WO2006112465A1

WO2006112465A1 - Phase difference compensation system

Info

Publication number: WO2006112465A1
Application number: PCT/JP2006/308168
Authority: WO
Inventors: Haruo Yago; Kenichi Nakagawa
Original assignee: Fujifilm Corporation
Priority date: 2005-04-14
Filing date: 2006-04-12
Publication date: 2006-10-26
Also published as: TW200702752A

Abstract

A liquid crystal projector (200) forms full color images by compositing three primary color light beams passed through liquid crystal devices for RGB (311R, 311G, 311B). In a light path of each liquid crystal device, a phase difference compensation element (400) is placed. The phase difference compensation element (400) includes a first optical anisotropic layer (401), which is made from an inorganic material and composed of high refractive index layers (401a) and low refractive index layers (401b), and a second optical anisotropic layer (402) including a polymerizable liquid crystal compound whose liquid crystal molecules are oriented to form hybrid orientation along the thickness direction of the liquid crystal device. The first and second optical anisotropic layers are adjusted in thickness (d1, d2) according to primary color light beams of RGB passing through the liquid crystal devices.

Description

DESCRIPTION

PHASE DIFFERENCE COMPENSATION SYSTEM

Technical Field

The present invention relates to a phase difference compensation system suitably applied to a liquid crystal projector with three liquid crystal devices corresponding to three primary color light beams .

Background Art

A three-panel type liquid crystal projector has three liquid crystal devices for three primary color light beams of red, green and blue. After modulated by these liquid crystal devices, the red, green and blue light beams are composited by a color combining prism and focused on a screen through a projection lens . The liquid crystal projectors are divided into two types, a front projection type that projects images from the front side of the screen and a rear projection type that projects from the rear side of the screen. Also, there are two types of the liquid crystal devices in the liquid crystal projectors, a transmissive type and a reflective type. While the liquid crystal projectors may have different optical systems because of such variations, they share a common projection mechanism in which the image for projection is displayed by each primary color on the liquid crystal devices , and these displayed images are then projected through the projection lens on the screen.

Depending on the operating methods, the liquid crystal devices are classified into TN (Twisted Nematic) mode, VA (Vertical Alignment) mode, IPS (In-Plane Switching) mode, OCB

(Optically Compensatory Bend) mode, ECB (Electrically Controlled Birefringence) mode and so forth. The most common liquid crystal device is a TFT (Thin Film Transistor) -LCD, and the most common operating manner is the TN mode . On the other hand, a recent growing demand for high contrast display encourages the development of the VA mode liquid crystal devices.

The TN mode liquid crystal device has nematic liquid crystals, which are sealed and twisted at 90° between two glass substrates . Disposed outside the glass substrates is a pair of polarizing plates arranged in a crossed nicols. When no voltage is applied, linearly polarized light passing through the first polarizing plate is induced to twist its polarization plane at 90° in the liquid crystal layer. The linearly polarized light then passes through the second polarizing plate and creates a white display. When a certain level of voltage is applied to selected pixels, the corresponding liquid crystals change their orientation directions to approximately perpendicular to a liquid crystal panel. Linearly polarized light does not change the polarization plane and reaches at the second polarizing plate. Thus, a black display is created. In contrast, the VA mode liquid crystal device includes nematic liquid crystals , which are sealed and aligned vertically or obliquely between two glass substrates. Disposed outside the glass substrates is a pair of polarizing plates, which are arranged in the crossed nicols. When no voltage is applied to the liquid crystal device, linearly polarized light passing through the first polarizing plate does not change the polarization plane as it passes through the liquid crystal layer. This light is finally blocked by the second polarizing plate, and the black display is created. When a certain level of voltage is applied, the liquid crystals twist themselves at 90° and change their orientation directions to approximately parallel with the liquid crystal panel. Linearly polarized light passing through the first polarizing plate is induced to twist its polarization plane at 90° in the liquid crystal layer. This light passes through the second polarizing plate, and creates the white display.

With these operating modes, the liquid crystal devices are sometimes unable to provide a complete black display to the viewers at certain angles, but allow light leakage instead. In other words , they pose a problem of view angle dependency, in which display quality is lowered because of deterioration in contrast and occurrence of tone reversal, a turnover of brightness in tonal expression.

Consequently, introduced to reduce the view angle dependency is an optical compensation film which gives a three dimensional optimization to the liquid crystal device in the black display state, so that the light leakage is prevented in any directions. The optical compensation film balances phase difference (or, retardation) of the light caused in the liquid crystal layer at the black display state and that caused in an optical anisotropic layer. The Japanese Patent laid-open publication No.08-50206 discloses such optical compensation film, constituted of a transparent support member made of a triacetylcellulose (TAC) film and the optical anisotropic layer formed on top of the support member. The transparent support member has the optical characteristic of approximately small negative refractive index ellipsoid, and the optical anisotropic layer is made of a compound with discoid (or, discotic) structure units. Every discotic structure units has a disc plane inclining to the upper surface of the transparent support member, and is treated to form a hybrid orientation structure, in which the angle between the disc plane of the discotic structure unit and the transparent support member changes in the thickness direction of the optical anisotropic layer. When this optical compensation film is employed, alignment of the disσotic structure units in the optical anisotropic layer are symmetrically compensatory to that of the liquid crystal layers in the black display state. The black display is therefore optimized and the light leakage is prevented over a wide range of view angle .

Recent increasing demand for big screen devices, however, calls for a wider view angle and higher contrast in the liquid crystal monitors and liquid crystal projectors. Among these, the liquid crystal projectors are designed to composite the light entering the liquid crystal device from different directions, using a projection lens, to project a magnified image on a screen. Therefore, they require still better contrast, and the optical compensation film should be improved further. In other words, the TAC film of the aforesaid optical compensation film hardly has a uniform thickness or a desired accuracy of optical property. It is therefore difficult to optically compensate the liquid crystal layer in the black display state with high accuracy so that the light leakage is prevented over a wide range of view angle . The U.S. Patent application publication No.2003/0112414 discloses a method of improving the contrast ratio of the liquid crystal projector, in which an optical film having a hybrid orientation liquid crystal layer is disposed between the two polarizing plates. This optical film includes a substrate film made of a polymer film with low birefringence, and the hybrid orientation liquid crystal layer placed above the substrate film. Even in this contrast ratio improving method, however, the optical film is inadequate to optically compensate the liquid crystal layer in the black display state with high accuracy so that the light leakage is prevented over a wide range of view angle.

The U.S. Patent application publication No.2004/0095535 discloses a liquid crystal projector which can deliver better contrast by the use of a phase difference compensation element composed of an alternating multilayer of a high refractive index layer and a low refractive index layer. However, it is still difficult to optically compensate the liquid crystal layer in the black display state with high accuracy so that the light leakage is prevented over a wide range of view angle.

In addition, the U.S. Patent application publication No .2004/0095535 discloses both a phase difference compensation element including a lamination of a first optical anisotropic layer made of an inorganic material and a second optical anisotropic layer made of a polymerizable compound, and a liquid crystal projector which incorporates this phase difference compensation element to offer better contrast . This phase difference compensation element provides a fine optical compensation to the liquid crystal layer for the black display, and prevents the light leakage over a wide range of view angle. Therefore, a better contrast, high image quality liquid crystal projector with wide view angle can be produced. For full color image projection, the liquid crystal projector has three liquid crystal devices for the three primary color light beams of red, green, and blue. The red, green and blue light beams are modulated by these liquid crystal devices, composited by the color combining prism, and focused on the screen through the projection lens. The liquid crystal projector disclosed in the U.S. Patent application publication No .2004/0095535 , however, uses the identical phase difference compensation elements for all the primary color light beams , and appropriate compensation cannot be achieved for all the light beams. If the black display is created on the screen in this case, the brightness, of black increases so that the contract ratio of the image will decrease. Moreover, the black state pixels may be colored because of incorrect color balance in low brightness areas .

In view of the above, an object of the present invention is to provide the phase difference compensation system which can increase the contrast of the images projected on the screen.

Another object of the present invention is to provide the phase difference compensation system which can keep the color balance in the low brightness areas .

Disclosure of Invention

In order to achieve the above and other objects, a phase difference compensation system made according to the present invention includes phase difference compensation elements each of which has a transparent support member, a first optical anisotropic layer of an inorganic material, and a second optical anisotropic layer of a polymerizable compound, both formed on the transparent support member. The phase difference compensation elements are individually placed on either a light incident surface side or a light exit surface side of liquid crystal devices , which are provided in every light paths for primary color light beams. The system uses at least two kinds of the phase difference compensation elements, one of which for the shortest wavelength light beam is different in physical structure from the others.

The first optical anisotropic layer is composed of a phase difference compensation film with an alternating lamination of at least high and low refractive index thin film layers . An optical thickness of each film layer is between one hundredth to one fifth of a reference wavelength of a corresponding primary color light beam. In addition, the phase difference compensation film for the shortest wavelength light beam has less numbers of film layers and/or less total film thickness than the phase difference compensation films for the other color light beams .

The second optical anisotropic layer is made of a polymerizable compound having liquid crystal molecules in hybrid orientation. The second optical anisotropic layer is adjusted of both or either of the thickness and the distribution of orientation angles according to the corresponding primary color light beam.

Two or more second optical anisotropic layers can be included in the phase difference compensation element , and they can be different from each other in at least one of the thickness, the distribution of orientation angle, and orientation direction. In addition, the first and the second anisotropic layers may be placed separately on the light incident surface side and the light exit surface side of the liquid crystal device. It should be appreciated that a liquid crystal projector having this phase difference compensation system lies within the scope of the present invention.

According to the present invention, the phase difference compensation element is constituted of the first and the second optical anisotropic layers , whose physical structures are changed according to the wavelength of the primary color light beams for full color display. It is therefore possible to improve the contrast of image on the screen throughout the visible light range .

Brief Description of Drawings

PIG.l is a conceptual diagram showing phase difference compensation action;

FIG.2 is a graph showing wavelength dependence of average retardation;

FIG.3 is an explanatory view of adjustment of the average retardation in a blue light region;

FIG.4 is an explanatory view of adjustment of the average retardation in the blue light region and a red light region;

FIG.5 is a cross sectional view of a phase difference compensation element with a first structure;

FIG.6 is a cross sectional view of another layer arrangement of the phase difference compensation element with the first structure;

FIG.7 is a cross sectional view of the phase difference compensation element with a second structure;

FIG.8 is a cross sectional view of the phase difference compensation element with a third structure;

FIG.9 is a cross sectional view of the phase difference compensation element with a fourth structure; FIG.10 is a cross sectional view of the phase difference compensation element with a fifth structure;

FIG.11 is a cross sectional view of the phase difference compensation element with a sixth structure;

FIG.12 is a cross sectional view of the phase difference compensation element with a seventh structure;

FIG.13 is a cross sectional view of the phase difference compensation element with an eighth structure;

FIG.14 is a schematic view of a liquid crystal display device with no voltage applied thereto; FIG.15 is a schematic view of the liquid crystal display device with a certain voltage applied thereto;

FIG.16 is a schematic view showing another embodiment of the liquid crystal display device for the present invention;

FIG.17 is a schematic view showing still another embodiment of the liquid crystal display device for the present invention;

FIG.18 is an external view of a liquid crystal projector of rear projection type; FIG.19 is a block diagram of a projection unit;

FIG.20 is a conceptual diagram of the phase difference compensation element;

FIG.21 is a table showing the wavelength dependency of the average retardation of a TN liquid crystal device;

FIG.22 is a table showing the wavelength dependency of the phase difference compensation element of a first embodiment;

FIG.23 is a graph showing average retardation characteristics of the TN liquid crystal device and the phase difference compensation element of the first embodiment;

FIG.24 is a graph showing the average retardation characteristic of the phase difference compensation element of a second embodiment;

FIG.25 is a table showing the wavelength dependency of the phase difference compensation element of the second embodiment ;

FIG.26 is a graph showing the average retardation characteristic of the phase difference compensation element of a third embodiment;

FIG.27 is a table showing the wavelength dependency of the phase difference compensation element of the third embodiment;

FIG.28 is a graph showing the average retardation characteristic of the phase difference compensation element of a fourth embodiment;

FIG.29 is a table showing the wavelength dependency of the phase difference compensation element of the fourth embodiment;

FIG.30 is an explanatory view of the phase difference compensation element which are divided for arrangement; and

FIGS.31A and 31B are explanatory views of the phase difference compensation element placed at an off-axis position to a reflective liquid crystal device.

Best Mode for Carrying Out the Invention In FIG.l, a liquid crystal device 2 has a liquid crystal layer 5 enclosed in between a transparent base substrates 3a and 3b, which have an orientation film on an interior surface individually. The liquid crystal device 2 is sometimes called a liquid crystal panel. The liquid crystal layer 5 is composed of liquid crystal molecules. In order to drive the liquid crystal layer 5 for each pixel, the substrates 3a and 3b are individually provided with matrix electrodes, common electrodes, and transparent electro-conductive films (all not shown) and the like. Disposed on an upstream side in the light path of the liquid crystal device 2 is a polarizer, by which incident light Sl is changed into linearly polarized light that enters the liquid crystal device 2.

As is well known, the liquid crystal layer 5 composed of rod-like liquid crystal molecules works as a positive retarder. Thus, during the passage through the liquid crystal layer 5, the incident light Sl is separated into an ordinary component So and an extraordinary component Se, and phase of the extraordinary component Se delays from that of the ordinary component So . The phase difference (or retardation) Pl is determined by a feature value "dpΔnp", which is the product of a birefringence value Δnp, i.e. the dependent value on optical anisotropy of the liquid crystals molecules, and a thickness dp of the liquid crystal layer 5. In terms of crystal optics, this feature value is defined as average retardation to an average incident angle. If an average retardation is represented as Rp, the retardation Pl becomes

dpΔnp) " . The coefficient a represents all external factors which vary depending on the conditions such as incident angle distribution of light, orientation of the liquid crystal molecules, and applied voltage. The coefficient a is no less than 0 and no more than 1.

An exit light S2 from the liquid crystal device 2 becomes a combination of the ordinary component So and the retarded extraordinary component Se. Thus, the exit light S2 has an elliptically polarized component related to the average retardation Rp, even if the incident light Sl is linearly polarized. Therefore, in order to prevent the occurrence of the elliptically polarized component, a phase difference compensation element 6 is employed between the light exit surface of the liquid crystal device 2 and an analyzer.

The phase difference compensation element 6 has an inorganic phase difference compensation film 8 formed on a transparent substrate 7 , and works as a negative retarder that causes phase delay in the ordinary component So against the extraordinary component Se. The phase difference compensation film 8 is composed of a first optical anisotropic layer 8a made from an inorganic material and a second optical anisotropic layer

8b made from a polymerizable compound. An average retardation Rq of the phase difference compensation element 6 is a sum of average retardations Rl(=dlΔnl) and R2(=d2Δn2) toward the average incident angles which are defined by the first and second optical anisotropic layers ' birefringence values Δnl, Δn2 and thickness dl, d2.

The retardation P2 of the ordinary component So against the extraordinary component Se is "P2=/?Rq( = /? dlΔnl + /?d2Δn2). If the condition P1=P2 is satisfied, the exit light S3 from the phase difference compensation element 6 becomes linearly polarized light because no retardation is there between the ordinary and extraordinary components to produce the elliptically polarized component. Consequently, the analyzer at downstream side of the phase difference compensation element 6 has an entry of the linearly polarized light, and the image contrast is effectively increased. Although the coefficients a and β will change depending on the incident angle distribution of light, influence of the incident angle may be disregarded if the light beam passes both the liquid crystal device 2 and the phase difference compensation element 6 at the same incident angle, as shown in FIG.l. Accordingly, in order to obtain the coefficient a to satisfy P1=P2, consideration has to be given only to the internal factors that depend on the liquid crystal device 2 itself, such as orientation of the liquid crystal molecules and the applied voltage. Note that the birefringence values Δnp and Δnq do not appear with positive or negative values basically for the sake of simplicity of explanation, but do appear with the positive or negative values if necessary.

As is clear from the above, it is effective in the present invention to make even the retardation Pl in the liquid crystal device 2 and the retardation P2 in the phase difference compensation element 6 as much as possible, in other words, the agreement of the average retardations Rp and Rq. The phase difference compensation elements 6 may, however, take other internal structures than the negative retarder, such as uniaxial structures (e.g. a-plate and o-plate) and other multilayer structures. That is, in order to satisfy the condition "Rp=Rq", the parameters (dl, Δnl, d2, Δn2) for the average retardation

Rq of the phase difference compensation film 8 has to be controlled. Hereinafter, a method for deciding these parameters is explained using a TN mode liquid crystals.

Depicted in FIG.2 is wavelength dependency of both an average retardation Rp (=dpΔnp) of a conventional liquid crystal layer 5 and the average retardation Rq (=dlΔnl + d2Δn2) of the phase difference compensation film 8. In the visible light range, the average retardation Rp is large in the short wavelength side, and becomes smaller gradually as it moves to the long wavelength side. Similarly, the average retardation Rq is large in the short wavelength side and small in the long wavelength side, but it changes steeply in the short wavelength side. Since the thickness is independent of the wavelength, it is the birefringence Δnp , Δnq ( Δnl + Δn2) that cause such wavelength dependency.

In FIG.2, the first and the second optical anisotropic layers 8a and 8b are adjusted for the thickness dl and d2 such that the average retardation Rq of the phase difference compensation film 8, which has a certain birefringence, comes close to the average retardation Rp of the liquid crystal layer 5 , and finally they agree at the standard wavelength of green light (550 nm, corresponding to the peak of visual sensitivity). Although the adjustment of the thickness dl and d2 allows to shift the average retardation Rq vertically in the graph, the slope in the graph can hardly be changed because it depends on the wavelength dependency of the birefringence Δnl and Δn2.

A three-plate type liquid crystal projector uses three identical liquid crystal devices for the primary color light beams . It is therefore necessary to change the average retardation Rq of the phase difference compensation element if the retardations Pl and P2 differ from one primary color to another. Therefore, in the present invention, the blue, green, and red wavelength ranges are defined as 400nm to 500nm, 500nm to 600nm, and 600nm to 700nm respectively, as shown in FIG.3. Then, in the phase difference compensation element 6 for blue light range, the thickness dl and d2 of the phase difference compensation film 8 is decreased to obtain the average retardation Rqs in the wavelength range of 400nm to 500nm. At the same time, the average retardation Rq_B is adjusted to correspond with the average retardation Rp of the liquid crystal layer 5 at the standard wavelength of blue light (450nm). As a result, the difference of the average retardations can be reduced to an acceptable level over the approximately entire visible light range, even if the wavelength dependency of the birefringence Δnl and Δn2 are not matched to the wavelength dependency of the birefringence Δnp of the liquid crystal layer 5. For additional improvement in the long wavelength side, it is possible to increase the thickness dl and d2 of the phase difference compensation film 8 used in the phase difference compensation element 6 for red light range, as shown in FIG.4, so that the average retardation Rq_R is obtained to correspond with the average retardation Rp of the liquid crystal layer 5 at the standard wavelength of red light (650nm) . The above method only requires to adjust the thickness dl and d2 according to the wavelength of the primary color light beams. Not requiring the adjustment of the birefringence Δnl and Δn2 which depend on the optical structure of the phase difference compensation film 8, the above method is suitable for mass production.

In the TN type liquid crystal, a certain voltage is applied to align the rod-like liquid crystal molecules perpendicular to the glass substrates for the black display. However, not all of the liquid crystal molecules near the substrates are aligned perpendicularly. Although higher voltage will align more liquid crystal molecules , a ratio of the perpendicularly aligned liquid crystal molecules in the black display state is generally 60% to 95%, or 65% to 80% to the thickness dp. Accordingly, it is necessary to decide the parameters of the phase difference compensation film 8 by considering that the retardation Pl of the liquid crystal layer 5 with the thickness dp becomes smaller than the value dpΔnp. In a simple method, the coefficient a is set to 0.7 to obtain the condition "0.7xdpΔnp=Rq" , which should be satisfied by the phase difference compensation film 8. Note that the OCB (Optically Compensatory Bend) type and STN (Super Twisted Nematic) type liquid crystal also have the similar characteristics . The phase difference compensation film 8 of the present invention is composed of the first optical anisotropic layer 8a made from an inorganic material and the second optical anisotropic layer 8b made from a polymerizable compound. Additionally, the first optical anisotropic layer has, for example, an alternate stacking structure of high refractive and low refractive thin film layers . The wavelength dependency of the birefringence in such phase difference compensation element 6 is further considered.

Provided that the standard wavelength of the blue, green, and ret light are 450nm, 550nm, and 650nm respectively while the birefringence of the phase difference compensation element at each standard wavelength are Δnq(₄₅o), Δnq(₅so), and Δnq(₆₅₀), the wavelength dependency Uq of the birefringence Δnq is defined as

Uq = {Δnq(₄₅₀) - Δnq(₆so)}/ Δnq(₅₅₀). Similarly , the wavelength dependency Up of birefringence

Δ np of the liquid crystal layer is defined as

Up = { Δnp (450) - Δ np (βso) }/ Δnp (ssoj -

Ideally, the condition Up=Uq is satisfied over the visible light range. There are, however, a limited kinds of the liquid crystal molecules for practical use, and it is difficult to drastically change the wavelength dependency Up of birefringence Δnp of the liquid crystal layer. Thus, it is the wavelength dependency Uq of the birefringence Δnq of the phase difference compensation element that is adjusted to come close to the wavelength dependency Up. The wavelength dependency Uq depends upon the characteristic of the thin film layers in the first and the second optical anisotropic layers. In addition, condition for correct retardation in each selected wavelength depends on thickness dl and d2. Accordingly, high and a low refractive index materials for the high and the low refractive index thin film layers in the first optical anisotropic layer and a polymerizing compound for the second optical anisotropic layer are selected such that the wavelength dependency Uq of the phase difference compensation film comes close to the wavelength dependency Up of the liquid crystal layer. Then, the thickness dl and d2 of the first and second optical anisotropic layers are adjusted in consideration of the retardation in the entire visible light range. Note that if the wavelength dependencies Up and Uq correspond with each other approximately, an appropriate retardation effect can be obtained over the visible light range only by adjusting the thickness dl and d2. In view of the high and low refractive index materials currently available, however, the wavelength dependency Up and Uq are different in any way. In this case, using the three-plate type liquid crystal projector with separate color channels for three primary colors , as shown in FIG .3 and FIG .4 , allows to adjust the thickness dl and d2 for each primary color light beams.

A major reason that the wavelength dependency Up and Uq do not correspond with each other is the difference in the wavelength dependency of the refractive index between the first and second optical anisotropic layers. Especially, the wavelength dependence becomes large as the refractive index increases, especially in the short wavelength range. However, the phase difference compensation element of the present invention allows to change both the high refractive and low refractive materials in the first optical anisotropic layer and the thickness of the polymerizable compound in the second optical anisotropic layer, and it is therefore able to provide more options for adjustment than the conventional phase difference compensation element which merely use either one of the first or the second optical anisotropic layer, in light of the above, the phase difference compensation system of the present invention is now explained. (Phase difference compensation element) The phase difference compensation element of the present invention is provided, on the transparent substrate, with the first optical anisotropic layer made of an inorganic material, a second optical anisotropic layer made of a polymerizable compound, and other layers where appropriate. ( 1 ) Transparent support member

The transparent support member may be made from any material, such as, for example, white plate glass, blue plate glass, quartz glass, sapphire glass, or organic polymer film. The organic polymer film is also made from any material, which is, for example, one or combination of polymers of polyalylate, polyester, polycarbonate, polyolefin, polyether, polysulfine, polysulphone , polyethersulphone , and cellulose-ester. Preferably, the organic polymer film is either a polycarbonate copolymer, a polyester copolymer, a polyester carbonate copolymer, or a polyalylate copolymer, and most preferable among these is the polycarbonate copolymer. It is preferable that the polycarbonate copolymer has fluorene skeletons, and more preferable from the viewpoint of transparency, thermostability, and productivity that the polycarbonate copolymer is made through a reaction of bisphenol with a carbonic ester compound such as phosgene or diphenyl carbonate. The polycarbonate copolymer will preferably have the fluorene skeleton contents of 1 to 99 mole percent. To the polycarbonate copolymer, it is possible to use the periodic unit described in the U.S. Patent No.6,565,974.

In order to obtain a smooth surface, it is preferable to manufacture the transparent support member with the glass made from either of the aforesaid inorganic materials.

Although there is no limitation on the thickness of the transparent support member, it is preferably no less than 0.1 μm. The upper limit of the thickness is preferably 0.3mm to 3mm, and more preferably 0.5mm to 1.5mm in view both of handling in the assembly work and mechanical strength. (2) First optical anisotropic layer

The first optical anisotropic layer can be any of those made from an inorganic material and being anisotropic in its entirety. For example, a preferable first optical anisotropic layer may be a periodic multilayer structure constituted of several regularly-repeated units (periodic units) , each of which has thin layers of different refractive index values stacked regularly in the normal direction of the transparent support member (i.e. a set of the repeated periodic units). Additionally, optical thickness of each periodic unit, in other words the thickness in the stacking direction thereof (hereinafter, "periodic structure pitch") is smaller than the wave length of light within a visible light range . These periodic units in the periodic multilayer structure are not necessarily to have the same thickness in the stacking direction, but able to be different in thickness according to the property of the light that the first optical anisotropic layer allows to pass. The periodic unit can have any number of the thin layers as long as they are different in refractive index. For example, a preferable periodic unit is constituted of two thin layers of different inorganic materials.

The thickness of each layer in the periodic multilayer structure has only to be smaller than the wavelength of light in the visible light range. Concretely, when the wavelength of light in the visible light range is represented by A , the thickness is preferably from A /100 to, A /5, more preferably from A /50 to A /5, and especially from A /30 to A /10. The periodic multilayer structure needs to prevent the interference of light between the stacked thin layers, and therefore requires these thin layers to be thin. However, such thin layers will result in increasing the number of the layering process to obtain the total thickness necessary. Also, consideration must be given to the optical characteristic needed in the first optical anisotropic layer and a problem of coloring caused by mutual interference of the thin layers. It is therefore preferable to decide the thickness of each thin layer based on the conditions such as the material to be used, the refractive index, a thickness ratio between the thin layers, and the total layer thickness necessary. The periodic structure pitch can be decided as appropriate according to the visible light range, as long as it is shorter than the wavelength of light within the visible light range. Hereinafter, the visible range means the wavelength range between 400nm to 700nm, unless otherwise stated. It is therefore preferably that the periodic structure pitch is decided between the range of 400nm to 700nm.

The periodic multilayer structure of the first optical anisotropic layer can be made from any material, which will be selected as appropriate according to the intended use. Provide, however, that the material should preferably be selected according to an intended refractive index difference Δn because the retardation caused by the birefringence of the first optical anisotropic layer is the product of the thickness d of the optical anisotropic layer and the refractive index difference Δn of each thin layer in the periodic unit. Particularly, the material is preferably be TiO₂ , ZrO₂ or the like as a high refractive material and SiO₂, MgF₂, or the like as a low refractive material.

It is preferable to combine these materials such that the refractive index difference Δn, which is the difference of the maximum and the minimum refractive index values in the visible light range, becomes 0.5 and above. More preferably, these materials are oxide films, and especially the combination of an SiO₂ (refractive index n = 1.4870 to 1.5442) film and a TiO₂ (refractive index n = 2.583 to 2.741) film is suitable.

If the difference Δn of the refractive index becomes less than 0.5, the optical anisotropic layer has to be adjusted in thickness so as to have the intended amount of the retardation. This leads to increase the number of the layering process for the periodic τmits and effects against manufacturability and productivity. While having uniform refractive index in the stacking direction of the thin layers (the normal direction of the transparent support member), the first optical anisotropic layer as a whole has the optical characteristic of a non-tilted uniaxial negative refractive index ellipsoid, due to an anisotropic function called form birefringence. It is thus possible to obtain an intended average retardation easily and precisely by smoothing the first optical anisotropic layer and appropriately deciding the options such as the material for the periodic multilayer structure, thickness of the thin layers, the number of the thin layers, and the periodic structure pitch.

Also, the first optical anisotropic layer is able to work as an anti-reflection film depending on the thickness ratio and total thickness of the thin layers.

(3) Second optical anisotropic layer

The second optical anisotropic layer in the phase difference compensation element of the present invention includes at least a polymerizable compound, and is able to have additional elements when needed. There is no limitation on the polymerizable compound. Nonetheless, the polymerizable compound may preferably contain liquid crystal molecules fixable in a certain orientation. It is more preferable that the liquid crystal molecules have either rod-like, disk, or bow shape, and the disk shaped (discotic) molecules are most preferable. The polymerizable compound can contain other components when needed. Hereinafter, the liquid crystal molecules are expressed as "in an oriented state" when their unique axes, the axis in the direction attribute to the molecular shape such as a long axis direction for a stick shape molecule or a normal direction of the plate for a plate like molecule, are almost in the same orientation inside a minute observation region. Additionally, the angle between the averaged orientation of the inherent axes of the oriented molecules in the minute observation region and the stacking direction of the phase difference compensation element (the normal direction at a boundary of the second optical anisotropic layer and the transparent support member) is called an orientation angle. Furthermore, a projection of the averaged orientation of the inherent axes on the boundary is called an orientation direction. It is preferable that the orientation angle inclines, in other words, neither parallel nor perpendicular to the thickness direction of the second optical anisotropic layer, and more preferable that the second optical anisotropic layer has a hybrid orientation structure, in which the orientation angle continuously varies in the thickness direction between the upper and lower surfaces of the layer.

In the hybrid orientation structure, the orientation angle is preferably controlled to change continuously within the range of 20° ±20° to 65° ±20° from the side of an orientation film toward the side of an air interface.

The oriented state of the polymerizable liquid crystal compound is determined by the orientation angle and the orientation direction, and is desirably controlled such that angle dependency of retardation in the liquid crystal layer at the black display state is compensated.

In these control, the orientation angle around the orientation film and at the air interface side as well as the average orientation angle in the second optical anisotropic layer are all estimated values obtained from an hybrid orientation refractive body model, which is simulated based on the average retardation measured from various directions with an ellipsometer (M-150 from JASCO corporation).

It is also possible to use the method described in "Design Concepts of Discotic Negative Birefringence Compensation Films, LP-J, SID98 SYMPOSIUMDIGEST (1998)" to calculate the orientation angle from the average retardation. In addition, the measurement on the second optical anisotropic layer can be conducted from any direction as appropriate for the purpose. The direction of the measurement may be, for example, the normal direction of the second optical anisotropic layer (ReO), a negative 40° angle (Re-40) and a positive 40° angle (Re+40) to the normal direction. The values of ReO, Re-40, and Re+40 are measured with the ellipsometer .

It is possible to use any polymerizable liquid crystal compound with rod-like liquid crystal molecules according to the purpose. The polymerizable liquid crystal compound may be, for example, one using a polymer binder to immobilize the orientation of the rod-like molecules or one with polymerizable groups which immobilize the orientation of the rod-like molecules by polymerization. Of these, the polymerizable liquid crystal compound with the polymerizable groups is preferable. Any kind of the rod-like liquid crystal molecule can be used according to the purpose. For example, it is either azomethines, azoxies, cyanobiphenyls , cyanophenyl esters, benzoic acid esters, σyclohexane carboxylic phenyl esters, cyanophenyl cyclohexanes , cyano substituted phenylpyrimidines , alkoxy substituted phenylpyrimidines, phenyl dioxianes, tolans , and alkenyl cyclohexyl benzonitriles.

The polymerizable liquid crystal compound with such rod-like liquid crystal molecules is a high polymer liquid crystal compound, which is formed by polymerization of the rod-like liquid crystal compounds having a low molecular polymerizable groups represented by, for example, a following structural formula 1. Q¹-L¹-A¹-L³-M-L⁴-A²-L²-Q² (STRACTURAL FORMULA 1)

In the structural formula 1, Q¹ and Q² represent polymerizable groups. While L¹, L², L³, and L⁴ represent either a single bond or a bifunctional connecting group respectively, at least one of the L² and L³ represents "-0-C0-0-". A¹ and A² individually represent a spacer group having 2 to 20 carbon atoms, and M represents a mesogen group.

It is possible to use any polymerizable liquid crystal compound with discotic liquid crystal molecules according to the purpose. For example, the polymerizable liquid crystal compound may be one using a polymer binder to immobilize the orientation of the discotic molecules or one with polymerizable groups which immobilize the orientation of the dicotic molecules by polymerization. Of these, one with the polymerizable groups is preferable. Such polymerizable liquid crystal compound with the polymerizable groups may have, for example, a connecting group between a discotic core and the polymerizable group. This polymerizable liquid crystal compound may preferably be represented by a following structural formula 2 described in the Japanese Patent laid-open publication No. 08-050206. D(-L-P)_n (STRACTURAL FORMULA 2)

In the structural formula 2 , D represents the discotic core, L represents a bifunctional connecting group, and P represents the polymerizable group. Additionally, n is an integer of 4 to 12. Although more than two kinds of Ls and Ps can be used, it is preferable to use a single kind of the connecting group L and the polymerizable group P. The discotic core D may be more than two kinds .

The discotic cores D in the structural formula 2 are those represented by following structural formulas Dl to D15 .

(Dl) (D2)

(D3) (D4)

(D9) (DlO)

(DIl)

(D12)

(D15)

In the structural formula 2 , any kind of the bifunctional connecting group L can be used according to the purpose. For example , an alkylene group, an alkenylene group, an arylene group , -CO-, -NH-, -O- , -S-, or a combination of these is preferable, and a combination of at least two of the bifunctional connecting groups selected from these is more preferable, and still more preferable is a combination of at least two of the bifunctional connecting groups selected from the alkylene group, the alkenylene group, the arylene group, -CO-, and -0- .

It is preferable that the alkylene group has 1 to 12 carbon atoms, and that the alkenylene group has 2 to 12 and the arylene group has 6 to 10 carbon atoms. The alkylene group, the alkenylene group, and the arylene group can include substituted groups of an alkyl, a halogen atom, a cyano, an alkoxy group, and an acyloxy group .

An exemplary bifunctional connecting group is -AL-CO-O-AL-, -AL-CO-O-AL-O-, -AL-CO-O-AL-O-AL-, -AL-CO-O-AL-O-CO-, -CO-AR-O-AL-, -CO-AR-O-AL-O-, -CO-AR-O-AL-O-CO-, -CO-NH-AL-, -NH-AL-O-, -NH-AL-O-CO-, -O-AL-, -O-AL-O-, -O-AL-O-CO-, -0-AL-O-CO-NH-AL- , -O-AL-S-AL-, -O-CO-AL-AR-O-AL-O-CO- , -O-CO-AR-O-AL-CO- ,

-O-CO-AR-O-AL-O-CO- , -O-CO-AR-O-AL-O-AL-O-CO- , -O-CO-AR-O-AL-O-AL-O-AL-O-CO-, -S-AL-, -S-AL-O-, -S-AL-O-CO-, -S-AL-S-AL-, -S-AR-AL-, or the like.

These examples connect on the left side to the discotic cores D, and on the right side to the polymerizable groups P. In addition, AL represents either the alkylene group or the alkenylene group, and AR represents the arylene group.

In the structural formula 2 , any kind of the polymerizable group P can be used according to the type of polymerization reaction. For example, an unsaturated polymerizable group or an epoxy group is preferable, and an ethylene unsaturated polymerizable group is more preferable. Particularly, the polymerizable groups may be those represented by following structural formulas Pl to P18. (Pl) (P2) (P3)

(M) (P5) (P6)

(P7) (P8) (P9)

-C=CH₂ "C H—*2 H"*CH₃ — N=C=S CH₃

(PlO) (PIl) (P12)

— 6H -CHO —OH

(P13) (P14) (P15)

-CO₂H — N=C=O "~~*Q H =C H "^2Hg

(¥16) (P17) (PIS)

^■~~TJPH^«~CH~~Π"C3Π7

It is noted that n in the examples Pl to P18 is an integer of 4 to 12, and determined by the kind of the discotic core D. According to the purpose, the polymerizable compound will include other components such as, for example, a polymerization initiator for starting the polymerization reaction of the polymerizable compound and a solvent for preparing a coating liquid of the polymerizable compound. The polymerization initiator, while there is no limitation thereon, may be a thermal polymerization initiator that starts a thermal polymerization reaction or a photopolymerization initiator that starts a photopolymerization reaction. Especially, the photopolymerization initiator is preferable.

An exemplary photopolymerization initiator is an a -carbonyl compound (disclosed in the U.S. Patent No. 2,367,661 and No.2, 367, 670) , acyloin ether (disclosed in the U.S. Patent No.2,448,828) , an a -hydrocarbon substituted aromatic acyloin compound (disclosed in the U.S. Patent No.2, 722 , 512) , a multiatom quinone compound (disclosed in the U.S. Patent No.3, 046, 127 and No.2, 951 , 758) , a combination of triarylimidazole dimmer and p-aminophenyl ketone (disclosed in the U. S. Patent No.3,549 , 367) , a compound of acridine and phenazine (disclosed in the Japanese Patent laid-open publication No. 60-105667 and the U.S. Patent No .4 , 239 , 850 ) , an oxadiazole compound (disclosed in the U.S. Patent No.4, 212, 970) , or the like. The amount of the photopolymerization initiator in the polymeraizable liquid crystal compound is not limited, and can be determined according to the purpose. Preferably, it is 0.01% to 20% by weight of dry solid contents in the coating liquid of the polymerizable compound, and more preferably 0.5% to 5% by weight .

It is possible to use any light irradiator for the photopolymerization reaction according to the purpose, and one preferable is an ultraviolet ray. Irradiation energy of the light irradiator is preferably 2OmJ to 50J/cm², and more preferably 10OmJ to 800mJ/cm².

Additionally, this irradiation operation may be conducted under a heat condition so that the photopolymerization is accelerated.

The solvent for preparing the coating liquid can be selected as appropriate, and organic solvents are preferable. For example, amide such as N or N-dimethylformamide, sulfoxide such as dimethylsulfoxide , a heterocyclic compound such as pyridine. hydrocarbon such as benzene or hexane, alkyl halide such as chloroform or dichloromethane , ester such as methyl acetate or butyl acetate, ketone such as acetone or methyl ethyl ketone, or ether such as tetrahydrofuran or 1, 2-dimethoxyethane is preferable, and more preferable among these is the alkyl halide or the ketone. Instead, it is possible to use more than two of these.

Any polymerization method can be used to the polymerizable liquid crystal compound according to the purpose. For example, the methods disclosed in the Japanese Patent laid-open publications NO.08-27284 and No.10-278123 can be used.

The second optical anisotropic layer can contain other components according to the purpose. For example, it may contain an orientation film that orients the liquid crystal molecules in the polymerizable compound. In this case, the polymerizable compound may preferably be placed on top of the orientation film by coating or the like.

There is no limitation on the orientation film, and it will be selected according to the purpose. For example, the orientation film may be either a rubbed film composed of organic compounds (polymers), a film with micro grooves, a film with organic compounds such as ω -tricosane, dioctadecyldimethylammonium chloride, and stearyl methyl accumulated made through Langmuir-Blodgett method (LB film), a film with inorganic compounds obliquely deposited, or a film that gives an orientation function by an electrical field, a magnetic field, or irradiation. Among these, the rubbed orientation film composed of organic compounds is preferable .

Any kind of rubbing process can be employed as appropriate, and the surface of the organic compound film may be rubbed, for example, several times in one direction with a paper or a fabric.

The organic compound can be selected as appropriate according to the oriented state (especially the orientation angle) of the liquid molecules . For example, a polymer that hardly decreases the surface energy of the orientation film will be selected so that the liquid crystal molecules are oriented horizontally.

If the liquid crystal molecules are to be oriented perpendicular to the rubbing direction, the orientation film-directed polymer will preferably be modified polyvinyl alcohol (disclosed in the Japanese Patent laid-open publication No. 2002-62427) , acrylic copolymer (disclosed in the Japanese Patent laid-open publication No. 2002-98836), polyimide, or polyamic acid (disclosed in the Japanese Patent laid-open publication No. 2002-268068).

The orientation film may preferably have reactive groups so as to improve adhesion to the polymerizable compound and the transparent support member. For example, the orientation film that adopts the reactive groups for the side chains of the periodic units of the polymer or the orientation film that adopts the substituent groups of cyclic groups for the polymer is preferable. Able to be used instead is the orientation film, disclosed in the Japanese laid-open publication No. 9-152509, which forms a chemical bond to the polymerizable compound and the transparent support member through the reactive groups .

The thickness of the orientation film is not limited, and preferably in the rage of O.Olμm to 5μm, more preferably in the range of 0.02μm to 2μm.

There is no specific method for manufacturing the second optical anisotropic layer, which is however preferably be manufactured by coating the orientation film with a coating liquid composed of the solvent, the polymerizable compound containing the liquid crystal molecules, and the polymerization initiator. The coating method is not limited either, and will be one of the un_¬

common methods such as the extrusion coating, direct gravure coating, reverse gravure coating, die coating, and spin coating.

The second optical anisotropic layer can also be manufactured as described below. At first, the optical anisotropic layer is formed of a polymerizable compound whose liquid crystal molecules are oriented by the orientation film and fixed as it is. Then, the optical anisotropic layer alone is transcribed on the transparent support member such as a polymer film to be the second optical anisotropic layer. In this method, no consideration is required for influence of the birefringence in the orientation film, and the liquid crystal layer in the black display state can be optically compensated with a high degree of accuracy.

( 4 ) Other layers As described above, the phase difference compensation element of the present invention is able to have other layers according to the purpose. One of the other layers an anti-reflection layer. As long as it lowers reflectance and increases transmittance, the anti-reflection layer can be of any material and structure such as a common AR film (Anti Reflection Coat Film) .

No specific combination of the first and second optical anisotropic layers is there for the structure the phase difference compensation element, and the structure can be selected as appropriate according to the purpose. It is preferable that the phase difference compensation element has one of following first to eight structures, even though the present invention is not limited to these structures .

(The first structure of the phase difference compensation element )

As shown in FIG.5, the phase difference compensation element 10 with the first structure is that a first optical anisotropic layer 12 is provided on a surface of a transparent support member 11. The other surface of the transparent support member 11 is provided with two of second optical anisotropic layer 13a and 13b, which have different orientation direction to each other. In particular, one surface of the transparent support member 11 has an orientation layer 14a, the second optical anisotropic layers 13a, another orientation layer 14b, another second optical anisotropic layer 13b, and an anti-reflection layer 15b stacked on top of the other in this order. The other surface of the transparent support member 11 has a first optical anisotropic layer 12 and an anti-reflection layer 15a stacked in this order.

The first optical anisotropic layer 12 is a periodic multilayer structure of a TiO₂ layer 12a and an SiO₂ layer 12b, each has the thickness of approximately 15nm. The orientation layers 14a and 14b are rubbed in one direction that is preferably at an angle of between 70° to 110° , centering around 90° , with the structure of the NT mode liquid crystal molecules . Hereinafter, this range of angle is described as approximate 90° . Such orientation films 14a and 14b enable to orient the liquid crystal molecules of the second optical anisotropic layers 13a and 13b in the direction to improve image contrast.

Additionally, the second optical anisotropic layers 13a and 13b have the same thickness so that view angle dependency in retardation is compensated in a liquid crystal device with TN mode liquid crystals at the black display state. It is also possible to allow an approximately 20% difference in thickness between these layers according to the structure and the orientation state of the liquid crystal device. Furthermore, it is preferable to optimize the orientation angle and the orientation direction of the second optical anisotropic layers 13a and 13b based on the structure and the orientation state of the liquid crystal device. A phase difference compensation element 10a, shown in

FIG.6, has almost the same structure as the phase difference compensation element 10 shown in FIG.5, except that it is provided with an anti-reflection layer 15c between the transparent support member 11 and the orientation layer 14a.

The phase difference compensation element 10a has a three layer structure of the anti-reflection layers, the anti-reflection layers 15a and 15b respectively disposed outermost on the transparent support member 11, and the anti-reflection layer 15c between the transparent support member 11 and the orientation layer 14a. Adding the anti-reflection layer in the middle of the multilayer structure gives anti-reflection function in a wider wavelength range.

(The second structure of the phase difference compensation element )

As shown in FIG.7, a phase difference compensation element with the second structure has both the first and the second optical anisotropic layers on at least one surface of the transparent support member. That is, the phase difference compensation element 20 with the second structure is provided on one surface of the transparent support member 21 with a first optical anisotropic layer 22, an orientation layer 24, a second optical anisotropic layer 23, and an anti-reflection layer 25b stacked on top of the other in this order. The other surface of the transparent support member 21 is provided with an anti-reflection layer 25a. The first optical anisotropic layer 22 is a periodic multilayer structure of a TiO₂ film 22a, as a high refractive index layer, and an SiO₂ film 22b, as a low refractive index layer. Formed in such periodic multilayer structure, the first optical anisotropic layer 22 becomes to give an anti-reflection function as well. Additionally, it is possible to stack two of the phase difference compensation element 20. In this case, they are preferably arranged such that their rubbing directions of the orientation layers are at approximately 90° to each other. While depending partly on the materials and the combination of the layers, handling and manufacturability are improved with the structure of the phase difference compensation element 20 which has most of the layers on one surface of the transparent support member .

(The third structure of the phase difference compensation element )

As shown in FIG.8, a phase difference compensation element with the third structure has two of the second optical anisotropic layers with different orientation directions on one surface of the transparent support member. Namely, the phase difference compensation element 30 with the third structure is provided on one surface of the transparent support member 31 with a first optical anisotropic layer 32, an orientation layer 34a, a second optical anisotropic layer 33a, another orientation layer 34b, another second optical anisotropic layer 33b, and an anti-reflection layer 35b stacked on top of the other in this order. The other surface of the transparent support member 31 is provided with an anti-reflection layer 35a. The first optical anisotropic layer 32 can take the same structure as the first optical anisotropic layer 12 of the phase difference compensation element 10.

Additionally, it is preferable to arrange the orientation layers 34a and 34b such that their rubbing directions are at approximately 90° to each other. Thereby, the orientation directions of the liquid crystal molecules in the second optical anisotropic layers 33a and 33b can be different from each other by 90° .

(The fourth structure of the phase difference compensation element )

As shown in FIG.9, a phase difference compensation element with the fourth structure has two of the second optical anisotropic layers with different orientation directions across the transparent support member.

Namely, the phase difference compensation element 40 with the fourth structure is provided on one surface of the transparent support member 41 with a first optical anisotropic layer 42, an orientation layer 44a, a second optical anisotropic layer 43a, and an anti-reflection layer 45b stacked on top of the other in this order. The other surface of the transparent support member 41 is provided with another orientation layer 44b, another second optical anisotropic layer 43b, and an anti-reflection layer 45a stacked in this order. The first optical anisotropic layer 42 can take the same structure as the first optical anisotropic layer 12 of the phase difference compensation element 10.

Additionally, it is preferable to arrange the orientation layers 44a and 44b such that their rubbing directions are at approximately 90° to each other. Thereby, the orientation directions of the liquid crystal molecules in the second optical anisotropic layers 43a and 43b can be different from each other by 90° .

(The fifth structure of the phase difference compensation element ) As shown in FIG.10, a phase difference compensation element with the fifth structure has the first and the second optical anisotropic layers on at least one surface of the transparent support member.

That is, the phase difference compensation element 50 with the fifth structure is provided on one surface of the transparent support member 51 with an orientation layer 54, a second anisotropic layer 53, a first optical anisotropic layer 52, and an anti-reflection layer 55b stacked on top of the other in this order. The other surface of the transparent support member 51 is provided with an anti-reflection layer 55a. The first optical anisotropic layer 52 is a periodic multilayer structure of a TiO₂ film 52a and an SiO₂ film 52b.

Additionally, it is possible to stack two of the phase difference compensation element 50. In this case, they are preferably arranged such that their rubbing directions of the orientation layers are at approximately 90° to each other. (The sixth structure of the phase difference compensation element)

As shown in FIG.11, a phase difference compensation element with the sixth structure has two of the second optical anisotropic layers with different orientation directions on one surface of the transparent support member.

Namely, the phase difference compensation element 60 with the sixth structure is provided on one surface of the transparent support member 61 with an orientation layer 64a, a second optical anisotropic layer 63a, another orientation layer 64b, another second optical anisotropic layer 63b, a first optical anisotropic layer 62, and an anti-reflection layer 65b stacked on top of the other in this order. The other surface of the transparent support member 61 is provided with an anti-reflection layer 65a. The first optical anisotropic layer 62 can take the same structure as the first optical anisotropic layer 52 of the phase difference compensation element 50 with the fifth structure.

Additionally, it is preferable to arrange the orientation layers 64a and 64b such that their rubbing directions are at approximately 90° to each other. Thereby, the orientation directions of the liquid crystal molecules in the second optical anisotropic layers 63a and 63b can be different from each other by 90° . (The seventh structure of the phase difference compensation element)

As shown in FIG.12, a phase difference compensation element with the seventh structure has two of the second optical anisotropic layers with different orientation directions across the transparent support member.

Namely, the phase difference compensation element 70 with the seventh structure is provided on one surface of the transparent support member 71 with an orientation layer 74a, a second optical anisotropic layers 73a, a first optical anisotropic layer 72, and an anti-reflection layer 75b stacked on top of the other in this order. The other surface of the transparent support member 71 is provided with another orientation layer 74b, another second optical anisotropic layer 73b, another first optical anisotropic layer 77, and an anti-reflection layer 75a stacked in this order.

The first optical anisotropic layers 72 and 77 can take the same structure as the first optical anisotropic layer 52 of the phase difference compensation element 50. Furthermore, the phase difference compensation element 70 has only to have either one of the first optical anisotropic layers 72 and 77, and the other can be omitted.

Additionally, it is preferable to arrange the orientation layers 74a and 74b such that their rubbing directions are at approximately 90° to each other. Thereby, the orientation directions of the liquid crystal molecules in the second optical anisotropic layers 73a and 73b can be different from each other by 90° .

(The eighth structure of the phase difference compensation element)

As shown in FIG.13, a phase difference compensation element with the eighth structure has the first and the second optical anisotropic layers respectively on the different surfaces of transparent support member.

Namely, the phase difference compensation element 80 with the eighth structure is provided on one surface of a transparent support member 81 with an orientation layer 84, a second optical anisotropic layer 83, and an anti-reflection layer 85 stacked on top of the other in this order. The other surface of the transparent support member 81 is provided with a first optical anisotropic layer 82 and another orientation layer 85a stacked in this order. The first optical anisotropic layer 82 is a periodic multilayer structure of a TiO₂ film 82a and an SiO₂ film 82b.

It is possible to stack two of the phase difference compensation element 80. In this case, they are preferably arranged such that their rubbing directions of the orientation layers are at approximately 90° to each other.

The optical characteristic of the first optical anisotropic layers 12, 22, 32, 42, 52, 62, 72, and 82 is determined by the periodic structure pitch of the periodic multilayer structure made from an inorganic material. Different, therefore, from uniaxially-stretched high polymer films, the first optical anisotropic layers allow to prevent problems of optical nonuniformity, such as variations in the refractive index and reduction in haze value in the high polymer film due to residual stress . The first optical anisotropic layers even increase the optical uniformity, and the liquid crystal layer in the black display state can therefore be compensated optically with a higher degree of accuracy.

In-plane thickness of the first optical anisotropic layers 12, 22, 32, 42, 52, 62, 72, and 82 is controlled in the range of ten and a few nm. With increased smoothness, the first optical anisotropic layer becomes to achieve more optical uniformity. Since the liquid crystal layer in the black display state is optically compensated with a higher degree of accuracy, the light leakage is reduced and shading streaks are prevented on the screen.

The first optical anisotropic layers 12, 22, 32, 42, 52, 62, 72, and 82 hardly expand or shrink over a long term use under high temperature and humidity conditions , and serve to minimize a change in the optical characteristic of the phase difference compensation element.

Especially, the second to fourth structured phase difference compensation elements 20, 30, and 40 have, on the transparent support members 21, 31, and 41, the first optical anisotropic layers 22, 32, and 42 whose in-plane thickness are controlled to the accuracy of ten and a few nm. Namely, the second optical anisotropic layers 23, 33, and 43 are placed on the smooth surface of the first optical anisotropic layers, and they are therefore prevented to have orientation defects. The phase difference compensation elements made in this manner allow the liquid crystal layer to be optically compensated with higher accuracy in the black display state, leading to prevent the light leakage over a wide view range . Such phase difference compensation element enables to produce high image quality and high image contrast liquid crystal devices and the liquid crystal projectors suitable for big screen display.

[Manufacturing method for the phase difference compensation element]

A manufacturing method for the phase difference compensation element is composed of, for example, a first optical anisotropic layer producing step and a second optical anisotropic layer producing step. In the first optical anisotropic layer producing step, several inorganic material-made layers with different refractive index are stacked on the transparent support member in a regular order. In the second optical anisotropic layer producing step, the polymerizable compound is polymerized while the oriented state of the liquid crystal is maintained.

It is possible to form the first optical anisotropic layer directly on the transparent support member, and the second optical anisotropic layer is then formed on the first optical anisotropic layer. Alternatively, the second optical anisotropic layer is firstly formed on the transparent support member through the orientation film, and the first optical anisotropic layer is then formed on this second optical anisotropic layer. Still instead, the first optical anisotropic layer may be formed directly on one surface of the transparent support member, and then the second optical anisotropic layer is formed on the other surface of the transparent support member.

Particularly, the phase difference compensation element is manufactured, for example, in the following method. Firstly, the anti-reflection layer and the second optical anisotropic layer are formed in sequence on a glass substrate of a predetermined size. Although there are no limitation in forming the anti-reflection layer and the second optical anisotropic layer, the anti-reflection layer may be formed by either coating or depositing an organic or inorganic material on the glass substrate, and then the TiO₂ film and the SiO₂ film are alternately deposit to form the periodic multilayer structure. Each layer of the first optical anisotropic layer can have any thickness according to the purpose.

On the formed first optical anisotropic layer, solution of the modified polyvinyl alcohol resin is coated to form the orientation film, the structure of which is then rubbed in one direction with a fabric to have the orientation function. Next , solution of the polymerizable compound containing the liquid crystal molecules is coated on the orientation film by using a bar coater, a spin coater, or a die coater. This coating layer is heated to dry, and the orientation of the liquidmolecules is then settled at a different heat temperature. Lastly, an ultraviolet ray is irradiated to polymerize the polymerizable compound and fix the orientation of the liquid crystal molecules so that the second optical anisotropic layer is obtained. Note that the heat temperature can be the same for the drying of the polymerizable compound and the settling of the orientation of the liquid molecules .

If two second optical anisotropic layers are to be formed on the same surface of the glass substrate, another orientation film should be formed, through the above film formation method, on one of the second optical anisotropic layers made through the above method. In addition, another second optical anisotropic layer is formed on the additional orientation film through the above method. In this case, these two second optical anisotropic layers are preferably arranged such that their rubbing directions become at approximately 90° to each other.

Finally, solution of an intended material is coated to form the anti-reflection layer on the second optical anisotropic layer, and thereby the phase difference compensation element is obtained.

(Liquid crystal display device)

A liquid crystal display of the present invention includes a liquid crystal device with at least a pair of the electrodes and the liquid crystal molecules enclosed between this electrode pair, one or two of the phase difference compensation element disposed on one or both sides of the liquid crystal device, polarizing devices facing the liquid crystal device and the phase difference compensation element, and other components when needed. The liquid crystal device works in, for example, the TN (Twisted Nematic) mode.

For better understanding on the liquid crystal display device of the present invention, in FIG.14 to FIG.17, light from the light source always moves from bottom to top. With regard to several identical components in the same drawing such as the polarizing plates or the optical anisotropic layers, one above in the drawing is called "upper" and one below is called "lower" for a descriptive purpose.

As shown in FIG.14, a liquid crystal display device 100 is composed of a pair of an upper polarizing element 101 (analyzer) and a lower polarizing element 116 (polarizer) arranged in crossed nicols where the absorption axes 102 and 115 are perpendicular to each other, a phase difference compensation element 108 and a liquid crystal device 114 (liquid crystal cell) in between the upper and lower polarizing elements 101 and 116. In place of the upper and lower polarizing elements 101 and 116, a polarization beam splitter such as a Glan-Thompson prism can be used and arranged to face the liquid crystal device 114.

The liquid crystal device 114 includes glass-made upper substrate 109 and lower substrate 113 facing to each other, and nematic liquid crystal 111 is enclosed between the upper and lower substrate 109 and 113. The facing surfaces of the upper and lower substrate 109 and 113 are both provided with several elements (not shown) such as picture electrodes and circuit elements (thin film transistor and the like). Each orientation film has a rubbed surface on the side facing to the nematic liquid crystal 111 for the orientation of the liquid crystal molecules . For the TN mode liquid crystal devices, the orientation films are arranged such that, for example, their rubbing directions 110 and 112 (the direction of the engraved grooves by the rubbing process) are approximately perpendicular to each other. FIG.14 shows the oriented state of the liquid crystal molecules at a normal state, in which no voltage is applied to the liquid crystal device 114. Near the upper and lower substrate 109 and 113, the nematic liquid crystal 111 is oriented in almost the same direction as the rubbing directions 110 and 112 by the function of the rubbed surfaces of the orientation films . Since the rubbing directions 110 and 112 are perpendicular to each other, the molecules of the nematic liquid crystal 111 are twisting their long axes at 90° from the upper substrate 109 toward the lower substrate 113.

It is preferable that the upper and lower polarizing elements 101 and 106 both have the light transmittance of 0.001% and below in crossed nicols, as the light transmittance in parallel nicols is 100%.

Each of the upper and lower polarizing elements 101 and 106 is provided with at least a polarization film, and able to have other elements when needed. Although there is no limitation, the polarization film may be, for example, a stretched and oriented film of hydrophilic polymer such as either polyvinyl alcohol, partially formal polyvinyl alcohol, or partially saponified ethylene-vinyl acetate copolymer, with a dichromatic material such as a dichromatic dye of iodine, azoles, anthraquinones , or tetrazines absorbed therein.

Any of the stretch-orientation process for the polarization films can be used for the polarization films , and it is preferable to use a horizontally uniaxial tenter machine, which aligns the absorption axis of the polarization film substantially perpendicular to a longitudinal direction. The horizontally uniaxial tenter machine has the advantage that foreign substances hardly enter at the time of laminating.

Instead, the polarizing films can be stretch-oriented by the stretching method disclosed in the Japanese Patent laid-open publication No.2002-131548.

The upper and the lower polarizing elements 101 and 106 may have other elements such as a transparent protection film, an anti-reflection film, and an anti-glare film on one or both surfaces of the polarizing film.

The upper and the lower polarizing elements 101 and 116 preferably take the form of a polarizing plate which has the transparent protection film on at least one surface of the polarizing film, or are formed integrally with the phase difference compensation element which, in this case, becomes the support member of the polarizing elements . The transparent protection film is not really specified, and may be made of , for example , cellulose esters such as cellulose acetate, cellulose acetate butyrate, and cellulose propionate, or polycarbonate , polyolefin, polystyrene, polyester or the like.

Particularly, the transparent protection film is preferably cellulose triacetate, polyolefin such as ZEONEX, ZEONOR (both from Zeon corporation), or ARTON (from JSR).

Also, the non-birefringent optical resin material disclosed in the Japanese Patent laid-open publications No.08-110402 and No.11-293116 can be used. While no specific direction is there for an orientation axis (slow axis) of the transparent protection film, the orientation axis is preferably in parallel to the longitudinal direction for the sake of workability. The angle between the slow axis (or orientation axis) of the transparent protection film and the absorption axis (or stretching axis) of the polarizing film is not limited particularly, and determined according to the purpose. It is noted that, if the horizontally uniaxial tenter machine is used, the slow axis (orientation axis) of the transparent protection film becomes substantially perpendicular to the absorption axis (stretching axis) of the polarizing film.

Retardation in the transparent protection film is not limited particularly, and it is however preferably no more than 4o

IOnm at 632.8nm wavelength, and more preferably no more than 5nm.

If the cellulose acetate is used, the retardation is preferably no more than 3nm, and more preferably no more than 2nm, in order to minimize the change in retardation due to environmental temperature and humidity.

While there is no limitation on the forming method, the polarizing plate is preferably manufactured by continuously laminating the polarization film, supplied as a long roll, on the transparent protection film such that the longitudinal directions of the two agree to each other.

To prevent misalignment of the optical axis and entry of foreign matters such as dust, the polarization film and plate are preferably fixed on the phase difference compensation element .

The anti-reflection layer is not really specified, and can be selected according to the purpose. For example, it may be a fluorene polymer coating layer or an optical interference film such as a multimetal deposited layer.

It is preferable that the upper and lower polarizing elements 101 and 116 have optical characteristic and durability (long and short term storage stability) as well or better than a commercially available super high contrast element (for example, HLC2-5618 from Sanritz cooporation) .

The phase difference compensation element 108 incorporates the phase difference compensation element of the present invention. The phase difference compensation element preferably has a ratio between white display transmittance Vw and black display transmittance Vb, i.e. a contrast ratio Vw:Vb of 100:1 or above at the front of the liquid crystal liquid crystal display device 100, more preferably of 200:1 and above, and further preferably of 300:1 and above.

Additionally, it is preferable that the maximum value of the black display transmittance Vb is no more than 10%, more preferably no more than 5% to Vw in all azimuth directions which incline at 60° to the normal direction of the display surface of the liquid crystal display device 100. Using such phase difference compensation element leads to produce a wide view angle and high image contrast liquid crystal display device that does not cause tone reversal.

Furthermore, in order to compensate the liquid crystal molecules with large residual torsion, it is preferable that the liquid crystal display device has no light extinction direction and the light transmittance is no less than 0.01% in all directions when the phase difference compensation element between the pair of polarizing plates in crossed nicols is rotated around its normal direction.

The phase difference compensation element 108 is placed between the upper polarizing element 101 and the liquid crystal device 114, and includes a first optical anisotropic layer 107, an upper second optical anisotropic layer 103, and a lower second optical anisotropic layer 105.

The optical anisotropic layers in the phase difference compensation element 108 are arranged such that the rubbing direction 104 of the orientation film on the upper second optical anisotropic layer 103 becomes at 180° to the rubbing direction 110 of the upper orientation film on the upper substrate 109 of the liquid crystal device 114. In addition, the other optical anisotropic layers are arranged such that the rubbing direction 106 of the orientation film on the lower second optical anisotropic layer 105 becomes at 180° to the rubbing direction 112 of the lower orientation film on the lower substrate 113 of the liquid crystal device 114. These relationships of the rubbing directions can be replaced. For example, the rubbing direction 106 of the orientation film on the lower second optical anisotropic layer 105 becomes at 180° to the rubbing direction 110 of the upper orientation film on the upper substrate 109 of the liquid crystal device 114, while the rubbing direction 104 of the orientation film on the upper second optical anisotropic layer 103 becomes at 180° to the rubbing direction 112 of the lower orientation film on the lower substrate 113 of the liquid crystal device 114.

Also, the first optical anisotropic layer 107 is preferably placed close to the liquid crystal device 114.

FIG.15 shows the black display state of the TN mode liquid crystal display device, namely the oriented state of the liquid crystal molecules when voltage is applied to the liquid crystal device 114. The voltage applied to the liquid crystal device 114 leads the liquid crystal molecules to shift the orientation direction such that their longitudinal axes become perpendicular to the light incident surface. Although ideal is that all the liquid crystal molecules become perpendicular to the light incident surface, the fact is, as shown in FIG.15, that the liquid crystal molecules gradually become perpendicular toward the centre region of the liquid crystal device 114. Therefore, the liquid crystal molecules near the boundaries to the upper and lower substrate 109 and 113 still incline their longitudinal axes to the light incident surface, even when the voltage is applied. These inclined liquid crystal molecules are not in the black display state at some view angles, and cause the light leakage. Generally, the TN mode liquid crystal display devices employ rod-like nematic liquid crystal, which is optically positive birefringent . Therefore, even the liquid crystal molecules completely perpendicular in the center region of the liquid crystal device 114 may give birefringency and cause the light leakage when the liquid crystal display device 100 is viewed from an angle.

Accordingly, the second optical anisotropic layers 103 and 105 are employed to optically compensate the light leakage caused by the birefringency of the liquid crystals in the black display state near the boundaries to the upper and lower substrates 109 and 113. In addition, the first optical anisotropic layer 107, which has the optical characteristic of a non-tilted uniaxial negative index ellipsoid, is employed to optically compensate the birefringency of the liquid crystals in the centre region of the liquid crystal device 114. In this manner, a three dimensional optical compensation is made on the liquid crystal device 114, and the light leakage can be prevented over a wide view angle .

As shown in FIG.16, the phase difference compensation element 108 can be placed on the lower surface of the liquid crystal device 114. Furthermore, as shown in FIG.17, the phase difference compensation element 108 can be divided into 108a and 108b and placed on the upper and lower surfaces of the liquid crystal device 114. In this case, one of first optical anisotropic layers 107a and 107b can be omitted.

It is possible to use the upper substrate 109 and the lower substrate 113 of the liquid crystal device 114 as support members of the phase difference compensation element 108. In this case, the first optical anisotropic layers 107a and 107b, shown in FIG.17, are formed directly on the upper substrate 109 and the lower substrate 113.

(Liquid crystal projector) As shown in FIG.18, a rear projection type liquid crystal projector 200 according to the present invention is provided, on the front surface of a housing 202, with a diffuse transmissive screen 203. Images are projected on the rear surface of the screen 203 and observed from the front side thereof. Incorporated inside the housing 202 is a projection unit 300, the projected images from which are reflected on mirrors 206, 207 and focused on the rear surface of the screen 203. Also, the housing 202 incorporates 5U

a tuner circuit and a well-known electrical circuit for video signals and audio signals. Able to display the reproduced video signal images onto a liquid crystal device of the projection unit 300, this liquid crystal projector also works as a big screen television.

As shown in FIG.19, the projection unit 300 is provided with three transmissive liquid crystal devices 311R, 311G, and 311B, and able to project full color images. Emission light of a light source 312 turns into white light including red, green and blue light essential to the full color image display, as it passes through a cut filter 313 which blocks ultraviolet rays and infrared rays . The white light goes along an illumination light axis , which extends between the light source and the liquid crystal device, and enters a glass rod 314. The light incident surface of the glass rod 314 is located near the focal position of a parabolic reflector used in the light source 312, and the light from the light source 312 effectively enters the glass rod 314.

The white light out of the glass rod 314 is turned into collimated light by a relay lens 315 and a collimate lens 316, and then enters a mirror 317. After reflected on the mirror 317, the collimated white light is separated into two light beams by a dichroic mirror 318R which only passes red light. The red light is reflected by a mirror 319 and illuminates the liquid crystal device 311R from behind. The blue and green light, reflected by the dichroic mirror 318R, is separated into two light beams again by a dichroic mirror 318G which only reflects the green light.

The reflected green light illuminates the liquid crystal device

311G from behind. The blue light passes through the dichroic mirror 318G and is reflected by mirrors 318B, 320, and then illuminates the liquid crystal device 311B from behind. The liquid crystal devices 3HR, 3HG, and 3HB contain the same specification of TN liquid crystals, and displays density pattern images of the red, green and blue images respectively. A combining prism 324 is located such that its center rests at optically equal distance from every liquid crystal devices 3HR, 3HG, and 3HB. Opposite to the light exit surface of the combining prism 324 is a projection lens system 325. Including two dichroic planes 324a and 324b, the combining prism 324 combines the red light from the liquid crystal device 3HR, the green light from the liquid crystal device 3HG, and the blue light from the liquid crystal device 311b and directs them to the projection lens 325. The projection lens 325 has an object side focal point tuned at the light exit surfaces of the liquid crystal devices 3HR, 3HG, and 3HB while its image side focal point is tuned on the screen 203. Therefore, full color images combined on the combining prism 324 are focused on the screen 203.

On the side of the light incident surfaces of the liquid crystal devices 3HR, 3HG, and 3HB, front polarizing plates 326R, 326G, and 326B are provided respectively. On the side of the light exit surfaces of the liquid crystal devices, phase difference compensation elements 327R, 327G, and 327B and rear polarizing plates 328R, 328G, and 328B are provided. The front polarizing plates 326R, 326G, and 326B are aligned in crossed nicols to the rear polarizing plates 328R, 328G, and 328B. The front polarizing plates 326R, 326G, and 326B work as polarizers while the rear polarizing plates 328R, 328G, and 328B work as analyzers. It is noted that the operation of the polarizing plate and the phase difference compensation element is basically the same in all the color channels, although some differences are there between the primary color light beams .

In FIG.20, the phase difference compensation element 327G has the same structure as, for example, the phase difference compensation element 20 (the above described second structure) , and includes a transparent support member 400 made of a glass substrate or the like, a first optical anisotropic layer 401 and a second optical anisotropic layer 402 both provided on top of the transparent support member, an orientation film 403 in between the first and the second optical anisotropic layers 401 and 402, and anti-reflection layers 404a and 404b respectively provided on the undersurface of the transparent support member 400 and the upper surface of the second optical anisotropic layer 402. Constituted of form birefringence bodies made of an inorganic material, the first optical anisotropic layer 401 is a multilayered film of dielectric high refractive index thin films 401a and low refractive index thin films 401b, which are alternately stacked to a total thickness dl . The optical thickness (the product of the physical thickness and the refractive index) of each thin film is smaller enough than the wavelength of light , and preferably from λ/100 to λ/5, more preferably from λ/50 to λ/5, and especially from λ /30 to λ/10. Such configuration enables an easy production of a negative σ-plate. This c-plate is used as a negative uniaxial birefringence plate with the birefringence value Δn2, and arranged such that the thin film forming face is perpendicular to the projection light axis.

The multilayered film with dielectric thin layers of different refractive indices is also used in dichroic mirrors , polarization beam splitters, color composition prisms and anti-reflection films. The multilayered film in such elements uses the thin films whose optical thickness is integer multiplication of λ /4, and works on utilizing optical interference. On the other hand, the multilayered film of the present invention uses the thin films 401a and 401b with the thickness of less than λ /4, and the birefringence Δ nl is determined by the ratio of the optical thickness between the two thin films. It can be said therefore that the multilayered film of the present invention does not utilize the optical interference .

A second optical anisotropic layer 402 is composed of the polymerizable liquid crystal compound which includes the liquid crystal molecules. The liquid crystal molecules are aligned in the hybrid orientation to the thickness direction of the layer, whose thickness is d2.

The phase difference compensation elements 327R and 327B have the same structure as the phase difference compensation element 327G, in which the first and second optical anisotropic layers are layered on the transparent support member. In the phase difference compensation elements 327B for the blue channel, however, one or both of the first and second optical anisotropic layers are thinner than those in the phase difference compensation elements 327R and 327G. Although the total thickness dl of the first optical anisotropic layer can be thinned easily by reducing the number of thin films, the same effect can be made by reducing the thickness of each thin film. The phase difference compensation elements 327R, 327G, and 327B provide negative phase difference compensation function to the color light passing through the liquid crystal devices 3HR, 311G, 311B and having the elliptically polarized components, leading the color light to turn into linearly polarized light and enter the polarizing plates 328R, 328G, and 328B. Thereby, the polarizing plates 328R, 328G, and 328B provide adequate light blocking function, and contrast of the black level is increased when a voltage is applied to the liquid crystal devices 328R, 328G, and 328B for the black display on the screen 203. Since the birefringence function of the liquid crystal devices 311R, -311G, and 311B depend on the wavelength, if the compensation elements 327R, 327G, and 327Bof identical structure are used for each primary color light beams , the phase difference compensation function is lowered to the blue light . In view of this problem, the phase difference compensation element 327B for the blue light has the first and second optical anisotropic layers both thinner than those of the other phase difference compensation elements 327R and 327G. Therefore, positive retardation in the liquid crystal device 3HB is cancelled by the negative retardation in the phase difference compensation element 327B, and good phase difference compensation is achieved. In cost terms , the phase difference compensation elements 327R and 327G may have the same structure. Also, in cost terms, the first optical anisotropic layers or either one of the second anisotropic layers may have the same structure in all the phase difference compensation elements 327R, 327G, and 327B. [Embodiment 1]

A specific embodiment of the phase difference compensation elements 327R, 327G, and 327B for the projection unit 300 of the above liquid crystal projector is explained in detail. [Liquid crystal device] The liquid crystal devices 3HR, 3HB, and 3HG of the projection unit 300 have the cell thickness d of 4.5μm. FIG.21 shows the wavelength dependency of both the birefringence Δn of the nematiσ liquid crystal of the TN liquid crystal device and the average retardation dΔn at 4.5μm cell thickness d. As shown in FIG. 21, the values depend on the wavelength. Also in the drawing, Re is an effective average retardation, which is relevant to 70% of the cell thickness d because all the liquid crystal molecules in the black display state do not alined perpendicularly, as mentioned above. In this embodiment, the liquid crystal material is cyanocyclohexanes nematic liquid crystal, known as "ZLI-1083" (Trade Name) from Merck Ltd. Note that the ratio of the liquid crystal to define the effective average retardation Re is not limited to 70%, but may be decided appropriately according to the composition and kind of the liquid crystal molecules , applied voltage to the substrates , and orientation distribution of the liquid crystal molecules.

[Manufacture of the phase difference compensation element ]

The phase difference compensation element was manufactured as follows . (1) Orientation film

100ml/m₂ of the orientation film coating liquid with a following composition was dropped and spin-coated at lOOOrpm on a glass substrate. This orientation film coating liquid was then dried for three minutes with hot air at 100° C to form an orientation film of 600nm thickness. The orientation film was rubbed to have a predetermined orientation direction.

< Orientation film coating liquid >

Modified polyvinyl alcohol with the following structural formula (3) : 2Og Water (solvent): 36Og Methanol: 12Og Glutaraldehyde (cross linking agent): l.Og

MODIFIED POLYVINYLALCOHOL

5b

(2) Second optical anisotropic layer

Firstly, coating liquid for polymerizable liquid crystal compound was prepared by dissolving 4.27g of discotic liquid crystal compound with the following structural formula (4) , 0.42g of ethylene oxide modified trimethylolpropane triacrylate (V#360 from Osaka organic chemical industry LTD.), 0.09g of cellulose acetate butyrate (CAB551-0.2 from Eastman chemical company), 0.02g of cellulose acetate butyrate (CAB531-1 from Eastman chemical company), 0.14g of photopolymerization initiator (irugacure 907 from Nihon Chiba-Geigy K. K), and 0.05g of sensitizer (kayacure DETX-S from Nippon kayaku Co., ltd.) into 15. Og of methyl ethyl ketone as a solvent .100ml/m² of the prepared coating liquid for polymerizable liquid crystal compound was dropped on the above orientation film and spin-coated at 1500rpm. This coating liquid was heated for five minutes in a constant temperature zone at 130° C to orient the polymerizable liquid crystal compound, which was then polymerized through UV irradiation by a high pressure mercury lamp with irradiation energy of 300mJ/cm² so that the oriented state of the liquid crystal molecules was fixed. Left to cool to room temperature, the second optical anisotropic layer was formed.

(STRUCTURALFORMULA4)

In the second optical anisotropic layer formed as above, the discotic liquid crystal compound was aligned in the hybrid orientation such that the angle between the normal to the plane of the discotic units and the normal to the glass substrate (i.e. orientation angle) was increased from 10° to 60° , toward the air interface side from the glass substrate side. By the method described in the "Design Concepts of Discotic Negative Birefringence Compensation Films, LP-J, SID98 SYMPOSIUM DIGEST (1998)", the orientation angle was calculated from a virtual hybrid orientation refractile body, which had been created from the average value of the retardation measured at several different angles with the ellipsometer (M- 150 from JASCO Corporation) . Then, on top of the second optical anisotropic layer, an additional orientation layer was placed such that its orientation direction became perpendicular to that of the previous orientation film. Furthermore, on top of the additional orientation layer, another second optical anisotropic layer was formed by the same method as the previous second optical anisotropic layer. In the another second optical anisotropic layer, the discotic liquid crystal compound was aligned in the hybrid orientation such that the angle between the normal to the plane of the discotic units and the normal to the glass substrate (i.e. orientation angle) was increased from 12° to 65° , toward the air interface side from the glass substrate side. In addition, the another second optical anisotropic layer was a uniform layer without any defect such as schlieren texture . (3) First optical anisotropic layer

On top of the another second optical anisotropic layer, SiO₂ and TiO₂ were alternately deposited under reduced pressure by a sputtering machine to form a periodic multilayer structure as the first optical anisotropic layer. (4) Anti-reflection layer

On top of the first optical anisotropic layer, SiO₂ and TiO₂ were alternately deposited under reduced pressure by a sputtering machine to form an anti-reflection layer. The anti-reflection layer had the thickness of, for example, 0.24μm.

[Liquid crystal display device]

The phase difference compensation element manufactured accordingly was placed on a normally white TN mode liquid crystal device which gave white display at 1.5V and black display at 3V, and thus a comparative example 1 was obtained.

The physical thickness of the high refractive index thin film layer and the low refractive index thin film layer are respectively 30nm and 20nm (physical thickness ratio is 3:2) in the first optical anisotropic layers of the phase difference compensation elements 327R, 327G, and 327B. Total 42 layers (21 layers each) were stacked to have the total physical thickness of 1.05μm. As shown in a table of FIG.22, the refractive indices of the TiO₂ film and SiO₂ film in the phase difference compensation element of the first embodiment had the wavelength dependency. Also, the birefringence Δnl was measured to prove that it had the wavelength dependency.

All the second optical anisotropic layers in the phase difference compensation elements 327R, 327G, and 327B were tuned to have the physical thickness of, for example, 3μm. As shown in a table of FIG.22, these second optical anisotropic layers exhibited the characteristics of wavelength dependency in the measurement of birefringence Δn2. The optical thickness of the Tiθ₂ film (physical thickness: 30nm) was 76.6nm even at the wavelength of 400nm where the refractive index is large. In addition, the optical thickness of the SiO₂ film (physical thickness: 20nm) was 29.6nm at the wavelength of 400nm. Both optical thicknesses were smaller than λ/5. This condition is satisfied at the blue standard wavelength 450nm and the standard wavelength of other primary colors. Therefore, unlike the conventional film which is based on the optical thickness of λ/4, the multilayered film of the present invention has the optical anisotropy essential to the system of the present invention. Meanwhile, if the optical thickness of each thin film is reduced to less than λ/100, the physical thickness becomes extremely thin. Accordingly, the number of the thin films has to be increased substantially to obtain the desired total physical thickness. This is unproductive and impractical.

Described hereinafter is the fact that the birefringence Δ nl of the first optical anisotropic layer with the above structure is in excellent agreement with the theoretical value derived from a form birefringence theory. When an electromagnetic wave enters perpendicular to the layered surface of the first optical anisotropic layer having two kinds of thin films (the refractive indices n_x, n₂ and the physical thicknesses a, b) stacked alternately at the pitch a+b shorter enough than the wavelength, the phase difference compensation film does not exhibit birefringence effect generally because the electromagnetic field only oscillates parallel to the layered surfaces (TE wave) . However, when electromagnetic wave obliquely enters the layered surface, the electromagnetic field oscillates parallel to the layered surface (TE wave component) and vertical to the layered surface (TM wave component), whose effective refractive indices N_TE and N_TM are expressed by the following equations .

N_TM =/^~ [(a+b)/{(a/n!²) + (b/n₂ ²)}]

The difference between N_TE and N_TM causes the birefringence Δn, which is defined as

Δn = N_TM - NTE If the birefringence Δn derived from the above equation is compared with the measured values shown in FIG.22, they are well agreed.

Since the average retardation dlΔnl of the first optical anisotropic layer is the product of the birefringence Δn at each wavelength and the thickness d (=1.05 μm) of the first optical anisotropic layer, it depends on the wavelength as shown in FIG.22. As will be clear from FIG.22, when the wavelength dependency of the TiO₂ film and the SiO₂ film are compared, the TiO₂ film is more influential to the wavelength dependency of the birefringence Δn than the SiO₂ film. Also, the average retardation d2Δn2 is obtained from the product of the birefringence Δ n2 at each wavelength and the thickness d2 (= 3μm) of the second optical anisotropic layer. Therefore, the average retardation of the whole phase difference compensation element is the sum of the average retardations dlΔnl and d2Δn2.

The graph in FIG.23 shows the effective average retardation Re (o) of the TN liquid crystal device shown in FIG.21 and the average retardation dΔn (A) of the phase difference compensation element of the first embodiment shown in FIG.22 for each wavelength. It means that the phase difference compensation effect becomes better as the effective retardation Re (o) and the average retardation [A.) come closer to each other. According to the graph in FIG.22, while the phase difference compensation element provides an acceptable effect in the wavelength range of 500nm to 600nm, it provides too much effect at the wavelength of less than 500nm, and less effect at the wavelength of more than 600nm. Accordingly, if the first and second optical anisotropic layers have the same sickness for the blue, green and red light, the retardation of blue light is not compensated sufficiently.

[Embodiment 2 ] ol

The wavelength dependency of the phase difference compensation elements can be reduced, without changing the birefringence Δ nl of the first optical anistropic layer, by adjusting the total thickness dl of the first optical anistropic layer such that, as shown in FIG.24, the average retardation (A) of the phase difference compensation element for blue light corresponds with the effective average retardation (o) at the standard wavelength of blue light (450nm). It is also possible to have better phase difference compensation effect for red light by increasing the total thickness dl of the first optical anistropic layer such that the average retardation (A) correspond with the effective average retardation (o) at the standard wavelength of red light (650nm).

FIG.25 shows the characteristics of the phase difference compensation element according to the second embodiment of the present invention. All the first optical anisotropic layers of the second embodiment had the same multilayer structure as described in the first embodiment, but each of them had different total thickness dl adjusted for the corresponding primary color light beam. More specifically, the total thickness dl of the first optical anisotropic layer was 0.85μm for the blue light, 1.05μm for the green light, and 1.1 μm for the red light. Thereby, as shown in FIG.24, the average retardation dΔn of the phase difference compensation element was adjusted according to the corresponding primary color light , and better compensation effect was achieved.

In this case, it is preferable that only one kind of the first optical anisotropic layer is prepared and the total number of layers is changed according to the corresponding primary color light beam. In the above second embodiment, the total number of the first optical anisotropic layers in the phase difference compensation element was 34 layers for the green light, 42 layers ΌΔ

for the blue light, and 44 layers for the red light. In this embodiment, the phase difference compensation films for blue, green, red light have 72, 80, 82 thin film layers, respectively, the average retardation (A) can be regarded as corresponding approximately with the effective average retardation (o) within the wavelength range of 500nm to 700nm, as shown in FIG.23, it is possible to use the green light phase difference compensation film to the red light so that the whole visible light region can be compensated by two kinds of the phase difference compensation elements.

Firstly prepared were three kinds of the phase difference compensation elements, in each of which the thickness of the film deposited on the glass substrate was adjusted according to the corresponding primary color light. These phase difference compensation elements were then closely fixed on the light exit side substrates of the TN liquid crystal devices in each color channel of a liquid crystal projector. Also prepared was a comparative liquid crystal projector equipped with conventional phase difference compensation elements in every color channel. An image signal for the black display was input to the both liquid crystal projectors, and the black displays were projected on the screens for comparison.

While the black display of the comparative liquid crystal projector included some blue components on the screen, the black display of the image liquid crystal projector of the present invention was intense black having almost no additional color components. In addition, when blue gradation images were displayed, the intensity of a low brightness area, the area of nearly black, went lower than that of the comparative liquid crystal projector. Moreover, the liquid crystal projector of the present invention was able to express the differences in the brightness level more clearly than the comparative one. The two liquid crystal projectors were also measured for the contrast ratio between the full screen white display and the full screen black display. While the comparative liquid crystal projector showed the contrast ratio of 500:1, the liquid crystal projector of the present invention showed an improvement of 700 : 1.

It is clear from these results that the phase difference compensation system of the present embodiment is able to give more power of expression especially in the low brightness areas, and also able to deepen the black color and improve the sharpness of the full color projection images.

[Embodiment 3]

In the third embodiment, the first optical anisotropic layers had the same total thickness (e.g. lμm) for every color, while the second optical anisotropic layers have different thickness (e.g. B: 2.5μm, G: 3.05μm, R: 3.3μm). The average retardation and the properties are shown respectively in a graph of FIG.26 and a table of FIG.27. As evidenced by this graph, optimum average retardation can be obtained by changing the thickness of the second optical anisotropic layer, instead of the first optical anisotropic layer.

[Embodiment 4]

In the first and second embodiments, one of the first and the second optical anisotropic layers is changed in thickness for each color. It is possible, however, to change the thickness of both the first and the second optical anisotropic layers for each color. FIG.28 and FIG.29 respectively show a graph of the average retardation and a table of the properties of the phase difference compensation element in which the first and the second optical anisotropic layers are changed in thickness as follows. As evidenced by this graph, an intended average retardation can be obtained by changing the thickness of both the first and second optical anisotropic layers. The first optical anisotropic layer (B: 1.05μm, G: 1.2μm, R: 1.25μm)

The second optical anisotropic layer (B: 2.25μm,G: 2.5μm, R: 2.6μm) [Embodiment 5]

Made by the method of the second embodiment , the liquid crystal display device of the fifth embodiment was provided on the upper surface of the transparent support member with the first optical anisotropic layer, the orientation layer, the second optical anisotropic layer, the another orientation layer, the another second optical anisotropic layer, and the anti-reflection layer formed in this order. The lower surface of the transparent support member was provided with the another anti-reflection layer . [Embodiment 6]

Made by the method of the second embodiment, the liquid crystal display device of the sixth embodiment was provided on the upper surface of the transparent support member with the orientation layer, the second optical anisotropic layer, the first optical anisotropic layer, the another orientation layer, the another second optical anisotropic layer, and the anti-reflection layer formed in this order. The lower surface of the transparent support member was provided with the another anti-reflection layer. [Embodiment 7]

Made by the method of the second embodiment , the liquid crystal display device of the seventh embodiment was provided on the upper surface of the transparent support member with the orientation layer, the second optical anisotropic layer, and the anti-reflection layer formed in this order. The lower surface of the transparent support member was provided with the another orientation layer, the another second optical anisotropic layer. the first optical anisotropic layer, and the another anti-reflection layer formed in this order.

[Embodiment 8 ]

Made by the method of the second embodiment, the liquid crystal display device of the eighth embodiment was provided on the upper surface of the transparent support member with the orientation layer, the second optical anisotropic layer, and the anti-reflection layer formed in this order. The lower surface of the transparent support member was provided with the first optical anisotropic layer, the another orientation layer, the another second optical anisotropic layer, and the another anti-reflection layer formed in this order.

[Embodiment 9 ]

The liquid crystal display device of the ninth embodiment was the same as that of the seventh embodiment , except that it used the orientation film coating liquid with a following composition.

[Orientation film coating liquid]

Sunever 150 (from Nissan chemical industries, ltd.): 2Og Polyimide thinner (from Nissan chemical industries, ltd. ) : 2Og

[Embodiment 10]

The liquid crystal display device of the tenth embodiment was the same as that of the eighth embodiment , except that the second optical anisotropic layer on the lower surface had 95% thickness of the second optical anisotropic layer on the upper surface.

[Embodiment 11 ]

The liquid crystal display device of the eleventh embodiment was the same as that of the eighth embodiment, except that the angle between the both second optical anisotropic layers was set at 92° . (Comparative example 1)

The liquid crystal display device of the comparative example 1 was the same as that of the second embodiment, except that a TAC (triacetate cellulose) film was used as the first optical anisotropic layer.

(Evaluation on view angle dependency of the liquid crystal display devices)

The liquid crystal display devices of the second to eleventh embodiments and the comparative example 1 were measured from a point on 20° angle of attack and 45° azimuth to the front of the display surface, by a conoscope (made by Autronic-Melcher) , for the contrast ratio. Here, the contrast ratio is a comparison of the white display transmittance and the black display transmittance to backlight (white display transmittance/black display transmittance). The test result is shown in TABLE 1.

(Evaluation on image contrast of the liquid crystal display devices)

The liquid crystal display devices of the second to eleventh embodiments accommodated for each RGB color and the liquid crystal display device of the comparative example 1 were individually installed in TN liquid crystal projectors to compose the liquid crystal projectors of twelfth to twenty first embodiments and a comparative example 2. These liquid crystal projectors were measured for luminance and contrast ratio (white display transmittance/black display transmittance) on the screen surface using the projection light for both the white display and the black display. The test result is shown in TABLE 1. [TABLE 1 ]

It is recognized, from the test results, that the liquid crystal display devices of the second to eleventh embodiments have an equivalent wider view angle and lower view angle dependency than the comparative example 1. Additionally, the image contrast is improved in the liquid crystal display devices of the twelfth to twenty first embodiments, compared to the comparative example 2. As described above, the phase difference compensation system according to the present invention improves the contrast and the color balance of the liquid crystal projectors . The phase difference compensation system is characterized that the physical structure of the phase difference compensation film in at least the blue color channel is different from those in the other color channels. Although the physical structure may be changed by the choice of either the materials of the thin films, the thickness of each thin film layer, or the total thickness of stacked layers. it is changed in the above embodiments by changing the total number of the high and the low refractive index layers in the first optical anisotropic layer or the thickness of the second optical anisotropic layer. In this manner, more than two kinds of the phase difference compensation elements can be produced from a single kind of each of the first optical anisotropic layer and the second optical anisotropic layer. Each layer in the optical anisotropic layers may have the same thickness. It is therefore possible to control the physical structure of the phase difference compensation elements on an easily controllable parameter such as the total number of layers or the total thickness of the layers , and thereby the mass productivity is increased without losing a certain level of quality. The birefringence Δnl may be controlled by changing the physical thickness ratio between the high and the low refractive index layers in the first optical anisotropic layer. In this case, the first optical anisotropic layers for the primary color light beams can be changed individually in the total thickness dl according to the values of the birefringence Δnl. It is also possible to change the combination of the high and the low refractive index materials in accordance with the color.

The high and low refractive index thin film layers in the first optical anisotropic layer are easily made to an intended thickness by the vacuum deposition operation or the sputtering operation. The deposition equipment has shutters to shield the substrate from the vapor source materials. The shutters are alternatively open and close while evaporating the source materials , so that the two kinds of thin film layers are alternately deposited on the substrate. Instead of the shutters, the substrate may be held on a holder that moves the substrate at a predetermined speed. The thin film layers are alternately deposited by passing the substrate above the evaporating source materials . As for the materials for inorganic thin film layers , any known materials for deposition may be utilized. Examples of the materials for the inorganic thin films are TiO₂, SiO₂, ZrO₂, MgO, CeO₂, SnO₂, Ta₂O₅, Y₂O₃, LiNbO₃, MgF₂, CaF₂, Al₂O₃, and Nb₂O₅.

If the optical anisotropic layer is made from thin film layers obtained by the deposition or sputtering process, a substrate for the supporting member can be attached to one of optical components, such as a lens that constitutes an illumination optical system or a projection optical system, and a glass substrate used in the liquid crystal device. Instead, it is possible to use these optical components as the support member of the thin film layers . This kind of technique leads to reduce the number of components and, thus, positioning and angle adjustment works .

If formed on the substrate of the liquid crystal device, the optical anisotropic layer can be on either interior or exterior surface of the substrate. However, the optical anisotropic layer, if formed on the interior surface, has less air interfaces and serves to prevent image deterioration or light intensity loss due to surface reflection. Noted that the liquid crystal device has two substrates , an active side substrate to be applied with signal voltage for each pixel and a counter substrate used as a common electrode. The optical anisotropic layer can be formed on either substrate. Additionally, it is preferable to apply the anti-reflection process on one or both surfaces of the optical anisotropic layer when needed. Especially, using the phase difference compensation element with stacked thin film layers leads to increase the manufacturability because it obtains the anti-reflection property of thin film interference during the film formation process. The thin film layers stacked in the first optical anisotropic layer do not necessarily meet the physical thickness ratio of 3:2, but meet the ratio of , for example , 1:1. Furthermore , the first optical anisotropic layer is not necessarily made by two kinds of thin layers stacked alternately on top of the other. For example, more than three kinds of thin layers with different refractive indices may be stacked in any order to any thickness, as appropriate according to the factors such as ease of film formation, absorption of deformation from the internal stress of each layer, wavelength dependency of the refractive index, and so forth. Also, it is within the scope of the present invention to combine any of the above described form birefringence bodies with phase difference compensation films which have the phase difference compensation function and are made of a durable polymer film.

When the phase difference compensation element composed of the multilayered film is combined with the transmissive liquid crystal device, as shown in FIG.19, the phase difference compensation elements 327R, 327G, and 327B are placed between the light exit surface side of the liquid crystal devices 3HR, 3HG, 311B and the front polarizing plates, i.e. the analyzers, 328R, 328G, and 328B respectively. However, the phase difference compensation elements 327R, 327G, and 327B can be placed between the light incidence surface side of the liquid crystal device 3HR, 311G, 311B and the rear polarizing plates, i.e. the polarizers, 326R, 326G, and 326B.

Furthermore, as shown in FIG.30, a first phase difference compensation element 452 may be provided between a polarizer 450 and the light incident surface of a liquid crystal device 451, and a second phase difference compensation element 454 may be provided between an analyzer 453 and the light exit surface of the liquid crystal device 451. In this case, the retardation in the liquid crystal device 451 is compensated by the combination of the first and the second phase difference compensation elements 452 and 454. This configuration has the advantage in thickness over the single phase difference compensation element whose total thickness sometimes becomes too much. Generally the multilayered film with too much thickness is easily cracked and lowers the yield. Separated phase difference compensation elements will easily solve such problem.

The phase difference compensation system according to the present invention is also applicable to the liquid crystal projector with reflective liquid crystal devices. The reflective liquid crystal device comprises a mirror behind the liquid crystal layer, so that incident light passes through the liquid crystal layer twice. Thus, it is necessary to design the parameters of the phase difference compensation system in considering that the retardation in the liquid crystal layer becomes double as the transmissive type having the same cell thickness. For example, as shown in FIG.3IA, when the reflective liquid crystal device takes an off-axis behavior (separated incident light axis and exit light axis), a phase difference compensation element 457 is disposed near a liquid crystal device 456 and used with a polarizer 458 and an analyzer 459. In this case, the incident light passes through the liquid crystal layer twice and also passes through the phase difference compensation element 457 twice. Accordingly, the design can be made simply based on the cell thickness (thickness d of the liquid crystal layer) of the liquid crystal device, similar to the above embodiments.

In the case where a phase difference compensation element

460 is placed near either the polarizer 458 or the analyzer 459, as shown in FIG.31B, it is necessary to design the retardation compensation element 460 based on a target thickness, which is twice as the cell thickness of the liquid crystal device 456. Additionally, it is possible to provide separate phase difference compensation elements near the polarizer 458 and the analyzer 459. In this case, the phase difference compensation elements are designed based on the cell thickness of the liquid crystal device 456. Of course, the phase difference compensation element is firstly made based on the thickness twice as liquid crystal device 456, and then divided into two pieces individually having an intended ratio of thickness. Note that since an actual thickness of the first and second optical anisotropic layers may be changed depending on the incident angle and the exit angle of light, the phase difference compensation element should be made in consideration of such conditions.

Industrial Applicability The phase difference compensation system of the present invention can be applied to a three-panel type liquid crystal device. The three-panel type liquid crystal device can be used in a liquid crystal projector, a rear projection type television which incorporates the liquid crystal projector, and the like.

Claims

1. A phase difference compensation system for compensating phase difference caused by birefringence of each three primary color light beam passing through one of first to third liquid crystal devices, said liquid crystal devices being provided separately in one of light paths for said three primary color light beams, said phase difference compensation system comprising: first to third phase difference compensation elements corresponding to said first to third liquid crystal devices , each of said phase difference compensation elements being placed at least one side of a light incident surface side and a light exit surface side of said liquid crystal device, each of said phase difference compensation elements including: a transparent support member; and a first optical anisotropic layer formed of an inorganic material and placed on said transparent support member; and a second optical anisotropic layer formed of a polymerizable compound and placed on said transparent support member, wherein said first phase difference compensation element having a different structure of said first optical anisotropic layer and/or said second optical anisotropic layer from at least one of said second and third phase difference compensation elements .

2. A phase difference compensation system described in claim 1, wherein said different structure is thickness of layer, said first and/or second optical anisotropic layer having different thickness among said first to third phase difference compensation elements . ^

3. A phase difference compensation system described in claim 1 , wherein said first optical anisotropic layer is composed at least of a high refractive index thin film layer and a low refractive index thin film layer stacked alternately on top of the other, each of said thin film layer having a thickness of no less than 1/100 and no more than 1/5 of standard wavelength of the corresponding primary color light beam.

4. A phase difference compensation system described in claim 3, wherein a total number or a total thickness of said high and low refractive index thin film layers is different among said first to third phase difference compensation elements .

5. A phase difference compensation system described in claim 1, wherein said second optical anisotropic layer is formed of a polymerizable liquid crystal compound having liquid crystal molecules, said liquid crystal molecules having hybrid orientation in which orientation angles of said liquid crystal molecules changes in the thickness direction of said second optical anisotropic layer.

6. A phase difference compensation system described in claim 5, wherein said second optical anisotropic layer is different in one or both of thickness and distribution of said orientation angles among said first to third phase difference compensation elements.

7. A phase difference compensation system described in claim 5, wherein each of said phase difference compensation elements has two ore more said second optical anisotropic layers, each of which is different in at least one of thickness, distribution of said orientation angles, and orientation direction among said first to third phase difference compensation elements .

8. A phase difference compensation system described in claim 1 , wherein said first optical anisotropic layer is placed on the side of said light incident surface of said liquid crystal device, while said second optical anisotropic layer is placed on the side of said light exit surface of said liquid crystal device.

9. A phase difference compensation system described in claim 1 , wherein said first to third phase difference compensation elements are placed in each of said light paths for three primary color light beams in a liquid crystal projector.