KR100688001B1 - Optical elements, lighting devices and liquid crystal displays - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the development of an optical element and an illumination device capable of forming a liquid crystal display device or the like which is difficult to change color due to a change in azimuth angle caused by strabismus.

The present invention is composed of a laminate having a reflective polarizing plate 1 and a dichroic polarizing plate 3 which separate incident light into polarized light through reflection and transmission, and is disposed so that the reflective polarizing plate is inward on a surface light source so as to transmit transmitted light. In the case of, where the color at any azimuth angle of the predetermined elevation angle is x1 and y1 and the color at the point where the azimuth angle is changed at the same elevation angle is x2 and y2, between two points calculated by Equation 1 below An optical element having a color change of less than or equal to 0.06, an illuminating device having the optical element on the surface side of a surface light source having a reflecting layer on the back side thereof so that its reflective polarizing plate is inward, and a liquid crystal cell on the light exit side of the illuminating device Provide a liquid crystal display device:

A large liquid crystal display device having a good display quality can also be advantageously formed.

Description

OPTICAL ELEMENT, ILLUMINATING DEVICE AND LIQUID-CRYSTAL DISPLAY DEVICE}             

1 is a cross-sectional view of an example of an optical element,

2 is a cross-sectional view of an example lighting device;

3 is a sectional view of another lighting device example;

4 is a sectional view of an example of a liquid crystal display device;

5 is a cross-sectional view of another liquid crystal display device example.

Explanation of symbols for main parts of the drawings

1: reflective polarizer,

11: supporting substrate,

12, l3: cholesteric liquid crystal layer,

2: 1/4 wave plate,

21, 22: retardation layer,

3: dichroic polarizer,

4: light guide plate (surface light source),                 

41: reflective layer,

42: light source,

5: prism array layer,

6: liquid crystal cell (liquid crystal display device),

61: dichroic polarizing plate.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element capable of forming a liquid crystal display device or the like which is difficult to change color due to a change in the azimuth azimuth and an illumination device using the same.

In the group to which the present inventors belong, first, the incident light has a function of separating the incident light into polarized light through reflection and transmission, and the deviation from the in-plane average of transmittance and color is 0.5 according to ΔE according to Hunter's color difference equation of Equation 2 below. And an optical element comprising a reflective polarizing plate having a quarter-wave plate and a dichroic polarizing plate, which are from 5.0 to 5.0, if necessary (Japanese Patent Laid-Open No. 99-311710).

Where                         

L is the brightness index;

a and b are the chromaticity indices.

This is for the purpose of improving luminance and preventing display unevenness by applying such ΔE to a liquid crystal display or the like. However, in the frontal direction, a good display is obtained, but there is a problem that the color is greatly changed due to the change of the azimuth angle by strabismus.

There is a proposal of a liquid crystal display device in which the amount of change in chromaticity in the color of the front and the strabismus is suppressed (Japanese Patent Laid-Open No. 98-319235), but the color change due to the change in the azimuth azimuth cannot be coped with. Certainly, even if the azimuth angle 0 ° or 45 ° due to the angle of elevation 70 ° and the front chromaticity change could be suppressed to the same 0.04, the chromaticities x and y were both positive in the azimuth 0 ° and in the negative direction in the opposite direction at 45 °. In the case of a change in color, the chromaticity is changed 0.08 by changing the azimuth angle from 0 ° to 45 °, thereby greatly changing the color. Therefore, the countermeasure cannot sufficiently cope with the color change due to the change in the azimuth azimuth when the coloring direction (government) differs from the azimuth azimuth.

An object of the present invention is to develop an optical element and an illumination device capable of forming a liquid crystal display device or the like which is difficult to change color due to a change in the azimuth angle.

The present invention is made up of a laminate having a reflective polarizing plate and a dichroic polarizing plate that separate incident light into polarized light through reflection and transmission, and when the reflective polarizing plate is disposed on the surface light source so as to be inward, a predetermined amount of light is transmitted. When the color at any azimuth angle of the elevation angle is x1 and y1 and the color at the point where the azimuth angle is changed at the same elevation angle is x2 and y2, the color change amount between two points calculated by Equation 1 below is 0.06 or less. An optical element comprising: an optical element on the surface side of a surface light source having a reflective layer on the back side thereof, so that the reflective polarizing plate thereof is inward; and a liquid crystal cell on the light exit side of the illumination device. Provided is a liquid crystal display device having:

Equation 1

The optical element according to the present invention is composed of a laminate having a reflective polarizing plate and a dichroic polarizing plate that separate incident light into polarized light through reflection and transmission, and is disposed so that the reflective polarizing plate is inward on the surface light source so as to transmit transmitted light. In one case, when the color at any azimuth angle of the predetermined elevation angle is x1 and y1 and the color at the point where the azimuth angle is changed at the same elevation angle is x2 and y2, the color between two points calculated by Equation 1 below The amount of change consists of not more than 0.06:

Equation 1

An example of the optical element is shown in FIG. 1. This element has at least a reflective polarizing plate 1 for separating incident light into polarized light through reflection and transmission, and a dichroic polarizing plate 3 stacked thereon. In addition, in the optical element of the illustrated example, the reflective polarizing plate 1 is configured as a circularly polarized light separating layer formed by superposing two cholesteric liquid crystals 12 and 13 on the supporting substrate 11, and a phase difference layer ( A quarter wave plate 2 consisting of 21 and 22 is installed. And the dichroic polarizing plate 3 is laminated on the quarter wave plate 2.

Reflective polarizers provide polarization to dichroic polarizers to suppress absorption losses and to improve luminance of liquid crystal displays by improving light utilization efficiency. For example, Japanese Patent Application Laid-Open No. 92-268505 or PCT Publication Reflects and transmits incident light such as natural light, such as a linearly polarized light splitting element that transmits linearly polarized light of a predetermined polarization axis and reflects other light composed of a multilayer thin film or the like described in Japanese Patent Application Publication No. 95/17691, or an alignment layer of cholesteric liquid crystal. It can be formed as a suitable material exhibiting the function of separating into polarized light through.

According to the alignment layer of the cholesteric liquid crystal, a circularly polarized light separation layer for separating natural light into left and right circularly polarized light through reflection and transmission can be obtained. The cholesteric liquid crystal exhibits a circular polarization separation function in which wavelength characteristics differ depending on the difference in the spiral pitch of the grandjean orientation, but in the present invention, the cholesteric liquid crystal may be a circular polarization separation layer having an appropriate layer form of a single layer or a multilayer.

In addition, as an example of the said layer form, the circle | corner which consists of a single layer or double layer circularly polarized light separating layer which a spiral pitch changes in thickness direction, and the superposition body of two or more layers of cholesteric liquid crystal layers from which the center wavelength of reflected light differs like the example of FIG. Or a circularly polarized light separating layer in which the helical pitch of two or more cholesteric liquid crystal layers above the spiral pitch in which they are combined, or the spiral pitch changes in the thickness direction is superimposed in the order of long and short lengths according to the central wavelength of the reflected light. have.

The superposition of two or three or more layers of the cholesteric liquid crystal layer in which the change in the thickness direction of the spiral pitch or the central wavelength of the reflected light is different, that is, the spiral pitch is different, is for the purpose of optical wavelength inversion of the separation function. That is, as a cholesteric liquid crystal layer of a single layer constant orientation, there is a limit in the wavelength range which shows selective reflectivity (circular polarization dichroism) normally, and the limit may be a wide range which affects the wavelength range of about 100 nm, but the wavelength Since the range does not reach the entire range of visible light expected when applied to a liquid crystal display or the like, an object thereof is to expand the wavelength range showing the circularly polarized dichroism by expanding the spiral pitch variation range.

In addition, by overlapping various kinds of spiral pitches of the cholesteric liquid crystal layer having a central wavelength of selective reflection in the range of 300 to 900 nm in a combination reflecting circular polarizations in the same direction, the visible region can be covered. The circularly polarized light separation layer can be efficiently formed. In addition, the overlapping point of reflecting circularly polarized light in the same direction is provided with a phase state of circularly polarized light reflected by each layer, and the polarization increase in a state that can be used by preventing the polarization state from being different in each wavelength range. For the purpose.

In addition, the superposition of the cholesteric liquid crystal layer in the order of long and short periods based on the central wavelength of the reflected light in the circularly polarized light separating layer is for the purpose of suppressing color change of transmitted light due to visual change. In this case, a cholester having the same helical pitch as a cholesteric liquid crystal layer having a different helical pitch between the cholesteric liquid crystal layers having the same helical pitch, having one or two or more layers interposed in the short and long order of the center wavelength. The layer structure etc. which contain 2 or more layers of a steric liquid crystal layer are also acceptable.

Although low molecular weight cholesteric liquid crystal etc. can also be used for formation of a circularly polarized light isolation layer, a cholesteric liquid crystal polymer can be used preferably from a viewpoint of the handleability, thin film property, etc. of the obtained reflective polarizing plate. In this case, the reflective polarizing plate can be obtained as a monolayer such as a cholesteric liquid crystal polymer film or a multilayer such as a plastic film or the like. A favorable circularly polarized light separating layer is oriented in a state in which the cholesteric liquid crystal polymer is oriented in a state in which there are few defects such as domains.

Moreover, as a cholesteric liquid crystal polymer, a suitable thing can be used and it is not specifically limited. Therefore, the conjugated linear atomic group (mesogen) which gives liquid crystal aligning property can use various things, such as main chain type or side chain type, introduce | transduced into the main chain or side chain of a polymer. The cholesteric liquid crystal polymer having a large birefringence difference can be preferably used in terms of widening the wavelength range of selective reflection and reducing the number of layers or the margin for wavelength shift at the dash-field angle. Moreover, as a liquid crystal polymer, it is preferable that glass transition temperature is 30-150 degreeC from a viewpoint of handleability or orientation stability in practical temperature.

In addition, examples of the main chain type liquid crystal polymer include, for example, polyesters, polyamides, and polycarbonates having a structure in which a mesogenic group composed of a para-substituted cyclic compound or the like is bonded through a spacer portion that provides flexibility. And polymers such as polyesterimide series.

In addition, examples of the side chain type liquid crystal polymer include polyacrylate, polymethacrylate, polysiloxane, polymalonate, and the like as a main chain skeleton, and as a side chain, a para-substituted cyclic compound, etc., as necessary, through a spacer portion composed of a conjugated atomic group. The thing which has a low molecular liquid crystal compound (mesogen part), the nematic liquid crystal polymer containing the low molecular chiral agent, the liquid crystal polymer of chiral component introduction, the mixed liquid crystal polymer of nematic system and a cholesteric system, etc. are mentioned.

As described above, for example, a nema composed of para-substituted aromatic units or para-substituted cyclohexyl ring units such as azomethine type, azo type, azoxy type, ester type, biphenyl type, phenylcyclohexane type and bicyclohexane type. Even in the case of having a para-substituted cyclic compound imparting tick orientation, cholesteric alignment may be performed by a method of introducing a suitable chiral component, a low molecular chiral agent, or the like composed of a compound having a subsidiary carbon or the like (Japanese Patent Laid-Open Publication No. 80-21479, US Pat. No. 5,332,522, etc.). In addition, as a terminal substituent of the para position in a para substituted cyclic compound, a cyano group, an alkyl group, an alkoxy group etc. may be suitable, for example.

Further, as the spacer showing the flexibility, for example, polymethylene chain - and the like can be - (CH _{2) n} -, a polyoxymethylene chain _{- (CH 2 CH 2 O)} m. The repeating number of the structural units forming the spacer portion is appropriately determined by the chemical structure of the mesogenic portion, etc., in general, n is 0 to 20, particularly 2 to 12, in the case of the polymethylene chain, and m is the polyoxymethylene chain. 0 to 10, in particular 1 to 3.

Formation of the circularly polarized light separating layer which consists of a cholesteric liquid crystal polymer can be performed by the method according to the orientation process of the conventional low molecular liquid crystal, etc., for example. I.e., including, for example, supporting the polyimide on a substrate, polyvinyl alcohol, polyester, polyarylate, polyamide-imide, an alignment film a polyester to form a film of polyetherimide such as rubbing treatment with rayon cloth or the like, all over the deposited layer of SiO ₂ , A liquid crystal polymer is developed on a suitable alignment film composed of an alignment film or the like by stretching treatment, heated to a glass transition temperature or more below the isotropic transition temperature, and cooled to below the glass transition temperature in a state in which the liquid crystal polymer molecules are oriented in a glass. The method of making it into the state and forming the solidified layer to which the said orientation was fixed is mentioned.

Examples of the supporting substrate include plastics such as triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyethersulfone, amorphous polyolefin, modified acrylic polymer and epoxy resin. Suitable ones, such as a single layer or lamination, a stretched film, or a glass plate, can be used. From a viewpoint of thickness reduction etc., a plastic film is preferable.

The development of the liquid crystal polymer is appropriate, for example, by sputter coating, roll coating, flow coating, printing, dip coating, cast film formation, bar coating, gravure printing, etc. It develops thin layer by the method and can implement this by the method of a drying process etc. as needed. As said solvent, suitable things, such as methylene chloride, cyclohexanone, trichloroethylene, tetrachloroethane, N-methylpyrrolidone, tetrahydrofuran, can be used, for example.

Further, a heating melt of the liquid crystal polymer, preferably a heating melt in a state showing an isotropic phase, is developed in accordance with the above, and, if necessary, does not use a solvent such as a method of expanding and solidifying again in a thin layer while maintaining the melting temperature. The liquid crystal polymer can be developed also by a method, and thus a method with good hygiene and the like of the working environment.

The heat treatment for orientating the developing layer of the liquid crystal polymer can be carried out by heating the temperature range from the glass transition temperature of the liquid crystal polymer to the isotropic transition temperature, that is, the temperature range in which the liquid crystal polymer shows a liquid crystal phase as described above. . In addition, fixation of an orientation state can be performed by cooling below glass transition temperature, and its cooling conditions are not specifically limited. Usually, the natural cooling system is generally employed since the heat treatment can be performed at a temperature of 300 ° C. or lower. Moreover, various additives, such as a stabilizer, a plasticizer, and metals, can be mix | blended with the developing solution of a cholesteric liquid crystal polymer as needed.

The thickness of the solidified layer of the liquid crystal polymer formed on the supporting substrate is 0.5 to 50 µm, particularly 1 to 30 µm, particularly preferably 2 in terms of prevention of confusion in orientation or lowering of transmittance, width of the wavelength range of selective reflection, and the like. To 10 µm. The liquid crystal polymer solidified layer on a support base material can be used as an integrated substance with a support base material, can also be peeled off from a support base material, and can also be used as a film. Moreover, when it has a support base material, the total thickness containing this base material is 2-500 micrometers, Especially 5-300 micrometers, Especially preferably, it is 10-200 micrometers.

The manufacture of the circularly polarized light separating layer in which the helical pitch changes in the thickness direction is performed by, for example, an operation of bonding two or three or more predetermined sheets of cholesteric liquid crystal polymer layers subjected to an alignment treatment by thermocompression bonding. can do. For the thermocompression treatment, a suitable method such as a method of heating the cholesteric liquid crystal polymer layer below the glass transition temperature and below the isotropic transition temperature through a suitable heat compression means such as a roll laminator and pressing the treatment may be adopted. In the case of the solidified layer of the liquid crystal polymer comprised by the integral substance with a support base material, the circularly-polarized light separation layer which a spiral pitch changes in the thickness direction can be obtained by superimposing according to the above so that the solidified layers may closely contact.

Further, the circularly polarized light separating layer whose spiral pitch is changed in the thickness direction may exhibit a wavelength range of continuous reflected light, or may show a wavelength range of discontinuous reflected light. The circularly polarized light separating layer which is preferable from a viewpoint of color nonuniformity prevention etc. shows the wavelength range of continuous reflected light. The production of such a circularly polarized light separation layer, for example, by heating the superposed body of the cholesteric liquid crystal polymer layer formed by the thermocompression operation or the like below the glass transition temperature or less than the isotropic transition temperature to form an upper and lower layers at the adhesion interface. It can carry out by the method of forming the layer which the cholesteric liquid crystal polymer mixed.

In the above, the cholesteric liquid crystal polymer layer formed by mixing the cholesteric liquid crystal polymer of the upper and lower layers forms a circularly polarized light separation layer in which the spiral pitch is different from the upper and lower layers, and the spiral pitch in the thickness direction is changed into a multi-stage layer. Usually, the said spiral pitch takes the intermediate value of the cholesteric liquid crystal polymer layer which forms an upper and lower layer, and forms the area | region which shows the wavelength range of continuous reflected light with an upper and lower layer. Therefore, when used in combination of the cholesteric liquid crystal polymer layer in which the wavelength range of the reflected light does not overlap in the upper and lower layers, that is, the combination in which the deficiency region due to discontinuity exists in the wavelength range of the reflected light, the collet formed by mixing of the upper and lower layers The steric liquid crystal polymer layer may fill the deficiency region to continue the wavelength region of the reflected light.

Thus, for example, using two cholesteric liquid crystal polymer layers having a reflection wavelength range of 500 nm or less and 600 nm or more, a circularly polarized light separation layer that also reflects light in a wavelength range of 500 to 600 nm, which is a discontinuous range of the reflection wavelength range, is obtained. This means that a small cholesteric liquid crystal polymer layer can be superimposed to form a circularly polarized light separation layer exhibiting a broad band of reflected wavelength range.

The reflective polarizing plate, especially the reflective polarizing plate having a circularly polarized light separating layer, may be used by adding a quarter wave plate 2 composed of one or two or more retardation layers on at least one side as in the example of FIG. 1. The quarter wave plate of the example is for linearly polarizing the circularly polarized light transmitted through the circularly polarized light separating layer. The quarter wave plate may be disposed on either the short wavelength side or the long wavelength side of the circularly polarized light separating layer. As the quarter wave plate (phase difference layer), in the visible region, the front phase difference is preferably used in the range of 100 to 180 nm in terms of linear polarization effect or compensation of color change by the transmitted light. That is, a quarter wave plate satisfying the following formula (3) is preferably used when the maximum refractive index in the plane is nx, the refractive index in the direction perpendicular thereto is ny, the refractive index in the thickness direction is nz, and the thickness is d:

The retardation layer used as necessary together with the retardation layer showing the quarter wave plate function preferably matches the color balance of the light transmitted through the retardation layer showing the quarter wave plate function with the color balance of the light transmitted vertically. , For compensation for the purpose of making the visual recognition through the polarizing plate a medium color with less color adhesion, and the like, and those having a front retardation (Δnd) of 100 to 720 nm are preferably used. The retardation layer, which is preferable in terms of compensation of color change, has a refractive index greater than one or both in the in-plane direction, or Nz of 5 or less, particularly 2 or less, particularly preferably 1.1 (All allow negative values):

(nx-nz) / (nx-ny)

It is preferable that the retardation layer is formed of an arbitrary material and is excellent in transparency, and in particular, exhibits a light transmittance of 80% or more to give a uniform retardation. Generally, polyolefins such as polycarbonate, polyester, polysulfone, polyethersulfone, polystyrene, polyethylene and polypropylene, polyvinyl alcohol, cellulose acetate polymer, polyvinyl chloride, polyvinylidene chloride, polyarylene Stretched films composed of plastics such as polymethyl methacrylate and polyamide, liquid crystal polymers, in particular liquid crystal polymers in a twisted orientation, and the like.

The retardation layer having a large refractive index in the thickness direction is a method of heating and stretching a film in which the polymer or the like is formed by a suitable method such as a casting method or an extraction method, for example, by uniaxial or biaxial bonding with a heat shrinkable film. It may be formed in a suitable manner such as. Characteristics such as Δnd or Nz in the retardation layer can be controlled by changing conditions such as the material of the film, the thickness, the stretching ratio, the stretching temperature, and the like. The general thickness of the retardation layer is 10 to 500 mu m, especially 20 to 200 mu m, based on the monolayer, but is not limited thereto.

Moreover, when forming retardation layers, such as a quarter wave plate, from a liquid crystal polymer, it has a suitable form, such as the alignment layer of the liquid crystal polymer supported by the orientation film of a liquid crystal polymer, or the transparent base material similarly to the case of the said circularly polarized light separation layer. Can be obtained. When the liquid crystal polymer is used, the desired retardation layer may be formed without stretching.

As described above, the quarter wave plate may be composed of a single phase retardation layer, or may be composed of a superposition of two or three or more retardation layers having different phase differences. The superposition of the phase difference layers having different phase differences is effective for expanding the wavelength range which functions as a desired quarter wave plate or a compensation plate. In the case of forming a superposed body of the retardation layer, it is preferable to arrange one or two or more layers of the retardation layer whose refractive index in the thickness direction is higher than at least one in-plane refractive index.

The reflective polarizing plate which is preferable in terms of a brightness improvement effect, etc. transmits linearly polarized light of a predetermined polarization axis, and reflects other light. As shown in FIG. 1, when the reflective polarizing plate 1 has a quarter wave plate 2, the optical element has a form in which the dichroic polarizing plate 3 is disposed thereon. Such an optical element can be applied to a liquid crystal cell as it is, since the dichroic polarizer of an optical element functions as a polarizer, without using a separate dichroic polarizing plate. The circularly polarized light separating layer or linearly polarized light separating layer to be used is preferably highly controlled in the uniformity of the alignment state due to the thickness accuracy, the orientation temperature, the stretching temperature, and the like. Highly suppressed is preferred.

As a dichroic polarizing plate, a suitable thing, such as an absorption type polarizing film containing a dichroic substance, a polyene oriented film, or what provided the transparent protective layer in these films, can be used. In addition, examples of the absorbing polarizing film include a dichroic substance such as iodine or dichroic dye on a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, and an ethylene / vinyl acetate copolymerized partial saponified film. And stretched. Moreover, the dehydration process of polyvinyl alcohol, the dehydrochlorination process of polyvinyl chloride, etc. are mentioned as an example of a polyene oriented film. In addition, although the thickness of a dichroic polarizing film is 5-80 micrometers normally, it is not limited to this.

The formation of a liquid crystal display device achieves a bright display, that is, a highly linearly polarized light through a quarter wave plate, if necessary, penetrates the dichroic polarizer while preventing absorption loss, and enters a highly linearly polarized light into the liquid crystal cell. In order to obtain an indication of a good contrast ratio, the high polarization degree is preferably used, such as an absorption type polarizing plate containing a dichroic substance. In particular, an absorption type polarizing plate containing a dichroic substance having a light transmittance of 40% or more and a polarization degree of 95.0% or more, particularly 99% or more is preferably used.

The transparent protective layer is provided for the purpose of protection, for example, when the water resistance is insufficient, such as a polarizing film containing a dichroic substance, and may be formed by a suitable method such as a plastic coating method or a film lamination method. In the case of forming a separate product such as a film, it is preferable to integrate the laminate into an adhesive layer from the viewpoint of preventing reflection loss. The thickness of a transparent protective layer can be suitably determined, and is generally 1 mm or less, especially 500 micrometers or less, Especially preferably, it is 1-300 micrometers. Moreover, although a suitable thing can be used as a plastic, what was illustrated by the transparent base material, retardation layer, etc. for supporting said liquid crystal polymer is generally used.

In addition, the transparent protective layer can also be formed in the form of surface fine uneven structure in the manner containing fine particles. Examples of the fine particles include conductive inorganic fine particles such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide and antimony oxide, organic fine particles such as crosslinked or uncrosslinked polymers having an average particle diameter of 0.5 to 20 µm. Of transparent particles are used. The content of the fine particles is generally 2 to 25% by weight, in particular 5 to 20% by weight.

When the dichroic polarizing plate 3 is disposed above the quarter wave plate 2 as in the example of FIG. 1, the arrangement angle of the dichroic polarizing plate relative to the quarter wave plate is a phase difference between the quarter wave plates. Although it can determine suitably according to the characteristic, the characteristic of circularly-polarized light which injects into it, etc., the dichroic polarizing plate of the dichroic polarizing plate with respect to the polarization direction (vibration direction) of the linearly polarized light through a quarter wave plate from the point of improvement of light utilization efficiency etc. It is preferable to arrange the transmission axes as parallel as possible.

As described above, the optical element is a reflective polarizing plate that separates incident light from a light source, such as natural light, into reflected light and transmitted light into left and right circularly polarized light or linearly polarized light in which the polarization axis is vertical, and circularly polarized light transmitted through the reflective polarizing plate. If necessary, the light is linearly polarized through the quarter wave plate and supplied to the dichroic polarizing plate so that absorption loss is reduced, thereby efficiently utilizing the incident light to improve luminance.

In the above, the optical element according to the present invention is disposed at a predetermined elevation angle, especially at an elevation angle at an elevation angle of 30 ° to 70 ° when the reflective polarizing plate is disposed on the surface light source so as to be inwardly transmitted. When the color at is x1 and y1, and the color at the point where the azimuth angle is changed at the same elevation is x2 and y2, the color change amount between the two points calculated by Equation 1 is 0.06 or less, especially 0.055 or less:

Equation 1

Thereby, the liquid crystal display device etc. which are hard to change a color by change of azimuth angle can be obtained.

The optical element which satisfies the color change amount is, for example, a laminated layer of a cholesteric liquid crystal layer and a quarter wave plate as an adhesive layer containing particles and exhibiting light diffusivity, and a collet having the light diffusing adhesive layer. A reflective polarizer using a steric liquid crystal layer or a quarter wave plate, a cholesteric liquid crystal layer containing particles, and a reflective polarizer using a quarter wave plate Similarly, it can obtain by the method using a light-diffusion reflective polarizing plate, etc.

Moreover, the optical element which can be used suitably for formation of a bright binocular liquid crystal display device etc. with little brightness nonuniformity and display nonuniformity, has the transmittance | permeability and the deviation from the in-plane average of color 0.5 in accordance with (DELTA) E by said Hunter color difference formula. To 5.0, in particular 4 or less, particularly preferably 3 or less, a reflective polarizing plate is used (Japanese Patent Laid-Open No. 99-311710).

As shown in Figs. 2 and 3, the optical element according to the present invention is disposed on a suitable surface light source 43 such as a side light guide plate or an EL lamp, which is suitable for forming a lighting device suitable as a backlight of a liquid crystal display device. Can be used. In addition, the surface light source of the example shown is comprised by arrange | positioning the light source 42 to the side surface of the light-guide plate 4 which has the reflective layer 41 on the back surface side, and an optical element is a reflection type polarizing plate (on the surface side (light emission side)). It is arrange | positioned so that 1) may become inner side.

According to the illuminating device of the above-described example, the light from the light source 42 is incident on the side of the light guide plate 4 and exits from the surface of the light guide plate through reflection on the back surface or the like, and the output light is disposed on the surface side of the light guide plate. Transmitted as a predetermined circular polarization (vertical) or elliptical polarization (aft) through the circularly polarized light separating layer 1, which is linearly polarized through the quarter wave plate 2 and enters the dichroic polarizing plate 3. . On the other hand, the light reflected by the circularly polarized light separating layer 1 as unplanned circularly polarized light is reflected back through the reflective layer 41 disposed on the back surface after being reentered into the light guide plate and returned to the circularly polarized light separating layer 1 again. Enter.

When the reflected light by the circularly polarized light separating layer is reflected from the back surface of the light guide plate, the polarization state is changed, and the reflected light is in a predetermined circularly polarized state through which some or all of the reflected light can pass through the circularly polarized light separating layer. Therefore, the reflected light by the circularly polarized light separating layer is trapped between the circularly polarized light separating layer and the light guide plate until there is a predetermined circularly polarized light that can penetrate the circularly polarized light separating layer, and the reflection is repeated between them. Therefore, in the side light type light guide plate, the reflected light is trapped between the circularly polarized light separating layer and the reflective layer of the light guide plate, and the polarization state is converted to transmit the circularly polarized light separating layer while the reflection is repeated therein, thereby initiating incident light. It is emitted together with the transmitted light, whereby unused portion of the light due to reflection loss is reduced. The same applies when a linearly polarized light separating layer is used instead of the circularly polarized light separating layer.

On the other hand, the circularly polarized light emitted from the circularly polarized light separating layer 1 is converted into linearly polarized light or elliptical polarized light with many linearly polarized light components through the quarter wave plate 2, and the converted light has dichroism in the linearly polarized light direction. When it coincides with the transmission axis of the polarizing plate 3, it is hardly absorbed and passes through the polarizing plate, whereby unused content of light due to absorption loss is also reduced. As a result, since the light which has conventionally been caused by reflection loss or absorption loss can be effectively used, the utilization efficiency of light can be improved. Therefore, as the surface light source, a light guide plate of side light type can be preferably used.

As the light guide plate, a suitable one having a reflective layer on the back surface and emitting light to the front surface side can be used. Preferably, what is emitted efficiently without absorbing light is used. A linear light source such as a cathode tube or a light source such as a light emitting diode is disposed on the side of the light guide plate 4, and the light transmitted through the light guide plate is diffused, reflected, diffracted, interference, etc. on one side of the plate. Examples thereof include a side light type backlight and the like which are known in a liquid crystal display device which emits light. The light guide plate to which the internal transmission light is radiate | emitted to the single side | surface is provided with the diffuser in the form of a dot or stripe on the light exit surface of the transparent or translucent resin plate, or its back surface, for example, The uneven structure on the back surface of the resin plate In particular, it can obtain by giving the uneven structure on a microprism array.

The light guide plate which emits light on one side of the light may have a function of polarizing conversion of light reflected by the circularly polarized light separating layer, but the reflection loss 41 may be almost completely prevented by providing the reflective layer 41 on the rear surface of the light guide plate. have. Reflective layers, such as a diffuse reflection layer or a specular reflection layer, are excellent in the function which polarizes the light reflected by the circularly polarized light separation layer, and are preferable in the present invention. In addition, in the diffuse reflection layer represented by the uneven surface or the like, the polarization states are randomly mixed with each other to diffuse the polarization state. In addition, the mirror-reflective layer represented by the metal surface which consists of vapor deposition layers, such as aluminum or silver, a resin plate, metal foil, etc. provided with this, reverses polarization state, when circularly polarized light is reflected.

At the time of forming the illumination device, as shown in Fig. 3, a prism array layer 5 composed of a prism sheet for controlling the emission direction of light or the like, a diffuser plate for obtaining uniform light emission, and reflection means for returning the leaked light And an auxiliary means such as a light source holder for guiding the light emitted from the linear light source to the side of the light guide plate at a predetermined position such as on the upper or lower surface or the side surface of the light guide plate 4 as necessary, in a suitable combination. can do.

In the above, the prism array layer, the diffuser plate, the dot applied to the light guide plate, etc. arranged on the surface side (light output side) of the light guide plate can function as polarization conversion means for changing the phase of the reflected light in the diffusion effect or the like. In addition, when arranging two or more prism array layers, it is preferable to arrange | position in the state which optical anisotropy is eliminated by twisting the arrangement | positioning angle of an array, such as orthogonal or crossing the prism array in each layer. The arrangement position of the prism array layer is usually between the reflective polarizing plate 1 and the surface light source or the light guide plate 4 as in the example of FIG. 3.

In the above, the optical element used in the formation of the lighting device has the ΔE of 0.5 to 9.0, in particular 8 or less, particularly preferably 7 or less, in view of suppressing luminance unevenness and display unevenness. In other words, by combining the reflective polarizing plate with the dichroic polarizing plate, the allowable range of ΔE is widened. This is because polarization cancellation, reflection inversion, etc. occur in optical layers such as a reflector, light guide plate, and diffuser plate when the illumination device or the like is used as described above, so that the deviation based on ΔE is allowed to increase.

In the present invention, each component such as a reflective polarizing plate such as a circularly polarized light separating layer or a linearly polarized light separating layer forming an optical element or an illuminating device, a quarter wave plate, a dichroic polarizing plate, a light guide plate, etc., may be formed through an adhesive layer as necessary. Lamination can be integrated. Stacking integration of the formed parts is effective in preventing reflection loss at each interface or preventing degradation of display quality due to prevention of intrusion of foreign matter and the like at each interface, and prevention of degradation such as compensation efficiency or polarization conversion efficiency due to optical system difference. . Therefore, even when the reflective polarizing plate, the quarter wave plate, the dichroic polarizing plate, the light guide plate, or the like are each formed of a plurality of layers, it is preferable that the respective layers be tightly integrated through the adhesive layer or the like.

A suitable adhesive agent etc. can be used for the said laminated integration. In particular, the adhesive layer having excellent stress relaxation property suppresses the stress generated in the circularly polarized light separating layer, the quarter wave plate, the dichroic polarizing plate, etc. due to the heat from the light source and the like, thereby preventing the change of the refractive index caused by the photoelastic deformation, It can be used suitably by the point which forms the liquid crystal display device which is bright and is excellent in visibility or reliability of display quality. In addition, an adhesive layer can also mix | blend the transparent particle etc. which were illustrated by said transparent protective layer, and can make it have a light-diffusion function. The light diffusing adhesive layer serves as a light diffusing layer, which is advantageous for thinning an optical element or an illuminating device, and in particular, when applied to an optical element, it is also advantageous to further reduce the amount of color change due to the homogenization effect by light diffusion.

For formation of the pressure-sensitive adhesive layer, a transparent pressure-sensitive adhesive composed of suitable polymers such as acrylic polymers, silicone polymers, polyesters, polyurethanes, polyethers, synthetic rubbers and the like can be used. In particular, acrylic pressure-sensitive adhesives can be preferably used in terms of optical transparency, adhesion characteristics, weather resistance, and the like. In addition, the pressure-sensitive adhesive layer has a relaxation modulus of from 2 x 10 ⁵ to 1 x 10 ⁷ dyn / cm 2, particularly from 2 x 10 ⁶ to the point of view of photoelastic deformation resistance due to relaxation of internal stress generated inside the laminate due to heat. It is preferable that it is 8x10 <^6> dyn / cm <2>.

The thickness of the adhesion layer can be determined suitably. Generally, it becomes 1-500 micrometers, especially 2-200 micrometers, Especially preferably, it is 5-100 micrometers in terms of adhesive force or thinning. In addition, the adhesive layer includes tackifiers such as petroleum resin, rosin resin, terpene resin, coumarone indene resin, phenol resin, xylene resin and alkyd resin, phthalic ester, phosphate ester, paraffin chloride, Softeners such as polybutene and poly isobutylene, or other suitable additives such as various fillers or anti-aging agents can be blended.

Formation of the laminated integrated optical element, for example, adheres an adhesive layer provided on a separator formed by surface treatment of a thin film such as a film with a release agent to an adhesive surface such as a circularly polarized light separating layer, and as necessary thereon. And a method in which a 1/4 wavelength plate is pressed and a dichroic polarizing plate is placed and pressed through an adhesive layer. In addition, the adhesive layer provided on the separator is adhered to an adhesive surface such as a light guide plate, and a reflective polarizing plate is disposed thereon and compressed thereon, and then the same adhesive layer is applied on the same, and the dichroic polarizing plate is sequentially pressed, or in advance. The method of laminating | stacking adherends, such as a reflective polarizing plate, a dichroic polarizing plate, and a light guide plate, in predetermined order via the adhesion layer provided in the predetermined | prescribed adhesive surface, and press-processing and crimping | compression-bonding collectively, etc. are mentioned.

In the optical element or the lighting apparatus according to the present invention, one or two or more layers of a suitable optical layer such as a light diffusion plate may be disposed at a suitable position between the surfaces or the layers. In that case, an optical layer can also be laminated integrally with a reflective polarizing plate etc. via the adhesion layer excellent in stress relaxation property. Such a pre-bonding method has the advantage of assembling to obtain an element having a more stable and reliable quality than the sequential bonding method in a line. In addition, in this invention, components, such as a reflective polarizing plate, a quarter wave plate, a dichroic polarizing plate, a light guide plate, an adhesive layer, and other optical layers which form an optical element or an illuminating device, are salicylic acid ester compounds, benzo, for example. It may have ultraviolet absorbing ability by the treatment with an ultraviolet absorber such as a phenone compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex salt compound or the like.

As described above, the lighting apparatus according to the present invention is excellent in light utilization efficiency, provides high brightness, easy to enlarge a large area, etc., and thus can be suitably used in various apparatuses as a backlight system in a liquid crystal display or the like. 4 and 5 show a liquid crystal display device using such a lighting device for a backlight system. This is done by arranging the liquid crystal cell 6 on the dichroic polarizing plate 3 side serving as the light output side of the lighting device. In the figure, 61 is a dichroic polarizing plate functioning as an analyzer, and 7 is a light diffusing plate for visual light diffusion.

The optical element or the lighting device according to the present invention can be particularly preferably used to form a liquid crystal display device of a type in which a dichroic polarizing plate which functions in a relationship between a polarizer and an analyzer is disposed on both sides of a liquid crystal cell as in the illustrated example. In that case, the dichroic polarizing plate in the optical element or the illumination device according to the present invention is used as a side functioning as a polarizer. A liquid crystal display device is generally formed by assembling a drive circuit by appropriately assembling components such as a dichroic polarizing plate, a liquid crystal cell, a backlight, and a compensation retardation plate as necessary. In the present invention, as described above, it is not particularly limited except that the optical element or the lighting device is disposed on the side of the illumination light incident on the liquid crystal cell, and can be formed according to the prior art. In that case, all or part of a component can be integrated integrally through adhesive layers, such as an adhesion layer.

In addition, the optical element or the lighting device according to the present invention can be suitably used for a liquid crystal cell, for example, a TN liquid crystal or an STN liquid crystal which needs to enter light in a polarized state as described above, but is a non-torsion type system. It can be used also for the liquid crystal of the liquid crystal, the thing of the guest host system liquid crystal, ferroelectric liquid crystal, etc. are used. In the formation of a liquid crystal display device, for example, a light diffusion plate, an anti-glare layer, an antireflection film, a protective layer, a protective plate, or a compensation retardation plate provided on a liquid crystal cell and a dichroic polarizing plate provided on the dichroic polarizing plate on the analyzer side. One or two or more suitable optical layers, such as these, can be arrange | positioned suitably.

Therefore, an optical layer (Japanese Patent Laid-Open Publication No. 92-268505, PCT Publication No. 95/17691) or the like, which is usually laminated with a plurality of polymer thin films disposed between a backlight and a liquid crystal cell for the purpose of luminance improvement, can also be disposed. . In addition, the compensation retardation plate is intended to improve the visibility by compensating the wavelength dependence of the birefringence. In this invention, it arrange | positions as needed between a dichroic polarizing plate and a liquid crystal cell on the analyzer side and / or a polarizer side. As the retardation plate for compensation, a suitable one can be used depending on the wavelength range or the like, and may be formed as an overlapping layer of one or two or more retardation layers. The compensation retardation plate can be obtained as the stretched film or the liquid crystal polymer layer exemplified in the quarter wave plate.

Example

Example 1

A 20% by weight tetrahydrofuran solution of an acrylic thermotropic cholesteric liquid crystal polymer was coated on a polyvinyl alcohol rubbing treated surface (about 0.1 μm thick) of a cellulose acetate acetate film having a thickness of 50 μm with a wire bar. A method of cooling at room temperature after heat alignment treatment at 2 ° C. for 5 minutes and having a thickness of 5 μm, which transmits left circularly polarized light having a wavelength range of selective reflection of 400 to 470 nm or 600 to 700 nm by a difference in the mesogen ratio. After forming two circularly polarized light separating layers, these liquid crystal layers were thermally compressed at 130 ° C. through a lamination roll to obtain circularly polarized light separating plates having a wavelength range of selective reflection of 400 to 700 nm.

Subsequently, a 1/4 phase plate having a front phase difference of 120 ± 5 nm and Nz -1.5 composed of a stretched film of polycarbonate on the side of the spiral pitch of the circularly polarized light separating plate was adhered through an acrylic adhesive layer having a thickness of 20 μm to reflect After obtaining a polarizing plate, the absorption type polarizing plate was adhere | attached on the 1/4 wavelength plate side through the acryl-type adhesive layer of 20 micrometers in thickness so that the polarization axis and the polarization axis of the transmitted light might correspond, and the optical element was obtained.

Example 2

An optical device was obtained in accordance with Example 1 except that the circularly polarized light separating plate and the quarter-wave plate were bonded to the light-diffusion type acrylic adhesive layer of silica.

Comparative example

An optical device was obtained in accordance with Example 1 except that a front wave difference of 120 ± 5 nm and a Nz of 1 were used as quarter wave plates.

Evaluation test

The optical elements obtained in Examples and Comparative Examples were placed on the surface light source so that the reflective polarizer was inward so that the transmitted light from the absorbing polarizer was front (another angle and azimuth angle of 0 °), an elevation angle of 70 ° at an elevation angle of 0 °, or an elevation angle. Colors x and y were measured at three points with an azimuth angle of 45 ° at 70 °, and the color change amount was calculated therefrom by the following equation (1) between each point:

Equation 1

The results are shown in the table below:

Elevation (°) Azimuth (°) x y Color change Car with the front Azimuth 0 0 0.312 0.331 - - Example 1 70 0 0.344 0.356 0.041 - 70 45 0.342 0.305 0.040 0.051 0 0 0.307 0.332 - - Example 2 70 0 0.343 0.338 0.036 - 70 45 0.331 0.300 0.040 0.040 0 0 0.305 0.330 - - Comparative example 70 0 0.334 0.355 0.038 - 70 45 0.276 0.302 0.040 0.079

According to the optical element or the illumination device according to the present invention, it is possible to form a liquid crystal display device which is less likely to change color due to a change in azimuth angle caused by strabismus, and also advantageously to form a large liquid crystal display device having good display quality. .

Claims (9)

It consists of a laminate having a reflective polarizing plate and a dichroic polarizing plate for separating incident light into polarized light through reflection and transmission, and when it is disposed so that the reflective polarizing plate is inward on the surface light source, the transmitted light is irradiated. When the color at the azimuth angle is x1 and y1 and the color at the point where the azimuth angle is changed at the same elevation angle is x2 and y2, the color change amount between two points calculated by Equation 1 below is 0.06 or less. Optical elements: Equation 1

The method of claim 1, Optical device having an elevation angle of 30 ° to 70 °. The method of claim 1, An optical element comprising a reflective polarizing plate having a cholesteric liquid crystal layer or a quarter wave plate therewith, or transmitting linearly polarized light of a predetermined polarization axis and reflecting other light. The method of claim 1, An optical element comprising all or part of the formation layer is in close contact with the adhesive layer. An illuminating device having the optical element according to any one of claims 1 to 4 on the surface side of a surface light source having a reflective layer on its back side such that its reflective polarizing plate is inward. The method of claim 5, wherein An illuminating device having one or two or more prism array layers between a reflective polarizer and a surface light source, and in the case of two or more layers, an array direction of the arrays intersects in an upper and lower layers. The method of claim 5, wherein A lighting device in which all or part of the forming layer is in close contact with the adhesive layer. A liquid crystal display device comprising a liquid crystal cell on the light output side of the lighting device according to claim 5. The method of claim 8, A liquid crystal display device in which all or part of the formation layer is in close contact with the adhesive layer.

Images