JPH09189811A - Polarizing element and elliptically polarizing element - Google Patents

Abstract

(57) Abstract: It is possible to form a liquid crystal display device which has low light reflection loss, excellent light utilization efficiency, is less likely to undergo photoelastic deformation due to heat from a light source, is highly reliable, and is excellent in brightness. Development of polarizing element. A polarization separation film (3) composed of a cholesteric liquid crystal layer, a quarter-wave plate (4), and a polarization film containing a dichroic substance as necessary, are used as an adhesive layer (2) having excellent stress relaxation property. ), A light guide plate (1) which has a reflection layer (11) on the back surface and emits light from the front surface, if necessary, on the polarization separation film side. 20) A polarizing element formed by adhering via. [Effect] The circularly polarized light reflected by the polarization splitting film is confined between the light guide plate and the reflection layer of the light guide plate, and is converted into a predetermined circularly polarized light while being repeatedly reflected. Usage is reduced. In addition, since the layers are integrated through the adhesive layer, the reflection loss at each interface is small, and the display unevenness is less likely to occur due to the heat from the light source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element excellent in light utilization efficiency and suitable for a transmissive liquid crystal display device and the like, and an elliptically polarizing element using the same.

[0002]

BACKGROUND OF THE INVENTION Conventionally, various means have been used to polarize light from a light source to improve light utilization efficiency in a liquid crystal display device and realize a bright display.
-127019, JP 61-122626, JP 63-121821, and JP 3-45.
906, JP-A-6-324333, JP-A-7-35925, and JP-A-7-36025 are proposed.

However, in any case, since it is formed of 3 to 4 constituent elements, the laminated body has 6 to 8 interfaces, and the optical loss due to the reflection loss at each interface is large, so that it is simply superposed arrangement. 70% to 80% in the case of simple calculation
However, there is a problem that the efficiency of light utilization is poor and the effect of improving the brightness of the display is poor.

Further, in a contact-type laminated body formed by adhesion, internal stress is generated in the laminated body by heat from a light source due to different linear expansion coefficients of constituent elements made of different materials, and photoelastic deformation is caused to cause birefringence. There is also a problem in that it occurs and causes display unevenness.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a liquid crystal display device which has a small light reflection loss, is excellent in light utilization efficiency, is less likely to undergo photoelastic deformation due to heat from a light source, is highly reliable, and is excellent in brightness. The challenge is to develop a polarizing element that can be formed.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a pressure-sensitive adhesive having a polarization separation film consisting of a cholesteric liquid crystal layer, a quarter-wave plate, and optionally a dichroic substance-containing polarization film, which is excellent in stress relaxation. It is composed of a laminated body which is sequentially adhered via layers, and further, if necessary, a polarizing plate which has a reflection layer on the back surface and emits light from the front surface is adhered to the polarization separation film side through the adhesive layer. The present invention provides a polarizing element characterized by the above.

[0007]

In the above structure, the polarization separation film is
Incident light passing through a light guide plate or the like is split into left and right circularly polarized light, one of which is transmitted and the other is reflected. As a result, the reflected light is confined between the polarization separation film and the reflection layer of the light guide plate,
While repeating the reflection in the meantime, it is converted into a predetermined circularly polarized light and can be transmitted through the polarization separation film, and is emitted together with the circularly polarized light in the predetermined state from the beginning of the incident light,
This reduces the unused portion of light due to reflection loss.

On the other hand, the circularly polarized light emitted from the polarization separation film is converted to a state having a large amount of linearly polarized light components such as linearly polarized light and flat elliptically polarized light through the quarter-wave plate. When the linear polarization direction of the converted light coincides with the transmission axis of the polarizing film, the converted light is hardly absorbed and passes through the polarizing film, thereby reducing unused light due to absorption loss. As a result, it is possible to effectively use the light, which has conventionally been a reflection loss or an absorption loss, and improve the light utilization efficiency.

In the above-mentioned polarizing element of the present invention, since it is laminated and integrated through the adhesive layer, the reflection loss at each interface is small, and foreign matter and the like are prevented from entering the interface, thus deteriorating the display quality. It is also possible to prevent the deterioration of the conversion efficiency due to the deviation of the optical system. In addition, it is possible to suppress the stress generated in the polarization separation film, the quarter-wave plate and the polarizing film due to the heat from the light source by integrating the layers through the adhesive layer, which has excellent stress relaxation property, and the refractive index generated by the photoelastic deformation. Can be prevented from changing. As a result, it is possible to form a liquid crystal display device which is bright and has excellent visibility and display quality reliability.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The polarizing element of the present invention comprises a polarization separation film composed of a cholesteric liquid crystal layer, a quarter-wave plate, and optionally a dichroic substance-containing polarizing film, which is excellent in stress relaxation. It is composed of a laminated body sequentially adhered via layers, and further, if necessary, on the polarization separation film side, a light guide plate having a reflection layer on the back surface and emitting light from the front surface is adhered via the adhesive layer. Become.

The polarizing element according to the present invention is illustrated in FIGS. 2, 20, 21, 22, 23, and 24 are adhesive layers, 3 is a polarization separation film, 4 is a quarter-wave plate, 1 is a light guide plate as needed, and 6 is a polarization film as needed. Is. In addition, 51 is a separator for protecting the adhesive layer.
As shown in FIG. 2, the polarization separation film 3 may be formed as a layer in which a plurality of cholesteric liquid crystal layers 31, 32 and 33 are superposed, and the quarter wavelength plate 4 is also formed into a plurality of retardation layers 41 and 4.
It may be formed as a superposed layer of two.

According to the polarizing element having the light guide plate arranged in the above-described example, a predetermined circularly polarized light of the light emitted from the surface of the light guide plate 1 is transmitted through the polarization separation film 3 arranged on the surface side of the light guide plate. Then, the light is transmitted to the outside through the quarter-wave plate 4.
On the other hand, the non-predetermined circularly polarized light is reflected by the polarization separation film 3, and the reflected light is re-incident on the light guide plate and is reflected on the rear surface of the reflection layer 1.
The light is reflected by the light beam No. 1 and enters the polarization separation film 3 again as return light.

The light reflected by the polarization separation film is
The polarization state is changed when reflected on the back surface of the light guide plate, and a part or all of the reflected light becomes a predetermined circularly polarized light that can be transmitted through the polarization separation film. Therefore, the light reflected by the polarization separation film is confined between the polarization separation film and the light guide plate until it becomes a predetermined circularly polarized light that can be transmitted through the polarization separation film, and is repeatedly reflected between them.

On the other hand, the circularly polarized light emitted from the polarization separation film is incident on the quarter-wave plate 4 to undergo a phase change, and the light having a wavelength corresponding to the quarter-wave phase change is converted into linearly polarized light. , Light of other wavelengths is converted into elliptically polarized light.
The elliptically polarized light becomes flatter elliptically polarized light as it approaches the wavelength of the light converted into the linearly polarized light. As a result, the light containing a large amount of linearly polarized light that can pass through the polarizing film is
It is emitted from the / 4 wavelength plate.

In the present invention, the polarization separation film and 1 /
The four-wave plate, and if necessary, each component of the polarizing film and the light guide plate are laminated and integrated via an adhesive layer having an excellent stress relaxation property. In that case, the arrangement position of each component is such that the polarization separation film 3 and the quarter-wave plate 4 are arranged to obtain a desired function.
The polarizing film 6 is on the side of the quarter-wave plate 4, the light guide plate 1 is on the side of the polarization separation film 3 and the surface of the light guide plate ( The light emission side is the polarization separation film side.

As the polarized light separating film, a film made of a cholesteric liquid crystal layer is used. The cholesteric liquid crystal layer has an advantage of being able to selectively separate left and right circularly polarized light into either one of them through transmission and reflection, and has an excellent wide viewing angle. Further, the cholesteric liquid crystal layer is suitable for a direct-viewing type liquid crystal display device in which a change in optical characteristics with respect to a change in viewing angle is small, and which is directly observed even in an oblique direction.

As the cholesteric liquid crystal, an appropriate one can be used, and there is no particular limitation. The use of a liquid crystal polymer is advantageous from the viewpoint of the superposition efficiency of the liquid crystal layer and the thinning of the liquid crystal layer. In addition, a cholesteric liquid crystal molecule having a large birefringence is preferable because the wavelength range of selective reflection becomes wider. Examples of the polarization separation film that can be preferably used include a film made of a liquid crystal polymer exhibiting a cholesteric phase, and a film provided with a layer made of a cholesteric liquid crystal polymer on a transparent substrate such as a film.

As the liquid crystal polymer, for example, a main chain type liquid crystal polymer such as polyester, a side chain type liquid crystal polymer including an acrylic main chain, a methacrylic main chain, a siloxane main chain, a nematic liquid crystal polymer containing a low molecular weight chiral agent, Examples include liquid crystal polymers having a chiral component introduced therein, and nematic and cholesteric mixed liquid crystal polymers. From the viewpoint of handleability, the glass transition temperature is 30 to 150.
The liquid crystal polymer of ° C. can be preferably used.

The cholesteric liquid crystal layer can be formed by a method according to a conventional alignment treatment. By the way, as an example, a film formed of polyimide or polyvinyl alcohol on a substrate and rubbed with rayon cloth or S,
A liquid crystal polymer is spread on an appropriate alignment film composed of an obliquely deposited layer of iO and heated to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature. Cooling to a glass state to form a solidified layer in which the orientation is fixed.

As the substrate, for example, an appropriate substrate such as a film made of plastic such as triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyether sulfone, or epoxy resin, or a glass plate Can be used. When the substrate is formed of a film, the solidified layer of the liquid crystal polymer formed on the substrate can be used as a polarization separation film as it is, or can be peeled off from the substrate and used as a polarization separation film formed of a film or the like. . When it is formed as an integral body with a film substrate, it is preferable to use a film having a phase difference as small as possible from the viewpoint of prevention of a change in the state of polarization.

The liquid crystal polymer can be developed by a heating and melting system or can be developed as a solution using a solvent. As the solvent, for example, an appropriate solvent such as methylene chloride, cyclohexanone, trichloroethylene, tetrachloroethane, N-methylpyrrolidone, tetrahydrofuran, or the like can be used. The development can be performed by an appropriate coating machine such as a bar coater, a spinner, a roll coater, or a gravure printing method. Upon development, a method of superposing a cholesteric liquid crystal layer with an alignment film interposed may be adopted if necessary.

The thickness of the cholesteric liquid crystal layer is from 0.5 to 100 μm, preferably from 1 to 100 μm, from the viewpoints of preventing alignment disorder and a decrease in transmittance, and selectively reflecting (wavelength range showing circular dichroism). 70 μm, particularly preferably 1 to 50 μm. The polarization separation film to be formed is preferably formed as a flat layer from the viewpoint of uniformization of separation performance including obliquely incident light, and each layer is flat even when formed as a superposed layer of two or more layers. It is preferable that it is When forming the cholesteric liquid crystal layer or the polarization separation film, various additives such as stabilizers, plasticizers, and metals can be blended as necessary.

The polarization separation film can also be formed as a laminate having two or more cholesteric liquid crystal layers as described above. The superposition is advantageous in that the separation function has a wider wavelength range and the wavelength shift of obliquely incident light is dealt with.
In that case, it is preferable that the light reflected as circularly polarized light outside the predetermined range be superimposed in a combination having different central wavelengths. That is, a single-layer cholesteric liquid crystal layer usually has a limit in the wavelength range exhibiting selective reflection (circular dichroism), and the limit may be a wide range extending to a wavelength range of about 100 nm. However, when it is applied to liquid crystal display devices, etc., it does not reach the entire range of visible light, so in such a case a wavelength range showing circular dichroism is expanded by overlapping cholesteric liquid crystal layers with different selective reflection properties. Can be made.

Incidentally, in the case of a cholesteric liquid crystal layer, the central wavelength of selective reflection based on the liquid crystal layer is 300 to 900.
A combination that reflects circularly polarized light of the same polarization direction with the nm one,
And the central wavelength of selective reflection is different, especially 50nm each.
It is possible to efficiently form a polarization separation film capable of covering a wide wavelength range by using the above different combinations and superposing 2 to 6 types thereof. For the superposition of the cholesteric liquid crystal layer, the use of a liquid crystal polymer is particularly advantageous from the viewpoints of production efficiency and thinning.

Therefore, as the polarized light separating film, one in which the wavelength range of the light which can be reflected as circularly polarized light outside the predetermined range matches the wavelength range of the outgoing light based on the light guide plate as much as possible can be preferably used. When the emitted light has a dominant wavelength such as an emission line spectrum, it is possible to match the wavelength of the reflected light based on the cholesteric liquid crystal phase or the like with one or more dominant wavelengths of the polarized light, such as the efficiency of polarization separation. From the point, it is the second best measure,
It is also advantageous for thinning the polarization separation film by reducing the required number of overlaps. In that case, it is preferable that the degree of coincidence of the wavelengths of the reflected light is within 20 nm with respect to one or more main wavelengths of the light guide plate.

In the above description, it was pointed out that when the polarization separation film was formed as a superposed layer of the cholesteric liquid crystal layer, it was used in combination with those which reflect circularly polarized light of the same polarization direction. This aligns the phase states of the circularly polarized light reflected by each layer to prevent different polarization states in each wavelength range,
The purpose is to increase the amount of polarized light in a usable state. As described above, an appropriate cholesteric liquid crystal may be used, but the wavelength range of selective reflection becomes wider as the cholesteric liquid crystal molecule having a larger phase difference, the number of layers is reduced, and the margin for wavelength shift at a large viewing angle is provided. Therefore, it can be preferably used.

The polarized light separating film used in the present invention is, for example, a cell form in which a cholesteric liquid crystal layer made of a low molecular weight material is sandwiched by a transparent substrate such as a film, a form in which a cholesteric liquid crystal layer made of a liquid crystal polymer is supported by a transparent substrate, The cholesteric liquid crystal layer may have a suitable form such as a film made of a liquid crystal polymer film or a form in which these forms are superposed in an appropriate combination. In that case, the cholesteric liquid crystal layer may be held by one or two or more supports depending on the strength and operability. When a support having two or more layers is used, the retardation is as small as possible, for example, a non-oriented film or a triacetate film having a small birefringence even when oriented, in order to prevent a change in the state of polarization. Those can be preferably used.

1/4 placed on one side of the polarized light separating film
The wave plate is intended to change the phase of the circularly polarized light emitted from the polarization separation film to convert it into a state having a large amount of linearly polarized light components as described above, and thereby, it is possible to obtain light easily transmitted through the polarizing film. .

Therefore, as the quarter-wave plate, the circularly polarized light emitted from the polarization separation film can form a large amount of linearly polarized light corresponding to the phase difference of 1/4 wavelength, and the light of other wavelengths can be linearly polarized. A material having a major axis in a direction as parallel as possible to the polarized light and capable of converting into a flat elliptically polarized light as close to linearly polarized light as possible is preferably used. By using such a 1/4 wavelength plate, the emitted light can be arranged so that the linear polarization direction of the emitted light and the major axis direction of the elliptically polarized light are as parallel as possible to the transmission axis of the polarization film, and the light can be transmitted through the polarization film. It is possible to obtain light with a large amount of linearly polarized light components.

The quarter-wave plate can be formed of an appropriate material,
Those which are transparent and give a uniform phase difference are preferred. The retardation of the quarter-wave plate can be appropriately determined according to the wavelength range of circularly polarized light emitted from the polarization separation film and the like. Incidentally, in the visible light region, a quarter wave plate for light having a wavelength of 550 nm is preferable.

The retardation layer may be colored depending on the viewing angle. From the viewpoint of preventing the coloring, the formula: N _z =
N _z defined by (n _x −n _z ) / (n _x −n _y ) is N _z <
A quarter-wave plate made of a refractive index ellipsoid satisfying 1.1 can be preferably used. Note in the above formulas, n _x is the maximum refractive index in the plane of the retardation layer, n _y is a refractive index in a direction perpendicular to n _x direction, n _z denotes a refractive index in the thickness direction.

The quarter-wave plate is composed of a single retardation layer, or has a different phase difference for the purpose of expanding the wavelength range capable of functioning as the quarter-wave plate as illustrated in FIG. It can be obtained as a laminate of two or more retardation layers.

Incidentally, as a superimposition type quarter-wave plate which can function as a quarter-wave plate in a wide range of the visible light range,
For example, a plurality of phase difference layers intersect their optical axes by a combination of a phase difference layer providing a phase difference of １ ／ wavelength and a phase difference layer providing a phase difference of ４ wavelength with respect to light having a wavelength of 550 nm. One that is superimposed in a state where it is made to occur is exemplified.

In the above, from the viewpoint of obtaining a superposed type quarter-wave plate in which coloring due to the viewing angle is prevented, N _z <1.
A retardation layer that gives a quarter-wave retardation satisfying 1;
It is preferable to use a superposed product using one or two or more retardation layers that give a retardation of ½ wavelength.

As described above, the quarter-wave plate can be obtained as a single layered product or a superposed product of retardation layers, and a retardation film or the like is used for forming the retardation layer. The retardation film can be obtained as a film obtained by appropriately stretching a polymer film uniaxially or biaxially, or a liquid crystal polymer film. Appropriate materials can be used as the polymer film or the liquid crystal polymer film.

Incidentally, specific examples of the above-mentioned polymer film include polycarbonate, polyester, polysulfone, polyethersulfone, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, cellulose acetate polymers, polyvinyl chloride, and polyvinyl chloride. Examples thereof include films made of a suitable transparent plastic such as arylate and polyamide.

In the present invention, as illustrated in FIG. 3, as the polarizing film to be bonded and arranged on the ¼ wavelength plate side in the polarizing element 5 consisting of the polarization separation film and the ¼ wavelength plate as necessary, an absorption type polarization film is used. An appropriate film such as a film or a polyene oriented film, or a film provided with a transparent protective layer may be used.

As an example of the absorption type polarizing film, a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, an ethylene / vinyl acetate copolymer partially saponified film is used, and iodine or dichroic dye is used. Examples include films stretched by adsorbing dichroic substances such as functional dyes. Examples of the oriented polyene film include dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. The thickness of the polarizing film is usually 5 to 80 μm
But is not limited to this.

In the formation of the liquid crystal display device, the achievement of bright display using the polarizing element according to the present invention, that is, absorption loss of highly linearly polarized light through the quarter-wave plate is prevented as much as possible. While having a high degree of polarization, such as an absorptive polarizing film containing a dichroic substance, from the viewpoint of transmitting a polarizing film and transmitting a high degree of linearly polarized light to a liquid crystal cell to obtain a good contrast ratio display. Is preferably used.

Above all, an absorptive polarizing film containing a dichroic substance having a light transmittance of 40% or more and a polarization degree of 99.0% or more, especially 99.5% or more is preferably used. The degree of polarization (P) is expressed by the formula: P = SQR [(T _p −T _c ) /
(T _p + T _c )]. In the formula, T _p is the light transmittance when the same polarizing films are arranged in parallel Nicols, T _p
c is the light transmittance when arranged in the crossed Nicols.

The above-mentioned transparent protective layer is provided for the purpose of protection particularly in the case of poor water resistance such as a polarizing film containing a dichroic substance, and is appropriately applied by a plastic coating method or a film laminating method. It may be formed by any method. When it is formed of a separated material such as a film, it is preferable that the adhesive layer is laminated and integrated to prevent reflection loss. The thickness of the transparent protective layer may be appropriately determined and is generally 1 mm or less, preferably 500 μm or less, particularly 1 to 300 μm.

The transparent resin layer can also be formed in the form of a fine surface uneven structure by a method of containing fine particles. The fine particles have, for example, an average particle size of 0.5 to 5 μm.
In a transparent resin layer such as inorganic fine particles that may be conductive such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide, and organic fine particles such as a crosslinked or uncrosslinked polymer. What shows transparency is used. The content of the fine particles is 2 to 25.
% By weight, especially 5 to 20% by weight.

When the polarizing film is bonded and arranged on the upper side of the quarter-wave plate, the arrangement angle of the polarizing axis of the polarizing film with respect to the fast axis or the slow axis of the quarter-wave plate is the position of the quarter-wave plate. It can be appropriately determined according to the phase difference characteristics and the characteristics of the circularly polarized light incident on it, but from the viewpoint of improving the light utilization efficiency, it is polarized with respect to the polarization direction of the linearly polarized light through the quarter-wave plate. It is preferred to arrange the transmission axes of the film as parallel as possible.

In the polarizing element of the present invention, as a light guide plate which is adhesively arranged as necessary on the polarization separation film side as shown in the figure, a reflection layer is provided on the back surface so that light is emitted to the front surface side. Any appropriate one can be used. Preferably, one that efficiently emits light without absorption is used. (cold,
A linear light source such as a cathode ray tube or a light source such as a light emitting diode is arranged on the side surface of the light guide plate 1, and the light transmitted through the light guide plate is diffused, reflected, diffracted, interfered, or the like on one side of the plate. An example thereof is a sidelight type backlight which is known in liquid crystal display devices and is configured to emit light to the side.

In the above, the light guide plate adapted to emit the transmitted light to the one side is provided with a diffuser in a dot shape or a stripe shape on the light emitting surface of the transparent or semitransparent resin plate or the back surface thereof. It can be obtained as a product or a resin plate having a back surface provided with an uneven structure.

The light guide plate that emits light to one surface side may have a function of converting the light reflected by the polarization separation film into polarization, but by providing the reflection layer 11 on the back surface of the light guide plate. Reflection loss can be almost completely prevented. A reflection layer such as a diffuse reflection layer or a specular reflection layer has an excellent function of converting the light reflected by the polarization separation film into polarization, and is preferable in the present invention. Incidentally, the diffuse reflection layer represented by an uneven surface or the like forms a depolarized state by randomly mixing polarization states based on the diffusion. When a circularly polarized light is reflected, the polarization state of a mirror reflection layer represented by a metal layer made of a vapor deposited layer of aluminum, silver, or the like, a resin plate provided with the layer, a metal foil, or the like is inverted.

When forming the light guide plate, a diffuser plate for obtaining uniform light emission, a prism sheet for controlling the emission direction of light, a reflecting means for returning leaked light, and a light emitted from a linear light source are guided. An auxiliary means such as a light source holder for guiding the light to the side surface of the light plate is arranged at a predetermined position as necessary to form an appropriate combination. Note that a diffusion plate or a prism sheet disposed on the surface side (light emission side) of the light guide plate, or a dot provided on the light guide plate can function as a polarization conversion unit that changes the phase of reflected light due to a diffusion effect or the like.

In the polarizing element of the present invention, the polarized light separating film, the quarter-wave plate, the polarizing film and the light guide plate, which are in a separated state, are bonded to each other through an adhesive layer having an excellent stress relaxation property to form a laminate. It is a thing. When the materials forming the polarized light separating film, the quarter-wave plate, the polarizing film and the light guide plate are not in the close contact and integrated state but in the separated state, the adhesive layer for the close contact and integration is used. .

For forming the pressure-sensitive adhesive layer, a transparent pressure-sensitive adhesive having excellent stress relaxation property, which is made of an appropriate polymer such as acrylic polymer, silicone polymer, polyester, polyurethane, polyether or synthetic rubber, is used. sell. Above all, an acrylic pressure-sensitive adhesive can be preferably used in terms of optical transparency, pressure-sensitive adhesive properties, weather resistance and the like. The adhesive layer has a relaxation elastic modulus of 2 × 10 ⁵ to 1 × 10 ⁷ dyne / cm ² , especially from the viewpoint of preventing photoelastic deformation due to relaxation of internal stress generated inside the laminate by heat. 2 x 10 ⁶ to 8 x
It is preferably 10 ⁶ dyne / cm ² .

Specific examples of the acrylic polymer forming the acrylic pressure-sensitive adhesive include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, pentyl group and isoamyl group, Alkyl groups such as hexyl group, heptyl group, cyclohexyl group, 2-ethylhexyl group, octyl group, isooctyl group, nonyl group, isononyl group, lauryl group, dodecyl group, decanyl group and isodecanyl group, especially having 2 to 2 carbon atoms. Examples thereof include those obtained by polymerizing one or two or more of acrylic acid esters and methacrylic acid esters having 14 alkyl groups with one or more modifying monomers as necessary.

When forming the acrylic copolymer, a modifying monomer copolymerizable with the (meth) acrylic acid ester may be used if necessary. Specific examples thereof include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6- (meth) acrylate.
A hydroxyl group-containing monomer such as hydroxyhexyl, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate or (4-hydroxymethylcyclohexyl) -methyl acrylate, Acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, carboxyl group-containing monomers such as itaconic acid, maleic acid and crotonic acid, acid anhydride monomers such as maleic anhydride and itaconic anhydride, 2-acrylamido-2-methyl Examples thereof include sulfonic acid group-containing monomers such as propanesulfonic acid and phosphoric acid group-containing monomers such as 2-hydroxyethylacryloyl phosphate.

Further, amide-based monomers such as (meth) acrylamide and N-substituted (meth) acrylamide, N-
Maleimide-based monomers such as cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide and N-phenylmaleimide, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2. Itaconimide-based monomers such as -ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide, N- (meth) acryloyloxymethylenesuccinimide, N- (meth) acryloyl-6-oxyhexamethylenesuccinimide, N- (meth) ) A succinimide-based monomer such as acryloyl-8-oxyoctamethylene succinimide can also be used as the modifying monomer.

Further, vinyl acetate, N-vinylpyrrolidone, vinyl monomers such as N-vinylcarboxylic acid amides and styrene, divinyl monomers such as divinylbenzene, 1,4-butyldiacrylate and 1,6-hexyldiene. Diacrylate-based monomer such as acrylate,
Glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, polyethylene glycol (meth) acrylate and polypropylene glycol (meth)
An acrylate monomer such as acrylate, fluorine (meth) acrylate or silicone (meth) acrylate, or an ester group different from the above-mentioned main component monomer such as methyl (meth) acrylate or octadecyl (meth) acrylate (meth) ) Acrylates and the like are also examples of the modifying monomer.

Among the above-mentioned modifying monomers, monomers having a functional group capable of reacting with the intermolecular crosslinking agent and capable of participating in the intermolecular crosslinking of the acrylic copolymer, such as the above-mentioned carboxyl group-containing monomer and acid anhydride Product monomers, glycidyl (meth) acrylate, hydroxyl group-containing monomers, and the like can be preferably used. Above all, monomers having high crosslinking reactivity such as carboxyethyl acrylate and 6-hydroxyhexyl (meth) acrylate can impart necessary crosslinking properties with a small amount of copolymerization. It is difficult to increase the relaxation modulus, and it is particularly preferably used.

The preparation method of the acrylic polymer is arbitrary, and an appropriate method such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, or a suspension polymerization method can be employed. In the polymerization, for example, hexanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) ) Polyfunctional monomers such as acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, epoxy acrylate, polyester acrylate and urethane acrylate may also be used.

In the polymerization treatment, a polymerization initiator may be used if necessary. The amount used can be according to the ordinary law,
Generally, 0.001 to 5% by weight of the monomer component is used. Examples of the polymerization initiator include benzoyl peroxide and t
-Butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-
Propyl peroxy dicarbonate, di (2-ethoxyethyl) peroxy dicarbonate, t-butyl peroxy neodecalate, t-butyl peroxy vivalate, (3,5,5-trimethylhexanoyl) peroxide and dipropionyl Organic peroxides such as peroxide and diacetyl peroxide can be mentioned.

Further, 2,2′-azobisisobutyronitrile and 2,2′-azobis (2-methylbutyronitrile),
1'-azobis (cyclohexane 1-carbonitrile)
And 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2,4-dimethyl-4-methoxyvaleronitrile) and dimethyl 2,2′-azobis (2
-Methylpropionate), 4,4'-azobis (4-cyanovaleric acid) and 2,2'-azobis (2-hydroxymethylpropionitrile), 2,2'-azobis [2-
An azo compound such as (2-imidazolin-2-yl) propane], potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like, or a redox initiator using a reducing agent in combination therewith, may be mentioned as the polymerization initiator.

The acrylic polymer which can be preferably used from the viewpoint of wet heat resistance and the like has a weight-average molecular weight of 10 or more, especially 200,000 or more, especially 400,000 or more. In addition, such an acrylic polymer may be subjected to a crosslinking treatment with an intermolecular crosslinking agent or the like, if necessary, to improve the adhesive properties by increasing the molecular weight or the like. Incidentally, examples of the intermolecular crosslinking agent include polyfunctional isocyanate crosslinking agents such as tolylene diisocyanate and trimethylolpropane tolylene diisocyanate, diphenylmethane triisocyanate, polyethylene glycol diglycidyl ether and diglycidyl ether, and trimethylolpropane triglycidyl ether. Suitable crosslinkers such as epoxy crosslinkers, melamine resin crosslinkers, metal salt crosslinkers, metal chelate crosslinkers, amino resin crosslinkers and the like can be used.

The thickness of the adhesive layer may be appropriately determined. Generally, the thickness is 1 to 500 μm, particularly 2 to 200 μm, particularly 5 to 100 μm from the viewpoint of adhesive strength and thinning. If necessary, a tackifier such as petroleum resin, rosin resin, terpene resin, coumarone indene resin, phenol resin, xylene resin, alkyd resin, phthalate ester or phosphorus An appropriate additive such as an acid ester, a softening agent such as chlorinated paraffin, polybutene, or polyisobutylene, or other various fillers or an antioxidant can be blended.

The polarizing element is formed by, for example, transferring an adhesive layer provided on a separator obtained by surface-treating a thin sheet such as a film with a release agent to the adhesive surface of the polarization separation film, and then applying a quarter wavelength on it. Method of crimping plate, or 1/4 of that
An example is a method in which an adhesive layer is similarly transferred onto a wave plate, a polarizing film is placed on the same, and pressure bonding is performed.

Further, the adhesive layer provided on the pallet is transferred to the adhesive surface of the light guide plate or the like, the polarization separation film is disposed on the adhesive layer and pressure-bonded, and then the adhesive layer is similarly transferred thereon. 1
/ 4 wavelength plate or polarizing film is sequentially pressure-bonded, or an adherend such as a polarization separation film, a 1/4 wavelength plate, a polarizing film or a light guide plate is attached in a predetermined manner via an adhesive layer provided on a predetermined adhesive surface in advance. There is also a method in which the layers are laminated in this order, and they are pressed and collectively pressure-bonded.

In the present invention, the processing order and the like are not particularly limited, except that each component forming the polarizing element is adhered and laminated in a predetermined arrangement order via a predetermined adhesive layer, and an appropriate method is used. The polarizing element may be formed of. Even when the polarization separation film, the quarter-wave plate, the polarization film, the light guide plate, and the like are formed of a plurality of separation materials, it is preferable to form them as an integrated adhesive product via an adhesive layer.

As described above, the polarizing element of the present invention is used in combination with an appropriate light source such as a light guide plate, and the circularly polarized light reflected by the polarization separation film is converted into polarized light and reused as outgoing light. Is prevented and the output light is phase-controlled through a quarter-wave plate to convert the linearly polarized light component of the polarizing plate to a rich state, thereby preventing the absorption loss by the polarizing film and improving the light utilization efficiency. It is intended to improve.

Therefore, since it provides light which is excellent in light utilization efficiency and can easily pass through the polarizing film and can be easily made large in area, it is preferably used in various devices such as a backlight system in a liquid crystal display device. You can
In that case, 65% of the linearly polarized light component that can be transmitted through the polarizing film as the long-axis component of the linearly polarized light or the elliptically polarized light is used rather than using the light emitted from the quarter-wave plate as the light source.
Above all, it is preferable to contain 70% or more.

The polarizing element according to the present invention can also be used by laminating appropriate optical elements such as a retardation film and a light diffusing plate at an appropriate position on the surface or between layers through an adhesive layer. Such a pre-adhesion method has an advantage that a device having stable quality and excellent reliability can be obtained as compared with a sequential adhesion method in an assembly line. In that case, as the pressure-sensitive adhesive layer used for lamination and integration, one having excellent stress relaxation property can be preferably used as in the case of the polarizing element.

In FIG. 4, an adhesive layer 24 is formed on the quarter wave plate 4.
An example of an elliptically polarizing element in which the retardation film 7 is adhered via the adhesive layer 25 on the polarizing film 6 adhered via to form an integrated laminate. Reference numeral 26 is an adhesive layer. FIG.
In the above, an example in which the light diffusion plate 8 is adhesively arranged on the adhesive layer 26 is illustrated.

The retardation film 7 disposed on the polarizing film 6 converts the linearly polarized light transmitted through the polarizing film into elliptically polarized light to adjust the plane of polarization of the light incident on the liquid crystal cell, or the liquid crystal cell. The object is to improve the visibility by compensating the optical characteristics due to the birefringence of the above.
As the retardation film, those exemplified above as the quarter-wave plate can be appropriately used according to the wavelength range or the like. The retardation film may be formed as one layer or two or more layers.

On the other hand, the light diffusing plate diffuses light for the purpose of homogenizing the brightness and expanding the light emitting direction. The light diffusing plate is, for example, one layer at an appropriate position between the surface of the polarizing element or the layers of the components forming the polarizing element, such as the upper side of the quarter-wave plate or the polarizing film, or the upper surface of the polarization separation film or the light guide plate. Two or more layers can be arranged.

As the light diffusing plate, a suitable one such as a transparent film having a diffusing structure by an appropriate method such as the fine concavo-convex structure exemplified by the transparent protective layer of the polarizing film or the diffusing structure exemplified by the light guide plate is used. It is possible to use any known light diffusing plate.

In the present invention, forming components such as an adhesive layer, a polarization separation film, a quarter-wave plate and a polarizing film, a light guide plate, a retardation film, and a light diffusing plate forming a polarizing element are made of, for example, salicylate-based ester. It is also possible to impart ultraviolet absorption ability by a method of treating with an ultraviolet absorber such as a compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex salt compound.

A liquid crystal display device using the polarizing element of the present invention in a backlight system is illustrated in FIGS. 6 and 7. This has a light source 12 on the side of the light guide plate 1 forming the polarizing element to form a backlight system. Further, 9 is a liquid crystal cell, 27, 28 and 29 are adhesive layers, 6 and 61 are polarizing films, 7 and 71 are retardation films, and 8 is a light diffusion plate. As shown in the figure, the liquid crystal cell is arranged on the quarter wavelength plate side of the polarizing element.

The polarizing element of the present invention can be particularly preferably used for forming a liquid crystal display device having polarizing films 6 and 61 on both sides of a liquid crystal cell 9. In the case of a polarizing element having a polarizing film on the upper side of the quarter wavelength plate, the polarizing film 6 on the side of the liquid crystal cell 9 on which the polarizing element is provided can be omitted.

A liquid crystal display device is generally formed by appropriately assembling components such as a polarizing film, a liquid crystal cell, a backlight, and a retardation film for compensation, if necessary, and incorporating a drive circuit. In the present invention, as described above, there is no particular limitation except that the liquid crystal cell having the necessary polarizing film is provided on the side of the quarter-wave plate in the polarizing element, and it can be formed according to the conventional method. Is preferably integrally bonded via a pressure-sensitive adhesive layer.

Further, the polarizing element of the present invention can be preferably used in a liquid crystal cell that needs to enter light in a polarized state, for example, one using twist nematic liquid crystal or super twist nematic liquid crystal, but non-twist liquid crystal or Guest-host liquid crystal in which dichroic material is dispersed in liquid crystal,
Alternatively, it can be used for a device using a ferroelectric liquid crystal.
The liquid crystal driving method is not particularly limited.

In forming the liquid crystal display device, for example, a light diffusion plate or an anti-glare layer, an antireflection film, a protective layer or a protective plate provided on the polarizing film on the viewing side, or the liquid crystal cell and the viewing side and / or the backlight. An appropriate optical element such as a retardation plate for compensation provided between the polarizing films on the side can be appropriately arranged.

Example 1 A light guide plate having a thickness of 5 mm and made of polymethylmethacrylate having a reflective layer made of an Al vapor-deposited layer on the back surface had a diameter of 4 mm.
After arranging a cold cathode tube of mm, and surrounding the side surface of the light guide plate and the cold cathode tube with an aluminum vapor deposition film, a polarized light separating film having a selective reflection property in the wavelength range of 400 to 700 nm is provided on the surface of the light guide plate. / 4 wave plates were sequentially arranged via an acrylic adhesive layer having a thickness of 20 μm, which were press-bonded to be laminated and integrated to obtain a polarizing element.

The polarized light separating film was prepared by adding a tetrachloroethane solution prepared by adding a chiral agent (CM-32, manufactured by Chisso Co.) to a side chain type nematic liquid crystal polymer having a methacrylic main chain, to form a 50 μm thick triacetyl cellulose film. It is applied to the polyimide rubbing treated surface of No. 3 by a spin coating method, dried and cured at 150 ° C. for 10 minutes to have a thickness of 5
A method for forming a cholesteric liquid crystal layer of μm, the selective reflection having a mirror-like selective reflection state has a central wavelength of 450 n.
It was obtained by obtaining three kinds of cholesteric liquid crystal layer-attached films of m, 550 nm, or 650 nm, and pressure-bonding and laminating them with an acrylic adhesive layer having a thickness of 20 μm. The adjustment of the central wavelength of the selective reflection is
It was performed by changing the addition amount of the chiral agent.

The 1/4 wave plate gives a phase difference of 1/4 wavelength to a light having a wavelength of 550 nm obtained by uniaxially stretching a polycarbonate film having a thickness of 100 μm at 160 ° C. by 1.05 times, Half of the retardation film cut so that the stretching axis is 17.5 degrees and a polycarbonate film having a thickness of 100 μm are uniaxially stretched 1.06 times at 160 ° C. to a light having a wavelength of 550 nm. It is obtained by pressure-bonding and laminating a retardation film, which is cut so that the stretching axis is 80 degrees and which gives a retardation of wavelength, with an acrylic adhesive layer having a thickness of 20 μm to be integrated.

Further, the acrylic adhesive layer was prepared by adding 99.9 parts by weight of butyl acrylate / 0.1 part by weight of 6-hydroxyhexyl acrylate / in a reaction vessel equipped with a cooling pipe, a nitrogen introducing pipe, a thermometer and a stirrer. 0.32 parts by weight of 2,2-azobisisobutyronitrile was added together with 120 parts by weight of ethyl acetate, and the mixture was put in a nitrogen gas stream at 60 ° C. for 4 hours and then at 70 ° C.
114% by weight of ethyl acetate was added to the solution obtained by the reaction for 2 hours to adjust the solid content concentration to 30% by weight, and 0.3 parts by weight of trimethylolpropane tolylene diisocyanate was added to 100 parts by weight of the solid content. The acrylic pressure-sensitive adhesive obtained in this way was applied onto a polyester film separator whose surface was treated with a silicone-based release agent, and the temperature was adjusted to 3 at 120 ° C.
It is formed by heating and drying for a minute. The relaxation elastic modulus of the acrylic pressure-sensitive adhesive layer was 6 × 10 ⁶ dyne / cm ² .

Comparative Example The same light guide plate, polarization separation film, and quarter wave plate as in Example 1 were laminated and integrated without interposing an adhesive layer therebetween.
The polarizing element was formed by simply stacking them.

Evaluation Test A liquid crystal display panel was adhered on the quarter-wave plate of the polarizing element obtained in Example 1 and Comparative Example through the acrylic adhesive layer having a thickness of 20 μm described above. The front luminance when the backlight was lit on the viewing side was measured with a luminance meter (manufactured by Minolta Camera Co., Ltd.), and the display state 5 hours after the start of lighting was examined. In the liquid crystal display panel, elliptical polarizing films (NRZ / EF / EG manufactured by Nitto Denko Corporation) are bonded to both sides of a liquid crystal cell via acrylic adhesive layers.

The above results are shown in the following table.

From the table, it can be seen that the liquid crystal display device using the polarizing element of the present invention has a small reflection loss of incident light, contains a large amount of light transmitting through the polarizing film, has a small absorption loss, and is excellent in utilization efficiency of the supplied light. It can be seen that, in addition to being excellent in brightness and bright, display unevenness is less likely to occur due to heat from the light source and visibility is excellent.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a polarizing element example.

FIG. 2 is a cross-sectional view of another example of a polarizing element.

FIG. 3 is a cross-sectional view of still another example of a polarizing element.

FIG. 4 is a cross-sectional view of an example of an elliptically polarizing element.

FIG. 5 is a sectional view of another example of an elliptically polarizing element.

FIG. 6 is a cross-sectional view of an example of a liquid crystal display device.

FIG. 7 is a cross-sectional view of another liquid crystal display device example.

[Explanation of symbols]

 1: Light guide plate 11: Reflection layer 5: Polarizing element 2, 20-29: Adhesive layer 3: Polarization separation film 31, 32, 33: Cholesteric liquid crystal layer 4: Quarter wave plate 41, 42: Phase difference layer 6, 61: polarizing film 7,71: retardation film 8: light diffusing plate 9: liquid crystal cell

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Naofumi Mihara 1-2-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation (72) Hideo Abe 1-2-1 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation

Claims (12)

[Claims] 1. A polarizing element comprising a laminated body in which a polarization separation film made of a cholesteric liquid crystal layer and a quarter-wave plate are bonded together via an adhesive layer having excellent stress relaxation property. 2. The polarizing element according to claim 1, wherein the polarization separation film is composed of an adhesive laminate of two or more layers of cholesteric liquid crystal layers having different central wavelengths of selective reflection. 3. The polarizing element according to claim 1, which has a dichroic substance-containing polarizing film adhered to the quarter-wave plate side via an adhesive layer having an excellent stress relaxation property. 4. The polarizing element according to claim 3, wherein the polarizing film has a transmission axis parallel to the polarized light transmitted through the quarter-wave plate. 5. The quarter-wave plate according to any one of claims 1 to 4, wherein the maximum refractive index in the film plane is n _x , the refractive index in the orthogonal direction is n _y , and the refractive index in the thickness direction is n _z . When the expression:
_{N z = (n x -n z} ) / (n x -n y) represented by N _z is, N
_A polarizing element using a retardation film satisfying _z <1.1. 6. The polarizing element according to claim 1, wherein the quarter-wave plate is composed of a single layer of a retardation film or two or more adhesively laminated products having different retardations. 7. The adhesive laminate according to claim 6, wherein the quarter-wave plate is a quarter-wave plate satisfying N _z <1.1 and one or more half-wave plates. A polarizing element consisting of. 8. The polarizing element according to claim 3, wherein the polarizing film has a light transmittance of 40% or more and a polarization degree of 99.0% or more. 9. The polarizing element according to claim 1, which has one or more light diffusion plates on the surface or between the layers. 10. The polarizing element according to claim 1, wherein a light guide plate having a reflective layer on the back surface and emitting light from the front surface is bonded to the polarization separation film side via an adhesive layer having excellent stress relaxation properties. . 11. The adhesive layer according to claim 1, wherein the adhesive layer is 2
A polarizing element having a relaxation elastic modulus of × 10 ⁵ to 1 × 10 ⁷ dyne / cm ² . 12. An elliptically polarizing element having a retardation film adhered to the polarizing film side of the polarizing element according to any one of claims 3 to 11 via an adhesive layer having an excellent stress relaxation property.