JPH10319233A - Elliptic polarizing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the elliptic polarizing element which has small reflection loss of light and superior utilization efficiency of light and can form a liquid crystal display device having superior lightness without causing any decrease in display quality due to the formation of a smear pattern and color unevenness. SOLUTION: This polarizing element is formed of a laminate obtained by adhering a polarized light separating film 3 formed of a cholesteric liquid crystal layer, a 1/4 wavelength plate 4, and a surface roughened film 5 in order across adhesive layers 2 and 21. On the side of the polarized light separation film 3, a light guide plate 1 which has a reflecting layer 11 on the reverse side and emits light from its surface is adhered across the adhesive layer 20 when necessary. Consequently, elliptic polarized light emitted by the polarized light separating film 3 is linearly polarized through the 1/4 wavelength plate 4 to prevent a decrease in the display quality due to a smear pattern, etc., of the liquid crystal display device by the presence of the polarizing plate across the surface roughened film 5, reflection loss on each boundary surface is small because of the laminate unification across the adhesive layers 20, and display unevenness due to heat from a light source is hardly generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

BACKGROUND OF THE INVENTION Hitherto, there has been known a polarization separation film utilizing a characteristic that a cholesteric liquid crystal layer separates incident light into left and right circularly polarized lights, transmits one of them, and reflects the other.
Attempts have been made to use it to improve the brightness of liquid crystal displays. By the way, circularly polarized light by the polarization separation film can be converted to linearly polarized light by transmitting through a 1/4 wavelength plate.
By making the vibration direction coincide with the transmission axis, the absorption loss by the polarizing plate can be reduced, and the brightness of the liquid crystal display can be improved by increasing the amount of transmitted light.

In the above case, the liquid crystal display device is formed by sequentially arranging a polarization separating film, a quarter-wave plate, a polarizing plate and a liquid crystal cell. However,
In the configuration in which the polarization separation film, the quarter-wave plate and the polarization plate are sequentially arranged, there is a problem that a spot pattern or color unevenness occurs in the liquid crystal display device, which causes a fatal defect in display quality.

[0004]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal display device which has a small reflection loss of light, is excellent in light use efficiency, and has excellent brightness without causing deterioration in display quality due to occurrence of spot patterns and color unevenness. The task is to develop an elliptically polarizing element that can be used.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a laminate comprising a polarizing separation film comprising a cholesteric liquid crystal layer, a quarter-wave plate and a surface-roughened film sequentially bonded via an adhesive layer having excellent stress relaxation properties. And an elliptically polarizing element characterized by further comprising, if necessary, a light guide plate having a reflective layer on the back surface and emitting light from the front surface adhered to the polarization separation film side via the adhesive layer. Is what you do.

[0006]

According to the above construction, the polarized light separating film comprises:
Light incident through the light guide plate or the like is separated into left and right circularly polarized lights, 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,
In the meantime, while being repeatedly reflected, 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 in the incident light,
This reduces the amount of unused light due to reflection loss.

On the other hand, the circularly polarized light emitted from the polarized light separating film is converted into a state having a large amount of linearly polarized light components such as linearly polarized light and flat elliptically polarized light through a quarter-wave plate. When the direction of the linearly polarized light coincides with the transmission axis of the polarizing plate, the converted light passes through the polarizing plate without being absorbed, thereby reducing unused light due to absorption loss. As a result, light that has conventionally been a reflection loss or an absorption loss can be effectively used, and the light use efficiency can be improved.

In the above, in the elliptically polarizing element of the present invention,
The polarizing plate on the viewing rear side of the liquid crystal cell comes into contact with the surface roughening film, thereby preventing a deterioration in display quality due to occurrence of a spot pattern or color unevenness in the liquid crystal display device. From this point, it is considered that the occurrence of the above-mentioned spot pattern and color unevenness is caused by the sticking phenomenon due to the close contact between the quarter-wave plate and the polarizing plate.

[0009] Further, by laminating and integrating through an adhesive layer, the reflection loss at each interface is small, foreign substances and the like can be prevented from entering the interface, and the display quality can be prevented from deteriorating. A decrease in efficiency can also be prevented. In addition, by laminating and unifying through an adhesive layer that is excellent in stress relaxation, the stress generated in the polarization separation film, quarter-wave plate, and even the polarizing plate due to heat from the light source can be suppressed, and the refractive index generated by photoelastic deformation Can be prevented from changing. As a result, a liquid crystal display device which is bright and has excellent visibility and reliability of display quality can be formed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The elliptically polarizing element of the present invention is a laminate in which a polarization separation film composed of a cholesteric liquid crystal layer, a quarter-wave plate and a surface roughened film are sequentially bonded via an adhesive layer having excellent stress relaxation properties. If necessary, 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 the adhesive layer, if necessary.

FIGS. 1 and 2 show an elliptically polarizing element according to the present invention. 2, 20, 21, 22, 23, and 24 are adhesive layers, 3 is a polarization separation film, 4 is a 波長 wavelength plate, 5 is a surface roughened film, and 1 is a light guide plate as needed. . As shown in FIG. 2, the polarization separating film 3 may be formed as a superimposed layer of a plurality of cholesteric liquid crystal layers 31, 32, and 33, and the quarter-wave plate 4 may include a plurality of retardation layers 4.
1, 42 may be formed as a superimposed layer.

According to the elliptically polarizing element having the light guide plate of the illustrated example, predetermined circularly polarized light out of the light emitted from the surface of the light guide plate 1 is converted by the polarization separation film 3 disposed on the surface side of the light guide plate. The light is transmitted through the 波長 wavelength plate 4 to the outside. On the other hand, 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, is reflected through the reflection layer 11 on the back surface, and re-enters the polarization separation film 3 as return light. .

The light reflected by the polarization splitting film is:
When the light is reflected by the back surface of the light guide plate, the polarization state is changed, and a part or all of the reflected light becomes a predetermined circularly polarized light that can pass through the polarization splitting film. Therefore, the light reflected by the polarized light separating film is confined between the polarized light separating film and the light guide plate until the light becomes a predetermined circularly polarized light that can pass through the polarized light separating film, and the light is repeatedly reflected between them.

On the other hand, the circularly polarized light emitted from the polarization splitting film enters the quarter-wave plate 4 and undergoes a phase change. Light having a wavelength corresponding to the quarter-wavelength change is converted into linearly polarized light. , Light of other wavelengths are converted to 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, light containing a large amount of linearly polarized light component that can be transmitted through the polarizing plate is emitted from the surface roughened film via the quarter-wave plate.

In the present invention, the polarized light separating film and 1 /
Each component of the four-wavelength plate, the surface-roughened film, and the light guide plate as required is laminated and integrated via an adhesive layer having excellent stress relaxation properties. In this case, the arrangement position of each component is such that a quarter-wave plate 4 is provided on the polarized light separating film 3 and a surface roughened film 5 is provided thereon, as shown in the figure, in order to obtain a desired function. Thus, the elliptically polarizing element 6 is provided. The light guide plate 1 is arranged on the polarization separation film 3 side of the elliptically polarizing element 6, and the surface (light emission) side of the light guide plate is the polarization separation film side.

As the polarized light separating film, a film composed of a cholesteric liquid crystal layer is used. According to the cholesteric liquid crystal layer, the left and right circularly polarized light can be selectively separated into either one of the two through transmission and reflection, and has an advantage of a wide viewing angle. In the case of a cholesteric liquid crystal layer, a change in optical characteristics with respect to a change in viewing angle is small, and thus the cholesteric liquid crystal layer is suitable for a direct-view type liquid crystal display device that can be directly observed even from 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. Cholesteric liquid crystal molecules having a large birefringence are preferable because the wavelength range of the selective reflection is widened. 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.

The liquid crystal polymer includes, for example, a main chain type liquid crystal polymer such as polyester, a side chain type liquid crystal polymer having an acrylic main chain, a methacryl main chain, a siloxane main chain, etc., a nematic liquid crystal polymer containing a low molecular weight chiral agent, and the like. Examples of the liquid crystal polymer include a chiral component-introduced liquid crystal and a mixed liquid crystal polymer of a nematic type and a cholesteric type. 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. Incidentally, examples thereof include a film formed by forming a film of polyimide or polyvinyl alcohol on a substrate and rubbing with a rayon cloth or the like,
A liquid crystal polymer is spread on an appropriate alignment film composed of an obliquely deposited layer of iO ₂ and heated to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature. A method of cooling to a glass state by cooling to a temperature lower than the temperature to form a solidified layer in which the orientation is fixed is exemplified.

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 a suitable coating machine such as a bar coater, a spinner, a roll coater, and a gravure printing method. Upon development, a cholesteric liquid crystal layer superimposing method via an alignment film may be used as 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 oblique incident light, and even when formed as two or more superposed layers, each layer is flat. Is preferable. When forming the cholesteric liquid crystal layer or the polarized light separating film, various additives such as stabilizers, plasticizers, and metals can be added as necessary.

As described above, the polarized light separating film can be formed as a superposed body having two or more cholesteric liquid crystal layers. The superimposition is advantageous from the point of increasing the wavelength range of the separation function and addressing the wavelength shift of obliquely incident light.
In that case, it is preferable to superimpose the light reflected as circular polarized light other than the predetermined wavelength in a different combination, and it is preferable to superimpose the light in the order of longer and shorter based on the central wavelength of the selective reflection. That is, in a single cholesteric liquid crystal layer, there is usually a limit to a wavelength region showing selective reflection (circular dichroism), and the limit may be a wide range up to a wavelength region of about 100 nm. However, since it does not cover the entire range of visible light desired when applied to a liquid crystal display device or the like,
In such a case, a cholesteric liquid crystal layer having different selective reflectivity can be superimposed to expand the wavelength region exhibiting circular dichroism.

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.
nm is a combination that reflects circularly polarized light in the same polarization direction,
And the central wavelength of selective reflection is different, especially 50nm each
By using different combinations as described above and superimposing two to six kinds thereof, it is possible to efficiently form a polarization separation film that can cover a wide wavelength range. 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. The cholesteric liquid crystal polymer layers having different central wavelengths of selective reflection and having a discontinuous wavelength range of selective reflection are brought into close contact with each other via thermocompression bonding or the like, and the width of the discontinuous wavelength range is reduced by heat treatment. It is also possible to form a polarized light separating film in which the wavelength range of selective reflection is continuous.

Therefore, as the polarized light separating film, a film in which the wavelength range of light that can be reflected as circularly polarized light other than the predetermined light as much as possible matches the wavelength range of emitted light based on the light guide plate can be preferably used. If the emitted light has a dominant wavelength such as a bright line spectrum, it is necessary to match the wavelength of the reflected light based on the cholesteric liquid crystal phase or the like to one or more dominant wavelengths such as efficiency of polarization separation. It is the next best solution from the point,
This is also advantageous for making the polarization separation film thinner by reducing the required number of superpositions. In this case, it is preferable that the degree of coincidence of the wavelengths of the reflected light is within a range of 20 nm or less for one or two or more types of main wavelength light of the light guide plate.

In the above, it has been pointed out that, when the polarization separation film is formed as a superposed layer of the cholesteric liquid crystal layer, a combination of those which reflect circularly polarized light having the same polarization direction is used. This aligns the phase state of the circularly polarized light reflected by each layer to prevent different polarization states in each wavelength range,
The aim is to increase the available polarization. As described above, a suitable cholesteric liquid crystal may be used, but a cholesteric liquid crystal molecule having a larger phase difference has a wider wavelength range of selective reflection, such as a reduction in the number of layers and a margin for a wavelength shift at a large viewing angle. It can be preferably used from the point of view.

The polarized light separating film used in the present invention is, for example, a cell type in which a cholesteric liquid crystal layer composed of a low molecular weight substance is sandwiched between transparent substrates such as a film, a form in which a cholesteric liquid crystal layer composed of a liquid crystal polymer is supported by a transparent substrate, An appropriate form such as a form composed of a film of a cholesteric liquid crystal polymer and a form in which these forms are superimposed in an appropriate combination can be adopted. In that case, the cholesteric liquid crystal layer can be held by one or more supports depending on the strength, operability and the like. 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.

A quarter arranged on one side of the polarized light separating film
The wavelength plate is intended to change the phase of the circularly polarized light emitted from the polarization splitting film as described above to convert it into a state having a large amount of linearly polarized light components. Can be obtained.

Accordingly, the quarter-wave plate can form a large amount of linearly polarized light corresponding to the phase difference of the quarter-wavelength circularly-polarized light emitted from the polarized light separating film, and can convert the light of other wavelengths into the linearly-polarized light. Those having a major axis direction as parallel as possible to polarized light and capable of converting into flat elliptically polarized light as close to linearly polarized light as possible can be preferably used. By using such a 波長 wavelength plate, the linearly polarized light direction and the major axis direction of the elliptically polarized light of the emitted light can be arranged so as to be as parallel as possible to the transmission axis of the polarizing plate, and can be transmitted through the polarizing plate. Light with a large amount of linearly polarized light components can be obtained.

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

Further retardation layer may be colored by the viewing angle, it is from the point of preventing the coloring of the formula: N _z =
_{(N x -n z) / (} n x -n y) is defined by N _z 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 has a single-layer retardation layer or, as illustrated in FIG. 2, has a different phase difference for the purpose of expanding the wavelength range that can function as a quarter-wave plate. 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.

[0034] In the above, from the viewpoint of obtaining a quarter-wave plate of superposition type for preventing coloration due viewing angle, the N _z ≦ 1.
A retardation layer that provides a quarter-wave retardation that satisfies 1.
It is preferable to use a superimposed body using one or two or more retardation layers that provide a half-wave retardation.

As described above, the quarter-wave plate can be obtained as a single layer or a superposed body of the retardation layer. For example, 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, when the liquid crystal cell is arranged on the elliptically polarizing element via the polarizing plate, the surface roughened film arranged on the quarter-wave plate can be used to adhere the elliptically polarizing element to the polarizing plate. The purpose of the present invention is to prevent the occurrence of a spot pattern or color unevenness due to the above. Therefore, an appropriate film having fine irregularities can be used as the surface roughened film.

The surface roughening film which can be preferably used is
A fine uneven structure is provided on one surface or both surfaces by a method in which fine particles are dispersed and fixed on the film or fine particles are contained in the film. Therefore, it may be a film conforming to an anti-glare treatment performed for the purpose of preventing glare on the viewing side of the liquid crystal display device. 1/4
The surface roughness is 0.1 μm or more based on the center line average roughness (Ra) for preventing adhesion of the wave plate and the polarizing plate.
A surface roughened film having a surface average roughness (Rz) of 1 μm or more is preferred.

The above-mentioned fine particles include, for example, inorganic materials which may be conductive such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide and antimony oxide having an average particle size of 0.5 to 20 μm. Fine particles,
Appropriate materials such as organic fine particles such as a crosslinked or uncrosslinked polymer can be used.

The surface roughened film is, for example, an unoriented film because it preserves the linearly polarized light through a quarter-wave plate as much as possible, that is, to prevent the polarization state from changing. A film having a retardation as small as possible, such as a triacetate film having a small birefringence even when oriented, particularly a film having a retardation of 50 nm or less, particularly 30 nm or less, can be preferably used. The thickness of the surface-roughened film may be determined as appropriate, and is generally 500 μm or less, especially 300 μm or less, particularly 5 to 100 μm.

In the elliptically polarizing element of the present invention, as shown in the drawing, the light guide plate which is adhered and arranged as necessary on the polarization separation film side has a reflection layer on the back surface and emits light to the front surface side. Any suitable one can be used. Preferably, one that efficiently emits light without absorption is used.
(Cold, hot) A linear light source such as a cathode ray tube or a light source such as a light emitting diode is disposed on the side surface of the light guide plate 1, and the light transmitted through the light guide plate is diffused, reflected, diffracted or interfered with the light guide plate. An example is a sidelight-type backlight known to liquid crystal display devices that emits light to one side of a plate.

In the above, the light guide plate for emitting the internal transmission light to one side is provided with a diffuser in the form of dots or stripes on the light emission surface of a transparent or translucent resin plate or on the back surface thereof. It can be obtained as a product or a product in which a concave and convex structure is provided on the back surface of a resin plate.

The light guide plate that emits light to one surface side can have a function of converting the light reflected by the polarization splitting film by itself, 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 is excellent in the function of converting the light reflected by the polarization separation film into a polarized light, and is preferable in the present invention.

Incidentally, in a diffuse reflection layer represented by an uneven surface or the like, polarization states are randomly mixed based on the diffusion to form a state in which polarized light is eliminated. 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.

In forming the light guide plate, a prism sheet for controlling the light emission direction, a diffusion plate for obtaining uniform light emission, a reflection means for returning leaked light, and a light guide for emitting light from the linear light source. Auxiliary means such as a light source holder for guiding to the side surface of the light plate may be arranged in one or more layers at predetermined positions as necessary to form an appropriate combination. In addition, a prism sheet or a diffusion plate disposed on the surface side (light emission side) of the light guide plate, or dots provided on the light guide plate can function as polarization conversion means for changing the phase of reflected light by a diffusion effect or the like.

The elliptically polarizing element of the present invention is an adhesive having excellent stress relaxation properties by separating each component of the polarized light separating film, the quarter-wave plate, the surface roughening film, and the light guide plate as required. The laminate is obtained by bonding through layers. When the materials forming the polarization separation film, quarter-wave plate, surface roughened film, and light guide plate are not in a tightly integrated state but in a separated state, the adhesive layer is also involved in the tightly integrated state. Is used.

For forming the pressure-sensitive adhesive layer, a transparent pressure-sensitive adhesive which is excellent in stress relaxation and 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 due to heat. 2 × 10 ⁶ -8 ×
Those having 10 ⁶ dyne / cm ² are preferred.

Specific examples of the acrylic polymer forming the acrylic pressure-sensitive adhesive include, for example, methyl group, ethyl group, n-propyl group and isopropyl group, n-butyl group and 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, isodecanyl group, especially those having 2 to 2 carbon atoms. One obtained by polymerizing one or more of acrylic acid esters and methacrylic acid esters having 14 alkyl groups together with one or two or more types of modifying monomers as necessary.

Specific examples of the modifying monomer include:
2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate,
12-hydroxylauryl (meth) acrylate and (4-
Hydroxyl group-containing monomers such as hydroxymethylcyclohexyl) -methyl acrylate, acrylic acid and methacrylic acid, carboxyethyl acrylate and carboxypentyl acrylate, carboxyl group-containing monomers such as itaconic acid, maleic acid and crotonic acid, maleic anhydride and itaconic anhydride Acid anhydride monomers such as
Examples thereof include sulfonic acid group-containing monomers such as acrylamide-2-methylpropanesulfonic acid, and phosphoric acid group-containing monomers such as 2-hydroxyethylacryloyl phosphate.

An amide monomer such as (meth) acrylamide or N-substituted (meth) acrylamide;
Maleimide monomers such as cyclohexylmaleimide and N-isopropylmaleimide, N-laurylmaleimide and N-phenylmaleimide, N-methylitaconimide and N-ethylitaconimide, N-butylitaconimide and N-octylitaconimide, N-2 -Ethylhexylitaconimide, N-cyclohexylitaconimide, itaconimide monomers such as N-laurylitaconimide, N- (meth) acryloyloxymethylene succinimide, N- (meth) acryloyl-6-oxyhexamethylene succinimide, N- (meta) S) A succinimide-based monomer such as acryloyl-8-oxyoctamethylene succinimide is also exemplified as a modifying monomer.

Further, vinyl monomers such as vinyl acetate, N-vinylpyrrolidone, N-vinylcarboxylic acid amides and styrene, divinyl monomers such as divinylbenzene, 1,4-butyldiacrylate and 1,6-hexyldiamine Diacrylate monomers such as acrylates,
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 method of preparing 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 can be used as required. 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, preferably 200,000 or more, and particularly 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 elliptically polarizing element is formed by, for example, transferring a pressure-sensitive adhesive layer provided on a separator obtained by surface-treating a thin film such as a film with a release agent to the bonding surface of the polarizing separation film, and then forming a ４ After the wave plate is pressed, a pressure-sensitive adhesive layer is similarly transferred onto the quarter-wave plate, and a surface-roughened film is placed thereon and pressed.

Further, an adhesive layer provided on a parator is transferred to an adhesive surface of a light guide plate or the like, and a polarization separation film is disposed thereon and pressed, and then the adhesive layer is transferred thereon in the same manner. 1
A method of sequentially pressing a / 4 wavelength plate or a surface roughened film,
Alternatively, an adherend such as a polarization separation film, a quarter-wave plate, a surface-roughened film, a light guide plate, or the like is laminated in a predetermined order via an adhesive layer provided on a predetermined adhesive surface in advance, and the laminate is pressed. And a method of pressing them all at once.

In the present invention, the processing order and the like are not particularly limited, except that the components forming the elliptically polarizing element are bonded and laminated in a predetermined arrangement order via a predetermined adhesive layer. The elliptically polarizing element may be formed in a manner.
In addition, even when the polarization separation film, the quarter-wave plate, the surface roughened 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 through an adhesive layer.

As described above, the elliptically polarizing element of the present invention is used in combination with an appropriate light source such as a light guide plate to convert the circularly polarized light reflected by the polarization splitting film into a polarized light and reuse the converted light as the outgoing light. Loss is prevented, the output light is phase-controlled through a quarter-wave plate, and converted to a state containing a linearly polarized component that is transparent to the polarizer, thereby preventing absorption loss by the polarizer and improving light use efficiency. It is intended to be able to measure improvement.

Therefore, it is possible to provide light that is excellent in light use efficiency and easily transmit through a polarizing plate, and it is easy to enlarge the area. Can be. In this case, 65% or more, especially 7%, of the linearly polarized light component that can be transmitted through the polarizing plate as linearly polarized light or elliptically polarized light in the major axis direction is used, rather than using the light emitted from the quarter wavelength plate as a light source.
It is preferable to contain 0% or more.

FIG. 3 illustrates a liquid crystal display device using the elliptically polarizing element of the present invention in a backlight system. this is,
The light source 12 is provided on the side surface of the light guide plate 1 provided on the elliptically polarizing element 6 to form a backlight system. 7, 71 are polarizing plates, 8 is a liquid crystal cell, and 13, 15, 25, 26, 2
7, 28 and 29 are adhesive layers, 14 and 92 are light diffusion plates, 16
Denotes a prism sheet, and 91 denotes a retardation film. As shown in the figure, the liquid crystal cell is arranged on the side of the surface roughening film 5 of the elliptically polarizing element 6.

A liquid crystal display device is generally formed by appropriately assembling components such as a polarizing plate, a liquid crystal cell, a backlight and, if necessary, a compensating retardation film and incorporating a drive circuit. In the present invention, there is no particular limitation except that the liquid crystal cell is provided on the surface roughened film side of the elliptically polarizing element via a polarizing plate, and a liquid crystal display device can be formed according to the related art. It is preferable that they are bonded and integrated via an adhesive layer. As shown in FIG. 3, the elliptically polarizing element of the present invention can be particularly preferably used for forming a liquid crystal display device having polarizing plates 7 and 71 on both sides of a liquid crystal cell 8.

The elliptically polarizing element of the present invention can be preferably used for a liquid crystal cell in which light in a polarized state needs to be incident, for example, a liquid crystal cell using a twisted nematic liquid crystal or a super twisted nematic liquid crystal. And a guest-host type liquid crystal in which a dichroic substance is dispersed in a liquid crystal, or a liquid crystal using a ferroelectric liquid crystal. There is no particular limitation on the driving method of the liquid crystal.

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

The above-mentioned light diffusing plate is intended to diffuse light and to make the luminance uniform and to expand the light emitting direction. Therefore, the light diffusion plate, for example, such as a polarization separation film or the upper surface of the light guide plate,
One layer or two or more layers can be arranged at appropriate positions on the surface or inside of the elliptically polarizing element. As the light diffusing plate, an appropriate one such as a transparent film having a diffusing structure by an appropriate method such as a fine uneven structure exemplified by a surface roughened film or a diffusing structure exemplified by a light guide plate can be used. Any of the light diffusion plates can be used. The compensating retardation plate is used for compensating birefringence of a liquid crystal cell or the like to prevent coloring of a display and the like, and can be obtained as a stretched film or the like according to the above-described quarter-wave plate.

In the arrangement of the liquid crystal cell and the elliptically polarizing element via the polarizing plate, the angle of arrangement of the polarizing axis of the polarizing plate with respect to the fast axis or slow axis of the quarter-wave plate is as follows. It can be appropriately determined according to the phase difference characteristic, the characteristic of the circularly polarized light incident on the phase difference characteristic, etc.
It is preferable to arrange the transmission axis of the polarizing plate as parallel as possible to the polarization direction of the linearly polarized light via the ／ wavelength plate.

Further, in the present invention, an adhesive layer or a polarization separation film for forming an elliptically polarizing element, a 波長 wavelength plate or a surface roughened film, or another light guide plate or retardation plate,
A component such as a light diffusion plate is provided with an ultraviolet absorbing ability by, for example, a method of treating with an ultraviolet absorbing agent such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex compound, or the like. You can also.

Example 1 A 5 mm-thick light guide plate made of polymethyl methacrylate having a reflective layer made of an Al vapor-deposited layer on the back surface has a diameter of 4 mm.
After placing a cold cathode tube of 1 mm in diameter and surrounding the side surface of the light guide plate and the cold cathode tube with an aluminum vapor-deposited film, a polarization separation film and a film having selective reflectivity in the wavelength range of 400 to 700 nm are placed on the surface of the light guide plate. A quarter-wave plate and a surface-roughened film are sequentially arranged via an acrylic adhesive layer having a thickness of 20 μm,
It was laminated by pressing and pressing to obtain an elliptically polarizing element.

The above-mentioned polarized light separating film is prepared by adding a tetrachloroethane solution obtained by adding a chiral agent (CM-32, manufactured by Chisso Corporation) to a side chain type nematic liquid crystal polymer having a methacrylic main chain, and forming a 50 μm-thick triacetyl cellulose film. Is applied by a spin coating method on a polyimide rubbed surface, and dried and cured at 150 ° C. for 10 minutes to obtain a thickness of 5 μm.
In the method of forming a cholesteric liquid crystal layer of μm, the central wavelength of selective reflection exhibiting a mirror-like selective reflection state is 450 n.
This is obtained by obtaining three types of films having a cholesteric liquid crystal layer of m, 550 nm, or 650 nm, and by crimping and laminating them through an acrylic adhesive layer having a thickness of 20 μm. The adjustment of the central wavelength of the selective reflection is as follows:
This was performed by changing the amount of the chiral agent added.

The 波長 wavelength plate is a film having a phase difference of １ ／ wavelength with respect to light having a wavelength of 550 nm obtained by uniaxially stretching a polycarbonate film having a thickness of 100 μm 1.05 times at 160 ° C. A phase difference film cut out to have an axis of 17.5 degrees, and a polycarbonate film having a thickness of 100 μm are uniaxially stretched by a factor of 1.09 at 160 ° C. to a wavelength of 550 nm, which is １ ／ wavelength. This is obtained by pressing and laminating a phase difference film cut to give a phase difference so that the stretching axis becomes 80 degrees via an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm and integrated.

On the other hand, the surface-roughened film was prepared by rapidly stirring 8 parts by weight of synthetic silica particles having an average particle diameter of 1.8 μm, 100 parts by weight of an ultraviolet-curable acrylic urethane oligomer and 3 parts by weight of benzophenone together with ethyl acetate. A 50% by weight mixed dispersion is prepared, and the thickness is 50 μm.
Is coated on one side of a triacetate film with a wire bar, and ethyl acetate is evaporated to form a coating layer having a thickness of 10 μm.
² is obtained by irradiating light and curing.
a was 0.33 μm and Rz was 3.5 μm.

Further, the acrylic pressure-sensitive adhesive layer was placed in a reaction vessel equipped with a cooling pipe, a nitrogen introduction pipe, a thermometer and a stirring device in an amount of 99.9 parts by weight of butyl acrylate / 0.1 part by weight of 6-hydroxyhexyl acrylate / 0.3 parts by weight of 2,2-azobisisobutyronitrile were added together with 120 parts by weight of ethyl acetate, and the mixture was placed at 60 ° C. for 4 hours under a nitrogen gas stream, then at 70 ° C.
To the solution obtained by reacting for 2 hours, 114 parts by weight of ethyl acetate was added to adjust the solid concentration to 30% by weight, and 0.3 parts by weight of trimethylolpropane tolylene diisocyanate was added to 100 parts by weight of the solids. The acrylic pressure-sensitive adhesive obtained above was coated on a polyester film separator surface-treated with a silicone-based release agent,
It was formed by heating and drying for minutes. The relaxation modulus of the acrylic pressure-sensitive adhesive layer was 6 × 10 ⁶ dyne / cm ² .

Comparative Example An elliptically polarizing element was obtained in the same manner as in Example 1 except that a surface roughening film was not provided on a quarter wavelength plate.

Evaluation Test A liquid crystal display panel was placed on the surface roughened film or １ ／ wavelength plate of the elliptically polarizing element obtained in Example 1 and Comparative Example.
The front luminance of the liquid crystal display panel on the viewing side when the backlight was turned on was measured, and the display state was examined. The above-mentioned liquid crystal display panel has an elliptically polarizing plate (manufactured by Nitto Denko Corporation, NRZ · E) with an acrylic adhesive layer on both sides of the liquid crystal cell.
F.EG).

As a result, the front luminance of Example 1 and that of Comparative Example were the same at 85 cd / cm ² . On the other hand, in the display state, Example 1 showed almost uniform display on the entire surface of the panel without occurrence of a stain pattern and color unevenness, but in the comparative example, a stain pattern and color unevenness occurred, and the display was partially displayed on the panel. Unevenness occurred.

In the liquid crystal display device using the elliptically polarizing element of the first embodiment, the reflection loss of incident light is small as described above,
Includes a large amount of light transmitted through the polarizing plate, minimizes absorption loss, excels in the use efficiency of the supplied light, provides high-brightness, bright display, and generates display unevenness including the influence of heat from the light source. And the visibility was excellent.

[Brief description of the drawings]

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

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

FIG. 3 is a cross-sectional view of an example of a liquid crystal display device.

[Explanation of symbols]

 1: light guide plate 11: reflection layer 14: light diffusion plate 16: prism sheet 6: elliptically polarizing element 2, 13, 15, 20 to 29: adhesive layer 3: polarization separation film 31, 32, 33: cholesteric liquid crystal layer 4: Quarter wavelength plates 41, 42: retardation layer 5: surface roughened film 7, 71: polarizing plate 8: liquid crystal cell 91: retardation plate 92: light diffusion plate

Claims (10)

[Claims] 1. An elliptically polarized light comprising a laminate in which a polarized light separating film composed of a cholesteric liquid crystal layer, a quarter-wave plate and a surface roughened film are sequentially bonded via an adhesive layer having excellent stress relaxation properties. element. 2. The elliptically polarizing element according to claim 1, wherein the polarized light separating film is formed of an adhesive laminate of two or more cholesteric liquid crystal layers having different central wavelengths of selective reflection. 3. The elliptically polarizing element according to claim 2, wherein the polarized light separating film has a wavelength range of continuous selective reflection. 4. The method of claim 1 to 3, 1/4 wave plate, a maximum refractive index in the film plane n _x, a refractive index of the direction perpendicular n _y, the refractive index in the thickness direction n _z Then, the formula:
_{N z = (n x -n z} ) / (n x -n y) represented by N _z is 1.
An elliptically polarizing element using a retardation film of 1 or less. 5. The elliptically polarizing element according to claim 1, wherein the quarter-wave plate is a single layer of a retardation film or a laminate of two or more adhesives having a retardation difference. 6. The superimposed body according to claim 5, wherein the quarter-wave plate is a quarter-wave plate satisfying N _z ≦ 1.1 and one or more half-wave plates. An elliptically polarizing element comprising: 7. The elliptically polarizing element according to claim 1, wherein the surface-roughened film is obtained by subjecting a triacetate film having a retardation of 50 nm or less to antiglare treatment. 8. The elliptically polarizing element according to claim 1, wherein the surface-roughened film has a center line average roughness of 0.1 μm or more and a 10-point average roughness of 1 μm or more. 9. The elliptically polarized light according to claim 1, wherein a light guide plate having a reflection 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. element. 10. The method according to claim 1, wherein the pressure-sensitive adhesive layer is 2 ×
An elliptically polarizing element having a relaxation modulus of 10 ⁵ to 1 × 10 ⁷ dyne / cm ² .