JPH11231130A - Polarizing element, optical element, lighting device, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element and a lighting device which can form the liquid crystal display device having superior luminance and field angle characteristics by obtaining the polarizing element which is superior in circular polarization dichroic performance, wide-band performance, and polarization degree and has superior alignment. SOLUTION: This lighting device has a polarizing element 1 consisting of cholesteric liquid crystal layers 12, 13, and 14 of <=5 μm in thickness and <=10% in haze which are stacked one over another, the optical element consisting of a stack of one or more layers of the polarizing element, a 1/4 wavelength plate, and a field angle compensating plate or polarizing plate, and the polarizing element or optical element and a surface light source or a liquid crystal cell. Consequently, the thickness can easily be increased by the stacking system of the cholesteric liquid crystal layer having excellent alignment and the polarizing element 1 is obtained which has superior circular polarization dichroic performance, wide-band performance, polarization, and alignment and also has small discoloration due to variation in field angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element suitable for improving luminance and suppressing display unevenness of a liquid crystal display device and the like, and an optical element and a lighting device using the same.

[0002]

2. Description of the Related Art Conventionally, as a polarizing element capable of improving the brightness of a liquid crystal display device by overcoming the drawbacks of a polarizing plate in which about half of incident light is absorbed and lost, circular dichroism, that is, natural light is circularly polarized. There has been known an element comprising a laminate of a cholesteric liquid crystal layer and a quarter-wave plate exhibiting a property of separating into reflected light and transmitted light. This element is arranged between the light source and the liquid crystal cell, converts the circularly polarized light transmitted through the cholesteric liquid crystal layer into linearly polarized light by a quarter-wave plate, and makes it incident on the polarizing plate with the polarization axis matched. This is to prevent absorption loss.

[0003] In the above, the usual cholesteric liquid crystal layer has a narrow wavelength range showing circular dichroism, so that a plurality of cholesteric liquid crystal layers having different wavelength ranges of circular dichroism are superposed for the purpose of broadening the band. In addition, there has been known a device in which a helical pitch is changed in a thickness direction (Japanese Patent Laid-Open No. 1-13 / 1990).
3003, JP-A-6-281814).

In addition, the cholesteric liquid crystal layer is enhanced in orientation to provide a wide viewing angle characteristic suitable for a monitor or the like, or a light collecting property in a viewing direction suitable for a notebook personal computer or the like (Japanese Patent Laid-Open No. 9-287677). No., JP-A-9-293
277, JP-A-9-314500 and JP-A-9-314501), and those in which the thickness of a cholesteric liquid crystal layer is increased to improve the degree of polarization of circular dichroism are also known (for example, Japanese Patent Application Laid-Open (JP-A) Nos. 9-181207 and 9-213873). J. Phys. D: Appl. Phys., 8, 1975).

[0005] However, in the above-mentioned prior art, when the thickness of the cholesteric liquid crystal layer is increased for the purpose of broadening the circular dichroism and improving the degree of polarization, for example, there is a problem that the degree of alignment is reduced. There is a problem that it is difficult to improve both the polarization and the degree of polarization.

[0006]

SUMMARY OF THE INVENTION The present invention provides an optical element which can obtain a polarizing element which is excellent in a broadband property and a degree of polarization of circular dichroism, and which is excellent in orientation, and can form a liquid crystal display device which is excellent in luminance and viewing angle characteristics. And the development of lighting devices.

[0007]

According to the present invention, there is provided a polarizing element comprising a superposed layer of a cholesteric liquid crystal layer having a thickness of 5 μm or less and a haze of 10% or less.
It is an object of the present invention to provide an optical element comprising a laminate of one or two or more layers of a 波長 wavelength plate, a viewing angle compensator or a polarizing plate.

According to the present invention, there is provided a liquid crystal display device comprising the above-mentioned polarizing element or optical element and a liquid crystal cell.
A lighting device having the polarizing element or the optical element above a surface light source; and a liquid crystal display device having a liquid crystal cell on a light emission side of the lighting device. .

[0009]

According to the present invention, the thickness can easily be increased by the superposition method of the cholesteric liquid crystal layer having excellent orientation, and the broadband property of circular dichroism, the degree of polarization and the orientation are excellent. In addition, it is possible to obtain a polarizing element having a small color change due to a change in viewing angle, and to obtain an optical element and a lighting device capable of forming a liquid crystal display device having excellent luminance and viewing angle characteristics using the polarizing element.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polarizing element according to the present invention has a thickness of 5 mm.
It is composed of a superposed layer of cholesteric liquid crystal layers having a size of not more than μm and a haze of not more than 10%. Examples thereof are shown in FIGS. 1
Is a polarizing element, 12, 13, 14, and 15 are cholesteric liquid crystal layers, and 11 is a transparent substrate as required. FIG. 2 illustrates an optical element in which a quarter-wave plate 2 is provided on a polarizing element 1.

The cholesteric liquid crystal layer used for superposition has a thickness of 5 μm or less and a haze of 10% or less.
Thereby, it is possible to obtain an excellent orientation. The cholesteric liquid crystal layer that can be preferably used from the viewpoint of orientation and the like has a thickness of 4.5 μm or less, preferably 1 to 4 μm, particularly 2 to 3 μm.
In μm, the haze is 9% or less, preferably 8% or less, particularly 5% or less. By using a polarizing element having excellent orientation, when applied to a liquid crystal display device in combination with a quarter-wave plate, it is possible to improve the luminance and suppress poor visibility such as display unevenness.

The cholesteric liquid crystal exhibits a circularly polarized light separating function of separating natural light into left and right circularly polarized light through reflection and transmission by means of Grandian alignment. In the present invention, the cholesteric liquid crystal appropriately exhibits such a circularly polarized light separating function. A cholesteric liquid crystal layer can be used. Accordingly, the cholesteric liquid crystal layer may be composed of a cell body of a low molecular weight cholesteric liquid crystal or the like, but is preferably composed of a cholesteric liquid crystal polymer in terms of handling properties and thin film properties.

In the above case, the cholesteric liquid crystal layer made of a cholesteric liquid crystal polymer used for forming the polarizing element can be obtained as a single layer such as a cholesteric liquid crystal polymer film or a multilayer having the cholesteric liquid crystal polymer film supported by a plastic film or the like. it can. A cholesteric liquid crystal layer, which is preferable from the viewpoint of expanding the viewing angle of a liquid crystal display device or the like, is a cholesteric liquid crystal polymer that is oriented in a Grand Jean state with few defects such as domains.

As the cholesteric liquid crystal polymer, an appropriate one may be used, and there is no particular limitation. Accordingly, various types such as a main chain type or a side chain type in which a conjugated linear atomic group (mesogen) imparting liquid crystal orientation is introduced into a main chain or a side chain of a polymer can be used. A cholesteric liquid crystal polymer having a larger birefringence difference has a wider wavelength range of circular dichroism (selective reflection), which is preferable in terms of reduction of the number of superposed layers and a margin for wavelength shift at a large viewing angle. As the liquid crystal polymer, those having a glass transition temperature of 30 to 150 ° C. are preferable from the viewpoints of handleability, stability of alignment at a practical temperature, and the like.

Incidentally, examples of the above-mentioned main chain type liquid crystal polymer include, for example, a polyester-based liquid crystal polymer having a structure in which a mesogen group composed of a para-substituted cyclic compound or the like is bonded via a spacer portion imparting flexibility as required. And polyamide-based, polycarbonate-based and polyesterimide-based polymers.

Examples of the side chain type liquid crystal polymer include:
A low-molecular liquid crystal compound (mesogen portion) composed of a para-substituted cyclic compound or the like with a main chain skeleton of polyacrylate, polymethacrylate, polysiloxane, polymalonate, or the like, and a spacer composed of a conjugated atomic group as a side chain, if necessary. , A nematic liquid crystal polymer containing a low molecular weight chiral agent, a liquid crystal polymer having a chiral component introduced, a mixed liquid crystal polymer of a nematic type and a cholesteric type, and the like.

As described above, the nematic orientation comprising para-substituted aromatic units and para-substituted cyclohexyl ring units such as azomethine, azo, azoxy, ester, biphenyl, phenylcyclohexane, and bicyclohexane forms can be used. Even those having a para-substituted cyclic compound to be imparted can be made to have cholesteric orientation by a method of introducing an appropriate chiral component such as a compound having an asymmetric carbon, a low molecular weight chiral agent, etc. No. 55-21479, U.S. Pat. No. 5,332,522). The terminal substituent at the para position in the para-substituted cyclic compound may be an appropriate one such as a cyano group, an alkyl group, or an alkoxy group.

Examples of the spacer include a polymethylene chain — (CH ₂ ) _n — and a polyoxymethylene chain — (CH ₂ CH ₂ O) _m — which exhibit flexibility. The number of repetitions of the structural unit forming the spacer portion is appropriately determined depending on the chemical structure of the mesogen portion and the like. In general, in the case of a polymethylene chain, n is 0 to 20, especially 2 to 12, and in the case of a polyoxymethylene chain. Has m of 0 to 10, especially 1 to 3.

The cholesteric liquid crystal layer formed of a cholesteric liquid crystal polymer can be formed by a method according to a conventional alignment treatment of a low-molecular liquid crystal. Incidentally, as an example, an alignment film formed by forming a film of polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, polyetherimide, or the like on a transparent substrate and rubbing with a rayon cloth or the like, or an oblique surface of SiO ₂ A liquid crystal polymer is developed on an appropriate alignment film such as an evaporation layer or an alignment film formed by a stretching process, and is 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 glass transition temperature to form a solidified layer in which the orientation is fixed is exemplified.

The transparent substrate is made of a plastic such as triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyether sulfone, amorphous polyolefin, modified acrylic polymer, or epoxy resin. An appropriate material such as a single-layer film, a laminated film, a stretched film, or a glass plate can be used. A plastic film is preferred from the viewpoint of thinning and the like.

The liquid crystal polymer can be developed by, for example, applying a solution of the liquid crystal polymer in a solvent by a spin coating method, a roll coating method, a flow coating method, a printing method, a dip coating method, a casting film forming method, a bar coating method, a gravure printing method, or the like. The method can be performed by a method of developing a thin layer by an appropriate method described above and drying it as necessary. Suitable solvents such as methylene chloride, cyclohexanone, trichloroethylene, tetrachloroethane, N-methylpyrrolidone, and tetrahydrofuran can be used as the solvent.

Further, a heated melt of the liquid crystal polymer, preferably a heated melt in a state exhibiting an isotropic phase, is developed in accordance with the above, and, if necessary, further developed into a thin layer and solidified while maintaining the melting temperature. Methods that do not use solvents, such as methods,
Therefore, the liquid crystal polymer can be developed by a method having good work environment hygiene and the like.

In the heat treatment for orienting the spread layer of the liquid crystal polymer, as described above, the liquid crystal polymer is heated to a temperature range from the glass transition temperature to the isotropic phase transition temperature, that is, to a temperature range in which the liquid crystal polymer exhibits a liquid crystal phase. It can be done by doing. The orientation can be fixed by cooling the glass to a temperature lower than the glass transition temperature, and the cooling conditions are not particularly limited. Usually, a natural cooling method is generally adopted because the above-mentioned heat treatment can be performed at a temperature of 300 ° C. or less. Various additives such as a stabilizer, a plasticizer, and metals can be added to the developing solution of the cholesteric liquid crystal polymer as needed.

In the above, the thickness of the solidified layer of the liquid crystal polymer formed on the transparent substrate is set to 5 μm or less from the viewpoint of preventing the alignment disorder and the decrease in transmittance as described above. The formed liquid crystal polymer solidified layer can be used as an integral body with the transparent substrate, or can be peeled off from the transparent substrate and used as a film or the like. Therefore, the polarizing element formed by superposing the cholesteric liquid crystal layers may have the transparent base material 11 in the middle or outside of the superposed layer as illustrated in FIG.

A part or all of the transparent substrate can be replaced with a transparent adhesive layer for superimposing a cholesteric liquid crystal layer or laminating a polarizing element with another member. Therefore, the polarizing element may have a transparent adhesive layer together with a transparent substrate as needed, in the middle or outside of the superposed layer. For forming the transparent adhesive layer, an appropriate adhesive such as an adhesive can be used. In the above description, when the cholesteric liquid crystal layer is used as an integral part of the transparent substrate, the total thickness is preferably 500 μm or less, more preferably 5 to 300 μm, particularly preferably 10 to 200 μm from the viewpoint of thinning.

The combination of the cholesteric liquid crystal layers to be superimposed is arbitrary, but the cholesteric liquid crystal layers having different center wavelengths of the circular dichroism are different from the point of expanding the wavelength range of the circular dichroism (broadening the band). It is preferable to use a combination of That is, the cholesteric liquid crystal exhibits a circularly polarized light separating function having different wavelength characteristics based on the difference in the helical pitch of the Clan-Jan orientation, and by superposing cholesteric liquid crystal layers having different central wavelengths of circular dichroism, those circularly polarized liquid crystals are superposed. The chromaticity is compounded, and the wavelength range of the separation function can be expanded.

Incidentally, the center wavelength of circular dichroism is 30.
By superimposing several types of cholesteric liquid crystal layers in the range of 0 to 900 nm in combinations with different helical pitches and in combinations that reflect circularly polarized light in the same direction, a polarizing element that can cover the visible light region is efficiently created. Can be formed. In addition, the point of superimposing in a combination of those that reflect circularly polarized light in the same direction is that the phase state of the circularly polarized light reflected by each layer is aligned to prevent different polarization states in each wavelength range, and that the state can be used. The purpose is to increase the amount of polarized light.

The superposition of the cholesteric liquid crystal layer is effective for improving the degree of polarization by increasing the thickness in addition to the above-mentioned broadening of the circular dichroism, and in terms of the degree of polarization, the superposition of the cholesteric liquid crystal layer The greater the value, the more advantageous. Therefore, the number of superposed cholesteric liquid crystal layers can be an appropriate number of two or more layers according to the intended circular dichroism broadband or the degree of polarization, and generally 20 layers or less,
In particular, the number of superimposition is 2 to 15 layers, especially 3 to 10 layers.

The superposition of the cholesteric liquid crystal layers can be performed by an appropriate method such as a mere superposition method or an adhesion treatment method via a transparent adhesive layer as described above. In this case, the order of superimposition of the cholesteric liquid crystal layer is in the superimposition direction from the point of suppression of color change due to the change of the viewing angle, and thus from the point of view angle characteristics when applied to a liquid crystal display device and the like.
That is, the order in which the helical pitch of the Grandian orientation increases or decreases based on the center wavelength of the circular dichroism of the cholesteric liquid crystal layer in the thickness direction is preferable.

In the above, if there is an inverted layer of the helical pitch based on the center wavelength of the circular dichroism in the superposition direction, that is, if the change in the helical pitch indicates a maximum point or a minimum point, the transmitted light will change the viewing angle. In this case, the viewing angle characteristic may be significantly deteriorated when applied to a liquid crystal display device or the like due to a large color change.

The cholesteric liquid crystal layer forming the polarizing element may or may not change the helical pitch in the thickness direction. The cholesteric liquid crystal layer in which the helical pitch changes in the thickness direction has an advantage of exhibiting a wide circular dichroic wavelength range based on the helical pitch having a width as described above.

In the production of a cholesteric liquid crystal layer in which the helical pitch changes in the thickness direction, for example, a predetermined number of two or three or more aligned cholesteric liquid crystal polymer layers differ in the center wavelength of circular dichroism. It can be performed by an operation such as bonding by thermocompression bonding in a combination of objects. The thermocompression bonding can be performed by an appropriate method such as a method of heating the cholesteric liquid crystal polymer layer to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature through an appropriate heating and pressing means such as a roll laminator and performing a pressure bonding process. .

In the case of a solidified layer of a liquid crystal polymer formed integrally with the above-mentioned transparent base material, the helical pitch is increased in the thickness direction by performing a superposition treatment according to the above so that the solidified layers are in close contact with each other. A changing cholesteric liquid crystal layer and thus a polarizing element according to the invention can be obtained.

The cholesteric liquid crystal layer in which the helical pitch changes in the thickness direction may exhibit a continuous wavelength range of circular dichroism or a discontinuous wavelength range of circular dichroism. It may be shown. A cholesteric liquid crystal layer that is preferable from the viewpoint of preventing color unevenness and the like exhibits a continuous wavelength range of circular dichroism.

For the production of a cholesteric liquid crystal layer exhibiting a continuous circular dichroic wavelength range, a laminate of a cholesteric liquid crystal polymer layer having a helical pitch changing in the thickness direction formed by, for example, the above-mentioned thermocompression bonding is used. Above the transition temperature,
It can be carried out by a method of heating below the isotropic phase transition temperature to form a layer in which the cholesteric liquid crystal polymer forming the upper and lower layers is mixed at the adhesive interface.

In the above, the cholesteric liquid crystal polymer layer formed by mixing the cholesteric liquid crystal polymer of the upper and lower layers is different from the upper and lower layers in the cholesteric liquid crystal layer in which the helical pitch changes in multiple steps in the thickness direction. The helical pitch usually takes an intermediate value of the cholesteric liquid crystal polymer layers forming the upper and lower layers, and forms a continuous circular dichroic wavelength region together with the upper and lower layers.

Therefore, a combination of cholesteric liquid crystal polymer layers in which the wavelength ranges of circular dichroism do not overlap in the upper and lower layers,
That is, when used in a combination in which a missing region due to discontinuity exists in the wavelength region of circular dichroism, the cholesteric liquid crystal polymer layer formed by mixing the upper and lower layers fills the missing region and circular dichroism. Can be made continuous.

Thus, for example, the wavelength range of circular dichroism is 5
Using two kinds of cholesteric liquid crystal polymer layers of a thing of 00 nm or less and a thing of 600 nm or more, a cholesteric liquid crystal layer showing circular dichroism also for light in the wavelength region of 500 to 600 nm, which is a discontinuous region of the wavelength region. This means that a cholesteric liquid crystal layer exhibiting a wide wavelength range of circular dichroism can be formed by superimposing a small number of cholesteric liquid crystal polymer layers.

The cholesteric liquid crystal layer used for forming the polarizing element and having a helical pitch that changes in the thickness direction has a helical pitch difference of 100 nm in order to prevent a decrease in circular dichroism.
Hereinafter, it is particularly preferably at most 85 nm, particularly preferably at most 80 nm. In addition, even in the case of a polarizing element using the cholesteric liquid crystal layer in which the helical pitch changes in the thickness direction partially or as a whole, the above-mentioned superimposed order structure in which the helical pitch increases or decreases in the thickness direction is satisfied. Is preferred.

The polarizing element according to the present invention can be preferably used for forming a liquid crystal display. In that case, the polarizing element
It can also be used as an optical element formed by laminating one or two or more appropriate optical layers such as a quarter-wave plate, a viewing angle compensator, or a polarizing plate. The optical layer can be arranged at an appropriate position on one side or both sides of the polarizing element.

FIGS. 2 and 3 show examples of the optical element. Reference numeral 2 denotes a 波長 wavelength plate, reference numerals 21 and 22 denote retardation layers, and reference numeral 3 denotes a polarizing plate. As shown in the figure, the 波長 wavelength plate 2 may be composed of a superposed body of one or two or more retardation layers 21 and 22,
The optical layer used for forming the optical element may have an appropriate layer form, such as a single layer or a multilayer.

The quarter-wave plate is provided on one or both sides of the polarizing element 1 as shown in FIGS. 2 and 3 to linearly polarize circularly polarized light transmitted through or reflected by the polarizing element. And is formed of one or two or more retardation layers.

The quarter-wave plate (retardation layer) preferably has a front phase difference of 100 to 180 nm in the visible light region in view of the effect of linear polarization and compensation of color change due to obliquely transmitted light. Can be used. That is, the maximum refractive indices n _x in the plane, the direction of the refractive index n _y perpendicular thereto, the refractive index n _z in the thickness direction, wherein the thickness of the case of the _{d: (n x -n y)} d
= △ nd = 100 to 180 nm can be preferably used.

The retardation layer optionally used together with the retardation layer exhibiting the quarter-wave plate function vertically transmits the color balance of the light obliquely transmitted through the retardation layer exhibiting the quarter-wave plate function. This is for compensation for the purpose of matching the color balance of light as much as possible, so that the visual recognition through the polarizing plate can be made into an intermediate color with less coloring.
Those having d) of 100 to 720 nm are preferably used.

In the above, the quarter-wave plate or the retardation layer, which can be preferably used from the viewpoint of reducing the angle dependence of the color change due to the change of the viewing angle, is composed of a cholesteric liquid crystal having a large helical pitch in the polarizing element. when placed on the polymer layer side, _{wherein: (n x -n z) /} (n x -n y)
In N _z is 1.1-1 represented, especially -0.2-0.
Eight. On the other hand, in the case of placing cholesteric the liquid crystal polymer layer side helical pitch is small in the polarization element, N _z is -0.5 2.5, especially -0.8～-
A 2.0 quarter wave plate or retardation layer is preferred.

The above-mentioned retardation layer may be formed of any material, and is preferably excellent in transparency, and preferably exhibits a light transmittance of 80% or more and gives a uniform retardation. In general, for example, plastics such as polycarbonate and polyester, polysulfone and polyether sulfone, polyolefin such as polystyrene and polyethylene, polypropylene, polyvinyl alcohol and cellulose acetate polymers, polyvinyl chloride and polyvinylidene chloride, polyarylate and polymethyl methacrylate, and polyamides A stretched film, a liquid crystal polymer, especially a twisted liquid crystal polymer is used.

The above-mentioned retardation layer having a large refractive index in the thickness direction is formed by forming a film obtained by forming the above-mentioned polymer or the like by an appropriate method such as a casting method or an extrusion method, for example, uniaxially while adhering to a heat-shrinkable film. It can be formed by an appropriate method such as a method of heating and stretching by a method such as heating or biaxial. Characteristics such as the △ nd and N _z in the phase difference layer can be controlled material and thickness of the film, by changing the conditions such as stretching ratio and stretching temperature. A typical thickness of the retardation layer is 10 to 500 μm based on a single layer material, preferably 20 to 20 μm.
0 μm, but not limited to this.

When a retardation layer such as a quarter-wave plate is formed of a liquid crystal polymer, an alignment film of a liquid crystal polymer or an alignment layer of a liquid crystal polymer supported by a transparent substrate may be appropriately formed according to the case of the cholesteric liquid crystal layer. It can be obtained as having any form. When a liquid crystal polymer is used, a target retardation layer can be formed without a stretching treatment.

The quarter-wave plate may be composed of a single-layer retardation layer as described above, or may be composed of a superposed body of two or three or more retardation layers having different retardations. Good. The superposition of the retardation layers having different retardations is effective for expanding the wavelength range that functions as a target quarter-wave plate or compensator. When a superimposed body of retardation layers is used, the retardation layer having a refractive index in the thickness direction higher than at least one of the in-plane refractive indices is referred to as one.
Arranging two or more layers is more preferable than the above-mentioned point.

An optical element which is preferable from the viewpoint of the effect of improving luminance and the like transmits linearly polarized light having a predetermined polarization axis and reflects other light. The optical element may have a configuration in which the polarizing plate 3 is disposed above the quarter-wave plate 2 as illustrated in FIG. In this case, the present invention can be applied to a liquid crystal cell without using a separate polarizing plate.

As the polarizing plate, an appropriate polarizing plate such as an absorption polarizing plate containing a dichroic substance, a polyene oriented film, or a film provided with a transparent protective layer can be used. By the way, examples of the absorption type polarizing plate include a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and an ethylene-vinyl acetate copolymer-based partially saponified film.
Examples include films stretched by adsorbing dichroic substances such as iodine and dichroic dyes. Examples of the oriented polyene film include dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. The thickness of the polarizing plate is usually 5 to 80 μm, but is not limited thereto.

In order to form a liquid crystal display device, it is necessary to achieve a bright display, that is, to transmit highly linearly polarized light through a quarter-wave plate through a polarizing plate while minimizing absorption loss. From the viewpoint of obtaining a display with a good contrast ratio due to the incidence of highly linearly polarized light on the liquid crystal cell, a material having a high degree of polarization such as an absorption type polarizing plate containing a dichroic substance is preferably used. Above all, an absorption type polarizing plate containing a dichroic substance having a light transmittance of 40% or more and a polarization degree of 95.0% or more, particularly 99% or more is preferably used.

The above-mentioned transparent protective layer is provided for the purpose of protection especially when water resistance is poor such as a polarizing plate containing a dichroic substance, and is appropriately applied by a plastic coating method or a film laminating method. Can be formed. When it is formed of a separated material such as a film, it is preferable to laminate and integrate with an adhesive layer from the viewpoint of preventing reflection loss and the like. The thickness of the transparent protective layer may be determined as appropriate, and is generally 1 mm or less, particularly 500 μm or less, particularly 1 to 300 μm. In addition, as the plastic, an appropriate plastic such as those exemplified for the above-mentioned transparent base material and retardation layer can be used.

The transparent resin layer can also be formed in the form of a fine surface unevenness by a method of incorporating 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 plate is arranged above the quarter-wave plate, the angle of the polarizing plate with respect to the quarter-wave plate is 1
Although it can be appropriately determined according to the phase difference characteristic of the 波長 wavelength plate and the characteristic of the circularly polarized light incident thereon, the light linearly polarized through the 波長 wavelength plate is improved from the viewpoint of improving the light use efficiency. It is preferable to arrange the transmission axis of the polarizing plate as parallel as possible to the polarization direction (vibration direction).

The polarizing element and the optical element according to the present invention can be preferably used for forming various devices such as a lighting device and a liquid crystal display device. It can be formed by combining liquid crystal cells. Incidentally, an optical element comprising the above-mentioned polarizing element and a quarter-wave plate, and optionally having a polarizing plate above the quarter-wave plate, transmits light from a light source, such as natural light, with reflected light through the polarizing element. Light is separated into left and right circularly polarized light, and circularly polarized light or elliptically polarized light transmitted through the polarizing element can be linearly polarized by a quarter-wave plate and supplied to a polarizing plate or the like.

Therefore, as illustrated in FIGS. 4 and 5, such a polarizing element or optical element is disposed above a suitable surface light source 4 such as a sidelight type light guide plate or an EL lamp to provide a backlight for a liquid crystal display device. As a preferred example, a lighting device can be formed. The surface light source in the illustrated example has a light source 42 disposed on the side surface of the light guide plate 4.

According to the illuminating device shown in the figure, the light from the light source 42 is incident on the side surface of the light guide plate 4 and is emitted from the front surface of the light guide plate through reflection on the back surface or the like. Is transmitted as predetermined circularly polarized light or elliptically polarized light, is linearly polarized through the quarter-wave plate 2, and enters the polarizing plate 3. On the other hand, the light reflected by the polarizing element 1 as non-predetermined circularly polarized light re-enters the light guide plate, is reflected via the reflective layer 41 disposed on the back surface or the like, and enters the polarizing element 1 again as return light.

The light reflected by the polarizing element changes its polarization state when reflected on the back surface of the light guide plate, and becomes a predetermined circularly polarized light that allows part or all of the reflected light to pass through the polarizing element. Therefore, the light reflected by the polarizing element is confined between the polarizing element and the light guide plate until the light becomes a predetermined circularly polarized light that can pass through the polarizing element, and the light is repeatedly reflected between them.

As described above, in the sidelight type light guide plate, the reflected light is confined between the polarizing element and the reflection layer of the light guide plate,
While the reflection is repeated during this time, the polarization state is changed to a state in which the light can be transmitted through the polarizing element, and is emitted together with the initially transmitted light of the incident light, thereby reducing unused light due to reflection loss.

On the other hand, the light emitted from the polarizing element is converted into linearly polarized light or elliptically polarized light having a large number of linearly polarized light components through a quarter-wave plate, and the converted light has its linear polarization direction coincident with the transmission axis of the polarizing plate. In this case, the light is transmitted through the polarizing plate without being absorbed, thereby reducing the amount of unused light due to the 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. Therefore, a side light type light guide plate can be preferably used as the surface light source.

As the light guide plate, an appropriate light guide plate having a reflective layer on the back surface to emit light to the front surface side 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 arranged on the side surface of the light guide plate 4, 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 in which the internal transmission light is emitted to one side is provided with, for example, 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 an object or a resin plate provided with a concave-convex structure on the back side, particularly, a fine prism array-shaped concave-convex structure.

The light guide plate which emits light to one surface side can have a function of converting the light reflected by the polarizing element by itself, but the light guide plate is provided with a reflection layer 41 on the back surface to reflect light. 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 polarizing element into a polarized light, and can be preferably used in the present invention.

Incidentally, the diffuse reflection layer represented by the uneven surface or the like cancels the polarization state by randomly mixing the 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 illumination device, as shown in FIG. 5, a prism array layer 5 composed of a prism sheet or the like for controlling a light emitting direction, a diffusion plate for obtaining uniform light emission, and returning leaked light, as illustrated in FIG. Means for reflecting light emitted from the linear light source to the side surface of the light guide plate, and auxiliary means such as a light source holder for one or more layers as required at predetermined positions on the upper and lower surfaces and side surfaces of the light guide plate 4. To form an appropriate combination.

In the above, the prism array layer and the diffusion plate disposed on the surface side (light emission side) of the light guide plate, or the dots provided on the light guide plate are used as polarization conversion means for changing the phase of the reflected light by a diffusion effect or the like. Can work. When two or more prism array layers are arranged, the prism arrays in each layer are orthogonally or intersected to shift the array arrangement angle so that the optical anisotropy is eliminated. Is preferred.

In the present invention, components such as a polarizing element, a quarter-wave plate, a polarizing plate, and a light guide plate which form an optical element and a lighting device can be laminated and integrated via an adhesive layer as necessary. . The integrated lamination of the formed components prevents reflection loss at each interface, prevents deterioration of display quality, etc. by preventing intrusion of foreign matter, etc., at each interface, and prevents reduction in compensation efficiency and polarization conversion efficiency, etc. due to misalignment of the optical system. It is effective for Therefore, even when each of the polarizing element, the quarter-wave plate, the polarizing plate, the light guide plate, and the like is formed of a plurality of layers, it is preferable that the respective layers be tightly integrated via an adhesive layer or the like.

An appropriate adhesive or the like may be used for the above-mentioned lamination and integration. In particular, an adhesive layer having excellent stress relaxation properties may be formed by a polarizing element, a 波長 wavelength plate, a polarizing plate, or the like by heat from a light source or the like. It can be more preferably used in that a liquid crystal display device which is bright and has excellent visibility and reliability of display quality can be formed by suppressing a stress generated in the liquid crystal display and preventing a change in refractive index caused by photoelastic deformation.

For forming the adhesive layer, a transparent adhesive made of an appropriate polymer such as an acrylic polymer, a silicone polymer, polyester, polyurethane, polyether or synthetic rubber can be used. 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 dy from the viewpoint of preventing photoelastic deformation due to relaxation of internal stress generated inside the laminate due to heat.
ne / cm ² , preferably 2 × 10 ⁶ to 8 × 10 ⁶ dyne / cm ² .

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.

As a method of forming an optical element or the like integrated by lamination, for example, a pressure-sensitive adhesive layer provided on a separator obtained by surface-treating a thin leaf such as a film with a release agent is transferred to the adhesive surface of the polarizing element. There is a method in which a 波長 wavelength plate is pressure-bonded thereon, an adhesive layer is similarly transferred onto the １ ／ wavelength plate, and a polarizing plate is placed thereon and pressure-bonded.

The adhesive layer provided on the separator was transferred to the bonding surface of the light guide plate or the like, and the polarizing element was placed thereon and pressed. After that, the adhesive layer was transferred and transferred in the same manner. A method of sequentially pressing a wavelength plate or a polarizing plate as needed, or attaching a polarizing element, a 波長 wavelength plate, a polarizing plate, a light guide plate, or the like via an adhesive layer previously provided on a predetermined adhesive surface. There is also a method in which the bodies are laminated in a predetermined order, pressed, and pressed together at once.

In the polarizing element, the optical element, and the lighting device according to the present invention, an appropriate optical layer such as a light diffusing plate can be disposed at an appropriate position on the surface or between the layers. In that case, the optical layer may be laminated and integrated with a polarizing element or the like via an adhesive layer or the like having excellent stress relaxation properties. 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 the present invention, a cholesteric liquid crystal layer and a 1/4
Components such as a wave plate, a polarizing plate, a light guide plate, an adhesive layer and other optical layers can be used to absorb ultraviolet rays such as salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, cyanoacrylate compounds, nickel complex compounds, etc. UV absorption can also be imparted by a method of treating with an agent.

As described above, the polarizing element and the optical element according to the present invention can be combined with an appropriate surface light source such as a side light type light guide plate to convert the circularly polarized light reflected by the polarizing element into polarized light and reuse it as emission light. To prevent the reflection loss, and to control the phase of the emitted light through a quarter-wave plate to convert the output light into a state containing a linearly polarized component that is transparent to the polarizing plate, thereby preventing the absorption loss by the polarizing plate and thereby improving the luminance. Can be improved.

Therefore, it provides light that is excellent in light use efficiency and easily transmits through the polarizing plate, and can be easily used in various devices as a backlight system in a liquid crystal display device and the like because it is easy to increase the area. . In that case, 1/4
Rather than using the light emitted from the wavelength plate as a light source, it is preferable that the linearly polarized light or the elliptically polarized light contains a linearly polarized light component that can be transmitted through the polarizing plate, such as 65% or more, particularly 70% or more.

FIGS. 6 and 7 illustrate a liquid crystal display device using the illumination device according to the present invention in a backlight system. This is one in which a liquid crystal cell 6 is arranged via a polarizing element or an optical element on the light emitting surface side of a light guide plate 4 forming an illuminating device. 4
It is arranged on the side of the wave plate 2, that is, on the light emission side of the illumination device. In the figure, 61 is a polarizing plate, and 7 is a light diffusion plate for diffusing visible light.

The optical element and the lighting device according to the present invention can be particularly preferably used for forming a liquid crystal display device having polarizing plates on both sides of a liquid crystal cell. In the case of an optical element having a polarizing plate above the quarter-wave plate, the polarizing plate on the side where the optical element is provided in the liquid crystal cell can be omitted.

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 viewing angle compensator and incorporating a drive circuit. In the present invention, as described above, there is no particular limitation except that an optical element or an illuminating device is arranged on the viewing back side of the liquid crystal cell via the polarizing element or the quarter-wave plate side or the polarizing plate side, and the conventional method is adopted. However, it is preferable that each component is bonded and integrated via an adhesive layer.

The polarizing element, the optical element and the illuminating device according to 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. A non-twist type liquid crystal, 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 can be used.

When a liquid crystal display device is formed, for example, a light diffusion plate or an anti-glare layer provided on a polarizing plate on the viewing side,
Appropriate optical layers such as an antireflection film, a protective layer or a protective plate, or a viewing angle compensator provided between a liquid crystal cell and a polarizing plate on the viewing side or the like can be appropriately disposed. Incidentally, for the purpose of improving the brightness and the like, an optical layer in which a plurality of polymer thin films are arranged between a backlight and a liquid crystal cell (Japanese Patent Laid-Open No.
268505, PCT Publication 95/17691) and the like can also be arranged.

The above-mentioned viewing angle compensating plate is intended to improve the visibility by compensating the wavelength dependence of birefringence, and the like. In the present invention, as described above, an optical element laminated with a polarizing element or the like is used. It can also be used as an element. The viewing angle compensator is disposed between the polarizing plate on the viewing side and / or the backlight side and the liquid crystal cell as necessary.

As the viewing angle compensating plate, an appropriate compensating plate can be used according to the wavelength range and the like, and it may be formed as a single layer or a superposed layer of two or more retardation layers. The viewing angle compensating plate can be obtained as a stretched film or a liquid crystal polymer layer as exemplified by the above-described quarter-wave plate.

[0085]

Example 1 A 20% by weight solution of an acrylic thermotropic cholesteric liquid crystal polymer in tetrahydrofuran was coated with a 50 μm thick film.
m on a polyvinyl alcohol rubbed surface (approximately 0.1 μm thick) of a cellulose triacetate film having a thickness of about 0.1 μm, and subjected to a heat orientation treatment at 150 ± 2 ° C. for 5 minutes, and then allowed to cool at room temperature to obtain a 2 μm thick film. In a method of forming a cholesteric liquid crystal layer, the wavelength range of circular dichroism is 400 to 500.
nm, 450-550 nm, 500-600 nm or 600-
Four types of cholesteric liquid crystal layers transmitting left circularly polarized light at 700 nm and having a haze of 2% were obtained.

Next, the wavelength range of the circular dichroism is 4
A cholesteric liquid crystal layer having a thickness of
A cholesteric liquid crystal layer of 0 nm
A cholesteric liquid crystal layer having a helical pitch difference in the thickness direction of 35 nm and exhibiting (superimposed) circular dichroism in the wavelength region of 400 to 550 nm was obtained by heating and aligning at 0 ± 2 ° C. for 2 minutes. The helical pitch difference in the thickness direction is 65 nm according to the above using a cholesteric liquid crystal layer having a circular dichroism wavelength range of 500 to 600 nm and a cholesteric liquid crystal layer having a wavelength range of 600 to 700 nm.
Thus, a (superimposed) cholesteric liquid crystal layer exhibiting circular dichroism in the wavelength region of 500 to 700 nm was obtained.

Next, on the side of the cholesteric liquid crystal layer (circularity) exhibiting circular dichroism in the wavelength region of 400 to 550 nm obtained as described above, the circular dichroism in the wavelength region of 500 to 700 nm is placed. The cholesteric liquid crystal layer (superimposed) was superimposed via a transparent acrylic adhesive layer having a thickness of 20 μm with the side having a small helical pitch as an adhesive surface to obtain a polarizing element.

On the side of the polarizing element obtained above having a large helical pitch, a quarter-wave plate having a front phase difference of 140 nm and an N _z -0.35 made of a stretched polycarbonate film having a thickness of 2
An optical element was obtained by bonding through an acrylic pressure-sensitive adhesive layer of 0 μm, and a surface light source was arranged on the polarizing element side to obtain an illumination device. The surface light source is 4 mm thick with dot printing on the back.
A 3 mm diameter cold cathode tube is placed on the side of an acrylic light guide plate, surrounded by an aluminum vapor-deposited film, and a reflection sheet made of a foamed polyester film is provided on the lower surface of the dot. It was arranged under the polarizing element via a system adhesive layer, and was press-compressed and laminated and integrated.

[0089] Example 2 N _z was obtained optical element and the illumination device except adhered smaller in helical pitch in accordance with Example 1 of the polarizing element a quarter wavelength plate -1.5.

Comparative Example 1 An optical element and an illuminating device were obtained in the same manner as in Example 1, except that a quarter-wave plate was adhered to the side of the polarizing element having a smaller helical pitch.

Comparative Example 2 The wavelength range of circular dichroism obtained according to Example 1 was 400 to
500 nm, 450-550 nm, 500-600 nm or 6
Four types of cholesteric liquid crystal layers having a haze of 2% and transmitting a circularly polarized light at a wavelength of 400 to 500 nm and a cholesteric liquid crystal layer having a wavelength range of 400 to 500 nm according to Example 1 were first used. After using a cholesteric liquid crystal layer of up to 550 nm to form a (superimposed) cholesteric liquid crystal layer, the cellulose triacetate film on the side with the larger helical pitch is peeled off, and the liquid crystal layer is adhered to the peeled surface. A cholesteric liquid crystal layer having a wavelength range of 500 to 600 nm and a cholesteric liquid crystal layer having a wavelength range of 600 to 700 nm are superposed in the same helical pitch order as described above, and the helical pitch difference in the thickness direction is 125 nm. After obtaining a polarizing element comprising a cholesteric liquid crystal layer of four superimposed layers exhibiting polarization dichroism, an optical element and a lighting device were obtained according to Example 1 using the polarizing element.

Evaluation Test Haze Haze of the (superimposed) cholesteric liquid crystal layer forming the polarizing element obtained in each of Examples and Comparative Examples was examined (NDH-20D, manufactured by Nippon Denshoku Industries Co., Ltd.).

Degree of Polarization The degree of polarization of the emitted light of the lighting devices obtained in the examples and comparative examples was examined.

Luminance Improvement A polarizing plate was provided on the light exit side of the lighting device obtained in each of the examples and comparative examples.
The brightness is adjusted according to the axis angle showing the maximum brightness, and the brightness in the front direction is checked (BM-7, manufactured by Topcon Corporation), and the brightness is improved by the ratio when the front brightness without the optical element is set to 100. I asked for degrees.

Viewing angle characteristics A polarizing plate was arranged on the light emitting side of the lighting device obtained in each of the examples and comparative examples so as to be adjusted to an axis angle at which the maximum luminance was obtained, and a color change due to a change in viewing angle was examined. The display unevenness was examined by observation, and the viewing angle characteristics were evaluated.

The results are shown in the following table.

[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 an example of an optical element.

FIG. 3 is a cross-sectional view of another example of an optical element.

FIG. 4 is a cross-sectional view of an example of a lighting device.

FIG. 5 is a cross-sectional view of another example of a lighting device.

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 example of a liquid crystal display device.

[Explanation of symbols]

 1: polarizing element 11: support base material 12, 13, 14, 15: cholesteric liquid crystal layer 2: quarter wave plate 21, 22: retardation layer 3: polarizing plate 4: light guide plate (surface light source) 41: reflection layer 42: light source 5: prism array layer 6: liquid crystal cell (liquid crystal display device) 61: polarizing plate

Claims (8)

[Claims] 1. A polarizing element comprising a superposed layer of a cholesteric liquid crystal layer having a thickness of 5 μm or less and a haze of 10% or less. 2. The method according to claim 1, wherein the helical pitch in the Grandian orientation changes in the thickness direction, and the helical pitch difference is 1
A polarizing element comprising a cholesteric liquid crystal layer having a thickness of 00 nm or less superposed in a combination having different center wavelengths of circular dichroism. 3. The polarizing element according to claim 1, wherein the helical pitch of the Grandian orientation increases or decreases in the thickness direction. 4. The polarizing element according to claim 1, further comprising a transparent substrate or a transparent adhesive layer in the middle or outside of the superposed layer. 5. A polarizing element according to claim 1, wherein
An optical element comprising a laminate of one or more layers of a wave plate, a viewing angle compensator or a polarizing plate. 6. The method of claim 5, when the maximum refractive indices n _x in the plane, the direction of the refractive index perpendicular thereto n _y, the refractive index in the thickness direction is n _z, wherein: (n _x - n _z) / (n _x -
N _z represented by n _y) has a quarter-wave plate of 1.1-1 to the cholesteric liquid crystal polymer layer side helical pitch is larger in the polarization element, or said N _z is -0.5～-
An optical element having a １ ／ wavelength plate of 2.5 on the side of a cholesteric liquid crystal polymer layer having a small helical pitch in a polarizing element. 7. A lighting device or a liquid crystal display device comprising the polarizing element according to claim 1 or the optical element according to claim 5 and a surface light source or a liquid crystal cell. 8. The liquid crystal display device according to claim 7, further comprising a liquid crystal cell on a light emitting side of the lighting device having the surface light source.