JPH11160539A - Polarizing element, polarized light source device and liquid crystal display device - Google Patents

Abstract

(57) [Abstract] [Problem] To develop a polarizing element excellent in luminance and stability. SOLUTION: At least a quarter-wave plate (2) is provided on a circularly polarized light separating layer (1) composed of one or two or more cholesteric liquid crystal polymer layers. A polarizing element in which the average molecular orientation direction on the surface of the cholesteric liquid crystal polymer layer on the four-wavelength plate side and the slow axis direction on the quarter-wavelength plate are in an intersecting state of 90 to 180 degrees, and the incident light from the side surfaces is A polarized light source device having the above-mentioned polarizing element on the exit surface side of a light guide plate emitting light from one side, and a liquid crystal display device having the polarized light source device disposed on one side of a liquid crystal cell. [Effect] A polarized light source device that has a high degree of polarization and a small color change through a quarter-wave plate with high conversion efficiency, is excellent in light use efficiency and is excellent in luminance, and is therefore bright and has little display unevenness. A liquid crystal display device having excellent properties can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element capable of forming a polarized light source device excellent in light use efficiency and a liquid crystal display device excellent in brightness and good visibility.

[0002]

2. Description of the Related Art Conventionally, a reflection layer is provided on the lower surface of a side light type light guide plate that allows incident light from the side to be emitted from one of upper and lower surfaces, and a circularly polarized light separating layer made of a cholesteric liquid crystal layer is provided on the emission surface. An illumination device that separates incident light into left and right circularly polarized transmitted light and reflected light through the circularly polarized light separating layer, reflects the reflected light through the lower reflective layer, and emits the reflected light again from the emission surface. A system has been proposed (JP-A-3-45906, JP-A-6-32433).
No. 3, JP-A-7-36032).

[0003] Such an illumination system is capable of supplying light as polarized light because non-polarized ordinary light absorbs about 55% of the light emitted from the light guide plate when transmitted through the polarizer, and thus is scarcely available light. Thus, absorption by a polarizing plate is prevented, thereby improving the light use efficiency, thereby improving the brightness of a liquid crystal display device or the like.

In the above, with respect to the circularly polarized light emitted from the circularly polarized light separating layer, absorption by the polarizing plate can be further reduced by transmitting the １ ／ wavelength plate to make it linearly polarized, and the transmittance can be improved. . Therefore, a liquid crystal display device or the like in which a quarter-wave plate is attached to a circularly polarized light separating layer to form a polarizing element can be preferably used.

[0005] However, when a quarter-wave plate is disposed in the circularly polarized light separating layer, there is a problem in that the luminance varies.

[0006]

The inventors of the present invention have conducted intensive studies to overcome the above-mentioned problems, and found that the orientation direction of the circularly polarized light separating layer and the optical axis of the quarter-wave plate have variations in luminance. I found something relevant. Therefore, an object of the present invention is to develop a polarizing element having excellent luminance and stability.

[0007]

According to the present invention, at least a quarter-wave plate is provided on a circularly polarized light separating layer composed of one or more cholesteric liquid crystal polymer layers, A polarizing element characterized in that the average molecular orientation direction on the surface of the cholesteric liquid crystal polymer layer on the four-wavelength plate side and the slow axis direction on the quarter-wavelength plate are in an intersecting state of 90 to 180 degrees, and incidence from the side. A polarized light source device comprising the above-mentioned polarizing element on the exit surface side of a light guide plate for emitting light from one of upper and lower surfaces, and a liquid crystal comprising the polarized light source device arranged on one side of a liquid crystal cell A display device is provided.

[0008]

According to the polarizing element of the present invention, linearly polarized light having a high degree of polarization and a small color change can be obtained with high conversion efficiency via a quarter-wave plate. As a result, it is possible to form a polarized light source device which is excellent in light use efficiency and excellent in luminance, and a liquid crystal display device which is bright and has small display unevenness and excellent visibility.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polarizing element of the present invention comprises at least a quarter-wave plate on a circularly polarized light separating layer composed of one or more cholesteric liquid crystal polymer layers. The average molecular orientation direction on the surface of the cholesteric liquid crystal polymer layer on the quarter wavelength plate side
The four-wavelength plate has a slow axis direction in an intersecting state of 90 to 180 degrees. Examples thereof are shown in FIGS.
1 is a circularly polarized light separating layer, 2 is a 1/4 wavelength plate,
Reference numerals 3 and 15 denote supporting substrates, and 12 and 14 denote cholesteric liquid crystal polymer layers.

The circularly polarized light separating layer can be formed using one or more appropriate cholesteric liquid crystal polymers that separate natural light into left and right circularly polarized light as transmitted light and reflected light by means of Grandian orientation. Therefore, as the cholesteric liquid crystal polymer, 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 the polymer can be used. .

A cholesteric liquid crystal polymer having a larger phase difference has a wider wavelength range of selective reflection, and can be preferably used in view of a margin for a wavelength shift at a large viewing angle. Further, the liquid crystal polymer has a glass transition temperature of 30 to 150 from the viewpoints of handleability and stability of alignment at a practical temperature.
° C can be preferably used.

Incidentally, examples of the above-mentioned main chain type liquid crystal polymer include a structure in which a mesogen group made of a para-substituted cyclic compound or the like is bonded via a spacer portion for imparting flexibility, if necessary, such as a polyester-based liquid crystal polymer. Examples thereof include 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 and 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 circularly polarized light separating layer is formed, for example, by forming a film of polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, polyetherimide or the like on a support substrate and rubbing with a rayon cloth or the like; Or, an appropriate alignment film made of an obliquely deposited layer of SiO ₂ or the like is provided, and a cholesteric liquid crystal polymer is developed on the alignment film, or on a molecularly-oriented support base material made of a stretched film or the like. A method in which a liquid crystal polymer molecule is heated to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature, and is cooled to a temperature lower than the glass transition temperature in a state in which the liquid crystal polymer molecules are oriented in a Grand-Jan state to form a solidified layer in which the orientation is fixed Can be performed.

As the above-mentioned supporting substrate, an appropriate material such as a single-layered product or a multi-layered product made of a transparent plastic film, a glass plate or the like can be used. The plastic is not particularly limited, and can be appropriately selected depending on physical properties according to the intended use such as moisture resistance, heat resistance and strength. Incidentally, examples of the plastic include polyolefins such as polyethylene and polypropylene, polyesters,
Polyimide, polycarbonate, polyethersulfone, polysulfone, cellulose, polyarylate, polystyrene, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, polyacryl, polyamide, epoxy, liquid crystal polymer 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.

A method in which a heated melt of a 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
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.

The cholesteric liquid crystal polymer layer to be formed is preferably oriented as uniformly as possible. In particular, in the present invention, since the arrangement state of the 波長 wavelength plate is regulated by the molecular orientation direction on the surface of the cholesteric liquid crystal polymer layer on which the 設 け る wavelength plate is provided, the orientation of the liquid crystal polymer is as uniform as possible; In particular, it is preferable that at least the above-mentioned surface is uniformly arranged in one direction. The cholesteric liquid crystal polymer layer having a uniform orientation provides reflected light without scattering, which is advantageous for expanding the viewing angle of a liquid crystal display device and the like, and particularly, for forming a direct-view type liquid crystal display device which can be directly observed even from an oblique direction. Suitable for.

The cholesteric liquid crystal polymer layer formed on one or both surfaces of the support substrate can be used for forming a circularly polarized light separation layer while being attached to the support substrate or separated from the support substrate. The cholesteric liquid crystal polymer layer forming the circularly polarized light separation layer may be a single layer or two or more layers. Therefore, the polarizing element of the present invention has the structure shown in FIG.
(A) and one or two or more cholesteric liquid crystal polymer layers 1, 12, 1 as shown in FIGS.
4, a single-layer or multi-layer support substrate 11,
It may have an appropriate layer form such as a form having 13, 15 or a form having no supporting base material.

In the above, the formation of the circularly polarized light separating layer by the arrangement of two or more cholesteric liquid crystal polymer layers aims at expansion of the reflection wavelength range and the like. That is, a single cholesteric liquid crystal polymer layer usually has a limit in a wavelength region showing selective reflection (circular dichroism), and the limit is about 100.
Although the wavelength range may be as wide as nm, the wavelength range does not reach the entire range of visible light desired when applied to, for example, a liquid crystal display device. The purpose is to extend the wavelength range showing circular dichroism, such as in the case where two or more cholesteric liquid crystal polymer layers are provided and the entire visible light range or the entire range is made the reflection wavelength range as much as possible. . Incidentally, a cholesteric liquid crystal polymer layer having a central wavelength of selective reflection of 300 to 900 nm is used in a combination for reflecting circularly polarized light having the same polarization direction, and a combination having different central wavelengths for selective reflection is used.
By overlapping the types, a circularly polarized light separation layer that can cover the visible light region can be efficiently formed.

From the standpoint of reducing the thickness of the circularly polarized light separating layer, it is preferable that the number of the cholesteric liquid crystal polymer layers is as small as possible, particularly, the number of the two cholesteric liquid crystal polymer layers shows the target reflection wavelength range. By the way, in the visible light range, the center wavelength of the reflected light is 400
Less than 550 nm and between 550 and 700 nm
The arrangement of the cholesteric liquid crystal polymer layers of the layers makes it possible to obtain a circularly polarized light separating layer having the whole or as much as possible the entire reflection wavelength range, and a more preferable combination is that the central wavelength of the reflected light is 450 to 540 nm. Medium 480-520 nm, especially about 500 nm, and 560-650 nm, especially 580-620 nm, especially about 600 nm.
Layer.

The combination of the two cholesteric liquid crystal polymer layers described above also has an advantage that the viewing angle, that is, the color change due to the oblique transmission light emission angle is small. In the case where three or more cholesteric liquid crystal polymer layers having different reflection wavelength ranges are provided, it is preferable to arrange the cholesteric liquid crystal polymer layers in a wavelength order based on the length of the central wavelength of the reflected light in order to suppress a color change of emitted light due to the change in the viewing angle. More preferred.

When two or more cholesteric liquid crystal polymer layers are arranged as described above, the combination of those that reflect circularly polarized light having the same polarization direction is different in that the phase state of the circularly polarized light reflected by each layer is uniform. An object is to prevent different polarization states in a wavelength range and increase the amount of polarized light in a usable state.

The difference in the center wavelength of the reflected light in the cholesteric liquid crystal polymer is based on the difference in the helical pitch of the clan-jang orientation, but in the present invention, the circularly polarized light separating layer in which the helical pitch changes in the thickness direction, Circularly polarized light of an appropriate form such as a circularly polarized light separating layer in which two or more cholesteric liquid crystal polymer layers having different helical pitches are superimposed in the order of length and length based on the central wavelength of reflected light and the helical pitch changes in the thickness direction. It may be a separation layer.

The above-described structure in which the helical pitch changes in the thickness direction is also effective for expanding the wavelength range of reflected light. In such a case, a cholesteric liquid crystal polymer layer having the same helical pitch is provided between the cholesteric liquid crystal polymer layers having the same helical pitch, and one or more cholesteric liquid crystal polymer layers having different helical pitches are interposed in the order of the central wavelength. A layer structure including two or more polymer layers is also acceptable.

The production of the circularly polarized light separating layer in which the helical pitch changes in the thickness direction is performed, for example, by forming the liquid crystal polymer on the alignment-treated cholesteric liquid crystal polymer layer in accordance with the above-mentioned cholesteric liquid crystal polymer layer forming operation. The cholesteric liquid crystal polymer layer is sequentially superimposed by developing the cholesteric liquid crystal polymer layer by performing the development of the cholesteric liquid crystal polymer layer and the operation of bonding two or three or more predetermined numbers of the aligned cholesteric liquid crystal polymer layers by thermocompression bonding. be able to.

In the case of a solidified layer of a liquid crystal polymer formed integrally with a substrate, circularly polarized light whose helical pitch changes in the thickness direction is obtained by performing a superposition treatment in accordance with the above so that the solidified layers are in close contact with each other. The separation layer and thus the polarizing element according to the invention can be obtained. The thermocompression bonding process employs an appropriate system such as a system in which the cholesteric liquid crystal polymer layer is heated to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature by an appropriate heating / pressing means such as a roll laminator to perform a compression bonding process. be able to.

The circularly polarized light separating layer whose helical pitch changes in the thickness direction may indicate the wavelength range of continuous reflected light or may indicate the wavelength range of discontinuous reflected light. Good. A circularly polarized light separating layer, which is preferable from the viewpoint of preventing color unevenness,
It shows the wavelength range of continuous reflected light. The cholesteric liquid crystal is manufactured by heating the cholesteric liquid crystal polymer layer formed by the above-mentioned thermocompression bonding operation or the like to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature, thereby forming upper and lower layers at the adhesion interface. It can be performed by a method of forming an alignment layer in which a polymer is mixed, or the like.

In the above, the cholesteric liquid crystal polymer layer formed by mixing the cholesteric liquid crystal polymers of the upper and lower layers has a helical pitch different from that of the upper and lower layers, and a circular polarization separation in which the helical pitch changes in multiple steps in the thickness direction. A layer is formed, and its helical pitch usually takes an intermediate value of the cholesteric liquid crystal polymer layers forming the upper and lower layers, and forms a region showing a continuous reflected light wavelength range together with the upper and lower layers.

Therefore, when used in a combination of cholesteric liquid crystal polymer layers in which the wavelength ranges of the reflected light do not overlap in the upper and lower layers, that is, in a combination in which there is a discontinuity in the wavelength range of the reflected light, mixing of the upper and lower layers is not possible. The cholesteric liquid crystal polymer layer formed by the above method can fill the missing area to make the wavelength range of the reflected light continuous.

Therefore, for example, using two types of cholesteric liquid crystal polymer layers having a reflection wavelength range of 500 nm or less and a reflection wavelength range of 600 nm or more, a reflection wavelength range of 5
It is possible to obtain a circularly polarized light separating layer that reflects light in the wavelength range of 00 to 600 nm, which can form a circularly polarized light separating layer that exhibits a broad band reflection wavelength range by superimposing a small amount of cholesteric liquid crystal polymer layer. Means

The thickness of each cholesteric liquid crystal polymer layer is 0.5 to 50 μm in view of prevention of disorder in alignment and reduction of transmittance, and a wide wavelength range of reflected light (reflection wavelength range).
m, preferably 1 to 30 μm, particularly preferably 1.5 to 10 μm. Further, the total thickness of the cholesteric liquid crystal polymer layer is 1 to 50 μm, preferably 2 to 3
It is preferably 0 μm, particularly preferably 3 to 10 μm.

Further, the total thickness of the cholesteric liquid crystal polymer layer including the supporting base material is 2 to 490 μm, preferably 10 to 10 μm.
It is preferably 300 μm, particularly preferably 20 to 200 μm. When forming the circularly polarized light separating layer, various additives such as stabilizers, plasticizers, and metals can be added to the cholesteric liquid crystal polymer layer as needed.

The polarizing element according to the present invention has at least a quarter-wave plate 2 above a circularly polarized light separating layer 1 as shown in the figure, and as shown by an arrow in FIG. The average molecular orientation direction on the surface of the cholesteric liquid crystal polymer layer on the １ ／ wavelength plate side of the layer and the slow axis direction of the ４ wavelength plate intersect at 90 to 180 degrees. The preferable intersection angle θ from the viewpoint of preventing luminance and color unevenness is 100 to 170 degrees.

The quarter-wave plate functions as a linearly polarized light converting means. The circularly polarized light emitted from the circularly polarized light separating layer enters the quarter-wave plate and undergoes a phase change. Is converted to linearly polarized light, and the other wavelength light is converted to elliptically polarized light. The converted elliptically polarized light becomes flat elliptically polarized light as it approaches the wavelength of the light converted into the linearly polarized light. As a result, light in a state containing a large amount of linearly polarized light component that can be transmitted through the polarizing plate is reduced to 1/4.
The light is emitted from the wave plate.

By converting the light into a state having a large amount of linearly polarized light components, light can be easily transmitted through the polarizing plate. This polarizing plate is, for example, in the case of a liquid crystal display device, an optical layer that maintains a display quality by preventing a decrease in polarization characteristics caused by a change in a viewing angle with respect to a liquid crystal cell, and a higher degree of polarization is better realized. It functions as an optical layer or the like for achieving display quality.

That is, in the above, it is possible to achieve the display by directly entering the polarized light emitted from the circularly polarized light separating layer into the liquid crystal cell without using the polarizing plate, but it is possible to achieve the display by using the polarizing plate. Since the quality can be improved, a polarizing plate is used as necessary. In this case, the higher the transmittance of the polarizing plate, the more advantageous in terms of display brightness, and the higher the transmittance, the more the linear polarization component in the polarization direction coinciding with the polarization axis (transmission axis) of the polarizing plate. Therefore, for that purpose, the polarized light emitted from the circularly polarized light separating layer is converted into a predetermined linearly polarized light via the linearly polarized light converting means.

Incidentally, when natural light or circularly polarized light is incident on a usual iodine-based polarizing plate, its transmittance is about 43%. However, when linearly polarized light is incident on the same polarization axis, it is 80%. %, So that the light use efficiency is greatly improved, and a liquid crystal display having excellent brightness can be realized. In such a polarizing plate, 99.99
% Can be achieved. It is difficult to achieve such a high degree of polarization by using the circularly polarized light separation layer alone, and particularly the degree of polarization with respect to obliquely incident light tends to decrease.

As the quarter-wave plate, the circularly-polarized light emitted from the circularly-polarized light separating layer is formed into a large amount of linearly-polarized light corresponding to the phase difference of quarter-wavelength, and the light of another wavelength is converted into the linearly-polarized light. It is preferable to use a material which has a major axis direction as parallel as possible and can be converted into flat elliptically polarized light close to linearly polarized light. With such a quarter-wave plate, the linear polarization direction of the emitted light and the major axis direction of the elliptically polarized light are arranged so as to be as parallel as possible to the transmission axis of the polarization plate, and a linear polarization component that can pass through the polarization plate. Light in many states can be obtained, and the brightness of the liquid crystal display can be improved.

The phase difference imparted by the quarter-wave plate can be appropriately determined according to the wavelength range of the circularly polarized light emitted from the circularly polarized light separating layer. By the way, in the visible light region, from the viewpoint of the wavelength range and conversion efficiency, etc., taking into account that most retardation plates show wavelength dispersion of positive birefringence from their material properties,
Those having a small phase difference, particularly those giving a phase difference of 100 to 180 nm, particularly 110 to 150 nm, can be preferably used.

The quarter-wave plate can be formed of an appropriate material.
Preferably, a transparent and uniform retardation is provided, and a retardation plate is generally used. The quarter-wave plate is shown in FIG.
As shown in FIG. 2A and FIG. 2A, it can be formed as a superposed layer of one or two or more retardation layers 21 and 22. In the case of a single-layer retardation layer, the smaller the wavelength dispersion of birefringence, the better the polarization state can be made uniform for each wavelength, which is preferable. On the other hand, the superposition of the retardation layers is effective for improving the wavelength characteristics in the wavelength range, and the combination thereof may be appropriately determined according to the wavelength range.

When a quarter-wave plate comprising two or more retardation layers in the visible light region is used, as described above, 100 to 100
It is preferable to include a layer giving a phase difference of 180 nm as one or more odd-numbered layers from the viewpoint of obtaining light having a large amount of linearly polarized light components. Layers other than the layer giving a phase difference of 100 to 180 nm are usually layers giving a phase difference of 200 nm or more, especially 1/2.
It is preferable to form a layer having a wavelength phase difference from the viewpoint of improving wavelength characteristics, but the present invention is not limited to this. When the quarter-wave plate is composed of two or more retardation layers,
The slow axis direction when disposing it on the circularly polarized light separating layer is 1
Based on a retardation layer that gives a retardation of 00 to 180 nm.

The above-mentioned retardation plate can be obtained as a stretched film made of the plastic exemplified as the above-mentioned supporting substrate. It is preferable that the error of the phase difference in the plane of the quarter-wave plate is smaller than that of maintaining the emission intensity and the emission color uniformly at a wide viewing angle.
It is preferably 0 nm or less.

The quarter-wave plate is disposed on the light exit side of the circularly polarized light separation layer. The position of the quarter wave plate is selected from the viewpoint of suppressing the color change of the emitted light due to the change of the viewing angle. It is preferably on the side where the center wavelength of the reflected light in the liquid crystal polymer layer is large (the long wavelength side). The thickness of the quarter-wave plate can be appropriately determined according to the phase difference and the like.
2 to 500 μm, especially 10 to 400 μm, especially 20 to 30
Preferably, the thickness is adjusted to be 0 μm.

The polarizing element of the present invention can be formed in various forms by arranging one or more suitable optical layers such as the diffusion layer 3 and the polarizing plate 4 thereon as illustrated in FIG. it can. The polarizing plate 4 is disposed above the quarter-wave plate 2 as shown in the figure because of the function of the quarter-wave plate.

The arrangement angle of the polarizing plate with respect to the quarter-wave plate is:
It is preferable that the transmission axis coincides with the vibrating plane of the linearly polarized light transmitted through the quarter-wave plate as much as possible from the viewpoint of improving the luminance. In the case of a polarizing element provided with a polarizing plate, the polarizing plate provided on the light source side of the liquid crystal cell can be omitted.

As the polarizing plate, an appropriate one can be used, but generally, a polarizing plate is used. Examples of the polarizing film include a film obtained by adsorbing iodine and / or a dichroic dye onto a hydrophilic polymer film such as a polyvinyl alcohol-based, partially formalized polyvinyl alcohol-based, or partially saponified ethylene / vinyl acetate copolymer. And polyene oriented films such as dehydration products of polyvinyl alcohol and dehydrochlorination products of polyvinyl chloride.

The thickness of the polarizing film is usually 5 to 80 μm, but is not limited to this. The polarizing plate may be one obtained by coating one or both sides of a polarizing film with a transparent protective layer or the like. Such a transparent protective layer or the like may have various purposes such as reinforcing the polarizing film, improving heat resistance, and protecting the polarizing film from humidity and the like. The transparent protective layer can be formed as a resin coating layer or a resin film laminate layer, and may contain fine particles for diffusion or surface roughening.

The diffusion layer provided on the polarizing element as required
An object of the present invention is to level out emitted light to suppress uneven brightness, and to prevent glare caused by moire due to interference with pixels when applied to a liquid crystal cell or the like. The diffusion layer, which can be preferably used from the viewpoint of maintaining the polarization state of the light emitted from the circularly polarized light separating layer and the quarter-wave plate, has a phase difference of 6
It is 30 nm or less, especially 0 to 20 nm, based on 33 nm vertically incident light, preferably incident light having an incident angle within 30 degrees.

The diffusion layer may be formed by, for example, a method of forming a particle-dispersed resin layer, a method of forming a surface unevenness such as sandblasting or chemical etching, a method of generating craze by mechanical stress or solvent treatment, or a mold provided with a predetermined diffusion structure. In any method such as a transfer forming method, a circularly polarized light separating layer, a coating layer on a 波長 wavelength plate or the like, a diffusion sheet, or the like can be appropriately formed. The diffusion layer is formed on one side or both sides of the circularly polarized light separating layer, between the quarter-wave plate and the polarizing plate, or on the upper surface thereof.
One layer or two or more layers can be arranged at an appropriate position adjacent to a circularly polarized light separating layer, a quarter-wave plate, a polarizing plate, or the like.

The polarizing element according to the present invention can be preferably used for forming a polarized light source device or a liquid crystal display device. An example is shown in FIG. The figure shows a liquid crystal display device 6, and 5 is a polarized light source device.

According to the above-mentioned polarized light source device 5, the light emitted from the light guide plate is incident on the circularly polarized light separating layer 1, which is disposed on the exit surface side of the light guide plate 51 which emits the incident light from the side surface from one of the upper and lower surfaces. Then, one of the left and right circularly polarized lights is transmitted, and the other circularly polarized light is reflected, and the reflected light is re-incident on the light guide plate as return light. The light re-entering the light guide plate is reflected by the reflection layer 5 on the lower surface.
The light is reflected by the reflection function portion composed of the second and the like, again enters the circularly polarized light separating plate 1, and is again separated into transmitted light and reflected light (re-incident light).

Accordingly, the re-incident light as the reflected light is confined between the circularly polarized light separating layer and the light guide plate until the light becomes a predetermined circularly polarized light that can pass through the circularly polarized light separating layer, and the reflection is repeated. In the present invention, from the viewpoint of the efficiency of use of the re-incident light, it is preferable that the first re-incident light be emitted with as few repetitions as possible, especially without repetition of reflection.

As the light guide plate, an appropriate one that emits the incident light from the side surface from one of the upper and lower surfaces can be used. Such a light guide plate is, for example, a transparent or translucent resin plate having a light emitting surface or a diffuser provided in a dot shape or a stripe shape on the back surface thereof, or a concave and convex structure on the back surface of the resin plate, especially from a fine prism array. It can be obtained, for example, as having a concavo-convex structure.

Therefore, the light guide plate is generally formed of a plate-like object having upper and lower surfaces, one of which is an emission surface, and an incident surface having at least one end surface between the upper and lower surfaces. As shown in FIG. 4, when a linear light source such as a (cold or hot) cathode tube or a light source 53 such as a light emitting diode is disposed on the side and light from the light source is incident, light transmitted through the plate is diffused or reflected. An example is a light guide plate 51 in a sidelight type backlight or the like known in liquid crystal display devices, which emits light to one side of the plate by diffraction, interference, or the like.

The circularly polarized light re-entered through the circularly polarized light separating layer was guided to the lower surface while maintaining its circularly polarized state without being affected by the phase difference, and the return light reflected by the lower surface was maintained in the circularly polarized state. A light guide plate that can be more preferably used, for example, a point where light is emitted as it is, has a phase difference due to birefringence in the thickness direction as small as possible as in the above-described diffusion layer, and is preferably 30 nm or less, particularly 0 to 20 nm. It is.

The light guide plate that emits light to the one surface side can itself have a function of converting the light reflected by the circularly polarized light separating layer, but the reflection layer 52 is provided on the back surface of the light guide plate. By providing them, 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 circularly polarized light separation layer into a polarized light, and is preferable in the present invention.

Incidentally, the diffuse reflection layer represented by the uneven surface or the like has a randomly mixed polarization state based on its diffusion.
Substantially eliminates the polarization state. 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 54 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.

When arranging two or more layers of prism sheets, it is preferable to arrange the prism arrays so that the directions of arrangement of the prism arrays in the upper and lower layers intersect, so as to make the luminance uniform by controlling the light emitting direction over the entire surface. It is more preferable than such points. A prism sheet or a diffusion plate disposed on the light exit side of the light guide plate, or a dot or the like provided on the light guide plate can function as a polarization conversion unit that changes the phase of reflected light due to a diffusion effect or the like.

The liquid crystal display device 6 illustrated in FIG. 4 uses the above-mentioned polarized light source device 5 in a backlight system, where 4 is a lower polarizing plate, 61 is a liquid crystal cell, and 62 is an upper polarizing plate. , 63 are diffusion plates. The lower polarizing plate 4 and the diffusion plate 63 are provided as needed. The polarized light source device using the polarizing element according to the present invention provides a bright liquid crystal display device which is excellent in light utilization efficiency, provides bright light, can be easily enlarged, and is bright and has excellent visibility.

In general, a liquid crystal display device has a liquid crystal cell functioning as a liquid crystal shutter and a driving device, a polarizing plate,
It is formed as an assembly of components such as a backlight and, if necessary, a compensating phase plate. In the present invention, there is no particular limitation except that the above-mentioned polarized light source device using a polarizing element is used, and it can be formed according to a conventional method, and particularly a direct-view type liquid crystal display device can be preferably formed.

Accordingly, the liquid crystal cell used is not particularly limited, and an appropriate one can be used. Above all, it is advantageously used for a display in which light in a polarization state is incident on a liquid crystal cell, and can be preferably used for a liquid crystal cell using, for example, a twisted nematic liquid crystal or a super twisted nematic liquid crystal. It can also be used for a guest-host type liquid crystal in which a dichroic dye is dispersed in a liquid crystal, or a liquid crystal cell 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 diffusion plate or an anti-glare layer provided on a polarizing plate on the viewing side, an antireflection film, a protective layer or a protective plate, or a compensating retardation plate provided between a liquid crystal cell and a polarizing plate. An appropriate optical layer such as the above can be appropriately arranged.

The purpose of the above-mentioned compensating retardation plate is to improve the visibility by compensating the wavelength dependence of birefringence and the like. In the present invention, it is arranged as needed between the polarizing plate on the viewing side and / or the backlight side and the liquid crystal cell. As the retardation plate for compensation, an appropriate retardation plate can be used according to a wavelength range and the like, and it may be formed as one or two or more superposed layers. The compensating retardation plate can be obtained as a stretched film or the like exemplified by the above-described quarter-wave plate.

In the present invention, the components forming the polarizing element, the polarized light source device and the liquid crystal display device may be laminated or integrated and fixed in whole or in part, or may be arranged in an easily separable state. May be done. It is preferable to fix the optical system from the viewpoint of preventing the optical system from shifting.
An appropriate adhesive may be used for the fixation, but an adhesive is preferably used from the viewpoint of preventing optical distortion due to heat.

When a liquid crystal display device or the like is formed, outgoing light having excellent perpendicularity and parallel light properties is supplied, and re-incident light passing through the circularly polarized light separating layer is reduced in loss and angle change due to scattering and the like. In addition, a polarized light source device that re-emits light with good coincidence with the direction of the initially emitted light and efficiently supplies emitted light in a direction effective for improving visibility can be preferably used.

[0071]

Example 1 A 20% by weight solution of an acrylic thermotropic cholesteric liquid crystal polymer in tetrahydrofuran was formed on a 50 μm-thick cellulose triacetate film having a polyvinyl alcohol rubbed surface (thickness: 0.1 μm) by spin coating. Thereafter, two types of circularly polarized light separating layers that transmit left-handed circularly polarized light with a thickness of 2 μm, a central wavelength of selective reflection of 500 nm or 600 nm are obtained by a method of cooling by heating at 160 ° C. for 5 minutes, and the liquid crystal polymer is obtained. After adhering the layers with each other via an acrylic adhesive layer, the center wavelength of the selective reflection is 600 nm, and a 位相 of a retardation of 115 nm made of polycarbonate is formed on the cholesteric liquid crystal polymer layer via the acrylic adhesive layer.
The wave plate was adhered to obtain a polarizing element. At this time, the intersection angle between the slow axis of the quarter-wave plate and the molecular orientation axis (rubbing direction) on the surface of the cholesteric liquid crystal polymer layer having a selective reflection center wavelength of 600 nm was set to 90 degrees.

Example 2 A polarizing element was obtained in the same manner as in Example 1, except that the intersection angle between the slow axis of the quarter-wave plate and the molecular orientation axis of the liquid crystal polymer layer was 135 degrees.

Example 3 A polarizing element was obtained in the same manner as in Example 1 except that the intersection angle between the slow axis of the quarter-wave plate and the molecular orientation axis of the liquid crystal polymer layer was 180 degrees.

Comparative Example A polarizing element was obtained in the same manner as in Example 1 except that the intersection angle between the slow axis of the quarter-wave plate and the molecular orientation axis of the liquid crystal polymer layer was 45 degrees.

Evaluation Test On the quarter-wave plate of the polarizing element obtained in each of Examples and Comparative Examples,
A polarizing plate (transmittance 43%, degree of polarization 99.9%) with the transmission axis coincident with the plane of oscillation of linearly polarized light via the quarter-wave plate.
Was arranged on a surface light source, and the transmittance and hue change (△ ab) on the polarizing plate were examined with a spectrophotometer (CMS-500, manufactured by Murakami Color Research Laboratory). The hue change was calculated from the following equation, where the hue of the reference polarizing plate was a ₀ and b ₀ , and the hue of the polarizing elements according to the above Examples and Comparative Examples were a ₁ and b ₁ . Δab = {(a ₀ −a ₁ ) + (b ₀ −b ₁ )}

The results are shown in the following table.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a polarizing element.

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

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

FIG. 4 is a cross-sectional view of a polarized light source device and an example of a liquid crystal display device.

[Explanation of symbols]

 1: Circularly polarized light separating layer 11, 13, 15: Support substrate 12, 14: Cholesteric liquid crystal polymer layer 2: Quarter wave plate 21, 22: Retardation layer 3: Diffusion layer 4: Polarizing plate 5: Polarized light source device 51: light guide plate 52: reflective layer 53: light source 6: liquid crystal display

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Naoki Takahashi 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (9)

[Claims] 1. A method according to claim 1, wherein a circularly polarized light separating layer comprising one or more cholesteric liquid crystal polymer layers has at least 1 /
It has a four-wavelength plate, and 1 /
A polarizing element, wherein the average molecular orientation direction on the surface of the cholesteric liquid crystal polymer layer on the four-wavelength plate side and the slow axis direction on the quarter-wavelength plate are in a crossing state of 90 to 180 degrees. 2. The polarizing element according to claim 1, wherein the direction of molecular orientation on the surface of the cholesteric liquid crystal polymer layer on the quarter wavelength plate side is substantially uniform. 3. The polarizing element according to claim 1, wherein a quarter-wave plate is located on a side of the circularly polarized light separating layer where the center wavelength of the reflected light is large. 4. A polarizing element according to claim 1, wherein a circularly polarized light separating layer is formed of a cholesteric liquid crystal polymer having a center wavelength of reflected light of 400 to less than 550 nm and a cholesteric liquid crystal polymer of 550 to 700 nm. 5. The cholesteric liquid crystal polymer layer according to claim 1, wherein the total thickness of the cholesteric liquid crystal polymer layer is 1 to 50 μm, and the total thickness is 2 to 50 μm.
A polarizing element having a size of 500 μm. 6. The polarizing element according to claim 1, wherein the circularly polarized light separating layer is formed of a cholesteric liquid crystal polymer layer whose helical pitch changes in the thickness direction. 7. The polarizing element according to claim 1, further comprising a polarizing plate above the quarter-wave plate. 8. A polarized light source device comprising the polarizing element according to claim 1 on the light-exiting surface side of a light guide plate that emits incident light from a side surface from one of upper and lower surfaces. 9. A liquid crystal display device comprising the polarized light source device according to claim 8 disposed on one side of a liquid crystal cell.