JPH10339867A - Liquid crystal polymer layer, circularly polarized light separation layer, optical element, and light source device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the liquid crystal polymer layer which can form a high- luminance light source device with superior light utilization efficiency or a light well-viewed liquid crystal display device with small display irregularity by performing orientation so that the mean number of domains per unit area on one surface is not more than a specific value. SOLUTION: The liquid crystal polymer layer 1 is oriented so that the means domain number of per unit area on one surface is <=100,000/mm<2> or/and variance in the number of domains per unit area is <=20,000/mm<2> . Various optical elements can be formed by arranging one or >=2 kinds of proper optical layer such as a 1/4-wavelength plate 2 and a polarizing plate 3 for this liquid crystal polymer layer 1 and a circularly polarized light separation layer. Further, a light source device, a liquid crystal display device, etc., can be formed by arranging a light source, a liquid crystal cell, etc. This 1/4-wavelength plate 2 is arranged on one side or both the sides of the circularly polarized light separation layer and functions directly as a polarized light converting means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal polymer layer capable of forming a light source device with high light use efficiency and a high brightness and a liquid crystal display device with good visibility, and a circularly polarized light separating layer and an optical element using the same.

[0002]

2. Description of the Related Art A polarized light source using a circularly polarized light separating layer composed of a cholesteric liquid crystal layer that separates natural light into left and right circularly polarized light through reflection and transmission has been known (Japanese Patent Application Laid-Open No. Sho 59-5959).
127019, JP-A-61-122626, JP-A-63-121821, JP-A-3-45
906, JP-A-6-324333, JP-A-7-35925, JP-A-7-36025 and JP-A-7-36032. However, there is a problem in that light utilization efficiency via the circularly polarized light separating layer is poor and display unevenness is large.

[0003]

The present invention is directed to the development of a liquid crystal polymer layer and a circularly polarized light separating layer capable of forming a light source device having excellent light use efficiency and high brightness, and a liquid crystal display device which is bright and has good visibility with little display unevenness. As an issue.

[0004]

According to the present invention, the average number of domains per unit area on one surface is 100,000 / mm ² or less, and / or the variation in the number of domains per unit area is 2 or less.
A liquid crystal polymer layer which is oriented in a state of 10,000 / mm ² or less,
In addition, the present invention provides a circularly polarized light separating layer composed of a cholesteric liquid crystal layer whose liquid crystal polymer layer has a Grand Jean orientation.

[0005]

According to the liquid crystal polymer layer of the present invention, it is possible to obtain a circularly polarized light separating layer which has little disturbance in optical characteristics, is excellent in light use efficiency and hardly causes display unevenness, and has a light source device excellent in luminance. As a result, a liquid crystal display device with good display with little display unevenness can be formed. This effect is considered to be based on an alignment state in which the liquid crystal polymer layer has less alignment defects and is excellent in homogeneity.

That is, according to the theory of the polarization separation mechanism of the cholesteric liquid crystal layer, it is possible to achieve a polarization degree of 100% by making the thickness infinite, but it is practically impossible to make the thickness infinite. is there. Therefore, it actually has a thickness, and the thickness is usually as thin as about 1 μm to several mm.
% Degree of polarization has not been achieved. By increasing the degree of alignment by reducing the discrimination (alignment defects) in the liquid crystal, it is not clear whether abnormal portions of the refractive index will decrease and this will lead to an improvement in the polarization separation ability, but the light use efficiency will improve. However, display unevenness is reduced.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The liquid crystal polymer layer of the present invention has an average number of domains per unit area on one surface of 100,000 / mm ² or less, and / or has a variation of 20,000 domains per unit area. / Mm ² or less.

The number of domains on the surface of the oriented liquid crystal polymer layer can be determined, for example, by measuring the liquid crystal polymer layer with an optical microscope or SE.
It can be checked by observing the surface with M or AFM. In that case, the domain is as shown in FIG.
It is observed as point and line patterns A and B due to difference in brightness. In addition, FIG. 1 is based on a microscopic photograph of the cholesteric liquid crystal polymer layer magnified 920 times, and the domain pattern appearing on the figure is considered to be based on the change in the refractive index due to the discrimination portion of the Grand Jean orientation. Can be

In the present invention, the domain count unit is based on the state shown in FIG. 1B. The number of domains can be determined by, for example, counting domains within an area of about 0.05 mm ² using a microscope or the like, and converting the number to about 1 mm ² .

[0010] The liquid crystal polymer forming the liquid crystal polymer layer of the present invention is not particularly limited, and may have a proper alignment characteristic such as a cholesteric liquid crystal phase, a nematic liquid crystal phase and a smectic liquid crystal phase. Oriented liquid crystal polymer layers can generally be preferably used as a retardation plate or the like because they exhibit birefringence. In addition, the cholesteric liquid crystal polymer layer having the Grand Jean orientation separates natural light into left and right circularly polarized light as transmitted light and reflected light, and can be used as a circularly polarized light separation layer. Furthermore, the twisted nematic liquid crystal polymer layer has the ability to rotate the plane of vibration of linearly polarized light and can be used as a rotator or the like. Therefore, the liquid crystal polymer used in the present invention may be used for various purposes based on its alignment characteristics.

The liquid crystal polymer layer can be formed by a method according to a conventional alignment treatment. 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 supporting base material and rubbing with a rayon cloth or the like, or an oblique surface of SiO ₂ Evaporation layer,
Alternatively, the liquid crystal polymer is spread on an appropriate alignment film composed of an alignment film or the like by a stretching treatment, and heated to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature, and the liquid crystal polymer is aligned in a predetermined state. A method of cooling to a glass state by cooling to a temperature lower than the transition temperature to form a solidified layer in which the orientation is fixed is exemplified.

The support substrate is made of a plastic such as triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyethersulfone, amorphous polyolefin, modified acrylic polymer, or epoxy resin. An appropriate material such as a single-layer or laminated film or a glass plate can be used. A plastic film is preferable from the viewpoint of thinning and the like, and a film having a phase difference due to birefringence as small as possible is preferable from the viewpoint of improving light use efficiency by preventing a change in optical characteristics such as a polarization state. .

The development of the liquid crystal polymer is performed 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 or a printing method, a dip coating method or a casting film forming method, a bar coating method or a gravure printing method. 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. When the liquid crystal polymer is developed, a method of superposing a cholesteric liquid crystal polymer layer via an alignment film or the like can be adopted as needed for the purpose of reducing the thickness.

As described above, the heat treatment for orienting the spread layer of the liquid crystal polymer is performed in a temperature range from the glass transition temperature to the isotropic phase transition temperature of the liquid crystal polymer, that is, in a temperature range in which the liquid crystal polymer exhibits a predetermined liquid crystal phase. It can be performed by heating. 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 solidified layer of the liquid crystal polymer formed on the supporting substrate can be used as it is with the supporting substrate for various purposes, as a liquid crystal polymer layer formed of a film or the like after peeling from the supporting substrate, or It can be used for various purposes as an appropriate form such as a form in which these forms are superimposed in an appropriate combination.

The separation of the solidified liquid crystal polymer layer from the support substrate can be easily performed by a method in which a release coat is provided on the support substrate from a release agent or the like. When formed as an integral part of the supporting base material, it may be preferable to use a supporting base material having a phase difference as small as possible from the viewpoint of maintaining the optical characteristics as described above.

In the above description, the liquid crystal polymer layer according to the present invention has a unit on one surface due to the fact that the optical characteristics are hardly disturbed, such as the improvement of luminance by providing reflected light without scattering and the prevention of display unevenness. The average number of domains per area is 100,000 / mm ² or less, especially 80,000 / mm ² or less,
In particular, it is 60,000 / mm ² or less, or the variation in the number of domains per unit area on one surface is 20,000 / mm ² or less,
In particular, it is oriented to a state of 15,000 / mm ² or less, particularly 10,000 / mm ² or less.

The liquid crystal polymer layer, which is preferable from the viewpoint of preventing disturbance of optical characteristics, has an average number of domains per unit area on one surface of 100,000 / mm ² or less, and especially 80,000 / mm ^2.
Less than 60,000 / mm ² , and the variation in the number of domains per unit area is less than 20,000 / mm ² , especially 15,000 / mm ² or less, especially 10,000 / mm ² It is oriented in the state of ² or less. A cholesteric liquid crystal layer having excellent alignment homogeneity is advantageous for expanding the viewing angle for good visibility while suppressing display unevenness of a liquid crystal display device or the like, and particularly for a direct-view type liquid crystal display device which is directly observed even from an oblique direction. Suitable for forming

The liquid crystal polymer layer according to the present invention may be composed of one liquid crystal polymer layer or a laminate of two or more liquid crystal polymer layers. Incidentally, by overlapping two or more cholesteric liquid crystal layers having different center wavelengths of reflected light, the reflection wavelength range can be expanded.

That is, in a single cholesteric liquid crystal layer, there is usually a limit in a wavelength range showing selective reflection (circular dichroism), and the limit may be a wide range up to a wavelength range of about 100 nm. Even in that wavelength range, it does not reach the entire range of visible light desired when applied to liquid crystal display devices, etc.,
By overlapping cholesteric liquid crystal layers having different selective reflectivity (reflection wavelength range), the wavelength range showing circular dichroism can be expanded.

When the above-mentioned cholesteric liquid crystal polymer layers are superimposed, it is preferable to use a combination of those that reflect circularly polarized light in the same direction. It is preferable from the point that the state of polarization is prevented and the amount of polarized light that can be used is increased. Further, it is more preferable that the cholesteric liquid crystal polymer layers are superposed in the order of the wavelength based on the center wavelength of the reflected light, from the viewpoint of suppressing the wavelength shift at the time of a large viewing angle.

The thickness of the liquid crystal polymer layer is 0.5 to 50 μm, preferably 1 to 30 μm, in view of prevention of disorder of alignment and decrease in transmittance, and widening of the wavelength range of selective reflection (reflection wavelength range).
m, particularly preferably 1.5 to 10 μm. In the present invention, the total thickness of the liquid crystal polymer layer is preferably 2 μm or more from the viewpoint of preventing disturbance of optical characteristics. Therefore, when the liquid crystal polymer layer is a single layer, its thickness is preferably 2 μm or more.

The circularly polarized light separating layer of the present invention utilizes the property that the cholesteric liquid crystal layer of the Grand Jean orientation separates natural light into left and right circularly polarized light as transmitted light and reflected light as described above. In the cholesteric liquid crystal polymer layer, for example, an appropriate one 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 layer, which is preferable in view of the size of the reflection wavelength range, has a helical pitch in the Grandian orientation that changes in the thickness direction. Cholesteric liquid crystal molecules having a larger phase difference have 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, a liquid crystal polymer having a glass transition temperature of 30 to 150 [deg.] C. can be preferably used from the viewpoint of handleability and stability of alignment at a practical temperature.

Incidentally, examples of the above-mentioned main chain type liquid crystal polymer include 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, for example, a polyester-based liquid crystal polymer. 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, for example, nematic orientation composed of para-substituted aromatic units and para-substituted cyclohexyl ring units such as azomethine, azo, azoxy and ester, biphenyl, phenylcyclohexane, and bicyclohexane forms can be obtained. 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 portion 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 above-mentioned main chain type liquid crystal polymer can be prepared, for example, by an appropriate method according to a conventional polymer synthesis, in which component monomers are copolymerized by a radical polymerization method, a cation polymerization method, an anion polymerization method or the like. it can.

The preparation of the side-chain type liquid crystal polymer is also described, for example,
A monomer addition polymerization method in which a monomer having a mesogen group introduced through a spacer group into a monomer for forming a vinyl-based main chain, such as an ester of acrylic acid or methacrylic acid, is polymerized by a radical polymerization method or the like, or polyoxymethylsilylene Of adding a vinyl-substituted mesogen monomer in the presence of a platinum-based catalyst via a Si-H bond, and introducing a mesogen group through an esterification reaction using a phase transfer catalyst via a functional group added to the main chain polymer And
The reaction can be carried out by an appropriate method such as a method of performing a polycondensation reaction between a diol and a monomer having a mesogen group introduced into a part of malonic acid via a spacer group, if necessary.

In the above description, the film formability, the good Gran-Jan orientation in the monodomain state, the short time of the alignment treatment, the stable fixation to the glass state, the controllability of the helical pitch of the cholesteric phase, the thin and light pitch The liquid crystal polymer whose orientation state is hardly changed at a practical temperature and which can be preferably used from the viewpoint of forming a circularly polarized light separating layer having excellent durability and storage stability is a monomer unit represented by the following general formula (a). And a copolymer containing a monomer unit represented by the general formula (b) as a component, particularly, a monomer unit 60 of the general formula (a)
To 95% by weight, and 40 to 5 monomer units of the general formula (b).
The composition comprises a copolymer consisting of 100% by weight (Japanese Patent Application No. 7-251818).

Formula (a): (However, R ¹ is hydrogen or a methyl group, m is an integer of 1 to 6, X ¹ is a CO ₂ group or an OCO group, p and q are 1 or 2, and p + q = 3 is satisfied.) Equation (b): (Where R ² is hydrogen or a methyl group, n is an integer of 1 to 6, X ² is a CO ₂ group or an OCO group, X ³ is —CO—R ³ or —R ⁴ , and R ³ is R ⁴ And R ⁵ is as follows. )

The acrylic monomer capable of forming the monomer units represented by the general formulas (a) and (b) can be synthesized by an appropriate method. For example, first, ethylene chlorohydrin and 4-hydroxybenzoic acid are heated and refluxed in an aqueous alkali solution using potassium iodide as a catalyst to obtain a hydroxycarboxylic acid, which is then subjected to a dehydration reaction with acrylic acid or methacrylic acid. (Meth) acrylate, and the (meth) acrylate
A method of obtaining a monomer belonging to the general formula (a) by esterification with -cyano-4'-hydroxybiphenyl in the presence of DCC (dicyclohexylcarbodiimide) and DMAP (dimethylaminopyridine).

As an example of the synthesis of an acrylic monomer belonging to the general formula (b), first, a hydroxyalkyl halide and 4-hydroxybenzoic acid are heated and refluxed in an aqueous alkali solution using potassium iodide as a catalyst to obtain a hydroxycarboxylic acid. After obtaining it, it is dehydrated with acrylic acid or methacrylic acid to obtain (meth) acrylate, and the (meth) acrylate is converted to a phenol having a R ³ group-containing CO group at the 4-position in the presence of DCC and DMAP. Esterification method, or after the above-mentioned dehydration reaction, the (meth) acrylate is converted into DCC and D with phenol having an asymmetric carbon group at the 4-position.
Examples of the method include esterification in the presence of MAP.

Accordingly, other monomers belonging to the above-mentioned general formulas (a) and (b) can be synthesized according to the above-mentioned method using an appropriate raw material having a target introduction group. The phenol having an R ³ group-containing CO group at the 4-position is, for example, first reacted with methyl chloroformate and 4-hydroxybenzoic acid in an aqueous alkali solution to form a carboxylic acid, which is then converted to an acid chloride with oxalyl chloride. after, is reacted with H-R ³ in pyridine / tetrahydrofuran to introduce an R ³ group, and then by a method for removing the processed protective groups with ammonia water thereto, also having an asymmetric carbon group at the 4-position Phenol can be obtained, for example, by a method of azeotropically dehydrating 4-hydroxybenzaldehyde and (S)-(-)-1-phenylethylamine in toluene.

The helical pitch of the cholesteric liquid crystal of the above copolymer can be changed by changing the content of the monomer unit represented by the general formula (b).
Therefore, the wavelength exhibiting circular dichroism can be adjusted by controlling the content of the monomer unit represented by the general formula (b), and an optical element exhibiting circular dichroism with respect to light in the visible light region can be easily obtained. Obtainable.

In order to reduce the thickness of the circularly polarized light separating layer, the total thickness of the cholesteric liquid crystal polymer layer should be 2 to 300 μm.
It is particularly preferably 3 to 100 μm, particularly preferably 5 to 50 μm. In the case of having a supporting substrate, the total thickness including the supporting substrate is 10 to 500 μm, preferably 22 to 300 μm, particularly 3
It is preferably from 0 to 100 μm. In 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.

In the above case, the cholesteric liquid crystal polymer layer can be held by one or two or more supporting substrates depending on the strength and operability. When using a support substrate having two or more layers, the phase difference is reduced as much as possible, such as a non-oriented film or a triacetate film having a small birefringence even when oriented, in order to prevent a change in the state of polarization. Small ones can be preferably used. Preferred forms from the viewpoint of thinning and the like include a form supported by a transparent base material and a form made of a liquid crystal polymer film. In the above,
The superposition treatment of the cholesteric liquid crystal polymer layer can be performed by an appropriate method such as mere superposition or adhesion through an adhesive such as an adhesive.

In the present invention, various optical elements are formed by arranging one or more suitable optical layers such as a quarter-wave plate or a polarizing plate on a liquid crystal polymer layer or a circularly polarized light separating layer. be able to. Further, a light source device, a liquid crystal display device, and the like can be formed by disposing a light source, a liquid crystal cell, and the like. Examples of the optical element are shown in FIGS. 1 is a circularly polarized light separating layer, 2 is a 1/4 wavelength plate, and 3 is a polarizing plate.

The 波長 wavelength plate is disposed on one side or both sides of the circularly polarized light separating layer, and functions as a linearly polarized light converting means. That is, circularly polarized light reflected by the circularly polarized light separating layer or transmitted through and emitted from the circularly polarized light separating layer is incident on a quarter-wave plate, undergoes a phase change, and has a phase change corresponding to a quarter wavelength. 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 pass through the polarizing plate is emitted from the １ ／ wavelength plate.

As described above, by converting the light into a state having a large amount of linearly polarized light components through the quarter-wave plate, light that can be easily transmitted through the polarizing plate can be obtained. This polarizing plate, for example, in the case of a liquid crystal display device, an optical layer that maintains display quality by preventing a decrease in polarization characteristics that occurs due to a change in the viewing angle with respect to the liquid crystal cell, and realizes a higher degree of polarization, It functions as an optical layer for achieving good display quality.

That is, in the above description, it is possible to achieve display by directly inputting the reflected polarized light or the output polarized light from the circularly polarized light separating layer to the liquid crystal cell without using the polarizing plate, but by using the polarizing plate. A polarizing plate is used as necessary because the above-described display quality can be improved. 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 reflected polarized light or the output polarized light from the circularly polarized light separating layer is converted into a predetermined linearly polarized light via the linearly polarized light converting means.

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

The quarter-wave plate can be formed as a single layer or as a superposed layer of two or more retardation plates. In the case of a quarter-wave plate composed of a single-layer retardation plate, the smaller the wavelength dispersion of birefringence, the more uniform the polarization state for each wavelength is preferable. On the other hand, the superposition of the retardation plates is effective for improving the wavelength characteristics in the wavelength range, and the combination may be determined as appropriate according to the wavelength range.

Incidentally, as a single-layer type quarter-wave plate which can be preferably used for light in the visible light region in terms of wavelength range, conversion efficiency, etc., those having a small phase difference, especially 100 to 1
It gives a phase difference of 80 nm, especially 110 to 150 nm or less. In the case of a quarter-wave plate composed of two or more retardation plates, a layer that provides a phase difference of 100 to 180 nm is included in one or more odd-numbered layers, and a layer that provides a retardation of 200 nm or more is included. It is preferable to combine them from the viewpoint of wavelength characteristics and the like.

The retardation plate forming the quarter-wave plate can be formed of an appropriate material, and preferably has a transparent and uniform retardation. In general, for example, a birefringent film obtained by stretching a film made of a suitable plastic such as polycarbonate, polysulfone, polyester, polymethyl methacrylate, polyamide, or polyvinyl alcohol, or a liquid crystal polymer layer is used.

In the present invention, a 1/4 wavelength plate made of a liquid crystal polymer layer or a retardation plate made of a liquid crystal polymer layer is used in order to efficiently convert circularly polarized light through the circularly polarized light separating layer into linearly polarized light. A quarter-wave plate having two or more layers is preferred. Further, as the liquid crystal polymer layer, a layer exhibiting a twisted alignment such as a twisted nematic liquid crystal is preferable. It is preferable that the liquid crystal polymer layer also satisfies the above-described average number and variation of the domains.

The optical element according to the present invention may have a polarizing plate on one or both sides of the liquid crystal polymer layer or the circularly polarized light separating layer. Further, as shown in FIG.
May be arranged on the 波長 wavelength plate 2 provided on the circularly polarized light separating layer. When the polarizing plate is arranged on the circularly polarized light separating layer without passing through the quarter wave plate, the circularly polarized light from the circularly polarized light separating layer is directly linearly polarized via the polarizing plate. on the other hand,
When a polarizing plate is arranged on a circularly polarized light separating layer via a quarter-wave plate, the polarizing plate can be used as a polarizing plate on the light source side of the liquid crystal cell.

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

As the polarizing plate provided on the liquid crystal polymer layer or the circularly polarized light separating layer, a type containing a dichroic dye is particularly preferably used from the viewpoint of the degree of polarization and the like. The thickness of the polarizing film is usually 5 to 80 μm, but is not limited thereto. The polarizing plate used may be one obtained by coating one or both sides of a polarizing film with a transparent protective layer or the like.

The liquid crystal polymer layer, the circularly polarized light separating layer and the optical element according to the present invention can be preferably used for forming a light source device.
The light source device can be formed by disposing a liquid crystal polymer layer, a circularly polarized light separating layer, and an optical element on a surface light source. When a circularly polarized light separating layer or an optical element having the same is used, a polarized light source device can be obtained. In that case,
When the helical pitch of the cholesteric liquid crystal layer changes in the thickness direction, or when the cholesteric liquid crystal layer is superimposed in the order of the center wavelength of the reflected light and the center wavelength of the reflected light is different on the front and back of the circularly polarized light separating layer, It is preferable to arrange the surface light source on the shorter wavelength side from the viewpoint of suppressing the wavelength shift and the like. As shown in FIGS. 2 and 3, the circularly polarized light separating layer
In the case where the wave plate 2 or the like is provided, it is preferable to arrange the surface light source on the side having no quarter wave plate or the like.

FIG. 4 shows an example of the light source device 4 according to the present invention. This shows a case where a polarized light source device is formed using an optical element having a circularly polarized light separating layer. 41 is a light guide plate, 4
2 is a light source, and the light guide plate 41 is a light source 42 arranged on the side.
From the top surface (on the side of the circularly polarized light separation layer) and functions integrally with the light source 42, and functions as a surface light source for supplying light to the circularly polarized light separation layer.

According to the light source device 4 described above, the incident light from the light source 42 is emitted from the upper surface of the light guide plate 41 and is incident on the circularly polarized light separating layer 1 disposed on the light emitting surface side, so that one of the left and right circularly polarized light is converted. The light is transmitted, the other circularly polarized light is reflected, and re-enters the light guide plate 41 as return light. The light that has re-entered the light guide plate is reflected by the reflection layer 44 on the lower surface and again enters the circularly polarized light separating layer 1.
The light is separated again into transmitted light and reflected light (re-incident light).

As described above, the light source in the light source device is preferably a light guide plate type surface light source that emits the incident light from the light source disposed on the side surface from one of the upper and lower surfaces, from the viewpoint of improving the light use efficiency. Can be As the light guide plate, an appropriate one can be used, but in general, one made of a plate-like material having an upper surface and an lower surface serving as an emission surface, and an incident surface formed of at least one side surface between the upper and lower surfaces is used. . A light guide plate in a conventional sidelight type backlight is an example.

The preferred form of the light guide plate is one that has excellent exit efficiency from the exit surface and that exit light has excellent perpendicularity to the exit surface and is easily used effectively. Further, in the case of a polarized light source device, it is excellent in the exit efficiency of the re-incident light through the circularly polarized light separation layer, and is excellent in the approximation of the exit direction to the initial exit direction. A light guide plate that is particularly preferable from the above point has a structure in which fine prism-shaped irregularities are formed on the surface opposite to the light emission surface, and in particular, a convex portion or a concave portion having a long side surface and a short side surface is periodically formed. (Japanese Patent Application No. 7-321036). Furthermore, it is preferable that the thickness of the side end portion facing the incident surface is thinner than that of the incident surface, particularly, the thickness is 50% or less.

The thinning of the end on the side opposite to the incident surface is effective in efficiently entering the short side surface of the prismatic uneven surface until the light incident from the incident surface reaches the end on the opposite side as the transmission end. However, it is advantageous in that incident light emitted from the exit surface via the reflection can be efficiently supplied to the target surface. Further, by adopting such a thin structure, the light guide plate can be reduced in weight. For example, when the prismatic uneven surface is linear, the weight can be about 75% of the light guide plate having a uniform thickness.

The pitch of the convex portions or concave portions on the prism-shaped concave-convex surface is determined from the viewpoints of suppressing uneven brightness and preventing moire with a liquid crystal cell since emitted light is usually emitted in a stripe shape through the convex portions or concave portions. Smaller is more preferable. A preferable period of the convex portion or the concave portion in consideration of manufacturing accuracy and the like is 500
μm or less, especially 300 μm or less, especially 5 to 200 μm.

The light guide plate can be formed of an appropriate material exhibiting transparency according to the wavelength range of the light source. By the way, in the visible light region, for example, acrylic resin such as polymethyl methacrylate, polycarbonate resin such as polycarbonate and polycarbonate / polystyrene copolymer, about 400 to 700 nm like transparent resin and glass represented by epoxy resin and the like. Those exhibiting transparency in the wavelength range are exemplified.

The light guide plate may be formed by an appropriate method. As a preferable production method from the viewpoint of mass productivity, for example, a method of performing a polymerization treatment by filling or casting a liquid resin that can be polymerized by heat, ultraviolet rays or radiation into a mold capable of forming predetermined prismatic irregularities, A method of transferring a shape by pressing a thermoplastic resin under heating to a mold capable of forming a predetermined prismatic unevenness under heating, a thermoplastic resin melted by heating or a resin fluidized through heat or a solvent is subjected to a predetermined method. Examples include a method such as injection molding in which a mold capable of being formed into a shape is filled.

The light guide plate may be formed as a laminate of different kinds of materials, such as a sheet in which a prism-like uneven surface forming sheet is adhered to a light guide portion for transmitting light, and may be made of one kind of material. It need not be formed as an integral monolayer. In the light guide plate described above, the characteristics such as the angle distribution and the in-plane distribution of the outgoing light are adjusted based on the control of the area ratio and the inclination angle of the short side surface and the long side surface, the shape and the curvature of the prismatic uneven surface, and the like. Can be.

The thickness of the light guide plate can be appropriately determined according to the size of the light guide plate and the size of the light source depending on the purpose of use. The general thickness of the light guide plate used in a liquid crystal display device or the like is 20 mm or less based on the incident surface, and is preferably 0.1 mm or less.
10 to 10 mm, especially 0.5 to 8 mm.

When a polarized light source device is formed, a reflection layer 44 is disposed on the surface of the light guide plate opposite to the light exit surface so that the return light from the circularly polarized light separation layer is incident on the circularly polarized light separation layer again through reflection. . The reflection layer 44 includes a plating layer, a metal deposition layer,
It can be appropriately formed of a metal foil, a metal deposition sheet, a plating sheet, or the like, may be integrated with the opposing surface of the light guide plate, or may be stacked as a reflection sheet or the like,
In the present invention, an appropriate arrangement form can be adopted. A metal reflecting surface is preferred over a point of inverting circularly polarized light via reflection. The reflection layer may be of a light diffusion type by, for example, providing a fine uneven structure on the surface.

A light guide plate type surface light source is generally formed by arranging a light source 42 on an incident surface of a light guide plate 41 as illustrated in FIG. As the light source, an appropriate one can be used. For example, a linear light source such as a (cold or hot) cathode tube, a point light source such as a light emitting diode, or a linear or planar array thereof can be preferably used. At the time of forming the backlight, as necessary, as shown in the figure, a light source holder 43 surrounding the light source for guiding the divergent light from the linear light source to the side surface of the light guide plate, and a suitable auxiliary such as a prism array layer. It can also be a combination in which means are arranged.

The purpose of the prism array layer is to control the light emission direction to obtain a large amount of light in a direction perpendicular to or close to the light source device, which is advantageous for visual recognition. As illustrated in FIG. 4, one or two or more layers of the prism array layer 5 can be arranged on the light emission side of the light guide plate 41 via the diffusion layer 45 as necessary.

The prism array layer can be provided by an appropriate method such as providing a prism structure to the light guide plate and arranging a prism sheet or the like. In the case where two or more prism array layers are arranged, it is preferable that the arrangement direction of the array in the upper and lower layers is orthogonal or another intersection state, from the viewpoint of canceling optical anisotropy.

A light guide plate which can be preferably used for forming a polarized light source device is capable of emitting incident light from the side surface with high efficiency from the exit surface, and directing the emitted light with high directivity, especially excellent perpendicularity to the exit surface. While exhibiting the property, it is excellent in the re-emission efficiency of the re-incident light through the circularly polarized light separation layer, and the directivity and the output angle of the re-output light match as much as possible with the directivity and the output angle of the initial output light, In addition, the re-incident light that has passed through the circularly polarized light separating layer is emitted with a small number of reflection repetitions, especially without repetition of reflection.

As described above, the polarized light source device according to the present invention prevents reflection loss and the like by reusing the reflected light (re-incident light) from the circularly polarized light separating layer as the outgoing light by polarization conversion, and If necessary, the light is converted into a light state containing a linearly polarized light component through a quarter-wave plate or the like to facilitate transmission through the polarizing plate and to prevent absorption loss, thereby improving light use efficiency, especially frontal luminance. It is like that.

Therefore, the light source device according to the present invention provides light which is excellent in light use efficiency as described above, is bright, has excellent perpendicularity of emitted light, and has less light and dark unevenness and display unevenness, and is easy to enlarge the area. Therefore, it can be preferably used for various devices as a backlight system in a liquid crystal display device or the like.

FIG. 5 illustrates a liquid crystal display device 6 using the light source device 4 according to the present invention in a backlight system. 61
Is a liquid crystal cell, 62 is an upper polarizing plate, and 63 is a diffusion plate. A liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell functioning as a liquid crystal shutter and an associated driving device, a polarizing plate, a backlight, and a compensating retardation plate as necessary. .

In the present invention, the liquid crystal display device is not particularly limited except that a liquid crystal cell is arranged on the liquid crystal polymer layer side or the circularly polarized light separating layer side with the polarizing plate interposed therebetween using the above-described light source device. Therefore, the liquid crystal display device can be formed according to a conventional method, and particularly, a direct-view liquid crystal display device can be preferably formed. When the light source device has no polarizing plate, a separate polarizing plate is disposed between the light source device and the liquid crystal cell.

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.

As described above, for example, an iodine-based or dye-based absorption-type linear polarizer is used as a polarizing plate, especially as a backlight-side polarizing plate, in order to obtain a display with a good contrast ratio due to the incidence of highly linearly polarized light. A liquid crystal display device using a material having a high degree of polarization such as, for example, is preferred.

In forming a liquid crystal display device, for example, a diffusion layer or an antiglare 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. One or two or more suitable optical layers can be arranged at appropriate positions.

The diffusion layer is arranged as necessary for the purpose of leveling outgoing light, suppressing uneven brightness, and preventing glare caused by moire due to interference with pixels when applied to a liquid crystal cell. Is done. The position of the liquid crystal polymer layer or the circularly polarized light separating layer, such as one side or both sides of the liquid crystal polymer layer or the circularly polarized light separating layer, between the １ ／ wavelength plate and the polarizing plate provided thereon, or the upper surface of the polarizing plate. One layer or two or more layers can be arranged at an appropriate position adjacent to a wavelength plate, a polarizing plate, or the like.

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 a solvent treatment, or a mold provided with a predetermined diffusion structure. In any method such as a transfer forming method, a coating layer on a liquid crystal polymer layer or a circularly polarized light separating layer, a diffusion sheet, or the like can be appropriately formed. The diffusion layer, which can be preferably used from the viewpoint of maintaining optical characteristics such as the polarization state of circularly polarized light via the circularly polarized light separating layer, is a vertically incident light having a phase difference of 633 nm, preferably an incident light having an incident angle within 30 degrees. 30 nm or less, especially 0 to 20 nm based on the

The above-mentioned compensating retardation plate is intended to improve the visibility by compensating for the wavelength dependence of the birefringence of the liquid crystal cell and the like. In the present invention,
It is arranged as necessary between the polarizing plate on the viewing side and / or the backlight side and the liquid crystal cell. In addition, as the compensation retardation plate, an appropriate one can be used according to a wavelength range or 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 a liquid crystal polymer layer as exemplified by the above-mentioned retardation plate for linear polarization conversion.

In the present invention, all or a part of the liquid crystal polymer layer, the circularly polarized light separating layer, the optical element, the light source device, and the components forming the liquid crystal display device are bonded through an adhesive layer. Alternatively, they may be arranged in an easily separable state. In the case where the arrangement angle of the optical axis becomes a problem as in the relationship between the quarter-wave plate and the polarizing plate, it is preferable to perform an adhesive treatment in order to prevent displacement or the like. The bonding process is also effective in preventing reflection loss at each interface, preventing deterioration of display quality by preventing foreign substances from entering the interface, and the like.

An appropriate adhesive layer can be used.
An adhesive layer is preferable from the viewpoint of simplicity of the bonding treatment and the like.
For forming the pressure-sensitive adhesive layer, a pressure-sensitive adhesive using an appropriate polymer such as an acrylic polymer, a silicone-based polymer, polyester, polyurethane, polyether, or synthetic rubber can be used. From the viewpoint of preventing reflection loss, it is preferable that the refractive index is an intermediate value of an object to be bonded.

[0080]

【Example】

Example 1 A 20% by weight solution of an acrylic thermotropic cholesteric liquid crystal polymer having a selected wavelength range of 500 to 600 nm in tetrahydrofuran is spin-coated on a polyvinyl alcohol rubbed surface (0.1 μm thick) of a 30 μm thick triacetyl cellulose film. Apply by method
The resultant was subjected to a heating alignment treatment at 60 ° C. for 5 minutes to obtain a circularly polarized light separating layer having a cholesteric liquid crystal polymer layer having a thickness of 3 μm.
This exhibits a mirror-like selective reflection state in the above wavelength range and transmits left-handed circularly polarized light, and a change in the helical pitch in the thickness direction was confirmed from TEM cross-section observation.

[0081] Then the exposed surface of the cholesteric liquid crystal polymer layer, a phase difference comprising a stretched film of polycarbonate is _{140nm, N z = (n x} -n z) / (n x -n y)
In being defined N _z is to obtain an optical element bonded via an acrylic adhesive layer having a thickness of 20μm quarter-wave plate 1. In the above _Nz calculation formula, _nx and _ny (where _nx ≧ _ny )
Is the in-plane refractive index, and _nz is the refractive index in the thickness direction.

Example 2 Depending on the difference in the ratio of mesogenic groups, 400 to 470 nm or 6
A cholesteric liquid crystal polymer having a thickness of 5 μm was applied by applying two kinds of acrylic thermotropic cholesteric liquid crystal polymers exhibiting a selected wavelength range of 00 to 700 nm according to Example 1, and heating and aligning at 160 ± 2 ° C. for 5 minutes. Two types of circularly polarized light separating films each having a layer were obtained. Each of them had a mirror-like selective reflection state in the above-mentioned wavelength range and transmitted left-circularly polarized light.

Next, the two types of circularly polarized light separating films are superposed on each other, and then thermocompression-bonded via a laminating roll at 130 ° C.
A circularly-polarized light separating layer showing a continuous selected wavelength range in the range of 00 to 700 nm is obtained, and a thickness of 20 μm
via an acrylic adhesive layer of m, the phase difference 135 nm, N _z 0.5 consisting of stretched polycarbonate film 1 /
An optical element was obtained by bonding a four-wavelength plate.

Comparative Example 1 A circularly polarized light separating layer was obtained in the same manner as in Example 1 except that the heating alignment treatment was performed at 140 ° C., and an optical element was obtained using the same.

COMPARATIVE EXAMPLE 2 The heating alignment treatment for forming the cholesteric liquid crystal layer was performed at 150 ±
A circularly polarized light separating layer was obtained in the same manner as in Example 2 except that the temperature was 20 ° C., and an optical element was obtained using the same.

Evaluation Test Number of Domains The surface of the cholesteric liquid crystal polymer layer in the circularly polarized light separating layer obtained in each of Examples and Comparative Examples was observed through a microscope, the number of domains per unit area was examined, and the average number and variation were determined. .

Luminance and Chromaticity Difference A cold cathode tube having a diameter of 3 mm is arranged on the side surface of a light guide plate having a fine prism structure formed on the lower surface, and the cold cathode tube is surrounded by a light source holder made of a silver-evaporated polyester film. On the upper surface of a sidelight-type surface light source in which a reflection sheet made of a silver-evaporated polyester film is disposed on the lower surface of a light plate, the optical elements obtained in Examples and Comparative Examples are disposed with the quarter-wave plate on the upper side. After that, a light source device was obtained by disposing a polarizing plate thereon at an angle at which the luminance became maximum, and the luminance improvement rate and the chromaticity difference causing display unevenness were examined. In addition, the measurement was performed in the case where the prism sheet was not arranged on the light guide plate, and in the case where the two-layer prism sheet was arranged with the array direction orthogonal to the array.

The above-mentioned luminance improvement rate was calculated based on the luminance of a surface light source device without an optical element.
Further, the chromaticity difference was calculated by the following formula by examining the chromaticity of the surface light source device without the optical element. Chromaticity difference = {(x ₁ −x ₀ ) ² + (y ₁ −y ₀ ) ² } (where x ₁ and y ₁ are when there is an optical element, x ₀ and y ₀ are when there is no optical element) Is.)

The results are shown in Tables 1 and 2.

[Table 1]

[0090]

[Table 2]

[Brief description of the drawings]

FIG. 1 is an enlarged surface view of an example of a liquid crystal polymer layer.

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 light source device.

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

[Description of Signs] 1: Circularly polarized light separating layer (liquid crystal polymer layer) 2: 1/4 wavelength plate 3: Polarizing plate 4: Light source device 41: Light guide plate 42: Light source 44: Reflective layer 5: Prism array layer 6: Liquid crystal Display device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02F 1/1337 G02F 1/1337 (72) Inventor Seiji Umemoto 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (16)

[Claims] 1. A liquid crystal polymer layer which is oriented in a state where the average number of domains per unit area on one surface is 100,000 / mm ² or less. 2. A liquid crystal polymer layer characterized in that the liquid crystal polymer layer is aligned in a state where the variation in the number of domains per unit area on one surface is 20,000 / mm ² or less. 3. The method according to claim 1, wherein an average number of domains per unit area on one surface is 100,000 / mm ² or less, and a variation in the number of domains is 20,000 / mm ² or less. Liquid crystal polymer layer. 4. The liquid crystal polymer layer according to claim 1, wherein the liquid crystal layer is composed of one or two or more superimposed bodies, and has a total thickness of 2 μm or more. 5. A circularly polarized light separating layer comprising the liquid crystal polymer layer according to claim 1, comprising a cholesteric liquid crystal layer having a Grandian orientation. 6. The circularly polarized light separating layer according to claim 5, wherein a helical pitch of the cholesteric liquid crystal layer changes in a thickness direction. 7. The circularly polarized light separating layer according to claim 5, wherein the cholesteric liquid crystal layer comprises two or more superimposed bodies formed by a combination of cholesteric liquid crystal polymers having different center wavelengths of reflected light. 8. An optical element, characterized in that at least one of the circularly polarized light separating layers according to claim 5 has a quarter-wave plate comprising one or two or more retardation plates. 9. The optical element according to claim 8, wherein the quarter-wave plate has at least one layer of a retardation plate made of a liquid crystal polymer. 10. The optical element according to claim 9, wherein the retardation plate made of a liquid crystal polymer is made of a twisted liquid crystal polymer. 11. The liquid crystal polymer layer according to claim 1, 4 or 7, or the circularly polarized light separation layer according to claim 5 to 7, or 8.
An optical element, characterized in that a polarizing plate containing a dichroic dye is provided on the optical element described in any one of (1) to (10). 12. A liquid crystal polymer layer according to any one of claims 1 to 4, a circularly polarized light separating layer according to any one of claims 5 to 7, or an optical element according to any one of claims 8 to 11, above the surface light source. A light source device characterized by the above-mentioned. 13. The light source device according to claim 12, wherein the light source device has one or more prism array layers. 14. The light source device according to claim 13, wherein two or more prism array layers are arranged so that the array direction of the upper and lower layers intersects. 15. A liquid crystal display device comprising a light source device according to claim 12 and a liquid crystal cell with a polarizing plate interposed on the liquid crystal polymer layer side. 16. The liquid crystal polymer layer according to claim 1, wherein all or a part of the formed part is subjected to an adhesive treatment via an adhesive layer. The optical element according to claim 8, the light source device according to claim 12, or the liquid crystal display device according to claim 15.