JP2007249027A - Polarized light conversion film and its manufacturing method, polarizing element, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarized light conversion film which can have a birefringent material aligned uniformly in a fixed direction by a rubbing method, and improves light use efficiency for a display such as a liquid crystal display and has high luminance improvement effect and superior productivity when used for reflection type and translucent type liquid crystal display elements, and to provide its manufacturing method, a polarizing element which is increased in light transmissivity using the polarized light conversion film, and a liquid crystal display device whose luminance is improved by using the polarized light conversion film. <P>SOLUTION: Disclosed are the polarized light conversion film which has a structure comprising a polarized light separating layer separating incident light into two linear polarized light beams having mutually orthogonal electric field vectors and a polarized light converting layer converting the polarized light states of the linear polarized light beams, the structure containing an optical isotropic material and having its surface brought into contact with a layer where the birefringent material is previously aligned; and its manufacturing method. Further, disclosed is the polarizing element which is increased in light transmissivity by using the polarized light conversion film; and the liquid crystal display device which is improved in luminance by using the polarized light conversion film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polarization conversion film capable of enhancing light utilization efficiency for a display such as a liquid crystal display device, a method for producing the same, a polarizing element using the polarization conversion film, and a liquid crystal display device.

  Polarizing elements can generate light in various polarization states, such as linearly polarized light, circularly polarized light, and elliptically polarized light, by transmitting natural light such as sunlight or light from a light source such as a lamp. It is used in a very wide range as an important member of a main liquid crystal display device such as a mode or a twisted nematic mode (see Non-Patent Document 1).

In general, iodine-based or dye-based dichroic polarizing elements are often used as the polarizing elements used in the liquid crystal display device. The dichroic polarizing element generates linearly polarized light by absorbing only one of two polarized components having orthogonal electric field vectors and not transmitting it, and transmitting the other polarized component. However, since linearly polarized light is generated by utilizing light absorption, when the degree of polarization is close to 100%, the upper limit of the light transmittance is 50% in principle.
Therefore, in an actual liquid crystal display device using the dichroic polarizing element, there is a problem that only half or less of the light source can be used and the display brightness is low.
Therefore, in order to improve the light use efficiency of the light source, several means for performing polarization conversion on the light from the light source have been proposed (see Patent Documents 1 to 3).
Further, in the application to the transmissive liquid crystal display device, the following 1. 1. Anisotropic reflection system and An anisotropic scattering type brightness enhancement film has already been industrialized and widely used.

1. Anisotropic reflection method For example, a polarizing element having anisotropy in reflectance and transmittance by laminating a uniaxially stretched film and an unstretched film in multiple layers and increasing the difference in refractive index in the stretching direction; This is a method of increasing the light use efficiency of the backlight by laminating a dichroic polarizing element and using it as a polarizing element on the backlight side (see Patent Documents 4 to 6). In this method, in order to increase the degree of polarization, it is necessary to increase the number of stacked layers to several tens of layers, and it is difficult to increase productivity, but the effect of improving the front luminance is great.
Also proposed is a method in which cholesteric liquid crystals having different pitch lengths are stacked in a vertically aligned state and combined with a quarter-wave plate (see Patent Documents 7 and 8).

2. Anisotropic Scattering Method An anisotropic scatterer is produced by blending a positive intrinsic birefringent polymer and a negative intrinsic birefringent polymer and uniaxially stretching, and used in combination with a normal dichroic polarizing element. This is a method for improving the light utilization efficiency of the backlight (see Patent Documents 9 to 14). This method has a feature that the viewing angle dependency of luminance is small, but the front luminance improvement degree is smaller than that of the anisotropic reflection method described above.

On the other hand, reflective liquid crystal display devices are used as displays for portable devices such as portable information terminals, portable game consoles and mobile phones because they do not require a backlight and consume less power. It is expected to expand.
The reflective liquid crystal display device has a basic structure in which a reflector, a liquid crystal cell, and a polarizing film are laminated in this order. As for the display mode of the liquid crystal cell, there are TN (Twisted Nematic), STN (Super Twisted Nematic), HAN (Hybrid Aligned Nematic), and HPDLC (Holographic Polymer Dispersed Liquid Display). Among these, TN mode and STN mode reflective liquid crystal display devices have already been put into practical use and widely used.
However, the reflection-type liquid crystal display device cannot be used when the external light is weakened because the reflection luminance decreases. For this reason, a transflective liquid crystal display device has been proposed that performs reflective display using reflected light of external light and performs transmissive display using transmitted light of a backlight, and is mainly used for portable terminal modules. ing.

  Here, in the above-described anisotropic reflection system and anisotropic scattering system brightness enhancement film, a part of incident light is reflected or scattered on the incident side. In the transmissive liquid crystal display device, the light can be reflected and reused by the backlight portion, so that the light use efficiency can be improved as a whole and the luminance can be improved. In the conventional transflective liquid crystal display device, light reflected or scattered on the light incident side is emitted into the atmosphere and cannot be reused, so that the luminance cannot be improved in principle.

  A method has been proposed in which an unpolarized beam can be almost completely converted into a polarized beam having the same polarization direction by a polarization element in which a polarization rotation layer is arranged between layers that control the direction of the polarization component. However, this polarizing element is a small area element for an image projection apparatus, and is difficult to manufacture as a large area element for a display such as a liquid crystal display apparatus.

  Also, luminance enhancement using a prism and a polarization separation layer using a birefringent layer having birefringence or a birefringent diffraction grating, and a polarization conversion layer in which a birefringent compound is tilted and oriented at a certain angle using a rod-like liquid crystal. Films have been proposed (see Patent Documents 16 and 17). However, in these methods, the efficiency of polarization conversion is not sufficient, and it takes time to incline and align at an almost constant angle with respect to the film surface. Is not enough.

Furthermore, in order to fabricate the prism and a birefringent layer having a birefringence or a polarization separation layer using a birefringent diffraction grating, a birefringent material is placed in a certain direction on the uneven surface having the prism structure or the diffraction grating structure. Must be oriented and laminated.
However, it is difficult to orient the birefringent material in a certain direction on the uneven surface. For example, when a liquid crystal compound is used as the birefringent material, a simple and general method for aligning the liquid crystal compound includes a rubbing method. In the rubbing method, when rubbing is performed, stripes can be made parallel to the surface, and the liquid crystalline compound is aligned along the stripes. However, if rubbing is applied to the uneven surface, there are slopes and steps in the depth direction. The generated lines are bent or cut in the middle, making it difficult to create a uniform line in parallel. Therefore, there is a problem that even if a liquid crystal compound is applied thereon, there is a portion where the alignment method is not aligned, and the performance of the polarization separation layer does not reach the prediction.
As a method for aligning the liquid crystalline compound, there are an electric field application method and a magnetic field application method in addition to the rubbing method, but they are complicated and not a general method.

  For this reason, in the rubbing method, the birefringent material can be aligned in a certain direction, and the light utilization efficiency is improved for a display such as a liquid crystal display device. In particular, the luminance improving effect is obtained in the reflective and transflective liquid crystal display elements. A polarization conversion film having high productivity and a method for producing the same, a polarizing element having increased light transmittance by using the polarization conversion film, and a liquid crystal display device having improved brightness by using the polarization conversion film are still proposed. However, the present situation is that further improvement and development is desired.

Sato Susumu “Liquid Crystal and its Applications”, published by Sangyo Tosho, pages 96-115 JP 63-121821 A Japanese Patent Laid-Open No. 5-224175 JP-A-5-232433 International Publication No. 95/17691 Pamphlet International Publication No. 95/17692 Pamphlet WO95 / 17699 pamphlet European Patent No. 606940 JP-A-8-271731 International Publication No. 97/32223 Pamphlet International Publication No. 97/32224 Pamphlet WO 97/32225 pamphlet WO 97/32226 pamphlet JP-A-9-274108 JP-A-11-174231 Japanese National Patent Publication No. 10-505435 Japanese Patent Laid-Open No. 2004-77899 JP 2004-77900 A

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, according to the present invention, in the rubbing method, birefringent materials can be aligned in a certain direction, and the light use efficiency is improved for a display such as a liquid crystal display device. A polarizing conversion film having a high improvement effect and excellent productivity, a method for producing the same, a polarizing element having increased light transmittance by using the polarizing conversion film, and a liquid crystal display device having improved brightness by using the polarizing conversion film The purpose is to provide.

Means for solving the above-mentioned problems are as follows. That is,
<1> A polarization separation layer that separates incident light into two linearly polarized light whose electric field vectors are orthogonal to each other, and a polarization conversion layer that converts a polarization state of the linearly polarized light, and the polarization separation layer is an optically isotropic material. A polarizing conversion film characterized in that the surface of the structure including the optically isotropic material is adhered to a layer in which the birefringent material is previously oriented.
<2> The polarization conversion film according to <1>, wherein the layer in which the birefringent material is previously aligned includes an alignment film.
<3> The polarization conversion film according to <2>, wherein the alignment film contains at least one of polyimide and polyvinyl alcohol.
<4> The polarization conversion film according to any one of <2> to <3>, wherein the alignment film has a thickness of 0.01 μm or more and 5 μm or less.
<5> The polarization conversion film according to any one of <1> to <4>, wherein the structure including the optically isotropic material is any one of a prism and a diffraction grating.
<6> The above <1> to <5>, wherein the surface of the structure including the optically isotropic material is adhered to a layer in which the birefringent material is previously oriented, and then the birefringent material is polymerized and fixed. The polarization conversion film according to any one of the above.
<7> The polarization conversion film according to <6>, wherein the alignment film is peeled after fixing.
<8> The polarization conversion film according to any one of <1> to <7>, wherein the polarization conversion layer includes a discotic liquid crystalline compound that is tilt-aligned with respect to the film surface.
<9> The polarization conversion film according to <8>, wherein the discotic liquid crystalline compound is hybrid-aligned.

  <10> A method for producing a polarization conversion film, wherein the polarization separation layer and the polarization conversion layer in the polarization conversion film according to any one of <1> to <9> are continuously produced in a roll shape. It is.

  <11> A polarizing element comprising the polarization conversion film according to any one of <1> to <9>.

<12> A liquid crystal display device comprising the polarizing element according to <11>.
<13> The liquid crystal display device according to <12>, which is a reflective liquid crystal display device in which a reflective plate, a liquid crystal cell, a quarter-wave plate, and a polarizing element are stacked in this order.
<14> The liquid crystal display device according to any one of <12> to <13>, further including a backlight, wherein a polarizing element is disposed on the backlight side.
<15> The liquid crystal display device according to <14>, which is a transflective liquid crystal display device including a circularly polarizing plate and a liquid crystal display element that can be used as a reflection type or a transmission type.

The optical compensation film of the present invention comprises a polarization separation layer that separates incident light into two linearly polarized light whose electric field vectors are orthogonal to each other, and a polarization conversion layer that converts the polarization state of the linearly polarized light. In the rubbing method, a structure having an optically isotropic material and the surface of the structure including the optically isotropic material are adhered to a layer in which the birefringent material is previously oriented. Refractive materials can be aligned in a certain direction.
Therefore, the light utilization efficiency can be increased for displays such as liquid crystal display devices, and in particular, the effect of improving luminance can be enhanced in reflective and transflective liquid crystal display elements.

  The manufacturing method of the polarization conversion film of the present invention can be manufactured as a large-area element with high production by continuously producing the polarization separation layer and the polarization conversion layer in the present invention in a roll form.

  Since the polarizing element of the present invention includes the polarization conversion film of the present invention, the light transmittance can be increased.

  Since the liquid crystal display device of the present invention includes the polarizing element of the present invention, the luminance can be improved.

  According to the present invention, the conventional problems can be solved. That is, in the rubbing method, the birefringent material can be aligned in a certain direction and the light use efficiency is improved for a display such as a liquid crystal display device, and in particular, the brightness improvement effect is high in the reflective and transflective liquid crystal display elements. Provided are a polarizing conversion film having excellent productivity, a method for producing the same, a polarizing element having increased light transmittance by using the polarizing conversion film, and a liquid crystal display device having improved brightness by using the polarizing conversion film. Can do.

(Polarization conversion film)
The polarization conversion film of the present invention comprises a polarization separation layer that separates incident light into two linearly polarized light whose electric field vectors are orthogonal to each other, and a polarization conversion layer that converts the polarization state of the linearly polarized light.

FIG. 1 shows an outline of the mechanism of polarization conversion in the polarization conversion film of the present invention.
When non-polarized incident light L enters the polarization separation layer 1, two linearly polarized lights (polarized light) whose electric field vectors (polarization directions) are orthogonal to each other at the interface between the structure containing the optically isotropic material and the birefringent material. Separating in directions a and b) with a separation angle θ.
At this time, in the first aspect, by adjusting the refractive index of the prism and the refractive index of the birefringent layer containing the birefringent material, one (polarized light L1; polarization direction a) is made to go straight, and the other (polarized light L2). The polarization direction b) can be refracted. In the second aspect, by adjusting the refractive index and shape of the diffraction grating and the refractive index of the birefringent material, one of the two linearly polarized light (polarized light L1; polarization direction a) goes straight and the other ( Polarization L2; polarization direction b) can be diffracted.
The two separated linearly polarized lights L 1 and L 2 enter the polarization conversion layer 2. The polarization conversion layer 2 includes a birefringent compound m that is inclined with respect to the film surface (inclination angle φ), and is refracted by the polarization separation layer 1 and is incident on the polarized light L2 that is inclined and incident on the polarization conversion layer 2. Acts and transforms its polarization state. By adjusting the intrinsic birefringence magnitude and the inclination angle φ of the birefringent compound m, the polarization direction of the polarized light L2 can be rotated from the direction b to the direction a ′ (≈a). A uniform linearly polarized light can be extracted.

<Polarized light separation layer>
The polarization separation layer has a structure including an optically isotropic material, and a surface of the structure including the optically isotropic material is a layer in which the birefringent material is previously oriented (hereinafter simply referred to as “birefringence”). Layer))).

-Optically isotropic material-
Although there is no restriction | limiting in particular as said optically isotropic material, For example, a transparent and optically isotropic polymer material is preferable.
Examples of the transparent and optically isotropic polymer material include polyolefin (eg, polyethylene), norbornene resin, polyethylene terephthalate, polyethylene naphthalate, polypropylene, polycarbonate, polystyrene, polyarylate, polysulfone, polyethersulfone, poly Vinyl chloride, polyvinyl alcohol, and cellulose ester (for example, cellulose acetate) are preferable. Among these, polyethylene terephthalate, polyethylene naphthalate, and polycarbonate are particularly preferable.
Specific examples of commercially available polymer materials include ZEONEX, ZEONOR (manufactured by Nippon Zeon Co., Ltd.), ARTON (manufactured by Nippon Synthetic Rubber Co., Ltd.), and Fujitac (manufactured by Fuji Photo Film Co., Ltd.). It is done. Among these, Fujitac (Fuji Photo Film Co., Ltd.) and ZEONOR (Nihon Zeon Co., Ltd.) are particularly preferable.

  Cellulose acetate raw material cotton, cellulose acetate solution and film preparation method, cellulose acetate solvent, plasticizer, anti-degradation agent, UV absorber, optical anisotropy control agent, fine particles, release agent and other additives, dissolution process, flow For the manufacturing process such as rolling, drying, and stretching process, surface treatment, undercoating, backing material, and functional layer, refer to the disclosure of the Japan Society of Invention and Innovation, 2001-1745, pages 7 to 59, Can be used. However, as for the cellulose acetate solvent, a halogenated hydrocarbon having 1 to 7 carbon atoms, particularly methylene chloride, can also be preferably used.

-Birefringent material-
The birefringent material is a material having a of the refractive index are different, i.e. the ordinary refractive index (n _o) and extraordinary refractive index (n _e) to the refractive index and the other for one of the linearly polarized light the polarization directions orthogonal to each other is there.
As the birefringent material, a liquid crystalline compound is preferably used. Examples of the liquid crystalline compound, ordinary large difference between the refractive index (n _o) and extraordinary refractive index (n _e), i.e. liquid crystal compound having a large intrinsic birefringence is preferable. The intrinsic birefringence is preferably 0.05 or more, and more preferably 0.08 or more.
The difference between the ordinary light refractive index n ₀ of the liquid crystalline compound and the refractive index of the optically isotropic material is preferably less than 0.05, and more preferably less than 0.03. It is preferable that the difference between the refractive index of the extraordinary refractive index n _e and the optical isotropic material of the liquid crystalline compound is 0.03 or more, more preferably 0.05 or more.

Examples of the liquid crystalline compound include low-molecular liquid crystals that exhibit a nematic or smectic phase at room temperature or when heated, for example, cyanobiphenyl liquid crystals, cyanophenylcyclohexane liquid crystals, cyanophenyl ester liquid crystals, benzoic acid phenyl ester liquid crystals, Examples thereof include phenylpyrimidine-based liquid crystals and mixtures thereof.
Alternatively, a polymer liquid crystal exhibiting a nematic phase or a smectic phase at room temperature or in a heated state can be used.

  As such a liquid crystalline compound, for example, a rod-shaped liquid crystalline compound is preferably exemplified. Examples of the rod-like liquid crystal compound and the composition thereof include, for example, Quarterly Chemical Review Vol. 22, Chapter 4 of Liquid Crystal Chemistry (1994), Chemical Society of Japan, Chapter 7, Chapter 10, and Liquid Crystal Device Handbook Japanese Studies Examples thereof include the compounds and compositions described in Chapter 3 of the 142th Committee of the Promotion Society. Of these, rod-like liquid crystalline compounds exhibiting a nematic phase are particularly preferable.

The alignment state of the liquid crystal compound is often difficult to maintain stably with respect to the period, temperature, humidity, mechanical deformation, and the like. Therefore, in order to maintain the alignment state over a long period of time, it is preferable to use a polymerizable liquid crystalline compound and polymerize in the alignment state to form a crosslinked network structure.
As the polymerization means for the polymerizable liquid crystalline compound, either thermal polymerization or photopolymerization can be used. In the present invention, photopolymerization using ultraviolet rays is preferably used.
The polymerizable group is preferably an ethylenically unsaturated group, and at least one ethylenically unsaturated group is preferably introduced per liquid crystalline compound.
As the liquid crystal compound, a bifunctional polymerizable liquid crystal compound having a photopolymerizable group at both ends of the rod-like liquid crystal molecule is particularly preferably used from the viewpoint of heat resistance and alignment uniformity.
Although there is no restriction | limiting in particular as a preferable specific example of the said liquid crystalline compound, For example, the compound (N1)-(N47) shown below is mentioned.

  The amount of the liquid crystal compound added is preferably 0.001 to 2.0 g, more preferably 0.01 to 1.5 g, per 1 g of the optically isotropic material.

When the liquid crystalline compound is radically polymerized using light, a photopolymerization initiator is preferably used.
Examples of the photopolymerization initiator include thioxanthone photopolymerization initiators such as 2,4-diethylthioxanthone and 2-chlorothioxanthone, and benzophenone light such as benzophenone and (4- (methylphenylthio) phenyl) phenylmethanone. Polymerization initiators, anthraquinone-based photopolymerization initiators such as ethyl anthraquinone, Ciba Specialty Chemicals. Inc. Irgacure 184, Irgacure 369, Irgacure 500, Irgacure 651, Irgacure 784, Irgacure 819, Irgacure 907, Irgacure1, 300, Irgacure1300, Irgacure1700, Irgacure1700, Irgacure1700, Irgacure1700
The addition amount of the photopolymerization initiator is preferably 0.01% by mass or more and 20% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less with respect to the total amount of the polymerizable liquid crystal compound.

Moreover, it is also preferable to add a photopolymerization accelerator, such as a spectral sensitizer, p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester, to the photopolymerizable initiator.
The addition amount in the case of adding the spectral sensitizer or the photopolymerization accelerator is preferably 10% by mass or more and less than 300% by mass, and more preferably 20% by mass or more and less than 200% by mass of the photopolymerization initiator.

-Birefringent layer-
The birefringent layer is produced, for example, by applying a coating solution containing the birefringent material onto a support on which an alignment film is formed, and then drying and orienting the birefringent material.

  As the support, for example, a transparent glass plate or a transparent and optically isotropic polymer material having a smooth surface is preferable. The transparent and optically isotropic polymer material is as described in the section of the optically isotropic material.

As a material for forming the alignment film, for example, a polymer such as polyimide or polyvinyl alcohol is preferably used. The birefringent material is preferably uniaxially aligned using the alignment film.
These alignment films are preferably provided with orientation by rubbing or linearly polarized light irradiation after coating. The thickness of the alignment film is preferably 0.01 μm or more and 5 μm or less. In addition, it is preferable to peel from the viewpoint which reduces the thickness after the fixing | fixed mentioned later and the support body formed with the said alignment film.

As a coating method, for example, a dip coating method, an air knife coating method, a curtain coating method, a roller coating method, a wire bar coating method, a gravure coating method, an extrusion coating method (US Pat. No. 2,681,294) is preferably used. It is done.
The coating method may be a method of coating two or more layers at the same time. Examples of such a simultaneous coating method include US Pat. Nos. 2,761,789, 2,941,898, 3,508,947, and 3,526,528. The description and Yuji Harasaki, Coating Engineering, page 253, Asakura Shoten (1973) can be referred to.

Before the birefringent material is fixed, the birefringent layer is brought into close contact with the surface of the structure containing the optically isotropic material. The direction of adhesion may be oriented in any direction with respect to the ridge line of the structure including the optical isotropic material, but is particularly aligned in a parallel state with respect to the ridge line of the structure including the optical isotropic material. Is preferred. Moreover, it is preferable to make it closely_contact | adhere by making the surface of the structure containing an optically isotropic material contact gradually from an end so that air may not enter. A roller is preferably used for the adhesion.
Specific conditions for the adhesion are, for example, preferably from 1 N to less than 50 N per 1 m of the roller width, and more preferably from 3 N to less than 30 N. Moreover, the temperature in the adhesion is preferably within 5 ° C., more preferably within 2 ° C., relative to the temperature aged for orienting the birefringent material.

  After the adhesion, the structure of the birefringent material, that is, the orientation state is fixed. The fixing is preferably performed by polymerizing the oriented birefringent material using, for example, the photopolymerizable initiator. More specifically, it is preferable to fix the alignment state by irradiating ultraviolet rays.

The wavelength of the irradiation light used for the irradiation can be suitably a wavelength region in which the photochemically reactive compound used has optical absorption, but is preferably 190 nm or more and less than 500 nm, more preferably 250 nm or more and less than 450 nm. preferable.
As the light source used for the irradiation, for example, an ultra-high pressure mercury lamp, a flash mercury lamp, a high-pressure mercury lamp, a low-pressure mercury lamp, a low-pressure mercury lamp, a deep UV lamp, a xenon lamp, a xenon flash lamp, a metal halide lamp and the like can be preferably cited. .
It is preferable that the ultraviolet rays emitted from the light source pass through a polarizing element to be linearly polarized light.
The polarizing element is preferably a prism-type element such as a Grand Taylor prism or a Glan-Thompson prism, or a reflective polarizing element using a Brewster angle.
The amount of the irradiation light is preferably 1~2,000mJ / cm ^2, more preferably 5~1,000mJ / cm ^2.
In order to develop optical anisotropy in a short time, irradiation with linearly polarized light is preferably performed while heating.
The temperature range of the substrate during linearly polarized light irradiation is preferably 0 ° C. or higher and lower than 200 ° C., more preferably 10 ° C. or higher and lower than 150 ° C.

  The thickness of the birefringent layer is preferably 1.1 times or more and less than 3 times the height of the structure including the optically isotropic material when the birefringent material is oriented. More than 2 times is more preferable.

-Structures containing optically isotropic materials-
The structure including the optically isotropic material is either a prism or a diffraction grating.

--Prism--
FIG. 2 shows a schematic cross-sectional view of the polarization separation layer 1 when a prism is used as a structure including the optically isotropic material.
The polarization separation layer 1 includes a prism 14 and a birefringent layer 11. The prism 14 is made of optically isotropic material (refractive index n _c), the birefringent layer 11 includes the birefringent material, more specifically having intrinsic birefringence Δn = n _e -n _o Made of material.
Here, n _e is the extraordinary refractive index, n _o is the ordinary refractive index. Perpendicular to the direction indicating the direction and n _o showing a n _e birefringent layer, directions corresponding respectively to the case of n _e> n _o is the slow axis, fast axis of the birefringent layer (hereinafter It is described on the assumption that the common _n e> _{n o,} becomes slow axis, fast axis as opposed to the case of _n e <n _o).
The prism 14 and the birefringent layer 11 are in direct contact with each other, the refractive index of the fast axis of the birefringent layer 11 and the refractive index of the prism 14 are substantially matched (n _o ≈n _c ), and the slow phase of the birefringent layer 11 is reached. It is preferable that the refractive index of the shaft and the refractive index of the prism are greatly different ( _ne ≠ n _c ).
As the orientation direction of the birefringent material, in FIG. 2, it is preferable that the fast axis direction is parallel to the paper surface (direction a) and the slow axis direction is perpendicular to the paper surface (direction b). . In this case, the polarized light in the fast axis direction of the birefringent layer 11 goes straight because there is no difference in refractive index between the prism and the birefringent layer (polarized light L1), but the polarized light in the slow axis direction of the birefringent layer 11 is Since the refractive index difference between the prism and the birefringent layer is large, the light is refracted (polarized light L2), so that two linearly polarized light whose electric field vectors (polarization directions) are orthogonal to each other can be separated.
The polarization separation angle θ depends on the magnitude of the intrinsic birefringence Δn, and θ increases as Δn increases. The intrinsic birefringence Δn is preferably 0.05 or more, and more preferably 0.10 or more. The polarization separation angle θ is preferably 3 ° or more, and more preferably 5 ° or more.

The shape of the prism is not particularly limited as long as a desired result can be obtained by polarization separation and subsequent polarization conversion, but the apex angle α (see FIG. 2) is preferably 20 to 150 °, and preferably 25 to 120 °. It is more preferable that Moreover, it is preferable that height h (refer FIG. 2) is 0.1-80 micrometers, and it is more preferable that it is 0.5-40 micrometers.
The prism may be manufactured by filling a mold with a transparent resin material or injecting a mold having a cavity in which a prism array having a triangular cross section is formed. Alternatively, an active energy ray-curable resin composition is applied to a mold on which a prism pattern is formed, a transparent base material that transmits active energy rays is stacked and laminated, and the active energy rays are irradiated and cured. May be produced.

  When a prism is used as the structure including the optically isotropic material, the birefringent layer is preferably formed to have a thickness of 0.1 to 100 μm from the apex of the prism, and the thickness is 0. 2 to 60 μm is more preferable.

--Diffraction grating-
FIG. 5 shows a schematic cross-sectional view of the polarization separation layer when a diffraction grating is used as a structure including the optically isotropic material.
The polarization separation layer is a diffraction grating in which an optically isotropic material 21 and a birefringent material 22 are arranged in a lattice shape.
Thus, since the birefringent material 22 exhibits birefringence, ordinary light (for example, a polarization component that vibrates in the X-axis direction in FIG. 5) and extraordinary light (for example, vibration in the Y-axis direction in FIG. 5). The refractive index differs depending on the polarization component). Accordingly, due to the action of the periodic grating, the diffraction efficiency of the generated diffracted light also differs between ordinary light and extraordinary light, and polarization separation can be achieved by adjusting the refractive index and the grating shape. Note that the birefringent material 22, to the extraordinary refractive index of the light n _e and ordinary index of refraction n _o, usually n _e> n _o, in this case, the polarization direction of the extraordinary light is anisotropic the slow axis of the medium 22, the polarization direction of the ordinary light becomes fast axis (i.e., in the case of n e _{<n o,} the polarization direction of the slow axis of the ordinary light, the polarization method of the extraordinary ray becomes fast axis .)

Here, for example, as shown in FIG. 6, the cross-sectional shape of the grating is a rectangular wave, the refractive index of ordinary light of the birefringent material 22 is n _o , and the refractive index of extraordinary light is n _e (the vibration direction is the same as FIG. 5). ), Where the refractive index of the optical isotropic material 21 is n _c , the grating depth is h, and the wavelength of the incident light is λ, the efficiency 0 _o0 of ordinary light and the ± first-order diffracted light of ordinary light The efficiency E _{o1 of} the extraordinary light, the efficiency E _e0 of the zero-order light of the extraordinary light, and the efficiency E _e1 of the ± first-order diffracted light of the extraordinary light are expressed by the following equations, where the incident light quantity is 1. In addition, the following calculation formula is "High efficiency of multiple beam grating" Wai-HonLee, Applied Optics Vol. 18, no. 13/1 July 1979 P2153.
〔formula〕
E _o0 = cos (2φ _o ) (1)
E _o1 = (2 / π) ² sin (2φ _o ) (2)
E _e0 = cos (2φ _e ) (3)
E _e1 = (2 / π) ² sin (2φ _e ) (4)
However, in the above formulas, φ _o = {h (n _o −n _c ) / λ} π, φ _e = {h (n _e −n _c ) / λ} π.

In order to separate the incident light L into ordinary light and extraordinary light whose electric field vectors (polarization directions) are orthogonal to each other, E _e0 = 1 when E _o0 = 1, or E _e0 = 1 _when E _o1 = 0. And it is sufficient.
Specifically, the phase term φ _{o of} ordinary light and the phase term φ _{e of} extraordinary light are expressed as follows: φ _e −φ _o = (l + 1/2) (l is 0 or a natural number), and φ _o = mπ / 2 (m is 0 or a natural number).
Here, there are many possible combinations of l and m. For _example, phi _o = 0 next by a n o = _{n c,} ordinary light travels straight, further, by setting the height h of the grating such that _{φ e = 1 / 2π, E} o0 = 1, E _o1 = 0, E _e0 = 0, E _e1 ≈0.41, thereby changing the incident light L into zero-order light L1 and ± first-order diffracted lights L2a and L2b and two linearly polarized light components whose polarization components are orthogonal to each other. Can be separated.

As the polarization separation layer, the fast axis of the birefringent material 22 (generally, the polarization direction of ordinary light) and the refractive index of the isotropic medium 21 are substantially matched (n _o ≈n _c ), and the retardation of the birefringent material 22 is delayed. refractive index of the axis (polarization direction generally extraordinary light) and an optical isotropic material 21 is preferably configured to differ (n _e ≠ n _c).
With this configuration, as described above, the polarization in the fast axis direction of the birefringent material 22 can be made to travel straight (polarized light L1), and the polarized light in the slow axis direction of the birefringent material 22 is diffracted ( Polarized light L2a, L2b) and two linearly polarized light whose electric field vectors (polarization directions) are orthogonal to each other can be separated.
Diffraction efficiency in the diffraction grating, i.e. the separation efficiency is primarily the depending on the size of the intrinsic birefringence Δn = n _e -n _o of the height h of the diffraction grating birefringent material 22, as [Delta] n is greater generally h Can be reduced. That is, the polarization separation layer can be thinned.
The intrinsic birefringence Δn is preferably 0.05 or more, and more preferably 0.08 or more. The polarization separation angle θ depends on the period P of the diffraction grating (see FIG. 6).
The shape (height h, period P) of the diffraction grating is determined so as to obtain the desired polarization separation as described above.

  When the diffraction grating is used as the structure including the optically isotropic material, the thickness of the polarization separation layer is preferably 0.1 to 100 μm, and more preferably 1 to 20 μm.

As described above, in the case where a diffraction grating is used as a structure including the optically isotropic material, the polarization separating layer includes the optically isotropic material and the birefringent material alternately arranged in a lattice shape as the diffraction grating. The example in which the optical axis of the birefringent material is arranged either perpendicularly or parallel to the rows of diffraction gratings has been described, but as an example of separating the optical path using the difference in diffraction efficiency due to polarization, Examples of these are also given, and these can also be used as the diffraction grating.
(1) An optical diffraction grating in the H ⁺ ion exchange region having a period is formed on the main surface of a lithium niobate crystal plate (Japanese Patent Laid-Open Nos. 5-249308, 6-18817, and 6-27320). (See the publications).
(2) One having a dielectric layer on the bottom surface of a periodic groove provided on the main surface of a crystal substrate having optical anisotropy (see JP-A-2-156205).
(3) A cholesteric liquid crystal spiral axis arranged in parallel to the cell plate (see Appl. Phys. Lett. 1997, 71, 1350-1352).

<Polarization conversion layer>
As shown in FIG. 1, the polarization conversion layer is a linearly polarized light (polarized light L1) that travels straight out of two kinds of linearly polarized light whose electric field vectors (polarization directions) are orthogonal to each other, that is, birefringence. The polarization state of the linearly polarized light in which the direction in which the refractive index of the layer and the refractive index of the prism coincide (generally the fast axis of the birefringent layer) is the polarization direction is not changed, but the polarized light (polarized light L2) travels at an inclination That is, the function of converting the polarization state of linearly polarized light (from b to a ′ polarization direction) in which the direction in which the refractive index of the birefringent layer and the refractive index of the prism do not match (generally the slow axis of the birefringent layer) is the polarization direction. Have

The polarization conversion layer contains a birefringent compound as a main component. As the birefringent compound, a discotic liquid crystalline compound is preferably used. In order to convert the polarization state of the polarized light L2, the birefringent compound needs to be tilted and oriented with respect to the film surface. What is necessary is just to incline with respect to the advancing direction of the coming light.
The slow axis of the birefringent compound is preferably tilted so that it is either parallel or perpendicular to the polarization direction of the polarized light L1 and is neither parallel nor perpendicular to the polarized light L2. .
The discotic liquid crystalline compound as the birefringent compound is preferably tilted at a substantially constant angle with respect to the film plane, and is preferably tilted in a hybrid orientation.
By adjusting the intrinsic birefringence of the discotic liquid crystalline compound, the tilt angle φ and the orientation state from the film surface, the layer thickness of the polarization conversion layer, etc., the polarization L2 matches the polarization state of the polarization L1. Can be converted. The inclination angle φ is preferably 30 to 80 °, for example.

Here, the fact that the discotic liquid crystalline compound is tilted and oriented with respect to the film surface can be measured, for example, by observing a section of the film cut into thin pieces in units of μm with a polarizing microscope.
“Hybrid orientation” means an orientation in which an angle formed between a major axis of liquid crystal molecules in the discotic liquid crystalline compound and the film surface continuously changes in the thickness direction of the liquid crystal layer, and the tilt It can be measured by the same method as the orientation.

  As the discotic liquid crystalline compound used in the present invention, various documents (C. Destrade et. Al., Mol. Crysr. Liq. Cryst., Vol. 71, page 111 (1981); edited by the Chemical Society of Japan, quarterly) Chemical Review, No. 22, Liquid Crystal Chemistry, Chapter 5, Chapter 10 Section 2 (1994); B. Kohne et.al., Angew.Chem.Soc.Chem.Com., Page 1794 (1985); J. Zhang et.al., J. Am.Chem.Soc., Vol.116, page 2655 (1994)) can be used. The polymerization of the discotic liquid crystalline compound is described in JP-A-8-27284.

The discotic liquid crystalline compound preferably has a polymerizable group so that it can be fixed by polymerization.
As the polymerizable group, for example, a structure in which a polymerizable group is bonded as a substituent to a discotic core of a discotic liquid crystalline compound can be considered, but when the polymerizable group is directly bonded to the discotic core, polymerization is performed. It becomes difficult to maintain the alignment state in the reaction. Therefore, a structure having a linking group between the discotic core and the polymerizable group is preferable. That is, the discotic liquid crystalline compound having a polymerizable group is preferably a compound represented by the following formula.
〔formula〕
D (-LP) _n
However, in said formula, D represents a disk shaped core, L represents a bivalent coupling group, P represents a polymeric group, and n represents the integer of 4-12.
Preferred specific examples of the discotic core (D), the divalent linking group (L) and the polymerizable group (P) in the above formula are (D1) to (D1) described in JP-A No. 2001-4837, respectively. D15), (L1) to (L25), and (P1) to (P18), and the contents described in the publication can be suitably used. In addition, the discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound is preferably 70 to 300 ° C, and more preferably 70 to 170 ° C.

  Examples of the tilt alignment means of the discotic liquid crystalline compound include photo alignment, electric field alignment, magnetic field alignment, and the like. The direction of light irradiation, the electrode and the magnetic pole are respectively inclined, and an electric field or a magnetic field is applied in an oblique direction. It is preferable to fix the alignment state by performing UV light irradiation or rapid cooling in the state. In the tilted alignment, when an alignment film is used, the liquid crystal may be tilted aligned using an alignment film having a large tilt angle.

(1) Photo-alignment method When the liquid crystalline compound is uniaxially aligned by light irradiation, it is preferable to add a compound containing a photochemically reactive group to at least one of the liquid crystalline compound and the optically isotropic binder.
The photochemically reactive group means a functional group that undergoes, for example, photolysis, photocrosslinking, photopolymerization, photooxidation reduction, phototransition, photoisomerization, etc. via an excited state by absorbing light energy. Among these, a functional group that performs at least one of photocrosslinking and photoisomerization can be particularly preferably used.

The functional group that performs photocrosslinking (hereinafter also referred to as “photocrosslinkable functional group”) is a radical generated by breaking a bond in a molecule or cleaving a part of the bond by light irradiation. It is a functional group that bonds active molecules such as each other (photodimerization) or radicalizes other molecules to perform a binding reaction.
Examples of the photocrosslinkable functional group include a cinnamoyl group, a cinnamylidene group, a diazo group, an azide group, an acryloyl group, a chalcone group, and a coumarin group. Among these, a cinnamoyl group, a cinnamylidene group, a chalcone group, Photodimerizable functional groups such as coumarin groups are particularly preferred.

  Examples of the functional group that performs the photoisomerization reaction include an azobenzene group (K. Ichimura et. Al, Langmuir. Vol. 4, 2; K. Ichimura et. Al, Appl.) That undergoes cis-trans isomerization by light irradiation. Phys.Lett.Vol.63, No.4, Page449 (1993); N.Ishizuki, Langmuir.Vol.9, Page3298 (1993); N.Ishizuki, Langmuir.Vol.9, Page857 (1993)), hydrazo-. β-keto ester group (S. Yamamura et.al, Liquid Crystal, Vol. 13, No. 2, page 189 (1993)), stilbene group (Kunihiro Ichimura et al., Polymer Journal, Vol. 47, No. 10, 771) Page (199 0)), spiropyran groups (K. Ichimura et.al, Chemistry Letters, Page 1063 (1992); K. Ichimura et.al, Thin Solid Films, Vol. 235, Page 101 (1993)). Among these, an azobenzene group and a stilbene group are preferable.

  The amount of the compound containing the photochemically reactive group (hereinafter sometimes referred to as “photochemically reactive compound”) is preferably 0.001 to 1 g, and 0.01 to 0.1 g per 1 g of the liquid crystalline compound. Is more preferable.

  Preferable specific examples of the photochemically reactive compound are not particularly limited, and examples thereof include compounds (WP-1) to (WP-4) shown below.

  The photo-alignment is preferably performed by linearly polarized light irradiation or oblique non-polarized light irradiation. The irradiation light wavelength, the irradiation light amount, the light source, and the substrate temperature at the time of irradiation in the case of the linearly polarized light irradiation are the same as in the case of fixing the orientation state of the birefringent material of the polarization separation layer by irradiating with ultraviolet rays.

  In the case of photo-alignment using oblique non-polarized light irradiation, Polym. Mater. Sci. Eng. 66, p263 (1992) can be preferably used.

(2) Electric field alignment method The liquid crystal compound can be uniaxially aligned by inserting a film coated with the liquid crystal compound between the electrodes and applying a voltage of 1 V or more and less than 50 kV. The voltage application is preferably performed in a temperature range in which the liquid crystalline compound forms a liquid crystal phase, and it is preferably performed by irradiating with ultraviolet rays in the alignment state to fix the alignment state.

(3) Magnetic field alignment method A film coated with the liquid crystalline compound is inserted between magnetic poles of a magnetic field alignment apparatus equipped with an electromagnetic coil, and a liquid crystal compound is uniaxially aligned by applying a magnetic field of 0.2 T or more and less than 10 T. can do. The magnetic field is preferably applied in a temperature range in which the liquid crystalline compound forms a liquid crystal phase, and it is suitably performed by irradiating with ultraviolet rays in the alignment state to fix the alignment state.

It is preferable that the liquid crystalline compound is uniaxially aligned using at least one of the above (1) to (3).
After aligning the liquid crystalline compound, it is preferable to fix the alignment state by irradiating ultraviolet rays.
The irradiation light wavelength, irradiation light amount, light source, and substrate temperature during irradiation in the ultraviolet irradiation polymerization are the same as in the case of the above-described photo-alignment method. When using the said photo-alignment method, it is preferable that the irradiation light wavelength used for photo-alignment differs from the irradiation light wavelength for photopolymerizing a polymerizable liquid crystalline compound.

  The thickness of the polarization conversion layer is preferably 0.1 to 100 μm, and more preferably 1 to 20 μm.

  The polarization conversion layer is, for example, coated on a polarization separation layer (birefringent layer) with a liquid added with a discotic liquid crystalline compound as a birefringent compound, a photopolymerization initiator, and the like, dried, and further aligned. It can be manufactured by fixing the orientation by light irradiation.

  The polarization conversion film of the present invention can be produced with high production by producing the polarization separation layer and the polarization conversion layer, which have been described above, in continuous production as long rolls, or in single sheets as large area sheets, respectively. .

(Polarizing element)
The polarizing element of the present invention comprises the polarization conversion film of the present invention. The polarization conversion film is preferably used in combination with a light absorption element.
In this case, the polarizing element comprises a light-absorbing polarizing element that absorbs one of two linearly polarized light whose electric field vectors are orthogonal to each other and substantially transmits the other, and the polarization conversion film of the present invention, It is preferable that the polarization transmission axis of the light-absorbing polarizing element and the polarization transmission axis of the polarization conversion film are arranged substantially in parallel.
Examples of the light-absorbing polarizing element include highly uniaxially oriented at least one of I ₃ ⁻ and I ₅ ⁻ and an organic dichroic dye in a polyvinyl alcohol film stretched 5 times or more and crosslinked with boric acid. A product obtained by sandwiching the product with a protective film such as cellulose triacetate is generally used.
The light absorbing polarizing element preferably has a degree of polarization represented by the following formula of 99% or more. It is preferable that the average light transmittance in 400-700 nm of the said light absorption type polarizing element is 40% or more.

In the above formula, P represents the transmittance of light transmitted through two polarizing elements whose transmission axes are parallel, and C represents the transmittance of light transmitted through the two polarizing elements whose transmission axes are orthogonal to each other. To express.

  As a combination with the polarization conversion film of the present invention, the polarization conversion film may be used as a separate polarizing element from the light absorbing polarizing element, or one of the protective films of the light absorbing polarizing element is replaced to absorb light. It may be integrated with the mold element.

  The polarization conversion film and the polarizing element of the present invention can be used for a display such as a liquid crystal display device. For example, a polarizing plate for LCD (for example, TN (Twisted Nematic), STN (Super Twisted Nematic), OCB (Optically) Compensatory Bend), ROCB (Reflective Optically Compensatory Bend), ECB (Electrically Controlled Birefringence), CPA (ContinuousPinwell Alignment), CPA (ContinuousPinwell Alignment) Mode, translucent (Over liquid crystal mode). Further, for example, it is also suitably used when used in combination with various optical members such as a retardation film such as a quarter-wave plate and a half-wave plate, a viewing angle widening film, an antiglare film, and a hard coat film. . In particular, the reflection type liquid crystal display element and the transflective type liquid crystal display element have a high luminance improvement effect and are preferably used.

(Liquid crystal display device)
The liquid crystal display device of the present invention comprises the polarizing element of the present invention. Although there is no restriction | limiting in particular as said liquid crystal display device, For example, it is preferable to provide a backlight and to arrange | position the polarizing element of this invention in this backlight side.
The liquid crystal display device is preferably either a reflective liquid crystal display device or a transflective liquid crystal display device.

The reflective liquid crystal display device includes a reflective plate, a liquid crystal cell, a quarter-wave plate, and a polarizing element laminated in this order.
More specifically, the liquid crystal cell has a circularly polarizing plate composed of a polarizing element and a quarter-wave plate, and has a reflective plate on the back surface of the liquid crystal cell, so that light taken from the front side can be obtained. While reflecting with a reflecting plate, the polarization state is modulated with a liquid crystal cell for display. In order to transmit light through the polarizing plate, the light use efficiency is low in the conventional polarizing element having a transmittance of about 40%. However, by using the polarizing element of the present invention, the light use efficiency is reduced. The luminance as a liquid crystal display device can be improved.
The light to be taken into the liquid crystal display device is not particularly limited and may be outside light. However, it is preferable to provide a front light including a light source and a light guide plate on the further front surface of the circularly polarizing plate and take in the light from the front light. .
Examples of the front light include SID '95 Digest p. 37, a tilted front light described in JP-A-11-218757, a prism continuous frontlight described in JP-A-2001-23424, and JP-A-11-184387. Examples thereof include the volume hologram type front light described.

The transflective liquid crystal display device includes a circularly polarizing plate and a liquid crystal display element that can be used as a reflective type or a transmissive type.
More specifically, a circularly polarizing plate and a backlight are also provided on the back side of the liquid crystal cell, and can be used as a reflective type that takes in external light and can be used as a transmissive type that utilizes light from the backlight. The liquid crystal display device is more preferable.
Similarly to the reflective liquid crystal display device, the transflective liquid crystal display device can improve the light use efficiency and improve the luminance as a display device by using the polarizing element of the present invention.

In the liquid crystal display device, as a quarter wavelength plate combined with a polarizing element to form a circularly polarizing plate, the retardation described in JP-A-5-27118 and JP-A-5-27119 is used. A retardation film obtained by laminating a large birefringent film and a birefringent film having a small retardation so that the optical axes thereof are orthogonal to each other, described in JP-A-10-68816, 1 at a specific wavelength A retardation film that can obtain a quarter wavelength in a wide wavelength region by laminating a polymer film that is a quarter wavelength and a polymer film that is made of the same material and has a half wavelength at the same wavelength, A retardation plate described in JP-A-10-90521, which can achieve a quarter wavelength in a wide wavelength region by laminating two polymer films, A phase difference plate capable of achieving a quarter wavelength in a wide wavelength region using a modified polycarbonate film described in International Publication No. 00/26705 pamphlet, and a cellulose acetate film described in International Publication No. 00/65384 pamphlet are used. A retardation plate or the like that can achieve a quarter wavelength in a wide wavelength range can be used.
The slow axis of the quarter-wave plate is determined in consideration of the liquid crystal material, the alignment direction, viewing angle characteristics, etc., and is arranged at an angle of 45 ° with the transmission axis (or absorption axis) of the polarizing plate. It is preferable. Further, a ½ wavelength plate may be disposed between the polarizing plate and the ¼ wavelength plate in order to compensate for a phase delay tolerance with respect to the wavelength of the light of the ¼ wavelength plate.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.
Example 1
(1) Preparation of polarized light separation layer i) Preparation of prism film An ultraviolet curable resin liquid 17 having the following composition was placed on an approximately A4 size plate made of approximately brass as shown in FIG. After injection into a prism mold 16 inscribed with a prism shape with a base angle of 60 °, a tack film 13 (manufactured by Fuji Photo Film Co., Ltd.) having a thickness of approximately 80 μm was overlaid. Next, the resin was cured by irradiating with ultraviolet rays for 30 seconds at an irradiation intensity of 6.4 kw and 80 w / cm ² with an ultraviolet lamp manufactured by Western Quartz Co., Ltd. installed at an upper portion of 300 mm of the tack film 13. The tack film 13 was peeled off to obtain a prism sheet. This was affixed to a roll to produce a long prism film by the embossing method.
[UV curable resin composition]
Bis (methacryloylthiophenyl) sulfide, 2,4-dibromophenyl (meth) acrylate ... 60 parts by weight Trimethylolpropane triacrylate ... 40 parts by weight Photocuring catalyst (Merck, Darocur 1173) ... above 1.5 parts by mass with respect to the sum of the two components (100 parts by mass) The refractive index after polymerization of the resin composition was n = 1.63.

ii) Preparation of birefringent layer A dilute solution of an alignment film (polyvinyl alcohol) is applied on an 80 μm thick tack film (Fuji Photo Film Co., Ltd.) as a support, and the 0.5 μm thick alignment film Formed. Next, after carrying out a rubbing treatment, a coating solution for forming a birefringent layer having the following composition was continuously applied by a bar coater, dried and heated (alignment aging). With heating, the prism surface is brought into contact with the ridge line direction of the prism so that the ridge line of the prism film prepared in i) is parallel to the direction of rubbing and orientation, and the birefringent material is 6 N per 1 m of roller width. Under the conditions controlled within 2 ° C. with respect to the temperature aged for aligning the film, the following liquid crystalline compound was polymerized by ultraviolet irradiation to fix the alignment direction. The tack film on which the alignment film was formed was peeled off to form a birefringent layer 11 as shown in FIG. The birefringent layer had a slow axis in a direction parallel to the ridgeline of the prism. In FIG. 4, 12 represents a tack film.
The intrinsic birefringence Δn at 550 nm of the polarization separation layer obtained as described above was 0.12.
[Coating solution composition for forming a birefringent layer]
The following rod-like liquid crystalline compound (1): 14.5 parts by mass The following sensitizer: 1.0 part by mass The following photopolymerization initiator: 3.0 parts by mass The following horizontal alignment accelerator ... 1.0 parts by mass Methyl ethyl ketone ... 80.5 parts by mass

(2) Production of Polarization Conversion Layer A diluted solution of an alignment film (polyvinyl alcohol) was applied on the polarization separation layer prepared in (1) to form an alignment film having a thickness of 0.5 μm. Next, a rubbing process was performed in parallel with the ridgeline of the prism. Thereafter, a coating liquid for a polarization conversion layer having the following composition was continuously applied and dried by a bar coater so that the film thickness after drying was 15 μm. Thereafter, the dried film was inserted between electrodes inclined by 60 ° with respect to the prism surface, and a voltage of 500 V was applied at 120 ° C. for 5 minutes. When the voltage was applied for 3 minutes, an irradiance of 200 mW / cm ² and an irradiation amount of 600 mJ were obtained using an air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd., wavelength range 200 to 500 nm, maximum wavelength 365 nm). The film was irradiated with UV light of / cm ² and cured while maintaining the tilted alignment state to produce a polarization conversion film. The liquid crystal molecules were measured by observing a cross section of the film cut into thin pieces in units of μm with a polarizing microscope. As a result, the liquid crystal molecules were parallel to the ridge line of the prism of the polarization separation layer and inclined by about 60 ° with respect to the film surface. Oriented.
[Coating solution composition for polarization conversion layer]
The following discotic liquid crystalline compound: 91.0 parts by mass Ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) ... 9.0 parts by mass .. 1.0 part by mass The above photopolymerization initiator ... 3.0 parts by mass The above horizontal alignment accelerator ... 1.0 part by mass Methyl ethyl ketone ... 195.0 parts by mass

(3) Production of Reflective Liquid Crystal Display Device Using an acrylic pressure-sensitive adhesive for the polarizing plate of a commercially available reflective liquid crystal display device (Color Zaurus MI-310, manufactured by Sharp Corporation), the produced polarization conversion film is used as a polarizing plate. Affixed so that the transmission axis and the polarization transmission axis of the polarization conversion film were parallel. In the reflective liquid crystal display device, a reflective plate, a liquid crystal cell, a quarter-wave plate, and a polarizing element are laminated in this order.
When the produced reflective liquid crystal display device was visually evaluated, it was confirmed that neutral gray was displayed without any color in any of white display, black display, and halftone.

(4) Evaluation of reflection type liquid crystal display device The following evaluation was performed about the produced reflection type liquid crystal display device.
[1] Measurement of reflection luminance The reflection luminance was measured using a measuring instrument (EZcontrast 160D, manufactured by Eldim). The results are shown in Table 1. The results in Table 1 are shown as relative values when the reflection luminance of Comparative Example 3 described later is 1.00.
[2] Evaluation of unevenness The following evaluation criteria were evaluated for unevenness that was prepared in a full black display and viewed from an elevation angle of 60 °. The results are shown in Table 1.
A: No unevenness is observed on the entire surface.
○: Slightly uneven.
Δ: Some unevenness has occurred.
X: Unevenness occurs on the entire surface.

(4) Production of transflective liquid crystal display device The transflective liquid crystal display device 141 shown in FIG. 9 was produced, and the produced polarization conversion film was placed on the upper side of the front side polarizing plate 108 and the lower side of the rear side polarizing plate 110. Each was bonded using an acrylic adhesive. In FIG. 9, 103 is a front side substrate, 104 is a back side substrate, 105 is a liquid crystal unit, 106 is a front electrode, 107 is a back electrode, 112 is a backlight, 113 is a two-terminal element, 122 is a signal electrode, 124 Denotes an insulating layer, 125 denotes an upper electrode in the two-terminal element, and 142 denotes a color filter.

(5) Evaluation of transflective liquid crystal display device The following evaluation was performed about the produced transflective liquid crystal display device.
[1] Display Quality in Reflection Mode Using a spectral colorimeter CM-2002 manufactured by Minolta Co., Ltd., the white display reflectance and black display reflectance of the liquid crystal display device were measured, and the contrast ratio was calculated. . The results are shown in Table 2.
[2] Display quality in the transmission mode Using the brightness meter BM-5A manufactured by TOPCOM, measure the brightness of the white display and the brightness of the black display when the backlight is lit, and calculate the contrast ratio. did. The results are shown in Table 2.

(Example 2)
A diluted solution of an alignment film (polyvinyl alcohol) was applied on the polarization separation layer prepared in (1) of Example 1 to form an alignment film having a thickness of 0.5 μm. Next, a rubbing process was performed in parallel with the ridgeline of the prism. Then, the coating liquid of the following composition was continuously apply | coated and dried so that it might become the film thickness 15 micrometers after drying with a bar coater. Thereafter, aging is performed at 120 ° C. for 5 minutes, and further using a 160 W / cm air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd., wavelength range 200 to 500 nm, maximum wavelength 365 nm), illumination intensity 200 mW / cm ² , irradiation The film was irradiated with ultraviolet rays in an amount of 600 mJ / cm ² and cured while maintaining the tilted alignment state, to produce a polarization conversion film. The liquid crystal molecules were measured by the same method as in Example 1. As a result, the discotic liquid crystal compound was in a hybrid orientation parallel to the prism ridge line of the polarization separation layer, and was tilted at an average tilt angle of about 60 degrees. Oriented.
[Coating solution composition for polarization conversion layer]
The above discotic liquid crystalline compound ... 91.0 parts by mass Ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) ... 9.0 parts by mass ..1.0 part by mass The above photopolymerization initiator ... 3.0 parts by mass Methyl ethyl ketone ... 193.0 parts by mass

Using the produced polarization conversion film, a reflective liquid crystal display device and a transflective liquid crystal display device were produced and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Moreover, when the produced reflective liquid crystal display device was visually evaluated, it was confirmed that neutral gray was displayed without any color in any of white display, black display, and halftone. .

(Example 3)
(1) Production of polarization separation layer A plurality of dies engraved with a diffraction grating shape having a height of h2.4 μm and a period of P3 μm shown in FIG. . After injecting an ultraviolet curable resin liquid 17 having the same composition as in Example 1 into a mold roll, an approximately 80 μm thick tack film 13 (manufactured by Fuji Photo Film Co., Ltd.) was superposed. Next, the resin was cured by irradiating with ultraviolet rays for 30 seconds at an irradiation intensity of 6.4 kw and 80 w / cm ² with an ultraviolet lamp manufactured by Western Quartz Co., Ltd. installed at an upper portion of 300 mm of the tack film 13. The tack film 13 was peeled off to obtain a diffraction grating sheet.

In the same manner as in Example 1, the groove direction of the diffraction grating sheet was rubbed and oriented while being heated on a film that had been continuously coated, dried, and heated (orientation-aged) with a coating solution for forming a birefringent layer in advance. The surface of the diffraction grating sheet is brought into contact with the ridge line direction of the diffraction grating so as to be parallel to the direction, and after contacted with a roller under the same conditions as in Example 1, the following liquid crystal compound is polymerized by ultraviolet irradiation. To fix the orientation direction. The tack film on which the alignment film was formed was peeled off to form a diffraction grating as shown in FIG. The obtained diffraction grating had a slow axis in a direction parallel to the groove direction.
The intrinsic birefringence Δn at 550 nm of the polarization separation layer obtained as described above was 0.12.

(2) Production of Polarization Conversion Layer A diluted solution of an alignment film (polyvinyl alcohol) was applied on the polarization separation layer prepared in (1) to form an alignment film having a thickness of 0.5 μm. Next, a rubbing process was performed in parallel with the groove direction of the diffraction grating. Thereafter, an optically anisotropic B coating solution having the same composition as in Example 1 was continuously applied and dried by a bar coater so that the film thickness after drying was 15 μm. Thereafter, a polarization conversion film was produced in the same manner as in Example 1 with respect to the surface of the polarized light separating layer. The liquid crystal molecules were measured by the same method as in Example 1. As a result, the liquid crystal molecules were parallel to the ridge line in the groove direction of the birefringent diffraction grating in the polarization separation layer and aligned in a state inclined by about 60 ° with respect to the film surface. It was.

Using the produced polarization conversion film, a reflective liquid crystal display device and a transflective liquid crystal display device were produced and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Moreover, when the produced reflective liquid crystal display device was visually evaluated, it was confirmed that neutral gray was displayed without any color in any of white display, black display, and halftone. .

Example 4
An alignment film (polyvinyl alcohol) dilution was applied on the polarization separation layer prepared in (1) of Example 3 to form an alignment film having a thickness of 0.5 μm. Next, a rubbing process was performed in parallel with the ridgeline in the groove direction of the diffraction grating. Thereafter, a polarization conversion film was produced in the same manner as in Example 2. The liquid crystal molecules were measured by the same method as in Example 1. As a result, the discotic liquid crystalline compound was parallel to the ridge line in the groove direction of the diffraction grating in the polarization separation layer, and the discotic liquid crystalline compound had a hybrid orientation, and the average tilt angle was about 60 degrees. It was oriented in an inclined state.

Using the produced polarization conversion film, a reflective liquid crystal display device and a transflective liquid crystal display device were produced and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Moreover, when the produced reflective liquid crystal display device was visually evaluated, it was confirmed that neutral gray was displayed without any color in any of white display, black display, and halftone. .

(Comparative Example 1)
In Example 1, the application liquid for forming the birefringent layer was directly applied on the prism film without using an alignment film, and then heated (alignment aging), and further irradiated with ultraviolet rays to produce a polarization separation layer. Except for the above, a polarization conversion film was produced in the same manner as in Example 1.
Using the produced polarization conversion film, a reflective liquid crystal display device and a transflective liquid crystal display device were produced and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.
In Comparative Example 1, the alignment of the liquid crystal compound was insufficient and unevenness occurred in the domain shape.

(Comparative Example 2)
In Example 3, without applying an alignment film, the birefringent layer forming coating solution was applied directly on the diffraction grating sheet, then heated (alignment aging), and further irradiated with ultraviolet rays to produce a polarization separation layer. A polarization conversion film was produced in the same manner as in Example 3 except that.
Using the produced polarization conversion film, a reflective liquid crystal display device and a transflective liquid crystal display device were produced and evaluated in the same manner as in Example 3. The results are shown in Tables 1 and 2.

(Comparative Example 3)
Evaluation was performed using a reflective liquid crystal display device and a transflective liquid crystal display device in the same manner as in Example 1 except that the polarization conversion film was not used. The results are shown in Tables 1 and 2.

From the results shown in Table 1, it was found that the front luminance of the liquid crystal display device using the polarization conversion film of the present invention was clearly improved as compared with a liquid crystal display device not using this. Furthermore, it has been found that the occurrence of unevenness can be suppressed.
The contrast ratio from the front of the liquid crystal display device is 23 in Example 1 and Example 3, 22 in Example 2 and Example 4, and the viewing angle at which the contrast ratio is 3 is Example 1 to Example 1. All four were 120 ° or more above and below and 120 ° or more left and right.

  From the results of Tables 1 and 2, it was found that the polarization conversion film of the present invention can improve the luminance with a simple configuration in both the reflection mode and the transmission mode.

The polarizing conversion film and the polarizing element of the present invention can be oriented by aligning birefringent materials in a certain direction in the rubbing method, and improve the light utilization efficiency for displays such as liquid crystal display devices, in particular, reflective liquid crystal display elements and The transflective liquid crystal display element has a high brightness improvement effect and is preferably used.
Since the liquid crystal display device of the present invention comprises the polarizing element of the present invention, it is particularly suitably used as a reflective liquid crystal display device and a transflective liquid crystal display device.

FIG. 1 is a schematic view showing a mechanism of polarization conversion in the polarization conversion film of the present invention. FIG. 2 is a schematic view of a cross section of the polarization separation layer. FIG. 3 is a diagram illustrating an example of manufacturing a prism. FIG. 4 is a schematic view of a cross section of the polarization separation layer produced in the example. FIG. 5 is a diagram illustrating an example of a birefringent diffraction grating. FIG. 6 is a diagram illustrating an example in which polarized light is separated by a birefringent diffraction grating. FIG. 7 is a schematic cross-sectional view of a translucent liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Polarization separation layer 2 ... Polarization conversion layer 11 ... Birefringence layer 12, 13 ... Tack film 14 ... Prism 16 ... Prism metal mold 17 ... Ultraviolet curable liquid 21. ··· Optically isotropic material 22 ··· Birefringent material 103 · · · Front side substrate 104 · · · Back side substrate 105 · · · Liquid crystal unit 106 · · · Front electrode 107 · · · Back electrode 108 ··· -Front side circularly polarizing plate 110 ... Back side circularly polarizing plate 112 ... Backlight 113 ... Two-terminal element 122 ... Signal electrode 124 ... Insulating layer 125 ... Upper part in two-terminal element Electrode 141... Transflective liquid crystal display device 142... Color filter a... Polarization direction of linearly polarized light traveling straight through the polarization separation layer b... Polarization direction of linearly polarized light refracted by the polarization separation layer L. -Incident light L1: Polarization separation layer Straight linearly polarized light L2 · · · polarization linearly polarized light m · · · birefringent compound refracted at the separation layer n _e · · · direction of the slow axis (if the intrinsic birefringence is positive)
θ ・ ・ ・ polarization separation angle φ ・ ・ ・ tilt angle of birefringent compound h ・ ・ ・ height α ・ ・ ・ vertical angle of prism P ・ ・ ・ period of diffraction grating

Claims (15)

  A structure comprising a polarization separation layer for separating incident light into two linearly polarized light whose electric field vectors are orthogonal to each other, and a polarization conversion layer for converting the polarization state of the linearly polarized light, wherein the polarization separation layer includes an optically isotropic material And a surface of the structure containing the optically isotropic material is adhered to a layer in which the birefringent material is previously oriented.   The polarization conversion film according to claim 1, wherein the layer in which the birefringent material is previously oriented includes an orientation film.   The polarization conversion film according to claim 2, wherein the alignment film contains at least one of polyimide and polyvinyl alcohol.   The polarizing conversion film according to claim 2, wherein the alignment film has a thickness of 0.01 μm or more and 5 μm or less.   The polarization conversion film according to any one of claims 1 to 4, wherein the structure containing the optically isotropic material is either a prism or a diffraction grating.   6. The surface of a structure containing an optically isotropic material is adhered to a layer in which the birefringent material is previously oriented, and then the birefringent material is polymerized and fixed. Polarization conversion film.   The polarization conversion film according to claim 6, wherein the alignment film is peeled after fixing.   The polarization conversion film according to any one of claims 1 to 7, wherein the polarization conversion layer contains a discotic liquid crystalline compound that is tilt-oriented with respect to the film surface.   The polarization conversion film according to claim 8, wherein the discotic liquid crystalline compound is hybrid-aligned.   A method for producing a polarization conversion film, wherein the polarization separation layer and the polarization conversion layer in the polarization conversion film according to claim 1 are continuously produced in a roll form.   A polarizing element comprising the polarization conversion film according to claim 1.   A liquid crystal display device comprising the polarizing element according to claim 11.   The liquid crystal display device according to claim 12, which is a reflective liquid crystal display device in which a reflector, a liquid crystal cell, a quarter-wave plate, and a polarizing element are laminated in this order.   The liquid crystal display device according to claim 12, further comprising a backlight, wherein a polarizing element is disposed on the backlight side. The liquid crystal display device according to claim 14, which is a transflective liquid crystal display device having a circularly polarizing plate and a liquid crystal display element that can be used as a reflective type and a transmissive type.