JP2009276398A - Laminated sheet polarizer, liquid crystal display device and polarized light scattering plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet polarizer, selectively transmitting only a specified polarization component to incident light, a liquid crystal display device including the sheet polarizer, and a polarized light scattering plate for use in these. <P>SOLUTION: This laminated sheet polarizer includes a reflection type sheet polarizer A and a polarized light scattering plate B, which are stacked, wherein the transmission axis of te reflection type sheet polarizer A and the transmission axis of the polarized light scattering plate B are arranged substantially in parallel, and the polarized light scattering plate B has a matrix phase and a domain phase disposed in the matrix phase. The matrix phase and the domain phase satisfy the following conditions (i) to (iii). In this laminated sheet polarizer, (i) the matrix phase is optically substantially isotropy, (ii) a slow axis of the domain phase is substantially vertical to the transmission axis of the reflection type sheet polarizer A in a plane of the polarized light scattering plate B, and (iii) the refractive index vertical to the slow axis of the domain phase is substantially the same as the refractive index of the matrix phase. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarizing plate that selectively transmits a specific polarization component of incident light, and a liquid crystal display device including the polarizing plate. In particular, the present invention relates to a laminated polarizing plate that increases the ratio of a specific polarization component of incident light and selectively transmits this polarization component, and a liquid crystal display device including the polarizing plate. The present invention also relates to a polarized light scattering plate that can be used for these applications.

  Optical elements that separate polarization components, that is, so-called polarizing plates, are widely used in liquid crystal display elements such as televisions, monitors, and mobile phones. In principle, the liquid crystal display element uses the liquid crystal to control the transmitted light of the polarization component, so that the polarizing plate is an indispensable member in the liquid crystal display device.

  Conventionally, many studies have been made to extract specific polarization components from ordinary light, and various forms of polarizing plates have been developed. As such a polarizing plate, for example, a birefringent polarizing plate using a birefringent (optically anisotropic) crystal such as calcite, a dichroic dye such as iodine or an organic dye (dye) is oriented and dispersed in a polymer. There are known a dichroic polarizing plate, a reflective polarizing plate having a characteristic of reflecting polarized light in one direction by a multilayer film having a controlled refractive index, and the like. In the liquid crystal display device which is one of the uses of the polarizing plate, the transmitted light can be controlled, and among these, a dichroic polarizing plate having a large dichroism has been preferably used.

  However, the dichroic polarizing plate transmits a maximum of 50% of the total incident light (for example, when the surface reflection is 4%, the maximum light transmittance is 46%), but the direction perpendicular to the transmission axis. Will absorb the ingredients. For this reason, the dichroic polarizing plate loses at least 50% of light, and is not satisfactory in terms of light utilization efficiency.

  Therefore, at present, in order to avoid light absorption into the dichroic polarizing plate and increase the light utilization efficiency, it is studied to use a combination of the dichroic polarizing plate and the reflective polarizing plate. In this method, light perpendicular to the transmission axis absorbed by the polarizing plate is reflected to the incident light side by the reflective polarizing plate, and transmitted again to the prism sheet, the light guide plate, and the diffusion plate installed on the light source side. Thus, depolarization is performed, and the light that has been depolarized is supplied to the polarizing plate again, thereby increasing the light utilization efficiency.

  Here, the reflection-type polarizing plate is an element mainly using optical reflection interference characteristics, and in the dichroic polarizing plate, polarized light that has been lost due to absorption is separated by using reflection characteristics.

  As such a reflective polarizing plate, for example, a combination of a cholesteric liquid crystal layer and a quarter-wave plate is known (see Patent Document 1). In the reflective polarizing plate described in Patent Document 1, the cholesteric liquid crystal layer transmits right (or left) circularly polarized light having a wavelength corresponding to the helical pitch, while reflecting left (or right) circularly polarized light. It has the characteristic to do. Circularly polarized light transmitted through such a reflective polarizing plate is converted to linearly polarized light by the quarter wavelength plate, and as a result, selective linearly polarized light can be created.

  Patent Document 2 describes a reflection type polarizing plate using interference of a multilayer film having birefringence. In the reflective polarizing plate described in Patent Document 2, polarization separation is performed by an alignment multilayer film of two types of polymer films made of a birefringent material. Such an oriented multilayer film is already commercially available from 3M as the D-BEF (brightness enhancement film) series.

  In recent years, a reflection type polarizing plate called a wire grid type polarizing plate has been proposed in which straight metal thin wires are arranged in parallel with each other at the same interval on a transparent substrate (see Patent Document 3).

  Further, Patent Document 4 proposes a polarizing plate in which a material having birefringence and a prism are combined. The polarizing plate described in Patent Document 4 has a configuration in which a prism is provided on the surface of a polymer substrate having birefringence, and by utilizing the difference in refractive index between the cross-sectional direction and the length direction of the prism, The prism angle is set so that the reflection angle at the prism is smaller than the critical angle for linearly polarized light, and the reflection angle at the prism is greater than the critical angle for the other linearly polarized light. With this setting, light with a critical angle or more is returned to the incident light side by total reflection, and polarization separation is performed.

  On the other hand, a technique relating to a scattering type polarizing plate that transmits a specific polarization component and scatters a polarization component perpendicular to the polarization on the other side has also been reported (see Patent Document 5). In this scattering type polarizing plate, a simple polymer blend is used to create a continuous phase and a discontinuous phase, and polarization separation is performed.

  In the method of improving the light utilization efficiency by using a single reflection type polarizing plate described in Patent Documents 1 to 4, the reflected light composed of a specific polarization component is returned to the incident light side, and a prism sheet, a diffusion plate The light is depolarized by transmission and reflection on the light guide plate and the reflection plate, and returned to the polarizing plate for reuse. However, in these methods, a part of the reflected light composed of a specific polarization component reflected by the reflection type is dissipated in the process of reuse as the number of members between the polarizing plate and the reflector increases. There is a problem that the use efficiency of the system is lowered. Further, it has been pointed out that the scattering efficiency of the scattering type polarizing plate according to Patent Document 5 is relatively low because there is a lot of scattered light due to scattering.

  For this problem, Patent Document 6 reports a technique in which a scattering film is laminated on a reflective polarizer. In this technique, a polarization component reflected in a specific direction reflected by a reflective polarizing element is re-reflected by a scattering film disposed immediately below the reflective polarizing element and returned to the reflective polarizing element, thereby reducing light dissipation. It is shown. According to Patent Document 6, the scattering film used here has high transmittance without reflection with respect to linearly polarized light in the transmission axis direction incident on the reflective polarizer from the light source, and on the other hand, the polarizer As for the linearly polarized light in the direction orthogonal to the transmission axis, the incident light from the light source has a certain transparency, and when the linearly polarized light returns after being reflected by the reflective polarizer. Linearly polarized light is depolarized by backscattering.

However, in the scattering film in this method described in Patent Document 6, the relationship between the three-dimensional refractive index of the matrix phase and the domain phase of the scattering film is not strictly defined. In particular, with respect to three-dimensional refractive index n _y and n _z in the yz plane of the matrix phase, as long as the difference between the average refractive index N _yz in the yz plane of their mean value and the domain phase is 0.05 or less Since it is only good, it can take a wide range of parameters. From a specific example, it can be seen that the three-dimensional refractive indexes _nx , _ny and _nz of the matrix phase are all different from each other. That is, three-dimensional refractive index N _y and n _y of the matrix phase and the domain phase of the transmission axis direction of the scattering film may take different values.

  In this case, since the interface between the matrix phase and the domain phase of the scattering film is recognized by the polarization in the transmission axis direction, the polarization component in the transmission axis direction is refracted according to the shape of the domain phase. This also causes the refracted polarization component to be affected by the phase difference corresponding to the product of the refractive index difference of the matrix phase and the path length. For this reason, a part of the polarized light in the transmission axis direction that passes through the scattering film cannot be kept linearly polarized until it reaches the reflective polarizing plate, and is therefore reflected by the reflective polarizer, and thus in the transmission axial direction. There is a problem that it cannot be effectively extracted as polarized light.

JP-A-8-271731 U.S. Pat. No. 3,610,729 Japanese Laid-Open Patent Publication No. 2005-195824 JP 2006-220879 A Special Table 2000-506994 JP 2007-298634 A

  The present invention has been made in view of the above problems, and its object is to increase the ratio of a specific polarization component of incident light and selectively transmit only this specific polarization component. The object is to provide a laminated polarizing plate. Still another object of the present invention is to provide a polarization scattering plate that can be used for these applications.

  Another object of the present invention is to provide a liquid crystal display device having high light utilization efficiency by using the laminated polarizing plate of the present invention.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies and as a result, have completed the present invention described below.

The laminated polarizing plate of the present invention has a reflective polarizing plate (A) and a polarizing scattering plate (B) laminated together, and the transmission axis of the reflective polarizing plate (A) and the transmission of the polarizing scattering plate (B). The polarization scattering plate (B) has a matrix phase (M) and a domain phase (D) disposed in the matrix phase (M), and the matrix phase A laminated polarizing plate in which (M) and the domain phase (M) satisfy the following conditions (i) to (iii):
(I) the matrix phase (M) is optically isotropic,
(Ii) The slow axis of the domain phase (D) is substantially perpendicular to the transmission axis of the reflective polarizing plate (A) in the plane of the polarization scattering plate (B), and (iii) the domain phase ( The refractive index in the direction perpendicular to the slow axis of D) is substantially the same as the refractive index of the matrix phase (M).

  A liquid crystal display device of the present invention is a liquid crystal display device comprising a first polarizing plate, a liquid crystal cell, a second polarizing plate, and a light source, wherein the first polarizing plate, the liquid crystal cell, the second polarizing plate, and The light sources are arranged in this order, and the laminated polarizing plate of the present invention is arranged between the second polarizing plate and the light source so that the polarization scattering plate (B) of the laminated polarizing plate is on the light source side. And the transmission axis of the laminated polarizing plate of the present invention and the transmission axis of the second polarizing plate are arranged substantially in parallel.

The polarized light scattering plate of the present invention has a matrix phase (M) and a domain phase (D) arranged in the matrix phase (M), and the matrix phase (M) and the domain phase (D) are the following: A polarized light scattering plate satisfying the following conditions (i) to (iii):
(I) the matrix phase (M) is optically isotropic,
(Ii) the slow axis of the domain phase (D) exists in the plane of the polarization scattering plate (B), and (iii) the refractive index in the direction perpendicular to the slow axis of the domain phase (D) is a matrix It is substantially the same as the refractive index of the phase (M).

  According to the laminated polarizing plate of the present invention, it is possible to increase the ratio of a specific polarization component in incident light and selectively transmit only this specific polarization component. This is because in the polarization scattering plate used in the laminated polarizing plate of the present invention, the incident polarized light in the transmission axis direction is maintained and transmitted to the reflective polarizing plate as it is, and the direction perpendicular to the transmission axis of the polarization scattering plate This is achieved by depolarizing the incident or reflected polarization component of the light by scattering, refraction and reflection inside the polarization scattering plate and transmitting it to the reflective laminate. In particular, according to the laminated polarizing plate of the present invention, by strictly controlling the three-dimensional refractive index of the matrix phase and the domain phase of the polarization scattering plate, the reflection of the polarization component in the transmission axis direction transmitted through the polarization scattering plate, Refraction and scattering can be eliminated, and the linear polarization can be maintained and transmitted to the reflective polarizing plate.

  In addition, according to the liquid crystal display device of the present invention, it is possible to increase luminance and / or reduce power consumption.

  According to the polarization scattering plate of the present invention, the polarization component incident in the transmission axis direction is maintained and transmitted as it is, and the polarization component incident or reflected in the direction perpendicular to the transmission axis of the polarization scattering plate is polarized and scattered. It can be depolarized and transmitted by scattering, refraction and reflection inside the plate. In particular, according to the polarization scattering plate of the present invention, by strictly controlling the three-dimensional refractive index of the matrix phase and the domain phase, reflection, refraction, and scattering of the polarization component in the transmission axis direction transmitted through the polarization scattering plate are reduced. And the linear polarization can be maintained.

<Reflective polarizing plate (A)>
The reflective polarizing plate constituting the laminated polarizing plate of the present invention may be a polarizing plate that transmits only linearly polarized light in one direction and reflects linearly polarized light in a direction perpendicular to this direction. Here, in the present invention, the polarization direction of linearly polarized light that is transmitted through the reflective polarizing plate is defined as the “transmission axis direction” of the reflective polarizing plate. Examples of such a reflective polarizing plate include a reflective polarizing plate using interference of a multilayer film having birefringence, and a wire grid polarizing plate in which linear fine metal wires are periodically arranged.

  A reflective polarizing plate using interference of a multilayer film having birefringence is composed of an alternating laminate of two types of thin films having different refractive index anisotropies. Specifically, two types of resins having different refractive indexes are laminated in a multilayer, and the obtained laminate is stretched to produce a uniaxially stretched optical multilayer film. Here, the refractive index difference between the two types of resins is controlled to increase the refractive index difference in the stretching direction between the two types of resins, and the refractive index difference in the direction perpendicular to the stretching direction is eliminated.

  The optical multilayer film thus obtained has no or small refractive index difference in the direction perpendicular to the stretching direction, so that light is transmitted in this direction. On the other hand, in the stretching direction, since the difference in refractive index is large, reflection due to the optical interference effect according to the total number and the film thickness occurs. This is the principle of a reflective polarizing plate made of an optical multilayer body.

  One of the resins used for the reflective polarizing plate using interference of a multilayer film having birefringence is preferably one that exhibits high birefringence due to stretching orientation, such as polyethylene terephthalate and polyethylene naphthalate. For example. The other resin is preferably one that exhibits low birefringence due to stretching orientation, such as nylon, a polymer material that does not have an aromatic ring in the molecular skeleton, a thermoplastic elastomer that does not generate birefringence upon stretching, and thermoplasticity. A resin and an elastomer mixture are appropriately selected.

  The thickness of each layer of the optical multilayer body needs to be a thickness that causes optical interference in which the phase difference calculated by the product of birefringence and the optical path length is λ / 2 for visible light (400 to 800 nm), This is approximately less than 500 nm. The total number of optical multilayer bodies requires 1000 to 2000 layers in order to obtain uniform reflection with visible light (400 to 800 nm).

  As a wire grid polarizing plate, there is usually a structure in which fine metal wires are periodically arranged on a substrate made of an optically uniform material such as a glass substrate. Here, the material of the metal wiring is preferably a metal having conductivity and high reflectivity, and examples thereof include aluminum and silver. The fine metal wires are linear and have a periodic structure arranged parallel to each other. The width of the fine metal wires and the pitch of the arrangement need to be sufficiently small with respect to visible light (400 to 800 nm), that is, for example, a width and interval of 100 nm or less. Regarding the thickness of the thin metal wire, a thickness that keeps the transmittance and the degree of polarization high is required, but is appropriately adjusted depending on the metal material and the arrangement pitch, and is, for example, less than 200 nm.

  The principle of the polarization characteristics of the wire grid polarizer is that linearly polarized light having an electric field vector orthogonal to the fine metal wire of the incident light when the pitch, which is the distance between the straight fine metal wires, is sufficiently shorter than the wavelength of the incident light. This is because linearly polarized light having an electric field vector that is transmitted through and parallel to the thin metal wire is reflected to separate the polarized light.

<Polarized light scattering plate>
The polarized light scattering plate (B) constituting the laminated polarizing plate of the present invention and the polarized light scattering plate of the present invention exhibit high transparency with respect to one linearly polarized light, and the linearly polarized light perpendicular to the linearly polarized light is polarized. The optical element reflects, refracts, and scatters and depolarizes by the domain phase (D) in the scattering plate. Here, with respect to the present invention, the polarization direction of linearly polarized light transmitted through the polarization scattering plate is defined as the “transmission axis direction” of the polarization scattering plate.

  The polarized light scattering plate of the present invention can have the same configuration as the polarized light scattering plate (B) constituting the laminated polarizing plate of the present invention. The following explanation about the polarization scattering plate (B) constituting the plate can be referred to.

(Matrix phase)
The matrix phase of the polarization scattering plate (B) constituting the laminated polarizing plate of the present invention is required to be optically transparent and optically isotropic. This is represented, for example, by the following equations (1) and (2):
_{| N y (M) -n z} (M) |
<0.01, preferably 0.005, more preferably 0.002 (1)
| _Nx (M)-( _ny (M) + _nz (M)) / 2 |
<0.01, preferably 0.005, more preferably 0.002 (2)
(N _x (M): Three-dimensional refractive index of matrix phase (M) in the slow axis direction of domain phase (D) in the plane of polarization scattering plate (B) n _y (M): Polarization scattering plate (B ) In the plane perpendicular to the slow axis of the domain phase (D), the three-dimensional refractive index _nz (M) of the matrix phase (M): the method with respect to the plane of the polarization scattering plate (B) 3D refractive index of the matrix phase (M) in the linear direction).

Further, the matrix phase needs to have a refractive index substantially the same as the refractive index in the direction perpendicular to the slow axis direction of the domain phase described later. Here, as described above, the matrix phase needs to be optically isotropic, and as described later, the slow axis of the domain phase may be in the plane of the polarization scattering plate (B). is necessary. Therefore, for example, the fact that the matrix phase has a refractive index substantially the same as the refractive index in the direction perpendicular to the slow axis direction of the domain phase is expressed by the following equation (6):
| ( _Ny (M) + _nz (M)) / 2- ( _ny (D) + _nz (D)) / 2 |
<0.01, preferably 0.005, more preferably 0.002 (6)
( _Ny (M) and _ny (D): the matrix phase (M) and the domain phase in the direction perpendicular to the slow axis of the domain phase (D) in the plane of the polarization scattering plate (B), respectively. (D) three-dimensional refractive index n _z (M) and n _z (D): of the matrix phase (M) and the domain phase (D) in the direction normal to the plane of the polarization scattering plate (B), respectively. 3D refractive index).

  As a single characteristic of the polarization scattering plate used in the present invention, the smaller the difference between the refractive index in the direction perpendicular to the slow axis of the domain phase and the refractive index of the matrix phase, the more in the slow axis direction of the domain phase. A high transmittance can be obtained for the polarization component in the vertical direction.

  As a material for the matrix phase, an optical transparent resin is preferable in consideration of refractive index control and workability. Also, the optically transparent resin for the matrix phase needs to have little or substantially no absorption in the visible region. Specifically, for example, when this optical transparent resin is a film having a thickness of 100 μm, the light transmittance of the film is 80% or more, preferably 85% or more, more preferably, in the wavelength range of 400 nm to 800 nm. It is necessary to be 90% or more.

  Moreover, it is preferable that the optical transparent resin of the matrix phase which comprises a polarized light scattering plate (B) shows favorable adhesiveness with respect to a domain phase. If sufficient adhesion between the matrix phase and the domain phase is not obtained, peeling occurs at the interface between the matrix phase and the domain phase during stretching, curing, etc. in producing the polarizing scattering plate (B), resulting in an air layer. As a result, light scattering by the air layer causes problems such as deterioration of polarization scattering characteristics.

  As described above, the matrix phase constituting the polarization scattering plate (B) must be optically substantially isotropic. If the matrix phase has birefringence, depolarization occurs due to the product of the optical path and birefringence for obliquely incident light, making it difficult to maintain linear polarization in the transmission axis direction. For this reason, as the optical transparent resin constituting the matrix phase of the present invention, those having low expression of birefringence are preferable. For example, a thermoplastic resin, or a curable resin such as a thermosetting resin or a photocurable resin is used. Can be mentioned. In these, it is preferable to use curable resin from a viewpoint which is excellent in workability, for example, it can apply | coat resin to a domain phase and can harden | cure rapidly after that.

  Examples of the thermoplastic resin that can constitute the optical transparent resin for the matrix phase of the polarized light scattering plate (B) include acrylic resins such as poly (methyl methacrylate), polyolefins such as polyethylene, polyesters such as polyethylene terephthalate, polyphenylene oxide, and the like. Polyether, polyvinyl alcohol such as polyvinyl alcohol, polyurethane, polyamide, polyimide, epoxy resin, or a copolymer using two or more monomers constituting these. The thermoplastic resin that can constitute the optically transparent resin for the matrix phase includes a mixture of poly (methyl methacrylate) and polyvinyl chloride in a weight ratio of 82:18, and weight of poly (methyl methacrylate) and polyphenylene oxide. Non-birefringent polymer blends such as a mixture having a ratio of 65:35 and a mixture of styrene / maleic anhydride copolymer and polycarbonate having a weight ratio of 77:23.

  A typical example of the curable resin that can form the matrix layer is a crosslinked resin that is cured through a crosslinking reaction or the like by external excitation energy. The curable resin includes an actinic radiation curable resin that is cured by irradiation with actinic rays such as ultraviolet rays and electron beams, and a thermally crosslinkable resin that initiates a crosslinking reaction by heat, both of which are preferable in the present invention. Can be used.

  A typical example of the actinic radiation curable resin that can form the matrix phase is an ultraviolet curable resin. Specifically, the actinic radiation curable resin that can form the matrix phase includes an ultraviolet curable polyester acrylate resin, an ultraviolet curable acrylic urethane resin, an ultraviolet curable methacrylate ester resin, and an ultraviolet curable polyester acrylate resin. And UV curable polyol acrylate resins. Among these, it is preferable to use an ultraviolet curable polyol acrylate resin from the viewpoint of processing stability. As photopolymerizable monomers (or oligomers), trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, alkyl-modified dipentaerythritol Pentaerythritol and the like can be preferably used.

  Examples of the electron beam curable resin that can form the matrix phase include those having an acrylate-based functional group, and specifically include relatively low molecular weight polyester acrylate resins, polyether acrylate resins, and acrylic acrylates. Examples thereof include resins, epoxy acrylate resins, urethane acrylate resins, polybutadiene acrylate resins, and the like.

  Examples of the thermosetting resin that can form the matrix phase include an epoxy resin, a phenoxy resin, a phenoxy ether resin, a phenoxy ester resin, an acrylic resin, a melamine resin, a phenol resin, a urethane resin, or a mixture thereof. it can.

(Domain phase)
The domain phase (D) constituting the polarization scattering plate (B) used in the laminated polarizing plate of the present invention is optically transparent and requires optical anisotropy of refractive index. Specifically, it is necessary that the slow axis of the domain phase is in the plane of the polarization scattering plate (B). According to this, the phase difference given to the linearly polarized light in the transmission axis direction that is obliquely incident on the polarization scattering plate (B) becomes small, and the linearly polarized light in the transmission axis direction can be relatively undisturbed. This can be represented, for example, by the following equations (3) and (4):
_{| N y (D) -n z} (D) |
<0.01, preferably 0.005, more preferably _{0.002 (3) n x (D} ) - (n y (D) + n z (D)) / 2
> 0.1, preferably 0.15, more preferably 0.20 (4)
_(N x (D): three-dimensional refractive index n _y in the slow the axis direction, a domain phase of the domain phase in the plane of polarized light scattering plate (B) (D) (D ) (D): polarized light scattering plate (B ) In the plane perpendicular to the slow axis of the domain phase (D), the three-dimensional refractive index _nz (D) of the domain phase (D): the method for the plane of the polarization scattering plate (B) 3D refractive index of the domain phase (D) in the linear direction).

  Reflection, refraction, and scattering of light occur at a portion where a difference in refractive index between the matrix phase and the domain phase occurs. As described above, since the refractive index of the matrix phase is substantially the same as the refractive index of the domain phase in the direction perpendicular to the slow axis of the domain phase, the refractive index of the matrix phase is perpendicular to the slow axis of the domain phase. The polarization component is transmitted without being reflected, refracted or scattered at the interface between the matrix phase and the domain phase.

  On the other hand, with respect to the polarization component in the slow axis direction of the domain phase, a refractive index difference occurs between the matrix phase and the domain phase. Therefore, at the interface between the matrix phase and the domain phase, the refractive index difference between the matrix phase and the domain phase, Depending on the shape of the domain phase, reflection, refraction, and scattering of the polarization component occur. Polarized components reflected, refracted and scattered at the interface between the matrix phase and the domain phase, and light traveling at an angle in the direction of the optical axis of the domain phase is transmitted through the domain phase. Under the influence of birefringence, it is depolarized.

A part of the polarization component depolarized by the polarization scattering plate in this way passes through the transmission axis of the reflective polarizing plate and is extracted as polarized light. When the number of domain phases is fixed, the depolarization effect of the polarization scattering plate is obtained by dividing the refractive index of the domain phase in the slow axis direction of the domain phase from the refractive index of the domain phase in the direction perpendicular to the slow axis. The difference increases, that is, the difference in refractive index between the domain phase and the matrix phase in the slow axis direction of the domain phase increases. Therefore, it is preferable that these differences are large. This can be represented, for example, by the following equations (4) and (5):
_nx (D)-( _ny (D) + _nz (D)) / 2
> 0.1, preferably 0.15, more preferably 0.20 (4)
_{n x (D) -n x (} M)
> 0.1, preferably 0.15, more preferably 0.20 (5)
( _Nx (M) and _nx (D): the third order of the matrix phase (M) and the domain phase (D) in the slow axis direction of the domain phase (D) in the plane of the polarization scattering plate (B), respectively. Original refractive index _ny (D): Three-dimensional refractive index _nz (D) of the domain phase (D) in the direction perpendicular to the slow axis of the domain phase (D) in the plane of the polarization scattering plate (B) ): The three-dimensional refractive index of the domain phase (D) in the normal direction to the surface of the polarization scattering plate (B).

  Examples of the material for the domain phase include a fiber made of a stretch-oriented polymer material.

  The material of the fiber used as the domain phase is not particularly limited. For example, a material that does not absorb or is small in the visible region, has no defects such as voids, and is oriented by stretching or the like to generate birefringence. If it is. In general, a polymer material having positive birefringence that easily develops birefringence has a skeleton having a high polarizability (for example, an aromatic ring or a naphthalene ring) in the molecular chain of the polymer material. In addition, it is a material in which high orientation of molecular chains is generated by stretching.

  As a material for the fiber used as the domain phase, from the viewpoint of optical transparency with respect to visible light, for example, aromatic polyester such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; polycarbonate, polymethyl methacrylate, etc. Examples thereof include methacrylates; polyvinyl ethers; polyolefins such as polyethylene and polypropylene; polystyrenes; aliphatic polyamides such as nylon 6. Further, from the viewpoint of the development of birefringence due to stretching orientation, the material for the fiber is preferably polycarbonate, polyethylene terephthalate, or polyethylene naphthalate, and among these, polyethylene naphthalate is particularly preferred because of its extremely high birefringence development. .

  For the purpose of improving the adhesion with the curable resin used for the matrix phase, various different adhesion treatments such as corona treatment may be applied to the surface of the fiber. Furthermore, for the purpose of improving the birefringence of the fiber, it is also a useful technique to make the fiber into a low molecular liquid crystal compound or a multifilament type polymer inter-aligned fiber.

  Low molecular liquid crystal compounds added to the fiber for the purpose of improving birefringence include biphenyl, phenylbenzoate, cyclohexylbenzene, azoxybenzene, azobenzene, azomethine terphenyl, and biphenylbenzoate. Examples thereof include compounds having a compound such as cyclohexylbiphenyl, phenylpyrimidine, cyclohexylpyrimidine, and cholesterol as a mesogen (a core unit for developing a liquid crystal in a molecular structure). These low-molecular liquid crystal compounds are preferably dissolved in the fiber as long as they are aligned in the long axis direction of the fiber.

  The thickness of the fiber used as the domain phase is preferably 0.7 μm to 100 μm, more preferably 0.8 μm to 80 μm, and still more preferably 1 μm to 50 μm. If the fiber thickness is 0.7 μm or less, fiber spinning and drawing techniques are difficult, and surface scattering at wavelengths in the visible region depending on the size of the fiber is likely to occur. Color display may not be possible. On the other hand, when the fiber thickness is 100 μm or more, since the fiber is too thick, a gap is formed when a polarizing plate having a desired thickness is formed in one direction, thereby causing a light leakage defect. In addition, a high degree of polarization may not be realized. Also, the fiber thickness does not need to be uniform, and a mixture of thin fibers and thick fibers may be used if there is no gap when arranged in one direction and a high degree of polarization is achieved. it can.

  The cross-sectional shape of the fiber used as the domain phase is not limited to a circular shape, and may be an elliptical shape, a triangular shape, a quadrangular shape, a pentagonal shape, a hexagonal shape, or a polygonal shape that is arranged in one direction. It is sufficient that there is no gap on the occasion and a high degree of polarization is achieved. In addition, the fiber shape need not be uniform, and a composite of various types of fibers may be used. However, in the case of a single shape fiber, it is not necessary to adjust the mixing ratio etc. uniformly. preferable.

  The optimum number of laminated fibers constituting the polarization scattering plate needs to be multi-layered as much as necessary to obtain the depolarization effect. When the fiber is used as the domain phase, the number of laminated layers is preferably 4 or more and 1000 or less, more preferably 6 or more and 500 or less, and most preferably 8 or more and 200 or less.

(Polarization scattering plate creation method)
The polarized light scattering plate used in the present invention is composed of, for example, the matrix phase and the domain phase described above. In the following, the method for producing a polarized light scattering plate is exemplified by a non-limiting example.

  Here, an ultraviolet curable resin is used as the matrix phase, and a fiber having birefringence obtained by uniaxial stretching is used as the domain phase. The materials for the matrix phase and the domain phase are appropriately selected so as to satisfy the above characteristics. Next, in order to form a multi-layered domain phase, the fibers are arranged so as to be multistage in one direction. A UV curable resin is dropped on a fiber aligned in one direction, vacuum degassed to eliminate bubbles, and irradiated with UV light to obtain a polarizing scattering plate in the form of a film consisting of a matrix phase and a domain phase. .

<Laminated polarizing plate>
The laminated polarizing plate of the present invention has a reflective polarizing plate (A) and a polarizing scattering plate (B) laminated together, and the transmission axis of the reflective polarizing plate (A) and the polarizing scattering plate (B). The transmission axis is arranged substantially in parallel. Here, the reflective polarizing plate and the polarizing scattering plate may be laminated directly or via an optional other layer such as an adhesive layer between them. For example, as shown in FIG. 1, the laminated polarizing plate 10 of the present invention is formed by laminating a reflective polarizing plate A and a polarizing scattering plate B, and reflects light from a backlight 21 such as a liquid crystal display device to a reflecting portion 22. The light utilization efficiency is improved by entering from the side of the polarization scattering plate B through the light guide plate 23 and an optional other layer 24 such as a prism.

  The principle of improving the light use efficiency in the laminated polarizing plate of the present invention is as follows.

  First, regarding the light incident from the backlight, the polarization component in the transmission axis direction of the laminated polarizing plate (that is, the transmission axis direction of the polarizing scattering plate and the reflective laminated plate) is considered to be a transparent body. If the surface reflection at is not considered, the amount of transmitted light is theoretically 50% (the amount of incident light is 100%).

  Next, with respect to the polarization component perpendicular to the transmission axis of the laminated polarizing plate, the incident light is incident on the polarization scattering plate and reflected back to the incident side, and the polarized light is depolarized into the reflective polarizing plate. It is divided into the part to go. For example, if there is no component that reflects to the incident side and the depolarization effect is 100%, the transmitted light amount obtained by transmitting through the reflective polarizing plate through this path is 25% (the incident light amount is 100%). ) Therefore, in this case, the reflected light from the laminated polarizing plate is 75% in one pass without considering that the reflected light travels back and forth through the prism sheet, the diffusion sheet, and the light guide plate reflector on the backlight side. A transmitted light amount (with an incident light amount of 100%) is obtained.

  In this case, the polarization component (25% (the amount of incident light is 100%)) incident on the reflection type polarizing plate in the direction perpendicular to the transmission axis of the reflection type polarizing plate is reflected by the reflection type polarizing plate and polarized Returning to the scattering plate, the light is reflected, scattered, depolarized, etc., and part of it is incident again on the reflective polarizing plate.

  Actually, the depolarization effect in the polarization scattering plate is not 100%, and the polarization scattering plate also reflects light on the incident side. Therefore, the ratio of the polarization component that can be extracted in one pass from the light incident on the laminated polarizing plate is It does not reach 75% (the amount of incident light is 100%). However, it is still considered that even if the recursion of the light reflected to the backlight side is not taken into account, a polarization component (a surface reflection is not taken into account) that is larger than 50%.

  In the laminated polarizing plate of the present invention, the refractive index in the direction of the transmission axis of the polarizing scattering plate is strictly controlled, that is, the refractive index in the direction perpendicular to the slow axis of the domain phase of the polarizing scattering plate, in particular, the refractive index of the matrix phase. By making the ratio substantially the same, the depolarization effect in the polarization component in the transmission axis direction that passes through the polarization scattering plate hardly occurs. Thereby, in the laminated polarizing plate of this invention, the ratio of the polarization component which can be taken out can be raised and the utilization efficiency of light can be implement | achieved.

  As described above, the laminated polarizing plate of the present invention can be obtained by laminating the reflective polarizing plate and the polarizing scattering plate with the transmission axes arranged in parallel. Here, the reflective polarizing plate and the polarizing scattering plate are made of a material having a refractive index substantially equal to the matrix phase of the polarizing scattering plate in order to eliminate the influence of reflection caused by the interface between the reflective polarizing plate and the polarizing scattering plate. It is preferable to adhere or eliminate the interface. In addition, when a wire grid polarizing plate is used as the reflective polarizing plate, a periodic structure made of a thin metal wire is formed on the polarizing scattering plate base material, perpendicular to the transmission axis of the polarizing scattering plate, using the polarizing scattering plate as a base material. May be processed directly.

[Use of laminated polarizing plate]
The laminated polarizing plate of this invention can be utilized for the same use as a reflective polarizing plate. For example, by arranging the reflective polarizing plate of the present invention on the opposite side (that is, the backlight side) of the liquid crystal panel sandwiching the liquid crystal cell with a polarizing plate such as a dichroic polarizing plate, Can improve the efficiency of use. According to this, a liquid crystal display device with high luminance and / or low power consumption can be obtained. The laminated polarizing plate of the present invention includes all backlights and dichroic polarizing plates of TFT liquid crystal display devices such as twisted nematic mode, vertical alignment mode, OCB (Optically Compensated Bend) alignment mode, and in-plane switching mode. It can be used for the liquid crystal mode.

  The laminated polarizing plate of the present invention can be used as a polarization separation element in a liquid crystal projector which is one of liquid crystal display devices. When the laminated polarizing plate of the present invention is used for a liquid crystal projector, by arranging the laminated polarizing plate between the light source and the RGB liquid crystal display panel, only one of the sp-polarized components can be selectively extracted with high efficiency. it can.

  Furthermore, the laminated polarizing plate of this invention can be utilized as an optical member which expresses various functions by laminating | stacking with the other optical layer which has an optical function. As an optical layer which can be laminated | stacked, an absorption type polarizing plate can be mentioned, for example. Here, the absorptive polarizing plate is a polarizing plate having a characteristic of absorbing polarized light in a certain direction and transmitting polarized light in a 90 ° direction with respect to the polarized light. Examples of the absorbing polarizing plate include a thermoplastic resin film in which a dichroic dye or the like is oriented and dispersed.

  Moreover, as another optical layer which can be laminated | stacked, a phase difference layer can be mentioned, for example. Here, the retardation layer is a layer which gives a retardation, and a retardation film obtained by stretching a transparent thermoplastic synthetic polymer film can be cited as an example. The other retardation layer is, for example, a birefringent material, and when the coating layer is formed, it has a slow axis in the normal direction with respect to the coating layer, and has a positive retardation wavelength dispersion characteristic. Twist-aligned polymerizable chiral nematic (cholesteric) liquid crystal layer with a reflection wavelength in the ultraviolet region, homeotropic-aligned polymerizable discotic liquid crystal layer, and phase difference in the normal direction to the coating layer when coated Examples thereof include a layer coated with a material having expression, or a retardation layer having a hybrid structure in which refractive index ellipsoids are arranged radially in the thickness direction. The laminated polarizing plate of the present invention can be combined with any of these retardation layers. A circularly polarizing film or an elliptically polarizing film can be provided by combining the laminated polarizing plate of the present invention with these retardation layers.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples as long as the gist thereof is not exceeded.

<Measurement and evaluation method>
In the examples, the following items were measured and evaluated by the following methods.

[Refractive index]
(1) Refractive index of matrix phase of polarized light scattering plate The refractive index of the matrix phase resin of the polarized light scattering plate was measured using a film processed to a thickness of 100 μm. The three-dimensional refractive index was measured at a wavelength of 589.3 nm using a refractometer (manufactured by Metricon, prism coupler).

(2) Refractive Index of Domain Phase of Polarization Scattering Plate Using a polarizing microscope, an interference filter (589 nm) was installed in the light source, and observation was performed using linearly polarized light. The fiber used for the domain phase was placed on a glass slide and placed so that the linearly polarized light for observation was parallel to the length direction of the fiber. Using the refraction adjusting liquid, while looking through the microscope, the refraction adjusting liquid having a refractive index of 1.500 to 1.800 is dropped successively onto the fiber, and the refraction adjusting liquid at the time when the outer shape of the fiber is no longer observed. Was the refractive index in the length direction of the fiber. Next, the fiber was installed so that the linearly polarized light was parallel to the vertical cross-sectional direction with respect to the length direction of the fiber. Similarly, while observing the microscope, the refractive adjustment liquid is sequentially dropped onto the fiber, and the refractive index of the refractive adjustment liquid at the time when the outer shape of the fiber is no longer observed is expressed in the direction perpendicular to the length direction of the fiber. Of the refractive index. At this time, since the shape was not confirmed even when the fiber was rotated in the refraction adjusting liquid, it was determined that the refractive index in the direction perpendicular to the length direction of the fiber was uniform.

[Light transmittance T]
The refractive index of the resin was measured using a film obtained by processing the resin to be measured into a thickness of 100 μm. Using a spectrophotometer (manufactured by Hitachi, Ltd., model: U-4000), a spectral transmittance t (λ) was obtained every 10 nm in a wavelength range of 400 nm to 700 nm. From the obtained result, the light transmittance T was calculated by the following formula (1). In the equation, P (λ) is a spectral distribution of standard light (C light source), and y (λ) is a color matching function based on the two-degree field of view X, Y, and Z systems.

[Polarization degree P]
An absorption type polarizing plate (product name: HLC2-2518, polarization degree: 99.9) is used as one polarizing plate, and the laminated polarizing plate of the present invention is used as the other polarizing plate. Two types of light transmittances were measured by arranging on the light source side of the meter (manufactured by Hitachi, Ltd., model: U-4000) and arranging the laminated polarizing plate of the present invention on the detector side. Here, the transmittance when the two polarizing plates are stacked so that the transmission axis directions are the same is Tp (paranicol transmittance), and the two polarizing plates are stacked so that the transmission axes are orthogonal to each other. The degree of polarization P was calculated by the following equation, where the transmittance in this case was Tc (crossed Nicol transmittance). Here, the “transmission axis” refers to an orientation in which the light transmittance of the polarizing plate is maximized with respect to linearly polarized light that is vertically incident.

[Thickness]
The thickness of the laminated polarizing plate of the present invention was measured with an electronic micrometer (manufactured by Anritsu).

[Brightness increase rate]
The luminance in the direction perpendicular to the liquid crystal display screen was measured with a luminance meter (manufactured by MINOLTA, model: LS-110). The case where a polarizing plate was used with respect to a liquid crystal display element and the case where it was not used were measured, and the luminance increase rate when a polarizing plate was used was calculated.

<Example 1>
[Polarized Scattering Plate-Domain Phase: Preparation of Polyethylene Naphthalate (PEN) Fiber]
100 parts by mass of 2,6-naphthalenedicarboxylic acid dimethyl ester and 60 parts by mass of ethylene glycol were subjected to an ester exchange reaction according to a conventional method using 0.03 parts by mass of cobalt acetate tetrahydrate as an ester exchange catalyst. Thereafter, 0.023 parts by mass of trimethyl phosphate was added to substantially complete the transesterification reaction. Subsequently, 0.024 parts by mass of antimony trioxide was added, and a polycondensation reaction was performed in a conventional manner under a high temperature and high vacuum to obtain an intrinsic viscosity (phenol / tetrachloroethane mixed solvent (mass ratio 1: 1) at 35 ° C. ) 0.62 dL / g of polyethylene naphthalate (PEN) was obtained. Using this PEN, melt spinning was performed at a spinning temperature of 295 ° C. to obtain a PEN fiber (diameter: 8 μm).

  The refractive index of this PEN fiber was 1.742 in the major axis direction, 1.556 in the minor axis direction, and the birefringence was 0.186.

[Polarized light scattering plate-matrix phase: UV curable resin]
The optical transparent resin for the matrix phase of the polarized light scattering plate is BPEF-A: 460 parts by weight, UA: 40 parts by weight, Irgacure 184: 15 parts by weight as a photoinitiator, and SH28PA as a leveling agent: 0.18 parts by weight. Parts were added sequentially, and the mixture was stirred and mixed until uniform.

BPEF-A: Bisphenoxyethanol full orange acrylate (manufactured by Osaka Gas)
UA: Urethane acrylate (Shin Nakamura Chemical "NK Oligo U-15HA")
Irgacure 184: Ciba Geigy SH28PA: Toray Dow Corning

  The refractive index of the optical transparent resin layer obtained by this configuration was 1.556.

[Preparation of polarization scattering plate]
The above-prepared PEN fiber as a domain phase is arranged on a glass plate with a thickness of 75 μm (about 10 layers as a fiber layer) side by side in the long axis direction of the glass, and the matrix phase created above from above As an ultraviolet curable resin was applied. After the PEN fiber was encapsulated with the ultraviolet curable resin in this manner, vacuum deaeration was performed to remove bubbles, so that the matrix phase encapsulated the domain phase without defects. This was irradiated with ultraviolet rays with a high-pressure mercury lamp to cure the ultraviolet curable resin as the matrix phase, and then peeled off from the glass to obtain a polarized light scattering plate having a thickness of 93 μm. The polarizing plate thus obtained had a transmittance of 45.1% and a polarization degree of 68.5%.

[Production of laminated polarizing plate]
Using the polarization scattering plate prepared above as a base material, metallic aluminum was sputtered to a thickness of 180 nm on one side of the polarization scattering plate. Next, patterning and etching were performed by a known method by a photolithography method to form a periodic structure in which the length direction of the fine metal wires was arranged to be orthogonal to the transmission axis of the polarization scattering plate. The line width of the fine metal wires was 60 nm, and the pitch was 80 nm.

[Measurement / Evaluation]
The obtained laminated polarizing plate had a light transmittance of 58.6% and a polarization degree of 99.3%. Thereby, it has confirmed that it was a laminated polarizing plate which has polarization separation performance.

[Production of liquid crystal display devices]
Using the obtained laminated polarizing plate and a commercially available transmissive liquid crystal display device, a liquid crystal display device having the following configuration is prepared, and the transmission of the absorption polarizing plate adjacent to the transmission axis of the laminated polarizing plate of the present invention. Arranged so that the axes coincide:
(Constitution) Absorption type polarizing plate / retardation film / liquid crystal cell / retardation film / absorption type polarizing plate / (reflection type polarizing plate side) laminated polarizing plate (polarization scattering plate side) / prism sheet / prism sheet / Diffusion film / Backlight / White reflective film

  When the rate of increase in luminance at the time of normally white before and after insertion of the polarizing plate was measured, a luminance increase effect of 153% was confirmed.

<Comparative Example 1>
An optically isotropic substrate having a thickness of 95 nm was obtained from the ultraviolet curable resin, which is the matrix phase material of Example 1. In addition, using this optical isotropic substrate instead of the polarization scattering plate of Example 1, a wire grid polarizing plate of metal thin wires made of aluminum is formed on the optical isotropic substrate in the same manner as in Example 1. Created.

[Measurement / Evaluation]
The obtained laminated polarizing plate had a light transmittance of 45.6% and a polarization degree of 99.1%. Thereby, although the polarization characteristic as a wire grid polarizing plate was able to be confirmed, the light transmittance did not exceed 50%.

[Production of liquid crystal display devices]
Using the obtained polarizing plate and a commercially available transmission type liquid crystal display device, a liquid crystal display device having the following configuration was prepared, and the transmission of the absorption type polarizing plate adjacent to the transmission axis of the polarizing plate of Comparative Example 1 was performed. Arranged so that the axes coincide:
(Structure) Absorption type polarizing plate / retardation film / liquid crystal cell / retardation film / absorption type polarizing plate / wire grid polarizing plate of comparative example / prism sheet / prism sheet / diffusion film / backlight / white reflective film

  When the luminance increase rate at the time of normally white before and after the insertion of the polarizing plate was measured, a luminance increase effect of 137% was confirmed, but the luminance increase effect obtained in the example was not as high as 153%.

It is a figure which shows the laminated polarizing plate of this invention.

Explanation of symbols

A Reflective polarizing plate B Polarized light scattering plate 10 Laminated polarizing plate 21 Backlight 22 Reflector 23 Light guide plate 24 Optional other layers

Claims (8)

A reflective polarizing plate (A) and a polarizing scattering plate (B) laminated on each other;
The transmission axis of the reflective polarizing plate (A) and the transmission axis of the polarization scattering plate (B) are arranged substantially in parallel,
The polarization scattering plate (B) has a matrix phase (M) and a domain phase (D) arranged in the matrix phase (M), and the matrix phase (M) and the domain phase (D) Which satisfies the following conditions (i) to (iii):
(I) the matrix phase (M) is optically isotropic,
(Ii) The slow axis of the domain phase (D) is substantially perpendicular to the transmission axis of the reflective polarizing plate (A) in the plane of the polarization scattering plate (B), and (iii) The refractive index in the direction perpendicular to the slow axis of the domain phase (D) is substantially the same as the refractive index of the matrix phase (M). The laminated polarizing plate according to claim 1, wherein the conditions (i) to (iii) are represented by the following formulas (1) to (6):
_{| N y (M) -n z} (M) | <0.01 (1)
| _Nx (M)-( _ny (M) + _nz (M)) / 2 | <0.01 (2)
_{| N y (D) -n z} (D) | <0.01 (3)
_nx (D)-( _ny (D) + _nz (D)) / 2> 0.1 (4)
_{n x (D) -n x (} M)> 0.1 (5)
| ( _Ny (M) + _nz (M)) / 2- ( _ny (D) + _nz (D)) / 2 | <0.01
(6)
( _Nx (M) and _nx (D): the matrix phase (M) and the domain phase (D) in the slow axis direction of the domain phase (D) in the plane of the polarization scattering plate (B), respectively. ) Three-dimensional refractive index _ny (M) and _ny (D): the direction perpendicular to the slow axis of the domain phase (D) in the plane of the polarization scattering plate (B), respectively. Three-dimensional refractive indexes _nz (M) and _nz (D) of the matrix phase (M) and the domain phase (D): the matrix phase that is normal to the plane of the polarization scattering plate (B), respectively. (M) and the three-dimensional refractive index of the domain phase (D).   The reflective polarizing plate (A) is a polarizing plate having an alternating laminate composed of two kinds of resins having different refractive index anisotropy, or a columnar structure made of a metal material is periodically arranged on a plane at regular intervals. The laminated polarizing plate according to claim 1, which is a wire grid polarizing plate.   The laminated polarizing plate according to any one of claims 1 to 3, wherein the matrix phase (M) of the polarized light scattering plate (B) is made of a curable resin.   The laminated polarizing plate according to any one of claims 1 to 4, wherein the domain phase (D) of the polarized light scattering plate (B) is made of a thermoplastic resin.   The laminated polarizing plate according to any one of claims 1 to 5, wherein the domain phase (D) of the polarized light scattering plate (B) is in a fiber form. A liquid crystal display device comprising a first polarizing plate, a liquid crystal cell, a second polarizing plate, and a light source,
The said 1st polarizing plate, the said liquid crystal cell, the said 2nd polarizing plate, and the said light source are arrange | positioned in this order, The said laminated polarizing plate in any one of Claims 1-6 is said 2nd. Between the polarizing plate and the light source, the polarizing scattering plate (B) of the laminated polarizing plate is disposed on the light source side, and the transmission axis of the laminated polarizing plate and the second polarizing plate A liquid crystal display device in which a transmission axis is arranged substantially in parallel. A matrix phase (M), and a domain phase (D) disposed in the matrix phase (M), and the matrix phase (M) and the domain phase (D) satisfy the following conditions (i) to Polarizing scattering plate satisfying (iii):
(I) the matrix phase (M) is optically isotropic,
(Ii) the slow axis of the domain phase (D) exists in the plane of the polarization scattering plate, and (iii) the refractive index in the direction perpendicular to the slow axis of the domain phase (D) is It is substantially the same as the refractive index of the matrix phase (M).

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