JP2009053624A - Reflecting/polarizing optical device, reflecting/polarizing optical unit equipped therewith, and liquid crystal display apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflecting/polarizing optical device by which luminance of a display device can be improved further. <P>SOLUTION: The reflecting/polarizing optical device 5 is provided with a reflection polarizer 2 and a retardation film 1. The retardation film 1 is arranged on the side of a light incident plane of the reflection polarizer 2. The retardation film 1 changes light of a predetermined polarized state into light mainly composed of the light of the polarized state different from the predetermined polarized state and transmits the transformed light. A smaller angle among the angles formed by the optical axis 71 of the retardation film 1 and the transmission axis 70 of the reflection polarizer 2 is in the ranges of 35-55°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reflective polarization optical device, a reflective polarization optical unit including the same, and a liquid crystal display device including the same.

  In recent years, various optical display devices have been used as printers and television receivers for personal computers. Examples of such an optical display device include a liquid crystal display device and a plasma display device. Optical display devices are strongly required to improve resolution and brightness in order to improve display quality.

For example, Patent Document 1 discloses a liquid crystal display device using a reflective polarizer. FIG. 10 is a schematic cross-sectional view of the liquid crystal display device 100 disclosed in Patent Document 1. The liquid crystal display device 100 includes an optical cavity 101, a reflective polarizer 102, an LCD assembly 103, and a front polarizer 104. Patent Document 1 discloses that the luminance of the liquid crystal display device 100 can be improved by disposing the reflective polarizer 102 between the optical cavity 101 and the LCD assembly 103 as shown in FIG. Has been.
Japanese Patent No. 3448626

  However, as described in Patent Document 1, there is a problem that it is difficult to sufficiently improve the luminance simply by disposing a reflective polarizer between the optical cavity and the LCD assembly.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a reflective polarization optical device that can further improve the luminance of a display device, and a reflective polarization optical device including the reflective polarization optical device. An object of the present invention is to provide a liquid crystal display device including an optical unit and a reflective polarization optical unit.

  A first reflective polarization optical device according to the present invention includes a reflective polarizer and an optical film. The reflective polarizer has a light incident surface and a light exit surface. The optical film is disposed on the light incident surface side of the reflective polarizer. The in-plane retardation of the optical film is 250 nm or more and 300 nm or less. Of the angles formed by the optical axis of the optical film and the transmission axis of the reflective polarizer, the smaller is 35 ° or more and 55 ° or less.

  The second reflective polarization optical device according to the present invention includes a reflective polarizer and an optical film. The reflective polarizer has a light incident surface and a light exit surface. The optical film is disposed on the light incident surface side of the reflective polarizer. The optical film converts light in a predetermined polarization state into light having a polarization state different from the predetermined polarization state as a main component and transmits the light. Of the angles formed by the optical axis of the optical film and the transmission axis of the reflective polarizer, the smaller is 35 ° or more and 55 ° or less.

  In the second reflective polarization optical device according to the present invention, the optical film gives an in-plane retardation of 5/11 wavelength or more and 6/11 wavelength or less to incident light of a predetermined wavelength. Is preferred.

  The optical film is preferably a half-wave plate.

  The optical film preferably has an Nz coefficient of 1 or less.

  It is preferable that the first and second reflective polarization optical devices according to the present invention further include a prism lens sheet disposed on the light exit surface side of the reflective polarizer.

  The reflective polarization optical unit according to the present invention includes a reflective polarization optical device configured according to the present invention, a light source, and a reflective element. The light source is disposed on the opposite side of the optical film from the reflective polarizer. The reflective element is disposed on the opposite side of the light source from the reflective polarizer, and reflects light from the light source side to the reflective polarizer side while changing the polarization state.

  Here, “reflect by changing the polarization state” means that the light of a predetermined polarization component is reflected after being converted into light having a polarization state different from that of the polarization component, and the light of the predetermined polarization component is reflected. The case where light is reflected as a mixed light of light having a polarization state different from that of the polarization component light and light having the same polarization state as the light of the polarization component is included. Specifically, for example, it includes a case where P-polarized light is converted into S-polarized light and reflected, and a case where P-polarized light is converted into light having a random polarization state (random polarized light) and reflected.

  A display device according to the present invention includes a reflective polarization type optical unit configured according to the present invention and a liquid crystal display cell. The liquid crystal display cell is disposed on the light exit surface side of the reflective polarization type optical unit.

  According to the present invention, it is possible to further increase the brightness of the display device.

<First Embodiment>
As a result of intensive studies, the present inventors have found that a reflection-polarization type optical device is arranged by arranging an optical film having an in-plane retardation on the light incident surface side of the reflection polarizer, compared with the case where only the reflection polarizer is arranged. For the first time, it was found that the amount of light extracted from can be increased. Specifically, the in-plane retardation of the optical film is set within a predetermined range, and the smaller one of the angles formed by the optical axis of the optical film and the transmission axis of the reflective polarizer is set within the predetermined range. As a result, it has been found that the amount of light extracted from the reflective polarization optical device can be increased, and as a result, the present invention has been achieved.

  Hereinafter, an example of a preferable embodiment in which the present invention is implemented will be described in detail with reference to FIG.

  FIG. 1 is a schematic diagram showing a reflective polarization optical unit 5 according to the first embodiment. As shown in FIG. 1, the reflective polarization optical unit 5 includes a reflective polarization optical device 5 a and a light source unit 6. The reflective polarization optical device 5a includes a reflective polarizer 2 and a retardation film 1 which is a kind of optical film. The reflective polarizer 2 includes a light incident surface 2a and a light exit surface 2b. The retardation film 1 is disposed on the light incident surface 2 a side of the reflective polarizer 2.

  In this specification, “reflective polarizer” refers to light that is incident on the reflective polarizer and transmits only light in a specific polarization state and reflects at least a part of light in other polarization states. Say. The reflective polarizer preferably reflects 80% of the light in other polarization states, and reflects 90% or more of the light in other polarization states. Particularly preferred. In the present embodiment, a case where only P-polarized light is transmitted and S-polarized light is reflected will be described as an example.

  In the first embodiment, an example in which the reflective polarization optical device 5a is configured by the retardation film 1 and the reflective polarizer 2 will be described. However, the present invention is not limited to this configuration, and the reflective polarization optical device may further include a prism sheet in addition to the retardation film 1 and the reflective polarizer 2.

(Structure and manufacturing method of the reflective polarizer 2)
The structure of the reflective polarizer 2 is not particularly limited. As the reflective polarizer 2, for example, the one shown in Patent Document 1 may be used.

  FIG. 3 is a schematic perspective view of the reflective polarizer 2. As shown in FIG. 3, the reflective polarizer 2 is formed by alternately laminating two different birefringent layers 80 and 81. Note that the number and form of the birefringent layers 80 and 81 are not particularly limited. The birefringent layers 80 and the birefringent layers 81 are usually laminated alternately in the tens to hundreds of layers.

  The refractive index with respect to the axis X direction of the birefringent layer 80 and the refractive index with respect to the axis Y direction are substantially the same. On the other hand, the refractive index in the axis X direction of the birefringent layer 81 and the refractive index in the axis Y direction are different from each other. Specifically, the refractive index with respect to the axis X of the birefringent layer 81 is substantially the same as the refractive index with respect to the direction of the axis X of the birefringent layer 80. The refractive index in the axis Y direction of the birefringent layer 81 is different from the refractive index in the axis Y direction of the birefringent layer 80.

  The manufacturing method of the reflective polarizer 2 is not particularly limited. The reflective polarizer 2 can be formed as follows, for example. First, a layered product is formed by alternately laminating a layer made of a material that changes the refractive index in the stretching direction by stretching and a layer made of a material that does not change the refractive index in the stretching direction even if stretched. Form. The refractive indexes of both layers before stretching are set to be substantially the same. The formed laminate is stretched, for example, in the axis X direction. Thereby, even if stretched, a layer made of a material whose refractive index in the stretching direction does not change is formed in the birefringent layer 80, and a layer made of a material in which the refractive index in the stretching direction changes by being stretched, The reflective polarizer 2 is obtained by being formed on the birefringent layer 81.

  The material of the birefringent layer 80 is not particularly limited. Examples of the material of the birefringent layer 80 include organic polymers. Specific examples of the organic polymer include polyethylene naphthalate (PEN) and its isomer, polyalkylene telenaphthalate such as polyethylene telenaphthalate, polyimide, polyetherimide, polycarbonate, poly (meth) acrylate, and the like. Specific examples of isomers of polyethylene naphthalate (PEN) include, for example, 2,6-PEN, 1,4-PEN, 1,5-PEN, 2,7-PEN, 2,3-PEN and the like. .

  The material of the birefringent layer 81 is not particularly limited. Examples of the material of the birefringent layer 81 include crystalline or semicrystalline organic polymers. Specific examples of the crystalline or semi-crystalline organic polymer include, for example, styrene copolymers such as PEN copolymer and styrene-butadiene copolymer. Specific examples of the copolymer of PEN include 2,6-naphthalenedicarboxylic acid or ester thereof, 1,4-naphthalenedicarboxylic acid or ester thereof, 1,5-naphthalenedicarboxylic acid or ester thereof, and 2,7-naphthalenedicarboxylic acid. An acid or an ester thereof, and one or more naphthalene dicarboxylic acids or an ester thereof selected from the group consisting of 2,3-naphthalenedicarboxylic acid or an ester thereof, terephthalic acid or an ester thereof, isophthalic acid or an ester thereof, or phthalic acid Or the copolymer with the ester is mentioned.

(Phase difference film 1)
-In-plane retardation of retardation film 1-
The retardation film 1 is disposed between the light source unit 6 and the reflective polarizer 2. The retardation film 1 and the reflective polarizer 2 may be integrated or separate. Further, the phase difference film 1 and the reflective polarizer 2 may be arranged apart from each other.

  The retardation film 1 is an optical film that converts light having a predetermined polarization state into light having a polarization state different from the predetermined polarization state as a main component and transmits the light. Specifically, for example, when P-polarized light is incident, the retardation film 1 converts S-polarized light different from P-polarized light into light having a main component and transmits the light. The retardation film 1 is preferably an optical film that substantially converts light having a predetermined polarization state into light having a polarization state different from the predetermined polarization state and transmits the light. More preferably, it is an optical film that gives an in-plane retardation of 11 / wavelength or less, more preferably an optical film that gives an in-plane retardation of 13/27 wavelength or more and 14/27 wavelength or less, 1/2 A wave plate is particularly preferable.

The “in-plane retardation” is expressed by the following mathematical formula (1).
Re = (nx−ny) × d (1)

here,
Re: In-plane retardation nx: Refractive index in the slow axis direction of the retardation film 1,
ny: refractive index in the fast axis direction of the retardation film 1,
d: thickness of retardation film 1,
Slow axis: An axis extending in the direction in which the in-plane refractive index of the retardation film 1 is maximized,
Fast axis: an axis extending in a direction perpendicular to the slow axis in the plane of the retardation film 1;
It is.

  A “½ wavelength plate” refers to a wavelength plate that provides an in-plane retardation of substantially ½ wavelength. That is, the half-wave plate is not limited to a wave plate that gives a half-wave in-plane phase difference strictly.

  For example, when used for a light source that emits so-called white light, when the light incident on the retardation film 1 includes light of various wavelengths, the retardation film 1 has a peak wavelength of incident light. It is preferable to design against. Here, the “peak wavelength” means a wavelength having the strongest intensity among the incident light.

  That is, the phase difference film 1 is designed so that light having a predetermined polarization state at the peak wavelength of incident light is converted into light having a polarization state different from the predetermined polarization state and transmitted. Is preferred.

  For example, in a display device such as a liquid crystal display device, a so-called white light source having a peak wavelength of about 550 nm is usually used. For this reason, when used in a display device using a white light source, the retardation film 1 is mainly composed of light in a predetermined polarization state having a wavelength of about 550 nm and light in a polarization state different from the predetermined polarization state. It is designed to be converted into light and transmitted. Specifically, the in-plane retardation of the retardation film 1 is set to 250 nm or more and 300 nm or less. The in-plane retardation of the retardation film 1 is preferably set to 265 nm or more and 285 nm or less, and more preferably set to about 275 nm.

-Relationship between optical axis 71 of retardation film 1 and transmission axis 70 of reflective polarizer 2-
As shown in FIG. 2, the retardation film 1 has a smaller one (θ) of an angle between the optical axis 71 of the retardation film 1 and the transmission axis 70 of the reflective polarizer 2 that is 35 ° or more and 55 ° or less. It is arranged to become. Of the angles formed by the optical axis 71 of the retardation film 1 and the transmission axis 70 of the reflective polarizer 2, the smaller one (θ) is preferably not less than 40 ° and not more than 50 °, and preferably about 45 °. Is more preferable, and 45 ° is particularly preferable.

~ Nz coefficient ~
In the present invention, the Nz coefficient of the retardation film 1 is not particularly limited, but for example, is preferably 1 or less, more preferably 0.9 or less, and particularly preferably 0.5 or less. , 0.4 or less is most preferable. The Nz coefficient is represented by the following mathematical formula (2).
Nz = (nx-nz) / (nx-ny) (2)

here,
Re: In-plane phase difference,
nx: refractive index in the slow axis direction of the retardation film 1,
ny: refractive index in the fast axis direction of the retardation film 1,
nz: refractive index in the thickness direction of the retardation film 1,
Slow axis: An axis extending in the direction in which the in-plane refractive index of the retardation film 1 is maximized,
Fast axis: an axis extending in a direction perpendicular to the slow axis in the plane of the retardation film 1;
It is.

The Nz coefficient is also expressed by the following mathematical formula (3).
Nz = (Rth / Re) +0.5 (3)

here,
Rth: retardation in the thickness direction of the retardation film 1,
Re: In-plane phase difference,
It is.

-Material of retardation film 1-
The material of the retardation film 1 is not particularly limited. Specific examples of the material of the retardation film 1 include cyclic olefin resins, polycarbonate resins, polysulfone resins and the like.

  The material of the phase difference film 1 is preferably a material having a low glossiness ratio and a phase difference that hardly changes due to external stress. Specifically, a cyclic olefin resin is preferable.

  A preferred specific example of the cyclic olefin resin is a norbornene resin. Specific examples of norbornene resins include, for example, hydrogenated products of ring-opening (co) polymers of norbornene monomers; addition copolymers of norbornene monomers and olefin monomers; addition copolymers of norbornene monomers Or these derivatives etc. are mentioned. These norbornene resins may be used alone or in combination.

  The norbornene-based monomer is not particularly limited as long as it has a norbornene ring. For example, norbornene; bicyclic ring such as norbornadiene; tricyclic ring such as dicyclopentadiene; Pentacycles such as pentadiene trimer; and heptacycles such as cyclopentadiene tetramer.

  The norbornene-based monomer may have a substituent. Specific examples of the substituent include alkyl groups, alkenyl groups such as vinyl groups, alkylidene groups such as ethylidene groups, hydrocarbon groups such as aryl groups; ester groups; ether groups; cyano groups; halogen atoms; alkoxycarbonyl groups; Group; hydroxyl group; carboxylic acid group; amino group; non-hydroxyl group; silyl group; epoxy group; acrylic group; Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. Specific examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group.

  In addition, since it is easily available, has excellent reactivity, and the resulting retardation film has excellent heat resistance, a polycyclic norbornene-based monomer having three or more rings is preferable, and among these, tricyclic and tetracyclic monomers are preferable. And pentacyclic norbornene monomers are more preferred.

  Specific examples of commercially available norbornene-based resins include, for example, the product name “ARTON” series manufactured by JSR, the product name “ZEONOR” series manufactured by ZEON CORPORATION, and the product name “APEL” manufactured by Mitsui Chemicals, Inc. "Series and the like.

  In addition, when the number average molecular weight of cyclic olefin resin is too small, the mechanical strength of the retardation film obtained may fall, and when too large, the workability | operativity at the time of film formation may fall. For this reason, it is preferable that the number average molecular weights of cyclic olefin resin are 5000-50000, and it is more preferable that it is 8000-30000. In addition, in this specification, the number average molecular weight of cyclic olefin resin means what was measured by the gel permeation chromatography method.

  Cyclic olefin resin improves the heat resistance, UV resistance, smoothness, etc. of the retardation film in order to prevent deterioration of the cyclic olefin resin during molding as long as the function of the retardation film is not impaired. In order to do so, phenol-based, phosphorus-based and other antioxidants; lactone-based and other thermal degradation inhibitors; velzophenone-based, benzotriazole-based, acrylonitrile-based UV absorbers; aliphatic alcohol esters, polyhydric alcohols Various additives such as partial ester-based and partial ether-based lubricants; amine-based antistatic agents and the like may be added. An additive may be used independently or 2 or more types may be used together.

-Formation method of retardation film 1-
As a method for forming a film from a cyclic olefin-based resin, a method that has been widely used has been used. Specifically, a so-called melt extrusion method or a melt casting method can be used. The melt extrusion method is a method of obtaining a resin film by supplying a cyclic olefin-based resin to an extruder, melting and kneading, and extruding the molten resin into a film form from a T die attached to the tip of the extruder. The solution casting method is a method in which a solution obtained by dissolving a cyclic olefin resin in an organic solvent is cast on a drum or a band, and then the organic solvent is evaporated to obtain a resin film.

  If the thickness of the cyclic olefin resin film is too thin, it is difficult to obtain a desired retardation Re. If it is too thick, it is disadvantageous for making the liquid crystal display device thin when incorporated in the liquid crystal display device. For this reason, it is preferable that the thickness of a cyclic olefin resin film is 50-200 micrometers.

  In addition, when the thickness of the cyclic olefin-based resin film is 80 μm or more, the use of the solution casting method may make it difficult to sufficiently evaporate and remove the organic solvent. It is preferable to produce a cyclic olefin resin film using

  Examples of the method for producing the retardation film 1 include a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, and a longitudinal and transverse simultaneous biaxial stretching method. These methods are properly used according to the performance of the target retardation film 1.

  For example, the retardation film 1 having an Nz coefficient of less than 1 can be produced, for example, in the following manner. First, heat shrinkable films having different MD shrinkage rates and TD shrinkage rates are attached to both surfaces of an optical film having a slow axis in the longitudinal direction to form a laminate. The laminate is uniaxially stretched at the free end in the longitudinal direction. Finally, the retardation film can be completed by peeling the heat-shrinkable film. In the case of this production method, for example, the Nz coefficient is adjusted by changing the MD shrinkage ratio / TD shrinkage ratio of the heat-shrinkable film to be used, the thickness of the heat-shrinkable film, the stretching conditions such as the stretching temperature and the stretching ratio, and the like. be able to.

  The retardation film 1 may be composed of a plurality of birefringent films. In that case, it is preferable that the Nz coefficient of the whole several birefringent film is 1 or less.

(Light source unit 6)
The light source unit 6 is disposed on the opposite side of the retardation film 1 from the reflective polarizer 2. The light source unit 6 includes a light source 3 and a reflective element 4. The reflective element 4 is disposed on the opposite side of the light source 3 from the reflective polarizer 2. The reflective element 4 reflects the light from the light source 3 side to the reflective polarizer 2 side while changing the polarization state. Here, the light from the light source 3 includes light emitted from the light source 3 and light reflected to the light source 3 by the reflective polarizer 2.

  For example, the reflecting element 4 may be one that reflects the polarization state of light from the light source 3 side at random. Specifically, for example, when P-polarized light is incident from the light source 3 side, the light may be converted into light mixed with P-polarized light and S-polarized light and reflected.

  The reflective element 4 may be a device that substantially converts light from the light source 3 side into light having a polarization state different from the polarization state and reflects the light. Specifically, for example, when P-polarized light is incident from the light source 3 side, the light may be substantially converted to S-polarized light and reflected.

(Light flow in the reflective polarization optical unit 5)
Next, the flow of light in the reflective polarization optical unit 5 will be described with reference to FIG. Here, the description will be made assuming that the reflection element 4 reflects the polarization state of light from the light source 3 side at random.

  In the reflective polarization type optical unit 5, the retardation film 1 is disposed between the reflective polarizer 2 and the light source 3. For this reason, among the lights emitted from the light source 3, the polarization state of P-polarized light is converted by the retardation film 1 twice in total. As a result, the P-polarized light emitted from the light source 3 returns to the light source 3 side as P-polarized light. That is, the light emitted from the light source 3 and reflected by the reflective polarizer 2 is emitted from the light source 3 and returns to the reflective element 4 in the same polarization state as that until the light is first transmitted through the retardation film 1.

  More specifically, with reference to FIG. 1, among the light emitted from the light source 3, P-polarized light 50 is converted into S-polarized light 51 in the retardation film 1. Here, the reflective polarizer 2 reflects S-polarized light. For this reason, the S-polarized light 51 is reflected by the reflective polarizer 2. The reflected light 52 that is S-polarized light is converted again to P-polarized light 53 in the retardation film 1. The P-polarized light 53 is reflected by the reflective element 4 with its polarization state randomized. Of the light reflected by the reflective element 4, the S-polarized light 54 is converted into P-polarized light 55 in the retardation film 1. Here, the reflective polarizer 2 transmits P-polarized light. Therefore, the P-polarized light 55 passes through the reflective polarizer 2 and is extracted from the reflective polarization type optical unit 5. On the other hand, P-polarized light 56 out of the light reflected by the reflective element 4 is converted into S-polarized light 57 in the retardation film 1. The S-polarized light 57 is reflected by the reflective polarizer 2 and reaches the reflective element 4 again via the retardation film 1.

  On the other hand, among the light emitted from the light source 3, the S-polarized light 59 is converted into the P-polarized light 60 in the retardation film 1. The P-polarized light 60 passes through the reflective polarizer 2 and is extracted from the reflective polarization optical unit 5.

(effect)
As described above, in the present embodiment, the reflective polarizer 2 is disposed, and light in a polarization state other than the polarized light extracted from the reflective polarization type optical unit 5 is reflected and reused. Accordingly, the amount of light extracted from the reflective polarization optical unit 5 can be increased.

  For example, as shown in FIG. 4, it is possible to arrange only the reflective polarizer 2 without arranging the retardation film 1. In that case, the P-polarized light 61 emitted from the light source 3 passes through the reflective polarizer 2 and is extracted from the reflective polarization-type optical unit 5. On the other hand, the S-polarized light 62 is reflected by the reflective polarizer 2. The reflected light 63 is reflected by the reflecting element 4 with its polarization state randomized. Among them, the P-polarized light 64 passes through the reflective polarizer 2 and is extracted from the reflective polarization type optical unit 5. On the other hand, the S-polarized light 65 is reflected by the reflective polarizer 2 and returns to the light source 3 side again.

  As described above, when the retardation film 1 is not disposed between the light source 3 and the reflective polarizer 2, the polarization state of the light reflected by the reflective polarizer 2 is the same as that before being reflected by the reflective polarizer 2. Different from polarization state.

  On the other hand, in this embodiment, the retardation film 1 is disposed on the incident surface side of the reflective polarizer 2. For this reason, the polarization state of the main light reflected and recycled by the reflective polarizer 2 is equal to the polarization state of the light before reaching the retardation film 1 before entering the reflective polarizer 2. Therefore, as demonstrated in the following examples, the amount of light emitted from the reflective polarization optical unit 5 can be made higher than in the case shown in FIG. As a result, a display device with high brightness can be realized by using the reflective polarization type optical unit 5.

  Further, the retardation film 1 is reflected so that the smaller one (θ) of the angle formed by the optical axis 71 of the retardation film 1 and the transmission axis 70 of the reflective polarizer 2 is 35 ° or more and 55 ° or less. By disposing the polarizer 2 on the incident surface side, the amount of polarized light extracted from the reflective polarization optical unit 5 can be further increased.

  The smaller one (θ) of the angles formed by the optical axis 71 of the retardation film 1 and the transmission axis 70 of the reflective polarizer 2 is 40 ° or more and 50 ° or less, further substantially 45 °, in particular 45. By setting the angle to 0 °, the amount of polarized light extracted from the reflective polarization optical unit 5 can be further increased.

  Further, from the viewpoint of increasing the amount of light extracted from the reflective polarization type optical unit 5, the retardation film 1 substantially converts light having a predetermined polarization state into light having a polarization state different from the predetermined polarization state. It is preferable that the light is converted to be transmitted and more preferably has an in-plane phase difference of 5/11 wavelength or more and 6/11 wavelength or less with respect to incident light of a predetermined wavelength. It is more preferable to provide an in-plane retardation of 27 wavelengths or more and 14/27 wavelengths or less, and a half-wave plate is particularly preferable.

  For example, when the light source 3 is a so-called white light source having a peak wavelength of about 550 nm, the in-plane retardation of the retardation film 1 is increased from the viewpoint of increasing the amount of light extracted from the reflective polarization optical unit 5. It is set to 250 nm or more and 300 nm or less. The in-plane retardation of the retardation film 1 is preferably 265 nm or more and 285 nm or less, and more preferably about 275 nm.

  In the present embodiment, the Nz coefficient of the retardation film 1 is set to 1 or less. For this reason, it is possible to suitably compensate for the polarization disturbance in the oblique direction. As a result, the proportion of the P-polarized light with respect to the recycled light reflected by the reflective polarizer 2 toward the light source 3 and transmitted through the retardation film 1 can be further increased. Therefore, the amount of polarized light extracted from the reflective polarization optical unit 5 can be increased. From the viewpoint of increasing the amount of polarized light extracted from the reflective polarizing optical unit 5, the Nz coefficient of the retardation film 1 is more preferably 0.9 or less, and particularly preferably 0.5 or less. Most preferably, it is 0.4 or less.

<Second Embodiment>
In the second embodiment, a backlight type liquid crystal display device using the reflective polarization type optical unit 5 described in the first embodiment will be described. In the description of the second embodiment, components having substantially the same functions are described with reference numerals common to those of the first embodiment, and description thereof is omitted.

(Liquid crystal display device 11)
FIG. 5 is an exploded perspective view of the liquid crystal display device 11 according to the second embodiment. The liquid crystal display device 11 includes a reflective polarization type optical unit 5. The reflective polarization optical unit 5 includes a light source unit 6, a diffusion sheet 13, and a reflective polarization optical device 5a. The reflective polarization optical device 5 a includes a retardation film 1, a reflective polarizer 2, and a prism lens sheet 7.

  The reflective polarization type optical unit 5 includes a light source unit 6 arranged on the most back side. The light source unit 6 includes a casing 8, a reflective element (reflective layer) 4, a light source 3, and a diffusion plate 12. The casing 8 is formed with a recess that opens toward the front. The reflective element 4 is formed in the recess. The light source 3 is disposed on the reflective element 4. In the second embodiment, the light source 3 is constituted by a plurality of fluorescent discharge tubes 3a arranged substantially in parallel with each other. The diffusion plate 12 is disposed on the light source 3.

  On the diffusion plate 12, a diffusion sheet 13 with beads is disposed. The diffusing plate 12 and the diffusing sheet 13 are for uniformizing the amount of light emitted from the plurality of fluorescent discharge tubes 3a in the plane. The diffusion plate 12 and the diffusion sheet 13 are not particularly limited, and for example, a conventional diffusion plate or diffusion sheet can be used. For this reason, the further detailed description regarding the diffusion plate 12 and the diffusion sheet 13 is abbreviate | omitted.

  On the diffusion sheet 13, the reflective polarization optical device 5 a is disposed. As shown in FIGS. 5 and 6, the reflective polarization optical device 5 a includes a retardation film 1, a reflective polarizer 2, and a prism lens sheet 7. The prism lens sheet 7 has a plurality of prism lens portions 7a extending in parallel to each other and having a substantially triangular cross section. By disposing the prism lens sheet 7, the front luminance of the liquid crystal display device 11 can be improved.

  In the present embodiment, the phase difference film 1, the reflective polarizer 2, and the prism lens sheet 7 are laminated, adhered, and integrated. For this reason, the assembly process can be simplified as compared with the case where the liquid crystal display device 11 is assembled using the retardation film 1, the reflective polarizer 2, and the prism lens sheet 7 provided separately.

  Above the prism lens sheet 7, a polarizing plate 14, a liquid crystal display cell 15 including a liquid crystal layer, and a polarizing plate 16 are arranged in this order from the light source unit 6 side. The polarizing plates 14 and 16 are attached to the liquid crystal display cell 15. The polarizing plates 14 and 16 and the liquid crystal display cell 15 are not specifically limited, For example, a conventional thing can be used and it can manufacture with the conventional manufacturing method.

(effect)
As described above, also in the reflective polarization optical unit 5 of the second embodiment, the retardation film 1 having a predetermined in-plane retardation is arranged under a predetermined arrangement condition. For this reason, the brightness of the reflective polarization optical unit 5 is increased. As a result, high brightness and high contrast of the liquid crystal display device 11 are realized.

(First embodiment)
The liquid crystal display device 11 shown in FIG. 5 was assembled in the following manner. A backlight of a liquid crystal television (product name: AQUAS LC-20S1) manufactured by Sharp Corporation was taken out, and the taken out backlight was used as the light source 3 and the casing 8. The diffusion plate 12 was a diffusion plate (grade MS, thickness 2 mm) manufactured by Asahi Kasei Chemicals. The diffusion sheet 13 with beads was manufactured by Kimoto Co., product number: 100DX2. In addition, the diffusion sheet 13 with beads having a product number of 100DX2 manufactured by Kimoto Co. was obtained by applying styrene beads dispersed in an acrylic binder to a polyethylene terephthalate (PET) substrate, and the thickness was 100 μm. The reflective polarizer 2 was a reflective polarizer (product name: DBEF, thickness 132 μm) manufactured by Minnesota Mining and Manufacturing Company. A retardation film 1 made of a uniaxially stretched film of ZEONOR (manufactured by Nippon Zeon Co., Ltd.) having a thickness of 35 μm is formed on one surface of the reflective polarizer 2 at an angle between the optical axis and the transmission axis of the reflective polarizer 2. It stuck together using the polyester-type adhesive agent so that the smaller one might be 45 degrees. A prism lens sheet 7 made of polycarbonate (PC) was bonded to the other surface of the reflective polarizer 2 using a polyester adhesive. The angle formed by the slope of the prism lens portion 7a of the prism lens sheet 7 was 93 degrees, the pitch from the prism lens portion 7a was 50 μm, the height from the top to the bottom of the prism lens portion 7a was 19 μm, and the thickness was 100 μm.

  As the liquid crystal display cell 15 and the polarizing plates 14 and 16, those mounted on the above liquid crystal television were used.

Prior to laminating the retardation film 1 on the reflective polarizer 2, an in-plane retardation (Re) and a thickness direction retardation (Rth) of the retardation film 1 were measured using a retardation measuring device. As a phase difference measuring device, a KOBRA-21ADH device manufactured by Oji Scientific Instruments was used. Further, the Nz coefficient was calculated from the obtained Re and Rth using the following mathematical formula (3).
Nz = (Rth / Re) +0.5 (3)

here,
Rth: retardation in the thickness direction of the retardation film 1,
Re: In-plane phase difference,
It is.

  Further, the front luminance and the integrated light quantity of the liquid crystal display device 11 produced as described above were measured with EZContrast 80 manufactured by ELDIM. The results are shown in Table 1 below.

(Second embodiment)
A liquid crystal display device 11 is produced in the same procedure as in the first embodiment, except that the retardation film 1 of the first embodiment is changed to a retardation film produced in the following manner. Similar evaluations were made. The results are shown in Table 1 below.

  First, a polypropylene heat-shrinkable film having a shrinkage rate of 30% at the stretching temperature was attached to both sides of a polycarbonate film (product number Panlite 1225ZE) manufactured by Teijin Ltd. so that the shrinking direction was perpendicular to the stretching direction. A laminate was formed. This laminate was uniaxially stretched at the free end in the longitudinal direction. The stretching temperature was 152 ° C. and the stretching ratio was 1.3 times. Subsequently, it cooled, hold | maintaining this state for 1 minute in 122 degreeC atmosphere, and also cooled to room temperature. Finally, the heat-shrinkable film was peeled off to obtain a retardation film used in the second example.

(First comparative example)
Except that the retardation of the used retardation film 1 was changed as shown in Table 1 below, a liquid crystal display device 11 was produced in the same manner as in the first example, and the same evaluation was performed. The results are shown in Table 1 below.

(Second comparative example)
The liquid crystal display device 11 is the same as the first embodiment except that a polycarbonate optical sheet manufactured by Teijin Ltd. whose surface is roughened by extrusion molding using a roll die is used instead of the retardation film 1. The same evaluation was performed. The results are shown in Table 1 below.

As shown in Table 1, in the first comparative example in which the in-plane retardation is 250 nm or less and the second comparative example in which the retardation film 1 is not used, only a relatively low front luminance of 420 cd / m ² or less is obtained. In contrast, in the first and second examples in which the in-plane retardation was 250 nm or more and 300 nm or less, a relatively high front luminance of 440 cd / m ² or more was obtained. In the first and second comparative examples, only a relatively low integrated light amount of 715 lm / m ² or less was obtained, whereas in the first and second examples, a relatively high amount of 735 lm / m ² or more was obtained. A high integrated light intensity was obtained.

  As a result, the retardation film 1 has an in-plane retardation of 250 nm or more and 300 nm or less, and the retardation film 1 is light mainly composed of light having a predetermined polarization state and light different from the predetermined polarization state. It was found that the front luminance and the integrated light quantity of the liquid crystal display device can be further increased by converting the light into a transparent light.

Further, in the first example in which the Nz coefficient is 1.0, the front luminance is 446 cd / m ² , the integrated light quantity is 738 m / m ² , while the Nz coefficient is 0.5. In this example, the front luminance was 467 cd / m ² and the integrated light amount was 773 m / m ² . From this result, it was found that the front luminance and the integrated light quantity of the liquid crystal display device can be further improved by making the Nz coefficient smaller than 1.

(Third embodiment)
The in-plane retardation (Re) of the retardation film 1 is changed to various values to produce a liquid crystal display device 11 similar to that of the first embodiment, and each liquid crystal display in the manner described in the first embodiment. The integrated light quantity of the apparatus 11 was measured. The measurement results are shown in FIG.

  As can be seen from the graph shown in FIG. 7, a high integrated light amount is obtained when the in-plane retardation of the retardation film 1 is 250 nm or more and 300 nm or less, and a high integrated light amount is obtained when the retardation film 1 is 265 nm or more and 285 nm or less. The highest integrated light intensity was obtained when the thickness was about 275 nm. Therefore, from this result, the in-plane retardation of the retardation film 1 is preferably 250 nm or more and 300 nm or less, more preferably 265 nm or more and 285 nm or less, and further preferably about 275 nm. all right.

(Fourth embodiment)
A liquid crystal display device similar to that of the first embodiment is obtained by changing the smaller one (arrangement angle: θ) of the angle formed by the optical axis of the retardation film 1 and the transmission axis of the reflective polarizer 2 to various values. 11 was manufactured, and the integrated light quantity of each liquid crystal display device 11 was measured in the manner described in the first example. The measurement results are shown in FIG.

  As can be seen from the graph shown in FIG. 8, a high integrated light amount is obtained when the arrangement angle of the retardation film 1 is 35 ° or more and 55 ° or less, and a higher integration is obtained when it is 40 ° or more and 50 ° or less. The highest integrated light amount was obtained when the amount of light was obtained and was about 45 °. Therefore, from this result, the arrangement angle (θ) of the retardation film 1 is preferably 35 ° or more and 55 ° or less, more preferably 40 ° or more and 50 ° or less, and about 45 °. It turned out to be more preferable.

(Fifth embodiment)
The Nz coefficient of the retardation film 1 is changed to various values to produce a liquid crystal display device 11 similar to that of the first embodiment, and the integrated light quantity of each liquid crystal display device 11 in the manner described in the first embodiment. Was measured. The measurement results are shown in FIG.

  As can be seen from the graph shown in FIG. 9, a high integrated light amount is obtained when the Nz coefficient of the retardation film 1 is 1 or less, and a high integrated light amount is obtained when it is 0.9 or less. When the ratio was less than or equal to, a higher integrated light quantity was obtained, and when it was 0.4 or less, the highest accumulated light quantity was obtained. Therefore, from this result, the Nz coefficient of the retardation film 1 is preferably 1 or less, more preferably 0.9 or less, further preferably about 0.5, and 0.4 or less. It turned out to be particularly preferred.

It is the schematic showing the reflective polarization type optical device which concerns on 1st Embodiment. It is a perspective view for demonstrating the relationship between the optical axis of retardation film, and the transmission axis of a reflective polarizer. It is a schematic perspective view of a reflective polarizer. It is sectional drawing for demonstrating the flow of the light in case the phase difference film is not arrange | positioned. It is a disassembled perspective view of the liquid crystal display device which concerns on 2nd Embodiment. It is sectional drawing of a reflective polarization type optical device. It is a graph showing the relationship between the in-plane phase difference measured in the 3rd example, and accumulated light quantity. It is a graph showing the relationship between the arrangement | positioning angle ((theta)) measured in the 4th Example, and integrated light quantity. It is a graph showing the relationship between the Nz coefficient measured in the 5th Example, and integrated light quantity. 1 is a schematic cross-sectional view of a liquid crystal display device disclosed in Patent Document 1. FIG.

Explanation of symbols

1 Optical film (retardation film)
2 reflective polarizer
2a Light incident surface
2b Light exit surface
4 reflective elements
5 Reflective polarization type optical unit
5a Reflective polarization type optical device
7 Prism lens sheet
11 Liquid crystal display device
12 Diffuser
15 Liquid crystal display cell
70 Transmission axis of reflective polarizer
71 Optical axis of retardation film

Claims (8)

A reflective polarization optical device comprising a reflective polarizer having a light incident surface and a light exit surface, and an optical film disposed on the light incident surface side of the reflective polarizer,
The in-plane retardation of the optical film is 250 nm or more and 300 nm or less,
The reflective polarization optical device, wherein the smaller one of the angles formed by the optical axis of the optical film and the transmission axis of the reflective polarizer is 35 ° to 55 °. A reflective polarization optical device comprising a reflective polarizer having a light incident surface and a light exit surface, and an optical film disposed on the light incident surface side of the reflective polarizer,
The optical film converts light having a predetermined polarization state into light mainly composed of light having a polarization state different from the predetermined polarization state, and transmits the light.
The reflective polarization optical device, wherein the smaller one of the angles formed by the optical axis of the optical film and the transmission axis of the reflective polarizer is 35 ° to 55 °.   The reflective polarizing optical device according to claim 2, wherein the optical film gives an in-plane retardation of 5/11 wavelength or more and 6/11 wavelength or less to incident light having a predetermined wavelength.   The reflective polarization type optical device according to any one of claims 1 to 3, wherein the optical film is a half-wave plate.   The reflective polarization type optical device according to any one of claims 1 to 4, wherein the optical film has an Nz coefficient of 1 or less.   The reflective polarization type optical device according to any one of claims 1 to 5, further comprising a prism lens sheet disposed on a light exit surface side of the reflective polarizer. The reflective polarization optical device according to any one of claims 1 to 6,
A light source disposed on the opposite side of the optical film from the reflective polarizer;
A reflective element that is disposed on the opposite side of the light source from the reflective polarizer side and reflects light from the light source side to the reflective polarizer side by changing a polarization state;
Reflective polarization type optical unit. The reflective polarization optical unit according to claim 7;
A liquid crystal display cell disposed on the light exit surface side of the reflective polarization optical unit;
A liquid crystal display device.

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