JP2007065314A - Circularly polarized light separating sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circularly polarized light separating sheet which realizes display of no coloring even when observed from an oblique direction and which is excellent in polarized light separating performance and to provide a liquid crystal display equipped with the circularly polarized light separating sheet. <P>SOLUTION: A solution containing a polymerizable liquid crystal compound having birefringence ▵n of ≥0.18 is applied onto a base material and then is irradiated with UV rays to polymerize the polymerizable liquid crystal compound. Thus a resin layer having cholesteric regularity and total thickness of ≤7 μm is formed to obtain the circularly polarized light separating sheet. Further the liquid crystal display which has a polarizer A, a liquid crystal cell, a polarizer B, a quarter wavelength plate and the polarized light separating sheet in this order is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a circularly polarized light separating sheet excellent in polarization separating performance and a liquid crystal display device provided with the circularly polarized light separating sheet, and more specifically, it can display without coloration when observed obliquely and has excellent polarized light separating performance. The present invention relates to a circularly polarized light separating sheet and a liquid crystal display device including the circularly polarized light separating sheet.

Liquid crystal display devices are used in many display devices. In addition, there is an increasing demand for display characteristics of liquid crystal display devices. Therefore, the performance of optical films, such as a polarizing plate, a viewing angle compensation film, a broadband quarter wave plate, and a brightness enhancement film, which constitute a liquid crystal display device, and a demand for productivity thereof are also increasing.
In particular, a brightness enhancement film for increasing display brightness is an indispensable component for suppressing power consumption of a liquid crystal display device, and a demand for its quality is high. The brightness enhancement film includes a polarization separation film for separating incident light into transmitted light and reflected light according to the polarization state as a component.

  For this polarization separation film, for example, a linear polarization separation film obtained by laminating a large number of anisotropic polymer layers disclosed in Patent Document 1, or a cholesteric liquid crystal layer disclosed in Patent Document 2 or Patent Document 3 is used. Known circularly polarized light separation membranes are known. Among these, the latter circularly polarized light separation film has a liquid crystal layer having a structure in which rod-like liquid crystal molecules or liquid crystal groups of side chain type liquid crystalline polymers are twisted in the thickness direction with a helical axis parallel to the layer normal as a rotation axis. Then, by utilizing the selective reflection characteristic, the circularly polarized light rotated left and right is separated into transmitted light and reflected light.

  The circularly polarized light separating film can be obtained, for example, by forming a superposed layer of a cholesteric liquid crystal layer having a thickness of 5 μm or less on the main surface of the substrate as described in paragraph 0014 of Patent Document 4. In the example of Patent Document 4, four types of cholesteric liquid crystal layers having a thickness of 2 μm (with wavelength ranges of 400 to 500 nm, 450 to 550 nm, 500 to 600 nm, and 600 to 700 nm; total thickness of 8 μm) are laminated. Patent Document 4 discloses that a suitable liquid crystal polymer constituting a cholesteric liquid crystal layer has a larger wavelength range of circular dichroism (selective reflection) as the birefringence is larger, thereby reducing the number of weight layers and a large visual field. It teaches that it is preferable in terms of a margin for a wavelength shift at the time of angular.

  In addition, the present applicant previously described in Patent Document 5 that a liquid containing a polymerizable liquid crystal compound having two ethylenic double bonds, a polymerization initiator, a surfactant, a chiral agent, and the like is made of polyvinyl alcohol. It is disclosed that a polarization separation sheet can be obtained by coating a base material on which an alignment film is formed and polymerizing the coating solution to form a cholesteric layer.

US Pat. No. 6,335,999 JP-A-6-235900 JP-A-8-271731 JP-A-11-231130 JP 2005-91825 A

However, it has been found that the circularly polarized light separation film described in Patent Document 4 is colored in the display when observed obliquely. In addition, even with the polarization separation sheet proposed in Patent Document 5, display coloration suppression in an oblique observation is not sufficient.
An object of the present invention is to provide a circularly polarized light separating sheet that can display without coloring when viewed obliquely and has excellent polarization separation performance, and a liquid crystal display device including the circularly polarized light separating sheet.

  As a result of studies to achieve the above object, the present inventors have obtained a resin layer having cholesteric regularity by using a polymerizable liquid crystal compound having a birefringence Δn of 0.18 or more, and the total thickness is obtained. By making the thickness 7 μm or less, it has been found that a circularly polarized light separating sheet can be obtained that can be displayed without being colored even when observed from an oblique direction and has excellent polarization separating performance, and the present invention is completed based on this finding. It has come.

Thus, according to the present invention,
(1) A circularly polarized light separating sheet having a cholesteric regularity and having a resin layer having a total thickness of 7 μm or less, obtained by using a polymerizable liquid crystal compound having a birefringence Δn of 0.18 or more is provided. The

As a preferred embodiment (2) the circularly polarized light separating sheet, wherein the resin layer is non-liquid crystalline,
(3) The circularly polarized light separating sheet, wherein the cholesteric regularity is in the thickness direction,
(4) The circularly polarized light separating sheet, wherein the cycle of cholesteric regularity changes stepwise in the thickness direction.
(5) The circularly polarized light separating sheet, wherein the resin layer is formed of two or more layers having different cholesteric regularity periods.
(6) The circularly polarized light separating sheet, wherein the period of cholesteric regularity is continuously changed in the thickness direction.
(7) The maximum wavelength of light having an incident angle of 0 degrees, wherein the resin layer has an average refractive index of 1.5 to 1.8, and / or (8) a reflectance of 30% or more. The circularly polarized light separating sheet having a thickness of 700 nm or more is provided.

  According to the present invention, (9) a solution containing a polymerizable liquid crystal compound having a birefringence Δn of 0.18 or more is applied to a substrate, and then irradiated with ultraviolet rays to polymerize the polymerizable liquid crystal compound. There is provided a method for producing a circularly polarized light separating sheet comprising forming a resin layer having a cholesteric regularity and having a total thickness of 7 μm or less.

Furthermore, according to the present invention, there is provided (10) a liquid crystal display device having a polarizer A, a liquid crystal cell, a polarizer B, a quarter wavelength plate and the circularly polarized light separating sheet in this order,
As a preferred embodiment, (11) the liquid crystal display device in which the polarizer B and the quarter-wave plate are integrated;
(12) The liquid crystal display device, wherein the surface of the circularly polarized light separating sheet on the quarter wavelength plate side has light diffusibility,
(13) The liquid crystal display device further including a diffusion sheet between the circularly polarized light separating sheet and the quarter wavelength plate is provided.

  The circularly polarized light separation sheet of the present invention has high polarization separation performance in the visible light region. In addition, the display is not colored even when observed obliquely. Therefore, the circularly polarized light separating sheet of the present invention is suitable as a brightness enhancement film for liquid crystal display devices.

The reason why the circularly polarized light separating sheet of the present invention does not cause coloration in the display by observation from an oblique direction is not clear, but the mechanism is estimated as follows.
The resin layer having cholesteric regularity has a structure in which rod-like liquid crystal molecules are twisted and rotated in a spiral shape. Refractive index of the resin layer having cholesteric regularity is its value changes in a cycle, such as cholesteric regularity, in _{general, n x = n y> n} z (n x, n y in-plane direction of the principal refractive index, n _z has a relationship of main refractive index in the thickness direction).

  The circularly polarized light reflected by the resin layer having cholesteric regularity that changes in the thickness direction is reflected at different locations, that is, in the thickness direction, depending on the wavelength. For example, when a resin layer having cholesteric regularity having a selective reflection wavelength region is laminated on each of 400 to 500 nm, 500 to 600 nm, and 600 to 700 nm, one circularly polarized light of 400 to 500 nm is incident on the resin layer. And the other circularly polarized light is transmitted through the resin layer. The circularly polarized light of 500 to 600 nm is reflected around the center of the resin layer, and the other circularly polarized light is transmitted through the resin layer. The circularly polarized light of 600 to 700 nm is reflected by the layer immediately before exiting from the resin layer, and the other circularly polarized light is transmitted through the resin layer. Thus, the distance that passes through the resin layer varies depending on the wavelength of the circularly polarized light. Since the distance passing through the resin layer is different, the amount of phase change at each wavelength is different. This difference in the amount of phase change is more noticeable in obliquely incident light.

It is known that the reflection coefficient Q in the resin layer is defined by a value of πΔn / n (Q is a reflection coefficient per pitch of a chiral structure described later). Δn of the polymerizable liquid crystal compound birefringent i.e. n _e -n o _{(n e} is the long axis direction of the refractive index of the polymerizable liquid crystal compound molecules, n _o is the refractive index along the short axis of the polymerizable liquid crystal compound molecules) of, n Is the average refractive index, i.e. (n _e + n _o ) / 2. When this Δn is 0.18 or more, the reflection coefficient Q increases. As a result, the total thickness d required to obtain the same reflectance can be reduced. Further, it is known that the reflection band Δλ is defined by N × Δn × p (N is the number of layers, p is a pitch length of a chiral structure described later), and the reflection band widens as Δn increases. As a result, it is possible to reduce the total thickness d (number of layers and number of chiral structure pitches) required to secure the same reflection band. If the total thickness d can be reduced, the difference in phase change due to wavelength can be greatly reduced. The present invention believes that such a mechanism can significantly suppress the phase change of obliquely incident light without degrading the polarization separation performance, and as a result, can suppress the coloring of the display in oblique observation. It is done.

  The circularly polarized light separating sheet of the present invention comprises a resin layer having a cholesteric regularity and having a total thickness of 7 μm or less, obtained using a polymerizable liquid crystal compound having a birefringence Δn of 0.18 or more. It is.

The resin layer constituting the circularly polarized light separating sheet of the present invention has cholesteric regularity.
Cholesteric regularity means that the molecular axes are aligned in a certain direction on one plane, but the direction of the molecular axis is slightly shifted on the next plane, and the angle is further shifted on the next plane. The structure is such that the molecular axes are shifted (twisted) one after another in the normal direction of the plane. Such a structure in which the direction of the molecular axis is twisted is called a chiral structure. The normal line (chiral axis) of the plane is preferably substantially parallel to the thickness direction of the resin layer having cholesteric regularity.

  A resin having cholesteric regularity (hereinafter sometimes referred to as cholesteric resin) has a circularly polarized light separation function. That is, it has a function of reflecting left-handed or right-handed circularly polarized light in a specific wavelength region and transmitting other circularly-polarized light. This is sometimes referred to as selective reflection.

  The total thickness d of the cholesteric resin layer is 7 μm or less, preferably 5 μm or less. By reducing the total thickness d, the difference in phase change amount depending on the wavelength is reduced. The total thickness means the total thickness when the cholesteric resin layers are separated, and the thickness when the cholesteric resin layers are integrated.

  The cholesteric resin layer used in the present invention is preferably a non-liquid crystalline resin layer. This is because the cholesteric regularity does not change depending on the ambient temperature, electric field, or the like when it is non-liquid crystalline. The non-liquid crystalline cholesteric resin layer can be obtained by polymerizing a composition containing a polymerizable liquid crystal compound having two or more polymerizable groups. By the polymerizable liquid crystal compound having two or more polymerizable groups, a relatively rigid cross-linked structure is introduced into the cholesteric resin, and a resin that does not produce liquid crystallinity is obtained. The cholesteric resin layer preferably has an average refractive index of 1.5 to 1.8.

  In this invention, it is preferable to provide the cholesteric resin layer which exhibits this circularly polarized light separation function over the entire wavelength region of visible light. Specifically, it is a cholesteric resin layer having a circularly polarized light separation function for light in any wavelength region of blue (wavelength 410 to 470 nm), green (wavelength 520 to 580 nm), and red (wavelength 600 to 660 nm). preferable.

  The wavelength that exhibits the circularly polarized light separation function depends on the pitch of the chiral structure in the cholesteric resin (= period of cholesteric regularity). The pitch of the chiral structure is a distance in the chiral axis direction until the angle of the molecular axis gradually shifts as it advances along the plane in the chiral structure and then returns to the original molecular axis direction again. By changing the pitch of this chiral structure, the wavelength at which the circularly polarized light separating function is exhibited can be changed.

  A cholesteric resin layer that exhibits a circularly polarized light separation function over the entire wavelength region of visible light includes, for example, (i) a cholesteric resin layer in which the pitch of the chiral structure is changed stepwise, and (ii) the pitch of the chiral structure. Examples thereof include a cholesteric resin layer whose size is continuously changed.

  (I) The cholesteric resin layer in which the pitch of the chiral structure is changed stepwise can be obtained, for example, by laminating two or more resin layers. Specifically, a cholesteric resin layer having a chiral structure pitch that exhibits a circularly polarized light separating function with light in the blue wavelength region, and a cholesteric material having a chiral structure pitch that exhibits a circularly polarized light separating function with light in the green wavelength region. It can be obtained by laminating a resin layer and a cholesteric resin layer having a chiral structure pitch that exhibits a circularly polarized light separation function with light in the red wavelength region. Further, different cholesteric resin layers are produced such that the central wavelengths of the circularly polarized light reflected are, for example, 470 nm, 550 nm, 640 nm, and 770 nm, and these cholesteric resin layers are arbitrarily selected, and the order of the central wavelengths of the reflected light Can be obtained by laminating 3 to 7 layers. When the cholesteric resin layers having different chiral structure pitches are laminated, it is preferable that the rotation directions of the circularly polarized light reflected by the cholesteric resin layers are the same. In order to obtain a liquid crystal display device having a wide viewing angle, the stacking order of the cholesteric resin layers having different chiral structure pitches is ascending or descending according to the chiral structure pitch. preferable. The lamination of these cholesteric resin layers may be merely overlaid, or may be fixed via an adhesive or an adhesive.

(Ii) The cholesteric resin layer in which the pitch of the chiral structure is continuously changed is not particularly limited by the manufacturing method. For example, it can be obtained by forming a layer containing a polymerizable liquid crystal compound for forming a cholesteric resin layer, a chiral agent, and an ultraviolet absorber and irradiating the layer with ultraviolet rays. Here, the polymerizable liquid crystal compound and the chiral agent are preferably compounds having different polymerizability in ultraviolet irradiation. The chiral agent is a compound that can give a chiral structure to the molecular arrangement.
Although the mechanism for continuously changing the pitch size by ultraviolet irradiation is not known in detail, it is said that the pitch is inclined by the following mechanism. The light receiving intensity of the ultraviolet ray irradiated to the layer containing the polymerizable liquid crystal compound, the chiral agent, and the ultraviolet absorber is strong on the surface (ultraviolet irradiation surface) side of the layer. In the layer, ultraviolet rays are absorbed by the ultraviolet absorber, so that the ultraviolet light receiving intensity decreases as the layer depth increases. Therefore, a difference in polymerization degree occurs as the depth of the layer increases from the surface of the layer (ultraviolet irradiation surface). Among the polymerizable liquid crystal compound and the chiral agent, the concentration of the compound having a high degree of polymerization is increased on the surface side of the layer, and the compound having a low degree of polymerization among the polymerizable liquid crystal compound and the chiral agent remaining as unreacted components is diffused. Move to the other side. Eventually, a concentration gradient is formed in which the concentration of the polymerizable liquid crystal compound or the chiral agent continuously changes in the depth direction of the layer. The amount of the chiral agent affects the pitch size of the chiral structure. In this way, a cholesteric resin layer in which the chiral structure pitch is continuously changed in the depth direction can be obtained.

  As this type of cholesteric resin layer, for example, SID '95, Asia Display. , P735 (1995); Liquid Crystal, Vol. 2, No. 2, p32-39 (1998); Japanese Patent Publication No. 11-514757, US Patent No. 2001001509, US Patent No. 6,638,449, US Patent No. 5,948,831 There are those described in publications.

The cholesteric resin layer constituting the present invention is obtained using a polymerizable liquid crystal compound having a birefringence Δn of 0.18 or more.
Polymerizable liquid crystal compound used in the present invention, the birefringence Δn ₍₌ n e -n _o) is 0.18 or more, preferably from 0.18 to 0.40, more preferably a 0.18 to 0.22 It is. Δn can be measured by the Cellnamon method. The polymerizable liquid crystal compound having Δn falling within the above range is preferably selected from rod-shaped polymerizable liquid crystal compounds.

Examples of the rod-like polymerizable liquid crystal compound include a compound represented by the formula (1).
R1-B1-A1-B3-M-B4-A2-B2-R2 Formula (1)
In addition, although A1 and A2 in Formula (1) are a coupling group so that it may mention later, this coupling group is abbreviate | omitted and B1 and B3 or B4 and B2 may couple | bond together directly.

  In formula (1), R1 and R2 represent a polymerizable group. Specific examples of R1 and R2 that are polymerizable groups include (r-1) to (r-15) shown in Chemical Formula 1, but are not limited thereto.

  B1, B2, B3 and B4 each independently represent a single bond or a divalent linking group. Moreover, it is preferable that at least one of B3 and B4 is a group containing —O—CO—.

  A1 and A2 represent a linking group having 1 to 20 carbon atoms. Examples of the linking group here include a polymethylene group and a polyoxymethylene group. The number of carbons contained in the structural unit forming the linking group is appropriately determined depending on the chemical structure of the mesogenic group, etc. In general, in the case of a polymethylene group, the number of carbons is 1 to 20, preferably 2 to 12, In the case of a polyoxymethylene group, the carbon number is 1 to 10, preferably 1 to 3.

  M represents a mesogenic group. The material for forming the mesogenic group M is not particularly limited, but azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines Alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.

  The cholesteric resin layer is usually obtained by polymerizing a polymerizable liquid crystal compound. The polymerizable liquid crystal compound is polymerized in the presence of a polymerization initiator and, if necessary, a chiral agent or a surfactant. As a specific example of a method for forming a cholesteric resin layer using a polymerizable liquid crystal compound, a polymerizable liquid crystal compound, a polymerization initiator and a chiral agent, and further, a surfactant, an alignment modifier, and the like were dissolved in a solvent as necessary. A coating solution is obtained, laminated on the substrate in the form of a film, dried, the dried film is polymerized, and a polymer having a cholesteric regularity is obtained by polymerizing a polymerizable liquid crystal compound. There is a method of laminating the material. Since the adjustment of the pitch of the chiral structure of the cholesteric resin layer is easy, the former method is preferred in which a coating liquid containing a polymerizable liquid crystal compound is laminated on a substrate and a dried film is polymerized.

The polymerization initiator includes a thermal polymerization initiator and a photopolymerization initiator, and a photopolymerization initiator is preferred because the polymerization reaction is fast.
Examples of the photopolymerization initiator include polynuclear quinone compounds (US Pat. No. 3,046,127, US Pat. No. 2,951,758), oxadiazole compounds (US Pat. No. 4,212,970), α-carbonyl compounds (US Pat. No. 2,367,661, US Pat. No. 2,367,670). No. 2), acyloin ether compounds (US Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (US Pat. No. 2,722,512), combinations of triarylimidazole dimers and p-aminophenyl ketones (US Pat. No. 3,549,367). And acridine and phenazine compounds (Japanese Patent Laid-Open No. 60-105667, US Pat. No. 4,239,850).

The amount of the polymerization initiator is preferably 1 to 10 parts by weight and more preferably 1 to 5 parts by weight with respect to 100 parts by weight of the polymerizable liquid crystal compound. When a photopolymerization initiator is used, it is preferable to use ultraviolet rays as irradiation light, and it is particularly preferable to use ultraviolet rays having a wavelength of 320 to 390 nm (hereinafter sometimes referred to as UV-A). The irradiation energy is preferably from ^{0.1mJ / cm 2 ~50J / cm 2} , further preferably 0.1~800mJ / cm ^2.

Although the ultraviolet irradiation method is not particularly limited, in order to widen the reflection band, first, the polymerizable liquid crystal compound is irradiated with an ultraviolet ray having an irradiation amount that does not cause the polymerization conversion rate to be 100%, and then the chiral structure pitch. The method of irradiating ultraviolet rays until the polymerization conversion rate reaches 100% is preferred. The irradiation dose such that the polymerization conversion rate of the polymerizable liquid crystal compound does not become 100% is appropriately selected depending on the type of the polymerizable liquid crystal compound. The irradiation dose such that the polymerization conversion does not reach 100% is usually 0.1 to 250 mJ / cm ² on a UV-A basis.
Examples of the method of changing the pitch of the chiral structure include a method of heating above the temperature showing the liquid crystal phase, a method of applying a composition containing a polymerizable liquid crystal compound to the photopolymerized resin layer, and further photopolymerizing, The method of apply | coating a non-liquid crystalline compound to the polymerized resin layer is mentioned. Of these, a method of heating to a temperature higher than the liquid crystal phase is preferred. The heating temperature can be appropriately selected depending on the type of the liquid crystal compound, and is usually 65 to 115 ° C. The heating time is usually 0.001 to 20 minutes, preferably 0.001 to 10 minutes, more preferably 0.001 to 5 minutes.
The amount of ultraviolet irradiation until the polymerization conversion rate reaches 100% is appropriately selected depending on the type of the polymerizable liquid crystal compound. The irradiation amount until the polymerization conversion rate reaches 100% is generally 200 to 1500 mJ / cm ² on the basis of UV-A based on the integration with the initial ultraviolet irradiation amount.

  As the chiral agent, those described in JP-A No. 2003-66214, JP-A No. 2003-313187, US Pat. No. 6,468,444, International Publication No. WO98 / 00428 and the like can be used as appropriate. From the viewpoint of economy, a large HTP that is an index representing the efficiency of twisting the liquid crystal compound is preferable. HTP is represented by the formula (I): HTP = 1 / p · c. Here, p represents the pitch length of the chiral structure, and c represents the concentration of the chiral agent. In order to avoid an unintended change in the phase transition temperature due to the addition of the chiral agent, it is preferable to use a chiral agent that exhibits liquid crystallinity.

  A surfactant may be used to adjust the surface tension of the coating liquid and the coating film laminated on the substrate. As the surfactant used here, a nonionic surfactant is particularly preferable, and an oligomer having a molecular weight of about several thousand is preferable. Examples of such a surfactant include KH-40 manufactured by Seimi Chemical Co., Ltd.

  The said orientation regulator is for controlling the orientation state of the air side surface of the cholesteric resin layer formed on the base material. Examples of the alignment modifier include polyvinyl alcohol, polyvinyl butyral, and modified products thereof.

  As the solvent used for preparing the coating solution, an organic solvent is preferably used. Specific examples of the organic solvent include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. In particular, ketones are preferable in consideration of environmental load. Two or more organic solvents may be used in combination.

  In order to laminate the coating liquid into a film, a known method such as an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, or a die coating method is performed.

  The substrate used for laminating the coating solution is not particularly limited as long as it is an optically transparent substrate, but is preferably optically isotropic in order to avoid polarization change. Examples of such a substrate include a transparent resin film and a glass substrate, and a long transparent resin film is more preferable from the viewpoint of efficiently producing a liquid crystal layer. The transparent resin film may be a single layer film or a multilayer film, but preferably has a thickness of 1 mm and a total light transmittance of 80% or more.

  The resin material of the transparent resin film includes an alicyclic structure-containing polymer resin, a chain olefin polymer such as polyethylene and polypropylene, triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, and polyether. Examples include sulfone, amorphous polyolefin, modified acrylic polymer, and epoxy resin. These can be used alone or in combination of two or more. Among these, alicyclic structure-containing polymer resins are preferable from the viewpoints of transparency, low hygroscopicity, dimensional stability, lightness, and the like.

  The alicyclic structure-containing polymer resin has an alicyclic structure in the repeating unit of the polymer resin, and the polymer resin having an alicyclic structure in the main chain and an alicyclic structure in the side chain. Any polymer resin can be used. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, and a cycloalkane structure is preferable from the viewpoint of thermal stability. Although there is no restriction | limiting in particular in carbon number which comprises an alicyclic structure, Usually, 4-30 pieces, Preferably it is 5-20 pieces, More preferably, it is 6-15 pieces.

  The proportion of the repeating unit having an alicyclic structure in the alicyclic structure-containing polymer resin is appropriately selected according to the purpose of use, but is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight. % Or more. When there are too few repeating units having an alicyclic structure, the heat resistance of the film may be reduced.

  Specifically, the alicyclic structure-containing polymer resin includes (1) a norbornene polymer, (2) a monocyclic olefin polymer, (3) a cyclic conjugated diene polymer, and (4) vinyl fat. Examples thereof include cyclic hydrocarbon polymers and hydrogenated products thereof. Among these, norbornene polymers and hydrogenated products thereof are more preferable from the viewpoints of transparency and moldability.

  Examples of the norbornene-based polymer include, for example, a ring-opening polymer of a norbornene-based monomer, a ring-opening copolymer of a norbornene-based monomer and another monomer capable of ring-opening copolymerization, and hydrogenated products thereof; Examples include addition polymers and addition copolymers with other monomers copolymerizable with norbornene-based monomers. Among these, from the viewpoint of transparency, a ring-opening polymer hydrogenated product of a norbornene-based monomer is most preferable. The polymer having the alicyclic structure is selected from known polymers disclosed in, for example, JP-A No. 2002-321302.

  The resin material of the transparent resin film suitable for the present invention has a glass transition temperature of preferably 80 ° C. or higher, more preferably 100 to 250 ° C. A transparent resin film made of a resin material having a glass transition temperature in such a range is excellent in durability without causing deformation or stress during use at high temperatures.

  The resin material of the transparent resin film suitable for the present invention has a molecular weight of gel permeation chromatography (hereinafter abbreviated as “GPC”) using cyclohexane (toluene when the resin material is not dissolved) as a solvent. The measured weight average molecular weight (Mw) in terms of polyisoprene (when the solvent is toluene, in terms of polystyrene) is usually 10,000 to 100,000, preferably 25,000 to 80,000, more preferably 25,000. ~ 50,000. When the weight average molecular weight is in such a range, the mechanical strength and moldability of the film are highly balanced and suitable.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the resin material of the transparent resin film suitable for the present invention is not particularly limited, but is usually 1 to 10, preferably 1 to 4, more preferably 1 The range is from 2 to 3.5.

  The resin material of the transparent resin film suitable for the present invention has a content of a resin component having a molecular weight of 2,000 or less (that is, an oligomer component), preferably 5% by weight or less, more preferably 3% by weight or less, and still more preferably Is 2% by weight or less. When the amount of the oligomer component is within the above range, fine convex portions are hardly generated on the surface, the thickness unevenness is reduced, and the surface accuracy is improved. In order to reduce the amount of the oligomer component, the selection of the polymerization catalyst and the hydrogenation catalyst, the reaction conditions such as polymerization and hydrogenation, and the temperature conditions in the step of pelletizing the resin as a molding material may be optimized. . The amount of oligomer components can be measured by GPC as described above.

  The thickness of the substrate used in the present invention is not particularly limited, but the thickness is usually 1 to 1000 μm, preferably 5 to 300 μm, more preferably 30 to 100 μm, from the viewpoint of productivity, thinning, and weight reduction.

  The base material used in the present invention is preferably surface-treated. By performing the surface treatment, the adhesion between the base material and the alignment film described later can be enhanced. Examples of the surface treatment include glow discharge treatment, corona discharge treatment, ultraviolet (UV) treatment, flame treatment) and the like. It is also preferable to provide an adhesive layer (undercoat layer) on the substrate in order to improve the adhesion between the substrate and the alignment film.

  Moreover, it is preferable that the base material used for this invention has an orientation film on the base-material surface, in order to adjust the orientation direction of the chiral structure of the cholesteric resin layer formed.

The alignment film used in the present invention is not particularly limited as long as the alignment direction of the cholesteric resin layer can be adjusted.
For the alignment film, for example, a coating liquid mainly composed of a resin such as polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, or polyetherimide is laminated on the base material in a film shape, dried, and then rubbed in one direction. It is obtained by doing. By rubbing the coating layer laminated in a film shape in one direction, it becomes possible to regulate the orientation of the resin layer having cholesteric regularity in one direction.

  The rubbing method is not particularly limited, and examples thereof include a method of rubbing the alignment film in a certain direction with a roll made of a synthetic fiber such as nylon or a natural fiber such as cotton or a felt. In order to remove fine powder (foreign matter) generated during rubbing and to clean the surface of the alignment film, it is preferable to clean the formed alignment film with isopropyl alcohol or the like. In order to give the alignment layer a function of regulating the alignment of the resin layer having cholesteric regularity in one direction in the plane, there is a method of irradiating the surface of the alignment film with polarized ultraviolet rays in addition to rubbing.

  Further, for example, a process for changing the pretilt angle by partially irradiating ultraviolet rays as disclosed in JP-A-6-222366 and JP-A-6-281937, or JP-A-5-107544. A resist film is partially formed on the rubbed alignment film as shown in the publication, and after the rubbing treatment is performed in a direction different from the rubbing direction performed previously, the resist film is A treatment that removes and changes the alignment ability of the alignment film is exemplified. These processes can improve the visual field characteristics of the liquid crystal display device.

  The thickness of the alignment film is preferably 0.01 to 5 μm, and more preferably 0.05 to 1 μm.

  In the circularly polarized light separating sheet of the present invention, the maximum wavelength of light with an incident angle of 0 degree at which the reflectance is 30% or more is preferably 700 nm or more, more preferably 730 nm or more. Further, the maximum wavelength of light with an incident angle of 60 degrees at which the reflectance is 30% or more is preferably 570 nm or more, more preferably 600 nm or more. When these maximum wavelengths are within the above range, coloring of the display when observed from an oblique direction can be eliminated.

  FIG. 1 schematically shows a circularly polarized light separating sheet 21 of the present invention. In FIG. 1, an alignment film 2 is stacked on a substrate 1, and a cholesteric resin layer 3 is stacked on the alignment film. The cholesteric resin layer 3 includes four layers having different pitches (each of the pitches P0, P1, P2, and P3). In FIG. 1, the pitch becomes wider in the order of P0, P1, P2, and P3. In FIG. 1, only a chiral structure for one cycle of each cholesteric resin layer P0, P1, P2, and P3 is shown, but the chiral structure may have two or more cycles.

  When light is incident on the cholesteric resin layer of this circularly polarized light separating sheet, only the left-handed or right-handed circularly polarized light in the specific wavelength region is reflected. Light other than the reflected circularly polarized light is transmitted. White light incident on the cholesteric resin layer of the circularly polarized light separating sheet at an incident angle θ1 is refracted on the surface of the cholesteric resin layer, passes through the cholesteric resin layer at a refraction angle θ2, and has a pitch P corresponding to the wavelength λ. One circularly polarized light is reflected by the layer at the reflection angle θ2, refracted on the surface of the cholesteric resin layer, and emitted at the emission angle θ1. Refraction is performed according to Snell's law.

As shown in FIG. 1, when the spiral axis 4 representing the rotation axis when the molecular axis is twisted in the chiral structure and the normal line of the cholesteric resin layer are parallel, the pitch p of the chiral structure and the reflected circularly polarized light The wavelength λ has the relationship of the formula (2).
λ = n × p × cos θ2 Formula (2)
Here, in _{n = (n e + n o} ) / 2 ( wherein, n _o represents the minor axis direction of the refractive index of the polymerizable liquid crystal compound, n _e represents the refractive index of long axis direction of the polymerizable liquid crystal compound , P represents the pitch length of the chiral structure.
Therefore, the reflection band of the circularly polarized light reflected by the cholesteric resin layer having the pitch p is expressed by Expression (3).
n _o × p × cos θ2 ≦ λ ≦ n _e × p × cos θ2 Formula (3)

  The circularly polarized light separating sheet of the present invention is attached to a liquid crystal display device having at least a polarizer A, a liquid crystal cell, and a polarizer B in combination with a quarter wavelength plate, and the polarizer A, the liquid crystal cell, the polarizer B, 1 The brightness of the liquid crystal display device can be improved by arranging the quarter-wave plate and the circularly polarized light separating sheet of the present invention in this order.

  Polarizers A and B used in the present invention are known polarizers used in liquid crystal display devices and the like. The polarizer used in the present invention transmits one of two linearly polarized light intersecting at right angles. For example, a hydrophilic polymer film such as a polyvinyl alcohol film or an ethylene vinyl acetate partially saponified film adsorbed a dichroic substance such as iodine or a dichroic dye and uniaxially stretched, the hydrophilic polymer film Examples include uniaxially stretched and dichroic substances adsorbed, and polyene oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Other examples include a polarizer having a function of separating polarized light such as grid polarizer and multilayer polarizer into reflected light and transmitted light. Of these, a polarizer containing polyvinyl alcohol is preferred.

Although the polarization degree of the polarizer used for this invention is not specifically limited, Preferably it is 98% or more, More preferably, it is 99% or more. The average thickness of the polarizer is preferably 5 to 80 μm.
The polarizing transmission axis of the polarizer A and the polarizing transmission axis of the polarizer B are usually arranged so as to sandwich the liquid crystal cell so as to be perpendicular to each other. Polarizer performance may change due to moisture absorption. In order to prevent this, a protective film is usually bonded to both sides of the polarizer A or B.

A liquid crystal cell is filled with a liquid crystal substance between two glass substrates provided with transparent electrodes facing each other with a gap of several μm, and a voltage is applied to this electrode to change the alignment state of the liquid crystal and pass through this. The amount of light to be controlled is controlled.
The liquid crystal cell is classified according to a method (operation mode) for changing the alignment state of the liquid crystal substance. For example, a TN (Twisted Nematic) type liquid crystal cell, a STN (Super Twisted Nematic) type liquid crystal cell, or a HAN (Hybrid Alignment Nematic) type. Examples include a liquid crystal cell, an IPS (In Plane Switching) type liquid crystal cell, a VA (Vertical Alignment) type liquid crystal cell, an MVA (Multiple Vertical Alignment) type liquid crystal cell, and an OCB (Optical Compensated Bend) type liquid crystal cell.

The quarter-wave plate used in the present invention gives a quarter-wave phase difference to incident light. Since the phase difference differs depending on the wavelength of the incident light, the one that gives a phase difference of ¼ wavelength at the center wavelength of visible light, for example, around 550 nm is generally called a ¼ wavelength plate. On the other hand, in the present invention, a broadband quarter-wave plate can be used. The broadband ¼ wavelength plate gives a phase difference of almost ¼ wavelength at any wavelength in the visible light region including wavelengths of 410 to 660 nm. Almost 1/4 means 0.15 to 0.40, preferably 0.18 to 0.36, more preferably 0.20 to 0.30.
Further, a quarter wavelength plate having a phase compensation function can be used. A quarter wavelength plate having a phase compensation function gives a phase difference of a quarter wavelength near 550 nm, and has a retardation Rth (= thickness direction of less than 0 nm, preferably −2000 to −10 nm). (( _Nx + _ny ) / 2- _nz ) * d); _nx and _ny are in-plane main refractive indexes, _nz is a main refractive index in the normal direction, and d is a thickness) .

  As a broadband quarter-wave plate, for example, a half-wave plate that gives a half-wave phase difference near a wavelength of 550 nm and a quarter-wave plate that gives a quarter-wave phase difference near 550 nm are stacked. One having a D layer made of a material having a positive intrinsic birefringence value and an E layer made of a material having a negative intrinsic birefringence value, wherein the D layer and the E layer are molecularly oriented in the same direction. Can be mentioned. Further, a commercially available broadband retardation film WRF (manufactured by Teijin Ltd.) or the like can be used.

In the preferable liquid crystal display device of the present invention, the polarizer B and the quarter-wave plate are integrated.
There is no particular limitation on the method of integrating the polarizer, for example, the polarizer B and the quarter wavelength plate may be directly bonded, and the quarter wavelength plate may function as the protective film; Further, a quarter wave plate may be bonded together. When pasting, an adhesive or an adhesive may be used. The polarizing transmission axis of the polarizer B is arranged so as to be substantially parallel to the direction of linearly polarized light emitted from the quarter wavelength plate. That the angle formed between the polarization transmission axis and the direction of linearly polarized light is substantially parallel means that the angle is an angle of 0 to 3 °.

In the liquid crystal display device of the present invention, when the quarter wavelength plate is not provided with the phase compensation function as described above, the liquid crystal display device does not substantially have in-plane retardation and has a thickness direction letter. Deshon _{Rth (Rth = {(n x} + n y) / 2-n z} × d: _{wherein, n x,} n _y represents a principal refractive index in the plane direction, _{n z} is a main refractive index in the thickness direction D represents a film thickness)) is a phase compensation element in the range of −20 nm to −1000 nm, preferably −50 nm to −500 nm, between the circularly polarized light separating sheet of the present invention and the quarter wavelength plate. It is preferable to provide. At this time, it is preferable that the phase compensation element and the quarter-wave plate are fixed.
The phase compensation element having Rth in such a range has a function of compensating for the phase difference of light incident obliquely on the quarter wavelength plate.

The phase compensation element is mainly refractive indices _n x, _{n y} and _{n z is,} it is necessary to satisfy _{n z> n x, n z} > n y y, and the relationship of _{n x} ≒ _{n y.} The main refractive index can be measured by an automatic birefringence meter [for example, “KOBRA series” manufactured by Oji Scientific Instruments Co., Ltd.]. Note that the _{n x} ≒ _{n y,} the refractive index difference is, usually within 0.0002, preferably 0.0001, more preferably within it within 0.00005.
Further, the phase compensation elements, the in-plane direction retardation _{Re (Re = (n x -n} y) × d:. N x, n y and d represent the same meaning as described above) is usually 20nm or less, Preferably it is 10 nm or less, More preferably, it is 5 nm or less.
A phase compensation element having such optical characteristics can be obtained by stretching and orientation of a film including a layer of a material having a negative intrinsic birefringence value.

FIG. 2 is a diagram showing an example of the liquid crystal display device of the present invention. As shown in FIG. 2, the reflecting plate 20, the cold cathode tube 19, the diffusion plate 18, the prism sheet (not shown) 17, the circularly polarized light separating sheet 21, the integrated phase compensation element 15 and the quarter wavelength plate 14. And the polarizer B 13, the liquid crystal cell 12, and the polarizer A 11 are arranged in this order. The light from the light source includes right polarized light and left polarized light. When the light is incident on the circularly polarized light separating sheet 21, the circularly polarized light separating sheet 21 is maintained while keeping the rotational direction of the circularly polarized light in one rotational direction (circularly polarized light rotated rightward in the drawing in the drawing). To Penetrate. The other circularly polarized light in the direction of rotation (circularly polarized light rotated counterclockwise toward the light traveling direction in the figure) is reflected by the circularly polarized light separating sheet (the reflected circularly polarized light remains rotated counterclockwise toward the light traveling direction). Is). The transmitted circularly polarized light is converted into linearly polarized light parallel to the transmission axis of the polarizer B by the quarter wavelength plate. On the other hand, the reflected circularly polarized light is reflected by a reflecting plate disposed behind the light source, and is incident on the circularly polarized light separating sheet again. In this way, the light emitted from the light source is effectively used, and the display brightness of the screen can be improved.
The diffusion plate is generally known as a plate having a function in which a particulate diffusion material is uniformly dispersed in a matrix such as a resin, thereby scattering and diffusing light. The prism sheet is generally known as a sheet having a function of narrowing light having a wide traveling direction due to scattering or the like in the normal direction of the sheet surface.
In FIG. 2, a diffusion sheet may be interposed between the phase compensation element and the circularly polarized light separating sheet. The diffusion sheet is generally laminated on a transparent film so that the particulate diffusion material is uniformly dispersed, and is known as a sheet having a function of scattering and diffusing light.
In the present invention, it is preferable that the surface of the circularly polarized light separating sheet on the quarter wavelength plate side has light diffusibility. The light diffusibility is a property of scattering and diffusing light. In order to provide light diffusibility, for example, a method of laminating a particulate diffusing material on the surface of a circularly polarized light separating sheet so as to uniformly disperse, a method of uniformly dispersing a particulate diffusing material on a substrate, Or the method of bonding the said diffusion sheet to a circularly polarized light separation sheet etc. are mentioned.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not restrict | limited to the following Example. Parts and% are based on weight unless otherwise specified.

<Reflection band> The collimated white light was incident on the circularly polarized light separating sheet at an incident angle of 0 degree and an incident angle of 60 degrees, and the spectroscope: [S-2600] manufactured by Soma Optical Co., Ltd. was used for measurement.
<Film thickness measurement> It measured using the surface shape measuring apparatus [DEKTAK6M] by ULVAC.
<Δn> According to the Sernamon method, measurement was performed using an Eclipse E-600POL IF lens 546 nm manufactured by Nikon Corporation.
<The refractive index of a phase compensation element> It measured using Oji Scientific Instruments Co., Ltd. [KOBRA].
<Refractive Index of Liquid Crystal Molecules> The refractive index of 633 nm laser light was measured using a prism coupler [Model 2010] manufactured by Metricon.

(¼ wavelength plate with phase compensation function (C))
A styrene-maleic anhydride copolymer (a material having a negative intrinsic birefringence value, Tg = 131 ° C.) and a norbornene-based polymer (“ZEONOR 1020”, manufactured by Nippon Zeon Co., Ltd., Tg = 105 ° C.) are coextruded. Molding was performed to obtain a multilayer film having a three-layer structure of norbornene polymer layer (thickness 50 μm) / styrene-maleic anhydride copolymer layer (thickness 200 μm) / norbornene polymer layer (thickness 50 μm).

Next, this multilayer film was successively biaxially stretched at 140 ° C. by 1.8 times in the vertical direction and 1.5 times in the horizontal direction to obtain a quarter-wave plate (C). The average thickness of the quarter-wave plate (C) 120 [mu] m, the main refractive indices _{n x} 1.5801, _{n y} is 1.5789, _{n z} was 1.5811. The in-plane retardation Re was 144 nm, and the thickness direction retardation Rth was -192 nm.

(Polarizing plate with phase compensation function (X))
The quarter wave plate (C) was bonded and fixed to one side of a polarizer B obtained by adsorbing iodine to polyvinyl alcohol. Further, a polarizing plate (X) was obtained by attaching and fixing a triacetyl cellulose film having an average thickness of 60 μm to the other surface of the polarizer.

(Polarizing plate (Y))
A polarizing plate (Y) was obtained by attaching and fixing a triacetyl cellulose film having an average thickness of 60 μm on both surfaces of a polarizer A obtained by adsorbing iodine to polyvinyl alcohol.

Example 1
One side of a ZEONOR film (ZF14-100 manufactured by Nippon Zeon Co., Ltd.) was corona discharged, and then a 5% by weight aqueous solution of polyvinyl alcohol (Kuraray Co., Poval MP203) was applied to the surface and dried at 100 ° C. for 3 minutes. The substrate was obtained by rubbing with a roll of felt to form an alignment film.
90.3 parts of a polymerizable liquid crystal compound having a birefringence Δn of 0.18, 6.7 parts of a chiral agent (LC756 manufactured by BASF), 3.1 parts of a polymerization initiator (IRGACURE907 manufactured by Ciba Specialty Chemicals), and an interface 0.1 parts of an activator (Surflon KH-40, manufactured by Seimi Chemical Co., Ltd.) is dissolved in methyl ethyl ketone so as to have a solid content of 40%, and then filtered through a polytetrafluoroethylene syringe filter having a pore size of 0.45 μm to polymerize. Sex solution was obtained.
This polymerizable solution was applied to the surface of the base material provided with the alignment film and dried to obtain a coating film. The ultraviolet coating film was 70 mJ / cm ² irradiated with UV-A standards, and left to 100 ° C. oven for 3 minutes, then ultraviolet rays to cure the coated film was irradiated 300 mJ / cm ² in UV-A standard Then, an optical element P1 having a thickness of 3 μm and having a cholesteric resin layer was formed. At this time, the thickness was controlled by adjusting the coating amount of the polymerizable solution.
In another substrate, 94.9 parts of a polymerizable liquid crystal compound having a birefringence Δn of 0.18, 5.1 parts of a chiral agent (LC756 manufactured by BASF), a polymerization initiator (IRGACURE907 manufactured by Ciba Specialty Chemicals) 3.1 parts and 0.1 part of a surfactant (Surflon KH-40, manufactured by Seimi Chemical Co., Ltd.) are dissolved in methyl ethyl ketone so as to have a solid content of 40%, and then a polytetrafluoroethylene syringe having a pore diameter of 0.45 μm A polymerizable solution obtained by filtration through a filter was applied, dried, and then cured by irradiating with ultraviolet rays in the same manner as above to form an optical element P2 having a thickness of 4 μm and having a cholesteric resin layer. ,
The optical element P1 is superposed so that the side with the larger pitch of the chiral structure of the cholesteric resin layer and the side with the smaller pitch of the chiral structure of the cholesteric resin layer of the optical element P2 face each other and have a total thickness of 7 μm. A circularly polarized light separating sheet having a cholesteric resin layer was obtained. This circularly polarized light separating sheet had a wavelength band of 405 to 743 nm for reflecting light with an incident angle of 0 degree by 30% or more.
The pitch of the chiral structure of the obtained optical elements P1 and P2 was confirmed by SEM observation. As for the optical elements P1 and P2, the pitch of the chiral structure was continuous from the surface on one side to the surface on the other side. It was changing. In addition, the average value of the pitch length of the chiral structure of the optical element was larger in the optical element P2 than in the optical element P1.

A polarized light source device was obtained by placing a circularly polarized light separating sheet and a polarizing plate (X) in this order on a backlight unit comprising a light reflecting plate, a cold cathode tube, a diffusion plate and a prism sheet. At this time, the surface of the circularly polarized light separating sheet having the larger pitch in the chiral structure and the surface of the polarizing plate (X) on the quarter wavelength plate (C) side were opposed to each other (of the circularly polarized light separating sheet). The surface on the cholesteric resin layer side of the optical element P1 is set to the cold cathode tube side). This polarized light source device has an ergoscope measurement in all directions at polar angles of 0 ° to 70 °. The x component variation Δx is 0.032, the y component variation Δy is 0.039, and the front luminance ratio is Was 1.25. The polar angle means an angle when tilted from the front direction when observing the polarized light source device. Further, it is shown that the smaller the chromaticity variations Δx and Δy, the better. The front luminance ratio is a ratio to luminance in a polarized light source device in which only a polarizer is placed on the backlight unit.
Furthermore, on the backlight unit composed of a light reflection plate, a cold cathode tube, a diffusion plate and a prism sheet, a circularly polarized light separating sheet, a polarizing plate (X), a liquid crystal cell, and a polarizing plate (Y) are placed in this order. A liquid crystal display device was obtained. Even when this liquid crystal display device was observed from an oblique direction, the color was the same as that observed from the front direction, and the screen was not colored.

Example 2
An experiment was performed in the same manner as in Example 1 except that the film thickness of the cholesteric resin layer P1 was 2 μm and the film thickness of the cholesteric resin layer P2 was 3 μm by adjusting the coating amount of the polymerizable solution. In addition, the obtained circularly polarized light separating sheet had a wavelength band for reflecting light of an incident angle of 0 degree by 30% or more of 410 to 738 nm.
In the same manner as in Example 1, a polarized light source device was obtained, and chromaticity variation and front luminance ratio were measured with an ergoscope. Δx was 0.027, Δy was 0.030, and the front luminance ratio was 1.21. Moreover, the liquid crystal display device was obtained similarly to Example 1, and the display performance was confirmed. Even when the liquid crystal display device was observed from an oblique direction, the color was the same as that observed from the front direction, and the screen was not colored.

Example 3
One side of a ZEONOR film (ZF14-100 manufactured by Nippon Zeon Co., Ltd.) was corona discharged, and then a 5% by weight aqueous solution of polyvinyl alcohol (Kuraray Co., Poval MP203) was applied to the surface, dried at 100 ° C. for 3 minutes, and felted. The base material which laminated | stacked the orientation film | membrane on the surface was obtained by rubbing with a roll.
93.9 parts of a polymerizable liquid crystal compound having a birefringence Δn of 0.20, 6.1 parts of a chiral agent (LC756 manufactured by BASF), 3.1 parts of a polymerization initiator (IRGACURE907 manufactured by Ciba Specialty Chemicals), and an interface 0.1 part of an activator (Surflon KH-40, manufactured by Seimi Chemical Co., Ltd.) is dissolved in methyl ethyl ketone so as to have a solid content of 40%, and is filtered through a polytetrafluoroethylene syringe filter having a pore size of 0.45 μm. A solution was obtained.
This polymerizable solution was applied to the surface of the base material provided with the alignment film and dried to obtain a coating film. The ultraviolet coating film was 40 mJ / cm ² irradiated with UV-A standards, and left to 100 ° C. oven for 3 minutes, then ultraviolet rays to cure the coated film was irradiated 300 mJ / cm ² in UV-A standard A cholesteric resin layer P3 having a thickness of 2 μm was formed.
In another substrate, 94.9 parts of a polymerizable liquid crystal compound having a birefringence Δn of 0.20, 5.1 parts of a chiral agent (LC756 manufactured by BASF), a polymerization initiator (IRGACURE907 manufactured by Ciba Specialty Chemicals) 3 .1 part and 0.1 part of a surfactant (manufactured by Seimi Chemical Co., Surflon KH-40) are dissolved in methyl ethyl ketone so as to have a solid content of 40%, and are added to a polytetrafluoroethylene syringe filter having a pore diameter of 0.45 μm. And filtered to obtain a polymerizable solution.
This polymerizable solution was applied to the surface of the base material provided with the alignment film and dried to obtain a coating film. The ultraviolet coating film was 40 mJ / cm ² irradiated with UV-A standards, and left to 100 ° C. oven for 3 minutes, then ultraviolet rays to cure the coated film was irradiated 300 mJ / cm ² in UV-A standard A cholesteric resin layer P4 having a thickness of 2 μm was formed.
The pitch of the chiral structure of the obtained optical elements P3 and P4 was confirmed by SEM observation. As for the optical elements P3 and P4, the chiral structure pitch was continuous from the surface on one side to the surface on the other side. It was changing. Moreover, the average value of the pitch length of the chiral structure of the optical element was larger in the optical element P4 than in the optical element P3.
Circularly polarized light separation having a cholesteric resin layer with a total thickness of 4 μm bonded so that the side with the larger pitch of the chiral structure of the cholesteric resin layer P3 faces the side with the smaller pitch of the chiral structure of the cholesteric resin layer P4 A sheet was obtained. This circularly polarized light separating sheet had a wavelength band for reflecting 30% or more of light rays with an incident angle of 0 degrees of 402 to 746 nm. In the same manner as in Example 1, a polarized light source device was obtained, and chromaticity variation and front luminance ratio were measured with an ergoscope. Δx was 0.022, Δy was 0.024, and the front luminance ratio was 1.22. Moreover, the liquid crystal display device was obtained similarly to Example 1, and the display performance was confirmed. Even when the liquid crystal display device was observed from an oblique direction, the color was the same as that observed from the front direction, and the screen was not colored.

Example 4
A diffusion sheet (Opulse PSS-010 manufactured by Ewasha Co., Ltd.) was bonded to the circularly polarized light separating sheet obtained in Example 3. In the same manner as in Example 1, a circularly polarized light separating sheet, a polarizing plate (a polarizing plate) in which the diffusion sheet is bonded onto the backlight unit including the light reflection plate 20, the cold cathode tube 19, the diffusion plate 18, and the prism sheet 17 The polarized light source device was obtained by placing in the order of X). At this time, the diffusion sheet was disposed between the circularly polarized light separating sheet and the polarizing plate (X). As a result of measuring the variation in chromaticity and the front luminance ratio, Δx: 0.017, Δy: 0.019, and front luminance ratio 1.20. In addition, a circularly polarized light separating sheet, a polarizing plate (X), a liquid crystal cell, and a polarized light obtained by bonding the diffusion sheet on the backlight unit including the light reflection plate 20, the cold cathode tube 19, the diffusion plate 18, and the prism sheet 17. The plate (Y) was placed in this order to obtain a liquid crystal display device. At this time, the diffusion sheet was disposed between the circularly polarized light separating sheet and the polarizing plate (X). As a result of confirming the display performance, even when observed from an oblique direction, the color was the same as that observed from the front direction, and the screen was not colored.

Comparative Example 1
94.0 parts of a polymerizable liquid crystal compound having a birefringence Δn of 0.14, 5.9 parts of a chiral agent (LC756 manufactured by BASF), 3.1 parts of a polymerization initiator (IRGACURE907 manufactured by Ciba Specialty Chemicals), and an interface 0.1 parts of an activator (Surflon KH-40, manufactured by Seimi Chemical Co., Ltd.) is dissolved in methyl ethyl ketone so as to have a solid content of 40%, and then filtered through a polytetrafluoroethylene syringe filter having a pore size of 0.45 μm to polymerize. Sex solution was obtained.
This polymerizable solution was applied to the surface of the base material provided with the alignment film and dried to obtain a coating film. The coating film is irradiated with ultraviolet rays at 0.2 mJ / cm ² on a UV-A basis, left in an oven at 100 ° C. for 3 minutes, and then irradiated with ultraviolet rays at 300 mJ / cm ² on a UV-A basis to cure the coating film. Thus, a cholesteric resin layer P5 having a thickness of 4 μm was formed.
In another substrate, 95.3 parts of a polymerizable liquid crystal compound having a birefringence Δn of 0.14, 4.7 parts of a chiral agent (LC756 manufactured by BASF), and a polymerization initiator (IRGACURE907 manufactured by Ciba Specialty Chemicals) 3 .1 part and 0.1 part of a surfactant (Surflon KH-40, manufactured by Seimi Chemical Co., Ltd.) were dissolved in methyl ethyl ketone so as to have a solid content of 40%, and then a syringe filter made of polytetrafluoroethylene having a pore size of 0.45 μm To obtain a polymerizable solution.
This polymerizable solution was applied to the surface of the base material provided with the alignment film and dried to obtain a coating film. The coating film is irradiated with ultraviolet rays at 0.2 mJ / cm ² on a UV-A basis, left in an oven at 100 ° C. for 3 minutes, and then irradiated with ultraviolet rays at 300 mJ / cm ² on a UV-A basis to cure the coating film. Thus, a cholesteric resin layer P6 having a thickness of 5 μm was formed.
Furthermore, 96.1 parts of a polymerizable liquid crystal compound having a birefringence Δn of 0.14, 3.9 parts of a chiral agent (LC756 manufactured by BASF), a polymerization initiator (IRGACURE907 manufactured by Ciba Specialty Chemicals) ) 3.1 parts and 0.1 part of a surfactant (Surflon KH-40, manufactured by Seimi Chemical Co., Ltd.) were dissolved in methyl ethyl ketone so as to have a solid content of 40%, and then made of polytetrafluoroethylene having a pore size of 0.45 μm Filtration with a syringe filter gave a polymerizable solution.
This polymerizable solution was applied to the surface of the base material provided with the alignment film and dried to obtain a coating film. The coating film is irradiated with ultraviolet rays at 0.2 mJ / cm ² on a UV-A basis, left in an oven at 100 ° C. for 1 to 5 minutes, and then irradiated with ultraviolet rays at 300 mJ / cm ² on a UV-A basis. The film was cured to form a cholesteric resin layer P7 having a thickness of 6 μm.
When the pitch of the chiral structure of the obtained optical elements P5, P6 and P7 was confirmed by SEM observation, the optical elements P5, P6 and P7 had a chiral structure pitch from the surface on one side to the surface on the other side. It was changing continuously toward. Moreover, the average value of the pitch length of the chiral structure of the optical element was optical element P7, optical element P6, and optical element P5 in order from the largest.
The one where the pitch of the chiral structure of the cholesteric resin layer P5 is larger and the side of the cholesteric resin layer P6 where the pitch of the chiral structure is larger and the side where the pitch of the chiral structure of the cholesteric resin layer P6 is smaller. Of the cholesteric resin layer P7 so that the side with the smaller pitch of the chiral structure faces each other to obtain a circularly polarized light separating sheet having a cholesteric resin layer with a total thickness of 15 μm. This circularly polarized light separating sheet had a wavelength band of 412 to 738 nm for reflecting a light beam having an incident angle of 0 degree by 30% or more.
In the same manner as in Example 1, a polarized light source device was obtained, and chromaticity variation and front luminance ratio were measured with an ergoscope. Δx was 0.047, Δy was 0.069, and the front luminance ratio was 1.27. Further, as in Example 1, the display performance of the liquid crystal display device was confirmed. When this liquid crystal display device was observed from an oblique direction, the hue was different from that observed from the front direction, and the screen was seen as yellow as a whole.

Comparative Example 2
Comparative Example 1 except that the film thickness of the cholesteric resin layer P5 is 2 μm, the film thickness of the cholesteric resin layer P6 is 2 μm, and the film thickness of the cholesteric resin layer P7 is 3 μm by adjusting the coating amount of the polymerizable solution. The experiment was conducted. The obtained circularly polarized light separating sheet had a wavelength band of 419 to 731 nm for reflecting light having an incident angle of 0 degree by 30% or more.
In the same manner as in Example 1, a polarized light source device was obtained, and chromaticity variation and front luminance ratio were measured with an ergoscope. Δx was 0.037, Δy was 0.040, and the front luminance ratio was 1.07. Moreover, the liquid crystal display device was obtained similarly to Example 1, and the display performance was confirmed. Even when this liquid crystal display device was observed from an oblique direction, the color was the same as that observed from the front direction, and the screen was not colored. However, the screen display of the liquid crystal display device obtained in Comparative Example 2 was significantly darker than the liquid crystal display devices obtained in Examples 1 to 4 and Comparative Example 1.

As shown in Table 1, from the results of Examples 1 to 4, when a polymerizable liquid crystal compound having Δn of 0.18 or more is used and the total thickness of the resin layer having cholesteric regularity is 7 μm or less, the visible light region (400 It can be seen that the light can be selectively reflected at ˜750 nm, and the chromaticity variation and luminance are also improved. In particular, in Examples 2 to 4 in which the total thickness is smaller than that of Example 1, it can be seen that the variation in chromaticity is small. Further, it can be seen from Example 3 that when Δn is large and the total thickness is small, the front luminance ratio is high and the chromaticity variation is small. It can also be seen that when the circularly polarized light separating sheet is provided with light diffusibility, the variation in chromaticity is further improved as compared to Example 3 (Example 4).
On the other hand, it can be seen that the dispersion of chromaticity increases in a resin layer having a cholesteric regularity of 15 μm in total thickness using a polymerizable liquid crystal compound having Δn of 0.14 (Comparative Example 1). It can also be seen that the front luminance ratio does not increase in a resin layer having a cholesteric regularity of 7 μm in total thickness using a polymerizable liquid crystal compound having Δn of 0.14 (Comparative Example 2).

It is a figure which shows an example of the circularly polarized light separation sheet of this invention. It is a figure which shows the structural example of the liquid crystal display device of this invention.

Explanation of symbols

1: Base material 2: Alignment film 3: Cholesteric resin layer 11: Polarizer A
12: Liquid crystal cell 13: Polarizer B
14: 1/4 wavelength plate 15: Phase compensation element 21: Circularly polarized light separating sheet 16: Base material 17: Cholesteric resin layer 18: Diffuser 19: Cold cathode tube 20: Light reflector

Claims (13)

A circularly polarized light separating sheet having a cholesteric regularity and having a resin layer having a total thickness of 7 μm or less, obtained by using a polymerizable liquid crystal compound having a birefringence Δn of 0.18 or more.   The circularly polarized light separating sheet according to claim 1, wherein the resin layer is non-liquid crystalline.   The circularly polarized light separating sheet according to claim 1, wherein the cholesteric regularity is in the thickness direction.   The circularly polarized light separating sheet according to claim 3, wherein the cycle of cholesteric regularity changes stepwise in the thickness direction.   The circularly polarized light separating sheet according to claim 4, wherein the resin layer is formed of two or more layers having different cholesteric regularity periods.   The circularly polarized light separating sheet according to claim 3, wherein the cycle of cholesteric regularity continuously changes in the thickness direction.   The circularly polarized light separating sheet according to claim 1, wherein the resin layer has an average refractive index of 1.5 to 1.8.   The circularly polarized light separating sheet according to any one of claims 1 to 7, wherein the maximum wavelength of light with an incident angle of 0 degrees at which the reflectance is 30% or more is 700 nm or more.   A solution containing a polymerizable liquid crystal compound having a birefringence Δn of 0.18 or more is applied to a substrate, and then the polymerizable liquid crystal compound is polymerized by irradiating with ultraviolet rays, and has a total thickness of 7 μm having cholesteric regularity. The manufacturing method of the circularly polarized light separation sheet | seat including forming the following resin layers. Polarizer A,
Liquid crystal cell,
Polarizer B,
The liquid crystal display device which has a quarter wave plate and the circularly-polarized-light separation sheet in any one of Claims 1-8 in this order.   The liquid crystal display device according to claim 10, wherein the polarizer B and the quarter-wave plate are integrated.   The liquid crystal display device according to claim 10, wherein the circularly polarized light separating sheet has a light diffusibility on a surface on a quarter wavelength plate side. The liquid crystal display device according to claim 10, further comprising a diffusion sheet between the circularly polarized light separating sheet and the quarter-wave plate.

Images