JP2006064758A - Optical laminated body, its manufacturing method and luminance improving film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical laminated body having a liquid crystal layer in a prescribed aligned state, which is excellent in selective reflection efficiency, and its manufacturing method, and to provide a luminance improving film using the optical laminated body, and a polarizing light source device and a liquid crystal display device. <P>SOLUTION: The luminance improving film includes the optical laminated body having two or more liquid crystal layers, all of which are layers (b) formed to partially include a part where a screw axis and a layer normal are not nearly parallel by deforming a cholesteric liquid crystal layer (a) after forming the cholesteric liquid crystal layer (a) so that the screw axis and the layer normal may be nearly parallel, a phase difference element in which Rth defined by an expression: Rth=[(nx+ny)/2-nz]×d (provided that nx is a maximum refractive index on a plane, ny is a refractive index in an axial direction orthogonal to nx on the plane, nz is a refractive index in a thickness direction, and d is the thickness of the phase difference element) is -20nm to -1,000nm, and a 1/4 wavelength plate. The polarizing light source device and the liquid crystal display device equipped with the luminance improving film are provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical laminate having two or more liquid crystal layers and a brightness enhancement film using the optical laminate.

  A polarizing plate is used in the liquid crystal display device. The light passing through this polarizing plate is only unidirectionally polarized light. Therefore, it is theoretically impossible for the light passing through the polarizing plate to exceed 50% of the incident light. A brightness enhancement film is known as a film for increasing the utilization efficiency of incident light to a liquid crystal panel and increasing the brightness of a liquid crystal display device. This brightness enhancement film is composed of a polarization separation film for separating incident light into transmitted light and reflected light according to the polarization state, and the light reflected by the polarization separation film is reflected by a reflecting plate or the like to form a polarization separation film. It is used to re-enter and reuse light.

  Examples of the polarization separation film include a linear polarization separation film in which a large number of anisotropic polymer layers are stacked (for example, see Patent Document 1) and a circular polarization separation film using a cholesteric liquid crystal layer (for example, Patent Document 2, Patent Document 3 and Patent). Reference 4) is known. Among these, the linearly polarized light separating film needs to be laminated with hundreds of anisotropic polymer layers and is very expensive.

  The latter circularly polarized light separation film has a so-called cholesteric phase liquid crystal layer in addition to the characteristics of nematic liquid crystal having the property that molecules are oriented in a certain direction. This cholesteric phase has a characteristic of separating circularly polarized light into transmitted light and reflected light according to the direction of rotation of the spiral structure, and the circularly polarized light separating film utilizes this characteristic. Since the circularly polarized light separating film composed of a simple cholesteric phase liquid crystal layer has a wavelength range of selective reflection of only a few tens of nanometers, the circularly polarized light separating film for a brightness enhancement film performs circularly polarized light separation over the entire visible light region. In addition, the reflection region is widened in the visible region.

  As methods for widening the bandwidth, there are known (Method 1) a method of laminating a plurality of liquid crystal layers having different selective reflection bands, and (Method 2) a method of gradually changing the helical pitch of the cholesteric liquid crystal layer in the thickness direction. It has been. However, the present situation is that both methods still have problems regarding productivity and cost.

Japanese Patent Laid-Open No. 9-506837 JP-A-8-271731 JP-A-6-281814 JP 11-248942 A

  The present invention has been made in view of such a background art, and is excellent in productivity, can be made at low cost, and has an excellent polarization separation characteristic, a method for manufacturing the same, and the manufacturing method thereof. The object of the present invention is to provide a brightness enhancement film using an optical laminate.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors are optical laminates having two or more liquid crystal layers, and each of the liquid crystal layers has a helical axis and a layer normal line substantially parallel to each other. An optical laminate which is a layer (b) formed by forming a cholesteric liquid crystal layer (a) so that the layer is deformed so as to partially include a portion where the helical axis and the layer normal are not substantially parallel As a result, it was found that a brightness enhancement film having excellent productivity and low cost and having excellent polarization separation characteristics can be obtained, and the present invention has been completed.

Thus, according to the present invention,
(1) An optical layered body having two or more liquid crystal layers, and after forming the cholesteric liquid crystal layer (a) so that the spiral axis and the layer normal line are substantially parallel to each other. An optical laminated body which is a layer (b) formed by deforming the layer so as to partially include a portion where the spiral axis and the layer normal are not substantially parallel.
(2) The optical laminate according to item (1), wherein at least one set of laminated cholesteric liquid crystal layers is in contact.
(3) A method for producing an optical laminate having two or more liquid crystal layers, wherein (A) the step of forming the cholesteric liquid crystal layer (a) so that the helical axis and the layer normal are substantially parallel to each other; B) A step of deforming the liquid crystal layer (a) so as to include a part in which the spiral axis and the layer normal are not substantially parallel; (C) a part in which the spiral axis and the layer normal are not substantially parallel; A method for producing an optical layered body comprising a step of laminating the cholesteric liquid crystal layer (b) formed so as to include two or more layers.
(4) The method for producing an optical laminate according to the item (3), wherein the step (C) is laminated so that at least one pair of cholesteric liquid crystal layers is in contact.
(5) In the step (B), a member having a convex portion in the surface is brought into contact with the cholesteric liquid crystal layer (a) formed in the step (A), and the liquid crystal layer (a) is deformed to form a spiral axis and a layer. The method for producing an optical layered product according to item (3) or (4), which is a step of including a part that is not substantially parallel to the normal line.
(6) The optical laminate according to (1) or (2) and the formula: Rth = [(nx + ny) / 2−nz] × d (where nx is the maximum refractive index in the plane, ny is A retardation element in which Rth is defined as -20 nm to -1000 nm defined by the refractive index in the axial direction orthogonal to nx in the plane, nz is the refractive index in the thickness direction, and d is the thickness of the retardation element. A brightness enhancement film comprising a quarter wave plate.
(7) A polarized light source device comprising the brightness enhancement film according to item (6).
(8) A liquid crystal display device comprising the polarized light source device according to item (7).

According to the present invention, it is possible to provide an optical laminate that is excellent in productivity, low in cost, and excellent in polarization separation characteristics over a wide wavelength region, and a method for manufacturing the same.
Further, according to the present invention, a brightness enhancement film that is suitably used as a backlight of a liquid crystal display device having high brightness and good viewing angle characteristics, a polarized light source device using the same, excellent brightness, and viewing field A liquid crystal display device with favorable angular dependency can be provided.

  The optical layered body of the present invention is an optical layered body having two or more liquid crystal layers, and each of the liquid crystal layers has a cholesteric liquid crystal layer (a The layer (b) is formed by deforming the layer after forming a part so that the spiral axis and the layer normal are not substantially parallel.

  The term “substantially parallel” means that the angle formed between the spiral axis and the layer normal is within ± 10 ° over the entire thickness direction from one surface of the cholesteric layer to the other surface.

  The production method of the present invention is a method for producing an optical laminate having two or more liquid crystal layers, wherein (A) the cholesteric liquid crystal layer (a) is formed so that the helical axis and the layer normal line are substantially parallel. (B) a step of deforming the liquid crystal layer (a) so as to include a part in which the spiral axis and the layer normal are not substantially parallel; (C) the spiral axis and the layer normal; The method includes a step of laminating the cholesteric liquid crystal layer (b) formed so as to partially include a portion that is not substantially parallel, so that two or more layers are formed. The production method of the present invention is particularly optimal for the production of the optical laminate of the present invention.

  In the step (A), the cholesteric liquid crystal layer (a) is formed so that the spiral axis and the layer normal line are substantially parallel. The cholesteric liquid crystal layer (a) can be formed by applying a coating liquid appropriately containing a cholesteric liquid crystal compound, a solvent, a polymerization initiator and the like on a substrate. Further, a surfactant, an alignment adjusting agent, etc. can be added to the coating solution as necessary.

  The cholesteric liquid crystal compound here is a compound or composition exhibiting cholesteric liquid crystallinity. For example, a cholesteric liquid crystal compound containing an optically active site alone, a composition of a cholesteric liquid crystal compound containing an optically active site and a chiral agent that is an optically active material, a nematic liquid crystal that does not have an optically active site, and an optical activity Examples include a composition with a chiral agent as a substance.

As the liquid crystal compound, a rod-like liquid crystal compound having a polymerizable functional group introduced in the molecule, a discotic liquid crystal compound, a polymer liquid crystal, or the like can be used.
Examples of the rod-like liquid crystal compound include compounds represented by the formula [1]: R1-L1-S1-L3-M-L4-S2-L2-R2.
In formula [1], R1 and R2 represent a polymerizable group. Specific examples of R1 and R2 include (r-1) to (r-15) shown below, but are not limited thereto.

  L1, L2, L3 and L4 each independently represent a single bond or a divalent linking group, and it is preferable that at least one of L3 and L4 is —O—CO—O—. S1 and S2 represent a spacer group having 2 to 20 carbon atoms, and M represents a mesogenic group. The mesogenic group M includes azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexyl carboxylic acid phenyl esters, cyanophenyl cyclohexanes, cyano substituted phenyl pyrimidines, alkoxy substituted phenyl pyrimidines, phenyl Dioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.

As discotic liquid crystalline compounds, various documents [C. Destrade et al. Mol. Cryst. Liq. Cryst. , vol. 71, page 111 (1981); edited by The Chemical Society of Japan, Quarterly Chemical Review, No. 22, Liquid Crystal Chemistry, Chapter 5, Chapter 10, Section 2 (1994); Liquid Crystal Handbook Editorial Committee, Liquid Crystal Handbook, Chapter 2, Section 2.1.1 (2000)] In addition, the same linking group, spacer group, and polymerization group as those described for the rod-like liquid crystal compound can be used.
As the polymer liquid crystal, those described in the edited edition of the Liquid Crystal Handbook, the Liquid Crystal Handbook, Chapter 3, Section 3.8 (2000) can be used, but are not limited thereto. Both main chain polymer liquid crystals and side chain polymer liquid crystals can be used.

The chiral agent is not particularly limited, and conventionally known agents can be used. Examples thereof include a chiral monomer described in JP-A-6-281814, a chiral agent described in JP-A-8-209127, and a photoreactive chiral compound described in JP-A-2003-131187.
As the chiral agent, in order to avoid an unintended change in the phase transition temperature of the composition exhibiting cholesteric liquid crystallinity, the chiral agent itself exhibits liquid crystallinity. Further, from the viewpoint of economy, those having a large HTP defined by the formula (II): HTP = 1 / P · c, which is an index representing the efficiency of twisting the liquid crystal compound, are preferable. Here, P represents the pitch length of the spiral of the cholesteric phase, and c represents the concentration of the chiral agent.

  As the solvent used in the coating solution, an organic solvent that dissolves the liquid crystal compound is preferably used. 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.

  Examples of the polymerization initiator include a thermal polymerization initiator and a photopolymerization initiator, and a photopolymerization initiator is preferred. Examples of photopolymerization initiators include aryl ketones such as acetophenones, benzophenones, alkylaminobenzophenones, benzyls, benzoins, benzoin ethers, benzyldimethylacetals, benzoylbenzoates, α-acyloxime esters Examples include initiators, sulfur-containing photopolymerization initiators such as sulfides and thioxanthones, and photopolymerization initiators such as acylphosphine oxides and anthraquinones. One or more photopolymerization initiators can be appropriately selected and used. It is preferable that the usage-amount of a photoinitiator is 0.01-20 weight% of solid content of a coating liquid. More preferably, it is 0.5 to 5% by weight.

  A surfactant can be used to adjust the surface tension of the coating liquid and the cholesteric liquid crystal layer (a) before the start of polymerization. Nonionic surfactants are preferred, and those composed of oligomers having a molecular weight of about several thousand are particularly preferred.

  The alignment regulator is for controlling the alignment state of the air interface of the cholesteric liquid crystal layer (a) formed on the substrate, and may also serve as the surfactant. As the alignment regulator, polyvinyl alcohol, polyvinyl butyral, or a modified product thereof is used, but not limited thereto.

  The substrate used for the production of the optical laminate is not particularly limited as long as it is an optically transparent substrate, but is preferably optically isotropic in order to avoid unnecessary changes in the polarization state. Examples of such a transparent substrate include a transparent resin film and a glass substrate. From the viewpoint that the liquid crystal layer can be produced efficiently, a long transparent resin film is more preferable. The transparent resin film may be a single layer film or a laminated film, but preferably has a total light transmittance of 80% or more at a thickness of 1 mm.

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

  The alicyclic structure-containing polymer has an alicyclic structure in the repeating unit of the polymer, and is a polymer having an alicyclic structure in the main chain and a polymer having an alicyclic structure in the side chain. Either can be used. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, but 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 5-15 pieces.

The amount of the repeating unit having an alicyclic structure in the polymer having an alicyclic structure is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more. If the number of repeating units having an alicyclic structure is too small, the heat resistance may be lowered.
Examples of the polymer having an alicyclic structure include norbornene polymers, monocyclic olefin polymers, cyclic conjugated diene polymers, vinyl alicyclic hydrocarbon polymers, and hydrogenated products thereof. . Among these, norbornene-based polymers are more preferable from the viewpoints of transparency and moldability.

Norbornene-based polymers include ring-opening polymers of norbornene-based monomers, ring-opening copolymers of norbornene-based monomers with other monomers that can be ring-opened copolymerized, hydrogenated products thereof, addition weights of norbornene-based monomers. Examples thereof include addition copolymers and addition copolymers of norbornene monomers and other monomers capable of addition copolymerization. Among these, from the viewpoint of heat resistance and transparency, a ring-opening polymer hydrogenated product of a norbornene-based monomer is most preferable.
The polymer having the above alicyclic structure is selected from known polymers disclosed in, for example, JP-A-2002-321302.

  It is desirable to provide an alignment layer for aligning the cholesteric liquid crystal compound on the substrate. The alignment layer can be provided by means such as rubbing treatment of a polymer film for alignment film, oblique vapor deposition of an inorganic compound, formation of a microgroup, or formation of an organic film by Langmuir-Blodgett method. Furthermore, it is also possible to use an alignment film in which an alignment function is generated by application of an electric field or a magnetic field or light irradiation. Further, in order to impart adhesion between the base material and the alignment layer, it is preferable to perform surface treatment on the base material in advance, and means for this purpose include glow discharge treatment, corona discharge treatment, ultraviolet (UV) treatment, flame treatment, etc. Is mentioned. It is also effective to provide an adhesive layer (undercoat layer) between the substrate and the alignment layer.

  From the viewpoint of continuous treatment, an alignment layer formed by rubbing the polymer film for alignment film is preferable. The rubbing treatment is achieved by rubbing the surface of the polymer film with a cloth in a certain direction. As the type of polymer for the alignment film used as such an alignment layer, a polymer suitable for production conditions can be selected from those capable of providing an alignment function. The alignment layer preferably has a polymerizable group for the purpose of imparting adhesion between the liquid crystal compound and the substrate. The thickness of the alignment layer is preferably 0.001 to 5 μm, and more preferably 0.01 to 2 μm.

  The method for coating the alignment film polymer coating solution on the substrate is not particularly limited, and spin coating, roll coating, flow coating, printing, dip coating, casting film forming, bar coating A known coating method such as a method or a gravure printing method can be employed.

  Further, the method for forming the cholesteric liquid crystal layer (a) in which the spiral axis and the layer normal line are substantially parallel was selected from the above-described known coating methods as the coating liquid for the cholesteric liquid crystal layer on the substrate. A cholesteric liquid crystal layer (a) can be formed by applying by the method and drying / heating the resulting coating layer. The temperature of heat processing is the temperature range used as a cholesteric phase.

  It is preferable that the cholesteric liquid crystal layer (a) in which the spiral axis and the layer normal are substantially parallel maintain the spiral structure of the cholesteric phase itself as much as possible in consideration of the subsequent step (B). For this purpose, it is preferable to fix the cholesteric liquid crystal layer (a) whose spiral axis and layer normal are substantially parallel to some extent. This fixing method includes a method of fixing by heating or irradiating with a cholesteric liquid crystal compound using a kind of polymerized group and a number of polymerized groups per molecule, a non-polymerizable liquid crystal and a polymerizable liquid crystal. By heating or light irradiation using a mixture of and a polymer liquid crystal, and by rapidly cooling when a cholesteric liquid crystal layer is formed in which the helical axis and the layer normal are substantially parallel Examples of the method include immobilization.

  The thickness of the cholesteric liquid crystal layer (a) obtained in the step (A) is usually 1 to 50 μm, preferably 2 to 30 μm, more preferably 2 to 10 μm, considering the function as a broadband circularly polarized light separating film. The total thickness of the substrate and the cholesteric liquid crystal layer (a) is usually 20 to 200 μm, preferably 25 to 150 μm, and more preferably 30 to 100 μm.

In the method of fixing by heating or light irradiation, when using a thermal polymerization initiator as a polymerization initiator, the coating layer is heated to a predetermined temperature, and when using a photopolymerization initiator, The liquid crystal compound can be polymerized by irradiating the coating layer with light. From the viewpoint of rapidity, a method using light irradiation is preferable, and a method using ultraviolet rays is more preferable. Light irradiation energy is usually ^{1mJ / cm 2 ~50J / cm 2} , it is preferable that 1~800mJ / cm ^2.

  FIG. 1 shows a schematic diagram of the cholesteric liquid crystal layer (a) in which the spiral axis and the layer normal produced in the step (A) are substantially parallel.

  The step (B) is a step in which the liquid crystal layer (a) is deformed to include a portion where the helical axis and the layer normal are not substantially parallel.

  When light is incident on the cholesteric liquid crystal layer (a) 1 in which the spiral axis and the layer normal are substantially parallel, the reflection characteristic (selective reflection) is exhibited with respect to either left or right circularly polarized light in a specific wavelength region. It is known. This will be described with reference to FIG. When the incident light is incident at the incident angle θ1, the white incident light L1 is refracted in the liquid crystal layer (a) 1 and when the incident angle θ2 is reached, the circularly polarized light L2 is selectively reflected by the liquid crystal layer (a). When the spiral axis 4 representing the rotation axis when the liquid crystal compound is twisted is perpendicular to the layer, the layer normal 3 and the spiral axis 4 are substantially parallel.

  The central wavelength λ of the circularly polarized light L2 subjected to selective reflection is expressed by the formula (III): λ = n × P × cos θ2, and the reflection band is expressed by the formula (IV): no × P × cos θ2 ≦ λ ≦ ne × P × cos θ2. It is represented by In the formula, no represents the refractive index in the minor axis direction of the rod-like liquid crystalline compound, ne represents the refractive index in the major axis direction of the rod-like liquid crystalline compound, P represents the helical pitch length, and n = (ne + no) / 2. Represents.

  As is clear from the formula (IV), the wavelength of the reflected light with respect to the light incident obliquely is shorter than the wavelength of the reflected light with respect to the light incident parallel (θ2 = 0) to the helical axis. Shift to the side. As a result, the transmission spectrum 5 with respect to light incident obliquely with respect to the helical axis has a peak position shifted to the short wave side with respect to the transmission spectrum 6 with respect to light incident in the parallel direction (θ2 = 0). This is shown in FIG. In FIG. 3, the horizontal axis indicates the measurement wavelength (nm), and the vertical axis indicates the light transmittance (%) when non-polarized light is incident.

Here, considering that the wavelength region Δλ of the reflection band is expanded to the entire visible region, there is a method of controlling cos θ2 in the above formula (IV). In the above formula (IV), θ2 is the angle formed between the incident light inside the liquid crystal and the helical axis, so the helical axis of the liquid crystal layer is inclined so that θ2 gradually changes along the path of the incident light inside the layer. In the case of the structure, the incident light is considered to have different reflection bands in different θ2 regions on the path.
As shown in the equations (III), (IV), and FIG. 3, the incident angle dependence of the wavelength of the selectively reflected light shifts to the shorter wavelength side as the incident angle, that is, θ2, increases. By adjusting the tilt angle and the helical pitch length over the entire path of incident light, it is possible to broaden the bandwidth. This is shown in FIG. FIG. 4 shows a state in which the angle θ2 formed by the spiral axis and L1 changes as a, b, and c (a>b> c) as the incident light L1 travels through the liquid crystal layer. Since the wavelength of the selectively reflected light is shifted to the shorter wavelength side as θ2 is larger, the wavelength of each reflected light is shorter when θ2 = a than when θ2 = c. Therefore, by setting the helical pitch length to the long wavelength side of visible light and controlling the tilt angle of the helical axis of the liquid crystal layer to reflect to the short wavelength side of visible light, it is possible to widen the band.

  For example, when the spiral pitch length P is set to 470 nm and n is set to 1.5, the tilt angle range necessary for tilting the spiral axis of the cholesteric liquid crystal layer to achieve a broad band with respect to visible light is expressed by the formula ( III) to θ2 (700) (inclination angle of the helical axis at 700 nm that is the upper limit wavelength of the reflection band) and θ2 (400) (inclination angle of the helical axis at 400 nm that is the lower limit wavelength of the reflection band) are θ2 ( 700) ≈0 ° and θ2 (400) ≈56 °. Therefore, it is preferable that the inclination θ2 of the spiral axis of the liquid crystal layer with respect to the traveling direction of incident light inside the layer has a distribution including at least 0 ° to 56 °.

  Therefore, in the present invention, a method of applying the step (B) after the step (A) is adopted. According to this method, a part in which the spiral axis and the layer normal are not substantially parallel can be included in a simple and reliable manner.

  The method in the step (B) is not particularly limited as long as it includes a portion in which the spiral axis and the layer normal are not substantially parallel. For example, a method in which an alignment layer having a function of aligning molecules of a liquid crystal compound obliquely with respect to a layer normal is brought into contact with the cholesteric liquid crystal layer produced in the step (A) from the reverse direction of the substrate, and particles (A) Examples thereof include a method of adding the cholesteric liquid crystal layer produced in the step from the reverse direction of the substrate, a method of bringing a member having a convex portion in the surface into contact with the cholesteric liquid crystal layer produced in the step (A), and the like. In view of the ease of controlling the tilt of the liquid crystal layer and the uniformity of orientation, a method in which a member having a convex portion in the surface is brought into contact with the cholesteric liquid crystal layer in which the spiral axis and the layer normal are substantially parallel is preferably mentioned. Can do.

  The material of the member having a convex portion in the surface is not particularly limited as long as it can be processed to be uneven, but an optically transparent material having a small phase difference due to birefringence is preferable. . As the optically transparent material that is optically isotropic with a small phase difference due to birefringence, the same materials as those described for the base material used in the production of the optical laminate are used.

  The shape of the convex portion is not particularly limited as long as it is within a range that causes the inclination of the spiral axis, but a polygonal columnar shape such as a cylinder, a triangular prism, a quadrangular prism, a polygonal pyramid shape such as a triangular pyramid, a quadrangular pyramid, Examples of the shape include a hemispherical shape and a dome shape. In order to prevent a phase difference from appearing even if the shape is changed, it is preferable that the rotational symmetry axis of the convex shape is in the normal direction of the substrate.

  As the height of the convex portion, the height from the bottom surface of the convex portion to the apex is preferably from 0.1 to 10 μm, and more preferably from 0.5 to 3 μm. Moreover, as an in-plane period of a convex part, 0.1-10 micrometers is preferable and 0.5-3 micrometers is more preferable.

  Sectional drawing of a state in which the member 7 having a convex portion in the plane is integrated with a cholesteric liquid crystal layer (b) formed so as to include at least a portion where the spiral axis and the layer normal are not substantially parallel to each other. As shown in FIG. Here, a curve 4 traversing the liquid crystal layer 1 represents the helical axis of the cholesteric phase. As shown in FIG. 5, first, the cholesteric liquid crystal layer (a) in which the spiral axis and the layer normal are substantially parallel is deformed by the member 7, and at least a portion where the spiral axis and the layer normal are not substantially parallel is formed. The cholesteric liquid crystal layer (b) formed so as to include the above has a structure in which the helical axis is inclined.

  As a means for bringing a member having a convex portion in the surface into contact with the liquid crystal layer (a), a member generally having a convex portion in the surface is opposed to the liquid crystal layer (a) with a press machine generally used. A method of pressing and a laminating method of heating and pressurizing between rolls can be applied. Moreover, the method etc. which pressure-bond an embossing roll etc. to a liquid crystal layer (a), and transcribe | transfer the convex part shape on an embossing roll, etc. are applicable.

As described above, after forming the cholesteric liquid crystal layer (a) in which the spiral axis and the layer normal are substantially parallel, the liquid crystal layer (a) is deformed, and the spiral axis and the layer normal are not substantially parallel. The cholesteric liquid crystal layer (b) formed so as to include a part can be easily and reliably formed.
Further, after the step (B), the member having a convex portion in the surface may be removed from the cholesteric liquid crystal layer (b) or may be left without being removed.

  The step (C) includes a step of laminating the cholesteric liquid crystal layer (b) formed so as to include two or more layers in which a part of the spiral axis and the layer normal is not substantially parallel. .

As a means for laminating the cholesteric liquid crystal layer (b) formed so as to include a part where the spiral axis and the layer normal are not substantially parallel in part,
(I) Another cholesteric liquid crystal layer (b2) formed in the steps (A) and (B) is prepared on the cholesteric liquid crystal layer (b1) formed in the steps (A) and (B). A means to stick sheets together. When this means is used, the two substrates may be bonded together with the base material used to obtain the liquid crystal layer (b) and a member having a convex portion in the surface remaining.
(Ii) A cholesteric liquid crystal layer (b1) having a convex portion in the surface produced in the step (B) is brought into contact with another cholesteric liquid crystal layer (a2) formed in the step (A) to obtain a liquid crystal. Means for laminating the layer (a2) while forming the cholesteric liquid crystal layer (b2) formed by deforming the layer (a2) so as to partially include a portion in which the spiral axis and the layer normal are not substantially parallel.
Etc. may apply.
Among these, the means shown in the above (ii) is preferable in consideration of a decrease in transmittance accompanying an increase in the refractive index interface and simplification of the process. When this means is used, at least one set of cholesteric liquid crystal layers is in contact with the optical layered body of the present invention.

  FIG. 6 shows a cross-sectional view of the optical laminate produced by the means (ii). Here, a curve 4 crossing the liquid crystal layer 1 represents the helical axis of the cholesteric liquid crystal layer.

  The shape of the optical laminate of the present invention is not particularly limited, but is preferably a film. The film-shaped optical laminate of the present invention is useful as a production material for a brightness enhancement film and a liquid crystal display device as described below.

  The brightness enhancement film of the present invention comprises the optical laminate and the formula: Rth = [(nx + ny) / 2−nz] × d (where nx is the one having the highest refractive index in the plane, ny is nx in the plane) A retardation element in which Rth is defined as -20 nm to -1000 nm, a quarter-wave plate, and a refractive index in an orthogonal axis direction, nz is a refractive index in a thickness direction, and d is a thickness of the retardation element. It is characterized by including.

  The quarter wavelength plate is not particularly limited as long as it gives a phase difference of almost ¼ wavelength to incident light having a wavelength of 550 nm, but a broadband quarter wavelength plate is preferable. Here, the broadband quarter-wave plate means a quarter-wave plate in which the retardation (retardation) is almost a quarter wavelength over the entire visible light region including the wavelength of 410 to 660 nm.

  The broadband quarter wave plate is, for example, a laminate of a half wavelength plate and a quarter wavelength plate described in JP-A-5-100114, JP-A-11-231132, etc., a broadband retardation film WRF [manufactured by Teijin Ltd.], WO03 / 107048, which is a laminate of two retardation films that have been obliquely stretched so that their slow axes intersect at a predetermined angle, and WO03 / 102639 The layer A has at least one layer (A layer) made of a material having a positive intrinsic birefringence value and a layer (B layer) made of a material having a negative intrinsic birefringence value. And those having the same orientation direction of molecular chains in the B layer. Among them, in consideration of in-plane luminance variation and production efficiency, at least one layer (A layer) made of a material having a positive intrinsic birefringence value and a layer made of a material having a negative intrinsic birefringence value (B It is particularly preferable that the layer has at least one layer) and the molecular chain orientation directions in the A layer and the B layer are the same.

  The retardation element used in the brightness enhancement film of the present invention is Rth = [(nx + ny) / 2−nz] × d (where nx is the maximum in-plane refractive index, ny is the axis orthogonal to nx in the plane) The refractive index in the direction, nz is the refractive index in the thickness direction, and d is the thickness of the retardation element.) Rth is in the range of −20 nm to −1000 nm. Such a retardation element having Rth has a function of compensating for the phase difference of light incident obliquely on the quarter-wave plate from the light source side.

  In the retardation element used in the brightness enhancement film of the present invention, it is preferable that the relationship between the main refractive indexes nx, ny and nz satisfies nz> nx, nz> ny, nx≈ny. When this retardation element is composed of a plurality of layers, the main refractive index of each layer is different, but in the present invention, it is preferable if the refractive index of the entire element satisfies the above relationship. This main refractive index can be measured by an automatic birefringence meter [for example, “KOBRA series” manufactured by Oji Scientific Instruments Co., Ltd.]. Note that nx≈ny means that the refractive index difference is usually within 0.0002, preferably within 0.0001, and more preferably within 0.00005.

  The in-plane retardation Re is defined by Re = (nx−ny) × d. Having substantially no in-plane retardation means that the Re is usually 20 nm or less, preferably 10 nm or less, more preferably 5 nm or less. The retardation Rth in the thickness direction is appropriately set according to the purpose of use, but in order to fulfill the function as a phase difference compensation member, it is in the range of −20 to −1000 nm, and in the range of −50 to −700 nm. preferable.

  Examples of the retardation element having such optical characteristics include those including a layer obtained by stretching and aligning a material having at least a negative intrinsic birefringence value.

A material having a negative intrinsic birefringence value refers to a material having a characteristic of optically negative uniaxiality when molecules are oriented in a uniaxial order. Examples of materials having a negative intrinsic birefringence value include discotic liquid crystals, discotic liquid crystal polymers, aromatic vinyl polymers, polyacrylonitrile polymers, polymethacrylate polymers, cellulose ester polymers, and their multiple ( Binary, ternary, etc.) copolymers. These can be used alone or in combination of two or more.
Among these, at least one selected from aromatic vinyl polymers, polyacrylonitrile polymers, and polymethacrylate polymers is preferable. Of these, aromatic vinyl polymers are more preferable from the viewpoint of high birefringence.

  The aromatic vinyl polymer refers to a polymer of an aromatic vinyl monomer or a copolymer of an aromatic vinyl monomer and a monomer copolymerizable therewith. Examples of the aromatic vinyl monomer include styrene, 4-methylstyrene, 4-chlorostyrene, 3-methylstyrene; styrene derivatives such as 4-methoxystyrene, 4-tert-butoxystyrene, and α-methylstyrene. It is done. You may use these individually or in combination of 2 or more types.

Examples of the copolymerizable monomer as the aromatic vinyl monomer include propylene, butene, acrylonitrile, (meth) acrylic acid, maleic anhydride, (meth) acrylic acid ester, maleimide, vinyl acetate, and vinyl chloride. .
Among the aromatic vinyl polymers, a copolymer of styrene and / or a styrene derivative and maleic anhydride is preferable from the viewpoint of high heat resistance.

  The glass transition temperature of a material having a negative intrinsic birefringence value is preferably 110 ° C. or higher, more preferably 120 ° C. or higher, from the viewpoint that excellent optical properties can be obtained.

  As the retardation element used in the present invention, the film or sheet made of the material having the negative intrinsic birefringence value is uniaxially stretched or unbalanced biaxially stretched, and the stretch direction (the refractive index becomes maximum or minimum). Use a single layer that is laminated with two (orientations) perpendicular to each other, or balanced biaxially stretched (stretched so that the refractive index is substantially equal in any direction in the plane). it can. However, in view of mechanical strength and the like, it is preferable to laminate a reinforcing layer (C layer) made of a transparent resin material on at least one surface of a layer obtained by stretching and orientation of the negative material.

The reinforcing layer (C layer) made of a transparent resin material is not particularly limited as long as it has a thickness of 1 mm and a total light transmittance of 80% or more. For example, a polymer having an alicyclic structure, polyethylene or polypropylene Chain olefin polymer, polycarbonate polymer, polyester polymer, polysulfone polymer, polyethersulfone polymer, polyvinyl alcohol polymer, cellulose acetate polymer, polyvinyl chloride polymer, etc. Examples include polymethacrylate polymers. Among these, a polymer having an alicyclic structure or a chain olefin polymer is preferable, and a polymer having an alicyclic structure is particularly preferable from the viewpoint of transparency, low hygroscopicity, dimensional stability, lightness, and the like. preferable.
About the polymer which has the said alicyclic structure, it is as having demonstrated in the base material of the above-mentioned optical laminated body.

In the present invention, the thickness of the reinforcing layer (C layer) made of a transparent resin material is not particularly limited, but is usually 15 to 250 μm, preferably 25 to 150 μm.
In the case where the retardation element used in the present invention has a laminated structure of a layer (D layer) made of a material having such a negative intrinsic birefringence value and a reinforcing layer (C layer) made of a transparent resin material, Although the thickness of this C layer is not specifically limited, Usually, 5-400 micrometers, Preferably it is 15-250 micrometers.
Further, the glass transition temperature Tg _C of the transparent resin material used for the glass transition temperature Tg _D and C layer of intrinsic birefringence is negative material used in the D layer is preferably a Tg _D> Tg _C, Tg More preferably, _D −20 (° C.) ≧ Tg _C (° C.). When Tg _D ≦ Tg _C , particularly when the intrinsic birefringence value of the transparent resin material used for the C layer is positive, the refractive index anisotropy of the D layer expressed by stretching is the refractive index anisotropy of the C layer. There is a risk that the relationship between the target refractive index in the plane direction and the refractive index in the thickness direction cannot be obtained.

Furthermore, when the retardation element used in the present invention includes a laminated structure of a layer (D layer) made of a material having a negative intrinsic birefringence value and a reinforcing layer (C layer) made of a transparent resin material, moisture absorption or temperature From the viewpoint of preventing warpage due to change or change over time, the C layer is preferably laminated on both sides of the D layer. In this case, the thickness of each C layer laminated on both sides of the D layer is substantially Is preferably equal to In addition, when the C layer is laminated on only one side, the number of D layers to be overlaid is not limited, but it is usually one layer.
For the material having a negative intrinsic birefringence value and / or transparent resin material used in the present invention, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, an antistatic agent, and a dispersing agent are optionally added. , Chlorine scavengers, flame retardants, crystallization nucleating agents, antiblocking agents, antifogging agents, mold release agents, pigments, organic or inorganic fillers, neutralizing agents, lubricants, decomposition agents, metal deactivators, contamination Known additive components such as an inhibitor, an antibacterial agent, other resins, and a heat-numerable elastomer can be added as long as the effects of the present invention are not impaired.

In the retardation element used in the present invention, an adhesive layer (E layer) may be provided between the D layer and the C layer.
The adhesive layer (E layer) can be formed from a material having an affinity for both the material having a negative intrinsic birefringence value used for the D layer and the transparent resin material used for the E layer. Specifically, ethylene- (meth) acrylic acid ester copolymers such as ethylene- (meth) acrylic acid methyl copolymer and ethylene- (meth) ethyl acrylate copolymer; ethylene-vinyl acetate copolymer And ethylene copolymers such as ethylene-styrene copolymer suspension; other olefin copolymers. In addition, modified products obtained by modifying these copolymers by oxidation, saponification, chlorination, chlorosulfonation or the like can also be used. The thickness of this adhesive layer (E layer) is preferably 1 to 50 μm, more preferably 5 to 30 μm.

Further the phase difference element for use in the present invention, the case comprising an adhesive layer (E layer) has a glass transition temperature or softening point Tg _E of the adhesive used in E layer, be a Tg _D> Tg _E Preferably, Tg _D −20 (° C.) ≧ Tg _E (° C.) is more preferable.

  The method for producing the retardation element used in the present invention is not particularly limited, but as a preferred production method, a transparent resin material is provided on at least one side of a layer (D layer) made of a material having a negative intrinsic birefringence value. There is a method of laminating a layer (E layer) consisting of the above to obtain an unstretched laminate, and uniaxially or biaxially stretching it.

As a method for obtaining an unstretched laminate, a coextrusion T die method, a coextrusion inflation method, a coextrusion molding method such as a coextrusion lamination method, a film lamination molding method such as dry lamination, and a base resin film A known method such as a coating molding method for coating a resin solution can be appropriately used. Among these, from the viewpoint of production efficiency and the like, a molding method by coextrusion is preferable.
The extrusion temperature may be appropriately selected according to the material having a negative intrinsic birefringence value, a transparent resin material, and the type of adhesive used as necessary.

There is no restriction | limiting in particular in the method of extending | stretching a laminated body, The conventionally well-known method of uniaxial or biaxial stretching can be applied.
The stretching temperature is not particularly limited, but when the retardation element has the above laminated structure, (Tg _D −10) (° C.) to (TTg) with respect to the glass transition temperature Tg _D of the material having a negative intrinsic birefringence. The range of ( _D + 20) (° C.) is preferable, and the range of (Tg _D −5) (° C.) to (Tg _D +15) (° C.) is more preferable. By setting the stretching temperature in the above range, it is possible to make it difficult for the E layer to exhibit refractive index anisotropy at the time of stretching, and to easily obtain the desired relationship between the in-plane orthogonal axis direction and the refractive index in the thickness direction. be able to.
Here, the draw ratio is usually 1.1 to 30 times, preferably 1.3 to 10 times. If the draw ratio is out of the above range, the orientation may be insufficient, the refractive index anisotropy and thus the retardation may be insufficiently exhibited, or the laminate may be broken.

  As described above, the optical element obtained by combining the optical laminate obtained by the method of the present invention with the quarter wavelength plate and the retardation element is suitably used as a polarized light source as a brightness enhancement film, a backlight unit of a liquid crystal display device, or the like. Used in devices and the like. A polarized light source device provided with a brightness enhancement film can provide a liquid crystal display device that has high brightness and is less likely to cause color unevenness with a wide viewing angle.

  An example of the layer structure of the brightness enhancement film of the present invention is shown in FIG. In FIG. 7, 9 is an optical laminated body having two or more cholesteric liquid crystal layers formed so as to partially include a portion where the spiral axis and the layer normal are not parallel, 12 is a retardation element, 10 is 1 / It is a 4-wavelength plate. For example, as shown in FIG. 8, the brightness enhancement film 14 shown in FIG. 8 can be used by sequentially arranging the light source A, the diffusion plate 8, the brightness enhancement film 14, the prism sheet 13, and the polarizing plate 11. The light beam L emitted from the light source A is converted into diffused light having a uniform distribution by passing through the diffusion plate 8. Next, a light beam incident on the optical laminate 9 having two or more cholesteric liquid crystal layers formed so as to partially include portions where the spiral axis and the layer normal are not parallel is circularly polarized in one rotational direction. Is transmitted, and circularly polarized light in the other rotational direction is reflected. The transmitted circularly polarized light is converted by the quarter wavelength plate 10 into linearly polarized light parallel to the transmission axis of the polarizing plate 11. On the other hand, the reflected circularly polarized light is depolarized by being depolarized by the diffusing plate 8 and then emitted again to the diffusing plate side by the reflecting plate B disposed on the back side of the light source A to be reused. As a result, the light emitted from the light source can be effectively used, and the luminance can be improved.

   The brightness enhancement film shown in FIG. 7 can be manufactured, for example, as follows. An optical laminated body having two or more cholesteric liquid crystal layers formed so as to partially include a portion in which the spiral axis and the layer normal are not substantially parallel is formed. Next, directly or through an adhesive layer or a pressure-sensitive adhesive layer, the formula: Rth = {(nx + ny) / 2−nz} × d (where nx is the maximum in-plane refractive index, ny is in-plane A retardation element in which Rth is defined as -20 nm to -1000 nm is laminated, in which the refractive index in the axial direction orthogonal to nx is, nz is the refractive index in the thickness direction, and d is the thickness of the retardation element. . Subsequently, the target brightness improvement film can be obtained by laminating | stacking a quarter wavelength plate to the phase difference element side directly or through an adhesive bond layer or an adhesive layer.

The present invention also provides a polarized light source device having the above-described brightness enhancement film of the present invention and a liquid crystal display device having the polarized light source device.
FIG. 9 is a cross-sectional view showing a configuration of an example of the polarized light source device of the present invention. In FIG. 9, 15 is a light source, 16 is a light source holder, 17 is a light guide plate, 18 is a reflection layer, 14 is a brightness enhancement film, and 11 is a polarizing plate. The brightness enhancement film 14 includes a cholesteric liquid crystal layer 9, a retardation element 12, and a quarter wavelength plate 10.

Light from the light source 15 disposed on the side surface enters the light guide plate 17 and exits upward (on the optical laminate 9 side of the present invention). The light that has entered the optical laminated body 9 is transmitted through one of the left and right circularly polarized light, the other circularly polarized light is reflected, and the reflected light reenters the light guide plate 17. The light that re-enters the light guide plate is reflected by the reflective layer 18 on the lower surface and enters the optical laminate 9 again, and is again separated into transmitted light and reflected light in the direction of circular polarization as described above. By repeating this, most of the light emitted from the light source 15 is converted into one circularly polarized light, so that there is no loss in the polarizing plate, effective use is achieved, and an excellent luminance improvement effect can be obtained. .
The light source 15 is not particularly limited, and a conventionally known light source 15 can be used.

  The light guide plate 17 preferably has a shape (wedge shape) in which the thickness of the side end facing the incident surface is thinner than that of the incident surface. Moreover, the thing of the structure which has fine prism-shaped unevenness | corrugation from a viewpoint of being excellent in the output efficiency from an output surface, and being excellent in the perpendicularity with respect to the output surface, and aiming at the effective utilization of an emitted light is preferable. The light guide plate 17 can be formed of a transparent material such as a norbornene polymer, polymethyl methacrylate, polycarbonate, or polystyrene. The light reflecting layer 2a can be appropriately formed by, for example, a plating layer, a metal vapor deposition layer, a metal foil, a metal vapor deposition sheet, a plating sheet, or the like. This light reflection layer may be integrated with the surface facing the light exit surface of the light guide plate, or may be formed as a light reflection sheet or the like superimposed on the light guide plate.

  The polarized light source device of the present invention has an excellent brightness enhancement effect and is provided with a phase difference element. Therefore, when used as a backlight unit of a liquid crystal display device, color unevenness with wide viewing angles in the front and perspective. It is possible to provide a high-brightness liquid crystal display device that is less likely to cause the phenomenon.

The liquid crystal display device of the present invention has the polarized light source device of the present invention as a backlight unit, and there is no particular limitation on the configuration thereof.
One example of the layer structure of the liquid crystal display device of the present invention is shown in FIG. The liquid crystal display device shown in FIG. 10 uses the polarized light source device of the present invention for a backlight system. In FIG. 10, 19 is a liquid crystal cell, 11a is a lower polarizing plate, 11b is an upper polarizing plate, and 8a and 8b are diffusion plates. The lower polarizing plate 11a and the diffusion plates (8a, 8b) can be excluded from the layer configuration.

The liquid crystal mode used is not particularly limited. As the liquid crystal mode, for example, TN (Twisted nematic) type, STN (Super Twisted Nematic) type, HAN (hybrid aligned nematic) type, VA (Vertical Aligned Bench type, IPS (In Plane Swing C, B) ) Type.
Moreover, it does not restrict | limit especially as a polarizing plate (8, 11), A conventionally well-known thing can be used.
Since the liquid crystal display device of the present invention has the polarized light source device of the present invention as a backlight unit, an excellent luminance improvement effect can be obtained and the luminance improvement effect can be stably exhibited over a long period of time. it can. In addition, the occurrence of color unevenness is suppressed at a wide viewing angle from the front and perspective, and the display quality is excellent.

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.
Example 1
(Preparation of an optical laminate having two cholesteric liquid crystal layers formed so as to partially include a portion in which the spiral axis and the layer normal are not substantially parallel)
95.53 parts by weight of a nematic liquid crystal compound represented by the following (Compound 1), 4.47 parts by weight of a chiral agent represented by the following (Compound 2), 3.10 of a light absorber represented by the following (Compound 3) Part by weight and 0.10 parts by weight of a surfactant were dissolved in 155.0 parts by weight of methyl ethyl ketone, and then filtered through a 0.5 μm filter to prepare a coating solution for cholesteric liquid crystals.

  Next, plasma treatment was performed on both surfaces of this substrate using a norbornene polymer film [manufactured by Zeon Corporation, trade name “Zeonor film ZF14-100”] having a thickness of 100 μm. And the orientation film coating liquid which consists of 10 weight part of polyvinyl alcohol and 371 weight part of water was apply | coated and dried on the single side | surface of this base material, and the 1-micrometer-thick orientation layer was formed. Thereafter, a rubbing treatment was performed on the alignment film. Next, the cholesteric liquid crystal coating solution is applied onto the rubbed substrate so as to have a dry thickness of 4 μm, and then heated at 100 ° C. for 5 minutes (alignment aging), so that the cholesteric liquid crystal layer (A) Formed. The cholesteric liquid crystal layer (A) had a helical axis in the layer normal direction.

For the cholesteric liquid crystal layer (A), a prism array having a vertex angle of about 90 °, a height of 2 μm, and a pitch of 4 μm is formed using a norbornene-based polymer [trade name “Zeonor 1420” manufactured by ZEON Corporation]. The surface on which the prism row is formed is arranged so as to face the surface of the cholesteric liquid crystal layer, and this is pressure-bonded so that the spiral axis and the layer normal are partially included. A cholesteric liquid crystal layer (B) formed in the above was prepared. Thereafter, (B) was cured by irradiating (B) with ultraviolet rays at 150 mW / cm ² for 2 seconds.

  The member in which the prism row in contact with (B) is peeled off, has the shape of a convex portion to which the prism row is transferred, and a portion where the spiral axis and the layer normal line are not substantially parallel A cholesteric liquid crystal layer (C) formed so as to be included in the portion was obtained.

  A norbornene polymer film [trade name “Zeonor film ZF14-100” manufactured by Nippon Zeon Co., Ltd.] different from the above was used as a substrate, and plasma treatment was performed on both surfaces of the substrate. And the orientation film coating liquid which consists of 10 weight part of polyvinyl alcohol and 371 weight part of water was apply | coated and dried on the single side | surface of this base material, and the 1-micrometer-thick orientation layer was formed. Thereafter, a rubbing treatment was performed on the alignment film. Next, the cholesteric liquid crystal coating solution is applied onto the rubbed substrate so as to have a dry thickness of 5 μm, and then heated at 100 ° C. for 5 minutes (alignment aging) to obtain a cholesteric liquid crystal layer (D ) Was formed.

The cholesteric liquid crystal layer (C) was pressure-bonded to the cholesteric liquid crystal layer (D) so that the prism rows were inside. At this time, the cholesteric liquid crystal layer is formed by pressure bonding so that the cholesteric liquid crystal layers are in contact with each other, deforming the cholesteric liquid crystal layer (D), and including a portion where the spiral axis and the layer normal are not substantially parallel. An optical laminated body (E) in which two layers were laminated was obtained. Thereafter, (E) was irradiated with ultraviolet rays at 150 mW / cm ² for 2 seconds to cure the uncured portion of (E). The total thickness of the liquid crystal layer was 8 μm.

For the optical layered body thus obtained, measurement of the selective reflection band is performed.
Measuring instrument: Otsuka Electronics Co., Ltd., “MCPD-3000”
Microscope used: Nikon Corporation, apparatus name “Eclipse E-600POL”
Made using. The measurement results are shown in FIG.
In addition, the selective reflection band was a band width of 60% or more of the reflectivity at which the maximum reflectivity was calculated by calculating “maximum transmittance−minimum transmittance” in a band of 400 to 700 nm.

Comparative Example 1
A cholesteric liquid crystal layer (A) was provided on the substrate in the same manner as in Example 1 except that coating was performed so that the dry thickness was 8 μm, and then cured by irradiation with ultraviolet rays at 150 mW / cm ² for 2 seconds. A cholesteric liquid crystal layer (A ¹ ) was prepared. The total thickness of the liquid crystal layer (A ¹ ) was 8 μm.
The selective reflection region of the cholesteric liquid crystal layer (A ¹ ) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

Comparative Example 2
Except for coating so as to have a dry thickness of 8 μm, in the same manner as in Example 1, after providing the cholesteric liquid crystal layer (A) on the substrate, a part where the spiral axis and the layer normal are not parallel is partially A cholesteric liquid crystal layer (B) formed so as to be included was prepared. Thereafter, (B) was irradiated with ultraviolet rays at 150 mW / cm ² for 2 seconds to produce a cholesteric liquid crystal layer (B ¹ ) in which (B) was cured. The total thickness of the liquid crystal layer (B ¹ ) was 8 μm.
The selective reflection region of the cholesteric liquid crystal layer (B ¹ ) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

From FIG. 11, according to Example 1, the selective reflection band of the optical layered body of the present invention is 125 nm, and the selection of the cholesteric liquid crystal layer (A ¹ ) (Comparative Example 1) in which the spiral axis and the layer normal are substantially parallel. The reflection band was 50 nm, and the selective reflection band of the cholesteric liquid crystal layer (B ¹ ) (Comparative Example 2) formed so as to partially include a portion where the spiral axis and the layer normal were not parallel was 90 nm.

The optical layered body of the present invention has a selective reflection band more than twice that of the cholesteric liquid crystal layer (A ¹ ) (Comparative Example 1) in which the spiral axis and the layer normal are substantially parallel, and has a wide selective reflection. You can see that it has an area. Further, the optical layered body of the present invention has a selective reflectance as compared with the cholesteric liquid crystal layer (B ¹ ) (Comparative Example 2) formed so as to partially include a portion where the spiral axis and the layer normal are not parallel. It can be seen that the selective reflection region is wide.

Example 2
(Production of retardation element)
A styrene-maleic anhydride copolymer [manufactured by Nopa Chemical Co., Ltd., trade name “DAILARK D332”] as a material having a negative intrinsic birefringence value, and a norbornene-based polymer [manufactured by Nippon Zeon Co., Ltd., trade name “ZEONOR 1020” as a transparent resin layer material. ]], And a laminate 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) by coextrusion method Got the body.

Next, the mixture was sequentially fed into a zone-heated longitudinal uniaxial stretching apparatus and a tenter stretching (transverse uniaxial stretching) apparatus to perform sequential biaxial stretching. The stretching temperature was 140 ° C. for both longitudinal stretching and lateral stretching, and the stretching ratio was 1.8 times for longitudinal stretching and 1.5 times for lateral stretching.
The average thickness of the phase difference element is 120 [mu] m, the refractive index of the surface direction is _{n X = 1.5732, n y =} 1.5731, the refractive index in the thickness direction was n _z = 1.5757. The retardation was in-plane Re = 10 nm and the thickness direction Rth = −300 nm.

(Preparation of broadband quarter wave plate)
As a material having a positive intrinsic birefringence value, a norbornene polymer [manufactured by Zeon Corporation, trade name “Zeonor 1420”], and as a material having a negative intrinsic birefringence value, a styrene-maleic anhydride copolymer [ The product name “DAILARK D332” manufactured by Nova Chemical Co., Ltd. was used. First, the norbornene-based resin and the styrene-maleic anhydride copolymer in a molten state were respectively stored in the extruders of the extrusion dies in which two extruders were integrally combined with the extrusion die. The extrusion flow path of the extruder storing the norbornene-based resin is branched into two, and the norbornene-based resin extruded from the branched flow path is styrene-maleic anhydride co-polymer extruded from another extruder. The union was sandwiched and a three-layer laminate was formed inside the extrusion die. In addition, a filter is disposed at a communication port to the extrusion die of the two extruders, and the norbornene resin and the styrene-maleic anhydride copolymer are passed through the filter and then pushed into the extrusion die. I put it out.
The thickness unevenness of the three-layer laminate extruded from the extrusion die was measured using a scanning thickness meter. The measurement was performed by continuously scanning in the longitudinal direction of the laminate. The obtained laminate had a thickness average of 120 μm, and the thickness unevenness was 2.5% with respect to the thickness average.

  Next, when the obtained laminate was longitudinally uniaxially stretched at 125 ° C. for 70%, the ratio of retardation to wavelength at wavelengths λ = 450 nm, 550 nm and 650 nm was 0.235, 0.250 and 0.232. A broadband ¼ wavelength plate was obtained.

(Preparation of an optical laminate having two cholesteric liquid crystal layers formed so as to partially include a portion in which the spiral axis and the layer normal are not substantially parallel)
In the same manner as in Example 1, an optical layered body having two or more cholesteric liquid crystal layers formed so as to partially include a portion where the spiral axis and the layer normal line are not substantially parallel was obtained.

(Production of brightness enhancement film)
The obtained optical laminated body having two cholesteric liquid crystal layers formed so as to partially include a portion in which the helical axis and the layer normal are not substantially parallel, the retardation element produced above, and the broadband quarter wavelength The plates were laminated in this order to obtain a brightness enhancement film.

A polarized light source device is manufactured by sequentially arranging a light diffusion sheet and the brightness enhancement film on the exit surface side of a general-purpose light guide plate in which a cold cathode tube is disposed on the incident end surface side and a light reflecting sheet is provided on the back surface side. did. Furthermore, a polarizing plate, a viewing angle widening film [manufactured by Fuji Photo Film Co., Ltd., “WV film”], a transmissive TN liquid crystal display element, and a polarizing plate are sequentially arranged on the 1/4 wavelength plate side of the brightness enhancement film, A display device was produced.
When the liquid crystal display device was observed in the white display mode from the light exit surface side, the brightness was 5 and the color viewing angle was good.
In the evaluation of the characteristics of the liquid crystal display device, the brightness is evaluated in five stages of 1, 2, 3, 4, and 5, with 5 being the brightest and 1 being the darkest.

Comparative Example 3
In the same manner as in Comparative Example 2, a cholesteric liquid crystal layer formed so as to partially include a portion where the cured helical axis and the layer normal line are not substantially parallel was produced.
In Example 2, instead of the optical laminate having two or more cholesteric liquid crystal layers formed so as to partially include a portion in which the spiral axis and the layer normal are not substantially parallel, a cured spiral axis and layer A brightness enhancement film and a liquid crystal display device were produced in the same manner as in Example 2 except that a cholesteric liquid crystal layer formed so as to partially include a portion not parallel to the normal line was used.
When this liquid crystal display device was observed from the light exit surface side in the white display mode, the brightness was 4 and the color viewing angle was good.

It is the schematic which shows a general cholesteric liquid crystal layer. It is the schematic which shows the selective reflection of a general cholesteric liquid crystal layer. It is the schematic which shows the viewing angle dependence of selective reflection. It is the schematic which shows the cholesteric liquid crystal layer in which the spiral axis inclined. It is the schematic which shows an example of the method of inclining a helical axis. It is the schematic which shows an example of the optical laminated body of this invention. It is the schematic which shows the principle and structure of a brightness enhancement film. It is a figure which shows the layer structure of the brightness enhancement film of this invention. It is a figure which shows the layer structure of the polarized light source device of this invention. It is a figure which shows the layer structure of the liquid crystal display device of this invention. It is a graph which shows the relationship between the wavelength in the optical laminated body obtained by Example 1, the comparative example 1, and the comparative example 2, and light transmittance.

Explanation of symbols

  1: cholesteric liquid crystal layer, 2: liquid crystal molecule, 3: layer normal, 4: spiral axis, 5: transmission spectrum for obliquely incident light, 6: transmission spectrum for parallel incident light, 7: member having a convex portion in the plane 8, 8a, 8b ... diffuser plate, 9: optical laminate, 10: 1/4 wavelength plate, 11, 11a, 11b: polarizing plate, 12: retardation element, 13: prism sheet, P: helical pitch, L1 : White incident light, L2: reflected circularly polarized light, θ1: incident angle with respect to the layer surface, θ2: incident angle inside the layer, a: incident angle inside the layer (upper layer), b: incident inside the layer (middle layer) Angle, c: Incident angle inside the layer (lower layer), A, 15: Light source, B, 18: Reflector (reflective layer), 16: Light source holder, 17: Light guide plate, 19: Liquid crystal cell

Claims (8)

An optical laminate having two or more liquid crystal layers, each of the liquid crystal layers is formed by forming the cholesteric liquid crystal layer (a) so that the spiral axis and the layer normal line are substantially parallel. An optical layered body which is a layer (b) formed so as to partially include a part that is deformed and includes a portion in which the spiral axis and the layer normal are not substantially parallel. The optical laminate according to claim 1, wherein at least one set of the laminated cholesteric liquid crystal layers is in contact. A method for producing an optical laminate having two or more liquid crystal layers, wherein (A) a step of forming a cholesteric liquid crystal layer (a) so that a helical axis and a layer normal line are substantially parallel, (B) A step of deforming the liquid crystal layer (a) to include a portion in which the spiral axis and the layer normal are not substantially parallel; (C) a portion in which the spiral axis and the layer normal are not substantially parallel; A method for producing an optical laminate including a step of laminating so that the cholesteric liquid crystal layer (b) formed to contain 2 or more layers. The manufacturing method of the optical laminated body of Claim 3 laminated | stacked so that the said (C) process may contact at least 1 set of a cholesteric liquid crystal layer. In step (B), a member having a projection in the surface is brought into contact with the cholesteric liquid crystal layer (a) formed in step (A), and the liquid crystal layer (a) is deformed so that the spiral axis and the layer normal line are The method for producing an optical laminate according to claim 3, wherein the optical laminate is a step of including a portion that is not substantially parallel. The optical laminated body according to claim 1 or 2, and a formula: Rth = [(nx + ny) / 2-nz] × d (where nx is a refractive index in the plane and ny is nx in the plane) A retardation element whose Rth is defined as -20 nm to -1000 nm, a quarter wavelength, and a refractive index in the axial direction perpendicular to the axis, nz is a refractive index in the thickness direction, and d is a thickness of the retardation element. A brightness enhancement film comprising a plate. A polarized light source device comprising the brightness enhancement film according to claim 6. A liquid crystal display device comprising the polarized light source device according to claim 7.

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