Stacked optical film, method for manufacturing the same, polarizing plate, and image display device

Abstract

The stacked optical film (10) of the present application has an alignment liquid crystal layer (3) formed by horizontally aligning rod-shaped liquid crystal compounds on a film substrate (1). The film substrate is a polymer film stretched in at least one direction. The film substrate is in contact with the alignment liquid crystal layer, and the slow axis direction of the film substrate is not parallel to the slow axis direction of the alignment liquid crystal layer. By the alignment adjustment force of the film substrate, the rod-shaped liquid crystal compounds can be horizontally aligned in a direction not parallel to the stretching direction of the film substrate.

Description

Technical Field

[0001] The present invention relates to a laminated optical film having an aligned liquid crystal layer on a film substrate and a method for manufacturing the same. Further, the present invention relates to a polarizing plate obtained by laminating the laminated optical film and a polarizer, and an image display device. Background Art

[0002] In a liquid crystal display device, polarizers are arranged on both sides of a liquid crystal cell due to its display principle, and a retardation plate is arranged between the liquid crystal cell and the polarizer for the purpose of optical compensation such as improving contrast and expanding the viewing angle. For example, when visually confirming a liquid crystal display device from an inclined direction, since the apparent angle between the absorption axis directions of the two polarizers deviates from 90°, light leakage occurs and the contrast decreases. Therefore, a retardation plate is used to compensate for the deviation of the apparent absorption axis directions of the two polarizers. In an organic EL display device, in order to suppress external light from being reflected by a metal electrode (cathode) and being visually recognized as a mirror surface, a circular polarizer (a laminate of a polarizer and a retardation film having a 1 / 4 wavelength retardation) is arranged on the visually confirming side surface of the cell.

[0003] As the retardation plate, a stretched film of a non-liquid crystal polymer or an aligned liquid crystal layer in which a liquid crystal compound is aligned in a predetermined direction is used. Ideally, the longer the wavelength of the retardation plate for compensating for the deviation of the apparent absorption axis direction of the polarizer and for antireflection of the circular polarizer, the greater the retardation, and the ratio of the wavelength to the retardation is constant over the entire visible wavelength region. However, materials having a greater retardation (so-called "reverse wavelength dispersion") as the wavelength increases are limited, and most polymers and liquid crystal materials show a smaller retardation (positive dispersion) or show a substantially constant retardation (low dispersion) regardless of the wavelength as the wavelength increases.

[0004] A method of adjusting the wavelength dispersion of retardation by laminating a plurality of retardation plates has been proposed. For example, Patent Document 1 proposes a method of laminating two retardation plates having different wavelength dispersions of retardation in such a manner that their slow axis directions are orthogonal to form a laminated retardation plate showing reverse wavelength dispersion of retardation. Patent Document 2 discloses that the wavelength dispersion can be adjusted by laminating the two retardation plates at an angle such that the slow axis directions of the two retardation plates are neither parallel nor orthogonal.

[0005] Patent Document 3 discloses a laminated retardation plate having an aligned liquid crystal layer in which a liquid crystal compound is horizontally aligned on a retardation plate formed of a stretched film of a polymer.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Laid-Open No. 5-27118

[0009] Patent Document 2: Japanese Patent Laid-Open No. 10-63816

[0010] Patent Document 3: WO2016 / 121856 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] In the roll-to-roll method, it is not easy to stack multiple stretched film layers in such a way that the slow axis direction is non-parallel. Therefore, it is difficult to consider that the productivity of the stacked retardation plates described in Patent Document 1 and Patent Document 2 is high. In addition, the thickness of the stacked retardation plate formed by stacking multiple stretched films with an adhesive or the like becomes large, making it unsuitable for thinning and lightening.

[0013] The birefringence of the aligned liquid crystal layer is larger than that of the stretched film of the polymer. In addition, as described in Patent Document 3, if the orientation adjusting force of the stretched film is utilized, the aligned liquid crystal can be stacked in contact with the stretched film, which is therefore advantageous for thinning and lightening. However, if the liquid crystal compound is oriented on the stretched film, the liquid crystal compound usually aligns parallel to the orientation direction (stretching direction) of the polymer. Therefore, in order to make the slow axis direction of the stretched film of the polymer non-parallel to the slow axis direction of the aligned liquid crystal layer, an alignment film having an alignment adjusting force in a direction non-parallel to the stretching direction of the polymer film needs to be provided. In terms of the method, grinding needs to be performed in a direction non-parallel to the stretching direction of the polymer film, so it is difficult to apply the roll-to-roll method, and it is difficult to consider that the productivity is high.

[0014] Means for Solving the Problems

[0015] The stacked optical film of the present invention has an aligned liquid crystal layer in which rod-like liquid crystal compounds are horizontally aligned on a polymer film substrate stretched in at least one direction. An alignment film is not provided on the surface of the film substrate, and the film substrate is in contact with the aligned liquid crystal layer. The slow axis direction of the film substrate is not parallel to the slow axis direction of the aligned liquid crystal layer. The angle formed by the slow axis direction of the film substrate and the slow axis direction of the aligned liquid crystal layer is, for example, 5° or more, and can also be greater than 45°.

[0016] By utilizing the alignment adjusting force of the film substrate, the rod-like liquid crystal compounds can be horizontally aligned in a direction non-parallel to the stretching direction of the film substrate. As the film substrate having such an alignment adjusting force, a film containing a polymer having an asymmetric carbon in the repeating unit of the main chain can be used.

[0017] The film substrate may contain an ester-based polymer. Examples of the ester-based polymer include polyester, polycarbonate, polyarylate, etc. The ester-based polymer may contain a cyclic diol having an asymmetric carbon as a diol component. Examples of the cyclic diol having an asymmetric carbon include isosorbide, isomannitol, isoidide, etc. The ester-based polymer may contain a diol component having no asymmetric carbon in addition to the diol component having an asymmetric carbon. The diol component having no asymmetric carbon may be an alicyclic diol.

[0018] The rod-shaped liquid crystal compound is preferably a thermotropic liquid crystal. The rod-shaped liquid crystal compound may be a liquid crystal polymer or a polymer of a polymerizable liquid crystal compound. In the case of a polymer of a polymerizable liquid crystal compound, it is sufficient that the monomer before polymerization exhibits liquid crystallinity, and it may also be a polymer that does not exhibit liquid crystallinity after polymerization.

[0019] For example, a liquid crystal composition containing a liquid crystal compound is coated on a film substrate, and the liquid crystal composition on the film substrate is heated to orient the liquid crystal compound in a liquid crystal state, whereby a laminated optical film can be obtained. In the case where the liquid crystal compound is a photopolymerizable liquid crystal monomer, it is preferable to heat the liquid crystal composition containing the photopolymerizable liquid crystal monomer on the film substrate to orient the liquid crystal monomer and then polymerize or crosslink the liquid crystal monomer by irradiating light.

[0020] The ratio Re(450) / Re(550) of the front retardation Re(450) at a wavelength of 450 nm to the front retardation Re(550) at a wavelength of 550 nm of the laminated optical film may be less than 1.00.

[0021] The ratio Re(450) / Re(550) of the front retardation Re(450) at a wavelength of 450 nm to the front retardation Re(550) at a wavelength of 550 nm of the film substrate may be 0.90 to 1.05. In this case, the Re(450) / Re(550) of the oriented liquid crystal layer is preferably larger than the Re(450) / Re(550) of the film substrate.

[0022] By laminating the above-mentioned laminated optical film with a polarizer, a polarizing plate with a retardation plate can be formed. The laminated optical film and the polarizing plate having the laminated optical film can be used as optical members for an image display device.

[0023] Advantages of the Invention

[0024] A laminated optical film in which a stretched film substrate and an oriented liquid crystal layer that can each function as a retardation plate alone are arranged such that the slow axis directions are not parallel can adjust the wavelength dispersion of retardation and can be used as a laminated retardation plate for optical compensation, antireflection, etc. of an image display device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a cross-sectional view of a laminated optical film according to an embodiment.

[0026] Figure 2 is a cross-sectional view of a polarizing plate according to an embodiment. Detailed Embodiment

[0027] Figure 1 is a cross-sectional view of a laminated optical film according to an embodiment of the present invention. The laminated optical film 10 includes a liquid crystal layer 3 that is closely laminated in contact with a film substrate 1.

[0028] [Liquid Crystal Compounds and Liquid Crystal Compositions]

[0029] Regarding the aligned liquid crystal layer, rod-like liquid crystal compounds are horizontally aligned in a specified direction. A liquid crystal composition is coated on the film substrate, and the liquid crystal composition is heated to align the liquid crystal compounds in a specified direction, and then the aligned state is fixed, thereby forming the aligned liquid crystal layer.

[0030] The rod-like liquid crystal compounds can be main-chain liquid crystals or side-chain liquid crystals. The rod-like liquid crystal compounds can be liquid crystal polymers or polymers of polymerizable liquid crystal compounds. If the liquid crystal compound (monomer) before polymerization exhibits liquid crystallinity, it can also be a compound that does not exhibit liquid crystallinity after polymerization.

[0031] As the polymerizable liquid crystal compound, for example, there can be mentioned: a polymerizable liquid crystal compound that can fix the alignment state of the rod-like liquid crystal compound using a polymer binder, a polymerizable liquid crystal compound having a polymerizable functional group that can fix the alignment state of the liquid crystal compound by polymerization, etc. Among them, a polymerizable liquid crystal compound having a photopolymerizable functional group is preferred.

[0032] The liquid crystal compound is preferably a thermotropic liquid crystal that exhibits liquid crystallinity upon heating. The thermotropic liquid crystal undergoes phase transitions among a crystalline phase, a liquid crystal phase, and an isotropic phase with temperature changes. As the rod-like liquid crystal compounds showing thermotropism, there can be mentioned: azomethines, azoxy compounds, cyanobiphenyls, cyanobenzoates, benzoates, phenyl cyclohexanecarboxylates, cyanophenyl cyclohexanes, cyanide-substituted phenyl pyrimidines, alkoxy-substituted phenyl pyrimidines, phenyl dioxanes, diphenylacetylenes, alkenyl cyclohexyl benzonitriles, etc.

[0033] The photopolymerizable liquid crystal compound (liquid crystal monomer) has a mesogenic unit and at least one photopolymerizable functional group in one molecule. The temperature at which the liquid crystal monomer exhibits liquid crystallinity (liquid crystal phase transition temperature) is preferably 40 to 200 °C, more preferably 50 to 150 °C, and further preferably 55 to 100 °C.

[0034] As mesogenic units of liquid crystal monomers, the following can be cited: cyclic structures such as biphenyl, phenyl benzoate group, phenyl cyclohexyl group, azoxy phenyl group, azomethine group, azo phenyl group, phenyl pyrimidine group, diphenyl ethynyl group, diphenyl benzoate group, dicyclohexyl group, cyclohexyl phenyl group, terphenyl group, etc. The terminals of these cyclic units may have substituents such as cyano group, alkyl group, alkoxy group, halogen group, etc.

[0035] As photopolymerizable functional groups, the following can be cited: (meth)acryloyl group, epoxy group, vinyl ether group, etc. Among them, (meth)acryloyl group is preferred. The photopolymerizable liquid crystal monomer preferably has two or more photopolymerizable functional groups in one molecule. By using a liquid crystal monomer containing two or more photopolymerizable functional groups, a bridging structure is introduced into the liquid crystal layer after photocuring, and thus the durability of the aligned liquid crystal layer tends to be improved.

[0036] As an example of a photopolymerizable thermotropic liquid crystal monomer having a mesogenic unit and a plurality of (meth)acryloyl groups in one molecule, a compound represented by the following general formula (I) can be cited.

[0037] Chemical formula 1

[0038]

[0039] In formula (I), R is a hydrogen atom or a methyl group, A and D are each independently 1,4-phenylene or 1,4-cyclohexylene, B is 1,4-phenylene, 1,4-cyclohexylene, 4,4'-biphenylene or 4,4'-dicyclohexylene, Y and Z are each independently -COO-, -OCO- or -O-. g and h are each independently an integer of 2 to 6.

[0040] As a commercially available product of the photopolymerizable liquid crystal monomer represented by the above general formula (I), “Paliocolor LC242” manufactured by BASF can be cited.

[0041] The liquid crystal composition may contain a photopolymerization initiator. In the case of curing the liquid crystal monomer by ultraviolet irradiation, in order to promote photocuring, the liquid crystal composition preferably contains a photopolymerization initiator (photo radical generator) that generates radicals by irradiated light. A photo cation generator or a photo anion generator may also be used according to the type of the liquid crystal monomer (the type of the photopolymerizable functional group). The amount of the photopolymerization initiator is about 0.01 to 10 parts by weight relative to 100 parts by weight of the liquid crystal monomer. A sensitizer etc. can also be used in addition to the photopolymerization initiator.

[0042] A liquid crystal composition can be prepared by mixing a liquid crystal monomer, a polymerization initiator, etc. with a solvent. The solvent is not particularly limited as long as it can dissolve the liquid crystal monomer and does not erode the film substrate (or has a low erosion rate), and examples include: halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, and o-dichlorobenzene; phenols such as phenol and p-chlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, and 1,2-dimethoxybenzene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, and N-methyl-2-pyrrolidone; ester solvents such as ethyl acetate and butyl acetate; alcohol solvents such as tert-butanol, glycerol, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, and 2-methyl-2,4-pentanediol; amide solvents such as dimethylformamide and dimethylacetamide; nitrile solvents such as acetonitrile and butyronitrile; ether solvents such as diethyl ether, dibutyl ether, and tetrahydrofuran; ethyl cellosolve, butyl cellosolve, etc. A mixed solvent of two or more solvents can also be used.

[0043] The solid content concentration of the liquid crystal composition is usually about 5 to 60% by weight. The liquid crystal composition can also contain additives such as surfactants and leveling agents.

[0044] [Film substrate]

[0045] By using the film substrate as the support for coating the liquid crystal composition, a series of processes from coating the liquid crystal composition to curing based on photopolymerization of the liquid crystal monomer can be carried out by roll-to-roll, so the productivity of the laminated optical film can be improved.

[0046] The film substrate 1 is a stretched film. By stretching the polymer film, the molecular chains of the polymer constituting the film are preferentially oriented in the stretching direction, and the orientation adjusting force for the liquid crystal compound of the alignment liquid crystal layer 3 provided on the film substrate 1 to be horizontally oriented in a specified direction comes into play.

[0047] The stretching ratio of the stretched film only needs to be at a level where the orientation adjusting force can be exerted, for example, about 1.05 times to 5 times. The stretched film can also be a biaxially stretched film. Even if it is a biaxially stretched film, as long as a stretched film with different stretching ratios in the longitudinal and transverse directions is used, it can have the effect of orienting the liquid crystal compound in a specified direction.

[0048] The front retardation of the stretched film used as the film substrate 1 is preferably 10 nm or more. When the film substrate is a stretched film with a front retardation of 10 nm or more, the polymer constituting the film is preferentially oriented in a specified direction, so the orientation adjusting force for the liquid crystal compound to be horizontally oriented in a specified direction is likely to come into play.

[0049] When the laminate of the film substrate 1 and the aligned liquid crystal layer 3 is used as a laminated retardation plate, the front retardation etc. of the film substrate 1 may be set according to the optical design of the laminated retardation plate. The front retardation Re(550) of the film substrate 1 at a wavelength of 550 nm is, for example, 10 to 1000 nm.

[0050] The thickness of the film substrate 1 is not particularly limited, and is preferably about 10 to 300 μm in consideration of workability etc. From the viewpoint of allowing the alignment adjusting force to act on the liquid crystal compound, the in-plane birefringence Δn (the value obtained by dividing the front retardation by the thickness) of the film substrate 1 is preferably 1×10 -5 or more, more preferably 3×10 -5 or more, and still more preferably 5×10 -5 or more. The in-plane birefringence Δn of the film substrate 1 may also be 1×10 -4 or more, 3×10 -4 or more, or 5×10 -4 or more.

[0051] As the polymer material constituting the film substrate, a material that does not dissolve in the solvent of the liquid crystal composition and has heat resistance during heating for aligning the liquid crystal compound is used. Examples of the polymer include: ester-based polymers having an ester bond in the main chain such as polyester, polyarylate, and polycarbonate; polyolefin, cyclic polyolefin, cellulose-based polymer, acrylic polymer, styrene-based polymer, etc.

[0052] The film substrate preferably has an alignment adjusting force that horizontally aligns the liquid crystal compound non-parallel to the stretching direction of the film (the orientation direction of the polymer). If a liquid crystal composition is coated on the film substrate having such an alignment adjusting force and becomes a liquid crystal phase by heating, the liquid crystal compound is horizontally aligned in a predetermined direction by the alignment adjusting force of the film substrate.

[0053] The stretched film of a general polymer has an alignment adjusting force that horizontally aligns the liquid crystal compound in a direction parallel to the stretching direction (the orientation direction of the polymer). If a rod-like liquid crystal compound is aligned on such a stretched polymer film, a laminated film is formed in which the stretching direction of the polymer film is parallel to the orientation direction of the liquid crystal compound.

[0054] In contrast, by using a film substrate having an action of aligning the rod-like liquid crystal compound non-parallel to the orientation direction of the polymer, the orientation direction of the polymer in the film substrate 1 and the orientation direction of the liquid crystal compound in the aligned liquid crystal layer 3 become non-parallel. Therefore, a laminated optical film in which the slow axis direction of the film substrate 1 and the slow axis direction of the aligned liquid crystal layer 3 are non-parallel is obtained.

[0055] As a polymer having an alignment adjusting force for aligning a liquid crystal compound non-parallel to the stretching direction, a polymer having an asymmetric carbon in the repeating unit of the main chain can be cited. A polymer having an asymmetric carbon in the repeating unit of the main chain is obtained by using a compound having an asymmetric carbon as a monomer component. It is considered that when the polymer constituting the film substrate contains a repeating unit having an asymmetric carbon in the main chain and the polymer is aligned in a specified direction, if a liquid crystalline compound is aligned thereon in the form of a liquid crystal phase, an action of aligning the liquid crystalline compound in a direction different from the alignment direction of the polymer molecules is generated by the interaction between the structural unit containing an asymmetric carbon (chiral center) and the liquid crystal compound.

[0056] The type of the polymer is not particularly limited, and from the viewpoint of easily controlling the alignment adjusting force for the liquid crystal compound, an ester-based polymer is preferred. An ester-based polymer is a polymer containing an ester bond in the main chain, and is obtained by condensation, addition polymerization, transesterification, etc. of a dihydroxy compound (diol) and a compound containing a carbonyl group. Examples of the ester-based polymer include: polyester, polycarbonate, polyarylate, etc. Among them, from the viewpoint of a high ratio of the structure derived from the diol component in the main chain, polycarbonate (carbonate) is preferred.

[0057] Examples of the diol component of the ester-based polymer include: alicyclic diol, diol having a cyclic ether structure, aliphatic diol, oxyalkylene diols, aromatic diol, etc. By using a diol having an asymmetric carbon, a polymer containing a repeating unit having an asymmetric carbon is obtained. Examples of the diol having an asymmetric carbon include cyclic diols. The cyclic diol is preferably a cyclic diol in which at least one of the carbon atoms constituting the ring is an asymmetric carbon, and is preferably a non-aromatic cyclic diol.

[0058] The ring structure of the cyclic diol may be an alicyclic structure having only carbon, or may be a non-aromatic heterocycle containing a heteroatom such as oxygen, nitrogen, sulfur. As the heterocycle, for example, a cyclic ether can be cited. The ring structure of the cyclic diol may be a monocyclic or polycyclic.

[0059] The cyclic diol may have a hydroxyl group directly bonded to the carbon atom constituting the ring, or may have a hydroxyl group bonded to the carbon atom constituting the ring via an alkylene group such as a methylene group or a propylene group. Examples of the cyclic diol having an asymmetric carbon include isosorbide and its optical isomers isomannitol and isoidide.

[0060] The ester-based polymer may contain, as the diol component, a diol having no asymmetric carbon in addition to the diol having an asymmetric carbon.

[0061] Examples of the alicyclic diols include cyclohexanedimethanol, tricyclodecanedimethanol, pentacyclopentadecanedimethanol, decahydronaphthalenedimethanol, 2,3-norbornanedimethanol, adamantanediol, cyclohexanediol, decahydronaphthalenediol, norbornanediol, adamantanediol, etc.

[0062] Examples of the aliphatic diols include ethylene glycol, propylene glycol, butylene glycol, heptylene glycol, hexylene glycol, etc. Examples of the oxyalkylene diols include diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, etc. Examples of the aromatic diols include bisphenols typified by 2,2-bis(4-hydroxyphenyl)propane (=bisphenol A).

[0063] The ester polymers such as polycarbonate preferably contain an alicyclic diol as a diol component in addition to the diol having an asymmetric carbon. By including an alicyclic structure in the main chain of the ester polymer, the heat resistance of the polymer tends to increase. In addition, by including an alicyclic structure in the main chain of the ester polymer, the retardation of the stretched film tends to exhibit a flat wavelength dispersion. Among the above alicyclic diols, cyclohexanedimethanol, tricyclodecanedimethanol, adamantanediol, and pentacyclopentadecanedimethanol are preferred, and among them, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, and tricyclodecanedimethanol are preferred.

[0064] In 100 mol% of the total amount of the diol component of the ester polymer, the amount of the diol having an asymmetric carbon is preferably 30 mol% or more, more preferably 40 mol% or more, and still more preferably 50 mol% or more. The ratio of the diol having an asymmetric carbon can also be 55 mol% or more or 60 mol% or more. If the amount of the diol having an asymmetric carbon is within the above range, the orientation adjusting force for the liquid crystal compound on the film substrate tends to increase. The amount of one or more diols selected from isosorbide, isomannitol, and isoidide can be within the above range, and the amount of isosorbide can also be within the above range.

[0065] The ratio of the diol having an asymmetric carbon can be 95 mol% or less, 90 mol% or less, 85 mol% or less, or 80 mol% or less. The ester polymer can also contain 5 mol% or more, 10 mol% or more, or 20 mol% or more of an alicyclic diol as a diol component.

[0066] The film substrate may contain various ester-based polymers. Additionally, polymers other than the ester-based polymers may also be included. With respect to a total of 100 parts by weight of the resin materials constituting the film substrate, the content of the ester-based polymer having an asymmetric carbon in the repeating unit of the main chain is preferably 50 parts by weight or more, more preferably 60 parts by weight or more, and further preferably 70 parts by weight or more. The content of the ester-based polymer having an asymmetric carbon in the repeating unit of the main chain may also be 80 parts by weight or more, 90 parts by weight or more, 95 parts by weight or more, or 100 parts by weight.

[0067] [Form an aligned liquid crystal layer on the film substrate]

[0068] A laminated optical film in which the film substrate 1 and the aligned liquid crystal layer 3 are closely laminated is formed by coating a liquid crystal composition on the film substrate and orienting the liquid crystal compound in a liquid crystal state by heating. The method of coating the liquid crystal composition on the film substrate is not particularly limited, and methods such as spin coating, die coating, roll kiss coating, gravure coating, reverse coating, spraying, Meyer bar coat, knife roll coating, and air knife coating can be used. After coating the solution, the solvent is removed to form a liquid crystal composition layer on the film substrate. The coating thickness is preferably adjusted so that the thickness of the liquid crystal composition layer (the thickness of the aligned liquid crystal layer) after drying the solvent is about 0.1 to 20 μm.

[0069] The liquid crystal phase is formed by heating the liquid crystal composition layer formed on the film substrate, and the liquid crystal compound is oriented. Specifically, the liquid crystal composition is coated on the film substrate and then heated to a temperature above the N (nematic phase)-I (isotropic liquid phase) transition temperature (hereinafter simply referred to as the N-I transition temperature) of the liquid crystal composition to make the liquid crystal composition in an isotropic liquid state. Then, slow cooling is performed as needed to make the nematic phase appear. At this time, it is desirable to temporarily maintain the temperature in the liquid crystal phase to grow the liquid crystal phase domains into a single domain. Alternatively, the liquid crystal composition can be coated on the film substrate and then the temperature can be maintained within the temperature range where the nematic phase appears for a certain period of time to orient the liquid crystal compound. As described above, by using a film substrate containing a specified polymer, the liquid crystal compound can be horizontally oriented in a direction different from the stretching direction of the film substrate.

[0070] The heating temperature when orienting the liquid crystal compound can be appropriately selected according to the type of the liquid crystal composition, and is usually about 40 to 200 °C. If the heating temperature is too low, the transition to the liquid crystal phase tends to be insufficient. If the heating temperature is too high, there is a case where the orientation defects increase. The heating time can be adjusted so that the liquid crystal phase domains grow sufficiently, and is usually about 30 seconds to 30 minutes.

[0071] Preferably, the liquid crystal compound is aligned by heating and then cooled to a temperature below the glass transition temperature. The cooling method is not particularly limited. For example, it can be taken out from the heating atmosphere to room temperature. Forced cooling such as air cooling or water cooling can also be performed.

[0072] By irradiating the liquid crystal layer with light, photocuring is carried out in a state where the photopolymerizable liquid crystal compound (liquid crystal monomer) has liquid crystal regularity. The irradiated light only needs to be able to polymerize the photopolymerizable liquid crystal compound. Usually, ultraviolet light or visible light with a wavelength of 250 - 450 nm is used. When the liquid crystal composition contains a photoinitiator, only light with a wavelength at which the photoinitiator has sensitivity needs to be selected. As the irradiation light source, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a xenon lamp, an LED, a black light, a chemical lamp, etc. are used. In order to promote the photocuring reaction, the irradiation of light is preferably carried out in an inert gas atmosphere such as nitrogen.

[0073] The irradiation intensity only needs to be appropriately adjusted according to the composition of the liquid crystal composition, the addition amount of the photoinitiator, etc. The irradiation energy (cumulative irradiation light amount) is usually about 20 - 10000 mJ / cm 2 preferably 50 - 5000 mJ / cm 2 more preferably 100 - 800 mJ / cm 2 . In order to promote the photocuring reaction, the irradiation of light can also be carried out under heating conditions.

[0074] The polymer obtained by photocuring the liquid crystal monomer is non-liquid crystalline and does not undergo transitions between liquid crystal phases, glass phases, and crystal phases based on temperature changes. Therefore, it is difficult for the liquid crystal layer photocured in a state where the liquid crystal monomer is aligned in a specified direction to undergo changes in molecular orientation based on temperature changes. In addition, the birefringence of the aligned liquid crystal layer is significantly larger than that of a film containing a non-liquid crystal material. Therefore, the thickness of the optical anisotropic element having the desired retardation can be significantly reduced. The thickness of the aligned liquid crystal layer only needs to be set according to the target retardation value, etc., and is usually about 0.1 - 20 μm, preferably 0.2 - 10 μm, more preferably 0.5 - 7 μm.

[0075] Coating the liquid crystal composition on the film substrate, alignment of the liquid crystal compound based on heating, and photocuring can be carried out in a roll-to-roll manner while transporting the long film substrate in the length direction. By forming an aligned liquid crystal layer on the film substrate in a roll-to-roll manner, a long laminated optical film can be obtained. The long laminated optical film can be wound up in a roll to form a wound body. The width of the long laminated optical film can be 300 mm or more, 500 mm or more, 800 mm or more, or 1000 mm or more. The length of the long laminated optical film can be 10 m or more, 50 m or more, 100 m or more, 300 m or more, or 500 m or more.

[0076] As described above, for the stacked optical film of the present invention, the aligned liquid crystal layer 3 is in contact with the stretched film substrate 1, and by utilizing the alignment adjusting force of the stretched film substrate 1, the liquid crystal compound in the aligned liquid crystal layer 3 is aligned in the in-plane direction (horizontal alignment) of the film substrate 1. The stretching direction of the film substrate 1 is not parallel to the alignment direction of the liquid crystal compound in the aligned liquid crystal layer 3. Therefore, the slow axis direction of the film substrate 1 is not parallel to the slow axis direction of the aligned liquid crystal layer 3.

[0077] The angle formed by the slow axis direction of the film substrate 1 and the slow axis direction of the aligned liquid crystal layer 3 is, for example, 5 to 90°. When the slow axis direction of the film substrate 1 is taken as a reference (0°), the slow axis direction θ of the aligned liquid crystal layer 3 can be 5° or more, 10° or more, 15° or more, 20° or more, 30° or more, or 40° or more. θ can be 45°, can also be greater than 45°, can also be 50° or more, 60° or more, or 70° or more. θ can be 90°, can also be 85° or less.

[0078] The film substrate 1 is a stretched film and can function as a retardation plate even alone. The aligned liquid crystal layer 3 can function as a retardation plate with a single layer due to the horizontal alignment of liquid crystal molecules. By making the slow axis direction of the film substrate 1 not parallel to the slow axis direction of the aligned liquid crystal layer 3, the retardation of the stacked retardation plate can be adjusted.

[0079] For example, when the front retardation of the film substrate 1 is larger than the front retardation of the aligned liquid crystal layer 3 and the slow axis direction of the film substrate 1 is orthogonal to the slow axis direction of the aligned liquid crystal layer 3, the front retardation of the stacked retardation plate becomes a value obtained by subtracting the front retardation of the aligned liquid crystal layer 3 from the front retardation of the film substrate 1. By utilizing such a characteristic, the wavelength dispersion of the retardation of the stacked retardation plate can be adjusted. The wavelength dispersion of the front retardation of the retardation plate can be evaluated by the ratio Re(450) / Re(550) of the front retardation Re(450) at a wavelength of 450 nm to the front retardation Re(550) at a wavelength of 550 nm.

[0080] When the front retardation of the film substrate 1 is larger than that of the aligned liquid crystal layer 3 and the Re(450) / Re(550) of the film substrate 1 is smaller than that of the aligned liquid crystal layer 3, the Re(450) / Re(550) of the laminated optical film can be made smaller than that of the film substrate 1 alone. The slow axis direction of the film substrate 1 and the slow axis direction of the aligned liquid crystal layer 3 are not necessarily orthogonal. When the angle θ is greater than 45°, the wavelength dispersion of the laminated retardation plate based on the "subtraction" as described above can be adjusted. When adjusting the wavelength dispersion of the laminated retardation plate by subtraction, the angle θ formed by the slow axis direction of the film substrate 1 and the slow axis direction of the aligned liquid crystal layer 3 is preferably 50° or more, more preferably 60° or more, and further preferably 70° or more.

[0081] By using the "subtraction" of the front retardation as described above, a laminated retardation plate with Re(450) / Re(550) less than 1 and a greater retardation as the wavelength increases can also be obtained. The Re(450) / Re(550) of the laminated retardation plate can be 0.75 to 0.99. The Re(450) / Re(550) of the laminated retardation plate can also be 0.95 or less, 0.92 or less, or 0.90 or less. The Re(450) / Re(550) can also be 0.80 or more. The Re(450) / Re(550) of the retardation plate showing an ideal inverse wavelength dispersion is 0.82.

[0082] When the wavelength dispersion of the front retardation of the film substrate 1 alone is small (for example, Re(450) / Re(550) is 0.90 to 1.05) and the Re(450) / Re(550) of the aligned liquid crystal layer is larger than that of the film substrate, a laminated retardation plate with a small Re(450) / Re(550) can be obtained.

[0083] The Re(450) / Re(550) of the film substrate 1 can be 0.95 to 1.03. The larger the Re(450) / Re(550) of the aligned liquid crystal layer 3, the greater the adjustment effect of the wavelength dispersion based on the subtraction of the front retardation. The Re(450) / Re(550) of the aligned liquid crystal layer 3 can be 1.05 or more, 1.08 or more, or 1.10 or more.

[0084] The front retardation of the laminated optical film can be appropriately set according to the purpose of use, for example, about 10 to 500 nm. When the laminated optical film is laminated with a polarizer to form a circular polarizer, the Re(550) of the laminated optical film is preferably 90 to 180 nm, more preferably 110 to 160 nm, and further preferably 120 to 150 nm.

[0085] [Applications of the Alignment Liquid Crystal Layer and the Stacked Optical Film]

[0086] A stacked optical film 10 having an alignment liquid crystal layer 3 disposed thereon in contact with a film substrate 1 can be directly used as a stacked retardation plate.

[0087] It is also possible to peel the alignment liquid crystal layer 3 from the film substrate 1 of the stacked optical film 10 and transfer it to another substrate. In the case of peeling the alignment liquid crystal layer 3 from the long stacked optical film 10 and transferring it to another substrate, it can also be carried out by a roll-to-roll method. Since the alignment liquid crystal layer 3 has a slow axis in a direction not parallel to the length direction of the film substrate, it can be applied to adjusting the wavelength dispersion of retardation, etc. even when laminated with other substrates. In addition, a circular polarizing plate or an elliptical polarizing plate can be formed by laminating the alignment liquid crystal layer with a polarizer.

[0088] A polarizer can be formed by laminating a polarizer on one main surface or both main surfaces of the stacked optical film. Figure 2 It is a cross-sectional view of a polarizer 50 in which a polarizer 20 is laminated on one main surface of a stacked optical film 10. For the polarizer 50, the stacked optical film 10 is laminated on one main surface of the polarizer 20 with an adhesive layer 41 interposed therebetween. Figure 2 In [the figure], the surface on the film substrate 1 side of the stacked optical film 10 is in contact with the polarizer 20, but the surface on the alignment liquid crystal layer 3 side can also be in contact with the polarizer 20. In addition, other films can be laminated between the stacked optical film 10 and the polarizer 20.

[0089] A transparent film 30 as a polarizer protective film is adhered to the other main surface of the polarizer 20 with an adhesive layer 42 interposed therebetween. In addition, the polarizer of the present invention only needs to have the stacked optical film 10 laminated on one main surface of the polarizer 20, and the transparent film 30 can also be omitted. Other optical films can also be laminated on the polarizer in addition to the stacked optical film and the polarizer protective film. Specific examples of the optical film can include functional films such as a retardation film, a viewing angle enlarging film, a viewing angle limiting (anti-peeping) film, and a brightness enhancing film. An adhesive layer or an adhesive layer for bonding to an image display unit or the like can also be laminated on the polarizer.

[0090] The stacked optical film and the polarizer having an alignment liquid crystal layer can be used as an optical film for an image display device. For example, an image display device is formed by disposing the stacked optical film or the polarizer having the stacked optical film on the surface of the image display unit.

[0091] In the case of a liquid crystal display device, a retardation plate as an optical compensation film is sometimes disposed between an image display unit (liquid crystal unit) and a polarizer for the purpose of appropriately converting the polarization state of light emitted from the liquid crystal unit to the visual confirmation side and improving the viewing angle characteristics. In the case of an organic EL display device, a quarter-wave plate is sometimes disposed between the unit and the polarizer in order to suppress the reflection of external light by the metal electrode layer so that it looks like a mirror. In addition, by disposing a quarter-wave plate on the visual confirmation side of the polarizer, the emitted light becomes circularly polarized light, and even for a visual confirmation person wearing polarized sunglasses, an appropriate image display can be visually confirmed.

[0092] Example

[0093] Hereinafter, examples will be given to explain the present invention in more detail, but the present invention is not limited to the following examples.

[0094] [Example 1]

[0095] <Fabrication of a stretched film substrate>

[0096] Pellets of a polycarbonate resin containing isosorbide and 1,4-cyclohexanedimethanol as diol components in a molar ratio of 70:30 were used to produce an unstretched film with a thickness of 100 μm by melt extrusion. A stretched polycarbonate film A with the width direction coinciding with the slow axis direction was obtained by stretching it 1.6 times in the width direction at a stretching temperature of 131 °C using a tenter stretching machine. The front retardation of this film at a wavelength of 590 nm was 360 nm.

[0097] <Preparation of an alignment composition>

[0098] 100 parts by weight of a photopolymerizable liquid crystal compound showing a nematic liquid crystal phase (“Paliocolor LC242” manufactured by BASF), 0.5 parts by weight of a surfactant (“BYK-361” manufactured by BYK-Chemie), 3 parts by weight of a photopolymerization initiator (“Irgacure 907” manufactured by BASF), and 200 parts by weight of toluene were mixed to prepare a liquid crystal composition solution A.

[0099] <Formation of an aligned liquid crystal layer>

[0100] The liquid crystal composition A was coated on the above-mentioned stretched polycarbonate film A using a bar coater, heated at 110 °C for 150 seconds, and then cooled to room temperature. Thereafter, ultraviolet rays were irradiated in a nitrogen atmosphere for photopolymerization to form an aligned liquid crystal layer with a film thickness of 2.7 μm.

[0101] [Example 2]

[0102] <Fabrication of a stretched film substrate>

[0103] Pellets of a polycarbonate resin containing isosorbide and tricyclodecane dimethanol as a diol component in a molar ratio of 70:30 were used to obtain an unstretched film with a thickness of 100 μm by melt extrusion. Using a roll stretching machine, it was uniaxially stretched freely at one end in the longitudinal direction at a stretching temperature of 133 °C to 2.1 times, thereby obtaining a stretched polycarbonate film B in which the longitudinal direction coincides with the slow axis direction. The film had a front retardation of 360 nm at a wavelength of 590 nm.

[0104] <Formation of the aligned liquid crystal layer>

[0105] The above-mentioned stretched polycarbonate film B was used instead of the stretched polycarbonate film A. Other than this, an aligned liquid crystal layer was formed on the stretched film substrate in the same manner as in Example 1.

[0106] [Comparative Example 1]

[0107] <Production of the stretched film substrate>

[0108] Using a linear motor type tenter that can arbitrarily set the moving speed of the clamp, a norbornene-based resin film with a thickness of 80 μm ("Zeonor Film" manufactured by Zeon Corporation, Japan) was obliquely stretched such that the slow axis direction was 45° with respect to the conveying direction, thereby obtaining a stretched norbornene film. The film had a front retardation of 69 nm at a wavelength of 590 nm.

[0109] <Preparation of the alignment composition and formation of the aligned liquid crystal layer>

[0110] Except that the solvent was changed from toluene to methyl ethyl ketone, a liquid crystal composition solution B was prepared in the same manner as in Example 1. The liquid crystal composition B was coated on the above-mentioned stretched norbornene film, and heating, cooling, and photopolymerization were carried out in the same manner as in Example 1, thereby forming an aligned liquid crystal layer.

[0111] [Evaluation]

[0112] For the measurement of retardation and the slow axis direction, a polarization light / phase difference measurement system (manufactured by Axometrics, product name "AxoScan") was used and the measurement was carried out in an environment of 23 °C. Unless otherwise specified, the retardation value is the measured value at a wavelength of 550 nm. For the measurement of the aligned liquid crystal layer (monomer), the aligned liquid crystal layer was transferred to the side with the adhesive on a glass plate having an adhesive on the surface, and the film substrate was peeled off and removed, and the resulting specimen was used as a specimen for retardation measurement.

[0113] <Orientational property of the liquid crystal layer>

[0114] In Example 1 and Example 2, the slow axis direction of the aligned liquid crystal layer is 80° with respect to the slow axis direction of the film substrate. The sample was rotated in the range of -70° to +70° centered on the slow axis direction, and the retardation was measured every 10°. As a result, the retardation on the positive side and the negative side was substantially symmetric centered on the rotation angle of 0° (normal incidence). From these results, it was confirmed that in Example 1 and Example 2, the aligned liquid crystal layer on the stretched film substrate was horizontally aligned in the direction of 80° with respect to the slow axis of the film substrate.

[0115] In Comparative Example 1, the slow axis direction of the aligned liquid crystal layer was parallel to the slow axis direction of the film substrate (obliquely stretched film). Similarly to the above, the sample was rotated in the range of -70° to +70° centered on the slow axis direction, and the retardation was measured. As a result, the retardation on the positive side and the negative side was substantially symmetric, and thus it was confirmed that the liquid crystal compound was horizontally aligned in the direction parallel to the slow axis of the film substrate.

[0116] <Wavelength dispersion of front retardation>

[0117] The front retardation Re(450) of the laminated retardation film of Example 1 was 118 nm at a wavelength of 450 nm, the front retardation Re(550) was 132 nm at a wavelength of 550 nm, Re(450) / Re(550) was 0.89, and it showed reverse wavelength dispersion characteristics. The Re(450) of the stretched film substrate (polycarbonate film A) monomer of Example 1 was 372 nm, Re(550) was 362 nm, and Re(450) / Re(550) was 1.02. It was found that by forming an aligned liquid crystal layer with a slow axis direction horizontally aligned at an 80° inclination on the stretched film substrate, Re(450) / Re(550) became smaller. The laminated retardation film of Example 2 was the same as Example 1, Re(450) / Re(550) was 0.89, and by forming an aligned liquid crystal layer with a slow axis direction horizontally aligned at an 80° inclination on the stretched film substrate (polycarbonate film B), Re(450) / Re(550) became smaller.

[0118] Symbol description

[0119] 1 Film substrate

[0120] 3 Aligned liquid crystal layer

[0121] 10 Laminated optical film

[0122] 20 Polarizer

[0123] 30 Transparent film

[0124] 41, 42 Adhesive layer

[0125] 50 Polarizing plate

Claims

1. A laminated optical film having an alignment liquid crystal layer formed by horizontally aligning a rod-shaped liquid crystal compound on a film substrate, Among them, wherein the film substrate is a polymer film stretched in at least one direction and contains a polymer having an asymmetric carbon in a repeating unit of the main chain, the film substrate is in contact with the alignment liquid crystal layer, the angle formed by the slow axis direction of the film substrate and the slow axis direction of the alignment liquid crystal layer is 5° or more.

2. The laminated optical film according to claim 1, wherein, The film substrate contains an ester-based polymer having an ester bond, which contains a cyclic diol having an asymmetric carbon as a diol component of the ester-based polymer.

3. The stacked optical film according to claim 2, wherein, The cyclic diol having an asymmetric carbon contains one or more selected from isosorbide, isomannitol, and isoidide.

4. The laminated optical film according to claim 2 or 3, further comprising an alicyclic diol as a diol component of the ester-based polymer.

5. The stacked optical film according to claim 2 or 3, wherein, The ester-based polymer is a polycarbonate.

6. The laminated optical film according to any one of claims 1 to 3, wherein, The rod-shaped liquid crystal compound is a polymer of a photopolymerizable thermotropic liquid crystal compound.

7. The laminated optical film according to any one of claims 1 to 3, wherein the ratio Re(450) / Re(550) of the front retardation Re(450) at a wavelength of 450 nm to the front retardation Re(550) at a wavelength of 550 nm is 0.75 to 0.

99.

8. The laminated optical film according to any one of claims 1 to 3, wherein, The front retardation Re(550) of the film substrate at a wavelength of 550 nm is larger than the front retardation Re(550) of the alignment liquid crystal layer at a wavelength of 550 nm, the ratio Re(450) / Re(550) of the front retardation Re(450) to the front retardation Re(550) of the film substrate at a wavelength of 450 nm and at a wavelength of 550 nm is 0.90 to 1.05, the Re(450) / Re(550) of the alignment liquid crystal layer is larger than the Re(450) / Re(550) of the film substrate.

9. The laminated optical film according to any one of claims 1 to 3, wherein, The angle formed by the slow axis direction of the film substrate and the slow axis direction of the alignment liquid crystal layer is greater than 45°.

10. A polarizing plate formed by laminating the laminated optical film according to any one of claims 1 to 9 and a polarizer.

11. An image display device having the laminated optical film according to any one of claims 1 to 9 on the surface of an image display unit.

12. A method for manufacturing a laminated optical film, which is the method for manufacturing the laminated optical film according to any one of claims 1 to 9, wherein, A liquid crystal composition containing a liquid crystal compound is coated on a film substrate, the liquid crystal composition on the film substrate is heated, and the liquid crystal compound is aligned in a liquid crystal state.

13. The manufacturing method of the laminated optical film according to claim 12, wherein, The liquid crystal compound is a photopolymerizable liquid crystal monomer, the photopolymerizable liquid crystal monomer is aligned on the film substrate, and then the photopolymerizable liquid crystal monomer is polymerized or crosslinked by irradiating light.

Images