JP6878662B1 - Manufacturing method of oriented liquid crystal film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oriented liquid crystal film having a small change in optical characteristics and excellent heating durability even when exposed to a high temperature environment for a long time. An oriented liquid crystal film (101) includes an oriented liquid crystal layer (1) in which liquid crystal molecules are oriented. A surface treatment is performed in which an organic solvent is brought into contact with the surface of the oriented liquid crystal layer. The oriented liquid crystal layer may contain a photocurable product of a photopolymerizable liquid crystal compound. The oriented liquid crystal layer (1) and the optical layer (4) after the surface treatment may be bonded to each other via an adhesive. [Selection diagram] Fig. 2

Description

The present invention relates to a method for producing an oriented liquid crystal film in which liquid crystal molecules are oriented.

A liquid crystal film (aligned liquid crystal film) in which a liquid crystal compound is oriented in a predetermined direction is used as an optical film having functions such as optical compensation for a liquid crystal display device and prevention of external light reflection of an organic EL element. Since the oriented liquid crystal film has a larger birefringence than the polymer stretched film, it is advantageous in reducing the thickness and weight. In the image display device, the oriented liquid crystal film is attached to an organic EL panel or a liquid crystal display panel as a polarizing plate integrally laminated with a polarizing element via an adhesive or an adhesive (for example, Patent Document 1).

With the liquid crystal compound, the liquid crystal molecules can be oriented in a predetermined direction by the shearing force when applied onto the substrate, the orientation regulating force of the alignment film, etc., and an oriented liquid crystal film having various optical anisotropies can be obtained. Be done. For example, a homogeneously oriented liquid crystal layer in which nematic liquid crystal molecules having a positive refractive index anisotropy are oriented parallel to a substrate surface can be used as a positive A plate having a refractive index anisotropy of nx> ny = nz.

When a thermorotopic liquid crystal is used, a solution containing a liquid crystal compound (liquid crystal composition) is applied onto a substrate and heated so that the compound contained in the composition is in a liquid crystal state to orient the liquid crystal molecules. When the liquid crystal composition contains a photopolymerizable liquid crystal compound (liquid crystal monomer), the orientation state is fixed by orienting the liquid crystal molecules and then curing the liquid crystal monomer by light irradiation.

Japanese Unexamined Patent Publication No. 2015-7700

Image display devices such as liquid crystal display devices and organic EL display devices are required to have higher durability, and the optical members constituting the image display device are exposed to a high temperature environment for a long time. , It is required that the change in optical characteristics is small. Patent Document 1 describes that by controlling the orientation parameter of the liquid crystal compound, the change in retardation of the oriented liquid crystal film in a high temperature environment can be reduced.

The optical characteristics of the oriented liquid crystal film may change in a high temperature environment due to the influence of not only the oriented state of the liquid crystal but also the layer arranged adjacent to the liquid crystal layer. For example, when the alignment liquid crystal layer and the polarizer are bonded to each other via an adhesive layer, the retardation change in a high temperature environment hardly occurs, whereas the alignment is performed through an ultraviolet curable adhesive. In the sample in which the liquid crystal layer and the polarizer were bonded, the retardation tended to increase in a high temperature environment.

In view of these problems, it is an object of the present invention to provide an oriented liquid crystal film having a small change in optical characteristics and excellent heating durability even when exposed to a high temperature environment for a long time.

The oriented liquid crystal film includes an oriented liquid crystal layer in which liquid crystal molecules are oriented in a predetermined direction. In the oriented liquid crystal layer, for example, a liquid crystal composition containing a photopolymerizable liquid crystal monomer is applied onto a support substrate, the liquid crystal composition on the support substrate is heated, and the liquid crystal monomer is oriented in a liquid crystal state to produce light. It is formed by polymerizing or cross-linking a liquid crystal monomer by irradiation.

In one embodiment of the present invention, a surface treatment is performed in which an organic solvent is brought into contact with the surface of the oriented liquid crystal layer. For the surface treatment, for example, an organic solvent having solubility in the photopolymerizable liquid crystal monomer and insoluble or sparingly soluble in the photocurable product of the photopolymerizable liquid crystal monomer is used. The liquid used for the surface treatment may contain a small amount of resin.

The organic solvent may be removed from the surface of the oriented liquid crystal layer by heating after the surface treatment. The heating temperature is, for example, 40 to 150 ° C.

Further, the oriented liquid crystal layer and the optical layer after the surface treatment may be bonded to each other via an adhesive. Examples of the optical layer include a polarizer, a transparent film, and an oriented liquid crystal layer. The adhesive used for bonding the oriented liquid crystal layer and the optical layer may be an active energy ray-curable adhesive.

The oriented liquid crystal film of the present invention has excellent heating durability, and the change in retardation is small even when exposed to a high temperature environment for a long time. Therefore, it is suitably used as an optical member for an image display device such as a liquid crystal display device or an organic EL display device.

It is sectional drawing of the oriented liquid crystal film provided with the liquid crystal layer on the support substrate. It is sectional drawing of the orientation liquid crystal film in which an optical layer is laminated on the surface of a liquid crystal layer. It is sectional drawing of the orientation liquid crystal film in which an optical layer is laminated on the surface of a liquid crystal layer. It is sectional drawing of the oriented liquid crystal film provided with a pressure-sensitive adhesive layer. It is sectional drawing of the orientation liquid crystal film in which an optical layer is laminated on the surface of a liquid crystal layer. It is sectional drawing which shows the laminated structure example of the image display apparatus.

The oriented liquid crystal film includes an oriented liquid crystal layer in which liquid crystal molecules are oriented. FIG. 1 is a cross-sectional view showing the configuration of the oriented liquid crystal film of one embodiment, and the aligned liquid crystal film 101 includes an oriented liquid crystal layer 1 on a support substrate 8. An oriented liquid crystal layer 1 is formed by applying a liquid crystal composition containing a liquid crystal compound on the support substrate 8, orienting the liquid crystal compound in a predetermined direction, and then fixing the oriented state.

<Liquid crystal composition>
Examples of the liquid crystal compound include a rod-shaped liquid crystal compound and a disk-shaped liquid crystal compound. A rod-shaped liquid crystal compound is preferable as the liquid crystal compound because it is easy to be homogenically oriented due to the orientation regulating force of the support substrate. The rod-shaped liquid crystal compound may be a main chain type liquid crystal or a side chain type liquid crystal. The rod-shaped liquid crystal compound may be a liquid crystal polymer or a polymer of a polymerizable liquid crystal compound. As long as the liquid crystal compound (monomer) before polymerization exhibits liquid crystallinity, it may not exhibit liquid crystallinity after polymerization.

The liquid crystal compound is preferably a thermotropic liquid crystal that develops liquid crystal properties by heating. The thermotropic liquid crystal undergoes a phase transition of a crystal phase, a liquid crystal phase, and an isotropic phase as the temperature changes. The liquid crystal compound contained in the liquid crystal composition may be any of a nematic liquid crystal, a smectic liquid crystal, and a cholesteric liquid crystal. A chiral agent may be added to the nematic liquid crystal to give it cholesteric orientation.

Examples of the rod-shaped liquid crystal compound exhibiting thermotropic properties include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidins, and alkoxy. Substituted phenylpyrimidines, phenyldioxans, trans, alkenylcyclohexylbenzonitriles and the like can be mentioned.

Examples of the polymerizable liquid crystal compound include a polymerizable liquid crystal compound capable of fixing the orientation state of the rod-shaped liquid crystal compound using a polymer binder, and a polymerizable functional group having a polymerizable functional group capable of fixing the orientation state of the liquid crystal compound by polymerization. Examples include liquid crystal compounds. Among these, a photopolymerizable liquid crystal compound having a photopolymerizable functional group is preferable.

The photopolymerizable liquid crystal compound (liquid crystal monomer) has a mesogen group and at least one photopolymerizable functional group in one molecule. The temperature at which the liquid crystal monomer exhibits liquid crystal properties (liquid crystal phase transition temperature) is preferably 40 to 200 ° C, more preferably 50 to 150 ° C, still more preferably 55 to 100 ° C.

Examples of the mesogen group of the liquid crystal monomer include a biphenyl group, a phenylbenzoate group, a phenylcyclohexane group, an azoxybenzene group, an azomethine group, an azobenzene group, a phenylpyrimidine group, a diphenylacetylene group, a diphenylbenzoate group, a bicyclohexane group and a cyclohexylbenzene group. A cyclic structure such as a terphenyl group can be mentioned. The terminal of these cyclic units may have a substituent such as a cyano group, an alkyl group, an alkoxy group, or a halogen group.

Examples of the photopolymerizable functional group include (meth) acryloyl group, epoxy group, vinyl ether group and the like. Of these, the (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 crosslinked structure is introduced into the liquid crystal layer after photocuring, so that the durability of the oriented liquid crystal film tends to be improved.

As the photopolymerizable liquid crystal monomer, any suitable liquid crystal monomer can be adopted. For example, International Publication No. 00/37585, US Pat. No. 5211877, US Pat. No. 4,388453, International Publication No. 93/22397, European Patent No. 02671712, German Patent No. 195042224, German Patent No. 4408171, U.S. Pat. No. 2,280,445, Japanese Patent Application Laid-Open No. 2017-206460, International Publication No. 2014/126113, International Publication No. 2016/114348, International Publication No. 2014/010325, Japanese Patent Application Laid-Open No. 2015-20877, Japanese Patent Application Laid-Open No. 2010- 31223, International Publication 2011/050896, Japanese Patent Application Laid-Open No. 2011-207765, Japanese Patent Application Laid-Open No. 2010-31223, Japanese Patent Application Laid-Open No. 2010-270108, International Publication No. 2008/119427, Japanese Patent Application Laid-Open No. 2008-107767 Examples thereof include the compounds described in Japanese Patent Application Laid-Open No. 2008-273925, International Publication No. 2016/125839, Japanese Patent Application Laid-Open No. 2008-273925, and the like. By selecting the liquid crystal monomer, the expression of birefringence and the wavelength dispersion of the retardation can be adjusted.

In addition to the liquid crystal monomer, the liquid crystal composition may contain a compound that controls the orientation of the liquid crystal monomer in a predetermined direction. For example, by including the side chain type liquid crystal polymer in the liquid crystal composition, the liquid crystal compound (monomer) can be homeotropically oriented. Further, by adding a chiral agent to the liquid crystal composition, the liquid crystal compound can be cholesterically oriented.

The liquid crystal composition may contain a photopolymerization initiator. When the liquid crystal monomer is cured by ultraviolet irradiation, the liquid crystal composition preferably contains a photopolymerization initiator (photoradical generator) that generates radicals by light irradiation in order to promote photocuring. Depending on the type of liquid crystal monomer (type of photopolymerizable functional group), a photocation generator or a photoanion generator may be used. The amount of the photopolymerization initiator used is about 0.01 to 10 parts by weight with respect to 100 parts by weight of the liquid crystal monomer. A sensitizer or the like may be used in addition to the photopolymerization initiator.

A liquid crystal composition can be prepared by mixing the liquid crystal monomer with a solvent, if necessary, various orientation control agents, polymerization initiators and the like. The solvent is not particularly limited as long as it can dissolve the liquid crystal monomer and does not erode the substrate (or has low erosion resistance), and is not particularly limited, and is chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene. , Orthodichlorobenzene and other halogenated hydrocarbons; Phenol, Barachlorophenol and other solvents; Aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, 1,2-dimethoxybenzene; Acetone, methylethylketone, methylisobutyl Ketone solvents such as ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, N-methyl-2-pyrrolidone; ester solvents such as ethyl acetate and butyl acetate; t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, Alcohol-based solvents such as ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2,4-pentanediol; amide solvents such as dimethylformamide and dimethylacetamide; nitrile solvents such as acetonitrile and butyronitrile Ether-based solvents such as diethyl ether, dibutyl ether and tetrahydrofuran; ethyl cell solve, butyl cell solve and the like can be mentioned. A mixed solvent of two or more kinds of solvents may be used.

The solid content concentration of the liquid crystal composition is usually about 5 to 60% by weight. The liquid crystal composition may contain additives such as a surfactant and a leveling agent.

<Support board>
Examples of the support substrate 8 to which the liquid crystal composition is applied include a glass plate, a metal plate, a metal belt, a resin film substrate, and the like. The support substrate has a first main surface and a second main surface, and the liquid crystal composition is applied on the first main surface.

By using a film substrate as the support substrate 8, a series of steps from application of the liquid crystal composition on the substrate to photocuring of the liquid crystal monomer and subsequent heat treatment can be carried out by roll-to-roll. The productivity of the oriented liquid crystal film can be improved. The resin material constituting the film substrate is not particularly limited as long as it is insoluble in the solvent of the liquid crystal composition and has heat resistance at the time of heating for orienting the liquid crystal composition, and is not particularly limited. Polyesters such as naphthalate; Polyethylenes such as polyethylene and polypropylene; Cyclic polyolefins such as norbornene polymers; Cellulosic polymers such as diacetylcellulose and triacetylcellulose; Acrylic polymers; Styrene polymers; Polycarbonates, polyamides, polyimides and the like. ..

The support substrate 8 may have an orientation ability for orienting liquid crystal molecules in a predetermined direction. For example, by using a stretched film as a support substrate, it is possible to homogenically orient the liquid crystal molecules along the stretching direction. The stretch ratio of the stretched film may be as long as it can exhibit the orientation ability, and is, for example, about 1.1 times to 5 times. The stretched film may be a biaxially stretched film. Even if it is a biaxially stretched film, if a film having different stretching ratios in the longitudinal direction and the horizontal direction is used, the liquid crystal molecules can be oriented along the direction in which the stretching ratio is large. The stretched film may be a diagonally stretched film. By using the stretched film as the support substrate 8, the liquid crystal molecules can be oriented in a direction that is not parallel to either the longitudinal direction or the width direction of the support substrate.

The support substrate 8 may have an alignment film on the first main surface. As the alignment film, an appropriate one may be appropriately selected depending on the type of the liquid crystal compound, the material of the substrate, and the like. As the alignment film for homogenically aligning the liquid crystal molecules in a predetermined direction, a polyimide-based or polyvinyl alcohol-based alignment film that has been subjected to rubbing treatment is preferably used. Further, a photoalignment film may be used. The resin film as the support substrate may be subjected to a rubbing treatment without providing the alignment film.

The support substrate 8 may include an alignment film for homeotropic alignment of liquid crystal molecules. Examples of the orientation agent for forming a homeotropic orientation film (vertical alignment film) include lecithin, stearic acid, hexadecyltrimethylammonium bromide, octadecylamine hydroxychloride, monobasic carboxylic acid chromium complex, and silane coupling agent. And organic silanes such as siloxane compounds, perfluorodimethylcyclohexane, tetrafluoroethylene, polytetrafluoroethylene and the like.

<Formation of oriented liquid crystal layer on the support substrate>
When the liquid crystal compound is a thermotropic liquid crystal, the liquid crystal composition is applied on the first main surface of the support substrate 8 and the liquid crystal compound is oriented into a liquid crystal state by heating.

The method of applying the liquid crystal composition on the support substrate 8 is not particularly limited, and spin coating, Daiko, kiss roll coating, gravure coating, reverse coating, spray coating, Meyer bar coating, knife roll coating, air knife coating and the like are applied. Can be adopted. After applying the solution, the solvent is removed to form a liquid crystal composition layer on the support substrate. The coating thickness is preferably adjusted so that the thickness of the liquid crystal composition layer (thickness of the oriented liquid crystal film) after drying the solvent is about 0.1 to 20 μm.

The liquid crystal compound is oriented by heating the liquid crystal composition layer formed on the support substrate to form a liquid crystal phase. Specifically, after applying the liquid crystal composition on the support substrate, the liquid crystal composition is heated to the N (nematic phase) -I (isotropic liquid phase) transition temperature or higher of the liquid crystal composition to obtain the liquid crystal composition or the like. Make it a directional liquid crystal state. From there, the nematic phase is expressed by slow cooling as needed. At this time, it is desirable to temporarily maintain the temperature at which the liquid crystal phase is exhibited and grow the liquid crystal phase domain to form a monodomain. Alternatively, after the liquid crystal composition is applied onto the support substrate, the liquid crystal molecules may be oriented in a predetermined direction while maintaining the temperature for a certain period of time within the temperature range in which the nematic phase appears.

The heating temperature at which the liquid crystal compound is oriented in a predetermined direction may be appropriately selected depending on the type of the liquid crystal composition, and is usually about 40 to 200 ° C. If the heating temperature is excessively low, the transition to the liquid crystal phase tends to be insufficient, and if the heating temperature is excessively high, orientation defects may increase. The heating time may be adjusted so that the liquid crystal phase domain grows sufficiently, and is usually about 30 seconds to 30 minutes.

After orienting the liquid crystal compound by heating, it is preferable to cool the liquid crystal compound to a temperature equal to or lower than the glass transition temperature. The cooling method is not particularly limited, and for example, it may be taken out from the heating atmosphere to room temperature. Forced cooling such as air cooling or water cooling may be performed.

By irradiating the liquid crystal layer with light, photocuring is performed in a state where the photopolymerizable liquid crystal compound (liquid crystal monomer) has liquid crystal regularity. The irradiation light may be any light as long as it is possible to polymerize a photopolymerizable liquid crystal compound, and usually ultraviolet or visible light having a wavelength of 250 to 450 nm is used. When the liquid crystal composition contains a photopolymerization initiator, light having a wavelength at which the photopolymerization initiator has sensitivity may be selected. As the irradiation light source, a low pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a metal halide lamp, a xenon lamp, an LED, a black light, a chemical lamp and the like are used. In order to promote the photocuring reaction, it is preferable that the light irradiation is carried out in an atmosphere of an inert gas such as nitrogen gas.

When the liquid crystal composition is photocured, the liquid crystal compound can be oriented in a predetermined direction by using polarized light in a predetermined direction. As described above, when the liquid crystal compound is oriented by the orientation restricting force of the support substrate 8, the irradiation light may be unpolarized light (natural light).

The irradiation intensity may be appropriately adjusted according to the composition of the liquid crystal composition, the amount of the photopolymerization initiator added, and the like. The irradiation energy (integrated irradiation light amount) is usually ^{about 20} to 10000 mJ / cm ² , preferably 50 to 5000 mJ / cm ² , and more preferably 100 to 800 mJ / cm 2. In order to promote the photocuring reaction, light irradiation may be carried out under heating conditions.

The polymer obtained by photocuring the liquid crystal monomer by light irradiation is non-liquid crystal, and the transition of the liquid crystal phase, the glass phase, and the crystal phase does not occur due to a temperature change. Therefore, the liquid crystal layer photo-cured with the liquid crystal monomer oriented in a predetermined direction is unlikely to change in molecular orientation due to a temperature change. Further, since the oriented liquid crystal film has a remarkably large birefringence as compared with a film made of a non-liquid crystal material, the thickness of the optically anisotropic element having a desired retardation can be remarkably reduced. The thickness of the oriented liquid crystal film (liquid crystal layer) may be set according to the target retardation value or the like, and is usually about 0.1 to 20 μm, preferably 0.2 to 10 μm, and 0.5 to 7 μm. More preferred.

The optical characteristics of the oriented liquid crystal layer are not particularly limited. The frontal retardation and the thickness direction retardation of the oriented liquid crystal layer may be appropriately set according to the intended use and the like. When the liquid crystal is homogenically oriented, the front retardation of the oriented liquid crystal layer is, for example, about 20 to 1000 nm. When the oriented liquid crystal layer is a 1/4 wave plate, the front retardation is preferably 100 to 180 nm, more preferably 120 to 150. When the oriented liquid crystal layer is a 1/2 wave plate, the front retardation is preferably 200 to 340 nm, more preferably 240 to 300 nm. When the liquid crystal is homeotropically oriented, the in-plane retardation of the oriented liquid crystal layer is approximately 0 (for example, 5 nm or less, preferably 3 nm or less), and the absolute value of the thickness direction retardation is about 30 to 500 nm. ..

(surface treatment)
As described above, the photocured liquid crystal layer does not undergo a phase transition even when heated, and therefore has excellent thermal stability as compared with the uncured oriented liquid crystal layer. However, if the photocured liquid crystal layer is exposed to a high temperature environment for a long time, the optical characteristics may change, and there is room for improvement in heating durability. In particular, an oriented liquid crystal film in which another optical layer is attached to the oriented liquid crystal layer via an adhesive tends to increase the retardation when heated for a long time, and has a problem in heating durability.

In the embodiment of the present invention, the surface treatment is carried out by bringing an organic solvent into contact with the surface of the oriented liquid crystal layer after fixing the orientation by photocuring or the like. By carrying out the surface treatment, the thermal stability of the optical characteristics of the oriented liquid crystal layer is improved.

The organic solvent used for the surface treatment is not particularly limited, but one that does not dissolve the oriented liquid crystal layer is preferable. For example, when the oriented liquid crystal layer contains a photocurable product of a photopolymerizable liquid crystal monomer, an organic solvent in which the cured product is insoluble or sparingly soluble is preferable. On the other hand, the organic solvent may be one that exhibits solubility in a liquid crystal compound (monomer) before photocuring. The organic solvent may be one kind of solvent or a mixed solvent of two or more kinds.

The liquid used for the surface treatment may contain a resin component in addition to the organic solvent. The resin component may be a liquid at room temperature and may become a solid resin by heat or photocuring. However, when the amount of the resin component is excessively large, the optical influence of the resin layer formed on the surface of the oriented liquid crystal layer may have a serious influence on the optical characteristics such as a decrease in transparency. Therefore, the amount of the resin component contained in the liquid used for the surface treatment is preferably 15% by weight or less, more preferably 10% by weight or less, and may be 5% by weight or less or 3% by weight or less. When the liquid used for the surface treatment contains a resin component, the glass transition temperature of the resin is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, and may be 40 ° C. or higher or 50 ° C. or higher. Further, the resin component is preferably a non-curable polymer which does not have photocurability and thermosetting property.

The method of bringing the above liquid into contact with the surface of the oriented liquid crystal layer is not particularly limited, and a dipping method and various coating methods can be appropriately adopted. The contact treatment time is not particularly limited, but from the viewpoint of improving the heating stability of the optical characteristics of the oriented liquid crystal layer, 10 seconds or more is preferable, and 20 seconds or more is more preferable. If the treatment time is excessively long, there is a concern that the productivity may decrease and the oriented liquid crystal layer may be dissolved in the organic solvent. Therefore, the treatment time is preferably 60 minutes or less, more preferably 30 minutes or less, and preferably 10 minutes or less. More preferably, it may be 5 minutes or less or 3 minutes or less.

After the surface treatment with the above liquid, it is preferable to remove the organic solvent adhering to the surface of the oriented liquid crystal layer. For example, the organic solvent is removed by heating. From the viewpoint of the removal efficiency of the organic solvent, the heating temperature is preferably 40 ° C. or higher, more preferably 50 ° C. or higher. If the heating temperature is excessively high, the heating stability of the oriented liquid crystal film may decrease due to heat damage to the base material, reorientation of the liquid crystal compound, and the like. Therefore, the heating temperature is preferably 150 ° C. or lower, more preferably 130 ° C. or lower, and may be 110 ° C. or lower or 100 ° C. or lower.

Instead of or in addition to the above heating, surface cleaning with water or an organic solvent may be performed. By cleaning the surface of the oriented liquid crystal layer after contacting it with an organic solvent, the monomers and additives precipitated from the oriented liquid crystal layer to the organic solvent are removed, which is expected to have the effect of suppressing contamination of the oriented liquid crystal layer surface. it can.

The reason why the heating durability of the oriented liquid crystal layer is improved by the surface treatment using an organic solvent is not clear, but the uncured monomer remaining in the liquid crystal layer after photocuring and the formation of a three-dimensional network structure are not possible. It is considered that one of the causes is that the free additives and the like contained in the sufficient portion are eluted with the organic solvent, and the substance causing the retardation change due to heating is removed from the oriented liquid crystal layer.

In the above embodiment, in the oriented liquid crystal film 101 in which the aligned liquid crystal layer 1 is closely laminated on the support substrate 8, the organic solvent is brought into contact with the surface (air surface) of the oriented liquid crystal layer 1 that is not in contact with the support substrate 8. However, after peeling the support substrate 8 from the oriented liquid crystal layer 1, the surface of the exposed oriented liquid crystal layer 1 may be surface-treated with an organic solvent. Further, both surfaces of the oriented liquid crystal layer may be surface-treated with an organic solvent.

<Lamination of optical layer on oriented liquid crystal layer>
The oriented liquid crystal film is not limited to the form shown in FIG. For example, as shown in FIG. 2, in the oriented liquid crystal film 102, another optical layer 4 is formed on a surface of the oriented liquid crystal layer 1 that is not in contact with the support substrate 8 via an appropriate adhesive layer 3 or an adhesive layer. It may be laminated.

The optical layer 4 is not particularly limited, and an optically isotropic or optically anisotropic film generally used as an optical film can be used without particular limitation. Specific examples of the optical layer 4 include transparent films such as retardation films and protector protective films, polarizers, viewing angle enlargement films, viewing angle limiting (peeping prevention) films, and functional films such as brightness improving films. Be done. The optical layer 4 may be a single layer or a laminated body. The optical layer 4 may be an oriented liquid crystal layer. For example, the optical layer 4 may be a polarizing plate in which a transparent protective film is bonded to one surface or both surfaces of a polarizing element. When the polarizing plate has a transparent protective film on one surface, the polarizer and the oriented liquid crystal layer may be bonded together, or the transparent protective film and the oriented liquid crystal layer may be bonded together.

For example, in a liquid crystal display device, an image display cell (liquid crystal cell) and a polarizer are used for the purpose of appropriately converting the polarization state of light emitted from the liquid crystal cell to the visual recognition side to improve viewing angle characteristics. A retardation plate as an optical compensation film may be arranged between them. In an organic EL display device, a 1/4 wave plate may be arranged between a cell and a polarizing plate in order to prevent external light from being reflected by a metal electrode layer and visually recognized as a mirror surface. ..

As described above, the heating durability of the oriented liquid crystal layer 1 in the aligned liquid crystal film 102 can be improved by treating the surface of the oriented liquid crystal layer 1 with an organic solvent and then laminating the optical layer 4. In particular, when the optical layer 4 is attached to the surface of the oriented liquid crystal layer 1 after the surface treatment via the adhesive layer 3, the heating durability of the oriented liquid crystal layer is improved as compared with the case where the surface treatment is not performed. Tends to be prominent.

The material of the adhesive constituting the adhesive layer 3 used for laminating the oriented liquid crystal layer 1 and the optical layer 4 is not particularly limited as long as it is optically transparent, and is an epoxy resin, a silicone resin, an acrylic resin, or a polyurethane. , Polyamide, polyether, polyvinyl alcohol and the like. The thickness of the adhesive layer 3 is, for example, about 0.01 to 20 μm, and is appropriately set according to the type of adherend, the material of the adhesive, and the like. When a curable adhesive that exhibits adhesiveness by a cross-linking reaction after coating is used, the thickness of the adhesive layer 3 is preferably 0.01 to 5 μm, more preferably 0.03 to 3 μm.

As the adhesive, various forms such as a water-based adhesive, a solvent-based adhesive, a hot melt adhesive, and an active energy ray-curable adhesive are used. Among these, a water-based adhesive or an active energy ray-curable adhesive is preferable because the thickness of the adhesive layer can be reduced.

Examples of the water-based adhesive include those containing a water-soluble or water-dispersible polymer such as vinyl polymer-based, gelatin-based, vinyl-based latex-based, polyurethane-based, isocyanate-based, polyester-based, and epoxy-based adhesive. The adhesive layer made of such a water-based adhesive is formed by applying an aqueous solution on the film and drying it. When preparing the aqueous solution, if necessary, a cross-linking agent, other additives, a catalyst such as an acid can be added.

Crosslinking agents to be added to water-based adhesives include boric acid and borax; carboxylic acid compounds; alkyldiamines; isocyanates; epoxies; monoaldehydes; dialdehydes; amino-formaldehyde resins; divalent metals or trivalents. Examples thereof include salts of valence metals and oxides thereof.

The active energy ray-curable adhesive is an adhesive capable of radical polymerization, cationic polymerization or anionic polymerization by irradiation with active energy rays such as electron beam and ultraviolet rays. Among them, a photoradical polymerizable adhesive in which radical polymerization is started by irradiation with ultraviolet rays is preferable because it can be cured with low energy.

Examples of the monomer of the radically polymerizable adhesive include a compound having a (meth) acryloyl group and a compound having a vinyl group. Of these, compounds having a (meth) acryloyl group are preferable. Compounds having a (meth) acryloyl group include _{alkyl (meth) acrylates such as C 1-20} chain alkyl (meth) acrylate, alicyclic alkyl (meth) acrylate, and polycyclic alkyl (meth) acrylate; hydroxyl group. Containing (meth) acrylate; Examples thereof include epoxy group-containing (meth) acrylate such as glycidyl (meth) acrylate. Radical-polymerizable adhesives include hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, (meth) acrylamide, and (meth) acryloylmorpholin. It may contain a nitrogen-containing monomer such as. The radically polymerizable adhesive contains tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecanedimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane glycol diacrylate, and EO-modified diacrylate as cross-linking components. It may contain a polyfunctional monomer such as glycerin tetraacrylate.

The photocurable adhesive such as a photoradical polymerizable adhesive preferably contains a photopolymerization initiator. The photopolymerization initiator may be appropriately selected depending on the reaction species. For example, it is preferable to add a photoradical generator that generates radicals by light irradiation to the radically polymerizable adhesive as a photopolymerization initiator. Specific examples of the photoradical generator will be described later. The content of the photoradical generator is usually about 0.1 to 10 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the monomer. When the radically polymerizable adhesive is used as an electron beam curable type, a photopolymerization initiator is not particularly required. A photosensitizer typified by a carbonyl compound or the like can be added to the radically polymerizable adhesive, if necessary. Photosensitizers are used to increase the curing rate and sensitivity of electron beams. The amount of the photosensitizer used is usually about 0.001 to 10 parts by weight, preferably 0.01 to 3 parts by weight, based on 100 parts by weight of the monomer.

The adhesive may contain an appropriate additive, if necessary. Examples of additives include coupling agents such as silane coupling agents and titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, deterioration inhibitors, dyes, processing aids, ion trap agents, and antioxidants. , Adhesive-imparting agent, filler, plasticizer, leveling agent, foaming inhibitor, antistatic agent, heat-resistant stabilizer, hydrolysis-resistant stabilizer and the like.

By applying an adhesive to one or both of the surface of the oriented liquid crystal layer 1 and the surface of the optical layer 4 and curing the adhesive, the oriented liquid crystal layer 1 and the optical layer 4 are laminated via the adhesive layer 3. .. Curing of the adhesive may be appropriately selected according to the type of the adhesive. For example, water-based adhesives can be cured by heating. The active energy ray-curable adhesive can be cured by irradiation with active energy rays such as ultraviolet rays.

The oriented liquid crystal film 102 in which the optical layer 4 is laminated on the oriented liquid crystal layer 1 may be used as it is as an optical member. In this case, the support substrate 8 constitutes a part of the oriented liquid crystal film. The support substrate may be peeled off from the oriented liquid crystal layer 1 as in the oriented liquid crystal film 103 shown in FIG. An appropriate adhesive layer 2 may be laminated as shown in FIG. 4 or an optical layer 5 may be laminated as shown in FIG. 5 on the surface of the oriented liquid crystal layer 1 exposed by peeling of the support substrate. .. Before laminating the pressure-sensitive adhesive layer or the optical layer on the exposed surface of the oriented liquid crystal layer 1 after the support substrate is peeled off, a surface treatment may be performed in which an organic solvent is brought into contact with the surface of the oriented liquid crystal layer.

The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer 2 is not particularly limited, and those using an acrylic polymer, a silicone-based polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine-based polymer, a rubber-based polymer, or the like as a base polymer are appropriately selected. Can be used. In particular, adhesives such as acrylic pressure-sensitive adhesives and rubber-based pressure-sensitive adhesives, which have excellent transparency, exhibit appropriate wettability, cohesiveness, and adhesiveness, and are excellent in weather resistance, heat resistance, and the like are preferable. The thickness of the pressure-sensitive adhesive layer is appropriately set according to the type of adherend and the like, and is generally about 5 to 500 μm.

The lamination of the pressure-sensitive adhesive layer 2 on the oriented liquid crystal layer 1 is performed, for example, by laminating a pressure-sensitive adhesive previously formed in a sheet shape on the surface of the oriented liquid crystal layer 1. After applying the pressure-sensitive adhesive composition on the oriented liquid crystal layer 1, the pressure-sensitive adhesive layer 2 may be formed by drying, cross-linking, photo-curing, or the like of the solvent. In order to increase the adhesive force (anchoring force) between the oriented liquid crystal layer 1 and the pressure-sensitive adhesive layer 2, a surface treatment such as corona treatment or plasma treatment or an easy-adhesion layer is formed on the surface of the oriented liquid crystal layer 1, and then the pressure-sensitive adhesive layer is formed. 2 may be laminated.

It is preferable that the separator 9 is temporarily attached to the surface of the pressure-sensitive adhesive layer 2. The separator 9 protects the surface of the pressure-sensitive adhesive layer 2 until the optical film with the pressure-sensitive adhesive is attached to the image display cell 50. As a constituent material of the separator, a plastic film such as acrylic, polyolefin, cyclic polyolefin, or polyester is preferably used. The thickness of the separator is usually about 5 to 200 μm. It is preferable that the surface of the separator is subjected to a mold release treatment. Examples of the release agent include silicone-based materials, fluorine-based materials, long-chain alkyl-based materials, fatty acid amide-based materials, and the like.

In the form shown in FIG. 4, the pressure-sensitive adhesive layer 2 is laminated on the exposed surface of the oriented liquid crystal layer 1 after the support substrate 8 is peeled off, but even if the pressure-sensitive adhesive layer is laminated on the air surface side of the oriented liquid crystal layer 1. Good.

Another optical layer may be laminated on the exposed surface of the oriented liquid crystal layer 1 after the support substrate 8 is peeled off, via an appropriate adhesive layer or an adhesive layer. For example, as shown in FIG. 5, another optical layer 5 may be laminated on the oriented liquid crystal layer 1 via an appropriate adhesive layer 7. An adhesive layer (not shown) may be further laminated on the optical layer 5, and a separator may be temporarily attached to the surface of the adhesive layer.

<Circular polarizing plate>
The oriented liquid crystal film can be used as an optical film for a display for the purpose of improving visibility and the like. For example, in a liquid crystal display device, an image display cell (liquid crystal cell) and a polarizer are used for the purpose of appropriately converting the polarization state of light emitted from the liquid crystal cell to the visual recognition side to improve viewing angle characteristics. A retardation plate as an optical compensation film may be arranged between them.

In one embodiment, the oriented liquid crystal film is a circularly polarizing plate in which a polarizing plate as an optical layer 4 is bonded to one surface of the oriented liquid crystal layer 1 via an adhesive layer 3. The circularly polarizing plate may include two or more oriented liquid crystal layers.

The polarizing plate may be composed of only one layer of a polarizing element, and as described above, a transparent protective film may be attached to one surface or both sides of the polarizing element. As the polarizer, a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymerization system partially saponified film, and a bicolor substance such as iodine or a dichroic dye are used. Examples thereof include those obtained by adsorbing and uniaxially stretching the film, and polyene-based oriented films such as a dehydrated product of polyvinyl alcohol and a dehydrogenated product of polyvinyl chloride.

Among them, since it has a high degree of polarization, polyvinyl alcohol or a polyvinyl alcohol-based film such as partially formalized polyvinyl alcohol is adsorbed with a dichroic substance such as iodine or a dichroic dye and oriented in a predetermined direction. Alcohol (PVA) -based polarizers are preferred. For example, a PVA-based polarizer can be obtained by subjecting a polyvinyl alcohol-based film to iodine dyeing and stretching. A PVA-based resin layer may be formed on the resin base material, and iodine dyeing and stretching may be performed in the state of the laminated body.

In a circularly polarizing plate in which a polarizing plate and an oriented liquid crystal layer are laminated, it is preferable that at least one oriented liquid crystal layer has liquid crystal molecules homogenically oriented. In the circular polarizing plate, the orientation direction of the liquid crystal molecules in the oriented liquid crystal layer in which the liquid crystal molecules are homogenically oriented is arranged so that the direction of the absorption axis of the polarizer is neither parallel nor orthogonal.

For example, when the circularly polarizing plate has only one oriented liquid crystal layer, the oriented liquid crystal layer 1 is a 1/4 wave plate, and the absorption axis direction of the polarizer and the orientation direction of the liquid crystal molecules (generally the slow phase axis direction). The angle between the two is set to 45 °. The angle formed by the absorption axis direction of the polarizer and the orientation direction of the liquid crystal molecules may be 35 to 55 °, 40 to 50 °, or 43 to 47 °.

In the configuration in which the polarizing plate 4 and the oriented liquid crystal layer 1 as the 1/4 wave plate are laminated so that the angle formed by the optical axes of both is 45 °, the liquid crystal molecules are further formed as the optical layer 5 as the substrate. An oriented liquid crystal layer that is vertically oriented (homeotropic oriented) with respect to the surface may be provided. By sequentially laminating the oriented liquid crystal layer 1 as a 1/4 wave plate and the homeotropic oriented liquid crystal layer 5 functioning as a positive C plate on the polarizing plate, reflected light is also reflected from external light from an oblique direction. It is possible to form a circularly polarizing plate that can shield the light. A homeotropically oriented liquid crystal layer (positive C plate) and a homogeneously oriented liquid crystal layer (a 1/4 wave plate which is a positive A plate) may be laminated in this order on the polarizing plate.

As shown in FIG. 5, in a circular polarizing plate in which a plurality of oriented liquid crystal layers 1 and 5 are laminated on a polarizing plate 4 as an optical layer, even if the oriented liquid crystal layers 1 and 5 are all homogeneous oriented liquid crystal layers. Good. In this case, it is preferable that the oriented liquid crystal layer 1 arranged on the side closer to the polarizing plate 4 is a 1/2 wavelength plate and the oriented liquid crystal layer 5 arranged on the side far from the polarizing plate is a 1/4 wavelength plate. .. In this laminated structure, the angle between the slow-phase axial direction of the 1/2 wave plate and the absorption axis direction of the polarizer is 75 ° ± 5 °, and the slow-phase axial direction of the 1/4 wave plate and the absorption axial direction of the polarizer. It is preferable to arrange them so that the angle between them is 15 ° ± 5 °. Since the circularly polarizing plate having such a laminated structure functions as a circularly polarizing plate over a wide wavelength range of visible light, it is possible to reduce the coloring of the reflected light.

[Image display device]
FIG. 6 is a cross-sectional view showing an example of a laminated configuration of an image display device, in which an oriented liquid crystal film including an oriented liquid crystal layer 1 is attached to the surface of an image display cell 50 via an adhesive layer 2. The oriented liquid crystal film may include two or more oriented liquid crystal layers. Examples of the image display cell 50 include a liquid crystal cell and an organic EL cell.

As described above, the heating durability of the oriented liquid crystal layer is improved by performing the surface treatment in which the surface of the oriented liquid crystal layer is brought into contact with the organic solvent. An image display device provided with a surface-treated oriented liquid crystal layer has a small change in visibility even when exposed to a heating environment for a long time, and therefore has excellent heating durability. There is.

Hereinafter, the present invention will be described in more detail with reference to examples of producing an oriented liquid crystal film, but the present invention is not limited to the following examples.

[Preparation of oriented liquid crystal film]
<Comparative example 1>
A photopolymerizable liquid crystal compound showing a nematic liquid crystal phase (“Pariocolor LC242” manufactured by BASF) was dissolved in cyclopentanone to prepare a solution having a solid content concentration of 30% by weight. A liquid crystal composition solution was prepared by adding a surfactant (“BYK-360” manufactured by BIC Chemie) and a photopolymerization initiator (“Omnirad 907” manufactured by IGM Resins) to this solution. The amount of the leveling agent and the polymerization initiator added was 0.01 part by weight and 3 parts by weight, respectively, with respect to 100 parts by weight of the photopolymerizable liquid crystal compound.

As a film base material, a biaxially stretched norbornene-based film (“Zeonor film” manufactured by ZEON Corporation, thickness: 33 μm, in-plane retardation: 135 nm) was used. The above liquid crystal composition was applied to the surface of the film substrate with a bar coater so that the thickness after drying was 1 μm, and the liquid crystal was oriented by heating at 100 ° C. for 3 minutes. After cooling to room temperature, the film was photo-cured by irradiating ultraviolet rays with an integrated light intensity of 400 mJ / cm ^{2 in} a nitrogen atmosphere to obtain a laminate in which a homogeneously oriented liquid crystal layer was formed on a film substrate.

<Example 1>
Cyclopentanone was applied to the surface of the oriented liquid crystal layer of the laminated body of Comparative Example 1 with a wire bar (# 10), and then heated at 110 ° C. for 1 minute to remove the solvent.

<Examples 2 and 3>
Treatment with cyclopentanone was carried out in the same manner as in Example 1 except that the heating temperature at the time of removing the solvent was changed as shown in Table 1.

<Example 4>
As a surface treatment liquid, a cyclopentanone solution (resin content: 3% by weight) of an acrylic resin (manufactured by Kusumoto Kasei, a copolymer of methyl methacrylate and butyl methacrylate, weight average molecular weight of 200,000) was prepared. The surface treatment liquid was applied to the surface of the oriented liquid crystal layer of the laminated body of Comparative Example 1 with a wire bar (# 10), and then heated at 85 ° C. to remove the solvent.

[Polarizing plate with oriented liquid crystal layer (manufacturing of circular polarizing plate]]
Prepare a laminate (single protective polarizing plate) in which a PVA-based polarizer with a thickness of 5 μm is provided on one side of an unstretched norbornene-based film with a thickness of 20 μm (“Zeonoa film” manufactured by Nippon Zeon) via a UV curable adhesive. did.

62 parts by weight of hydroxyethyl acrylamide (“HEAA” manufactured by Kojin), 25 parts by weight of acryloylmorpholin (“ACMO” manufactured by Kojin), 7 parts by weight of PEG400 # diacrylate (“Light Acrylate 9EG-A” manufactured by Kyoeisha Chemical Co., Ltd.), and UV curable adhesive composition by mixing 3 parts by weight of photopolymerization initiator (“Omnirad 907” manufactured by IGM Resins) and 3 parts by weight of 2,4-diethylthioxanthone (“Kayacure DETX-S” manufactured by Nippon Kayaku). Was prepared. This adhesive is applied to the surface of the above-mentioned single protective polarizing plate to a thickness of about 1 μm, and the surface of the laminated body of Examples and Comparative Examples on the oriented liquid crystal layer side is bonded onto the coating layer of the adhesive. The adhesive was cured by irradiating with ultraviolet rays having an integrated light amount of 1000 mJ / cm ^2. At the time of bonding, the angle formed by the absorption axis direction of the polarizer and the orientation direction of the liquid crystal molecules in the alignment liquid crystal layer (the slow axis direction of the film substrate) was set to 45 °.

The film base material is peeled off from the oriented liquid crystal film, an acrylic pressure-sensitive adhesive sheet having a thickness of 15 μm is attached to the surface of the oriented liquid crystal film, and the oriented liquid crystal layer is placed on the polarizer of the single-protective polarizing plate via a UV curable adhesive layer. Was bonded together, and a polarizing plate provided with an acrylic pressure-sensitive adhesive sheet was obtained.

[Evaluation]
The pressure-sensitive adhesive layer of the above polarizing plate was attached to a glass plate to prepare a sample for evaluation. After measuring the in-plane retardation having a wavelength of 590 nm with a phase difference meter (“KOBRA21-ADH” manufactured by Oji Measuring Instruments), the evaluation sample was put into an air circulation type constant temperature oven at 85 ° C. for 120 hours. After taking out the sample from the oven, the in-plane retardation was measured again, and the rate of change of the retardation before and after the heating test was calculated.

Table 1 shows the surface treatment conditions (type of treatment liquid and heating temperature) of the oriented liquid crystal layer of each of the above Examples and Comparative Examples, and the rate of change of the in-plane retardation Re before and after the heating test.

In Comparative Example 1 in which the surface treatment of the oriented liquid crystal layer was not carried out, the amount of Re change before and after the heating test was 3%, whereas in Examples 1 to 3 in which the treatment with cyclopentanone was carried out, comparison was made. The rate of change in Re was reduced as compared with Example 1, and excellent heating durability was exhibited. Also in Example 4 using the treatment liquid containing the resin, the Re change before and after the heating test was suppressed as in Examples 1 to 3.

1 Oriented liquid crystal layer 8 Support substrate 4 Optical layer (polarizing plate)
5 Optical layer (aligned liquid crystal layer)
3, 7 Adhesive layer 2 Adhesive layer 9 Separator 50 Image display cell

Claims (8)

A method for producing an oriented liquid crystal film having an oriented liquid crystal layer in which liquid crystal molecules are homogenically oriented.
A method for producing an oriented liquid crystal film, in which a surface treatment is performed in which an organic solvent is brought into contact with the surface of the oriented liquid crystal layer. The method for producing an oriented liquid crystal film according to claim 1, wherein after the surface treatment, heating is performed at 40 to 150 ° C. to remove the organic solvent from the surface of the oriented liquid crystal layer. The method for producing an oriented liquid crystal film according to claim 1 or 2, further comprising a step of bonding the aligned liquid crystal layer and the optical layer after the surface treatment via an adhesive. The method for producing an oriented liquid crystal film according to claim 3, wherein the optical layer is a polarizer, a transparent film, or another oriented liquid crystal layer. The method for producing an oriented liquid crystal film according to claim 3 or 4, wherein the adhesive is an active energy ray-curable adhesive. A coating step of applying a liquid crystal composition containing a photopolymerizable liquid crystal monomer onto a support substrate;
It has an alignment step of heating the liquid crystal composition on the support substrate to homodiasically align the liquid crystal monomer in a liquid crystal state; and a photocuring step of polymerizing or cross-linking the liquid crystal monomer by light irradiation.
The method for producing an oriented liquid crystal film according to any one of claims 1 to 5 , wherein the surface treatment is carried out after the photocuring step. The method for producing an oriented liquid crystal film according to claim 6 , wherein the supporting substrate is a resin film. The sixth or seven claim, wherein the organic solvent used for the surface treatment has solubility in the photopolymerizable liquid crystal monomer and is insoluble or sparingly soluble in the photocurable product of the photopolymerizable liquid crystal monomer. A method for producing an oriented liquid crystal film.

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