JP6769921B2 - Manufacturing method of liquid crystal alignment film - Google Patents

Description

The present invention relates to a process for the manufacture of liquid crystal alignment fill-time.

Optical films (phase difference films) having various refractive index anisotropies are used for the purpose of optical compensation of liquid crystal display devices, prevention of external light reflection of organic EL elements, and the like. As the retardation film, a stretched polymer film is generally used. From the viewpoint of thinning and weight reduction, a liquid crystal alignment film in which liquid crystal molecules are oriented in a predetermined direction is also used.

As the liquid crystal alignment film, a film in which liquid crystal molecules are homogenically or homeotropically oriented on a substrate provided with an alignment film is known. Patent Document 1 describes a liquid crystal composition that spontaneously orients homeotropically on a substrate that does not have a vertically oriented film.

In a retardation film in which the refractive index nz in the thickness direction is an intermediate value between the refractive index nz in the slow axis direction in the plane and the refractive index ny in the phase advance axis direction, the retardation changes due to the change in the viewing direction. It is small and is used for viewing angle compensation of displays. In order to realize the refractive index anisotropy of nx> nz> ny in one film, it is necessary to orient the molecules in the in-plane direction and the thickness direction in the film.

In the polymer film, a heat-shrinkable film is attached to both sides, and the polymer film is stretched so as to expand in the thickness direction by the shrinkage force of the heat-shrinkable film to obtain refractive index anisotropy of nx> nz> ny. A retardation film having is obtained. On the other hand, it is not easy to orient liquid crystal molecules in multiple directions. As the liquid crystal alignment film having a refractive index anisotropy of nx> nz> ny, an example in which a plurality of liquid crystal alignment films are laminated (for example, Patent Document 2) and an example in which a plurality of types of lyotropic liquid crystal compounds are used (for example, Patent Document 3). ) Etc. are few.

Patent No. 4174192 Japanese Unexamined Patent Publication No. 2008-122851 WO2011 / 138869 Pamphlet

An object of the present invention is to provide a liquid crystal alignment film which can be made thinner and whose refractive index anisotropy is controlled.

The present invention relates to a liquid crystal alignment film containing a side chain type thermotropic liquid crystal polymer and a polymer of a thermotropic liquid crystal compound. As the side chain type thermotropic liquid crystal polymer, one having a monomer unit containing a liquid crystal fragment side chain and a monomer unit containing a non-liquid crystal fragment side chain is preferably used. The content of the polymer of the thermotropic liquid crystal compound is preferably 1.2 to 20 times the content of the side chain type thermotropic liquid crystal polymer.

In one embodiment of the liquid crystal alignment film of the present invention, the refractive index nx in the slow axis direction in the plane, the refractive index ny in the phase advance axis direction in the plane, and the refractive index nz in the thickness direction are nx> nz> ny. Meet. Preferably, the NZ coefficient represented by NZ = (nx-nz) / (nx-ny) is 0.2 to 0.8.

Liquid crystal alignment film, the Oriented film is not provided a film on a substrate, coating a liquid crystal composition containing a side chain type thermotropic liquid crystal polymer and photopolymerizable the thermotropic liquid crystal compound (coating step), the side It can be produced by heating and aligning a chain-type thermotropic liquid crystal polymer and a thermotropic liquid crystal compound (liquid crystal alignment step), and polymerizing or cross-linking the thermotropic liquid crystal compound by light irradiation (photopolymerization step).

In the present invention, a stretched film is used as the film substrate. The in-plane retardation of the stretched film used as the film substrate is preferably 10 to 1000 nm, for example. The larger the in-plane retardation and the in-plane birefringence of the film substrate, the larger the NZ coefficient of the liquid crystal alignment film tends to be (approaching 1). As the film substrate, for example, a norbornene-based polymer film is used.

The higher the heating temperature at the time of liquid crystal alignment by heating, the higher the homogenous orientation of the liquid crystal molecules, and the larger the NZ coefficient of the liquid crystal alignment film tends to be. It is preferable that the heating temperature T (° C.) at the time of liquid crystal orientation and the in-plane birefringence Δn of the film substrate satisfy T ≧ 90-5 × 10 ³ Δn. By adjusting the heating temperature T to this range, it is easy to obtain a liquid crystal alignment film having an NZ coefficient larger than 0.

According to the present invention, a liquid crystal oriented film having controlled refractive index anisotropy can be obtained.

The liquid crystal alignment film of the present invention contains a polymer of a side chain type liquid crystal polymer and a liquid crystal compound. Both the side chain type liquid crystal polymer and the liquid crystal compound (photopolymerizable liquid crystal monomer) exhibit thermotropic liquid crystal properties. The liquid crystal alignment film is produced by applying a liquid crystal composition containing a liquid crystal polymer and a liquid crystal monomer on a substrate and fixing the orientation thereof.

[Liquid crystal composition]
The liquid crystal composition used for producing the liquid crystal alignment film contains a side chain type thermotropic liquid crystal polymer and a photopolymerizable thermotropic liquid crystal compound (monomer).

<Side chain type liquid crystal polymer>
As the side chain type thermotropic liquid crystal polymer, a copolymer having a monomer unit containing a thermotropic liquid crystal fragment side chain and a monomer unit containing a non-liquid crystal fragment side chain is used. Since the polymer has a thermotropic liquid crystal fragment in the side chain, the side chain type liquid crystal polymer is oriented when the liquid crystal composition is heated to a predetermined temperature. Further, when the side chain type polymer has a non-liquid crystal fragment in the side chain, the non-liquid crystal fragment interacts with the photopolymerizable liquid crystal monomer to cause a homeotropic orientation of the photopolymerizable liquid crystal monomer.

Examples of the monomer having a liquid crystal fragment side chain include a polymerizable compound having a nematic liquid crystalline substituent containing a mesogen group. The mesogen group includes 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, a cyclohexylbenzene group and a terphenyl group. And the like, an annular structure 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. Among them, those having a biphenyl group and a phenylbenzoate group are preferable as the mesogen group.

Examples of the monomer having a non-liquid crystal fragment side chain include a polymerizable compound having a linear substituent such as a long-chain alkyl having 7 or more carbon atoms. Examples of the polymerizable functional group of the liquid crystalline monomer and the non-liquid crystalline monomer include a (meth) acryloyl group.

As the side chain type thermotropic liquid crystal polymer, a copolymer having a liquid crystal monomer unit represented by the general formula (I) and a non-liquid crystal monomer unit represented by the general formula (II) is preferably used.

In formula (I), R ¹ is a hydrogen atom or a methyl group, R ² is a cyano group, a fluoro group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms, and X ¹ Is -CO _2- or -OCO-. a is an integer of 1 to 6, and b and c are independently 1 or 2, respectively.

In the formula (II), R ³ is a hydrogen atom or a methyl group, and R ⁴ is represented by an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or the following general formula (III). It is a base.

In formula (III), R ⁵ is an alkyl group having 1 to ⁵ carbon atoms, and d is an integer of 1 to 6.

The ratio of the liquid crystal monomer unit to the non-liquid crystal monomer unit in the side chain type liquid crystal monomer is not particularly limited, but when the ratio of the non-liquid crystal monomer unit is small, the photopolymerizable liquid crystal monomer accompanying the orientation of the side chain type liquid crystal polymer When the proportion of the liquid crystal monomer unit is small, it becomes difficult for the side chain type liquid crystal polymer to exhibit the liquid crystal monodomain orientation. Therefore, the ratio of the non-liquid crystal monomer to the total of the liquid crystal monomer unit and the non-liquid crystal monomer unit is preferably 0.05 to 0.8, more preferably 0.1 to 0.6, and 0.15 in terms of molar ratio. ~ 0.5 is more preferable. From the viewpoint of achieving both film formation property and orientation of the liquid crystal composition, the weight average molecular weight of the side chain type liquid crystal polymer is preferably about 2000 to 100,000, more preferably about 2500 to 50000.

The side chain type liquid crystal polymer can be polymerized by various known methods. For example, when the monomer unit has a (meth) acryloyl group as a polymerizable functional group, a side chain type liquid crystal polymer having a liquid crystal fragment and a non-liquid crystal fragment can be obtained by radical polymerization using light or heat.

<Photopolymerizable thermotropic liquid crystal monomer>
The photopolymerizable thermotropic liquid crystal monomer has a mesogen group and at least one photopolymerizable functional group in one molecule. Examples of the mesogen group include those described above as liquid crystal fragments of the side chain type liquid crystal polymer. 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 photopolymerization, so that the durability of the liquid crystal alignment film tends to be improved.

Examples of the photopolymerizable liquid crystal compound having a mesogen group and a plurality of (meth) acryloyl groups in one molecule include a compound represented by the following general formula (IV).

In formula (IV), R is a hydrogen atom or a methyl group, A and D are independently 1,4-phenylene groups or 1,4-cyclohexylene groups, and B is a 1,4-phenylene group, 1 , 4-Cyclohexylene group, 4,4'-biphenylene group or 4,4'-bicyclohexylene group, where Y and Z are independently -COO-, -OCO- or -O-, respectively. g and h are independently integers of 2 to 6.

As a commercially available product of the photopolymerizable liquid crystal monomer represented by the above general formula (IV), "Pariocolor LC242" manufactured by BASF Corporation can be exemplified.

<Composition>
The ratio of the photopolymerizable liquid crystal compound to the side chain type liquid crystal polymer in the liquid crystal composition is not particularly limited. When the content of the side chain type liquid crystal polymer is high, the homeotropic orientation due to the interaction with the polymer becomes predominant, and the NZ coefficient represented by (nx-nz) / (nx-ny) tends to be small. is there. On the other hand, when the content of the photopolymerizable liquid crystal compound is large, the homogeneous orientation of the liquid crystal compound due to the orientation regulating force of the substrate becomes predominant, and the NZ coefficient represented by (nx-nz) / (nx-ny) becomes large. Tend. In order to obtain a liquid crystal alignment film having an NZ coefficient in the range of 0.2 to 0.8, the content of the photopolymerizable liquid crystal compound is preferably 1.2 to 20 times the content of the side chain type liquid crystal polymer. In order to obtain a liquid crystal alignment film having an NZ coefficient close to 0.5, the content of the photopolymerizable liquid crystal compound is preferably 1.3 to 10 times the content of the side chain type liquid crystal polymer, and 1.4 to 9 times. Double is more preferable, and 1.5 to 8 times is further preferable.

In order to accelerate the curing of the photopolymerizable liquid crystal compound by light irradiation, the liquid crystal composition preferably contains a photopolymerization initiator. Examples of the photopolymerization initiator include Irgacure 907, Irgacure 184, Irgacure 651, and Irgacure 369 manufactured by BASF. The content of the photopolymerization initiator in the liquid crystal composition is usually about 0.5 to 20 parts by weight, preferably about 3 to 15 parts by weight, more preferably about 3 to 15 parts by weight, based on 100 parts by weight of the photopolymerizable liquid crystal compound. Is about 5 to 10 parts by weight.

A liquid crystal composition can be prepared by mixing a side chain type liquid crystal polymer, a photopolymerizable liquid crystal compound, a photopolymerization initiator and a solvent. The solvent is not particularly limited as long as it can dissolve the side chain type liquid crystal polymer and the photopolymerizable liquid crystal compound and does not erode the film substrate (or has low erosion resistance), and chloroform, dichloromethane, carbon tetrachloride, etc. Halogenized hydrocarbons such as dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene and orthodichlorobenzene; solvents such as phenol and barachlorophenol; aromatics such as benzene, toluene, xylene, methoxybenzene and 1,2-dimethoxybenzene. Hydrocarbons; Ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl 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, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2,4-pentanediol and other alcohol solvents; dimethylformamide, dimethylacetamide and other amide-based solvents. Solvents; nitrile solvents such as acetonitrile and butyronitrile; ether solvents such as diethyl ether, dibutyl ether and tetrahydrofuran; ethyl cell solves, butyl cell solves and the like can be mentioned. The concentration of the liquid crystal composition is usually about 3 to 50% by weight, preferably about 7 to 35% by weight.

[Film substrate]
To obtain a liquid crystal alignment film having a refractive index anisotropy of nx>nz> ny is used as the substrate for coating the liquid crystalline composition, it is preferable to use a stretched film Oriented film is not provided. By using the stretched film substrate, the photopolymerizable liquid crystal compound has a homeotropic orientation action due to interaction with the side chain type liquid crystal polymer and a homogeneous alignment action due to the molecular orientation of the polymer constituting the stretched film substrate. .. By balancing these orientation actions, the orientation of the photopolymerizable liquid crystal compound can be adjusted and the refractive index anisotropy of the liquid crystal alignment film can be controlled.

The in-plane retardation R ₀ of the stretched film used as the film substrate is generally 10 nm or more. The larger the in-plane retardation of the film substrate, the greater the orientation of the polymer constituting the film in a predetermined direction (late phase axis direction or phase advance axis direction), and the liquid crystal orientation formed on the film substrate accordingly. The homogeneous orientation of the layer tends to increase, and the NZ coefficient tends to increase (approach 1). If the in-plane retardation of the stretched film is excessively large, it tends to be difficult to control the orientation of the liquid crystal molecules. Therefore, the in-plane retardation R ₀ of the stretched film is preferably 1000 nm or less, more preferably 500 nm or less. It is preferable, and 400 nm or less is more preferable.

The thickness of the film substrate is not particularly limited, but is usually about 10 to 200 μm in consideration of handleability and the like. The in-plane birefringence Δn (value obtained by dividing the in-plane retardation R ₀ by the thickness) of the stretched film is preferably 0.0001 to 0.05, more preferably 0.0005 to 0.03, and 0.001 to 0. .02 is more preferred.

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. Polyethylene terephthalate, polyethylene 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. .. Above all, it is particularly preferable to use a norbornene-based polymer film as a film substrate because it is easy to obtain a film having excellent fluidity during molding and high smoothness. A norbornene-based polymer film is preferable because it has excellent peelability when the liquid crystal alignment film is transferred to another substrate or the like. Examples of the norbornene-based polymer include Zeonoa and Zeonex manufactured by Zeon Corporation of Japan, and Arton manufactured by JSR.

The film substrate has a first main surface and a second main surface, and the liquid crystal composition is applied on the first main surface. The arithmetic average roughness Ra of the first main surface of the film substrate is preferably 3 nm or less, more preferably 2 nm or less, still more preferably 1.5 nm or less. By applying the liquid crystal composition to the surface of the film substrate having a small Ra and high smoothness, the orientation defects of the liquid crystal alignment film tend to be reduced.

By stretching the film, irregularities such as die lines during film formation are leveled, so that Ra of the film substrate tends to be small. Therefore, by using the stretched film substrate, in addition to being able to control the refractive index anisotropy of the liquid crystal alignment film, orientation defects tend to be reduced. It is particularly preferable to use a biaxially stretched film as the film substrate because the surface uniformity is high.

In order to keep the arithmetic mean roughness in the above range, it is preferable that the film substrate does not contain a filler inside. A film that does not contain a filler and has a high surface smoothness has low slipperiness, which may cause blocking, transfer failure in a roll-to-roll process, and winding failure. Examples of prevention of blocking and poor transport due to high smoothness include a method of attaching another highly slippery film to the film substrate and a method of providing an easy-slip layer on the film substrate. When another film is attached to the film substrate, defects caused by transfer of the adhesive layer, etc. to the first main surface (the surface on which the liquid crystal composition is applied) (such as poor alignment of the liquid crystal and optical defects) are suppressed. From the viewpoint of this, it is preferable to bond it to the second main surface (the surface opposite to the coated surface of the liquid crystal composition). However, in the roll-to-roll process, when the film substrate is wound, the adhesive or the like adhering to the second main surface may be transferred to the first main surface, which may cause misalignment or optical defects.

Therefore, it is preferable to improve the slipperiness by providing the slippery layer on at least one surface of the film substrate. Examples of the slippery layer include those in which a binder such as polyester or polyurethane contains a fine filler having an average particle size of 100 nm or less. From the viewpoint of maintaining the peelability when transferring the homeotropic-oriented liquid crystal film to another substrate or the like, and suppressing defects such as transfer of the slippery layer to the homeotropic-oriented liquid crystal film when peeling from the film substrate. The film substrate preferably does not have an easy-slip layer on the surface to which the liquid crystal composition is applied. That is, it is preferable to use a film substrate having an easy-slip layer on the second main surface and no easy-slip layer on the first main surface.

[Formation of liquid crystal alignment film on film substrate]
A liquid crystal alignment film is formed by applying a liquid crystal composition on a film substrate, aligning the liquid crystal molecules in a liquid crystal state by heating, fixing the orientation by cooling, and polymerizing or cross-linking the liquid crystal monomers by light irradiation. can get. Therefore, the liquid crystal alignment film contains a liquid crystal polymer and a polymer of a liquid crystal compound.

The method of applying the liquid crystal composition on the film substrate is not particularly limited, and spin coating, die coating, kiss roll coating, gravure coating, reverse coating, spray coating, Meyer bar coating, knife roll coating, air knife coating, etc. are adopted. it can. After applying 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 (thickness of the liquid crystal alignment film) after drying the solvent is about 0.5 to 5 μm. Since the in-plane retardation of the liquid crystal alignment film is represented by the product of the in-plane birefringence (nx-ny) and the thickness, the larger the thickness, the larger the in-plane retardation. Further, as shown in the experimental examples described later, the larger the coating thickness, the larger the NZ coefficient of the liquid crystal alignment film tends to be.

By heating the liquid crystal composition layer formed on the film substrate to form a liquid crystal phase, the side chain type liquid crystal polymer is homeotropically oriented. At that time, the photopolymerizable liquid crystal compound undergoes a homeotropic orientation effect due to the interaction with the non-liquid crystal fragment of the side chain type liquid crystal polymer. When an unstretched film substrate is used, the orientation regulating force of the substrate does not act, so that both the side chain type liquid crystal polymer and the photopolymerizable liquid crystal compound are homeotropically oriented to form a homeotropic oriented liquid crystal layer. On the other hand, when a stretched film substrate is used, the refractive index anisotropy of the liquid crystal alignment film differs depending on the heating temperature, and the higher the temperature, the smaller the refractive index nz in the thickness direction, and (nx-nz) / (nx-). The NZ coefficient represented by ny) tends to increase.

It is considered that the higher the heating temperature, the smaller the refractive index nz in the thickness direction is due to the difference in the orientation behavior of the photopolymerizable liquid crystal compound depending on the heating temperature. That is, when the heating temperature is low, the interaction between the non-liquid crystal fragment of the liquid crystal monomer and the photopolymerizable liquid crystal compound is strong, and the photopolymerizable liquid crystal compound is predominantly homeotropic orientation, whereas the heating temperature is high. Therefore, it is considered that the influence of the orientation restricting force of the stretched film substrate becomes stronger, and the homogeneous orientation of the photopolymerizable liquid crystal compound becomes predominant. One of the reasons why the influence of the orientation restricting force of the film substrate increases as the temperature rises is that the polymerizable liquid crystal compound undergoes an isotropic phase transition at high temperature and is easily affected by the orientation regulating force of the film substrate when returning to the liquid crystal phase by cooling. Can be considered.

In the present invention, by utilizing the above findings, the orientation of the liquid crystal composition is controlled, and the refractive index nz in the thickness direction is the refractive index nz in the slow axis direction in the plane and the refractive index ny in the phase advance axis direction. A liquid crystal oriented film having an intermediate value between and (NZ coefficient is greater than 0 and less than 1) can be produced.

When a stretched film substrate is used, in addition to the heating temperature, the composition of the liquid crystal composition, the in-plane retardation of the stretched film substrate, and the in-plane birefringence also affect the refractive index anisotropy of the liquid crystal oriented film. Therefore, it is not possible to unconditionally determine an appropriate temperature range for aligning the liquid crystal compound after applying the liquid crystal composition on the stretched film substrate, but the heating temperature for obtaining a liquid crystal oriented film having an NZ coefficient greater than 0. T is preferably 70 ° C. or higher, more preferably 75 ° C. or higher, and even more preferably 80 ° C. or higher. Further, it is preferable that the heating temperature T (° C.) and the in-plane birefringence Δn of the film substrate satisfy T ≧ 90-5 × 10 ³ Δn. The heating temperature T (° C.) is more preferably 95-5 × 10 ³ Δn or more, more preferably 100-5 × 10 ³ Δn or more, and further preferably 105-5 × 10 ³ Δn or more.

When the liquid crystal molecules are uniformly homogenically oriented, the liquid crystal oriented film becomes a positive A plate of nx = nz> ny (NZ = 1). The heating temperature T for coexisting the homeotropic alignment component and the homogenius alignment component to obtain a liquid crystal alignment film of nx> nz (NZ <1) is preferably 150 ° C. or lower, more preferably 140 ° C. or lower, and 130 ° C. or lower. Is even more preferable. Further, it is preferable that the heating temperature T (° C.) and the in-plane birefringence Δn of the film substrate satisfy T ≦ 150-3 × 10 ³ Δn. Heating temperature T (° C.) is more preferably 140-3 × 10 ³ [Delta] n or less, more preferably 135 - 3 × 10 ³ [Delta] n or less, more preferably 130-3 × 10 ³ [Delta] n or less.

From the same viewpoint as above, in order to obtain a liquid crystal oriented film having an NZ coefficient greater than 0 and smaller than 1, the heating temperature T (° C.) is (90-0.1 × R ₀ ) to (150-0.06 ×). R ₀ ) is preferable, (95-0.1 × R ₀ ) to (140-0.06 × R ₀ ) is more preferable, and (100-0.1 × R ₀ ) to (135-0.06 × R). ₀ ) is more preferable, and (105-0.1 × R ₀ ) to (130-0.06 × R ₀ ) are particularly preferable. R ₀ is the in-plane retardation (nm) of the stretched film substrate.

After heating the liquid crystal composition layer, the orientation of the liquid crystal compound is fixed by cooling it to a temperature equal to or lower than the glass transition temperature of the liquid crystal polymer. 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 composition layer having a fixed orientation with light to polymerize or crosslink the photopolymerizable liquid crystal compound, the orientation of the photopolymerizable liquid crystal compound is fixed and the durability of the liquid crystal alignment film is improved. As the light to be irradiated, light having a wavelength at which the photopolymerization initiator cleaves may be selected, and ultraviolet rays are generally used. In order to promote the photopolymerization reaction, it is preferable that the light irradiation is carried out in an atmosphere of an inert gas such as nitrogen gas.

[Characteristics and applications of liquid crystal alignment film]
The liquid crystal alignment film obtained as described above has a refractive index anisotropy of nx>ny> nz and can be used as an optical film for a display for the purpose of compensating the viewing angle and the like. The in-plane retardation of the liquid crystal alignment film is, for example, 50 to 500 nm. In the present invention, it is desired by adjusting the composition of the liquid crystal composition, the in-plane retardation and in-plane birefringence of the stretched film substrate, the coating thickness of the liquid crystal composition, the heating temperature at the time of liquid crystal orientation, and the like. A liquid crystal alignment film having the above retardation and NZ coefficient is obtained. According to the present invention, using the same film substrate and liquid crystal composition, a liquid crystal oriented film having various front retardations and NZ coefficients can be produced only by adjusting the heating temperature at the time of liquid crystal alignment, so that productivity can be obtained. It is possible to improve, and it is easy to handle small lot production.

In order to reduce the change in retardation depending on the viewing direction, the NZ coefficient of the liquid crystal alignment film is preferably 0.2 to 0.8, more preferably 0.3 to 0.7, and is 0. It is more preferably 0.4 to 0.6, and particularly preferably 0.45 to 0.55.

The preferable ranges of the in-plane retardation Ro and the NZ coefficient of the liquid crystal alignment film differ depending on the purpose of use and the like. For example, when Ro is 200 to 350 nm and the NZ coefficient is 0.4 to 0.6, it is suitable as a λ / 2 retardation plate with little change in retardation depending on the viewing direction, and is suitable for an IPS liquid crystal display device. It is preferably used for a viewing angle compensation film or the like. When Ro is 120 to 170 nm and the NZ coefficient is 0.4 to 0.6, it is suitable as a λ / 4 retardation plate in which there is little change in retardation depending on the viewing direction, and by laminating it with a polarizing plate. A wide viewing angle circular polarizing plate can be obtained. The wide viewing angle circular polarizing plate is preferably used as an external light reflection antireflection film for OLEDs.

The liquid crystal alignment film may be used in a state of being laminated with the film substrate, or may be peeled off from the film substrate and used. The liquid crystal alignment film may be peeled off from the film substrate and laminated with a substrate such as a retardation film, a polarizing plate, or glass.

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

[Evaluation method]
(Arithmetic mean roughness)
The arithmetic mean roughness was determined from an AFM observation image of 1 μm square using a scanning probe microscope (AFM).

(Letteration)
For the measurement of the retardation, a polarization / phase difference measurement system (product name "AxoScan" manufactured by Axometrics) was used, and the value at a wavelength of 590 nm was measured in an environment of 23 ° C. For the measurement of the liquid crystal alignment film retardation, a sample obtained by transferring the liquid crystal alignment film onto the adhesive-attached surface of a glass plate provided with an adhesive on the surface was used, and the in-plane retardation R ₀ and when tilted by 40 ° The refractive index nz, ny, nz was calculated from these measured values, assuming that the average refractive index of the liquid crystal alignment film was 1.52, and NZ = (nx-nz) / (nx-ny). Asked.

[Preparation of liquid crystal compositions 1 to 8]
A side-chain liquid crystal polymer having a weight average molecular weight of 5000 having the following chemical formula (n = 0.35, which is shown as a block polymer for convenience) and a polymerizable liquid crystal monomer showing a thermotropic nematic liquid crystal phase (BASF "Pariocolor"). A liquid crystal composition was prepared by dissolving 100 parts by weight of LC242 ") and 5 parts by weight of a photopolymerization initiator ("Irgacure 907" manufactured by BASF) in 400 parts by weight of cyclopentanone. As shown in Table 1, the ratio of the polymer to the monomer was changed to a ratio of 100/0 to 20/80 to obtain liquid crystal compositions 1 to 8.

[Preparation of liquid crystal composition 9]
50 parts by weight of a side chain liquid crystal polymer having a repeating unit represented by the following chemical formula and a weight average molecular weight of 5000, 50 parts by weight of BASF's "Pariocolor LC242", and 5 parts by weight of BASF's "Irgacure 907" are cyclopentanone. The liquid crystal composition 9 was prepared by dissolving in 400 parts by weight.

[Experimental Example 1]
Biaxially stretched norbornene film having an I Ching layer on one surface (“Zeonor film” manufactured by Nippon Zeon, thickness: 52 μm, in-plane retardation: 50 nm, arithmetic mean roughness of non-I Ching layer non-formed surface: 1.2 nm ), The above liquid crystal compositions 1 to 9 were applied to the non-slip layer non-forming surface using a Meyer bar (# 4), and heated at 100 ° C. for 2 minutes to orient the liquid crystal. Then, the film was cooled to room temperature to fix the orientation, and irradiated with ultraviolet rays of 700 mJ / cm ² in a nitrogen atmosphere to photocure the liquid crystal monomer to prepare a liquid crystal alignment film.

[Experimental Examples 2 and 3]
The liquid crystal compositions 1 to 8 were coated, heated, cooled and photocured in the same manner as in Experimental Example 1 except that # 8 was used in Experimental Example 2 and # 12 Meyer Bar was used in Experimental Example 3. To prepare a liquid crystal alignment film.

[Experimental Example 4]
Biaxially stretched norbornene film having an easy-slip layer on one surface (“Zeonor film” manufactured by Nippon Zeon, thickness: 34 μm, in-plane retardation: 270 nm, arithmetic mean roughness of non-slip layer non-formed surface: 0.9 nm ), The liquid crystal compositions 1 to 8 were applied to the non-slip layer non-forming surface using # 12 Meyer bar roll to prepare a liquid crystal alignment film in the same manner as in Experimental Example 3.

[Experimental Example 5]
Liquid crystal composition 4 using # 12 Meyer bar roll on an unstretched norbornene film (Zeon Corporation "Zeonoa film", thickness; 34 μm, in-plane retardation: 0 nm, arithmetic mean roughness 2.3 nm). Was applied to prepare a liquid crystal alignment film in the same manner as in Experimental Example 3.

Experimental Examples 1-5 plane retardation R ₀ of the base material used _for, thickness of the liquid crystal alignment film, and retardation of the measurement results of the liquid crystal alignment film (in-plane retardation R ₀ and NZ), are shown in Table 1 ..

[Experimental Examples 6-8]
Liquid crystal composition 4 (polymer / monomer ratio of 80/20) was applied onto a biaxially stretched film having an in-plane retardation of 50 nm, which was the same as in Experimental Examples 1 to 3, using a # 12 Meyer bar. After that, the heating temperature was changed in the range of 70 to 120 ° C. A liquid crystal alignment film was produced in the same manner as in Experimental Example 3 except for the above. The measurement results of the heating temperatures of Experimental Examples 6 to 8 and the retardation of the liquid crystal alignment film are shown in Table 2 together with the results of Experimental Example 3 (reposted).

In Table 1, when the liquid crystal compositions 7 and 8 having a small proportion of the thermotropic liquid crystal compound in the liquid crystal composition were applied onto the stretched film substrate, the obtained liquid crystal alignment film was obtained in any of Experimental Examples 1 to 4. Was a positive C plate with an in-plane retardation R ₀ of approximately 0 and a negative NZ coefficient. In Experimental Examples 1 to 4, as the proportion of the thermotropic liquid crystal compound increased, R _{0 of the} liquid crystal alignment film increased, and the NZ coefficient tended to increase accordingly. On the other hand, in Experimental Example 5 using the non-stretched film, R _{0 of the} liquid crystal oriented film was approximately 0 even when the proportion of the thermotropic liquid crystal compound was large (monomer / polymer = 80/20).

Comparing Experimental Examples 1 to 3, even when the same liquid crystal composition was used, the NZ of the liquid crystal alignment film tended to increase as the coating thickness increased. From the comparison between Experimental Example 3 and Experimental Example 4, it can be seen that the larger the in-plane birefringence of the stretched substrate film, the more the homogeneous orientation component increases, and the larger the NZ coefficient of the liquid crystal alignment film.

From the results shown in Table 2, it can be seen that even when the same liquid crystal composition is used, the higher the heating temperature after coating the liquid crystal composition, the larger the NZ coefficient of the liquid crystal alignment film.

From the above results, the refractive index of the liquid crystal alignment film is anisotropic by adjusting the heating temperature after coating the liquid crystal composition containing the side chain type thermotropic liquid crystal polymer and the thermotropic liquid crystal compound on the stretched film substrate. It turns out that the sex can be controlled. That is, according to the present invention, various in-planes are adjusted by adjusting the composition of the liquid crystal composition, the in-plane retardation (in-plane birefringence) of the substrate on which the liquid crystal composition is applied, the coating thickness, the heating temperature, and the like. It can be seen that a liquid crystal oriented film having a retardation and an NZ coefficient can be obtained.

Claims (7)

A method for producing a liquid crystal alignment film composed of a liquid crystal layer containing a side chain type thermotropic liquid crystal polymer and a polymer of a thermotropic liquid crystal compound .
A coating step of applying a liquid crystal composition containing a side chain type thermotropic liquid crystal polymer and a photopolymerizable thermotropic liquid crystal compound on the first main surface of a film substrate having a first main surface and a second main surface;
A liquid crystal alignment step in which the side chain thermotropic liquid crystal polymer and the photopolymerizable thermotropic liquid crystal compound are heated and oriented; and
A photopolymerization step of polymerizing or cross-linking the photopolymerizable thermotropic liquid crystal compound by light irradiation.
Have,
The film substrate is a stretched film that does not have an alignment film.
The side chain type thermotropic liquid crystal polymer has a monomer unit containing a liquid crystal fragment side chain and a monomer unit containing a non-liquid crystal fragment side chain.
The photopolymerizable thermotropic liquid crystal compound has a mesogen group and a plurality of (meth) acryloyl groups in one molecule.
The liquid crystal layer is a single layer, and has an in- plane refractive index nx in the slow axis direction, an in-plane refractive index ny in the phase advance axis direction, and a refractive index nz in the thickness direction of 0.2 ≦ (nx-nz). ) / (Nx-ny) ≤ 0.8,
A method for producing a liquid crystal alignment film. The side chain type thermotropic liquid crystal polymer has a liquid crystal monomer unit represented by the following general formula (I) and a non-liquid crystal monomer unit represented by the following general formula (II), according to claim 1. Manufacturing method of liquid crystal alignment film:

R ¹ and R ³ are independently hydrogen atoms or methyl groups, respectively.
X ¹ is a -CO _2- or -OCO- group and
R ² is a cyano group, a fluoro group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms.
a is an integer from 1 to 6, and b and c are independently 1 or 2, respectively.
R ⁴ is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or a group represented by the following general formula (III).

R ⁵ is an alkyl group having 1 to ⁵ carbon atoms, and d is an integer of 1 to 6. The liquid crystal composition according to claim 1 or 2, wherein the content of the photopolymerizable thermotropic liquid crystal compound is 1.2 to 20 times the content of the side chain type thermotropic liquid crystal polymer. A method for producing a liquid crystal alignment film. The method for producing a liquid crystal oriented film according to any one of claims 1 to 3, wherein the in- plane retardation of the liquid crystal layer is 50 to 500 nm. The method for producing a liquid crystal oriented film according to any one of claims 1 to 4 , wherein the film substrate has an in-plane retardation of 10 to 1000 nm. The invention according to any one of claims 1 to 5 , wherein the heating temperature T (° C.) in the liquid crystal alignment step and the in-plane birefringence Δn of the film substrate satisfy T ≧ 90-5 × 10 ³ Δn. A method for producing a liquid crystal alignment film. The method for producing a liquid crystal oriented film according to any one of claims 1 to 6 , wherein the film substrate is a norbornene-based polymer film.