TWI645020B - Manufacturing method of vertical alignment liquid crystal film - Google Patents

Abstract

In the present invention, a liquid crystal composition containing a side chain liquid crystal polymer and a photopolymerizable liquid crystal monomer is coated on a film substrate without a vertical alignment film, so that the liquid crystal polymer and the liquid crystal monomer are carried out in a liquid crystal state. Vertical alignment and polymerization or cross-linking of liquid crystal monomers by light irradiation can obtain a vertical alignment liquid crystal film. The side chain liquid crystal polymer of the present invention has a monomer unit containing a liquid crystal segment side chain and a monomer unit containing a non-liquid crystal segment side chain. In the present invention, it is preferable to use an stretched film as a film substrate, and set the heating temperature when the liquid crystal compound is aligned to a specific range.

Description

Manufacturing method of vertical alignment liquid crystal film

The invention relates to a vertical alignment liquid crystal film and a manufacturing method thereof.

As an optical film having the functions of optical compensation of a liquid crystal display device and organic EL (Electroluminescence) elements' resistance to external light reflection, the industry uses a liquid crystal film in which liquid crystal compounds are aligned in a specific direction. Since the birefringence of the alignment film of the liquid crystal compound is larger than that of the stretched film of the polymer, it is advantageous for thinning or lightening. For example, regarding a vertically aligned liquid crystal film in which liquid crystal molecules having positive refractive index anisotropy are aligned along the normal direction (thickness direction) of the substrate surface, the refractive index (abnormal light refractive index) in the thickness direction of the alignment direction of the liquid crystal molecules nz is larger than the in-plane refractive index (ordinary light refractive index) nx and ny, and can be used as a positive C plate with refractive index anisotropy of nz> nx = ny.

The substances that spontaneously perform vertical alignment are very limited. Usually, a vertical alignment liquid crystal film is produced by coating a liquid crystal compound on a substrate provided with a vertical alignment film. Patent Document 1 discloses that a composition containing a specific side chain liquid crystal polymer and a photopolymerizable liquid crystal monomer is vertically aligned on a substrate without a vertical alignment film. Specifically, the liquid crystal composition is coated on a substrate, and the liquid crystal polymer is heated in a liquid crystal state, and then cooled to fix the alignment, and the liquid crystal monomer is polymerized or crosslinked by light irradiation. This can obtain a vertical alignment liquid crystal film.

Patent Document 1 describes A method for coating a liquid crystal composition on a film having a small optical anisotropy, such as an olefin film, to prepare a vertically aligned liquid crystal film, or transferring an aligned liquid crystal film formed on a plastic film or a metal film having optical anisotropy Method for plastic film with less optical anisotropy. In Patent Document 1, as an example, the following example is described: Yu Jiang A liquid crystal composition is applied to an olefin-based polymer film or a glass substrate, the liquid crystal is aligned by heating to 130 ° C, and then ultraviolet rays are irradiated to produce a vertically aligned liquid crystal film.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 4174192

With the high definition or high brightness of the display, higher in-plane uniformity is required for the optical film for the display, and in the liquid crystal alignment film, alignment defects of minute regions are regarded as a problem. When the vertical alignment liquid crystal film described in Patent Document 1 is observed under a polarizing microscope, local light leakage caused by minute alignment defects is observed. In view of this problem, an object of the present invention is to provide a vertically aligned liquid crystal film with fewer alignment defects.

In view of the above, the present inventors conducted research, and found that, by adjusting a film substrate for coating a liquid crystal composition or conditions for aligning liquid crystal molecules, a vertically aligned liquid crystal film with fewer alignment defects can be obtained, thereby The present invention has been completed.

The present invention relates to a vertical alignment liquid crystal film having a side chain liquid crystal polymer and a polymer of a photopolymerizable liquid crystal compound, and a method for manufacturing the same.

A liquid crystal composition containing a side chain liquid crystal polymer and a photopolymerizable liquid crystal monomer is coated on a first main surface of a film substrate on which a vertical alignment film is not provided (coating step), and the liquid crystal polymer and the liquid crystal are coated. The monomers are aligned vertically in the liquid crystal state (liquid crystal alignment step), and the liquid crystal monomers are polymerized or cross-linked by light irradiation (photopolymerization step) to form vertically aligned liquid crystals on the film substrate. membrane.

The side chain liquid crystal polymer is preferably one having a monomer unit containing a liquid crystal segment side chain and a monomer unit containing a non-liquid crystal segment side chain. The content of the photopolymerizable liquid crystal monomer in the liquid crystal composition is preferably 1.1 to 10 times the content of the side chain liquid crystal polymer.

The heating temperature T (° C) during the liquid crystal alignment and the in-plane birefringence Δn of the film substrate preferably satisfy T ≦ 100-3.5 × 10 ³ Δn. By lowering the heating temperature during liquid crystal alignment, a vertical alignment liquid crystal film with less alignment defects and higher uniformity can be obtained.

By using a smooth film substrate as the first main surface (the surface to which the liquid crystalline composition is applied), there is a tendency that alignment defects are reduced. The arithmetic mean roughness of the first main surface of the film substrate is preferably 3 nm or less. As a film substrate having a small arithmetic average roughness and excellent smoothness, it is preferable to use an stretched film. The in-plane retardation of the stretched film is, for example, 10 to 500 nm. When the liquid crystal composition is coated on the stretched film substrate, the alignment restriction force of the substrate may hinder the vertical alignment of the liquid crystal composition, but if the heating temperature for liquid crystal alignment is lowered as described above, It can reduce alignment defects.

The film substrate may have an easy-slip layer on the second main surface. It is preferable that no slippery layer is provided on the first main surface of the film substrate. As the film substrate, for example, Ethylene polymer film.

The vertical alignment liquid crystal film preferably has an arithmetic average roughness of at least one side of 3 nm or less. The number of alignment defects per 1 cm ² of the vertical alignment liquid crystal film is preferably 1 or less.

According to the present invention, a vertical alignment liquid crystal film with few minute alignment defects and excellent in-plane uniformity can be obtained.

A liquid crystal alignment film is obtained by coating a substrate with a liquid crystal composition and fixing the alignment thereof. Production.

[Liquid Crystal Composition]

The liquid crystal composition used in the production of the vertical alignment liquid crystal film includes a side chain liquid crystal polymer and a photopolymerizable liquid crystal monomer.

<Side-chain liquid crystal polymer>

As the side chain liquid crystal polymer, a copolymer having a monomer unit containing a liquid crystal segment side chain and a monomer unit containing a non-liquid crystal segment side chain can be used. Since the polymer has a liquid crystal segment in a side chain, the polymer is vertically aligned when the liquid crystal composition is heated to a specific temperature. In addition, since the polymer has a non-liquid crystalline segment in the side chain, the photo-polymerizable liquid crystal monomer contained in the liquid crystalline composition and the polymer are aligned with the vertical alignment force. By aligning the liquid crystal monomer with the alignment of the side chain liquid crystal polymer and fixing the alignment state, a vertically aligned liquid crystal film can be obtained.

Examples of the monomer having a liquid crystal segment side chain include a polymerizable compound having a nematic liquid crystal substituent having a mesogen group. Examples of the mesogen include biphenyl, phenylbenzoate, phenylcyclohexane, azophenyloxy, methineazo, azophenyl, phenylpyrimidinyl, Ring structures such as diphenylethynyl, diphenylbenzoate, dicyclohexane, cyclohexylphenyl, and tritriphenyl. The ends of these cyclic units may have substituents such as cyano, alkyl, alkoxy, and halo. Among them, the mesogen is preferably one having a biphenyl group or a phenylbenzoate group.

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

As the side chain liquid crystal polymer, liquid crystallinity having a general formula (I) can be preferably used. A copolymer of a monomer unit and a non-liquid crystalline monomer unit represented by general formula (II).

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 from 1 to 6, and b and c are each independently 1 or 2.

In formula (II), R ³ is a hydrogen atom or a methyl group, and 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) .

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

The ratio of the liquid crystalline monomer unit to the non-liquid crystalline monomer unit in the side chain liquid crystal polymer is not particularly limited. When the ratio of the non-liquid crystalline monomer unit is small, there is a side chain liquid crystal polymer. The alignment of the aligned photopolymerizable liquid crystal compound becomes insufficient, and the alignment of the liquid crystal layer after photo-hardening becomes uneven. On the other hand, when the ratio of the liquid crystalline monomer units is small, the side chain liquid crystal polymer is unlikely to exhibit liquid crystal single-domain alignment. Therefore, the ratio of the non-liquid crystalline monomer to the total of the liquid crystalline monomer unit and the non-liquid crystalline monomer unit is preferably 0.01 to 0.8, more preferably 0.1 to 0.6, and still more preferably 0.15 to 0.5 in terms of molar ratios. . Just at the same time From the viewpoint of the film-forming property and the alignment property of the liquid crystal composition, the weight average molecular weight of the side chain liquid crystal polymer is preferably about 2,000 to 100,000, and more preferably about 2500 to 50,000.

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

<Photopolymerizable liquid crystal compound>

The photopolymerizable liquid crystal compound (monomer) has a mesogen group and at least one photopolymerizable functional group in one molecule. Examples of the mesogenic group include those described above as the liquid crystal segment of the side chain liquid crystal polymer. Examples of the photopolymerizable functional group include a (meth) acrylfluorenyl group, an epoxy group, and a vinyl ether group. Among these, (meth) acrylfluorenyl is preferred.

The photopolymerizable liquid crystal monomer is preferably one having two or more photopolymerizable functional groups in one molecule. By using a liquid crystal monomer containing two or more photopolymerizable functional groups and introducing a crosslinked structure into the liquid crystal layer after photopolymerization, the durability of the vertically aligned liquid crystal film tends to be improved.

Examples of the photopolymerizable liquid crystal monomer having a mesogen and a plurality of (meth) acrylfluorenyl groups in one molecule include compounds 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 or 1,4-cyclohexyl, and B is 1,4-phenylene, 1, 4-Cyclohexyl, 4,4'-biphenyl, or 4,4'-bicyclohexyl, and Y and Z are each independently -COO-, -OCO-, or -O-. g and h are each independently an integer of 2-6.

Examples of the commercially available photopolymerizable liquid crystal monomer represented by the general formula (IV) include: "Paliocolor LC242" manufactured by BASF.

<Composition>

The ratio of the photopolymerizable liquid crystal compound (monomer) to the side chain liquid crystal polymer in the liquid crystal composition is not particularly limited. From the viewpoint of obtaining a vertically aligned liquid crystal film having high durability, the content of the photopolymerizable liquid crystal compound is preferably more than the content of the side chain liquid crystal polymer. From the viewpoint of obtaining a vertically aligned liquid crystal film with higher durability and higher alignment uniformity, the content (weight) of the photopolymerizable liquid crystal compound in the liquid crystal composition is preferably the content of the side chain liquid crystal polymer. 1.5 to 15 times, more preferably 2 to 10 times, and even more preferably 2.5 to 6 times.

In order to promote hardening 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, and more preferably 5 to 100 parts by weight of the photopolymerizable liquid crystal compound. About 10 parts by weight.

A liquid crystal composition can be prepared by mixing a side chain liquid crystal polymer, a photopolymerizable liquid crystal compound, and a photopolymerization initiator with a solvent. The solvent is not particularly limited as long as it dissolves the side chain liquid crystal polymer and the photopolymerizable liquid crystal compound and does not erode the film substrate (or has low erodibility), and examples thereof include chloroform, dichloromethane, and tetrachloride. Halogenated hydrocarbons such as carbonized carbon, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, o-dichlorobenzene; phenols such as phenol and p-chlorophenol; benzene, toluene, xylene, methyl chloride Aromatic hydrocarbons such as oxybenzene, 1,2-dimethoxybenzene; acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, N- Ketone solvents such as methyl-2-pyrrolidone; ester solvents such as ethyl acetate and butyl acetate; tertiary butanol, glycerol, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, and diethyl ether Glycol dimethyl ether, propylene glycol, dipropylene glycol Alcohol solvents such as alcohols and 2-methyl-2,4-pentanediol; amine solvents such as dimethylformamide and dimethylacetamide; nitrile solvents such as acetonitrile and butyronitrile; diethyl ether, Ether solvents such as dibutyl ether and tetrahydrofuran; ethyl cyrus, butyl cyrus and the like. The concentration of the liquid crystal composition is usually about 3 to 50% by weight, and preferably about 7 to 35% by weight.

[Film substrate]

In the present invention, as the substrate for applying the liquid crystal composition, a film substrate without a vertical alignment film can be used. As described above, since the side chain liquid crystal polymer in the liquid crystal composition is vertically aligned by heating, there is no need to provide a vertical alignment film on the substrate. By using a film substrate, a series of steps of applying a liquid crystal composition on a self-directed substrate to a liquid crystal monomer and curing by photopolymerization can be performed by a roll-to-roll process, so that the productivity of a vertically aligned liquid crystal film can be improved. .

The film substrate has a first main surface and a second main surface, and the liquid crystal composition is coated on the first main surface. The resin material constituting the film substrate is not particularly limited as long as it does not dissolve in the solvent of the liquid crystal composition and has heat resistance during heating to align the liquid crystal composition. Examples include polyethylene terephthalate. Polyesters such as diesters and polyethylene naphthalates; polyolefins such as polyethylene and polypropylene; Cyclic polyolefins such as olefin polymers; Cellulose polymers such as diacetyl cellulose and triethyl cellulose; Acrylic polymers; Styrene polymers; Polycarbonate, Polyamine, Polyamide Amine, etc. Among them, in terms of easily obtaining a film which is excellent in fluidity at the time of molding and has high smoothness, it is particularly preferable to reduce the use. An olefin-based polymer film is used as a film substrate. It is also preferred that the vertical alignment liquid crystal film has excellent peelability when transferred to other substrates. Ethylene polymer film. As drop Examples of the olefin polymer include Zeonor manufactured by Zeon Japan, Zeonex, Arton manufactured by JSR, and the like.

As the film substrate, a stretched film may be used. By extending the film, the irregularities such as mold lines during film formation are smoothed, so the smoothness of the film substrate is improved, and the arithmetic average roughness Ra is reduced. The tendency. In terms of higher surface uniformity, it is particularly preferable to use a biaxially stretched film as the film substrate.

The in-plane retardation R ₀ of the stretched film used as a film substrate is usually 10 nm or more. In the case where the film substrate is an extended film having an in-plane retardation of 10 nm or more, the polymers constituting the film are preferentially aligned in a specific direction (late phase axis direction or advance axis direction), so the liquid crystal molecules are aligned horizontally. The alignment restricting force tends to work, and hinders the vertical alignment of the liquid crystal composition. As described in detail below, by lowering the heating temperature when the liquid crystal molecules are aligned vertically, when a stretched film substrate is used, a vertically aligned liquid crystal film with fewer alignment defects can also be obtained.

If the in-plane retardation of the film substrate is too large, the temperature at which alignment defects can be reduced may be low, and it may be difficult to cause side-chain liquid crystal polymers to undergo liquid crystal phase transfer within this temperature range. Therefore, the in-plane retardation R _{0 of the} film substrate is preferably 500 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less.

The thickness of the film substrate is not particularly limited, and in consideration of handleability and the like, it is usually about 10 to 200 μm. The in-plane birefringence Δn (a value obtained by dividing the in-plane retardation R ₀ by the thickness) of the stretched film is preferably 0.01 or less, more preferably 0.008 or less, and even more preferably 0.006 or less.

The arithmetic mean roughness Ra of the first main surface of the film substrate is preferably 3 nm or less, more preferably 2 nm or less, and even more preferably 1.5 nm or less. By coating a liquid crystal composition on the surface of a film substrate having a small Ra and a high smoothness, there is a tendency that the alignment defects of the vertically aligned liquid crystal film are reduced. As described above, by stretching the film, the Ra of the film tends to decrease. Therefore, by using the stretched film substrate, there is a tendency that the alignment defects of the vertically aligned liquid crystal film are reduced.

Since the surface shape of the first main surface of the film substrate is transferred to the vertical alignment liquid crystal film formed thereon, the Ra of the substrate surface of the vertical alignment liquid crystal film and the Ra of the first main surface of the substrate are approximately equal. Therefore, when a film substrate having a Ra of the first main surface of 3 nm or less is used, Ra of the substrate surface of the liquid crystal alignment film also becomes 3 nm or less in many cases. In addition, Ra of the air surface at the time of application of the liquid crystal composition tends to be smaller than Ra of the substrate surface. Therefore, if a film substrate having a Ra of the first main surface of 3 nm or less is used, the arithmetic average roughness of both sides of the vertically aligned liquid crystal film in most cases becomes 3 nm or less.

In order to set the arithmetic mean roughness to the above range, it is preferable that the film substrate does not contain a filler inside. Films that do not contain fillers and have high surface smoothness have low sliding properties, which may cause blocking, or may cause poor conveyance or poor winding during the roll-to-roll process. In order to prevent blocking or poor transportation due to high smoothness, a method of attaching another film having a high sliding property to the film substrate, or a method of providing an easy-slip layer on the film substrate can be cited. In the case where a film substrate is bonded to another film, it is possible to suppress defects (such as poor alignment of the liquid crystal or optical defects) caused by the transfer of an adhesive layer or the like to the first main surface (the surface on which the liquid crystal composition is applied). From the viewpoint of), it is preferably bonded to the second main surface (the surface opposite to the coating surface of the liquid crystalline composition). Among them, in the roll-to-roll manufacturing process, when the film substrate is rolled, the adhesive or the like attached to the second main surface is transferred to the first main surface, which may cause poor alignment or optical defects.

Therefore, it is preferable to improve the sliding property by providing an easy slip layer on at least one side of the film substrate. Examples of the slippery layer include those containing a fine filler having an average particle diameter of 100 nm or less in an adhesive such as polyester and polyurethane. From the viewpoint of maintaining the releasability when transferring the vertically-aligned liquid crystal film to other substrates, and suppressing the troubles such as the transfer of the easy-sliding layer to the vertically-aligned liquid crystal film when peeling from the film substrate, the film substrate is preferably There is no slippery layer on the surface to which the liquid crystal composition is applied. That is, it is preferably used for a film substrate having an easy-slip layer on the second main surface and not having an easy-slip layer on the first main surface.

[Formation of vertical alignment liquid crystal film on film substrate]

A liquid crystal composition is coated on a film substrate, the liquid crystal polymer is brought into a liquid crystal state by heating, the liquid crystal molecules are aligned vertically, and then the alignment is fixed by cooling, and the liquid crystal monomer is irradiated with light. Polymerization or crosslinking is performed, whereby a vertically aligned liquid crystal film can be obtained.

The method for coating the liquid crystal composition on the film substrate is not particularly limited, and spin coating, die coating, contact roll coating, gravure coating, reverse coating, spray coating, and Meyer bar coating can be used. Cloth, roll knife coating, air knife coating, etc. After the solution is applied, 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 crystalline composition layer (thickness of the vertical alignment liquid crystal film) after the solvent is dried becomes about 0.5 to 5 μm.

The liquid crystal composition layer formed on the film substrate is heated to form a liquid crystal phase, and the liquid crystal composition is vertically aligned. The heating temperature is not particularly limited, but is usually about 40 to 200 ° C. If the heating temperature is too low, the transition to the liquid crystal phase tends to be insufficient, and if the heating temperature is too high, the alignment defects tend to increase. Therefore, the heating temperature is preferably 45 to 100 ° C, more preferably 50 to 95 ° C, and even more preferably 55 to 90 ° C. The heating time may be adjusted so that the transition to the liquid crystal phase becomes sufficient, and is usually about 30 seconds to 30 minutes.

When a stretched film substrate is used, the horizontal alignment restricting force caused by the molecular alignment of the film substrate tends to act as the heating temperature increases, and the vertical alignment liquid crystal film tends to have increased alignment defects. Therefore, when the stretched film substrate is used, it is preferable to perform heating at a low temperature within a temperature range where the liquid crystal compound is transferred to the liquid crystal phase. The heating temperature T (° C) during liquid crystal alignment is preferably 100-3.5 × 10 ³ Δn or less. Δn is the in-plane birefringence of the stretched film substrate. The heating temperature T is more preferably 100-4 × 10 ³ Δn or less, and still more preferably 100-4.5 × 10 ³ Δn or less. Further, the heating temperature T is preferably 100-0.1R ₀ or less, more preferably 100-0.12R ₀ or less, and further preferably 100-0.13R ₀ or less. R ₀ is the in-plane retardation of the stretched film substrate.

After heating the liquid crystal composition layer, it is cooled to the glass transition temperature of the liquid crystal polymer. At a temperature of less than or equal to 50 ° C, the alignment of the liquid crystal compound is fixed. The cooling method is not particularly limited, and for example, it may be taken out from a heating atmosphere to room temperature. Forced cooling such as air cooling and water cooling are also available.

The vertical alignment fixed liquid crystal composition layer is irradiated with light to polymerize or crosslink the photopolymerizable liquid crystal compound, thereby fixing the alignment of the photopolymerizable liquid crystal compound and improving the durability of the vertical alignment liquid crystal film. As the light to be irradiated, light having a wavelength at which the photopolymerization initiator is cleaved may be selected, and usually ultraviolet rays may be used. In order to promote the photopolymerization reaction, light irradiation is preferably performed in an inert gas atmosphere such as nitrogen.

[Characteristics and uses of vertical alignment liquid crystal film]

The in-plane retardation of the vertically aligned liquid crystal film obtained by the above is approximately 0 (for example, less than 5nm, preferably less than 3nm), and the retardation in the thickness direction is negative (having a refractive index anisotropy of nz> nx = ny). Positive C plate. The thickness direction retardation R _t represented by the product of (nx-nz) and thickness of the vertical alignment liquid crystal film is, for example, about -50 to -500 nm.

The light leakage (poor alignment) observed in the vertically aligned liquid crystal film under a polarizing microscope is preferably 1 or less per 1 cm ² , more preferably 0.7 or less, and even more preferably 0.5 or less. The number of misalignments is determined as an average value obtained by observing 10 locations in the film surface. As described above, by using a stretched film substrate having high smoothness and setting the heating temperature during liquid crystal alignment to a specific range, a vertical alignment liquid crystal film with fewer alignment defects can be obtained.

The vertical alignment liquid crystal film can be used as an optical film for a display for the purpose of viewing angle compensation and the like. The vertical alignment liquid crystal film can be used in a state of being laminated with a film substrate, or can be used by being peeled from the film substrate. The vertical alignment liquid crystal film can also be peeled from the film substrate and laminated with a substrate such as a retardation film, a polarizing plate, and glass to be used.

[Example]

Hereinafter, the present invention will be described in more detail by making examples of the vertical alignment liquid crystal film, but the present invention is not limited to the following examples.

[Preparation of liquid crystal composition]

20 parts by weight of a side-chain liquid crystal polymer having a weight average molecular weight of 5000 and a nematic liquid crystal phase (BASF) having a weight average molecular weight of 5,000 and a chemical formula (n = 0.35, for convenience of explanation) 80 parts by weight of "Paliocolor LC242" manufactured and 5 parts by weight of a photopolymerization initiator ("Irgacure 907" manufactured by BASF) were dissolved in 400 parts by weight of cyclopentanone to prepare a liquid crystal composition.

[Experimental Example 1]

Using a bar coater, apply the above-mentioned liquid crystal composition to the unstretched film so that the thickness after drying becomes 1 μm. Ethylene-based film ("Zeonor Film" manufactured by Zeon, Japan, thickness: 50 μm, in-plane retardation: 0 nm, arithmetic mean roughness: 2.3 nm), heated at the temperature (50 to 100 ° C) shown in Table 1 for 2 minutes, and Align the liquid crystal. Thereafter, the alignment was fixed by cooling to room temperature, and 700 mJ / cm ² of ultraviolet light was irradiated in a nitrogen atmosphere to light-harden the liquid crystal monomer to produce a liquid crystal alignment film.

[Experimental Example 2]

Biaxial extension with slip layer on one side Ethylene-based film ("Zeonor Film" manufactured by Zeon, Japan, thickness: 52 μm, in-plane retardation: 50 nm, arithmetic average roughness of the surface where no slip layer is formed: 1.2 nm) The liquid crystal composition was produced in the same manner as in Experimental Example 1 to produce a liquid crystal alignment film.

[Experimental Example 3]

Biaxial extension with slip layer on one side Ethylene-based film ("Zeonor Film" manufactured by Zeon, Japan, thickness: 33 μm, in-plane retardation: 135 nm, arithmetic average roughness of the surface where no slip layer is formed: 1.0 nm) The liquid crystal composition was produced in the same manner as in Experimental Example 1 to produce a liquid crystal alignment film.

[Experimental Example 4]

Biaxial extension with slip layer on one side Ethylene-based film ("Zeonor Film" manufactured by Zeon, Japan, thickness: 34 μm, in-plane retardation: 270 nm, arithmetic average roughness of the surface where no slip layer is formed: 0.9 nm) The liquid crystal composition was produced in the same manner as in Experimental Example 1 to produce a liquid crystal alignment film.

[Experimental Example 5]

The liquid crystal composition was coated on a biaxially stretched polyethylene terephthalate film ("DIAFOILT 302" manufactured by Mitsubishi Chemical Corporation, thickness: 75 µm), and a liquid crystal alignment film was produced in the same manner as in Experimental Example 1.

[Experimental Example 6]

A liquid crystal composition having a composition changed to 50 parts by weight of a side chain type liquid crystal polymer and 50 parts by weight of a polymerizable liquid crystal compound was coated on a biaxially stretched film the same as the user used in Experimental Example 2 at 80 ° C. After heating for 2 minutes, cooling and photo-hardening were performed to prepare a liquid crystal alignment film.

[Evaluation] (Arithmetic average roughness)

Obtain an image from a 1 μm square AFM observation image using a scanning probe microscope (AFM). Find the arithmetic mean roughness.

(delay)

The retardation was measured using a polarized retardation measurement system (product name "AxoScan" manufactured by Axometrics) in a 23 ° C environment at a wavelength of 590 nm. The measurement of the retardation of the liquid crystal alignment film is a sample in which a liquid crystal alignment film is transferred on the adhesive attachment surface of a glass plate provided with an adhesive on the surface, and the in-plane retardation R ₀ and the retardation at a tilt of 40 ° are measured, and Based on these measured values, the thickness-direction retardation R _t was calculated by setting the average refractive index of the liquid crystal alignment film to 1.52.

(Alignment defect)

On the adhesive attachment surface of the glass plate provided with an adhesive on the surface, a liquid crystal alignment film is transferred, and an area of 1 cm ² is observed under a polarizing microscope with crossed polarized light, and the number of local light leaks is counted. Polarized light microscope observation was performed at 10 locations (total 10 cm ² ) per sample, and the average number of light leaks was set to the number of alignment defects per 1 cm ² . Table 1 shows the number of alignment defects per 1 cm ² of the liquid crystal alignment film obtained in each experimental example.

(Durability test)

The liquid crystal alignment film prepared at a heating temperature of 80 ° C. in Experimental Example 2 and the liquid crystal alignment film of Experimental Example 6 were transferred to an adhesive attachment surface of a 5 cm square glass plate with an adhesive on the surface, and 100 cycles were performed. Thermal cycling between -40 ° C and 85 ° C. The thickness direction retardation after the thermal cycle test relative to the thickness direction retardation before the thermal cycle test (phase difference retention ratio), and the number of cracks confirmed by visual observation of the sample after the thermal cycle test, and per 1 cm ^The number of alignment defects of 2 is shown in Table 2.

From the results shown in Table 2, it can be seen that in Experimental Example 2 and Experimental Example 6, no alignment defect was confirmed before and after the thermal cycle test, and the vertical alignment of the liquid crystal was fixed. However, in Experimental Example 6 in which the content of the photopolymerizable liquid crystal monomer was small, cracks occurred after the thermal cycle test, and the retardation retention ratio was lower than that in Experimental Example 2. From this result, it is understood that by increasing the ratio of the photopolymerizable liquid crystal monomer in the liquid crystal composition, a vertically aligned liquid crystal film having high temperature cycle durability can be obtained.

In Experimental Example 5 using a biaxially stretched PET film having a large in-plane birefringence, more than 10 alignment defects were confirmed per 1 cm ² at any heating temperature ranging from 50 to 100 ° C. On the other hand, in Experimental Examples 1 to 4, there are fewer alignment defects than Experimental Example 5. It can be seen that the lower the heating temperature, the fewer the number of alignment defects. From these results, it can be seen that by using a film substrate having a specific range of in-plane birefringence and lowering the heating temperature during liquid crystal alignment, a vertically aligned liquid crystal film with fewer alignment defects can be obtained.

If Experimental Example 1 is compared with Experimental Example 2, the alignment defects in Experimental Example 2 are reduced in the temperature range of 50 to 90 ° C. On the other hand, at temperatures of 95 ° C and 100 ° C, the number of alignment defects in Experimental Example 2 increased. In Experimental Example 2 using an extended film substrate with an in-plane retardation R ₀ of 50 nm, alignment defects were reduced at a temperature below 90 ° C. compared to Experimental Example 1. In contrast, an extended film substrate with R ₀ of 135 nm was used. In Experimental Example 3, the temperature range for reducing alignment defects is 50 to 80 ° C. In Experimental Example 3 using an extended film substrate with R ₀ at 270 nm, the temperature range for reducing alignment defects is 50 to 70 ° C.

Since Ra of the film substrate used in Experimental Examples 2 to 4 is the same, it can be said that the smaller R _{0 of the} stretched film is, the wider the temperature range in which alignment defects can be reduced. This is considered to be because the alignment of the polymer constituting the film substrate in a specific direction increases with an increase in R ₀ , and the alignment limiting force for horizontal alignment of the liquid crystal molecules due to the film substrate is likely to act.

From the above results, it can be seen that by adjusting the heating temperature when the liquid crystal is aligned, a vertical alignment liquid crystal film with fewer alignment defects can be obtained. In addition, it is considered that the smaller Ra of the surface of the stretched film substrate on which the liquid crystal composition is applied also contributes to the reduction of alignment defects.

Claims (8)

A method for manufacturing a vertically-aligned liquid crystal film, comprising: a coating step of coating on a first main surface of a film substrate having a first main surface and a second main surface without a vertical alignment film, and containing a side chain; Liquid crystal composition of a liquid crystal polymer and a photopolymerizable liquid crystal monomer; a liquid crystal alignment step that vertically aligns the liquid crystal polymer and the liquid crystal monomer in a liquid crystal state; and a photopolymerization step by The liquid crystal monomer is polymerized or cross-linked by light irradiation; and the side chain liquid crystal polymer has a monomer unit containing a liquid crystal segment side chain and a monomer unit containing a non-liquid crystal segment side chain. The film substrate has For an in-plane retardation stretched film having a thickness of 10 to 500 nm, the heating temperature T (° C) in the liquid crystal alignment step and the in-plane birefringence Δn of the film substrate satisfy T ≦ 100-3.5 × 10 ³ Δn. The method for manufacturing a vertically-aligned liquid crystal film according to claim 1, wherein the side chain liquid crystal polymer has a liquid crystalline monomer unit represented by the following general formula (I) and a non-liquid crystal represented by the following general formula (II) Sex monomer unit, [Chemical 2] R ¹ and R ³ are each independently a hydrogen atom or a methyl group, X ¹ is a -CO ₂ -group or -OCO- group, and R ² is a cyano group, a fluoro group, an alkyl group having 1 to 6 carbon atoms, or a carbon number 1 to 6 alkoxy groups, a is an integer of 1 to 6, b and c are independently 1 or 2, 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 from 1 to 6; For example, the method for manufacturing a vertically aligned liquid crystal film according to claim 1 or 2, wherein the arithmetic average roughness of the first main surface of the film substrate is 3 nm or less. For example, the method for manufacturing a vertically aligned liquid crystal film according to claim 1 or 2, wherein the film substrate has an easy-sliding layer on the second main surface and does not have an easy-sliding layer on the first main surface. The method for manufacturing a vertically aligned liquid crystal film as claimed in item 1 or 2, wherein the above-mentioned film substrate is Ethylene polymer film. The method for manufacturing a vertically aligned liquid crystal film according to claim 1 or 2, wherein the content of the photopolymerizable liquid crystal monomer in the liquid crystal composition is 1.1 to 10 times the content of the side chain liquid crystal polymer. The method for manufacturing a vertically aligned liquid crystal film according to claim 1 or 2, wherein the film substrate is a biaxially stretched film. For example, the method for manufacturing a vertical alignment liquid crystal film according to claim 1 or 2, wherein the heating temperature T in the above liquid crystal alignment step is 75 ° C or lower.