KR101975402B1 - Homeotropotropic alignment liquid crystal film and manufacturing method thereof - Google Patents

Abstract

A liquid crystal composition containing a side chain type liquid crystal polymer and a photopolymerizable liquid crystal monomer is applied onto a film substrate on which a vertical alignment film is not provided and the liquid crystal polymer and the liquid crystal monomer are subjected to homeotropic alignment in a liquid crystal state, By polymerizing or crosslinking the liquid crystal monomer, a homeotropic alignment liquid crystal film is obtained. The side chain type 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. It is preferable that the heating temperature at the time of orienting the liquid crystal compound using a stretched film as the film substrate is set to a predetermined range.

Description

Homeotropotropic alignment liquid crystal film and manufacturing method thereof

The present invention relates to a homeotropic alignment liquid crystal film and a method of manufacturing the same.

A 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 of a liquid crystal display device and prevention of reflection of external light of an organic EL element. Since the orientation film of the liquid crystal compound is larger in birefringence than the stretched film of the polymer, it is advantageous for thinning and lightening. For example, a homeotropic alignment liquid crystal film in which liquid crystal molecules having positive refractive index anisotropy are oriented in the normal direction (thickness direction) of the substrate surface has refractive index (extraordinary refractive index) (nz) in the thickness direction, which is the alignment direction of liquid crystal molecules, (Ordinary refractive index) (nx and ny) in the refractive index anisotropy index nx and refractive index anisotropy of nz > nx = ny.

Materials which are spontaneously homeotropic are very limited. Generally, a homeotropic alignment liquid crystal film is produced by applying a liquid crystal compound on a substrate having a vertical alignment film. Patent Document 1 discloses a composition comprising a predetermined side chain type liquid crystal polymer and a photopolymerizable liquid crystal monomer in homeotropic orientation on a substrate having no vertical alignment film. Specifically, a liquid crystal composition is coated on a substrate, the liquid crystal polymer is heated to be in a liquid crystal state, and then cooled and cooled to fix the alignment, and a liquid crystal monomer is polymerized or crosslinked by light irradiation to obtain a homeotropic alignment liquid crystal film .

Patent Document 1 discloses a method for producing a homeotropic alignment liquid crystal film by coating a liquid crystalline composition on a film having a small optical anisotropy such as a norbornene based film or a method for producing a homeotropic alignment oriented liquid crystal film by using an alignment liquid crystal film Is transferred onto a plastic film having a small optical anisotropy. Patent Literature 1 discloses, as an example, an example in which a liquid crystal composition is applied onto a norbornene polymer film or a glass substrate, the liquid crystal is aligned by heating at 130 캜, and ultraviolet rays are irradiated to produce a homeotropic alignment liquid crystal film .

Japanese Patent No. 4174192

As the display has high definition and high brightness, a higher in-plane uniformity is required for a display optical film, and an alignment defect in a micro-area is a problem in a liquid crystal orientation film. When the homeotropic alignment liquid crystal film described in Patent Document 1 is observed under a polarization microscope, local light leakage due to minute alignment defects is observed. In view of these problems, the object of the present invention is to provide a homeotropic alignment liquid crystal film having few alignment defects.

As a result of the investigation by the present inventors in view of the above, it has been found that a homeotropic alignment alignment liquid crystal film with few alignment defects can be obtained by adjusting film substrates to which the liquid crystal composition is applied and conditions for aligning the liquid crystal molecules, .

TECHNICAL FIELD The present invention relates to a homeotropic alignment liquid crystal film in which a polymer of a side chain type liquid crystal polymer and a photo polymerizable liquid crystal compound is homeotropically aligned, and a method for producing the same.

A liquid crystal composition containing a side chain type liquid crystal polymer and a photopolymerizable liquid crystal monomer is coated (coating step) on a first main surface of a film substrate on which a vertical alignment film is not provided, and a liquid crystal polymer and a liquid crystal monomer (Liquid crystal aligning step) and polymerizing or crosslinking the liquid crystal monomer by light irradiation (photopolymerization step), a homeotropic alignment liquid crystal film is formed on the film substrate.

The side chain type liquid crystal polymer preferably has a monomer unit containing a liquid crystal fragment side chain and a monomer unit containing a non-liquid crystal fragment 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 type liquid crystal polymer.

Liquid heating temperature (T) (℃) and the in-plane birefringence of the film substrate at the time of orientation (△ n) is preferably satisfies the T≤ 100-3.5 × 10 ³ △ n. By lowering the heating temperature at the time of liquid crystal alignment, the alignment defect of the liquid crystal is reduced and a homotropic alignment oriented liquid crystal film having high uniformity is obtained.

Alignment defects tend to be reduced by using a film substrate having a smooth first surface (the surface to which the liquid crystal composition is applied). The arithmetic average roughness of the first main surface of the film substrate is preferably 3 nm or less. It is preferable to use a stretched film as a film substrate having a small arithmetic mean roughness and excellent smoothness. The in-plane retardation of the stretched film is, for example, 10 to 500 nm. When the liquid crystal composition is applied onto the stretched film substrate, the alignment restraining force of the substrate sometimes hinders the homeotropic alignment property of the liquid crystal composition. However, if the heating temperature for aligning the liquid crystal is lowered as described above, .

The film substrate may have a lubricating layer on the second main surface. It is preferable that the lubricant layer is not provided on the first main surface of the film substrate. As the film substrate, for example, a norbornene polymer film is used.

It is preferable that the homeotropic alignment liquid crystal film has an arithmetic mean roughness of at least 3 nm. It is preferable that the number of alignment defects per 1 cm ^{2 of} the homeotropic alignment liquid crystal film is one or less.

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

A liquid crystal orientation film is prepared by applying a liquid crystal composition on a substrate and fixing the orientation thereof.

[Liquid Crystalline Composition]

The liquid crystal composition used for preparing the homeotropic alignment liquid crystal film includes a side chain type liquid crystal polymer and a photo polymerizable liquid crystal monomer.

≪ Side chain type liquid crystal polymer &

As the side chain type liquid crystal polymer, a copolymer having a monomer unit containing a liquid crystal fragment side chain and a monomer unit containing a non-liquid crystal fragment side chain is used. When the polymer has a liquid crystal fragment in the side chain, the polymer is homeotropically aligned when the liquid crystal composition is heated to a predetermined temperature. Further, since the polymer has a non-liquid crystalline fragment in the side chain, an orientation force for homeotropic alignment of the photo-polymerizable liquid crystal monomer contained in the liquid crystal composition acts together with the polymer. The liquid crystal monomer is aligned with the orientation of the side chain-type liquid crystal polymer, and the orientation state is fixed to obtain a homeotropic alignment liquid crystal film.

Examples of the monomer having a liquid crystal fragment side chain include a polymerizable compound having a nematic liquid crystal substituent group containing a mesogen group. Examples of mesogens include biphenyl, phenylbenzoate, phenylcyclohexane, azoxybenzene, azomethine, azobenzene, phenylpyrimidine, diphenylacetylene, diphenylbenzoate, bicyclohexane, cyclo Hexylbenzene group, terphenyl group, and the like. 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, mesogen groups preferably have a biphenyl group and a phenylbenzoate group.

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

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

[Formula (I)]

[Formula (II)] <

Wherein 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, X ¹ is -CO _{2 -} Or -OCO-. a is an integer of 1 to 6; b and c are each independently 1 or 2;

In the 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 formula (III).

(III)

In the 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 crystalline monomer unit to the non-liquid crystalline monomer unit in the side chain-type liquid crystal polymer is not particularly limited, but when the ratio of the non-liquid crystalline monomer unit is small, the orientation of the photo-polymerizable liquid crystal compound Becomes insufficient, and the alignment of the liquid crystal layer after photo-curing may become uneven. On the other hand, when the proportion of the liquid crystalline monomer unit is small, the side chain type liquid crystal polymer is less likely to exhibit the liquid crystal mono domain orientation property. Accordingly, the ratio of the non-liquid crystalline monomer to the sum 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 even more preferably 0.15 to 0.5. The weight average molecular weight of the side chain type liquid crystal polymer is preferably from about 2,000 to 100,000, and more preferably from about 2,500 to about 500,000, from the viewpoint of achieving both the film forming property and the orientation property of the liquid crystalline composition.

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 is obtained by radical polymerization using light or heat.

≪ 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 mesogen group include the liquid crystal fragments of the side chain type liquid crystal polymer described above. Examples of the photopolymerizable functional group include a (meth) acryloyl group, an epoxy group, and a vinyl ether group. Among them, a (meth) acryloyl group is preferable.

The photopolymerizable liquid crystal monomer preferably has at least two photopolymerizable functional groups in one molecule. The use of a liquid crystal monomer containing two or more photopolymerizable functional groups tends to improve the durability of the homeotropic alignment liquid crystal film because a cross-linking structure is introduced into the liquid crystal layer after photo polymerization.

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

(IV)

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

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

<Composition>

The ratio of the photopolymerizable liquid crystal compound (monomer) and the side chain type liquid crystal polymer in the liquid crystal composition is not particularly limited. From the viewpoint of obtaining a highly durable homeotropic alignment liquid crystal film, it is preferable that the content of the photopolymerizable liquid crystal compound is larger than the content of the side chain type liquid crystal polymer. The content (weight) of the photopolymerizable liquid crystal compound in the liquid crystal composition is preferably from 1.5 to 15 times the content of the side chain type liquid crystal polymer, more preferably from 2 to 5 times the content of the side chain type liquid crystal polymer in view of obtaining a homeotropic alignment liquid crystal film having high durability and high orientation uniformity. To 10 times, and more preferably 2.5 to 6 times.

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 5 to 10 parts by weight, per 100 parts by weight of the photopolymerizable liquid crystal compound Respectively.

A liquid crystal composition can be prepared by mixing a side chain type 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 can dissolve the side chain type liquid crystal polymer and the photopolymerizable liquid crystal compound and does not corrode the film substrate (or has low erosion resistance), and may be any solvent such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, Halogenated hydrocarbons such as trichlorethylene, tetrachlorethylene, chlorobenzene, and orthodichlorobenzene; Phenols such as phenol and para-chlorophenol; Aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, and 1,2-dimethoxybenzene; Ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone and N-methyl-2-pyrrolidone; Ester solvents such as ethyl acetate and butyl acetate; alcohols such as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol and 2-methyl-2,4-pentanediol; Amide solvents such as dimethylformamide and dimethylacetoamide; Nitrile solvents such as acetonitrile and butyronitrile; Ether solvents such as diethyl ether, dibutyl ether and tetrahydrofuran; Ethyl cellosolve, butyl cellosolve 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, a film substrate on which a vertical alignment film is not provided is used as a substrate to which the liquid crystal composition is applied. As described above, since the side chain type liquid crystal polymer in the liquid crystal composition is homeotropically aligned by heating, it is not necessary to provide a vertical alignment film on the substrate. A series of steps from the application of the liquid crystal composition onto the substrate to the curing by the photo-polymerization of the liquid crystal monomer can be carried out by roll-to-roll using the film substrate, so that the productivity of the homeotropic alignment liquid crystal film Can be improved.

The film substrate has a first major surface and a second major surface, and the liquid crystalline composition is applied on the first major 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 at the time of heating to align the liquid crystal composition, and may be polyester such as polyethylene terephthalate and polyethylene naphthalate; Polyolefins such as polyethylene and polypropylene; Cyclic polyolefins such as norbornene-based polymers; Cellulosic polymers such as diacetylcellulose, triacetylcellulose and the like; Acrylic polymer; Styrene-based polymers; Polycarbonate, polyamide, polyimide and the like. Among them, 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 at the time of molding and high smoothness. The norbornene-based polymer film is preferable in that it is excellent in peelability when the homeotropic alignment liquid crystal film is transferred onto another substrate or the like. Examples of the norbornene-based polymer include Zeonoa manufactured by Nippon Zeon Co., Zeonex, and Aton manufactured by JSR Corporation.

A stretched film may be used as the film substrate. Since the unevenness of the die lines and the like at the time of film formation is leveled by stretching the film, the smoothness of the film substrate is improved and the arithmetic average roughness Ra tends to be small. It is particularly preferable to use a biaxially stretched film as the film substrate in view of high surface uniformity.

The in-plane retardation (R ₀ ) of a stretched film used as a film substrate is generally 10 nm or more. In the case where the film substrate is a stretched film having an in-plane retardation of 10 nm or more, since the polymer constituting the film is preferentially oriented in a predetermined direction (a phase-axis direction or a phase-advance axis direction) The alignment regulating force for homogeneously orienting the liquid crystal molecules tends to act and the homeotropic alignment of the liquid crystal composition tends to be inhibited. As described later in detail, the heating temperature at the time of homeotropic alignment of the liquid crystal molecules is lowered, so that a homeotropic alignment liquid crystal film with less alignment defects can be obtained even when a stretched film substrate is used.

If the in-plane retardation of the film substrate is excessively large, the temperature at which alignment defects can be reduced is low, and it may be difficult to cause the liquid crystal phase transition of the side chain type liquid crystal polymer within the 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 further preferably 200 nm or less.

The thickness of the film substrate is not particularly limited, but is usually about 10 to 200 占 퐉 in view of handleability and the like. The in-plane birefringence (n) (value obtained by dividing in-plane retardation (R ₀ ) by the thickness) of the stretched film is preferably 0.01 or less, more preferably 0.008 or less, still 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 further preferably 1.5 nm or less. The alignment defects of the homeotropic alignment alignment liquid crystal film tend to be reduced by applying the liquid crystal composition to the surface of the film substrate having a small Ra and high smoothness. As described above, when the film is stretched, the Ra of the film tends to be reduced. Therefore, by using the stretched film substrate, alignment defects of the homeotropic alignment alignment liquid crystal film tend to be reduced.

The surface shape of the first main surface of the film substrate is transferred to the homeotropic alignment liquid crystal film formed thereon, so that Ra of the substrate surface of the homeotropic alignment liquid crystal film becomes approximately equal to Ra of the first main surface of the substrate. Therefore, in the case of using a film substrate having an Ra of 3 nm or less on the first main surface, Ra of the substrate surface of the liquid crystal alignment film is often 3 nm or less. 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, when a film substrate having Ra of the first major surface of 3 nm or less is used, the arithmetic average roughness of both surfaces of the homeotropic alignment liquid crystal film is often 3 nm or less.

In order to keep the arithmetic average roughness within the above range, it is preferable that the film substrate does not contain a filler therein. A film having no smoothness and high surface smoothness without a filler has a low slidability, which may result in blocking, or may cause poor conveyance or poor winding in a roll-to-roll process. A method of bonding another film having high slidability to the film substrate to prevent blocking or conveyance failure due to high smoothness, and a method of providing a lubricant layer on the film substrate. In the case of sticking another film to the film substrate, from the viewpoint of suppressing troubles (defective alignment of the liquid crystal, optical defects, etc.) due to transfer of the adhesive layer or the like to the first main surface (surface to which the liquid crystal composition is applied) (The surface opposite to the application side of the liquid crystalline composition). However, in the roll-to-roll process, the adhesive or the like adhering to the second main surface at the time of winding the film substrate may be transferred to the first main surface, which may result in orientation defects or optical defects .

Therefore, it is preferable to improve the slidability by providing a lubricity layer on at least one surface of the film substrate. Examples of the lubricity layer include those containing a micropiller having an average particle diameter of 100 nm or less in a binder such as polyester or polyurethane. From the viewpoint of maintaining the peeling property when transferring the homeotropic alignment liquid crystal film to another substrate or the like and suppressing troubles such as transfer of the lubricant layer to the homeotropic alignment liquid crystal film upon peeling from the film substrate, It is preferable that the surface on which the liquid crystal composition is applied does not have a lubricity layer. That is, it is preferable to use a film substrate having a lubricating layer on the second main surface and no lubricating layer on the first main surface.

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

A liquid crystal composition is coated on a film substrate, the liquid crystal polymer is subjected to homeotropic alignment in a liquid crystal state by heating, followed by cooling to fix the alignment, and the liquid crystal monomer is polymerized or crosslinked by light irradiation, A homeotropic alignment liquid crystal film is obtained.

The method of applying the liquid crystal composition on the film substrate is not particularly limited and may be any one of a spin coat, a die coat, a kiss roll coat, a gravure coat, a reverse coat, a spray coat, a Meyer bar [wire bar] coat, A coat or the like can be adopted. After applying the solution, the solvent is removed to form a liquid crystalline composition layer on the film substrate. The coating thickness is preferably adjusted so that the thickness of the liquid crystalline composition layer after drying (thickness of the homeotropic alignment liquid crystal film) is about 0.5 to 5 mu m.

By heating the liquid crystalline composition layer formed on the film substrate to form a liquid crystal phase, the liquid crystalline composition is homeotropic aligned. The heating temperature is not particularly limited, but is usually about 40 to 200 占 폚. 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, alignment defects tend to increase. Therefore, the heating temperature is preferably 45 to 100 占 폚, more preferably 50 to 95 占 폚, and still more preferably 55 to 90 占 폚. The heating time may be adjusted so that the transition to the liquid crystal phase is sufficient, and is usually about 30 seconds to 30 minutes.

When a stretched film substrate is used, the homogeneous alignment restoring force due to the molecular orientation of the film substrate tends to act as the heating temperature rises, and alignment defects of the homeotropic alignment liquid crystal film tend to increase. Therefore, in the case of using a stretched film substrate, it is preferable to perform heating at a low temperature within a temperature range where the liquid crystalline compound transitions to the liquid crystal phase. The heating temperature at the time of liquid crystal alignment (T) (℃) is preferably from 100-3.5 × 10 ³ △ n or less. DELTA n is the in-plane birefringence of the stretched film substrate. The heating temperature (T) is a 100-4 × 10 ³ △ n or less are more preferred, and 100-4.5 × 10 ³ △ n or less is more preferred. The heating temperature (T) is, 100-0.1R ₀ and less are preferred, 100-0.12R ₀ and less are more preferred, 100-0.13R is ₀ or less is more preferable. And R ₀ is in-plane retardation of the stretched film substrate.

The orientation of the liquid crystalline compound is fixed by cooling the liquid crystalline composition layer to a temperature below the glass transition temperature of the liquid crystal polymer after heating. The cooling method is not particularly limited, and may be taken out at room temperature in a heating atmosphere, for example. Or forced cooling such as air cooling or water cooling may be performed.

The alignment of the photo polymerizable liquid crystal compound is fixed and the durability of the homeotropic alignment liquid crystal film is improved by irradiating light to the liquid crystalline composition layer having fixed homeotropic alignment and polymerizing or crosslinking the photo polymerizable liquid crystal compound do. As the light to be irradiated, light having a wavelength at which the photo polymerization initiator cleaves (cleaves) can be selected, and ultraviolet rays are generally used. In order to promote the photopolymerization reaction, the light irradiation is preferably performed in an inert gas atmosphere such as nitrogen gas.

[Characteristics and uses of homeotropic alignment liquid crystal film]

The homeotropic alignment liquid crystal film obtained by the above process is a positive C (having refractive index anisotropy of nz> nx = ny) whose in-plane retardation is approximately 0 (for example, 5 nm or less, preferably 3 nm or less) Plate. The retardation (R _t ) in the thickness direction represented by the product of (nx-nz) and the thickness of the homeotropic alignment liquid crystal film is, for example, about -50 to-500 nm.

The homeotropic alignment liquid crystal film is preferably one or less per 1 cm ^{2 of} light leakage (defective alignment) observed under a polarization microscope, more preferably 0.7 or less, further preferably 0.5 or less. The defective orientation number is obtained as an average value obtained by observing ten portions in the film surface. As described above, a homeotropic alignment liquid crystal film with few alignment defects can be obtained by using a stretched film substrate having a high smoothness and by setting the heating temperature at the time of aligning the liquid crystal within a predetermined range.

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

Example

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

[Production of liquid crystal composition]

20 weight parts of a side chain type liquid crystal polymer having a weight average molecular weight of 5000 and having the following formula (n = 0.35, for the sake of convenience, represented by a block polymer body), 80 weight parts of a polymerizable liquid crystal compound ("Paliocolor LC242" And 5 parts by weight of a photo polymerization initiator (" Irgacure 907 ", manufactured by BASF) were dissolved in 400 parts by weight of cyclopentanone to prepare a liquid crystal composition.

[Experimental Example 1]

The above liquid crystalline composition was applied to a non-stretched norbornene-based film ("Zeonoa Film" manufactured by Nippon Zeon Co., Ltd., thickness: 50 탆, in-plane retardation: 0 nm, arithmetic mean roughness: 2.3 nm) Coated with a coater and heated at the temperature (50 to 100 DEG C) shown in Table 1 for 2 minutes to orient the liquid crystal. Thereafter, the film was cooled to room temperature, fixed in the direction, and irradiated with ultraviolet light of 700 mJ / cm ² under a nitrogen atmosphere to photo-cure the liquid crystal monomer to prepare a liquid crystal orientation film.

[Experimental Example 2]

A biaxially oriented norbornene-based film having a lubricity layer on one side ("Zeonoiafilm" manufactured by Nippon Zeon Co., Ltd., thickness: 52 μm, in-plane retardation: 50 nm, arithmetic mean roughness of the non- The above liquid crystalline composition was coated on the non-layered surface, and a liquid crystal orientation film was produced in the same manner as in Experimental Example 1. [

[Experimental Example 3]

(Manufactured by Nippon Zeon Co., Ltd., thickness: 33 탆, in-plane retardation: 135 nm, arithmetic average roughness of the non-lubricating layer surface: 1.0 nm) having a lubricity layer on one side and a biaxial oriented norbornene- The above liquid crystalline composition was coated on the non-layered surface, and a liquid crystal orientation film was produced in the same manner as in Experimental Example 1. [

[Experimental Example 4]

(Manufactured by Nippon Zeon Co., Ltd., thickness: 34 占 퐉, in-plane retardation: 270 nm, arithmetic average roughness of the non-supported layer surface: 0.9 nm) having a lubricity layer on one side The above liquid crystalline composition was coated on the non-layered surface, and a liquid crystal orientation film was produced in the same manner as in Experimental Example 1. [

[Experimental Example 5]

The liquid crystal composition was coated on a biaxially stretched polyethylene terephthalate film ("Diaformil T302" manufactured by Mitsubishi Chemical Co., Ltd., thickness: 75 μm), and a liquid crystal orientation film was produced in the same manner as in Experimental Example 1.

[Experimental Example 6]

50 parts by weight of the side chain type liquid crystal polymer and 50 parts by weight of the polymerizable liquid crystal compound were coated on the same biaxially stretched film as used in Experimental Example 2, and after cooling for 2 minutes at 80 DEG C, To prepare a liquid crystal alignment film.

[evaluation]

(Arithmetic mean illuminance)

The arithmetic mean illuminance was obtained from the observation image of 1 mu m square AFM using a scanning probe microscope (AFM).

(Retardation)

The retardation was measured at a wavelength of 590 nm under an environment of 23 캜 by using a polarization / phase difference measurement system (manufactured by Axometrics, product name "AxoScan"). In order to measure the retardation of the liquid crystal orientation film, the in-plane retardation (R ₀ ) and the retardation at the time of 40 ° inclination were measured using a sample on which the liquid crystal orientation film was transferred onto the adhesive surface of the glass plate on which the pressure- From these measured values, the thickness direction retardation (R _t ) was calculated by setting the average refractive index of the liquid crystal orientation film to 1.52.

(Alignment defect)

The liquid crystal orientation film was transferred onto the adhesive surface of the glass plate on which the pressure-sensitive adhesive was formed, and the area of 1 cm ² was observed under a polarizing microscope of Cross-Nicol, and the local leakage of light was counted. Polarization microscope observation was carried out at 10 portions (total 10 cm ² ) per sample, and the average number of blasts was determined as the number of alignment defects per 1 cm ² . Table 1 shows alignment defects per 1 cm &lt; ² &gt; of the liquid crystal alignment film obtained in each Experimental Example.

[Table 1]

(Durability test)

The liquid crystal orientation film produced at a heating temperature of 80 캜 and the liquid crystal orientation film of Experimental Example 6 in Experimental Example 2 were transferred onto a pressure sensitive adhesive surface of a 5 cm square glass plate having a pressure-sensitive adhesive formed thereon, The cycle was carried out for 100 cycles. Table 2 shows the values of the retardation in the thickness direction after the heat cycle test (retardation retention) and the number of cracks observed by visual observation of the sample after the heat cycle test and the alignment defects per 1 cm ² for the thickness direction retardation before the heat cycle test .

[Table 2]

From the results shown in Table 2, in Experimental Examples 2 and 6, it was found that alignment defects were not observed before and after the heat cycle test, and the homeotropic 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 were generated after the heat cycle test, and the retardation retention ratio was lower than in Experimental Example 2. [ From this result, it can be seen that a homeotropic alignment liquid crystal film having high temperature cycle durability can be obtained by increasing the proportion of the photopolymerizable liquid crystal monomer in the liquid crystal composition.

In Experimental Example 5 using a biaxially stretched PET film having a large in-plane birefringence, at least 10 alignment defects were observed per 1 cm ² at any heating temperature in the range of 50 to 100 ° C. On the other hand, in Experimental Examples 1 to 4, the number of alignment defects was smaller than that of Experimental Example 5, and the number of alignment defects tended to decrease as the heating temperature was lower. From these results, it can be seen that a filmotropic alignment liquid crystal film with less alignment defects can be obtained by lowering the heating temperature at the time of liquid crystal alignment by using a film substrate having an in-plane birefringence in a predetermined range.

As compared with Experimental Example 1 and Experimental Example 2, the alignment defects in Experimental Example 2 were reduced in the temperature range of 50 to 90 占 폚. On the other hand, at 95 ° C and 100 ° C, the number of alignment defects in Experimental Example 2 was increased. In Experimental Example 2 using a stretched film substrate having an in-plane retardation (R ₀ ) of 50 nm, alignment defects were reduced at a temperature of 90 ° C or lower compared to Experimental Example 1, while in Experimental Example 3 using a stretched film substrate having R ₀ of 135 nm the orientation temperature range and is 50~80 ℃ to defects is reduced, the temperature range was 50~70 ℃ which R ₀ is reduced alignment defect in example 3 using the stretched film substrate 270nm.

It can be said that the Ra of the film base used in Experimental Examples 2 to 4 is equivalent, and the smaller the R ₀ of the stretched film, the wider the temperature range in which the alignment defects can be reduced. It is considered that this is because the orientation of the polymer constituting the film substrate in a predetermined direction increases with increasing R ₀ , and the alignment regulating force for homogeneously aligning the liquid crystal molecules due to the film substrate is likely to act.

From the above results, it can be seen that a homeotropic alignment liquid crystal film with less alignment defects can be obtained by adjusting the heating temperature at the time of aligning the liquid crystal. It is also believed that the stretched film substrate contributes to reduction of alignment defects even if the Ra of the surface to which the liquid crystal composition is applied is small.

Claims (14)

A method for producing a homeotropic alignment liquid crystal film,
A coating step of coating a liquid crystal composition containing a side chain type liquid crystal polymer and a photopolymerizable liquid crystal monomer on a first main surface of a film substrate having a first main surface and a second main surface without a vertical alignment film;
A liquid crystal alignment step of subjecting the liquid crystal polymer and the liquid crystal monomer to homeotropic alignment in a liquid crystal state; And
And a photopolymerization step of polymerizing or crosslinking the liquid crystal monomer by light irradiation,
Wherein the side chain type 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,
Wherein the film substrate is a stretched film having an in-plane retardation of 10 to 500 nm,
And the heating temperature (T) (℃) in the liquid crystal orientation process, the in-plane birefringence (△ n) is T≤100-3.5 × 10 ³ △ n homeotropic alignment method of producing a liquid crystal film that satisfies the above film substrate. The method according to claim 1,
Wherein the side chain type liquid crystal polymer comprises a liquid crystalline monomer unit represented by the following formula (I) and a non-liquid crystalline monomer unit represented by the following formula (II):
[Formula (I)]

[Formula (II)] &lt;

In the above formulas (I) and (II)
R ¹ and R ³ are each independently a hydrogen atom or a methyl group,
X ¹ is a -CO ₂ - group or a -OCO- 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,
a is an integer of 1 to 6, b and c are each 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 formula (III)
(III)

In the above formula (III)
R ⁵ is an alkyl group having 1 to ⁵ carbon atoms, and d is an integer of 1 to 6. delete 3. The method 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. 3. The method according to claim 1 or 2,
Wherein the film substrate has a lubricant layer on a second main surface and a lubricant layer on the first main surface. 3. The method according to claim 1 or 2,
Wherein the film substrate is a norbornene polymer film. 3. The method 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 type liquid crystal polymer. delete delete delete delete delete 3. The method according to claim 1 or 2,
Wherein the film substrate is a biaxially stretched film. 3. The method according to claim 1 or 2,
Wherein the heating temperature (T) in the liquid crystal alignment step is not more than 75 占 폚.