JPH0769490B2 - How to make an alignment film - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a uniaxially highly oriented film. A highly uniaxially oriented film has a high mechanical strength in the orientation direction, and is not only used for a packaging film and a reinforced film laminated facing each other by utilizing this strength, but also in the orientation direction and the direction perpendicular to it. Utilizing the optical anisotropy in the above, it can be used as a retardation film or by adding a dichroic dye to a polarizing film, or as an optical filter, an optical stitching element, a recording material or a display material. Used.

[Prior Art] A uniaxially highly oriented film has heretofore been melt-extruded or solution-cast in a solvent which is uniaxially stretched or appropriately swelled at a temperature not lower than its glass transition temperature and not higher than its melting point. It is generally made by stretching in one direction.
The uniaxially stretched film produced by these stretching methods is likely to have pinholes, and distortion is likely to occur in the manufacturing method. A heat treatment may be performed to relax the strain, but it may not always be sufficiently relaxed, the flatness may be impaired, the film may be optically nonuniform, or opaque due to crystallization.

On the other hand, as a method for producing an oriented film different from the above method, A composition containing AIBN (2,2'-azobisisobutyronitrile) added to a system monomer is sandwiched between rubbing-treated Nesa glass, and a voltage of 100 V is applied to both ends of the cell while heating at 150 ° C for 5 hours. A method of polymerizing a liquid crystal composition by leaving it to form a polarizing film is disclosed in JP-A-58-58.
It is described in Japanese Patent No. 102205. In such a thermal polymerization, it is difficult to control the polymerization initiation temperature, and since the polymerization is bulk polymerization, it is necessary to orient and polymerize at a high temperature of 100 ° C. or higher. It requires complicated and sophisticated technology. A photopolymerization method can be mentioned as a means for solving this. Regarding the photopolymerization method, although there is a description in the claims of the above-mentioned publication that "a liquid crystal vinyl monomer is polymerized by irradiating with ultraviolet rays or sunlight," such a light is used in the detailed description of the invention. No mention is made of polymerization. Therefore, the type of photopolymerization initiator, the conditions for photopolymerization, etc. are unknown. According to the photopolymerization method, polymerization can be performed by freely selecting a temperature range from room temperature to around 100 ° C. Therefore, it is possible to use a liquid crystalline monomer that exhibits a liquid crystal state at a relatively low temperature. Is greatly simplified.

However, in order to carry out photopolymerization, it is necessary to add a photopolymerization initiator. For example, depending on the type of photopolymerization initiator such as general benzophenone, the liquid crystal region of the liquid crystalline monomer becomes narrow, and a stable alignment state is obtained. There may be a problem that it cannot be obtained.

(Object of the invention) An object of the present invention is to solve the above problems in photopolymerization, and to provide a method for producing a highly uniaxially oriented alignment film which is free of pinholes and distortions, excellent in transparency and highly transparent. And

(Structure of the Invention) According to the present invention, a liquid crystalline monomer having the following general formula [I] and at least one carbon-carbon double bond in the molecule, and at least one aromatic group in the molecule By carrying a mixture of a photopolymerization initiator having a ring or a heteroaromatic ring on or between the supports subjected to the alignment treatment, while maintaining the liquid crystal state of the mixture, by irradiating with light to polymerize, It was found that a highly uniaxially oriented film excellent in optical transparency without pinholes, distortion or unevenness can be obtained. Furthermore, by using the photopolymerization initiator, the liquid crystal region of the liquid crystalline monomer is not narrowed,
It was found that a stable alignment state was obtained.

In the general formula [I], R is H or CH ₃ , and n
Can take an integer value of 1 to 11, and X represents a group containing two or more aromatic rings or hetero rings each having a CN group in the para position. X is preferably an aromatic ring or a group shown below. It is a para-substitution of a heterocycle.

The above liquid crystalline monomers may be used alone or in combination of two or more.

According to the present invention, by using a photopolymerization initiator having a double bond and an aromatic ring or a heterocycle in the molecule, the liquid crystal region of the liquid crystalline monomer is not restricted and the alignment at a relatively low temperature is achieved. , The polymerization can be performed, and the film production process is greatly simplified.

The structure of the photopolymerization initiator used in the present invention, as described above,
It has a double bond and at least a heteroaromatic ring in the molecule, and among them, those represented by the general formulas [II] and [III] are preferable.

Ar: substituted or unsubstituted aromatic or heterocyclic nucleus W: hydrogen atom, alkyl, aryl group Z: chlorine or bromine atom Z: chlorine or bromine atom X: -CZ ₃ , -NH ₂ -NHR, -NR ₂ or -OR (R is phenyl or a lower alkyl group not larger than 11 carbon atoms) n: 1, 2, 3 Y: optionally A substituted aromatic or heterocyclic nucleus, specifically
A compound belonging to the general formula [II] is disclosed in JP-A-54-74728.
However, the following are preferable ones.

Particularly preferred compounds belonging to the general formula [III] are listed below.

As the support used in the present invention, it is also possible to use glass, a plastic sheet, or a belt or drum formed by plating or vapor-depositing a metal such as stainless steel, chromium, or aluminum on one of the supports.

Examples of the plastic sheet include cellulose, cellulose triacetate, cellulose diacetate, cellulose derivatives such as cellulose acetate butyrate, polyethylene terephthalate,
Polyester such as polyethylene naphthalate, polycarbonate, polypropylene, polyolefin such as polyethylene, polyvinyl alcohol, polyvinyl chloride,
Polyvinylidene chloride, nylon, polystyrene and the like can be used.

The orientation treatment is carried out on the support surface with metal, cotton, natural fibers such as wool,
Rubbing may be performed with synthetic fibers such as nylon, polyester, acrylonitrile, etc., polyimide, polyamide, polyvinyl, alcohol, etc. may be applied and the surface may be rubbed with the above fibers, or an appropriate surface active The agent may be applied.

In order to keep the monomer in the liquid crystal state, the temperature of the atmosphere may be controlled to be not less than the liquid crystal liquid crystal transition temperature (Tc) of the liquid crystalline monomer and not more than the liquid crystal isotropic liquid transition temperature (Ti).

Among these liquid crystalline monomers, there are materials that do not destroy the liquid crystallinity of the monomer, and to the extent that they do not destroy the dichroic dye,
Ultraviolet absorbers Addition of low molecular weight liquid crystal, gearing agents such as ordinary acrylate or methacrylate monomer glass beads which do not exhibit liquid crystallinity, etc., does not cause any problems.

As the dichroic dye, it is possible to use, for example, an anthraquinone-based or azo-based dye which is used as a guest of a normal guest-host liquid crystal.

The film obtained by the method of the present invention may be used while being sandwiched between supports, or may be used after being peeled off from the support after polymerization.

As the light used for the polymerization, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp or an ultra-high pressure mercury lamp can be used, but it is desirable to use a high-pressure or ultra-high pressure mercury lamp in order to accelerate the polymerization.

Examples will be described below, in which the birefringence measurement is
The letter size was measured with a polarizing microscope equipped with a compensator using white light, and this value was divided by the thickness of the film.

First, the synthesis of the liquid crystalline monomer will be described.

Synthesis example Liquid crystalline monomer, Synthesis of [abbreviated as 5H below] 4-hydroxy-4'-cyanobiphenyl 200g (1.02mol) and 5-bromo-1-pentanol 170g (1.02mol) in 1methanol solution in which 68g (1.03mol) of KOH was dissolved.
Was added, and the mixture was heated under reflux for 11 hours, poured into ice water and extracted with ethyl acetate. The extract was concentrated under reduced pressure using an evaporator and then subjected to column treatment (carrier: Wakogel C-20
0, 4- (6-hydroxypentyloxy) -4'-cyanobiphenyl, 172 g, via developing solvent hexane / THF)
(Yield 60%) was obtained.

This 4- (6-hydroxypentyloxy) -4'-cyanobiphenyl 110 g (0.39 mol) and triethylamine 48
g (0.47 mol) is dissolved in 600 ml of THF, and this solution is
After cooling to 5 ° C and stirring with a stirrer, 39 g (0.43 mol) of acrylic acid chloride was added dropwise over 30 minutes, and the mixture was further reacted at 5 to 10 ° C for 1 hour, then poured into ice water and extracted with ethyl acetate. . The yellow solid obtained by concentrating the extract to dryness was recrystallized twice from a mixed solvent of hexane / THF to obtain 4
-[Ω (propenoyloxy) pentyloxy] -4'-
102 g of cyanobiphenyl (yield 72%) was obtained.

[Example 1] As a polyimide-based aligning agent, PIX-1400-04 (manufactured by Hitachi Chemical Co., Ltd.) was applied by a spin coater and heat-treated, and then liquid crystallinity was applied between glass plates that were rubbed in a certain direction with nylon cloth. As a photopolymerization initiator for monomer 5H, The glass cell was loaded with a mixture containing 1 wt% of
The mixture was heated to 0.degree. C., the mixture was made an isotropic liquid, and then allowed to cool. 55 ° C
Orientation occurred from the position, and this orientation was maintained up to room temperature (up to 30 ° C). Photopolymerization at 50 ° C. using a 2 KW ultra-high pressure mercury lamp and ultraviolet irradiation for 5 seconds gave a uniform alignment film, and the birefringence was 0.18.

[Example 2] As a polyimide-based aligning agent, PIX-1400-04 (manufactured by Hitachi Chemical Co., Ltd.) was applied by a spin coater, heat-treated, and then rubbed in a certain direction with nylon cloth. 5H as a photopolymerization initiator, The glass cell was loaded with 1 wt% of the mixture, and the glass cell was once heated to 80 ° C. to make the mixture an isotropic liquid and then allowed to cool. Orientation occurred at around 55 ° C and this orientation was maintained up to room temperature (30 ° C). Photopolymerization was carried out at 50 ° C. using a 2 KW ultra-high pressure mercury lamp for 7 seconds to irradiate ultraviolet rays, and a uniform alignment film was obtained with a birefringence of 0.17.

[Comparative Example 1] A cell was prepared in the same manner as in Example 1 using benzophenone (2 wt% vs. monomer) and ethyl Michler's ketone (0.2 wt% vs. monomer) as the photopolymerization initiator, and heated to 75 ° C once. Then, the mixture was made into an isotropic liquid and then allowed to cool. Orientation started to occur at 53 ℃, but almost simultaneously a fan-like structure was generated, and uniform orientation could not be obtained.

[Comparative Example 2] The same as Example 1 except that no photopolymerization initiator was used and AIBN (2,2'-azobisisobutyronitrile) was used as a thermal polymerization initiator in an amount of 2 wt% with respect to the monomer. Then, a cell was prepared, and the mixture was heated once to 75 ° C. to make the mixture an isotropic liquid and then polymerized. After the completion of the polymerization, the cell was gradually cooled to prepare an alignment film. However, since the polymerization reaction started at the time of heating to 75 ° C., the obtained alignment film did not show uniform alignment.

Claims (2)

[Claims] 1. A photopolymerization having a liquid crystalline monomer having the following general formula [I] and at least one carbon-carbon double bond in the molecule and having at least one heteroaromatic ring in the molecule. A method for producing an alignment film characterized by carrying a mixture of an initiator on a support subjected to an alignment treatment or between the supports, and polymerizing the mixture by irradiating with light while keeping the mixture in a liquid crystal state in general. Formula [I]: (However, R represents H or CH ₃ , n represents an integer of 1 to 11, and X represents a group containing two or more aromatic rings or heterocycles having a CN group in the para position.) . 2. The method for producing an alignment film according to claim 1, wherein X in the above general formula [I] represents any one of the following groups.