JP2852789B2 - Composition for liquid crystal alignment film - Google Patents

Description

The present invention relates to a composition for a liquid crystal alignment film capable of forming a liquid crystal alignment film.

[Conventional technology]

2. Description of the Related Art In a liquid crystal element used in a liquid crystal display device, a liquid crystal alignment film is generally formed on the surface of a transparent electrode on the inner side surface of a transparent substrate which is disposed so as to have a predetermined gap. In the case of a conventional TN type liquid crystal device, a polyimide film is often used as the liquid crystal alignment film. The polyimide film is formed by applying a composition for a liquid crystal alignment film obtained by dissolving a precursor polyamic acid in an organic solvent onto a transparent electrode, and heating and dehydrating and closing the ring.

Conventionally, a polyimide film using a wholly aromatic diamine as a raw material has been used as a polyimide for a liquid crystal alignment film. For example, a polyimide film obtained by subjecting a composition for a liquid crystal alignment film composed of a polyamic acid obtained by a reaction between pyromellitic anhydride and 4,4'-diaminodiphenyl ether to dehydration-closing is used. This kind of polyimide has advantages such as excellent orientation, but cannot be applied to a liquid crystal display device utilizing a super-twisted birefringence effect (STBE), which has recently attracted attention. This display device has a feature that contrast and visual characteristics are extremely excellent as compared with the conventional TN type. It is necessary to increase the pretilt angle of the alignment film used for this purpose. However, in the conventional polyimide, the pretilt angle is 2 ° or less, and good display characteristics such as generation of domains and generation of line defects called disclination cannot be obtained. . Therefore, at present, an inorganic obliquely evaporated film of silicon oxide or the like has been mainly used as an alignment film capable of obtaining satisfactory display characteristics in an STBE display device.

[Problems to be solved by the invention]

However, the inorganic obliquely deposited film has selectivity to liquid crystal, and it is difficult to properly align all liquid crystal compositions. In addition, there is a disadvantage that the orientation becomes uneven due to the high-temperature heat treatment at the time of assembly, the yield is reduced, and the productivity is deteriorated.
The contrast and visual characteristics required for the alignment film could not be satisfied.

[Means for solving the problem]

The present inventors have studied the development of a polyimide film having a relatively high pretilt angle in place of the inorganic oblique deposition film having various problems as described above. Because the conventional polyimide film has a planar structure, it is considered that the pretilt angle is low, and to prototype a polyimide film in which some of the constituent molecules stand from the plane,
The composition for a liquid crystal alignment film was studied.

As a result, the pretilt angle is higher than the conventional product,
The inventors have invented a composition for an excellent liquid crystal alignment film capable of forming a polyimide alignment film capable of oblique alignment.

That is, the present invention provides a compound represented by the general formula (I) (Wherein, R ₁ is an aromatic ring or an alicyclic ring, R ₂ is a substituted or unsubstituted azobenzene group, R ₃ is an alkyl group, an alkoxy group, or a halogen atom, X is an alkyl group,
O, S, NR ₄ (R ₄ is a hydrogen atom or an alkyl group), Wherein n is a positive integer. A composition for a liquid crystal alignment film, comprising the polyamic acid represented by the formula (1).

The composition for a liquid crystal alignment film of the present invention mainly comprises a polyamic acid of the general formula (I) and an organic solvent capable of dissolving the same, and the organic solvent is volatilized simultaneously with dehydration ring closure to form a polyimide film.

Here, the polyamic acid of the general formula (I) will be described in detail. This polyamic acid is obtained by the reaction of an acid anhydride and an aromatic diamine having a chain substituent. Examples of the acid anhydride include pyromellitic anhydride, 3,3 ′, 4,
4'-biphenyltetracarboxylic acid, 3,3 ', 4,4'-anhydride
Benzophenonetetracarboxylic acid, cyclopentanetetracarboxylic anhydride, 2,3,5-tricarboxycyclopentylacetic anhydride, 5- (2,5-dioxotetrahydro-3-furanyl) -3-cyclohexene-1,1-dicarboxylic anhydride Acids and the like. The aromatic diamine having a chain substituent has the general formula (II) (Wherein R ₂ , R ₃ and X are the same as described above), for example, the following compounds. Incidentally, Compound No.
Is commonly used in the embodiments.

One or two or more of the above-mentioned acid anhydrides and aromatic diamines having a chain substituent are reacted in an organic solvent under anhydrous conditions, preferably at a temperature of 50 ° C. or lower, to obtain a polyamic acid solution.

The organic solvent used here is a polar solvent that is relatively easy to volatilize and can dissolve the generated polyamic acid, for example, N,
N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethylsulfoxide and the like are used.

Further, there is no doubt that a silane coupling agent or diaminosiloxane is used in combination as a reaction component for the purpose of improving the adhesion to a glass substrate, metals, and the like. Examples of the silane coupling agent include γ-aminopropyltriethoxysilane, N- (β-aminoethyl) -γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ -Methacryloxypropyltrimethoxysilane and the like.

1,3-bis (3-aminopropyl) -1,1,3,3-tetramethyldisiloxane, α, ω
-Bis (3-aminopropyldimethylsilyl) benzene and the like.

A method for forming an alignment film using the composition for a liquid crystal alignment film containing the polyamic acid of the present invention obtained as described above is as follows.

That is, a 0.1 to 20% by weight solution of the polyamic acid in an organic solvent is applied to an electrode constituting a liquid crystal by a dipping method, a spinner method, a spraying method, a printing method, or the like. After the application, the polyamic acid is subjected to a heat treatment at 100 to 400 ° C., preferably 150 to 250 ° C. to dehydrate and ring-close the polyamic acid to obtain a polyimide coating. This film is rubbed to form a liquid crystal alignment film. The pretilt angle between the liquid crystal alignment film and the liquid crystal was 2 ° or less in the conventional polyimide film, but in the liquid crystal alignment film obtained from the composition of the present invention, the pretilt angle was increased, and it was possible to reach about 40 °. . The composition for a liquid crystal alignment film containing a polyamic acid of the present invention is suitable for a liquid crystal display device of the STBE mode.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples. In addition,
Parts in Examples are parts by weight.

Example 1 A solution of 4.19 parts of the diamine of Compound No. 2 in 64 parts of N, N-dimethylacetamide was added under an atmosphere of nitrogen under an equimolar amount of anhydrous 3,3.
Add 2.94 parts of 3 ', 4,4'-biphenyltetracarboxylic acid and add 2
The reaction was carried out at 0-30 ° C for 24 hours. N, N-dimethylacetamide was added to the obtained polyamic acid solution to prepare a 5% by weight solution to prepare a liquid crystal alignment film composition. Using a spin coater, the transparent glass substrate of ITO (3cm x 3cm thickness 1)
mm). After coating, the coating was heated at 250 ° C. for 1 hour to effect dehydration and ring closure to form a slightly yellowish polyimide coating.

Next, a liquid crystal display (thickness: 6 μm) was prepared by enclosing a liquid crystal ZLI-2214 (manufactured by Merck) using a pair of substrates rubbed with this film. When the pretilt angle was measured, it was 8 °. When a voltage was applied to the device and the rising characteristics and contrast were observed, the results were extremely good.

Examples 2 to 5 Example 1 was repeated using the compounds shown in Table 1 in place of the diamine and acid anhydride of compound No. 2 used in Example 1.
The same operation as described above was performed to measure the pretilt angle. Table 1 shows the results.

In each case, good rising and contrast were observed as in Example 1.

In Table 1, PMDA is pyromellitic anhydride, BPDA is 3,3 ', 4,4'-biphenyltetracarboxylic anhydride, BZDA
Represents 3,3 ', 4,4'-benzophenonetetracarboxylic anhydride and CPDA represents cyclopentanetetracarboxylic anhydride.

Example 6 N, N-Dimethylacetamide (57 parts) was combined with the compound No. 2 diamine (4.15 parts) and 1,3-bis (3-aminopropyl)-.
Under a nitrogen atmosphere, 2.18 parts of pyromellitic anhydride were added, and the mixture was reacted at 20 to 30 ° C. for 24 hours under the condition of dissolving 0.025 parts of 1,1,3,3-tetramethyldisiloxane (1 mol% of the entire diamine). N, N-dimethylacetamide was added to the obtained polyamic acid solution to prepare a 5% by weight solution to prepare a liquid crystal alignment film composition. Using this composition, a polyimide film was obtained in the same manner as in Example 1, and a liquid crystal display device was further prepared. The pretilt angle was measured. In addition, good rising and contrast were observed as in Example 1.

Example 7 In the reaction solution obtained in Example 2 in the same manner as in Example 1, 1 mol% of γ-aminopropyltriethoxysilane based on diamine was added, and the same operation as in Example 1 was performed to measure the pretilt angle. Then it was 15 ゜. In addition, good rising and contrast were observed as in Example 1.

Example 8 9.52 parts of diamine and 4,4'-diaminodiphenyl ether of Compound No. 13 were added to 59 parts of N, N-dimethylacetamide.
Dissolve 0.8 part, under a nitrogen atmosphere, pyromellitic anhydride 4.36
Then, the mixture was reacted at 20 to 30 ° C. for 24 hours. N, N-dimethylacetamide was added to the obtained polyamic acid solution to prepare a 5% by weight solution to prepare a liquid crystal alignment film composition. Using this composition, a polyimide film was obtained in the same manner as in Example 1, and a liquid crystal display device was further prepared. The pretilt angle was measured. In addition, good rising and contrast were observed as in Example 1.

(Comparative example)

In Example 2, instead of the diamine of compound 2,
The same operation as in Example 2 was performed using 4,4'-diaminodiphenyl ether to measure the pretilt angle.
It was 2 ゜.

〔The invention's effect〕

By using the composition for a liquid crystal alignment film of the present invention for alignment control, a display device having excellent contrast and visual characteristics can be obtained.

Continuation of front page (72) Inventor Makoto Ebisawa 2470 Handa, Shibukawa-shi, Gunma Japan Central Research Institute of Carlit Co., Ltd. (58) Fields investigated (Int.Cl. ⁶ , DB name) G02F 1/1337

Claims (1)

(57) [Claims] 1. The compound of the general formula (I) (Wherein, R ₁ is an aromatic ring or an alicyclic ring, R ₂ is a substituted or unsubstituted azobenzene group, R ₃ is an alkyl group, an alkoxy group, or a halogen atom, X is an alkyl group,
O, S, NR ₄ (R ₄ is a hydrogen atom or an alkyl group), Wherein n is a positive integer. A composition for a liquid crystal alignment film, comprising the polyamic acid represented by the formula (1).