JPH0483563A - Formation of thin polyimide film with liquid crystal orientation - Google Patents

Abstract

PURPOSE:To obtain a thin polyimide film oriented uniformly and in a predetermined direction by a method wherein the polyimide precursors synthesized from a polyamic acid having a specific composition are accumulated on a base plate by Landmuir-Blodgett's technique, followed by imidation. CONSTITUTION:A polyimide precursor represented by the formula II is synthetically produced using as a material the polyamic acid having an intrinsic viscosity of at least 1.20dl/g represented by the formula I. In such formulas, R1 represents the formulas I, II, III, IV, V, VI, VII and VIII, R2 and R3 are the aliphatic hydrocarbon or amine containing at least three carbon atoms and n is a positive integer. The polyimide precursors are accumulated on a base plate by the Langmuir-Blodgett's technique, followed by imidation. This method can produce a thin polyimide film having liq. crystal oriented uniformly and in a predetermined direction.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a method for forming a polyimide thin film for liquid crystal alignment, and more specifically, a method for forming a polyimide thin film for liquid crystal alignment by the Langmuir-Blodgett I method using a polyimide precursor. The present invention relates to a method for forming polyimide 1M.

[Conventional technology]

Conventionally, polyimide thin films for liquid crystal alignment have generally been produced by applying a solution containing polyamic acid to a substrate by spin-casting or transfer, heating it to form a polyimide thin film, and then rubbing the surface in a certain direction with a cloth or the like. (rubbing) treatment. However, in recent years, as the area of substrates has become larger, problems have arisen, such as the uniformity of thin films being impaired and the film not exhibiting sufficient properties as an alignment film for new liquid crystals such as ferroelectric liquid crystals.

In order to overcome these problems, the Journal of the Chemical Society of Japan no.

11, 2174 (1987), Journal of the Japanese Society of Applied Physics (J
pn, J.

^pp1. Phys, )27(4), L475(1
988), Journal of the Japanese Society of Applied Physics (Jpn, J, ^pp
1. Phys, ) 27(5), L729 (1988
), or published patent publication Sho 63-23131.
As described in Figure 1, a polyimide precursor (1) synthesized from polyamic acid is spread and compressed on a water surface by the Langmuir-Blodgett method and transferred onto a substrate (2). A polyimide thin film for liquid crystal alignment formed by performing an imidization reaction after the preparation is being studied.

In forming a polyimide thin film for liquid crystal alignment by the Langmuir-Blodgett method, when a polyimide precursor is transferred from above the water surface to a substrate, the polyimide precursor molecules are uniaxially aligned in the direction of pulling up (or pulling down) the substrate due to flow. Therefore, the polyimide thin film obtained by imidizing the film transferred to the substrate also has a uniaxially oriented polymer structure.

A polyimide thin film having such a structure is used, for example, as a liquid crystal alignment film (2) of a liquid crystal display element having the structure shown in FIG.
When used as a liquid crystal, the liquid crystals are aligned along the uniaxial direction, and the initial state of the liquid crystal can be kept constant. In other words,
The polyimide thin film formed by the Langmuir-Blodgett method can function as a liquid crystal alignment film without rubbing treatment, and it is easy to make the film thickness uniform and can align various liquid crystals. I can do it, etc.
Industrially important effects were expected.

[Problem that the invention seeks to solve]

However, polyimide thin films for liquid crystal alignment produced by the conventional Langmuir-Blodgett method have a problem in that the uniformity of liquid crystal alignment is inferior to films obtained by the rubbing method. In addition, the characteristics of liquid crystal display elements created using polyimide thin films for liquid crystal alignment vary among individuals, and it is impossible to always achieve uniform liquid crystal alignment. There were some problems, such as the display not showing.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a method for forming a polyimide thin film for liquid crystal alignment, which always achieves uniform liquid crystal alignment in a certain direction.

[Means for solving problems]

That is, in the present invention, a polyimide precursor represented by the formula (2) synthesized using a polyamic acid represented by the following formula (1) and having an intrinsic viscosity (η) of 1.20 dN/g or more as a raw material is used. This invention provides a method for forming a polyimide thin film for liquid crystal alignment, characterized in that polyimide thin films are deposited on a substrate by the Langmuir-Blodgett method and then imidized. It represents an aliphatic hydrocarbon or an aliphatic amine, and n represents a positive integer].

The present invention will be explained in more detail below.

In order to achieve uniform liquid crystal alignment in a fixed direction, it is necessary that the polymer chains in the polyimide thin film be uniaxially aligned. The present inventors have discovered that this uniaxial orientation depends on the intrinsic viscosity (molecular weight) of polyamic acid as a raw material. That is, FIG. 3 shows the GP of polyamic acid.
Elution volume (El
This shows the relationship between the value of the equation volume (Elution Volume), the degree of orientation of the polyimide thin film obtained from this polyamic acid raw material, and the extinction ratio of the liquid crystal cell using the same. It was found that the larger the values of intrinsic viscosity and molecular weight, the larger the extinction ratio (r) of the liquid crystal cell, and the better the liquid crystal orientation. Furthermore, as shown in Fig. 3, the larger the molecular weight and intrinsic viscosity, the smaller the carbonyl characteristic absorption intensity ratio (A /// A) in the direction parallel to and perpendicular to the substrate pulling direction, which indicates the uniaxial orientation of the polymer chains in the polyimide thin film. was found to be higher. Good liquid crystal alignment properties can be achieved with a polyamic acid raw material having an equation volume of about 7.30 or less.

This corresponds to using a polyamic acid raw material having an intrinsic viscosity of 1.20 dl/g or more.

Therefore, a polyimide precursor for liquid crystal alignment obtained by forming a film by the Langmuir-Projet method using a polyimide precursor obtained from a high molecular weight polyamic acid having an intrinsic viscosity of 1.20 dZ/ or more as a raw material, and imidizing the film. The thin film can stably achieve good liquid crystal alignment characteristics.

In addition, even when using polyamic acid raw materials that have been stored for a long period of time, by checking their intrinsic viscosity before film formation and using materials with a value of 1.20 dN/g or higher, good liquid crystal alignment can always be achieved. It is possible to obtain a polyimide thin film that achieves this.

[Effect]

As mentioned above, a polyimide precursor synthesized using a polyamic acid having an intrinsic viscosity (η) of 1.20 dl/fI or more as a raw material is accumulated on a substrate by the Langmuir-Blodgett method, and then imidized, resulting in an extremely A polyimide thin film with a high degree of orientation can be obtained, and a liquid crystal cell with a high extinction ratio can be obtained.

〔Example〕

Hereinafter, specific examples of the present invention will be described.

Dog] L Sha-1 0.4 g of diaminodiphenyl ether was dissolved in 10 ml of well-dehydrated dimethylformamide. This solution was heated at 5°C.
0.436y of pyromellitic anhydride was gradually added and reacted while introducing nitrogen, and then reprecipitated with methanol and thoroughly dried to obtain a structure having the structure of formula (3) with an intrinsic viscosity of 1.
A polyamic acid of 30 dN/H was obtained.

Subsequently, this polyamic acid is dissolved in a dimethylformamide/benzene mixture to make a lXl0-'mol/1 solution, and mixed with N,N-dimethylhexadecylamine of the same concentration to form a solution having the structure of formula (4). A solution containing a polyimide precursor was obtained.

111N/III, substrate pulling speed 101/min, water temperature 2
It was 0°C.

Subsequently, the obtained thin film was heated at 150°C for 30 minutes at 300"C30
The polyimide thin film for liquid crystal alignment having the structure of formula (5) was obtained by imidization under the following conditions.

CHlCH.

The obtained solution was spread and compressed on a clean water surface, and IT○ (Indium
A thin film consisting of five monomolecular layers of a polyimide precursor was formed on a (Tin Oxide) substrate. The conditions for the Langmuir-Blodgett method are: Cumulative surface pressure 25 Carbonyl characteristic absorption intensity ratio of polymer chains in this thin film (an indicator of the degree of orientation)
A///A soil was 0.60, and a nematic liquid crystal display element with a cell gap of 5.5 μm using this thin film as a liquid crystal alignment film had an extinction ratio r of 620, indicating a good liquid crystal alignment function.

Large 410-noparaphenylenediamine 0.108y 10m&N-
Dissolved in methyl 2-pyrrolidone and reacted with 024 g of pyromellitic anhydride in the same manner as in Example 1,
A polyamic acid having an intrinsic viscosity of 1.20 dl/FI was obtained.

This polyamic acid was esterified with stearyl alcohol in an N-methyl 2-pyrrolidone/benzene solvent to obtain a polyimide precursor solution having a structure represented by formula (6).

C[I3 CL The obtained polyimide precursor solution was spread on a water surface and compressed, and a polyimide precursor thin film consisting of 20 monomolecular layers was formed on a Sn 02 substrate by the Langmuir-Blodgett method.

The formation conditions at this time were a cumulative surface pressure of 32 IIIN/m, a substrate pulling rate of 11 nllZ, and a water temperature of 5°C. Subsequently, the polyimide precursor thin film was immersed in an acetic anhydride/pyridine mixed solution for 20 hours to perform imidization, thereby obtaining a polyimide thin film for liquid crystal alignment having a structure represented by formula (7).

Using this thin film as an alignment film for ferroelectric liquid crystal, a ferroelectric liquid crystal switching element was fabricated, and as a result, the applied voltage lOv
Good switching characteristics with 100% memory performance were observed.

3 and 4 Polyamic acids having structures represented by formulas (8) and (9) were synthesized in the same manner as in Examples 1 and 2.

The intrinsic viscosities were 1.20 and 1.25 dl'/g, respectively.

O Polyimide precursors represented by formulas (10) and (11) were prepared from polyamines and nic acid represented by formulas (8) and (9), respectively, and heated and imidized at 250°C for 1 hour. A polyimide thin film for liquid crystal alignment with a thickness of 5n+* was obtained (Example 3, Example 4).

CH, CHz Uniform alignment of ferroelectric liquid crystal and nematic liquid crystal was confirmed in the obtained polyimide thin film for liquid crystal alignment.

[0.4 g of diaminodiphenyl ether as in Example 1]
was dissolved in 10 ml of dimethylformamide.

While keeping this solution at 5°C and introducing nitrogen, 0.46 g of pyromellitic anhydride was gradually added and reacted, and then reprecipitated with methanol and thoroughly dried.
) A polyamic acid having the structure of the formula was obtained. The intrinsic viscosity of this polyamic acid was 1.05 dl/g.

Using the obtained polyamic acid as a raw material, a polyimide thin film for liquid crystal alignment was formed by the same method as in Example 1, and its properties as a liquid crystal alignment film were investigated.

As a result, the value of A /// A was 0.9 and the extinction ratio r was 0.03, indicating that uniform liquid crystal alignment was not exhibited.

〔Effect of the invention〕

As described above, according to the present invention, since a material with an intrinsic viscosity of 1.20 dN/g or more is used as a raw material for a polyimide thin film for liquid crystal alignment, it is possible to always achieve uniform liquid crystal alignment. became.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the Langmuir-Blodgett thin film forming method used in the present invention. FIG. 2 is a diagram showing an example of a cross-sectional view of a liquid crystal display device. FIG. 3 is a diagram showing the relationship between the extinction ratio (r) and orientation degree of the polyimide thin film for liquid crystal alignment obtained in Example 1 and the elution volume of the raw material polyamic acid. In Figure 1, 1: Polyimide precursor 2: Substrate 3: Water In Figure 2, Substrate 2: Polyimide thin film for liquid crystal alignment 3 Liquid crystal 4: Transparent electrode 5, sealing material 6: Polarizing plate In Figure 3, The horizontal axis shows the equation volume, the left vertical axis shows the logarithm of the extinction ratio, and the right vertical axis shows the carbonyl characteristic absorption intensity ratio. Figure 2 1: Rolled plate 2: Polyimide for hyper-crystal alignment Thickening 3: Liquid crystal 4: Transparent moon 154 at 1 5: Sealing material 6: Polarizing plate 1, polyimide front body 24 [Temporary 3: Point ( Figure 3 Elution volume (m()

Claims (1)

[Claims] It is represented by the following formula (1), and its intrinsic viscosity (η) is 1.20d.
A polyimide precursor represented by formula (2) synthesized using polyamic acid having a value of 1/g or more as a raw material is accumulated on a substrate by the Langmuir-Blodgett method, and then imidized. , method of forming a polyimide thin film for liquid crystal alignment: ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(1) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(2) [In formulas (1) and (2), R_1 represents ▲There are mathematical formulas, chemical formulas, tables, etc.▼, or ▲There are mathematical formulas, chemical formulas, tables, etc.▼, and R_2 and R_3 are aliphatic hydrocarbons or aliphatic amines with 3 or more carbon atoms, which may be the same or different. where n represents a positive integer].