JPH081497B2 - Alignment treatment agent for liquid crystal cells - Google Patents

Description

The present invention relates to an alignment treatment agent for a liquid crystal cell,
More specifically, the present invention relates to an alignment treatment agent for liquid crystal cells, which is made of a polyimide resin having a higher dielectric constant than conventional ones.

(Prior Art) Alignment treatment agents conventionally used for aligning liquid crystal molecules such as nematic liquid crystals or smectic liquid crystals in a certain direction are excellent in heat resistance, liquid crystal resistance, mechanical properties, and electrical properties. In this respect, the polyimide resin is industrially widely used as a highly reliable resin.

In general, a polyimide resin is a polyamic acid solution obtained by reacting an organic tetracarboxylic dianhydride and a diamine in a solvent, and polymerizing the solution, and then applying this to a glass substrate with a transparent electrode or a plastic film to form a polyimide resin by dehydration ring closure. Then, by rubbing the surface of the polyimide resin with a cloth or the like, the liquid crystal molecules sandwiched between the substrates are aligned in a certain direction and used as an alignment treatment agent for liquid crystal cells.

Generally, in a liquid crystal cell, a liquid crystal layer is sandwiched between polyimide resins formed on two substrates, and the polyimide resin and the liquid crystal layer are sandwiched between transparent electrodes.

(Problems to be Solved by the Invention) When such a liquid crystal cell structure is adopted, the voltage applied to the liquid crystal layer itself when a voltage is applied between the transparent electrodes is subject to voltage loss due to the polyimide resin layer. However, there is a problem in that the liquid crystal cell cannot be efficiently driven in terms of responsiveness.

Here, in the configuration of the liquid crystal cell, when the capacitances of the polyimide resin layer and the liquid crystal layer are C _P and C _L , respectively, and when a voltage of V _O is applied between the electrodes, the voltage V _L applied to the net liquid crystal layer is It is generally expressed by the following equation.

That is, when the thicknesses of the polyimide resin layer and the liquid crystal layer are constant, the voltage applied to the liquid crystal layer increases as the dielectric constant of the polyimide resin increases, so that the liquid crystal cell can be driven more efficiently.

However, a polyimide resin conventionally used as an alignment treatment agent for liquid crystal cells generally has a dielectric constant of 3 to 4
However, it is not so satisfactory in driving a liquid crystal cell, and development of a polyimide resin having a higher dielectric constant is desired.

Furthermore, as a component that constitutes the conventional polyimide resin,
There are aromatic tetracarboxylic dianhydrides typified by pyromellitic dianhydride and biphenyltetracarboxylic dianhydride, and diamines typified by diaminodiphenyl ether and diaminodiphenylmethane. The polyimide resin obtained using the compound has a low content of polar groups, and generally has a small polarity because the uneven distribution of electrons in the polyimide resin structure is small, and depending on the type of liquid crystal, it may not always be satisfactory in terms of its orientation. is there.

Furthermore, the ferroelectric liquid crystal having spontaneous polarization found in recent years has excellent characteristics such as high-speed response or memory property as compared with conventional nematic liquid crystals, but it is not easy to obtain uniform alignment. There is a problem, and a highly polar alignment treatment agent having stronger interaction with the spontaneous polarization of the ferroelectric liquid crystal is desired.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an alignment treatment agent for liquid crystal cells, which is made of a polyimide resin having a higher dielectric constant and higher polarity than conventional ones.

(Means for Solving Problems) The present inventors have completed the present invention as a result of intensive studies to solve the above problems.

That is, the present invention is applied to a transparent substrate with a transparent electrode,
In the alignment treatment agent for a liquid crystal cell, which is cured by heating at ℃ to 250 ℃, and then subjected to a rubbing treatment to form an alignment treatment layer, the treatment agent is represented by the general formula [I]. (R ¹ and R ² are the same or different divalent organic groups, and R ³ is a tetravalent organic group having 4 carbon atoms which constitutes tetracarboxylic acid or a derivative thereof.) The present invention relates to an alignment treatment agent for a liquid crystal cell, which comprises forming an alignment treatment layer made of a polyimide resin containing

The alignment treatment agent of the present invention is prepared by formula (I) on a transparent substrate such as glass or plastic film having a transparent electrode.
Forming a polyimide resin film containing a repeating unit of
Then, it is used as an alignment treatment agent for liquid crystal cells by subjecting it to rubbing treatment.

Here, the polyimide resin containing the repeating unit of the general formula [I] can be generally obtained by using the dianhydride of tetracarboxylic acid and diamine as starting materials.

Represented (R ¹ and R ² are the same.) In formula (II) ^{_{H 2 N-R 1 -CONH-}} R 2 -NH 2 (II) as the diamine component used for the alignment treating agent of the present invention in It is necessary to use the diamines mentioned.

Specific examples of the diamine of the general formula [II], H ₂ NCH _{2 3} CONHCH _{2 3} NH ₂ However, the present invention is not limited to these.

Further, one kind or a mixture of two or more kinds of these diamines can be used.

Further, as the diamine component used in the alignment treatment agent of the present invention, a diamine other than the diamine of the general formula [II] can be used as long as the effect of the present invention is not impaired.

 Specific examples thereof include the following diamines.

p-phenylenediamine, m-phenylenediamine,
Diaminodiphenylmethane, diaminodiphenyl ether, 2,2-diaminodiphenylpropane, diaminodiphenyl sulfone, diaminobenzophenone, diaminonaphthalene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, Four,
Examples thereof include aromatic diamines such as 4'-di (4-aminophenoxy) diphenyl sulfone and 2,2'-bis [4 (4-aminophenoxy) phenyl] propane.

Other alicyclic diamines and aliphatic diamines may be used depending on the purpose.

Further, one kind or a mixture of two or more kinds of these diamines can be used.

Here, the use ratio of the diamine of the general formula [II] in the diamine component is at least 30 mol% with respect to the total amount of diamine.
It is preferable that the content be more than 30 mol%, and if it is less than 30 mol%, sufficient effects may not be obtained in terms of the dielectric constant and polarity of the polyimide resin produced, which is not preferable.

Further, specific examples of the tetracarboxylic acid or a derivative thereof which represents a tetravalent organic group having 4 carbon atoms of R ³ which constitutes the repeating unit of the general formula [I], include butanetetracarboxylic acid, cyclobutanetetracarboxylic acid and the like. And the dicarboxylic acid dihalides thereof.

The reaction and polymerization method of the tetracarboxylic acid dianhydride and its derivative and the diamine component are not particularly limited, but generally, the diamine component is dissolved in a polar solvent such as N-methylpyrrolidone, and tetracarboxylic acid is added thereto. A method is employed in which dianhydride is added in an approximately equimolar number with respect to the total amount of diamine, the mixture is sufficiently stirred to form a polyamic acid intermediate, and then dehydration ring closure is performed on the intermediate.

Here, the reaction temperature for producing the polyamic acid intermediate can be selected from any temperature from −20 ° C. to 150 ° C., but especially −
The range of 5 ° C to 100 ° C is preferable.

Further, in order to convert the polyamic acid intermediate into a polyimide resin, a method of dehydration and ring closure by heating is usually adopted.

The heat dehydration ring-closing temperature is 150 ° C to 350 ° C, preferably
Any temperature from 170 ° C to 350 ° C can be selected.

The time required for this dehydration ring closure is usually 30 seconds to 10 hours, preferably 5 minutes to 5 hours, depending on the above reaction temperature.

As another method for converting the polyamic acid intermediate into a polyimide resin, a known dehydration ring-closing catalyst can be used for ring closure.

The polyimide resin or polyamic acid intermediate solution in the present invention is applied on a transparent substrate such as glass or plastic film with a transparent electrode by a spin coating method or a printing method, and then cured at 150 to 250 ° C. for 1 minute to 2 hours. Form a polyimide resin film with a thickness of 200 to 3000Å.
Then, the polyimide resin film layer can be rubbed to be used as an alignment treatment agent for liquid crystal cells.

(Effect of the invention) When the alignment treatment agent for a liquid crystal cell of the present invention is used, since it has a -CONH- group in the molecular skeleton of the formed polyimide resin film, its dielectric constant is higher than that of a conventional polyimide resin. Since the film polarity is high and the film polarity represented by the surface tension is higher than in the conventional case, the liquid crystal molecules can be aligned more uniformly, and the liquid crystal cell can be efficiently driven.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

Example 1 4,4'-Diaminobenzanilide (12.077 g, 0.053 mol) was added to 50 g of N-methylpyrrolidone, and the mixture was stirred and dissolved in a nitrogen atmosphere at 50 ° C until uniform.

Furthermore, butanetetracarboxylic dianhydride 10.422 at room temperature
g (0.053 mol) and N-methylpyrrolidone (130 g) were added and reacted for 4 hours to obtain a uniform solution having a viscosity of 47 poise.

This solution was spin coated on a stainless steel plate and heated at 170 ° C.
A polyimide resin film having a thickness of 10 μm was formed by heating at 60 ° C. for 60 minutes.

When an aluminum electrode was vapor-deposited on this polyimide resin film and the dielectric constant was measured, it was 5.5, which was an extremely high value as compared with the conventional polyimide resin.

The surface tension of the polyimide resin film obtained by the contact angle method was as high as 59 dyne / cm.

Furthermore, a solution with a viscosity of 47 poise was diluted with N-methylpyrrolidone to a concentration of 4%, spin-coated on two glass electrodes with transparent electrodes, and heated at 170 ° C for 60 minutes to prepare a 1000Å polyimide resin film. Was formed. Next, a rubbing process was performed, a spacer was sandwiched, and the rubbing directions were made orthogonal to each other to assemble a cell.

Liquid crystal (Merck, ZLI-2293) was injected into this cell and the alignment state was observed. As a result, a very uniform alignment was obtained.

Furthermore, in order to see the effectiveness of the alignment treatment agent according to the present invention,
The rise response speed when a rectangular wave with a pulse frequency of 5 V and a pulse frequency of 100 Hz was applied at a temperature of 23 ° C was measured at various cell thicknesses. Table 1 shows the results.

Comparative Example 1 4,4'-diaminodiphenyl ether 10.613 g (0.053
Mol) in 50 g of N-methylpyrrolidone and uniformly dissolved at room temperature in a nitrogen atmosphere, 10.394 g (0.053 mol) of butanetetracarboxylic dianhydride and 140 g of N-methylpyrrolidone are added and reacted for 4 hours or more. To obtain a uniform solution.

This solution was treated in the same manner as in Example 1 to form a polyimide resin film, and the dielectric constant was measured to be 3.3. The surface tension was as low as 44 dyne / cm.

Furthermore, a cell was prepared in the same manner as in Example 1 and the rising response speed was measured.

From Table 1, it can be seen that the polyimide resin film of Example 1 containing the repeating unit represented by the general formula [I] has higher responsiveness of the liquid crystal cell than Comparative Example 1 containing no polyimide resin film of the general formula [I]. There is a clear improvement.

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Claims (1)

[Claims] 1. A transparent substrate with a transparent electrode, which is coated at 150 ° C to 2 ° C.
In the alignment treatment agent for liquid crystal cells, which is cured by heating at 50 ° C. and then rubbed to form an alignment treatment layer, the treatment agent is represented by the general formula [I]. (R ¹ and R ² are the same or different divalent organic groups, and R ³ is a tetravalent organic group having 4 carbon atoms which constitutes tetracarboxylic acid or a derivative thereof.) An alignment treatment agent for a liquid crystal cell, which comprises forming an alignment treatment layer made of a polyimide resin containing