JPH02287324A - Orientation treating agent for liquid crystal cell - Google Patents

Abstract

PURPOSE:To obtain an excellent voltage holding characteristic at the time of driving of a liquid crystal cell by forming the above agent of a polyimide resin having a specific repeating unit. CONSTITUTION:This treating agent is formed of the polyimide resin having the repeating unit expressed by formula I. This resin formed by bringing 3, 4-dicarboxy-2, 3, 3, 4-tetrahydro-1-naphthalene succinid dianhydride and primary diamine into reaction and polymn. to form a polyamic acid intermediate, then imidizating the same by a dehydration ring closure to >=20% imidization rate is used as the above-mentioned resin. In the formula, R denotes bivalence org. group; n denotes 4 to 1,000 integers. The polyimide resin film is formed on a transparent substrate deposited with transparent electrodes and is subjected to a rubbing treatment, by which the orientation treating agent for the liquid crystal cell is obtd. The excellent voltage holding characteristic at the time of the driving of the liquid crystal cell is obtd. in this way.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to an alignment treatment agent for liquid crystal cells, and more specifically, an alignment treatment agent for liquid crystal cells that provides excellent voltage holding characteristics when driving a liquid crystal cell. It is related to.

(b) Conventional technology A liquid crystal cell is a display element that utilizes electro-optical changes in liquid crystal, and has attracted attention for its characteristics such as small size and light weight, and low power consumption.In recent years, it has been used as a display element for various displays. It is making remarkable progress.

In particular, a nematic liquid crystal with positive dielectric anisotropy is used, and the liquid crystal molecules are aligned parallel to the substrates at each interface of a pair of opposing electrode substrates, and the orientation directions of the liquid crystal molecules are orthogonal to each other. A typical twisted nematic type (hereinafter abbreviated as TN type) field effect liquid crystal cell is a combination of both types of plates.

In such a TN type liquid crystal cell, it is important to align the long sleeve direction of the liquid crystal molecules uniformly and parallel to the substrate surface.

The following two methods are conventionally known as typical methods for aligning liquid crystals.

The first method is to form an inorganic film on a substrate by depositing an inorganic substance such as silicon oxide from an oblique direction to the substrate,
This method aligns liquid crystal molecules in the direction of vapor deposition. Although this method provides stable orientation, it is not industrially efficient.

The second method is to provide an organic film on the surface of the substrate, rub the surface with cloth such as cotton, nylon, or polyester in a certain direction, and orient the liquid crystal molecules in the rubbing direction.

This method is relatively easy to obtain stable orientation, so
This method is exclusively used industrially.

Examples of organic films include polyvinyl alcohol, polyoxyethylene, polyamide, polyimide, etc.
Polyimide is most commonly used in terms of chemical stability, thermal stability, etc.

(c) Problems to be solved by the invention In recent years, liquid crystal cells have been required to display a large amount of information such as image display, and for this reason, the structure has changed from a segment type display to a dot matrix type. has transitioned to

Furthermore, two types of dot matrix type display are known: a simple matrix type and an active matrix type.

In the former, the electrodes on two opposing substrates are each divided into strips, and each intersection of each electrode group is divided into cells that are arranged perpendicularly to each other, with one being a scanning electrode and the other a signal electrode. By forming a plurality of electrodes and selectively applying a voltage to these electrode groups, arbitrary information can be displayed.

This method has the advantage that the structure of the display is simple and can be easily manufactured even with a large area, but has the disadvantage that as the cell area becomes large, the crosstalk phenomenon becomes noticeable and it is difficult to obtain clear images. .

On the other hand, the latter has the disadvantage that each pixel is equipped with active elements such as transistors and diodes, and the element structure is complicated, but it is possible to obtain clear images even with large screen cells, making it suitable for LCD TVs. It is currently being actively developed as a display method for various large-sized liquid crystal displays.

In the case of this active matrix method, each pixel is switched on when a scanning voltage is applied, but the circuit is completely cut off until the next scanning voltage is applied, and during this time, each pixel is switched on. The ON state must be maintained.

That is, the so-called voltage holding characteristic of a cell, in which a voltage is held for a certain period of time, is an important factor in determining the sharpness of the display.

The factors that affect this voltage holding characteristic are the purity of the liquid crystal,
Although impurity ions in the cell, moisture, polarization due to interfacial interactions, etc. are considered, it is also known that the liquid crystal alignment film has a large influence.

In general, when an inorganic film is used as a liquid crystal alignment film, good voltage holding characteristics can be obtained, but when an organic film, which is used exclusively in industry, is used as a liquid crystal alignment film, the voltage holding property deteriorates significantly. That was a big problem.

(d) Means for Solving the Problems The present inventor has made earnest efforts to solve the above problems, and as a result, has completed the present invention.

That is, the present invention provides (1) a liquid crystal cell made of a polyimide resin having a repeating unit represented by the general formula [I] (wherein R represents a divalent organic group and n represents an integer from 4 to 1000). and (2) a polyimide resin having a repeating unit represented by the general formula [I] is 3,4-dicarboxy-1,2゜3.4-tetrahydro-1-naphthalenesuccinic dianhydride. After reacting and polymerizing a substance with a primary diamine to form a polyamic acid intermediate, it is dehydrated and ring-closed to imidize it.
The present invention relates to an alignment treatment agent for liquid crystal cells, characterized in that its imidization rate is 20% or more.

The alignment treatment agent of the present invention is used as an alignment treatment agent for liquid crystal cells by forming a polyimide resin film on a transparent substrate such as glass or plastic film with a transparent electrode, and then subjecting the film to a rubbing treatment.

By using the alignment treatment agent of the present invention, excellent voltage holding characteristics can be obtained when driving a liquid crystal cell.

The polyimide resin having a repeating unit of the general formula CI] of the present invention is generally 3,4-dicarboxy-1,2°3.
It can be obtained by reacting and polymerizing 4-tetrahydro-1-naphthalenesuccinic acid dimhydrate and a primary diamine to obtain a polyamic acid intermediate, which is then dehydrated and ring-closed and imidized.

At this time, the primary diamine used is not particularly limited, but specific examples include p-phenylenediamine, m-phenylenediamine, diaminodiphenylmethane, diaminodiphenyl ether, 2.2-
Diaminodiphenylpropane, diaminodiphenyl sulfone, diaminobenzophenone, diaminonaphthalene,
1.4-bis(4-aminophenoxy)benzene, 1.
3-bis(4-aminophenoxy)benzene, 4.4°
-bis(4-aminophenoxy)diphenylsulfone,
2. Aromatic diamines such as 2'-bis[4(4-aminophenoxy)phenyl]propane, alicyclic diamines such as bis(4-aminocyclohexyl)methane, bis(4-niamino-3-methylcyclohexyl)methane, and Examples include aliphatic diamines such as tetramethylene diamine and hexamethylene diamine, and silicone diamines such as (wherein n represents an integer of 1 to 10).

Further, these diamines may be used alone or in combination of two or more.

The tetracarboxylic dianhydride used in the alignment treatment agent of the present invention is 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride (hereinafter referred to as T
(abbreviated as DA), but other tetracarboxylic dianhydrides may be used in combination as long as the purpose of the present invention is not impaired.

Specific examples include aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, and biphenyltetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, and cyclopropane tetracarboxylic dianhydride. Examples include alicyclic tetracarboxylic dianhydrides such as carboxylic dianhydride and cyclohexane tetracarboxylic dianhydride, and aliphatic tetracarboxylic dianhydrides such as butane tetracarboxylic dianhydride.

After reacting and polymerizing TDA and a primary diamine to form a polyamic acid intermediate, there is no need to particularly limit the method of dehydrating and ring-closing imidization of the intermediate.

At this time, the molar ratio of both TDA and primary diamine used is 0.
．． It is preferable that it is 8-1.2. As in normal polycondensation reactions, the closer the molar ratio of these two components is to 1, the higher the degree of polymerization of the produced polymer.

If the degree of polymerization is too low, the strength of the polyimide resin film will be insufficient when used as an alignment agent, and the alignment of liquid crystals will become unstable.

Furthermore, if the degree of polymerization is too large, workability during formation of the polyimide resin film may deteriorate.

Therefore, the degree of polymerization n of the product in this reaction is 4 to 1000.
It is preferable that

A general method of reacting and polymerizing TDA and a primary diamine to form a polyamic acid intermediate and then dehydrating and ring-closing imidization of the intermediate includes N-methylpyrrolidone, N,N
- React and polymerize in an organic polar solvent such as dimethylacetamide, N,N-dimethylformamide, or T-butyrolactone to obtain a polyamic acid intermediate solution, apply the polyamic acid intermediate solution as it is on a substrate, and heat it on the substrate. A polyimide film can be formed by imidization.

The reaction temperature for reacting and polymerizing TDA and primary diamine to form a polyamic acid intermediate can be any temperature in the range of -20 to 150°C, but is particularly preferably in the range of 5 to 100°C.

Also, the temperature for heating imidization on the substrate is 150 to 400.
Any temperature between 150 and 350 degrees Celsius can be adopted, especially between 150 and 350 degrees Celsius.
A range of is preferred.

If the imidization temperature is 150° C. or lower, the imidization rate will be 20% or lower, and the alignment of the liquid crystal will become unstable.

Moreover, if the temperature is 350° C. or higher, the coating film will be colored, which will cause display problems on the liquid crystal cell.

The polyimide resin of the present invention has the characteristic that it is soluble in a solvent. Therefore, the obtained polyamic acid intermediate can be directly imidized in the solution to form a polyimide solution, and the obtained polyimide can be isolated and It can also be dissolved in a solvent to form a polyimide solution.

A polyimide film can also be formed on the substrate by applying this solution onto the substrate and volatilizing the solvent.

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

The ring-closing temperature by this heating dehydration can be selected from any temperature from 100 to 350°C, preferably from 120 to 250°C.

Another method for converting the polyamic acid intermediate into a polyimide resin is chemical ring closure using a known dehydration ring closure catalyst.

In this way, a polyimide resin film with a thickness of 200 to 300 layers is formed on a transparent substrate such as glass or plastic film with a transparent electrode, and then the polyimide resin layer is rubbed to form an alignment treatment agent for liquid crystal cells. can do.

(E) Effects of the Invention The liquid crystal cell alignment treatment agent of the present invention can uniformly distribute liquid crystal molecules by forming a polyimide resin film on a transparent substrate such as glass or plastic film with a transparent electrode, and then performing a rubbing treatment. - and can be oriented in parallel, and furthermore, excellent voltage holding characteristics can be obtained when driving a liquid crystal cell.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto.

(f) Example The method for measuring voltage holding characteristics and imidization rate will be described below.

a) Method for measuring voltage holding characteristics of a liquid crystal cell A substrate with a transparent electrode on which a polyimide film was formed was rubbed with a cloth, and then assembled with a 7 μm spacer in between, with the rubbing directions perpendicular to each other, and a liquid crystal cell (Merck & Co.: ZLI-229) was assembled.
3) is implanted to produce a TN cell.

This cell is rotated in a crossed nicol, and the orientation of the cell is visually determined from the reversal of brightness and darkness.

Further, a pulse voltage of 9 volts/1 hertz and a pulse width of 5 milliseconds is applied to this cell, the voltage drop after 1 second is measured, and the voltage relaxation time is calculated from the following equation as the voltage holding characteristic.

'J = V, e x p (-t/τ) Vo: Initial applied voltage (9V) t: Time (1 second) v: Terminal voltage of sand diameter (V) τ: Voltage relaxation time (seconds) b) Measurement of imidization rate IR spectrum measurement (KBr method) of each sample was performed.
The imidization rate is calculated from the absorbance of the peak derived from the imide group at 85 cm-'.

Example 1 2.2-bis[4-(4-aminophenoxy)phenyl]propane 41.05 g (0.1 mol) and TDA
29.88g (0,0995 mol) of N-methyl-
A polyamic acid intermediate solution was prepared by reacting in 400 g of 2-pyrrolidone (hereinafter abbreviated as NMP) at room temperature for 10 hours.

Reduced viscosity η of the obtained polyamic acid intermediate.

/C was 1.14 dl/g (0.5% by weight NMP solution, 30°C).

After diluting this solution with NMP to a total solid content of 2%, it was coated on a glass substrate with a transparent electrode at 350 rpm.
A polyimide resin film was formed by heat treatment at 170° C. for 60 minutes. The imidization rate was 45% from the IR spectrum of the obtained polyimide resin.

Example 2 50 g of polyamic acid intermediate solution obtained in Example 1
and 10.8 g of acetic anhydride as an imidization catalyst.

5.0 g of pyridine was added and reacted at 50° C. for 3 hours to prepare a polyimide resin solution.

This solution was poured into 500 ml of methanol, and the resulting white precipitate was filtered and dried to obtain a white polyimide resin powder.

Reduced viscosity η5 of the obtained polyimide resin. /C is 1.0
4 dl/g (0.5% by weight NMP solution, 30°C).

Moreover, the imidization rate was 100% from this IR spectrum.

0.68 of this powder was dissolved in 29.4 g of T-butyrolactone, the total solid content was 2%, and 3.0 g of this powder was placed on a glass substrate with a transparent electrode.
It was spin coded at 50 rpm and heat treated at 170° C. for 60 minutes to form a polyimide resin film.

Example 3 Diaminophenylmethane 19.83 g (0.1 mol)
, and 29.88 g (0,0995 mol) of TDA were reacted in 280 g of NMP at room temperature for 10 hours to prepare a polyamic acid intermediate solution.

The reduced viscosity η sp/C of the obtained polyamic acid intermediate was 1.08 cIjl/g (0.5% by weight NMP solution, 30° C.).

This solution was diluted with NMP to a total solid content of 2%, spin-coded at 3500 rpm onto a glass substrate with a transparent electrode, and heat-treated at 170° C. for 60 minutes to form a polyimide resin film.

The imidization rate was 40% from the IR spectrum of the obtained polyimide resin.

Comparative Example 1 41.05 g (0.1 mol) of 2.2-bis[4-(4-aminophenoxy)phenyl]propane and 21.95 g (0,099 mol) of pyromellitic dianhydride were mixed with 350 g of NMP. The mixture was reacted at room temperature for 5 hours to prepare a polyamic acid intermediate.

The reduced viscosity ηsp/C of the obtained polyamic acid intermediate was 1.10 dll/g (0.5 wt% NMP solution, 3
0°C).

After diluting this solution with NMP to a total solid content of 2%, spin code was applied to a glass substrate with a transparent electrode at 350 rpm.
A polyimide resin film was formed by heat treatment at 170° C. for 60 minutes.

The imidization rate was 35% from the IR spectrum of the obtained polyimide resin.

Comparative Example 2 The polyamic acid intermediate solution obtained in Example 1 was treated with NMP.
After diluting the total solid content to 2% by
C. for 60 minutes to form a polyimide resin film.

The imidization rate was 10% from the IR spectrum of the obtained polyimide resin.

Table 1 shows the liquid crystal cell characteristics of Examples 1 to 3 and Comparative Examples 1 to 2.

From Table 1, it can be seen that the alignment agent of the present invention has excellent voltage holding characteristics.

Table-1 Liquid crystal cell characteristics Orientation Voltage relaxation time τ (seconds)

Claims (2)

[Claims] (1) General formula [I] ▲There are mathematical formulas, chemical formulas, tables, etc.▼[I] (In the formula, R represents a divalent organic group, and n represents an integer from 4 to 1000.) Represented by An alignment treatment agent for liquid crystal cells made of polyimide resin having repeating units. (2) A polyimide resin having a repeating unit represented by the general formula [I] is 3,4-dicarboxy-1,2,3
, 4-tetrahydro-1-naphthalenesuccinic anhydride and primary diamine are reacted and polymerized to form a polyamic acid intermediate, which is then dehydrated and ring-closed to imidize it, and the imidization rate is 20% or more. An alignment treatment agent for liquid crystal cells characterized by the following.