JP2548730B2 - Liquid crystal display element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an improvement in a parallel alignment type liquid crystal display element, and more specifically, it has excellent heat resistance and moisture resistance and good adhesion to a substrate. In addition, the present invention relates to a liquid crystal alignment element having a large pretilt angle (angle formed by liquid crystal molecules and a substrate).

[Conventional technology]

Conventionally, as a display for portable computers, word processors, etc., a twisted nematic liquid crystal display element (hereinafter TN) in which liquid crystal molecules are twisted by 90 degrees when no voltage is applied
Liquid crystal display elements) have been used.

Although TN liquid crystal display elements have been researched in various ways, they have limitations in display capacity and display quality.

Therefore, it is desired to develop a liquid crystal display device with further improved display capacity and display quality, and a Sparts nematic liquid crystal display device (hereinafter referred to as STN liquid crystal display device) with a larger twist angle of liquid crystal molecules has been developed. There is.
In this STN liquid crystal display element, it is particularly important to orient the liquid crystal molecules uniformly and to have a constant pretilt angle (the angle at which the liquid crystal molecules rise from the substrate surface due to the orientation). Is necessary to improve the display capacity and display quality.

Generally, a film formed by using an organic polymer such as polyimide and oriented by rubbing in one direction can obtain a pretilt angle of only 0.5 to 3 °. To obtain a pretilt angle higher than this, oxidation is required. A method of providing a pretilt angle by oblique vapor deposition of silicon or the like is known.
According to the oblique deposition of silicon oxide, the pretilt angle is 0-40.
An orientation having an arbitrary pretilt angle can be formed in the range of °. However, it is difficult to make a large-scale element by the method of obliquely vapor-depositing silicon oxide, etc., and since it is obliquely vapor-deposited, it is physically formed on a part (around the circuit end portion, etc.) to be vapor-deposited on a circuit board on which electrodes are formed. It has an important drawback that it cannot be vapor-deposited and the image is lacking in sharpness.Because of the vapor-deposition method, continuous steps cannot be taken, and there is no choice but to make it a batch type, and it becomes a complicated step and a certain degree. It is difficult to produce a large quantity of quality products, and an expensive vapor deposition device or the like must be used, resulting in a high cost.

Various methods have also been investigated such as adding a surface treatment agent to an organic polymer to form a film and increasing the pretilt angle by rubbing, but these methods have low heat resistance of the film. However, there is a drawback that the film deteriorates due to heat during the assembly of the device and the orientation decreases. There is also a method of using polyimide, which has excellent heat resistance among organic polymers, but it is difficult to further increase the pretilt angle with conventional polyimide, and if the twist angle is increased like STN liquid crystal display element, it is equivalent to inside the liquid crystal. And the display is defective. Further, since these polyimides have a high water absorption rate of 2 to 5%, water easily penetrates into the interface between the alignment film surface and the substrate, and the adhesion between the alignment layer and the substrate decreases, resulting in poor moisture resistance. There was a problem with.

[Object of the Invention]

As a result of earnest studies for solving the above-mentioned drawbacks, the present inventors have obtained an alignment film having a large pretilt angle and excellent heat resistance and moisture resistance, improving display capacity and display quality, and having long life and high performance. The present invention provides a liquid crystal display device.

[Structure of Invention]

Of the organic tetracarboxylic dianhydride component and the silicon-based diamine represented by the general formula (1), the number of siloxane bonds (m) is in the range of 1 to 10 in all diamine components.
A diamine component containing 0.05 to 10 mol% in the range of 05 to 10 mol% and 11 to 150 is reacted at a temperature of 0 to 200 ° C., and coated on a transparent substrate made of glass or plastic and heat treated to form a film. The liquid crystal display device is characterized in that it is a liquid crystal alignment film formed by subjecting the film to an alignment treatment, and has a pretilt angle of 5 to 20 °.

R ₁ : Methylene group, phenylene group or substituted phenylene group R ₂ : Methyl group, phenylene group or substituted phenylene group n: _1, when R ₁ is phenylene group or substituted phenylene group
In the case of a methylene group, 3 or 4. As the diamine component used in the present invention, in addition to the above-mentioned silicon-based diamine, the following aromatic diamine can of course be used together in order to impart various characteristics.

For example, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminenodiphenylpropane and the like.

The organic tetracarboxylic dianhydride component used in the present invention may be one kind or a mixture of two or more kinds, but as the tetracarboxylic dianhydride used, pyromellitic dianhydride, 3,3 ′, 4 Examples include 4,4'-benzophenone tetracarboxylic acid dianhydride and 2,3,6,7-naphthalene tetracarboxylic acid dianhydride.

Number of siloxane bonds among silicon-based diamines (m)
Is in the range of 1 to 10 has the effect of improving the adhesion of the substrate, and the amount used is preferably 0.05 to 10 mol%. 0.
If it is less than 05 mol%, the adhesion will not be improved, and if it is more than 10 mol%, the flexibility of the polyimide film will be lost. Further, those having a number (m) of siloxane bonds in the range of 11 to 150 have the effects of increasing the pretilt angle and decreasing the water absorption rate, and the amount used is preferably 0.05 to 10 mol%. If it is 0.05 mol% or less, the pretilt angle is as small as 5 ° or less and the water absorption rate is large, and if it is 10 mol% or more, the pretilt angle becomes large, but the performance as a film deteriorates and the heat resistance particularly lowers. Therefore, the pretilt angle can be adjusted to 5 to 20 ° by adding 0.05 to 10 mol% of siloxane bonds having a number (m) of 11 to 150.

The application of the polyamic acid to the substrate, N, N- dimethylformamide, N, N- dimethylacetamide, 0.01-40 wt% solution of N-methyl-2-pyrrolidone, etc., the polyamic acid as a spinner, wheeler, It is applied by using a roll coater or the like. After application 100 ℃ ~ 400
Heat treatment is performed at ℃ to form a polyimide-based polymer film. The coating film thus formed is rubbed in a certain direction by rubbing it with a cloth or the like to form a liquid crystal alignment film of extremely good quality, which has a high display capacity and high display quality and a long-life liquid crystal display. An element can be obtained.

〔The invention's effect〕

According to the present invention, the plane tilt angle is 5 to 20 °,
Furthermore, a liquid crystal display element having excellent heat resistance and moisture resistance can be easily obtained. In addition, since the liquid crystal has excellent uniformity of alignment and can generate a large pretilt angle in the liquid crystal,
High-performance liquid crystal display devices such as STN type liquid crystal display devices with improved display quality can be easily obtained.

〔Example〕

Example 1 In a four-neck separable flask equipped with a thermometer, a stirrer, a raw material charging port and a dry nitrogen gas inlet port, 4,4′-diaminediphenyl ether (19.02 g, 95 mol%), 1.24 g (0.5 mol%), An amount of 17.46 g (4.5 mol%) was taken, and anhydrous N-methyl-2-pyrrolidone was added and dissolved in such an amount that the solid content ratio of all the charged materials was 15% by weight. Next, the flask was immersed in a water bath at 0 to 50 ° C., and 21.81 g (0.1 mol, 100 mol%) of purified pyromellitic dianhydride was added while suppressing heat generation. After the tetracarboxylic dianhydride was dissolved, the temperature of the system was kept at 20 ° C. and the reaction was continued for 10 hours. The dry nitrogen gas was allowed to flow in all steps from the reaction preparation stage to the product removal. The obtained product was a pale yellow viscous solution.

The above varnish was applied to a glass substrate on which an electrode of indium oxide was formed by using a spinner. 1 at 250 ℃ after coating
After heating and ring closure for a period of time, a polyimide-based polymer film was formed to a thickness of 800Å. This coating film had excellent adhesion to the substrate, and the result of the substrate eye test (JIS-D-0202) was 0/100 (number of peelings / total number). After that, the film was rubbed in a certain direction with gauze to prepare a liquid crystal display device using a pair of substrates, and the alignment was good. Even if the liquid crystal display device was subjected to a humidity resistance test (80 ° C., 90% RH) for 1000 hours, the alignment characteristics did not deteriorate. The pretilt angle measured by the zero magnetic field capacitance method was 10 to 11 °.

[Examples 2 and 3 and Comparative Examples 1 and 2] The reaction composition of the acid anhydride diamine was set as shown in Table 1, and the reaction was carried out by the same apparatus and operation as in Example 1. Further, using these varnishes, a liquid crystal display device was produced in the same manner as in Example 1, and various characteristics were obtained. The results are shown in Table 1. As is clear from the results shown in Table 1, the liquid crystal display device obtained according to the present invention has excellent adhesiveness between the polyimide-based polymer film and the substrate and also has a low water absorption rate, and thus has excellent moisture resistance. Moreover, since the pretilt angle is large, a high-performance STN type liquid crystal display device without alignment defects was obtained. In Comparative Example 1, the adhesion between the polyimide-based polymer film and the substrate was poor, and the water absorption rate was large, so that a defect occurred in the moisture resistance test for 200 hours. Since Comparative Example 2 has a small pretilt angle, when applied to an STN type display element, an alignment defect was generated.

Claims (1)

(57) [Claims] 1. An organic tetracarboxylic dianhydride component and a silicon-based diamine represented by the following general formula (1):
A polyimide resin comprising a diamine component containing 0.05 to 10 mol% of siloxane bonds (m) in the range of 1 to 10 and 0.05 to 10 mol% of total diamine components in the range of 11 to 150. A liquid crystal display device, which is a liquid crystal alignment film obtained by applying a heat treatment to a transparent substrate from glass or plastic to form a film, and subjecting the film to an alignment treatment, and having a pretilt angle of 5 to 20 °. R ₁ : Methylene group, phenylene group or substituted phenylene group R ₂ : Methyl group, phenylene group or substituted phenylene group n: _1, when R ₁ is phenylene group or substituted phenylene group
3 or 4 for methylene group