JPH0361168B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" This invention relates to an alignment film for a liquid crystal display device. "Conventional Example" and "Problems to be Solved by the Present Invention" It is well known that polyimide resin, which has excellent durability, is used as an alignment film for liquid crystal display devices. However, polyimide films have a high volume resistivity and a low dielectric constant, so if the film is thick enough to be durable (300 Å or more), the impedance will be high, resulting in a large voltage drop and the need for a high driving voltage. be. Furthermore, the change in impedance with respect to frequency is large, which causes deterioration of drive frequency characteristics. "Means for Solving the Problems" This invention was proposed in view of the above circumstances, and its purpose is to obtain an alignment film with a small amount of voltage drop and good frequency characteristics. . In order to achieve the above object, the present invention uses an alignment film made of a polyimide resin precursor (prepolymer).
NMP (N-methyl-pyrrolone) solution, or
A mixed solution in which a predetermined amount of a polymer with a higher dielectric constant than a polyimide resin or a polymer with a lower volume resistivity is added to a DMF (di-methyl-formamide) solution.
It is formed from an imidized thin film of. In order to obtain an alignment film, the above-mentioned mixed solution is applied onto a glass substrate, and then imidization treatment and alignment treatment are performed, which is no different from the conventional technique. The amount of the above added polymer is the amount of the polyimide resin precursor.
Approximately 10 to 50% by weight is appropriate. Also, the film thickness is 300
Approximately Å to 1500 Å is suitable. “Example” First, a precursor (prepolymer) of polyimide resin was prepared.
Phenol resin, melamine resin, methacrylic resin, polyamide resin, polychloroprene, epoxy resin, polyester resin, polybutadiene resin, polyethylene terephthalate in NMP (N-methyl-pyrrolone) solution or DMF (di-methyl-formamide) solution at 15% by weight. Any one of the resins
A mixture is obtained by adding 15% by weight of 1 and stirring thoroughly. If the polymer added as described above is not dissolved in NMP or DMF, a liquid mixture is obtained in which the polymer is uniformly and finely dispersed and mixed in the solution. The mixture thus obtained was placed on a glass substrate on which transparent electrodes had already been formed using a spinner for 300 min.
Form a film with a thickness of Å to 1500 Å and further heat treatment at 200 °C for 60 min.
The film is subjected to imidization treatment by partial baking, and orientation treatment is performed on the surface of this film by a rubbing method. Using the alignment film thus formed on the glass substrate, a normal liquid crystal display panel as shown in FIG. 1 is prepared, and its frequency characteristics and voltage drop are measured. That is, in FIG. 1, an alignment film is formed on the glass substrate 1 on which the transparent electrode 3 is formed by the method described above, and two glass substrates 1 are placed so that the alignment films 4 face each other. They are made to face each other with a gap of about 10 μm maintained by a spacer 2, and the liquid crystal material is filled in the gap. Also, front and back polarizing plates 6a6b
constitute a so-called TN-FEM type liquid crystal display device, which is arranged so that their polarization axes are perpendicular to each other.
Using an alignment film added with each of the above-mentioned additive polymers,
The results of measuring the voltage drop and frequency characteristics of the liquid crystal panel shown in FIG. 1 above are shown in rows and rows of Table 1. Furthermore, as is not clear from the model shown in Fig. 2, the amount of voltage drop is the voltage V applied between the two electrodes 3,
The value obtained by subtracting the voltage drop V _LC of the liquid crystal itself from 2Vpi is 2Vpi = (V - V _LC ). In addition, the frequency characteristics are based on the case of using a single polyimide film (1000 Å) shown in Figure 3 (1st
As shown in the bottom column of the table, mark △ if it is better than that, mark ○, and mark △ if it is the same.
It was shown in In addition, a sandwich cell was separately prepared in which the above alignment film of 1000 Å was sandwiched between 1 cm ² electrodes, and the impedance at a frequency of 100 Hz was measured. The results are shown in the first row of the table. The volume resistivity and dielectric constant of the additive polymer such as phenolic resin are shown in the rows and rows of Table 1, and the above-mentioned properties of the polyimide resin alone are shown in the bottom column of Table 1. As is clear from Table 1, among the alignment films to which one of the aforementioned nine types of polymers was added, the alignment films to which six types of polymers other than epoxy resin, polybutadiene resin, and polyethylene terephthalate resin were added, A voltage drop that is two orders of magnitude smaller than that of an alignment film made of polyimide alone is obtained, and the frequency characteristics are also excellent. It can also be seen that the alignment film to which the above six types of polymers are added naturally has excellent impedance characteristics. Although Table 1 shows only the case where the film thickness is 1000 Å, similar results are obtained for any film thickness from 300 Å to 1500 Å.

【table】

[Table] "Effects of the Invention" As explained above, this invention has a lower volume resistivity than polyimide resin as an alignment film material.
Or, since it contains a polymer with a low dielectric constant, it has excellent impedance characteristics and a small voltage drop.
Moreover, as a result of being able to obtain an alignment film with excellent frequency characteristics, it is possible to obtain a liquid crystal panel that requires only a low applied voltage.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing an example of a liquid crystal panel;
The figure is a schematic diagram showing a model of voltage drop in a liquid crystal panel, and FIG. 3 is a graph showing impedance characteristics of an alignment film.

Claims (1)

[Claims] 1. A predetermined amount of NMP as a precursor of polyimide resin.
(N-methyl-pyrrolone) solution or DMF (di-methyl-formamide) solution mixed with a predetermined amount of a polymer that has a lower volume resistivity than polyimide resin or a higher dielectric constant than polyimide resin. An alignment film for a liquid crystal display device, characterized in that: 2. The alignment film for a liquid crystal display device according to claim 1, wherein the amount of the polymer mixed with the polyimide resin precursor is 10 to 50% by weight.