JPH048772B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field> The present invention relates to improvement of an alignment film for a liquid crystal display element, and particularly to an alignment film suitable for aligning liquid crystal molecules in a horizontal direction with respect to a substrate. <Prior Art> Conventionally, a polyimide film is used as a material for an alignment film that aligns liquid crystal molecules in a horizontal direction with respect to a substrate. An example of this polyimide film is the tetracarboxylic acid with the structural formula in Table 1 below.

【table】 Diamines with the structural formula in Table 2 below

【table】

Examples include polyimide films obtained by applying a prepolymer obtained by synthesizing [Table] onto an electrode substrate and then baking it. It has been confirmed that such a polyimide film has excellent optical properties and reliability (heat resistance). However, the above-mentioned polyimide film does not have a steep threshold characteristic and has poor dynamic driving characteristics such as line sequential driving, and therefore has the disadvantage that sufficient contrast cannot be obtained at a high duty ratio. <Purpose> The present invention has been made to solve the above-mentioned conventional problems, and by improving the alignment film, it is particularly excellent in dynamic drive characteristics and has sufficient contrast even at high duty ratios. The purpose is to obtain a novel liquid crystal display element. <Example> Hereinafter, one example of the liquid crystal display element according to the present invention will be described in detail using the drawings. First, an example of the alignment film of an embodiment of the liquid crystal display element according to the present invention will be described.
BTDA is a diamine with the structural formula shown in Table 3 below.

[Table] NMP (N-
An example of this is a polyimide film obtained by an imidization reaction by coating a glass substrate surface previously covered with a transparent electrode pattern with a methylpyrrolidone solution and baking it at 300° C. for 60 minutes. In order to conduct a characteristic test on the polyimide film according to the present invention, the film thickness of the polyimide film was
The electrode substrate coated with the polyimide film was subjected to a rubbing treatment, and two electrode substrates subjected to such treatment were prepared and bonded together with an epoxy resin while maintaining an appropriate cell gap. In this state, an ECH-based and PCH-based blended liquid crystal was injected into the gap between the electrode substrates using a vacuum impregnation method to construct an element. FIG. 1 is a side sectional view of one embodiment of a liquid crystal display element according to the present invention obtained in this manner. In the figure, 1 and 1' are glass substrates, 2,
2' is a base film, 3 and 3' are transparent electrodes, 4 and 4' are polyimide films that have been rubbed in directions perpendicular to each other, and 5 is a sealing material made of epoxy resin.
6 is a liquid crystal, and 7 and 7' are polarizing plates. The electro-optical characteristics of a field-effect liquid crystal display device using a twisted nematic liquid crystal having the above structure were measured and evaluated. The γ value was used as the evaluation parameter. Here γ
The value is 90% at a viewing angle of θ = 40°, where θ is the viewing angle with respect to the liquid crystal display element 8 as shown in Figure 2.
It is defined as Vsat/Vth, where Vth is the applied voltage that gives 20% transmission at a viewing angle of θ=0°, and Vsat is the applied voltage that gives 20% transmission (see the graph in Figure 3). Further, the above applied voltage is a 100 Hz rectangular wave. The smaller the γ value, the better the dynamic drive characteristics, and a difference of about 0.1 in the γ value will result in a large difference in contrast. The following Table 4 shows the γ values when using the polyimide film according to the present invention described above.

[Table] Table 5 also shows the conventional polyimide film (4
The γ value is shown when using the following species.

[Table] Comparing Tables 4 and 5, it can be seen that the γ value of the liquid crystal display element using the polyimide film according to the present invention is smaller and improved compared to the liquid crystal display element using the conventional polyimide film. I understand that. <Effects> According to the present invention described above, it is possible to obtain a liquid crystal display element with improved electro-optical characteristics and a high contrast ratio even through dynamic driving with a high duty ratio. Therefore, it is possible to improve the appearance of liquid crystal display devices containing a large amount of information, such as graphic displays and television displays. Of course, since the reliability as polyimide is maintained, it is possible to obtain a liquid crystal display element with high reliability, wide viewing angle characteristics, and less visible electrode patterns.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an embodiment of a liquid crystal display element according to the present invention, FIG. 2 is a side view showing the viewing angle for the liquid crystal display element, and FIG. 3 is a diagram showing changes in transmittance when the applied voltage is changed. It is a graph diagram. In the figure, 1, 1': glass substrate, 2, 2': base film, 3, 3': transparent electrode, 4, 4': polyimide film, 5: sealant, 6: liquid crystal, 7, 7': polarized light Board.

Claims (1)

[Scope of Claims] 1. An alignment film that is coated on an electrode substrate that supplies a driving voltage to the liquid crystal and provides alignment in a predetermined direction to the liquid crystal. 1. A line-sequential drive type liquid crystal display element comprising a polyimide resin which is a polymer of a polycarboxylic acid represented by the following structural formula and a diamine represented by the following structural formula () or ().