JPS62159117A - Liquid crystal display element with plastic substrate - Google Patents

Abstract

PURPOSE:To prevent an interference color due to the birefringence of substrates from appearing and to obtain a liquid crystal display element of high quality which has no coloring by specifying the optical main-axis direction of the substrates, the orientation direction of liquid crystal, and the directions of transmission axes of polarizing plates. CONSTITUTION:The degree of surface orientation films is >=-0.01 and the angle of the transmission axis of the polarizing plate 17 on the side of the 1st substrate 11 to the orientation processing direction of the surface of the 1st substrate is <=0+ or -5 deg. or <=90+ or -5 deg.. Further, the angle of the transmission axis of the polarizing plate 27 on the side of the 2nd substrate 21 to the orientation processing direction of the surface of the 2nd substrate is <=0+ or -20 deg. or <=90+ or -20 deg.. The angle between the optical main-axis direction in which the refractive index of the 1st substrate is largest and the orientation processing direction is <=0+ or -20 deg. or <=90+ or -20 deg.. The angle between the optical main-axis direction in which the refractive index of the 1st substrate is largest and the orientation processing direction is <=0+ or -2.5 deg. or <=90+ or -2.5 deg. and the angle between the optical main-axis direction in which the refractive index of the 2nd substrate is largest and the orientation processing direction is <=0+ or -2.5 deg. or <=90+ or -2.5 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device using a plastic film as a substrate.

Traditionally, glass substrates have been mainly used as substrates for liquid crystal display elements, but in recent years, liquid crystal display elements using plastic films have been developed from the viewpoints of weight reduction, larger size, improved strength, and curved display. is attracting attention.

As plastic film substrates, plastic films with low optical anisotropy obtained from low crystallinity polymers such as polyether sulfone, polycarbonate, polysulfone, polyether ketone, cellulose acetate, and epoxy-modified polyester are known. However, such plastic films have poor dimensional stability, making it difficult to create high-precision cells.

Due to poor solvent resistance and liquid crystal resistance, it is necessary to overcoat the side or both surfaces in contact with the liquid crystal, which increases the number of steps and increases costs. Furthermore, plastic films such as polyether sulfone have poor surface properties as substrates for liquid crystal display element layers, making it difficult to accurately control the gap.

By using a uniaxially stretched plastic film such as polyester, dimensional stability and chemical resistance can be improved, and gap control becomes easier, but there is a problem that interference colors occur and display quality deteriorates. be. Planar orientation degree is -0.03 as a method to prevent interference color.
It has been proposed to use the above uniaxially stretched polyester film (Japanese Unexamined Patent Publication No. 59-95513).

This is not always sufficient, and interference colors may occur depending on the method of arranging the polarizing plates, for example.

An object of the present invention is to improve display quality by preventing coloring in a liquid crystal display element in which a liquid crystal cell using a plastic film substrate is sandwiched between polarizing plates.

A liquid crystal display device using the plastic film of the present invention has a liquid crystal sealed between a first substrate and a second substrate made of a uniaxially stretched translucent plastic film. The film is a plastic film in which a liquid crystal cell is sandwiched between a pair of polarizing plates, and the liquid crystal molecules are aligned approximately horizontally, and the direction of the liquid crystal molecules is rotated approximately 90 degrees between the two plates. In substrate liquid crystal display elements.

The degree of plane orientation of the film is -0.01 or more, and the first
The angle that the transmission axis of the polarizing plate on the substrate side makes with the orientation treatment direction of the first substrate surface is within 0 degrees ± 5 degrees or 90 degrees ±
Within 5 degrees, and the angle that the transmission axis of the polarizing plate on the second substrate side makes with the alignment processing direction on the surface of the second substrate is 0 degrees ± 20 degrees.
degree or within 90 degrees ± 20 degrees, and the first
The angle between the optical principal axis direction with the highest refractive index of the substrate and the orientation processing direction is within 0 degrees ± 2.5 degrees or 90 degrees ±
2.5 degrees or less, and the direction of the optical principal axis having the largest refractive index of the second substrate and the orientation processing direction are within 0 degrees ± 2.5 degrees or within 90 degrees ± 2.5 degrees. Features.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 3 is a sectional view showing an example of the configuration of a liquid crystal display device of the present invention. A first substrate 11 having a transparent electrode 13 on which an alignment film 15 is formed and subjected to an alignment treatment, and a similar second substrate 21 are placed apart and facing each other, and a liquid crystal is sealed between them. (twisted nematic) type liquid crystal cell 31
is configured. 23 is a transparent electrode, and 25 is an alignment film. As the first and second substrates, a uniaxially stretched translucent plastic film such as a uniaxially stretched polyester film is used. The first substrate 11 and the second substrate 21 are subjected to alignment treatment so that liquid crystal molecules are aligned in a substantially horizontal direction. The alignment treatment is performed by an appropriate method such as rubbing the alignment film, and the liquid crystal molecules are aligned along the direction of the alignment treatment. Further, the first substrate 11 and the second substrate 21 are arranged so that the directions of the alignment process are substantially perpendicular to each other so that the direction of the liquid crystal molecules is rotated by about 90 degrees between the two substrates. 33 represents a sealant. liquid crystal cell 31
is sandwiched between the first polarizing plate 17 and the second polarizing plate 27 to form a TN type liquid crystal display element.

By controlling the degree of plane orientation of the plastic film of such a liquid crystal display element, the arrangement method of the polarizing plate, and the orientation treatment direction, interference caused by the use of a birefringent substrate in a TN type liquid crystal display device when no voltage is applied can be reduced. It is possible to prevent coloring caused by That is, coloring can be prevented by satisfying the following conditions (1) to (2).

■ The degree of plane orientation of the plastic film substrate is -0.01
Must be above. The degree of plane orientation is defined by the following formula, and if this value is too small, coloring will occur.

The larger they get, the harder it becomes to color them. If it exceeds 0.05, the mechanical strength of the film will decrease.

n + n plane orientation degree = 2 - n2 nX: refractive index in the direction of the largest refractive index of the film substrate ny: refractive index of the direction perpendicular to the direction of the largest refractive index of the film substrate within the film plane n2: film substrate The refractive index in the thickness direction ■ The transmission axis (direction of the electric field vector of transmitted light) of the polarizing plate on the first substrate 11 side (the first polarizing plate 17) is the orientation processing direction of the surface of the first substrate 11 The angle α1 with respect to These figures show the case where the transmission axes P and P2 of the pair of polarizing plates 17 and 27 are orthogonal to each other, but of course it is also possible to arrange the transmission axes so that they are substantially parallel. In Figure 1, α is O″±5＠
In the case where the first polarizing plate 17 is rotated by 90'' in FIG. 1, it is necessary to satisfy 90''±5''.

■ The angle α2 formed by the transmission axis P2 of the polarizing plate (second polarizing plate 27) on the second substrate 2 side with respect to the alignment treatment direction on the surface of the second substrate 21 is within 90''±20'' or O#±2
Must be within 0".

Note that the first substrate 11 and the second substrate 2I are the same.

Either direction may be in the viewing direction.

■ The liquid crystal molecules are aligned approximately horizontally on the surface of both plates.

(2) The angle β1 between the optical principal axis direction [and 100, which has the highest refractive index on the first substrate side] is within 0°±2°56 or within 90″±2.5°.

■ The angle β2 between the optical principal axis direction B, which has the largest refractive index on the second substrate side, and the direction B.

Within 0''±2.5° or within 90''±2.5'.

■ The angle ν between Dl and D2 is approximately 906.

By satisfying all of the above, coloring due to interference can be prevented, and even if one condition is missing, coloring will occur.

Further, when α2 is set to 5 degrees or more, the viewing angle range is widened and is effective in static drive and low multiplex drive up to about 1/33 duty.

Setting α2 to 15 degrees or less improves the steepness of the threshold characteristic, and is effective in improving contrast in high multiplex driving of 1/32 duty or more.

In this way, a high-quality display can be realized by controlling α2 according to the required display quality.

Furthermore, it is preferable that the optical principal axis directions X and X2 of both substrates are substantially parallel. If they are not substantially parallel, the cells will be deformed by the heat during cell processing due to the anisotropy of the thermal elongation rate, making it difficult to maintain an accurate cell gap.

According to the present invention, in a liquid crystal display device using a uniaxially stretched plastic film as a substrate, it is possible to specify the optical principal axis direction of the substrate, the orientation direction of liquid crystal molecules, and the transmission axis direction of a polarizing plate. As a result, interference colors due to birefringence of the substrate can be prevented, and a high-quality liquid crystal display element without coloring can be realized.

EXAMPLE A cell was formed using uniaxially stretched polyester films of 100 μm thickness as the upper and lower substrates, and polyamide coatings subjected to rubbing treatment as an alignment treatment to form a liquid crystal cell. The liquid crystal is RO-TN- manufactured by Hoffmann U. Roche.
Use 619.

The liquid crystal layer thickness was 8.5 μm. Table 1 shows the results of evaluating the characteristics of this liquid crystal cell sandwiched between two polarizing plates.

(Margin below)

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the structure of a liquid crystal display element according to the present invention. FIG. 2 is an exploded perspective view showing the relationship between the substrate and the polarizing plate. FIG. 3 is a diagram showing the angular relationship of each axis 611...
First substrate 17...First polarizing plate 21...Second substrate 27...Second polarizing plate Patent applicant Ricoh Co., Ltd.

Claims (1)

[Claims] 1. A liquid crystal is sealed between a first substrate and a second substrate made of a uniaxially stretched translucent plastic film,
The film is a plastic film in which a liquid crystal cell is sandwiched between a pair of polarizing plates, and the liquid crystal molecules are aligned approximately horizontally, and the direction of the liquid crystal molecules is rotated approximately 90 degrees between the two substrates. In the substrate liquid crystal display element, the degree of plane orientation of the film is -0.01 or more, and the angle between the transmission axis of the polarizing plate on the first substrate side and the orientation treatment direction of the first substrate surface is 0 degrees. The transmission axis of the polarizing plate on the second substrate side should be within ±5 degrees or within 90 degrees ±5 degrees, and the angle that the transmission axis of the polarizing plate on the second substrate side makes with respect to the alignment processing direction on the surface of the second substrate should be within 0 degrees ±20 degrees or 90 degrees ± within 20 degrees, and the angle between the optical principal axis direction with the highest refractive index of the first substrate and the orientation treatment direction is within 0 degrees ± 2.5 degrees or within 90 degrees ± 2.5 degrees, and , the direction of the optical principal axis with the largest refractive index of the second substrate and the orientation treatment direction are within 0 degrees ± 2.5 degrees or 9 degrees.
A plastic film substrate liquid crystal display element characterized in that the angle is within 0 degrees ±2.5 degrees.