JPH0593907A - Liquid crystal display element - Google Patents

Abstract

(57) [Abstract] [Purpose] Considering the optical anisotropy of the plastic film, the viewing angle in the lateral viewing angle direction can be determined by optimal placement with the polarizing plate.
An object of the present invention is to provide a liquid crystal display device having improved brightness. [Structure] Plastic film substrates 1 arranged to face each other
For this, uniaxially stretched polyethylene terephthalate (1-PET) having a thickness of about 100 μm is used. An electrode 2 and an orientation control film 3 are adhered and formed on the inner surface of the plastic film substrate 1, and a peripheral portion of the plastic film substrate 1 is sealed with a sealing material 4, and a liquid crystal 5 is sealed therein. The liquid crystal 5 is a nematic liquid crystal to which chiral is added, the thickness of the liquid crystal layer is 8,25 μm, and the twist angle is 200 °.
I am trying. In addition, polarizing plates 6 are formed on the outer surfaces of the upper and lower substrates 1, respectively.
Affix. The relationship between the stretching direction (TD) of the substrate 1 and the rubbing direction of the alignment control film 3 attached to the substrate 1 is approximately 45 ° for both the upper and lower substrates 1.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a super twisted nematic (ST) using a plastic film as a substrate.
The present invention relates to an N) type liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, Twisted Nematic (TN)
When a plastic film is used as a substrate for a liquid crystal display element of a type, since the plastic film itself has optical anisotropy, the birefringence of the plastic film causes color unevenness in the display, resulting in deterioration of display quality. May be invited. Therefore, according to JP-A-56-97318 and the like, the above-mentioned problems are solved by making the extending axis direction of the plastic film, the rubbing direction of the alignment control film and the polarizing axis direction of the polarizing plate parallel or perpendicular. is doing.

This TN display mode has drawbacks in that when it is driven in a high time division manner in order to increase the display capacity, the contrast is lowered and the viewing angle is narrowed. Therefore, a Super Twisted Nematic (STN) type liquid crystal display device in which the twist angle of liquid crystal molecules is further increased has been proposed. The liquid crystal display element performs display by utilizing the birefringence of the liquid crystal layer, and as shown in FIG.
When the directions C and D of the polarization axes of the polarizing plates are set to about 45 ° with respect to the rubbing directions E and F of the substrate and the twist angle of the liquid crystal from the lower substrate to the upper substrate is ω, the upper and lower polarizing plates are opened. The angle Δβ is optimally set to Δβ = ω−180 °.

[0004]

However, the above-mentioned S
Although it is preferable to use a glass substrate as a substrate for a TN type liquid crystal display element, if a plastic film having optical anisotropy is used as the substrate, the viewing angle becomes narrow or the brightness is reduced due to the birefringence effect of the plastic film. Therefore, it is necessary to optimize the absorption axis (or polarization axis) of the polarizing plate with respect to the axial direction in which the in-plane refractive index of the plastic film is maximum.

An object of the present invention is to provide a liquid crystal display device in which the viewing angle and the brightness in the lateral viewing angle direction are improved by optimally arranging it with a polarizing plate in consideration of the optical anisotropy of a plastic film.

[0006]

DISCLOSURE OF THE INVENTION The present invention comprises two plastic films having an electrode and an orientation control film on the inner surface,
A super twisted nematic (STN) type liquid crystal display device comprising a liquid crystal sandwiched between the plastic films and having a twist angle of 160 ° or more, and a polarizing plate disposed outside the plastic films, wherein the plastic film is used. The absorption axis direction of the polarizing plate is substantially parallel to the axial direction having a large in-plane refractive index.

The liquid crystal display element according to the present invention is characterized in that uniaxially stretched polyethylene terephthalate is used as the plastic film.

[0008]

With the above structure, since the axial direction of the plastic film substrate having a large refractive index and the absorption axial direction of the polarizing plate are substantially parallel to each other, the birefringence effect does not occur in the light passing therethrough. The viewing angle in the direction becomes wider and the brightness of the display surface also increases.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a liquid crystal display device which is an embodiment of the present invention. Uniaxially stretched polyethylene terephthalate (1-PET) having a thickness of about 100 μm is used for the plastic film substrates 1 arranged to face each other, and the refractive index in the stretching direction (TD) of the film substrate 1 is 1.708. The refractive index in the direction perpendicular to this is 1.
Since it is 601, the in-plane birefringence anisotropy is 0.10.
7 (= 1.708-1.601). Further, an electrode 2 and an orientation control film 3 are adhered and formed on the inner surface of the plastic film substrate 1, and a peripheral portion of the plastic film substrate 1 is sealed with a sealing material 4, and a liquid crystal 5 is sealed therein. The liquid crystal 5 is a nematic liquid crystal added with chiral, its retardation is 0.9, the thickness of the liquid crystal layer is 8,25 μm, and the twist angle is 200 °. Polarizing plates 6 are attached to the outer surfaces of the upper and lower plastic film substrates 1, respectively.

As shown in FIG. 2, the relationship between the stretching direction (TD) of the plastic film substrate 1 and the rubbing direction of the orientation control film 3 attached to the substrate 1 is as shown in FIG. A, B and rubbing direction A'of the upper and lower substrate 1,
Each of them has an angle of about 45 ° with B ', and the opening angle of the upper and lower substrates 1 is 20 °.

The stretching direction (TD) of the upper and lower substrates 1 and the polarizing plate 6
The characteristics as a liquid crystal display device were compared between the case where the absorption axis of the liquid crystal display device was substantially parallel and the case where the absorption axis was substantially orthogonal. However, an omnidirectional reflective film was adhered to the outer surface of the lower substrate 1 so that the liquid crystal display element was in the reflective mode. Figure 3
As shown in Fig. 4, when they are made substantially parallel, the good viewing angle direction θ = 4
The angle was 0 °, and the lateral viewing angle direction was ψ = 50 °. When they were made substantially orthogonal, the good viewing angle direction θ = 40 ° and the lateral viewing angle direction ψ = 30 °. As a definition of the viewing angle, the contrast was set to 10 or less, and the brightness at the time of non-lighting was set as a limit point at which it was 1/3 or more of the brightness at the front. As a result, there is no difference between substantially parallel and substantially orthogonal in the good viewing angle direction, but it is better that the arrangement is substantially parallel in the lateral viewing angle direction.

As described above, the stretching direction (TD) of the substrate 1
By making the absorption axis of the polarizing plate 6 and the absorption axis of the polarizing plate 6 substantially parallel to each other, the viewing angle (contrast, brightness) in the lateral viewing angle direction could be improved.

[0014]

As described above, according to the present invention,
When constructing a super twist nematic liquid crystal display device using a plastic film having optical anisotropy, the axial direction with the maximum in-plane refractive index of the plastic film and the absorption axis direction of the polarizing plate are substantially parallel. Therefore, the display characteristics in the lateral viewing angle direction can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display element of an embodiment of the present invention.

FIG. 2 is a diagram showing a stretching direction and a rubbing direction of a substrate.

FIG. 3 is a diagram showing a viewing angle direction of a liquid crystal display element.

FIG. 4 is a diagram showing a relationship between a rubbing direction of a substrate of a super twist nematic liquid crystal display element and a polarization axis direction of a polarizing plate.

[Explanation of symbols]

 1 plastic film (substrate) 2 electrode 3 orientation control film 5 liquid crystal 6 polarizing plate

Claims (2)

[Claims] 1. A two-layer plastic film having an electrode and an orientation control film on its inner surface, a liquid crystal sandwiched between the plastic films and having a twist angle of 160 ° or more, and a polarizing plate arranged outside the plastic film. In a super twisted nematic (STN) type liquid crystal display device including :, the absorption axis direction of the polarizing plate is substantially parallel to the axial direction of the plastic film having a large in-plane refractive index. Liquid crystal display device. 2. The liquid crystal display device according to claim 1, wherein uniaxially stretched polyethylene terephthalate is used as the plastic film.