JPH01217317A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the generation of such inconveniences as the generation of an uneven color, etc., by sticking the lower side polarizing plate or the lower side polarizing plate provided with a reflecting plate, to the lower side of a liquid crystal cell and sticking the upper side polarizing plate to the lower face of a third substrate provided separately on the liquid crystal cell. CONSTITUTION:With regard to a polarizing plate provided on both sides of a liquid crystal cell 11, the lower side polarizing plate 18 is stuck directly to the lower side of the liquid crystal cell 11, but the upper side polarizing plate 20 is stuck to the lower face of the third substrate 21 provided separately on the upper part of the liquid crystal cell 11. Accordingly, even if the substrate consists of a flexible film such as a plastic film and a liquid crystal cell gap is apt to be fluctuated, a gap fluctuation caused by providing the upper side polarizing plate 20 does not occur and the cell gap being in a cell simple substance state can be maintained. In such a way, no uneven color is generated, and also, brightness of a display screen caused by providing the polarizing plate, the elimination of a floating sense of a display picture element and the decrease of an illuminating reflected light, etc., can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a liquid crystal display device using a flexible film such as a plastic film or an extremely thin glass substrate for at least one of the substrates.

Conventional technology Conventionally, this type of liquid crystal display element was of the TN type (twisted type).
The mainstream is one using a nematic type (nematic type) liquid crystal cell. This is composed of a liquid crystal cell in which a liquid crystal layer having a 90' spiral structure is provided between two substrates with transparent electrodes, and a pair of upper and lower polarizers disposed to sandwich this liquid crystal cell. However, this TN type has a limit in display capacity.

Therefore, when considering the recent increase in the size of dot matrix type liquid crystal display elements, this is insufficient.

Therefore, recently, instead of such a TN type,
A liquid crystal display device using a display method called SBE or STN in which the twist angle is 180° or more has been proposed and has already been put into practical use.

FIG. 2 shows a schematic external configuration of the cell. Upper and lower cell substrates (transparent electrodes are formed inside each other so as to form a dot matrix) 2 sandwiching the liquid crystal layer 1.
, 3 are provided with an upper polarizing plate 5 and a lower polarizing plate 6 with a reflecting plate 6a attached above and below the liquid crystal cell 4. Here, drive circuit boards 8 each carrying a drive LSI 7 are connected and mounted on the boards 2 and 3.

Here, in the display system of the mode called SBE or STN, Δn・d(Δn−ne
n□, ne Refractive index in the long axis direction of one liquid crystal molecule, n
Since the color changes due to a slight change in o: refractive index in the minor axis direction of the liquid crystal molecules, d: cell gap - thickness of the liquid crystal layer, unevenness in the gap d within the cell causes color unevenness.

For this reason, in this type of liquid crystal cell, polished glass plates or the like, whose cell gap can be easily controlled, are used as the upper and lower substrates. However, recently, the use of plastic films as the substrates 2 and 3 has attracted attention from the viewpoint of making liquid crystal display devices thinner and lighter, easier to process, and lower in cost.

Further, the pair of polarizing plates 5 and 6 disposed to sandwich the liquid crystal cell 4 are also usually film-like with a thickness of 100 to 200 I1 m.

These polarizing plates 5 and 6 are directly attached to both sides of a liquid crystal cell using a glass substrate in view of brightness, contrast, viewing angle characteristics, floating feeling of display pixels, and the like. However, the liquid crystal cell 4 constructed from a plastic film substrate
On the other hand, when the polarizing plate 5゜6 is attached directly, due to uneven thickness of the polarizing plate, uneven thickness of the adhesive, uneven bonding, etc.
The plastic film substrate of the liquid crystal cell 4 is also deformed and unevenness occurs. Therefore, color unevenness (generally, the second
A striped pattern (as shown by symbol A in the figure) occurs, and the display quality is significantly impaired.

Purpose The present invention was made in view of the above points, and even in the case of a liquid crystal cell using a flexible film such as a plastic film as a substrate, it is possible to prevent color unevenness due to the attachment of a polarizing plate. An object of the present invention is to obtain a liquid crystal display device that does not cause the following disadvantages.

Structure In order to achieve the above object, the present invention provides upper and lower polarizing plates for a liquid crystal cell in which a liquid crystal is sandwiched between a pair of substrates, at least one of which is made of a flexible film and each of which has a transparent electrode inside. and a lower polarizing plate or a lower polarizing plate with a reflective plate, the lower polarizing plate or the lower polarizing plate with a reflective plate is attached to the lower side of the liquid crystal cell,
It is characterized in that the upper polarizing plate is attached to the lower surface of a third substrate separately disposed above the liquid crystal cell.

An embodiment of the present invention will be described below with reference to FIG. The basic components are the same as in FIG.

First, a liquid crystal cell 11 with a mode display system called STN etc. has two substrates 12 and 13 made of plastic film.
A liquid crystal layer 14 is sealed and sandwiched between them with a sealing material 15. Transparent electrodes (I
TO) are formed so that both constitute a dot matrix. Also, for the substrates 12 and 13, the drive LS
A drive circuit board 17 on which components 116 and the like are mounted is connected and mounted by thermocompression bonding using an anisotropic conductive film having hot-melt properties.

A lower polarizing plate 18 including a reflecting plate 18a is directly attached to the lower surface of the substrate 13 below the liquid crystal cell 11 using an adhesive 19.

On the other hand, an upper polarizing plate 20 is also provided on the upper part of the substrate 12 above the liquid crystal cell 11.
2. There is no direct conclusion above. That is, the upper polarizing plate 20 is attached to the lower surface of the liquid crystal cell protection plate 21 as the third substrate provided above so as to cover the entire liquid crystal cell 11 with an adhesive 22, so that the upper polarizing plate 20 is positioned above the substrate 12. has been done.

In a configuration like B, generally the liquid crystal N of the liquid crystal cell 11
If the range of variation in the thickness-cell gap d of 1-5 is △d, if the straightness of Δd〕・d exceeds ±0.005 μm, color unevenness that can be seen with the naked eye will occur within the liquid crystal cell 1. It has been shown through simulations and experiments that this phenomenon occurs. 80 varies depending on the type of liquid crystal used,
Normally, it is about O.1, so the target Δn-d≦
To achieve 0.005μm, Δd≦0.05μ
Must be m.

If a commonly used polarizing plate is attached to both sides of the liquid crystal cell as shown in Figure 2, the change in △d will be 10, 1.
micrometer or more, and striped color unevenness occurred. However, according to this embodiment, since the polarizing plate 20 is not pasted on the second substrate 2, the cell gap in the liquid crystal cell alone does not change and is less than the allowable value (
Δd≦0°051 im), and therefore good display quality was obtained. Further, according to this embodiment, since the upper polarizing plate 20 is attached to the lower surface of the liquid crystal cell protection plate 2, there is no interface between the two. Therefore, diffuse reflection of incident light and reflection of external objects on the two surfaces of the upper polarizing plate 20 can be prevented. However, an interface is formed between the upper polarizing plate 20 and the substrate 12 of the liquid crystal cell 11, but since the transmittance of the polarizing plate is generally less than 50% and the light is polarized, this interface has no adverse effects. It can be almost ignored. That is, the function of providing brightness and eliminating the floating feeling of display pixels, which is achieved by providing the polarizing plate, is not impaired. Furthermore, in the case of liquid crystal cells made of glass substrates, if pasting of the polarizing plate fails, the pasting work can be redone;
In the case of a liquid crystal cell made of a plastic film substrate, the polarizing plate cannot be reattached. Considering this point, as in this embodiment, since the second polarizing plate 20 is not directly attached to the plastic film substrate 2,
The yield will also go up. In particular, considering that a glass substrate or the like may be used for the substrate 3 to which the polarizing plate is directly attached, this is an effect that cannot be ignored.

Note that the substrate 32.13 is not limited to one made of a plastic film, but can be similarly applied to one made of a flexible film material made of ultra-thin glass, but it is particularly effective in the case of a plastic film. be.

Further, in this embodiment, the lower polarizing plate 1 with the reflecting plate 18a is
Although the explanation has been made using an example using the reflector 8a, the present invention can be similarly applied to an example without a reflector plate], 8a.

Effect As described above, the present invention has polarizing plates disposed on both sides of the liquid crystal cell, and the lower polarizing plate is attached directly to the lower side of the liquid crystal cell, but the two side polarizing plates are separately disposed above the liquid crystal cell. Since the third substrate is attached to the lower surface of the third substrate, even if the substrate is made of a flexible film such as a plastic film and the liquid crystal cell gap is likely to fluctuate, the gap can be reduced by providing the two-side polarizing plate. There is no fluctuation and the cell gap can be maintained in the state of a single cell, so there is no color unevenness.In addition, by providing a polarizing plate, the brightness of the display screen can be improved, the floating feeling of display pixels can be removed, and the reflected light from lighting can be improved. It is possible to reduce the amount of

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is an external perspective view showing a conventional example. 11・Liquid crystal cell, 1.2, 1.3...Substrate, 15 Liquid crystal layer, 18 Lower polarizing plate, 20 Second polarizing plate, 2]・Third substrate

Claims (1)

[Claims] A liquid crystal cell has a liquid crystal sandwiched between a pair of substrates, at least one of which is made of a flexible film, and each has a transparent electrode on the inside. In the liquid crystal display device, the lower polarizing plate or the lower polarizing plate with a reflector is attached to the lower side of the liquid crystal cell, and the upper polarizing plate is separately arranged above the liquid crystal cell. A liquid crystal display device characterized in that it is attached to the bottom surface of a substrate.