JPS6223848B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device using a pair of plastic film substrates and a polarizing plate.

2. Description of the Related Art Liquid crystal display devices in which a liquid crystal is filled between an upper glass substrate and a lower glass substrate having electrodes, and a polarizing plate is disposed outside both glass substrates are widely used. However, in recent years, liquid crystal display devices have become increasingly lightweight and
There is a trend toward smaller and thinner devices, but as long as glass is used as a substrate, there are limits due to mechanical strength and manufacturing constraints. Additionally, glass has the drawback of being sensitive to impact and easily causing breakage during the assembly process of the elements and the completed display device. Therefore, it may be possible to use plastic film instead of glass, but using plastic film has its own problems that do not occur with glass substrates, such as alignment processing methods and liquid crystal sealing methods. These are in the direction of successive solutions.

However, even if a plastic film is used as a substrate and the alignment treatment and sealing are successful, when an electric field is applied to the liquid crystal to block the transmitted (reflected) light,
A phenomenon occurs in which a portion of the light passes through the orthogonal polarizing plates, reducing the contrast of the display device. This phenomenon does not occur with glass substrates, but is thought to be a problem unique to plastic film substrates.The reason for this is that plastic films are stretched during the manufacturing process, which makes them optically anisotropic, due to the following reasons. The reason is that the contrast decreases. In other words, when light passes through an optically anisotropic object, only two polarized waves having mutually orthogonal vibration directions and different velocities pass. The polarized light wave with amplitude A that is polarized in the PO direction through the polarizing plate 1 as shown in FIG. Even if the lower polarizing plate 3 is made perpendicular to the lower polarizing plate 3, light in the AO direction and light in the QQ' direction of the light in the BO direction will pass through, resulting in a decrease in contrast.

In order to prevent this decrease in contrast, the angle between the direction of the polarized wave passing through the polarizing plate and the vibration direction of the light wave passing through the plastic substrate (angle θ in Figure 2) should be set to 0° or 90°. One possible method is to match both directions. However, it is difficult to match the polarization directions of these two light waves because the directions of the optical axes of the film are not uniform, and the larger the area, the greater the deviation, and there is also the effect of work errors. However, some deviation is likely to occur. If a shift occurs, the contrast will decrease accordingly.

An object of the present invention is to provide a liquid crystal display device with no misalignment between the two as described above, and the object thereof is to fill a liquid crystal between an upper plastic film substrate and a lower plastic film substrate having electrodes, and In a liquid crystal display device in which polarizing plates are provided on the outside of both substrates, this is achieved by arranging the two substrates so that their long optical axes are perpendicular to each other.

The present invention will be explained in detail below with reference to the drawings.
In the present invention, plastic films such as polyethylene terephthalate film, polybutylene terephthalate film, polyether sulfonate film, and polycarbonate film are used as substrates, and a transparent conductive film of indium oxide, tin oxide, etc. is provided on these films by known means. Further, an alignment treatment film is formed using a reaction product of nylon, epoxy resin, organic titanate, etc., and a rubbing treatment is performed to obtain a substrate.

The above plastic films are stretched during the manufacturing process and each has its own optical axis, but the present invention is characterized in that the long axes of the optical axes 4 are arranged in combination so that they are perpendicular to each other. do.

With this arrangement, the upper substrate 2 and the lower substrate 5
The phases of the lights that have passed through will be shifted by π, and they will cancel each other out.

The reason for this can be explained using a mathematical formula and FIG. 2 as follows. That is, after passing through the upper polarizing plate 1
When the light |OP|=A polarized in the PO direction passes through the upper substrate 2 and the lower substrate 5, which are optically anisotropic bodies, it is divided into the AO direction and the BO direction. And the polarization components AO and BO are expressed as follows.

AO=Acosθ BO=Asinθ When this light passes through the lower polarizing plate 3, the polarized light component
Among AO and BO, light polarized in the QQ' direction is expressed as follows.

AO...A cos θ sin θ = 1/2 As in 2 θ BO... As in θ cos θ = 1/2 As in 2 θ The lights separated by the substrates 2 and 5 have the same amplitude after passing through the lower polarizing plate 3, but the vibration directions are shifted by π.

On the other hand, the wavelength of light in the air is λ ₀ , the wavelength of the polarization component in the substrate in the AO direction is λ ₁ , and the wavelength in the BO direction is λ
_2. If the combined thickness of the substrates 2 and 5 is d, the deviation in the frequency of light while passing through the substrates 2 and 5 is d/λ ₂ −d/n ₁ .

If the refractive index of light in air is n ₀ = 1, the wavelength of ordinary light is λ ₁ , and the wavelength of extraordinary light is λ ₂ , then 1/λ ₁ = n ₁ /λ ₀ 1/λ ₂ = n ₂ /λ ₀ Therefore, the phase shift δ is as follows.

δ=2πd/λ ₀ (n ₂ − n ₁ ) The amplitudes of the ordinary light and extraordinary light are A ₁ , A ₂ , the phase difference considering the difference in vibration direction is δ′, and the lower polarizing plate 3
Let A′ be the amplitude of the composite wave that has passed through A′ ² =A ₁ ² +A ₂ ² +2A ₁ A ₂ cosδ′ δ′=(π−δ), so A′ ² =A ² (sin2θ) ² {sinπd(n ₂ - n ₁ )/λ ₀ } ² ...(1) In equation (1), (sin2θ) The angle that makes the term ² 0, that is, θ, is 0, π/2, π, 3/2π, etc. If θ is set to 0° or 90°, the composite wave will be extinguished, but as mentioned above, it is difficult to set θ to 0° or 90°. Therefore, if n ₂ = n ₁ , the term {sinπd(n ₂ - n ₁ )/λ ₀ } ² becomes 0 and the composite wave is extinguished. If the long axes of the optical axes of the upper substrate 2 and the lower substrate 5 are perpendicular to each other, n ₂ =n ₁ , so the composite wave is extinguished, no light leaks, and the contrast does not deteriorate.

Arrange the upper and lower substrates 2 and 5 as described above, fill the space between them with the liquid crystal 6, seal the liquid crystal with a sealant made of nylon, epoxy resin, hexafluoropropanol, etc., and polarize the polarized light onto the outside of the substrates 2 and 5. Plates 1 and 3 are provided to form a liquid crystal display device.

As detailed above, the liquid crystal display device of the present invention uses a plastic film as a substrate, and the upper and lower plastic films are arranged so that their optical axes are perpendicular to each other. They can be mass-produced more easily than display devices, have increased mechanical strength, and solve the problem of reduced contrast, making it possible to further expand the applications of liquid crystal display devices.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing an example of a liquid crystal display device, and FIG. 2 is a schematic diagram showing how light is polarized. 1... Upper polarizing plate, 2... Upper plastic film substrate, 3... Lower polarizing plate, 4... Optical axis,
5... lower plastic film substrate, 6... liquid crystal.

Claims (1)

[Claims] 1. In a liquid crystal display device in which a liquid crystal is filled between an upper plastic film substrate and a lower plastic film substrate having electrodes, and a polarizing plate is provided on the outside of both substrates, the two substrates are connected to each other. A liquid crystal display device characterized in that the optical axes of the two are arranged so that they are perpendicular to each other. 2. The liquid crystal display device according to claim 1, wherein the upper plastic film substrate and the lower plastic film substrate are polyethylene terephthalate film, polybutylene terephthalate film, polyether sulfonate film, or polycarbonate film.