JPS629319A - Liquid crystal display cell - Google Patents

Abstract

PURPOSE:To suppress a decrease in the quantity of transmitted light and to prevent a contrast ratio and visibility from deteriorating by providing a layer of a birefringent material to a vision-side polarizing plate more on a surface side than the polarizer. CONSTITUTION:The polarizing plate 1 composed of a polarizer 3 with a layer 2 of a birefringent medium is stuck on the vision side of the liquid crystal cell 4 formed by charging liquid crystal 7 between substrates 5 having a transpar ent conductive layer 6, and a polarizing plate 8 having a polarizer 9 is stucked on the other surface. The axis of absorption of the polarizer 3 is at an angle thetaof 45 deg. to the horizontal direction, the axis of absorption of the polarizing plate 8 is crossed at an angle theta+90 deg., and the angle of the layer 2 is set to theta/2 which is 0.4-0.6 time the angle of othe polarizer 3. Thus, the layer 2 is interposed, so a decrease in the quantity of transmitted light due to anticoincidence between polarizers and polarizing media of polarizing sunglasses, etc., is suppressed to prevent effectively the contrast ratio and visibility from deteriorating.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention provides a novel liquid crystal display cell that is suitable for automotive liquid crystal display devices and has improved visibility when viewed through a polarizing medium such as polarized sunglasses. It is related to.

With the proliferation of conventional techniques and open point liquid crystal display devices in various fields, new challenges have arisen. For example, in a vehicle-mounted liquid crystal display device, there is a problem in that the visibility of display contents on the liquid crystal display device decreases when a driver wears polarized sunglasses.

In other words, in a conventional liquid crystal display cell in which polarizing plates having only a polarizing function are provided on the front and back surfaces of the cell, when viewed through a polarizing medium such as polarized sunglasses, the displayed characters, etc. There was a problem that the visibility was greatly reduced due to a decrease in contrast, etc. Wearing polarized sunglasses blocks reflected light etc. through the polarizing medium, thereby improving the visibility of objects. In view of the fact that the device is intended for .

Means for Solving the Problems The present invention overcomes the above problems by using a polarizing plate on the viewing side of a liquid crystal display cell having a layer made of a birefringent medium.

That is, the present invention provides a liquid crystal display cell in which the polarizing plate on the viewing side has a layer made of a birefringent medium on the surface side of the polarizer.

By interposing a layer made of a birefringent medium between a working polarizer and a polarizing medium such as polarized sunglasses, a decrease in the amount of transmitted light due to mismatch of absorption axes between the polarizer and the polarizing medium is suppressed.

Example FIG. 1 shows an example of the structure of a liquid crystal display cell according to the present invention.

This is done by placing a birefringent medium on the viewing side of a liquid crystal cell 4 in which a liquid crystal 7 is sealed between a substrate 5 having a transparent conductive film layer 6 in a predetermined form and arranged with the transparent conductive film layer sides facing each other. A polarizing plate 1 consisting of a polarizer 3 having a layer 2 of
A polarizing plate 8 consisting of a polarizer 9 is attached to the other side of the liquid crystal cell so that the absorption axis of the polarizer 9 is perpendicular to the absorption axis of the polarizer 3 in the viewing side polarizing plate 1. It is formed by pasting. In addition, in the examples, the angle θ that the absorption axis of the polarizer 3 in the polarizing plate 1 on the viewing side makes with the lower side direction of the polarizing plate and the lower side direction of the liquid crystal display cell (usually corresponds to the horizontal direction) is based on the general configuration. There are 45
degree. Therefore, the angle between the absorption axis of the polarizing plate 8 on the other surface of the cell and the direction of the lower side of the cell is 135 degrees.

Furthermore, the layer 2 made of a birefringent medium in the polarizing plate 1 is
It is provided so that its leading axis intersects the lower side direction of the polarizing plate 1 at an angle of 22.5 degrees. FIG. 2 shows the relationship between the absorption axis and the optical axis (both indicated by arrows). Note that IO in the figure is a polarizing medium such as polarized sunglasses, and the arrow indicates the absorption axis of the polarizing medium. In this way, in the present invention, the layer made of a birefringent medium is such that the angle between its optical axis direction and the lower side direction of the polarizing plate on the viewing side of the liquid crystal display cell is the absorption axis direction of the polarizer. 0.4 to 0.6 times the angle (θ) with the lower side direction of the cell, that is, the angle (
From the viewpoint of the intensity of light when viewed through a polarizing medium, and therefore the visibility, it is desirable that the value be 1/2 times as large as θ) or a value close to this value.

Incidentally, the respective absorption axes of the polarizing medium and the polarizer in the polarizing plate on the viewing side intersect at an angle θ, and a layer made of a birefringent medium is provided between the polarizing medium and the polarizer, and its leading axis is When the light is interposed in a state that occupies the middle (θ/2) between the respective absorption axes, the intensity (1) of the light as visibility is expressed by the following formula (a).

1 =Ao” (cos2 θ +sin” θ
・ cos2 (Δnd ・ π/λ ) ) ・
(a) On the other hand, the intensity of light when there is no intervening layer made of a birefringent medium is expressed by the following equation (b).

I=A'cos θ... (mouth) Generally, θ is not O, so by comparing equations (a) and (b), the intensity of light for visibility can be improved by interposing a layer made of a birefringent medium. increases.

In addition, in the above equations (a) and (b), Ao is the amplitude of light, Δ
nd is the retardation value defined by the product of the refractive index difference in birefringence (Δn) and the thickness d) of the layer made of the birefringent medium, and λ is the wavelength of light.

In the liquid crystal display cell of the present invention, as the polarizing plate on the viewing side, one having a layer made of a birefringent medium on the surface side of the polarizer is used.

The polarizer may be anything that can be molded into a plate or sheet, and a typical example thereof is a polarizing film. Specific examples of polarizing films include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and saponified ethylene-vinyl acetate copolymer films that are coated with iodine and/or dichroic dyes. Examples of t) include oriented polyene films such as dehydrated polyvinyl alcohol and dehydrochloric acid treated polyvinyl chloride, which are adsorbed and oriented. The thickness of the polarizer is usually 10 to 8
It is generally 0 μm, but is not limited to this.

On the other hand, the layer made of a birefringent medium may be made of, for example, a birefringent plastic film, a modified layer of a polarizer, a birefringent coating, etc., depending on the formation method. There are no limitations. The system using a birefringent plastic film is advantageous in terms of ease of production and control of the optical axis direction of the layer. An example of a birefringent plastic film is polyvinyl alcohol.
Examples include stretched films made of plastics such as /1 type, cellulose type, polyvinyl chloride type, polypropylene type, polystyrene type, acrylic copolymer type, polycarbonate type, polyester type, and polyamide type. In the case of a method using this plastic film, a bonding method using an adhesive is generally adopted. Those with good quality are preferably used.

The thickness d) of the layer made of birefringent medium is 1+W (,
If and/λ) is small, the occurrence of interference color will be noticeable, so it is preferable to set the value to be large, preferably 15 or more, and to set the value so that the divided value is an integer value. It is desirable to set it to . The upper limit of the thickness of this layer is generally about several mm in practice, but there is no particular limit.

In the present invention, the layer made of the birefringent medium may be in contact with the polarizer in the polarizing plate at an interface, or may be in a state in which, for example, a glass plate, a surface protective layer, etc. are interposed between the layer and the polarizer. may be provided.

On the other hand, the polarizing plate on the other side of the liquid crystal display cell of the present invention may be the same as conventional ones, such as the above-described polarizing film, or a polarizing plate added with a surface protective layer, a glass plate, etc. It will be done.

Effects of the Invention According to the liquid crystal display cell of the present invention, a polarizing plate having a polarizing function and a birefringence function on the viewing side is used. Can you increase the brightness when viewing the displayed contents?

Therefore, it is possible to effectively prevent a decrease in contrast ratio and a decrease in visibility when viewing the display contents of the liquid crystal display cell through polarized sunglasses, etc., and it can be advantageously applied for use in cars, wristwatches, etc. , its practical significance is great.

Specific example: A polarizing plate with a light transmittance of 39% made by laminating a stretched polyester film with a thickness of 85mm and a refractive index difference of 0.11 in birefringence and a polyvinyl alcohol/iodine polarizing film with a thickness of 50μm is used as the viewing side. A liquid crystal display cell was obtained by laminating one side of a liquid crystal cell and a polarizing plate having a light transmittance of 41%, which was made by laminating a cellulose film having a thickness of 80 μm and the above-mentioned polarizing film, to the other side of the cell. The polarizing plates on the front and back surfaces of the liquid crystal display cell are arranged so that the absorption axes of the polarizing films are perpendicular to each other, and the polarizing plates on the viewing side are at an angle (θ) of 45 degrees with respect to the lower side (horizontal direction) of the cell. ) Pasted together so that there were seven. Further, the stretched polyester film of the polarizing plate on the viewing side was attached to the front side. Note that the stretched polynisder film is bonded to the polarizing film so that its leading axis forms an angle of 22.5 degrees (θ/2) with respect to the lower side of the cell.

Comparative Example A liquid crystal display cell was obtained in the same manner as in the Hagaba specific example except that instead of the polarizing plate having a stretched polynisder film, a polarizing plate equivalent to the facing side having a cellulose film was used as the viewing side.

Evaluation Test Regarding the cells of the specific examples and comparative examples, the brightness was measured when the display section of the cell was viewed as it was or through polarized sunglasses when the drive voltage was in the OFF, OFF, or ON state, and the contrast ratio thereof was determined. The results are shown in the table.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an embodiment of the present invention, and FIG. 2 is an exploded explanatory diagram thereof. 1.8: Polarizing plate, 2: Layer made of birefringent medium, 3.9
: Polarizer, 4: Liquid crystal cell, lO: Polarizing medium Patent applicant
Nitto Electric Industry Co., Ltd. Agent Tsutomu Fujimoto Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A liquid crystal display cell characterized in that the viewing side polarizing plate has a layer made of a birefringent medium on the surface side of the polarizer. 2. The cell according to claim 1, wherein the polarizer is a polarizing film and the layer made of a birefringent medium is a plastic film having birefringence. 3. The angle between the optical axis direction of the layer made of birefringent medium and the lower side direction of the liquid crystal display cell is between 0.4 and 0.4 of the angle between the absorption axis direction of the polarizer and the lower side direction of the liquid crystal display cell. The cell according to claim 1, which is 6 times larger.