JPS63257723A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To make the brightness of a display surface uniform by providing a scattering layer for light to between a polarizing film at the rear side of a liquid crystal display device and a light shielding film of a liquid crystal cell. CONSTITUTION:An electrode 2A and an orientation film 3A are formed on a substrate 1A, and a light shielding film 4 and an orientation film 3B are superposed in addition to an electrode 2B and a display pattern on a substrate 1B. Both substrates are arranged to face oppositely and sealed with a sealing agent 5 at the periphery, and nematic liquid crystals are injected into the inside. A pair of polarization films 7A, 7B are arranged to both surfaces of the cell wherein the axes of polarization of the polarizing films are arranged to form 90 deg. angle with each other. By providing a light scattering layer 8 in between a polarizing film 7B at the rear side of the cell and the light shielding film 4, the reflectance of a display segment is increased and the difference of the intensity from surface reflected light at the light shielding part is reduced. The light scattering layer is formed by providing unevennesses on the surface of the substrates or by using a light scattering high molecular film. By this constitution, a transparent type liquid crystal display is obtd. with high contrast ratio. If it is used as a reflection type display, there is no fear for causing misconception. More distinct display may be obtained when a dichroic dye is added to the liquid crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a liquid crystal display device that performs negative type display in which a light shielding film is formed.

[Prior Art] Conventionally, liquid crystal display devices used for displaying automobile instruments or clocks, etc. have bright characters on a dark display surface.
Negative type displays for displaying figures, etc. are often used.

In negative-tone liquid crystal display devices, no voltage is applied to the liquid crystal layer in the background area, so the liquid crystal molecules are twisted, and the light travels along this twisted path, aligning the polarization axes of the pair of polarizing films in parallel. This prevents light from passing through the background area. However, in the back part of a normal negative-type liquid crystal display device, light travels in a twisted manner, and since the refractive index differs depending on the color of the light, there is a problem that a certain amount of light of a certain color will pass through. Ta. The ratio (contrast ratio) between when a pair of polarizing films are arranged with the polarizing axes perpendicular to each other and when the polarizing axes are arranged in the opposite direction is 100.
0 or more” can also be 2. However, in a normal negative type liquid crystal display device, when a liquid crystal layer is sandwiched between the layers, as mentioned above, the light travels in a distorted manner in the throat and background areas, making it impossible to obtain sufficient polarization for all colors. Light leakage occurs in some areas,
This was the problem.

For this reason, it has been proposed to form a light shielding film on this background portion to prevent light leakage from the background portion.

However, if a light-shielding film is provided in the IIT to eliminate light leakage from the background part, the background part will become dark, but the non-display pattern will prevent light from passing through the display pattern part. In this area, light leaks to a certain extent, causing the same problem as the background area described above, and when the ratio of darkness between the background area and this non-display pattern area increases, the area where light should not originally be passing through becomes invisible. There is a risk of misreading the display if light is transmitted through it.

For this reason, the Applicant provided a light-shielding film in the background area, and also added a polarizing film in a positive direction so that light would pass through the areas where no voltage was applied to the liquid crystal, as in the case of liquid crystal display devices. It is proposed that a voltage be applied to the portion of the liquid crystal that prevents light from passing through to drive the display pattern. As a result, since the liquid crystal stands up in the part where a voltage is applied to the liquid crystal, there is no effect of color. A high light-shielding property was obtained by making full use of the polarization performance, and a high contrast ratio of 100 or more was obtained.

However, in a display device drawn in this way, under strong external illumination light, the light reflectance of the display segment and the light shielding film portion C are different, and the segment that becomes darker due to voltage application appears blacker than the surrounding light shielding film1. There was a problem that display quality was impaired. FIG. 2 is a plan view showing an example of the appearance in such a state. In the figure, the reflected light intensity differs between the part masked by the light-shielding film and the part In darkened by voltage application, resulting in a difference in the brightness of the display surface, which is unfavorable in terms of appearance.

[Problem to be solved by the invention]

An object of the present invention is to solve the problem that the brightness of the display surface varies due to the low light reflectance of the display segment portions to which a voltage is applied. was developed to solve the above-mentioned problems, and a nematic liquid crystal layer is sandwiched between substrates provided with electrodes,
A light-shielding film is provided in areas other than those corresponding to the display pattern, and a voltage greater than the voltage that excites the nematic liquid crystal is applied to the electrodes in the display pattern area other than the desired display pattern.The polarization axis of the polarizing film is applied to both sides of the liquid crystal cell. In a negative type liquid crystal display device in which a pair of polarizing films are arranged so that light is transmitted through a portion where no electric current is applied, a light scattering layer is provided between the polarizing film on the back side and the light shielding film. The present invention provides a liquid crystal display device characterized in that:

The present invention will be explained with reference to the drawings.

FIG. 1 shows a cross-sectional view of a basic example of a negative-tone twisted nematic liquid crystal display device of the present invention.

In FIG. 1, IA is a substrate, 2A is an electrode formed thereon, and an alignment film 38 is further formed thereon. On the other hand, on the other substrate IB, an electrode zn is formed on the second side, a light shielding film 4 is formed on the portion other than the display pattern, and an alignment film 3B is formed on the second side of the substrate IB. These two substrates are arranged so that their electrode surfaces face each other, their peripheries are sealed with a sealing material 5, and nematic liquid crystal is injected inside to form a liquid crystal layer 6 to form a liquid crystal cell.

A pair of polarizing films 7A are provided on both sides of this liquid crystal cell.

7B is arranged, and its polarization axis is such that light is blocked at the portion to which a voltage is applied, as in the case of a normal positive type liquid crystal display element.

Specifically, the alignment film is formed so that the twist is approximately 90", and the liquid crystal molecules twist approximately 90" when no voltage is applied.
The polarizing film may be placed in a twisted state so that the polarization axes of the polarizing films are parallel or perpendicular to the respective orientation directions. That is, the polarizing axes of the polarizing films are arranged at approximately 90° to each other. The light scattering layer 8 is provided between the polarizing film 7B and the light shielding film 4 on the back surface of the cell.

When the external irradiation light from the polarizing film 7A side is strong, the surface reflection of the light shielding film 4 cannot be ignored, and there is a problem that the display segment becomes brighter than the display segment to which voltage is applied. The reflectance of the light-shielding film portion increases, and the difference from the light reflected from the surface of the light-shielding film portion can be reduced.

Note that the light scattering position may be between the light shielding film and the back polarizing film, and may be provided on the outer surface of the cell as shown in FIG.
It can also be provided on the inner surface of the cell. If the light-scattering layer has an uneven surface, it is not always preferable to provide the light-shielding film and the reflective layer on the same surface, as this may increase the surface reflectance of the light-shielding layer and reduce the effect of the reflective layer. do not.

The light scattering layer can be formed by scratching the surface of the substrate to form irregularities, by inserting a light scattering polymer film, or by spraying a solution onto the substrate and then heating and baking it to create an uneven layer of inorganic oxide. However, it is necessary to control the reflectance of the light scattering layer so that the reflectance of the display segment and the reflectance of the light-shielding film almost match. The light scattering layer has a light reflectance of about 0.1 to 10%, but display quality is usually improved by making the light scattering layer approximately the same reflectance as the light shielding film. If it is less than 0.1%, there is almost no point in providing the light scattering layer, and if it exceeds 10%, the contrast ratio will decrease, which is not preferable.

For example, if the reflectance of the light shielding film is 1%, it is preferable that the reflectance of the light scattering layer is also about 1%.

Also, even if the orientation direction is 90°, the twist of the liquid crystal is 90°.
Instead of 270' or 450', the orientation direction may not be exactly 90° but 85° or 100°. Also, the angle between the polarization axis and the alignment direction is not limited to being parallel or perpendicular, but may be slightly shifted from that by 5 degrees or 8 degrees.
It may be 5 degrees.

The substrate used in the present invention may be a transparent substrate made of glass, plastic, etc., and has InJ*-5n on its inner surface.
A transparent electrode is formed using a transparent conductive film such as Oz (I T O), 5nOa, or the like. In addition, a film of a low-resistance conductive material such as metal or conductive paste may be formed on the transparent electrode in the form of thin lines, a grid, or the like.

The alignment film is made of organic polymers such as polyimide, polyamide, polyvinyl alcohol, SiO□, TiO□, Al2
Any alignment film that aligns the liquid crystal may be used, such as rubbing a film made of an inorganic material such as Oa or diagonally depositing the film, and it may be one layer or two layers as required.

The light shielding film of the present invention may be provided on the inner surface of the liquid crystal cell, or
It may be provided on the outer surface, and its light transmittance is 0.02 to 1.0.
%. However, it is preferable to form the light-shielding film on the inner surface of the liquid crystal cell because it is less likely to cause misalignment between the display pattern and the light-shielding film when viewed from an oblique direction.

This light-shielding film is formed on the background portion of the display, and usually only needs to be formed on one substrate. Of course, it may be formed separately on both substrates, but forming on one substrate requires fewer steps and is more productive.

This light-shielding film is formed by depositing or plating a metallic light-shielding film of aluminum, nickel, or chrome cap through a transparent electrode and an insulating film, or by printing a light-shielding ink of carbon paste cap. It is sufficient if it is formed.

In a positive display liquid crystal display element, the contrast ratio changes depending on the viewing angle, and there is a part that shows the maximum contrast ratio near an angle of 0°, and a part slightly deviated from there in the main viewing angle direction is about 10% of the maximum contrast ratio. There are parts with gentle curves that do not have a high contrast ratio. For this reason, the light transmittance of the light shielding film is adjusted so that the contrast ratio of this gentle curved portion and the light transmittance of the light shielding film almost match within the range of light transmittance of 0.02 to 1.0%. This setting is preferable because it prevents the non-display portion from being confused with the display portion and causing misunderstanding not only when viewed from the front direction but also from an oblique direction.

In this case, it is sufficient to use a light-shielding film with a light-shielding degree lower than the maximum contrast ratio of the polarizing film, so it is possible to reduce the thickness of the light-shielding film that tends to cause short circuits, such as carbon ink, or to use non-conductive three colors such as cyan, magenta, and yellow. Since ink with a low degree of light shielding, such as ink containing colored pigments, can be used, one advantage is that short circuits between the upper and lower substrates are less likely to occur.

The thickness of this light-shielding film varies depending on the material and forming method, but in the printing method using light-shielding ink, the thickness may be approximately 0.2 to 3 μm.

The sealing material may be an ordinary epoxy resin or silicone resin cap sealing material, and usually, after opening [1 part] and forming a cell, during that time [liquid crystal is injected from 1 part, and the The opening may be sealed 11-.

The liquid to be injected may be an ordinary nemagic liquid crystal, which usually has a twist of about 90'', but as mentioned above,
A chiral substance may be added to give a twist of 270° or 450″.

In addition, a single layer of color filter may be formed on the inner or outer surface of the substrate, the substrate may be a polarizing film substrate, a touch switch, an ultraviolet cut filter, or a non-reflection filter may be laminated on the outer surface of the substrate. The technique applied to ordinary liquid crystal display elements may be applied within a range that does not impair the effects of the invention.

Although the present invention is a negative type display as a whole, voltage is applied to the electrodes in the same way as a positive type display.

That is, voltage is not applied to the portions of the liquid crystal that are desired to transmit light, but voltage is applied to portions of the liquid crystal that are desired to be blocked from light. Thereby, the light transmittance of the liquid crystal in the portion where the voltage is applied can be made 0.1% or less in the front direction. Furthermore, even when viewed from an oblique direction, the difference in light transmittance between the light-blocking portion of the liquid crystal and the background portion is not excessive, making it difficult to cause *J recognition.

In the present invention, in the background portion where the light shielding film is present, light leaks by approximately 0.02 to 1.0%, which is the light transmittance of the light shielding film.

At this time, in a display pattern without a light-shielding film,
Light is blocked from the non-display pattern portion where the voltage is applied. At this time, by setting the light shielding degree of the light shielding film to be lower than the light shielding degree of the non-display part of the liquid crystal, the contrast ratio in the front direction will be slightly lower, but there is a risk of misidentification when viewed from an oblique direction. sex is significantly reduced.

[Function] When the liquid crystal display device of the present invention is used in a transmissive type in a dark environment, a high contrast ratio can be obtained regardless of the presence or absence of a light scattering layer. This is because the light scattering layer does not eliminate polarized light, so the light is only slightly scattered, and even in areas where voltage is applied and no light passes through, the light transmission rate due to the surrounding light shielding film is 0.5%. A contrast ratio of 200 or more, which is equivalent to or higher than that of 200, can be obtained.

Also, if this is placed in a bright surrounding, light from the outside will be reflected by the light shielding film, but in the present invention, a light scattering layer is provided and a voltage is applied to prevent light from passing through. Reflections occur even in parts of the image, lowering the apparent contrast ratio, making it difficult to misidentify.

Therefore, even if the surrounding area 11a is bright, it is possible to obtain an easy-to-read liquid crystal display device that does not cause misidentification.

[Example] Example I With the configuration shown in Fig. 1, Merck ZL was used as the liquid crystal.
I-2978-000, Nitto Denko G- as a polarizing film
1220Du, and the cell gap was 5.7 μm.

A light shielding film was formed on the inner surface of the cell and printed with carbon ink to have a thickness of about 2 μm and a light transmittance of about 0.5%. Also,
The driving voltage was IOV.

A cellulose acetate membrane with a scratched surface was used as the light scattering layer. Table 1 shows the intensity of reflected light from the light shielding film portion and the display segment portion along with comparative examples. Comparative Example I shows the case where no damaged cellulose acetate membrane was inserted. Also, the external lighting is 20
000 lux.

As shown in Table 1, the presence of the light scattering layer made it possible to make the intensity of reflected light almost the same between the light shielding film portion and the segment portion, resulting in a display surface with a uniform appearance.

Table 1 Example 2 A cell similar to Example 1 was constructed, and as a light scattering layer, a polynisder resin containing fine silica particles was printed on a glass substrate and dried to form irregularities. When the reflected light intensity was measured in the same manner as in Example 1, it was found that 50
It was a unit.

Example 3 A solution of ethyl silicate (Ethyl silicate 40 manufactured by Multilayer Chemical Co., Ltd.) 18% by weight, 1% by weight of acetic acid, 1% by weight of methanol 64% by weight was sprayed onto a glass substrate after being left for 7 days, and heated to 500°C. After heating for 30 minutes to form irregularities on the substrate surface, a transparent electrode was deposited, and a cell similar to that of Example 1 was constructed. The intensity of the reflected light at the voltage application segment was 45 units.

[Effects of the Invention] The present invention uniformizes the reflectance of externally incident light on the display surface by providing a light scattering layer between the light-shielding film and the back polarizing plate, resulting in a uniform appearance. .

In particular, when a cellulose acetate film is damaged to make it light scattering and inserted between the layers, the product of the refractive index anisotropy (Δn) in the film thickness direction and the film surface direction of the cellulose acetate film and the film thickness (d) (△nd)
Optimization also has the effect of making it possible to improve the viewing angle.

This makes it possible to obtain a display with a high contrast ratio when viewed as a transmissive type, and also reduces the possibility of misidentification when viewed as a reflective type.
High contrast ratio display can be obtained in both dark and bright places.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a basic example of the invention. FIG. 2 is a plan view showing the appearance of a conventional display. Board: IA, IB Group electrode: 2A, 2B Alignment film: 38, 3B Light shielding film: 4 Seal material = 5 Liquid crystal layer 26 Polarizing film Near A, 7B Light scattering layer: 8

Claims (7)

[Claims] (1) A nematic liquid crystal layer is sandwiched between substrates provided with electrodes, and a light-shielding film is provided in areas other than those corresponding to the display pattern.
A voltage higher than that which excites the nematic liquid crystal is applied to the electrodes of display pattern parts other than the desired display pattern.A pair of polarizing films are attached to both sides of the liquid crystal cell so that the polarizing axis of the polarizing film is set so that light passes through the part where no voltage is applied. What is claimed is: 1. A liquid crystal display device with a negative type display provided with a polarizing film, characterized in that a light scattering layer is provided between the polarizing film on the back surface and the light shielding film. (2) The liquid crystal display device according to claim 1, wherein the nematic liquid crystal is twisted approximately 90 degrees, and the pair of polarizing films are arranged so that their polarization axes are substantially perpendicular to each other. (3) The liquid crystal display device according to claim 1 or 2, wherein the light transmittance of the light-shielding film is approximately the same as a contrast ratio that provides a substantially constant contrast over a wide range of visual field of the liquid crystal display device. (4) The liquid crystal display device according to claim 1, wherein illumination means is provided behind the polarizing film on the back side. (5) The liquid crystal display device according to claim 1, wherein the light scattering layer is formed by forming irregularities on the surface of the substrate. (6) The liquid crystal display device according to claim 1, wherein the light scattering layer is made of a light scattering polymer film. (7) The liquid crystal display device according to claim 1, which uses a liquid crystal obtained by adding a dichroic dye to a nematic liquid crystal.