JPH0527224A - Liquid crystal display device and its production - Google Patents

Abstract

PURPOSE:To reduce variation in parallax by making one of substrates thin so that a color filter can be disposed outside of the cell and the productivity is improved, and to solve such problems concerning to gap control which are caused by the thin substrate, by selecting the coefft. of thermal expansion and elastic constant of the two substrates. CONSTITUTION:One of substrates 2 is made enough thin compared to an electrode pitch. A color filter 5 is provided outside of the thin substrate 2 for a color display device, while a reflecting plate is provided outside of the thin substrate 2 for a monochromatic reflecting type display. The thin substrate 2 has high coefft. of thermal expansion and low elastic constant. A sealing material 8 is hardened under pressure in a heated state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color STN (super twisted nematic) liquid crystal display device having excellent display uniformity and productivity, a reflective monochrome STN liquid crystal display device capable of high-definition display, and their manufacture. Concerning the law.

[0002]

2. Description of the Related Art A conventional color STN liquid crystal display device has a liquid crystal molecule alignment (for example, 180 to 360) having a large twist angle.
Degree), a phase compensating plate that eliminates birefringence interference color and enables black and white display, and a mosaic color filter that produces three primary colors. However, since the color filter is arranged between the substrates, the color filter Surface irregularities cause display irregularities. This is because the unevenness of the color filter surface makes the gap between the substrates non-uniform and the threshold voltage varies. Therefore, there has been proposed a method of applying a transparent flattening film on the filter in order to suppress unevenness on the surface of the color filter (Japanese Patent Laid-Open No. 2-67502).

On the other hand, in the case of the reflection type monochrome STN liquid crystal display device, the thickness of the substrate constituting the panel is about 0.5 mm or more and the thicknesses of the two substrates are substantially equal.

[0004]

[Problems to be Solved by the Invention] However, JP-A-2-675
Also in the publication No. 02, the degree of display unevenness is remarkably high as compared with the case of monochrome in which neither a color filter nor a flattening film is provided. In addition, problems such as an increase in production cost due to the addition of the flattening film coating process and a decrease in productivity due to a decrease in adhesion strength between the flattening film and the transparent electrode have occurred.

On the other hand, in the case of the reflection type monochrome STN liquid crystal display device which is the other conventional technique, there is a problem of blurring of the display pattern due to the position of the display pixel portion and its shadow appearing to be displaced. This problem becomes more serious as the pixel pitch becomes shorter and the display becomes finer.

A first object of the present invention is to provide a color STN liquid crystal display device having reduced display unevenness and production cost and improved productivity, and a manufacturing method thereof.

A second object of the present invention is to provide a reflection type monochrome STN liquid crystal display device with less blurring due to shadows, particularly a high definition liquid crystal display device and a manufacturing method thereof.

[0008]

Means for Solving the Problems The gist of the present invention to achieve the above objects is as follows: (1) A liquid crystal composition having a pair of substrates, at least one of which is transparent, and positive dielectric anisotropy and a chiral substance between the substrates. The liquid crystal molecules on the physical layer, the XY matrix electrode, and the interface are provided with a tilt angle of 2 degrees or more, and the twist angle of the liquid crystal molecules is 1 between the substrates.
Alignment film having an angle of 80 to 360 degrees, a liquid crystal panel sandwiching a spacer for providing a constant gap between substrates, a polarizing means for changing light transmission or reflection characteristics according to the molecular alignment state of the liquid crystal, the XY matrix electrode In a liquid crystal display device including drive means for applying electric charge to drive the liquid crystal layer, the thickness of the pair of substrates is different, and the thickness d of the thinner substrate is represented by the following equation. Liquid crystal display device.

[0009]

D <t / [2 · tan {sin ⁻¹ (1 / 2n ₂ )}] where t is the pitch of the matrix electrodes and n ₂ is the refractive index of the thinner substrate. Further, (2) a thicker substrate that opposes a substrate made of a transparent organic polymer film having a thickness d represented by the following formula, a liquid crystal composition layer having a positive dielectric anisotropy and a chiral substance between the substrates, X
The liquid crystal molecules on the Y matrix electrode and the interface are given a tilt angle of 2 degrees or more, and the twist angle of the liquid crystal molecules between the substrates is 180 to
Alignment film of 360 degrees, liquid crystal panel sandwiching a spacer that gives a certain gap between substrates, polarizing means for changing light transmission or reflection characteristics according to the molecular alignment state of the liquid crystal, charge on the XY matrix electrodes In the method of manufacturing a liquid crystal display device including a driving means for driving the liquid crystal layer, the coefficient of thermal expansion α ₁ and the coefficient of elasticity E _{1 of the} transparent organic polymer film, Between the coefficient of thermal expansion α ₂ and the coefficient of elasticity E ₂ , α ₁ > α ₂ , E
_The method for manufacturing a liquid crystal display device is characterized in that there is a relationship of ₁ <E ₂ .

[0010]

D <t / [2 · tan {sin- ¹ (1 / 2n ₂ )}] where t is the pitch of the matrix electrode and n ₂ is the refractive index of the thinner substrate.

In the STN liquid crystal display which is widely used as a flat display having a large display capacity at present, high time division driving is performed by giving a steep threshold characteristic by a large twist alignment. In order to fully utilize this steep threshold characteristic, it is necessary to control the cell gap and the pretilt angle extremely uniformly. On the other hand, there is an increasing demand for color display, and a multi-color display device has been manufactured which has a mosaic color filter inside a cell and is combined with the above-mentioned STN liquid crystal. However, the incorporation of the color filter increases the factor of variation in the cell gap, which makes the threshold value non-uniform and causes display unevenness. Therefore, in order to suppress the influence of the unevenness of the color filter, a step of newly applying a flattening film was added and countermeasures were taken.
A significant increase in production costs is inevitable.

In the present invention, in order to solve these problems caused by incorporating the color filter, the color filter is arranged outside the cell. Further, when the color filter is simply arranged outside the cell, when viewed from an oblique direction, the pixel electrode portion and the corresponding mosaic color filter pixel portion appear to be displaced due to the refraction phenomenon of light in the substrate (hereinafter, It is called parallax shift), and color display becomes impossible. Therefore, the parallax shift is reduced by making the substrate on the side where the color filter is installed thinner than the substrate facing it. Further, the thicker counter substrate has a function of obtaining a uniform cell gap and sufficient mechanical strength. That is, a highly practical liquid crystal display device can be obtained for the first time by the present invention in which two substrates having different properties and shapes are combined.

[0013]

First, the first operation of the present invention will be described with reference to FIG.

FIG. 2 shows a partial cross section of the liquid crystal panel of the present invention. A transparent substrate having a thickness d and a refractive index n ₂ is provided with a transparent electrode having a pitch t on one side and a color filter having the same pitch on the other side. Consider a case where this panel is viewed from a medium having a refractive index of n ₁ at an angle θ ₁ with respect to the substrate normal. At this time, in the transparent substrate, the light ray propagates at an angle θ ₂ with the substrate normal due to the refraction phenomenon of the light, and reaches the corresponding pixel electrode with a relative positional deviation Δx.

By the way, there exists the following relationship as Snell's law among the refractive indices n ₁ and n ₂ and the refraction angles θ ₁ and θ ₂ at this time.

[0016]

[Formula 5] n₁・ Sin θ₁= N₂・ Sin θ₂ The relative positional deviation Δx is expressed by the following equation.

[0017]

[Equation 6] Δx = d · tan θ₂ From the equations (1) and (2),

[0018]

[Expression 7] Δx = d · tan {sin ⁻¹ (n ₁ · sin θ ₁ / n ₂ )} If the ratio of the light passing through the color filter to the corresponding electrode is not at least 50% or more, the pixel of the adjacent pixel It can no longer be distinguished from color. Therefore, it is necessary that Δx <(t / 2), and the thickness of the substrate must satisfy the following equation.

[0019]

[Equation 8] d <t / [2 · tan {sin ⁻¹ (n ₁ · sin θ ₁ / n ₂ )}] Note that since generally viewed in air, n ₁ = 1.0.
In addition, assuming a normal application, it is approximately 30 degrees (θ ₁ = 30
It is good if there is no parallax shift when viewed from the direction of (°). Therefore,
Practically, the following formula should be satisfied.

[0020]

D <t / [2 · tan {sin ⁻¹ (1 / 2n ₂ )}] For example, when the pixel pitch t is 100 μm, the refractive index n _{2 of the} substrate is
Is 1.6, the substrate thickness is

[0021]

[Equation 10] d <172 μm It must be

In the above analysis, the peripheral structural materials such as the counter substrate and the polarizing plate are ignored, but even if they are taken into consideration, the value of the deviation between the color filter and the pixel electrode, that is, the condition of the equation (9) does not change. .

In order to make the first effect of the present invention more remarkable, it is preferable to use an organic polymer film as the thin substrate. For example, diagonal size of 10 inches, number of pixels 480
Assuming a general color liquid crystal display of × 640 × 3, the pixel pitch t is almost 100 μm, so the substrate thickness must be 200 μm or less. An organic polymer film is optimal for achieving sufficient strength with such a thinness. Of course, when the area is large and the pixel pitch is rough, the present invention can be applied to an inorganic substrate such as a relatively thick glass.

Further, in order to make the effect of the present invention more remarkable when an organic polymer film is used as a thin substrate,
A glass substrate thicker than the organic polymer film may be used as the counter substrate. The glass substrate is superior to the organic polymer film in terms of rigidity and flatness. Therefore,
The thicker glass substrate can maintain the shape, and the opposing thin substrates can prevent parallax displacement, resulting in a uniform cell gap and a uniform threshold value.

On the other hand, it suffices that the color filter is arranged on the outer side of the thin substrate without any gaps.
The same effect can be obtained by applying it directly or by applying it to another transparent plate and adhering and laminating it.

Further, the present invention can be applied to a color STN liquid crystal display, whether it is a transmissive display having a light source on the back or a reflective display having a reflector on the back.

Further, the present invention can be applied to a reflection type monochrome STN liquid crystal display device. In the case of color display, there is an effect of suppressing the parallax shift between the color filter and the pixel electrode. Similarly, in the case of monochrome, the shift between the pixel electrode and the shadow of the display pixel formed on the reflection plate can be reduced, and the image is blurred due to the shadow. Can be suppressed. As a result, a high-definition reflective monochrome STN liquid crystal display device becomes possible.

Next, the second operation of the present invention will be described with reference to FIG.

The second function is to provide a method for solving the following problems that occur when using a thin substrate as described above. That is, since one of the substrates is thin, the shape retaining ability is deteriorated and a uniform cell gap cannot be obtained. At this time, if a transparent organic polymer film is used as the thin substrate, its coefficient of thermal expansion α ₁ , its elastic coefficient E ₁ , between the coefficient of thermal expansion α ₂ of its thicker substrate and its elastic coefficient E ₂ , The relationship of α ₁ > α ₂ and E ₁ <E ₂ is used. First, the sealing material is applied to one substrate at a predetermined temperature, then the temperature is raised, and then the two substrates are pressurized, The problem can be solved by hardening the sealing material at a temperature almost equal to or higher than the temperature at this time and then cooling it to a predetermined temperature. This is because the difference in the coefficient of thermal expansion causes the thin substrate to be constantly stretched in the substrate surface direction at the operating temperature, and the elastic coefficient of the transparent organic polymer film, which is the thinner substrate, is low. As a result, it is stretched slightly and as a result it does not bend significantly,
This is because the surface of the organic polymer film is almost as flat as the thick substrate.

In order to make this effect more conspicuous, if a part of the spacers has adhesiveness and the adhesive spacers are heated to a temperature at which they soften, then both substrates are brought into pressure contact with each other and cooled in that state. Good. By doing so, the degree of adhesion between both substrates is increased and the flatness of the gap is further increased. Further, in order to enhance this effect, the liquid crystal panel may be placed upright in a state in which it is brought into close contact with pressure and heated. As shown in Figure 3, the adhesive spacer
Since the two substrates contact each other substantially evenly without being biased to one substrate, the two substrates are more effectively adhered.

[0031]

EXAMPLES The present invention will be specifically described with reference to examples.

Example 1 First, FIG. 1 shows an example of providing a color STN liquid crystal display device with reduced display unevenness and production cost, which is the first object of the present invention, and improved in productivity. As the substrate, a glass substrate having a thickness of 1.1 mm and having a polished surface and an organic polymer film (polyether sulfone, hereinafter abbreviated as PES) having a thickness of 0.1 mm are used. PES
Has a refractive index of 1.60 (wavelength: 589 nm). A liquid crystal composition in which a small amount of chiral substance S-811 (manufactured by Merck) was added to nematic liquid crystal RDP-91206-1 (manufactured by Roddick) was sandwiched between these substrates. The natural pitch of the composition is 11.6 μm, and the gap between the substrates is 7.
It is 5 μm. Matrix-shaped transparent electrodes connected to the driver IC are formed inside the substrate (640 × 3)
× 400 pixels are formed. The signal electrodes are alternately taken out from the upper and lower two directions and driven at a duty of 1/400. A polyimide-based alignment film LQ-1 is formed on the electrode.
800 (manufactured by Hitachi Chemical) is approximately 500Å by spin coating
It is applied in the thickness of. The surface treatment is performed by the rubbing method, and the liquid crystal material has a tilt angle of 4 degrees (pretilt) and a twist angle of 240 degrees. 7.6 μm diameter bead spacer (made of divinylbenzene) and the original diameter is 1
Two kinds of polyethylene, which are crushed in the cell at 0 μm and adhered to both substrates, are mixed and act as a spacer to keep a constant gap of 7.5 μm. The pitch t of the striped electrodes on the thin substrate is 100 μm, and the color filters of the three colors RGB are formed on the outside of the substrate in alignment with the pitch t.

Configuration conditions of this embodiment, t = 100 μm, n
Substituting ₂ = 1.60 into the right side of the equation (1), d <152
μm. Since the thickness d of the substrate is 100 μm as described above, this embodiment satisfies the formula (1) and the parallax shift is suppressed to a practical level.

<Embodiment 2> As shown in FIG. 4, in this embodiment, the color filters of three RGB colors formed on the outside of the thin substrate constituting the liquid crystal panel in Embodiment 1 are mounted on another transparent substrate. And the side where the filter is formed faces toward the side of the thin substrate that constitutes the liquid crystal panel, and is laminated in close contact. The color filter is made of pigment and is applied by a printing method. Other configurations are the same as those in the first embodiment. The parallax shift can be suppressed to a practical level as in the first embodiment.

<Embodiment 3> This embodiment is an example of a monochrome reflective display. As shown in FIG. 5, there is no color filter, and the phase plate is arranged only outside the thick substrate. Further, a reflection plate is adhered and laminated on the outer side of the thin substrate via a polarizing plate. The total thickness of the thin substrate and the polarizing plate (the thickness d of the thin substrate defined in the present invention is this value) is 150.
μm, and each has a refractive index of 1.6. The number of pixels is 1280 × 780, and the pixel pitch t is 125 μm.
The other basic configuration is almost the same as in the first and second embodiments.

Similarly, substituting the constituent conditions into the equation (1) gives d <190 μm. Actually, since d is 150 μm, this condition is satisfied, and the parallax shift between the shadow and the pixel is suppressed to a practical level as in the first and second embodiments, and a clearer image can be obtained.

<Embodiment 4> This embodiment relates to a manufacturing method, and the constitutions of materials such as a substrate and a spacer are the same as those in Embodiments 1 to 3. Glass substrate and organic polymer film (PE
S) The respective physical property values are as follows. α ₁ = 40
× 10 ^-6 , α ₂ = 9 × 10 ^-6 , E ₁ = 0.5 × 10 ¹⁰ P
a, E ₂ = 8 × 10 ¹⁰ Pa.

As described above, α which is the constituent feature of claim 7
The relationship of ₁ > α ₂ and E ₁ <E ₂ is satisfied.

First, a sealing material for sealing (manufactured by Yoshikawa Kako, SE-4500) is screen-printed on an organic polymer film substrate and pre-dried at 70 ° C. for 30 minutes. During this time, the same bead spacers and polyethylene beads as those in Examples 1 to 3 dispersed in water are dispersed by a spinner on a glass substrate facing each other. Next, the two substrates are put together and piled up, heated to 120 ° C., and quickly applied with a load of 1000 kg by a press. At this time, the substrate is erected vertically. In this state, the sealing material is left for 60 minutes to cure, and then gradually cooled to room temperature of 25 ° C. for about 30 minutes. Although two kinds of spacers are used in this embodiment, the same effect can be obtained even if, for example, a bead-shaped spacer is coated with a hot-melt adhesive.

Since the liquid crystal panel thus formed is stressed so as to stretch on a thin substrate, a uniform gap is formed and display unevenness is sufficiently suppressed.

[0041]

According to the present invention, it is possible to provide a color STN liquid crystal display device with reduced display unevenness and production cost and improved productivity, and a method for manufacturing the same. Further, it is possible to provide a reflection type monochrome STN liquid crystal display device, in particular, a high-definition liquid crystal display device in which blurring due to a shadow is small, and a manufacturing method thereof.

[Brief description of drawings]

FIG. 1 is a side sectional view schematically showing a liquid crystal display device of the present invention.

FIG. 2 is an explanatory view of the operation of the present invention.

FIG. 3 is an explanatory view of the operation of the present invention.

FIG. 4 is a sectional view schematically showing a liquid crystal display device according to another embodiment of the present invention.

FIG. 5 is a sectional view schematically showing a monochrome reflective liquid crystal display device of the present invention.

[Explanation of symbols]

1 ... Thick substrate, 2 ... Thin substrate, 3 ... Liquid crystal, 4 4 '... Transparent electrode, 5 ... Color filter, 6 ... Adhesive material, 7 ... Bead spacer, 8 ... Seal material, 9, 9' ... Phase plate, 10, 1
0 '... Polarizing plate, 11 ... Light source, 12 ... Light guide.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Osamu Ito             4026 Kujimachi, Hitachi City, Ibaraki Japan             Tachi Works Hitachi Research Laboratory (72) Inventor Seiyoshi Tanno             4026 Kujimachi, Hitachi City, Ibaraki Japan             Tachi Works Hitachi Research Laboratory (72) Inventor Naoki Kikuchi             Hitachi, Ltd. 3300 Hayano, Mobara-shi, Chiba             Mobara Factory

Claims (10)

[Claims] 1. A pair of substrates, at least one of which is transparent, a liquid crystal composition layer having a positive dielectric anisotropy and a chiral substance between the substrates, an XY matrix electrode, and a tilt angle of 2 degrees or more for liquid crystal molecules on the interface. And the twist angle of liquid crystal molecules between the substrates is 18
Alignment film having an angle of 0 to 360 degrees, a liquid crystal panel sandwiching a spacer for giving a constant gap between substrates, a polarizing means for changing light transmission or reflection characteristics according to the molecular alignment state of the liquid crystal, the XY matrix electrode In a liquid crystal display device including a driving unit that applies electric charge to the liquid crystal layer to drive the liquid crystal layer, the thickness of the pair of substrates is different, and the thickness d of the thinner substrate is represented by the following equation. Liquid crystal display device. ## EQU1 ## d <t / [2tan {sin- ¹ (1 / 2n ₂ )}] where t is the pitch of the matrix electrodes and n ₂ is the refractive index of the thinner substrate. 2. The thermal expansion coefficient α _{1 of} a thinner substrate, its elastic coefficient E ₁ , the thermal expansion coefficient α ₂ of an opposite thicker substrate, and its elastic coefficient E ₂ between α ₁ > α. ₂ , E
_A liquid crystal display device having a relationship of ₁ <E ₂ . 3. The liquid crystal display device according to claim 2, wherein the thinner substrate is made of a transparent organic polymer film. 4. The liquid crystal display device according to claim 3, wherein the thick substrates facing each other are glass substrates. 5. A liquid crystal display device according to claim 1, 2, 3 or 4, wherein a plurality of color filters are applied to the outside of the thinner substrate. 6. A liquid crystal display device according to claim 1, 2, 3 or 4, wherein a transparent body coated with a plurality of color filters is closely laminated on the outer side of the thinner substrate. 7. A liquid crystal display device according to claim 1, 2, 3 or 4, wherein a medium having a light-scattering property or a light-reflecting property is closely laminated on the outer side of the thinner substrate. 8. A substrate made of a transparent organic polymer film having a thickness d represented by the following formula, a thicker substrate facing the substrate,
A liquid crystal composition layer having a positive dielectric anisotropy and a chiral substance between the substrates, an XY matrix electrode, an inclination angle of 2 degrees or more is given to liquid crystal molecules on the interface, and a liquid crystal molecule twist angle between the substrates is 180 to Alignment film of 360 degrees, liquid crystal panel sandwiching spacers that give a certain gap between substrates, polarization means for changing light transmission or reflection characteristics according to the molecular alignment state of the liquid crystal, charge on the XY matrix electrodes In the method of manufacturing a liquid crystal display device including a driving means for driving the liquid crystal layer, the transparent organic polymer film has a coefficient of thermal expansion α ₁ , an elastic coefficient of E ₁ , Using a material having a relationship of α ₁ > α ₂ and E ₁ <E ₂ between the coefficient of thermal expansion α _{2 of} the substrate and its elastic coefficient E ₂ , first apply the sealing material to one substrate at a predetermined temperature and then Raise the temperature Next, the two substrates under pressure,
After that, the method for producing a liquid crystal display device is characterized in that the sealing material is cured at a temperature substantially the same as or higher than the temperature at this time, and then cooled to a predetermined temperature. ## EQU2 ## d <t / [2tan {sin- ¹ (1 / 2n ₂ )}] where t is the pitch of the matrix electrodes and n ₂ is the refractive index of the thinner substrate. 9. A liquid crystal display device according to claim 8, wherein at least a part of said spacers has adhesiveness, and both substrates are pressed and brought into close contact after being heated to a temperature at which said adhesive spacers are softened and then cooled in that state. Manufacturing method. 10. The method for manufacturing a liquid crystal display device according to claim 9, wherein the liquid crystal panel is arranged substantially vertically in the state of being brought into close contact with the pressure.