JP2645166B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device, and more particularly to a spacer for a liquid crystal cell of the liquid crystal display device.

(Related Art) In recent years, liquid crystal display devices are not only devices having a small display such as a clock and a calculator, but also devices having a large display such as a word processor, a personal computer, and a television. Is used as a display device.

In general, in a liquid crystal display device, two electrode substrates on which an alignment layer is formed are overlapped with each other via a spacer for regulating the distance between the substrates, and the periphery is sealed to form a liquid crystal cell. It has a structure sandwiching a liquid crystal material. In this case, in a large-sized liquid crystal display device, it is important to obtain a uniform and stable alignment of the liquid crystal over the entire display surface.

However, in such a large-sized liquid crystal display device,
It has been difficult to obtain uniform and stable alignment of the liquid crystal over the entire display surface. That is, particularly in a large-sized liquid crystal display device, spacer particles are scattered at a high density in the display region in order to make uniform the substrate spacing over the entire large display region. In such a case, the orientation of the liquid crystal molecules is disturbed on the spacer surface, and the display quality may be significantly reduced.

For example, in a so-called super twist (ST) type liquid crystal display device in which liquid crystal molecules are twisted at an angle of 180 ° or more between a pair of electric domain substrates, after the liquid crystal is injected into the liquid crystal cell, in addition to normal alignment, Various alignment defects, for example, a different alignment state of a twist angle or a twist direction (hereinafter referred to as a reverse twist alignment defective region) may appear. In order to eliminate the misalignment region, the liquid crystal display device is usually heated and cooled until the liquid crystal becomes isotropic.

However, even in this method, the reverse twist alignment defective area may not be erased. The boundary between these two orientation states becomes a defect line called a disclination line. The disclination line moves as the reverse twist misalignment area decreases.

The spacer hinders the movement of the disclination and, in turn, hinders the disappearance of the reverse twist misalignment region. For this reason, an alignment defect region remains, and display quality is significantly impaired. Further, if the lighting display is continuously performed, a state in which the tilt direction of the liquid crystal molecules is different from the spacer in the lighting pixel (hereinafter referred to as a reverse tilt alignment defective area) may occur, which also significantly reduces the display quality. Lower.

Such a problem is remarkable in the ST type liquid crystal display device, but similarly occurs in various liquid crystal display devices other than a twisted nematic (TN) liquid crystal display device having a 90 ° twist and an ECB type liquid crystal display device.

The above problem can be mitigated by reducing the number of spacers to be scattered, since the spacer is often the core in the poorly-aligned region. However, if the number of spacers is reduced, a problem arises in that the electrode substrate interval cannot be kept uniform over a large area.

On the other hand, the inventors have found through many experiments that the degree of occurrence of the reverse orientation is different depending on the surface properties of the spacer. That is, when the surface of the spacer is vertically aligned with the liquid crystal (a so-called vertical alignment surface), occurrence of the reverse alignment defect can be suppressed. Whether a surface vertically aligns the liquid crystal depends on the surface tension of the surface and depends on the liquid crystal used.
Generally, when the surface is low energy with a surface tension of about 30 dyn / cm or less, a vertical orientation is obtained.

However, such low energy surface area
In the case of using a semiconductor, there is a practically serious problem. In other words, the low-energy surface spacer has a weak adhesive force to the substrate, and the spacer easily moves and dissipates during the assembly of the liquid crystal panel after the spacer is scattered on the substrate, so that the spacer has a uniform distribution density. The liquid crystal panel cannot be assembled in a state where the liquid crystal panel is scattered, so that the distance between the substrates (cell thickness) of the liquid crystal panel is not uniform. This causes unevenness in contrast and display color of the liquid crystal display device, which is a serious problem in practical use.

On the other hand, an attempt was made to cover the spacer with an adhesive for the purpose of preventing spacer movement and preventing cell thickness unevenness by bonding and fixing the substrates with an adhesive spacer (Japanese Patent Application Laid-Open No.
52-29754, JP-A-58-102922, JP-A-59-218425 and JP-A-63-94224. These are all made by coating the whole spacer with some resin. In this case,
Poor reverse orientation caused a problem and was not practical.

(Problems to be Solved by the Invention) As described above, when a normal spacer is used, poor reverse alignment occurs. When a spacer having a low energy surface is used, occurrence of reverse orientation defects can be suppressed, but the adhesion to the substrate is weak, and the spacer moves and dissipates, so that the distance between the substrates (cell thickness) is not uniform. Was. Further, the method of coating the entire spacer with the adhesive causes poor reverse orientation.

The present invention has been made in order to solve the above problems, and has as its object to provide a liquid crystal display device having good alignment and a uniform cell thickness.

[Structure of the Invention] (Means for Solving the Problems) In the liquid crystal display device of the present invention, a liquid crystal composition and a spacer having a surface tension of about 30 dyn / cm or less are sandwiched between a pair of opposed electrode substrates. In the liquid crystal display device described above, an adhesive substance is attached to a part of the surface of the spacer.

(Operation) In the liquid crystal display device of the present invention, an adhesive substance is attached to a part of the surface of the spacer having a low surface tension.

For this reason, the reverse orientation defect is suppressed by the surface having a small surface tension, and the adhesive force is obtained by the adhesive substance partially covering the spacer.

When the surface tension is 30 dyn / cm or less, the effect of suppressing the reverse orientation defect is produced.

At this time, the ratio of the area between the low energy surface (the surface having a small surface tension) and the surface of the adhesive substance on the spacer surface is practically important. That is, the ratio of the adherent substance is made as small as possible to the extent that the adhesion of the spacer to the substrate is practically acceptable, and the surface of the spacer in contact with the liquid crystal exposes as much low-energy surface as possible, and the reverse It is important to control the occurrence.

The adhesion to the substrate may be due to electrostatic force or adhesion. Further, it may be based on adhesiveness.

The spacer may be either an organic substance or an inorganic substance. For example, polystyrene, divinylbenzene, silica, alumina, or the like, or a surface-treated one thereof can be used. As the surface treatment at this time, for example, a treatment agent such as a long-chain alkylsilane coupling agent, a fluorine-based coupling agent, a monobasic chromium complex, or hydrogen fluoride is preferably used so as to minimize the surface tension. And a spacer surface-treated with these.
Needless to say, a material having a small surface energy, for example, a fluorine resin may be used as the material of the spacer itself.

On the other hand, as the adhesive substance for improving the adhesive force to the substrate, divinylbenzene, benzoguanamine, polyolefin, PMMA (polymethyl methacrylate)
Although various types of thermoplastic or thermosetting resins such as epoxy resins and epoxy resins can be used, a stable resin that does not adversely affect the liquid crystal is selected.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 1 is a sectional view of a liquid crystal cell which is an embodiment in which the present invention is applied to a super twist type liquid crystal display device.

In the figure, reference numerals 1a and 1b denote glass substrates arranged to face each other. Transparent electrodes 2a and 2b made of ITO are provided on the surfaces of these glass substrates, respectively. Then, alignment films 3a and 3b made of rubbed polyimide are provided on the surfaces of the transparent electrodes 2a and 2b. These alignment films 3a,
The rubbing direction 3b is such that the twist angle of the liquid crystal is 240 °. Further, polarizing plates 4a and 4b are provided on the outer surfaces of the glass substrates 1a and 1b, respectively.

As a liquid crystal composition 5 having a positive dielectric anisotropy, ZLI-2293 (manufactured by E. Merck) is injected between the alignment films 3a and 3b. Further, a plurality of particulate spacers 6 are fixed between the alignment films 3a and 3b. The periphery of the liquid crystal composition is sealed with an epoxy adhesive 7.

As the spacer 6, spherical silica having a spherical diameter of 6.5 μm is treated with a monobasic chromium complex FC-805 (manufactured by Sumitomo 3M Limited) to form a low-tensile surface 8, and the low-tensile surface 8 is further formed.
A polymethyl methacrylate (PMMA) 9 partially adhered to the upper portion in a patch-like manner was used. At this time, the area to which PMMA is attached is assumed to be approximately 30% of the total surface area of the spacer.
The −805 surface was exposed to the remaining 70%.

Such a spacer can be produced by combining silica spheres having a diameter of 6.5 μm previously treated with FC-805 and PMMA spheres having a diameter of 0.1 μm using a mechanofusion system. . This is a silica sphere and PMMA
It is considered that the PMMA sphere adheres around the silica sphere due to the mechanochemical effect generated between the two during the mixing with the sphere. At this time, the adhesion amount of the PMMA spheres can be controlled by the production conditions, for example, the stirring time, and the ratio of the FC-805 surface to the PMMA surface can be controlled.

The spacer thus produced is mixed with Freon,
This spacer mixed liquid is atomized by a spraying device, the chlorofluorocarbon is evaporated, and the mixture is sprayed using a method of dropping only the spacer onto the substrate. Thereafter, the entire substrate was heated at 160 ° C. for 5 minutes, and then the cell was assembled. This heating melts the PMMA and adheres to the substrate, resulting in a fairly strong air blow.
The spacer did not move or scatter even when sprayed on the substrate or when vibration was applied to the substrate.

The plate-like silica was treated with FC-805, and the surface tension was measured by an ordinary method. As a result, it was 21 dyn / cm. Further, when a liquid crystal cell was prepared using the plate-like silica treated with FC-805, vertical alignment was exhibited.

The liquid crystal display device manufactured in this manner did not have a twist strip, a tilt strip, etc., had a very uniform cell thickness, and provided high-contrast and even display over the entire surface of the cell.

Example 2 Divinylbenzene was used in place of PMMA in Example 1, and the other conditions were the same as in Example 1. However, the space
Even if the substrate was not heated after spraying, the spacer did not move or scatter during assembly of the cell, and sufficient adhesion strength was obtained.

The liquid crystal display device manufactured in this manner did not have a twist strip, a tilt strip, etc., had a very uniform cell thickness, and provided a high-contrast and even display over the front surface of the cell.

Example 3 The surface of the silica spacer was covered with fluorine by treating the silica spheres with hydrofluoric acid as a spacer, and further around the silica spacer,
As shown in FIG. 1, a material to which polymethyl methacrylate (PMMA) was partially adhered was produced in the same manner as in Example-1.

The hydrofluoric acid treatment of the silica spheres was performed as follows. First, silica spheres are dispersed in methanol to form a slurry (20 wt.
%)did. While stirring, a solution of hydrogen fluoride in methanol (0.5 M / l) was added dropwise to the slurry at a concentration of 10 mol% with respect to the silica spheres, followed by stirring for 12 hours. Thereafter, the silica spheres were decanted and washed with methanol,
Heat treatment was performed at 0 ° C. for 5 hours. The area to which PMMA was attached was approximately 35% of the total surface area of the spacer, so that the remaining 65% of the fluorine surface was exposed.

Using this spacer, a liquid crystal display device was manufactured in the same manner as in Example 1.

The plate-like silica was treated with hydrofluoric acid, and the surface tension was measured by an ordinary method. As a result, it was 19 dyn / cm. Further, when a liquid crystal cell was prepared using the plate-like silica treated with hydrofluoric acid, vertical alignment was exhibited.

The liquid crystal display device manufactured in this manner did not have a twist strip, a tilt strip, etc., had a very uniform cell thickness, and provided a high-contrast and even display over the entire surface of the cell.

Comparative Example On the other hand, as a spacer, a cell obtained by simply treating spherical silica with FC-805 was assembled.
In this case, the substrate was not heated at 160 ° C. for 5 minutes.
Other conditions were the same as those of Example-1.

In this case, the adhesion of the spacer to the substrate is weak, and the air blows to the substrate, and the spacer moves and scatters due to the vibration of the substrate at the time of assembly. Density unevenness occurred. As a result, the cell thickness becomes non-uniform, and the contrast and the unevenness appear, which is a practical problem.

Further, using a spacer having PMMA adhered to the entire periphery of a spherical silica, after spraying, the whole substrate was heated at 160 ° C.
After heating for 1 minute, a cell was produced under the same conditions as in Example-1. In this case, the spacer adheres to the substrate, and the spacer does not move or scatter even when a considerably strong air blow is blown on the substrate or when the substrate is vibrated, and the cell thickness is extremely large. Was uniform.

However, twisting and tilting reverse occurred, and became a practical problem.

[Effects of the Invention] As described above, according to the liquid crystal display device of the present invention, a reverse alignment defect does not occur, and a uniform cell thickness is obtained by fixing the spacer. High display quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a liquid crystal display device of the present invention. 1a, 1b: glass substrate, 2a, 2b ... transparent electrode, 3a, 3b ...
... Alignment film, 4a, 4b ... Polarizer, 5 ... Liquid crystal composition, 6 ...
… Spacer, 6a …… spacer low tension surface, 6b …… polymethyl methacrylate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinichi Kamagami 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Akio Murayama 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Corporation Inside Yokohama Works (72) Inventor Shoichi Matsumoto 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside Toshiba Yokohama Works Co., Ltd. (72) Inventor Takeo Suzuki 3506 Nakamura, Night Market, Tokuyama-shi, Yamaguchi Prefecture (72) Genji Taga Yamaguchi Prefecture 22-24 Misasa-cho, Shinnanyo-shi (72) Inventor Shozo Takeno 1059-8 Nakano-cho, Sakae-ku, Yokohama-shi, Kanagawa (56) References JP-A-57-613 (JP, A) JP-A-63-94224 ( JP, A) Japanese Utility Model Showa 60-8933 (JP, U)

Claims (1)

(57) [Claims] 1. A liquid crystal display device in which a liquid crystal composition and a spacer having a surface tension of about 30 dyn / cm or less are sandwiched between a pair of opposing electrode substrates. A liquid crystal display device comprising a conductive material.