JPH04264427A - Spacer for liquid crystal display - Google Patents

Abstract

PURPOSE:To provide such a spacer for a liquid crystal display that can prevent the liquid crystal near the spacer from regularily orienting near the spacer surfaces, that can widen the area for the liquid crystal to freely orient, and that can improve contrast of the liquid crystal display CONSTITUTION:The spacer for a liquid crystal display consists of composite particles comprising spherical particles of 1-10mum average particle size with <=5% variation coefficient of the particle size and other particles depositing on the particles above mentioned, having <=10% average particle size of the average particle size of the former particles. For example, the composite particles consist of polystyrene or silica particles with deposition of smaller particles which do not melt in the process of assembling the liquid crystal, for example, the same material as the spherical particles above mentioned.

Description

Detailed Description of the Invention [0001] The present invention is used to adjust the gap between two transparent plates constituting a liquid crystal display element, and is used to improve the contrast of a liquid crystal display. This invention relates to a spacer for liquid crystal display elements that can be used. 2. Description of the Related Art A liquid crystal display element is composed of two transparent plates sandwiching a liquid crystal and a spacer. The above-mentioned spacer is used to adjust the gap between the two transparent plates to enable alignment of liquid crystal between the two transparent plates. 2
In order to satisfactorily adjust the gap between the transparent plates, the spacer must be particles with small variation in particle size. Currently, spherical particles such as polystyrene and silica are used as the spacer. [0003] The above-mentioned spherical particles of polystyrene and silica are suitably used as spacers because of their small variation in particle diameter. However, the use of such a spacer has the disadvantage that the contrast of the liquid crystal display is insufficient. [0004] The present inventors have studied the cause of the adverse effect of the above-mentioned spacer on the contrast of a liquid crystal display. As a result, the liquid crystals are regularly arranged on the surface of the spacer particles, and the liquid crystals arranged in this way do not function as liquid crystals even when a voltage is applied.As a result, a region that does not function as a liquid crystal is generated near the surface of the spacer. It was found that the wider the area, the poorer the contrast. [Means for Solving the Problems] Therefore, the present inventors
As a result of intensive research to develop a spacer that is a particle with small variation in particle size and a small area for orientation of liquid crystal formed on the particle surface, we succeeded in achieving the above objective and developed the present invention. I came up with a proposal. That is, in the present invention, the average particle diameter is 1 to 10 μm.
m, the coefficient of variation of the particle diameter is 5% or less, and the surface of the spherical particles that does not melt in the liquid crystal assembly process has an average particle diameter of 10% or less of the average particle diameter of the spherical particles, and the liquid crystal This is a spacer for a liquid crystal display element made of composite particles made up of a large number of attached particles that do not melt during the assembly process. [0007] In the present invention, the spherical particles have an average particle diameter of 1 to 10 μm and a coefficient of variation of particle diameter of 5% or less. Particles having an average particle diameter outside the range of 1 to 10 μm cannot be used as a spacer for a liquid crystal display element because the gap between the two transparent plates cannot be adjusted to be suitable for alignment of the liquid crystal. Further, particles having a coefficient of variation of particle diameter exceeding 5% cannot be used as a spacer for a liquid crystal display element because the variation in particle diameter is too large. Spherical particles having an average particle diameter of 2 to 8 μm and a particle diameter variation coefficient of 3% or less are particularly suitable as spacers for liquid crystal display elements, and are therefore preferably used in the present invention. [0008] The shape of the above-mentioned spherical particles is preferably true spherical, but it does not necessarily have to be true spherical, and if the sphericity is 0.9 or more, it can be used satisfactorily as a spacer for liquid crystal display elements. be able to. Incidentally, the sphericity in the present invention is expressed by the ratio of the short axis to the long axis of a spherical particle observed with an electron microscope. [0009] The material of the above-mentioned spherical particles must be one that does not melt when heated during the sealing process of liquid crystal assembly, generally at a temperature of 150 to 200°C. Such materials include synthetic resins such as polystyrene, styrene-divinylbenzene copolymer, benzoguanamine resin, and polytetrafluoroethylene; alumina, silica, titania,
Examples include inorganic oxides such as zirconia. [0010] On the surface of the spherical particles, a large number of particles are attached which have an average particle diameter of 10% or less of the average particle diameter of the spherical particles and which do not melt during the liquid crystal assembly process. The average particle diameter of the particles attached to the surface of the spherical particles must be 10% or less of the average particle diameter of the spherical particles. When the average particle diameter exceeds 10%, it is impossible to reduce the area in which the liquid crystals formed on the surface of the spacer of the present invention are oriented. The average particle diameter of the particles attached to the surface of the spherical particles may be 10% or less of the average particle diameter of the spherical particles, but if the area where the liquid crystals formed on the spacer surface are oriented is made smaller, It is preferably in the range of ~5%. [0011] Such particles usually have a particle size of 0.01
Those having an average particle diameter of ~0.5 μm are employed. The material of the particles attached to the surface of the spherical particles is as follows:
Similar to the spherical particles, the material must not melt during the sealing process of liquid crystal assembly. Therefore, the material of the particles can be the same as that of the spherical particles described above. [0013] The shape of the particles adhering to the surface of the spherical particles is
There is no particular restriction, and any shape may be adopted. [0014] The particles adhering to the surface of the spherical particles have a surface area coverage of 80% or more, and moreover 90%.
% or more is preferable in order to further reduce the area where the liquid crystals formed on the spacer surface are aligned. The above particles may be attached to the surface of the spherical particles in the form of one or more layers. [0015] The above-mentioned composite particles having particles attached to the surface of the spherical particles may be synthesized by any method, but preferably can be obtained by the following method. [0016] Synthesized by a known method, the average particle diameter is 1~
Spherical particles having a diameter of 10 μm and a coefficient of variation of particle diameter of 5% or less are mixed with particles having an average particle diameter of 10% or less of the average particle diameter of the spherical particles, and the heat generated thereby causes the particles to A method of melting the surfaces and adhering the particles to each other, for example, a method using the Mechanofusion system manufactured by Hosokawa Micron Co., Ltd., or a method of mixing the above particles in a solvent and then drying to increase the cohesive force between the particles. Examples include a method of adhering using. [Effects] In the spacer for a liquid crystal display element of the present invention, since the alignment of the liquid crystal is disturbed by the particles attached to the surface of the spherical particles, the liquid crystal near the surface of the spacer can perform its original function as a liquid crystal. The area that does not function as a liquid crystal can be narrowed down. Therefore, by using the spacer for a liquid crystal display element of the present invention, the contrast of a liquid crystal display can be improved. [Examples] In order to describe the present invention in more detail, Examples and Comparative Examples are listed below, but the present invention is not limited to these Examples. Example 1 Black silica particles (manufactured by Tokuyama Soda Co., Ltd.) with an average particle diameter of 5.9 μm, a coefficient of variation of 1.0%, and a sphericity of 1.0 were synthesized by a sol-gel method with an average particle diameter of 0.2 μm. of monodispersed silica at a weight ratio of 10:1 was charged into a Mechanofusion system (manufactured by Hosokawa Micron Co., Ltd.).
rpm for 5 minutes. As a result of observing the obtained particles with an electron microscope, it was confirmed that monodisperse silica was attached to the surface of the black silica particles at a coverage rate of 95%. The particles thus prepared were sprayed onto a glass substrate provided with a transparent electrode and an oriented polyimide using a dry spraying device. After that, stack the same glass substrates and
The surroundings were sealed at 50° C., and liquid crystal was injected into the obtained cell to create a liquid crystal cell. In order to evaluate the obtained liquid crystal cell, the width of the area around the spacer where the liquid crystal was oriented was measured. That is, light was irradiated from the back side of the liquid crystal cell, the light transmitted through the liquid crystal cell was observed with a microscope, and the light transmission area around the spacer was defined as the area around the spacer where the liquid crystal was oriented. As a result, the light transmission area around the spacer was within 0.1 μm from the surface of the spacer. Example 2 In the same manner as in Example 1, except that the particles shown in Table 1 were used instead of the spherical particles and adhered particles used in Example 1, the liquid crystal oriented area around the spacer was The width of the area was measured. The results are shown in Table 1. [Table 1] Example 3 The black silica and monodispersed silica used in Example 1 were mixed in a Freon-ethanol mixed solvent (with a weight ratio of 10:1 so that the particle concentration was 20%). After dispersing at a volume ratio of 1:1), the mixture was dried and the solvent was evaporated. When the obtained particles were observed with an electron microscope, the coverage of the black silica surface with monodisperse silica was 80%. When the obtained particles were measured in the same manner as in Example 1, it was found that the area around the spacer where the liquid crystal was oriented was within a range of 0.3 μm from the spacer surface. Comparative Example 1 The procedure of Example 1 was repeated except that black silica to which no monodispersed silica was attached was used. the result,
The liquid crystal was oriented around the spacer, and the area within 1.5 μm from the surface of the spacer was transparent and appeared white. Comparative Example 2 The same procedure as in Example 1 was carried out except that polymethyl methacrylate having an average particle diameter of 0.2 μm was used instead of monodisperse silica. Small particles were observed to adhere to the spacer surface until the cell was sealed at 150°C, but after sealing, the polymethyl methacrylate melted due to the heat generated by sealing, and small particles adhered to the spacer surface. is no longer found. Also,
As a result of measuring the area of the oriented liquid crystal around the spacer in the same manner as in Example 1, the area within 1 μm from the surface of the spacer was transparent and appeared white.

Claims (1)

[Claims] Claim 1: A spherical particle having an average particle diameter of 1 to 10 μm, a coefficient of variation of the particle diameter of 5% or less, and 10% of the average particle diameter of the spherical particle, which does not melt during the liquid crystal assembly process, is applied to the surface of the spherical particle. A spacer for a liquid crystal display element made of composite particles having the following average particle diameter and having a large number of attached particles that do not melt during the liquid crystal assembly process.