JPS62112641A - Pressure-sensitive, electrically conductive elastomer composition - Google Patents

Abstract

PURPOSE:To remarkably stabilize the electrical conductivity characteristics under pressure of a compsn. and to facilitate the production thereof, by mixing electrically conductive particles obtd. by firing and carbonizing a spherical high-molecular material with an insulating matrix material having rubbery elasticity and dispersing them therein. CONSTITUTION:Electrically conductive particles obtd. by firing and carbonizing a high-molecular material in the form of spherical particles are mixed with and dispersed in an insulating matrix material having rubbery elasticity. Examples of said matrix material are natural rubbers, synthetic rubbers such as chloroprene, silicone rubber, etc., thermoplastic elastomers such as urethane, EVA, etc., and liquid rubbers such as urethane, silicone, etc., and silicone rubber is preferred. Examples of the spherical high-molecular material are spherical particles obtd. by suspension-polymerizing styrene, vinyl chloride, vinylidene chloride, methyl methacrylate, etc. and spherical particles obtd. by chemically powdering a resol resin, etc. The electrically conductive particles have particle sizes of pref. 50-100mum and are used in an amount of 20-60vol% based on the total amount of the compsn.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a pressure-sensitive conductive elastomer composition, and more specifically, it exhibits high resistance (insulating properties) in a non-pressurized state and decreases in pressure as pressure is applied. This invention relates to a pressure-sensitive conductive elastomer composition whose resistance value changes depending on its size.

[Conventional technology]

BACKGROUND ART Conventionally, as a material having pressure-sensitive conductivity, a conductive composition in which a conductivity imparting agent is blended with an elastic material such as rubber is known. As the conductivity imparting agent, metal particles such as Ni-Kel, conductive carbon black, graphite particles, etc. are used. These compositions are currently widely used in the form of rods or sheets as pressure-sensitive elements for switch elements, pressure sensors, tactile sensors, and the like.

The conventional conductive compositions described above have the following drawbacks. In other words, those that use metal particles as a conductivity imparting agent have the disadvantage that their properties tend to change over time due to oxidation of the particles, resulting in a lack of stability and the generation of chattering phenomena and noise. However, the particle diameter was extremely small, 20 to 30 mμ, and the resistance change during heating was small, making it impractical. Furthermore, if conductive carbon black granules are used, the resistance change can be increased, but the particles may break when pressurized, resulting in poor durability and
Stability was lacking.

When graphite particles are used as a conductivity imparting agent, stable characteristics cannot be obtained if the particle shape is asymmetric, as is the case with natural graphite. It is known that the characteristics are stabilized using particles. Products using artificial graphite particles are superior in terms of stability of properties, durability, and low noise, but the operations to obtain the desired particles are difficult and complicated, and the yield is also low. There was a problem.

[Problem that the invention seeks to solve]

The present invention has been made in view of the above-mentioned difficulties in the prior art, and its purpose is to provide a pressure-sensitive conductive elastomer composition that has very stable pressure conductive properties and is easy to manufacture. It is about providing.

Another object of the present invention is to provide a pressure sensitive conductive elastomer composition whose pressure conductive properties can be varied without changing the mechanical properties of the composition.

[Means for solving problems]

The technical means taken by the present invention to achieve the above object are as follows.

That is, conductive particles obtained by firing and carbonizing a polymeric material in the form of spherical particles are mixed and dispersed in an insulating, rubber-like elastic matrix material.

Examples of matrix materials having insulating rubber-like elasticity include natural rubber, chloroprene, SBR, NBR,
Synthetic rubbers such as silicone rubber, thermoplastic elastomers such as urethane, polyester, and EVA, and liquid rubbers such as urethane and silicone can be used;
Spherical polymer materials preferably include silicone rubber with excellent electrical properties and chemical resistance, and include spherical particles made by suspension polymerization of styrene, vinyl chloride, vinylidene chloride, methyl methacrylate, furfuryl alcohol, etc., or resol. Spherical particles made by chemically powdering resin or the like are used.

Suspension polymerization is a process in which a polymerization catalyst is added to monomers, and the mixture is vigorously stirred in water containing a dispersant so that the seven polymers are dispersed in the form of oil droplets, and then polymerized under heat and pressure. Powdering refers to cooling a resin dissolved in a solvent or adding a precipitant to precipitate a fine powder.

The particle diameter of the conductive particles is 30 to 120 μm, preferably 5 μm.
0 to 100 μm, and its blending amount is 20 to 100 μm in the total composition.
It is 60% by volume. This is because if the particle size is smaller than 30 μm, the resistance change of the composition will be small, and if the particle size is larger than 120 μm, it will be difficult to disperse in the matrix. Also,
The blending amount is determined depending on the desired characteristics, sensitivity, type of matrix material, etc., but if it is less than 20% by volume, the composition will not exhibit sufficient conductivity, and if it is more than 60% by volume, it will not be able to be compressed. The change in conductivity (resistance value) during operation becomes small, making it impractical.

[Effect]

Since conductivity is imparted to the particles by firing the spherical particles made of a polymeric material and carbonizing all or part of the particles, it is easy to select the particle size of the conductive particles. Therefore, since particles of uniform particle size can be used, the pressurized conductive properties of the composition can be extremely stabilized, and manufacturing is also easy.

In addition, by changing the degree of firing of the particles, the amount of carbonization of the particles (1) as shown in Figure 1 (the spherical shell-shaped carbonized part (2) in Figure 1) can be changed.
) thickness (1) is easily obtained, particles of various conductivity grades can be easily obtained, which allows the pressure conductivity properties to be varied without changing the mechanical properties of the composition. Note that (3) is the non-carbonized part of the particle (1).

〔Example〕

Example I Hereinafter, the present invention will be specifically explained with reference to Examples.
.

Spherical microparticles of polystyrene resin crosslinked with divinylbenzene with a particle size of approximately 70 to 130 μm were heated at 300 μm in an air stream.
The mixture was heated to 1000°C and then fired in an inert gas to 1000°C. When measuring the particle size of the obtained carbonized particles,
It was 53 to 105 μm. 100 parts by weight of the carbonized particles were mixed with silicone rubber (manufactured by Shuga Silicone Co., Ltd., TSE
210-40) to produce a 0.5 mm thick sheet by press molding.

The surface of the sheet was pressed with a pressing electrode having a diameter of 5 mm, and the relationship between the pressing force and the resistance value was measured. The results are shown in FIG. 2, showing good resistance change characteristics and small hysteresis.

The spherical microparticles of polystyrene resin were manufactured in the following manner. That is, hendiyl peroxide or lauroyl peroxide is dissolved in a monomer mixture of styrene and divinylbenzene, stirred vigorously in water containing a dispersant such as fully saponified polyvinyl alcohol or incompletely saponified polyvinyl alcohol, and then heated to 80°C. So 6~
This was obtained by suspension polymerization for 8 hours.

Example 2 A spherical phenolic resin with a particle size of about 60 to 100 μm was heated and fired at 800″C in an inert gas. The particle size of the obtained glass spherical carbonized particles was 44 to 74 μm. 100 parts by weight of particles were kneaded with 100111i parts of the same silicone rubber as in Example 1, and press molded to give 0.
A sheet with a thickness of 5 mm was produced.

When the pressure resistance characteristics were measured in the same manner as in Example 1, the results were as shown in the graph (a) of FIG. In this case as well, good characteristics were exhibited and hysteresis was small.

Spherical phenolic resin is manufactured by dissolving resol resin in acetone, adding a precipitant while stirring to precipitate microspherical resin, filtering and drying this microspherical resin, and then heating and curing it. It is.

Example 3゜The same spherical phenol resin as in Example 2 was heated at 600°C.
Fired. The particle size of the obtained glass spherical carbonized particles is 44~
It was 74 μm. 120 parts by weight of the carbonized particles were kneaded with 100 parts by weight of the same silicone rubber as in Example 1, and a sheet with a thickness of 0.5 mm was prepared by press molding.

The results measured in the same manner as in Example 1 are shown in graph (b) of FIG. In this case, the resistance value changes are almost the same as in Example 2, but the range of change is different. This means that the electrical conductivity of the spherical phenolic resin changes depending on the firing temperature, and the reason for this is presumed to be that the degree of carbonization differs depending on the firing temperature, and the carbonized portion increases as the firing temperature increases. Ru. That is, it is thought that this is because the thickness (t) of the spherical shell-shaped carbonized portion (2) in FIG. 1 increases, and the conductivity of the particles increases.

〔Effect of the invention〕

The present invention has the above-mentioned configuration, and has very stable pressurized conductive properties and is easy to manufacture, and furthermore, the pressurized conductive properties can be changed without changing the mechanical properties of the composition. The present invention provides a pressure-sensitive conductive elastomer composition that can

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view showing the carbonized state of spherical particles made of polymeric material, in which (a) only the vicinity of the surface is carbonized, (b) almost the entire part is carbonized, and (c) is completely carbonized. FIG. 2 is a graph showing the pressure resistance value characteristics of Example 1. FIG. 3 is a graph showing the pressure car resistance characteristics of Example 2 and Example 3, where (a) is Example 2 and (b) is Example 3.
This is a graph of (1)... Spherical particles (2)... Carbonized part (3)
・・・Non-carbonized part

Claims (1)

[Claims] 1. A pressure-sensitive conductive elastomer composition characterized in that conductive particles obtained by firing and carbonizing a polymeric material in the form of spherical particles are mixed and dispersed in an insulating rubber-like elastic matrix material.