JPH04296362A - Electro-conductive silicone rubber composition - Google Patents

Abstract

PURPOSE:To provide the electro-conductive silicone rubber composition not only having sufficient electro-conductivity but also having semi-transparency or a dyeable white color. CONSTITUTION:In an electro-conductive silicone rubber composition containing an electro-conductive filler, the composition is characterized in that an indium compound such as indium oxide or indium hydroxide as the electro-conductive filler is compounded with a silicone-based polymer e.g. in a wt. ratio of 5-500: 100. The indium compound can impart a good conductive performance to the composition but does not color the composition.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to conductive silicone rubber compositions, and more particularly to translucent or colorable conductive silicone rubber compositions.

0003

[Prior Art] Silicone compositions that cure into silicone rubber have been well known, and their weather resistance,
Utilizing its excellent properties such as heat resistance, cold resistance, and electrical insulation, it is widely used as a potting material for electrical and electronic parts, a coating material, and a molding material for molding. Furthermore, silicone compositions, which are originally insulating materials, are also used by imparting electrical conductivity to them.

[0004] As a method of imparting electrical conductivity to the silicone composition as described above, a method of blending electrically conductive carbon black is commonly used. Naturally, in a system containing such carbon black, the compound becomes black. Even in conductive silicone rubber,
In order to meet the diversification of their uses, there is a demand for compounds that are translucent or capable of being colored.

In order to meet these demands, fillers other than carbon black have been investigated as conductivity imparting agents. The use of various fillers coated with antimony oxide and tin oxide, various fillers whose surfaces are coated with metal, metal powder, etc. is being considered.

[0006]

However, the above-mentioned conductive fillers other than carbon black each have the following drawbacks. In other words, with various fillers whose surfaces are coated with antimony oxide and tin oxide, the color of the compound becomes gray.
It was not possible to make the color white enough to easily adjust the color. In addition, the color often changed to a dark color when exposed to ultraviolet light. Metal powder and various fillers whose surfaces are coated with metal also turn gray, and their properties deteriorate over time when exposed to water or high humidity. However, no bright color development could be expected.

[0007] For these reasons, a conductive filler that can easily make the compound color white or translucent and that can impart sufficient conductivity to silicone rubber is needed. is strongly desired.

[0008] The present invention has been made to address these problems, and it is possible to make the compound translucent or colorable white while imparting sufficient conductivity, and furthermore, it is possible to avoid compounding restrictions and The object of the present invention is to provide a conductive silicone rubber composition that has no restrictions on use.

[Configuration of the invention]

0010

[Means and effects for solving the problems] That is, the conductive silicone rubber composition of the present invention is a conductive silicone rubber composition containing a conductive filler, in which an indium compound is added as the conductive filler. It is characterized by the fact that it is blended with

The conductive silicone rubber composition of the present invention is
Basically, (B) an indium compound is blended with (A) a polyorganosiloxane composition which becomes a rubber elastic body by curing at room temperature or by heating.

The polyorganosiloxane composition of component (A) above is a composition in which (a) a polyorganosiloxane base polymer, (b) a curing agent, and various additives as necessary are uniformly dispersed. be. Among the various components used in such a composition, (a) the silicone base polymer and (b) the curing agent are appropriately selected depending on the reaction mechanism for obtaining the rubber elastic body. The reaction mechanism includes (1) crosslinking method using an organic peroxide vulcanizing agent;
(2) A method using a condensation reaction, (3) A method using an addition reaction, etc. are known, and the preferred combination of components (a) and (b), that is, a curing catalyst or a crosslinking agent, is determined by the reaction mechanism. is well known.

[0013] That is, when applying the crosslinking method (1) above, the base polymer of component (a) is usually one in which at least two of the organic groups bonded to silicon atoms in one molecule are vinyl. The base polydiorganosiloxane is used. In addition, as the curing agent of component (b), benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-
2,5-di-t-butylperoxyhexane, di-
Various organic peroxide vulcanizing agents such as t-butyl peroxide are used; dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5- Di-t-butyl peroxyhexane and di-t-butyl peroxide are preferred. In addition, these organic peroxide vulcanizing agents are: 1
It is used as a species or a mixture of two or more species.

The blending amount of the organic peroxide which is the curing agent of the component (b) is as follows: 1 of the silicone base polymer of the component (a)
The range is preferably from 0.05 to 15 parts by weight per 00 parts by weight. If the amount of organic peroxide blended is less than 0.05 parts by weight, vulcanization will not be performed sufficiently, and if it is blended in excess of 15 parts by weight, not only will there be no particular effect, but the obtained silicone rubber will be This is because it may have an adverse effect on physical properties.

When the condensation reaction (2) above is applied, a polydiorganosiloxane having hydroxyl groups at both ends is used as the base polymer of component (a). As the curing agent for component (b), first, as a crosslinking agent, ethyl silicate, propyl silicate, methyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, methyltris(methoxyethoxy)silane, vinyltris( Alkoxy type such as methoxyethoxysilane and methyltripropenoxysilane; acetoxy type such as methyltriacetoxysilane and vinyltriacetoxysilane; methyltri(acetoneoxime)silane, vinyltri(acetoneoxime)silane, methyltri(methylethylketoshiquim)silane , vinyltri(methylethylketoxime)silane, and partially hydrolyzed products thereof. In addition, hexamethyl-bis(diethylaminoxy)cyclotetrasiloxane, tetramethyldibutyl-bis(diethylaminoxy)cyclotetrasiloxane, heptamethyl(diethylaminoxy)cyclotetrasiloxane, pentamethyl-tris(diethylaminoxy)cyclotetrasiloxane, hexamethyl-bis(diethylaminoxy)cyclotetrasiloxane, Examples include cyclic siloxanes such as methylethylaminoxy)cyclotetrasiloxane and tetramethyl-bis(diethylaminoxy)-mono(methylethylaminoxy)cyclotetrasiloxane. Thus, the crosslinking agent may have either a silane or siloxane structure, and the siloxane structure may be linear, branched, or cyclic. Furthermore, when using these, it is not necessary to be limited to one type, and two or more types can be used in combination.

[0016] Among the curing agents of component (b), as curing catalysts, carboxylic acid metal salts such as iron octoate, cobalt octoate, manganese octoate, tin naphthenate, tin caprylate, and tin oleate;
Dimethyltin dioleate, dimethyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin dioleate, diphenyltin diacetate, dibutyltin oxide, dibutyltin dimethoxide, dibutylbis(triethoxysiloxy)tin, dioctyltin dilaurate Such organic tin compounds are used.

Among the curing agents as component (b), the amount of the crosslinking agent blended is preferably 0.1 to 20 parts by weight per 100 parts by weight of the base polymer as component (a). If the amount of the crosslinking agent used is less than 0.1 parts by weight, the cured rubber will not have sufficient strength, and if it exceeds 20 parts by weight, the resulting rubber will become brittle, and both are difficult to put into practical use. Further, the amount of the curing catalyst blended is preferably 0.01 to 5 parts by weight per 100 parts by weight of the base polymer (a). If the amount is less than this, it will be insufficient as a curing catalyst, and curing will take a long time, and curing will be poor in areas far from the contact surface with air. On the other hand, if the amount is more than this, the storage stability will deteriorate. A more preferable blending amount range is from 0.1 to 3 parts by weight.

When the addition reaction in (3) above is applied, the same base polymer as the base polymer in (1) above is used as the base polymer for component (a). As the curing agent for component (b), platinum-based catalysts such as chloroplatinic acid, platinum olefin complexes, platinum vinyl siloxane complexes, platinum black, and platinum triphenylphosphine complexes are used as curing catalysts, and as crosslinking agents. A polydiorganosiloxane having an average number of at least two hydrogen atoms bonded to a silicon atom in one molecule is used.

Among the curing agents (b), the curing catalyst is preferably blended in an amount ranging from 1 to 1000 ppm in terms of platinum element based on the base polymer (a). If the content of the curing catalyst is less than 1 ppm as the amount of platinum element, curing will not proceed sufficiently, and if it exceeds 1000 ppm, no improvement in the curing rate can be expected. The amount of the crosslinking agent is such that 0.00 hydrogen atoms bonded to silicon atoms in the crosslinking agent per one alkenyl group in component (a).
The amount is preferably 5 to 4.0, more preferably 1.0 to 3.0. If the amount of hydrogen atoms is less than 0.5, the curing of the composition will not proceed sufficiently and the hardness of the cured composition will decrease, and if the amount of hydrogen atoms is less than 4.0. If it exceeds this, the physical properties and heat resistance of the cured composition will deteriorate.

The organic group in the polyorganosiloxane as the base polymer of component (a) used in the various reaction mechanisms described above is a monovalent substituted or unsubstituted hydrocarbon group, such as a methyl group or an ethyl group. , unsubstituted hydrocarbon groups such as alkyl groups such as propyl, butyl, hexyl, and dodecyl groups, aryl groups such as phenyl groups, and aralkyl groups such as β-phenylethyl and β-phenylpropyl groups. , chloromethyl group, 3
, 3,3-trifluoropropyl group and the like are exemplified. Note that, in general, a methyl group is often used due to ease of synthesis.

In the conductive silicone rubber composition of the present invention, the curing mechanism and the polysiloxane base polymer are not particularly limited, but from the viewpoint of conductive properties, the addition reaction of (3) or the addition reaction of (1) is preferred. It is preferable to use organic peroxide vulcanization, and it is preferable that the polysiloxane base polymer has a degree of polymerization of 1000 or more, that is, a so-called millable type. This is presumably because the shear stress during mixing is appropriate, so that the above-mentioned effects are more effectively achieved depending on the blending.

The indium compound as component (B) in the composition of the present invention is a conductive filler that can impart conductivity to the silicone rubber and suppress coloring of the compound, and is a characteristic of the present invention. It is a component of

Examples of the indium compound include compounds containing monovalent indium, such as InX (X is Cl, Br
, I, etc.)
, In2Y (Y represents at least one element selected from O, S, Se, Te, etc.) Compounds containing divalent indium, such as InX2, InY
etc., compounds containing trivalent indium, such as In2
Oxides such as O3, hydroxides, sulfides, and various salts are known. In the present invention, a compound containing divalent indium or a compound containing trivalent indium is used from the viewpoint of color development and conductivity. In particular, it is preferable to use indium oxide because it has little coloring and can effectively impart conductive properties.

[0024] Furthermore, when attempting to obtain a translucent compound, it is preferable to use an indium compound powder having a primary particle size of 20 μm or less and having a uniform particle size. A more preferable primary particle size of this indium compound powder is 10 μm or less.

The amount of the indium compound as component (B) can be arbitrarily selected depending on the degree of polymerization of the polysiloxane base polymer and the characteristics of the silicone rubber to be obtained, and is not particularly limited. No, but
Generally, it is used in an amount of 5 to 500 parts by weight, preferably 20 to 150 parts by weight, per 100 parts by weight of the silicone base polymer as component (a).

The conductive silicone rubber composition of the present invention may optionally contain various additives such as reinforcing fillers, heat resistance improvers, and flame retardants. However, as additives to be added, those that clearly have coloring properties such as carbon black and Bengara shall be excluded. Such materials usually include fumed silica, precipitated silica, reinforcing charging agents such as diatomaceous earth, aluminum oxide, mica, clay, zinc carbonate, glass beads, polydimethylsiloxane, alkenyl group-containing polysiloxane, etc. is exemplified.

[0027]

[Examples] Examples of the present invention will be described below. Note that all "parts" in the following text indicate "parts by weight."

Examples 1 and 2 Average primary particles as an indium compound were added to 100 parts of a vinyl group-containing polydimethylsiloxane (degree of polymerization of about 6000) whose ends were blocked with trimethylsilyl groups and contained 0.15 mol% of methylvinylsiloxane units. Diameter is 5μm
of indium oxide powder with an average primary particle size of 8
Indium hydroxide powder of .mu.m was individually blended in the proportions shown in Table 1, charged into a kneader, kneaded, and taken out after the compound was formed. Next, 2 parts of 2,5-dimethyl-2,5-di-t-butylperoxyhexane as a crosslinking agent was uniformly mixed thereto to prepare a conductive silicone rubber composition.

[0029] Also, as a comparison with the present invention, SnO2 ・Sb2 O, which is also used as a transparent conductive agent,
A conductive silicone rubber composition was prepared in the same manner as in Example 1, except that fine mica powder having an average particle diameter of 3 nm and having a surface coated with No. 3 was used.

Each conductive silicone rubber composition (compound) thus obtained was made into a 1 mm thick sheet.
After press curing at 170°C for 10 minutes,
Secondary vulcanization was performed at 200° C. for 4 hours, and the temperature was returned to room temperature to obtain silicone rubber sheets. The volume resistivity of these silicone rubber sheets was measured using a multimeter (manufactured by Advantest Co., Ltd.). The results are shown in Table 1 together with the blending ratio of each composition.

[0031]

[Table 1]

As is clear from the results shown in Table 1, the silicone rubbers according to each example using an indium compound as a conductive filler had not only sufficient conductivity but also transparency. . On the other hand, the silicone rubber according to the comparative example has insufficient conductivity and also loses transparency. This is because the transparent conductive agent decomposes due to the shear stress applied during mixing.
This seems to be because it was not possible to obtain the desired conductivity.

Example 3 Polydimethylsiloxane having a viscosity of 4000 cP at 25° C., with both molecular chain ends blocked with silanol groups.
100 parts, 20 parts of indium hydroxide powder with an average primary particle size of 20 μm and 2 parts of rutile titanium dioxide powder were added, and 2 parts of ethyl silicate was added as a crosslinking agent.
0.2 parts, dibutyltin dilaurate as a curing catalyst
A conductive silicone rubber composition was prepared by thoroughly mixing with a kneader.

In addition, as a comparison with the present invention, conductive silicone was prepared in the same manner as in Example 3, except that zinc oxide whiskers (manufactured by Matsushita Amtech Co., Ltd.) were used as the white conductive material instead of the indium hydroxide powder. A rubber composition was prepared.

Each of the conductive silicone rubber compositions thus obtained was left to cure in an atmosphere of 25° C. and 60% relative humidity for one week to obtain a silicone rubber sheet. The volume resistivity of these silicone rubber sheets was measured in the same manner as in Example 1, and the Hunter whiteness was also measured. The results are shown in Table 2 together with the blending ratio of each composition.

[0036]

[Table 2]

[0037]

Effects of the Invention As explained above, according to the conductive silicone rubber composition of the present invention, it is possible to impart sufficient conductivity without coloring the compound, so that it has good conductivity. It becomes possible to stably provide a white silicone rubber that is translucent or can be easily colored.

Claims (2)

[Claims] Claim 1. In a conductive silicone rubber composition containing a conductive filler, the conductive filler comprises:
A conductive silicone rubber composition characterized by containing an indium compound. 2. The conductive silicone rubber composition according to claim 1, wherein the indium compound is indium oxide.