JP2000336273A - Conductive silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent compatibility of a silver powder and a silicone rubber composition without coagulation of the silver powder by making the composition contain a polyorganosiloxane having at least 2 unsaturated aliphatic groups, conductive powder obtained in advance by mixing at least a specific amount of a powder selected from an inorganic filler and a spherical organic resin with the silver powder. SOLUTION: This composition contains 100 pts.wt. of a polyorganosiloxane represented by the formula, 0 to 800 pts.wt. of a conductive powder containing at least 0.2 wt.% of an inorganic filler, a spherical organic resin and the like and a hardening agent, the amount of the hardening agent being sufficient enough to harden the organopolysiloxane (wherein R1 is identical or different non-substituted or substituted monovalent hydrocarbon group; and n is a positive number of 1.98 to 2.02). The organopolysiloxane preferably has an average degree of polymerization of 100 to 10,000 and the diameter of the silver powder is in the range of 0.05 to 100 μm, particularly 0.1 to 10 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive silicone rubber composition and, more particularly, to a conductive silicone rubber which contains a silver powder which hardly agglomerates over time and provides a silicone rubber having excellent resistance stability. Composition.

[0002]

2. Description of the Related Art Since silver powder has a high electric conductivity, it has an addition reaction-curable silicone rubber composition, a condensation reaction-curable silicone rubber composition,
It is used as a conductive filler for silicone rubber compositions such as peroxide-cured silicone rubber compositions.
A silicone rubber composition containing silver powder is cured to form a low-resistance silicone rubber, and is therefore used in fields requiring heat resistance and conductivity. Normally, silver powder used in the silicone rubber composition is in the form of granules or flakes.

However, there is a problem that these silver powders are strongly agglomerated and cannot be added to the silicone rubber composition when stored for a long time. Further, it is difficult to disperse the aggregated silver powder during the compounding, and an improvement thereof has been desired. Further, there is another problem that the silicone rubber obtained by curing has an unstable volume resistivity.

[0004] In particular, flake silver powder used for forming a silicone rubber having a low resistance (high conductivity) is generally mixed with lauric acid and myristine when the silver powder is ground. Acid, palmitic acid, stearic acid, a method of treating with a saturated or unsaturated higher fatty acid such as oleic acid, a metal soap, a higher aliphatic amine, polyethylene wax, etc. It may cause vulcanization inhibition when added.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has an excellent affinity with a silicone rubber composition of a silver powder by preventing agglomeration of the silver powder. An object of the present invention is to provide a conductive silicone rubber composition excellent in stability of rubber volume resistivity.

[0006]

Means for Solving the Problems and Embodiments of the Invention The present inventors have made intensive studies to achieve the above object, and as a result, at least 0.2% by weight of an inorganic filler and a spherical By using a conductive powder obtained by mixing powders selected from organic resins, a silver powder having excellent dispersibility (conductive powder) can be obtained, so that the above-described problems in the case of using a simple silver powder can be solved. I found that.

That is, 100 parts (parts by weight, hereinafter the same) of an organopolysiloxane represented by the following average composition formula (1):
Is mixed with 100 to 800 parts of a conductive powder obtained by previously mixing at least 0.2% by weight of a powder selected from an inorganic filler and a spherical organic resin in the silver powder, whereby the silver powder with the passage of time is mixed. It has little coagulation and is excellent in dispersibility when blended into a silicone rubber composition, so that a stable volume resistivity can be obtained, and the obtained silicone rubber composition contains an organic peroxide or an organohydrogenpolysiloxane / A platinum-based catalyst alone or a combination of an organic peroxide and an organohydrogenpolysiloxane / platinum-based catalyst can be cured, and the resulting molded article is stable and has a low electric resistance (high conductivity). ) Since it is a member and can withstand long-term use, it was found that it is most suitable for conductive contact members, connectors, roll members for office machines, and electromagnetic wave shielding gasket materials. Leading to the completion of the invention.

Accordingly, the present invention provides: (A) the following average composition formula (1) R ¹ _n SiO _{(4-n) / 2} (1) (wherein R ¹ is the same or different unsubstituted or substituted 1 And n is a positive number from 1.98 to 2.02.) 100 parts by weight of an organopolysiloxane having at least two aliphatic unsaturated groups, And 100 to 800 parts of a conductive powder obtained by mixing at least 0.2% by weight of a powder selected from an inorganic filler and a spherical organic resin, and (C) a curing agent in an amount capable of curing the component (A). Provided is a conductive silicone rubber composition characterized by comprising:

Hereinafter, the present invention will be described in more detail. The organopolysiloxane as the first essential component of the silicone rubber composition according to the present invention is represented by the following average composition formula (1). R ¹ _n SiO _{(4-n) / 2} (1) (wherein, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.98 to 2.02) Is.)

In the above formula, R ¹ is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, a cycloalkyl group such as a cyclohexyl group, a vinyl group, an allyl group, a propenyl group. Group, butenyl group,
Alkenyl groups such as hexenyl groups, phenyl groups, aryl groups such as tolyl groups, benzyl groups, aralkyl groups such as phenylethyl groups, and the like, and some or all of the hydrogen atoms bonded to carbon atoms of these groups are halogen atoms, The same or different, preferably unsubstituted or substituted monovalent carbon having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms selected from a chloromethyl group, a trifluoropropyl group, a cyanoethyl group and the like substituted with a cyano group and the like. It is a hydrogen group. In this case, R ¹ needs to have at least two aliphatic unsaturated groups (alkenyl groups), and the content of the aliphatic unsaturated group in R ¹ is 0.001 to 20 mol%. , Especially 0.025-5
Preferably it is mol%. Also, n is 1.98-
It is a positive number of 2.02. The organopolysiloxane of the above formula (1) is preferably basically linear, but may be one kind or a mixture of two or more kinds having different molecular structures.

Further, the above-mentioned organopolysiloxane preferably has an average degree of polymerization of 100 to 10,000.

Next, the silver powder will be described. The silver powder used in the present invention is not particularly limited, and may be produced by, for example, an electrolytic method, a pulverizing method, a heat treatment method, an atomizing method, a chemical manufacturing method, or the like. , Granules, dendrites, flakes and the like. Further, a material obtained by plating silver on glass beads or a phenol resin may be used.

The particle size of the silver powder used in the present invention is not particularly limited.
The range is preferably 100 μm, particularly 0.1 to 10 μm.

The shape of the silver powder of the present invention is not particularly limited, and may be, for example, granular, dendritic, flake, or irregular shapes, and may be a mixture of silver powders having these shapes. In order to form a low-resistance silicone rubber, it is desirable that the silver powder is not completely independent but is partially connected to silver powder.

The apparatus for crushing the silver powder is not particularly limited.
For example, known devices such as a stamp mill, a ball mill, a vibration mill, a hammer mill, a rolling roller, a mortar and the like can be used. In addition, reduced silver, atomized silver, electrolytic silver or a mixture thereof
The conditions for rolling the silver powder composed of a mixture of more than one kind are not particularly limited, and it is necessary to select the conditions according to the particle size and shape of the silver powder to be used.

In the present invention, a conductive filler obtained by previously mixing one or more powders selected from an inorganic filler and a spherical organic resin with the silver powder is blended into the silicone rubber composition. In this case, as the inorganic filler,
Examples thereof include silica, alumina, titanium dioxide, mica, barium sulfate, and carbon black. Among these, silica, alumina and carbon black are preferred,
Particularly, silica is preferable. Also, as the spherical organic resin,
Polyethylene, polyvinyl chloride, polypropylene, polyolefins such as polystyrene, styrene-acrylonitrile copolymers, acrylic resins such as polymethyl methacrylate, amino resins, fluorine-containing resins, nitrile resins and the like, with polymethyl methacrylate being particularly preferred. Used. The average particle diameter of the inorganic filler and the spherical organic resin is preferably 0.005 to 50 μm, more preferably 0.01 to 30 μm.

As the above-mentioned inorganic filler, silica, particularly finely divided silica is preferred. Finely divided silica mixed with the above silver powder is for the purpose of preventing aggregation of the silver powder, and has a specific surface area (BET method) of 50 m. ² / g or more, especially 100 to 30
It is preferably 0 m ² / g. The specific surface area is 50m ² /
If it is less than g, a sufficient aggregation-preventing effect may not be obtained. Examples of the finely divided silica include fumed silica and precipitated silica, and those obtained by hydrophobizing the surface thereof with chlorosilane, hexamethyldisilazane, organopolysiloxane, alkoxysilane, or the like are also preferably used.

The powder selected from the inorganic filler and the spherical organic resin is used in an amount of 0.2% by weight or more, preferably 0.5 to 5% by weight, based on 100 parts of the silver powder, using a turbula stirrer or the like. Mixing for about a minute to 5 hours is recommended. When the amount of the powder added is less than 0.2% by weight, the aggregation effect is reduced. If the content exceeds 5% by weight, the electric resistance may increase.

Instead of using a conductive powder obtained by previously mixing silver powder with the above-mentioned powder as described above, even if silver powder and the above-mentioned powder are mixed with the above-mentioned organopolysiloxane at the time of preparing the composition, the present invention can be used. The effect of the invention cannot be obtained.

The amount of the conductive powder is 100 to 800 parts, preferably 200 to 600 parts, per 100 parts of the organopolysiloxane. If the amount is too small, it may not be possible to impart sufficient conductivity. If the amount is too large, there may be a problem in the compoundability.

In the present invention, as the curing agent of the third essential component, a known organohydrogenpolysiloxane / platinum-based catalyst (curing agent for addition reaction) or an organic peroxide catalyst can be used.

As the platinum-based catalyst, known catalysts can be used. Specifically, platinum element simple substance, platinum compound, platinum complex, chloroplatinic acid, alcohol compound of chloroplatinic acid, aldehyde compound, ether compound, various olefins And the like. The amount of the platinum-based catalyst to be added is desirably in the range of 1 to 2,000 ppm as platinum atoms with respect to the organopolysiloxane of the first component.

On the other hand, the organohydrogenpolysiloxane has at least two hydrogen atoms directly bonded to silicon atoms.
It not particularly limited as long as it has more than five, linear, branched, may or cyclic, R ² _a H _b Si
O _{(4-ab) / 2} (R ² is the same unsubstituted or substituted monovalent hydrocarbon group as R ¹ and preferably does not have an aliphatic unsaturated bond. A and b are 0 ≦ a <3, 0 <b <3, 0 <a
+ B <3. ) Are preferable, and those having a polymerization degree of 300 or less are particularly preferable. In particular,
Diorganopolysiloxane having a terminal blocked by a dimethylhydrogensilyl group, a copolymer of a dimethylsiloxane unit, a methylhydrogensiloxane unit and a terminal trimethylsiloxy unit, a dimethylhydrogensiloxane unit (H (CH ₃ ) ₂ SiO _0.5 Unit) and SiO ₂
Low-viscosity fluid consisting of units, 1,3,5,7-tetrahydrogen-1,3,5,7-tetramethylcyclotetrasiloxane, 1-propyl-3,5,7-trihydrogen-1, Examples thereof include 3,5,7-tetramethylcyclotetrasiloxane and 1,5-dihydrogen-3,7-dihexyl-1,3,5,7-tetramethylcyclotetrasiloxane.

The amount of the organohydrogenpolysiloxane used as the curing agent is such that the hydrogen atoms directly bonded to silicon atoms are 50 to 500 with respect to the aliphatic unsaturated groups (alkenyl groups) of the first component organopolysiloxane. It is desirable to use the compound in a ratio of mol%.

Examples of the organic peroxide catalyst include, for example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane,
Di-t-butyl peroxide, t-butyl perbenzoate and the like. The amount of the organic peroxide catalyst to be added may be 0.1 to 5 parts based on 100 parts of the first component organopolysiloxane.

The silicone rubber composition according to the present invention includes:
In addition to the above essential components, a reinforcing silica powder may be added as necessary, as long as the effect of the present invention is not impaired. The reinforcing silica powder is added in order to obtain a silicone rubber having excellent mechanical strength. For this purpose, the specific surface area is 50 m ² / g or more, preferably 100 to 300 m ² / g. Needs to be If the specific surface area is less than 50 m ² / g, the mechanical strength of the cured product will be low. As such reinforcing silica,
For example, fumed silica, precipitated silica and the like can be mentioned, and those whose surfaces are hydrophobized with chlorosilane, hexamethyldisilazane or the like are also preferably used.

The addition amount of the reinforcing silica powder is 3 to 70 parts with respect to 100 parts of the organopolysiloxane of the first component.
In particular, it is preferably 10 to 50 parts, and if it is less than 3 parts, the amount of addition may be too small to obtain a reinforcing effect,
If the amount exceeds 70 parts, the workability is deteriorated and the mechanical strength may be reduced.

Further, in combination with silver powder, a conductive material such as conductive carbon black, conductive zinc oxide, and other conductive inorganic oxides such as conductive titanium oxide, which are conventionally known, and silicone as an extender can be used. Fillers such as rubber powder, red iron oxide, crushed quartz, and calcium carbonate may be added.

Further, an inorganic material for forming a sponge,
An organic foaming agent may be added. As this blowing agent,
Examples thereof include azobisisobutyronitrile, dinitropentamethylenetetramine, benzenesulfone hydrazide azodicarbonamide and the like, and the addition amount thereof is preferably in the range of 1 to 10 parts with respect to 100 parts of the organopolysiloxane (A). Thus, when a foaming agent is added to the composition of the present invention, a sponge-like silicone rubber can be obtained.

It is optional to add various additives such as a coloring agent and a heat resistance improving agent, a reaction controlling agent, a release agent or a dispersant for a filler to the composition of the present invention, if necessary. However, diphenylsilanediol, various alkoxysilanes, carbon functional silane, silanol group-containing low molecular weight siloxane, etc. used as a filler dispersant may be added in a minimum amount so as not to impair the effects of the present invention. It is preferable to stop.

Further, in order to make the silicone rubber composition of the present invention flame-retardant and fire-resistant, platinum-containing materials, platinum compounds and titanium dioxide, platinum and manganese carbonate, platinum and γ-Fe
Known additives such as ₂ O ₃ , ferrite, mica, glass fiber and glass flake may be added.

In the silicone rubber composition according to the present invention, the above-mentioned components are uniformly mixed using a rubber kneading machine such as a two-roll mill, a Banbury mixer or a dough mixer (kneader), and a heat treatment is performed if necessary. It can be obtained by applying.

The silicone rubber composition thus obtained can be molded to the required application by various molding methods such as mold pressure molding, extrusion molding, calender molding and the like. The curing can be appropriately selected depending on the curing method and the thickness of the molded product, but can be usually performed at 80 to 400 ° C. for 10 seconds to 30 days.

The cured product of the obtained silicone rubber composition has a volume resistivity of 0.1 Ω · cm or less, especially 1.1 × 10 5
^-3 Ω · cm or less, and can be used as a connector or an electromagnetic wave shielding material.

[0035]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following examples, all parts are parts by weight.

[Examples 1 to 5, Comparative Examples 1 and 2] A fine powder of hydrophobic silica [R] was added to silver powder having an average particle size of 1.5 to 1.7 μm.
−972 (specific surface area: 130 m ² / g, manufactured by Nippon Aerosil Co., Ltd.)] in an amount of 0.5% by weight, 1.0% by weight, and 3.0% by weight. Stir and mix. Next, each of the obtained silica-treated silver powders was allowed to stand at room temperature for 30 days, and then passed through a 150-mesh sieve. In addition, R-972 containing no silica was added in an amount of 0.1%.
A powder to which 1% by weight was added was used as a comparative sample (Table 1).

[0037]

[Table 1]

Next, the obtained conductive powder was mixed with 99.85 mol% of dimethylsiloxane units and 0.15 mol% of methylvinylsiloxane units to have an average degree of polymerization of about 8,000.
As shown in Table 2, 0.5 part of dicumyl peroxide was added to 100 parts of the obtained compound, and heated and pressed at 170 ° C. for 10 minutes. A 1 mm sheet was obtained, and the electrical characteristics and the aggregates in the sheet were observed. Table 2 shows the results.

[0039]

[Table 2]

Examples 6 to 10 and Comparative Example 3 Instead of the hydrophobic silica R-972 used in Example 1, the specific surface area was 2
A silver powder was obtained in the same manner except that 00 m ² / g of fumed silica [Erosil 200 (manufactured by Nippon Aerosil Co.)] and 180 m ² / g of wet silica [Nipsil LP (manufactured by Nippon Silica)] were used. (Table 3). Each of the obtained silica-treated silver powders was allowed to stand at room temperature for 30 days, and then passed through a 150-mesh sieve.

[0041]

[Table 3]

Next, it was added to the siloxane polymer in the same manner as in Example 1, and the electrical resistance and the aggregates in the sheet were observed in the same manner. Table 4 shows the results.

[0043]

[Table 4] Note: Dicumyl peroxide, C-19A, C-19B
Is a siloxane polymer / amount added to 100 parts of conductive powder C-19A Shin-Etsu Chemical Co., Ltd. product name (addition catalyst, platinum-based catalyst) C-19B Shin-Etsu Chemical Co., Ltd. product name (addition crosslinking agent, methyl Hydrogen polysiloxane)

For comparison, a conductive silicone rubber composition in which 450 parts of conductive powder D, 3 parts of Erosil 200, and 0.5 part of dicumyl peroxide were mixed in 100 parts of a siloxane polymer was evaluated in the same manner as described above. (Comparative Example 3). The results were as follows. Volume resistivity (Ω · cm): Aggregate in 7 × 10 ^-4 sheet: Yes [Examples 11 and 12] 1.5 average particle diameter used in Example 1
~ 1.7 μm silver powder with an average primary particle size of 20 nm
Of aluminum oxide (Oxide C, trade name of Nippon Aerosil Co., Ltd.) was added thereto, and silver powder and aluminum oxide were stirred and mixed for 30 minutes using a turbula stirrer to obtain conductive powder K. Further, instead of aluminum oxide, a spherical polymethyl methacrylate resin having an average particle diameter of 1 micron was added to obtain a conductive powder L. The resulting treated silver powder was allowed to stand at room temperature for 30 days, and then passed through a 150-mesh sieve. Next, it was added to the siloxane polymer used in Example 1, and the electrical properties and the aggregates in the sheet were observed. The results shown in Table 5 were obtained.

[Table 5]

[0045]

The conductive silicone rubber composition of the present invention has excellent affinity with the silicone rubber composition by preventing aggregation of silver powder over time, and the silicone rubber obtained by curing the composition can be obtained. Is excellent in stability of volume resistivity.

Continued on the front page (72) Inventor Tsutomu Nakamura 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture Inside Silicone Electronic Materials Research Laboratory, Shin-Etsu Chemical Co., Ltd. Shinano Polymer Co., Ltd.

Claims (4)

[Claims] (A) The following average composition formula (1): R ¹ _n SiO _{(4-n) / 2} (1) (wherein, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group) And n is a positive number from 1.98 to 2.02.) 100 parts by weight of an organopolysiloxane having at least two aliphatic unsaturated groups, (B) inorganic filler previously in silver powder 0 to 800 parts by weight of a conductive powder obtained by mixing at least 0.2% by weight of a powder selected from an agent and a spherical organic resin, and (C) a curing agent containing an amount capable of curing the component (A). A conductive silicone rubber composition, comprising: 2. The silicone rubber composition according to claim 1, wherein the powder of the component (B) is finely divided silica. 3. The conductive silicone rubber composition according to claim 2, wherein the fine silica powder mixed with the silver powder has a specific surface area of 50 m ² / g or more. 4. The conductive silicone rubber according to claim 1, wherein the amount of the component (B) mixed with the silver powder is 0.5 to 5% by weight. Composition.