Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-11-01
2002-04-30
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C528S014000, C528S015000, C528S024000, C528S031000, C528S032000, C528S033000, C428S405000, C525S478000, C524S437000
Reexamination Certificate
active
06380301
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermally conductive silicone rubber composition and more particularly to a thermally conductive silicone rubber composition possessing excellent handling properties and moldability even though it contains a large amount of thermally conductive filler.
BACKGROUND OF THE INVENTION
In recent years, following advances in the degree of density and integration of hybrid ICs and printed circuit boards, on which transistors, ICs, memory elements, and other electronic parts are mounted, various thermally conductive silicone rubber compositions have been employed in order to enhance the efficiency of heat dissipation. Addition-curable thermally conductive silicone rubber compositions are known in the art. For example, Japanese Laid-Open Patent Application No. Sho 61[1986]-157569 discloses a thermally conductive silicone rubber composition comprising a vinyl group-containing organopolysiloxane, an organohydrogenpolysiloxane, a thermally conductive filler, a tackifier selected from an alkyl titanate, an epoxysilane, and an aminosilane, and a platinum catalyst.
Japanese Laid-Open Patent Application No. Sho 62[1987]-184058 discloses a thermally conductive silicone rubber composition comprising an organopolysiloxane containing, on the average, two alkenyl groups per molecule, an organopolysiloxane containing, on the average, three or more silicon-bonded hydrogen atoms per molecule, a thermally conductive filler comprising zinc oxide and magnesium oxide, a filler treating agent, and a platinum catalyst.
Japanese Laid-Open Patent Application No. Sho 63[1988]-251466 discloses a thermally conductive silicone rubber composition comprising an organopolysiloxane containing at least 0.1 mol of alkenyl groups per molecule, an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms in one molecule, a spherical alumina powder with an average particle size of from 10 &mgr;m to 50 &mgr;m, a spherical or non-spherical alumina powder with an average particle size of less than 10 &mgr;m, and platinum or a platinum compound.
Japanese Laid-Open Patent Application No. Hei 02[1990]-041362 discloses a thermally conductive silicone rubber composition comprising an alkenyl group-containing an organopolysiloxane, an organohydrogenpolysiloxane, an alumina powder having no definite shape with an average particle size of from 0.1 &mgr;m to 5 &mgr;m, a spherical alumina powder with an average particle size of from 5 &mgr;m to 50 &mgr;m, and a platinum catalyst.
Japanese Laid-Open Patent Application No. Hei 02[1990]-097559 teaches a thermally conductive silicone rubber composition comprising an organopolysiloxane containing at least two silicon-bonded alkenyl groups in one molecule, an organohydrogenpolysiloxane containing at least three silicon-bonded hydrogen atoms in one molecule, a thermally conductive filler with an average particle size of from 5 &mgr;m to 20 &mgr;m, an adhesion assistant, and platinum or a platinum compound.
The problem with such thermally conductive silicone rubber compositions, however, is that the content of the thermally conductive fillers, which are added to the compositions in order to improve the coefficient of thermal conductivity of the silicone rubber obtained by curing them, must of necessity be high, which leads to a deterioration in the handling properties and moldability of the resultant silicone rubber compositions.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thermally conductive silicone rubber composition possessing excellent handling properties and moldability even though it contains a large amount of thermally conductive filler added in order to obtain silicone rubber of high thermal conductivity.
The present invention is directed to a thermally conductive silicone rubber composition comprising:
(A) a curable organopolysiloxane;
(B) a curing agent; and
(C) a filler prepared by treating the surface of a thermally conductive filler with an oligosiloxane having a formula selected from (i) (R
1
O)
a
Si(OSiR
2
3
)
(4−a)
and (ii) (R
1
O)
a
R
2
(3−a)
SiO[R
2
2
SiO]
n
Si(OSiR
2
3
)
b
R
2
(3−b)
wherein R
1
is alkyl, each R
2
is independently a monovalent hydrocarbon group free of aliphatic unsaturation, subscript a is an integer from 1 to 3, b is an integer from 1 to 3, and n is an integer having a value greater than or equal to 0.
The thermally conductive silicone rubber composition of the present invention is characterized by excellent handling properties and moldability even though it contains a large amount of thermally conductive filler added in order to obtain silicone rubber of high thermal conductivity.
DETAILED DESCRIPTION OF THE INVENTION
A thermally conductive silicone rubber composition according to the present invention, comprises:
(A) a curable organopolysiloxane;
(B) a curing agent; and
(C) a filler prepared by treating the surface of a thermally conductive filler with an oligosiloxane having a formula selected from (i) (R
1
O)
a
Si(OSiR
2
3
)
(4−a)
and (ii) (R
1
O)
a
R
2
(3−a)
SiO[R
2
2
SiO]
n
Si(OSiR
2
3
)
b
R
2
(3−b)
wherein R
1
is alkyl, each R
2
is independently a monovalent hydrocarbon group free of aliphatic unsaturation, subscript a is an integer from 1 to 3, b is an integer from 1 to 3, and n is an integer having a value greater than or equal to 0.
There are no limitations concerning the cure mechanism of the present composition; thus, one may suggest a hydrosilation reaction, a condensation reaction, or a free radical reaction, among which a hydrosilation reaction or a condensation reaction are preferred.
The curable organopolysiloxane of component (A) is the main component of the present composition, and when the present composition is hydrosilation-curable, component (A) is an organopolysiloxane having, on the average, not less than 0.1 silicon-bonded alkenyl groups per molecule, preferably, an organopolysiloxane having, on the average, not less than 0.5 silicon-bonded alkenyl groups per molecule, and especially preferably, an organopolysiloxane having, on the average, not less than 0.8 silicon-bonded alkenyl groups per molecule. When the average number of silicon-bonded alkenyl groups per molecule is lower than the lower limit of the above-mentioned range, the resultant composition does not completely cure. Examples of silicon-bonded alkenyl groups include vinyl, allyl, butenyl, pentenyl, and hexenyl, of which vinyl is preferred. Examples of silicon-bonded groups in the organopolysiloxane other than the alkenyl include methyl, ethyl, propyl, butyl, pentyl, hexyl, and other alkyl groups; cyclopentyl, cyclohexyl, and other cycloalkyl groups; phenyl, tolyl, xylyl, and other aryl groups; benzyl, phenetyl, and other aralkyl groups; and 3,3,3-trifluoropropyl, 3-chloropropyl, and other halogenated alkyl groups. Among these groups, alkyl and aryl are preferred, and methyl and phenyl are particularly preferred.
Although there are no limitations concerning the viscosity of the organopolysiloxane, its viscosity at 25° C. should preferably be within the range of from 50 mPa·s to 100,000 mPa·s, and, especially preferably, within the range of from 100 mPa·s to 50,000 mPa·s. When its viscosity at 25° C. is lower than the lower limit of the above-mentioned range, the physical characteristics of the resultant silicone rubber tend to markedly deteriorate, and, on the other hand, when it exceeds the upper limit of the above-mentioned range, the handling properties of the resultant silicone rubber composition tend to markedly deteriorate.
There are no limitations concerning the molecular structure of this type of organopolysiloxane, and, for example, it may be a linear, branched, partially branched linear, or dendritic configuration; preferably, it is a linear or partially branched linear configuration. In addition, the organopolysiloxane can be a homopolymer having such a molecular structure, a copolymer made up of such molecular structures, or a mixt
Amako Masaaki
Enami Hiroji
Okawa Tadashi
Onishi Masayuki
Brown Catherine
Dawson Robert
Dow Corning Toray Silicone Co. Ltd.
Milco Larry A.
Peng Kuo-Liang
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