Compositions – Electrically conductive or emissive compositions – Free metal containing
Reexamination Certificate
2000-07-20
2002-03-26
Dawson, Robert (Department: 1712)
Compositions
Electrically conductive or emissive compositions
Free metal containing
C524S398000, C524S261000, C524S266000, C524S267000, C524S588000, C525S479000, C528S015000, C528S031000, C528S032000
Reexamination Certificate
active
06361716
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a curable silicone composition for preparing a silicone adhesive and more particularly to an addition-curable silicone composition containing an electrically conductive filler and a hydroxy-functional organic compound. The present invention also relates to an electrically conductive silicone adhesive produced from such composition.
BACKGROUND OF THE INVENTION
Silicone adhesives are useful in a variety of applications by virtue of their unique combination of properties, including high thermal stability, good moisture resistance, excellent flexibility, high ionic purity, low alpha particle emissions, and good adhesion to various substrates. For example, silicone adhesives are widely used in the automotive, electronic, construction, appliance, and aerospace industries.
Addition-curable silicone compositions comprising an alkenyl-containing polydiorganosiloxane, an organohydrogenpolysiloxane, an electrically conductive filler, and a hydrosilylation catalyst are known in the art. Illustrative of such compositions are U.S. Pat. No. 5,075,038 to Cole et al.; U.S. Pat. No. 5,227,093 to Cole et al.; European Patent Application No. 0 653 463 to Mine et al.; U.S. Pat. No. 5,384,075 to Okami; U.S. Pat. No. 5,932,145 to Mitani et al.; U.S. Pat. No. 5,498,644 to Reo; and U.S. Pat. No. 6,017,587 to Kleyer et al. However, none of the aforementioned references teach the hydroxy-functional organic compound of the present invention.
SUMMARY OF THE INVENTION
The present inventors have discovered that an addition-curable silicone composition containing an electrically conductive filler and a hydroxy-functional organic compound cures to form an adhesive having unexpectedly superior electrical conductivity. Specifically, the present invention is directed to a curable silicone composition for preparing a silicone adhesive, the composition comprising:
(A) an organopolysiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule;
(B) an organohydrogenpolysiloxane containing an average of at least two silicon-bonded hydrogen atoms per molecule in a concentration sufficient to cure the composition;
(C) an electrically conductive filler in an amount sufficient to impart electrical conductivity to the silicone adhesive, wherein the filler comprises particles having at least an outer surface of a metal selected from silver, gold, platinum, palladium, and alloys thereof;
(D) an effective amount of a hydroxy-functional organic compound having a molecular weight up to about 1000 and containing at least one hydroxy group per molecule, provided the compound is free of acetylenic hydroxy groups and the compound does not substantially inhibit cure of the composition; and
(E) a catalytic amount of a hydrosilylation catalyst.
The present invention is also directed to a silicone adhesive comprising a reaction product of the above-described composition.
The present invention is further directed to a multi-part curable silicone composition comprising components (A) through (E) in two or more parts, provided components (A) (B), and (E) are not present in the same part.
The silicone composition of the present invention has numerous advantages, including good flow, low VOC (volatile organic compound) content, and adjustable cure. Moreover, the present silicone composition cures to form a silicone adhesive having good adhesion and unexpectedly superior electrical conductivity as evidenced by a low contact resistance.
The silicone composition of the present invention is useful for preparing an electrically conductive silicone adhesive. The silicone adhesive of the present invention has numerous uses, including die attach adhesives, solder replacements, and electrically conductive coatings and gaskets. In particular, the silicone adhesive is useful for bonding electronic components to flexible or rigid substrates.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a curable silicone composition for preparing a silicone adhesive, the composition comprising:
(A) an organopolysiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule;
(B) an organohydrogenpolysiloxane containing an average of at least two silicon-bonded hydrogen atoms per molecule in a concentration sufficient to cure the composition;
(C) an electrically conductive filler in an amount sufficient to impart electrical conductivity to the silicone adhesive, wherein the filler comprises particles having at least an outer surface of a metal selected from silver, gold, platinum, palladium, and alloys thereof;
(D) an effective amount of a hydroxy-functional organic compound having a molecular weight up to about 1000 and containing at least one hydroxy group per molecule, provided the compound is free of acetylenic hydroxy groups and the compound does not substantially inhibit cure of the composition; and
(E) a catalytic amount of a hydrosilylation catalyst.
Component (A) of the present invention, also referred to herein as the “polymer,” is at least one organopolysiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule. The structure of the organopolysiloxane can be linear, branched, or resinous. The organopolysiloxane can be a homopolymer or a copolymer. The alkenyl groups typically have from 2 to about 10 carbon atoms and are exemplified by, but not limited to, vinyl, allyl, butenyl, and hexenyl. The alkenyl groups in the organopolysiloxane may be located at terminal, pendant, or both terminal and pendant positions. The remaining silicon-bonded organic groups in the organopolysiloxane are independently selected from monovalent hydrocarbon and monovalent halogenated hydrocarbon groups free of aliphatic unsaturation. These monovalent groups typically have from 1 to about 20 carbon atoms, preferably from 1 to 10 carbon atoms, and are exemplified by, but not limited to alkyl such as methyl, ethyl, propyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl; and halogenated hydrocarbon groups such as 3,3,3-trifluoropropyl, 3-chloropropyl, and dichlorophenyl. Preferably, at least 50 percent, and more preferably at least 80%, of the organic groups free of aliphatic unsaturation in the organopolysiloxane are methyl.
The viscosity of the organopolysiloxane at 25° C., which varies with molecular weight and structure, is typically from 0.05 to 200 Pa·s, preferably from 0.5 to 100 Pa·s, and more preferably from 2 to 50 Pa·s.
A preferred organopolysiloxane according to the present invention is a polydiorganosiloxane having the formula R
2
R
1
2
SiO(R
1
2
SiO)
a
SiR
1
2
R
2
wherein each R
1
is independently selected from monovalent hydrocarbon and monovalent halogenated hydrocarbon groups free of aliphatic unsaturation, as defined above; R
2
is alkenyl, as defined above; and subscript a has a value such that the viscosity of the polydiorganosiloxane at 25° C. is from 0.05 to about 200 Pa·s. Preferably, R
1
is methyl and R
2
is vinyl.
Examples of organopolysiloxanes useful in the present invention include, but are not limited to, polydiorganosiloxanes having the following formulae:
ViMe
2
SiO(Me
2
SiO)
a
SiMe
2
Vi, ViMe
2
SiO(Me
2
SiO)
0.25a
(MePhSiO)
0.75a
SiMe
2
Vi,
ViMe
2
SiO(Me
2
SiO)
0.95a
(Ph
2
SiO)
0.05a
SiMe
2
Vi,
ViMe
2
SiO(Me
2
SiO)
0.98a
(MeViSiO)
0.02a
SiMe
2
Vi,
Me
3
SiO(Me
2
SiO)
0.95a
(MeViSiO)
0.05a
SiMe
3
, and PhMeViSiO(Me
2
SiO)
a
SiPhMeVi,
where Me, Vi, and Ph denote methyl, vinyl, and phenyl respectively and a is as defined above.
Component (A) can be a single organopolysiloxane or a mixture comprising two or more organopolysiloxanes that differ in at least one of the following properties: structure, viscosity, average molecular weight, siloxane units, and sequence.
Methods of preparing organopolysiloxanes suitable for use in the compositio
Kleyer Don Lee
Lutz Michael Andrew
Brown Catherine
Dawson Robert
Dow Corning Corporation
Milco Larry A.
Zimmer Marc S.
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