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
2000-03-28
2002-08-13
Moore, Margaret G. (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...
C524S785000, C524S780000, C524S588000, C252S514000
Reexamination Certificate
active
06433057
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a silicone composition and more particularly to an addition-curable silicone composition containing an electrically conductive filler and a specific concentration of an organopolysiloxane resin. 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 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 assembly of automotive parts, toys, electronic circuits, and keyboards.
Addition-curable silicone compositions comprising a polydiorganosiloxane, organohydrogenpolysiloxane, electrically conductive filler, and hydrosilylation catalyst are known in the art. For example, U.S. Pat. No. 5,075,038 to Cole et al. discloses an electrically conductive silicone composition, comprising (A) a silicone polymer having greater than 5 percent of the silicon atoms having a phenyl radical attached, or having greater than 5 mole percent vinyl radicals, or having greater than 5 mole percent phenyl and vinyl radicals in combination, said polymer being curable through an addition reaction with a silicon hydride in the presence of a platinum catalyst; and (B) from 12.5 to 50 volume percent of the total composition of silver particles or particles having an outer surface of silver, said composition being free of carbon black and having an electrical resistivity of less than 1×10
−2
ohm-cm, and which electrical resistivity is stable to thermal aging. However, Cole et al. do not teach the specific combination of the organopolysiloxane resin and polymer of the present invention.
U.S. Pat. No. 5,227,093 to Cole et al. discloses, inter alia, an improved curable organosiloxane composition exhibiting electrical conductivity in the cured form, said composition comprising the product obtained by blending to homogeneity an organopolysiloxane containing at least two alkenyl radicals per molecule, an organohydrogensiloxane containing an average of at least two silicon-bonded hydrogen atoms per molecule, an amount of finely divided silver particles sufficient to impart electrical conductivity to said cured material, and a platinum-containing catalyst, the improvement comprising the presence on the surface of said silver particles of a coating of at least one esterified fatty acid. However, Cole et al. do not teach the specific combination of the organopolysiloxane resin and polymer of the present invention.
European Patent Application No. 0 653 463 to Mine et al. discloses (Example 1) an electrically conductive silicone rubber composition prepared by blending to homogeneity 450 parts by weight of a silver powder; 100 parts of a mixture containing 1) a dimethylvinylsiloxy-terminated dimethylpolysiloxane and 2) a silicone resin consisting essentially of (CH
3
)
3
SiO
1/2
units, (CH
2
═CH)(CH
3
)
2
SiO
1/2
units, and SiO
4/2
units; 1 part by weight of a trimethylsiloxy-terminated methylhydrogensiloxane; 10 parts of a hydrophobic fumed silica; 500 ppm, based on the total weight of the composition, of phenylbutynol; a curing catalyst; and 7 parts of an adhesion-promoting organosilicon compound. However, Mine et al. do not teach the specific concentration of the organopolysiloxane resin of the present invention.
U.S. Pat. No. 5,384,075 to Okami discloses an organopolysiloxane composition having a volume resistivity of 10
7
&OHgr;cm or below, comprising (A) an organopolysiloxane having at least two alkenyl groups in its molecule and a viscosity at 25° C. of from 100 to 200,000 cSt, (B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms in its molecule, (C) a platinum group metal catalyst, (D) an organosilicon compound which has at least one silicon-bonded hydrogen atom in its molecule and in which at least one member selected from the group consisting of epoxy group-containing organic groups and alkoxy groups is attached to a silicon atom, and (E) an electrically conductive filler. Okami also discloses an organopolysiloxane resin as an optional ingredient. However, Okami does not teach the specific concentration of the organopolysiloxane resin of the present invention.
Although silicone adhesives produced from the aforementioned compositions exhibit a wide range of electrical properties, there is a continued need for silicone adhesives having improved electrical performance.
SUMMARY OF THE INVENTION
The present inventors have discovered that a silicone composition containing an electrically conductive filler and a specific concentration of an organopolysiloxane resin cures to form an adhesive having unexpectedly superior electrical properties, contact resistance and volume resistivity. Specifically, the present invention is directed to a silicone composition, comprising:
(A) 10 to 50 parts by weight of a polydiorganosiloxane having the formula:
R
1
3
SiO(R
1
2
SiO)
n
SiR
1
3
wherein each R
1
is independently a monovalent aliphatic hydrocarbon group or a monovalent halogenated aliphatic hydrocarbon group, n has a value such that the polydiorganosiloxane has viscosity from 0.1 to 200 Pa·s at 25° C., and the polydiorganosiloxane contains an average of at least two alkenyl groups per molecule;
(B) 50 to 90 parts by weight of an organopolysiloxane resin consisting essentially of R
2
3
SiO
1/2
siloxane units and SiO
4/2
siloxane units wherein each R
2
is independently alkyl or alkenyl, the mole ratio of R
2
3
SiO
1/2
units to SiO
4/2
units is from 0.65 to 1.9, the resin contains an average of from about 3 to 30 mole percent of alkenyl groups, and the total amount of components (A) and (B) is 100 parts by weight;
(C) an organohydrogenpolysiloxane having an average of at least two silicon-bonded hydrogen atoms per molecule in an amount sufficient to cure the composition;
(D) an electrically conductive filler in an amount sufficient to impart electrical conductivity to the composition, wherein the filler comprises particles having at least an outer surface of a metal selected from the group consisting of silver, gold, platinum, palladium, and alloys thereof; and
(E) a catalytic amount of a hydrosilylation catalyst.
The present invention is also directed to an electrically conductive silicone adhesive comprising a reaction product of the above-described composition.
The present invention is further directed to a multi-part silicone composition comprising components (A) through (E) in two or more parts, provided neither component (A) nor component (B) are present with components (C) and (E) 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 properties.
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.
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
A silicone composition according to the present invention comprises:
(A) 10 to 50 parts by weight of a polydiorganosiloxane having the formula:
R
1
3
SiO(R
1
2
SiO)
n
SiR
1
3
wherein each R
1
is independently a monovalent aliphatic hydrocarbon group or a monovalent halogenated aliphatic hydrocarbon group, n has a value such that the polydiorganosiloxane has a viscosity from 0.1 to 200 Pa·s at 25° C., and the polydiorganosiloxane contains an average of at least
Bhagwagar Dorab Edul
Kleyer Don Lee
Lutz Michael Andrew
Brown Catherine U.
Dow Corning Corporation
Milco Larry A.
Moore Margaret G.
Troy Timothy J.
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