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
2000-07-20
2003-03-18
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...
C252S514000, C524S379000, C524S398000, C524S266000, C524S268000, C524S439000, C524S440000, C524S588000, C524S858000, C528S018000, C528S034000, C528S038000
Reexamination Certificate
active
06534581
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a curable silicone composition for preparing a silicone adhesive and more particularly to a condensation-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.
Condensation-curable silicone compositions comprising an organopolysiloxane containing silicon-bonded hydroxy groups, a crosslinking agent, and a curing catalyst are known in the art. Illustrative of such compositions are U.S. Pat. Nos. 3,769,064; 2,902,467; 2,843,555; 2,927,907; 3,065,194; 3,070,559; 3,127,363; 3,070,566; 3,305,502; 3,575,917; 3,696,090; 3,702,835; 3,888,815; 3,933,729; 4,388,433; 4,490,500; 4,547,529; 4,962,152; and European Patent Application No. 0816437A2. However, the aforementioned references do not teach the electrically conductive filler and the hydroxy-functional organic compound of the present invention.
Furthermore, Japanese Laid-Open Patent Application (Kokai) No. 8-302196 to Fujiki et al. discloses a silicone composition comprising a silanol group-containing organopolysiloxane, a hydrolysable organosilicon compound, a conductive filler composed of silver particles or silver-covered particles surface-treated with a silicone compound, and a curing catalyst. However, the preceding patent application does not teach the hydroxy-functional organic compound of the present invention.
SUMMARY OF THE INVENTION
The present inventors have discovered that a condensation-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 prepared by mixing:
(A) an organopolysiloxane containing an average of at least two silicon-bonded hydroxy groups per molecule;
(B) a crosslinking agent in an amount sufficient to cure the composition; wherein the agent is selected from (i) at least one silane having the formula R
2
n
SiX
4−n
wherein each R
2
is independently selected from monovalent hydrocarbon and monovalent halogenated hydrocarbon groups having from 1 to about 8 carbon atoms, n is 0 or 1, and X is —OR
2
or —OCH
2
CH
2
OR
2
; (ii) a partial hydrolyzate of (i), and (iii) mixtures comprising (i) and (ii);
(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 the group consisting of 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 does not substantially inhibit cure of the composition; and
(E) a catalytic amount of a condensation catalyst comprising a metal salt of a carboxylic acid.
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 neither component (A) nor component (D), are present with components (B) 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 conductivity as evidenced by low contact resistance and/or volume resistivity.
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 prepared by mixing:
(A) an organopolysiloxane containing an average of at least two silicon-bonded hydroxy groups per molecule;
(B) a crosslinking agent in an amount sufficient to cure the composition; wherein the agent is selected from (i) at least one silane having the formula R
2
n
SiX
4−n
wherein each R
2
is independently selected from monovalent hydrocarbon and monovalent halogenated hydrocarbon groups having from 1 to about 8 carbon atoms, n is 0 or 1, and X is —OR
2
or —OCH
2
CH
2
OR
2
; (ii) a partial hydrolyzate of (i), and (iii) mixtures comprising (i) and (ii);
(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 the group consisting of 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 does not substantially inhibit cure of the composition; and
(E) a catalytic amount of a condensation catalyst comprising a metal salt of a carboxylic acid.
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 hydroxy groups (silanol groups) per molecule. The structure of the organopolysiloxane can be linear, branched, or resinous. The organopolysiloxane can be a homopolymer or a copolymer. The silicon-bonded organic groups in the organopolysiloxane are independently selected from monovalent hydrocarbon and monovalent halogenated hydrocarbon groups. 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 cylcohexyl; alkenyl such as vinyl, allyl, butenyl, and hexenyl; 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 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
2
to 100 Pa·s, and more preferably from 5 to 50 Pa·s.
A preferred organopolysiloxane according to the present invention is a hydroxy-terminated polydiorganosiloxane having the general formula HOR
1
2
SiO(R
1
2
SiO)
m
SiR
1
2
OH wherein each R
1
is independently selected from monovalent hydrocarbon and monovalent halogenated hydrocarbon groups, as defined above; and subscript m has a value such that the viscosity of the polydiorganosiloxane at 25° C. is from 0.05 to 200 Pa·s. Preferably, R
1
is methyl.
Examples of organopolysiloxanes
Kleyer Don Lee
Lutz Michael Andrew
Brown Catherine U.
Dawson Robert
Dow Corning Corporation
Milco Larry A.
Zimmer Marc S
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