Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2002-08-23
2004-12-14
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S025000, C524S379000, C524S385000, C524S386000, C524S387000, C524S439000, C524S440000, C524S588000
Reexamination Certificate
active
06831145
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a silicone composition and more particularly to a silicone composition containing an electrically conductive filler and a hydroxy-functional organic compound. The present invention also relates to an electrically conductive, cured silicone product formed from the silicone composition.
BACKGROUND OF THE INVENTION
Silicone compositions containing an epoxy-functional organopolysiloxane, curing agent, and electrically conductive filler are known in the art. For example, Japanese Patent Application (Kokai) 63-161014 to Akinobu et al. discloses an electrically conductive resin paste consisting of (A) silver powder, (B) an epoxy resin, (C) a hardening agent, and (D) a dimethylsiloxane compound containing epoxy, amino, or alcohol groups.
Japanese Patent Application (Kokai) 30-43482 to Oura et al. discloses a conductive adhesive containing (A) an epoxy-modified silicone compound obtained by reaction of a carboxyl-capped dimethylsiloxane and an epoxy resin having at least 2 epoxy groups per molecule, wherein the dimethylsiloxane has the general formula:
wherein R is a divalent organic group and n is an integer from 1 to 500; (B) a curing agent; and (C) a conductive filler.
WO9002768 to Ohura et al. discloses an electrically conductive adhesive comprising a silicone-epoxy resin having the formula:
wherein R
1
, R
2
, R
3
, and R
4
are selected from alkyl having 1 to 4 carbon atoms, alkenyl having 2 to 4 carbon atoms, and phenyl; R
5
and R
6
are selected from hydrogen and methoxy; and n is from 1 to 100; a hardening agent; and an electrically conductive filler.
Although the aforementioned silicone compositions cure to form products exhibiting a range of electrical properties, there is a persistent need for silicone products having improved conductivity.
SUMMARY OF THE INVENTION
The present inventors have discovered that a curable silicone composition containing an electrically conductive filler and a hydroxy-functional organic compound cures to form a silicone product having unexpectedly superior electrical conductivity. Specifically, the present invention is directed to a silicone composition for preparing a cured silicone product, the composition prepared by mixing:
(A) an organopolysiloxane containing an average of at least two epoxy-functional organic groups per molecule;
(B) a curing agent in an amount sufficient to cure the composition, provided the curing agent is free of phenolic hydroxy groups;
(C) an electrically conductive filler in an amount sufficient to impart electrical conductivity to the silicone product, wherein the filler comprises particles having at least an outer surface of a metal selected from silver, gold, platinum, palladium, and alloys thereof; and
(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.
The present invention is also directed to a cured silicone product 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 (D) in two or more parts, provided component (A) and component (D) 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 product 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 has numerous uses, including the manufacture of electronic, construction, appliance, and aerospace products. Moreover, the silicone composition of the present invention is useful for preparing an electrically conductive, cured silicone product, such as an electrically conductive coating, adhesive, or gasket.
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 silicone composition for preparing a cured silicone product, the composition prepared by mixing:
(A) an organopolysiloxane containing an average of at least two epoxy-functional organic groups per molecule;
(B) a curing agent in an amount sufficient to cure the composition, provided the curing agent is free of phenolic hydroxy groups;
(C) an electrically conductive filler in an amount sufficient to impart electrical conductivity to the silicone product, wherein the filler comprises particles having at least an outer surface of a metal selected from silver, gold, platinum, palladium, and alloys thereof; and
(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.
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 epoxy-functional organic groups per molecule. The structure of the organopolysiloxane can be linear, branched, or resinous. The organopolysiloxane can be a homopolymer or a copolymer. The epoxy-functional organic groups typically have from 2 to about 10 carbon atoms and are exemplified by, but not limited to, vinyl, allyl, butenyl, and hexenyl. The epoxy-functional organic groups in the polydiorganosiloxane may be located at terminal, pendant, or both terminal and pendant positions. Examples of epoxy-functional organic groups include, but are not limited to, 2-glycidoxyethyl, 3-glycidoxypropyl, 4-glycidoxybutyl, 2-(3,4-epoxycyclohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl, 2,3-epoxypropyl, 3,4-epoxybutyl, and 4,5-epoxypentyl.
The remaining 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 cyclohexyl; 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 0.5 to 100 Pa·s, and more preferably from 2 to 50 Pa·s.
Organopolysiloxanes useful in the silicone composition of the present invention include a linear organopolysiloxane having the general formula R
2
R
1
2
SiO(R
1
R
2
SiO)
m
(R
1
R
2
SiO)
n
SiR
1
2
R
2
wherein each R
1
is independently selected from monovalent hydrocarbon and monovalent halogenated hydrocarbon groups, as defined and exemplified above; each R
2
is independently an epoxy-functional organic group or R
1
; m is 0 or a positive integer; n is 0 or a positive integer; the sum of m and n is such that the organopolysiloxane has a viscosity of from 0.05 to 200 Pa·s at 25° C.; and the organopolysiloxane contains an average of at least two epoxy-functional organic groups per molecule. Examples of linear organopolysiloxanes include, but are not limited to, organopolysiloxanes having the following formulae: R
3
Me
2
SiO(Me
2
SiO)
p
SiMe
2
R
3
, R
3
Me
2
SiO(Me
2
SiO)
0.25p
(MePhSiO)
0.75p
SiMe
2
R
3
, R
3
Me
2
SiO(Me
2
SiO)
0.95p
(Ph
2
SiO)
0.05p
SiMe
2
R
3
, R
3
Me
2
SiO(Me
2
SiO)
0.98p
(RMeSiO)
0.02p
SiMe
2
R
3
, and R
3
Me
2
SiO(Me
2
Kleyer Don Lee
Lutz Michael Andrew
Brown Catherine U.
Dow Corning Corporation
Moore Margaret G.
Zimmer Marc S
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