Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-06-25
2003-07-15
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C525S474000, C525S479000, C524S432000, C524S433000, C524S430000, C524S403000, C524S404000, C524S437000, C524S413000, C524S588000, C528S033000, C528S024000, C528S027000, C528S032000, C528S038000
Reexamination Certificate
active
06592997
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to silicone compositions. More particularly, the present invention is related to low viscosity, curable polydiorganosiloxane compositions.
Dispensible materials that can cure and give high thermal conductivity are typically used in the electronics industry. Currently, there are two classes of cured articles used as thermally conductive sinks. Sakamoto et al., Japanese Patent No. 05117598, discuss highly filled matrices that are cured to make a pad. The pad can be cut and physically placed in an electronics device. Toya, Japanese Patent No. 02097559, discuss a filled matrix that is dispensed and cured in place. The dispensable approach requires that the material have a viscosity that is low enough such that the material can be forced through an orifice for rapid manufacture of many parts. However, the final cured product must have sufficiently high thermal conductivity.
There remains a need to find a material that has a sufficiently low viscosity such that it can be rapidly placed on a small device with high power requirements. The high power requirement needs a way to remove more heat. This requirement necessitates a thermally conductive material. Thus, dispensable, curable, and high thermally conductive materials are constantly being sought.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a polydiorganosiloxane comprising the general formula:
(R
4
)
2
R
5
SiO[(R
4
)
2
SiO]
m
[R
4
R
5
SiO]
n
Si(R
4
)
2
R
5
wherein R
5
is a polar radical with a dipole moment great than about 2 debye; R
4
comprises C
1-8
alkyl radicals, phenyl radicals, vinyl radicals or mixtures thereof; and “m”+“n” has a value sufficient to provide a polydiorganosiloxane composition with an initial viscosity in a range between about 100 centipoise and about 50,000 centipoise at 25° C.
The present invention further provides a silicone composition comprising a curable adhesive formulation which comprises
(A) a polydiorganosiloxane comprising the general formula:
(R
4
)
2
R
5
SiO[(R
4
)
2
SiO]
m
[R
4
R
5
SiO]
n
Si(R
4
)
2
R
5
wherein R
5
a polar radical with a dipole moment greater than about 2 debye; R
4
comprises C
1-8
alkyl radicals, phenyl radicals, vinyl radicals or mixtures thereof; and “m”+“n” has a value sufficient to provide a polydiorganosiloxane with an initial viscosity in a range between about 100 centipoise and about 50,000 centipoise at 25° C.;
(B) at least one thermally conductive filler; and
(C) at least one diluant
wherein the total silicone composition has a viscosity in a range between about 10,000 centipoise and about 250,000 centipoise at 25° C.
In yet a further embodiment of the present invention, there is provided a method for substantially increasing the thermal conductivity of a silicone composition comprising:
providing at least one polydiorganosiloxane wherein the polydiorganosiloxane has the general formula:
(R
4
)
2
R
5
SiO[(R
4
)
2
SiO]
m
[R
4
R
5
SiO]
n
Si(R
4
)
2
R
5
wherein R
5
a polar radical with a dipole moment great than about 2 debye; R
4
comprises C
1-8
alkyl radicals, phenyl radicals, vinyl radicals or mixtures thereof; and “m”+“n” has a value sufficient to provide a polydiorganosiloxane with an initial viscosity in a range between about 100 centipoise and about 50,000 centipoise at 25° C.; and combining into the polydiorganosiloxane at least one thermally conductive filler in a range between about 60% by weight and about 95% by weight of the total composition wherein the total silicone composition has a viscosity in a range between about 10,000 centipoise and about 250,000 centipoise at 25° C.
In yet a further embodiment of the present invention, there is provided a thermal interface material comprising:
(A) at least one polydiorganosiloxane comprising
(R
4
)
2
R
5
SiO[(R
4
)
2
SiO]
m
[R
4
R
5
SiO]
n
Si(R
4
)
2
R
5
wherein R
5
a polar radical with a dipole moment greater than about 2 debye; R
4
comprises C
1-8
alkyl radicals, phenyl radicals, vinyl radicals or mixtures thereof; and “m”+“n” has a value sufficient to provide a polydiorganosiloxane with an initial viscosity in a range between about 100 centipoise and about 50,000 centipoise at 25° C.;
(B) at least one thermally conductive filler; and
(C) at least one diluant
wherein the thermal interface material provides adhesion to at least one substrate.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that the use of a polydiorganosiloxane with polar-functional groups provides a substantially lower initial viscosity. “Substantially lower initial viscosity” as used herein refers to a polydiorganosiloxane with a viscosity in a range between about 100 centipoise (cps) and 50,000 centipoise at 25° C. When the polydiorganosiloxane of the present invention is combined with a diluant, at least one thermally conductive filler, and optionally, a cure catalyst, a total silicone composition is formed with a substantially higher thermal conductivity.
“Substantially higher thermal conductivity” as used herein refers to a composition with a thermal conductivity greater than about 1.5 Watts per meter per degree Kelvin (W/mK). The “viscosity of the total silicone composition” as used herein typically refers to a viscosity before cure of the composition in a range between about 10,000 centipoise and 250,000 centipoise and preferably, in a range between about 20,000 centipoise and about 100,000 centipoise at 25° C.
The polar-containing polydiorganosiloxane has the general formula (I),
(R
4
)
2
R
5
SiO[(R
4
)
2
SiO]
m
[R
4
R
5
SiO]
n
Si(R
4
)
2
R
5
(I)
wherein R
5
is a polar radical with a dipole moment greater than about 2 debye; R
4
comprises C
1-8
alkyl radicals, phenyl radicals, vinyl radicals, or mixtures thereof; and “m”+“n” has a value sufficient to provide an initial viscosity in a range between about 100 centipoise and about 50,000 centipoise at 25° C. and a polar content in a range between about 1% by weight and about 10% by weight of the polar-containing polydiorganosiloxane. Radicals represented by R
4
are preferably C
1-4
alkyl radicals and more preferably, methyl. Typically, the polar-containing polydiorganosiloxane is present in a range between about 0.5% by weight and about 5% by weight of the total composition, and more typically in a range between about 1% by weight and about 2% by weight of the total composition.
The polar radical is typically a cyano functional group, an epoxy functional group such as cyclohexyloxy and 7-oxabicyclo[4,1,0]hept-3-yl, and glycidoxy, an acryloxy functional group, a methacryloxy functional group, a urethane group or combinations thereof. Most typically, the polar radical is an acryloxy, methacryloxy, or epoxy functional group.
Additionally, a reactive organic diluant may be added to the silicone composition to decrease the viscosity of the composition. Examples of diluants include, but are not limited to, styrene monomers such as tert-butyl styrene (t-Bu-styrene), (meth)acrylate monomers such as methylmethacrylate and hexanedioldiacrylate, methacryloxy-containing monomers such as methacryloxypropyltrimethoxysilane, epoxy-containing monomers such as biscyclohexaneoxypropyldimethylsiloxane, and glycioxy-containing monomers such as glycidoxypropyltrimethoxysilane. It is to be understood that (meth)acrylate includes both acrylates and methacrylates. The mixture of the diluant and the polar-containing polydiorganosiloxane lowers the viscosity, which allows for higher loading of filler. The amount of filler in the silicone composition is directly proportional to the thermal conductivity. Thus, the higher the amount of filler in the silicone composition, the greater the thermal conductivity of the silicone composition.
The thermally conductive fillers in the present invention include all common thermally conductive solids. Examples of thermally conductive filler include, but are not limited to, aluminum oxide, aluminum nitride, boron nitride, diamond,
Gifford Steven Kenneth
Lewis Larry Neil
Bennett Bernadette M.
Dawson Robert
General Electric Company
Johnson Noreen C.
Peng Kuo-Liang
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