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
2001-11-27
2003-10-28
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...
C524S404000, C524S428000, C524S430000, C524S431000, C524S432000, C524S439000, C524S440000, C528S025000, C528S026000, C528S027000, C528S032000, C528S038000
Reexamination Certificate
active
06639008
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.
Dispensable 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 electronic device. Toya, Japanese Patent No. 02097559, discusses 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 a 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 silicone composition comprising a curable adhesive formulation which comprises
(A) a functionalized polydiorganosiloxane having the general formula:
(R
1
)
3-p
R
2
p
SiO[(R
1
)
2
SiO]
m
[R
1
R
2
SiO]
n
Si(R
1
)
3-q
R
2
q
wherein R
2
is independently at each occurrence vinylcyclohexeneoxy, silane, epoxy, glycidoxy, acryloxy, imide, urethane, vinyl, or combinations thereof; R
1
is independently at each occurrence a C
1-8
alkyl radical, phenyl radical, vinyl radical, or combination thereof; “p” is 0 or 1; “q” is 0 or 1; “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 reactive diluant;
(C) at least one cure catalyst; and
(D) at least one thermally conductive filler;
wherein the total silicone composition has a viscosity in a range between about 10,000 centipoise and about 250,000 centipoise at 25° C. before cure.
The present invention further provides a method for increasing the thermal conductivity of a silicone composition comprising:
(A) providing at least one functionalized polydiorganosiloxane having the general formula:
(R
1
)
3-p
R
2
p
SiO[(R
1
)
2
SiO]
m
[R
1
R
2
SiO]
n
Si(R
1
)
3-q
R
2
q
wherein R
2
is independently at each occurrence vinylcyclohexeneoxy, silane, epoxy, glycidoxy, acryloxy, imide, urethane, vinyl, or combinations thereof; R
1
is independently at each occurrence a C
1-8
alkyl radical, phenyl radical, vinyl radical, or combination thereof; “p” is 0 or 1; “q” is 0 or 1; “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.;
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 silicone composition;
combining into the polydiorganosiloxane at least one diluant; and
combining into the polydiorganosiloxane at least one cure catalyst wherein the total silicone composition has a viscosity in a range between about 10,000 centipoise and about 250,000 centipoise at 25° C. before cure.
In yet a further embodiment of the present invention, there is provided a thermal interface material comprising:
(A) at least one polydiorganosiloxane having the general formula:
(R
1
)
3-p
R
2
p
SiO[(R
1
)
2
SiO]
m
[R
1
R
2
SiO]
n
Si(R
1
)
3-q
R
2
q
wherein R
2
is independently at each occurrence vinylcyclohexeneoxy, silane, epoxy, glycidoxy, acryloxy, imide, urethane, vinyl, or combinations thereof; R
1
is independently at each occurrence a C
1-8
alkyl radical, phenyl radical, vinyl radical, or combination thereof; “p” is 0 or 1; “q” is 0 or 1; “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 reactive diluant;
(C) at least one cure catalyst; and
(D) at least one thermally conductive filler;
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 at least one functionalized polydiorganosiloxane, at least one reactive diluant, at least one cure catalyst, and at least one thermally conductive filler provides a formulation with a low viscosity of the total silicone composition before cure and whose cured parts have a high thermal conductivity. “High thermal conductivity” as used herein refers to a cured total silicone composition with a thermal conductivity greater than about 1.5 Watts per meter per degree Kelvin (W/mK). “Low viscosity of the total silicone composition before cure” typically refers to a viscosity of the composition in a range between about 10,000 centipoise and about 250,000 centipoise and preferably, in a range between about 20,000 centipoise and about 100,000 centipoise at 25° C. before the silicone composition is cured. “Cured” as used herein refers to a total silicone composition with reactive groups wherein in a range between about 50% and about 100% of the reactive groups have reacted.
The functionalized polydiorganosiloxane has the general formula (I),
(R
1
)
3-p
R
2
p
SiO[(R
1
)
2
SiO]
m
[R
1
R
2
SiO]
n
Si(R
1
)
3-q
R
2
q
(I)
wherein R
2
is independently at each occurrence vinylcyclohexeneoxy, silane, epoxy, glycidoxy, acryloxy, imide, urethane, vinyl, or combination thereof; R
1
is independently at each occurrence a C
1-8
alkyl radical, phenyl radical, vinyl radical, or combination thereof; “p” is 0 or 1; “q” is 0 or 1; “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 a functional content in a range between about 1% by weight and about 10% by weight of the functionalized polydiorganosiloxane. Radicals represented by R
1
are preferably C
1-4
alkyl radicals and more preferably, methyl. Typically, the functionalized polydiorganosiloxane is present in a range between about 0.5% by weight and about 5% by weight of the total silicone composition, and more typically in a range between about 1% by weight and about 2% by weight of the total silicone composition.
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 biscyclohexaneoxyethylenetetramethylsiloxane, glycidoxy-containing monomers such as glycidoxypropyltrimethoxysilane, hydride-stopped polydimethylsiloxanes, and vinyl ethers. It is to be understood that (meth)acrylate includes both acrylates and methacrylates. Vinyl ethers include mono-, di-, and poly-vinyl ethers containing carbon atoms in a range between about 2 and about 20. The preferred reactive diluants are methacryloxypropyltrimethoxysilane and vinyl ethers. The mixture of the diluant and the functionalized polydiorganosiloxane lowers the viscosity, which allows for higher loading of thermally conductive filler. The amount of thermally conductive filler in the silicone composition is directly proportional to the thermal conductivity. Thus, the higher the amount of thermally conductive filler in the silicone composition, the greater the thermal conductivity of the silicone composition.
The
Gifford Steven Kennth
Lewis Larry Neil
Rubinsztajn Slawomir
Bennett Bernadette M.
Dawson Robert
Zimmer Marc S
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