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
2000-04-13
2001-07-24
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...
C524S261000, C524S265000, C524S366000, C524S386000, C524S492000, C524S847000, C524S862000, C523S212000, C523S213000
Reexamination Certificate
active
06265480
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a silicone gel composition and more particularly to a silicone gel composition having reduced spreadabity after application that cures to form a silicone gel having excellent cold-resistant properties.
BACKGROUND OF THE INVENTION
Curing of silicone gel compositions produces silicone gels with excellent electric, heat-resistant, weather-proof, and stress-relaxation properties. Therefore, such compositions find application as sealants, cushioning agents, shock-absorbing agents, or fillers for electric and electronic components. An example of such silicone gel compositions is a composition comprising a branch-chained organopolysiloxane having a molecular terminal capped with a silicon-bonded vinyl group, a diorganopolysiloxane having both molecular terminals capped with silicon-bonded vinyl groups, an organopolysiloxane having silicon-bonded hydrogen atoms, and a platinum catalyst (see Japanese Laid-Open Patent Application [Kokai] Sho 62-181,357).
However, the aforementioned silicone gel composition does not possess thixotropic properties and has a tendency to spreading out during application. Therefore, when this composition is used for sealing some electric and electronic components, it may [accidentally] seal other electric and electronic components for which sealing is undesirable.
On the other hand, silicone gel compositions with thixotropic properties are known. Examples of such compositions are a silicone gel composition comprising an organopolysiloxane having a silicon-bonded vinyl group on a molecular terminal and a 3,3,3-trifluopropyl group in a side molecular chain, an organopolysiloxane having a silicon-bonded hydrogen atom on a molecular terminal and/or in a side molecular chain and a 3,3,3,3-trifluoropropyl group in a side molecular chain, a platinum-type catalyst, and a hydrophobized silica (see Japanese Laid-Open Patent Application [Kokai] HEI-7-324,165) and a two-liquid type silicone gel composition comprising the following components in a mixed state: an organopolysiloxane having at least two silicon-bonded alkenyl groups in one molecule, an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, an inorganic filler, an organopolysiloxane having a silicon-bonded alkoxy group, and a platinum-type catalyst (see Japanese Laid-Open Patent Application [Kokai] HEI-9-132,718).
However, after application onto the surfaces of electric or electronic devices, these silicone gel compositions with thixotropic properties spread out over the surface when cured by heat and seal the areas of the electric or electronic device which are not supposed to be sealed. Furthermore, the silicone gels obtained as a result of curing the aforementioned compositions have poor resistance to cold temperatures. For example, they rapidly loose their gel-like state at such low temperatures as −40° C. and thus lead to breakage in conductive patterns or to cracking in soldered areas.
SUMMARY OF THE INVENTION
The present invention is directed to a silicone gel composition comprising:
(A) 100 parts by weight of an organopolysiloxane comprising 80 to 98 mole % of R(CH
3
)SiO
2/2
units, 0.1 to 10.0 mole % of RSiO
3/2
units, and 0.1 to 10 mole % of R(CH
3
)
2
SiO
1/2
units, wherein R is methyl, phenyl, or alkenyl, provided that 0.25 to 4.0 mole % of the R groups in the organopolysiloxane are alkenyl;
(B) an organopolysiloxane having an average of at least 2 silicon-bonded hydrogen atoms per molecule in an amount sufficient to provide from 0.1 to 5 silicon-bonded hydrogen atoms per alkenyl group in component (A);
(C) a platinum catalyst;
(D) 0.01 to 10 parts by weight of a silica powder; and
(E) 0.01 to 5 parts by weight of a thixotropic agent selected from at least one epoxy compound, at least one polyhydric alcohol, and mixtures thereof; wherein the silicone gel composition has an apparent viscosity ratio of 2.0 to 10.0 and cures to form a silicone gel having a ¼ consistency of 10 to 200.
DETAILED DESCRIPTION OF THE INVENTION
Component (A) of the present invention is an organopolysiloxane comprising R(CH
3
)SiO
2/2
units, RSiO
3/2
units, and R(CH
3
)
2
SiO
1/2
units. Although the presence of only these three units in component (A) is sufficient, this component may contain other units in small quantities, such as HO(CH
3
)
2
SiO
1/2
units, RO(CH
3
)
2
SiO
1/2
units, HO(CH
3
)SiO
2/2
units, and RO(CH
3
)SiO
2/2
units. The organopolysiloxane can contain one or a combination of two or more of these other units. In the above formulae, R is methyl, phenyl, or alkenyl, provided that 0.25 to 4.0 mole % of all R groups in the organopolysiloxane are alkenyl. If the organopolysiloxane contains alkenyl groups in an amount below the lower limit of the aforementioned range, the composition will not cure to a sufficient degree. If, on the other hand, the organopolysiloxane contains alkenyl groups in an amount that exceeds the upper limit of the range, the cured product will loose its gel-like properties. Examples of alkenyl groups represented by R include, but are not limited to vinyl, allyl, isopropenyl, butenyl, pentenyl, and hexenyl. A vinyl group is most preferable. Furthermore, the polysiloxane should contain 80 to 98 mole % of R(CH
3
)SiO
2/2
units, 0.1 to 10.0 mole % of RSiO
3/2
units, and 0.1 to 10 mole % of R(CH
3
)
2
SiO
1/2
units. If the organopolysiloxane contains RSiO
3/2
units in an amount below the lower limit of the aforementioned range, the resulting silicone gel tends to exhibit a decrease in cold-resistant properties. If, on the other hand, the organopolysiloxane contains R(CH
3
)SiO
2/2
units in an amount that exceeds the upper limit of the range, the silicone gel composition will acquire a very high viscosity and will lose its flowability. Although there are no special limitations with regard to the viscosity of component (A), it is recommended that its viscosity be within the range of 10 to 100,000 mPa·s at 25° C.
Component (B) of the present invention is an organopolysiloxane having an average of at least two silicon-bonded hydrogen atoms per molecule. The molecular structure of component (B) may be a linear, branch-chained, a partially branch-chained linear, cyclic, net-like, or a resin-like molecular chain. Component (B) may comprise a single polymer with the aforementioned molecular structure, or a copolymer, or a mixture of the above. Furthermore, apart from the silicon-bonded hydrogen atoms, component (B) may contain other silicon-bonded groups, e.g., substituted or unsubstituted groups, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, or a similar alkyl group; cyclopentyl, cyclohexyl, or a similar cycloalkyl group; phenyl, tolyl, xylyl, or a similar aryl group; benzyl, phenethyl, or a similar aralkyl group; 3,3,3-trifluoropropyl, 3-chloropropyl, or a similar halogenated alkyl group. Among the above, the methyl and phenyl groups are preferable. Although there are no special limitations with regard to the viscosity of component (B), the composition can be prepared with improved application properties if the viscosity is within the range of 1 to 100,000 mPa·s at 25° C.
The concentration of component (B) in the composition of the present invention is sufficient to provide from 0.1 to 5 silicon-bonded hydrogen atoms per alkenyl group in component (A). If the concentration of component (B) is below the lower limit of the recommended range, the composition tends to cure incompletely. If, on the other hand, the concentration of component (B) exceeds the upper limit of the range, the cured product of the composition either cannot be obtained in a gel form or tends to exhibit a decrease in heat-resistant properties.
Component (C) of the present invention is a platinum catalyst, which is used to accelerate curing. This component can be represented by a chloroplatinic acid, an alcoholic solution of a chloroplatinic acid, an olefin complex of platinum, a 1,3-divinyltetramethyl disiloxane complex of platinum, a carbonyl complex of platinum, a dik
Enami Hiroji
Nakamura Akihiro
Dawson Robert
Dow Corning Toray Silicone Company, Ltd.
Milco Larry A.
Robertson Jeffrey B.
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