Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-03-29
2001-10-09
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S134000, C521S154000, C521S079000, C521S081000
Reexamination Certificate
active
06300383
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a silicone rubber sponge composition, a silicone rubber sponge, and a process for making the sponge. More particularly, it relates to a silicone rubber sponge composition that gives a silicone rubber sponge having fine, uniform cells, a silicone rubber sponge, and a process for making the silicone rubber sponge.
BACKGROUND OF THE INVENTION
Due to their outstanding heat and weather resistance and light weight, silicone rubber sponges are used for automotive parts, such as packings, gaskets, and O-rings; as sheath materials for rollers in copiers, and as sealing materials of various kinds. A number of silicone rubber sponge compositions have been proposed to date. Patent Publication (Kokoku) 44-461 and Unexamined Patent Application Laying Open 7-247436, for example, teach silicone rubber sponge compositions containing thermally decomposable organic blowing agents such as azobisisobutyronitrile. However, silicone rubber sponges produced from these compositions tend to have coarse cells, making it difficult to consistently produce silicone rubber sponges having fine, uniform cells. Accordingly, there is a need for a silicone rubber sponge composition having finer cells.
It is an object of the present invention to provide a silicone rubber sponge composition that gives a silicone rubber sponge having fine, uniform cells, a silicone rubber sponge, and a process for production of the sponge.
SUMMARY OF THE INVENTION
The present invention relates to a silicone rubber sponge composition, a silicone rubber sponge, and a process for making the silicone rubber sponge. The silicone rubber sponge composition comprises (A) 100 parts by weight organopolysiloxane gum described by average structural unit R
a
SiO
(4−a)/2
, where R is a monovalent hydrocarbon group or haloalkyl and a is 1.8 to 2.3 and having a viscosity of 1,000,000 mPa·s or above at 25° C., (B) 1 to 400 parts by weight inorganic filler, (C) 0.01 to 50 parts by weight hollow thermoplastic resin particles, (D) 0.1 to 10 parts by weight liquid compound with a boiling point above room temperature, and (E) a curing agent in an amount sufficient to cure the composition.
DESCRIPTION OF THE INVENTION
A first embodiment of the present invention is a silicone rubber sponge composition comprising
(A) 100 parts by weight organopolysiloxane gum described by average structural unit R
a
SiO
(4−a)/2
, where R is a monovalent hydrocarbon group or haloalkyl and a is 1.8 to 2.3 and having a viscosity of 1,000,000 mPa·s or above at 25° C.,
(B) 1 to 400 parts by weight inorganic filler,
(C) 0.01 to 50 parts by weight hollow thermoplastic resin particles,
(D) 0.1 to 10 parts by weight liquid compound with a boiling point above room temperature, and
(E) a curing agent in an amount sufficient to cure the composition.
A second embodiment of the present invention is a silicone rubber sponge produced by heat curing of the silicone rubber sponge composition. A third embodiment of the present invention is a process for production of a silicone rubber sponge composition comprising the steps of combining components (A) and (B) to produce a silicone rubber base compound, and incorporating component s (C), (D), and (E) into the silicone rubber base compound. A fourth embodiment of the present invention is a process for production of a silicone rubber sponge comprising the step of curing the composition by heating to a temperature equal to or above the softening point of the thermoplastic resin of component (C).
Component (A) is the principal component of the present composition. It must have a viscosity at 25° C. of 1,000,000 mPa·s or above, and preferably 5,000,000 mPa·s or above. Since component (A) is a gum, it will have Williams plasticity of 50 or greater, and preferably 100 or greater. The degree of polymerization of component (A) is typically 3,000 to 20,000, with the weight-average molecular weight being 20×10
4
or above. The class of compounds known as organopolysiloxane gums used as principals in organic peroxide-curing millable compositions can be used for component (A). Component (A) consists of an organopolysiloxane gum described by the following average unit formula R
a
SiO
(4−a)/2
, where R is a monovalent hydrocarbon group or haloalkyl and a is 1.8 to 2.3. Monovalent hydrocarbon groups represented by R include alkyls such as methyl, ethyl, and propyl; alkenyls such as vinyl and allyl; cycloalkyls such as cyclohexyl; aralkyls such as &bgr;-phenylethyl; and aryls such as phenyl and tolyl. Haloalkyl groups represented by R include 3,3,3-trifluoropropyl and 3-chloropropyl.
Where the curing agent consists of either an alkyl peroxide or a platinum catalyst used concomitantly with a organopolysiloxane containing silicon-bonded hydrogen atoms, the organopolysiloxane gum molecule must have at least two silicon-bonded alkenyls. Alkenyl here refers, for example, to vinyl, ally, propenyl, and hexenyl groups. Silicon-bonded organic groups other than alkenyl include alkyls such as methyl, ethyl, and propyl; aryls such as phenyl and tolyl; and haloalkyls such as 3,3,3-trifluoropropyl and 3-chloropropyl. The molecular structure of component (A) may be linear or linear containing branches. Component (A) may be a homopolymer, copolymer, or a blend of polymers. Specific examples of the siloxane units of component (A) are dimethylsiloxane, methylvinylsiloxane, methylphenylsiloxane, and (3,3,3-trifluoropropyl)methylsiloxane units. Examples of molecular chain terminal endgroups of component (A) are trimethylsiloxy, dimethylvinylsiloxy, methylvinylhydroxysiloxy, and dimethylhydroxysiloxy groups. Examples of such organopolysiloxane gums include methylvinylpolysiloxane gum that is endblocked at both terminals with trimethylsiloxy groups, a copolymer gum of methylvinylsiloxane and dimethylsiloxane that is endblocked at both terminals with trimethylsiloxy groups, dimethylpolysiloxane gum that is endblocked at both terminals with dimethylvinylsiloxy groups, a copolymer gum of methylvinylsiloxane and dimethylsiloxane that is endblocked at both terminals with dimethylvinylsiloxy groups, a copolymer gum of methylvinylsiloxane and dimethylsiloxane that is endblocked at both terminals with dimethylhydroxysiloxy groups, a copolymer gum of methylphenylsiloxane, methylvinylsiloxane, and dimethylsiloxane that is endblocked at both terminals with methylvinylhydroxysiloxy groups, and a copolymer gum of (3,3,3-trifluoropropyl)methylsiloxane, methylvinylsiloxane, and dimethylsiloxane that is endblocked at both terminals with methylvinylhydroxysiloxy groups.
Examples of the inorganic filler of component (B) are reinforcing fillers such as finely divided silica (e.g. dry process silica or wet process silica) and finely divided silica whose surfaces have been treated with an organochlorosilane, organoalkoxysilane, hexaorganodisilazane, organosiloxane oligomer, or the like; and semi-reinforcing or extending fillers such as powdered quartz, diatomaceous earth, heavy calcium carbonate, light calcium carbonate, magnesium oxide, calcium silicate, mica, aluminum oxide, aluminum hydroxide, carbon black, and the like. In excessively large amounts, component (B) is difficult to incorporate into component (A) and accordingly the range 1 to 400 parts by weight per 100 parts by weight of component (A) is preferred, preferably using from 1 to 100 parts by weight for the reinforcing fillers and from 1 to 150 parts by weight for the semi-reinforcing or extending fillers.
The hollow thermoplastic resin particles used for component (C) serve as nuclei for cell formation, and also make cell distribution uniform. An exemplary component (C) is a material consisting of thermoplastic resin shells having an inert gas enclosed therein. Thermoplastic resins include silicone resins, acrylic resins, and polycarbonate resins. In preferred practice, the thermoplastic resin will have a softening point of from 40 to 200° C., and especially 60 to 180° C. Inert gases include air, nitrogen gas, helium gas, and the like. Component (C) average
Baba Katsuya
Honma Hiroshi
Nakamura Akito
Cesare James L. De
Dow Corning Toray Silicone Company, Ltd.
Foelak Morton
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