Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-04-05
2002-02-12
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...
C521S064000, C521S065000, C521S079000, C521S081000, C521S134000, C521S154000
Reexamination Certificate
active
06346556
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a silicone rubber sponge composition, to a silicone rubber sponge, and to a process for production thereof. More particularly, it relates to a silicone rubber sponge composition that gives a silicone rubber sponge having fine, uniform cells, to a silicone rubber sponge, and to a process for production thereof.
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; sheath materials for rollers in copiers; gaskets for construction use such as joint fillers and sealers; and various sealing and cushioning applications. A number of silicone rubber sponge compositions have been proposed to date. Patent Publication 44-461 and Patent Application Laying Open 7-247436, for example, teach heat curing silicone rubber sponge compositions containing thermally decomposable organic blowing agents such as azobisisobutyronitrile. However, these compositions give rise to harmful decomposition products during sponge production and thus pose an environmental problem. Patent Publication 7-122000 proposes a silicone rubber sponge composition comprising an oil-in water type emulsion consisting of dimethylpolysiloxane, an emulsifier, water, and a thickener. However, this composition does not readily give silicone rubber sponges with uniform cells. Further, since oil-in water type emulsions and silicone rubber compositions are basically immiscible, the process of evenly dispersing the silicone rubber composition throughout the silicone rubber composition is time consuming and throughput is poor.
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 thereof.
SUMMARY OF THE INVENTION
The present invention relates to a silicone rubber sponge composition, a silicone rubber sponge, and a process for production thereof. 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 at 25° C. of 1,000,000 mPa·s or above, (B) 1 to 400 parts by weight inorganic filler, (C) 0.01 to 50 parts by weight hollow thermoplastic resin particles, (D) 0.01 to 10 parts by weight water-in-oil emulsion with silicone oil as an oil phase, 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 at 25° C. of 1,000,000 mPa·s or above,
(B) 1 to 400 parts by weight inorganic filler,
(C) 0.01 to 50 parts by weight hollow thermoplastic resin particles,
(D) 0.01 to 10 parts by weight water-in-oil emulsion with silicone oil as an oil phase, 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 components (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 present 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 mnPa·s or above. Component (A) is a gum at normal temperature and has a Williams plasticity of 50 or greater, preferably 100 or greater, and more preferably 120 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 the principle component in organic peroxide-curing millable compositions can be used for component (A). Component (A) consists of an organopolysiloxane gum described by 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 an 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. 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. Endgroups present on the molecular chain terminals of component (A) include, for example, trimethylsiloxy, dimethylvinylsiloxy, methylvinylhydroxysiloxy, and dimethylhydroxysiloxy groups. Examples of such organopolysiloxane gums include methylvinylpolysiloxane gum endblocked at both terminals with trimethylsiloxy groups, a copolymer gum of methylvinylsiloxane and dimethylsiloxane endblocked at both terminals with trimethylsiloxy groups, dimethylpolysiloxane gum endblocked at both terminals with dimethylvinylsiloxy groups, a copolymer gum of methylvinylsiloxane and dimethylsiloxane endblocked at both terminals with dimethylvinylsiloxy groups, a copolymer gum of methylvinylsiloxane and dirnethylsiloxane endblocked at both terminals with dimethylhydroxysiloxy groups, a copolymer gum of methylphenylsiloxane, methylvinylsiloxane and dimethylsiloxane 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 rendered hydrophobic through treatment 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 preferred range is 1 to 400 parts by weight per 100 parts by weight of component (A), preferably 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 the cell distribution uniform. An exemplary component (C) is a material consisting of thermoplastic resin shells having an inert gas enclosed therein. Thermoplastic resins include sil
Baba Katsuya
Nakamura Akito
Suto Manabu
Cesare James L. De
Dow Corning Toray Silicone Company, Ltd.
Foelak Morton
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