Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-06-06
2001-10-09
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S402210, C428S313500, C521S091000, C521S092000, C521S134000, C524S268000, C524S272000, C524S492000, C528S032000, C264S045900
Reexamination Certificate
active
06299952
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates to a moldable silicone rubber sponge composition, to silicone rubber sponge, and to a method for producing silicone rubber sponge.
Silicone rubber sponge, by virtue of its excellent resistance to heat and weathering and its light weight, is used for automotive components such as packings, gaskets, and O-rings; as a surface covering for the rolls used in copiers; and for a variety of sealing materials. A large number of moldable silicone rubber sponge compositions have already been disclosed. For example, Japanese Published Patent Application Sho 44-461 (461/1969) and Japanese Laid Open Patent Application Hei 7-247436 (247,436/1995) teach moldable silicone rubber sponge compositions that contain a thermally decomposable blowing agent as typified by azobisisobutyronitrile. Japanese Laid Open Patent Application Number Hei 10-36544 (36,544/1998) teaches a composition comprising hollow thermoplastic silicone resin particles blended into a liquid silicone rubber composition that evolves gas during its cure. In the case of the former two compositions, however, the decomposition products produced by the thermally decomposable blowing agent during foaming are harmful to humans and thus are problematic from the standpoint of environmental pollution. The silicone rubber sponge produced by the composition taught in Japanese Laid Open Patent Application Number Hei 10-36544 has a poor mechanical strength and hence suffers from limitations in its applications.
The inventors achieved the present invention as the result of investigations directed to solving the problems described above. More specifically, the object of this invention is to provide a moldable silicone rubber sponge composition that during foaming does not generate gas harmful to humans and that curcs to give a silicone rubber sponge that has uniform and microfine cells and a high mechanical strength.
SUMMARY OF INVENTION
A moldable silicone rubber sponge composition comprising
(A) 100 weight parts silicone rubber base compound with a Williams plasticity at 25° C. of 50 to 600 comprising
(a) 100 weight parts diorganopolysiloxane gum that contains at least 2 alkenyl groups in each molecule and
(b) 1 to 120 weight parts wet-process silica,
(B) 0.01 to 50 weight parts hollow gas-containing thermoplastic resin powder, and
(C) curing agent in an amount sufficient to effect curing of the composition. The invention is further a silicone rubber sponge afforded by the thermosetting of the above-defined moldable silicone rubber sponge composition and a method for producing the silicone rubber sponge.
DESCRIPTION OF INVENTION
A moldable silicone rubber sponge composition comprising
(A) 100 weight parts silicone rubber base compound with a Williams plasticity at 25° C. of 50 to 600 comprising
(a) 100 weight parts diorganopolysiloxane gum that contains at least 2 alkenyl groups in each molecule and
(b) 1 to 120 weight parts wet-process silica,
(B) 0.01 to 50 weight parts hollow gas-containing thermoplastic resin powder, and
(C) curing agent in an amount sufficient to effect curing of the composition. The invention is further the silicone rubber sponge afforded by the thermosetting of the above-defined moldable silicone rubber sponge composition and the method for producing the silicone rubber sponge, said method being characterized by curing the composition by heating to at least the softening point of the thermoplastic resin.
To explain the preceding in greater detail, the silicone rubber base compound (A) used in this invention is the base component of the present composition. The diorganopolysiloxane gum (a) encompassed by component (A) must contain at least 2 silicon-bonded alkenyl groups in each molecule. This alkenyl can be exemplified by vinyl, allyl, propenyl, and hexenyl. The non-alkenyl silicon-bonded organic groups can be exemplified by alkyl groups such as methyl, ethyl, and propyl; aryl groups such as phenyl and tolyl; and halogenated alkyl groups such as 3,3,3-trifluoropropyl and 3-chloropropyl. The molecular structure of component (a) can be straight chain or branch-containing straight chain. This component in general will have a degree of polymerization of 3,000 to 20,000 and will be a gum. Component (a) can be a homopolymer or copolymer or a mixture of these polymers. The units constituting component (a) can be specifically exemplified by the dimethylsiloxane unit, methylvinylsiloxane unit, methylphenylsiloxane unit, and 3,3,3-trifluoropropylmethylsiloxane unit. The molecular chain terminals of component (a) are preferably capped by a triorganosiloxy group or the hydroxyl group. The group present at the molecular chain terminal position in this component can be exemplified by trimethylsiloxy, dimethylvinylsiloxy, methylvinylhydroxysiloxy, and dimethylhydroxysiloxy. The diorganopolysiloxane gum can be exemplified by dimethylvinylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxane copolymer gums, dimethylvinylsiloxy-endblocked dimethylpolysiloxane gums, hydroxyl-endblocked dimethylsiloxane-methylvinylsiloxane copolymer gums, and methylvinylhydroxysiloxy-endblocked dimethylsiloxane-methylvinylsiloxane copolymer gums.
The wet-process silica (b) functions to promote formation of the foam cells during foaming and curing of the present composition and also functions to impart mechanical strength to the cured silicone rubber sponge. Wet-process silica denotes the microparticulate silica produced by a wet process, for example, by neutralization of sodium silicate with acid or decomposition of an alkaline earth metal silicate with acid. Wet-process silicas are already well-known as reinforcing fillers for silicone rubber compositions and are readily acquired in commerce. They are marketed, for example, under such trade names as Nipsil LP (Nippon Silica Kogyo Kabushiki Kaisha), Tokusil USA (Tokuyama Kabushiki Kaisha), and Carplex 50S (Kabushiki Kaisha Shionogi). Wet-process silicas with a BET specific surface area of at least 50 m
2
/g are preferred. The wet-process silica (b) also includes wet-process silica whose surface has been treated with, for example, methylchlorosilane, organoalkoxysilane, a silane coupling agent, or hexamethyldisilazane. The wet-process silica (b) preferably has a water content less than 4 weight %. This component is added at from 1 to 120 weight parts and preferably at from 5 to 100 weight parts, in each case per 100 weight parts component (a).
The Williams plasticity at 25° C. of component (A) must be in the range from 50 to 600 and preferably is in the range from 150 to 450. A high tackiness occurs at a Williams plasticity below 50, while a Williams plasticity in excess of 600 results in reduced extrusion moldability.
Component (A) can be exemplified by the material afforded by intermixing components (a) and (b) and subjecting the mixture to aging for an extended period of time; the material afforded by intermixing components (a) and (b) while heating; and the material afforded by intermixing components (a) and (b) while heating and applying reduced pressure thereto. During this preparative step, silanol-functional organosiloxane oligomer, silanol-functional organosilane, or hexaorganodisilazane may also be introduced and admixed as a surface-treatment agent for component (b). This organosiloxane oligomer can be exemplified by hydroxyl-endblocked dimethylsiloxane oligomers, hydroxyl-endblocked methylvinylsiloxane oligomers, hydroxyl-endblocked dimethylsiloxane-methylvinylsiloxane co-oligomers, hydroxyl-endblockcd methylphenylsiloxane oligomers, and hydroxyl-endblocked dimethylsiloxane-methylphenylsiloxane co-oligomers. The silanol-functional organosilane can be exemplified by dimethylsilanediol and diphenylsilanediol. The hexaorganodisilazane can be exemplified by hexamethyldisilazane. This component should generally be added at from 0.01 to 5 weight parts for each 100 weight parts component (a).
The curing agent (C) can be an organoperoxide or the combination of a platinum group catalyst with SiH-functional organopolysiloxane crosslinker. The organoperoxid
Hamada Mitsuo
Honma Hiroshi
Boley William F.
Dawson Robert
Dow Corning Toray Silicone Company, Ltd.
Zimmer Marc S.
LandOfFree
Moldable silicone rubber sponge composition, silicone rubber... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Moldable silicone rubber sponge composition, silicone rubber..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Moldable silicone rubber sponge composition, silicone rubber... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2562437