Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2000-09-06
2001-06-26
Wu, David W. (Department: 1713)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S046600, C528S015000, C528S031000, C528S032000
Reexamination Certificate
active
06251327
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to organosiloxane compositions that are curable to form organosiloxane elastomers. More particularly this invention relates to organosiloxane compositions that are curable to form organosiloxane elastomers that exhibit extended moldlife.
2. Description of the Related Art
The prior art also describes organosiloxane compositions that cure to yield crosslinked elastomers by the reaction of a polyorganosiloxanes containing at least two alkenyl groups per molecule with organosilicon compounds containing at least three silicon-bonded hydrogen atoms per molecule as the crosslinker. This reaction is typically catalyzed by platinum containing compounds.
In U.S. Pat. No. 4,879,339, which issued on Nov. 7, 1989, Yoshino et al. disclose a composition comprising a vinyl containing organopolysiloxane; an organohydrogenpolysiloxane; a platinum compound; an aliphatic hydrocarbon; and an antioxidant.
In U.S. Pat. No. 4,654,408, which issued on Mar. 31, 1987, Okinoshima discloses a composition comprising vinyl containing organosilicon compound; a platinum compound; and an antioxidant.
Yet another reference is European Patent Publication 0 531 009 A1, which published on Mar. 10, 1993 in the name of Judith stein, in which there is disclosed a silicone release composition comprising a polydiorgansiloxane containing unsaturated groups, a crosslinking agent containing Si-H groups and a hydrosilation catalyst, which release composition also contains at least one free radical inhibitor to prevent “acrylic weld” to acrylic surfaces.
The compositions of the present invention contain a free radical scavenger for radicals that participate in the free radical polymerization of styrene monomers. These free radical scavengers may be antioxidants. The present inventors discovered compositions containing selected free radical scavengers yield elastomers having unexpectedly improved moldlife.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that adding certain free radical scavengers to hydrosilylation reaction curable organosiloxane compositions extends the mold life of the resulting elastomers.
The present invention relates to a hydrosilylation reaction curable organosiloxane composition comprising:
A) an alkenyl-containing polyorganosiloxane having an average of at least two silicon-bonded alkenyl groups per molecule;
B) an organohydrogensiloxane having an average of at least two silicon-bonded hydrogen atoms per molecule;
C) a hydrosilylation reaction catalyst, in an amount sufficient to accelerate the curing of the composition; and
D) a free radical scavenger for radicals that participate in the free radical polymerization of styrene; wherein the sum of the average number of silicon-bonded alkenyl groups in Component (A) and the average number of silicon-bonded hydrogen atoms per molecule in Component (B) is great than 4.
The present invention also relates to a method of increasing the moldlife of a silicone elastomer mold, said method comprising the steps of:
I. preparing a hydrosilylation reaction curable organosiloxane composition containing a free radical scavenger and,
curing the curable organosiloxane composition to form a silicone elastomer mold having an increased moldlife.
This invention also deals with a method of molding polyester parts from a mold having enhanced mold life, and finally, this invention deals with molds prepared from silicone Elastomers, wherein the molds have enhanced moldlife.
REFERENCES:
patent: 3419593 (1968-12-01), Willing
patent: 4654408 (1987-03-01), Okinoshima
patent: 4879339 (1989-11-01), Yoshino et al.
patent: 5118735 (1992-06-01), Burnier
patent: 5519082 (1996-05-01), Yoshino
patent: 0 531 009 A1 (1993-03-01), None
patent: 0 787 766 A1 (1997-08-01), None
Brandrup et al., “Polymer Handbook”, 3rd Ed., pp. 11-67 to 11-142.
Brandrup et al., “Polymer Handbook”, 2nd Ed., p. 11-80.
Bentz Peter Otto
McMahon Daniel Francis
Nakahara Hideki
Scott Edward Burton
Dow Corning Asia Ltd.
Lu Caixia
McKellar Robert L.
Milco Larry A.
Wu David W.
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