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
2001-02-07
2002-06-25
Moore, Margaret G. (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...
C524S262000, C525S477000, C427S387000, C106S287110
Reexamination Certificate
active
06410641
ABSTRACT:
This invention relates to silica-filled, cured rubber, and more particularly, to cured rubber having improved compression set and a treating method for manufacturing the same.
BACKGROUND OF THE INVENTION
The compression set of silica-filled rubber largely differs with the amount and type of silica filler, wettability of silica filler with rubber, and other factors. For the purpose of improving the compression set, investigations have heretofore been made on the amount and type of silica filler and a variety of wetters for improving the wettability of silica filler.
Prior art approaches are successful in improving the compression set to some extent, however, better compression sets are required in some applications. There is a desire to have cured rubber having an improved compression set.
SUMMARY OF THE INVENTION
It has been found that when a cured rubber made of a curable rubber composition comprising a curable organopoly-siloxane or perfluoropolyether group-containing organosilicon compound, a curing agent therefor, and a silica filler having a mean particle size of 0.001 to 10 &mgr;m is post treated by immersing it in a hydrolyzable aminosilane or amidosilane having a Si—N bond, preferably in the presence of a rubber swelling solvent, the cured rubber is significantly improved in compression set.
In a first aspect, the invention provides a cured rubber made of a curable rubber composition comprising a curable organopolysiloxane, a curing agent therefor, and a silica filler having a mean particle size of 0.001 to 10 &mgr;m, the cured rubber being post treated with a hydrolyzable aminosilane or amidosilane having a Si—N bond.
In a second aspect, the invention provides a cured rubber made of a curable rubber composition comprising a curable perfluoropolyether group-containing organosilicon compound, a curing agent therefor, and a silica filler having a mean particle size of 0.001 to 10 &mgr;m, the cured rubber being post treated with a hydrolyzable aminosilane or amidosilane having a Si—N bond.
In a third aspect, the invention provides a method for treating a cured rubber obtained by curing a curable rubber composition as set forth above. The method involves the step of immersing the cured rubber in a hydrolyzable aminosilane or amidosilane having a Si—N bond in the presence of a rubber swelling solvent.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The cured rubber of the invention is made of either (I) a silicone rubber composition comprising a curable organopolysiloxane, a curing agent therefor, and a silica filler, or (II) a fluororubber composition comprising (A) a curable perfluoropolyether group-containing organosilicon compound, (B) a curing agent therefor, and (C) a silica filler.
In the silicone rubber composition (I), the curable organopolysiloxane is preferably of the following average compositional formula.
R
n
SiO
(4−n)/2
In the formula, R, which may be the same or different, stands for substituted or unsubstituted monovalent hydrocarbon groups, preferably of 1 to 12 carbon atoms and more preferably 1 to 8 carbon atoms, for example, alkyl groups such as methyl, ethyl, propyl and butyl; cycloalkyl groups such as cyclohexyl; alkenyl groups such as vinyl, allyl, butenyl and hexenyl; aryl groups such as phenyl and tolyl; aralkyl groups such as benzyl and &bgr;-phenylpropyl; and substituted ones of the foregoing groups in which some or all of the hydrogen atoms attached to carbon atoms are replaced by halogen atoms, cyano groups or the like, such as chloromethyl, trifluoropropyl and cyanoethyl. The organo-polysiloxane should preferably have at least two alkenyl groups per molecule. Of the R groups, alkenyl groups, especially vinyl groups should preferably account for 0.001 to 10 mol %, especially 0.01 to 5 mol %. The organopolysiloxane is usually end-capped with trimethylsilyl, dimethylvinylsilyl, dimethylhydroxysilyl or trivinylsilyl groups. The letter n is a positive number from 1.98 to 2.02.
The organopolysiloxane preferably has a degree of polymerization of at least about 100, more preferably about 100 to 100,000, and most preferably about 3,000 to 20,000.
Exemplary organopolysiloxanes are given by the structural formulas below.
The curing agent used herein is selected as appropriate for the curing mechanism of silicone rubber. For the heat vulcanization type, for example, a curing method using an organic peroxide and an addition curing method using an addition reaction curing agent combined with a catalyst are useful. Typical for the room temperature vulcanization type is a condensation curing method using a condensation crosslinker and a condensation reaction promoting catalyst.
The organic peroxide curing method uses organic peroxide curing agents, for example, chlorine-free organic peroxides such as benzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butylperoxybenzoate, dicumyl peroxide, and cumyl t-butyl peroxide. Especially for atmospheric hot air vulcanization, acyl organic peroxides such as benzoyl peroxide, p-methylbenzoyl peroxide, and o-methylbenzoyl peroxide are preferred.
These organic peroxides may be used alone or in admixture of two or more. An appropriate amount of the organic peroxide added is about 0.1 to 10 parts, and especially about 0.3 to 5 parts by weight per 100 parts by weight of the organopolysiloxane. Too small an amount of the organic peroxide may provide short crosslinking whereas too large an amount may bring no further increase in cure rate.
In the addition reaction curing method, conventional addition reaction curing agents are used. Often an organo-hydrogenpolysiloxane having at least two, preferably at least three Si—H groups per molecule is used. It is typically represented by the formula:
R′
a
H
b
SiO
(4−a−b)/2
wherein R′ is as defined for R, preferably methyl, phenyl or trifluoropropyl, most preferably methyl, and letters “a” and “b” are positive numbers satisfying 0≦a<3, 0<b≦3, and 0<a+b≦3. Examples are methylhydrogenpolysiloxane and copolymers of methylhydrogenpolysiloxane with dimethyl-polysiloxane. The organohydrogenpolysiloxane used herein usually has less than about 400 silicon atoms per molecule. Typical organohydrogenpolysiloxanes are exemplified by the following formula.
The organohydrogenpolysiloxane is preferably added in such amounts that 0.5 to 3 mol of Si—H groups are available per mol of alkenyl groups in the organopolysiloxane.
For the rubber to be cured through addition reaction or hydrosilylation reaction, addition reaction promoting catalysts, typically platinum group compounds are preferably used. The platinum group compound serves to promote the addition reaction or hydrosilylation reaction of the curing agent to the polymer backbone. Since noble metal compounds are generally expensive, commercially readily available platinum compounds are often used. Examples include chloroplatinic acid, complexes of chloroplatinic acid with olefins such as ethylene, complexes of chloroplatinic acid with alcohols or vinylsiloxanes, and solid catalysts in the form of platinum on silica, alumina or carbon. To obtain more uniform cured products, a solution of chloroplatinic acid or a complex thereof in a suitable solvent is admixed with the first component prior to use.
Known catalysts in the form of platinum group compounds other than the platinum compounds include rhodium, ruthenium, iridium and palladium compounds, for example, RhCl(PPh
3
)
3
, RhCl(CO)(PPh
3
)
2
, RhCl(C
2
H
4
)
2
, Ru
3
(CO)
12
, IrCl(CO)(PPh
3
)
2
, and Pd(PPh
3
)
4
.
The amount of the catalyst used is not critical. Partially because of expensiveness, the catalyst is usually used in an amount of about 1 to 1,000 ppm, desirably about 10 to 500 ppm based on the organopolysiloxane.
For the rubber to be cured through condensation reaction, any of acetic acid, alcohol, oxime and acetone type curing agents may be selected so as to comply with a particular curing mechanism. Specifically, suitable condensation reaction curing agents are shown below
Arai Masatoshi
Sato Shin'ichi
Millen White Zelano & Branigan P.C.
Moore Margaret G.
Shin-Etsu Chemical Co., Ltd
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