Low modulus one-component RTV compositions and processes
AssigneeGeneral Electric Company
InventorDale M. Beers
Life of this patent
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Abstract
A one-component alkoxy-functional RTV silicone rubber composition which is made shelf-stable by the incorporation of scavengers in the composition to absorb hydroxy groups. The present composition is made low modulus by the incorporation of various additives in the composition such as a trifunctional fluid and a linear diorganopolysiloxane fluid. There is also disclosed the use of sag control additives in the uncured composition to impart to it thixotropic properties.
Claims34
A mixture comprising
- (a) 100 parts of a silanol-terminated organopolysiloxane consisting essentially of chemically combined units of the formula ##STR31## (b) a stabilizing amount of a silane scavenger for hydroxy functional groups of the formula ##STR32## (c) 0 to 10 parts of a cross-linking silane of the formula ##STR33## (d) an effective amount of a condensation catalyst, and (e) where ingredient (b) is enoxy functional, 0.1 to 5 parts of a curing accelerator selected from the group consisting of substituted guanidines, amines and mixtures thereof, where R is selected from C.sub.(1-13) monovalent substituted and unsubstituted hydrocarbon radicals, R.sup.1 is a C.sub.(1-8) aliphatic organic radical selected from the group consisting of alkyl, alkylether, alkylester, alkylketone and alkylcyano radicals and a C.sub.(7-13) aralkyl radical, R.sup.2 is a C.sub.(1-13) monovalent substituted or unsubstituted hydrocarbon radical, X is a hydrolyzable leaving group selected from the group consisting of amido, amino, carbamato, enoxy, imidato, isocyanato, oximato, thioisocyanato and ureido radicals, and a is an integer equal to 1 or 2, b is a whole number equal to 0 or 1, and
- the sum of a+b is equal to 1 or 2;
- and from 2 to 20 parts by weight per 100 parts by weight of said organopolysiloxane of a first plasticizer fluid siloxane containing a high degree of trifunctionality and mixtures of tri- and tetra-functionality comprising
- (i) from 5 to 60 mole percent of monoalkylsiloxy units, siloxy units or a mixture of such units;
- (ii) from 1 to 6 mole percent of trialkylsiloxy units and
- (iii) from 34 to 94 mole percent of dialkyl siloxy units, said polysiloxane containing from about 0.1 to 2% by weight of silicon-bonded hydroxyl groups.
In the method of making a substantially acid-free room temperature vulcanizable organopolysiloxane composition under substantially anhydrous conditions utilizing an effective amount of a condensation catalyst with a silanol-terminated organopolysiloxane and a polyalkoxysilane cross-linking agent, the improvement which comprises adding to the silanol-terminated organopolysiloxane a stabilizing amount of a polyalkoxysilane which is both a scavenger for hydroxy functional groups and a cross-linking agent of the formula ##STR38## where R.sup.1 is a C.sub.(1-8) aliphatic organic radical selected from the group consisting of alkyl, alkylether, alkylester, alkylketone and alkylcyano radicals, or a C.sub.(7-13) aralkyl radical, R.sup.2 is a C.sub.(1-13) monovalent substituted or unsubstituted hydrocarbon radical, X is a hydrolyzable leaving group selected from the group consisting of amido, amino, carbamato, enoxy, imidato, ixocyanato, oximato, thioisocyanato and ureido radicals, and a is an integer equal to 1 or 2, b is an integer equal to 0 or 1, and the sum of a+b is equal to 1 or 2, and thereafter adding an effective amount of a condensation catalyst, whereby improved stability is achieved in the resulting room temperature vulcanizable organopolysiloxane composition, and where X is enoxy, adding before or with the scavenger an effective amount of a curing accelerator selected from the group consisting of substituted guanidines, amines and mixtures thereof and from 2 to 20 parts by weight per 100 parts by weight of said organopolysiloxane of a first plasticizer fluid polysiloxane containing a high degree of trifunctionality and mixtures of tri- and tetra-functionality and comprising
- (i) from 5 to 60 mole percent of monoalkylsiloxy, siloxy units or a mixture of such units;
- (ii) from 1 to 6 mole percent of trialkylsiloxy units and
- (iii) from 34 to 94 mole percent of dialkyl siloxy units, said polysiloxane containing from about 0.1 to about 2% by weight of silicone-bonded hydroxyl groups.
Dependencies are inferred from the claim text.