Organopolysiloxane elastomers admixed with fillers subjected to mechanical stress

Claim 2

AN ORGANOPOLYSILOXANE COMPOSITION CAPABLE OF BEING VULCANIZED TO AN ELASTOMER CONTAINING A DIORGANOPOLYSILOXANE HAVING A VISCOSITY OF AT LAST 10**6 CST AT 250*C. IN WHICH THE ORGANIC GROUPS SELECTED FROM THE CLASS CONSISTING OF MONOVALENT HYDROCARBON RADICALS, HALOGENATED MONOVALENT HYDROCARBON RADICALS AND CYANOALKYL RADICALS, AN AGENT CAPABLE OF FORMING FREE RADICALS SELECTED FROM THE CLASS CONSISTING OF PEROXIDES, AZO COMPOUNDS AND HIGH ENERGY RADIATION AND A FILLER IN WHICH AT LEAST A PORTION OF SAID FILLER IS FINELY DIVID SILICON DIOXIDE PARTICLES HAVING A SURFACE AREA OF AT LEAST 50 M2/G. WHICH HAVE BEEN SUBJECTED TO MECHANICAL STRESS AND REACTED WITH AN ORGANSILICON COMPOUND TO INCREASE THE BULK WEIGHT OF THE SILICON DIOXIDE TO A RANGE OF FROM ABOUT 120 TO ABOUT 500 GRAMS PER LITER, SAID ORGANSILICON COMPOUND HAVING THE FORMULA (R2SI)AZ'', WHREREIN R IS SELECTED FROM THE CLASS CONSISTING OF MONOVALENT HYDROCARBON RADICALS, HALOGENATED MONOVALENT HYDROCARBON RADICALS AND CYANOALKYL RADICALS, Z'' IS SELECTED FROM THE CLASS CONSISTING OF HYDROGEN, HALOGEN, OH, OR'', NR''X, ONR''2, SR'', OOCR'',O, N(CX) AND S WHEREIN R'' IS SELECTED FROM THE CLASS CONSISTING OF ALKYL RADICALS AND ARYL RADICALS, X IS SELECTED FROM THE CLASS CONSISTING OF HYDROGEN AND R'' AND A IS 1 OR 2.

Claim 3

The composition of claim 1 wherein the bulk weight of the treated silicon dioxide is from 150 to 320 grams per liter.

Claim 4

The composition of claim 1 wherein the organosilicon compound is trimethylethoxysilane.

Claim 5

The composition of claim 1 wherein the treated silicon dioxide is subsequently subjected to mechanical stress to reduce the bulk weight of the silicon dioxide.

Claim 6

A process for preparing a vulcanizable organopolysiloxane having reduced structure formation which comprises mixing a filler with a diorganopolysiloxane having a viscosity of at least 106 cSt at 25*C. in which the organic groups are selected from the class consisting of monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals, and cyanoalkyl radicals, and an agent capable of forming free radicals selected from the class consisting of peroxides, azo compounds and high energy radiation, said filler contains finely divided silicon dioxide particles having a surface area of at least 50 m2/g which have been subjected to mechanical stress and reacted with an organosilicon compound to increase the bulk weight of the silicon dioxide to a range of from about 120 to 150 grams per liter, said organosilicon compound having the formula (R3Si)aZ'' wherein R is selected from the class consisting of monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals and cyanoalkyl radicals, Z'' is selected from the class consisting of hydrogen, halogen, OH, OR'', NR''X, ONR''2, SR'', OOCR'', O, N(CX) and S where R'' is selected from the class consisting of alkyl radicals and aryl radicals, X is selected from the class consisting of hydrogen and R'' and a is 1 or 2.

Claim 7

A process for preparing a vulcanizable organopolysiloxane having reduced structure formation which comprises mixing a filler with a diorganopolysiloxane having a viscosity of at least 106 cSt at 25*C. in which the organic groups are selected from the class consisting of monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals, and cyanoalkyl radicals, and an agent capable of forming free radicals selected from the class consisting of peroxides, azo compounds and high energy radiation, said filler contains finely divided silicon dioxide particles having a surface area of at least 50 m2/g which have been subjected to mechanical stress and reacted with an organosilicon compound to increase the bulk weight of the silicon dioxide to a range of from about 120 to 150 grams per liter, said organosilicon compound having the formula (R3Si)aZ'' wherein R is selected from the class consisting of monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals and cyanoalkyl radicals, Z'' is selected from the class consisting of hydrogen, halogen, OH, OR'', NR''X, ONR''2, SR'', OOCR'', O, N(CX) and S where R'' is selected from the class consisting of alkyl radicals and aryl radicals, X is selected from the class consisting of hydrogen and R'' and a is 1 or 2.

Claim 8

The process of claim 5 wherein the treated silicon dioxide is subsequently subjected to mechanical stress to reduce its bulk weight prior to mixing with the diorganopolysiloxane and the radical forming agent.

Claim 9

The process of claim 5 wherein the silicon dioxide is treated with the organOsilicon compound while being subjected to mechanical stress in a ball mill.