Patent GB-1433461-A (GB)
Title: Release characteristics of substrates
IPC: C08L83/00
Filed: 1974-02-07
Abstract: 1433461 Vinyl-containing siloxane polymers cured by ultra-violet radiation DOW CORNING CORP 7 Feb 1974 [28 Sept 1973] 05610/74 Headings C3P and C3T [Also in Division B2] The release of adhesive materials from a solid substrate is improved by applying to the substrate a composition comprising (A) a siloxane consisting essentially of 0À5-100 mole per cent of vinyl-containing siloxane units of formula wherein R is a monovalent hydrocarbon or monovalent halogenated hydrocarbon radical which contains 1-30 carbon atoms and n is 0, 1 or 2, any non-vinyl-containing siloxane units present having the formula wherein R<SP>1</SP> is as defined for R and m is 0-3, (B) a siloxane containing at least one siliconbonded hydrogen atom per molecule, the ratio of silicon-bonded vinyl groups in (A) to the silicon-bonded hydrogen groups in (B) being in the range of 1 : 100 to 100 : 1, and (C) a photo- , sensitizer (preferably 0À1-20% by weight), and curing said composition by exposure to ultraviolet light of wavelength less than 3650 Š. R and R<SP>1</SP> are preferably selected from methyl, ethyl, phenyl, chloropropyl and 3,3,3-trifluoropropyl radicals with n and m having average values of about 1 and 2 respectively. Especially preferred (A) is one which is composed of 100 mole per cent of the vinyl-containing siloxane units. Siloxane (B) may have the general formula wherein a is 0-99 (especially 0), b is 1-100, the sum of a and b being 1-100. A preferred composition is (A) a siloxane of vinylmethylsiloxane units and dimethylsiloxane units end-blocked with trimethylsiloxy units or vinyldimethylsiloxy units and (B) a siloxane of general formula wherein b is 1-100. The composition may also contain a mercapto-functional silicone (D) which comprises any silane or siloxane containing at least one mercapto group (HS-) attached to a silicon atom through one or more carbon atoms, which accelerates the cure of the composition. The silane (D) is of formula wherein R<SP>3</SP> is a divalent (p is 1) or trivalent (p is 2) hydrocarbon radical of 1-18 carbon atoms, one bond of which is attached to the silicon atom and the other bonds attached to the mercapto group, q is 1 or 2, R<SP>4</SP> is a monovalent hydrocarbon radical of 1-30 carbon atoms, s is 0-3, and X is a hydrolysable group, the sum of q and s being 1-4. A preferred silane is one in which R<SP>3</SP> is propylene, p is 1, q is 1, s is 0, and X is a methoxy group. The siloxane (D) is of formula wherein R<SP>3</SP> and R<SP>4</SP> are defined as above, v is 0-2, p and q are defined as above, the sum of q and v being 1-3, any other siloxane units present having the general formula wherein Q is a monovalent hydrocarbon or monovalent halogenated hydrocarbon radical of 1-30 carbon atoms, and t is 0-3. A preferred siloxane is one in which R<SP>3</SP> is a propylene radical, p, q and v are 1, R<SP>4</SP> and Q are methyl radicals, and t is 3. The invention also includes a composition for treating a solid substrate to improve its release characteristics, said composition comprising (1) a siloxane consisting essentially of 0À1-100 mole per cent of mercaptofunctional containing siloxane units having the formula wherein R<SP>2</SP> is an alkylene radical, y is 1 or 2, R<SP>5</SP> is a monovalent hydrocarbon or monovalent halogenated hydrocarbon radical of 1-30 carbon atoms, x is 0-2, and the sum of x and y is 1-3, any non-mercapto functional siloxane units present having the formula wherein R<SP>4</SP> is a monovalent hydrocarbon or monovalent halogenated hydrocarbon radical of 1-30 carbon atoms and z is 0-3, and (2) a siloxane consisting essentially of 0À1-100 mole per cent of vinyl-containing siloxane units of formula wherein R is a monovalent hydrocarbon or a monovalent halogenated hydrocarbon radical of 1-30 carbon atoms and n is 0-2, any non- vinyl containing siloxane units present in (2) having the formula wherein R<SP>1</SP> is defined as for R and m is 0-3, the ratio of mercapto groups in (1) to the vinyl groups in (2) being 1 : 100 to 100 : 1, and (3) a photosensitizer, the composition being applied to a substrate and cured with ultra-violet light of wavelength 2537 Š. Preferred compositions are those in which y is 1, R and R<SP>1</SP> contain 1-6 carbon atoms (especially methyl), R<SP>2</SP> is a propylene radical, R<SP>4</SP> and R<SP>5</SP> are methyl radicals, z and m are 2, n is 1, and x is 0 or 1.