Silicone pressure sensitive adhesives having enhanced adhesion to low energy substrates

A solventless silicone pressure sensitive adhesive composition consisting essentially of:

• (A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M.sub.n value of about 950 to 1,600 and consisting essentially of R.sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units wherein each R denotes a monovalent radical selected from the group consisting of hydrocarbon and halogenated hydrocarbon radicals, at least 1/3 of all R radicals being methyl and the mole ratio of R.sub.3 SiO.sub.1/2 siloxane units to SiO.sub.4/2 siloxane units in the soluble organopolysiloxane having a value of from 1.1/1 to 1.4/1;
• and
• (B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula R.sup.1.sub.2 R.sup.2 SiO(R.sup.1 R.sup.2 SiO).sub.n SiR.sup.2 R.sup.1.sub.2 wherein each R.sup.1 individually is a radical selected from the group consisting of methyl, ethyl, propyl and phenyl, each R.sup.2 individually is an olefinic radical or any R.sup.1 as defined above with the proviso that at least two R.sup.2 radicals per molecule must be olefinic and n has an average value of 50 to 200;
• (C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B) and having an average of at least 2 silicon-bonded hydrogen atoms per molecule, the amount of (C) present in the adhesive composition being sufficient to provide from 1 to 30 silicon bonded hydrogen atoms for every olefinic radical in (B);
• and
• (D) a platinum containing catalyst in sufficient quantity to provide at least 0.1 part by weight platinum for every one million parts by weight of the combined weight of (A), (B) and (C).

A solventless silicone pressure sensitive adhesive composition comprising:

• (A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M.sub.n value of about 950 to 1,600 and consisting essentially of Me.sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units in a mole ratio of 1.1/1 to 1.4/1, wherein Me denotes a methyl radical;
• (B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula CH.sup.2 .dbd.CH(R.sup.1.sub.2 SiO).sub.n R.sup.1.sub.2 SiCH.dbd.CH.sub.2 wherein each R.sup.1 individually is a radical selected from the group consisting of methyl, ethyl, propyl and phenyl, and m has an average value of 50 to 200;
• (C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B) and having an average of at least 3 silicon-bonded hydrogen atoms per molecule, the amount of (C) present in the adhesive composition being sufficient to provide from 1 to 30 silicon bonded hydrogen atoms for every olefinically unsaturated radical in the total of (A) plus (B);
• and
• (D) a platinum containing catalyst in sufficient quantity to provide at least 0.1 part by weight platinum for every one million parts by weight of the combined weight of (A), (B) and (C).

A process for preparing a solventless silicone pressure sensitive adhesive composition comprising:

• (I) preparing an organic solvent solution of
• (A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M.sub.n value of about 950 to 1,600 and consisting essentially of Me.sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units in a mole ratio of 1.1/1 to 1.4/1, in which Me denotes a methyl radical;
• (B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula R.sup.2 (R.sup.1.sub.2 SiO).sub.n SiR.sup.1.sub.2 R.sup.2 wherein R.sup.1 is independently selected from the group consisting of methyl, ethyl, propyl and phenyl, R.sup.2 is an olefinically unsaturated radical and m has an average value of 50 to 200;
• and
• (C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B) and having an average of at least 3 silicon-bonded hydrogen atoms per molecule, the amount of (C) present in the adhesive composition being sufficient to provide from 1 to 30 silicon bonded hydrogen atoms for every olefinically unsaturated radical in the total of (A) plus (B);
• (II) removing organic solvent from the solution to obtain a devolatilized mixture containing less than one percent by weight, based on the total weight of devolatilized mixture, of volatiles;
• and
• (III) mixing the devolatilized mixture with
• (D) a platinum containing catalyst in sufficient quantity to provide at least 0.1 part by weight platinum for every one million parts by weight of the combined weight of (A), (B) and (C).

A process for preparing a solventless silicone pressure sensitive adhesive composition comprising;

• (I) preparing an organic solvent solution of
• (A) 60 to 90 parts by weight of a soluble organopolysiloxane having a M.sub.n value of about 950 to 1,600 and consisting essentially of Me.sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units in a mole ratio of 1.1/1 to 1.4/1, in which Me denotes a methyl radical, and
• (B) 10 to 40 parts by weight of a polydiorganosiloxane having the general formula R.sup.2 (R.sup.1.sub.2 SiO).sub.n SiR.sup.1.sub.2 R.sup.2 wherein R.sup.1 is independently selected from the group consisting of methyl, ethyl, propyl and phenyl, R.sup.1 is an olefinically unsaturated radical and m has an average value of 50 to 200;
• (II) removing organic solvent from the solution to obtain a devolatilized mixture containing less than one percent of volatiles based on the total weight of devolatilized mixture;
• and
• (III) mixing the devolatilized mixture with
• (C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B) and having an average of at least 3 silicon-bonded hydrogen atoms per molecule, the amount of (C) present in the adhesive composition being sufficient to provide from 1 to 30 silicon bonded hydrogen atoms for every olefinically unsaturated radical in the total of (A) plus (B) and
• (D) a platinum containing catalyst in sufficient quantity to provide at least 0.1 part by weight platinum for every one million parts by weight of the combined weight of (A), (B) and (C).