Low-foaming water-based printing ink composition

Claim 1

A low-foaming water-based printing ink composition which comprises, as a uniform blend: (A) an organic polymer in the form of an aqueous solution or in the form of an aqueous emulsion; (B) a coloring agent; and (C) a silicone-based defoaming composition, in an amount in the range from 0.01 to 10% by weight, comprising: (a) 100 parts by weight of a polyoxyalkylene group-containing organopolysiloxane represented by the average unit formula G.sub.a R.sup.1.sub.b SiO(.sub.4-a-b )/2, in which R 1 is a monovalent hydrocarbon group having 1 to 18 carbon atoms, G is a polyoxyalkylene group represented by the general formula --R.sup.2 --O--(--R.sup.3 --O--).sub.p --Q, R 2 being a divalent hydrocarbon group having 1 to 10 carbon atoms, R 3 being an ethylene group --C 2 H 4 -- or a propylene group --C 3 H 6 --, Q being an atom or group selected from the class consisting of a hydrogen atom, alkyl groups having 1 to 8 carbon atoms, acetyl group and isocyanato group --NCO and the subscript p being a positive integer not exceeding 200, the subscript a is a positive number in the range from 0.005 to 0.5 and the subscript b is a positive number in the range from 1.4 to 2.195 with the proviso that a +b is in the range from 1.9 to 2.2; (b) from 2 to 200 parts by weight of a polydimethylsiloxane having a viscosity in the range from 100 to 1,000,000 centistokes at 25° C.; (c) from 0.1 to 40 parts by weight of a finely divided silica powder having a specific surface area of at least 50 m 2 /g; and (d) from 0.05 to 60 parts by weight of an organopolysiloxane resin soluble in an organic solvent which consists of the siloxane units of the unit formula R 4 8 SiO 0 .5, siloxane units of the unit formula SiO 2 , siloxane units of the unit formula R 4 2 SiO and siloxane units of the unit formula R 4 SiO 1 .5, R 4 in the unit formulas being a monovalent hydrocarbon group having 1 to 6 carbon atoms, of which the combined molar fraction of the siloxane units of the formula R 4 3 SiO 0 .5 and the siloxane units of the formula SiO 2 is at least 80% and the molar ratio of the siloxane units of the formula R 4 3 SiO 0 .5 to the siloxane units of the formula SiO 2 is in the range from 0.5 to 1.5.