LOW FOAMING PAPER SURFACE SIZING COMPOSITION

The present invention refers to a paper surface sizing composition comprising a copolymer having: a) structural units derived from ethylenically unsaturated hydrocarbons; b) structural units derived from monomers selected from esters of ethylenically unsaturated mono-carboxylic acids, half-esters of ethylenically unsaturated dicarboxylic acids, allylethers and vinylethers and mixtures thereof bearing a substituent R linked to the oxygen atom of either the ester groups of the ether groups that is at each occurence selected from: (i) polyalkyleneoxide groups corresponding to formula: (1) wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, R2 is C1-C44 hydrocarbyl, t is 0 or 1 and m is an integer in the range of 5 to 200, with the proviso that if R2 is C1-C5 alkyl the polyalkyleneoxide group does not contain more than 50 weight percent ethyleneoxide moieties based on the weight of the polyalkyleneoxide group; and (ii) groups corresponding to formula: (2) wherein t is 0 or 1 and Q is a polysiloxane residue; whereby the substituents R of said half-esters are additionally selected from: (iii) C1C24 alkyl, with the proviso that if R comprises a C1-C9 alkyl, at least 1 mole percent of the substituents R of said half-esters are selected from substituents (i) and (ii); optionally c) structural units derived from ethylenically unsaturated monomers selected from monocarboxylic acids as well as salts and amides thereof, dicarboxylic acids as well as salts, amides and half-amides thereof, and cyclic anhydrides and imides of dicarboxylic acids and mixtures thereof; and optionally d) structural units derived from alkyl or amino-substituted alkyl acrylates or methacrylates with the proviso, that if no structural units c) are present, the structural units b) are derived from monomers selected from half esters of ethylenically unsaturated dicarboxylic acids.