Patent ID: 7851542

Claim:
A formaldehyde-free aqueous binder having a broad molecular weight distribution and comprising a mixture of polymers composed of monomers A) and B), comprising (A) from 5 to 50% by weight of an ethylenically unsaturated acid anhydride or ethylenically unsaturated dicarboxylic acid whose carboxylic acid groups can form an anhydride group, or mixtures thereof [monomers A)], (B) from 50 to 95% by weight of at least one ethylenically unsaturated compound different from monomers A) [monomers B)], and (C) at least one polyfunctional crosslinker or mixtures thereof, the polymers of monomers A) and B) obtained by free-radical addition polymerization, when classified in a coordinate system by way of their average molecular weight Mw and their polydispersity, being situated in the area above a straight line which is defined by the linear equation y=1.25x+20 000 and has been shifted in y direction parallelwise by at least +3 000, the x axis denoting the weight-average molecular weight and the y axis the polydispersity times 10 000, wherein the polymers are prepared: (a) in situ in one step by first synthesizing either a low molecular mass fraction at a particular initiator concentration and temperature and then, after lowering the initiator concentration in the reaction mixture and/or reducing the temperature, synthesizing a high molecular mass fraction, or by first synthesizing a high molecular mass fraction at a particular initiator concentration and temperature and then, after raising the initiator concentration in the reaction mixture and/or increasing the temperature, synthesizing a low molecular mass fraction, (b) by mixing polymers having different molecular weights, or (c) by synthesizing one polymer of low or high molecular weight in the presence of a second polymer with high or low molecular weight, respectively.