The invention relates to a polymer dispersion which contains water, at least one polymer that has been produced by emulsion polymerisation, at least one protective colloid, at least one water-soluble acidic metallic salt and at least one cross-linking resin that is based on phenol-formaldehyde condensation products, hydroxymethyl-substituted imidazolidinones, such as 1,3-dimethylol-4,5-dihydroxy-imidazolidinone (4,5-dihydroxy-N,N'-dimethylolethylene urea), hydroxymethyl-substituted pyrimidinones, or hydroxymethyl-substituted triazinones or their auto-condensation products, or mixed condensates from two or more of the aforementioned compounds, or a mixture of two or more of the aforementioned compounds.