The present invention relates to the use of a heat-curable aqueous
composition comprising dispersed polymer particles of at least a) one
polymer A1 comprising, 98-100% by weight of ethylenically unsaturated
monomers A, it being possible for up to 20% by weight of the monomers A
to comprise glycidyl and/or hydroxyl groups and/or amino/amido groups,
and the polymer comprising, incorporated in the form of polymerized
units, .ltoreq.5% by weight of an .alpha.,.beta.-ethylenically
unsaturated mono- or dicarboxylic acid and at least 1% by weight of
acrylonitrile, and 0-5% by weight of a bi- or polyfunctional monomer and
b) a polymer A2 which is soluble in the serum and comprises,
incorporated in the form of polymerized units, 60-100% by weight of at
least one .alpha.,.beta.-ethylenically unsaturated mono- or dicarboxylic
acid whose carboxyl groups can form an anhydride group, salts or mixtures
thereof c) and a polyfunctional crosslinking agent or mixtures thereof d)
and, if appropriate, divalent or trivalent metal ions which are added in
the form of hydroxides, oxides, carbonates or bicarbonatesas a binder for
substrates.