The present invention provides an additive comprising A) a copolymer of
ethylene and 8-21 mol % of at least one acrylic or vinyl ester having a
C.sub.1-C.sub.18-alkyl radical and B) a comb polymer containing
structural units of B1) at least one olefin as monomer 1, which bears at
least one C.sub.8-C.sub.18-alkyl radical on the olefinic double bond, and
B2) at least one ethylenically unsaturated dicarboxylic acid as monomer
2, which bears at least one C.sub.8-C.sub.16-alkyl radical bonded via an
amide and/or imide moiety, wherein the sum Q
.times..times..times..times..times..times. ##EQU00001## of the molar
averages of the carbon chain length distributions in the alkyl radicals
of monomer 1 on the one hand and the alkyl radicals of the amide and/or
imide groups of monomer 2 on the other hand is from 23 to 27, where
w.sub.1 is the molar proportion of the individual chain lengths in the
alkyl radicals of monomer 1, w.sub.2 is the molar proportion of the
individual chain lengths in the alkyl radicals of the amide and/or imide
groups of monomer 2, n.sub.1 are the individual chain lengths in the
alkyl radicals of monomer 1, n.sub.2 are the individual chain lengths in
the alkyl radicals of the amide and/or imide groups of monomer 2, i is
the serial variable for the individual chain lengths in the alkyl
radicals of monomer 1, and j is the serial variable for the individual
chain lengths in the alkyl radicals of the amide and/or imide groups of
monomer 2.