Process for Preparing Vinyl Acetate-Ethylene Copolymers by Means of Emulsion Polymerization

The invention provides a process for preparing vinyl acetate-ethylene copolymers by means of free-radically initiated emulsion polymerization of vinyl acetate and 18% to 34% by weight of ethylene, based on the total weight of the vinyl acetate and ethylene monomers, and, optionally, further comonomers, characterized in that polymerization takes place in the presence of at least one protective colloid and of 0.5% to 4% by weight, based on the total amount of monomers, of at least one nonionic, ethoxylated emulsifier with a branched or linear alkyl radical or in the form of ethylene oxide-propylene oxide copolymers, and in the absence of chain transfer agent, and, before the initiation of the polymerization, 10% to 70% by weight of the vinyl acetate monomer and 40% to 100% by weight of the ethylene monomer are included in the initial charge, up to 100% by weight of the protective colloid fraction is included in the initial charge, at least 25% by weight of the emulsifier fraction is included in the initial charge, and the remaining fractions of monomers, protective colloid and emulsifier are metered in during the polymerization, the procedure being such that the criterion of process COP meets the condition 2.5 COP 70, where COP=100×(ETM2.5×ETV1.25×EA2.5×EV1.5×VV−1), where ETM=MEt/MM, ETV=MEtV/MEt, EA=100 ME/MM, EV=MEV/ME and VV=MVacV/MVac, where MEt=total mass of ethylene in kg, MM=total mass of monomer in kg, MEtV=mass of ethylene charge in kg, ME=total mass of emulsifier in kg, MEV=mass of emulsifier charge in kg; MVacV=mass of vinyl acetate charge in kg, and MVac=total mass of vinyl acetate in kg.