Process for preparing aqueous vinyl polymer dispersions

Abstract

The invention relates to a process for the preparation of aqueous vinyl polymer dispersions having good film forming properties, good stability and in can clarity, to the polymer dispersions obtainable by the process and coating compositions prepared from said polymer dispersions and the use thereof. The process comprising, (1) a first polymerization step comprising (1a) preparing an emulsion (1A) in water of a first monomer mixture (1a1) comprising carboxylic acid functional monomers, a surfactant (1a2) and water soluble inorganic salt (1a3) wherein surfactant (1a2) is a sulfur based anionic surfactant containing less than 60 wt % ethylene oxide and wherein the salt (1a3) content at the start of polymerization (1b) is between 0.01 and 3 gr/kg water, (1b) emulsion polymerizing the obtained emulsion 1A forming a hydroplasticizable first stage polymer particle dispersion (1B) said first stage polymer having a Tg from 10 to 125°, (2) a second polymerization step comprising (2a) adding to dispersion 1B a second monomer mixture (2a1) wherein carboxylic acid functional monomers is present in an amount such that the acid value of the resulting polymer is less than 23 KOH/g and wherein the amount of monomer mixture (2a1) is between 10 and 90 wt % of the total weight of monomers (1a1) plus (2a1), (2b) polymerizing second monomer mixture (2a1) to form a second stage polymer in the first particle dispersion (1B) to form a multiphase particle dispersion (2B).