Preparation Of Core-shell Polymer Particles Containing Voids

Paint has many applications in people's routine life, such as in furniture, architecture, paper and appliance etc, and inorganic extender takes an important proportion in paint. For the bad tolerance between inorganic extender and organic material which causes bad dispersion, core-shell particles with voids are used in some high quality paints and paper coatings and it is still a vacancy in this field in our country. The main aim of this article is to research the synthesis method of core-shell emulsion polymerization and opacifying ability of the emulsion.At the first of the experiment a seed latex was prepared, then preparing a core on its surface with core monomer such as (meth) acrylic eater, unsaturated carboxylic, cross-linking and optionally vinyl aromatic monomer. At certain weight ratio of core polymer to shell polymer, shell particles were prepared encapsulating said core, then swelling at elevated temperature the resultant core-shell particles with volatile base such as ammonia to produce an aqueous dispersion of particles which when dried contained a microvoid which caused opacity in compositions in which they were contained.During the preparation of seed latex, to gain a stable latex, anionic surfactant sodium lauryl sulphate (SDS) was used which was preferably 2-3% weight parts of seed monomer mixture. When preparing core particles, glass transition temperature (Tg) of core polymer was adjusted to research the effect of Tg on the contrast ratio of core-shell polymer. Experiment proved that when Tg of the core was 75℃, the polymer had a higher opacifying ability. Otherwise incorporation of vinyl aromatic monomer (such as styrene) units into the core polymer provided the preparation of core polymer latex completely free of coagulate. Anionic surfactant and nonionic surfactant were used during the preparing core particles whose weight ratio was preferably at 1:1. When core monomer comprising of single styrene and 1% weight parts of shell monomer of anionic surfactant used, stable latex and higher opacifying ability were gained. Before neutralization and swelling, addition of 20 parts of shell monomer by weight, based on 100 parts by weight core-shell polymer improved stability of latex and contrast ratio. When the weight ratio of core polymer to shell polymer being 1:3.5, contrast ratio reaches 0.755.Considering the effects of the weight ratio of core polymer to shell polymer, monomer component and synthesis method, a method of double-layer shell was attempted. Preparation of double-layer polymer mainly adopted the synthesis method of single-layer shell and contrast ratio of 0.75 was gained by changing the weight ratio of core polymer to shell polymer to be 1:2:2.