| Environment-friendly acrylic emulsion coatings have been widely used in the construction industry, while they are seldom researched and used in wood coating. Because they can't meet the properties requirement of wood coating, such as low film-forming temperature, high hardness, good adhesion, excellent water resistance, etc. In order to get the acrylic emulsion with low emulsifier content and high solid content, which can meet the special requirement of wood coating, the traditional acrylic emulsion needs to be improved.In this paper, on the basis of "particle design", the microemulsion with hard-core and soft-shell structure was prepared by seed emulsion polymerization, choosing suitable monomer. And then, styrene acrylic microemulsion was modified. Mainly in the following areas:Using the improved polymerization method and whole dropping way in core shell step, styrene acrylic core-shell microemulsion was prepared with the particle size of 78.7nm and polydispersity index (PDI) of 0.059. According to particle size, adhesion, hardness, water absorption and contact angle, the influence of monomer ratio, emulsifier category, proportion and concentration, initiator concentration, polymerization method, reaction temperature and other factors on the emulsion and coating film were studied. The results showed that when the ratio of soft and hard monomers was 1/2, the monomer content was 45%, emulsifier ratio of Dow/NP-10 was 2/1 and the percentage was 2%, initiator concentration was 0.3%, the reaction temperature was 78℃, the emulsion polymerization had good stability and chemical stability ,the coating film had good water absorption, hardness, water resistance and contact angle.By the measurement of latex particle size in different steps by dynamic light scattering (DLS), the polymerization mechanism has been discussed. The results showed that the polymerization carried out mainly in the micelle. The monomer got into the micelle under the action of the emulsifier and stirring, then it was captured by the free radicals in the micelles. By calculating the number of latex particles in the two stages, the result showed the microemulsion polymer had the core-shell structure and there was little new latex particles in the shell step.By the influence of AA adding methods on the effects of emulsion viscosity, the microemulsion styrene-acrylic alkali thickening mechanism was studied. The results showed that when AA was added mainly in the latter part of accession, the carboxyl would be distributed on the surface of the polymer chain, getting the greatest effect of the alkali thickening.The structure of the polymer particles was characterized by FTIR, TEM and other means, the results showed that styrene acrylic microemulsion prepared by core-shell whole dropping method had the core-shell structure, and monomers of MMA, St, BA and AA had copolymerized, with low film forming temperature, good adhesion and hardness.To enhance the water resistance, adhesion and hardness of the microemulsion film further, the microemulsion has been modified in two ways: the first is to add the functional monomers for cross-linking reaction; the second is microsoap modification by reaction emulsifier.NMA could enable cross-linking reaction of the polymer, performing interpenetrating polymer network structure and improving the film hardness and water resistance. When dosage of A-172 was 20g, the water absorption value of the film fell to 2.84% , with contact angle of 76.5°. When the dosage of HPAA was 10g, the water absorption value was 10.37%, with particle size of 74.8nm and translucent appearance of emulsion. The performance of emulsion has been improved to varying degrees. Microsoap emulsion was mainly carried though reactive emulsifying agent taking place of the conventional emulsifier. When the dosage of COPS-1 was 1.0g, the water absorption of the coating film was 13.61%.The emulsion formulation was optimized by orthogonal experiments. Orthogonal experiments showed that when adding NMA 1.0g, A-172 20g, emulsifier1.75% and HPAA 5g, comprehensive performance was relatively good, with adhesion of 1 level, pencil hardness of 2-3H and 24h not blanching in water.
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