| In recent years,countries have paid more and more attention to the environment,and have put more and more stringent requirements on the emission of volatile organic compounds(VOC)in the chemical industry.Therefore,the development of water-based environmental protection coatings has also become a trend in the coating industry.Among them,water-borne acrylic resin coatings were developed and used in1950 s,and developed rapidly in the early 1970 s.Compared with general solvent-borne coatings,water-borne acrylic resin coatings have the advantages of relatively low price,safe application,saving capital and energy consumption,and reducing pollution and public hazards,so they have become one of the key areas of current water-borne coatings technology research and development.Waterborne acrylic resin coatings mainly include water-soluble acrylic resin,waterborne acrylic emulsion and waterborne acrylic secondary dispersion.Among them,the VOC of water-soluble acrylic resin is still high,and its application is limited to some extent.The molecular weight of acrylic emulsion is large,which makes some hydroxyl groups covered inside the particles,and the effective hydroxyl concentration can not reach the theoretical hydroxyl concentration,which seriously affects the performance of paint film.Therefore,waterborne acrylic secondary dispersion is widely used in coating industry.In this paper,the production of waterborne acrylic secondary dispersion and the application of waterborne acrylic amino baking varnish were studied emphatically.Using methyl methacrylate,styrene,butyl methacrylate,butyl acrylate,2-ethylhexyl acrylate and methacrylic acid as comonomers,2-hydroxyethyl methacrylate as functional monomer,tert-butyl benzoate as initiator and mercaptoethanol as chain transfer agent,the aqueous acrylic secondary dispersion with excellent core-shell structure was prepared by solution polymerization and phase inversion.The effects of solvent,initiator,chain transfer agent,hydroxyl content,hydrophilic monomer,core-shell ratio and neutralization degree on the properties of the dispersion were studied.Finally,it was determined that when the amount of solvent was 10% of the solid content,initiator was 2% of the total monomer,chain transfer was 1% of the total monomer,hydrophilic monomer(MAA:SR-10=2:1)was3% of the total monomer,and hydroxyl group content was 4% of the total monomer,a better acrylic secondary dispersion could be obtained.The water resistance and adhesion to the matrix of acrylic acid secondary dispersion can be further enhanced by modifying it with alkyl acrylate phosphate accounting for 1% of the total monomer.The chemical structure of the polymer segment was confirmed by infrared spectrum analysis,which ensured that all the comonomers used were connected to the polymer and reached the expected requirements.Differential thermal analysis shows that the actual glass transition temperature of acrylic acid dispersion is about 57℃,and thermogravimetric analysis shows that the synthesized polymer begins to decompose at about 300℃,which has excellent thermal stability.The transmission electron microscope shows that the polymer has obvious core-shell structure,and the particles are spherical structure with regular shape and uniform size.The specific particle size of the synthesized acrylic acid secondary dispersion was determined by the particle size map,which was only 97.97 nm and distributed evenly.The effects of the mixing ratio of acrylic acid secondary dispersion and amino resin,the ratio of pigment to base,the amount of additives,the glass transition temperature of acrylic acid secondary dispersion and baking conditions on the properties of paint film were studied.The reference formula of acrylic amino baking paint coating is given: acrylic secondary dispersion and amino resin are mixed according to the solid ratio of 4: 1,and pigments and fillers are added according to the ratio of 1: 1,and then 0.3% wetting dispersant(Digao 750),0.5% defoamer(BYK028),0.2% leveling assistant(BYK333)and 0.2% are added.The results show that the performance of acrylic amino baking varnish film is excellent,with gloss of 94.1,hardness of 3H,water resistance of more than 20 days,adhesion of 0 grade,impact resistance of 50kg·cm,flexibility of 1mm,and excellent acid and acetone resistance,which can meet the use requirements of anticorrosive coatings.The electrochemical workstation technology is used to detect that the coating has very good electrochemical corrosion resistance. |
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