Preparation And Modification Of Aqueous Polyacrylate Secondary Dispersion Containing Hydroxyl Group

Polyurethane coatings have excellent mechanical and chemical properties.They are widely used in wood coatings,automotive repair coatings,floor coatings,electronic coatings and so on.The two-component waterborne polyurethane coating is composed of an isocyanate curing agent and a hydroxyl-containing resin.Aqueous polyacrylate secondary dispersion containing hydroxyl group is a commonly used hydroxyl-containing resin,which has excellent weather resistance,gloss retention,high hardness and flexibility,and becomes a hot issue in this field.However,at present,the application of aqueous polyacrylate secondary dispersion containing hydroxyl group is severely limited across the world by the problems of low solid content,low hydroxyl content,high viscosity and high production cost.In view of these problems,choosing acrylic dispersion and its film properties as the research topic has theoretical significance and great practical value.In the synthesis process,the hydrophilic solvent acetone and the hydrophobic solvent propylene glycol butyl ether were used as a mixed solvent.The hydrophilic monomer methacrylic acid and the reactive emulsifier were used in combination,and the viscosity-reducing monomer isobornyl acrylate was added to prepare a high-solid low-viscosity,high hydroxyl value aqueous polyacrylate secondary dispersion containing hydroxyl group.The prepared dispersion has a milky white appearance with blue light,a solid content of 47.5%,viscosity of 135 cp and a dispersion particle size of 165 nm.Its number-average molecular weight is 5788 Da with a polydispersity as 1.71.The dispersion and polyurethane curing agent G610 were used to prepare a film coating.The properties of the film were as follows: surface drying time 50 min,pencil hardness H,adhesion level 2,flexibility 1 mm,gloss 95.4 °,water resistance more than 7 days,acid resistance more than 48 hours,alkali resistance more than 72 hours.In order to further improve the adhesion and hardness of the film,the dispersion was modified with various modifiers such as epoxy resins,phosphate esters,siloxane monomers,?-carboxyethyl acrylates.The experiments show that the dispersion modified with 1% silicone KH-570 has the best performances.The solid content of the dispersion is 47.5% and the viscosity is 193 cp.The pencil hardness of paint film is 2H,the adhesion is 0 class and the alkali resistance meets the national standard requirements.The performance of aqueous polyacrylate secondary dispersion containing hydroxyl group products was studied across the world.The effects of NCO/OH ratio,dosage of additives and drying time were studied.Experiments show that the ratio of NCO/OH is 1.5-1.75:1 and the paint prepared with 0.4% defoamer,0.5% leveling agent and 0.5% substrate wetting agent is easy to be used.The hardness and gloss of the paint film increase rapidly.