| Acrylic resin coatings have been widely utilised due to its well performance on metal protection,but until now,existing organic coatings still have many deficiencies,such as corrosion-resistance,etc.In addition,it is limited to understand and recognize the protection process and mechanism of organic films on metal surface up to today.Therefore,it is valuable in academic and practical application to investigate the influence of protection performance and metal protection mechanism for coating films on metal.In this paper,the water resistance,acid resistance,alkali resistance and other physical properties of acrylic resin films were investigated by changing hydroxyl value,acid value and glass transition temperature(T_g)of hydroxyl acrylic resin.The weight factors to impact on the molecular weights and distribution of the resin were studied using the uniform design experiment and gray correlation theory.Based on the results from a comparative study on different anti-corrosive pigments how to affect the anti-corrosion of epoxy-modified acrylic resin coatings on metal surface using electrochemical impedance spectroscopy(EIS)and salt spray test,a mechanism model was proposed for organic coating on metal surface how to protect metal.The main conclusions are listed as followings:(1)In reaction the data discloses that polymerization temperature,rate of adding monomer and the amount of chain transfer agent have great influence on the average molecular weight and polydispersity index of hydroxyl acrylic resin,while the amount of initiator has relatively little impact.(2)There are visible cracks on surface for the film from the resin with higher T_g.The higher the hydroxyl value and acid value,the more densification the film surface is.T_g has little difference in acid resistance,alkali resistance and water resistance for the films from these resin T_g between 15°C and 35°C,but these resistances will show sharp drop phenomenon when T_g above 45°C.Furthermore,the impact resistance of the paint film decrease with the increase of T_g.(3)The influences of acid value,hydroxyl value and T_g on the main protective properties of the resin film are different:for the film pendulum hardness and acid resistance,their influence order is T_g>acid value>hydroxyl value,and for water resistance the order is acid value>T_g>hydroxyl value.(4)It can further improve corrosion resistance of epoxy-modified acrylic resin coatings to add anti-corrosion pigment;the anti-corrosion pigment of iron-zinc phosphate has little work to improving anti-corrosion performance of epoxy-modified acrylic resin coating films when the addition exceeds 10%.(5)Based on the results from electrochemical impedance spectroscopy(EIS)and salt spray test of the coating films,the protection of the epoxy-modified acrylic coatings is divided into three stages.The first stage:the paint film is equivalent to a physical shielding layer which isolates the metal substrate from the corrosion medium solution;The second:the corrosion medium solution gradually penetrates the coating/metal interface,which destroys the adhesion between the coating and the metal substrate.The third:the coating fails with appearing rusty spots on the paint film. |
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