Surface Modification Of Aluminum Powder And Its Application In Waterborne Coatings

Flaky aluminum powder is an important metal pigment due to its excellent metallic luster,angular heterochromic effect,floatability,covering performance and shielding effect.Therefore,it is widely used in automotive coatings,industrial coatings,printing ink,plastic coatings and corrosion resistant coatings.With the gradual improvement of human requirements for environment,life and health and the need for sustainable social development,the state is strictly controlling VOCs emissions from enterprises.Now,the traditional solvent-based coatings are gradually replaced by water-based coatings.Water-based coatings are safe,non-toxic,and have low VOCs emissions,which have been widely used in daily life.However,the aluminum pigments used in oil-based coatings are not satisfied with the use of water-based coatings.Aluminum pigments are easy to react with water molecules in water-based coatings,resulting in the corrosion of the surface of aluminum powder and the decrease of the gloss of aluminum pigments,which do not meet the application standards in coatings.Moreover,hydrogen generated by chemical reactions becomes an unsafe factor,and brings potential safety hazards to industrial production and storage processes.In addition,the pristine aluminum pigments still have some practical problems,such as poor dispersion and easy agglomeration in the water-borne paint system.Aiming at the above problems,three kinds of aluminum pigments used inwaterborne coatings were designed and prepared in this paper.The glossiness of the prepared waterborne aluminum pigments remained basically unchanged under the condition of good water resistance.In addition,the dispersibility of aluminum pigments in waterborne coatings was excellent,which met the industry application standards.The details are as follows:1.A waterborne aluminum pigment coated with multi-layer structure was designed.Firstly,molybdate passivation solution was used to treat the surface of aluminum powder,and a chemical passivation film was formed on the surface of aluminum powder.Then,the preparation of silica film on the surface of flaky aluminum powder was realized by hydrolysis-condensation of tetraethyl orthosilicate under the action of alkaline catalyst.In order to further improve the dispersion of aluminum pigments in water-borne resins,silane coupling agent gamma-aminopropyl triethoxysilane(KH550)was used to modify the corrosion resistant layer on the surface of aluminum powder.The results show that the water-borne aluminum pigments coated with multi-layer structure have no hydrogen to produce through HG/T2456.5-2016 standard to test,which indicates that the prepared microencapsulated flaky aluminum powder has excellent corrosion resistance.The results of electron microscopy showed that the dispersibility of aluminum pigments in water solution was excellent and there was no agglomeration.2.A waterborne aluminum pigments with self-assembly of polydopamine film on the surface of flaky aluminum powder was designed.The structure of microcapsules with flaky aluminum powder as core and polydopamine film as corrosion resistant film was studied.The aluminum powder was placed in the Tris-HCl buffer solution with dopamine,and the polydopamine corrosion resistant film was prepared on the surface of the flaky aluminum powder at 8.5 pH,so as to protect the surface of the flaky aluminum powder.According to the industry standard HG/T 2456.5-2016,the results show that the corrosion resistance of the self-assembled aluminum pigments with polydopamine film is better than that of the pristine aluminum powder,and the modified aluminum pigments have excellent dispersion in water-borne coatings.3.Water-borne aluminum pigment coated with polysiloxane film by grafting and curing on the surface of flaky aluminum powder was designed.Firstly,a layer of triethanolamine molecule was adsorbed on the surface of flaky aluminum powder by electrostatic adsorption.Hydroxyl groups of triethanolamine could react with Si-H groups of polysiloxane under the action of alkaline catalyst,and the grafted polysiloxane can form anticorrosion film by in situ polymerization method on the surface of aluminum powder.According to the water resistance test of industry standard HG/T 2456.5-2016,the amount of hydrogen evolution of polysiloxane graft-cured aluminum pigments is 0 ml in 2 hours,which shows that the prepared silicone-coated aluminum pigments have good corrosion resistance.The prepared water-borne aluminium pigments were applied to automotive paint.The results of gloss and corrosion resistance showed that the water-borne aluminium pigments prepared in the laboratory met the application standard of water-borne automotive paint.