| Since the industrial revolution,steel materials have played an increasingly important role in our daily life,and have been applied in all aspects of national production.In order to protect the steel and prolong its service life,the most common method is coating pretreatment its surface.A pretreatment process is necessary before coating.On the one hand,the pretreatment layer can protect the steel substrate and slow down the corrosion,on the other hand,it can play a role of "double-sided tape" to improve the adhesion between the organic coating and the steel substrate.However,there are serious pollution problems in the pretreatment layer technology adopted widely in the past.The polluting heavy metal ions(such as Ni2+,Mn2+,Cu2+)present in the chromate passivation solution will give rise to carcinogenic side effects on human body.Phosphating process can produce nitrite and polluting sediment.For the above reasons,these pretreatment layer technologies are gradually banned by Chinese government.In this context,exploring and establishing new environmentally friendly pretreatment technologies turn into new challenges to relevant researchers and pretreatment companies at home and abroad.At present,there are three kinds of environmental protection pretreatment products:silane pretreatment technology,ceramic pretreatment technology and silane-zirconium composite pretreatment technology.Its main core technologies were mastered by Henkel,BASF of Germany and Parker of Japan,respectively.Their products occupied a large market share in China.In the past decades,research on the above three pretreatment technologies have been made by Chinese researchers,and breakthroughs and progress have been made.People have studied the effect of silanes containing different functional groups on metal anticorrosion,but there are few studies on the synergy of aminosilane,zirconate and epoxy silane.In the first part of this paper,aminosilane and zirconate were used to prepare the pretreatment layer on the cold rolled steel sheets through synergistic effect,and a series of adhesion application tests were carried out on the sample sheet after electrostatic spraying.In the second part,the water-free pretreatment layer was prepared on the cold rolled steel surface by using the synergistic effect between bis-aminosilane and epoxy silane,in which the treatment liquid was alkaline;and the corrosion resistance and adhesion evaluation and analysis of the sample sheets after electrostatic spraying were carried out.The main research contents and experimental results are as follows:(1)Preparation and application of zirconium aminosilane composite pretreatment coating on cold rolled steel.The amino functional group of aminosilane can strengthen the bonding force with cold rolled steel substrate.Fluorozirconate and zirconate can form zirconia nanofilms on the surface of cold rolled steel at specific pH environment.By combining them to prepare a pretreatment layer on the surface of cold rolled steel,excellent corrosion resistance and good adhesion of paint film can be obtained.In this part,through exploring the electrochemical impedance data under four kinds of film-forming conditions:pH of treatment solution,dosage of aminosilane,temperature and pretreatment time,the best film-forming conditions of pretreatment layer were obtained,that is,pH was 4.5,dosage of aminosilane was 0.11 ml/L,treatment time was 120 s,and temperature was 35?.The adhesion of cold rolled steel sample obtained under the best conditions was evaluated by electrostatic spraying.The results of electrochemical impedance spectroscopy and polarization curve show that the prepared pretreatment layer has strong corrosion resistance and the highest protection efficiency can reach 91.7%.In addition,the adhesion test results show that:the grid test is grade 0,the heavy hammer impact test can resist the impact of 60 cm height,the salt water immersion test has a slight diffusion after 48 h,the neutral salt spray test of all samples can meet the requirements of 500 h,and some of them can meet the requirements of 800 h,which has a good application prospect.(2)Study on Preparation and application properties of a new environmental friendly and water free silane pretreatment layer on cold rolled steel surface.Epoxy functional group of epoxy silane can enhance the interaction with epoxy organic coating layer,and the amino functional group of aminosilane can combine with hydroxyl group of cold rolled steel substrate through hydrogen bond.In this part,the basic silane pretreatment layer was prepared on the surface of cold rolled steel by the synergistic effect of the two additives,epoxy vinyl resin and waterborne polyurethane,and were pretreated for 3 min,6 min and 9 min respectively.The corrosion resistance of the pretreated samples was evaluated by electrochemical impedance spectroscopy and steady-state polarization curve,and the adhesion of the cold rolled samples after epoxy powder spraying was evaluated and analyzed.The electrochemical results show excellent corrosion resistance when the pretreatment time is 9 min.Adhesion test results show that the pretreatment layer can enhance the adhesion between the cold rolled steel substrate and the organic coating.When the pretreatment time is 9 min,the adhesion level of the scratch test is 0,the heavy impact test can resist the impact height of 60 cm,and the neutral salt spray test can meet the requirements of 500 h.Adhesion test results showed that the pretreatment layer can enhance the adhesion between the cold rolled steel substrate and the organic coating,the adhesion grade of the grid test was grade 0,the heavy hammer impact test can resist the impact of 60 cm height,and the neutral salt spray test can meet the requirements of 500 h.In addition,the pretreatment layer can be coated directly without water washing process,which reduces one process and reduces the production cost.Moreover,the treatment solution does not add any heavy metal ions and polluting substances,which has the prospect of industrial application. |
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