Coated Steel Sheet. Present Situation and Future Prospect. Recent Development in Prepainted Steel Sheets.

Abstract

Recent development in prepainted steel sheet production is reviewed in terms of the control of heterogeneity of resin composition, morphology, and structures of the coatings. The former two are mainly controlled by surface tension or reaction rate differences between resins, and the latter one by design of the resins themselves. Relationship between mechanical properties of the coatings and press formability of prepainted steel sheets is also described. In bending mode, the higher the elongation of films is, the higher the integrity of painted films on steel is, while in drawing mode, the lower the elastic strain energy is, the higher the integrity of panted films is. Development of galvanized steel sheets is also important to improve corrosion resistance of products. 55 ％ Al-Zn alloy-coated and new Zn-Al alloy-coated steel sheets containing Mg have excellent corrosion resistance as prepainted steel sheet substrates. Finally, recent topics on environmentally friendly products without hexa-valent chromium or polyvinyl chloride, are introduced.