The Growing Procedure of Zirconium-Type Chemical Conversion Coatings and Their Adhesion with Paint Film

Abstract

Zirconium-type chemical conversion coatings were studied as a pretreatment of the organic coatings on the surface of aluminum cans. The structure of the chemical conversion coatings and adhesion capability on to the organic coatings were investigated by using Auger electron spectroscopy (AES). Chemical conversion coatings consist of a layer that is mainly composed of PO₄ on a solid-liquid interface, although the layer is chiefly composed of chemical compounds of PO₄ and Zr or Al. It was found that aluminum oxide (or hydroxide) and aluminum fluoride are present at the interface between chemical conversion coatings and the aluminum substrate. The mechanism of development the chemical conversion coatings can also be considered as the result of a solid-liquid reaction between chemical conversion coatings and the liquid phase. The composition of chemical conversion coatings reflects the composition of the solid-liquid interface, and when the concentration of Al or HF in the bath is high the quantity of Al in the chemical conversion coatings increases. It is concluded that the reasons for the good adhesion between zirconium-type chemical conversion coatings and phenolic-epoxy systems are the penetration of the macromolecure chains composing the organic coating into the chemical conversion coatings, as well as interaction between the functional groups of macromolecular chains and Zr, PO₄ and their compound which may be formed in the chemical conversing coatings.