This paper deals with the establishment of a method for the estimation of the service lifetime of PVC-sol coating. The depth profile of the outdoor-exposed coating films was determined by various analytical techniques. With the exposure time, the film thickness decreased due to the loss of DOP as well as the decomposition of PVC. The degradation of the PVC film proceeded from the surface toward interior of the film, accompanied with the generation of various functional groups. When the degradation of PVC film reached to the bottom of the film, at where carbonyl groups generated at the same time, its lifetime was regarded as having been over. The reduction of the film thickness and the depth profile of carbonyl group concentration are useful for the prediction of the service life time of PVC-sol coating. Determination of the thickness of unaffected part of the exposed film was very important for the prediction of its durability. This concept is expected to be applicable to other coating films.
It is known that a brown-colored film is obtained by the D. C. electrolytic coloring of anodic oxide film on aluminum in a electrolyte of a mixture of nickel (II) sulfate and boric acid. This brown film was found to turn to a red purple, blue or yellow green film by the A. C. electrolysis in an aluminum sulfate bath. This phenomenon was also observed in the electrolysis in a dilute sulfuric acid bath (pH=3.0). However, the brown film was decolorized when 0.1 mol/l sulfuric acid bath was used. These results suggested that a partion of nickel, deposited in the brown film pores as a metallic state, was anodicdissolved by the A. C. electrolysis and converted to its hydrate or oxide by OH-in pores.
In order to elucidate the mechanism of electrolytic coloring, the effect of the quality of aluminum as an anode was studied. Five kinds of aluminum material were used for this purpose, i. e., high purity Al (99.99%), pure Al (A 1050), Al-Mn (A 3003), Al-Mg (A 5052), and Al-Mg-Si (A 6063). In the experiment, an anodic oxide film on the aluminum was intended to be colored white by the electrolysis in an electrolyte containing Al13+ and Mg2+. As the anodic oxide film, an ordinary film formed in a sulfuric acid bath and a double layered film, which was obtained by another anodization on top of the ordinary film in a phosphoric acid bath, were used. In the results, the ordinary film from a sulfuric acid bath on any aluminum was not colored white. However, the double layered films became white when A 3003, A 5052 and A 6063 were used. On the high purity Al and A 1050, the double layered films were whitened slightly and spalled easily. A film with more defects, which tended to be whitened easily, spalled less. It was concluded that the electrolytic white-coloring in the Al3+-Mg2+ bath was not caused by the reduction of the metals but caused by the hydrolysis of the metals with OH- generated by the electrolysis of water. Then the metals deposited in pores of the films as their oxide or hydroxide form.