The effect of tannic acid on the paint adhesion of zinc was investigated, since our previous investigations showed that the adhesion was improved by a treatment with an aqueous solution of tannic acid. The structure of the film formed on zinc in the tannic treatment was determined with IR, ESCA, and UV. Experimental data suggested that the film was composed of zinc carboxylate and that OH groups of tannic acid were strongly attached to zinc surface by hydrogen bonding between zinc surface and OH groups. Therefore, it is concluded that adhesion of paint on zinc depends on the effect of the functional group contained in the tannic acid film lying between zinc substrate and a paint film.
The effects of solvents on the radiation graft polymerization of styrene onto γ-alumina and anodic oxide film on aluminum were investigated by concurrent irradiating method in an attempt provide hydrophobic anodic oxide film surfaces. Styrene monomer was grafted on γ-alumina under all treating conditions, but the amount of grafted styrene depends on the kind of solvent and on the ratio of monomer and solvent. Treating with equal volume ratio of styrene and methanol (SM-25) yielded the highest amount of grafting. Treated γ-alumina was found to show hydrophobicity by dispersion grade measurement. The anodic oxide film on aluminum treated under the same conditions as SM-25 also showed hydrophobicity.
Reliability of the paint coatings on zinc plated steels is not sufficient enough for corrosion prevention, because in spite of the initial good adhesion of the coatings to the base metals, peeling might take place with the lapse of time. This study has been made, therefore, to elucidate the causes for the adhesion failure and to find out the methods to prevent the deterioration of the coatings. Five different paints classified according to the kinds of resins contained were directly applied, with and without zinc chromate corrosion prevention pigment, to the surfaces of electroplated zinc plates, fresh and stored, and hot-dipped plates, respectively. Each specimen was subjected to the salt spray test to accelerate the adhesion failure of the coatings, while the permeability of water for clear paint films was measured separately. Results indicate that water which can pass through the coatings reacts with ZnO and Zn(OH)2 on zinc metal surfaces to cause liberation of hydrogen and subsequent pin-hole formation in the coatings. Peeling also takes place because the corrosion products push the coatings upward as the corrosion products grow. It is shown that the deterioration of the coatings is accelerated with increasing thickness of the natural oxide layers on zinc surfaces, while zinc chromate can retard the growth of Zn(OH)2 under the coatings through which adequate amount of water can pass.
Raported are the effect of humidity on the photodegradation of PVC. Photodegradation rate of PVC films slowed down under high percentage of humidity in weathering atomosphere. It is shown that main chain scission was retarded by the existence of water, which would start next to oxidation. Further experiments using copper sulfate with various contents of crystal water suggested that crystal water also restrained photodegradation.