| 摘要 |
<p>An aqueous acidic solution (preferably pH <2.3) for the treatment of bare or conversion coated surfaces of metal consisting wholly or predominately of iron, zinc or aluminium comprises at least 0.25% (preferably 1-10%) by weight of the product of the reaction of an aqueous acid solution containing 50-800 grams of Cr6+ (expressed as CrO3) per litre with formaldehyde in a molar ratio of at least 0.03 (preferably 0.5-5) to 1 (expressed at HCHO/CrO3) and a polymeric resinous compound which is one or more of the following:- (a) at least 0.25% polyacrylic acid compound(s) (b) at least 0.25% polyvinyl alcohol compound(s) or (c) at least 0.1% of water soluble polymer(s) of hydroxyethyl ethers of cellulose. The concentration of the resinous polymeric compound may be up to 5% (preferably up to 2%) by weight, and the weight ratio of the reaction product to the resinous polymeric compound is from 0.5-5 to 1. The pH of the solution may be adjusted by the blending of acids such as formic or phosphoric into the solution. In order to improve the dispersability and viscosity of the solution aliphatic alcohols and ketones having up to 4 carbon atoms and aliphatic ether alcohols having 4-8 carbon atoms may be added as co-solvents. Wetting agents may also be added to the solution.</p> |
