Increasing topcoat adhesion for solvent phosphatized surfaces

A methylene chloride and water containing liquid phosphatizing composition having a continuous and homogeneous liquid phase containing water in a minor amount, said composition being adapted for forming a phosphate coating on a metal substrate that provides enhanced topcoat adhesion, the composition being maintained during phosphatizing at a temperature within the range of from about 95.degree. to about 105.degree. F and having the proportion of the composition constituents present in amounts providing said liquid phase with a specific gravity between about 1.12 and about 1.14 at said phosphatizing temperature, wherein the composition constituency comprises methylene chloride, aprotic polar organic compound, C.sub.1 -C.sub.4 alcohol, a phosphatizing proportion of phosphoric acid and an amount of water above about 4 weight percent, basis total weight of the composition, while being sufficient for said composition to provide a phosphatized coating of substantial water insolubility.

The method of preparing a methylene chloride and water-containing liquid phosphatizing composition having a continuous and homogeneous liquid phase containing water in minor amount and being adapted for forming a phosphate coating on a metal substrate that provides enhanced topcoat adhesion, wherein said phosphatizing composition is prepared by combining a precursor solution with an adjuvant, with the precursor solution containing methylene chloride, a solubilizing solvent capable of solubilizing phosphoric acid in methylene chloride and water, said adjuvant containing solubilizing solvent and water, which method comprises mixing precursor solution and adjuvant together in proportion providing said liquid phosphatizing composition with an augmented amount of adjuvant.

In the process of preparing a coated metal substrate wherein the surface of the metal receives a phosphatized coating and the resulting phosphatized surface is subsequently topcoated, the improvement for enhancing topcoat adhesion to a phosphatized surface of low coating weight which comprises contacting said low coating weight phosphatized surface with a methylene chloride and water-containing liquid phosphatizing composition having a continuous and homogeneous liquid phase and containing water in minor amount which composition has an augmented constituency selected form the group consisting of water, aprotic polar organic compound, solubilizing solvent capable of solubilizing phosphoric acid in methylene chloride, and mixtures thereof, thereby preparing a phosphatized surface of augmented coating weight.

A coated ferruginous substrate having an adherent and water-insoluble surface coating that is a complex coating of the iron phosphate type, said surface coating containing, in addition to trace elements, the elements, iron, phosphorus, oxygen, carbon, and nitrogen and having a coating surface ratio of carbon atoms to phosphorus atoms of above about 5:1, with said coating being obtained by contacting said ferruginous substrate with a methylene chloride and water-containing liquid phosphatizing composition, maintained at a temperature within the range of from about 95.degree. F to about 105.degree. F, said composition containing water in an amount above about 4 weight percent, basis total weight of the composition, and with said composition having a specific gravity between about 1.12 and about 1.14 within said temperature range.