Abstract An organic composite coated steel strip having well-balanced corrosion resistance, coating properties including adaptability to electrophoretic coating and water resistant secondary coating adherence, and spot weldability is provided. The organic composite coated strip comprises a zinc or zinc base alloy plated steel substrate; a chromate layer on the substrate containing up to 70% by weight of Cr⁶⁺ based on the total chromium quantity, said chromate layer being coated in a weight of 5 to 500 mg/m² in terms of elemental chromium; and an organic composite layer on said chromate layer mainly comprising silica and an organic high molecular weight resin. In the organic composite coated steel strip, (a) silica has an average primary particle diameter of 5 to 30 nm; (b) silica is agglomerated into agglomerates of an average thickness of 0.2 to 2 µm and an average apparent diameter of 5 to 300 µm; and (c) the organic composite layer has been coated to a dry weight of 0.1 to 3 g/m². The organic composite coated steel strip of the invention has various uses including automobile bodies.
An organic composite coated steel strip having improved corrosion resistance and spot weldability, comprising a zinc or zinc base alloy plated steel substrate, a chromate layer on the substrate containing up to 70% by weight of Cr⁶⁺ based on the total chromium quantity, said chromate layer being coated in a weight of 5 to 500 mg/m² in terms of elemental chromium, and an organic composite layer on said chromate layer mainly comprising silica and an organic high molecular weight resin, wherein (a) said silica has an average primary particle size of 5 to 30 nm, (b) said silica is agglomerated in said organic composite layer into agglomerates of an average thickness of 0.2 to 2 µm and an average apparent diameter of 5 to 300 µm, and (c) said organic composite layer has been coated to a dry weight of 0.1 to 3 g/m².
Claim 2
Dependent Claim
47 words
The organic composite coated steel strip having improved corrosion resistance and spot weldability according to claim 1 wherein said organic composite layer is formed by applying a coating composition having blended therein an organic solvent-dispersed silica sol having an average agglomerate diameter of 0.05 to 2 µm.
Claim 3
Dependent Claim
35 words
The organic composite coated steel strip having improved corrosion resistance and spot weldability according to claim 1 wherein said organic composite layer is formed by applying a coating composition having blended therein hydrophobic fumed silica.
Claim 4
Dependent Claim
41 words
The organic composite coated steel strip having improved corrosion resistance and spot weldability according to claim 1 wherein said organic high molecular weight resin primarily comprises an epichlorohydrin-bisphenol A epoxy resin having a number average molecular weight of at least 2,000.
Claim 5
Dependent Claim
55 words
The organic composite coated steel strip having improved corrosion resistance and spot weldability according to claim 1 wherein said organic composite layer contains the silica and the organic resin in such a dry weight ratio that 10 to 100 parts by weight of the silica is present per 100 parts by weight of the resin.