Abstract: The surface-treated steel sheet has a zinc-based plated steel sheet, a surface-treatment coating being formed on the surface of the zinc-based steel sheet by applying and drying a surface treatment coating composition thereon, and a top coating being formed by applying and drying a coating composition for top coating on the surface-treatment coating. The surface treatment coating composition contains a water-epoxy resin dispersion, a silane coupling agent, and phosphoric acid and/or a hexafluorometal acid. The coating composition for top coating contains a high molecular weight epoxy group-containing resin having number average molecular weights ranging from 6000 to 20000.

Abstract: The invention is to provide a surface-treated steel sheet of good white rust resistance with no chromium in its surface treatment film, and it has realized a surface-treated steel sheet of higher-level corrosion resistance by forming a reaction layer of plating metal with a barrier layer effective for anticorrosion not in a two-layered film but in a single-layered film.

Abstract: A coated steel sheet having excellent corrosion resistance comprises: a zinc or a zinc alloy plated steel sheet or an aluminum or an aluminum alloy plated steel sheet; a composite oxide coating formed on the surface of the plated steel sheet; and an organic coating formed on the composite oxide coating. The composite oxide coating contains a fine particle oxide and a phosphoric acid and/or a phosphoric acid compound. The organic coating has thickness of from 0.1 to 5 &mgr;m.

Abstract: Steel sheet having organic coating comprises: a zinc or a zinc alloy plated steel sheet or an aluminum or an aluminum alloy plated steel sheet; a composite oxide coating formed on the surface of the plated steel sheet and containing at least one metal selected from the group consisting of Mn and Al; and an organic coating formed on the composite oxide coating and containing a rust-preventive additive component.

Abstract: This invention provides an organic composite coated steel sheet comprising, as the base, a zinc or zinc alloy coated steel sheet, which can be used in automobile bodies and electric appliances. The coated steel sheet has excellent press formability with oil, while having excellent perforation corrosion resistance and excellent corrosion resistance in a rust-contaminated environment. The coated steel sheet comprises a zinc or zinc alloy plated steel sheet having, on its surface, a chromate layer and an organic film formed in that order, in which the organic film has a thickness of from 0.1 to 3.0 .mu.

Abstract: An organic composite coated steel sheet having an excellent corrosion resistance in a rust-contaminated environment. The sheet contains a chromate film on a zinc or zinc alloy plated sheet and an organic resin film on the chromate film. The resin film has a thickness of 0.2-2.0 microns. The resin film contains (a) a base resin obtained by adding at least one basic nitrogen atom and at least two primary hydroxyl groups to the ends of molecules of an epoxy resin, (b) a polyfunctional polyisocyanate compound having at least six isocyanate groups per molecule, and (c) a rust-preventing additive of a sparingly soluble chromate or a mixture of silica and a sparingly soluble chromate.

Abstract: A black steel sheet having a sufficiently small coating thickness to allow the welding of the steel sheet, and yet exhibiting an excellently black surface. It is a steel sheet having a surface plated with zinc or a zinc alloy, and carrying a chromate film formed on its plated surface, and a black film formed on the chromate film from a composition comprising specific proportions of a thermosetting resin and a black dye, which are both soluble in an organic solvent, and having a sufficiently small thickness. The composition may further contain a solid lubricant, or a granular rust-inhibitive pigment, or both.

Abstract: A colored steel sheet having a coating thickness which is sufficiently small to permit welding therethrough, and yet exhibiting an excellently colored and lustrous surface. It is a steel sheet having a surface plated with zinc or a zinc alloy, and carrying a chromate film formed on its plated surface, and a colored film formed on the chromate film from a composition comprising specific proportions of a thermosetting resin and a dye, which are both soluble in an organic solvent. The composition may further contain a solid lubricant, or a granular rust-inhibitive pigment, or both. The colored film has a specific range of thickness, and a color other than black.

Abstract: A black steel sheet having a sufficiently small coating thickness to allow the welding of the steel sheet, and yet exhibiting an excellently black surface, but also having high corrosion resistance, adhesive strength and formability. It is a steel sheet having a surface plated with zinc or zinc alloy, and carrying a chromate film formed on its plated surface, and a black film formed on the chromate film from a composition comprising specific proportions of a water-soluble or water-dispersible thermosetting resin and a water-soluble black dye, and having a sufficiently small thickness. The composition may further contain a solid lubricant, or a granular rust-inhibitive pigment, or both.

Abstract: A colored steel sheet having a coating thickness which is sufficiently small to permit welding therethrough, and yet exhibiting an excellent colored and lustrous surface. It is a steel sheet having a surface plated with zinc or zinc alloy, and carrying a chromate film formed on its plated surface, and a colored film formed on the chromate film from a composition comprising specific proportions of a water-soluble or water-dispersible thermosetting resin and a water-soluble dye. The composition may further contain a solid lubricant, or a granular rust-inhibitive pigment, or both. The colored film has a specific range of thickness, and a color other than a black.

Abstract: A steel sheet plated with zinc or a zinc alloy carries a chromate film formed on each side thereof and having a coating weight of 1 to 200 mg/m.sup.2 in terms of metallic chromium, and a black film formed at least on the chromate film on one side thereof. The black film contains 100 parts by weight of a thermosetting resin which is soluble in an organic solvent, 1 to 200 parts by weight of a black dye which is also soluble in an organic solvent, and 1 to 100 parts by weight of organic resin particles. It may further contain 1 to 100 parts by weight of fine inorganic particles, or a solid lubricant, or both. The black film has a thickness of 0.3 to 5.0 microns which is sufficiently small to permit the welding of the sheet, and yet has an excellently black surface. The organic resin particles, etc., which are used as a matting agent, give the film a surface of low gloss which resists visible staining by fingerprints.