Surface-treated steel sheet and method for producing surface-treated steel sheet

Patent metadata

Field	Value
Publication number	US-11091839-B2
Application number	US-201716066863-A
Country	US
Kind code	B2
Filing date	Mar 9, 2017
Priority date	Mar 9, 2016
Publication date	Aug 17, 2021
Grant date	Aug 17, 2021

Abstract

The object of the invention is to provide a surface-treated steel sheet having a coating having fine adhesiveness to an adhesive on the surface and having excellent corrosion resistance, and a production method thereof. Provided is a surface-treated steel sheet including: a steel sheet; a plated layer containing zinc on the steel sheet; and a coating on the plated layer, wherein the coating contains an acrylic resin, zirconium, vanadium, phosphorus and cobalt, and the acrylic resin has an area ratio of 80 to 100 area % in an area from a surface to a thickness of one-fifth of a film thickness of the coating, and an area ratio of 5 to 50 area % in an area including areas from the film thickness center of the coating to a thickness of one-tenth of the film thickness toward the surface side and toward the plated layer side.

First claim

The invention claimed is:

1. A surface-treated steel sheet comprising:
a steel sheet;
a plated layer that contains zinc and is formed on the steel sheet; and
a coating formed on the plated layer,
wherein the coating contains an acrylic resin, zirconium, vanadium, phosphorus and cobalt,
the acrylic resin has an area ratio of 80 to 100 area % in an area from a surface of the coating to a thickness of one-fifth of a film thickness of the coating on a cross-section of the coating, and the acrylic resin has an area ratio of 5 to 50 area % in an area including an area from the film thickness center of the coating to a thickness of one-tenth of the film thickness toward the surface side and an area from the film thickness center to a thickness of one-tenth of the film thickness toward the plated layer side,
wherein the zirconium is contained in the coating by 4 to 400 mg/m 2 in terms of metal.

2. The surface-treated steel sheet according to claim 1 , wherein
a plurality of island projections is present on the surface of the coating in a planar view, and
when three or more virtual straight lines each having a length of equal to or more than 10 μm and extending in any direction are drawn on any positions on the surface of the coating in a planar view, a length of each island projection is 0.1 to 5.0 μm, where the length of each island projection is defined as an average value of lengths of a plurality of line segments, which are portions of the virtual straight lines passing through the projections.

3. The surface-treated steel sheet according to claim 2 , wherein the surface of the coating in an area of 1 μm by 1 μm has an arithmetic mean roughness Ra of 5 to 50 nm, a maximum cross-sectional height Rt of a roughness curve of 50 to 500 nm, and a root mean square roughness Rq of 10 to 100 nm.

4. The surface-treated steel sheet according to claim 2 , wherein a concentration of the zirconium in an area between adjacent island projections on the surface of the coating is less than a concentration of the zirconium in an area on which the island projections are formed.

5. The surface-treated steel sheet according to claim 2 , wherein a concentration of the acrylic resin in an area between adjacent island projections on the surface of the coating is more than a concentration of the acrylic resin in an area on which the island projections are formed.

6. The surface-treated steel sheet according to claim 1 , wherein
the coating has a mass ratio of a mass of the vanadium to a mass of the zirconium of 0.07 to 0.69,
a mass ratio of a mass of the phosphorus to the mass of the zirconium of 0.04 to 0.58, and
a mass ratio of a mass of the cobalt to the mass of the zirconium of 0.005 to 0.08.

7. The surface-treated steel sheet according to claim 1 , wherein the acrylic resin has an area ratio of 20 to 60 area % on a cross-section of the coating.

8. The surface-treated steel sheet according to claim 1 , wherein the plated layer consists of, in mass %, one or more of Al: less than or equal to 60%, Mg: less than or equal to 10%, and Si: less than or equal to 2%; zinc; and impurities.

9. The surface-treated steel sheet according to claim 1 , wherein the acrylic resin is a copolymer of, in mass %, styrene: 15 to 25%, (meth)acrylic acid: 1 to 10%, (meth)acrylic acid alkyl ester: 40 to 58% and acrylonitrile: 20 to 38%, and the acrylic resin has a glass transition temperature of −12 to 24° C.

10. The surface-treated steel sheet according to claim 1 , wherein the coating contains less than or equal to 5% by mass of a fluoride ion.

11. A method for producing the surface-treated steel sheet according to claim 1 , comprising:
a step of forming a plated layer containing zinc on a steel sheet;
a step of forming a coating by applying an aqueous surface treating agent containing an acrylic resin, zirconium, vanadium, phosphorus and cobalt on the plated layer by using a roll coater;
a step of retaining the coating for equal to or more than 0.5 seconds from the formation of the coating to initiation of heating of the coating; and
a step of heating the coating to dry the coating,
wherein, in the step of applying the aqueous surface treating agent, a viscosity of the aqueous surface treating agent measured at 25° C. is equal to or more than 1 mPa·s and equal to or less than 4 mPa·s.

12. The method for producing the surface-treated steel sheet according to claim 11 , wherein, in the step of applying the aqueous surface treating agent, a temperature of the steel sheet when the steel sheet enters into the roll coater is equal to or more than 5° C. and equal to or less than 80° C.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Shoji Hiromasa
• Toshin Kunihiko
• Ueda Kohei
• Morishita Atsushi

Classifications

• C09D5/10

  containing metal dust · CPC title

• C23C2/40

  Plates; Strips · CPC title

• C23C22/05

  using aqueous solutions · CPC title

• B05D3/0254

  After-treatment · CPC title

• C09D5/106

  containing Zn · CPC title