Paint composition for pre-coated metal and method of curing treatment of pre-coated metal by using the composition

Patent metadata

Field	Value
Publication number	US-9505947-B2
Application number	US-201213883992-A
Country	US
Kind code	B2
Filing date	Feb 16, 2012
Priority date	Feb 18, 2011
Publication date	Nov 29, 2016
Grant date	Nov 29, 2016

Abstract

Provided is a paint composition for a two-step curing process including a binder resin containing a hydroxyl group and a hardener having a functional group reactable with the hydroxyl group. The paint composition includes: one or more binder resins selected from the group consisting of a polyester resin, an alkyd resin, an acryl resin, and a modified resin thereof; and a hardener including one or more selected from an isocyanate group and one or more selected from a melamine group, wherein mechanical processing is performed on a steel sheet coated with the composition and primarily cured, and then mechanical and chemical properties of a coating layer damaged during the mechanical processing are recovered through secondary curing.

First claim

The invention claimed is:

1. A method of treating a surface of a steel sheet, the method comprising the steps of:
(a) forming a coating layer by coating the surface of the steel sheet with a paint composition comprising a binder resin selected from the group consisting of a polyester resin, an alkyd resin, an acrylic resin, and a modified resin thereof, wherein the binder has a hydroxyl value of 5 mgKOH/g to 100 mgKOH/g and a molecular weight of 1,000 to 25,000;
(b) performing primary curing on the coating layer by heating within a temperature range of 180° C. to 300° C.;
(c) molding the steel sheet having the primarily cured coating layer formed thereon by mechanical processing; and
(d) performing secondary curing on the molded steel sheet by heating within a temperature range of 140° C. to 200° C. to recover physical properties of the coating layer damaged in the molding.

2. The method according to claim 1 , wherein the primary curing of the step (b) is performed for a time range of 10 seconds to 5 minutes and the secondary curing of the step (d) is performed for a time range of 5 minutes to 50 minutes.

3. The method according to claim 1 , wherein the paint composition comprises
a hardener selected from one or more of an isocyanate group and a melamine group.

4. The method according to claim 3 , wherein the isocyanate group is one or more selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and xylene diisocyanate, or a blocked isocyanate group.

5. The method according to claim 3 , wherein a stoichiometric ratio of the isocyanate group to a hydroxyl group of the resin is in a range of 0.6 to 1.4.

6. The method according to claim 3 , wherein the melamine group is one or more selected from the group consisting of alkylate, imino, and carboxylate.

7. The method according to claim 3 , wherein a weight ratio of the melamine group to a total resin content of the paint composition is in a range of 10% to 50%.

Assignees

• Park Jong Myung
• Kim Jung Teag
• Jung Ho Su
• Postech Academy-Industry Found

Inventors

• Park Jong Myung
• Kim Jung Teag
• Jung Ho Su

Classifications

• C09D175/04

  Polyurethanes · CPC title

• C23C26/00 Primary

  Coating not provided for in groups C23C2/00 - C23C24/00 · CPC title

• C09D167/00 Primary

  Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain (based on polyester-amides C09D177/12; based on polyester-imides C09D179/08); Coating compositions based on derivatives of such polymers · CPC title

• C08L61/28

  with melamine · CPC title

• B05D3/0209

  Multistage baking · CPC title