Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-03-27
2003-09-09
La Villa, Michael (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S659000, C428S334000, C428S339000, C428S416000, C428S458000, C427S385500, C427S388100
Reexamination Certificate
active
06617048
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a prepainted steel sheet and a method for preparation thereof. The prepainted steel sheet of the present invention is used as materials of, for example, household electric appliances such as a refrigerator and a fan heater, building materials and automobile parts.
2. Description of the Related Arts
The prepainted steel sheet usually used is painted in two-coat. Such type of prepainted steel sheet maintains adhesiveness to a base steel sheet, corrosion resistance and the like by mainly using a modified polyester resin or an epoxy resin as a primer, and gives mainly contamination-resistance, design-ability, flaw-resistance, barrier property and the like by using polyester and acrylic paints as a topcoat paint. On the other hand, since preparation of two-coat-prepainted steel sheet needs many processes when painting and baking, it takes longer time for them. Therefore, one-coat coating and thin coating are desirable from the viewpoints of rationalization of painting work and conservation of resources.
However, when using a paint itself for a conventional prepainted steel sheet as one-coat in solvent-type-paint, use of a primer only is insufficient for contamination-resistance, design-ability and the like, while use of topcoat paint only is insufficient for adhesiveness to a base steel sheet and corrosion resistance. In addition, a one-coat-painting steel sheet with a powder paint has been already manufactured, there are, however, drawbacks that the powder paint thickens the coating and takes longer time to cure.
Accordingly, it is required to design a thin coating film which has both functions of a primer layer and a topcoat layer of a two-coat-prepainted steel sheet and is capable of curing in a short time in order to adopt a one-coat-prepainted steel sheet by a solvent-type paint, considering rationalization of the painting work, the resource-saving and the like.
Incidentally, the prepainted steel sheet requires various properties such as high hardness, high workability, contamination-resistance, chemical resistance, water-resistance, corrosion resistance and the like. Among them, the molding workability is extremely important capability for the prepainted steel sheet to perform molding process after painting and baking. Herein, molding workability means that there is little damage of coating in processes such as bending, drawing and cutting when processing to different shapes from a planar metal sheet. In a molding process such as relatively mild bending process, the higher the degree of the spread and softening of coating itself are, the better the workability becomes. Further, in severe molding process such as drawing process, it becomes significant to have the strength endurable to deformation or stress when processing and flaw-resistance as well as spread and softness of the coating.
To such required properties of the prepainted steel sheet, for example, a paint composition combining a specific polyester resin, a melamine resin (curing agent) and the like and a painted steel sheet by use thereof have been proposed in Japanese Unexamined Patent Publication No. 8-100150 in order to obtain the coating excellent in hardness, contamination-resistance and weather resistance.
It has been also proposed in Japanese Unexamined Patent Publication No. 9-111183 that another painted steel sheet fulfils workability, corrosion resistance, adhesiveness, shock resistance, scratch-resistance and design-ability by being painted with a paint composition combined with a polyester resin, a melamine resin (a curing agent), a rust preventive pigment, an organic polymeric microparticles and the like, However, in the art of Japanese Unexamined Patent Publication No. 8-100150 of such prior arts, the polyester resin has not been designed so as to obtain a strong coating endurable to stress when molding a severe process such as a drawing process in one-coat, resulting in insufficient molding workability.
Also in the art of Japanese Unexamined Patent Publication No. 9-111183, the polyester resin has not been designed so as to obtain a strong coating endurable to stress when molding a severe process such as a drawing process in one-coat, resulting in insufficient molding workability.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a one-coat-prepainted steel sheet and a method for producing the same of which hardly generate flaws to a severe working process such as drawing process and enable fast operations when manufacturing.
To attain the object, first, the present invention provides the one-coat-prepainted steel sheet comprising a chemically conversion-treated zinc-plated steel sheet and a coating containing polyester resin (A) and melamine resin (D) formed on the surface of said zinc-plated steel sheet.
A thickness of dried film of said coating is not more than 10 &mgr;m. Said coating is formed by painting and baking of a solvent-type-paint composition composed of 100 parts by weight (a ratio of solid content) of polyester resin (A) and 5-30 parts by weight (a ratio of solid content) of melamine resin (D) as main components.
Said polyester resin (A) has a number-average molecular weight of 5000-25000, a glass transition temperature of 20-80° C., a hydroxyl value of 3-30 KOH mg/g, and an acid value of 0-10 KOH mg/g. A 20-70 mol % of polyalcohol components in polyester resin (A) is cyclohexanedimethanol.
Secondly, the present invention provides the one-coat-prepainted steel sheet comprising a chemically conversion-treated zinc-plated steel sheet and a coating containing polyester resin (A), epoxy resin (B) and melamine resin (D) formed on the surface of said zinc-plated steel sheet.
A thickness of dried film of said coating is not more than 10 &mgr;m. Said coating is formed by painting and baking of a solvent-type-paint composition composed of 100 parts by weight (a ratio of solid content) of polyester resin (A), 5-25 parts by weight (a ratio of solid content) of epoxy resin (B) having 180-1000 epoxy equivalents, and 5-30 parts by weight (ratio of solid content) of melamine resin (D) as main components.
Said polyester resin (A) has a number-average molecular weight of 5000-25000, a glass transition temperature of 20-80° C., a hydroxyl value of 3-30 KOH mg/g, and an acid value of 0-10 KOH mg/g.
20-70 mol % of polyalcohol components in polyester resin (A) is cyclohexanedimethanol.
The first and second one-coat-prepainted steel sheets are produced by a method comprising the steps of:
painting a solvent-type-paint composition on the surface of a chemically conversion-treated zinc-plated steel sheet; and
forming a curing coating by baking a painted paint composition on said plated steel sheet at 200-250° C. of an reaching sheet temperature in 20-90 sec of baking time.
Thirdly, the present invention provides the one-coat-prepainted steel sheet comprising a chemically conversion-treated zinc-plated steel sheet and a coat containing polyester (A) and a curing agent formed on the surface of said zinc-plated steel sheet.
A thickness of dried film of said coating is not more than 10 &mgr;m. Said coating is formed by painting and baking of a solvent-type-paint composition composed of 100 parts by weight (a ratio of solid content) of polyester resin (A) and 3-20 parts by weight (a ratio of solid content) of a curing agent as main components.
Said curing agent containing blocked polyisocyanate compound (C) and melamine resin (D) is composed of a mixing weight ratio (C)/(D) of 100/0-15/85 in the solid content.
Said polyester resin (A) has a number-average molecular weight of 5000-25000, a glass transition temperature of 20-80° C., a hydroxyl value of 3-30 KOH mg/g, and an acid value of 0-10 KOH mg/g.
A 20-70 mol % of polyalcohol components in polyester resin (A) is cyclohexanedimethanol.
Fourthly, the present invention provides the one-coat-prepainted steel sheet comprising a chemically conversion-treated zinc-plated steel sheet and a coating containing polyester resin (A), epoxy resin (B) and a curing
Ito Kazumi
Kajita Yasuyuki
Kato Hiroyuki
Kato Nobuyoshi
Ogawa Susumu
Frishauf Holtz Goodman & Chick P.C.
La Villa Michael
NKK Corporation
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