Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1998-09-21
2001-08-28
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S472000, C427S405000, C427S407100, C205S319000, C205S320000
Reexamination Certificate
active
06280852
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a surface-treated steel sheet for a laminate being excellent in tenacious adhesion of surface-treated steel sheet to a film after forming, and relates to a process for producing it.
BACKGROUND ART
Heretofore, as one used for a base plate of laminated steel sheet in which films are laminated on a steel sheet, there is a surface-treated steel sheet as disclosed in Japanese Patent Laid Open No. 138786 of 1995 (Heisei 7).
However, the above-mentioned surface-treated steel sheet was difficult to be applied for uses such as in deep-drawn can, can end and others in which it is hard to be formed, since the performance of tenacious adhesion of the surface-treated steel sheet to thermoplastic resin film was not specifically examined. Particularly, in thin deep-drawn can and others, it particularly needs to be excellent in tenacious adhesion of surface-treated steel sheet to a film in order that excellent corrosion resistance can be secured even after forming.
Accordingly, it is the object of the present invention to provide a surface-treated steel sheet used as a base sheet for manufacturing a laminated steel sheet being excellent in tenacious adhesion of the surface-treated steel sheet to film after forming, while improving drawbacks of conventional surface-treated steel sheet.
DISCLOSURE OF INVENTION
The process for producing a laminated steel sheet of the present invention is characterized in that a surface-treated steel sheet having an outermost chromium oxide layer with a specific surface area of 1.08 to 1.35 is used as a base sheet, and a plastic film is laminated on at least one side of said base sheet.
According to this process, a laminated steel sheet in which a surface-treated steel sheet having an outermost chromium oxide layer with a specific surface area of 1.08 to 1.35 is used as a base sheet, and a laminated steel sheet, produced by laminating at least one side of the said base sheet with a plastic film is provided.
And a specific surface area of an outermost chromium oxide layer in a surface-treated steel sheet as a base sheet is desirable to be 1.08 to 1.35.
The above-mentioned surface-treated steel sheet can be produced by forming an outermost chromium oxide layer on a steel sheet, and thereafter rinsing the outmost chromium oxide layer with water or warm water so that the value of a specific surface area of the outermost chromium oxide layer comes to 1.08 to 1.35.
A laminated steel sheet of the present invention has an excellent tenacious adhesion of surface-treated steel sheet to film after forming and can be applied for uses such as in thin deep-drawn can in which it is severely formed.
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention is explained in detail referring examples. A surface-treated steel sheet of the present invention comprises a steel sheet as a material for the surface-treated steel sheet, with a metallic chromium layer and a chromium oxide layer formed on at least one side. For a steel sheet as a material for the surface-treated steel sheet, conventional low carbon steel, hyper low carbon steel and high carbon steel and others are used.
Metallic chromium of from 30 mg/m
2
to 300 mg/m
2
, desirably of from 30 mg/m
2
to 200 mg/m
2
, is applied for metallic chromium layer. The lower limit is set to be 30 mg/m
2
by reason of giving corrosion resistance, and the upper limit is set to be 300 mg/m
2
by reason that even when the amount of metallic chromium is increased exceeding 300 mg/m
2
, the effect of corrosion resistance is saturated and it is not economical.
Chromium oxide of from 5 mg/m
2
to 40 mg/m
2
as chromium is applied for chromium oxide layer. The lower limit is set to be 5 mg/m
2
by reason that when decreasing the amount of chromium oxide below it, tenacious adhesion of surface-treated steel sheet to film becomes poor, and the upper limit is set to be 40 mg/m
2
by reason that even when increasing the amount of chromium oxide exceeding it, the effect of corrosion resistance is saturated and the appearance comes to be darkened.
In order to secure excellent performance of a laminated steel sheet even after severe forming such as for thin deep-drawn can, the tenacious adhesion of surface-treated steel sheet to a film is particularly an important matter. There are several methods for improving the tenacious adhesion of surface-treated steel sheet to a film. However, in the present invention, the inventors noticed the condition of the surface of a surface-treated steel sheet which is brought into direct contact with a film. Namely, it was found that for the surface condition of a surface-treated steel sheet which is brought into direct contact with a film, the one having a certain surface area is excellent in the tenacious adhesion of it to a film. The concept of “surface area” hereon is different from that of the surface roughness measured by a profile measuring method, and is more approximate to the concept of what is called “surface activity”.
A specific surface area mentioned in claims according to the present invention means a state of surface having extremely fine roughness which cannot be measured by a conventional profile measuring method, wherein by restricting a specific surface area of a surface-treated steel sheet within a certain range, tenacious adhesion of surface-treated steel sheet to a film is increased. Namely, in the present invention, the restriction of a specific surface area between 1.08 and 1.35 resulted in the remarkable improvement of tenacious adhesion of surface-treated steel sheet to a film. The value of the specific surface area is expressed by the ratio of the surface area of an example of the present invention (real area) to that of an assumed sample having no surface roughness (projected area=reference).
As thermoplastic resin film which is laminated on a surface-treated steel sheet of the present invention, the following can be given: (1) olef in resin film such as polyethylene, polypropylene, ethylene propylene copolymer, ethylene vinylacetate copolymer, ethylene acrylic ester copolymer, ionomer and others; (2) polyester such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, ethylene terephthalate/isophthalate copolymer and others; (3) polyamide such as nylon
6
, nylon
66
, nylon
11
, nylon
12
and others, and;
(4) Polyvinyl Chloride, Polyvinylidene Chrolide and Others
These thermoplastic resin films have different characteristics in terms of heat resistance, corrosion resistance, adhesion of film to steel sheet, and can be used properly according to contents of a food can. Further, when the adhesion of these thermoplastic resin film with a base sheet is not sufficient, for example, epoxy resin adhesive, phenol resin adhesive, amide resin adhesive, urethane resin adhesive, acid modified olefin resin adhesive, copolyamide resin adhesive, copolyester resin adhesive and a blend thereof can be laid between a thermoplastic resin layer and a surface-treated steel sheet.
Further, the thickness of thermoplastic resin films is desirable to be between 3 &mgr;m and 50 &mgr;m in general. When the thickness thereof is below 3 &mgr;m, the laminating efficiency is remarkably lowered, and besides pinholes are apt to be caused so that sufficient corrosion resistance cannot be obtained. On the other hand, when the thickness thereof exceeds 50 &mgr;m, it is not economical as compared with paints used widely in the field of can manufacturing. There are cases where thermoplastic resin films are laminated on both sides of a base sheet and where a thermoplastic resin film is laminated on one side of it.
Next, a method for producing a surface-treated steel sheet of the present invention is explained. First, a cold-rolled steel sheet is degreased and pickled. Thereafter, metallic chromium is deposited on the steel sheet as a cathode in a treating bath for electrolytic chromate coating mainly composed of chromic anhydride, in which small amount of one or more of sulfuric acid, sulfate, fluoric acid, fluoride, silicofluo
Komai Masao
Shimizu Nobuyoshi
Taniguchi Ayumu
Browdy and Neimark
Jones Deborah
Toyo Kohan Co. Ltd.
Young Bryant
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