U.S. patent application number 14/006837 was filed with the patent office on 2015-05-14 for surface treatment agent composition, method for producing surface-treated steel sheet, surface-treated steel-sheet, surface-treated steel sheet with organic coating, can lid, can body, and seamless can.
This patent application is currently assigned to Nippon Paint Co., Ltd.. The applicant listed for this patent is Tomio Hirano, Munemitsu Hirotsu, Seitaro Kanazawa, Wataru Kurokawa, Masahiko Matsukawa, Naomi Taguchi, Shinichi Taya, Miwa Uchikawa, Kunihiro Yoshimura. Invention is credited to Tomio Hirano, Munemitsu Hirotsu, Seitaro Kanazawa, Wataru Kurokawa, Masahiko Matsukawa, Naomi Taguchi, Shinichi Taya, Miwa Uchikawa, Kunihiro Yoshimura.
Application Number | 20150129453 14/006837 |
Document ID | / |
Family ID | 46930840 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150129453 |
Kind Code |
A1 |
Uchikawa; Miwa ; et
al. |
May 14, 2015 |
SURFACE TREATMENT AGENT COMPOSITION, METHOD FOR PRODUCING
SURFACE-TREATED STEEL SHEET, SURFACE-TREATED STEEL-SHEET,
SURFACE-TREATED STEEL SHEET WITH ORGANIC COATING, CAN LID, CAN
BODY, AND SEAMLESS CAN
Abstract
A surface treatment agent composition for non-chromium steel
sheets for removing iron ions without reducing the amount of
aluminum ions when subjecting the steel sheet to surface treatment
by means of cathodic electrolysis using a surface treatment agent
containing aluminum ions as the main component; and a method for
producing a surface-treated steel sheet using the composition. A
surface-treated steel sheet exhibiting high corrosion resistance, a
surface-treated steel sheet with an organic coating, and a can lid,
can body and seamless can produced using the surface-treated steel
sheets. A surface treatment agent composition for steel sheets
contains aluminum ions, fluorine ions and polycarboxylic acid and
is used as the surface treatment bath used for forming a surface
treatment coating film on the surface of the steel sheet by
cathodic electrolysis.
Inventors: |
Uchikawa; Miwa; (Tokyo,
JP) ; Matsukawa; Masahiko; (Tokyo, JP) ;
Hirano; Tomio; (Tokyo, JP) ; Kurokawa; Wataru;
(Yokohama-shi, JP) ; Hirotsu; Munemitsu;
(Yokohama-shi, JP) ; Kanazawa; Seitaro;
(Yokohama-shi, JP) ; Yoshimura; Kunihiro;
(Kudamatsu-shi, JP) ; Taya; Shinichi;
(Kudamatsu-shi, JP) ; Taguchi; Naomi;
(Kudamatsu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Uchikawa; Miwa
Matsukawa; Masahiko
Hirano; Tomio
Kurokawa; Wataru
Hirotsu; Munemitsu
Kanazawa; Seitaro
Yoshimura; Kunihiro
Taya; Shinichi
Taguchi; Naomi |
Tokyo
Tokyo
Tokyo
Yokohama-shi
Yokohama-shi
Yokohama-shi
Kudamatsu-shi
Kudamatsu-shi
Kudamatsu-shi |
|
JP
JP
JP
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
Nippon Paint Co., Ltd.
Osaka-shi
JP
Toyo Kohan Co., Ltd.
Tokyo
JP
Toyo Seikan Kaisha, Ltd.
Tokyo
JP
|
Family ID: |
46930840 |
Appl. No.: |
14/006837 |
Filed: |
March 22, 2012 |
PCT Filed: |
March 22, 2012 |
PCT NO: |
PCT/JP2012/057349 |
371 Date: |
January 29, 2014 |
Current U.S.
Class: |
206/524.3 ;
205/320; 428/219; 524/429 |
Current CPC
Class: |
C09D 5/4411 20130101;
C25D 9/10 20130101; C09D 133/02 20130101; B65D 25/36 20130101; C25D
11/34 20130101; C09D 5/103 20130101; C25D 9/02 20130101 |
Class at
Publication: |
206/524.3 ;
205/320; 524/429; 428/219 |
International
Class: |
C25D 9/02 20060101
C25D009/02; B65D 25/36 20060101 B65D025/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2011 |
JP |
2011-067939 |
Claims
1. A surface treatment agent composition for a steel sheet, the
composition being used in electrolytic surface treatment of a steel
sheet having a surface to which iron is at least partially exposed,
and the composition comprising aluminum ions, fluorine ions, and a
polycarboxylic acid.
2. The surface treatment agent composition for a steel sheet
according to claim 1, wherein the polycarboxylic acid is a
homopolymer containing a monomer selected from the group consisting
of acrylic acid, methacrylic acid, maleic acid, and itaconic acid
as a constitutional unit or a copolymer containing at least one of
these monomers as the constitutional unit.
3. The surface treatment agent composition for a steel sheet
according to claim 1, wherein a ratio [carboxyl group]/[Al] of a
molar concentration [carboxyl group] of carboxyl groups contained
in the polycarboxylic acid to a molar concentration [Al] of the
aluminum ions is 0.005 to 2.0.
4. The surface treatment agent composition for a steel sheet
according to claim 1, wherein the polycarboxylic acid is
polyitaconic acid.
5. The surface treatment agent composition for a steel sheet
according to claim 1, wherein a ratio [F]/[Al] of a molar
concentration [F] of the fluorine ions to a molar concentration
[Al] of the aluminum ions is 1 to 4.
6. The surface treatment agent composition for a steel sheet
according to claim 1, wherein a mass concentration of the aluminum
ions is 100 to 10000 ppm.
7. The surface treatment agent composition for a steel sheet
according to claim 1, wherein the surface treatment agent
composition has a pH value of 1 to 5 at 25.degree. C.
8. The surface treatment agent composition for a steel sheet
according to claim 1, wherein the surface treatment agent
composition contains iron ions having a mass concentration of 200
ppm or less.
9. A method of producing a surface-treated steel sheet, comprising
subjecting a steel sheet having a surface to which iron is at least
partially exposed to cathodic electrolysis in a surface treatment
bath containing aluminum ions, fluorine ions, and a polycarboxylic
acid to form a treatment film on the surface of the steel sheet,
wherein the treatment film contains a metal-oxygen compound and a
polycarboxylic acid; the metal-oxygen compound contains oxygen
compounds of aluminum and iron in which the main component is the
aluminum-oxygen compound; and the treatment film has an aluminum
amount of 5 to 150 mg/m.sup.2 and a carbon amount of 0.1 to 5.0
mg/m.sup.2, in terms of metal element.
10. The method of producing a surface-treated steel sheet according
to claim 9, wherein the polycarboxylic acid is a homopolymer
containing a monomer selected from the group consisting of acrylic
acid, methacrylic acid, maleic acid, and itaconic acid as a
constitutional unit or a copolymer containing at least one of these
monomers as the constitutional unit.
11. The method of producing a surface-treated steel sheet according
to claim 9, wherein in the surface treatment bath, a ratio
[carboxyl group]/[Al] of a molar concentration [carboxyl group] of
carboxyl groups contained in the polycarboxylic acid to a molar
concentration [Al] of the aluminum ions is 0.005 to 2.0.
12. The method of producing a surface-treated steel sheet according
to 9, wherein the polycarboxylic acid is polyitaconic acid.
13. The method of producing a surface-treated steel sheet according
to claim 9, wherein in the surface treatment bath, a ratio [F]/[Al]
of a molar concentration [F] of the fluorine ions to a molar
concentration [Al] of the aluminum ions is 1 to 4.
14. The method of producing a surface-treated steel sheet according
to claim 9, wherein in the surface treatment bath, a mass
concentration of the aluminum ions is 100 to 10000 ppm.
15. The method of producing a surface-treated steel sheet according
to claim 9, wherein the surface treatment bath has a pH value of 1
to 5 at 25.degree. C.
16. The method of producing a surface-treated steel sheet according
to 9, wherein the surface treatment bath contains iron ions having
a mass concentration of 200 ppm or less.
17. A surface-treated steel sheet comprising a surface treatment
film containing a metal-oxygen compound and a polycarboxylic acid
formed on a steel sheet having a surface to which iron is at least
partially exposed, wherein the metal-oxygen compound contains
aluminum and iron and mainly includes an aluminum-oxygen compound;
and the surface treatment film has an aluminum amount of 5 to 150
mg/m.sup.2 and a carbon amount of 0.1 to 5.0 mg/m.sup.2, in terms
of metal element.
18. The surface-treated steel sheet according to claim 17, wherein
the surface treatment film has an atomic ratio (Fe/Al) of iron to
aluminum of 0.5 or less.
19. The surface-treated steel sheet according to claim 17, wherein
the polycarboxylic acid is a homopolymer containing a monomer
selected from the group consisting of acrylic acid, methacrylic
acid, maleic acid, and itaconic acid as a constitutional unit or a
copolymer containing at least one of these monomers as the
constitutional unit.
20. A surface-treated steel sheet with an organic coating,
comprising a surface-treated steel sheet according to claim 17 and
a thermoplastic resin laminated on at least one surface of the
steel sheet.
21. A surface-treated steel sheet with an organic coating,
comprising a surface-treated steel sheet according to claim 17 and
a thermosetting resin laminated on at least one surface of the
steel sheet.
22. A can lid molded from a surface-treated steel sheet with an
organic coating according to claim 20.
23. A can body molded from a surface-treated steel sheet with an
organic coating according to claim 20.
24. A seamless can molded from a surface-treated steel sheet with
an organic coating according to claim 20 by
drawing/bending-stretching and/or ironing.
Description
TECHNICAL FIELD
[0001] The present invention relates to a surface treatment agent
composition for producing a surface-treated steel sheet, a method
for producing a surface-treated steel sheet using the surface
treatment agent composition, a surface-treated steel-sheet, a
surface-treated steel sheet with an organic coating, a can lid, a
can body, and a seamless can. More specifically, the invention
relates to a surface treatment agent composition that allows
production of a surface-treated steel sheet having excellent
high-speed processing ability, corrosion resistance, and coating
adhesion and exhibiting excellent processing adhesion even in
severe processing thereof and that is a chromium-free composition
having excellent bath stability, a method for producing a
surface-treated steel sheet using the surface treatment agent
composition, a surface-treated steel sheet, surface-treated steel
sheet with an organic coating, a can lid, a can body, and a
seamless can.
BACKGROUND ART
[0002] Chromate treatment has heretofore been known as treatment
for improving the adhesion between a steel sheet and an organic
coating and has therefore been widely used in the fields of home
electric appliances, building materials, vehicles, aircrafts, and
containers and other fields because of its provision of excellent
corrosion resistance and adhesion.
[0003] The chromate treatment is roughly classified based on the
treatment methods into a chemical conversion-type (reaction
type.cndot.coating type) and an electrolytic type and is roughly
classified based on the film formation into a type of which end
product contains a small amount of residual hexavalent chromium for
more highly utilizing the self-repair effect and a type of which
end product does not contain hexavalent chromium.
[0004] Even if the chromate treatment is employed for metal
materials for metal containers, the chromate treatment is a type in
which hexavalent chromium does not remain in end products. The
treatment liquid, however, contains hexavalent chromium, which is a
harmful material, and therefore involves various environmental
problems. That is, it is necessary to perform, for example,
completely drainage and exhaust of the--treatment liquid containing
the hexavalent chromium not to discharge to the outside, and
therefore a huge amount of money is necessary for drainage and
exhaust processing facilities and waste disposal. Furthermore,
regulations against transfer and exhaust of wastewater treatment
sludge have become strict, and therefore there is a demand for
developing a chromium-free surface treatment that is comparable to
the conventional chromate treatment.
[0005] As chromium-free surface treatment for steel sheet
materials, immersion treatment and cathodic electrolytic treatment
using a treatment liquid containing Zr (zirconium) or Ti (titanium)
have been proposed (Patent Literatures 1, 2, and 3).
[0006] Cathodic electrolytic treatment using a treatment liquid
containing Al (aluminum) ions has also been proposed (Patent
Literature 4). [0007] [Patent Document 1] PCT International
Application, Publication No. 2002/103080 [0008] [Patent Document 2]
Japanese Unexamined Patent Application, Publication No. 2004-190121
[0009] [Patent Document 3] Japanese Unexamined Patent Application,
Publication No. 2005-97712 [0010] [Patent Document 4] Japanese
Unexamined Patent Application, Publication No. 2006-348360
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0011] The present inventors have found this time that in the case
of using a treatment liquid containing aluminum ions, the corrosion
resistance of the resulting film is deteriorated with an increase
in concentration of iron ions in a treatment bath eluted from a
steel sheet as the base material. Accordingly, in order to maintain
the corrosion resistance of the resulting film, it is necessary to
remove the iron ions from the treatment bath.
[0012] However, it is difficult to selectively remove iron ions,
and, usually, aluminum ions are also removed together with the iron
ions. In such a case, since the aluminum ions, which are a film
forming component, are also removed, the film deposition efficiency
of aluminum decreases to reduce the film amount, resulting in a
problem of reducing the corrosion resistance of the film.
[0013] Accordingly, it is an object of the present invention to
provide a chromium-free surface treatment agent composition for a
steel sheet allowing removal of iron ions without reducing the
amount of the aluminum ions in the surface treatment of the steel
sheet by cathodic electrolysis using the surface treatment agent
composition mainly containing aluminum ions, and to provide a
method of producing a surface-treated steel sheet using the
composition.
[0014] In addition, it is an object of the present invention to
provide a surface-treated steel sheet and a surface-treated steel
sheet with an organic coating having high corrosion resistance
compared to those of conventional technologies and to provide a can
lid, a can body, and seamless can produced from these steel
sheets.
Means for Solving the Problems
[0015] (1) The present invention relates to a surface treatment
agent composition for a steel sheet, the composition being used in
electrolytic surface treatment of a steel sheet having a surface to
which iron is at least partially exposed, and the composition
including aluminum ions, fluorine ions, and a polycarboxylic
acid.
[0016] The polycarboxylic acid is preferably a homopolymer
containing a monomer selected from acrylic acid, methacrylic acid,
maleic acid, and itaconic acid as a constitutional unit or a
copolymer containing at least one of these monomers as the
constitutional unit.
[0017] A ratio [carboxyl group]/[Al] of a molar concentration
[carboxyl group] of carboxyl groups contained in the polycarboxylic
acid to a molar concentration [Al] of the aluminum ions is
preferably 0.005 to 2.0.
[0018] The polycarboxylic acid is preferably polyitaconic acid.
[0019] A ratio [F]/[Al] of a molar concentration [F] of the
fluorine ions to a molar concentration [Al] of the aluminum ions is
preferably 1 to 4.
[0020] A mass concentration of the aluminum ions is preferably 100
to 10000 ppm.
[0021] The surface treatment agent composition preferably has a pH
value of 1 to 5 at 25.degree. C.
[0022] The surface treatment agent composition preferably contains
iron ions having a mass concentration of 200 ppm or less.
[0023] (2) The present invention relates to a method of producing a
surface-treated steel sheet. The method comprises subjecting a
steel sheet having a surface to which iron is at least partially
exposed to cathodic electrolysis in a surface treatment bath
containing aluminum ions, fluorine ions, and a polycarboxylic acid
to form a treatment film on the surface of the steel sheet,
wherein
[0024] the treatment film contains a metal-oxygen compound and a
polycarboxylic acid;
[0025] the metal-oxygen compound contains oxygen compounds of
aluminum and iron in which the main component is the
aluminum-oxygen compound; and
[0026] the treatment film has an aluminum amount of 5 to 150
mg/m.sup.2 and a carbon amount of 0.1 to 5.0 mg/m.sup.2, in terms
of metal element.
[0027] The polycarboxylic acid is preferably a homopolymer
containing a monomer selected from acrylic acid, methacrylic acid,
maleic acid, and itaconic acid as a constitutional unit or a
copolymer containing at least one of these monomers as the
constitutional unit.
[0028] In the surface treatment bath, a ratio [carboxyl group]/[Al]
of a molar concentration [carboxyl group] of carboxyl groups
contained in the polycarboxylic acid to a molar concentration [Al]
of the aluminum ions is preferably 0.005 to 2.0.
[0029] The polycarboxylic acid is preferably polyitaconic acid.
[0030] In the surface treatment bath, a ratio [F]/[Al] of a molar
concentration [F] of the fluorine ions to a molar concentration
[Al] of the aluminum ions is preferably 1 to 4.
[0031] In the surface treatment bath, a mass concentration of the
aluminum ions is preferably 100 to 10000 ppm.
[0032] The surface treatment bath preferably has a pH value of 1 to
5 at 25.degree. C.
[0033] The surface treatment bath preferably contains iron ions
having a mass concentration of 200 ppm or less.
[0034] (3) The present invention relates to a surface-treated steel
sheet having a surface treatment film containing a metal-oxygen
compound and a polycarboxylic acid formed on a steel sheet having a
surface to which iron is at least partially exposed, wherein
[0035] the metal-oxygen compound contains aluminum and iron and
mainly includes an aluminum-oxygen compound; and
[0036] the surface treatment film has an aluminum amount of 5 to
150 mg /m.sup.2 and a carbon amount of 0.1 to 5.0 mg/m.sup.2, in
terms of metal element.
[0037] The surface treatment film preferably has an atomic ratio
(Fe/Al) of iron to aluminum of 0.5 or less.
[0038] The polycarboxylic acid is preferably a homopolymer
containing a monomer selected from acrylic acid, methacrylic acid,
maleic acid, and itaconic acid as a constitutional unit or a
copolymer containing at least one of these monomers as the
constitutional unit.
[0039] (4) The present invention relates to a surface-treated steel
sheet with an organic coating, wherein a thermoplastic resin is
laminated on at least one surface of the surface-treated steel
sheet.
[0040] (5) The present invention relates to a surface-treated steel
sheet with an organic coating, wherein a thermosetting resin is
laminated on at least one surface of the surface-treated steel
sheet.
[0041] (6) The present invention relates to a can lid molded from
the surface-treated steel sheet with an organic coating according
to the aspect (4) or (5).
[0042] (7) The present invention relates to a can body molded from
the surface-treated steel sheet with an organic coating according
to the aspect (4) or (5).
[0043] (8) The present invention relates to a seamless can molded
from the surface-treated steel sheet with an organic coating
according to the aspect (4) or (5) by
drawing.cndot.bending-stretching and/or ironing.
[0044] In the present invention, the surface treatment agent
composition for a steel sheet contains a polycarboxylic acid.
Accordingly, in a treatment bath using this surface treatment agent
composition for a steel sheet, the polycarboxylic acid captures
iron ions eluted into the treatment bath from the steel sheet to
maintain the concentration of iron ions in the treatment bath to be
a certain level or less, resulting in formation of a film having
high corrosion resistance.
[0045] The polycarboxylic acid used in the present invention
captures and precipitates iron ions eluted into a treatment bath to
reduce the iron ion concentration in the treatment bath to 200 ppm
or less, which is a level that does not affect the characteristics
of the resulting film, and also the polycarboxylic acid does not
affect the aluminum ion concentration in the treatment bath.
Consequently, a stable treatment bath can be maintained.
[0046] Furthermore, in the present invention, a film having
controlled amounts of aluminum ions and a polycarboxylic acid is
formed, which allows retaining of the conditions of the outermost
surface of the film to maintain the stable surface even under a
high-temperature high-humidity environment. Even though the film is
chromium-free, the film can retain the corrosion resistance of the
surface-treated steel sheet and can inhibit a reduction in adhesion
to the organic coating.
Effects of the Invention
[0047] The present invention provides a chromium-free surface
treatment agent composition for a steel sheet allowing removal of
iron ions without reducing the amount of the aluminum ions, in the
surface treatment of the steel sheet by cathodic electrolysis using
the surface treatment agent composition mainly containing aluminum
ions, and provides a method of producing a surface-treated steel
sheet using the composition.
[0048] The present invention provides a surface-treated steel sheet
and a surface-treated steel sheet with an organic coating having
high corrosion resistance compared to those of conventional
technologies and a can lid, a can body, and seamless can produced
from these steel sheets.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
(Steel Sheet)
[0049] The steel sheet used in the present invention may be any
steel sheet used in can manufacturing, such as a cold rolled steel
sheet. In can manufacturing, the thickness of the steel sheet is
preferably about 0.07 to 0.4 mm.
[0050] Throughout the specification, the term "steel sheet" refers
to one whose iron exposed to at least a part of a surface other
than the end faces.
(Surface Treatment Agent Composition for Steel Sheet and Surface
Treatment Bath)
[0051] The surface treatment agent composition for a steel sheet of
the present invention contains aluminum ions and a polycarboxylic
acid, which is an important characteristic of the invention. In the
case of using such a surface treatment agent composition for a
steel sheet as a surface treatment bath, the polycarboxylic acid
contained in the treatment bath captures the iron ions eluted into
the treatment bath from the steel sheet, but hardly capture
aluminum ions. Consequently, the iron ion concentration in the
treatment bath can be maintained to be a certain level or less
without decreasing the aluminum ion concentration in the treatment
bath. That is, the polycarboxylic acid contained in the surface
treatment bath forms chelates with iron ions to inhibit iron ions
from being excessively introduced into a film and partially becomes
a constituent component of the film and contributes to the adhesion
of the organic coating.
[0052] The "surface treatment bath (hereinafter may be also
referred to as simply "treatment bath")" described in the following
description mainly includes the surface treatment agent composition
for a steel sheet of the present invention and is used in
electrolytic surface treatment of a steel sheet having a surface to
which iron is at least partially exposed. In the following
description, the surface treatment agent composition for a steel
sheet is also referred to as simply "surface treatment agent
composition".
[0053] The concentration of the polycarboxylic acid in the surface
treatment agent composition is controlled such that the ratio
[carboxyl group]/[Al] of the molar concentration [carboxyl group]
of the carboxyl groups contained in the polycarboxylic acid to the
molar concentration [Al] of the aluminum ions is preferably in a
range of 0.005 to 2.0, more preferably 0.01 to 1.0, and most
preferably 0.017 to 0.069. That is, as described above, the
polycarboxylic acid has a function of forming chelates with iron
ions to inhibit iron ions from being excessively introduced into a
film and partially becomes a constituent component of the film.
However, a concentration of the polycarboxylic acid higher than the
above-mentioned range may excessively introduce the polycarboxylic
acid into a film to reduce the corrosion resistance and is
disadvantageously uneconomical. In contrast, a concentration of the
polycarboxylic acid lower than the above-mentioned range may not
sufficiently introduce to capture iron ions in the treatment bath
and may reduce the adhesion with the organic coating.
[0054] Note that throughout the specification, the molar
concentration of aluminum ions is the molar concentration in terms
of aluminum metal. Aluminum ions in the surface treatment agent
composition are partially in forms of complexes in which fluorine
ions described below or various ligands are coordinated. In the
present invention, these complexes are included in the definition
of aluminum ions.
[0055] The treatment bath contains iron ions eluted from the steel
sheet. As described above, a large amount of iron ions in the
treatment bath reduces the corrosion resistance of the resulting
film. Accordingly, in the present invention, it is preferred to
maintain the iron ion concentration in the treatment bath to be 200
ppm or less, in particular, 100 ppm or less.
[0056] The surface treatment agent composition of the present
invention is preferably an aqueous solution having a pH value of 1
to 5 at 25.degree. C., more preferably 2.0 to 4.5, and most
preferably 2.5 to 3.5. A pH value lower than the above-mentioned
range causes excessive etching of the steel sheet to increase the
iron ion concentration in the treatment bath, whereas a pH value
higher than the range causes lack of etching to prevent efficient
formation of a film and to make the treatment bath unstable.
[0057] Examples of the aluminum ion source for supplying aluminum
ions to the surface treatment agent composition include aluminum
nitrate, potassium aluminum sulfate, aluminum sulfate, aluminum
dihydrogen phosphate solution, aluminum dihydrogen phosphate,
aluminum lactate, aluminum fluoride, aluminum hydroxide, aluminum
oxide, aluminum silicate, aluminate salts such as sodium aluminate,
and sodium hexafluoroaluminate. These aluminum ion sources may be
used alone or in combination of two or more thereof.
[0058] The mass concentration of aluminum ions in the surface
treatment agent composition is preferably 100 to 10000 ppm. A
content of aluminum ions of 100 ppm or more in the surface
treatment agent composition allows formation of a film having
sufficiently high corrosion resistance on the surface of a steel
sheet, which is preferable, and a content of 10000 ppm or less can
maintain satisfactory solubility of the aluminum ions in the
surface treatment agent composition to form a uniform film on the
surface of a steel sheet. The content of aluminum ions in the
surface treatment agent composition is more preferably 1000 to 5000
ppm and most preferably 1500 to 5000 ppm in terms of aluminum
metal.
[0059] The polycarboxylic acid contained in the surface treatment
agent composition is, for example, a homopolymer containing a
monomer selected from acrylic acid, methacrylic acid, maleic acid,
and itaconic acid as a constitutional unit or a copolymer
containing at least one of these monomers as the constitutional
unit. Examples of the homopolymer include polyacrylic acid,
polymethacrylic acid, polymaleic acid, and polyitaconic acid. Among
these homopolymers, in particular, polyitaconic acid can be
preferably used.
[0060] These polycarboxylic acids may be alkali metal salts or
ammonium salts thereof.
[0061] The polycarboxylic acid preferably has a molecular weight in
a range of 90 to 1000000, in particular, 1000 to 70000.
[0062] In a case of using a copolymer mentioned above as the
polycarboxylic acid, the copolymer may be a copolymer of two or
more of the above-mentioned monomers or a copolymer of one or more
of the above-mentioned monomers and another monomer. Examples of
such "another monomer" include vinyl compounds such as
N-vinylpyrrolidone, N-vinylcarbazole, N-vinyloxazoline,
N-vinyl-1,2,4-triazole, N-vinylcarbazole, N-vinylphthalimide,
N-vinyl succinimide, N-vinylimidazole, vinyl sulfonic acid,
2-sulfoethyl(meth)acrylate, and vinyl sulfonic acid; vinyl ketones
such as methyl vinyl ketone, phenyl vinyl ketone, and divinyl
ketone; acrylamide-based monomers such as (meth)acrylamide,
N-methylol(meth)acrylamide, N,N-dimethyl(meth)acrylamide,
N,N-dibutyl(meth)acrylamide, N,N-dioctyl(meth)acrylamide,
N-monobutyl(meth)acrylamide, N-monooctyl(meth)acrylamide,
N-isopropylacrylamide, acryloyl morpholine, N,N-dimethylaminopropyl
acrylamide, diacetone acrylamide, N-2-hydroxyethyl acrylamide, and
2-acrylamide-2-methylsulfonic acid; (meth)acrylate ester monomers
such as methyl(meth)acrylate, ethyl(meth)acrylate,
n-butyl(meth)acrylate, isobutyl acrylate, tert-butyl(meth)acrylate,
2-ethylhexyl(meth)acrylate, lauryl methacrylate, phenyl acrylate,
isobornyl(meth)acrylate, cyclohexyl methacrylate,
tert-butylcyclohexyl(meth)acrylate,
dicyclopentadienyl(meth)acrylate,
dihydrodicyclopentadienyl(meth)acrylate, N,N-dimethylaminoethyl
acrylate, 2-methacryloyloxyethylsuccinic acid, ethylene glycol
dimethacrylate, glycerin dimethacrylate, methoxytriethylene
glycol-2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,
4-hydroxybutyl(meth)acrylate, methoxy polyethylene glycol
methacrylate, and methoxy polyethylene glycol dimethacrylate;
polymerizable nitriles such as acrylonitrile and methacrylonitrile;
alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether,
n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether,
isobutyl vinyl ether, and tert-butyl vinyl ether; polymerizable
aromatic compounds such as styrene, .alpha.-methylstyrene,
tert-butylstyrene, para-chlorostyrene, vinyl naphthalene, and
p-styrene sulfonic acid; vinyl esters such as vinyl acetate, vinyl
propionate, vinyl butyrate, vinyl trimethylacetate, vinyl caproate,
vinyl caprylate, vinyl laurate, and vinyl stearate; conjugated
dienes such as butadiene and isoprene; olefins such as ethylene,
propylene, 1-butene, isobutylene, and 3-methyl-1-butene; and allyl
compounds such as allyl chloride, diallyl phthalate, allyl alcohol,
and allylsulfonic acid. These monomers may be used alone or in
combination of two or more thereof as the "another monomer".
[0063] The surface treatment agent composition of the present
invention further contains fluorine ions. Examples of the fluorine
ion source for supplying fluorine ions to the surface treatment
agent composition include hydrofluoric acid, sodium fluoride,
ammonium fluoride, ammonium hydrogen fluoride, sodium hydrogen
fluoride, and potassium fluoride. These fluorine ion sources may be
used alone or in combination of two or more thereof. The ratio
[F]/[Al] of the molar concentration [F] of the fluorine ions to the
molar concentration [Al] of the aluminum ions is preferably 1 to 4.
A ratio [F]/[Al] of 1 or more sufficiently solubilizes the aluminum
ions in the surface treatment agent composition to advantageously
allow an improvement of uniformity of the film formed on the
surface of a steel sheet. A ratio of 4 or less can inhibit
excessive etching of the steel sheet by fluorine ions and allows
formation of a film having sufficient corrosion resistance on the
surface of the steel sheet. The ratio [F]/[Al] is more preferably
1.5 to 3.5 and most preferably 0.65 to 2.16. The concentration of
aluminum ions is the mass concentration in terms of aluminum metal,
and the concentration of fluorine ions is mass concentration in
terms of fluorine. The molar ratio [F]/[Al] of fluorine ions to
aluminum ions is calculated from molar concentrations (mmol/L) of
the aluminum ions and the fluorine ions determined from their mass
concentrations (ppm). The concentration of aluminum ions can be
measured with an inductively coupled plasma emission spectrometer
(ICP). The concentration of fluorine ions can be measured by ion
chromatography.
[0064] The surface treatment agent composition of the present
invention may further contain nitrate ions, a peroxide, and a
complexing agent, as necessary. The nitrate ions have an effect of
maintaining the stability of a precipitation state for a long-term
electrolysis. Usable examples of the ion source include nitric
acid, sodium nitrate, potassium nitrate, and ammonium nitrate. The
peroxide generates oxygen in an aqueous solution and thereby shows
an effect of inhibiting concentration polarization in the periphery
of the surface of a cathode and is particularly useful when the
stirring in the bath is weak. Usable examples of the peroxide
include hydrogen peroxide, ammonium peroxodisulfate, potassium
peroxodisulfate, sodium peroxoborate, sodium peroxocarbonate, and
sodium peroxodisulfate. The complexing agent works so as to inhibit
generation of precipitate in the bath, and usable examples thereof
include ethylenediaminetetraacetic acid, sodium
ethylenediaminetetraacetate, citric acid, sodium citrate, boric
acid, nitrilotriacetic acid, sodium nitrilotriacetate,
cyclohexanediaminetetraacetic acid, glycine, citric acid, gluconic
acid, malonic acid, succinic acid, tartaric acid, phosphonic acid,
and ethylenediaminetetraacetic acid. Note that too high
concentrations of the nitrate ions, the peroxide, and the
complexing agent tend to reduce the deposition efficiency.
[0065] The surface treatment agent composition of the present
invention may further contain an antibacterial agent, a surfactant,
a corrosion inhibitor, and other components, as necessary. Usable
examples of these components include alcohols such as ethanol and
isopropanol, guanidine group-containing compounds such as
polyhexamethylene biguanidine hydrochloride, benzimidazole-based
antibacterial agents such as 2-(4-thiazolyl)-benzimidazole and
methyl-2-benzimidazole carbamate, phenol-based antibacterial agents
such as p-chloro-m-xylenol and p-chloro-m-cresol, nitrile-based
antibacterial agents such as 2,4,5,6-tetrachloroisophthalonitrile
and 1,2-dibromo-2,4-dicyanobutane, pyridine-based antibacterial
agents such as sodium (2-pyridylthio-1-oxide) and zinc
bis(2-pyridylthio-1-oxide), isothiazolone-based antibacterial
agents such as 2-methyl-4-isothiazolin-3-one and
5-chloro-2-methyl-4-isothiazolin-3-one, quaternary ammonium salts
such as benzalkonium chloride and benzethonium chloride, benzoic
acid, ethyl p-oxybenzoate, sorbic acid, potassium sorbate, sodium
dehydroacetate, sodium propionate, nonionic surfactants, cationic
surfactants, anionic surfactants, tannic acid, imidazoles,
triazines, guanines, hydrozines, and biguanide. In order to improve
the adhesion with an organic resin film, the surface treatment
agent composition may further contain a silane-coupling agent,
colloidal silica, an amine, and a water-soluble phenol-based
organic compound containing a phenolic resin.
[0066] The surface treatment agent composition of the present
invention may contain an inorganic material, as necessary, in
addition to aluminum, fluorine, and iron. Examples of the inorganic
material include, but not limited to, zirconium and titanium.
(Method of Producing Surface-Treated Steel Sheet)
[0067] Prior to surface treatment, a steel sheet is pretreated.
Examples of the pretreatment include, as common processes,
degreasing and water washing and, as necessary, cleansing of the
surface through pickling and water washing.
[0068] A surface-cleaned steel sheet is subjected to cathodic
electrolysis in a current density range of 0.5 to 100 A/dm.sup.2 in
a treatment bath at a temperature of 30.degree. C. to 65.degree. C.
with stirring. The steel sheet is washed with water into a
surface-treated steel sheet having a suitable surface structure. As
described above, the treatment bath is constituted of the surface
treatment agent composition of the present invention.
[0069] As the counter electrode plate corresponding to the anode
side, a titanium plate covered with iridium oxide can be suitably
used. The counter electrode plate is required to be made of a
material that is not dissolved into the treatment liquid during
electrolysis and is desirably an insoluble anode having a low
oxygen overvoltage.
[0070] Such a production process forms a treatment film containing
a metal oxide and a polycarboxylic acid on the surface of the steel
sheet. The treatment film will be described in detail in the
description of the surface-treated steel sheet below.
[0071] As described above, the treatment bath (surface treatment
agent composition) in the present invention is preferably
constituted of an aqueous solution having a pH value of 1 to 5,
more preferably 2.0 to 4.5, at 25.degree. C. In general, there is a
tendency that a low pH value of the treatment bath increases the
allowable dissolved iron ion concentration, whereas a high pH value
decreases the allowable dissolved iron ion concentration. Iron ions
exceeding the allowable dissolved iron ion concentration float or
precipitate in the treatment bath as oxides or hydroxides, which
may be caught in the treatment film to reduce the corrosion
resistance of the resulting film. Accordingly, it is desirable to
promptly remove the iron ions deposited in the treatment bath.
[0072] Accordingly, in the method of producing the surface-treated
steel sheet of the present invention, it is desirable to perform
recycling treatment of the treatment bath by removing iron ions by
increasing the pH value of the surface treatment agent composition
in the treatment bath by about 0.2 to 0.5 for precipitating the
chelate of polycarboxylic acid and iron ion as an iron compound,
turning the pH value of the treatment bath to the original level,
and then adding a polycarboxylic acid to the treatment bath so that
the ratio [carboxyl group]/[Al] of the molar concentration
[carboxyl group] of the carboxyl groups contained in the
polycarboxylic acid to the molar concentration [Al] of the aluminum
ions in the treatment bath is in a range of 0.005 to 2.0 to control
the iron ion concentration in the treatment bath to be constantly
200 ppm or less. The polycarboxylic acid contained in the treatment
bath is as described in the description about the surface treatment
agent composition of the present invention.
[0073] The recycling treatment may be performed in another tank by
transferring the treatment liquid thereto or may be performed in
the circulation path of the surface treatment agent
composition.
[0074] In the case of performing the recycling treatment in another
tank, the pH value of the surface treatment agent composition is
increased with ammonia to precipitate the iron ions captured by the
polycarboxylic acid, and the precipitate is removed by a filter,
for example. Subsequently, the pH value of the treatment liquid is
decreased to the original level with nitric acid, and then a
polycarboxylic acid is added to the treatment bath so that the
ratio [carboxyl group]/[Al] of the molar concentration [carboxyl
group] of the carboxyl groups contained in the polycarboxylic acid
to the molar concentration [Al] of the aluminum ions in the
treatment bath is in a range of 0.005 to 2.0.
[0075] In the case of performing the recycling treatment in the
circulation path, it is preferable to adjust the pH value during
the treatment bath operation to be higher than that in the
recycling treatment in another tank to reduce the concentration of
iron ions that can be dissolved in the treatment bath within a
range that does not affect the film performance. The precipitated
iron compounds are continuously removed with, for example, a filter
provided in the circulation path, resulting in maintenance of the
concentration of iron ions dissolved in the treatment bath to be
200 ppm or less.
[0076] The surface treatment agent composition constituting the
treatment bath used in the method of producing a surface-treated
steel sheet is the same as that described above, and the
description thereof is omitted here.
(Surface-Treated Steel Sheet)
[0077] The surface-treated steel sheet of the present invention is
a steel sheet provided with a treatment film on at least one
surface thereof. The treatment film contains an oxide mixture of an
iron-oxygen compound and an aluminum-oxygen compound and a
polycarboxylic acid. The amount of aluminum is preferably 5 to 150
mg/m.sup.2 and more preferably 17.2 to 102.1 mg/m.sup.2 in terms of
aluminum metal, and the carbon amount (hereinafter also referred to
as "C amount") is preferably 0.1 to 5.0 mg/m.sup.2 and more
preferably 0.1 to 3.2 mg/m.sup.2. Thus, the treatment film is
mainly made of an aluminum-oxygen compound. Such a treatment film
is formed on the surface of a steel sheet by performing cathodic
electrolysis in a treatment bath containing the above-described
surface treatment agent composition. An amount of aluminum
contained in the treatment film less than the above-mentioned range
deteriorates the corrosion resistance of the surface-treated steel
sheet, whereas an amount higher than the above-mentioned range is
uneconomical due to saturation of the performance. Consequently,
the amount of aluminum in the film is preferably within the
above-mentioned range. A C amount contained in the treatment film
less than the above-mentioned range deteriorates the adhesion
between the organic coating and the surface-treated steel sheet,
whereas a C amount higher than the above-mentioned range
deteriorates the corrosion resistance of the surface-treated steel
sheet. Consequently, the C amount in the film is preferably within
the above-mentioned range.
[0078] In addition, in the treatment film formed on the
surface-treated steel sheet of the present invention, the atomic
ratio, Fe/Al, of iron to aluminum, which can be measured by a
method described in the following examples, is preferably 0.5 or
less from the viewpoint of corrosion resistance.
[0079] A treatment film containing an appropriate amount of
fluorine together with aluminum has a stabilization structure such
as represented by AlO.sub.X(OH).sub.Y-ZF.sub.Z to inhibit a
structural change of the treatment layer under a high-temperature
high-humidity environment. As a result, a further stable surface
can be retained. A treatment film containing an excessive amount of
fluorine may be washed with water after electrolytic treatment. The
washing may be performed with warm water or hot water. The water
used in the washing may be adjusted to have a pH value in the
alkaline side. The pH value may be controlled with any chemical
species. It is thought that the film characteristics can be
improved by controlling the fluorine amount in the film.
(Surface-Treated Steel Sheet with an Organic Coating)
[0080] In the surface-treated steel sheet with an organic coating
of the present invention, the organic coating provided on the
above-described surface-treated steel sheet is not specifically
limited, and examples thereof include resin coatings composed of
various thermoplastic resins and coating films composed of
thermosetting resins. In these cases, a thermoplastic resin or a
thermosetting resin is laminated on at least one surface of the
surface-treated steel sheet to give a surface-treated steel sheet
with an organic coating.
[0081] The resin coating composed of a thermoplastic resin may be
an unstretched or biaxially stretched thermoplastic resin film, of
which examples include films of olefin-based resins such as
polyethylene, polypropylene, ethylene-propylene copolymers,
ethylene-vinyl acetate copolymers, ethylene-acrylic ester
copolymers, and ionomers; films of polyesters such as polyethylene
terephthalate and polybutylene terephthalate; films of polyamides
such as nylon 6, nylon 6,6, nylon 11, and nylon 12; polyvinyl
chloride films; and polyvinylidene chloride films.
[0082] In formation of the organic coating, a layer of a known
adhesive priming agent or adhesive can be provided between the
surface-treated steel sheet and the thermoplastic resin coating.
The adhesive priming agent has excellent adhesion to both a metal
material and a film. Examples of the priming coating having
excellent adhesion and corrosion resistance include phenol
epoxy-based coatings composed of resol-type phenol aldehyde resins
derived from various phenols and formaldehydes and bisphenol-type
epoxy resins. In particular, a coating containing a phenol resin
and an epoxy resin at a weight ratio of 50:50 to 1:99, particularly
40:60 to 5:95, can be preferably used. The adhesive priming agent
is usually applied so as to have a thickness of 0.01 to 10 .mu.m.
The adhesive priming agent may be applied onto the surface-treated
steel sheet in advance or may be applied to the thermoplastic resin
film.
[0083] Preferred examples of the adhesive include urethane-based
adhesives, epoxy-based adhesives, acid-modified olefin resin-based
adhesives, copolyamide-based adhesives, and copolyester-based
adhesives (thickness: 0.1 to 5.0 .mu.m). Alternatively, a
thermosetting coating may be applied to the surface-treated metal
sheet side or the film side at a thickness range of 0.05 to 2 .mu.m
as an adhesive layer.
[0084] The coating film may be a thermosetting coating, for
example, a modified epoxy coating such as phenol epoxy or
amino-epoxy, a vinyl chloride-vinyl acetate copolymer, a saponified
vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl
acetate-maleic anhydride copolymer, an epoxy modified-, epoxyamino
modified-, or epoxyphenol modified-vinyl coating, a modified vinyl
coating, an acrylic coating, or a synthetic rubber-based coating
such as a styrene-butadiene-based copolymer. These thermosetting
coatings may be used alone or in combination of two or more
thereof.
[0085] Among these resins, a resin coating composed of a polyester
resin is most preferably used as a container material. Examples of
the polyester resin include thermoplastic polyesters derived from
an alcohol component mainly including ethylene glycol or butylene
glycol and an aromatic dibasic acid derived from an acid component
such as terephthalic acid, isophthalic acid, or naphthalene
dicarboxylic acid.
[0086] Though polyethylene terephthalate itself can be used as a
polyester, it is desirable to reduce the highest degree of
crystallization to which a film can reach from the viewpoints of
shock resistance and workability, and in order to achieve the
reduction, it is desirable to introduce a copolymer ester unit
other than the ethylene terephthalate into the polyester. It is
particularly preferred to use a copolymer polyester mainly
including ethylene terephthalate units or butylene terephthalate
units and containing a small amount of other ester units and having
a melting point of 210.degree. C. to 252.degree. C. Note that
homopolyethylene terephthalate generally has a melting point of
255.degree. C. to 265.degree. C.
[0087] In general, preferably, in the copolymer polyester, 70% by
mol or more, in particular, 75% by mol or more of the dibasic acid
component is a terephthalic acid component; 70% by mol or more, in
particular, 75% by mol or more of the diol component is ethylene
glycol or butylene glycol; and 1% to 30% by mol, in particular, 5%
to 25% by mol of the dibasic acid component is a dibasic acid
component other than terephthalic acid.
[0088] Examples of the dibasic acid other than terephthalic acid
include aromatic dicarboxylic acids such as isophthalic acid,
phthalic acid, and naphthalene dicarboxylic acid; alicyclic
dicarboxylic acids such as cyclohexane dicarboxylic acid; aliphatic
dicarboxylic acids such as succinic acid, adipic acid, sebacic
acid, and dodecanedioic acid; and dimer acids obtained through
dimerization of unsaturated fatty acid having 10 to 25 carbon
atoms. These dibasic acids can be used alone or in combination of
two or more thereof. Examples of the diol component other than
ethylene glycol and butylene glycol include propylene glycol,
diethylene glycol, 1,6-hexylene glycol, cyclohexane dimethanol, and
ethylene oxide adduct of bisphenol A. These diol compounds can be
used alone or in combination of two or more thereof. In the
combination of these comonomers, it is preferable to control the
melting point of the copolymer polyester within the above-mentioned
range.
[0089] In order to improve the melt flowability in molding, the
polyester can contain at least one branched or crosslinked
component selected from the group consisting of tri- or
more-functional polybasic acids and polyols. The amount of these
branched or crosslinked component is 3.0% by mol or less,
preferably, within a range of 0.05% to 3.0% by mol.
[0090] Examples of the tri- or more-functional polybasic acids and
polyols include polybasic acids such as trimellitic acid,
pyromellitic acid, hemimellitic acid, 1,1,2,2-ethane
tetracarboxylic acid, 1,1,2-ethane tricarboxylic acid,
1,3,5-pentane tricarboxylic acid, 1,2,3,4-cyclopentane
tetracarboxylic acid, and biphenyl-3,4,3',4'-tetracarboxylic acid;
and polyols such as pentaerythritol, glycerol, trimethylolpropane,
1,2,6-hexanetriol, sorbitol, and
1,1,4,4-tetrakis(hydroxymethyl)cyclohexane.
[0091] In the surface-treated steel sheet with an organic coating
of the present invention, particularly preferred examples of the
polyester resin that can be used as a material for manufacturing a
can include polyethylene terephthalate/isophthalate containing 5%
to 25% by mol of an isophthalic acid component and
polyethylene/cyclohexylene dimethylene terephthalate containing 1%
to 10% by mol of a cyclohexane dimethanol component.
[0092] The homopolyester and the copolymer polyester each should
have a molecular weight within the film-forming range and
preferably have an intrinsic viscosity [.eta.] measured using a
solvent mixture of phenol and tetrachloroethane within a range of
0.5 to 1.5, in particular, 0.6 to 1.5.
[0093] The thermoplastic resin coating used for the surface-treated
steel sheet with an organic coating of the present invention may be
formed from any single polyester or copolyester mentioned above, a
mixture of two or more of the polyesters and/or the copolyesters,
or a mixture of the polyester and/or the copolyester and another
thermoplastic resin. Examples of the mixture of two or more of the
polyesters and/or the copolyesters include, but not limited to,
combinations of two or more selected from polyethylene
terephthalate, polybutylene terephthalate, polyethylene
terephthalate/isophthalate, and polyethylene/cyclohexylene
dimethylene terephthalate.
[0094] Examples of another thermoplastic resin that can be
contained in the polyester include ethylene-based polymers,
thermoplastic elastomers, polyacrylates, and polycarbonates. The
addition of at least one of these modified resin components can
further improve the heat and humidity resitance and the shock
resistance. The amount of the modified resin component is generally
up to 50 parts by weight, most preferably 5 to 35 parts by weight,
based on 100 parts by weight of the polyester.
[0095] Examples of the ethylene-based polymer include low-,
medium-, and high-density polyethylenes, linear low density
polyethylenes, linear ultra low density polyethylene,
ethylene-propylene copolymers, ethylene-butene-1 copolymers,
ethylene-propylene-butene-1 copolymers, ethylene-vinyl acetate
copolymers, ionically crosslinked olefin copolymers (ionomers), and
ethylene-acrylate copolymers. Among these polymers, preferred are
ionomers, of which base polymers are, for example,
ethylene-(meth)acrylate copolymers and
ethylene-(meth)acrylate-(meth)acrylic acid copolymers and of which
ion species are, for example, Na, K, and Zn. Usable examples of the
thermoplastic elastomer include styrene-butadiene-styrene block
copolymers, styrene-isoprene-styrene block copolymers, hydrogenated
styrene-butadiene-styrene block copolymers, and hydrogenated
styrene-isoprene-styrene block copolymers.
[0096] The polyarylate is defined as a polyester derived from a
dihydric phenol and a dibasic acid. Usable examples of the dihydric
phenol include bisphenols such as 2,2'-bis(4-hydroxyphenyl)propane
(bisphenol A), 2,2'-bis(4-hydroxyphenyl)butane (bisphenol B),
1,1'-bis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)methane
(bisphenol F), 4-hydroxyphenyl ether, and p-(4-hydroxy)phenol.
Bisphenol A and bisphenol B are preferred. Usable examples of the
dibasic acid include terephthalic acid, isophthalic acid,
2,2-(4-carboxyphenyl)propane, 4,4'-dicarboxydiphenyl ether, and
4,4'-dicarboxybenzophenone. The polyarylate may be a homopolymer
derived from the above-mentioned monomer component or may be a
copolymer.
[0097] Alternatively, the polyarylate may be a copolymer with an
ester unit derived from an aliphatic glycol and a dibasic acid
within a range that does not deteriorate the essential qualities.
These polyarylates are available, for example, as U-series or
AX-series of U-polymers of Unitika Ltd., Ardel D-100 of UCC Co.,
APE of Bayer Co., Durel of Hoechst Co., Arylon of Du Pont Co. and
NAP Resin of Kaneka Corp.
[0098] The polycarbonate is a carbonate ester resin derived from a
bicyclic dihydric phenol and phosgene and is characterized by its
high glass transition temperature and high heat resistance.
Preferred examples of the polycarbonate include bisphenols, e.g.,
those derived from 2,2'-bis(4-hydroxyphenyl)propane (bisphenol A),
2,2'-bis(4-hydroxyphenyl)butane (bisphenol B),
1,1'-bis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)methane
(bisphenol F), 1,1-bis(4-hydroxyphenyl)cyclohexane,
1,1-bis(4-hydroxyphenyl)cyclopentane,
1,1-bis(4-hydroxyphenyl)-1-phenylmethane,
1,1-bis(4-hydroxyphenyl)-1-phenylethane, and
1,2-bis(4-hydroxyphenyl)ethane.
[0099] The thermoplastic resin coating of the surface-treated steel
sheet with an organic coating of the present invention may be a
resin monolayer or a resin multilayer formed by, for example,
coextrusion. In a polyester resin multilayer, advantageously, it is
possible to select a polyester resin having a composition excellent
in adhesion as an underlying layer, i.e., as the layer on the
surface-treated steel sheet side and to select a polyester resin
having a composition excellent in content resistance, i.e.,
excellent in extraction resistance and non-adsorption of flavor
component, as the surface layer.
[0100] Examples of the polyester resin multilayer being shown as
surface layer/underlying layer include, but not limited to,
polyethylene terephthalate/polyethylene
terephthalate.cndot.isophthalate, polyethylene
terephthalate/polyethylene.cndot.cyclohexylene
dimethylene.cndot.terephthalate, polyethylene
terephthalate.cndot.isophthalate (in which the content of the
isophthalate is low)/polyethylene terephthalate.cndot.isophthalate
(in which the content of the isophthalate is high), and
polyethylene terephthalate.cndot.isophthalate/(a mixture of
polyethylene terephthalate.cndot.isophthalate and polybutylene
terephthalate.cndot.adipate). The thickness ratio, the surface
layer:the underlying layer, is desirably within a range of 5:95 to
95:5.
[0101] The organic coating can contain known additives for resin,
for example, an anti-blocking agent such as amorphous silica, an
inorganic filler, various anti-static agents, a lubricant, an
antioxidant, and an UV absorber, in accordance with known
prescriptions.
[0102] In particular, tocopherol (vitamin E) is preferably used.
Tocopherol is known as an antioxidant that prevents a decrease in
molecular weight caused by degradation of a polyester resin in heat
treatment and thereby improves the dent resistance. In particular,
addition of the tocopherol to a polyester composition including a
polyester resin and the above-mentioned ethylene-based polymer as a
modified resin component can provide an effect of significantly
improving not only dent resistance but also corrosion resistance,
and even if a film has cracks due to severe conditions such as
retort sterilization or hot bender, corrosion from the cracks can
be prevented from progressing.
[0103] The amount of the tocopherol is preferably 0.05% to 3% by
weight, in particular, 0.1% to 2% by weight.
[0104] In the present invention, the thickness of the organic
coating is desirably within a range of 3 to 50 .mu.m, in particular
5 to 40 .mu.m, in the case of a thermoplastic resin coating. In the
case of a coating film, the thickness after baking is preferably
within a range of 1 to 50 .mu.m, in particular 3 to 30 .mu.m. A
thickness smaller than the above-mentioned range provides
insufficient corrosion resistance, whereas a thickness larger than
the range tends to cause a problem in workability.
[0105] In the present invention, the organic coating can be formed
on the surface-treated steel sheet by any arbitrary process. For
example, a coating with a thermoplastic resin can be performed by
extrusion coating, cast film thermobonding, or biaxially stretched
film thermobonding. In the extrusion coating, a polyester resin in
a molten state is extruded onto the surface of a surface-treated
steel sheet and thermally adheres to the surface. That is, a
polyester resin is molten and kneaded with an extruder and is then
extruded from a T-die into a thin film, and the extruded molten
resin film is allowed, together with a surface-treated steel sheet,
to pass between a pair of laminating rollers. The resin film and
the steel sheet are unified by pressing with cooling and are then
quenched. In extrusion coating of a polyester resin multilayer, an
extruder for a surface layer and an extruder for an underlying
layer are used. The resin flows from the extruders are joined in a
multiple multilayer die, followed by extrusion coating as in a
resin monolayer. Alternatively, a coating layer of a polyester
resin can be formed on each of both surfaces of a surface-treated
steel sheet by allowing the surface-treated steel sheet to
perpendicularly pass between a pair of laminating rollers and
supplying molten resin webs on both sides thereof.
[0106] Specifically, in extrusion coating, the surface-treated
steel sheet with an organic coating composed of a polyester resin
is produced as follows. A surface-treated steel sheet is pre-heated
with a heater as necessary and is supplied to a nip position
between a pair of laminating rollers. A polyester resin is extruded
from the die head of an extruder into a thin film form. The thin
film is supplied between a laminating roller and the
surface-treated steel sheet and is pressure bonded to the
surface-treated steel sheet with laminating rollers. The laminating
rollers are maintained at a certain temperature and press-bond a
thin film composed of a thermoplastic resin such as polyester to a
surface-treated steel sheet to thermally bond the both and also
cool them from both sides to provide a surface-treated steel sheet
with an organic coating. In general, the resulting surface-treated
steel sheet with an organic coating is further quenched by being
introduced into, for example, a water tank for cooling to prevent
thermal crystallization.
[0107] In the extrusion coating, the polyester resin layer has a
low degree of crystallization, i.e., the density difference from
the amorphous density is suppressed to 0.05 g/cm.sup.3 or less, by
appropriately selecting the resin composition and quenching with
rollers and a cooling tank. Consequently, sufficient workability
for the subsequent processes such as can manufacturing processing
and lid processing is guaranteed. The process of quenching is not
limited to those described above. For example, the resulting
surface-treated steel sheet with an organic coating can also be
quenched by spraying a cooling water or rapidly cooling the
laminated sheet.
[0108] The thermobonding of a polyester resin to a surface-treated
steel sheet is achieved by the thermal energy of the molten resin
layer and the thermal energy of the surface-treated steel sheet.
The heating temperature of the surface-treated steel sheet is
preferably 90.degree. C. to 290.degree. C., in particular,
100.degree. C. to 280.degree. C., whereas the heating temperature
of the laminating rollers is preferably in a range of 10.degree. C.
to 150.degree. C.
[0109] The surface-treated steel sheet with an organic coating of
the present invention can also be produced by thermally bonding a
polyester resin film formed in advance by a T-die method or an
inflation film forming method to a surface-treated steel sheet. The
film may be an unstretched, non-orientation film formed by a
casting method through quenching an extruded film or may be a
biaxially stretched film formed by sequential or simultaneous
biaxial stretching of the cast film at an elongation temperature
and subsequent heat setting of the film.
(Can Body and Can Lid)
[0110] The can body of the present invention may be produced by any
method from the above-described surface-treated steel sheet with an
organic coating and can be formed into a three-piece can. The
three-piece can is formed by bending the surface-treated steel
sheet with an organic coating such that the organic coating is the
inside of the can and welding or heat sealing the ends and
therefore has a seam in the side wall. The can is produced by any
known process.
[0111] The can lid of the present invention may be produced by any
known method from the above-described surface-treated steel sheet
with an organic coating. In general, the can lid can be applied to
a stay-on-tab type or full-open type easy-open can lid or a flat
lid.
(Seamless Can)
[0112] The seamless can (e.g., two-piece can or DR can) of the
present invention can also be produced by any method from the
above-described surface-treated steel sheet with an organic coating
and is produced so as to have the organic coating inside the can by
a known procedure such as a drawing process, a
drawing.cndot.redrawing process, a bending-stretching process
(stretching process) through drawing.cndot.redrawing, a
bending-stretching.cndot.ironing process through
drawing.cndot.redrawing, or a drawing.cndot.ironing process. In
particular, the organic coating is preferably a thermoplastic resin
coating formed by extrusion coating. That is, since the
surface-treated steel sheet with an organic coating has excellent
processing adhesion, the surface-treated steel sheet exhibits
excellent coating adhesion even in severe processing and can
thereby provide a seamless can having excellent corrosion
resistance.
(Exposure of Iron to the Steel Sheet Surface)
[0113] As described above, in the steel sheet to be treated in the
present invention, iron is exposed to at least a part of a surface
other than the end faces. In such a steel sheet, iron may be
exposed to the entire surface. That is, the steel sheet may be a
cold rolled steel sheet. In a case of using a cold rolled steel
sheet as the steel sheet, the effects of the present invention can
be particularly high.
EXAMPLES
[0114] The present invention will now be more specifically
described by examples, but is not limited to these examples. The
materials to be treated, the degreasing agent, and the organic
coating used in the following examples were appropriately selected
from commercially available materials and do not limit the actual
treatment liquid for surface treatment and surface treatment
process of the present invention.
[Types of Treatment Bath]
[0115] Surface treatment agent compositions each having an
unadjusted pH value were prepared by mixing the respective
components such that the resulting aqueous solution contains
aluminum ions and a polycarboxylic acid at concentrations shown in
the columns "Al" and "Polyitaconic acid", respectively, in Table 1.
Polyitaconic acid, aluminum nitrate, and sodium fluoride were used
as the polycarboxylic acid, the aluminum agent, and the fluorine
agent, respectively. Based on the mass concentrations (ppm) of
these components, the molar concentrations (mmol/L) of aluminum
ions, fluorine, and the carboxyl groups contained in the
polycarboxylic acid and the molar ratio ([carboxyl group]/[Al]) of
the molar concentrations (mmol/L) of the carboxyl groups contained
in the polycarboxylic acid to the aluminum ions were calculated.
The results are shown in Table 1. The concentration of the carboxyl
groups contained in the polycarboxylic acid (polyitaconic acid) can
be calculated by dividing the mass concentration (ppm) of the
polyitaconic acid by a half of the molecular weight of itaconic
acid as the constitutional unit. The pH value is a level at
25.degree. C. (the same applies to the following).
TABLE-US-00001 TABLE 1 [Carboxylic [Carboxylic Mixture Al F
Polycarboxylic Glycine [Al] [F] group] group]/[Al] No. (ppm) (ppm)
acid (ppm) (ppm) (mmol/L) (mmol/L) (mmol/L) (Molar ratio) A 1500
2300 500 0 56 121 4 0.069 B 1500 2300 250 0 56 121 2 0.035 C 1500
2300 125 0 56 121 1 0.017 D 5000 2300 500 0 185 121 4 0.021 XA 1500
2300 0 0 56 121 0 0 XB 1500 2300 0 4100 56 121 0 0 XC 0 0 500 0 0 0
4 --
[Production of Surface-Treated Steel Sheet]
[0116] The samples used in the following examples and comparative
examples were low-carbon cold rolled steel sheets each having a
thickness of 0.225 mm, unless specifically mentioned. Pretreatment
was performed by electrolytic degreasing in an aqueous solution of
a commercially available degreasing agent (Surf Cleaner 322N8,
manufactured by Nippon Paint Co., Ltd.), water washing, pickling
through immersion in an aqueous sulfuric acid solution, and then
water washing. Subsequently, surface treatment by providing
electricity with a current density of 1 to 10 A/dm.sup.2 for 0.15
seconds and no electricity for 0.50 seconds was repeated one to ten
cycles, followed by water washing and then drying to give a
surface-treated steel sheet. On this occasion, the water washing or
pure water washing may be performed with warm water or hot water
and may be performed so as to reduce excessive fluorine in the film
to further improve the characteristics of the film for some
applications.
[Process of Producing Surface-Treated Steel Sheet with an Organic
Coating]
[0117] The surface-treated steel sheets prepared above were each
laminated with a non-orientation polyethylene terephthalate film
(polyester film having a thickness of 20 .mu.m) copolymerized with
15 mol % of isophthalic acid for the inner surface of a can and a
non-orientation polyethylene terephthalate film (polyester film
having a thickness of 13 .mu.m and containing titanium oxide as a
white pigment) copolymerized with 15 mol % of isophthalic acid for
the outer surface of the can to produce a surface-treated steel
sheet with an organic coating.
[0118] The lamination of a polyester film was performed by
thermocompression bonding of the polyester film to a heated
surface-treated steel sheet with laminating rollers and immediately
cooling them. The heating temperature for this process was
250.degree. C. In the case of laminating a stretched film, the
heating temperature of the surface-treated steel sheet and the
temperature of the laminating rollers were controlled such that the
film after the lamination had appropriate orientation.
[Measurement of Treatment Bath Component]
[0119] The concentrations of aluminum and iron in the film formed
on a surface-treated steel sheet were measured with an ICP emission
spectrometer, ICPE-9000 (manufactured by Shimadzu Corporation), and
the organic carbon amount (C amount) in the film was measured with
a total organic carbon analyzer, TOC-5000 (manufactured by Shimadzu
Corporation).
[Measurement of Film Amount]
[0120] The amount of aluminum in the film formed on a
surface-treated steel sheet was measured with an X-ray fluorescence
spectrometer, ZSX100e (manufactured by Rigaku Corporation), and the
C amount in the film was measured with a
carbon.cndot.hydrogen/water analyzer, RC612 (manufactured by LECO
Corporation).
[Spot Measurement of Atomic Ratio (Fe/Al) of Iron to Aluminum in
Film]
[0121] The surface-treated steel sheet after the surface treatment
was cut out and was subjected to analysis with FE-AES (JAMP-9500F,
manufactured by JEOL Ltd.) to measure the atomic ratio (Fe/Al) of
iron to aluminum in the film. The analyses of iron and aluminum
were each performed by point analysis in the depth direction at an
accelerating voltage of 10 kV in a visual field of 30 k
magnification. The etching rate was 2.5 nm/once in terms of
SiO.sub.2. The peaks of iron and aluminum used in the analysis were
approximately 712 eV and 1390 eV, respectively. Each difference
between the maximum value and the minimum value obtained by
differentiation of the resulting spectrum by the analysis was used
as the signal strength. Based on the obtained signal strengths,
atomic concentrations were calculated by quantitative analysis
using known relative sensitivity factors, and atomic ratio Fe/Al of
iron to aluminum was determined. The atomic concentration was
calculated with analytical software, Specta Investigater
(manufactured by JEOL Ltd.). The calculation can also be performed
using another similar analytical software. The atomic ratios Fe/Al
at the film surface portion and the film central portion were
determined.
[Evaluation of Cross-Cut Corrosion Resistance]
[0122] A cross-cut having a length of 4 cm and reaching the base
material was formed with a cutter on the surface corresponding to
the inner side of a can of the surface-treated steel sheet with an
organic coating. The steel sheet was immersed in commercially
available coffee (trade name: Blendy.cndot.Bottle Coffee Low Sugar,
manufactured by Ajinomoto General Foods, Inc.) at 37.degree. C.,
and the condition of corrosion over time was evaluated. During the
evaluation, the coffee was regularly replaced by fresh one for
reducing the growth of mold as much as possible.
[0123] Each test strip was evaluated for spread of discoloring to
one side from the cross-cut portion by the following evaluation
criteria: a spread of less than 0.5 mm: 5 points, a spread of 0.5
mm or more and less than 1 mm: 4 points, a spread of 1 mm or more
and less than 2 mm: 3 points, a spread of 2 mm or more and less
than 3 mm: 2 points, and a spread of 3 mm or more: 0 point. A test
strip of 3 points or more was determined to be usable.
[Adhesion Evaluation]
[0124] Each surface-treated steel sheet with an organic coating
prepared above was cut into a strip having a width of 15 mm and a
length of 70 mm. A cut reaching the base material was made in the
strip at the position of 30 mm from one end of the strip on the
surface opposite to the measurement surface. The test strip was
subjected to hot-water retort treatment at 120.degree. C. for 30
minutes and was then immersed in water and the test strip was
pulled up from the water immediately before the measurement. Only
the metal piece of the test strip was broken into two pieces from
the cut formed in advance to give a site at which the two pieces
are connected to each other with only the resin film corresponding
to the inner side of a can. The test strip was folded in the
direction of 180 degrees such that the site is the inner side and
was subjected to a peeling test by peeling in the direction of 180
degrees at a tensile rate of 5 mm/min with a tensile tester. The
results were used as the adhesion strengths. In the evaluation, a
maximum tensile load of 5 N/15 mm or more when a test strip was
peeled off was determined as a satisfactory range. Note that the
term "N/15 mm" refers to the strength (N) of a test strip having a
width of 15 mm.
[0125] .smallcircle.: adhesion strength of 5 N/15 mm or more,
[0126] .DELTA.: adhesion strength of 1 N/15 mm or more and less
than 5 N/15 mm, and
[0127] .times.: adhesion strength of less than 1 N/15 mm.
Example 1
[0128] A solution containing 100 ppm (mass concentration, the same
applies to the following) of iron ions was prepared by adding an
aqueous iron nitrate solution to mixture A shown in Table 1 as a
treatment bath. In the preparation, ammonia or nitric acid was
added to the solution for maintaining the PH value to be 2.5. This
solution is a mimic condition of a treatment bath containing iron
ions eluted from a steel sheet as a result of surface treatment of
the steel sheet. Note that also in the following examples and
comparative examples, in order to produce a mimic condition of a
treatment bath containing iron ions eluted from a steel sheet, iron
ions may be added to a solution (treatment bath) as shown in each
Table.
[0129] Subsequently, the solution was put in a container having an
internal diameter of 45 mm and was adjusted to a pH value of 3.0 or
3.5 with ammonia, followed by leaving to stand for 6 hours. The
precipitation height was visually measured. In addition, the
concentrations of aluminum ions and iron ions in the supernatant
were measured. The results are shown in Table 2. In the column of
"Presence of precipitation" in Table 2, the numerical value shown
in parentheses after "Yes" indicates the height of the resulting
precipitate.
Example 2
[0130] Example 2 was performed as in Example 1 except that mixture
B was used as the treatment bath.
Example 3
[0131] Example 3 was performed as in Example 1 except that the
solution put in a container was adjusted so as to have a pH value
of 3.5.
Examples 4 and 5
[0132] Examples 4 and 5 were performed as in Example 3 except that
mixtures B and C were respectively used as the respective treatment
baths.
Example 6
[0133] Example 6 was performed as in Example 2 except that the
solution had an iron ion concentration of 150 ppm.
Examples 7 and 8
[0134] Examples 7 and 8 were performed as in Example 1 except that
mixture C was used as the treatment bath and that the solution had
an iron ion concentration of 200 ppm or 250 ppm.
Comparative Examples 1 to 3
[0135] Comparative Examples 1 to 3 were performed as in Example 1
except that mixtures XA, XB, and XC were respectively used as the
treatment baths.
TABLE-US-00002 TABLE 2 Concentration in supernatant Removal Mixture
Initial Fe content pH after Presence of (ppm) of iron No. pH (ppm)
adjustment precipitation Al Fe from bath Example 1 A 2.5 100 3.0
Yes (10 mm) 1500 40 effective Example 2 B 2.5 100 3.0 Yes (7 mm)
1500 50 effective Example 3 A 2.5 100 3.5 Yes (12 mm) -- --
effective Example 4 B 2.5 100 3.5 Yes (10 mm) -- -- effective
Example 5 C 2.5 100 3.5 Yes (9 mm) -- -- effective Example 6 B 2.5
150 3.0 Yes (12 mm) 1500 90 effective Example 7 C 2.5 200 3.0 Yes
(7 mm) -- -- effective Example 8 C 2.5 250 3.0 Yes (10 mm) 1500 190
effective Comparative XA 2.5 100 3.0 No 1500 100 ineffective
Example 1 Comparative XB 2.5 100 3.0 No 1500 100 ineffective
Example 2 Comparative XC 2.5 100 3.0 No 0 100 ineffective Example
3
Example 9
[0136] A steel sheet was subjected to degreasing and pickling and
then subjected to cathodic electrolytic treatment at a current
density of 1 A/dm.sup.2 three cycles with mixture A shown in Table
1 as the treatment bath in accordance with the method of producing
a surface-treated steel sheet described above to produce a
surface-treated steel sheet. The resulting surface-treated steel
sheet was heated to a sheet temperature of 250.degree. C. with a
hot plate, and then polyester films were laminated to both surfaces
of the steel sheet by the above-described procedure, followed by
quenching in water to produce a surface-treated steel sheet with an
organic coating. Subsequently, the surface-treated steel sheet with
an organic coating was cut into a 45-mm square. The end faces were
covered with tape, and a sample was produced in accordance with the
cross-cut corrosion resistance evaluation described above. The
degree of corrosion in coffee under an atmospheric pressure at
37.degree. C. was evaluated after four weeks. Evaluation results
are shown in Table 3.
Examples 10 to 12
[0137] Examples 10 to 12 were performed as in Example 9 except that
the cathodic electrolytic treatment at a current density of 4
A/dm.sup.2 was performed one, five, or ten cycles.
Examples 13 to 18
[0138] Examples 13 to 18 were performed as in Example 9 except that
an aqueous iron nitrate solution was added to the treatment bath
such that the iron ion concentration was 50, 100, or 200 ppm and
that the cathodic electrolytic treatment was performed at a current
density of 4 A/dm.sup.2 one cycle or five cycles.
Example 19
[0139] Example 19 was performed as in Example 9 except that the pH
value of the treatment bath was adjusted to be 3.5 and that the
cathodic electrolytic treatment was performed two cycles.
Example 20
[0140] Example 20 was performed as in Example 9 except that the pH
value of the treatment bath was adjusted to be 3.0 and that the
cathodic electrolytic treatment at a current density of 1
A/dm.sup.2 was performed 12 cycles.
Examples 21 and 22
[0141] Examples 21 and 22 were performed as in Example 9 except
that mixture B shown in Table 1 was used as the treatment bath and
that the cathodic electrolytic treatment was performed one cycle or
five cycles.
Examples 23 to 28
[0142] Examples 23 to 28 were performed as in Examples 21 and 22
except that the iron ion concentration in the treatment bath was
50, 100, or 200 ppm.
Examples 29 and 30
[0143] Examples 29 and 30 were performed as in Example 9 except
that mixture C shown in Table 1 was used as the treatment bath and
that the cathodic electrolytic treatment was performed one cycle or
three cycles.
Examples 31 and 32
[0144] Examples 31 and 32 were performed as in Examples 29 and 30
except that the iron ion concentration in the treatment bath was 50
ppm.
Comparative Example 4
[0145] Comparative Example 4 was performed as in Example 1 except
that the steel sheet was merely immersed in the bath for 30 seconds
without performing cathodic electrolysis.
Comparative Example 5
[0146] Comparative Example 5 was performed as in Comparative
Example 4 except that the iron ion concentration in the treatment
bath was 200 ppm.
Comparative Example 6
[0147] Comparative Example 6 was performed as in Example 1 except
that mixture XA shown in Table 1 was used as the treatment bath and
that the cathodic electrolytic treatment at a current density of 4
A/dm.sup.2 was performed five cycles.
Comparative Example 7
[0148] Comparative Example 7 was performed as in Comparative
Example 6 except that the iron ion concentration in the treatment
bath was 200 ppm.
Comparative Example 8
[0149] A steel sheet was subjected to degreasing, water washing,
pickling, and water washing and then subjected to treatment with
130 mg /m.sup.2 of chromium and 20 mg/m.sup.2 of chromium hydrous
oxide for one surface and was then immediately washed with water,
followed by drying to give a steel sheet treated with chromate on
the surface. Subsequently, lamination with polyester films was
performed as in Example 9. In the column of "Mixture" in Tables 3,
5, and 6, the term "TFS" indicates that a chromium-based treatment
bath was used.
TABLE-US-00003 TABLE 3 Electrolysis conditions Atomic Electro-
Current Number Immer- Film ratio Fe/Al Fe lytic Current flow of
sion amount Film Film Mix- content treat- density time cycles time
(mg/m.sup.2) surface central Crosscut ture pH (ppm) ment
(A/dm.sup.2) (sec) (times) (sec) Al C portion portion corrosion
Adhesion Note Example 9 A 2.5 0 Done 1 0.15 3 0 32.8 1.1 5
.smallcircle. Example 10 0 Done 4 0.15 1 0 28.6 1.4 5 .smallcircle.
Example 11 0 Done 4 0.15 5 0 57.0 1.2 0.11 0.11 5 .smallcircle.
Example 12 0 Done 4 0.15 10 0 102.1 3.2 5 .smallcircle. Example 13
50 Done 4 0.15 1 0 28.6 1.5 5 .smallcircle. Example 14 50 Done 4
0.15 5 0 68.9 1.2 5 .smallcircle. Example 15 100 Done 4 0.15 1 0
28.7 0.8 5 .smallcircle. Example 16 100 Done 4 0.15 5 0 63.9 0.4 5
.smallcircle. Example 17 200 Done 4 0.15 1 0 25.5 0.3 3
.smallcircle. Example 18 200 Done 4 0.15 5 0 65.7 0.1 0.37 0.34 3
.smallcircle. Example 19 3.5 0 Done 4 0.15 2 0 42.5 0.2 5
.smallcircle. Example 20 3.0 0 Done 1 0.15 12 0 40.8 0.4 5
.smallcircle. Example 21 B 2.5 0 Done 4 0.15 1 0 27.9 0.9 5
.smallcircle. Example 22 0 Done 4 0.15 5 0 66.9 0.6 5 .smallcircle.
Example 23 50 Done 4 0.15 1 0 19.0 0.1 5 .smallcircle. Example 24
50 Done 4 0.15 5 0 69.7 0.3 5 .smallcircle. Example 25 100 Done 4
0.15 1 0 17.7 0.1 4 .smallcircle. Example 26 100 Done 4 0.15 5 0
61.9 0.1 4 .smallcircle. Example 27 200 Done 4 0.15 1 0 17.2 0.3 3
.smallcircle. Example 28 200 Done 4 0.15 5 0 51.1 0.1 3
.smallcircle. Example 29 D 2.5 0 Done 4 0.15 1 0 36.4 0.9 5
.smallcircle. Example 30 0 Done 4 0.15 3 0 57.6 0.5 5 .smallcircle.
Example 31 50 Done 4 0.15 1 0 35.0 0.1 5 .smallcircle. Example 32
50 Done 4 0.15 3 0 50.8 0.1 5 .smallcircle. Comparative A 2.5 0
None -- -- -- 30 44.4 1.3 0.13 0.23 3 .smallcircle. Example 4
Comparative 200 None -- -- -- 30 41.2 0.7 0.33 0.55 2 .DELTA.
Example 5 Comparative XA 2.5 0 Done 4 0.15 5 0 66.1 0 0.06 0.06 4
.smallcircle. Example 6 Comparative 200 Done 4 0.15 5 0 66.1 0 0.51
0.51 2 .DELTA. Example 7 Comparative TFS -- -- Done -- -- -- -- --
-- 5 .smallcircle. Chromate Example 8
Examples 33 and 34
[0150] A solution containing 200 ppm of iron ions was prepared by
adding an aqueous iron nitrate solution to mixture A shown in Table
1 as a treatment bath. In the preparation, ammonia water or nitric
acid was added to the solution for maintaining the pH value to be
2.5. This solution was used as the treatment bath. A steel sheet
was subjected to degreasing, water washing, pickling, and water
washing and was then subjected to cathodic electrolytic treatment
at a current density of 4 A/dm.sup.2 five cycles. Subsequently, the
treatment bath was transferred to another tank and was controlled
to have a pH value of 3.0 with ammonia water. The precipitate was
removed with filter, and the pH value was adjusted to 2.5 again
with nitric acid. Subsequently, a surface-treated steel sheet was
produced in the same way as before the removal of the precipitate
and was laminated with polyester films, followed by cross-cut
corrosion resistance evaluation as in Example 9. This test is
carried out on the assumption of continuous operation and evaluates
the effect of surface treatment in a recycled treatment bath.
Accordingly, a surface-treated steel sheet produced for the first
time was not used, and a surface-treated steel sheet produced for
the second time (after removal of precipitate from the treatment
bath) was laminated and was evaluated. Table 4 shows the bath
concentrations before and after the removal of precipitate and the
evaluation results.
Comparative Examples 9 and 10
[0151] Comparative Examples 9 and 10 were performed as in Examples
33 and 34 except that mixture XA shown in Table 1 was used as the
treatment bath.
TABLE-US-00004 TABLE 4 Atomic Concen- ratio Fe/Al tration Film Film
Bath (ppm) surface central Crosscut Continuous Mixture condition pH
Al Fe portion portion corrosion operation Example 33 A Before 2 5
1500 230 0.37 0.34 3 .smallcircle. filtration Example 34 A After
2.5 1500 100 0.19 0.23 4 .smallcircle. filtration Comparative XA
Before 2.5 1500 260 0.51 0.51 3 x Example 9 filtration Comparative
XA After 2.5 1500 260 0.50 0.49 3 x Example 10 filtration
Examples 35 and 36
[0152] Solutions having iron ion concentrations of 0 ppm and 200
ppm were prepared by adding an aqueous iron nitrate solution to
mixture A shown in Table 1 as treatment baths. Steel sheets
subjected to electrolytic degreasing, water washing, pickling, and
water washing were immersed in the respective treatment baths for
cathodic electrolysis at a current density of 4 A/dm.sup.2 five
cycles. Subsequently, the resulting surface-treated steel sheets
were each coated with an epoxy acrylic water based paint such that
the thickness after baking was 5 .mu.m, followed by hardening by
baking in a hot air drying furnace at 200.degree. C. for 10 minutes
to give a surface-treated steel sheet with an organic coating.
[Evaluation of Coating Film Adhesion of Surface-Treated Steel Sheet
with an Organic Coating]
[0153] The produced surface-treated steel sheet with an organic
coating was provided with a grid-like cut with a cutter and was
subjected to a tape-peeling test. The peeling ratio was determined
by visual inspection. The evaluation criteria are as follows. The
results are shown in Table 5.
[0154] .circleincircle.: a peeling ratio of 5% or less,
[0155] .smallcircle.: a peeling ratio of higher than 5% and not
higher than 10%,
[0156] .DELTA.: a peeling ratio of higher than 10% and not higher
than 20%, and
[0157] .times.: a peeling ratio of higher than 20%.
[Processing Adhesion of Surface-Treated Steel Sheet with an Organic
Coating]
[0158] A cross-cut reaching the steel sheet face was formed on the
surface of the surface-treated steel sheet with an organic coating
with a cutter, and Erichsen bulging was performed using the
intersection of the cross-cut as the center with a bulging height
of 5 mm. After the bulging processing, peeling with tape was
performed, and the degree of peeling was visually evaluated. The
results are shown in Table 5.
[0159] .circleincircle.: no peeling,
[0160] .smallcircle.: peeling of not more than 20% of the bulging
portion,
[0161] .DELTA.: peeling of more than 20% and not more than 50% of
the bulging portion, and
[0162] .times.: peeling of more than 50% of the bulging
portion.
Comparative Example 11
[0163] A steel sheet was subjected to degreasing, water washing,
pickling, and water washing and then subjected to treatment with
130 mg /m.sup.2 of chromium and 20 mg/m.sup.2 of chromium hydrous
oxide for one surface and was then immediately washed with water,
followed by drying to give a steel sheet treated with chromate on
the surface.
[0164] Subsequently, the resulting surface-treated steel sheet was
coated with an epoxy acrylic water based paint as in Example 35 to
obtain the surface-treated steel sheet with an organic coating.
TABLE-US-00005 TABLE 5 Film Fe amount Coating content (mg/m.sup.2)
film Processing Mixture pH (ppm) Al C adhesion adhesion Note
Example 35 A 2.5 0 41 1.3 .circleincircle. .circleincircle. Example
36 A 2.5 200 48 0.3 .circleincircle. .circleincircle. Comparative
TFS -- -- -- -- .circleincircle. .circleincircle. Chromate Example
11
Examples 37 and 38
[0165] Solutions having iron ion concentrations of 0 ppm and 200
ppm were prepared by adding an aqueous iron nitrate solution to
mixture A shown in Table 1 as treatment baths. Steel sheets
subjected to degreasing, water washing, pickling, and water washing
were immersed in the respective treatment baths for cathodic
electrolysis at a current density of 4 A/dm.sup.2 five cycles.
Subsequently, the resulting surface-treated steel sheets were each
heated on a hot plate so as to have a surface temperature of
250.degree. C. and were each laminated with a polyester film with
laminating rollers and quenched in water to give a surface-treated
steel sheet with an organic coating.
[Production of Metal Can]
[0166] Paraffin wax was applied to both surfaces of the resulting
surface-treated steel sheet with an organic coating for
electrostatic oiling. The steel sheet was punched into a circle
having a diameter of 143 mm, which was formed into a cup by
shallow-drawing in accordance with a common method. Subsequently,
this shallow drawn cup was subjected to a simultaneous drawing and
ironing process twice to be formed into a cup having a small
diameter and a large height. The thus prepared cup had the
following characteristics:
[0167] Cup diameter: 52.0 mm,
[0168] Cup height: 111.7 mm, and
[0169] The thickness ratio of the can wall to the original sheet
thickness: -30%.
[0170] The cup was subjected to doming and then heat treatment at
220.degree. C. for 60 seconds to remove the distortion of the resin
film, followed by trimming of the open end, curved surface
printing, neck-in processing into dimension 200, and flange
processing to produce a 200-g seamless can.
[Evaluation of Metal Can Processing Adhesion]
[0171] A linear cut was formed on the outer surface of the shallow
drawn cup at the position 15 mm from the top. The cup was peeled
off in the direction of 180 degrees in the can height direction in
accordance with adhesion evaluation described above with a tensile
tester to measure the adhesion strength. The retort treatment of
the test strips was omitted.
[0172] When a test strip was peeled off with a tensile tester, one
having a maximum tensile strength of 3 N/15 mm or more was
determined as .circleincircle., one having a maximum tensile
strength of 0.5 N/15 mm or more and less than 3.0 N/15 mm was
determined as .smallcircle., and one having a maximum tensile
strength of less than 0.5 N/15 mm was determined as .times..
[Evaluation of Metal Can Cross-Cut Corrosion Resistance]
[0173] A can side wall portion was cut out from the resulting metal
can, and the end faces were coated with tape. A cross-cut having a
length of 4 cm was formed with a cutter at the position 50 mm from
the can bottom. The can was immersed in commercially available
coffee (trade name: Blendy.cndot.Bottle Coffee Low Sugar,
manufactured by Ajinomoto General Foods, Inc.). After four weeks,
the can was evaluated as in the evaluation of cross-cut corrosion
resistance described above. The results are shown in Table 6.
Comparative Example 12
[0174] A steel sheet was subjected to degreasing, water washing,
pickling, and water washing and then subjected to treatment with
130 mg /m.sup.2 of chromium and 20 mg/m.sup.2 of chromium hydrous
oxide for one surface and was then immediately washed with water,
followed by drying to give a steel sheet treated with chromate on
the surface. Subsequently, the resulting steel sheet was laminated
with a polyester film as in Example 37 to produce a surface-treated
steel sheet with an organic coating.
TABLE-US-00006 TABLE 6 Film Metal can amount crosscut Metal can Fe
(mg/m.sup.2) corrosion processing Mixture pH concentration Al C
resistance adhesion Note Example 37 A 2.5 0 41 1.3 5
.circleincircle. Example 38 A 2.5 200 48 0.3 3 .circleincircle.
Comparative TFS -- -- -- -- 5 .circleincircle. Chromate Example
12
[0175] As shown in Table 2, in a treatment bath containing a
polycarboxylic acid, i.e., polyitaconic acid, when the
concentration of iron ions in the treatment bath was 100 ppm,
precipitation occurred at a pH value 3.0 (Examples 1 and 2). In the
treatment bath not containing polyitaconic acid, the treatment bath
composed of polyitaconic acid only, and the treatment bath
containing a relatively common complexing agent glycine, no
precipitation occurred even at a pH value of 3.0 (Comparative
Examples 1, 2, and 3). Accordingly, it was revealed that a
polycarboxylic acid, i.e., polyitaconic acid, induces precipitation
of iron ions to allow removal of iron components at a pH value
level near that in treatment conditions from the early stage. In
addition, it was revealed that in a treatment bath containing a
polycarboxylic acid, i.e., polyitaconic acid, the precipitation
height was further increased by raising the pH value level to be
higher than 3.0 to effectively remove the iron components (Examples
3 to 5). In addition, the precipitation height was increased with
an increase in proportion of polyitaconic acid in the treatment
bath, which demonstrates that iron components can be removed by
adding a large amount of polyitaconic acid to the treatment bath
(Examples 1 and 2, 3 to 5). In addition, it was revealed that the
precipitation height increases with the concentration of iron ions
(Examples 6 to 8). As obvious from the concentrations of aluminum
ions and iron ions in the treatment bath after a change in pH value
of the bath, it was revealed that the addition of polyitaconic acid
can reduce the Fe concentration in the bath without decreasing the
aluminum concentration. In the case of glycine, which does not
cause precipitation, the same effect cannot be obtained even if the
pH value was raised.
[0176] As obvious from Table 3, in a surface-treated steel sheet
having a film containing 10 to 150 mg/m.sup.2 of aluminum and 0.1
to 3.5 mg/m.sup.2 of carbon prepared by electrolytic treatment,
corrosion hardly occurred in the steel sheets with cross-cuts by
immersion. Thus, the steel sheets all had excellent corrosion
resistance (Examples 9 to 32), cross-cut corrosion resistance
equivalent to that of TFS containing chromium was obtained. In
contrast, in the surface-treated steel sheet prepared by only
immersion treatment without performing electrolytic treatment, the
cross-cut corrosion resistance was low (Comparative Examples 4 and
5) to make application to a can difficult. Even if the treatment
bath did not contain polyitaconic acid, corrosion resistance with
an applicable level could be obtained when the iron ion
concentration of the treatment bath was 0 ppm (Comparative Example
6), but an increase in iron ion concentration in the bath
deteriorated the cross-cut corrosion resistance regardless of
electrolytic treatment (Comparative Example 7). Accordingly, the
proportion of iron atoms in a film increases with the iron ion
concentration in the treatment bath to show a tendency of
deterioration in cross-cut corrosion resistance. However, the
presence of polyitaconic acid in the treatment bath shows an effect
of preventing the film from being contaminated with iron atoms. It
is obvious that a further increase of the iron ion concentration in
the treatment bath increases the proportion of iron atoms in the
film to deteriorate the cross-cut corrosion resistance.
Accordingly, the iron ion concentration in the treatment bath is
desirably 200 ppm or less.
[0177] As also obvious from Table 4, in a treatment bath containing
polyitaconic acid, the aluminum ion concentration in the treatment
bath hardly varied before and after removal of precipitate with a
filter, whereas the iron ion concentration decreased. The atomic
ratio Fe/Al of the film of an electrolytic treatment steel sheet
prepared with a treatment solution after filtration was lower than
that of the film prepared with a treatment solution before the
filtration, and the cross-cut corrosion resistance was improved.
Accordingly, recycling treatment can maintain the performance
necessary for a surface-treated steel sheet, such as cross-cut
corrosion resistance, and therefore allows continuous operation. In
contrast, in a treatment bath not containing polyitaconic acid,
precipitate is not generated. Accordingly, iron ions in the
treatment bath cannot be removed even by performing filtration
treatment, and iron ions increase with the area of electrolytic
treatment, resulting in a difficulty of continuous operation.
[0178] As also obvious from Tables 5 and 6, in the surface-treated
steel sheet with an organic coating of the present invention, the
processing adhesion was satisfactory both in application of epoxy
acrylic water based paint and in lamination with a polyester film.
In addition, the can had satisfactory metal can processing adhesion
and metal can cross-cut corrosion resistance at the side wall
portion and also had performance equivalent to that of TFS
containing chromium.
INDUSTRIAL APPLICABILITY
[0179] The surface treatment bath of the present invention contains
a polycarboxylic acid, which captures iron ions eluted into the
treatment bath from a steel sheet, to maintain the concentration of
iron ions in the treatment bath to be a certain level or less.
Consequently, the surface treatment bath of the present invention
can form a film having excellent corrosion resistance on the
surface of the steel sheet and can produce a surface-treated steel
sheet having excellent corrosion resistance and excellent adhesion
with a coating film. In particular, the treatment bath can be
suitably used in production of an organic surface-treated steel
sheet for can manufacturing.
[0180] The surface treatment bath of the present invention and the
surface-treated steel sheet with an organic coating produced using
the surface treatment bath are excellent in processing adhesion in
coating and can therefore be suitably used not only in three-piece
cans and can lids but also in seamless cans that are produced by a
known procedure that requires advanced process such as a
bending-stretching process (stretching process) through
drawing.cndot.redrawing, a bending-stretching.cndot.ironing process
through drawing.cndot.redrawing, or a drawing.cndot.ironing
process.
[0181] Furthermore, the can body and the can lid of the present
invention have excellent corrosion resistance and therefore can be
suitably used as containers and lids for highly corrosive contents
or contents requiring retort sterilization.
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