U.S. patent application number 14/006843 was filed with the patent office on 2014-12-25 for surface treatment agent composition for tin-plated steel, and tin-plated steel subjected to surface treatment.
This patent application is currently assigned to NIPPON PAINT CO., LTD.. The applicant listed for this patent is Tomio Hirano, Masahiko Matsukawa, Miwa Uchikawa. Invention is credited to Tomio Hirano, Masahiko Matsukawa, Miwa Uchikawa.
Application Number | 20140377581 14/006843 |
Document ID | / |
Family ID | 46930839 |
Filed Date | 2014-12-25 |
United States Patent
Application |
20140377581 |
Kind Code |
A1 |
Uchikawa; Miwa ; et
al. |
December 25, 2014 |
SURFACE TREATMENT AGENT COMPOSITION FOR TIN-PLATED STEEL, AND
TIN-PLATED STEEL SUBJECTED TO SURFACE TREATMENT
Abstract
A surface treatment agent composition which contains aluminum as
the coating film formation component and exhibits excellent
properties for removing tin ions within a treatment bath when
subjecting a tin-plated steel to electrolytic surface treatment,
thereby forming a coating film exhibiting excellent corrosion
resistance and yellowing resistance. This surface treatment agent
composition is used for subjecting a tin-plated steel or a
tin-based alloy-plated steel to electrolytic surface treatment and
contains aluminum ions, fluorine ions, and polycarboxylic acid. The
tin ions that eluted from the tin-plated steel are precipitated
within and removed from the treatment bath by using this surface
treatment agent composition.
Inventors: |
Uchikawa; Miwa; (Tokyo,
JP) ; Matsukawa; Masahiko; (Tokyo, JP) ;
Hirano; Tomio; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Uchikawa; Miwa
Matsukawa; Masahiko
Hirano; Tomio |
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP |
|
|
Assignee: |
NIPPON PAINT CO., LTD.
Osaka-shi
JP
|
Family ID: |
46930839 |
Appl. No.: |
14/006843 |
Filed: |
March 22, 2012 |
PCT Filed: |
March 22, 2012 |
PCT NO: |
PCT/JP2012/057348 |
371 Date: |
January 29, 2014 |
Current U.S.
Class: |
428/632 ;
205/199; 205/320 |
Current CPC
Class: |
C23C 28/34 20130101;
C23C 28/32 20130101; C09D 5/103 20130101; Y10T 428/12611 20150115;
C25D 7/0614 20130101; C25D 5/48 20130101; C23C 28/345 20130101;
C25D 9/10 20130101; C09D 131/00 20130101; C09D 5/4411 20130101;
C25D 5/505 20130101; C25D 9/08 20130101; C25D 9/04 20130101; C25D
3/44 20130101; C09D 133/02 20130101 |
Class at
Publication: |
428/632 ;
205/320; 205/199 |
International
Class: |
C25D 3/44 20060101
C25D003/44; C25D 9/04 20060101 C25D009/04; C23C 28/00 20060101
C23C028/00; C25D 7/06 20060101 C25D007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2011 |
JP |
2011-067962 |
Claims
1. A surface treatment agent composition for tin-plated steel to be
used for electrolytic surface treatment of a tin- or tin-based
alloy-plated steel, comprising aluminum ions, fluorine ions and a
polycarboxylic acid.
2. The surface treatment agent composition for tin-plated steel
according to claim 1, wherein the polycarboxylic acid is a
homopolymer containing a monomer selected from tl.sup.-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 tin-plated steel
according to claim 1, wherein a ratio [C group]/[Al] of a molar
concentration [C 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 tin-plated steel
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.
5. The surface treatment agent composition for tin-plated steel
according to claim 1, wherein a mass concentration of the aluminum
ions is 100 to 10,000 ppm.
6. The surface treatment agent composition for tin-plated steel
according to claim 1, wherein a pH value of the surface treatment
agent at 25.degree. C. is 1 to 5.
7. The surface treatment agent composition for tin-plated steel
according to claim 1, comprising tin ions, wherein a mass
concentration of the tin ions is 500 ppm or less.
8. A tin-plated steel which is surface-treated with the surface
treatment agent composition for tin-plated steel according to claim
1.
9. A method for electrolytic surface treatment of a tin- or
tin-based alloy-plated steel, comprising electrolytically treating
said tin- or tin-based alloy-plated steel with a surface treatment
agent comprising aluminum ions, fluorine ions and polycarboxylic
acid.
10. The method according to claim 9, wherein the polycarboxylic
acid is 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.
11. The method according to claim 9, wherein a ratio [C group]/[Al]
of a molar concentration [C 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 according to claim 9, 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.)
13. The method according to claim 9, wherein a mass concentration
of the aluminum ions is 100 to 10,000 ppm.
14. The method according to claim 9, wherein a pH value of the
surface treatment agent at 25.degree. C. is 1 to 5.
15. The method according to claim 9, comprising tin ions, wherein a
mass concentration of the tin ions is 500 ppm or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a surface treatment agent
composition for tin-plated steel, more specifically, to a surface
treatment agent composition for tin-plated steel capable of
imparting blackening resistance to a tin-plated steel when used in
an electrolytic surface treatment of the steel.
BACKGROUND ART
[0002] The chromate treatment has heretofore been known as a
treatment for improving adhesion of a steel or a tin-plated steel
to an organic film such as a coating film while imparting corrosion
resistance to the steel or tin-plated steel. The chromate treatment
has widely been employed in the fields of home electric appliances,
building materials, vehicles, air crafts, containers, and the like
due to its excellent corrosion resistance and adhesion to organic
films.
[0003] Usages of a tin- or tin-based alloy-plated steel include a
metal container such as a beverage can, for example, and the
chromate treatment of subjecting the tin- or tin-based alloy-plated
steel to cathode electrolysis in a solution of sodium dichromate
has been performed as a surface treatment for the metal container.
In this case, since the chromate-treated surface expresses
excellent adhesion to an organic resin coating, the chromate
treatment is remarkably useful for forming a barrier layer such as
a coating film or a laminate on the surface of the metal
container.
[0004] However, hexavalent chromium, which is used for the chromate
treatment, is toxic and has a heavy environmental burden. Since the
finished product is subjected to a treatment for removing
hexavalent chromium, use of the product is not problematic.
However, there has been a trend toward a reduction and abolishment
of the use of compounds containing chromium such as hexavalent
chromium in recent years. Also, since a large amount of cost is
required for wastewater and exhaust treatments and disposal caused
by performing the chromate treatment, there has a trend toward
omitting the chromate treatment which has been performed on the
tin- or tin-based alloy-plated steels in recent years. Therefore,
there is a demand for development of a surface treatment with
non-chromium which is an alternative for the chromate
treatment.
[0005] For instance, Patent Literature 1 proposes an immersion
treatment as a non-chromium-based surface treatment of steel, in
which a treatment solution containing zirconium or titanium is
used. In this case, a coating film including oxide of zirconium or
titanium is formed on a surface of the steel. However, the steel
which is surface-treated by treatment of immersing the steel into a
treatment solution containing zirconium or titanium is inferior in
corrosion resistance of a formed coating film and, slow in
deposition of the coating film compared to a steel with the
electrolytic chromate treatment which has been employed for metal
containers. Therefore, the immersion treatment has a problem of
considerably poor productivity. Accordingly, as a high speed
treatment process to replace the immersion treatment, a zirconium
and/or titanium treatment utilizing cathode electrolysis has been
proposed (for example, see Patent Literatures 2 and 3).
[0006] Further, there has been proposed a surface-treated metal
sheet in which a coating film of aluminum oxide having corrosion
resistance is formed on a surface of a steel by performing cathode
electrolysis using a treatment solution containing aluminum as a
coating film-forming component (for example, see Patent Literature
4).
[0007] [Patent Document 1] Pamphlet of PCT International
Publication No. WO2002/103080
[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] By the way, in the case of forming on a surface of a
tin-plated steel a coating film of a metal component contained in a
treatment solution by utilizing the cathode electrolysis, tin ions
are contained in a treatment bath due to elution of the tin ions
from the tin-plated steel which is the treated substrate during the
treatment. Accordingly, the tin ions in the treatment bath are
incorporated into the coating film to be formed or is deposited on
a surface of the coating film, and a sulfur component contained in
a beverage housed in a container of the treated substrate reacts
with the tin ions in the coating film, or oxygen penetrated into
the coating film from a small defect of the formed coating film
oxidizes the tin ions in the coating film, thereby causing an
abnormal appearance such as blackening or yellowing on the formed
coating film. It is therefore necessary to remove the tin ions from
the treatment bath by increasing pH of the treatment bath during
the treatment, but, zirconium, titanium, or aluminum which is the
component forming the coating film is undesirably precipitated
together with the tin ions when pH of the treatment bath is
increased. Therefore, a problem that it is difficult to efficiently
remove the tin ions eluted from the treated substrate into the
treatment bath is raised.
[0012] The present invention was accomplished in view of the
above-described circumstances, and an object of the present
invention is to provide a surface treatment agent composition
including aluminum as a coating film-forming component, the surface
treatment agent composition being capable of forming a coating film
excellent in blackening resistance and yellowing resistance due to
its excellent tin ion-removing property in a treatment bath.
Means for Solving the Problems
[0013] The inventors conducted extensive researches in order to
solve the above-described problems and accomplished the present
invention based on the findings that, by performing a surface
treatment on a tin-plated steel with the use of a surface treatment
agent composition containing aluminum ions as a coating
film-forming component and, further, polycarboxylic acid, the
polycarboxylic acid selectively reacts with tin ions to cause
precipitation of the tin ions, and a concentration of the tin ions
in the treatment bath can be kept to a level which does not exert
adverse influence on properties of the coating film.
[0014] The present invention is a surface treatment agent
composition for tin-plated steel, to be used for electrolytic
surface treatment of a tin- or tin-based alloy-plated steel,
including aluminum ions, fluorine ions, and polycarboxylic
acid.
[0015] The polycarboxylic acid may preferably be 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.
[0016] Also, a ratio [C group]/[Al] of a molar concentration [C
group] of carboxyl groups contained in the polycarboxylic acid to a
molar concentration [Al] of the aluminum ions may preferably be
0.005 to 2.0.
[0017] Further, a ratio [F]/[Al] of a molar concentration [F] of
the fluorine ions to a molar concentration [Al] of the aluminum
ions may preferably be 1 to 4.
[0018] Further, a mass concentration of the aluminum ions may
preferably be 100 to 10,000 ppm.
[0019] Further, a pH value at 25.degree. C. of the surface
treatment liquid for tin-plated steel may preferably be 1 to 5.
[0020] Further, a mass concentration of tin ions contained in the
surface treatment liquid for tin-plated steel may preferably be 500
ppm or less.
[0021] The present invention provides a tin-plated steel which is
surface-treated with the surface treatment agent composition for
tin-plated steel.
Effects of the Invention
[0022] According to the present invention, there is provided a
surface treatment agent composition comprising aluminum as a
coating film-forming composition, which enables to form a coating
film excellent in blackening resistance and yellowing resistance
due to its excellent property of removing tin ions in a treatment
bath in an electrolytic surface treatment of a tin-plated
steel.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
[0023] Hereinafter, one embodiment of a surface treatment agent
composition for tin-plated steel of the present invention will be
described. The surface treatment agent composition for tin-plated
steel of the present invention (hereinafter simply referred to as
"surface treatment agent composition" in some cases) is used for
subjecting tin- or tin-based alloy-plated steel to an electrolytic
surface treatment and includes aluminum ions, fluorine ions, and
polycarboxylic acid.
[0024] The tin- or tin-based alloy-plated material (hereinafter
collectively referred to as "tin-plated steel" in some cases) which
is an object to be treated with the surface treatment agent
composition is a steel of which a surface is plated with tin or a
tin-based alloy. An amount of the tin- or tin-based-plating formed
on a surface of a steel is not particularly limited. Also, examples
of the tin-based alloy to be used for fabrication of the tin-based
alloy-plated steel include, but are not limited to, a tin-silicon
alloy, a tin-silver alloy, a tin-indium alloy, a tin-copper alloy,
a tin-aluminum alloy, a tin-germanium alloy, and the like.
[0025] The tin-plated steel which is the object to be treated is
immersed into the surface treatment agent composition to undergo
the electrolytic surface treatment. In the electrolytic surface
treatment, the tin-plated steel is immersed into a treatment bath
of the surface treatment agent composition and becomes a cathode
when a negative electric charge is applied thereto. On the other
hand, in the bath of the surface treatment agent composition, an
anode to which a positive electric charge is applied is provided as
a counter electrode of the tin-plated steel to be treated. An
electrolysis reaction occurs when a voltage is applied between the
anode and the cathode, and the pH of the solution around the
cathode which is the treatment object is increased. Thus, as is
well-known to those skilled in the art, the aluminum ions or an
aluminum complex contained in the surface treatment agent
composition, which is described later in this specification, can no
longer maintain the dissolved state and is deposited as a coating
film of an aluminum compound on a surface of the treatment object.
The deposited coating film imparts blackening resistance to the
treatment object. A preferred example of a quantity of electric to
be applied between the anode and the cathode includes, but is not
limited to, 1 to 24 cycles when a cycle consists of 0.15 second of
a current application time at a current density of 1 to 10
A/dm.sup.2 and 0.50 second of a halt time, and more preferred
example thereof is 1 to 10 cycles. After the electrolytic surface
treatment, washing with water or washing with pure water may be
performed by using warm water or hot water, and properties of the
coating film may be further improved by reducing excessive fluorine
in the coating film depending on the usage. A pH level of the water
used for the washing with water may be adjusted to be within the
alkali range. A chemical species to be used for the pH adjustment
is not limited.
[0026] The surface treatment agent composition may preferably be an
aqueous solution but may contain an aqueous solvent such as alcohol
and ketone in order to dissolve the components. Next, the
components contained in the surface treatment agent composition
will be described.
[Aluminum Ion]
[0027] The surface treatment agent composition includes aluminum
ions. The aluminum ions serve as a coating film-forming component
in the electrolytic surface treatment as described above and, also,
is present as compounds with components such as nitrate ions,
fluorine ions, sulfate ions, and various ligands described later in
this specification (hereinafter, the aluminum ion and the compounds
(complexes) are collectively referred to as "aluminum ion(s)") in
the surface treatment agent composition. The aluminum ions through
the electrolytic surface treatment deposit on a surface of a
tin-plated steel as a composition including aluminum oxide or
aluminum hydroxide as a main component to form a coating film. The
coating film imparts the blackening resistance to the tin-plated
steel.
[0028] A content of aluminum ions in the surface treatment agent
composition may preferably be 100 to 10,000 ppm. The content of
aluminum ions being 100 ppm or more in the surface treatment agent
composition enables to form the coating film having satisfactory
blackening resistance on the surface of the tin-plated steel and,
therefore, is preferred. The content of 10,000 ppm or less enables
to maintain good aluminum ion solubility in the surface treatment
agent composition, thereby enabling to form the homogeneous coating
film on the surface of the tin-plated steel. A content of aluminum
ions when expressed in terms of metal in the surface treatment
agent composition may more preferably be 1000 to 5000 ppm, most
preferably 1500 to 3000 ppm.
[0029] Examples of an aluminum ion source include aluminate such as
sodium aluminate, fluoroaluminum such as sodium fluoroaluminate,
aluminum hydroxide, aluminum fluoride, aluminum oxide, aluminum
sulfide, aluminum nitrate, aluminum silicate, aluminum potassium
sulfate, aluminum dihydrogenphosphate, aluminum lactate, and the
like. These aluminum ion sources may be used alone or in
combination of two or more species thereof. The aluminum nitrate is
preferred as the aluminum ion source.
[Fluorine Ion]
[0030] The surface treatment agent composition includes fluorine
ions. The fluorine ions coordinate to the aluminum ions which are
the coating film-forming component to solubilize the aluminum ions.
Therefore, the fluorine ions enable the surface treatment agent
composition to contain a sufficient amount of the aluminum ions and
to be a homogeneous solution, thereby contributing improvement of
homogeneity of the coating film to be formed.
[0031] A fluorine ion source may be a salt of each of various
fluorides such as hydrofluoric acid, sodium fluoride, ammonium
fluoride, ammonium hydrogen fluoride, sodium hydrogen fluoride
(HFNaF), and potassium fluoride or may be fluoroaluminum, aluminum
fluoride, or the like which is exemplified above as the aluminum
ion source. The fluorine ion sources may be used alone or in
combination of two or more species thereof. These sodium fluoride
and/or ammonium fluoride is preferred as the fluorine ion
source.
[0032] As described in the foregoing, the fluorine ions homogenize
the surface treatment agent composition by solubilizing the
aluminum ions through the complex formation and thus improve the
homogeneity of the coating film to be formed on the surface of the
tin-plated steel. From the above-described viewpoint, [F]/[Al]
which is a ratio of a molar concentration [F] of the fluorine ions
to a molar concentration [Al] of the aluminum ions contained in the
surface treatment agent composition may preferably be 1 to 4. The
[F]/[Al] of 1 or more enables to sufficiently solubilize the
aluminum ions in the surface treatment agent composition and to
improve the homogeneity of the coating film to be formed on the
surface of the tin-plated steel and, therefore, is preferred. The
[F]/[Al] of 4 or less enables to suppress excessive etching of the
tin-plated steel which is otherwise caused by the fluorine ions,
thereby enabling to form the coating film having the satisfactory
blackening resistance on the surface of the tin-plated steel. The
[F]/[Al] may more preferably be 1.5 to 3.0, most preferably 1.9 to
2.6. The aluminum ion concentration and the fluorine ion
concentration are an aluminum mass concentration expressed in terms
of metal and a mass concentration expressed in terms of fluorine,
respectively. The molar ratio [F]/[Al] of fluorine to aluminum ions
is calculated by detecting the molar concentrations (mmol/L) of
aluminum ions and fluorine from the mass concentrations (ppm) of
aluminum ions and fluorine. It is possible to measure the aluminum
ion concentration by using an ICP (inductively-coupled plasma
spectrometry device) and the fluorine ion concentration by ion
chromatography.
[Polycarboxylic Acid]
[0033] The surface treatment agent composition includes
polycarboxylic acid. As described above, the tin ions are eluted
into the treatment bath from the tin-plated steel which is the
treatment object during the electrolytic surface treatment, and
absorption of the tin ions by a coating film formed on the surface
of the tin-plated steel leads to deterioration of blackening
resistance and yellowing resistance of the coating film. The
inventors conducted researches in order to solve the problems and
found that polycarboxylic acid added to the surface treatment agent
composition captures and precipitates the tin ions eluted into the
treatment bath, thereby suppressing a concentration of the tin ions
in the treatment bath to 500 ppm or less which does not exert any
influence on the properties of the coating film, more preferably
less than 300 ppm, particularly preferably less than 50 ppm.
Further, the inventors found that the polycarboxylic acid hardly or
never captures the coating film-forming components such as the
aluminum ions and, therefore, does not exert any influence on
formation of the coating film. The present invention was
accomplished based on the above-described findings, and the surface
treatment agent composition of the present invention includes
polycarboxylic acid. In the case of removing the tin ions from the
treatment bath by using polycarboxylic acid, since it is
unnecessary to increase a pH value of the treatment bath, it is
possible to selectively remove the tin ions while hardly or never
precipitating the coating film-forming components such as the
aluminum ions contained in the treatment bath, and it is possible
to stably maintain the treatment bath, thereby contributing to
improvement in long-term continuous productivity. Iron ions derived
from the steel can sometimes be eluted from the tin-plated steel in
addition to the tin ions, and, in such a case, the eluted iron ions
can be the cause of deterioration of blackening resistance and
yellowing resistance of the coating film as is the case with the
tin ions. Polycarboxylic acid selectively removes the iron ions,
too.
[0034] Further, polycarboxylic acid has a chelate effect on the
aluminum ions. Therefore, polycarboxylic acid aids dissolution of
the aluminum ions which are the coating film-forming component in
the surface treatment agent composition as is the case with the
above-described fluorine ions. Furthermore, since the aluminum ions
form a chelate with an organic substance such as polycarboxylic
acid, deposition rate on a surface of the tin-plated steel which is
caused by an increase in pH value is slowed down. Thus, deposition
of a coarse substance otherwise caused by local excessive
deposition on the surface of the tin-plated steel is suppressed, so
that the homogeneous and dense coating film is formed on the
tin-plated steel surface. Also, since the aluminum ions form a
chelate with an organic substance such as polycarboxylic acid, a
fluctuation in deposition behavior which is caused by a pH
fluctuation of the treatment bath is reduced, thereby facilitating
pH value control of the treatment bath in continuous
production.
[0035] As the polycarboxylic acid, a polymer may preferably be
used. Preferred examples of the polymer include a homopolymer
containing a monomer selected from acrylic acid, methacrylic acid,
maleic acid, and itaconic acid as a constitutional unit and a
copolymer containing at least one species of these monomers as the
constitutional unit. Polyitaconic acid and/or polyacrylic acid is
preferred as the polycarboxylic acid.
[0036] In the case of using the copolymer as polycarboxylic acid, a
copolymer obtained by copolymerization of two or more species of
the above-described monomers may be used, or a copolymer obtained
by copolymerization of one or more species of the above-described
monomers and another monomer may be used. Examples of "another
monomer" include a vinyl compound such as N-vinylpyrrolidone,
N-vinylcarbazole, N-vinyloxazoline, N-vinyl-1,2,4-triazole,
N-vinylcarbazole, N-vinylphthalimide, N-vinylsuccinimde,
N-vinylimidazole, vinylsulfonic acid, 2-sulfoethyl(meth)acrylate,
and vinil compound such as vinylsulfonic acid; vinyl ketones such
as methyl vinyl ketone, phenyl vinyl ketone, and divinyl ketone; an
acrylamide monomer 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-isopropyl acrylamide, 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-methacryloyloxyethyl succinic acid, ethylene glycol
dimethacrylate, glycerin dimethacrylate,
methoxytriethyleneglycol-2-hdyroxyethyl(meth)acrylate,
2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,
methoxypolyethylene glycol methacrylate, and methoxypolyethylene
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; a polymerizable aromatic compound such as styrene,
.alpha.-methylstyrene, tert-butylstyrene, parachlorostyrene,
vinylnaphthalene, and p-styrenesulfonic 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; an allyl compound such as ally
chloride, diallyl phthalate, allyl alcohol, and allylsulfonic acid;
and the like. These monomers as the "another monomer" may be used
alone or in combination of two or more species thereof.
[0037] As described above, since polycarboxylic acid has the
chelate effect on the aluminum ions, polycarboxylic acid attains
the effects of aiding dissolution of the aluminum ions, enabling to
form the homogeneous coating on the surface of the tin-plated
steel, and facilitating the control of the surface treatment in the
continuous production. The chelate effect is attributable to
carboxyl groups contained in polycarboxylic acid. From the
above-described viewpoint, a ratio [C group]/[Al] of a molar
concentration [C group] of the carboxyl groups contained in
polycarboxylic acid to the molar concentration [Al] of the aluminum
ions contained in the surface treatment agent composition may
preferably be within a predetermined range. A preferred example of
the [C group]/[Al] may be 0.005 to 2.0, a more preferred example
thereof may be 0.01 to 1.0, and a most preferred example thereof
may be 0.02 to 0.5. The aluminum ion concentration is a mass
concentration of the aluminum expressed in terms of metal. The
molar ratio [C group]/[Al] of the carboxyl groups contained in
polycarboxylic acid to the aluminum ions is calculated by detecting
the molar concentrations (mmol/L) of the aluminum ions and the
carboxyl groups contained in polycarboxylic acid from mass
concentrations (ppm) of the aluminum ions and the carboxyl
groups.
[Other Components]
[0038] Other components may be added to the surface treatment agent
composition in addition to the aluminum ions, fluorine ions, and
polycarboxylic acid in order to improve various other required
properties. Examples of such components include an antibacterial
agent, a surfactant, a chelating agent, an anticorrosion agent, and
the like.
[0039] Examples of the antibacterial agent include alcohols such as
ethanol and isopropanol; a guanidine group-containing compound such
as polyhexamethylene biguanidine hydrochloride; a
benzimidazole-based compound such as 2-(4-thiazolyl)benzimidazole
and methyl-2-benzimidazole carbamate; A phthalimide-based compound
such as N-(trichloromethylthio) tetrahydrophthalimide and
N-(fluorochloromethylthio)phthalimide; a phenol-based compound such
as p-chloro-m-xylenol and p-chloro-m-cresol; a nitrile-based
compound such as 2,4,5,6-tetrachloroisophthalonitrile and
1,2-dibromo-2,4-dicyanobutane; a pyridine-based compound such as
(2-pyridylthio-1-oxide)sodium and bis(2-pyridylthio-1-oxide)zinc;
an isothiazolone-based compound 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 paraoxybenzoate; sorbic acid; potassium sorbate; sodium
dehydroacetate; sodium propionate; and the like. The antibacterial
agents may be used alone or in combination of two or more species
thereof. A concentration of the antibacterial agent in the surface
treatment agent composition may appropriately be set depending on
the required property and, for example, may be 50 to 10,000
ppm.
[0040] The surfactant is not particularly limited, and a publicly
known nonionic surfactant, cationic surfactant, and/or anionic
surfactant may be used. The surfactants may be used alone or in
combination of two or more species thereof. A concentration of the
surfactant in the surface treatment agent composition may
appropriately be set depending on the required property and, for
example, may be 50 to 10,000 ppm.
[0041] The chelating agent is added in order to maintain the stable
dissolution state of the aluminum ions as is the case with the
above-described fluorine ions and polycarboxylic acid. Also, the
chelating agent acts as a scavenger for an impurity with which the
treatment bath is contaminated. The chelating agent is not
particularly limited, and examples thereof include citric acid,
gluconic acid, malonic acid, succinic acid, tartaric acid,
phosphoric acid, ethylene diamine tetra-acetic acid, and the like.
The chelating agents may be used alone or in combination of two or
more species thereof. A concentration of the chelating agent in the
surface treatment agent composition may appropriately be set
depending on the required property and, for example, may be 50 to
10,000 ppm.
[0042] The anticorrosion agent is not particularly limited, and
examples thereof include tannic acid, imidazoles, triazines,
guanines, hydrazines, biguanide, a silane coupling agent, colloidal
silica, amines, a phenol-based water-soluble organic compound
including a phenol resin, and the like. The anticorrosion agents
may be used alone or in combination of two or more species thereof.
A concentration of the anticorrosion agent in the surface treatment
agent composition may appropriately be set depending on the
required property and, for example, may be 10 to 10,000 ppm.
[Preparation of Surface Treatment Agent Composition]
[0043] The surface treatment agent composition is prepared by
dissolving the above-described components into water, followed by
stirring until homogeneity. The water into which the components are
dissolved is not particularly limited, and examples thereof include
tap water, well water, industrial water, ion exchanged water, and
the like. Also, publicly known water-based solvent may be added to
the water in order to aid the dissolution of the components.
Examples of the water-based solvent include methanol, ethanol,
isopropanol, methyl ethyl ketone, and the like.
[0044] As described in the foregoing, the surface treatment agent
composition is decomposed by an electric current when subjecting
the treatment object to the electrolytic surface treatment.
Therefore, the surface treatment agent composition necessarily has
certain electric conductivity, and a preferred example of the
electric conductivity is, 10 to 60 mS/cm at 20.degree. C. When the
surface treatment agent composition has the above-specified
electric conductivity, the balance between electrolytic surface
treatment efficiency and electricity usage becomes favorable, and
it is possible to speed up the electrolytic surface treatment and
to reduce electricity usage.
[0045] Examples of a method for adjusting the electric conductivity
of the surface treatment agent composition include a method for
adding a salt to the surface treatment agent composition. Examples
of the salt include, but are not limited to, sodium nitrate, sodium
sulfate, ammonium nitrate, ammonium sulfate, lithium nitrate, and
the like. An amount of the salt to be added is not particularly
limited and may be decided by appropriately adjusting the amount to
keep the electric conductivity of the surface treatment agent
composition to a desired value.
[0046] A pH value of the surface treatment agent composition at
25.degree. C. may preferably be 1 to 5. With the pH value of the
surface treatment agent of 1 or more, excessive etching of the
tin-plated steel which is the substrate is suppressed to make it
possible to form the coating film having favorable properties on
the surface of the substrate. Also, with the pH value of the
surface treatment agent of 5 or less, the solubility of the
aluminum ions is maintained, so that the aluminum ions can be
incorporated into the surface treatment agent in an amount
sufficient for forming the coating film having favorable
properties. The pH value of the surface treatment agent composition
may more preferably be 2.5 to 3.6.
[0047] An acidic or basic compound may be added to the surface
treatment agent to adjust the pH value of the surface treatment
agent composition. Examples of the compound include, but are not
particularly limited to, hydrochloric acid, sulfuric acid, nitric
acid, sodium hydroxide, ammonium water, amino alcohols such as
triethanolamine and dimethylethanolamine, potassium hydroxide, and
the like. An amount of each of the compounds to be added is not
particularly limited and may be decided by appropriately adjusting
the amount to keep the pH value of the surface treatment agent
composition to a desired value.
[0048] As described above, when the tin-plated steel is subjected
to the electrolytic surface treatment by using the surface
treatment agent composition of the present invention, the tin ions
eluted from the tin-plated steel is precipitated and removed from
the treatment bath. Therefore, the mass concentration of the tin
ions in the treatment bath is suppressed to 500 ppm or less, and
the coating film formed on the surface of the tin-plated steel is
excellent in blackening resistance and is suppressed in yellowing
with time.
[0049] Also, a tin-plated steel which is subjected to the surface
treatment with the surface treatment agent composition for
tin-plated steel is provided according to another aspect of the
present invention. As described in the foregoing, the tin-plated
steel has favorable blackening resistance and yellowing resistance
since the coating film of the aluminum compound is formed on a
surface thereof.
EXAMPLES
[0050] The present invention will hereinafter be described in more
details by giving examples, but the present invention is not
limited to the following examples at all.
[Surface Treatment Agent Composition]
[0051] Polyitaconic acid (manufactured by Iwata Chemical Co., Ltd.;
trade name: PIA-728; molecular weight: about 3000), polyacrylic
acid (manufactured by Nippon Shokubai Co., Ltd.; trade name:
Aqualic HL-415; molecular weight: 10,000), aluminum nitrate
[Al(NO.sub.3).sub.39H.sub.2O], and sodium fluoride (NaF) were
blended and dissolved into tap water in such a manner as to obtain
a solution having aluminum ions, polycarboxylic acid, and fluorine
concentrations as shown in Table 1 as mass concentrations (ppm),
thereby preparing each of surface treatment agent compositions of
Examples 1 to 16 and Comparative Examples 1 to 4 of which pH values
were not yet adjusted. Polyitaconic acid and polyacrylic acid were
used as polycarboxylic acid. Polyitaconic acid was used as
polycarboxylic acid in each of the examples and comparative
examples except Example 11. Polyacrylic acid was used as
polycarboxylic acid only in Example 11. In other words, the surface
treatment agent composition of Example 11 is the same as the
surface treatment agent composition of Example 1 except for using
polyacrylic acid as polycarboxylic acid in place of polyitaconic
acid.
[0052] Aluminum nitrate and sodium fluoride were used as the
aluminum ion source and the fluorine source, respectively, and the
aluminum concentration and the fluorine concentration shown in
Table 1 are the mass concentration of aluminum expressed in terms
of metal and the mass concentration expressed in terms of fluorine,
respectively. Further, a molar concentrations (mmol/L) of the
aluminum ions, fluorine, and carboxyl groups contained in
polycarboxylic acid, a molar ratio [F]/[Al] of fluorine to the
aluminum ions, and a molar ratio [C group]/[Al] of the carboxyl
groups contained in polycarboxylic acid to the aluminum ions were
calculated and are shown in Table 1. It is possible to calculate
the concentration of the carboxyl groups contained in
polycarboxylic acid with, for example, a mass concentration (ppm)
of polyitaconic acid/(1/2 of a molecular weight of itaconic acid
which is the constitutional unit) when polyitaconic acid is
used.
[Table 1]
[Evaluation of Tin Ion-Removing Property]
[0053] After adjusting the pH value to 2.5 of each of the surface
treatment agent compositions of Examples 1 to 16 and Comparative
Examples 1 to 4, 80 mL of each of the surface treatment agent
compositions was transferred to a container having an inner
diameter of 45 mm, and tin sulfide (II) was added so as to adjust
the mass concentration of the tin ions to the value shown in Table
2, thereby preparing a simulant treatment bath. The reason for
adding tin sulfide is to reproduce a state in which the tin ions
are eluted into a treatment bath from a tin-plated steel during a
surface treatment. Then, after adjusting the pH value of each of
the treatment baths to the one shown in Table 2, the treatment
baths were left to stand still for 6 hours, and then height of
precipitates generated at the bottoms of the treatment baths was
measured. The generated precipitates were derived from the tin ions
contained in the treatment baths. As the evaluation, the sample in
which the height of the precipitation was 0.5 mm or more was
evaluated to be capable of tin ion removal (o), and the sample in
which the height of the precipitation was 0.5 mm or less was
evaluated to be incapable of tin ion removal. The results are shown
in Table 2. Each of the pH values shown in Table 2 is the one
detected at 25.degree. C., and nitric acid and ammonium water were
used for the pH adjustment.
[Residual Tin Ion Concentration Measurement]
[0054] A supernatant liquid of the solution of the treatment bath
in which the precipitate was generated was collected, and the
precipitate was removed by using a filter paper. After confirming
that there was no solid matter in the liquid by visual observation,
the liquid was diluted with ion exchanged water in such a manner
that a tin ion concentration is within the measureable
concentration range while adjusting a pH value by using nitric acid
or ammonium water in such a manner as to avoid a fluctuation in pH
value. After that, the tin ion concentration was measured by using
an inductively-coupled plasma emission spectrometry device
(ICPE-9000, product of Shimadzu Corporation). From the obtained
results, a tin ion concentration (ppm) remaining in the supernatant
liquid was calculated based on the dilution ratio. As the
evaluation, the sample in which a supernatant concentration was 300
ppm or more and 500 ppm or less was evaluated to be preferable; the
sample in which a supernatant concentration was 50 ppm or more and
less than 300 ppm was evaluated to be more preferable; and the
sample in which a supernatant concentration was less than 50 ppm
was evaluated to be most preferable.
[Table 2]
[0055] As shown in Table 2, it is understood that, since each of
the surface treatment agent compositions containing polycarboxylic
acid as one of the essential components according to the present
invention has the favorable tin ion-removing property, even when
the tin ions are eluted into the treatment bath during the surface
treatment of the tin-plated steel, the diluted tin ions are
precipitated and removed from the treatment bath, and absorption of
the tin ions by a coating film formed on a surface of the
tin-plated steel is suppressed. Though each of the surface
treatment agent compositions of Comparative Examples 1 and 2
containing polycarboxylic acid also exhibits the favorable tin
ion-removing property (Comparative Test Examples 1 and 2), the
surface treatment agent compositions cause the problem in terms of
coating film-forming property as described later in the test
results since they do not contain the aluminum ions or fluorine
which is one of the essential components of the present
invention.
[0056] The supernatant concentrations of all of the samples were
within the range of less than 500 ppm, and each of Examples 1, 2,
13, 14, 17, and 18 attained the supernatant concentration of less
than 50 ppm.
[Fabrication of Test Sheet]
[0057] A low carbon cold-rolled steel sheet (sheet thickness: 0.225
mm) was subjected to degreasing through immersion into a 3%
solution of an alkaline degreasing agent (Surfcleaner 322N8
manufactured by Nippon Paint Co., Ltd.) at 70.degree. C. for 15
seconds.
[0058] The steel sheet after the degreasing was subjected to
washing with water through spraying with tap water for 30 seconds,
followed by pickling through immersion into a pickling solution (5%
sulfuric acid solution) at 70.degree. C. for 5 seconds. After
subjecting the steel sheet to washing with water through spraying
with tap water for 30 seconds, a tin-plated layer having a plate
thickness of 2.8 g/m.sup.2 was formed on a surface of the steel
sheet using publicly known Ferrostan bath under the below-described
conditions, followed by washing with water and reflow, thereby
obtaining a tin-plated steel. (Plating Conditions)
[0059] Temperature: 40.degree. C.
[0060] Stirring: as required
[0061] Current density: 10 A/dm.sup.2
[0062] Anode material: commercially available 99.999% metal tin
[0063] Treatment time: the number of cycles of 5 to 15 by setting 1
second of a current application time+0.50 second of a halt time as
a cycle
[0064] Reflow: the obtained tin-plated steel sheet was heated to a
temperature equal to or more than a melting point of tin by
induction heating, followed by quenching by pouring ion exchanged
water
[0065] The obtained tin-plated steel sheets were respectively
immersed into to the treatment baths (bath temperature: 45.degree.
C.) comprising the surface treatment agent compositions of Examples
1 to 16 and Comparative Examples 1 to 4 each having the
predetermined pH value. A cathode electrolysis (electrolysis
conditions: the number of cycles was adjusted to be 1 to 7 cycles
by setting a cycle as 0.15 second of a current application time at
a current density of 4 A/dm.sup.2+0.50 second of a halt time and in
such a manner as to maintain a coating film amount to 5 to 10
mg/m.sup.2 in terms of aluminum which was measured by fluorescent
X-ray measurement) was performed with stirring the treatment bath
and by using as an anode an iridium oxide-coated titanium plate
positioned at 17 mm from the cathode. A post-treatment including
washing with running water, washing with pure water, and drying was
performed immediately after the cathode electrolysis. Warm water or
hot water may be used for the washing with water and washing with
pure water, and properties of the coating film may be improved by
reducing excessive fluorine in the coating film depending on the
usage. The surface treatment agent compositions used as the
treatment baths and the pH values of the treatment baths are shown
in Table 3. Each of the pH values shown in Table 3 is the one
detected at 25.degree. C., and nitric acid and ammonium water were
used for the pH adjustment of the treatment baths. In Test Example
42 and Test Example 43 shown in Table 3, the treatment baths which
were respectively prepared by removing the precipitates from the
simulant treatment baths of Example 4 and Example 16 (Table 2) were
used for performing the tests described below. Test Example 42 and
Test Example 43 were performed in order to confirm the surface
treatment capability in the treatment bath from which the tin ions
diluted from the tin-plated steel was precipitated and removed and
to verify the treatment capability in the case of continuously
performing the surface treatment.
[Coating Film Amount Measurement]
[0066] After drying a coating film formed on each of the test
sheets fabricated by the method described in [Fabrication of Test
Sheet], an aluminum amount in the coating film was measured by
using a fluorescent X-ray device (XRF-1500, product of Shimadzu
Corporation), and a carbon amount (C amount) in the coating film
was measured by using a carbonhydrogen/moisture analysis device
(RC612, product of Leco Japan Corporation). The results are shown
in the column of "Coating film amount" of Table 3.
[Evaluation of Coating Film Appearance]
[0067] In each of the test sheets fabricated by the method
described in [Fabrication of Test Sheet], absence/presence of
contaminant deposition in the form of a sludge on a surface of the
coating film was investigated to evaluate homogeneity of the
coating film. The contaminant deposition is observed particularly
when the treatment bath develops white turbidity (i.e. is not a
homogeneous solution). As the evaluation, the sample in which the
contamination deposition was not observed on the coating film
surface was evaluated as o, and the sample in which the
contamination deposition was observed on the coating film surface
or in which no coating film was formed on the test sheet was
evaluated as x. The results are shown in the column of "Coating
film appearance" of Table 3.
[Coating Film Deposition Property]
[0068] The number of cycles required for depositing a coating film
of 5 mg/m.sup.2 in terms of aluminum on the surface of the
tin-plated steel sheet in the cathode electrolysis (electrolysis
conditions: 4A/dm.sup.2) described in [Fabrication of Test Sheet]
was measured. The results are shown in the column of "Deposition
property" of Table 3. As the evaluation, productivity was
determined to be preferable when the required number of treatment
cycles was 1 to 10 cycles; 1 to 6 cycles was considered to be more
preferable; and less than 3 cycles was considered to be most
preferable. The sample which required 10 or more cycles for
depositing the coating film of 5 mg/m.sup.2 (including the one
which could not form any coating film) was considered to have poor
productivity and is indicated as ">10".
[Adhesion property Evaluation]
[0069] In the state where each of the test sheets fabricated by the
method described in [Fabrication of Test Sheet] was heated to
230.degree. C., a polyester film (Teflex FT-20 manufactured by
Teijin DuPont Films Japan Limited; thickness: 20 .mu.m) was
thermocompression-bonded to the test sheet via a laminate roll.
Water cooling was performed immediately after the thermocompression
bonding to obtain a polyester-coated test sheet. Each of the
polyester-coated test sheets was cut into strips each 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 a 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. The results are shown in the column of
"Adhesion property" of Table 3. As the evaluation, maximum tensile
strength of 1N/15 mm or more when the test strip was peeled off by
the tension tester (LST-200N-S100 and a load cell "LTTU-200N",
products of Minebea Co., Ltd.) was evaluated to be favorable, 3N/15
mm or more was evaluated to be excellent, and 5N/15 mm or more was
evaluated to be particularly excellent.
[Sulfide Blackening Resistance Evaluation]
[0070] An epoxyphenol-based coating material was coated on each of
test sheets fabricated by the method described in [Fabrication of
Test Sheet] in such a manner that a coating film thickness after
annealing and drying was 70 mg/dm.sup.2, followed by baking at
200.degree. C. for 20 minutes. The test sheet was cut to obtain a
sheet of 70 mm square, and each of the cut sections was protected
with a tape having a width of 3 mm, followed by 3 mm extension
processing by using an Erichsen tester (product of Coating Tester
K. K.). The extended part formed by the extension processing was
immersed into a model solution comprising a solution containing 4.5
g/L of potassium dihydrogenphosphate (KH.sub.2PO.sub.4), 12 g/L of
sodium hydrogenphosphate (Na.sub.2HPO.sub.412H.sub.2O), and 2 g/L
of an L-cysteine hydrochloride monohydrate and then subjected to a
retort treatment in a hermetically sealed container at 115.degree.
C. for 60 minutes. After that, sulfide blackening resistance was
evaluated. The evaluation was conducted by determining a change in
appearance by visual observation, and the sample in which a
considerable change was not observed was evaluated as o, and the
sample in which considerable change was observed was evaluated as
x. The results are shown in the column of "Blackening resistance"
in Table 3.
[Yellowing Resistance Evaluation]
[0071] Each of the test sheets fabricated by the method described
in [Fabrication of Test Sheet] was cut to obtain a sheet of 70 mm
square, and the thus-obtained test sheet was heated in a
200.degree. C. oven for an hour. A degree of a change in color of
the test sheet from the color before the heating to the color after
the heating was investigated by using a colorimeter (product of
Konica Minolta Sensing, K. K.; trade name: CM-2500d) to evaluate
the yellowing resistance. The evaluation was conducted by using as
a standard a color difference between colors before and after the
heating in the test sheet (Reference Test Example 1) made by a
chromate treatment described later in this specification and
calculating a difference between a color difference before and
after the heating of the test sheet as the evaluation object and
the color difference used as the standard, and the sample having
the difference of 1.9 or less is evaluated as o, the sample having
the difference exceeding 1.9 and less than 3 is evaluated as
o.sup.-, and the sample having the difference of 3 or more is
evaluated as x. The results are shown in the column of "Yellowing
resistance" of Table 3. The color difference was calculated with
(.DELTA.L.sup.2+.DELTA.a.sup.2+.DELTA.b.sup.2).sup.0.5.
[Reference Test Examples 1 and 2]
[0072] The above-described evaluations were conducted on a
commercially available chromate-treated (311 treated) tinplate (Sn
amount: 2.8 g/m.sup.2), and the results are shown in Table 3 as
Reference Test Example 1. Also, the above-described evaluations
were conducted on an untreated tin-plated steel sheet (a steel
sheet described in [Fabrication of Test Sheet] on which only the
tin-plating was performed), and the results are shown in Table 3 as
Reference Test Example 2.
[Electric Conductivity]
[0073] Electric conductivity of each of the surface treatment agent
compositions of Examples 1 to 16 and Comparative Examples 1 to 4
after adjusting the pH value at 25.degree. C. of each of the
compositions to 3.5 was measured. The results are shown in Table 4.
Nitric acid and ammonium water were used for the pH adjustment.
[Table 3]
[0074] *1 PIA stands for polyitaconic acid, and PAA stands for
polyacrylic acid. [0075] *2 Each of the values shown in the column
of deposition property is the number of treatment cycles of the
cathode electrolysis required for forming the coating film having
the predetermined thickness on the test sheet; the smaller the
value is, the better the deposition property. The samples having
the value ">10" include the sample on which no effective coating
film was formed by the cathode electrolysis. [0076] *3 Each of Test
Examples 42 and 43 shows the result of the test conducted by using
the treatment bath which was obtained by removing the precipitate
from the treatment bath after the test in each of Test Examples 4
and 16. [0077] *4 Comparative Example 9 shows the result of the
test conducted by using the treatment bath after the test in
Comparative Test Example 3. Since no precipitate was generated in
the treatment bath after the test in Comparative Test Example 3, no
precipitation-removing operation was performed.
[Table 4]
[0078] As shown in Table 3, it is understood that the coating film
excellent in blackening resistance and yellowing resistance is
formed on the surface of the tin-plated steel sheet by performing
the electrolytic surface treatment on the tin-plated steel sheet
(steel) using each of the surface treatment agent compositions of
the present invention. Referring to Table 3, it is understood that
the coating films formed by using the surface treatment agent
compositions of the present invention have the properties equal to
or better than the coating film formed by the conventional chromate
treatment. From such results, it is proved that the surface
treatment agent compositions of the present invention are
remarkably effective in the electrolytic surface treatment of
tin-plated steels.
* * * * *