U.S. patent application number 13/003091 was filed with the patent office on 2011-07-14 for tin-plated steel sheet and method for manufacturing the same.
This patent application is currently assigned to JFE STEEL CORPORATION. Invention is credited to Hiroki Iwasa, Norihiko Nakamura, Takeshi Suzuki.
Application Number | 20110168563 13/003091 |
Document ID | / |
Family ID | 41507153 |
Filed Date | 2011-07-14 |
United States Patent
Application |
20110168563 |
Kind Code |
A1 |
Suzuki; Takeshi ; et
al. |
July 14, 2011 |
TIN-PLATED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME
Abstract
A tin-plated steel sheet includes a steel sheet; an
Sn-containing plating layer in which the mass per unit area of Sn
is 0.05 to 20 g/m.sup.2 disposed on at least one surface of the
steel sheet; a first chemical conversion coating which contains P
and Sn, in which the mass per unit area of P is 0.3 to 10
mg/m.sup.2, disposed on the Sn-containing plating layer; and a
second chemical conversion coating which contains P and Al, in
which the mass per unit area of P is 1.2 to 10 mg/m.sup.2 and the
mass per unit area of Al is 0.24 to 8.7 mg/m.sup.2, disposed on the
first chemical conversion coating.
Inventors: |
Suzuki; Takeshi; (Chiba,
JP) ; Nakamura; Norihiko; (Chiba, JP) ; Iwasa;
Hiroki; (Kanagawa, JP) |
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
|
Family ID: |
41507153 |
Appl. No.: |
13/003091 |
Filed: |
July 2, 2009 |
PCT Filed: |
July 2, 2009 |
PCT NO: |
PCT/JP2009/062493 |
371 Date: |
March 31, 2011 |
Current U.S.
Class: |
205/50 ;
205/170 |
Current CPC
Class: |
C25D 3/30 20130101; C23C
2/08 20130101; C25D 5/10 20130101; C23C 28/321 20130101; C25D 5/48
20130101; C25D 11/36 20130101; C23C 2/28 20130101; C23C 22/20
20130101; C23C 2/26 20130101; C23C 22/08 20130101; C23C 22/73
20130101; C23C 28/34 20130101; C23C 28/322 20130101 |
Class at
Publication: |
205/50 ;
205/170 |
International
Class: |
C25D 11/36 20060101
C25D011/36; C25D 7/00 20060101 C25D007/00; C25D 5/10 20060101
C25D005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2008 |
JP |
2008-179680 |
Claims
1. A tin-plated steel sheet comprising: a steel sheet; an
Sn-containing plating layer in which the mass per unit area of Sn
is 0.05 to 20 g/m.sup.2 disposed on at least one surface of the
steel sheet; a first chemical conversion coating which contains P
and Sn, in which the mass per unit area of P is 0.3 to 10
mg/m.sup.2, disposed on the Sn-containing plating layer; and a
second chemical conversion coating which contains P and Al, in
which the mass per unit area of P is 1.2 to 10 mg/m.sup.2 and the
mass per unit area of Al is 0.24 to 8.7 mg/m.sup.2, disposed on the
first chemical conversion coating.
2. A method for manufacturing a tin-plated steel sheet comprising:
forming an Sn-containing plating layer on at least one surface of a
steel sheet so that the mass per unit area of Sn is 0.05 to 20
g/m.sup.2; immersing the steel sheet in a chemical conversion
solution containing tetravalent tin ions and phosphate ions or
cathodically electrolyzing the steel sheet in the chemical
conversion solution; immersing the steel sheet in a chemical
conversion solution containing 5 to 200 g/L of aluminum phosphate
monobasic and having a pH of 1.5 to 2.4 or cathodically
electrolyzing the steel sheet in the chemical conversion solution;
and drying the steel sheet.
3. The method according to claim 2, wherein the drying is performed
at a temperature lower than 60.degree. C.
Description
RELATED APPLICATIONS
[0001] This is a .sctn.371 of International Application No.
PCT/JP2009/062493, with an international filing date of Jul. 2,
2009 (WO 2010/005042 A1, published Jan. 14, 2010), which is based
on Japanese Patent Application No. 2008-179680, filed Jul. 10,
2008, the subject matter of which is incorporated by reference.
TECHNICAL FIELD
[0002] This disclosure relates to tin-plated steel sheets for use
in DI cans, food cans, beverage cans, and the like, and
particularly relates to a tin-plated steel sheet having a chemical
conversion coating containing no chromium (Cr) on the surface and a
method for manufacturing the same.
BACKGROUND
[0003] As surface-treated steel sheets for use in cans, tin-plated
steel sheets referred to as "tinplates" have been widely used.
Generally in such tin-plated steel sheets, a chromate coating is
formed on the tin-plated surface of the steel sheets by chromate
treatment such as immersing the steel sheet in an aqueous solution
containing a hexavalent chromium compound such as dichromic acid,
or electrolyzing the steel sheet in the solution. This is because,
by formation of the chromate coating, oxidation of the tin-plated
surface that is likely to occur due to long-term storage or the
like can be prevented, and a degradation of appearance (yellowing)
can be suppressed. In addition, when lacquer is applied to the
tin-plated steel sheet before use, cohesive failure due to the
growth of a tin (Sn) oxide layer is prevented and adhesion with
organic resin such as paints, (hereinafter simply referred to as
"paint adhesion") is ensured.
[0004] In contrast, considering recent environmental problems,
restriction of the use of chromium has proceeded in various fields,
and some chemical conversion treatment techniques in stead of the
chromate treatment have been proposed also for the tin-plated steel
sheets for cans.
[0005] For example, Japanese Examined Patent Application
Publication No. 55-24516 discloses a method for surface-treating a
tin-plated steel sheet. The method includes forming a chemical
conversion coating by performing direct current electrolysis using
the tin-plated steel sheet as a cathode in a phosphoric acid
solution. Japanese Examined Patent Application Publication No.
58-41352 discloses a chemical conversion solution containing
phosphate ions, one or more of chlorates and bromates, and tin ions
and having a pH of 3 to 6. Japanese Unexamined Patent Application
Publication No. 49-28539 discloses a surface treatment method, for
tinplates, including applying one or more of calcium phosphates,
magnesium phosphates, and aluminum phosphates so that the coating
thickness is 15 .mu.g/m.sup.2 or lower. Japanese Unexamined Patent
Application Publication No. 2005-29808 discloses a surface-treated
steel sheet, for containers, successively having an iron
(Fe)-nickel (Ni) diffusion layer, an Ni layer, and an Ni--Sn alloy
layer, a non-alloyed Sn layer and further having 1 to 100
mg/m.sup.2 of a phosphate coating layer in terms of phosphorus (P)
on the steel sheet surface.
[0006] However, the chemical conversion coatings disclosed in JP
'516, JP '352, JP '539 and JP '808 cannot suppress degradation of
appearance or reduction in paint adhesion caused by oxidization of
the tin-plated surface compared to conventional chromate
coatings.
[0007] In contrast, Japanese Unexamined Patent Application
Publication No. 2007-239091 discloses a method for manufacturing a
tin-plated steel sheet including plating a steel sheet with tin,
immersing the tin-plated steel sheet in a chemical conversion
solution containing tin ions and phosphate ions or subjecting the
steel sheet to cathodic electrolysis in a chemical conversion
solution, and then heating the same to 60 to 200.degree. C. to form
a chemical conversion coating, thereby suppressing degradation of
appearance and reduction in paint adhesion caused by oxidization of
the tin-plated surface to a degree equal to or higher than the
suppression degree obtained by conventional chromate coatings.
[0008] However, the method disclosed in JP '091 has a problem that
a heating unit used subsequently to chemical conversion is
necessary and therefore the cost of chemical conversion is
high.
[0009] It could therefore be helpful to provide a tin-plated steel
sheet, without using Cr, that can suppress degradation of
appearance and reduction in paint adhesion caused by oxidization of
the tin-plated surface and can be subjected to chemical conversion
treatment at low cost and a method for manufacturing the same.
SUMMARY
[0010] We conducted extensive research on a tin-plated steel sheet,
without using Cr, that can suppress degradation of appearance and
reduction in paint adhesion caused by oxidization of the tin-plated
surface and that can be subjected to chemical conversion treatment
at low cost. We found that when a tin-plated steel sheet having a
Sn-containing plating layer on the steel sheet surface, a first
chemical conversion coating containing P and Sn on the
Sn-containing plating layer, and a second chemical conversion
coating containing P and aluminum (Al) on the first chemical
conversion coating is achieved, the degradation of appearance and
the reduction in paint adhesion can be suppressed without heating
after the chemical conversion treatment.
[0011] We thus provide a tin-plated steel sheet including an
Sn-containing plating layer in which the mass per unit area of Sn
is 0.05 to 20 g/m.sup.2 and which is disposed on at least one
surface of the steel sheet; a first chemical conversion coating
which contains P and Sn, in which the mass per unit area of P is
0.3 to 10 mg/m.sup.2, and which is disposed on the Sn-containing
plating layer; and a second chemical conversion coating which
contains P and Al, in which the mass per unit area of P is 1.2 to
10 mg/m.sup.2 and the mass per unit area of Al is 0.24 to 8.7
mg/m.sup.2, and which is disposed on the first chemical conversion
coating.
[0012] A tin-plated steel sheet can be manufactured by the
following method: a method including forming an Sn-containing
plating layer on at least one surface of a steel sheet such that
the mass per unit area of Sn is 0.05 to 20 g/m.sup.2, immersing the
steel sheet in a chemical conversion solution containing
tetravalent tin ions and phosphate ions or cathodically
electrolyzing the steel sheet in the chemical conversion solution,
immersing the steel sheet in a chemical conversion solution
containing 5 to 200 g/L of aluminum phosphate monobasic and having
a pH of 1.5 to 2.4 or cathodically electrolyzing the steel sheet in
this chemical conversion solution, and then drying the steel
sheet.
[0013] Drying is preferably performed at a temperature of lower
than 60.degree. C.
[0014] It is now possible to manufacture a tin-plated steel sheet,
without using Cr, that can suppress degradation of appearance and
reduction in paint adhesion caused by oxidization of the tin-plated
surface, requires no special heating facility, and can be subjected
to chemical conversion treatment at low cost. A chemical conversion
coating of the tin-plated steel sheet can be formed at a high line
speed of 300 m/minute or more similarly as in the case of the
current chromate treatment.
DETAILED DESCRIPTION
[0015] A tin-plated steel sheet successively includes an
Sn-containing plating layer, a first chemical conversion coating
containing P and Sn, and a second chemical conversion coating
containing P and Al on at least one surface of a general
cold-rolled steel sheet for cans using low carbon steel or
extremely low carbon steel. Hereinafter, the details will be
described.
(1) Sn-Containing Plating Layer
[0016] First, to provide corrosion resistance, the Sn-containing
plating layer is formed on at least one surface of the steel sheet.
In this case, the mass per unit area of Sn needs to be 0.05 to 20
g/m.sup.2. This is because when the mass per unit area of Sn is
lower than 0.05 g/m.sup.2, the corrosion resistance is poor and
when the mass per unit area of Sn exceeds 20 g/m.sup.2, the plating
layer thickness increases, which causes an increase in cost. The
mass per unit area of Sn can be measured by coulometry or surface
analysis using fluorescence X-rays.
[0017] The Sn-containing plating layer is not particularly limited
and is preferably a plating layer such as a plating layer
containing an Sn layer (hereinafter referred to as "Sn layer"), a
plating layer having a two-layer structure in which an Sn layer is
formed on an Fe--Sn layer (hereinafter referred to as "Fe--Sn
layer/Sn layer"), a plating layer having a two-layer structure in
which an Sn layer is formed on Fe--Sn--Ni layer (hereinafter
referred to as "Fe--Sn--Ni layer/Sn layer"), or a plating layer
having a three-layer structure in which an Fe--Sn--Ni layer and an
Sn layer are successively formed on an Fe--Ni layer (hereinafter
referred to as "Fe--Ni layer/Fe--Sn--Ni layer/Sn layer").
[0018] The Sn-containing plating layer may be a continuous plated
layer or a discontinuous layer with a dotted pattern.
[0019] The Sn-containing plating layer can be formed by a known
process. For example, the Sn-containing plating layer can be formed
by electroplating a steel sheet with Sn using a usual tin
phenolsulfonate plating bath, tin methanesulfonate plating bath, or
tin halide plating bath such that the mass per unit area is 2.8
g/m.sup.2, performing reflow treatment at a temperature equal to or
higher than the melting point of Sn, that is, 231.9.degree. C., to
form a plating layer of Fe--Sn layer/Sn layer, performing cathodic
electrolysis at 1 to 3 A/dm.sup.2 in a 10 to 15 g/L aqueous sodium
carbonate solution to remove an Sn oxide film formed on the surface
after the reflow treatment, and washing the steel sheet with water.
The plating layer containing Ni among the above-described
Sn-containing plating layers can be formed by plating a steel sheet
with nickel before tin plating and, as required, performing
annealing treatment or performing reflow treatment or the like
after tin plating.
(2) First Chemical Conversion Coating
[0020] Next, the first chemical conversion coating, which contains
P and Sn, is provided on the Sn-containing plating layer. This is
because, to efficiently form a chemical conversion coating at a
high line speed of 300 m/minute or more, a chemical conversion
solution containing tetravalent tin ions and phosphate ions is used
as described in detail below, similarly as in the current chromate
treatment. In this case, the mass per unit area of P in the
chemical conversion coating needs to be 0.3 to 10 mg/m.sup.2. This
is because, when the mass per unit area of P is lower than 0.3
mg/m.sup.2, the surface coverage of the coating becomes
insufficient. Thus, an effect of suppressing the oxidization of the
tin-plated surface becomes insufficient and, when the mass per unit
area of P exceeds 10 mg/m.sup.2, the cohesive failure of the
coating is likely to occur. Thus, the appearance is likely to
deteriorate and the paint adhesion is likely to decrease.
[0021] The first chemical conversion coating can be formed by
immersing the plated steel sheet in a chemical conversion solution
containing tetravalent tin ions and phosphate ions or cathodically
electrolyzing the plated steel sheet in the chemical conversion
solution. The steel sheet may be washed with water after the
immersion treatment or the cathodic electrolysis treatment. The
reason why the chemical conversion solution containing tetravalent
tin ions and phosphate ions is used is to form the chemical
conversion coating at a high line speed of 300 m/minute or more as
described above. More specifically, tetravalent tin ions have high
solubility and a larger number of tetravalent tin ions can be added
compared with the case of divalent tin ions. Moreover, since
tetravalent tin ions are reduced to divalent tin ions near the tin
surface by electrons emitted with the dissolution of the tin
surface, high-concentration divalent tin ions are generated near
the tin-plated surface, and thus a reaction is accelerated.
Furthermore, when cathodic electrolysis treatment is performed,
reduction of tetravalent tin ions to divalent tin ions is
accelerated and also a reduction reaction of protons is also
accelerated to increase the pH near the tin-plated surface to
thereby promote precipitation deposition of insoluble tin (II)
hydrogen phosphate or tin (II) phosphate. Thus, the reaction is
further accelerated. Accordingly, when the chemical conversion
solution containing tetravalent tin ions and phosphate ions is
used, the chemical conversion coating is efficiently formed in a
short period of time.
[0022] As the chemical conversion solution containing tetravalent
tin ions and phosphate ions, an aqueous solution containing 0.5 to
5 g/L of stannic chloride pentahydrate and 1 to 80 g/L of
orthophosphoric acid is mentioned.
(3) Second Chemical Conversion Coating
[0023] Finally, the second chemical conversion coating containing P
and Al is provided on the above-described first chemical conversion
coating. This is because when a chemical conversion coating
containing P and Al is formed, degradation of appearance and
reduction in paint adhesion can be suppressed to a degree equal to
or higher than the suppression degree obtained by conventional
chromate coatings simply by drying at low temperatures without
positively heating after chemical conversion treatment. The reason
is not clear, but is believed to be because a dense chemical
conversion coating of phosphate having stronger barrier properties
to the oxidization of the tin-plated layer is formed by
introduction of Al into the chemical conversion coating. In this
case, the mass per unit area of P in the chemical conversion
coating needs to be 1.2 to 10 mg/m.sup.2 and the mass per unit area
of Al therein needs to be 0.24 to 8.7 mg/m.sup.2. This is because
when the mass per unit area of P is lower than 1.2 mg/m.sup.2 or
the mass per unit area of Al is lower than 0.24 mg/m.sup.2, an
effect of suppressing oxidization of the tin-plated surface becomes
insufficient. Thus, the appearance deteriorates and paint adhesion
decreases with time and when the mass per unit area of P exceeds 10
mg/m.sup.2, the cohesive failure of the coating itself occurs.
Thus, the paint adhesion is likely to decrease. The upper limit of
the mass per unit area of Al of 8.7 mg/m.sup.2 is a
stoichiometrically derived value when the total amount of the
coating is occupied by aluminum phosphate tribasic. When the mass
per unit area of P is lower than 10 mg/m.sup.2, the value does not
exceed this value. The mass per unit area of P or the mass per unit
area of Al in the chemical conversion coating can be measured by
surface analysis using fluorescence X-rays.
[0024] The second chemical conversion coating can be formed by
immersing the steel sheet having the first chemical conversion
coating in a chemical conversion solution containing 5 to 200 g/L
of aluminum phosphate monobasic and having a pH of 1.5 to 2.4 or
cathodically electrolyzing the steel sheet having the first
chemical conversion coating in this chemical conversion solution,
and then drying the steel sheet. After the immersion or cathodic
electrolysis treatments, the steel sheet may be washed with water,
and then may be dried. In this case, based on the following reason,
the chemical conversion solution containing 5 to 200 g/L of
aluminum phosphate monobasic and having a pH of 1.5 to 2.4 is
used.
[0025] More specifically, when the content of the aluminum
phosphate monobasic is lower than 5 g/L, the mass per unit area of
Al in the coating is not sufficient and strong barrier properties
to the oxidization of the tin-plated layer is not obtained. When
the content of the aluminum phosphate monobasic exceeds 200 g/L,
the stability of the chemical conversion solution is deteriorated,
a precipitate is formed in the chemical conversion solution and
adheres to the surface of the tin-plated steel sheet, which causes
a degradation of appearance and a reduction in paint adhesion.
Moreover, when the pH of the chemical conversion solution is lower
than 1.5, the deposition of the coating becomes difficult and a
sufficient mass per unit area cannot be secured even when the
treatment time is extremely prolonged to several 10 seconds. When
the pH of the chemical conversion solution exceeds 2.4, the
deposition of the coating rapidly occurs and thus the control of
the mass per unit area becomes difficult.
[0026] Drying is preferably performed at a temperature lower than
60.degree. C. This is because the chemical conversion coating
formed by the manufacturing method can sufficiently suppress
oxidization of the tin-plated layer even when the drying
temperature is lower than 60.degree. C. Thus, a particular heating
facility is unnecessary. The drying temperature is the peak
temperature of the steel sheet.
[0027] To allow the mass per unit area of P to reach 1.2 to 10
mg/m.sup.2 in a short period of time, the amount of the aluminum
phosphate monobasic is preferably adjusted to 60 to 120 g/L. To
adjust the mass per unit area of P to 1.2 to 10 mg/m.sup.2 at a
high line speed, the cathodic electrolysis treatment is more
preferable than the immersion treatment. It is more preferable to
generate hydrogen gas by cathodic electrolysis to consume protons
near the interface between the tin-plated surface and the chemical
conversion solution to thereby forcibly increase the pH.
Furthermore, to the chemical conversion solution, 1 to 20 g/L of
orthophosphoric acid can be blended to adjust the pH or increase
the reaction rate described below.
[0028] The pH of the chemical conversion solution can be adjusted
by adding acid or alkali such as phosphoric acid, sulfuric acid or
sodium hydroxide. To the chemical conversion solution, a promoter
such as FeCl.sub.2, NiCl.sub.2, FeSO.sub.4, NiSO.sub.4, sodium
chlorate, or nitrite salt; an etching agent such as a fluorine ion;
and/or a surfactant such as sodium lauryl sulfate or acetylene
glycol can be appropriately added. The temperature of the chemical
conversion solution is preferably set to 70.degree. C. or more.
This is because when the temperature is set to 70.degree. C. or
more, the reaction rate increases with an increase in temperature
and treatment at a higher line speed can be achieved. However, when
the temperature is excessively high, the evaporation rate of
moisture from the chemical conversion solution increases and the
composition of the chemical conversion solution changes with time.
Thus, the temperature of the chemical conversion solution is
preferably 85.degree. C. or lower.
[0029] As disclosed in JP '091, when a steel sheet is subjected to
the immersion treatment or the cathodic electrolysis treatment in a
chemical conversion solution containing tin ions and phosphate ions
to form a single-layer chemical conversion coating, the steel sheet
needs to be heated to 60 to 200.degree. C. after the chemical
conversion treatment. However, as in the case of our tin-plated
steel sheet, when the second chemical conversion coating is formed
on the first chemical conversion coating formed using the chemical
conversion solution containing tin ions and phosphate ions by
further performing immersing treatment in a chemical conversion
solution containing aluminum phosphate monobasic or cathodic
electrolysis in the chemical conversion solution, the steel sheet
need not to be positively heated after the chemical conversion
treatment. Thus, a heating facility is not necessary and the
chemical conversion treatment can be performed at low cost.
[0030] As described above, considering that the current chromate
treatment is usually performed at a line speed of 300 m/minute or
more and the productivity is very high, it is preferable that new
chemical conversion treatment in place of the chromate treatment
can be performed at least at the current line speed. This is
because when the treatment time is prolonged, the size of a
treatment tank needs to be enlarged or the number of the tanks
needs to be increased, which causes an increase in facility cost or
the maintenance cost thereof. To perform the chemical conversion
treatment at a line speed of 300 m/minute or more without
reconstructing the facility, the treatment time is preferably set
to 2.0 seconds or lower in total similarly as in the current
chromate treatment. The treatment time is more preferably 1 second
or lower.
[0031] When the immersion treatment or the cathodic electrolysis
treatment is performed in the above-described chemical conversion
solution, the treatment can be performed at the current line speed
of 300 m/minute or more. The current density during the cathodic
electrolysis treatment is preferably adjusted to 10 A/dm.sup.2 or
lower. This is because when the current density exceeds 10
A/dm.sup.2, changes in the mass per unit area to changes in the
current density become high, which makes it difficult to secure a
stable mass per unit area. To form a chemical conversion coating,
there is a method using application or anode electrolysis treatment
in addition to the immersion treatment or the cathodic electrolysis
treatment. However, the former treatment is likely to cause surface
reaction unevenness, which makes it difficult to obtain uniform
appearance and, in the latter method, the coating is likely to be
deposited in a powder shape. Thus, degradation of appearance or
degradation of paint adhesion is likely to occur. Thus, these
methods are not preferable.
EXAMPLES
[0032] The raw material used to form a steel sheet was: [0033]
Steel sheet A: a low carbon cold-rolled steel sheet having a sheet
thickness of 0.2 mm; or [0034] Steel sheet B: a steel sheet
obtained by forming a nickel-plated layer on both surfaces of a low
carbon cold-rolled steel sheet having a sheet thickness of 0.2 mm
and a mass per unit area of 100 mg/m.sup.2 using a Watts bath, and
then annealing the steel sheet at 700.degree. C. in an atmosphere
containing 10% by volume H.sub.2 and 90% by volume N.sub.2 for
diffusing nickel in the steel sheet. Then, an Sn layer was formed
using a commercially-available tin plating bath with the mass per
unit area of Sn shown in Table 3. Then, the Sn layers were reflowed
at a temperature equal to or higher than the melting point of Sn,
thereby forming a plated layer containing Sn of Fe--Sn layer/Sn
layer on the steel sheet A and forming a plated layer containing Sn
of Fe--Ni layer/Fe--Ni--Sn layer/Sn layer on the steel sheet B.
[0035] Next, to remove a surface Sn oxide film formed by reflowing,
cathodic electrolysis was performed at a current density of 1
A/dm.sup.2 in an aqueous 10 g/L sodium carbonate solution having a
bath temperature of 50.degree. C. Thereafter, immersion treatment
was performed at a treatment time shown in Tables 1 and 2 or
cathodic electrolysis treatment was performed at a current density
and a treatment time shown in Tables 1 and 2 using a chemical
conversion solution containing orthophosphoric acid and stannic
chloride pentahydrate and having a temperature as shown in Tables 1
and 2. Then, wringing was performed by a wringer roll, followed by
washing with water was performed. Subsequently, immersion treatment
was performed at a treatment time shown in Tables 1 and 2 or
cathodic electrolysis treatment was performed at a current density
and a treatment time shown in Tables 1 and 2 using a chemical
conversion solution containing orthophosphoric acid and aluminum
phosphate monobasic and having a pH and a temperature as shown in
Tables 1 and 2. Then, wringing was performed by a wringer roll, and
then washing with water was performed. Then, the steel sheets were
dried at room temperature using a general blower or dried using
70.degree. C. hot air, thereby producing samples Nos. 1 to 22 of a
tin-plated steel sheet having a first chemical conversion coating
and a second chemical conversion coating. In the production
thereof, the pH of the chemical conversion solutions shown in Table
1 and 2 was adjusted with acid or alkali.
[0036] Then, after each layer or coating was formed, the mass per
unit area of Sn in the Sn-containing plating layer, the mass per
unit area of P in the first chemical conversion coating, and the
mass per unit area of P and the mass per unit area of Al in the
second chemical conversion coating were measured by the
above-described method. Moreover, the produced tin-plated steel
sheets were evaluated for the appearance immediately after the
production, the amount of the Sn oxide film and the appearance
after long-term storage, the paint adhesion, and the corrosion
resistance by the following methods.
[0037] Appearance immediately after production: The appearance of
the tin-plated steel sheets immediately after the production was
visually observed and evaluated as follows. Then, when evaluated as
A or B, the appearance was good. [0038] A: Excellent appearance in
which no powdery deposit is present on the surface and metallic
luster is maintained [0039] B: Excellent appearance in which no
powdery deposit is present on the surface but the surface is
slightly whitish [0040] C: Uneven appearance in which a powdery
deposit is locally present on the surface and the surface is
slightly whitish [0041] D: Whitish appearance in which a large
amount of powdery deposits is present on the surface
[0042] Amount of Sn oxide film and appearance after long-term
storage: The tin-plated steel sheets were stored for 10 days under
an environment of 60.degree. C. and a relative humidity of 70%.
Then, the appearance was visually observed and also the amount of
the Sn oxide film formed on the surface was evaluated as follows by
electrolyzing with a current density of 25 uA/cm.sup.2 in an
electrolysis solution which was a 1/1000 N HBr solution, and
determining the amount of electricity required for electrochemical
reduction. When evaluated as A or B, the amount of Sn oxide film
after long-term storage was small and the appearance was also good.
[0043] A: Electric quantity for reduction of lower than 2
mC/cm.sup.2, excellent appearance (better than that in the case of
a chromate treated material) [0044] B: Electric quantity for
reduction of 2 mC/cm.sup.2 or more and lower than 3 mC/cm.sup.2,
excellent appearance (equivalent to that in the case of a chromate
treated material) [0045] C: Electric quantity for reduction of 3
mC/cm.sup.2 or more and lower than 5 mC/cm.sup.2, slightly
yellowish appearance [0046] D: Electric quantity for reduction of 5
mC/cm.sup.2 or more, clear yellowish appearance
[0047] Paint adhesion: An epoxy phenol paint was applied to the
tin-plated steel sheets immediately after production so that the
mass per unit area was 50 mg/dm.sup.2, and then cured at
210.degree. C. for 10 minutes. Subsequently, the two painted
tin-plated steel sheets were laminated so that the coated surfaces
face each other with a nylon adhesion film interposed therebetween,
and pressure-bonded to each other under the bonding conditions of a
pressure of 2.94.times.10.sup.5 Pa, a temperature of 190.degree.
C., and a pressure-bonding time of 30 seconds. Then, the laminate
was divided into test pieces having a width of 5 mm. Then, the test
pieces were torn off using a tensile testing machine and evaluated
as follows by measuring the strength. When evaluated as A or B, the
paint adhesion was good. The same paint adhesion evaluation was
also performed after the tin-plated steel sheets were stored for
six months at a room temperature environment. [0048] A: 19.6 N (2
kgf) or more (equivalent to that in the case of a chromate treated
material for welding cans) [0049] B: 3.92 N (0.4 kgf) or more and
lower than 19.6 N (equivalent to that in the case of a chromate
treated material for welding cans) [0050] C: 1.96 N (0.2 kgf) or
more and lower than 3.92 N [0051] D: Lower than 1.96 N (0.2
kgf)
[0052] Corrosion resistance: An epoxy phenol paint was applied to
the tin-plated steel sheets so that the mass per unit area was 50
mg/dm.sup.2, and then cured at 210.degree. C. for 10 minutes.
Subsequently, the steel sheets were immersed in a
commercially-available tomato juice at 60.degree. C. for 10 days.
Then, the stripping of the paint and the generation of rust were
visually evaluated. When evaluated as A or B, the corrosion
resistance was good. [0053] A: No stripping of the paint and no
generation of rust [0054] B: No stripping of the paint but
generation of very slight dot-like rust (equivalent to that in the
case of a chromate treated material) [0055] C: No stripping of the
paint but generation of slight rust [0056] D: Stripping of the
paint and generation of rust
[0057] The results are shown in Table 3. In all the samples Nos. 1
to 17 as our tin-plated steel sheets, the appearance immediately
after the production and after long-term storage is good and the
amount of the Sn oxide film after long-term storage is small, which
shows that the samples have excellent paint adhesion and corrosion
resistance.
TABLE-US-00001 TABLE 1 Conditions for forming first Conditions for
forming second chemical conversion coating chemical conversion
coating Conversion solution Conversion solution Amount Amount
Amount Amount of of Cathodic of of Cathodic Drying ortho- stannic
electrolysis ortho- stannic electrolysis Peak Raw phos- chloride
(immersion) phos- chloride (immersion) sheet Sam- material phoric
penta- Temper- Current phoric penta- Temper- Current temper- ple
steel acid hydrate ature density Time acid hydrate ature density
Time ature No. sheet (g/L) (g/L) (.degree. C.) (A/dm.sup.2)
(second) (g/L) (g/L) pH (.degree. C.) (A/dm.sup.2) (second) Method
(.degree. C.) Remarks 1 A 6.0 0.7 60 Immer- 1.0 8.5 18.0 1.74 70 4
1.0 Blower Room Inventive sion temper- example ature 2 A 6.0 2.7 60
5 1.0 4.2 18.0 1.97 70 4 1.0 Blower Room Inventive temper- example
ature 3 A 3.0 0.7 60 Immer- 0.5 3.0 18.0 2.08 70 4 1.0 Blower Room
Inventive sion temper- example ature 4 A 6.0 2.7 60 5 1.0 3.0 54.0
2.12 80 6 1.0 Blower Room Inventive temper- example ature 5 A 3.0
0.7 60 Immer- 0.5 20.0 18.0 1.60 60 4 1.0 Blower Room Inventive
sion temper- example ature 6 A 6.0 0.7 60 Immer- 1.0 8.5 18.0 1.74
50 4 1.0 Blower Room Inventive sion temper- example ature 7 A 3.0
0.7 60 Immer- 0.5 8.5 60.0 1.80 50 4 1.0 Blower Room Inventive sion
temper- example ature 8 A 6.0 2.7 60 3 1.0 8.5 80.0 1.80 50 4 1.0
Blower Room Inventive temper- example ature 9 A 6.0 2.7 60 3 1.0
8.5 120.0 1.80 50 4 1.0 Blower Room Inventive temper- example ature
10 A 6.0 2.7 60 3 1.0 8.5 200.0 1.80 50 4 1.0 Blower Room Inventive
temper- example ature 11 A 3.0 0.7 60 Immer- 0.5 1.0 60.0 2.00 50 4
0.5 Blower Room Inventive sion temper- example ature 12 A 6.0 0.7
60 Immer- 1.0 8.5 60.0 1.80 50 4 1.0 Hot air 70 Inventive sion
drying example 13 A 6.0 0.7 60 Immer- 1.0 8.5 60.0 1.80 70 Immer-
1.0 Blower Room Inventive sion sion temper- example ature 14 A 6.0
0.7 60 Immer- 1.0 8.5 18.0 1.74 70 5 1.0 Blower Room Inventive sion
temper- example ature 15 B 6.0 0.7 60 Immer- 1.0 8.5 18.0 1.74 70 5
1.0 Blower Room Inventive sion temper- example ature 16 A 3.0 0.7
60 Immer- 0.5 8.5 18.0 1.74 70 3 1.0 Blower Room Inventive sion
temper- example ature 17 B 3.0 0.7 60 Immer- 0.5 8.5 18.0 1.74 70 3
1.0 Blower Room Inventive sion temper- example ature
TABLE-US-00002 TABLE 2 Conditions for forming first Conditions for
forming second chemical conversion coating chemical conversion
coating Conversion solution Conversion solution Amount Amount
Amount of of Cathodic of Amount Cathodic Drying Raw ortho- stannic
electrolysis ortho- of electrolysis Peak mate- phos- chloride
(immersion) phos- aluminum (immersion) sheet Sam- rial phoric
penta- Temper- Current phoric phosphate Temper- Current temper- ple
steel acid hydrate ature density Time acid monobasic ature density
Time ture No. sheet (g/L) (g/L) (.degree. C.) (A/dm.sup.2) (second)
(g/L) (g/L) pH (.degree. C.) (A/dm.sup.2) (second) Method (.degree.
C.) Remarks 18 A 6.0 0.7 60 Immer- 1.0 8.5 1.0 1.73 70 4 1.0 Blower
Room Compar- sion temper- ative ature example 19 A 6.0 0.7 60
Immer- 1.0 8.5 250.0 2.00 70 4 2.0 Blower Room Compar- sion temper-
ative ature example 20 A 6.0 0.7 60 Immer- 1.0 8.5 60.0 1.30 85 4
10.0 Blower Room Compar- sion temper- ative ature example 21 A 6.0
0.7 60 Immer- 1.0 8.5 60.0 2.50 50 4 0.5 Blower Room Compar- sion
temper- ative ature example Room Compar- 22 A 6.0 2.7 60 5 1.0 Not
used Blower temper- ative ature example
TABLE-US-00003 TABLE 3 Sn- containing First Amount of plating
chemical Sn oxide layer conversion Second chemical film and Mass
per coating conversion coating Appearance appearance Paint adhesion
Sam- unit area Mass per Mass per Mass per immediately after
Immediately Six ple of Sn unit area unit area unit area after
long-term after months Corrosion No. (g/m.sup.2) of P (mg/m.sup.2)
of P (mg/m.sup.2) of Al (mg/m.sup.2) production storage production
later resistance Remarks 1 2.8 1.00 3.20 1.70 A A B B A Inventive
example 2 2.8 8.50 4.50 2.39 A A B B A Inventive example 3 2.8 0.32
6.50 3.45 A A B B A Inventive example 4 2.8 8.50 9.50 5.13 B A B B
B Inventive example 5 2.8 0.32 1.25 0.64 A B B B A Inventive
example 6 2.8 1.00 2.50 1.38 A A B B A Inventive example 7 2.8 0.32
4.50 2.43 A A B B A Inventive example 8 2.8 6.50 6.00 3.30 A A B B
A Inventive example 9 2.8 6.50 7.50 4.28 A A B B A Inventive
example 10 2.8 6.50 7.60 4.41 A A B B A Inventive example 11 2.8
0.34 9.80 5.30 A A B B A Inventive example 12 2.8 1.00 4.50 2.43 A
A B B A Inventive example 13 2.8 1.00 1.80 1.40 A A B B A Inventive
example 14 1.1 1.00 3.30 1.75 A A B B A Inventive example 15 1.1
1.00 3.40 1.77 A A B B A Inventive example 16 0.1 0.32 3.60 1.94 A
A A A B Inventive example 17 0.1 0.33 3.70 1.96 A A A A B Inventive
example 18 2.8 1.00 2.50 0.22 A C B C B Comparative example 19 2.8
1.00 11.00 7.59 D A D D C Comparative example 20 2.8 1.00 1.00 0.52
A C B D D Comparative example 21 2.8 1.00 12.00 6.72 C A C C C
Comparative example 22 2.8 8.50 0 0 A D B D A Comparative
example
INDUSTRIAL APPLICABILITY
[0058] We have made it possible to manufacture, without using Cr, a
tin-plated steel sheet that can suppress degradation of appearance
and reduction in paint adhesion caused by oxidization of the
tin-plated surface and that requires no special heating facility
and thus can be subjected to chemical conversion treatment at low
cost. Moreover, the chemical conversion coating of the tin-plated
steel sheet can be formed at a high line speed of 300 m/minute or
more similarly as in the case of the current chromate treatment.
Therefore, our steel sheets and methods can greatly contribute to
the industry.
* * * * *