STEEL SHEET FOR CONTAINERS, AND METHOD FOR
PRODUCNG STEEL SHEET FOR CONTAINERS
[Technical Field of the Invention]
[OOOl]
The present invention relates to a steel sheet for containers and a niethod for
producing a steel sheet for containers.
Priority is claimed on Japanese Patent Application No. 2013-107304, filed on
May 21, 2013, tlie content of which is incorporated herein by reference.
[Related Art]
[0002]
As containers for beverages and foods, metal containers that are made into
cans fiom steel sheets such as a nickel mi)-coated steel sheet, a tin (S1i)-coated steel
slieet, or a tin alloy-based steel sheet have been widely used. hi many cases, such
steel sheets for metal containers are subjected to a ~ustproofingtr eatment using
chromate such as hexavalent chromate or the like in order to ensure adhesion between
the steel slieet and the coating or between the steel sheet and the film and to ensure
co~rosiotrie sistance. However, since hexavalent chronlate used for tlie rustproofing
treattnetit using chromate is envirotin~etitallyh ar~nfiili,n stead of tlie rustproofing
treatment using chromate that hitherto has been performed on steel sheets for
containers, a treattnent using a chemical treatment film such as a zirconium (Zr)-
pliospliorus (P) filn~o r the like lias been developed (for example, refer to Patetit
Document 1 below).
[Prior At Document]
[Patent Document]
[0003]
[Patent Docun~ent I] Japanese Unexamitled Patent Application, First
Publication No. 2007-284789
[Disclosure of tlie Invention]
[Problems to be Solved by the Invention]
[0004]
When a metal container formed by using the above-described steel sheet for
containers is used for foods such as meat and vegetables including an amino acid
containing sulfur (S), the foods are heated at the time of sterilization treattilent. At
this time, sulfur is bonded with tin, iron (Fe) and the like and the steel sheet becomes
black. This phenomenon is called sulfide stain and due to this sulfide stain, a
problem of the design of the inner surface of the metal container becoming deteriorated
arises.
[OOOS]
In order to deal with such sulfide stain, in the related art, by using chromate
for forming a dense film even with a stnall amount of film, sulfide stain resistance of
the metal container has been achieved. However, in the case in which a chemical
treatnletit film suc11 as a zirconium-phosphotus film is used instead of using chromate,
when tlie atnoutlt of film is small, a large nutnber of film defects are generated.
Therefore, in order to exhibit excellent corrosion resistance, the atnoutlt of film cannot
be reduced and cost reduction is difficult.
[0006]
Therefore, there has been a demand for a technique capable of achieving both
sulfide stain resistance and cost reduction using a chemical treatment filni.
[0007]
The preselit illvention has been made in consideratio~o~f the above-described
problenis and an object thereof is to provide a steel slieet for co~itai~ietrhsa t is capable
of achieving sulfide stain resistance aud cost reduction usi~iga clietnical treatnient film
and a method for producing a steel sheet for containers.
[Means for Solving the Problem]
[0008]
In order to solve the above-described problems, as a result of an intensive
investigatio~ci onducted by the inventors, it has been found that all of the abovedescribed
problems cat1 be solved by forming an oxide layer includirig ti11 oxide
(SnOx) between a chemical treatment film and a Sn coated layer. The gist thereof is
as follows.
[0009]
(1) According to an aspect of tlie present invention, a steel sheet for containers is
provided, including: a steel sheet; an underlying Ni layer fortned by performing a Ni
coating or a Fe-Ni alloy coating containing Ni it1 an amount of 5 nig/m2 to 150 nig/n12
it1 terms of an amount of metal Ni on at least one surface of tlie steel sheet; a Sn coated
layer formed by performing Sn coating cotitaining Sn in an amount of 300 nig/n12 to
3,000 tng/t$ in terms of at1 amount of metal Sn on the underlying Ni layer and
iricludirig an island-shaped Sn formed by alloying the Sn coating and at least a part of
the underlyitig Ni layer by a reflow treatment; an oxide layer formed 011 the Sn coated
layer atid containing titi oxide; and a cliemical treatment layer fortned on the oxide
layer and containing Zr in an amoulit of 1 mg/m2 to 500 mg/niz it1 terms of an alnount
of metal Zr atid phosphate acid in an amount of 0.1 tng/n12 to 100 nigh2 in ternis of an
amount of P, wherein the oxide layer cotitaitis tin oxide in such at1 amount that an
amount of electricity required for reduction of tlie oxide layer is 0.3 mc/ctn2 to 10
tn~/cni~.
(2) In the steel slieet for containers according (I), the oxide layer tilay contain tin oxide
in such an amount that an anioulit of electricity required for reduction of the oxide
layer is 5.5 m ~ / c tno ~10~ IU C/CI~~~.
(3) In the steel sheet for containers according (1) or (2), after a lacquer is applied to the
surface of the steel sheet for containers atid the steel slieet is baked to form a lacquer,
the steel sheet for containers in which the lacquer is formed riiay be placed and fixed
onto an opening of a heat-resistant bottle in which a 0.6% by mass L-cysteine solution,
which is boiled for 1 hour, is stored, the heat-resistant bottle may be capped with a lid,
a heat treatment is performed at llO°C for 30 minutes in a state of the lid being upside
down, and then when an appearance of a contact portion of the steel sheet for
containers in which the lacquer is forn~edw ith the heat-resistant bottle is observed, a
stain may not occur in 50% or more of an area of the contact portion.
(4) According to another aspect of the invention, there is a method for producing a
steel sheet for containers including: forming an underlying Ni layer containing Ni in an
amount of 5 tilg/rnz to 150 mg/m2 in terms of an aniount of metal Ni by performing a
Ni coating or a Fe-Ni alloy coating on at least one surface of a steel sheet; performing
a Sn coating containing Sn in an amount of 300 nig/ni2 to 3,000 nig/m2 in terms of an
atiiount of metal Sn on the underlying Ni layer; fonning an oxide layer containing tin
oxide by oxidizing a surface of a Sn coated layer, while forming the Sn coated layer
including an island-shaped Sn formed by alloying the St1 coating and at least a part of
the underlying Ni layer by performitig a reflow treatment at a teniperature of 200°C or
higher and 300°C or lower for 0.2 seconds to 20 seconds; and forming a chemical
treatment layer on the oxide layer by performing an electrolysis treatment at a current
density of 1.0 A/dtn2 or more atid 100 A/dm2 or less for an electrolysis treatment time
of 0.2 seco~idso r longer and 150 seconds or sho~teirt 1 a clietnical treatmelit solutio~l
iticludi~ig 10 ppni or more and 10,000 ppni or less of Zr ions, 10 ppni or lnore atid
10,000 ppm or less of fluoride ions, 10 ppni or more and 3,000 pptii or less of
phosphate ions, and 100 pprn or Inore atid 30,000 ppm or less of nitrate ions andlor
sulfate ions atid having a temperature of 5°C or higher and lower than 90°C.
[Effects of the Invention]
[OO lo]
Accorditig to the above aspects, it is possible to achieve sulfide stain
resistance atid cost reductionusing a cheniical treatment layer by forming an oxide
layer between tlie chemical treatment layer and tlie S11 coated layer.
[Brief Description of the Drawings]
[OOll]
FIG. 1A is an explanatory view schematically showing a steel sheet for
colitainers accorditig to an embodiment of tlie presetit invention.
FIG 1B is an expla~iatoryv iew sche~ilaticallys howing the steel sheet for
containers according to the present embodiment.
FIG 2A is an explanatory view showing a method for measuritig a tin oxide
content it1 an oxide layer.
FIG 2B is an explatiato~yv iew showing the method for measuring a tin oxide
content in tlie oxide layer.
FIG 3Ais a flow chart explaining at1 example of a flow of a method for
evaluating sulfide stain resistance.
FIG 3B is an explanatory view showing the method for evaluating sulfide
stain resistance.
FIG 4 is a flow chart explaining an example of a flow of a method for
producing a steel sheet for cotitai~iersa ccorditig to the present embodiment.
FIG 5A is a diagram plotting the relationship between the atnoulit of ti11 oxide
and a yellowness index (YI).
FIG. 5B is a diagram plottiiig tlie relationship between the evaluation results
of sulfide stain resistance and a yellowness index (YI).
[Emboditiient of the Invention]
[0012]
I-Iereinafier, a preferred embodiment of the present inventioti will be described
with reference to the attached drawings. In addition, in the specification and
drawings, the same reference numerals will be give11 to components having
substantially the same ht~ctiona nd configuration, atid redundant descriptions will be
omitted by imparting the same reference numerals.
[0013]

First, a configuratio~oi f a steel sheet for containers according to an
embodiment of the present invention will be described in detail with reference to FIGS.
1Aand 1B. FIGS. 1Aatid 1B are explanatory views schematically showing a
configuration of a steel sheet for containers according to the present ernboditnetlt when
viewed from tlie side of the steel sheet.
[0014]
As showti it1 FIGS. 1Aand lB, a steel sheet for containers 10 according to the
present embodiment includes a steel sheet 101, an underlying Ni layer 103, a Sn coated
layer 105, an oxide layer 107, and a chemical treatment layer 109. The underlying Ni
layer 103, tlie St1 coated layer 105, the oxide layer 107 atid tlie chemical treatment
layer 109 may be formed oti only one surface of the steel sheet 101, as shown in FIG
1 A, or may be fornled on two opposite surfaces of the steel sheet 101, as shown in FIG
1B.
[0015]
[Regarding Steel Sheet 1011
The steel sheet 101 is used as a base metal of the steel sheet for containers 10
in the present embodiment. The steel sheet 101 used in the present embodiment is not
particularly limited and ktiowtl steel sheets that are typically used as a tl~ateriafl or
containers can be used. The methods for producing these known steel sheets and
materials are not particularly limited and the steel sheets may be produced through
known processes of hot rolling, pickling, cold rolling, annealing, temper rolling, and
the like from a typical steel piece production process.
[0016]
[Regarding Underlying Ni Layer 1031
The underlying Ni layer 103 is formed on the surface of the steel sheet 101, as
shown in FIGS. lAand 1B. The underlying Ni layer 103 is a Ni-based coated layer
composed of Ni or a Fe-Ni alloy and at least containing Ni in an amount of 5 nlg/m2 to
150 rng/m2 in terms of the amount of metal Ni. The underlyit~gN i layer 103 is
formed by performing Ni coating or Fe-Ni alloy coating on the steel sheet 101.
[00 171
The Ni-based coated layer co~nposedo f Ni or a Fe-Ni alloy is formed to
ensure lacquer adhesion, film adhesion, corrosion resistance, and weldability. Since
Ni is a highly corrosiotl-resistant metal, the corrosion resistance of an alloy layer
i~icludingF e and Sn formed by Ni coating at the time of reflow treatment, which will
be described later, can be improved. The effect of improving the lacquer adhesion,
film adhesion, corrosion resistance, and weldability of the alloy layer by Ni begins to
be exhibited when the amount of metal Ni in the underlying Ni layer 103 is 5 tng/tn2 or
more. As the Ni content increases, the effect of itnproving the corrosion resistance of
the alloy layer increases. Therefore, the anlount of tnetal Ni in the underlying Ni
layer 103 is set to 5 111g/111~ or Inore.
[00 181
In addition, the atnout~to f metal Ni in the underlying Ni layer 103 is set to
150 mglm2 or less. This is because when the amount of metal Ni in the underlying Ni
layer 103 is n~oreth an 150 mg/tn2, not only is the effect of improving lacquer adhesion,
film adhesion, corrosion resistance, and weldability saturated, but it is also
ecot~omicallyd isadvantageous to perform Ni coating in an amount of nlore than 150
mg/m2 due to the fact that Ni,is an expensive metal.
[00 191
The amount of metal Ni in the underlying Ni layer 103 is hrther preferably 5
mg/~nto~ 1 00 mg/m2.
[0020]
Further, when Ni diffusion coating is performed, Ni coating is performed and
then a diffusion treattne~ltis performed in an annealing furnace to form a Ni diffusion
layer. After, before, or coincident with the Ni difhsion treatment, a nitriding
treatment may be performed. Even when the uitridiug treatment is performed, both
the effect of Ni and the effect of a nitriding treatment layer can be exhibited in the
ut~derlyingN i layer 103 in the present embodiment.
[0021]
As a Ni coating or Fe-Ni alloy coating method, for example, known methods
performed in general electrocoating n~ethodsc an be'used.
[0022]
[Regarding Sn Coated Layer 1051
As sliown in FIGS. 1Aat1d IB, the Sn coated layer 105 is formed on the
underlying Ni layer 103 by Sn coating. The Sn coated layer 105 is a coated layer at
least containing Sn in an amount of 300 lng/m2 to 3,000 mg/1n2 in terms ofthe atnount
of metal Sn.
[0023]
"Sn coating" used in the specification refers to not only coating by metal tin
but also coating by metal tin with inevitable impurities or metal tin to which trace
elements are added. A Sn coating method is not patticularly limited and for example,
a known electrocoating method is preferably used. Acoatitg nlethod of dipping a
steel sheet into molten Sn tnay be used.
[0024]
The Sn coated layer 105 by the Sn coating is fortiled to ensure corrosion
resistance and weldability. Since the corrosion resistance of Sn itself is high,
excellent corrosion resistance and weldability can be exhibited in tnetal tin or an alloy
formed by the reflow treatment, which will be described later
[0025]
The excellent corrosion resistance of Sn becomes remarkable when the
amount of metal Sn is 300 tng/m2 or more, and as the Sn content increases, the degree
of corrosion resistance also increases. Accordingly, the amount of metal Sn in the Sn
coated layer 105 is set to 300 tng/n12 or more. In addition, since the corrosion
resistance-improving effect is saturated when the amount of metal Sn is more than
3,000 mg/n2, the amount of Sn is set to 3,000 mng/m2 or less from the ecotiomic
viewpoint.
[0026]
In addition, since Sn having a low electric resistance is soft and spreads by
being pressurized between electrodes at the time of welding, a stable electrification
region can be reliably ensured. Thus, particularly excellent weldability is exhibited.
This excellent weldability is exhibited when the anlount of metal Sn is 100 1ng/mZ or
more. Further, in the above-described range of the amount of metal Sn exhibiting
excellent corrosion resistance, the effect of improving weldability is not saturated.
Fro111 the above reasons, in order to ensure excellent corrosion resistance and
weldability, the amount of metal Sn is set to 300 mg/n12 or more and 3,000 mg/m2 or
less.
[0027]
The amount of metal Sn in the Sn coated layer 105 is further preferably 300
tng/tn2 to 2,000 nlg/n12.
[0028]
After the above-described Sn coating is performed, a molten tin treatment
(reflow treatment) is performed. The reflow treatnlent is perfo~n~etod improve the
corrosion resistance of an alloy layer that is a Sn-Fe or Sn-Fe-Ni alloy layer formed by
melting Sn and forming an alloy with the underlying steel sheet 101 or the underlying
Ni layer 103, and to form a Sn alloy composed of island-shaped Sn (island-shaped tin).
This island-shaped Sn alloy can be fornled by appropriately controlling the reflow
treatment. 111 addition, the surface of the Sn coated layer 105 (the surface opposite to
the interface with the underlying Ni layer 103) is oxidized by the appropriately
controlled reflow treatment, and the oxide layer 107, which will be described later, is
fornled on the Sn coated layer 105.
[0029]
[Regarding Oxide Layer 1071
As shown in FIGS. 1A and lB, the oxide layer 107 cotitaitling ti11 oxide is
formed on the Sn coated layer 105. This oxide layer 107 contains tin oxide in such at1
amoutit that the amount of electricity required for the reduction of the oxide layer 107
is 0.3 nlC (millicro~i)/cmt~o 10 m ~ / c m ~B. y formi~igs uch an oxide layer 107 on the
Sn coated layer 105, the sulfide stain resistance of the steel sheet for containers 10 can
be improved.
[0030]
The sulfide stain occurs by black SnS formed by reaction of metal SII with
sulfur S. Accordingly, in the case oftlie steel sheet for colitainers having tlie Sn
coated layer, sulfur S included in an object to be prese~ved in a corltainer such as foods
reacts with metal Sn in the Sn coated layer to cause sulfide stain. Therefore, by
forrnitig the oxide layer 107 including tin oxide on the Sn coated layer 105, diffusion
of sulfitr atoms S to the interface with the St1 coated layer105 cat1 be inhibited and thus
sulfide stain resistance is improved. As a result, even when the amount of the
chemical treatment layer coated onto the oxide layer 107 is reduced, excellent sulfide
stain resistatice can be achieved.
[0031]
The above-described sulfide stain resistance is remarkably exhibited whet1 the
ti11 oxide content (the amount of tin oxide) included in the oxide layer 107 is equal to
or more than the amount corresponditlg to an amount of 0.3 ~CICIIoIf~ e lectricity
required for the reductioti of the oxide layer 107. Accordingly, the atnourit of tin
oxide contained in the oxide layer 107 is set to be equal to or more than the allloutlt
corresponditig to an amount of 0.3 ni~lcllolf~ e lectricity required for the reduction of
tlie oxide layer 107. 011 the other hand, the oxide layer including tin oxide is a brittle
film and when the atnoutit of fill11 coated is excessively increased, the chemical
treatnlent layer 109 to be fonned on the oxide layer 107 is easily peeled off.
Accordingly, fi-on] the viewpoint of adhesion between the oxide layer 107 and the
cl~emicatlr eattnent layer 109, the amount of tin oxide included in the oxide layer 107
is set to be equal to or less than the amount corresponding to an amount of 10 mc/cn12
of elect~icityr equired for the reduction of the oxide layer 107. The amount of metal
Sn in the oxide layer 107 is further preferably an amount corresponding to an amount
of 5.5 ~ C / C ItIoI 1~0 m~/cmn~.
[0032]
A method for measuring the amount of electricity required for the reduction of
the oxide layer 107 will be described below again.
[0033]
In the related art, sulfide stain resistance of a steel sheet for containers which
had been coated with Sn was achieved by using a film containing Cr Therefore,
there were a lot of uncertainties in techniques of achieving sulfide stain resistance
without using Cr. However, in the present embodiment, by forming the oxide layer
107 including tin oxide in the above-described anlount in terms of metal Sn on the Sn
coated layer 105, sulfide stain resistance can be easily improved without using Cr.
[0034]
The oxide layer 107 can be formed by performing a reflow treatment,for
forming island-shaped Sn in the Sn coated layer 105 at an appropriate temperature for
an appropriate time as described above. The term "island-shaped" refers to a state in
which the surface of the underlying layer is not completely covered by an upper layer
and the underlying layer is partially exposed. That is, the "island-shaped Sn coated
layer" refers to a state in which the surface of the underlying Ni layer including alloy
coating is not completely covered by the Sn coated layer and is paltially exposed.
Tlie reflow treatment in wliicl~th e Sn coated layer 105 and the oxide layer 107 can be
appropriately fortlied is performed in such a way that, after Sn coating, the tetnperature
is raised to 200°C or higher and 30OoC or lower by heating such as electric resistance
heating, inductiotl heating, or the like for 0.2 seconds or longer atld 20 seconds or
shorter, and rapid cooli~lgto about roo111 temperature (for example, about 50°C) is
performed by cold water im~nediatelya fter a metal gloss is obtained.
[0035]
[Regarding Chemical Treatment Layer 1091
As shown in FIGS. 1A and lB, the chemical treatnletit layer 109 is formed on
the oxide layer 107. The chemical treatment layer 109 is a composite film layer
mainly including a zirco~~iuctno tl~pounda t least containing Zr in an amount of 1
tng/tn2 to 500 mg/n12 in ternis of the amount of metal Zr, and phosphoric acid in an
amount of 0.1 mg/n12 to 100 tng/m2 in terms of the amount of P (it1 other words, at
least containitlg a Zr compolient and a phosphoric acid component).
[0036]
When each of the above-described Zr cotnponent and the phosphoric acid
cotnponent individually forms a Zr filn~o r a phospl~orica cid film, a certain degree of
effect related to corrosiotl resistance and adhesion is recogtlized but sufficient practical
perfortnar~cec annot be exhibited. However, when the chenlical treatment layer 109 is
formed as a composite fill11 obtained by compoundir~ga Zr cotilponent with a
pliosphoric acid component as the chemical treatment layer 109 of the present
embodiment, excellent practical performance cat1 be exhibited.
[0037]
The Zr conipouent iticluded in the chemical treatmetit layer 109 in the present
enibodimet~ht as a function of iniprovit~gc orrosion resistance, adhesion and working
adhesion. The Zr coliiponent in the present e~~~hodiri~si ceo~mipt osed of, for example,
plural Zr conipounds such as zirconium hydroxide and zirconiun~f luoride, in addition
to zirconium oxide or zirconium phosphate. Since such a Zr cotllponetlt has excelletit
corrosion resistance and adhesion, as the amount of the Zr component contained in the
chemical treatment layer 109 increases, the corrosion resistance and adhesion of the
steel sheet for containers 10 are improved.
[0038]
Specifically, when the Zr component content as the chen~icatlr eatment layer
109 coated onto the oxide layer 107 is 1 mg/m2 or more in terms of the amount of
metal Zr, corrosion resistance and lacquer adhesion at a level causing no practical
problen~sa re ensured. On the other hand, as the Zr colnponent content increases, the
effect of improving corrosion resistance and coating adhesion increases. However,
when the Zr conlponent content is more than 500 mg/n12 in terrns of the amount of
metal Zr, the thickness of the cl~en~ictarel atment layer 109 is excessively increased
and the adhesion of the chemical treatment filn~it self is deteriorated (niainly caused by
cohesive flacture). Also, electric resistance increases and weldability is deteriorated.
In addition, when the Zr component content is more than 500 n1g/m2 in terms of the
amount of metal Zr, uneven coating of the chemical treatment film is exhibited with an
uneven appearance. Accordingly, the Zr component content (that is, the Zr content)
in the steel sheet for containers 10 of the present etnhodirnent is set to 1 mg/nl2 to 500
mg/m2 in terms of the amount of metal Zr. The Zr component content is preferably 2
tng/td to 50 mg/m2 in terms of the amount of metal Zr.
[0039]
Further, the above-described chemical treatment layer 109 further includes a
phospl~orica cid cornpotlent formed of one or two or more of phosphoric acid
compounds in addition to the above-described Zr component
[0040]
The phosphoric acid component in the present e~nboditnenth as a function of
improving corrosion resistance; adhesion, and working adhesion. The phosphoric
acid colnponetit in the present enibodiment is composed of a con~positec omponent of
one pliosphoric acid cotnpound or two or more phosphoric acid compounds, such as
iron phosphate, nickel phosphate, tin phosphate, and zirconium pliosphate, formed by
reaction with the underlying layers (the steel sheet 101, underlying Ni layer 103, Sn
coated layer 105, and oxide layer 107) or the Zr component. Since such a phosplioric
acid component has excellent corrosion resistance and adhesion, as the atnount of the
phosphoric acid component to be formed increases, the corrosion resistance and
adhesion of the steel sheet for containers 10 are improved.
[0041]
Specifically, when the phosphoric acid component content in the chen~ical
treatment layer 109 is 0.1 mg/m2 or more in ternis of the aamunt of P, corrosion
resistance and lacquer adhesion at a level causing no practical problems are ensured.
On the other hand, as the phosphoric acid component content increases, the effect of
improving corrosion resistance and lacquer adhesion also increases. However, when
the pliosplioric acid component content is more than 100 mg/m2 in term of the amount
of P, the thickt~esso f the chemical treatment layer 109 is excessively increased and the
adhesion of the chemical treatnlent layer itself (mainly caused by cohesive failure) is
deteriorated. Also, electric resistance increases and weldability is deteriorated. In
addition, when the phosphoric acid component content is nlore than 100 mg/m2 in
terms of the amount of P, uneven coating of the chemical treatment layer is exhibited
with an uneven appearance. Accordingly, the phosphoric acid component content in
- 15 -
the steel sheet for containers 10 of the present embodi~nenits set to 0.1 mn/nl2 to 100
1ii~lni1n ~te rnis of the amount of P. TIie phosphoric acid colnponelit content is more
preferably 0.5 nigln? to 30 mgl~i? in terms of the atnount of P.
[0042]
In the steel sheet for containers 10 of tlie presetit embodiment, in order to
form the oxide layer 107 on the lower layer of the above-described chemical treatment
layer 109, for example, even when the amourit of metal Zr is a low film amount of 2
nidm2 01: ltke, excellent sulfide stain resistance can be achieved. As a result, since
the adhesion amount of the chemical treatment layer 109 can be hrther reduced, cost
reduction cat1 be achieved.
[0043]
TIie clien~icatlr eatment layer 109 including the above-described Zr
component and phosphoric acid component is formed by an electrolysis treatment (for
example, cathodic electrolysis treatment). In order to form tlie chetnical treatment
layer by an electrolysis treatment, it is necessary to determitie conlponents in a
chen~icatlr eatment solution according to the type of the chemical treatment layer to be
formed. Specifically, a chemical treatment solution it~cluding1 0 pytn or more and
10,000 ppm or less of Zr ions, 10 ppm or more and 10,000 ppm or less of fluoride ions
(F'), 10 pprn or more and 3,000 ppni or less of phosphate ions, and 100 ppm or more
atid 3,000 pptn or less of nitrate ions andlor sulfate io~isis used. In addition, as
required, a phenolic resit1 or the like may he hrther added to tlie chemical treatment
solution thereof
[0044]
The temperature of the chetuical treatnlent solution is set to 5'C or higher and
lower than 90°C. When the temperature of the chemical treatment solution is lower
than 5"C, the film forming efficie~icyis poor aid is not econoniical. Thus, this case is
not preferable. In addition, when the temperature of the chemical treatment solution
is 90°C or higher, tlie stiucture of the film to be formed is not even, and thus defects,
cracks, microcracks and tlne like are generated. As a result, dense fi1111 formatio~is~
difficult and defects, cracks, microcracks and the like easily serve as origins for
corrosiotn and the like. Tlius, this case is not preferable.
[0045]
Such an electrolysis treatment is performed at a current density of 1.0 A / ~ I I I ~
or more and 100 ~ / d n ?o r less for at1 electrolysis treatment time of 0.2 seco~ndso r
longer atnd 150 seconds or shorter. When the current density is less tlnan 1.0 A / ~ I I I ~ ,
tlie adhesion amoulit of the chemical treatment layer is reduced and a long electrolysis
treatment time is required so that the productivity is deteriorated. Thus, this case is
not preferable. In addition, when the current density is more than 100 A/dm2, the
adhesion amount of the chemical treatment layer is more than a required amount and
becomes saturated. In some cases, the i~isuficientlya dhered film may be washed off
(peeled off) in a washing process by rinsing or the like after electrolysis chemical
treatment. Thus, this case is not economical. Further, when tlie electrolysis
treatment time is shorter than 0.2 seco~ndst,l ne adhesiotn amount of film is reduced and
corrosion resistance, lacquer adhesion and the like are deteriorated. Thus, this case is
not preferable. When the electrolysis treatment time is longer than 150 seconds, the
adliesion amount of film is tnore tlnan a required amount and the adhesion amount
becomes saturated. In some cases, tlne insuficiently adhered film niay be washed off
(peeled oQ iin a washing process by rinsing or tlne like after electrolysis che~nical
treatment. Thus, this case is not econoinical.
[0046]
In addition, the pH is preferable in a range of 3.1 to 3.7, and Illore preferably
around 3.5. Further, nitric acid, amnionia, or tlie like may be added to adjust the pH
as required.
[0047]
Wlieti tlie electrolysis treatment is performed at the above-described
electrolysis current-density for the above-described energizing time, it is possible to
form a film with an appropriate adhesion amount on tlie surface of tlie steel sheet.
[0048]
When the chemical treatment layer of tlie present etnbodimet~ti s formed,
tannic acid may be further added to an acid solution used for the electrolysis treatment.
By adding tannic acid to the acid solution, the tannic acid reacts with iron (Fe) oti the
surface of the steel sheet during the above-described treatment and a film of iron
tannate is formed on the surface of the steel sheet. Sitice this film of iron tamate
improves rust resistance and adhesion, as required, formation of the chemical treatment
layer may be performed in at1 acid solution to which ta~inica cid is added.
[0049]
In addition, as tlie solvetit of the acid solution used for formation of the
chemical treatment layer, for example, distilled water and tlie like can be used.
However, the solve~lto f the acid solution in the present embodiment is not limited
thereto and can be appropriately selected depending on dissolved materials, fortiiatioti
methods, formation cot~ditionso f chemical treatmetit layers, and tlie like. However, it
is preferable to use distilled water in terms of stable industrial productivity, cost, and
tlie etivirot~tnent.
[0050]
I11 the chemical treatmetit solution used for forming the chemical treattiletit
layer of the present iuvention, for exatnple, a Zr complex such as H2ZrF6 can be used
as the supply source of Zr Zr in the above-described Zr cotnplex becomes zP+ due
to a hydrolysis reaction resulting from an increase in pH at the cathodic electrode
interface and is present in the chemical treatment solution. Such Zr ions more rapidly
react with the chen~icatlr eatment solution and fonn a co~npout~sudc h as Zr02 or
Zr3(P04)4. The conlpound is subjected to a dehydration condensation reaction with a
hydroxyl group (-OH) present on the surface of the metal orthe like and thus a Zr film
can be formed. In addition, when a pl~enolicre sin is added to the chemical treatment
solution, the phenolic resin may be subjected to amino alcol~oml odification to be made
soluble to water.
[OOSl]
The above-described steel sheet for containers 10 of the present embodiment
exhibits excellent sulfide stain resistance even when the adhesion amount of the
chemical treatment layer on the oxide layer 107 is reduced. For example, a lacquer is
applied to the surface of the steel sheet for containers 10 and baked to form a lacquer.
Then, the steel sheet for containers 10 in which a lacquer is formed is placed and fixed
onto the opening of a heat-resistant bottle in which a 0.6% by mass L-cysteine solution
which has been boiled for 1 hour is stored as a lid and a heat treattnent is perforn~ed at
llO°C for 30 minutes. hl this case, when the appearance of a contact portion where
the steel sheet is brought into contact with the heat-resistant bottle is observed in the
steel sheet for containers 10 in which the lacquer is formed after the heat treatment, the
steel sheet for containers 10 of the present embodiment exhibits excellent sulfide stain
resistance in which 50% or more of the area of the contact portion does not become
black.
[0052]

The amount of tnetal Ni in the underlying Ni layer 103 or the amount of metal
Sn in the St1 coated layer 105 can be lneasured by, for example, a fluorescent X-ray
atlalysis. In this case, a calibration curve related to the amount of metal Ni is
specified in advance using a sample for the amount ofNi coated in which the amount
of r~letaNl i is already known, and the amount of tnetal Ni is relatively specified using
the same calibration cutve. Sin~ilatro the amount of tnetal Sn, a calibration curve
related to the amount of metal Sn is specified in advance using a sample for the amount
of Sn coated in which the atnount of metal Sn is already known, and the amount of
metal Sn is relatively specified using the same calibration curve.
[0053]
The amount of electricity required for the reduction of the oxide layer 107 cat1
be determined from a potential-time curve obtained by cathodic electrolysis of the steel
sheet for containers 10 of the present embodiment at a constant current of 0.05
mA/cm2 in 0.001 mol/L of a hydrobromic acid solutiot~fi -om which dissolved oxygen
is removed by means of such as bubbling of nitrogen gas. Hereinafter, a method for
measuring the alnount of electricity required for the reduction will be described simply
with reference to FIGS. 2A and 2B.
[0054]
FIGS. 2Aand 2B are explanatory views showing a method for measuring a tin
oxide content (the atnount of tin oxide) in an oxide layer. As shown in FIG 2A, in
the measurement of the amount of tin oxide, first, a bath for electrolysis treatrlletlt in
which a hydrohromic acid aqueous solution (HBr aqueous solution) with the abovedescribed
detlsity fro111 which dissolved oxygen is removed is stored is prepared. In
the bath for electrolysis treatment, an anode and a cathode provided with a
nieasurement sample (that is, tlie steel sheet for containers 10) are arranged. The
material for the anode and the cathode is not particularly liniited and for example, fot
the anode and tlie cathode, platinum electrodes can be used. In addition, tlie test piece
as it is can be used for the cathode.
[0055]
Next, a cathodic electrolysis treatment is performed at a constant current of
0.05 mklcm2 and a potential-time curve is measured. The full-scale length LFS (unit:
mtn) of the obtained nieasuring chart of the potential-time curve (hereinafter, also
simply referred to as a "chart") and the feeding speed TFS (unit: sec) of the full-scale
chart are specified in advance.
[0056]
FIG. 2B schematically shows a measuring chart that can be obtained. In the
obtained chart, as shown in FIG 2B, each of a tangent on the potential axis side and a
tangent on the time axis side is specified and the position ofthe intersection of the
tangents is specified. The length of a perpendicular line drawn from this intersection
to the potential axis is set to a chart length L (unit: mnl), as shown in FIG 2B.
[0057]
When the amount of electricity required for the reduction of the oxide layer
107 (unit: mc/cm2) is refelred to as an amount of tin oxide Q, the amount of tin oxide
Q can be calculated by the following equation 101. In the following equation 101, 1
represents a current density (unit: mA), S represents an area of a sati~ple(u nit: cm2),
and T represents the time required for completely removing the oxide layer 107 (that is,
completely reducing the oxide layer 107) (unit: sec). In addition, the titlie T required
for con~pletelyre moving the oxide layer 107 can be calculated by the followitig
equation 102 using the full-scale length LFS, the feeding speed TFS of the full-scale
chart, and the chart length L obtained from the measuring chatt. Accordingly, the
amount of tin oxide Q can be calculated by using the following equations 101 and 102.
[OOSS]
[Equation I]
1
Q = - x T ... Equation 101
S
FS T = - x L ... Equation 102
L~~
[0059]
Further, the aulount of metal Zr and the amount of P in the chemical treatment
layer 109 can be measured by, for example, a quantitative analysis method such as
fluorescent X-ray analysis or the like.
[0060]
The method for measuring the amount of each of the above-described
components is not limited to the above-described method and other known
nleasure~nenmt ethods can be used.
[0061]

Next, with reference to FIGS. 3A and 3B, a method for evaluating sulfide
stain resistance will be described in detail. FIG 3A is a flow chart explaining an
example of a flow of a method for evaluating sulfide stait~re sistance. FIG 3B is an
explanatory view showing the method for evaluating sulfide stain resistance.
[0062]
In the method for evaluating the sulfide stain resistance of the present
etnbodiment, a gold lacquer (28S93MB, manufactured by Valsper Corporation) is
applied to tlie surface of tlie sariiple and tlie saliiple is baked to form a lacquer (Step
S101). For the sample, the steel sheet for containers in which the underlying Ni layer,
the Sn coated layer, the oxide layer, and the cheniical treatment layer are formed on tlie
surface of the steel sheet by the above-described niethod is used.
[0063]
A 0.6% by niass L-cysteine solution which has been boiled for 1 hour is
poured into a heat-resistant bottle 201 (a 100 tnL heat resistance bottle, 017260-IOOA,
manufactured by SCHOTT AG) and tlie bottle is sealed (Step S102).
[0064]
An O-ring 202, a packing silicone rubber 203, a sample 204 (42 @) prepared
in Step S201, and a packing silicone rubber 205 are placed and fixed onto the opening
of the heat-resistant bottle in this order (Step S103).
[0065]
The heat-resistant bottle is capped with a lid 206 (GL45, manufactured by
SIBATA SCIENTLFIC TECHNOLOGY LTD., inner diameter: 450, outer diameter:
55@) and is put into a soaking furnace such that tlie lid is directed downward (Step
S104).
[0066]
In tlie soaking furnace, the heat-resistant bottle is subjected to a heat treatment
at llO°C for 30 tninutes (Step S105).
[0067]
The heat-resistant bottle is taken out fiom the soaking fitrnace, the degree of
stain at the contact poltion of the sample and the L-cysteine solution is observed with
the naked eye (Step SlO6).
[0068]

When a yellowness index (YI) deterniined according to JIS K-7373 is used to
evaluate sulfide staiti resistance, in the above-described Step S101, a gold lacquer
(28S93ME3, matiufactured by Valsper Corporation) is applied to tlie surface of tlie
sample 204 atid tlie sample is baked to form a lacquer.
[0069]
Steps S102 to 105 are conitnon to the method for evaluatitig sulfide stain
resistatice with the naked eye and the niethod for evaluating sulfide stain resistance by
YI.
[0070]
In tlie method for evaluating sulfide stain resistance by YI, it1 the abovedescribed
Step S106, the yellowness index of the sample after reacting with the Lcysteine
solution is measured using a spectral colorinieter. It is preferable to use a
spectral coloritiieter according to the conditioti c of JIS 2-8722 in the measurement of
tlie yellowness index, and as the measuretnetit method, SCI (including regular
reflection light) tneasurenletit which is hardly affected by surface properties is
performed.
The measurelnent has to be performed under predeter~nined conditions of a
light source, luimidity, temperature and the like as for tlie tneasurelnent conditions.
[0071]
In the above description, the configuration of the steel sheet for containers 10
of the present et~ibodimeriht as been described in detail with reference to FIGS. lAt o
3B.
[0072]

Next, a metliod for producing the steel sheet for containers 10 of the present,
embodiment will be described in detail with reference to FIG 4. FIG 4 is a flow
cliart explaining an example of a flow of a nietliod for producing a steel sheet for
containers according to the present embodiment.
[0073]
In tlie metliod for producing tlie steel slieet for containers 10 of the present
embodiment, first, Ni coating or Fe-Ni alloy coating is perfortiled on the steel sheet
101 to form an underlying Ni layer 103 (Step S201).
[0074]
Next, Sn coating is performed on tlie steel sheet 101 in which the underlying
Ni layer 103 is fornied (Step S203). Then, an oxide layer 107 is fornied by surface
oxidation while forming a Sn coated layer 105 including island-shaped Sn by a molten
tin treatment (reflow treatment) (Step S205).
[0075]
Then, a chemical treatment layer 109 is formed on tlie oxide layer 107 by an
electrolysis treatment (Step S207).
[0076]
The steel sheet for containers 10 of the present embodinlent is produced by
perfor~ningt he treatment by this flow.
[Exan~ples]
[0077]
Hereinafter, the steel sheet for containers and the method for producing a steel
sheet for containers of the present invention will be described in detail while sliowing
Examples and Comparative Exan~ples. Examples shown below are merely examples
of the steel sheet for containers and the tnetliod for producing a steel sheet for
containers of the present i~iventiona nd the steel sheet for containers and the method for
producing a steel sheet for containers of the present invention are not litiiited to
Examples shown below.
[0078]
(Examples)
A steel sheet generally used as a steel sheet for containers was used and Ni
coating and Sn coating were sequentially performed on the steel sheet by a known
method. Subsequently, a reflow treatment was performed under the conditions shown
in Table 1 below and a St1 coated layer and an oxide layer were formed. Then, a
chemical treattilent layer was formed under the conditions shown in Table 1 below.
COO791
The atnoutt of metal Ni in tlie formed underlying Ni layer and the amount of
metal St1 in the Sn coated layer were measured by fluorescent X-ray analysis atid the
results are shown in Table 2 below. In addition, the amount of tin oxide in the oxide
layer was measured by the metliod described with reference to FIGS. 2Aand 2B and
tlie results are shown in Table 2 below. In addition, the amount of eacli component in
the chemical treatment layer was n~easuredb y fluorescent X-ray analysis and tlie
results are shown in Table 2 below.
[OOSO]
In the evaluation of sulfide stain resistance, the sulfide stain resistance of
samples of each level was observed with tlie naked eye and evaluated by tlie method
described with reference to FIGS. 3A and 3B. In the samples of eacli level, the
appearance of the contact portion in which the steel sheet was brought into contact
with the heat-resistant bottle was observed and evaluation points of 1 to 10 were
assigned to the sa~iiplesa ccording to a ratio of a portion with stain occupied with tlie
cotitact portion (area ratio). In this evaluatioli method, when the evaluatioli poilit was
8 or higher (that is, wlieti staiti did not occur in 50% or more ofthe contact portion),
the steel sheet for contaitiers exhibited excelletit sulfide stain resista~ice.
[0081]
10 Points: The area of a portion with staiti was less that1 10%.
9 Points:-The area of a portion with staiti was 10% or Inore and less than 30%.
8 Points: The area of a portion with stain was 30% or tiiore and less than 50%.
7 Points: The area of a portioti with stain was 50% or more and less than 60%.
6 Points: The area of a portion with stain was 60% or Inore atid less that1 65%.
5 Points: Tlie area of a portioli with stain was 65% or tiiore and less than 75%.
4 Points: The area of a portioti with stain was 75% or more and less than 85%.
3 Poitits: The area of a portioti with stain was 85% or more and less than 90%.
2 Points: Tlie area of a portiot~w ith stain was 90% or more and less than 95%.
1 Point: The area of a portion with stain was 95% or more.
[0084]
Next, under the conditions sliown in Table 3 below, samples of each level
were produced. The amount of each coniponetit of the san~plesw as measured in tlie
sanie manner as in tlie case of the above Table 2 and the sulfide stain resistance was
evaluated with the naked eye by tlie same method as in the case of tlie above Table 2.
The obtained results are sliown in Table 4 below.
[0087]
Next, under the conditions shown in Table 5 below, sanlples of each level
were produced. The anlount of each corliponent of the samples was measured in the
same tnantier as in the case of the above Tables 2 and 4 and the sulfide stain resistance
was evaluated with the naked eye by the same method as in the case of the above
Tables 2 and 4. The obtained results are shown in Table 6 below.
[0090]
In each test exanlple shown in Tables 1 and 2, tests were perforn~ed while
mainly focusing on each condition at the time of producing the steel sheets for
containers and in each test exan~plesh own in Tables 3 and 4, tests were performed
while mainly focusing on the properties of the produced steel sheets for containers.
In each test example shown in Tables 5 and 6, tests were performed while changing the
amount of tin oxide by changing a reflow treatment time.
As can be clearly seen from the above Tables 1 to 6, it was found that the steel
sheets of the present invention exhibited sulfide stain resistance through the abovedescribed
evaluation test of sulfide stain resistance.
[0091]
Next, under the conditions shown in Table 7 below, samples of each level
were produced. The coated amount of tin oxide was measured in the sanle nlantier as
in the case of the above Tables 2,4, and 6. The sulfide stain resistance was evaluated
by the evaluation method with the naked eye shown in the above Tables 2,4, and 6 arid
the evaluation method based on YI. The obtained results are sshown in Table 8 and
FIGS. SA and SB.
[0094]
As can be clearly seeti from the above Table 8 and FIGS. 5Aa11d 5B, it was
found that the nu~ilericavl alues of YI correspotided well to sensory evaluation results
with the naked eye and Y1 could be used as an itidex for quantitatively indicating a
surface color cliange due to sulfide stain.
[0095]
While the preferable embodiment of the present itlve~itiothi as beeti described
in detail with reference to tlie drawings, the present invetition is not limited to the
present embodiment. It should be noted by those skilled in the art to which the
present invetitio~bi elongs that various changes and modification examples can be
made in the scope of tlie tecli~iicaild ea described in the appended claims, and these
examples tiaturally belong to the technical range of tlie present invention.
[Industrial Applicability]
[0096]
According to the present inventioti, it is possible to achieve sulfide stain
resistance and cost reduction using a chemical treatment film by forming an oxide
layer between the chemical treatment layer and a Sn coated layel:
[Brief Description of the Reference Symbols]
[0097]
10: STEEL SHEET FOR CONTAINERS
10 1 : STEEL SHEET
103 : UNDERLYING Ni LAYER
105: Sn COATED LAYER
107: OXIDE LAYER
109: CHEMICAL TREATMENT LAYER

CLAIMS
1. Asteel sheet for contaitiers, comprising:
a steel slieet;
an underlying Ni layer formed by performing a Ni coating or a Fe-Ni alloy
coating cotitaining Ni in an amount of 5 mg/n~to~ 1 50 mng/~ni~n terms of an aniount of
metal Ni on at least one surface of the steel slieet;
a Sn coated layer forrned by performing a St1 coating containing Sn in an
amount of 300 mg/mn2 to 3,000 nig/m2 in terms of an amount of metal Sn 011 the
underlying Ni layer and including an island-shaped Sn for~iiedb y alloying the Sn
coating and at least a part of the underlying Ni layer by a reflow treatment;
an oxide layer formed on the Sn coated layer and containing tin oxide; and
a chemical treatment layer for~iiedo n the oxide layer and containing Zr in an
amount of 1 mg/m2 to 500 mg/n? in tertns of an amount of metal Zr and phospliate
acid in an amount of 0.1 mg/m2 to 100 tng/ni2 in terms of an amount of P,
wherein the oxide layer contains tin oxide in such an amount that an amount
of electricity required for reduction of the oxide layer is 0.3 n l ~ f c r nto~ 1 0 mc/cm2.
2. The steel sheet for co~itainersa ccording to Claim 1,
wherein the oxide layer contains tin oxide in such an amount that tlie amount
of electricity required for reduction of the oxide layer is 5.5 111~lcmto~ 10 m~lcn?.
3. The steel slieet for co~itainersa ccording to Claim 1 or 2,
wherein afier a coating is applied to the surface of tlie steel sheet for
containers and the steel sheet is baked to form a lacquel; the steel sheet for cotitairiers
in which the lacquer is fom~edis placed and fixed onto an ope~lit~ogf a heat-resistant
bottle in which a 0.6% by mass L-cysteit~es olution, which is boiled for 1 hour, is
stored, the heat-resistant bottle is capped with a lid, a heat treatment is perfor~neda t
110°C for 30 minutes in a state of the lid beiug upside down, and the11 when an
appearance of a contact portion of the steel sheet for containers in which the lacquer is
formed with the heat-resistant bottle is observed, a stain does not occur in 50% or more
of an area of the contact portion.
4. A method for producing a steel sheet for containers, comprisitlg:
fornling an ut~derlyit~Ngi layer containing Ni in an amount of 5 mg/tn2 to 150
mg/m2 in terms of an amount of metal Ni by performi~~ag N i coating or a Fe-Ni alloy
coating on at least oue surface of a steel sheet;
perfortnit~ga Sn coating containing Sn it1 an amount of 300 mg/m2 to 3,000
mg/m2 in terms of an amount of metal Sn on the underlying Ni layer;
for~nitlga n oxide layer containing tin oxide by oxidizing a surface of a Sn
coated layer, while forming the St1 coated layer including an island-shaped Sn formed
by alloying the SII coating and at least a part of the underlying Ni layer by performing
a reflow treatment at a temperature of 200°C or higher and 300°C or lower for 0.2
secotlds to 20 seconds; and
forming a chemical treatment layer on the oxide layer by performing an
electrolysis treatment at a current density of 1.0 A/dm2 or more and 100 A/dm2 or less
for an electrolysis treatnletlt time of 0.2 seconds or lo~lgera nd 150 seconds or shorter
in a chetnical treatment solution including 10 ppnl or Inore and 10,000 ppn~o r less of
Zr ions, 10 ppm or more and 10,000 ppm or less of fluoride ions, 10 ppm or more and
3,000 pprn or less of phosphate ions, aud 100 ppnl or more and 30,000 ppm or less of
nitrate ions and/or sulfate ions and having a temperature of 5°C or higher and lower
than 90°C.