Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
DEEPLY DRAWN CAN AND METHOD OF PRODUCING
THE SAME
Background of the Invention
Field of the Invention:
The present invention relates to a seamless can
obtained by deeply drawing a steel plate having an
organic coating and to a method of producing the same.
More particularly, the present invention relates to a
deeply drawn corrosion-resistant can made of a laminated
material of a metal substrate having a tin-containing
metal that is coated at a rate that lies within a
predetermined range and an organic coating layer, the
can being suited for containing acidic beverages and
sports beverages, and to a method of producing the same
can.
Prior Art:
Side-seamless can have heretofore been produced by
subjecting a metal material such as an aluminum plate, a
tin plate or a tin-free steel plate to the drawing of at
least one stage between a drawing die and a punch to
form a cup which consists of a drum portion with no seam
on the side surface thereof and a bottom portion
connected integrally to the drum portion without forming
seam, and then,as required, squeezing the drum portion
between a drawing punch and a squeezing die in order to
reduce the thickness of the drum portion of the can. It
has also been known to produce the side-seamless cans by
using a material obtained by laminating a thermoplastic
resin film such as a polypropylene or a thermoplastic
polyester on the metal material.
Japanese Patent Publication Laid-Open No.
258822/1989 filed by the present inventors discloses a
method of reducing the thickness of side walls of cans
by effecting the bend-stretching at the time of the deep
drawing, i.e., discloses a redrawing method wherein a
predrawn cup of a coated metal plate is held by an
annular holding member inserted in the cup and a
redrawing die, a redrawing punch and the redrawing die
are moved relative to each other in mesh with each
other, the redrawing punch and the redrawing die being
provided in concentric with the holding member and the
redrawing die so as to be inserted in or come out from
the holding member, thereby to form a deeply drawn cup
having a diameter smaller than that of the predrawn cup,
and wherein the radium of curvature (RD) of the action
corner of the redrawing die is 1 to 2.9 times as great
as the thickness (tB) of the metal plate, the radius of
curvature (RD) of the holding corner of the holding
member ls 4.1 to 12 times as great as the thickness (tB)
of the metal plate, the plane engaging portions of the
holding member and the redrawing die that engage with
the predrawn cup have a dynamic coefficient of friction
of 0.001 to 0.2, at least one stage of drawing is
effected so that the redrawing ratio defined as a ratio
of the diameter of a shallowly drawn cup to the diameter
of a deeply drawn cup lies over a range of 1.1 to 1.5,
the whole side wall of the cup is uniformly bent in the
direction of the height in order to reduce the
thickness. It has also been proposed to use a tin-free
steel ~TFS: steel plate electrolytically treated with
chromic acid) as a coated metal plate.
A material of cans consisting of TFS as a base
material coated with an organic resin allows a resin
coating layer to be intimately adhered thereto, and does
not develop such a problem that the resin coating
material is peeled off during the deep drawing or while
the thickness is being as a result of drawing, during
: the neck-in treatment, double seaming relative to the
cover, heat-sterilization treatment, or while the
: 35 contents are being preserved. Therefore, the deeply
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drawn can made of such a material exhibit excellent
processing properties.
In mass-producing the cans, however, defects and
damages by the treatment may often develop in the
organic resin coating material at a predetermined
frequency permitting, sometimes, the underlying metal to
be exposed. The coating on the TFS surface has a
limited resistance against corrosion. Therefore, if the
underlying metal is exposed, iron is abnormally eluted
out or holes are formed resulting in the leakage when
there are contained acidic beverages and spots beverages
that cause the steel plate to be vigorously corroded.
In order to cope with the above problem, it can be
contrived to treat the surface of the steel plate with
tin or a tin alloy which exhibits corrosion-preventing
effect that stems from the sacrificial dissolution of
tin in order to impart corrosion-resistant property to
the surface coating of the steel plate.
With the presently available tin-plated steel
plates, however, intimacy or adhesiveness to the organic
resin coating material is exhibited to a degree which is
just enough to withstand a light degree of processing
such as shallow drawing, but is not exhibited to a
degree large enough to withstand the deep drawing and
the subsequent neck-in processing and double lap-
seaming.
Summary of the Invention
The object of the present invention therefore is to
provide a deeply drawn can having excellent corrosion
resistance which is capable of containing acidic
beverages or sports beverages having large corrosion-
promoting property and which can be deeply drawn or can
be subjected to the treatment for reducing the
thickness.
According to the present invention, there is
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provided a deeply drawn can having excellent corrosion
resistance made of a laminated material which comprises:
a metal substrate having a steel plate, a tin-
containing metal applied thereon at a coating rate
defined by the formula,
PSn = 100~1 - (VFe/VFeo)3 --- (1)
wherein VFe represents a photoelectric intensity of
iron at a moment when the photoelectric intensity
of iron (Fe) and the photoelectric intensity of tin
(Sn) have entered into nearly a steady state while
subjecting the surface of the steel plate to be
coated an X-ray photoelectric spectroscopic method
to etch the surface of said steel plate, and VFeo
represents a photoelectric intensity of iron at a
moment when the etching is further carried out and
the photoelectric intensity of tin (Sn) becomes
substantially zero,
of 20 to 80%, metal chromium and a hydrated chromium
oxide which are applied onto the whole surface of the
steel plate coated with the tin-containing metal; and
an organic resin coating applied onto the surface
of said metal substrate.
In the material of cans used in the present
`~ invention, the tin-containing metal layer should be
homogeneously and uniformed distributed on the steel
plate substrate as a plated layer having a sea-island
relationship with an average size in the plane direction
of from 0.1 to 10 ,um and, particularly, 0.2 to 5 ~m.
Further, the tin-containing metal layer should contain
tin in an amount of greater than 20%, and should be in
the form of a tin-plated layer, a tin-iron alloy layer,
or a tin-nickel-plated layer.
According to the present invention, furthermore,
there is provided a redrawing method wherein the
laminated member is drawn into a shallow predrawn cup,
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said predrawn cup is held by an annular holding member
inserted in said cup and by a redrawing die, a redrawing
punch and the redrawing die are moved relative to each
other and in mesh with each other, said redrawing punch
and said redrawing die being provided in concentric with
said holding member and said redrawing die so as to move
into and come out of the holding member, in order to
form a deeply drawn cup having a diameter smaller than
that of said predrawn cup, and the whole side wall of
the cup is uniformly bent in the direction of the height
to decrease the thickness of the side wall of the cup.
According to the method of the present invention,
the radius of curvature (RD) of the action corner of the
redrawing die is 1 to 2.9 times as great as the
thickness (tB) of the metal plate, the radius of
curvature (RD) of the holding corner of the holding
member is 4.1 to 12 times as great as the thickness (tB)
of the metal plate, the plane engaging portions of the
holding member and the redrawing die that engage with
the predrawn cup have a dynamic coefficient of friction
of 0.001 to 0.2, and at least one stage of draw-molding
is effected so that a redrawing ratio defined as a ratio
of the diameter of the shallowly drawn cup to the
diameter of the deeply drawn cup lies over a range of
25 from 1.1 to 1.5.
A distinguished feature of the present invention is
that the tin-containing metal is not applied as a
completely continuous coating onto the steel plate
substrate, but is applied in such a manner that the
surfaces of the tin-containing metal and the steel
surfaces exist being mixed together on the surface of
the steel plate substrate, and that metal chromium and a
surface-treated layer of a chromium oxide are formed on
the above surface that is incompletely coated with the
tin-containing metal. This makes it possible to greatly
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increase the corrosion resistance of the metal substrate
itself as well as to greatly improve the adhesiveness
between the metal substrate and the organic resin
coating material to be capable of withstanding severe
deep drawing and the reduction of thickness by bending
and stretching the side walls.
Usually, the distribution of atoms on the metal
substrate and the chemical composition can be measured
by the X-ray photoelectric spectroscopic method. In the
present invention, satisfactory results are obtained
when the coating rate of the above-mentioned equation
(1) lies from 20 to 80% and, preferably, from 30 to 60%
as measured by the photoelectric spectroscopic method.
Fig. 1 shows the measure results of the metal
substrate used in the present invention by the X-ray
photoelectric spectroscopic method, wherein the abscissa
represents the treatment time of when the steel plate is
sputtered with argon ions. The sputtering for about 20
minutes corresponds to the etching quantity of about 300
angstroms. The ordinate represents the photoelectric
intensities of the elements emitted by the irradiation
with X-rays, i.e., represents the kinds and compositions
of the metals exposed on the surface of the metal
substrate. In the initial stage of etching as shown in
Fig. 1, the electrons that are emitted are mostly those
of chromium and chromium oxide, from which it is
recognized that the outermost surface of the steel plate
has been completely coated with chromium and chromium
oxide. Then, as the etching proceeds, the emission of
electrons from chromium and chromium oxide decreases,
and the emission of electrons from tin and iron
increase. That is, when the coating of the tin-
containing metal is complete and is continuous, no
electron is emitted from iron. However, the fact that
the electrons are emitted from both tin and iron
indicates that the iron-phase and the tin-phase exist
being mixed together in the steel plate which is coated
with the tin-containing metal but which is not coated
with chromium yet. As the sputtering proceeds, the
photoelectric intensity of tin and the photoelectric
intensity of iron become nearly horizontal (steady
state). In this case, it can be regarded that the
intensities are related to a ratio of areas of the two
metals on the reference surface (before being plated) of
the steel plate. In the measurement of the present
invention, the photoelectric intensity of iron at this
moment is denoted by VFe. As the sputtering is further
carried out, tin is removed by etching and the
photoelectric intensity of tin becomes almost zero. At
this moment, the surface of the steel plate consists
almost all of iron. If the photoelectric intensity of
iron at this moment is denoted by VFeo, then the ratio
VFe/VFe represents the ratio of exposed areas of the
steel plate. Therefore, a value obtained by subtracting
the above ratio from 1 represents a coating factor of
tin.
In the steel plate coated with the tin-containing
metal used in the present invention, the steel plate
assumes the sea-like distribution and the tin-containing
metal layer assumes the island-like distribution. In
addition, the tin-containing metal layer exists in a
homogeneous and minute condition. Fig. 3 is a
microphotograph of a tin plate having a coating rate PSn
of a tin-containing metal of 47~ at a magnification of
400 times, wherein black portions are seas of the steel
and white portions are islands of the tin-containing
metal layer. The steel portions help increase the
adhesive force of the organic resin coating layer via a
metal chromium-chromium oxide layer, and the tin-
containing metal layer portions elute out to prevent the
underlying steel from corroding and to prevent the metalfrom eluting out. Therefore, even when the above can
material is subjected to the deep drawing or to the
treatment for reducing the thickness, the organic resin
coating material does not at all peel off. Moreover,
even when the organic resin coating material is partly
damaged by the treatment, the damaged portions are not
corroded by the acidic beverages or sports beverages.
Fig. 4 is a diagram of characteristics showing a
change in the corrosion resistance tdiscoloration
evaluation) when the coating rate PSn of the tin-
containing metal is changed and a change in the adhesive
force of the organic resin and chromium coating. It
will be understood from Fig. 4 that the corrosion
resistance suddenly increases as the coating rate PSn
exceeds 20% and that the corrosion resistance decreases
as the coating rate PSn exceeds 80~ to make it difficult
to perform the deep drawing. When the coating rate PSn
is 100%, the adhesive force so decreases that the deep
drawing can no longer be carried out even though the tin
and metal chromium coatings are perfect (point P in Fig.
4).
Brief Description of the Drawings
Fig. 1 is a graph showing the measured results of a
surface-treated can material used in the present
invention as measured by the X-ray photoelectric
spectroscopic method;
Fig. 2 is a schematic diagram of the can material
in cross section;
Fig. 3 is a microphotoghraph showing a particulate
structure on the surface of the steel plate coated with
the tin-containing metal that is used in the present
~; invention;
Fig. 4 is a diagram showing correlations among the
coating rate of tin on the can material, adhesive force
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of the organic coating material, and the corrosion
resistance; and
Fig. 5 is a diagram of steps for drawing the can
material.
Description of a Preferred Embodiment
A preferred embodiment of a deeply drawn can
according to the present invention will now be described
in conjunction with the accompanying drawings.
Fig. 2(A) is a schematic sectional view of the can
material used in the present invention, wherein a
surface-treatment layer 4 of a tin-containing metal is
formed on the surface of a steel plate 2, and a surface-
treatment layer 6 of metal chromium and a hydrated
chromium oxide is further formed thereon. The layer 6
of metal chromium and hydrated chromium oxide is formed
to completely cover the surface of the steel plate 2 and
the surface of the tin-containing metal layer 4, and an
organic resin layer 8 is further formed on the surface
of the layer 6 of metal chromium and hydrated chromium
oxide. The layer of chromium and hydrated chromium
oxide and the organic resin layer 8 are drawn in Fig.
2(A) exaggerating the thickness. In the present
invention, furthermore, the surface treatment layer 4 of
the tin-containing metal is applied onto the surface of
the steel plate 2 at a coating rate PSn over a range of
-~ from 20 to 80% as shown in Fig. 3.
Fig. 2(B) schematically illustrates the state in
which the photoelectric intensities of tin and iron
remain constant as measured by the X-ray photoelectric
spectroscopic method mentioned earlier and wherein
islands 9 of the tin-containing metal are floating on
the sea of steel.
The steel plate substrate should generally be a
rolled steel plate such as the one that has heretofore
been used for producing cans. The steel plate should
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have a thickness of, usually, from 0.05 to 0.35 mm, and
particularly from 0.07 to 0.30 mm though it varies
depending upon the size of the final cans.
It is desired that the tin-containing metal is
applied to the steel plate in an amount of 100 to 5000
mg/m and, particularly, in an amount of lO0 to 4000
mg/m 2. When the coating amount becomes smaller than
the above range, the tin-containing metal layer 4 shown
in Fig. 2(A) is not sufficiently formed, and the coating
rate PSn may often become smaller than 20%. When the
coating amount exceeds the above range, on the other
hand, the coating rate PSn becomes too great and the
adhesive force decreases.
The tin-containing metal may be an alloy with iron,
nickel or any other metal, but its content should at
least be greater than 20~. When the content of tin is
smaller than the above-mentioned range, the corrosion
resistance of the deeply drawn can is not sufficiently
enhanced.
In order to form the tin-containing metal layer
maintaining the sea-island relationship according to the
present invention, the plated layer is precipitated in a
granular form, and the plated steel plate is not
subjected to the reflow processing but is washed with,
for example, hydrochloric acid or a like acid of 1 to
7 N, so that the coating rate PSn lies within a range
specified by the present invention.
In general, the coating rate PSn decreases with an
increase in the degree of washing with acid. Therefore,
the hydrochloric acid concentration, temperature of
processing and the processing time should be suitably
set on this basis.
Coating layer of metal chromium and hydrated chromium
` oxide.
The coating layer of chromium and a hydrated
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chromium oxide should be so provided as to sufficiently
cover the surface of the steel plate and the surface of
the tln-containing coating layer. A preferred example
of the surface treatment is the electrolytic treatment
with chromic acid to provide a metal chromium layer in
an amount of 10 to 200 mg/m 2 and a chromium oxide layer
in an amount of 1 to 50 mg/m 2 (reckoned as metal
chromium). This layer is excellent in both organic film
adhesion and corrosion resistance.
Organic resin coating layer.
Examples of the organic resin coating include a
variety of thermoplastic resin films and thermosetting
or thermoplastlc resin films. Furthermore, preferred
examples of the crystalline thermoplastic resin film
include olefin-type resin films such as of polyethylene,
polypropylene, ethylene-propylene copolymer, ethylene-
vinyl acetate copolymer, ethylene-acrylic ester
copolymer and ionomer; polyester films such as of
polyethylene terephthalate, polybutylene terephthalate,
ethylene terephthalate/isophthalate copolymer, ethylene
terephthalate/adipate copolymer, ethylene
terephthalate/sebacate copolymer, and butylene
terephthalate/isophthalate copolymer; polyamide films
such as nylon 6, nylon 6,6, nylon 11 and nylon 12;
polyvinyl chloride films; and polyvinylidene chloride
films. These films may be unstretched or may be
biaxially stretched. Their thicknesses should generally
be from 3 to 50,um and, particularly, from 5 to 40,um.
The film is laminated on the metal plate by the
heat-melting method, the dry lamination or the extrusion
coating method. When the adhesiveness (melt-adhering
property) is poor, there can be interposed, for example,
an urethane-type adhesive, an epoxy-type adhesive, an
adhesive of the type of an acid-modified olefin resin, a
copolyamide-type adhesive, a copolyester-type adhesive
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or an adhesive primer that is described below between
the film and the metal plate. As the adhesive primer,
there can be used a coating material that exhibits
excellent adhesiveness to the metal plate, excellent
anti-corroding property, and excellent adhesiveness to
the resin film. As the adhesive primer, there can be
used an epoxy resin and a curing resin for the epoxy
resin, such as a coating material consisting of a
combination of a phenol resin, an amino resin, an
acrylic resin and a vinyl resin, and particularly an
epoxy-phenol coating material, or an organosol-type
coating material composed of a vinyl chloride copolymer
resin and an epoxy resin-type coating material. The
adhesive primer or the adhesive agent should have a
thickness of from 0.1 to 5 ~m.
To effect the lamination, the adhesive primer or
the adhesive agent is applied to either one or both of
the metal and the film followed, as required, by drying
or partial curing. Then, the two are pressed and
adhered together into a unitary form under the
application of heat. During the step of lamination, the
biaxial molecular orientation in the film may slightly
be loosened which, however, does not at all affect the
- drawing or the redrawing and may often turn out to be
desirable from the standpoint of drawing operation.
Other compositions.
An inorganic filler (pigment) can be contained in
the film for outer surface for the purpose of concealing
;~ the metal plate and assisting the transmission of
wrinkle-suppressing force to the metal plate at the time
of drawing and redrawing. Examples of the inorganic
filler include inorganic white pigments such as rutile-
type or anatase-type titanium dioxide, zinc flower,
gloss white and the like; white body pigments such as
barite, sedimenting barite sulfate, calcium carbonate,
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gypsum, sedimenting silica, aerosil, talc, sintered or
unsintered cray, barium carbonate, alumina white,
synthetic or natural mica, synthetic calcium silicate,
and magnesium carbonate; black pigments such as carbon
black, magnetite, and the like; red pigments such as red
iron oxide, yellow pigments such as sienna, and the
like; and blue pigments such as ultramarine, cobalt
blue, and the like. These inorganic fillers can be
blended in an amount of 10 to 500~ by weight and,
particularly, in an amount of 10 to 300~ by weight with
respect to the resin.
A protective coating material that can be used
instead of, or together with, the film may be any
protective coating material comprising thermosetting and
thermoplastic resins. Examples include modified epoxy
coating materials such as phenol-epoxy coating material,
amino-epoxy coating material; vinyl or modified vinyl
coating materials such as vinyl chloride-vinyl acetate
copolymer, partially saponified product of vinyl
chloride-vinyl acetate copolymer, vinyl chloride-vinyl
acetate-maleic anhydride copolymer, epoxy-modified,
epoxyamino-modified, or epoxyphenol-modified vinyl
coating material; acrylic resin-type coating material;
and synthetic rubber-type coating material such as
styrene-butadiene-type copolymer, and the like, which
can be used alone or in a combination of two or more
kinds.
These coating materials are applied to the metal
material in the form of an organic solvent solution such
as enamel, lacquer or the like, in the form of an
aqueous dispersion or aqueous solution, or by the roller
coating, spray coating, immersion coating, electrostatic
coating, or electrophoretic coating. The above resin
coating material is baked, as required as a matter of
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~ 35 course, when it has a thermosetting property. From the
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standpoint of corrosion resistance and processability,
it is desired that the protective coating material has a
thickness (dry state) which is usually from 2 to 30 ~m
and, particularly, from 3 to 20 ,um. In order to improve
S the drawing-redrawing property, furthermore, a variety
of lubricating agents may be contained in the coated
film.
Drawing.
In the steps of drawiny and redrawing as shown in
Fig. 5, a coated metal plate 10 is punched into a disc,
a predrawn cup 13 having a bottom portion 11 and a side
wall 12 is formed in a predrawing step using a
predrawing punch of a large diameter and a die, the
predrawn cup 13 is held by an annular ho~ding member
which is inserted in the cup and a redrawing die (not
shown), a deeply drawn cup 16 having a diameter smaller
than that of the predrawn cup is formed by moving a
redrawing punch and the redrawing die in mesh with each
other and relative to each other, the redrawing punch
and the redrawing dies being provided in concentric with
the holding member and the redrawing die so as to go
into and come out from the holding member, and a cup 19
having a smaller diameter is formed by similarly
effecting the drawing.
Reference numerals 14 and 17 denote bottom portions
of the cups 16 and 19, and reference numerals 15 and 18
denote side walls of the cups 16 and 19. In carrying
out the redrawing, it is desired to bend and stretch the
coated metal plate by the action corner of the redrawing
die in order to reduce the thickness, or to slightly
squeeze the coated metal plate between the redrawing
punch and the redrawing die during the redrawing step in
order to reduce the thickness.
In Fig. 5, the side walls of the cups usually have
a relationship,
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tw'''~ tw''~ tw'~ tB
It is desired that the drawing ratio defined by an
equation,
Drawing ratio = (diameter of material plate)/
(diameter of punch) --- (2)
usually lies within a range of from 1.2 to 2.0 and,
particularly, from 1.3 to 1.9. It is further desired
that the redrawing ratio defined by an equation,
Redrawing ratio = (diameter of drawing punch)/
(diameter of redrawing punch) (3)
usually lies within a range of from 1.1 to 1.6 and,
particularly, from 1.15 to 1.5.
Furthermore, the degree of reduction of thickness
of the side wall should usually be about 5 to 45% and,
particularly, about 5 to 40% of the thickness of the
material plate (thickness of the bottom portion). It is
desired that the drawing and redrawing are carried out
under the conditions where molecular orientation takes
place in the resin layer. For this purpose, the drawing
and redrawing should be carried out at a stretching
temperature of the resin layer, such as at a temperature
of 20 to 200C in the case of the PET.
In carrying out the drawing and redrawing, it is
desired that the coated metal plate or the cup is
; 25 further coated with various lubricants such as liquid
paraffin, synthetic paraffin, edible oil, hydrogenated
edible oil, palm oil, various natural waxes or
polyethylene wax. The lubricant should be applied in an
amount of usually from 0.1 to 10 mg/dm 2 and,
particularly, in an amount of 0.2 to 5 mgtdm 2 though it
may vary depending on the kind thereof. The lubricant
is applied to the surface in a molten state by spray
coating. The deeply drawn can that is obtained is them
subjected to the after-treatment such as washing with
water and drying, and is further subjected to the
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doming, trimming, neck-in treatment, bead treatment and
flange treatment, in order to obtain a final barrel of
can. Even in the above treatment steps, the organic
resin coating material excellently follows the steel
plate.
Examples and Comparative Examples
Example 1:
A cold-rolled steel plate having a thickness of
0.15 mm and a tempering degree of DR-9 was was~ed with
an acid and on which tin was plated using an ordinary
stannous phenol sulphonate bath at a current density of
O.S A/m 2 followed by washing with hydrochloric acid in
order to obtain a tin-plated steel plate having a tin
amount of 1.2 g/m 2 and a tin coating rate of 50~.
The tin-plated steel plate was then subjected to
the ordinary electrolytic treatment with chromic acid to
plate metal chromium in an amount of 120 mg/m and to
plate a hydrated chromium oxide in an amount of 15
mg/m 2 in a laminated form. The tin coating rate was
calculated from the formula (1) by effecting the
analysis based on the XPS (X-ray photoelectric
spectroscopic) method.
A biaxially stretched polyethylene terephthalate
film (melting point, 230C) having a thickness of 20~um
to which has been applied an epoxyphenol-type adhesive
primer was thermally adhered to a surface of the thus
obtained steel plate that would become the inner surface
of the can and, at the same time, a titanium dioxide-
containing biaxially stretched polyethylene
terephthalate/isophthalate film (melting point, 230C)
; having a thickness of 15 ~um to which has been applied a
` similar adhesive primer was thermally adhered to the
surface of the steel plate that would become the outer
surface of the can, in order to obtain a metal plate
` 35 coated with resin. The palm oil was applied to the thus
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coated metal plate which was then punched into a disk
having a diameter of 187 mm to form a shallowly drawn
cup in accordance with the customary method. In the
above drawing step, the drawing ratio was 1.4.
In the subsequent first, second and third redrawing
steps, the cup was preheated at 80C, and the redrawing
was carried out. In the first to third redrawing steps,
the redrawing conditions were as follows:
First redrawing ratio 1.25
Second redrawing ratio 1.25
Third redrawing ratio 1.25
Radius of curvature (Rd) of action
corner of the redrawing die 0.40 mm
In order to reduce the thickness of the drum of
can, the redrawing was effected by bending. The drawing
and redrawing thus effected developed no problem in the
processability, and the deeply drawn cup exhibited the
following properties.
Diameter of the cup66 mm
Height of the cup140 mm
Rate of change in the
thickness of side wall -20%
Thereafter, the doming was effected according to a
customary method, the palm oil was removed by washing
with water and, then, the trimming was effected. Next,
in the step of printing, printing was effected to the
outer surface using an ordinary ink and a finishing
varnish, followed by baking and neck-in/flange
treatment, in order to obtain a deeply drawn coated can
having a reduced thickneæ~.
In this case, the rate of metal tin in the tin
layer was 70% as measured by an electrochemical method
(supplement to JIS-G3303) by using the bottom portion of
the deeply drawn coated can as a sample and after the
organic resin coating material was removed by being
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immersed in an aqueous solution of peroxide at 90C.
The thus obtained deeply drawn coated can could be
treated without permitting the coating material to be
peeled off during the step of treatment. Thereafter, an
orange juice was contained therein being heated at 95C
while permitting liquid nitrogen to drop thereon, and
the cover was seamed. The orange juice was preserved
fro extended periods of time at 37C to observe the
corroding condition on the inner surface of the can pit
corrosion and the leakage through the pore. No abnormal
condition, however, was recognized. The results were as
shown in Table 1.
Example 2:
A deeply drawn can was obtained by effecting the
coating and treatment in the same manner as in Example 1
but plating tin in an amount of 3.2 g/m 2 and changing
the tin coating rate into 76%. The results were as
shown in Table 1.
Example 3:
A deeply drawn can was obtained by effecting the
coating and treatment in the same manner as in Example 1
but plating tin in an amount of 520 mg/m 2 and changing
the tin coating rate into 26%. The results were as
shown in Table 1.
Example 4:
A deeply drawn can was obtained by effecting the
coating and treatment in the same manner as in Example 1
except that an alloy layer was formed on the interface
between the tin layer and the steel and the ratio of
metal tin in the tin layer was 45% since the biaxially
stretched polyethylene terephthalate/isophthalate film
was heat-adhered onto the plated steel plate at a
~ temperature that was as high as nearly the melting point
;' of the film. The results were as shown in Table 1.
Example 5:
'
- 19 -
A deeply drawn can was obtained by effecting the
coating and treatment in the same manner as in Example l
except that an epoxyphenol resin coating material was so
applied and baked on the surface of the plated steel
plate that would become the inner surface of the can
that the thickness of the coated film after drying was
15,um and the epoxyphenol resin coating material was so
applied and baked on the surface that would become the
outer surface of the can that the thickness of the
coated film after drying was 15 ~m, the ratio of metal
tin in the tin layer being 55%. The results were as
shown in Table l.
Comparative Example 1:
The coating and treatment were carried out in the
same manner as in Example 1 except that the cold-rolled
steel plate having a thickness of 0.15 mm and a
tempering degree of DR-9 was washed with an acid and on
which tin was plated using an ordinary stannous phenol
sulphonate bath at a current density of 1.5 A/m 2 to
obtain a tin-plated steel plate having a tin amount of
3.7 g/m 2 and a tin coating rate of 100%, and then the
tin-plated steel plate was subjected to the ordinary
electrolytic treatment with chromic acid to plate metal
chromium in an amount of 120 mg/m 2 and to plate a
hydrated chromium oxide in an amount of 15 mg/m 2 in a
laminated form. After the redrawing of the third time,
however, the resin coating layer was partly peeled off
on the drum portion of the cup, and the subsequent
treatment could not be carried out.
Comparative Example 2:
A deeply drawn can was obtained by effecting the
coating and treatment in the same manner as in Example 1
with the exception of using a so-called steel plate
without tin that was obtained by washing the cold-rolled
steel plate having a thickness of 0.15 mm and a
`:
- 20 -
tempering degree of DR-9 with an acid and subjecting the
steel plate to an ordinary electrolytic treatment with
chromic acid to plate metal chromium in an amount of 120
mg/m 2 and a hydrated chromium oxide in an amount of lS
mg/m 2 in a laminated form. The results were as shown
in Table 1.
Comparative Example 3:
A deeply drawn can was obtained by effecting the
coating and treatment in the same manner as in Example 1
except that tin was plated in an amount of 400 mg/m and
tin coating rate was 15%. The results were as shown in
Table 1.
Comparative Example 4:
A deeply drawn coated can was obtained by effecting
the coating and treatment in the same manner as in
Example 1 except that in was plated in an amount of 3.8
g/m 2 and a tin coating rate was 85%. At the time of
deep drawing, neck-in treatment and seaming, however, it
was observed that the resin coating had been partly
peeled off. The results obtained were as shown in Table
1.
;
~'
` 35
:.
~ 8 N N N N N o o N
~3 o c o o o x x
'~ o o o o o
~, a~
.~, . O O O O O G G ~ ~^
.
O G O O O ~ O
.~
~ O O O O G X G G <I
,,1 ~
C
~,,) b ~13 0 t~0 P. 0 0 0
E O 6 o~ o X ~ 0 ~o E0 ,o 0 ~
~, co 0 c~ 0cq 0 a~ ~ ~ 0 ~q 0 ~q 0
~o~ o cO a~ O o o u~ o
1~ ~ t ~ ~ co
~6
O ~D ~ O O O O 1-~
~_ L~ D co O ~I CO
, ~
o ~0 ~ 0 a~ 0 ~ 0 o
0 ~ a~ ~ 0 ~ 0
~` ¦ E0 0 E0 E0E~ e 60 E E0 e E0 6 E0
~ ~ ~3 ~
.
- 22 -
According to the present invention, a tin-
containing metal is applied onto the surface of the
steel plate at a coating rate or 20 to 80%, and then
metal chromium and a hydrated chromium oxide are applied
thereon, in order to form an organic resin coating layer
on the steel plate which is then deeply drawn to obtain
a can. Therefore, the organic resin coating layer of
the deeply drawn can remains sufficiently adhered to the
surface of the steel plate despite the presence of the
tin-containing metal layer, and is not peeled off at all
even after the aforementioned deep drawing, doming,
trimming, neck-in treatment, beading and flange
treatment. Moreover, since the tin-containing metal
exists in an amount larger than a required amount, there
takes place sacrificial dissolution of tin lending the
cans well suited for storing even acidic beverages that
have highly corrosive properties.
.~
:
:,
'
~ 35
':~
