U.S. patent application number 10/545395 was filed with the patent office on 2006-10-19 for metal band having metallic appearance excellent in forming stability and seamlessly formed can body and method for production thereof.
Invention is credited to Toru Chichiki, Takaharu Kataoka, Osamu Miyamae, Hiroshi Nishida, Masayoshi Suehiro, Hirokazu Yokoya.
Application Number | 20060230800 10/545395 |
Document ID | / |
Family ID | 32866299 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060230800 |
Kind Code |
A1 |
Chichiki; Toru ; et
al. |
October 19, 2006 |
Metal band having metallic appearance excellent in forming
stability and seamlessly formed can body and method for production
thereof
Abstract
A metal band having metallic appearance and being excellent in
forming stability is provided. The metal band includes a coating
film containing not less than 20 mass % in the coated and dried
state, of filler of aluminum or aluminum alloys on the side thereof
corresponding to the outside of a can. The metal band also has a
resin-rich portion containing not more than approximately 5 mass %
of the filler, approximately 0.1 to 20 .mu.m in thickness in the
coated surface far from the metal strip surface, seamlessly-formed
can bodies made of such strips. Methods for manufacturing such
strips and can bodies are also provided.
Inventors: |
Chichiki; Toru;
(Kitakyushu-shi, JP) ; Suehiro; Masayoshi;
(Futtsu-shi, JP) ; Nishida; Hiroshi; (Fukuoka,
JP) ; Miyamae; Osamu; (Fukuoka, JP) ; Yokoya;
Hirokazu; (Fukuoka, JP) ; Kataoka; Takaharu;
(Fukuoka, JP) |
Correspondence
Address: |
DORSEY & WHITNEY LLP;INTELLECTUAL PROPERTY DEPARTMENT
250 PARK AVENUE
NEW YORK
NY
10177
US
|
Family ID: |
32866299 |
Appl. No.: |
10/545395 |
Filed: |
July 7, 2003 |
PCT Filed: |
July 7, 2003 |
PCT NO: |
PCT/JP03/08615 |
371 Date: |
March 27, 2006 |
Current U.S.
Class: |
72/46 |
Current CPC
Class: |
B05D 2252/10 20130101;
B05D 5/067 20130101; B05D 2490/50 20130101; B05D 2252/02 20130101;
B05D 2202/25 20130101 |
Class at
Publication: |
072/046 |
International
Class: |
B21D 51/26 20060101
B21D051/26 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2003 |
JP |
2003-35588 |
Claims
1. A metal strip with metallic-appearance excellent in forming
stability, having a single coated film layer on the side thereof
corresponding to an external side of a can, the metal strip
comprising: a filler-rich portion containing not less than
approximately 20 mass %, in the coated and dried state, of a filler
of at least one of aluminum or aluminum alloys; and a resin-rich
portion containing not more than approximately 5 mass % of said
filler and approximately 0.1 to 20 .mu.m in thickness provided upon
the filler-rich portion, wherein the filler-rich portion is
dilutely distributed in the direction of thickness of the coated
film layer.
2. A metal strip with metallic-appearance excellent in forming
stability, having a single coated film layer on the side thereof
corresponding to an external side of a can, the metal strip
comprising: a filler-rich portion containing not less than
approximately 20 mass %, in the coated and dried state, of a filler
of at least one of aluminum or aluminum alloys; and a resin-rich
portion containing not more than approximately 5 mass % of said
filler and approximately 0.3 to 10 .mu.m in thickness provided upon
the filler-rich portion, wherein the filler-rich portion is
dilutely distributed in the direction of thickness of the coated
film layer.
3. A metal strip of claim 1, further comprising a resin film not
less than approximately 8 .mu.m thick which is laminated on the
side thereof corresponding to an internal side of said can.
4. A metal strip of claim 1, further comprising at least one of a
polyester or polyolefin resin film which is laminated on the side
thereof corresponding to an the internal side of said can.
5. A metal strip with of claim 1, wherein the coated film layer on
the external side of said can contains one or more of polyester,
epoxyphenol and vinyl organosol.
6. A method for manufacturing at least one metal strip with a
metallic-appearance excellent in forming stability, comprising:
setting a the ratio a/(a+b) at 20% to 45%, where a sum of weights
of a filler of at least one of aluminum or aluminum alloys and
resin in a paint, and (a+b) is a sum of a and b of organic solvent
for dissolving the paint, and at least one of roll-coating or
photogravure-coating at a linear pressure of at least approximately
3 kg/cm between the metal strip and rolls by using coating-rolls
having a diameter of at most approximately 500 mm.PHI..
7. A method of claim 6, wherein a statistic viscosity of the paint
applied by roll-coating is approximately 20 to 350 centipoise at
20.degree. C.
8. A seamlessly-formed can body, comprising: a filler-rich portion
containing not less than 5 mass %, in the coated and dried state,
of a filler of at least one of aluminum or aluminum alloys on a
side thereof corresponding to an outside of a can, and a resin-rich
portion containing at most approximately 5 mass % of said filler,
and approximately 0.03 .mu.m in thickness Provided upon the
filler-rich portion, wherein the filler-rich portion is dilutely
distributed in the direction of a coated layer thickness.
9. A seamlessly-formed can body, comprising: a filler-rich portion
containing not less than 20 mass %, in the coated and dried state,
of a filler of at least one of aluminum or aluminum alloys on a
side thereof corresponding to an outside of a can, and a resin-rich
portion containing at most approximately 5 mass % of said filler,
and approximately 0.03 .mu.m in thickness provided upon the
filler-rich portion, wherein the filler-rich portion is dilutely
distributed in the direction of a coated layer thickness.
10. A seamlessly-formed can body of claim 8, wherein the body has a
laminated resin film.
11. A seamlessly-formed can body of claim 8, wherein the body has a
resin film of one or more of polyester, epoxyphenol and vinyl
organosol.
12. A method for manufacturing a seamlessly-formed can body, by
comprising: applying multistage ironing to a metal strip with a
thickness reduction ratio .gamma. by using two or more dies such
that a Total thickness reduction ratio .gamma.<58+11d0.35
(wherein d is a thickness (.mu.m) of the resin-rich portion
containing at most approximately 5 mass % of filler in a coated
surface at distance from a coated side), wherein the metal strip
has a single coated film layer on the side thereof corresponding to
an external side of a can, the metal strip comprising: a
filler-rich portion containing not less than approximately 20 mass
%m, in the coated and dried state, of a filler of at least one of
aluminum or aluminum alloys, and a resin-rich portion containing
not more than approximately 5 mass % of said filler and
approximately 0.1 to 20 .mu.m in thickness provided upon the
filler-rich portion, and wherein the filler-rich portion is
dilutely distributed in the direction of thickness of the coated
film layer.
13. A method of claim 12, wherein the ironing is performed by using
a die whose intersection point between the entry and exit half
angles has a radius of curvature not less than 0.02 mm.PHI., and an
entry half angle is set at 2.degree. to 10.degree..
14. A method of claim 12, wherein the ironing is performed by using
a die whose intersection point between the entry and exit half
angles has a radius of curvature not less than 0.1 mm.PHI., and an
entry half angle set at 2.degree. to 18.degree..
15. A metal strip of claim 2, further comprising a resin film not
less than approximately 8 .mu.m thick which is laminated on the
side thereof corresponding to an internal side of said can.
16. A metal strip of claim 2, further comprising at least one of a
polyester or polyolefin resin film which is laminated on the side
thereof corresponding to an internal side of said can.
17. A metal strip of claim 2, wherein the coated film layer on the
external side of said can contains one or more of polyester,
epoxyphenol and vinyl organosol.
18. A seamlessly-formed can body of claim 9, wherein the body has a
laminated resin film.
19. A seamlessly-formed can body of claim 9, wherein the body has a
resin film of one or more of polyester, epoxyphenol and vinyl
organosol.
20. A method for manufacturing a seamlessly-formed can body,
comprising: applying multistage ironing to a metal strip with a
thickness reduction ratio .gamma. by using two or more dies such
that a Total thickness reduction ratio .gamma.<58+11d0.35
(wherein d is a thickness (.mu.m) of the resin-rich portion
containing at most approximately 5 mass % of filler in the a coated
surface at distance from a coated side), wherein the metal strip
has a single coated film layer on the side thereof corresponding to
an external side of a can, the metal strip comprising: a
filler-rich portion containing not less than approximately 20 mass
%, in the coated and dried state, of a filler of at least one of
aluminum or aluminum alloys, and a resin-rich portion containing
not more than approximately 5 mass % of said filler and
approximately 0.3 to 10 .mu.m in thickness provided upon the
filler-rich portion, and wherein the filler-rich portion is
dilutely distributed in the direction of thickness of the coated
film layer.
21. A method of claim 12, wherein the ironing is performed by using
a die whose intersection point between the entry and exit half
angles has a radius of curvature not less than 0.02 mm.PHI., and an
entry half angle is set at 2.degree. to 10.degree..
22. A method of claim 12, wherein the ironing is performed by using
a die whose intersection point between the entry and exit half
angles has a radius of curvature not less than 0.1 mm.PHI., and an
entry half angle set at 2.degree. to 18.degree..
Description
TECHNICAL FIELD
[0001] The present invention relates to metal strips permitting
stable ironing, cans bodies made of such metal strips, and method
for manufacturing such metal strips and cans.
BACKGROUND ART
[0002] Drawn and ironed cans have conventionally been used widely
for beverage containers because of the ease of low-cost mass
production. Drawn and ironed cans are generally manufactured, in
order to insure good ironing, by ironing tinplates and aluminum
sheets while applying lubricants on the surface thereof.
[0003] In order to prevent rusting on the external surface and
secure corrosion resistance on the internal surface, however, this
method must apply a coating on the surfaces. Therefore, it has
involved a problem that each can must pass a low-productivity step
to remove the lubricant with alkali or other detergent after
ironing and, then, apply a coating after the chemical
treatment.
[0004] As a technique to improve productivity by eliminating the
low-productivity step required for each can, it has been proposed
to pre-apply a resin film lamination or resin-coating on both
surfaces of metal strips.
[0005] When metal strips are laminated with resin film, it is
necessary to secure a film strength which will withstand ironing
and permit mass production. This necessitates the use of at least
10 .mu.m or thicker films, which, in turn, which unavoidably
results in a cost increase.
[0006] When coating resin paint on metal strips, it is relatively
easy to reduce the thickness of coated film. Not having as high a
degree of polymerization as a film resin, however, coated film has
low resistance to ironing and, therefore, does not provide adequate
forming stability at high speed.
[0007] Methods to apply a paint containing aluminum filler on one
side of steel sheet and a paint containing lubricant on the other
have been proposed as a technique to improve ironing formability.
For example, Japanese Unexamined Patent Publication No. 02-303633
discloses a technique of forming a coated film containing aluminum
filler on the inside of cans.
[0008] On the outside of cans, however, the force to change a form
associated with a thickness reduction during ironing is much
greater than on the inside. As a result, aluminum filler is
sometimes exposed to the surface layer of a coated film where heavy
ironing is applied. The exposed aluminum filler at the surface
layer of coated film sometimes adheres to ironing dies, induces
troubles and makes continuous volume production difficult.
[0009] Many studies have been made on optimum conditions for metal
dies used in the ironing of metal strips applied with common resin
paints and those coated with resin films in the dry state.
[0010] Japanese Unexamined Patent Publications Nos. 09-285826,
09-285827 and 09-285828 disclose techniques for achieving stability
in ironing by specifying the entry and exit half angles of dies and
the radius of curvature of the bearing portion between the entry
and exit half angles. However, no study has been done on optimum
conditions for metal dies used in the ironing of metal strips
coated with metallic-appearance coatings containing aluminum
fillers.
[0011] As such, it has been desired that a study be done on the
optimum profile of metal dies for the ironing of steel sheets
coated with metallic-appearance coated films.
[0012] While roll-coating methods to apply common resin paints on
the external surface of steel sheets have been established, no
study has yet been done on coating conditions for controlling the
distribution of filler in S the direction of thickness coating in
one roll coating.
SUMMARY OF THE INVENTION
[0013] The present invention avoids the defects in said prior arts
and provides metal strips having greater forming stability for
forming seamless cans having a coated film containing metal fillers
on the external surface thereof by ironing, cans made of said metal
strips, and methods for manufacturing said metal strips and
cans.
[0014] In order to solve said conventional problems, the present
invention provides one-side coated metal strips having dramatically
increased stability in ironing obtainable by adding aluminum filler
at an appropriately controlled thickness to the paint to be coated
on the outside of cans and strictly controlling the individual
ironing steps and the quality of base material and seamlessly
formed cans made thereof and method for manufacturing said metal
strips and cans.
[0015] The gist of the present invention is as given below:
[0016] (1) A metal strip with metallic-appearance excellent in
forming stability, having a only one coated film layer on the side
thereof corresponding to the outside of a can, characterized
by;
[0017] comprising a filler-rich portion containing not less than 20
mass %, in the coated and dried state, of a filler of aluminum or
aluminum alloys,
[0018] and a resin-rich portion containing not more than 5 mass %
of said filler 0.1 to 20 .mu.m in thickness upon the filler-rich
portion,
[0019] wherein the filler is dilutely distributed in the direction
of the coated layer thickness.
[0020] (2) A metal strip with metallic-appearance excellent in
forming stability, having a only one coated film layer on the side
thereof corresponding to the external side of a can, characterized
by;
[0021] comprising a filler-rich portion containing not less than 20
mass %, in the coated and dried state, of a filler of aluminum or
aluminum alloys,
[0022] and a resin-rich portion containing not more than 5 mass %
of said filler 0.3 to 10 .mu.m in thickness upon the filler-rich
portion,
[0023] wherein the filler is dilutely distributed in the direction
of the coated layer thickness.
[0024] (3) A metal strip with metallic-appearance excellent in
forming stability described in (1) or (2) above, wherein a resin
film not less than 8 .mu.m thick is laminated on the side thereof
corresponding to the internal side of said can.
[0025] (4) A metal strip with metallic-appearance excellent in
forming stability described in any of (1) to (3) above, wherein a
polyester or polyolefin resin film is laminated on the side thereof
corresponding to the internal aide of said can.
[0026] (5) A metal strip with metallic-appearance excellent in
forming stability described in any of (1) to (4) above, wherein the
coated film on the external side of said can contains one or more
of polyester, epoxyphenol and vinyl organosol.
[0027] (6) A method for manufacturing metal strip with
metallic-appearance excellent in forming stability, characterized
by;
[0028] setting the ratio a/(a+b) at 20 to 45%, where a is the sum
of the weights of the filler of aluminum or aluminum alloys and
resin in the paint and (a+b) is the sum of said sum a and the mass
b of organic solvent for dissolving the paint, and
[0029] roll-coating or photogravure-coating at the linear pressure
of not less than 3 kg/cm between the metal strip and rolls by using
coating-rolls having a diameter of not more than 500 mm.
[0030] (7) A method for manufacturing metal strip with
metallic-appearance excellent in forming stability described in (6)
above, wherein the statistic viscosity of the paint applied by
roll-coating is 20 to 350 centipoise at 20.degree. C.
[0031] (8) A seamlessly-formed can body, characterized by;
[0032] comprising a filler-rich portion containing not less than 5
mass %, in the coated and dried state, of a filler of aluminum or
aluminum alloys on the side thereof corresponding to the outside of
a can,
[0033] and a resin-rich portion containing not more than 5 mass %
of said filler 0.03 Am in thickness upon the filler-rich
portion,
[0034] wherein the filler is dilutely distributed in the direction
of the coated layer thickness.
[0035] (9) A seamlessly-formed can body, characterized by;
[0036] comprising a filler-rich portion containing not less than 20
mass %, in the coated and dried state, of a filler of aluminum or
aluminum alloys on the side thereof corresponding to the outside of
a can,
[0037] and a resin-rich portion containing not more than 5 mass %
of said filler 0.03 .mu.m in thickness upon the filler-rich
portion,
[0038] wherein the filler is dilutely distributed in the direction
of the coated layer thickness.
[0039] (10) A seamlessly-formed can body described in (8) or (9)
above, wherein the body has a laminated resin film.
[0040] (11) A seamlessly-formed can body described in any of (8) to
(10) above, wherein the body has a resin film of one or more of
polyester, epoxyphenol and vinyl organosol.
[0041] (12) A method for manufacturing seamlessly-formed can body,
characterized by;
[0042] applying multistage ironing to the metal strip described in
any of (1) to (5) above with a thickness reduction ratio y by using
two or more dies:
[0043] Total thickness reduction ratio .gamma.<58+11d.sup.0.35
(d: thickness (.mu.m) of the resin-rich portion containing not more
than 5 mass % of filler in the coated surface far from the coated
side).
[0044] (13) A method for manufacturing seamlessly-formed can body
described in (12) above, wherein ironing is performed by using a
die whose intersection point between the entry and exit half angles
has a radius of curvature not less than 0.02 mm.phi., with the
entry half angle set at 2 to 10.degree..
[0045] (14) A method for manufacturing seamlessly-formed can body
described in (12) above, wherein ironing is performed by using a
die whose intersection point between the entry and exit half angles
has a radius of curvature not less than 0.01 mm.phi., with the
entry half angle set at 2 to 18.degree..
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 shows the cross-sectional surface structure of a
metal strip according to the present invention.
[0047] FIG. 2 shows a coating process to apply resin on a metal
strip according to the present invention.
[0048] FIG. 3 shows the cross-section of a metal die used in the
ironing of a metal strip according to the present invention.
THE MOST PREFERRED EMBODIMENT
[0049] Details of the invention are described below with reference
to the attached drawings.
[0050] First, the metal strips of the present invention will be
explained. FIG. 1 shows the cross-sectional surface structure of a
metal strip according to the present invention. As is illustrated,
a coated film 2 containing a filler of aluminum or aluminum alloys
is formed on the surface of a metal strip 1, with a filler-free
layer (a resin-rich portion) 3 formed on top thereof and a coated
film or resin film 4 is formed on the other side.
[0051] Although the thickness of the metal strip need not be
specified, 0.15 to 0.35 mm thick steel sheets suited for can making
are commonly used.
[0052] So long as adhesiveness to resin and ironing formability are
secured, surface properties of the metal strip need not be
specified. In order to secure adhesiveness, however, it is desired
to apply surface pretreatment with chromic acid, dichromic acid,
phosphoric acid, organic acids, etc.
[0053] The metal strips of the present invention may be of
aluminum, aluminum alloys, tin-free steel, chromium-coated steel,
nickel-coated steel, phosphated steel, phosphated resin-coated
steel, tin-coated steel, tin-nickel coated steel, etc.
[0054] Before ironing, a coated film (hereinafter sometimes
referred to as the "filler-containing coated film) containing not
less than 5 mass %, preferably not less than 20 mass %, of filler
of aluminum or aluminum alloys is formed on the side corresponding
to the external side of cans. If the content of the filler is less
than 5 mass %, the filler-containing coated film does not provide
sufficient coating on the surface subjected to ironing. Then,
resistance to ironing becomes uneven, which, in turn, damages the
coated film by galling or other problem.
[0055] Fillers consisting of aluminum or aluminum alloys are used
because aluminum or aluminum alloys excel in drawability, which
facilitates deformation and elongation during ironing and avoids
the concentration of ironing stress to certain specific parts on
the external side.
[0056] Purity enhancement, alloying, crystalline structure control
and annealing further increase the formability of aluminum.
Therefore, resistance to ironing can be decreased by applying said
treatments. This effect is prominent when the filler content is not
less than 20 mass %.
[0057] The resins used for the purpose of the present invention are
not particularly limited to any specific ones so long as surface
hardness is high enough to withstand ironing. It is preferable to
use any of polyester, epoxyphenol and vinyl organosol that have
good formability.
[0058] The surface hardness of resins is preferably not more than 2
H in terms of pencil hardness rating. The color of resins can be
changed by adding chemical pigments and dyes other than aluminum
pigments.
[0059] In the structure of resin film, the distribution of filler
is controlled so that the portion containing not more than 5 mass %
of filler formed in the coated film far from the metal strip
surface (hereinafter referred to as the filler-free portion) is 0.1
to 20 .mu.m, preferably 0.3 to 10 .mu.m, in thickness before
ironing. While the thickness of the filler-free portion (resin-rich
portion) before ironing is not less than 0.1 .mu.m, the thickness
of the filler-free portion in the can body portion after ironing is
not less than 0.03 .mu.m.
[0060] The content of aluminum filler in the coated film is
determined based on the mass ratio derived by measuring the areas
of the aluminum filler and resin in electron photomicrographs of
magnification not less than 2000 of not fewer than 50 specimens
taken at random, with specific gravity correction.
[0061] If the thickness of the filler-free portion before ironing
is less than 0.1 .mu.m, the surface deforming force resulting from
thickness change induced by ironing prompts the exposure of filler
to the formed surface and makes difficult the execution of stable
high-speed ironing.
[0062] If the thickness of the filler-free portion before ironing
exceeds 10 .mu.m, propagation of ironing force to the metal surface
becomes uneven and induces surface galling.
[0063] In order to realize stable high-speed ironing, the
pre-ironing thickness of the filler-free portion is preferably not
less than 0.3 .mu.m and more preferably 1 to 8 .mu.m.
[0064] As the present invention does not require any particular
adhesiveness between the filler and metal strip, the density
distribution of filler in the coated film is not particularly
specified. However, highly adhesive primary resin to increase the
adhesiveness between the filler and metal strip may be applied
before the pigment containing aluminum filler is applied.
[0065] The coating on the side of metal strips corresponding to the
internal side of cans is not particularly limited so long as it
withstands ironing and provides enough corrosion resistance
required of the formed inside. Commonly, pigments containing any of
polyester, epoxyphenol and vinyl organosol are applied to a
thickness of not less than 1 .mu.m or resin film is laminated.
[0066] Any kind of metal strips can be used so long as adequate
formability to withstand ironing is obtainable. If the coated side
is the side corresponding to the internal side of cans, it is
preferable that material hardness is under 57 in terms of
HR30T.
[0067] If material hardness is greater than 57 in terms of HR30T,
resistance to ironing increases, which, in turn, induces an
increase in surface ironing force and makes it difficult to secure
adequate coating adhesiveness on both sides of cans.
[0068] The use of any of polyester, epoxyphenol and vinyl organosol
for the coating film on the external side further stabilizes
ironing formability.
[0069] Compared with the coating on the side of metal strips
corresponding to the internal side of cans, laminating not less
than 8 .mu.m resin film on that side provides greater ironing
force. This permits using harder metal strips and, as a
consequence, facilitates weight reduction of cans through reduction
of metal strip thickness.
[0070] Metal strips whose hardness is up to 73 in terms of HR30T
can be used. Preferable resin films are of polyester or polyolefin
having high enough formability to withstand ironing.
[0071] If film thickness is less than 8 .mu.m, resistance to
surface galling decreases to such an extent as to destabilize the
ironing of hard metals.
[0072] The use of any of polyester, epoxyphenol and vinyl organosol
for the coating on the external side of metal strips further
stabilizes ironing formability.
[0073] Next, details of coating method to secure adequate coating
thickness in the filler-free portion is described at length. FIG. 2
shows a coating process to apply resin on a metal strip. As is
illustrated, a film of resin is formed on a metal strip 1 by
applying a pressure L on coating rolls 6 and the film is then dried
in a drying oven 5.
[0074] In this coating, the ratio of the solid content to the total
sum of the solid content of organic solvent is 20 to 45 mass %.
Though the solvent need not be particularly limited, mixed solvents
of toluene, benzene, ether, etc. are commonly used,
[0075] If the ratio of the solid content to the total sum of the
solid content of organic solvent exceeds 45 mass %, viscosity
increases and high-speed coating becomes difficult. If the ratio is
less than 20 mass %, the position of-the filler is destabilized in
the drying process, which makes the formation of the filler-free
portion difficult and facilitates the dissipation of the filler
throughout the entire thickness of the coating.
[0076] In order to gather the filler as close as possible to the
surface of the metal strip in coating and realize the desired
filler distribution in the coated film, it is necessary to adjust
the pressure applied to the strip by the coating rolls.
[0077] The pressure on the strip is governed by the diameter and
linear pressure of the rolls. Here, the roll linear pressure was
evaluated from L/W, wherein L is the axial load determined by a
load cell disposed in the roll bearing and W is the width of the
metal strip to be coated.
[0078] The coated film according to the present invention is formed
with the use of rolls whose diameter is not more than 500 mm.phi.
and linear pressure not less than 3 kg/cm. While the roll linear
pressure can be secured by several methods such as the use of
backup rolls in coating, the present intention imposes no
particular limitation.
[0079] If the roll linear pressure is less than 3 kg/cm, the force
to keep the filler in close contact with the surface of the metal
strip, which, in turn, impairs parallelism of the filler in the
coated film with respect to the surface of the metal strip and
facilitates the dissipation of the filler in the direction of the
thickness of the coated film. As a consequence, it becomes
difficult to secure the thickness of the filler-free portion.
[0080] The viscosity (static viscosity) of the paint applied is
preferably 20 to 350 centipoise at 20.degree. C. If the viscosity
is less than 20 centipoise, the aluminum filler disperses just
after coating, which, in turn, tends to result in poor appearance.
If the viscosity exceeds 350 centipoise, adhesion between the
filler and base metal decreases.
[0081] The above description is based on a method that forms the
filler-free portion in one roll coating. In order to insure the
formation of the filler-free portion, a resin-rich layer containing
not more than 5% aluminum filler may be added after a coated film
containing not less than 5% aluminum filler has been formed.
[0082] Next, methods to form the metal strips according to the
present invention are described.
[0083] FIG. 3 shows the cross section of a metal die used for
ironing the metal strip according to the present invention. FIG. 3
shows a metal strip 1 formed by an upper die 7 that comes in
contact with the external side of a can and a lower die 8.
[0084] In order to achieve stable ironing of the coated metal strip
1, it is necessary to control the surface forming force within the
limit of the tensile shear strengths of the resin at the forming
temperature.
[0085] While the strength of the coated film generally varies with
the composition and crystalline condition thereof and the
temperature, the coated film is hardened by the forming heat. Thus,
the inventors took note of the fact that the heat generation due to
ironing influences the limit of the total thickness reduction ratio
that indicates the possibility of ironing and investigated the
relationship between the heat value or the total thickness
reduction ratio in ironing and the condition of the coated
film.
[0086] The investigation led to the finding that, for the
prevention of occurrence of coating film damage during ironing, the
thickness and total thickness reduction ratio of the aluminum
filler layer must satisfy the relationship expressed by the
following equation:
[0087] Total thickness reduction ratio
.gamma.<58+11d.sup.0.35
[0088] wherein total thickness reduction ratio .gamma.(%) is the
reduction in thickness between before and after forming divided by
the original strip thickness, and
[0089] d is the thickness (.mu.m) of the resin-rich (thickness of
the filler-free layer) portion containing not more than 5 mass % of
filler in the coated surface far from the coated side.
[0090] When iron is applied to the coated surface, the total
thickness reduction ratio .gamma. that permits ironing depends
greatly on the thickness d of the filler-free layer at the
surface.
[0091] If the thickness d of the filler-free layer is small and
severe ironing beyond said total thickness reduction ratio is
applied, the resin at the surface can no longer adequately cover
the filler, as a result of which the filler becomes exposed to the
uppermost layer of the can, builds up on the surface of the metal
dies, and increases the heat volume generated thereby. This, as a
result, impairs the efficiency of the ironing work.
[0092] In the forming of seamless cans, securing of can height and
reduction of wall thickness are commonly achieved by combining
drawing, ironing and stretching. If work design is made to keep the
total thickness reduction ratio in ironing within the limit defined
by the equation given earlier, cans having the desired height can
be stably manufactured in large volume without damaging the coated
film and causing metal die trouble.
[0093] In order to achieve stable ironing by forming a coated film
containing a controlled smaller amount of aluminum or aluminum
filler on the outermost side of said can, it is necessary, unlike
in the ironing of conventional coated metal strips, to avoid, as
much as possible, a stress concentration between the coated film
and aluminum filler that is induced by the ironing stress on the
resin at the surface of the coated film.
[0094] For this purpose, it is necessary to minimize the entry half
angle (see a in FIG. 3) and inhibit the swelling of the coated film
in the vicinity of the metal dies during ironing.
[0095] Study of appropriate conditions for the minimization and
inhibition led to a finding that if the entry half angle exceeds
18.degree. the swelling of the coated film just before ironing can
not be sufficiently inhibited and, as a consequence, galling or
exposure of the aluminum filler becomes likely to occur.
[0096] If the entry half angle is smaller than 2.degree., the
contact area between the dies and coated film becomes unstable and
resistance to ironing tends to vary. This leads to the creation of
uneven ironing and other appearance defects at the surface of the
formed surface.
[0097] Though the present invention does not particularly limit
exit half angle (see .beta. in FIG. 3), it is preferable, for the
assurance of stable surface gloss, to keep the exit half angle
between 1.degree. and 25.degree.. If the radius of curvature of the
curved surface at the point of intersection between the entry and
exit half angles (see .gamma. in FIG. 3) is smaller than 0.1
mm.phi., surface contact becomes so great that the appearance of
the can surface tends to become impaired as a result of heat
generation. If the entry half angle is smaller than 10.degree., the
curvature can be reduced to 0.02 mm.phi..
[0098] Though the ironing work according to the present invention
is based on dry ironing without lubricant, ironing with solid
lubricant, such as Vaseline, or wet ironing with lubricant is also
applicable.
[0099] Examples of the present invention are concretely described
below.
EXAMPLE 1
[0100] Tin-free steel sheets, 0.22 mm thick, bright finished,
temper T3 and total chromium amount 80 mg/m.sup.2, with the
external and internal surfaces coated under the conditions shown in
Table 1 were subjected to ironing under the conditions shown in
Table 1. Table 1 also shows the appearance of the cans thus
obtained. The steel sheets according to the present invention also
had good appearance.
[0101] As to the appearance of cans, the degree of glossiness was
measured twice at randomly selected 10 points. The cans whose
difference between the maximum and minimum measurements falls
within .+-.10% of the overall average were classed as
.circleincircle. (best) and those whose difference between the
maximum and minimum measurements exceeds .+-.10% and falls within
.+-.15% as .largecircle. (practically usable).
[0102] The degree of glossiness was determined by measuring the
light reflected at an angle of 60.degree. with respect to the
direction in which coating is done on the metal strip.
TABLE-US-00001 TABLE 1 External Side Dry Filler- Coating Conditions
Weight free Internal Side Boll Linear Ratio Layer Thickness
Diameter Pressure Pigment Resin (%) (.mu.m) Condition Resin (.mu.m)
(nm) (kg/cm) 1 Aluminum Polyester 20 3 Laminated PET 25 300 3 2 30
3 Laminated PET 25 300 3 3 40 3 Laminated PET 25 300 3 4 50 3
Laminated PET 25 300 3 5 50 1 Laminated PET 25 300 3 6 50 3
Laminated PET 25 300 3 7 50 5 Laminated PET 25 300 3 8 50 10
Laminated PET 25 300 3 9 Epoxyphenol 30 3 Laminated PET 25 300 3 10
Vinyl 30 3 Laminated PET 25 300 3 organosol 11 Polyester 50 3
Coated Epoxyphenol 6 300 3 12 50 3 Coated Vinyl 6 300 3 organosol
13 20 0.05 Laminated PET 25 300 2 14 30 0.05 Laminated PET 25 300 2
15 40 0.05 Laminated PET 25 300 2 16 50 0.05 Laminated PET 25 300 2
17 50 0.05 Laminated PET 25 300 3 18 50 0.05 Laminated PET 25 300 3
19 50 0.05 Laminated PET 25 300 3 20 50 22 Laminated PET 25 300 3
21 30 0.05 Laminated PET 25 300 3 22 50 0.05 Coated Epoxyphenol 6
300 3 23 50 0.05 Coated Epoxyphenol 6 300 3 Ironing Metal Dies
Total Entry Exit Ironing Half Half Radius of Appearance Ratio 58 +
11d.sup. Angle Angle Curvature of Can Remarks 1 70 74.2 10 10 0.2
.largecircle. Example 2 70 74.2 10 10 0.2 .largecircle. of the 3 70
74.2 10 10 0.2 .largecircle. present 4 70 74.2 10 10 0.2
.largecircle. invention 5 65 69.0 10 10 0.2 .largecircle. 6 70 74.2
10 10 0.2 .largecircle. 7 75 77.3 10 10 0.2 .largecircle. 8 78 82.6
10 10 0.2 .largecircle. 9 70 74.2 10 10 0.2 .largecircle. 10 72
74.2 10 10 0.2 .largecircle. 11 72 74.2 10 10 0.2 .largecircle. 12
72 74.2 10 10 0.2 .largecircle. 13 70 61.9 10 10 0.2 Galling
Examples 14 70 61.9 10 10 0.2 for 15 70 61.9 10 10 0.2 comparison
16 70 61.9 10 10 0.2 17 72 61.9 10 10 0.2 18 75 61.9 10 10 0.2 19
80 61.9 10 10 0.2 20 60 90.5 10 10 0.2 Galling mark 21 60 61.9 10
10 0.2 Aluminum 22 72 61.9 20 10 0.2 ironing power 23 72 61.9 0.5
10 0.2 Galling mark
EXAMPLE 2
[0103] Coating was done with the viscosities shown in Table 2 under
the conditions for Example 1 of the present invention shown in
Table 1. The appearance in Table 2 was evaluated by the same method
as in Example 1. Nos. 1 to 5 in Table 2 are examples for comparison
in which the filler could moved in the paint with relative ease
because the viscosity thereof was as low as under 20 centipoise.
This impaired the parallelism of the filler in the coated film with
respect to the surface of the metal strip and, therefore, caused
somewhat great variations in the degree of glossiness.
[0104] Nos. 11 to 15 were also examples for comparison in which the
viscosity of the paint exceeded 350 centipoise. While the thickness
of coating applied by the coater tended to vary, the resulted
unevenness was difficult to level off under gravity because of the
high viscosity. As a consequence, the degree of glossiness varied
rather extensively.
[0105] Nos. 6 to 6 were examples of the present invention in which
the viscosity of the paint was between 20 centipoise and 350
centipoise. Therefore, poor appearances due to the movement of the
filler and uneven coating were avoided. The viscosity was
determined with the E-type viscometer after heating the paints to
20.degree. C. TABLE-US-00002 TABLE 2 Paint Parameters Coating
Conditions Dry Roll Linear Weight Paint Diameter Pressure Ratio
Viscosity No (mm.phi.) (kg/cm) Pigment Resin (%) (cp) Appearance
Remarks 1 300 3 Aluminum Polyester 20 1 .largecircle. Examples for
2 300 3 Aluminum Polyester 20 5 .largecircle. comparison 3 300 3
Aluminum Polyester 20 10 .largecircle. 4 300 3 Aluminum Polyester
20 15 .largecircle. 5 300 3 Aluminum Polyester 20 18 .largecircle.
6 300 3 Aluminum Polyester 20 20 .circleincircle. Examples of 7 300
3 Aluminum Polyester 20 50 .circleincircle. the present 8 300 3
Aluminum Polyester 20 100 .circleincircle. invention 9 300 3
Aluminum Polyester 20 300 .circleincircle. 10 300 3 Aluminum
Polyester 20 350 .circleincircle. 11 300 3 Aluminum Polyester 20
360 .largecircle. Examples for 12 300 3 Aluminum Polyester 20 380
.largecircle. comparison 13 300 3 Aluminum Polyester 20 400
.largecircle. 14 300 3 Aluminum Polyester 20 420 .largecircle. 15
300 3 Aluminum Polyester 20 450 .largecircle.
INDUSTRIAL APPLICABILITY
[0106] The present invention dramatically improves the forming
stability in heavy ironing of one-side coated steel sheets and,
thus, provides metal strips with metallic-appearance excellent in
forming stability, seamlessly-formed cans made of such steels, and
methods for manufacturing such metal strips and cans.
[0107] As such, the present invention has great contributions to
the development of can manufacturing and utilizing industries.
* * * * *