Note: Descriptions are shown in the official language in which they were submitted.
Z()OU356
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a copolyester resin film
laminated metal sheet having excellent formability and its method
of production. The process comprises laminating a biaxially
oriented copolyester resin fil~m, having specified characteristics,
precoated with a small amount of a resin composite, the resin
composite containing at least one radical, such as an epoxy radical
or a hydroxyl radical on one or both sides of a surface treated
metal sheet which has been heated to the melting point of the
copolyester resin film + 50C just before the lamination of the
copolyester resin film. The side of the copolyester resin film
precoated with the resin composite is in contact with the surface
treated metal sheet.
BRIEF DESCRIPTION OF THE PRIOR ART
At present, metal sheets, such as electrotinplate, tin
free steel and aluminum sheets are widely used for can stock after
being coated, at least once, with lacquer. This lacquer coating
is disadvantageous from an energy standpoint as significant time
is required for curing the lacquer and large volumes of solvent
discharged during the lacquer curing process must be burned in
another furnace in order to prevent air pollution.
- 2 -
- ~OU3S6
-~ Recently, lamination of thermoplastic resin film on a
metal sheet was attempted in order to avoid these problems. See
for example, Laid-Open Japanese Patent Application No. Sho 53-
141786, Japanese Patent Publication No. Sho 60-47103, Laid-Open
Japanese Patent Application Nos. Sho 60-168643, Sho 61-20736 and
Sho 61-149341.
Laid-Open Japanese Patent Application No. Sho 53-141786
discloses a metal can produced from a metal sheet covered with
polyolefin resin film, using an adhesive containing polyolefin
resin modified with a carboxyl radical. However, this polyolefin
film laminated metal sheet cannot be used as a material for can
stock as the metal sheet can become corroded by the packed contents
due to the poor permeability resistance of the laminated polyolefin
resin film. Furthermore, even if the polyolefin resin film
laminated metal sheet is used as a material for can stock, cans
having satisfactory appearance cannot be obtained because the
laminated polyolefin resin film is melted during heating at
temperatures of from 160 to 200C . These temperatures are
required for curing the printing ink or the coated lacquer.
Japanese Patent Publication No. Sho 60-47103 relates to
a process for lamination of a crystalline polyester resin film to
a metal sheet by heating the sheet above the melting point of said
polyester resin film and thereafter immediately quenching the
20(3{~351~i
laminate. In this patent, the crystalline polyester film is
sufficiently adhered to the metal sheet by an amorphous and non-
oriented polyester resin film that is formed at the interface of
the crystalline polyester film and the metal sheet as a result of
the heating step. However, when the polyester film laminated metal
sheet is reheated to 160 to 200C for 10 to 30 minutes, as required
for curing the printing ink or lacquer applied on the other side
of the metal sheet before forming, adhesion of the polyester resin
film deteriorates. This is due to the amorphous non-oriented
polyester resin layer recrystallizing upon heating. As a result,
corrosion resistance also deteriorates.
Laid-Open Japanese Patent Application No. Sho 60-168643
relates to a thermoplastic resin film laminated steel sheet for a
drawn and ironed can (DI can) and the production method therefor.
In said patent, the side of the steel sheet to be employed for the
inside of the DI can is laminated with a thermoplastic resin film,
such as polyethylene terephthalate, without any adhesives. The
side of the steel sheet to be employed for the outside of the DI
can is plated with a ductile metal, such as tin, nickel or
aluminum.
The steel sheet according to said patent has the same
defects as those in Japanese Patent Publication No. Sho 60-47103,
i.e., as a result of the reheating to the 160 to 200C for 10 to 30
ZOOQ356
minutes required for curing the printing ink and the lacquer on the
outside of the DI can, the adhesion of the polyester resin film
noticeably deteriorates.
Laid-Open Japanese Patent Application Nos. Sho 61-20736
and Sho 61-149341 relate to lamination of a precoated biaxially
oriented polyester resin film~ to a metal sheet heated below the
melting point of said polyester resin film. The film is precoated
with a special adhesive, such as an epoxy resin containing a curing
agent. In said patents, an amorphous and non-oriented polyester
resin layer as shown in Japanese Patent Publication No. Sho 60-
47103 and Laid-Open Japanese Patent Application No. Sho 60-168643
is not formed. This is because the lamination of biaxially
oriented polyester resin film to the metal sheet is carried out
below thè melting point of said polyester resin film. Therefore,
the corrosion resistance and the adhesion of polyester resin film
to the metal sheet does not deteriorate, even if it is reheated at
temperatures of 160 to 200C for the time required for curing
printing ink and lacquer. However, if said laminated metal sheet
is used for some applications requiring more severe formability,
such as a deep drawn can having a drawing ratio higher than 2.0,
many cracks occur in the polyester resin film.
Recently, the use of a polyester resin film having
specified characteristics has been proposed in order to improve the
Z{~ 356
formability of the polyester resin film laminated metal sheet
(Laid-Open Japanese Patent Application No. Sho 64-22530 and
Japanese Patent Application No. Sho 63-75837). However, when these
polyester resin film laminated metal sheets are formed in processes
such as deep drawing or bending at high speed, many cracks arise
or the laminated polyester resin film is peeled off in the formed
area of said polyester resin film.
SUMMARY OF THE INVENTION
Accordingly, it is the first objective of the present
invention to provide a surface treated metal sheet covered with
copolyester resin film having excellent corrosion resistance in a
part formed under severe conditions, such as a deeply drawn can,
a drawn and partially ironed can and a drawn and stretch formed can
having high can height above 2.0 in drawing ratio, even after
reheating to cure overcoated color printing ink or lacquer.
It is the second objective of the present invention to
provide a method for continuous high speed lamination of
copolyester resin film on one or both sides of the surface treated
metal sheet.
The first objective of the present invention can be
accomplished by the formation of a film consisting of an outer
2000356
layer and an inner layer on the surface of a metal
layer. The outer layer is comprised of a
copolyester resin film possessing specific
characteristics and is produced by stretching and
heat setting a copolyester resin film consisting of
75 to 99 mole % of polyethylene terephthalate and 25
to 1 mole % of a polyester resin produced by
esterification of at least one saturated
polycarboxylic acid with at least one saturated
polyalcohol. The inner layer comprises a thin resin
composite containing in its molecular structure, at
least one radical, such as epoxy radical and
hydroxyl radical. The composite layer is present on
one or both sides of the surface treated metal
sheet.
More specifically, the invention relates to
a copolyester resin film laminated metal sheet,
comprising:
(i) a biaxially oriented copolyester resin
film having a melting point of from about 210C to
about 250C, an index of refraction of from about
1.5000 to about 1.5500 relative to the thickness of
said film and an index of refraction of from about
1.6000 to about 1.6600 relative to its planar
dimensions,
(ii) a resin composite applied to one side
of said copolyester resin film which contains at
least one radical selected from the group consisting
of an epoxy, a hydroxyl, an amide, an ester, a
carboxyl, a urethane, an acryl and an amino radical,
and
(iii) a surface treated metal sheet, wherein
the side of said copolyester resin film coated with
said resin composite is laminated to said surface
treated metal sheet, wherein at least one side of
-
2000356
said surface treated metal sheet has said
copolyester resin film laminated thereto.
The second objective of the present
invention can be accomplished by continuous high
speed lamination of the copolyester resin film
precoated with resin composite, onto one or both
sides of a surface treated metal sheet that has been
heated to + 50C of the melting point of the
copolyester resin film, with the precoated side of
the copolyester resin film being in contact with the
metal sheet.
More specifically, the invention also
relates to a method for production of a copolyester
resin film comprising:
(i) precoating a side of a copolyester resin
film with a resin composite containing at least one
radical selected from the group consisting of an
epoxy, a hydroxyl, an amide, an ester, a carboxyl, a
urethane, an acryl and an amino radical wherein said
copolyester film has a melting point of from about
210 to about 250C and an index of refraction of
from about 1.5000 to about 1.5500 relative to the
thickness of said film and an index of refraction of
from about 1.6000 to about 1.6600 relative to its
planar dimensions,
(ii) heating a surface treated metal sheet
to a temperature within the melting point of said
copolyester resin film + 50C, and
(iii) contacting the side of said
copolyester resin film treated with said resin
composite to at least one side of said surface
treated metal sheet so as to laminate said
copolyester resin film thereto.
- 7a -
~ ~- 2000356
The specific characteristics referred to
suPra are:
(1) melting temperature;
(2) refractive index of the film's
thickness;
(3) refractive index of the film's planar
dimensions; and
- 7b -
2000356
(4) amount and average particle size of added
lubricant, when lubricant is added
thereto.
The copolyester resin film laminated metal
sheet having an excellent formability according to the
present invention can be obtained by controlling all of
these factors in the optimum ranges as disclosed below
The copolyester resin film laminated metal
sheet according to the present invention can be used in
applications where excellent corrosion resistance is
required after severe forming. Examples are deeply
drawn cans, drawn and partially ironed cans, drawn and
stretch formed cans having high can height and a high
drawing ratio and can ends where a tab for easy opening
is attached. In these applications, the cans are
exposed to hot water or hot steam for sterilization
after packing food, such as fruit juices, coffee
drinks, meats and fish. For example, fruit juices are
immediately packed in the can after sterilization, at a
temperature of 90 to 100C Coffee drinks, meats and
fish are sterilized by hot steam at a temperature above
100C in a retort after being packed in the can.
Furthermore, the metal sheet according to the present
invention can be used for screwed caps and crown caps.
~)(~U356
In these applications, color printing ink or lacquer
coating on one or both sides of the metal sheet used for the
outside or inside of these cans is often carried out before or
after forming. In these cases, the laminated copolyester resin
film in the present invention is not peeled off in the severely
formed areas, even after reheating for curing color printing ink
or lacquer and subsequent treatment by hot water or hot steam.
BRIEF DESCRIPTION OF THE FIGURE
Figure 1 depicts, graphically, the relationship between
the index of refraction of a given copolymer and the degree of
elongation possible before the copolymer film breaks.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a laminated metal sheet where
the metal sheet is laminated with copolyester resin film having
specified characteristics, consisting of 75 to 99 mole % of
polyethylene terephthalate and 25 to 1 mole ~ of a polyester resin
produced by the esterification of at least one saturated
polycarboxylic acid with at least one saturated polyalcohol
selected from the following polycarboxylic acids and polyalcohols.
_ g
-
zol)Q356
Saturated polycarboxylic acids are selected from phthalic
acid, isophthalic acid, terephthalic acid, succinic acid, azelaic
acid, adipic acid, sebacic acid, diphenyl carboxylic acid, 2,6-
naphthalene dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid
and trimellitic acid anhydride.
Saturated polyalcohols are selected from ethylene glycol,
1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, propylene
glycol, polytetramethylene glycol, trimethylene glycol, triethylene
glycol, neopenthyl glycol, 1,4-cyclohexane dimethanol, trimethylol
propane and pentaerythritol.
Furthermore, in the present invention, the use of
biaxially oriented copolyester resin film having all of the
following factors in some optimum range is indispensable from the
viewpoint of corrosion resistance after severe forming. These
factors are:
(1) melting temperature;
(2) refractive index of the film's thickness;
(3) refractive index of the film's planar dimensions;
and
(4) amount and average particle size of added lubricant,
when lubricant is added thereto.
In some cases, additives such as antioxidants,
stabilizer, pigments, antistatic agents and corrosion inhibitors
-- 10 --
20~U356
are added during the manufacturing process of the copolyester resin
film.
The melting temperature of the employed copolyester resin
film is defined as the temperature at which the endothermic peak
is obtained at a heating rate of 10 C/minute in the differential
scanning calorimeter (SS10) made by Seiko Denski Kogyo Co. It is
preferred that a copolyester resin film having a melting
temperature of from about 210 to about 250C should be used. The
use of a copolyester resin film having a melting temperature above
250C is not suitable in the present invention as such rigid
copolyester resin films have poor formability. A copolyester resin
film having a melting temperature below 210C is not practical as
its mechanical property deteriorates upon the reheating required
to cure the color printing ink or lacquer applied to the outside
or inside of the can.
The refractive indexes, the second and third factors
mentioned, are measured by using a polarized monochromatic light
in Abbe`s refractometer at 25C.
In the biaxially oriented copolyester resin film used in
the present invention, the refractive indexes in the thickness
direction and all planar dimensions in the plane should be in the
range of from about 1.5000 to about 1.5500 and from about 1.6000
~03~
to about 1.6600, respectively. These refractive
indexes change slightly depending upon conditions used
to laminate the copolyester resin film to the metal
sheet, as well as reheating conditions necessary to
cure the color printing ink or lacquer applied to the
copolyester resin film laminated metal sheet. The
degree of change in the refractive index of said
copolyester resin film also depends on the stretching
conditions and heat setting conditions for the
production of thin and wide copolyester resin film.
For example, if the laminating temperature of the
copolyester resin film is higher, the refractive index
of the laminated copolyester resin film decreases. The
refractive index of the copolyester resin film produced
under lower stretching and heat setting at higher
temperature decreases. On the other hand, the
refractive index produced under higher stretching and
heat setting at lower temperature increases.
As described above, the refractive index of
the copolyester resin film is dependant upon the
manufacturing conditions of copolyester resin film, the
laminating conditions and the reheating conditions.
- 12 -
2000356
In the present invention, it is necessary
that the refractive indexes in the thickness direction
and all planar dimensions of the copolyester resin film
should be controlled in the range of from about 1.5000
to about 1.5500 and from about 1.6000 to about 1.6600,
respectively, after the lamination to the surface
treated metal sheet. It is preferred that the
refractive index in all directions in the plane of the
copolyester resin film be maintained in the range of
1.6100 to 1.6500 after lamination, in order to obtain a
copolyester resin film laminated metal sheet having
excellent formability.
Copolyester resin films having refractive
indexes beyond the optimum range described above, are
not practical for some applications where severe
formability is required. Many cracks may arise in said
copolyester resin film or the laminated copolyester
resin film may be peeled off in the severe formed area
as a result of the deterioration in formability.
Laid-Open Japanese Patent Application No. Sho
64-22530 and Japanese Patent Application No. Sho 63-
5837 disclose polyester resin film laminated metal
sheet having excellent formability.
20Q0356
The former patent application shows that a
polyester resin film with excellent formability is
obtained by controlling the planar orientation
coefficient in the range of from 0.130 to 0.160. This
planar orientation coefficient, which is defined as the
degree of the planar coefficient of the polyester resin
film, is determined by using a refractometer and is
shown by the following equation:
- 13a-
-
2()0U3~
A = (B+C)/2-D,
where, A represents the planar orientation coefficient of the
polyester resin film,
B represents the refractive index in the lengthwise direction
of the polyester resin film,
C represents the refractive index in the widthwise direction
of the polyester resin film, and
D represents the refractive index in the thickness direction
of the polyester resin film.
Usually, the thin and wide polyester resin film is
produced continuously by stretching the extruded thick polyester
resin film in the lengthwise and widthwise directions. Therefore,
the characteristics in the center position of the wide polyester
resin film are different from those in the edge position,
particularly, the mechanical property and the coefficient of
expansion by heat in the oblique direction in the edge position of
the wide film.
Even if the planar orientation coefficient in the center
position of the wide polyester resin film is the same as that in
the edge position, the characteristics in the center position are
different from that in the edge position, because the planar
orientation coefficient calculated by the equation described above
is defined without consideration of the refractive index in the
- 14 -
-
~ZOOU356
oblique direction of the polyester resin film. The latter patent
application shows that a polyester resin film having excellent
formability is obtained by controlling the melting temperature, the
softening temperature and the elongation at break within the range
of 210 to 250C, 175 to 235C and 150 to 400%, respectively.
Recently, it has been found that the elongation at break
is related to the refractive index in the plane of the copolyester
resin film as shown in Figure 1. In particular, the elongation at
break declines if the refractive index in the plane falls below
1.6100. Even the copolyester resin film to be laminated on the
metal sheet has above 150% of the elongation at break and excellent
formability with a refractive index below 1.6100 in the plane. The
corrosion resistance of the metal sheet covered with this
copolyester resin film becomes poor in the areas formed under
severe conditions, because thè amorphous and non-oriented parts in
this copolyester resin film increase if the refractive index
decreases. Furthermore, the gradual decrease in the elongation at
break when the refractive index is above 1.6200 depends upon the
increase in the degree of the orientation in the copolyester resin
film.
Even if a copolyester resin film having above 150% of the
elongation at break with a refractive index of 1.6700 in the plane
is laminated on the metal sheet, a copolyester resin film laminated
~ Q3S6
metal sheet having excellent formability is not always obtained.
This is because the elongation at break of said copolyester resin
film decreases after lamination.
Therefore, a copolyester resin film laminated metal sheet
having excellent formability is not always obtained by using the
copolyester resin film according to Japanese Patent Application No.
Sho 63-75837, as the characteristics of the copolyester resin film
change depending upon the laminating and reheating conditions.
This problem has been solved by the present invention by
controlling the characteristics of the employed copolyester resin
film before and after lamination. According to the present
invention, in a copolyester resin film laminated metal sheet, where
formability under severe conditions is required, it is
indispensable that the mechanical property, thermal property and
chemiçal property of the employed copolyester resin film are
uniform throughout.
Therefore, the copolyester resin film used in the present
invention is characterized by the restriction in the range of the
refractive indexes in the thickness direction and all directions
in the plane as has been described above.
- 16 -
Q3S6
In order to produce a copolyester resin film having
excellent formability in all positions of the wide copolyester
resin film, it is necessary that the extruded thick copolyester
r~sin film is biaxially stretched with a lower ratio compared to
that in usual polyethylene terephthalate film. For instance, it
is desireable to stretch the extruded copolyester resin film 2.7
to 3.7 times in the lengthwise~direction and about 3.0 to 3.8 times
in the widthwise direction and that the temperature be set at from
about 150 to about 230C.
Additionally, the amount and the particle size of a
lubricant in the copolyester resin are important factors when a
lubricant is used. At least one lubricant selected from
silica(SiO2), alumina, titanium dioxide, calcium carbonate, barium
sulfate and organic silicon compound is usually added during the
manufacturing process of the copolyester resin film, and it is
desirable to use a lubricant having an average particle size below
2.5 ~m, preferably 0.5 to 2.0 ~m. It is not practical to use a
lubricant having a particle size above 2.5 ~m, as it acts as the
starting point for the growth of many cracks in the laminated
copolyester resin film during severe forming. Generally, the
amount of lubricant added into the copolyester resin film is
determined by the quality in coiling the produced copolyester resin
film and formability of the copolyester resin film laminated metal
sheet. If the lubricant is not added into the copolyester resin
~ 2~0Q3S6
film, it is not possible to wind the produced copolyester resin
film smoothly. Usually, the addition of lubricant having a large
particle size is effective in small amounts. On the other hand,
a lubricant having a small particle size, must be added in a larger
quantity. For example, silica having an average particle size of
2.3 ~m is effective with the addition of 0.001 to 0.05 weight % to
the weight of the copolyester~resin. In case of silica having an
average particle size of 0.3 ~m, the addition of 0.05 to 5 weight
% to the weight of the copolyester resin is necessary.
Copolyester resin films to be used for the outside of
cans, containing inorganic color pigment such as titanium dioxide
(Tio2 powder), instead of coating a white enamel on the clear
copolyester resin film laminated metal sheet and then curing the
coated white enamel. It is desirable that the amount of the color
pigment added to the copolyester resin film be 2 to 20 weight %
relative to the weight of the copolyester resin. If the amount of
color pigment is below 2 weight %, a satisfactory appearance is not
obtained. The copolyester resin film containing color pigment
above 20 weight % is not suitable in the present invention, as the
formability of said film becomes noticeably poor.
Measurement of refractive indices of the copolyester
resin film containing color pigment is not possible as the
- 18 -
(735fi
polarized monochromatic light used for measurement does not pass
through the pigmented film. Therefore, it is necessary to produce
the copolyester resin film containing color pigment under the same
conditions as those for the clear copolyester resin film having the
refractive indexes described above.
The thickness of the copolyester resin film used in the
present invention should be 5 to 50 ~m, preferably 10 to 30 ~m.
If the thickness of the employed copolyester resin film is below
5 ~m, the excellent corrosion resistance after severe forming of
the copolyester resin film laminated metal sheet is not obtained
and continuous lamination of thin copolyester resin film to the
surface treated metal sheet becomes noticeably difficult.
Moreover, the use of the copolyester resin film having a thickness
above 50 ~m is not economically suitable for lamination on surface
treated metal sheet, as the copolyester resin film used for the
present invention is expensive compared with epoxy phenolic
lacquers widely used in the can industry.
One side of the copolyester resin film selected by the
various characteristics described above, is precoated with 0.1 to
5.0 g/m2 of a resin composite containing at least one radical
selected from the group consisting of an epoxy radical, a hydroxyl
radical, an amide radical, an ester radical, a carboxyl radical,
a urethane radical, an acryl radical and an amino radical. Epoxy
-- 19 --
~noo3~fi
resin, phenol resin, nylon resin, polyester resin, modified vinyl
resin, urethane resin, acryl resin and urea resin are examples of
such resin composites.
It is desirable that the resin composite be coated on one
side of the copolyester resin film as uniformly and thinly as
possible. This is because the bonding strength of resin composite
layer to the surface treated metal sheet and the copolyester resin
film becomes gradually poorer with an increase in the thickness of
the precoated resin composite. However, it is very difficult to
uniformly coat in amounts below 0.1 g/m2 of the resin composite on
the copolyester resin film. Furthermore, when the amount of the
resin composite is below 0.1 g/m2 or above 5.0 g/m2, the bonding
strength of the resin composite layer to the surface treated metal
sheet and the copolyester resin film becomes noticeably poor in
severely formed areas. It is preferable that the resin composite
be diluted by a solvent and then coated by a roller or spray method
in order to form a uniform and thin resin composite layer on the
copolyester resin film. The temperature for drying a resin
composite diluted by a solvent which is coated on one side of the
copolyester resin film is one of the important factors in the
present invention. If the temperature is below 60C, a long time
is required for the removal of solvent and the formed resin
composite layer becomes tacky. When the drying temperature is
above 150C, the chemical reaction of resin composite coated on the
- 20 -
~ 3~fi
copolyester resin film is accelerated, and the bonding strength of
the resin composite to the surface treated metal sheet becomes
noticeably poor. It is preferable that the drying time of the
resin composite solution coated on the copolyester resin film be
5 to 30 seconds at a temperature of 60 to 150C. If the drying
time is less than 5 seconds, the solvent is not sufficiently
removed. On the other hand, ~rying times of more than 30 seconds
result in poor productivity.
A solvent having low boiling point is preferred for
dissolving the resin composite as it is easily removed by heating
at 60 to 150C. The solvent has no other specific limitations. In
some cases, a coloring agent, such as a dye, may be added to the
resin composite dissolved into the solvent.
The surface treated metal sheet should be selected from
the group consisting of a tin free steel having double layers of
an upper layer of hydrated chromium oxide and a lower layer of
metallic chromium, electrotinplate covered with the double layer
as described above, electrotinplate covered with hydrated chromium
oxide and an aluminum sheet treated in a solution containing
chromate, phosphate or zirconium salt which is usually used for the
treatment of aluminum drawn and ironed cans, as the metal sheet of
the present invention is contemplated for use as sanitary food
cans. The optimum range of hydrated chromium oxide and metallic
- 21 -
2000356
chromium in a tin free steel is 5 to 25 mg/m2 as
chromium and 10 to 150 mg/m2 as metallic chromium,
respectively. If the amount of hydrated chromium oxide
is below 5 mg/m2 or above 25 mg/m2 as chromium, the
bonding strength to the copolyester resin film
precoated with said resin composite becomes noticeably
poor in severely formed areas. Although the corrosion
resistance in the formed part becomes gradually poorer
with a decrease in the amount of metallic chromium,
even tin free steel having about 10 mg/m2 of metallic
chromium can be used for some applications where mild
corrosion resistance is required. The electrotinplate
should be cathodically treated in an electrolyte for
producing an ordinary tin free steel or treated by
immersion in a solution containing about 30 g/l of
sodium dichromate in water. By said cathodic
treatment, a double layer consisting of an upper layer
of hydrated chromium oxide and a lower layer of
metallic chromium is formed on the electrotinplate. It
is desirable that the amount of hydrated chromium oxide
and metallic chromium on electrotinplate be almost the
same as that in tin free steel. However, it is
preferable that the amount of metallic chromium be 10
to 50 mg/m2, in order to facilitate high speed
production.
.,;'
- 22-
- 2000356
In the case of immersion treatment of
electrotinplate in sodium dichromate solution, a thin
layer of hydrated chromium oxide in an almost constant
amount (1 to 4 mg/m2 as chromium) is formed on the
electrotinplate. The thin hydrated chromium oxide on
- 22a -
zoa~3s6
electrotinplate is necessary for excellent adhesion of the
copolyester resin film precoated with said resin composite in
severely formed area. If electrotinplate is not treated by
immersion into sodium dichromate solution, the adhesion of the
copolyester resin film precoated with said resin composite becomes
gradually poorer during storage in an atmosphere having high
humidity. If hydrated chro~ium oxide, having above 5 mg/m2 as
chromium, is formed on electrotinplate by cathodic treatment in
sodium dichromate solution, adhesion of the copolyester resin film
precoated with resin composite becomes noticeably poor in severely
formed areas. It is considered that the difference in the adhesion
of the copolyester resin film to electrotinplate depends on the
guality of the hydrated chromium oxide. The hydrated chromium
oxide formed by cathodic treatment in an electrolyte, for producing
a tin free steel, has better adhesion to said copolyester resin
film precoated with resin composite compared with that by an
immersion treatment into sodium dichromate solution.
It is desirable in the present invention that the amount
of plated tin in electrotinplate be from O.S to S.6 g/m2. If the
amount of plated tin is less than O.S g/m2, the effect of plated
tin on the corrosion resistance is hardly apparent, despite further
plating process. An amount of above 5.6 g/m2 of tin is not
economical.
- 23 -
2000356
The temperature of the surface treated metal
sheet heated just before the lamination of the
copolyester resin film precoated with resin composite,
is also an important factor. This should be maintained
at the melting point of said copolyester resin film +
50C. If the temperature is above the melting point +
50C, corrosion resistance becomes noticeably poor as
the copolyester resin film deteriorates by post heating
after lamination
The copolyester resin film used in the
present invention cannot be easily recrystallized by
the heating temperature required for curing the color
printing ink or lacquer applied on the metal sheet,
although a non-oriented amorphous copolyester resin
layer is formed by heating. Therefore, the metal sheet
maintains excellent corrosion resistance, even if it is
heated at 160 to 200C. If the lamination of the
copolyester resin film precoated with resin composite
to the surface treated metal sheet is carried out below
the melting temperature of the copolyester resin film
-50C the copolyester resin film is easily peeled off
from the surface of the surface treated metal sheet.
- 24 -
2 0 0 0 3 ~ 6
In the present invention, the method for
heating the surface treated metal sheet to which the
copolyester resin film is laminated is not limited.
However, from the standpoint of
,..~
- 24a -
2~Q35fi
continuous and stable production of the metal sheet at high speed,
conduction heating by a roller heated by induction heating and
induction heating and/or resistance heating which are used for
reflowing electrotinplate in the production process of
electrotinplate, is suitable as the method for heating the surface
treated metal sheet to be laminated. This is because the surface
treated metal sheet can be rapidly heated and the temperature of
the heated metal sheet can be easily controlled. Furthermore, it
is also preferable that heating by rollers heated by hot steam or
heating for preheating the surface treated metal sheet to be
laminated.
The surface temperature of the laminating roller is also
an important factors. The surface temperature of the laminating
roller should be in the range of 80 to 180 C. Below 80C, air
bubbles may easily occur between the copolyester resin film
precoated with resin composite and the surface treated metal sheet,
when the copolyester resin film is laminated to the metal sheet.
On the other hand, at temperatures above 180 DC~ production of the
metal sheet at high speed is prevented, because the copolyester
resin film easily adheres to the laminating roller. The use of a
chromium plated, ceramic or rubber laminating roller is preferable.
A roller made with silicon rubber or fluorine rubber, which are
excellent in heat conductivity and heat resistance, should be
selected.
2~C3~6
Usually, the copolyester resin film is
laminated on the surface treated metal under the
conditions described above, and then the copolyester
resin film laminated metal sheet is gradually or
rapidly cooled. In some applications, where more
severe formability is required, it is preferable to
post-heat the copolyester resin film laminated metal
sheet at a temperature in the range of from the melting
point -80C to the melting point of the copolyester
resin film for 5 to 1000 seconds, in order to improve
the formability of the copolyester resin film laminated
metal sheet. Heating for curing the color printing ink
or lacquer applied on the copolyester resin film
laminated metal sheet before forming is also effective
in improving the formability of the copolyester resin
film laminated metal sheet. Heating to cure the color
printing ink or lacquer applied on the copolyester
resin film laminated metal sheet before forming, is
also effective in improving the formability of the
copolyester resin film laminated metal sheet.
It is considered that this effect depends on
the relaxation of the residual stress of the laminated
copolyester by the post heating. When this post
heating is applied to the copolyester resin film
laminated metal sheet before forming, the laminated
2000356
-
copolyester resin film is not peeled off from the
surface of the metal sheet and cracks in the laminated
copolyester resin film is almost non-existent in
severely formed areas.
~`
`' - 26a -
Z~ 3S~;
The present invention is explained in further detail by
reference to the following examples. These examples do not limit
the scope of the invention.
EXAMPLE 1
A cold rolled steel~strip having a thickness of 0.21 mm
and a width of 300 mm was electrolytically degreased in a solution
of 70 g/l of sodium hydroxide and then pickled in a solution of 100
g/l of sulfuric acid. The steel strip, after being rinsed with
water, was cathodically treated by using an electrolyte containing
60 g/l of CrO3 and 3 g/l of NaF in water under 20 A/d* of cathodic
current density at an electrolyte temperature of 50 C. The
treated steel strip was rinsed with hot water having a temperature
of 80 C and dried.
After that, a biaxially oriented copolyester resin film
produced from a condensation polymerization of ethylene glycol and
polycarboxylic acid consisting of 85 mole % of terephthalic acid
and 15 mole % of sebacic acid having characteristics shown in (A),
which was precoated with a resin composite under following
condition (B), was continuously laminated on both surfaces of the
treated steel strip under the following condition (C).
(A) Characteristics of the employed copolYester resin film
Thickness : 25 ~m
- 27 -
2000356
Melting temperature: 229C
Refractive index in thickness direction: 1.5311
Refractive index in all planar dimensions:
Maximum: 1.6411
Minimum: 1.6210
Type of added lubricant: Silica (SiO2)
Average particle size of added lubricant: 2.0 ~m
Amount of lubricant: 0.07 weight % relative to
the weight of the employed copolyester
(B) Conditions for Precoating of resin composite
to the co~olYester resin film
Composition of precoated material:
Epoxy resin having an epoxy equivalentof 3000:
80 parts
Resol product from paracresol: 20 parts
Drying temperature of precoated resin composite:
100 C
Drying time of precoated resin composite:
10 seconds
Amount of resin composite after drying: 0.2 g/m2
(C) Conditions for lamination of coPolyester resin
film precoated under condition (B)
Method for heating the treated steel strip:
Roller heated by induction heating
., .
- 28 -
2000356
Temperature of the treated steel strip just before
lamination: 200C
Material of laminating roller: Silicon rubber
Surface temperature of laminating roller:
Max. 180C
Method for cooling after lamination: Rapid cooling
Post heating of the laminate: 215C for 1 minute
EXAMPLE 2
Two kinds of biaxially oriented copolyester resin
films produced from a condensation polymerization of
ethylene glycol and polycarboxylic acid consisting of
88 mole % of terephthalic acid and 12 mole % of
isophthalic acid having characteristics shown in (A),
which were precoated with resin composite by the
following condition (B), were simultaneously laminated
on each side of the same treated steel strip as in
Example 1 under the following condition (C).
(A) Characeristics of the emPloYed coPolyester
resin film
Clear film
Thickness: 25 ~m
Meltin~3 temperature: 229C
Refractive index in thickness direction:
1.5405
J~J`
- 29 -
2000356
Refractive indexes in all planar dimensions:
Maximum 1.6500
Minimum 1.6305
Type of added lubricant: Silica (SiO2)
Average particle size of added lubricant:
1.5 ~m
Amount of added lubricant: 0.12 weight % relative
to the weight of the employed copolyester resin
White film
Thickness: 20 ~m
Melting temperature: 229C
Type of color pigment: TiO2
Average particle size of added color pigment:
0.3 ~m
Amount of added color pigment: 15 weight %
relative to the weight of the employed
copolyester resin
(B) Conditions for precoatinq of resin comPosite to
the coPolyester resin films
Composition of precoated material:
Epoxy having an epoxy equivalent of 3000: 70 parts
Resol product from paracresol: 30 parts
Drying temperature of precoated resin composite:
120C
- 30 -
2000356
Drying time of precoated resin composite:
5 seconds
Amount of resin composite after drying: 1.1 g/m2
(C) Conditions for lamination of coPolYester resin
film Precoated under condition (B)
Method for heating the treated steel strip:
Roller heated by induction heating
Temperature of the treated steel strip just before
lamination: 230C
- 30a -
35fi
Temperature of the treated steel strip just before
lamination : 230 C
Material of laminating roller : Silicon rubber
Surface temperature of laminating roller
: Max. 210 C
Method for cooling after lamination : Rapid cooling
Post heating of the laminate : 210 C for 5 minutes
EXAMPLB 3
The same steel strip pretreated as in Example 1 was
electroplated with 2.8 g/m2 of tin by using an electrolyte
containing 80 g/l of SnSO4, 60 g/l of phenolsulfonic acid (60%)
aqueous solution) and 5 g/l of ~-naphthol sulfonic acid in water
under 15 A/dm2 of cathodic current density at an electrolyte
temperature of 40 C. After reflowing of tin and rinsing with
water, the tin plated steel strip was treated by using an
electrolyte containing 30 g/l of CrO3 and 0.3 g/l of H2SO4 in water
under 40 A/dm2 of cathodic current density at an electrolyte
temperature of 50 C. The thus treated electrotinplate was rinsed
with water and dried.
After that, a biaxially oriented copolyester resin film
produced from a condensation polymerization of ethylene glycol and
polycarboxylic acid consisting of 88 mole % terephthalic acid and
12 mole % of sebacic acid having characteristics shown in (A),
- 31 -
~ 200~356
which ~as precoated with resin composite by the
following condition (B), was continuously laminated on
both surfaces of thus treated steel strip under the
following condition (C).
(A) Characteristics of the emPloYed coPolYester resin
film
Thickness: 25 ~m
Melting temperature: 243C
Refractive index in thickness direction: 1.5218
Refractive indexes in all planar dimensions:
Maximum 1.6312
. Maximum 1.6228
Type of added lubricant: Silica (SiO2)
Average particle size of added lubricant: 0.3 ~m
Amount of added lubricant: 0.81 weight % relative
to the weight of the employed copolyester resin
(B) Conditions for precoatinq of resin comPosite to
the coPolyester resin film
Composition of precoated resin composite
Epoxy resin having an epoxy equivalent of 2500:
75 parts
Resol product from paracresol: 25 parts
Drying temperature of precoated resin composite:
75C
,. "
- 32 -
200U356
Drying time of resin composite after drying
:15 sec.
Amount of resin composite after drying: 1.2 g/m2
(C) Conditions for lamination of copolYester resin film
precoated under condition fB)
Method for hea~ing the treated steel strip
: Resistance Heating
Temperature of the treated steel strip just before
lamination : 228 C
Material of laminating roller : Silicon rubber
Surface temperature of laminating roller : 200 C
Method for cooling after lamination: Gradual
cooling
Post heatiffg of the laminate: 220C for 30 seconds
EXAMPLE 4
The same steel strip pretreated as in Example 1 was
electroplated with 1.5 g/m2 of tin by using an electrolyte
containing 10 g/l of SnS04, 20 g/l of phenolsulfonic acid (60%
aqueous solution) and 4 g/l of ethoxylated ~-naphthol in water
under 3 A/dm2 of cathodic current density at an electrolyte
temperature of 45 C. After rinsing with water, the tin plated
steel strip was treated by an immersion into 30 g/l of sodium
dichromate solution for 3 seconds at a temperature of 45 C. The
`_ 2000356
thus treated electrotinplate strip was rinsed with
water and dried.
After that, a biaxially oriented copolyester
resin film produced from a condensation polymerization
of ethylene glycol and polycarboxylic acid consisting
of 80 mole % of terephthalic acid and 20 mole % of
sebacic acid having characteristics shown in (A), which
was precoated with the same resin composite as in
Example 3, was continuously laminated on both surfaces
of thus treated steel strip under the following
condition (C).
(A) Characteristics of the emPloYed copolYester resin
film
Thickness: 25 ~m
Melting temperature: 215C
Refractive index in thickness direction: 1.5100
Refractive indexes in all planar dimensions:
Maximum 1.6211
Minimum 1.6110
Type of the added lubricant: TiO2
Average particle size of added lubricant: 0.5 ~m
Amount of added lubricant: 0.52 weight % relative
to the weight of the employed copolyester resin
(B) Conditions for lamination of copolYester resin
film Precoated under condition (B) of ExamPle 3
- 34 -
~)~35~;
Method for heating the treated steel strip
: Resistance heating
Temperature of the treated steel strip just before
lamination : 234C
Material of laminating roller: Fluorine rubber
Surface temperature of laminating roller: 180C
Method for cooling ~after lamination: Rapid cooling
Post heating of the laminate: 190C for 30 seconds
EXAMPLB 5
. An aluminum strip (JIS 3004) having a thickness of 0.23
mm was cathodically degreased in a solution of 30 g/l of sodium
carbonate. After being rinsed with water, the aluminum strip was
immersed into 5% Alodine 401-41 (Chromate-Phosphate type) solution
made by Nippon Paint Co., Ltd. for 20 seconds at 45C and then
rinsed with water and dried.
After that, the same biaxially oriented copolyester resin
film as shown in (A) of Example 1, which was precoated with the
same resin composite as in (B) of Example 1, was continuously
laminated on both surfaces of thus treated aluminum strip under the
same conditions as in condition (C) of Example 1.
COMPARATIVE EXAMPLE 1
- 35 -
2000356
A biaxially oriented copolyester resin film
produced from a condensation polymerization of ethylene
glycol and polycarboxylic acid consisting of 85 mole %
of terephthalic acid and 15 mole % of sebacic acid
having characteristics shown in (A), which was
precoated with the same resin composite as in Example
1, was continuously laminated on both surfaces of the
same treated steel strip as in Example 1 under the same
condition as in (C) of Example 1.
(A) Characteristics of the emPloYed coPolyester resin
film
Thickness: 25 ~m
Melting temperature: 229C
Refractive index in thickness direction: 1.5334
Refractive indexes in all planar dimensions:
Maximum 1.6473
Minimum 1.6022
Type of added lubricant: Silica (SiO2)
Average particle size of added lubricant: 2.0 ~m
Amount of added lubricant: 0.07 weight % relative
to the weight of the employed copolyester resin
~e
- 36 -
_ 20~03~
COMPARATIVB BXAMPLB 2
A biaxially oriented copolyester resin film
produced from a condensation polymerization of the
ethylene glycol and polycarboxylic acid consisting of
88 mole % of terephthalic acid and 12 mole % of
isophthalic acid having characteristics shown in (A),
which was precoated with the same resin composite as in
Example 1, was continuously laminated on both surfaces
of the same treated steel strip as in Example 1 under
the same conditions as in condition (C) of Example 1.
(A) Characteristics of the emPloyed coPolYester resin
film
Thickness: 25 ~m
Melting temperature: 229C
Refractive index in thickness direction: 1.5110
Refractive indexes in all planar dimensions:
Maximum 1.6720
Minimum 1.6390
Type of added lubricant: Silica
Average particle size of added lubricant: 2.0 ~m
Amount of added lubricant: 0.07 weight % relative
to the weight of the employed copolyester resin
- 37 -
200~356
COMPARATIVE EXAMPLE 3
A biaxially oriented copolyester resin film
produced from a condensation polymerization of ethylene
glycol and polycarboxylic acid consisting of 83 mole %
of terephthalic acid and 17 mole % of isophthalic acid
having characteristics shown in (A), which was
precoated with the same resin composite as in Example
3, was continuously laminated on both surfaces of the
same treated steel strip as in Example 3 under the same
conditions as in condition (C) of Example 3.
(A) Characteristics of the emPloYed coPolYester resin
film
Thickness: 25 ~m
Melting temperature: 212C
Refractive index in thickness direction: 1.5442
Refractive indexes in all directions in the plane:
Maximum 1.6041
Minimum 1.5986
Type of added lubricant: Silica
Average particle size of added lubricant: 2.3 ~m
Amount of added lubricant: 0.07 weight % relative
to the weight of the employed copolyester resin
- 38 -
~ 2000356
COMPARATIV~ EXAMPLE 4
A biaxially oriented copolyester resin film
produced from a condensation polymerization of ethylene
glycol and polycarboxylic acid consisting of 85 mole %
of terephthalic acid and 15 mole % of sebacic acid
having characteristics shown in (A), which was
precoated with the same resin composite as in Example
3, was continuously laminated on both surfaces of the
same treated steel strip as in Example 4 under the same
conditions as the condition (B) of Example 4.
(A) Characteristics of the employed coPolYester resin
film
Thickness: 25 ~m
Melting temperature: 215C
Refractive index in thickness direction: 1.5311
Refractive indexes in all directions in the plane:
Maximum 1.6331
Minimum 1.6098
Type of added lubricant: Silica
Average particle size of added lubricant: 2.9 ~m
Amount of added lubricant: 0.05 weight % relative
to the weight of the employed copolyester resin
- 39 -
200~356
COMPARATIVE EXAMPLE 5
The same biaxially oriented copolyester resin film
as in Example 1, which was precoated with the same
resin composite as in Example 1, was continuously
laminated on both surfaces of the same treated aluminum
strip as in Example 5 under the same conditions as in
Example 1, except the temperature of the treated
aluminum strip just before lamination being 162C.
The formability and the corrosion resistance of
the resultant metal sheet were evaluated by the
following testing methods after the measurement of the
coating weight on the resultant metal sheet by X-ray
fluorescent method. The results are shown in the
Table.
(1) Formability by deep drawing
The resultant metal sheet was cut by a punch
press, to a circular blank having a diameter of 158 mm.
The blank was deeply drawn to form a cylindrical cup at
a drawing ratio of 2.92. The formability of the
resultant metal sheet was evaluated by the degree of
cracks in the copolyester resin film and the degree in
the peeling off of the copolyester resin film in the
formed area and then divided into 5 ranks. 5 was
excellent, 4 was good, 3 was fair, 2 was poor and 1 was
bad.
- 40 -
2000356
~2) Formability by impact bending
The resultant metal sheet was cut to a size of
30 mm x 50 mm. The sample was pre-bent by a rod having
a diameter of 3 mm and was then bent by dropping a load
weighing 2.3 kg from a height of 30 cm. The
formabiiity, by bending the resultant metal sheet, was
evaluated by th~ degree of cracks in the copolyester
resin film in the bent area by use of a microscope. It
was then divided into the 5 ranks, as described above.
(3) Corrosion resistance after cup drawing
The resultant metal sheet was cut by a punch press
to a circular blank having a diameter of 85 mm. The
blank was deeply drawn to form a cylindrical cup at a
drawing ratio of 2.15. The drawn cup was filled with
Coca Cola and stored at 20C. After 3 months, iron
pick-up was measured by using an atomic absorption
method.
- 40a -
2~0~35~
The terms and expression which have been employed are
used as terms of description and not of limitation, and there is
no intention in the use of such terms and expressions of excluding
any equivalents of the features shown and described or portions
thereof, it being recognized that various modifications are
possible within the scope of the invention.
2~)0Q356
. 0 ~
. u~ ~ o _ ~ cn e
~ o ~ ~ _ _ U~
E X
O ~ ~ O . . .
- _ ~o o
o~ o ~ - o o
O .~,~ O.~ ~ o u~ ~ ~ a
8 K ~. ,~
O ~u~a _ ~ o - - ~ N K
a~ C.~ _ _ _ ~ o
U~ oO O O
~ 0_ _~n~D O
t~ ~ O ~ O O ~ N -- -
~ K ' ' o ' ~ ' ~ ~ ~
ow ~a~ L.o ~o . <u-~ ~
o ~ o o _ L~
~ C~J ~N ~ ~ O _ t'~ ''a
o ~_ o ~
e K ' -n u~
o ~ ~n~L o~~ o . . 0 0
_. _ _ ~ ~ C
o U~ o _ o
. ~ ~ ~ _ N -- O
_ OU~
e ~ , O ~ o
o ~ a~~ o ~ o
~ ~ C
0 o o U~ ~
u~ ~ o a~
- _a. o c~ n o
K ~: + - u~ ~ ~ ~
O - -- O
t,~ _ ~ _ ~S - O
O ~ u~
~r o o ~ _ o ~ L~
- ~ U~ O _ _ O U~ U~ O C
K ~ ~ u~
_ _ _ ~ o ~.n .
O O ~ O -- ~
m ~ o _ _ a~ o ~ ~ 3
~ ~ O O _t'~ t.) O
E~ K ~ o
~ cna~ ~o ~o
-- o _ ~
O ~ U~ O_I L. _ _
O~ o ~ U~ o o
cn~ o ~ o - ~ ~ o o
o U~ o U~ O
~ 0 ~ C C
O_ o ~ n o ~ o
O ~ O o o~ ~ ~1
~ ~ ` oo ~ ~ o c
o~ a a co~
-- o ~ 0 _~ CC ~
~ -- -- 3D--~ :J_ L. o
-- e a ~ CL
~ ~~ c~y
~:
O00 ~ -- -- O -- _ __ D7--
ec s~
~J -- ~ ~ ~ D OD O-- ~n
0 ~ 1~ 1 ~ 0
~) 3 -- ~ ' - EEi ~
-- K C ~~ EL- ~ a1
o -- O DO--O ~ E
oe~ aa~,~e sald~es ~o
~aalls le~aw ~IIT~ UTsa.~ sal~JadJd
Ja~sa~odo
-- 4~
