Note: Descriptions are shown in the official language in which they were submitted.
39 ~ 59
FIELD OF THE INVENTION
The present invention relates to a method for
producing a surface treated steel sheet covered with a
copolyester resin film. The method comprises laminating the
copolyester resin film, precoated on one side with a resin
composite containing in its molecular structure at least one
radical such as epoxy radical or hydroxyl, to both sides of
a surface-treated steel sheet such as tin-free steel and
electrotinplate which has been heated to a temperature of
the melting point of said copolyester resin film + 50~C.
The side of said copolyester resin film precoated with said
resin composite contacts the surface-treated steel sheet.
BACKGROUND OF THE INVENTION
At present, metal sheets such as electrotinplate,
tin-free steel and aluminum sheets are widely used for can
stock after coating with lacquer one or several times. The
lacquer coating is disadvantageous from the standpoint of
energy cost because a long time is required for curing the
lacquer and a large volume of solvent discharged during
lacquer curing must be burned in another furnace in order to
prevent air pollution.
*
1339459
Recently, the lamination of thermo,; _stic resin
film on a metal sheet was attempted in order to avert these
problems. For example, the methods shown in Laid-Open
Japanese Patent Application No. Sho 53-141786, Japanese
Patent Publication No. Sho. 60-47103, Laid-Opqn Japanese
Patent Application Nos. Sho. 60-168643, Sho 61-29736 and
Sho 81-149341 have been already known.
Laid-Open Japanese Patent Application No. Sho
53-141786 relates to a metal can produced from a metal sheet
covered with polyolefin resin film by using an
adhesive-containing polyolefin resin modified with a
carboxyl radical. However, this polyolefin film laminated
metal sheet cannot be used for a material for can stock
because the metal sheet can be corroded by the packed
contents as a result of the laminated polyolefin resin film
having poor permeability resistance. Furthermore, even if
the polyolefin resin film laminated metal sheet is used as a
material for can stock, cans having a satisfactory
appearance cannot be obtained because the laminated
polyolefin resin film is melted during heating at the 160~
to 200~C temperatures required for curing printing ink or
coated lacquer.
1~39459
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
to above the melting point of said polyester resin film and
thereafter immediately quenching the laminate. In this
patent, the crystalline polyester film is sufficiently
adhered to the metal sheet by an amorphous non-oriented
polyester resin film which 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
laminated metal sheet according to said patent is reheated
to the temperature of 160~ to 200~ C for 10 to 30 minutes
required for curing the printing ink or lacquer placed on
the other side of the metal sheet before forming, adhesion
of the polyester resin film becomes noticeably poor because
the amorphous non-oriented polyester resin film is
recrystallized upon reheating. Therefore, the filiform
corrosion resistance becomes also poor.
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
1339459
laminated with a thermoplastic resin film, such as
polyethylene terephthalate resin film without any adhesives
and 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 temperature of 160~ to 200~ C for 10 to 30
minutes required for curing the printing ink or lacquer on
the outside of the DI can, the adhesion of the polyester
resin becomes noticeably poor.
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 to 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, because-the lamination of biaxially oriented
polyester resin film to the metal sheet is carried out
below the temperature of the melting point of said polyester
resin film. Therefore, the corrosion resistance and the
13394~9
adhesion of polyester resin film to the metal sheet does
not deteriorate, even if it is reheated at the
temperature of 160~ to 200~C for the time required for
curing printing ink and lacquer. However, if said
laminated metal sheet is used for some applications in
which 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.
Accordingly, it is a first objective of the
present invention to provide a surface-treated steel
sheet covered with copolyester resin film having
excellent adhesion of copolyester resin film to said
steel sheet and excellent corrosion resistance in a
severely formed part such as a deeply drawn can, a drawn
and partially ironed can, or 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 the continuous
lamination at high speed of copolyester resin film on
both sides of a surface-treated steel sheet.
1339~a9
BRIEF DESCRIPTION OF THE INVENTION
The first objective of the present invention can
be accomplished by the formation on a surface treated
steel sheet of double coating layers consisting of: an
outer layer of a copolyester resin film produced by
stretching and heat setting of a copolyester resin
consisting of 75 to 99 mole % of polyethylene
terephthalate and 1 to 25 mole % of a polyester which is
produced by esterification of at least one saturated
polycarboxylic acid with at least one saturated
polyalcohol; and an inner layer of thin resin composite
containing in its molecular structure at least one
radical, such as an epoxy radical or hydroxyl, on both
sides of the surface treated steel sheet.
The second objective of the present invention can
be accomplished by continuously laminating, at high
speed, said copolyester resin film, precoated with said
resin composite, onto both sides of a surface-treated
steel sheet heated to the temperature of the melting
point of said copolyester film +50~C, with the precoated
side of the copolyester resin film in contact with the
steel sheet
1339~9
The present invention is characterized by the
lamination of the copolyester resin film to both sides of
the surface-treated steel sheet heated to the temperature of
the melting point of said copolyester resin film ~ 50~ C,
said film having been precoated with the thin resin
composite which contacts the surface of the steel sheet.
The copolyester resin film laminated steel sheet
according to the present invention can be used in
applications wherein excellent corrosion resistance is
required after severe forming, such as deeply drawn cans,
drawn and partially ironed cans, and drawn and stretch-
formed cans having high can height and high drawing ratio.
In these applications, the cans are exposed to hot water or
hot steam for sterilization after packing foods such as
fruit juices, coffee beverages, meats and fish, except for
carbonated beverages and beer. For example, fruit juices
are immediately packed in the can after sterilization at a
temperature of 90~ to 100~ C and coffee drinks, meats and
fish are sterilized by hot steam at a temperature above
100~ C in a retort after being packed in the can.
In these applications, color printing or lacquer
coating on one or both sides of the steel sheet used for the
4 5 9
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 the color
printing ink or lacquer and subsequent treatment by
hot water or hot steam.
Generally, the present invention relates to a
method for producing a surface-treated steel sheet
laminated with a copolyester film onto a film which
comprises the steps of (1) producing a copolyester
resin film from a copolyester resin consisting
essentially of 75 to 99 mole % of polyethylene
terephthalate and 1 to 25 mole % of a polyester
resin produced by the esterification of at least one
saturated polycarboxylic acid and at least one
saturated polyalcohol, (2) precoating said
copolyester resin film on one side with a resin
composite containing in its molecular structure at
least one radical selected from the group consisting
of an epoxy radical hydroxyl, an amide radical, an
ester radical, a carboxyl radical, a urethane
radical, an acryl radical and an amino radical, (3)
heating a surface-treated steel sheet to the
temperature of the melting point of said copolyester
film +50 ~C, and (4) laminating said copolyester
resin film onto both sides of said steel sheet
wherein the side of said copolyester resin film
precoated with said resin composite contacts said
steel sheet.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the copolyester
resin film employed is prepared by processing
according to known methods a copolyester resin
1~3~59
consisting of 75 to 99 mole % of polyethylene
terephthalate and 1 to 25 mole % of a polyester
resin which is 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.
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.
- 9a -
13~g~9
Saturated polyalcohols are selected from ethylene
glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,
propylene glycol, polytetramethylene glycol,
trimethylene glycol, triethylene glycol, neopentyl
glycol, 1,4-cyclohexane dimethanol, trimethylol propane
and pentaerythritol.
In some cases, additives such as antioxidants,
stabilizers, pigments antistatic agents and corrosion
inhibitors are added during the manufacturing process of
the copolyester resin film used for the present
invention.
In the present invention, the use of copolyester
resin film which is biaxially stretched and then heat
set is especially desirable from the viewpoint of
corrosion resistance, compared with non-stretched
copolyester resin film.
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, good
corrosion resistance after severe forming of the steel
sheet according to the present invention is not obtained
-- 10 --
1339459
and the continuous lamination of thin copolyester resin
film to the metal sheet becomes noticeably difficult.
The use of copolyester resin film having a thickness
above 50 ~m is not economically suitable for the film to
be laminated to the surface treated steel sheet, because
the copolyester resin film used for the present
invention is expensive as compared with epoxy phenolic
lacquers widely used in the can industry.
In the present invention, the softening
temperature and the melting temperature of the
copolyester resin film are also important factors. The
softening temperature is defined as the temperature at
which the insertion of the needle into the copolyester
resin film starts at a heating rate of 10~C/min. in the
thermal mechanical analyzer (TMA 100) made by Seiko
Denshi Kogyo Co. The melting temperature is defined as
the temperature at which the endothermic peak is
obtained at a heating rate of 10~C/min. in the
differential scanning calorimeter (SS10) made by Seiko
Denshi Kogyo Co.
In the present invention, a copolyester resin
film having a softening temperature of 170 to 235~C and
a melting temperature of 210 to 250~C should be used. A
13~3~59
copolyester resin Lilm having a softening temperature of
above 235~ C becomes poor in formability, and many cracks
occur in the severely formed copolyester resin film. On the
other hand, if a copolyester resin film having a softening
temperature below 170~ C is used, the efficiency in the
production process of deeply drawn cans becomes noticeably
poor because the copolyester resin film soften as a result
of the reheating require to cure color printing ink lacquer
applied to the outside or the inside of the drawn can which
is done at a higher temperature than the softening
temperature of the film.
The use of a copolyester resin film having a
melting temperature above 250~ C is not suitable in the
present invention because such rigid copolyester resin films
show poor formability. If a copolyester resin film having a
melting temperature below 210~ C is applied to the surface-
treated steel sheet, many cracks are observed in the resin
film after severe forming, because the mechanical property
of those copolyester resin films deteriorates upon the
reheating require to cure the color printing ink or lacquer
applied to the outside or the inside of the can.
Furthermore, the mechanical properties of the copolyester
resin film are also very important factors from the
~i339459
standpoint of formability o he copolyester resin film.
Specifically, an elongation at break of the copolyester
resin film, which is determined at the speed of 100mm/min.
at 25~ C in an ordinary tensile testing machine, should be
within the range of 150 to 400 %. If a copolyester resin
film having below 150% of elongation at break is used in the
present invention, many cracks arise in the film after
severe forming, because the formability of said film becomes
noticeably poor. On the other hand, if a copolyester resin
film having above 400 % of elongation at break is used in
the present invention, the film is easily damaged by severe
forming because the thickness of this copolyester resin film
becomes non-uniform during extrusion; in particular, the
film can be easily cut off in the biaxial stretching
process.
In the present invention, one side of the
copolyester resin film described above is precoated with 0.1
to 5.0 g/m2 of a resin composite containing in its molecular
structure at least one radical selected from the group
consisting of an epoxy radical, hydroxyl, an amide radical,
an ester radical, a carboxyl radical, a urethane radical, an
acryl radical and an amino radical. Epoxy resin, phenol
resin, nylon resin, polyester resin, modified vinyl resin,
urethane resin, acryl resin and urea resin are examples of
such resin composites.
~9~59
It is desirable in the present invention that the
resin composite be coated on the one side of the
copolyester resin film as uniformly and thinly as
possible because the bonding strength of the resin
composite layer to the surface-treated steel 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 an amount below 0 1 g/m2 of 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 resin composite layer to the
surface treater steel sheet and the copolyester resin
film becomes noticeably poor in severely formed areas.
It is preferable in the present invention that
the resin composite be diluted with 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 the
resin composite diluted by a solvent which is coated
on the copolyester resin film is also one of the
important factors in the present invention. If the
temperature is below 60~C, a long time is required for
the removal of solvent and the resin composite layer
1~394S9
becomes tacky. When the drying temperature is above 150~ C,
the chemical reaction of resin composite coated on the
copolyester resin film is accelerated, and then the bonding
strength of resin composite layer to the steel sheet becomes
noticeably poor.
It is suitable in the present invention that the
drying time of the resin composite solution coated on the
copolyester resin film be from 5 to 30 seconds at a
temperature of 60~ to 150~ C. If the drying time is less
than 5 seconds, the solvent is not sufficiently removed. On
the other hand, long time drying of more than 30 seconds
results in poor productivity.
In the present inventlon, a solvent having low
boiling point should be used for the dissolution of resin
composite because it is easily removed by heating at 60~ to
150~ C, although the solvent is not otherwise specially
limited. In some cases, a color agent such as a dye may be
added to the resin composite dissolved in a solvent.
As described above, it is suitable in the present
invention for the resin composite to be coated on the
copolyester resin film and, after dissolution of the low
1339~9
boiling solvent for the coated film to be dried at 60~ to
150~ C for 5 to 30 seconds.
The surface-treated steel sheet should be selected
from the group consisting of a double layer tin-free steel
having an upper layer of hydrated chromium oxide and a lower
layer of metallic chromium, electrotinplate covered with the
double layer as described above and electrotinplate
covered with hydrated chromium oxide, because the steel
sheet according to the present invention is contemplated for
use as sanitary food cans. The optimum range of hydrated
chromium oxide and metallic chromium in a tin-free steel is
5 to 25 mg/m2 as chromium and 10 to 150 mg/m2 as chromium,
respectively. If the amount of hydrated chromium oxide is
below 5 mg/m 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 the tin-free steel having about 10
mg/m of metallic chromium can be used for some applications
where mild corrosion resistance is required. The
electrotinplate used in the present invention should be
cathodically treated in an electrolyte for producing an
16
133!~59
ordinary tin-free steel or treated by immersion into a
solution containing about 30 g/liter 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
electrotinplate. It is suitable in the present invention
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 more preferable that the
amount of metallic chromium be 10 to 50 mg/m2 in order to
facilitate high speed production.
In the case of immersion treatment of
electrotinplate into sodium dichromate solution, a thin
layer of hydrated chromium oxide having almost constant
amount ~1 to 4 mg/m2 as chromium) is formed on
electrotinplate. The thin hydrated chromium oxide on
electrotinplate is necessary for excellent adhesion of the
copolyester resin film precoated with said resin composite
in severely formed areas. If electrotinplate is not treated
by immersion into sodium dichromate solution, the adhesion
of the copolyester resin film precoated with resin composite
becomes gradually poorer during storage in an atmosphere
having high humidity. If hydrated chromium oxide having
above ~ mg/m2 as chromium is formed on elect-rotinplate by
~ 1339459
cathodic treatment in sodium dichromate solution, adhesion
of the copolyester resin film precoated with resin composite
becomes noticeably poor in the severely formed areas. It is
considered that the difference in the adhesion of the
copolyester resin film to electrotinplate depends on the
quality of the hydrated chromium oxide. Namely, the
hydrated chromium oxide fonned by cathodic treatment in an
electrolyte for producing a tin-free steel has better
adhesion to said copolyester resin film compared with that
by an immersion treatment into sodium dichromate solution.
It is suitable in the present invention that the
amount of plated tin in electrotinplate be 0.5 to 5.6 g/m2.
If the amount of plated tin is less than 0.5 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 economically preferable.
The temperature of the surface-treated steel sheet
heated just before the lamination of the copolyester resin
film precoated with resin composite, which is also one of
the important factors in the present invention, should be
maintained in the range of the melting point of said
copolyester resin film +50~ C. If the temperature is above
18
1~39~9
the melting point + 50~ C, corrosion resistance becomes
noticeably poor because the copolyester resin film is
deteriorated by heating. The copolyester resin film used in
the present invention cannot be easily recrystallized at the
heating temperature required for curing the color printing
ink or lacquer applied on the steel sheet, although a
non-oriented amorphous copolyester resin layer is formed by
heating. Therefore, the steel sheet according to the
present invention maintains excellent corrosion resistance,
even if it is heated at 160~ to 200~ C. If the lamination
of the copolyester resin film precoated with resin composite
to the surface treated steel sheet is carried out below the
melting point of the copolyester resin film - 50~ C, the
copolyester resin film is easily peeled off from the surface
of the surface-treated steel sheet.
In the present invention, the method for heating
the surface-treated steel sheet to which the copolyester
resin film is laminated is not especially limited. However,
from the standpoint of continuous and stable production of
steel sheets according to the present invention at high
speed, conduction heating by a roller heated by induction
heating, induction heating and/or resistance heating which
are used for reflowing electrotinplate in the production
.. . ..
13~34~9
process of electrotinplate is suitable as the method for
heating the surface-treated steel sheet to be laminated,
because the surface-treated steel sheet can be rapidly
heated and the temperature of the heated steel sheet can be
easily controlled. Furthermore it is also preferable in the
present invention that heating by roller heated by hot steam
or heating in an electric oven be used as an auxiliary
method for preheating~the surface-treated steel sheet to be
laminated.
The surface temperature of laminating roller is
also one of the important factors in the present invention.
The surface temperature of the laminating roller should be
controlled in the range of 80~ to 180~ C. At below 80~ C,
an air bubble occurs easily between the copolyester resin
film precoated with resin composite and the surface-treated
steel sheet during the lamination of the copolyester resin
film to the steel sheet. On the other hand, at a
temperature of the laminating rolls above 180~ C, production
of the steel sheet according to the present invention at
high speed is prevented, because the copolyester resin film
readily adheres to the laminating roller. As the laminating
roller, the use of a chromium plated roller, a ceramic
roller or a rubber roller is preferable in the present
invention. In the use of a rubber roller, a roller made
~3'~9~59
with silicon rubber or fluorine rubber, which is an
excellent in heat conductivity and heat resistance, should
be selected.
The present invention is explained in further
detail by reference to the following examples.
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/liter of sodium hydroxide and then
pickled in a solution of 100 g/liter of sulfuric acid. The
steel strip, after being rinsed with water, was cathodically
treated by using an electrolyte containing 60 g/liter of
CrO3 and 3 g/liter of NaF in water under 20 A/dm of
cathodic current density at an electrolyte temperature of
50~ C. The thus 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 of ethylene glycol and
polycarboxylic acid consisting of 80 mole % of terephthalic
_ .
13~9 459
a~ia and 20 mole % of isophthalic acid having a thickness of
25 um, softening temperature of 176~ C, melting temperature
of 215~ C, and elongation at break of 330%, which was
precoated with resin composite by the following condition
(A), was continuously laminated on both surfaces of thus
treated steel strip under the following condition (B).
(A) Conditions for precoating of resin composite to
the copolyester resin film
Composition of precoated material:
1339459
Epoxy resin having an epoxy equivalent of 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 at 100~ C:
0.2 g/m
(B) Conditions for lamination of copolyester resin film
precoated by under condition (A)
Method for heating the treated steel strip:
Roller heated by induction heating
Temperature of the treated steel strip just before
lamination: 185~ C
Material of laminating roller: Silicon rubber
Surface temperature of laminating roller: Max. 154~ C
Method for cooling the laminate: Gradual cooling
1339459
EXAMPLE 2
The same steel strip pretreated as in Example 1
was cathodically treated in an electrolyte containing 80
g/liter of CrO3, 0.8 g/liter of HBF4 and 0.5 g/liter of
H2SO4 in water under 50 A/dm2 of cathodic current density at
an electrolyte temperature of 60~ C. The thus treated steel
sheet 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 isophthalic acid having a
thickness of 25 ~m, softening temperature of 192~ C, melting
temperature of 239~ C and elongation at break of 210%, which
had been precoated with resin composite by the following
condition (A), was continuously laminated on both sides of
the thus treated steel strip under the following condition
(B).
(A) Conditions for precoating of resin composite to
the copolyester resin film
Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 3000 -
70 parts
24
1339459
Resol product from paracresol - 30 parts
Drying temperature of precoated resin composite: 120~ C
Drying time of precoated resin composite: 7 seconds
Amount of resin composite after drying at 120~ C:
0.6 g/m
(B) Conditions for lamination of copolyester resin film
precoated by under condition (A)
Method for heating the treated steel strip:
Roller heated by induction heating
Temperature of the treated steel strip just before
lamination: 219 ~C
Material of laminating roller: Silicon rubber
Surface temperature of laminating roller: Max. 176~ C
Method for cooling the laminate: Gradual cooling
1~39~S9
EXAMPLE 3
The same steel strip pretreated as in Example 1
was electroplated with 1.7 g/m2 of tin by using an
electrolyte containing 10 g/liter of SnSO4, 20 g/liter of
phenolsulfonic acid (60% aqueous solution) and 5 g/liter of
ethoxylated ~-naphthol sulfonic acid in water under 5 A/dm
of cathodic current density at an electrolyte temperature
of 40~ C. After rinsing with water, the tin plated steel
sheet was cathodically treated by using an electrolyte
containing 30 g/liter of CrO3 and 0.3 g/liter of H2SO4 in
water under 50 A/dm of cathodic current density at an
electrolyte temperature of 50~ C. The thus treated
electrotinplated 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 90 mole ~ of
terephthalic acid and 10 mole ~ of isophthalic acid having a
thickness of 16 ~m, softening temperature of 212~ C, melting
temperature of 241~ C and elongation at break of 172%, which
had been precoated with resin composite by the following
condition (A), was continuously laminated on both sides of
26
13~g4~9
the thus treated steel strip under the followi..~- condition
(B).
(A) Conditions for precoating of resin composite to
the copolyester resin film
Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 2500 -
70 parts
Polyamide resin (Trade name: Versamide 115) - 30
parts
Drying temperature of precoated resin composite: 80~ C
Drying time of precoated resin composite: 15 seconds
Amount of resin composite after drying at 80~ C: 1.5
g/m2
(B) Conditions for lamination of copolyester resin film
precoated by under condition (A)
Method for heating the treated steel strip:
Roller heated by induction heating
Temperature of the treated steel strip just before
lamination: 255~ C
Material of laminating roller: Fluorine rubber
Surface temperature of laminating roller: Max. 128 ~ C
Method for cooling the laminate: Gradual cooling
27
133g4~9
EXAMPLE 4
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/liter of SnSO4, 60 g/liter of
phenolsulfonic acid (60% aqueous solution) and 5 g/liter of
ethoxylated ~-naphthol sulfonic acid in water under 15
A/dm2 of cathodic current density at an electrolyte
temperature of 45~ C. After reflowing of tin and rinsing
with water, the tin plated steel sheet was treated by
immersion into 30 g/liter of sodium dichromate solution for
3 seconds at a temperature of 45~ C. The thus treated
electrotinplate strip was rinsed with water and dried.
After that, the same biaxially oriented
copolyester resin film as in Example 1 precoated with resin
composite by the following condition (A) was laminated on
the thus treated steel strip under the following condition
(B).
(A) Conditions for precoating of resin composite to
the copolyester resin film
Composition of precoated resin composite;
Copolyester resin (Trade name Vylon 200) -
75 parts
Urethane resin (Trade name Coronate L) - 25 parts
1339459
Drying temperature of precoated resin composite: 80~C
Drying time of precoated resin composite: 20 seconds
Amount of resin composite after drying at 80~C: 2.0 g/m2
(B) Conditions for lamination of coPolyester resin film
precoated bY under condition (A)
Method for heating the treated steel strip:
Roller heated by induction heating
Temperature of the treated steel strip just before
lamination: 215~C
Material of laminating roller: Silicon rubber
Surface temperature of laminating roller: Max. 165~C
Method for cooling the laminate: Gradual cooling
. 29-
133~ iS9
EXAMPLE 5
The same steel strip pretreated as in Example 1
was electroplated with metallic chromium by using a Sargent
bath containing 250 g/liter of CrO3 and 2.5 g/liter of H2SO4
in water under 30 A/dm2 of cathodic current density at a
bath temperature of 55~ C. After rinsing with water, a
chromium plated steel strip was cathodically treated by
using an electrolyte containing 30 g/liter of CrO3 and 1.2
g/liter of NH4F in water under 20 A/dm of cathodic current
density at an electrolyte temperature of 40~ C and then
rinsed with hot water having a temperature of 80~ C and
dried.
After that, a copolyester resin film produced from
a condensation polymerization of ethylene glycol and
carboxylic acid consisting of 96 mole % of terephthalic acid
and 4 mole % of isophthalic acid having a thickness of 30
~m, softening temperature of 235~ C, melting temperature of
250~ C and elongation at break of 155~ precoated with resin
composite by the following condition (A) was continuously
laminated on both surface of the treated aluminum strip
under the following condition (B).
(A) Conditions for precoating of resin composite to
the copolyester resin film
13394~9
Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 3000 -
80 parts
Urea resin - 20 parts
Drying temperature of precoated resin composite: 135~ C
Drying time of precoated resin composite: 10 seconds
Amount of resin composite after drying at 135~ C:
1.5 g/m
(B) Conditions for lamination of copolyester resin film
precoated by under condition (A)
Method for heating the treated steel strip:
Roller heated by induction heating
Temperature of the treated steel strip just before
lamination: 245~ C
Material of laminating roller- Silicon rubber
Surface temperature of laminating roller: Max. 160~ C
Method for cooling the laminate: Rapid cooling
13394~9
COMPARATIVE EXAMPLE 1
A biaxially oriented polyethylene terephthalate
film (Trademark Lumirror made by Toray Co. Ltd.) having
a thickness of 25 ~m, softening temperature of 240~C,
melting temperature of 257~C and elongation at break of
125% precoated with the same resin composite as shown in
condition (A) of Example 1 was continuously laminated on
both surfaces of the same treated steel strip as in
Example 1 under the same condition (B) as in Example 1.
COMPARATIVE EXAMPLE 2
A biaxially oriented polyethylene terephthalate
film (Tradename Enblett made by Unichika Co. Ltd.)
having a thickness of 25 ~m, softening temperature of
238~C, melting temperature of 257~C and elongation at
break of 138~ precoated with the same resin composite as
shown in condition (A) of Example 2 was continuously
laminated on both sides of the same treated steel strip
as in Example 2 under condition (B) of Example 2.
COMPARATIVE EXAMPLE 3
A non-oriented polyethylene terephthalate film
(Trademark Tetoron made by Teijin Co. Ltd.) having a
- 32-
1339~59
thickness of 30 ~m, softening temperature of 242~ C, melting
temperature of 254~ C and elongation at break of 110%
precoated with the same resin composite as shown in
condition (A) of Example 3 was continuously laminated on
both surface of the same treated electrotinplate strip as in
Example 3 under condition (B) of Example 3.
COMPARATIVE EXAMPLE 4
The same copolyester resin film as in Example 2
precoated with the same resin composite as shown in the
condition (A) of Example 2 was continuously laminated on
both sides of the same treated steel strip as in Example 1
under the same condition (B) of Example 2, except for the
temperature of the treated steel strip just before the
lamination.
Temperature of the treated steel strip just before
the lamination: 175~ C
COMPARATIVE EXAMPLE 5
The same polyethylene terephthalate film as in
Comparative Example 1 was laminated on the same treated
steel strip as in Example 5 without the resin composite
1339 159
adhesive under the following conditions:
Conditions for the lamination of polyethylene
terephthalate film
Temperature of the treated steel strip just before
the lamination: 280~ C
Material of laminating roller: Silicon rubber
Surface temperature of laminating roller: Max.
105~ C
Method for cooling the laminate: Rapid cooling
The adhesion of polyester resin film in the
resultant steel sheet was evaluated by the following testing
methods, after the measurement of the coating weight on the
resultant steel sheet by the X-ray fluorescent method. The
results are shown in the Table.
(1) Degree of cracks in polyester resin film after forming
The resultant steel sheet was cut to a circular
blank having a diameter of 140 mm by a punch press after
heating for 10 minutes at 190~ C. The blank was deeply
drawn to form a cup at a drawing ratio of 2.55. After that,
1% of sodium chloride solution was filled in the drawn cup.
The degree of cracks of polyester resin film in the formed
34
1339459
part was evaluated by a current value flowing between an
anode of the steel exposed through cracks of polyester resin
film in said drawn cup and a cathode of stainless steel rod
inserted in said drawn cup at constant voltage of 6.3
volts.
(2) Stretch formability of polyester resin film
The resultant steel sheet was cut to a size of 10
cm (width~ x 30 cm (length) after reheating for 10 minutes
at 190~ C. After that, the sample was stretched by cold
rolling in the transverse direction to the cold rolling
direction of steel strip after coating palm oil on both
sides of the sample. The limiting reduction ratio in which
cracks in polyester resin film on the sample is observed was
determined by the following equation after cold rolling of
several times.
R (%) = x 100
to
where R = limiting reduction ratio (%)
to = thickness of the sample before cold rolling (mm)
t = thickness of the sample after cold rolling (mm)
1339459
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