Laminated sheet metal for container manufacture and primer used in conjunction with same

A laminated sheet metal for the manufacture of containers is made from a sheet metal and, a layered thermoplastic resin film wherein the primer resin includes from about 50 to about 98 weight percent of polyamidodicarboxylic acid-modified epoxy resin, from about 2 to about 50 weight percent of curing agent resin, and from about 0.05 to about 10 weight percent of curing catalyst; also disclosed is a primer resin composition for use in the manufacture of laminated sheet metal for use in the manufacture of containers, made from about 50 to about 98 weight percent of polyamidodicarboxylic acid-modified epoxy resin, from about 2 to about 50 weight percent of curing agent resin, and from about 0.05 to about 10 weight percent of curing catalyst.

BACKGROUND OF THE INVENTION 
The present invention relates to a laminated sheet metal used for container 
manufacture and a primer used in conjunction with same. More particularly, 
the present invention relates to a laminated sheet metal and a novel 
primer used to bind a thermoplastic resin film to the sheet metal 
resulting in enhanced processability and corrosion resistance. 
Conventional methods used to produce cans result in two general types. A 
three piece can is known having a can body with a seam on the side. The 
seam is formed by soldering, adhesion, welding or similar processes. A top 
cover and a bottom cover are crimped on to the top and the bottom of the 
can body, respectively. 
A conventional two-piece can has a seamless can body. The seamless can body 
is formed by drawing, deep-drawing with bending, drawing and ironing, 
impact forming (or stamping), and by similar methods. A container having a 
flange with a heat-sealed cover is also known. This known can is used as a 
light-weight container. A drawing process is used to form this 
conventional two piece can from coated metallic foil. 
Metallic materials used for any of the cans above require protective 
coatings on both inside and outside surfaces. This is required to prevent 
corrosion and leaching of the metal. In order to reduce material costs and 
increase productivity, most metallic materials are now pre-coated prior to 
processing the metallic materials into cans. 
Coated metallic materials used to make cans thus require superior endurance 
properties. These coated metallic materials have endurance properties that 
must be maintained in the face of severe processing conditions. Coated 
metallic materials also need superior sealing and corrosion resistance 
properties. 
Generally, prior art methods of manufacturing cans utilize epoxy resins as 
coating materials. The use of epoxy resins is preferred due to their 
corrosion resistance and their ability to adhere to metallic materials. An 
epoxy resin may be used in combination with other curing resins, such as a 
phenol resin. The phenol resin is added to cure the epoxy resin. 
Japanese Laid Open Patent Publications Nos. 59-15458, 1-284431 and 
2-286709, disclose examples of prior art epoxy resins. These disclosures 
include a variety of epoxy resins modified by at least one of an aliphatic 
acid, a dibasic acid, a polyamidodicarboxylic acid and similar acids. 
Conventional processes for metal sheet formation now include the step of 
laminating thermoplastic resin films to metallic materials with a primer, 
instead of coating thermosetting resins directly onto the metallic 
materials. Japanese Laid-open Patent Publication No. 62-10188 discloses 
such a process for use in the packaging industry. 
Similarly, Japanese Laid Open Patent Publication No. 62-10188 discloses a 
process which includes the formation of a layered body. The layered body 
includes a polyester based film thermally adhesed to a metallic foil 
substrate. A thermosetting primer is sandwiched between the foil substrate 
and the film. The polyester based film is heat-sealable. The thermosetting 
primer further includes an epoxy resin component. The epoxy resin 
component includes about 450 to about 5500 units of an epoxy equivalent. 
The epoxy resin component further includes a curing resin component having 
one or more functional groups effective to react with the epoxy resin 
component to form a coating. 
Japanese Laid Open Patent Publication No. 62-10188, further describes a 
thermosetting primer having a gel fraction ranging from about 50 to about 
100 percent. The thermosetting primer is extracted in chloroform at 
60.degree. C. for 60 minutes. In order to improve corrosion resistance 
properties of the layered body the polyester based film is disposed in a 
continuous, unbroken skin thereupon. The thermosetting primer formed from 
the epoxy-phenol resin exhibits improved adherence properties. 
The layered body according to Japanese Laid-open Patent Publication No. 
62-10188 endures severe processing conditions. This includes the retort 
sterilization step required for the canning process. However, the process 
according to Japanese Laid Open Patent Publication No. 62-10188 is plagued 
by numerous drawbacks. Chief among these are leaching of the involved 
metal and under-film corrosion. These difficulties occur when laminating a 
thermoplastic resin film on a metallic sheet containing a epoxy-phenol 
resin primer. 
Forming cans by prior art processes (by stretching, deep-stretching, and 
deep-stretching with thin wall formation at side walls of the container) 
creates products having serious durability limitations. 
Generally, products manufactured according to conventional processes, such 
as drawing or re-drawing yield inferior cans. A major drawback with the 
known processes is that cans are produced having an uneven height, and an 
improperly sized circumference (generally smaller than the desired 
dimension). It is thought that plastic flow of the sheet metal during the 
process is responsible for the uneven height and circumference of cans. 
Further, cans manufactured according to conventional bending and stretching 
processes also have bodies with thinner walls than desired. Such thinner 
walls have low endurance properties and are easily deformed when subjected 
to stresses. 
Finally, in a deep drawing process designed to form cans with thin walls, a 
conventional, epoxy-phenol resin-based primer tends to break and peel off. 
This is again due to the plastic flow of the sheet metal and the poor 
quality of adherence to resin films. Under-film corrosion and the leaching 
of metals are similarly caused by these drawbacks of the prior art. 
Many similar problems exist during the manufacture of cans having 
conventionally known "easy open ends". Generally, scoring and riveting are 
employed during the manufacture of cans having such easy open ends. 
Scoring is used with dies and pre-coated can covers. Riveting is employed 
at the coated can cover to fasten tabs with rivets. The inside surface of 
the processed area tends to be damaged easily. This also results in more 
serious under-film corrosion and leaching problems, as discussed above. 
OBJECTS AND SUMMARY OF THE INVENTION 
The present invention overcomes the problems in the previous practice by 
disposing a layered thermoplastic resin film over a primer resin layer 
consisting of polyamidodicarboxylic acid-modified epoxy resin. This 
approach allows for a more effective and durable chemical structure, which 
results in containers capable withstanding even the most severe of 
industrial conditions. 
Accordingly, it is an object of the invention to provide a laminated sheet 
metal consisting of a sheet metal having a primer resin layer, and a 
layered thermoplastic resin film for container manufacture which overcomes 
the drawbacks of the prior art. 
It is a further object of the invention to provide a laminated sheet metal 
consisting of a sheet metal having a primer resin layer, and a layered 
thermoplastic resin film for container manufacture, wherein the primer 
resin layer has enhanced adherence and coating properties on the 
thermoplastic resin film and the metal substrate, even under severe 
processing conditions. 
It is a still further object of the invention to provide a laminated sheet 
metal consisting of a sheet metal having a primer resin layer, and a 
layered thermoplastic resin film for can manufacture, wherein the primer 
resin layer has enhanced adherence and coating properties on the 
thermoplastic resin film under severe conditions of retort sterilization 
which are included in the canning process. 
Briefly stated, there is provided a laminated sheet metal for the 
manufacture of containers which is made from a sheet metal and, by way of 
a primer resin layer, a layered thermoplastic resin film wherein the 
primer resin comprises from about 50 to about 98 weight percent of a 
polyamidodicarboxylic acid-modified epoxy resin, from about 2 to about 50 
weight percent of curing agent resin, and from about 0.05 to about 10 
weight percent of curing catalyst; also disclosed is a primer resin 
composition for use in the manufacture of laminated sheet metal which is 
for use in the manufacture of containers, the resin is made from about 50 
to about 98 weight percent of polyamidodicarboxylic acid-modified epoxy 
resin, from about 2 to about 50 weight percent of curing agent resin, and 
from about 0.05 to about 10 weight percent of curing catalyst. 
In accordance with these and other objects of the invention, there is 
provided a laminated sheet metal, comprising; a sheet metal, a 
thermoplastic resin film, a primer resin layer being disposed between said 
sheet metal and said thermoplastic resin film, the primer resin layer 
being composed of a primer resin composition and, the primer resin 
composition containing, in weight percent, from about 50 to about 98 of a 
polyamidodicarboxylic acid modified epoxy resin from about 2 to about 50 
of a curing agent resin, and from about 0.05 to about 10 of a curing 
catalyst. 
According to a feature of the invention, there is provided a laminated 
sheet metal comprising; a sheet metal, a thermoplastic resin film, a 
primer resin layer being disposed between said sheet metal and said 
thermoplastic resin film, said primer resin layer being composed of a 
primer resin composition, and said primer resin composition containing, in 
weight percent, from about 50 to about 98 of a polyamidodicarboxylic acid 
modified epoxy resin, from about 2 to about 50 weight percent of a curing 
agent resin, and from about 0.05 to about 10 weight percent of a curing 
catalyst, said polyamidodicarboxylic acid modified epoxy resin includes an 
epoxy skeleton of bisphenol A type, wherein the concentration of said 
polyamidodicarboxylic acid modified epoxy resin per said epoxy skeleton is 
from about 1 to about 10 weight percent. 
According to a further feature of the invention, there is provided a primer 
for use in the preparation of a laminated sheet metal, comprising; from 
about 50 to about 98 weight percent of polyamidodicarboxylic acid modified 
epoxy resin, from about 2 to about 50 weight percent of curing agent 
resin, and from about 0.05 to about 10 weight percent of curing catalyst. 
The above, and other objects, features and advantages of the present 
invention will become apparent from the following description read in 
conjunction with the accompanying tables, in which letters and sample 
numbers designate the involved resins.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention is directed to a laminated sheet metal, consisting of 
a sheet metal having a sheet metal and a coating having at least two 
layers. The two layers include at least a primer resin layer and a 
thermoplastic resin film or layer useful for manufacturing containers. 
The primer layer is composed of a primer composition which includes a 
polyamidodicarboxylic acid modified epoxy resin. This resin has a chemical 
structure having a high molecular weight polyamide chain. The chain is 
bound to an epoxy resin skeleton through an ester group. 
The present inventors have discovered that the enhanced properties of the 
primer layer of the present invention are derived from intrinsic effects 
of the polyamide as a linear polymer. 
Generally, adherence of epoxy resins to metallic substrates or resin films 
is highly problematic. This is because adherence of the epoxy resins to 
metallic substrates substantially deteriorates when the modified epoxy 
resin is a high molecular weight polymer. 
However, the polyamidodicarboxylic acid modified epoxy resin of the present 
invention is an exception to this general rule. The adherence of the 
polyamidodicarboxylic acid modified epoxy resin is enhanced because of its 
excellent hot-melt adhesion. It is likewise noted that the modified epoxy 
resin provides this enhanced hot-melt adhesion both to metallic substrates 
and resin films. 
The primer composition may be combined with a curing agent resin 
(hereinafter curing resin) and a curing catalyst. Combining the curing 
resin, however, and the curing catalyst provides a hard and brittle epoxy 
resin. The primer composition according to the present invention maintains 
superior processability and enhanced adherence under cured conditions. 
The primer composition imparts superior corrosion resistance to the 
metallic substrate. This property results from the plasticization effect 
of the terminal carboxyl groups of the polyamidodicarboxylic acid modified 
epoxy resin. 
The primer resin composition according to the present invention includes 
from about 50 to about 98 weight percent of polyamidodicarboxylic acid 
modified epoxy resin. The primer resin composition further includes from 
about 2 to about 50 weight percent of the curing resin, and from about 
0.05 to about 10 weight percent of the curing catalyst. It is preferable 
that the content of the curing catalyst range from about 0.1 to about 5 
weight percent of curing catalyst. 
The primer layer becomes brittle when the amount of the 
polyamidodicarboxylic acid modified epoxy resin falls below 50 weight 
percent. On the other hand, when the amount of the polyamidodicarboxylic 
acid modified epoxy resin exceeds 98 weight percent, the boundary between 
the primer layer and the metallic substrate becomes weak and easily breaks 
during processing. 
Furthermore, when the amount of the polyamidodicarboxylic acid modified 
epoxy resin exceeds 98 weight percent, the hardness of the resulting 
primer layer is too low. Under these conditions, the primer layer breaks 
down by aggregation and the strength of the primer layer is substantially 
reduced. This reduction in strength, in turn, reduces the adherence and 
corrosion resistance property of the primer layer. 
The primer layer becomes brittle when the amount of the curing catalyst 
exceeds 10 weight percent. The boundary between the primer layer and the 
metallic substrate weakens and breaks during processing when the amount of 
the curing catalyst exceeds 10 weight percent. 
When the amount of the curing catalyst falls below about 0.05 weight 
percent, the hardness of the resulting primer composition is insufficient. 
The primer composition tends to break down by aggregation and the overall 
strength of the primer composition is substantially reduced. These 
conditions, in turn, substantially weaken adherence and corrosion 
resistance of the resulting primer layer. 
It is preferable that the molecular weight of the polyamidodicarboxylic 
acid modified epoxy resin be from about 20,000 to about 100,000 and the 
epoxy equivalent of the polyamidodicarboxylic acid modified epoxy resin be 
from about 2500 to about 8000. 
When the molecular weight and the epoxy equivalent of the 
polyamidodicarboxylic acid modified epoxy resin exceed falls below the 
aforementioned ranges, the toughness of the resulting primer composition 
and resulting primer layer deteriorates substantially. On the other hand, 
when the molecular weight and the epoxy equivalent of the 
polyamidodicarboxylic acid modified epoxy resin exceeds the aforementioned 
ranges, the adherence and corrosion resistance properties of the resulting 
primer composition and primer layer are compromised. 
It is preferable that the polyamidodicarboxylic acid modified epoxy resin 
have an epoxy skeleton of bisphenol A type with from about 1 to about 10 
weight percent of polyamidodicarboxylic acid modifier per skeleton. When 
the amount of the modifier falls below about 1 weight percent per 
skeleton, the toughness of the resulting primer composition and primer 
layer deteriorates substantially. When the amount of the modifier exceeds 
10 weight percent, the adherence and corrosion resistance properties of 
the resulting primer composition and primer layer deteriorate, and the 
glass transition temperature (Tg) also decreases. 
The present invention is described in detail with reference to the 
individual components which form the laminating sheet according to the 
present invention. Described hereinafter, are the individual components of 
the laminating sheet of the present invention. 
Polyamidodicarboxylic Acid Modified Epoxy Resin 
The polyamidodicarboxylic acid modified epoxy resin according to the 
present invention has a chemical structure in which a 
polyamidodicarboxylic acid is bound to an epoxy resin skeleton through an 
ester group. 
The polyamidodicarboxylic acid is a polyamide containing two terminal 
carboxyl groups according to the primer composition of the present 
invention it functions as a modifier. The polyamidodicarboxylic acid is 
formed by the condensation of a dibasic acid and diamine. It is important 
that a carboxyl group is attached to the terminal of the polyamide chain 
so that the high molecular weight polyamide chain can be introduced to the 
epoxy skeleton through an ester group. 
The polyamide chain is prepared using a dibasic acid which may be one of 
aliphatic, alicyclic, and aromatic. Preferably, a dibasic acid having from 
about 4 to about 48 carbon atoms is used. Alternately, a dimeric dibasic 
acid having from about 4 to about 48 carbon atoms may be used. A dimeric 
acid may be obtained from the dimerization of a highly unsaturated 
aliphatic acid. 
Highly unsaturated aliphatic acids include, for example, an aliphatic acid 
obtained from the purification of a plant oil or similar types of oil. The 
plant oils further include one of a drying oil (a natural oil that hardens 
on exposure to air, having unsaturated fatty acids which polymerize on 
oxidation), a semi-drying oil, and similar types of oil. 
Linoleic acid, linolenic acid, and oleic acid are examples of C.sub.18 
ununsaturated aliphatic acids. The dimeric acid according to the present 
invention includes an oligomer (for example, a trimer of an unsaturated 
acid and a monomeric aliphatic acid), in addition to a dimer of an 
unsaturated acid. 
The chemical structure of a dimeric acid varies depending upon the kind of 
the monomeric aliphatic acid and the method used in polymerization. The 
dimeric acids with the structures shown below are known and may be used in 
the present invention. 
##STR1## 
where, R.sub.0 is a --(CH.sub.2).sub.7 COOH group and R.sub.1 is a 
--(CH.sub.2).sub.4 CH.sub.3 group 
##STR2## 
where, R.sub.0 is a --(CH.sub.2).sub.7 COOH group and R.sub.1 is a 
--(CH.sub.2).sub.4 CH.sub.3 group. 
##STR3## 
where, R.sub.0 is a --(CH.sub.2).sub.7 COOH group and R.sub.1 is a 
--(CH.sub.2).sub.7 CH.sub.3 group. 
Referring to The above structures, it is clear that each of the dimeric 
acids contain at least one carbon double bond (C.dbd.C) in its chain. 
Before being used in the present invention, the double bond (C.dbd.C) 
portions may be saturated by hydrogenation in order to maintain their 
aromaticity. 
The diamine for use in the preparation of the polyamidodicarboxylic acid 
includes at least one of aliphatic and aromatic diamines. Aliphatic 
diamines for use in the present invention are exemplified by at least one 
of ethylene diamine, tetramethylene diamine, hexamethylene diamine. 
decamethylene diamine. dodecamethylene diamine, tridecamethylene diamine, 
N-oleyl-1,3-propane aliamine, and related compounds. 
The aromatic diamines include at least one of a p-phenyl diamine, 
bis(4-aminophenyl)methane, 2,2-bis(4-aminophenyl)propane, and similar 
compounds. It is preferred that ethylene diamine and 
bis(4-aminophenyl)methane be used. 
The polyamidodicarboxylic acid is synthesized by polycondensation of the 
aforementioned dicarboxylic acid and diamine using conventional methods. 
Namely, in order to form a polyamidodicarboxylic acid having two terminal 
carboxyl groups, an excessive amount of dicarboxylic acid is reacted with 
a diamine in an inert atmosphere to produce a nylon salt. 
The polyamidodicarboxylic acid modified epoxy resin according to the 
present invention includes an epoxy resin synthesized by the condensation 
of an aromatic diol component, particularly a bisphenol, and an 
epihalohydrin. The bisphenol for use in the constitution of the epoxy 
resin according to the present invention may be a divalent phenol 
represented by the structure below: 
EQU HO--Ph--R--Ph--OH 
where Ph is a phenyl group, more particularly a p-phenyl group, and R is a 
divalent bridging group or a direct bonding. 
In the divalent phenol shown above, where the divalent bridging group 
includes at least one of an alkylidene group represented by --CR.sub.1 
R.sub.2 --, an --O-- group, a --S-- group, a --SO.sub.2 -- group, and a 
--NR.sub.3 -- group. 
Here, the R.sub.1 and R.sub.2 in the alkylidene may be one of a hydrogen 
atom, a halogen atom, an alkyl group with 1 to 4 carbon atoms, and a 
perhaloalkyl group. 
R.sub.3 in the --NR.sub.3 -- may be a hydrogen atom or an alkyl group with 
1 to 4 carbon atoms. Generally, use of at least one of alkylidene groups 
and the ether groups are preferred. 
A suitable divalent phenol is exemplified by 
2,2'-bis(4-hydroxyphenyl)propane which is also known as bisphenol A, 
2,2'-bis(4-hydroxyphenyl)butane which is also known as bisphenol B, 
1,1'-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)methane which is 
also known as bisphenol F, 4-hydroxyphenyl ether, p-(4-hydroxy)phenol and 
related compounds. Bisphenol A is preferred. 
The polyamidodicarboxylic acid modified epoxy resin of the present 
invention may be formed by a direct reaction between the aforementioned 
polyamidodicarboxylic acid and an epoxy resin of the bisphenol type. 
However, in order to effectively synthesize a polyamidodicarboxylic acid 
modified epoxy resin (with the aforementioned desired molecular weight and 
epoxy equivalent under homogeneous conditions), it is preferable to use a 
high molecular weight epoxy resin. The high molecular weight epoxy resin 
is synthesized by reacting a bisphenol with a low molecular weight liquid 
epoxy resin. 
During synthesis of the high molecular weight epoxy resin, 
polyamidodicarboxylic acid is added. Thus, the modification and the 
conversion to high polymer by the polyamidodicarboxylic acid proceed 
simultaneously. 
In general, the low molecular weight liquid epoxy resin for use in the 
aforementioned reaction has an epoxy equivalent of from about 180 to about 
500, and a numerical average molecular weight of about 340 to about 1000. 
Various methods may be used for this reaction. 
For example, the liquid epoxy resin, the bisphenol, and the 
polyamidodicarboxylic acid may be added simultaneously to start the 
reaction. Likewise, the liquid epoxy resin can be reacted with the 
polyamidodicarboxylic acid, followed by the reaction of the semi-solid of 
the resulting epoxy ester with the bisphenol. Moreover, the 
polyamidodicarboxylic acid can be reacted with the bisphenol to form a 
polyamide ester having terminal hydroxyl groups. 
This is then followed by the reaction of the resulting polyamide ester with 
liquid epoxy resin. All of the above mentioned reactions can be carried 
out in a multiple stage fashion. 
The aforementioned reactions can be carried out in an organic solvent 
including at least one of a glycol, glycol ether, glycol ester, acetate, 
alcohol, ketone, and various aromatics. The temperature for this reaction 
may range from about 100.degree. to about 220.degree. C. The presence of a 
catalyst is optional. The catalyst can be one of a hydroxide, a carbonate, 
a sulfonium salt, a chloride, and an amine of alkali and alkaline earth 
metals. 
Curing (Agent) Resin 
According to the present invention, a curing agent resin may be combined 
with the primer composition. This curing resin is a resin which includes a 
reactive functional group. This reactive functional group can react with 
one of an epoxy group and a hydroxyl group of an epoxy resin. 
The curing resin can include at least one of a phenol aldehyde resin, an 
amino resin (such as one of a urea resin, a melamine resin, and a 
guanamine resin), a xylene-formaldehyde resin, an acrylic resin and 
related resins. 
The curing resin may also be a resorcinol type phenol resin. If the curing 
resin is a resorcinol type phenol resin it is preferable that the 
concentration of one of a methylol group and an esterified methylol group 
be from about 50 to about 1000 millimole per 100 g of resin. It is 
preferred to use resorcinol type phenol resin to achieve coating material 
having enhanced physical properties and adhesion properties. 
If the curing agent resin is an aminoaldehyde resin, it is preferable that 
the concentration of one of the methylol group and esterified methylol 
group be from about 50 to about 500 millimole per 100 g of resin. 
If the curing resin is an acrylic resin, the preferred concentration of at 
least one of a carboxylic group, an acid anhydride group, and a hydroxyl 
group ranges from about 10 to about 500 millimole per 100 g of resin. A 
phenol aldehyde resin or amino resin is preferably used as the curing 
agent resin. 
Curing Catalyst 
The primer resin composition according to the present invention contains a 
curing catalyst in addition to the aforementioned components. Although 
both inorganic and organic acids can be used as curing catalysts with the 
present invention, phosphoric acid and toluene sulfonic acid are 
preferred. 
Primer Composition 
The primer resin composition is composed of at least a 
polyamidodicarboxylic acid modified epoxy resin, a curing resin, and a 
curing catalyst. The primer resin composition includes from about 50 to 
about 98 weight percent of polyamidodicarboxylic acid modified epoxy 
resin. The primer resin composition further includes from about 2 to about 
50 weight percent of the curing resin, and from about 0.05 to about 10 
weight percent of the curing catalyst. It is preferred that the primer 
resin composition according to the present invention be used with a 
solution having an organic solvent. 
The organic solvent can include at least one of an aromatic hydrocarbon, a 
ketone, an alcohol, a cellosolve, an ester, a glycol and a glycol ether. 
Examples of an aromatic hydrocarbon include at least one of toluene, 
xylene and similar compounds, while ketones for use in the present 
invention include at least one of an acetone, methyl ethyl ketone, methyl 
isobutyl ketone, cyclehexanone and related compounds. 
Examples of alcohol for use as an organic solvent include one of an 
ethanol, propanol, butanol and related hydroxyl group containing 
compounds, while the cellosolve is exemplified by at least one of a ethyl 
cellosolve, butyl cellosolve, and related glycol ethers. Examples of 
esters for use as organic solvents include at least one of an ethyl 
acetate, butyl acetate and the like. 
The above noted organic solvent can be used alone or together with one or 
more other solvents. 
The solid content of the solution containing the organic solvent preferably 
ranges from about 2 to about 40 weight percent, optimally from about 2 to 
about 30 weight percent. A variety of additives for use in coating can be 
added to the solution containing the organic solvent. Such additives 
include plasticizer, lubricants, pigments, fillers, stabilizers, and the 
like. Optionally, a preliminary condensation can be performed to improve 
the coating properties of the solution. Preliminary condensation of the 
solution containing the solvent helps prevent the solution from thickening 
during storage. 
Laminated sheet metal 
The sheet metal according to the present invention includes a variety of 
surface treated steel sheets. The sheet metal according to the present 
invention also includes sheets of light metals such as aluminum. 
The surface treated steel sheets may be cold stretching steel sheets having 
at least one surface treatment after annealing and secondary cold 
stretching. The surface treatment includes at least one of zinc plating, 
tin plating, nickel plating, electrolytic chromic acid treatment, chromic 
acid treatment, and related plating types. 
An example of a preferred surface treated steel sheet is an electrolytic 
chromic acid treated steel sheet containing from about 10 to about 200 
mg/m.sup.2 of a metallic chromium layer and a chromium oxide layer. The 
chromium oxide content of this layer is from about 1 to about 50 
mg/m.sup.2. Such an electrolytic chromic acid treated steel sheet is 
superior to others in terms of both adherence with coating materials and 
corrosion resistance. 
Another preferred surface treated steel sheet is exemplified by a hard tin 
plate consisting of from about 0.5 to about 11.2 mg/m.sup.2 of tin, 
electroplated on the steel sheet. Chromic acid treatment (with or without 
phosphoric acid) is preferred to give the tin plate is a metallic chromium 
ranging from about 1 to about 30 mg/m.sup.2. 
Other than conventionally known "pure" aluminum sheets, aluminum alloy 
sheets may be used as the light metal sheets to practice the present 
invention. In addition to aluminum, aluminum alloy sheets preferably 
contain from about 0.2 to about 1.5 weight percent of Mn, from about 0.8 
to about 5 weight percent of Mg, from about 0.25 to about 0.3 weight 
percent of Zn, and from about 0.15 to about 0.25 weight percent of Cu. 
Such aluminum alloy sheets exhibit superior corrosion resistance and 
processability. 
According to the present invention, such aluminum alloy sheet are treated 
by chromic acid (with or without phosphoric acid) resulting in a metallic 
chromium content ranging, from about 20 to about 300 mg/m.sup.2. 
Bare metal ranging in thickness from about 0.10 to about 0.50 mm can also 
be used. The preferred thickness of the bare metal varies with the type of 
containers produced according to the present invention. 
The thickness of the bare, surface treated steel sheet preferably ranges 
from about 0.10 to about 0.30 min. The thickness of a bare, light metal 
sheet preferably ranges from about 0.15 to about 0.40 mm. 
According to a feature of the present invention, a thermoplastic resin film 
can be used in the layered laminate. This thermoplastic resin film is at 
least one of a polyolefin resin film, a polyester resin film, a polyamide 
film, a polyvinyl chloride film, a polyvinyliene chloride film and similar 
films. 
The polyolefin resin film includes resin films of polyethylene, 
polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate 
copolymer, ethylene-acrylate copolymer, and reacted films. The polyester 
film is at least one of polyethylene terephthalate, polyethylene adipate, 
polybutylene terephthalate, ethylene-terephthalate/isophthalate copolymer, 
ethylene terephthalate/adipate copolymer, blended copolymer, ionomer and 
similar films. 
Films of nylon 6; nylon 6,6; nylon 11; nylon 12; and comparable nylons can 
also be used for the polyamide film of the present invention. Such a film 
may be one of an original film, a one-directionally drawn film, or a 
two-directionally drawn film. Preferably, the thickness of the film ranges 
from about 3 to about 100/.mu.m. A superior film ranges from about 5 to 
about 50/.mu.m in thickness. Among these films, a two-directionally drawn 
film of polyethylene terephthalate or of a polyethylene terephthalate 
based polyester copolymer is preferable for practicing the present 
invention. 
The primer resin composition is first applied with a viscosity suitable for 
coating. The primer resin coating material is applied to at least one of 
the surfaces of the aforementioned metallic material and the thermoplastic 
resin film. This application can be effectuated by means of roller 
coating, or brush coating. 
Alternately, the primer resin composition may be applied by coater coating 
using a docter coater, an air-knife coater, a reverse coater, or similar 
device, and by spray coating, by static coating, and the like. 
The primer resin composition may be used to form a layered laminate by 
means of hot melt adhesion. This can be accomplished either after drying, 
when the material is no longer tacky, or after curing. In the former case, 
where the uncured primer resin layer is used to form the laminate, the 
primer resin composition is simultaneously cured by heat during hot melt 
adhesion. 
The primer resin composition can be cured at a relatively low temperature 
ranging from about 100.degree. to about 250.degree. C. in a short time. 
For example, at 150.degree. C. (a relatively low temperature), heating for 
between 10 and 100 seconds is sufficient to completely cure the primer 
resin composition. A 200.degree. C. (a relatively high temperature), the 
curing is completed by heating for an even shorter time period--between 1 
and 15 seconds. The step of hot-melt adhesion may be performed by 
conducting heat using heated rollers or similar mechanisms. It may 
likewise be performed with convection of heat using an electrical oven, a 
gas-burning oven, a hot-air oven or related devices. Hot-melt adhesion may 
also be performed using the heat of resistance of the metallic substrate. 
Conventional inductive, induced or guided heating may also be used to 
facilitate hot-melt adhesion. 
The temperature for hot-melt adhesion is based upon the melting point (mp) 
of each involved resin. Preferably, this temperature ranges from about 
100.degree. C. below mp to about 50.degree. C. above mp. 
Described hereinafter is one method of manufacturing containers using the 
laminated sheets of the present invention. 
The method includes cutting the laminated sheet metal into small 
disk-shaped pieces. The disk shaped pieces are then stretched using dies 
and a puncher to form shallow cups having wide mouths. The resulting 
shallow cups are then re-stretched to form deep cups with narrow mouths. 
Enhanced corrosion resistance is obtained with the present invention, even 
when the laminated sheet metal is deformed by stretching. 
Enhanced corrosion resistance was demonstrated although the laminated sheet 
metal of the present invention was subjected to a stretch ratio ranging 
from about 2.0 to about 4.0. Similarly, satisfactory corrosion resistance 
was obtained even when the laminated sheet metal was re-stretched with 
bending and stretching. 
This step, according to the process of the present invention, produces thin 
walled cans having side walls which are about 70 to about 100 percent of 
the thickness of bottom wall. 
The laminated sheet metal according to the present invention is processed 
to form can covers by punching and pressing. The laminated sheet metal is 
further processed to form an easy-open can cover. This involves the step 
of scoring, button formation, and tab disposition after punching and 
pressing. 
The present invention is described by the Examples which follow. These 
examples describe resin synthesis for use in conjunction with the 
laminated metal sheet of the present invention. The methods used for 
measurement and evaluation are described in detail below, prior to 
Examples 1-7 and Comparisons 1-7. 
EXAMPLES 
1. Synthesis of Polyamidodicarboxylic Acid 
947 g of HARIDAIMA/HARIDIMER 300 (a dimeric acid obtained from Harima Kasei 
Kogyo Sha) and 53 g of ethylene diamine were added to a reactor equipped 
with an agitator, a thermometer, a cooler and supplied with nitrogen gas. 
The above components were maintained at 60.degree. C. for 30 minutes under 
flowing nitrogen in order to facilitate a reaction between the above 
components. The temperature of the reactor was then raised to 120.degree. 
C. in 1 hour. The reactor was maintained at 120.degree. C. for 2 hours and 
cooled down to room temperature to produce 968 g of polyamidodicarboxylic 
acid with an amine value of 1 and an acid value of 91. 
The resulting polyamidodicarboxylic acid was diluted with SORUBBESO/SOLVESO 
100 (a hydrocarbon solvent obtained from EXXON) to provide a 50% 
polyamidodicarboxylic acid solution containing 50% solid components. 
To a reactor equipped with an agitator, a thermometer, a cooler and a 
nitrogen gas supply, EPIKOTO/EPICOAT 828 (a liquid epoxy resin obtained 
from Yuka Shell KK), bisphenol A, polyamidodicarboxylic acid solution, and 
SORUBBESO/SOLVESO 100 (a hydrocarbon solvent obtained from EXXON) are 
added in predetermined amounts as listed in TABLE 1. 
TABLE 1 
__________________________________________________________________________ 
Modified Epoxy Resin 
A B C D E F G H 
__________________________________________________________________________ 
Amount 
Used (g) 
Epicoat 828 
638 630 624 644 598 640 623 544 
Bisphenol A 
332 340 340 346 327 330 373 156 
Polyamidodicarboxylic 
60 60 60 20 150 60 0 300 
Acid Solution 
Solveso 100 
80 80 80 100 35 80 110 80 
Reaction 
Conditions 
Reaction Temperature 
160 160 160 160 160 160 160 160 
(.degree.C.) 
Reaction Time 
3 4 7 2 3 2 10 4 
(Hour) 
Charac- 
teristics 
of Resin 
Content of Polyamido- 
3 3 3 1 7.5 3 0 15 
dicarboxylic Acid 
(%) 
Epoxy Equivalent 
3000 
4000 
5000 
3200 
2990 
1400 
33000 
4200 
(g/eq) 
Weight Averaged 
25000 
40500 
65000 
23000 
31000 
15400 
118000 
50000 
Molecular Weight 
__________________________________________________________________________ 
2. Preparation of High Molecular Weight Modified Epoxy Resin 
After adding 0.5 g of ethyl triphenyl phosphonium phosphate, reactions 
under conditions specified in TABLE 1 were conducted. Flowing nitrogen was 
used to give high molecular weight, modified epoxy resins A to H. The 
characteristics of these high molecular weight, modified epoxy resins 
(including the weight averaged molecular weight, the epoxy equivalent, the 
acid value, and the amine value) are summarized in TABLE 1. 
3. Weight Averaged Molecular Weight 
High molecular weight epoxy resin and high molecular weight modified epoxy 
resin samples were dissolved in tetrahydrofuran (THF) to form solutions 
containing 0.3 weight percent of resin. The solution were analyzed by GPC 
using HLC 8020 (a GPC measurement equipment obtained from Toyo Soda Kogyo) 
with an RI detector and a TSK gel G4000HXL/G3000HXL/G2000HXL/G1000HXL 
column at 40.degree. C. 
THF was used as the solvent at 1 ml/min. About 20 microliters of the resin 
solution were analyzed to give a GPC chart. The weight averaged molecular 
weight was determined based on a standard polystyrene reference. 
4. Epoxy Equivalent 
About 4 g of epoxy resin sample was placed in a 100-ml beaker and dissolved 
in about 50 ml of methylene chloride. After adding 10 ml of tetraethyl 
ammonium bromide/acetic acid solution and 2 to 3 drops of crystal violet 
indicator, the solution was titrated by 0.1 N perchloric acid/acetic acid 
solution. The end point of the titration was determined by the color 
change of the indicator. With a blank test run in the same way, the epoxy 
equivalent was calculated from the following formula: 
##EQU1## 
where, W: Weight of sample (g) 
.alpha.: Weight fraction of resin 
V: Volume of 0.1 N perchloric acid/acetic acid solution used in titration 
(ml) 
B: Volume of 0.1 N perchloric acid/acetic acid solution used in blank test 
(ml) 
N: Normality of 0.1 N perchloric acid/acetic acid solution (eq/1) 
F: Factor of 0.1 N perchloric acid/acetic acid solution 
5. Acid Value 
A polyamidodicarboxylic acid sample was dissolved in a mixed solvent 
(tetrahydrofuran (THF)/methylene chloride=1/5), and titrated with 0.1 N 
ethanolic KOH solution using phenolphthalein as indicator. The acid value 
was given by the formula below: 
##EQU2## 
where, A: Volume of 0.1 N ethanolic KOH solution used in titration (ml) 
W: Weight of polyamidodicarboxylic acid sample (g) 
6. Amine Value 
A polyamidodicarboxylic acid sample was dissolved in tetrahydrofuran (THF) 
and titrated with 0.02 N aqueous HCl solution using bromophenol blue as 
indicator. The amine value was given by the formula below: 
##EQU3## 
where, A: Volume of 0.02 N aqueous HCl solution used in titration (ml) 
W: Weight of polyamidodicarboxylic acid sample (g) 
7. Preparation of Phenol Formaldehyde Resin 
One (1.0) mole of bisphenol A and 2.4 moles of formaldehyde from a 37 
percent aqueous solution are added to a reactor. The resulting combination 
is heated to 50.degree. C. with agitation to form a solution. After adding 
0.1 mole of magnesium hydroxide, the temperature is raised to 90.degree. 
C. and kept constant for one hour. 
Subsequently, a mixed solvent consisting of 30 parts by weight of methyl 
ethyl ketone, 20 pans by weight of cyclehexanone, and 50 parts by weight 
of xylene was added to extract the products of the condensation reaction. 
After washing twice with deionized water and removing the aqueous layer, 
the residual water in the oil layer was removed by azeotropic 
distillation. After cooling, a 30 percent solution of phenol aldehyde 
resin was obtained. 
8. Primer 
The 30 percent solution of phenol aldehyde resin (resol type) was mixed 
with the high molecular weight, modified epoxy resins A to H obtained from 
EXAMPLE 1 and curing catalyst according the predetermined ratio shown in 
TABLE 2. A mixed solvent (cyclehexanone: MIBK: MEK=1:1:1) was added to 
give a primer containing 20 weight percent of coating resin components. 
TABLE 2 
__________________________________________________________________________ 
Primer Resin Composition Cola Storage Test 
(Weight %) 37.degree. .times. 1 Year 
Modified Can Body 
Concentration of 
Sample Epoxy 
Phenol Resin 
Curing 
Formation of Laminated 
Adherence 
iron Dissolved 
Corrosion at inside 
Number Resin 
Curing Agent 
Catalyst 
Sheet Metal Body 
(%) Cola (ppm) 
Surface of 
__________________________________________________________________________ 
Can 
Example 
1 Resin A 
48 4 Good 0 0.86 No Corrosion 
48 Observed 
Example 
2 Resin B 
24 2 Good 0 0.12 No Corrosion 
74 Observed 
Example 
3 Resin B 
9.5 0.5 Good 0 0.08 No Corrosion 
90 Observed 
Example 
4 Resin C 
4.8 0.2 Good 0 0.30 No Corrosion 
95 Observed 
Example 
5 Resin D 
19 1 Good 0 0.15 No Corrosion 
80 Observed 
Example 
6 Resin E 
9.5 0.5 Good 0 0.45 No Corrosion 
90 Observed 
Example 
7 Resin B 
24 2 Good 0 0.08 No Corrosion 
74 Observed 
Comparison 
1 Resin B 
70 0 Film Peels Off Due to 
65 -- Corrosion in upper 
30 Aggregation of Primer portion of can. 
Holes formed. No. 
of leaking can 
found: 62/100 
Comparison 
2 Resin B 
3 0 Film Peels Off Due to 
84 -- Corrosion in upper 
97 Aggregation of Primer portion of can. 
Holes formed. No. 
of leaking can 
found: 62/100 
Comparison 
3 Resin B 
20 15 Film Peels Off at 
100 -- Corrosion in upper 
65 Boundary between portion of can. 
Metal and Primer Holes formed. No. 
of leaking can 
found: 62/100 
Comparison 
4 Resin F 
19 1 Film Peels Off Due to 
83 -- Corrosion in upper 
80 Aggregation of Primer portion of can. 
Holes formed. No. 
of leaking can 
found: 62/100 
Comparison 
5 Resin G 
24 2 Film Peels Off at 
100 -- Corrosion in upper 
74 Boundary between portion of can. 
Metal and Primer Holes formed. No. 
of leaking can 
found: 62/100 
Comparison 
6 Resin H 
24 2 Good 0 4.66 Under-film corro- 
74 sion found under 
primer layer inside 
the can 
Comparison 
7 -- -- -- Good 6 9.72 Under-film corro- 
sion found under 
polyester film 
inside 
the 
__________________________________________________________________________ 
can 
However, in EXAMPLE 7, a primer with a predetermined composition shown in 
TABLE 2 was prepared with an additional, preliminary condensation reaction 
at 100.degree. C. for 2 hours. 
9. Can Body Adherence Test 
The adherence of the primer coating film was evaluated by a can body 
adherence test using a cross cut adhesion test. A cutting means was 
centered at a position 30 mm away from the front the flange edge of an 
empty can. Then the primer coating film inside the empty can was crosscut 
to form 100 subdivided square areas. Each square area was 1 mm by 1 mm. 
Subsequently, SCOTCH 610 (TM) (an adhesive tape obtained from 3M) was 
applied to these crosscut areas and peeled off. The percentage of the 
crosscut areas losing their coated film was used to evaluate the can body 
adhesion of the coating material. 
10. Cola Storage Test 
100 cans filled with cola were used per test. The cans were kept at room 
temperature for one week. Subsequently, a steel bar with a diameter of 10 
mm was placed on the bottom of each can and impacted by a weight of 500 g 
falling from a height of 60 mm. Following these steps, the cans were 
stored at 37.degree. C. for one year. After one year, the average amount 
of iron leached out by the cola was measured with 5 cans by atomic 
absorption (AA) and the inside of each can was observed. 
EXAMPLE 1 
Laminated Sheet Metal 
A two directionally oriented polyester film, about 25 .mu.m thick of 
terephthalic acid (PET)--isophthalic acid (I) copolymer (PET:I=88:12) was 
coated by the primer solution set forth in TABLE 2. The film was then 
dried at 100.degree. C. forming a primer-coated film with about 0.6 
g/m.sup.2 of dried primer. 
The primer-coated side of the resulting film was then thermally laminated 
onto both sides of a tin-free steel (TFS) sheet. The tin-free steel (TFS) 
sheet was about 0.165 mm thick, and made up of DR-9 tin-free steel (TFS). 
The resulting film was laminated onto both sides of the sheet at the 
melting point of the polyester film. This was cooled immediately by water 
producing a laminated sheet metal. 
The laminated sheet metal was coated by petrolatum and punched to form a 
disk having a diameter of about 179 mm. Using a conventional method, the 
disk was drawn at about 80.degree. C. with a drawing ratio of 1.56 to form 
a shallow cup. 
The shallow cup which obtained was preheated at 80.degree. C. and re-drawn 
twice to form a deep cup having thin walls. The drawing ratio of the first 
redrawing was 1.37 while the drawing ratio of the second re-drawing was 
1.27. The deep cup having thin walls was about 128 mm tall and about 66 mm 
wide. The deep cup which was obtained was 20 percent thinner than the 
thickness of the original bare metal sheet. 
After doming at 80.degree. C. by a conventional method, the deep cup was 
heat-treated at 220.degree. C. and left to cool at room temperature. After 
trimming the edge of the open end, priming on a curved surface, and 
processing the flange--a two-piece can was obtained. The two-piece can 
which was obtained weighed about 350 g. 
One hundred such resulting cans were filled with cola. The cans underwent a 
storage test, in which they were maintained at 37.degree. C. for one year. 
After one year, the average amount of iron leached out by the cola was 
measured. Similarly, the inside conditions and the leakage of the cans 
were observed. As shown in TABLE 2, no particularly abnormal conditions 
were observed. 
EXAMPLE 2 
Laminated Sheet Metal 
A laminated metal sheet was obtained through the processes described at 
length above (in EXAMPLE 1). The laminated metal sheet had a primer 
composition as shown in TABLE 2. As can be seen in TABLE 2, no 
particularly abnormal conditions were observed following the 1 year cola 
storage test. 
EXAMPLE 3 
Laminated Sheet Metal 
A laminated metal sheet was obtained through the processes described at 
length above (in EXAMPLE 1). The laminated metal sheet has a primer 
composition as shown in TABLE 2. As can be seen in TABLE 2, no 
particularly abnormal conditions were observed following the 1 year 
storage test. 
EXAMPLE 4 
Laminated Sheet Metal 
A primer with the composition shown in TABLE 2 was applied onto the inside 
surface of a tin-free steel sheet to form a 2 .mu.m thick, dry film. Right 
after baking at about 225.degree. C. for about 5 seconds, both sides of 
the tin-free steel sheet were thermally laminated. The two sides of the 
tin-free sheet were thermally laminated by a 25 .mu.m thick, two 
directionally oriented polyester film of terephthalic acid 
(PET)--isophthalic acid (I) copolymer (PET:I=88:12). 
Subsequently, a laminated sheet metal was obtained as fully described in 
EXAMPLES 1-3. As can be seen in TABLE 2, no particularly abnormal 
conditions were observed after the storage test. 
EXAMPLE 5 
Laminated Sheet Metal 
A laminated metal sheet is obtained through the processes described at 
length above (in EXAMPLE 1) having a primer composition as shown in TABLE 
2, and a two directionally oriented polyester film of terephthalic acid 
(PET)--isophthalic acid (I)--polybutylene terephthalate (PBT) copolymer 
(PET:I:PBT--66:9:25). 
As can be seen in TABLE 2, no particularly abnormal conditions were 
observed after the storage test. 
EXAMPLE 6 
Laminated Sheet Metal 
A laminated metal sheet was obtained through the processes described at 
length above (in EXAMPLE 1). The laminated metal sheet had a primer 
composition as shown in TABLE 2. As can be seen in TABLE 2, no 
particularly abnormal condition were observed after the storage test. 
EXAMPLE 7 
Laminated Sheet Metal 
A primer with a composition as shown in TABLE 2 was prepared with an 
additional, preliminary condensation reaction at 100.degree. C. for 2 
hours. Subsequently, a laminated sheet metal was obtained as per the 
processes described in EXAMPLE 3. As can be seen in TABLE 2, no 
particularly abnormal condition were observed after the storage test. 
COMISON 1 
Laminated Sheet Metal 
With a predetermined primer composition, as shown in TABLE 2, a laminated 
sheet metal was obtained by the processes and procedures detailed at 
length in EXAMPLE 1 (above). As can be seen from TABLE 2, during the 
formation of the laminated sheet metal, the primer-coated film was peeled 
off due to the aggregation of primer material. Furthermore, remarkable 
corrosion at the upper portion of the can is observed after the cola 
storage test. Among the 100 cans tested, 62 cans leaked after the storage 
test. The amount of dissolved iron inside the can was not measured. 
COMISON 2 
Laminated Sheet Metal 
With a primer composition as shown in TABLE 2, a laminated sheet metal was 
obtained according to the steps described at length in EXAMPLES 1-3. As 
evident from TABLE 2, during the formation of the laminated sheet metal 
the primer-coated film was peeled off due to aggregation of the primer 
material. Furthermore, remarkable corrosion at the upper portion of the 
cans was observed following the cola storage test. Among the 100 cans 
tested 75 cans leak after the storage test. As above, the amount of the 
dissolved iron inside the can required no measurement. 
COMISON 3 
Laminated Sheet Metal 
With a primer composition as shown in TABLE 2, a laminated sheet metal was 
obtained according to the steps described at length in EXAMPLES 1-3. As 
evident from TABLE 2, during the formation of the laminated sheet metal 
the primer-coated film was peeled off due to aggregation of the primer 
material. Furthermore, remarkable corrosion at the upper portion of the 
cans was observed following the cola storage test. Among the 100 cans 
tested 99 cans leaked after the storage test. The amount of the dissolved 
iron inside the can was not measured for the reasons set forth above. 
COMISON 4 
Laminated Sheet Metal 
With a primer composition as shown in TABLE 2, a laminated sheet metal was 
obtained according to the steps described at length in EXAMPLES 1-3. As 
evident from TABLE 2, during the formation of the laminated sheet metal 
the primer-coated film was peeled off due to aggregation of the primer 
material. Furthermore, remarkable corrosion at the upper portion of the 
cans was observed following the cola storage test. Among the 100 cans 
tested, 68 cans leak after the storage test. Likewise, in this case, the 
amount of dissolved iron inside the can was not measured. 
COMISON 5 
Laminated Sheet Metal 
With a primer composition as shown in TABLE 2, a laminated sheet metal was 
obtained according to the steps described at length in EXAMPLES 1-3. As 
evident from TABLE 2, during the formation of the laminated sheet metal 
the primer-coated film was peeled off due to aggregation of the primer 
material. Furthermore, remarkable corrosion at the upper portion of the 
cans was observed following the cola storage test. Among the 100 cans 
tested 99 cans leak after the storage test. The amount of dissolved iron 
inside the can was not measured for the reasons set forth above. 
COMISON 6 
Laminated Sheet Metal 
With a primer composition shown in TABLE 2, a laminated sheet metal was 
obtained following the above described processes, as set forth in EXAMPLE 
3. As can be seen from TABLE 2, good laminate formation and can body 
adherence were observed during the formation of the laminated sheet metal. 
However, remarkable corrosion on the inside film and the under-film 
corrosion were observed after the cola storage test. Since a significant 
amount of dissolved iron inside the can was detected (4.66 ppm), it was 
determined that these cans are not suitable for use as containers for cola 
or related substances. 
COMISON 7 
Laminated Sheet Metal 
Without primer, both sides of a tin-free steel sheet were thermally 
laminated with a 25 micron thick, two directionally oriented polyester 
film of terephthalic acid (PET)--isophthalic acid (I)copolymer 
(PET:I=88:12). Subsequently, a laminated sheet metal was obtained 
following the processes described at length in EXAMPLE 3. As can be seen 
in TABLE 2, good laminate formation and can body adherence were observed 
during the formation of the laminated sheet metal. 
However, remarkable corrosion under the inside film was observed after the 
cola storage test. Since a significant amount of dissolved iron inside the 
can was detected (9.72 ppm), these cans were likewise determined to be not 
suitable for use as containers for cola or related substances. 
Having described preferred embodiments of the invention with reference to 
the accompanying drawings, it is to be understood that the invention is 
not limited to those precise embodiments, and that various changes and 
modifications may be effected therein by one skilled in the art without 
departing from the scope or spirit of the invention as defined in the 
appended claims.