Note: Descriptions are shown in the official language in which they were submitted.
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PAT 92 354 FILE. ~ttN TH!S ~r1r`~ L L' ~;
7~ TRANSL~ N
22.04.1993
BASF Lacke + Farben Aktiengesellschaft, Munster
Metal sheeting/polyurethane adhe~ive layer/poly-
propylene copolymer pla~tic film co~posite, proce~s for
its production, and its use for the production of
packagi~g container~
. '
The present invention relates to a metal
sheeting/ polyurethane adhesive layer/polypropylene
copolymer plastic film composite in which the adhesive
layer is obtained from a solvent-containing two-
component polyurethane adhesive. The present inventionfurthermore relatec to a process for the production of
the composite and to the use of the composite for the
production of packaging containers.
In the productio~ of a can or a closure for use
as a packaging material, in particular for the packag-
ing of foodstuff B ~ metal sheeting made from tinplate, ;-
chromated steel, such as ECCS (electrolytic chromium-
coated steel~ and aluminum in sheet or tape form are -
coated. The lacquer film acts as a protective coating, ~-
;~25 on the one hand for protecting the metal against attack
by the contents and consequent corrosion and on the
other hand for preventing the contents being affected
by corrosion products from the metal. Naturally, the
lacquer film it~elf, for example through di~solved-out
lacquer constituents, must not affect or impair the
6992
~ 2
contents, neither during the sterilization of the
contents carried out after filling nor during
subsequent storage of the packaged contents, in parti-
cular food~tuffs.
Furthermore, the lacquers must be built up in
such a way that they withstand the mechanical stresses
which occur during further conversion of the coated
sheeting to cans or closures, for example during
shaping, stamping, flanging, creasing etc. of the
sheeting.
In addition, the high solvent emissions during
drying of the lacquer film mean that precautions must
be taken to keep these emissions and the consequent
environmental pollution as low as pos~ible.
An advantageous process for the coating of
metal sheeting employed, in particular, for the
production of foodstuff packaging has proved to be the
coating of metal sheeting with films. Thus,
DE-A 3 128 641, for example, describes a process for
the production of laminates for foodstuff packaging in
which the metal sheeting and a thermoplastic resin film
together with an adhesive based on a carboxyl-
containing polyolefin arranged between these layers is
heated to temperatures above the melting point of the
adhesive and then cooled together with application of
precsure~ producing the metal/plastic composite.
Furthermore, DE-A 2 912 023, GB-A-2,027,391 and
EP-B-31 701 disclose laminates and foodstuff packaging
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containers, in particular bags, produced from these
laminates.
A multiplicity of composites of metal foils
with polyolefin or polypropylene films is known.
Examples of adhesion promoter~ employed are polar-
modified polypropylenes, eg. polypropylenes grafted
with carboxylic acids or carboxylic anhydrides. Com-
posites of this type are described, for example, in
EP-A-101 250 and EP-A-312 306. It is furthermore known
that metal sheeting/polypropylene plastic film compo-
sites can be produced using solvent-containing two-
component polyurethane adhesives. However, the problem
occurs in polypropylene plastic film/metal sheeting
composites that the plastic films bonded to the metal
tend toward stress whitening. Otherwise, polypropylene
plastic films have greater chemicals resistance than
polyethylene plastic films.
The present invention thus had the object, in
particular, of developing polypropylene plastic
film/metal sheeting composites which do not exhibit
stress whitening after shaping to form a packaging
container. In addition, the adhesion of the plastic
film to the metal sheeting should of course be excel-
lent. Naturally, the thermoplastic polypropylene film
should pro~ect the metal in an optimum manner against
attack by the contents and consequent corrosion and
prevent the contents being affected by corrosion
products from the metal. Furthermore, the plastic film
itself, for example through dissolved-out constituents,
- 4 -
should of course not affect or impair the contents,
neither during sterilization of the contents carried
out after filling nor during subsequent storage of the
packaged goods, in particular foodstuffs. In addition,
it should be ensured that the bonding of the plastic
film to the metal sheeting can be carried out at
conventional lamination rates at temperatures above the
melting point of the polypropylene plastic.
Surprisingly, this object is achieved by a
metal sheeting/polyurethane adhesive layer/polypropyl-
ene copolymer plastic film composite in which the
adhesive layer is obtained from a solvent-containing
two-component polyurethane adhesive. The composite is
characterized in that the polypropylene copolymer
plastic film essentially or fully comprises random
polypropylene copolymer obtainable by random copoly-
merization of from 1 to 8% by weight of ethylene and/or
further ~-monoolefins, with the exception of propylene,
and from 99 to 92% by weight of propylene, based on the
total weight of the monomer composition, the
polypropylene copolymer having a molecular weight
distribution MW:Mn in the range from 2 to 8 and a melt
flow index MFI 230C/2.16 kg in the range from 5 to
10 g/10 min, preferably in the range from 6 to
10 g/10 min.
The invention also relates to a process for the
production of the composite and to the use of the
coated metal sheeting for the production of packaging
containers.
'~3~9~ :
The advantages of the metal sheeting/two-
component polyurethane adhesive layer/polypropylene
copolymer plastic film composites according to the
invention are, in particular, that the composites have
no tendency toward stress whitening after shaping to
form a packaging container.
Metal sheeting which is suitable for the pro-
duction of the coated metal sheeting according to the
invention is sheeting having a thickness of from 0.04
to 1 mm made from tin-free steel, tinplate, aluminum
and various iron al oys, which may have been provided
with a passivation coating based on compounds of
nickel, chromium and zinc. Depending on the applica-
tion, metal thicknesses of greater than 1 mm are also
possible.
The metal sheeting is coated with thermoplastic
polypropylene plastic film, the adhesion of the film to
the metal sheeting being accomplished by means of a
polyurethane adhesive.
The thermoplastic polypropylenes used to
produce the plastic film are random polypropylene
copolymers in the form of a film. These may also be
composite films (multilayer films) obtained, for
example, by joint extrusion of the polypropylene random
copolymers.~ Polypropylene films of this type are pro-
duced by known processes (blow processes, chill-roll
processes, etc.) from granules of the polypropylenes.
The polypropylene copolymer plastic film of the
composite according to the invention fully or
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-- 6 --
essentiall~ comprises random polypropylene copolymer
obtainable by random copolymerization of from 1 to 8%
by weight of ethylene and/or further ~-monoolefins,
with the exception of propylene, and from 99 to 92% by
weight of propylene, based on the total weight of the
monomer composition. Examples of further ~-monoolefins
with the exception of propylene are, for example, C4-
to C12- ~-monoolefins, such as 1-butene, 4-methyl-
1-pentene, 1-hexene, 1-n-octene, 1-n-decene and
1-n-dodecene.
The polypropylene copolymer plastic film of the
composite according to the invention is particularly
preferably produced from a propylene copolymer obtained
exclusively from the abovementioned amounts of ethylene
and propylene.
The polypropylene copolymers have a molecular
weight distribution MW:Mn in the range from 2 to 8 and
a melt flow index MFI 230C/2.16 kg in the range from 5
to 13 g/10 min, preferably in the range from 6 to
20 10 g/10 min (measured in accordance with DIN 53 735).
The copolymer can be prepared by the polymeri-
zation process described in DE-A 37 30 022 using a
Ziegler-Natta catalyst system. For example, they are
prepared by the so-called gas-phase polymerization
25 process at temperatures of from 20 to 160C and at a
pressure of from 1 to 100 bar. The molecular weights of
the polymers can be regulated by generally known
measures, for example by means of hydrogen as poly-
merization regulator or by peroxidic degradation.
._.. .. .
.~: ~. : .
213~992
-- 7 --
The plastic films of the composites according
to the invention are preferably obtained from poly-
propylene copolymers prepared by random copolymeriza-
tion of from 2 to 4% by weight of ethylene and from 98
to 96% by weight of propylene, based on the total
weight of the monomer composition, the random copoly~
mers having a molecular weight distribution MW:Mn in
the range from 2 to 5, particularly preferably in the
range from 3 to 4, and a melt flow index MFI
230C/2.16 kg in the range from 5 to 10 g/10 min,
particularly preferably in the range from 7 to
9 g/10 min (measured in accordance with DIN 53 735).
The polypropylene copolymers used in accordance
with the present invention for the production of the
metal/plastic film composites have a melting range of
from about 135C to about 150C (determined by DSC).
They are obtainable, for example, under the trads name
Novolen~ 3225 MCX (BASF AG).
The plastic of the plastic film used in the
composite according to the invention preferably fully
comprises the polypropylene copolymer described above.
However, it is also possible within the scope of the
invention to extrude mixtures of the copolymer
described and small amounts of other thermoplastics,
preferably polypropylenes, to give a plastic film which
can be employed in the composite. It is furthermore
possible to employ multilayer films of said propylene
copolymers which are obtainable by coextrusion.
~,. ~,.,_. .. - - - - - -
3 5 9 ~ 2
- 8 -
~ he thermoplastic polypropylene plastic film of
the composite according to the invention may also
contain conventional additives, such as, for example,
internal and external lubricants, antiblocking agents,
stabilizers, antioxidants, pigments, crystallization
assistants and the like. These additives are employed
in the amounts necessary for preparation, processing,
make-up and use, in the form of powders, dusts, beads
or a concentrate which is incorporated directly into
the polymer. Further details on the amounts convention-
ally employed and examples of suitable additive~ are
given, for example, in Gachter-MUller, Kunststoff-
additive, Carl-Hanser Verlag.
It is particularly advantageous if the thermo-
plastic polypropylene films of the composites containup to 0.5% by weight, based on the total weight of the
film, of erucamide and/or oleamide as lubricant and up
to 0.2% by weight, based on the total weight of the
plastic film, of antiblocking agent, preferably silicon
dioxide, and if desired, antioxidants and, if desired,
further processing stabilizers and further additives.
Preferred antioxidants are phenol derivatives.
Further suitable additives are titanium dioxide,
calcium carbonate, diatomaceou~ earth, metal stearates
and primary and secondary fatty acid amides. Examples
of the W stabilizers employed are W stabilizers of
the HALS type.
The adhesive layer arranged between the poly-
propylene copolymer plastic film and the metal sheeting
~_.. ,, .. .. , . . , . . , . , -
'~ 9 2
g
may likewise contain the abovementioned additives.
However, these are preferably incorporated into the
polypropylene plastic film.
The adhesive layer arranged between the metal
sheeting and the polypropylene copolymer plastic film
is obtained from a two-component, solvent-containing
polyurethane adhesive. Any suitable proce~s can be used
to apply the adhesive to the metal sheeting. The two-
component polyurethane adhesive is applied by
application from solutions in organic solvents. The
solutions generally have an adhesive content of from 5
to 80% by weight. The amount of adhesive applied is
generally from about 1 to 15 g/m2 [sic] of area.
The two-component polyurethane adhesive com-
prises an OH-containing component (I), for example
polyester-polyols, polyether-polyols or low-molecular-
weight polyols, and an isocyanate group-containing
component (II). The two components are mixed with one
another immediately before application to the
substrate.
Component (I) of the 2-component adhesive
preferably comprises polye~ter-polyols. These are pre-
pared by esterifying dicarboxylic acids by means of
excess diols or polyols.
The esterification proceeds at elevated tem-
perature in solution or in the melt. Dicarboxylic acids
and glycols give linear polyesters, while esterifica-
tion in the presence of triols and/or higher-functional
polyols gives polyesters with a certain degree of
~13~992
- 10 --
branching. The polyester-polyols are obtainable by
reacting polycar~oxylic acids or esterification-capable
derivatives thereof, if desired together with mono-
carboxylic acids, polyols, if desired together with
monools, and, if desired, further modifying components.
Examples of suitable polycarboxylic acids are
phthalic acid, isophthalic acid, terephthalic acid,
halophthalic acids, adipic acid, glutaric acid, azelaic
acid, sebacic acid, fumaric acid, maleic acid,
trimellitic acid, pyromellitic acid, tetrahydrophthalic
acid, hexahydrophthalic acid, 1,2-cyclohexanedicar-
boxylic acid, 1,3-cyclohexanedicarboxylic acid,
1,4-cyclohexanedicarboxylic acid, 4-methylhexahydro-
phthalic acid, endomethylenetetrahydrophthalic acid,
cyclohexanetetracarboxylic acid and cyclobutanetetra-
carboxylic acid,
Also suitable are the esterifiable derivatives
of the abovementioned polycarboxylic acids, such as,
for example, their monoesters or polyesters with
aliphatic alcohols having 1 to 4 carbon atoms or
hydroxy alcohols having 1 to 4 carbon atoms. In
addition, the anhydrides of the abovementioned acids,
if they exist, may also be employed.
If desired, monocarboxylic acids may also be
employed together with the polycarboxylic acids;
examples are benzoic acid, tert-butylbenzoic acid,
lauric acid, isononanoic acid and fatty acids of
naturally occurring oils. The preferred monocarboxylic
acid employed i~ isononanoic acid.
~1~6992
Suitable alcohol components for the preparation
of the polyesters are polyhydric alcohols, such as
ethylene glycol, propanediols, butanediols,
hexanediols, neopentyl glycol, diethylene glycol,
cyclohexanediol, cycloh~xanedimethanol, trimethyl-
pentanediol, ethylbutylpropanediol, ditrimethylol-
propane, trimethylolethane, trimethylolpropane,
glycerol, pentaerythritol, dipentaerythritol, tris-
hydoxyethyl [sic] isocyanurate, polyethylene glycol,
polypropylene glycol, if desired together with
monohydric alcohol~, such as, for example, butanol,
octanol, lauryl alcohol, ethoxylated or propxylated
[sic] phenols.
Suitable modifying components are polyiso-
cyanates and/or diepoxide compounds, if desired alsomonoiQocyanates and/or monoepoxide compounds.
Suitable OH components (I) of the two-component
polyurethane adhesive are also polyether polyols, which
are obtainable, for example, by adduction of ethylene
oxide or propylene oxide with suitable polyols.
Suitable isocyanate group-containing components
(II) of the polyureth~ne adhesive are, for example:
aromatic isocyanates, such as, for example, 2,4- and
2,6-tolylene diisocyanate and mixtures thereof,
4,4'-diphenylmethane diisocyanate, m-phenylene,
p-phenylene, 4,4-diphenyl, 1,5-naphthalene, 1,4-naph-
thalene, 4,4-toluidine and xylylene diisocyanate, and
substituted aromatic systems, such as, for example,
dianisidine diiqocyanates, 4,4-diphenyl ether
- `` ~ 9 9 2
- 12 -
diisocyanates or chlorodiphenylene diisocyanates, and
higher-functional aromatic isocyanates, such as, for
example, 1,3,5-triisocyanatobenzene, 4,4',4"-triiso-
cyanattriphenylmethane [sic], 2,4,6-triisocyanato-
toluene and 4,4'-diphenyldimethylmethane 2,2',
5,5'-tetraisocyanate; cycloaliphatic isocyanates, such
as, for example, 1,3-cylocopentane [sic~ diisocyanate,
1,4-cyclohexane diisocyanate, 1,2-cyclohexane diiso~
cyanate and isophorone diisocyanate; aliphatic
isocyanates, such as, for example, trimethylene,
tetramethylene, pentamethylene, hexamethylene and
trimethylhexamethylene l,~-diisocyanate and tris(hexa-
methylene) triisocyanate.
Furthermore, the isocyanate group-containing
component (II) can also be a prepolymer of relatively
high molecular weight. Compounds which may be mentioned
here are adducts of tolylene diisocyanate and
trimethylolpropane, a biuret formed from 3 molecules of
hexamethylene dii~ocyanate, and the trimers of
hexamethylene diisocyante and of 3,5,5-trimethyl-
1-isocyanato-3-isocyanatomethylcyclohexane.
.
The amount of component (II) is selected so
that the ratio between the isocyanate groups of (II~
and the OH groups (I) is generally in the range from
~- 25 1:3 to 3:1. -~
Suitable isocyanate components (II) are, for
:: , - -
example, the isocyanate solutions commercially
available under the name Desmodur0 N and Desmodur~ L
(Bayer AG). Suitable solvents for the isocyanate
~ . ~ ~ . ~ :, . - - : ~ . ,.: ~: ~ - . ::, , : ,
- ~136992
components are, for example, butyl acetate and ethyl
acetate. A further suitable 2-component polyurethane
adhesive is the adhesive obtainable under the trade
name Adcote 549 B/Catalyst F from Morton International
B.V.
The two-component adhesive used is particularly
preferably an OH-containing polyester in which the
carboxylic acid component is essentially or fully
iæophthalic acid and/or terephthalic acid and the
isocyanate component is a polyurethane prepolymer based
on tolylene diisocyanate. The polyester may have been
modified by means of diepoxide and/or monoepoxide
compounds.
The production of the metal sheeting/poly-
urethane adhesive layer/polypropylene copolymer plasticfilm composites i8 a process which i8 known in general
terms. In this process, the two-component polyurethane
adhesive BOlUtion i8 applied to the metal sheeting, and
the polypropylene plastic film produced by extrusion is
laminated onto the heated metal sheeting coated with
the adhesive.
The coating of the metal sheeting or of the
,! ; film!adhesive composite produced generally has a total
dry film thickness of less than 500 ~m, preferably from
;, :: : - - .: ~-
10 to 200;~m and particularly preferably less than
100 ~m. The thickness of the adhesive layer is between
0.5 and 100 ~m. The thickness of the polypropylene film
layer is correspondingly at values between 10 and
499.5 ~m.
-. - ....:.
-` 2~3~92
Finally, it should be pointed out that it is
also possible to coat the metal sheeting on the side
facing away from the contents with a preferably flat,
thermoplastic composite film or alternatively with a
liquid or pulverulent coating composition.
The composites according to the invention are
employed for the production of packaging containers, in
particular for the production of bases and lids of
cans, valve disks or aerosol cans and of closure~. The
closure parts are produced by conventional methods (cf.
for example, VR-INTERPACK 1969, pages 600-606
W. Panknin, A. Breuer, M. Sodeik, ~Abstreckziehen als
Verfahren zum Herstellen von Dosen aus Wei~blech"
[Ironing as a Method for the Production of Cans from
Tinplate], S~EET METAL INDUSTRIES, August 1976
W. Panknin, CH. Schneider, M. Sodeik, ~Plastic Deforma~
tion of tinplate in Can Manufacturing~; Verpackungs-
Rundschau, i~sue 4/1971, pages 450-458- M. Sodeik,
I. Siewert, "Die nahtlose Dose aus Wei~blech" [The
Seamless Can Made from Tinplate]; Verpackungs-
Rundschau, issue 11/1975, pages 1402-1407: M. Sodeik,
K. Haa~, I. Siewert, "Herstellen von Dosen aus Wei~blech
durch Tiefziehen" [Production of Cans from Tinplate by
Deep Drawing], Arbeitsmappe fur den
Verpackungspraktiker, Metalle, Part II, Group 2,
Wei~blech [Tinplate], Serial No. 220.042 to 220.048 in
neue Verpackung 12/87, page B 244 to B 246 and neue
Verpackung 1/88, pages B 247 to B 250).
~ ~.
'~1369~2
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For further details, reference is therefore
made to the literature.
The polypropylene film/adhesive layer/metal
sheeting composites according to the invention no
longer have any significant stress whitening, and in
addition the adhesion between the metal and the
polyurethane adhesive on the one hand and the
~ polypropylene plastic film and/or polyurethane adhesive
on the other hand is extremely good. The polypropylene
outer layer protects the metal very well against attack
by the contents, and effects on the contents by cor~
rosion products from the metal are likewise prevented.
Impairment of the contents by dissolved-out con-
stituents of the polypropylene outer layer film is not
observed during sterilization and storage of the
packaged goods. In addition, the composites according
to the invention can readily be produced since the
bonding (lamination) of the polypropylene plastic film
to the metal sheeting by means of the polyurethane
adhesive at below the melting point of the polypropy-
lene plastic can be carried out at the lamination rates
which are usual in practice.
The invention is described below in greater
~ detail with reference to working examples~
-~ ~ 25 Example 1:
The polypropylene copolymer obtainable under
the trade name Novolen 3225 MCX (BASF AG) is extruded
by flat film die extrusion to give a 200 ~m thick
plastic film. A two-component polyurethane adhesive
-, ~.
,:
- 16 _ ~136~2
(Adcote 549 B/Catalyst F from Morton International
B.V.) is knife-coated onto metal sheeting (12 g
wet/m2), the adhesive-coated sheeting is placed in an
oven (oven temperature 150C), and the pla~tic film is
subsequently laminated at 100C onto the adhesive
before the latter has cured completely. After 5 days,
the adhesion is tested. It is greater than 20 N/25 mm.
After the composite has been stamped to give a
can, no stress whitening is observed.
. - ~
~.,
