Note: Descriptions are shown in the official language in which they were submitted.
2 ~
~ugust 8, l99l
BASF Lacko + Farben AG
Profiled-~urface metal-plastic compo~te~_p~oce~es
for their prepar~tion_and_tha u~e o~ th~
composites for producinq packa~ing containers
Th~ pre~ent invention rela~es to a sheet m~tal
10~
¦ having a laminated-on thermoplastic film, the film having
I a repeating pattern of thickenings.
The invention furthermorc relates to proce~ses
for producing tho ~heet metal~, to the thermopla~tic
composite film~ u~ed for coating the sheet metals and to
the U80 of the coated sheet metals for the production of
packaging containers.
A can or a clo~ure for use as packaging matsrial,
in particular for the packaging of food, is produced by
coating sheet metals compoqed of tinplate, chromium-
coated steel such a~ ECCS (electrolytic chromium-coated
stcel) or aluminu~ in the form of panels or in continuous
form. The coatlng act3 a~ a protective layer to protect
the metal from attack by the contents and from the
resulting corro~ion, on the one hand, and, on the other
hand, tojprevent the content9 from becoming affected by
corro~ion products of the metal. Ob~iously, it i8 e~en-
ti~l that the coating itself doe9 not affect or damage
35 Ithe conten~, for example by rel9asing the coating
constituents, either during ~ter~llzation of the content~
ub~equent ~o filling or on sub8equent ~torage of the
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packaged goods, in particular food.
Furthermore, the compoRition of the coatings must
be such that they withstand the mechsnical ~tresses which
occur on further processing of the coated sheet metal to
give cans or closures, for example the proce~ses of
shaping, stamping, flanging, crimping and the like,
applied to the sheet metal.
In the production of lid~ and bases of can~, and
with closures, an additional sealing material i8 needed
to seal either between the metal parts or between metal
and glass, or the like. Thi~ ~ealing iY achieved by
applying a sealant to the coated and already shaped
packaging component~ (base~, lid~, clo~ures) and by
gelation or drying of the sealant at elevated
temperatures.
However, tha production of lids and ba~e~ of
cans, and of closures, con3umes a large amount of energy,
since coating and sealant are eeparately baked. Ow$ng to
the large number of finished lids, bases and closures,
this additional process 9tep al80 represents a con~ider-
able cost element.
Moreover, owing to the high solvent emissions not
only on drying the coating but al80 on drying the seal-
ant, precaution~ must be taken to minimize these emis-
sions and the associated environmental pollution.
A process which h2s proven advantageous forcoating sheet metals, in particular for producing food
packaging, is the film-coating of ~heet metals. For
instance, DE-A-3,128,641 describes a process for the
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preparation of laminates for food packaging in which the
sheet metal and a thermopla~tic reRin film, together with
a carboxyl-cont~ining polyolefin-ba~ed adhesive arranged
between these layer~, are heated to temperatures of above
the melting point of the adhesive and then cooled to-
gether under pressure, the metal-pla~tic composite being
formed by this means.
However, in the production of lids and bases, and
also of closures, even by this procedure, the sealant
mu~t be introduced, in a further process step, into the
previou ly shaped lids and bases and hardened.
Furthermore, DE-A-2,912,023, GB-A-2,027,391 and
EP-B-31,701 have disclosed laminates and food packaging
containers produced from these laminates, in particular,
bags. However, the use of these laminates for producing
closure component~ for packaging container~ is not
described.
EP-B-41,512 then di~closes a process for the
production of containers, in which process laminates are
likewise used, in particular to produce the lids and
ba~e3 of the cans and to produce the valve caps of
aerosol cans. The polymer layer of these laminates then
acts ~imultaneously during the production of the con-
tai.ners as a seal and as a protective layer so that in
this process it is not necessary to apply a sealant to
the clo~ure components. However, this proce~ has the
disadvantage that a very high layer thickne~ of the
laminated-on polymeric layer, about 200 ~m, i8 necessary
to ensure sealing. The high material consumption
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1 a~sociated with this layer thickness lead~ to a pronoun-
ced increase in manufactur~ng co~t3 for the contalnersand is consequently a considerable economic diYadvantage
of thi~ proce~, the more 30 on taking $nto account that
the container3 are high-volum~ ma~3 produced product~.
Patent Application ZA-A-880,198 di~close~, in the
production of cans, ansuring the ~eal of the ~oint
between can body and can lid by in~erting a ~ealing
laminate between lid and body. This proce~s al~o i~ very
~expen~ive ~ince first the laminate~ acting as sealing
Imaterial must be cut to size and mu~t then be fitted into
tha clo~ur~ component.
Finally, EP-B-l67,775 de~cribes a proce~ and an
apparatus for the continuou~ production of ob~ects or
coatings havlng contours of complex ~hapo, for example
for remolding of car tire3, ln which process a liqu~d
material i3 applied between at lea~t two moving, con-
¦tinuous, shaping surfaces and cured. However, the prep-
aration of thermoplastic composite films or ~he applica-
tion of the proces~ for the production of ~heet metals
for use a3 closure component~ of packaging containers is
not de~cribed.
30~ U.S. Patent 3,265,785 describes a process for the
production of closure components and packaging
container~, in which expanding vinyl resin pla~tisol is
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8150 ST 1.91 20090
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introduced, as a sealant, into the preshaped clo~ure
component and is ~haped in such a way that the plasti~ol
layer ha3 an annular (~O-ring~) collar-like thickening.
To perform the sealing function, the plastisol i8 h~ated
to a ~ufficiently high temperature before, during or
after the shaping proce3s, in order to decompose the
foaming agent present in the plastisolO
1o Furthermore, German Laid-Open Application DOS
1,903,783 describe~ a process for coating ub~trate~ with
a thermo-plastic film, the thermo-pla~tic coæting having
~ a pre~elected profile of zones of different thicknes~es.
~his proces~ is used for the production of coated box or
carton blank3 which are used for packing liquid~, for
example, milk or juice. The coated box or carton blanks
have a greater layer thickness in the region of the ~eal~
or weld seams to enable them to ba made leak-proof.
The object of the present invention i9 therefore
to provide coated sheet metals which are suitable for u~e
as a packaging material. In particular, the use of these
coated sheet m~tals as a closure component such as, for
example, can lid, can base, valved cap and screw closure
must allow the packagin~ containers to be produced by
means of a simple and economical process, this process
6160 ST 1.91 200aO
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not having the abovementioned disadvantage~ of the prior
art. Furth~rmore, the~e coated ~heet metal~ must ~ati~ ~ ~6 5 ~ 2 6
1 the abovementioned requirffments concerning mechanical
properties and concerning compatibility with and
protective actlon toward the contents.
Surprisingly, this object i8 achieved by a
thermoplastic composite film comprising at least one
adhe~ion-promoting layer and at least one other
Ithermoplastic layer arranged on the adhesion-promoting
9 layer, wherein the thexmoplastic compo~ite film has
¦ annular or discoid collar-like thickenings of the adhe-
¦ sion-promoting layer and/or top layer and wherein the
15 collar-like thickenings form a pattern, this pattern
recurring in both the tran~ver~e and the longitudinal
directions .
The present invention furthermore provides a
20 sheet metal having the thermopla~tic composite film, a
¦ process for producing the ~heet metals according to the
invention and the use of the sheet metals according to
I the invention for producing packaging container~ and
25l clo~ure component~ of packaging container~.
The advantages of the coated sheet metals accord-
ing to the invention ar~ essentially that they arecomponents of packaging containers 3uch as, for example,
3q lids, bases and closures, it being of particular ad-
vanta~e that the built-in sealing action of the coated
~heet metals allow~ the ~limination of the process step
of applying a sealant, this otherwise being nece3sary in
the production of closure components. The u8e of the
sheet metals which have been coated according to the
invention accordingly allows thc production of packaging
containers using a Rimple and in particular economical
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The subsequent text fir3t explain~ in more deta1l
the materials which ars suitable for the preparation of
the coated sheet metals according to the invention. Thi~
i9 followed by the description of the preparation of the
sheet metals according to the inventi4n.
Sheet metal:
I Sheet metal~ which are suitable for preparing the
10 coated ~heet metals according to the invention are tho~e
having a thickness of 0.04 to 1 mm, compo~ed of tin-free
steel, tinplate, aluminum and variou~ iron alloys, which
may optionally be provided with a pa~ivating layer based
15 on compound~ of nickel, chromium and zinc.
TheYe sheet metals have been coated with one or
more, optionally different, resin layers, it being
essential to the invention that the coated sheet metal
20 has collar-shaped thickenings which as3ume the sea1ing
function.
However, most particular preference is given to
Isheet metals which have been obtained by coating ~heet
25lmetals with thermoplastic composite films which are
composed of at least one adhe~ion-promoting layer and at
lea~t one other thermoplastic layer arranged on the
adhesion-promoting layer.
9160 ST 1.91 20080
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1 Thermopla~tic_top layer of the compoRite films
The thermopla~tic resin film~ or coatings used
according to th~ invention as a top layer include poly-
olefin~, polyam1des, polyester~, polyvinyl chlorite,
polyvinylidene chloride and polycarbonateo, each in th2
form of a film or coating. They also include multilayer
f ilm8 and coatings (composite films and coatings) which
are obtained, for example, by co-extrusion of at leaRt
two of the abovementioned resin3. Tha preferred
thermopla~tic film or thermopla~t$c coating which act~ as
the inmost layer (this is the layer which i~ in contact
with the contents) of the metal-pla~tic compo~ite~
preferably compriRes a film or a coating compo~ed of a
polyolefin, polye~ter or polyamide. Films and coating~ of
this type are known and are commercially availabl~ in
larg~ num~ers.
; Polyolefin films of this type are produced by
known proces~es tfilm blowing, chill roll proceR~ etc.)
25 Ifrom granules of homopolymers of ethylene and propylene
~and from copolyer~. Examples of these are~low dens$ty
- ~ polyethylene (LDP~), medium den~ity polyethylene (MDPE),
~ high densLty polyethylene (HDP~), linear low density and
30 ~ linear very low density polyethylene (LLDPE, VLDP~)
polypropylene, copolymers thereof with ethylene and the
copolymer~ o~ ethylene with one or more comonomer8 from
the group8 compri3ing vinyl e~ters, vinyl alkyl ethers,
unsaturated mono- and di-carboxylic acid~, and ~alts,
anhydrides and ester8 thereof.
These polyolefin~ are commarcially a~ailable, for
example, under the following tradenamess
8160 ST 1.91 20080
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Escorene, Lupolen, Lotader, Lacqtene, Orerac, Lucalen,
Dowlex, Primacor, Surlyn, Admer, Novatex, Sclair "
Stamylan, and so on.
Examples of polyamides which are suitable for the
S top layer are polyamide 6 (polyamide prepared from ~-
aminocaproic acid), polyamide 6,6 (polyamide prepared
from hexamethylenediamine and ~ebacic acid), poly-
amide 66,6 (copolyamide composed of polyamide 6 and
polyamide 6,6), polyamide 11 ~polyamide prepared from ~-
aminoundecanoic acid) and polyamide 12 (polyamide pre-
pared from ~-aminolauric acid or from laurolactam).
Example~ of commercial products are Grilon, Sniamid and
Ultramid.
Preference is given to the use of the following
polyesters: polyethylene terephthalate, polybutylene
terephthalate and polyesters ba~ed on terephthalic acid,
ethylene glycol and butylene glycol. However, other
suitable polyester~ are tho~e based on terephthalic acid,
isophthalic acid and phthalic acid and various polyols
such as, for example, polyethylene glycol and polytetra-
methylene glycols of various degrees of polymerization.
Example~ of suitable commercial products are
Ho~taphan, Melinex and Ho~tadur.
Adhesion-~romoting layer of the thermoplastic compo~ite
~5 film
The polymers used as the adhesion-promoting layer
in the process according to the invention may ~e copoly-
mer~, terpolymers, graft copolymer~ or ionomers, with the
provision that they carry carboxyl or anhydride groups or
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group~ which are hydrolyzable to give carboxyl groups,
and that the melt index of the polymers, measured at
190C and under a load of 2.16 kg is between 0.1 and
30 g/10 min, preferably between 0.2 and 25 g/10 min and
par~icularly preferably between 0.5 and 20 g/10 min.
Suitable copolymers and terpolymers can be
prepared by copolymerization of ethylene with ~ unsatu-
rated carboxylic acids such as, for example, acrylic
acid, methacrylic acid, itaconic acid, crotonic acid,
i~ocrotonic acid, maleic acid and fumaric acid, the
corre~ponding anhydrides or the corre~ponding esters or
semiesters which have 1 to 8 carbon atoms in the alcohol
radical ~uch a~, for example, the methyl, ethyl, propyl,
butyl, pentyl, hexyl, cyclohexyl, heptyl, octyl and 2-
ethylhexyl e~ters of the li~ted acids. Likewise usable
are the corresponding salts of the listed carboxylic
acids, for example the sodium, potassium, lithium,
magnesium, calcium, zinc and ammonium salts. Preference
is given to the use of the carboxylic acids and the
anhydride~ thereof.
Furthermore, it is possible, in the copolymeriza-
tion, to use still other monomar~ which are copolymeriz-
able with ethylene and with the unsaturated carbonyl
compounds. Suitable examples of these are -olefins
having 3 to 10 carbon atoms, vinyl acetate and vinyl
propionate.
The amounts of monomers used in thi~ copoly-
meri~ation are sslected 80 that the resulting polymer ha~
a carboxyl content of 0.1 to 30 % by weight, preferably
lo- 2~
2 to 20 % by wsight, and the proportion of ethylene units
in the polymer is between [lacuna] 99.9 % by weight,
preferably between 75 and 95 % by weight.
Suitable graft copolymers can be prspared by
grafting at lea~t one polymer from the group comprising
polyolefins, with up to 10 ~ by weight, preferably up to
5 ~ by weight, relativa to the total weiqht of monomer~
of at lea~t one monomer from the group compri3ing ~
unsaturated carboxylic acids, or anhydrides, esters or
salt~ thereof in the presence or absence of peroxides.
Example~ of suitable polyolefins are those polyolefins
which have already been li~ted in the description of the
top layers on page 6 of this description. Examples of
suitable carbonyl compounds are the carbonyl compounds
which have been listed above in tha description of the
copolymer-based adhesion-promoters.
The ionomers used a3 the adhe~ion-promoting layer
can be prepared by the already abovementioned copolymer-
ization of ethylene and optionally other monomers with
salts of ~,~-unsaturated carboxylic acids or by partial
neutralization of the already abovementioned carboxylic
acid-containing copolymers, terpolymers and graft poly-
mers with salts, oxides and hydroxide~ of sodium, potas-
~ium, lithium, magnesium, calcium, zinc and ammonium.
Thi3 neutralization can be carried out in the melt or in
solution. In carrying out this neutralization, the amoun~
of ba~ic compound i~ ~elected 80 that the degree of
neutralization of the polymer i8 between~ 0.1 and 99 %,
preferably between 0.1 and 75 % and mo~t particularly
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preferably between 0.1 and 40 ~.
Not only the adhe~ion-promoting layer but also
the thermoplastic top layer may contain other customary
additive~ such as, for example, internal and external
lubricants, antiblocking agents, ~tabilizers, antioxid-
ants, pigments, crystallization auxiliarie~ and the like.
These additive~ are used in the amounts nece~sary for
preparation, processing, conversion and use, in the form
of pulverulent materials, powder~, beads or in the form
of a concentrate which has been directly incorporated in
the corresponding polymer. Further details concerning the
amounts customarily used and examples for suitable
additives are given, for example, in G~chter-M~ller,
gunststoffadditive, Carl-Hanser Verlag. The~e additiveR
are preferably incorporated in the top layer.
Preparation of com~o3ite films havina a textured surface:
There are various methods of preparation for the
textured-surface composite films composed of the mater-
ials ju~t described:
1.) Monofilms or composite films are prepared by ext-
rusion through flat film die~ or annular dies. These
flat films are then shaped by the application of
heat and pressure 80 that one surface of the film i8
flat and the other surface has the collar-shaped,
preferably periodically recurring, thickenings
according to the invention. This ~haping can be
introduced by mæans of a mask which is laid on the
film or by mean~ of a profiled platen which is laid
on the film, with the use of a press or a roll.
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Preference i~ given to the use of roll~ since in
thi~ way it is pos~lble to continuously produce the
textured film. Obviou ly, it i~ al~o possible to use
presses having a profiled platen, prsferably having
an interchangeable, surface-textured press platen,
and rolls having a - preferably interchangeable -
textured surface. Moreover, it is preferable if the
pres~ or the roll i tsmperature-controllable,
preferably heatable, so a~ to shape the film at the
required temperature. The temperature used for the
shaping operation i~ obviously dependent on the
applied pressure of the roll or press and i~ gene-
rally between 50C and the melting point of the
film, the temperature being correspondingly higher
the lower the pressure. The applied pressure i8
generally between 1 and 400 bar.
A film which has been textured in this manner i~
then ~oated with an adhesion-promoter or with a
coextruded laminar polymer composite having identi-
cal or different adhesion-promoter~ on the two
~urfaces of the polymer composite, in the form of a
film or a melt. ~he temperature for this operation
is selected 80 that the adhesion-promoter forms a
firm and stable bond with the textured monofilm and
composite film, without the textured film ~elting
or losing its embossed structure.
2. In a similar manner to the process which ha~ just
been described, it is also pos~ible to shape a flat
monofilm or composite film using a press or rolls
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in such a way that one curf ace has the collar-
shaped, preferably periodically recurring, thicksn-
ing~ according to the invention (positive profile),
while the other surface hac the corresponding
S geometrical pattern in negative profile, i.e. in the
form of depressions. This textured film is then
likewise coated on ~he negative side, by the proce-
dure of procecs 1 with an adhesion-promoter 80 that
the embo-~sed tructure (positive side) is retained.
3. Besides the multi-stage processes 1 and 2, the
thermopla~tic composite film can also be prepared
by extruding a ~in the ca~e of a monofilm) polymer
or a plurality (in the case of composite films) of
polymers using one or more extruders through a flat
film die, a dual slit die or a feed block die
directly onto a thermostatically controllable roll
having a - preferably interchangeable -textured
surface and thus directly producing a film having a
textured surface. This i8 followed by lamination,
lining or coating with an adhesion- promoting film,
an adhesion-promoting melt or with an optionally
molten, laminar polymer composite film, care being
taken to ensure that the surface texture of the
thermoplastic layer i8 retained. ~his application of
the adhesion-promoting layer can be carried out
either onto the molten, smoothed, surface of the
thermoplastic top layer on the reverse side of the
taxtured surface, in the vicinity of the surface-
textured roll or onto the ~moothed, cooled surface
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of the top layer. This gives thermopla~tic compo3ite
film-Q corre~ponding to tho e films wh~ch were
prepared in accordance with process 1.
4. The thermoplastic textured-surface composite film
S can al~o be prepared by coextruding the thermoplas-
tic top layer together with the adhe~ion-promoting
layer through flat film dies or annular die~. The
resulting, flat thermopla~tic compofiite film i8 then
shaped usins the apparatuseY described in proce~s 1,
80 that one surface is flat and the other surface
has the collar-~haped, preferably recurring, thick-
ening~ according to the invention.
5. However, it i~ also possible to bond a flat thermo-
plastic monofilm, or a composits with an adhesion-
promoting layer or a polymer composite in which at
least one ~urface consists of an adhe~ion-promoting
layer, and to shape the re~ulting flat thermoplastic
composite film by the procedure of proces~ 4 80 that
one surface is flat and the other ~urface has the
collar-shaped, preferably periodically recurring,
thickenings according to the invention.
Thermop~astic textured-surface composite films in which
at l~ast one layer consists of a foamed plastic
In the process according to the invention, it is
also pos~ible to use textured-surface thsrmoplastic
compo~ite films in which at leaat one layer consists of
a foamed plastic. Composita films of this type can be
prepared, for example, by the follo~ing processess
- I. A polymer is melted in an extruder in the presence
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of a chemical (thermally decompo~ing compound such
aq, for example, azodicarbonamide, ~odium dicarbon-
ate) or of a physical blowing aqent (blowing gases
such as, for example, freon, carbon dioxide, butane)
5and is extruded onto a temperature-controlled roll
having a - preferably interchangeable - textured
surface. If necessary, the non-textured surface of
the foam film is smoothed with a knife or a roll and
then an adhe~ion~promoting film or a polymer com-
10posite film which has, at least on one surface, an
adhe~ion-promoting layer i laminated or extruded
onto the polymer film.
II. a) Similarly to proce~ l, a polymer i~ melted in an
extruder in the presence of a chemical or physi-
lScal blowing agent and extruded onto a smooth roll
and then, optionally aftar subsequent smoothing
- of the surface, i8 coated 3Lmilarly to process I
with an adhesion-promoting layer or a polymer
CompositQ film.
20This untextured, flat composite film iq then,
as described in the film preparation according to
process l, shaped between pres3es or ralls which
are heated on one or both sides, resulting in a
composite having coll2r-shaped thickenings on the
25foamed surface layer.
II. b) A composite film having at lea~t one ~urface
composed of an adhesion-promoter or an adhesion-
promoting film is coated with expandinq polymer
fil~. The foamed surface layer i3 shaped on
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pre~se~ or roll~ a~ de~cribed in II a).
II.c~ A coextruded composlte film having a foamed
: surface layer and an adhesion-promoter a the
second surface is ~haped betwean presse~ or xolls
which are heated on one or both ~ides re~ulting
in a composite having collar-shaped thickening~
on the foamed surface layer.
III. A composite film corresponding to the composite film
prepared according to process II i~ prepared by
first shaping a flat thermoplastic foamed monofilm
or composite film having at least one foamed surface
layer between temperature-controlled rolls (for
example an embos~ing unit) having a textured surface
on one or both sides, this re~ulting in a film
having the collar-~haped thickenings according to
the invention on the foamed surface layer, and then
applying the adhe3ion-promoting layer or a composite
having at lea3t one adhesion-promoting layer on the
surface to the non-textured surface in such a way
that the textured surface i~ retained.
IV. The depressions of a temperature-controllable
roll (W) are filled with an expanding re~in and
excess material is ramoved u~ing a knife or a roll.
Immediately afterwards, a pre-heated laminating film
or a melt film composed either of an adhasion-
promoter or of a coextruded polymer composite having
an adhesion-promoting layer on at lea~t one of its
surfaces is pres~ed on by means of a roll. After
being partially wrapped around the roll (W) in the
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range of 40 to 90 ~ of the circumferenc~ of the
roll (W), the composite is drawn off.
Production_of textured-surface metal-plastic composi5es
The sheet metal is covered with the textured-
surface thermoplastic composite film which has beendescribed by bringing into contact the adhe~ion-promoting
layer of the composite and the metal surface. The
application of pressure and heat either by means of a
temperature-controllable pre~ or in the nip of a roll
mill or calender using temperature-controllable roll3
gives the metal-pla~tic composite. In this procedure, the
pressure and the temperature must be ~elected 80 that, on
the one hand, the adhesion-promoter forms a firm and
stable bond to the metal foil or ~heet metal and, on the
other hand, the thermoplastic top layer does not melt or
105e its embossed texture.
Besides this process for the production of the
structured-surface metal-plastic composites, it is also
possible first to produce a composite from a sheet metal
and a flat thermopla~tic composite film and then to shape
this metal-plastic composite 80 that the top layer
consisting of the thermoplastic material has collar-
shaped thickening~ which preferably form a geometrical
pattern, this pattern preferably recurring in both the
transverse and longitudinal directions.
Finally, it i8 al~o possible to coextrude the
thermopla3tic composite film directly onto the sheet
metsl and, subsequent to the coextrusion, to directly
shape the re3ulting composite so that the top layer
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1 con~i~ting of the thQrmoplastlc material has collar-
~haped thickenings whic~ preferably fonm a geometrical
pattern, this pattern preferably recurring in both the
5 transver~e and longitudinal d~rections.
The apparatu~os u~ed to ~hape the me~al-plastlc
compo~ites are identical with the apparatu~es for prepar-
ing the profiled-surfac~ composits fil~. Consequently,
reference i3 merely made at this point to page~ 10 - 16
of the pre~ent de~cription.
Moreover, the sealant~ may al90 be applied in the
form of lamlnates to the ~heet metals which have been
coated but not yet shaped into closure components.
In these production methods for the coated ~heet
metal~ according to the invention, the top layer may also
.
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con3ist of a foam~d polym~r. 2 ~ 2 6
1 Th~ coating of the sheet metal or the
thermoplastic composite film generally ha~ an overall try
film thickn~ss (without thic~nings) of la~ than 500 ~m,
preferably lO to 200 ~m and particularly preferably le~
th~n lO0 ~m. The thickne3s of the adhesion-promoting
layer in the case o~ the compo~ite films i~ ~tween 0.5
and lO0 ~m. The thicknes3 of the top layer is
10 corre~pondingly
Ibetween lO and 499.5 ~m. A~ already mentioned, it
is possible to u~e thermoplastic composite film3 which
ara compo~ed only of one adhesion-promoting layer and one
15 top layer, but it i~ also pos3ible to u~e composite films
consi~ting of a plurality of layer~. In thi~ case, not
only tha various adhesion-promoting layer~ but also the
variou~ thermoplastic layer~ each may be composed of
identical or diffsrent material in identical or different
layer thickne~se3.
The collar-shaped thicXenings essential to the
invention of the coated sheet metal are annular or
discoid having a regular or irregular periphery and have
a thickness of at least 2 ~m, prsferably at least 5 ~m
and most particularly preferably thlcknesses of at least
30 50 ~ to achieve good sealing characteristics. The
intern~l angle of the flanks with the film web ls 1 to
90-C, preferably 3 to 85-. The width o~ the annular
collar-~haped thickenings varie~ according to the in-
35 tended u~e of the ooated sheet metal~ generally between1 and 20 ~ and i~ preferably between 2 and lO m~.
It rem~in~ to be pointed out that it i~ also
a1~
~;
- 20 - 2~ 26
pos~iblQ to coat the ~heet metal on the side facing away
from the contents likewise with a preferably flat,
thermopla~tic composite film or else with a liquid or
powder coating composition.
Use of_the coated sheet metals to produce packaainq
containers
The coated sheet matals according to the inven-
tion are used to produce packaging containers, in par-
ticular for the production of base~ or lid~ or cans,
valve caps of aerosol cans and closure4. The closure
component~ are produced by cu~tomary methods tcf., for
example, VR-INTERPACR 1969, pages 600 - 606: W. Panknin,
A. Breuer, M. Sodeik, "Abstreckziehen als Verfahren zum
Hex~tellen von Dosen au~ WeiAblech"; SHEET METAL
INDUSTRIES, August 1976: W. Panknin, Ch. Schneider,
M. Sodeik, "Plastic Deformation of Tinplate in Can
Manufacturing"; Verpackungs-Rund chau, Volume 4/1971,
pas~es 450-458: M. Sodeik, I. Siewert, "Die nahtlose Dose
au~ WeiBblech~'; Verpackungs-Rundschau~ Voll~me 11/1975,
pages 1402 to 1407; M. Sodeik, K. HaaA, I. Siewert,
~'Herstellen von Dosen aus WeiAblech durch Tiefziehen";
Arbeitsmappe fUr den Verpackungspraktiker, Metalle,
Part II, Group 2, 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).
Further details can therefore be obtained from
tha literature.
The invention i~ now explained in~more detail by
maans of d$agrams.
2 ~ 2 6
Fig. 1 shows a section of a textured thermopla~-
tic composite film (1) comprising a thermoplastic top
layer (2) and an adhe~ion-promoting layer (3)t the
thermoplastic top layer (2) having the collar-shaped
thickenings. A composite film of this type can be pre-
pared by the process 1 outlined in the present
de~cription~
Fig. 2 shows a ~ection of a textured thermoplas-
tic composite film (1) comprising a thermoplastic top
layer (2) and an adhe ion-promoting layer (3), the
adhesion-promoting layer (3) having the collar-~haped
thickenings. A composite film of this type can be pre-
pared by the process 2 outlined in the present descrip-
tion.
Fig. 3 shows a section of a textured thermo-
pla~tic compo~ite film (1) comprising an adhe~ion-promot-
ing layer (3) and a thermoplastic top layer (4) of foamed
plastic. A compo~ite film of this type can be prepared by
the process IV outlined in the present description.
Fig. 4 shows a section of a coated sheet metal
having annular collar-shaped thickenings (5) in the top
layer (2), revealed in perspective. Furthermore, a
punched-out section of the sheet metal which is required
for the production of a closure component i8 indicated.
Fig. 5 shows a section along the line A-B. The
~heet metal (6), the adhe3ion-promoting layer (3) and the
top layer (21 having the collar-shaped thickenings (5)
can be ~een.
Figs. 4 and 5 ware based on the following typical
.~ ,
_ 22 - 2~65~2~
parameter~ for the coated ~heet metal:
Height of the thickening~ = 0.05 mm
Width of the thickening~ = 4 mm
Thickness of the compo~ite film = 0.1 mm
Sheet metal thickness = 0.2 mm
Lid diameter = 73 mm
Distance between 2 ad~acent thickenings = 1 mm.
The invention is explained in more detail below
with the aid of exemplary embodiments. All data concern-
ing part~ and percentages are given by weight unless
explicitly stated otherwi3e.
I. Preparation of thermopla~tic composite film~
I.l. Preparation of the thermoplastic composite film I
A coextruded film comprising a 0.20 mm thick
layer of high density polyethylene (dansity
= 0.960 g/cm3, melt index, mea~ured at 190C under a load
of 2.16 kg (i.e. MFI 190/2.16) = 8 g/10 min), melting
point 135C) and a 0.05 mm thick layer of an
ethylene-acrylic copolymer (density = O.931 g/cm3, MFI
190/2.16 = 6 g/10 min, 6.5 % by weight of acrylic acid)
i9 shaped in a heated embossing unit. The embossing roll
is heated to a temperature 5 to 20C below the melting
point of the polyethylene, and the smooth pressure roll
is heated to 40C below the temperature of the embossing
roll. The coextruded film i8 wrapped around the Qmbo~sing
roll to an extent of up to 80 ~ of the roll circumference
to ensure optimal heat transfsr. The pressure roll has a
Teflon- or rubber-coated surface to avoid ~ticking. ~he
embos~ing roll has annular depressions (O.05 mm deep,
- 23 - 20~
5 mm wide~. The contact pres~ure i~ 200 N/mm of nip
length.
I.2. _reparation of thQ thermopla~tic com osite film 2
An embossed polyamide film (polyamide 6, film
thickne~s 0.06 mm) having, on one side, rai~ed annular
structures (O.06 mm in height) i coated in a coating
unit on the reverse side from this profLle with ethylene-
acrylic acid copolymer ~density = 0.938 g/cm3, MFI
190/2.16 = lO g/10 min, 10 % by weight of acrylic acid.
Material temperature: 180Ct coating speed
lS0 m/min, chill-roll temperature 5C, layer thickness
0.1 mm.
I.3. Preparation of the thermopla~tLc composite film 3
An embossed polyamide film (polyamide 6, thick-
ne~ 0.06 mm) having, on ons side, raised annular struc-
tures (O.02 mm in height) is coated in a coating unit on
the reverse side to this profile with a coextruded
polymer film comprising 0.02 mm of Zn-ionomer (density
= 0.940 g/cm3~ MFI 190/2.16 = 2 g/10 min, 1.7 % by w~ight
of zinc acrylate and 6.8 % by weight of acrylic acid),
0.06 mm of LDPE - low density polyethylene - (den~lty
= O.934 g/cm3~ MFI 190/2.L6 - O.3 g/10 min) and 0.03 mm
of zinc Lonomer.
Material temperature 170C, coat~ng speed
100 m/min, chill-roll temperature 5C, layer thickness
0.11 nun.
I.4 Preparation of the thermoplastic composite films 4-6
HDPE - high dGnsity polyqthylene - ~density
O.952 g/cm3~ NFI l90/2.16 = 6 g/10 min~, grafted LLDPE -
2065~2~
- 24 -
linear low density poly~thylene - (density 0.920 q/cm3~
MFI 190/2.16 = 4 g/10 min, 0.3 ~ by weight of maleic
anhydride) and ethylene-vinyl alcohol copolymer (density
1.19 g~cm3, MFI 190/2.16 = 1.3 g/10 min, 30 mol % of
ethylene) are coextruded u.Ring a feed block die to give
a surface-textured compo~ite film. The HDPE layer of the
composite is textured by extruding the melt (290C,
150 m/min) onto a chill roll (15C) having interchange-
able surface components. The interchangeable components
are 2 mm thick chrome-plated half-shells in which annular
depre~sions (width 7 mm and 3 mm, depth with film 4
0.15 mm, with film 5 0.1 mm, and with film 6 0.01 mm)
ha~e been introduced before chrome-plating by spark
erosion. The composite comprises 0.1 mm of HDPE, 0.02 mm
of g-LLDPE, 0.05 mm of ethylene-vinyl alcohol copolymer
and 0.03 mm of g-LLDPE.
I.5. Preparation of the thermoplastic composite film 7
A polypropylene of density 0.908 g/cm3 and melt
index NFI 230~2.16 = 11 g/10 min is melted in a single
screw extruder (~ = 45 mm, screw length L = 30 D (D = ~),
material temperature 290C) and extruded onto a chill
roll cylinder (surface temperature 15C). On the surface
of the chill roll was fastened a 2.5 mm thick Teflon film
having annular depre~sion~ (0~05 mm deep and 5 mm wide).
The polypropylene film (thicknes~ 0.15 mm) extruded onto
this ~urface is ~moothed by means of a pre~sure roll and,
after being wrapped half-way round said chill roll, is
drawn off. The flat ~urface of the textured film i3
pretreated using industrially known proce~ses (electric
_ 25 - 2~
dischargs, corona and pla~ma treatment, flame treatment),
so that a ~urface tension of 45 to 65 mN/m is achieved.
This textured-surface polypropylene film is
coated with a coextruded film (0.05 mm thick) comprising
an ethylene-vinyl acetate copolymer (28 % by weight of
vinyl acetate, MFI 190/2.16 = 20 g/10 min, 0.01 mm thick)
and an ethylene-acrylic acid copolymer (8 ~ by weight of
acrylic acid, MFI 190/2.16 = 17 g/10 min, 0.04 mm thick)
so that the ethylene-vinyl acetate copolymer 1 yer i8
arranged on the polypropylene film. The material tempera-
ture is 205C, and the coating speed i~ 100 m/min.
I.6. Preparation of the thermopla~tic composite film 8
A thermopla~tic compo~ite film 8 i~ prepared by
a procedure similar to that for composite film 7 with the
sole difference from the preparation of composite film 7
being that now the annular deprecsions of the Teflon film
on the chill roll are 0.03 mm deep (instead of 0.05 mm).
I.7. Preparation of the thermoplastic composite film 9
A thermoplastic composite film 9 i3 prepared by
a procedure ~Lmilar to that for composite film 7 with the
sole difference thst now the annular depre~sions of the
Teflon film on the chill roll are 0.005 mm deep instead
of 0.05 mm.
I~8. Preparation of the thermoplastic composite film 10
A polypropylene (density - 0.898 g/cm3, MFI
230/2.16 - 5 g/10 min) is coextruded together with a
grafted random polypropylene (density = 0.89 g/cm3, NFI
230/2.16 = 12 g/10 min, melting point 15~C, 0.21 % by
weight of maleic anhydride) onto a chill roll to which a
~: . , -; .
,
- 26 - 2~ 6
Teflon film (2 mm thick, annular depre~ion 0.1 mm, 5 mm
wide, internal diam. 73 mm) i8 attached. The depressions
are filled at a material temperatur~ of 250C and a speed
of 120 m/min to give a compo~ite film 0.24 mm thick
(O.2 mm of polypropylene, 0.04 mm of graft copolymer)
having 0.08 mm high collar-shaped thickenings on the
polypropylene side.
I.9. Preparation of the thermopla~tic composite film 11
The graft copolymer side of the compogite film 10
is coated with a 0.05 mm thick layer of a copolymer (87 %
of ethylene, 9 % of butyl acrylate, 4 % of acrylic acid,
MFI lg0/2.16 = 7 g/10 min) at a material temperature of
270C-
I.10. Preparation of the thermopla~tic compo~ite film 12
A polyester film (commercial product MelinexR 870
from ICI) of thicknes~ 0.012 mm i8 given annular textures
(O.04 mm deep, external diamO 11.57 cm, internal diam.
10.57 cm) in a heated thermoforming tool (T = 150C).
Thi~ film i~ coated with grafted LLDPE (linear low
density polyethylene - densitys 0.918 g/cm3, ~PI 190/2.16
= 4 g/10 min, 0.27 % by weight of maleic anhydride).
Material temperature 290C, amount applied 50 g/mZ.
Exa~E~e 1
A polyethylQne (PE) of density 0.918 g/cm3 and
melt index ~MFI 190/2.16) of 1.7 g/10 min i8 melted in an
extruder (diam. 60 mm, L - 25 D). The matarial tempera-
ture i~ 220C. In a sQcond extruder (diam. 35 mm,
L = 25 D) an ethylene-acrylic acid copolymer (8 % by
weight of acrylic acid, den~ity - 0.935 g/cm3,
.
- 27 - 20~ 6
MFI 190/2.16 = 7 g/10 min~ is melted at a temperature of
210C. The two melt stream~ are brought together in the
feed block nozzle and extruded onto a smooth chill roll
(temperature 15C). The 0.2 mm thick film is compo~ed of
0.15 mm of polyethylene and 0.05 mm of copolymer. In a
second process step, the copolymer side of this film is
laid on a degreased steel sheet (O.3 mm ECCS, electro-
lytic chremium-coated steel). On the polyethylene side i~
laid a Teflon film (2 mm thick) having annular depres-
sions. The rings have an internal diameter of 54 mm and
an external diameter of 59 mm with various depth~ of
0.003, 0.01, 0.05 and 0.1 mm. A gentle preliminary
pressure of ~ 0.5 kg/cm2 is applied for 1 min at 200C and
then a pres ure of 5 kg/cma is applied for 3 min and then
the composite is cooled under pre~ure to room tempera-
ture. The annular depression~ are completely filled. The
peel te3t, conforming to AST~ D 1876 (angle 90C [sic])
gives an adhesion of 45 N~15 mm ~trip width (cf.
Table 1). The adhesions of the adhesion-promoting layer
on other substrates is [8iC] given in Table 2.
Example 2
A coated steel shaet is produced by the process
described in Example 1, but, contrsry to Example 1,
polyethylene of density = 0.924 g/cm3 and melt index
MFI 190/2.16 = 7 g/10 min and ethylene-acrylic acid
copolymer of density = 0.932 g/cm3 and melt index
MFI 190/2.16 - 7 g/10 min containing 4 ~ by w~ight of
acrylic acid and 8 % by w~ight of butyl acrylate i8 [sic]
used. The thickne3s distribution of the composite fil~ i8
- 28 ~ 2~ 2~
0~20 mm of polyethylene to 0.05 mm of copolymer. The
copolymer is bond~d to 0.2 mm tinplate E 5.6/5.6 [ 8iC ]
with an adhesion of 69 N/15 mm. The result~ of other
adhesion tests of the adhesion-promoting layer on other
substrates are given in Table 2.
Example 3
An untextured coextruded film comprising an LDPE-
low density polyethylene (density = 0.918 g/cm3,
MEI 190/2.16 = 7 g/10 min, thicknes~ 0.1 mm) and an
ethylene copolymer (den3ity = 0.94Q g/cm3, NFI 190/2.16
= 11 g/10 min, 16 % by weight of vinyl acetate, 0.6 % by
weight of maleic anhydride, 0.02 mm thick) i~ bonded in
a heated embossing unit under a roll pressure of 100 N/mm
and at a speed of 10 m/min with a preheated tinplate
strip with simultaneous embossing of the LDPE layer. The
embossing roll has regular annular depressions of width
5 mm and depth 0.01 mm. The temperature of the preheating
roll of the film is 80C and the temperatures of the
embossing roll and pre~sure roll are 15Co The sheet
metal ~trip is preheated to 150C. The re3ults of the
adhesion tests are given in Table 1 and 2.
Example 4
Polyethylene glycol terephthalate (density
1.41 g/cm3, melting points 255C, glass transition tem-
peratures 75~C) is coextruded toge~her with an ethylene-
vinyl acetate-maleic anhydride terpolymer (8 % by weight
of vinyl acetate, 3 % by weight of maleic anhydride,
MEI 190/2.16 = 6 g/10 min) at 270C. The composite
co~prise~ 0.01 mm of polye~ter and 0.07 mm of terpolymer.
2065~2~
- 29 -
In a 3econd process step, the copolymer sid~ of this film
is laid on a degreased ~teel sheet (0.2 mm TFS). On the
polyester side i~ laid a steel sheet (O.2 mm thick)
having annular depressions. The ring~ have an internal
diameter of 25 mm and an external diameter of 32 mm with
different depths of 0.01 and 0.05 mm. A gentle prelimin-
ary pres ure of < O.5 kg/cm2 is applied for 1 min at
250C, and then a pres~ure of 5 kg~cm2 is applied for
3 min and then the compo~ite is cooled under pressure to
room temperature. The annular depressions are completely
filled. The re~ult~ of variou~ adhesion te~ts are given
in Table 1 and 2.
Examples 5 to 15 (process a)
A 35 cm wide metal strip i~ heated to a tempera-
tuxe between the melting point of the adhe~ion promoter
and 250C (for individual temperatures, cf. also Tables
1 and 2) by ~uitable method~ (HF heating, treatment with
a gas flame, etc.) and then the strip is covered with the
adhesion-promoting side of a 35 cm wide strip taken from
composite fiLms 1 to 11 and bonded between the rolls of
an embossing unit to give a metal-plastic laminate. The
pressure roll is rubber~lined and the roll pressure
(< 50 N of roll pressure per mm of nip length) i~ ~elec-
ted 80 that the reduction in the height of the textures
is less than 10 % of the original height. A peel tQst in
accordance with ASTM D 1876 was carried out on some
sslected composite~. The test results are given in
Table 1 and 2.
.
'' '
~' .
~ 3~ ~ 2~65~6
Exam~les 16 to 2~ LPrCe~ bL
A 35 cm wide metal ~trip is covered with the
adhesion-promoting side of a 35 cm wide trip taken from
composite filmY 1 to 11, the metal ~ide i8 heated by
suitable method~ (HF heating, heating with a gas flame,
etc.) to a temperature higher than the melting point of
the adhesion promoter (for individual temperatures cf.
Table 1) and thi~ laminate is pres~ed between a smooth
metal roll and a rubber roll (textured polymer side) of
an embossing unit to give a metal-pla~tic laminate. The
roll pre~sure i3 ad~u~ted ~o that the diminution in the
height of the textures i8 less than 10 % of the original
height. A peel te~t in accordance with ASTM D 1876 wa~
likewise carried out on some selected composite~. The
test results are given in Tabls 1 and 2.
Example rsic] 27 to 37 (proce~s c)
A 35 cm wide metal ~trip i~ heated using suitable
method~ (HF heating, treatment with a ga~ flame, etc.) to
a temperature of < 300C (for the particular temperature,
cf. Table 1) and bonded in the nip of an embossing unit
with the adhesion-promoting side of one of the composite
films 1 to 11 to give a metal-plastic laminate. The
pre~sure roll is rubber-lined and the roll pressure
(~ 100 N of roll pres~ure per mm of nip length) is
selected ~o that the reduction in the height of the
textures is less than 10 ~ of the original height. A peel
te3t in accordance with ASTM D 1876 was likewise carried
on some selected composites. The test results are given
in Table 1 and 2.
' ' ' ' "'
. ~
- 31 - 20~ 6
Example 38
Coated ~heet metals are produced using the
thermoplastic composite film 12, process b being
employed. A peel test in accordance with ASTM 1876 was
likewise carried out on some composite The re~ults are
given in Table 1 and 2.
;- ' ' ' ~ . ' ':,
. -
- 32 ~ 6
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m I O O O U~ U~ o co
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.
: ' ' ''
- 33 - 2~6~2~
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~ 34 ~ 2~6~2~
Notes to Table 1:
1) ProcQss used to produce the composite comprising
sheet metal and thermoplastic composite film
2) Surface temperature of the sheet metal during
production of the composite comprising sheet metal
and thermplastic composite film
3) TFS = tin-free steel
ECCS = electrolytic chromium - coated steel
4) Tinplate E5.6/5.6 (DIN 1616)
~ . ~
- 35 - 2~ 126
~ _
O ~ U~ O ~ r~ _I
o ~
.,, .,,
E~
U~ ~ I~ o~ D N
U~ U 10 1''7 ~ I I I ~ CO
~ E~l U
a~ ~
_I co r~ 1~ ~ ~D
rl ~ 1~ 1~ N ~ I I ~
~o E-l u~
a _ !~ :
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~ ~ ~ ~ ~ g ~
~ ta ~ 8 dP ~ ~ ~ o
X ~ ~ CD ~ O
~ ID ~ N~ :.
~ OO ~
Pl P13 14 P3 ~ 3 H tJI
a~ o _
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E.1 ~ ~1 ~I N t~ N
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O ~ 1:1 --I N ~ ~ I N --I
~: :
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- - ~
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- 37 ~ 3 1~ 2 ~
Key to Table 2:
1. Production of the composite comprising sheet metal
and adhesion-promoting layer by the process des-
cribed in Example 1
2. Abbreviation~:
E = ethylene
BA = butyl acrylate
AA = acrylic acid
ZnAA = zinc acrylate
g = grafted
LLDPE = linear low density polyethylene
PP = polypropylene
VA = vinyl acetate
MA = maleic anhydride
5 3. Sur~ace temperature of the sheet metal during
production of the compo~ite comprising sheet metal
and adhesion-promoting layer
4. TFS = tin-free steel
ECCS = electrolytic chromium-coated steel
5. Tinplate E5.6/5.6 (DIN 1616)
~ .
:
.. . : .
- 38 - 20~5~2~
Examples 39 to 42
Food can lids were punched from the plastic-metal
compo~ite of Example~ 15, 19, 20 and 21 which had been
produced according to processes a-c, and the ~uitability
of these lid~ for use as food can material wa4 tested in
the abbreviated te~t. The test indicate~ a good re~is-
tance toward the cu~tomary te~t ~olutions (lactic acid,
acetic acid, common ~alt solution, H20) under sterili-
zation conditions of 121C for 30 min.
Examples 43 to 44
Cup~ of diameter 33 mm and height 25 mm were
drawn using the composites from Examples 1 and 3. The
cup~ were then exposed to methylene chloride. The adhe-
sion before commencement of the test and after 72 hours
was tested u~ing the Te~a test. No diminution in the
adhesion was observed.
Examples 45 to 47
A cup of diameter 33 mm and height 25 mm was
drawn from the composites of Example~ 6, 17 and 28 which
had bsen prepared according to process A-C ~sic], and
this cup was then stored in isopropanol, xylsne, solvent
naphtha 100 and solvent naphtha 150. Before commencement
of this test and after 72 hours, the adhesion wa~ tested
using the Tesa test. No diminution in the adhesion was
observed.
Examples 48 and 49
Beverage can shells were stamped from the compos-
ites of Examples 4 and 38. These were sterilized for~
30 min at 78C and at 100C in water. The te~t shows that
:
., - :
- 39 - 2~
the composite i~ completely re~i~tant (no water absorp-
tion, no loss of adhe~ion).
:
.: . . - , ., , : . - , :
