CA2065426A1 - Metal-plastic composites, process for producing them and their use - Google Patents

Abstract

(57) Abstract The invention relates to sheet metal coated with one or more layers (2) of possibly different resins, characterized by annular or disk-shaped bead-like thickenings (5) in at least one of the layers of resins. The invention also relates to processes for coating sheet metal, the thermoplastic composite films used to coat the sheet metal and the use of the coated sheet metal in the manufac-ture of packaging containers.

Description

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~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 REPLACEMENT PAGB

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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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- 3 - 2 ~ 2 6 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 REPLACEMENT PAGE

8150 ST 1.91 20090 ' : :

~0~5~6 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 proceg 9 -.
' 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 S' `` ' ' ' , a- 20~5~
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 :' ' ~ ' ' . ' -9- 20~5~6 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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- 13 - 2~ 6 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 - 14 - 2~5~
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 .: -. : . - . .
.~. ' '' ~ '. - ' - 15 - 2~ 2~
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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206542~

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 - . . . . . . .

- 17 - 2~ 6 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 - 18 - ~065~
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 .

a1605T ~.91 200ao ` :' ~' '' ~' ' ' '~ - . :' ' ~ ' ' ~' ~ - ..
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l9 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~
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- 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~

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 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~

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.

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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~

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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).

:

.: . . - , ., , : . - , :

Claims (15)

Claims

1. A thermoplastic composite film comprising at least one adhesion-promoting layer and at least one other thermoplastic layer arranged on the adhesion-promoting layer, wherein the thermoplastic composite film has annular or discoid collar-like thickenings of the adhe-sion-promoting layer and/or top layer and wherein the collar-like thickenings form a pattern, this pattern recurring in both the transverse and the longitudinal directions.

2. A sheet metal having a laminated-on thermoplastic film, the film having a repeating pattern of thickenings, wherein a thermoplastic composite film as claimed in claim 1 has been laminated on.

3. A sheet metal or a thermoplastic composite film as claimed in claim 1 or 2, wherein the collar-like thickenings have a thickness of at least 2 µm, preferably of at least 50 µm.

4. A sheet metal or a thermoplastic composite film as claimed in any one of claims 1 to 3, wherein the thermoplastic composite film has an overall thickness of less than 500 µm, preferably 10 to 300 µm.

5. A sheet metal or a thermoplastic composite film as claimed in any one of claims 1 to 4, wherein the thickness of the adhesion-promoting layer of the thermoplastic composite films is between 0.5 and 100 µm, preferably between 1 and 70 µm, and the thickness of the top layer of the thermoplastic composite film is between 10 and 499.5 µm, preferably between 10 and 200 µm.

6. A sheet metal or a thermoplastic composite film as claimed in any one of claims 1 to 5, wherein the adhesion-promoting layer of the thermoplastic composite film comprises at least one carboxyl-containing polymer, optionally in combination with other polymers.

7. A sheet metal or a thermoplastic composite film as claimed in any one of claims 1 to 6, wherein the top layer of the thermoplastic composite film consists of a foamed polymer.

8. A process for producing a sheet metal as claimed in any one of claims 2 to 7, wherein either a) a thermoplastic composition film is laminated on which has annular or discoid collar-like thickenings of the adhesion-promoting layer and/or top layer, or b) the thermoplastic composition film is initially laminated on in a uniform layer thickness and then annular or discoid thickenings are produced in at least one of the resin layers by embossing and pressing.

9. A process as claimed in claim 8, wherein the thermoplastic composite film prepared by 1. extruding a thermoplastic film or a composite film comprising adhesion-promoting and top layers, said film being shaped either during or after the extr-usion in such a way that one surface of the film has the collar-like thickenings and the other surface is either flat or contains the collarlike thickenings in negative profile, i.e. as depressions and 2. coating the thus prepared surface-textured film on its flat surface or on the surface having the depressions with an adhesion promoter or a coextru-ded laminar polymer composite having identical or different adhesion-promoting layers on the two surfaces of the polymer composite, in such a way that the surface texture of the thermoplastic top layer is retained.

10. A process as claimed in claim 8, wherein the thermoplastic composite film is prepared by coextrusion of the adhesion-promoting layer and top layer followed by shaping of the thermoplastic composite film in such a way that the top layer has the collar-like thickenings.

11. A process as claimed in claim 8, wherein the thermoplastic composite film has been prepared by first bonding a flat thermoplastic monofilm or a composite having an adhesion-promoting layer or a polymer composite in which at least one surface consists of an adhesion-promoting layer, and then shaping the resulting flat thermoplastic composite film in such a way that one surface is flat and the other surface has the collar-like thickenings.

12. A process as claimed in any one of claims 8 to 10, wherein the sheet metal is coated with the thermo-plastic composite film by A) laying on top of one another the thermoplastic composite film having the collar-like thickenings and the sheet metal in such a way that an adhesion-promoting layer is arranged on the metal surface, B) heating the adhesion-promoting layer to a tempera-ture which is at least equal to the melting point of the adhesion-promoting layer but which is below the melting point of the thermoplastic layer arranged on the adhesion-promoting layer and C) laminating on the thermoplastic composite film under pressure, the pressure being selected so that the reduction in the height of the collar-like thicken-ings during lamination is at most 10 % of the original height of the thickenings.

13. A process as claimed in claim 8 or 11, wherein the sheet metal is coated with the thermoplastic composite film by A) laying on top of one another a thermoplastic compos-ite film which has no collar-like thickenings and the sheet metal in such a way that an adhesion-promoting layer is arranged on the metal surface, B) heating the adhesion-promoting layer to a temperature which is at least equal to the melting point of the adhesion-promoting layer but which is below the melting point of the thermoplastic layer which is arranged on the adhesion-promoting layer and C) laminating the thermoplastic composite film under pressure in such a way that the collar-like thicken-ings are produced during lamination of the composite film or immediately after lamination of the comp-osite film.

14. The use of the sheet metals as claimed in any one of claims 2 to 7 for the production of packaging containers.

15. The use of the sheet metals as claimed in any one of claims 2 to 7 for the production of closure components for packaging containers.