IE63937B1

IE63937B1 - Profiled-surface metal-plastic composites processes for their preparation and the use of the composites for producing packaging containers

Info

Publication number: IE63937B1
Application number: IE318590A
Authority: IE
Inventors: Hans-Henning Hub; Siegfried Krause
Original assignee: Basf Lacke & Farben
Priority date: 1989-09-08
Filing date: 1990-08-31
Publication date: 1995-06-28
Also published as: PT95238A; DE59003269D1; WO1991003373A1; CA2065426A1; NO920891D0; ES2047341T3; EP0490949A1; YU47086B; NO920891L; ATE96376T1; PT95238B; NO178722C; YU169890A; DE3929942A1; IE903185A1; DK0490949T3; EP0490949B1; NO178722B

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 manufacture of packaging containers.

Description

The present invention relates to a metal sheet laminated with a thermoplastic film, where the film has a recurring pattern of thickenings. The invention furthermore relates to processes for producing metal sheets, to the thermoplastic composite films used for coating the metal sheets and to the use of the coated metal sheets for the production of packaging containers and of closure components for packaging containers.

A can or a closure for use as packaging material, in particular for the packaging of food, is produced by coating metal sheets composed of tinplate, chromiumcoated steel such as ECCS (electrolytic chromium-coated steel) or aluminum in the form of panels or in continuous form. The coating acts as a protective layer to protect the metal from attack by the contents and from the resulting corrosion, on the one hand, and, on the other hand, to prevent the contents from becoming affected by corrosion products of the metal. Obviously, it is essential that the coating itself does not affect or damage the contents, for example by releasing the coating constituents, either during sterilisation of the contents subsequent to filling or on subsequent storage of the packaged goods, in particular food.

Furthermore, the composition of the coatings must be such that they withstand the mechanical stresses which occur on further processing of the coated metal sheet to give cans or closures, for example the processes of shaping, stamping, flanging, crimping and the like, applied to the metal sheet.

In the production of lids and bases of cans, and with closures, an additional sealing material is needed to seal either between the metal parts or between metal and glass, or the like. This sealing is achieved by applying a sealant to the coated and already shaped packaging components (bases, lids, closures) and by gelation or drying of the sealant at elevated temperatures .

However, the production of lids and bases of cans, and of closures, consumes a large amount of energy, since coating and sealant are separately baked. Owing to the large number of finished lids, bases and closures, this additional process step also represents a considerable cost element.

Moreover, owing to the high solvent emissions not only on drying the coating but also on drying the sealant, precautions must be taken to minimise these emissions and the associated environmental pollution.

A process which has proven advantageous for coating metal sheets, in particular for producing food packaging, is the film-coating of metal sheets. For instance, DE-A-3,128,641 describes a process for the preparation of laminates for food packaging in which the metal sheet and a thermoplastic resin film, together with a carboxyl-containing polyolefin-based adhesive arranged between these layers, are heated to temperatures of above the melting point of the adhesive and then cooled together under pressure, the metal-plastic composite being formed by this means.

However, in the production of lids and bases, and also of closures, even by this procedure, the sealant must be introduced, in a further process step, into the previously 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 components for packaging containers is not described.

EP-B-41,512 then discloses a process for the production of containers, in which process laminates are likewise used, in particular to produce the lids and bases of the cans and to produce the valve caps of aerosol cans. The polymer layer of these laminates then acts simultaneously during the production of the containers as a seal and as a protective layer so that in this process it is not necessary to apply a sealant to the closure components. However, this process has the disadvantage that a very high layer thickness of the laminated-on polymeric layer, about 200 μία, is necessary to ensure sealing. The high material consumption associated with this layer thickness leads to a pronounced increase in manufacturing costs for the containers and is consequently a considerable economic disadvantage of this process, the more so on taking into account that the containers are high-volume mass produced products.

Patent Application ZA-A-880,198 discloses, in the production of cans, ensuring the seal of the joint between can body and can lid by inserting a sealing laminate between lid and body. This process also is very expensive since first the laminates acting as sealing material must be cut to size and must then be fitted into the closure component.

Finally, EP-B-167,775 describes a process and an apparatus for the continuous production of objects or coatings having contours of complex shape, for example for remoulding of car tyres, in which process a liquid material is applied between at least two moving, con25 tinuous, shaping surfaces and cured. However, the preparation of thermoplastic composite films or the application of the process for the production of metal sheets for use as closure components of packaging containers is not described.

US-A-3,265,785 describes a process for the production of closure parts for packaging containers in which, as sealant composition, a foamable vinyl resin plastisol is introduced into the pre-shaped closure part and is shaped in such a manner that the plastisol layer has an annular (0-ring, collar-like thickening. In order to achieve the sealing function, the plastisol is heated, before, during or after the shaping, to a sufficiently high temperature to decompose the foaming agent present in the plastisol.

Furthermore, DE-A-19 03 783 describes a process for the coating of substrates with a thermoplastic film in which the thermoplastic film has a preselected profile of zones of different thickness. This process serves to produce coated packet or box sections which are employed for packaging liquids, such as, for example, milk or juice. These coated packet or box sections have an increased layer thickness in the region of the seal or weld seams so that it is possible for them to be made leak-tight.

The object of the present invention is therefore to provide coated metal sheets which are suitable for use as a packaging material. In particular, the use of these coated metal sheets as a closure component such as, for example, can lid, can base, valved cap and screw closure must allow the packaging containers to be produced by means of a simple and economical process, this process not having the abovementioned disadvantages of the prior art. Furthermore, these coated metal sheets must satisfy the abovementioned requirements concerning mechanical properties and concerning compatibility with and protective action toward the contents.

Surprisingly, this object is achieved by a thermoplastic composite film comprising at least one adhesion-promoter layer and at least one further, thermoplastic layer arranged on the adhesion-promoter layer, characterised in that the thermoplastic composite film has annular or discoid, collar-like thickenings of the adhesion promoter and/or top layer, and in that the collar-like thickenings form a pattern which recurs in both the transverse and longitudinal directions.

The present invention furthermore relates to a metal sheet laminated with the thermoplastic composite film, to a process for the production of the metal sheets according to the invention, and to the use of the metal sheets according to the invention for the production of packaging containers and closure parts for packaging containers .

The advantages of the coated metal sheets according to the invention are essentially that they are eminently suitable for the finishing of closure components of packaging containers such as, for example, lids, bases and closures, it being of particular advantage that the built-in sealing action of the coated metal sheets allows the elimination of the process step of applying a sealant, this otherwise being necessary in the production of closure components. The use of the metal sheets which have been coated according to the invention accordingly allows the production of packaging containers using a simple and in particular economical process.

The subsequent text first explains in more detail the materials which are suitable for the preparation of the coated metal sheets according to the invention. This is followed by the description of the preparation of the metal sheets according to the invention.

Metal sheet: Metal sheets which are suitable for preparing the coated metal sheets according to the invention are those having a thickness of 0.04 to 1 mm, composed of tin-free steel, tinplate, aluminium and various iron alloys, which may optionally be provided with a passivating layer based on compounds of nickel, chromium and zinc.

These metal sheets have been coated with one or more, optionally different, resin layers, it being essential to the invention that the coated metal sheet has collar-shaped thickenings which assume the sealing function. According to the invention metal sheets are obtained by coating metal sheets with thermoplastic composite films which are composed of at least one adhesion-promoting layer and at least one other thermoplastic layer arranged on the adhesion-promoting layer.

Thermoplastic top layer of the composite film: The thermoplastic resin films or coatings used according to the invention as a top layer include polyolefins, polyamides, polyesters, polyvinyl chloride, polyvinylidene chloride and polycarbonates, each in the form of a film or coating. They also include multilayer films and coatings (composite films) which are obtained, for example, by co-extrusion of at least two of the abovementioned resins. The preferred thermoplastic film or thermoplastic coating which acts as the inmost layer (this is the layer which is in contact with the contents) of the metal-plastic composites preferably comprises a film or a coating composed of a polyolefin, polyester or polyamide. Films and coatings of this type are known and are commercially available in large numbers.

Polyolefin films of this type are produced by known processes (film blowing, chill roll process etc.) from granules of homopolymers of ethylene and propylene and from copolyers. Examples of these are low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density and linear very low density polyethylene (LLDPE, VLDPE) polypropylene, copolymers thereof with ethylene and the copolymers of ethylene with one or more comonomers from the groups comprising vinyl esters, vinyl alkyl ethers, unsaturated mono- and di-carboxylic acids, and salts, anhydrides and esters thereof.

These polyolefins are commercially available, for example, under the following tradenames: Escorene, Lupolen, Lotader, Lacqtene, Orerac, Lucalen, Dowlex, Primacor, Surlyn, Admer, Novatex, Sclair, Stamylan, and so on.

Examples of polyamides which are suitable for the top layer are polyamide 6 (polyamide prepared from «aminocaproic acid), polyamide 6,6 (polyamide prepared from hexamethylenediamine and sebacic acid), polyamide 66,6 (copolyamide composed of polyamide 6 and polyamide 6,6), polyamide 11 (polyamide prepared from ω7 aminoundecanoic acid) and polyamide 12 (polyamide prepared from ω-aminolauric acid or from laurolactam). Examples of commercial products are Grilon, Sniamid and Ultramid.

Preference is given to the use of the following polyesters: polyethylene terephthalate, polybutylene terephthalate and polyesters based on terephthalic acid, ethylene glycol and butylene glycol. However, other suitable polyesters are those based on terephthalic acid, isophthalic acid and phthalic acid and various polyols such as, for example, polyethylene glycol and polytetramethylene glycols of various degrees of polymerisation.

Examples of suitable commercial products are Hostaphan, Melinex and Hostadur.

Adhesion-promoting layer of the thermoplastic composite film The polymers used as the adhesion-promoting layer in the process according to the invention may be copolymers, terpolymers, graft copolymers or ionomers, with the provision that they carry carboxyl or anhydride groups or groups which are hydrolysable to give carboxyl groups, and that the melt index of the polymers, measured at 190°C 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 particularly preferably between 0.5 and 20 g/10 min.

Suitable copolymers and terpolymers can be prepared by copolymerisation of ethylene with α,^-unsaturated carboxylic acids such as, for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and fumaric acid, the corresponding anhydrides or the corresponding esters or semiesters which have 1 to 8 carbon atoms in the alcohol radical such as, for example, the methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, heptyl, octyl and 2ethylhexyl esters of the listed 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 anhydrides thereof.

Furthermore, it is possible, in the copolymerisation, to use still other monomers which are copolymerisable with ethylene and with the unsaturated carbonyl compounds. Suitable examples of these are a-olefins having 3 to 10 carbon atoms, vinyl acetate and vinyl propionate.

The amounts of monomers used in this copolymerisation are selected so that the resulting polymer has a carboxyl content of 0.1 to 30 % by weight, preferably 2 to 20 % by weight, 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 prepared by grafting at least one polymer from the group comprising polyolefins, with up to 10 % by weight, preferably up to 5 % by weight, relative to the total weight of monomers of at least one monomer from the group comprising α,βunsaturated carboxylic acids, or anhydrides, esters or salts thereof in the presence or absence of peroxides. Examples of suitable polyolefins are those polyolefins which have already been listed 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 the description of the copolymer-based adhesion-promoters.

The ionomers used as the adhesion-promoting layer can be prepared by the already abovementioned copolymerisation of ethylene and optionally other monomers with salts of a,£-unsaturated carboxylic acids or by partial neutralisation of the already abovementioned carboxylic acid-containing copolymers, terpolymers and graft polymers with salts, oxides and hydroxides of sodium, potassium, lithium, magnesium, calcium, zinc and ammonium. This neutralisation can be carried out in the melt or in solution. In carrying out this neutralisation, the amount of basic compound is selected so that the degree of neutralisation of the polymer is between 0.1 and 99 %, preferably between 0.1 and 75 % and most particularly preferably between 0.1 and 40 %.

Not only the adhesion-promoting layer but also the thermoplastic top layer may contain other customary additives such as, for example, internal and external lubricants, antiblocking agents, stabilisers, antioxidants, pigments, crystallisation auxiliaries and the like. These additives are used in the amounts necessary for preparation, processing, conversion and use, in the form of pulverulent materials, powders, 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 Gachter-Muller, Kunststoffadditive, Carl-Hanser Verlag. These additives are preferably incorporated in the top layer.

Preparation of composite films having a textured surface: There are various methods of preparation for the textured-surface composite films composed of the materials just described: 1.) Monofilms or composite films are prepared by extrusion through flat film dies or annular dies. These flat films are then shaped by the application of heat and pressure so that one surface of the film is flat and the other surface has the collar-shaped, periodically recurring, thickenings according to the invention. This shaping can be introduced by means of a mask which is laid on the film or by means of a profiled platen which is laid on the film, with the use of a press or a roll. Preference is given to the use of rolls since in this way it is possible to continuously produce the textured film. Obviously, it is also possible to use presses having a profiled platen, preferably having an interchangeable, surface-textured press platen, and rolls having a preferably interchangeable -textured surface. Moreover, it is preferable if the press or the roll is temperature-controllable, preferably heatable, so as to shape the film at the required temperature. The temperature used for the shaping operation is obviously dependent on the applied pressure of the roll or press and is generally between 50°C and the melting point of the film, the temperature being correspondingly higher the lower the pressure. The applied pressure is generally between 1 and 400 bar.

A film which has been textured in this manner is then coated with an adhesion-promoter or with a coextruded laminar polymer composite having identical or different adhesion-promoters on the two surfaces of the polymer composite, in the form of a film or a melt. The temperature for this operation is selected so that the adhesion-promoter forms a firm and stable bond with the textured monofilm and composite film, without the textured film melting or losing its embossed structure. 2. In a similar manner to the process which has just been described, it is also possible to shape a flat monofilm or composite film using a press or rolls in such a way that one surface has the collarshaped, periodically recurring, thickenings according to the invention (positive profile), while the other surface has the corresponding geometrical pattern in negative profile, i.e. in the form of depressions. This textured film is then likewise coated on the negative side, by the procedure of process 1 with an adhesion-promoter so that the embossed structure (positive side) is retained. 3. Besides the multi-stage processes 1 and 2, the thermoplastic composite film can also be prepared by extruding a (in the case 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 is 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 is retained. This 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 textured surface, in the vicinity of the surfacetextured roll or onto the smoothed, cooled surface of the top layer. This gives thermoplastic composite films corresponding to those films which were prepared in accordance with process 1. 4. The thermoplastic textured-surface composite film can also be prepared by coextruding the thermoplastic top layer together with the adhesion-promoting layer through flat film dies or annular dies. The resulting, flat thermoplastic composite film is then shaped using the apparatuses described in process 1, so that one surface is flat and the other surface has the collar-shaped, periodically recurring, thickenings according to the invention.

. However, it is also possible to bond a flat thermoplastic monofilm, or a composite with an adhesionpromoting layer or a polymer composite in which at least one surface consists of an adhesion-promoting layer, and to shape the resulting flat thermoplastic composite film by the procedure of process 4 so that one surface is flat and the other surface has the collar-shaped, periodically recurring, thickenings according to the invention.

Thermoplastic textured-surface composite films in which at least one layer consists of a foamed plastic In the process according to the invention, it is also possible to use textured-surface thermoplastic composite films in which at least one layer consists of a foamed plastic. Composite films of this type can be prepared, for example, by the following processes: I. A polymer is melted in an extruder in the presence of a chemical (thermally decomposing compound such as, for example, azodicarbonamide, sodium dicarbonate) or of a physical blowing agent (blowing gases such as, for example, freon, carbon dioxide, butane) and 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 adhesion-promoting film or a polymer composite film which has, at least on one surface, an adhesion-promoting layer is laminated or extruded onto the polymer film.

II. a) Similarly to process 1, a polymer is melted in an extruder in the presence of a chemical or physical blowing agent and extruded onto a smooth roll and then, optionally after subsequent smoothing of the surface, is coated similarly to process I with an adhesion-promoting layer or a polymer composite film.

This untextured, flat composite film is then, as described in the film preparation according to process 1, shaped between presses or rolls which are heated on one or both sides, resulting in a composite having collar-shaped thickenings on the foamed surface layer.

II. b) A composite film having at least one surface composed of an adhesion-promoter or an adhesionpromoting film is coated with expanding polymer film. The foamed surface layer is shaped on presses or rolls as described in II a).

II.c) A coextruded composite film having a foamed surface layer and an adhesion-promoter as the second surface is shaped between presses or rolls which are heated on one or both sides resulting in a composite having collar-shaped thickenings on the foamed surface layer.

III. A composite film corresponding to the composite film prepared according to process II is 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 embossing unit) having a textured surface on one or both sides, this resulting in a film having the collar-shaped thickenings according to the invention on the foamed surface layer, and then applying the adhesion-promoting layer or a composite having at least one adhesion-promoting layer on the surface to the non-textured surface in such a way that the textured surface is retained.

IV. The depressions of a temperature-controllable roll (W) are filled with an expanding resin and excess material is removed using a knife or a roll. Immediately afterwards, a pre-heated laminating film or a melt film composed either of an adhesionpromoter or of a coextruded polymer composite having an adhesion-promoting layer on at least one of its surfaces is pressed on by means of a roll. After being partially wrapped around the roll (W) in the range of 40 to 90 % of the circumference of the roll (W), the composite is drawn off.

Production of textured-surface metal-plastic composites The metal sheet is covered with the texturedsurface thermoplastic composite film which has been described by bringing into contact the adhesion-promoting layer of the composite and the metal surface. The application of pressure and heat either by means of a temperature-controllable press or in the nip of a roll mill or calender using temperature-controllable rolls gives the metal-plastic composite. In this procedure, the pressure and the temperature must be selected so that, on the one hand, the adhesion-promoter forms a firm and stable bond to the metal foil or metal sheet and, on the other hand, the thermoplastic top layer does not melt or lose 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 metal sheet and a flat thermoplastic composite film and then to shape this metal-plastic composite so that the top layer consisting of the thermoplastic material has collarshaped thickenings which form a geometrical pattern, this pattern recurring in both the transverse and longitudinal directions.

Finally, it is also possible to coextrude the thermoplastic composite film directly onto the metal sheet and, subsequent to the coextrusion, to directly shape the resulting composite so that the top layer consisting of the thermoplastic material has collarshaped thickenings which form a geometrical pattern, this pattern recurring in both the transverse and longitudinal directions.

The apparatuses used to shape the metal-plastic composites are identical with the apparatuses for preparing the profiled-surface composite film. Consequently, reference is merely made at this point to the appropriate places of the present description.

Moreover, the sealants may also be applied in the form of laminates to the metal sheets which have been coated but not yet shaped into closure components.

In these production methods for the coated metal sheets according to the invention, the top layer may also consist of a foamed polymer.

The coating of the metal sheet or the thermoplastic composite film generally has an overall dry film thickness (without thickenings) of less than 500 gm, preferably 10 to 200 gm and particularly preferably less than 100 gm. The thickness of the adhesion-promoting layer in the case of the composite films is between 0.5 and 100 gm. The thickness of the top layer is correspondingly between 10 and 499.5 gm. As already mentioned, it is possible to use thermoplastic composite films which are composed only of one adhesion-promoting layer and one top layer, but it is also possible to use composite films consisting of a plurality of layers. In this case, not only the various adhesion-promoting layers but also the various thermoplastic layers each may be composed of identical or different material in identical cr different layer thicknesses.

The collar-shaped thickenings essential to the invention of the coated metal sheet are annular or discoid having a regular or irregular periphery and have a thickness of at least 2 pm, preferably at least 5 μτα and most particularly preferably thicknesses of at least 50 pm to achieve good sealing characteristics. The internal angle of the flanks with the film web is 1 to 90eC, preferably 3 to 85’. The width of the annular collar-shaped thickenings varies according to the intended use of the coated metal sheets generally between 1 and 20 mm and is preferably between 2 and 10 mm.

It remains to be pointed out that it is also possible to coat the metal sheet on the side facing away from the contents likewise with a preferably flat, thermoplastic composite film or else with a liquid or powder coating composition.

Use of the coated metal sheets to produce packaging containers The coated metal sheets according to the invention are used to produce packaging containers, in particular for the production of bases or lids or cans, valve caps of aerosol cans and closures. The closure components are produced by customary methods (cf., for example, VR-INTERPACK 1969, pages 600 - 606: W. Panknin, A. Breuer, M. Sodeik, Abstreckziehen als Verfahren zum Herstellen von Dosen aus WeiBblech; Metal sheet INDUSTRIES, August 1976: W. Panknin, Ch. Schneider, M. Sodeik, Plastic Deformation of Tinplate in Can Manufacturing; Verpackungs-Rundschau, Volume 4/1971, pages 450-458: M. Sodeik, I. Siewert, Die nahtlose Dose aus WeiBblech; Verpackungs-Rundschau, Volume 11/1975, pages 1402 to 1407; M. Sodeik, K. Haafi, I. Siewert, Herstellen von Dosen aus WeiBblech 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 the literature.

The invention is now explained in more detail by means of diagrams.

Fig. 1 shows a section of a textured thermoplastic composite film (1) comprising a thermoplastic top layer (2) and an adhesion-promoting layer (3), the thermoplastic top layer (2) having the collar-shaped thickenings. A composite film of this type can be prepared by the process 1 outlined in the present description.

Fig. 2 shows a section of a textured thermoplastic composite film (1) comprising a thermoplastic top layer (2) and an adhesion-promoting layer (3), the adhesion-promoting layer (3) having the collar-shaped thickenings. A composite film of this type can be prepared by the process 2 outlined in the present description.

Fig. 3 shows a section of a textured thermoplastic composite film (1) comprising an adhesion-promoting layer (3) and a thermoplastic top layer (4) of foamed plastic. A composite film of this type can be prepared by the process IV outlined in the present description.

Fig. 4 shows a section of a coated metal sheet having annular collar-shaped thickenings (5) in the top layer (2), revealed in perspective. Furthermore, a punched-out section of the metal sheet which is required for the production of a closure component is indicated.

Fig. 5 shows a section along the line A-B. The metal sheet (6), the adhesion-promoting layer (3) and the top layer (2) having the collar-shaped thickenings (5) can be seen.

Figs. 4 and 5 were based on the following typical parameters for the coated metal sheet: Height of the thickenings = 0.05 mm Width of the thickenings = 4 mm Thickness of the composite film = 0.1 mm Metal sheet thickness = 0.2 mm Lid diameter — 73 mm Distance between 2 adjacent thickenings = 1 mm. The invention is explained in more detail below with the aid of exemplary embodiments. All data concerning parts and percentages are given by weight unless explicitly stated otherwise.

I. Preparation of thermoplastic composite films 1.1. Preparation of the thermoplastic composite film I A coextruded film comprising a 0.20 mm thick layer of high density polyethylene (density = 0.960 g/cm3, melt index, measured at 190eC under a load of 2.16 kg (i.e. MFI 190/2.16) = 8 g/10 min), melting point 135eC) and a 0.05 mm thick layer of an ethylene-acrylic copolymer (density = 0.931 g/cm3, MFI 190/2.16 = 6 g/10 min, 6.5 % by weight of acrylic acid) is shaped in a heated embossing unit. The embossing roll is heated to a temperature 5 to 20eC below the melting point of the polyethylene, and the smooth pressure roll is heated to 40°C below the temperature of the embossing roll. The coextruded film is wrapped around the embossing roll to an extent of up to 80 % of the roll circumference to ensure optimal heat transfer. The pressure roll has a Teflon- or rubber-coated surface to avoid sticking. The embossing roll has annular depressions (0.05 mm deep, 5 nun wide). The contact pressure is 200 N/mm of nip length. 1.2, Preparation of the thermoplastic composite film 2 An embossed polyamide film (polyamide 6, film thickness 0.06 nun) having, on one side, raised annular structures (0.06 mm in height) is coated in a coating unit on the reverse side from this profile with ethyleneacrylic acid copolymer (density * 0.938 g/cm3, MFI 190/2.16 = 10 g/10 min, 10 % by weight of acrylic acid.

Material temperature: 180°C, coating speed 150 m/min, chill-roll temperature 5°C, layer thickness 0.1 mm. 1.3-. Preparation of the thermoplastic composite film 3 An embossed polyamide film (polyamide 6, thickness 0.06 mm) having, on one side, raised annular structures (0.02 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 weight of zinc acrylate and 6.8 % by weight of acrylic acid), 0.06 mm of LDPE - low density polyethylene - (density = 0.934 g/cm3, MFI 190/2.16 = 0.3 g/10 min) and 0.03 mm of zinc ionomer.

Material temperature 170®C, coating speed 100 m/min, chill-roll temperature 5°C, layer thickness 0.11 mm. 1.4 Preparation of the thermoplastic composite films 4-6 HDPE - high density polyethylene - (density 0.952 g/cm3, MFI 190/2.16 = 6 g/10 min), grafted LLDPE linear low density polyethylene - (density 0.920 g/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 using a feed block die to give a surface-textured composite film. The HDPE layer of the composite is textured by extruding the melt (290°C, 150 m/min) onto a chill roll (15®C) having interchangeable surface components. The interchangeable components are 2 mm thick chrome-plated half-shells in which annular depressions (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) have 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. 1.5. Preparation of the thermoplastic composite film 7 A polypropylene of density 0.908 g/cm3 and melt index MFI 230/2.16 = 11 g/10 min is melted in a single screw extruder (φ = 45 mm, screw length L = 30 D (D = φ) , material temperature 290°C) and extruded onto a chill roll cylinder (surface temperature 15°C). On the surface of the chill roll was fastened a 2.5 mm thick Teflon film having annular depressions (0.05 mm deep and 5 mm wide). The polypropylene film (thickness 0.15 mm) extruded onto this surface is smoothed by means of a pressure roll and, after being wrapped half-way round said chill roll, is drawn off. The flat surface of the textured film is pretreated using industrially known processes (electric discharge, corona and plasma treatment, flame treatment), so that a surface 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 layer is arranged on the polypropylene film. The material temperature is 205°C, and the coating speed is 100 m/min. 1.6. Preparation of the thermoplastic composite film 8 A thermoplastic composite film 8 is 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 depressions of the Teflon film on the chill roll are 0.03 mm deep (instead of 0.05 mm). 1.7. Preparation of the thermoplastic composite film 9 A thermoplastic composite film 9 is prepared by a procedure similar to that for composite film 7 with the sole difference that now the annular depressions of the Teflon film on the chill roll are 0.005 mm deep instead of 0.05 mm. 1.8. 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, MFI 230/2.16 = 12 g/10 min, melting point 158eC, 0.21 % by weight of maleic anhydride) onto a chill roll to which a Teflon film (2 mm thick, annular depression 0.1 mm, 5 mm wide, internal diam. 73 mm) is attached. The depressions are filled at a material temperature of 250°C and a speed of 120 m/min to give a composite film 0.24 mm thick (0.2 mm of polypropylene, 0.04 mm of graft copolymer) having 0.08 mm high collar-shaped thickenings on the polypropylene side. 1.9. Preparation of the thermoplastic composite film 11 The graft copolymer side of the composite 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 190/2.16 = 7 g/10 min) at a material temperature of 270eC. 1.10. Preparation of the thermoplastic composite film 12 A polyester film (commercial product MelinexR 870 from ICI) of thickness 0.012 mm is given annular textures (0.04 mm deep, external diam. 11.57 cm, internal diam. 10.57 cm) in a heated thermoforming tool (T = 150°C). This film is coated with grafted LLDPE (linear low density polyethylene - density: 0.918 g/cm3, MFI 190/2.16 - 4 g/10 min, 0.27 % by weight of maleic anhydride). Material temperature 290°C, amount applied 50 g/m2. Example 1 A polyethylene (PE) of density 0.918 g/cm3 and melt index (MFI 190/2.16) of 1.7 g/10 min is melted in an extruder (diam. 60 mm, L = 25 D). The material temperature is 220°C. In a second extruder (diam. 35 mm, L = 25 D) an ethylene-acrylic acid copolymer (8 % by weight of acrylic acid, density = 0.935 g/cm3, MFI 190/2.16 = 7 g/10 min) is melted at a temperature of 210eC. The two melt streams are brought together in the feed block nozzle and extruded onto a smooth chill roll (temperature 15°C). The 0.2 mm thick film is composed 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 (0.3 mm ECCS, electrolytic chromium-coated steel). On the polyethylene side is laid a Teflon film (2 nun thick) having annular depressions. The rings have an internal diameter of 54 nun and an external diameter of 59 mm with various depths 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 200°C and then a pressure of 5 kg/cm2 is applied for 3 min and then the composite is cooled under pressure to room temperature. The annular depressions are completely filled. The peel test, conforming to ASTM D 1876 (angle 90°C [sic]) gives an adhesion of 45 N/15 mm strip width (cf. Table 1). The adhesions of the adhesion-promoting layer on other substrates are given in Table 2.

Example 2 A coated steel sheet is produced by the process described in Example 1, but, contrary 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 weight of acrylic acid and 8 % by weight of butyl acrylate is [sic] used. The thickness distribution of the composite film is 0.20 mm of polyethylene to 0.05 mm of copolymer. The copolymer is bonded to 0.2 mm tinplate E 5.6/5.6 [sic] with an adhesion of 69 N/15 mm. The results 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 LDPElow density polyethylene (density = 0.918 g/cm3, MFI 190/2.16 = 7 g/10 min, thickness 0.1 mm) and an ethylene copolymer (density = 0.940 g/cm3, MFI 190/2.16 = 11 g/10 min, 16 % by weight of vinyl acetate, 0.6 % by weight of maleic anhydride, 0.02 mm thick) is 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 80eC and the temperatures of the embossing roll and pressure roll are 15°C. The metal sheet strip is preheated to 150°C. The results of the adhesion tests are given in Table 1 and 2.

Example 4 Polyethylene glycol terephthalate (density 1.41 g/cm3, melting point: 255°C, glass transition temperature: 7 5 °C) is coextruded together with an ethylenevinyl acetate-maleic anhydride terpolymer (8 % by weight of vinyl acetate, 3 % by weight of maleic anhydride, MFI 190/2.16 = 6 g/10 min) at 270°C. The composite comprises 0.01 mm of polyester and 0.07 mm of terpolymer. In a second process step, the copolymer side of this film is laid on a degreased steel sheet (0.2 mm TFS). On the polyester side is laid a steel sheet (0.2 mm thick) having annular depressions. The rings 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 preliminary pressure of <0.5 kg/cm2 is applied for 1 min at 250°C, and then a pressure of 5 kg/cm2 is applied for 3 min and then the composite is cooled under pressure to room temperature. The annular depressions are completely filled. The results of various adhesion tests are given in Table 1 and 2.

Examples 5 to 15 (process a) A 35 cm wide metal strip is heated to a temperature between the melting point of the adhesion promoter and 250°C (for individual temperatures, cf. also Tables 1 and 2) by suitable methods (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) is selected so that the reduction in the height of the textures is less than 10 % of the original height. A peel test in accordance with ASTM D 1876 was carried out on some selected composites. The test results are given in Table 1 and 2.

Examples 16 to 26 (process bl A 35 cm wide metal strip is covered with the adhesion-promoting side of a 35 cm wide strip taken from composite films 1 to 11, the metal side is heated by suitable methods (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 this laminate is pressed between a smooth metal roll and a rubber roll (textured polymer side) of an embossing unit to give a metal-plastic laminate. The roll pressure is adjusted so that the diminution in the height of the textures is less than 10 % of the original height. A peel test in accordance with ASTM D 1876 was likewise carried out on some selected composites. The test results are given in Table 1 and 2.

Examples 27 to 37 (process c) A 35 cm wide metal strip is heated using suitable methods (HF heating, treatment with a gas flame, etc.) to a temperature of < 300°C (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 pressure roll is rubber-lined and the roll pressure (< 100 N of roll pressure per mm of nip length) is selected so that the reduction in the height of the textures is less than 10 % of the original height. A peel test in accordance with ASTM D 1876 was likewise carried on some selected composites. The test results are given in Table 1 and 2.

Example 38 Coated metal sheets 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 composites. The results are given in Table 1 and 2.

Table 1: Results of the peel test in accordance with ASTM D 1876 for testing the adhesion of the composite film to metal sheets Example Composite film Process 1) T (°C)2 1 Metal Thickness of metal (mm) Adhesion (N/15 mm) 1 — - — TFS-ECCS33 0.30 45 2 - - - Tinplate*3 0.20 69 3 - - - Tinplate*3 0.20 7.8 4 - - - 5 1 a 180 Tinplate*3 0.35 7.5 1 0 17 2 b 210 Tinplate*3 0.25 10.4 29 3 c 200 Tin-free 0.50 4.1 steel 19 4 b 210 ECCS3 3 0.28 8.0 t hj σι ι Example Composite film Process 1) T (°C)2 20 5 b 210 21 6 b 210 5 33 7 c 180 34 8 c 180 35 9 c 180 15 10 a 220 37 11 c 170 10 38 12 b 250 Metal Thickness of metal (mm) Adhesion (N/15 mm) ECCS3’ 0.28 9.0 ECCS3’ 0.28 8.5 Tinplate*’ 0.21 11.5 Tinplate*’ 0.21 11.0 Tinplate*’ 0.21 11.5 Tinplate*’ 0.18 4.5 Tinplate*’ 0.20 9.1 Aluminum 0.28 7.0 Notes to Table 1: 1) Process used to produce the composite comprising metal sheet and thermoplastic composite film 2) Surface temperature of the metal sheet during production of the composite comprising metal sheet and thermplastic composite film 3) TFS = tin-free steel ECCS = electrolytic chromium - coated steel 4) Tinplate E5.6/5.6 (DIN 1616) Results of peel tests in accordance with ASTM D 1876 for testing the adhesion of the adhesionpromoting layer to various metal sheets Table 2 Example τ(·ο3) Adhesion promoter2’ Comonomer content (% by wt.2’) Tin-free steel TFS/ eccs*’ Tinplate Aluminum 1 180 E/AA 8 AA 38 66 85 34 2 180 E/BA/AA 4 AA, 8 BA 57 37 69 38 3 180 E/VA/MA 16 VA, 0.6 MA 27 49 79 22 1 0 4 180 E/VA/MA 8 VA, 3 MA 24 - - 27 5 180 E/AA 6.5 AA - - 70 28 17 210 E/AA 10 AA - - 83 - 29 200 Ionomer 6.8 AA, 1.7 Zn AA 36 46 77 26 1 5 19 210 g-LLDPE 0.3 MA 82 61 43 Example T(*C)3’ Adhesion promoter2’ Comonomer content (% by wt.2’) Tin-free steel TFS/ ECCS*’ Tinplate Aluminum 20 210 g-LLDPE 0.3 MA - 82 61 43 21 210 g-LLDPE 0.3 MA - 82 61 43 33 180 E/AA 8 AA 35 60 - - 34 180 E/AA 8 AA 35 60 - - 35 180 E/AA 8 AA 35 60 - - 15 220 g-PP 0.21 MA 31 - - - 37 170 E/BA/AA 9 BA, 4 AA - 39 74 - 38 250 g-LLDPE 0.27 MA — 75 80 - I Key to Table 2: 1. Production of the composite comprising metal sheet and adhesion-promoting layer by the process described in Example 1 2. Abbreviations: 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 3. Surface temperature of the metal sheet during production of the composite comprising metal sheet and adhesion-promoting layer 4. TFS = tin-free steel ECCS = electrolytic chromium-coated steel . Tinplate E5.6/5.6 (DIN 1616) Examples 39 to 42 Food can lids were punched from the plastic-metal composite of Examples 15, 19, 20 and 21 which had been produced according to processes a-c, and the suitability of these lids for use as food can material was tested in the abbreviated test. The test indicates a good resistance toward the customary test solutions (lactic acid, acetic acid, common salt solution, H20) under sterilisation conditions of 121 °C for 30 min.

Examples 43 to 44 Cups of diameter 33 mm and height 25 mm were drawn using the composites from Examples 1 and 3. The cups were then exposed to methylene chloride. The adhesion before commencement of the test and after 72 hours was tested using the Tesa 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 Examples 6, 17 and 28 which had been prepared according to process A-C [sic], and this cup was then stored in isopropanol, xylene, solvent naphtha 100 and solvent naphtha 150. Before commencement of this test and after 72 hours, the adhesion was tested using the Tesa test. No diminution in the adhesion was observed.

Examples 48 and 49 Beverage can shells were stamped from the composites of Examples 4 and 38. These were sterilised for 30 min at 78*C and at 100eC in water. The test shows that the composite is completely resistant (no water absorption, no loss of adhesion).

Claims

Claims:

1. Thermoplastic composite film, comprising at least one adhesion-promoter layer (3) and at least one further, thermoplastic top layer (2, 4) arranged on the adhesionpromoter layer, characterised in that the thermoplastic composite film has annular or discoid, collar-like thickenings (5) of the adhesion-promoter and/or top layer, and in that the collar-like thickenings form a pattern which recurs in both the transverse and longitudinal directions.

2. Metal sheet laminated with a thermoplastic film, where the film has a recurring pattern of thickenings, characterised in that a thermoplastic composite film according to Claim 1 has been laminated on.

3. Metal sheet or thermoplastic composite film according to Claim 1 or 2, characterised in that the collar-like thickenings have a thickness of at least 2 μία, preferably of at least 50 μτα·

4. Metal sheet or thermoplastic composite film according to any one of Claims 1 to 3, characterised in that the thermoplastic composite film has an overall thickness (dry) of less than 500 μτα, preferably 10 to 300 pm.

5. Metal sheet or thermoplastic composite film according to any one of Claims 1 to 4, characterised in that the thickness of the adhesion-promoting layer of the thermoplastic composite films is between 0.5 and 100 pm, preferably between 1 and 70 pm, and the thickness of the top layer of the thermoplastic composite film is between 10 and 499.5 pm, preferably between 10 and 200 pm.

6. Metal sheet or thermoplastic composite film according to any one of Claims 1 to 5, characterised in that the adhesion-promoting layer of the thermoplastic composite film comprises at least one carboxyl-containing polymer, optionally in combination with other polymers.

7. Metal sheet or thermoplastic composite film according to any one of Claims 1 to 6, characterised in that the top layer of the thermoplastic composite film consists of a foamed polymer.

8. Process for the production of metal sheets according to one of Claims 2 to 7, characterised in that either _ a) a thermoplastic composite film which has annular or discoid, collar-like thickenings of the adhesionpromoter and/or top layer is laminated on, or b) the thermoplastic composite film is first laminated on in a uniform layer thickness, and annular or discoid, collar-like thickenings of at least one of the resin layers are produced by embossing and pressing.

9. Process according to Claim 8, characterised in that the thermoplastic composite film is 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 extrusion 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 collar-like 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 coextruded 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. Process according to Claim 8, characterised in that 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. Process according to Claim 8, characterised in that the thermoplastic composite film is 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. Process according to any one of Claims 8 to 10, characterised in that the metal sheet is coated with the thermoplastic composite film by A) laying on top of one another the thermoplastic composite film having the collar-like thickenings and the metal sheet in such a way that an adhesionpromoting 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 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 thickenings during lamination is at most 10 % of the original height of the thickenings.

13. Process according to Claim 8 or 11, characterised in that the metal sheet is coated with the thermoplastic composite film by A) laying on top of one another a thermoplastic composite film which has no collar-like thickenings and the metal sheet in such a way that an adhesionpromoting 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 thickenings are produced during lamination of the composite film or immediately after lamination of the composite film.

14. Use of the metal sheets according to any one of Claims 2 to 7 for the production of packaging containers.

15. Use of the metal sheets according to any one of Claims 2 to 7 for the production of closure components for packaging containers.

16. A thermoplastic composite film according to Claim 1, substantially as hereinbefore described and exemplified.

17. A thermoplastic composite film according to Claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

18. A metal sheet according to Claim 2, substantially as hereinbefore described and exemplified.

19. A metal sheet according to Claim 2, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

20. A process according to Claim 8, substantially as hereinbefore described and exemplified.

21. A metal sheet whenever produced by a process claimed in a preceding claim.

22. Use according to Claim 14 or 15, substantially as hereinbefore described and exemplified.