GB2125733A

GB2125733A - Polyolefin coated cardboard

Info

Publication number: GB2125733A
Application number: GB08323051A
Authority: GB
Inventors: Roland Fink; Edgar Fleischmann; Dr Heinrich Heitz; Rainer Hemberger
Original assignee: Alkor GmbH Kunstoffverkauf
Current assignee: Alkor GmbH Kunstoffverkauf
Priority date: 1982-08-28
Filing date: 1983-08-26
Publication date: 1984-03-14
Also published as: FR2532343B1; IT8322649A0; DK163255C; SE8304590D0; DK163255B; GB2125733B; NL8302706A; DK390983D0; SE8304590L; IT1169784B; SE458213B; ATA305483A; BE897598A; DK390983A; FR2532343A1; CH667889A5; AT384444B; GB8323051D0

Abstract

Cardboard is directly provided with a polyolefine coating consisting of a composite polyolefin film made up of at least two layers, which is applied on at least one side of the cardboard. The composite polyolefin film is made up of a fusibly adherent film as an inner film, and of at least one surface film, the films being of particular specified compositions and properties. The coated cardboard is made by applying the composite polyolefin film onto one side of the cardboard, completely covering it, with at least one strip-shaped overlap of the cardboard on the other side, a and preferably the other side of the cardboard is covered with a second composite polyolefin film, with strip-shaped or frame-shaped overlapping of the first polyolefin composite film. The product is suitable for files, ring binders and office and stationery requisites.

Description

SPECIFICATION Cardboard provided with a polyolefin coating, preferably for files, ring binders and other organisational. office and stationery requisites and method of producing same This invention relates to a cardboard provided with a polyolefin coating, preferably for files, ring binders and other organisational, office and stationery requisites, and the method of producing the same.

It is already known to coat paper or cardboard material with a body of paper or cardboard on at least one surface with a low density polyethylene resin and to apply a second coating of a high density resin on the outer surface of the low density resin (cf. DE-OS 25 30 477). This method serves for sealing the paper and cardboard material, in order to produce, with the aid of the resulting coating, a fluid-tight material, e.g. for milk packaging and other packaging in dairies.

These seals for fluid-tight packaging, with the aid of coatings with particular polyethylene resin take place between the layers of high density polyethylene, but are not suitable if the cardboard is to be supplied for another use and is to be enclosed according to different methods. In particular, fluid-tight seals according to DE-OS 2530477 are not suitable, because if a subsequent precisely contoured stamping is required as in the manufacture of surface-coated cardboards for organisational purposes, e.g. in the case of files, ring binders, book covers and suchlike, temperatures over 90"C are necessary. Here, the humidity contained in the cardboard would lead to bubbles on stamping without cooling under pressure.

It is an object of the present invention to avoid an additional application of adhesive onto the cardboard and/or polyolefin coating or film, but nevertheless to achieve a good adhesion of the surface layer and if possible to achieve, with shorter production time, improved properties of the film and composite, preferably an improved amenability to stamping of the composite of film and cardboard, while reducing risk of embrittlement. Through the elimination of the use of additional adhesives, the pre-warming or after-heating of layers or adhesive layers for the purpose of predrying or vaporization of a solvent or thinning agent of the adhesive could largely be dispensed with.

According to one aspect of the present invention, there is provided cardboard provided with a polyolefin coating and suitable for files, ring binders and organisational, office and stationery requisites, wherein a layer of cardboard having a thickness of 0.3 to 5 mm has adhered thereto by fusion a composite polyolefin film comprising at least an inner layer and an outer layer, the film having been applied directly on at least one side of the layer of cardboard or having been applied so as completely to cover said one side and overlap it to provide at least one stripshaped or a frame-shaped overlap of the cardboard on the other side, with said inner layer of the flim in contact with the cardboard, and wherein the composite polyolefin film comprises (1) a fusibly adherent inner layer which a) consists of an olefin homopolymer or copolymer or mixture of such homopolymer(s) and/or copolymer(s) which, in relation to the total weight of the inner layer, contains from 33 to 5% by weight of a polar monomer or mixture of polar monomers in the form of solid or liquid, monomeric or copolymerised compound(s), b) has a melting point or melting range of 50 to 95on, c) has a density greater than that of the outer layer, and d) has a melt index 190/2.16 of less than 10 g/10 minutes, and (2) at least one outer layer which a) consists of an olefin homopolymer, an olefin copolymer, an olefin copolymer having polar groups, or a mixture of olefin homopolymer(s) and/or olefin copolymer(s), b) has a melting range greater than 1 00,C c) has a melt index 190/2.1 6 of less than 10 g/ 10 minutes, d) has a hardness of less than 65 Shore D, and e) has a density of 0.89 to 0.93 g/cm3.

The composite polyolefin film comprises a fusibly adherent film as the inner or lower layer, consisting of an olefin homo-, -copolymer or olefin homo- or -copolymer mixture, which as a whole (in relation to the total synthetic material mixture for the inner layer) contains preferably 30 to 7% by weight of a polar monomer or polar monomer mixture in the form of the solid or liquid monomeric or copolymerisable compounds, preferably as polar comonomer(s). The inner layer has a melting point or melting range of preferably 60 to 90"C, and a density which is greater than the density of the outer or upper film.The composite polyolefin film also comprises at least one surface or outer film consisting of an olefin homo-, olefin copolymer, an olefin copolymer having polar groups or an olefin homo- or olefin copolymer mixture, and has a melting point or melting range greater than 100"C, preferably greater than 105"C, a hardness of preferably less than 50 Shore D and a density of preferably 0.915 to 0.926 g/cm3. The cardboard is directly connected with the fusibly adherent inner layer without the additional use of layer of adhesive, and the cardboard preferably has a thickness of 1 to 3 mm.

In the use or additional use of propylene homo- or copolymers for the surface film, a density of 0.89 to 0.915 g/cm3 results, preferably 0.90 to 0.915 g/cm3, and a hardness of less than 65 Shore D, so that as a whole for the surface film (in the use of propylene- and/or ethylene homo- or -copolymers), a hardness of less than 65 Shore D, preferably less than 50 Shore D and a density range of 0.89 to 0.93 g/cm3, preferably 0.90 to 0.926 g/cm3, is to be taken as a basis.

In the application of the composite polyolefin film, an additional application of adhesives onto the cardboard and/or film is therefore dispensed with; likewise a pre-warming of the adhesive layer to vaporize a thinning agent of an adhesive is not necessary. Shorter production times are achieved. Pre-drying of the cardboard is likewise not necessary, because the sealing point of the fusibly adherent film layer lies below the volatilization temperature of the humidity contained in the cardboard. A good adhesion of the inner film on the cardboard and on the surface film at the seam point is produced.

Owing to the high viscosity of the inner layer, the composite of foil and cardboard can be stamped, on lamination coating, without an accelerated cooling being necessary, with or without the action of pressure.

Preferably, the composite polyolefin film, composed of the fusibly adherent inner film and at least one surface film, has a thickness of 50 to 400 ym, more preferably 80 to 300,um, and the fusibly adherent inner film itself has a thickness of 5 to 50 jum, preferably 10 to 30,us.

Preferably, the olefin copolymer, which has polar groups, or olefin copolymer mixture consists of at least one ethylene- and/or propyiene copolymer or contains the latter, whereby as a whole 33 to 5% by weight, preferably 30 to 7% by weight of a polar monomer or of a polar monomer mixture are contained as comonomer(s) or as polar units in the total synthetic material mixture for the fusibly adherent film. The olefin copolymer or olefin copolymer mixture is preferably produced through copolymerisation of the polar monomer mixture with an ethylene and/or propylene homo- and/or -copolymer.

In another embodiment, the olefin copolymer mixture, having polar groups, may consist of an ethylene- and/or propylene homo- and/or -copolymer containing non-polar groups, and an olefin copolymer containing polar groups, preferably an ethylene copolymer containing polar groups, which is produced through copolymerisation with 10 to 70% by weight, preferably 25 to 60% by weight of a polar monomer or polar monomer mixture, provided that as a whole 33 to 5% by weight, preferably 30 to 7% by weight of a polar monomer or of a polar monomer mixture are contained as comonomer(s) or as polar units in the total synthetic material mixture for the fusibly adherent film.

In addition, the melt index (1 90/2.1 6) of the polyolefin copolymerised with one or more polar monomers, and/or mixture of polyolefins with copolymers with polar monomers of the fusibly adherent film is preferably less than 8 g/10 min.

Preferably, the fusibly adherent film contains in addition an inorganic filler material as an antiblocking agent. Also, the surface film expediently contains an inorganic filler material, which may serve as a delustering agent.

Preferably, per 100 parts by weight of the synthetic resin or synthetic resin mixture present in the fusibly adherent film and/or the surface film, 0 to 40 parts by weight, preferably 0.5 to 20 parts by weight of filler material are present. The filler material should consist of very fine particles.

The inorganic filler material may be chalk, talcum, silicon dioxide, glass pellets or a mixture of two or more thereof and the average grain size of the filler material is preferably less than 40 more more preferably less than 20 ym.

Per 100 parts by weight of the synthetic resin or synthetic resin mixture present in the fusibly adherent film and/or surface film 0.3 to 5 parts by weight, preferably 0.5 to 3 parts by weight of one or more processing adjuvants may be added. Since both the outer film and also the fusibly adherent inner film are deficient in plasticisers (plasticiser content less than 3% by weight), and are preferably free of primary or fluid plasticisers, the films have the advantage that a loss of plasticiser can not occur, or can only occur to a very reduced extent.

"Free of plasticisers" is understood to mean, within the framework of the present invention, that the preparations are free of primary or fluid plasticisers or are free of other external plasticisers. "Deficient in plasticisers" is understood to mean that they only have a very smali content of primary fluid plasticisers, for example in preparations which also contain pigments, colorants or fillers.

The preferred polyolefins copolymerised with polar monomers or olefin copolymers containing polar groups are those which contain ethylene vinyl acetate copolymer with a vinyl acetate content of 33 to 5% by weight, preferably 30 to 7% by weight, and/or alkyl- or alkylene acrylates, in particular ethylene acrylate and/or butyl- and/or isobutyl acrylate.

These required properties can also be achieved with mixtures of polyolefins and copolymers with a higher proportion of the above-mentioned monomers in a ratio such that the proportion amounts to 33 to 5% by weight, preferably 30 to 7% by weight of these monomers in the mixture.

The polyolefin mixtures or olefin copolymer mixtures can also contain a proportion of other synthetic substances in quantities of up to 15% by weight, preferably up to 10% by weight, for example EPDM (terpolymer of ethylene, propylene and a diene, with an unsaturated part of the diene in the side chain), EPM (ethylene-propylene-copolymers) etc.

The surface or upper film preferably consists of polyethylene, preferably high pressure polyethylene, polypropylene or a copolymer thereof or a mixture with a-olefin polymers, in which the modulus of elasticity is less than 104 kp/cm2, preferably less than 103 kp/cm2 and the Shore D hardness is less than 65, preferably less than 50.

The composite polyolefin film composed of the fusibly adherent inner film or layer and at least one surface or outer film or layer, is preferably a coextruded film.

The film may be produced with the use of a subsequent treatment and cooling according to the chill rolling method.

Alternatively, the composite polyolefin film may be stamped jointly with the cardboard.

The composite polyolefin film composed of the fusibly adherent film or layer and at least one surface film preferably has a modulus of elasticity less than 104 kp/cm2, more preferably less than 103 kp/cm2, and a Shore D hardness less than 65, preferably less than 50.

According to another aspect of the present invention there is provided cardboard with a polyolefin coating, wherein a composite polyolefin film comprising at least an inner layer and an outer layer is applied on at least one side of a layer of cardboard having a thickness of 0.3 to 5 mm or is applied so as completely to cover said one side of said layer of cardboard and overlap it to provide at least one strip-shaped or a frame-shaped overlap of the cardboard on the other side, the film being applied with its inner layer directly in contact with the cardboard under pressure and at a temperature of 50 to 95"C to effect adhesion to the cardboard by fusion, and wherein the composite polyolefin film comprises (1) a fusibly adherent inner layer which a) consists of an olefin homopolymer or copolymer or mixture of such homopolymer(s) and/or copolymer(s) which, in relation to the total weight of the inner layer, contains from 33 to 5% by weight of a polar monomer or mixture of polar monomers in the form of solid or liquid, monomeric or copolymerised compound(s), b) has a melting point or melting range of 50 to 95"C, c) has a density greater than that of the outer layer, and d) has a melt index 190/2.16 of less than 10 g/10 minutes, and (2) at least one outer layer which a) consists of an olefin homopolymer, an olefin copolymer, an olefin copolymer having polar groups, or a mixture of olefin homopolymer(s) and/or olefin copolymer(s), b) has a melting range greater than 1 00 C c) has a melt index 190/2.16 of less than 10 g/10 minutes, d) has a hardness of less than 65 Shore D, and e) has a density of 0.89 to 0.93 g/cm3.

The fusibly adherent film or inner layer preferably contains 30 to 7% by weight of said polar monomer or polar monomer mixture and preferably has a melting point or melting range of 60-90"C. The surface film or outer layer preferably has a melting point or melting range of greater than 105"C. In carrying out the present method, the composite polyolefin film is laminated onto the cardboard without the additional use of a layer of adhesive, directly by means of the fusibly adherent film or inner layer. The application or lamination takes place at a temperature of 50 to 95"C, preferably 70 to 90"C, under the action of pressure.

In one preferred form of embodiment of the method, the cardboard, which preferably has a thickness of 1 to 3 mm is cut to the desired measurement and a composite polyolefin film with larger dimensions than those of the cardboard is applied on one side of the cardboard fully covering it, whilst maintaining at least one free composite polyolefin film edging strip and is then flapped around the cardboard, so that the polyolefin film, overlapping the cardboard on the other side in the form of a strip or frame, preferably fully encloses the cardboard with a second composite polyolefin film with strip- or frame-shaped overlapping of the first composite polyolefin film.

After completion of the desired, e.g. rectangular or square cut, the cardboard is either directly passed on to further processing, or is stacked and/or stored in a warehouse. The composite polyolefin film is cut to the required dimensions in, for example, a book covering machine, preferably unwinding from a roll. The flapping over of the free composite polyolefin edging strip projecting over the cardboard takes place by means of mechanical devices or methods, preferably with the use of brushes.

The lamination coating takes place preferably by means of plates and/or rolls pressed to shape.

In pressing by means of plates, the amount of pressure applied is conveniently 0.3 to 5 kp/cm2, and in roll lamination coating the line pressure is 3 to 30 kp/cm, the application of the film under heat and pressure conveniently being effected for 0.5 to 5 seconds.

Additional measures for the fixing of the stamping are not necessary in the present method.

The heat is conveniently transferred through permanently heated plates or rolls onto the layers or films which are to be connected, and these plates or rolls may stamp the composite, without additional measures for fixing the stamping being used.

The invention will now be illustrated by the following Examples.

Example 1 The composite polyolefin film is a coextruded film in which the upper or outer film consists of polypropylene ("ELTEX" PKS 404-" ELTEX" is a Registered Trade Mark of Solvay a Cie) and the lower or inner film consists of an olefin copolymer mixture containing polar groups, containing 9% by weight of a mixture of high molecular weight acrylic ester and a polyethylene.

The thickness of the upper film or layer is 120,um, and that of the inner film or layer is 30 yam.

Sealing temperature: 90 C Welded joint strength: 6 N/15 mm Sealing time: 3 seconds Adhesion to cardboard: inseparable; delamination of the cardboard at increased loading in tensile test.

Example 2 The composite polyolefin film is a coextruded film of polyolefin base, in which the upper film consists of high pressure polyethylene (LDPE 1018 of BASF) and the lower film consists of a copolymer of ethylene with ethylene vinyl acetate, containing polar groups (EVA content 30% by weight).

Sealing temperature: 90"C Welded joint strength: 2.5 N/15 mm Sealing time: 3 seconds Adhesion to cardboard: Tearing of the cardboard at increased loading in tensile test.

Example 3 The composite polyolefin film consisted of an upper film of a linear high pressure polyethylene (linear-low-density polyethylene), and a lower film comprising a mixture of copolymers of ethylene with ethylene vinyl acetate containing polar groups, and consisting of 50 parts by weight with a vinyl acetate content of 20% by weight and of 50 parts by weight with a vinyl acetate content of 30% by weight.

Sealing temperature: 88"C Welded joint strength: 1.2 N/15 mm Sealing time: 3.5 seconds Adhesion to cardboard: Partial tearing of the cardboard at increased loading in tensile test.

Example 4 The composite polyolefin film consisted of an upper film of 50 parts by weight of a iinear high pressure polyethylene and 50 parts by weight of an ethylene copolymer containing polar groups with an ethylene vinyl acetate content of 30% by weight, and a lower film comprising 100 parts by weight of an ethylene copolymer containing polar groups with an ethylene vinyl acetate content of 30% by weight.

Sealing temperature: 92"C Welded joint strength: 3.2 N/1 5 mm Sealing time: 2.8 seconds Adhesion to cardboard: Tearing of the cardboard on increased loading in tensile test.

Examples 5-8 A composite polyolefin film was used which, in each of these Examples, the upper film was respectively the same as described in Examples 1 to 4. In addition, 0.5 to 3% by weight of filler material was added to the synthetic material or synthetic material mixture of the lower film, as an anti-blocking agent. With a sealing time of 3 seconds and a sealing temperature of 90"C, adhesions of 2.5 to 3.5 N/15 mm were measured. In all the adhesion tests, tearing of the cardboard occurred on increased loading in the tensile test.

Examples 9-12 In each of these Examples the respective lower film was the same as described in Examples 1 to 4. In addition, 0.5 to 3% by weight of filler material was added to the upper film as antiblocking agent. These correspond to the respective upper films of Examples 1 to 4 (without the addition of fillers) or Examples 5 to 8.

Example 12 The composite polyolefin film comprised a lower film as described in Example 2 and an upper film which was the same as that in Example 2, but which, in addition, contained 7 parts by weight EPDM (terpolymer of ethylene, propylene and a diene with an unsaturated part of the diene in the side chain), to set the degree of sheen of the foil.

Sealing temperature: 87"C Sealing time: 2 seconds Adhesion to cardboard: Partial delamination of the cardboard in the adhesion test.

Example 14 A coextruded film was used in which the upper film consisted of high pressure polyethylene and the lower film consisted of a mixture of 60 parts by weight of linear high pressure polyethylene and 40 parts by weight of an ethylene vinyl acetate copolymer containing polar groups, with a vinyl acetate content of 60% by weight.

Hardness: 48 Shore D Sealing temperature: 94"C Sealing time: 2.5 seconds Adhesion to cardboard: Tearing of the cardboard at increased loading in tensile test.

In order to enable the invention to be more readily understood reference will now be made to the accompanying drawing which illustrates diagrammatically and by way of example an embodiment thereof, and which is a section through part of a cardboard, provided with a polyolefin coating, for files, ring binders or similar organisational, office and stationery requisites.

Referring now to the drawing there is shown a piece of cardboard 3 with a polyolefin coating in the form of a composite polyolefin film comprising a fusibly adherent lower film 1, which together with a surface or upper film 2 is produced by a coextrusion process. The cardboard 3, cut to the desired dimension, is enclosed by the composite film so that on the under side of the cardboard 3 a composite polyolefin film with larger dimensions than those of the cardboard is applied, whilst maintaining at least one free edging strip or polyolefin composite foil, and the film is subsequently flapped around the cardboard, so that the composite polyolefin film furnishes the cardboard on the upper side with a strip- or frame-shaped overlap 4. According to a preferred embodiment, a second composite polyolefin film is applied on the upper side of the cardboard, with a strip- or frame-shaped overlap 5 of the first composite polyolefin film overlap.

Claims

1. Cardboard provided with a polyolefin coating and suitable for files, ring binders and organisational, office and stationery requisites, wherein a layer of cardboard having a thickness of 0.3 to 5mm has adhered thereto by fusion a composite polyolefin film comprising at least an inner layer and an outer layer, the film having been applied directly on at least one side of the layer of cardboard or having been applied so as completely to cover said one side and overlap it to provide at least one strip-shaped or a frame-shaped overlap of the cardboard on the other side, with said inner layer of the film in contact with the cardboard, and wherein the composite polyolefin film comprises (1) a fusibly adherent inner layer which a) consists of an olefin homopolymer or copolymer or mixture of such homopolymer(s) and/or copolymer(s) which, in relation to the total weight of the inner layer, contains from 33 to 5% by weight of a polar monomer or mixture of polar monomers in the form of solid or liquid, monomeric or copolymerised compound(s), b) has a melting point or melting range of 50 to 95"C, c) has a density greater than that of the outer layer, and d) has a melt index 190/2.16 of less than 10 g/10 minutes, and (2) at least one outer layer which a) consists of an olefin homopolymer, an olefin copolymer, an olefin copolymer having polar groups, or a mixture of olefin homopolymer(s) and/or olefin copolymer(s), b) has a melting range greater than 100"C c) has a melt index 190/2.16 of less than 10 g/10 minutes, d) has a hardness of less than 65 Shore D, and e) has a density of 0.89 to 0.93 g/cm3.

2. Cardboard as claimed in claim 1, wherein the inner layer contains from 30 to 7% by weight of said polar monomer or mixture of polar monomers.

3. Cardboard as claimed in claim 1 or 2, wherein the inner layer has a melting point or melting range of 60 to 90"C.

4. Cardboard as claimed in any one of claims 1 to 3, wherein said outer layer has a hardness of less than 50 Shore D.

5. Cardboard as claimed in any one of claims 1 to 4, wherein said outer layer has a melting range greater than 105"C.

6. Cardboard as claimed in any one of claims 1 to 5, wherein said outer layer has a density of 0.90 to 0.926 g/cm3.

7. Cardboard as claimed in any one of claims 1 to 6, wherein said layer of cardboard has a thickness of 1 to 3 mm.

8. Cardboard as claimed in any one of claims 1 to 7, wherein said composite polyolefin film has a thickness of 50 to 400 ym.

9. Cardboard as claimed in any one of claims 1 to 8, wherein said composite polyolefin film has a thickness of 80 to 300,us.

10. Cardboard as claimed in any one of claims 1 to 9, wherein said inner layer has a thickness of 5 to 50 ym.

11. Cardboard as claimed in any one of claims 1 to 10, wherein said inner layer has a thickness of 10 to 30,us.

12.. Cardboard as claimed in any one of claims 1 to 11, wherein the inner layer comprises at least one ethylene- and/or propylene copolymer and from 33 to 5% by weight of polar monomer or polar monomer mixture as comonomer(s) or polar units.

1 3. Cardboard as claimed in any one of claims 1 to 11, wherein the inner layer comprises an ethylene and/or propylene homo- and/or copolymer containing non-polar groups and an olefin copolymer which contains polar groups and which has been produced by copolymerisation of an olefin copolymer and 10 to 70% by weight of a polar monomer or mixture of monomers.

14. Cardboard as claimed in claim 13, wherein said copolymerisation has been effected with 25 to 60% by weight of said polar monomer or mixture of monomers.

15. Cardboard as claimed in any one of claims 1 to 14, wherein the melt index 190/2.

16 of said inner layer is less than 8 g/10 minutes.

1 6. Cardboard as claimed in any one of claims 1 to 15, wherein the inner layer and/or the outer layer of said composite polyolefin film contain(s) an inorganic filler material.

1 7. Cardboard as claimed in claim 16, wherein the inorganic filler material is chalk, talcum, silicon dioxide, glass pellets or a mixture of two or more thereof.

1 8. Cardboard as claimed in claim 1 6 or 17, wherein the inorganic filler material has an average grain size less than 40 ym.

1 9. Cardboard as claimed in any one of claims 1 6 to 18, wherein the inorganic filler material has an average grain size less than 20 pom.

20. Cardboard as claimed in any one of claims 1 to 16, wherein the outer layer comprises polyethylene, polypropylene, a copolymer thereof or a mixture thereof with a-olefin polymer(s), and has a modulus of elasticity of less than 104 kp/cm2.

21. Cardboard as claimed in claim 18, wherein the outer layer has a modulus of elasticity of less than 103 kp/cm2.

22. Cardboard as claimed in any one of claims 1 to 21, wherein-the composite polyolefin film is a coextruded film.

23. Cardboard as claimed in claim 22, wherein the composite polyolefin film is manufactured by the flat film method with subsequent cooling.

24. Cardboard as claimed in any one of claims 1 to 23, wherein the composite polyolefin film has a modulus of elasticity of less than 104 kp/cm2.

25. Cardboard as claimed in any one of claims 1 to 24, wherein the composite polyolefin film has a modulus of elasticity of less than 103 kp/cm2.

26. Cardboard as claimed in any one of claims 1 to 25, wherein the other side of the cardboard is covered with another layer of said composite polyolefin film overlapping the first so as completely to envelop said layer of cardboard in said film.

27. Cardboard provided with a polyolefin coating and suitable for files, ring binders and organisational, office and stationery requisites substantially as hereinbefore described with reference to the accompanying drawing and/or in any one of the foregoing Examples.

28. A method of producing cardboard with a polyolefin coating, wherein a composite polyolefin film comprising at least an inner layer and an outer layer is applied on at least one side of a layer of cardboard having a thickness of 0.3 to 5mm or is applied so as completely to cover said one side of said layer of cardboard and overlap it to provide at least one strip-shaped or a frame-shaped overlap of the cardboard on the other side, the film being applied with its inner layer directly in contact with the cardboard under pressure and at a temperature of 50 to 95"C to effect adhesion to the cardboard by fusion, and wherein the composite polyolefin film comprises (1) a fusibly adherent inner layer which a) consists of an olefin homopolymer or copolymer or mixture of such homopolymer(s) and/or copolymer(s) which, in relation to the total weight of the inner layer, contains from 33 to 5% by weight of a polar monomer or mixture of polar monomers in the form of solid or liquid, monomeric or copolymerised compounds(s), b) has a melting point or melting range of 50 to 95"C, c) has a density greater than that of the outer layer, and d) has a melt index 190/2. 16 of less than 10 g/ 10 minutes, and (2) at least one outer layer which a) consists of an olefin homopolymer, an olefin copolymer, an olefin copolymer having polar groups, or a mixture of olefin homopolymer(s) and/or olefin copolymer(s), b) has a melting range greater than 100"C c) has a melt index 190/2.16 of less than 10 g/10 minutes, d) has a hardness of less than 65 Shore D, and e) has a density of 0.89 to 0.93 g/cm3,

29.A method as claimed in claim 28, wherein the inner layer contains from 30 to 7% by weight of said polar monomer or mixture of polar monomers.

30. A method as claimed in claim 28 or 29, wherein the inner layer has a melting point or melting range of 60 to 90"C.

31. A method as claimed in any one of claims 28 to 30, wherein said outer layer has a melting range of greater than 105"C.

32. A method as claimed in any one of claims 28 to 31, wherein said outer layer has a hardness of less than 50 Shore D.

33. A method as claimed in any one of claims 28 to 32, wherein the film is applied at a temperature of 70 to 90"C.

34. A method as claimed in any one of claims 28 to 33, wherein the film is applied so as completely to envelop the cardboard.

35. A method as claimed in any one of claims 28 to 34, wherein the composite polyolefin film is produced by coextrusion and subsequently applied to the cardboard.

36. A method as claimed in any one of claims 28 to 35, wherein the film is applied to the cardboard under pressure by means of plates at a pressure of 0.3 to 5 kp/cm2.

37. A method as claimed in any one of claims 28 to 35, wherein the film is applied to the cardboard under pressure by means of rolls at a line pressure of 3 to 20 kp/cm2.

38. A method as claimed in claim 36 or 37, wherein the plates or rolls are heated.

39. A method as claimed in any one of claims 36 to 38, wherein the plates or rolls stamp or cut the composite film to shape.

40. A method as claimed in any one of claims 28 to 39, wherein the application of the film under heat and pressure is effected for 0.5 to 5 seconds.

41. A method as claimed in any one of claims 28 to 40, wherein the cardboard is cut to the desired shape, and the composite polyolefin film having dimensions larger than those of the cardboard is applied on one side of the cardboard so as completely to cover it, whilst maintaining at least one free edge of the composite film as an edging strip which is subsequently flapped around the cardboard, so that the composite film surrounds the cardboard on the other side, overlapping in the form of a strip or frame, and wherein the cardboard is completely enveloped by applying a second composite polyolefin film with strip- or frameshaped overlapping of the first composite film.

42. A method of producing cardboard with a polyolefin coating substantially as hereinbefore described with reference to the accompanying drawing and/or in any of the foregoing Examples.