IE912895A1

IE912895A1 - Stretch-formable laminate

Info

Publication number: IE912895A1
Application number: IE289591A
Authority: IE
Original assignee: Alusuisse Technology And Man L
Priority date: 1990-08-16
Filing date: 1991-08-15
Publication date: 1992-02-26
Also published as: CA2047951A1; PT98689B; DE59109179D1; EP0474587A1; EP0474587B1; CH679656A5; ATE188906T1; DK0474587T3; PT98689A

Abstract

A stretch-formable metal/plastic composite laminate, for example for the production of containers, in which the laminate has a metal layer and a plastic layer on both sides of the metal layer, the metal layer having a thickness x and the plastic layers each having a thickness of from 0.7 x to 1.4 x, and x being from 30 to 70 mu m, and the plastic layers contain or comprise olefin-based thermoplastics, for example polypropylene.

Description

The invention relates to a stretch-formable metal-plastic composite laminate, the use of the laminate and container therefrom.

It is known to use stretch-formed aluminium moulded packs for pharmaceutical products and foodstuffs, for example as press-through packs, containers, under-seal trays, double moulds and the like. They are able to meet to maximum effect the high requirements for the protection of the goods against diffusion of oxygen, steam and light, or escape of, for example fragrances, and to improve the user-friendliness of the pack.

In addition, sterilisability, pasteurisabi1ity or suitability for hot-filling often belong to the stated requi rements.

The state of the art is to produce stretch-formed containers from laminates which have a central aluminium layer, an outer layer of oriented polyamide and an inner layer of polyvinyl chloride. Today the use of polyvinyl chloride should be limited due to reasons relating to environmental protection. Polyvinyl chloride-free layers or those low in polyvinyl chloride have the advantage that if they are energy-recycled as opposed to materialrecycled, they produce no pollutants or only few pollutants on combustion. It is also advantageous for disposal and recycling of laminates of this type if there are as few as possible different types of material.

Composite laminates for packs containing no polyvinyl chloride are known per se.

European Application 0 317 818 describes a packaging laminate for tobacco products which has barrier properties. However, the material is only envisaged for packing, for example cigarettes and is therefore very thin, that is having a maximum thickness limit of 2.5 mils, corresponding to 63.5 pm. A material of this type is not suitable for stretch-forming.

United States patents 4 085 244 and 4 216 268 describe a laminated packaging film comprising an outer biaxially oriented polyamide film, a flexible metal foil, a biaxially oriented polypropylene and an inner sealing layer for the manufacture of pouches.

This film is less suitable as a stretch-form laminate because of its asymmetric construction with a relatively strong inner sealing layer. Furthermore, recycling is made more difficult by the use of two types of plastic.

German Patentschrift 3 436 412 describes a metal sheet laminated on one side or both sides with a biaxially oriented polyester film which ought to be suitable for drawing tins. To achieve secure bonding of metal to the polyester film, the metal sheet must have a double layer of hydrated chromium oxide. A metal sheet of this type is complex to manufacture and chromium oxide layers are undesirable, for example in foodstuffs packaging, or may be prohibited.

None of these film composites or laminates described hitherto can be combined to give optimum properties required for stretch-forming. This also applies to the properties required for reasons relating to environmental protection, which promote, for example recyclability of laminates or the objects prepared therefrom, such as packages .

A suitable composite laminate must support the stretching of the metal layer during the stretch-forming process, so that surface extensions of 80 % and higher may be achieved without damage, such as perforation of the metal layer. Protection of the metal layer with regard to damage by cracks or perforation has greater significance since the metal layer serves primarily as a barrier layer against the diffusion of gases, such as oxygen, steam and light, and against the escape of fragrances and aromatic substances.

The object of the present invention is to provide a stretch-formable metal-plastic composite laminate which does not have the disadvantages mentioned. The stated aim is achieved in accordance with the invention by means of a stretch-formable laminate, the laminate having a metal layer and a plastic layer on both sides of the metal layer, the metal layer having a thickness x and the plastic layers each having a thickness of 0.7 x to 1.4 x, and x being a thickness of 30 to 70 pm, and the plastic layers containing thermoplastics based on olefin or consisting of them.

The metal layer of the laminate may be, for example iron, steel or copper, a preferred metal layer is aluminium or an aluminium alloy. A metal layer is advantageously aluminium having a purity of 98.6 % and higher, preferably 99.2 % and higher, and particularly preferably 99.5 % and higher. Aluminium alloys, for example of the type AA 8079 or AA 8101, are also advantageous.

A soft-annealed, fine-grain and/or largely texture-free (isotropic) aluminium thin tape, in particular having at least 5 and particularly preferably 7 grain layers over the thickness of the tape, is particularly preferred as a metal layer.

The surface of the metal layer and in particular the aluminium layer is preferably homogeneous, without residual greases and having a defined surface. The aluminium surfaces may be treated, for example with stoving lacquers based on epoxide or phenol, or with conversion layers, such as mixed oxide and/or hydrate layers. Furthermore, the surfaces may be pretreated by means of a corona discharge treatment.

The plastic layers contain a thermoplastic based on olefin or consist of it.

The thermoplastics based on olefin are advantageously a polyethylene, polypropylene, poly-(1-butene), poly-(3methylbutene), poly-(4-methylpentene) or copolymers thereof .

Preferred examples of thermoplastics based on olefin are polyolefins, such as polyethylene and in particular high density polyethylene (HDPE, density greater than 0.944 g/cm3), moderate density polyethylene (MDPE, density 0.926-0.940 g/cm3), linear moderate density polyethylene (LMDPE, density 0.926-0.940 g/cm3), low density polyethylene (LDPE, density 0.910-0.925 g/cm3) and linear low density polyethylene (LLDPE, density 0.916-0.925 g/cm3), and polypropylene, polypropylene being most particularly preferred.

The plastic layers may be oriented and are advantageously uniaxially oriented and preferably biaxially oriented. In particular the plastic layers may contain uniaxially oriented and preferably biaxially oriented thermoplastics based on olefin or consist of them. Uniaxially oriented or in particular biaxially oriented polypropylene is most particularly preferred.

The flow behaviour of the plastic layers in the form of films, and in particular of the biaxially oriented polypropylene films, is advantageously as isotropic as possible.

Preferred plastic layers or films below are those in which the yield behaviour shows high strengthening.

High strengthening means that with increasing extension of the film, the tension in the machine direction and in the transverse direction increases.

Films with a yield behaviour characterised by a positive strengthening increase, at least in the machine direction or the tranverse direction, are also preferred. The positive strengthening increase expresses the quotient of the tension increment over the extension increment and is therefore preferably above a value 0, that is the value is preferably positive.

Particularly suitable plastic layers have a high R value, an R value lying in particular above 1. The R value expresses whether the material yields preferably from the width or from the thickness of the particular film. An R value above 1 denotes that the material yields preferably from the width of the sample.

The preferred films include, for example biaxially oriented polypropylene films having a tensile strength in both directions of more than 150 MPa, preferably more than 200 MPa.

The extension to break of preferred films is, for example above 40 % and in particular above 50 %.

The tension in the extension region of 5 to 15 % in preferred films is advantageously between 40 and 120 MPa and in particular between 50 and 100 MPa.

The thickness x mentioned is the thickness for the metal layer and the thickness x may preferably be 40 to 60 pm.

The thickness of each of the plastic layers is preferably 0.75 x to 1.35 x and particularly preferably 0.9 x to 1.2 x.

The plastic layers disposed on both sides of the metal layer and in particular the thermoplastics based on olefin may each be provided additionally with a sealable layer on one side or on both sides independently of one another. The sealing layers may be, for example coextruded. Coextrusion is advantageously carried out before the orientation process. The type of sealable layer is not critical and may contain, for example polyethylene, polypropylene or a polypropylene/polyethylene copolymer, or may consist of them. Other suitable sealing layers are made from, for example polyvinylidene chloride or acrylates, or contain these materials. The thickness range for the sealing layers is, for example 1 to 10 pm, and preferably 1 to 5 pm.

A composite which can be sealed on both sides is obtained both by single-sided and double-sided coextrusion of the plastic layer using, for example a polypropylene/polyethylene copolymer.

The coextruded layer may be directed, for example towards the aluminium. This is a preferred example because in this way, improved adhesive properties and adhesive conditions may be imparted to the adhesive.

It is therefore advantageous that the plastic layers contain a thermoplastic based on olefin or consist of it and at least one of the thermoplastics based on olefin or consist of it provided with a sealing layer on at least one side. That is, each layer of thermoplastic based on olefin may be covered with a sealable layer on one side or on both sides independently of other layers.

The surface of the plastic films should advantageously have at least 35 mN/m and preferably at least 38 mN/m surface tension, so that the application of adhesive onto the plastic surface may be carried out in optimum manner.

The surface tensions, and hence also the adhesive properties, may be controlled by corona pretreatment of the plastic films and/or of the aluminium surfaces.

A laminating adhesive is advantageously used to join the plastic films to the aluminium or the plastic films to one another. The laminating adhesive may be applied to the surface to be adhered by lacquer laminating.

Examples of suitable adhesives are vinyl chloride copolymers, vinyl chloride-vinyl acetate copolymers, polymerisable polyesters, vinylpyridine polymers, vinylpyridine polymers in combination with epoxy resins, butadiene-acrylonitrile-methacrylic acid copolymers, phenol resins, rubber derivatives, acrylic resins, acrylic resins with phenol or epoxy resins or acrylate copolymers, or organosilicon compound, such as organosilanes .

The organosilanes are preferred. Examples of these are alkyltrialkoxysilanes having an amino functional group, alkyltrialkoxysilanes having an epoxy functional group, alkyltrialkoxysilanes having an ester functional group. alkyltrialkoxysilanes having an aliphatic functional group, alkyltrialkoxysilanes having a glycidoxy functional group, alkyltrialkoxysilanes having a methacryloxy functional group, and mixtures thereof. Examples of those'organosilanes are γaminopropyltriethoxysilane and Ν-β-(aminoethyl)-γaminopropyltrimethoxysilane, γ-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane. These compounds are known per se in the specialist field.

Further suitable adhesion promoters are adhesives, such as for example nitrile rubber-phenol resins, epoxides, acrylonitrile-butadiene rubber, urethane-modified acrylics, polyester co-polyamides, hot-melt polyesters, polyisocyanates cross-linked with hot-melt polyesters, polyisobutylene-modified styrene-butadiene rubbers, polyurethanes, ethylene-acrylic acid mixed polymers and ethylene-vinyl acetate mixed polymers.

The polyurethanes are particularly preferred. Depending on the type, the adhesives may be used with or without solvents or from aqueous solution.

As a rule the adhesive layer thickness is kept to 1 to 12 pm and preferably 1.5 to 9 pm. Instead of the layer thickness, the amount of adhesive, especially between the metal layer and the plastic layers arranged right next to both sides of the metal layer, can be expressed by the amount of laminating adhesive. The amount is, for example 1.0 to 14 g/m2, advantageously 1.5 to 9 g/m2, and preferably 1.5 to 6 g/m2. The amount is given without miscellaneous solvent. The plastic films may be heatlaminated on the aluminium surface or also on the opposite surface.

Typical layer constructions for metal laminates according to the present invention contain, for example a) a central layer of aluminium having a thickness of, for example 30 to:70 pm, and preferably 40 to 60 pm, and on both sides of the aluminium layer b) and b') each a layer of a laminating adhesive having a thickness of 1.5 to 9 pm c) and c') each a layer of a polyethylene-polypropylene copolymer having a thickness of, for example 1 to 10 pirn, and preferably 1 to 5 pm, d) and d') each a layer of a biaxially oriented polypropylene film, for example having a thickness of 20 to 90 pm, preferably 35 to 70 pm, and in particular 40 to 50 pm, and e) and e') each a layer of a polyethylene-polypropylene copolymer having a thickness of, for example 1 to 10 pm, and preferably 1 to 5 pm.

In other layer constructions according to the present invention, the layers c) and/or c') and/or the layers e) and/or e') may be omitted. Such advantageous metal laminates then contain, for example only the layer a), the layers b) and b') and d) and d'), or the layer a), the layers b) and b'), d) and d') and the layers e) and e'), or the layer a), the layers b) and b'), the layers c) and c') and the layers d) and d').

Packages produced from the metal-plastic laminates of the invention must be heat-resistant in many cases. For example the package must endure a sterilising or pasteurising process, or the package acts simultaneously as a boiling vessel and must withstand the heating and/or fermentation process of the contents. The individual components of the laminate are therefore advantageously heat-resistant both on their own as well as in interdependent composite.

This property applies in particular to the individual plastic films, where applicable coextrudates or laminates, and the adhesives and adhesion promoters used.

The invention also relates to the use of the stretchformable laminates of the invention for producing stretch-formed containers.

The stretch-formable metal-plastic laminates according to the present invention are particularly suitable for producing stretch-formed containers with a ratio of height to diameter of 1 to 3.7 to 3.2, in particular for a flat container base.

For containers which do not have a round base, diameter has the meaning of the length of the diagonal or the average lengths of the diagonals.

The stretch processes for producing containers from the stretch-formable metal-plastic laminates of the invention are known per se. As a rule, a section of the laminate is placed on a die while cold. The laminate is retained on the edge of the die with the aid of a holding-down device and a stamp is lowered into the die while deforming the laminate.

The laminate is stretched since no material can flow from the edge region. As a result the thickness of the laminate decreases.

The composite construction of the laminate of the invention described has optimum suitability for stretchforming with controlled mechanical properties which aid the extension of the aluminium layer during the stretchforming process, so that surface extensions of 80 % and higher may be achieved without damaging the metal layer.

Extensions up to 40 % and higher may be achieved without damaging the aluminium layer in the uniaxial tension state.

Finally, the stretch-formable metal-plastic laminate according to the present invention can be heat-sterilised in the stretched or non-stretched state, in particular under standard conditions of 121°C for 30 minutes.

The present invention also includes containers of the stretch-formable laminate of the invention, advantageously with a ratio of height to diameter of 1 to 3.7 to 1 to 3.2, in particular for a flat container base.

The containers produced from the stretch-formable metalplastic composite of the invention are in turn suitable, for example to store foodstuffs for humans or animals. Other intended uses are, for example containers for pharmaceutical products, such as coated tablets, tablets, powders and the like, and cosmetic products, such as perfumed serviettes, colorants and the like.

Example A polyurethane laminating adhesive having an application weight of 5.5 to 6.5 g/m2 is applied to an aluminium thin tape having a thickness of 45 pm and a clean surface without pretreatment.

The laminating adhesive solvent is evaporated in the drying channel and then laminated in the laminating gap under pressure with a biaxially oriented oPP film coextruded on both sides from a polypropylenepolyethylene copolymer and having a thickness of 50 pm, and rolled-up or further processed immediately.

Further processing is carried out in identical manner to the above, only now the other side of the aluminium thin tape is laminated under the same conditions.

The finished product is cured at 40 to 50° for a few days and then tested: The composite adhesion is approximately 10 N/15 mm strip.

The deforming properties may be outlined as follows: A break depth of more than 9 mm may be achieved by stretch-forming using a flat stamp of diameter 27 mm and a die of diameter 30 mm.

A break depth of more than 13 mm may be achieved by stretch-forming using a semi-spherical stamp with radius 13.5 mm and a die of diameter 30 mm.

Adequate thermal sealing against an identical sealing layer may be carried out starting at a temperature of 140°C.

Sterilisation at a temperature of 121°C for 30 minutes after deformation and ageing for three months at 45°C did not lead to delamination of the plastic layers.

Claims

1. Stretch-formable metal-plastic composite laminate characterised in that the laminate has a metal layer and a plastic layer oh both sides of the metal layer, the metal layer having a thickness x and the plastic layers each having a thickness of 0.7 x to 1.4 x, and x being a thickness of 30 to 70 pm, and the plastic layers containing thermoplastics based on olefin or consisting of them.

2. Stretch-formable laminate according to claim 1, characterised in that the metal layer is an aluminium layer.

3. Stretch-formable laminate according to claim 1, characterised in that the thermoplastics based on olefin are a polyethylene, polypropylene, poly-(1-butene), poly(3-methylbutene), poly-(4-methylpentene) or copolymers thereof .

4. Stretch-formable laminate according to claim 1, characterised in that the thermoplastics based on olefin are biaxially oriented.

5. Stretch-formable laminate according to claim 1, characterised in that the thermoplastic based on olefin is a polypropylene.

6. Stretch-formable laminate according to claim 1, characterised in that the plastic layers contain a thermoplastic based on olefin or consist of it, and at least one of the thermoplastics based on olefin or consist of it is provided with a sealing layer on at least one side.

7. Stretch-formable laminate according to claim 1, characterised in that x is a thickness of 40 to 60 pm.

8. Stretch-formable laminate according to claim 1, characterised in that the thickness of each of the plastic layers is 0.75 x to 1.35 x.

9. Stretch-formable laminate according to claim 1, characterised in that the thickness of each of the plastic layers is 0.9 x to 1.2 x.

10. Use of the stretch-formable laminate according to claim 1 for producing stretch-formed containers.

11. Container produced from a stretch-formable laminate according to claim 1.

12. A method of producing a stretch-formable laminate according to claim 1, substantially as described herein by way of example.