GB1584531A

GB1584531A - Metal-plastics flexible laminates

Info

Publication number: GB1584531A
Application number: GB11756/78A
Authority: GB
Original assignee: Vaw Leichtmetall GmbH
Current assignee: Vaw Leichtmetall GmbH
Priority date: 1977-03-25
Filing date: 1978-03-23
Publication date: 1981-02-11
Also published as: IT1156935B; CH628587A5; FR2384617A1; IT7867680A0; DE7709445U1; FR2384617B1

Abstract

The composite material for producing cylindrical containers for packaging aggressive filling material consists of a metal film laminated on both sides with thermoplastic films by means of a laminating adhesive. The material is suitable in particular for tubes for fluorine-containing toothpaste and provides thermally welded seams of high strength and low thickness and makes possible perfect thermal welding to the tube head part.

Description

(54) METAL PLASTICS FLEXIBLE LAMINATES (71) We, VAW LEICHTMETALL GmbH, a German Body Corporate of Dellweg 1, D 5300 Bonn 1, Federal Republic of Germany do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a laminate for use in the manufacture of ductile containers, e.g.

tubes, which can be squeezed and/or folded for dispensing their contents.

Ductile containers of that kind are known which are formed mainly of metal or alternatively of one or more plastics foils. The known containers are not suitable or not entirely suitable for holding certain substances, for example fluoride-containing tooth paste. Very strict requirements must be satisfied in the packaging of such materials.

The inner surfaces of the known metal tubes are usually protected by a sprayed-on protective paint or lacquer but this coating inevitably has pores so that it cannot prevent corrosion of the metal.

The known tubes made of one or more plastics layers provide less resistance than metal tubes to outward diffusion of substances contained in the tubes and they allow penetration of light into the tubes. Furthermore certain substances contained in tooth pastes can penetrate into the plastics and degrade it so that its protective function is further impaired.

Attempts have been made to overcome these difficulties, by forming containers for fluoride-containing tooth pastes from multilayer laminates of paper, plastics and metal, using up to six layers. Such tubes function well enough but the manufacturing costs are too high, partly due to the number of manufacturing steps involved.

When making squeezable and/or foldable tubes from a ribbon of sheet metal, the two margins of the ribbon are usually joined together by overlap welding to form a hollow cylinder which is subsequently welded to the tube head. When the margins of a ribbon of a six-layer laminate are welded together in that way the resulting twelve-layer structure at the weld is so thick compared with the remainder of the cylinder wall that mechanical difficulties arise in welding the cylinder to the tube head and a tight joint cannot be ensured.

There is therefore a need for a material from which squeezable and/or foldable containers, such as tubes, can be satisfactorily produced at low cost. The material should be resistant to penetration by light and foreign substances and resistant to outward migration of substances to be stored in the containers, and particularly fluoride-containing substances. The material should be weldable for forming it into containers which are mechanically strong, particularly at the welding seam and where the container body is joined to another part or to other parts of the container.

According to the present invention there is provided a laminate suitable for use in forming ductile containers, e.g. tubes, which can be squeezed or folded for dispensing their contents, such laminate incorporating a metal layer and synthetic plastics layers, characterised in that the laminate comprises a ductile ply of metal, 0.03 to 0.15 mm in thickness, which on each face bears a preformed polyolefin foil 0.03 to 0.10 mm in thickness, which foils, after folding the laminate to bring portions of such foils into contact with each other, can be fusion-jointed together, at least one of said plastics foils being bonded to the metal ply by an intervening layer formed from a two-component adhesive composition based on polyurethane.

Preferably the metal ply has a tensile strength of 5 to 10 kp/mm and an elongation at rupture of 7 to 15%. Such properties are very suitable for laminates to be used in forming ductile containers, such as squeezable tubes.

In preferred embodiments of the invention the metal ply is made of aluminium.

The plastics foils, are each 0.03 to 0.10 mm in thickness and one at least of these foils is bonded to the metal by a polyurethane adhesive layer. The two plastics foils need not be identical but they should be compatible in the sense that they can be firmly welded (fusion jointed) together to make a stable welded seam. In certain embodiments of the invention the two polyolefin foils are polyethylene foils. For example both foils can be formed of high density polyethylene.

In other embodiments, polypropylene foils are used. The two foils can be of different thicknesses, as hereafter exemplified.

If only one of the polyolefin foils is bonded to the metal by a layer formed from a twocomponent polyurethane adhesive composition that foil should be disposed at the inside of a container when it is formed from the laminate. The second polyolefin foil can be secured to the metal in a different way, e.g.

by means of an adhesive foil.

Preferably at least one of the polyolefin foils is bonded to the metal ply by a said polyurethane adhesive layer having a dry weight of 4 to 8g/m2. Said foil is thereby made very resistant to separation from the metal substrate. The different polyolefin foils can be bonded to the metal substrate by adhesive layers of different thicknesses as hereinafter exemplified.

In order to give a container an attractive outer surface, promoting saleability, a white exterior is often preferred. A convenient and economic way of achieving this whiteness is to incorporate a white pigment in the polyolefin composition used for the outer ply. The whiteness can be accentuated by incorporating a white pigment filler into an adhesive layer underlying that outer ply.

The outer plastics layer can be given a matt or a glossy surface, according to market preferences, and by applying a suitable surface treatment, for example by a corona or flame treatment, the outer surface can be conditioned for printing on by conventional methods, for example by flexographic printing, rotogravure or offset processes.

A laminate according to the invention, particularly in its preferred embodiments, affords a number of advantages, as follows: 1. A hollow cylinder or tube can be made from the laminate by the simple method of overlap welding (heat welding) for example by hot contact heating or by high-frequency heating. The weld seam can have the following characteristics: (a) The bare cut edges of the metal can be completely covered by plastics due to flow of molten plastics over such edges from the plastics plies during the welding. This effect can be clearly seen in a micrograph of a transverse section at 200 x magnification.

Nevertheless there is only insignificant reduction in thickness of the plastics layers in the region of the weld seam. The protection of the metal edges by plastics in that manner prevents corrosion of metal or delamination from occurring at that place.

(b) The weld seam, which is preferably not more than 3mm wide, can have a tensile strength of more than 2 kp/mm2.

(c) The seam in the body of a container made from a three-ply laminate according to the invention is much thinner than that formed in tubes made from the commercially available six-layer laminates made of paper, metal and various plastics layers. This has the advantage that a cylinder formed by welding in that manner can easily be welded to a tube head, which is usually a plastics injection moulding, giving a strong and tight joint, even at the region of the overlap weld seam.

This is important because a joint which is defective at the critical region of the overlap body seam can leave open channels leading to degradation of the substance in the container. Furthermore when a tube is being squeezed or folded the tube body can easily part from the head piece.

(d) The seam can be almost invisible from the outside.

2. At the inside of a tube or other container formed from the laminate, the inner plastics ply and the polyurethane adhesive underlying that ply are able to provide a high resistance to the action of corrosive fluorides in tooth paste. Corrosion of the metal would of course impair its protective properties.

Moreover a secure bond is achieved between the plastics and the metal. A test was performed on a sample of a laminate according to the invention which comprised the following layers, beginning with the outermost one: (i) a high density polyethylene foil charged with white pigment and having a thickness of 0.050 mm (the outer surface of this foil bearing printed matter) (ii) adhesive layer formed from a 2-component polyurethane adhesive composition of a thickness such that the dry weight of the layer is 4 g/m2.

(iii) aluminium foil 0.050 mm in thickness (iv) adhesive layer as above but having a dry weight of 6 g/m2.

(v) a high density polyethylene foil 0.070 mm in thickness.

In the test a fluoride-containing tooth paste was brought into contact with the thicker (non-pigmented) plastics ply (thickness 0.070 mm) and the sample with the tooth paste thereon was stored for 6 weeks at 38"C. The adhesion of the non-pigmented plastics foil to the metal was tested on a 15 mm wide sample of the laminate by measur ing the force necessary to separate the plastics foil from the metal substrate. The adhesion, after the described storage, was found to be 680 g/15 mm. The underlying metal surface showed no signs of corrosion.

3. An overlap welded joint can be formed of such high mechanical strength that it is possible to deform an initially cylindrical tube formed from the laminate into the conventional conical shape with the help of apparatus conventionally used in manufacturing metal tubes. This has the advantage that the still-empty tubes can be stacked in nested condition, reducing by about 80% the space occupied during transportation and storage, minimizing mechanical damage to the tubes during transportation, and simplifying the packaging boxes or the like as compared with what is required for cylindrical tubes.

4. Tube bodies made from the laminate can, if desired, be printed using conventional all-round printers. But a further great advantage can be obtained by printing the ribbon of laminate while it is still flat, using one of the ordinary printing processes such as flexographic printing rotogravure or offset. The surface of the outer polyolefin foil should first be treated, for example by corona discharge or a flame treatment. Only in special cases is it necessary to protect the print by an overcoating of clear lacquer. And even then it is still possible, due to the thinness of the protective coating, to obtain a satisfactory overlap weld seam between the printed outer surface and the inner surface of the laminate without it being necessary to apply a further plastics layer over the print in order to form a good seal against the said inner surface.

The present invention includes tubes and other containers, and particularly fluoridecontaining tooth paste tubes and containers, having a body made of a laminate according to the invention as hereinbefore defined. For promoting a high resistance of a container to fluoride-containing substances or other material to be held in the container, for a given thickness of the laminate, the interior plastics ply of the laminate can be thicker than the exterior plastics ply. In addition or alternatively, for promoting the same purpose, the adhesive layer underlying the interior plastics ply can be thicker than the adhesive layer beneath the interior plastics ply.

In the specific example given earlier in this specification the same kind of adhesive composition is used for bonding both plastics foils to the metal substrate. That is not of course an essential feature of the invention. The two thermoplastics foils of a laminate according to the invention can be held by different adhesives. By way of modification of the foregoing example the thinner polyurethane adhesive layer could be replaced by a layer of adhesive based on polyethylene.

WHAT WE CLAIM IS: 1. A laminate suitable for use in forming ductile containers which can be squeezed or folded for dispensing their contents, such laminate incorporating a metal layer and synthetic plastics layers, characterised in that the laminate comprises a ductile ply of metal 0.03 to 0.15 mm in thickness, which on each face bears a pre-formed polyolefin foil 0.03 to 0.10 mm in thickness, which foils, after folding the laminate to bring portions of such foils into contact with each other, can be fusion-jointed together, at least one of said foils being bonded to the metal ply by an intervening layer formed from a twocomponent adhesive composition based on polyurethane.

2. A laminate according to claim 1, wherein the metal ply has a tensile strength of 5 to 10 kp/mm2 and an elongation at rupture of 7 to 15%.

3. A laminate according to claim 1 or 2, wherein the metal ply is made of aluminium.

4. A laminate according to any preceding claim, wherein each of said plastics foils is a polyethylene foil.

5. A laminate according to claim 4, wherein each of said plastics foils is a high density polyethylene foil.

6. A laminate according to any of claims 1 to 3, wherein each of said plastics foils is a polypropylene foil.

7. A laminate according to any preceding claim, wherein at least one of said plastics foils is bonded to the metal ply by a said polyurethane adhesive layer having a dry weight of 4 to 8 g/m2.

8. A laminate according to any preceding claim, wherein one of said polyolefin foils incorporates a white pigment.

9. A laminate according to claim 8, wherein the non-pigmented polyolefin foil is bonded to the metal ply by an adhesive layer whose dry weight per unit area is greater than that of the adhesive layer beneath the white-pigmented foil.

10. A container or container body formed from a laminate according to any preceding claim.

11. A container or container body according to claim 10 wherein opposed margins of a strip or ribbon of the laminate have been overlap-heat-welded together causing plastics to flow and to cover the edges of the metal ply along the region of the seam.

12. A tooth-paste tube having a body according to claim 10 or 11.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ing the force necessary to separate the plastics foil from the metal substrate. The adhesion, after the described storage, was found to be 680 g/15 mm. The underlying metal surface showed no signs of corrosion. 3. An overlap welded joint can be formed of such high mechanical strength that it is possible to deform an initially cylindrical tube formed from the laminate into the conventional conical shape with the help of apparatus conventionally used in manufacturing metal tubes. This has the advantage that the still-empty tubes can be stacked in nested condition, reducing by about 80% the space occupied during transportation and storage, minimizing mechanical damage to the tubes during transportation, and simplifying the packaging boxes or the like as compared with what is required for cylindrical tubes. 4. Tube bodies made from the laminate can, if desired, be printed using conventional all-round printers. But a further great advantage can be obtained by printing the ribbon of laminate while it is still flat, using one of the ordinary printing processes such as flexographic printing rotogravure or offset. The surface of the outer polyolefin foil should first be treated, for example by corona discharge or a flame treatment. Only in special cases is it necessary to protect the print by an overcoating of clear lacquer. And even then it is still possible, due to the thinness of the protective coating, to obtain a satisfactory overlap weld seam between the printed outer surface and the inner surface of the laminate without it being necessary to apply a further plastics layer over the print in order to form a good seal against the said inner surface. The present invention includes tubes and other containers, and particularly fluoridecontaining tooth paste tubes and containers, having a body made of a laminate according to the invention as hereinbefore defined. For promoting a high resistance of a container to fluoride-containing substances or other material to be held in the container, for a given thickness of the laminate, the interior plastics ply of the laminate can be thicker than the exterior plastics ply. In addition or alternatively, for promoting the same purpose, the adhesive layer underlying the interior plastics ply can be thicker than the adhesive layer beneath the interior plastics ply. In the specific example given earlier in this specification the same kind of adhesive composition is used for bonding both plastics foils to the metal substrate. That is not of course an essential feature of the invention. The two thermoplastics foils of a laminate according to the invention can be held by different adhesives. By way of modification of the foregoing example the thinner polyurethane adhesive layer could be replaced by a layer of adhesive based on polyethylene. WHAT WE CLAIM IS:

1. A laminate suitable for use in forming ductile containers which can be squeezed or folded for dispensing their contents, such laminate incorporating a metal layer and synthetic plastics layers, characterised in that the laminate comprises a ductile ply of metal 0.03 to 0.15 mm in thickness, which on each face bears a pre-formed polyolefin foil 0.03 to 0.10 mm in thickness, which foils, after folding the laminate to bring portions of such foils into contact with each other, can be fusion-jointed together, at least one of said foils being bonded to the metal ply by an intervening layer formed from a twocomponent adhesive composition based on polyurethane.

12. A tooth-paste tube having a body according to claim 10 or 11.