Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1989-06-09
1990-09-18
Morris, Theodore
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
428626, 428629, 428667, 428458, 428483, 156 69, 1562722, 1562735, 1563082, 1563099, B28C 3502, B32B 1508
Patent
active
049578200
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for producing laminated metal sheet and to laminated metal sheet so produced.
Lamination of polymer materials to metal sheet such as metal strip is a well known and well documented technique. The resultant laminates have many applications such as, for example, use for the manufacture of can bodies and can ends for containers for foodstuffs and beverages, and end components and valve cups for aerosol containers.
For many applications, a polymer film is laminated to each of the two major surfaces of the metal sheet. In general, most of the known lamination techniques are concerned either with the simultaneous application of polymer films of the same or similar composition to opposite faces of a metal sheet, or describe the lamination of polymer films having different compositions to the opposite faces of a metal sheet, each of the two different polymers being applied to the metal sheet in a separate step rather than simultaneously.
Whereas metal laminates having similar polymer coatings on both sides of the metal sheet or strip have many advantages, they are not suitable for all purposes. Thus, for example, while polyester coatings of the type described in GB No. 2123746 have excellent formability, they are not readily receptive to heat sealed closures, they are difficult to pigment to an acceptable level of opacity at viable cost, and they change in appearance on retorting.
Polypropylene or polyethylene coatings such as those described, for example, in GB No. 1324952 and EP No. 0062385 impart acceptable corrosion resistance to the metal sheet but are relatively soft, damage easily, have low melting points and relatively low gloss.
No single polymer embodies all of the various physical properties desired in coatings for metal/polymer laminates which are intended for use as can stock. Consequently it is found to be advantageous to use a combination of different polymers in a single polymer/metal/polymer laminate and utilize appropriately the properties conferred to the laminate by each polymer.
It is desirable, in many cases, to use dissimilar polymers laminated to the two surfaces of the metal sheet thereby making use of the different properties of the different polymers.
It is preferable, from an economic point of view, to apply the different polymer coatings to the metal sheet in a simultaneous operation, thereby reducing operational costs. The simultaneous application of the two different polymers can be achieved by the use of adhesives which are applied separately to the two different polymeric films followed by laminating these films simultaneously to the metal sheet. Alternatively, the required polymer films can be extrusion coated simultaneously in one single operation onto the two surfaces of the metal strip.
However, the first method is undesirable because it requires the use of solvent based materials which may contain biologically hazardous chemicals such as isocyanates and also involves lengthy cure schedules. The second method, which requires co-extrusion of molten polymers, would destroy the excellent properties of biaxially oriented polyester materials such as polyethylene terephthalate (PET), since such biaxially oriented materials cannot be extrusion coated and retain their excellent properties.
Thermal lamination of biaxially oriented PET to metal strip is known, for example from GB No. 2123746. Similarly, thermal lamination of polypropylene films to metal strip is disclosed for example, in GB No. 1324952 and U.S. Pat. No. 3679513, while thermal lamination of polyethylene films to metal strip is described, for example in EP No. 0062385 and U.S. 4452375. However, the conditions described in these documents for thermal lamination of polymer films having such varied properties are not suitable for the simultaneous thermal lamination of a polyester film, especially biaxially oriented polyethylene terephthalate film, to one side of a metal strip, while at the same time thermally laminating to the other side of the metal strip a polyolefin or polyamide-c
REFERENCES:
patent: 4058647 (1977-11-01), Inoue et al.
patent: 4631155 (1986-12-01), Caines
Heyes Peter J.
Middleton Nicholas J.
CMB Foodcan plc
Morris Theodore
Wyszomierski George
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