Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1989-06-09
1990-07-31
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, 4284763, 428515, 156 69, 1562722, 1562735, 1563082, 1563099, B29C 3502, B32B 110, B32B 1508
Patent
active
049450085
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to laminated metal sheet and to a process for producing laminated metal sheet.
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.
The lamination of polyolefin film to metal sheet has been described in many patents. However, although polyolefin coatings have many useful attributes, they have significant limitations as can coatings. Thus, for example, polypropylene or polyethylene coatings such as those described 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.
Polypropylene and polyethylene coatings are relatively soft materials compared with conventional lacquers used in can stock coating. The softness of polyolefin coatings results in a tendency for the coatings to fibrillate when laminates incorporating such coatings are subjected to can end double seaming. Although the polyolefin coating forms well, it is found to develop unacceptable polymer filaments on the extremities of the seaming panel.
For many applications it is necessary to use relatively thick polyolefin coatings. Thus, when it is desired to incorporate white pigments in a polyolefin coating so as to obtain a white external coating on a can body or a can end, it is found necessary to utilize a relatively thick polypropylene layer, suitably pigmented, in order to achieve acceptable opacity and appearance. However, increasing the thickness of the polyolefin coating tends to exacerbate the problem of fibrillation mentioned above, and thick white polypropylene coatings are found to fibrillate when subjected to double seaming in a can making process. This is a considerable disadvantage.
A further disadvantage of white pigmented polyolefin coated metal sheet is that such sheet is not readily susceptible to draw redraw processes for manufacturing cans nor for use in the manufacture of partially wall ironed cans. Such processes tend to disrupt the polyolefin coatings on the metal sheet and the resultant cans are found to be unsuitable for packaging human food products. Cans made by such processes are found to have limited shelf life and corrode quickly when packed with human food products.
We have now found that by forming composite polyolefin film incorporating an external polyamide layer, the above-mentioned problems and disadvantages can be overcome.
Accordingly the present invention provides a laminated metal sheet having adhered to one of its major surfaces a composite co-extruded polyolefin-containing film (B) comprising a plurality of layers in the following order: resin containing carboxyl or anhydride groups, and
We have found that the four layer composite film used in the laminates of the present invention has excellent lamination characteristics. The laminates of the present invention can readily be formed into draw redraw cans or partially ironed cans. The composite film laminated to the metal sheet is found to provide excellent protection to the metal sheet whether used as an internal coating or external coating.
This is a surprising attribute of the laminates of the invention given that when the laminates are formed into cans, the polyamide layer is in direct contact with aqueous media and is unprotected from moisture.
Furthermore, the composite film used in the present laminates does not have the fibrillation problems encountered with prior polyolefin coatings.
The polyamide layer (B4) in the laminated metal sheet of the invention is preferably Nylon 6, Nylon 66, Nylon 11 or Nylon 12.
Preferably the polyolefin in layer (B2) is polypropylene, or polyethylene, or an ethylene-propylene copolymer. If desired other polyolefins such as polymethyl pentene may be used.
The bonding resin in each of lay
REFERENCES:
patent: 4009312 (1977-02-01), Hayashi et al.
patent: 4058647 (1977-11-01), Inoue et al.
patent: 4504531 (1985-03-01), Murata et al.
patent: 4741957 (1988-05-01), Park
patent: 4762737 (1988-08-01), Lu
patent: 4810434 (1989-03-01), Caines
Heyes Peter J.
Middleton Nicholas J.
CMB Packaging (UK) Limited
Morris Theodore
Wyszomierski George
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