Stock material or miscellaneous articles – Hollow or container type article – Nonself-supporting tubular film or bag
Patent
1989-06-09
1992-01-07
Herbert, Jr., Thomas J.
Stock material or miscellaneous articles
Hollow or container type article
Nonself-supporting tubular film or bag
1563082, 1563099, 156327, 156332, 428 359, 428216, 428336, 428458, 428461, 4284763, 428480, 428516, B65D 100, B32B 1508, B32B 3126
Patent
active
050790528
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.
Although polyolefin coatings do in many cases impart acceptable corrosion resistance to the metal sheet, such coatings nevertheless can have limited ability to protect the underlying metal sheet from corrosion; this is particularly true of steel based substrates.
It is likely that this drawback of polyolefin coatings is due to the high oxygen permeability of such materials and their relatively poor resistance to some solvents.
It is known that although polyamides such as Nylon 6 have a higher permeability to moisture than polyolefins, they have better solvent resistance with some solvents and are less permeable to oxygen than polyolefin coatings. It is known to combine the favorable properties of the two types of polymer by forming composite laminates incorporating a layer of a polyamide and a layer of polyolefin, usually having a tie layer--typically an acid modified polyolefin--between the Polyamide layer and the polyolefin layer. Such a composite laminate is found to act as a good barrier both to oxygen and moisture and has the desired low oxygen permeability and low moisture permeability.
However, such simple three layer composites do not form satisfactory coatings for metal sheet because neither nylon nor polypropylene will directly bond satisfactorily to a metal sheet.
We have now found that a four-layer composite film incorporating an inner layer of polyamide of a particular thickness adheres readily to a metal sheet and minimizes the permeability of the coating to water, oxygen and solvent. We have found that the good oxygen barrier properties of the polyamide are most effective when the polyamide is laminated between the metal sheet and the polyolefin, thereby maintaining the polyamide in an environment which is relatively free of moisture.
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, 9 microns, and
We have found that the thickness of the polyamide layer used in the laminates of the present invention is crucial. Although thicker polyamide layers should give improved barrier properties, it is found that if polyamide layers which have a thickness of 10 microns or more are used, unacceptable blistering occurs during lamination of the composite film (B) to the metal sheet. This blistering is probably caused by the release of moisture from the hygroscopic polyamide layer, said moisture being trapped by the external layer of polyolefin. However if polyamide layers having a thickness which is 10 microns or less are used, no blistering occurs during lamination and a protective coating which imparts excellent corrosion resistance is obtained.
The polyamide layer (B2) in the laminated metal sheet of the invention is preferably Nylon 6, Nylon 66, Nylon 11 or Nylon 9; particularly preferred polyamides are Nylon 6 and amorphous nylon.
The polyamide layer (B2) has a thickness which is not greater than 9 microns. Preferably the thickness of the layer (B2) is from 3 to 5 microns.
Preferably the polyolefin in layer (B4) is polypropylene, or polyethylene, or an ethylene-propylene copolymer. If desired other polyolefins such as polymethyl pentene may be used.
The outer, polyolefin layer is typically 10 to 200 microns in thickness depending on the requirements
REFERENCES:
"Packaging", Reference Issue Including the 1986 Encyclopedia, pp. 76-79 and 86-89.
"Modern Packaging Encyclopedia and Planning Guide 1972-1973", pp. 102-103.
Heyes Peter J.
Middleton Nicholas J.
CMB Foodcan plc
Herbert, Jr. Thomas J.
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