Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1995-12-04
1997-12-09
Sells, James
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
1562722, 156282, 1563082, 1563099, 156324, B32B 3100
Patent
active
056955790
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process and apparatus for producing laminated materials comprising a metal sheet laminated on one or both sides to a polymer film or films.
U.S. Pat. No. 3,679,513 describes a process for applying polyethylene films to a steel substrate during a pre-determined heating cycle. The steel substrate is coated with chromium/chromium oxide and preheated so as to soften the polyethylene films which are applied to either side of the substrate between nip rolls. The resultant laminate is then reheated and temperature is maintained for from 5 to 240 seconds. Rapid cooling then takes place firstly by forced air to lower the temperature of the laminate to below the softening point of the polyethylene films, and finally by a water spray. In situations where fast line speeds are not of commercial importance, U.S. Pat. No. 3,679,513 suggests cooling in still air.
Both the rapid and the still air cooling methods of U.S. Pat. No. 3,679,513 lead to the polymeric film becoming at least partially crystalline. In particular, it has been found that forced air cooling below approximately 180.degree. C. or spray quenching from a higher temperature leads to "spotting" of coating. These cooling methods cool only where the air or spray strikes the coating so that only local cooling occurs and a mottled, partially crystalline coating results. Crystallinity is particularly to be avoided when laminated materials are to be shaped into articles such as cans or can ends. In the case of a polypropylene film, "crystallinity" means .alpha.-form (rather than smectic) crystallinity.
EP-B-0312309 seeks to overcome the problems of U.S. Pat. No. 5,679,513 and describes a process for laminating polypropylene film to a metal substrate. The resultant laminate is reheated to a temperature above the melting point of polypropylene and then uniformly and rapidly quenched by flooding the laminate with continuously cooled water which travels on the laminate to a collecting tank. Such rapid and uniform cooling seeks to prevent the polypropylene from having an x-form crystallinity and indeed provides a substantially smectic form of polypropylene. This form is less susceptible to deformations when shaped.
A problem which arises on start-up of lamination processes when line speed is slow is that recrystallisation or, in the case of polypropylene, the formation of an x-form crystallinity can take place as cooling occurs after leaving the reheat zone prior to quenching. This recrystallisation is also exhibited when cooled in still air as suggested in U.S. Pat. No. 3,679,513.
This invention therefore seeks to provide a process and apparatus in which partial crystallinity and development of discontinuities are avoided.
EP-A-0402004 describes a process for laminating aluminium and polyester in which the laminate is cooled by forced air after a reheat stage and prior to rapid quenching in water. In order to ensure the desired polyester structure in the laminate, the laminate should enter the water at a specific temperature T3. This temperature will, however, vary according to the line speed of the lamination process.
According to the present invention, there is provided a process for producing a polymer/metal laminate comprising the steps of:
(a) heating a metal strip in a first heater to a first temperature T1;
(b) feeding to a lamination nip both a strip of polymer film and the metal strip at said temperature T1, which is above the initial adhesion point of the polymer film, to cause intimate contact of the film with the metal strip;
(c) reheating the resultant laminate in second heater to a second temperature T2 to cause the film to interact with and bond to the metal strip;
(d) passing the laminate through a heat/cool zone to heat and/or cool the laminate across its width, according to the line speed, to an exit temperature T3;
(e) allowing bonding to develop between the film and the metal strip in said heat/cool zone; and
(f) quenching the laminate rapidly and uniformly, the laminate entering this quenching stage at the temperature T
REFERENCES:
patent: 3679513 (1972-07-01), Addinall et al.
patent: 5059460 (1991-10-01), Heyes et al.
patent: 5318648 (1994-06-01), Heyes et al.
CarnaudMetalbox plc
Sells James
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