Process and apparatus for producing laminated materials

Details Process and apparatus for producing laminated materials Process and apparatus for producing laminated materials

1995-12-08

1997-10-21

Stemmer, Daniel

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

1563099, 156322, 156324, 156555, B32B 1508, B32B 3126

Patent

active

056792000

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a process and apparatus for producing a laminated metal sheet or strip. In particular, it relates to a thermal lamination process for laminating a polymer film to a metal strip.
Thermal lamination of polypropylene films to metal strip, or sheet, is known from GB-1324952, for example, for imparting corrosion resistance to the metal strip. Simultaneous lamination of composite polyester films to each major surface of a metal strip is taught in EP-0312303 and simultaneous lamination of a polyester film to one side of a metal strip and a polyolefin or polyamide-containing film to the other side is described in EP-0312302.
Simultaneous lamination is achieved by applying one or more polymer films to a metal strip at a first temperature or laminating temperature T.sub.1 which does not damage the outer surface of the polymer film(s) as the metal strip and polymer film(s) pass through a lamination nip. There is, however, a limit to this metal temperature, because excessive heat will cause the polymer film to stick to the laminating nip roll. This is known as "pick-up".
Polyester films, in particular, suffer micro-blistering at production laminating speeds. Whilst these defects are not thought to affect the integrity of the PET film, they detract from the appearance and thus the commercial viability of the film. Such micro-blistering can be avoided by increasing the lamination temperature but this may then lead to sticking, or pick-up, of the film on the laminating roll.
Pick-up is more pronounced for polypropylene film and will start to occur above a laminating temperature T.sub.1 of only 180.degree. C., dependent on the film gauge. When thin polypropylene is to be laminated to one side of a metal sheet with polyester, such as PET, simultaneously laminated to the other side of the metal sheet, pick-up of the polypropylene will occur if the laminating temperature is only 180.degree. C., but micro-blistering of the PET film will start to occur at lower temperatures than 180.degree. C.
This tendency to form micro-blisters under the polymer film is particularly pronounced when the metal sheet has high surface roughness values and varies according to the type and gauge of film used. It is believed that blistering arises due to air trapped beneath a film, particularly when the metal sheet has high surface roughness.
There is therefore a need for a lamination process which does not lead to micro-blistering of a polymer film or to pick-up of a polymer film on the laminating roll.
According to the present invention, there is provided a process for producing a laminate of strip metal and a polymeric film comprising the steps of: heating the metal strip to a first temperature T.sub.1 above the initial adhesion point of the polymeric film; applying the polymeric film to the preheated metal by passing the metal and film between nip rolls; reheating the metal laminate to a second temperature T.sub.2 to cause the film to interact with and bond to the metal sheet; and quenching the laminate rapidly and uniformly; in which the laminating nip rolls impose a nip force in excess of 15 kN/m.
Previous commercial lamination processes, such as those described in EP-0312302 and EP-0312303, have used a lamination nip force of up to 12.5 kN/m. The use of higher nip forces as in the present invention is particularly advantageous when the polymer film is of polyester, particularly polyester having pigment therein, since these forces have been found to reduce and/or eliminate micro-blistering under the polyester film which arises when commercial lamination speeds of 30 m/min and above are used.
Typically, polyester films of 15 .mu.m thickness for clear polyester and 25 .mu.m thickness for pigmented polyester were used but blistering arose both above and below these values when commercial lamination speeds were used.
The problem of microblistering has not been apparent before since lower line speeds were used. Furthermore, nip forces were limited by the apparatus used, heavier duty equipment being both bulkier and more e

REFERENCES:
patent: 3679513 (1972-07-01), Addinall et al.
patent: 4289559 (1981-09-01), Murphy
patent: 4748070 (1988-05-01), Beechler
patent: 5093208 (1992-03-01), Heyes
patent: 5238517 (1993-08-01), Heyes

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