Laminating film for metal, laminated metal sheet and metal container

DETAILED DESCRIPTION OF THE INVENTION It has been found that a thermoplastic resin film cannot afford a pinhole having a size of 0.
1 mm .
phi.
or above to accomplish the aforementioned objects.
In other words, a pinhole having a size of less than 0.
1 mm .
phi.
does not impair rust proof property of a metal sheet, since such pinhole present just before lamination can be blocked as a result of, for example, a very small size variation caused by the heat history of the film during heat pressure lamination of the film on a metal sheet, or a slight flow caused by the heat history during lamination of an adhesive and/or an adhesive layer present in between the film and the metal sheet.
It is essential that at least the portion laminated on a metal be devoid of a pinhole having a size of 0.
1 mm .
phi.
or above.
In particular, irrespective of the size of the production lot of the film, that is, be it a small lot, medium lot or large lot, the film of one production lot desirably has no pinhole having a diameter of not less than 0.
1 mm .
phi.
.
To be specific, the number of pinhole having a diameter of not less than 0.
1 mm .
phi.
is desirably zero, i.
e.
, 0 pinhole/not more than 1,000 m.
sup.
2, 0 pinhole/not more than 10,000 m.
sup.
2, 0 pinhole/not more than 100,000 m.
sup.
2, 0 pinhole/.
infin.
m.
sup.
2.
Pinholes are detected using a detector based on high voltage application.
This detector enables detection of every pinhole having a diameter of not less than 0.
1 mm .
phi.
.
A detector capable of detecting every pinhole having a diameter of not less than 0.
01 mm .
phi.
is more preferable.
FIG.
1 shows one example of a pinhole detector to be used in the present invention, which is based on high voltage application.
A film is unrolled and run toward a guide roller 2 from the film roll attached to an unrolling shaft 1.
If a pinhole is contained in the film, a discharge phenomenon occurs at the detection electrode 4 when the film runs between the detection roller 3 and a detection electrode 4 set above the detection roller 3, and said pinhole is detected by a high voltage generator and pinhole detection data processor of 8