The quality modern Stamping Part is rapidly
approaching. There are many benefits of this process, and some disadvantages,
although cold foiling has progressed a lot since then. The benefits in reel to
reel printing are obvious. If hot foiling is carried out in-line at the end of
the printing process, then the press speed is limited by the foiling speed
which is relatively slow. If the printing was maintained and the foil applied
as a separate pass, there is a corresponding cost impact. Furthermore, the cost
of hot foil dies is relatively high compared to a printing plate or sleeve and
energy is needed to heat the die. Reel to reel cold foiling involves printing a
UV curable adhesive in the foil design needed, laminating the foil to the
adhesive through a nip, curing the adhesive with UV lamps and separating the
foil from the printed web. The foil that is removed from its carrier film is in
the design of the printed adhesive, since that has been UV cured and so adheres
to the foil.
By using a cold foil,
the speed is limited only by the strength of the UV lamps or the optical
density of the foil. True, this is irrelevant when the foiling is carried out
directly to transparent films since the light can be directed through the back
of the film onto the adhesive, but this is frequently not the case. The foiling
is often carried out over an opaque white ink which can be silk screened onto
to the label prior to the adhesive and then the foil applied. This places an
opaque layer between the film and the foil, so that the beam has to pass
through the lacquer layer or top coat of the cold foil. The UV beam passes
through the lacquer and aluminum layers to reach the adhesive, so the aluminum
must be as transparent as possible. The more opaque it is, the more lamps are
needed or the slower the running speed. Since printers want the lamps set in a
fixed position, and not changed around for each type of job, all curing is
generally carried out through the foil than through the film being printed.
Given that this can be done, then cold foiling is much faster than hot foiling,
and of course there is no need for a die, thus saving not only on die-cutting
costs but also on energy.
Cold foiling is
generally not as brilliant as hot foiling, and also most stamping foil manufacturers
offer a very limited range. They have also tended not be very print receptive.
If the overprint is small enough, it can adhere, though the cold foil surface
tends to be fairly low in surface energy (low dyne level). Larger printed areas
tend to have poor scratch resistance and tape adhesion, though many customers
accept this in return for the lower costs. Modern developments, however, are
tending to overcome these problems though truly over printable cold foils are
very difficult to find and depend very much on the type of ink being used. This
process is currently patented. Further developments involve offset UV adhesives
and inks, though the adhesion of the UV ink to the foil surface is still an
issue here. The volumes of cold foil being used worldwide are increasing at a
rapid rate, and much of this is in the offset field, where the major European
printing machine suppliers are offering purpose build equipment, and add-ons
that can be retrofitted to a printer's existing equipment. Browse nbstampingparts
now!
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