Set-off on one part of asheet and arough finish on other
parts, is almost certainly due to uneven spraying. will also
cause an uneven stack.) Check regularly that applicator nozzles
are spraying properly. To test this, hold a black sheet
underneath the nozzle, allow it to spray two or three times and
then examine the spray on the sheet.
It is always tempting to over·spray in an effort to 'insure'
against but this will cause many problems later. If the ideal
dosage results in then it would be better to increase the
particle size rather than the amount of powder. If the grains
are distributed widely enough on the sheet, they should not
Using the incorrect powder can result in pinholing after
varnishing or lifting of the laminate from the sheet. If these
operations are subsequently to be carried out, use a powder
which is compatible and will 'wet-out' in oil based substances,
hydrophobic powder, or one which can be removed from the
sheet entirely such as a vanishing/soluble type.
If using conventional inks prior to ultraviolet varnishing,
a conventional powder can cause loss of gloss. Instead, use a
soluble powder and pass the work through the press with the
damping system engaged to clean the sheets.
Never use a soluble spray powder with an infra-red drying
unit because this will result in a build-up of a brown sticky
material - the powder melts at low temperature - which also
sticks to the drier and can eventually damage it. With this
type of system use a hydrophobic powder.
If you have a problem with your spray powder
equipment and you still have not found the answer having read
this far, it is best to call a qualified engineer. If you
operate the equipment on a single shift it is wise to have it
serviced once ayear; if on adouble shift then twice ayear.
Always keep equipment clean and dry, have it fitted only by
aqualified engineer and buy the best system you can