All possible plastic film defects ought to be detected and
eliminated by the extruder operator before the roll gets
shipped to the customer. But in practice, through oversight
and inattention to detail defects can slip by that may be
all too easily spotted by the customer or the customer's
customer. I have found a variety of unrelated faults that
fit into this category.
First is the appearance and a good looking finished plastic
roll of film this aspect can be half of the battle. Keep in
mind is that first impression what you see is what you get!
A superficially ugly looking roll which may convert on the
filling machine or bag machine can have the operator
looking at the roll much closer for the entire lot for real
or imaginary defects.
A roll that has a machine cylinder look means no scuff
marks, damaged edges, and fuzzy ends, protruding or buried
core ends, or crushed cores. The solutions to these
problems are self evident. There are other finer detailed
defects that can be buried in the roll, and may be if the
production line is never approached by the operator except
during a roll change. There is no excuse for the customer
being the first to see these.
I have a couple of areas for helping prevent roll defects:
How to Tackle Blocking of the Plastic Film - a common
reason for blocking is too much winding tension. This maybe
over looked unless tension is so great as to crush the core
as the film is being wound on the roll. This makes it
impossible for the operator to remove the roll from the
winder shaft. With a case of crushed cores, the rolls may
be hard to get off of the shaft, only to have the customer
find them impossible to remount on a un-wind stand. Just as
bad of a problem can arise if the winding tension is too
light, no blocking but the film may telescope from one end
of the roll, making it impossible to convert into finished
product. Hot weather can bring its share of blocking
problems. Plastic Film is insufficiently cooled and the
inner surface blocks as they pass through the nip rolls.
For a cure you must reduce the output, raise the tower
height or nip rolls, or use refrigerated air or other means
of improving cooling efficiency. It also can be an
inefficient air ring. An entirely different cause of
blocking can be using a resin to produce 1 mil film that
has a slip and anti-block additive level designed for
heavier gauges like 4 mil. There just isn't enough additive
to do the proper job. Over-treatment and or high gloss can
aggravate if not cause blocking with any of the above
conditions.
Tendency to Split - Plastic Film with splits tendencies can
also be overlooked unless samples are taken to examine, or
actually tested. Insufficient cooling, a high frost line or
to low of a blow up ratio, separately or a combination can
accentuate the machine direction or orientation of the film
causing the film to become splits. Also your nips in the
tower maybe to tight particularly with an old and hardening
nip roll which can deform the plastic film in the edge
crease and make it splits. Die lines or another name is
weld lines from the extrusion die make splits film as can
scratches from the collapsing frame in the extrusion tower
or a bur that has developed if using wooden collapsing
frames. But not so readily detected are the fine weld lines
caused by degraded particles of resin or dirt lodged under
or in the die lips that make the film extremely split at
the weld.
Good operator observations to equipment maintenance,
quality testing of roll samples and putting the proper
procedures in place will help in building customer loyalty.
----------------------------------------------------
David Banig has been in the Flexographic printing industry
for 32 years and has had various patents along with hands
on experience. If you are looking for someone to improve
your packaging P&R Flexible is the inovator and consultant
of todays packaging.
http://www.prflexbag.com
No comments:
Post a Comment