Plastic Film defects ought to be detected and eliminated by the extruder operator before the rolls get shipped to the customer.
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.
There are 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. There is an area over looked and it is the tension which is set 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. The cause of blocking can be using to much additive when producing 1 mil that has slip and anti-block additive level designed for heavier guages like 3 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.
Copyright (c) 2008 David Banig
David Banig has been in the Flexographic printing industry for 32 years and has had various patents along with hands on experience. Need turn around help P&R does consulting to improve manufacturing processes.