Roll defects versus film defects
There are so many sources of defects in plastic film processing. By segmenting according to roll or film, root causes can be addressed. The table below looks at providing an exhaustive list for the both blown and it can also be applied to cast processes also.
Tips on dealing with roll defects
A common converter complaint is wrinkled film near the core of the roll. This problem can be due to operator error. How much skill does the operator have in cutting the film from the finished roll to a new core? Was there a fixed reference mark to locate the core or was it “eye-balled” for position on the winder shaft with the resultant buried and protruding core ends? Or, was the damaged roll just too heavy for the operator to handle?
Other, non-operator, conditions can contribute to roll and film defects, including the location and/or the accessibility of winder nips, slitting, and trimming stations, treating stations, gusseting equipment, etc. Telescoping or crushed cores, with possible blocking, are the result of too little or too much winding tension. Again, defective cores could be the result of inattention to tension control as the roll builds or a need for maintenance work on the drive.
Color in the roll ends of natural film results from three unrelated problems. Blue/gray coring in the first inch (or less) of film around the core is caused by too much initial winding tension and can indicate crushed cores if severe enough. If blue/gray coring occurs, some cores may collapse at a later time, as the film ages, shrinks and increases the stress on the core. Making a roll change too soon after changing resins can also cause a color change in the roll end from the core to the finished diameter. There is nothing inherently wrong with the film, but such transition rolls should be scheduled to meet orders where such a roll is acceptable. For instance, such a roll of film might be quite acceptable as the last roll of a general purpose clarity order rather than the first roll of a high clarity order.
Finally, on some equipment it is very difficult to purge color, particularly white. Liner, rather than clarity orders, should be scheduled following orders for colored film. A clarity film scheduled after a white film appears clear in single thickness, but on the roll the residual color, still purging from the extruder and die, whitens the end of one or several rolls of otherwise clear film. Care should always be taken to know and not exceed the number of splices allowed in a roll and the number of spliced rolls acceptable to the customer in an order. Splices are costly in the time they take to check and thread through converting equipment. Uniform roll diameters, consistent weights and good appearance are important customer requirements.
OneBoxVision's core competence is the identification of roll and folm defects using automated machine vision solutions. We also produce manufacturing analytics that can be used by your customer service to reduce complaints. If the defects above are issues for your organisation, click below and download our white paper on plastic film inspection.