From pinholes to burn out, find out what your shrink wrap is telling you.
Nothing is more satisfying than a perfect shrink wrap when the package comes out of the shrink tunnel. Experienced operators know that when, on the other hand, a package comes out with imperfections, the result itself provides clues on how to adjust the system configuration to correct the problem. If you’re having problems with shrink film, all you need to do is “read” these clues about the film.
The article “Problems with Shrink Film” explains the potential underlying cause of six of the most common film problems, including burnout and pinholes, as well as the configuration adjustments that usually resolve the issue.
Three variables that affect the results of shrink wrap
Prima di esaminare questi sei problemi comuni, è importante comprendere le variabili che influenzano il processo di retrazione. Queste tre variabili sono: dimensione del sacco, evacuazione dell’aria/perforazioni e temperatura o velocità del tunnel.
Diamo un’occhiata a come queste tre variabili influenzano il film.
During the shrinking process, the bag must be large enough to allow the film to peel away from the product and collapse just before exiting the tunnel chamber. If the bag size is too tight, the film will contact the product too soon, resulting in fish eyes or crow’s feet. The film must first swell from the product and then collapse.
Air evacuation (drilling)
Bleeding the air out too quickly does not allow the film to inflate properly, resulting in wrinkles, crow’s feet or fish eyes. Bleeding the air out too slowly will cause bubbles, a cloudy film and potential burns. Placement of Perforations: Checking which part of the bag holds air the longest can help control shrinkage. The most critical element for the appearance of the package is the control of the air evacuation!
Tunnel temperature and speed
For a good appearance of the package, it must spend 3 to 4 seconds in the tunnel chamber. The size of the tunnel depends on the productivity. Always adjust the speed and temperature of the tunnel conveyor so that the film balloon collapses just before exiting the tunnel chamber.
Six common shrink films problems
Now that we have an understanding of the three most important variables in the shrink process, let’s look at how an incorrect machine or film setting can be seen in the final package, the most common cause, and how to correct the problem by adjusting the set up.
Burnt problems with shrink wrap
BURNOUT: Holes or cracks in the film outside the weld line
COMMON CAUSE: Insufficient air exhaust
ADJUSTMENT: Add some perforations so that the air escapes more quickly
CLOUD: Film is foggy/blurred
COMMON CAUSE: The tunnel temperature is too high
ADJUSTMENT: Adjust the temperature or try speeding up the conveyor belt. You may also need to add some perforations.
CROW’S FEET: Wrinkles at the corners and near the edges
COMMON CAUSE: Inadequate bag size: bag is too small or has too many perforations
REGULATION: The bag should inflate away from the product during the shrinking process. Adjust the size of the bag and remove some of the perforations.
DOG EARS: curled film protruding at the end of the seal
COMMON CAUSE: incorrect bag size, too many perforations, time and temperature in the tunnel
ADJUSTMENT: Make adjustments to ensure the bag has 3 to 4 seconds of dwell time inside the tunnel chamber.
FISH EYES: Rounded spots near the edges
COMMON CAUSE: Inadequate bag size and/or too many perforations
REGULATION: The bag should inflate away from the product during the shrinking process. If there are too many holes, the bag won’t inflate properly, or if the bag is too small, it will contact the product too quickly. It will help to adjust the size of the bag and remove some of the perforations.
PIN HOLE: Small holes along the gasket
COMMON CAUSE: An installation problem where there is too much tension on the film during the sealing process
ADJUSTMENT: Try making a bigger bag and loosening the tension on the film.
Do you have one or more of these problems with shrink films?
Learning to read the film markings and properly adjusting bag size, perforations and tunnel settings are the keys to ensuring proper film retraction and flawless presentation. We at Pactur have a very long experience in setting up heat-shrink machines in relation to the various products and therefore if you have problems with heat-shrink films we advise you to call us immediately if you have problems packaging your products: we will find a solution together!