Shrink wrap packaging, sometimes referred to as shrink wrap is a method of forming shrink film around a product then exposing it to regulated heat to shrink it tightly around the product. The end result in the film should be a tight fit with no or very little wrinkles to ensure good product appearance.

When certain mistakes are made the most common appearance is a wrinkled wrap finish that in some industries are not acceptable shrink wrap packaging. Following is a list of common mistakes that cause poor appearance: This refers to a complete wrap, typically used in L bar type shrink wrap packaging machines.

1. Machine using the incorrect seal blade to seal the shrink wrap film

Most automatic wrapping machines use a constant heat sealing head that uses a specially shaped seal blade that cuts and seals the shrink wrap film when put under pressure. The specially shaped seal blade has a flat (or sometimes slightly curved) on the cutting edge that is made to suit specific types of film. This flat surface is what creates the seal width that also determines the strength of the seal. When the blade is 'too sharp' or the flat surface is too narrow, the seal that it creates in the film is too weak. When the product enters the heat or shrink cycle, the pressure that is created in the shrink film bag from the shrink will put tension on the seals and will tear it open. The end result is a wrinkled finish in the film with a clear visible tear along the seal.

2. Sealing too tight around the product

When the shrink wrap machine is set up incorrectly the product can be positioned incorrectly in the seal area causing the sealing head to come down too close to it. This can cause the film to be wrapped too tightly causing tension on the seals during the seal cycle. In most cases this will cause the seals to be weak and will tear open during the shrink cycle.

3. Insufficient perforation in the shrink wrap film

The main purpose of the perforating pins is to pierce the shrink film with multiple rows of small holes while it is being fed into the wrapping machine. The holes will allow the air to escape from the bag during the shrink cycle. If the bag has insufficient perforating holes, the air cannot escape quick enough to allow the shrink to complete. This will cause a loose or uncompleted wrap or in some cases the bag will pop at the seals due to too much pressure.

4. Too much perforation in the shrink wrap film

If there are too many perforating holes the air will escape the shrink wrap bag too quick that will cause a wrinkled finish. The key to getting a good result in the shrink wrap packaging is to have the correct balance of shrink rate to perforation.

5. Incorrect heat used during the shrink cycle

If the shrink packaging tunnel temperature is set too high it will cause the shrink film to shrink too fast and the air in the bag might not be able to escape quick enough. This will cause the bag to pop and will result in a wrinkled finish. Sometimes the excessive heat will cause the film to melt causing a big hole to appear. If the shrink tunnel temperature is set too low, the film will not complete the shrink cycle and will cause a loose wrap.

6. Incorrect shrink wrap film used, not a suitable packaging for certain products

There are many different types of shrink film on the market and the suitability is determined by the product or application. Choosing the wrong type can cause inadequate protection, poor appearance or even unnecessary packaging costs (over wrapping). It is recommended that the correct product trials and cost analysis are completed before any commitment is made on purchasing shrink wrap packaging film.

By: Marius Liebenberg
Technical Support and Service