1. The type of shrink wrap film will greatly determine the end quality of the finished product

As a general rule the film type will be determined by the packaging machine being used to wrap the film on the package and what type of heat tunnel, if any, is used to do the shrinking.

• PVC (Poly Vinyl Chloride) shrink wrap films are generally better if hand shrinking is done via a heat gun. Also on older hood machines that do not generate sufficient heat to shrink POF film
• POF (Polyolefin) shrink wrap films are more widely used on semi-automatic and automatic lines with good quality shrink tunnels.

Shrink wrap film gauge or thickness is usually determined by the puncture resistance or film strength required and weight of the package.

POF shrink wrap films range between 7.5um to 38um.  Typically 15um is a good standard for a “chocolate box” type package. POF shrink films generally have a high bi-axial shrink percentage rate, typically 60% or higher.

• Crossed linked films generally give stronger seals and are have a better puncture resistance than non-crossed linked films.
  
• Non-crossed linked films seal quicker but have less puncture resistance than crossed linked shrink films
  
• Soft shrink films can be helpful with products that will bend easily and will not tolerate the shrinking process or need higher air transmission rates eg, mould ripened cheeses.
  
• Anti-Fog films are available for refrigerated display products.
  
• Anti-Slip films are required when packs are prone to moving when palletised without shippers
  
• Hot slip films that make packing into shippers directly after shrinking easier.
  
• High performance films, that shrink at lower temperatures than standard POF films.

2. The next most important tip, in achieving good quality shrink wrap packaging, is the seal quality of the pre-shrunk film. The seals must be strong and without holes otherwise shrink quality will not be consistent.

3. The next most important tip is the air escape holes that allow trapped air within the package to escape during the shrink process. Some films are pre-perforated for this purpose but I recommend that the perforating process usually controlled by the packaging machine is critical in the end result.

The rule to use is the perforation holes should allow the air to escape from the shrink wrap film just before the package exits from the shrink tunnel.  So if the seal has holes or the air escape holes are too large then the “balloon effect” and slow air escape will not happen thus affecting the shrink wrap film appearance.

4. When we have achieved the 1st 3 steps then using a good quality shrink wrap tunnel that has the following critea is critical.

a)High velocity air flow
b)Adjustable air flow patterns to direct air at the package
c)Variable speed conveyor
d)Accurate temperature control (Maximum of 5oC variation)
e)Live roller conveyor design is preferred if the bottom of the package is also critical

5. Shrink wrap film shrinking temperature and time varies with brand and type of shrink film, as a general rule the shrink tunnel should be set to 150oC for POF film and along with the conveyor speed set to give an equal pack space ratio in the tunnel with the wrapping machine at the maximum packs per minute possible. The temperature can then be varied to achieve a fully shrunk pack just before the package exits for the tunnel.

6. Package to Film ratio “Bag size” is important, as this will affect the volume of air entrapment and thus the shrink time due to air escape. With automatic lines this is normally controlled. Some machines are set up to increase the amount of trapped air in the shrink wrap film usually to keep the film away from the product, this is useful with wet of sticky packages that will smear or mark the film.

7. The operator should be looking at the shrink action as the product passed through the shrink wrap tunnel. Here are some final tips that will help achieve great shrink wrap results.

On package entry into the tunnel the shrink wrap film should balloon hard without bursting the film, then slowly and evenly shrink down, until full shrink is achieved just before exiting the tunnel.

If the film does not balloon hard then

a)Shrink wrap film has weak seals or holes
b)Shrink wrap film has too many or too large air escape holes
c)Tunnel temperature is too low
d)Tunnel air velocity is too low or air flow direction is not aimed at pack

If film bursts i.e., does not slowly and evenly reduce the balloon size then

a)Tunnel temperature is too high
b)No air escape holes in film

If shrink film finishes its balloon and slow collapse action too soon then.

a)Reduce air escape holes size or number
b)Tunnel temperature is too high
c)Tunnel speed is too slow

Kerry O’Brien
New Business Development