Top 10 Heat Shrink Wrap Problems and Solutions

A variety of heat shrink wrap problems can arise when shrinking wrapping products with shrink film.

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We will cover common problems and solutions when wrapping with shrink wrap machines.

Most of these issues are familiar and easy to resolve by adjusting machine settings.

Among them are often adjustments of shrink tunnel temperature, circulating air speed, conveyor belt speed, number of vent holes, and changing shrink film.

Ⅰ. Shrink Film Ballooning heat shrink wrap problems

Excess air trapped inside the sealed shrink film.

The reason is that shrink film is exposed to hot air after sealing.

Solution:

1. You can buy pre-punched heat shrink film. There are many small needle-sized vent holes in this type of film.

Or add the number of vent holes to the film you have already purchased.  Increase air escape velocity when shrink film wraps product.

At KEEPTOP Packaging We sell pre-perforated shrink film rolls and bags to prevent.

2. Slow down conveyor speed of shrink wrap machine and shrink tunnel.

Helps hot air have more time to escape from shrink wrap.

3. Raise the temperature of the shrink tunnel to increase the speed at which the air is expelled from the heat shrink wrap.

Ⅱ. Burn Holes On Shrink Films

A cloudy appearance or burn Holes through the heat shrink film after passing through the heat shrink tunnel.

The reason is that too much heat is applied to the shrink film.

Solution:

1. Reduce the temperature of the shrink tunnel machine.

2. Increase the conveyor speed of shrink wrap machines and shrink tunnels.

3. Increase the number of vent holes in shrink wrap rolls.

Ⅲ. Dog Ears On Shrink Wrap

Shrink film is bunched up in the corners of the package. They resemble a dog ear.

It is a widespread problem when shrink wrapping.

Solution:

1. Utilizing a larger film width than necessary can result in dog ears appearing on the corners of your finished goods.

Packaging products with less shrink film roll to reduce the width of the film.

2. If the temperature of the heat tunnel is too low, Increase the temperature.

3. The heat tunnel blower speed is too low. Increase the blower speed.

4. If using PVC shrink film, switch to POF shrink film. PVC is more brittle after heated.

5. If the product is irregularly shaped, it can also cause dog ears after heating.

6. Problems with the quality of shrink film.

Unwanted protruding corners are often found in low quality shrink film.

However, by using KEEPTOP’s Polyolefin shrink film, especially our cross linked shrink film, the likelihood of these issues is significantly reduced.

Our advanced film technology ensures a tighter and more consistent wrap, almost eliminating the occurrence of such corners, providing a smoother and more aesthetically pleasing finish.

This makes our cross linked POF shrink film an ideal choice for high-quality packaging.

Ⅳ. Fish Eyes On Shrinkable Film

There are circular or oval patterns on the surface of shrink wrap film, and the shrinking effect is poor.

The reason is lack of heat.

This is also a common problem in shrink wrapping. When solving for dog ears, you will often solve for crow feet too.

Solution:

1. Increase the temperature of the heat shrink tunnel.

2. Reduce the speed of shrink wrapping machine and heat tunnel conveyor belt. Increase heating time.

3. If the air speed of the heat shrink tunnel blower is too low, increase the airspeed.

The wrap doesn’t shrink consistently if your heat source is not pushing enough air when applying heat.

4. Problems with the shrink film, replacement of high quality POF shrink film.

Ⅴ. Crow’s Feet heat shrink wrap problems

Crow’s feet are wrinkles extending from the corners of your packages.

Solution:

1. Using a smaller heat shrink wrap roll. Excessive film on the corners of the product occurs if there is too much film wrapping the product.

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2. Temperature of shrink tunnel machine is too low Increase temperature.

3. Decrease the speed of the conveyor belt to allow enough time for the shrink film to heat.

4. Increase the air speed of the heat shrink tunnel blower.

5. There are too many vent holes on the shrink film, reduce the number or replace the film.

The hot air can fully heat the shrink wrap film and help it to shrink consistently.

Ⅵ. Weak Sealing Line On Heat Shrink Wraps

The reason is that the seal bar sealing effect is not good.

Solution:

1. Reduce the temperature of the shrink wrapping machine’s hot knife.

2. The height of the sealing line should be in the middle of the package height.

3. The seal bar pressure applied to the film is not uniform. Adjust the seal bar to be level. Replace the gasket if it is damaged.

4. Clean the surface of the hot knife and seal base.

5. Replace the thermal pad if it is damaged.

6. The hot knife sealing time is too short. There is not enough time to complete the sealing. Extend sealing time.

Ⅶ. The Sealing Line Is Not In The Center Of The Package Height

Solution:

1. The height of the sealing table or conveyor belt on the shrink wrappers is incorrect. Adjust the height of the sealing table or conveyor belt.

2. The direction of the shrink tunnel blower is incorrect. Adjust the direction of the blower.

3. Packaging products with less shrink film roll to reduce the width of the film.

Ⅷ. Angel Hair heat shrink wrap problems

There are very thin strands of melted plastic between the product and the film.

The reason is the seal bar not being hot enough.

Solution:

1. Increase the temperature of the hot knife of the seal bar.

2. The seal bar pressure applied to the film is not uniform. Adjust the seal bar to be level.

Ⅸ. Deformed Or Crushed Product

The shrinking force is too large, and the product is crushed by the heat shrink film.

Solution:

1. The temperature of the shrink tunnel is too high, decrease the heat.

2. The speed of the shrink tunnel conveyor belt is too slow. Increase the speed.

3. The size of the shrink film is too small, use a large shrink film.a

The Importance Of Regular Maintenance Of Shrink Wrappers

The above article shows that you need to understand the equipment‘s structure fully. Know which parts to adjust when problems are found during the packaging process.

And proper regular maintenance of your packaging line can greatly reduce the number of damaged goods you see.

The following takes the automatic L sealer as an example of regularly maintaining the machine.

7. Waste File Recycling Wheel Maintenance

1. Maintenance once a month

2. Remove the recovery wheel nut, take out the spring, and recovery wheel

3. Apply butter on the contact surface between the shaft and the recovery wheel to ensure smooth operation.

4. Put the recovery wheel and spring back, and tighten the nut

Design Inputs

The first design input to consider is the activation temperature. This is defined as the minimum temperature the heat seal coating must be exposed to before it can exhibit tack and adherence to the substrate. In addition to temperature, design inputs for seal pressure and dwell time are also important. Seal pressure is a measurement of pressure applied onto the coating during sealing, and dwell time accounts for temperature exposure time and how long pressure is applied during sealing. Collectively, these are known as sealing conditions. 

The next design inputs to consider are the substrates that the heat seal will be coated onto and the substrates that the coated film will be sealed to. The desired peel force is another design input to note. Peel force is usually measured in grams/inches and is a measurement of the force needed to open the seal applied to the package. The adhesive mode of failure required should also be considered.

The final two design inputs are specific to certain types of heat seals. First, it is important to note the requirement of hot tack, which is the actual strength of the heat seal when heated during the sealing process. This is critical for bottle applications where the shape may change during the cooling process. Second, it is prudent to know if the application or storage conditions create a specific blocking requirement. Blocking can occur when the heat seal coating begins to adhere to the top side of the film it is applied to in the roll form.

EVA Copolymers and Terpolymers

With the above design inputs in mind, basic resin systems used in heat seal coatings can be compared. The broadest chemistry used in heat seals is EVA (ethylene vinyl acetate) copolymers and terpolymers. These polymers are available in water-based and solvent-based carriers and are typically used in food, medical, and industrial packaging. Medical packaging applications usually require breathable EVA-based heat seal coatings that can facilitate EtO and gamma sterilization processes. EVA-based heat seal coatings are also widely used for in-mold labeling as well as shrink and heat transfer label applications. Solvent-based EVA heat seal coatings are especially useful in hot fill condiment packaging. In general, EVA-based heat seal products have broad compatibility with various apply-to and seal-to substrates, where there is often good adhesion to olefins, polyester, paper, polystyrene, PVC, HIPS, and many others.

If higher chemical resistance is needed, other chemistries may be considered. EAA (ethylene acrylic acid) polymers are available in a water-based carrier with higher grease and oil resistance, improved moisture resistance, and excellent hot tack properties. They are often used in aseptic packaging and as primers for foil. SURLYN™ ionomers may also be used in similar applications to the EAA products. Unlike EVA polymers, the seal-to and apply-to substrates for EAA and SURLYN™ ionomer-based coatings are narrower, typically limited to foil and paper. Nylon, PET, and PVDC-coated HIPS may be included as appropriate substrates. 

Vinyl, Modified Vinyl, PET, and Modified Polyester Polymers

Vinyl polymers are predominantly used as foil primers or wash coats to prevent corrosion. They can also be used for heat seals, offering good chemical, oil, and moisture resistance. Modified vinyl polymers are seen in pill blister packaging and provide good adhesion to foil, paper, and PVC blisters. PET and modified polyester polymers are used in heat seal coatings. These products will offer the highest heat and chemical resistance for aggressive food packaging, retortable packaging, and dual ovenable applications. PET and modified polyester coatings are more restrictive in their seal-to and apply-to substrate list, mainly compatible with PET, foil, PVC, APET, CPET, and ETP steel. 

Conclusion

Many heat seal coating chemistries are available, from the carrier system to the types of backbones in coating polymers. Understanding these and knowing the design inputs of the heat seal’s final packaging can help guide a converter in the correct direction. A list of Bostik's heat seal coatings can be reviewed here. Working closely with the heat seal coating supplier for these choices is recommended. This will allow the converter to optimize their heat seal choice based on their applications and equipment assets. Click below to talk to a specialist at ChemPoint for Bostik's heat seal coatings. 

EVA Co and Terpolymers

Next let’s begin to review, compare and contrast the basic resin systems used in heatseal coatings. By far the broadest chemistry used in heatseals are products based on EVA (Ethylene Vinyl Acetate) co and terpolymers. These polymers are available in water-based and some solvent-based carriers. These products are used in a wide variety of end uses from food and medical packaging to some Industrial packaging. The medical packaging applications are usually for breathable coatings used in EtO and gamma sterilization packages. Products are also widely used in IML (In-Mold Labeling), shrink and heat transfer labeling applications. These products have a very broad apply to and seal to the substrate list (see above).

Good adhesion is often seen to olefins, polyester, paper, polystyrene, PVC, HIPS and many others. If higher chemical resistance is needed over the EVA products other chemistries may be looked at. EAA (Ethylene Acrylic Acid) polymers are available in a water-based carrier. These show higher grease and oil resistance. Improved moisture resistance and excellent hot tack properties. They are often used in aseptic packaging and as primers for foil. Surlyn™ Ionomers are often used in similar applications to the EAA products. Unlike EVA polymers the seal to and adhesive to the substrate list is narrower and is often limited to foil and paper. Nylon, pet, and PVDC coated HIPS may also be included.

Vinyl, Modified Vinyl, PET, and Modified Polyester Polymers

When moving over to strictly solvent-based carriers, the EVA polymers have already been discussed above. The primary uses in those cases are labeling and food packaging, especially hot fill condiments. Vinyl polymers are often seen and used predominantly as foil primer or wash coat to prevent corrosion. They can also be used as a heatseal offering chemical, oil and moisture resistance. Modified vinyl polymers are also seen in pill blister packaging offering good adhesion to foil, paper and PVC blisters. The last common chemistries are PET (Polyester) and modified polyester polymers. These are more restrictive in their seal to and apply to the substrate list focusing on pet, foil, PVC, APET and CPET surfaces and ETP steel. These products will offer the highest heat and chemical resistance for aggressive food packaging, retortable packaging, and dual ovenable applications.

Conclusion

As one can see that there are many chemistry options available. From the carrier system to the types of backbones available. Having a very basic understanding of these will help guide the converter in the correct direction. Working closely with the adhesive manufacturer on these choices is essential. This will allow the converter to best optimize their heatseal choice for the range of applications and the equipment assets they have available.

For more information, please visit Heat Sealable Pet Film.