Heat Transfer Films: Hot, Warm or Cold Peel

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After you heat press an applique to a garment, how long should you wait before peeling the carrier or the hot mask from the applique?  A number of variables come into play. The answer depends in part on the physical properties of the hot melt adhesive and the type of carrier used on the heat transfer film. Of course, there’s more to it than that.

Each film is a little different from one manufacturer to the next, from one product line to the next.  You should refer to the information that the manufacturer provides. A list of SEF Processing and Application Bulletins is available on this blog.  

In most cases the manufacturer’s guidelines are a good starting point.  For example, you can remove the carrier from most of the SEF polyurethane films, such as FlexCut Sticky and Tatoo, in three to five seconds after heat pressing. VelCut flock films require more cool down time after heat pressing. For the flock appliques, you should wait at least 20 seconds before removing the carrier.   These guidelines work for applications to most garments.

This general rule may not work for every application, though.  How a hot melt adhesive adheres to a fabric can vary from one garment manufacturer to another. Fabrics colored with some dyes, may require modification of your heat press process. The weight of the fabric also affects the rate at which the garment and applique will cool down. Heavier fabric will require more time to cool down than thinner, lighter weight materials. That means you will probably need to wait a little longer before peeling the carrier.

The Role of the Liner or Carrier

The release value of the liner or carrier also plays an important role in determining the optimal peel temperature. Here’s why. When the heat press opens the hot melt adhesive is still in a very liquid. In this liquid state, the adhesive bond to the fabric is very low. As the hot melt adhesive cools, it re-solidifies very quickly and the adhesion builds.

The strength of adhesive bond to the fabric is opposed by the peel adhesion value of the liner. Peel adhesion is the amount of force, measured in grams, required to remove the film from its carrier. Peel adhesion of the liner depends on its physical properties, such as surface finish (glossy or matte), acrylic mass, silicone mass, high release chemical components.

Manufacturers use a variety of release liners with a wide range of release values.  If the release value of the carrier is low, a hot peel is generally possible, immediately after the heat press opens. If the release liner has a medium release value, a warm peel is recommended after three to five seconds after heat pressing.  The higher the peel adhesion value is, the longer you will need to wait before removing the liner or carrier. When the release strength of the liner or carrier is high, a cold peel is recommended, which can take twenty to thirty seconds.

Not all liners perform according in the manner that I just described. Some liners have unusual performance characteristics. For example, in some cases a liner can exhibit very low release strength when it is hot, but the release value can build dramatically as it cools. In this instance, a hot peel is required. Conversely, another liner may  have  very high release strength, when it is hot, but the release can decrease as it cools. In this case, a cold peel would be recommended.

What’s important, is that you carefully qualify the products that you are working with so that you understand the performance characteristics, before you use these materials in production.

When an applique does not adhere properly, here are some remedies that you may try:  

• Heat pressing is a function of time, temperature and pressure. First, check your heat press settings for time and temperature.  If these are set at the specified levels, then increase the pressure.  You may also need to test actual temperature of the platen with an IR temperature gun.

• Unusually large appliques may require an increase of the heat pressing time.  This will give the hot melt adhesive more time to transition from a solid non-sticky mass to a liquid that will flow out onto the surface of the fabric. I like to compare this to grilling a steak. It takes more time to cook a thick steak than a hamburger. Generally, increasing the press temperature will not help.

• Cool down time is important. After the adhesive flows into the texture of the garment, you must allow it time to solidify and mechanically grab onto or adhere to the garment.

ABOUT SEF: For more than 35 years, SEF has provided the screen printing and garment industries with high quality flex films and flock films. Manufacturing at SEF is totally integrated. The factory formulates, casts and adhesive coats its own polyurethane (PU) films. SEF even manufactures its own flock fibers. With a corporate commitment to a greener environment, all of its film and adhesive formulations are water based. This ensures that no solvents pollute the atmosphere. Its only emission is water vapor. Today, SEF is recognized as a leading producer of heat transfer films for used in the fabrication of heat press appliqués for textile decoration. Its ultra-thin polyurethane films and super soft flock films are easy to plotter cut and digitally print.

FOR TECHNICAL SUPPORT: SEF Americas provides a toll-free technical support service at 844-720-9601. NOTE:  If your call is not answered by a tech support person during normal business hours, 8am to 5pm EST (Eastern Standard Time), please leave a message and we will do our best to return your call within an hour.  Should you need to contact us after business hours, an alternate tech support number is 480-987-8028.  You can also get answers to your technical questions by emailing: techsupport@SEFamericas.com.

About this blog: SEF Americas Heat Transfer Blog is dedicated to providing technical information about flex and flock films for heat pressing appliques to textiles. SEF, a leader in flock materials and polyurethane films, serves the garment, sign and screen print industries. SEF brands include Tatoo, Classicprint, Clearflex, Fiberplus, Metalflex and Reflexcut.

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© 2015 Jim Hingst