Thin bonding is a huge category of adhesives with many applications, so we’re continuing our efforts to share what we know in our ongoing series. You’re invited to check out an overview of thin bonding and details about double sided tape.
First off, when you think of adhesive transfer tapes, think about flexibility. The “thinnest” of thin bonding tapes (sub 1 mil), adhesive transfer tapes are conformable to elastic, printed circuit boards, thin plastic, and many other materials, even irregular shapes and sizes. And, because they’re so thin, they’re perfect for products that need to be aesthetically pleasing.
Second, what is being bonded together (the substrates) and their composition are the determining factors in which thin bonding product to use. Adhesive transfer tape manufacturers offer thousands of types of transfer tapes, yet it’s the converter that helps determine that the form meets the function.
Third, (speaking of converting) it takes an experienced converter to properly handle adhesive transfer tapes. The materials themselves and how they’re being converted often make for a challenging manufacturing process, which we’ll get into later.
No Carrier Presents Opportunities and Challenges
As we did with double sided tape, let’s first explore how adhesive transfer tape is constructed. Adhesive transfer tape (also called ATT) is simply a thin film of adhesive with a release liner over the top. The liner makes handling easy, and it just peels off when applying to the second substrate.
Unlike double sided tapes, adhesive transfers tapes have only one type of adhesive and no carrier, a material that separates and holds two adhesives. If the product requires the tape to provide a significant stiffness to function properly, only a tape with a carrier (double sided) can do that. If, however, the stiffness comes from the materials being bonded, the right adhesive transfer tape can do the job.
The thinness of transfer tape has some design advantages yet some potential problems in the converting process. Think of a delicate sheet that’s being pulled off a release liner. Too much tension can pull the liner off too easily or break the adhesive, and not enough tension makes the adhesive stay with the liner. There is a fine line when a pressure sensitive adhesive (PSA) tape is so stretchy.
Surface and Environment Meet Transfer Tapes’ Strengths
As previously mentioned, the substrates’ composition helps converters decide what adhesive transfer tape to use. Yet, there’s also the surface’s three-dimensional characteristics to consider and where transfer tape really shines. A physical surface is rarely completely flat, yet some surfaces have quite a bit of irregularity. These require a flexible tape, obviously one without a carrier.
Another advantage of adhesive transfer tapes is their low profile, which allows for easier stacking atop one another to perform different functions. Plus, with no carrier, a transfer tape is not dependent on the carrier’s ability to withstand various temperatures as it is with double sided tape. Sub-zero temperatures can affect an adhesive solution’s effectiveness as much as extremely warm environments, or a tape constantly exposed to the sun’s UV rays or moisture.
If the application demands optical clarity, an optically clear adhesive (OCA) transfer tape is the most appropriate product because of its thinness and minimal construction material used. When looking good is a priority, adhesive transfer tapes step up to replace bulky rivets, bolts, and other mechanical fasteners. An ultra-thin transfer tape is low profile and nearly unnoticeable.
Challenges
- Adds no significant stiffness (no carrier)
- Cannot easily bond two dissimilar materials
- Handling strength is minimal
- Thinness requires expert converting
Advantages
- Flexible and conformable to irregular shapes
- Design flexibility and clean aesthetics
- Low profile allows for stacking
- Not limited to the temperature resistance of a carrier
- Optical clarity solutions
- Replace mechanical fasteners
- Converters can combine adhesive transfer tapes with a carrier to make a custom double sided tape
Experienced Engineers Make the Difference
While adhesive transfer tapes are thin and flexible, they’re not very sturdy, so converting them requires more expertise. Consistently converting to exact dimensions or complex shapes at low tensions is not something every converter can do.
For example, if the task is to die cut shapes in transfer tape and then remove sections of adhesive for a tab, not having a carrier in the middle makes that tricky. Experienced engineers at high-end converters have designed processes to ensure that adhesive transfer tapes meet specified dimensions and tolerances while being designed for manufacturability. As mentioned, a stretchy adhesive transfer tape provides opportunities and challenges, and the earlier an engineer is involved, the more successful that project will be.
Some aspects of transfer tape present unique, surprising challenges, such as storage. If a transfer tape is improperly stored for a long period of time, gravity will cause the adhesive to flow downward off the release liner, creating a pool of adhesive.
Oftentimes it’s experience and expertise that makes a material incredibly useful instead of frustrating. How do you know if the converter you’re considering embraces adhesive transfer tape or avoids it? Our checklist, How to Choose an Adhesive Converter, is a great guide.
