Adhesives and adhesive tapes often have contradictory requirements: they need to adhere firmly yet be easily and cleanly removed. These requirements exist for several applications where there is a need for fixation for a limited time — a time period that can vary from seconds to years.

Adhesive requirements depend on the application. For some, the main purpose is to be able to easily separate two adhered surfaces for recycling or repair. For others, the ability to remove the adhesive bond without damaging the application surface is most important. The greatest benefit for some applications is the ability to easily remove the adhesive without having to clean the application surface afterwards. Yet for an additional group, the greatest benefit is the ability to reduce the adhesive bond to enable removal of tapes and adhesives in automated systems. Technologies that can satisfy these requirements open up many new application areas, thereby expanding the entire market for adhesives.

Several adhesive technologies try to meet the requirements of strong fixation in combination with easy removal. All have benefits and disadvantages. Often, the adhesive systems work with a “switch” mechanism that changes the adhesive properties. The switch can, for example, be triggered by heat, electricity or light.

Light-Switchable Adhesives

Enlarge this picture Figure 1. Peel force test performed on two different light-switchable adhesives. One version has a peel force of 35 N/25 mm before exposure to light, which is reduced to ~4 N/25 mm within a few seconds after the light is turned on. The other version has a peel force of ~2.5 N/25 mm and decreases to less than 0.5 N/25 mm after exposure to light. The Adhelight technology can be tailored to meet requirements of different adhesive properties such as peel force strength.

Innovation-based startup company Lumina Adhesives has developed a new technology platform of switchable pressure-sensitive adhesives called Adhelight^TM that enables debonding on demand. The adhesives adhere strongly to the application surface but can — within a few seconds of exposure to visible light — be easily removed without leaving any residue. The light-switchable adhesive technology has been developed to satisfy the need for secure fixation in combination with pain- and irritation-free removal of wound dressings and other human skin applications. The adhesive is cleared for biocompatibility safety.

The light-switchable adhesive has attracted interest in the electronics, paper and graphics industries as well.

Working with Visible Light

Working with an adhesive that reacts to visible light presents a challenge: the light must be kept away from the adhesive until removal time, then the light needs to be led to the adhesive to get a “switch.”

In production, the solution to restricting the light conditions to not let the adhesive switch is easier than one might expect. As the Adhelight adhesives are triggered only by wavelengths >550 nm, it is possible to use light filters that shield the unwanted light wavelengths. The light filters also provide decent working light conditions; the light is bright yellow (not white), similar to regular indoor light.

Tape Design

Enlarge this picture Figure 2. Medical dressing design.

Designing tapes with the light-switchable adhesive is tricky; no universal design solution exists for all kinds of tape. Instead, one must look at the requirements for a specific application and design the tape with these particular needs in mind.

For medical dressings, the tape design comprises a transparent film onto which the light-switchable adhesive is laminated. On top of the transparent film is a light-protective film that is adhered to the transparent film with a breathable adhesive. At the removal time, the light-protective film is peeled off and the adhesive is exposed to light through the transparent film. When the adhesive is “switched,” it can easily be removed together with the transparent backing film without causing skin irritation or pain for the user.

For many non-medical products, such as labels and posters, the design can be simplified. Adhelight can be laminated directly onto a light-blocking backing material. When it is time for removal, the backing material (such as a label or a poster) is removed and any remaining adhesive is exposed to light. After a few minutes of ambient light exposure, the adhesive has “switched” and can easily be rubbed off — saving much time and effort cleaning.

When using the adhesive in manufacturing processes, using light filters to shield indoor light sources (as opposed to working with light-protective films) is easiest. For such applications, the light-switchable adhesive is laminated onto a transparent film, such as PET, then stored in a light-protective package until it is applied. At the manufacturing site, all direct light sources that will come in contact with the tape in use are covered with light filters. The ambient light can, after quality inspection, usually be left unaffected, as the Adhelight tape used for manufacturing processes does not switch because of low-energy light. For automated systems, light tables with blue LEDs can be used to switch the adhesive in a few seconds, thus enabling automated and easy removal of tape — and no cleaning is necessary.

Choosing the Right Switchable Adhesive

Choosing the appropriate switchable adhesive depends on the desired application and convenience of use. Switchable adhesives triggered by visible light offer many benefits in that the energy source used to “switch” the adhesive is readily available everywhere and no additional machinery is required. In addition, UV light or heat is not required. By tailoring the adhesive properties (such as time for switch), using light filters (if necessary), and allowing for a flexible tape design, switchable adhesives can bring value to many applications.

For more information, contact Daniel Jacobsson at Daniel.jacobsson@luminaadhesives.com or visit www.luminaadhesives.com.