Protective Shield for Screens

Release Force Is Key

Source: Gartner, May 2017

Whether the protective films are applied by manufacturers or consumers, or films are employed permanently or as temporary protection during transportation, it is essential to bond them effectively on the surface. For this purpose, the films are treated with pressure sensitive adhesives (PSA). These self-adhesive coatings only need to be pressed on gently. To enable the films to be easily peeled off completely as required, the release force of the PSA film is adjusted precisely. The release force indicates how much force is required to peel a film off its backing.

Customizable

The manufacturers decide whether it has to be easy or difficult to peel off, depending on the specific requirements. The best systems should be capable of being individually tailored to the application. With our new DEHESIVE® PSA 765 silicone, that is exactly what we have achieved,” explains Ki-Eon Kim of the Group’s applications technology center in Seongnam-si, near Seoul in South Korea. Like his colleague Timo Hagemeister, the WACKER expert works in the beating heart of the electronics industry. East Asia is not only where many smartphone manufacturers have their production sites, but is also the home of their subcontractors – including protective-film manufacturers.

Sandwich Structure

The exact properties of the self-adhesive films are determined by their structure and chemical composition. The protective films have a multilayer sandwich structure. A key role is played by the PSA layer, “It may be made of polyacrylic, polyurethane or rubber – or silicones, as in this case,” explains Hagemeister. The PSA layer is usually between 15 and 25 micrometers thick, and has to perform several different functions, such as anchoring firmly to the glass surface of the display. At the same time, the layer must remain bonded to the backing material, usually a polyethylene terephthalate (PET) film. The adhesive film is thus the connecting element between the PET layer of the film and the glass surface of the smartphone.

“However, the materials have very different chemical and physical properties,” says Hagemeister. “That is why it is a challenge to formulate the silicone PSAs such that they remain anchored to both materials – but with different adhesion strengths.” It should be possible to strip the adhesive film off the glass surface, though not off the PET layer. Manufacturers of protective film need a higher adhesion strength here.

This is the balancing act that the new product DEHESIVE® PSA 765 is required to perform. Its properties have convinced a South Korean protective-film manufacturer – which now uses WACKER’s silicone PSAs.