Protective Shield for Screens
Market share of different PSA grades (in the markets of Greater China and South Korea) – WACKER estimate
“Silicones are more expensive on the whole. That is why they only command some 8% of the market. Our customers therefore only use silicones where they offer a performance advantage,” says Kim, explaining the challenges facing developers. “In practical terms, our silicone PSAs show ideal behavior in the production process. To ensure rapid processing workflows, the viscosity and curing behavior must be precisely matched,” adds Hagemeister.
Other important criteria that the protective-film manufacturers use to choose their adhesive suppliers include storage stability, abrasion resistance and surface adhesion. In addition, the handling also plays an important role. “The adhesive layer must ensure that the protective film conforms to the display surface without troublesome air bubbles,” says Kim. The silicones achieve all that – as well as another advantage: they do not yellow and they retain their properties both at high and low temperatures.
The chemical and physical properties of the release coating can be tested at WACKER’s technical center in South Korea.
Silicone PSAs are multicomponent systems, including high-adhesion and less high-adhesion silicones, various additives and a platinum catalyst. This catalyst triggers the crosslinking of the silicones to form a three-dimensional polymer structure. This step only takes place during manufacture of the protective films, after the silicone PSA has been applied to the backing material. “The platinum catalyst is thus sold as part of the product – and makes up a significant share of the total price. The less precious metal that is needed for the curing reaction, the better,” explains Hagemeister. “We managed to reduce the platinum content of DEHESIVE® PSA 765 to the point where we have a competitive product that performs very well on various PET films, and which protective-film manufacturers can tailor to their requirements,” he adds.
We exploit the special talents of silicones here, since, by artfully functionalizing them – that is to say introducing special chemical groups and combining different silicone grades – we can produce complementary properties, with low or high adhesion, and flexible or stiff characteristics. The reason lies in their chemical structure. Whereas silicone fluids consist of linear molecular chains, silicone resin chains are highly branched, and introduce a high degree of crosslinking into the adhesive layer. And that has an effect on the release force: where the degree of curing is higher, the film remains strongly bonded. Thus, the release force can be precisely adjusted by adding silicone resins. This opens up a wide range of applications for DEHESIVE® PSA 765 coatings on protective films: in display production as a whole, various protective films are used – for example to protect the components against damage during manufacture. “Our goal is to develop a product family that supplies the entire value chain with solutions for self-adhesive films,” explains Kim, summarizing his future development ambitions.