Low optical interaction, high strength

A precondition for high component quality is low optical interaction between the adhesive and photopolymer. Because of this, adhesives are chemically adapted so they do not shift the absorption into other wavelength ranges when they are combined with the photopolymer. Therefore, they must ensure color fidelity under all conditions.

Until now, silicones have been the primary adhesive material for foil layers as they are versatile and high-performance. However, this is offset by lower strength, slower curing and—in some cases—strong outgassing, emitting particles during curing. Due to the potential impact this may have on adjacent manufacturing processes, many automotive suppliers strive for silicone-free production. DELO PHOTOBOND UV acrylates, tested by DELO and Covestro, show vastly improved outgassing behavior compared to silicones, reaching full strength within seconds under UV light.

The right products for film integration

Automotive taillights are one possible future application for holographic films. DELO PHOTOBOND OB4116 can be used to attach them to the most commonly used substrates in their assemblies. This UV acrylate has low outgassing and excellent reliability, particularly evident in its high adhesion values after storage in industry-standard temperature and humidity (+85 °C / 85 % r. h.) as well as climatic cycling tests (-45 °C to +100 °C).

In addition, it enables high precision with active alignment with LED matrix or reflector systems, and requires no additional heat curing, thus protecting temperature-sensitive components as well as the environment during production.

Another potential candidate for this application is DELO PHOTOBOND OB4189. In addition to AR, this adhesive is used for other optical automotive functions, namely LED headlights. It exhibits particular reliability, with low yellowing and high demonstrable durability under climate change testing ranging between -45 and +100 °C. It also demonstrates low outgassing and a high aspect ratio for accurate lens alignment. In addition, DELO PHOTOBOND OB4120 demonstrates similar yellowing resistance, withstanding 500 hours at 140 °C before any physical effects take place.