DELO PHOTOBOND UV-curing acrylates for optoelectronics enable fast and true-color bonding of holographic foils manufactured by Covestro, one of the leading suppliers of foils for holographic applications. The automotive industry, as well as many others, will benefit from rapid roll-to-roll manufacturing and better integration of the foils into holographic end-use applications.
Augmented reality head-up displays (AR-HUDs) represent one of the most important future applications for holographic films, like Bayfol® HX from Covestro. As these foils are integrated into the windshield, projections merge with reality so that the navigation appears to be displayed directly on the road. The films allow for brighter and larger images while reducing installation space.
This holographic film technology also offers design freedom and reduced space requirements in the rear lights of cars and other automotive lighting applications. Customized holograms, like a warning message that says ‘Stop’ in the driver’s field of vision, can be designed to increase safety.
No matter the application, holographic films are thin, lightweight and completely invisible under so-called off-bragg conditions – whenever the coupled light does not meet certain requirements, like the correct wavelength. The films usually consist of RGB-sensitive photopolymers on a transparent carrier film and are embedded between two protective cover layers.
Low optical interaction, high strength
A precondition for high component quality is low optical interaction between adhesive and photopolymer. Because of this, the adhesives are chemically adapted in such a way that 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, mainly silicones have been used to fix the foil layers. Silicones are versatile and high-performance materials; however, this is offset by lower strength, slower curing and, in some cases, strong outgassing. During curing, they emit particles to their surroundings. Due to the potential impact on adjacent manufacturing processes, many automotive suppliers are striving for silicone-free production. The DELO PHOTOBOND UV acrylates tested by DELO and Covestro show a highly improved outgassing behavior compared to silicones and reach full strength within seconds under UV light.
"Our holographic films have the potential to push the existing boundaries of automotive lighting capabilities," says Richard Meisenheimer, Application Development Holographic LightGuiding at Covestro. "With UV adhesives, DELO gives our customers another manufacturing option and helps them process the products in their application."
Richard Meisenheimer, Application Development Holographic LightGuiding bei Covestro
The right product for integrating films into end applications
Rear lighting is one of the possible future automotive applications for holographic films. To attach them to the most common substrates in this area, DELO PHOTOBOND OB4116 can be used. The UV acrylate has low outgassing and excellent reliability. This is particularly evident in its high adhesion values after storage, for example in industry-standard tests under temperature and humidity (+85 °C / 85 % r. h.) and climatic cycling tests (-45 °C to +100 °C).
In addition, it enables high-precision, active alignment of the optics to the LED matrix or reflector systems. DELO PHOTOBOND OB4116 requires no additional heat curing, and thus protects temperature-sensitive components as well as the CO2 budget in production. You can find more technical specifications of the product in its technical data sheet.
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