Optical adhesives play an important role in eliminating reflections and extending the service life of a display. Liquid adhesives are better than tapes due to their superior tolerance to particles and flexibility. Acrylates are the best choice, but silicones are available when the customer requires specific performance.
Fremont, CA: Ambient light-hitting displays create unwanted reflections that can greatly degrade readability. This can be mitigated, however, with optical adhesives. In display bonding, the cover glass is fixed to the surface of a display, usually an LCD, using an optically clear adhesive. This prevents dust and moisture from getting behind the cover glass and makes the display more shock-resistant, thus making it stronger against impacts. Additionally, the refractive index of the adhesive is optimized to minimize solar reflections for enhanced viewability.
Originally applied in the consumer electronics market, display bonding is now gaining ground in the industrial and automotive industries. Many companies currently qualify suitable materials, but the variety of options makes the selection process difficult.
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Difference between Adhesives or Tapes
Manufacturers wishing to bond displays first must choose between tapes and adhesives. Tapes are easy to use and have a clean application process. However, despite requiring more expertise, liquid adhesives offer some advantages over tapes. Liquid adhesives have higher particle tolerance; thus, small particles that enter the adhesive layer during bonding are less noticeable than those caught under tapes. The particles "sink" into the liquid adhesive, which mixes them rather than causing blemishes.
Liquid adhesives also offset production tolerances, such as surface irregularities on a display bezel. They bond with the black mask of the cover glass seamlessly and permit curved cover glass and flat displays. Tapes often result in small air bubbles on screen-printed edges, which sometimes cannot be removed easily. Liquid adhesives allow one to align components post-attachment, making manufacturing more versatile. They further allow different display sizes without purchasing distinct equipment, while tapes have to be pre-set and pre-cut.
Good Product Features in Acrylates and Silicones
Once a manufacturer has decided to use a liquid adhesive, choosing between silicones and acrylates is the next decision. Both types have excellent optical and mechanical properties. Silicones are available in UV-curable or two-component systems, while acrylates are available in light- or light- and humidity-curing systems.
Silicones are softer and reduce the effects of tensions causing image defects, known as "Mura effects." On the other hand, acrylates have an advantage in adhesion, especially at low temperatures, avoiding delamination. The choice between the two is usually determined by the application's specific requirements and the production process.
Differences in the Production Process
High process reliability in the production process for adhesives is vital. Two-component silicones must be mixed carefully, are sensitive to contamination and can hinder proper curing. One-component acrylates eliminate mixing problems and offer reliable curing even in shadowed areas through dual light- and humidity-curing options.
Silicones normally cure in ovens. It is a batch-curing process, whereas acrylates cure fast under the light. Therefore, they are preferred for high-volume production using less cycle time. In contrast, silicones require huge investments in facilities and equipment, while acrylates require less space and power, hence being environmentally friendly and resource-efficient.
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