Displays are omnipresent nowadays. Not only are they found in portable devices such as mobile phones and tablet PCs, but they are also used in parking ticket terminals, ticket machines, and ATMs. Display requirements have escalated as continuously as the variety of applications; users now expect complete transparency and the utmost quality.
However, liquid crystal displays (LCDs) are difficult to read in bright surroundings (e.g., in direct sunlight). The reason for this is that the displays are often covered by a glass plate to protect them against vandalism. The sunlight is partly reflected at the interfaces, and these reflections superpose the generated image. This effect can be reduced by bonding the glass cover directly to the LCD using an index-matched adhesive. For this purpose, innovative adhesives have been developed that cure by a combination of light and humidity.* Reliable curing of adhesive in shadowed areas is possible.
Bonding provides additional benefits beyond improved readability. Contamination caused by dust between the glass plates is prevented. In addition, the glass plate will not fog up in humid surroundings. The ruggedness and resistance to vibrations and shock is also increased. Typical application areas include large-area displays in the automotive, aircraft and military industries.
*Developed by DELO Industrial Adhesives.
INDEX-MATCHED LCD ADHESIVES
The refractive index of these newly developed adhesives is matched to glass, which improves the readability of the display. This circumstance is confirmed by the following calculation based on the Fresnel formulas. If a light beam vertically hits a glass surface, the formula for the reflection coefficient R is applied: