Bonding Materials

Because most types of glass have a refractive index of 1.5, most adhesives used for optical bonding have a similar refractive index. Depending on the application, silicone, epoxy, acrylated urethane or PSA may offer the optimized mechanical and thermal properties.

Silicones are commonly used in optical bonding because they have high transparency, good thermal range and can be reworked if a problem occurs (such as debris entrapment) during the bonding process. The drawback of silicones is that they are soft material and can fail at low temperatures or high altitudes. Consequently, they may not be suitable for applications where high mechanical strength and stability are required.

Epoxies are also used in optical bonding and provide very good thermal durability, but often form a permanent bond that cannot be easily reworked. They can be applied in a thinner bond line and shorter curing time than silicones. Epoxies can have some issues when bonding dissimilar materials.

Acrylated urethanes are now used in optical bonding in the electronic display industry because they exhibit desirable properties such as clean bond lines, very wide thermal range and short curing times.

Dontech can develop custom formulations are often developed and used for specific display applications and bonding configurations (e.g., over-frame, under-frame and rear-surface display bonding).

Selecting the proper optical bonding adhesive is dictated by the application including the type and surface treatment of the display, mechanical configuration, components to be bonded to the display, cost concerns, thermal range and optical performance criteria.