Optically Clear Adhesive (OCA)

Photo elasticity based stress analysis

Mechanic deformation can lead to the optical property change in an optical media, which is called photo elasticity. Therefore, this principle is commonly adopted to investigate the stress distribution in a material.

Optical path for reflection/transmission measurement in Perkin Elmer spectrophotometer

The following figure from Perkin Elmer shows the optical path for transmission and reflection measurements using an integrating sphere.

Photo elastic modulator

photo elastic modulator

Photo elastic modulator (PEM) is one the critical components in a phase modulated ellipsometer, which modulates phase and amplitude changes in detected signal, based on that Psi and Delta will be measured and n, k, d, and others accordingly in principle.

Transmittance/Haze/Clarity measurement-ASTM D 1003

As a simplified view, light is incident upon a sample, three processes occur: transmission, absorption, and reflection, as schematically shown in the follow figure, including retroflection, diffuse reflection, specular reflection, diffuse transmission, and specular transmission.

OCA for good gap filling

Patent application, WO 2017/058499 Al, teaches a method to formulate OCA with good gap filling property for display applications.

initiators

In optically clear adhesive synthesis, free radical initiators can be photoinitators or thermal initiators. The amount of the free radical initiator is often in a range of 0.05 to 5 weight percent based on a total weight of monomers used. The following are some examples of initiators including both thermal and photo-initiators:

OCA formulation

Due to better refractive index matching between optical film and OCA, optically clear adhesive, compared to only air gap, OCA dramatically enhances display performances; there it have been broadly applied in the displays, solar cells, automobiles, buildings, et. al. In addition to provide suitable adhesion, it is also required to be optically transparent, colorless, weathering/aging resistant (no yellowing, no bubbles), and sometimes it requires to able to sustain high temperature, dissipate stress and more as required by specific applications.