Patent application, WO 2017/058499 Al, teaches a method to formulate OCA with good gap filling property for display applications.
The application is summarized as in the above figure. And more details can be obtained from the original description. A couple of good points in the application are cited and can be used as guide lines for OCA development:
- G’ of less than 10^5 Pascal (Pa) (100 kPa), at at 1 radian/second frequency, tends to favor good ink wetting, as well as quick deformation and compliance to the sharp edge of the ink-step contour.
- The shear storage modulus is no greater than 300 kPa (this is often the upper limit for a pressure -sensitive adhesive but heat activated adhesives can be higher such as up to 400 kPa, up to 500 kPa, or up to 600 kPa); typically in a range of 50to 125 kPa.
- A high tan delta value (e.g., tan δ of at least 0.6 between 40°C to 80°C or even slightly higher) ensures sufficient flow to wet the ink surface. Sufficient flow often correlates with lamination, autoclaving and others.
- High creep compliance can cause boundary control issues; during assembly of the display, for example, the adhesive may flow too much under lamination or autoclave conditions.