ULTEM® polyetherimide (PEI) resins have been used in opto-electronic markets since the optical properties of these materials enable the design of critical components under tight tolerances. PEI resins are the material of choice for injection molded integrated lens applications due to good dimensional stability, near infrared (IR) optical transparency, low moisture uptake and high heat performance. In most applications, parts must be produced consistently with minimal deviations to insure compatibility throughout the lifetime of the part. With the large number of lenses needed for this market, injection molding has been optimized to maximize the production rate. These optimized parameters for high throughput may or may not translate to an optimized optical performance.
In this paper, we evaluate and optimize PEI injection molding processes with a focus on optical property performance. A commonly used commercial grade was studied to determine factors and conditions which contribute to optical transparency, color, and birefringence. Melt temperature, mold temperature, injection speed and cycle time were varied to develop optimization trials and evaluate optical properties. These parameters could be optimized to reduce in-plane birefringence from 0.0148 to 0.0006 in this study. In addition, we have studied an optically smooth, sub-10nm roughness mold to re-evaluate material properties with minimal influence from mold quality and further refine resin and process effects for the best optical performance.
SABIC’s ULTEMTM (polyetherimide) resin has been the choice of material for injection moldable micro lenses and lens arrays in optical communication components such as transceivers due to its unique combination of physical, thermal and optical properties including high refractive index, low absorption in near IR range, good dimensional stability and high heat performance. It's known that processing conditions affect properties of final parts. Often the processing conditions are optimized for best mechanical properties, while their effect on optical properties is sidelined. In this study, the effect of injection molding processing conditions on optical properties of polyetherimide resin is discussed.