ISO 25178 Surface Parameters for Injection Moulding Optical Components
ISO 25178 areal parameters define 3D optical surface texture to control stray light and guide injection moulding process windows for precision lenses.
Stray Light Reduction
Meaning
An optical design objective minimizes unwanted internal reflections in molded transparent parts to ensure image clarity. The stray light reduction is achieved by optimizing both the mold surface finish and the molded part geometry to prevent light scattering. In clear polymer molding, this process is critical for producing lenses and sensor housings that operate in demanding optical environments.
Optical Clarity
Prevention of internal scattering requires high-gloss mold surfaces with extremely low roughness. In injection molding, stray light reduction is achieved by polishing the mold cavities to a mirror finish. Any microscopic roughness or surface defects on the mold will be replicated on the plastic part, creating scattering sites that degrade optical performance.
Molding Precision
High-precision molding processes must control resin properties and processing parameters to minimize internal stresses that cause birefringence. This stress-induced birefringence generates phase shifts in the transmitted light, compromising stray light reduction efforts. Moulders must utilize high melt temperatures and slow injection speeds to reduce shear stress in the polymer.
Furthermore, using virgin optical-grade resins rather than regrind ensures the absence of impurities that would otherwise cause scattering and increase stray light.
Quality Assessment
Measurement of the scattering behavior of the finished parts confirms the efficacy of the reduction techniques. Using specialized optical goniophotometers, the stray light reduction is verified under simulated operating conditions. This ensures that every molded lens meets the strict performance requirements of the optical system.