Birefringence techniques for the characterization of residual stresses in injection-moulded micro-lens arrays

The presence or absence of residual stresses is a major concern in the injection moulding of plastic products used in precision optical and medical applications. Micro-lens arrays are critical components of LED displays that are produced by micro-injection moulding. Due to their small size, residual stresses in these micro-lens arrays are difficult to measure and characterize. The birefringence method was used in this paper to evaluate residual stresses in injection-moulded micro-lens arrays and the finite element simulation method was also employed to predict their distribution. Comparable results from both experiments and simulation were obtained. It is found that the mould temperature is the most significant processing parameter. The value of maximum residual stress is smaller when the mould temperature is higher. The birefringence method is applicable and efficient for the measurement of residual stress in injection-moulded plastic micro-optics.