Birefringence in injection‐compression molding of amorphous polymers: Simulation and experiment

Abstract

The influence of the processing variables on the residual birefringence was analyzed for polystyrene and polycarbonate disks obtained by injection‐compression molding under various processing conditions. The processing variables studied were melt and mold temperatures, compression stroke, and switchover time. The modeling of flow‐induced residual stresses and birefringence of amorphous polymers in injection‐compression molded center‐gated disks was carried out using a numerical scheme based on a hybrid finite element/finite difference/control volume method. A nonlinear viscoelastic constitutive equation and stress‐optical rule were used to model frozen‐in flow stresses in moldings. The filling, compression, packing, and cooling stages were considered. Thermally‐induced residual birefringence was calculated using the linear viscoelastic and photoviscoelastic constitutive equations combined with the first‐order rate equation for volume relaxation and the master curves for the Young's relaxation modulus and strain‐optical coefficient functions. The residual birefringence in injection‐compression moldings was measured. The effects of various processing conditions on the measured and simulated birefringence distribution Δn and average transverse birefringence <nrr−nθθ> were elucidated. Comparison of the birefringence in disks manufactured by the injection molding and injection‐compression molding was made. The predicted and measured birefringence is found to be in fair agreement. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers

An experimental study on the effects of injection-molding types for the birefringence distribution in polycarbonate discs

“…et al(2009) predicted the in-plane direction birefringence and residual stress in a PMMA micro-lens using a commercial code, Moldflow, in various injection molding conditions. Recently, Kim(2009) showed the effects of compression and co-injection on the birefringence structure by experiments and numerical simulation. However, compression process was used for filling which is somewhat different from the process used in the industry.…”

Polystyrene Foam with High Cell Density and Small Cell Size by Compression‐Injection Molding and Core Back Foaming Technique: Evolution of Cells in Cavity

“…However, the application of the packing pressure may cause heterogeneous structures in the direction of the flow, although the combination of packing pressure and packing time is sufficient to re‐dissolve the cells . Injection–compression molding is a technique which will cause a quick increase of cavity pressure after filling through a controlled mold compression in the injection molding . In the normal core‐back process, the cavity generally expands in the direction perpendicular to the flow for a certain distance at a set opening speed, once the filling stage is completed .…”

“…[43] Injection-compression molding is a technique which will cause a quick increase of cavity pressure after filling through a controlled mold compression in the injection molding. [44,45] In the normal core-back process, the cavity generally expands in the direction perpendicular to the flow for a certain distance at a set opening speed, once the filling stage is completed. [36,46,47] For the technology of core-back, a fast pressure drop in cavity can be achieved easily.…”

Optical properties of high‐density polyethylene in injection press molding for IR system lenses

“…Then the clamping process is conducted during or after injection. This method is used to produce thin‐walled parts such as compact disks and optical lenses produced from a transparent amorphous polymer because of transcriptional improvement, uniform pressure distribution, reduction of the residual stresses, and reduction of warpage . The method by which polymer melt is injected in the state of the suitably opened cavity is called injection press molding (IPM) .…”