Injection molding of a diffractive optical element

Abstract

The injection molding of a microfeatured component, a diffractive optical element, was studied. The component has a wave‐like pattern on the surface, with amplitude 0.5 μm and wavelength 3 μm. Two different polymers were used: a polymethylmethacrylate and an ethylene‐norbornene copolymer (cyclic olefin copolymer). The topography was investigated using white light interferometry (WLI), atomic force microscopy (AFM), and scanning electron microscopy (SEM). A new WLI‐based technique is proposed for rapid quantification of the replication of periodic surface patterns. This technique gives almost the same information regarding the degree of replication as AFM but can be performed much faster. Quantitative data on the degree of replication as function of processing conditions are presented. At optimal conditions, almost perfect replication is obtained using both materials. At suboptimal conditions, it is observed that the degree of replication increases with increasing injection velocity and increasing mold temperature, with similar characteristics for both materials. The difference in replication quality between the two materials seems to be related to the different temperature dependencies of the viscosities. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Multiscale Simulation of Injection Molding of Parts with Low Aspect Ratio Microfeatures

“…The purpose of the macroscale simulation is to obtain the cavity pressure for the microscale simulation and this is the only information passed from the macroscale to the microscale. This pressure was also measured using a pressure sensor mounted in the mold half opposite the microfeatures, and the measurements showed good agreement with the simulated pressure as was shown earlier (Tofteberg et al, 2008). An illustration of the situation when the polymer melt hits the microstructured nickel shim (mold insert) is illustrated in Fig.…”

“…The DOR is defined as in the experimental paper, and is based on the Fourier transform of the replicated grating (Tofteberg et al, 2008). It is found by first transforming the shape of the periodic grating into the frequency domain.…”

“…To reconstruct the degree of replication as defined in the experimental paper (Tofteberg et al, 2008), the following procedure was used;…”

“…The aim of the present simulation study is to capture the observations in a previous experimental study in which a part with a micrometer scaled grating was injection molded. (Tofteberg et al, 2008). The part is illustrated in Fig.…”

“…COC has, because of its biocompatibility and good water barrier properties (Shin et al, 2005) become popular for producing labon-a-chip devices and has optical properties that make it attractive in for example waveguides (Khanarian and Celanese, 2001). In the experimental study (Tofteberg et al, 2008), the injection velocity and the mold temperature were varied, while keeping all other settings constant. After production, the degree of replication of the grating was characterized and it varied greatly with processing settings.…”