Accessible Requires Authentication Published by De Gruyter April 6, 2013

Effects of Injection Molding Holding Pressure on the Replication of Surface Microfeatures

T. R. Tofteberg, H. Amédro, F. Grytten and E. Andreassen

Abstract

The injection molding of an optical grating was studied using two different polycarbonates. The grating had period 10 μm and peak-to-valley distance ∼1 μm. Parts were molded using different holding pressures and mold temperatures. After production, the parts were annealed at 100°C. The replication was investigated using white light interferometry (WLI) before and after annealing. WLI was performed using high definition vertical-scanning interferometry (HDVSI) to resolve the details of the molded gratings with a noise level below 2 nm.

It was observed that increasing the holding pressure could have either a positive or a negative effect on the replication. When the microfeatures were not fully filled, an increased holding pressure improved the definition of the features. However, for both polymers, it was observed that the replication as a function of holding pressure started to drop when the holding pressure was increased above an optimal value. This could be due to an elastic recoil occurring after releasing the holding pressure.

The peak-to-valley distance of the grating was reduced after annealing. This effect was larger for parts molded using a low mold temperature. This is probably due to a higher cooling rate giving higher internal stresses, which will relax during annealing.


Mail address: Terje Rosquist Tofteberg, SINTEF Materials and Chemistry, Oslo, Norway. E-mail:

References

Aasetre, S., Andreassen, E., “Packing of Material along Flow Path in Injection Moulded Container”, Plast. Rubber Compos., 31, 2027(2002), DOI: 10.1179/146580101125000475 Search in Google Scholar

Arlø, U. R., Kjær, E. M., “Transcription of Small Surface Structures in Injection Molding – An Experimental Study”, in Specialized Molding Techniques, Heim, H.-P., Potente, H. (Eds.), Plastics Design Library, Ontario(2001) Search in Google Scholar

Carpenter, B., et al., “Effect of Machine Compliance on Mold Deflection during Injection and Packing of Thermoplastic Parts”, Polym. Eng. Sci., 46, 844852(2006), DOI: 10.1002/pen.20527 Search in Google Scholar

Chen, D., U.S. Patent 7605925-B1 (2009) Search in Google Scholar

Ding, Y., et al., “Relaxation Behavior of Polymer Structures Fabricated by Nanoimprint Lithography”, ACS Nano, 1, 8492(2007)10.1021/nn700014p Search in Google Scholar

Han, X., Yokoi, H., “Visualization Analysis of the Filling Behavior of Melt into Microscale V-Grooves during the Filling Stage of Injection Molding”, Polym. Eng. Sci., 46, 15901597(2006), DOI: 10.1002/pen.20615 Search in Google Scholar

Han, X., et al., “Effects of Cavity Conditions on Transcription Molding of Microscale Prism Patterns using Ultra-high-speed Injection Molding”, Int. Polym. Proc., 21, 473479(2006) Search in Google Scholar

Jansen, K. M. B., et al., “Effect of Processing Conditions on Shrinkage in Injection Molding”, Polym. Eng. Sci., 38, 838846(1998), DOI: 10.1002/pen.10249 Search in Google Scholar

Jansen, K. M. B., et al., “Comparison of Residual Stress Predictions and Measurements Using Excimer Laser Layer Removal”, Polym. Eng. Sci., 39, 20302041(1999), DOI: 10.1002/pen.11596 Search in Google Scholar

Kalima, V., et al., “Transparent Thermoplastics: Replication of Diffractive Optical Elements using Micro-injection Molding”, Opt. Mater., 30, 285291(2007), DOI: 10.1016/j.optmat.2006.11.046 Search in Google Scholar

Kambour, R. P., et al., “Tensile Stresses in the Edges of Injection Moldings: Roles of Packing Pressure, Machine Compliance, and Resin Compression”, Polym. Eng. Sci., 36, 28632874(1996), DOI: 10.1002/pen.10687 Search in Google Scholar

Li, J. H., Young, W. B., “Study on Mold Filling Behaviors of Micro Channels in Injection Molding”, Int. Polym. Proc., 24, 421427(2009), DOI: 10.3139/217.2289 Search in Google Scholar

Madou, M. J.: Fundamentals of Microfabrication: The Science of Miniaturization, 2nd Edition, 2nd Ed., CRC Press, Boca Raton(2002) Search in Google Scholar

Murakami, O., et al., “Effect of Molecular Weight and Molding Conditions on the Replication of Injection Moldings with Micro-scale V-Groove Features”, Polym. Eng. Sci., 48, 697704(2008), DOI: 10.1002/pen.21002 Search in Google Scholar

Mönkkönen, K., et al., “Replication of Sub-micron Features Using Amorphous Thermoplastics”, Polym. Eng. Sci., 42, 16001608(2002), DOI: 10.1002/pen.11055 Search in Google Scholar

Nguyen-Chung, T., Mennig, G., “Does Fountain Flow Influence Molecular Orientation in Injection Moulded Parts?”, Plast. Rubber Compos., 35, 418424(2006), DOI: 10.1179/174328906X149709 Search in Google Scholar

Pham, H. T., et al., “Residual-stresses in Injection-molded Polycarbonate Rectangular Bars”, Polym. Eng. Sci., 33, 16341643(1993), DOI: 10.1002/pen.760332408 Search in Google Scholar

Sha, B., et al., “Investigation of Micro-injection Moulding: Factors Affecting the Replication Quality”, J. Mater. Process. Tech., 183, 284296(2007), DOI: 10.1016/j.jmatprotec.2006.10.019 Search in Google Scholar

Theilade, U., Hansen, H., “Surface Microstructure Replication in Injection Molding”, Int. J. Adv. Manuf. Tech., 33, 157166(2007), DOI: 10.1007/s00170-006-0732-y Search in Google Scholar

Titomanlio, G., et al., “Mechanism of Cooling Stress Build-up in Injection Molding of Thermoplastic Polymers”, Int. Polym. Proc., 1, 5559(1987) Search in Google Scholar

Tofteberg, T., et al., “Injection Molding of a Diffractive Optical Element”, Polym. Eng. Sci., 48, 21342142(2008), DOI: 10.1002/pen.21154 Search in Google Scholar

Tofteberg, T. R., Andreassen, E., “Multiscale Simulation of Injection Molding of Parts with Low Aspect Ratio Microfeatures”, Int. Polym. Proc., 25, 6374(2010), DOI: 10.3139/217.2318 Search in Google Scholar

Xu, G., et al., “Experimental and Numerical Studies of Injection Molding with Microfeatures”, Polym. Eng. Sci., 45, 866875(2005), DOI: 10.1002/pen.20341 Search in Google Scholar

Yao, D., et al., “Rapid Thermal Cycling of Injection Molds: An Overview on Technical Approaches and Applications”, Adv. Polym. Technol., 27, 233255(2008), DOI: 10.1002/adv.20136 Search in Google Scholar

Yokoi, H., et al., “Effects of Molding Conditions on Transcription Molding of Microscale Prism Patterns Using Ultra-high-speed Injection Molding”, Polym. Eng. Sci., 46, 11401146(2006), DOI: 10.1002/pen.20519 Search in Google Scholar

Yoshii, M., et al., “Experimental-Study of Transcription of Minute Width Grooves in Injection-Molding”, Polym. Eng. Sci., 34, 12111218(1994), DOI: 10.1002/pen.760341507 Search in Google Scholar

Zoetelief, W. F., et al., “Residual Thermal Stresses in Injection Molded Products”, Polym. Eng. Sci., 36, 18861896(1996), DOI: 10.1002/pen.10585 Search in Google Scholar

Received: 2010-01-10
Accepted: 2010-02-27
Published Online: 2013-04-06
Published in Print: 2010-07-01

© 2010, Carl Hanser Verlag, Munich