A novel method for improving the surface quality of microcellular injection molded parts

Microcellular injection molding is the manufacturing method used for producing foamed plastic parts. Microcellular injection molding has many advantages including material, energy, and cost savings as well as enhanced dimensional stability. In spite of these advantages, this technique has been limited by its propensity to create parts with surface defects such as a rough surface or gas flow marks. Methods for improving the surface quality of microcellular plastic parts have been investigated by several researchers. This paper describes a novel method for achieving swirl-free foamed plastic parts using the microcellular injection molding process. By controlling the cell nucleation rate of the polymer/gas solution through material formulation and gas concentration, microcellular injection molded parts free of surface defects were achieved. This paper presents the theoretical background of this approach as well as the experimental results in terms of surface roughness and profile, microstructures, mechanical properties, and dimensional stability.

[1]  R. Flumerfelt,et al.  Nitrogen solubilities in low-density polyethylene at high temperatures and high pressures , 1995 .

[2]  S. Cha,et al.  The Relationship of Mold Temperatures and Swirl Marks on the Surface of Microcellular Plastics , 2005 .

[3]  R. Reid,et al.  The Properties of Gases and Liquids , 1977 .

[4]  C. Panayiotou,et al.  Foaming of polymers with supercritical CO2: An experimental and theoretical study , 2007 .

[5]  E. Beckman,et al.  Nucleation and growth in microcellular materials: Supercritical CO2 as foaming agent , 1995 .

[6]  Michel Vert,et al.  Biodegradable polymers and plastics , 1992 .

[7]  G. Steinbichler,et al.  Polycarbonate Microfoams with a Smooth Surface and Higher Notched Impact Strength , 2004 .

[8]  S. Cha,et al.  Bubble growth in mold cavities during microcellular injection molding processes , 2009 .

[9]  Donald G. Baird,et al.  Polymer Processing: Principles and Design , 1995 .

[10]  S. Cha,et al.  A Mold Surface Treatment for Improving Surface Finish of Injection Molded Microcellular Parts , 2004 .

[11]  L. Turng,et al.  Mathematical modeling and numerical simulation of cell growth in injection molding of microcellular plastics , 2004 .

[12]  Jonathan S. Colton,et al.  The nucleation of microcellular thermoplastic foam with additives: Part II: Experimental results and discussion , 1987 .

[13]  L. Turng,et al.  Development of a Hybrid Solid-Microcellular Co-injection Molding Process , 2004 .

[14]  Zhongbao Chen,et al.  Effect of processing conditions on shrinkage and warpage and morphology of injection moulded parts using microcellular injection moulding , 2006 .

[15]  L. Turng,et al.  Improving surface quality of microcellular injection molded parts through mold surface temperature manipulation with thin film insulation , 2010 .

[16]  Sung Woon Cha,et al.  Influence of Mould Temperature on the Thickness of a Skin Layer and Impact Strength in the Microcellular Injection Moulding Process , 2005 .

[17]  A. Laaksonen,et al.  Nucleation: measurements, theory, and atmospheric applications. , 1995, Annual review of physical chemistry.

[18]  L. Turng,et al.  Study of Shrinkage and Warpage in Microcellular Co-Injection Molding , 2006 .

[19]  Chul B. Park,et al.  Measurement of gas solubility in linear/branched PP melts , 2007 .

[20]  E. Beckman,et al.  Generation of microcellular polymeric foams using supercritical carbon dioxide. I: Effect of pressure and temperature on nucleation , 1994 .

[21]  Chul B. Park,et al.  Solubility measurements of N2 and CO2 in polypropylene and ethene/octene copolymer , 2007 .

[22]  T. Chong,et al.  Study on the Accuracy of Injection Molded Plastic Gear with the Assistance of Supercritical Fluid and a Pressurized Mold , 2007 .

[23]  Jung Joo Lee,et al.  Characteristics of the Skin Layers of Microcellular Injection Molded Parts , 2006 .

[24]  Jonathan S. Colton,et al.  The nucleation of microcellular thermoplastic foam with additives: Part I: Theoretical considerations , 1987 .

[25]  David L. Tomasko,et al.  Development of CO2 for polymer foam applications , 2009 .

[26]  D. Rodrigue,et al.  The effect of injection molding conditions on the morphology of polymer structural foams , 2009 .