Effect of Gas Counter Pressure on the Surface Roughness, Morphology, and Tensile Strength between Microcellular and Conventional Injection-Molded PP Parts

Microcellular injection-molded parts have surface defect problems. Gas counter pressure (GCP) is one of the methods to reduce surface defects. This study investigated the effect of GCP on the surface roughness, morphology, and tensile strength of foamed and conventional injection-molded polypropylene (PP) products. GCP is generated by filling up the mold cavity with nitrogen during the injection-molding (IM) process. It can delay foaming and affect flow characteristics of microcellular and conventional injection-molding, which cause changes in the tensile strength, flow length, cell morphology, and surface quality of molded parts. The mechanism was investigated through a series of experiments including tuning of GCP and pressure holding duration. Surface roughness of the molded parts decreased with the increase in GCP and pressure holding duration. Compared to microcellular IM, GCP-assisted foaming exhibited much better surface quality and controllable skin layer thickness.

[1]  Patrick C. Lee,et al.  Improved Cell Morphology and Surface Roughness in High-Temperature Foam Injection Molding Using a Long-Chain Branched Polypropylene , 2021, Polymers.

[2]  S. Chen,et al.  Using P(Pressure)-T(Temperature) Path to Control the Foaming Cell Sizes in Microcellular Injection Molding Process , 2021, Polymers.

[3]  Guoqun Zhao,et al.  Polypropylene/talc foams with high weight-reduction and improved surface quality fabricated by mold-opening microcellular injection molding , 2021 .

[4]  Jiachang Wang,et al.  Experimental investigation on the forming and evolution process of cell structure in gas counter pressure assisted chemical foaming injection molded parts , 2020 .

[5]  Hongfu Zhou,et al.  Thermoplastic polyurethane (TPU) modifier to develop bimodal cell structure in polypropylene/TPU microcellular foam in presence of supercritical CO2 , 2020, Journal of Vinyl and Additive Technology.

[6]  C. Griffiths,et al.  A Design of Experiment Approach for Surface Roughness Comparisons of Foam Injection-Moulding Methods , 2020, Materials.

[7]  W. Zhai,et al.  Preparation of microcellular thermoplastic polyurethane (TPU) foam and its tensile property , 2018 .

[8]  Xiangfang Peng,et al.  In-situ fibrillated polytetrafluoroethylene (PTFE) in thermoplastic polyurethane (TPU) via melt blending: Effect on rheological behavior, mechanical properties, and microcellular foamability , 2018 .

[9]  Chul B. Park,et al.  Study of the foaming mechanisms associated with gas counter pressure and mold opening using the pressure profiles , 2017 .

[10]  C. Hopmann,et al.  Surface roughness and foam morphology of cellulose acetate sheets foamed with 1,3,3,3‐tetrafluoropropene , 2017 .

[11]  M. Vincent,et al.  Polypropylene structural foams: Measurements of the core, skin, and overall mechanical properties with evaluation of predictive models , 2017 .

[12]  Guang-hong Hu,et al.  Microcellular Foam Injection Molding Surface Improvement Methods , 2016 .

[13]  Guoqun Zhao,et al.  Influence of relative low gas counter pressure on melt foaming behavior and surface quality of molded parts in microcellular injection molding process , 2014 .

[14]  Shyh-Shin Hwang,et al.  Foaming morphology control of microcellular injection molded parts with gas counter pressure and dynamic mold temperature control , 2014 .

[15]  S. Chen,et al.  The effects of gas counter pressure and mold temperature variation on the surface quality and morphology of the microcellular polystyrene foams , 2013 .

[16]  Y. Yoo,et al.  Injection molding without prior drying process by the gas counter pressure , 2012 .

[17]  M. Vijayan,et al.  Effect of the Surface Roughness of Conducting Polypyrrole Thin-Film Electrodes on the Electrocatalytic Reduction of Nitrobenzene , 2012 .

[18]  Jian Wang.  Some Critical Issues for Injection Molding , 2012 .

[19]  H. Guanghong,et al.  Microcellular Foam Injection Molding Process , 2012 .

[20]  Wei Min Yang,et al.  Effect of Processing Conditions on the Shrinkage and Warpage of Glass Fiber Reinforced PP Using Microcellular Injection Molding , 2012 .

[21]  S. Chen,et al.  Rheological characterization of polystyrene melts dissolved with supercritical nitrogen fluid during microcellular injection moulding , 2010 .

[22]  A. Chate,et al.  Correlation Between Morphology and Notched Impact Strength of Microcellular Foamed Polycarbonate , 2010 .

[23]  L. Turng,et al.  Processing and characterization of microcellular PHBV/PBAT blends , 2010 .

[24]  S. Chen,et al.  Using thermally insulated polymer film for mold temperature control to improve surface quality of microcellular injection molded parts , 2008 .

[25]  Shyh-Shin Hwang,et al.  The dimensional stability of a microcellular injection molded gear shaft , 2008 .

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

[27]  L. Turng,et al.  Microcellular Injection Molding , 2005 .

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

[29]  D. Rodrigue,et al.  The Effect of Skin Thickness on the Mechanical Properties of Structural Foams , 2004 .

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

[31]  Andrea Sorrentino,et al.  Molecular orientation in injection molding: experiments and analysis , 2004 .

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

[33]  M. Ohshima.  A new technique of supercritical CO2-asisted surface coating injection molding , 2004 .

[34]  Jon Rigelsford,et al.  Injection Molding Handbook. 3/e , 2003 .

[35]  Jonathan S. Colton,et al.  Nucleation of microcellular foam: Theory and practice , 1987 .