开发一种超临界流体辅助微孔发泡注塑新技术，研制相应的超临界流体发生与计量控制技术系统，构建超临界流体辅助微孔发泡注塑试验线，并对超临界流体辅助微孔发泡注塑熔体的发泡行为进行研究。结果表明，超临界流体辅助微孔发泡注塑熔体的发泡过程包括“填充过程中发泡”和“填充结束后发泡”两个过程，分别对应成型产品内部的变形椭球形泡孔和规则球形泡孔两种不同的泡孔结构形态，而熔体“填充过程中发泡”形成的泡孔，受熔体剪切和喷泉流动行为的影响而发生变形，并在熔体流动前锋处破裂、涌出，与冷的模具表面接触后冷凝遗留在产品表面，形成表面气泡痕。所揭示的发泡演变过程和缺陷产生机理对微孔发泡注塑工艺原理和质量控制有较高的参考意义和工程应用价值。
董桂伟
,
赵国群
,
管延锦
,
王桂龙
,
侯俊吉
,
吴昊
. 超临界流体辅助微孔发泡注塑技术及其熔体发泡行为[J]. 机械工程学报, 2018
, 54(18)
: 42
-48
.
DOI: 10.3901/JME.2018.18.042
A new supercritical fluid assisted microcellular injection molding technique and the corresponding supercritical fluid generation, measurement and monitoring systems are developed. The supercritical fluid assisted microcellular injection molding test line is constructed. The melt foaming behaviors in supercritical fluid assisted microcellular injection molding are investigated. The results show that the melt foaming process in supercritical fluid assisted microcellular injection molding contains two processes:"foam during injection" and "foam after injection", respectively corresponding to the two different cell morphologies of distorted ellipsoidal cells and the regular spherical cells in the microcellular injection molded parts. The cells formed in "foam during injection" process are stretched by the shear flow and fountain flow behaviors, then broken, pushed out and turned over to both sides of the melt flow front, and finally contacted with the cold mold cavity surface and solidified to form surface bubble marks on the molded parts. The revealed foaming processes and defects generation mechanism have higher reference significance and engineering application value for technological principle and quality control of microcellular injection molding.
[1] MARTINI J E,WALDMAN F A,SUH N P. The production and analysis of microcellular thermoplastic foam[J]. SPEANTEC Tech Papers,1982,28:674-676.
[2] AMELI A,JAHANI D,NOFAR M,et al. Development of high void fraction polylactide composite foams using injection molding:Mechanical and thermal insulation properties[J]. Composites Science & Technology,2014,90(2):88-95.
[3] MI H Y,JING X,SALICK M R,et al. Fabrication of thermoplastic polyurethane tissue engineering scaffoldby combining microcellular injection molding and particle leaching[J]. Journal of Materials Research,2014,29(8):911-922.
[4] LIVI S,LINS L C,SAR G,et al. Supercritical CO2-Ionic liquids:A successful wedding to prepare biopolymer foams[J]. Acs Sustainable Chemistry & Engineering,2016,4(2):461-470.
[5] MILLER D,KUMAR V. Microcellular extrusion of PLA utilizing solid-state nucleation in the gas-saturated pellet extrusion process[J]. Journal of Applied Polymer Science,2013,127(3):1967-1973.
[6] DING W D,JAHANI D,CHANG E,et al. Development of PLA/cellulosic fiber composite foams using injection molding:crystallization and foaming behaviors[J]. Composites Part A-Applied Science and Manufacturing,2016,83:130-139.
[7] YUSA A,YAMAMOTO S,GOTO H,et al. A new microcellular foam injection-molding technology using non-supercritical fluid physical blowing agents[J]. Polymer Engineering and Science,2017,57(1):105-113.
[8] XU J Y. Microcellular Injection molding[M]. New Jersey:Wiley Series on Polymer Engineering and Technology,2010.
[9] TURNG L S,KHARBAS H. Development of a hybrid solid-microcellular co-injection molding process[J]. International Polymer Processing,2004,19(1):77-86.
[10] YOON J D,HONG S K,KIM J H,et al. A mold surface treatment for improving surface finish of injection molded microcellular parts[J]. Cellular Polymers,2004,23(1):39-47.
[11] CHEN S C,LIN Y W,CHIEN R D,et al. Variable mold temperature to improve surface quality of microcellular injection molded parts using induction heating technology[J]. Advances in Polymer Technology,2008,27(4):224-232.
[12] CHEN S C,HSU P S,HWANG S S. The effects of gas counter pressure and mold temperature variation on the surface quality and morphology of the microcellular polystyrene foams[J]. Journal of Applied Polymer Science,2013,127(6):4769-4776.
[13] 李帅,赵国群,管延锦,等. 模具型腔气体压力对微发泡注塑件表面质量的影响[J]. 机械工程学报,2015,51(10):79-85. LI Shuai,ZHAO Guoqun,GUAN Yanjin,et al. Influence of mold cavity gas pressure on the surface quality of a microcellular injection molding part[J]. Journal of Mechanical Engineering,2015,51(10):79-85.
[14] HOU J J,ZHAO G Q,WANG G L,et al. A novel gas-assisted microcellular injection molding method for preparing lightweight foams with superior surface appearance and enhanced mechanical performance[J]. Materials & Design,2017,127(5):115-125.
[15] ZHAI M,XIE Y. Investigation of the effect of process conditions on cell size of microcellular injection molded part[J]. Kgk-Kautschuk Gummi Kunststoffe,2010,63(3):85-88.
[16] GOMEZ-GOMEZ J F,ARENCON D,SANCHEZ-SOTO M A,et al. Influence of the injection moulding parameters on the microstructure and thermal properties of microcellular polyethylene terephthalate glycol foams[J]. Advances in Polymer Technology,2013,49(1):47-63.
[17] LI K,CUI Z X,SUN X F,et al. Effects of nanoclay on the morphology and physical properties of solid and microcellular injection molded polyactide/poly(butylenes adipate-co-terephthalate) (PLA/PBAT) nanocomposites and blends[J]. Journal of Biobased Materials and Bioenergy,2011,5(4):442-451.
[18] KUBOKE T. Mechanical properties and foaming behavior of injection molded cellulose fiber reinforced polypropylene composite foams[J]. Journal of Cellular Plastics,2014,50(2):129-143.
