MuCell微发泡注塑成型技术应用

MuCell微发泡注塑成型技术的使用日趋普及,其制品主要集中在品质要求较高、材料较贵的产品上。近年来,选用微发泡注塑成型技术的中国企业数目快速增长,其应用领域也正在扩大。     

成核剂对聚丙烯微发泡行为及力学性能的影响

将自制的发泡母料添加到共聚聚丙烯(PP)中,采用化学发泡注塑工艺制得微发泡材料。通过SEM和TGA分析,研究了不同成核剂制得的发泡母料对PP微发泡材料力学性能和泡孔行为的影响。结果表明:发泡母料含量为5%时,制得的发泡PP复合材料性能优异;以硫酸钙作为成核剂时,所得制品泡孔直径较小,且均匀性最好。     

PP/GF/EPDM微发泡复合材料制备及性能研究

通过微发泡注塑成型制备了聚丙烯/玻纤/三元乙丙橡胶(PP/GF/EPDM)复合材料,并研究了EPDM对微孔发泡PP/GF/EPDM复合材料微观形态和力学性能的影响。结果表明:随着EPDM用量的增加,泡孔直径呈先变小后变大、泡孔密度呈先变大后变小的趋势;当EPDM用量为15%时,微发泡制品的微观形态最好。同时,随着EPDM用量的增加,微发泡制品的拉伸强度有所降低,而冲击强度有所提高,且拉伸强度和冲击强度下降比值均呈先减小后增大的趋势;当EPDM用量为15%时,强度下降比值最小。此时PP/GF/EPDM微发泡制品的综合性能最好,其多项性能指标优于纯PP微发泡制品,达到了增强增韧的预期目的。     

注塑工艺对PP板材结构发泡的影响

介绍PP结构发泡注塑的加工工艺过程、机理及特点,分析各工艺参数对结构发泡制品性能的影响。     

结构发泡成型技术

介绍了结构发泡的工艺过程，并将该工艺与普通注塑工艺作了比较，阐述了结构发泡成型技术和优点及装置的关键技术和产品特点。结构发泡了工艺的多点喷嘴顺序注射技术决定了设备低压、低锁模力的特性，从而允许模具使用低成本铝模，增大模板尺寸，增强模塑能力，并能保证尺寸差异较大的制品质量，减轻制品质量，提高制品强度。     

塑料注塑成型--结构发泡

简要介绍了用于塑料的发泡注塑成型技术，并重点描述了结构发泡中的低压发泡法、高压发泡法、双组份发泡法和反压发泡法及影响发泡注塑的因素。     

热塑性聚酯弹性体减振材料注塑发泡研究

以偶氮二甲酰胺(AC)、950DU、碳酸氢钠组成发泡剂体系,采用注塑成型工艺制备热塑性聚酯弹性体发泡材料.研究了三种发泡剂对发泡材料孔径、静刚度及动静刚度比的影响,并探讨了注塑温度等工艺参数对产品性能的影响.结果表明,采用复合发泡剂能制得性能优良的发泡材料,当AC母粒用量为1.7份、NaHCO30.9份、950DU0.5份时,发泡制品静刚度及动静刚度比均较低;注塑温度在一定范围内升高可降低制品静刚度及动静刚度比;成型后退火处理有助于降低动静刚度比.     

微发泡聚丙烯复合材料发泡行为研究

以PP(聚丙烯)为基体材料,分别添加发泡剂母粒、发泡剂和助剂母粒及发泡剂、助剂、成核剂母粒,在二次开模条件下注塑制备微发泡PP复合材料,分析了发泡助剂及成核剂对微发泡复合材料发泡行为的影响规律。结果表明,添加发泡助剂以后,PP体系的发泡质量得到明显改善;助剂和成核剂同时添加,微发泡PP体系的发泡质量最好,泡孔平均直径为26.79μm,泡孔密度达到4.76×106个/cm3。     

PBT含量对PLA/PBT原位微纤复合材料流变及发泡性能的影响

聚乳酸(PLA)是用量最大的可生物降解材料之一,由于其拉伸流变性能较差,难于发泡。本文采用聚合物微纳层叠共挤装置制备PLA/聚对苯二甲酸丁二醇酯(PBT)原位微纤复合材料(PLA/PBT-MRC),研究了PLA/PBT-MRC的微纤形态、熔体的动态流变性能和拉伸流变性能。PLA、PLA/PBT-MRC注塑发泡后的泡孔形貌、注塑发泡制品的拉伸、缺口冲击和弯曲力学性能。研究表明：PLA/PBT-MRC中微纤宽度低至0.72μm,宽度随PBT含量增加而增大;随PBT含量增加PLA/PBT-MRC的储能模量、损耗模量和复数黏度都增大;PBT含量增加可以明显改善PLA熔体的拉伸流变性能,相对PLA表现出明显的拉伸应变硬化;PLA/PBT-MRC注塑发泡后泡孔直径比PLA注塑发泡泡孔直径减小800%,泡孔密度增加600%,发泡制品的拉伸强度、缺口冲击强度、弯曲强度分别提高22.2%、10.1%和26.4%。     

微孔发泡注塑注气量控制的理论和实验

微孔发泡注塑是1种新型成型工艺,能够在基本保持制品原有力学性能的前提下明显减轻制品质量。在注塑过程中,注气量的多少对制品特性有很大影响。通过对微孔发泡注塑系统注气量的实验和模拟,利用现代控制理论及数据分析方法,建立注气系统的数学模型,得到一定工艺条件下注气量与注气压力及熔体压力之间的关系。     

Effects of nano‐ and micro‐fillers and processing parameters on injection‐molded microcellular composites

The effects of submicron core‐shell rubber (CSR) particles, nanoclay fillers, and molding parameters on the mechanical properties and cell structure of injection‐molded microcellular polyamide‐6 (PA6) composites were studied. The experimental results of PA6 nanocomposites with 5.0 and 7.5 wt% nanoclay loadings and of CSR‐modified PA6 composites with 0.5 and 3.1 wt% CSR loadings were compared to their neat resin counterparts. This study found that nanoclay was more efficient in promoting a smaller cell size, larger cell density, and higher tensile strength for microcellular injection molding parts. A higher nanoclay loading led to more brittle behavior for microcellular parts. It was found that a proper amount of CSR particles could be added to the microcellular injection‐molded PA6 to reduce the cell size, increase the cell density, and enhance the toughness of the molded part. However, CSR particles were less effective cell nucleation agents as compared to nanoclay for producing desirable cell structures, and a higher CSR loading was found to have diminishing effects on the process and on the properties of the parts. POLYM. ENG. SCI., 45:773–788, 2005. © 2005 Society of Plastics Engineers     

Improving surface quality of microcellular injection molded parts through mold surface temperature manipulation with thin film insulation

Microcellular injection molding offers many advantages such as material and energy savings, reduced cycle times, and excellent dimensional stability. However, typical surface characteristics of microcellular injection molded parts—such as gas flow and swirl marks and a lack of smoothness—have precluded the process from being used for applications where surface appearance is important. This article presents an insulator‐assisted method that has been shown to improve the surface quality of microcellular injection molded parts significantly. By incorporating a thin film (75–225 μm) of polytetrafluoroethylene (PTFE) insulator on the mold surface, the polymer melt–insulator interfacial temperature can be manipulated and can be kept high enough during mold filling to reduce or eliminate swirl marks on the surface. The experimental results in terms of surface roughness and surface profile of conventional and microcellular injection molded parts with and without the insulator film are discussed. Thermal analyses of the corresponding microcellular injection molding experiments were performed to elucidate the correlation between film thickness, interfacial temperature, and the surface quality. The effect of insulator on the cooling time increase is also analyzed and presented. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

The cell forming process of microcellular injection‐molded parts

In this article, we studied the cell forming process of microcellular injection‐molded parts. Using a modified injection molding machine equipped with a Mucell^® SCF delivery system, microcellular‐foamed acrylonitrile–butadiene–styrene parts with different shot sizes were molded. The cell structure on the fractured surfaces along the direction both vertical and parallel to melt flow in the molded parts was examined. The results showed that a regular spherical cells region and a distorted ellipsoidal cells region exist in the molded parts simultaneously. The length of the distorted cells region along the melt flow direction in the molded parts remained basically unchanged for different shot sizes and it is about 195 mm away from the flow front in this study's conditions. The cell formation mechanism was analyzed, two cell forming processes in microcellular injection molding, the “foam during filling” process and the “foam after filling” process, were proposed. It was also found that the melt pressure in the filling stage is the dominant factor affecting the cell forming process, and there is a critical melt pressure value in the filling stage, 20.9 MPa, as the dividing line of the two cell forming processes in this study. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40365.     

A new microcellular injection molding process for polycarbonate using water as the physical blowing agent

This article presents a new process for producing microcellular injection molded plastic parts using water as the physical blowing agent and micro‐scaled particles as the cell nucleating agents. Distilled water with dissolved salt were fed through the hopper of an injection molding machine at a preset rate and mixed with polycarbonate (PC) in the machine barrel. Microcellular PC tensile bars were then injection molded with different shot volumes, water/salt solution feed rates, and salt concentrations. Tiny salt crystals of 10–20 μm recrystallized during molding acted as nucleating agents in the PC foamed parts. The surface roughness, mechanical properties, and microstructure of the solid and foamed parts were measured and compared with microcellular injection molded parts using supercritical fluid (SCF) nitrogen as the physical blowing agent. At a similar weight reduction of about 10%, the water foamed PC parts have a smooth surface comparable to that of solid injection molded parts. They also possess similar, if not better, mechanical properties compared to SCF nitrogen foamed PC parts. Without the nucleating agent, PC/water foamed parts exhibit much larger and fewer bubbles within the molded parts. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Characteristics of the Skin Layers of Microcellular Injection Molded Parts

The cross-section of products made with the microcellular injection molding process shows the skin layer and the core region where the formation of pores takes place. The cell size, cell density, and cell morphology were found to depend on pressure drop rate, viscosity, cell growth period, and cell coalescence. However, research on the actual mechanisms of the skin layer is rare.

Cell morphology and skin layer are of importance as a factor influencing the density and strength of microcellular injection molded parts. Especially, as size of the injection molded parts becomes large, the skin layer size changes, resulting in variation of the foaming rate. Therefore, there is the need to study factors that influence the formation of the skin layer and its thickness.

This research proposes a hypothesis on the mechanism of the skin layer formation in microcellular injection molding process and addresses factors influencing skin layer thickness. In addition, the experimental design method was utilized to identify the factors, and the variation in physical properties with skin layer thickness was reported.     

Effect of process conditions on the weld‐line strength and microstructure of microcellular injection molded parts

This study was aimed at understanding how the process conditions affect the weld‐line strength and microstructure of injection molded microcellular parts. A design of experiments (DOE) was performed and polycarbonate tensile test specimens were produced for tensile tests and microscopic analysis. Injection molding trials were performed by systematically adjusting four process parameters (i.e., melt temperature, shot size, supercritical fluid (SCF) level, and injection speed). For comparison, conventional solid specimens were also produced. The tensile strength was measured at the weld line and away from the weld line. The weld‐line strength of injecton molded microcellular parts was lower than that of its solid counterparts. It increased with increasing shot size, melt temperature, and injection speed, and was weakly dependent on the supercritical fluid level. The microstructure of the molded specimens at various cross sections were examined using scanning electron microscope (SEM) and a light microscope to study the variation of cell size and density with different process conditions.     

Quantitative study of shrinkage and warpage behavior for microcellular and conventional injection molding

This research investigated the effects of processing conditions on the shrinkage and warpage (S&W) behavior of a box‐shaped, polypropylene part using conventional and microcellular injection molding. Two sets of 2^6‐1 fractional factorial design of experiments (DOE) were employed to perform the experiments and proper statistical theory was used to analyze the data. After the injection molding process reached steady state, molded samples were collected and measured using an optical coordinate measuring machine (OCMM), which had been evaluated using a proper R&R (repeatability and reproducibility) measurement study. By analyzing the statistically significant main and two‐factor interaction effects, the results show that the supercritical fluid (SCF) content (nitrogen in this case, in terms of SCF dosage time) and the injection speed affect the S&W of microcellular injection molded parts the most, whereas pack/hold pressure and pack/hold time have the most significant effect on the S&W of conventional injection molded parts. Also, this study quantitatively showed that, within the processing range studied, a reduction in the S&W could be achieved with the microcellular injection molding process. POLYM. ENG. SCI., 45:1408–1418, 2005. © 2005 Society of Plastics Engineers     

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.     

Spatial orientation of nanoclay and crystallite in microcellular injection molded polyamide‐6 nanocomposites

Three different types of characteristic structures‐microcells, nanoclay, and crystallite lamella‐exist in injection molded polyamide‐6 microcellular nanocomposites. These structures are in completely different scales. The spatial orientation of these microscale structures crucially determines the material's bulk properties. Based on scanning electron microscopy, transmission electron microscopy, and two‐dimensional X‐ray diffractometry measurements, it was found that the nanoclay and the crystallite formed special geometric structures around the microcells and near the part skins. The nanoclay platelets lay almost parallel to the surfaces of the molded parts. Preferred orientation of the crystallites was induced by the presence of the nanoclay. A molecular‐based model is proposed to describe the structural hierarchy and correlations among the microcells, nanoclay, and crystallite lamella. From the small‐angle X‐ray scattering experiments, it was found that microcellular injection molding produces relatively smaller crystallite lamella than that of conventional injection molding, and that for both solid and microcellular neat resin parts the crystallite lamella thickness at the part skin is smaller than that at the core. Polarized optical microscopy results also indicated that the size of crystallites in the microcellular neat resin and nanocomposite parts is smaller than that in the corresponding solid parts. POLYM. ENG. SCI., 47:765–779, 2007. © 2007 Society of Plastics Engineers     

Microstructure and mechanical properties of microcellular injection molded polyamide-6 nanocomposites

The microstructure and mechanical properties of microcellular injection molded polyamide-6 (PA6) nanocomposites were studied. Cell wall structure and smoothness were determined by the size of the crystalline structure, which, in turn, were based on the material system and molding conditions. The correlation between cell density and cell size of the materials studied followed an exponential relationship. Supercritical fluid (SCF) facilitated the intercalation and exfoliation of nanoclays in the microcellular injection molding process. The orientation of nanoclays near the surface of microcells and between microcells was examined and a preferential orientation around the microcells was observed. Nanoclays in the microcellular injection molding process promoted the γ-form and suppressed the α-form crystalline structure of PA6. Both nanoclays and SCF lowered the crystallinity of the parts. Microcells improved the normalized toughness of the nanocomposites. Both microcells and nanoclay had a significant influence on the mechanical properties of parts depending on the molding conditions.