内容简介：: 注塑成型工艺期间颗粒填充聚丙烯的冷却反应 xxx译摘要在一个注塑成型的过程中，影响散热性能的是各种填料（磁铁矿，重晶石，铜，滑石，玻璃纤维和锶铁氧体），调查在不同比例下对聚丙烯复合材料的冷却反应。在注塑成型时，热电偶在型腔模具表面的复合纪录气温。测量室温和高温时，从斜坡的冷却曲线和热扩散的复合来估计，热扩散系数是一个暂时性的数据。由于后压力，冷却曲线显示不同的合并路段，扩散的综合和扩散的聚丙烯基体。冷却的反应，就看异性热扩散的复合材料，其原因是该路的填充材料，其注射成型工艺和互联的灌装机粒子。热扩散表明，最高值为30的滑石粉填充聚丙烯，在最短的冷却时间可以发现35铜填充聚丙烯。系统性变化的热传递性能的复合材料，由于不同的填充材料和填充比例，使模过程优化，并定制热流性能。此外，较强的滑石粉填充聚丙烯通过异性热传递性质，使设计的复合材料比较预定的最高热流能力，以此来确定热传递的首选方向。关键词：聚合物基复合材料热学性能注塑成型颗粒灌装机1. 导言常用的塑料，如聚丙烯和聚酰胺，有一个低导热系数。不过，新的应用主要是在汽车行业，为传感器或执行器，需要新的材料与强化，或具有高导热性。通过增加合适的填料，比如塑料，其热行为聚合物是可以改变的，系统的热扩散大于1.2/秒，从0.2/秒多为补聚丙烯. 这种填充聚合物具有较高的热导率，由于广泛的应用在电子封装，越来越多的成为一个重要的研究领域，。较高的热导率可以通过使用一个合适的填料达到，如铝，碳纤维和石墨，铝氮化物或磁铁矿颗粒。此外，在注塑机上模具的冷却反应，是受聚合物填料的热性能影响。然而，填充材料比较能体现出热导率的价值观。因此，聚丙烯样品不同于挤出商用填料制备和各种体积分数的注塑成型。磁铁矿和重晶石一般是用来增加重量的聚丙烯，锶铁氧体是用聚合物粘结磁体，玻璃纤维是用于加固的新材料，滑石粉是一种反阻断剂。然而，铜被选为额外灌装机，因为它具有高度的对于其他材料热导率相。2. 实验2.1 材料试验材料是由minelco bv准备合作的RTP有限公司供应的，聚丙烯化合物与各种填料在挤出过程相似，即给出了填充材料是常用的材料，是工业产品。填料粒子不具备的表面涂层能影响热性能。2.2 热扩散率测量热扩散的高分子材料，是一个暂时性的衡量方法，密切相关的是雷射闪光试验。用过的瞬态技术尤其适合用于测量多相粒料。温度信号转移到上侧的样本及马上注册一个热电偶。温度信号被转让时，启动一个热平衡过程中的标本，由热电偶作为区别样品的背面，和相对恒定的温度一比，这就叫热扩散率。最小二乘算法是用来确定热扩散率，而不同系统的热扩散率值在一个特别设计的差分计划之内。2.3注塑成型测量注塑机标准样品拉伸性能时，连接一直径10毫米和长度130毫米的热棒，配合后放入一个模具。开始测试在腔内的铝镍合金试验以及热电偶棒拉伸应用。在注塑成型实验温度记录：每0.5秒一个数字万用表，并储存在一台个人电脑中。它的结果是在腔喷射，热电偶淹没大约0.2毫米进入腔，并开始观察。从而得到结论：一个良好的热接触，聚合物接触热电偶后，保证会收缩成型。为更好地比较，多记录温度-时间曲线，同时还要记录注射成型参数。挑选所有复合材料用过的注射成型参数列，由此提交注塑成型周期产生的时间曲线图。3. 结果与讨论颗粒填充聚丙烯的冷却反应与各部分的磁铁矿填料没有任何关系。测量时间=0时，温度热电偶达到最高值约200.随着观测越来越多的时间，温度也随之下降。模子在t=54s打开，冷却反应随热电偶改变，因为它不再接触注射成型的材料。这段时间，由于棒的直径大，直到模具被打开，注射成型零件跳伞选择的相对较高，以确保该部分肯定被凝固。斜率曲线变化写着T=9s ，这相当于时间一到，压力就被拆除。此外指出，这种复合材料在腔降温速度较快，分开磁铁矿。要达到温度T = 60温度远远低于凝固的样品，这样才能达到聚丙烯的需求，在描述T = 5 0.5s这段实验时间时， 5 0的聚丙烯冷却时间降低至T = 3 0.9s 。是在良好的配合下，减少冷却时间，增加磁铁矿填充复合材料，由于高的热扩散粒子是其中的主要成分，可以增加冷却速度。温度时间并不遵循一个简单的温度-时间曲线，根据对照，填补聚丙烯实测值可在单一直线之间达到大约15S到54s。其他测量冷却曲线：聚丙烯-磁铁矿复合交叉到两个区域，为高温和低温区。估计热扩散系数，斜坡上的回归线（ 15秒t 40秒） = 0.24 / 秒和（ 41秒 t 54秒） = 0.19 /秒的PP对应15的四氧化三铁，（ 12秒 t 33秒） = 0.29 /秒和（ 34秒 t 54秒） = 0.19 /秒的PP对应30的四氧化三铁和（ 9秒 t 22秒） = 0.33 / 秒和（ 28秒 t1.2/s.from0.2/s.for.unfilled polypropylene.Such filled polymers with higher thermal conductivities than unfilled ones become more and more an important area of study because of the wide range of applications,e.g.in electronic packaging.The higher thermal conductivity can be achieved by the use of a suitable filler such as aluminium,carbon fibres and graphite,aluminium nitrides or magnetite particles.Also,the cooling behaviour in the mould of the injection moulding machine is influenced by the thermal properties of the polymer-filler composite. However,published values of thermal conductivities of the same filler materials in different polymer matrices vary drastically and a comparison of different materials is difficult or at least impossible.Therefore,polypropylene samples with different commercially available fillers were prepared by extrusion and injection moulding using various volume fractions.Magnetite and barite are generally used to increase the weight of polypropylene,e.g.for bottle closures,strontium ferrite is used in polymer bonded magnets,glass fibres are used for the reinforcement of materials,and talc is an anti-blocking agent.However,copper was chosen as additional filler because of its high thermal conductivity compared to the other materials.2. Experimental2.1.Materials Test materials were supplied by Minelco B.V.Minelco B.V.prepared in cooperation with RTP s.a.r.l several polypropylene compounds with various fillers in an extrusion process similar to that described.The filler materials are commonly used materials in industrial products.The filler particles do not have a surface coating which can affect thermal properties.2.2.Thermal diffusivity measurementsThe thermal diffusivity of the polymers is measured by a transient method,closely related to laser-flash experiments.The used transient technique is especially optimized for measurements of polyphase aggregates.A temperature signal is transferred to the upper side of the sample and registered by a thermocouple.The transferred temperature signal starts a thermal equilibration process in the specimen,which is recorded by a thermocouple as the difference between samples rear surface and a constant temperature in a furnace and which is used for the evaluation of thermal diffusivity.A least squares algorithm is used to determine the thermal diffusivity,while varying systematically the thermal diffusivity value in an especially designed finite-difference scheme.A detailed description of the apparatus is given by Schilling.2.3.Injection moulding With an injection moulding machine standard samples for measuring tensile properties together with a rod for thermal measurements of 10 mm diameter and 130 mm length were prepared in one mould.In the cavity of the tensile test bar a chromel alumel thermocouple was applied.During injection moulding experiments the temperature was recorded every 0.5 s by a digital multimeter and stored in a personal computer.The position of the thermocouple at the sample surface and its position in the cavity of the ejector are shown,respectively.The thermocouple submerges approximately0.2mm into the cavity.Therefore,a good thermal contact between polymer and thermocouple even after shrinkageof the moulding is ensured. For a better comparison of the recorded temperature-time curves the same injection moulding parameters for all composite materials were chosen.The used injection moulding parameters are listed.The resultant characteristic times of the injection moulding cycle are tabled.3. Results and discussionThe cooling behaviour of polypropylene without and with various fractions of magnetite filler are presented. At a time =0s the temperature measured by the thermocouple reaches a maximum value around 200.With increasing time the observed temperature decreases. After t=54 s the mould opens and the cooling behaviour recorded with the thermocouple changes because it is no longer in contact with the injection moulded material.Due to the large diameter of the rod,the time until the mould is opened and the injection moulded parts are ejected is chosen relatively high to ensure that the parts are surely solidified.The slope of the curve changes significantly after t=9 s,which corresponds to the time where the after pressure is removed.Additionally, points out that the composite in the cavity cools down faster with increasing magnetite fraction.To reach a temperature of T=60a temperature far below the solidification of the samplethe polypropylene needs in the described experiment a time of t=50.5 s,whereas cooling time of polypropylene with 50%is reduced to t=30.9 s.The reduced cooling time is in good agreement with the increased thermal diffusivity of magnetite filled composites due to the high thermal diffusivity of the particles which leads,to an increased cooling rate.The temperature time dependence does not follow a simple linear behaviour expected for temperaturetime curves in a logarithmic plot.Only for the unfilled polypropylene the measured values can be fitted with a single straight line between approximately 15 and 54 s. The other measured cooling curves of the polypropylene-magnetite composites are fitted in each case with two straight lines,for the high temperature and low temperature region.The thermal diffusivities estimated from the slopes of the regression lines are (15st40s)=0.24/s and (41st54s)=0.19/s for PP with 15 %,(12st33s)=0.29 /s and (34st54s)=0.19 /sfor PP with 30 %,and (9st22s)=0.33/s and(28st54 s)=0.16 /s forPP with 50 %.It is remarkable that the calculated thermal diffusivitiesof the higher temperature parts of the cooling curves are a little bit lower than the diffusivities measured with the transient technique,while the calculated thermal diffusivities of the lower temperature parts of the cooling curves meet the measured diffusivity values of unfilled polypropylene quite well.The measured thermal diffusivity data of the investigated samples at ambient conditions.It can be seen that the thermal diffusivity of the magnetite-polypropylene composite is increased from =0.19 for unfilled polypropylene up to=0.48(PPC50 %Fe3O4)with increasing magnetite loading.Therefore,the cooling time becomes shorter for higher magnetite filler fractions One reason for the change in the slope of the cooling curves is a change of the thermal diffusivity with temperature which is shown for magnetite and barite polypropylene composites with 45 %filler fraction.With increasing temperature thermal diffusivity decreases.Therefore,the values derived from mould experiments should be smaller than the measured values of the composites at room temperatures.Above the solidification temperature of the PP matrix the thermal diffusivity of the matrix is reduced due to the lowered bulk modulus K which results in a reduced phonon velocity and reduced mean free path length of phonons in a liquid.Furthermore,above solidification temperature TS no crystallites in the polypropylene matrix are present,but below TS a crystallization in the polypropylene matrix appears,and the degree of crystallization as well as the bulk modulus of the composite is dependent on the amount of filler.The presence or absence of crystallites affects the bulk modulus K and the phonon free path.Other reasons for the discrepancy between diffusivity values of the different experiments are the non-isobaric conditions in the injection moulding process and the non-isothermal conditions along the samples thickness.The cooling behaviour of magnetite,barite,glass fibre,talc,hard ferrite and copper fillers in comparison with the unfilled polypropylene are plotted.Only the cooling behaviour of the unfilled and the copper filled polypropylene show significant differences to the other composites.The copper filled composite cools down much faster than the other investigated composites.The temperature of the unfilled polypropylene is during the whole injection moulding process higher than the temperature of the other investigated materials.The cooling behaviour of the other composite materials does not show large differences.The temperatures of the magnetite loaded PP is a little bit lower than the temperatures of the barite filled PP at the same cooling time.The temperatures of the strontium ferrite polypropylene composite again are a little bit lower than those of the magnetite filled polymers.While the measured thermal diffusivity of the talc filled polypropylene is much higher than the thermal diffusivity of the other investigated materials and even much higher than that of the copper filled polypropylene,the cooling behaviour of talc is smaller than that of the other investigated materials.Weidenfeller et al.report in the talc filled composite an alignment of the talc particles oriented along their direction of highest thermal conductivity in the direction of the flow,due to the moulding process.The measurements of thermal diffusivity are made parallel to this axis of highest thermal conductivity,whereas the temperature measurements in the injection moulding process reveal the diffusivity perpendicular to the flow direction.This implies that the talc filled PP samples have a strong anisotropy with a maximum in the flow direction and a minimum perpendicular to the flow.The anisotropy of the injection moulded specimens due to the geometry of the particles is shown.In spite of the high thermal conductivity of the copper compared to the other used filler materials,the cooling behaviour is relative poor and the measured temperatures in the cavity are not as significant different from those of the other composites as could be expectedfrom the thermal conductivity which is approximately 40 times higher than that of talc.This might be related to the poor interconnectivity of the particles in the composite,which was shown by Weidenfeller et al.It was shown that the interconnectivity,which is a relative measure to an ideally interconnected network of high conductivity particles,is for copper in a polypropylene matrix lower than 1%and very poor compared to interconnectivity of magnetite with 55%or the interconnectivity of barite with 46%.The authors also discussed influences of particle size and shape on the interconnectivity in a polypropylene matrix.The necessary time to cool down the surface of the composite in the cavity to 60 . The cooling time is linearly dependent on the filler volume fraction in the polypropylene matrix.The data of the calculated regression lines are listed.It can be clearly seen that the copper filled polypropylene cools down much faster than the other investigated composites. The cooling behaviour of polypropylene with barite,strontium ferrite and magnetite is similar,whereas the magnetite cools down a little bit faster than all other materials.4. Conclusions The cooling behaviour of polypropylene in the injection moulding process can be reduced by the used magnetite,barite,strontium ferrite,glass fibre,talc and copper fillers.The cooling behaviour cannot solely be explained by a si

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