注塑成型中颗粒填充物聚丙烯的冷却情况@中英文翻译@外文翻译

ofstryacceptedAbstractTherefore, polypropylene samples with different com-Composites: Part A 36The effects of thermal properties of various fillers (magnetite, barite, copper, talc, glass fibres and strontium ferrite) in various proportionson the cooling behaviour of polypropylene matrix composites are investigated in an injection moulding process. A thermocouple in the cavityof the mould records the temperatures at the surface of the composite during injection moulding. From the slope of the cooling curves thethermal diffusivities of the composites are estimated and compared with thermal diffusivities at room temperature and elevated temperaturesmeasured with a transient technique. The cooling curves show different merging sections affected by the after pressure, the diffusivity of thecomposite and the diffusivity of polypropylene matrix. The cooling behaviour depends on the anisotropic thermal diffusivity of the usedcomposite, which is caused by the alignment of filler material due to the injection moulding process and the interconnectivity of the fillerparticles. The thermal diffusivity shows the highest value for 30 vol% talc filled polypropylene, whereas the shortest cooling time was foundfor 35 vol% copper filled polypropylene. The knowledge of the systematic variation of thermal transport properties of composites due todifferent filler material and filler proportions allows to optimize the mould process and to customize the heat flow properties. Furthermore, thestrongly anisotropic thermal transport properties of talc filled polypropylene allow the design of composites with a predefined maximum heatflow capability to transport heat in a preferred direction.Keywords: A. Polymermatrix composites (PMCs); B. Thermal properties; E. Injection moulding; Particulate filler1. IntroductionCommonly used plastics, such as polypropylene andpolyamide, have a low thermal conductivity. However, newapplications, mainly in automotive industries, e.g. forsensors or actuators, require new materials with anenhanced or high thermal conductivity 1. By the additionof suitable fillers to plastics, the thermal behaviour ofpolymers can be changed systematically up to significanthigher thermal diffusivity of O1.2 mm2/s from 0.2 mm2/sfor unfilled polypropylene 2,3. Such filled polymers withhigher thermal conductivities than unfilled ones becomemore and more an important area of study because ofthe wide range of applications, e.g. in electronic packaging46. The higher thermal conductivity can be achieved bythe use of a suitable filler such as aluminium 1, carbonfibres and graphite 7, aluminium nitrides 6,8 ormagnetite particles 2. Also, the cooling behaviour in themould of the injection moulding machine is influenced bythe thermal properties of the polymer-filler composite.However, published values of thermal conductivities of thesame filler materials in different polymer matrices varydrastically and a comparison of different materials isdifficult or at least impossible 2.Cooling behaviour of particleinjection mouldingBernd Weidenfellera,*, MichaelaInstitute of Polymer Science and Plastics Processing, Technical UniversitybGeoForschungsZentrum Potsdam, Section 4.1 Experimental GeochemiReceived 25 June 2004;filled polypropylene duringprocessHoferb, Frank R. SchillingbClausthal, Agricolastrasse 6, D-38678 Clausthal-Zellerfeld, Germanyand Mineral Physics, Telegrafenberg, D-14473 Potsdam, Germany4 July 2004(2005) 345351talc and SrFe12O19) were prepared by extrusion and injectionmoulding using various volume fractions (050%). Magne-tite and barite are generally used to increase the weight ofKoch-Str. 42, D-38678 Clausthal-Zellerfeld, Germany. Tel.: C49-5323-723708; fax: C49-5323-723148.E-mail address: bernd.weidenfellertu-clausthal.de (B. Weidenfeller).* Corresponding author. Present address: Institute of Metallurgy, Robert-mercially available fillers (Fe3O4, BaSO4, Cu, glass fibres,3. ExperimentalTalc, Mg3Si4O10OH2Strontiumferrite,SrFe12O19Copper,CuGlassfibresl11:1.76G0.00,l33:10.69G1.35,a:2.97,a:3.00G0.10,a:6.10G0.90l11:401 l:1.21.513 14 152.0 1.5 15 11Platelet Irregular Irregular Fibre2.78 5.11 8.94 2.58aretes: Part A 36 (2005) 3453512. Theoretical considerationsThe Fourier law of heat transport in one dimension isgiven byvTvtZ av2Tvx2(1)with temperature T, time t, position x and thermal diffusivity a.In an homogeneous body, thermal diffusivity a andthermal conductivity l are interrelated by specific density rpolypropylene, e.g. for bottle closures (cosmetics industry,cf. Ref. 10), strontium ferrite is used in polymer bondedmagnets, glass fibres are used for the reinforcement ofmaterials, and talc is an anti-blocking agent. However,copper was chosen as additional filler because of its highthermal conductivity compared to the other materials.The thermal properties of these injection mouldedsamples and the injection moulding behaviour wereinvestigated and correlated to the amount and the kind offiller material.Table 1Selected properties of filler materialsMagnetite, Fe3O4Barite, BaSO4Thermal conduc-tivity (W/(m K)a:4.61G0.42,a:5.10,l11:9.7l11:2.07G0.02,l33:2.92G0.07,a:1.72G0.04Reference 13 13Mean particle diam-eter (mm)9 1.5Particle shape Irregular IrregularDensity (g/cm3) 5.1 4.48a denotes measurements on monomineralic aggregates. Directions of anisotropyand l33are parallel to the crystallographic axes a, b and c, respectively.B. Weidenfeller et al. / Composi346and specific heat capacity cpaccording tol Z cpra (2)Assuming an injection moulding process with anisothermal filling stage for a polymer with a temperatureTPand a constant temperature of the mould TMas well as atemperature independent thermal diffusivity a, an analyticalsolution of Eq. (1) results in 9T ZTMC4pTPKTM!XNnZ012nC1exp Ka2nC12p2ts2C26C27sin2nC1pxsC18C19(3)In Eq. (3), s denotes the wall thickness of the injectionmoulded part and T the temperature of the moulding after3.1. MaterialsTest materials were supplied by Minelco B.V. (TheNetherlands). Minelco B.V. prepared in cooperation withRTP s.a.r.l (France) several polypropylene (PP) compoundswith various fillers (Fe3O4, BaSO4, Cu, glass fibres, talc andSrFe12O19) in an extrusion process similar to that describedin Ref. 2. The filler materials are commonly used materialsin industrial products. The filler particles do not have atime t after injection. Neglecting higher order terms, Eq. (3)can be reduced for the position xZs/2 toT ZTMC4pTPKTM expKap2ts2C18C19C26C27(4)Eq. (4) gives a relation between cooling rate and thermaldiffusivity in an injection moulding process, where highthermal diffusivities result in a higher cooling rate andshorter process cycles.specified by the thermal conductivity tensor (l11, l22, l33), where l11, l22surface coating which can affect thermal properties. Someselected properties of the filler materials are listed inTable 1.Fig. 1. Photograph of the used mould for the injection mouldingexperiments. The mould consists of a standard tensile test sample and atest bar for the measurement of thermal diffusivity.time curves the same injection moulding parameters for allcomposite materials were chosen. The used injectionmachine. The position of the thermocouple for temperature measurements isPart A 36 (2005) 345351 3473.2. Thermal diffusivity measurementsThe thermal diffusivity of the polymers is measured by atransient method 12, closely related to laser-flash experi-ments 11. The used transient technique is especiallyoptimized for measurements of polyphase aggregates. Atemperature signal is transferred to the upper side of thesample and registered by a thermocouple. The transferredtemperature signal starts a thermal equilibration process inthe specimen, which is recorded by a thermocouple as thedifference between samples rear surface and a constanttemperature in a furnace and which is used for theevaluation of thermal diffusivity. A least squares algorithmis used to determine the thermal diffusivity, while varyingsystematically the thermal diffusivity value in an especiallyFig. 2. Mold with cavity for preparing test samples in an injection mouldingmarked by an arrow.B. Weidenfeller et al. / Composites:designed finite-difference scheme. A detailed description ofthe apparatus is given by Schilling 12. The accuracy of themeasurements of the polyphase aggregates is 3%.For thermal diffusivity measurements, small cylinders of10 mm diameter and 56 mm height were cut out of theinjection-moulded rods (cf. Fig. 1).3.3. Injection mouldingWith an injection moulding machine (Allrounder 320C600-250, Arburg, Germany) standard samples for measuringtensile properties together with a rod for thermal measure-ments of 10 mm diameter and 130 mm length were preparedin one mould (cf. Fig. 1). In the cavity of the tensile test bar achromel alumel (Type K) thermocouple was applied.During injection moulding experiments the temperaturewas recorded every 0.5 s by a digital multimeter and storedin a personal computer. The position of the thermocouple atthe sample surface and its position in the cavity of theejector are shown in Figs. 1 and 2, respectively.The thermocouple submerges approximately 0.2 mm intomoulding parameters are listed in Table 2. The resultantcharacteristic times of the injection moulding cycle aretabled in Table 3.4. Results and discussionIn Fig. 3, the cooling behaviour of polypropylene withoutand with various fractions of magnetite filler are presented.the cavity. Therefore, a good thermal contact betweenpolymer and thermocouple even after shrinkage 10 of themoulding is ensured.For a better comparison of the recorded temperatureTable 3Characteristic times in one injection moulding cycle starting with theinjection of the polymer into the cavity at time tiZK8.5 s until the ejectionof the mould at tfZ68 sInjection time (s) K8.52Dwell time (s) 29Cooling time (s) 954Open/close time ejection time (s) 5468Total cycle time (s) 76.5These times define the time axis (abscissa) of Figs. 3 and 6.Table 2Injection moulding parameters during preparation of sample rods formeasurements of thermal diffusivity by transient techniqueMass (polymer) temperature (8C) 200Mould temperature (8C) 20Cycle time (s) 76.5Injection time (s) 10.5Dosing time (s) 12.4Holding pressure time (s) 7.0Injection pressure (Pa) 6!107ylene composites with various filler fractions of Fe3O4. The symbols are measuredtes: Part A 36 (2005) 345351At a time t0Z0 s the temperature measured by thethermocouple reaches a maximum value around 200 8C.With increasing time the observed temperature decreases.After tZ54 s the mould opens and the cooling behaviourrecorded with the thermocouple changes because it is nolonger in contact with the injection moulded material. Dueto the large diameter of the rod, the time (54 s) until themould is opened and the injection moulded parts are ejectedis chosen relatively high to ensure that the parts are surelysolidified.It can be seen in Fig. 3 that the slope of the curve changessignificantly after tz9 s, which corresponds to the timeFig. 3. Comparison of cooling curves of unfilled polypropylene with polypropvalues; the lines are regression lines (cf. text).B. Weidenfeller et al. / Composi348where the after pressure is removed. Additionally, Fig. 3points out that the composite in the cavity cools down fasterwith increasing magnetite fraction. To reach a temperature ofTZ60 8Ca temperature far below the solidification of thesamplethe polypropylene needs in the described exper-iment a time of tZ50.5 s, whereas cooling time ofpolypropylene with 50 vol% Fe3O4is reduced to tZ30.9 s(cf. Table 4). The reduced cooling time is in good agreementwith the increased thermal diffusivity of magnetitefilled composites due to the high thermal diffusivity ofthe particles (cf. Table 1) which leads, regarding Eq. (4), to anincreased cooling rate. The temperature time dependence inFig. 3 does not follow a simple linear behaviour expected fortemperaturetime curves by Eq. (4) in a logarithmic plot.Only for the unfilled polypropylene the measured values canbe fitted with a single straight line between approximately 15and 54 s. The slope of this line leads to a diffusivity ofaz0.21 mm2/s (cf. Eq. (4). The other measured coolingcurves of the polypropylene-magnetite composites are fittedin each case with two straight lines, for the high temperature(a1) and low temperature (a2) region. The thermal diffusiv-ities estimated from the slopes of the regression linesare a1(15 s!t!40 s)z0.24 mm2/s and a2(41 s!t!54 s)z0.19 mm2/s for PP with 15 vol% Fe3O4, a1(12 s!t!33 s)z0.29 mm2/s and a2(34 s!t!54 s)z0.19 mm2/sfor PP with 30 vol% Fe3O4,anda1(9 s!t!22 s)z0.33 mm2/s and a2(28 s!t!54 s)z0.16 mm2/s forPP with 50 vol% Fe3O4(cf. Table 5).It is remarkable that the calculated thermal diffusivitiesa1of the higher temperature parts of the cooling curvesare a little bit lower than the diffusivities measured withthe transient technique, while the calculated thermaldiffusivities a2of the lower temperature parts of thecooling curves meet the measured diffusivity valuesTable 4Time t to cool down a polypropylene-filler composite from a mass(polymer) temperature of TMZ200 down to 60 8CComposite Filler fraction(vol%)t (from 200 to 60 8C)(s)PP 0 50.5PPCFe3O415 46.4PPCFe3O430 40.5PPCFe3O445 34.6PPCFe3O450 34.9PPCBaSO415 44.3PPCBaSO430 40.7PPCBaSO445 35.6PPCCu 15 40.5PPCCu 30 33.8PPCCu 35 29.0PPCglass fibres 15 46.0PPCglass fibres 30 41.8PPCglass fibres 35 40.8PPCtalc 15 45.7PPCtalc 30 42.5PPCSrFe12O1930 40.9The cooling is measured in situ within a cavity of the mould by a K-typethermocouple.of unfilled polypropylene quite well (cf. Table 5 andFig. 4).Fig. 4 shows the measured thermal diffusivity data of theinvestigated samples at ambient conditions. It can be seenthat the thermal diffusivity of the magnetite-polypropyleneAbove the solidification temperature of the PP matrix(around 110 8C, DSC measurements) the thermaldiffusivity of the matrix is reduced due to the loweredbulk modulus K which results in a reduced phonon velocity(vz(K/r)0.5) and reduced mean free path length of phononsin a liquid (Einstein approximation). Furthermore, aboveTable 5Thermal diffusivity estimated from the cooling behaviour of injection moulded polypropylene-filler composites using the slope of the regression lines (a1, a2)(cf. Fig. 3) compared to thermal diffusivity values measured by the transient method (a)Composite Regression lines Transient methoda1(mm2/s) a2(mm2/s) a (mm2/s)PP 0.21 (12055 8C) 0.19 (26 8C)PPC15 vol% Fe3O40.24 (12067 8C) 0.19 (6751 8C) 0.27 (26 8C)PPC30 vol% Fe3O40.29 (12068 8C) 0.19 (6845 8C) 0.35 (26 8C)PPC50 vol% Fe3O40.33 (12577 8C) 0.16 (6745 8C) 0.48 (26 8C)The temperature values in parenthesis give the temperature region of the regression lines and the ambient temperature during the measurement with thetransient technique.B. Weidenfeller et al. / Composites: Part A 36 (2005) 345351 349composite is increased from aZ0.19 for unfilled poly-propylene up to aZ0.48 (PPC50 vol% Fe3O4) withincreasing magnetite loading. Therefore, the cooling timebecomes shorter for higher magnetite filler fractions(Fig. 3).One reason for the change in the slope of the coolingcurves shown in Fig. 3 is a change of the thermaldiffusivity with temperature which is shown in Fig. 5 formagnetite and barite polypropylene composites with45 vol% filler fraction. With increasing temperaturethermal diffusivity decreases. Therefore, the valuesderived from mould experiments should be smaller thanthe measured values of the composites at room tempera-tures. Thermal diffusivity of the PP matrix is mainlycaused by phonons and is related to the mean soundvelocity v and mean free path length l of phononsaccording toa Z13vl (5)Fig. 4. Thermal diffusivity values of injection moulded polypropylenesamples with different fillers and various filler proportions measured by atransient technique at room temperature (cf. text). Solid lines are plotted toguide eyes.solidification temperature TSno crystallites in the poly-propylene matrix are present, but below TSa crystallizationin the polypropylene matrix appears, and the degree ofcrystallization as well as the bulk modulus of the compositeis dependent on the amount of filler 16. The presence orabsence of crystallites affects the bulk modulus K and thephonon free path. Other reasons for the discrepancybetween diffusivity values of the different experimentsare the non-isobaric conditions in the injection mouldingprocess and the non-isothermal conditions along thesamples thickness.The cooling behaviour of magnetite, barite, glass fibre,talc, hard ferrite and copper fillers in comparison withthe unfilled polypropylene are plotted in Fig. 6. Only thecooling behaviour of the unfilled and the copper filledpolypropylene show significant differences to the othercomposites.Fig. 5. Temperature dependence of thermal diffusivity of magnetite andbarite filled polypropylene with a filler content of 45 vol%. The symbolsrepresent measured values, the lines are deduced by linear regression.tes: Part A 36 (2005) 345351The copper filled composite cools down much faster thanthe other investigated composites. The temperature of theunfilled polypropylene is during the whole injectionmoulding process higher than the temperature of the otherinvestigated materials. The cooling behaviour of the othercomposite materials does not show large differences. Thetemperatures of the magnetite loaded PP is a little bit lowerthan the temperatures of the barite filled PP at the samecooling time. The temperatures of the strontium ferritepolypropylene composite again are a little bit lower thanthose of the magnetite filled polymers.While the measured thermal diffusivity of the talc filledFig. 6. Comparison of the cooling behaviour of polypropylene matrix compositesmachine.B. Weidenfeller et al. / Composi350polypropylene is much higher than the thermal diffusivity