IL45057A - High performance composites of polymeric and conductive filler materials - Google Patents

Description

High performance composites of polymeric and conductive filler materials IMI INSTITUTE FOR RESEARCH The Leonard Marshall Shorr Waterman Mani Ravey The present invention concerns novel bodies that are electrically thermally magnetic or which composite bodies comprise a matrix of a setting polymeric material and a property imparting The polymeric materials are used as materials in accordance with the invention are characterized by the They have zero flow according to the ASTM 62T test at and at above their melting a description of the ASTM test see 65 book ASTM Part General Methods of Their cohesive energy density is greater than 40 They have an entanglement factor least 322 T where T is the glass transition S temperature in is tabulated for most for example Van of Correlation with Chemical Elsevier Publishing Amsterdam The entanglement factor is defined by the equation where is the molecular weight and is the critical molecular weight which 3 a critical value of the molecular weight at which a sudden transition of the slope of the logarithm of the melt viscosity against the logarithm of the molecular or which is attributed to the onset of chain t The critical molecular weight has been lished for many polymers from weight data is in Van p Table and Properties of 2nd Wiley and pp Where these data are they can be calculated from the equation where Mark coefficient which is related to theta the intrinsic viscosity IV by the following equation holding under theta conditions where is viscosity average molecular values are tabulated in Van pp Table or can be calculated from the structure the polymer via group contributions Van Table The entanglement factor stands for the number of entanglement points per molecule and the higher the factor the more difficult it becomes to process the as the entanglements impede the relative movements of the polymer From the above three criteria it follows clearly that the polymeric materials which are used as matrices in accordance with the invention are extremely difficult to degree of entanglement between polymer Examples of such polymera given in following In Table the cohesive energy densities at and the factors are In this ultra high molecular weight polyethylene chlorinated PAH high molecular weight high molecular weight polypropylene All these are exceedingly difficult to process by extrusion or to compound by and are no suitable for injection Cohesive Energy Density Entanglement Factor Hostalen x ex Allied AO x 105 Folyvinylidene 149 chloride 97 on ex Mcrite ex 97 237 150 PVC 39 PP 300 Ipivyl the trade name of resins ffianufaotured by the Haifav flow characteristics as herein before predetermined electrical heat conductivity magnetic and also the purpose of electroplating an essentially Hitherto compositeshave been fabricated from plastic materials by the common techniques of injection moulding and extrusion and conventional from mixtures of particulate plastic materials and conductive fillers for US Patent Specifications and These techniques require the use of readily flowing plastic materials and the use of such materials has several for the ready flow of the matrix forming plastics under the forming conditions causes disruption of contacts between metal the retained flow properties of the plastic used give rise to considerable particle both during fabrication and in particularly at elevated and thus introduces a degree of instability in those properties which depend on filler Since the filler particles are largely coated with resin in a molten state during they become and remain isolated from each other and unexposed at the surface of the moulded unless very high loadings are excessively high loadings weaken the Attempts to come filler particle migration by curing with the aid of heat treatment or exposure to have not been entirely satisfactory due to deterioration of the plastic material or the occurrence of a certain degree of usually result from side reactions in the curing She use of thermosetting resins as polymers leads to composite bodies with variations in ductivity properties along the to a tendency of the filler particles to be coated by such resins during Such coating also leads to poor filler particle A further disadvantage inherent in the use of thermosetting materials is the bility of For all these reasons thermosetting resins are unsatisfactory polymers in the duction of composite bodies of the kind One attempt to produce an improved composite body comprising a plastic matrix and a metallic filler is disclosed in US Patent Specification In accordance with that specification composite bodies comprising a plastic matrix consisting of adhering plastic particles having an average size from 20 to microns and at least by volume of a conductive are prepared by pressure moulding in the heat of a mixture of the matrix material and both in particulate the temperature being above the glass transition temperature and below the melting temperature of the plastic The plastic matrix employed ance with patent is of a type that flows above the melting point as follows column lines 58 where the following is should be carefully noted that the plastic material is not permitted to The same also follows from lines 65 to 67 of the same column where the following is the other hand if the plastic material is heated above its melting point the plastic will The only plastic material whose use is illustrated PVC having a molecular weight of It is known that the critical molecular weight for PVC is and therefore the entanglement factor this 1 5 which is below the lower limit of the entanglement factor stipulated for the thermoplastic polymeric materials employed i accordance with the present By for PVC the minimum It is thus that the plastic materials employed in accordance wit US Patent Specification are distinguished from those employed in accordance with the invention by two critical as can be see from the following Table II Plastic material Plastic material used according to according to US Patent present cation invention Plows upon meltin Zero flow at and at 10 C above melting point than 23 In view of the composite bodies according to US Patent suffer from insufficient stability which is a drawback common to all prior art composite bodies of the kind This lack of stability is manifested in some cases in the flow of particles under pressure even in the or and in tion in the e cold flow or compressive creep may disrupt contact which leads to instability in the properties depending The heat in shape which even when they are only slight may he All this may in certain cases bring about such as loss of desirable properties in the Plastic materials which have the characteristics of no cohesive density and entanglement factor as stipulated in accordance with the are very difficult to process and when in the particulate state can only be shaped by very drastic mechanical such as isostatlc wedge rolling or sintering under relatively high This difficulty of processing prima incompatible with the basic requirement that in composite bodies comprising a plastic material matrix and a conductive the filler has to be properly distributed in the plastic matrix with proper particle contacts to provide the required degree of cohesion and It is no doubt this apparent incompatibility which accounts for the fact that hitherto no attempt has been made to use plastic materials of the kind specified for the fabrication of composite bodies comprising a plastic material and a conductive Quite surprisingly it has been found in accordance with the present invention that polymeric materials of the kind specified render themselves in the particulate state to the formation of composite bodies with particulate conductive and that such bodies possess an intimate contact such as to provide desired degree of stability and in many instances the impact strength of the composite bodies according to the invention is superior to that of the polymeric Hereinaf er the property to conduct electricity or heat to be magnetic or magnetizable will be to for short and indiscriminately as and the filler as In accordance with the invention there is provided a conductive body of compressed particulate comprising a matrix of polymeric material and embedded therein a conductive filler material the polymeric material being characterized zero flow according to the teat at and at above its melting a cohesive energy density greater than 40 and an entanglement factor of at least g where is the glass transition temperature 8 in If two or more different polymeric materials may be used in admixture for the formation of the Also if two or more different conductive filler materials may be The conductive filler is either noble alloys such as rare metal or conductive carbon size of the polymer particles and the filler particles have an influence on the properties of the the filler particles are of a smaller average size than the particles of shape of the filler particles vary and they may he of different shaped fillers may fibers The filler particles may be or have a core of material covered by a conductive particles may also be of size and in such a case a high degree of conductivity may be achieved at a relatively low filler volume Other characteristics that are of importance for the ultimate properties of the composite are surface state of pore surface properties and the degree of free surface of which should preferably be more than of the The fabrication of a body according to the invention comprises mixing the particulate polymeric material with the desired amount of a particulate conductive filler subjecting the mixture preferably at an elevated Such treatment may be effected for in a falling hammer forging press of the kind described in British Patent Specification the compacting may be achieved by sintering under relatively high pressure or isostatic the latter purpose the particulate mixture is placed in a bag of flexible material and pressed in all directions and simultaneously in a hydraulic Depending on the forming conditions the bodies may be porous or be substantially free of When they are impregnation with waxes or solids for lubrication purposes is 11 reduce its porosity and produce the final form by skiving from a suitable ram or screw polishing or etching in order to produce If bonding or conditioning oxidizing may be incorporated in the mix to treat or activate the surface of the plastic particles to promote adhesion to the metal The surface of the composite bodies may be treated or activated with known ditioning or activating such as oxidizing various organic if desired in aqueous solutions or dispersions of metallic catalysts with or without Addition of a lubricant may reduce friction and friction between the powder and the wall of the Quite surprisingly it has been found that composite bodies according to the invention that contain an electrically conductive filler material render themselves readily to electroplating in a single stage operation under substantially constant current and voltage to produce adhering metal In other in an electroplating system in which such a body is connected as it behaves like a This observation was unexpected having regard to the fact that the conductive filler in such a body is By it is known from French Patent Specification i to electroplate a posite body prepared by injection moulding and comprising a readily flowing thermoplastic matrix and a carbon black This electroplating proceeds in stages in the first of which a weak current in which the current is is shown in this patent specification Example that in the absence of preliminary the coating does not adhere well to the substrate and is therefore of no practical So no satisfactory explanation could be suggested for the unexpected results achieved in the electroplating of composite bodies according to the It believed that this phenomenon results from the nature of the materials employed in accordance with the which have never been employed the invention also provides electroplated composite bodies comprising a matrix of a thermosettlng polymeric material and embedded therein a ductive filler the polymeric material being characterized zero flow according to the D teat at and at above its melting a cohesive energy density greater than 40 and an entanglement factor of at least T where is the glass transition s temperature in The invention further provides a method for producing the electroplated composite bodies comprising preparing a composite body as hereinbefore introducing the body as cathode into an electrolytic bath and subjecting it to a single stage electroplating The invention is illustrated by the following Examples to which it is not EXAMPLE 1 Preparation of the composite bodies general The plastic material is mixed with appropriate conductive filler particles and compacted to a high density in a Palling Hammer Forging Press of the kind described in our British Patent Specification Mould release agents can be used as The Falling Hammer Press consists essentially of an iron weight of which is repeatedly released to fall free from a certain delivering a number of blows to the top piston of the The cylindrical steel mould used in the experiments consists of a stationary cylinder as mould and movable top and bottom pistons which the material is Prior to the the mixture to be introduced into the mould cylinder was mixed a The polymer particles are introduced first and the agglomerates are crushed if The powders are added The resulting mixture is transferred into a cylindrical plastic box rotated at an nclined In this way no segregation is pointing to efficient The of coating of the mixture and the percentage of the free surface of the plastic particles was mined b inspecting them unde a microscope at a magnification of In all moulding mixtures in the following Examples the particles had a free surface of at least is introduced into the mould and prepressed at at ambient The feed mixtures are preheated to about not otherwise s ecified in the followin Exam and is subjected to four from a height of with a weight of 2 impact E is calculated n x h x A n number of h falling falling A surface of the cm E x 1 kgm Examination of the bodies Density If the pellets obtained according to part are purely density is determined from weight and otherwise by a buoyancy method or by Microscopic study Particle sizes of fillers and polymers are determined Microscopy the sections is performed on polished surfaces by reflected light observations a metallographic The conductive samples are in the filler particles being segregated along the surfaces of the plastic Electrical resistivity Measurements are carried out on formed two pressed between two aluminium with electrodes on the top and bottom Hardness determined with a Barcol Impressor 935 Standard C Impact Resistance The determinations are performed also on samples prepared by cutting slabs from parallel to the axis of the sample dimensions are 15 1 The impact resistance is measured by a pendulum impact tester built according to the Tester 573 BAM manufactured by Earl Franck Electroplating Electroplating is carried out in a conventional Such methods are described in the in the Kenneth Electroplating Engineering 2nd pp Plating pp Electroplating and lifcal Finishing pp Geest Leipzig pp and by the same author Verlag Weinheim p Average thickness of coating is determined from weight increase and The good quality of the plating is surprising in view of the appearance of the EXAMPLE An dendritic Cu powder composite was prepared from a Ziegler type polymer whose melt flow according to AST D was The copper powder was electrolytically dendritic ex 20 and The mixture used had a Cu polymer I weight ratio of corresponding to a filler volume fraction of and was preheated at about pellet was density Electrical resistivity was Machinability was EXAMPLE 3 A chlorinated graphite powder composite was prepared from a sample of chlorinated PVC containing and of melt zero Condition and dered graphite ex Particle size distributions for the for the 0 The weight ratio was corresponding to a filler volume fraction of Preheating was carried out at 2 The resulting pellet had a density of electrical Barcol hardness 30 or 45 From the same chlorinated PVC as above with lytically dendritic Cu as used in Example at a weight ratio of corresponding to a similar volume fraction as in the previous Example heating the same a pellet of perfect shape was an electrical resistivity of cm and a Barcol hardness of EXAMPLE 4 with a size distribution of and was used as the polymeric The fillers were in one instance lytically prepared dendritic Cu powder in Example 2 and in other instance bronze ex rich with particle size distribution of than 3 and The filler PAN weight ratiowas corresponding to a filler volume fraction of and The free surface of the particles was in the first instance and in the second The mixtures were preheated at The composites were shaped into pellets having densities of and and electrical resistivities of and 1 The pellet containing bronze powder was electroplated in a bath with excellent Thickness of plating was A PAN without run under the same preheating conditions had an impact strength of only kg cm whereas the sample with the dendritic Cu had an impact strength of 1 kg 10 g of the same as above was mixed with a mixed filler consisting of 5 g graphite ex Merck characteristics see Example 4 and 18 g of ex sample was prepared with a similar PAN weight ratio as in above corresponding to a filler volume of surface of particles was and under identical conditions of which yielded a magnetizable pellet with an electrical resistivity of This pellet electroplated well in a conventional plating thickness of plating 1 The same PAN was used as above to form composite bodies with powdered ex The particle size distribution of the filler was and Two samples were prepared with filler levels and filler PAN weight The higher level corresponded to similar filler volume fraction as in The lower graphite level corresponded to a filler volume fraction of and the free surface of the particle was The respective sities were and and the electrical ies were and Both samples behaved excellently at Thickness of plating was mil in the case of the high filler level and mil in the case of the low filler and both showed excellent adhesion in a conventional thermal cycling test cycles of 40 seconds each EXAMPLE 5 of a weight average molecular weight of about x 10 and of intrinsic viscosity showing no melt flow at Condition density and a particle size distribution corresponding to and was used to form a composite body at filler polymer weight ratio of corresponding to a filler volume fraction of The resulting pellet had a density of an electrical resistivity of and behaved excellently at thickness of plating The top plane machined and also plated excellently after The adhesion in the thermoeyeling test was excellent Example 6 A high molecular weight unplasticized and of zero melt Condition by weight of an mercaptide stabilizer known by the commercial name Mark 292 with an intrinsic viscosity of consisting of and particles used to form a composite with graphite Merck characteristics see Example 3 at a filler polymer weight ratio of corresponding to a ller volume fraction of The obtained pellet had a density of an electrical resistivity of only and behaved excellently at thickness of 7 A PAN with the composition as given in Example was prepared by pressure moulding at 12 under in a mould a diameter of with a preheating of 15 minutes and another minutes of She resulting pellet had a density of which compares favourably with the density of tained for the same composition by a forging Applying a pressure of only under the same conditions of heating and the density of the resulting pellet was At half the level of bronze loading g to g correspondirg a filler weight ratio and a filler volume fraction of the density of the pellet obtained by forming by means of a falling hammer forging press at was equal to that obtained by pressure sintering under at 120 d 8 A composite of chlorinated PVC showin no melt flow in with graphite was prepared at a level of graphite loading of g to g in the same way as in Example but a instead of The resulting pellet had a density d 1 EXAMPLE 9 parts by weight of powdered chlorinated showing no melt flow in an ASTM test and 1 part by weight of Silicon Carbide mesh Buehler were mixed in a the polymer particles were added and subsequently the Silicon Carbide powder was added The resulting mixture introduced into a cylindrical plastic container which rotated at an inclined The free surface of the particles was 20 A pellet of this mixture was prepared in a hea pellet using a carbon steel mould of 13 mm Glycerine from a thermostatically controlled bath was pumped through the press The bath temperature was set at After minutes a pressure of ton was applied for an stopped and water was to cool the The pressure was then released and the pellet The pellet had a smooth perfect sharp edges and a high Its Barcol hardness was its density and it was a good conductor for EXAMPLE 10 A composite of 18 g of PAN and 2 g of extra ductive carbon black corresponding to a filler volume fraction of was prepared by pressure moulding at 190 C under in a mould with a diameter of with a preheating of 15 minutes and another 1 minutes of The resulting hard pellet had electrical resistivity of EXAMPLE 11 A composite body was prepared from 3 g of PAN and g of Al by high pressure moulding for minutes at under a pressure of in a circular mould of 13 mm Prior to moulding the mixture was preheated for 1 minutes at The resulting pellet ha a density of and was a good conductor for EXAMPLE Two composites of PAN characteristics see Bxample 4 and a fine particle size Barium Perrite were pared at filler s polymer weight ratios of 2 and 4 by high pressure sintering at under in a mould of preheating the mixture at for 15 In a composite of teristics see Example and the same ferrite was prepared under the same conditions but at and perfect sharp edges a high They could be magnetized in a capacitor discharge EXAMPLE 13 A ternary composite of chlorinated containing CI characteristics see Example 3 PAN characteristics see Example 4 and graphite ex Merck characteristics see Example was prepared using a falling hammer forging press at a chlorinated PVC PAN graphite weight of 1 1 The forming technique is described in Example Preheating was carried out at The resulting pellet had a density of an electrical resistivity of a Barcol hardness of 42 and was electroplated in a bath with excellent thickness of plating EXAMPLE 4 From the pellet of a composite of UHMWPE dendritic Cu prepared according to Example 2 a cylindrical billet was by of diameter cm and density This billet was entered into a steel mould of diameter 0 consisting of a stationary cylinder as mould body and movable top and bottom pistons between which the billet was Prior to forging the billet was heated in the mould to whereafter it was pressed in a hydraulic press at 1 for 10 minutes and next at subjected to two blows from heights of and with a weight of 130 Then the die was opened and the finished pellet It had a diameter of cm and had completely filled the mould Its density was insufficientOCRQuality

Claims (2)

CLAIMS.

1. A conductive composite body of compressed particulate material, comprising a matrix of non-theroosetting polymeric material and embedded therein a conductive filler material, the matrix-forming polymeric material being characterized by: (a) zero flow according to the AST D1238-62T test (Condition P) at 190°C and at 10°C above its melting point; (b) a cohesive energy density greater than 40 cal/cm ; and (c) an entanglement factor of at least 322-0.84 T_, s where Ϊ is the glass transition temperature 6 in °K. 2. A composite body according to Claim 1 , comprising at least two different matrix-forming polymeric materials. 3· A composite body according to Claim 1 or 2, comprising at least two different filler materials, 4· A composite body according to any one of Claims 1 to 3» wherein the filler is metallic. 5· A composite body according to any one of Claims 1 to 3» wherein the filler is non-metallic* 6· A composite body according to Claim 5, wherein the filler is graphite, a conductive carbon black, a carbide or a ferrite. 7· A method of making a composite body according to any one of the preceding Claims, comprising mixing a particulate matrix-forming polymeric material of the kind defined - 24 - 45057/2 material, and subjecting the particulate mix to a compacting treatment at an elevated temperature. '^m * 8. A method according to Claim 7 , wherein an initially produced composite body is subjected to further shaping, 9. A method according to Claim 7 or 8 , wherein an initially produced composite body is sintered to reduce its porositye 1 0· A method according to any one of Claims 7 to 9 » wherein a bonding and/or conditioning agent and/or a lubricant is incorporated in the particulate mix. 1 1 . A method according to any one of Claims 7 to 1 0 , wherein the compacting method used is impact-forming.

2. A method according to any one of Claims 7 to 1 0 , wherein the compacting method used is sintering under high pressure. 13· Composite bodies according to any one of Claims -1 to 6 comprising an electrolytically produced metal coat. 14· A method of producing a metal coated body according to Claim 1 3 comprising preparing a composite body by the method according to any one of Claims 7 to 1 2 , introducing the body as cathode into an electrolytic bath and subjecting it to a single stage electroplating operation. C:mz