ELECTRICALLY CONDUCTIVE SHAPED BODY WITH A POSITIVE TEMPERATURE COEFFICIENT

Abstract

The invention describes electrically conductive shaped bodies with an inherent positive temperature coefficient (PTC), produced from a composition which contains at lest one organic matrix polymer (compound component A), at least one submicroscale or nanoscale, electrically conductive additive (compound component B) and at least one phase-change material with a phase-transition temperature in the range from 42 C. to +150 C. (compound component D). The phase-change material is incorporated into an organic network (compound component C). The electrically conductive shaped body with an inherent PTC effect is, in particular, a filament, a fibre, a spun-bonded web, a foam, a film, a foil or an injection-moulded article. The switching point for the PTC behavior is dependent on the type and also the phase-conversion temperature of the phase-change material. By way of example, a self-regulating surface heater in the form of a film, foil and/or textile can be realized in this way.

Claims

1. An electrically conductive molding with inherent positive temperature coefficient made of a polymer composition which comprises at least one organic matrix polymer as compound material component A, at least one submicro- or nanoscale electrically conductive additive as compound material component B and at least one phase-change material with a phase-transition temperature in the range from 42 C. to +150 C. as compound material component D, and the melting range of the polymer composition is within the range from 100 C. to 450 C., wherein the phase-change material is used without further treatment or has been bound into an organic network made of at least one copolymer based on at least two different ethylenic monomers as compound material component C, the phase-change material has been selected in a manner such that the positive temperature coefficient intensity of the polymer composition exhibits a significant rise in the temperature range of the main melting peak of the phase-change material, and the positive temperature coefficient effect results from an increase in the volume of the phase-change material as a consequence of the temperature increase, and when the positive temperature coefficient takes effect the electrically conductive molding does not experience any changes in the morphology of the crystalline structures and does not melt, and there is no impairment of the service properties of the electrically conductive molding, where the molding comprises from 10 to 90% by weight of matrix polymer, from 0.1 to 30% by weight of the electrically conductive additive, from 2 to 50% by weight of the phase-change material with a phase-transition temperature in the range from 42 C. to 150 C., from 0 to 10% by weight of stabilizers, modifiers and dispersing agents and from 0 to 10% by weight of processing aids, based in each case on the total weight of the molding, where the sum of the percentages by weight of the individual constituents is 100% by weight.

2. The molding as claimed in claim 1, wherein the molding is a monofilament, a multifilament, a fiber, a nonwoven fabric, a foam, a film, a foil or an injection molding.

3. The molding as claimed in claim 1, wherein the organic matrix polymer that is compound material component A is polyethylene an ethylene copolymer, atactic, syndiotactic or isotactic polypropylene, a propylene copolymer, a polyimide, a copolyamide, a homopolyester, an aliphatic, cycloaliphatic or semi-aromatic copolyester, a modified polyester, polyvinylidene fluoride, a copolymer having vinylidene fluoride units, a thermoplastic elastomer, a crosslinkable thermoplastic polymer or copolymer, or a mixture or blend of two or more of the foregoing polymers.

4. The molding as claimed in claim 1, wherein the submicro- or nanoscale, electrically conductive additive that is compound material component B comprises submicro- or nanoscale particles, flakes, needles, tubes, platelets and/or spheroids.

5. The molding as claimed in claim 1, wherein the organic copolymer based on at least two different ethylenic monomers that is compound material component C is a block copolymer having at least two different polymer blocks, a random or grafted copolymer, where the compound material component C optionally additionally comprises amorphous polymers.

6. The molding as claimed in claim 1, wherein the phase-change material is a native or synthetic paraffin; a native or synthetic wax, a polyalkylene glycol, a native or synthetic fatty alcohol; a native or synthetic wax alcohol; a polyester alcohol, an ionic liquid or a mixture of two or more of the foregoing materials.

7. The molding as claimed in claim 1, wherein the phase-change material has a phase transition in the range from 42 C. to +150 C., which is associated with a reversible change of its volume.

8. The molding as claimed in claim 1, wherein the polymer composition comprises stabilizers, modifiers, dispersing agents and/or processing aids.

9. The molding as claimed in claim 1, wherein the melting point or melting range of the matrix polymer alone or in conjunction with processing aids and/or modifiers is within the range from 100 C. to 450 C.

10. The molding as claimed in claim 1, wherein the melting point or melting range of the phase-change material is below the melting range of the matrix polymer by at least 10 C.

11. The molding as claimed in claim 1, wherein the molding resistivity at a temperature of 24 C. is from 0.001 .Math.m to 3.0 .Math.m.

12. The molding as claimed in claim 1, wherein in the temperature range 24 C.T90 C. the molding temperature-dependent resistivity is (T), where the ratio (T)/(24 C.) increases with increasing temperature T from 1 to a value of from 1.1 to 30.

13. The molding as claimed in claim 1, wherein in the temperature range 24 C.T90 C. the molding temperature-dependent resistivity is (T), where the ratio (T)/(24 C.) increases with increasing temperature T from 1 to a value of from 1.1 to 21 and the average value of the increase gradient [(T+T)(T)]/[(24 C.).Math.T] in the increase range is from 0.1/ C. to 3.5/ C.

14. The molding as claimed in claim 1, wherein the molding has been crosslinked with the aid of a chemical crosslinking agent, via heating and/or via treatment with high-energy radiation.

15. A process for the production of a molding as claimed in claim 1, comprising processing the phase-change material that is compound material component D with the copolymer that is the compound material component C to give a masterbatch and then mixing the masterbatch with the other components.

16. The molding as claimed in claim 3, wherein the polyethylene is LDPE, LLDPE or HDPE, the polyamide is PA 6, PA 11 or PA 12, the copolyamide is PA 6.6, PA 6.66, PA 6.10 or PA 6.12; the cycloaliphatic or semi-aromatic copolyester is polyethylene terephthalate, polybutylene terephthalate or polytrimethylene terephthalate and the modified polyester is a glycol-modified polyethylene terephthalate.

17. The molding as claimed in claim 4, wherein the submicro- or nanoscale particles, flakes, needles, tubes, platelets and/or spheroids are (i) submicro- or nanoscale particles made of carbon black, graphite, expanded graphite or graphene; (ii) submicro- or nanoscale metal flakes or particles made of Ni, Ag, W, Mo, Au, Pt, Fe, Al, Cu, Ta, Zn, Co, Cr, Ti, Sn or an alloy or mixture thereof; (iii) electrically conductive polymers, (iv) single- or multiwall, open or closed, unfilled or filled carbon nanotubes, or metal-filled carbon nanotubes.

18. The molding as claimed in claim 5, wherein the block copolymer having at least two different polymer blocks is styrene-butadiene-styrene block copolymer, a styrene-isoprene-styrene block copolymer, a styrene-ethylene-propylene-styrene block copolymer, a styrene-poly(isoprene-butadiene)-styrene block copolymer or an ethylene-propylene-diene block copolymer; and the random or grafted copolymer is ethylene-vinyl acetate-vinyl alcohol copolymer, an ethylene-methyl acrylate-maleic anhydride copolymer, an ethylene-ethyl acrylate-maleic anhydride copolymer, an ethylene-propyl acrylate-maleic anhydride copolymer, an ethylene-butyl acrylate-maleic anhydride copolymer, an ethylene-(methyl, ethyl, propyl or butyl) acrylate-glycidyl methacrylate copolymer, an acrylic-butadiene-styrene graft copolymer, an ethylene-maleic anhydride copolymer, an ethylene-glycidyl methacrylate copolymer, an ethylene-vinyl acetate copolymer, an ethylene-vinyl alcohol copolymer, an ethylene-acrylate copolymer or a polyethylene graft copolymer or polypropylene graft copolymer, and the amorphous polymers are cycloolefin copolymers, polymethyl methacrylates, amorphous polypropylene, amorphous polyamide, amorphous polyester or polycarbonates.

19. The molding as claimed in claim 18, wherein the ethylene-acrylate copolymer is an ethylene-(methyl, ethyl, propyl or butyl acrylate) copolymer.

20. The molding as claimed in claim 6, wherein the synthetic wax is a highly crystalline polyethylene wax and the polyalkylene glycol is polyethylene glycol.

21. The molding as claimed in claim 10, wherein the melting point or melting range of the phase-change material is below the melting range of the matrix polymer by at least 20 C.

22. The molding as claimed in claim 10, wherein the melting point or melting range of the phase-change material is below the melting range of the matrix polymer by at least 30 C.

Description

[0105] The invention is explained in more detail with reference to figures.

[0106] FIG. 1a shows electrical current as a function of time in a heating textile comprising PTC filament yarn;

[0107] FIG. 1b shows the temperature of the heating textile of FIG. 1a as a function of time;

[0108] FIG. 2 shows the standardized electrical resistance R(T)/R(24 C.) of PTC mono- and multifilaments.

[0109] The temperature range and the intensity of the PTC effect can be adjusted via variation of compound material components A, B, C, D and optionally E. This behavior is documented by FIG. 1a and FIG. 1b. FIG. 1a shows electrical current I, and FIG. 1b shows temperature T, in each case as a function of time, for a self-regulating heating textile. The self-regulating heating textile was produced with use of a PTC monofilament of the invention with diameter 300 m as weft in a carrier textile made of polyester multifilaments. A heat output up to 248 watts per square meter can be generated by the heating textile when a voltage of 24 volts is applied.

[0110] FIG. 1a shows current as a function of time in a heating textile which comprises PTC filament yarn of the invention, to which an electrical voltage U of either 24 V or 30 V is applied. According to Ohm's law, the power output generated in the heating textile or in the PTC filament yarn present therein is calculated from the relationship P.sub.=U/R.sup.2. The electrical energy consumed in the heating textile during a period T, or the resultant electrical work W, where W=P.sub.. t, is almost entirely converted into heat, increasing the temperature of the heating textile. Some of the heat generated in the heating textile is dissipated to the environment via radiated heat and convection. The heat remaining in the heating textile causes a continuous temperature increase, in particular in the PTC filaments. As soon as the temperature of the heating textile approaches the phase-transition temperature of the phase-change material present in the PTC filament yarn, some of the phase-change material begins to melt. Associated with this is decreased density of the phase-change material and correspondingly increased volume thereof. This progressive volume increase results in increased electrical resistance of the PTC filament yarn, and decreased heat output P.sub.=U/R.sup.2. At a certain temperature, and a resistance corresponding thereto, a thermal equilibrium is established, where the electrical energy introduced into the heating textile per unit of time balances the heat generated by the heating textile. In the thermal equilibrium, with a certain electrical voltage applied, the resultant current, as illustrated by FIG. 1a, and the electrical resistance, and consequently the temperature of the heating textile, are constant. As can be seen from FIG. 1a, after a relatively short period of about 4 to 5 minutes not only the current but also the electrical resistance of the heating textile is constant, the value assumed by the latter in the thermal equilibrium being either R=24 V/0.13 A=185 or R=30 V/0.1 A=300, depending on the electrical voltage. The corresponding electrical heat output is P.sub.=(24 V).sup.2/185=3.1 W and, respectively, P.sub.=(30 V).sup.2/300=3.0 W. From the abovementioned electrical power, this textile generates, in the thermal equilibrium, a constant quantity of heat per unit of time. In this condition, the temperature of the heating textile is therefore also constant.

[0111] FIG. 1b shows the temperature of this specific heating textile as a function of time. With an applied voltage of 24 V and, respectively, 30 V the temperature in the thermal equilibrium assumes values of 63 C. and, respectively, 59 C.

[0112] FIG. 2 shows the standardized electrical resistance R(T)/R(24 C.) of PTC mono- and multifilaments produced in the invention, as a function of temperature. The maximal value and the gradient of the standardized resistance R(T)/R(24 C.) on the region of the phase transition are subsumed in the technical literature under the term PTC intensity. The respective measured curves are denoted by the numerals 1a, 1b and 2 to 7 in FIG. 2, the numerals being abbreviations for the filaments in the examples of the invention: [0113] 1a=PTC monofilament_01a [0114] 1b=PTC monofilament_01b [0115] 2=PTC monofilament_02 [0116] 3=PTC monofilament_03 [0117] 4=PTC monofilament_04 [0118] 5=PTC monofilament_05 [0119] 6=PTC monofilament_06 [0120] 7=PTC monofilament_07.

[0121] As can be seen from FIG. 2, the temperature at which the resistance of the filament increases can be varied, for example in the range of about 20 C. to 90 C., via selection of a suitable phase-change material and the corresponding conductivity additive. We describe below the phase-change material present in each filament, the corresponding conductivity additive, and the relevant mass fractions of these, and also of the other components of the polymer composition which can be used to influence the PTC intensity, and also the linear density of each filament.

[0122] By varying the concentration of the constituents of the composition, it is possible to produce mono- and multifilaments with differing PTC characteristic or resistance-temperature profile.

[0123] The monofilaments denoted by PTC monofilament_01a) and PTC monofilament_01b comprise a phase-change material (PCM) with melting range from 45 C. to 63 C. and with main melting peak at a temperature of 52 C. The proportion of the phase-change material was 5.25% by weight. The two curves (a) and (b) provide evidence of the good reproducibility of the production process. Although PTC monofilament_01a and PTC monofilament_01b derive from different filament wheels, the difference between the curves (a) and (b) is negligible. The monofilaments denoted by PTC monofilament_02 and PTC monofilament_03 used a phase-change material with main melting peak at a temperature of 35 C. and, respectively, 28 C. The PTC effect in both monofilaments is therefore observable at correspondingly lower temperatures than for PTC monofilament_01. The monofilaments denoted by PTC monofilament_05, PTC monofilament_04 and PTC monofilament_07 used the same phase-change material as PTC monofilament_01, in each case with a proportion by weight of 5.25% by weight, and the phase-change material therefore exhibited a main melting peak at a temperature T=52 C. However, the monofilaments PTC monofilament_05, PTC monofilament_04 and PTC monofilament_07 differ in their electrical conductivity because in each case their nature, composition and proportion of the conductivity component B varies. This has a significant effect on the starting level of the electrical resistance of the filaments at 24 C.: The resistance of the monofilament PTC monofilament_07 was only R=0.6 M/m, whereas the resistance of PTC monofilament_04 is 17.9 M/m, of PTC monofilament_05 is R=22.0 M/m and of PTC monofilament_01 is R=26.1 M/m. The sample denoted by PTC multifilament_06 is a multifilament with linear density 307 dtex (36-filament). It was produced from a material that, by virtue of the nature and the proportion of the conductivity component B, gives relatively good electrical conductivity and at the same time permits production of multifilaments. The electrical resistance of the multifilament yarn PTC multifilament_06 at 24 C. was 13.1 M/m, which was therefore lower than for the monofilaments with linear density 760 dtex and diameter 300 m. The PTC intensity of the multifilament yarn in essence corresponded to the behavior observed for monofilaments.

[0124] There are many different possible uses and applications of the moldings of the invention with PTC, because they can be used either with low voltages of from 0.1 volt to 42 volts or with relatively high electrical voltages of up to 240 volts, and also with direct or alternating voltage, and frequencies of up to 1 megahertz, and they have electrical and thermal properties that exhibit long-term stability.

[0125] It is preferable to use carbon black as conductivity additive. Carbon black is produced by various processes. Terms also used for the resultant carbon black, these being dependent on production process or starting material, are furnace black, acetylene black, plasma black and activated carbon. Carbon black consists of what are known as primary carbon black particles with mean diameter in the range from 15 to 300 nm. As a result of the production process, a large number of primary carbon black particles in each case forms what is known as a carbon black aggregate in which sinter bridges having very high mechanical stability connect adjacent primary carbon black particles to one another. Electrostatic attraction causes clumping of the carbon black aggregates, to give agglomerates exhibiting various levels of binding. Carbon black suppliers differ in respect of optional additional granulation or pelletization of the carbon black aggregates and carbon black agglomerates.

[0126] During the processing of polymer compositions comprising carbon black as additive in processes involving melting, for example extrusion, melt spinning and injection molding, the carbon black aggregates and carbon black agglomerates are exposed to shear forces. The maximal shear force acting in a polymeric melt depends in a complex manner on the geometry and the operating parameters of the extruder or gelling assembly used, and also on the rheological properties of the polymeric composition and its temperature. The maximal shear force acting in the process can exceed the electrostatic binding force and split carbon black agglomerates into carbon black aggregates, which become dispersed in the melt. On the other hand, increased agglomeration or flocculation can occur in low-viscosity polymeric melts or solutions where there is high mobility of the carbon black aggregates and low shear force.

[0127] The conductivity of a polymer molding comprising carbon black is decisively influenced by the proportion, distribution and morphology of the carbon black agglomerates and carbon black aggregates. As explained above, the distribution and morphology of carbon black in a polymer molding produced by processes involving melting depends on the nature of the carbon black additive, the rheological properties of the polymer composition and the process parameters. It is necessary to adjust the process parameters in a suitable manner, as required by the proportion and nature of the carbon black additive and of the other components of the polymer composition, in a manner that provides the prescribed conductivity to the molding. The influence exerted by, and the interaction between, the physical properties of the carbon black additive, the other constituents of the polymer composition and the process parameters is an extremely complex matter which hitherto has not been adequately understood.

[0128] The technical literature contains indications that break-up of carbon black agglomerates and uniform dispersion of carbon black aggregates by high shear forces in polymer melts prevents formation of a network of carbon black agglomerates and reduces conductivity by several orders of magnitude.

[0129] Surprisingly, the experiments carried out by the inventors lead to the obvious conclusion that use of phase-change materials in various polymer matrices can achieve fine and uniform dispersion of carbon black agglomerates and carbon black aggregates in polymer moldings and that conductivity is improved. It has therefore been possible to produce polymer moldings which, with a prescribed upper limit of 30% by weight for the proportion of carbon black, have conductivity up to 100 S/m (corresponding to resistivity =0.01 .Math.m) and in particular cases up to 1000 S/m (=0.001 .Math.m).

[0130] In the examples below, all of the starting materials or components, i.e. all of the polymers, polymer blends and additives, were processed only after careful drying in vacuum drying cabinets. As already explained above, the phase-change material can comprise one or more substances. The phase-change material in the examples comprises a compound material component C functioning as network-former and stabilizer, and a compound material component D which is a substance, in particular a paraffin, with a phase transition in the temperature range from about 20 C. to about 100 C. Unless otherwise stated or obvious from the context, percentages are percentages by weight.

EXAMPLE 1

Monofilament

[0131] The matrix polymer, or compound material component A, consists of a mixture with a proportion of 39.8% by weight of Moplen 462 R polypropylene and a proportion of 22.5% by weight of Lupolen low-density polyethylene (LDPE), and a proportion of 22.5% by weight of Super Conductive Furnace N 294 conductive carbon black was used as conductivity additive or compound material component B. Compound material component C consisted of a blend of styrene block copolymer and poly (methyl methacrylate), the proportion of each being 2.25% by weight. 10.5% by weight of Rubitherm RT52 paraffin with main melting peak at a temperature of 52 C. was used as compound material component D or phase-change material in the narrower sense. 0.2% by weight of a mixture of 0.06% by weight of Irganox 1010, 0.04% by weight of Irgafos 168 and 0.10% by weight of calcium stearate was used as further compound material component E.

[0132] In a separate step, compound material component D, i.e. the paraffin, is first plastified and homogenized together with the styrene block copolymer and the poly (methyl methacrylate) in a kneading assembly equipped with a granulator, and the mixture is then granulated. The composition of the PCM granulate was as follows: [0133] 70*% by weight PCM (Rubitherm RT52, Rubitherm Technologies GmbH); [0134] 15*% by weight SEEPS (Septon styrene block copolymer, Kuraray Co. Ltd); [0135] 15*% by weight PMMA (PMMA 7N uncolored, Evonik AG);
where the quantitative data in * % by weight are based on the total weight of the PCM granulate. The mean grain diameter of the PCM granulate was 4.5 mm.

[0136] This PCM granulate, the matrix polymers polypropylene (Moplen 462 R) in granulate form and polyethylene (Lupolen LDPE) in granulate form, and also compound material component E, were mixed together and charged to an extruder hopper. The conductive carbon black, or the compound material component B, was charged to metering equipment connected to the extruder. The metering equipment permits uniform introduction of the conductive carbon black into the polymer melt. The extruder is a Rheomex PTW 16/25 corotating twin-screw extruder from Haake with standard configuration, i.e. with segmented screws without back-conveying elements. The contents of the hopper, and the conductive carbon black, were plastified, homogenized and extruded by the extruder. During the entire extrusion process, the hopper extruder and the metering equipment were blanketed with nitrogen. The screw rotation rate was 180 rpm, and the mass throughput was about 1 kg/h. The temperature of the extruder zones were as follows: 220 C. at the intake, 240 C. in zone 1, 260 C. in zone 2, 240 C. in zone 3 and 220 C. at the strand die. The internal diameter of the strand die was 3 mm. The extruded and cooled polymer strand was granulated in a granulator. The composition of the polymer granulate thus obtained was as follows: [0137] 39.8% by weight of polypropylene as part of compound material component A; [0138] 22.5% by weight of low-density polyethylene (LDPE) as part of compound material component A; [0139] 22.5% by weight of conductive carbon black as compound material component B; [0140] 15.0% by weight of PCM granulate with 10.5% by weight of paraffin as compound material component D, and also respectively 2.25% by weight of SEEPS and PMMA as compound material component C; [0141] 0.2% by weight of additives as compound material component E.

[0142] This granulate was dried and served as starting material for the production of monofilaments in a filament extrusion system from FET Ltd., Leeds. The filament extrusion system comprises a single-screw extruder with screw diameter 25 mm and length-to-diameter ratio L/D=30:1. The mass throughput of polymer melt was 13.7 g/min. The following composition temperature regime was implemented: 200 C. in zone 1, 210 C. in zone 2, 220 C. in zone 3, 230 C. in zone 4, 240 C. in zone 5, 250 C. in zone 6 and 260 C. at the filament die. The die perforation diameter was 1 mm. The extruded polymer melt was cooled in a water bath at 20 C. and the solidified monofilament was drawn in-line in a process step using three draw units. The circumferential velocity here was 58.2 m/min for the godets of the first draw unit and 198 m/min for those of the second draw unit. A draw bath ranged between the first and second draw unit contained water at 90 C. After the second draw unit, the monofilament was passed via a heating oven onto the third draw unit. The circumferential velocity of the godets of the third draw unit was likewise 198 m/min. The drawn monofilament was then wound on a K 160 shell. The winder was operated at a velocity of 195 m/min. The draw ratio was 1:3.4. The diameter of the monofilament thus produced is 300 m.

[0143] Characterization of the monofilament in respect of its physical properties gave elongation 23%, tensile strength 62 mN/tex and initial modulus 1024 MPa.

[0144] The electrical resistance of the monofilament as a function of temperature was measured in a four-point device arranged in a controlled-temperature andhumidity chamber. The temperature was increased here stepwise from 24 C. (room temperature) to values of 30 C., 40 C., 50 C., 60 C., 70 C. and 80 C. 8 pieces of the monofilament were tested simultaneously, the test distance or test length in each case being 75 mm. The electrical resistance of the monofilament at room temperature is R(24 C.)=2.6 M/m. Heating of the monofilament to a temperature of 80 C. increases the resistance to R(80 C.)=19.0 M/m. Resistance returned to the initial value after cooling of the monofilament to room temperature. At a temperature of 80 C., the resistance ratio R(T)/R(24 C.) shown in FIG. 2 as a function of the temperature, and therefore as a measure of PTC intensity, is R(80 C.)/R(24 C.)=7.3. This is a consequence of the comparatively moderate electrical conductivity, i.e. of the relatively high electrical resistance at room temperature of 2.6 M/m for this monofilament produced as described with use of the specific polymer composition.

EXAMPLE 2

Multifilament

[0145] A blend of a proportion of 34.3% by weight of Moplen 462 R polypropylene and a proportion of 30% by weight of Lupolen low-density polyethylene (LDPE) was used as matrix polymer or compound material component A, and a proportion of 28.0% by weight of Super Conductive Furnace N 294 conductive carbon black was used as conductivity additive or compound material component B. Compound material component C consisted of a blend of styrene block copolymer and poly (methyl methacrylate), the proportion of each being 1.125% by weight. 5.25% by weight of Rubitherm RT55 paraffin with main melting peak at a temperature of 55 C. were used as compound material component D or phase-change material in the narrower sense. 0.2% by weight of a mixture of 0.06% by weight of Irganox 1010, 0.04% by weight of Irgafos 168 and 0.10% by weight of calcium stearate was used as further compound material component E.

[0146] In a separate step in a kneading assembly equipped with a granulator, a PCM granulate was first produced, consisting of paraffin as phase-change material, and also styrene block copolymer and poly(methyl methacrylate) as binder or stabilizer. The composition of the PCM granulate was as follows: [0147] 70*% by weight PCM (Rubitherm RT55, Rubitherm Technologies GmbH); [0148] 15*% by weight SEEPS (Septon styrene block copolymer, Kuraray Co. Ltd.); [0149] 15*% by weight PMMA (PMMA 7N uncolored, Evonik AG);
where the quantitative data in * % by weight are based on the total weight of the PCM granulate. The mean grain diameter of the PCM granulate was 4.5 mm.

[0150] This PCM granulate, the matrix polymers polyethylene (Lupolen LDPE) in granulate form, polypropylene (Moplen 462 R) in granulate form, and the compound material component E were mixed together and charged to an extruder hopper. The conductive carbon black, or the compound material component B, was charged to metering equipment connected to the extruder. The metering equipment permits uniform introduction of the conductive carbon black into the polymer melt. The extruder is a Rheomex PTW 16/25 corotating twin-screw extruder from Haake with standard configuration, i.e. with segmented screws without back-conveying elements. The contents of the hopper, and the conductive carbon black, were plastified, homogenized and extruded by the extruder. During the entire extrusion process, the hopper extruder and the metering equipment were blanketed with nitrogen. The screw rotation rate was 180 rpm, and the mass throughput was about 1 kg/h. The temperature of the extruder zones were as follows: 220 C. at the intake, 240 C. in zone 1, 260 C. in zone 2, 240 C., in zone 3 and 220 C. at the strand die. The internal diameter of the strand die was 3 mm. The extruded and cooled polymer strand was granulated in a granulator. The composition of the granulate thus obtained was as follows: [0151] 34.3% by weight of polypropylene as part of compound material component A; [0152] 30.0% by weight of low-density polyethylene (LDPE) as part of compound material component A; [0153] 28.0% by weight of conductive carbon black as compound material component B; [0154] 7.5% by weight of PCM granulate with 70% by weight of paraffin as compound material component D, and also respectively 15% by weight of SEEPS and PMMA as parts of compound material component C; [0155] 0.2% by weight of additives as compound material component E.

[0156] This granulate was dried and served as starting material for the production of multifilament yarn in a filament extrusion system from FET Ltd., Leeds. The granulate was processed in a filament extrusion system from FET Ltd., Leeds. The filament extrusion system comprises a single-screw extruder with screw diameter 25 mm and length-to-diameter ratio L/D=30:1. The mass throughput of polymer melt was 20 g/min. The following composition temperature regime was implemented: 190 C. in zone 1, 190 C. in zone 2, 190 C. in zone 3, 190 C. in zone 4, 190 C. in zone 5, 190 C. in zone 6 and 190 C. at the spinning die. The spinning die has 36 perforations each of diameter 200 m. The polymer melt emerging from the spinning die was cooled at an air temperature of 25 C. in a cooling shaft, and the multifilament thus solidified was drawn in-line in a step using four godet pairs. Circumferential velocity here was 592 m/min for the take-off godet, 594 m/min for the first godet pair, 596 m/min for the second godet pair, 598 m/min for the third godet pair and 600 m/min for the fourth godet pair. The multifilaments were then wound on a K 160 shell. The winder was operated at a velocity of 590 m/min. The linear density of the resulting multifilament yarn was 307 dtex (36-filament).

[0157] In a downstream step, the multifilament yarn was subjected to afterdrawing in a three-stage draw unit. Circumferential velocity was 60 m/min for the godets of the first draw stage and 192 m/min respectively for those of the second and third draw stage. Between the first and second draw stage, the multifilament was passed through a water-filled draw bath at 90 C. Between the second and third draw stage, the multifilament yarn was passed through a heating tunnel. The multifilament yarn was then wound on a K 160 shell. The winder was operated at a velocity of 190 m/min. The draw ratio of the multifilament yarn thus treated, with linear density 96 dtex (36-filament) was 1:3.2.

[0158] Characterization of the flat multifilament yarn processed in this way in respect of its physical properties gave elongation 19%, tensile strength 136 mN/tex and initial modulus 1431 MPa. The diameter of the individual filaments of the multifilament yarn was 17 m.

[0159] Properties measured on the multifilament yarn not subjected to afterdrawing, with linear density 307 dtex (36-filament) were: 192%, tensile strength 38 mN/tex and initial modulus 1190 MPa. The diameter of the individual filaments of the multifilament yarn not subjected to afterstretching was 31 m.

[0160] The electrical resistance of the non-stretched multifilament yarn was measured as a function of temperature by a four-point device arranged in a controlled-temperature andhumidity chamber. The temperature was increased here stepwise from 24 C. (room temperature) to values of 30 C., 40 C., 50 C., 60 C., 70 C. and 80 C. 8 pieces of the multifilament yarn were tested simultaneously, the test distance or test length in each case being 75 mm. The electrical resistance of the multifilament yarn at room temperature is R(24 C.)=13 M/m. Heating of the multifilament yarn to a temperature of 80 C. increases the resistance to R(80 C.)=119 M/m. Resistance returned to the initial value after cooling of the multifilament yarn to room temperature. At a temperature of 80 C., the resistance ratio R(T)/R(24 C.) shown in FIG. 2 as a function of the temperature, and therefore as a measure of PTC intensity, is R(80 C.)/R(24 C.)=9.1. This value increased to R(90 C.)/R(24 C.)=17.8 at a temperature of 90 C.

[0161] This multifilament yarn was produced by using a polymer composition that, by virtue of the proportion, and also the nature, of conductivity component B gave relatively good electrical conductivity and nevertheless could be used to produce multifilaments amenable to drawing. The electrical resistance of the multifilament yarn with linear density 307 dtex (36-filament) at a temperature of 24 C., based on linear density or cross-sectional area, is smaller by a factor of 4.6 than that of the monofilament with linear density 760 dtex (diameter 300 m). As can be seen from FIG. 2, the PTC intensity of the multifilament yarn substantially corresponds to that of monofilaments.

EXAMPLE 3

Foil

[0162] A blend of a proportion of 34.3% by weight of Moplen 462 R polypropylene and a proportion of 30% by weight of Lupolen low-density polyethylene (LDPE) was used as matrix polymer or compound material component A, and a proportion of 28.0% by weight of Super Conductive Furnace N 294 conductive carbon black was used as conductivity additive or compound material component B. Compound material component C consisted of a blend of styrene block copolymer and poly (methyl methacrylate), the proportion of each being 1.125% by weight. 5.25% by weight of Rubitherm RT55 paraffin with main melting peak at a temperature of 55 C. were used as compound material component D or phase-change material in the narrower sense. 0.2% by weight of a mixture of 0.06% by weight of Irganox 1010, 0.04% by weight of Irgafos 168 and 0.10% by weight of calcium stearate was used as further compound material component E.

[0163] In a separate step in a kneading assembly equipped with a granulator, a PCM granulate was first produced, consisting of paraffin as phase-change material, and also styrene block copolymer and poly(methyl methacrylate) as binder or stabilizer. The composition of the PCM granulate was as follows: [0164] 70*% by weight PCM (Rubitherm RT55, Rubitherm Technologies GmbH); [0165] 15*% by weight SEEPS (Septon 4055, Kuraray Co. Ltd); [0166] 15*% by weight PMMA (PMMA 7N uncolored, Evonik AG);
where the quantitative data in * % by weight are based on the total weight of the PCM granulate. The mean grain diameter of the PCM granulate was 4.5 mm.

[0167] This PCM granulate, the matrix polymers polyethylene (Lupolen LDPE) in granulate form, polypropylene (Moplen 462 R) in granulate form, and the compound material component E were mixed together and charged to an extruder hopper. The conductive carbon black, or the compound material component B, was charged to metering equipment connected to the extruder. The metering equipment permits uniform introduction of the conductive carbon black into the polymer melt. The extruder is a Rheomex PTW 16/25 corotating twin-screw extruder from Haake with standard configuration, i.e. with segmented screws without back-conveying elements. The contents of the hopper, and the conductive carbon black, were plastified, homogenized and extruded by the extruder. During the entire extrusion process, the hopper extruder and the metering equipment were blanketed with nitrogen. The screw rotation rate was 180 rpm, and the mass throughput was about 1 kg/h. The temperature of the extruder zones were as follows: 220 C. at the intake, 240 C. in zone 1, 260 C. in zone 2, 240 C. in zone 3 and 220 C. at the strand die. The internal diameter of the strand die was 3 mm. The extruded and cooled polymer strand was granulated in a granulator. The composition of the granulate thus obtained was as follows: [0168] 34.3% by weight of polypropylene as part of compound material component A; [0169] 30.0% by weight of low-density polyethylene (LDPE) as part of compound material component A; [0170] 28.0% by weight of conductive carbon black as compound material component B; [0171] 7.5% by weigt of PCM granulate with 70% by weight of paraffin as compound material component D, and also respectively 15% by weight of SEEPS and PMMA as parts of compound material component C; [0172] 0.2% by weight of additives as compound material component E.

[0173] This granulate was ground to powder in a planetary ball mill under a blanket of nitrogen, and the resultant powder was dried for 16 hours in a vacuum drying cabinet. The dried powder served as starting material for the production of foil by a vertical Randcastle Microtruder single-screw extruder with seven regulatable temperature zones (3 zones at the extruder head, 3 zones between the extruder head and the flat-film die and 1 zone at the flat-film die). The single-screw extruder has a screw with diameter 0.5 inch (=1.27 cm) and length-to-diameter ratio L/D=24:1. The capacity or melt volume of the extruder is 15 cm.sup.3, and the maximal compression ratio is 3.4:1.

[0174] The powder was charged to the extruder hopper under a blanket of nitrogen. The temperatures in the seven extruder zones were 190 C. in zone 1, 200 C. in zone 2, and respectively 210 C. in zone 3, 4, 5, 6 and 220 C. at the flat-film die. The slot width of the flat-film die was 50 mm and its gap size was 300 m. The single-screw extruder was operated with a screw rotation rate of 8 revolutions per minute and with a mass throughput of 3.5 g/min. The polymer melt or polymer web emerging from the flat-film die was drawn off by way of a chill roll and downstream belt-take-off equipment at a velocity of 0.6 m/min. The temperature of the chill roll was 36 C. Foil webs of width from 40 to 50 mm and thickness from 160 to 240 m could be produced continuously via variation of the above process parameters. The elongation of a foil thus produced with width 45 mm and thickness 180 m was 448%, and its tensile strength was 34 N/mm.sup.2.

[0175] The electrical resistance of the resultant foils as a function of temperature was determined in accordance with DIN EN 60093:1993-12 in a chamber under controlled conditions of temperature and humidity. The temperature was increased in 10 C. steps from 24 C. (room temperature) to values of 30 C., 40 C., 50 C., 60 C., 70 C. and 80 C. Resistance values of R(24 C.)=18.4 m and R(80 C.)=48.0 m were measured on a foil sample of thickness 180 m and area 28.3 cm.sup.2 at 24 C. and 80 C. After cooling of the foil from 80 C. to 24 C. resistance returned to its initial value. The resistance ratio R(T)/R(24 C.) as a function of temperature serves as indicator for PTC intensity, and was R(T)/R(24 C.)=2.6.

[0176] The following methods are used to measure the physical properties of the molding of the invention and of the conductivity additive present therein:

TABLE-US-00001 Property Method Filament: diameter DIN EN ISO 137: 2016-05 Filament: maximum tensile DIN EN ISO 2062: 2010-4 force and elongation, modulus of elasticity Filament: resistivity Measurement of resistance in chamber under controlled conditions of temperature and humidity Foil: thickness DIN 53370: 2006 Foil: modulus of elasticity DIN EN ISO 527: 2012 (tensile modulus), elongation at break Foil: tensile impact DIN EN ISO 8256: 2005 resistance Foil: resistivity DIN EN 60093: 1993-12, measurement of resistance by two-electrode device in chamber under controlled conditions of temperature and humidity Conductivity additive: ASTM D1510-16 specific surface area (iodine adsorption) Conductivity additive: oil ASTM D2414-16 absorption number Conductivity additive: oil ASTM D3493-16 absorption number after compression Conductivity additive: void ASTM D6086-09a, at a geometric- volume under compression mean pressure of 50 MPa, using a Micromeritics DVVA II dynamic volume analyzer Conductivity additive: ASTM D3849-14a equivalent diameter of primary carbon black particles and carbon black aggregates Conductivity additive: ASTM D3849-14a, using a equivalent diameter of primary solution of the polymeric particles and aggregates in sample polymeric samples

[0177] In the table above, and for the purposes of the present invention, the term equivalent diameter means the diameter of an equivalent spherical particle having the same chemical composition and areal section (electron microscope imaging) as the particle under consideration. In practical terms, the areal section of each (irregularly shaped) particle under consideration is assigned to a spherical particle having a diameter commensurate with the measured signal.

[0178] The distribution of carbon black agglomerates and carbon black aggregates in the moldings of the invention is determined in accordance with ASTM D3849-14a. For this, a volume of about 1 ml of the molding under consideration is first dissolved in a suitable solvent, for example hexafluoroisopropanol, m-cresol, 2-chlorophenol, phenol, tetrachloroethane, dichloroacetic acid, dichloromethane or butanone. If required by the nature of the matrix polymer, the solution is prepared at elevated temperature and over a period of up to 24 h. The resultant polymeric solution is dispersed or diluted with the aid of ultrasound in about 3 ml of chloroform, and applied to sample grids for analysis by scanning transmission electron microscope (STEM). The images produced by the STEM from the dilute polymeric solutions are evaluated by image-analysis software, for example ImageJ in order to determine the area or equivalent diameter of the carbon black agglomerates and carbon black aggregates.