MXPA99001160A - Method of making a laminate comprising a conductive polymer composition - Google Patents

Abstract

A method of making a laminate from a conductive polymer composition in which a particulate filler is dispersed in a polymeric component. The method comprises the following steps conducted sequentially in a single continuous procedure:(A) loading the polymeric component and the conductive filler into a mixing apparatus;(B) mixing the polymeric component and the conductive filler to form a molten mixture;(C) transporting the mixture from the mixing apparatus through a die;(D) forming a polymeric sheet;and (E) attaching metal foil to a least one side of the sheet to form a laminate. The laminate can be used to prepare circuit protection devices or heaters.

Description

METHOD FOR FORMING A LAMINATE MATERIAL THAT MEANS A POLYMER CONDUCTIVE COMPOSITION BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method for forming a sheet material comprising a polymer conductive composition and electrical devices comprising said sheet material. I ntroduction of the invention Conductive polymer compositions exhibiting CTP (positive temperature coefficient of resistance) are well known for use in electrical devices such as circuit protection devices. Said compositions comprise a polymer component and therein, a particulate conductive filler such as carbon black or metal is dispersed. The amount and type of filler in the composition is determined by the resistivity required for each application, as well as by the nature of the polymer component. Compositions suitable for use in circuit protection devices have resistivities below room temperature, v. gr. , less than 100 ohm-cm, and generally comprise relatively high levels of conductive filler. When said high filler compositions are prepared by conventional methods such as melt mixing, they are subjected to substantial shear stress. Said shear stress generates heat, which can degrade the polymer and result in increased resistivity. The additional shear stress and / or heat exposure result from the subsequent processing steps, v. gr. , extrusion, fusion formation and union of electrodes, v. gr. , by rolling. Conventional processing techniques provide that some of these steps, eg. extrusion and lamination can be performed in a continuous process, but, due to the desire to ensure adequate dispersion of the filler in the polymer, it is common to divide the manufacturing process into several discrete steps, that is, separate. The more times the composition is heated, cooled and subjected to shear stress, the greater the chances of degradation and resistivity change. Compositions with low resistivity are suitable for use in circuit protection devices that respond to changes in ambient temperature and / or current conditions. Under normal conditions, a circuit protection device remains in a low temperature, low resistance state, in series with a load in an electrical circuit. However, when exposed to an overcurrent or over-temperature condition, the device increases its resistance, effectively closing the flow of current to the load in the circuit. For many applications it is desirable that the device have a resistance as low as possible in order to minimize the effect of the resistance of the electrical circuit during normal operation. Although low resistance devices can be formed by changing the dimensions, v. gr. , forming the very small distance between the electrodes or the area of the very large device, small devices are preferred because they occupy less space in a circuit board and generally have suitable thermal properties. The most common technique for achieving a small device is to use a composition that has a low resistivity. The resistivity of a conductive polymer composition can be decreased by adding more confectionary filler, but this process can affect the processability of the composition, v. gr. , increased viscosity. In addition, the addition of conductive filler generally reduces the size of the CTP anomaly, i.e. the size of the increase in resistivity of the composition in response to an increase in temperature, generally on a relatively small temperature scale. The required CTP anomaly is determined by the applied voltage and the application. Thus, it is necessary to reduce to the minimum the processing effects that result in increases in resistivity, in order to achieve a composition with acceptable size and electrical properties. COMPLETION OF THE NONVENTION We have now found that through the use of a process in which a lamellar material in which a polymer conductive composition is attached to a sheet metal electrode (and preferably is sandwiched between two electrodes of sheet metal) is conducted in a simple continuous process, devices which have low resistivity, adequate CTP anomaly and good electrical performance can be prepared. The continuous process for producing the sheet material allows non-molten polymer, raw and filler ingredients to be introduced into a mixing apparatus, v. gr. , like an extruder and that is formed by fusion in a laminar material, reducing the number of steps required to produce a device. Unlike conventional processes in which the raw ingredients are melt-mixed, they are formed into pellets, then dried and extruded into a sheet to be laminated, the method of the invention allows the elimination of the pelletizing step, together with the drying of the pellets before the leaf forming step. This means that the composition is exposed to a process with less heat and less shear stress. In a first aspect this invention provides a method for forming a sheet material of a polymer conducting composition comprising (i) a polymer component and (ii) a particulate conductive filler dispersed in the polymer component, the method comprising: (A) Charging the polymer component and conductive relay in a mixing apparatus; (B) mixing the polymer component and the conductive base in the mixing apparatus to form a molten mixture; (C) transporting the molten mixture from the mixing apparatus through a die; (D) forming the molten mixture in a polymer sheet; and (E) joining the sheet metal to at least one side of the sheet to form a sheet material, the steps (A) to (E) being carried out sequentially in a single continuous process. In a second aspect, this invention provides an electrical device, which (1) comprises (a) a resistive element that is composed of a polymer conductive composition exhibiting CTP behavior and comprising (i) a polymeric component having a melting temperature Tm and (ii) a particulate conductive filler is dispersed in the polymer component; and (b) two electrodes which (i) are connected to the resistive element, (ii) which comprises a metal foil and (ii i) can be connected to a source of electrical energy; (2) has a resistance at 20 ° C, R20, at most 50.0 ohm; (3) has a resistivity at 20 ° C, p20, at most 50.0 ohm-cm; and (4) is formed by a method comprising: (A) charging the polymer component and the conductive filler in a mixing apparatus; (B) mixing the polymer component and the conductive base in the mixing apparatus to form a molten mixture.

(C) transporting the molten mixture from the mixing apparatus through a die; (D) forming the molten mixture in a polymeric sheet; (E) joining the metal sheet to two sides of the sheet to form a sheet material; and (F) cutting the sheet material to form the device, steps (A) to (E) being carried out sequentially in a single continuous process. DETAILED DESCRIPTION OF THE INVENTION The method of the invention is used to form a sheet material of a polymer conductive composition. The polymer conductive composition comprises a polymer component and is dispersed in the polymer component, a particulate conductive filler. The polymer component of the composition comprises one or more polymers, one of which preferably is a crystalline polymer having a crystallinity of at least 20% in its non-filled state as measured by a differential scanning calorimeter. Suitable crystalline polymers include polymers of one or more olefins, particularly polyethylene such as high density polyethylene; copolymers of at least one olefin and at least one monomer copolymerizable therewith such as ethylene / acrylic acid copolymer, ethylene / ethyl acrylate, ethylene / vinyl acetate and ethylene / butyl acrylate; fluoropolybleable melt-forming polymers such as polyvinylidene fluoride and ethylene / tetrafluoroethylene copolymers (including terpolymers); and mixtures of two or more of said polymers. For some applications it may be convenient to mix a crystal polymer with another polymer, v. gr. , an elastomer or an amorphous thermoplastic polymer, in order to achieve specific physical or thermal properties, v. gr. , flexibility or temperature at maximum exposure. The polymer component has a melting temperature, as measured by the peak of the endotherm of a differential scanning calorimeter of Tm. When there is more than one peak, for example, in a mixture of polymers, Tm is defined as the temperature of the highest temperature peak. The polymer component generally comprises from 40 to 90% by volume, preferably from 45 to 80% by volume, especially from 50 to 75% by volume of the total volume of the composition. The particulate conductive filler which is dispersed in the polymer component may be any suitable material, including carbon black, graphite, metal, metal oxide, conductive coated glass or ceramic beads, particulate conductive polymer or a combination thereof. The filler may have the form of powder, beads, flakes, fibers or any other suitable form. The amount of conductive filler required is based on the required resistivity of the composition and the resistivity of the conductive filler itself. For many compositions the conductive filler comprises from 10 to 60% by volume, preferably from 20 to 55% by volume, especially from 25 to 50% by volume of the total volume! of the composition. The polymeric conductive composition may comprise additional components, such as antioxidants, inert fillers, non-conductive fillers, radiation entanglement agents (often referred to as pro-radians or entanglement enhancers, eg, triallyl isocyanurate), stabilizers, dispersing agents, coupling agents, acid scavengers (eg, CaCO3) or other components. These components generally comprise a maximum of 20% by volume of the total composition. The composition generally exhibits a positive temperature coefficient (CTP) behavior that is, they show sharp increase in resistivity with temperature over a relatively small temperature scale, although the method of the invention can be used to prepare compositions exhibiting performance of zero temperature coefficient (CTC). In this application, the term "CTP" is used to mean a composition or device having a value of R14 of at least 2.5 and / or a value of R 10o of at least 10., and it is preferred that the composition or device have a value of R30 of at least 6, where R .4 is the ratio of the resistivities at the end and at the beginning of a scale of 14 ° C, R .oo is the ratio of the resistivities at the end and beginning of a scale of 100 ° C and R30 is the ratio of resistivities at the end and at the beginning of a scale of 30 ° C. Generally the compositions used in devices of the invention that exhibit CTP behavior show increases in resistivity that are much greater than those minimum values. It is preferred that the compositions used to form the devices of the invention have a CTP anomaly in at least one temperature on the scale of 20 ° C to (Tm + 5 ° C) of at least 104, preferably at least 1 04 5, particularly of at least 105, especially at least 105 5, that is, the log [resistance (Tm + 5 ° C) / resistance 20 ° C] is at least 4.0, preferably at least minus 4.5, particularly of at least 5.0, especially at least 5.5. if the maximum resistance is achieved at a temperature Tx that is below (Tm + 5 ° C), the CTP anomaly is determined by log (resistance to Tx / resistance at 20 ° C). The resistivity of the composition depends on the application and what type of electrical device is required. As preferred, when the composition is used to form lamellar material for circuit protection device. The composition has a resistivity of 20 ° C, p20, of at least 100 ohm-cm, preferably at most 50 ohm-cm, more preferably at least 20, more particularly at least 10 ohm-cm, more particularly at most mo 4 ohm-cm, especially at most 2.0 ohm-cm, more especially at most 2.0 ohm-cm. When the composition is used in a heater, the resistivity of the polymer conducting composition preferably is higher, eg, at least 102 ohm-cm, preferably at least 103 ohm-cm. Suitable polymeric conductive compositions are described in U.S. Pat. Nos. 4,237,441 (van Konynenburg and others), 4,388,607 (Toy and others), 4,534,889 (van Konynenburg and others), 4,545,926 (Fouts and others), 4,560,498 (Horsma and others), 4,591,700 (Sopory), 4,724,417 (Au and others) , 4,774,024 (Deep and others), 4,935,156 (van Konynenburg and others), 5,049,850 (Evans and others), and 5,250,228 (Baigrie and others), 5,378,407 (Chandler and others), 5,451,919 (Chu and others) and 5,582,770 (Chu and others). ) and in International Publications Nos. WO96 / 29711 (Raychem Corporation, published September 26, 1996) and WO96 / 30443 (Raychem Corporation, published October 3, 1996). The method of the invention comprises five steps, steps (A) to (E), which are carried out sequentially in a single procedure. Additional process steps, eg, heat treatment or irradiation, can be carried out between two steps of the invention while the process remains continuous. At least, the two-step parts can be carried out simultaneously, eg, by transporting the molten mixture through a die (step (C)) having a configuration that forms the molten mixture in a polymeric sheet ( step (D)). In step (A), the polymeric component and the particulate conductive filler are charged to a mixing apparatus, in a preferred embodiment, both the polymer component and the conductive filler are in the form of dry powder, flakes, fibers or pellets that are they can easily feed into the mixing apparatus, although these two components can be fed separately into the mixing apparatus, preferably the polymeric component and the conductive filler are "pre-mixed" in the dry state, v. gr. , by means of a mixer such as Henschel ™ mixer, to improve the uniformity and flow of the components during the loading step. The additional components, in the form of powder, pellets or liquid, can be premixed with the polymer component and the particulate component., or they can be added at different points in the process. The loading can be achieved by any means, although weight loss feeders such as those sold by K-Tron America under the tradename "K-Tron" are preferred to ensure consistent feeding in the apparatus. The mixing apparatus is preferably an extruder, although other types of mixing equipment can be used, including internal mixers, such as Banbury ™ mixers, Brabender ™ mixers and Moriyama ™ mixers, with suitable joints to complete the required steps of the invention . Suitable extruders include single screw extruders, co-rotating twin screw extruders, rotating double screw extruders in the opposite direction or reciprocating single screw extruders, v. gr. , a Buss ™ mixer. When the extruder is used, additive vials can be added, eg. , entangling agents such as peroxide, continuously downstream of the feed port from the door into which the polymeric conductive filler component is introduced. Unlike conventional methods in which an entanglement agent is added to one composition, it could result in an interlaced mass which can not easily be formed in a uniform sheet or otherwise, the method of invention is particularly suitable for in-line chemical entanglement. The continuous process allows the interlacing agent to be added just before the material is transported through a die. In step (B), the polymeric component and conductive filler are mixed in the mixing apparatus to form a molten mixture, i.e. one having a temperature above the melting temperature Tm of the polymer component. During step (B), the conductive filler, as well as other components such as inorganic fillers or pigments, is dispersed in the polymer component. To ensure that proper mixing and dispersion is achieved, the screw of an extruder can be designed to have mixing or kneading sections, as well as transport sections. For example, we have found that incorporating kneading sections into at least 10% of the total screw length for a rotating twin screw extruder has produced acceptable dispersion. When an extruder is used, it is preferred that the ratio of the length of the bolt to its diameter, ie L / D ratio, is at least 10: 1, preferably at least 15: 1, particularly at least 20: 1, especially at least 30: 1, v.gr. , 40: 1, in order to achieve adequate dispersion of conductive filler. The mixing apparatus can be heated, v. gr. , electrically or with oil, in one or more sections (zones). A vacuum apparatus, for removing volatiles generated during mixing, can be appropriately placed in combination with the mixing apparatus. In step (C), the molten mixture is transported from the mixing apparatus through a die. The term "given" is used in this specification to mean any element that has a hole through which the molten material can pass. Therefore, a die can be a mold, a nozzle or an article with an opening or space of a particular shape through which the molten material passes. The die can be attached directly to an output port of the mixing apparatus, e.g. , by means of an adapter or can be separated from the mixing apparatus by one or more pieces of equipment, e.g. , a gear pump or a vacuum device. When the mixing apparatus is an extruder, the "transport" of the molten mixture occurs during normal operation of the extruder. Other means of transporting the molten mixture may be required if another type of mixing apparatus is used. In step (D), the fumed mixture is formed into a polymeric sheet. This can be easily achieved by extrusion through a die or calender of the molten mixture., ie, passing the molten mixture through rolls or plates to thin it into a sheet. The thickness of the calendered sheet was determined by the distance between the plates or rollers, as well as the rate at which the rollers rotate. Generally, the polymeric sheet has a thickness of 0.025 to 3.8 mm, preferably 0.051 to 2.5 mm. The polymeric sheet can have any width. The width is determined by the shape and width of the die or the volume of the material and calendering regime and is often 0.15 to 0.31 m.

In step (E), a sheet material is formed by joining a metal sheet to at least one side, preferably both sides, of the polymer sheet. When the lam inar material is cut into an electrical device, the layers of sheet metal act as an electrode. The metal sheet generally has a thickness of a maximum of 0.13 mm, preferably a maximum of 0.076 mm, particularly at a maximum of 0.051 mm, v. gr. , 0.025 mm. The width of the metal sheet is generally about the same as that of the polymer sheet, but for some applications, it may be convenient to apply the metal sheet in the form of two or more narrow strips, each having a width that is less than the polymeric sheet. Suitable metal sheets include nickel, copper, brass, aluminum, molybdenum and alloys, or sheets comprising two or more of these materials in the same layer or in different layers. Particularly suitable metal sheets have at least one surface that is electrodeposited, preferably nickel or electrodeposited copper. Suitable metal sheets are described in the E Patents. U .A. Do not . 4,689,475 (Matthiesen) and 4, 800,253 (Kleiner et al.) And in International Publication No. WO95 / 34081 (Raychem Corporation, published December 14, 1995). In a preferred embodiment, the metal sheet is contacted with the polymer sheet and then passed through the rolls, v. gr. , via u na pi la de rodi llos, to promote good lamination of the sheet to the polymer. In addition to minimizing the cooling of the sheet as it leaves the die, it is preferred that the distance between the die and the roll stack will be relatively small, v. gr. , less than 0.61 m, preferably less than 0.31 m. For some applications, an adhesive composition (i.e., an interlaced layer) can be applied to the polymeric lam, v. gr. , by spraying or brushing, before putting in contact with the metal sheet. The sheet material resulting from step (E) may be wound on a rail or cut into discrete pieces for further processing or storage. The thickness of the sheet material is generally 0.076 to 4.1 mm. The method of the invention can be used to produce a minar material with more than one polymeric sheet using two or more mixing / transport apparatuses / forming structures that produce polymeric sheets based on the same components or different components and conductive fillers. When the sheet material comprises two metal sheets, it can be used to form an electrical device, particularly a circuit protection device. The device can be cut from the lam inar material in step (F). In this application the term "cut" is used to include any method of isolating or separating the device from the sheet material, e.g., cutting into cubes, chopping, tearing, cutting, graveling and / or breaking as described. in the International Publication NO. WO95 / 34084 (Raychem Corporation, published December 4, 1995), or any other suitable means. Step (F), but not necessarily, can be part of a single continuous procedure of steps (A) or (E). The additional metallic charges, eg, in the form of wires or strips, can be attached to the electrodes of the sheet to allow electrical connection to a circuit. In addition, the elements for controlling the thermal output of the device, e.g., one or more conductive terminals, can be used. These terminals may be in the form of metal plates, e.g., steel, copper, or brass or fins, which are attached either directly or by means of an intermediate layer such as a solder or a conductive adhesive to the electrodes. See, for example, US Patents. Nos. 5,089,801 (Chan et al.) And 5,436,609 (Chan et al.). For some applications, it is preferred to attach the devices directly to a circuit board. Examples of such joining techniques are shown in International Publications Nos. WO94 / 01876 (Raychem Coporation, published January 20, 1994) and WO95 / 31816 (Raychem Corporation, published November 23, 1995). In order to improve the electrical stability of the device, it is often convenient to subject the device to various processing techniques, e.g., interlacing and / or heat treatment. The interlacing can be achieved by chemical means or by irradiation, e.g. , using an electron beam or a source of irradiation? of Co60. The level of entanglement depends on the application required for the composition, but is generally less than the equivalent of 200 Mrads and preferably substantially smaller, i.e. 1 to 20 Mrads, preferably 1 to 16 Mrads, particularly 2 to 10 Mrad for applications Low voltage circuit protection (ie less than 60 volts). Generally, the devices are interlaced to the equivalent of at least 2 Mrads. Processing procedures for devices are described in International Publication No. WO96 / 2971 1 (published September 26, 1996). The devices of the invention are preferably circuit protection devices that generally have a resistance at 20 ° C, R20, less than 100 ohm, preferably less than 50 ohm, particularly less than 20 ohm, more particularly less than 10 ohm, especially lower at 5 ohm, more especially less than 1 ohm. Because the laminar material prepared by the method of the invention comprises a polymer conducting composition which may have a low resistivity, it can be used to produce devices with low resistance, v. gr. , from 0.001 to 0.100 ohm. The devices that are heaters generally have a resistance of at least 100 ohms, preferably at least 250 ohms, particularly at least 500 ohms.

It should be understood that the sheet material made by the method of this invention can be used for any type of device, v. gr. , heaters or sensors, as well as circuit protection devices. The invention is illustrated by the following Examples, in which Examples 1, 2, 4, 6, 8 and 10 are Comparative Examples. Examples 1 to 7 For each example, the following ingredients, in percentages by weight based on the weight of the total composition listed in Table I, were mixed at 1500 rpm for three minutes using a Henschel ™: PVDF mixer (KF ™ 1000W , polyvinylidene fluoride in powder form with a melting temperature of about 177 ° C, available from Kureha), ETFE (Tefzel ™ HT 2163, ethylene / tetrafluoroethylene / perfluorinated butyl ethylene terpolymer with a melting temperature of about 235 ° C, available from DuPont), CB (Raven ™ 430, carbon black, available from Columbian Chemical), TA IC (triazyl isocyanurate) and CaCO3 (Atomite ™ powder, calcium carbonate, available from John K. Bice Co.). The mixed dry ingredients are subjected to a two-step process (comparative) or to a one-step process of the invention. Two Step Process For Comparative Examples 1, 2, 4 and 6, the mixed dry ingredients were fed into a co-rotating twin screw extruder using a screw with an L / D ratio of 40: 1 (ZSK- 40, available from Warner-Pfleiderer), mixed, extruded into threads and cut into pellets. For Example 1, the pellets were dried at 80 ° C for at least 24 hours and then extruded through a 25 mm single screw extruder adapted with a nozzle with a diameter of 9.5 mm. The molten material was extruded from the nozzle and fed into a roller stack positioned approximately 25 mm from the end of the nozzle. The roller stack was used to calender the material in a sheet with a thickness of approximately 0.250 mm and a width of approximately 14-145 mm and to join the electrodeposited nickel / copper sheet (Type 31, sheet of 1 oz. a thickness of approximately 0.44 mm available from Fukuda) on both sides of the calendered sheet. The resulting sheet material had a thickness of approximately 0.34 mm. For Examples 2, 4 and 6, pellets were extruded through a co-rotating twin-screw extruder in the opposite direction (ZSE-27, available from Leistritz) in a co-rotating mode using a screw without kneading elements. and having an L / D ratio of 40: 1. The extruder was adapted with a gear pump having a capacity of 10 cm3 / revolutions (Pep I I, available from Zenith) and then with a nozzle as before. The material was extruded, calendered and laminated following the same procedure as for Example 1. Step Process The mixed dry ingredients were fed into a ZSE-27 extruder used in a co-rotating mode and having a screw configuration in which 1 1% of the total screw length were kneading elements. The screw had an L: D ratio of 40: 1. The extruder was adapted with a gear pump and a nozzle as in Examples 2, 4 and 6. The material was mixed, and the mixed material was extruded through a gear pump and nozzle, calendered and rolled following the Same procedure as for Examples 2, 4 and 6. Device Preparation For Examples 2 to 7, the laminar material was irradiated in a continuous process using a 3.5 MeV electron beam to a total of 7.5 Mrad. The sheet material was then coated in a continuous process with welding (using a weld of approximately 250 ° C) and the devices with dimensions of 11 × 15 mm were bitten from the sheet material. Two copper tips coated with 20 AWG tin approximately 25 mm long were attached to the device and the device was cycled by temperature at a rate of 10 ° C / minute from 40 ° C to 160 ° C at 40 ° C during six cycles, with a dilation time of 30 minutes at the extreme temperatures for each cycle. For Example 1, devices with dimensions as before were cut from the sheet material and irradiated as discrete pieces and not coated by solder. The tips were joined and the devices cycled by temperature as before.

TABLE * Comparative Examples Device Test The resistance of the device at 20 ° C was measured and the resistivity was calculated. The properties of resistance against temperature of the device were determined by placing the device in an oven and measuring the resistance at intervals on the temperature scale from 20 to 200 at 20 ° C. The height of the CTP anomaly, CTP, was determined after the first temperature cycle as log (resistance at 175 ° C / resistance at 20 ° C). The results, shown in Table I I, indicate that the devices made by the method of the invention had lower initial resistances than the devices made by the conventional process. In addition, the method of the invention produces devices that have PTC anomalies similar to those by the conventional method although the composition for the devices of the invention contained less conductive filler (compare Example 5 with Example 6 and Example 7 with the Example 2). TA BLA I I Comparative Examples Examples 8-1 The following ingredients, in the weight percentages listed in Table III, were mixed in a Henschel mixer: H PDE (Petrothene ™ LB832, high density polyethylene having a melting temperature of about 135 ° C, available from Quantum Chemical), EBA (Enanthene ™ 705-009, ethylene / n-butyl acrylate copolymer having a melting temperature of about 105 ° C, available from Quantum Chemical) and CB (Raven 430). The mixed dry ingredients were subjected to a two-step process or a one-step process. Two-Step Process For Comparative Examples 8 and 10, the mixed dry ingredients were placed in a 70 mm Buss Kneader kneader (a single-screw reciprocating extruder), mixed, entruded into yarns and cut into pellets. The extruder ZSE-27 in a co-rotating mode with a screw having no kneading elements and an L: D ratio of 40: 1 was adapted with a gear pump at the exit port of the extruder as in Example 2 The gear pump was attached to a rolling die having an opening of 1 52 mm in width and 0.038 in thickness. The pellets were extruded through the die of the sheet to form a polymer sheet and the polymer sheet was removed from the die on a stack of rollers spaced approximately 12.7 mm from the die lip and having rubber coated rollers heated to approximately 155 °. C. The nickel / copper plate as described in Example 1 was laminated to the polymeric sheet. The resultant sheet material had a thickness of approximately 0.127 mm. Step Process For Examples 9 and 11, the mixed dry ingredients were fed into a ZSE-27 extruder used in a co-rotating mode and having a screw configuration in which 1 1% of the total length of the screw were kneading elements and the L: D ratio was 40: 1. The material was mixed in the extruder and continuously extruded and laminated using the given gear pump and the rolling process described for Example 8. Preparation of Devices The sheet material was coated welding in a continuous process (using a temperature of welding of approximately 220 ° C) and devices with dimensions of 5 x 12 mm were bitten from the sheet material. The devices were heat treated in a process that exposed them to a temperature of 185 to 215 ° C for about 4 seconds. The devices were then interlocked at 10 Mrad using a Co60 range irradiation source. Poles with dimensions of 0.13 x 5 x 13.5 mm were attached to the electrodes on both sides of the device by welding reflow and the devices cycled in six cycles from 40 ° C to 85 ° C with a time of dilation of 30 minutes at extreme temperatures. Device Test The devices were tested as before, except that the CTP anomaly was measured on a temperature scale of 20 to 160 at 20 ° C. The height of the CTP anomaly was determined at three different temperatures, 105 ° C, 125 ° C and 140 ° C as log (resistance to Ty ° C / resistance at 20 ° C) for the second cycle, where y was the measurement temperature. (The measurement at 140 ° C was closer to the actual melting point of the polymer conductive composition). The results, shown in Table III, indicated that similar CTP anomalies could be achieved, but with a much lower resistance, for a composition made with the one-step continuous process instead of a conventional two-step process (compare Examples 8 and 9).

TABLE III 'Comparative Examples

Claims (10)

1. RECIPE N D ICAC ION ES 1. A method for forming a sheet material of a polymer conductive composition comprising (I) a polymer component and (ii) a particulate conductive resin dispersed in the polymer component, the method comprising: (A) charging the polymer component and the conductive filler in a mixing apparatus; (B) mixing the polymer component and the conductive filler in the mixing apparatus to form a molten mixture; (C) transporting the molten mixture from the mixing apparatus through a die; (D) forming the molten mixture in a polymeric sheet; and (E) joining the sheet metal to at least one side of the sheet to form a sheet material, the steps (A) to (E) being carried out sequentially in a single continuous process.
2. 2. A method according to claim 1, wherein the mixing apparatus is an extruder, preferably a single-screw extruder, a co-rotating double-screw extruder, a rotating double-screw extruder in the opposite direction, or an extruder. of a single reciprocal screw.
3. 3. A method according to claim 1, wherein the die is a nozzle.
4. 4. A method according to claim 1, wherein the die is attached directly to an outlet port of the mixing apparatus.
5. 5. A method according to claim 1, wherein step (E) comprises joining the metal sheet to two sides of the sheet.
6. 6. A method according to claim 1, wherein the conductive polymer composition in the sheet material has a resistivity of less than 20 ohm-cm, preferably less than 10 ohm-cm.
7. 7. A method according to claim 1, wherein the polymeric sheet has a thickness of 0.025 to 3.8 mm and is formed by extrusion or calendering.
8. 8. An electrical device which (1) comprises (a) a resistive element that is composed of a polymer conductive composition which exhibits CTP behavior and which comprises (i) a polymeric component which has a melting temperature Tm , and (ii) a particulate conductive filler dispersed in the polimeric component; and (b) two electrodes which (i) are attached to the resistive element, (i i) comprises metal plates, and (ii) can be connected to an electrical power source; (2) has a resistance at 20 ° C, R20, at most 50.0 ohm: (3) has a resistivity at 20 ° C, p2o, at most 500 ohm-cm; and (4) it has been formed by a method according to claim 5 further comprising (F) cutting the laminar material to form the device.
9. 9. A device according to claim 8, wherein the polymer component comprises a crystalline polymer which is a polyethylene, a copolymer of ethylene, a fluoropolymer, or a mixture of these polymers and the particle repel comprises black carbon.
10. 10. A device according to claim 8, which has a CTP anomaly of at least 104 °.