MXPA96006205A - Electrical devices containing polymers duct - Google Patents

Abstract

The present invention relates to an electrical device, which comprises: an element composed of a conductive polymer, and at least one metal foil electrode which comprises: a base layer comprising a first metal, an intermediate metal layer, which is placed between the base layer and a surface layer, and comprises a metal that is different from the first metal, and a surface layer comprising a second metal, has an average roughness of the center line Ra of at least 1.3, and has a reflex density Rd of at least 0.60, and placed in such a way that the surface layer is in direct physical contact with the polymer element

Description

ELECTRICAL DEVICES CONTAINED »CONDUCTIVE POLYMERS BACKGROUND OF THE INVENTION Field of the Invention This invention relates to electrical devices that comprise conductive polymeric compositions, and to circuits comprising these devices.

Introduction to the Invention Electrical devices comprising conductive polymeric compositions are well known. These devices comprise an element composed of a conductive polymer. The element is physically and electrically connected to at least one suitable electrode for connection to a source of electrical energy. These factors that determine the type of electrode used include the specific application, the configuration of the device, the surface to which the device is to be connected, and the nature of the conductive polymer. Among these types of electrodes that have been used are solid and braided wires, metal foils, perforated and expanded metal sheets, and conductive inks and paints. When the conductive polymer element is in the form of a sheet or web, metal sheet electrodes which directly attach to the surface of the conductive polymer, sandwiching the element are particularly preferred. Examples of these devices are found in U.S. Patent Nos. 4,426,633 (Taylor), 4,689,475 (Matthiesen), 4,800,253 (Kleiner et al.), 4,857,880 (Au et al.), 4,907,340 (Fang et al.), And 4,924,074. (Fang et al.), Whose descriptions are incorporated herein by reference. As described in the Patents of the States United States of North America Numbers 4,689,475 (Matthiesen) and 4,800,253 (Kleiner et al.), Microrough metal sheets having certain characteristics give excellent results when used as electrodes in contact with conductive polymers. Accordingly, U.S. Patent No. 4,689,475 discloses the use of metal foils having surface irregularities, e.g., nodules, which protrude from the surface by 0.1 to 100 microns, and have at least one dimension parallel to the surface which is at most 100 microns, and U.S. Patent No. 4,800,253 discloses the use of metal foils with a microrough surface comprising macronodules which themselves comprise micronodules. Other documents describing the use of metal foils having rough surfaces, but not describing the characteristics of the foils described in U.S. Patent Nos. 4,689,475 and 4,800,253, are Japanese Patent Kokai Number 62-113402 (Murata, 1987), Japanese Patent Kokoku H4-18681 (Idemitsu Kosan, 1992), and German Patent Application Number 3,707,494A (Nippon Mektron Ltd.). The description of each of these documents from the United States of America, Japan and Germany is incorporated herein by reference.

COMPENDIUM OF THE INVENTION We have discovered that even better results can be obtained for electrodes that are in contact with a conductive polymer, by using metal sheets of rough surfaces having one or both of two characteristics that are not found in the metal sheets. that have been used, or that have been proposed to be used, in the past. These characteristics are: (1) The protuberances from the surface of the sheet must have a certain average minimum height (and preferably a certain maximum average height), expressed by a value known as the "average roughness of the central line", whose measurement is In addition, the protuberances from the surface of the sheet have some minimal irregularity (or "structure"), expressed by a value known as the "reflection density", whose measurement is also described below. (2) The base of the sheet comprises a first metal, and the protuberances from the surface of the sheet comprise a second metal. The first metal is selected to have a high thermal and electrical conductivity, and is preferably easily manufactured at a relatively low cost. In addition, the first metal is often more likely to cause degradation of the conductive polymer than the second metal. The fracture of the protuberances, caused by the thermal cycle of the device, and / or the thermal diffusion of the metals at elevated temperature, exposes the second metal rather than the first metal. It is believed that feature (1) is important, because it ensures that the conductive polymer penetrates the surface of the sheet, enough to provide a good mechanical bond. However, if the height of the protuberances is too large, the polymer will not completely fill the cracks between the protuberances, leaving a gap of air, which will result in accelerated aging of the conductive polymer, and / or faster corrosion of the polymer. polymer / metal interface that surrounds the air gap. Characteristic (2) is based on our discovery that the thermal cycle of the device will cause the fracture of some of the protuberances as a result of the different thermal expansion characteristics of the conductive polymer and the sheet, so it is important that this fracture does not expose the conductive polymer to a metal that promotes polymer degradation. In addition, it is important that a sufficient thickness of the second metal is in contact with the conductive polymer, so that, even when the first metal diffuses into the second metal at an elevated temperature, there is little opportunity for the first Metal make contact with the conductive polymer. In a first aspect, this invention describes an electrical device comprising: (A) an element composed of a conductive polymer; (B) at least one metal sheet electrode that: (1) comprises: (a) a base layer comprising a first metal, (b) an intermediate metal layer that (i) is placed between the base layer and a layer surface, and (ii) comprises a metal that is different from the first metal, and (c) a surface layer that (i) comprises a second metal, (ii) has an average roughness of the center line Ra of at least 1.3, and (iii) has a reflection density Rd of at least 0.60, and (2) is positioned in such a way that the surface layer is in direct physical contact with the conductive polymeric element. In a second aspect, this invention provides a circuit protection device, which comprises: (A) an element composed of a conductive polymer that exhibits a positive temperature coefficient behavior; and (B) two metal foil electrodes positioned on opposite sides of the conductive polymer element, each of which electrodes comprises: (1) a base layer comprising copper, (2) an intermediate layer which (a) is adjacent to the base layer, and (b) comprises nickel, and (3) a surface layer which (a) comprises nickel, (b) has an average roughness of the center line Ra of at least 1.3, and at most 2.5, (c) has a reflection density Rd of at least 0.60, and (d) is in direct physical contact with the conductive polymer element. In a third aspect, this invention provides an electrical circuit comprising: (A) a source of electrical energy; (B) a load; and (C) an electrical device, for example, a circuit protection device, of the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 shows a plan view of a device of the invention. Figure 2 shows a schematic cross-sectional view of a conventional metal foil. Figure 3 shows a schematic cross-sectional view of a metal sheet used in devices of the invention.

DETAILED DESCRIPTION OF THE INVENTION The electrical devices of the invention are prepared from an element composed of a conductive polymeric composition. The conductive polymer composition is one in which a particulate conductive filler is dispersed or distributed in a polymeric component. The composition exhibits in general a positive temperature coefficient (PTC) behavior, ie it shows an acute increase in resistivity with temperature over a relatively small temperature scale, although for some applications, the composition may exhibit a coefficient behavior of zero temperature (ZTC). In this specification, the term "PTC" is used to mean a composition or device having an R14 value of at least 2.5, and / or an R100 value of at least 10, and it is preferred that the composition or device have a value R30 of at least 6, where R1 is the proportion of the resistivities at the end and at the beginning of a scale of 14 ° C, R100 is the proportion of the resistivities at the end and at the beginning of a scale of 100 ° C, and R30 is the proportion of resistivities at the end and at the beginning of a scale of 30 ° C. In general, the compositions used in the devices of the invention, which exhibit a positive temperature coefficient behavior, show increases in resistivity that are much greater than these minimum values. The polymer component of the composition is preferably a crystalline organic polymer. Suitable crystalline polymers include polymers of one or more olefins, particularly polyethylene; copolymers of at least one olefin and at least one monomer copolymerizable therewith, such as copolymers of ethylene / acrylic acid, ethylene / ethyl acrylate, ethylene / vinyl acetate and ethylene / butyl acrylate; melt-configurable fluoropolymers, such as polyvinylidene fluoride and ethylene / tetrafluoroethylene copolymers (including terpolymers); and mixtures of two or more of these polymers. For some applications, it may be desirable to mix a crystalline polymer with another polymer, for example, an elastomer, an amorphous thermoplastic polymer, or another crystalline polymer, in order to achieve specific physical or thermal properties, for example, flexibility or exposure temperature maximum. The electrical devices of the invention are particularly useful when the conductive polymer composition comprises a polyolefin, due to the difficulty of bonding conventional metal foil electrodes with non-polar polyolefins. For applications where the composition is used in a circuit protection device, it is preferred that the crystalline polymer comprises polyethylene, particularly high density polyethylene, and / or an ethylene copolymer. The polymer component generally comprises 40 to 90 percent by volume, preferably 45 to 80 percent by volume, especially 50 to 75 percent by volume, of the total volume of the composition. The particulate conductive filler that is dispersed in the polymer component can be any suitable material, including carbon black, graphite, metal, metal oxide, conductive coated glass or ceramic granules, conductive particulate copolymer, or a combination thereof. same. The filler may be in the form of powder, granules, 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 percent by volume, preferably from 20 to 55 percent by volume, especially from 25 to 50 percent by volume, of the total volume of the composition. When used for circuit protection devices, the conductive polymer composition has a resistivity at 20 ° C, p20, of less than 10 ohm-cm, preferably less than 7 ohm-cm, particularly less than 5 ohm-cm, especially less than 3 ohm-cm, for example, from 0.005 to 2 ohm-cm. When the electrical device is a heater, the resistivity of the conductive polymer composition is preferably higher, for example, from 102 to 105 ohm-cm, preferably from 102 to 104 ohm-cm. The conductive polymer composition may comprise additional components, such as antioxidants, inert fillers, non-conductive fillers, radiation crosslinking agents (often referred to as prorads or crosslinking improvers), stabilizers, dispersing agents, coupling agents, acid scavengers ( example, CaC03), or other components. These components generally comprise at most 20 percent by volume of the total composition.

The dispersion of the conductive filler and other components can be achieved by melt processing, mixing with solvent, or any other suitable mixing element. Following the mixing, the composition can be fused by any suitable method to produce the element. Suitable methods include melt extrusion, injection molding, compression molding and sintering. For many applications, it is desirable that the compound be extruded into a sheet, from which the element can be cut, maked or otherwise removed. The element can be of any shape, for example, rectangular, square or circular. Depending on the intended end use, the composition can undergo different processing techniques, for example, crosslinking or heat treatment, next to the configuration. The crosslinking can be done by chemical elements, or by irradiation, for example, using an electron beam or a Co60 irradiation source, and can be done either before or after the electrode connection. The conductive polymer element may comprise one or more layers of a conductive polymer composition. For some applications, for example, where it is necessary to control the location in which a hot line or a hot zone corresponding to a region of high current density is formed, it is desirable to prepare the element from conducting polymer layers having different values of resistivity. Alternatively, it may be beneficial to apply a conductive bonding layer to the surface of the element to improve bonding to the electrode. Suitable conductive polymeric compositions are described in U.S. Patent Nos. 4,237,441 van Konynenburg et al.), 4,388,607 (Toy et al., 4,534,889 (van Konynenburg et al.), 4,545,926 (Fouts et al.), 4,560,498 (Horsma et al. ), 4,591,700 (Sopory), 4,724,417 (Au et al.), 4,774,024 (Deep et al.), 4,935,156 (van Konynenburg et al.), 5,049,850 (Evans et al.), And 5,250,228 (Baigrie et al.), And in Patent Applications. of the pending United States of America Numbers 07 / 894,119 (Chandler et al., filed on June 5, 1992), 08 / 085,859 (Chu et al., filed June 29, 1995), 08 / 173,444 (Chandler et al., filed on December 23, 1993), and 08 / 255,497 (Chu et al., filed on June 8, 1995.) The description of each of these patents and applications is incorporated herein. as reference. The devices of the invention comprise at least one electrode that is in direct physical contact with, and generally linked directly to, the conductive polymer element. For many devices of the invention, two electrodes are present, sandwiching the conductive polymer element. The electrode is generally in the form of a solid metal foil, for example, a foil, although for some applications, the electrode may be perforated, for example, it may contain holes or grooves. The electrode comprises at least two layers, that is, a base layer comprising a first metal, and a surface layer comprising a second metal. In addition, as discussed below, there may be one or more intermediate metallic layers present, each of which is placed between the base layer and the surface layer. The first metal, used in the base layer, can be any suitable material, for example, nickel, copper, aluminum, brass or zinc, but more often it is copper. Copper is preferred due to its excellent thermal and electrical conductivity, which allows a uniform distribution of electrical current through a device, the reproducibility of its production process, the ease of its manufacture that allows the production of continuous sections exempt from defects, and its relatively low cost. The base layer can be prepared by any suitable method. Copper, for example, can be prepared by lamination or electrodeposition. For some applications, it is preferred to use laminated nickel, produced by a powder metallurgical process, as the base layer. This nickel is more conductive than nickel prepared by a conventional electrodeposited process, due to the higher purity. The surface of the base layer may be relatively smooth, or it may be micro-rough. Microrough surfaces are generally those that have irregularities or nodes protruding from the surface by a distance of at least 0.03 microns, preferably at least 0.1 microns, particularly from 0.1 to 100 microns, and having at least one dimension parallel to the surface which is at most 500 microns, preferably at most 100 microns, particularly at 10 microns, and preferably at least 0.03 microns, particularly at least 0.1 microns. Each irregularity or nodule can be made up of smaller nodules, for example, in the form of a cluster of grapes. These micro-roughnesses are often produced by electrodeposition, where a metal foil is exposed to an electrolyte, but a microrough surface can also be achieved by removing material from a smooth surface, for example, by etching; by chemical reaction with a smooth surface, for example, by galvanic deposit; or by contacting a smooth surface with a surface in patterns, for example, by rolling, pressing, or embossing. In general, a sheet is said to have a smooth surface if its average roughness of the center line Ra is less than 1.0, and a microrough surface if Ra is greater than 1.0. It is often preferred that the surface of the base layer in contact with the intermediate layer have a Ra value of less than 1.0, preferably less than 0.9, particularly less than 0.8, especially less than 0.7. Metal foils with that smooth surface are generally difficult to bond to conductive polymeric compositions, especially if the conductive polymer composition has a high level of filler, and / or comprises a non-polar polymer. Ra is defined as the arithmetic average deviation of the absolute values of the roughness profile from the average line or center line of a surface, when measured using a profilometer having a style with a radius of 5 microns. The value of the center line is such that the sum of all the areas of the profile above the center line is equal to the sum of all the areas below the center line, when viewed at right angles to the sheet. Appropriate measurements can be made by using a Tencor P-2 profilometer available in Tencor Therefore Ra is a caliber of the height of the protuberances from the surface of the sheet. The surface layer is in direct physical contact with the base layer, or preferably, is separated from the base layer by one or more intermediate conductive layers, preferably metallic. The surface layer comprises a second metal that is different from the first metal. Suitable second metals include nickel, copper, brass or zinc, but for many devices of the invention, the second metal is more often nickel, or a material containing nickel, for example, zinc-nickel. Nickel is preferred because it provides a diffusion barrier for a copper base layer, thereby minimizing the rate at which copper comes in contact with the polymer, and serves to degrade the polymer. In addition, a surface layer of nickel will naturally comprise a thin nickel oxide covering layer, which is stable to moisture. The surface layer is in direct physical contact with the conductive polymer element. To improve adhesion to the conductive polymeric element, the surface layer has a microrough surface, that is, it has an average roughness of the centerline Ra of at least 1.3, preferably when 1.4, particularly at least 1.5. Although it is desirable that the protuberances from the surface be sufficiently high to allow adequate penetration of the polymer into the voids to produce a good mechanical bond, it is not desirable that the height of the protuberances be so large that the polymer can not fill the void. completely. This air gap results in an aging malfunction when a device is exposed to a high temperature or an applied voltage. Accordingly, it is preferred that Ra be at most 2.5, preferably at most 2.2, particularly at a lot 2.0. We have discovered that, in addition to the required Ra, the surface layer must also have a particular reflection density Rd. The reflection density is defined as the logarithm (1 /% of reflected light) when the light on the visible scale (is say, 200 to 700 nanometers) is directed towards the surface. An average of measurements is calculated, each one taken over an area of 4 mm2. Appropriate measurements can be made using a Macbeth Model 1130 Color Checker in the automatic filter selection mode "L" with calibration of a black standard at 1.61 before measurement. For a surface with a perfect reflection the value Rd is 0; the value increases as the amount of light absorbed increases. Higher values indicate a greater structure in the protuberances from the surface. For the devices of the invention, the value Rd is at least 0.60, preferably at least 0.65, particularly at least 0.70, especially at least 0.75, and more especially at least 0.80. When an intermediate layer is present, as preferred, it may comprise the second metal or a third metal. The metal of the intermediate layer may not be the same as the first metal. It is preferred that the intermediate layer comprises the second metal. In a preferred embodiment, the intermediate layer comprises a generally smooth layer bonded to the base layer. The intermediate layer then serves as a base, from which a microrough surface layer can be prepared. For example, if the base layer is copper, the intermediate layer can be a generally smooth layer of nickel, from which nickel nodules can be produced on the electrodeposition, to provide a surface layer. The metal electrodes can be attached to the conductive polymer element by any suitable element, for example, compression molding or clamping lamination. Different types and thicknesses of metal sheets may be suitable depending on the viscosity of the conductive polymer and the conditions of the lamination. To provide adequate flexibility and adhesion, it is preferred that the metal sheet has a thickness of less than 50 microns (0.002 inches), particularly less than 44 microns (0.00175 inches), especially less than 38 microns (0.0015 inches), and more especially less than 32 microns (0.00125 inches) ). In general, the thickness of the base layer is 10 to 45 microns (0.0004 to 0.0018 inches), preferably 10 to 40 microns (0.0004 to 0.0017 inches). The thickness of the surface layer is generally 0.5 to 20 microns (0.00002 to 0.0008 inches), preferably 0.5 to 15 microns (0.00002 to 0.0006 inches), particularly 0.7 to 10 microns (0.00003 to 0.0004 inches). If an intermediate layer is present, it generally has a thickness of 0.5 to 20 microns (0.00002 to 0.0008 inches), preferably 0.8 to 15 microns (0.00003 to 0.0006 inches). When the layer comprises a microrough surface, the term "thickness" is used to refer to the average height of the nodes. A measurement of the property of the union of the metal electrode to the conductive polymeric composition is by the resistance to separation. The resistance to separation, as described below, is measured by holding one end of a sample in the jaw of a tester, and then separating the sheet at a constant speed of 127 millimeters / minute (5 inches / minute), and at an angle of 90 °, that is, perpendicular to the surface of the sample. The amount of force in pounds / linear inch required to remove the sheet of conductive polymer is recorded. It is preferred that the electrode have a separation strength of at least 3.0 pli, preferably at least 3.5 pli, particularly at least 4.0 pli, when attached to the conductive polymer composition. The electrical devices of the invention can comprise circuit protection devices, heaters, sensors or resistors. Circuit protection devices generally have a resistance of less than 100 ohms, preferably less than 50 ohms, particularly less than 30 ohms, especially less than 20 ohms, and more especially less than 10 ohms. For many applications, the resistance of the circuit protection device is less than 1 ohm, for example, 0.010 to 0.500 ohms. The heaters generally have a resistance of at least 100 ohms, preferably at least 250 ohms, particularly at least 500 ohms. The electrical devices of the invention are often used in an electrical circuit comprising a source of electrical energy, a load, for example, one or more resistors and the device. In order to connect an electrical device of the invention to the other components of the circuit, it may be necessary to join one or more additional metal conductors, for example, in the form of wires or cables, to the metal foil electrodes. In addition, elements can be used to control the thermal output of the device, i.e., one or more conductive terminals. These terminals may be in the form of metal plates, for example, of steel, copper or brass, or fins that are attached, either directly or by means of an intermediate layer, such as welding or a conductive adhesive, to the electrodes . See, for example, U.S. Patent No. 5,089,801 (Chan et al.), And pending U.S. Patent Application No. 07 / 837,527 (Chan et al.), Filed on February 18, 1992. For some applications, it is preferred to attach the devices directly to a circuit board. Examples of these connection techniques are shown in U.S. Patent Applications Serial Nos. 07 / 910,950 (Graves et al., Filed July 9, 1992), 08 / 121,717 (Siden et al., Filed on September 15, 1993), and 08 / 242,916 (Zhang et al., filed May 13, 1994), and in International Application Number PCT / US93 / 06480 (Raychem Corporation, presented on July 8, 1993). The description of each of these patents and applications is incorporated herein by reference. The invention is illustrated by the drawing, wherein the Figure 1 shows a plan view of the electrical device 1 of the invention, wherein the metal foil electrodes 3, 5 are directly joined to a conductive polymer element of positive temperature coefficient 7. The element 7 may comprise a single layer, as it is shown, or two or more layers of the same compositions or of different compositions. Figure 2 shows a schematic cross-sectional view of a conventional metal sheet to be used as an electrode 3, 5. A base layer 9 comprising a first metal, eg, copper, has a microrough surface preferably produced by electrodeposition. The nodules 11 comprising the microrough surface are composed of the first metal. A surface layer 13 of a second metal, eg, nickel, covers the nodes 11. Figure 3 shows a schematic cross-sectional view of a metal sheet used as an electrode 3.5 in the devices of the invention. A base layer 9 comprising a first metal, for example copper, is in contact with an intermediate layer 15 comprising a second metal, for example, nickel. The surface of the intermediate layer forms the basis for a surface layer 17, which has a micro-rough surface. As shown in Figure 3, the nodes comprising the surface layer 17 are formed from the second metal. The invention is illustrated by the following Examples 1 to 9, in which Examples 1, 2, 4, 7 and 8 are comparative examples.

Composition For each of the compositions A and B, the ingredients mentioned in Table I were previously mixed in a Henschel mixer, and then mixed in a Buss-Condux mixer. The composite was granulated and extruded through a die of sheet to give a sheet with dimensions of approximately 0.30 m x 0.25 mm (12 x 0.010 inches).

TABLE I Compositions in Percentage in Weight Sheet Type The characteristics of the metal sheets used in the Examples are shown in Table II. Each metal sheet was approximately 35 microns thick.

TABLE II Characteristics of the Metal Sheet ' Preparation of the Device 0 The extruded sheet was laminated to the metal sheet, either by compression molding (C), in a press, or by tightening lamination (N). In the compression molding process, the extruded sheet was cut into pieces with dimensions of 0.30 x 0.41 meters (12 x 16 inches), and was sandwiched between two pieces of sheet. The pressure-absorbing silicone sheets were placed on the sheet, and the sheet was joined by heating in the press at 175 ° C for 5.5 minutes, at 13.16 kg / cm2, and by cooling at 25 ° C for 6 minutes at 13.16 kg. / cm2, to form a plate. In the tightening lamination process, the extruded sheet was laminated between two layers of sheet at a set temperature of 177 ° C to 198 ° C (350 ° F to 390 ° F). The laminate was cut into plates with dimensions of 0.30 x 0.41 meters (12 x 16 inches). The plates made by both processes were irradiated at 10 Mrad, using a 3.5 MeV electron beam. Individual devices were cut from the irradiated plates. For the tests of durability to the shot and life of the cycle, the devices were circular discs with an external diameter of 13.6 millimeters (0.537 inches), and an internal diameter of 4.4 millimeters (0.172 inches). For the humidity test, the devices had dimensions of 12.7 x 12.7 millimeters (0.5 x 0.5 inches). Each device was placed at the temperature from -40 ° C to + 80 ° C six times, keeping the device at each temperature for 30 minutes.

Shock Durability Test The devices were tested for trip durability by using a circuit consisting of the serial device with a switch, a 15 volt DC power source, and a fixed resistor that limited the initial current to 40A. The initial resistance of the device at 25 ° C, Ri was measured. The device was inserted into the circuit, fired and then kept in its fired state for the specified period of time. Periodically, the devices were removed from the circuit, and cooled to 25 ° C, and the final resistance was measured at 25 ° C, Rf.

Cycle Life Test The devices were tested for cycle life using a circuit consisting of a serial device with a switch, a 15 volt DC power source, and a fixed resistor that limited the initial current to 50A. Before the test, resistance at 25 ° C, R¿ was measured. The test consisted of a series of test cycles. Each cycle consisted in closing the switch for 3 seconds, firing the device in this way, and then opening the switch and allowing the device to cool down for 60 seconds. The final resistance Rf was recorded after each cycle.

Moisture Test After measuring the initial resistance R? at 25 ° C, devices were inserted in an oven maintained at 85 ° C and with 85 percent humidity. Periodically, the devices were removed from the furnace, cooled to 25 ° C, and the final resistance Rf was measured. Then the ratio of Rf / Rj was determined ..

Resistance to Separation Resistance to separation was measured by cutting samples with dimensions of 25.4 x 254 millimeters (1 x 10 inches), from the extruded sheet attached to the metal sheet. One end of the sample was held in a Tinius Olsen tester. At the other end, the sheet was separated from the conductive polymer at a 90 ° angle and at a speed of 127 millimeters / minute (5 inches / minute). The amount of force in pounds / linear inch required to remove the sheet of conductive polymer was recorded.

TABLE III * Example 2 was tested at 85 ° C / 90% humidity.

Examples 8 v 9 Following the above procedures, and using a tightening / laminating process at 185 ° C, devices were prepared from a composition comprising 28.5 weight percent of ethylene / butyl acrylate copolymer Enathene EA 705, 23.4 percent by weight of Petrothene high density polyethylene LB832; and 48.1 percent by weight of Raven 430 carbon black. The devices were tested as described above for shot durability, cycle life and humidity. An additional test was conducted following the cycle test up to 3,500 cycles and in storage at room temperature (25 ° C) for approximately three months. Ten devices of each type, which had cycled 3,500 cycles at 15 VDC and at 40A, were aged in a circulating air oven at 100 ° C for 600 hours, or at 85 ° C / 85 percent humidity for 600 hours. Periodically, the devices were cooled to 25 ° C, and their resistances were measured. The devices of the invention (Example 9) wherein the nodules were nickel, showed a better aging behavior than the devices prepared with conventional metal foil electrodes, where the nodes were copper (Example 8). The results are shown in Table IV. A metal electrode of a device of each of Examples 8 and 9, which had been aged at 100 ° C for 170 hours, was separated from the polymeric element, and the surface that had been in contact with the conductive polymer composition was analyzed by this, to determine the elemental composition of the surface (ie, the top 10 nanometers). The average of the measurements for two different regions of the surface is shown in Table V. As a control, the samples of the metal sheet used to prepare the electrode were aged in air for 24 hours at 200 ° C, to simulate the exposure Thermal film during processing and testing. The results are shown in Table V. The detection limit of the equipment was 0.1 atomic percent.

TABLE IV TABLE V ESCA Test Results * Less than 0.1% atomic

Claims (10)

1. An electrical device (1), which comprises: (A) an element (7) composed of a conductive polymer; and (B) at least one metal foil electrode (3) which: (1) comprises: (a) a base layer (9) comprising a first metal, (b) an intermediate metal layer (15), which (i) is placed between the base layer (9) and a surface layer (17), and (ii) comprises a metal that is different from the first metal, and (c) a surface layer (17) which (i) comprises a second metal, (ii) has an average roughness of the centerline Ra of at least 1.3, and (iii) has a reflection density Rd of at least 0.60, and (2) is positioned in such a manner that the surface layer (17) ) is in direct physical contact with the conductive polymer element (7).

2. A device according to the claim 1, where the first metal is copper or brass.

3. A device according to claim 1, wherein the second metal is nickel.

4. A device according to claim 1, 2 or 3, wherein the metal of the intermediate layer (15) is the same as the metal of the surface layer (17).

5. A device according to claim 1, 2 or 3, wherein Ra is at most 2.5.

6. A device according to claim 1, 2 or 3, wherein the base layer (9) has a surface that (a) has an average roughness of the center line Ra of less than 1.0, and (b) makes contact with the intermediate layer.

A device according to claim 1, 2 or 3, wherein the conductive polymer (a) exhibits a positive temperature coefficient behavior, and (b) comprises a polyolefin or a fluoropolymer, and dispersed therein, a conductive filler in particles.

8. A device according to claim 1, 2 or 3, which comprises two metal foil electrodes (3, 5), and is (a) a circuit protection device that has a resistance less than 50 ohms, or (b) a heater that has a resistance of at least 100 ohm.s

9. A device in accordance with claim 1, 2 or 3, wherein the surface layer (17) is composed of nodules (11), each of which is composed of a number of smaller nodes.

10. An electrical circuit, which comprises: (A) a source of electrical energy; (B) a load; and (C) a circuit protection device according to claim 1.