Conductive polymeric article

Abstract: A tubular heat recoverable article comprises electri­ cally conductive polymeric material and can be recovered by passing an electric current therethrough. The article comprises two or more elongate electrodes extending at least part way along the article. One or more of the electrodes are interrupted so that so that separate lengths of the article can be connected to an electrical power source and heated and or recovered independently.

Description: This invention relates to an article which comprises a conductive polymeric material, which can be heated by passing electrical current through the conductive polymeric material, and particularly to an article in which heat is generated in a selected area only of the article. Conductive polymeric materials and devices incorporating them are also well known. Reference may be made for example U.S. Patents Nos. 2,952,761, 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,658,976, 3,757,086, 3,793,716, 3,823,217, 3,858,144, 3,861,029, 3,950,604, 4,017,715, 4,072,848, 4,085,286, 4,117,312, 4,151,126, 4,177,376, 4,177,446, 4,188,276, 4,237,441, 4,242,573, 4,246,468, 4,250,400, 4,252,692, 4,255,698, 4,271,350, 4,272,471, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,314,231, 4,315,237, 4,317,027, 4,318,881, 4,327,351, 4,330,704, 4,334,351, 4,352,083, 4,361,799, 4,388,607, 4,398,084, 4,413,301, 4,425,397, 4,426,339, 4,426,633, 4,427,877, 4,435,639, 4,429,216, 4,442,139, 4,459,473, 4,470,898, 4,481,498, 4,476,450, 4,502,929; 4,514,620, 4,517,449, 4,534,889, and 4,560,498; J. Applied Polymer Science 19 , 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18 , 649-653 (1978), Narkis et al; European Application Nos. 38,713, 38,714, 38,718, 74,281, 92,406, 119,807, 133,748, 134,145, 144,187, 157,640, 158,410, 175,550 and 176,284; and Japanese Published Patent Application No. 59-122,524. We have discovered a new conductive polymeric article which can be heat recoverable and used as a heat recoverable cover, and/or can be an electrically powered article. A heat-recoverable article is an article the dimensional configuration of which may be made subtantially to change when subjected to heat treatment. Usually these articles recover, on heating, towards an original shape from which they have previously been deformed, but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed. Heat recoverable articles are known. In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Patents 2,027,962, 3,086,242 and 3,597,372. As is made clear in, for example, U.S. Patent 2,027,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form. In other applications, a preformed dimensionally heat stable article is deformed to a dimensionally heat unstable form in a separate stage. In other articles, an elastomeric member is held in a stretched state by a second member, which, upon heating weakens and thus allows the elastomeric member to recover. Heat-recoverable articles of this type are described, for example, in British Patent 1,440,524 in which an outer tubular elastomeric member is held in a stretched state by an inner tubular member. Alternatively, the "hold-out" layer could be on the outside. Heat-recoverable articles which comprise conductive polymeric materials, and which use ohmic heating of those materials to cause heat recovery are also known. Reference may be made for example to GB 1265194 (MPO99), US 4085286 (MP192), US 4017715 (MP0212), US 4421582 (MP0219), European Patent Publication No. 0157640 (MP0922) and US 4570055 (MP0939). A heater which comprises a conductive polymeric material and which is arranged so that pre-selected areas only of the heater are heated is described in EP-A-0128664. This patent forms the basis of the preamble of the claims of the present invention The heater of EP-A-0128664 (which may also be heat recoverable) comprises two laminar electrodes having a conductive polymeric laminar heating element sandwiched therebetween. Electrical power supplied to the electrodes causes electrical current to flow through the thickness of the article. An electrical discontinuity in the form of a channel is cut in one or both of the electrodes, so that when the electrical power is applied, pre-selected areas only of the heater are heated. It is also known to be desirable to use for a conductive recoverable article, a material which exhibits a PTC (positive temperature coefficient of resistivity) effect, that is a sharp rise in resistivity at a particular, or over a short range of temperatures. This temperature or temperature range is known as the anomaly or switching temperature. Typically the material is selected to exhibit the sharp rise in temperature at or slightly above the recovery temperature of the article. The PTC effect minimises overheating and consequent so-called "thermal runaway" of the material. Materials which exhibit a PTC effect are typically referred to simply as PTC materials. An article according to the invention is tubular and has elongate electrodes extending along its length which when connected to a source of electrical power causes electrical current to flow between the electrodes around the circumference of the article. In order to heat and/or recover selected parts only of the article, the electrode (which extends along the entire length of the article) may be interrupted. Thus a first aspect of the invention provides an article comprising conductive polymeric material having two or more electrodes each in electrical contact with the conductive polymeric material, the article being arranged so that when the electrodes are connected to an electrical power source a selected part only of the article is heated by the passage of electrical current from the power source, characterised in that the article is tubular, and the electrodes are elongate and extend at least part way along the length of the article, and at least one of the electrodes is interrupted so that the electrical power source can be selectively connected to the article to cause electrical current to pass between the electrodes around the circumference of the article and through a first length only of the article. The term "interrupted" means that there is a discontinuity in the length of the electrode. The interrupted electrode may have been made by starting with a longer continuous electrode and removing part of its length (other than at one end). Alternatively the "interrupted" electrode may be made by applying two discrete electrode lengths. There is no direct, low resistance, electrical connection between the parts of the interrupted electrode. Tubular articles according to the invention may be of open (wraparound) or closed cross-section. When tubular articles are used they may be open at one or both ends. As used herein the term "wraparound" means a cover which can be wrapped around a substrate, with longitudinal edges secured together to form a tubular article around the substrate. The term does not include wrapped tape. A feature of this article is that it can be made in a continuous process in long lengths and then later cut to the desired length. The above arrangement enables the first length of the interrupted electrode(s), on one side of the interruption, to be connected to a source of electrical power independently of the remaining part of the electrode. Several interruptions may be made in the electrodes if desired. This invention is advantageous where it is desirable to heat or recover only one part of the tubular article, or where it is desired to heat or recover that portion at a different time. For example, one part of an article may be heated to activate or cure an underlying adhesive or sealant before a second part is heated. One or more parts of the article can be used to deliver adhesive or sealant to an area before another part of the article is heated. The article according to the invention may be expanded to render it recoverable or it may be non expanded, and hence heat-stable. Thus the article may be a recoverable cover and/or heater or a heat stable heater. European publication no. EP-A-0307206 (DK003 EP) describes a heat recoverable article (preferably tubular) which comprises electrically conductive recoverable material, and is provided with at least two integrally formed spaced apart support elements. The support elements also comprise electrically conductive material and are dimensionally heat stable, so that they remain undeformed during recovery, other than bending to accommodate transitions. The arrangement ensures good contact is maintained throughout recovery of the article. This arrangement is suitable for use in the present invention, the electrodes (which are interrupted, or are to be interrupted) being positioned on or in the support elements, which are typically in the form of elongate flanges. European publication no. EP-A-0207200 (DK004 EP) describes a heat recoverable conductive polymeric, preferably tubular, article with longitudinal electrodes extending part way only along its length. European publication no EP-A-0307207 (DK005 EP), discloses articles comprising a material with specific electrical properties to control the direction of current flow. One article according to European publication no EP-A-0307207 (DK005 EP) has been expanded from X% to Y% to make it heat recoverable, the article comprising a conductive polymeric material the resistivity of which decreases on expansion, as measured in the direction of current flow, in at least part of the X - Y% expansion range. Another article according to the invention is heat recoverable and comprises a conductive polymeric material which has a resistivity which increases on recovery, as measured in the direction of current flow, throughout the temperature range 20°C to Te ( extrapolated end temperature, as measured according to ASTM D3418-82). Other articles according to that invention have a so-called pseudo-PTC ratio (peak resistivity: resistivity at 25°C in the range 1% to 10), and are connected to electrodes so that current flows parallel to the faces of the article. Preferred articles are expanded to render them recoverable and the resistivity of the composition of the articles decreases in at least part of the expansion range when expanded by 25% or more, for example by 25 - 500%. European publication no EP-A-0307197 (RK352-A EP) describes a tubular article which comprises a conductive polymeric material and is preferably heat recoverable and which can apply a radially inward force on a substrate therein This can be used to join or repair a substrate e.g. a cable or a pipe. It can, for example, melt a polymeric patch between the article and the substrate. It is preferably multi-part or wraparound, for easy installation European publication no EP-A-0307199 (DK006 GB) describes a tubular conductive polymeric article which has particular application as a duct seal, and which increases in thickness on recovery. It preferably has three Longitudinal sections, which are all electroded separately. The end sections shrink radially, and the central section increases in thickness. According to the present invention, the longitudinal sections may comprise interrupted elongate electrodes. The interrupted electrodes of the present invention may be used in any of the above described articles. As mentioned above, in preferred embodiments the electrodes are provided in or on longitudinal flanges extending along the length of the article. Such an arrangement is described in European publication no. EP-A-0307206 (DK003 EP). In these cases the interruption in the electrodes is preferably effected by making a cut through the flanges and associated electrodes, so that there is an electrically insulating space between the cut ends of the electrode. A second aspect of the invention provides a method of making a selectively heatable or selectively recoverable article comprising: forming an article comprising conductive polymeric material; providing two or more electrodes in electrical contact with the conductive polymeric material; and interrupting the electrical continuity of at least one electrode, characterised in that: (a) the conductive polymeric article is formed in tubular configuration; (b) the electrodes are longitudinal and arranged to extend along the article; and (c) the electrical discontinuity provided in at least one of the electrodes defines a first electrode part and a remaining electrode part, one or both of which can be separately connected to an electrical power source to cause electrical current to pass between the electrodes around the circumference of the article, thereby separately heating or recovering the said first and the said remaining electrode part. In a preferred embodiment the tubular article is provided with longitudinal conductive polymeric flanges extending along at least part of the length of the article, and the electrodes are provided in or on these flanges. In this case the electrical continuity of the electrode(s) may be interrupted, for example, by cutting and removing a section of each flange, part-way along the length of the electrode(s). Where the electrodes are provided on the surface of the flanges or the surface of the body of the article, e.g. by silver conductive ink or paint, they may be mechanically removed, e.g. by abrading. As an alternative the electrodes may be provided interrupted in the first instance. In this case the article is a selectively heatable or selectively recoverable tubular article comprising: (a) a tubular article comprising conductive polymeric material, and (b) three or more longitudinal electrodes extending along the article, at least two of which extend along the same line but are separated from each other. The two electrodes that are separated from each other may nonetheless be electrically connected via a higher resistivity medium (ie the conductive polymeric material of the main body of the article). There is however no direct low resistance electrical connection between the electrodes. Also there may be a mass of insulating material between the separated electrodes. The invention also envisages a method of making this article comprising providing the constituent parts thereof. In use, to heat or to recover selected parts of a tubular article according to the invention, a first part of each electrode is preferably connected to a source of electrical power to cause current to flow between said first parts. Optionally the remaining parts of each electrode (if both contain a discontinuity) are separately connected to an electrical power source to cause electrical current to flow between said remaining electrode parts. The concept of independently electroding and heating/recovering different sections of a conductive polymeric article is an important aspect of the present invention. Preferred compositions for use in the present invention are described in European publication no. EP-A-0307205 (RK365 EP). One material that can be used is 59.4 parts by weight Elvax 460 (an E.V.A. of 18% by weight vinyl acetate content and a melt flow index of 2.5, as supplied by Du Pont), 39.6 parts by weight of Vulcan P (a carbon black supplied by Cabot Corporation) and 1 part by weight antioxidant. Other suitable examples are: Polymer (parts by weight) Carbon Black (parts by weight) Antioxidant (parts by weight) Marlex HXM 50100 (59.4) Vulcan P (39.6) (1.0) Elvax 460 (59.4) Sevalco N110 (39.6) (1.0) Sclair 11D-1 (59.4) Ensaco MS (39.6) (1.0) Elvax 770 (59.4) Vulcan P (39.6) (1.0) The polymeric materials used as follows: Marlex is a HDPE supplied by Phillips Elvax 460 - described earlier Sclair 11D-1 is a LLDPE supplied by Du Pont, Canada Elvax 770 is an EVA supplied by Du Pont. Vulcan P, Ensaco MS and Sevalco N110 carbon blacks are supplied by Cabot Corporation, Ensagri Willebroek NV and Sevalco Ltd respectively. One preferred article according to the invention is a tubular article which has been expanded radially and has two or more, preferably three separately radially shrinkable sections. The article preferably comprises longitudinally separated pairs of electrodes (one pair for each separately radially shrinkable section) arranged to shrink each of the sections. One example of such an article is for cable blocking a cable splice, e.g. a splice between optical fibres. For this application there are three separately radially shrinkable sections. The central section contains a large mass of adhesive or other sealant, for cable blocking. The end sections are lined with adhesive, e.g. a hot melt adhesive, for bonding to the cables. For cable blocking and similar applications, there is not necessarily a requirement for the inner surface of the article to be smooth (since the substrate may not be). Thus in the preferred case where the electrodes are provided on heat stable flanges projecting from the surface of the article (as described in British Patent Application 8810522 (DK003 GB5) these flanges may project outwardly from or inwardly into the article, or both. Another preferred article, which is recoverable, comprises a conductive polymeric hold-out layer which holds in a stretched state an elastomeric layer. The hold-out layer may be the inner or outer layer. The elastomeric layer is allowed to recover when the conductive layer heats. Where the article is tubular with one or more open ends, it may be desirable to seal between two or more substrates exiting the open end. This can be achieved using a branch-off clip (e.g. as disclosed in US 4648924) which brings together circumferentially spaced portions of the walls of the article between the substrates. Preferably an electrically heated branch-off clip is used. As an alternative an electrically heated filling piece may be used. The electrically heated clip and filling piece may be powered by the same power supply that is used to heat and recover the article. In articles according to the invention, the wall thickness of the article may be varied along its length. Also two or more layers of different materials may be used. The second or additional layer may extend along the whole or along part of the length of the article. They may have electrical properties e.g. room temperature resistivity and resistivity/temperature behaviour, that are the same as, or different to, that of the first material. As an example, the second or subsequent layers may comprise a material that exhibits traditional PTC behavlour or ZTC (zero temperature coefficient of resistivity) behaviour. The effect of the additional layer(s) is that it (they) provide additional material through which electrical current can flow, and hence provide additional heating. By appropriate choice of the resistivity of the material of the additional layer(s) greater heating can be achieved than would be the case were a similar additional thickness of the first material used. This may be advantageous, for example to decrease recovery times in certain regions, or where a higher temperature is required. Therefore in some preferred embodiments second or subsequent layers of material different to the first material are added in selected regions. Another example of using two layers of different materials is where certain properties, e.g. flame retardancy, solvent resistance, abrasion resistance, electrical insulation, impact resistance, colour coding are required. Where two or more layers are used these may be applied separately, for example by sequential extrusion or may be coextruded. The present invention may be utilised in a variety of articles of different shapes. They are generally tubular, including wraparounds, and may be open at one or both ends. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 shows a recoverable article according to the invention; Figure 2 shows the article of Figure 1, with separated electrodes; Figure 3 shows the article of Figure 2, one end of which has been recovery onto a substrate; and Referring now to the drawings, Figure 1 shows a tubular article 2 and comprising a conductive polymeric material. The main body of the article has been expanded to make it recoverable. Electrodes 4 in the form of wires 4 extend in heat stable conductive polymeric flanges 6 along the length of the article. Figure 2 shows the article of Figure 1, in which the electrodes have been interrupted by a notch 8. This enables section 10 (to the left of notch 8 in the drawings) to be heated/recovered independently of part 12 (to the right of notch 8 in the drawings.) Notch 8 can be made with a suitable cutting tool. The flanges 6 are cut back at one end to bare projecting portions 4 which can be connected to a power source 15. As an alternative method of contacting the electrodes, insulation - displacement type devices could be used. Figure 3 shows the article 2' with one end 10' recovered onto pipe 16, (superscript indicates recovered part).

Claims: An article (2) comprising conductive polymeric material having two or more electrodes (4) each in electrical contact with the conductive polymeric material, the article being arranged so that when the electrodes are connected to an electrical power source (15) a selected part only of the article is heated by the passage of electrical current from the power source, characterised in that the article is tubular, and the electrodes are elongate and extend at least part way along the length of the article, and at least one of the electrodes is interrupted so that the electrical power source (15) can be selectively connected to the article to cause electrical current to pass between the electrodes around the circumference of the article and through a first length only of the article. An article according to claim 1, wherein the electrodes (4) are provided in or on longitudinal conductive polymeric flanges (6) extending at least part way along the length of the article. An article according to claim 2, wherein the electrodes are interrupted by cutting through the flange so that there is an electrically insulating space between the cut ends of the electrodes. An article according to any preceding claim, which is heat recoverable. An article according to claim 1 which comprises three or more longitudinal electrodes extending along the length of the article, at least two of which extend along the same line, but are separated from each other. An article according to claim 5 comprising three selectively heatable and recoverable longitudinal sections, each of which is provided with a pair of longitudinal electrodes arranged so that electrical current flows around the circumference of the article, each of the pairs of electrodes being separated from the adjacent pair(s) of electrodes, so that each pair can be separately connected to a source of electrical power and hence each of said longitudinal sections can be heated and/or recovered independently of the other of said sections. An article according to claim 5 or 6, wherein one of the sections of the article can be used to deliver adhesive or sealant before a second section is recovered. An article according to any preceding claim comprising a material which has been expanded by 25% or more to render it recoverable, wherein the material decreases in resistivity in at least part of the expansion range on said expansion, or the material exhibits a pseudo PTC ratio in the range 1.5 to 10. An article according to any preceding claim, wherein at least one end of at least one electrode terminates in a body of conductive polymeric material, thereby defining an inwardly directed electrode end. A method of making a selectively heatable or selectively recoverable article comprising: forming an article (2) comprising conductive polymeric material; providing two or more electrodes (4) in electrical contact with the conductive polymeric material; and interrupting the electrical continuity of at least one electrode, characterised in that: (a) the conductive polymeric article is formed in tubular configuration; (b) the electrodes are longitudinal and arranged to extend along the article; and (c) the electrical discontinuity provided in at least one of the electrodes defines a first electrode part and a remaining electrode part, one or both of which can be separately connected to an electrical power source (15) to cause electrical current to pass between the electrodes around the circumference of the article, thereby separately heating or recovering the said first and the said remaining electrode part. A method according to claim 10, wherein the tubular article is provided with longitudinal conductive polymeric flanges (6) extending along at least part of the length of the article, with electrodes (4) provided in or on the flanges. A method according to claim 11, wherein the electrical continuity is interrupted by cutting and removing a section of at least one flange, part-way along the length of at least one electrode.

Inventors: GANSBUEHLER GEORGE MICHAEL JOH, JENSON PER, GANSBUEHLER, GEORGE MICHAEL JOHN, JENSON, PER
Applicants: RAYCHEM LTD, RAYCHEM LIMITED
Application year: 1988
Main classification: B29C61
IPC codes: B29C65, G02B6, H05B3, B29C63, H01C7, H02G15, B29D23, B29C61, B29K105