DOUBLE WALLED TUBULAR ARTICLE

Abstract: A tubular article comprises a double walled tube (1), preferably of an elastomeric material having a friction reducing means (4) between the two walls (23) of the double wall. The friction reducing means comprising a liquid containing dispersed particles, preferably solid particles, having an average particle size of about 0.1 to about 1000 microns. The liquid is preferably a low viscosity liquid and is preferably dimethyl siloxane. The particles are preferably of sodium stearate.

Description: DOUBLE WALLED TUBULAR ARTICLE Background of the Invention This invention relates to a double wall elastomeric tubular article and to its use in covering an elongate substrate, such as a cable or pipe. Double wall tubular article of the type of this invention are disclosed in U.S. Patent No. 4,868,967 to Holt et al and European published patent application EP281,353 to Chang, the entire disclosures of which are incorporated herein by reference. As taught in these references a friction reducing means is provided between the walls of the double walled article. Particularly preferred friction reducing means are pituitous liquids, such as solutions of high molecular weight polymers. The articles are useful for covering substrates such as cables, pipelines or the like. In certain instances it is desirable that only a single layer of elastomeric material be applied over the substrate, for example when the article is used to repair the jacket on a cable subject to abrasion. As taught in U.S. Patent No.4,868,967 and EP281,353, an annular ring cut may be made in the outer wall which can then be unfolded, or slid, into contact with the substrate. It has been found that if a pituitous liquid or silicone oil, as preferred in the prior disclosures, is used, the amount of friction reducing means required to install the article over the substrate results in an undesirably messy application. This is particularly true if the friction reducing means is a pituitous liquid. However, it has been found that if a low viscosity liquid is used, the article is extremely difficult to install and cannot be installed over substrates of different diameters. It has now been found that by the appropriate selection of friction reducing means significantly less friction reducing means is required and an attractive low profile product results. Summary of the Invention One aspect of this invention comprises a tubular article comprising a double walled tube having a friction reducing means between the two walls of the double wall, the friction reducing means comprising a liquid having dispersed therein particles having an average particle size of about 0.1 to about 1000 microns, the particles being substantially insoluble in the liquid. Another aspect of this invention comprises a method of covering an elongate substrate which comprises revolving onto the substrate a tubular article comprising a double walled tube having a friction reducing means between the two wall of the double wall, the friction reducing means comprising a liquid having dispersed therein particles having an average particle size of about 0.1 to about 1000 microns, the particles being substantially insoluble in the liquid. Brief Description of the Drawings Figure la is a perspective view of a first embodiment of the invention comprising a double-walled article; Figure lb is a transverse cross-sectional view of the article; Figure lc is an axial cross-sectional view of the article; Figure 2 illustrates a preferred method of forming the article; Figure 3a illustrates an initial revolving action; Figure 3b illustrates subsequent revolving action; Figure 3c illustrates the installed article; Detailed Description of the Invention A key feature of the article of this invention is the friction reducing means, or lubricant, used between the walls of a double wall tubular article. The friction reducing means utilized in the practice of this invention comprises a liquid having insoluble particles dispersed therein . The liquid is preferably a low viscosity liquid, for example a liquid having a viscosity of about 1 to about 1000 centistokes, more preferably about 5 to about 500 and most preferable about 5 to about 250 centistokes. Preferred liquids are low viscosity liquid silicones, for example dimethyl siloxane, aqueous or glycol solutions of soluble polymers, mineral oils, vegetable oils, polyols, water, surfactants, liquid high molecular weight alcohols and the like. Dispersed in the liquid are particles having an average particle size of about 1 to about 1000 microns.preferably about 50 to about 500 and more preferably about 50 to about 300 microns. The particles are preferable solid and should be substantially insoluble in the liquid. In an alternative embodiment, the particles may be droplets of a second liquid substantially insoluble in the first. The term substantially insoluble means that less than about 50%, preferably less than about 40% and most preferably less that about 30%, of the particulate substance dissolves in the liquid. Preferred particles are particulate salts of fatty acids, such as stearic or oleic acid, for example, sodium stearate, etc., PTFE powder, talc, particulate graphite, molybdenum disulfide and the like. The particles are preferably present in the friction reducing means in an amount of about 2 to about 40%, more preferably about 5 to about 35 and most preferable about 10- to about 25%, by weight, based on the weight of the liquid. The intended use of the article of the invention may restrict the liquid that can be used. For example, if the article has to be installed at high temperatures or will experience high temperatures once installed, the liquid selected should have a relatively low vapor pressure at such temperatures. A particular instance is the use of the article over a high voltage cable. Such cables are intended to operate at about 90°C, but higher temperatures can arise and accessories used in conjunction with such cables are expected to be operable up to 130°C. In embodiments of the invention where the article is intended to such use the liquid should have a boiling point of greater than 130°C and preferably its vapor pressure is less than 1 bar at 130°C. Further, if the article is to be used to install a single layer cover on the substrate by cutting the outer wall and sliding it down onto the substrate, it is preferred that both the liquid and particles be non-toxic or non-irritating to the person installing the article. As mentioned above, the amount of friction reducing means required according to the instant invention is significantly less than that required if a pituitous liquid or silicone oil is used in accordance with the teaching of U.S. Patent No. 4,868,353, mentioned above. U.S. Patent No. 4,868,967 discloses a double-walled tubular article of the same general type as the article of this invention. The tube can be revolved along a substrate by relative sliding motion between the two walls of the double wall, substantially without relative sliding motion between a wall adjacent the substrate and the substrate. This revolving action may cause the walls to stretch, and thus the tube can be installed over substrates of larger dimension than its relaxed dimension, resulting in tight engagement. The term "revolving" means that relative sliding motion or shear between first and second walls of the double wall can be continued such that the first and second walls exchange position and can preferably then return to their original configuration. Such a complete revolution may be achievable only once, although we prefer that it can be continued as many times as desired. Thus, the article may be revolved along an elongate member and left in any desired position. The first and second walls may of course be indistinguishable from one another, except for the fact that at any given time one is an inner wall adjacent the substrate and one is an outer wall overlying the inner wall. Then the portion of wall material that constitutes each wall will continuously change as the revolving action takes place. Revolving involves stretching a wall portion as it passes from an inner position, and relaxing another wall portion as it passes from an outer position to an inner position. Reference to a first, second, inner or outer wall merely refers to a portion of wall identifiable for the time being by its position and does not imply that it has any structural uniqueness. The revolving action may be pictured best perhaps by imagining a longitudinal axial section of the double-walled tube over a cylindrical substrate. The tube will appear as a caterpillar-track on either side of the substrate (Caterpillar is a trade mark). The tube can progress along the substrate by the caterpillar- tracks revolving. This involves shear between the inner and outer walls constituting the caterpillar-track, and will generally avoid shear between the inner wall and the substrate. When the article has reached the desired position, it may simply be left there as it is. Alternatively, as mentioned above, an outer wall may be cut (which term includes any suitable technique for parting two parts of it) and a resulting separated outer wall portion revolved such that the double walled article becomes (at least in part) a single walled article extended along the substrate. Reference to the double- walled tube does not preclude additional walls or layers, providing the revolving action is still able to take place. The a icle of this invention may be of any length, and it will generally be less than 30 m (100 feet) and more frequently less than 15 m (50 feet). Typically articles of this invention are from about 5 cm (2 inches) to about 130 cm (50 inches) in length, and in particular are from 13 cm (5 inches) to 80 cm (30 inches) in length depending on the substrate over which they are to be used. The outer diameter of the article similarly can be of any desired size, and typically is less than 125 cm (50 inches) generally less than 50 cm (20 inches), preferably from 2.5 cm (1 inch) to 15 cm (6 inches) depending on intended use. The inner diameter is preferably from 0.2 cm- 120 cm, more preferably 0.5 cm-50 cm, especially 1 cm to 10 cm. The ratio between the length and outer diameter of the article will also depend on the use to which it is to be put. Preferably that ratio is more than 5, more preferably more than 7, especially more than 8. Typical values are from 5-12. Articles of such shape will tend to buckle (rather than revolve) if subjected to an axial compressive force applied between an outer wall at one extreme end and an inner wall at an opposite extreme end. as a result a preferred technique whereby articles of the invention are installed is as follows: the revolving action is at least initiated by applying a shear force between the inner wall at one extreme end (by means for example of an end of a substrate to be covered) and the outer wall at a position a short distance, say less than 7 cm, preferably from 0.5-5 cm, from that same end (by means for example of an installer's hand). This technique is particularly relevant to a preferred use of the article where both the inner and outer walls are under tension when the article is installed on the substrate, as is required if an environmental seal is to be reliably achieved. Both the inner and outer walls must therefore be expanded as the article is revolved onto the substrate, and that portion of the outer wall which is over the substrate will generally be under greater tension than the remainder that has yet to reach the substrate. This difference in tension will tend to drive any fluid separating the inner and outer walls towards the end of the article yet to reach the substrate, i.e. towards the end of less tension. The inner and outer walls at the end over the substrate will cease to be separated, and friction will bring the revolving action to a stop. Hence the need for an effective friction reducing means. The inner and outer walls are each preferably from 0.0025 to 1.3 cms (0.001 to 0.5 inches) thick, more preferably from 0.05 to 0.65 cms (0.02 to 0.25 inches), and most preferably from 0.15 to 0.25 cm (0.05 to 0.1 inch) thick. The material comprising the walls should of course be sufficiently flexible that the revolving action may take place, and it preferably has an elongation to break of at least 20%, more preferably at least 40%, especially at least 100%, more especially at least 200%, particularly at least 500%, more particularly at least 700%. These figures relate to the ASTM test D412-83. The degree to which the walls of the article may be stretched will determine the maximum size of substrate over which the article may be installed. Preferably, the outer diameter of the substrate is from 1.0 to 8 times the inner diameter of the article of the invention. Preferred ranges are from 1.1 to 5, especially from 1.1 to 2.5. The ease with which the article can be installed over a substrate of larger size will depend on the tensile stress of the material comprising the walls. Preferable, the article can be installed by hand over substrates having the size ranges given above, using the technique disclosed above whereby a shear force is applied between the end of the article and a position close to that end. The material comprising the double-wall will be chosen from at least three considerations. Firstly it must allow the revolving action necessary for installation onto or use along a substrate of a certain size or shape or substrates of a certain range of sizes and shapes. The properties of interest here will include flexibility, tensile stress at a chosen elongation, elongation to break and ability to retain the friction- reducing means. The second consideration is the functional requirement of the installed product. For example, it may need a certain mechanical strength, abrasion resistance, cut resistance, moisture impermeability, etc. If it is to have an electrical function it may be required to be of high resistivity as an insulator, of low resistivity as a screen or other conductor, of intermediate resistivity as for stress- grading. It may have a certain specific impedance at a certain frequency, it may need anti-tracking properties, or it may need resistance to corrosion under high electrical discharge, etc. Where it is to be used in difficult environments it may need compatibility with certain sealing materials, U.V. resistance, fungal resistance, oxidation resistance, resistance to stress-relaxation, flame resistance, resistance to solvents, or low water up-take, etc. Such features are known to be required of certain prior art products, for example heat shrinkable sleeves, and one of skill in the art of polymer formulation will know how to prepare suitable materials. After reading this specification he will be able to prepare various new and inventive articles that combine the ability to be installed by the revolving action described herein, and any one or more of the above functional requirements. The material is preferably an elastomeric material containing appropriate additives to provide the desired properties. Preferably, the material comprises neoprene, EPDM, natural rubber, silicone rubber, styrene/butadiene copolymer rubber, butyl rubber.chlorosulfonated polyethylene or the like. The article of this invention can be used to cover any elongate substrate, such as electrical and fiber optic cables, cable splices, damaged cable jackets, pipelines, bus bars, bushings, fuses, elbow connectors and various other electrical connections, electrical wires, pipes and pipe lines, including hose and irrigation pipes, particularly over weld areas and damaged sections, pylons of off-shore oil rigs, flag poles, and other articles of circular or other cross-sectional shapes. In certain embodiments, it may be desirable that its physical properties, such as tear-strength, surface hardness and rigidity be able to be changed after installation by, for example, by further curing the elastomeric material as taught in European published patent application No. 281,353, mentioned above, the disclosure of which is incorporated by reference. In this embodiment, the article can be easily installed due to the elastomeric nature of its walls, and when in position it may be cured preventing or restricting further movement. In certain embodiment, a sealing material may be provided between the inner wall and the substrate or between the outer wall and some other object with respect to which movement is to be prevented. Such sealing material may be supplied on a surface of the substrate, on a wall of the article or as a discrete component that is positioned as desired during installation of the article. The double-walled tube is able to apply a compressive force to a sealing material, forcing it against a substrate, whilst avoiding any shear that would tend to displace it during installation. Illustrative sealing materials that may be used with the article for sealing or locking purposes include adhesives, sealants, gels. The sealing material may be provided in sheet form (which includes tapes, strips and bands), either alone or on a backing material, which may be wrapped around the substrate. As will be apparent, this invention is extremely versatile. Situations where the double-walled tubular article of this invention can be substituted for a prior art article can be found in the following, the disclosures of which are incorporated herein by reference: U.S. Patent Nos. 3,610,291 to Heslop, 3,950,604 to Penneck, 4,118,260 to Boettcher, 4,142,592 to Brusselmann, 4,194,082 to Campbell, 4,350,842 to Nolf, 4,400,579 to Nolf, 4,409,426 to Nolf, 4,426,413 to Fentress, 4,431,861 to Clabburn et al, 4,466,843 to Shimirak, 4,467,137 to Paget et al, 4,485,269 to Steinberg, 4,478,486 to Fentress, 4,498,732 to Fentress, 4,499,129 to Kridl, 4,511,611 to Moisson and 4,518,819 to Larsson Great Britain 2,110,479 to Link et al, and 2,125,637 to Clabburn et al, and EP 0,210,807, 0,212,851, 0,209,399 and 0,210,061 (Raychem Corporation). The invention will now be understood with reference to the accompanying drawings. A typical article is illustrated in Figures la, lb and lc which provide respectively perspective, transverse cross-sectional and longitudinal cross-sectional views. The article 1 comprises an outer wall 2 and an inner wall 3. The walls are joined to form a continuous, closed double-walled tubular structure. A friction-reducing means 4 is located within the double wall, separating the walls and allowing relative sliding motion between them. An article of this invention, generally tubular in shape, can be made by a variety of methods. The manner in which it is made is generally not critical. A preferred method of manufacture is illustrated in Fig. 2. In this method, a tube approximately double the desired length of the tubular article is formed by, for example, extrusion. The ends 6 and 7 of the tube 5 are folded over until they form an overlap region as illustrated. The friction reducing means can be added at this point. Because of the low viscosity of the friction reducing means it has been found to be desirable to mount the tube on a mandrel provided with a longitudinally extending groove. A vacuum can be applied to the groove creating a pocket between the walls. The low viscosity friction means can then be inserted into this pocket. The ends 6 and 7 may be secured together, for example by means of an adhesive , forming the continuous wall of the double wall structure. The adhesive between the walls of the article can then be cured, generally by placing the article in an oven or, if the friction reducing means is volatile, in an autoclave. Another preferred method comprises extruding individual tubes, one of smaller diameter than the other, arranging the tubes in concentric relationship and then bonding the ends of the tubes together. To apply the double-walled tubular article 1 to a substrate 8, an end 9 of the article is expanded to the outer diameter of the substrate and an end of the substrate is inserted into the expanded open end 9 of the article, as shown in Figures 3a and 3b. The force on the article will generally be applied at line 10, i.e. close to the applied at position 11. From Figure 3b it can be seen that, for the relative size of substrate and article illustrated, the circumferential tension in the right hand end 9 of the outer wall 2 will be greater than in the left hand end which would cause the friction reducing means 4 to be driven away from where it is needed, were it not for some means to restrict such displacement. Continued axial force causes the tubular article to move axiaily along the substrate as shown in Figure 3c until the desired position is reached. Thus, the article can be used to cover, for example a cable joint. Before the cables are joined, the tubular article is positioned over one of the cables and axiaily revolved away from the cable end. The cables are then joined and the tubular article is positioned over the joint by applying an opposite axial force relative to the outer wall. Figure 3c illustrates, partially in cross-section, article 1 when fully on an elongate substrate. Article 1 comprises outer wall 2, inner wall 3 and friction reducing means 4. In Fig. 3c the arrows indicate movement of the outer wall 2 while substrate 8 substantially prevents axial motion of inner wall 3. As a result outer wall 2 progressively revolves into contact with the surface of substrate 8 resulting in moving the article 1 in an axial direction from left to right in the drawing. The following examples illustrate preferred embodiments of the invention and show its improvement resulting from the use of insoluble particles in a Hquid friction reducing means in a double wall tubular article. Example 1 This example illustrates the use of insoluble particles in a low viscosity liquid as the friction reducing means for a double walled tubular article. For each sample, a tube of neoprene about 18 inches long and having a wall thickness of .12 inch, an internal diameter was positioned on a mandrel and folded over itself. A friction reducing means (FRM) in the amounts specified in Table I and consisting of a liquid dimethyl siloxane having a viscosity of 100 centistokes (DC-200, lOOcs commercially available from Dow Corning) and varying amounts of particles of sodium stearate, as designated in Table I, was introduced into the space between the walls. The ends of the tube were overlapped and secured together with adhesive to provide a double wall tubular article about 8.5 inches in length. The article was placed in an oven to cure the neoprene adhesive. Sample articles were installed onto a 1.38 inch diameter mandrel or a 1.76 inch diameter mandrel and the force necessary to revolve the article along the mandrel was measured. The results are shown in Table I. Table I These results show the significant improvement when insoluble particles are added to a low viscosity liquid, friction reducing means. The reduced force required to revolve the article along the mandrel makes it possible to utilize less friction reducing means when particles are dispersed in the liquid. Example 2 This example illustrates the use of insoluble particles in a pituitous liquid as the friction reducing means for a double walled tubular article. The procedure of Example 1 was repeated using as the friction reducing means (FRM) an aqueous solution of a water soluble high molecular weight polymer (Polywater F from Polywater Corp., of Minnesota) optionally containing particles of polytetrafluoroethylene (PTFE). As in Example 1, sample articles were installed onto a 1.38 inch or a 1.76 inch mandrel and the force necessary to revolve the article along the mandrel was measured. The results are shown in Table H. TABLE II *The article could not be revolved along the mandrel. These results show the significant improvement when insoluble particles are added to a pituitous liquid, friction reducing means. Example 3 This example illustrates the heat aging performance of double wall articles containing a liquid/dispersed particle friction reducing means in accordance with this invention. The procedure of Example 1 was repeated using 1.5 ml of a friction reducing means comprising dispersions of sodium stearate, in the amounts specified in Table III, in dimethyl siloxane having a viscosity of 100 centistokes. In this example, the articles used were somewhat larger, having an internal diameter of 1.025, the other dimensions being the same as in Example 1. Sample articles were installed onto a 1.38 inch diameter mandrel or a 1.76 inch diameter mandrel and the force necessary to revolve the article along the mandrel was measured. The samples were then placed in an oven maintained at 70°C for the times indicated in Table III. The samples were removed from the oven, cooled and the force required to revolve the article along the mandrel was measured. The results are listed in Table III. After 32 days under the above accelerated aging test, the articles could be readily revolved along the substrate. This demonstrates that the article can be installed over the substrate in use and can be removed if desired, e.g. to modify or repair an underlying cable splice.

Claims: WHAT IS CLAIMED IS: 1. A tubular article comprising a double walled tube having a friction reducing means between the two wall of the double wall, the friction reducing means comprising a liquid having dispersed therein particles having an average particle size of about 0.1 to about 1000 microns, the particles being substantially insoluble in the liquid. 2. An article in accordance with claim 1, wherein the liquid is selected from the group consisting of liquid silicones, aqueous or glycol solutions of soluble polymers, mineral oils, vegetable oils, polyols, water, surfactants, and liquid high molecular weight alcohols. 3. An article in accordance with claim 1, wherein the liquid has a viscosity of about 1 to about 1000 centistokes. at 25°C. 4. An article in accordance with claim 1, wherein the liquid is a low viscosity liquid silicone. 5. An article in accordance with claim 4, wherein the liquid is dimethyl siloxane. 6. An article in accordance with claim 1, wherein the hquid is a pituitous liquid. 7. An article in accordance with claim 5, wherein the pituitous liquid comprises an aqueous or glycol solution of a high molecular weight polymer. 8. An article in accordance with claim 1, wherein the particles are present in an amount of about 2 to about 40% by weight, based on the weight of the liquid. 9. An article in accordance with claim 1, wherein the particles selected from the group consisting of salts of fatty acids, PTFE powder, talc, particulate graphite and molybdenum disulfide 10. An article in accordance with claim 9, wherein the particles comprise sodium stearate particles. 11. An article in accordance with claim 1, wherein the low viscosity liquid is a a low viscosity liquid silicone and the particles are sodium stearate particles. 12. An article in accordance with claim l.wherein the material of the wall of the double walled article is an elastomer. 13. An article in accordance with claim 12, wherein the elastomer is selected from the group consisting of neoprene, EPDM, natural rubber, silicone rubber, styrene/butadiene copolymer rubber, butyl rubber and chlorosulfonated polyethylene. 14. A method of covering an elongate substrate which comprises revolving onto the substrate to be covered a tubular article comprising a double walled tube having a friction reducing means between the two walls of the double wall, the friction reducing means comprising a liquid having dispersed therein particles having an average particle size of about 0.1 to about 1000 microns, the particles being substantially insoluble in the liquid. 15. A method in accordance with claim 14, which further comprises the steps of cutting the outer wall of the article after it has been installed on the substrate and then sliding the outer wall into contact with the substrate. 16. A method in accordance with claim 14 which further comprises positioning a sealing material between the substrate and the article. 17. A method in accordance with claim 14 in which the substrate is a cable splice. 18. A method in accordance with claim 14, wherein the Hquid is selected from the group consisting of Hquid silicones, aqueous or glycol solutions of soluble polymers, mineral oils, vegetable oils, polyols, water, surfactants, Hquid high molecular weight alcohols. 19. A method in accordance with claim 14, wherein the Hquid has a viscosity of about 1 to about 1000 centistokes. at 25°C. 20. A method in accordance with claim 14, wherein the Hquid is a low viscosity liquid silicone. 21. A method in accordance with claim 20, wherein the Hquid is dimethyl siloxane. 22. A method in accordance with claim 14, wherein the liquid is a pituitous liquid. 23. A method in accordance with claim 22, wherein the pituitous liquid comprises an aqueous or glycol solution of a high molecular weight polymer. 24. A method in accordance with claim 14 wherein the partides are present in an amount of about 2 to about 40% by weight, based on the weight of the Hquid. 25. A method in accordance with claim 14, wherein the particles selected from the group consisting of salts of fatty adds, PTFE powder, talc, particulate graphite and molybdenum disulfide 26. A method in accordance with claim 25, wherein the particles comprise sodium stearate particles. 27. A method in accordance with claim 14, wherein the low viscosity Hquid is a a low viscosity liquid silicone and the particles are sodium stearate particles. 28. A method in accordance with claim 14, wherein the material of the wall of the double walled article is an elastomer. 29. A method in accordance with claim 28, wherein the elastomer is selected from the group consisting of neoprene, EPDM, natural rubber, silicone rubber, styrene/butadiene copolymer rubber, butyl rubber and chlorosulfonated polyethylene.

Inventors: YOUNG RICHARD ALAN, YOUNG, RICHARD, ALAN
Applicants: RAYCHEM CORP, RAYCHEM CORPORATION
Application year: 1991
Main classification: F16L47
IPC codes: F16L5, F16L47, F16N15, H02G15