HEAT-SHRINKABLE ARTICLE

Abstract: Fabric (10) with HDPE shrinkable fibres (12) in wraparound direction laminated to LDPE film (14) on outside and coated with adhesive (16) on inside curls around small diameter object such as wire splice to resist unwrapping during heat shrinking and thus provides side-entry splice (SES) especially suitable for automotive wiring assembly.

Description: Heat-shrinkable Article This invention relates to a heat shrinkable article for wrapping around an object of up to 25 millimetres diameter, which article is especially useful for protecting wiring splices from environmental contamination, for example, in automotive wiring harnesses. Heat shrinkable tubes of plastics material have been used for such purposes for many years, but such tubes have the disadvantage that they must be slipped on over a free end of the wire, which is not always convenient in practice. Attempts to wrap heat shrinkable plastic sheeting around small diameter objects such as wiring splices have been commercially unacceptable in the past owing to the difficulty of securing the ends of the sheet around the object to be enclosed. Clamping devices of the kind well known for large cable wraparound enclosures are impracticable on the small scale of wiring splices, and attempts to secure the sheet by means of adhesive tend to fail owing to the tendency of the sheet to unwrap from around the object during heat shrinking. The present invention provides an ingenious and relatively low-cost route to alleviating these problems. The invention provides a heat-shrinkable article for wrapping around an object of up to 25 millimetres diameter, comprising: (i) a fabric having heat-shrinkable fibres extending in the wrapping direction, (ii) a flexible layer of cross-linked plastics material laminated to one major surface of the fabric to face outwards away from the said object in use, and (iii) heat-activatable adhesive carried on the other major surface of the fabric to face inwards toward the said object in use, the construction of the article being such that heat recovery of the fabric in use curls the article around the said object and towards the surface carrying the said adhesive and activates the said adhesive. The flexible layer (ii) and adhesive (iii) may be carried (preferably adhered) directly on the fabric, or on other intervening layers in direct contact with the fabric. By thus placing the heat-shrinkable fabric as the inner layer (in use) of a two- component laminate with the cross-linked plastics material, the present invention takes advantage of the asymmetric shrinkage force generated in the laminate by the heat- shrinkable fibres shrinking in the wraparound direction to curl the article during shrinkage in a manner which reinforces the wrapping action and thus counteracts the tendency toward unwrapping on heat shrinking. It has been surprisingly found that an article according to this invention can survive recovery after initial securing around the object by means of an overlap joint using pressure-sensitive adhesive, without unacceptable opening, even though the overlap may slip by up to 50% of its original overlap width during such shrinking. Preferably the fabric will have the heat-shrinkable fibres extending substantially only in the wrapping direction. The heat-shrink ratio of the article (that is the ratio of the length in the wrapping direction before heat shrinking to that after complete heat shrinking) is preferably within the range 1.10:1 to 5:1, more preferably 1-3:1 to 3:1, especially 1-5:1 to 2:1. The article may conveniently be provided in the form of a strip or roll for example anything between 1 and 1000 metres in length in the wrapping direction, and it will be understood that such a roll or strip may advantageously be fed to automated installation equipment or other suitable equipment for enclosing relatively small articles such as wiring splices on a production-line basis. Alternatively, the article according to this invention could be provided in the form of a pre-cut strip or sheet carrying pressure-sensitive adhesive on at least one of its end regions capable of securing the article wrapped around the said object in use prior to heat shrinking of the article. Various forms of fabric containing heat-shrinkable fibres may be selected to suit end use requirements the heat-shrinkable fibres in one preferred form of this invention being formed of high density polyethylene, preferably cross-linked by irradiation. Suitable materials for the said layer of plastics material laminated to the fabric may also be selected by trial and error, a preferred material being low-density polyethylene, preferably cross-linked by irradiation after lamination to the fabric. The fabric may have been irradiated prior to lamination to the plastics layer thereto, but is preferably irradiated together with the plastics laminate after lamination and prior to coating with the adhesive. Any heat-activatable adhesive may be carried on the surface of the fabric facing away from the laminated plastics material, preferred adhesives being hot melts or heat curable adhesives, the adhesive naturally being selected to suit the end use of the article. The materials, dimensions and construction of the article are all selected and balanced to suit the end use in question, and for automotive wiring splices, for example, will be selected to render the article shrinkable in less than 30 seconds, preferably less than 20 seconds, more preferably in 10 to 15 seconds, by application of hot air or infrared heating, preferably at a temperature of 250 to 270°C at the outer surface of the article. Examples of adhesives which may be suitable for the present purposes are described in WO-A- 8707755 (RK310), GB-A-2104800 (RK149), EP-A-0157478 (RK232) and co-pending International Application PCT/GB95/00731 (B247), the disclosures of all of which are incorporated herein by reference. Methods of forming the fabric, preferably by weaving, applying the laminate of plastics material and applying the adhesive will be known to those familiar with this field. The fabric article may be made from heat-shrinkable fibres and other fibres as described generally in GB-A-2134334 but preferably with omission of the second plastics laminate and the metallised Mylar laminate described therein. For example, the fabric could use a plain weave (1 over and 1 under) of shrinkable warp fibres of cross-linked high-density polyethylene of 0.2 - 0.3 mm diameter at 35.4 ends per centimetre (90 ends per inch) and weft fibres of glass 3 x 68 g/km or 0.1 mm PET monofilaments (2 per pick) at 3.9 picks per centimetre (10 picks per inch). The weft fibres will be spaced apart so as not to interfere to an unacceptable extent with the shrinkage of the warp fibres. Alternative fabric designs are indicated in the following table. Fabric Construction Warp Waφ Diameter Weft Weft Diameter Weave Design Ends/cm or picks or (Ends/inch) Linear Density per cm Linear Density & (picks & Material per inch) Material #1 15.7 HDPE 4.7 Ryton (trademark) 2/2 (40) fibrillated tape (12) PPS HOPSAK 200 g/km 0.2 mm #2 27.6 PVDF 3.1 PET 2/2 (70) monofilament (8) monofilament BROKEN TWILL 0.35 mm 0.1 mm # 3 35.4 HDPE 3.5 E-Glassfibre PLAIN WEAVE Pref (90) monofilament (9) 2 x 68 g/km 0.25 mm # 4 47.2 LLDPE 4.7 Hoechst Warp Interchange (120) monofilament (12) Trevira 0.3 mm (Trade mark) 2 ply WEAVE Type 711 polyester multifil 110 g/km Preferably, the fabric article includes adherent polymeric material, preferably an adherent polymeric film laminate (preferably a polyethylene film), which renders the fabric article substantially non-porous. For example, a low-density polyethylene film of about 0.2 mm thickness may be laminated by known lamination methods to one side of the woven fabric. After laminating, the film and fabric are preferably irradiated by the usual means (known per_S£), preferably to a dosage of at least 10, preferably at least 12, especially at least 14, megarads, to enhance the temperature performance and the bonding together of the laminated article. Suitable irradiation methods and equipment, for example electron beams, are well known. Doses over 20 Mrads are preferably not used, and little added advantage is gained by does above 15 Mrads. The fabric article may be rendered resistant to transmission of liquids in the plane of the fabric sheet, usually known as making the article "planar tight", by methods including those described in EP-A-0324630. The invention also provides a kit of parts comprising an article as hereinbefore described according to the invention and pressure-sensitive adhesive for securing the article wrapped around an object in use prior to heat shrinking of the article Another aspect of the invention provides a method for enclosing an object comprising wrapping an article according to this invention as hereinbefore described around the object and heat shrinking the article. Such a method preferably includes the step of securing the article wrapped around the object, preferably by pressure sensitive adhesive, prior to heat shrinking the article. As aforementioned, the invention is particularly applicable where the enclosed object is an electrical wiring splice, especially an automotive wiring splice. The average diameter of the enclosed object is preferably less than 20 mm, more preferably within the range from 5 to 15 mm. Articles having lower installation temperature ranges may be prepared by using linear low density polyethylene fibres in place of the currently preferred high density polyethylene heat-shrinkable fibres. Higher temperature ratings may be achievable by using fluoropolymers such as PVDF as the recoverable fibres, possibly in combination with glass fibres, and higher temperature adhesives and laminate materials which can readily be selected by suitably skilled persons, for example as described in GB-A- 2133740, the disclosure of which is incorporated herein by reference. An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, wherein Figure 1 shows schematically the structure of an article according to this invention; Figure 2 shows an article according to the present invention wrapped around a wiring splice with the heat-shrinkable fibres of the article lying in the wrapping direction; Figures 3 A to 3D represent schematically the formation of the fabric (i) with flexible laminate (ii); Figures 4A and 4B illustrate schematically the application of the hot-melt and pressure-sensitive adhesives to the laminated fabric; Figures 5A to 5E illustrate in more detail the adhesives application, and the wrapping of the adhesive-bearing heat-shrinkable article around a wiring joint; and Figure 6 illustrates schematically the heat shrinking of the article around the wiring joint. As shown in exploded form in Fig. 1, the article according to this invention consists of the fabric 10 having heat-shrinkable fibres 12 lying in the wrapping directed, with a layer of low-density polyethylene film 14 laminated to one major surface of the fabric and a coating of polyamide hot melt adhesive 16 on the other major surface. The article 20 in Fig. 2 is secured in the wrapped configuration around a splice (not visible) in wires 25 by means of a pressure-sensitive adhesive 20 in an overlap joint. On heat- shrinking of the article the hot melt adhesive 40 flows and on cooling solidifies to seal the enclosed wiring splice against contamination and/or short circuiting. Figure 3A indicates a plain weave fabric made of heat-shrinkable 0.25 mm diameter high density polyethylene warp monofilaments 30 with 0.1 mm diameter polyethylene terephthalate weft monofilaments 32. This fabric 34 is laminated on one side with a 0.25 mm thick extruded layer of low density polyethylene, as schematically indicated in Fig. 3B, and the resulting laminated article 35 is subjected to 14 Mrads of ionising radiation from an electron beam 36 in known manner, as schematically indicated in Fig. 3C. The irradiated fabric laminate 38 is then slit longitudinally into rolls 39 of 50 mm width and 100 metres length, or other dimensions to suit end use requirements, as indicated in Fig. 3D. Figure 4A indicates schematically the application of a strip of known polyamide hot melt adhesive 40 and a strip of known double-side pressure-sensitive adhesive (PSA) tape 41 to the fabric laminate fed from a roll 42 similar to those produced in Fig. 3D. The application equipment 43 of any convenient design applies sufficient heat and pressure to adhere the hot melt adhesive and the PSA to the side of fabric remote from the LDPE laminate. The resulting structure is shown in more detail in Fig. 4B, wherein the fabric 45, with LDPE laminate 46 on one main surface, has the hot melt adhesive 47 on most of its other main surface, with an edge strip free of hot melt carrying the PSA 48. The thickness of this whole heat-recoverable adhesive-coated article is about 0.7 mm. Figure 5A gives an enlarged schematic indication of the hot melt adhesive 50 and pressure-sensitive adhesive 51 being applied to the fabric side of the fabric/LDPE laminate 52, with the hot melt 50 ending adjacent to an end strip of the fabric to which the PSA 51 is applied. Figure 5B shows the adhesive-bearing laminate 53 with a wiring splice 54 positioned over it, after which a suitable length of the laminate 53 is cut off, as indicated in Fig. 5C, and fed together with the splice to suitable wrapping means indicated by guide 55 in Fig. 5D, which fastens the laminate 53 around the splice 54 by means of an overlap bond with the PSA 51, as indicated in Fig. 5E. These processes can be readily automated by suitably skilled persons for efficient use in automotive wiring production. Figure 6 shows schematically the wiring splice 60, with the heat- shrinkable adhesive-carrying fabric laminate 61 wrapped and fastened around it, being fed to a known belt heater 62 which shrinks the wrapped article 61 around the wiring splice 60 to produce the finished protected wiring assembly 63.

Claims: Claims 1. A heat-shrinkable article for wrapping around an object of up to 25 millimetres diameter, comprising: (i) a fabric having heat-shrinkable fibres extending in the wrapping direction, (ii) a flexible layer of cross-linked plastics material laminated to one major surface of the fabric to face outwards away from the said object in use, and (iii) heat-activatable adhesive carried on the other major surface of the fabric to face inwards toward the said object in use, the construction of the article being such that heat recovery of the fabric in use curls the article around the said object and towards the surface carrying the said adhesive and activates the said adhesive. 2. An article according to claim 1, having the heat-shrinkable fibres extending substantially only in the wrapping direction. 3. An article according to claim 1 or 2, wherein the ratio of its length in the wrapping direction before heat shrinking to that after complete heat shrinking is within the range from 1.10:1 to 5:1, preferably 1-3:1 to 3:1, more preferably 1-5:1 to 2:1. 4. An article according to any preceding claim wherein the surface of the fabric carrying the heat-activatable adhesive has at least one region which is free of that adhesive, which region may be bonded to the other main surface of the heat- shrinkable article to secure the article wrapped around the object in use prior to heat shrinking of the article. 5. An article according to claim 4 in the form of a strip or sheet carrying on the said region, which is preferably one of its edge regions, pressure-sensitive adhesive capable of securing the article wrapped around the said object in use prior to heat shrinking of the article. 6. An article according to any preceding claim, wherein the heat-shrinkable fibres are formed of high-density polyethylene, preferably cross-linked by irradiation. « 7. An article according to any preceding claim, wherein the said layer of plastics material is formed of low-density polyethylene, preferably cross-linked by irradiation after lamination to the fabric. 8. An article according to any preceding claim wherein, the fabric has been irradiated prior to lamination of the plastics layer thereto. 9. An article according to any preceding claim, wherein the said adhesive is a hot melt adhesive or a heat-curable adhesive. 10. An article according to any preceding claim, whose materials, dimensions and construction are selected to render it shrinkable in less than 30 seconds, preferably less than 20 seconds, more preferably in 10 to 15 seconds, by application of hot air or infrared heating, preferably at a temperature of 250 to 270°C at the outer surface of the article. 11. A kit of parts comprising an article according to any preceding claim and pressure- sensitive adhesive for securing the article wrapped around an object in use prior to heat shrinking of the article. 12. A method of enclosing an object comprising wrapping an article according to any of claims 1 to 10 around the object and heat shrinking the article. 13. A method according to claim 12, comprising securing an article according to claim 4 or 5 wrapped around the object by means of pressure-sensitive adhesive prior to heat shrinking the article. 14. A method according to claim 12 or 13, wherein the enclosed object is an electrical wiring splice. 15. A method according to any of claims 12 to 14, wherein the average diameter of the said object is less than 20 millimetres, preferably within the range from 5 to 15 millimetres. 16. An article, kit or method according to any preceding claim, wherein the said fabric is substantially as described in any one of the examples 1 to 4 in the foregoing table, preferably example 3.

Inventors: LOWE FRANK JAMES, RYDER ALAN GEORGE, LOWE, FRANK, JAMES, RYDER, ALAN, GEORGE
Applicants: LOWE FRANK JAMES, RAYCHEM LTD, RYDER ALAN GEORGE, LOWE, FRANK, JAMES, RAYCHEM LIMITED, RYDER, ALAN, GEORGE
Application year: 1996
Main classification: B29C61
IPC codes: B29C61, B29C63, B29K105, B32B5, B32B7, B32B37, H01B17, H02G15