This invention relates to a method of adhering a sleeve to an elongate article.

The term "sleeve" includes the preferred tubular articles of substantially round cross-sectional profile, but does not necessarily exclude articles having an angular, for example, triangular, rectangular or polygonal profile either for their interior surface or their exterior surface or both, and may include other hollow shapes of regular or irregular profile. The sleeve may be adhered to the elongate article for various purposes, for example, for electrical or environmental protection, for spacing the article from adjacent surfaces, for vibration damping, or for impact buffering. The invention ingeniously avoids problems that may arise with conventional methods of adhering sleeves to elongate articles.

The invention provides a method of adhering a sleeve to an induction-heatable (preferably metallic) elongate article, comprising the steps of:

(a) placing a substantially non-heat-transmitting sleeve at least partly around the elongate article with a heat-activatable adhesive between die sleeve and die elongate article, the said sleeve comprising polymeric material, preferably elastomeric material, of a thickness which substantially precludes activation of the adhesive by application of heat directly to the exterior of the sleeve, and

(b) causing induction heating of the elongate article within the sleeve to a temperature which activates the adhesive, thereby adhering the sleeve to the elongate article.

By thus ingeniously taking advantage of the induction-heatable property of the elongate article, the invention avoids die problems which could arise in trying to activate the adhesive by applying heat to the outside of die sleeve, notably the problem of heat damage of me exterior of the sleeve before sufficient heat is transmitted to activate the adhesive.

The elongate article may comprise any induction-heatable material, for example, an electrically insulating polymeric material with a suitable induction-heatable filler, but is preferably a metallic elongate article. The article may have a metallic outer surface, or may have a covering layer of polymeric material to which the sleeve will be adhered on activation of die adhesive. For example, d e elongate article may be one or more electrical

wires or an electrical cable. Alternatively, die elongate article may be a pipe or hose, preferably a metallic pipe or hose.

It will be understood that die sleeve is "non-heat-transmitting" in the sense that direct application of heat to die exterior of the sleeve eidier will not result in transmission of sufficient heat to activate the adhesive inside d e sleeve, or will not result in transmission of sufficient heat widiout unacceptable heat damage to die sleeve. This is particularly relevant when the sleeve comprises polymeric material, preferably elastomeric material, of a d ickness which substantially precludes activation of die adhesive by application of heat directly to die exterior of die sleeve, either due to insufficient transmission per se or due to heat damage as aforesaid. An especially useful form of sleeve comprises foamed polymeric material, for example, of die kind used for water pipe lagging.

The sleeve may have a longitudinal slit or opening whereby it can be applied laterally around the elongate article. In this case, it is preferred that die sleeve extend at least half way round the article, preferably substantially more man half way round die article, and more preferably substantially all the way round die article, especially so that the longitudinal slit will substantially close togedier after the sleeve is applied around die article. The sleeve will preferably fit closely around the article so as to ensure good adhesion on activation of die adhesive. Sleeves which extend only partially around die article will therefore preferably be shaped and sufficiently resilient to grip die article. Slit sleeves will preferably be of a size such that they close around the article with as little clearance as possible between the article and the sleeve and between die opposed faces of the slit.

When d e opposed faces of a longitudinally slit sleeve substantially close together after the sleeve is applied around the elongate article, the slit may be adhered closed by means of a suitable adhesive, preferably an induction-heatable heat-activatable adhesive, between die opposed faces. Such an adhesive will be activated by the induction heating step (b).

If desired, the adhesive between d e sleeve and the elongate article may also be induction-heatable, and may for convenience be the same as the adhesive between die opposed faces of the slit, when present. Different adhesives could however be used if desired.

For convenience, die sleeve may be pre-coated widi the adhesive or adhesives. Alternatively, the adhesive(s) may be provided separately from the sleeve, preferably as a pre-formed profile shaped to fit against the sleeve surface to which it is intended to adhere after activation.

In a preferred embodiment of the invention, the sleeve, preferably of foamed polymeric material, is positioned to act as a buffer against vibration or rattling of the elongate article in use. This is particularly useful, for example, in vehicles where ratding of pipes, hoses, or cables maybe irritating or unacceptable.

The invention includes a sleeve of foamed polymeric material, preferably having a longitudinal slit or opening, which sleeve has an coating of heat-activatable adhesive on its interior surface. Such a sleeve may have a longitudinal slit widi a coating of induction- heatable heat-activatable adhesive on at least one of the opposed surfaces of the slit. It will be understood diat such sleeves are uniquely suited for use in the method hereinbefore described.

The invention also includes a kit of parts for use in the method hereinbefore described, comprising the said sleeve and a separate quantity of the said adhesive, preferably a pre-formed profile of the said adhesive shaped to fit against die sleeve surfaces which it is intended to adhere after activation. When die sleeve in such kits has a longitudinal slit, the adhesive profile may be shaped to fit inside the sleeve and to extend between the opposed surfaces of the slit, at least die part of die profile shaped to extend between the said surfaces of die slit comprising induction-heatable heat-activatable adhesive.

May suitable kinds of heat-activatable adhesive are known, the preferred kind for the present invention being hot melt adhesives. Heat-activatable adhesives have been found to be more efficient than pressure sensitive or solvent-based adhesives for the present purposes, especially where induction-heating equipment is already available. Suitable induction-heating methods and equipment are known, for example, as described in WO -A- 94/24837 (MP1474), the disclosure of which is incorporated herein by reference.

Suitable heat-activatable adhesives are also known, and will be selected wid melting points and flow characteristics to suit the amount of heat which can be generated by the

induction heating of the elongate article and die desired end-use temperatures to which the adhesive may subsequently be exposed in use of the elongate article. Adhesives which cure after flowing to effect die necessary adhesion may be used if desired. When it is desired to use an adhesive which is itself induction-heatable, suitable adhesives may be selected, for example, from diose described in d e aforementioned WO 94/24837.

Methods of forming suitable sleeves and methods of coating them with the adhesive or providing die adhesive separately in suitable forms are sufficiently well known to require no further description here.

Specific embodiments of the invention will now be described by way of example, widi reference to die accompanying drawings, wherein:-

Figure 1 shows schematically a sleeve for use in the ediod of die present invention;

Figure 2 shows schematically the sleeve of figure 1 in position on a metal pipe or hose;

Figure 3 shows schematically a longitudinally-slit sleeve for use in die mediod according to tiiis invention;

Figure 4 shows schematically in perspective a shaped adhesive profile for use with a slit sleeve; and

Figure 5 shows the profile of figure 4 in position in a sleeve.

Referring to figure 1, a relatively diick sleeve 10 of plastics material is shown in end view having a substantially circular outer circumference and a substantially circular inner circumference with a layer of heat-activatable adhesive 12 on the inner surface. The relatively great thickness of the plastics material 10 would make it difficult or impossible to activate the adhesive 12 by applying heat from the outside of the sleeve. Figure 2 shows in end view the sleeve of figure 1 which has been slid over the end of a pipe or hose 20, shown for clarity widi exaggerated space between the pipe or hose 20 and die sleeve. Figure 3 shows schematically in end view a sleeve 30 of foamed polymeric material suitable for thermal insulation of pipes, having a longitudinal slit 32 which can be opened, due to the flexibility of the material, to allow the sleeve to be fitted laterally onto the pipes. The interior surface of the sleeve and d e opposed faces of d e slit carry an induction-heatable heat-activatable adhesive 34. After tiiis sleeve has been fitted around a metal pipe or hose, actuation of the adhesive by induction heating of die pipe or hose will be augmented by

induction heating generated within die adhesive itself. Pre-coating of die adhesive on an article as shown may be inconvenient, owing to the tendency of die slit to close before the coating is tack free, and it may dierefore be preferable to use a separate adhesive profile as shown in figure 4.

Figure 4 shows schematically in perspective an extruded adhesive profile suitable for placing within a slit sleeve to achieve a structure similar to that shown in Figure 3 or suitable for pre-positioning around the article to which the sleeve is to be adhered following by placing of the slit sleeve around the pre-positioned adhesive. In diis embodiment, it can be imagined mat only die flat portions 42 of the adhesive profile 40 are made of induction- heatable adhesive, while die tubular portion 44 of die profile is made of ordinary hot melt adhesive. When this profile 40 has been positioned within a slit sleeve 30 as shown in figure 5, and around an elongate metal article such as a pipe or hose (not shown), heat generated by induction heating of d e pipe or hose will activate die hot melt portion 44 of die adhesive profile, while the slit-closing portions 42 of the profile will be activated by induction heating within the adhesive itself, this being advantgeous because the portions 42 are relatively remote from the heat-generating pipe or hose.

Other aspects of this invention follow. Heating of the elongate article may be effected by means other than induction, for example by passing hot gas or liquid inside a pipe or by applying heat to the article adjacent to die sleeve and allowing conduction of heat to activate the adhesive.

These mediods of heating and/or induction-heating could be used to shrink heat- shrinkable sleeves of any kind, with or without adhesives, around elongate articles, especially when sleeves having a relatively low shrinkage ratio of, say, 10-20%, calculated as (starting diameter - shrunk diameter)/ starting diameter, are fitted fairly closely over the article. The sleeves may have adhesive linings or may be used widi separate adhesives as hereinbefore described. Sleeves of suitable foamed (preferably cross-linked) polymeric material could be made to grip the article by expanding the inner sleeve diameter while warm (above Tg), cooling to fix the expanded state, placing die expanded sleeve on die article, and heating as hereinbefore described to recover the sleeve towards the original unexpanded inner diameter. These aspects individually, and in any appropriate combination widi each odier or with features described hereinbefore, are included as inventions in this application.