It is known to use heat shrinkable protective sleeves to protect electrical cables and joints. These give both mechanical and electrical protection. Where a total seal is required to prevent water ingress and subsequent corrosion and electrocution hazard, the sleeve is lined with a thermoplastic hot melt adhesive and sealant. When the sleeve is heat shrunk, this hot melt adhesive melts and forms a seal. Typically polyisobutylene is used as the hot melt adhesive. This gives good performance characteristics albeit at a high price.

GB-A-2297984 discloses a sleeve for protecting wooden objects from decay.

The sleeve is formed of heat shrinkable plastics material which is coated with a bituminous substance prior to application to the object.

The use of a bituminous sealant gives a valid low cost alternative to thermoplastic hot melt adhesive for other applications as well as for protecting wooden objects from decay. Such applications include the protection of electrical cables, joints and lead-outs and the protection of elongate metal sections e.g.

underwater or underground piping, against corrosion.

Standard and modified bitumens have the disadvantage of being soft and sticky at room temperature whilst exhibiting a tendency to self stick at relatively low

temperatures (approximately 350C). This means that the sleeves have to be stored and used in cool conditions and even then bitumen tends to stick to an operator's hands when applied to the object.

The present invention seeks to provide a sleeve which overcomes this drawback.

According to the invention there is provided a heat shrinkable plastics sleeve having an internal coating of a bituminous substance to which coating has been applied an agent in liquid form for reducing the stickiness of the exposed inner surface of the bituminous substance.

Preferred and/or optional features of the invention are set forth in claims 2 to 9, inclusive.

For the avoidance of doubt, the term "bituminous substance" used herein includes, for example, bitumen, tar, pitch, coal tar, asphalt, gilsonite or any combination thereof in straight or modified form.

In one example, a heat shrinkable thermoplastics sleeve (typically low or high density U.V. stabilised polyethylene or polyvinylchloride) is internally hot coated with a molten bituminous substance comprising one or more of the group comprising bitumen, tar, pitch, coal tar, asphalt or gilsonite, in straight or modified form. The bituminous substance should be sufficiently fluid to bond to an object at a temperature

lower than the temperature at which the thermoplastics sheet is heat shrinkable.

Bitumen has been found to be particularly suitable and typically the thickness of the bitumen solution is about 0.3mm but this may depend on the particular application for which the sleeve is to be used.. The bituminous substance may include wood preservatives (if the sleeve is to be used to protect wooden objects) and/or adhesion promoters. It may also include fillers, extenders, plasticisers and/or elastomers. It may also include reinforcing fibres. However, the total of any wood preservative, adhesion promotors, fillers, extenders, plasticisers and elastomers preferably should not exceed 20% by weight. Indeed, if any wood preservative is to be used it may well be desirable to overcoat the bituminous substance with it.

The sleeve of thermoplastics material, typically, has a thickness of 100 - 600 microns, but can be thicker. It may be necessary to cool the outer surface of the sleeve during hot coating with the bituminous substance to prevent the sleeve reaching a temperature at which shrinking will occur. Also, it may be desirable to pretreat the sleeve using corona discharge or a flame to improve adhesion of the bituminous substance to the film.

It has been found that a blend of 50% by weight of 50 PEN grade bitumen + 50% by weight of 85/40 oxidized grade bitumen (BS3690 Part 2 1994) will operate satisfactorily over a temperature range of 0 to 30° C without cracking at low temperatures. For a larger temperature range it may be necessary to use a very sticky layer of 200 - 800 PEN grade bitumen adjacent to the thermoplastics sheet with a second less sticky top layer of 25 - 50 PEN grade bitumen.

It has subsequently been found that an 85/40 oxidized grade bitumen with added temperature dependent viscosity modifier allows the characteristics of the bitumen to be maintained to 400C whilst giving a rapid reduction in viscosity above this temperature thereby ensuring excellent bond to an object. A grade of bitumen with a straight viscosity modifier has also proved effective.

In order to reduce the surface stickiness of the bituminous substance, the exposed surface of the bituminous substance is coated with a concentrated or dilute soap solution. Fairy Liquid (RTM) has been found to be particularly suitable. It has been found that a mixture of 50% Fairy Liquid and 50% water works satisfactorily, although improved results can be obtained if the mixture has a larger proportion of Fairy Liquid. Fairy Liquid includes anionic surfactants (15-30%), nonionic surfactants (5-15 %), amphoteric surfactants < 5 %), denatured ethanol (5-15 %) and hydrotrope (<5%).

The application of this soap solution increases the temperature at which self stick occurs when bitumen faces come into contact with another and typically this temperature is increased by 300C or more.

As stated previously, the sleeve can be used to protect a wooden object, such as a fence post or a pole, from decay.

The sleeve is placed over the fence post (which may or may not be previously treated with conventional preservative) and positioned so that, when heat

shrunk, it will encapsulate the required area of the post.

The sleeve is then heated (typically using hot air or infra red heating or possibly even a blow torch) at a temperature of between 800 - 2500 C. This temperature will be sufficient to ensure that the bituminous substance has melted to a sufficiently liquid state to intimately bond to the post prior to shrinkage of the sleeve. Thus, when the sleeve shrinks, an airtight sleeve is formed around the post.

The sleeve is advantageously heated from one end in order to ensure that all air is expelled. However, the sleeve could be perforated to allow air to escape, the perforations being sealed by the bitumen.

The sleeve, together with the bituminous substance, will prevent oxygen, micro-organisms, nitrogen and termites from the surrounding soil and air entering that portion of the post which has been encapsulated and will also greatly reduce the leaching of preservatives from the posts into the surrounding soil.

Also, the presence of the sleeve below ground effectively moves the entry point for moisture by the length of the sleeve below ground level. Thus, in the encapsulated area, the moisture content is considerably lower than a non-encapsulated area. Depending on sleeve length and ground conditions, it is possible to reduce the moisture content below the 20% level needed for decay to occur within the encapsulated portion. The overall effect of the sleeve is to dramatically reduce the likelihood of decay and resultant premature post or pole failure.

A strap could be tied around the top and bottom of the sleeve where the sleeve is most vulnerable and/or the top and bottom of the sleeve could be folded into the remainder of the sleeve prior to heat shrinking. This will result in a higher clamping force at the top and bottom of the sleeve when the sleeve is heat shrunk.

The sleeve could extend beyond the bottom of the post where it can be sealed to form a boot.

The above method of encapsulation can also be used to protect other wooden objects in other applications.

The coated sleeve may also be used for other purposes, for example, to protect electrical cables, joints and lead-outs and to protect elongate metal sections, e.g. underwater or underground piping, against corrosion.