Recoverable Fabric Sleeve

This invention relates to a wraparound, heat- recoverable fabric sleeve for enclosing an elongate object, such as a pipe or a cable, or joints or splices between pipes or cables. In particular the invention relates to such a wraparound sleeve, having longitudinal edges which overlap to close the wraparound.

Heat recoverable articles are well known. They are articles whose dimensional configuration may be made to change when subjected to an appropriate treatment. Typically heat recoverable articles comprise a heat shrinkable sleeve made from a polymeric material that exhi¬ bits the property of elastic or plastic memory as described, for example in US patents 2027962, 3086242 and 3597,372. More recently heat recoverable articles comprising fabrics have become known, as described for example in EP-A-0116393 (MP0790) and EP-A-0117026 (RK176) and EP-A-0116392 (RK178). These comprise a recoverable fabric in conjunction with a polymeric matrix formed by laminating a polymeric material to one or both sides of the fabric to render it impervious.

Wraparound heat-recoverable sleeves for enclosing elongate objects are also well known. They typically comprise a sheet of material which is wrapped around the object, and then the longitudinal edges held together in some way to close the wraparound to form a tubular article. In some known wraparound sleeves the longitudinal edges overlap. They may then be secured together by bonding eg. by adhesive, by fus..on or by a penetrating closure such as stitching or rivetting. Where the longitudinal edges overlap in this way an additional patch closure strip may be used, bonded over the overlapped edges. Again the bond bet¬ ween the patch and each of the overlapped edges may be by

adhesive, by fusion or by a penetrating closure means. The bond between the patch on each of the overlapped edges maybe instead of, but is usually additional to, the bond between the overlapped edges themselves. Other types of clsoure are also known for wraparound sleeves. One common closure, known as a "rail and channel" closure, comprises forming the longitudinal edges of the sleeve into upstanding rails, and providing a channel which slides over the rails to hold the wraparound article closed. Typically the "rail and channel" closure and other similar mechanical - type closures can withstand significantly higher recovery forces than the overlapped and patch type closures: the latter being liable to pull out at the closure as a result of the shear forces between the lapped edges, or between the lapped edges and the patch, generated by the hoop stresses of recovery.

Known wraparound, heat recoverable fabric sleeves are described in EP-A-0116392 (RK178) and EP-A-0278707 (B137). The latter patent application describes a particular type of fabric design which is particularly applicable for heat recoverable articles having a recovery ratio of greater than 40% eg. up to 75%, and which are advantageously closed by a rail and channel type closure that is able to withstand recovery forces up to 30N per 50mms.

We have now designed a new recoverable wraparound fabric sleeve that is particularly suitable for use for covering an object where recovery ratios less than 40% are required eg. 20-30%, and where the edges of the closure are closed by overlapping, optionally with an auxiliary patch, where it is desirable to minimise the shear, hoop, recovery forces at the closure.

The present invention provides a recoverable wra¬ paround article having a recovery ratio of between 15 - 40%, and comprising

(a) a fabric having 7 to 13 heat recoverable fibres per cm in one direction and 4 to 8 fibres, some of

which are heat recoverable, and some of which are heat stable, in a substantially perpendicular direc¬ tion, and

(b) polymeric material laminated to at least one side of the fabric.

Heat stable fibres are those which are not inherently dimensionally recoverable on heating.

The recovery ratio in the present invention is defined in terms of a percentage. The ratio represents the change in a dimension as a percentage of the same dimension before recovery. The recovery ratio of the article of the present invention is in the range of 15-40%. Preferably the recovery ratio is in the range 2 -30%. The minimum ratio of 15% is sufficient to allow the article to be fitted over and shrunk to encapsulate number of objects, in a variety of applica¬ tions. It is not sufficient for sealing onto some of the objects described in EP-A-0278707 (B173), which have a large variation in diameter along their length, but these are not the subject of the present applicaiton. The maximum ratio is 40%, preferably 35% more preferably 30%. A maximum is specified because we have found that for a wraparound article comprising a lap bond, if the recovery ratio is too high, the portion of the sleeve forming the underside of the lapped region becomes too thick on recovery, tending to weaken the bond in the closure region. Preferably the sleeve has a thickness after recovery which is at most 1.2-1.4 times its thickness before recovery. In absolute terms, the thickness before recovery is preferably about 1.8mm, and the thickness after recovery is preferrably about 2.4mm.

The recoverable fabric is preferably provided by interlinking (preferably weaving) fibres that are already recoverable, rather than by deforming a fabric woven from dimensionally stable fabrics. In the preferred case, the

recovery ratio of the article depends at least on the following features: (a) the recovery ratio and the recovery force of the fibres per se , (b) the number of recoverable fibres per unit length in the fabric, (c) the nature of the laminated polymeric material, in particular its viscosity, and (d) the fabric design. Thus the desired recovery ratio can be achieved by balancing features (a) to (d) above.

Features (a) to (d) discussed in the previous paragraph are also to be balanced to achieve the desired recovery force of the article of the present invention, which is preferably less than 25N per 25mm, more preferably less then 15N per 25mm. As described above where a wra¬ paround is closed by a lap bond, on recovery hoop forces are generated at the closure region. These tend to shear the overlapping edges apart. Where a patch is used over the overlapped edges they tend to shear the patch from the sheet edges. Hence the desire to limit the maximum recovery force of the article.

A preferred method of making the fabric according to the invention comprises weaving the fibres into a fabric, laminating them on both sides with a polymeric material and cross-linking the article preferably by irradiating it with a beam of high energy electrons. The irradiation step cross-links both the recoverable fibres of the fabric and the matrix polymer. This increases the viscosity of the matrix, and increases the post recovery strength of the fibres.

The viscosity increase is preferably sufficiently high not only to prevent dripping or running during heat- recovery, particularly during heat recovery by means of a torch, but also sufficiently high to act against the reco¬ very forces of the fibres to achieve a recovery ratio in the ratio 15-40%, and preferably also the desired recovery force. Thus the viscosity of the matrix acts in conjunction

with the fibres to achieve the desired recovery ratio and force.

In the prior art reference EP-A-0278707 (B137) dif¬ ferent extents of cross-linking are required by the fibres of the fabric and the polymer of the matrix, and accordingly a two-step process is preferred. In the present invention a simple one step beam is sufficient by appropriate selection of the density of the recoverable fibres.

Chemical peroxide cross-linking agents may be used in place of irradiation.

The article comprises a polymeric material laminated to at least one side of the fabric. The purpose of the polymeric material is to render the fabric substantially impervious. The extent to which the fabric need be imper¬ vious depends on the use of the sleeve. For example, imper- viousness to water, oil, fuel or hydraulic fluids may be required. A degree of perviousness will, in general, be tolerable depending on the nature of the substrate on the length of time that the assembly will be in use.

The polymeric material is laminated to, and preferably extends throughout the recoverable fabric. We prefer that a true composite structure be formed between the recoverable fabric and a polymeric material by means of which it is ren¬ dered impervious. We prefer that the polymeric material provides a matrix -saterial through which the fabric material be chemically physically compatible with the poly¬ meric material. By physically compatible we mean that the relevant properties of the two materials are similar or identical during lamination, recovery and use. Chemically similar materials are preferred, for example both reco¬ verable fibres and matrix may be polyolefins, and preferred materials are high density and low density polyethylene respectively.

Other thermoplastic or elastomeric materials can be used. Examples of thermoplastic materials include: ethylene/vinyl acetate copolymers, ethylene/εthyl acrylate copolymers, LLDPE, LDPE, MDPE, HDPE, polypropylene, polybu- tylene, polyesters, polyamides , polyetheramides, perfluoroethylene/ethylene copolymers, and polyvinylidene fluoride. The following is a list of preferred elastomeric materials: ABS block copolymers, acrylics including acryla- tes, methacrylates and their copolymers, high vinyl acetate copolymers with ethylenes, polynorbornene, polyurethanes and silicone elastomers.

The sleeve of the invention thus preferably comprises a composite structure of a heat-recoverable fabric an po¬ lymer matrix material as defined in EP-A-0116393 (MP0790 EP) wherein:

(a) the heat recoverable fabric comprises fibres that will recover when heated, the fibres having a recovery stress Y of at least 1 X 10-2, preferably at least 5 X 10 ^-2 more pre¬ ferably at least 1 MPa at a temperature above their recovery temperature; and

(b) the polymer matrix material has a elongation/temp¬ erature profile such that there exists a temperature (T) which is at or above the recovery temperature of the fibres at which temperature the polymeric matrix material has a elongation to break of greater then 20% preferably greater then 100%, especially from 400-700% and a 20% secant modulus X of at least 10~2 MPa (measured at a strain rate of 300% per minutes), and at which temperature the inequality is satisfied:

X (1-R) , is less then one, preferabley Y R less then 0.5, more preferabley less than 0.05.

wherein R is the mean effective volume fraction of heat- recoverable fibres in the composite structure along a given

direction based on the total volume of the composite struc¬ ture, or relevant portion thereof.

The precise technique by means of which the fabric is rendered substantially impervious will of course depend on whether, for example, the polymeric material is simply used in conjunction with the fabric, is adhered to a surface (preferably an inner surface) of the fabric, extends throughout the fabric, or is introduced in some other way. The extent of mechanical interaction required between the fabric and the polymeric material will depend on the extent of bonding that can be achieved during manufacture, and this is a function of the difference between the melt or sof¬ tening temperature of the polymeric material and the reco¬ very temperature of the fabric. Unless a further stretching operation is to be carried out later, recovery should not occur at this stage. Recovery could of course be avoided by mechanically holding the fabric, but this tends to make incorporation of the polymeric material rather complex. Suitable techniques for coating the fabric with a polymeric material which achieve at least some penetration include press lamination, hot coating the fabric with a polymeric material which achieve at least some penetration include press lamination, hot coating from the melt between rollers, spray coating, dip coating and powder coating.

The amount of polymeric material used should be suf¬ ficient to render the fabric sleeve substantially impervious to air when it is recovered. It is possible, therefore, for the polymeric material to be a discontinuous coating or impregnation before recovery, and optionally to melt or sof¬ ten sufficiently to be brought together on recovery to pro¬ vide a substantially impervious barrier. We prefer, however, that the composite of fabric and polymeric material be substantially impervious before as well as after reco¬ very. The thickness of the polymeric material should be great enough to counteract the recovery forces of the fabric

to achieve the desired recovery ratio (also dependant on viscosity as described above) , but small enough to allow the fabric to recover to the desired extent. The composite desirably recovers as a unit with no appreciable drawing- through of fabric within the matrix. A suitable thickness of polymeric material is 0.5 - 1.5mm preferably about 1mm on the inside of the fabric and about 0.5mm on the outside of the fabric. Such a polymeric layer will generally soften during recovery but has a sufficiently high viscosity that it is retained by the fabric. A polymeric material ini¬ tially having a sufficiently high viscosity may be used, or the viscosity of a low viscosity material may be increased by cross-linking, particularly by beaming.

Where two layers of polymeric material are provided one on each side of the sleeve, both layers may be cross- linked, for example by irradiation, or only the layer on the outer surface of the sleeve.

The preferred article according to the invention is recoverable predominantly in one direction. Thus for a heat shrinkable wraparound sleeve, the sleeve is recoverable pre¬ dominantly along the direction corresponding to the circum¬ ference of the sleeve. However it has been found advantageous in the present invention to include non- recoverable fibres, and also a smaller number of heat- recoverable fibres in the substantially perpendicular direction. This finding is based on the observation that when the sleeve shrinks predominantly in one direction, the tightening of the shrinkable fibres in said one direction around the non-shrinkable fibres in the substantially per¬ pendicular direction causes the end to end length of the non-shrinkable fibres to appear to increase. This is thought to be due to the shrinking fibres tightening onto, and reducing any undulations in the non-shrinkable fibre caused by their winding path, in and out of the shrinkable fibres. In a lap wraparound closure, this is disadvan-

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tageous since it results in wirnkling at the lap. This effect is particularly apparent where a heat stable patch is used at the lap since the increase in length of the sleeve is not matched by the patch, and their difference in lengths causes wrinkling at the patch edges. By incorporating a number of shirnkable fibres into the said substantially per¬ pendicular direction the lengthening effect in that direc¬ tion on recovery of the fibres in the said one direction is counter-balanced. Preferably the article comprises less than 0.5, preferably less then 0.25 times as many heat reco¬ verable fibres in said perpendicular direction as in said one direction. Preferably the article comprises more, pre¬ ferably about twice as many heat-stable, non recoverable fibres as recoverable fibres in said perpendicular direc¬ tion.

The said one direςtion, ie. the predominant recovery direction, may constitute either the warp or the weft of the fabric. In some applications, particularly where large diameter sleeves are requried it preferably constitutes the warp, enabling it to be made on reasonably sized machines.

The preferred fabric used according to the invention is a weave. Other designes eg. knits may be used.

Different effects, in terms of for example, final recovery ratio, strength and flexibility, will result from different types of weave even if the same fibres are used. Examples of type of weave include broken twill and twill, especially broken twill 2/2 (two up, two down) and twill 2/2 (two up, two down), satin 4, and satin 5 and related complex designs. Certain weaves are said to have a "float". A "float" is the number of fibres in one direction (say the weft) which a fibre in the other (say warp) direction passes over, before passing under again. The weave may be single ply, or if higher density or thicker fabrics are desired multiple ply weaves may be used.

According to the invention there are 7-13 recoverable fibres per cm in the said one direction (the predominent recovery direction), preferably about 10 per cm. Preferably the heat recoverable fibres are 0.3-0.5mm in diameter, espe¬ cially about 0.4mm. Preferably the heat recoverable fibres have a tex (weight in g per cm) of 50 to 200. Each reco¬ verable fibre may comprise, for example, a shrinkable polyethylene fibre.

The non-recoverable fibres in the substantially per¬ pendicular direction preferably have a tex of 60-220. Each non recoverable "fibre" may comprise for example a bundle of glass fibres. Preferably there are 2-6 non-recoverable fibres per cm in the substantially perpendicular direction preferably about 4 per cm. Preferably there are about half as many recoverable fibres as non-recoverable fibres in the substantially perpendicular direction, ie. about 1-3 per cm, preferably about 2 per cm. Preferably the recoverable and the non-recoverable fibres are uniformly arranged. One par¬ ticular arrangement is a repitition of two recoverable fibres/one recoverable fibre etc. The two non-recoverable fibres may be two glass fibre bundles wrapped together.

The fibres used to produce the recoverable fabric may be monofilaments, multifilaments spun staple yarns or yarns produced by fibrillation, for example from film. Greater flexibility can be attained using multifilament yarns, although problems can be encountered in cross-linking due to the high surface area. Examples of polymeric materials that may be used as the recoverable fibres include polyolefins such as polyethylene (especially HDPE) and polypropylene, polyamids, polyesters and fluoropolymers such as FEP, ethy¬ lene perfluoro copolymers, polyvinylidine fluoride and TFE copolymers. The recovery temperature, by which we mean the temperature at which recovery will go substantially to completion, is preferably 60°C or more, more preferably from 80-250°C, most preferably from 100-150°C.

The heat recoverable fibres may be provided indivi¬ dually, or in bundles.

Non-recoverable fibres are used together with the recoverable fibres. The following non-recoverable materials may be regarded as illustrative: glassfibres, carbon fibres, wires or other metal fibres, polyesters, aromatic polymers such as aromatic polyamides for example Kevlar (trade name) , imides and ceramics. The non-recoverable component may be permanent, giving the recovered article enhanced strength etc., or may be present in discrete form only to locate the recoverable component during installation.

The polymeric embedded fabric sleeve is preferably coated with an adhesive on its inside, ie. on that side which will face the substrate to be enclosed, although the polymeric material providing imperviousness may alone pro¬ vide the desired adhesiveness under installation conditions. Heat-activatable adhesives are preferred, especially hot- melt adhesives such as polyamides and EVAs.

The invention is further illustrated by reference to the accompanying drawings, by way of example, in which:

Figure 1 is a perspective view showing a recoverable wraparound sleeve according to the invention, positioned around aa object to be covered;

Figure 2 is a cross-sectional view through the cover of Figure 1; and

Figure 3 and 4 are schematic views showing the fabric design used in the cover of figures 1 and 2.

Referring to the drawings, Figure 1 shows an object 2 surrounded by a heat shrinkable, wraparound cover 4, the longitudinal edges 6 of which overlap to form a tubular

article. A heat stable patch 8 extends along the article overlying the overlapped longitudinal edges 6.

The heat shrinkable wraparound cover 4 comprises a fabric 8. The warp of the fabric comprises 10 heat- shrinkable high density polyethylene fibres per cm, each having a diameter of 0.4mm. The weft of the fabric compri¬ ses 4 heat-stable glass fibres and 2 heat shrinkable polyethylene fibres (identical to those in the warp). The glass and polyethylene are arranged uniformly, in a pattern two glass, one polythylene etc. The fabric is predominently shrinkable in its warp direction. Hence the warp is arranged to extend around the circumference of the wrapped cover to provide a radially heat shrinkable cover.

As best seen in Figure 2, the fabric 8 is embedded in a matrix of low density polyethylene 10 which is achieved by laminating the fabric oh both sides. One surface of the embedded fabric is coated with a hot melt adhesive layer 12. This forms the inner surface of the wrapped cover.

The heat-shrinkable fabric cover is manufactured by weaving the recoverable fibres, laminating with low density polyethlene, cross-linking the matrix and fibres by irra¬ diating with a beam of electrons and then coating with adhe¬ sive.

The heat stable patch 6 comprises a polymeric material that may be reinforced, eg. with glass fibres. It may comprise an inner coating of adhesive or it may comprise a suitable material which fuses to the wrapped cover on heating. An especially preferred patch 6 is described in EP-A-85303716 (B104 EPC Babyseal) the disclosure of which is incorporated by reference.

For installation the cover 4 is wrapped around the object, the patch positioned, and then the whole heated, first in the patch region to bond the patch to the cover 4

to form the closure, and then around the body of the cover to effect shrinkage. As the recoverable fibres in the warp of the fabric 8 (around the circumference) shrink, the end- to-end glass length tends to increase, caused by eliminating the undulations in the glass where the glass passed over and under the shrinkable fibres. This increase is counter¬ balanced by shrinkage of the recoverable fibres in the weft. Thus there is no overall increase in the fabric length, and hence no wrinkling at the join between the patch and the cover. Thus the behaviour of the sleeve in its longitudinal direction corresponds to the behaviour of the patch.

The overall shrinkage ratio is 25%. This is suf¬ ficiently low that the underlapped portion 14 of the wrapped cover 4 (see fig 1) does not increase unduly in thickness, and therefore does not impair the bond.

The overall shrinkage force is less than 15N/25mm. This is not sufficient to cause shear between the patch 6 and the wrapped cover 4.

The fabric design is illustrated in Figures 3 and 4. Figure 3 is a block diagram as used in the fabrication industry. The 4 by 4 square block illustrates the sub¬ sequent passage of 4 adjacent fibres in each of the warp and the weft. In the diagram the weft extends horizontally, and the warp vertically. A white square illustrates a fibre passing over the fibre in the other direction, and a hatched square a fibre passing under the fibre in the opposite direction. This is also illustrated in the more literal diagram Figure 4 in which the heat recoverable polyethylene fibres are referenced 16 and each pair of non recoverable glass fibres are referenced 18. In the weft there is one recoverable polyethylene fibres for each pair of glass fibre bundles. Thus each of rows 1 and 3 of the weft represents passage of a single polyethylene fibre, and each of rows 2 and 4 of the weft represent passage of a pair of glass fibre

oundles. Each row cf tr.e warp ' ^' represented by vertical columns in Fig.3) represents a single polyethylene fibre. It will be seen that in the weft, eacn glass fibre (rows 2 and 4) has a float of 2, that is t passes alternately under and over two warp fibres. Each polyethylene fibre in the weft however (rows 1 and 3) has a float of 1, passing alter¬ natively under and over a single warp fibre.

The float of 2 for the glass fibres reduces the amount of extension of the overall length cf the weft caused by uncrimping of the glass fibres on recovery, compared to a similar design in which the glass fibres have only a float of 1 in the weft. All the polyethylene fibres in the warp have a float of 2.

The following example is given to illustrate a wra¬ paround built from preferred materials.

Example

The following HDPE monofilament was chosen to provide the recoverable component,

Mn 24500

Mw 135760

Mz 459000

Mp 64400

D 5.378

Initial Modulus (MPa) 3881.3

Tensile Strength (MPa) 534.4

% Elongation (21°C) 21

Monofilament dia (MM) 0.38

This fibre had the following properties

Fibre Properties

Radiation Dosage (Mrads)

Property 8 16 32

100% Modulus (MPa) 0.13

Tensile strength (MPa) 0.93

Elongation to Break (%) 1480

Gel Content (%) 27.0

Recovery Force (MPa) 1.17

Recovery (%) 89

The HDPE fibres were woven with non-recoverable glass fibres to produce the fabric design illustrated in figure 3, The recoverable HDPE fibres were the only fibres in the warp. Recoverable HDPE 'fibres and glass were in the weft.

The glass fibres are preferably ones having the designation EC 9 34 tex x 25152. This type of designation is standard and will be understood by those in the art. Briefly it has the following meaning EC refers to the tex value of the bundles of filaments, x 2S refers to the number of monofilaments in the bundle, 152 refers to 152 twists in the bundles per metre.

The warp density was 10 ends/cm, and the weft density was about 6 per cm (4 glass bundles and 2 HDPE in a 2 glass bundles: 1 HDPE repeating pattern. Hence the warp was the predominant shrink direction.

The fabric was rendered substantially impervious by laminating to it a low density polyethylene at a thickness of 0.5mm on one side and 1mm on the other side. Lamination was carried out at such a temperature, pressure and processing speed that the material permeated the interstices of the fabric but no recovery occurred.

The resulting composite was subjected to an irra¬ diation step with 16 MeV electrons in air at room tem¬ perature for times sufficient to ^" produce the required recovery and product functionally.

The resulting composite material had a recovery of 25%.

The composite material was used to produce a wra¬ paround sleeve suitable for use for covering a pipe in con¬ junction with a closure patch.

The sleeve was arranged with the predominant shrink direction around the circumference.

The composite material was coated with a hot-melt adhesive on that side which would be inwardly facing when the sleeve was in the wrapped around configuration. The adhesive used was applied to a thickness of 1.2mm.