Abstract:
A fibrous closure comprises a dimensionally stable, heat resistant fibrous backing layer and a layer of high shear strength pressure sensitive adhesive. The closure is used in conjunction with a heat shrinkable, wraparound sleeve for sealing cable jackets, connectors and joints between lengths of pipe or other elongate objects. The sleeve is wrapped around the object such that its ends overlap. The closure is then applied over the overlapping ends of the sleeve to prevent slippage of the overlapping ends during heat shrinking, and to prevent subsequent creeping of the overlap joint due to hoop stresses in the shrunken sleeve. The closure avoids use of a relatively inflexible polymeric backing layer, and is therefore able to conform to objects having a relatively small diameter or irregular shape.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to closures for joining the ends of polymeric sheet materials, and specifically relates to closures for joining and sealing the overlapping edges of dimensionally recoverable covers, such as heat-shrinkable polymeric sleeves.  
         BACKGROUND OF THE INVENTION  
         [0002]    Thin-walled polymeric sleeves are known for sealing cable jackets, connectors and the joints between lengths of pipe or other elongate objects, for example to provide environmental sealing protection. Heat-shrinkable tubular sleeves formed by extrusion are commonly used for this purpose, but suffer from the disadvantage that they require access to a free end, which is often not readily available. In addition, it is difficult to produce heat-shrinkable sleeves by extrusion, particularly where the sleeves are for relatively large diameter pipes.  
           [0003]    To overcome these difficulties, so called “wraparound sleeves” have been developed. These wraparound sleeves are more versatile than tubular sleeves in that they can be readily applied to regularly-shaped, elongate articles, including cables and large diameter pipes, which may or may not have an accessible exposed end.  
           [0004]    Wraparound sleeves typically comprise an outer layer of heat-shrinkable polymeric material and an inner layer of mastic or adhesive, which adheres the sleeve to the substrate and fills any voids. The sleeve is wrapped around the substrate such that its ends overlap. The sleeve is subsequently heated, for example by a torch, causing it to shrink into intimate contact with the substrate.  
           [0005]    In order to prevent slippage of the overlapping ends during heat shrinking, and to prevent subsequent creeping of the overlap joint due to hoop stresses in the shrunken sleeve, a closure patch is applied to the overlap joint prior to heat shrinking of the sleeve.  
           [0006]    A number of different types of closure patches are known. One type of closure comprises a polymeric backing material to which a high shear strength hot melt adhesive is applied. In order to provide the closure with dimensional stability, the closure also incorporates a layer of reinforcing material, such as a mesh or fabric. One example of this type of closure is disclosed in U.S. Pat. No. 4,200,676 (Caponigro et al.). This patent discloses a layer of crosslinked hot melt adhesive applied to a polymer layer which is reinforced with glass cloth. The reinforcing layer may either be sandwiched between two layers of polymer or the polymer may be extruded about the reinforcement. Strips of pressure sensitive adhesive or two-sided tape are provided on the adhesive layer for initial adhesion to the wraparound sleeve. U.S. Pat. No. 4,803,104 (Peigneur et al.) discloses a closure patch comprising a laminate of two polymeric layers with an intermediate reinforcing layer. One polymeric layer functions as a backing, and the second layer contacts and bonds to the overlapping edges of the wraparound sleeve. U.S. Pat. No. 4,961,978 (Doheny, Jr. et al.) discloses a closure comprising a dimensionally stable backing layer, a pressure sensitive adhesive, and a heat-shrinkable film having an area smaller than that of the adhesive layer, the heat-shrinkable film layer preferably comprising the same material as the wraparound sleeve.  
           [0007]    Another type of closure is known which does not utilize a reinforcing layer. One example of such a closure is disclosed in U.S. Pat. No. 4,472,468 (Tailor et al.). This patent discloses a wraparound sleeve with an integral closure, the sleeve comprising a heat-shrinkable polymeric layer and a hot melt adhesive layer. The hot melt adhesive layer covers only a portion of the sleeve, leaving a bare area near one end. This bare area forms a closure which welds to the heat-shrinkable sleeve in the region of the overlap joint. U.S. Pat. No. 5,175,032 (Steele et al.) discloses a closure in which the hot melt adhesive layer is eliminated. The polymeric layer is merely provided with strips of a pressure sensitive hold down adhesive near its ends to retain the closure patch in place while it is being fused to the wraparound sleeve. U.S. Pat. No. 5,411,777 (Steele et al.) discloses a sleeve with an integral closure which is provided with a removable susceptor strip to permit induction heating of the polymer layer.  
           [0008]    Known closures for wraparound sleeves suffer from disadvantages which limit their utility. For example, the polymeric backing layers of known closures tend to be relatively thick and stiff. While the backing layer may require only limited flexibility where the closure is used for sealing wraparound sleeves to regularly shaped articles of relatively large diameter (typically greater than 12 inches), such closures may not be flexible enough to conform to the dimensions of objects having an irregular shape or a relatively small diameter. As a result, peeling of the closure can occur. Furthermore, the application of multi-layered closures with relatively thick polymeric backing layers requires large amounts of heat in cause the inner adhesive layer to flow, and bond the closure to the wraparound sleeve. As this heating is typically performed in the field with a gas torch, it is difficult to apply the correct amount of heat, and failure of the closure may result.  
           [0009]    Accordingly, the need exists for an improved closure for wraparound heat-shrinkable sleeves.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention overcomes the disadvantages of the prior art by providing a fibrous closure for a wraparound sleeve comprising a dimensionally stable heat resistant fibrous backing layer and a layer of high shear strength pressure sensitive adhesive. The closure of the present invention avoids use of a polymeric backing layer, and is therefore able to conform to substrates of relatively small diameter or of irregular shape.  
           [0011]    The fibrous backing layer is dimensionally stable so as to prevent deformation of the closure patch during heat shrinking of the wraparound sleeve, and is flame resistant and temperature resistant so that it will not be damaged during heating of the closure patch by a flame. Most preferably, the fibrous backing material comprises an inorganic fabric such as a mat of woven or non-woven glass fibers.  
           [0012]    The pressure sensitive adhesive is preferably partially or completely crosslinked and is highly temperature resistant, flame resistant and shear resistant. Contrary to the teachings of the prior art, the inventors have discovered that pressure sensitive adhesives can be effective to provide initial adhesion of the closure to the wraparound sleeve and also to permanently bond the closure to the sleeve.  
           [0013]    In another aspect, the present invention provides a wraparound sleeve comprised of an outer heat-shrinkable polymeric material and an inner adhesive layer. The wraparound sleeve is preferably in the form of a rectangular sheet, one end of which is provided with a closure as described above comprising a fibrous backing material and a pressure sensitive adhesive layer. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The invention will now be described, byway of example only, with reference to the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 is a side view of a preferred closure according to the invention;  
         [0016]    [0016]FIG. 2 is a top plan view of the closure of FIG. 1;  
         [0017]    [0017]FIG. 3 shows the closure of FIG. 1 immediately before it is applied to a wraparound sleeve which has been applied to a pipe;  
         [0018]    [0018]FIG. 4 shows the overlapped ends of a wraparound sleeve;  
         [0019]    [0019]FIG. 5 shows a closure according to the invention initially adhered to the wraparound sleeve of FIG. 4;  
         [0020]    [0020]FIG. 6 shows the closure of FIG. 5 being bonded to the wraparound sleeve by application of heat from a torch; and  
         [0021]    [0021]FIG. 7 shows a wraparound sleeve according to the invention with an integral closure. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]    The invention will now be described with reference to FIGS.  1  to  7 . It is to be noted that the FIGS.  1  to  7  are not drawn to scale with respect to the relative thicknesses of the closures, sleeves and the substrate to which they are applied, or with respect to the thicknesses of the layers comprising the closures and the sleeves.  
         [0023]    [0023]FIGS. 1 and 2 illustrate a preferred closure  10  according to the present invention. As shown in FIG. 1, closure  10  comprises a backing layer  12 , a layer of adhesive  14  applied to the backing layer, and a release film  16  applied to the adhesive layer  14 . Closure  10  preferably has an elongate, rectangular shape for application along the length of an overlapping joint formed by the ends of a wraparound sleeve.  
         [0024]    The backing layer  12  is comprised of a fibrous material and has a first surface  18  and an opposed second surface  20 . The backing layer  12  has sufficient dimensional stability such that, during heat shrinking of the wraparound sleeve to which the closure will be applied, the backing layer will resist substantial deformation which would result in pulling apart of the overlapping joint formed by the ends of the wraparound sleeve. Furthermore, the backing layer possesses sufficient resistance to heat such that it will retain its integrity and dimensional stability when it is heated during application to a wraparound sleeve. Preferably, the backing layer should be of a composition able to resist the heat and flame of a torch for a time sufficient to allow the closure to be applied to the underlying wraparound sleeve.  
         [0025]    Preferably the backing layer is comprised of an inorganic fibrous material, such as glass fibers (also referred to herein as “fiberglass”). The fibrous material may comprise either a woven or non-woven material. Where it is non-woven, it is preferably in the form of a random mat. Most preferably, the backing layer comprises a woven mat, having either an open weave or a closed weave. An open weave may be more preferred where the substrate to which the wraparound sleeve is applied has a small diameter or an irregular shape, or where there is some axial shrinkage of the sleeve, since a fabric with an open weave may be more flexible and therefore better able to conform to the contours of the sleeve and the underlying substrate. One example of a suitable backing layer comprises a 10 ounce or 14 ounce woven fiberglass fabric.  
         [0026]    The backing layer may preferably be coloured, for example by incorporation of a colourant such as a dye, or by including other types of fibers in the backing layer for colouring purposes.  
         [0027]    The adhesive layer  14  is applied to the first surface  18  of backing layer  12 , preferably by lamination, such that it is in direct contact with the fibrous material comprising backing layer  12 . The adhesive comprising layer  14  has sufficient shear resistance such that it resists slippage of the closure  10  relative to the wraparound sleeve during heat shrinking of the sleeve, and so as to resist creeping of the closure relative to the sleeve after heat shrinking of the sleeve is completed.  
         [0028]    The adhesive preferably has sufficient tack (pressure sensitivity) at ambient temperatures so that it can be applied to the contours of the wraparound sleeve prior to heating of the closure. As used herein, the term “ambient temperature” refers to the temperatures at which the closure is applied to a heat shrinkable sleeve, the lower limit of the ambient temperature being at least as low as about 0° C. Furthermore, the adhesive also has sufficient pressure-sensitivity at elevated temperature such that it forms a permanent bond between the backing layer and the wraparound sleeve upon application of sufficient heat.  
         [0029]    The pressure-sensitive adhesive comprising layer  14  can be selected from one or more adhesive materials selected from the group comprising iso-butylene polymers such as polyisobutylene, polybutene and butyl rubber. These polymers are preferably at least partially crosslinked in order to increase their shear strength, particularly at elevated temperatures. Other preferred adhesive materials include silicones.  
         [0030]    One particularly preferred pressure-sensitive adhesive is the partially crosslinked butyl mastic RSL-091 manufactured by RPD Inc. of Evansville, Ind. This adhesive is preferably applied to the fibrous backing layer  12  in a thickness of about 0.03 inches.  
         [0031]    The release film  16  preferably comprises a self supporting strippable polymer film which is removed prior to use of the closure  10 . Thus, immediately prior to application of the closure  10  to a wraparound sleeve, the adhesive layer  14  has an exposed surface  22  which is available for adhesion to the sleeve, the area of the exposed surface  22  being substantially equal to the total area of the adhesive layer  14 .  
         [0032]    The following is a description of a preferred method of applying a close-fitting protective covering to an article, and in particular a method of applying a heat-shrinkable wraparound sleeve  24  to a joint at which two lengths of pipe  26  are connected, as illustrated in FIGS.  3  to  6 . It will be noted that details of the pipe  26  are omitted from FIGS.  4  to  6 , as are details of the layers of material comprising the wraparound sleeve  24 .  
         [0033]    The heat-shrinkable sleeve comprises a flexible sheet  28  having a first surface  30 , an opposed second surface  32 , a first end portion  34  and a second end portion  36 , the end portions being spaced from one another in a longitudinal direction (when the sheet is laid flat).  
         [0034]    The flexible sheet  28  is comprised of a dimensionally heat unstable material, preferably a polymer, the material having been stretched in the longitudinal direction from an original heat stable form to a dimensionally heat unstable form capable of moving in the longitudinal direction toward its original heat stable form by the application of heat. As used herein, the term “longitudinal direction” refers to the direction along an axis extending between the end portions  34  and  36  of the flexible sheet  28 .  
         [0035]    The flexible sheet  28  is wrapped around the pipe  26  by laying the sheet  28  against the pipe  26  and overlapping the first end portion  34  of the sheet  28  over the second end portion  36 . This is illustrated in FIGS. 3 and 4.  
         [0036]    Next, the closure  10  is applied to the overlapped end portions  34 ,  36  of flexible sheet  28 . The closure  10 , with the release film  16  removed, is applied to the overlapped end portions  34 ,  36  with the exposed surface  22  of adhesive layer  14  directly contacting the sleeve  24 . As mentioned above, the adhesive has sufficient pressure sensitivity at ambient temperature such that it initially adheres to the sleeve  24  prior to application of heat. The closure  10  has a first edge  38  which is applied to the first end portion  34  of sheet  24 , and an opposed second edge  40  which is applied on the underlapping second portion  36  of the flexible sheet  28 . This is illustrated in FIG. 5.  
         [0037]    After application of the closure  10  to the sleeve  24 , the closure  10  is heated for a sufficient time and to a sufficient temperature to cause the adhesive layer  14  to bond the closure  10  to the first and second end portions  34 ,  36  of the flexible sheet  28 . As illustrated in FIG. 6, heat is preferably applied directly to the second surface  18  of backing layer by a flame from a torch, from example a propane torch.  
         [0038]    After the closure  10  is bonded to the sheet  28 , the flexible sheet  28  is heated, causing it to shrink in the longitudinal direction toward its original heat stable form and into close-fitting relation with the underlying pipe  26 .  
         [0039]    Preferably, the first surface of the flexible sheet  28  is provided with a functional coating  42  to improve contact between the flexible sheet  28  and the underlying substrate and to fill any voids. The functional coating preferably comprises a hot-melt adhesive or a mastic.  
         [0040]    As mentioned above, the adhesive layer  14  has sufficient shear resistance to prevent substantial slippage and creeping of the closure  10  relative to the flexible sheet  28  during and after heating thereof, and the dimensional stability of the backing layer is sufficient to resist substantial deformation in the longitudinal direction during and after heating of the flexible sheet.  
         [0041]    The closure discussed above with reference to FIGS.  1  to  6  is in the form of an elongate strip which is applied to the sleeve  24  after it is wrapped around pipe  26 . FIG. 7 illustrates an alternate type of closure in which the closure is attached to the sleeve before the sleeve is wrapped around the substrate. The sleeve/closure  100  illustrated in FIG. 7 comprises a closure strip  110  and a flexible sheet  128 . The closure strip  110  has a first edge  138  which is disposed on the first end portion  134  of the flexible sheet  128 . The second edge  140  of closure strip  110  comprises a free edge extending beyond the first end portion  134 . In the embodiment shown in FIG. 7, a release film  116  (shown partially peeled from adhesive layer  114 ) is provided between the free edge  140  and the first end portion  134  of flexible sheet  128 , thereby preventing premature adhesion of adhesive layer  114  to the second end portion  136  of flexible sheet  128 . As with sleeve  24  described above, the flexible sheet  128  has a first surface  130  and a second surface  132 , wherein a functional coating  142  is provided on the first surface  130 .  
         [0042]    Although the invention has been described by reference to certain preferred embodiments, it is not to be limited thereto. Rather, the invention is intended to include all embodiments which may fall within the scope of the following claims.