Abstract:
An adhesive tape having a perforated carrier carrying on opposite sides a structural adhesive with tack such that two articles can be connected by the adhesive tape. The two articles are initially held together by pressure. A direct bond from one article to the other through the perforations in the carrier is subsequently formed to secure the two articles together.

Description:
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    Not Applicable. 
       CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    This application claims priority in Great Britain Appln. No. 1506261.5, filed Apr. 13, 2015 and Great Britain Appln. No. 1506413.2, filed Apr. 15, 2015, both of which are entitled “Adhesive Tape”. The full disclosures of these applications are hereby incorporated by reference. 
       MICROFICHE/COPYRIGHT REFERENCE 
       [0003]    Not Applicable. 
       FIELD OF THE INVENTION 
       [0004]    The invention relates to an adhesive tape. 
       BACKGROUND OF THE INVENTION 
       [0005]    It is known to use double-sided adhesive tapes to connect two or more articles. The applications for which such double-sided adhesive tapes can be used are limited by both the strength of the connection to hold the articles together during assembly (the initial adhesion strength) and the strength of the connection to hold the articles together during use (the final adhesion strength). 
         [0006]    Known adhesive tapes are not suitable for structural bonding applications, for example automotive, aerospace or constructions applications, which require significant initial and final adhesion strengths along with a cohesive strength equivalent to liquid adhesives such as epoxy and polyurethane (PU). 
       SUMMARY OF THE INVENTION 
       [0007]    According to a first aspect of the present invention there is provided an adhesive tape comprising a perforated carrier carrying on opposite sides a structural adhesive with tack such that two articles can be connected by the adhesive tape, the two articles being initially held together by pressure and subsequently bonded by the structural adhesive so that the structural adhesive forms a direct bond from one article to the other through the perforations in the carrier. 
         [0008]    The structural adhesive with tack advantageously ensures that the initial adhesion strength of the adhesive is sufficient to hold the two articles in position during assembly, prior to formation of the structural bond between the two articles. This facilitates transportation of articles during manufacture, for example along a manufacturing line. The present invention is also advantageous as the formation of a direct bond from one article to the other through the perforations in the carrier enables a high final adhesion and cohesion strength to be achieved through a homogenous reinforced bond line. 
         [0009]    Providing the adhesive in tape form advantageously provides a uniform bond thickness, as the risk of the adhesive running or slumping prior to final assembly of components is eliminated. 
         [0010]    The perforated carrier may be woven and/or may comprise a plurality of reinforcement fibres, for example, reinforcement fibres including glass. The reinforcement fibres further increase the strength of the bond or connection between the two articles, and advantageously provides impact resistance. 
         [0011]    The structural adhesive may be cross-linkable and the bond between the two articles may be a cross-linked bond. The cross-linked bond further increases the final adhesion strength. 
         [0012]    The structural adhesive may comprise a polymer, for example, a thermosetting polymer. The polymer may comprise a polyepoxide, for example, polyepoxyacrylate. 
         [0013]    The structural adhesive may include a tackifier. Molecules of a tackifier may be distributed throughout the structural adhesive. Alternatively, the structural adhesive may be inherently tacky. The tackifier increases the initial adhesion strength. 
         [0014]    The structural adhesive may comprise a release layer on one side, for example a release layer having a silicone coating. The release layer advantageously enables the adhesive tape to be rolled up for storage and/or transportation. 
         [0015]    According to a second aspect of the present invention there is provided a structure comprising two articles connected by an adhesive tape according to the first aspect of the present invention. 
         [0016]    According to a third aspect of the present invention there is provided a vehicle comprising two panels connected by an adhesive tape according to the first aspect of the present invention. 
         [0017]    According to a fourth aspect of the present invention there is provided a method of connecting two articles comprising the steps a) providing an adhesive tape comprising a perforated carrier carrying a structural adhesive with tack on opposite sides; b) placing adhesive tape between the two articles and applying pressure to hold two articles in a desired position; c) activating the adhesive so that a direct bond is formed from one article to the other through the perforations in the carrier. 
         [0018]    The structural adhesive may comprise a polymer, and the step of activating the adhesive so that a direct bond is formed from one article to the other may include curing the polymer. 
         [0019]    According to a further aspect of the invention there is provided a method of forming a structure using the method of connecting two articles according to the fourth aspect of the present invention. 
         [0020]    Other objects, features, and advantages of the invention will become apparent from a review of the entire specification, including the appended claims and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1  is a perspective view of an adhesive tape according to a first embodiment of the present invention; 
           [0023]      FIG. 2  is a side view of a structure comprising two articles connected by the adhesive tape of  FIG. 1 ; 
           [0024]      FIG. 3  is a plan view of a perforated carrier for use in the adhesive tape of  FIG. 1 ; 
           [0025]      FIG. 4  is a side view of the adhesive tape of  FIG. 1  being applied to an article; 
           [0026]      FIG. 5  is a side view of the structure of  FIG. 2  during assembly; and 
           [0027]      FIG. 6  is an alternative side view of the structure of  FIG. 2  during assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    Referring now to  FIG. 1  there is shown a piece of adhesive tape  10  according to the present invention. The adhesive tape  10  has a perforated carrier  20 , a first adhesive layer  22  and a second adhesive layer  24 . As shown in  FIG. 1 , the adhesive tape  10  also has a protective release layer  26 . 
         [0029]    The carrier  20  is a scrim carrier and has a pair of opposing surfaces  28   a ,  28   b  and a mesh of interconnected fibres  30  that are separated by a plurality of perforations  32 , as shown in  FIG. 3 . The carrier  20  is in the form of a tape or ribbon. The fibres  30  are glass fibres. 
         [0030]    The first adhesive layer  22  is a polymeric adhesive  34  with inherent tack properties, for example a thermosetting rubber or polyepoxyacrylate. The first adhesive layer has a pair of opposing surfaces  38   a,    38   b.    
         [0031]    The second adhesive layer  22  is also a polymeric adhesive  34  with inherent tack properties, for example a thermosetting rubber or polyepoxyacrylate. The second adhesive layer has a pair of opposing surfaces  40   a,    40   b.    
         [0032]    The release layer  26  has a pair of opposing surfaces  42   a,    42   b.  Surface  42   a  and  42   b  of the release layer  26  each have a silicone coating (not shown). 
         [0033]    The adhesive tape  10  is prepared as follows. 
         [0034]    The first adhesive layer  22  is applied to the carrier  20  such that surface  28   a  of the carrier  20  is in contact with and adhered to surface  38   b  of the first adhesive layer  22 . 
         [0035]    The second adhesive layer  24  is applied to the carrier  20  such that surface  28   b  of the carrier  20  is in contact with and adhered to surface  40   a  of the second adhesive layer  24 . 
         [0036]    A release layer  26  is applied to the first adhesive layer  22  such that surface  42   b  of the release layer  26  is in releasable contact with surface  38   a  of the first adhesive layer  22 . 
         [0037]    The adhesive tape  10  is wound into rolls up to 1600 mm wide and up to 1000 m in length and processed into smaller rolls using known slit/rewind or rewind/slit equipment for transportation and/or storage and/or application. 
         [0038]    Use of the adhesive tape  10  to form a structure  80  by connecting two carbon-fibre composite articles  44 ,  46  will now be described with reference to  FIGS. 4 to 6 . 
         [0039]    The first carbon-fibre composite article  44  has an inner surface  48  and an outer surface  50 . 
         [0040]    The second carbon-fibre composite article  46  has an inner surface  52  and an outer surface  54 . 
         [0041]    The adhesive tape  10  is applied to the first article  44  such that surface  40   b  of the second adhesive layer  24  is in contact with the inner surface  48  of the first article  44 . The tackiness (shown by arrows A) of the second adhesive layer  24  adheres the adhesive tape  10  to the first article  44 . 
         [0042]    The protective release layer  26  is removed from the first adhesive layer  22  by peeling surface  42   b  of the release layer  26  away from surface  38   a  of the first adhesive layer  22  in the direction of arrow B. 
         [0043]    The second article  46  is positioned in a desired position relative to the first article  44  and pressed into contact with the adhesive tape  10 . The inner surface  52  of the second article  46  is pressed into contact with surface  38   a  of the first adhesive layer  22 . The tackiness (shown by arrows C) of the first adhesive layer  22  adheres the adhesive tape  10  to the second article  46 . 
         [0044]    In this way the first and second articles  44 ,  46  are held in the desired position to form structure  80 . The tack properties of the first and second adhesive layers  22 ,  24  advantageously provides the initial adhesion strength required to retain the first and second articles  44 ,  46  in the desired position. 
         [0045]    Once the first and second articles  44 ,  46  are in the desired position, an activator, for example heat or ultra violet radiation, is applied to the structure  80 . 
         [0046]    The activator causes the formation of cross-links (depicted by arrows D) in the polymeric adhesive  34  of both the first and second adhesive layers  22 ,  24 . The cross-links are formed through the perforations  32  in the carrier  20  to the first and second articles  44 ,  46  to provide a homogenous bond line. 
         [0047]    In this way a structural bond is formed between the first and second articles  44 ,  46  of the structure  80 . The formation of the cross-linked bond through the perforations  32  in the carrier  20  provides the high final adhesion strength required for high performance applications. The carrier  20  acts as a reinforcement within the bond, providing additional strength. The final adhesion strength of the adhesive tape  10  is 6 to 12 KN/25 mm2. 
         [0048]    The first and second articles  44 ,  46  may be panels for a vehicle, for example a car. The adhesive tape  10  may be up to 25 mm in width and used in lengths up to 10 m, for example having 0.05 mm-0.1 mm thick carrier and 0.05 mm-0.1 mm adhesive on each side. 
         [0049]    In the example described above, the first and second adhesive layers comprise a polymeric adhesive with inherent tack properties. In alternative embodiments, the first and second adhesive layers may be formed from a polymer matrix in which molecules of a tackifier, a chemical compound that increases the tack or stickiness of the surface of an adhesive, are dispersed. 
         [0050]    In the example described above, the carrier is formed from a mesh of interconnected fibres that are separated by a plurality of perforations. In alternative embodiments, the carrier may be formed from any woven or knitted structure in which the fibres are separated by perforations or openings. 
         [0051]    In the example described above, the first and second articles are carbon-fibre composite articles. In alternative embodiments, the first and/or second article may be manufactured from any material.