Abstract:
Embodiments of the present invention generally relate to adhesive tapes having high tensile strength properties. In particular, embodiments of the present invention relate to adhesive tapes having tensile strength greater than 50 pounds/inch, while maintaining hand tearability characteristics. In one embodiment, a high tensile strength adhesive tape comprises a backing layer, and an adhesive layer affixed to a surface of the backing layer, wherein the adhesive tape has a tensile strength of at least about 50 pounds per inch, and a tear strength of less than about 10 pounds.

Description:
PRIORITY CLAIM 
       [0001]    This is a continuation of U.S. application Ser. No. 12/013,424, filed Jan. 12, 2008, which claims the benefit of US Provisional Application No. 60/884,802, filed Jan. 12, 2007, both of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention generally relate to adhesive tapes having high tensile strength properties. In particular, embodiments of the present invention relate to adhesive tapes having tensile strength greater than 50 pounds/inch, while maintaining hand tearability characteristics. 
         [0004]    2. Description of the Related Art 
         [0005]    Adhesive tapes, specifically duct tapes and film/woven cloth tapes, are designed for applications based on their material properties. Many of the material properties are determined by the combination of adhesive type and the strength of the backing material. For example, standard adhesive tapes typically have tensile strengths in the range of 20-35 pounds/inch. Such tapes are beneficial for most household uses, and are desirable for their easy-to-tear characteristics, i.e., low tear strength. However, these tapes may fail when a significant tensile force is applied. 
         [0006]    Tapes designed for “high strength” applications generally have a tensile strength in a range of 35-45 pounds/inch. While useful for many industrial applications, these tapes generally have high tear strength characteristics, thus requiring a tool, such as a knife, to tear. Also, these tapes may fail when subjected to very high tensile forces, i.e., greater than 50 pounds/inch. 
         [0007]    Therefore, there is a need for a high tensile strength tape capable of withstanding high tensile forces greater than 50 pounds/inch, while maintaining hand tearability characteristics. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments of the present invention generally relate to a high tensile strength tape having hand tearability characteristics. In one embodiment, A high tensile strength adhesive tape comprises a backing layer, and an adhesive layer affixed to a surface of the backing layer, wherein the adhesive tape has a tensile strength of at least about 50 pounds per inch, and a tear strength of less than about 10 pounds. 
         [0009]    In another embodiment of the present invention, a high tensile strength adhesive tape comprises a backing layer comprising a woven cloth scrim, and a pressure-sensitive adhesive layer disposed on a surface of the backing, wherein the adhesive tape has a tensile strength of between about 50 pounds per inch and about 100 pounds per inch, and a tear strength of between about 0.05 pounds and about 10 pounds. 
         [0010]    In yet another embodiment, a high tensile strength adhesive tape comprises a woven cloth scrim comprising a plurality of interlaced threads arranged in a grid density of about 28×44 threads per square inch, and a rubber-based pressure-sensitive adhesive layer disposed on a surface of the scrim, wherein the adhesive tape has a tensile strength of at least 50 pounds per inch and a tear strength of less than about 10 pounds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    So the manner in which the above recited features of the present invention can be understood in detail, a more particular description of embodiments of the present invention, briefly summarized above, may be had by reference to embodiments, which are illustrated in the appended drawings. It is to be noted, however, the appended drawings illustrate only typical embodiments of embodiments encompassed within the scope of the present invention, and, therefore, are not to be considered limiting, for the present invention may admit to other equally effective embodiments, wherein: 
           [0012]      FIG. 1  depicts an adhesive tape in accordance with one embodiment of the present invention; and 
           [0013]      FIG. 2  depicts a flowchart for a method of producing adhesive tape in accordance with one embodiment of the present invention. 
       
    
    
       [0014]    The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including but not limited to. To facilitate understanding, like reference numerals have been used, where possible, to designate like elements common to the figures. 
       DETAILED DESCRIPTION 
       [0015]      FIG. 1  depicts an adhesive tape in accordance with an embodiment of the present invention. The adhesive tape  100  may be a duct tape, electrical tape, cloth tape, masking tape, packing tape, stationary tape, or the like. In one embodiment, the adhesive tape  100  is a duct tape. 
         [0016]    The adhesive tape  100  generally comprises a backing layer  101  and an adhesive layer  104 . The adhesive tape  100  may optionally comprise a release liner material  106  applied to the layer of adhesive  104 . The release liner  106  prevents the adhesive layer  104  from unnecessarily adhering to unintended objects, and allows for easy unwinding if packaged in roll form. However, omitting the release liner  106  facilitates the tape  100  to be manufactured and packaged as a self-wound roll. 
         [0017]    In some embodiments of the present invention which do not comprise a release liner, the unwind force of the adhesive tape on the roll is between about 50 ounce-force/inch (about 5.5 N/cm) and about 200 ounce-force/inch (about 22 N/cm) when the adhesive tape is exposed to a temperature of 180° F. and is being unwound at a rate of about 12 in/min (30.5 cm/min). Additionally, in some embodiments of the present invention, the unwind force of the tape on the roll is between about 5 ounce-force/inch (about 0.55 N/cm) and about 75 ounce-force/inch (about 8.20 N/cm) when subjected to an unwind rate of about 100 ft/min (about 30.5 m/min). 
         [0018]    In one embodiment of the present invention, the adhesion of the adhesive  104  to the backing layer  101  is between about 50 ounce-force/inch (about 5.5 N/cm) and about 150 ounce-force/inch (about 16.5 N/cm). In another embodiment of the present invention, the adhesion of the adhesive  104  to the backing layer  101  is between about 75 ounce-force/inch (about 8 N/cm) and about 125 ounce-force/inch (about 14 N/cm). 
         [0019]    The backing layer  101  generally comprises at least a scrim  102 , and optionally a film layer  108 . The scrim  102  comprises a woven or non-woven material. The material may be any natural or synthetic textile material. In one embodiment, the scrim  102  is a cloth material such as cotton, and the like. Alternatively, the scrim  102  may comprise a woven or non-woven scrim material, including, but not limited to, cotton, polyester, nylon, one or more polymeric materials, and the like. 
         [0020]    In one embodiment of the present invention, the scrim  102  is a woven cloth material. The woven cloth material is comprised of a plurality of interlaced threads. The interlaced threads may be formed such that when a tensile force is positively applied in either a machine direction or cross direction, or both, the threads reinforce one another, thereby resisting failure. The interlaced threads may be arranged in any conceivable fashion, including, but not limited to, grid patterns, aligned in parallel, randomly distributed, traditional woven patterns, and the like. 
         [0021]    In one embodiment, the threads are arranged in a grid having a grid density in a range of about 5×10 threads per square inch to about 50×100 threads per square inch. In one embodiment, the threads are arranged in a grid having a grid density of about 28×44 threads per square inch. 
         [0022]    The film layer  108  is disposed on one side of the scrim  102 , or optionally encompassing the entire scrim  102 . The film layer  108  is generally a polyethylene film. However, any polymer film is contemplated. Optionally, the film layer  108  may be multilayered. In one embodiment, the film layer  108  includes a tying layer (not shown) against the scrim  102 . The tying layer may include ethylene methacrylate, ethylene vinyl acetate, or the like. The film layer  108  protects the backing layer  102  from moisture and abrasion, and effectively seals the backing layer  102 . The film layer  108  provides enhanced surface area to which the adhesive layer  104  may adhere. 
         [0023]    Some embodiments of the present invention provide abrasion resistant materials and/or toughness modifiers to the backing layer  102 . Such materials include, but are not limited to, styrene block copolymers, polypropylene, K-resins, and the like. Other known protective materials may be added as well. 
         [0024]    The adhesive layer  104  may be any adequate adhesive. In one embodiment, the adhesive layer  104  is a pressure-sensitive adhesive comprising at least one of silicone, natural or synthetic rubber, thermal plastic elastomer, polyurethane, water or solvent based acrylic, or the like. In one embodiment, the adhesive layer  104  is a rubber-based pressure-sensitive adhesive. Other embodiments of the present invention utilize a residue-free adhesive layer  104 . Exemplary residue-free adhesives include, but are not limited to, acrylic, silicone, polyurethane, rubber, or the like. The adhesive layer  104  may also be an aggressive compounded adhesive, such as, for example, those described in U.S. Pat. Nos. 4,880,880; 4,997,709; and 5,405,703; each of which is incorporated herein by reference in its entirety. The adhesive layer  104  may be applied to a side of the backing layer  102  or film layer  108 . 
         [0025]    In other embodiments of the present invention, the adhesive layer  104  includes a tackifying resin to improve application of the adhesive tape  100  in cold temperatures. The tackifying resin may be any adequate tackifying resin. In one embodiment, the adhesive layer  104  includes about 5 percent to about 30 percent by weight of the tackifying resin. In another embodiment, the adhesive layer  104  comprises at least one of a terpene phenolic resin, a rosin ester resin, a C 5  or C 9  hydrocarbon resin or blends thereof. In another embodiment, the adhesive layer  104  includes about 5 percent to about 30 percent by weight of a rosin ester resin. 
         [0026]    The optional release liner  106  may be applied to an exposed side of the adhesive layer  104 . The release liner material  106  may be a silicone liner material, or non-silicone release liner material, such as polyvinyl octadecylcarbamate. Other types of release liners  106  include, but are not limited to polyvinyl stearylcarbamate, vinyl acrylic emulsion release liner material, and a fluorochemical emulsion with an acrylic backbone. 
         [0027]    In alternative embodiments, the release liner  106  may be provided as a layer applied on the backing  101 . In such an embodiment, when the adhesive tape  100  is provided in a roll, the force required to unroll the adhesive tape  100  is substantially less than it would be on an adhesive tape  100  of the present invention provided without such a release liner. In one embodiment, the release liner  106  may comprise a non-silicone material, for example polyvinyl octadecylcarbamate or polyvinyl stearylcarbamate. 
         [0028]    The force at which the adhesive tape  100  breaks when a tensile force is applied is commonly denoted as the tensile strength. In one embodiment, the adhesive tape  100  has a minimum tensile strength of at least about 50 pounds/inch. In another embodiment, the adhesive tape  100  has a tensile strength in a range of about 50-100 pounds/inch. In yet another embodiment, the adhesive tape  100  has a tensile strength of at least one of about 50, 55, 60, 65, 70, 75, or 80 pounds/inch. 
         [0029]    Despite high tensile strength, embodiments of the present invention provide adhesive tapes with relatively low tear strength, i.e., the force at which the interlaced threads fail due to a tear force, such that the adhesive tapes are hand-tearable. Generally, a hand-tearable tape is a tape that may be torn by hand without the use of a cutting or tearing tool. In one embodiment, the adhesive tape  100  has a tear strength in a range of about 0.01 pounds to about 10 pounds. In another embodiment, the adhesive tape has a tear strength in a range of about 0.05 pounds to about 5 pounds. 
         [0030]    In an alternate embodiment, stabilizers may be added to either the backing layer  101  and/or the adhesive layer  104  to improve the UV resistance and deter thermal degradation. Where multiple film layers  108  exist in the backing layer, a stabilizer may be added to one of the film layers  108 . The stabilizers may be applied in at least single or multiple layers. 
         [0031]    In one embodiment, the stabilizers include any high molecular weight stabilizer. In another embodiment, the stabilizers comprise at least a hindered amine light stabilizer (HALS). In another embodiment, the stabilizer comprises an ultraviolet light absorbing agent, such as 3,5-di-t-Butyl-4-Hydroxybenzoic Acid, Hexadecyl Ester, and a solvent. In yet another embodiment, the stabilizer comprises an ultraviolet light absorbing agent and free radical scavenger, commercially available under the name CYASORB® UV-2908. Additional embodiments provide the stabilizer comprises a UV light stabilizer, commercially available under the name Tinuvin 765. 
         [0032]    Antioxidants may also be added to either the backing layer  101  and/or the adhesive layer  104 . The antioxidants may include hindered phenols or multifunctional phenols such as those containing sulfur or phosphorus. The performance of either the UV stabilizers or the antioxidants may be further enhanced by utilizing synergists such as, for example, thiodipropionate esters and phosphites, and/or chelating agents and metal deactivators, for example, ethylenediamine tetraacetic acid, salts thereof, and disalicylalpropylenediimine. 
         [0033]    In other embodiments, other agents may be incorporated into the adhesive tape  100 . In one embodiment, a fungicide is applied to the adhesive tape to resist fungal growth. Exemplary fungicides include miconazol, amphotericin B, nystatin, griseofulvin, and the like. Embodiments of the present invention may further comprise any bioactive agent or the like, to prevent any undesirable biological growth or presence in the adhesive tape  100 . 
         [0034]      FIG. 2  depicts a flowchart of a method for making an adhesive tape in accordance with one embodiment of the present invention. The method  200  begins at step  202 . At step  204 , an adhesive is prepared. In one embodiment, the adhesive is compounded in an intensive mixer such as a banbury or extruder. Where a rubber-based adhesive is utilized, the rubber compounds are introduced in pellet, slab, liquid, or solid (e.g., flakes, powders, etc.) form, then heated and mixed until they are melted and substantially homogeneous. Other ingredients are added to the blend tank as specified in the formulation, including any tackifying agents, viscosity modifiers, antioxidants, or the like. The final mixture is thick but smooth enough to be pumped to a holding tank connected to the coating equipment. 
         [0035]    At step  206 , the adhesive and the backing layer  101  are combined using sophisticated coating equipment. In one embodiment, the adhesive is softened by heat on a roller mill. A roller mill typically consists of closely spaced hollow rollers made of heavy gauge stainless steel. The rollers are attached to high torque gears and a motor, and are rotated at a predetermined speed. The temperature of the rollers is continuously regulated by pumping water through the center of the rollers. In one embodiment, a top roller is held at a temperature between about 230° F. and about 290° F. and a center roller is maintained between about 80° F. and about 120° F. The rollers are generally fixed in a position that allows only a small gap or nip between them. As the rollers rotate, the adhesive is fed into this space, which in turn, heats and softens the adhesive. This arrangement allows the molten adhesive to form a thin sheet across the surface of the rollers. 
         [0036]    In one embodiment, the backing layer  101  is fed into a coating machine through a second set of rollers. A third roller, maintained between about 180° F. and about 230° F., places the backing layer  101  in contact with the adhesive. At this stage in the process, generally known as coating, the adhesive is transferred to the backing layer  101 , forming an adhesive layer  104 . By controlling the gaps between the rollers, the thickness of the adhesive layer  104  can be regulated. Adhesive layers as thin as about 0.002 inch can be created, but it become difficult to retain uniformity below about 0.004 inch. 
         [0037]    At step  208 , the backing layer  101  and adhesive layer  104 , collectively forming an adhesive tape  100 , may optionally be wound onto large cores. When a sufficient length of adhesive tape  100  is on a core, it is removed and cut to the proper size. The method  200  ends at step  210 , resulting in an adhesive tape  100  as described in connection with  FIG. 1  above. 
         [0038]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.