Abstract:
The present invention relates to improved self-adhesive labels which are suitable far use in adhering to wet surfaces or wet irregularly shaped surfaces such as that found on fruits and vegetables. The self-adhesive label is made of a water absorbent backing layer having opposing sides and a rubber-based pressure sensitive adhesive applied on one side of the backing layer. The adhesive is discontinuously coated as a pattern onto the backing layer to provide areas of the adhesive interspersed with areas which are free of adhesive.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to pressure sensitive adhesive labels and more particularly, a label adapted to conform to wet, irregularly shaped surfaces that may include texturing found on the surface of raw fruits and vegetables. 
     In recent years, it has been deemed desirable to apply labels to identify source, as well as grade or quality of raw fruits and vegetables. For many years, growers and packers have sought to apply labels to individual fruit such as apples, avocados, cantaloupe, grapefruit, melons, kiwifruit, lemons, limes, nectarines, oranges, pears, pineapples, plums, tangerines, and watermelons, and to individual vegetables such as bell peppers, celery, cucumber, onions, potatoes, radishes, and squash. Growers and packers wish to affix a recognizable label to the individual products in order to distinguish them from the products of competitors and provide them with a unique identifying mark. Typical processing of fruits and vegetables includes washing the items after they have been picked and before they are shipped. Conventional labels are designed to adhere to dry, relatively smooth surfaces. The presence of water between the label and the surface of the fruit or vegetable will typically cause adhesion failure. Consequently, before a label is applied to these products, they must be thoroughly dried so that the label will effectively adhere to their surface. No known adhesive label can effectively be used on wet fruit and vegetable surfaces. As a result, there is a need to develop an adhesive label which is suitable for use under wet conditions. 
     Another shortcoming of conventional labels is that they often do not conform to the surface of irregular surfaced fruits and vegetable such as, for example, cantaloupe, melons, pineapples, tangerines, potatoes, and some squashes. They become easily creased and/or folded because of the planar nature of the label. Therefore, it would be desirable to provide labels which readily adhere to irregularly shaped or curved surfaces of fruit and vegetables. 
     There is a need in the art for improved labels that address at least some of the above concerns, and other concerns related to manufacture and use of the labels. 
     SUMMARY OF THE INVENTION 
     The present invention is concerned with self-adhesive labels which are suitable for use in adhering to a wet surface. The present invention is also concerned with self-adhesive labels suitable for use in adhering to a wet, irregular surface. The self-adhesive label is made of a water absorbent backing layer having opposing sides and a rubber-based pressure sensitive adhesive applied on one side of the backing layer. The adhesive is discontinuously applied as a pattern onto the backing layer to provide areas of the adhesive interspersed with areas of uncoated backing. The areas of the backing layer which are not covered by adhesive can be at most 90 percent of the total available area of the backing layer. It is believed that the areas of uncoated backing layer provide a means for moisture to be absorbed by the backing layer rendering the label flexible and pliable to conform to nonplanar surfaces having irregularities. It is further believed that the passage of water away from the adhesive improves adhesion between label and the target surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a cross-sectional view of one embodiment of the present invention. 
         FIG. 2   a - 2   c  depict different embodiments of a discontinuous pattern of adhesive for use in the present invention. 
         FIG. 3  depicts a cross-sectional of another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now more particularly to  FIG. 1  of the drawings, a preferred embodiment of label  10  embodying the present invention is shown. The label  10  comprises a water absorbent backing layer  20  having a first surface  21  and an opposing second surface  22 . The label  10  further comprises a layer of pressure sensitive adhesive  30 . In accordance with an important aspect of the present invention, the pressure sensitive adhesive is applied to the first surface  21  of backing layer  20  in a discontinuous manner so as to provide areas of adhesive interspersed with areas of uncoated backing  40 . Application of the adhesive may be accomplished according to techniques known in the art. Such techniques include spray application, roller printing, screen printing and similar single contact techniques. Preferably, the amount of pressure sensitive adhesive  30  applied per unit area of the entire backing layer surface  21  is at least 10 percent of the total available area of the backing layer  20 . 
     In a preferred embodiment, the amount rubber-based pressure sensitive on the backing layer is between 1.6 and 9.0 grams per 100 square inch, and more preferably, between 3.5 and TO grams per 100 square inch. It is also preferred that the area which is adhesive-free  30  is between 5 percent and 90 percent of the total available area of the backing layer, and even more preferred, between 15 percent and 50 percent of the total available area of the backing layer. As depicted in  FIGS. 2   a - 2   c  the pressure sensitive adhesive  30  may be applied to backing layer  20  as a straight strip pattern creating alternating lanes of adhesive  30  and lanes of adhesive-free areas  40 . Alternatively, the strip pattern may be formed as curved lines, zigzag lines or combinations thereof (not shown). Alternatively, pressure sensitive adhesive  30  may be applied to backing layer  20  as circular islands of adhesive  30  surrounded by adhesive-free areas  40  as shown in  FIG. 2   b . Alternatively, the islands of adhesive may have the shape of squares, torus, rectangles, or diamonds. In still other embodiments, adhesive  30  may be applied to backing layer  20  in a cross-hatch pattern 2c. 
     Evaluation of Backing Materials 
     Various materials were evaluated as a possible backing layer candidates with respect to their flexibility when wet and their water wicking capability. Specimen samples were constructed by coating a synthetic rubber-based pressure sensitive adhesive mixture, MP-735 supplied by Morgan Adhesives Company, Inc., onto a release liner in a strip pattern having a width of approximately 0.0625 inch (0.159 centimeter) similar to that described in  FIG. 3  above. After the excess solvent was removed by drying coated release lines, the backing layer candidate material to be tested was then transfer coated onto the adhesive to form a label laminate. A 1-inch diameter circular specimen was die cut from each label laminate. The surface of a fresh cantaloupe was treated with running water for five minutes after which time the circular specimen was immediately applied. Observations were rated on a relative scale of 0 to 5 with respect to how easily the label specimen conformed to the surface of the cantaloupe and how well moisture was absorbed by the specimen. The results are shown in TABLE 1 below. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Evaluation of Backing Materials 
               
             
          
           
               
                   
                   
                   
                   
                 Transverse  
               
               
                   
                 Coat Weight 
                 Thickness  
                 Wet Flex- 
                 Wicking  
               
               
                   
                 of Adhesive 
                 of Back- 
                 ibility (Con- 
                 (Absorp- 
               
               
                 Material 
                 (g/100 in2) 
                 ing (mil) 
                 formability) 
                 tivity) 
               
               
                   
               
               
                 Wet Strength  
                 3.5 
                 4.8 
                 2 
                 4 
               
               
                 Uncoated Paper 
                   
                   
                   
                   
               
               
                 Matte Litho  
                 3.5 
                 4.7 
                 3 
                 4 
               
               
                 Paper 
                   
                   
                   
                   
               
               
                 Uncoated Laser  
                 3.5 
                 3.7 
                 5 
                 5 
               
               
                 Paper 
                   
                   
                   
                   
               
               
                 Semi-Gioss  
                 3.5 
                 3.0 
                 4 
                 4 
               
               
                 Coated Paper 
                   
                   
                   
                   
               
               
                 Semi-Gioss  
                 3.5 
                 2.5 
                 4 
                 4 
               
               
                 Coated Paper 
                   
                   
                   
                   
               
               
                 Biaxially  
                 3.5 
                 2.3 
                 2 
                 0 
               
               
                 Oriented  
                   
                   
                   
                   
               
               
                 Polypropylene 
               
               
                   
               
               
                 0 = very poor; 1 = poor; 2 = fair; 3 = good; 4 = very good; and 5 = excellent. 
               
             
          
         
       
     
     An example of a commercially available uncoated laser type paper includes 50# Laser Layflat II supplied by Domtar. Corporation, Fort Mill, S.C. 
     An example of a commercially available semi-gloss coated paper includes 60# Sterling Ultra C1S supplied by NewPage Corporation, Miamisburg, Ohio. 
     In a preferred embodiment, backing layer  20  is formed from paper face stock. The properties that enable backing layer  20  to absorb water are provided in paper face stock having a basis weight of less than 70 pounds per ream as measured in accordance with TAPPI T-410 test method; and/or a thickness of less than 0.0050 inch (121 microns) as measured in accordance with TAPPI T-411 test method. In a more preferred embodiment, backing layer  20  is formed from paper face stock having a basis weight equal to or less than 60 pounds per ream as measured in accordance with TAPPI T-410 test method, a thickness of between 0.0030 inch (72.6 microns) and 0.0048 inch (121.9 micron) as measured in accordance with TAPPI T-411 test method, TAPPI T-410, and T-411 test methods are incorporated herein by reference in their entities. 
     Pressure Sensitive Adhesive 
     Various adhesive materials were examined for use in the present invention based on their ability to function as an adhesive even in the presence of large amounts of water. Different types adhesives may be suitable for use in the present invention which may include acrylic-based pressure sensitive adhesives, butyl rubber-based pressure sensitive adhesives, hydrocarbon-based pressure sensitive adhesives, natural rubber-based pressure sensitive adhesives, synthetic rubber-based pressure sensitive adhesives or combinations thereof. Synthetic rubber-based pressure sensitive adhesives may include a styrene-butadiene copolymer (SB), styrene-isoprene copolymer (SI), a styrene-isoprene-styrene copolymer (SIS), freezer-grade hot melt rubber or combinations thereof. Examples of a commercially available acrylic-based pressure sensitive adhesives include AROSET® 383M self-crosslinking acrylic polymer supplied by Ashland Inc., Columbus, Ohio; DURO-TAK™ AH 115 acrylic-rubber hybrid adhesive supplied by Henkel Corporation, Rocky Hill, Conn.; Acronal® N—CR-1139 all temperature acrylic adhesive supplied by BASF Corporation, Charlotte, N.C.; and FLEXCRYL™ LC-18 water-based acrylic adhesive supplied by Ashland Inc., Columbus, Ohio. An example of a commercially available freezer-grade hot melt rubber adhesive includes Themiogrip H2259-01 adhesive supplied by Bostik, Inc, Wauwatosa, Wis. 
     In one embodiment, the adhesive  30  is a synthetic rubber-based pressure sensitive adhesive mixture comprising a polystyrene-butadiene copolymer and a styrene-isoprene-styrene copolymer and, preferably, a mixture comprising a polystyrene-butadiene copolymer, a styrene-isoprene-styrene copolymer, and an aromatically-modified aliphatic tackifier, and most preferably, a mixture comprising a polystyrene-butadiene copolymer, a styrene-isoprene-styrene copolymer, and an aromatically-modified aliphatic tackifier having a 2-methyl-1-propene comonomer moiety and a 1,3-pentadiene comonomer moiety or an aromatically-modified aliphatic tackifier having a di-cyclopentadiene moiety. Suitable synthetic rubber-based pressure sensitive adhesive mixtures as described above are produced by Morgan Adhesives Company, Inc. Stow. Ohio under the product identifier MP-735, MP-172S, and MP-894S. 
     Commercially available styrene-isoprene-styrene copolymers are sold under the product family Quintac® by Zeon Chemicals Corporation, Louisville, Ky. Commercially available styrene-butadiene copolymers are sold under the product family name Solprene® by Dynasol Elastomers, Houston, Tex. 
     Any of the adhesives described above may include a tackifier, plasticizer, antioxidant/thermal stabilizer, solvent and combinations thereof. None of the ingredients described above are limited to any specific commercially available product mentioned herein. 
     Two different adhesives on two different backing layers were evaluated with respect to their dry adhesion, damp adhesion and wet adhesion on a fresh cantaloupe. Specimen samples were constructed by coating the adhesive candidate material onto a release liner in either a continuous coating of adhesive or a discontinuous strip pattern having a width of approximately 0.0625 inch (0.159 centimeter). The discontinuous pattern coating of adhesive was a straight strip pattern similar to that described in  FIG. 3  above. After the excess solvent was removed by drying coated release lines, a backing layer of either a 50# Laser Layflat II supplied by Domtar Corporation, Fort Mill, S.C., or a polypropylene film was then transfer coated onto the adhesive to form a label laminate. A 1-inch diameter circular specimen was die cut from each label laminate. For damp conditions, the cantaloupe was placed under running water for 1 minute then allowed to dry for 5 minutes before applying the specimen label was applied to its surface. For wet conditions, the cantaloupe was placed under running water for 5 minutes then the specimen label was applied to its surface. Observations were rated on a relative scale of 0 to 5 with respect to its adhesive properties. The results are shown in TABLE 2 below. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Evaluation of Adhesive &amp; Backing Material 
               
             
          
           
               
                   
                   
                 Adhesive coat 
                   
                   
                   
               
               
                   
                   
                 weight/Patten 
                   
                   
                   
               
               
                   
                 Backing 
                 (grams/100 
                 Dry 
                 Damp 
                 Wet 
               
               
                 Adhesive 
                 Material 
                 inch 2 ) 
                 Adhesion 
                 Adhesion 
                 Adhesion 
               
               
                   
               
             
          
           
               
                 A 1   
                 B 1   
                 7.0/P 1   
                 4 
                 2 
                 3 
               
               
                 A 1   
                 B 1   
                 7.0/P 2   
                 5 
                 2 
                 1 
               
               
                 A 1   
                 B 1   
                 3.5/P 1   
                 3 
                 1 
                 2 
               
               
                 A 1   
                 B 1   
                 3.5/P 2   
                 5 
                 2 
                 1 
               
               
                 A 1   
                 B 2   
                 7.0/P 1   
                 4 
                 2 
                 2 
               
               
                 A1 
                 B2 
                 3.5/P 2   
                 4 
                 3 
                 0 
               
               
                 A 2   
                 B 1   
                 7.0/P 2   
                 3 
                 0 
                 1 
               
               
                 A 2   
                 B 1   
                 7.0/P 2   
                 3 
                 0 
                 0 
               
               
                 A 2   
                 B 1   
                 3.5/P 1   
                 2 
                 0 
                 0 
               
               
                 A 2   
                 B 1   
                 3.5/P 2   
                 3 
                 0 
                 0 
               
               
                   
               
               
                 0 = very poor; 1 = poor; 2 = fair; 3 = good; 4 = very good; and 5 = excellent. 
               
             
          
         
       
     
     Adhesive A 1  was a synthetic rubber-based mixture comprising a polystyrene-butadiene copolymer, a styrene-isoprene-styrene copolymer, and an aromatically-modified aliphatic tackifies having a 2-methyl-1-propene comonomer moiety and a 1,3-pentadiene comonomer moiety. 
     Adhesive A 2  was Aroset 383M, an acrylic adhesive supplied by Ashland Inc., Columbus, Ohio. 
     Backing layer B 1  was Layflat II an uncoated laser type 50# Laser paper, supplied by Domtar Corporation, Fort Mill, S.C. 
     Backing layer B 2  was a 2.3 mil polypropylene film. 
     Pattern P 1  was a discontinuous strip pattern onto the backing layer. 
     Pattern P 2  was a continuous coating onto the backing layer. 
     Turning now to  FIG. 3 , it is further contemplated that label  10  embodying the present invention may further comprise a layer of printed indicia  50  applied to the second surface  22  of backing layer  20 . A protective topcoat or primer (not shown) may be provided over printed indicia  50 . Layer  50  may be produced by any printing technique known in the art. Specifically, layer  50  may be applied to backing layer  20  using direct thermal printing method. Direct thermal printing is well known in the art and has been described in U.S. Pat. Nos. 5,292,713; 5,508,247; 5,661,099; 5,773,386; and U.S. Patent Application Publication No. 2008/0160233, all of which are incorporated herein by reference in their entireties. Alternatively, layer  50  may be applied to backing layer  20  using thermal transfer printing techniques. Thermal transfer printing methods are well known in the art and have been described U.S. Pat. Nos. 5,292,713; 5,750,192; 6,309,498 and U.S. Patent Application Publication No. 2004/0018322, all of which are incorporated herein by reference in their entireties. Ink jet printing method may also be used to produce layer  50 . Ink jet printing is well known in the art and has been described in U.S. Pat. No. 8,133,342 which is incorporated herein by reference. 
     The following example illustrates a certain particular method of producing a pressure sensitive adhesive label of the present invention and is not to be interpreted as limiting. In the following example, a rubber-based pressure sensitive adhesive is coated onto a 50# super calendared Kraft release liner having a low release platinum cured silicone release system. A modified roll coater is used to apply the adhesive in a 0.0625 inch straight striped pattern onto the release liner. In areas where the coating shim had been cut away, the adhesive stays on the casting roll and returns to the adhesive pan. The adhesive coated release liner is then placed into a forced air oven where excess solvent is removed by heat. After exiting the drying oven, a paper face stock backing layer is laminated onto the surface containing the adhesive coating. The adhesive is now permanently adhered to the backing layer. This laminated product may then be wound onto larger rolls for further processing. 
     The larger rolls of laminated produce are typically slit down into smaller rolls for easier handling on printing and converting equipment. A solvent flexographic press is used to print indicia onto the outer face of the label web which is then die cut into the finished label. The shape and dimensions of the label may vary. In one embodiment, the label is a circle having a diameter from 0.25 inch to 2 inch. The finished label may then be applied to the fruit or vegetable items by being hand applied, blown onto the item or machine applied. 
     Alternative methods of coating the adhesive as a pattern onto the release liner or directly onto the backing layer may be used. For example, a die coater utilizing a cut-away shim could be used to coat a solvent-based, an emulsion-based or a hot-melt adhesive into a stripe pattern. Rotogravure printing, nozzles or other methods could also be used to form discontinuous patterns of adhesive onto the backing layer.