Abstract:
A label for use as an in-mold label and including a radio frequency identification device (RFID) is disclosed. The label includes an RFID having opposed first and second surfaces; a first layer of heat-activated adhesive disposed on the first surface of the RFID; a second layer of heat-activated adhesive disposed on the second surface of the RFID; and a surface layer comprising a polymeric film disposed on a surface of the first layer of heat-activated adhesive opposite the first surface of the RFID. The label is placed in a mold with the surface layer contacting the mold. A polymer is molded in the mold such that the second layer of heat-activated adhesive (or a surface layer over the second layer of heat-activated adhesive) adheres to the polymer thereby producing a labeled article that can be identified using the radio frequency identification device in the label.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to labels including a radio frequency identification device, and more particularly to labels including a radio frequency identification device wherein the label is compatible with an in-mold process. This allows the label to be incorporated into plastic parts, such as bins and pallets, for durable tracking purposes. 
     2. Description of the Related Art 
     It is well known that items, such as plastic bins and pallets in a factory, can be tracked and identified using a radio frequency identification device (RFID). An RFID generally includes an antenna connected to an integrated circuit chip in which digital information is stored. The RFID transmits stored data by reflecting varying amounts of an electromagnetic field provided by an RFID interrogator. An RFID can now be manufactured in a very small, light weight and inexpensive unit. 
     A problem exists in finding a durable and cost-effective way of attaching an RFID to items to be tracked. One means for attaching an RFID to an item is an externally fastened tag. However, such tags are prone to being torn away from the item during transport. Self adhesive labels for an RFID have also been used in numerous applications where the performance and convenience of a pressure sensitive adhesive is suitable. See, for example, U.S. Pat. Nos. 6,281,795, 6,163,260 and 5,982,284. However, these labels may also be susceptible to being torn away from an item. To provide a smooth finish and excellent resistance to detachment in a molded article, embedding or in-molding of an RFID in a molded article has been proposed. See, for example, U.S. Pat. Nos. 6,302,461 and 6,206,282. 
     Many injection molded plastic products are manufactured from the family of polyolefins including polyethylene and polypropylene. These materials are used to produce rugged products, especially containers. The molding process includes heating a polyolefin resin to a melt-flow temperature (as high as 270° C.) and injecting under pressure into a temperature controlled mold. Depending upon mold size and complexity, this is done under pressure as high as hundreds of pounds per square inch. Typically, an in-mold label is placed in position on the wall of a mold, the mold is closed and the injection process begins. The wall temperature of the mold prevents the label from exceeding its own melt temperature. The in-mold label material is often made from an olefinic material treated for adhesion. Being similar in nature to the olefinic plastic used in the molding process, high adhesion is developed to the finished, molded article. The plastic used in the molding process is softened by heat and flows with molding pressure to fill the mold and capture the edges of the in-mold label. The surface of the mold itself retains the dimension of the finished product so the in-mold label is flush with the surface of the finished product. 
     A standard pressure sensitive RFID label is made using a pressure sensitive adhesive on one side of an RFID and a film or paper label stock laminated to the other, usually with another pressure sensitive adhesive. Typically, an RFID is somewhat fragile, especially in the area of the integrated chip. Inexpensive RFIDs for general label purposes are usually supplied with the antenna and chip attached to a flexible polyester film substrate. If a standard pressure sensitive RFID label is used in an in-mold process, the melt/flow temperature of typical pressure sensitive adhesives is exceeded and the label moves out of position and is distorted, delaminated or otherwise damaged a high percentage of the time. Even high performance acrylic pressure sensitive adhesives do not function well during the exposure to heat and pressure of an injection molding process. They soften excessively and lose their bond. 
     Thus, there exists a need for a label including a radio frequency identification device wherein (i) the label protects the radio frequency identification device chip during and after in-molding of the label in an article, (ii) the label includes a protective outer sheet that resists mechanical and chemical damage, (iii) the label provides for improved structural integrity during an in-molding process, and (iv) the label allows for improved bonding to an article during an in-molding process. 
     SUMMARY OF THE INVENTION 
     The foregoing needs are met by a label according to the invention. The label comprises a radio frequency identification device having opposed first and second surfaces; a first layer of heat-activated adhesive disposed on the first surface of the radio frequency identification device; a second layer of heat-activated adhesive disposed on the second surface of the radio frequency identification device; and a surface layer comprising a polymeric film disposed on a surface of the first layer of heat-activated adhesive opposite the first surface of the radio frequency identification device. The label according to the invention is particularly suited for use as an in-mold label. In a method according to the invention, the label is placed into a mold such that the surface layer contacts the mold. A moldable polymer is then introduced into the mold, and the polymer is molded in the mold such that the second layer of heat-activated adhesive contacts and adheres to the polymer thereby producing a labeled molded polymeric article that can be tracked or identified using the radio frequency identification device included in the in-molded label. 
     In another form, the label comprises a radio frequency identification device having opposed first and second surfaces; a first layer of heat-activated adhesive disposed on the first surface of the radio frequency identification device; a second layer of heat-activated adhesive disposed on the second surface of the radio frequency identification device; a first surface layer comprising a first polymeric film disposed on a surface of the first layer of heat-activated adhesive opposite the first surface of the radio frequency identification device; and a second surface layer comprising a second polymeric film disposed on a surface of the second layer of heat-activated adhesive opposite the second surface of the radio frequency identification device. This label according to the invention is also particularly suited for use as an in-mold label. In another method according to the invention, this label is placed into a mold such that the first surface layer contacts the mold. A moldable polymer is then introduced into the mold, and the polymer is molded in the mold such that the second surface layer contacts and adheres to the polymer thereby producing a labeled molded polymeric article that can be tracked or identified using the radio frequency identification device included in the in-molded label. 
     It has been discovered that: (1) the side of a radio frequency identification device label with the chip attached should face to the inside of a mold to prevent damage due to extensive heat and pressure during in-molding and the resultant deformation of the flexible radio frequency identification device; (2) providing a label including a radio frequency identification device with a protective outer sheet resists mechanical and chemical damage to the label when molded in an article; (3) laminating a radio frequency identification device with heat activated adhesives greatly improves the resistance to the heat of an in-mold labeling process compared to pressure sensitive adhesive lamination, and (4) using an olefinic label stock suitable for in-mold labels in a label including a radio frequency identification device offers great improvements to the adhesion of the label to a molded article. 
     Thus, the invention satisfies a need for a way to track reusable plastic items, such as bins and pallets, in a factory. Simple adhesion of a radio frequency identification device label to these items is a poor solution, because the label would be rendered inoperative from normal long-term wear. This invention provides a way to protect the radio frequency identification device label and greatly extend its lifespan by incorporating the label within the plastic part itself during an in-molding process. 
     It is therefore an advantage of the present invention to provide a label including a radio frequency identification device wherein the label protects the radio frequency identification device chip during and after in-molding of the label in an article. 
     It is another advantage of the present invention to provide a label including a radio frequency identification device wherein the label includes a protective outer sheet that resists mechanical and chemical damage. 
     It is yet another advantage of the present invention to provide a label including a radio frequency identification device wherein the label provides for improved structural integrity during an in-molding process. 
     It is still another advantage of the present invention to provide a label including a radio frequency identification device wherein the label allows for improved bonding to an article during an in-molding process. 
     These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings, and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side cross-sectional view of a first embodiment of a label according to the invention. 
         FIG. 2  shows a side cross-sectional view of a second embodiment of a label according to the invention. 
         FIG. 3  shows a side cross-sectional view of a third embodiment of a label according to the invention. 
     
    
    
     Like reference numerals will be used to refer to like or similar parts from Figure to Figure in the following description. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning first to  FIG. 1 , there is shown a first embodiment of a label according to the invention. The label, indicated generally at  10 , includes a radio frequency identification device which comprises an integrated circuit chip  32  connected to an antenna  28 . The radio frequency identification device is mounted on a flexible substrate  22 , which typically comprises a polyester film. The term “radio frequency identification device” as used herein and in the appended claims, is to be construed as any device capable of communicating by radio frequency. For example, the term “radio frequency identification device” should be construed as encompassing devices that transmit or receive any data by radio frequency, not just identification data. The radio frequency identification device is of any conventional construction such as described in U.S. Pat. No. 5,497,140. 
     A first layer  18  of heat-activated adhesive is disposed on the surface of substrate  22  of the radio frequency identification device, and a second layer  24  of heat-activated adhesive is disposed on the surface of the integrated circuit chip  32  and antenna  28  of the radio frequency identification device. A polymeric film  16  is disposed on the surface of the first layer  18  of heat-activated adhesive opposite the radio frequency identification device. On the side of the polymeric film  16  opposite the first layer  18  of heat-activated adhesive, there is disposed a third layer  14  of heat-activated adhesive. A protective polymeric film  12  is disposed on the surface of the third layer  14  of heat-activated adhesive opposite the polymeric film  16 . Thus, in the embodiment of  FIG. 1 , a surface layer comprising the protective polymeric film  12 , the third layer  14  of heat-activated adhesive, and the polymeric film  16  is disposed over the first layer  18  of heat-activated adhesive on the surface of substrate  22  of the radio frequency identification device. A polymeric film  26  comprising a second surface layer is disposed on the surface of the second layer  24  of heat-activated adhesive opposite the radio frequency identification device. 
     Turning now to  FIG. 2 , there is shown a second embodiment of a label according to the invention. The label, indicated generally at  10 A, includes a radio frequency identification device comprising a flexible substrate  22  and an integrated circuit chip  32  connected to an antenna  28  as in the embodiment of  FIG. 1 . In the second embodiment of  FIG. 2 , a first layer  18  of heat-activated adhesive is disposed on the surface of substrate  22  of the radio frequency identification device, and a second layer  24  of heat-activated adhesive is disposed on the surface of the integrated circuit chip  32  and antenna  28  of the radio frequency identification device. A protective polymeric film  12  is disposed on the surface of the first layer  18  of heat-activated adhesive opposite the radio frequency identification device. A polymeric film  26  comprising a second surface layer is disposed on the surface of the second layer  24  of heat-activated adhesive opposite the radio frequency identification device. It can be seen that the polymeric film  16  and the third layer  14  of heat-activated adhesive shown in  FIG. 1  are not included in the second embodiment of  FIG. 2 . In other words, in the embodiment of  FIG. 2 , a surface layer comprising the protective polymeric film  12  is disposed over the first layer  18  of heat-activated adhesive on the surface of substrate  22  of the radio frequency identification device. 
     Turning now to  FIG. 3 , there is shown a third embodiment of a label according to the invention. The label, indicated generally at  10 B, includes a radio frequency identification device comprising a flexible substrate  22  and an integrated circuit chip  32  connected to an antenna  28  as in the embodiment of  FIGS. 1 and 2 . In the third embodiment of  FIG. 3 , a first layer  18  of heat-activated adhesive is disposed on the surface of substrate  22  of the radio frequency identification device, and a second layer  24  of heat-activated adhesive is disposed on the surface of the integrated circuit chip  32  and antenna  28  of the radio frequency identification device. A protective polymeric film  12  is disposed on the surface of the first layer  18  of heat-activated adhesive opposite the radio frequency identification device. It can be seen that the polymeric film  16 , the polymeric film  26  and the third layer  14  of heat-activated adhesive shown in  FIG. 1  are not included in the third embodiment of  FIG. 3 . Thus, in the embodiment of  FIG. 3 , a surface layer comprising the protective polymeric film  12  is disposed over the first layer  18  of heat-activated adhesive on the surface of substrate  22  of the radio frequency identification device. However, a surface layer comprising the protective polymeric film  12 , the third layer  14  of heat-activated adhesive, and the polymeric film  16  as shown in  FIG. 1  could alternatively be disposed over the first layer  18  of heat-activated adhesive on the surface of substrate  22  of the radio frequency identification device. 
     Having detailed the layered construction of three embodiments of the invention, non-limiting examples of materials that can be used in the first layer  18  of heat-activated adhesive, the second layer  24  of heat-activated adhesive, and the third layer  14  of heat-activated adhesive can now be described. The heat-activated adhesive used in the first layer  18 , the second layer  24 , and the third layer  14  (all of which may or may not be present in the labels  10 ,  10 A and  10 B of the present invention as detailed above) may comprise any heat-activated adhesive that does not significanitly effect the performance of the radio frequency identification device and that provides structural integrity during the application of heat and pressure in an in-molding process. 
     Non-limiting examples of suitable heat-activated adhesives include polyester resins, polyethylene, copolymers of ethylene and an ethylenically unsaturated carboxylic acid or ester. The ethylenically unsaturated carboxylic acid or ester may be, for example, acrylic acid, methacrylic acid, methylmethacrylate, butyl acrylate, and vinyl acetate. One specific example of a heat-activated adhesive is a polyester resin sold under the trademark “Mor-Ester” by Rohm and Haas. The heat-activated adhesive may be applied to the radio frequency identification device and polymeric films  12 ,  16  and  26  in a coating solution. Any suitable solvent or solvent mixtures may be employed to form a coating solution. Typical solvents include tetrahydrofuran, toluene, methylene chloride, cyclohexanone, and the like, and mixtures thereof. Conventional techniques for applying the coating mixture to the radio frequency identification device and polymeric films  12 ,  16  and  26  include spraying, dip coating and roll coating. 
     The heat-activated adhesive in the first layer  18 , the second layer  24 , and the third layer  14  may be the same or different, and may comprise a single heat-activated adhesive or a mixture of heat-activated adhesives. Satisfactory results may be achieved with a first layer  18  thickness between about 0.0001 inches and about 0.002 inches, a second layer  24  thickness between about 0.0001 inches and about 0.002 inches, and a third layer  14  thickness between about 0.0001 inches and about 0.002 inches. In an example embodiment, the first layer  18 , the second layer  24  and the third layer  14  of heat-activated adhesive have a thickness of about 0.0002 inches. 
     Non-limiting examples of materials that can be used in the protective polymeric film  12  can also now be described. The protective polymeric film  12  can be designed of a selection of materials of adequate strength and toughness (such as 0.0005″, 0.003″, 0.005″, or 0.007″ thick polyester or polyethylene terephthalate film sold as Mylar® by DuPont) to help the radio frequency identification device resist mechanical damage. The protective polymeric film  12  can also be designed of a material with excellent outdoor durability (such as polyvinyl fluoride film sold as Tedlar® by DuPont) to allow the finished article to be used for a long period of time outdoors. The protective polymeric film  12  can also be designed of an inexpensive printable film such as the porous silica filled polyolefin (typically polyethylene) film sold as Teslin® by PPG Industries to give it excellent printability. The protective polymeric film  12  can also be made from numerous other film materials for specific properties desired, such as the polyimide film sold as Kapton® by DuPont and the polyethylene naphthalate film sold as Kaladex® by DuPont. 
     The polymeric film used in the protective polymeric film  12  may be the same or different, and may comprise a single polymeric film or a coextruded or coated polymeric film. Satisfactory results may be achieved with a protective polymeric film  12  thickness between about 0.0005 inches and about 0.020 inches. In an example embodiment, the protective polymeric film  12  is a polyester or polyethylene terephthalate film having a thickness of about 0.0005 inches. 
     Non-limiting examples of materials that can be used in the polymeric film  16  and the polymeric film  26  can also now be described. The polymeric film  16  and the polymeric film  26  may comprise a polyester or polyethylene terephthalate film, a polyvinyl fluoride film, a polyolefin (typically polyethylene) film, a polyimide film or a polyethylene naphthalate film. The polymeric films used in the polymeric film  16  and the polymeric film  26  may be the same or different, and may comprise a single polymeric film or a coextruded or coated polymeric film. The film must have sufficient heat-sealable properties. Satisfactory results may be achieved with a polymeric film  16  thickness between about 0.002 inches and about 0.020 inches, and a polymeric film  26  thickness between about 0.002 inches and about 0.020 inches. In an example embodiment, the polymeric film  16  and the polymeric film  26  each comprise a porous silica filled polyolefin, typically polyethylene, film (sold as Teslin® by PPG Industries) having a thickness of about 0.0070 inches. Using a porous silica filled polyolefin, typically polyethylene, offers great improvements to the adhesion of an in-molded label to a molded article. 
     The labels  10 ,  10 A and  10 B described above can be supplied in either continuous rolls, scored or perforated rolls, or individual cut tags, and are particularly suited for use as an in-mold label in an in-molding process that produces a polymeric article that is desired to be tracked or identified in subsequent use. The labels  10 ,  10 A and  10 B are suitable for conventional inmolding processes such as those described in U.S. Pat. Nos. 6,422,605, 6,044,682, 5,868,986 and 5,193,711 which are incorporated herein by reference. 
     Typically, at the site of polymeric article manufacture, stacks of individual labels  10  or  10 A or  10 B are loaded in a dispensing magazine and a label is picked-off the magazine and applied to the interior surface of a mold with the protective polymeric layer  12  of the label  10  or  10 A or  10 B oriented in facing (and typically contacting) relationship with the inner surface of the mold wall. This orientation of the labels  10  or  10 A or  10 B with the protective polymeric film  12  towards the mold wall assures that the radio frequency identification device remains flat through the molding process and prevents the high mold pressure from distorting the antenna around the integrated circuit chip and damaging its functionality. The cool, temperature controlled mold wall also helps protect the radio frequency identification device from exceeding its reliable temperature range during the molding cycle. 
     The label may be held accurately in position within the mold by a vacuum applied through holes in the mold wall. There may or may not be a recess on the interior mold surface to accommodate the label. A hot fluid thermoplastic resin (or hot resins that react to form a thermoset material) is fed into the mold, and as the hot resin contacts the polymeric film  26  of the label  10  or  10 A, or the second layer  24  of heat-activated adhesive of the label  10 B, heat transferred from the hot resin activates the heat-activated adhesive layers. When the molded polymeric article is sufficiently cooled, it is ejected from the mold. The radio frequency identification device functionality is thereby included in the molded article and the protective film is exposed at the surface of the article, optionally bearing graphics. 
     There is sometimes warping distortion that can occur as the heated molten plastic cools in the mold adhered to the in-mold label construction. This is known in the art and can be offset by compensation in the mold dimension or label materials. For example, the films can be selected such that the annealing temperature of the in-mold label film exceeds the service temperature in the mold in order to avoid label shrinkage or distortion. To assure a uniform joining of the label and container, it is also desirable that the softening temperature of the in-mold label film be close to the service temperature. If, as is preferred, the label is on, not in, the interior surface of the mold, the label becomes embedded in the article to which it is adhered, thus advantageously providing an inset label that is flush with the container surface without diminishing the structural integrity of the article to any detected degree. 
     EXAMPLES 
     The following examples serve to further illustrate the invention. The examples are not intended to limit the invention in any way. 
     Example 1 
     A label  10  as shown in  FIG. 1  was prepared as follows. The label  10  was made by: (1) solvent coating, at about 2 to 6#/ream, two 0.0070″ thick polyolefin films (Teslin® brand porous silica filled polyethylene available from PPG Industries) with a thermoplastic heat activated adhesive polyester resin (MorEster® 49000 brand polyester resin available from Rohm and Haas); (2) heat laminating a flexible radio frequency identification device to the polyolefin layers at 275° F. at a speed that is slow enough to soften the polyolefin so it can form around the irregular profile of the integrated circuit chip and antenna of the radio frequency identification device; and (3) heat laminating a 0.001″ polyester film with a polyethylene heat laminating adhesive to the flat side (non-chip side) of the polyolefin-radio frequency identification device laminate. The end product can be supplied in either continuous rolls, scored or perforated rolls, or individual cut tags. 
     Fifty labels were prepared using the methods of Example 1. These fifty labels were in-molded in a polypropylene crate using conventional methods. Fifty out of fifty samples tested by in-molding into a polypropylene crate were fully functional. Thus, the label of Example 1 provides a construction that withstands molding temperatures and pressures and results in a label with high adhesion to a molded article, undamaged by the molding process. Due to the fact that the radio frequency identification device label is insert molded, it is encased in the plastic molding compound. This provides the extra protection required to use a flexible radio frequency identification device. 
     Example 2 
     A label  10 A as shown in  FIG. 2  was prepared as follows. The label  10 A was made by: (1) solvent coating, at about 2 to 6#/ream, a 0.002″ thick white pigmented polyester film (e.g., Mylar® brand pigmented polyester film available from DuPont) and a 0.0070″ thick polyolefin film (Teslin® brand porous silica filled polyethylene available from PPG Industries) with a thermoplastic heat activated adhesive polyester resin (Mor-Ester® 49000 brand polyester resin available from Rohm and Haas); (2) heat laminating the chip side of a radio frequency identification device to the polyolefin layer at 275° F. at a speed that is slow enough to soften the polyolefin so it can form around the irregular profile of the integrated circuit chip and antenna of the radio frequency identification device; and (3) heat laminating the polyester film to the flat side (non-chip side) of the polyolefin-radio frequency identification device laminate. The end product can be supplied in either continuous rolls, scored or perforated rolls, or individual cut tags. 
     Therefore, it can been seen that a radio frequency identification device label according to the invention will withstand plastic molding temperatures and pressures and result in a label with high adhesion to the molded article. It has been discovered that: (1) laminating a radio frequency identification device with heat activated adhesives greatly improves the resistance to the heat of an in-mold labeling process compared to pressure sensitive adhesive lamination, (2) using an olefinic label stock suitable for in-mold labels in a label including a radio frequency identification device offers great improvements to the adhesion of the label to a molded article, and (3) the side of a radio frequency identification device with the chip attached should face to the inside of a mold to prevent damage due to extensive heat and pressure during in-molding and the resultant deformation of the flexible radio frequency identification device. The invention is advantageous in that inexpensive, flexible radio frequency identification devices can be incorporated in injection molded articles, especially where resistance to heat and pressure are critical. Maximizing resistance to heat and pressure allows the use of the thinnest and consequently least expensive materials in designs where available molded wall thickness is minimal. 
     Although the present invention has been described in considerable detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     INDUSTRIAL APPLICABILITY 
     This invention relates to labels including a radio frequency identification device, and more particularly to labels including a radio frequency identification device wherein the label is compatible with an in-molding process. This allows the label to be incorporated in plastic parts for durable tracking and identification purposes.