Abstract:
The present invention provides a sheet-shaped material containing an RFID thread. The RFID thread comprises a strip-shaped film onto one side of which a semiconductor chip containing plural bits of memory and provided with an antenna wire is bonded. The strip-shaped film has plural openings formed therethrough except where the semiconductor chip is bonded. Since intertwining occurs between paper fibers via the openings, the RFID thread is strongly fixed in the paper.

Description:
The present application claims priority from Japanese patent application JP2007-208226 filed on Aug. 9, 2007, the content of which is hereby incorporated into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to RFID threads, which are attached to or rolled in securities, banknotes and the like to prevent forgery thereof, and sheet-shaped materials using them. In particular, the invention relates to semiconductor chip-incorporated ones which allow at least contactless retrieval of information. 
     2. Description of the Related Art 
     Conventionally, to provide a thin sheet of paper or the like with an RFID, it is common to affix the RFID to a seal-like tag coated beforehand with gum or the like and then affix this seal to the objective thin sheet. 
     In other known methods, an RFID tag formed beforehand into a thread shape is rolled in paper (Patent Document 1) and an RFID tag is fixed with gum between two sheets of paper (Patent Document 2). In these methods, the RFID can be held therein enough strongly due to the stiffness of the paper if the paper is thick enough or the RFID tag is thin enough. 
     Also known is a thread comprising a strip-shaped first sheet substrate on which an IC chip allowing at least contactless retrieval of information is mounted and a strip-shaped second sheet substrate laminated on the first sheet substrate, characterized in that holes are bored from the top to the bottom outside the IC chip area (Patent Document 3). If a thread of this construction is affixed to securities, banknote or other sheet with an adhesive, the adhesive penetrates into the through holes and thereby causes wedge effect between the thread and the adhesive, making the thread less likely to separate from the sheet. 
     [Patent Document 1] JP-A-2002-319006 
     [Patent Document 2] JP-A-2005-350823 
     [Patent Document 3] JP-A-2005-284389 
     SUMMARY OF THE INVENTION 
     In the common method of affixing an RFID tag to a thin sheet of paper or the like as mentioned above, its anti-counterfeit effect is low since the presence of the affixed RFID tag can easily be recognized from the appearance. This method also has a disadvantage that restrictions are imposed on the design of the appearance. 
     In the method described in Patent Document 1 or Patent Document 2, specifically, if a 30 μm-thick base film  20  made of PET having a 3 mm-wide RFID formed thereon as shown in  FIG. 7  is developed to a paper sheet with a total uniform thickness of 0.1 mm, stiffness is not so given to the RFID as expected since covering layer of the RFID with paper is very thin. Further, since the cellulose-based glue for paper cannot fix the polyester film enough strongly, external force during use may detach the internal RFID from the upper and lower paper layers  40  and causes the upper and lower paper layers  40  to float as shown in a cross sectional view of  FIG. 8 . In an extreme case, the RFID base film  20  falls off. 
     The method described in Patent Document 3 also has a problem that since the adhesive penetrates into the through holes when the thread is affixed to a sheet with an adhesive, hardening of the adhesive causes a decrease in flexibility and therefore lowers the easiness of handling and it is difficult to thin the tag like a thin sheet. 
     Any of the above-mentioned prior art techniques has a problem that although an RFID base film must be bonded to paper in order to fix the RFID, it is difficult to attain sufficiently strong bonding if the tag is thinned like a thin sheet. 
     To solve the above-mentioned problem, the present invention provides a sheet-shaped material comprising a strip-shaped film onto one side of which a semiconductor chip containing plural bits of memory and provided with an antenna wire is bonded and a paper sheet, wherein the strip-shaped film is rolled in the paper sheet so that the upper layer and lower layer of the paper sheet are bonded together by means of intertwining between upper paper fibers and lower paper fibers. 
     The film may have plural openings disposed therethrough except where the semiconductor chip is mounted so that intertwining occurs between upper paper fibers and lower paper fibers of the paper sheet. 
     The openings may be arranged in two rows of round holes formed at the same pitch by punch-out. 
     The openings may be plural U-shaped notches whose internal areas are lifted up. 
     The film may have dimples formed except where the semiconductor chip is mounted. 
     The dimples may be obtained by forming plural non-open impressions. 
     Further, the present invention provides an RFID thread comprising a strip-shaped film onto one side of which a semiconductor chip containing plural bits of memory and provided with an antenna wire is bonded, wherein the strip-shaped film has plural openings formed therethrough so that when the strip-shaped film is rolled in a paper sheet, intertwining occurs between upper paper fibers and lower paper fibers of the paper sheet via the plural openings or the strip-shaped film has dimples formed thereon. 
     The openings may be plural U-shaped notches whose internal areas are lifted up. 
     The dimples may be obtained by forming plural non-open impressions. 
     The size of the semiconductor chip is not larger than 0.5-by-0.5 mm and the width of the strip-shaped film is not larger than 3 mm. 
     According to the present invention, since the RFID base film and antenna portion have plural openings or bumps/pits, the upper paper layer and lower paper layer of the RFID tag can be united together strongly due to enhanced adhesion between the paper portion and the RFID portion or between the gum portion and the RFID portion. By this structure, the thickness of an RFID-incorporated paper card can be reduced down to about 0.1 mm. Such a thin paper card is difficult to realized by prior art structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an RFID thread in accordance with a first embodiment; 
         FIG. 2  is a schematic diagram for illustrating how RFID threads in accordance with the first embodiment are rolled in paper by using a cylinder paper machine; 
         FIG. 3A  illustrates the condition of a paper sheet which has gone through the dewatering/drying process and  FIG. 3B  is an enlarged explanatory partial view where the upper section of the paper sheet is cut off to expose the inside; 
         FIG. 4A  is a partly enlarged cross sectional view of a paper sheet containing one base film and  FIG. 4B  is a perspective view of the sheet where the sheet is partly cut off to show openings and paper fibers included in the cross section; 
         FIG. 5  is a schematic diagram for illustrating how an RFID thread in accordance with the first embodiment is rolled in by using a Fourdrinier paper machine; 
         FIG. 6  is a schematic diagram for illustrating how an RFID sheet in accordance with the first embodiment is sandwiched by milled paper sheets; 
         FIG. 7  is a perspective view of a conventional RFID thread; 
         FIG. 8  is a cross sectional view of a sheet with the conventional RFID thread structure not in accordance with the present invention, indicating the internal RFID is detached from the upper and lower paper layers; 
         FIG. 9  is a perspective view of an RFID thread, a variant of the first embodiment; 
         FIG. 10  is a perspective view of an RFID thread in accordance with a second embodiment; and 
         FIG. 11  is a perspective view of an RFID thread in accordance with a third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The best mode for carrying out the present invention will be described below with reference to the drawings. 
     Embodiment 1 
     Firstly, a first embodiment of the present invention is described by using  FIGS. 1 through 6 .  FIG. 1  is a perspective view of an RFID thread to which the present embodiment is applied. On a 30 μm-thick base film  20  made of PEN (polyethylene naphthalate), a 7 μm-thick aluminum wire antenna  30  is formed. This antenna has a slit  31  formed thereon. A cut-out RFID chip  10  of at most 0.5 by 0.5 mm is bonded so as to straddle (stride over) this slit  31 . An RFID circuit is constructed from the antenna  30  and RFID chip  10 . This RFID portion is repeatedly disposed on the strip-shaped base film  20 . In the present embodiment, the base film  20  has a width of 3 mm and each antenna  30  is 55 mm long. Since the RFID portion is repeated at a pitch of 57 mm, the base film  20  is repeatedly exposed by 2 mm. Note that the thickness of the base film  20  and that of the antenna  30  are not depicted. Also note that the RFID chip  10  and slit  31  are depicted larger since they can not be recognized if depicted on the same scale as the others. 
     The base film  20  and antenna  30  have many openings  21  formed therethrough except where the above-mentioned slit  31  and RFID chip  10  are located. The openings  21  are round holes formed by means of punch out and arranged in two rows at the same pitch. Due to the roundness and the same pitch, stress concentration is less likely to occur from external force, which reduces the possibility that external force may break the antenna  30  or detach the RFID chip  10  during paper manufacture process or practical use. 
     In addition, since the openings  21  are formed so as not to interfere with the periphery of the antenna  30  or the slit  31 , the deterioration of the antenna  30  in communication performance due to the openings  21  is minimized. 
       FIG. 2  shows how this base film  20  having the RFID portion repeatedly thereon is rolled in paper. When the roll-in is done with a plurality of paper layers, it is common to use a cylinder paper machine as shown in  FIG. 2 . A two-tank type cylinder paper machine is exemplarily shown in  FIG. 2 . Dipped in a pulp solution in the first reservoir tank  51 , a cylindrical wire mesh  51   a  is rotating. Pulped material adheres to the wire mesh  51   a , forming a wet film of dewatered paper material on the wire mesh  51   a . Since this film is pressed against the blanket  54 , this film is detached from the wire mesh  51   a  and driven by the blanket  54  toward the second wire mesh  52   a . In this process, a strip-shaped base film  20  having RFID portions formed thereon beforehand is supplied externally. Consequently, the base film  20  is sandwiched between the wet film on the blanket  54   a  and another wet film which is formed similarly on the wire mesh  52   a  in the second reservoir tank. In this process, upper and lower fibers (pulped materials) of the wet films intertwine with each other through openings  21  of the base film  20  since the pulped material is not yet sufficiently dewatered. The amount of material attached to the top side and that to the bottom side can be adjusted respectively by changing the material concentrations in the reservoir tanks  51  and  52 . 
     Then, the damp-dry paper sheet  40  is detached from the blanket  54  and sent to the subsequent dewatering/drying stage. Needless to say, although a two-tank type cylinder paper machine is used in this embodiment, it is also possible to use a cylinder paper machine provided with more tanks, for example, if the paper sheet  40  must be made thicker or another perforated sheet layer is added in order to suppress the projection of RFID chips  10 . 
       FIG. 3A  shows the condition of the paper sheet  40  which has gone through the dewatering/drying stage. In the paper sheet  40 , a plurality of base films  20  are included. Substantially, they are arranged in parallel at the same pitch. Note that although the base films  20  are depicted clearly in  FIG. 3A  for the purpose of explanation, it is actually difficult to recognize them in appearance since they are incorporated in the paper.  FIG. 3B  is an enlarged partial view of the paper sheet  40 . In  FIG. 3B , the front upper section of the paper sheet  40  is removed so as to expose an incorporated base film  20 . As shown, this base film  20  has plural openings  20  formed therethrough and an RFID chip  10  mounted thereon. 
       FIG. 4A  is an enlarged cross sectional view of the paper sheet  40  including one base film  20 . The upper and lower paper layers are united since paper fibers  40   a  which basically constitute the paper sheet  40  go through openings  21  of the base film  20 , resulting in strong adhesion between the paper sheet  40  and the base film  20 .  FIG. 4B  is a perspective view of the paper sheet  40 , wherein the upper paper layer of the paper sheet  40  is partly removed in order to observe the openings  21  and paper fibers  40   a  included in the cross section. When the base film  20  is rolled in, paper fibers on each side thereof go through the openings  21  and intertwine with those on the opposite side. Since the openings  21  bored through both the base film  20  and the alumina antenna  30  layer thereon are arranged almost overall, it is possible to unite the paper sheet  40  and the RFID portion. Finally, this paper sheet  40  is cut into pieces each containing at least one RFID portion in order to obtain an anti-counterfeit RFID thread-used paper set. 
     The aforementioned manufacture method uses a cylinder paper machine. The following describes a variant of this manufacture method.  FIG. 5  is a schematic diagram for illustrating how an RFID thread in accordance with the present embodiment is rolled in by using a Fourdrinier paper machine. Two band-shaped wire meshes  61   b  and  62   b  are stretched by rollers  61   a  and  62   a  so that a wedge-shaped gap is formed. Pulp slurry is injected into this wedge-shaped portion by a slit nozzle  63 . In addition, a strip-shaped base film  20  is supplied externally into this wedge-shaped portion. Therefore, the paper materials are altogether sandwiched between the wire meshes  61   a  and  62   b  and almost completely dewatered. Then, a wet paper sheet  40  drawn onto the wire mesh  61   b  is detached therefrom and conveyed to the next dewatering/drying stage. 
     This method also can attain the same effect as the previously described method. In addition, this method has an advantage that since the pulped material is molded together with a base film  20  by one sandwiching operation, higher unity can be attained between paper pulp on top side of the base film  20  and that on the bottom side thereof. 
     As another manufacture method, the above method may be modified so as to laminate two milled paper sheets together.  FIG. 6  illustrates this manufacture method. Two paper sheets  40   d  each milled to a thickness of, for example, 45 μm, are fed. Each paper sheet  40   d  is pulled in by a pair of rollers; an application roller  71   a  and a pressure roller  71   b . A holding roller  71   c  is disposed behind the application roller  71   a  and a cellulose-based glue solution  40   c  is stored between the two rollers. Therefore, the glue is applied to one side of each of the two paper sheets  40   d . In this state, a strip-shaped base film  20  is sent. As pressed between rollers, the three elements are laminated into a paper sheet  40 . Then, the paper sheet  40  is sent to the drying stage. 
     In this method, since the fluidity of the glue solution  40   c  is sufficiently high, the upper and lower layers of the paper sheet  40  can be bonded together satisfactorily through fine openings  21  of the base film  20 . This is advantageous in designing the antenna since the openings  21  can be designed smaller. 
     As mentioned so far, an RFID thread in accordance with the present embodiment has many openings bored through its base film and antenna except where a slit is formed and where an RFID chip is mounted. Therefore, when the RFID thread is developed to a paper sheet, paper fibers on the upper side of the thread and those on the lower side go thorough the openings and intertwine with paper fibers on the opposite side. Since the upper and lower layers of the paper sheet can thus be united via the openings, it is possible to prevent the RFID thread from floating even if the paper sheet is deformed by external force. 
     In the case of a conventional RFID thread structure as shown in  FIG. 7 , the above-mentioned openings are not formed. The base film  20  is made of such a polyester material as PEN (Polyethylene naphthalate) which is difficult to attain adhesion with cellulose or paper fiber. Likewise, the antenna  30  made of aluminum is difficult to attain adhesion with them. Therefore, if this RFID thread is developed to a paper sheet  40 , external force may cause the upper and lower layers of the paper sheet  40  to separate from the non-perforated base film  20   b , resulting in a lift  40   b  as indicated in the cross sectional view of  FIG. 8 . In an extreme case, the base film  20   b  may slip in the length direction and fall off from the paper sheet  40 . 
     Note that the openings  21  in the present embodiment may be modified in arrangement, shape and structure.  FIG. 9  shows a modified embodiment where openings  21  are arranged in a row along the center of the antenna  30 . Advantageously, since the openings  21  are decreased, this embodiment can reduce the possibility that the antenna  30  may be elongated or broken due to tension or the like when the thread is developed to a paper sheet or when the paper sheet is used. 
     Embodiment 2 
     The following describes a second embodiment of the present invention. The second embodiment is characterized in that semi-open U-shaped notches  22  are formed instead of openings  21 .  FIG. 10  is its perspective view. The other components are the same as in the first embodiment and therefore description thereof is omitted. Unlike the openings  21 , any part of the thread is not cut away to form them. Advantageously, the notching process does not produce scraps. Such scraps may be left and sandwiched, resulting in poor adhesion or abnormal appearance. 
     Embodiment 3 
     The following describes a third embodiment of the present invention. The third embodiment is characterized in that dowel-shaped projections  23  are formed on the base film  20  and antenna  30  by a dimpling process instead of the openings  21 .  FIG. 11  is its perspective view. The other components are the same as in the first embodiment and therefore description thereof is omitted. Although adhesion with paper fibers is somewhat weaker, this embodiment has the advantage that the projections  23  serve to prevent the base film  20  from falling off even if the paper sheet  40  has a lift  40   b . This embodiment is also advantageous in that the antenna performance is not lowered since no holes are formed through the antenna  30 . In addition, this embodiment has the advantage that no scraps are produced similar to the second embodiment.