Abstract:
An RFID tag includes: a first sheet; a conductor pattern provided on the first sheet and at least partially forming a communication antenna; a circuit chip electrically connected to the antenna formed by the conductor pattern and performing radio communication via the antenna. The RFID tag further includes: a second sheet detachably attached to the first sheet by covering the conductor pattern and the circuit chip so as to be detached together with a part of the pattern when detached from the first sheet; and a release layer provided between the part of the conductor pattern and the first sheet.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an RFID (Radio_Frequency_Identification) tag for exchanging information with an external device in a noncontact manner. There are the cases where those in the art refer to the “RFID tag” used herein as an “RFID tag inlay” regarding it as an inlay for the “RFID tag.” There are also the cases where the “RFID tag” is referred to as a “Radio Frequency IC tag.” The “RFID tag” also includes a noncontact IC card.  
         [0003]     2. Description of the Related Art  
         [0004]     In recent years, there are proposals of various kinds of RFID tags for exchanging information with an external device represented by a reader-writer in a noncontact manner via radio waves. There is a proposal of a kind of the RFID tag having a configuration in which an antenna pattern for radio communication and an IC chip are mounted on a base sheet consisting of plastic or paper. As for such a type of the RFID tag, there is a considered usage wherein it is attached to an article or the like and the information on the article is exchanged with the external device to identify the article.  
         [0005]     In the case of such a usage of the RFID tag, there may occur an unauthorized use of causing the external device to misidentify the article by detaching the RFID tag attached to a certain article from that article and attaching it to another article so as to obtain an expensive article for sale as an inexpensive article for sale for instance. Thus, a technique for avoiding such an unauthorized use is expected.  
         [0006]     Concerning such a status, there is a technique configured to break a circuit by detaching a part of a conductor pattern configuring the antenna and the like and the IC chip upon detachment of the RFID tag (refer to Japanese Patent Laid-Open No. 2004-227273, for instance).  
         [0007]     The RFID tag of Japanese Patent Laid-Open No. 2004-227273 has an adhesive layer including the circuit and the like on the entire undersurface of an uppermost sheet. The adhesive layer is attached to the article. The RFID tag has a release agent in a part between the uppermost sheet and the adhesive layer. Thus, if the uppermost sheet is detached after being attached to the article, an adhesive force works on the article side in the part having the release agent while the adhesive force works on the sheet side in the part having no release agent. And then a shearing force is generated in the adhesive layer so that the adhesive layer is torn off. Consequently, the circuit and the like included in the adhesive layer are also torn off so as to break the circuit.  
         [0008]     However, there are the cases where the part of the circuit to be eliminated cannot be securely eliminated by the configuration in which the adhesive layer is torn off by the shearing force working in the adhesive layer to indirectly break the circuit inside the adhesive layer.  
         [0009]     There is also a problem that the configuration having the circuit and the like included in the adhesive layer becomes a complicated configuration including lamination of the adhesive layer and the like, which leads to increased cost.  
         [0010]     In view of the circumstances, the present invention provides the RFID tag having a simple configuration and securely breaking an internal circuit.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention provides an RFID tag including: 
        a first sheet;     a conductor pattern provided on the first sheet and at least partially forming a communication antenna;     a circuit chip electrically connected to the antenna formed by the conductor pattern and performing radio communication via the antenna;     a second sheet detachably attached to the first sheet by covering the conductor pattern and the circuit chip so as to be detached together with a part of the conductor pattern when detached from the first sheet; and     a release layer provided between the part of the conductor pattern and the first sheet.        
 
         [0017]     According to the RFID tag of the present invention, the release layer is formed between the first sheet and the conductor pattern. Therefore, the pattern portion on the release layer is easily separable from the first sheet, and a part of the conductor pattern is eliminated from the first sheet by adhesion of the second sheet if the second sheet is detached from the first sheet. Consequently, a circuit consisting of the conductor pattern and the circuit chip is broken. Thus, the circuit can be easily broken by a simple configuration having the release layer between the part of the conductor pattern and the first sheet. As the second sheet adheres directly to the portion to be broken of the conductor pattern, the portion to be broken can be securely broken.  
         [0018]     In the RFID tag of the present invention, preferably, the circuit chip also detects destruction to a predetermined pattern portion of the conductor pattern; 
        the second sheet is detachable together with at least a detachable portion of the pattern portion when detached from the first sheet; and     the release layer is provided between the detachable portion and the first sheet.        
 
         [0021]     According to this RFID tag, if the first sheet is detached, the pattern portion for detecting detachment is surely destroyed, and the destruction of the pattern portion is securely detected by the circuit chip. For this reason, it is possible to obtain the RFID tag of high security capable of securely detecting unauthorized detachment of the RFID tag and the like.  
         [0022]     As described above, the RFID tag of the present invention has a simple configuration and securely breaks an internal circuit. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a sectional view of an unused RFID tag;  
         [0024]      FIG. 2  is an explanatory diagram of a circuit pattern of the RFID tag;  
         [0025]     FIGS.  3 ( a ) and  3 ( b ) are sectional views of the RFID tag in use; and  
         [0026]     FIGS.  4 ( a ) and  4 ( b ) are diagrams showing another embodiment of the RFID tag of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     Embodiments of the present invention will be described with reference to the attached drawings.  
         [0028]      FIG. 1  is a sectional view of an unused RFID tag  1 , and  FIG. 2  is an explanatory diagram of a circuit pattern of the RFID tag  1 .  FIG. 1  shows an X to X cross section of  FIG. 2 , and  FIG. 2  omits a protective layer and an adhesion layer of  FIG. 1  for convenience of illustration.  
         [0029]     The configuration of the RFID tag  1  will be described by using  FIGS. 1 and 2 . The RFID tag  1  is configured by multiple layers as in  FIG. 1 .  
         [0030]     As shown in  FIG. 1 , the RFID tag  1  is provided with a base material layer  11  which is equivalent to an example of a first sheet according to the present invention. The base material layer  11  is the layer as a base on which the layers are formed, and is configured by a plastic resin or the like. As a lower layer to the base material layer  11 , an adhesive layer  12  configured by an adhesive is formed to be attached to an object such as an article. As the lower layer to the adhesive layer  12 , a release layer  13  for protecting the adhesive layer  12  when the RFID tag  1  is unused and being detached when the RFID tag  1  is used is formed.  
         [0031]     As upper layers of the base material layer  11 , an adhesion layer  14  and a protective layer  15  are formed. The protective layer  15  protects the surface of the RFID tag  1 . The adhesive of the adhesion layer  14  has higher adhesion to the protective layer  15  than to the base material layer  11 , and the adhesion of the adhesion layer  14  to the base material layer  11  is lower than an adhesive force of the adhesive layer  12  to an object. For this reason, the adhesion layer  14  and the protective layer  15  are integrally formed and detachable from the base material layer  11 . The protective layer  15  and the adhesion layer  14  configure an example of a second sheet according to the present invention.  
         [0032]     A circuit portion  20  is formed on the base material layer  11 . The circuit portion  20  includes an antenna pattern  21 , a detection pattern  22  and an IC chip  23 . The circuit portion  20  is fixed to the base material layer  11  more firmly than the adhesion of the adhesion layer  14 . The antenna pattern  21  and detection pattern  22  configure an example of a conductor pattern according to the present invention, and the IC chip  23  is equivalent to an example of a circuit chip according to the present invention.  
         [0033]     The base material layer  11  has a circuit pattern shown in  FIGS. 1 and 2  transferring-printed in conductive ink thereon. The circuit pattern includes the antenna pattern  21  playing a role of the antenna for sending and receiving radio wave and the detection pattern  22  provided to detect detachment of the protective layer  15 . As shown in  FIG. 2 , the IC chip  23  is placed on the antenna pattern  21  and detection pattern  22  and under the adhesion layer  14  to connect to both the antenna pattern  21  and detection pattern  22 . The IC chip  23  performs communication with an external device via the antenna pattern  21 , and detects destruction to the detection pattern  22  if it occurs so as to notify the external device thereof as described below.  
         [0034]     The base material layer  11  has a release layer  31  formed at a position under a release portion  22   a  provided to a part of the detection pattern  22 . The release layer  31  is formed before transferring-printing the circuit pattern on the base material layer  11 , and the release portion  22   a  transferring-printed on the release layer  31  is in an easily detachable state not being firmly fixed to the release layer  31 . The release layer  31  is equivalent to an example of the release layer according to the present invention.  
         [0035]     Next, a use situation of the RFID tag  1  will be described.  
         [0036]     FIGS.  3 ( a ) and  3 ( b ) are sectional views of the RFID tag  1  in use. FIGS.  3 ( a ) and  3 ( b ) also show the X to X cross section of  FIG. 2 .  
         [0037]     As shown in  FIG. 3 ( a ), when the RFID tag  1  is used, the release layer  13  is eliminated first, and then the RFID tag  1  is attached to an article A which is an article for sale, a container of the article for sale or the like by the adhesive layer  12 . In this state, the detection pattern  22  is in a conductive status as shown in  FIG. 2 , and the IC chip  23  recognizes that the protective layer  15  is not detached in this state.  
         [0038]     Next, in the case where the RFID tag  1  is no longer necessary after the use or in the case where an unauthorized user tries to detach the RFID tag  1  from the article A, the protective layer  15  is detached from the base material layer  11  in the state where the base material layer  11  is attached to the article A by the adhesive layer  12  as shown in  FIG. 3 ( b ). Here, the adhesion of the adhesion layer  14  integrally formed with the protective layer  15  is not high enough to separate the circuit patterns (the antenna pattern  21  and the detection pattern  22  shown in  FIG. 2 ) and the IC chip  23  from the base material layer  11 . For this reason, the adhesion layer  14  and protective layer  15  separate in the state where the antenna pattern  21 , detection pattern  22  and IC chip  23  are left on the base material layer  11 .  
         [0039]     However, the release layer  31  is formed between the release portion  22   a  of the detection pattern  22  and the base material layer  11  so that the release portion  22   a  is easily separable from the release layer  31 . For this reason, the release portion  22   a  is separated from the release layer  31  by the adhesion of the adhesion layer  14 .  
         [0040]     Here, most of the detection pattern  22  is left on the base material layer  11  as described above while only the release portion  22   a  is separated from the release layer  31  on the base material layer  11  by the adhesion layer  14 . For this reason, the detection pattern  22  is broken by having only the portion of the release portion  22   a  eliminated from the base material layer  11 . If the detection pattern  22  is thus broken, the IC chip  23  recognizes that the protective layer  15  is detached based on change in resistance of the detection pattern  22  and the like.  
         [0041]     The IC chip  23  having thus recognized the detachment of the protective layer  15  prohibits reading and writing to data of an internal memory so as to prevent an unauthorized use.  
         [0042]     The present invention may adopt control for rendering the data of the internal memory of the IC chip  23  readable and writeable if the detection pattern  22  is in a conduction state and rendering the data from the internal memory of the IC chip  23  readable only if the detection pattern  22  is in an insulation state. If such control is adopted, it is possible, when transporting the article for sale for instance, to attach the RFID tag  1  to the article for sale and read and write during the transportation so that a worker can read the information on the article for sale and record the status of the transportation. It is also possible, by detaching the protective layer  15  after the transportation of the article, to read only the information on the article so as to help quality control.  
         [0043]     According to the embodiment described above, the antenna pattern  21 , detection pattern  22  and IC chip  23  are left on the article A side by detaching the protective layer  15 . However, the RFID tag of the present invention is not limited thereto. For instance, if the protective layer  15  is detached from the base material layer  11 , the antenna pattern  21 , detection pattern  22  and IC chip  23  may be left on the protective layer  15  side as with another embodiment described below.  
         [0044]     FIGS.  4 ( a ) and  4 ( b ) are diagrams showing another embodiment of the RFID tag of the present invention.  
         [0045]      FIG. 4 ( a ) shows a sectional view of an unused RFID tag  2 , and  FIG. 4 ( b ) shows a sectional view of the RFID tag  2  in use.  
         [0046]     As shown in  FIG. 4 ( a ), the RFID tag  2  is provided with the base material layer  11  which has the protective layer  15  formed as an upper layer thereof and the adhesion layer  14  formed as a lower layer thereof. The antenna pattern  21 , detection pattern  22  (only the release portion  22   a  which is a part of the detection pattern is shown in  FIG. 4 ( a )) and IC chip  23  configuring the circuit portion are formed under the base material layer  11  and on the adhesion layer  14 . The release layer  31  is formed between the release portion  22   a  and the base material layer  11 . The release layer  13  for protecting the adhesion layer  14  when unused and being detached in use is formed under the adhesion layer  14 .  
         [0047]     In the case of the embodiment shown in FIGS.  4 ( a ) and  4 ( b ), an example of the first sheet according to the present invention is formed by the base material layer  11  and protective layer  15 . The adhesion layer  14  is equivalent to an example of the second sheet according to the present invention.  
         [0048]     As shown in  FIG. 4 ( b ), when using the RFID tag  2 , the release layer  13  is eliminated, and the RFID tag  2  is attached to the article A which is an article for sale, a container of the article for sale or the like by the adhesion layer  14 . And if the protective layer  15  is detached thereafter, the base material layer  11  integral with the protective layer  15  and the antenna pattern  21 , detection pattern  22  and IC chip  23  firmly fixed to the base material layer  11  are separated from the adhesion layer  14  together with the protective layer  15 . In this case, the release layer  31  is formed between the release portion  22   a  of the detection pattern  22  and the base material layer  11 . As the release portion  22   a  is easily separable from the release layer  31 , the release portion  22   a  is separated from the release layer  31  by the adhesion of the adhesion layer  14  so as to remain on the adhesion layer  14 . Consequently, the detection pattern  22  is broken, and the IC chip  23  recognizes that the protective layer  15  is detached.  
         [0049]     Thus, the detection pattern  22  is broken and the detachment of the protective layer  15  is recognized even if the part of the circuit portion left on the article side and the detached part are reversed.