Abstract:
The anti-counterfeit method of the invention conceals an authentication pattern in a retarder by means of specific treatments that achieve different phase retardation on the retarder. To authenticate the authentication pattern, the invention provides an identification system that can produce and filter polarized light projected through the retarder to display the authentication pattern. To improve protection against counterfeits, the invention further conceals the authentication pattern in a plurality of retarders that must be assembled with one another to display the authentication pattern. One retarder carrying a part of the authentication pattern and the polarizer can be therefore incorporated within the identification system to achieve a more effective anti-counterfeit effect.

Description:
FIELD OF THE INVENTION 
     The invention relates to an anti-counterfeit method that can protect confidential documents or sales articles against counterfeit. More particularly, the invention provides a method that can conceal the authentication mark of the article in such a manner that it is visible only with the use of a specific identification system. 
     BACKGROUND OF THE INVENTION 
     Along with the technical progress in various fields such as mechanical processing, electro-forming, scanning techniques, or printing techniques, effective anti-counterfeit measures have to be continuously improved. 
     Presently, commonly used anti-counterfeit methods are based on the use of a transparent protecting film that covers laser holographic layers or laser anti-counterfeit structures of diffraction optical grating that are attached on the article to conceal an authentication pattern. Concealed by means of the laser holographic layers or laser anti-counterfeit structures of diffraction optical grating, the authentication pattern however can be displayed via light projection thereon. Moreover, a counterfeiter can remove the transparent protecting film easily and copy the authentication pattern concealed in the laser holographic layers or laser anti-counterfeit structures of diffraction optical grating by electro-forming. In addition, the counterfeiter can desirably produce a falsification to replace the authentic laser label, but common people are usually incapable of distinguishing this falsification without a comparison with the authentic label. Furthermore, as printing techniques and digital acquision techniques progress, accurate printing anti-counterfeit patterns can be also easily reproduced through high resolution scanning and printing to obtain a falsified version hardly discernable. 
     Another method known in the prior art is the use of two optical gratings or two holographic layers among which one is an authentication element. The authentication pattern becomes visible only once the authentication optical grating or holographic element is properly superposed over the other optical grating or holographic layer. Such a method thus favorably allows the user to easily authenticate an article. However, the fabrication of holographic elements or optical gratings is difficult to achieve and not economical. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an anti-counterfeit method that overcomes the above problems by concealing the authentication pattern in a manner not to be directly visible, and that is difficult to falsify. 
     To achieve the above and other objectives, the anti-counterfeit method of the invention conceals an authentication pattern in a retarder where the authentication pattern is incorporated in a concealed pattern region and a background region of different phase retardation. To authenticate the authentication pattern, the invention further provides an identification system in which the patterned retarder and one or more polarizers are to be assembled. The identification system polarizes the light that passes through the retarder and produces different transmittances of the concealed pattern region and background region, and thereby displays the authentication pattern. To improve protection against counterfeits, the invention further conceals the authentication pattern in a plurality of retarders that must be assembled with one another to display the authentication pattern. The retarder carrying a part of the authentication pattern with the polarizers can therefore assembled within the identification system to achieve a more effective anti-counterfeit measure. 
     To provide a further understanding of the invention, the following detailed description illustrates embodiments and examples of the invention, this detailed description being provided only for illustration of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings included herein provide a further understanding of the invention. A brief introduction of the drawings is as follows: 
     FIG. 1 is a schematic view illustrating a phase retardation anti-counterfeit method according to an embodiment of the invention; 
     FIG. 2 is a schematic view of a retarder according to an embodiment of the invention; 
     FIG. 3 is a schematic view illustrating a phase retardation anti-counterfeit method using two retarders according to an embodiment of the invention; 
     FIG. 4 is a schematic view of a stripe-patterned retarder according to an embodiment of the invention; 
     FIG. 5 is a schematic view illustrating the assembly of the retarder with the identification system according to an embodiment of the invention; 
     FIG. 6 is a schematic view illustrating the assembly of a transmissive type identification system with a single retarder according to an embodiment of the invention; 
     FIG. 7 is a schematic view illustrating the light travels through the transmissive type identification system and the single retarder according to an embodiment of the invention; 
     FIG. 8 is a schematic view illustrating the assembly of the transmissive type identification system with two retarders according to an embodiment of the invention; 
     FIG. 9 is a table showing different transmittances of the concealed pattern region and background region obtained for various configurations of the retarders once assembled with the transmissive type identification system according to the invention; 
     FIG. 10 is a schematic view of a transmissive type identification system according to another embodiment of the invention; 
     FIG. 11 is a schematic view illustrating the assembly of a reflective-type identification system with a single retarder according to an embodiment of the invention; 
     FIG. 12 is a schematic view of the assembly of the reflective-type identification system with two retarders according to an embodiment of the invention; and 
     FIG. 13 is a schematic view of a reflective-type identification system according another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Wherever possible in the following description, like reference numerals will refer to like elements and parts unless otherwise illustrated. 
     FIG. 1 is a schematic view of a phase retardation anti-counterfeit method according to an embodiment of the invention. In accordance with the invention, the phase retardation anti-counterfeit method provides a retarder  10  that has an authentication pattern  11  incorporated in the retarder  10  in a concealed pattern region  12  and a background region  13 , as shown in FIG.  2 . By combining the retarder  10  with the identification system  20  that can generate and filter polarized light, and the different transmittances from the concealed pattern region  12  and the background region  13  will show the authentication pattern  11 . The authentication pattern  11  hence can be authenticated via human eyes or specific authentication machines. 
     In FIG.  1  and FIG. 2, the concealed pattern region  12  and the background region  13  are formed by means of specific treatments (such as the chemical treatments or thermal treatments to either partially or entirely elimate the phase retardation in the processing regions) applied on the phase retardation regions of the retarder  10 . Before assembling with the identification system  20 , the concealed pattern region  12  and the background region  13  are both transparent. Therefore, it is impossible for an observer to directly see the authentication pattern  11  of the retarder  10 . Even by using an ordinary light source projected on the retarder  10 , the observer cannot read the authentication pattern  11 . Anti-counterfeit is therefore effectively achieved. 
     As described above, the authentication pattern  11  is incorporated in at least one retarder  10 . As shown in FIG. 3, the invention also envisages a retarder  10  that is formed via the lamination of a first retarder  10 A and a second retarder  10 B. Hence, the phase retardation of each retardation region on the retarder  10  is the result of accumulating phase retardation in the corresponding position on the first retarder  10 A and the second retarder  10 B. The authentication pattern  11  can be thereby dispersed on two or more different retarders (such as the first retarder  10 A and the second retarder  10 B). Hence, one retarder (for example first retarder  10 A) may be disposed on the article to be protected while the other retarder (for example second retarder  10 B) is disposed on the identification system  20 . Hence, the authentication pattern  11  appears only when both retarders are properly superposed over each other. Therefore, if a counterfeiter tries to access to the authentication pattern  11  from the article, only an incomplete part of the authentication pattern  11  may be unveiled since the other part lies on the identification system  20 . Counterfeit of the authentication pattern thus is prevented. In addition, the authentication pattern  11  of the first retarder  10 A and the second retarder  10 B may be further concealed in random-dot pattern (FIG. 3) or stripe pattern (FIG. 4) so that the distinction of the authentication pattern  11  through visual perception, before assembling with the identification system  20 , is even more difficult. Besides the binary retardation processing (the processed regions having zero retardation), the production of the random-dot pattern may be also generated in gray-scale and the retarder may be processed in a gray-scale retardation processing manner accordingly. With respect to stripe pattern, the stripe directions can be achieved according to a random-period irregular manner. When random-dot pattern is used to conceal the authentication pattern  11 , a counterfeiter that obtains one of the retarders  10 A,  10 B can only see random dots and cannot distinguish the corresponding part of the authentication pattern  11 . The random-dot pattern and the stripe pattern therefore contribute to increase the efficiency of the anti-counterfeit effect. 
     FIG. 5 is a schematic view illustrating the assembly of the identification system  20  with the retarder  10  according to an embodiment of the invention. The polarized light  21  of the identification system  20  is projected on the retarder  10 , and travels through the concealed pattern region  12  and the background region  13  of different phase retardation. The First and the second polarized lights  21 A,  21 B of different polarization directions respectively come out from the concealed pattern region  12  and the background region  13 , and travel through the identification system  20  to produce different transmittances of the concealed pattern region  12  and background region  13 . The authentication pattern  11  is thereby displayed. 
     Depending on whether the article protected by the anti-counterfeit method of the invention is transparent or not, the identification system  20  of the invention may be either of transmissive or reflective type as described hereafter. 
     Transmissive Type Identification System 
     As shown in FIG. 6, a transmissive type identification system  20 A according to an embodiment of the invention comprises an upper polarizer  22 A and a lower polarizer  22 B that are respectively placed above and below the retarder  10 . The upper and lower polarizers  22 A,  22 B may be, for example, linear polarizers, elliptical polarizers, or circular polarizers. In addition, the upper polarizer  22 A and the lower polarizer  22 B may be further assembled with other elements into integrated optical modules (not shown). As illustrated in the schematic view of FIG. 7, once the transmissive type identification system  20 A is assembled with the retarder  10 , a polarized light  21  is generated via light projection from a light source  23  through the lower polarizer  22 B. The polarized light  21  travels through the concealed pattern region  12  and background region  13  of the retarder  10  with different phase retardation, thereby generating the first and the second polarized lights  21 A,  21 B of different polarization directions that then travel through the upper polarizer  22 A. Due to the polarization characteristic of the upper polarizer  22 A, the polarized lights  21 A,  21 B while penetrating there through are also subjected to absorption that results in different transmittances with respect to the concealed pattern region  12  and the background region  13 . Via the contrast of the above different transmittances, the authentication pattern  11  is thereby displayed. The higher the contrast of the concealed pattern region  12  and the background region  13 , the clearer the display of the authentication pattern  11 . The authentication pattern  11  may be also displayed via light projection inversely from the light source  23  on the upper polarizer  22 A, through the retarder  10  to the lower polarizer  22 B. 
     As shown in FIG. 6, the upper and lower polarizers  22 A,  22 B respectively can be, for example, horizontally linear and vertically linear polarizers, and the retarder  10  is a ½λ(half wavelength) retarder. By means of specific treatments (such as chemical treatments, thermal treatments, or laser treatments), the phase retardation of the concealed pattern region  12  hence is set to ½λ while the phase retardation of the background region  13  is set to 0. Meanwhile, the lower polarizer  22 B is a vertical linear polarizer, and the stretching direction of the retarder  10  is adjusted to tilt 45° from the polarized direction of the lower polarizer  22 B. Hence, the vertically polarized light, generated via light projection through the lower polarizer  22 B, respectively becomes horizontally polarized after traveling through the concealed pattern region  12  of the retarder  10  and remains unchanged after traveling through the background region  13 . The horizontally polarized light from the concealed pattern region  12  then passes through the horizontal direction upper polarizer  22 A, so that the concealed pattern region  12  is entirely transparent. Meanwhile, the vertically polarized light is absorbed by the upper polarizer  22 A, so that the background region  13  appears to be black. Because contrast between the concealed pattern region  12  (entirely transparent) and the background region  13  (black color) is highest consequently, the authentication pattern  11  is therefore clearly displayed. FIG. 9 is a table illustrating various transmittances of the concealed pattern region  12  and background region  13  obtained with different phase retardation in combination with polarizers of different polarization directions. 
     As shown in FIG. 8, the transmissive type identification system  20 A can also accommodate the use of two retarders. The first retarder  10 A can be attached to one polarizer, for example the upper polarizer  22 A, while the second retarder  10 B is attached to the other polarizer, for example the lower polarizer  22 B. Provided with the first retarder  10 A thereon, the upper polarizer  22 A then is attached to a transparent article to be protected against counterfeit, thereby a part of the authentication pattern  11  is concealed on the article. The other part of the authentication pattern  11  is in turn concealed in the transmissive type identification system  20 A. Hence arranged, the authentication pattern  11  is visible only once the first retarder  10 A and the second retarder  10 B are properly superposed over each other and light is projected from the light source  23  through the lower polarizer  22 B. Counterfeit is therefore more difficult since the unique possession of the transparent article or the transmissive type identification system  20 A is insufficient to obtain the authentication pattern  11 . 
     According to a variant example, the transmissive type identification system  20 A can be equipped with a polarized light emitter as substitution for the light source  23  and the lower polarizer  22 B of FIG.  7 . As illustrated in FIG. 10, the transmissive type identification system  20 A hence comprises a polarized light emitter  25  and a lower polarizer  22 B placed below the retarder  10 . Once the retarder  10  is assembled with the transmissive type identification system  20 A, the polarized light emitter  25  projects a polarized light on the upper surface of the retarder  10 , thereby displaying the authentication pattern. With the retarder  10  attached thereto, the lower polarizer  22 B can be further attached to an article to conceal the authentication pattern  11  thereon. 
     Reflective Type Identification System 
     As schematically shown in FIG. 11, a reflective type identification system  20 B comprises a polarizer  22  disposed above the retarder  10  and a polarization reserved reflective layer  24 . The polarizer  22  can be, for example, a linear polarizer, an elliptical polarizer or a circular polarizer, while the reflective layer  24  can be, for example, metallic. In addition, the polarizer  22  and the reflective layer  24  may be possibly assembled with other elements into integrated optical modules (not shown). Once the reflective type identification system  20 B is assembled with the retarder  10 , a polarized light  21  is generated via light projection from the light source  23  through the polarizer  22 . The polarized light  21  travels through the concealed pattern region  12  and the background region  13  of the retarder  10  with different phase retardation, and becomes polarized light of different polarization directions that reflect from the reflective layer  24 . After reflection from the reflective layer  24 , the polarized light travel again through the concealed pattern region  12  and the background region  13 , thereafter generating the first polarized light  21 A and the second polarized light  21 B that arrives on the polarizer  22 . Due to the polarization characteristic of the polarizer  22 , the first and second polarized lights  21 A,  21 B while penetrating there through are also subjected to absorption that generates different reflectivity with respect to the concealed pattern region  12  and the background region  13 . Via the contrast of the above different reflectivity, the authentication pattern  11  is thereby displayed. The higher the contrast of the concealed pattern region  12  and the background region  13 , the clearer the display of the authentication pattern  11 . 
     As schematically shown in FIG. 11, the polarizer  22  can be, for example, a horizontally linear polarizer and the retarder  10  a ¼λ retarder. By means of specific treatments (such as chemical treatments, thermal treatments, or laser treatments), the phase retardation of the concealed pattern region  12  hence is set to ¼λ. while the phase retardation of the background region  13  is set to 0. Meanwhile, the polarizer  22  is adjusted in a manner to have the polarization direction thereof forming 45° with the stretching direction of the retarder  10 . Hence, the horizontally polarized light, generated via light projection through the polarizer  22 , respectively becomes circularly polarized after traveling through the concealed pattern region  12  and remains unchanged after traveling through the background region  13 . The circularly polarized light from the concealed pattern region  12  then reflects from the polarization reserved reflective layer  24  toward the concealed pattern region  12  of ¼λ phase retardation after which it becomes vertically polarized. As a result, the concealed pattern region  12  appears in black color. Meanwhile, the horizontally polarized light from the background region  13 , after reflection from the reflective layer  24 , passes through the background region  13  again and remains horizontally polarized. The background region  13  is consequently completely transparent. Because the hue of the concealed pattern region  12  (black color) and the background region  13  (reflective) then has the highest contrast, the authentication pattern  11  is therefore clearly displayed. 
     As shown in FIG. 12, the reflective type identification system  20 B can also accommodate the use of two retarders. The first retarder  10 A can be attached to one polarizer  22 , while the second retarder  10 B is attached to the reflective layer  24 . Provided with the second retarder  10 B thereon, the reflective layer  24  then is attached to a non-transparent article to be protected against counterfeit, thereby a part of the authentication pattern  11  is concealed on the article. The other part of the authentication pattern  11  is in turn concealed in the reflective type identification system  20 B. Hence arranged, the authentication pattern  11  is visible only once the first retarder  10 A and the second retarder  10 B are properly superposed over each other and light is projected from the light source  23  through the polarizer  22 . Counterfeit is therefore more difficult since only possessing the non-transparent article or reflective type identification system  20 B is insufficient to obtain the authentication pattern  11 . 
     According to another example schematically illustrated in FIG. 13, the reflective type identification system  20 B may alternatively comprise a polarized light emitter  25  and a reflective polarizer  26  disposed below the retarder  10 . The reflective polarizer  26  is a polarizer with a reflective layer that only reflects the light of a specific polarization direction, and the light of other polarization directions either are absorbed or passes there through. Once the retarder  10  is assembled with the reflective type identification system  20 B, the polarized light emitter  25  projects a polarized light through the upper surface of the retarder  10  to the reflective polarizer  26 . The polarized light that reaches the reflective polarizer  26  with a polarization direction similar to that of the reflective polarizer  26  is reflected while the light of other polarization directions either is absorbed or passes there through. Because the concealed pattern region  12  and the background region  13  have different phase retardation, the polarized light that respectively passes there through becomes polarized light of different polarization directions. As a result, the light that reaches the reflective polarizer  26  reflects differently with different reflectivities, thereby causing the authentication pattern to be displayed. Hence, with the retarder  10  attached thereto, the reflective polarizer  26  can be further attached to an article to conceal the authentication pattern thereon. 
     In another example of reflective type identification system illustrated in FIG. 13, the general phase retardation of the retarder  10  is ½λ, the phase retardation of the concealed pattern region  12  is ½λ and the phase retardation of the background region  13  is consequently 0. Furthermore, if the direction of the polarized light from the polarized light emitter  25  is horizontal, the polarization direction of the reflective polarizer  26  is also horizontal. The polarization direction of the reflective polarizer  26  and the stretching direction of the retarder  10  are set to form 45°. With the above disposition, once the horizontally polarized light is projected from the polarized light emitter  25  through the retarder  10 , the resulting light passes through the concealed pattern region  12  is vertically polarized while that passes through the background region  13  remains horizontally polarized. Once the above two polarized lights reach the reflective polarizer  26 , the vertically polarized light passes through the concealed pattern region  12  is either entirely absorbed or entirely passes through the reflective polarizer  26 : an observer then sees a corresponding black region. Meanwhile, the horizontally polarized light passes through the background region  13  is entirely reflected via the reflective polarizer  26 : an observer then sees a reflective region. By means of the above disposition, a maximum contrast is favorably obtained. 
     It should be apparent to those skilled in the art that the above description is only illustrative of specific embodiments and examples of the invention. The invention should therefore cover various modifications and variations made to the herein-described structure and operations of the invention, provided they fall within the scope of the invention as defined in the following appended claims.