Information storage medium

Abstract: An information storage medium (1) has a base portion (2) and a code storage portion (3). The code storage portion (3) is disposed on the base portion (2) and contains an infrared absorber which absorbs substantially only infrared rays within a narrow wavelength band. If a real information storage medium (1) is produced like that, subject mediums (1, 11) are judged real or not by a method including the steps of emitting rays to the subject medium (1, 11) , receiving rays reflected from the subject medium (1, 11), detecting a first reflectance at the peak absorption wavelength (λ 0 ) and a second reflectance at a comparison wavelength (λ 1 ) near the peak wavelength (λ 0 ), and judging if the subject medium (1, 11) is real or not. The rays at the comparison wavelength (λ 1 ) are not very much absorbed by the absorber.

Description: The present invention relates to an information storage medium including a code storage portion, e.g., a bar code portion. The invention also relates to a method and an apparatus for judging if a subject information storage medium is authentic or forged. Identity cards having bar-code markings are described in US-A-4,359,633 and US-A-4,853,525. US-A-4,359,633 discloses an information storage medium comprising a base portion and a bar code storage portion disposed on the base portion. The bar code storage portion contains an infrared absorber made from black ink containing carbon. The storage medium also comprises a transparent red filter for absorbing blue light and transparent blue filter for absorbing red light. Both filters allow infrared light to pass through unabsorbed. Hence, the filters filter out the visible light and allow only infrared light to be transmitted to the bar code. Although the carbon black ink used to print the bar code absorbs in the visible and infrared regions, only infrared light can be received by the bar code because of the filters. US-A-4,853,525 discloses an information storage medium comprising a base portion and a code storage portion disposed on the base portion. The medium also comprises a cover layer exclusively permeable to infrared light, and an additional layer which is generally transparent but absorbs infrared light within a narrow wavelength band. This film is used to form the pattern of the code. The reading apparatus comprises IR emitters and wide band IR phototransistors for reading the code in the IR range, and IR phototransistors for reading the narrow band absorption. The output signals from the wide band phototransistors and the narrow band phototransistors are compared in an AND gate in order to detect a forgery. In recent years, code storage portions, for example, bar codes, which may be detected by optical readers, have been attached to various goods. Information recorded at such code storage portions may be utilized for merchandise management, e.g., distinction of items in POS (point of sale) system and so on. Usually, a bar code is constituted of black and white bars having different widths which cooperate to represent codes or information. An optical reader emits rays within a specific range of wavelength and receives the rays reflected from the bar code. Then, the reader can detect the widths of the black and white bars since the reflectance from the black bars and the reflectance from the white bars are significantly different from each other. However, the application of such bar codes including black or dark bars may cheapen the appearance of the goods so that it is not appropriate to attach the visible bar codes to expensive, sophisticated or aesthetically pleasing goods. Therefore, bar codes, which absorb infrared but which do not absorb visible rays, so as to be invisible for human beings, have been developed. JP-A-57-201963 (published in 1982) and JP-A-1-305484 (published in 1989) disclose a bar code which is transparent for visible rays and absorbs infrared rays. However, conventional infrared absorbers absorb a wide range of wavelengths. Thus, they are not in fact completely transparent to visible rays. Accordingly, in order to conceal such bar codes, a cover layer, made of infrared-transparent and invisible materials, was proposed in JP-A-58-45999 (published in 1983). Moreover, JP-A-3-154187 (published in 1991) discloses that a cover layer, made of infrared-transparent and invisible materials, is mounted on a bar code made of an infrared absorber which absorbs infrared rays in a specific wavelength range between 700 nm and 1000 nm. These known techniques may resolve the above-described problem since the bar codes are difficult to detect by human beings and do not cheapen the appearance of the goods. On the other hand, it is a very important consideration to prevent the code storage portions, e.g., bar codes or the like, from being forged or counterfeited. The above-described prior art techniques for concealing may be one of the means for protecting against forgers or counterfeiters since the bar codes are invisible. However, if a forger uses infrared scopes, the concealed bar codes can be inspected easily since the conventional infrared absorbers absorb a wide range of wavelength. In addition, since there are many kinds of infrared absorbers, it is not difficult following such inspection to forge such bar codes using known infrared absorbers. An object of the present invention is to provide an information storage medium which is extremely difficult to forge or counterfeit. Another object of the present invention is to provide a method and an apparatus for judging if a subject information storage medium is authentic or not. In accordance with one aspect of the present invention, an information storage medium comprises a base portion and a code storage portion disposed on said base portion, said code storage portion containing an infrared absorber, said infrared absorber being capable of absorbing substantially only infrared radiation within a narrow wavelength band, wherein said infrared absorber has an infrared absorption peak at a first wavelength of said narrow wavelength band, characterized in that said infrared absorber is adapted to have substantially no absorption for infrared at a second wavelength of said narrow wavelength band, the difference between the first wavelength and the second wavelength being less than or equal to 100 nm; and in that said infrared absorber is capable of substantially reflecting visible rays. With such a construction, since the infrared absorber absorbs substantially only infrared within a narrow wavelength band, the code storage portion is extremely difficult to detect by means of infrared scopes in comparison with the conventional infrared absorbers which absorbs a wide range of wavelength of infrared rays. In addition, such an absorber absorbing substantially only specific rays within the narrow wavelength band is extremely difficult to produce using other components, and thus, forgery or counterfeiting of the information storage medium is largely prevented. Besides, since the infrared absorber absorbs visible rays little, the code storage portion can be made invisible, and therefore may not cheapen the appearance of expensive, sophisticated or aesthetically pleasing goods. In another aspect of the present invention there is provided a method for judging if a subject information storage medium is authentic or forged, where an authentic information storage medium includes a base portion and a code storage portion disposed on said base portion, said code storage portion containing a light absorber, said light absorber being capable of absorbing substantially only specific rays within a narrow wavelength band, the narrow wavelength band including a peak wavelength (λ 0 ) at which the light absorption curve has a peak value, the method comprising the steps of emitting rays to said subject information storage medium; receiving rays reflected from said subject medium; detecting a first reflectance at said peak wavelength (λ 0 ) and a second reflectance at a comparison wavelength (λ 1 ) near said peak wavelength (λ 0 ), rays at the comparison wavelength being substantially unabsorbed by said light absorber, the difference between said peak wavelength (λ 0 ) and said comparison wavelength (λ 1 ) being less than or equal to 100 nm; and judging if said subject medium is authentic or not on the basis of said first reflectance and said second reflectance. By the method according to the present invention, since the comparison wavelength is near the peak absorption wavelength and the rays at the comparison wavelength are substantially unabsorbed, accurate detection of a forged medium is ensured. In other words, whether an information storage medium is authentic or not is judged with improved reliability. Preferably, in the judging step, a difference between the first reflectance and second reflectance is obtained, and the subject medium is judged authentic if the difference between the first reflectance and the second reflectance is greater than a certain value. But, the subject medium is judged as a forgery if the difference is equal to or less than the certain value. In this case, if the certain value is variable, it will be determined high for expensive goods which need high reliability. On the other hand, the certain value will be determined low for inexpensive goods which do not need high reliability. The light absorber is preferably an infrared absorber being capable of absorbing substantially only infrared within a narrow wavelength band, but absorbing visible rays little, so that the code storage portion may be concealed. In this case, the rays used at the emitting step contain at least infrared rays which are absorbed by said light absorber. It is preferable that the difference between the peak wavelength and the comparison wavelength is prescribed greater than 10 nm. This means that the narrow wavelength band, which the light absorber absorbs, is very much narrow since the comparison wavelength is near or at the critical point of the narrow wavelength band as mentioned above. Such a light absorber may be made of only specific components practically, and thus subject information mediums will be judged as a forged one when the components are different from those of the authentic medium. Accordingly, the accuracy of the judgement is further improved. In another aspect of the present invention, there is provided an apparatus for judging if a subject information storage medium is authentic or forged, where an authentic information storage medium includes a base portion and a code storage portion disposed on said base portion, said code storage portion containing a light absorber, said light absorber being capable of absorbing substantially only specific rays within a narrow wavelength band, the narrow wavelength band including a peak wavelength (λ 0 ) at which the light absorber absorbs the most, the apparatus comprising: an emitting means for emitting rays to said subject information storage medium, said rays containing at least rays of said peak wavelength and rays of a comparison wavelength (λ 1 ) near said peak wavelength (λ 0 ), rays at the comparison wavelength (λ 1 ) being substantially unabsorbed by said light absorber, the difference between said peak wavelength (λ 0 ) and said comparison wavelength (λ 1 ) being less than or equal to 100 nm; receiving means for receiving rays reflected from said subject medium, and providing a first output signal in accordance with a first reflectance at said peak wavelength (λ 0 ) and a second output signal in accordance with a second reflectance at said comparison wavelength (λ 1 ); and a judging means for obtaining the difference between said first signal and said second signal, and judging if said subject medium is authentic or not on the basis of said difference between said first signal and said second signal. More preferably, the judging means judges the subject medium authentic if the difference between the first signal and the second signal is greater than a certain value, and judges the subject medium as a forgery if the difference is equal to or less than the certain value. Preferably, the emitting means emits at least infrared rays for inspecting the subject medium when the light absorber of the authentic information storage medium is an infrared absorber, the infrared absorber being capable of absorbing substantially only infrared within a narrow wavelength band, but absorbing visible rays little. It is also preferable that a difference between the peak wavelength and the comparison wavelength, by which the receiving means provides the first and second output signals, is prescribed greater than 10 nm. These and other objects and advantages of the present invention will be appreciated by the description hereinafter with reference to the accompanying drawings, in which: Figure 1 is an enlarged cross sectional view showing an information storage medium according to an embodiment of the present invention; Figure 2 is a graph showing an absorption spectrum of an infrared absorber which is ideal for the usage in the information storage medium in Fig. 1; Figure 3 is a schematic view showing a judging apparatus according to an embodiment of the present invention; Figure 4 is a graph showing the change of signals processed in the judging apparatus during the conveyance of the real information storage medium in Figure 1; Figure 5 is a graph showing an absorption spectrum of another light absorber which will be judged as a forgery by the apparatus shown in Figure 3; Figure 6 is a graph showing the change of signals processed in the judging apparatus during the conveyance of an information storage medium using with the light absorber of which the absorption characteristic is shown in Figure 5; Figure 7 is a graph showing an absorption spectrum of a light absorber in a specimen of an information storage medium which will be preferably used as a real medium for the apparatus in Figure 3; Figure 8 is a graph showing an absorption spectrum of another light absorber in another specimen of an information storage medium which will be judged as a forgery by the apparatus shown in Figure 3; and Figure 9 is a graph showing an absorption spectrum of another light absorber in a second embodiment of an information storage medium according to the present invention. Figure 1 shows an information storage medium 1 according to an embodiment of the present invention. The medium 1 includes a card-like base 2 and a code storage portion (bar code) 3 disposed on the upper surface on the base 2. The code storage portion 3 is constituted of absorber portions 3A and blank portions 3B arranged alternately. The absorber portions 3A are made of an infrared absorber printed on the base 2, and the widths of the absorber portions 3A and the blank portions 3B cooperate to represent codes or information. In Figure 1, although the thickness of the absorber portions 3A is enlarged very much than the base 2 for easy understanding, the absorber portions 3A is very thin actually. Figure 2 shows an absorption spectrum of the infrared absorber which is ideal for the usage in the code storage portion 3 of the information storage medium 1 in Fig. 1. In Figure 2 and so on, the absorption spectrum is represented by the reflectance of the absorber portion 3, and it is assumed that the base 2 reflects all the rays between 300 nm and 1100 nm. As shown in Figure 2, the reflectance of the infrared absorber is almost uniform when the wavelength of the rays emitted to the absorber is less than a value λ 2 (approximately 670 nm) and when the wavelength is greater than an upper value λ 1 (approximately 840 nm). More specifically, the absorption by the absorber material is little when the wavelength is less than a value λ 2 or when the wavelength is more than a value λ 1 . On the other hand, the infrared absorber absorbs rays in a range from the wavelength λ 2 to the wavelength λ 1 very much. Usually, rays having a wavelength between 700 nm and 10 6 nm are called infrared, and rays having a wavelength between 400 nm and 700 nm are visible. Accordingly, the infrared absorber absorbs substantially only infrared within a narrow wavelength band, but absorbs visible rays little. The narrow wavelength band includes a peak value λ 0 (780 nm) at which the infrared absorber absorbs the most. CONSTRUCTION OF JUDGING APPARATUS Next, referring to Figure 3, an apparatus for reading subject information storage mediums, where the above described medium 1 is preferably the authentic information storage medium, will be described. In Figure 3, a subject information storage medium 11 is shown, and reference signs 12 and 13 designate a card-like base and a code storage portion, respectively. The code storage portion 13 is constituted of absorber portions 13A and blank portions 13B arranged alternately. As represented in Figure 3, the apparatus comprises a ray emitter 30, a first ray receiver 31, a second ray receiver 32 and a comparing means 33. The ray emitter 30 emits rays to the subject medium 11, the rays containing at least rays of the peak wavelength λ 0 and the rays of the wavelength λ 1 . The first receiver 31 includes a photoelectric conversion element 312 and an optical filter 311 mounted on the light receiving surface of the photoelectric conversion element 312. Through the optical filter 311, substantially only rays of the wavelength λ 0 (780 nm) pass, so that the photoelectric conversion element 312 receives substantially only those rays, and provides a first output signal 31a in accordance with the reflectance of the subject medium 11 at the peak wavelength λ 0 . The second receiver 32 also includes a photoelectric conversion element 322 and an optical filter 321 mounted on the light receiving surface of the photoelectric conversion element 322. Through the optical filter 321, substantially only rays of the wavelength λ 1 (840 nm) pass, so that the photoelectric conversion element 322 receives substantially only those rays, and provides a second output signal 32a in accordance with the reflectance of the subject medium 11 at the wavelength λ 1 . The comparing means 33 provides a judgment signal 33A on the basis of the first signal 31a and second signal 32a and a prescribed standard value R stored in a memory (not shown). The judgment signal 33a is transmitted to an alarm 34. Also, the comparing means 33 inspects the widths of the absorber portions 13A of the code storage portion 13 on the subject medium 11 and produces a readout code signal 33b based on the inspection of the widths. The readout code signal 33b is transmitted to a data processor 35. OPERATION OF THE JUDGING APPARATUS Next, the operation of the judging apparatus will be described with reference to Figures 3 and 4. The subject medium 11 is conveyed along the arrow in Figure 3 by a conveyor (not shown). During the conveyance of the subject medium 11, the rays are emitted from the ray emitter 30 to the code storage portion 13, and are reflected from it. The reflected rays are received by the first and second receivers 31 and 32, and are converted to the first and second output signals 31a and 32a, respectively. Now, it is assumed that the subject medium 11 is the authentic medium 1 and that the medium 1 includes code storage portion 3 in which the absorber portions 3A are arranged as in the lower section of Figure 4. Since the absorber portions 3A pass one by one during the conveyance of the information storage medium 1, the first signal 31a, representing the reflectance at the peak wavelength λ 0 , changes as represented by the solid line in the upper section of Figure 4. The second signal 32a, representing the reflectance at the wavelength λ 1 , also changes as by the dotted line in Figure 4. If the subject medium 11 is authentic, the amplitude of the second signal 32a is much smaller than that of the first signal 31a since many of the rays at the wavelength λ 1 are not absorbed by the absorber portions 3A although many of the rays at the wavelength λ 0 are absorbed. The comparing means 33 calculates a difference signal in accordance with the difference between the first signal 31a and second signal 32a, and compares the amplitude of the difference signal with the standard value R. In this case, if the amplitude is greater than the standard value R, the comparing means 33 provides the judgment signal 33a indicating that the subject medium 11 is authentic. For example, the output judgment signal 33a is "one" when the alarm 34 is driven to sound by "zero" signal in the binary system. The standard value R is determined in connection with the difference T (shown in Figure 2) of the reflectance of the absorber portions 3A at the wavelength λ 0 and the reflectance at the wavelength λ 1 . Thus, the comparing means 33 can recognize the subject medium 11 as authentic, and produces the judgment signal 33a representing that it is authentic. Besides, the comparing means 33 compares the changing first signal 31a with the standard value R to compensate the pulse of the first signal 31a, and provides the readout code signal 33b which represents the codes or information stored in the code storage portion 3. On the contrary, if the subject medium 11 includes the absorber portions 13A made of another light absorber of which the absorption characteristic is shown in Figure 5, the reflectance at the wavelength λ 0 and the reflectance at the wavelength λ 1 are not very much different, so that not only many of the rays at the wavelength λ 0 , but many rays at the wavelength λ 1 are absorbed by the light absorber. Now, it is assumed that the subject medium 11 is forged and that the light absorber thereof has the absorption characteristic in Figure 5. The medium 11 includes absorber portions 13A arranged in the lower section of Figure 6. Since the absorber portions 13A pass one by one, the first signal 31a, representing the reflectance at the peak wavelength λ 0 , changes as represented by the solid line in the upper section of Figure 6. The second signal 32a, representing the reflectance at the wavelength λ 1 also changes as by the dotted line in Figure 6. In this case, the amplitude of the second signal 32a is also smaller than that of the first signal 31a, however the difference therebetween is less than the standard value R. Therefore, the comparing means 33 provides the judgment signal 33a indicating that the subject medium 11 is forged. For example, the judgment signal 33a is "zero", so that the alarm 34 sounds. The reason why the judging apparatus utilizes the reflectance at the peak wavelength λ 0 and the reflectance at the wavelength λ 1 is that the reflectance-difference should be prescribed as great as possible since there is likelihood that some kinds of noises will be measured at the above-mentioned inspection of the reflectance-difference. As described above, the authentic absorbing material absorbs the rays at the peak wavelength λ 0 the most, and does not absorb many of the rays at the wavelength λ 1 . Therefore, the reflectance-difference can be great, so that the signal-noise ratio can be excellent. Accordingly, an accurate judgement can be realized. In addition, the wavelength λ 1 is near the peak wavelength λ 0 and at the critical point of the narrow wavelength band, so that the reflectance of the absorber differs remarkably between two wavelengths. Such an absorber, absorbing substantially only specific rays within the narrow wavelength band, is extremely difficult to produce using other components. In other words, forging or counterfeiting of the information storage medium 1 is largely prevented. Also, utilizing with the wavelength λ 1 , which is near the peak wavelength λ 0 and is at the critical point of the narrow band, ensures an accurate detection of a forged medium. In the practical use, the difference between the wavelength λ 0 and the wavelength λ 1 is small, i.e., equal to or less than 100 nm in order to prevent the information storage medium from being forged. On the other hand, it is in practice very difficult even for those skilled in the art to produce a light absorber if the difference between the wavelengths λ 0 and λ 1 is prescribed less than 10 nm. Therefore, if the difference between the wavelengths λ 0 and λ 1 is prescribed less than 10 nm, the signal-noise ratio will be bad. Accordingly, the difference between the wavelengths λ 0 and λ 1 is prescribed greater than 10 nm and equal to or less than 100 nm. PREFERABLE EXAMPLE OF INFORMATION STORAGE MEDIUM A specimen of the information storage medium which will be preferably used for the above-described apparatus was produced. In the specimen, a polyethylene terephlate sheet having a thickness of 188 µm was used for the base 2. The infrared absorber of the code storage portion 3 was a special ink for screen printing, constituted of a resin belonging to polyester at 50% by weight, infrared absorbing material belonging to phthalocyanine at 1% by weight, and cyclohexane at 49% by weight. The infrared absorber was formed on the base 2 by screen-printing, so that the information storage medium 1 having a bar-code-like code storage portion 3 was prepared. Figure 7 shows the absorption spectrum of the absorber portions 3A of the specimen. As shown in Figure 7, the absorber portions 3A of the specimen absorbed substantially only infrared rays within a narrow wavelength band and especially absorbed rays at the wavelength λ 0 (780 nm) most. The reflectance at the peak wavelength λ 0 and the reflectance at the wavelength λ 1 (840 nm) were very different and greater than the difference T (shown in Figure 2). Accordingly, it will be appreciated that the amplitude of the difference between first signal 31a and the second signal 32a is greater than the standard value R, and this specimen can be judged authentic by the judging apparatus. COMPARISON EXAMPLE OF INFORMATION STORAGE MEDIUM On the other hand, a specimen, which will not be preferable for the medium by the invention, was produced. In this specimen, only the infrared absorbing material belonging to phthalocyanine was replaced by a pigment belonging to cianine, and other materials and components were the same as in the above-described specimen. Figure 8 shows the absorption spectrum of the absorber portions 3A of the specimen. As shown in Figure 8, although the absorber portions 3A of the specimen have an absorbtion peak at the wavelength λ 0 (780 nm), the reflectance at the wavelength λ 1 is much smaller than that shown in Figure 7. Therefore, this specimen will be judged as a forgery by the judging apparatus since the difference between the reflectance at the peak wavelength λ 0 and the reflectance at the wavelength λ 1 (840 nm) were not very different. SECOND EMBODIMENT Figure 9 shows an absorption spectrum of another light absorber in a second embodiment of an information storage medium according to the present invention. The light absorber was a special ink for screen printing, constituted of an ink medium, "SS8800-medium" manufactured by Toyo Ink Seizo Kabusiki Kaisha (Toyo Ink Manufacturing Co., Ltd.), at 99.5% by weight, and an infrared absorbing material, "NK-2911" manufactured by Kabushiki Kaisha Nihon Kanko Shikiso Kenkyusho (Japan Photosensitive Pigment Institute Co., Ltd), at 0.5% by weight. The infrared absorber was formed on the base 2 by screen-printing, so that the information storage medium 1 having a bar-code-like code storage portion 3 was prepared. The screen-printing was conducted using with a tetron screen having 300 fibers per one inch. On the screen, the portions which did not correspond to the bar-code like absorber portions 3A were coated with a non-penetration emulsion of 7 µm thickness, so that the portions were prevented from being penetration of the special ink. The thickness of the completed absorber portions 3A was 2.5 µm. As shown in Figure 9, the reflectance of the light absorber was great when the wavelength of the rays emitted to the light absorber was less than approximately 600 nm and when the wavelength was greater than a value λ 1 (approximately 950 nm). More specifically, the absorption by the absorber material was little when the wavelength was less than 600 nm or when the wavelength was more than 950 nm. On the other hand, the light absorber absorbed rays in a range from 600 nm to 950 nm very much. Accordingly, the light absorber absorbed substantially only infrared within a narrow wavelength band, but absorbed visible rays little. The narrow wavelength band includes a peak value λ 0 (850 nm) at which the infrared absorber absorbed the most. In this embodiment, the wavelength λ 1 (approximately 950 nm) is near the peak wavelength λ 0 (850 nm), i.e., the difference is approximately 100 nm. In addition, the wavelength λ 1 is at the critical point of the narrow wavelength band, so that the reflectance of the absorber differs remarkably between two wavelengths. Therefore, the information storage medium in accordance with the second embodiment may be utilized for an authentic medium. In this case, the judging apparatus should be modified for detecting the peak wavelength λ 0 and the comparison wavelength λ 1 which are respectively 850 nm and about 950 nm. ALTERATIONS AND MODIFICATIONS Although the various features of the present invention have been described hereinbefore, it is to be understood that the invention is not limited to the foregoing description and the various modifications may be made in the invention without departing from the scope thereof as defined by the appended claims. It is possible to provide the information storage medium 1 with a surface layer for concealing the code storage portion 3 and/or a protection layer for improving the durability of the code storage portion 3 if necessary. For the purpose of the protection layer, a resin, which is transparent for both visible rays and infrared rays, may be used. The base 2 may be manufactured of any kind of materials as long as the materials reflect the rays of at least the wavelength λ 1 . For instance, it is possible to use vinylchloride, polyethylene terephlate, paper, metals and the like. In addition, many kinds of merchandise may be used for base 2. That is, the code storage portion 3 can be formed on the merchandise directly. The absorber portions 3A may be formed on the base 2 by means of various methods, for example, offset printing, gravure, letterpress printing, intaglio printing, thermal transferring and pressure transferring. The components of the absorber portions 3A may include various additives although the absorber portions 3A can be produced of at least a light absorber and resin for fixing the light absorber on the base 2. The resin, which should be decided in relation to the base 2 and to the light absorber, may be selected from natural or artificial resin. As described above, the ray emitter 30 should emit rays containing at least rays of the peak wavelength λ 0 and the rays of the wavelength λ 1 . In regard to this, it is possible that the ray emitter 30 emits rays of which the intensity is uniform in a wide range of wavelength including the wavelengths λ 0 and λ 1 . Alternatively, it is possible that the intensity of the rays is not uniform, i.e., the intensity may have peaks at the wavelengths λ 0 and λ 1 . Besides, it is possible that the ray emitter emits the rays of the wavelength λ 0 and the rays of the wavelength λ 1 at different times. In this case, a single ray receiver, which can detect the rays at both wavelengths λ 0 and λ 1 , may be used and a memory should be used for storing at least the primarily detected reflectance at the wavelength λ 0 or λ 1 , so that the comparing means 33 can evaluate reflectance at both wavelength. Although it is described above that the comparing means 33 emits the code signal 33b after the compensation of the pulse of the first signal 31a, the comparing means 33 may be manufactured or adjusted to output the received first signal 31a as it is. In addition, in the above description, the reflectance at the peak absorption wavelength λ 0 and the reflectance at the wavelength λ 1 are detected to prescribe the reflectance-difference T (Figure 2) great value and obtain the difference signal having an excellent signal-noise ratio. In the judging apparatus, it is possible that the standard value R is variable. In this case, the standard value R will be determined high for expensive goods which need high reliability. On the other hand, the standard value R will be determined low for inexpensive goods which do not need high reliability.

Claims: An information storage medium (1,11) comprising: a base portion (2,12); and a code storage portion (3,13) disposed on said base portion (2,12), said code storage portion (3,13) containing an infrared absorber, said infrared absorber being capable of absorbing substantially only infrared radiation within a narrow wavelength band, wherein said infrared absorber has an infrared absorption peak at a first wavelength (λ 0 ) of said narrow wavelength band, characterized in that said infrared absorber is adapted to have substantially no absorption for infrared at a second wavelength (λ 1 ) of said narrow wavelength band, the difference between the first wavelength and the second wavelength being less than or equal to 100 nm; and in that said infrared absorber is capable of substantially reflecting visible rays. An information storage medium according to Claim 1, wherein said base portion (2,12) is arranged to reflect rays within said narrow wavelength band. A method for judging if a subject information storage medium (1,11) is authentic or forged, where an authentic information storage medium (1,11) includes a base portion (2,12) and a code storage portion (3,13) disposed on said base portion (2,12), said code storage portion (3,13) containing a light absorber, said light absorber being capable of absorbing substantially only specific rays within a narrow wavelength band, the narrow wavelength band including a peak wavelength (λ 0 ) at which the light absorption curve has a peak value, the method comprising the steps of: emitting rays to said subject information storage medium (1,11); receiving rays reflected from said subject medium (1,11); detecting a first reflectance at said peak wavelength (λ 0 ) and a second reflectance at a comparison wavelength (λ 1 ) near said peak wavelength (λ 0 ), rays at the comparison wavelength being substantially unabsorbed by said light absorber; and judging if said subject medium (1,11) is authentic or not on the basis of said first reflectance and said second reflectance, characterized in that the difference between said peak wavelength (λ 0 ) and said comparison wavelength (λ 1 ) is less than or equal to 100 nm. A method according to Claim 3, wherein said judging step comprising obtaining the difference between said first reflectance and said second reflectance, and judging said subject medium (1,11) authentic if said difference between said first reflectance and said second reflectance is greater than a certain value (R), but judging said subject medium (1,11) as a forgery if said difference is equal to or less than said certain value (R). A method according to Claim 3 or 4, wherein said light absorber is capable of absorbing substantially only infrared within a narrow wavelength band, but substantially reflecting visible rays, said rays used at said emitting step containing at least infrared rays which are absorbed by said light absorber. A method according to any one of Claims 3 to 5, wherein the base portion (2) reflects rays within said narrow wavelength band. An apparatus for judging if a subject information storage medium (1,11) is authentic or forged, where an authentic information storage medium (1,11) includes a base portion (2,12) and a code storage portion (3,13) disposed on said base portion (2,12), said code storage portion (3,13) containing a light absorber, said light absorber being capable of absorbing substantially only specific rays within a narrow wavelength band, the narrow wavelength band including a peak wavelength (λ 0 ) at which the light absorber absorbs the most, the apparatus comprising: an emitting means (30) for emitting rays to said subject information storage medium (1,11), said rays containing at least rays of said peak wavelength and rays of a comparison wavelength (λ 1 ) near said peak wavelength (λ 0 ), rays at the comparison wavelength (λ 1 ) being substantially unabsorbed by said light absorber; receiving means (31,32) for receiving rays reflected from said subject medium (1,11), and providing a first output signal (31a) in accordance with a first reflectance at said peak wavelength (λ 0 ) and a second output signal (32a) in accordance with a second reflectance at said comparison wavelength (λ 1 ); and a judging means (33) for obtaining the difference between said first signal (31a) and said second signal (32a), and judging if said subject medium (1,11) is authentic or not on the basis of said difference between said first signal (31a) and said second signal (32a), characterized in that the difference between said peak wavelength (λ 0 ) and said comparison wavelength (λ 1 ) is less than or equal to 100 nm. An apparatus according to Claim 7, wherein said judging means (33) is arranged to judge said subject medium (1,11) as authentic if said difference between said first signal (31a) and said second signal (32a) is greater than a certain value (R) and to judge said subject medium (1,11) as a forgery if said difference is equal to or less than said certain value (R). An apparatus according to Claim 7 or 8, wherein said emitting means (30) is arranged to emit at least infrared rays for inspecting said subject medium (1,11) when said light absorber of said authentic information storage medium (1,11) is an infrared absorber, said infrared absorber being capable of absorbing substantially only infrared within a narrow wavelength band, but substantially reflecting visible rays. An apparatus according to any one of Claims 7 to 9, wherein said base portion (2,12) is arranged to reflect rays within said narrow wavelength band.

Inventors: ITOH NORIYUKI, OHTA HARUKI, SUZUKI MANABU, WAKANA MASAHIKO, ITOH, NORIYUKI, OHTA, HARUKI, SUZUKI, MANABU, WAKANA, MASAHIKO
Applicants: TOPPAN PRINTING CO LTD, TOPPAN PRINTING CO., LTD.
Application year: 1996
Main classification: G06K7
IPC codes: G06K7, G06K1, B42D15