SEALED-TYPE OPTICAL CARD

Abstract: Technology of optical card having high data recording density. Among the optical cards, the additionally recorded optical card must have particularly excellent writing characteristics. When the additionally recorded-type optical card is sealed, the writing characteristics are deteriorated. In this invention, a sensitizing layer (50) is provided on the back of the optical recording portion (30) so that a molten recording material may escape thereon at the time of writing; i.e., an optical card is obtained having excellent characteristics in both resistance against environment and writability. The sensitizing layer (50) is composed of a self-oxidizing or a thermoplatic resin and an absorbing agent dispersed in the resin. The absorbing agent not only improves the writing characteristics in combination with the resin but also helps improve designing the card and readability.

Description: TECHNICAL FIELD This invention relates to an optical card, that is, an optical recording card in which information is optically written to an optical recording section in or on the card, and the written information is optically read out and, more particularly, to an optical card of closed type in which an optical recording section, onto which information is recorded, is isolated from the outside environment. BACKGROUND ART Generally, an optical card has extremely high information recording density as compared with other recording cards such as a magnetic card, an IC card and so on. The optical card has an optical recording section on one side of a substrate. Information is recorded onto the optical recording section by an optical energy, chiefly, a laser light. On the basis of a difference in optical reflectivity between a recorded portion and a portion on which recording is not made, the recorded information is optically reading back. The general background of the optical card constructed as described above is disclosed in US-A-4,680,460 or US-A-4,673,626, for example. As will be seen from these patents, the optical card is broadly divided into two categories. One of them is an read only optical card in which a user performs only reading-out, that is, an optical card of ROM (Read Only Memory) type. The other is an additional recording optical card in which the user performs also writing, that is, an optical card of WO (Write Once) type. A first characteristic required for a recording material in the optical card of WO type is a writing characteristic. In view of this, a recording material of boring type is preferable whose representative is a low-melting-point metal such as tellurium, bismuth or the like or its alloy. Conversely, however, the more the writing characteristic is superior, the more the recording material tends to be subjected to an influence due to the outside environment, so that there is such a tendency that a difficult point occurs in other characteristics such as durability and so on. As a method of improving the environmental resistance, there is known means for isolating the optical recording section made of boring-type recording material, from the outside environment. For example, as one of optical discs, there already exists an optical disc in which an optical recording section is enclosed between a pair of substrates of the optical disc while providing an air gap. Here, the air gap is provided for escaping the recording material melted due to heat, to the air gap, in order to prevent the writing characteristic from being deteriorated. There is also seen a technique in which the closing method having such air gap is applied to an optical card (Japanese Patent Provisional Publication JP-A-61-96539). It cannot be said, however, that the technique is suitable in a wide usability such as carrying or the like of the optical card, because there is a fear that the air gap causes such another problem as to reduce characteristics such as compactness and strength as the card. JP-A-61.220.148 which reflects the subject matter of the preamble of claim 1 and JP-A-61.115.186 both disclose an optical card comprising a sensitizing layer provided between the substrate and the recording layer. DISCLOSURE OF THE INVENTION It is an object of this invention to provide a new or novel technique of an optical card in which, in spite of the fact that the card is of a closed construction superior in environmental resistance, the optical card is superior also in a writing characteristic and card characteristics. This invention is widely applicable to various kinds of optical cards of WO type of a construction in which an optical recording section is closed. As a method of closing the optical recording section, there are a method covering the optical recording section on one side of a light-transmittance substrate by a protective layer as a whole, a method of closing the optical recording section between a pair of card substrates in a sandwich fashion, a method in which a substrate supporting the optical recording section is made of a flexible sheet, and the optical recording section on the sheet is closed between a pair of reinforcing substrates together with the sheet in a sandwich fashion, or the like. This invention is applicable also to an optical card taking any one of the aforementioned closed methods. In either case, a sensitizing layer made of a self-oxidizable or thermoplastic resin is laminated onto the optical recording section made of a boring-type recording material directly adjacent the same. It is of course that the self-oxidizable resin indicates a resin lower in decomposition (oxidizing) point than the melting point. The sensitising layer is located in rear of the optical recording section, when viewed from one side of the substrate upon which a recording light is incident. This specific positional relationship is important in practicing formation of pits due to writing superiorly in reproducibility or repeatability and, further, is important also in producing high contrast at reading. The sensitizing layer functions such that, when information is written to the optical recording section, a recording material solved due to energy of the recording light escapes into a layer of the recording material. For this reason, an attempt can be made to improve the writing characteristic. This improvement in the writing characteristic is particularly noticeable or remarkable when an absorbing agent effectively absorbing optical energy of the recording light is contained in the sensitizing layer and, slightly more specifically, when green to blue dyes or black dyes in complementary-color relation to a laser light in a near-infrared range is contained in the sensitizing agent. Here, description will be made along experimental examples, regarding improvement in the writing characteristic. In this connection, a laser light, which is used in each of experiments, is an infrared laser light whose wavelength is 830 nm and whose spot size is 6.5 µm. As will be seen from the table 1, in the case where there is no sensitizing layer, variation in contrast ratio (ten (10) point measurement) is large, whereas, by provision of the sensitizing layer, the variation can be reduced. Effects due to the reduction of the variation can be seen in the self-oxidizable resin such as nitrocellulose, and also in the thermoplastic resin. As will be seen from comparison of the results of the table 2 with those of the aforesaid table 1, addition of the near-infrared absorbing dyes to the sensitizing layer enables the writing sensitivity to be improved (pits to be enlarged), and enables the contrast ratio to be further raised. The more an amount of addition of the dyes, the more preferable, in order to raise the contrast ratio. It is sufficient, however, if there is of the order of 5% by weight ratio. As described above, the sensitizing layer located adjacent the optical recording section has such a function as to improve the writing characteristic with respect to the optical recording section, and can effectively make the most of the function of the environmental resistance due to closure which the optical card of closed type has. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing a first embodiment of a hermetic-type or closed-type optical card according to this invention; Fig. 2 is a view showing a cross-sectional construction of the optical card illustrated in Fig. 1; Fig. 3 is a cross-sectional view showing a second embodiment of the optical card according to the invention; Fig. 4 is a cross-sectional view showing a third embodiment of the optical card according to the invention; and Fig. 5 is a cross-sectional view showing a fourth embodiment of the optical card according to the invention. BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment...Figs. 1 and 2 An optical card 10 is of such a construction that an optical recording section 30 having a pre-format pattern is put between a transparent card substrate 12 on the front-surface side and an opaque card substrate 14 on the rear-surface side in a sandwich fashion, and is closed. It is required that a laser light for writing and reading is sufficiently transmitted through at least one of the pair of card substrates 12 and 14. The card substrate 12 on the front-surface side is made of polycarbonate sheet having light transmittance and having its thickness of 0.4 mm. The substrate 12 has two sides 12a and 12b which extend in parallel relation to each other. A hard coat layer 16, whose thickness is about 5 µm, is formed on the first side 12a which is one of the two sides 12a and 12b. The side of the first side 12a having the hard coat layer 16 is the side upon which the laser light L is incident for writing and reading. The hard coat layer 16 protects the surface of the first side 12a of the card substrate 12. On the other hand, an anchor layer 18, whose thickness is of the order of 0.5 µm, is formed on the other second side 12b of the card substrate 12. The optical recording section 30 is formed on the anchor layer 18. The anchor layer 18 is provided for improving adhesiveness between the card substrate 12 and the optical recording section 30, and is made of a silicon acrylic resin layer, for example. Further, the optical recording section 30 is made of Te whose thickness is of the order of 350 Å. A predetermined format pattern is beforehand formed on the optical recording section 30 per se by photoetching. On the other hand, the card substrate 14 on the rear side is made of a hard vinyl chloride sheet whose color is white and whose thickness is 0.35 mm. The card substrate 14 has also two sides 14a and 14b which extend in parallel relation to each other. Printing such as silk-screen printing, UV-offset printing or the like is applied to one of the two sides 14a, while an urethane adhesive layer 40 of normal-temperature hardened type, whose thickness is about 20 µm, is formed on the other side 14b as a whole. The thus formed card substrate 14 on the rear side is stuck to the card substrate 12 on the front side with the adhesive layer 40. Forming of the adhesive layer 40 by adhesives of normal-temperature hardened type enables the card substrates 12 and 14 on the front and rear sides to be stuck together without the use of heat press. For this reason, the card substrates 12 and 14 on the front and rear sides are not subject to influence of heat shrinkage due to a difference in material between the card substrates 12 and 14. Thus, it is possible to beforehand avoid such a problem that the card is curled. The optical recording section 30 is formed on the second side 12b of the card substrate 12 on the front side, to which the card substrate 14 on the rear side is stuck. A sensitizing layer 50 is covered on the optical recording section 30. As a material of the sensitizing layer 50, it is possible to use various thermoplastic resins and self-oxidizable resins. In this example, however, polyvinylidene chloride paint containing near-infrared absorbing dyes was used. Silk-screen printing was employed in formation of the sensitizing layer 50, and its thickness was about 2 µm. In this case, the sensitizing layer 50 has its area broader than the optical recording section 30. However, the sensitizing layer 50 is narrower than the optical recording section 30 in dimension as a card. For this reason, when both the card substrates 12 and 14 on the front and rear sides are stuck together, the optical recording section 30 is protected double by both the sensitizing layer 50 and the adhesive layer 40. By such double protecting, the optical recording section 30 is effectively isolated from the outside environment, so that anti-environment or environmental resistance is ensured to be improved. Further, in the interior of the optical card 10, not only an attempt is made for the sensitizing layer 50 to improve a writing characteristic of the optical recording section 30, but also the sensitizing layer 50 cooperates with printing characters 60 or the like which are provided on the card substrate 12 or the like, to raise design effects or advantages of the optical card 10 per se . In practice, the results of experiments conducted on the optical card 10 regarding the writing characteristic and the durability indicated superior characteristics. For example, regarding the writing, when the aforesaid infrared laser light was used whose wavelength was 830 nm, it was possible to produce a sufficiently large contrast ratio by writing power of the order of 8 mW for irradiation time of 150 µsec and of the order of 11 mW for irradiation time of 50 µsec. Further, at immersion test of medicine resistance known in the field of magnetic cards, that is, when the card was immersed, for forty-eight (48) hours at the room temperature, in each of liquids such as a 5% saline solution, a 5% acetic solution, a 1% sodium hydroxide solution and a 1% sodium carbonate decahydrate solution, an error rate did not change from the beginning of the immersion to completion of the immersion, and was of the order of 10⁻⁵. Second Embodiment...Fig. 3 An optical card 200 according to this second embodiment utilizes a protective layer 210 due to coating, in place of the card substrate 14 on the rear side and the adhesive layer 40 in the optical card 10 according to the first embodiment. As the protective layer 210, a material is used which can uniformly cover the surface of the sensitizing layer 50 as a whole to isolate the outside humidity and the like, for example, a general resin is employed such as UV hardening type, acrylic type or the like. A commercially available resin can be used as the resin of UV hardening type as it is. Also for the resin of acrylic type, the viscosity can be regulated or adjusted for coating by the use of a solvent (alcohol, toluene or the like) which does not exert a bad influence to the sensitizing layer 50. In the case of the optical card 200, since an adhesive step between the substrates can be omitted or dispensed with, manufacturing is more easy. Third Embodiment...Fig. 4 For an optical card 300 according to the third embodiment, the substrate 12 in the optical card 10 according to the first embodiment is formed by a flexible sheet 312 and, after an optical recording section 330 and a sensitizing layer 350 have been formed on the sheet 312, the sheet 312 including the optical recording section 330 and the sensitizing layer 350 is put between a light-transmittance first reinforcing substrate 301 and an opaque second reinforcing substrate 302 in a sandwich fashion. For the optical card 300, the sheet 312 is formed slightly smaller in dimension than the first and second reinforcing substrates 301 and 302, whereby it is possible to fill up also gap portions occurring on the lateral sides of the card, by an adhesive layer 340. Accordingly, it is possible to close the optical recording section 330 in the interior of the card with sufficient environmental resistance. Further, for the optical card 300, since the sheet 312 is flexible, it is possible to form the optical recording section 330 and the sensitizing layer 350 by rolling the sheet 312. Furthermore, since the sheet 312 forming the optical recording section 330 and the sensitizing layer 350 can be treated or handled as a semi-product, it is easy to apply known processing such as printing or the like to the first and second reinforcing substrates 301 and 302. Fourth Embodiment...Fig. 5 An optical card 400 according to the fourth embodiment is a so-called modification of the third embodiment. Here, a sheet 412, which supports an optical recording section 430 and a sensitizing layer 450, has a dimension which is the same as those of first and second reinforcing substrates 401 and 402. It is possible, however, to close double the lateral sides of the optical recording section 430 by the sensitizing layer 450 and a pair of adhesive layers 440. In connection with the above, the material and the technical specification of the first and second reinforcing substrates 301 and 401; and 302 and 402 in the third and fourth embodiments are the same as those of the light-transmittance substrate 12 and the card substrate 14 in the first embodiment. INDUSTRIAL APPLICABILITY As described above, it is possible for the invention to still produce the superior writing characteristic even if the optical card of WO type, whose recording material is tellurium easy in writing, its alloy or the like, is of a closed construction high in environmental resistance. Thus, the optical card is extremely high in practicability as an optical card superior in both sides of the writing characteristic and the environmental resistance, and is useful in diffusion of the optical card.

Claims: An enclosed type optical card comprising a parallel sided light transmitting substrate (12, 312, 412) having first (12a) and second (12b) sides, the first side (12a) being a writing side upon which in use, a writing light (L) is incident, an optical recording section (30, 330, 430) located on the second side (12b) of the substrate, the optical recording section (30, 330, 430) being operative by cavities formed by optical energy of the writing light (L), the optical recording sections (30, 330, 430) including a thin membrane layer made of a light reflective recording material, a sensitizing layer (50, 350, 450) directly laminated on the optical recording section characterised in that the sensitizing layer (50, 350, 450) is made of a self-oxidizable or thermoplastic resin containing an absorbing agent dispersed in the resin for absorbing writing light (L), the sensitizing layer providing an escape for molten recording material when cavities are formed in the thin membrane layer, and closing means (40, 340, 440) including a coating layer coating the sensitizing layer (50, 350, 450). An optical card according to claim 1 characterised in that the first side (12a) of the substrate (12, 312, 412) is both a writing and a reading side upon which a reading light (L) is incident. An optical card according to claim 1 or 2 characterised in that the absorbing agent is a near-infrared absorbing agent. An optical card according to claim 1, 2 or 3 characterised in that the closing means consists of only a protective layer (210) which serves as a coating layer coating the sensitizing layer (50, 350, 450). An optical card according to claim 1, characterised in that the coating layer (40) is an adhesive layer, the optical recording section being sandwiched between the adhesive layer and a second card substrate (14). An optical card according to claim 5 characterised in that the light-transmitting substrate (12), the card substrate (14), the optical recording section (30) and the sensitizing layer (50) each define an area, the areas defined by the optical recording section (30) and the sensitizing layer (50) being less than those areas defined by the two substrates (12, 14). An optical card according to claim 6, characterised in that the adhesive layer (40) coats the sensitizing layer as a whole and fills up a gap between the light-transmitting substrate (12) and the second card substrate (14) at a peripheral edge portion of the sensitizing layer. An optical card according to claim 1 characterised in that the light-transmitting substrate is made from a flexible sheet (312, 412), a light-transmitting reinforcing substrate (301, 401) being attached to the first side of the sheet through an adhesive layer, the second card reinforcing substrate (302, 402) being attached onto the sensitizing layer on the second side of the sheet by an adhesive layer. An optical card according to claim 8 characterised in that the flexible sheet (312) is smaller in dimension than the light-transmitting substrate and the second card substrate. An optical card according to claim 1 to 9 characterised in that the recording material is made from a low-melting point metal or its alloy. An optical card according to claim 11 characterised in that the recording material is made from tellurium or its alloy.

Inventors: FUJITA MINORU, FUKUSHIMA YOICHI, KAKINUMA YUJI, FUJITA, MINORU, FUKUSHIMA, YOICHI, KAKINUMA, YUJI
Applicants: KYODO PRINTING CO LTD, KYODO PRINTING CO., LTD.
Application year: 1990
Main classification: G11B7
IPC codes: B42D15, G11B7