Magnetic card

A magnetic card in which a magnetic layer is successfully concealed without lowering the magnetic output of the magnetic layer and giving any restriction to the design of the card. Such a magnetic card can be produced in the following manner. A magnetic layer (magnetic stripe) 12 is formed on a substrate 11 by means of thermal transfer, and a thin film layer 13 is formed, by vacuum deposition or the like, on the entire surface of the substrate 11 including the surface of the magnetic layer 12 to conceal the magnetic layer 12. Patterns, etc. are printed on the surface of the thin film layer 13 to form a print layer 14, and a light-diffractive structure layer 15 is further formed on the print layer 14 of thermal transfer. On the other hand, a print layer 14A is provided on the back surface of the substrate 11, and a reverse side protective layer 16 is further provided on the print layer 14A to cover it. After these layers are formed to obtain a laminate, a card of a predetermined shape is punched from the laminate, and subjected to a post-treatment to finally obtain a magnetic card 10.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a magnetic card comprising a substrate,
 and a magnetic layer provided thereon, in which information is
 magnetically recorded in such a manner that the recorded information can
 be mechanically read.
 2. Description of Related Art
 A magnetic card is produced by providing, on a substrate, a magnetic layer
 in which the ID number of the user of the card, and the like are
 magnetically recorded in such a manner that the recorded data can be
 mechanically read. Magnetic cards of this type are widely used as bank
 cards, credit cards, and the like.
 It has conventionally been known that the magnetic layer is concealed in
 order to ensure the security of the magnetic card. Conventional methods
 for concealing the magnetic layer are as follows:
 a first method in which a specific ink is applied, by means of printing, to
 the entire surface of the substrate including the surface of the magnetic
 layer provided on the substrate, thereby concealing the magnetic layer;
 a second method in which an ink is applied, by means of printing, to the
 surface of the magnetic layer provided on the substrate, wherein the color
 of the ink is the same as that of the substrate, thereby concealing the
 magnetic layer; and
 a third method in which an ink is applied, by means of printing, to the
 surface of the substrate excluding the surface of the magnetic layer
 provided on the substrate, wherein the color (dark color) of the ink is
 the same as that of the magnetic layer, thereby concealing the magnetic
 layer.
 However, the conventional magnetic cards have had the following problem.
 Namely, when the thickness of the ink layer which is provided on the
 magnetic layer by means of printing is increased, the magnetic output of
 the magnetic layer is lowered, so that reading errors can be made when the
 information recorded in the magnetic layer is read. Under the
 circumstances, it has been impossible to form, on the magnetic layer by
 means of printing, an ink layer whose thickness is larger than
 approximately 6 micrometers. Therefore, there has been such a problem
 that, when an ink is applied to the magnetic layer by means of printing to
 conceal the magnetic layer by the above-described first or second method,
 and when patterns, etc. are further printed on the surface of this ink
 layer, the number of colors which can be used for printing the patterns,
 etc. is limited.
 On the other hand, in the case of the above third method, an ink is not
 applied to the surface of the magnetic layer by means of printing, so that
 this method is free from the aforementioned problem. However, the card
 produced by the third method is entirely darkish in color. The design of
 the card is therefore restricted.
 SUMMARY OF THE INVENTION
 The present invention has been accomplished in the light of the foregoing
 problems. An object of the present invention is therefore to provide a
 magnetic card in which a magnetic layer is successfully concealed without
 lowering the magnetic output thereof and restricting the design of the
 card.
 A first aspect of the present invention is a magnetic card comprising a
 substrate, a magnetic layer provided on the substrate, in which
 information is magnetically recorded in such a manner that the recorded
 information can be mechanically read, and a thin film layer made from a
 metal or metallic compound having the property of concealing the
 underlying layer, provided to cover at least the magnetic layer. Both the
 recording of information in the magnetic layer, and the reading of the
 information recorded in the magnetic layer being performed through the
 thin film layer provided on the magnetic layer.
 A second aspect of the present invention is a magnetic card whose structure
 is the same as that of the above-described magnetic card except that a
 first protective layer into which the above magnetic layer is embedded is
 further provided between the substrate and the thin film layer.
 In the present invention, it is preferable that the above-described thin
 film layer be simply formed by means of vapor deposition,
 electrodeposition or sputtering. Further, it is preferable that a print
 layer, and/or a light-diffractive structure layer having a
 light-diffractive pattern be provided on the surface of the thin film
 layer. Furthermore, it is preferable that the print layer and the
 light-diffractive structure layer be provided by allowing them to at least
 partly overlap each other in the direction of thickness and that such a
 part of the light-diffractive structure layer that overlaps the print
 layer in the direction of thickness be made either transparent or
 semitransparent so that the print layer can be visually seen through the
 light-diffractive structure layer. In addition, it is preferable that, in
 the region where the print layer and the light-diffractive structure layer
 overlap each other in the direction of thickness, these layers be so
 provided that at least a part of the image reconstructed from the
 light-diffractive structure layer by the diffraction of light will align
 with the image formed in the print layer in order to make the magnetic
 card more aesthetic.
 Further, it is preferable to provide a transparent or semitransparent
 second protective layer on the surface of the above-described print layer
 or light-diffractive structure layer in order to protect the print layer
 or the light-diffractive structure layer. Furthermore, it is preferable to
 color the light-diffractive structure layer or the second protective layer
 to a predetermined color in order to make the magnetic card still more
 aesthetic.
 According to the first and second aspects of the present invention, the
 thin film layer can be made extremely thin as compared with the print
 layer or the light-diffractive structure layer. This means that the
 magnetic layer can be concealed by an extremely thin layer. Thus, it
 becomes possible to produce magnetic cards without undergoing the
 limitation on the number of colors which can be used for the print layer
 to be provided on the magnetic layer, while sufficiently retaining the
 magnetic output of the magnetic layer.

DETAILED DESCRIPTION OF THE INVENTION
 First Embodiment
 By referring now to the accompanying drawings, embodiments of the present
 invention will be explained. FIG. 1 is a plan view showing the first and
 second embodiments of a magnetic card according to the present invention.
 FIG. 2 is a sectional view showing the formation of layers in the first
 embodiment of a magnetic card according to the present invention.
 As shown in FIGS. 1 and 2, a magnetic card 10 comprises a substrate 11, and
 on the surface of this substrate 11 are laminated a magnetic layer 12, a
 thin film layer 13, a print layer 14 and a light-diffractive structure
 layer 15 in the mentioned order. Further, on the back surface of the
 substrate 11, a print layer 14A and a reverse side protective layer 16 are
 successively laminated.
 Substrate
 Materials that can be used for making the substrate 11 include vinyl
 chloride resins, vinyl chloride-vinyl acetate copolymers, polyester
 resins, and papers. These materials can be used either singly or in
 combination of two or more. The thickness of the substrate 11 is
 approximately 0.1 mm to 2.0 mm. If it is desired to make the magnetic card
 10 conformable to the ISO standard, the thickness of the substrate 11 is
 selected so that the total thickness of the magnetic card 10 will be
 approximately 0.76 mm.
 Magnetic Layer
 On the surface of the substrate 11, a strip of the magnetic layer 12 is
 provided. The magnetic layer 12 is made from a magnetic material. In this
 layer, data such as the ID number of the user of the magnetic card 10 are
 magnetically recorded in such a manner that the recorded data can be
 mechanically read.
 Thin Film Layer
 The thin film layer 13 is provided on the entire surface of the substrate
 11 including the surface of the magnetic layer 12 provided on the
 substrate 11. The thin film layer 13 is for concealing the magnetic layer
 12. It is an extremely thin film of an opaque metal or metallic compound
 having the property of concealing the underlying layer.
 To form the thin film layer 13, metals such as Al, Cr, Fe, Co, Ni, Cu, Ag,
 Au, Ge, Mg, Sb, Pb, Cd, Bi, Sn, Se, In, Ga and Rb, and compounds of these
 metals (metallic oxides, metallic nitrides, etc.) can be used either
 singly or in combination of two or more. Of these metals, Al, Cr, Ni, Ag
 and Au are particularly preferred.
 Vapor deposition, electrodeposition, sputtering or the like can be
 mentioned as a method for forming the thin film layer 13. "Vapor
 deposition" is a method for adhering a film of a metal or metallic
 compound to the surface of an adherend; more specifically, a method in
 which a metal or metallic compound that is dissolved and evaporated in
 vacua by directly applying thereto an electric current is deposited to the
 surface of an adherend placed in the vacuum system. Vapor deposition
 includes aluminum vapor deposition and gold vapor deposition.
 "Electrodeposition" is a method in which a metal or metallic compound is
 allowed to separate out on an electrode by means of electrolysis.
 Electrodeposition includes electroplating. "Sputtering" is a method in
 which glow discharge is caused in argon gas under reduced pressure to
 impinge ionized gas atoms upon a target, and those target-constituting
 atoms which are driven out from the target by the impingement are
 deposited on the surface of an adherend.
 The thickness of the thin film layer 13 is approximately 200 to 1,000
 angstroms, preferably about 500 angstroms. The thin film layer 13 is
 opaque, so that the magnetic layer 12 is concealed when the thin film
 layer 13 is provided thereon.
 Print Layer
 The print layer 14 is provided on the almost entire surface of the thin
 film layer 13 which has been provided on the surface of the substrate 11.
 The print layer 14 is for indicating letters, figures, or symbols, or a
 combination thereof. In FIG. 1, the designation of a bank, and the
 logotype "CASH" that shows the use of the magnetic card 10 are printed.
 When the print layer 14 is formed by printing letters or the like, the
 above-described thin film layer 13, which is positioned under the print
 layer 14, can be seen through the print layer 14. It is also possible to
 provide a first print layer to cover the underlying thin film layer 13,
 and to further provide thereon a second print layer by printing letters or
 the like.
 The print layer 14 is formed by means of silk screen printing or the like.
 The thickness of the print layer 14 is approximately 1 micrometer.
 Light-Diffractive Structure Layer
 The light-diffractive structure layer 15 is provided on the almost entire
 surface of the substrate 11 including the surface of the print layer 14.
 The light-diffractive structure layer 15 has a light-diffractive pattern
 such as a surface relief pattern, or a pattern of the distribution of
 refractive index difference, from which a two- or three-dimensional image
 can be reconstructed by the diffraction of light. The image reconstructed
 from the light-diffractive structure layer 15 by the diffraction of light
 is expressed by letters, figures, symbols, or a combination thereof, or a
 combination of these ones and colors. It is preferable that the
 light-diffractive structure layer 15 and the print layer 14 be so provided
 that at least a part of the image reconstructed from the light-diffractive
 structure layer 15 by the diffraction of light can align with at least a
 part of the letters or the like shown by the print layer 14. Specifically,
 it is preferable to form the print layer 14 by printing the same letters,
 figures, etc. as those in the image to be reconstructed by the diffraction
 of light so that these two images can be seen as a single image or that
 the figures (flat ones) formed in the print layer 14 which are the same as
 those in the image reconstructed by the diffraction of light can be seen
 even from an angle which is outside the range of image reconstruction
 angles.
 The surface relief pattern for the light-diffractive structure layer 15
 includes relief holograms, relief diffraction gratings, etc., in which the
 distribution of the intensities of the light of interference fringes
 formed by the interference between object wave and reference wave is
 recorded as a relief pattern. Specifically, there can be mentioned
 holograms from which an image is reconstructed by using white light, such
 as rainbow hologram; color hologram, computer hologram and holographic
 stereogram which utilize the principle of the above holograms; and
 holographic diffraction grating which is formed by utilizing a holographic
 recording means. Besides these holograms and diffraction gratings, there
 can also be mentioned such a hologram or diffraction grating that any
 diffracted light can be obtained by calculation by using a diffraction
 grating which is mechanically made by an electron beam imaging apparatus.
 It is noted that one of or a plurality of these holograms or diffraction
 gratings may also be recorded in the light-diffractive structure layer 15.
 Further, the pattern of the distribution of refractive index difference for
 the light-diffractive structure layer 15 includes Lippmann hologram or
 Denisyuk hologram.
 FIG. 3 is a sectional view showing the formation of layers in the
 light-diffractive structure layer 15. As shown in FIG. 3, the
 light-diffractive structure layer 15 is composed of a resin layer 17
 serving as a substrate layer, a reflecting layer 18 provided on the back
 surface of the resin layer 17, and an adhesive agent layer 19 provided to
 cover the outer surface of the reflecting layer 18.
 Resin Layer of Light-Diffractive Structure Layer
 As a material for forming the resin layer 17 of the light-diffractive
 structure layer 15, it is possible to use such a synthetic resin that fine
 irregularities can be provided on the surface thereof to form the
 above-described surface relief pattern.
 Examples of such a synthetic resin include thermoplastic synthetic resins
 such as polyvinyl chloride, acrylic resins (e.g., polymethylmethacrylate,
 etc.), polycarbonate and polystyrene, and thermosetting synthetic resins
 such as unsaturated polyesters, melamine resins and epoxy resins. Mixtures
 of these thermoplastic synthetic resins and thermosetting synthetic resins
 may also be used.
 It is preferable to use such synthetic resins that fine irregularities can
 be provided on the surfaces thereof to form the surface relief pattern and
 that, after the formation of the fine relief pattern, the resins are cured
 to show sufficiently high durability. Ultraviolet-curing resins,
 electron-beam-curing resins, and reactive resins of thermosetting type or
 of hardening type can also be used.
 Information recorded in the magnetic layer 12 of the magnetic card 10 is
 read by a magnetic head by sliding it on the surface of the
 light-diffractive structure layer 15. In order to prevent the
 light-diffractive structure layer 15 from being worn out, it is preferable
 to form the resin layer 17 of the light-diffractive structure layer 15 by
 using a resin having wear-resistant properties such as an
 ultraviolet-curing acrylic resin.
 The resin layer 17 is formed either by a conventional coating method such
 as gravure, die, knife or roll coating method, or by an ordinary printing
 method such as offset, silk screen or type printing method so that the
 thickness will be from 0.1 to several micrometers.
 Reflecting Layer of Light-Diffractive Structure Layer
 The reflecting layer 18 which is provided on the underside surface of the
 resin layer 17 of the light-diffractive structure layer 15 is for
 imparting reflecting properties to the image-diffractive pattern. It is
 required that the print layer 14 on which the light-diffractive structure
 layer 15 is provided can be seen through the reflecting layer 18 of the
 light-diffractive structure layer 15. Therefore, a material having both
 reflecting properties and transparency is used for forming the reflecting
 layer 18.
 Examples of materials useful for forming the reflecting layer 18 include
 metallic thin film, or continuous thin film made from substances whose
 refractive indexes are different from that of the resin layer 17. The
 continuous thin film may have any thickness as long as it is transparent.
 In general, however, the thickness of the continuous thin film is
 preferably in the range of 100 to 1,000 angstroms. Such a continuous thin
 film is formed on the underside surface of the resin layer 17 by a
 conventional method for forming a thin film such as vacuum deposition,
 sputtering or ion plating.
 The refractive index of the continuous thin film which is used as the
 reflecting layer 18 can be either higher or lower than that of the resin
 layer 17. It is however preferable that the difference between the
 refractive indexes of these two layers be preferably 0.3 or more, more
 preferably 0.5 or more, most preferably 1.0 or more. Examples of
 continuous thin films whose refractive indexes are higher than that of the
 resin layer 17 include thin films of ZnS, TiO.sub.2 and Al.sub.2 O.sub.3).
 Examples of continuous thin films whose refractive indexes are lower than
 that of the resin layer 17 include thin films of LiF, MgF.sub.2 and
 AlF.sub.3.
 The metallic thin film useful as the reflecting layer 18 includes a film
 made from a single metal of Al, Te or the like. Such a metallic thin film
 slightly shows light-transmitting properties when the thickness thereof is
 as thin as 200 angstroms or less, so that it can be used as the reflecting
 layer 18 having transparency.
 A transparent layer made from such a synthetic resin as
 polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl acetate,
 polyethylene, polypropylene or polymethylmethacrylate, having a refractive
 index different from that of the resin layer 17 can also be used as the
 reflecting layer 18.
 Adhesive Agent Layer of Light-Diffractive Structure Layer
 The adhesive agent layer 19 which is provided to cover the outer surface of
 the reflecting layer 18 of the light-diffractive structure layer 15 is for
 adhering the light-diffractive structure layer 15 to the print layer 14.
 Various types of adhesive agents can be used for forming the adhesive
 agent layer 19. For example, it is possible to use an adhesive agent
 comprising as its main component(s) one or more materials selected from
 thermosetting resins including phenolic resins, thermoplastic resins
 including polyvinyl acetate resins, rubbers including
 butadiene-acrylonitrile rubber, and other materials such as glues, natural
 resins, caseins, sodium silicate, dextrins, starches and gum arabic.
 These adhesive agents may be of any type such as a solution, emulsion,
 powder or film type. Moreover, they may also be of any type such as a
 cold-setting type, solvent type or hot-melt type.
 Further, it is also possible to use heat sensitive adhesive agents (heat
 sealing agents) which reveal adhesiveness when heated. Examples of
 materials which can be used for producing heat sensitive adhesive agents
 include thermoplastic resins such as polyethylene, polyvinyl acetate,
 polyethylene-polyvinyl acetate copolymers and acrylic resins, and
 thermosetting resins such as epoxy resins and phenolic resins, which are
 unhardened.
 The adhesive agent layer 19 is formed by applying such an adhesive agent to
 the surface of the reflecting layer 18 by means of silk screen printing so
 that the thickness will be approximately 2 to 3 micrometers.
 If the light-diffractive structure layer 15 includes Lippmann hologram or
 Denisyuk hologram having the pattern of the distribution of refractive
 index difference, the reflecting layer 18 provided on the surface of the
 resin layer 17 made from photopolymers or dichromate gelatin having the
 distribution of refractive index difference may be omitted, and the
 adhesive agent layer 19 may be provided directly on the resin layer 17.
 The light-diffractive structure layer 15 composed of the aforementioned
 layers is formed so that the total thickness of the layer 15 will be
 approximately 5 micrometers or less. This is because, when the total
 thickness of the layers provided on the magnetic layer 12 is approximately
 6 micrometers or less, sufficiently high magnetic field intensity can
 generally be secured on the light-diffractive structure layer 15 although
 it depends on the intensity of the magnetic field formed by the magnetic
 layer 12, and the data recorded in the magnetic layer 12 can be read
 accurately.
 Next, a method for producing a magnetic card 10 having the aforementioned
 structure will now be explained.
 A magnetic layer (magnetic stripe) 12 is firstly formed on a substrate 11
 by means of thermal transfer. A thin film layer 13 is then formed on the
 entire surface of the substrate 11 including the surface of the magnetic
 layer 12 by means of vapor deposition or the like, thereby concealing the
 magnetic layer 12. Thereafter, patterns, etc. are printed on the surface
 of the thin film layer 13 to form a print layer 14. A light-diffractive
 structure layer 15 is further formed on the surface of the print layer 14
 by means of thermal transfer.
 On the other hand, on the back surface of the substrate 11, a print layer
 14A is provided. The print layer 14A is then covered with a reverse side
 protective layer 16. The reverse side protective layer 16 is for
 protecting the print layer 14A, and formed by using, for example, a
 transparent or semitransparent resin such as a vinyl chloride resin.
 After all of the layers are thus formed to make a laminate, a card of a
 predetermined shape is punched from the laminate, and then subjected to a
 post-treatment to finally obtain a magnetic card 10.
 Thus, according to the first embodiment of the present invention, the
 magnetic layer 12 is concealed by the thin film layer 13. This means that
 the magnetic layer 12 can be concealed by an extremely thin layer unlike
 the conventional magnetic cards in which the magnetic layer 12 is
 concealed by an ink layer formed thereon by means of printing. Thus, it
 becomes possible to produce magnetic cards without undergoing the
 limitation on the number of colors which can be used for the print layer
 14 to be provided on the magnetic layer 12, while sufficiently retaining
 the magnetic output of the magnetic layer 12.
 Further, through the light-diffractive structure layer 15, the underlying
 layer can be seen. Therefore, letters, figures, or the like expressed by
 the print layer 14 can be visually seen through the light-diffractive
 structure layer 15. Furthermore, by aligning the image which is
 reconstructed from the light-diffractive structure layer 15 by the
 diffraction of light and the image in the print layer 14 with each other,
 it is possible to make the magnetic card more aesthetic. It is also
 possible to color the light-diffractive structure layer 15 to a
 predetermined color (e.g., a metallic color, etc.). By doing so, the
 magnetic card becomes still more aesthetic.
 In addition, since the light-diffractive structure layer 15 is formed on
 the almost entire surface of the substrate 11, the positioning between the
 light-diffractive structure layer 15 and the substrate 11 becomes
 difficult. It is thus possible to prevent the forgery of the magnetic
 card, which is committed, for example, by separating the light-diffracting
 structure layer 15 from the magnetic card, and by applying it to other
 magnetic card.
 Further, even when the print layer 14 and the light-diffractive structure
 layer 15 are provided by allowing them to overlap each other in the
 direction of thickness, both the image reconstructed from the
 light-diffractive structure layer 15 by the diffraction of light and the
 image in the print layer 14 can be visually seen. It is therefore possible
 to freely form images on the substrate 11 without any restriction.
 Furthermore, the print layer 14 or the light-diffractive structure layer
 15 can be provided on the almost entire surface of the substrate 11
 without being restricted by the magnetic layer 12. This is also favorable
 from the viewpoint of design.
 Second Embodiment
 By referring to FIGS. 1, 4 and 5, the second embodiment of the present
 invention will now be explained. FIG. 4 is a sectional view showing the
 formation of layers in the second embodiment of a magnetic card according
 to the present invention; and FIG. 5 is a sectional view showing a thermal
 transfer sheet which comprises the first laminated structure shown in FIG.
 4. The second embodiment of the present invention is almost the same as
 the first embodiment of the present invention as shown in FIGS. 1 to 3,
 except that an inner protective layer (first protective layer) into which
 the magnetic layer is embedded is provided between the substrate and the
 thin film layer and that a transparent protective layer (second protective
 layer) is provided on the light-diffractive structure layer. In the second
 embodiment of the present invention, the same parts as those in the first
 embodiments shown in FIGS. 1 to 3 are indicated by like reference
 numerals, and detailed explanations for these parts will not be given any
 more.
 As shown in FIGS. 1 and 4, a magnetic card 20 comprises a substrate 11, and
 on the surface of this substrate 11 are laminated an inner protective
 layer 16A, a magnetic layer 12, a thin film layer 13, a print layer 14, a
 light-diffractive structure layer 15 and a transparent protective layer 21
 in the mentioned order. On the other hand, a print layer 14A and a reverse
 side protective layer 16 are successively provided on the back surface of
 the substrate 11. The transparent protective layer 21, the
 light-diffractive structure layer 15, the print layer 14 and the thin film
 layer 13 constitute a first laminated structure 30 in the magnetic card
 20, whereas the magnetic layer 12, the inner protective layer 16A, the
 substrate 11, the print layer 14A and the reverse side protective layer 16
 constitute a second laminated structure 40 in the magnetic card 20.
 Inner Protective Layer (First Protective Layer)
 As shown in FIG. 4, the inner protective layer 16A is provided between the
 substrate 11 and the thin film layer 13. The inner protective layer 16A
 contains therein the magnetic layer 12 which is embedded so that the
 surface of the magnetic layer 12 will be level with that of the inner
 protective layer 16A. The inner protective layer 16A is formed by using
 the same material as that for forming the reverse side protective layer
 16, for instance, a transparent or semitransparent resin such as a vinyl
 chloride resin.
 Transparent Protective Layer (Second Protective Layer)
 The transparent protective layer 21 is provided on the light-diffractive
 structure layer 15 for the protection thereof. It is preferable to use, as
 a material for the transparent protective layer 21, a mixture of the
 material useful for the inner protective layer 16A and reverse side
 protective layer 16, for instance, a transparent or semitransparent resin
 such as a vinyl chloride resin, and an ultraviolet- or electron
 beam-curing resin. Further, it is also preferable to color the transparent
 protective layer 21 to a predetermined color (e.g., a metallic color,
 etc.). By doing so, it is possible to make the magnetic card more
 aesthetic.
 In terms of constitution (material, thickness, etc.), the substrate 11, the
 magnetic layer 12, the thin film layer 13, the print layer 14, the
 light-diffractive structure layer 15, the print layer 14A, and the reverse
 side protective layer 16 are almost the same as those in the
 aforementioned first embodiment as shown in FIGS. 1 to 3 except that the
 light-diffractive structure layer 15 is composed of a resin layer and a
 reflecting layer only and does not contain an adhesive agent layer.
 Next, a method for producing a magnetic card 20 having the above-described
 structure will now be explained.
 A thermal transfer sheet comprising the first laminated structure 30, and
 the second laminated structure 40 which is useful for conventional cards
 are separately prepared.
 As shown in FIG. 5, a thermal transfer sheet comprising the first laminated
 structure 30 is prepared by successively laminating, on a substrate 25 for
 a release sheet, a release layer 26, a transparent protective layer 21, a
 light-diffractive structure layer 15, a print layer 14, a thin film layer
 13 and an adhesive agent layer 27.
 The second laminated structure 40 is prepared in the following manner. An
 inner protective layer 16A is provided on the surface of a substrate 11. A
 print layer 14A is provided on the back surface of the substrate 11, and a
 reverse side protective layer 16 is formed on the print layer 14A to cover
 it. A magnetic layer (magnetic stripe) 12 is formed, by means of thermal
 transfer, on the surface of the inner protective layer 16A, which has been
 provided on the surface of the substrate 11. The thus-obtained laminate
 consisting of the magnetic layer 12, the inner protective layer 16A, the
 substrate 11, the print layer 14A and the reverse side protective layer 16
 is hot-pressed, whereby the layers are adhered to each other by the
 autohesion of the inner protective layer 16A and that of the reverse side
 protective layer 16. By this hot pressing, the magnetic layer 12 is
 embedded into the inner protective layer 16A, and the surface of the
 magnetic layer 12 becomes level with that of the inner protective layer
 16A.
 The thermal transfer sheet comprising the first laminated structure 30 is
 superposed on the second laminated structure 40 so that the adhesive agent
 layer 27 of the thermal transfer sheet and the inner protective layer 16A
 of the second laminated structure 40 can face each other. These two are
 integrated by means of hot pressing. A card of a predetermined shape is
 punched from this integrated material, and then subjected to a
 post-treatment to finally obtain a magnetic card 20.
 Thus, according to the second embodiment of the present invention, the
 strength and design of the magnetic card 20 can be improved by providing
 the transparent protective layer 21 while obtaining actions and effects
 which are comparable to those obtainable from the previously-mentioned
 first embodiment; and it also becomes possible to produce magnetic cards
 more easily and accurately.
 Although some embodiments of the invention have been disclosed and
 described, it is apparent that the present invention is not limited to the
 foregoing first and second embodiments and that various modifications
 which come within the spirit and the scope of the present invention are
 possible. For instance, although the thin film layer 13 is provided on the
 almost entire surface of the substrate 11 in the aforementioned first and
 second embodiments, it can also be provided only on the surface of the
 magnetic layer 12 to cover it. Further, the print layer 14 and the
 light-diffractive structure layer 15 are provided as needed, and can be
 formed on any region on the surface of the substrate 11. Furthermore, a
 coloring layer may also be provided in addition to the print layer 14 or
 to the light-diffractive structure layer 15. Moreover, it is also possible
 to impart the function of IC card, optical card, or the like by providing
 an IC module, an optical recording section, or the like to the back
 surface of the substrate 11.
 EXAMPLES
 Specific examples of the aforementioned first and second embodiments will
 be described below.
 Example 1
 One example of the magnetic card 10 as shown in FIGS. 1 to 3, which is the
 first embodiment of the present invention, will be shown below.
 On a substrate 11 made from a white-colored vinyl chloride resin, having a
 thickness of 0.56 mm, a magnetic layer (magnetic stripe) 12 having a
 thickness of 20 micrometers, capable of forming a magnetic field with an
 intensity of 600 Oe was formed by means of thermal transfer. A thin film
 layer 13 (the thickness of the thin film layer 13 on the magnetic layer
 12: 500 angstroms) was formed on the entire surface of the substrate 11
 including the surface of the magnetic layer 12 by depositing aluminum by
 means of vacuum deposition, thereby concealing the magnetic layer 12.
 Thereafter, patterns, etc. were printed on the surface of the thin film
 layer 13 by means of silk screen printing to form a print layer 14 having
 a thickness of 1 micrometer. A light-diffractive structure layer 15 was
 further formed on the print layer 14 by means of thermal transfer.
 Preparation of Light-Diffractive Structure Layer
 The light-diffractive structure layer 15 was made in the following manner.
 A hologram original plate was placed on an ultraviolet-curable acrylic
 resin layer having a thickness of 2 micrometers. This one was hot-pressed
 for 1 minute under the conditions of 150.degree. C. and 50 kg/cm.sup.2,
 thereby stamping the hologram relief on the surface of the resin layer.
 The hologram original plate was then separated. Ultraviolet light was then
 applied to the resin layer to cure the layer. A resin layer 17 with the
 hologram relief was thus formed.
 On this hologram-relief-formed surface of the resin layer 17, a thin film
 of titanium oxide having a thickness of 200 angstroms was formed by means
 of vacuum deposition, thereby providing a reflecting layer 18.
 Onto the surface of this reflecting layer 18, an
 adhesive-agent-layer-forming coating liquid having the following
 composition was coated by means of gravure reverse coating so that the
 thickness of the resulting layer after dried would be 2 micrometers, and
 then dried, thereby forming an adhesive agent layer 19.

Composition of Coating Liquid for Forming Adhesive
 Agent Layer:
 (1) Vinyl chloride-vinyl acetate copolymer 20 parts by weight
 (2) Acrylic resin 10 parts by weight
 (3) Solvent: ethyl acetate 20 parts by weight
 (4) Solvent: toluene 50 parts by weight
 Production of Magnetic Card
 The thus-prepared light-diffractive structure layer 15 consisting of the
 resin layer 17, the reflecting layer 18 and the adhesive agent layer 19
 was adhered to the surface of the print layer 14.
 On the other hand, patterns, instructions for use, etc. were printed on the
 back surface of the substrate 11 by means of silk screen printing, thereby
 forming a print layer 14 A having a thickness of 1 micrometer. This print
 layer 14 A was then covered with a reverse side protective layer 16 made
 from a transparent vinyl chloride resin, having a thickness of 0.1 mm.
 After all of the layers were thus formed, the resulting laminate was
 hot-pressed by a hot stamping press for 1 minute under the conditions of
 150.degree. C. band 10 kg/cm.sup.2. A card of a predetermined shape was
 punched from the hot-pressed laminate, and then subjected to a
 post-treatment to finally obtain a magnetic card 10.
 In the magnetic card 10 of Example 1, produced in the above-described
 manner, the magnetic layer 12 was able to be successfully concealed by the
 thin film layer 13 having a thickness of as extremely small as 500
 angstroms, and the total thickness of the layers provided on the magnetic
 layer 12 became approximately 5 micrometers. Thus, it became possible to
 produce magnetic cards without undergoing the limitation on the number of
 colors which can be used for the print layer 14 to be provided on the
 magnetic layer 12, while retaining the magnetic output of the magnetic
 layer 12.
 Example 2
 Next, one example of the magnetic card 20 as shown in FIGS. 1, 4 and 5,
 which is the second embodiment of the present invention, will be shown
 below.
 Preparation of Thermal Transfer Sheet Comprising First Laminated Structure
 A release sheet shown in FIG. 5 was prepared in the following manner: a
 biaxially oriented transparent PET film having a thickness of 25
 micrometers was used as the substrate 25 of the release sheet; one surface
 of this substrate was subjected to a corona discharge treatment; and a
 release-layer-forming coating liquid having the following composition was
 coated onto this corona-discharged surface by means of gravure reverse
 coating so that the thickness of the resulting layer after dried would be
 0.5 micrometers, thereby forming a release layer 26 to obtain the desired
 release sheet.

Composition of Coating Liquid for Forming Release Layer:
 (1) Melamine resin 5 parts by weight
 (2) Solvent: methyl alcohol 25 parts by weight
 (3) Solvent: ethyl alcohol 45 parts by weight
 (4) Cellulose acetate resin 1 part by weight
 (5) para-Toluenesulfonic acid 0.05 parts by weight
 Onto the surface (in FIG. 5, the underside) of the release layer 26 of the
 release sheet, a transparent-protective-layer-forming coating liquid
 having the following composition was coated by means of gravure reverse
 coating so that the thickness of the resulting layer after dried would be
 0.5 micrometers. Ultraviolet light was then applied to the coated layer by
 an ultraviolet-light irradiator (twin high-pressure mercury vapor lamp,
 power output=160 W/cm) in an irradiation dose of 500 mJ/cm.sup.2 to cure
 the layer. Thus, a transparent protective layer 21 was formed.

Composition of Coating Liquid for Forming Transpar-
 ent Protective Layer:
 (1) Polyurethane acrylate (prepolymer) 20 parts by weight
 (2) Dipentaerythritol hexaacrylate 100 parts by weight
 (3) 2-Hydroxyethylacrylate 5 parts by weight
 (4) Photopolymerization initiator 1 part by weight
 (5) Sensitizer 1 part by weight
 Onto the surface (in FIG. 5, the underside) of the transparent protective
 layer 21, a resin-layer-forming coating liquid having the following
 composition was coated by means of gravure reverse coating so that the
 thickness of the resulting layer after dried would be 2 micrometers, and
 then dried at 100.degree. C. for 1 minute, thereby forming a resin layer,
 a constituent of a light-diffractive structure layer 15.

Composition of Coating Liquid for Forming Resin
 Layer of Light-Diffractive Structure Layer:
 (1) Acrylic resin 40 parts by weight
 (2) Melamine resin 10 parts by weight
 (3) Solvent: cyclohexanone 50 parts by weight
 (4) Solvent: methyl ethyl ketone 25 parts by weight
 On the surface of this resin layer of the light-diffractive structure
 layer, a hologram original plate was placed. This one was hot-pressed for
 1 minute under the conditions of 150.degree. C. and 50 kg/cm.sup.2,
 thereby stamping the hologram relief to the resin layer. The hologram
 original plate was then separated. Ultraviolet light was then applied to
 the resin layer to cure the layer. A resin layer with the hologram relief
 was thus formed.
 On this hologram-relief-formed surface of the resin layer of the
 light-diffractive structure layer 15, a thin film of titanium oxide having
 a thickness of 200 angstroms was formed by means of vacuum deposition,
 thereby forming a reflecting layer.
 Patterns, etc. were then printed on the surface of this reflecting layer of
 the light-diffractive structure layer 15 by means of silk screen printing,
 thereby forming a print layer 14 having a thickness of 1 micrometer.
 Aluminum was further deposited on the surface of this print layer 14 by
 vacuum deposition to form a thin film layer 13 having a thickness of 500
 angstroms.
 Onto the surface (in FIG. 5, the underside) of this thin film layer 13, an
 adhesive-agent-layer-forming coating liquid having the following
 composition was coated by means of gravure reverse coating so that the
 thickness of the resulting layer after dried would be 2 micrometers, and
 the dried. An adhesive agent layer 27 was thus formed.

Composition of Coating Liquid for Forming Adhesive
 Agent Layer:
 (1) Vinyl chloride-vinyl acetate copolymer 20 parts by weight
 (2) Acrylic resin 10 parts by weight
 (3) Solvent: ethyl acetate 20 parts by weight
 (4) Solvent: toluene 50 parts by weight
 Preparation of Second Laminated Structure
 On the other hand, a second laminated structure 40 was prepared in the
 following manner. Namely, on the surface of a substrate 11 made from a
 white-colored vinyl chloride resin, having a thickness of 0.56
 micrometers, an inner protective layer 16A made from a transparent vinyl
 chloride resin, having a thickness of 0.1 mm was provided. On top of this
 inner protective layer 16A, a magnetic layer (magnetic stripe) 12 having a
 thickness of 20 micrometers, capable of producing a magnetic field with an
 intensity of 600 Oe was formed by means of thermal transfer.
 On the back surface of the substrate 11, patterns, instructions for use,
 etc. were printed by means of silk screen printing, thereby forming a
 print layer 14A having a thickness of 1 micrometer. This print layer 14A
 was covered with a reverse side protective layer 16 made from a
 transparent vinyl chloride resin, having a thickness of 0.1 mm. After all
 of these layers were formed, the resulting laminate was hot-pressed by a
 hot stamping press for 1 minute under the conditions of 150.degree. C. and
 10 kg/cm.sup.2. The layers were thus adhered to each other by the
 autohesion of the inner protective layer 16A and that of the reverse side
 protective layer 16. By this hot pressing, the magnetic layer 12 was
 embedded into the inner protective layer 16A, and the surface of the
 magnetic layer 12 became level with that of the inner protective layer
 16A.
 Production of Magnetic Card
 The thermal transfer sheet comprising the first laminated structure 30 was
 superposed on the second laminated structure 40 so that the adhesive agent
 layer 27 of the thermal transfer sheet and the inner protective layer 16A
 of the second laminated structure 40 would face each other. These two were
 integrated by hot pressing conducted by a hot stamping press for 1 minute
 under the conditions of 150.degree. C. and 10 kg/cm.sup.2. A card of a
 predetermined shape was punched from this hot-pressed laminate, and then
 subjected to a post-treatment to finally obtain a magnetic card 20.
 In the magnetic card 20 of Example 2, produced in the above-described
 manner, the magnetic layer 12 was able to be successfully concealed by the
 thin film layer 13 having a thickness of as extremely small as 500
 angstroms, and the total thickness of the layers provided on the magnetic
 layer 12 became approximately 5.5 micrometers. Thus, it became possible to
 produce magnetic cards without undergoing the limitation on the number of
 colors which can be used for the print layer 14 to be provided on the
 magnetic layer 12, while retaining the magnetic output of the magnetic
 layer 12.
 Example 3
 The procedure of Example 2 was repeated except that the
 transparent-protective-layer-forming coating liquid used in Example 2 for
 forming the transparent protective layer 21 was replaced with a coating
 liquid having the following composition, thereby obtaining a magnetic card
 20.

Composition of Coating Liquid for Forming Transpar-
 ent protective Layer:
 (1) Polyurethane acrylate (prepolymer) 100 parts by weight
 (2) Photopolymerizable monomer 5 parts by weight
 (monofunctional)
 (3) Photopolymerization initiator 1 part by weight
 (4) Sensitizer 1 part by weight
 In the magnetic card 20 of Example 3, produced in the above-described
 manner, the magnetic layer 12 was able to be successfully concealed by the
 thin film layer 13 having a thickness of as extremely small as 500
 angstroms, and the total thickness of the layers provided on the magnetic
 layer 12 became approximately 5.5 micrometers. Thus, it became possible to
 produce magnetic cards without undergoing the limitation on the number of
 colors which can be used for the print layer 14 to be provided on the
 magnetic layer 12, while retaining the magnetic output of the magnetic
 layer 12.
 As explained hereinbefore, according to the present invention, it is
 possible to make the thin film layer extremely thin as compared with the
 print layer and the light-diffractive structure layer. This means that the
 magnetic layer can be concealed by an extremely thin layer. It is
 therefore possible to produce magnetic cards without undergoing the
 limitation on the number of colors which can be used for forming the print
 layer to be provided on the surface of the magnetic layer, while
 sufficiently retaining the magnetic output of the magnetic layer.