Magnetic recording medium and method of manufacture of same

Abstract: A magnetic recording medium is made by applying a coating mixture having magnetic particles dispersed in a binder and drying the coating mixture so as to produce a coding layer containing tamper-proof identifier coding information comprising designed patterns, letters, numerals and bar-code type patterns. Another magnetic layer for recording regular magnetic data can be provided above or below the coding layer. The coding information can neither be read or altered by ordinary magnetic reader. The magnetic recording medium is therefore useful for such applications as shopping cards, pre-paid cards, retail store cards; financial cards including credit cards, insurance cards; travelling cards including transit passes, tickets; and identification cards including passports, birth certificates and other personal identification cards. A method of making such a magnetic recording medium is also presented in which the coating mixture is applied on a non-magnetic base material, and while the coating mixture is still wet, i.e. while the magnetic particles are mobile, suitable coding information is magnetically recorded. The coating mixture is then dried to fixate the identifier coding information in the coding layer to produce fixated coding information which is non-erasable and non-alterable.

Description: The present invention relates to a magnetic recording medium for use in magnetic cards, magnetic sheets and magnetic roll papers for such applications as shopping cards including pre-paid cards, retail store cards; financial cards including credit cards, insurance cards; travelling cards including transit passes, tickets; and identification cards including passports, birth certificates and other personal identification cards. The fields of application of consumer cards containing magnetically recorded information have expanded rapidly in recent years, and the uses of such cards are expanding greatly. The basic structure of such magnetic cards comprises a non-magnetic base material and a magnetic layer formed on top of the non-magnetic base material, and the magnetic layer is used to magnetically record proprietary information. It is essential to prevent unlawful uses enabled by copying or altering of the proprietary information on such media, and there have been many methods which are being used to prevent illegal uses of magnetic cards. Representative examples of counterfeit preventing measures can be divided into two broad categories: the first method is to make reproduction of magnetic information difficult; and the second method is to incorporate a piece of identifier coding data so as to identify counterfeited cards. The first method is based on making the reproduction of magnetic information difficult, and there are known examples such as providing a multilayer section for magnetic recording in which to hide the correct information, or providing superfluous information to make analysis of the correct information difficult. However, such methods suffer from the disadvantages of complexity of manufacturing, and the requirement for special equipment to read/write the correct information. Furthermore, once the details of the technique of hiding the correct information are discovered, it is not possible to prevent someone skilled in the art to analyze the data, and to easily duplicate the information or to produce a counterfeit product. The second method is based on including a special identifier codes in the magnetic card, and such a card cannot be put to actual use unless the card is certified to be genuine, even though the card may contain duplicated magnetic information. However, such cards also suffer from disadvantages of difficult manufacturing process, and the requirement of special reading devices for the identifier codes. Also, this type of card has another major disadvantage that it is not possible to prevent unlawful uses of a genuine card in which the proprietary information has been altered. US-A-4 114 029 discloses a magnetic recording medium having a magnetic layer containing magnetic particles having a coercive force of no less than 500 Oe and a magnetic layer containing magnetic particles having a coercive force of no less than 250 Oe and no more than 500 Oe. The present invention was made in consideration of the state of the existing state of the art of magnetic recording media, and the objective of the first invention is to present a magnetic recording medium, based on the second approach, having the capability to make it virtually impossible to produce a counterfeit magnetic recording medium by forgery, i.e. an incorporation of an identifier coding information which is non-alterable and non-erasable, and a method of making such a magnetic recording medium. Another objective of the present invention is to present a magnetic recording medium, based on the second approach, having the capability to provide a different identifier coding information for each recording medium, and the identifier coding information cannot subsequently be altered or deleted, thereby presenting a magnetic recording medium which is superior to the conventional magnetic recording media and is, therefore, highly effective for preventing forgery of proprietary information. According to a first aspect of the invention, there is provided a magnetic recording medium according to claim 1,2 or 3; according to another aspect there is provided a method for making a magnetic recording medium according to claim 12 or 18; ancillary features are defined in the dependent claims. The following description of particular embodiments refers to the attached drawings, wherein: Figure 1 (A) is a plan view of a magnetic recording medium in a first embodiment; and Figure 1 (B) is a longitudinal cross sectional view of the magnetized section seen at the line X-X' in Figure 1 (A); and Figure 1 (C) is a longitudinal cross sectional view of the demagnetized first magnetic layer one seen at the line X-X' in Figure 1 (A). Figure 2 is an illustration of the coating process for the first magnetic layer in the first embodiment. Figure 3 is an illustration of the coating process for the second magnetic layer in the second embodiment. Figure 4 (A) is a plan view of a magnetic recording medium in a second embodiment; and Figure 4 (B) is a longitudinal cross sectional view of the magnetized section seen at the line X 1 -X 2 in Figure 4 (A); and Figure 4 (C) is a magnified view of the longitudinal cross section between the first magnetic layer and the second magnetic layer at line X 1 -X 2 in Figure 4 (A). Figure 5 is an illustration of the coating process of the first magnetic layer of the second embodiment. Figure 6 is an illustration of the coating process of the second magnetic layer of the second embodiment. Figure 7 is a third embodiment of the magnetic recording medium. Figure 8 (A) is a transverse cross sectional view of the magnetic recording medium along line Y-Y' shown in Figure 7; and Figure 8 (B) is a transverse cross sectional view of another example of the third embodiment. Figure 9 is a magnified view of the transverse cross section of the magnetic medium at line X 3 -X 4 shown in Figure 7. Figure 10 is a longitudinal cross sectional view of another example of the third embodiment. Figure 11 is an example of the bar-code-type patterns produced in experimental example 1 observed under direct current biasing magnetic field. Figure 12 is an exempla of the bar-code-type patterns produced in experimental examples 3,8 and 9 observed under direct current biasing magnetic field. A first embodiment of the present invention will be explained with reference to the drawings. Figure 1 (A) is a plan view of a magnetic recording medium (magnetic card) of the second embodiment having a magnetic recording track T 1 . Figure 1 (B) is a cross sectional view through the track T 1 at the line X-X. The track T 1 comprises: a base material 21; a first magnetic layer 22, containing magnetic particles of coercivity between 250 to 4,000 oersted and a binder, overlayed on the base material 21; and a second magnetic layer 23, containing magnetic particles of coercivity over 4,500 oersted, for recording the identifier coding information which cannot be erased or altered. As necessary, a protective covering layer (not shown) can be applied on top of the second magnetic layer 23. The material of construction of the first embodiment will be explained. The base material 21 can be made from a non-magnetic material in a sheet form of 150 µm to 1 mm thickness such as polyester film, vinyl chloride, synthetic paper, wood pulp paper, laminated paper. The magnetic particles for use in the first magnetic layer 22 can be made from γ-iron oxide, cobalt doped γ-iron oxide, chrome oxide, barium ferrite, strontium ferrite and the like. The powder of such magnetic particles is dispersed, together with an additive such as a pigment, in a binder, such as vinyl chloride·vinyl acetate group copolymer, vinyl chloride·vinyl chloride·vinyl acetate·vinyl alcohol group copolymers, polyurethane group resins, polyester group resins, epoxy group resins, polyisocyanate group resins, to make a coating mixture. The coating mixture is applied to the base material 21 and dried to produce the first magnetic layer 22. The magnetic particles for use in the second magnetic layer 23 can be made from barium ferrite, strontium ferrite and related compound with the replaced metal ions. The magnetic particles are dispersed, together with an additive such as a pigment, in a binder as in the case of making the magnetic layer, and the coating mixture thus made is applied on top of the first magnetic layer 22 to produce a second magnetic layer. A protective covering layer 23 can be applied as necessary on top of the second magnetic layer 23. The protective covering layer, depending on the need, can be made from: (a) a coloring layer containing such material as aluminum powder or white pigment to hide the coloring of the magnetic layer; (b) a print magnetic layer comprised of a thermal magnetic layer made of leuco dye type, or a discharge magnetic layer made by metal vapor depositing of such metals as tin or aluminum. (c) a protective covering layer comprising a UV-hardenable resin. One or more of the above mentioned layer can be applied as a single or a multiple layer. Next, the method of manufacturing the magnetic recording medium of the first embodiment will be explained. For example, as shown in Figure 2, the base sheet material 21 is sent from the forwarding reel 31, and is coated with the coating mixture in the coating apparatus 32 having a coating head 33 for forming the first magnetic layer 22. The undried coated sheet material is passed over an idler roll 34 to reach the magnetic orientation station 35, and after passing through the dryer section 36, and an idler roll 37 to be picked up by the take-up reel 38. The stock sheet has only the first magnetic layer 22 thereon. Incidentally, magnetic orientation may or may not be carried out on the first magnetic layer at this time. Next, as shown in Figure 3, the pick-up reel 38 loaded with the stock sheet containing the first magnetic layer is made to be the forwarding reel 39. In this processing step, the stock sheet is first processed with a magnetic head 40 to record information on the first magnetic layer 22. The stock sheet then proceeds to a second magnetic layer coating apparatus 41 for applying a second magnetic layer 23 with a coating head 42. Then, passing through an idler roll 43, and, after going through a dryer section 45 and an idler roll 46, the stock sheet is picked up by the pick-up reel 47 to produce the magnetic recording medium of the second embodiment. If a protective covering layer is required, it can be easily applied in another apparatus(not shown). In the above method, because the first magnetic layer 22 has a coercive force of between 250 to 4,000 oersted which is the same strength as the ordinary magnetic recording medium, magnetic information can readily be inputted using ordinary magnetic recording devices. When the second magnetic layer 23 is applied, the coercive force of the layer 23 while still wet with the coating mixture is temporarily lower than the final coercive force of 4,500 oersted. Therefore, the magnetically recorded information on the first magnetic layer 22 is transferred onto the still undried second magnetic layer 23, and is duplicated in the layer 23. When the second magnetic layer 23 is dried, the magnetically recorded information is fixated in the medium having a high magnetic force of 4,500 oersted, and the recorded information cannot be erased or altered subsequently using ordinary magnetic head, thus enabling to provide tamper-proof magnetic information to the recording medium. For conventional magnetic cards, it is impossible to provide individual tamper-proof coding to individual card. However, according to the recording medium of the second invention, individual identifier coding can be provided on the second magnetic layer 23 by copying of the individual identifier coding recorded on the first magnetic layer 22, and the duplicated identifier coding can be fixated in arid become tamper-proof after the second recording is fixated. A second embodiment will be explained below with reference to the drawings. Figure 4 (A) is a plan view of a magnetic recording medium (magnetic card) of the third embodiment having a magnetic recording track T 2 . Figure 4 (B) is a cross sectional view through the track T 2 at the line X 1 -X 2 . The track T 2 comprises: a base material 51; a first magnetic layer 52, containing magnetic particles of coercivity between 250 to 4,000 oersted and a binder, overlayed on the base material 51; and a second magnetic layer 53, containing magnetic particles having a coercive force of less than 100 oersted, for recording the identifier coding information which cannot be erased or altered. As necessary, a protective covering layer (not shown) can be applied on top of the second magnetic layer 53. After the magnetic recording of the first magnetic layer 52 and the second magnetic layer 53 as shown in Figure 4 (B), the magnetic particles in the second magnetic layer 53 collect at the boundaries of alternating polarities in the magnetic layer 52, as shown in Figure 4 (C). The resulting pattern is a bar code like pattern, which becomes fixated in the second magnetic layer 53. The materials of construction of the second embodiment will be explained. For the base material 51, the same type of materials mentioned in the previous embodiments can be used. For the magnetic particles in the first magnetic layer 52, the same type of materials used for the first magnetic layer 22 in the previous embodiment can be used. For the magnetic particles in the second magnetic layer 53, a magnetic powder such as carbonyl/iron powder, zinc ferrite, manganese zinc ferrite, nickel, magnetite, Permalloy (Ni-Fe), Sendust (Fe-Si-Al), and Alperm (Fe-Al). The powder material is dispersed, together with an additive such as a pigment, in a binder as in the previous embodiments, and the coating mixture thus made is applied on top of the first magnetic layer 52, and dried to produce the second magnetic layer 53. The protective covering layer provided on top of the second magnetic layer 53 can be selected from the same type of materials mentioned in the previous embodiment. Next, the method of manufacturing of the recording medium of the second embodiment will be explained. For example, as shown in Figure 14, the base sheet material 51 is sent from the forwarding reel 61, and is coated in the coating apparatus 62 having a coating head 63 for forming the first magnetic layer 52. The coated sheet material is passed over an idler roll 64 to reach the magnetic orientation station 65, and after passing through the dryer section 66, and an idler roll 67 to be picked up by the pick-up reel 68. It is preferable that the first magnetic layer 52 be magnetically oriented at this time, but it is not mandatory. Next, as shown in Figure 6, the pick-up reel 68 loaded with the stock sheet containing the first magnetic layer is made to be the forwarding reel 69. In this processing step, the stock sheet is first processed with a magnetic head 70 to record magnetic information on the first magnetic layer 52. The stock sheet then proceeds to a second magnetic layer coating apparatus 71 for applying a second magnetic layer 53 with a coating head 72. Then, passing through an idler roll 73, the dryer section 74, and another idler roll 75 is picked up by the pick-up reel 76 to produce the magnetic recording medium of the third embodiment. If a protective covering layer is required, it can be easily applied in another facility (not shown). In the above method, because the coercive force of the first magnetic layer 52 is between 250 to 4,000 oersted which is the force for regular magnetic recording medium, magnetic information can be inputted with an ordinary magnetic recording head after forming the first magnetic layer 52. If the force is less than 250 oersted, there is a danger of having the recorded information erased by an external magnetic field, and if the force is over 5,000 oersted, it becomes impossible to record with an ordinary magnetic recording head. Also, the coercive force of the second magnetic layer 53 is low, less than 100 oersted. This is because if it is stronger than 100 oersted, the magnetic particles are difficult to be collected in a form as shown in Figure 4 (C), as well as the fact that the magnetic patterns can be recognized with a magnetic viewer. In this embodiment, the second magnetic layer 53 is applied over the first magnetic layer 52, and before the second magnetic layer 53 dries, the magnetic patterns in the first magnetic layer 52 are duplicated in the second magnetic layer 53 by the low coercivity particles. When the second magnetic layer 53 is dried, the magnetic patterns, produced by the low coercive magnetic particles of less than 100 oersted, become fixated in the second magnetic layer 53, thereby providing tamper-proof identifier coding which cannot be erased or altered subsequently with an ordinary magnetic head. According to this embodiment, the magnetic information on the first magnetic layer 52 is duplicated in accordance with the patterns thereon. In other word, although it is not possible in the conventional type cards to provide individual tamper-proof coding to each card individually, according to the recording medium of this embodiment, individual identifier coding can be provided on the second magnetic layer 53 by copying of the individual identifier coding recorded on the first magnetic layer 52, and the duplicated identifier coding can be fixated in and become tamper-proof after the second magnetic layer is dried. A third embodiment will be explained in the following with reference to the drawings Figure 7 is an example of the third embodiment which comprises a recording medium A having a card-type base material 81 and a magnetic recording stripe member 82 formed longitudinally on one side of the top surface of the base material 81. Figure 8 (A) is a cross sectional view of the transverse section taken along the line Y-Y' of the recording medium A, including the magnetic stripe member 82 embedded in a groove 83 on one side. The stripe member 82 comprises an adhesive layer 84 formed at the bottom of the groove 83, and a successive overlay layers of first magnetic layer 85, a second magnetic layer 86 and a protective covering layer 87. The protective covering layer 87 is for the protection of the second magnetic layer 86, and may be deleted in some cases. It is also permissible to form a coloring layer or a metallic vapor deposition layer between the protective covering layer 87 and the second magnetic layer 86, depending on the need. Further, this type of magnetic recording medium A is made by thermal bonding of the adhesive layer 84, the first magnetic layer 85, the second magnetic layer 86 and the protective covering layer 87 together to form a unitized member, It is also permissible to have a recording medium, as shown in Figure 8 (B) such that the stripe member 82, comprising the adhesive layer 84, the first magnetic layer 85, and the second magnetic layer 86, is overlayed on top of the base material 81'. The base material 81 can be made from a non-magnetic material in sheet form of 150 µm to 1 mm thickness such as polyester film, vinyl chloride, synthetic paper, wood pulp paper, laminated paper. Any material to suit the purpose may be used, and therefore, sheet or film type material generally known to be used for magnetic recording purposes, singly or in laminated form are applicable. The adhesive layer 84 can be a hot melt type adhesive, for example, adhesives of vinyl chloride·vinyl acetate group copolymers, polyester group resins, polyamide group resins, polyurethane group resins may be used singly on mixed. The second magnetic layer 86 comprises a binder in which magnetic powder particles having a coercive force of over 250 oersted, for example, between 250 to 5,000 oersted, are dispersed therein. The magnetic particles can be selected suitably from γ-iron oxide having a coercive force of 250-400 oersted; cobalt-clad γ-iron oxide of 600-700 oersted; barium ferrite of 1,600-1,900 oersted or 2,500-3,000 oersted. It is, of course, permissible to use known magnetic powder particles such as chromium oxide and strontium ferrite. The first magnetic layer 85 comprises a binder in which magnetic powder particles having a coercive force of less than 100 oersted are dispersed therein. The magnetic particles may be selected from powders of carbonyl iron powder, zinc ferrite, manganese zinc ferrite, nickel, magnetite, Permalloy (Ni-Fe), Sendust (Fe-Si-Al), and Alperm (Fe-Al). The binder for use in dispersing the magnetic particles and anchoring them in the first magnetic layer 85 and the second magnetic layer 86 may be selected from vinyl chloride·vinyl acetate group copolymers, polyurethane group resins, polyester group resins, epoxy group resins, with a small amount of an additive such as pigment. Other known binders for magnetic particles may also be used. In addition, the additive may be selected from inorganic materials such as silica, alumina or organic materials such as wax and silicone oil. The bottom surface of the first magnetic layer 85 is provided with a plurality of uniformly spaced protrusions 85a as shown in Figure 9. These protrusions 85a are formed by the magnetic particles and the binder in the first magnetic layer 85 collecting in such a way to form the protrusions. The magnetic particles collect densely at and near the protrusions 85a. Accordingly, the bottom surface of the first magnetic layer 85 is provided with a type of magnetic patterns formed by the protrusions 85a. The protective covering layer 87 can be selected from acrylic group resins, cellulose group resins, urethane group resins, epoxy group resins, vinyl chloride·vinyl acetate group copolymers used singly or mixed. Figure 9 is an enlarged view of a longitudinal section taken through a line X 3 -X 4 in Figure 16, and shows the layered structure having the base material 81, the adhesive layer 84, the first magnetic layer 85, the second magnetic layer 86 and the protective covering layer 87. Next, an example of the method of manufacturing the recording medium of the third embodiment will be presented. In this embodiment, the method involves a step of making a magnetic transfer tape member first followed by a step of making the magnetic recording medium B. The magnetic recording medium B is made, as illustrated in Figure 10, of a holding substrate material 90 and a peeling layer 91 formed thereon, and the protective covering layer 93 is formed on top of the peeling layer 91. The holding substrate material 90 used in this embodiment is made of a polyester film of thickness of 5 to 500 µm, for example. The peeling layer 91 can be selected from silicone group resins, fluorinated group resins, acrylic group resins, cellulose group resins, urethane group resins, epoxy group resins, vinyl chloride·vinyl acetate copolymers used singly or mixed. Next, a magnetic coating containing magnetic particles and binder so as to generate a coercive force of 250-5,000 oersted is applied on top of the protective covering layer 93, then the solvent in the coating mixture is vaporized and the magnetic coating is dried to produce a stock sheet having the second magnetic layer 95. In this case, magnetic orientation treatment may be applied to the second magnetic layer 95 while the magnetic coating is still undried. Next, magnetic information is recorded on the second magnetic layer 95 produced by the above step. The recording can be performed from the front or the back surface of the second magnetic layer 95 using an ordinary magnetic head following a usual magnetic recording procedure. In this case, the recording magnetic head may comprise a plurality of magnetic head members to suit the total width of the stock sheet or it may comprise one magnetic head having a magnetic core of a width to correspond with the sheet width. The result of the above recording is a reversing magnetic polarity pattern in the second magnetic layer 95 as shown in Figure 10. This step is followed by a step of forming the first magnetic layer 96 on top of the second magnetic layer 95. The first magnetic layer 96 comprises a coating made by mixing magnetic particles having a coercive force of less than 100 oersted and the binder. While the solvent is present in the magnetic coating, the magnetic particles in the first magnetic layer 96 will collect at the locations of strong magnetic force, that is, the boundaries 97 of reversing magnetic polarities, and form a plurality of protrusions 96a, as shown in Figure 10, to correspond with the patterns of magnetic recording made in the second magnetic layer 95. When the first magnetic layer 95 is dried, a bar-code type of patterns serving as identifier coding information is formed in the first magnetic layer 96. Finally, an adhesive layer 98 is formed on top of the first magnetic layer 96, thus producing a stock sheet for magnetic tape. The tape is slit into narrow strips to produce magnetic transfer tapes 99 of the fourth embodiment. Next, the tape 99 is attached to a non-magnetic base material 81 as shown in Figure 10, and the holding substrate material 90 and the peeling layer 91 are peeled off to produce the magnetic recording medium B shown in Figure 8 (B). In this case, the second magnetic layer 95, the first magnetic layer 96 and the protective covering layer 93 shown in Figure 19 correspond, respectively, to the second magnetic layer 86, the first magnetic layer 85 and the protective covering layer 87 shown in Figure 8 (B). Also, it is possible to make the recording medium A by applying a heat processing treatment such as hot rolling to the recording medium B. For the second magnetic layer 86 in the magnetic recording media A and B, re-recording is possible with an ordinary magnetic head, thus making it possible to use this type of recording medium for ordinary applications. The magnetic information recorded at the time of manufacturing of the second magnetic layer 86 can be erased with DC- or AC-demagnetization techniques prior to the use, but if the old information is left in the recording medium, it will not interfere with proper writing of new information, as the new information writes over the old information. The magnetic information inputted in the first magnetic layer 85 can be read with a magnetic head with an external biasing magnetic field so as to generate reproduction signals. Further advantage of the recording media A, B is that since the bar-code-type patterns serving as the coding information are protrusions 85a disposed on the bottom surface of the first magnetic layer 85, and the protrusion 85a are embedded in the adhesive layer 84 facing the base material, the protrusions 85a do not appear on the surface of the stripe member 82. Therefore, it is impossible to detect the presence of the bar-code-type magnetic patterns by examining from outside. Therefore, the recording media A, B are provided with invisible magnetic identifier coding information beneath the second magnetic layer 86 which can be magnetically recorded in the usual way. In addition, the protrusions 85a are formed during the process of applying the first magnetic layer while the magnetic particles are still mobile in the undried coating mixture (before the solvent is vaporized). Therefore, after the solvent is vaporized and the magnetic particles are fixated, the magnetic information recorded in the first magnetic layer becomes fixated coding information which can neither be erased or altered subsequently to the formation of the first magnetic layer. Furthermore, the magnetic information on the first magnetic layer 85 can be freely selected by freely selecting the recording pattern at the time of making the second magnetic layer 86. In other words, a pattern can be repeated many times by such fixed reproduction method as printing, or random patterns which would not be possible by the fixed method may be recorded. Such random information is useful as finger print data by providing individual identifier coding to the final product, such as consumer credit card. This means that it becomes impossible to make a counterfeit card by duplicating the magnetic information on some magnetic card on another magnetic card. Therefore, the method enables to present the recording media A, B which are tamper-proof and counterfeit-proof. Further, in the above embodiment, magnetic information was recorded internally in the second magnetic layer 86; however, for some types of magnetic layer, magnetic information can be recorded by vertical magnetization. Therefore, the identifier coding information can be inputted in the first magnetic layer 85 by recording the coding information by perpendicular recording in the second magnetic layer 86. Experimental Examples In the following sections, various experimental examples of the embodiments presented above will be demonstrated by means of some experimental examples. The compositions are all given in weight percentage. The following experimental examples are based on the first embodiment of the present invention. Experimental Example 1 The first magnetic layer was made in the following blending ratio. Barium ferrite powder (BaO·6Fe 2 O 3 ) (coercive force 2750 oersted; Specific surface area 8 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts After blending the above coating mixture in a ball mill for eight hours, five parts by weight of polyisocyanate resin was added and the mixture was further blended for one hour to produce a coating mixture for a first magnetic layer. The coating procedure was the regular one used for making magnetic recording medium. That is, as shown in Figure 2, coating a white polyester film of 188 µm thickness with the coating mixture, and before the coating is dry, applying magnetic orientation processing, and drying the film in the dryer to form a magnetic layer of 12 µm thickness, and the sheet is rolled up as a stock sheet. Next, a coating mixture for a second magnetic layer was prepared by mixing the ingredients in the following proportion. Strontium ferrite powder (SrO·6Fe 2 O 3 ) (coercive force 8,000 oersted; Specific surface area 5 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Isophorone 60 weight parts After blending the above coating mixture in a ball mill for eight hours, five parts by weight of polyisocyanate resin was added and the mixture was further blended for one hour to produce a coating mixture for the second magnetic layer. The coating procedure was to overlay the second coating on the first magnetic layer in the same way as in the coating process for the first magnetic layer. However, magnetic orientation processing is carried out on the first magnetic layer as shown in Figure 3, before the second coating is applied. Magnetic recording was performed with a a magnetic recording head having a 50 µm gap, using pulsed recording current at a force to sufficiently saturate the first magnetic layer. The recording method was FM recording at 100 BPI. Next, as shown in Figure 3, the second coating mixture was applied, followed by drying the coating in the dryer to make the second magnetic layer of 6 µm thickness to produce the recording medium of the present invention. The recording medium was made into cards conforming to the JIS (54x84 mm), and the cards were evaluated as follows. As shown in Figure 1 (A), magnetic recordings were made on the first magnetic layer at the time of coating the first magnetic layer. This was followed by the formation of the second magnetic layer as shown in Figure 1 (B), and after the track T 1 was DC-erased at a coercive force suitable for a magnetic layer of 2750 oersted which is sufficient to saturate the track T 1 , the magnetic information was read with a read magnetic head. The result was that the magnetic information on the first magnetic layer was erased as shown in Figure 1 (C), but the information on the first magnetic layer was transferred to the magnetic layer having the coercive force of 8000 oersted and was fixated thereon, thus permitting this information to be read. This information was not able to be erased with a magnetic head capable of recording on a magnetic layer of 2,750 oersted force. An example of the bar-type coding pattern obtained is shown in Figure 11. On the regions of the card other than the track T 1 , magnetic recordings were made using the magnetic head capable of recording on a magnetic layer of 4,000 oersted coercive force was used to FM record at 100 BPI. It was possible to carry out normal recording and reproduction, i.e. the cards were useable as ordinary magnetic cards. Experimental Example 2 The first magnetic layer was made in the following blending ratio. Barium ferrite powder (BaO·6Fe 2 O 3 ) (coercive force 2750 oersted; Specific surface area 8 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts After blending the above coating mixture in a ball mill for eight hours, five parts by weight of polyisocyanate resin was added and the mixture was further blended for one hour to produce a coating mixture for a first magnetic layer. The coating method was the normal method for making magnetic recording medium. That is, as shown in Figure 2, a white polyester film of 188 µm was used as the base material, and the film was coated with the above mixture, was magnetically oriented while wet, while the magnetic particles are mobile, dried in the dryer to produce a magnetic layer of 12 µm thickness to make a stock sheet. The magnetic stock sheet was magnetically recorded using a magnetic recording device. The recording process was performed using a magnetic head of 50 µm head gap at the recording pulsed current which is sufficient to saturate the first magnetic layer. The method was FM recording at 100 BPI. On top of the pre-recorded magnetic stock sheet thus produced, a second magnetic layer was applied by screen printing. The coating mixture for the second magnetic layer had the following blending ratio. Strontium ferrite powder (SrO·6Fe 2 O 3 ) (coercive force 8,000 oersted; Specific surface area 5 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Isophorone 60 weight parts After blending the above coating mixture in a ball mill for eight hours, five parts by weight of polyisocyanate resin was added and the mixture was further blended for one hour to produce a screen printing mixture for the second magnetic layer. The screen printing ink thus obtained was used to form the screen printed (coding) layer on the first magnetic layer on the stock sheet which has been magnetically pre-recorded, and it was dried to make the second magnetic layer of 6 µm thickness (to become a coding layer) to produce the magnetic recording medium of the present invention. The recording medium was punched out to produce JIS size (54x84 mm) magnetic cards, and the cards were evaluated according to the following methods. That is, the regions forming the second magnetic layer was DC-erased at a saturation magnetic field suitable for the 2,750 oersted layer, and the magnetic information was read with a magnetic read head. The information on the first magnetic layer was erased, but the information from the first magnetic layer was transferred and fixated in the 8,000 oersted (coding) layer, and it was possible to read this information. This information was not able to be erased with a magnetic head capable of recording on a a magnetic layer of 4,000 oersted force. On the regions of the card other than the track T 2 , magnetic recordings were made using the magnetic head capable of recording on a magnetic layer of 4,000 oersted was used to FM record at 100 BPI. It was possible to carry out normal recording and reproduction, i.e. the cards were useable as ordinary magnetic cards. In the following, experimental examples of the second embodiment of the invention will be presented. Experimental Example 5 The first magnetic layer was produced at the following blending ratio. Barium ferrite powder (BaO·6Fe 2 O 3 ) (coercive force 2750 oersted; Specific surface area 8 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts After blending the above coating mixture in a ball mill for eight hours, five parts by weight of polyisocyanate resin was added and the mixture was further blended for one hour to produce a coating mixture for a first magnetic layer. The coating method was the normal method for making magnetic recording medium. That is, as shown in Figure 5, a white polyester film of 188 µm was used as the base material, and the film was coated with the above mixture, was magnetically oriented while wet, dried in the dryer to produce a magnetic layer of 12 µm thickness to make a stock sheet. The coating mixture for a second magnetic layer had the following blending ratio. Carbonyl iron powder (coercive force 10 oersted; Specific surface area 1 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts After blending the above coating mixture in a ball mill for eight hours, five parts by weight of polyisocyanate resin was added and the mixture was further blended for one hour to produce a coating mixture for a second magnetic layer. The stock sheet having the first magnetic layer was coated with the second magnetic layer in the same way as the coating process for first magnetic layer. However, as shown in Figure 6, before forming the second magnetic layer, magnetic recording is performed using a magnetic head 20 having a head gap of 50 µm at a pulsed current sufficient to saturate the first magnetic layer. The method was FM recording at 100 BPI. Next, as shown in Figure 6, coating was applied in the coating section to produce a second magnetic layer, the coating was dried to form the second magnetic layer of 6 µm thickness to serve as the coding layer, and the stock sheet was picked up. Cards of JIS size (54x84 mm) were punched out from the stock sheet, and were evaluated as follows. That is, the regions where the second magnetic layer is formed, as shown in Figure 4 (A), was DC-erased at a magnetic force suitable for the 3,000 oersted magnetic layer. The region was read with a magnetic read head under a 500 gauss biasing magnetic field. It was found that the information on the first magnetic layer was erased, but the information from the first magnetic layer was transferred and fixated in the second magnetic layer thus serving as the coding layer, and it was possible to read this information. An example of the signals from the bar-code-type patterns obtained is shown in Figure 12. On the regions of the card other than the track T 2 , magnetic recordings were made using the magnetic head capable of recording on a magnetic layer of 3,000 oersted by FM recording at 100 BPI. It was possible to carry out normal recording and reproduction, i.e. the cards were useable as ordinary magnetic cards. Experimental Example 4. Except for the first magnetic layer which was made using the coating mixture of the following blending ratio, the conditions for making the magnetic recording medium were the same as in Example 3. -iron oxide powder (coercive force 300 oersted; Specific surface area 20 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts From the stock sheet thus produced, JIS size cards (54x84 mm) were punched out, and evaluated in the same way as in Example 3. The results similar to Experiment 3 were obtained. On the regions of the card other than the track T 2 , magnetic recordings were made using the magnetic head capable of recording on a magnetic layer of 3,000 oersted was used to FM record at 100 BPI. It was possible to carry out normal recording and reproduction, i.e. the cards were useable as ordinary magnetic cards. Experimental Example 5 The coating mixture for the first magnetic layer was made in the following blending ratio. Barium ferrite powder (BaO·6Fe 2 O 3 ) (coercive force 2750 oersted; Specific surface area 8 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts After blending the above coating mixture in a ball mill for eight hours, five parts by weight of polyisocyanate resin was added and the mixture was further blended for one hour to produce a coating mixture for a first magnetic layer. That is, as shown in Figure 5, a white polyester film of 188 µm was used as the base material, and the film was coated with the above first coating mixture, was magnetically oriented while wet, dried in the dryer to produce a magnetic layer of 12 µm thickness to make a stock sheet. The stock sheet was subjected to recording using a magnetic recording device. That is, recordings were made using a recording head having a 50 µm head gap at a pulsed current sufficient to saturate the first magnetic layer. The recording was performed by FM recording at 100 BPI. The pre-recorded magnetic tracks were provided with a second magnetic layer to serve as the coding layer using a screen printing technique to produce the second magnetic layer. The magnetic ink was produced according to the following blending ratio. Carbonyl iron powder (coercive force 10 oersted; Specific surface area 1 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts After blending the above coating mixture in a ball mill for eight hours, five parts by weight of polyisocyanate resin was added and the mixture was further blended for one hour to produce a screen printing ink for the second magnetic layer to serve as the coding layer. Using a screen printing technique, the above screen printing ink was used to form the coding layer, by forming the coding layer on the first magnetic layer on the stock sheet which had been magnetically recorded, and printing and drying to form the coding layer of 6 µm thickness. Cads of JIS size (54x84 mm) were punched out from the stock sheet, and were evaluated as follows. After the regions of the track T 2 , where the coding layer is formed, was DC-erased at a magnetic force suitable for a 3,000 oersted force magnetic layer. the region was read with a magnetic read head under a 500 gauss biasing magnetic field. The recorded information on the first magnetic layer was erased, but the information from the first magnetic layer was transferred and fixated in the second magnetic layer thus forming the coding information, and it was possible to read this coding information. On the regions of the card other than the track T 2 , magnetic recordings were made using the magnetic head suitable for saturation of a magnetic layer at 3,000 oersted by FM recording at 100 BPI. It was possible to carry out normal recording and reproduction, i.e. the cards were useable as ordinary magnetic cards. Experimental Example 6 Except for using the coating mixture of the following blending mixture for the second magnetic layer, production conditions remained the same as in Example 5. Manganese-Zinc ferrite powder (coercive force 20 oersted; Specific surface area 10 m 2 /g) parts 100 weight Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts From the stock sheet thus produced, cards of JIS size (54x84 mm) were punched out, and were evaluated in the same way as in Example 4. The results were similar to those obtained in Example 3. On the regions of the card other than the track T 2 , magnetic recordings were made using the magnetic head capable of recording on a magnetic layer of 3,000 oersted by FM recording at 100 BPI. It was possible to carry out normal recording and reproduction, i.e. the cards were useable as ordinary magnetic cards. Experimental Example 7 Except for using the coating mixture of the following blending ration for the second magnetic layer, production conditions remained the same as in Example 3. Permalloy powder (coercive force 0.006 oersted; specific surface area 1 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts The coating mixture was blended in a ball mill for eight hours, and after adding polyisocyanate resin by 5 weight parts, the mixture was blended further for one hour to obtain a coating mixture for the second magnetic layer. Coating was carried out by coating the first magnetic layer on top of the stock sheet, and applying the second coating on top of the first magnetic layer. The procedure was the same as that for making the first magnetic layer. However, as shown in Figure 6, before applying the second coating, magnetic pre-recording is made on the first magnetic layer using magnetic recording head. The magnetic recording was made with a recording head 70 having a head gap of 50 µm with a pulsed current sufficient to saturate the first magnetic layer at a FM rate of 100 BPI. Next, as shown in Figure 6, the coating head was used to apply the coating for the second magnetic layer for the coding layer, and the coated sheet was dried in the dryer section to produce the second magnetic layer of 6 µm thickness serving as the coding layer and the stock sheet was rolled up. Cards of JIS size (54x84 mm) was punched out from the stock sheet, and were evaluated as follows. That is, after the regions where the second magnetic layer is formed, as shown in Figure 4 (A), was DC-erased at a magnetic force suitable for 3,000 oersted force magnetic layer, the region was read with a magnetic read head under a 500 gauss biasing magnetic field. The information on the first magnetic layer was erased, but the information from the first magnetic layer was transferred and fixated in the second magnetic layer thus forming the coding information, and it was possible to read this information. On the regions of the card other than the track T 2 , magnetic recordings were made using the magnetic head capable of recording on a magnetic layer of 3,000 oersted by FM recording at 100 BPI. It was possible to carry out normal recording and reproduction, i.e. the cards were useable as ordinary magnetic cards. Experimental Example 8 The coating mixture for making peeling layer was made in the following blending ratio. Acrypolyol resin 15 weight parts Isocyanate hardener 1 weight parts Silicone oil 1 weight parts Toluene 40 weight parts Methyethylkeytone 40 weight parts Next, the peeling layer of 1 µm was produced on a polyester film of 25 µm thickness by applying the above coating mixture with the Gravure coater, and by drying the coating. A coating mixture for the protective covering layer was produced by blending the following materials. Nitrocellulose resin 10 weight parts Polyurethane resin 9 weight parts Isocyanate resin 1 weight parts Toluene 40 weight parts Methyethlkeytone 40 weight parts Next, the protective covering layer of 1 µm thickness was produced by applying the above mixture on top of the above peeling layer with a Gravure coater. Next, a coating mixture for the second magnetic layer was made in the following blending ratio. Barium ferrite powder (BaO·6Fe 2 O 3 ) (coercive force 2750 oersted; Specific surface area 8 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts The coating mixture was blended in a ball mill for eight hours, and after adding 5 weight parts of polyisocyanate, the mixture was further blended for one hour to make the coating mixture for the second magnetic layer. The coating was performed using the ordinary method for making a magnetic recording medium. That is, coating was applied on top of the protective covering layer with a Gravure coater, and before the coating is dried, magnetic orientation was performed. The coating was dried to produce a magnetic layer of 12 µm thickness, and this stock sheet was rolled up. The first magnetic layer was produced from the following coating mixture. Carbonyl iron powder (coercive force 40 oersted; Specific surface area 1 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts The coating mixture was blended in a ball mill for eight hours, and after adding 5 weight parts of polyisocyanate hardener, the mixture was further blended for one hour to make the coating mixture for the first magnetic layer. The first magnetic layer was produced applying the above coating mixture on top of the second magnetic layer with a Gravure coater. Before applying the first magnetic layer (before Gravure coating to make the first magnetic layer on top of the stock sheet having the second magnetic layer already coated), magnetic recording is made on the second magnetic layer using a magnetic recording head with, for example, a recording head having a 50 µm head gap at a pulsed current capable of saturating the second magnetic layer. The recording was made by arranging the magnetic recording head in the width direction of the stock sheet, because the sheet was eventually cut into tapes. The magnetic recording was performed by FM recording at 100 BPI. The recorded data on the second magnetic layer generated bar-code type patterns on the first magnetic layer. Next, the coating was applied to make the first magnetic layer, and the coating was dried in the dryer to make the coding layer of 6 µm thickness. Thus, the bar-code type patterns were formed and fixated in the first magnetic layer serving as the coding layer containing the bar-code-type patterns 96a shown in Figure 10. Next, the coating mixture for the adhesive layer was produced in the following blending ratio. Vinyl chloride·vinyl acetate· copolymer resin 5 weight parts Polyester resin 15 weight parts Toluene 40 weight parts Methyethylkeytone 40 weight parts The above coating mixture was applied on top of the first magnetic layer, and the coating was dried in the dryer to make a hot melt adhesive layer of 10 µm thickness. The stock sheet thus produced was cut into strips of 6.5 mm width to obtain magnetic transfer tape. Using this magnetic transfer tape, the magnetic layer was thermally transferred onto a polyvinyl sheet of 100 µm thickness, and the holding base material of a polyester film of 25 µm thickness was peeled off. The vinyl chloride sheet with the double magnetic layers thus produced, center core material of 560 µm thickness and the overlaying sheet of vinyl chloride of 100 µm thickness was piled on top of each other, and were thermally compressed to a thickness of 760 µm. The stock sheet was punched out to make JIS size recording medium (cards) with magnetic stripes. The above produced cards were evaluated as follows. The magnetic stripe regions were DC-erased at a saturation magnetic field suitable for the 2750 oersted layer, and the magnetic card was read with a magnetic read head with a biasing magnetic field of 1 KG. The bar-code type patterns fixated in the coding layer and the signals from the card shown in Figure 12 were identified. This coding information corresponded to those inputted in the second magnetic layer before the coding layer was applied. This information was neither alterable or erasable afterwards. Next, using the recording magnetic head, magnetic recordings were made using current pulses to sufficiently saturate the second magnetic layer. The information was subsequently read with a read head without any problems. Experimental Example 9 A coating mixture for making the magnetic transfer layer was made in the following blending ratio. Barium ferrite powder (BaO·6Fe 2 O 3 ) (coercive force 2750 oersted; Specific surface area 8 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts The coating mixture was blended in a ball mill for eight hours, and after adding 5 weight parts of polyisocyanate hardener, the mixture was further blended for one hour to make the coating mixture for the magnetic transfer layer. The coating operation was according to the usual method for making magnetic recording medium. Before the coating is dried, magnetic orientation was performed. The coating was dried in the dryer to make the magnetic transfer layer of 12 µm thickness. Next, a coating mixture for the peeling layer was produced in the following blending ratio. Acrylpolyole resin 15 weight parts Isocyanate hardener 1 weight parts Silicone oil 1 weight parts Toluene 40 weight parts Methylethylkeytone 40 weight parts The above coating mixture was applied on top of the magnetic transfer layer with a Gravure coater to make the peeling layer of 1 µm thickness. Next, a coating mixture for the protective covering layer was produced in the following blending ratio. Nitrocellulose resin 10 weight parts Polyurethane resin 9 weight parts Isocyanate hardener 1 weight parts Toluene 40 weight parts Methylethylkeytone 40 weight parts Next the above coating mixture for the protective covering layer was applied on top of the peeling layer with a Gravure coater, and dried to make the protective covering layer of 1 µm thickness. Next, a coating mixture for the second magnetic layer to serve as the coding layer was made in the following blending ratio. Carbonyl iron powder (coercive force 40 oersted; Specific surface area 1 m 2 /g) 100 weight parts Carbon black 3 weight parts Lecithin 1 weight parts Vinyl chloride·vinyl acetate· vinyl alcohol copolymer 20 weight parts Polyurethane resin 20 weight parts Toluene 60 weight parts Methyethylkeytone 60 weight parts Methyisobutylketone 60 weight parts The coating mixture was blended in a ball mill for eight hours, and after adding 5 weight parts of polyisocyanate hardener, the mixture was further blended for one hour to make the coating mixture for the second magnetic layer to serve as the coding layer. This coating mixture was applied on the protective covering layer with a Gravure coater, and dried to make the coding layer of 6 µm. Before applying the second magnetic layer (before Gravure coating to make the second magnetic layer on top of the stock sheet having the protective covering layer already printed), magnetic recording is made on the magnetic transfer layer using a recording magnetic head with, for example, a recording head having a 50 µm head gap at a pulsed current capable of saturation recording on the magnetic transfer layer. The recording was made by arranging the magnetic recording heads in the width direction of the stock sheet, because the sheet was eventually cut into tapes. The magnetic recording was performed by FM recording at 100 BPI. The recorded data on the magnetic transfer layer generated bar-code type patterns on the second magnetic layer. The results demonstrated that bar-code type patterns were formed and fixated in the second magnetic layer. Next, a coating mixture for the adhesive layer was made in the following blending ratio. Vinyl chloride·vinyl acetate· copolymer resin 5 weight parts Polyester resin 15 weight parts Toluene 40 weight parts Methyethylkeytone 40 weight parts The above coating mixture for the adhesive layer was applied with a Gravure coater on the coding layer, and dried to make the hot melt adhesive layer of 10 µm thickness. The stock sheet thus produced was cut into strips of 6.5 mm width to obtain the magnetic transfer tape. Using these magnetic transfer tapes, the magnetic transfer layer was thermally compressed on the coding layer. That is, the holding base material of polyester film of 25 µm thickness, the magnetic transfer layer and the peeling layer were peeled off, thus forming the coding layer having the fixated identifier coding information on the vinyl chloride sheet base material. Also, to provide regular magnetic recording stripes, the regular magnetic transfer tape was used to thermally transfer on the other region of the vinyl sheet to make the first magnetic layer, thus making stripes for regular magnetic layer. The stock sheet was produced by piling the vinyl chloride sheet having the stripes for fixated identifier coding information and for regular magnetic recording, the vinyl chloride sheet of 560 µm for the center core, the overlay sheet of 100 µm thickness on top of each other and thermally pressing to make a thickness of 760 µm. The stock sheet was punched out to make JIS size cards (54x84 mm) to produce magnetic recording medium (magnetic cards) having magnetic stripes. The cards were evaluated as follows. The magnetic stripe section having the identifier coding information was read with a magnetic read head under an external biasing magnetic field of 1KG. The identifier coding information in the second magnetic layer serving as the coding layer containing bar-code type patterns were observed. The patterns corresponded to the patterns which were inputted on the magnetic transfer layer of high coercivity before applying the second magnetic layer. The signals of the coding information, of the bar-code-type patterns shown in Figure 12, could neither be altered or erased subsequently. Next, using a recording magnetic head, regular magnetic recordings were made with a regular recording head at current pulses sufficient to saturate the first magnetic layer of the recording magnetic stripe, and the information was later read with a magnetic read head. There was not problem in reading the information.

Claims: A magnetic recording medium for preventing forgery of magnetically recorded proprietary information, comprising a non-magnetic base material (1a) and a magnetic layer (1b, 1d) containing magnetic particles dispersed in a binder, characterized in that said magnetic layer comprises a first magnetic layer having a coercive force of 100 oersted or less which is provided on the non-magnetic base material, and a second layer having a larger coercive force in a range of 250 to 5000 oersted which is provided on the first magnetic layer, said first magnetic layer containing pre-recorded identifier coding information for forgery prevention which is fixated in said first magnetic layer, so that said identifier coding information is readable magnetically but is neither erasable or alterable subsequent to the manufacture of said magnetic recording medium, said identifier coding information being formed by localized regions of different concentrations of magnetic particles. A magnetic recording medium for preventing forgery of magnetically recorded proprietary information, comprising a non-magnetic base material (1a) and a magnetic layer (1b, 1d) containing magnetic particles dispersed in a binder, characterized in that said magnetic layer comprises a first magnetic layer having a coercive force in a range of 250 to 4,000 oersted which is provided on the non-magnetic base material, and a second magnetic layer having a larger coercive force of 4,500 or more oersted which is provided on the first magnetic layer, said second magnetic layer containing magnetically pre-recorded identifier coding information for forgery prevention which is fixated in said second magnetic layer, so that said identifier coding information is readable magnetically but is neither erasable or alterable subsequent to the manufacture of said magnetic recording medium. A magnetic recording medium for preventing forgery of magnetically recorded proprietary information, comprising a non-magnetic base material (51) and a magnetic layer containing magnetic particles dispersed in a binder, characterized in that said magnetic layer comprises a first magnetic layer (52) having a coercive force in a range of 250 to 4,000 oersted which is provided on the non-magnetic base material, and a second magnetic layer (53) having a coercive force of less than 100 oersted which is provided on the first magnetic layer, said second magnetic layer containing magnetically pre-recorded identifier coding information for forgery prevention which is fixated in said second magnetic layer, so that said identifier coding information is readable magnetically but is neither erasable or alterable subsequent to the manufacture of said magnetic recording medium. A recording medium as claimed in claim 1 or 3, wherein said coding layer contains magnetic particles dispersed in a binder so as to produce a coding layer of a coercive force of not more than 100 oersted, and said identifier coding information is formed by a plurality of protrusions in said magnetic layer comprising designed patterns, letters or bar-code-type patterns formed by localized regions of different concentrations of magnetic particles, and said protrusions protrude away from said non-magnetic base material. A recording medium as claimed in claim 1, wherein said first magnetic layer is formed on top of said non-magnetic base material and said second magnetic layer is formed on top of said first magnetic layer, wherein said first magnetic layer defines the coding information as designed patterns, letters or bar-code-type patterns, pre-recorded and fixated for forgery prevention. A magnetic recording medium as claimed in claim 1, wherein said magnetic layer is attached to said base material with an adhesive layer, said identifier coding information is formed by a plurality of protrusions of said magnetic layer and said plurality of protrusions protrude into said adhesive layer. A magnetic recording medium as claimed in claim 1, 2 or 3, wherein said non-magnetic base material is selected from the group consisting of papers, laminated papers, resins such as polyester resins, synthetic polymer sheets, films and their laminated products. A magnetic recording medium as claimed in claim 1, 2 or 3, wherein said binder is selected from the group consisting of vinyl chloride·vinyl acetate group copolymers, polyurethane group resins, polyester group resins, epoxy group resins. A magnetic recording medium as claimed in claim 4 or 3 wherein the magnetic particles constituting the primary component in said coding layer are selected from the group consisting of the powders of at least one of carbonyl iron powder, zinc ferrite, manganese zinc ferrite, nickel, magnetite, Permalloy comprising Ni-Fe, Sendust comprising Fe-Si-Al, and Alperm comprising Fe-Al. A magnetic recording medium as claimed in claim 1, wherein the magnetic particles constituting the primary component in said magnetic layer, are selected from the group consisting of at least one powder of γ-iron oxide, cobalt doped γ-iron oxide, chromium oxide, barium ferrite, strontium ferrite. A magnetic recording medium as claimed in claim 2, wherein the magnetic particles constituting the primary component in said coding layer is selected from the group consisting of at least one of barium ferrite, strontium ferrite and related compound with replaced metal ions. A method for making a magnetic recording medium, comprising the steps of: for forming a first magnetic layer, applying a coating mixture comprising magnetic particles dispersed in a wet coating mixture on a non-magnetic base material to produce a wet coated sheet and drying the coating mixture; subjecting said coated sheet to a magnetic encoding process for recording identifier coding information on said first magnetic layer; applying a second coating mixture on said first magnetic layer to produce a second magnetic layer so as to duplicate the identifier coding information recorded in said first magnetic layer in said second magnetic layer, and drying said second magnetic layer to produce a coding layer containing non-erasable and non-alterable fixated identifier coding information comprising designed patterns, letters or bar-code-type patterns fixated for forgery prevention. A method for making a magnatic recording medium, comprising the steps of: forming a first magnetic layer having a coercive force of not less than 250 oersted and not more than 4,000 -oersted by applying a coating mixture comprising magnetic particles dispersed in a wet coating mixture on a non-magnetic base material to produce a wet coated sheet; and drying the coating mixture; recording magnetic information on said first magnetic layer; applying a second coating mixture having a coercive force of not more than 100 oersted on said first magnetic layer to produce a second magnetic layer so as to form protrusions in said second coating mixture by the magnetic field generated by said first magnetic layer; and drying said second magnetic layer to produce said protrusions forming designed patterns, letters or bar-code-type patterns formed by localizes regions of different concentrations of magnetic particles, pre-recorded and fixated for forgery prevention. A method as claimed in claim 13, wherein said magnetic information recording process is applied with a permanent magnet or an electromagnet from the back surface of said wet coated sheet opposite to the coating mixture while the magnetic particles in said coating mixture is mobile. A method as claimed in claim 13 or 14, wherein said layer of a coercive force of not more than 100 oersted is overlaid with the magnetic layer having a coercive force of not less than 250 oersted and not more than 4,000 oersted. A method as claimed in claim 13 or 14, wherein said magnetic layer having a coercive force of not less than 250 oersted and not more than 4,000 oersted is overlaid with the layer of a coercive force of not more than 100 oersted. A method as claimed in claim 12, wherein said first magnetic layer has a coercive force of not less than 250 oersted and not more than 4,000 oersted coating mixture; and said second coating mixture has a coercive force of not less than 4,500 oersted. A method for making a magnetic recording medium, having pre-recorded and fixated identifier coding information for forgery prevention, comprising the steps of: forming a first magnetic layer comprising a dried binder medium and magnetic particles having a high coercive force of not less than 250 oersted and not more than 5,000 oersted on a non-magnetic holding material; recording identifier coding information on said first magnetic layer magnetically; forming a second magnetic layer comprising a binder medium and magnetic particles of a coercive force of not more than 100 oersted so as to serve as a coding layer by duplicating said magnetic information recorded on said first magnetic layer in said second magnetic layer; forming an adhesive layer on top of said second magnetic layer to produce a magnetic transfer tape; transferring said first magnetic layer and said second magnetic layer defining the coding layer from said magnetic transfer tape to a non-magnetic base material to make said magnetic recording medium. A method as claimed in claim 18, wherein said identifier coding information duplicated in said second magnetic layer is produced by forming protrusions having localized regions of different concentrations of magnetic particles in said second magnetic layer while the magnetic particles are mobile within said binder medium; and fixating said protrusions by removing a solvent from said binder medium by evaporation.

Inventors: KAWASHIMA HIROSHI, MOCHIZUKI TUYOSHI, SUZUKI MASAYASU, KAWASHIMA, HIROSHI, MOCHIZUKI, TUYOSHI, SUZUKI, MASAYASU, KAWASHIMA, HIROSHI, C/O TOMOEGAWA PAPER CO., LTD., MOCHIZUKI, TUYOSHI, C/O TOMOEGAWA PAPER CO., LTD., SUZUKI, MASAYASU, C/O TOMOEGAWA PAPER CO., LTD.
Applicants: TOMOEGAWA PAPER CO LTD, TOMOEGAWA PAPER CO. LTD.
Application year: 1993
Main classification: G06K19
IPC codes: G06K1, G06K19