JP2000268353A - Magnetic recording medium and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make surely discriminable a magnetic recording medium from other magnetic recording media and prevent an unauthorized action by making the magnetic recording medium include a magnetic material composed of a hard magnetic substance (A), a hard magnetic substance (B) of a smaller coercive force than the hard magnetic substance (A) and a soft magnetic substance (C), in a predetermined dense-and-thin pattern into a second magnetic layer. SOLUTION: A base material 2 is formed of polyester such as PET, PET-G, PEN or the like, vinyl chloride, or the like. A first magnetic layer 3a uses magnetic fine particles such as γ-Fe2O3, Co applied γ-Fe2O3, Fe3O4, CrO2 or the like including a magnetic material of a coercive force in the range of 300-6000 (e). A second magnetic layer 3b contains three kinds of magnetic materials in a predetermined dense-and-thin pattern. A hard magnetic material A is Ba ferrite, Sr ferrite or a rare earth-based material for forming permanent magnets which has a coercive force of 6,000 (e) or larger, a hard magnetic material B is γ-Fe2O3, Co-applied γ-Fe2O3 or the like having a coercive force in the range of 100-5,000 (e), and a soft magnetic material C is Al, Si, Fe or the like having a coercive force of 200 (e) or smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium which is difficult to forge and alter, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A magnetic recording medium in which a magnetic recording layer is formed in an entire area on one side or both sides of a substrate or in a stripe shape is provided.
For example, prepaid cards, commuter passes, tickets, admission tickets,
It is widely used as vouchers, securities, such as car tickets, betting tickets, gift certificates, stock certificates, certificates, passbooks, magnetic tags, etc., cards such as ID cards, cash cards, credit cards, membership cards, and magnetic labels. Conventionally, such a magnetic recording medium writes information on a magnetic recording layer at a high recording density,
The recorded information cannot be easily read from outside.

[0003] However, due to the characteristics of the magnetic recording layer, the recorded information can be freely rewritten and erased, so that forgery and falsification are possible. In recent years, it has been highlighted as a major social problem. In particular, since it is now easy to obtain a magnetic stripe, it is possible to manufacture a similar card, and if the magnetic recording layer is exposed on the surface of the magnetic recording medium as in the current specification. There is also a problem that magnetic recording information can be easily read or magnetic recording information can be easily transferred to another magnetic recording layer by a magnetic transfer technique.

[0004] In order to solve the problem based on the essential drawback of the reversibility of magnetically recorded information, various methods for making it difficult to rewrite magnetically recorded information have been proposed. For example, by using a high coercive force magnetic material such as Ba ferrite or Sr ferrite, a high coercive force low Curie point (high Hc and low Tc) magnetic material, a magnetic material containing MnBi, or the like, magnetic information is hardly erased. Medium is being developed.

Further, a magnetic recording medium has been developed in which magnetic recording information is provided by giving a physical change to a magnetic layer so that magnetic rewriting becomes impossible. For example, a magnetic recording medium provided with a magnetic barcode by printing,
Examples include a magnetic recording medium in which marking is performed on a magnetic layer with a laser or the like.

Further, a first magnetic layer containing a magnetic material having a relatively low coercive force is formed on a base material, and after performing magnetic recording on the first magnetic layer, a second magnetic layer containing a magnetic material having a high coercive force is formed. Magnetic recording media in which layers are applied and laminated are also being developed. In this magnetic recording medium, since the magnetic recording pattern of the first magnetic layer is copied (so-called magnetic transfer) to the second magnetic layer, it is difficult to rewrite with a magnetic head for forgery or falsification.

[0007]

However, a magnetic recording medium using only a high coercivity magnetic material as described above is
Although it is possible to prevent the erasure of magnetically recorded information due to the influence of an external magnetic field, it is difficult to magnetize when writing information with a magnetic head, which causes a new problem that the writing device can be limited. .

On the other hand, in a magnetic recording medium having a high Hc / low Tc magnetic material or a magnetic material containing MnBi, magnetic writing can be performed by utilizing a sudden decrease in coercive force due to temperature. Was insufficient.

Further, in a magnetic recording medium in which a magnetic layer is physically changed like a magnetic barcode, if the magnetic material contained in the magnetic layer has a low coercive force, demagnetization can be performed by an AC magnetic field, There is a problem that information can be erased.

Further, a magnetic recording medium having magnetic recording information magnetically transferred to the second magnetic layer has a problem that when a very strong magnetic field is applied, the magnetic recording of the second magnetic layer by the magnetic transfer is erased. In order to solve this, if the second magnetic layer contains a magnetic material having a higher coercive force,
This time, it is difficult to efficiently perform magnetic transfer to the second magnetic layer, and there is a problem that a magnetic output required for reading cannot be obtained from the second magnetic layer.

The present invention has been made in view of such circumstances, and has fixed information whose output level and waveform can be variously changed in reading by a magnetic head.
A magnetic recording medium capable of reliably discriminating from other magnetic recording media, preventing fraudulent acts such as forgery and falsification, and capable of rewriting variable information, and a method of manufacturing this magnetic recording medium. Aim.

[0012]

In order to achieve the above object, a magnetic recording medium of the present invention has a base material and a magnetic recording layer on the base material, and the magnetic recording layer has a base material. A first magnetic layer and a second magnetic layer are laminated in order from the material side, and the second magnetic layer includes a hard magnetic material A, a hard magnetic material B having a smaller coercive force than the hard magnetic material A, and The magnetic material was composed of three kinds of soft magnetic materials C in a predetermined density pattern.

In the magnetic recording medium of the present invention, the coercive force of the hard magnetic material A is 6000 Oe or more, the coercive force of the hard magnetic material B is in the range of 100 to 5000 Oe, The configuration was such that the coercive force was 20 Oe or less.

According to the method of manufacturing a magnetic recording medium of the present invention, a first magnetic layer is formed on a base material, a desired magnetic recording is performed on the first magnetic layer, and a hard magnetic layer is formed on the first magnetic layer. A magnetic paint containing a magnetic material A, a hard magnetic material B having a lower coercive force than the hard magnetic material A, and a soft magnetic material C is applied, and the magnetic coating film is subjected to magnetic orientation treatment by a bias magnetic field. Or performing a magnetic orientation treatment and then drying to form a second magnetic layer having fixed information composed of a dense / dense pattern of a magnetic material corresponding to the magnetic recording pattern of the first magnetic layer, The configuration was such that a magnetic recording layer comprising a first magnetic layer and the second magnetic layer was formed.

In the method for manufacturing a magnetic recording medium of the present invention, the strength of the bias magnetic field is in a range of 50% or less of the coercive force of the magnetic material contained in the first magnetic layer.

In the present invention as described above, the hard magnetic material A constituting the dense / dense pattern of the second magnetic layer imparts stability to an external AC magnetic field to the fixed information, and the hard magnetic material B is applied to the magnetic recording medium. Variable information can be written, and the soft magnetic material C
Has the effect of changing the obtained magnetic output level and waveform depending on the presence or absence of a bias magnetic field and its direction when reading the second magnetic layer with a magnetic head.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of the embodiment of the magnetic recording medium of the present invention. In FIG. 1, a magnetic recording medium 1 of the present invention includes a base material 2 and a magnetic recording layer 3 formed on the entire surface of one surface of the base material 2, and the magnetic recording layer 3 is a first magnetic layer. 3a and the second magnetic layer 3b are laminated.

Base material 2 constituting magnetic recording medium 1 of the present invention
Considering heat resistance, strength, rigidity, etc. required as a base material, polyester such as PET, PET-G, PEN,
Resin such as vinyl chloride, polycarbonate, polyethylene, polypropylene, polystyrene, polylactic acid, etc., biodegradable resin, metals such as copper and aluminum, paper, impregnated paper, synthetic paper, etc. Or a composite. The thickness of the substrate 2 is 100 μm to 1 mm, preferably 1 μm.
It can be about 50 to 250 μm.

The first magnetic layer 3a constituting the magnetic recording layer 3 contains a magnetic material having a coercive force in the range of 300 to 6000 Oe. The coercive force of this magnetic material is 300 Oe
If it is less than 600, a sufficient magnetic output required for forming a dense / dense pattern of a magnetic material of the second magnetic layer 3b, which will be described later, cannot be obtained, or the resistance to an external magnetic field is insufficient.
If it exceeds 0 Oe, stable recording by the magnetic head becomes difficult, which is not preferable. If the recording by the magnetic head can be performed stably, a magnetic material having a coercive force exceeding 6000 Oe can be used.

Examples of the magnetic material constituting the first magnetic layer 3a and having a coercive force in the range of 300 to 6000 Oe include γ-Fe ₂ O ₃ and γ-Fe ₂ O coated with Co.
_{3, Fe 3 O 4, CrO} 2, Fe, Co, Ni, Fe-
Co, Co-Ni, Fe-Ni, Ba ferrite, Sr
Magnetic fine particles such as ferrite are exemplified.

The first magnetic layer 3a is formed by dispersing one or more of the above-mentioned magnetic fine particles in a suitable resin or ink vehicle by a gravure method, a roll method, a knife edge method or the like. It can be formed by coating and drying according to a known coating method. In addition, using the above magnetic material, a vacuum evaporation method, a sputtering method,
The first magnetic layer 3a can also be formed by a plating method or the like. When formed by a coating method, the thickness of the first magnetic layer 3a is 1 to 50 μm, preferably 3 to 50 μm, after drying.
It is about 20 μm.

The second magnetic layer 3b constituting the magnetic recording layer 3 is made of a hard magnetic material A, a hard magnetic material B having a smaller coercive force than the hard magnetic material A, and a soft magnetic material C. Magnetic material in a predetermined density pattern. That is, the three types of magnetic materials (hard magnetic material A, hard magnetic material B, and soft magnetic material C) each form a dense / dense pattern,
The magnetic output when reading the magnetic recording layer 3 with a magnetic head is a combination of the magnetizations of the three types of magnetic materials.

The hard magnetic material A has a coercive force of 60
A magnetic material of 00 Oe or more can be used, and the upper limit of the coercive force is not particularly limited. As such a magnetic material,
For example, Ba ferrite, Sr ferrite, rare earth permanent magnet materials and the like can be mentioned. These hard magnetic materials A can be used alone or in combination of two or more.

As the hard magnetic material B, a magnetic material having a coercive force in the range of 100 to 5000 Oe can be used. If the coercive force of the hard magnetic material B is less than 100 Oe, a sufficient magnetic output cannot be obtained in reproducing variable information described later, or the resistance to an external magnetic field is insufficient. It is not preferable because the recorded data becomes difficult. As such a hard magnetic material B, for example, γ-Fe ₂ O ₃ ,
_{-Fe 2 O 3, Fe 3 O} 4, CrO 2, Fe, Co, N
i, Fe-Co, Co-Ni, Fe-Ni, Ba ferrite and the like. These hard magnetic materials B can be used alone or in combination of two or more.

Further, as the soft magnetic material C, a magnetic material having a coercive force of 20 Oe or less, preferably in the range of 0.5 to 20 Oe can be used. By setting the coercive force of the soft magnetic material C to 20 Oe or less as described above, it is possible to saturate the soft magnetic material C or to reverse the magnetization with a low bias magnetic field, and it is necessary to apply an excessive current to the magnetic head. Disappears. If the coercive force of the soft magnetic material C exceeds 20 Oe, the control stability of the magnetization of the soft magnetic material C depending on the presence or absence of the bias magnetic field at the time of reading is undesirably reduced.
If an error occurs during reading due to the influence of the terrestrial magnetism, it is desirable to set the lower limit of the coercive force to 0.5 Oe as described above.

As such a soft magnetic material C, for example,
Magnetic metal material made of Al, Si, Fe, etc., metal high permeability material such as Permalloy, Sendust, Fe, etc., Mn-Zn
Ferrites such as ferrite, Co—Zn ferrite, and Ni—Zn ferrite, and metal amorphous materials can be given. These soft magnetic materials C can be used alone or in combination of two or more.

The second magnetic layer 3b is formed by coating a magnetic paint in which the above-described hard magnetic material A, hard magnetic material B, and soft magnetic material C are dispersed in an appropriate resin or ink vehicle with a desired magnetic material. The gravure method is applied on the recorded first magnetic layer 3a,
It can be formed by applying according to a known coating method such as a roll method or a knife edge method and performing a magnetic alignment treatment with a predetermined bias magnetic field, or after performing a magnetic alignment treatment and then drying the magnetic coating film. it can. In addition, as the orientation device used for the orientation treatment, a solenoid type electromagnet orientation device is preferable.

The ratio (weight ratio) of the contents of the hard magnetic material A, the hard magnetic material B, and the soft magnetic material C in the second magnetic layer 3b.
Although it greatly depends on the performance of the magnetic material used, it can be set, for example, in the range of A: B: C = 1 to 5: 1: 0.1 to 1. The thickness of the second magnetic layer 3b is
It can be appropriately set depending on the performance, content, and the like of the magnetic material used, and for example, can be in the range of 1 to 50 μm.

In the magnetic recording medium 1 of the present invention having such a configuration, the second magnetic layer 3b of the magnetic recording layer 3 is made of a magnetic material composed of three types of hard magnetic material A, hard magnetic material B and soft magnetic material C. The material is contained in a predetermined density pattern, and has fixed information composed of the density pattern. Then, the second magnetic layer 3b
The fixed information composed of the dense / dense pattern becomes extremely stable with respect to an external magnetic field due to the hard magnetic material A contained in the hard magnetic material A.
In other words, the magnetic information based on the dense / dense pattern is not erased by the DC magnetic field, and conversely, the output increases due to the magnetization.However, when only a magnetic material having a low coercive force is used, the magnetic information can be demagnetized by the AC magnetic field. Can be erased. However, in the magnetic recording medium of the present invention, since the hard magnetic material A exists, the fixed information cannot be completely erased even when an AC magnetic field is applied.

Since the hard magnetic material B is contained in the second magnetic layer 3b, normal rewritable magnetic information (variable information) can be handled by the magnetic recording medium 1 of the present invention.
For example, a rewritable magnetic track can be provided in an area other than the area where the fixed information composed of the above-mentioned dense / dense pattern is recorded.

Further, since the soft magnetic material C is contained in the second magnetic layer 3b, almost no residual magnetization occurs in the dense / dense pattern. However, since magnetization occurs in a magnetic field, the output of the soft magnetic material C component changes depending on the reading conditions. For example, if the hard magnetic material A and the hard magnetic material B are magnetized at a magnetic field intensity sufficient to be magnetized, and then a normal bias-free reading without applying a bias magnetic field is performed, the soft magnetic material C component hardly contributes to the output. Instead, the sum of the hard magnetic material A component and the hard magnetic material B component is the magnetic output. On the other hand, in the bias reading in which the bias magnetic field is applied, when the soft magnetic material C is magnetized and the soft magnetic material C is magnetized in the same direction as the magnetization directions of the hard magnetic materials A and B, 3 If the soft magnetic material C is magnetized in a direction opposite to the magnetization direction of the hard magnetic material A and the hard magnetic material B, the sum of the kinds of magnetic material components becomes a magnetic output. The magnetic output of the magnetic body C) is obtained. That is, by using the soft magnetic material C, the reproduction waveform and its output level can be changed depending on the reading conditions. In addition, the fixed information in the second magnetic layer 3b can be arbitrarily set for each magnetic recording medium by magnetic recording on the first magnetic layer 3a. Therefore, the magnetic recording medium can be distinguished from another magnetic recording medium, and the authenticity of the magnetic recording medium can be reliably determined.

In the magnetic recording medium of the present invention, the magnetic recording layer 3 is formed on the entire surface of one side of the base material 2. As shown in FIG. May be formed in a stripe shape on a part of the base material. Further, in the present invention, the magnetic recording layer 3 of the magnetic recording medium 1 is used.
An intermediate layer may be provided between the first magnetic layer 3a and the second magnetic layer 3b, or a protective layer, a colored layer, or a pattern for providing protection, hiding, and decorative effects may be provided on the magnetic recording layer 3. .

The intermediate layer, the protective layer, the colored layer and the pattern are made of a cellulose derivative such as ethyl cellulose, cellulose nitrate, ethyl hydroxyethyl cellulose, cellulose acetate propionate or cellulose acetate, a styrene resin such as polystyrene or poly-α-methylstyrene, or Acrylic resin such as styrene copolymer resin, polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, polybutyl acrylate, etc. or methacrylic resin alone or copolymer resin, rosin, rosin-modified maleic resin, rosin-modified phenol resin Rosin ester resin such as polymerized rosin, polyvinyl acetate resin, coumarone resin, vinyl toluene resin, vinyl chloride resin, polyester resin, polyurethane resin, butyral resin, etc. As the Te adding various pigments, it imparts a cleaning effect of the magnetic head as required,
Add titanium oxide, alumina powder, micro silica, etc., and further, if necessary, a plasticizer, a stabilizer, a wax,
After adding a grease, a drying agent, a drying aid, a curing agent, a thickening agent, and a dispersing agent, using a coloring paint or ink which is sufficiently kneaded with a solvent or a diluent, a normal gravure method, a roll method, A desired portion can be formed by a coating method such as a knife edge method or an offset method or a printing method.
The thickness of the intermediate layer is preferably about 1 to 3 μm, and the thickness of the protective layer and the colored layer is preferably about 1 to 5 μm.

Next, an embodiment of a method for manufacturing a magnetic recording medium according to the present invention will be described with reference to FIG. First, the first magnetic layer 3a is formed on the base material 2 (see FIG. 3).
(A)). The first magnetic layer 3a is formed by applying a magnetic paint obtained by dispersing a magnetic material having a coercive force in the range of 300 to 6000 Oe in an appropriate resin or an ink vehicle by a gravure method, a roll method, a knife edge method, or the like. Can be formed by coating and drying according to the known coating method described above. As the resin or ink vehicle, butyral resin, vinyl chloride / vinyl acetate copolymer resin,
A urethane resin, a polyester resin, a cellulose resin, an acrylic resin, a styrene / maleic acid copolymer resin or the like is used, and a rubber-based resin such as a nitrile rubber or a urethane elastomer is added as necessary. Further, in consideration of heat resistance, a resin having a high glass transition temperature (Tg) such as polyamide, polyimide, or polyethersulfone, or a system in which Tg increases by a curing reaction can be used. If necessary, a dispersing agent, a plasticizer, a curing agent, an antistatic agent, a pigment, and the like may be appropriately contained in the magnetic paint in which the magnetic material is dispersed in the resin or the ink vehicle as described above. Further, the first magnetic layer 3a can also be formed by using the above magnetic material by a vacuum deposition method, a sputtering method, a plating method, or the like.

Next, desired magnetic recording is performed on the first magnetic layer 3a (FIG. 3B). Thus, a magnetic pattern having a different magnetization direction is formed on the first magnetic layer 3a. Next, the second magnetic layer 3b is formed. First, a magnetic coating material in which the hard magnetic material A, the hard magnetic material B, and the soft magnetic material C are dispersed in an appropriate resin or an ink vehicle as described above is applied to a first magnetic material on which desired magnetic recording has been performed. On the layer 3a, a magnetic coating film 3'b is formed by applying a known coating method such as a gravure method, a roll method, and a knife edge method (FIG. 3).
(C)). As the resin or ink vehicle used for the magnetic paint, those mentioned in the formation of the first magnetic layer 3a can be used, and if necessary, a dispersant, a plasticizer, a curing agent, an antistatic agent, A pigment or the like may be appropriately contained in the magnetic paint.

Next, a magnetic field is applied by applying a bias magnetic field in a fixed direction (FIG. 3D). Thereby, the first
The magnetic coating 3'b
The magnetic material moves and gathers at a portion where the direction of the magnetization existing therein matches the direction of the bias magnetic field, and a dense portion of the magnetic material is formed in the undried magnetic coating film 3'b. That is, by performing the magnetic orientation treatment, the first magnetic layer 3a
The intensity of the magnetic lines of force generated in the magnetic coating film 3'b that is generated from the undried magnetic film 3'b is changed, and a dense / dense pattern of the magnetic material is formed. The magnetic orientation treatment also has the effect of magnetizing the magnetic material, inducing agglomeration of the magnetic materials, and facilitating the formation of a dense / dense pattern. The intensity of the applied bias magnetic field is
To prevent the magnetic recording of the magnetic layer 3a from being erased, the coercive force of the magnetic material contained in the first magnetic layer 3a should be 50% or less.
The coercive force of the magnetic material of the first magnetic layer to be used, and the second
It can be set as appropriate according to the viscosity of the magnetic coating material for the magnetic layer.

Thereafter, by drying the magnetic coating film 3'b, a second magnetic layer 3b having fixed information composed of a dense / dense pattern of a magnetic material corresponding to the magnetic recording pattern of the first magnetic layer 3a is formed. When the bias magnetic field is removed from the dense / dense pattern formed on the magnetic coating film 3'b, the state of distribution of the magnetic material changes. Therefore, the dense / dense pattern is quickly dried to fix the dense / dense pattern. It is most preferable to perform drying while applying a bias magnetic field.

The squareness ratio of the hard magnetic material B component contained in the second magnetic layer 3b is improved by the magnetic orientation treatment performed at the time of forming the second magnetic layer 3b, and the variable Recording and reproduction of information can be performed reliably.

Next, a bias magnetic field for erasing the magnetic recording of the first magnetic layer 3a is applied in a fixed direction to erase the magnetic recording of the first magnetic layer 3a, and to erase the magnetic recording of the second magnetic layer 3b.
The fixed information is magnetized to obtain the magnetic recording medium 1 (FIG. 3E). Note that the direction of the bias magnetic field is the same as the direction of the bias magnetic field in the above magnetic alignment processing.
Conversely, either may be used.

In the magnetic recording medium 1 of the present invention manufactured as described above, since the dense / dense pattern of the magnetic material fixed in the second magnetic layer 3b of the magnetic recording layer 3 is nothing but a pattern of magnetization change. Used as information. Since this magnetic information is due to the physical change of the density of the magnetic material, it becomes fixed information that cannot be magnetically rewritten. The magnetic output waveform when read by the magnetic head corresponds to the dense / dense pattern due to a change in magnetization generated at the dense / dense boundary of the magnetic material (shown by a chain line in FIG. 3E). It changes depending on the state of magnetization of each of the hard magnetic material A, the hard magnetic material B, and the soft magnetic material C contained in the magnetic layer 3b, the presence or absence of the read bias magnetic field, and the direction thereof. For example, if the hard magnetic material A and the hard magnetic material B are magnetized at a magnetic field intensity sufficient to be magnetized, and then a normal bias-free reading without applying a bias magnetic field is performed, the soft magnetic material C component hardly contributes to the output. Instead, the sum of the hard magnetic material A component and the hard magnetic material B component is the magnetic output. On the other hand, in the bias reading in which the bias magnetic field is applied, when the soft magnetic material C is magnetized and the soft magnetic material C is magnetized in the same direction as the magnetization directions of the hard magnetic materials A and B, 3 If the soft magnetic material C is magnetized in a direction opposite to the magnetization direction of the hard magnetic material A and the hard magnetic material B, the sum of the kinds of magnetic material components becomes a magnetic output. The magnetic output of the magnetic body C) is obtained.

In the present invention, the fixed information in the second magnetic layer 3b can be arbitrarily set for each magnetic recording medium by magnetic recording on the first magnetic layer 3a. It is possible to determine.

Incidentally, a resin film such as a polyethylene terephthalate film is used as a base material, and a first magnetic layer and a second magnetic layer are sequentially laminated on the base material by the above-described manufacturing method to form a magnetic recording layer. The magnetic recording medium may be manufactured by preparing a magnetic tape by providing the magnetic tape and bonding the magnetic tape to the entire surface or a part of a card base material or the like.

[0043]

Next, the present invention will be described in more detail with reference to examples. First, a 188 μm-thick polyethylene terephthalate (E-22 manufactured by Toray Industries, Inc.) was prepared as a base material, and a magnetic paint for forming a first magnetic layer having the following composition was coated on one surface of the base material by a gravure coating method. And dried to form a first magnetic layer having a thickness of 10 μm.

(Coating liquid for forming first magnetic layer) Ba ferrite (coercive force = 4000 Oe): 80 parts by weight Vinyl chloride / vinyl acetate copolymer resin: 10 parts by weight Urethane resin: 10 parts by weight Methyl ethyl ketone 50 parts by weight Toluene 50 parts by weight Methyl isobutyl ketone 50 parts by weight Isocyanate-based curing agent 3 parts by weight Next, magnetic recording M was performed on the first magnetic layer at a write current of 1000 mA. The recording density at this time is 200 bpi
(FM recording).

Next, a magnetic paint for forming a second magnetic layer having the following composition was applied by gravure coating on the first magnetic layer to form a magnetic coating film. The magnitude relationship of the saturation magnetization per unit weight of each magnetic material used is as follows.
Hard magnetic material A (coercive force = 8000 Oe) <hard magnetic material B (coercive force = 1800 Oe) <soft magnetic material C (coercive force = 8 Oe)
Met.

(Coating solution for forming second magnetic layer) Hard magnetic material A (Sr ferrite): 60 parts by weight (coercive force = 8000 Oe) Hard magnetic material B (Ba ferrite): 30 parts by weight (coercive force) = 1800 Oe)-Soft magnetic material C (permalloy) ... 10 parts by weight (coercive force = 8 Oe)-Vinyl chloride / vinyl acetate copolymer resin ... 10 parts by weight-Urethane resin ... 10 parts by weight-Methyl ethyl ketone ... 50 parts by weight-Toluene ... 50 parts by weight-Methyl isobutyl ketone ... 50 parts by weight-Isocyanate curing agent ... 3 parts by weight

Next, a DC bias magnetic field of 2000 G solenoid was applied to the above magnetic coating film in one direction along the recording direction of the first magnetic layer to perform a magnetic orientation treatment. Then, the magnetic coating film is dried to obtain a second 10 μm thick film.
A magnetic layer was formed. This second magnetic layer comprises a hard magnetic material A, a hard magnetic material B and a soft magnetic material C, wherein A: B: C = 2: 1:
The fixed information M ′ which is contained at a weight ratio of 0.33 and is composed of a dense / dense pattern of a magnetic material corresponding to the magnetic recording M of the first magnetic layer.
It had the following. Thereby, the first magnetic layer and the second magnetic layer
A magnetic recording layer composed of a laminate with a magnetic layer was formed on a substrate.

Next, a coating liquid for a protective layer having the following composition was applied on the magnetic recording layer by a gravure coating method and dried to form a protective layer having a thickness of 2 μm. (Coating liquid for protective layer) ・ Aluminum powder 10.5 parts by weight ・ Titanium oxide powder 10.5 parts by weight ・ Polyurethane resin 4 parts by weight ・ Methyl ethyl ketone 75 parts by weight

The substrate on which the magnetic recording layer was formed as described above was punched into a card having a size of 86 mm × 54 mm to obtain a magnetic recording medium of the present invention.

Next, a DC bias magnetic field of 25000 G by a solenoid is applied to the magnetic recording layer of the magnetic recording medium in one direction along the recording direction of the first magnetic layer to erase the magnetic recording M of the first magnetic layer. At the same time, magnetization was performed on the fixed information M 'portion composed of the dense / dense pattern of the magnetic material of the second magnetic layer.

The magnetic recording medium was subjected to the following three conditions (I
-III) using a card reader, and the relative value (%) of the magnetic output is shown below. Reading conditions Condition I: no bias reading Condition II: forward bias reading (magnetization directions of hard magnetic material A and hard magnetic material B, and soft magnetic material C by bias magnetic field)
Condition III: Reverse bias reading (the magnetization direction of the hard magnetic material A and the hard magnetic material B is opposite to the magnetization direction of the soft magnetic material C due to the bias magnetic field)

From this, the fixed information of the second magnetic layer of the magnetic recording medium of the present invention is based on the presence or absence of a bias magnetic field,
It was confirmed that the magnetic output changed depending on the direction.

Next, alternating current demagnetization of the dense / dense pattern formation region (fixed information) of the second magnetic layer is performed using a magnetic head.
Thereafter, reading was performed under the three conditions as described above.
As a result, the coercive force was 800 under any of the reading conditions.
The output of the hard magnetic material A of 0 Oe was detected, and it was confirmed that the fixed information could not be magnetically erased. From this, it was confirmed that the fixed information of the second magnetic layer of the magnetic recording medium of the present invention can be used as magnetic information that cannot be magnetically erased.

In the magnetic recording layer other than the dense / dense pattern formation region (fixed information) of the second magnetic layer, the hard magnetic material B
Magnetic information was written under the condition that saturation writing was possible for (coercive force of 1800 Oe). Thereafter, the magnetic information was reproduced by a magnetic head using a card reader, and as a result, a reproduced waveform having a sufficient output was obtained.

[0055]

As described in detail above, according to the present invention, the magnetic recording layer provided on the substrate is obtained by laminating the first magnetic layer and the second magnetic layer on the substrate in this order, Since the second magnetic layer has fixed information composed of a dense / dense pattern of three types of magnetic materials, a hard magnetic material A, a hard magnetic material B having a smaller coercive force than the hard magnetic material A, and a soft magnetic material C, Stability to an external AC magnetic field is imparted to the fixed information by the hard magnetic material A constituting the dense / dense pattern of the two magnetic layers, and variable information can be written to the magnetic recording medium by the hard magnetic material B. When the magnetic recording layer is read by the magnetic head due to the existence of the pair C, the obtained magnetic output level and waveform change depending on the presence or absence and the direction of the bias magnetic field, thereby making it possible to discriminate the magnetic recording medium from other magnetic recording media. Possible and true With determination can be performed reliably, it is possible to a magnetic recording medium capable of writing variable information necessary from time to time.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an embodiment of a magnetic recording medium of the present invention.

FIG. 2 is a schematic sectional view showing another embodiment of the magnetic recording medium of the present invention.

FIG. 3 is a process chart showing an example of an embodiment of a method for manufacturing a magnetic recording medium according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Magnetic recording medium 2 ... Base material 3 ... Magnetic recording layer 3a ... 1st magnetic layer 3b ... 2nd magnetic layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Hiroyuki Yamaguchi 1-1-1, Ichigaya-Kagacho, Shinjuku-ku, Tokyo Inside Dai Nippon Printing Co., Ltd. (72) Nobuaki Wakamatsu 1-1-1, Ichigaga-cho, Shinjuku-ku, Tokyo No. 1 Dai Nippon Printing Co., Ltd. F term (reference) 2C005 HA02 JA03 KA08 KA19 KA21 KA40 LA11 LB18 5B035 AA15 BA03 BA05 BB02 BB09 BC00 BC02 CA01 5D006 BA01 BA06 BA08 BA19 BA20 DA01 EA01 FA00

Claims (4)

[Claims] 1. A magnetic recording layer comprising: a base material; and a magnetic recording layer on the base material, wherein the magnetic recording layer is formed by laminating a first magnetic layer and a second magnetic layer in order from the base material side. The second magnetic layer includes a hard magnetic material A and a hard magnetic material B having a smaller coercive force than the hard magnetic material A.
And a magnetic material comprising three kinds of soft magnetic materials C in a predetermined density pattern. 2. The coercive force of the hard magnetic material A is 6000 Oe.
The coercive force of the hard magnetic material B is 100 to 500
0 Oe, and the coercive force of the soft magnetic material C is 20 Oe.
The magnetic recording medium according to claim 1, wherein e is equal to or less than e. 3. After forming a first magnetic layer on a base material and performing desired magnetic recording on the first magnetic layer, a hard magnetic material A and a hard magnetic material A are formed on the first magnetic layer. A magnetic paint containing a hard magnetic material B and a soft magnetic material C having a smaller coercive force than the magnetic material, and applying a magnetic alignment treatment by a bias magnetic field to the magnetic coating film, or a magnetic alignment treatment. And then drying to form a second magnetic layer having fixed information composed of a dense / dense pattern of a magnetic material corresponding to the magnetic recording pattern of the first magnetic layer. The first magnetic layer and the second magnetic layer A method for manufacturing a magnetic recording medium, comprising forming a magnetic recording layer composed of layers. 4. The method according to claim 3, wherein the intensity of the bias magnetic field is 50% or less of a coercive force of a magnetic material contained in the first magnetic layer.