JPH0855338A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent forgery and alteration by forming a second magnetic layer having the coercive force lower than the coercive force of a first magnetic layer on this first magnetic layer and permanently recording the prescribed identification signals recorded on the first magnetic layer as fixed patterns of the second magnetic layer. CONSTITUTION:A magnetic coating material consisting of Ba ferrite magnetic powder of the coercive force of 27500e is applied by a coating head 11 on a nonmagnetic substrate which consists of a PET, has a thickness of 188mum and is emitted from a delivery device 10. The coating is then dried by a drying device 13, by which the first magnetic layer having a thickness of 8mum is obtd. The prescribed identification signals, for example, continuous signals of 25FCI and 400FCI and FM signals of 105BPI are respectively saturation recorded by a magnetic head 15 on the first magnetic layer and the substrate is taken up on a take-up device 14. This raw sheet is again placed in the delivery device 10 and is coated with the magnetic coating material consisting of flaky high-permeability magnetic metallic powder, such as 'permalloy (R)'and having the coercive force of eta40000e by the coating head 11. Magnetic field orientation of 6000e is applied thereon by an orienting magnetic field generator 12 consisting of a solenoid coil and thereafter, the raw sheet is dried by the drying device 13, by which the second magnetic layer having the thickness of 10mum is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, such as a prepaid card, which is required to have high security against unauthorized use such as forgery and alteration.
In particular, the present invention relates to a method of manufacturing a magnetic recording medium which is formed by laminating a plurality of magnetic layers, and in which at least one magnetic layer has a fixed pattern that cannot be rewritten.

[0002]

2. Description of the Related Art With the spread of magnetic cards such as prepaid cards that have rapidly spread in recent years, there is a strong demand for safety against unauthorized use such as forgery and alteration. As a means for improving the safety of a magnetic recording medium, it has been proposed to add identification information unique to the medium, which is difficult to rewrite, to a location different from the normal magnetic recording / reproducing area. Specifically, Japanese Patent Publication Sho 49
Japanese Patent Laid-Open No. 37529/1975, a method of providing a magnetic pattern by regularly changing the arrangement direction of the easy axis of magnetization of needle-like magnetic powder with respect to the reading direction of the medium, and Japanese Patent Laid-Open No.
As disclosed in Japanese Patent No. 79311, a magnetic paint in which magnetic particles are dispersed is applied under the action of a magnetic field of information normally magnetically recorded in a magnetic layer to physically orient the orientation of the magnetic particles dominated by the information in the lower layer. Or the fixed information is used for identification, or the information magnetically recorded in a normal magnetic layer has a coercive force of 4500 Oersted or more as described in JP-A-5-318974. There is known a method of imparting to a medium information which is difficult to be rewritten by a magnetic head which is usually used, by transferring the magnetic layer having a high coercive force to a magnetic layer.

[0003]

However, as in Japanese Patent Publication No. 49-37529, a method of providing a magnetic pattern by regularly changing the arrangement direction of the easy axis of magnetization of the needle-shaped magnetic powder with respect to the reading direction of the medium. Has a drawback that the manufacturing cost and the cost of the reading device are increased because the reading requires special parts and devices and a special orientation device for manufacturing. On the other hand, among the methods for transferring the unique information to the magnetic layer having a high coercive force, the method disclosed in Japanese Patent Laid-Open No. 50-79311 has a drawback that the identification output is low. As will be described below, it has been found that this drawback can be solved by using an orienting magnetic field according to the present invention, but it is presumed that the orienting magnetic field will have a detrimental effect on the transfer of fixed information in the method of the publication. It should have been done, but it gives surprisingly good results. Further, in Japanese Unexamined Patent Publication No. 5-318974, when a magnetic head having a core material of a magnetic material having a saturation magnetic flux density of about 22 kilogauss, such as an Fe-Co alloy, is used, a high coercive force up to about 8000 Oersted is obtained. It is well known that the magnetic layer can be rewritten sufficiently, and in the above-mentioned conventional technique, the magnetic layer having a higher coercive force is arranged closer to the magnetic head than the ordinary magnetic layer. Since it is exposed to a strong magnetic field, there has been a problem that there is a high risk of falsification and forgery of the medium due to rewriting of the unique information. Further, in this method, not only is it difficult to transfer a signal to a magnetic layer having magnetic particles having a coercive force of 4500 oersteds or more, but also a magnetic particle having an ultra-high coercive force generally has a low saturation magnetization amount, and thus a read output of a transfer signal is performed. It also had the drawback of being low.
It has been found according to the invention that this drawback is solved by using magnetic particles of low coercivity.

[0004]

In order to solve the above-mentioned problems, the present invention is a method for manufacturing a magnetic recording medium comprising at least two magnetic layers laminated on a non-magnetic substrate. A first magnetic layer made of a magnetic material capable of magnetic recording is formed on a substrate, and then a predetermined signal is magnetically recorded on the first magnetic layer, and then a magnetic substance having a coercive force of 4000 oersted or less is placed in a binder. A magnetic coating material prepared by dispersion is applied, and before the magnetic coating material is dried and solidified, a DC orientation magnetic field having a magnetic field strength lower than the coercive force of the first magnetic layer and having a substantially constant direction on the application surface is applied. By applying a direct current orientation treatment and then drying and solidifying the magnetic paint, a non-rewritable fixed signal formed by the influence of the magnetic field recorded on the first magnetic layer and the orientation magnetic field is applied to the second magnetic layer. Forming to provide a method of manufacturing a magnetic recording medium characterized. Conveniently, the orienting means for orienting the second magnetic layer is at least partially provided in the drying means for drying the second magnetic layer. In order to obtain the effects intended by the present invention, it is essential to use a direct-current directing magnetic field in a constant direction. A direct-current orientation magnetic field by a homopolar facing magnet that has been conventionally used for magnetic orientation causes reversal in the magnetic field applied to the magnetic particles, so that the desired effect cannot be sufficiently obtained.

[0005]

According to the method of the present invention, a non-rewritable fixed pattern is formed on the second magnetic layer. For that purpose, first, a signal for producing a fixed pattern, which is alternately magnetized with different polarities, is recorded in the first magnetic layer. The second magnetic coating material is applied onto the first magnetic layer, and a direct current in a predetermined direction, which is as constant as possible, is applied before drying. When the direction of the signal magnetic field generated from the first magnetic layer and the direction of the orientation magnetic field are the same, the two strengthen each other and the strength of the magnetic field applied to the second magnetic layer 4 becomes strong, while the directions of both are opposite. The magnetic fields of the two cancel each other out in the direction, and the strength of the magnetic field applied to the second magnetic layer becomes weak. Therefore, the magnetic particles in the fluidized state are concentrated in a place where the magnetic field is strong. Therefore, when dried in this state, the magnetic particles are concentrated in the second magnetic layer and the content ratio of the magnetic particles is high.
Therefore, a portion having a high magnetic output per unit area and a portion having a low magnetic particle content rate and thus a low magnetic output per unit area are alternately formed. In this way, the first
The signal pattern recorded on the magnetic layer is reproduced in the second magnetic layer as a fixed pattern encoded by the difference in magnetic output per unit area.

[0006]

The present invention will be described in detail below with reference to the accompanying drawings. FIG. 5 is a sectional view showing an example of a magnetic recording medium manufactured by the manufacturing method according to the present invention. In FIG. 5, the magnetic recording medium 1 is composed of a non-magnetic substrate 2, a first magnetic layer 3 and a second magnetic layer 4. The second magnetic layer 4 is formed of a magnetic paint in which a ferromagnetic powder having a coercive force of 4000 oersted or less is dispersed in a polymer resin binder. The second magnetic layer 4 has a portion 4a having a high magnetic particle content and thus a high magnetic output per unit area, and a portion 4b having a low magnetic particle content and thus a low magnetic output per unit area. Is provided with non-rewritable fixed patterns alternately formed with predetermined dimensions.

The non-magnetic substrate 2 is made of polyethylene terephthalate (PET), hard vinyl chloride (PVC), synthetic paper,
Materials used for ordinary magnetic cards, magnetic tapes, magnetic sheets, etc. such as paper are used. The first magnetic layer 3 may be the same as a coating for a magnetic recording medium such as a normal magnetic card or a magnetic tape, and is made of a known magnetic material such as Co-adhered γFe ₂ O ₃ , Ba ferrite, Sr ferrite. Chosen,
It is formed by a known method to have a thickness of about 4 to 20 μm. However, the coercive force of the magnetic material used for the first magnetic layer 3 needs to be higher than the orientation magnetic field applied when the second magnetic layer 4 is formed, and may be 600 oersted or more. preferable.

On the first magnetic layer 3, a magnetic paint having the same or different structure as that thereof and having a coercive force of 4000 oersted or less dispersed in a polymer resin binder is applied and coated. A second magnetic layer 4 formed by drying is provided. When applying and drying the second magnetic layer 4, it is necessary that a predetermined signal is magnetically recorded at a predetermined position on the first magnetic layer 3. This signal represents identification information such as a number for specifying the medium. For example, a magnetic head is used so that the polarity of the residual magnetization in a predetermined region is alternately inverted with respect to the traveling direction of the medium. It is formed by magnetic recording. The identification signal is R
It is encoded by a known method such as Z, FM, PM, MFM or PWM.

FIG. 1 is a schematic sectional view showing an example of a method for manufacturing a magnetic recording medium of the present invention. First, the delivery device 10
The coating head 11 is applied to the non-magnetic substrate roll sent out from
To apply the first magnetic layer, and then the orientation magnetic field generator 1
2. The first magnetic layer is formed through the tunnel dryer 13. A predetermined signal is magnetically recorded on the first magnetic layer by the magnetic head 15 before being wound by the winding device 14. Next, the original roll on which the first magnetic layer is formed is again fed from the feeding device 10, the second magnetic layer is coated by the coating head 11, and then the orientation magnetic field generating device 12,
It is taken up by the winding device 14 through the tunnel drying device 13. Particularly, as the orientation magnetic field generator 12 used when applying the second magnetic layer, it is desirable that the magnetic field direction does not change with respect to the application surface during passage, and a solenoid coil or a magnet as shown in FIG. 3 is used. Is preferred. In the above method, it is preferable that the first magnetic layer has the above-mentioned magnetic field orientation, but this is not a necessary condition. The recording of the signal on the first magnetic layer is not limited to being performed immediately after the first magnetic layer is applied and dried, and may be performed immediately before the application of the second magnetic layer. It is also possible to separately provide only the step of recording.

FIG. 2 is a schematic cross-sectional view showing another example of the method for manufacturing a magnetic recording medium of the present invention.
1 is the same as that in FIG. 1, but a part thereof is provided in the tunnel dryer 13.

FIG. 4 is a schematic diagram showing a process of forming a non-rewritable fixed pattern on the second magnetic layer by the method of the present invention. FIG. 4- (a) shows a state before the second magnetic layer 4 is applied, and the first magnetic layer 3 has alternating polarities with different polarities as shown by the arrow directions. A signal for producing a magnetized fixed pattern is recorded with a predetermined size. FIG. 4- (b) shows the first magnetic layer 3
Is a schematic representation of the strength of the magnetic field applied to the second magnetic layer 4 when a second magnetic coating material is applied on top of it and an orientation magnetic field in a predetermined direction is applied before drying. . Reference number 5
At the position indicated by a, the direction of the signal magnetic field generated from the first magnetic layer 3 and the direction of the orientation magnetic field (indicated to the right in FIG. 4- (b)) match, so the magnetic field applied to the second magnetic layer 4 is the same. Are stronger than each other, and at the location indicated by reference numeral 5b, the direction of the signal magnetic field generated from the first magnetic layer 3 and the direction of the orientation magnetic field cancel each other out, and The strength of the applied magnetic field is weak. That is, in the second magnetic layer 4, the strong magnetic field portions 5a and the weak magnetic field portions 5b appear alternately according to the signal pattern recorded in the first magnetic layer 3. Since the magnetic particles in the fluidized state are concentrated in the place where the magnetic field is strong, the magnetic particles in the second magnetic paint are
As shown in (c), the magnetic field concentrates on the portion 5a to which a strong magnetic field is applied. When dried in this state, the magnetic particles are concentrated in the second magnetic layer 4 and the content of the magnetic particles is high. Therefore, the portion 4a where the magnetic output per unit area is high and the content of the magnetic particles is low. The portions 4b having a low magnetic output per unit area are formed alternately. In this way, the signal pattern recorded in the first magnetic layer 3 is duplicated in the second magnetic layer 4 as a fixed pattern encoded by the difference in magnetic output per unit area.

As described above, it is particularly preferable to use a solenoid coil that does not reverse the polarity of the magnetic field during passage as the orienting device used when forming the second magnetic layer. Generally, as an orienting device for a magnetic recording medium, a device in which the same poles of permanent magnets are arranged parallel to each other is often used. However, this device is not suitable for use in the manufacturing method of the present invention because the polarity of the orientation magnetic field is reversed on the way. Further, the magnetic particles aggregated while passing through the aligning device tend to become random again because the force for holding the magnetic particles after passing through the aligning device is weakened. Therefore, it is particularly preferable to dry under the condition that the orientation magnetic field is applied. However, in order to maintain the aggregated state of the magnetic particles, a low magnetic field of several hundred Oersted or less is sufficiently effective.

The magnetic powder used in the second magnetic layer 4 may be any that can be magnetized by the magnetic field generated from the signal recorded in the first magnetic layer 3, such as permalloy, sendust, and amorphous. Scale-like high magnetic permeability magnetic metal powder, soft magnetic metal powder such as iron powder, and Mn-Zn, Ni
Soft magnetic ferrite powder such as -Zn can be used. When these magnetic materials are used, since the residual magnetization does not occur in the fixed pattern portion after reading, it is impossible to visually observe the fixed pattern with a magnetic developer or the like.
It is also particularly preferable because it has a special effect of magnetically shielding the magnetic information recorded in the first magnetic layer. Also γ
Even for materials used for magnetic recording, such as Fe ₂ O ₃ , Co-deposited γFe ₂ O ₃ , and Ba ferrite, the fluidity of the magnetic particles in the paint state is high, and the strength of the orientation magnetic field is appropriately selected. As a result, magnetic particles are concentrated by the signal magnetically recorded on the first magnetic layer 3. The coercive force of a magnetic paint in a fluid depends on the shape of the magnetic particles, but is generally much lower than the coercive force after being dried and solidified.
Therefore, the coercive force of the second magnetic layer 4 after drying need not be lower than the coercive force of the first magnetic layer 3 after drying. However, when the second magnetic layer 4 is magnetized and read, a sufficient read output cannot be obtained unless the second magnetic layer 4 is easily magnetized. The upper limit of coercive force is 4000 Oersted.

The following method is used to read the fixed pattern of the magnetic recording medium manufactured by the manufacturing method of the present invention. First, the fixed pattern forming signal recorded in the first magnetic layer 3 is DC erased. Next, while generating a bias magnetic field from the read head (not shown), the second
The fixed pattern portion formed on the magnetic layer 4 is scanned.
At this time, since the magnetic resistance changes at the boundary between the portion 4a having a high magnetic output per unit area of the second magnetic layer 4 and the portion 4b having a low magnetic output, an output waveform proportional to the change of the magnetic flux is generated in the coil of the read head. To do. In this way, the fixed pattern formed at the predetermined location on the second magnetic layer 4 can be read. Moreover, since this fixed pattern is formed as a difference in the physical structure of the magnetic layer, it cannot be erased or rewritten by the magnetic head at all.

The method according to the present invention is not limited to the above-mentioned example, and a colored concealing layer, a printing layer, a protective layer, etc. may be appropriately provided on the second magnetic layer, and a printing layer may be provided if necessary. It is clear that it is okay. Further, for example, in a magnetic recording medium having three or more magnetic layers, it is apparent that the above-mentioned non-rewritable fixed pattern can be formed in any magnetic layer other than the first magnetic layer formed. Further, for a card in which at least a first magnetic layer and a second magnetic layer including a non-rewritable fixed pattern are formed by a method described above on a substrate coated with a release agent such as silicon, and an adhesive is coated thereon. It can also be applied to a method of manufacturing a transfer tape.

Hereinafter, the present invention will be described in more detail with reference to specific examples. Example 1 A Ba ferrite magnetic powder having a coercive force of 2750 Oersted is mixed and dispersed with a binder resin, a dispersant, a curing agent, and other additives and a solvent on the entire surface of one side of a white polyester film substrate having a thickness of 188 μm. The magnetic paint prepared by applying the gravure method, the thickness after drying is 8μm
The first magnetic layer of was formed. In a predetermined area of the first magnetic layer, a continuous signal having a recording density of 25 FCI and 400 FCI and an FM-modulated signal of 105 BPI were saturation recorded. A magnetic coating material prepared by mixing and dispersing a scale-like powder of a high magnetic permeability Fe-Si alloy having a coercive force of 20 Oersted or less with a binder resin, a dispersant, a curing agent, and other additives and a solvent. Was applied by a knife coating method, and immediately thereafter, a magnetic field orientation having a maximum strength of 600 oersted was applied by an orientation device using a solenoid coil, and then dried by a drying device to form a second magnetic layer having a thickness of 10 μm.

(Embodiment 2) The same as Embodiment 1 except that a part of the solenoid coil for carrying out the orientation treatment on the second magnetic layer is arranged in the drying device.

(Example 3) A signal was recorded on the first magnetic layer manufactured by the same method as in Example 1 by the same method as in Example 1. In addition, γFe ₂ with a coercive force of 300 oersted
A magnetic paint prepared by mixing and dispersing O ₃ with a binder resin, a dispersant, a curing agent, and other additives and a solvent is applied by a gravure method, and immediately after that, a maximum orientation of 1000 Oersted is obtained with an orienting device using a solenoid coil. Magnetic field orientation,
Then, it was dried by a drying device to form a second magnetic layer having a thickness of 8 μm.

(Embodiment 4) The same operation as in Embodiment 3 is carried out except that a part of the solenoid coil for carrying out the orientation treatment on the second magnetic layer is arranged in the drying apparatus.

(Comparative Example 1) In Example 1, before applying and drying the second magnetic layer, a magnetic field orientation with a maximum strength of 600 oersted was performed with an orientation device in which the same poles of permanent magnets were arranged in parallel and opposite each other. The same procedure as in Example 1 was carried out except that it was applied.

(Comparative Example 2) In Example 3, before applying and drying the second magnetic layer, a magnetic field orientation with a maximum strength of 1000 oersted was performed with an orientation device in which the same poles of permanent magnets were arranged in parallel and opposite each other. Same as Example 3 except that it was applied.

The magnetic sheets produced in Examples 1 to 4 and Comparative Examples 1 and 2 were punched out to a size of 86 × 54 mm to produce magnetic cards, which were read by the following method. First, the signal written in the first magnetic layer was DC erased by a reader / writer equipped with a magnetic head capable of saturation writing a magnetic medium having a coercive force of 2750 Oersted. Next, a bias current is applied to a read head having a bias coil attached to the same reader / writer to apply a bias magnetic field of about 800 oersted from the front gap of the head while reproducing output (peak-pee) of each card.
ak) was read. 25 FCI and 40 for each card
Table 1 shows a list of the reproduction output level of the 0 FCI continuous signal and the demodulation result of the 105 BPI FM signal.

[0023]

[Table 1]

In each of Examples 1 to 4, 25 FCI
And 400 FCI signal, a sufficient output level is obtained,
The 105 BPI modulated signal also had a good SN ratio and could be demodulated without any problem. Further, comparing Examples 1 and 2 with Comparative Example 1 and Examples 3 and 4 with Comparative Example 2, the effectiveness of applying orientation with a solenoid coil when applying the second magnetic layer and in a drying device The effectiveness of applying the orientation was confirmed.

[0025]

As described in detail above, according to the method of manufacturing a magnetic recording medium of the present invention, the first magnetic layer is the second magnetic layer of the magnetic recording medium in which at least two magnetic layers are laminated. The non-rewritable fixed pattern formed by the influence of the signal magnetic field and the orientation magnetic field magnetically recorded on the disk can be permanently recorded. If this fixed pattern is used as identification information for identifying the medium, the pattern cannot be rewritten by a medium processing device or the like, and there is no choice but to destroy the medium in order to erase it. It is possible to supply a magnetic recording medium that is extremely safe against changes and alterations. Further, the method of the present invention can manufacture a medium at a low cost without requiring a special material or a complicated process, as compared with a conventional method in which a fixed signal such as a magnetic barcode or an optical barcode is provided by printing or the like. It also has the feature.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a method for manufacturing a magnetic recording medium of the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of the method for manufacturing a magnetic recording medium of the present invention.

FIG. 3 is a diagram showing another example of an apparatus for generating a DC orientation magnetic field that can be used in the present invention.

FIG. 4 is a schematic view showing a method of the present invention, (a) shows a step of forming a first magnetic layer, (b) shows a step of forming a second magnetic layer, and (c). Indicates a state in which magnetic particles are alternately present at different densities as a result of step (b).

FIG. 5 is a cross-sectional view of a magnetic recording medium obtained by the method of the present invention.

[Explanation of symbols]

1: magnetic recording medium 2: non-magnetic substrate 3: first magnetic layer 4: second magnetic layer 4a: high content of magnetic particles and high magnetic output per unit area 4b: content of magnetic particles A portion having a low magnetic output per unit area 10: Sending device 11: Coating head 12: DC magnetic field generating device 13: Tunnel drying device 14: Winding device 15: Magnetic head

Claims (3)

[Claims] 1. A method of manufacturing a magnetic recording medium comprising at least two magnetic layers laminated on a non-magnetic substrate, wherein a first magnetic layer made of a magnetic material capable of magnetic recording is first formed on the non-magnetic substrate. And then magnetically recording a predetermined signal on the first magnetic layer, and then applying a magnetic paint prepared by dispersing a magnetic material having a coercive force of 4000 oersted or less in a binder, and drying the magnetic paint. Before being solidified, it has a magnetic field strength lower than the coercive force of the first magnetic layer and is subjected to a DC orientation treatment with a DC orientation magnetic field in a substantially constant direction on the coating surface, after which the magnetic coating material is dried and solidified. By doing so, a non-rewritable fixed signal formed due to the influence of the magnetic field and the orientation magnetic field due to the signal recorded in the first magnetic layer is formed in the second magnetic layer. . 2. The orienting means for orienting the second magnetic layer is at least partially provided in a drying means for drying the second magnetic layer. 1. The method for manufacturing a magnetic recording medium according to 1. 3. The method of manufacturing a magnetic recording medium according to claim 1, wherein the orientation magnetic field for orienting the second magnetic layer is applied by a solenoid coil.