JPH09244556A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which indicates the brightness and darkness by the parts impressed with magnetism and the parts not impressed with the magnetism on a magnetic recording layer and is capable of reversibly displaying bright images having high resolution and the excellent sensitivity and contrast of printing recording and the images having excellent stability. SOLUTION: This magnetic recording medium is constituted by dispersing and arranging the microcapsules 14, into which flaky magnetic particles having coercive force of at least <=50Oe (measured magnetic field: 5kOe) and dispersion media formed by dispersing these particles and exhibiting a solid phase state at ordinary tap. are included, into a binder 15, thereby forming a magnetic recording layer. Further, the particle size of the flaky magnetic particles is made smaller and the aspect ratio thereof made larger, by which the contrast in the microcapcules is increased, the rotation (orientation) in the microcapsules is facilitated and the sensitivity is improved.

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 for displaying a pattern such as an image by applying a magnetism with heating, and more particularly, a reversible magnetic recording medium excellent in contrast, sensitivity, resolution and image stability. Regarding the body

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium utilizing magnetism, a magnetic field is applied to a suspension in which magnetic particles are dispersed in a coloring dispersion medium, as described in, for example, JP-A-48-56393. By doing so, a method is known in which the magnetic particles are moved to change the color of the colored dispersion medium and display is performed.

However, in such a magnetic recording medium, when the suspension is sealed between two substrates and one of the substrates draws characters and patterns with a magnetic pen to apply magnetism, the magnetic particles of the suspension are attracted. Although the characters and patterns are obtained as they are, since the specific gravity of the magnetic particles is much larger than that of the dispersion medium, the attracted magnetic particles have the drawback that the characters and patterns cannot be retained for a long time because they settle with time. .

Further, since all the magnetic particles magnetized by the magnetic pen are attracted to the magnetic pen, the magnetic particles existing apart from the magnetic pen are also attracted, so that only unclear characters and patterns are obtained. It also had drawbacks. In order to prevent sedimentation of magnetic particles, for example, if the magnetic particles are made finer or the magnetic particles are coated with a polymer having a low specific gravity, and the apparent specific gravity of the magnetic particles approximates that of the dispersion medium, the magnetic particles Since the force becomes extremely small, it becomes difficult to be sucked by the magnetic pen, which causes a defect that it is not possible to obtain a clear character or pattern with high density.

Further, if the apparent specific gravity of the magnetic particles is approximated to that of the dispersion medium, the magnetic particles are difficult to be attracted to the opposite side of the substrate even when characters and patterns are erased, and the particles cannot be completely erased. Repeatedly, it turned black overall, which was not practical.

As a mode for solving these drawbacks, for example, Japanese Patent Publication No. 57-27463 and Japanese Patent Laid-Open No. 62-53.
As described in Japanese Patent No. 359, as a dispersion medium,
By using a liquid that has a yield value of a certain value or more, or by using a thickener, clear and high-contrast characters and images without blur can be displayed, and the display can be kept stable for a long time, and erasure can be completed completely. There are known magnetic recording media that can be neatly cleaned.

However, this magnetic recording medium is formed by forming honeycomb cells each having a side and a depth of about 2 mm on the entire surface of a transparent plastic sheet, and the magnetic particles and the white pigment are contained in the cells. The suspension was injected into a dispersion medium, and the suspension was sealed with a transparent sheet, which had the following drawbacks. That is, since the image is formed by moving the magnetic particles from the back surface to the front surface in the honeycomb-shaped cell, it is impossible to make the resolution of the image smaller than that of the honeycomb-shaped cell. Further, it is difficult to form honeycomb cells, to make the honeycomb cells large or very small, and to inject a suspension into the honeycomb cells.

As another form, for example, Japanese Patent Laid-Open No. Hei 2
As described in JP-A-146082 and JP-A-4-233581, unlike a magnetic recording medium in which magnetic particles and pigments are sealed in a honeycomb-shaped cell as described above,
A magnetic recording medium is known in which magnetic particles are enclosed in microcapsules and coated on a support. According to this method, the resolution can be increased by controlling the particle size of the microcapsules, and the manufacturing process is easy. Further, various films and the like can be selected as the substrate on which the microcapsules are applied, and the shape and size can be freely selected.

However, the image formation shown here is performed by the following method. First, the permanent magnet attracts the light-absorbing magnetic particles in the microcapsule to the back surface side of the magnetic recording medium, and the light-reflecting non-magnetic particles remain on the surface of the magnetic recording medium. It becomes the color of non-magnetic particles and is in an erased state. Then, by applying and recording magnetism from the surface of the magnetic recording medium by a permanent magnet, the light-absorbing magnetic particles are magnetically attracted to the surface, and desired characters and images are formed. Therefore, in such image formation, it takes a long time to attract the magnetic particles, resulting in a magnetic recording material having poor sensitivity.

Further, as another embodiment utilizing the microcapsules, for example, JP-A-1145637, JP-A-63-153197, JP-B-4-7518, JP-A-6-79986 and JP-A-6-79986. 6-9206
No. 8, or Eyne S. Trumble
P. S. & E. 7 213 (1963), there is known a magnetic recording medium in which light-absorbing magnetic particles and light-reflecting non-magnetic particles are encapsulated in microcapsules.

In the image forming method of this embodiment, first, when the magnetic recording medium is manufactured, the magnetic particles in the coated capsules are orientated in advance in parallel with the plane of the magnetic recording medium so that all the incident light is reflected to make it appear bright. Next, magnetic recording causes magnetic particles to rotate and scatter incident light.
It becomes absorbed, and contrast is generated, and a black image is formed.

However, the magnetic recording material thus obtained has a magnetic force over a wide range, and therefore has a resolution extremely inferior to that of recording by other heat or light. Furthermore, since the magnetic recording medium can be easily printed and erased by magnetic force, the image may be fogged in the unprinted portion or the image may be erased by just touching the magnet. It has the drawback of poor stability.

Therefore, the present applicant has the following drawbacks.
For example, JP-A-7-29145 and JP-A-7-291
46, JP-A-7-104685, JP-A-7-
No. 129104, etc., microcapsules encapsulating at least flake-shaped magnetic particles and a dispersion medium that is in a solid state at room temperature and is formed by dispersing the flaky magnetic particles on a support made of a non-magnetic material. We have proposed a magnetic recording medium that is dispersed in a binder to form a magnetic recording layer.According to this, the flaky magnetic particles in the microcapsules disperse the magnetic recording layer except when recording or erasing an image. The dispersion medium is in a solid state and the flaky magnetic particles do not move even when affected by a magnetic field due to external magnetism, so fogging and image deletion do not occur in the unprinted area. The above problem is solved.

[0014]

However, when the coercive force of the flake-shaped magnetic particles used in the above-mentioned magnetic recording medium is large, it is necessary to increase the applied magnetic field at the time of recording / erasing. The magnetic recording layer has a problem that the response to a magnetic field becomes slow when the coercive force is large, and the recording sensitivity to the magnetic recording layer formed by dispersing in a binder in a microcapsule is deteriorated. The microcapsules arranged in the recording layer have a large size (particle size, thickness, etc.) of the flake-shaped magnetic particles, and the size of the microcapsules also increases. There is a problem that the movement of the particles becomes slow and the sensitivity and contrast of print recording are lowered.

Therefore, according to the present invention, microcapsules are obtained by making flaky magnetic particles, which display an image by the darkness and darkness of a portion to which a magnetic field is applied to the magnetic recording layer, into a low coercive force material and small pieces. Because of its small size and fast reactivity to the magnetism of flaky magnetic particles, it has a high resolution and a clear image with excellent print recording sensitivity and contrast, and reversible display with excellent image stability. It is intended to provide a magnetic recording body.

[0016]

The present invention has been made to achieve the above object, and the invention described in claim 1 has a coercive force of 50 Oe or less on a support made of a nonmagnetic material. (Measurement magnetic field: 5 kOe) Flake-like magnetic particles and a dispersion of the particles have a viscosity of 10 at room temperature.
0000 cps or more, and viscosity when heated is 500
A magnetic recording medium is characterized in that microcapsules containing a dispersion medium of 0 cps or less are dispersed in a binder to form a magnetic recording layer.

According to a second aspect of the present invention, in the magnetic recording medium according to the first aspect, the average major axis of the flaky magnetic particles is 5 μm.
It is characterized in that it is between m and 50 μm, and the average thickness is between 0.1 μm and 3 μm.

According to a third aspect of the present invention, in the magnetic recording medium according to the first aspect, the average particle size of the microcapsules is 10 μm.
It is characterized by being between m and 100 μm.

According to a fourth aspect of the present invention, in the magnetic recording medium according to the first aspect, a protective layer is formed on the magnetic recording layer.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. 1 is a sectional view showing an embodiment of a magnetic recording medium of the present invention, FIG. 2 is a sectional view showing an embodiment of a microcapsule used in the magnetic recording layer of the present invention, and FIG. 3 is a sectional view of the present invention. 5 is a cross-sectional view showing an unrecorded state (the flake-shaped magnetic particles are in the horizontal direction) of the magnetic recording medium of FIG. is there.

FIG. 1 shows the structure of the magnetic recording medium 1 of the present invention, in which a magnetic recording layer coated with a coating material in which a support 11 and microcapsules 14 containing flaky magnetic particles are dispersed in a binder 15. 12 and the protective layer 13 are sequentially stacked.

FIG. 2 is a sectional view showing an embodiment of the microcapsules 14 used in the magnetic recording layer 12 in the present invention. The microcapsule 14 has a core substance 21 mainly composed of suspension dispersed in a dispersion medium (for example, wax) 23 in which flake-shaped magnetic particles 22 are in a solid state at room temperature, and a shell substance 24 made of a polymer or the like.
The configuration is encapsulated in.

The flake-shaped magnetic particles 22 have a low coercive force (coercive force of 50 Oe or less: measurement magnetic field of 5 kOe) and a high contrast color tone, for example, iron (Fe) -silicon (Si) type amorphous, iron-nickel alloy. Therefore, in order to increase the affinity with organic solvents and the like, those subjected to fatty acid treatment, higher ester treatment, silane coupling treatment, coating treatment with various resins, and the like are used. By this treatment, the flaky magnetic particles 22 can be stably dispersed in the dispersion medium without coming out of the wall of the microcapsule 14 or the outside of the microcapsule 14. The flake-like magnetic particles 22 used here have a low coercive force and thus have excellent responsiveness to a magnetic field, excellent mobility (rotation, orientation) in the microcapsules, and high sensitivity. Furthermore, the size of the flake-shaped magnetic particles 22 is set to have an average major axis of 5 to 50 μm.
(Particularly, particles larger than the desired microcapsule diameter should be cut in advance.), Average thickness 0.1 to 3
By increasing the μm and average aspect ratio to 80,
Mobility (rotation, orientation) is improved and high contrast is obtained. When the average major axis is less than 5 μm and when the average thickness is more than 3 μm, the difference in the reflectance of light when oriented in the horizontal direction and the vertical direction is small, and the contrast is lowered. If the average major axis exceeds 50 μm,
Although it depends on the microcapsule diameter, the movement inside the microcapsule becomes slow and the response speed becomes slow. If the average thickness is less than 0.1 μm, the flake-shaped magnetic particles become weak, the flake-shaped magnetic particles are damaged by repeated recording and erasing, the image cannot be displayed accurately, and the contrast is lowered. Note that a metal such as aluminum may be vapor-deposited in order to increase the surface reflectance of the flaky magnetic particles and increase the contrast. In the production of the flaky magnetic particles 22, for example, fine particles are formed into flakes by an atomizer or a hammer mill.

The dispersion medium 23 is at room temperature (about 10-35).
Viscosity range of 100,000 cps or more,
And, if it is heated to room temperature or higher (in the range of about 40 to 100 ° C.), the temperature may be 5000 cps or less,
For example, organic compounds such as paraffin wax, carnauba wax, natural wax or carboxylic acid wax,
Commonly known substances such as fatty acid esters, synthetic waxes such as petrolatum, natural resins and synthetic resins that satisfy the above conditions can be used alone or in combination.

Further, a hydrophobic solvent such as an aliphatic hydrocarbon, an aromatic hydrocarbon or an alicyclic hydrocarbon which is a liquid substance at room temperature in the above organic compound, such as an alkylated biphenyl or an alkylated naphthalene, or an aliphatic acid ester. Aromatic acid ester, alcohol ester, oxy acid ester, for example, polar solvents such as dimethyl phthalate and dioctyl sebacate may be mixed and used. By mixing these, the volume change of the dispersion medium due to temperature change can be suppressed, so there is little volume change between normal temperature and heating during recording / erasing, and the shape of the magnetic recording medium is reduced. In particular, the smoothness of the surface can be maintained.

When a liquid substance at room temperature is mixed as the dispersion medium, a thermoplastic resin such as polyvinyl chloride, polyvinyl butyral, polymethacrylic acid ester, polyvinyl acetate, ethyl cellulose or acetyl cellulose may be added. . During the microcapsule production process (generally performed in a heated state) due to the addition of a thermoplastic resin, it exhibits a certain degree of viscosity, so that flaky magnetic particles with a large specific gravity go out of the microcapsule wall or the microcapsule. Without, it can be stably dispersed in the dispersion medium, and the microcapsules can be stably manufactured. A coloring agent (not shown) made of a pigment or a dye may be added to the dispersion medium 23 for coloring.

The colorant in this case comprises a pigment or a dye, and is used as a pigment alone, a mixture of several pigments, a mixture of a pigment and a polymer, a dye alone, a mixture of several dyes and the like. For example, in the case of a pigment, fine particles such as an inorganic pigment such as titanium dioxide, zinc sulfide, lead titanate, zirconium oxide, lead white, cadmium red, or cadmium yellow, or an organic pigment such as a phthalocyanine pigment (for example, the size is 1 nm to 1 μm), and in the case of dyes, various known dyes such as azo dyes, quinoline dyes and phthalocyanine dyes can be used. When the pigment or dye is used as a mixture with the polymer as the colorant, the pigment or dye and the polymer are kneaded and then pulverized. Alternatively, the colorant may be prepared by a method of polymerizing a pigment or a dye using a method such as emulsion polymerization, suspension polymerization or dispersion polymerization of a monomer. In this case, the polymer should be crosslinkable. Is preferred.

The core substance 21 containing the above-mentioned flaky magnetic particles 22, the dispersion medium 23 and the like as main components is covered with a shell substance 24 such as a polymer to be microencapsulated. This shell substance 2
Examples of the resin used as 4 include commonly used resins such as acrylic resin, methacrylic resin, polystyrene, polyester resin, polyurethane resin, polyurea resin, polyamide resin, epoxy resin, and natural resin. It is also possible to use them alone or in combination of two or more.

Microcapsules 1 having the above-mentioned shell material
The production method of 4 is a phase separation method in which a concentrated phase of the polymer is separated around the core substance dispersed in the polymer solution, and a liquid for curing the polymer around the core substance in the polymer solution with a curing test agent for the polymer or the like. Medium-cure coating method, in-situ polymerization method in which the surface of the core material is covered with a polymer by supplying a monomer or a polymerization catalyst from either one of the emulsion in which the core material is dispersed, or the external phase, and the emulsion in which the core material is dispersed. A microencapsulation technique such as an interfacial polymerization method in which a monomer is supplied from both the internal phase and the external phase is suitable, but the method is not limited to these methods.

In particular, the flake-shaped magnetic particles 22 as the core substance 21 are uniformly dispersed in the dispersion medium 23 by the in-situ polymerization method in which the monomer is supplied from the outer phase of the suspension, or by the phase separation method to produce particles. It is possible to manufacture the microcapsules 14 having uniform diameters and in which the flake-shaped magnetic particles 22 can be easily moved. The polymerizable monomer used here is preferably acrylic acid ester, methacrylic acid ester, styrene and its derivatives, isocyanate, various amines, compounds having an epoxy group, and the like.

Next, in the magnetic recording medium 1 of the present invention, as shown in FIG. 1, the microcapsules 14 having the above-mentioned structure are coated on a support 11 together with a binder 15 to form the magnetic recording layer 1.
2 is formed, and the protective layer 13 is further laminated to produce the layer.

The support 11 is a synthetic resin such as polyvinyl chloride, polyester, polycarbonate, polymethylmethacrylate, polystyrene, polyethylene terephthalate, natural resin, paper, synthetic paper, metal, ceramics, etc., alone or in combination. Can be used. In addition, its shape can be selected according to the application such as a card shape or a sheet shape, a film shape, and further considering the physical properties required according to the application, for example, strength, rigidity, hiding power, light opacity, etc. It can be appropriately selected.

As the binder 15 in which the microcapsules 14 are dispersed, a water-based binder, a solvent-based binder, an emulsion-based binder or the like is appropriately used.
Further, as the protective layer 13, an epoxy resin, tetrafluoroethylene, or the like, or a synthetic resin such as polyvinyl chloride, polyester, polycarbonate, polymethyl methacrylate, polystyrene, or polyethylene terephthalate,
Natural resin or the like can be used. The protective layer 13 needs to hold the microcapsules 14 formed on the support 11 and have a light-transmitting property such that the flaky magnetic particles 22 in the microcapsules 14 can be seen from the outside. Any material can be used as long as it satisfies necessary conditions such as strength.

The protective layer 13 may be colored in a range that does not affect the display / reading of the lower magnetic recording layer, or may be provided with a light-transmitting colored layer (not shown). For coloring the protective layer, mix a pigment or dye,
When a colored layer (not shown) is provided, a pigment or dye dispersed or dissolved in a binder or the like is applied and formed between the magnetic recording layer 12 and the protective layer 13.

The magnetic recording layer 12 and the protective layer 13 may be formed by a known printing method such as offset printing, gravure printing, silk screen printing, or roll coating or knife-edge coating. Method, a transfer method using a transfer sheet having a transfer layer containing the microcapsules 14 described above, an ink jet method in which the ink containing the microcapsules 14 described above is sprayed on a substrate, and between the support 11 and the protective layer 13. It can be manufactured by a forming method such as a method of filling a solution in which the microcapsules 14 are mixed, and can be appropriately selected from the above methods according to the use and quantity of the information recording medium to be manufactured.

Next, a method of forming a display image on the magnetic recording medium of the present invention will be described. FIG. 1 shows a part of the magnetic recording body 1 of the present invention, which is obtained by coating the support 11 with the microcapsules 14 containing the suspension in which the flaky magnetic particles 22 shown in FIG. 2 are dispersed in the dispersion medium 23. It is an expanded sectional view. Initially, the flake-shaped magnetic particles 22 are fixed in the dispersion medium 23 in a uniformly dispersed state inside the microcapsules 14 at room temperature.

FIG. 3 shows a state where no image is recorded, that is, the flake-shaped magnetic particles 22 are usually in the magnetic recording layer 12.
FIG. 7 is an explanatory diagram showing a state in which the image is erased or unrecorded, which is oriented parallel (horizontal direction) with respect to. When the magnetic recording layer 12 is heated by the thermal / magnetic recording head 30,
The dispersion medium 23 in the microcapsule is in a low viscosity state,
The flaky magnetic particles 22 can be oriented or moved (rotated). Then, by applying magnetism, the orientation state becomes the same as the direction of magnetism application. Therefore, in the drawing, the magnetic recording layer 12 is heated uniformly and the magnetic field applied in the horizontal direction causes the flaky magnetic particles 2 in the microcapsules 14 to move.
2 is oriented horizontally in the magnetic recording layer 12. This allows
Since most of the incident light is reflected by the flake-shaped magnetic particles 22 on the surface of the magnetic recording body, a bright and uniform color tone is obtained.

FIG. 4 is a sectional view showing a recording state of the magnetic recording medium 1 of the present invention, and the magnetic recording layer 12 of the magnetic recording body 1.
On the other hand, the magnetic recording layer 12 is partially heated, the dispersion medium 23 of the heated microcapsules 14 is brought into a molten state, and the flaky magnetic particles 22 become movable (rotatable). , Its orientation is the same as the direction of magnetic application. Therefore, in the drawing, the dispersion medium 23 is heated to a molten state, and the horizontally oriented flake-shaped magnetic particles 22 in the microcapsules 14 of the magnetic recording layer 12 are generated by the magnetic field applied in the vertical direction. 12 is oriented vertically. The flake-shaped magnetic particles 22 oriented in the vertical direction hardly reflect the incident light, and the incident light is transmitted through the magnetic recording layer 12 and scattered / absorbed to have a dark color tone, or the incident light is magnetically recorded. The color of the support is displayed due to the reflection of the support surface through the layer. The support 11 is, for example, black if it is a dark color here.

Flake-shaped magnetic particles 22 of the microcapsules 14 to which a magnetic force is applied in the vertical direction along with this heating.
Since only the flake-shaped magnetic particles 22 in the other microcapsules 14 are oriented in the horizontal direction, the difference in reflected light due to the difference in the orientation direction of the flake-shaped magnetic particles 22, that is, the contrast. And the visible display information can be recorded.

Although not shown, the flaky magnetic particles 22 in the microcapsules 14 are vertically oriented over the entire surface of the magnetic recording layer 12, and the flakes are partially heated and horizontally applied with the flakes. Magnetic particles 2
By orienting 2 in the horizontal direction, a difference in reflected light due to a difference in the orientation direction of the flake-shaped magnetic particles 22, that is, a contrast can be obtained in the same manner as described above, whereby visible display information can be recorded.

Heat used for recording the magnetic recording medium 1 of the present invention
The magnetic head 30 is, for example, a method in which heat is applied only to a recording portion after forming a uniform magnetic field to perform recording, and a magnetic field is formed only to a recording portion after uniformly applying heat to the entire recording portion. (1) Specifically, an optical head capable of converting heat such as laser light and magnetic field forming means capable of applying a uniform magnetic field, and (2) application of a uniform magnetic field to the thermal head. There is a magnetic field forming means capable of applying heat, (3) a heat applying means capable of applying heat uniformly to the magnetic head, and the constitution may be such that the heat and the magnetic field are scanned in a line shape, and should be appropriately selected according to the application. You can In particular, the heating means for applying heat may have a heating capacity such as wax for melting the dispersion medium 23.

Since this image formation is simple due to heat with low energy to the extent that magnetism and the viscosity of the dispersion medium are lowered, recording is easy, and the resolution can be improved by controlling the particle size of the microcapsules. High image formation is possible. An image formed by a thermal / magnetic head has a high viscosity state as soon as the dispersion medium returns to room temperature, so the recording stability is good, and an image can only be formed by magnetism except in a low viscosity state. Therefore, the fogging does not occur when the magnet is touched. The magnetic recording medium according to the present invention has the mobility (rotation) of the contained flake-shaped magnetic particles during recording, that is, both good recording reactivity and stable recorded image.

Furthermore, since the microcapsules can be made into a coating solution by mixing with a binder, they can be applied to various supports and can be processed into various shapes, and the manufacturing process is simple. Therefore, the range of applications can be expanded. Further, by appropriately selecting the coloring of the flake-shaped magnetic particles, the coloring of the dispersion medium, the coloring of the protective layer, etc., it is possible to obtain a magnetic recording material capable of displaying various colors.

The image recorded on the magnetic recording medium of the present invention is various visible information such as letters, numbers, marks, patterns, pictures and photographs, and the incident light is transmitted through the magnetic recording layer and is reflected by the surface of the support. Visible information is displayed by the contrast between the body color and the display of a bright image by the flaky magnetic particles oriented in the horizontal direction, and a clear image is obtained.
The entire surface of the magnetic recording layer can be erased or partially erased by heating the entire surface of the magnetic recording layer with a heat / magnetic recording head at a temperature slightly higher than the melting point of the dispersion medium and applying magnetism in the horizontal or vertical direction. Yes, reversible recording and erasing can be performed.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to specific embodiments. <Example 1> Flake-shaped Fe-Si type amorphous magnetic particles (average particle size: 12) that have been subjected to silane coupling treatment.
μm, average aspect ratio: 60, coercive force: 15 Oe / measuring magnetic field: 5 kOe) 15 parts by weight were heated to 80 ° C. and melted into a mixture of 60 parts by weight of paraffin wax having a melting point of 60 ° C. and 20 parts by weight of dibutyl phthalate. 20% of 10% gelatin aqueous solution which was uniformly dispersed and heated at 80 ° C.
A homogenizer was used in 0 parts by weight to rotate at 200 rpm.
The particles were dispersed at 0 rpm for about 5 minutes so that the average particle diameter was 70 μm. A 10% aqueous solution of gum arabic was added to the resulting dispersion.
00 parts by weight was mixed, 1000 parts by weight of water was further added, and the mixture was kept at 40 ° C. and a 10% acetic acid aqueous solution was added dropwise to adjust pH to 4. Then, the liquid temperature was cooled to 7 ° C., 10 parts by weight of a 30% formalin aqueous solution was added, and a 10% sodium hydroxide aqueous solution was added dropwise to adjust the pH to 9 to prepare microcapsules 22 having a gelatin-arabic gum wall.

Next, the obtained microcapsules 2 were formed on a transparent polyethylene terephthalate (PET) film.
A magnetic recording layer is formed by applying a coating liquid in which 2 is uniformly dispersed in a polyvinyl alcohol aqueous solution, and a protective layer made of an acrylic resin in which a black pigment (for example, carbon black , graphite, acetylene black, naphthol blue black, etc.) is kneaded. Then, the magnetic recording material of the present invention was obtained.

The entire surface of this magnetic recording medium is heated to 80 ° C.,
A horizontal magnetic field is applied to the magnetic recording layer from the outside, and the flaky magnetic particles in all the microcapsules are oriented so as to be parallel to the surface of the magnetic recording layer, leaving the magnetic recording layer in an unrecorded state. Next, the magnetic recording layer is partially heated to 80 ° C. in accordance with the visible display information to be recorded, and a magnetic field is applied in the perpendicular direction of the magnetic recording layer so that the flaky magnetic particles become perpendicular to the magnetic recording layer. When the image was oriented and recorded with visible display information, a clear image with clear contrast of light and dark could be formed.

Although not shown, an image can be recorded or erased from the support (PET) side, and the support (PET) side can be fitted into a concave portion of another medium so that the magnetic recording portion is formed. It can also be used as a display means for forming a. Further, although not shown, the support may be a dark color system such as black and the protective layer may be transparent.

Example 2 Flake Fe-Ni alloy magnetic particles treated with oleic acid (average particle size: 15 μm,
Average aspect ratio: 75, coercive force: 15 Oe / measuring magnetic field: 5 kOe) 15 parts by weight of 50 parts by weight of stearyl stearate melted by heating at 60 ° C., diisopropyl naphthalene 15 parts by weight, dibutyl phthalate 15 parts by weight and ethyl cellulose 1 Evenly dispersed in 80 parts by weight of mixed solvent of 80 parts by weight, this dispersion is dispersed in 200 parts by weight of 5% polyvinyl alcohol heated to 60 ° C., and an average particle diameter of 75 μm is obtained at a rotation speed of 2000 rpm using a homogenizer. For about 5 minutes. 100 parts by weight of a melamine-formalin prepolymer aqueous solution was mixed with the obtained dispersion, and a 20% acetic acid aqueous solution was added dropwise to adjust the pH to 6.
Then, the liquid temperature was raised to 65 ° C. and a polymerization reaction was carried out for 6 hours to prepare melamine-formalin wall microcapsules.

Next, the obtained microcapsules 2 were formed on a transparent polyethylene terephthalate (PET) film.
A magnetic recording layer is formed by applying a coating liquid in which 2 is uniformly dispersed in a polyvinyl alcohol aqueous solution, and a protective layer made of an acrylic resin in which a black pigment (for example, carbon black , graphite, acetylene black, naphthol blue black, etc.) is kneaded. Then, the magnetic recording material of the present invention was obtained.

The entire surface of this magnetic recording medium is heated to 70 ° C.,
A magnetic field perpendicular to the magnetic recording layer is applied from the outside, and the flaky magnetic particles in all the microcapsules are oriented parallel to the surface of the magnetic recording layer, leaving the magnetic recording layer in an unrecorded state. Next, the magnetic recording layer is heated to 70 ° C. and a magnetic field is partially applied in the direction perpendicular to the magnetic recording layer in accordance with the visible display information to be recorded so that the flaky magnetic particles become perpendicular to the magnetic recording layer. When the image was oriented and recorded with visible display information, a clear image with clear contrast of light and dark could be formed.

Although not shown, an image can be recorded or erased from the side of the support (PET), and the support (PET) side can be fitted into a concave portion of another medium so that the magnetic recording portion can be recorded. It can also be used as a display means for forming a. Further, although not shown, the support may be a dark color system such as black and the protective layer may be transparent.

[0053]

According to the magnetic recording medium of the present invention, magnetic particles are formed by dispersing and arranging microcapsules containing flake-shaped magnetic particles and a dispersion medium that disperses the flake-shaped magnetic particles and shows a solid state at room temperature in a binder. An image is recorded by the contrast of the reflected light by having the recording layer and aligning the flaky magnetic particles of these microcapsules horizontally or vertically with respect to the magnetic recording layer. 50 Oe or less (measurement magnetic field: 5 kOe)
As a result, the response to the magnetic field is excellent and the mobility (rotation, orientation) within the microcapsule even in a low magnetic field.
It is a magnetic recording material with excellent sensitivity and high sensitivity. Further, by decreasing the particle size of the flake-shaped magnetic particles and increasing the aspect ratio, the contrast in the microcapsules is high, the rotation (orientation) in the microcapsules is facilitated, and the sensitivity is improved.

Further, the magnetic recording medium of the present invention can easily form an image by heating at a low temperature and applying a magnetism, so that the energy consumption is low, and by using the microcapsule for the recording layer, the microcapsule can be used. The resolution can be increased by controlling the particle size of the. Moreover, since the magnetic particles are dispersed in the dispersion medium that is in a solid state at room temperature in the microcapsule and are fixed except during recording and erasing, even if external magnetism is applied after recording the information, the inside of the microcapsule remains Stable recording can be obtained without causing movement of the magnetic particles. Since the movement (orientation) of the magnetic particles can be substantially limited only to the portion to which heating / magnetism is applied, the stability of the image is excellent by using a dispersion medium having a high resolution and showing a solid state at room temperature.

Further, since the step of applying the coating liquid containing the microcapsules can be carried out, the manufacturing step of the magnetic recording body can be simplified.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a magnetic recording body of the present invention.

FIG. 2 is a cross-sectional view showing an example of microcapsules used in the magnetic recording layer of the magnetic recording medium of the present invention.

FIG. 3 is a cross-sectional view showing an unrecorded state (flake-shaped magnetic particles in a horizontal direction) of the magnetic recording medium of the present invention.

FIG. 4 is a cross-sectional view showing a recorded state (the flake-shaped magnetic particles are in a vertical direction) of the magnetic recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 11 Support 12 Magnetic recording layer 13 Protective layer 14 Microcapsule 15 Binder 21 Core substance 22 Flake-like magnetic particles 23 Dispersion medium 24 Shell substance 30 Thermal magnetic head

Claims (4)

[Claims] 1. A flaky magnetic particle having a coercive force of 50 Oe or less (measurement magnetic field: 5 kOe) and a dispersion thereof on a support made of a non-magnetic material, having a viscosity at room temperature of 100,000 cps or more and at the time of heating. A magnetic recording medium comprising microcapsules containing a dispersion medium having a viscosity of 5000 cps or less and dispersed in a binder to form a magnetic recording layer. 2. The average major axis of the flaky magnetic particles is 5 μm.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of m to 50 μm and an average thickness of 0.1 μm to 3 μm. 3. The average particle size of the microcapsules is 10 μm.
2. It is between m and 100 μm.
The magnetic recording material described. 4. The magnetic recording medium according to claim 1, wherein a protective layer is formed on the magnetic recording layer.