JPH07271315A - Magnetic recording medium and recording and erasing method for the same - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium to enable reversible display with which an image having high contrast, high resolution, sharpness and stability is obtd., by forming a magnetic recording layer having microcapsules with a specified constitution dispersed in a binder. CONSTITUTION:A magnetic recording layer 12 formed by applying a coating material having microcapsules 14 dispersed in a binder 15 and a protective supporting body 13 are successively formed on a supporting body 11. The microcapsule 14 contains such suspension in which magnetic particles 22, pigment 23, and IR absorbent 24 are dispersed in a dispersion medium which shows a solid phase at a normal temp. When the medium is irradiated with IR laser light, the IR absorbent 24 generates heat to change the dispersion medium in the microcapsule into a molten state. Magnetic particles 22 are attracted upward in the microcapsule 14 by an magnetic field applied. On the other hand, magnetic particles 22 in an area not heated with IR laser light do not move but the pigment 23 is present in the upper part of the microcapsule 14.

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 recording an image by heating and applying a magnetic field, and more particularly to a reversible display type magnetic recording medium excellent in resolution and image stability and a recording / erasing method thereof. .

[0002]

2. Description of the Related Art Conventionally, as a display 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. 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 display, when a suspension is sealed between two substrates and a magnetic pen is used to draw characters and a pattern from one substrate to apply magnetism, magnetic particles of the suspension are attracted, Although the characters and patterns can be 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 a drawback that the characters and patterns cannot be retained for a long time because they settle out 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 displays that can be used beautifully.

However, this display is formed by forming a honeycomb-shaped cell having a side and a depth of about 2 mm on the entire surface of a transparent plastic sheet, and magnetic particles and a white pigment are dispersed in the cell. The suspension dispersed in a medium was injected, 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 the honeycomb-shaped cells, increase the size of the honeycomb-shaped cells, or make the honeycomb-shaped cells very small, and the process of injecting the suspension into the honeycomb-shaped cells.

As another mode, for example, Japanese Patent Laid-Open No. 1-14
5637 or Eyne S. et al. Trumb
le P.L. S. & E. No. 7 213 (1963), unlike a display in which magnetic particles and a pigment are sealed in a honeycomb-shaped cell as described above, the magnetic particles are encapsulated in microcapsules and coated on a support. Display is known. According to this method
By controlling the particle size of the microcapsules, the resolution can be increased and the manufacturing process is easy. Also,
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, in the image forming method shown here, first, at the time of manufacturing a display, the magnetic particles in the coated capsules are orientated in advance in parallel with the plane of the display so that all the incident light is reflected to make it appear bright. Next, by magnetically recording, the magnetic particles rotate to scatter and absorb the incident light, and a contrast is produced, so that a black image is formed. That is, the magnetic particles used here are generally limited to flat particles such as nickel, iron and barium-ferrite, and since the principle of image formation is based on the orientation of the magnetic particles, it is It is necessary to always orient the flat surface in parallel with the plane of the magnetic recording medium, but it is difficult to orient it uniformly and in a certain direction in this way. The result is an unclear image of light and dark.

Further, as another mode using the microcapsules, for example, Japanese Patent Laid-Open No. 2-146082,
As described in JP-A-4-233581, a display in which light-absorbing magnetic particles and light-reflecting non-magnetic particles are enclosed in microcapsules is known.

In the image formation of this form, first, the permanent magnet attracts the light-absorbing magnetic particles in the microcapsules to the back surface side of the display, and accordingly, the light-reflecting non-magnetic particles remain on the surface of the display. By doing so, the surface becomes the color of the non-magnetic particles and the erased state is achieved. Next, apply magnetism from the display surface with a permanent magnet.
By recording, the light absorbing magnetic particles are attracted to the surface by magnetism, and desired characters and images are formed.

However, since the display thus obtained has a wide range of magnetic force, its resolution is very inferior to that of recording by other heat or light. Furthermore, since the above-mentioned display can be easily printed and erased by magnetic force, the stability of the image may be caused by fogging the unprinted part or erasing the image just by touching the magnet. Has the disadvantage of being bad.

From the above, the conventional magnetic recording medium using the magnetic material as the display means cannot record an image with high resolution, and the recorded image is partially or legible due to the influence of external magnetism. Since the image is erased in an impossible state or the unprinted portion is fogged, stable recording cannot be performed. Also, the mobility of the encapsulated magnetic particles,
That is, there has been no magnetic recording material having both good recording reactivity and recorded image stability.

Therefore, the present applicant has filed Japanese Patent Application No. 5-15344.
No. 5, Japanese Patent Application No. 5-153446 and the like, magnetic particles are dispersed in a wax that is solid at room temperature, and a method of encapsulating the wax in microcapsules is used to apply heat and magnetism to image recording at the same time. It proposes a magnetic recording medium in which wax is melted and magnetic particles are further moved, and erasing is also carried out by melting wax by heating and moving magnetic particles by applying magnetism.

[0015]

However, since it is necessary to transfer heat from the outside of the magnetic recording medium to the microcapsules, it is not possible to increase the distance from the surface of the magnetic recording medium to the microcapsules. It is difficult to thicken the protective layer for the purpose of improving, and deterioration of the protective layer due to contact with a heating source, and further, when heat is conducted through the protective layer, diffusion of heat occurs in the in-plane direction, There is a problem that recording at higher resolution becomes difficult. Therefore, the present invention provides a reversible display magnetic recording medium in which a portion to which magnetism is applied has a clear brightness and darkness different from a non-application portion, has high resolution, is clear, and has excellent image stability, and a reversible display. The purpose is to provide a recording / erasing method.

[0016]

The present invention has been made to achieve the above object, and the invention according to claim 1 is one in which at least one is made of a nonmagnetic material having transparency. To form a magnetic recording layer in which at least magnetic particles, a pigment, an infrared absorbing agent, and microcapsules containing the infrared absorbing agent and a dispersion medium showing a solid state at room temperature are dispersed in a binder. The magnetic recording medium is characterized by the above.

According to a second aspect of the present invention, in the magnetic recording medium according to the first aspect, the dispersion medium is a wax.

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 1000 μm.

According to a fourth aspect of the present invention, in the magnetic display according to the first aspect, the average particle size of the magnetic particles is between 0.1 μm and 10 μm.

According to a fifth aspect of the present invention, in the magnetic recording medium according to the first aspect, the average particle diameter of the pigment is 0.01 μm to 1 μm.
It is characterized by being between 0 μm.

According to a sixth aspect of the present invention, in the magnetic recording medium according to the first aspect, the refractive index of the pigment is 1.5 or more.

According to a seventh aspect of the present invention, at least magnetic particles, a pigment, and an infrared absorber are provided on a support made of a non-magnetic material.
Microcapsules containing a dispersion medium having a solid state at room temperature, which is formed by dispersing these, are dispersed in a binder, and a recording layer is partially or entirely applied with a magnetism by a magnetism generating means and an infrared irradiating means. The recording / erasing method of the magnetic recording medium is characterized in that the recording / erasing of the recording layer is carried out by melting the dispersion medium and moving the magnetic particles from the heat generation of the infrared absorbent caused by the irradiation of the infrared rays.

An eighth aspect of the invention is the magnetic recording medium according to the seventh aspect, wherein the infrared irradiating means is an infrared laser.

[0024]

The magnetic recording medium of the present invention has a magnetic recording layer containing microcapsules in which magnetic particles, a pigment and an infrared absorbing agent are dispersed and which contains a dispersion medium exhibiting a solid state at room temperature. The magnetic particles are attracted to the back side which is one side of the recording body, that is, below the microcapsules, and the surface of the magnetic recording body which is the other side is the color of the dispersion medium,
Alternatively, since the color of the magnetic particles is hidden by the light scattering due to the difference in the refractive index, a uniform color tone is obtained.

Further, the recording on the magnetic recording medium of the present invention is performed by scanning from the surface side of the magnetic recording medium with a magnetism generating means having an infrared irradiating means, and the infrared ray radiating heat causes the infrared absorbing agent to generate heat to lower its viscosity. The magnetic particles in the part of the dispersion medium that has become
Moving to the surface of the magnetic generation means, an image is formed by magnetic particles, and for erasing, the entire surface of the magnetic recording material is heated by infrared irradiation in the same manner, and the entire surface of the magnetic recording material is magnetized from the back surface, or infrared rays are applied. By scanning the back surface with a magnetism generating means having an irradiation means, the magnetic particles are attracted to the magnetism generating means side below the microcapsules, and the surface of the magnetic recording medium becomes a uniform color tone (pigment color) again. The image is erased.

[0026]

The present invention will be described in detail below with reference to the drawings. 1 is a sectional view showing an embodiment 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. It is explanatory drawing which shows the state at the time of manufacture of a magnetic recording body, and FIG.
FIG. 6 is an explanatory diagram showing a non-recorded state by the erasing operation of the magnetic recording body of the present invention, and FIG. 5 is an explanatory diagram showing a recording state of the magnetic recording body of the present invention.

FIG. 1 shows the structure of the magnetic recording medium 1 of the present invention, in which a support 11 and microcapsules 14 containing magnetic particles, a pigment and an infrared absorber are dispersed in a binder 15 to apply a coating agent. The magnetic recording layer 12 and the protective support 13 are sequentially laminated.

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 microcapsules 14 include magnetic particles 22 and pigments 2.
3. A structure in which the infrared absorbing agent 24 has a core substance 21 mainly composed of suspension dispersed in a dispersion medium (for example, wax) 25 showing a solid state at room temperature and encapsulated with a shell substance 26 made of a polymer. Is.

The magnetic particles 22 may be magnetic particles alone, a mixture of several kinds of magnetic particles, or a mixture of magnetic particles and a polymer. For example, magnetite, ferrite and other iron, cobalt,
A metal exhibiting ferromagnetism such as nickel, an alloy containing these elements, or fine particles of a compound is used. In this case, the magnetic particles may be subjected to surface hydrophobizing treatment such as silane coupling treatment in order to enhance affinity with wax or the like. When a mixture of magnetic particles and a polymer is used, the above-mentioned magnetic particles and a polymer are kneaded and then pulverized, or a monomer in which the magnetic particles are dispersed is subjected to a method such as emulsion polymerization, suspension polymerization, or dispersion polymerization. A method such as polymerization is used. In this case, the polymer is preferably crosslinkable. The size of the magnetic particles is 0.1 μm in consideration of the ease of movement due to magnetism and the image density.
It is preferably between 1 and 10 μm.

As the pigment 23, a single pigment, a mixture of several pigments, or a mixture of a pigment and a polymer can be used. For example, fine particles of commonly known inorganic pigments such as titanium dioxide, zinc sulfide, lead titanate, zirconium oxide, lead white, cadmium red, and cadmium yellow, and organic pigments such as phthalocyanine pigments are used. In this case, the pigment may be subjected to surface treatment such as silane coupling treatment in order to enhance affinity with wax or the like. When a mixture of pigment and polymer is used, the above pigment and polymer are kneaded and then pulverized.
Alternatively, a method in which a monomer in which a pigment is dispersed is polymerized using a method such as emulsion polymerization, suspension polymerization, or dispersion polymerization is used. In this case, the polymer is preferably crosslinkable. The size of the pigment is preferably 0.01 μm to 10 μm in consideration of hiding the magnetic powder.
Further, the refractive index of the pigment is preferably 1.5 or more in order to conceal the color of the magnetic particles more strongly.

The infrared absorber 24 has a function of absorbing infrared rays, particularly in the near infrared region 780 to 2000 nm and converting it into heat, and an organic or inorganic near infrared absorber can be used. . For example, in the organic system, polymethine dyes, naphthoquinone dyes, anthraquine dyes, triphenylmethane dyes, aminium dyes, diimmonium dyes, and metal complex dyes such as phthalocyanine dyes, naphthalocyanine dyes, and diol dyes are available. Can be mentioned. Examples of inorganic materials include glass materials containing Fe ²⁺ and / or Cu ²⁺ , metal oxides, metal hydroxides, metal sulfates, metal carbonates, metal silicates, metal nitrates and metal complex compounds. To be In each case, a material is selected that can efficiently absorb infrared rays having an emission wavelength of an infrared laser that irradiates the magnetic recording body and convert it into heat.

The dispersion medium 25 is at room temperature (about 10-40
It should be solid (in the range of 0 ° C.) (in a substantially solid state) and be in a fluid state when heated to a temperature higher than room temperature (in the range of approximately 50 to 80 ° C.), for example, an organic compound. As the synthetic or natural wax such as paraffin wax or carnauba wax, a natural or synthetic resin, or a carboxylic acid ester, a generally known one satisfying the above conditions can be appropriately used.

A core substance 21 containing the above-mentioned magnetic particles 22, pigment 23, infrared absorbing agent 24, dispersion medium 25 and the like as main components.
Is covered with a shell substance 26 such as a polymer to be microencapsulated. Examples of the resin used as the shell material 26 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 these alone or in combination of two or more.

Microcapsule 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, an in-situ polymerization method or a phase separation method in which a monomer is supplied from an outer phase of a suspension in which a magnetic particle 22, a pigment 23, and an infrared absorbing agent 24, which are core materials 21, are uniformly dispersed in a dispersion medium 25, is used. By manufacturing, the magnetic particles 22 and the pigment 2 having a uniform particle size are obtained.
3. The microcapsule 14 in which the infrared absorbent 24 can be easily moved can be manufactured. The polymerizable monomer used here is acrylic acid ester, methacrylic acid ester,
Styrene and its derivatives, isocyanate, various amines, compounds having an epoxy group and the like are preferable.

The magnetic recording medium 1 of the present invention is produced by coating the support 11 with the microcapsules 14 having the above-mentioned structure together with the binder 15 to form the magnetic recording layer 12, and further laminating the protective support 13. It

The support 11 is a composite of synthetic resins such as polyvinyl chloride, polyester, polycarbonate, polymethylmethacrylate, polystyrene and polyethylene terephthalate, natural resin, paper, synthetic paper, metal and ceramics, 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 support 13, epoxy resin, tetrafluoroethylene, etc., or polyvinyl chloride, polyester, polycarbonate, polymethyl methacrylate,
It is possible to use synthetic resins such as polystyrene and polyethylene terephthalate, and natural resins. This protective support 13
Is required to hold the microcapsules 14 formed on the support 11 and be transparent so that the microcapsules 14 can be seen from the outside. be able to.

These forming methods include well-known printing methods such as an offset printing method, a gravure printing method, a silk screen printing method, a coating method such as a roll coating method and a knife edge method, and the microcapsules 14 described above. A transfer method using a transfer sheet in a transfer layer, an ink jet method in which ink containing the above-mentioned microcapsules 14 is sprayed onto a base material, and a solution containing the above-mentioned microcapsules 14 between a support 11 and a protective support 13. Can be prepared by a forming method such as a filling method, and can be appropriately selected from the above-mentioned methods according to the use and quantity of the information recording body to be prepared.

Next, an image forming method for the magnetic recording medium of the present invention will be described. FIG. 3 is a cross-sectional view showing an enlarged cross-section of a part of the magnetic recording body 1 of the present invention in which the microcapsules 14 containing the suspension in which the magnetic particles 22 are dispersed in the dispersion medium 25 are applied on the support 11. . Initially, the magnetic particles 22, the pigment 23, and the infrared absorbing agent 24 are fixed in the dispersion medium 25 in the microcapsule 14 in a state of being uniformly dispersed.

FIG. 4 is an explanatory view showing a state when a normal image is erased or when no image is recorded. The entire surface of the magnetic recording medium is uniformly heated, the dispersion medium 25 in the microcapsules is in a molten state, and the magnetic particles 22 in the microcapsules of the magnetic recording layer 12 are generated by the magnetism uniformly applied from the back surface of the magnetic recording medium. The magnetic recording medium surface is attracted to the lower side of the microcapsule and has a uniform color tone mainly due to the color of the pigment 23.

FIG. 5 is an explanatory diagram showing a state in which recording is performed from above the magnetic recording medium 1 by heating the infrared laser irradiating means 27 by irradiation with an infrared laser and applying magnetism by the magnetism generating means 28. Infrared laser irradiation means 27
The infrared laser 27 is irradiated by the infrared laser / magnetic head device 29 having the magnetic field generating means 28 and the infrared absorbent 24 in the microcapsule 14 generates heat, and the dispersion medium 25 in the microcapsule at the heated portion is generated.
For example, the wax is in a molten state, and the magnetic particles 22 in the microcapsules are attracted above the microcapsules by the applied magnetism. On the other hand, in the portion which is not heated by the infrared laser / magnetic head device 29, the magnetic particles 22 do not move inside the microcapsule, and the pigment 23 exists above the microcapsule. Therefore, an image of the color of the magnetic particles in the recorded portion can be obtained in the color of the pigment in the unrecorded portion by heating and magnetically applying the recording portion by laser irradiation according to the recorded information. The infrared laser / magnetic head device 29 is a combination of a normal magnetic head and a laser, and the infrared laser irradiation means 27 and the magnetic generation means 28 may be separately provided. Further, the magnetism generating means 28 may be a simple permanent magnet or an electromagnet as long as the magnetic field strength necessary for the movement of the magnetic particles 22 can be obtained even if it does not have the form of a magnetic head.

The infrared laser irradiating means 27 is heated by the infrared absorbing agent 24 such that the dispersion medium 24 such as wax is dissolved.
The output of the infrared laser can be recorded even at several milliwatts to ten and several milliwatts. When importance is attached to the recording speed, a laser having a relatively high output is used, and a semiconductor laser is preferable in terms of price and shape.

Since this image formation is simple due to heat of low energy which lowers the magnetism and viscosity of the dispersion medium, recording is easy, and the resolution can be improved by controlling the particle size of the microcapsules. High image formation is possible.
Further, since the pigment has a high refractive index, it is possible to hide the color of the magnetic powder when the magnetic powder is attracted to the back surface of the magnetic recording medium. Further, the formed image has a fixed state as soon as the dispersion medium returns to room temperature, and thus has good recording stability,
Moreover, since the image cannot be formed only by magnetism when the dispersion medium is not in a fluid state, fogging does not occur when the magnet is touched. The magnetic recording medium according to the present invention has the mobility of the magnetic powder contained therein at the time of recording, that is, both good recording reactivity and stability of the recorded image. Further, due to the heat generated by the infrared absorbent, the magnetic particles can move only in the portion of the dispersion medium that is in a fluidized state, so an image with high resolution can be obtained.

Furthermore, since the microcapsules can be made into a coating liquid 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. In particular, when applied on paper, it can be used as information recording paper for household faxes, etc. It can be used as recycled paper because printing and erasing can be done easily and reversibly by applying laser light (heat) and magnetism. Is.

The present invention will be described below with reference to specific examples.
The details will be described. <Example 1> 50 parts by weight of titanium dioxide having an average particle size of 0.5 μm subjected to silane coupling treatment, 10 parts by weight of magnetite magnetic powder having an average particle size of 1 μm subjected to oleic acid treatment, and an absorption peak at a wavelength of 830 nm. And 10 parts by weight of the infrared absorbent having the above were uniformly dispersed in 80 parts by weight of liquid paraffin melted by heating at 60 ° C. 6 this dispersion
Using a homogenizer, 300 parts by weight of a 10% aqueous gelatin solution heated to 0 ° C. was dispersed at a rotation speed of 2000 rpm for about 5 minutes so that the average particle diameter was 100 μm. To the obtained dispersion liquid, 10% aqueous solution of gum arabic 300
By mixing 1 part by weight, 1500 parts by weight of water was added, the temperature was kept at 40 ° C., and a 10% acetic acid aqueous solution was added dropwise to adjust the pH to 4. Then, the liquid temperature was cooled to 5 ° C., 10 parts by weight of 30% formalin aqueous solution was added, and 10% aqueous sodium hydroxide solution was added dropwise to adjust pH to 9 to obtain gelatin-arabic gum microcapsules.

A recording layer using the above-mentioned microcapsules is provided on plain paper, and a protective layer made of acrylic resin is further provided. Then, the entire surface of the magnetic recording medium is heated, and a magnetic force is applied from below to obtain a white color. A magnetic recording paper was obtained. Irradiate this with a lasing semiconductor laser with a wavelength of 830 nm,
At the same time, by applying magnetism with the magnetic head, a clear image with a bright and dark black color on a white background was obtained.

Example 2 50 parts by weight of cadmium red having an average particle size of 0.5 μm, which has been subjected to a silane coupling treatment,
10 parts by weight of magnetite magnetic powder having an average particle size of 1 μm and treated with oleic acid, and 10 parts by weight of an infrared absorbing agent having an absorption peak at a wavelength of 830 nm are heated to 60 ° C. and uniformly melted in 80 parts by weight of paraffin wax. Dispersed. This dispersion was heated to 60 ° C. and dispersed in 200 parts by weight of a 5% aqueous solution of polyvinyl alcohol using a homogenizer at a rotation speed of 2000 rpm so that the average particle diameter was 100 μm for about 5 minutes. 100 parts by weight of a melamine-formalin prepolymer aqueous solution was added to 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 30 minutes to obtain melamine-formalin resin microcapsules.

A recording layer using the above-mentioned microcapsules is provided on plain paper, and a protective layer made of acrylic resin is further provided. Then, the entire surface of the magnetic recording medium is heated and magnetized from below to give a red color. A magnetic recording paper was obtained. Irradiate this with a lasing semiconductor laser with a wavelength of 830 nm,
At the same time, by applying magnetism with a magnetic head, a clear image with a bright and dark black color on a red background was obtained.

Example 3 50 parts by weight of titanium oxide having an average particle size of 0.5 μm which has been subjected to silane coupling treatment, and magnetite 5 having an average particle size of 1 μm which has been subjected to oleic acid treatment.
0 parts by weight and 10 parts by weight of an infrared absorber having an absorption peak at a wavelength of 830 nm were uniformly dispersed in 80 parts by weight of paraffin wax melted by heating at 60 ° C. This dispersion was heated to 60 ° C. and dispersed in 200 parts by weight of a 5% aqueous solution of polyvinyl alcohol using a homogenizer at a rotation speed of 2000 rpm for about 5 minutes so that the average particle diameter was 100 μm. A 10% aqueous sodium carbonate solution was added dropwise to adjust the pH to 8-9. The liquid temperature was cooled to 25 ° C., and a 20% urea-formalin prepolymer aqueous solution 200 was prepared.
Part by weight was added, and acetic acid was added dropwise to adjust the pH to 4. Then, the reaction was carried out at 30 ° C. for 3 hours and at 50 ° C. for 2 hours to obtain urea-formalin resin microcapsules.

A recording layer using the above-mentioned microcapsules is provided on plain paper, and a protective layer made of acrylic resin is further provided. Then, the entire surface of the magnetic recording medium is heated, and a magnetic force is applied from below to obtain a white color. A magnetic recording paper was obtained. Irradiate this with a semiconductor laser emitting a wavelength of 830 nm,
At the same time, by applying magnetism with the magnetic head, a clear image with a bright and dark black color on a white background was obtained.

[0052]

The magnetic recording medium and the recording / erasing method of the magnetic recording medium of the present invention have a magnetic recording layer containing microcapsules containing a dispersion medium in which magnetic particles are dispersed and which exhibits a solid phase state at room temperature. In the non-recording state, the magnetic particles are attracted to the back side which is one side of the magnetic recording body, and the surface of the magnetic recording body which is the other side shows a uniform color tone due to the color of the pigment. Scan from the surface side of the magnetic recording medium with an infrared laser / magnetic head device having infrared irradiation means and magnetism generation means, and heat the dispersion medium by infrared laser irradiation and magnetize the inside of the dispersion medium melted by the application of magnetism. The particles move to the surface side of the magnetic recording body, and a black image is formed by the magnetic particles. For erasing, heating the entire surface and applying magnetism from the back surface of the magnetic recording material to the entire surface, or heating and applying magnetism to scan the back surface of the magnetic recording material, magnetic particles are attracted below the microcapsules and the magnetic recording The body surface again becomes pigmentary and the image is erased.

That is, in the magnetic recording medium of the present invention, the portion to which magnetism is applied is clearly different from the portion to which no magnetism is applied, the contrast is clear, the resolution is high, the image is sharp, and the image stability is excellent. And so on.

In the present invention, since image formation can be easily performed by heating at low temperature and applying magnetism, the energy consumption is low, and by using microcapsules for the recording layer, the particle size of the microcapsules can be controlled. By doing so, the resolution can be increased. Moreover, since the magnetic particles are dispersed in the dispersion medium that shows a solid state at room temperature in the microcapsule and are fixed except during recording, even if magnetism is externally applied after recording the information, the microcapsule can be Stable recording can be obtained without causing the magnetic particles inside to move. In addition, since the area affected by magnetism does not expand by encapsulating microcapsules, the movement of magnetic particles can be almost limited only to the part where heating and magnetism is applied, so the dispersion medium has high resolution and shows a solid state at room temperature. By using, the image stability is also excellent.

Further, since the dispersion medium is heated from the outside by the photothermal conversion effect by the infrared absorption of the infrared absorbing agent inside, the protective layer can have a sufficient thickness and the durability of the magnetic recording medium can be improved. Since the property can be improved and the irradiation is performed in a non-contact manner, no heating mark is left on the surface of the protective layer.

When paper is used as the support, printing and erasing can be performed easily, safely, and reversibly by heating at low temperature by infrared laser irradiation and application of magnetism. Therefore, it can be used as a recycled paper for household fax machines, etc. Can be used as information recording paper.

Further, since the step of applying the coating liquid containing the microcapsules can be performed, the manufacturing steps 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 an explanatory view showing a state at the time of manufacturing the magnetic recording body of the present invention.

FIG. 4 is an explanatory diagram showing a non-recorded state by an erasing operation of the magnetic recording body of the present invention.

FIG. 5 is an explanatory diagram showing a recording state of the magnetic recording medium of the present invention.

[Explanation of symbols]

 1 Magnetic Recording Material 11 Support 12 Magnetic Recording Layer 13 Protective Support 14 Micro Capsule 15 Binder 21 Core Material 22 Magnetic Particle 23 Pigment 24 Infrared Absorber 25 Dispersion Medium 26 Shell Material 27 Laser Irradiation Means 28 Magnetic Generation Means 29 Infrared Laser Magnetic head device

Claims (8)

[Claims] 1. A dispersion medium having at least one magnetic particle, a pigment, an infrared absorber, and a solid dispersion at room temperature, which are dispersed between supports made of a non-magnetic material, at least one of which is transparent. A magnetic recording medium, comprising a magnetic recording layer comprising microcapsules containing and dispersed in a binder. 2. The magnetic recording medium according to claim 1, wherein the dispersion medium is wax. 3. The average particle size of the microcapsules is 10 μm.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is between m and 1000 μm. 4. The magnetic recording medium according to claim 1, wherein the average particle diameter of the magnetic particles is between 0.1 μm and 10 μm. 5. The average particle diameter of the pigment is 0.01 μm to 1
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of 0 μm. 6. The magnetic recording medium according to claim 1, wherein the pigment has a refractive index of 1.5 or more. 7. A binder comprising microcapsules containing at least magnetic particles, a pigment, an infrared absorber, and a dispersion medium which is in a solid phase state at room temperature and is dispersed on a support made of a non-magnetic material. Due to the application of magnetism to the magnetic layer by the magnetic generation means and the heat generation of the infrared absorbent by the infrared irradiation means, the melting of the dispersion medium and the magnetic particles A recording / erasing method for a magnetic recording medium, characterized in that recording / erasing is performed on the recording layer by moving. 8. The recording method for a magnetic recording medium according to claim 7, wherein the infrared irradiation means is an infrared laser.