WO2020110768A1

WO2020110768A1 - Magnetic recording medium and method for producing same

Info

Publication number: WO2020110768A1
Application number: PCT/JP2019/044806
Authority: WO
Inventors: 笹栗　大助; 西村　直樹
Original assignee: キヤノン株式会社
Priority date: 2018-11-30
Filing date: 2019-11-15
Publication date: 2020-06-04
Also published as: JP2020087497A

Abstract

A magnetic recording medium 100 according to the present invention is provided with: a recording layer 30 which contains a plurality of magnetic particles 10 that contain hard magnetic bodies 15 and a soft magnetic body 20 that is in contact with the plurality of magnetic particles 10; and a support layer 70 which is flexible and supports the recording layer 30.

Description

Magnetic recording medium and manufacturing method thereof

The present invention relates to a magnetic recording medium. In particular, it relates to a magnetic recording medium having a composite magnetic body in which at least one of a hard magnetic body and a soft magnetic body is dispersed in the other, in a recording layer.

Conventionally, as a magnetic recording medium, a magnetic film and a magnetic disk in which a recording layer containing a magnetic material is laminated on a sheet-shaped resin base material are known. By moving relative to the magnetic head, such a recording medium can be formed in the recording layer as a magnetic domain corresponding to time-series data and can be reproduced. Therefore, there is a demand for a technique for increasing recording density by arranging finely divided magnetic particles in the recording layer with high density. Japanese Unexamined Patent Publication No. 2016-130208 discloses a magnetic recording medium provided with a recording layer in which iron-based magnetic particles containing ε-Fe2O3 having an average particle diameter of 10-30 nm are arranged. In JP-A-2016-130208, a vehicle in which iron-based magnetic particles are coated with a resin binder such as urethane is applied to a base film to form a magnetic recording film, and magnetic field orientation is performed by an external magnetic field immediately after application. , Are disclosed.

JP, 2016-130208, A

Magnetic recording media are required to have electromagnetic conversion characteristics having high coercive force Hc and high residual magnetic flux density (residual magnetization) Br. The high coercive force Hc brings about an effect that the magnetization is not easily inverted due to the influence of the adjacent magnetic domains even if the high coercive force is mounted. The high magnetization Br makes it possible to increase the SN ratio when the magnetic head performs magnetoelectric conversion even when the magnetic domain becomes small.

On the other hand, the recording layer described in Japanese Unexamined Patent Application Publication No. 2016-130208 has a form in which the functional component that contributes to magnetic recording includes only iron-based magnetic particles. There is a problem that it is difficult to increase the magnetization Br of the recording film. In the specification of the application, the coercive force Hc includes a case where Oe is used as a unit, and the residual magnetic flux density Br includes a case where it is paraphrased as a magnetization Br when emu/g is used as a unit.

An object of the present invention is to provide a magnetic recording medium exhibiting high coercive force Hc and high magnetization Br by a simple method.

A magnetic recording medium according to the first aspect of the present invention, a recording layer including a plurality of magnetic particles containing a hard magnetic material and a soft magnetic material in contact with the plurality of magnetic particles, and exhibits flexibility to support the recording layer. And a support layer.

Further, the method for producing a magnetic recording medium according to the second aspect of the present invention is a recording method comprising a support layer having flexibility, a plurality of magnetic particles containing a hard magnetic material, and a soft magnetic material in contact with the plurality of magnetic particles. And a magnetic field applying step of magnetizing the soft magnetic material and the magnetic particles in a predetermined direction by an external magnetic field applied from the outside of the laminated body. And

It is a figure which shows typically the laminated form of the magnetic recording medium which concerns on 1st Embodiment. FIG. 3 is a partially enlarged view of the recording layer of the magnetic recording medium according to the first embodiment. It is a figure which shows typically the laminated|stacked form of the magnetic recording medium which concerns on 2nd Embodiment. FIG. 6 is a partially enlarged view of a recording layer of the magnetic recording medium according to the second embodiment.

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments, and is appropriately modified from the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. Those with improvements and the like are also included in the scope of the present invention.

<First Embodiment>
A magnetic recording medium 100 according to the first embodiment of the present invention includes a recording layer 30 including a plurality of magnetic particles 10 including a hard magnetic material 15 and a soft magnetic material 20 in contact with the plurality of magnetic particles 10, and a flexible layer. And a support layer 70 that supports the recording layer 30.

Since the recording layer 30 includes the magnetic particles 10 including the supporting hard magnetic material 15 and the soft magnetic material 20, the recording layer 30 may be referred to as a composite magnetic material. The hard magnetic body 15 of the present embodiment contains ε iron oxide. In other words, the magnetic particles 10 of the present embodiment contain ε iron oxide as a main component. In addition, the ε iron oxide contained in the magnetic particles 10 of the present embodiment includes a case where ε-Fe ₂ O ₃ is represented by a composition formula. In the present specification, the main component is assumed to be more than 50% by weight.

Further, ε iron oxide includes a form containing a substitution metal substituting iron. Such a substitution metal includes at least one of Co, Ni, Ti, and Ga. Therefore, the ε iron oxide contained in the magnetic particles 10 may be described as ε-P _x Q _y R _z Fe _(2-3x-1.5yz) O ₃ . Here, P, Q, and R each represent a monovalent, divalent, and trivalent metal, and parameters x, y, and z are 0≦x<1.5, 0≦y<2/3, and 0≦z<2. , 0≦3x−1.5y−z<2.

Further, although the magnetic particles 10 including the ε iron oxide particles included in the recording layer 30 are magnetic particles exhibiting a high coercive force Hc, the magnetic recording medium containing the ε iron oxide particles alone has a too large coercive force Hc. It may be difficult to record. Further, in a magnetic recording medium containing ε iron oxide particles alone, the magnetization Br (remanent magnetization) is small, so that the signal-to-noise ratio (SNR) during recording/reproduction may be reduced. Therefore, the soft magnetic body 20 is arranged to supplement the magnetization Br that is insufficient when only the magnetic particles 10 are used as the magnetic recording layer, and exchange coupling by contacting with the plurality of magnetic particles 10 including the hard magnetic body 15. Is playing. The soft magnetic body 20 of the present embodiment covers the magnetic particles 10 so as to bridge the plurality of magnetic particles 10 that include the hard magnetic body 15 and are bonded to each other by sintering. In other words, the soft magnetic body 20 of the present embodiment covers the plurality of magnetic particles 10 so that the plurality of magnetic particles 10 are sandwiched between the soft magnetic body 20 and the support layer 70. It is also said that the soft magnetic body 20 covers the plurality of magnetic particles 10 on the side opposite to the surface where the magnetic particles 10 face the support layer 70.

The soft magnetic body 20 of the present embodiment contains α-Fe as a main component. The soft magnetic body 20 may contain iron in another crystalline form such as β-Fe in the range where exchange coupling with the magnetic particles 10 is possible. The soft magnetic body 20 may contain amorphous iron having no crystallinity other than α-Fe. The recording layer 30 may contain additives such as a binder, a lubricant, an abrasive and a rust preventive.

When the layer thickness of the soft magnetic body 20 is increased or the content of the soft magnetic body 20 with respect to the hard magnetic body 15 is increased, the magnetization Br of the recording layer 30 increases and the coercive force Hc decreases. However, in the range where the concentration ratio of [soft magnetic material 20]/[hard magnetic material 15] satisfies the predetermined upper limit, the effect of increasing the magnetization is greater than the decrease of the coercive force Hc. That is, when the relative content [soft magnetic body 20]/[hard magnetic body 15] of the soft magnetic body 20 is not more than the upper limit, the effect of increasing the magnetization Br can be prioritized. In this respect, the layer thickness of the soft magnetic body 20 is preferably 500 nm or less, more preferably 200 nm or less. As the magnetization Br, an optimum thickness can be appropriately selected from design values such as the characteristics of the magnetic head, the recording magnetization amount, and the coercive force.

On the other hand, the recording layer 30 may contain a binder (not shown) for the purpose of improving the binding property between the magnetic particles 10 or for promoting the adhesion between the magnetic particles 10 and the soft magnetic body 20. .. The binder may be a homopolymer or a copolymer. The binder contained in the recording layer 30 is selected from polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, epoxy resin, phenoxy resin and polyvinyl acetal. Further, the recording layer 30 can also be selected from an acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate and the like, a cellulose resin such as nitrocellulose, and a polyvinyl alkaryl resin such as polyvinyl butyral. Furthermore, the recording layer 30 can be used by mixing a plurality of resins. The recording layer 30 is particularly preferably made of polyurethane resin, acrylic resin, cellulose resin and vinyl chloride resin.

In addition, the recording layer 30 may be added with additives as required. Examples of the additive applied to the recording layer 30 include an abrasive, a lubricant, a dispersant, a dispersion aid, an antifungal agent, an antistatic agent, an antioxidant, and carbon black. Further, the recording layer 30 includes a form containing a curing agent and a plasticizer.

On the other hand, the support layer 70 supports the recording layer 30 so that the laminated body of the support layer 70 and the recording layer 30 has flexibility. By thus forming the magnetic recording medium 100 as a laminated body having flexibility, it becomes possible to wind the magnetic recording medium 100 on a reel, thereby increasing the recording capacity, portability and storability. Etc. can be improved. Further, it becomes possible to continue to apply a tension for pressing the magnetic recording medium 100 to the magnetic head during an operation such as recording and reproducing, and there is an effect that the magnetic head and the recording medium 100 slide stably during such an operation.

The support layer 70 has a flexibility to stably support the recording layer 30 even if the support layer 70 is deformed by an external force. The support layer 70 has tensile strength, chemical stability with respect to environment, thermal stability, insensitivity to magnetic field, layer thickness, surface roughness, and antistatic property in consideration of portability of the recording medium 100, scanning form, and the like. The material and dimension can be selected in consideration of conductivity for the above. The support layer 70 includes a form that is a resin layer that does not exhibit magnetism, and such a configuration can reduce a magnetic field that becomes a background and affects the recording layer 30. Embodiments that do not exhibit magnetism include paramagnetism. The aspect which does not exhibit magnetism may be paraphrased as nonmagnetic.

The support layer 70 of the present embodiment includes a substrate 40 made of a flexible resin, an intermediate layer 50 having adhesiveness or plastic deformability for supporting the recording layer 30, a winding property, and a support layer 70. And a back layer 60 that provides a peeling property that reduces sticking between the recording layer 30 and the recording layer 30.

The base material 40 is a flexible, long film, and can be in the form of a roll. As the material of the base material 40, polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, metals, ceramics and the like are selected.

Polyethylene terephthalate PET is selected for polyesters, and polyethylene, polypropylene, etc. are selected for polyolefins. The cellulose derivative is selected from cellulose triacetate, cellulose diacetate, cellulose butyrate and the like, and the vinyl resin is selected from polyvinyl chloride, polyvinylidene chloride and the like. As the metal, a paramagnetic metal or alloy such as titanium or aluminum is selected. Alumina or the like formed from a green sheet is selected as the ceramic. As the support layer, a thin film containing an oxide of Al or Cu may be disposed on at least one of the front and back surfaces of the base material 40 in order to increase the mechanical strength of the base material 40.

The back layer 60 preferably contains carbon black and inorganic powder. The layer thickness of the back surface layer is preferably 0.9 μm or less, and more preferably 0.1 μm or more and 0.7 μm or less.

Between the base material 40 and the recording layer 30, it has a function of an adhesion layer for ensuring the adhesion of the magnetic particles 10 to the base material 40, a relaxation layer for relaxing the difference in the physical properties of the base material 40 and the recording layer 30, and the like. A mode in which the intermediate layer 50 is added is included in the modification of the present embodiment.

The magnetic recording medium 100 of this embodiment can be manufactured by a manufacturing method including at least the following steps 1 and 2.
(Step 1) Laminated body in which a support layer 70 having flexibility and a recording layer 30 including a plurality of magnetic particles 10 including a hard magnetic body 15 and a soft magnetic body 20 in contact with the plurality of magnetic particles 10 are laminated. (Step 2) Magnetic field applying step of magnetizing the magnetic particles 10 in a predetermined direction by an external magnetic field applied from the outside of the laminated body

The magnetic particle 10 is an aspherical body including a long axis and a short axis, and the plurality of magnetic particles 10 include a form in which the long axis is oriented in a predetermined direction as shown in FIG. The predetermined direction may coincide with the direction along the easy axis of magnetization. In this step, the soft magnetic material 20 may be magnetized not only by the magnetic particles 10 but also by the external magnetic field.

Next, a method for manufacturing the magnetic particles 10 according to the present embodiment will be described below by using an example in which the hard magnetic body 15 is ε iron oxide. The magnetic particles 10 containing ε iron oxide as the hard magnetic material 15 are produced by producing nanoparticles of iron oxide or iron hydroxide using a chemical process in a solution and heating the produced nanoparticles in an oxidizing atmosphere. can get. The chemical process in the solution can be obtained, for example, by subjecting precursor particles formed by a reverse micelle method or a sol-gel method using iron nitrate hydrate as a starting material to heat treatment in an oxidizing atmosphere.

Next, a method for manufacturing the magnetic recording medium 100 according to this embodiment will be described below.

The method of manufacturing the magnetic recording medium 100 according to the present embodiment includes a support layer 70 having flexibility, a plurality of magnetic particles 10 including the hard magnetic material 15, and a soft magnetic material 20 in contact with the plurality of magnetic particles 10. The recording layer 30 and the recording layer 30 are laminated to form a laminated body.

The method for manufacturing the magnetic recording medium 100 according to the present embodiment includes a magnetic field applying step of magnetizing the magnetic particles 10 including the hard magnetic material 15 in a predetermined direction by an external magnetic field applied from the outside of the stacked body. The magnetic field applying step can be performed after the step of forming the laminated body. 1B and 2B are partially enlarged views of the recording layer 30. In each embodiment, the magnetic particles 10 are magnetized in the vertical direction of the paper surface. In other words, the hard magnetic material 15 contained in the magnetic particles 10 is oriented in the upper limit direction of the paper surface. The easy axis of magnetization in the magnetic domain due to the application of the magnetic field can be identified by measuring the magnetic characteristics while varying the direction and strength of the external magnetization and taking the squareness ratio. 1B and 2B show a mode in which the magnetization direction is aligned with the short axis of the magnetic particle 10. However, a form in which the shape of the magnetic particles 10 and the magnetization direction do not necessarily match is included as a modification of the present embodiment.

(Step of preparing the material for the support layer)
A backing layer 60 is provided and a tape-shaped substrate 40 is prepared.

(Process of preparing recording layer material)
The recording layer coating material is prepared by kneading and dispersing the magnetic particles 10 containing ε iron oxide and the additive substance in a solvent. The additive substance includes conductive particles and a binder. When the recording layer 30 is a composite of a hard magnetic material and a soft magnetic material in which the soft magnetic material 20 is contained as the binder matrix of the magnetic particles 10, the soft magnetic material is kneaded and dispersed in the coating material for the recording layer.

The solvent used for the coating material for the recording layer is selected in consideration of the dispersibility of the magnetic particles 10 and the added substance, and examples thereof include a ketone solvent, an alcohol solvent, an ester solvent, an ether solvent, an aromatic solvent, and a halogen. A solvent containing a hydrocarbon and the like are included. These may be used alone or may be appropriately mixed and used. As a kneading device used for preparing such a coating material, for example, a kneading device such as a continuous biaxial kneading machine, a continuous biaxial kneading machine capable of diluting in multiple stages, a kneader, a pressure kneader, or a roll kneader can be used. A roll mill, a ball mill, a homogenizer, an ultrasonic disperser, or the like is selected as the dispersing device used for the above-mentioned coating material preparation.

(Intermediate layer forming step)
The intermediate layer 50 is formed on the base material 40 by applying the intermediate layer coating material to the surface of the base material 40 on which the back surface layer 60 is not formed and drying it. Through this step and the step of preparing the material for the support layer, the support layer 70 having flexibility is created.

(Laminating step, recording layer forming step)
The magnetic particles 10 are formed on the intermediate layer 50 by applying the coating material for the recording layer on the intermediate layer 50 and drying it. Subsequently, the soft magnetic body 20 is formed on the surface on which the magnetic particles 10 are arranged, and the recording layer 30 is formed. This step is in other words the step of stacking the recording layer 30 on the support layer 70.

The soft magnetic material 20 can be deposited on the magnetic particles 10 by using a sputtering method or a vacuum evaporation method. It is preferable to form the soft magnetic material 20 by a sputtering method because of its controllability of the layer thickness.

(Roll forming)
Next, the support layer 70 is wound around the cylindrical core and cured. Next, after calendering the support layer 70, the support layer 70 is cut into a predetermined width to obtain a long tape-shaped support layer 70 cut into a predetermined width. The predetermined width corresponds to the length of the core in the tube axis direction. The step of forming the back surface layer 60 may be performed after the calendar treatment.

<Second Embodiment>
As shown in FIG. 2, the present embodiment is related to the first embodiment in that the soft magnetic body 20 is a binder matrix that is in contact with the periphery of the magnetic particles 10 and binds the plurality of magnetic particles 10. It is different from the magnetic recording medium 100. In other words, the magnetic particles 10 of this embodiment are bound to each other via the soft magnetic body 20.

Hereinafter, the present invention will be described in more detail using examples, but the technical scope of the present invention is not limited to the following examples. All “%” used below are based on mass unless otherwise specified.

[Example 1]
(Preparation of ε-Fe2O3 particles)
ε-Fe ₂ O ₃ particles were produced by the following procedure.

(1) First, two types of micelle solutions (micelle solution (A) and micelle solution (B)) were prepared as follows.

(1-1) Pure water 30 mL, n-octane 92 mL, and 1-butanol 19 mL were placed in a reaction vessel and mixed. There, iron nitrate hydrate _{_{(Fe (NO 3) 3 ·}} 9H 2 O) was added 6 g, was sufficiently dissolved with stirring. Next, cetyltrimethylammonium bromide as a surfactant was added in an amount such that the molar ratio represented by (mol number of pure water)/(mol number of surfactant) was 30, and the mixture was stirred. Dissolved. Thereby, the micelle solution (A) was obtained.

(1-2) In another reaction container, 10 mL of 28% ammonia water was mixed with 20 mL of pure water and stirred, and then 92 mL of n-octane and 19 mL of 1-butanol were added and well stirred. Cetyltrimethylammonium bromide as a surfactant is added to the solution so that the molar ratio represented by ((the number of moles of pure water+water in ammonia water))/(the number of moles of the surfactant) is 30. The amount was added and dissolved by stirring. Thereby, the micelle solution (B) was obtained.

(2) The micellar solution (B) was added dropwise to the micellar solution (A) while thoroughly stirring the micellar solution (A). After the dropping was completed, stirring was continued for 30 minutes.

(3) While stirring the obtained mixed solution, 7.5 mL of tetraethoxysilane (TEOS) was added to the mixed solution, and the stirring was continued for 1 day. In this step, a silica layer was formed on the surface of the iron-containing particles in the mixed solution.

(4) The obtained solution was set in a centrifuge and centrifuged at 4500 rpm for 30 minutes to collect the precipitate. The collected precipitate was washed multiple times with ethanol.

(5) After drying the obtained precipitate, it was placed in a firing furnace in an air atmosphere and heat-treated at 1150° C. for 4 hours.

(6) The powder after heat treatment was dispersed in an aqueous NaOH solution having a concentration of 2 mol/L and stirred for 24 hours to remove the silica layer on the particle surface. Then, filtration, washing with water and drying were performed to obtain ε-Fe ₂ O ₃ particles. Further, as a result of analyzing the crystal structure of the obtained ε-Fe ₂ O ₃ particles by XRD, the diffraction peak of ε-Fe ₂ O ₃ was confirmed, and the diffraction peaks derived from other crystal structures were not confirmed. . When the magnetic properties of the particles alone in the non-oriented state were measured with an applied magnetic field strength of 50 kOe using a vibrating sample type magnetometer, the coercive force was 20.1 kOe and the residual magnetization (Mr) was 6 emu/g.

(Ε-Fe2O3 particle layer forming paint)
6 g of vinyl chloride resin (30% cyclohexanone solution), 0.5 g of aluminum oxide powder, and 0.2 g of carbon black were weighed and sufficiently mixed with 10 g of the ε-Fe2O3 particles produced as described above.

Next, 3 g of vinyl chloride resin (resin solution: resin content 30%, cyclohexanone 70%), n-butyl stearate 2 g, methyl ethyl ketone 12 g and toluene 12 g were weighed and mixed sufficiently. These were mixed to obtain a coating material for forming ε-Fe2O3 particle layer.

(Paint for forming the intermediate layer 50)
Next, 6 g of vinyl chloride resin (resin solution: resin content 30%, cyclohexanone 70%) and carbon black 1 g were weighed and mixed sufficiently with 10 g of α-Fe2O3 particles.

Next, 1.9 g of polyurethane resin, 0.2 g of n-butyl stearate, 11 g of methyl ethyl ketone, toluene: 10.8 g and 1.9 g of cyclohexanone were weighed and thoroughly mixed. These were mixed to obtain a coating material for forming the intermediate layer 50.

Next, 0.4 g of polyisocyanate and 0.2 g of myristic acid were added as a curing agent to each of the coating material for forming the recording layer 30 and the coating material for forming the intermediate layer 50 produced as described above.

(Magnetic tape)
Next, using these coating materials, the intermediate layer 50 and the recording layer 30 were formed as follows on the polyethylene naphthalate film (PEN film) which is a non-magnetic support. First, the intermediate layer 50 was formed on the PEN film by applying and drying the intermediate layer 50 forming coating material on the PEN film having a thickness of 6 μm which is a non-magnetic support. Next, the recording layer 30 forming coating material was applied onto the intermediate layer 50 and dried to form the recording layer 30 on the intermediate layer 50. The drying was performed in a coil that generates a magnetic field of 6 kOe, and the ε-Fe2O3 particles were fixed while being aligned in the direction along the easy axis of magnetization. Next, the PEN film on which the intermediate layer 50 and the recording layer 30 were formed was calendered to smooth the ε-Fe2O3 particle layer. The average thickness of the intermediate layer 50 after calendering was 1 μm, and the average thickness of the ε-Fe 2 O 3 particle layer was in the range of 20 to 50 nm.

Next, an Fe film was formed as a soft magnetic material on the ε-Fe2O3 particle layer by a sputtering method (DC magnetron sputtering apparatus). First, the PEN film on which the ε-Fe 2 O 3 particle layer was formed was placed in a vacuum chamber, and vacuum evacuation was performed until the degree of vacuum reached 3×10 ⁻⁴ Pa. Next, while supplying argon gas at a flow rate of 30 sccm, the pressure was adjusted to 0.5 Pa. Next, pre-sputtering was performed at a discharge power of 100 W for 3 minutes, and then an Fe film was deposited to 200 nm on the ε-Fe 2 O 3 particle layer for 1 minute to form the recording layer 30.

Next, 10 g of carbon black, 10 g of polyester polyurethane, 50 g of methyl ethyl ketone, 40 g of toluene and 10 g of cyclohexanone were weighed and mixed to obtain a mixture. On the surface opposite to the recording layer 30, the mixed portion was coated with a coating material having the following composition to a film thickness of 0.6 μm and dried to form a back surface layer 60.

Next, a fluorine-based lubricant was applied on the recording layer 30 to form a top coat layer. Next, the PEN film on which the intermediate layer 50, the recording layer 30, and the back layer 60 are formed as described above is cut into a width of 0.5 inch (12.65 mm) to obtain a magnetic tape as a magnetic recording medium. It was

Next, a part of the magnetic tape was cut out and a magnetic field was applied in the vertical direction of the magnetic tape to evaluate the characteristics. The measurement magnetic field was set at 50 kOe as a magnetic field sufficient to saturate the hysteresis curve of the magnetic tape. Since the obtained hysteresis curve includes background noise other than that of the recording layer 30, the hysteresis curve of only the recording layer 30 is obtained by linearly approximating the area where the hysteresis curve is saturated and subtracting from the hysteresis curve. And The magnetization upon application of 50 kOe was calculated as saturation magnetization Ms(emu) and residual magnetization Mr(emu) to obtain the squareness ratio (Mr/Ms) of the magnetic signal. Further, the magnetic field at which the magnetization is zero was defined as the coercive force (Oe).

[Comparative Example 1]
In the same manner as in Example 1, a film in which an ε-Fe2O3 particle layer was formed on a PEN film was produced, and a back surface layer 60 was formed on the back surface.

Next, as described above, the PEN film having the intermediate layer 50, the recording layer 30 having only the ε-Fe2O3 particle layer, and the back layer 60 formed thereon was cut into a 0.5 inch (12.65 mm) width, and magnetic recording was performed. A magnetic tape as a medium was obtained.

Next, a part of the magnetic tape was cut out and the MH curve was measured in the vertical direction of the magnetic tape. The measurement magnetic field was 50 kOe as a magnetic field sufficient to saturate the MH curve of the magnetic tape. Since the obtained MH curve contains background noise other than that of the recording layer 30, the MH curve of only the recording layer 30 is obtained by linearly approximating the area where the MH curve is saturated and subtracting it from the MH curve. And The magnetization upon application of 50 kOe was calculated as saturation magnetization Ms(emu) and residual magnetization Mr(emu) to obtain the squareness ratio (Mr/Ms) of the magnetic signal.

[Examples 2 to 5]
A magnetic tape was produced using the same ε-Fe2O3 particle layer forming coating material and intermediate layer 50 forming coating material as in Example 1. However, a magnetic tape was produced by setting the thickness of the Fe film of the soft magnetic material to 20 to 100 nm and the other configurations being the same as in Example 1, and the magnetic characteristics were evaluated.

[Examples 6 to 9]
Using the production method of ε-Fe2O3 particles of Example 1 as a basic production method, ε-Fe2O3 particles in which a part of Fe element was replaced with another metal element (Co, Ni, Ti or Ga) were synthesized. For each metal element, cobalt nitrate hydrate is used for Co, nickel nitrate hydrate is used for Ni, titanium sulfate hydrate is used for Ti, and gallium nitrate hydrate is used for Ga. % Replaced.

Next, in the same manner as in Example 1, a coating material for forming an ε-Fe2O3 particle layer and a coating material for forming the intermediate layer 50 were prepared, and a magnetic tape was prepared by depositing a Fe film to a thickness of 200 nm on the ε-Fe2O3 particle layer to prepare a magnetic tape. The characteristics were evaluated.

[Comparative Examples 2 to 5]
ε-Fe2O3 particles were produced by substituting a part of Fe element of ε-Fe2O3 particles with another metal element (Co, Ni, Ti or Ga), and a magnetic tape having only the ε-Fe2O3 layer as a recording layer was prepared to produce a magnetic tape. The characteristics were evaluated. The amount of substitution of the metal element was selected such that the coercive force of the ε-Fe2O3 particles was about 3000 Oe.

As shown in Table 1, in Examples 1 to 9, both the residual saturation magnetization and the residual magnetization were improved as compared with Comparative Examples 1 to 5. From the above results, it was found that the magnetic recording medium having ε-Fe2O3 and the soft magnetic material in the recording layer 30 can provide a magnetic recording medium having excellent electromagnetic conversion characteristics.

The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are attached to open the scope of the present invention.

The present application claims priority based on Japanese Patent Application No. 2018-225870 filed on November 30, 2018, and the entire content of the description is incorporated herein.

Claims

A recording layer comprising a plurality of magnetic particles containing a hard magnetic material and a soft magnetic material in contact with the plurality of magnetic particles, and a support layer exhibiting flexibility and supporting the recording layer, and a magnetic field comprising: recoding media.
The magnetic recording medium according to claim 1, wherein the hard magnetic material contains ε iron oxide.
The magnetic recording medium according to claim 2, wherein the magnetic particles contain ε iron oxide as a main component.
The magnetic recording medium according to claim 2 or 3, wherein the ε iron oxide contains trivalent iron.
The magnetic recording medium according to any one of claims 2 to 4, wherein the ε iron oxide contains a substituted metal.
The magnetic recording medium according to claim 5, wherein the substitution metal contains at least one of Co, Ni, Ti, and Ga.
7. The ε-iron oxide is described as ε-P x Q y R z Fe (2-3x-1.5y-z) O 3 , according to any one of claims 2 to 6. Magnetic recording medium.
However, each of P, Q, and R is a monovalent, divalent, or trivalent metal, and 0≦x<1.5, 0≦y<2/3, 0≦z<2, 0≦3x−1.5y− It is a number that satisfies z<2.
The magnetic recording medium according to any one of claims 1 to 7, wherein the soft magnetic material contains α-Fe.
The magnetic recording medium according to claim 8, wherein the soft magnetic material contains α-Fe as a main component.
The magnetic recording medium according to any one of claims 1 to 9, wherein the magnetic particles are bound to each other via the soft magnetic material.
The magnetic recording medium according to any one of claims 1 to 10, wherein the magnetic particles are sandwiched between the soft magnetic material and the support layer.
12. The soft magnetic material covers the plurality of magnetic particles on the side opposite to the surface where the magnetic particles face the supporting layer, according to claim 1. Magnetic recording media.
13. The supporting layer supports the recording layer so that the laminate of the supporting layer and the recording layer has flexibility, and the supporting layer supports the recording layer. Magnetic recording medium.
The magnetic recording medium according to any one of claims 1 to 13, wherein the support layer is a resin layer that does not exhibit magnetism.
15. The magnetic particle is an aspherical body having a long axis and a short axis, and in the plurality of magnetic particles, the long axis is oriented in a predetermined direction. A magnetic recording medium according to item.
The magnetic recording medium according to claim 15, wherein the predetermined direction is a direction along an easy axis of magnetization.
A step of forming a laminated body by laminating a support layer having flexibility, a recording layer containing a plurality of magnetic particles containing a hard magnetic material and a soft magnetic material in contact with the plurality of magnetic particles;
A magnetic field applying step of magnetizing the soft magnetic material and the magnetic particles in a predetermined direction by an external magnetic field applied from the outside of the laminated body.