JP2009087475A - Method for manufacturing magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which is excellent in durability even though it is excellent in a high recording density characteristic. <P>SOLUTION: In this method for manufacturing a magnetic recording medium having at least a magnetic layer on a non-magnetic supporting body, the magnetic layer is formed by applying a magnetic paint containing magnetic powder, a polishing agent and a binder, wherein the average particular diameter is 10 to 40 nm. The magnetic paint is adjusted by going through a step for adjusting a magnetic liquid containing the magnetic powder and the binder, a step for preparing a polishing liquid containing the polishing agent and the binder, and a step for mixing and dispersing the magnetic liquid and the polishing liquid by colliding them by a collision type dispersion mixer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a coating type magnetic recording medium excellent in durability while having excellent high recording density characteristics suitable for a magnetic recording / reproducing system using, for example, a magnetoresistive reproducing head (MR head).

  Magnetic tapes have various uses such as audio tapes, video tapes, computer tapes, etc., especially in the field of data backup tapes, with the increase in capacity of hard disks to be backed up, several tens to 800 GB per volume. The one with the recording capacity is commercialized. In the future, a large-capacity backup tape exceeding 1 TB has been proposed, and its high recording density is indispensable.

  As a means for increasing the recording capacity, the approach from the recording / reproducing apparatus uses a shorter recording signal wavelength or a narrower track pitch, which reduces the leakage flux from the magnetic tape, thereby reducing the reproduction. It has become the mainstream to use an MR head that can obtain a high output even with a minute magnetic flux.

  In the approach from the medium, the magnetic properties are improved along with the fine particles of the magnetic powder. Conventionally, ferromagnetic iron oxide and Co-modified ferromagnetic oxidation used for video tapes for audio and home use. Magnetic powders such as iron and chromium oxide have been the mainstream, but at present, acicular ferromagnetic iron-based metal powders with a particle size of about 25 to 65 nm have been proposed as computer tapes.

  In addition, in order to prevent a decrease in output due to demagnetization during short wavelength recording, a high coercive force of the magnetic powder is achieved, and a coercive force of about 198.9 kA / m is realized by the alloying of iron-cobalt. Yes.

  In addition, as a magnetic powder for realizing low noise, the particle shape is plate-like, and the particle size (particle diameter) is a fine particle of barium ferrite magnetic powder having a particle size (particle diameter) of about 10 to 40 nm, and having crystal magnetic anisotropy, As a magnetic powder capable of achieving both a fine particle size and a high coercive force, iron nitride magnetic powder (eg, Patent Document 1) having a spherical or granular shape and a particle size of about 5 to 50 nm has been proposed.

  On the other hand, in the approach from the medium manufacturing technology side, a magnetic layer component containing fine magnetic powder is kneaded and dispersed (Patent Document 2, etc.), a nonmagnetic undercoat layer (hereinafter simply referred to as a nonmagnetic layer, an undercoat) under the magnetic layer. Improvements in techniques such as simultaneous multilayer coating (also referred to as Patent Document 3), which improve the short wavelength recording characteristics by improving the filling property and surface smoothness of the magnetic layer and making the magnetic layer thinner. ing.

  Further, in order to improve the durability of the recording medium, a medium manufacturing method has been proposed in which an abrasive is made into a paste separately from the magnetic liquid and mixed with the magnetic liquid to form a magnetic coating (Patent Document 4 or the like). Various devices for mixing two liquids have been disclosed (for example, Patent Documents 5 to 7).

Japanese Patent No. 3886968 JP 2004-22158 A JP-A 63-187418 JP 2002-352423 A JP 2000-153142 A JP-A-8-103642 JP 7-144122 A

  However, even when a magnetic coating is prepared using magnetic powder with fine coercive force and fine magnetic layers are applied simultaneously on the nonmagnetic undercoat layer, the magnetic powder becomes finer and the surface of the magnetic layer becomes smoother. The durability of the recording medium tends to decrease as the performance is improved. The abrasive that improves the durability is made into a paste separately from the magnetic liquid, and finally mixed with the magnetic liquid and mixed to form a magnetic paint. A method of manufacturing a medium has been proposed. However, in the conventional technique such as Patent Document 4, it is difficult to mix the abrasive paste and the magnetic liquid sufficiently uniformly. The magnetic layer is formed by agglomerating the abrasive particles, and the durability is improved. However, the MR head is damaged by the frictional heat due to the collision of the protrusions even if the MR head is damaged or not damaged. US Noise there has been a case that occurs utility occurs. In view of the above problems, an object of the present invention is to provide a magnetic recording medium excellent in durability while being excellent in high recording density characteristics.

  As a result of intensive studies in a method for producing a magnetic recording medium having at least a magnetic layer on a nonmagnetic support, it is possible to provide a magnetic recording medium excellent in durability while having excellent high recording density characteristics with the following configuration. As a result, the present inventors have made the present invention.

  That is, the magnetic layer is formed by applying a magnetic paint containing magnetic powder, an abrasive, and a binder, and the magnetic powder has an average particle size of 10 to 40 nm. A step of adjusting a magnetic liquid containing powder and a binder, a step of preparing a polishing liquid containing an abrasive and a binder, and the magnetic liquid and the polishing liquid are collided by a collision type disperser and mixed and dispersed. It adjusts through a process, It is characterized by the above-mentioned.

  The collision type disperser was ejected from each orifice, a first orifice that ejects the magnetic liquid at a first predetermined pressure, a second orifice that ejects the polishing liquid at a second predetermined pressure, and the like. A mixing chamber having an inner diameter larger than the inner diameter of each of the orifices for mixing the liquid, and the liquid contact surface of the orifice and the mixing chamber is made of a wear-resistant material.

  In the method for producing a magnetic recording medium having at least a magnetic layer on a nonmagnetic support, the magnetic layer is formed by applying a magnetic paint containing magnetic powder, an abrasive and a binder, and the magnetic powder is Since the average particle diameter is 10 to 40 nm, noise is small and the magnetic coating material prepares a polishing liquid containing a polishing agent and a binder, and a step of adjusting a magnetic liquid containing the magnetic powder and the binder. And the step of causing the magnetic liquid and the polishing liquid to collide with a collision-type disperser to mix and disperse, so that each paint can be suitably mixed and dispersed. By mixing and dispersing, a magnetic paint in which the abrasive is uniformly dispersed can be obtained. As a result, it is possible to provide a magnetic recording medium excellent in durability while being excellent in high recording density characteristics.

  Further, the collision type disperser ejects the magnetic liquid at a first predetermined pressure, the second orifice that ejects the polishing liquid at a second predetermined pressure, and the respective orifices. A mixing chamber having an inner diameter larger than the inner diameter of each of the orifices for mixing the liquid, and the liquid contact surface of the orifice and the mixing chamber is made of a wear-resistant material. Since the liquid can be mixed and dispersed, and the wear of each orifice and the mixing chamber is reduced, the magnetic recording medium can be manufactured for a long time.

  As a method of mixing a magnetic liquid in which magnetic powder is dispersed in a binder and a polishing liquid (abrasive paste) in which an abrasive is dispersed in the binder, (1) a disperser which is a so-called stirring type mixing device. However, since this method has a small shearing force, the particle size of the powder contained, the particle surface properties, the resin adsorption form, and the viscosity of the magnetic liquid are completely different. It is difficult to uniformly mix with the polishing liquid, and when viewed microscopically, the polishing liquid exists in the form of droplets in the magnetic liquid, so that the abrasive exists as an aggregate in the formed magnetic layer. Become a shape. To that end, (2) An attempt to finely disperse the liquid droplets of the polishing liquid in the magnetic liquid using an ultrasonic disperser or collision type disperser having a larger shearing force after mixing in the disperser. Has been proposed, but it has not been fully effective. There has also been proposed an attempt to finely disperse the liquid droplets of the polishing liquid in the magnetic liquid using a media-type disperser after mixing in the disperser. Although a magnetic coating material in which the agent is dispersed can be obtained, there is a problem that the magnetic properties are deteriorated due to mixing of media wear components or the magnetic powder is damaged, and the electromagnetic conversion properties are deteriorated.

  According to the study by the present inventors, the magnetic liquid and the polishing liquid are premixed with a device having a relatively small shearing force such as a disper, and then another mixing and dispersing device with a relatively high shearing force is prepared. It has been found that it is difficult for the conventional mixing / dispersing method used to effectively exhibit the performance of the subsequent high-shearing mixing / dispersing device.

  That is, it was found that the abrasive liquid can be uniformly mixed and dispersed in the magnetic liquid by colliding the magnetic liquid in which the magnetic powder is dispersed in the binder with the polishing liquid in which the abrasive is dispersed in the binder. It is.

  A commercially available collision disperser can be used to cause the magnetic liquid and the polishing liquid to collide. The impact disperser pressurizes the paint to be dispersed at a high pressure by a high-pressure pressurizing means, and ejects the paint from a narrow gap to cause shearing and grinding action due to collision between the paints to be dispersed or between the paint to be dispersed and the inner wall of the apparatus. Since it is an apparatus for finely dispersing using it and does not use dispersion media, it is characterized by no contamination due to dispersion.

  Collision type dispersers such as Sugino Machine Optimizer, Yoshida Machine Industries Co., Ltd. Nanomizer, Sanwa Machine Co., Ltd. Homogenizer, Microfluidics Co., Ltd., Microfluidizer These devices can be used as they are or after modification.

  A normal collision type disperser pressurizes one liquid with a plunger pump, and ejects it from a narrow gap so that it collides with the inner wall of the apparatus or branches into two paths after pressurization so as to face the narrow gap (orifice). The liquid is ejected to cause the liquids to collide and disperse.

  In order to use the above-described collision type disperser in the present invention, at least a plunger pump for pressurizing the magnetic liquid is required. The magnetic liquid and the polishing liquid are mixed and dispersed by colliding a magnetic liquid ejected at a high pressure and a high speed with a polishing liquid ejected from another orifice. In this case, it is not always necessary to pressurize the polishing liquid at a high pressure, and the magnetic liquid can be jetted and collided with the supplied polishing liquid to perform mixing and dispersion. Further, it is preferable to appropriately adjust the magnitude of the pressure for pressurizing the liquid and the gap (orifice) for ejecting the liquid in accordance with the mixing ratio of the magnetic liquid and the polishing liquid.

  Hereinafter, an example of a mixing and dispersing apparatus used in the method for manufacturing a magnetic recording medium of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a main part of an example of a collision type disperser used in the mixing and dispersing apparatus of the present example. The collision type disperser 10 of this example includes a first supply nozzle 1 for introducing a magnetic liquid, a second supply nozzle 2 for introducing a polishing liquid, a mixing chamber 4 for mixing and dispersing the liquid, and discharging the mixed and dispersed two liquids. The discharge nozzle 3 is configured.

  The first supply nozzle communicates with a magnetic liquid supply tank (not shown) that supplies the magnetic liquid via a plunger pump (not shown). A first orifice having a diameter smaller than the nozzle diameter of the first supply nozzle 1 is disposed at the outlet of the first supply nozzle 1 on the mixing chamber 4 side, and the magnetic liquid is ejected from a small gap.

  The second supply nozzle 2 communicates with a polishing liquid supply tank (not shown) for supplying a polishing liquid via a plunger pump (not shown) or a normal supply pump. A second orifice 12 having a diameter smaller than the nozzle diameter of the second supply nozzle 2 is disposed at the outlet of the second supply nozzle 2 on the mixing chamber 4 side, and the polishing liquid is ejected from a small gap.

  The mixing chamber 4 forms a space whose inner diameter is larger than the inner diameter of each orifice. By forming such a space, the magnetic liquid and the polishing liquid ejected from the first orifice and the second orifice turbulently flow. The two liquids can be efficiently mixed and dispersed.

  The discharge nozzle 3 is provided with a third orifice 13 having a diameter smaller than the nozzle diameter of the discharge nozzle 3 at the entrance from the mixing chamber 4, and the mixed liquid can be supplied while maintaining a constant pressure in the mixing chamber 4. It can be discharged.

  FIG. 2 is a schematic configuration diagram of an example of a mixing and dispersing apparatus used in the method for manufacturing a magnetic recording medium of the present invention. The magnetic liquid that has entered the first tank 20 is pressurized to the pressure P1 and sent to the first supply nozzle 1 of the collision disperser 10 via the first pump 21 (plunger pump). The polishing liquid that has entered the second tank 30 is pressurized to the pressure P2 via the second pump 31 (for example, a normal supply pump such as a plunger pump or a Mono pump) or collides without being particularly pressurized. It is sent to the second supply nozzle 2 of the disperser 10. The magnetic liquid pressurized by the plunger pump is ejected from the first orifice 11 having an inner diameter D1 into the mixing chamber 4. The polishing liquid is jetted into the mixing chamber 4 from the second orifice 12 having an inner diameter D2. The supply nozzles 1 and 2 are arranged such that the magnetic liquid ejection direction and the polishing liquid ejection direction form an angle θ. The magnetic liquid and the polishing liquid ejected from the supply nozzles 1 and 2 collide with each other at an angle θ, and are mixed and dispersed instantaneously in the mixing chamber 4. The mixed and dispersed magnetic liquid and polishing liquid are discharged from the discharge nozzle 3 as a magnetic paint through the third orifice 13 having an inner diameter of D3.

  Each of the orifices (particularly, the first orifice 11 and the second orifice 13) and the liquid contact surface of the mixing chamber 4 are preferably made of a wear resistant material. The liquid contact surface is made of a wear resistant material. As a result, deformation due to wear of the wetted surface can be reduced, so that the service life of the collision type disperser can be extended. Conventionally known materials can be used as the wear resistant material, but super steel, ceramic, DLC, and the like can be used.

  The pressure received by the magnetic liquid in the first tank from the first plunger pump and the pressure received by the polishing liquid in the second tank from the second plunger pump are the first pressure gauge 22 and the second pressure, respectively. Measurement is possible with a total of 32.

  The pressure P1 of the magnetic liquid is preferably 50 to 250 MPa, more preferably 50 to 200 MPa, and most preferably 50 to 150 MPa. This range is preferable because if the pressure is less than 50 MPa, the pressure is too low to obtain uniform mixing, and if it exceeds 250 MPa, the heat generated at the time of collision is too large, and the paint may become too hot and change its quality. It is. The inner diameter D1 of the first orifice 11 for ejecting the magnetic liquid may be appropriately selected according to the desired amount of the magnetic liquid to be processed, but is usually preferably 0.01 to 1 mm, more preferably 0.05 to 0.8 mm. 0.1 to 0.6 mm is most preferable. This range is preferable because if the thickness is less than 0.01 mm, the processing amount becomes too small, and if it exceeds 1 mm, the capacity of the pump required for pressurization becomes too large.

The polishing liquid is not particularly pressurized, and a predetermined amount may be sent to the mixing chamber 4 with a metering pump. However, by applying pressure, the magnetic liquid and the polishing liquid can be mixed more uniformly. When pressurizing, the applied pressure P2 is preferably 50 to 250 MPa, more preferably 50 to 200 MPa, and most preferably 50 to 150 MPa. This range is preferable if the pressure is too small at less than 50 MPa, and the effect of pressurization cannot be obtained, and if it exceeds 250 MPa, the heat generated at the time of collision is too great, and the paint may become too hot and change its quality. Because. The inner diameter D2 of the second orifice 12 for ejecting the polishing liquid may be appropriately selected according to the desired amount of polishing liquid treatment, but is usually preferably 0.01 to 1 mm, more preferably 0.05 to 0.8 mm. 0.1 to 0.6 mm is most preferable. This range is preferable because if the thickness is less than 0.01 mm, the throughput is too small, and if it exceeds 1 mm, the capacity of the pump required for pressurization becomes too large.
The inner diameter D3 of the third orifice 13 that discharges the mixed liquid from the mixing chamber 4 may be appropriately selected according to the desired amount of magnetic paint to be treated, but is usually preferably 0.5 to 5 mm, more preferably 1 to 3 mm. 1 to 2 mm is most preferable. This range is preferred because if it is less than 0.05 mm, the amount of treatment is too small, and if it exceeds 5 mm, the pressure of the jet flow may escape and mixing may be insufficient.

  The angle θ formed between the magnetic liquid jet flow and the polishing liquid jet flow is preferably 5 to 175 °, more preferably 45 to 135 °, and most preferably 70 to 110 °. This range is preferable because when the angle θ is less than 5 °, the collision effect between the jet flows becomes insufficient, and uniform mixing is not performed, and when the angle θ exceeds 175 °, the jet flows are too opposite to each other and are polished. This is because the jet flow of the liquid is pushed back to the jet flow of the magnetic liquid, and on the contrary, the mixing effect is lowered.

  In the method for producing a magnetic coating material of the present invention, it is preferable to provide a mixing step, a kneading step and a mixing step, a dispersing step, a dilution and a mixing and dispersing step in this order. The manufacturing process of these magnetic paints is demonstrated using FIG.

  First, in the mixing step 41, as a pre-step of the kneading step, the magnetic powder granules are crushed with a high-speed stirring mixer, and subsequently, phosphoric acid-based or sulfonic acid-based organic acid-based with a high-speed stirring mixer. The surface treatment of the magnetic powder is performed by mixing with a dispersant, a binder resin and a solvent. The above high-speed agitating mixers include gas blow-up type agitators using the rolling flow effect such as Hosokawa Micron's Agromaster, the company's cyclomix and mechano-fusion system, and Sugiyama Heavy Industries' axial mixer. A rotary mixer, a Henschel mixer manufactured by Mitsui Mining Co., etc. can be used.

  Next, in the kneading step 42, the magnetic liquid component obtained in the mixing step 41 is kneaded by a batch kneader or a continuous biaxial kneader. The continuous twin-screw kneader includes KEX-30, KEX-40, KEX-50, KEX-65, KEX-80 manufactured by Kurimoto Steel Works, TEX30αII, TEX44αII, TEX65αII, TEX77αII, TEX90αII manufactured by Nippon Steel. Can be used.

  In the mixing step 43, the magnetic liquid component that has passed through the kneading step 42 is adjusted and diluted to a paint viscosity that facilitates dispersion, and the coarse agglomerates contained in the magnetic liquid component obtained in the kneading step 42 are pulverized and dispersed The previous paint is made uniform. As the high-speed stirrer, conventionally known apparatuses such as a dissolver, a homomixer, and cleamics are used.

  The magnetic liquid component that has undergone the above-described steps is dispersed by a conventionally known disperser (magnetic liquid dispersion step 44). In addition, a polishing agent component containing a polishing agent and a binder is dispersed by a conventionally known disperser (polishing liquid dispersion step 46).

  The magnetic liquid dispersion step 44 and the polishing liquid dispersion step 46 are preferably performed by a media type disperser. Media-type dispersers include discs (including holes, notches, grooves, etc.), pins, and rings provided on the agitation shaft, and rotors that rotate, such as nano mills, pico mills, sand mills, dyno mills, etc. A conventionally well-known thing can be used.

  The particle diameter of the dispersion medium is preferably 0.05 to 2.0 mm, more preferably 0.2 to 1.6 mm. This range is preferable because when the particle diameter is less than 0.05 mm, separation from the paint becomes difficult, and when it exceeds 2.0 mm, the dispersibility with respect to the fine magnetic powder decreases.

Conventionally known media such as glass, ceramic, and metal (including those whose surfaces are covered with resin) can be used as the dispersion media, but the density is particularly large (3 g / cm 3) for fine magnetic powder. ³ or more) is preferable. The filling amount of the dispersion medium into the mill container is preferably 50 to 90% in terms of an apparent volume ratio with respect to the mill internal volume. This range is preferable because if the ratio is less than 50%, the dispersion efficiency decreases, and if it exceeds 90%, not only does the movement of the dispersion medium worsen, but also the amount of heat generation increases.

  The rotation speed of the stirring shaft is preferably 6 to 15 m / s as the outer peripheral speed (circumferential speed) of the rotating part. This range is preferable because the dispersion energy of the dispersion medium is small at less than 6 m / s, and the dispersion medium is destroyed when it exceeds 15 m / s.

  Although the residence time at the time of dispersion of the paint varies depending on the constituents and applications of the magnetic paint, it is usually preferably 30 to 90 minutes. When performing paint dispersion using two or more sand mills, the dispersion conditions for each series may be changed. For example, it is more preferable to use a medium for dispersing large particles at the beginning and a medium for dispersing small particles at the end.

  After passing through the magnetic liquid dispersion step 44 and the dilution step 45, the magnetic liquid is collided with the polishing liquid obtained in the polishing liquid dispersion step 46 by a collision type disperser and mixed and dispersed to obtain a magnetic paint (mixing dispersion step). 47).

  Next, the magnetic paint is filtered as necessary to obtain a final magnetic paint.

<Magnetic powder>
Conventionally known magnetic powder can be used as the magnetic powder used in the production of the magnetic coating in the present invention, such as ferromagnetic iron-based metal magnetic powder, iron nitride magnetic powder, and plate-shaped hexagonal ferrite magnetic powder. Preferably used. Those having an average particle size of less than 40 nm, usually those having an average particle size of 10 nm or more are preferred, and those having a range of 15 to 40 nm are more preferred. This range is preferable because when the average particle size is 40 nm or more, particle noise based on the particle size increases, and when the average particle size is less than 10 nm, the coercive force decreases and the surface energy of the particles increases. This is because dispersion in the paint becomes difficult.

  The particle diameter as used in the present application refers to the average major axis diameter when the particles are needle-shaped, and refers to the length of the larger sheet diameter when the particles are plate-shaped, and the ratio of the major axis length to the minor axis length is 1 to 1. In the case of a spherical or elliptical shape of 3.5, it indicates the maximum passing diameter. The average particle size is obtained by measuring the particle size of a photograph taken with a transmission electron microscope (TEM) and calculating the average number of 300 particles.

<Binder>
Binders used in the magnetic layer, nonmagnetic layer, and back coat layer include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol. A polyurethane resin, at least one selected from a copolymer resin, a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and a cellulose resin such as nitrocellulose; And a combination of these.

  Among these resins, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination.

  Examples of the polyurethane resin include polyester polyurethane resin, polyether polyurethane resin, polyether polyester polyurethane resin, polycarbonate polyurethane resin, polyester polycarbonate polyurethane resin, and the like.

Such a binder includes —COOH, —SO ₃ M, —OSO ₃ M, —P═O (OM) ₃ , —O—P═O (OM) ₂ (in these formulas, M Represents a hydrogen atom, an alkali metal base or an amine salt), —OH, —NR ₁ R ₂ , —N ⁺ R ₃ R ₄ R ₅ (in these formulas, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ represents hydrogen or a hydrocarbon group), and those having an epoxy group are preferably used.

This is because the use of such a binder improves the dispersibility of the magnetic powder and the like. When two or more kinds of resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

  These binders are usually used in an amount of 7 to 50 parts by weight, preferably 10 to 35 parts by weight, based on 100 parts by weight of the magnetic powder. In particular, when a vinyl chloride resin and a polyurethane resin are used in combination, it is preferable to use 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin.

  Moreover, it is preferable to use together with these binders, the thermosetting crosslinking agent couple | bonded with the functional group etc. which are contained in a binder, and bridge | crosslinks.

  Examples of such crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates such as are preferably used.

  These crosslinking agents are usually used in a proportion of 1 to 50 parts by weight with respect to 100 parts by weight of the binder. More preferably, it is 15 to 35 parts by weight.

  Further, instead of the thermosetting binder resin as described above, a radiation curable resin may be used. As the radiation curable resin, those obtained by acrylic modification of the thermosetting resin to give a radiation sensitive double bond, acrylic monomers, and acrylic oligomers are used.

<Organic solvent>
Examples of the organic solvent used in the production of the magnetic coating in the present invention include ketone solvents such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, and acetates such as ethyl acetate and butyl acetate. And glycol solvents such as ethylene glycol, propylene glycol, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether. These organic solvents are used alone or in combination, and are used in a mixture with toluene or the like.

  In the present invention, abrasives, lubricants, and dispersants can be used as additives used in the production of magnetic paints.

<Abrasive>
As an abrasive, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, boron nitride For example, those having a Mohs hardness of 6 or more can be used alone or in combination. The particle size of these abrasives is usually preferably 10 to 200 nm as an average particle size.

  In addition, conventionally known carbon black may be added to the magnetic coating material for the purpose of improving conductivity and surface lubricity, if necessary. As carbon black, acetylene black, furnace black, thermal black, and the like can be used. Those having an average particle diameter of 10 to 100 nm are preferred. This range is preferable because when the average particle size is less than 10 nm, it is difficult to disperse carbon black. When the average particle size exceeds 100 nm, it is necessary to add a large amount of carbon black. Because it becomes. If necessary, two or more carbon blacks having different average particle diameters may be used.

<Lubricant>
For magnetic paints, 0.5-5% by weight fatty acid, 0.2-3% by weight ester of fatty acid, 0.5-5.0% by weight fatty acid based on the total powder contained in the paint. It is preferable to contain an amide. The addition of the fatty acid in the above range is preferable because if the amount is less than 0.5% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 5% by weight, the toughness may be lost.

  It is preferable to add an ester of fatty acid within the above range. If the amount is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3% by weight, the amount transferred to the magnetic layer is too large. This is because side effects such as sticking may occur. The addition of the fatty acid amide within the above range is preferable when the amount is less than 0.5% by weight, and direct contact at the head / magnetic layer interface occurs and the effect of preventing seizure is small. This is because defects such as the above may occur. As the fatty acid, it is preferable to use a fatty acid having 10 or more carbon atoms. The fatty acid having 10 or more carbon atoms may be any of isomers such as linear, branched and cis / trans, but is preferably a linear type having excellent lubricating performance. These fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable.

As the fatty acid ester, the fatty acid ester is preferably used. As the fatty acid amide, a fatty acid amide having 10 or more carbon atoms such as palmitic acid and stearic acid can be used.

<Dispersant>
A dispersing agent can be used to satisfactorily disperse additives such as magnetic powder, abrasive and carbon black. Examples of such a dispersant include 12 to 12 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and stearic acid. 18 fatty acids [RCOOH (R is an alkyl group or alkenyl group having 11 to 17 carbon atoms)], a metal soap composed of an alkali metal or an alkaline earth metal of the fatty acid, a compound containing fluorine of the fatty acid ester, Fatty acid amide, polyalkylene oxide alkyl phosphate ester, lecithin, trialkyl polyolefinoxy quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, sulfonate, phosphoric acid Various conventionally known dispersants such as salts and copper phthalocyanine And either can be used. These may be used alone or in combination. In any layer, the dispersant is usually added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  In the present invention, together with the magnetic powder and binder described above, an organic solvent and the additive component described above are used to produce a magnetic paint by dispersion treatment according to the above method. According to a conventional method, a magnetic recording medium is produced by coating on a nonmagnetic support, drying, forming a magnetic layer, and passing through a required processing step.

  Here, the thickness of the magnetic layer is preferably 0.01 μm or more and 0.15 μm or less. This range is preferable because if the output is small if it is less than 0.01 μm, it is difficult to apply a uniform magnetic layer, and if it exceeds 0.15 μm, the resolution of the short wavelength signal is deteriorated. is there. In order to further improve the short wavelength recording characteristics, the thickness of the magnetic layer is more preferably 0.01 to 0.1 μm, most preferably 0.02 to 0.06 μm.

  In the present invention, the above magnetic layer can be formed directly on the nonmagnetic support, but it is usually desirable to form it through the nonmagnetic layer. Further, a topcoat layer (the uppermost nonmagnetic layer) may be provided on the magnetic layer as necessary for the purpose of protecting the magnetic layer. Further, the above magnetic layer may be formed on both sides of the nonmagnetic support in order to increase the capacity of the magnetic recording medium. On the other hand, when a magnetic layer is formed only on one side of a nonmagnetic support, it is usually desirable to form a backcoat layer on the back side.

<Non-magnetic support>
Although the thickness of a nonmagnetic support body changes with uses, a 1.5-11 micrometers thing is normally used. The thickness of the nonmagnetic support is more preferably 2 to 7 μm. The non-magnetic support having a thickness in this range is used when the thickness is less than 1.5 μm because it becomes difficult to form a film and the tape strength decreases. When the thickness exceeds 11 μm, the total thickness of the tape is increased. This is because the recording capacity per tape roll is reduced.

The longitudinal Young's modulus of the nonmagnetic support, preferably 5.8GPa (590kg / mm ²⁾ or more, 7.1GPa (720kg / mm ²⁾ or more is more preferable. The reason why the Young's modulus in the longitudinal direction of the nonmagnetic support is preferably 5.8 GPa or more is that the tape running becomes unstable when the Young's modulus in the longitudinal direction is less than 5.8 GPa.

  In the helical scan type, the Young's modulus (MD) in the longitudinal direction / Young's modulus (TD) in the width direction is preferably in the range of 0.6 to 0.8, and more preferably in the range of 0.65 to 0.75. The Young's modulus in the longitudinal direction / Young's modulus in the width direction is good when the range is less than 0.6 or more than 0.8. The mechanism is currently unknown, but from the entrance side of the magnetic head track. This is because the output variation (flatness) between the output sides increases. This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.7. In the linear recording type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.7 to 1.3, although the reason is not clear.

The temperature expansion coefficient in the width direction of the nonmagnetic support is preferably −10 to 10 × 10 ⁻⁶ , and the humidity expansion coefficient is preferably 0 to 10 × 10 ⁻⁶ . The reason why this range is preferred is that if it is outside this range, off-track occurs due to changes in temperature and humidity, and the error rate increases.

  Examples of the non-magnetic support that satisfies the above characteristics include biaxially stretched polyethylene terephthalate film, polyethylene naphthalate film, aromatic polyamide film, and aromatic polyimide film.

<Nonmagnetic layer>
In order to obtain a magnetic layer having a high recording density, it is desirable to reduce the thickness of the magnetic layer, and in order to stably obtain a durable thin magnetic layer, a magnetic layer and a nonmagnetic support are used. It is preferable to provide a nonmagnetic layer between them. The thickness of the nonmagnetic layer is preferably 0.2 μm or more and 1.5 μm or less, more preferably 1 μm or less, and even more preferably 0.8 μm or less. The reason why this range is preferable is that when the thickness is less than 0.2 μm, the effect of reducing the thickness unevenness of the magnetic layer and the effect of improving the durability are reduced, and when it exceeds 1.5 μm, the total thickness of the magnetic tape becomes too thick. This is because the recording capacity per tape roll is reduced. As the binder resin (or crosslinking agent) used for the nonmagnetic layer and the coating solvent for forming the nonmagnetic layer, the same ones as in the case of the magnetic coating are used.

  Nonmagnetic powders used for the nonmagnetic layer include titanium oxide, iron oxide, and aluminum oxide. Iron oxide alone or a mixed system of iron oxide and aluminum oxide is preferable. The particle shape of the non-magnetic powder may be any of spherical, plate-like, needle-like and spindle-like, but in the case of needle-like and spindle-like, the major axis length is usually 20 to 200 nm and the minor axis length is 5 to 200 nm. Are preferred. In many cases, non-magnetic powder is used as a main component, and if necessary, carbon black having a particle size of 0.01 to 0.1 μm and aluminum oxide having a particle size of 0.05 to 0.5 μm are supplementarily contained. In order to apply the nonmagnetic layer smoothly and with little thickness unevenness, it is preferable to use the nonmagnetic particles and carbon black having a sharp particle size distribution.

  A nonmagnetic plate-like powder having an average particle size of 10 to 100 nm can also be added to the nonmagnetic layer. As the component of the non-magnetic plate-like powder, rare earth elements such as cerium, oxides or complex oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used.

  For the purpose of improving conductivity, a plate-like carbonaceous powder such as graphite having an average particle size of 10 to 100 nm or a plate-like ITO (indium tin composite oxide) powder having an average particle size of 10 to 100 nm is added. Also good. By adding the non-magnetic plate-like powder, film thickness uniformity, surface smoothness, rigidity, and dimensional stability are improved.

<Back coat layer>
In the present invention, a back coat layer is provided on the other surface of the nonmagnetic support constituting the magnetic tape (the surface opposite to the surface on which the magnetic layer is formed) for the purpose of improving running performance. be able to.

  The thickness of the back coat layer is preferably 0.2 to 0.8 μm. This range is good because if the thickness is less than 0.2 μm, the effect of improving the runnability is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape becomes thick and the recording capacity per roll becomes small. The center line average surface roughness Ra of the backcoat layer is preferably 3 to 8 nm, and more preferably 4 to 7 nm.

  The back coat layer usually contains carbon black. As carbon black, acetylene black, furnace black, thermal black, and the like can be used. Usually, small particle size carbon black and large particle size carbon black are used. The total addition amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 100% by weight, more preferably 70 to 100% by weight based on the weight of the inorganic powder.

  As the small particle size carbon black, those having an average particle size of 5 to 200 nm are used, and those having an average particle size of 10 to 100 nm are more preferable. This range is more preferable when the average particle diameter is less than 10 nm, it becomes difficult to disperse the carbon black, and when the average particle diameter exceeds 100 nm, it is necessary to add a large amount of carbon black, both of which become rough. This is because it causes a back-off (embossing) to the magnetic layer. When a large particle diameter carbon black having a large particle diameter of 5 to 15% by weight and an average particle diameter of 200 to 400 nm is used as the large particle diameter carbon black, the surface is not roughened and the effect of improving running performance is increased.

  A nonmagnetic plate-like powder having an average particle size of 10 to 100 nm can be added to the backcoat layer for the purpose of improving strength, temperature / humidity dimensional stability, and the like. As the component of the nonmagnetic plate-like powder, in addition to aluminum oxide, rare earth elements such as cerium, oxides or complex oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used.

  For the purpose of improving conductivity, a plate-like carbonaceous powder having an average particle size of 10 to 100 nm, a plate-like ITO powder having an average particle size of 10 to 100 nm, or the like may be added. Moreover, you may add the granular iron oxide powder whose average particle diameter is 0.1-0.6 micrometer as needed. The addition amount is preferably 2 to 40% by weight, more preferably 5 to 30% by weight, based on the weight of the total inorganic powder in the backcoat layer. Moreover, it is preferable to add alumina having an average particle size of 0.1 to 0.6 μm because durability is further improved.

  In the backcoat layer, the same binder resin as that used in the magnetic paint can be used. Among these, in order to reduce the coefficient of friction and improve the runnability, it is preferable to use a cellulose resin and a polyurethane resin in combination.

  The content of the binder resin is usually 40 to 150 parts by weight, preferably 50 to 120 parts by weight, more preferably 60 to 110 parts by weight with respect to 100 parts by weight of the total amount of carbon black and inorganic nonmagnetic powder. More preferably, it is 70 to 110 parts by weight. The above range is preferable because if the amount is less than 40 parts by weight, the strength of the backcoat layer is insufficient, and if it exceeds 150 parts by weight, the friction coefficient tends to increase. It is preferable to use 30 to 70 parts by weight of cellulose resin and 20 to 50 parts by weight of polyurethane resin.

  In the backcoat layer, it is preferable to use a crosslinking agent such as a polyisocyanate compound in order to cure the binder resin. As the crosslinking agent, the same one as in the magnetic layer can be used. The amount of the crosslinking agent is usually 10 to 50 parts by weight, preferably 10 to 35 parts by weight, and more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the binder resin. The above range is preferable because if less than 10 parts by weight, the coating strength of the backcoat layer tends to be weak, and if it exceeds 35 parts by weight, the dynamic friction coefficient against SUS increases.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, the part in an Example and a comparative example is a weight part. Moreover, the average particle diameter in an Example and a comparative example is a number average particle diameter.

[Example 1]
<Non-magnetic paint component>
(1) Component Acicular iron oxide 68 parts Carbon black 20 parts Granular alumina powder 12 parts Methyl acid phosphate 1 part Vinyl chloride-hydroxypropyl acrylate copolymer 9 parts
(Contained -SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g)
Polyester polyurethane resin 5 parts
(Glass transition temperature: 40 ° C., contained —SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
Tetrahydrofuran 13 parts Cyclohexanone 63 parts Methyl ethyl ketone 137 parts (2) Component Butyl stearate 2 parts Cyclohexanone 50 parts Toluene 50 parts (3) Component Polyisocyanate 6 parts Cyclohexanone 9 parts Toluene 9 parts

<Magnetic paint component>
(1) Component Granular iron nitride magnetic powder 100 parts
(Al—Y—Fe—N) [σs: 70 Am ² / kg (70 emu / g)
Hc: 175.1 kA / m (2200 Oe) average particle size 16 nm]
Vinyl chloride-hydroxypropyl acrylate copolymer 20 parts Polyester polyurethane resin 6.7 parts Methyl acid phosphate 6.0 parts Carbon black 2.0 parts Methyl ethyl ketone 22.4 parts Toluene 11.2 parts (2) Methyl ethyl ketone 50 parts Toluene 50 Part (3) component Alumina powder 15 parts Vinyl chloride-hydroxypropyl acrylate copolymer 1.7 parts Methyl ethyl ketone 50 parts (4) Component Palmitic acid amide 1 part Butyl stearate 1 part Methyl ethyl ketone 185 parts (5) Component Polyisocyanate 8. 0 parts Methyl ethyl ketone 10 parts Cyclohexanone 139.2 parts

In the above non-magnetic component, (1) is kneaded with a batch kneader, (2) is added and stirred, then dispersion treatment is performed with a sand mill for a residence time of 60 minutes, and (3) is added to this and stirred and filtered. After that, a non-magnetic coating material (non-magnetic layer coating material) was obtained.

  Separately, among the above magnetic coating components, first, the component (1) is premixed at a high speed in a high-speed stirring mixer as a magnetic powder pretreatment step (mixing step), and the mixed powder is The mixture was kneaded with a pressure kneader, and the component (2) was added and taken out (kneading step). Next, the component (4) was added and diluted with stirring (mixing step). As a magnetic liquid dispersion step, dispersion was performed with a nanomill (manufactured by Asada Tekko Co., Ltd.) with a residence time of 60 minutes. Next, the component (5) was added and stirred for dilution (dilution step) to obtain a magnetic liquid.

  In addition to the magnetic liquid, the component (3) is mixed and stirred as a polishing liquid dispersion step, and then dispersed in a sand mill in which the stirring shaft and the inner surface of the container are ceramic-coated to obtain a polishing liquid. It was.

  The collision type dispersion device shown in FIG. 2 is prepared using a collision type dispersion machine in which the liquid contact surfaces of the orifices and the collision chamber shown in FIG. 1 are coated with ceramic, and under the conditions shown in Table 1, The magnetic liquid and the polishing liquid were collided so as to have the ratio shown in the magnetic paint component, and mixed and dispersed to obtain a magnetic paint. This magnetic paint was filtered through a filter having a pore diameter of 0.8 μm before application.

  The nonmagnetic paint is applied onto a nonmagnetic support made of a polyethylene naphthalate film having a thickness of 8 μm so that the thickness after drying and calendering becomes 0.9 μm, and the above magnetic layer is applied on the nonmagnetic layer. The paint was applied wet-on-wet with an extrusion type coater so that the thickness after drying and calendering was 0.08 μm, and the magnetic field orientation (NN counter magnet (398 kA / m) + solenoid coil ( 398 kA / m)) After the treatment, it was dried using a dryer and far infrared rays to produce a magnetic sheet.

<Backcoat layer paint component>
Carbon black (average particle diameter 25 nm) 80 parts Carbon black (average particle diameter 350 nm) 10 parts Granular iron oxide (average particle diameter 50 nm) 10 parts Nitrocellulose 45 parts Polyurethane resin 30 parts Cyclohexanone 260 parts Toluene 260 parts Methyl ethyl ketone 525 parts After the backcoat layer coating component was dispersed by a sand mill, 15 parts of polyisocyanate was added to adjust the back layer coating material. After filtration, the coating was applied to the opposite surface of the magnetic layer of the magnetic sheet prepared above and dried.

  The magnetic sheet thus obtained was mirror-finished (calendar treatment) under the conditions of a temperature of 100 ° C. and a linear pressure of 196 kN / m with a seven-stage calendar made of a metal roll, and the magnetic sheet was wound around the core in a state of 60 A magnetic sheet for evaluation was prepared by aging at 48 ° C. for 48 hours.

[Example 2]
A magnetic sheet for evaluation was produced in the same manner as in Example 1 except that the conditions of the mixing and dispersing apparatus were changed to the conditions shown in Table 1.

[Example 3]
Instead of the plunger pump, the pump for sending the polishing liquid of the mixing / dispersing device is changed to a metering pump, and the polishing liquid is sent without significantly increasing the pressure, and the second orifice diameter D2 is changed as shown in Table 1. A magnetic sheet for evaluation was produced in the same manner as in Example 1 except that.

[Example 4]
The magnetic powder is converted into a ferromagnetic iron-based metal magnetic powder (Al—Y—Fe—Co) (σs: 110 Am ^{2 /} kg (110 emu / g, Hc: 170.1 kA / m (2250 Oe), average particle diameter: 40 nm)). A magnetic sheet for evaluation was produced in the same manner as in Example 1 except that the change was made.

[Comparative Example 1]
Magnetic powder is converted into ferromagnetic iron-based metal magnetic powder (Al—Y—Fe—Co) (σs: 116 Am ^{2 /} kg (116 emu / g, Hc: 169.9 kA / m (2135 Oe), average particle diameter: 45 nm)) In Example, except that (2) the polishing liquid component was mixed with the (1) kneading component and the kneading step was performed, and the magnetic liquid and polishing liquid were not mixed and dispersed by collision. In the same manner as in Example 1, a magnetic sheet for evaluation was produced.

[Comparative Example 2]
Magnetic powder is converted into ferromagnetic iron-based metal magnetic powder (Al—Y—Fe—Co) (σs: 116 Am ^{2 /} kg (116 emu / g, Hc: 169.9 kA / m (2135 Oe), average particle diameter: 45 nm)) A magnetic sheet for evaluation was produced in the same manner as in Example 1 except that the change was made.

[Comparative Example 3]
Instead of using a collision type disperser, the magnetic liquid and the polishing liquid were mixed with a stirrer, and then mixed and dispersed in a sand mill in which the stirring shaft and the inner surface of the container were coated with a ceramic, with a residence time of 20 minutes. In the same manner as in Example 1, a magnetic sheet for evaluation was produced.

[Comparative Example 4]
A magnetic sheet for evaluation was produced in the same manner as in Comparative Example 3 except that the mixing and dispersing treatment by the sand mill was not performed.

[Comparative Example 5]
The magnetic liquid and the polishing liquid are mixed with a stirrer to make one liquid, and then the nozzle of the collision type disperser is set and mixed and dispersed as shown in FIG. Thus, a magnetic sheet for evaluation was produced.

  The obtained magnetic sheet for evaluation was evaluated by the following method.

<Surface roughness of magnetic layer>
The magnetic layer of the magnetic sheet for evaluation was measured at a scan length of 5 μm by scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer NewView 5000 manufactured by ZYGO. The measurement visual field is 350 μm × 260 μm. The center line average surface roughness of the magnetic layer was determined as Ra.

<C / N measurement>
A drum tester was used to measure the electromagnetic conversion characteristics of the magnetic sheet for evaluation. The drum tester was equipped with an electromagnetic induction head (track width 25 μm, gap 0.1 μm) and an MR head (track width 8 μm), and recording was performed with the induction head and reproduction was performed with the MR head. Both heads are installed at different locations with respect to the rotating drum, and tracking can be adjusted by operating both heads in the vertical direction. A length of 60 cm was cut from the magnetic sheet in the longitudinal direction, further processed to a width of 4 mm, and wound around the outer periphery of the rotating drum.

  For output and noise, a rectangular wave with a wavelength of 0.2 μm was written by a function generator, and the output of the MR head was read into a spectrum analyzer. The carrier value of 0.2 μm was set as the medium output C. Further, when a rectangular wave of 0.2 μm was written, an integrated value obtained by subtracting the output and system noise was used as the noise value N. Furthermore, the ratio between the two was taken as C / N, and the relative value to the value of the magnetic sheet of Comparative Example 1 used as a reference for both C and C / N was obtained.

<Running test>
A magnetic sheet for evaluation was cut into a 1/2 inch width, and a servo signal was written with a servo writer, and then a predetermined length was incorporated into an LTO3 cartridge. Using an LTO3 drive, 200 passes of writing and playback were performed in an environment of 25 ° C. and 50% RH, and an average error rate in each pass was measured to obtain an error rate of each pass. The number of passes (X) when the error rate increases and the value of log (error rate of the X-th pass) −log (initial error rate) exceeds 0.5 is defined as the error rate increase start pass number. After the running test, the surface of the magnetic head was observed to check for dirt and scratches.

<Evaluation of dirt>
◎: No head contamination is observed. Good: Head contamination occurs on the head with an area ratio of less than 10%. △: Head contamination occurs on the head with an area ratio of 10 to 20%. X: Head dirt is generated at an area ratio of 20% or more on the head. <Scratch Evaluation>
○: No scratch on the head, good △: Only one scratch on the head occurred ×: Two or more scratches on the head occurred

As is apparent from Tables 1 and 2, the magnetic paint comprises a step of preparing a magnetic liquid containing magnetic powder and a binder, a step of preparing a polishing liquid containing an abrasive and a binder, When the polishing liquid is adjusted through a step of colliding with a collision type disperser and mixing and dispersing, a magnetic recording medium having good surface properties, high C / N, and excellent durability can be obtained.

It is sectional drawing which shows the structure of the collision type disperser of an example used with the coating-material manufacturing method of this invention. It is a figure which shows the structure arrangement | positioning including a collision type disperser in the case of processing a magnetic coating material using two tanks of another example used with the coating material manufacturing method of this invention. It is a figure which shows the structure arrangement | positioning including a collision type disperser in the case of processing a magnetic coating material using one tank used with the coating material manufacturing method of a comparative example. It is a flowchart which shows the coating-material manufacturing process of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st supply nozzle 2 2nd supply nozzle 3 Discharge nozzle 4 Collision mixing processing chamber 10 Collision type dispersion machine 11 1st orifice 12 2nd orifice 13 3rd orifice

Claims (2)

In a method for producing a magnetic recording medium having at least a magnetic layer on a nonmagnetic support,
The magnetic layer is formed by applying a magnetic paint containing magnetic powder, an abrasive and a binder,
The magnetic powder has an average particle size of 10 to 40 nm, and the magnetic paint
Adjusting a magnetic liquid containing the magnetic powder and a binder;
Preparing a polishing liquid comprising the abrasive and a binder;
A step of causing the magnetic liquid and the polishing liquid to collide with a collision type disperser to mix and disperse;
The method of manufacturing a magnetic recording medium, characterized by being adjusted through   The collision type disperser was ejected from the first orifice for ejecting the magnetic liquid at a first predetermined pressure, the second orifice for ejecting the polishing liquid at a second predetermined pressure, and each orifice. 2. A mixing chamber having an inner diameter larger than an inner diameter of each orifice for mixing the liquid, and the liquid contact surface of the orifice and the mixing chamber is made of a wear-resistant material. A method for producing the magnetic recording medium according to 1.

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