JP2009230779A - Method of manufacturing magnetic recording medium, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in short wavelength recording characteristics. <P>SOLUTION: In a method of manufacturing a magnetic recording medium which is obtained by forming a magnetic layer by applying magnetic paint which contains magnetic powder and a binder on one main surface of a nonmagnetic support, the magnetic paint is manufactured by: a kneading process of kneading the magnetic powder and the binder with a first solid content concentration in a batch type kneading device to obtain a magnetic kneading object; and a dilution process which performs dilution even to a second solid content concentration lower than the first solid content concentration to obtain a dilution paint by using a batch type kneading device and a consecutive kneading apparatus arranged in series thereto. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a manufacturing method of a coating type magnetic recording medium excellent in high recording density characteristics suitable for a magnetic recording / reproducing system using a magnetoresistive reproducing head (MR head), and a magnetic recording medium obtained by the manufacturing method. .

  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 production technology side, with respect to the production method of magnetic paint, a method using a batch kneading apparatus (Patent Document 2), a method using a continuous kneading apparatus (Patent Document 3 etc.), Improved magnetic layer fillability, surface smoothness, magnetic layer by improving techniques such as simultaneous multi-layer coating (Patent Document 4, etc.) to provide a nonmagnetic undercoat layer (hereinafter also simply referred to as nonmagnetic layer or undercoat layer) The improvement in short wavelength recording characteristics is achieved by making the layer thinner.

Japanese Patent No. 3886968 JP 2000-195043 A JP-A-2-178364 JP-A 63-187418

  However, as the magnetic powder becomes finer, it becomes more difficult to sufficiently disperse the magnetic powder particles to the primary particles. Therefore, a magnetic coating is prepared using magnetic powder having a high coercive force and is formed on the nonmagnetic undercoat layer. Even if the magnetic layers are applied simultaneously, if the magnetic powder contained in the magnetic coating is not well dispersed, desired short wavelength recording characteristics cannot be obtained. In order to satisfactorily disperse the magnetic powder, it has been proposed to use a batch-type or continuous kneader (Patent Documents 2 and 3). However, in this method, the fine-particle magnetic powder is favorably dispersed. It was inadequate.

In view of the above problems, an object of the present invention is to provide a magnetic recording medium excellent in short wavelength recording characteristics.

  In order to achieve the above object, the present inventors have intensively studied a method of manufacturing a magnetic recording medium suitable for a magnetic recording / reproducing system using an MR head. As a result, the manufacturing process of the magnetic paint can be configured as follows. The present inventors have found that the above object can be achieved and have made the present invention.

  That is, in a method of manufacturing a magnetic recording medium in which a magnetic layer is formed by applying a magnetic paint containing magnetic powder and a binder to one main surface of a non-magnetic support, the magnetic paint comprises a batch kneader. A kneading step of kneading the magnetic powder and the binder at a first solid content concentration to obtain a magnetic kneaded product, the batch kneading device, and a continuous kneading device arranged in series therewith, And a dilution step of diluting to a second solid content concentration lower than the first solid content concentration to obtain a diluted paint.

  The diluting step is performed by circulating the diluted paint a plurality of times in the batch kneader and the continuous kneader arranged in series.

  A magnetic paint is kneaded with the magnetic powder and the binder at a first solid content concentration in a batch kneader to obtain a magnetic kneaded product, and the batch kneader and the batch kneader are arranged in series. And a dilution step of diluting to a second solid content concentration lower than the first solid content concentration using a continuous kneading apparatus provided to obtain a diluted paint. Since it can be kneaded well and the magnetic kneaded material can be efficiently and well diluted, a magnetic recording medium excellent in short wavelength recording characteristics can be obtained.

  In the production of a magnetic paint, usually, first, magnetic powder, a binder, and other additives are mixed (mixing step), and then an organic solvent is added in a kneading apparatus to obtain a relatively high first solid content. Kneading by applying high shear force at the concentration (kneading step). By performing this kneading step, a highly viscous magnetic kneaded material in which the binder resin is highly filled with magnetic powder is obtained. In this kneading step, a batch kneader such as a kneader having a pair of blades in a kneading tank or a continuous kneader such as a twin screw extruder is used.

  Next, an organic solvent and a resin liquid are added and diluted to the second solid content concentration to obtain a diluted paint having a relatively low viscosity (dilution step). Dilution is performed by further adding an organic solvent and a resin liquid in the kneading apparatus.

  The diluted paint is dispersed by a media-type disperser in which a dispersion medium is filled in a dispersion tank, and the paint is dispersed by forcibly stirring with a stirring blade (dispersing step).

  Usually, in a dispersion | distribution process, dispersion | distribution is performed by solid content concentration (30-60 weight%) lower than solid content concentration (70-90 weight%) of the coating material in a kneading | mixing process. Therefore, the magnetic paint is inevitably diluted before the dispersion step, but the prior art did not pay attention to the method of dilution of the paint after the kneading step, so that sufficient dilution was not performed and the dispersion in the subsequent dispersion step was not performed. The efficiency decreased and sufficient dispersion could not be achieved. The present invention efficiently and satisfactorily performs the dilution step of obtaining a relatively low-viscosity diluted paint by adding an organic solvent or resin liquid to the magnetic kneaded material, and in a well dispersed state in the subsequent dispersion step. The present invention relates to a method for obtaining a paint.

  FIG. 1 shows a schematic diagram of an example production line used in the kneading step and dilution step of the method for producing a magnetic recording medium of the present invention.

  In this production line, a batch kneader 1 which is a batch kneading apparatus and a biaxial extruder 2 which is a continuous kneading apparatus are connected in series by a pipe. The batch kneader 1 is provided with a raw material blending tank 3 and a take-off valve 6. A liquid feed pump 5 is disposed in a pipe connecting the batch kneader 1 and the biaxial extruder 2 which is a continuous kneader. The biaxial extruder 2 is provided with a plurality of dilution tanks 4. A three-way valve 7 is disposed in the downstream pipe of the biaxial extruder 2 so that the diluted paint can be returned to the batch kneader 1 or sent to the next process.

  The batch type kneader is not particularly limited, and a conventionally known one can be used, and a commercially available batch type kneader manufactured by Moriyama Co., Ltd. or Inoue Seisakusho Co., Ltd. can be used. It is more preferable to use a pressure kneader that can knead with a high shear force while pressing the magnetic kneaded material from above.

  There is no restriction | limiting in particular as a continuous kneading apparatus, A conventionally well-known thing can be used, Commercially available biaxial extruders, such as Nippon Steel Works, Kurimoto Steel Works, etc., can be used.

  Next, a manufacturing procedure will be described. From the raw material blending tank 3, magnetic powder, a binder, other additives, and an organic solvent are blended into the batch kneader 1. Thereafter, the blade 11 is rotated to mix the compound uniformly. After mixing for a predetermined time, a predetermined amount of organic solvent is blended from the raw material blending tank 3, and the blend is set to the first solid content concentration. As a result, the blend is changed from a powder form so far to a high-viscosity paste, and a high shearing force is applied. The preferred range of the first solid content concentration varies depending on the type and composition of the magnetic powder and binder used, but is preferably 70 to 90% by weight. This range is preferred when the viscosity is less than 70% by weight and sufficient shearing force is not applied, and when it exceeds 90% by weight, the kneaded material does not gather into a kneaded shape, and sufficient shearing force is not applied. Because.

  After kneading for a predetermined time, the organic solvent is added a plurality of times from the raw material blending tank 3 while rotating the blade 11, thereby diluting the batch type kneader 1 to the second solid content concentration. The number of additions of the organic solvent is preferably 5 to 20 times. A larger number of additions is preferable because the magnetic kneaded material can be diluted more uniformly, but if the number of additions is too large, the operation becomes complicated and the operation time becomes longer, so the above range is preferable. The dilution in the batch kneader 1 may be carried out to such an extent that the paint obtained by diluting the magnetic kneaded material can be taken out from the take-off valve 6 and fed by the liquid feed pump 5, and the solid content concentration is 30 to 60% by weight. The range of is preferable.

  Next, the take-out valve 6 is opened, the liquid feed pump 5 is driven, and the paint diluted in the batch kneader 1 is fed to the biaxial extruder 2. When the paint passes between the barrel (not shown) of the twin screw extruder 2 and a rotating screw (not shown), the paint receives a shearing force and is further uniformized. The paint that has passed through the biaxial extruder 2 can be selected by a three-way valve 7 and can be sent to the next process, or sent to a pipe that returns to the batch kneader 1 and returned to the batch kneader 1, It may be circulated for a predetermined time.

  Thus, after diluting with the batch kneader 1, the paint is further uniformly diluted by passing through the twin screw extruder 2. This is because the rotational speed of the screw of the twin-screw extruder 2 (50 to 2000 rpm) can be made much larger than the rotational speed of the blade of the batch kneader 1 (3 to 60 rpm). This is because a high shear force can be applied. The coating material diluted in this way is circulated through the batch type kneader 1 → the twin screw extruder 2 → the batch type kneader 1 for a predetermined time to obtain a uniform diluted coating material having a desired level.

  As another embodiment of the present invention, in the batch kneader 1, the first solid content concentration is not diluted from the first solid content concentration to the second solid content concentration, but in the batch kneader 1. Is diluted to a solid content concentration between 1 and 2 and the batch type kneader 1 → the twin screw extruder 2 → the batch type kneader 1 and the coating material are circulated to finally reach the second solid content concentration. There is a way to dilute until. In this case, the organic solvent is added continuously from the raw material blending tank 3 and / or the dilution tank 4 or divided into a plurality of times while the paint is circulated to dilute to the second solid content concentration. . When dilution is performed from the dilution tank 4, it is preferable to provide a plurality of dilution tanks 4 because dilution can be performed more efficiently.

  The diluted paint obtained in this manner may be further diluted while stirring with a stirrer in a tank in the next step, if necessary.

  The diluted paint is produced by finely dispersing the magnetic powder by a conventionally known technique and method such as a dispersion process using a media type dispersing machine. According to the study by the present inventors, when sufficiently uniform dilution is not performed in the above-described dilution step, the dispersion efficiency is lowered even in the subsequent dispersion step, and a desired dispersion level cannot be obtained. Therefore, the magnetic recording medium manufactured using the magnetic paint obtained by the kneading and dilution method of the present invention can be obtained with excellent short wavelength recording characteristics.

  Next, the components of the magnetic recording field obtained by the method for manufacturing a magnetic recording medium of the present invention will be described in further detail.

<Nonmagnetic layer>
The thickness of the nonmagnetic layer is preferably 0.2 μm or more and less than 1.0 μm, and more preferably 0.9 μm or less. This range is preferably less than 0.2 μm, the effect of reducing the thickness unevenness of the magnetic layer, the effect of improving the durability is reduced, and when it is 1.0 μm or more, the total thickness of the magnetic tape becomes too thick, This is because the recording capacity per tape roll is reduced.

  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 preferably used. The particle shape of the non-magnetic powder may be spherical, plate-like, needle-like, or spindle-like, but in the case of needle-like or spindle-like, the major axis length is usually 50 to 200 nm and the minor axis length is 5 to 100 nm. Is preferred. In the case of a granular shape, a particle size of 5 to 200 nm, more preferably 5 to 100 nm is used.

  Furthermore, it is preferable to add carbon black having a particle size of 0.01 to 0.1 μm for the purpose of improving conductivity. In order to apply the nonmagnetic layer smoothly and with little thickness unevenness, it is particularly preferable to use the nonmagnetic powder and carbon black having a sharp particle size distribution. Instead of carbon black, plate-like ITO (indium and tin composite oxide) powder having an average particle diameter of 10 to 100 nm may be used.

  In order to control the temperature / humidity expansion coefficient, elastic modulus, and magnetic layer smoothness of the magnetic recording medium, a nonmagnetic plate-like powder having an average particle diameter of 10 to 100 nm may be added. As the nonmagnetic 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.

  In addition, as a binder (binder resin) used for a nonmagnetic layer, the thing similar to a magnetic layer mentioned later can be used.

<Magnetic powder>
The average particle size of the magnetic powder contained in the magnetic layer is preferably in the range of 10 to 40 nm, and more preferably in the range of 15 to 30 nm. This range is preferable because when the average particle size is less than 10 nm, the surface energy of the particles becomes large and dispersion becomes difficult, and when the average particle size exceeds 40 nm, noise increases. As the magnetic powder, ferromagnetic iron-based metal magnetic powder, iron nitride magnetic powder, plate-shaped hexagonal Ba-ferrite magnetic powder, and the like are preferable.

  The ferromagnetic iron-based metal magnetic powder may contain transition metals such as Mn, Zn, Ni, Cu, and Co as an alloy. Among these, Co and Ni are preferable, and Co is particularly preferable because it can improve saturation magnetization most. As a quantity of said transition metal element, it is preferable to set it as 5-50 atomic% with respect to iron, and it is more preferable to set it as 10-30 atomic%. Further, at least one rare earth element selected from yttrium, cerium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium, terbium, and the like may be included. Among these, when cerium, neodymium and samarium, terbium, and yttrium are used, a high coercive force is obtained, which is preferable. The amount of the rare earth element is 0.2 to 20 atomic%, preferably 0.3 to 15 atomic%, more preferably 0.5 to 10 atomic% with respect to iron.

  As the iron nitride magnetic powder, a known one can be used, and the shape can be an irregular shape such as a spherical shape or a cubic shape in addition to the needle shape. Regarding the particle diameter and specific surface area, in order to clear the required characteristics as a magnetic powder for magnetic recording, it is necessary to set the production conditions of the limited magnetic powder.

The coercive force of the ferromagnetic iron-based metal magnetic powder and the iron nitride magnetic powder is preferably 160 to 320 kA / m, and more preferably 200 to 300 kA / m. Saturation magnetization preferably ^{60~200A · m 2 / kg (60~200emu} / g) ^{is, 80~180A · m 2 / kg (} 80~180emu / g) is more preferable.

The average particle size of the ferromagnetic iron-based metal magnetic powder and the iron nitride magnetic powder is preferably 10 to 40 nm, and more preferably 13 to 20 nm. This range is preferable when the average particle diameter is less than 10 nm, the coercive force is decreased, the surface energy of the particles is increased, so that dispersion in the paint becomes difficult, or the average particle diameter is larger than 40 nm. This is because the particle noise based on the particle size becomes large. Further, BET specific surface area of the ferromagnetic powder is preferably at least ^35m 2 / g, more preferably at least ^{40 m} 2 / g, most preferably at least ^{50 m} 2 / g. Usually 100 m ² / g or less.

  The ferromagnetic iron metal magnetic powder and iron nitride magnetic powder may be used after being surface-treated with Al, Si, P, Y, Zr or an oxide thereof.

The coercive force of the hexagonal Ba-ferrite magnetic powder is preferably 120 to 320 kA / m, and the saturation magnetization is preferably 40 to 60 A · m ² / kg (40 to 60 emu / g). The particle size (size in the plate surface direction) is preferably 10 to 30 nm, more preferably 10 to 25 nm, and further preferably 10 to 20 nm. When the particle size is less than 10 nm, the surface energy of the particles increases, so that dispersion in the paint becomes difficult. When the particle size exceeds 30 nm, particle noise based on the particle size increases. The plate ratio (plate diameter / plate thickness) is preferably less than 3, and more preferably 2 or less. The BET specific surface area of the hexagonal Ba-ferrite magnetic powder is preferably 1 to 100 m ² / g.

  Note that the magnetic properties of these ferromagnetic powders all refer to values measured with an external magnetic field of 1273.3 kA / m (16 kOe) using a sample vibration magnetometer.

In addition, the average particle diameter is determined by measuring the maximum diameter of each particle (major axis diameter for needle-like powder and plate diameter for plate-like powder) from a cross-sectional photograph of the magnetic layer taken with a scanning electron microscope (SEM). , And the average value of 100 pieces.
<Non-magnetic support>
Although the thickness of a magnetic support body changes with uses, a 2-5 micrometers thing is used normally. More preferably, it is 2.5-4.5 micrometers. Nonmagnetic supports with a thickness in this range are used because film formation is difficult if the thickness is less than 2 μm, and the tape strength is low. If the thickness exceeds 5 μm, the total thickness of the tape increases, and the recording capacity per tape roll This is because becomes smaller.

The Young's modulus in the longitudinal direction of the nonmagnetic support is preferably 9.8 GPa (1000 kg / mm ² ) or more, and more preferably 10.8 GPa (1100 kg / mm ² ) or more. The longitudinal Young's modulus of the non-magnetic support is preferably 9.8 GPa (1000 kg / mm ² ) or more. If the Young's modulus in the longitudinal direction is less than 9.8 GPa (1000 kg / mm ² ), the tape running becomes unstable. Because. 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 a specific range of 0.60 to 0.80. The Young's modulus in the longitudinal direction / Young's modulus in the width direction is more preferably in the range of 0.65 to 0.75. The specific range of Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably in the range of 0.60 to 0.80. When the ratio is less than 0.60 or exceeds 0.80, the mechanism is currently unknown. This is because the output variation (flatness) between the entrance side and the exit side of the track of the magnetic head increases. This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.70. Further, in the linear recording type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.70 to 1.30, although the reason is not clear. Nonmagnetic supports that satisfy these characteristics include biaxially stretched aromatic polyamide base films and aromatic polyimide films.

<lubricant>
The nonmagnetic layer contains 0.5 to 5.0% by weight of higher fatty acid based on the total powder contained in the magnetic layer and nonmagnetic layer, and 0.2 to 3.0% by weight of higher fatty acid ester. If it is contained, the coefficient of friction with the head becomes small, which is preferable. The addition of higher fatty acids within this range is preferable when the content is less than 0.5% by weight, and the effect of reducing the friction coefficient is small. When the content exceeds 5.0% by weight, the nonmagnetic layer may be plasticized and the toughness may be lost. Because. The addition of higher fatty acid esters within this range is preferable because the effect of reducing the friction coefficient is small if it is less than 0.2% by weight, and the amount transferred to the magnetic layer is too large if it exceeds 3.0% by weight. This is because side effects such as sticking to the head 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. Examples of such 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. The amount of fatty acid added to the magnetic layer is not particularly limited because the fatty acid is transferred between the non-magnetic layer and the magnetic layer, and the amount of fatty acid added to the magnetic layer and the non-magnetic layer is the above-mentioned amount. And it is sufficient. If fatty acids are added to the nonmagnetic layer, it is not always necessary to add fatty acids to the magnetic layer.

  When the magnetic layer contains 0.5 to 3.0% by weight of fatty acid amide with respect to the magnetic powder and 0.2 to 3.0% by weight of higher fatty acid ester, the friction coefficient during tape running Is preferable. Fatty acid amides in this range are preferred if less than 0.5% by weight, the direct contact at the head / magnetic layer interface tends to occur, and the effect of preventing seizure is small. This is because defects such as out may occur. 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. Also, the addition of higher fatty acid esters in the above range is preferred because the effect of reducing the friction coefficient is small if it is less than 0.2% by weight, and if it exceeds 3.0% by weight, it may cause side effects such as sticking to the head. It is. The mutual movement of the lubricant in the magnetic layer and the lubricant in the nonmagnetic layer is not excluded.

<Dispersant>
The nonmagnetic powder, carbon black, and magnetic powder contained in the nonmagnetic layer and magnetic layer include phosphoric acid dispersants, carboxylic acid dispersants, amine dispersants, chelating agents, and various silane cups. A ring agent or the like is preferably used. These dispersants are preferably blended after the kneading pretreatment step, the kneading step and the initial dispersion step. Examples of phosphate dispersants include alkyl phosphates such as monomethyl phosphate, dimethyl phosphate, monoethyl phosphate, and diethyl phosphate, and aromatic phosphates such as phenylphosphonic acid and monooctylphenylphosphonic acid. As commercial products, “GARFAC RS410” manufactured by Toho Chemical Co., Ltd., “JP-502”, “JP-504”, “JP-508” manufactured by Johoku Chemical Industry Co., Ltd., and the like can be used. Examples of the carboxylic acid dispersant include benzoic acid, phthalic acid, tetracarboxyl naphthalene, dicarboxyl naphthalene, and fatty acids having 12 to 22 carbon atoms.

  Examples of the amine dispersant include aliphatic amines having 8 to 22 carbon atoms, aromatic amines, alkanolamines, and alkoxyalkylamines. Further, examples of chelating agents include 1,10-phenanthroline, EDTA, dimethylglyoxime, acetylacetone, glycine, dithiazone, nitrilotriacetic acid and the like. The amount of the dispersant used is preferably 0.5 to 5 parts by weight per 100 parts by weight of the magnetic powder.

  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 in any layer.

<Magnetic layer>
The thickness of the magnetic layer is preferably 0.01 μm or more and less than 0.1 μm, more preferably 0.06 μm or less, and even more preferably 0.04 μm or less. This range is preferable because if the output is less than 0.01 μm, it is difficult to apply a uniform magnetic layer, and if it exceeds 0.1 μm, the resolution for short wavelength recording is reduced. .

  The binder resin used for the magnetic layer (the same applies to the nonmagnetic layer) includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer. A combination of a polyurethane resin and at least one selected from a cellulosic resin such as a polymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer, and nitrocellulose. Can be mentioned. Among these, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer and a polyurethane resin in combination. Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane.

As a functional _{group, -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′R ″, —N + R ′ ″ R ″ ″ R ′ ″ ″ [in these formulas, R ′, R ″, R ′ ″. , R ″ ″ and R ′ ″ ″ represent hydrogen or a hydrocarbon group], and a binder resin such as a urethane resin made of a polymer having an epoxy group is used. The reason why such a binder resin is used is that the dispersibility of the magnetic powder and the like is improved as described above. When two or more 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 binder resins are used in the range of 7 to 50 parts by weight, preferably 10 to 35 parts by weight with respect to 100 parts by weight of the magnetic powder. In particular, as the binder resin, it is most preferable to use a composite of 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin.

  It is desirable to use together with these binder resins a thermosetting cross-linking agent that bonds and bonds with functional groups contained in the binder resin. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are usually used in a proportion of 1 to 30 parts by weight with respect to 100 parts by weight of the binder resin. More preferably, it is 5 to 20 parts by weight. However, when a magnetic layer is applied on the nonmagnetic layer by wet-on-wet, a certain amount of polyisocyanate is diffused and supplied from the nonmagnetic coating material. Cross-linked.

  In addition, nonmagnetic plate-like particles having a particle size (number average particle size) of 10 nm to 100 nm may be added to the magnetic layer. In addition, conventionally known abrasives can be added as necessary. Examples of these abrasives include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, and corundum. Those having a Mohs hardness of 6 or more, such as artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. The particle size of the abrasive is preferably 10 nm to 150 nm in terms of the normal particle size (number average particle size) in a thin magnetic layer having a thickness of 0.01 to 0.09 μm. The addition amount is preferably 5 to 20% by weight with respect to the magnetic powder. More preferably, it is 8 to 18% by weight.

  Furthermore, in order to improve conductivity, the magnetic layer of the present invention has a plate-like ITO particle, plate-like carbon black prepared by the above-described manufacturing method, and a conventionally known carbon black (for improving conductivity and surface lubricity) CB) can be added, and as these carbon blacks, acetylene black, furnace black, thermal black and the like can be used. The thing with a particle diameter (number average particle diameter) of 10 nm-100 nm is preferable. This range is preferable because it is difficult to disperse carbon black when the particle diameter is 10 nm or less, and it is necessary to add a large amount of carbon black when the particle diameter is 100 nm or more. Because it becomes. The addition amount is preferably 0.2 to 5% by weight with respect to the magnetic powder. More preferably, it is 0.5 to 4% by weight.

<Back coat layer>
A back coat layer is provided on the other surface (the surface opposite to the surface on which the magnetic layer is formed) of the non-magnetic support constituting the magnetic recording medium of the present invention for the purpose of improving running performance. Can do. 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 running property 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. As carbon black (CB), acetylene black, furnace black, thermal black, etc. can be used. Usually, small particle size carbon black and large particle size carbon black are used. As the small particle size carbon black, those having a particle size (number average particle size) of 5 nm to 200 nm are used, and those having a particle size of 10 nm to 100 nm are more preferable. This range is more preferable, when the particle size is 10 nm or less, it is difficult to disperse carbon black, and when the particle size is 100 nm or more, it is necessary to add a large amount of carbon black, and in any case, the surface becomes rough, This is because it causes a back-off (embossing) to the magnetic layer. When 5 to 15% by weight of the small particle size carbon black and the large particle size carbon black having a particle size of 300 to 400 nm are used as the large particle size carbon black, the surface is not roughened and the effect of improving running performance is increased. The total addition amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 98% by weight, more preferably 70 to 95% by weight based on the weight of the inorganic powder. The center line average surface roughness Ra is preferably 3 to 8 nm, and more preferably 4 to 7 nm. Since the magnetic signal of the magnetic recording layer may be disturbed if the backcoat layer is magnetic, the backcoat layer is usually nonmagnetic.

  In addition, non-magnetic plate-like particles having a particle diameter (number average particle diameter) of 10 nm to 100 nm as described above are added to the back coat layer for the purpose of improving strength, temperature / humidity dimensional stability, and the like. Can do. The component of the nonmagnetic plate-like particles is not limited to aluminum oxide, and 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, plate-like ITO (indium, tin composite oxide) particles or plate-like carbon black prepared by the above-described production method may be added. To the backcoat layer, based on the weight of the total inorganic powder in the backcoat layer, plate-like ITO particles and carbon black are added so that the total amount is 60 to 98% by weight. Carbon black preferably has a particle size (number average particle size) of 10 nm to 100 nm. Moreover, you may add the iron oxide whose particle diameter is 0.1 micrometer-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.

  For the back coat layer, the same resin as that used for the magnetic layer and the non-magnetic layer described above can be used as the binder resin. Among these, in order to reduce the coefficient of friction and improve the runnability, cellulose resin and polyurethane resin are used. It is preferable to combine and use resin. 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 the carbon black and the 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 50 parts by weight, the strength of the backcoat layer is insufficient, and if it exceeds 120 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. Further, in order to further cure the binder resin, it is preferable to use a crosslinking agent such as a polyisocyanate compound.

  For the back coat layer, the same cross-linking agent as that used for the magnetic layer and the non-magnetic layer is 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.

<Organic solvent>
Examples of organic solvents used in magnetic paints, nonmagnetic paints, and back coat paints include ketone solvents such as methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, and acetic acid such as ethyl acetate and butyl acetate. Examples include ester solvents. These solvents are used alone or in combination, and further mixed with toluene or the like.

  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) A component Acicular iron oxide 80 parts Carbon black 17 parts Granular alumina powder 3 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 B butyl stearate 2 parts Stearic acid 1 part Cyclohexanone 50 parts Toluene 50 parts (3) Component C Polyisocyanate 6 parts Cyclohexanone 9 parts Toluene 9 parts

<Magnetic paint component>
(1) Component a 100 parts of ferromagnetic iron-based metal magnetic powder (Al—Y—Fe—Co) [σs: 120 Am2 / kg (120 emu / g)
Hc: 176.3 kA / m (2215 Oe) average particle diameter: 45 nm, true density ρ: 5.7 g / cc]
Vinyl chloride-hydroxypropyl acrylate copolymer resin 17 parts Polyester polyurethane resin 6 parts Granular alumina powder (average particle size: 0.2 μm) 10 parts Methyl acid phosphate 4 parts Methyl ethyl ketone 4 parts Toluene 4 parts Tetrahydrofuran 8 parts (2) Component b Methyl ethyl ketone 8 parts Cyclohexanone 8 parts (3) c component Methyl ethyl ketone 52 parts Cyclohexanone 52 parts Toluene (4) d component Palmitic acid amide 4 parts Cyclohexanone 38 parts Toluene 38 parts (5) e component Polyisocyanate 6 parts Methyl ethyl ketone 20 parts Cyclohexanone 160 parts Toluene 20 copies

  In the above nonmagnetic component, the A component is kneaded with a batch kneader, the B component is added and stirred, and then the dispersion is performed with a sand mill with a residence time of 60 minutes. Got.

  Apart from this, among the above-mentioned magnetic paint components, first, the a component is first mixed at a high speed with a high-speed stirring mixer (mixing step), and the b component is added to the mixed powder to obtain a solid content concentration of 81 Using the batch-type kneader 1 shown in FIG. 1 at weight% (first solid content concentration), the blade 11 was kneaded for 4 hours while rotating at a low speed (30 rpm) (kneading step). Thereafter, the component c was divided into 5 portions and added in 5 portions over 3 hours from the raw material blending tank 3, and the solid content concentration was diluted to 50% by weight while rotating the blade at high speed (45 rpm). The diluted product was taken out and the valve 6 was opened, and the solution was fed to the biaxial extruder 2 by the solution feeding pump 5. Next, d component is divided into three parts, added from the dilution tank 4, and further diluted while rotating the screw at high speed (1300 rpm) to dilute by diluting the solid concentration to 40% by weight (second solid concentration) A paint was obtained (dilution step). The diluted paint was dispersed in a nanomill (manufactured by Asada Tekko Co., Ltd.) with a residence time of 60 minutes (dispersing step). Finally, component e was added and stirred for blending (blending step) to obtain a magnetic paint.

  The non-magnetic coating material is applied onto a non-magnetic support made of a polyethylene naphthalate film having a thickness of 5 μm so that the thickness after drying and calendering becomes 0.9 μm, and the above magnetic layer is applied on the non-magnetic layer. The paint was applied by wet-on-wet (simultaneous multi-layer coating) with an extrusion type coater so that the thickness after drying and calendering was 0.08 μm, and 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 dispersing the above coating component for the backcoat layer with a sand mill, 15 parts of polyisocyanate is added to adjust the coating material for the back layer, and after filtration, on the opposite surface of the magnetic layer of the magnetic sheet prepared above, It was applied and dried to a thickness of 0.5 μm.

  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:
In the magnetic paint production process, the diluted product diluted to a solid content concentration of 40% by weight with the twin screw extruder 2 is returned to the batch kneader 1 by operating the valve 7 and circulated for 2 hours to obtain a diluted paint. A magnetic sheet for evaluation of Example 2 was produced in the same manner as Example 1 except that.

Example 3:
In the magnetic coating production process, the diluted 50% by weight solid content diluted with the batch kneader 1 is fed to the twin screw extruder 2, and the valve 7 is operated to pass through the twin screw extruder 2. The product was returned to the batch kneader 1 and circulated for 2 hours. At this time, the d component was divided into 9 parts, and the magnetic sheet for evaluation of Example 3 was prepared in the same manner as in Example 1 except that the diluted component was obtained by adding the diluted component 4 from the dilution tank 4 and performing dilution. did.

Comparative Example 1:
In the magnetic coating production process, after diluting the solid content to 50% by weight with the batch kneader 1, the component d is divided into three parts and added to the raw material blending tank over three hours, The solid content concentration was diluted to 40 wt% while rotating at a high speed (60 rpm), and then the diluted paint was obtained by making it uniform in a tank equipped with a stirrer without passing through the biaxial extruder 2. In the same manner as in Example 1, a magnetic sheet for evaluation of Comparative Example 1 was produced.

Comparative Example 2:
In the magnetic paint manufacturing process, instead of a batch kneader, a continuous kneader equipped with a kneading part and a dilution part is used, and the mixed powder obtained through the mixing process is blended into the continuous kneader, and the components b, c, d Were mixed sequentially from each dilution tank of a continuous kneader, kneaded and diluted in a continuous kneader, and uniformed in a tank equipped with a stirrer to obtain a diluted paint having a solid content concentration of 40% by weight. In the same manner as in Example 1, a magnetic sheet for evaluation of Comparative Example 2 was produced.

  The evaluation method was performed as follows.

<Dispersed state of diluted paint>
The diluted paint is applied onto a PET film using an applicator so that the dry thickness is 90 μm. After drying, the surface of the coating film is observed with an optical microscope at a magnification of 100 times, and a 5 mm × 5 mm visual field is observed. The number of aggregates having a size of 50 μm or more was counted. The number of aggregates was evaluated as ◯, 10 or less, Δ from 11 to 20, and × from 21 or more.

<Surface roughness of magnetic layer>
Using a general-purpose three-dimensional surface structure analyzer NewView 5000 manufactured by ZYGO, the surface roughness was measured by a scanning white light interferometry, and the 10-point average roughness Rz was evaluated. In the measurement, a 50 × objective lens was used and the measurement was performed at 2 × zoom. Therefore, the magnification is 100 times. The measurement visual field is 72 μm × 54 μm.

<Magnetic properties>
The square shape (Br / Bs) was measured according to a conventional method in which an external magnetic field of 0.8 MA / m (10 kOe) was applied to the evaluation magnetic sheet. For the measurement, a sample vibration type magnetometer VSM-P7 manufactured by Toei Industry Co., Ltd. was used.

Table 1 shows the evaluation results of the magnetic sheets for each evaluation. As is clear from the table, the magnetic sheets of Examples 1 to 3 according to the present invention are those obtained by kneading and diluting by combining a batch kneader and a continuous kneader, and do not satisfy Claim 1. Compared to the magnetic sheets of Comparative Examples 1 and 2 which are not the subject of the invention, there is less aggregation after dilution, and they are kneaded and diluted well, so that the smoothness and magnetic properties of the magnetic sheet are good. A magnetic sheet excellent in short wavelength recording characteristics has been obtained.

As is clear from Table 1, by providing a dilution step for dilution using a batch-type kneader and a continuous kneader arranged in series with this, smoothness and a short wavelength with good square shape are provided. A magnetic recording medium having excellent recording characteristics can be manufactured.

It is a block diagram of an example kneading | mixing and dilution apparatus used for the manufacturing method of the magnetic recording medium of this invention.

Explanation of symbols

1 Batch kneader (batch kneader)
2 Twin screw extruder (continuous kneader)
3 Raw material compounding tank 4 Dilution tank 5 Liquid feed pump 6 Take-out valve 7 Three-way valve 11 Blade

Claims (3)

  In a method of manufacturing a magnetic recording medium in which a magnetic layer is formed by applying a magnetic coating containing magnetic powder and a binder to one main surface of a nonmagnetic support, the magnetic coating is applied to a batch kneader. A kneading step of kneading the magnetic powder and the binder at a first solid content concentration to obtain a magnetic kneaded product, and the batch kneader and a continuous kneader arranged in series therewith. And a diluting step of diluting to a second solid content concentration lower than the first solid content concentration to obtain a diluted paint, and producing the magnetic recording medium.   The method of manufacturing a magnetic recording medium, wherein the dilution step is performed by circulating the diluted paint a plurality of times in the batch kneading apparatus and the continuous kneading apparatus arranged in series.   A magnetic recording medium manufactured by the manufacturing method according to claim 1.

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