JP4562671B2 - Method for producing magnetic paint - Google Patents

Description

The present invention relates to the production how the magnetic coating, in particular, relates to the production how magnetic coating composition containing ultrafine magnetic powders.

  There are various uses for magnetic recording media. In particular, computer tapes and hard disks are mainly used for data backup magnetic recording media. Data backup computer tapes with a storage capacity of 100 GB or more per volume are commercialized. ing. On the other hand, since the storage capacity of the hard disk will further increase in the future, it is essential to increase the capacity of the backup tape. In addition, in order to increase the capacity of a magnetic recording medium, it is indispensable to make the recording wavelength shorter and the track width smaller.

  High-capacity computer tapes are generally manufactured by applying a magnetic coating material in which magnetic powder is dispersed in a binder resin onto a flexible support. Corresponding to the increase in the density of magnetic recording media, the particle size of the magnetic powder to be used is reduced, and a ferromagnetic metal powder having a large magnetic energy represented by saturation magnetization σs is being used. However, it is known that as the magnetic powder becomes finer and has higher magnetic energy, the cohesive strength of individual particles increases.

  In addition, the magnetic recording medium can reduce the spacing loss by smoothing the surface, thin the magnetic layer, reduce the dropout due to surface defects, uniform the coercive force distribution of the magnetic powder, and can be used many times for a long time. It is required to have both high durability that can be withstood. In order to satisfy these requirements, it is necessary that the magnetic coating material is sufficiently dispersed.

  In general, magnetic coating materials are needle-shaped, granular, plate-shaped magnetic powders, binder resins, organic solvents and other necessary components, and dispersion media such as metals, ceramics, and glass are placed in a dispersion container. Dispersed and manufactured using a media-type disperser such as a filled ball mill or sand mill.

  However, as described above, the cohesion of the magnetic powder is increased by making the magnetic powder finer and the magnetic energy with the increase in capacity of the magnetic recording medium, and the magnetic powder can be uniformly dispersed in the magnetic paint. It has become difficult.

In order to solve such a problem, a proposal has been made to combine a media-type disperser and other dispersion processes. For example, a magnetic coating material is mixed and an attempt is made to uniformly disperse the composition for magnetic coating that has been dispersed by irradiating ultrasonic waves (Patent Document 1), or after dispersion by a sand mill, Attempts have been made to provide a dispersion process such as sonic dispersion and high-pressure homogenizer (Patent Document 2), and an attempt to combine a process of dispersing by a sand mill and a process of dispersing by ultrasonic waves (Patent Document 3).

Japanese Patent Laid-Open No. 10-251561 JP 2003-115107 A JP 2005-146187 A

  However, in order to disperse ultrafine magnetic powder having an average particle diameter of less than 50 nm, even if the ultrasonic wave is irradiated after dispersion of the sand mill, the improvement of the dispersion is not sufficient, and the improvement of the magnetic properties is not satisfactory. However, the characteristics of the ultrafine magnetic powder could not be sufficiently extracted. In particular, sufficient dispersion of granular ultrafine magnetic powder has been difficult with conventional dispersion techniques.

The present invention is, in light of these circumstances, ultra-fine magnetic powder is intended for and provide child a method of manufacturing a well-dispersed magnetic coating.

  In order to achieve the above-mentioned problems, the present inventors have intensively studied the dispersion process of a magnetic paint containing a magnetic powder having an average particle size of less than 50 nm and a binder resin. Thus, the above object was achieved and the present invention was made.

That is, the method for producing a magnetic coating material comprising a magnetic powder having an average particle diameter of less than 50 nm and a binder resin according to the present invention performs a dispersion step using a media-type disperser, and thereafter, faces a predetermined interval, The dispersion step is performed by a disperser having a pair of dispersive surfaces that move relatively at a speed.

In the method for producing a magnetic coating material of the present invention, since it includes a dispersion step by a disperser having a pair of dispersive surfaces facing each other at a predetermined interval and relatively moving at a predetermined speed, and a dispersion step by a media type disperser, The dispersion of the paint by the media type dispersing machine is efficiently performed, and a highly dispersed magnetic paint can be provided. By using this magnetic paint, a magnetic layer having a smooth roughness and excellent magnetic properties is formed. be able to. As a result, a magnetic recording medium having excellent short wavelength recording characteristics can be provided.

  A disperser (referred to as a micro-interval high-speed shearing disperser) having a pair of dispersive surfaces facing each other at a predetermined interval and relatively moving at a predetermined speed, which is used in the method for producing a magnetic coating material of the present invention, will be described. FIG. 1 shows a cross-sectional view of an example of a fine gap high-speed shearing disperser. The disperser includes a rotating rotor 4 that is driven and rotated by a motor (not shown) in a dispersing container 5, and the rotating rotor 4 is provided with an annular second dispersing portion 2 having a second dispersing surface 2a. Yes. An annular first dispersion part 1 having a first dispersion surface 1 a so as to overlap the second dispersion part 2 is attached to a dispersion container 5 via a spring 3 so as to be movable in the direction of the rotation axis of the rotary rotor 4. The second dispersion unit 2 is urged. The first dispersion surface 1a and the second dispersion surface 2a overlap each other. The first dispersion surface 1a and the second dispersion surface 2a are mirror-finished and smooth. The first dispersion surface 1a and the second dispersion surface 2a are made of a wear-resistant material such as wear-resistant steel or ceramic. In the dispersion container 5, a paint supply hole 5 a for supplying magnetic paint (not shown) to the space surrounded by the rotary rotor 4, the first dispersion part 1, and the second dispersion part 2 in the dispersion container 5 and the paint are discharged. A paint discharge hole 5b is provided.

  The operation of this dispersing machine will be described. After supplying the magnetic coating material for the dispersion process from the coating material supply hole 5a, the space surrounded by the rotary rotor 4, the first dispersion unit 1 and the second dispersion unit 2 in the dispersion container 5 is filled with the magnetic coating material. The rotating rotor 4 is rotated at a predetermined number of rotations. Due to the supply pressure, the magnetic coating material starts to enter the gap formed by the first dispersion surface 1a and the second dispersion surface 2a. The contact surface between the first dispersion surface 1a and the second dispersion surface 2a is expanded by a magnetic paint to form a pair of dispersion surfaces having a predetermined interval. Since the first dispersion surface 1a is stationary and the second dispersion surface 2a rotates at a high speed, the pair of dispersion surfaces move at a relatively high speed and are sandwiched between the pair of dispersion surfaces. The magnetic coating is subjected to a high shearing force, and the magnetic powder and other non-magnetic powder particles in the magnetic coating are dispersed. The distance between the pair of dispersion surfaces is determined by the supply pressure of the magnetic paint, the elasticity of the spring 3, the viscosity of the magnetic paint, and the like, and can be set to a desired value by controlling them. In addition, this interval can be monitored by providing a position sensor that detects the movement of the first dispersion unit 1 in the rotation axis direction.

  Although the space | interval of a pair of said dispersion | distribution surface can be arbitrarily set according to the objective and a use, it is preferable that it is 1-100 micrometers. This range is preferable, if the distance is less than 1 μm, the interval is too small and the amount of paint processed per unit time becomes too small, or the supply pressure when the paint is processed with this disperser becomes too large to be practical. If the thickness exceeds 100 μm, the shearing force becomes small and the coating cannot be sufficiently dispersed.

  The relative movement speed of the pair of dispersion surfaces is preferably 10 to 100 m / s. This range is preferable because if the shear force is less than 10 m / s, the coating force cannot be dispersed sufficiently, and if it exceeds 100 m / s, the power for moving the dispersion surface becomes extremely large and becomes impractical. is there. The shape of the pair of dispersion surfaces can also be set arbitrarily, and may be, for example, a double cylinder in addition to the two circular rings described above.

  A specific example of such a disperser is CLEA SS5 manufactured by M Technique Co., Ltd.

  The distance between the pair of dispersion surfaces may be set by the above-described mechanism, or may be a mechanism that is mechanically adjusted by a screw or the like as shown in FIG. Usually, when an interval of several tens of μm or more is formed, it is preferably mechanically adjusted, and when it is less than that, it is preferably adjusted by the above-described mechanism.

  The shape of the pair of dispersion surfaces may be the one where the distance on the paint entrance side is not wide as shown in FIG. 4A, but the first dispersion portion 1 and the second dispersion as shown in FIG. 4B. It is preferable to taper at least one part of the portion 2 to widen the distance on the entrance side of the paint because secondary particles having a particle diameter larger than the target dispersion level can be easily drawn and dispersed. The taper shape may be linear as shown in (b), may be curved as shown in (c), or may be stepped.

  As shown in FIG. 3, the moving path of the magnetic coating material in the dispersion container 5 can be set from the outside to the inside of the rotary rotor 4. In this case, when the paint passes through the pair of dispersion surfaces formed by the first dispersion surface 1a and the second dispersion surface 2a, secondary particles having a relatively large particle diameter are subjected to the action of centrifugal force. Is preferable because it becomes difficult to pass and cannot pass or it takes a long time to pass, so that a well-dispersed paint with a better dispersion level can be obtained.

  Since such a finely spaced high-speed shearing type disperser does not use a dispersion medium, there is no contamination due to media wear, and by appropriately selecting the distance between the pair of dispersion surfaces, it is larger than that distance. Since the coarse particles are not allowed to pass through, the upper limit value of the particle size of the coarse particles in the paint can be set, so that the dispersion efficiency in the dispersion step by the media type disperser in the next step is dramatically improved. In addition, after the dispersion step by the media type disperser, if the dispersion step is performed by the fine interval high-speed shearing disperser with the distance between the pair of dispersion surfaces being 10 μm or less, an extremely high shearing force can be applied to the paint. Effects such as reduction of re-aggregation, suppression of re-aggregation, and improvement of magnetic properties.

  The method for producing a magnetic paint according to the present invention includes the step of dispersing the paint with the above-mentioned fine gap high-speed shearing disperser and the step of dispersing the paint with a media type disperser.

  The media-type disperser is used to disperse the paint by stirring the paint together with the dispersion medium in a dispersion container, and is widely used for dispersing magnetic paint. In particular, in dispersing fine magnetic powder, a method of reducing the particle diameter of the media and increasing the density is effective, and zirconia beads having a particle diameter of 2 mm or less are preferably used. However, reducing the particle size of the media is effective for the dispersion of magnetic powder with a small particle size, but the magnetic powder and other non-magnetic powders in the magnetic coating before the dispersion process by the media-type disperser is performed. When the particle diameter of the secondary particles (coarse particles) is large, the dispersion ability tends to decrease. That is, in order to effectively disperse the paint using the fine particle dispersion medium, it is preferable to sufficiently reduce the secondary particle diameter of the magnetic paint before dispersion. For this purpose, a mixing process, a kneading process and a dilution process, which will be described later, are provided. However, when fine magnetic powder having an average particle diameter of less than 50 nm is dispersed, the secondary particle diameter of the magnetic coating material before dispersion is sufficient. It was difficult to reduce the size, and it could not be said that the dispersion by the media-type disperser was sufficiently effective. In addition, the magnetic paint that has been subjected to the dispersion process by the media type disperser has a relatively high viscosity, and when a magnetic layer is formed by applying the magnetic paint to a nonmagnetic support, a large amount of solvent is used to adjust the viscosity of the paint. In this case, re-aggregation of the magnetic powder occurs, and the performance of the magnetic recording medium may be deteriorated.

In the manufacturing method of the magnetic coating material of the present invention, after a dispersion process by the media-type dispersing machine, it intends rows dispersion step by minute distance high speed shearing type dispersing machine. The distance between the pair of dispersion surfaces of the fine gap high-speed shearing disperser is preferably 1 to 10 μm. This range is preferable, if the distance is less than 1 μm, the interval is too small and the amount of paint processed per unit time becomes too small, or the supply pressure when the paint is processed with this disperser becomes too large to be practical. This is because if it exceeds 10 μm, the shearing force becomes small, and the dispersion of the paint cannot be sufficiently performed.

  After passing through the dispersion step with a media-type disperser, the dispersion step with a fine gap high-speed shearing disperser is effective in reducing paint viscosity, suppressing re-agglomeration, and improving magnetic properties. A magnetic layer having good characteristics can be obtained, and a magnetic recording medium having excellent high recording density characteristics can be obtained.

  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 dilution step before the coating material dispersion step. Among these steps, in the mixing step, 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 using a high-speed stirring mixer. It is mixed with an organic acid or the like or a binder resin to perform surface treatment of the magnetic powder or mixing with the binder resin.

  The high-speed agitating mixers mentioned above include gas blow-up type agitators utilizing the rolling flow effect such as Hosokawa Micron's Agromaster, Cyclomix and Mechano-Fusion Systems made by the company, and Axial Mixers made by Sugiyama Heavy Industries. A rotary mixer, a Henschel mixer manufactured by Mitsui Mining Co., etc. can be used.

  Next, in the kneading step, kneading is performed by a batch kneader or a continuous biaxial kneader, and in the dilution step, a batch kneader, a continuous biaxial kneader, or another type is performed as a subsequent step of the kneading step. It is used for kneading and diluting using a diluting device.

  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 manufactured by Nippon Steel. TEX90αII or the like can be used.

  In the present invention, the paint (undispersed paint) that has undergone such a pre-process is dispersed by a high-pressure spray impingement minute interval high-speed shearing disperser. By performing this treatment, coarse secondary particles in the undispersed paint can be solved, and dispersion by a media-type disperser can be facilitated, and a paint excellent in smoothness and magnetic properties can be produced.

  In the process of processing the undispersed paint with a high-pressure spray collision fine interval high-speed shearing disperser, the solid content concentration is usually 10 to 30% by weight, and the ratio of the binder resin to 100 parts by weight of the magnetic powder is 15 to 30 parts by weight. The viscosity of the coating material before dispersion is usually preferably 0.5 to 3.0 Pa · s (500 to 3000 cP). Moreover, it is preferable to process after filtering with a 50-100 micrometers filter previously.

  Thereafter, dispersion is performed with a media-type disperser. Normally, when the paint is dispersed by a media type disperser, the viscosity increases. However, in the method for producing a magnetic paint according to the present invention, the increase in the viscosity of the paint can be suppressed. Further, since the dispersion is performed at a high pressure and high energy, dispersion in a short time is possible. Furthermore, the magnetic properties can be greatly improved by fine dispersion. 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 ability to disperse fine particles 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 paint dispersion is performed using two or more media-type dispersers, the dispersion conditions for each train 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.

<Magnetic powder>
In the present invention, the magnetic powder used for the production of the magnetic coating is preferably a ferromagnetic iron metal magnetic powder, an iron nitride magnetic powder, a plate-shaped hexagonal ferrite magnetic powder or the like. Those having an average particle size of less than 50 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 50 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.

<Binder>
As binder resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-anhydrous Examples include a combination of a polyurethane resin and at least one selected from a maleic acid copolymer resin, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and a cellulose resin such as nitrocellulose.

  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 resin has —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 resin improves the dispersibility of 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 binder resins 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.

  In addition to these binder resins, it is preferable to use in combination with a thermosetting crosslinking agent that is bonded to a functional group contained in the binder resin and crosslinked.

  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 at a ratio of 1 to 50 parts by weight with respect to 100 parts by weight of the binder resin. 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>
In the magnetic coating material, 0.5 to 5 parts by weight of higher fatty acid, 0.2 to 3 parts by weight of higher fatty acid ester, and 0.5 to 5 parts by weight with respect to 100 parts by weight of the total powder contained in the coating material. It is preferable to contain 0 part by weight of a fatty acid amide. The addition of higher fatty acids within the above range is preferable because if the amount is less than 0.5 parts by weight, the effect of reducing the friction coefficient is small, and if it exceeds 5 parts by weight, the toughness may be lost. The ester addition of higher fatty acids within the above range is preferable because if the amount is less than 0.2 parts by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3 parts by weight, the amount of transfer 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 because if the amount is less than 0.5 parts by weight, direct contact at the head / magnetic layer interface occurs and the effect of preventing seizure is small. This is because defects may occur. As the higher 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 higher fatty acid ester, the higher 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 in order 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 resin described above, an organic solvent, the above additive components, etc. are used to produce a magnetic coating material by dispersing the above method, and then the magnetic coating material is used. According to a conventional method, a magnetic recording medium is produced by coating on a non-magnetic 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 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 magnetic layer can be directly formed on the nonmagnetic support, but it is usually desirable to form it through an undercoat 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 nonmagnetic support having a thickness in this range is used because if it is less than 1.5 μm, it becomes difficult to form a film and the tape strength is reduced. If it 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 nonmagnetic support satisfying the above-described characteristics include biaxially stretched polyethylene terephthalate film, polyethylene naphthalate film, aromatic polyamide film, and aromatic polyimide film.

<Undercoat 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 an undercoat layer (nonmagnetic layer) between them. The thickness of the undercoat layer is preferably 0.2 μm or more and 1.5 μm or less, more preferably 1 μm or less, and further 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 undercoat layer and the coating solvent for forming the undercoat layer, the same ones as in the case of the magnetic paint are used.

  Nonmagnetic powders used for the undercoat 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 undercoat layer smoothly and with little thickness unevenness, it is preferable to use non-magnetic 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 undercoat 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. If the backcoat layer is magnetic, the magnetic signal of the magnetic recording layer may be disturbed, so that the backcoat layer is usually nonmagnetic.

  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 parts by weight, more preferably 5 to 30 parts by weight, with 100 parts by 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 back coat layer, the same binder resin as in the case of 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 70-110 weight part. 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 50 parts by weight, the coefficient of dynamic friction against SUS increases.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this 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. Furthermore, the viscosity of the paint in the examples and comparative examples was measured by using a Bisco Tester (“VT-04E” manufactured by Lyon Co., Ltd.) (using No. 1 rotor), and taking the paint within 1 minute after dispersion in a 300 ml beaker. The viscosity is determined from the indicated value 30 seconds after the start.

[Example 1]
<Undercoat 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) Components of kneading process Granular iron nitride magnetic powder 100 parts
(Al—Y—Fe—N) [σs: 95 Am ² / kg (95 emu / g)
Hc: 214.9 kA / m (2700 Oe) average particle size 15 nm]
Vinyl chloride-hydroxypropyl acrylate copolymer 17 parts Polyester polyurethane resin 6 parts Alumina powder 10 parts Methyl acid phosphate 4 parts Methyl ethyl ketone 35 parts Cyclohexanone 110 parts Toluene 110 parts (2) Dilution step components Palmitic acid amide 1 part Butyl stearate 1 Part Cyclohexanone 70 parts Toluene 70 parts (3) Blending process component Polyisocyanate 6 parts Methyl ethyl ketone 2 parts Cyclohexanone 8 parts Toluene 8 parts In the above primer, knead (1) with a batch kneader, add (2) and stir Thereafter, a dispersion treatment was performed using a sand mill with a residence time of 60 minutes, and after adding (3), stirring and filtering, an undercoat paint (undercoat paint) was obtained.

  Apart from this, among the above-mentioned magnetic paints, first, (1) kneading process components are kneaded with a batch kneader. Next, (2) dilution process components were added and diluted with stirring (undispersed paint). Subsequently, as pre-dispersion treatment, the dispersion treatment was performed three times with a fine gap high-speed shearing disperser shown in FIG. After dispersion treatment with a nanomill (manufactured by Asada Tekko Co., Ltd.) with a residence time of 90 minutes, as a post-dispersion treatment, the dispersion spacing is 2 μm and the dispersion surface peripheral speed is again measured with the fine spacing high-speed shearing disperser shown in FIG. The dispersion treatment was performed 3 times at 50 m / s. Furthermore, (3) the compounding process component was added, and it stirred and filtered and adjusted the magnetic coating material.

  The undercoat 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 magnetic paint is applied onto the undercoat layer. Apply wet-on-wet with an extrusion type coater so that the thickness after drying and calendering is 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 the backcoat layer coating component was dispersed with 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. A magnetic sheet for evaluation was prepared by aging at 48 ° C. for 48 hours.

[Example 2]
The fine gap high-speed shearing disperser was changed from the one shown in FIG. 3 to the one shown in FIG. 1, and the paint flow path in the dispersion container was changed from “outer → inner” to “inner → outer”. A magnetic sheet for evaluation of Example 2 was produced in the same manner as Example 1 except that.

[Example 3]
A magnetic sheet for evaluation of Example 3 was produced in the same manner as in Example 1 except that the pre-dispersion treatment was not performed with a fine gap high-speed shearing disperser.

[Example 4]
A magnetic sheet for evaluation of Example 4 was produced in the same manner as Example 3 except that the distance between the dispersion surfaces was changed from 2 μm to 11 μm.

[Example 5]
A magnetic sheet for evaluation of Example 5 was produced in the same manner as in Example 1 except that the post-dispersion treatment using a fine gap high-speed shearing disperser was not performed.

[Example 6]
A magnetic sheet for evaluation of Example 6 was produced in the same manner as Example 5 except that the distance between the dispersion surfaces was changed from 90 μm to 110 μm.

[Comparative Example 1]
A magnetic sheet for evaluation of Comparative Example 1 was produced in the same manner as in Example 1 except that the dispersion treatment was not performed using a fine gap high-speed shearing disperser.

  The evaluation method of the obtained magnetic sheet was performed as follows.

<Surface roughness of magnetic layer>
The scan length of the magnetic layer of the magnetic sheet was measured at 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.

<Dispersion stability>
For the evaluation of dispersion stability, a magnetic sheet was prepared using the magnetic coating compounded for multi-layer coating described above and the paint left for 3 hours after blending, and the rate of change in surface roughness of the obtained magnetic sheet was measured. Used as.
Here, the rate of change in surface roughness was determined from (Ra (after leaving) −Ra (before leaving for 3 hr)) / Ra (before leaving) × 100.

<C / N measurement>
A drum tester was used to measure the electromagnetic conversion characteristics of the magnetic sheet. 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.

<Magnetic properties>
The magnetic properties are values measured using a sample vibration type magnetometer at 25 ° C. and an external magnetic field of 1273.3 kA / m according to a conventional method. The measurement sample was adjusted by sticking 20 magnetic sheets and punching them into a diameter of 8 mm.

  As is clear from the results in Table 1 above, each of the magnetic sheets of Examples 1 to 6 of the present invention has better magnetic properties than the magnetic sheet of Comparative Example 1, and the surface roughness of the magnetic layer. It can also be seen that a magnetic recording medium that is smooth and excellent in high recording density characteristics is obtained. In addition, it can be seen that the stability of the paint is also excellent because the decrease in the surface property due to leaving the paint is small.

It is sectional drawing which shows the structure of the fine space | interval high-speed shearing disperser of an example used with the coating-material manufacturing method of this invention. It is sectional drawing which shows the structure of the fine space | interval high-speed shearing disperser of another example used with the coating-material manufacturing method of this invention. It is sectional drawing which shows the structure of the fine space | interval high-speed shearing disperser of another example used with the coating-material manufacturing method of this invention. It is an expanded sectional view of a pair of dispersion | distribution surface part of a micro space | interval high-speed shearing-type disperser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st dispersion | distribution part 1a 1st dispersion | distribution surface 2 2nd dispersion | distribution part 2a 2nd dispersion | distribution surface 3 Spring 4 Rotating rotor 5 Dispersion container 5a Paint supply hole 5b Paint discharge hole 6 Position adjustment screw

Claims (3)

In a method for producing a magnetic coating material comprising a magnetic powder having an average particle size of less than 50 nm and a binder resin, a dispersion step is performed by a media-type disperser, and then opposed at a predetermined interval and relatively moved at a predetermined speed. A method for producing a magnetic paint, comprising performing a dispersion step using a disperser having a pair of dispersion surfaces. The method for producing a magnetic paint according to claim 1, wherein an interval between the pair of dispersion surfaces is 1 to 10 μm . The method for producing a magnetic paint according to claim 1 or 2, wherein a relative moving speed of the pair of dispersion surfaces is 10 to 100 m / s .

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