JP2011148657A - Production method for hexagonal ferrite particle powder, hexagonal ferrite particle powder and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hexagonal ferrite particle powder, which has an average plate surface diameter of above 20.5 nm and at most 30 nm and is obtained by using hydrothermal synthesis process with excellent productivity in industry. <P>SOLUTION: In a production method, the hexagonal ferrite particle powder is obtained by: adding a suspension, which is composed of a mixture of a metal salt containing at least one kind of metal ion selected from Ba, Sr and Ca, an iron compound and one or two kinds or more of metal salts selected from di- to pentavalent metal elements, to an alkaline aqueous solution; allowing to react by using an autoclave; filtering out and drying an obtained precursor of hexagonal ferrite particles; and after calcinating the particles in the presence of a flux, removing the flux. When the suspension is added to the alkaline aqueous solution, the addition should be gradually performed over at least 20 minutes to obtain the hexagonal ferrite particle powder, having an average plate surface diameter of above 20.5 nm and at most 30 nm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to hexagonal ferrite particle powder, and more specifically, hexagonal ferrite particle powder having an average plate surface diameter of more than 20.5 nm and not more than 30 nm by a hydrothermal synthesis method excellent in industrial productivity. It is about.

  Conventionally, magnetic recording technology has been widely used in various fields including audio, video, and computer. In recent years, there has been a demand for smaller and lighter devices, longer recording time, increased recording capacity, and the like, and further improvement in recording density is desired for recording media.

  In order to perform high-density recording on a conventional magnetic recording medium, a high C / N ratio is required, noise (N) is low, and reproduction output (C) is required to be high. In recent years, high-sensitivity heads such as magnetoresistive heads (MR heads) and giant magnetoresistive heads (GMR heads) have been developed in place of the inductive magnetic heads used so far. Since it is easy to obtain a reproduction output as compared with the head, in order to obtain a high C / N ratio, it is more important to reduce the noise than to increase the output.

  The noise of the magnetic recording medium is roughly classified into particulate noise and surface noise generated due to the surface property of the magnetic recording medium. In the case of particulate noise, the influence of the particle size is large, and the finer the particle, the better the noise reduction. Therefore, the magnetic particle powder used in the magnetic recording medium needs to be as small as possible. Since the particle volume is reduced by miniaturization, the ratio of magnetic anisotropy energy and thermal energy (KuV / kT) representing the thermal stability of magnetization (Ku: magnetic anisotropy constant, V: particle volume) , K: Boltzmann constant, T: absolute temperature) becomes small, and is susceptible to thermal fluctuations.

  Generally, as magnetic particles having fine particles and a high coercive force value, metal magnetic particle powders mainly composed of iron, hexagonal ferrite particle powders, and the like are known, and hexagonal ferrite particle powders are acicular metal. Compared with magnetic particle powder, it has a feature that a high output can be obtained in a short wavelength region, and is very promising as a magnetic powder for high-density recording magnetic recording media using an MR head or GMR head for reproduction.

  As the hexagonal ferrite particles by hydrothermal synthesis, an alkaline suspension having a desired ferrite composition is heated in a liquid phase at 100 ° C. or higher, washed and dried, heat treated at about 900 ° C., and pulverized to obtain hexagonal ferrite particles. A method for obtaining particle powder (Patent Document 1), an alkaline suspension having a desired ferrite composition is heated in a liquid phase in a temperature range of 50 to 150 ° C., and the resulting coprecipitate is washed and dried, followed by 680 to 900 ° C. Heat treatment and pulverization to obtain hexagonal ferrite particle powder (Patent Document 2), an alkaline suspension having a desired ferrite composition is heated at a temperature exceeding 100 ° C. using an autoclave, washed and dried. A method of obtaining hexagonal ferrite particle powder (Patent Document 3) is known.

Japanese Patent Laid-Open No. 2-9723 JP-A-7-172839 JP-A-2-120236

  A fine hexagonal ferrite particle powder having an average plate surface diameter of more than 20.5 nm and not more than 30 nm by a hydrothermal synthesis method has not yet been obtained.

  That is, in the above-mentioned Patent Document 1, a plate-like composite ferrite fine particle powder obtained by a hydrothermal synthesis method is described. A suspension composed of a metal salt constituting the hexagonal ferrite particle powder is made into an alkaline aqueous solution. Slow addition is not considered, and in the conventional hydrothermal synthesis method, hexagonal ferrite particles having an average particle size of 30 nm or less and a coercive force (Hc) of 95.5 kA / m or more are obtained. It was difficult to get.

  In addition, Patent Document 2 described above describes a hexagonal ferrite particle powder obtained by a coprecipitation-firing method or a hydrothermal synthesis method. However, the suspension is composed of a metal salt constituting the hexagonal ferrite particle powder. It is not considered that the solution is gradually added to the alkaline aqueous solution. Therefore, the hexagonal ferrite particle powder obtained in the examples has the smallest average particle size of 53 nm, and the magnetic recording for high-density recording. A particle size that is too large for use in a medium and a coercive force (Hc) of 95.5 kA / m or more has not been obtained.

  In addition, in the above-mentioned Patent Document 3, a plate-like composite ferrite fine particle powder obtained by a hydrothermal synthesis method is described. A suspension made of a metal salt constituting the hexagonal ferrite particle powder is made into an alkaline aqueous solution. Slow addition is not taken into consideration, so the hexagonal ferrite particle powder obtained in the examples has the smallest average particle diameter of 50 nm, and is used for a magnetic recording medium for high-density recording. A particle having a particle size that is too large and a coercive force (Hc) of 95.5 kA / m or more has not been obtained.

  Then, this invention makes it a technical subject to obtain the hexagonal ferrite particle powder whose average plate surface diameter exceeds 20.5 nm and is 30 nm or less by a hydrothermal synthesis method.

  The technical problem can be achieved by the present invention as follows.

  That is, the present invention provides a metal salt and an iron compound containing at least one metal ion selected from barium, strontium, and calcium, and one or more selected from divalent to pentavalent metal elements. The suspension in which the metal salt is mixed is added to the alkaline aqueous solution, then reacted in the temperature range of 100 to 300 ° C. using an autoclave, and the resulting hexagonal ferrite particle precursor is filtered and dried, In the method for producing hexagonal ferrite particles obtained by removing the flux after firing at a temperature of 600 to 800 ° C. in the presence of the flux, when adding the suspension to the aqueous alkaline solution, This is a method for producing hexagonal ferrite particle powder having an average plate surface diameter of more than 20.5 and 30 nm or less, characterized by being gradually added over 20 minutes (Invention 1).

  Further, the present invention is a hexagonal ferrite particle powder obtained by the method of the present invention 1 having a coercive force (Hc) of 95.5 kA / m (1200 Oe) or more (Invention 2).

Further, the present invention is characterized in that the average plate surface diameter (L) (nm) of the hexagonal ferrite particle powder and the BET specific surface area value (SSA) (m ² / g) are in the relationship of the following formula (1): This is the hexagonal ferrite particle powder of the present invention 2 (present invention 3).
−1.0 × L (nm) + 120 ≧ SSA (m ² /g)≧−1.0×L (nm) +90 (1)

  The present invention also relates to a magnetic recording medium comprising a magnetic recording layer comprising a magnetic particle powder formed on a nonmagnetic support and a binder resin, wherein the magnetic particle powder is one of the present invention 2 or the present invention 3. A magnetic recording medium using any one of the hexagonal ferrite particle powders (Invention 4).

  The method for producing hexagonal ferrite particle powder by the hydrothermal synthesis method according to the present invention can industrially advantageously provide fine hexagonal ferrite particle powder having an average plate surface diameter of more than 20.5 nm and not more than 30 nm. It is suitable as a method for producing magnetic particle powder for high-density magnetic recording media.

  The hexagonal ferrite particle powder obtained by the production method according to the present invention has an average plate surface diameter of more than 20.5 nm and 30 nm or less, and an average plate surface diameter (L) and a BET specific surface area value (SSA). Since it is in a specific range and is excellent in dispersibility, it is suitable as a magnetic particle powder for a high-density magnetic recording medium.

  The configuration of the present invention will be described in more detail as follows.

  First, a method for producing hexagonal ferrite particle powder according to the present invention will be described.

  The hexagonal ferrite particle powder according to the present invention is a metal salt containing at least one metal ion selected from barium, strontium, and calcium, an iron compound, and one kind selected from divalent to pentavalent metal elements. Alternatively, a suspension obtained by mixing two or more metal salts is added to an alkaline aqueous solution, and then subjected to a hydrothermal reaction in a temperature range of 100 to 300 ° C. using an autoclave, and the obtained precursor of hexagonal ferrite particles. In the process for producing hexagonal ferrite particle powder obtained by removing the flux after filtering and drying, then firing at a temperature of 600 to 800 ° C. in the presence of the flux, When it is added to the alkaline aqueous solution, it can be obtained by gradually adding it over 20 minutes.

Further, as a more preferable production method of the hexagonal ferrite particle powder according to the present invention, in addition to the above production method, a slurry after reaction in a temperature range of 100 to 300 ° C. using an autoclave is used. What is subjected to dispersion treatment until the volume behavior particle diameter (D ₅₀ ) of the particle precursor is 30 μm or less is used for firing.

  As the iron compound in the present invention, one or more selected from water-soluble iron salts such as halides such as chloride, bromide and iodide, nitrates, sulfates, carbonates, organic acid salts and complex salts are used. Can be used. Considering solubility in water and economy, ferric chloride and ferric nitrate are preferable.

  As the metal salt containing at least one metal ion selected from barium, strontium and calcium in the present invention, water-soluble chlorides, bromides, iodides and other halides or nitrates can be used. In view of solubility in water and economy, chloride is preferred.

  As one or more metal salts selected from divalent to pentavalent metal elements (substitution elements) in the present invention, water-soluble chlorides, bromides, iodides and other halides or nitrates may be used. it can. Specific examples of divalent to pentavalent metal elements include Co, Ni, Zn, Mn, Mg, Ti, Sn, Zr, Cu, Mo, La, Ce, V, Si, Sc, Sb, Y, and Rh. , Pd, Nd, Nb, B, P, Ge, Al, Ru, Pr, Bi, W, Re, or the like can be used.

  As the aqueous alkali solution in the present invention, an aqueous alkali hydroxide solution such as sodium hydroxide or potassium hydroxide can be used, and sodium hydroxide is preferable.

  The concentration of the alkaline aqueous solution is preferably 2.5 to 10 times, more preferably 4 to 8 times the total amount of metal salts (iron salt and metal salt) constituting the hexagonal ferrite particles. . As the concentration of the aqueous alkali solution increases, the obtained hexagonal ferrite particle powder tends to become fine particles. However, since the effect is saturated at about 10 times, addition beyond that is industrially disadvantageous.

  In the present invention, one or more metals selected from metal salts and iron compounds containing at least one metal ion selected from barium, strontium, and calcium, and divalent to pentavalent metal elements. When adding the suspension mixed with the salt to the alkaline aqueous solution, it is important to gradually add over 20 minutes, and by adding gradually, it is possible to obtain fine hexagonal ferrite particle powder. Become. When the suspension is added to the alkaline aqueous solution at once, coarse particles are likely to be generated, and it becomes difficult to obtain fine hexagonal ferrite particle powder. Further, since the powder SFD becomes large due to the mixed coarse particles, it is difficult to obtain good magnetic properties.

  The suspension is gradually added to the aqueous alkali solution over 20 minutes and then reacted in the temperature range of 100 to 300 ° C. using an autoclave to obtain a slurry containing a precursor of hexagonal ferrite particles. The reaction temperature is preferably 110 to 280 ° C, more preferably 120 to 250 ° C. The reaction time is preferably 30 minutes to 24 hours, more preferably 1 hour to 20 hours.

  The obtained slurry containing the precursor of hexagonal ferrite particles was washed with water in accordance with a conventional method, the salt produced by the reaction and the unreacted alkali, and the pH value was adjusted to less than 10 using acids such as hydrochloric acid, nitric acid and acetic acid. To do.

The precursor of hexagonal ferrite particles used for firing is dispersed in advance until the volume behavior particle size (D ₅₀ ) of the precursor of hexagonal ferrite particles in the slurry containing the precursor of hexagonal ferrite particles is 30 μm or less. It is preferable to keep it, more preferably 20 μm or less. The dispersion treatment may be performed either before or after adjusting the pH value, but more preferably after adjusting the pH value. As a dispersion method of the slurry containing the precursor of hexagonal ferrite particles, for example, a bead mill can be used. By setting the volume behavior particle diameter (D ₅₀ ) of the precursor of hexagonal ferrite particles in the slurry to 30 μm or less and loosening the aggregation of the particles in advance, sintering between the particles is suppressed even in the subsequent firing step. Therefore, fine hexagonal ferrite particle powder can be obtained.

  Next, after adding a flux to the slurry containing the hexagonal ferrite particle precursor whose pH value has been adjusted, stirring and mixing, drying and grinding the slurry containing the hexagonal ferrite particle precursor with the flux added In accordance with conventional methods. As the flux, it is preferable to use chlorides such as sodium chloride and barium chloride, preferably sodium chloride. Moreover, 100-200 degreeC is preferable for drying temperature, More preferably, it is 120-180 degreeC.

  Firing of the precursor of the obtained hexagonal ferrite particles is performed in a temperature range of 600 to 800 ° C. When the firing temperature is less than 600 ° C., it is difficult to obtain hexagonal ferrite particle powder having good magnetic properties. When the firing temperature exceeds 800 ° C., the particles tend to be coarse, which is not preferable. A preferable firing temperature is 650 to 750 ° C. The firing time is preferably 30 minutes to 6 hours, more preferably 1 hour to 5 hours.

  The obtained crystallized product is pulverized by wet pulverization, and the slurry containing the pulverized crystallized product is pickled using an acid such as hydrochloric acid, acetic acid, and nitric acid. For wet pulverization, a ball-type kneader, a blade-type kneader, a wheel-type kneader, or a roll-type kneader can be used. Blade type kneaders such as planetary mixers and nauter mixers can be used more effectively.

  An aqueous alkali solution such as sodium hydroxide is added to the acid-washed slurry to adjust the pH to 5, followed by washing, drying and pulverization according to a conventional method to obtain hexagonal ferrite particle powder according to the present invention.

  The hexagonal ferrite particle powder according to the present invention is one or more selected from the group consisting of an aluminum hydroxide, an aluminum oxide, a silicon hydroxide and a silicon oxide. (Hereinafter referred to as “aluminum hydroxide or the like”).

  The hexagonal ferrite particle powder coated with an aluminum hydroxide is added to an aqueous suspension obtained by dispersing the hexagonal ferrite particle powder, and the aluminum compound, the silicon compound or both of the compounds are mixed and stirred. Or, if necessary, by adjusting the pH value after mixing and stirring, the particle surface of the hexagonal ferrite particle powder is oxidized with aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon. It can be obtained by coating with one or two or more kinds of surface coatings selected from products, and then filtering, washing, drying and pulverizing.

  As the aluminum compound, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride, and aluminum nitrate, and alkali aluminates such as sodium aluminate can be used.

  As the silicon compound, No. 3 water glass, sodium orthosilicate, sodium metasilicate and the like can be used.

  Next, the hexagonal ferrite particle powder according to the present invention will be described.

  The hexagonal ferrite particle powder for magnetic recording media according to the present invention is obtained by the hydrothermal synthesis method described above, and has an average plate surface diameter of more than 20.5 nm and 30 nm or less.

  The hexagonal ferrite particle powder according to the present invention is a magnetoplumbite type (M type) ferrite fine particle powder or W type ferrite fine particle powder containing one or more elements selected from Ba, Sr and Ca, or these This is hexagonal ferrite particle powder in which some of the atoms are substituted with other elements. Specific examples of substitution elements include Co, Ni, Zn, Mn, Mg, Ti, Sn, Zr, Cu, Mo, La, Ce, V, Si, Sc, Sb, Y, Rh, Pd, Nd, and Nb. , B, P, Ge, Al, Ru, Pr, Bi, W, Re, and the like can be used alone or in combination.

  The average plate surface diameter of the hexagonal ferrite particle powder according to the present invention is more than 20.5 nm and not more than 30 nm, preferably more than 20.5 nm and 28 nm, more preferably more than 20.5 nm and 26 nm. When the average plate surface diameter of the hexagonal ferrite particle powder exceeds 30 nm, the particle size is large, so that it is difficult to reduce particulate noise, and it is difficult to obtain a magnetic recording medium having a high C / N ratio. Become. Moreover, when the average plate surface diameter is 20.5 nm or less, the influence of thermal fluctuation accompanying the refinement of the magnetic particle powder becomes large, which is not preferable.

  The plate ratio of the hexagonal ferrite particles according to the present invention (the ratio of the average plate surface diameter to the average thickness) (hereinafter referred to as “plate ratio”) is preferably 1.5 to 10.0, more preferably 1. .75 to 8.0, and still more preferably 2.0 to 6.0. When the plate ratio exceeds 10, stacking between particles increases, dispersibility in the vehicle during production of the magnetic coating material decreases, and viscosity may increase, which is not preferable.

The relationship between the average plate surface diameter (L) (nm) and the BET specific surface area value (SSA) (m ² / g) of the hexagonal ferrite particle powder according to the present invention is represented by the following formula (1).
−1.0 × L (nm) + 120 ≧ SSA (m ² /g)≧−1.0×L (nm) +90 (1)

  When the relationship between the average plate surface diameter (L) and the BET specific surface area value (SSA) is in the range of the above formula (1), the dispersibility in the magnetic coating material is improved when a magnetic recording medium is produced using this. Therefore, a magnetic recording medium having excellent surface properties can be obtained. When the relationship between the average plate surface diameter (L) and the BET specific surface area value (SSA) exceeds the upper limit value of the above formula (1), aggregation is likely to occur due to an increase in intermolecular force due to particle refinement. Dispersibility in the vehicle during production of the magnetic coating is reduced.

As for the magnetic properties of the hexagonal ferrite particles according to the present invention, the coercive force (Hc) is preferably 95.5 to 397.9 kA / m, more preferably 119.4 to 318.3 kA / m, and the saturation magnetization value. Is preferably 40 to 70 Am ² / kg, more preferably 45 to 70 Am ² / kg. The powder SFD is preferably 1.5 or less, more preferably 1.4 or less.

  In the hexagonal ferrite particle powder according to the present invention, the surface of the hexagonal ferrite particle powder is selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide, if necessary. You may coat | cover with the seed | species or 2 or more types of compounds (henceforth "the hydroxide of aluminum etc."). By carrying out a coating treatment with aluminum hydroxide or the like, when dispersed in a magnetic paint, it is well-familiar with the binder resin and a desired degree of dispersion is more easily obtained.

  Next, the magnetic recording medium according to the present invention will be described.

  The magnetic recording medium according to the present invention is formed by forming a magnetic recording layer containing the hexagonal ferrite particle powder according to the present invention and a binder resin on a nonmagnetic support. Further, if necessary, a nonmagnetic underlayer may be formed between the nonmagnetic support and the magnetic recording layer, and further, with respect to the magnetic recording layer formed on one surface of the nonmagnetic support, A back coat layer may be formed on the other surface of the nonmagnetic support. In particular, in the case of a backup tape for computer recording, it is preferable to provide a nonmagnetic underlayer or a backcoat layer from the viewpoint of preventing winding disturbance and improving running durability.

  As the nonmagnetic support in the present invention, polyesters such as polyethylene terephthalate and polyethylene naphthalate that are currently widely used in magnetic recording media, polyolefins such as polyethylene and polypropylene, polycarbonate, polyamide, polyamideimide, polyimide, aromatic Synthetic resin films such as polyamide, aromatic polyimide, aromatic polyamideimide, polysulfone, cellulose triacetate, and polybenzoxazole, metal foils and plates such as aluminum and stainless steel, and various papers can be used.

  As the binder resin, a thermoplastic resin, a thermosetting resin, an electron beam curable resin, etc. that are widely used in the production of magnetic recording media can be used alone or in combination.

  In the magnetic recording medium of the present invention, when a nonmagnetic underlayer is formed between the nonmagnetic support and the magnetic recording layer, the nonmagnetic underlayer contains nonmagnetic particle powder and a binder.

  Nonmagnetic particle powders used for the nonmagnetic underlayer include alumina, hematite, goethite, titanium oxide, silica, chromium oxide, cerium oxide, zinc oxide, silicon nitride, boron nitride, silicon carbide, calcium carbonate, and barium sulfate. Can be used alone or in combination. Hematite, goethite and titanium oxide are preferred, and hematite is more preferred.

  The particle shape of the non-magnetic particle powder may be any shape such as needle shape, spindle shape, rice grain shape, spherical shape, granular shape, polyhedron shape, flake shape, scale shape and plate shape. The particle size is preferably 0.005 to 0.30 μm, more preferably 0.010 to 0.25 μm. If necessary, the particle surface may be coated with one or more compounds selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. Compared with the case of not coating, dispersibility in the nonmagnetic paint can be improved.

  As the binder resin, the binder resin used for producing the magnetic recording layer can be used.

  In the magnetic recording medium of the present invention, when a backcoat layer is formed on the other surface of the nonmagnetic support relative to the magnetic recording layer formed on one surface of the nonmagnetic support, It is preferable to contain an antistatic agent and inorganic particle powder together with the binder resin for the purpose of improving the surface electrical resistance value and strength of the backcoat layer.

  As the inorganic powder, one or more selected from alumina, hematite, goethite, titanium oxide, silica, chromium oxide, cerium oxide, zinc oxide, silicon nitride, boron nitride, silicon carbide, calcium carbonate, barium sulfate, etc. Can be used. The particle size is preferably 0.005 to 1.0 [mu] m, more preferably 0.010 to 0.5 [mu] m.

  As the antistatic agent, conductive powder such as carbon black, graphite, tin oxide, titanium oxide-tin oxide-antimony oxide, a surfactant, and the like can be used. In addition to antistatic properties, carbon black is preferably used as the antistatic agent since effects such as reduction of the friction coefficient and improvement of the strength of the magnetic recording medium can be expected.

  As the binder resin, the binder resin used for producing the magnetic recording layer and the nonmagnetic underlayer can be used.

  In the magnetic recording layer, nonmagnetic underlayer and backcoat layer in the present invention, lubricants, abrasives, dispersants, antistatic agents, etc., which are usually used in the production of magnetic recording media are added as necessary. May be.

  The magnetic recording medium according to the present invention has a coercive force (Hc) of 95.5 to 358.1 kA / m, preferably 51.7 to 318.3 kA / m, and a coercive force distribution SFD (Switching Field Distribution) of 0. 70 or less, preferably 0.67 or less, more preferably 0.65 or less.

  Next, a method for manufacturing a magnetic recording medium in the present invention will be described.

  Solvents used in the formation of the nonmagnetic underlayer, magnetic recording layer, and backcoat layer include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and tetrahydrofuran, toluene, xylene, etc. that are widely used in magnetic recording media. Aromatic hydrocarbons, alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol and isopropyl alcohol, esters such as methyl acetate, butyl acetate, isobutyl acetate and glycol acetate, glycol dimethyl ether, glycol monoethyl ether and dioxane Glycol ethers and mixtures thereof can be used.

  The nonmagnetic underlayer, the magnetic recording layer, and the backcoat layer are kneaded and dispersed with a kneader and a disperser that generally use components and solvents that constitute each layer, thereby preparing each paint. Using each of the coating materials, a nonmagnetic underlayer and a magnetic recording layer are applied in this order on one surface of the nonmagnetic support, dried, and then calendared. As a coating method at that time, either the Wet on Wet method in which the magnetic layer and the nonmagnetic layer are applied almost simultaneously, or the Wet on Dry method in which the nonmagnetic underlayer is applied and dried and then the magnetic recording layer is applied thereon. But you can. If necessary, if a backcoat layer is provided, a backcoat layer coating is applied on the nonmagnetic support opposite to the nonmagnetic underlayer and the magnetic recording layer, dried, calendered, and magnetically treated. A recording medium is obtained.

<Action>
The important point in the present invention is that one or two metal salts and iron compounds containing at least one metal ion selected from barium, strontium and calcium, and one or two metal elements selected from divalent to pentavalent metal elements are used. The suspension obtained by mixing the above metal salts is added to an alkaline aqueous solution, then reacted in an autoclave at a temperature range of 100 to 300 ° C., and the obtained hexagonal ferrite particle precursor is filtered and dried. Then, in the method for producing hexagonal ferrite particle powder obtained by firing at a temperature of 600 to 800 ° C. in the presence of a flux and then removing the flux, the suspension is added to an aqueous alkaline solution. In addition, by gradually adding over 20 minutes, hexagonal ferrite particle powder having an average plate surface diameter of more than 20.5 nm and 30 nm or less can be obtained. It is.

  As a reason why the fine hexagonal ferrite particle powder having an average plate surface diameter of more than 20.5 nm and 30 nm or less can be obtained by the method for producing the hexagonal ferrite particle powder according to the present invention, the present inventor I think like that. When the suspension is added to the alkaline aqueous solution all at once, coarse particles are likely to be generated, but by gradually adding over 20 minutes, the obtained hexagonal ferrite particle precursor becomes fine particles, It is considered that fine hexagonal ferrite particle powder could be obtained by using this as a precursor.

  Examples of the present invention are shown below, and the present invention will be specifically described.

  The average plate surface diameter and average thickness of the hexagonal ferrite particle powder and the magnetic fine particle powder for a magnetic recording medium are obtained by taking a photograph of the particles using a transmission electron microscope and using the photograph for the plate surface of 360 or more particles. The diameter and the thickness were measured, and the average value of the average plate surface diameter and the average thickness of the particles was shown. In addition, as a selection criterion for particles, particles that overlap each other and whose boundaries are not clear are not measured.

  The plate ratio was shown as the ratio between the average plate surface diameter and the average thickness.

  The specific surface area was shown by the value measured by BET method using “Monosorb MS-11” (manufactured by Kantachrome Co., Ltd.).

  The content of various elements contained in the hexagonal ferrite particle powder is measured using a “fluorescence X-ray analyzer 3063M type” (manufactured by Rigaku Denki Kogyo Co., Ltd.) according to “General X-ray fluorescence analysis rules” of JIS K0119. did.

The volume-based average particle diameter (D ₅₀ ) of the precursor of hexagonal ferrite particles contained in the slurry is determined using a wet dispersion unit of “Laser diffraction particle size distribution measuring device model HELOS LA / KA” (manufactured by SYMPATEC). It was measured.

  The magnetic properties of the hexagonal ferrite particle powder and the magnetic tape were measured using a “vibrating sample magnetometer VSM SSM-5-15” (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of 1193.7 kA / m. The powder SFD and the SFD of the magnetic tape have a sweep speed of 79.6 (kA / m) / min when the applied magnetic field is in the range of 0 to 397.9 kA / m, and is 397.9 to 1,193.7 kA / min. In the range of m, the sweep rate was measured as 397.9 (kA / m) / min.

  The glossiness of the coating film surface of the magnetic tape is a value measured at an incident angle of 45 ° using “Gloss meter UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.), and the standard plate gloss is 86.3%. The hour value is shown in%.

  Surface roughness Ra measured the centerline average roughness of the coating film using "ZYGO NewView600S" (made by ZYGO Corporation).

  The thickness of each of the nonmagnetic support and the magnetic recording layer constituting the magnetic recording medium was measured using a digital electronic micrometer K351C (manufactured by Anritsu Electric Co., Ltd.).

<Example 1-1: Production of hexagonal ferrite particle powder for magnetic recording medium>
Pure water was added and dissolved in BaCl ₂ .2H ₂ O 0.08 mol, FeCl ₃ .6H ₂ O 0.60 mol, NiCl ₂ 0.018 mol, TiCl ₄ 0.018 mol to prepare a 0.7 L mixed solution. Next, while stirring 0.5 L of 18.55 mol / L NaOH aqueous solution, the mixed solution was added at 20 mL / min. Was added to an aqueous NaOH solution at a flow rate of 35 minutes, followed by reaction at 150 ° C. for 240 minutes using an autoclave.

Next, the obtained slurry of the hexagonal ferrite particle precursor is sufficiently washed with pure water to obtain a 1 L slurry containing the hexagonal ferrite particle precursor, and then the pH value is adjusted with hydrochloric acid. The mixture was adjusted to 8.5 and stirred for 10 minutes using an ultrasonic homogenizer (Sonifier II model 450D manufactured by BRANSON Co., Ltd.) for dispersion treatment. The volume behavior particle diameter (D ₅₀ ) of the precursor of hexagonal ferrite particles in the slurry at this time was 1.6 μm.

  Next, 30 parts by weight of NaCl as a flux with respect to 100 parts by weight of the hexagonal ferrite particle precursor is added to the slurry containing the hexagonal ferrite particle precursor, followed by filtration and drying. A precursor was obtained. The drying temperature was 150 ° C.

  The obtained precursor of the dried hexagonal ferrite particles was fired in air at a temperature of 700 ° C. for 120 minutes, and 1 L of pure water was added to the fired product to obtain a dispersed slurry. The obtained slurry was wet pulverized, acid-treated by adjusting the pH value to 2 with hydrochloric acid and maintaining for 60 minutes, adjusted to pH value 5 with an aqueous sodium hydroxide solution, and then washed with water. -Filtration, drying, and pulverization gave the hexagonal ferrite particle powder of Example 1-1.

The obtained hexagonal ferrite particle powder has a plate shape, an average plate surface diameter of 22.7 nm, an average thickness of 6.7 nm, a plate ratio of 3.4, and a BET specific surface area value (measured value) of 73.8 m. ^The coercive force (Hc) was 188.3 kA / m, the saturation magnetization (σs) was 48.0 Am ² / kg, and the powder SFD was 0.84.

<Example 2-1: Production of magnetic recording medium>
Nonmagnetic coating composition for nonmagnetic underlayer formation 100.0 parts by weight of hematite particle powder for nonmagnetic underlayer,
11.8 parts by weight of a vinyl chloride copolymer resin having a potassium sulfonate group,
11.8 parts by weight of a polyurethane resin having a sodium sulfonate group,
78.3 parts by weight of cyclohexanone,
195.8 parts by weight of methyl ethyl ketone,
117.5 parts by weight of toluene,
Curing agent (polyisocyanate) 3.0 parts by weight,
Lubricant (butyl stearate) 1.0 part by weight.

  A non-magnetic underlayer hematite particle powder, a binder resin solution (vinyl chloride copolymer resin having potassium sulfonate group 30 wt% and cyclohexanone 70 wt%) and cyclohexanone are mixed so that the solid content is 72 wt%; A kneaded product was obtained by kneading for 30 minutes using an automatic mortar.

  Next, the kneaded product and an additional binder resin solution (30% by weight of a polyurethane resin having a sodium sulfonate group, 70% by weight of a solvent (methyl ethyl ketone: toluene = 1: 1)) so that the nonmagnetic coating composition is obtained. The mixture was added to a 140 ml glass bottle together with 95 g of cyclohexanone, methyl ethyl ketone and toluene 1.5 mmφ glass beads, and mixed and dispersed in a paint shaker for 6 hours to obtain a nonmagnetic coating composition. Thereafter, a lubricant and a curing agent were added, and further mixed and dispersed for 15 minutes with a paint shaker, followed by filtration using a filter having an average pore diameter of 3 μm to prepare a nonmagnetic paint for a nonmagnetic underlayer.

  The nonmagnetic coating for the nonmagnetic underlayer was applied onto an aromatic polyamide film having a thickness of 4.5 μm, and then dried to form a nonmagnetic underlayer.

100.0 parts by weight of a magnetic coating composition hexagonal ferrite particle powder for forming a magnetic recording layer,
12.5 parts by weight of a vinyl chloride copolymer resin having a potassium sulfonate group,
7.5 parts by weight of a polyurethane resin having a sodium sulfonate group,
Abrasive (AKP-50) 5.0 parts by weight,
2.0 parts by weight of carbon black,
Lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight,
Curing agent (polyisocyanate) 5.0 parts by weight,
170.0 parts by weight of cyclohexanone,
170.0 parts by weight of methyl ethyl ketone.

  Hexagonal ferrite particles, abrasive, carbon black, binder resin solution (30% by weight of vinyl chloride copolymer resin having potassium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone so that the solid content becomes 76% by weight. They were mixed and kneaded for 40 minutes using an automatic mortar to obtain a kneaded product.

  Next, the kneaded product and an additional binder resin solution (30% by weight of a polyurethane resin having a sodium sulfonate group, 70% by weight of a solvent (methyl ethyl ketone: toluene = 1: 1)) so that the magnetic coating composition is obtained, The mixture was added to a 140 ml glass bottle together with 95 g of cyclohexanone, methyl ethyl ketone and toluene 1.5 mmφ glass beads, and mixed and dispersed for 6 hours with a paint shaker to obtain a nonmagnetic coating composition. Thereafter, a lubricant and a curing agent were added, and further mixed and dispersed for 15 minutes with a paint shaker, followed by filtration using a filter having an average pore diameter of 3 μm to prepare a magnetic coating material for a magnetic recording layer.

  The magnetic recording layer coating composition was applied on the nonmagnetic underlayer so that the thickness after drying was 1.5 μm, and then oriented and dried in a magnetic field. Thereafter, a curing reaction was performed at 60 ° C. for 24 hours, and a magnetic recording medium was obtained by slitting to a width of 12.7 mm.

  The obtained magnetic recording medium had a coercive force Hc of 197.9 kA / m, a Br / Bm of 0.81, a coercive force distribution SFD of 0.56, a glossiness of 177%, and a surface roughness Ra of 10.1 nm. there were.

  A hexagonal ferrite particle powder and a magnetic recording medium were prepared according to Example 1-1 and Example 2-1. Various production conditions and various properties of the obtained hexagonal ferrite particle powder and magnetic recording medium are shown.

Examples 1-2 to 1-3 and Comparative Example 1-1
Hexagonal ferrite particle powders were obtained by variously changing the conditions for the formation reaction of the precursors of the hexagonal ferrite particles and the firing of the precursors.

  The production conditions at this time are shown in Table 1, and various properties of the obtained hexagonal ferrite particle powder are shown in Table 2.

<Manufacture of magnetic recording media>
Examples 2-2 to 2-3 and Comparative Example 2-1
A magnetic tape was produced according to the method for producing a magnetic recording medium of Example 2-1 except that the type of hexagonal ferrite particle powder was variously changed.

  Table 3 shows various characteristics of the obtained magnetic tape.

  The method for producing hexagonal ferrite particle powder by the hydrothermal synthesis method according to the present invention can industrially advantageously provide fine hexagonal ferrite particle powder having an average plate surface diameter of more than 20.5 nm and not more than 30 nm. It is suitable as a method for producing magnetic particle powder for high-density magnetic recording media.

The hexagonal ferrite particle powder obtained by the production method according to the present invention has an average plate surface diameter of more than 20.5 nm and 30 nm or less, and an average plate surface diameter (L) and a BET specific surface area value (SSA). Since it is in a specific range and is excellent in dispersibility, it is suitable as a magnetic particle powder for a high-density magnetic recording medium.

Claims (4)

A metal salt containing at least one metal ion selected from barium, strontium, and calcium, an iron compound, and one or two or more metal salts selected from divalent to pentavalent metal elements. After adding the turbid solution to the aqueous alkaline solution, the reaction is carried out in the temperature range of 100 to 300 ° C. using an autoclave, the obtained hexagonal ferrite particle precursor is filtered and dried, and then in the presence of a flux. In the method for producing hexagonal ferrite particles obtained by firing at 600 to 800 ° C. and then removing the flux, the suspension is gradually added over 20 minutes when added to the alkaline aqueous solution. A method for producing hexagonal ferrite particle powder having an average plate surface diameter of more than 20.5 and not more than 30 nm, which is characterized by being added. The hexagonal ferrite particle powder obtained by the method according to claim 1, wherein the coercive force (Hc) is 95.5 kA / m (1,200 Oe) or more. The average plate surface diameter (L) (nm) of the hexagonal ferrite particle powder and the BET specific surface area value (SSA) (m ² / g) are in a relationship represented by the following formula (1). Hexagonal ferrite particle powder.
−1.0 × L (nm) + 120 ≧ SSA (m ² /g)≧−1.0×L (nm) +90 (1) 6. The hexagon according to claim 3, wherein the magnetic particle powder is a magnetic recording medium comprising a magnetic recording layer including a magnetic particle powder formed on a nonmagnetic support and a binder resin. A magnetic recording medium using crystal ferrite particle powder.