JP2006331539A - Magnetic recording medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium having ferromagnetism and excellent running durability, and to provide its manufacturing method. <P>SOLUTION: The magnetic recording medium having a magnetic layer containing a CuAu type or Cu<SB>3</SB>Au type ferromagnetic ordered alloy and a matrix agent is characterized in that pores are formed in the magnetic layer. Its manufacturing method includes a degreasing step for performing degreasing as a step prior to a thermal treatment step for performing thermal treatment for forming the CuAu type or the Cu<SB>3</SB>Au type ferromagnetic ordered alloy. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a magnetic recording medium and a manufacturing method thereof, and more particularly to a magnetic recording medium including a CuAu type or Cu ₃ Au type ferromagnetic ordered alloy in a magnetic layer and a manufacturing method thereof.

  It is necessary to reduce the particle size of the magnetic substance contained in the magnetic layer in order to increase the magnetic recording density. For example, in a magnetic recording medium widely used as a video tape, a computer tape, a disk, etc., if the mass of the ferromagnetic material is the same, the noise decreases as the particle size is reduced.

The CuAu type or Cu ₃ Au type hard magnetic ordered alloy has a large magnetocrystalline anisotropy due to strain generated during ordering, a small particle size, and exhibits hard magnetism even in what is called a metal nanoparticle. Therefore, it is a promising material for improving the magnetic recording density (see, for example, Patent Document 1).

As a method of synthesizing metal nanoparticles capable of forming a CuAu type or Cu ₃ Au type alloy, when classified by precipitation method, (1) alcohol reduction method using primary alcohol, (2) secondary, tertiary, divalent Alternatively, there are a polyol reduction method using a trivalent alcohol, (3) thermal decomposition method, (4) ultrasonic decomposition method, and (5) strong reducing agent reduction method (for example, see Patent Document 1). Further, when classified by reaction system, there are (6) polymer existence method, (7) high boiling point solvent method, (8) normal micelle method, and (9) reverse micelle method.

  The structure of the metal nanoparticles synthesized by the above method is a face-centered cubic crystal. Face-centered cubic crystals are usually soft or paramagnetic. Soft magnetism or paramagnetism is not suitable for recording media. In order to obtain a hard magnetic ordered alloy having a coercive force of 95.5 kA / m (1200 Oe) or more necessary for a magnetic recording medium, it is necessary to perform an annealing treatment at a temperature higher than the transformation temperature at which the transformation from the disordered phase to the ordered phase occurs. The annealing temperature is generally a high temperature of 500 ° C. or higher.

  In the magnetic recording medium, the surface of the medium needs to be smooth in order to make the head slide on the surface of the medium, or to make the head fly over at a distance of about 10 nm from the surface of the medium. Further, since the rough surface causes noise, the surface needs to be smooth.

On the other hand, since magnetic nanoparticles have a small particle size, they have a larger surface area than conventional magnetic materials and are likely to aggregate, so the surface may not be smooth, and it is difficult to obtain a smooth surface with good reproducibility. . As a result, there is a problem that the running durability is lowered.
JP 2003-73705 A

  In view of the above, an object of the present invention is to provide a magnetic recording medium exhibiting ferromagnetism and excellent running durability and a method for manufacturing the same.

As a result of intensive studies to solve the above problems, the present inventors have conceived the following present invention and found that the problems can be solved. That is, the present invention is a magnetic recording medium having a magnetic layer containing a CuAu type or Cu ₃ Au type ferromagnetic ordered alloy and a matrix agent, wherein the magnetic layer has pores formed therein. It is a recording medium. The pores are preferably at least one of micropores and mesopores.

The present invention is also a method for producing a magnetic recording medium according to the present invention, wherein a degreasing treatment is performed as a pre-step of a heat treatment step for performing a heat treatment for obtaining the CuAu type or Cu ₃ Au type ferromagnetic ordered alloy. A method for producing a magnetic recording medium, comprising a degreasing treatment step. As a pre-process of the degreasing process, it is preferable to include a curing process for curing the matrix agent.

  According to the present invention, it is possible to provide a magnetic recording medium exhibiting ferromagnetism and excellent in running durability and a method for manufacturing the same.

[Magnetic recording medium]
The magnetic recording medium of the present invention has a magnetic layer containing a CuAu type or Cu ₃ Au type ferromagnetic ordered alloy (hereinafter sometimes referred to as “ferromagnetic ordered alloy”) and a matrix agent. A pore is formed. Since the pores are formed in the magnetic layer, the pores become a place for collecting the lubricant, and the running durability can be improved.

  The pores are preferably at least one of micropores and mesopores. The micropore means a pore having an average pore diameter of 2 nm or less. The mesopore means a pore having an average pore diameter of 2 to 50 nm. By forming these micropores and mesopores, a lubricant pool can be formed.

  The occupied volume ratio of pores (preferably at least one of micropores and mesopores) in the magnetic layer (total volume of pores / volume of magnetic layer) is preferably 0.03 to 0.3, More preferably, it is 0.05-0.2. By being 0.03 to 0.3, an effective lubricant pool can be formed.

  The average pore diameter and the pore volume can be determined by measuring by a gas adsorption method or a mercury intrusion method. Further, the volume of the magnetic layer can be determined from the average thickness and width of the layer measured by TEM and the length in the longitudinal direction after cutting the end face by FIB.

The magnetic layer contains a CuAu type or Cu ₃ Au type ferromagnetic ordered alloy and a matrix agent. By including a CuAu type or Cu ₃ Au type ferromagnetic ordered alloy, ferromagnetism (hard magnetism) can be exhibited. In addition, the inclusion of the matrix agent can prevent the fusion of particles made of the CuAu type or Cu ₃ Au type ferromagnetic ordered alloy. The matrix agent is preferably a nonmagnetic metal oxide matrix agent.

  The nonmagnetic metal oxide matrix is preferably composed of at least one matrix agent selected from silica, titania and polysiloxane. Moreover, it is preferable to add at least one matrix agent selected from organosilica sol, organotitania sol and silicone resin. In addition, if the said matrix agent is a main component (50 mass% or more), you may add together various well-known additives besides these.

The CuAu type or Cu ₃ Au type ferromagnetic ordered alloy is not particularly limited, but at least two metals selected from Group VIII of the short periodic table and, if necessary, I of the short periodic table. It is preferable to contain at least one metal selected from Group III, Group III, Group IV and Group V.

  Examples of binary or ternary alloys composed of Group VIII of the short periodic table include FePt, FePd, FeNi, FeRh, CoNi, CoPt, CoPd, CoRh, FeNiPt, FeCoPt, CoNiPt, FeCoPd, FeNiPd, and the like. Is mentioned. In addition, other metals selected from Group I, Group III, Group IV, and Group V of the short periodic table may be selected from Cu, Ag, B, In, Sn, Pb, P, Sb, Bi, and the like. preferable. The ferromagnetic ordered alloy is preferably a ternary or higher alloy. Examples of the ternary or higher alloy include FePtCu, FePtIn, FePtPb, FePtBi, FePtAg, CoPtCu, FePdCu, FeCoPtCu, FeNiPtCu, FePtCuAg, and FeNiPdCu.

  The content of each metal forming the ferromagnetic ordered alloy can be appropriately determined according to the type of metal to be configured. Preferably, the content of at least one metal selected from Group I, Group III, Group IV and Group V of the short periodic table is 0 to 35 atomic%, and 10 to 35 atomic%. It is preferable that it is 15 to 30 atomic%. When the metal content is 35 atomic% or less, an ordered phase exhibiting hard magnetism can be formed even after annealing at 400 ° C. or less. As a result, by using the ferromagnetic ordered alloy, a magnetic recording medium with high smoothness can be produced, and a polymer support can be used.

  The transformation temperature of FePt, CoPt, FePd, etc. is usually as high as 550 ° C. or higher. At such high transformation temperatures, there is a risk of distortion in the case of glass supports as well as that they cannot be used for polymer supports. This distortion may destroy the head in a hard disk on which the head is recorded and reproduced with a flying height of 10 nm or less. Therefore, a reduction in transformation temperature is desired.

  The ferromagnetic ordered alloy includes a ferromagnetic ordered alloy whose surface is oxidized or a ferromagnetic ordered alloy whose portion is oxidized.

The CuAu type or Cu ₃ Au type ferromagnetic ordered alloy can take various forms, but is preferably in the form of particles. The shape is preferably substantially spherical. This is because spherical particles are easier to increase the filling rate than needle-like or plate-like particles. Increasing the degree of filling of the magnetic material is advantageous in terms of output. For this purpose, it is important not to fuse the particles during annealing in order to synthesize spherical particles and obtain a hard magnetic material. Polycrystalline particles in which these particles are fused cause noise and are not preferable. In the present specification, particles before annealing are referred to as alloy nanoparticles, and after annealing, that is, ordered particles are referred to as magnetic particles.

  The variation coefficient of the particle size and composition of the magnetic particles is preferably 20% or less (1 to 20%), more preferably 15% or less (2 to 15%), and 10% or less (2 to 10%). More preferably it is. When the variation coefficient is 20% or less, the variation in coercive force is small, and the decrease in output and the increase in noise during magnetic recording / reproduction are reduced.

  In the present specification, the “coefficient of variation in particle size” means a value obtained by calculating a standard deviation of the particle size distribution with an equivalent circle diameter and dividing this by the average particle size. The “composition variation coefficient” means a value obtained by calculating a standard deviation of the composition distribution of the alloy nanoparticles and dividing this by the average composition in the same manner as the particle diameter variation coefficient. In the present invention, these values are multiplied by 100 to display%.

  The coefficient of variation of the particle size is 100,000 times with TEM (JEOL 1200EX) after drying diluted alloy nanoparticles (magnetic particles after annealing, the same applies below) on Cu200 mesh with a carbon film attached. The photographed negative can be calculated from the arithmetic average particle diameter measured with a particle size measuring instrument (KS-300 manufactured by Carl Zeiss).

  On the other hand, the coefficient of variation of the composition was measured by FE-TEM while observing the diluted alloy nanoparticles on Ni300 mesh with a carbon film and drying it with FE-TEM (Hitachi HF-2210) at 500,000 times. / EDS composition analysis (accumulate particle area for 30 seconds and calculate the composition of each metal in atomic% using the Filter Fit method of EDS built-in software from the obtained spectrum) and calculate with composition ratio be able to. In addition, the said average particle diameter can measure a TEM photograph with the image analyzer KS-300 by Carl Zwis.

  The alloy nanoparticles as described above can be preferably produced by the following production method.

(1) A reduction process in which a reverse micelle solution (I) containing at least one metal compound and a reverse micelle solution (II) containing a reducing agent are mixed and subjected to a reduction treatment; and an aging treatment after the reduction treatment The manufacturing method of the alloy nanoparticle which has an aging process to apply.
(2) The production method according to (1), wherein the metal contained in the metal compound is at least one metal selected from the group consisting of Group VIII, Group I, Group III, Group IV and Group V.
(3) The manufacturing method as described in (1) or (2) whose temperature of the said reduction | restoration process is -5-30 degreeC.
(4) The production method according to any one of (1) to (3), wherein the temperature of the aging step is 30 to 90 ° C. and is higher than the temperature of the reduction.
(5) The manufacturing method according to any one of (1) to (4), including an annealing treatment step.
(6) The manufacturing method according to (5), wherein the temperature of the annealing treatment step is higher than the transformation temperature of the alloy forming the alloy nanoparticles.

  Below, the manufacturing method of an alloy nanoparticle is demonstrated in detail. In the present specification, “to” is used as a meaning including numerical values described before and after the lower limit value and the upper limit value.

  The alloy nanoparticles are subjected to a reduction process in which a reverse micelle solution (I) containing at least one metal compound and a reverse micelle solution (II) containing a reducing agent are mixed and subjected to a reduction process, and an aging process is performed after the reduction process. It can be manufactured by an aging process. By this production method, nanoparticles made of a multi-component alloy are produced. Hereinafter, each step will be described.

(Reduction process)
First, a reverse micelle solution (I) is prepared by mixing a water-insoluble organic solvent containing a surfactant and an aqueous solution containing one or more metal compounds. The reverse micelle solution (I) may contain a plurality of types of metal salts used to form a multi-component alloy, and each of the reverse micelle solutions ((I ′), (I '') Etc.) may be prepared and each may be a reverse micelle solution. For example, a reverse micelle solution (I) containing a metal selected from Group VIII and a reverse micelle containing a metal selected from Group I, Group III, Group IV and Group V separately The solution (I ′) may be prepared separately, and these may be mixed as appropriate to form a reverse micelle solution.

  An oil-soluble surfactant is used as the surfactant. Specifically, sulfonate type (for example, aerosol OT (manufactured by Wako Pure Chemical Industries), quaternary ammonium salt type (for example, cetyltrimethylammonium bromide), ether type (for example, pentaethylene glycol dodecyl ether) and the like can be mentioned. It is done.

Preferable water-insoluble organic solvents for dissolving the surfactant are alkanes and ethers. The alkane is preferably an alkane having 7 to 12 carbon atoms. Specific examples include heptane, octane, nonane, decane, undecane, and dodecane. On the other hand, the ether is preferably diethyl ether, dipropyl ether, or dibutyl ether.
The addition amount of the surfactant in the water-insoluble organic solvent is preferably 20 to 200 g / liter.

  Metal compounds contained in an aqueous solution of a metal compound include nitrates, sulfates, hydrochlorides, acetates, metal complex hydrogen acids with chloride ions as ligands, and metal complex potassiums with chloride ions as ligands. Examples include salts, sodium salts of metal complexes having a chloride ion as a ligand, ammonium salts of metal complexes having an oxalate ion as a ligand, etc. Can do.

  The concentration of the metal compound in each metal compound aqueous solution is preferably 0.1 to 2000 μmol / ml, and more preferably 1 to 500 μmol / ml.

  It is preferable to add a chelating agent to the aqueous metal compound solution so that the resulting particles have a uniform composition. Specifically, DHEG (dihydroxyethylglycine), IDA (iminodiacetic acid), NTP (nitrilotripropionic acid), HIDA (dihydroxyethyliminodiacetic acid), EDDP (ethylenediamine dipropionic acid dihydrochloride), BAPTA It is preferable to use (diaminophenylethylene glycol tetraacetic acid tetrapotassium salt hydrate) or the like as a chelating agent. The chelate stability constant (log K) is preferably 10 or less. The addition amount of the chelating agent is preferably 0.1 to 10 mol, and more preferably 0.3 to 3 mol, per 1 mol of the metal compound.

  Next, reverse micelle solution (II) containing a reducing agent is prepared. The reverse micelle solution (II) can be prepared by mixing a water-insoluble organic solvent containing a surfactant and a reducing agent aqueous solution. When two or more reducing agents are used, they may be mixed together to form a reverse micelle solution (II). However, in consideration of the stability and workability of the solution, each is separately added to a water-insoluble organic solvent. It is preferable that they are mixed and prepared as separate reverse micelle solutions ((II ′), (II ″), etc.), which are appropriately mixed and used.

Examples of the reducing agent aqueous solution include alcohols; polyalcohols; H ₂ ; HCHO, S ₂ O ₆ ²⁻ , H ₂ PO ₂ ⁻ , BH ₄ ⁻ , N ₂ H ₅ ⁺ , H ₂ PO ₃ ^{− and the} like and water. These reducing agents are preferably used alone or in combination of two or more. The amount of the reducing agent in the aqueous solution is preferably 3 to 50 mol with respect to 1 mol of the metal salt.

  Examples of the surfactant and non-aqueous organic solvent used in the reverse micelle solution (II) include those used in the reverse micelle solution (I).

  The mass ratio of water and surfactant (water / surfactant) contained in each of the reverse micelle solutions (I) and (II) is preferably 20 or less. If the mass ratio is 20 or less, precipitation is unlikely to occur and uniform particles can be obtained. In order to obtain particles having a particle size of 4 to 12 nm, the mass ratio is more preferably 15 or less, and further preferably 0.5 to 10.

  The mass ratio of water and surfactant in the reverse micelle solutions (I) and (II) may be the same or different, but the mass ratio is preferably the same in order to make the system uniform.

  The reverse micelle solutions (I) and (II) prepared as described above are mixed. The mixing method is not particularly limited, but it is preferable to add and mix the reverse micelle solution (II) while stirring the reverse micelle solution (I) in consideration of the reduction uniformity. After the mixing is completed, the reduction reaction is allowed to proceed, and the temperature at that time is a constant temperature in the range of -5 to 30 ° C. If the reduction temperature is −5 ° C. or higher, the reduction reaction can be made uniform without condensation of the aqueous phase, and if it is 30 ° C. or lower, aggregation or precipitation hardly occurs and the system is stabilized. be able to. A preferable reduction temperature is 0 to 25 ° C, and more preferably 5 to 25 ° C.

  Here, the “constant temperature” means that the temperature is in a range of T ± 3 ° C. when the set temperature is T (° C.). Even in this case, the upper and lower limits of T are in the range of the reduction temperature (−5 to 30 ° C.).

  The time for the reduction reaction needs to be appropriately set depending on the amounts of the reverse micelle solutions (I) and (II), but is preferably 1 to 30 minutes, and more preferably 5 to 20 minutes.

  Since the reduction reaction has a great influence on the monodispersity of the particle size distribution of the alloy, it is preferable to carry out the reduction reaction while stirring as fast as possible (for example, about 3000 rpm or more). A preferred stirring device is a stirring device having a high shearing force. Specifically, the stirring blade basically has a turbine-type or paddle-type structure, and a sharp blade is attached to the end of the blade or a position in contact with the blade. It is a stirring device that has a structure and rotates blades with a motor. Specifically, devices such as a dissolver (manufactured by Special Machine Industries), an omni mixer (manufactured by Yamato Kagaku), and a homogenizer (manufactured by SMT) are useful. By using these apparatuses, monodisperse nanoparticles can be synthesized as a stable dispersion.

  After the reaction of the reverse micelle solutions (I) and (II), at least one dispersant having 1 to 3 amino groups or carboxy groups is added in an amount of 0.001 to 10 per mole of alloy nanoparticles to be prepared. It is preferable to add a molar amount. If the addition amount of a dispersing agent is 0.001-10 mol, the monodispersity of an alloy nanoparticle can be improved more and aggregation will not occur.

  The dispersant is preferably an organic compound having a group that adsorbs to the surface of the alloy nanoparticles. Specifically, it has 1 to 3 amino groups, carboxy groups, sulfonic acid groups or sulfinic acid groups, and these can be used alone or in combination.

As structural formulas, R—NH ₂ , H ₂ N—R—NH ₂ , H ₂ N—R (NH ₂ ) —NH ₂ , R—COOH, HOCO—R—COOH, HOCO—R (COOH) —COOH , R—SO ₃ H, HOSO ₂ —R—SO ₃ H, HOSO ₂ —R (SO ₃ H) —SO ₃ H, R—SO ₂ H, HOSO—R—SO ₂ H, HOSO—R (SO ₂ H) a compound represented by -SO ₂ H, R in the formula is a hydrocarbon residue of a straight, branched or cyclic, saturated or unsaturated.

  A particularly preferred compound as a dispersant is oleic acid. Oleic acid is a well-known surfactant in colloidal stabilization and has been used to protect iron nanoparticles. The relatively long chain of oleic acid gives an important steric hindrance that counteracts the strong magnetic interaction between particles (oleic acid has 18 carbon chains, about 2 nm in length (about 20 angstroms), double bond 1). Oleic acid is preferred because it is an inexpensive natural resource that can be easily obtained from, for example, olive oil. In addition, oleylamine derived from oleic acid is a useful dispersant like oleic acid.

  In addition, similar long-chain carboxylic acids such as erucic acid and linoleic acid can be used similarly to oleic acid (for example, long-chain organic acids having 8 to 22 carbon atoms can be used alone or in combination). .

  The addition timing of the dispersant is not particularly limited, but is preferably between immediately after the reduction reaction and the start of the following aging step. By adding such a dispersant, it is possible to obtain more monodisperse and non-aggregated alloy nanoparticles.

(Aging process)
The manufacturing method further includes an aging step of raising the temperature of the solution after the reaction to the aging temperature after the reduction reaction is completed.
The aging temperature is preferably a constant temperature between 30 and 90 ° C., and the temperature is suitably higher than the temperature of the reduction reaction. The aging time is preferably 5 to 180 minutes. When the aging temperature and aging time are within the above ranges, aggregation and precipitation are unlikely to occur, the reaction is completed, and the composition can be made constant. More preferable aging temperature and aging time are 40 to 80 ° C. and 10 to 150 minutes, and further preferable aging temperature and aging time are 40 to 70 ° C. and 20 to 120 minutes.

  Here, the “constant temperature” is synonymous with the temperature of the reduction reaction (where “reduction temperature” is the “aging temperature”), but in particular, the range of the above aging temperature (30 It is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, than the temperature of the reduction reaction. By increasing the temperature by 5 ° C. or more, a composition as prescribed can be obtained.

In the aging process as described above, a noble metal is deposited on the base metal that has been reduced and deposited in the reduction process. That is, the reduction of the noble metal occurs only on the base metal, and the base metal and the noble metal do not separate separately, so that the nanoparticles capable of forming the CuAu type or Cu ₃ Au type hard magnetic ordered alloy according to the desired composition, It can be produced efficiently and with a high yield. Moreover, the alloy nanoparticle which has a desired particle size can be produced by adjusting a stirring speed suitably with the temperature at the time of ripening.

  After the aging, the solution after aging is washed with a mixed solution of water and a primary alcohol, and then subjected to a precipitation treatment with a primary alcohol to generate a precipitate. It is preferable to provide a washing / dispersing step for dispersing with a solvent. By providing such a cleaning / dispersing step, impurities can be removed, and the coating property when forming the magnetic layer of the magnetic recording medium can be further improved. The washing and dispersion are each performed at least once, preferably twice or more.

  The primary alcohol used for washing is not particularly limited, but methanol, ethanol, and the like are preferable. The volume mixing ratio of water and primary alcohol (water / primary alcohol) is preferably in the range of 10/1 to 2/1, and more preferably in the range of 5/1 to 3/1. When the ratio of water is high, the surfactant may be difficult to remove, and conversely, when the ratio of primary alcohol is high, aggregation may occur.

  As described above, alloy nanoparticles dispersed in a solution are obtained. Since the alloy nanoparticles are monodispersed, even when applied to a support, they can be kept uniformly dispersed without agglomeration. Therefore, even if the alloy nanoparticles are subjected to an annealing treatment, the respective nanoparticles do not aggregate, so that they can be made ferromagnetic (hard magnetic) efficiently and have excellent coating suitability.

  The particle diameter of the alloy nanoparticles before annealing is preferably 7 to 12 nm. When used as a magnetic recording medium, it is preferable to close-pack the alloy nanoparticles in order to increase the recording capacity.

If the particle size of the alloy nanoparticles is too small, it becomes superparamagnetic due to thermal fluctuation, which is not preferable. Although the minimum stable particle size varies depending on the constituent elements, it is effective to synthesize by changing the mass ratio of H ₂ O / surfactant in order to obtain the required particle size.

  A transmission electron microscope (TEM) can be used for particle size evaluation of the manufactured alloy nanoparticles. To determine the crystal system of the alloy nanoparticles hardened by heating, electron beam diffraction by TEM may be used, but X-ray diffraction should be used for accuracy. It is preferable to evaluate by FE-TEM / EDS which can narrow down an electron beam for the compositional analysis inside the hardened alloy nanoparticles. Evaluation of the magnetic properties of the hard magnetized nanoparticles can be performed using VSM.

  The coercive force (Hc) of the magnetic particles after annealing described below is preferably 110 to 1200 kA / m (1382 to 15079 Oe), more preferably 160 to 800 kA / m (2010 to 10052 Oe). .

  The method of heating the alloy nanoparticles to the transformation temperature or higher (annealing method) is not particularly limited, but in order to avoid fusion of the alloy nanoparticles, it is preferable to heat the alloy nanoparticles after application to the support.

  Since the alloy nanoparticles have a low transformation temperature, they can be suitably used for an organic support having a low heat resistance temperature. In this case, examples of the means for heating to the transformation temperature include a pulse laser. By using a pulse laser, it is possible to more efficiently prevent the organic support from being altered or deformed by heat.

[Method of manufacturing magnetic recording medium]
Next, a method for manufacturing the magnetic recording medium of the present invention using the above-described alloy nanoparticles will be described.

In the magnetic recording medium of the present invention, a magnetic layer containing at least the above-described alloy nanoparticles and a matrix agent is formed on a support, and another layer is formed as necessary (coating process) to form a CuAu type. or as pre-process heat treatment step of performing heat treatment for the Cu ₃ Au-type ferromagnetic ordered alloy is manufactured by the degreasing treatment step of performing degreasing treatment. The magnetic layer is formed by applying a coating solution in which alloy nanoparticles and a matrix agent are dispersed on a support and performing an annealing treatment. As a pre-process of the degreasing process, it is preferable to include a curing process for curing the matrix agent.

  Examples of the other layers include a nonmagnetic layer provided between the magnetic layer and the support. In the case of a disk, the other side of the support is similarly provided with a magnetic layer, and if necessary, a magnetic layer and a non-magnetic layer. A magnetic layer may be provided. In the case of a tape, a backcoat layer is provided on the support opposite to the side on which the magnetic layer is formed. Hereinafter, each process will be described in detail.

(Coating process)
As the coating liquid in which the alloy nanoparticles are dispersed, a solution containing the alloy nanoparticles after production can be used. Actually, known additives and various solvents are added to the coating solution containing the alloy nanoparticles, and the content of the alloy nanoparticles is adjusted to a desired concentration (for example, 0.01 to 0.1 mg / ml). It is preferable to do.

  This coating solution is applied onto a support to form a lower coating layer or a magnetic layer. In the production of the magnetic recording medium using the alloy nanoparticles of the present invention, for example, the coating solution is applied to the surface of the support, preferably the thickness of the magnetic layer after drying is in the range of 5 to 200 nm, more preferably 5 It coat | coats so that it may become in the range of -100nm. In this application, a plurality of application liquids may be applied successively or simultaneously.

  Examples of the method for applying the coating liquid on the support include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, A cast coat, a spray coat, a spin coat, and the like can be mentioned. Among them, a spin coat, a blade coat, and an impregnation coat are preferable.

  According to the study by the present inventor, it was confirmed that when the particle size of magnetic particles made of FePt or the like is increased, the medium surface tends to become rough. The addition of the matrix agent was effective for obtaining the surface property (average surface roughness described above) preferable for the present invention. It has also been found that the presence of fatty acids and aliphatic amines in the coating solution in which alloy nanoparticles and a matrix agent are dispersed is effective in smoothing the surface. In addition, fatty acids are preferably used for fatty acids and aliphatic amines.

  The fatty acid is preferably an unsaturated fatty acid, more preferably a monounsaturated fatty acid. Specifically, myristoleic acid, palmitoleic acid, and oleic acid are preferable, and oleic acid is most preferable. As the aliphatic amine, a monoalkylamine is preferable and a long chain is preferable. Specifically, myristylamine, stearylamine and oleylamine are preferable, and oleylamine is most preferable. It is preferable that it is aliphatic, and it could also be achieved by adding oleic acid or oleylamine.

  The amount of additives such as fatty acid and aliphatic amine added is preferably 1 to 20% by mass in total and more preferably 5 to 15% by mass in the coating solution.

  From the viewpoint of smoothing the surface during coating, it is preferable that fatty acids and aliphatic amines are present, but when annealing, excess fatty acids and aliphatic amines form cracks on the surface. There is.

  In such a case, it is effective in the present invention to remove fatty acids and aliphatic amines by degreasing treatment. Specifically, it is preferable to degrease after the matrix agent is cured. This is because if the degreasing treatment is performed before the matrix agent is cured, cracks may occur, which is not industrially preferable.

(Curing process)
The curing process is a process for performing a curing process on the matrix agent. Examples of the curing treatment include heat treatment, irradiation treatment with UV light and electron beam. Since the matrix agent preferably used in the present invention is thermosetting, when using a thermosetting agent, it is preferable to perform heat treatment at 150 ° C. to 300 ° C., and heat treatment at 200 ° C. to 250 ° C. More preferably. The heat treatment time is preferably 10 minutes to 60 minutes, and more preferably 15 minutes to 40 minutes.

(Degreasing process)
The degreasing treatment step is a step of performing a degreasing treatment in order to prevent cracking of the cured matrix agent. In the degreasing treatment, vacuum degassing is preferably performed to about 5 × 10 ⁻¹ Pa to ¹ × 10 ⁻¹ Pa, and it is preferable to perform vacuum degassing while heating at 50 to 250 ° C. in order to shorten the time.

  As another degreasing treatment method, the fat can be removed (degreased) by dissolving the fat in an organic solvent such as chloroform, carbon tetrachloride, benzene, and acetone. Furthermore, the method of immersing in sodium hydroxide and sodium carbonate, decomposing | disassembling fat, and degreasing can also be used.

  When the degreasing process is performed, or when the degreasing process is performed after the curing process, pores such as micropores or mesopores are formed. Since these pores become places where lubricant is accumulated, it can also contribute to improvement in running durability.

  As the support used in the magnetic recording medium of the present invention, both inorganic and organic substances can be used. As the inorganic support, Mg alloy such as Al, Al—Mg alloy, Mg—Al—Zn, glass, quartz, carbon, silicon, ceramics, or the like can be used. These supports are excellent in impact resistance and have rigidity suitable for thinning and high-speed rotation. Moreover, it has the characteristic strong against a heat | fever compared with an organic substance support body.

  Examples of organic supports include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide (including aromatic polyamides such as aliphatic polyamide and aramid), polyimide, polyamideimide, poly Sulfone, polybenzoxazole, and the like can be used.

(Annealing process)
Since the alloy nanoparticles before the annealing treatment are in an irregular phase, it is necessary to anneal them to obtain an ordered phase in order to develop ferromagnetism. As the annealing treatment, it is preferable to heat the substrate after coating in order to prevent fusion of the alloy nanoparticles. As for the heating temperature in the annealing treatment, the order-disorder transformation temperature of the alloy constituting the alloy nanoparticles is obtained by using differential thermal analysis (DTA), and it is necessary to set the temperature higher than that temperature.

  When an organic support is used, the annealing method is effective by heating only the magnetic layer using the pulse laser described above. When a pulse laser is used, the laser wavelength can be from ultraviolet to infrared. However, since the organic support has absorption in the ultraviolet region, it is preferable to use laser light in the visible to infrared region.

  The laser output of the pulse laser is preferably 0.1 W or more, and more preferably 0.3 W or more in order to heat the coating film in a short time. If the output is too high, the organic support may be affected by heat, so 3 W or less is preferable.

  From the viewpoint of the laser wavelength and laser output of the pulse laser, preferably used pulse lasers are Ar ion laser, Cu vapor laser, HF chemical laser, dye laser, ruby laser, YAG laser, glass laser, titanium sapphire laser, and alexandrite laser. And GaAlAs array semiconductor laser.

  The linear velocity at the time of scanning with laser light is preferably 1 to 10 m / second, more preferably 2 to 5 m / second, in order to obtain an effect that annealing occurs sufficiently and does not cause ablation. .

  In magnetic recording media, a very thin protective film is formed on the magnetic layer to improve wear resistance, and a lubricant is applied on the magnetic layer to increase slipperiness to ensure sufficient reliability. It is effective to do.

  Examples of the protective film include oxides such as silica, alumina, titania, zirconia, cobalt oxide, and nickel oxide; nitrides such as titanium nitride, silicon nitride, and boron nitride; carbides such as silicon carbide, chromium carbide, and boron carbide; graphite A protective film made of carbon such as amorphous carbon can be mentioned, and a carbon protective film made of carbon is preferable. In addition, hard amorphous carbon generally called diamond-like carbon is particularly preferable for the carbon protective film.

  As a method for producing the carbon protective film, in the case of a hard disk, a sputtering method is generally used. However, for products that require continuous film formation such as video tape, a number of methods using plasma CVD having a higher film formation rate are proposed. Has been. Among them, it has been reported that the plasma injection CVD (PI-CVD) method has a very high film formation rate, and the obtained carbon protective film is hard and has a good quality protective film with few pinholes (for example, JP-A-61-61). No. 130487, JP-A 63-279426, JP-A 3-113824, etc.).

The carbon protective film is a hard carbon film having a Vickers hardness of 1000 kg / mm ² or more, preferably 2000 kg / mm ² or more. Further, the crystal structure is an amorphous structure and non-conductive. When a diamond-like carbon film is used as the carbon protective film, the structure can be confirmed by detecting a peak at 1520 to 1560 cm ⁻¹ when the structure is measured by Raman spectroscopy. When the film structure deviates from the diamond-like structure, the peak detected by Raman spectroscopic analysis deviates from the above range, and the film hardness also decreases.

  As raw materials for producing the carbon protective film, carbon-containing compounds such as alkanes such as methane, ethane, propane, and butane; alkenes such as ethylene and propylene; and alkynes such as acetylene can be used. Further, a carrier gas such as argon or an additive gas such as hydrogen or nitrogen for improving the film quality can be added as necessary.

  When the carbon protective film is thick, the electromagnetic conversion characteristics are deteriorated and the adhesion to the magnetic layer is deteriorated. When the carbon protective film is thin, the wear resistance is insufficient. For this reason, it is preferable that the film thickness of a carbon protective film is 2.5-20 nm, and it is more preferable that it is 5-10 nm. In addition, in order to improve the adhesion between the carbon protective film and the ferromagnetic metal thin film as a support, the surface of the ferromagnetic metal thin film is etched in advance with an inert gas or exposed to a reactive gas plasma such as oxygen. It can also be modified.

  The magnetic layer may have a multilayer structure in order to improve electromagnetic conversion characteristics. Moreover, you may have a nonmagnetic base layer and an intermediate | middle layer.

  In the magnetic recording medium of the present invention, in order to improve running durability and corrosion resistance, it is preferable to apply a lubricant or a rust preventive agent on the magnetic layer or protective film. As the lubricant to be added, a known hydrocarbon lubricant, fluorine lubricant, extreme pressure additive and the like are used.

  Examples of hydrocarbon lubricants include carboxylic acids such as stearic acid and oleic acid; esters such as butyl stearate; sulfonic acids such as octadecyl sulfonic acid; phosphate esters such as monooctadecyl phosphate; stearyl alcohol and oleyl alcohol. Alcohols such as stearamide, amines such as stearylamine, and the like.

  Examples of the fluorine-based lubricant include a lubricant in which part or all of the alkyl group of the hydrocarbon-based lubricant is substituted with a fluoroalkyl group or a perfluoropolyether group.

Examples of perfluoropolyether groups include perfluoromethylene oxide polymer, perfluoroethylene oxide polymer, perfluoro-n-propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n , perfluoroisopropylene oxide polymer (CF (CF ₃ ) CF ₂ O) _n or a copolymer of these. A compound having a polar functional group such as a hydroxyl group, an ester group, or a carboxyl group at the terminal or in the molecule is preferable because it has a high effect of reducing frictional force. The molecular weight is preferably 500 to 5000, and more preferably 1000 to 3000. A molecular weight of 500 or more is preferable because volatility increases and lubricity does not decrease. Further, if the molecular weight is 5000 or less, a moderate viscosity is obtained, the slider and the disk are adsorbed, and there is no occurrence of running stop or head crash.

  Specific examples of the lubricant substituted with the perfluoropolyether include those commercially available under trade names such as FOMBLIN from Augmond and KRYTOX from DuPont.

  Extreme pressure additives include phosphate esters such as trilauryl phosphate, phosphites such as trilauryl phosphite, thiophosphites and thiophosphates such as trilauryl trithiophosphite, dibenzyl disulfide And sulfur-based extreme pressure agents such as

  The above lubricants may be used alone or in combination. As a method for applying these lubricants on the magnetic layer or the protective film, the lubricant is dissolved in an organic solvent and applied by a wire bar method, a gravure method, a spin coating method, a dip coating method, or a vacuum deposition method. Can be attached.

  Antirust agents include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine and pyrimidine, and derivatives in which an alkyl side chain is introduced into the mother nucleus, benzothiazole, 2-mercapton benzothiazole, tetrazaindene Examples thereof include nitrogen- and sulfur-containing heterocycles such as ring compounds and thiouracil compounds and derivatives thereof.

  When a backcoat layer (backing layer) is provided on the surface of the support on which the magnetic layer is not formed, the backcoat layer is formed on the surface of the support on which the magnetic layer is not formed, such as an abrasive or an antistatic agent. A back coat layer-forming coating material in which the particulate component and the binder are dispersed in an organic solvent can be applied and provided.

Various inorganic pigments and carbon black can be used as the particulate component, and nitrocellulose, phenoxy resin, vinyl chloride resin, polyurethane and other resins can be used alone or in combination as binders. Can do.
In addition, the adhesive layer may be provided in the application surface of the dispersion liquid of the nanoparticle of a support body, and a backcoat layer formation coating material.

  The magnetic recording medium as described above has an extremely smooth surface having a surface centerline average roughness of 0.1 to 3 nm, preferably 0.3 to 2 nm, at a cutoff value of 0.25 mm. It is preferable as a magnetic recording medium for high density recording. This is because when Ra is large, noise increases, and when it is too small, the head and the medium stick to each other. In order to obtain such a surface, it is preferable to perform a calendar treatment after applying the magnetic layer. Moreover, you may perform a varnish process.

  Further, the obtained magnetic recording medium can be used by being punched with a punching machine or cut into a desired size using a cutting machine or the like.

  The present invention will be described in more detail based on the following examples, but the present invention is not limited thereto.

(Preparation of alloy nanoparticles)
The following operation was performed in high purity N ₂ gas.
Triammonium iron oxalate (Fe (NH ₄ ) ₃ (C ₂ O ₄ ) ₃ ) (manufactured by Wako Pure Chemical Industries) 0.35 g and potassium chloroplatinate (K ₂ PtCl ₄ ) (manufactured by Wako Pure Chemical Industries) 0.35 g And an aqueous solution of metal salt dissolved in 24 ml of H ₂ O (deoxygenated), an alkane solution in which the amount shown in Table 1 below for aerosol OT is dissolved in 80 ml of decane is added and mixed to obtain a reverse micelle solution (I). Prepared.

In an aqueous reducing agent solution in which 0.57 g of NaBH ₄ (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 12 ml of H ₂ O (deoxygenated), the amount of aerosol OT (manufactured by Wako Pure Chemical Industries, Ltd.) was decanted (Wako Pure Chemical Industries, Ltd.) Alkane solution dissolved in 40 ml) was added and mixed to prepare reverse micelle solution (II).

While the reverse micelle solution (II) was stirred at a high speed with an omni mixer (manufactured by Yamato Kagaku) at a temperature of 22 ° C., the reverse micelle solution (I) was added instantaneously. Five minutes after the completion of the addition, the stirring was changed to magnetic stirrer and the temperature was raised to 40 ° C., followed by aging for 120 minutes. After cooling to room temperature, 2 ml of oleic acid (manufactured by Wako Pure Chemical Industries) was added, mixed, and taken out into the atmosphere. In order to destroy the reverse micelle, a mixed solution of 200 ml of H ₂ O and 200 ml of methanol was added to separate into an aqueous phase and an oil phase. A state in which the metal nanoparticles were dispersed on the oil phase side was obtained. The oil phase side was washed 5 times with “H ₂ O 600 ml + methanol 200 ml”. Thereafter, 1300 ml of methanol was added to cause flocculation of the alloy nanoparticles and to precipitate them. The supernatant was removed, and 20 ml of heptane (manufactured by Wako Pure Chemical Industries, Ltd.) was added for redispersion, followed by precipitation by adding 100 ml of methanol. This was repeated twice, and finally 5 ml of heptane (manufactured by Wako Pure Chemical Industries, Ltd.) and 50 μl of oleylamine were added, and then 50 μl of oleic acid was added, and a FePt alloy nanoparticle dispersion having the particle size and composition shown in Table 1 Got. In Table 1, those having a particle diameter of 6 nm of the alloy nanoparticles are those of the magnetic body No. No. 1 having a particle size of 8 nm 2.

  The dispersion (alloy nanoparticle dispersion) was vacuum degassed, and the prepared alloy particle-containing liquid was concentrated, diluted with decane to 4 wt%. Then, Toray's Trefil R910 as a matrix agent was dissolved in a decane solution to a concentration of 1% by weight, and the amount shown in Table 1 below was added to 1 ml of the alloy particle dispersion and stirred. Thereafter, oleylamine and oleic acid shown in Table 1 below were added in the amounts shown in Table 1 below per 1 ml of the alloy particle dispersion and stirred. Thereafter, the solution was filtered in a clean room to obtain a coating solution.

(Support)
A glass substrate for HD (hard disk) (65 / 20-0.635t glass polished substrate manufactured by Toyo Kohan Co., Ltd.) was used as a support, washed with pure water, and dried at 100 ° C. Thereafter, the surface was cleaned with decane.

(Application of magnetic layer: Application process)
An alloy nanoparticle dispersion (coating solution) was applied to the HD glass substrate with a spin coater and dried at 25 ° C. for 1 minute. At this time, the magnetic layer thickness was 50 nm.

(Curing process)
It was kept in air at 25 ° C. for 1 minute and the one with matrix agent was cured at this stage.

(Degreasing process)
Degreasing treatment with acetone:
The sample after the curing treatment was immersed in acetone for 25 minutes, and then the surface was washed with acetone.

Degreasing treatment by "heating + vacuum degassing":
The sample after the curing treatment was heated at 200 ° C. and held for 25 minutes under a pressure of 1 × 10 ⁻¹ Pa while being evacuated with a rotary pump.

(Annealing process)
After coating, annealing is performed at a temperature increase rate of 50 ° C./min in an infrared image furnace in an atmosphere of “5% H ₂ + 95% Ar” for 30 minutes at a temperature of 450 ° C. and then cooled to room temperature at 50 ° C./min. The magnetic layer (film thickness: 50 nm) containing a magnetic particle and a matrix agent was formed, and the magnetic recording medium (Samples 1-9 and 10-15 in Table 1) was produced.

(Magnetic properties)
The magnetic characteristics were measured for each substrate of the magnetic layer. Using a high-sensitivity magnetization vector measuring machine manufactured by Toei Kogyo Co., Ltd. and a DATA processing apparatus manufactured by the same company, it was performed under the condition of an applied magnetic field of 790 kA / m (10 kOe).

(Surface property)
The surface property (Ra) was evaluated using AFM (manufactured by NanoScope III Digital Instruments).

(Confirmation of pores)
Measurement was performed by an N ₂ adsorption method using a fully automatic gas adsorption device “AUTOSORB” manufactured by Quanta Chrone.

(Driving durability)
The head was attached with a CSS tester manufactured by OLYMPUS, and a running test was conducted for 24 hours. As a result, it was confirmed that the sample of the example can run for 24 hours and there is no scratch on the surface of the medium. The sample of the comparative example was able to run for less than 6 hours.

  From the results of Table 1, Samples 1 to 9 as examples had good running durability because micropores were formed in the magnetic layer. Also, the surface roughness was small and a smooth surface was formed.

Claims (4)

A magnetic recording medium having a magnetic layer containing a CuAu type or Cu ₃ Au type ferromagnetic ordered alloy and a matrix agent,
A magnetic recording medium, wherein pores are formed in the magnetic layer.   The magnetic recording medium, wherein the pore is at least one of a micropore and a mesopore. A method of manufacturing a magnetic recording medium according to claim 1 or 2, as a pre-process heat treatment step of performing heat treatment to said CuAu type or Cu ₃ Au-type ferromagnetic ordered alloy, degreasing process for degreasing treatment A method of manufacturing a magnetic recording medium, comprising a step.   4. The method of manufacturing a magnetic recording medium according to claim 3, further comprising a curing process step of curing the matrix agent as a pre-process of the degreasing process.