JP2010086605A - Magnetic recording medium and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which contains ferromagnetic powder composed mostly of iron and has excellent storage stability and traveling durability. <P>SOLUTION: The magnetic recording medium has a magnetic layer containing ferromagnetic powder and a binder on a nonmagnetic support. The magnetic layer contains the ferromagnetic powder which is composed mostly of iron and contains a phosphate compound and a hydroxy dicarboxylic acid compound at a mass ratio of 90:10 to 10:90 while the total amount of compounds is 1.5-7 pts.mass per 100 pts.mass of the ferromagnetic powder. The method for manufacturing the magnetic recording medium including the magnetic layer containing the ferromagnetic powder and the binder on the nonmagnetic support includes forming the magnetic layer on the nonmagnetic support by applying and drying an application liquid for generating the magnetic layer which contains the ferromagnetic powder composed mostly of iron and contains the phosphate compound and the hydroxy dicarboxylic acid compound at the mass ratio of 90:10 to 10:90 while the total amount of compounds is 1.5-7 pts.mass per 100 pts.mass of the ferromagnetic powder. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium and a method for producing the same, and more particularly to a magnetic recording medium capable of exhibiting excellent storage stability and durability and a method for producing the same.

  Data backup tapes for computers used to store large volumes of data have a recording capacity of several TB (terabytes) per volume of magnetic tape as the volume of data such as documents, images, and videos to be backed up increases. Magnetic tape has been commercialized. In addition, with the increase in the capacity of the world's weather satellites, military satellites, video information, etc., it is required to store a large amount of data exceeding PB (petabyte). Along with this, the capacity per tape of the tape used for backing up these data is further increased. As of 2008, a road map of a computer magnetic tape having a capacity exceeding 6 TB is shown. In the future, higher density will be required, and in the future, it is expected that an age exceeding 20TB / volume will come.

  As a means for increasing the recording capacity, techniques for increasing the recording density such as smoothing the recording surface, thinning the tape, and improving the recording density have been proposed as approaches from the magnetic tape side. Improvement of the recording density includes making the magnetic powder fine particles. However, the magnetic powder is more likely to aggregate and become difficult to disperse as it becomes finer.

  For example, Patent Document 1 proposes to add higher fatty acid esters such as succinic acid as a dispersant to magnetic coatings as a countermeasure against dispersibility degradation. However, if a magnetic material containing iron as a main component is used as the fine particle magnetic material, there arises a problem of a decrease in storage stability as well as a decrease in dispersibility. This is probably because the specific surface area increases as the magnetic powder becomes finer and the iron component is more easily corroded.

As means for improving the dispersibility and storage stability of magnetic materials containing iron as a main component such as ferromagnetic metal powder and iron nitride powder, Patent Documents 2 and 3 bind a phosphate compound to the surface of the magnetic powder. It has been proposed to use a phosphate compound as a magnetic layer component.
Japanese Patent Laid-Open No. 11-235576 JP 2008-84418 A JP 2006-31751 A

  However, when a phosphoric acid compound is used as a magnetic layer component as described in Patent Documents 2 and 3 with respect to iron-based ferromagnetic powder, storage stability and running durability during time, long-term storage, repeated running, etc. There is a problem that the performance is lowered.

  Accordingly, an object of the present invention is to provide a magnetic recording medium containing a ferromagnetic powder containing iron as a main component and having excellent storage stability and running durability.

As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge.
When a ferromagnetic powder containing iron as a main component and a phosphoric acid compound are used in combination as the magnetic layer component, it is considered that the dispersibility is improved by the phosphoric acid compound covering the surface of the ferromagnetic powder and being interposed between the binder. In addition, it is considered that the phosphoric acid compound is covered with the surface of the ferromagnetic powder, thereby providing corrosion resistance and improving storage stability. However, phosphoric acid compounds produce iron phosphate by binding with iron components in the magnetic material during time-lapse, long-term storage, and repeated running, and if this precipitates in a large amount on the surface of the magnetic layer, running durability decreases. Become. Furthermore, since the iron content in the magnetic material decreases due to the formation of iron phosphate, the demagnetization rate with time increases and the storage stability decreases.
In contrast, the present inventors have newly found that a magnetic recording medium having both running durability and storage stability can be obtained by using a predetermined amount of a phosphoric acid compound and a hydroxydicarboxylic acid compound in combination. The inventor presumes this reason as follows.
The carboxyl group is an acid having a weak acid dissociation constant as compared with the phosphoric acid group and the phosphonic acid group. According to HSAB theory (hard and sot acids and bases) proposed by Pearson, it is considered to be a relatively soft acid compared to a phosphate group or a phosphonate group, and when ionized on the Fe atom surface, Fe ⁺⁺ , Fe ⁺⁺⁺ generates, by coexistence of a less hard acid and hard acid when these acids are present, is assumed that can be stabilized of the magnetic surface. That is, the pKa1 of the phosphoric acid group and the phosphonic acid group of the phosphoric acid compound is approximately 1 to 2, and pKa2 is approximately 6 to 7. If a compound having a pKa of about 4 to 5 of the carboxyl group is present here, the complex adsorption state in the competitive adsorption with the iron ion results in the desorption due to the compound formation by the single bond of the iron ion and the phosphate group or the phosphonate group. It is thought that separation can be avoided. Furthermore, it is speculated that the hydroxyl group contained in the carboxyl group gives an unexpected effect when considering the affinity and reactivity with the binder. That is, it is considered that the hydroxyl group present in the magnetic layer reacts with the polyisocyanate contained as a binder component (crosslinking agent or curing agent) to keep the binder in the system. It is speculated that these can suppress the release of iron ions from the iron surface that is accelerated over time, long-term storage, and repeated running, maintain magnetic properties, and suppress the generation of dirt components due to running. The
As a result of further studies based on the above findings, the present inventors have completed the present invention.

That is, the above object was achieved by the following means.
[1] A magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic layer contains a ferromagnetic powder containing iron as a main component, and the ferromagnetic powder 100 contains a phosphate compound and a hydroxydicarboxylic acid compound in a mass ratio of 90/10 to 10/90 and a total amount of the compound. A magnetic recording medium comprising 1.5 to 7 parts by mass with respect to parts by mass.
[2] The magnetic layer contains a ferromagnetic powder containing iron as a main component in a proportion of 90/10 to 10/90 by mass ratio of phosphoric acid compound and hydroxydicarboxylic acid compound with respect to 100 parts by mass of the powder. The magnetic recording medium according to [1], wherein the magnetic recording medium is a layer formed using a ferromagnetic powder surface-treated with 1.5 to 7 parts by mass of a surface treatment agent.
[3] The magnetic recording medium according to [1] or [2], wherein the hydroxydicarboxylic acid compound is represented by the following general formula (1).
^{HOOC- (CR 1 R 2) n} -C (R 3 R 4) m-COOH ... (1)
[In General Formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represents a hydrogen atom, an alkyl group or a hydroxyl group, provided that at least one of R ¹ , R ² , R ³ and R ⁴ One represents a hydroxyl group. n and m represent integers satisfying 2 ≦ (n + m) ≦ 18. ]
[4] The magnetic recording medium according to [3], wherein the hydroxydicarboxylic acid compound is at least one selected from the group consisting of tartaric acid, mesotartaric acid, and malic acid.
[5] The magnetic recording medium according to any one of [1] to [4], wherein the ferromagnetic powder containing iron as a main component is an iron nitride powder containing Fe ₁₆ N ₂ as a main component.
[6] The magnetic recording medium according to any one of [1] to [4], wherein the ferromagnetic powder containing iron as a main component is a ferromagnetic metal powder.
[7] The magnetic recording medium according to any one of [1] to [6], wherein the magnetic layer is a layer formed using a coating solution for forming a magnetic layer containing a polyurethane resin and an isocyanate compound.
[8] A method for producing a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
A ferromagnetic powder containing iron as a main component on a non-magnetic support, and the ferromagnetic compound and the hydroxydicarboxylic acid compound in the ratio of 90/10 to 10/90 by mass ratio and the total amount of the compound. The said manufacturing method including forming a magnetic layer by apply | coating and drying the coating liquid for magnetic layer formation included in the quantity of 1.5-7 mass parts with respect to 100 mass parts of powders.
[9] For the magnetic layer forming coating solution, a ferromagnetic powder containing iron as a main component, and a phosphoric acid compound and a hydroxydicarboxylic acid compound in a mass ratio of 90/10 to 10/90 with respect to 100 parts by mass of the powder. [8] The method for producing a magnetic recording medium according to [8], wherein the magnetic powder is prepared using a ferromagnetic powder surface-treated with 1.5 to 7 parts by mass of a surface treating agent contained in a ratio of
[10] The method for producing a magnetic recording medium according to [8] or [9], wherein the hydroxydicarboxylic acid compound is represented by the following general formula (1).
^{HOOC- (CR 1 R 2) n} -C (R 3 R 4) m-COOH ... (1)
[In General Formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group or a hydroxyl group, provided that at least one of R ¹ , R ² , R ³ and R ⁴ One represents a hydroxyl group. n and m represent integers satisfying 2 ≦ (n + m) ≦ 18. ]
[11] The method for producing a magnetic recording medium according to [10], wherein the hydroxydicarboxylic acid compound is at least one selected from the group consisting of tartaric acid, mesotartaric acid, and malic acid.
[12] ferromagnetic powder based on the iron, an iron nitride powder mainly composed of Fe ₁₆ N ₂ [8] ~ method of manufacturing a magnetic recording medium according to any one of [11].
[13] The method for manufacturing a magnetic recording medium according to any one of [8] to [11], wherein the ferromagnetic powder containing iron as a main component is a ferromagnetic metal powder.
[14] The method for producing a magnetic recording medium according to any one of [8] to [13], wherein the coating liquid for forming a magnetic layer further contains a polyurethane resin and an isocyanate compound.

  According to the present invention, it is possible to provide a magnetic recording medium that can exhibit excellent electromagnetic conversion characteristics and durability over a long period of time.

[Magnetic recording medium]
The present invention relates to a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support. The magnetic recording medium of the present invention includes a ferromagnetic powder containing iron as a main component in a magnetic layer, and a phosphoric acid compound and a hydroxydicarboxylic acid compound in a mass ratio of 90/10 to 10/90 and the total of the compounds. It is contained in an amount of 1.5 to 7 parts by mass with respect to 100 parts by mass of the ferromagnetic powder.
By using the phosphoric acid compound in combination with a predetermined amount of the dihydroxycarboxylic acid compound, it is possible to obtain excellent durability and storage stability over a long period of time as well as excellent electromagnetic conversion characteristics due to the dispersibility improvement effect of the phosphoric acid compound.
Hereinafter, the magnetic recording medium of the present invention will be described in more detail.

Phosphoric acid compound, hydroxydicarboxylic acid compound In the magnetic recording medium of the present invention, a phosphoric acid compound and a hydroxydicarboxylic acid compound are used in combination in a magnetic layer containing a ferromagnetic powder containing iron as a main component. High electromagnetic conversion characteristics can be obtained by an action such as improvement of dispersibility by using a phosphoric acid compound, and by using a hydroxydicarboxylic acid compound in combination, excellent storage stability and durability can be exhibited over a long period of time. The reason for this is presumed by the inventors as described above. However, when the total amount of the phosphoric acid compound and the hydroxydicarboxylic acid compound is less than 1.5 parts by mass with respect to 100 parts by mass of the ferromagnetic powder, the dispersibility improvement / storage stability improvement effect by adding the phosphoric acid compound and the hydroxydicarboxylic acid The effect of the combined use of the compound cannot be sufficiently obtained, and when it exceeds 7 parts by mass, the component that cannot be bonded to the surface of the ferromagnetic powder is liberated, and the free component precipitates during storage or running, resulting in durability. Decreases. Therefore, in the present invention, the total amount of the above compounds is in the range of 1.5 to 7 parts by mass per 100 parts by mass of the ferromagnetic powder. From the viewpoint of further improving the electromagnetic conversion characteristics and durability while suppressing the occurrence of deposits and deposits on the magnetic tape surface and magnetic head, the preferred range is 2.0 to 6.5 parts by mass, and more preferred range. Is 3.0 to 6.5 parts by mass.

  Furthermore, in the present invention, the ratio of the phosphoric acid compound and the hydroxydicarboxylic acid compound in the magnetic layer is in the range of 90/10 to 10/90 in terms of phosphoric acid compound / hydroxydicarboxylic acid compound (mass ratio). If the amount of the hydroxydicarboxylic acid compound used relative to the phosphoric acid compound is excessively small, it will be difficult to obtain the effect of the combined use of the hydroxydicarboxylic acid compound, and if it is excessively large, the corrosion inhibition and electromagnetic conversion characteristics improving effect by the phosphoric acid compound will be obtained. This is because it becomes difficult. In order to obtain the addition effect of both compounds more effectively, the above range is preferably 79/21 to 15/85, and more preferably 79/21 to 21/79.

  In the present invention, the phosphoric acid compound refers to a derivative of phosphoric acid, and is preferably an organic phosphoric acid compound from the viewpoint of improving storage stability and improving electromagnetic conversion characteristics. Examples of the organic phosphate compound include nitrilomethyl phosphate, phenyl phosphate, monomethyl phosphate, dimethyl phosphate, monoethyl phosphate, and alkyl phosphate esters such as diethyl phosphate, phenylphosphonic acid, monooctylphenylphosphonic acid, and the like. Aromatic phosphonic acids, methylphosphonic acid and the like can be mentioned.

Any hydroxydicarboxylic acid compound may be used as long as it has two carboxyl groups and a hydroxyl group, and specific examples thereof include compounds represented by the following general formula (1).
^{HOOC- (CR 1 R 2) n} -C (R 3 R 4) m-COOH ... (1)

Hereinafter, the general formula (1) will be described.
In general formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group or a hydroxyl group, provided that at least one of R ¹ , R ² , R ³ and R ⁴ Represents a hydroxyl group. The number of hydroxyl groups contained in the general formula (1) is not particularly limited as long as it is one or more. The alkyl group may be linear or branched, but is preferably a lower alkyl group having 3 or less carbon atoms from the viewpoint of adsorptivity to the surface of the ferromagnetic metal powder. Group, ethyl group and propyl group. From the viewpoint of adsorptivity to the surface of the ferromagnetic powder, R ^{1 to} R ⁴ are preferably a hydroxyl group or a hydrogen atom.

  In the general formula (1), when (n + m) is 2 or more, it can react well on the surface of the ferromagnetic powder. However, if (n + m) exceeds 18, the melting point becomes high and it is difficult to sufficiently dissolve in the coating solvent. Therefore, in the general formula (1), (n + m) is 2 or more and 18 or less. From the viewpoint of solubility and reactivity, (n + m) is preferably 2 or more and 14 or less, more preferably 2 or more and 8 or less. Specific examples of the hydroxydicarboxylic acid compound represented by the general formula (1) include malic acid, tartaric acid, mesotartaric acid and 2-oxyglutaric acid. Among these, preferred specific examples include malic acid, tartaric acid, Mesotartaric acid can be mentioned.

  Both the phosphoric acid compound and the hydroxydicarboxylic acid compound used in the present invention can be synthesized by known methods, and are also available as commercial products.

Ferromagnetic powder In the magnetic recording medium of the present invention, the magnetic substance contained in the magnetic layer is a ferromagnetic powder containing iron as a main component. Here, “having iron as a main component” means that the content of other elements when iron is 100 atomic% is 49 atomic% or less. About the ferromagnetic metal powder mentioned later, it is preferable that Co is contained 40 atomic% or less with respect to 100 atomic% of iron as elements other than iron from the point of a magnetic characteristic, and 1-40 atomic% is contained. It is more preferable that the content of atoms other than iron and Co is 12 atomic percent or less with respect to 100 atomic percent of iron.

  Ferromagnetic powders containing iron as a main component are more likely to be corroded as they become finer, and storage stability decreases. On the other hand, according to the present invention, by using a phosphoric acid compound together with a hydroxydicarboxylic acid compound in the above-mentioned predetermined range, a ferromagnetic material mainly composed of iron while suppressing a decrease in durability due to iron phosphate generation. A decrease in storage stability of the powder can be suppressed.

  Examples of the ferromagnetic powder containing iron as a component include iron nitride powder and ferromagnetic metal powder. Hereinafter, the ferromagnetic powder will be described.

(Ii) Iron nitride powder The iron nitride powder in the present invention means a magnetic powder containing at least an Fe ₁₆ N ₂ phase, preferably an iron nitride powder containing Fe ₁₆ N ₂ as a main component. In the present invention, “having Fe ₁₆ N ₂ as a main component” indicates a profile showing the Fe ₁₆ N ₂ phase in X-ray diffraction, and the nitrogen content relative to iron is in the range of 7.0 to 14 atomic%. It means that. The nitrogen content can be measured by fluorescent X-ray analysis, X-ray electron spectroscopy, nitrogen analyzer or the like.

The iron nitride powder preferably contains no iron nitride phase other than the Fe ₁₆ N ₂ phase. This is because the magnetic anisotropy of iron nitride (Fe ₄ N or Fe ₃ N phase) is about 1 × 10 ⁵ erg / cc (1 × 10 ⁻² J / cc), whereas Fe ₁₆ N _2. This is because the phase has a high magnetocrystalline anisotropy of 2 × 10 ^{6 to} 7 × 10 ⁶ erg / cc (2 × 10 ^{−1 to} 7 × 10 ⁻¹ J / cc). Thereby, a high coercive force can be maintained even when the particles are made fine. This high magnetocrystalline anisotropy results from the crystal structure of the Fe ₁₆ N ₂ phase. The crystal structure is a body-centered tetragonal system in which N atoms regularly enter the Fe interstitial positions of Fe, and the strain when N atoms enter the lattice is considered to be the cause of high crystal magnetic anisotropy. . The easy axis of magnetization of the Fe ₁₆ N ₂ phase is the C axis extended by nitriding.

The shape of the particles containing the Fe ₁₆ N ₂ phase is preferably granular or elliptical. More preferably, it is spherical. This is because one of three equivalent directions of cubic α-Fe is selected by nitriding and becomes the c-axis (magnetization easy axis). Therefore, if the particle shape is acicular, the easy magnetization axis is the minor axis. This is because particles in the direction and the major axis direction are mixed, which is not preferable. Therefore, the average value of the axial ratio of major axis length / minor axis length is preferably 2 or less (for example, 1 to 2), more preferably 1.5 or less (for example, 1 to 1.5).

In general, the particle size is determined by the particle size of the iron particles before nitriding, and is preferably monodispersed. This is because, in general, monodispersion reduces the medium noise. The particle size of the iron nitride magnetic powder containing Fe ₁₆ N ₂ as the main phase is usually determined by the particle size of the iron particles, and the particle size distribution of the iron particles is preferably monodisperse. This is because the degree of nitriding differs between the large and small particles, and the magnetic properties are different. From this point of view, the particle size distribution of the iron nitride magnetic powder is preferably monodispersed.

The average particle size of iron nitride is preferably less than 35 nm. If the average particle diameter is less than 35 nm, there is little noise based on the particle size, which is suitable for high density recording. However, if the average size of the magnetic powder is too small, it is difficult to ensure the residual magnetization due to heat, and the coercive force is lowered and the intermolecular attractive force of the particles is increased, which makes it difficult to disperse in the magnetic layer coating liquid. Therefore, it is preferable to select an iron nitride powder having a suitable average particle size in consideration of the above points. Specifically, the average particle size of the iron nitride powder is more preferably 5 to 20 nm, and still more preferably 10 to 18 nm. The average particle diameter of the iron nitride in the present invention refers to an average particle size of the Fe ₁₆ N ₂ phase, if the layer on the surface of the Fe ₁₆ N ₂ particles are formed does not include the layer Fe ₁₆ N _It shall mean the average size of the _two particles themselves. The Fe ₁₆ N ₂ particles can optionally have a layer such as an antioxidant layer on the surface.

The average size of the ferromagnetic powder can be measured by the following method.
The ferromagnetic powder is photographed with a transmission electron microscope H-9000, manufactured by Hitachi, at a photographing magnification of 100,000, and printed on a photographic paper so that the total magnification is 500,000 times to obtain a particle photograph. The target magnetic material is selected from the particle photograph, the outline of the powder is traced with a digitizer, and the particle size is measured with the image analysis software KS-400 manufactured by Carl Zeiss. Measure the size of 500 particles. Let the average value of the particle size measured by the said method be an average size of a ferromagnetic powder.

In the present invention, the size of the powder such as a magnetic material (hereinafter referred to as “powder size”) is (1) the shape of the powder is needle-like, spindle-like, or column-like (however, the height is the bottom surface). In the case of larger than the maximum major axis, etc., it is represented by the length of the major axis constituting the powder, that is, the major axis length, and (2) the shape of the powder is plate-shaped or columnar (however, the thickness or height is (Smaller than the maximum major axis of the plate surface or the bottom surface), and (3) the shape of the powder is spherical, polyhedral, unspecified, etc. When the major axis constituting the body cannot be specified, it is represented by the equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.
The average powder size of the powder is an arithmetic average of the above powder sizes, and is obtained by carrying out the measurement as described above for 500 primary particles. Primary particles refer to an independent powder without aggregation.

The average acicular ratio of the powder is determined by measuring the short axis length of the powder in the above measurement, that is, the short axis length, and calculating the arithmetic average of the values of (long axis length / short axis length) of each powder. Point to. Here, the minor axis length is defined by the above-mentioned powder size in the case of (1), the length of the minor axis constituting the powder, and in the case of (2), the thickness or height, respectively. In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.
When the shape of the powder is specific, for example, in the case of the definition (1) of the powder size, the average powder size is referred to as an average major axis length, and in the case of the definition (2), the average powder size Is called the average plate diameter, and the arithmetic average of (maximum major axis / thickness to height) is called the average plate ratio. In the case of definition (3), the average powder size is referred to as an average diameter (also referred to as an average particle diameter or an average particle diameter).

  The particle size distribution of iron nitride is preferably monodispersed. This is because, in general, monodispersion reduces the medium noise. The variation coefficient of the particle size is 15% or less (preferably 2 to 15%), more preferably 10% or less (preferably 2 to 10%). In the present invention, the “particle size variation coefficient” means a value obtained by calculating a standard deviation of the particle size distribution at the equivalent circle diameter and dividing this by the average particle size.

In the particles containing the Fe ₁₆ N ₂ phase, the content of nitrogen with respect to iron is preferably 1.0 to 20.0 atomic%, more preferably 5.0 to 18.0 atomic%, more preferably 8.0 to 8.0. 15.0 atomic%. This is because if the amount of nitrogen is too small, the amount of Fe ₁₆ N ₂ phase formed decreases, the increase in coercive force is caused by strain due to nitriding, and the amount of nitrogen decreases, the coercive force decreases. This is because if the amount of nitrogen is too large, the Fe ₁₆ N ₂ phase is a metastable phase and therefore decomposes into other nitrides that are stable phases, resulting in excessive reduction in saturation magnetization.

The surface of the iron nitride powder mainly composed of Fe ₁₆ N ₂ is preferably covered with an oxide film. This is because the fine particles Fe ₁₆ N ₂ are easily oxidized and require handling in a nitrogen atmosphere.

  The oxide film preferably contains a rare earth element and / or an element selected from silicon and aluminum. This is because it has the same particle surface as so-called metal particles mainly composed of iron and Co as a main component, and the affinity with the process for handling the metal particles is increased. As the rare earth element, Y, La, Ce, Pr, Nd, Sm, Tb, Dy, and Gd are preferably used, and Y is particularly preferably used from the viewpoint of dispersibility.

  Further, in addition to silicon and aluminum, boron or phosphorus may be included as necessary. Furthermore, carbon, calcium, magnesium, zirconium, barium, strontium and the like may be contained as effective elements. By using these other elements in combination with rare earth elements and / or silicon and aluminum, it is possible to obtain higher shape maintainability and dispersion performance.

  Regarding the composition of the surface compound layer, the total content of rare earth elements or boron, silicon, aluminum and phosphorus with respect to iron is preferably 0.1 to 40.0 atomic%, more preferably 1.0 to 30.0 atomic%, More preferably, it is 3.0-25.0 atomic%. If the amount of these elements is too small, it becomes difficult to form the surface compound layer, and not only the magnetic anisotropy of the magnetic powder is reduced, but also the oxidation stability tends to be poor. Moreover, when there are too many of these elements, the saturation magnetization will fall excessively easily.

  The thickness of the oxide film is preferably 1 to 5 nm, and more preferably 2 to 3 nm. This is because if the thickness is smaller than this range, the oxidation stability tends to be low, and if the thickness is thick, the particle size may be hardly reduced.

As the magnetic properties of the iron nitride powder containing Fe ₁₆ N ₂ as a main component, the coercive force (Hc) is preferably 79.6 to 318.4 kA / m (1,000 to 4,000 Oe), More preferably, it is 159.2 to 278.6 kA / m (2000 to 3500 Oe). More preferably, it is 197.5-237 kA / m (2500-3000 Oe). This is because, if Hc is low, for example, in the case of in-plane recording, it is likely to be affected by the adjacent recording bit and may not be suitable for high recording density, and if it is too high, it may be difficult to record. It is.

The “Ms · V” of the iron nitride powder is preferably 5.2 × 10 ^{−16 to} 6.5 × 10 ⁻¹⁶ . The saturation magnetization Ms in “Ms · V” can be measured using, for example, a vibration type magnetometer (VSM). The volume V can be obtained by observing particles using a transmission electron microscope (TEM), obtaining the particle size of the Fe ₁₆ N ₂ phase, and converting the volume.

Saturation magnetization of the iron nitride powder ^{80~160Am 2 / kg (80~160emu / g} ) are ^{preferable, 80~120Am 2 / kg (80~120emu /} g) is more preferable. This is because if the signal is too low, the signal may be weakened. If the signal is too high, for example, in the case of in-plane recording, the adjacent recording bit is likely to be affected, and the recording density is not suitable.

The iron nitride powder preferably has a BET specific surface area of 40 to 100 m ² / g. This is because if the BET specific surface area is too small, the particle size increases, and when applied to a magnetic recording medium, the particulate noise increases, the surface smoothness of the magnetic layer decreases, and the reproduction output tends to decrease. is there. Further, if the BET specific surface area is too large, particles containing the Fe ₁₆ N ₂ phase are likely to aggregate, and it is difficult to obtain a uniform dispersion and it is difficult to obtain a smooth surface.

  The iron nitride that can be used in the present invention can be synthesized by a known method, and some iron nitrides are commercially available. For details of the iron nitride that can be used in the present invention, reference can be made to, for example, JP-A-2007-36183, JP-A-2007-305221, and the like.

(Ii) Ferromagnetic metal powder The ferromagnetic metal powder used in the magnetic layer is not particularly limited, but it is preferable to use a ferromagnetic metal powder containing α-Fe as a main component. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, other than predetermined atoms. Atoms such as Ta, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B may be included. In particular, at least one of Al, Si, Ca, Y, Ba, La, Nd, Co, Ni, and B is preferably included in addition to α-Fe, and further includes at least one of Co, Y, and Al. preferable. The Co content is preferably 0 atomic percent or more and 40 atomic percent or less, more preferably 1 atomic percent or more and 40 atomic percent or less, and even more preferably 15 atomic percent or more and 35 atomic percent or less with respect to 100 atomic percent of Fe. Hereinafter, it is more preferably 20 atomic% or more and 35 atomic% or less. The Y content is preferably from 1.5 atomic percent to 12 atomic percent, more preferably from 3 atomic percent to 10 atomic percent, and particularly preferably from 4 atomic percent to 9 atomic percent. Al is preferably from 1.5 atomic percent to 12 atomic percent, more preferably from 3 atomic percent to 10 atomic percent, and even more preferably from 4 atomic percent to 9 atomic percent.

  These ferromagnetic metal powders may be treated in advance with a dispersant, lubricant, surfactant, antistatic agent, etc. described later before dispersion. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-22062, Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. 46-28466, Japanese Patent Publication No. 46-38755. No. 47, No. 47-4286, No. 47-12422, No. 47-17284, No. 47-18509, No. 47-18573, No. 39-10307 No. 46-39639, U.S. Pat. Nos. 3,026,215, 3,031,341, 3,100,194, 3,342,005 and 3,389,014.

  The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. As the ferromagnetic metal powder, those obtained by a known production method can be used, and the following methods can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles, a metal carbonyl compound A method of thermal decomposition, a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite, or hydrazine to an aqueous solution of a ferromagnetic metal, and evaporating the metal in a low-pressure inert gas to form a fine powder. How to get. The ferromagnetic metal powder obtained in this manner is a known gradual oxidation treatment, that is, a method of drying after immersing in an organic solvent, an oxygen-containing gas is sent after immersing in an organic solvent, and an oxide film is formed on the surface. Thereafter, either a drying method or a method of adjusting the partial pressures of oxygen gas and inert gas without using an organic solvent to form an oxide film on the surface can be applied.

The specific surface area by BET method of the ferromagnetic metal powder employed in the magnetic layer is preferably 45~100m ² / g, more preferably 50-80 m ² / g. If it is 45 m ² / g or more, low noise is obtained, and if it is 100 m ² / g or less, good surface properties can be obtained. The crystallite size of the ferromagnetic metal powder is preferably 80 to 180 mm, more preferably 100 to 180 mm, and still more preferably 110 to 175 mm. The long axis length of the ferromagnetic metal powder is preferably 0.01 μm or more and 0.15 μm or less, more preferably 0.02 μm or more and 0.15 μm or less, and further preferably 0.03 μm or more and 0.12 μm or less. . The average major axis length of the ferromagnetic metal powder is preferably 40 nm or less. If the average major axis length is 40 nm or less, there is little noise based on the particle size, which is suitable for high density recording. However, as explained above, if the average size of the magnetic powder is too small, it is difficult to ensure the residual magnetization due to heat, and the coercive force is lowered and the intermolecular attractive force of the particles is increased. Is difficult to disperse. Therefore, it is preferable to select a ferromagnetic metal powder having a suitable average particle size in consideration of the above points. Specifically, the average major axis length is preferably 10 to 40 nm, and more preferably 15 to 34 nm.

The average needle ratio of the ferromagnetic metal powder is preferably 3 or more and 15 or less, more preferably 5 or more and 12 or less. Σs of the ferromagnetic metal powder is preferably from 100~180A · m ² / kg, more preferably 110~170A · m ² / kg, and more preferably from 125~160A · m ² / kg. The coercive force of the ferromagnetic metal powder is preferably 2000 to 3500 Oe (160 to 280 kA / m), more preferably 2200 to 3000 Oe (176 to 240 kA / m).

  The moisture content of the ferromagnetic metal powder is preferably 0.01 to 2%. It is preferable to optimize the moisture content of the ferromagnetic metal powder depending on the type of the binder. The pH of the ferromagnetic metal powder is preferably optimized depending on the combination with the binder used. The range can be 4-12, preferably 6-10. The ferromagnetic metal powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they hardly affect the characteristics. The ferromagnetic metal powder used in the present invention preferably has fewer vacancies, and its value is 20% by volume or less, more preferably 5% by volume or less. As for the shape, any of needle shape, rice grain shape, and spindle shape may be used as long as the above-described characteristics regarding the particle size are satisfied. It is preferable that it is a shape. The acicular ferromagnetic metal powder preferably has an average acicular ratio in the above range.

  The SFD of the ferromagnetic metal powder itself is preferably small and is preferably 0.8 or less. It is preferable to reduce the Hc distribution of the ferromagnetic metal powder. When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, the magnetization reversal is sharp, and the peak shift is small, which is suitable for high density digital magnetic recording. In order to reduce the distribution of Hc, there are methods such as improving the particle size distribution of getite in the ferromagnetic metal powder and preventing sintering.

  In the magnetic recording medium of the present invention, the magnetic layer contains the above components. In order to effectively obtain the modification effect of the surface of the ferromagnetic powder by the phosphoric acid compound and the hydroxydicarboxylic acid compound, the magnetic layer is made of a ferromagnetic powder mainly composed of iron and phosphoric acid with respect to 100 parts by mass of the powder. It is preferable to use a ferromagnetic powder surface-treated with 1.5 to 7 parts by mass of a surface treatment agent containing a compound and a hydroxydicarboxylic acid compound in a mass ratio of 90/10 to 10/90. The details of the method for forming the magnetic layer of the magnetic recording medium of the present invention are as described later for the method of manufacturing the magnetic recording medium of the present invention.

[Method of manufacturing magnetic recording medium]
The method for producing a magnetic recording medium of the present invention is a method for producing a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, and the method mainly comprises iron on the nonmagnetic support. A phosphoric acid compound and a hydroxydicarboxylic acid compound in a mass ratio of 90/10 to 10/90 and a total amount of the compound of 1.5 to 7 mass with respect to 100 mass parts of the ferromagnetic powder. It includes forming a magnetic layer by applying and drying a magnetic layer forming coating liquid (hereinafter also referred to as “magnetic layer coating liquid”) contained in an amount of parts. Details of the ferromagnetic powder, the phosphoric acid compound and the hydroxydicarboxylic acid compound are as described above.
Hereinafter, the method for producing a magnetic recording medium of the present invention will be described in more detail.

  The coating liquid for forming the magnetic layer can be prepared through a kneading step, a dispersing step, and a mixing step provided as necessary before and after these steps. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powder, phosphoric acid compound, hydroxydicarboxylic acid compound, binder, and various additives and solvents that are optionally added may be added at the beginning or during any step. In addition, individual raw materials may be added in two or more steps. For example, polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, a conventional known manufacturing technique can be used as a partial process. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, glass beads can be used to disperse each layer forming coating solution. Other than such glass beads, zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media, are suitable. The particle diameter and filling rate of these dispersion media are optimized. A well-known thing can be used for a disperser.

  In the present invention, the presence of a phosphoric acid compound together with the hydroxydicarboxylic acid compound on the surface of the ferromagnetic powder provides a corrosion prevention effect and a dispersibility improvement effect due to the phosphoric acid compound while suppressing a decrease in durability due to iron phosphate formation. Can do. Therefore, in the present invention, it is preferable that the phosphoric acid compound and the hydroxydicarboxylic acid compound are favorably adsorbed on the surface of the ferromagnetic powder in the magnetic layer coating solution. In addition, it is preferable that the added compound is adsorbed on the surface of the ferromagnetic powder with a high adsorption rate in order to suppress the occurrence of contamination due to free components. In order to enhance the adsorptivity of the compound to the surface of the ferromagnetic powder, it is preferable to treat the surface of the ferromagnetic powder with a phosphoric acid compound and a hydroxydicarboxylic acid compound. That is, a surface treatment agent 1.5 to 1.5 containing a ferromagnetic powder mainly containing iron in a proportion of 90/10 to 10/90 by mass ratio of phosphoric acid compound and hydroxydicarboxylic acid compound with respect to 100 parts by mass of the powder. It is preferable to prepare a magnetic layer coating solution after surface treatment with 7 parts by mass. For this purpose, it is preferable to mix the ferromagnetic powder and the above compound before the kneading step for preparing the magnetic layer coating solution. From the viewpoint of improving the dispersibility by interposing a phosphate compound between the ferromagnetic powder and the binder, the phosphate compound is preferably mixed with the ferromagnetic powder before adding the binder. From this viewpoint, it is preferable that the phosphoric acid compound is mixed with the ferromagnetic powder at least before the kneading step. The hydroxydicarboxylic acid compound may be mixed with the ferromagnetic powder at the same time as the phosphoric acid compound, or may be added and mixed after mixing the phosphoric acid compound and the ferromagnetic powder. From the viewpoint of obtaining the effect of addition more effectively, the hydroxydicarboxylic acid compound is preferably mixed with the ferromagnetic powder and the phosphoric acid compound before adding the binder.

  Next, various components contained in the magnetic layer coating solution will be described.

As the binder, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. As the thermoplastic resin, those having a glass transition temperature of −100 to 150 ° C., a number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and a polymerization degree of about 50 to 1000 are used. can do.

  Examples of such include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a structural unit, polyurethane resins, and various rubber resins. Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, polyester resins. And a mixture of a polyester and an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like. These resins are described in detail in “Plastic Handbook” published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. These examples and their production methods are described in detail in JP-A No. 62-256219. The above resins can be used alone or in combination, but are preferably selected from vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate vinyl maleic anhydride copolymer. A combination of at least one selected from the above and a polyurethane resin, or a combination of these with a polyisocyanate.

As the polyurethane resin, those having a known structure such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and _{durability, -COOM, -SO 3 M, -OSO} 3 M, -P = O (OM) 2, - O—P═O (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), —OH, —NR ₂ , —N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, —SH, — It is preferable to use one in which at least one polar group selected from CN and the like is introduced by copolymerization or addition reaction. The amount of such a polar group is, for example, 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.

  The binder used for this invention is compoundable by a well-known method, and is also available as a commercial item.

In the magnetic layer coating liquid and the nonmagnetic layer coating liquid described later, a binder can be used in the range of, for example, 5 to 50% by mass, preferably 10 to 30% by mass, based on the nonmagnetic powder or the magnetic powder. . It is preferable to use a combination of 5 to 30% by mass when using a vinyl chloride resin, 2 to 20% by mass when using a polyurethane resin, and 2 to 20% by mass of polyisocyanate. However, for example, when head corrosion occurs due to a small amount of dechlorination, it is possible to use only polyurethane or only polyurethane and isocyanate. When polyurethane is used, the glass transition temperature is −50 to 150 ° C., preferably 0 ° C. to 100 ° C., the breaking elongation is 100 to 2000%, the breaking stress is 0.05 to 10 kg / mm ² (0.49 to 98 MPa), The yield point is preferably 0.05 to 10 kg / mm ² (0.49 to 98 MPa).

  In order to increase the strength of the coating film, an isocyanate compound is usually added as a crosslinking agent (curing agent) to the magnetic layer coating liquid containing a polyurethane resin as a binder resin. The present inventor presumes that the use of a hydroxydicarboxylic acid compound in a magnetic layer coating solution containing an isocyanate compound is effective in maintaining magnetic properties and durability. This is because the hydroxyl group contained in the carboxyl group reacts with the NCO group in the isocyanate compound to keep the binder on the surface of the ferromagnetic powder, and the surface of the ferromagnetic powder is covered with the binder layer. This is considered to be due to the effects of (1) suppressing the release of iron ions from the ferromagnetic powder, and (2) suppressing the occurrence of dirt due to the release of the binder component during running. The equivalent ratio of the NCO group to the hydroxyl group contained in the hydroxydicarboxylic acid compound and the polyurethane resin is preferably an excessive amount in consideration of the influence of moisture and the like present in the system.

  As the isocyanate compound, a polyfunctional polyisocyanate compound is preferable, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, Isocyanates such as triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, polyisocyanates formed by condensation of isocyanates, and the like can be used. These isocyanates are commercially available, and can be used for each layer alone or in combination of two or more using the difference in curing reactivity. In addition, by using an isocyanate compound as a binder component of the coating solution for forming a nonmagnetic layer described later, the lower layer isocyanate compound migrates to the magnetic layer located in the upper layer, and the hydroxydicarboxylic acid compound on the surface of the ferromagnetic powder and It is also possible to obtain the above action by reacting.

Additives can be added to the additive magnetic layer coating solution as necessary. Examples of additives include abrasives, lubricants, dispersants / dispersing aids, antifungal agents, antistatic agents, antioxidants, solvents, various additives usually used in magnetic layers such as carbon black. it can. These are easily available as commercial products. In addition, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. Amphoteric interfaces such as cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, and sulfate ester groups, amino acids, aminosulfonic acids, sulfuric or phosphate esters of aminoalcohols, and alkylbetaines An activator or the like can also be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.).

  The additive is not necessarily pure, and may contain impurities such as isomers, unreacted products, side reaction products, decomposed products, and oxides in addition to the main components. These impurities are preferably 30% by mass or less, more preferably 10% by mass or less.

Moreover, carbon black can be added to the magnetic layer coating solution as necessary. Examples of carbon black that can be used in the magnetic layer include rubber furnace, rubber thermal, color black, and acetylene black. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle size is 5 to 300 nm, pH is 2 to 10, moisture content is 0.1 to 10%, tap density is 0.1 to 1 g / ml is preferred. Carbon black may be surface-treated with a dispersant, or may be used after being grafted with a resin, or may be obtained by graphitizing a part of the surface. Carbon black may be dispersed with a binder in advance before being added to the magnetic layer coating solution. These carbon blacks can be used alone or in combination. When using carbon black, it is preferable to use 0.1-30 mass% with respect to the mass of a ferromagnetic powder. Carbon black functions to prevent the magnetic layer from being charged, reduce the coefficient of friction, impart light-shielding properties, and improve the film strength. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the magnetic layer and the non-magnetic layer, and are based on the above-mentioned characteristics such as particle size, oil absorption, conductivity, pH, etc. Of course, it is possible to use them properly according to the purpose, but rather they should be optimized in each layer. Carbon black that can be used in the present invention is available as a commercial product. For details, for example, “Carbon Black Handbook” edited by Carbon Black Association can be referred to.

As an abrasive, α-alumina, β-alumina, α-alumina, 90% or more α-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, industrial diamond, silicon nitride, silicon carbide titanium carbide, titanium oxide Known materials having a Mohs hardness of 6 or more, such as silicon dioxide and boron nitride, can be used alone or in combination. Moreover, you may use the composite_body | complex (what surface-treated the abrasive | polishing agent with the other abrasive | polishing agent) of these abrasive | polishing agents. The said abrasive | polishing agent is easily available as a commercial item. These abrasives may contain compounds or elements other than the main component, but the effect is not affected if the main component is 90% or more. The particle size of these abrasives is preferably from 0.01 to 2 [mu] m, and in particular, the narrower particle size distribution is preferable in order to improve electromagnetic conversion characteristics. Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as necessary, or to obtain the same effect by widening the particle size distribution even with a single abrasive. The tap density is preferably 0.3 to ² g / cc, the water content is preferably 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, a dice shape, and a plate shape, but those having a corner in a part of the shape are preferable because of high polishing properties. Abrasives can also be added to the nonmagnetic layer as required. By adding to the nonmagnetic layer, the surface shape can be controlled, and the protruding state of the abrasive can be controlled. The particle size and amount of the abrasive added to these magnetic and nonmagnetic layers should of course be set to optimum values.

A known organic solvent can be used for the solvent magnetic layer coating solution. As the organic solvent, specifically, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, in any ratio Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene , Aromatic hydrocarbons such as cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethyl Nkuroruhidorin, chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane.

  These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% by mass or less, more preferably 10% by mass or less. The organic solvent used in the present invention is preferably the same in the magnetic layer and the nonmagnetic layer. The amount added may be changed. Use non-magnetic layers with high surface tension solvents (cyclohexanone, dioxane, etc.) to increase coating stability. Specifically, the arithmetic average value of the upper layer solvent composition may not fall below the arithmetic average value of the nonmagnetic layer solvent composition. It is essential. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that 50% by mass or more of the solvent having a dielectric constant of 15 or more is included in the solvent composition. Moreover, it is preferable that a solubility parameter is 8-11.

  The various additives used in the present invention can be properly used in the magnetic layer and further in the nonmagnetic layer, which will be described later, according to need. For example, since the lubricant exists in a free state, fatty acids with different melting points are used in the non-magnetic layer and the magnetic layer, and bleeding is controlled on the surface using esters with different boiling points and polarities. It is conceivable that the stability of coating is improved by controlling the amount of the surfactant, and the lubricating effect is improved by increasing the amount of lubricant added in the nonmagnetic layer. All or a part of the additives used in the present invention may be added in any step during the production of the coating liquid for the magnetic layer or nonmagnetic layer. For example, when mixing with a ferromagnetic powder before the kneading step, when adding at a kneading step with a ferromagnetic powder, a binder and a solvent, when adding at a dispersing step, when adding after dispersing, when adding just before coating, etc. There is.

Nonmagnetic Layer Forming Coating Liquid In the method of manufacturing a magnetic recording medium of the present invention, a magnetic recording medium having a nonmagnetic layer and a magnetic layer can be manufactured. The coating solution for forming a nonmagnetic layer can be prepared by mixing a nonmagnetic powder, a binder and optionally used various additives in a solvent. The nonmagnetic powder may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides.

Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α-alumina, β-alumina having an α conversion ratio of 90 to 100% , Γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , carbonized Silicon, titanium carbide, or the like can be used alone or in combination of two or more. The non-magnetic powder can be synthesized by a known method, and can also be obtained as a commercial product. Preferred are α-iron oxide and titanium oxide.

  The shape of the nonmagnetic powder may be any of acicular, spherical, polyhedral and plate shapes. The crystallite size of the nonmagnetic powder is preferably 4 nm to 500 nm, more preferably 40 to 100 nm. If the crystallite size is in the range of 4 nm to 500 nm, it is preferable because dispersion does not become difficult and it has a suitable surface roughness. The average particle size of these non-magnetic powders is preferably 5 nm to 500 nm. However, if necessary, non-magnetic powders having different average particle sizes may be combined, or a single non-magnetic powder may have a wide particle size distribution. It can also have an effect. The average particle size of the particularly preferred nonmagnetic powder is 10 to 200 nm. The range of 5 nm to 500 nm is preferable because the dispersion is good and the surface roughness is suitable.

The specific surface area of the nonmagnetic powder is, for example, 1 to 150 m ² / g, preferably 20 to 120 m ² / g, and more preferably 50 to 100 m ² / g. A specific surface area in the range of 1 to 150 m ² / g is preferred because it has a suitable surface roughness and can be dispersed with a desired amount of binder. The oil absorption using dibutyl phthalate (DBP) is, for example, 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is, for example, 1 to 12, preferably 3 to 6. The tap density is, for example, 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. When the tap density is in the range of 0.05 to 2 g / ml, there are few particles to be scattered, the operation is easy, and there is a tendency that it is difficult to adhere to the apparatus. The pH of the non-magnetic powder is preferably 2 to 11, and particularly preferably 6 to 9. When the pH is in the range of 2 to 11, it is possible to prevent the friction coefficient from increasing due to high temperature, high humidity, or liberation of fatty acids. The water content of the nonmagnetic powder is, for example, 0.1 to 5% by mass, preferably 0.2 to 3% by mass, and more preferably 0.3 to 1.5% by mass. A water content in the range of 0.1 to 5% by mass is preferable because the dispersion is good and the viscosity of the paint after dispersion is stable. The ignition loss is preferably 20% by mass or less, and the ignition loss is preferably small.

When the nonmagnetic powder is an inorganic powder, the Mohs hardness is preferably 4-10. If the Mohs hardness is in the range of 4 to 10, durability can be ensured. The stearic acid adsorption amount of the nonmagnetic powder is preferably 1 to 20 μmol / m ² , more preferably ² to 15 μmol / m ² . The heat of wetting of the nonmagnetic powder into water at 25 ° C. is preferably in the range of 200 to 600 erg / cm ² (200 to 600 mJ / m ² ). Moreover, the solvent which exists in the range of this heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C. is suitably 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 9. It is preferable that Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ and ZnO are present on the surface of these nonmagnetic powders by surface treatment. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ , and more preferred are Al ₂ O ₃ , SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface-treated layer co-precipitated according to the purpose may be used, or a method of treating the surface layer with silica after first treating with alumina, or vice versa may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

Carbon black can be mixed in the nonmagnetic layer together with nonmagnetic powder to lower the surface electrical resistance, reduce the light transmittance, and obtain a desired micro Vickers hardness. The micro-Vickers hardness of the nonmagnetic layer is generally 25~60kg / mm ² (245~588MPa), preferably in order to adjust the head contact, a 30~50kg / mm ² (294~490MPa), thin film hardness meter ( Using a HMA-400 manufactured by NEC, measurement can be performed using a diamond triangular pyramid needle having a ridge angle of 80 degrees and a tip radius of 0.1 μm at the tip of the indenter. For details, refer to Realize Co., Ltd. It is standardized that the light transmittance is generally 3% or less for absorption of infrared rays having a wavelength of about 900 nm, for example, 0.8% or less for a VHS magnetic tape. For this purpose, rubber furnace, rubber thermal, color black, acetylene black and the like can be used.

The specific surface area of the carbon black employed in the nonmagnetic layer is, for example, 100 to 500 m ² / g, preferably from 150 to 400 m ² / g, DBP oil absorption, for example, 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g is there. The particle size of carbon black is, for example, 5 to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. Carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml. Carbon black may be surface-treated with a dispersant, or may be grafted with a resin, or may be obtained by graphitizing a part of the surface. Moreover, before adding carbon black to a coating material, you may disperse | distribute with a binder beforehand. These carbon blacks can be used, for example, in a range not exceeding 50% by mass with respect to the inorganic powder and in a range not exceeding 40% by mass of the total mass of the nonmagnetic layer. These carbon blacks can be used alone or in combination. Carbon black used in the coating solution for forming the nonmagnetic layer is readily available as a commercial product. For details, see, for example, “Carbon Black Handbook” edited by Carbon Black Association.

  Further, an organic powder can be added to the nonmagnetic layer according to the purpose. Examples of such organic powder include acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin, and the like. Resin powder and polyfluorinated ethylene resin can also be used. As the production method, those described in JP-A Nos. 62-18564 and 60-255827 can be used.

  As the binder, lubricant, dispersant, additive, solvent, dispersion method, etc. of the coating liquid for forming the nonmagnetic layer, those of the coating liquid for forming the magnetic layer can be applied. In particular, known techniques relating to the magnetic layer can be applied to the amount of binder, type, additive, and amount of dispersant added, and type. Regarding the method for preparing the coating solution for forming the nonmagnetic layer, the above description regarding the method for preparing the coating solution for the magnetic layer can be referred to.

Undercoat layer In the method for producing a magnetic recording medium of the present invention, an undercoat layer may be formed. By providing the undercoat layer, the adhesive force between the support and the magnetic layer or the nonmagnetic layer can be improved. As the undercoat layer, a solvent-soluble polyester resin can be used.

Nonmagnetic support As nonmagnetic support, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aromatic polyamide, polybenzoxazole and the like are known. Can be used. It is preferable to use a support having a glass transition temperature of 100 ° C. or higher, and it is particularly preferable to use a high-strength support such as polyethylene naphthalate or aramid. Moreover, in order to change the surface roughness of a magnetic surface and a base surface as needed, the laminated type support body as shown in Unexamined-Japanese-Patent No. 3-224127 can also be used. These supports may be subjected in advance to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like.

As the non-magnetic support, the center surface average surface roughness (Ra) measured with a light interference type surface roughness meter HD-2000 manufactured by WYKO is 8.0 nm or less, preferably 4.0 nm or less, more preferably 2. It is preferable to use one having a thickness of 0 nm or less. These supports preferably have not only a small center plane average surface roughness (Ra) but also no coarse protrusions of 0.5 μm or more. The surface roughness shape is freely controlled by the size and amount of filler added to the support as required. Examples of these fillers include organic fine powders such as acrylic, in addition to oxides and carbonates such as Ca, Si, and Ti. The maximum height Rmax of the support is 1 μm or less, the ten-point average roughness Rz is 0.5 μm or less, the center surface mountain height Rp is 0.5 μm or less, the center surface valley depth Rv is 0.5 μm or less, and the center surface area ratio Sr is preferably 10% or more and 90% or less, and the average wavelength λa is preferably 5 μm or more and 300 μm or less. In order to obtain the desired electromagnetic conversion characteristics and durability, the surface protrusion distribution of these supports can be arbitrarily controlled by fillers, each having a size of 0.01 μm to 1 μm, 0 pieces per 0.1 mm ² Can be controlled in the range of 2,000 to 2,000.

The F-5 value of the support used in the present invention is preferably 5 to 50 kg / mm ² (49 to 490 MPa). The heat shrinkage rate of the support at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage rate at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0. .5% or less. Breaking strength 5~100kg / mm ² (49~980MPa), it is preferred that each elastic modulus is 100~2000kg / mm ² (0.98~19.6GPa). The temperature expansion coefficient is preferably 10 ⁻⁴ to 10 ⁻⁸ / ° C., more preferably 10 ⁻⁵ to 10 ⁻⁶ / ° C. The humidity expansion coefficient is preferably 10 ⁻⁴ / RH% or less, more preferably 10 ⁻⁵ / RH% or less. These thermal characteristics, dimensional characteristics, and mechanical strength characteristics are preferably substantially equal with a difference within 10% in each in-plane direction of the support.

The thickness of the layered magnetic recording medium is such that the thickness of the nonmagnetic support is preferably 3 to 80 μm, more preferably 3 to 50 μm, and particularly preferably 3 to 10 μm. When an undercoat layer is provided between the nonmagnetic support and the nonmagnetic layer or the magnetic layer, the thickness of the undercoat layer is, for example, 0.01 to 0.8 μm, preferably 0.02 to 0.6 μm.

  The thickness of the magnetic layer is preferably 5 to 300 nm, more preferably 10 to 150 nm, and still more preferably 15 to 80 nm, and can be optimized depending on the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used. preferable. The thickness variation rate of the magnetic layer is preferably within ± 50%, more preferably within ± 30%. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.

  The thickness of the nonmagnetic layer is, for example, 0.1 to 3.0 μm, preferably 0.3 to 2.0 μm, and more preferably 0.5 to 1.5 μm. Note that the nonmagnetic layer of the magnetic recording medium of the present invention exhibits its effect if it is substantially nonmagnetic. For example, it includes impurities or intentionally contains a small amount of magnetic material or soft magnetic material. However, this shows the effect of the present invention and can be regarded as substantially the same configuration as the magnetic recording medium of the present invention. Note that “substantially the same” means that the residual magnetic flux density of the nonmagnetic layer is 10 mT or less or the coercive force is 7.96 kA / m (100 Oe) or less, and preferably has no residual magnetic flux density and coercive force. Means.

Backcoat layer In the method for producing a magnetic recording medium of the present invention, a backcoat layer can be provided on the surface of the nonmagnetic support opposite to the surface having the magnetic layer. The back coat layer preferably contains carbon black and inorganic powder. For the binder and various additives for forming the backcoat layer, the formulation of the magnetic layer and the nonmagnetic layer can be applied. The thickness of the back coat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm. The surface magnetic resistance is preferably 10 ⁻⁴ to 10 ⁻⁷ Ω / in ² at 25 ° C. and 50% RH.

  In the method of manufacturing a magnetic recording medium, for example, the magnetic layer is applied to the surface of a nonmagnetic support under running so that the magnetic layer is applied to a predetermined thickness. Here, a plurality of magnetic layer forming coating solutions may be sequentially or simultaneously applied, or the nonmagnetic layer forming application solution and the magnetic layer forming application solution may be applied successively or simultaneously. Note that sequential multi-layer coating (wet-on-dry) is a coating method in which an upper layer forming coating solution is applied after drying the lower layer, and simultaneous multi-layer coating (wet-on-wet) Is a coating method in which a coating solution for forming an upper layer is applied while is in a wet state. The coating machines that apply the magnetic layer coating solution or non-magnetic layer coating solution 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, cast coat, spray coat, spin coat, etc. can be used. As for these, for example, “Latest Coating Technology” (May 31, 1983) issued by General Technology Center Co., Ltd. can be referred to.

  It is preferable to be able to control the drying position of the coating film by controlling the temperature, air volume, and coating speed of the drying air in the drying process after coating the coating liquid. The coating speed is 20 m / min to 1000 m / min, drying The wind temperature is preferably 60 ° C. or higher. Moreover, moderate preliminary drying can also be performed before entering a magnet zone.

The coating material after the drying step is usually once taken up by a take-up roll, and then unwound from the take-up roll and can be subjected to a calendar process.
For the calendar process, for example, a super calendar roll or the like is used. The calendering improves the surface smoothness and eliminates the voids generated by the removal of the solvent during drying and improves the filling rate of the ferromagnetic powder in the magnetic layer. Obtainable. The step of calendering is preferably performed while changing the calendering conditions according to the smoothness of the surface of the coating raw material.

  As the calender roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyamideimide or the like can be used. Moreover, it can also process with a metal roll. As the calendering conditions, for example, the temperature of the calender roll is in the range of 60 to 100 ° C., preferably in the range of 70 to 100 ° C., particularly preferably in the range of 80 to 100 ° C., and the pressure is 100 to 500 kg / cm (98 ˜490 kN / m), preferably 200 to 450 kg / cm (196 to 441 kN / m), and particularly preferably 300 to 400 kg / cm (294 to 392 kN / m). The calendar treatment has an effect of increasing the surface smoothness of the magnetic layer. In the magnetic recording medium of the present invention, the surface of the magnetic layer has a center surface average surface roughness (Ra) of 0.1 to 4 nm, more preferably 1 to 3 nm as measured with an optical interference surface roughness meter HD-2000 manufactured by WYKO. It is preferable to have an extremely excellent surface smoothness of the range.

  Apart from this, the magnetic recording media obtained before and after the calendering process can be thermo-treated to proceed with thermosetting. Such thermo treatment may be appropriately determined depending on the formulation of the magnetic layer coating solution, and is, for example, 35 to 100 ° C, and preferably 50 to 80 ° C. The thermo treatment time is, for example, 12 to 72 hours, preferably 24 to 48 hours.

  The obtained magnetic recording medium can be cut into a desired size using a cutting machine or the like. The cutting machine is not particularly limited, but is preferably provided with a plurality of pairs of rotating upper blades (male blades) and lower blades (female blades). The slitting speed, the engagement depth, and the upper blade (male blade) are appropriately selected. The peripheral speed ratio (upper blade peripheral speed / lower blade peripheral speed) between the blade and the lower blade (female blade), the continuous use time of the slit blade, and the like are selected.

The coercive force (Hc) of the physical property magnetic layer is preferably 143.2 to 318.3 kA / m (1800 to 4000 Oe), more preferably 159.2 to 278.5 kA / m (2000 to 3500 Oe). The coercive force distribution is preferably narrow, and SFD and SFDr are 0.8 or less, more preferably 0.5 or less. The squareness ratio is preferably closer to 1 in both the longitudinal direction and the vertical direction with respect to the support, and a tape of 0.6 to 0.9 can be realized.

The coefficient of friction with respect to the head of the magnetic recording medium is, for example, 0.50 or less, preferably 0.3 or less, in the range of temperature −10 to 40 ° C. and humidity 0 to 95%. The surface resistivity is preferably 10 ⁴ to 10 ⁸ Ω / sq of the magnetic surface, and the charging position is preferably within −500 V to +500 V. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 0.98 to 19.6 GPa (100 to 2000 kg / mm ² ) in each in-plane direction, and the breaking strength is preferably 98 to 686 MPa (10 to 70 kg). / Mm ² ), the elastic modulus of the magnetic recording medium is preferably 0.98 to 14.7 GPa (100 to 1500 kg / mm ² ) in each in-plane direction, and the residual spread is preferably 0.5% or less, 100 ° C. The thermal shrinkage at any of the following temperatures is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.

Glass transition temperature of magnetic layer (maximum point of loss elastic modulus of dynamic viscoelasticity measurement measured at 110 Hz by a dynamic viscoelasticity measuring device (for example, Leo Vibron manufactured by A & D Corporation)) is 50 to 180 ° C. The nonmagnetic layer preferably has a temperature of 0 to 180 ° C. The loss elastic modulus is preferably in the range of 1 × 10 ⁷ to 8 × 10 ⁸ Pa (1 × 10 ⁸ to 8 × 10 ⁹ dyne / cm ² ), and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. These thermal characteristics and mechanical characteristics are preferably almost equal within 10% in each in-plane direction of the medium.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less. The porosity of the coating layer is preferably 40% by volume or less, more preferably 30% by volume or less for both the nonmagnetic layer and the magnetic layer. The porosity is preferably small in order to achieve high output, but it may be better to ensure a certain value depending on the purpose. For example, in the case of a disk medium in which repeated use is important, a larger void ratio is often preferable for running durability.

  In the present invention, these physical characteristics can be changed between the nonmagnetic layer and the magnetic layer according to the purpose. For example, the elastic modulus of the magnetic layer can be increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer can be made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

  Hereinafter, the present invention will be described more specifically with reference to examples. It should be noted that the components, ratios, operations, order, and the like shown here can be changed without departing from the spirit of the present invention, and should not be limited to the following examples. Further, “parts” and “%” in the examples indicate parts by mass and mass% unless otherwise specified.

Magnetic layer coating solution component A
100 parts of ferromagnetic iron nitride powder mainly composed of Fe ₁₆ N ₂ (Hc: 209 kA / m, σs: 85 A · m ² / Kg, average particle size: 19 nm, coefficient of variation of particle size: 19%, average needle shape Ratio: 1.0, specific surface area (S _BET ): 55.0 m ² / g, composition: Al / Y / V / Fe = 7.7 / 2.0 / 9.5 / 100 (atomic%))
Compound a / Compound b See Table 1. 7 parts of vinyl chloride copolymer (containing 1.2 × 10 ⁻⁴ eq / g of —SO ₃ K group, degree of polymerization: 300)
Polyester polyurethane resin 3.5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, —SO ₃ Na group: 1 × 10 ⁻⁴ eq / g contained)
α-alumina (average particle size: 0.05 μm) 8 parts carbon black (average particle size: 18 nm) 4.0 parts sec butyl stearate 1.5 parts stearic acid 2.5 parts methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 300 Part

  The iron nitride powder was put into a container, and the lump of powder was pulverized in the container. Thereafter, compounds a and b were simultaneously added to the container and mixed with iron nitride powder. Next, carbon black, vinyl chloride copolymer, 130 parts of 1: 1 mixed solvent of methyl ethyl ketone and cyclohexanone were added, kneaded with a kneader, the above remaining components were added and mixed, and then 0.4 mmφ zirconia beads were used. Dispersed for 1 hour with a sand grinder. Add 5 parts of polyisocyanate (Nippon Polyurethane Industrial Co., Ltd. Coronate L) to the resulting dispersion, add 4 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone 1: 1, and filter using a filter having an average pore diameter of 1 μm. A layer coating solution was prepared.

Magnetic layer coating solution component B
100 parts of ferromagnetic metal powder (Hc: 186 kA / m, σs: 106 A · m ² / kg, specific surface area (S _BET ): 63 m ² / g, average major axis length: 35 nm, coefficient of variation of major axis length: 19% , Composition: Fe / Co / Al / Y = 100/24 / 6.0 / 7 (atomic%), sintering inhibitor: Al ₂ O ₃ , Y ₂ O ₃ )
Compound a / Compound b See Table 2. 11 parts of vinyl chloride copolymer (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ K group, degree of polymerization: 300)
5 parts of polyester polyurethane resin (neopentyl glycol / caprolactone polyol / MDI = 0.8 / 2.5 / 1, —SO ₃ Na group: 1.8 × 10 ⁻⁴ eq / g contained)
α-alumina (average particle size: 0.08 μm) 7 parts Carbon black (average particle size: 20 nm 4.0 parts sec butyl stearate 3 parts stearic acid 3 parts methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 350 parts

  The ferromagnetic metal powder was put into a container, and the powder lump was pulverized in the container. Thereafter, compounds a and b were simultaneously added to the container and mixed with iron nitride powder. Next, carbon black, vinyl chloride copolymer, 130 parts of 1: 1 mixed solvent of methyl ethyl ketone and cyclohexanone were added, kneaded with a kneader, the above remaining components were added and mixed, and then 0.4 mmφ zirconia beads were used. Dispersed for 1 hour with a sand grinder. Add 5 parts of polyisocyanate (Nippon Polyurethane Industrial Co., Ltd. Coronate L) to the resulting dispersion, add 4 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone 1: 1, and filter using a filter having an average pore diameter of 1 μm. A layer coating solution was prepared.

Nonmagnetic layer coating liquid component acicular hematite (nonmagnetic powder) 40 parts Carbon black (Conductex SC manufactured by Columbia Carbon Co.) 60 parts Vinyl chloride copolymer (MR110 manufactured by Nippon Zeon Co., Ltd.) 10 parts Polyurethane resin (UR8200 manufactured by Toyobo Co., Ltd.) ) 4 parts stearic acid 3 parts sec butyl stearate 1 part isooctyl stearate 1 part methyl ethyl ketone and cyclohexanone 8: 2 mixed solvent 250 parts

  After kneading 150 parts of the above acicular hematite, carbon black, vinyl chloride copolymer, methyl ethyl ketone and cyclohexanone 8: 2 with a kneader, the above remaining components were added and mixed, and then 0.4 mmφ zirconia beads were added. Dispersed and prepared for 1 hour using a sand grinder. To the obtained dispersion, 8 parts of polyisocyanate (Nippon Polyurethane Industry Co., Ltd. Coronate L) and 30 parts of cyclohexanone are added, and the resulting dispersion is filtered using a filter having an average pore diameter of 1 μm, and a non-magnetic layer coating solution Was prepared.

Backcoat layer coating liquid component of carbon black (average particle diameter: 18m) 40.5 parts Carbon black (average particle size: 370 nm) 0.3 parts Barium sulfate 2.5 parts Nitrocellulose 25 parts Polyurethane resin (SO ₃ Na group-containing ) 25 parts cyclohexanone 100 parts toluene 100 parts methyl ethyl ketone 100 parts

  The nonmagnetic layer coating solution obtained above was used as a nonmagnetic support and a polyethylene naphthalate film having a thickness of 4 μm (105 ° C., 30 minutes thermal shrinkage ratio of 0.8% in the vertical direction and 0% in the horizontal direction). 0.6%, center plane average roughness 2.0 nm) so that the thickness of the non-magnetic layer after drying was 0.8 μm, and dried in a multistage bath at 80 to 100 ° C. Furthermore, the magnetic layer coating solution was applied (wet-on-dry coating) so that the thickness after drying was 60 nm, and dried in a multistage bath at 40 to 100 ° C. Next, the backcoat layer coating solution prepared by mixing the above components on the side opposite to the surface on which the nonmagnetic layer and magnetic layer of the nonmagnetic support are formed is dried and calendered. The coating was applied to a thickness of 0.5 μm and dried. Thereafter, a surface smoothing treatment was performed at a speed of 100 m / min, a linear pressure of 269.5 kN / m, and a temperature of 90 ° C. using a seven-stage calendar composed only of metal rolls. The back coat layer was prepared by dispersing 7.0 parts of the above components in a sand mill and then adding 7.0 parts of polyisocyanate (Nippon Polyurethane Industry Co., Ltd. Coronate L), followed by stirring and filtration, and a film thickness of 0.5 μm when dried. It was made with. The magnetic sheet thus obtained was mirror-finished with a seven-stage calendar (temperature 90 ° C., linear pressure 294 kN / m), and thermo-treated for 48 hours at 60 ° C. and 40% RH. Then, the magnetic layer surface was ground with a diamond wheel (rotation measurement + 150%, winding angle 30 °) while being cut at a width of 1/2 inch and running at 100 m / min to produce a magnetic tape.

Evaluation method 1. Demagnetization rate: Measure residual magnetic flux density (Bm) of magnetic tape with a vibrating sample magnetometer (VSM manufactured by Toei Kogyo Co., Ltd.), measure again after storage at 60 ° C. and 90% RH for 30 days, and values before aging The rate of change from was calculated.
2. Electromagnetic conversion characteristics: After storing the magnetic tape at 60 ° C. and 90% RH for 30 days, a MIG head having a track width of 6 μm, a gap length of 0.10 μm and a Bs of 1.5 T is used as a recording head, and a track is used as a reproducing head The SNR was determined using a GMR head having a width of 4.5 μm and SH-SH: 0.12 μm. The SNR was measured by measuring the reproduction output (S) and broadband noise (N) at a recording density of 250 kfci using a spectrum analyzer with a relative speed of the tape and the head of 5.0 m / min, and reproducing output (S) / It was calculated as the ratio of broadband noise (N). The reproduction output, noise level, and SNR in Table 1 are shown as relative values with the value of the tape of Comparative Example 1 being 0 dB.
3. Durability pass number: After the magnetic tape was stored at 60 ° C. and 90% RH for 30 days, a sticking durability test was performed using an LTO-G3 drive. Table 1 shows the number of times of running at the time when the tape stopped and started running every 100 passes, and the running friction coefficient increased and could not withstand running.

Evaluation results As shown in Tables 1 and 2, in Examples 1 to 14 in which a predetermined amount of a phosphoric acid compound and a hydroxydicarboxylic acid compound was used, (1) superior storage stability (reduced magnetic susceptibility), (2) Electromagnetic conversion characteristics and (3) running durability could be achieved. (1) is the effect due to the suppression of iron corrosion due to the use of phosphoric acid compound, (2) is the effect due to the improved dispersibility of the magnetic material due to the use of the phosphoric acid compound, and the magnetic material due to the use of the phosphoric acid compound. It is considered that the effect of preventing the deterioration of magnetic properties by inhibiting corrosion and preventing oxidation, and (3), the effect of inhibiting the formation of iron phosphate by the combined use of hydroxydicarboxylic acid compounds. The reactivity of the hydroxyl group of the hydroxydicarboxylic acid compound and the NCO group of the polyisocyanate compound is also considered to contribute to the above (3).

  According to the present invention, it is possible to provide a magnetic recording medium that can exhibit excellent performance over a long period of time. The magnetic recording medium of the present invention is suitable as a backup tape or the like that requires high reliability over a long period of time.

Claims (14)

A magnetic recording medium having a magnetic layer comprising a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic layer contains a ferromagnetic powder containing iron as a main component, and the ferromagnetic powder 100 contains a phosphate compound and a hydroxydicarboxylic acid compound in a mass ratio of 90/10 to 10/90 and a total amount of the compound. A magnetic recording medium comprising 1.5 to 7 parts by mass with respect to parts by mass. The magnetic layer comprises a surface treatment agent comprising a ferromagnetic powder containing iron as a main component and a phosphoric acid compound and a hydroxydicarboxylic acid compound in a mass ratio of 90/10 to 10/90 with respect to 100 parts by mass of the powder. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a layer formed using a ferromagnetic powder surface-treated with 1.5 to 7 parts by mass. The magnetic recording medium according to claim 1, wherein the hydroxydicarboxylic acid compound is represented by the following general formula (1).
^{HOOC- (CR 1 R 2) n} -C (R 3 R 4) m-COOH ... (1)
[In General Formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represents a hydrogen atom, an alkyl group or a hydroxyl group, provided that at least one of R ¹ , R ² , R ³ and R ⁴ One represents a hydroxyl group. n and m represent integers satisfying 2 ≦ (n + m) ≦ 18. ] The magnetic recording medium according to claim 3, wherein the hydroxydicarboxylic acid compound is at least one selected from the group consisting of tartaric acid, mesotartaric acid, and malic acid. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder containing iron as a main component is an iron nitride powder containing Fe ₁₆ N ₂ as a main component. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder containing iron as a main component is a ferromagnetic metal powder. The magnetic recording medium according to claim 1, wherein the magnetic layer is a layer formed using a coating solution for forming a magnetic layer containing a polyurethane resin and an isocyanate compound. A method of manufacturing a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
A ferromagnetic powder containing iron as a main component on a non-magnetic support, and the ferromagnetic compound and the hydroxydicarboxylic acid compound in the ratio of 90/10 to 10/90 by mass ratio and the total amount of the compound. The said manufacturing method including forming a magnetic layer by apply | coating and drying the coating liquid for magnetic layer formation included in the quantity of 1.5-7 mass parts with respect to 100 mass parts of powders. The magnetic layer forming coating solution is made of a ferromagnetic powder containing iron as a main component, and the phosphoric acid compound and the hydroxydicarboxylic acid compound in a mass ratio of 90/10 to 10/90 with respect to 100 parts by mass of the powder. The method for producing a magnetic recording medium according to claim 8, wherein the magnetic recording medium is prepared using ferromagnetic powder surface-treated with 1.5 to 7 parts by mass of a surface treating agent. The method for producing a magnetic recording medium according to claim 8, wherein the hydroxydicarboxylic acid compound is represented by the following general formula (1).
^{HOOC- (CR 1 R 2) n} -C (R 3 R 4) m-COOH ... (1)
[In General Formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represents a hydrogen atom, an alkyl group or a hydroxyl group, provided that at least one of R ¹ , R ² , R ³ and R ⁴ One represents a hydroxyl group. n and m represent integers satisfying 2 ≦ (n + m) ≦ 18. ] The method for producing a magnetic recording medium according to claim 10, wherein the hydroxydicarboxylic acid compound is at least one selected from the group consisting of tartaric acid, mesotartaric acid, and malic acid. The method of manufacturing a magnetic recording medium according to claim 8, wherein the ferromagnetic powder containing iron as a main component is an iron nitride powder containing Fe ₁₆ N ₂ as a main component. The method for manufacturing a magnetic recording medium according to claim 8, wherein the ferromagnetic powder containing iron as a main component is a ferromagnetic metal powder. The method for manufacturing a magnetic recording medium according to claim 8, wherein the coating liquid for forming a magnetic layer further contains a polyurethane resin and an isocyanate compound.