JP2009009646A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating type magnetic recording medium suitable for a system in which a signal is reproduced using an MR head. <P>SOLUTION: The magnetic recording medium, in which a signal is reproduced by a reproducing head using a magnetoresistance effect element, includes a non-magnetic support, a magnetic layer including a granular iron nitride-based magnetic powder with an average particle size of 5 to 50 nm, a binder, and a nitro-triazole derivative on the non-magnetic support. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coating type magnetic recording medium having a magnetic layer in which iron nitride magnetic powder is dispersed in a binder, and more particularly to a magnetic recording medium on which a signal is reproduced by a reproducing head using a magnetoresistive element. .

  A coating-type magnetic recording medium having a magnetic layer in which magnetic powder is dispersed in a binder is required to further improve the recording density as the recording / reproducing method shifts from an analog method to a digital method. In particular, this demand is increasing year by year for magnetic recording media used for high-density digital video tapes, computer backup tapes, and the like.

  In order to cope with the short wavelength recording in order to improve the recording density, the magnetic powder has been made finer year by year. At present, acicular iron-based metal magnetic powder having a particle length of 0.1 μm or less is practically used. It is used for conversion. In addition, in order to prevent a decrease in output due to demagnetization in short wavelength recording, a higher coercivity of magnetic powder has been achieved year by year. For example, an iron-cobalt alloy powder having a coercive force of about 199.0 kA / m (2,500 Oe) has been realized (Patent Document 1).

However, in the magnetic recording medium using these needle-shaped particles, since the coercive force depends on the shape of the magnetic powder, it is difficult to make a large particle from the particle length.
Therefore, the present applicant has previously proposed a magnetic recording medium using granular iron nitride magnetic powder having an average particle diameter of 5 to 50 nm (Patent Document 2).
Japanese Patent Laid-Open No. 3-49026 JP 2004-273094 A

  By the way, in a computer data recording system, an anisotropic magnetoresistive element (AMR), a giant magnetoresistive element (GMR) is used as a magnetic head for reproducing recorded information, instead of a conventional induction head. ), Or magnetic heads using magnetoresistive elements such as tunnel magnetoresistive elements (TMR) (hereinafter collectively referred to as “MR heads”) have been studied. In a system using such a head, noise caused by the system can be greatly reduced, and it is known that medium noise derived from a magnetic recording medium dominates the S / N ratio of the system. . Therefore, in order to improve the S / N ratio of the system in future high-density recording, it is necessary to reduce the medium noise.

  In order to reduce medium noise, it is effective to use fine magnetic powder. However, in the magnetic layer using iron nitride magnetic powder as the particle size is reduced, the aggregation of the magnetic powder becomes prominent, and the magnetic properties such as coercive force and square shape are likely to deteriorate, and the iron nitride type having high coercive force with fine particles. It became clear that the characteristics of magnetic powder could not be fully demonstrated.

  Further, since the MR head or the like reads the recorded signal while being in sliding contact with the magnetic layer, the surface of the head is easily corroded by the sliding contact. When such corrosion occurs, in the MR head or the like, the electrical resistance of each layer forming the head changes, and the head characteristics deteriorate.

  The present invention has been made to solve the above-described problems, and improves the dispersibility of the iron nitride-based magnetic powder and provides an MR head or the like produced by sliding contact with the magnetic layer containing the iron nitride-based magnetic powder. An object of the present invention is to provide a coating type magnetic recording medium suitable for a system that prevents corrosion and reproduces a signal by using an MR head or the like.

  The present invention is a magnetic recording medium in which a signal is reproduced by a reproducing head using a magnetoresistive element, and has a nonmagnetic support and an average particle diameter of 5 to 50 nm on the nonmagnetic support. A magnetic recording medium comprising a granular iron nitride magnetic powder, a binder, and a magnetic layer containing a triazole derivative having a nitro group. The iron nitride magnetic powder preferably contains at least one element selected from the group consisting of rare earth elements, boron, silicon, aluminum, and phosphorus.

  According to the present invention, it is possible to form a magnetic layer in which iron nitride-based magnetic powder is well dispersed, and to suppress corrosion of the MR head and the like due to sliding contact with the magnetic layer. Thereby, it is possible to provide a magnetic recording medium suitable for a system in which a signal is reproduced using an MR head or the like.

  The magnetic recording medium of the present embodiment includes a magnetic layer containing fine iron nitride magnetic powder as a magnetic powder, a binder, and a triazole derivative having a nitro group. By using the triazole derivative having a nitro group together with the iron nitride magnetic powder, the fine iron nitride magnetic powder can be highly dispersed, and a magnetic layer excellent in coercive force and square shape can be formed. In addition, in order to improve the corrosion resistance of magnetic powder, addition of an anticorrosive agent such as an unsubstituted or triazole derivative having an amino group to the magnetic layer has been studied, but as shown in the examples described later, triazole Even if the derivative is used together with the iron nitride magnetic powder, the effect of improving the corrosion resistance of the iron nitride magnetic powder itself is small. Even if the above-mentioned unsubstituted or triazole derivative having an amino group is used, the iron nitride magnetic powder It has been confirmed that the effect of improving dispersibility cannot be sufficiently obtained. The magnetic recording medium having a magnetic layer containing an unsubstituted or amino group-containing triazole derivative as described above has a low effect of suppressing corrosion of an MR head or the like, whereas a triazole having a nitro group as a substituent. A magnetic recording medium provided with a magnetic layer containing a derivative has an excellent effect of reducing the corrosion of an MR head or the like.

  Examples of the triazole derivative having a nitro group include triazole derivatives in which a part of a compound having a triazole ring structure such as triazole or benzotriazole is substituted with a nitro group. Among these, 5-nitrobenzotriazole Is preferred.

  The content of the triazole derivative having a nitro group is preferably 2 to 10 parts by mass and more preferably 4 to 8 parts by mass with respect to 100 parts by mass of the iron nitride magnetic powder. If the content is less than 2 parts by mass, the effect of improving the dispersibility of the iron nitride-based magnetic powder cannot be sufficiently obtained. If the content is more than 10 parts by mass, the effect of improving the dispersibility is saturated, rather the coercive force and the angle. The mold tends to drop.

As the iron nitride magnetic powder, granular iron nitride magnetic powder having an average particle diameter of 5 to 50 nm can be used. In addition, granular means a substantially spherical or substantially ellipsoidal shape having an average axial ratio [major axis diameter / short axis diameter] of 1 to 2, and the particle diameter is a spherical powder. In the case of powder having an anisotropy such as an ellipsoid, the diameter means a major axis diameter. Further, the iron nitride magnetic powder may have irregularities on the surface of the powder as long as the shape is granular, or may have some deformation. The average particle diameter is an average value obtained by photographing the iron nitride magnetic powder with a transmission electron microscope and actually measuring the particle diameters of 300 iron nitride magnetic powders in the photograph. Such an iron nitride magnetic powder is described in, for example, Japanese Patent Application Laid-Open No. 2000-277311. The iron nitride magnetic powder is preferably an iron nitride magnetic powder mainly containing iron nitride whose main phase is an Fe ₁₆ N ₂ phase. Since the Fe ₁₆ N ₂ phase is excellent in crystallinity, a magnetic layer having a high coercive force can be formed by using an iron nitride magnetic powder having an Fe ₁₆ N ₂ phase as a main phase.

  The iron nitride magnetic powder preferably contains at least one element selected from the group consisting of rare earth elements, boron, silicon, aluminum, and phosphorus. An iron nitride-based magnetic powder containing such an element is preferable because it exhibits high dispersibility and excellent shape retention while having a high coercive force. Specific examples of such rare earth elements include yttrium, ytterbium, cesium, praseodymium, lanthanum, europium, and neodymium. These may be contained alone or in combination. Among these, yttrium, samarium, and neodymium are preferable because the effect of maintaining the particle shape during reduction is great. The content of the above elements is preferably 0.05 to 20 atomic%, more preferably 0.1 to 15 atomic%, and most preferably 0.5 to 10 atomic% with respect to iron. If it is the range of the said content, while being able to improve a dispersibility further, coercive force and saturation magnetization can be improved. Note that the iron nitride magnetic powder may contain carbon, calcium, magnesium, zirconium, barium, strontium, or the like, if necessary. By using these elements and rare earth elements in combination, high shape retention and dispersibility can be obtained.

The iron nitride-based magnetic powder of the present embodiment is a two-layer iron nitride-based structure having an inner layer portion mainly containing iron nitride mainly composed of an Fe ₁₆ N ₂ phase and an outer layer portion mainly containing the rare earth element. Magnetic powder may be used. Such an iron nitride-based magnetic powder is preferable because it exhibits high dispersibility and excellent shape retention while having a high coercive force. Such a two-layered iron nitride-based magnetic powder can be produced, for example, by the method described in JP-A-2004-273094.

  In the iron nitride magnetic powder, a part of iron may be substituted with another transition metal element. Specific examples of such other transition metal elements include manganese, zinc, nickel, copper, and cobalt. Among these, nickel and cobalt are preferable, and cobalt is particularly preferable because saturation magnetization can be most improved. However, the content of these transition metal elements is preferably 10 atomic% or less with respect to iron. If the content of the transition metal element is excessive, nitriding tends to take a long time.

Examples of the binder include at least one selected from the group consisting of a vinyl chloride resin, a nitrocellulose resin, an epoxy resin, and a polyurethane resin. Specific examples of the vinyl chloride resin include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, vinyl chloride. -Vinyl acetate-maleic anhydride copolymer resin, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and the like. Among these, the combined use of a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin is more preferable. In addition, these binders preferably have a functional group in order to improve the dispersibility of the iron nitride magnetic powder and increase the filling property. Specific examples of such functional groups include COOM, SO ₃ M, OSO ₃ M, P═O (OM) ₃ , and O—P═O (OM) ₂ (M is a hydrogen atom, alkali metal) Salt or amine salt), OH, NR ¹ R ² , NR ³ R ⁴ R ⁵ (R ¹ , R ² , R ³ , R ⁴ and R ⁵ are hydrogen or a hydrocarbon group, usually having 1 carbon atom) 10), and an epoxy group. When two or more resins, it is preferable to match the polarity of the functional groups, among others, a combination of a resin having a -SO 3 _M group. These binders are preferably 7 to 50 parts by mass and more preferably 10 to 35 parts by mass with respect to 100 parts by mass of the iron nitride magnetic powder. In particular, the combined use of 5 to 30 parts by mass of vinyl chloride resin and 2 to 20 parts by mass of polyurethane resin is preferable.

  Moreover, it is preferable to use together with said binder the thermosetting crosslinking agent which couple | bonds with the functional group etc. which are contained in a binder, and forms a crosslinked structure. Specific examples of the crosslinking agent include isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate; reaction products of isocyanate compounds and compounds having a plurality of hydroxyl groups such as trimethylolpropane; Examples include various polyisocyanates such as condensation products. A crosslinking agent is normally used in 10-50 mass parts with respect to 100 mass parts of binders.

  In the present embodiment, the magnetic layer may contain additives such as carbon black, a lubricant, and nonmagnetic powder for the purpose of improving characteristics such as conductivity, surface lubricity, and durability. Specifically, carbon black such as acetylene black, furnace black, and thermal black can be used as the carbon black. The content of carbon black is preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the iron nitride magnetic powder. Specific examples of the lubricant that can be used include fatty acids, fatty acid esters, and fatty acid amides having 10 to 30 carbon atoms. The content of the lubricant is preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the iron nitride magnetic powder. Specifically, for example, nonmagnetic powders such as alumina and silica can be used as the nonmagnetic powder. The content of the nonmagnetic powder is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the iron nitride magnetic powder.

  As the nonmagnetic support, conventionally used nonmagnetic supports for magnetic recording media can be used. For example, a plastic film having a thickness of usually 2 to 20 μm made of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide, etc. It is done.

  In the magnetic recording medium of the present embodiment, an undercoat layer may be provided between the nonmagnetic support and the magnetic layer. For the undercoat layer, non-magnetic powders such as titanium oxide, iron oxide, aluminum oxide, etc. for the purpose of controlling paint viscosity and tape rigidity; γ-iron oxide, Co-γ-iron oxide, magnetite, chromium oxide, Fe-Ni Alloy, Fe-Co alloy, Fe-Ni-Co alloy, barium ferrite, strontium ferrite, Mn-Zn ferrite, Ni-Zn ferrite, Ni-Cu ferrite, Cu-Zn ferrite, Mg-Zn ferrite, etc. The magnetic powder can be included. These may be used alone or in combination. The undercoat layer may contain carbon black such as acetylene black, furnace black, or thermal black in order to impart conductivity. As the binder used for the undercoat layer, the same resin as the binder used for the magnetic layer can be used.

  The magnetic layer is prepared by mixing an iron nitride-based magnetic powder, a binder, a triazole derivative containing a nitro group, and, if necessary, other additives with a solvent to prepare a magnetic paint, and then applying the magnetic paint on a nonmagnetic support. It can form by apply | coating to. In preparing the magnetic coating material, a coating material preparation method conventionally used in the manufacture of magnetic recording media can be used. In applying a magnetic coating material on a nonmagnetic support, conventional coating methods used in the production of magnetic recording media, such as gravure coating, roll coating, blade coating, and extrusion coating, can be used.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples. In the following, “part” means “part by mass”.

[Example 1]
(Preparation of iron nitride magnetic powder)
Substantially spherical magnetite particles (average particle diameter: 20 nm) having an yttrium and aluminum oxide layer formed on the surface were used as raw materials. The contents of yttrium and aluminum in this raw material were 1.2 atomic% and 9.8 atomic%, respectively, with respect to iron. This raw material was reduced by heating in a hydrogen stream at 450 ° C. for 2 hours to obtain an iron-based magnetic powder containing yttrium and aluminum. Next, the temperature was lowered to 150 ° C. over about 1 hour in a state where hydrogen gas was allowed to flow. When the temperature reached 150 ° C., the gas was switched to ammonia gas, and nitriding was performed for 30 hours while maintaining the temperature at 150 ° C. Thereafter, the temperature was lowered from 150 ° C. to 90 ° C. with ammonia gas flowing, and at 90 ° C., the ammonia gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours. Next, the temperature was lowered from 90 ° C. to 40 ° C. while flowing the mixed gas, and the mixture was held at 40 ° C. for about 10 hours, and then taken out into the air to prepare an iron nitride magnetic powder containing yttrium and aluminum. This iron nitride magnetic powder was confirmed to have an Fe ₁₆ N ₂ phase as a main phase by X-ray diffraction. Moreover, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was confirmed that the powder was a substantially spherical powder with an average particle diameter of 18 nm. Further, when the magnetic properties of the iron nitride magnetic powder were measured by applying a magnetic field of 1,270 kA / m (16 kOe), the saturation magnetization was 135.2 Am ² / kg (105.8 emu / g) and the coercive force. Was 219.7 kA / m (2,760 Oe).

(Preparation of magnetic paint)
A magnetic paint having the composition shown in Table 1 below was prepared using the iron nitride magnetic powder prepared above. In the preparation of the magnetic paint, a planetary ball mill (dispersion medium: zirconia beads) manufactured by Frichche was used to disperse the magnetic paint for 10 hours.

次に、この磁性塗料に５−ニトロベンゾトリアゾールを４部添加し、さらに２時間分散させた。分散後、ポリイソシアネート（日本ポリウレタン工業社製の「コロネートＬ」）を４部添加し、さらに１５分間分散させて磁性層形成用の磁性塗料を調製した。

Next, 4 parts of 5-nitrobenzotriazole was added to this magnetic coating material and further dispersed for 2 hours. After the dispersion, 4 parts of polyisocyanate (“Coronate L” manufactured by Nippon Polyurethane Industry Co., Ltd.) was added and further dispersed for 15 minutes to prepare a magnetic coating for forming a magnetic layer.

(Production of magnetic recording media)
The magnetic coating material prepared as described above was applied to the magnetic layer after drying while applying a magnetic field of 318.4 kA / m (4,000 Oe) onto a polyethylene terephthalate film having a thickness of 20 μm as a nonmagnetic support. The magnetic recording medium was manufactured by coating so that the thickness was about 2 μm.

[Example 2]
A magnetic recording medium was produced in the same manner as in Example 1 except that 8 parts of 5-nitrobenzotriazole was added.

[Example 3]
A magnetic recording medium was produced in the same manner as in Example 1 except that 2 parts of 5-nitrobenzotriazole was added.

[Example 4]
A magnetic recording medium was produced in the same manner as in Example 1 except that 10 parts of 5-nitrobenzotriazole was added.

[Comparative Example 1]
A magnetic recording medium was produced in the same manner as in Example 1 except that 5-nitrobenzotriazole was not added.

[Comparative Example 2]
A magnetic recording medium was produced in the same manner as in Example 1 except that 4 parts of 1,2,3-benzotriazole was added instead of 4 parts of 5-nitrobenzotriazole.

[Comparative Example 3]
A magnetic recording medium was produced in the same manner as in Example 1 except that 4 parts of 3-amino-1,2,4-triazole was added instead of 4 parts of 5-nitrobenzotriazole.
Each magnetic recording medium produced as described above was evaluated for the following magnetic characteristics and corrosivity of the GMR head. Table 2 shows the results.

(Magnetic properties)
A measurement sample was prepared by cutting each magnetic recording medium into a 1 cm square, and the coercive force and the square shape in the longitudinal direction were measured. Further, the coercive force and the square shape in the longitudinal direction after the measurement sample was stored at 60 ° C. and 90% RH for 168 hours were measured, and the coercive force before storage and the deterioration amount (%) from the square shape were examined.

(Head corrosive)
A magnetic recording medium was wound around a rotating drum equipped with a GMR head, and the rotating drum was rotated at 25 ° C. and 60% RH for 1 hour. After rotation, the presence or absence of corrosion on the surface of the GMR head was observed with an optical microscope, and the case where there was no corrosion was evaluated as ◯ and the case where there was corrosion was evaluated as x.

上記表２に示されるように、５−ニトロベンゾトリアゾールを２〜１０部、特に４〜８部用いた実施例の磁気記録媒体は高保磁力及び高角型を有することが分かる。また、実施例の磁気記録媒体は、ＧＭＲヘッドの腐食も抑えられていることが分かる。これに対して、比較例１の磁気記録媒体は、トリアゾール誘導体を使用していないため、窒化鉄系磁性粉末の分散性を向上することができず、保磁力及び角型が低くなっている。また、無置換あるいはアミノ基を有するトリアゾール誘導体を用いた比較例２及び３の磁気記録媒体は、同量のニトロ基を有するトリアゾール誘導体を用いた実施例１の磁気記録媒体に比べ、保磁力及び角型の向上効果が少なく、またヘッドの腐食を抑えられないことが分かる。

As shown in Table 2, it can be seen that the magnetic recording media of Examples using 2 to 10 parts, particularly 4 to 8 parts of 5-nitrobenzotriazole have a high coercive force and a high angle type. It can also be seen that the magnetic recording medium of the example also suppresses the corrosion of the GMR head. On the other hand, since the magnetic recording medium of Comparative Example 1 does not use a triazole derivative, the dispersibility of the iron nitride magnetic powder cannot be improved, and the coercive force and the square shape are low. Further, the magnetic recording media of Comparative Examples 2 and 3 using a triazole derivative having no substitution or an amino group had a coercive force and a magnetic recording medium in comparison with the magnetic recording medium of Example 1 using a triazole derivative having the same amount of a nitro group. It can be seen that the effect of improving the square shape is small and the corrosion of the head cannot be suppressed.

Claims (2)

  A magnetic recording medium on which a signal is reproduced by a reproducing head using a magnetoresistive element, a nonmagnetic support, and granular iron nitride having an average particle diameter of 5 to 50 nm on the nonmagnetic support And a magnetic layer containing a triazole derivative having a nitro group.   The magnetic recording medium according to claim 1, wherein the iron nitride magnetic powder contains at least one element selected from the group consisting of rare earth elements, boron, silicon, aluminum, and phosphorus.