JP2009245565A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium capable of surely compatibly achieving head wear reduction and excellent durability, in a high density magnetic recording and reproducing system using an MR head as a reproduction head. <P>SOLUTION: The magnetic recording medium has ferromagnetic powder, a binder, and a magnetic layer containing non-magnetic powder in this order on a non-magnetic support. The non-magnetic powder contains cubic crystal boron nitride powder whose average particle diameter is 0.01 to 0.10 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium having excellent running durability.

  In recent years, as a reproducing head suitable for higher density, a reproducing head based on an operating principle of magnetoresistance (MR) has been proposed and has begun to be used in a hard disk or the like. For example, Patent Documents 1 and 2 disclose a magnetic recording medium for use in a high-density recording / reproducing system using a magnetoresistive head (MR head) as a reproducing head. MR heads / TMR heads can reproduce output several times as much as conventional induction type magnetic heads and do not use induction coils, which significantly reduces equipment noise such as impedance noise and magnetic properties. By reducing the noise of the recording medium, a large S / N ratio can be obtained, and the high density recording characteristics can be dramatically improved.

An MR head is an essential head for high-density recording, but since a hard material such as AlTiC (alumina titanium carbide) is used for the head substrate, the MR element, shield layer, insulating layer portion between the head substrates is used. Step wear (partial wear) occurs that selectively wears only, and the output tends to decrease in a high-density recording area. Also, since the MR element is a thin film, if the entire head is worn much, the MR element itself is worn away.
On the other hand, if the amount of non-magnetic powder in the magnetic layer is extremely reduced or excessively soft non-magnetic powder is used to prevent head wear, the true contact area between the head and tape increases when sliding with the head. When the sliding resistance is increased or the hardness of the tape surface is excessively softer than that of the head, there is a problem that the tape is damaged and durability is deteriorated. For this reason, there has been a demand for a magnetic recording medium that does not cause uneven head wear or overall head wear but has good durability.

Patent Document 3 discloses a magnetic recording medium containing boron nitride having a particle diameter of 0.04 μm in the magnetic layer, and Patent Document 4 discloses magnetic recording containing boron nitride having a particle diameter of 0.01 to 1 μm as an abrasive in the magnetic layer. Patent Document 5 discloses a magnetic recording medium containing carbide having a particle size of 0.02 to 0.10 μm as an abrasive.
JP 2003-22515 A JP 2003-272124 A JP-A-10-79116 JP 2006-277837 A JP 2007-26564 A

However, the boron nitride used in the technologies described in Patent Document 3 and Patent Document 4 are both amorphous in terms of their particle diameters based on the common general knowledge at the time of filing them, Further, neither Patent Document 3 nor Patent Document 4 discloses anything about achieving both head wear suppression and medium durability when an MR head is used as a reproducing head. Further, the technique described in Patent Document 5 aims to achieve both the suppression of head wear and the durability of the medium when an MR head is used as a reproducing head, but it has not been satisfactory.
Under such circumstances, an object of the present invention is to provide a magnetic recording medium capable of more reliably achieving both head wear reduction and excellent durability in a high-density magnetic recording / reproducing system using an MR head as a reproducing head. .

Nanoparticles are being developed in anticipation of high functionality, but it is known that the synthesis of nitride and carbide nanoparticles is difficult compared to inorganic oxide nanoparticles. Boron nitride nanoparticles are difficult to synthesize and there are few examples of synthesis. On a commercial basis, boron nitride nanoparticles: nanoparticles having a particle size of 200 nm or less, particularly 100 nm or less, have not been put to practical use. In addition, amorphous particles are likely to be produced at nanoparticle size, and control of crystallinity is one of the important issues for high functionality. In particular, it was more difficult to control the crystallinity of boron nitride with the nanoparticle size. Boron nitride nanoparticles and their crystallinity control method are under intensive study. Recently, researches on the synthesis of cubic boron nitride nanoparticles and hexagonal boron nitride nanoparticles with high crystallinity have been advanced, and small-scale synthesis Cases have been reported.
Using the present crystalline / cubic boron nitride nanoparticles and / or hexagonal boron nitride nanoparticles as a nonmagnetic powder in a magnetic layer of a magnetic recording medium having a magnetic layer on a nonmagnetic support I found that it can be solved.

Means for achieving the object is as follows.
(1) A magnetic recording medium having a magnetic layer containing a ferromagnetic powder, a binder, and a nonmagnetic powder on a nonmagnetic support, wherein the nonmagnetic powder has an average particle size of 0.01 to 0.10 μm. A magnetic recording medium comprising a cubic boron nitride powder.
(2) The magnetic recording medium according to (1) above, which has a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer.
(3) The magnetic recording medium according to (1) or (2), wherein the nonmagnetic powder of the magnetic layer contains hexagonal boron nitride powder having an average particle size of 0.01 to 0.10 μm.
As described above, the magnetic recording medium of the present invention uses cubic boron nitride nanoparticles or cubic boron nitride nanoparticles in addition to cubic boron nitride nanoparticles as nonmagnetic powder contained in the magnetic layer. .

  According to the present invention, it is possible to provide a magnetic recording medium for high density recording suitable for a high density magnetic recording / reproducing system using an MR / TMR head as a reproducing head.

Hereinafter, the present invention will be described in more detail.
The magnetic recording medium of the present invention is a magnetic recording medium having a magnetic layer containing a ferromagnetic powder, a binder and a nonmagnetic powder on a nonmagnetic support, and the nonmagnetic powder has an average particle size of 0.01. A magnetic recording medium comprising ˜0.10 μm cubic boron nitride powder.

[Nonmagnetic powder (contained in magnetic layer)]
The magnetic recording medium of the present invention contains a cubic boron nitride powder (hereinafter also simply referred to as cubic boron nitride) having an average particle size of 0.01 to 0.10 μm as a nonmagnetic powder in a magnetic layer. As a result, head wear, particularly uneven wear of the MR head, can be suppressed. This is presumably because the balance between the hardness of the magnetic layer and the MR head was maintained by using cubic boron nitride having properties close to those of members (such as Altic) constituting the MR head. By adopting cubic boron nitride, the hardness of the non-magnetic powder (cubic boron nitride) contained in the head and the magnetic layer is kept at the same level, and it is possible to prevent mutual wear, so that the head does not wear, It is thought that the effect which does not damage a tape can also be acquired.

  The cubic boron nitride has an average particle size in the range of 0.01 to 0.10 μm. If the average particle size is less than 0.01 m, the head wear can be suppressed, but the medium is damaged and the durability is lowered. On the other hand, when the average particle diameter of the cubic boron nitride exceeds 0.10 μm, head wear becomes remarkable and there is a risk of causing a decrease in output. The average particle size of the cubic boron nitride is preferably 0.02 to 0.09 μm, and more preferably 0.02 to 0.08 μm.

  The cubic boron nitride preferably has a Mohs hardness of 8 or more and less than 10, and more preferably has a Mohs hardness of 9 or more and less than 10. As the shape, a spherical shape, a cubic shape, an indeterminate shape, or the like can be appropriately selected.

  In the magnetic recording medium of the present invention, the content of the cubic boron nitride in the magnetic layer can be 0.1 to 15 parts by mass per 100 parts by mass of the ferromagnetic powder. If the cubic boron nitride content is within the above range, head wear can be suppressed while maintaining durability. The content is preferably 0.2 to 10 parts by mass, more preferably 0.3 to 7 parts by mass.

In the magnetic recording medium of the present invention, as the nonmagnetic powder contained in the magnetic layer, in addition to the cubic boron nitride, a hexagonal boron nitride powder having an average particle size of 0.01 to 0.10 μm (hereinafter simply referred to as hexagonal crystal). (Also referred to as boron nitride) is preferably used in combination. It is thought that lubricity is imparted by hexagonal boron nitride.
When the average particle size of the hexagonal boron nitride is less than 0.01 μm, dispersion is difficult. On the other hand, if the average particle size of the hexagonal boron nitride exceeds 0.10 μm, the magnetic layer surface protrusions may increase, causing a decrease in output. The average particle diameter of the hexagonal boron nitride is preferably 0.02 to 0.09 μm, and more preferably 0.02 to 0.08 μm.
The content of the hexagonal boron nitride in the magnetic layer can be 0.1 to 15 parts by mass per 100 parts by mass of the ferromagnetic powder. If the hexagonal boron nitride content is within the above range, head wear can be suppressed while maintaining durability. The content is preferably 0.2 to 8 parts by mass, more preferably 0.3 to 5 parts by mass.

  In the present invention, the crystallinity, particle size, hardness, etc. of cubic boron nitride and / or hexagonal boron nitride added to the magnetic layer are determined according to the particle synthesis conditions (reaction conditions in the case of high-frequency plasma method, thermal plasma method, CVD method ( (E.g., temperature, time, etc.), laser method (e.g., laser irradiation conditions in the case of liquid phase laser method), and to narrow down the desired particle size and / or particle size distribution, centrifugal classification, etc. The particle size and particle size distribution can be set to the above ranges by combining the classification treatments.

In the present invention, nonmagnetic powders other than cubic boron nitride and hexagonal boron nitride can be used in combination as the nonmagnetic powder contained in the magnetic layer. As the nonmagnetic powder used in combination, conventionally used nonmagnetic powder, for example, α-alumina, β-alumina, fine particle diamond, chromium oxide, cerium oxide, α-iron oxide, corundum having an α conversion ratio of 90% or more, Mention may be made of carbides composed of titanium oxide, silicon dioxide, TiC, SiC, ZrC, B ₄ C, WC, and VC. The particle size of the nonmagnetic powder used in combination is preferably about the same as that of cubic boron nitride (0.02-0.10 μm). When non-magnetic powder other than cubic boron nitride is used in combination, in order not to impair the effect of cubic boron nitride, which is a non-magnetic powder that exhibits the main effects in the present invention, the amount is equal to or less than cubic boron nitride. Can be used in combination.

[Magnetic layer]
In the present invention, examples of the ferromagnetic powder contained in the magnetic layer include ferromagnetic metal powder and hexagonal ferrite powder.

  As the ferromagnetic metal powder, it is preferable to use a ferromagnetic metal powder containing α-Fe as a main component. In addition to predetermined atoms, ferromagnetic metal powder includes Al, Si, Ca, Mg, Ti, Cr, Cu, Y, Sn, Sb, Ba, W, La, Ce, Pr, Nd, P, Co, Mn, An atom such as Zn, Ni, Sr, or B may be contained. In particular, at least one of Al, Ca, Mg, Y, Ba, La, Nd, Sm, Co, and Ni is preferably included in addition to α-Fe. Co is particularly preferable when making an alloy with Fe because saturation magnetization is increased and demagnetization is improved. The Co content is preferably 1 atom% to 40 atom%, more preferably 15 atom% to 35 atom%, and more preferably 20 atom% to 35 atom% with respect to Fe. The content of rare earth elements such as Y is preferably 1.5 atom% to 18 atom%, more preferably 3 atom% to 16 atom%, more preferably 4 atom% to 15 atom% with respect to Fe. It is. The Al content is preferably 1.5 atomic percent to 12 atomic percent with respect to Fe, more preferably 3 atomic percent to 10 atomic percent, and more preferably 4 atomic percent to 9 atomic percent. The rare earth and Al containing Y function as a sintering inhibitor, and when used in combination, a higher sintering prevention effect can be obtained. These ferromagnetic metal powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent or the like, which will be described later. 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. Examples of the method for producing the ferromagnetic metal powder include the following methods. Reduction of hydrous iron oxide and iron oxide with anti-sintering treatment with reducing gas such as hydrogen to obtain Fe or Fe-Co particles, reduction of complex organic acid salt (mainly oxalate) and hydrogen A method of reducing with a reactive gas, a method of thermally decomposing a metal carbonyl compound, a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal, a metal at a low pressure For example, the powder is obtained by evaporating in an inert gas. The ferromagnetic metal powder thus obtained can be subjected to a known slow oxidation treatment. As the gradual oxidation treatment, there is a method in which hydrous iron oxide or iron oxide is reduced with a reducing gas such as hydrogen, and an oxide film is formed on the surface by controlling the partial pressure, temperature and time of the oxygen-containing gas and the inert gas. It is preferable because the amount of demagnetization is small.

The specific surface area by BET method of the ferromagnetic metal powder (S _BET) is preferably 40 to 100 m ² / g, more preferably 45~90m ² / g. If it is 40 m ² / g or more, low noise is obtained, and if it is 100 m ² / g or less, the surface smoothness is high and preferable. The crystallite size of the ferromagnetic metal powder is preferably 60 to 180 mm, preferably 70 to 170 mm, and more preferably 80 to 165 mm. The average major axis length of the ferromagnetic metal powder is preferably 20 to 50 nm, more preferably 30 to 45 nm. If the average major axis length of the ferromagnetic metal powder is 20 nm or more, there is no loss of magnetization due to thermal fluctuation, and if it is 50 nm or less, the error rate deterioration due to noise rise can be avoided. The average acicular ratio {average of (major axis length / minor axis length)} of the ferromagnetic metal powder is preferably 2 to 15, and more preferably 3 to 10. Saturation magnetization σs of the ferromagnetic metal powder is preferably from 60~170A · m ² / kg, more preferably 70~160A · m ² / kg, and more preferably from 80~160A · m ² / kg. The coercive force of the ferromagnetic metal powder is preferably 1400 to 3500 oersted (111 to 279 kA / m), more preferably 1600 to 3000 oersted (127 to 239 kA / m).

The moisture content of the ferromagnetic metal powder is preferably 0.1 to 2% by mass. 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 6-12, preferably 7-11. Ferromagnetic metal powder SA (stearic acid) adsorption amount (a measure of the basic points of the surface) may be a 1~15μmol / m ^2, preferably 2~10μmol / m ^2, more preferably 3 to 8 [mu] mol / m ² . When a ferromagnetic metal powder having a large amount of stearic acid adsorption is used, it is preferable to produce a magnetic recording medium by modifying the surface of the ferromagnetic metal powder with an organic substance that strongly adsorbs to the surface. The ferromagnetic metal powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, Sr, NH ₄ , SO ₄ , Cl, NO ₂ and NO ₃ . Although it is preferable that these are essentially not present, the characteristics are not affected if the total sum of the ions is about 300 ppm or less. In addition, the ferromagnetic metal powder used in the present invention preferably has fewer vacancies, and its value is preferably 20% by volume or less, and more preferably 5% by volume or less. Further, the shape may be any of needle shape, rice grain shape, and spindle shape as long as the powder size and magnetic characteristics shown above are satisfied, and needle shape is particularly preferable. It is preferable that the ferromagnetic metal powder itself has a small SFD (switching-field distribution). When the SFD of the magnetic recording medium is small, the magnetization reversal is sharp and the peak shift is small, which is suitable for high-density digital magnetic recording. It is preferable to reduce the Hc distribution of the ferromagnetic metal powder. In order to reduce the Hc distribution, there are methods such as improving the particle size distribution of goethite in the ferromagnetic metal powder, using monodispersed αFe ₂ O ₃ , and preventing sintering between particles.

  Examples of the hexagonal ferrite powder used in the present invention include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and various substitutes thereof, Co substitutes, and the like. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and composite magnetoplumbite-type barium ferrite and strontium ferrite partially containing a spinel phase. In addition to predetermined atoms, Al, Si, S, Nb, Sn, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, W, Re, Au, Bi , La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, B, Ge, and Nb may be included. Generally, Co-Zn, Co-Ti, Co-Ti-Zr, Co-Ti-Zn, Ni-Ti-Zn, Nb-Zn-Co, Sn-Zn-Co, Sn-Co-Ti, Nb-Zn, etc. Those added with these elements can be used. Some raw materials and manufacturing methods contain specific impurities. The average plate diameter is preferably 10 to 40 nm, more preferably 10 to 30 nm. In particular, when reproducing with a magnetoresistive head (MR head) in order to increase the track density, it is necessary to reduce the noise, and the average plate diameter is preferably 40 nm or less. I can't expect magnetization. If it is larger than 40 nm, the noise is high and none is suitable for high-density magnetic recording. The average plate thickness is preferably 4 to 15 nm. If the average plate thickness is 4 nm or more, stable production is possible, and if the average plate thickness is 15 nm or less, sufficient orientation can be obtained.

The plate ratio (plate diameter / plate thickness) is preferably 1 to 15, more preferably 1 to 7. When the plate ratio is small, the filling property in the magnetic layer is preferably high, but sufficient orientation cannot be obtained. When it is larger than 15, noise increases due to stacking between powders. The specific surface area according to the BET method in this powder size range is 30 to ²⁰⁰ m ² / g. The specific surface area is generally referred to as an arithmetic calculation value from the powder plate diameter and plate thickness. The narrower the distribution of the powder plate diameter and plate thickness, the better. Although it is difficult to digitize, it can be compared by randomly measuring about 500 powder TEM (transmission electron microscope) photographs. In many cases, the distribution is not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average powder size = 0.1 to 1.5. In order to sharpen the powder size distribution, the powder generation reaction system is made as uniform as possible, and the generated powder is subjected to a distribution improvement process. For example, a method of selectively dissolving ultrafine powder in an acid solution is also known. According to the vitrification crystal method, a more uniform powder can be obtained by performing heat treatment a plurality of times to separate nucleation and growth.

In general, hexagonal ferrite powder having a coercive force Hc of about 500 to 5000 oersted (40 to 398 kA / m) can be produced. Higher Hc is more advantageous for high density recording, but is limited by the capacity of the recording head. Hc can be controlled by powder size (plate diameter / plate thickness), type and amount of contained elements, element substitution site, powder generation reaction conditions, and the like. The saturation magnetization σs can be 30 to 70 A · m ² / kg. σs tends to decrease as the powder becomes finer. In order to improve σs, heat treatment temperature is set stepwise to increase crystallinity, temperature rise due to exothermic reaction accompanying crystallization is uniformly controlled, or compensated and crystallized at uniform temperature, hexagonal system There are methods such as controlling the substitution site and spin (↑ ↓) by the substitution element of Fe in ferrite and further densifying the surface coating by surface treatment. It is also possible to use W-type hexagonal ferrite. When the hexagonal ferrite powder is dispersed, the surface of the hexagonal ferrite powder is treated with a material suitable for the dispersion medium and the polymer. As the surface treatment agent, an inorganic compound or an organic compound can be used. Typical examples of the main compound include oxides or hydroxides such as Si, Al, and P, various silane coupling agents, and various titanium coupling agents. The amount can be 0.1 to 10% by mass relative to the hexagonal ferrite powder. The pH of the hexagonal ferrite powder is also important for dispersion. Usually, about 4 to 12 has optimum values depending on the dispersion medium and polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Moisture contained in the hexagonal ferrite powder also affects the dispersion. Although there is an optimum value depending on the dispersion medium and the polymer, 0.1 to 2.0% by mass is usually selected.

  The hexagonal ferrite is manufactured by mixing (1) a metal oxide that replaces barium carbonate, iron oxide, and iron with boron oxide as a glass-forming substance so as to have a desired ferrite composition, and then melting and quenching. Vitrification crystal method to obtain barium ferrite crystal powder after making it amorphous and then reheating, (2) neutralizing barium ferrite composition metal salt solution with alkali, Hydrothermal reaction method to obtain barium ferrite crystal powder by liquid phase heating at 100 ° C or higher after removal, washing, drying and grinding, (3) neutralizing barium ferrite composition metal salt solution with alkali, by-product There is a coprecipitation method in which barium ferrite crystal powder is obtained by drying, treating at 1100 ° C. or less, and pulverizing, but the production method is not limited.

In the present invention, examples of the carbon black that can be used in the magnetic layer include a furnace for rubber, a thermal for rubber, a black for color, conductive carbon black, and acetylene black. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, average particle size is 5 nm to 300 nm, pH is 2 to 10, moisture content is 0.1 to 10% by mass, tap density is 0. It is preferably 1 to 1 g / cc. Specific examples of carbon black used in the magnetic layer include Cabot's BLACKPEARLS 2000, 1300, 1000, 900, 905, 800, 700, VULCAN XC-72, Asahi Carbon # 80, # 60, # 55, # 50, # 35, Mitsubishi Chemical # 2400B, # 2300, # 900, # 1000 # 30, # 40, # 10B, Colombian Carbon CONDUCTEXSC, RAVEN 150, 50, 40, 15, RAVEN-MT-P, Akzo Ketjen Black EC made by the company, etc. are mentioned. Carbon black may be surface-treated with a dispersant or the like, 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 carbon black is used, it is preferably used in an amount of 0.1 to 30% by mass with respect to the ferromagnetic powder. Carbon black functions to prevent the magnetic layer from being charged, reduce the friction coefficient, impart light-shielding properties, and improve the film strength. These differ depending on the carbon black used. Therefore, in the present invention, it is possible to select the type and amount of carbon black to be used based on the above-mentioned characteristics such as particle size, oil absorption, electrical conductivity, pH, etc. so as to obtain desired physical properties. preferable. For the carbon black that can be used in the present invention, for example, “Carbon Black Handbook (Edited by Carbon Black Association)” can be referred to.

  In the present invention, examples of the binder used in the magnetic layer include conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. 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, Examples thereof include polymers or copolymers containing vinyl ether as a constituent 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, polyesters. Examples thereof include a mixture of resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like. These resins are described in detail in “Plastic Handbook” issued by Asakura Shoten. It is also possible to use a known electron beam curable resin. 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, known ones 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, CN, etc. It is preferable to use one in which at least one polar group is introduced by copolymerization or addition reaction. The amount of such a polar group can be 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.

  Specific examples of these binders used in the present invention include VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYES, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC, PKFE, Union Carbide, MPR-TA, MPR-TA5, MPR-TAL, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, MPR-TAO, manufactured by Nissin Chemical Industry Co., Ltd. 1000 W, DX80, DX81, DX82, DX83, 100FD, Nippon Zeon MR-104, MR-105, MR110, MR100, MR555, 400X-110A, Nippon Polyurethane Nipporan N2301, N2302, N2304, Dainippon Ink Pandex T-5105, T-R3080, T-5201 ,bar D-400, D-210-80, Crisbon 6109, 7209, Toyobo's Byron UR8200, UR8300, UR-8700, RV530, RV280, Daiichi Seika's Daiferamin 4020, 5020, 5100, 5300, 9020, 9022, 7020 , Mitsubishi Chemical MX5004, Sanyo Kasei Samprene SP-150, Asahi Kasei Saran F310, F210, and the like.

The binder used in the magnetic layer can be generally used in the range of 5 to 50% by mass, preferably in the range of 10 to 30% by mass with respect to the ferromagnetic 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. In the present invention, when polyurethane is used, the glass transition temperature is usually −50 to 150 ° C., preferably 0 to 100 ° C., the breaking elongation is 100 to 2000%, and the breaking stress is 0.05 to 10 kg / mm ² (0. 49 to 98 MPa) and a yield point of 0.05 to 10 kg / mm ² (0.49 to 98 MPa) is preferably used.

  Polyisocyanates used in the present invention include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate. And the like, products of these isocyanates and polyalcohols, polyisocyanates produced by condensation of isocyanates, and the like can be used. Commercially available product names of these isocyanates include: Nippon Polyurethane Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Takenate D-102, Takenate D-110N, Takenate D -200, Takenate D-202, Sumitomo Bayer's Death Module L, Death Module IL, Death Module N, Death Module HL, etc., which are used alone or in combination of two or more using the difference in curing reactivity Can be used.

  In the present invention, additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, and the like can be used for the magnetic layer. Specifically, molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, poly Glycol, alkyl phosphate ester and alkali metal salt thereof, alkyl sulfate ester and alkali metal salt thereof, polyphenyl ether, phenylphosphonic acid, α-naphthyl phosphoric acid, phenyl phosphoric acid, diphenyl phosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones , Various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds or branched And a metal salt thereof (Li, Na, K, Cu, etc.) or a monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol (unsaturated) having 12 to 22 carbon atoms. A bond may be included or branched), an alkoxy alcohol having 12 to 22 carbon atoms (which may include an unsaturated bond or branched), and a monobasic group having 10 to 24 carbon atoms Fatty acids (which may contain unsaturated bonds or may be branched) and any one of monovalent, divalent, trivalent, tetravalent, pentavalent and hexavalent alcohols having 2 to 12 carbon atoms (unsaturated) Mono-fatty acid ester or di-fatty acid ester or tri-fatty acid ester, fatty acid ester of monoalkyl ether of alkylene oxide polymer, fatty acid having 8 to 22 carbon atoms, which may contain a saturated bond or may be branched) Amides, aliphatic amines having 8 to 22 carbon atoms, and the like can be used.

  Specific examples of these fatty acids include capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, isostearic acid, and the like. . Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, 2-octyldodecyl palmitate 2-hexyldecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleyl, oleyl alcohol, stearyl for alcohols Alcohol, lauryl alcohol, etc. are mentioned. 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. Cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, Amphoteric surfactants such as alkylbedine type can also be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides in addition to the main components. Absent. These impure amounts are preferably 30% by mass or less, more preferably 10% by mass or less. In general, the total amount of lubricant can be in the range of 0.1 to 50% by weight, preferably 2 to 25% by weight, with respect to the ferromagnetic powder.

[Nonmagnetic layer]
The magnetic recording medium of the present invention may have a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The nonmagnetic powder contained in the nonmagnetic layer can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Examples of inorganic compounds include α-alumina, β-alumina, γ-alumina, α-alumina of 90 to 100%, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, oxidation Titanium, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like can be used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate, and more preferred is titanium dioxide.

The average particle size of these nonmagnetic powders is preferably 0.005 to 2 μm, but if necessary, nonmagnetic powders having different average particle sizes can be combined, or even a single nonmagnetic powder can have a wide particle size distribution. The same effect can be given. Particularly preferably, the non-magnetic powder has an average particle size of 0.01 μm to 0.2 μm. The pH of the nonmagnetic powder is particularly preferably between 6 and 9. The specific surface area of the nonmagnetic powder is preferably 1 to 100 m ² / g, more preferably 5 to 50 m ² / g, more preferably from 7~40m ² / g. The crystallite size of the nonmagnetic powder is preferably 0.01 μm to 2 μm. The amount of oil absorption using DBP is preferably 5 to 100 ml / 100 g, more preferably 10 to 80 ml / 100 g, still more preferably 20 to 60 ml / 100 g. The specific gravity is preferably 1 to 12, more preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedron shape, and a plate shape.

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 first treating with alumina and then treating the surface layer with silica, or vice versa. 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 into the nonmagnetic layer to reduce Rs, which is a known effect, and to obtain a desired micro Vickers hardness. For this purpose, furnace black for rubber, thermal black for rubber, carbon black for color, acetylene black and the like can be used. The specific surface area of the carbon black is 100 to 500 m ² / g, preferably 150~400m ² / g, DBP oil absorption 20 to 400 ml / 100 g, preferably it is respectively suitable is a 30 to 200 ml / 100 g. The average particle size of carbon black is 5 to 80 nm (mμ), preferably 10 to 50 nm (mμ), more preferably 10 to 40 nm (mμ). 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. Specific examples of carbon black used in the present invention include BLACKPEARLS 2000, 1300, 1000, 900, 800, 880, 700, VULCAN XC-72, manufactured by Cabot Corporation, # 3050B, 3150B, 3250B, # 3750B, # 3950B, # 950, # 650B, # 970B, # 850B, MA-600, Columbia Carbon Corporation CONDUCTEXSC, RAVEN 8800, 8000, 7000, 5750, 5250, 3500, 2100, 2000, 1800, 1500, 1255, 1250, Ketjen Black EC manufactured by Akzo Corporation, and the like.

The binder, lubricant, dispersant, additive, solvent, dispersion method, etc. used for the nonmagnetic layer can be those of the magnetic layer. 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.
A nonmagnetic layer coating solution prepared from the above materials can be applied onto a nonmagnetic support to form a nonmagnetic layer.

  All or part of the additives used in the present invention may be added in any step of producing the magnetic layer coating solution and nonmagnetic layer coating solution, for example, when mixed with the ferromagnetic powder before the kneading step In addition, when adding in a kneading step with a ferromagnetic powder, a binder and a solvent, adding in a dispersing step, adding after dispersing, adding in just before coating, and the like. Moreover, after applying a magnetic layer according to the purpose, the object may be achieved by applying a part or all of the additive by simultaneous or sequential application. Depending on the purpose, a lubricant can be applied to the surface of the magnetic layer after calendering or after completion of the slit. In the present invention, a known organic solvent can be used, and for example, a solvent described in JP-A-6-68453 can be used.

[Layer structure]
In the magnetic recording medium of the present invention, the thickness of the nonmagnetic support is, for example, 2 to 100 μm, preferably 2 to 80 μm. In the case of computer tape, the nonmagnetic support has a thickness in the range of 3.0 to 6.5 μm (preferably 3.0 to 6.0 μm, more preferably 4.0 to 5.5 μm). Can be used.

  An undercoat layer may be provided between the nonmagnetic support and the nonmagnetic layer or magnetic layer to improve adhesion. The undercoat layer thickness is, for example, 0.01 to 0.5 μm, preferably 0.02 to 0.5 μm. The magnetic recording medium of the present invention may be a disk-shaped medium in which a nonmagnetic layer and a magnetic layer are provided on both sides of a support, or a tape-shaped medium or a disk-shaped medium provided only on one side. In this case, a back coat layer may be provided on the side opposite to the non-magnetic layer and the magnetic layer in order to obtain effects such as antistatic and curl correction. This thickness is, for example, 0.1 to 4 μm, preferably 0.3 to 2.0 μm. Known undercoat layers and backcoat layers can be used.

  In the magnetic recording medium of the present invention, the thickness of the magnetic layer is optimized by the saturation magnetization amount of the head to be used, the head gap length, and the band of the recording signal, preferably 0.03 to 0.10 μm, more preferably 0.03 to 0.08 μm. 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 usually 0.2 to 5.0 μm, preferably 0.3 to 3.0 μm, and more preferably 1.0 to 2.5 μm. The non-magnetic layer exhibits its effect if it is substantially non-magnetic. For example, even if a small amount of magnetic material is included as an impurity or intentionally, the effect of the present invention is exhibited. Needless to say, the configuration can be considered substantially the same as the invention.

[Back coat layer]
Generally, a magnetic tape for recording computer data is strongly required to have repeated running characteristics as compared with a video tape and an audio tape. In order to maintain such high running durability, the back coat layer preferably contains carbon black and inorganic powder.

  As carbon black, it is preferable to use a combination of two types having different average particle diameters. In this case, it is preferable to use a combination of fine particle carbon black having an average particle size of 10 to 50 nm and coarse particle carbon black having an average particle size of 70 to 300 nm. In general, by adding fine carbon black as described above, the surface electrical resistance of the backcoat layer can be set low, and the light transmittance can also be set low. Some magnetic recording devices utilize the light transmittance of the tape and are used for the operation signal. In such a case, the addition of particulate carbon black is particularly effective. In addition, particulate carbon black is generally excellent in retention of liquid lubricants, and contributes to reduction of the friction coefficient when used in combination with lubricants.

Specific products of the particulate carbon black include the following. In addition, the average particle size is shown in parentheses.
BLACK PEARLS 800 (17 nm), BLACK PEARLS 1400 (13 nm), BLACK PEARLS 1300 (13 nm), BLACK PEARLS 1100 (14 nm), BLACK PEARLS 1000 (16 nm), BLACK PEARLS 900 (15 nm), BLACK PEARLS 8 PEARLS 4630 (19 nm), BLACK PEARLS 460 (28 nm), BLACK PEARLS 430 (28 nm), BLACK PEARLS 280 (45 nm), MONARCH 800 (17 nm), MONARCH 14000 (13 nm), MONARCH 1300 (13 nm), MONARCH 1 MONARCH 1000 (16nm MONARCH 900 (15 nm), MONARCH 880 (16 nm), MONARCH 630 (19 nm), MONARCH 430 (28 nm), MONARCH 280 (45 nm), REGAL 330 (25 nm), REGAL 250 (34 nm), REGAL 99 (38 nm), REGAL 400 (25 nm), REGAL 660 (24 nm) (above, manufactured by Cabot), RAVEN2000B (18 nm), RAVEN1500B (17 nm), Raven 7000 (11 nm), Raven 5750 (12 nm), Raven 5250 (16 nm), Raven 3500 (13 nm) ), Raven 2500 ULTRA (13 nm), Raven 2000 (18 nm), Raven 1500 (17 nm), Rav n 1255 (21 nm), Raven 1250 (20 nm), Raven 1190 ULTRA (21 nm), Raven 1170 (21 nm), Raven 1100 ULTRA (32 nm), Raven 1080 ULTRA (28 nm), Raven 1060 ULTRA 30 nm, Raven 1060 ULTRA 30 nm Raven 880 ULTRA (30 nm), Raven 860 (39 nm), Raven 850 (34 nm), Raven 820 (32 nm), Raven 790 ULTRA (30 nm), Raven 780 ULTRA (29 nm), Raven 760 UL TR Manufactured by Asahi Co., Ltd.), Asahi # 90 (19 nm), Asahi # 80 (22 nm), Asahi # 70 (28 nm), Asahi F-200 ( 5 nm), Asahi # 60 HN (40 nm), Asahi # 60 (45 nm), HS-500 (38 nm), Asahi # 51 (38 nm) (above, manufactured by Asahi Carbon Co., Ltd.), # 2700 (13 nm), # 2650 (13 nm) # 2400 (14 nm), # 1000 (18 nm), # 950 (16 nm), # 850 (17 nm), # 750 (22 nm), # 650 (22 nm), # 52 (27 nm), # 50 (28 nm), # 40 (24 nm), # 30 (30 nm), # 25 (47 nm), # 95 (40 nm), CF9 (40 nm) (manufactured by Mitsubishi Chemical Corporation), PRINTEX90 (14 nm), PRINTEX95 (15 nm), PRINTEX85 (16 nm) , PRINTEX 75 (17 nm) (above, manufactured by Degussa), # 3950 (16 nm) (Mitsubishi Chemical Industry ( ) Co., Ltd.).

  Examples of specific products of the coarse particle carbon black include BLACKPEARLS 130 (75 nm), MONARCH 120 (75 nm), Regal 99 (100 nm) (manufactured by Cabot Corporation), Raven 450 (75 nm), Raven 420 (86 nm), Raven 410 (101 nm), Raven 22 (83 nm), Raven MTP (275 nm) (above Colombian Carbon), Asahi 50H (85 nm), Asahi # 51 (91 nm), Asahi # 50 (80 nm), Asahi # 35 (78 nm), Asahi # 15 (122 nm) (above, manufactured by Asahi Carbon Co., Ltd.), # 10 (75 nm), # 5 (76 nm), # 4010 (75 nm) (above, manufactured by Mitsubishi Chemical Corporation), thermal black (270 nm) (Manufactured by Khan Calve).

When two types of backcoat layers having different average particle sizes are used, the content ratio (mass ratio) of fine particle carbon black having an average particle size of 10 to 50 nm and coarse particle carbon black having an average particle size of 70 to 300 nm The former / the latter is preferably in the range of 100 / 0.5 to 100/100, and more preferably in the range of 100/1 to 100/50.
The content of carbon black in the backcoat layer (the total amount when two types are used) is usually in the range of 30 to 100 parts by mass with respect to 100 parts by mass of the binder, It is the range of 45-95 mass parts.

  It is preferable to use two types of inorganic powders having different hardnesses. Specifically, it is preferable to use a soft inorganic powder having a Mohs hardness of 3 to 4.5 and a hard inorganic powder having a Mohs hardness of 5 to 9. By adding a soft inorganic powder having a Mohs hardness of 3 to 4.5, the friction coefficient can be stabilized by repeated running. Moreover, when the hardness is within this range, the sliding guide pole is not scraped. Moreover, it is preferable that the average particle diameter of this inorganic powder exists in the range of 30-50 nm.

  Examples of the soft inorganic powder having a Mohs hardness of 3 to 4.5 include calcium sulfate, calcium carbonate, calcium silicate, barium sulfate, magnesium carbonate, zinc carbonate, and zinc oxide. These can be used alone or in combination of two or more.

  The content of the soft inorganic powder in the backcoat layer is preferably in the range of 10 to 140 parts by mass, more preferably 35 to 100 parts by mass with respect to 100 parts by mass of carbon black.

  By adding a hard inorganic powder having a Mohs hardness of 5 to 9, the strength of the backcoat layer is enhanced and the running durability is improved. When these inorganic powders are used together with carbon black or the soft inorganic powder, there is little deterioration even with repeated sliding, and a strong backcoat layer is obtained. In addition, the addition of the inorganic powder provides an appropriate polishing force and reduces the adhesion of shavings to the tape guide pole and the like. In particular, when used in combination with soft inorganic powder, the sliding characteristics with respect to the guide pole having a rough surface are improved, and the friction coefficient of the backcoat layer can be stabilized. The average particle size of the hard inorganic powder is preferably in the range of 80 to 250 nm (more preferably 100 to 210 nm).

Examples of the hard inorganic powder having a Mohs hardness of 5 to 9 include α-iron oxide, α-alumina, and chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Of these, α-iron oxide or α-alumina is preferred. Content of hard inorganic powder is 3-30 mass parts normally with respect to 100 mass parts of carbon black, Preferably, it is 3-20 mass parts.

  When the soft inorganic powder and the hard inorganic powder are used in combination in the backcoat layer, the difference in hardness between the soft inorganic powder and the hard inorganic powder is 2 or more (more preferably 2.5 or more, particularly preferably 3 or more). It is preferable to select and use a soft inorganic powder and a hard inorganic powder. It is preferable that the back coat layer contains the two types of inorganic powders having different specific Mohs hardnesses each having a specific average particle size and the two types of carbon blacks having different average particle sizes.

  The back coat layer can contain a lubricant. The lubricant can be appropriately selected from the lubricants listed above as the lubricant that can be used for the nonmagnetic layer or the magnetic layer. In the backcoat layer, the lubricant is usually added in the range of 1 to 5 parts by mass with respect to 100 parts by mass of the binder.

[Non-magnetic support]
In the present invention, examples of the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyaramid, polyamideimide, polysulfone, aromatic polyamide, polybenzoxazole, and the like. Any known film 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 polyaramid. 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 by 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 2.0 nm or less. Are preferably used. These supports preferably have not only a small center plane average surface roughness 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 peak height is Rp of 0.5 μm or less, the center face valley depth Rv is 0.5 μm or less, and the center surface area The rate Sr is preferably 10% to 90%, and the average wavelength λa is preferably 5 μm to 300 μm. In order to obtain the desired electromagnetic conversion characteristics and durability, the surface protrusion distribution of these supports can be arbitrarily controlled by a filler, and each of those having a size of 0.01 μm to 1 μm can be reduced from 0 per 0.1 mm ^2. It can be controlled in the range of 2000.

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.

[Production method]
The step of preparing the magnetic layer coating solution used for producing the magnetic recording medium of the present invention, and further the non-magnetic layer coating solution, is at least a kneading step, a dispersing step, and before and after these steps as necessary. It consists of a provided mixing step. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powder, nonmagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention 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. When a kneader is used, the range is 15 to 500 parts by mass with respect to 100 parts by mass of ferromagnetic powder or non-magnetic powder and all or part of the binder (however, preferably 30% by mass or more of the total binder) and ferromagnetic powder. Can be kneaded. 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 the magnetic layer coating solution and the nonmagnetic layer coating solution, and it is preferable to use zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media. 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 magnetic layer coating liquid can be formed by uniformly dispersing the above-described crystalline boron nitride together with each component for the magnetic layer coating liquid. Alternatively, the crystalline boron nitride can be slurried together with an abrasive and a solvent, and uniformly dispersed in advance with a sand mill or an ultrasonic disperser, and then mixed with the magnetic layer coating solution.

As a method of applying a magnetic recording medium having a multi-layer structure in the present invention, a method of applying a coating solution for forming a nonmagnetic layer and drying, and then applying and drying a coating solution for forming a magnetic layer thereon (Wetton dry) Is preferably used. This method is suitable for increasing the density because the variation in thickness of the magnetic layer is reduced and the S / N is improved.
In addition, when using a method (Weton wet) in which the magnetic layer forming coating solution is applied and dried while the nonmagnetic layer coating solution is in a wet state, the following method is preferably used. . First, a nonmagnetic layer is first applied by a gravure coating, a roll coating, a blade coating, an extrusion coating device or the like generally used in the coating of a magnetic paint. A method of applying a magnetic layer by a support pressure type extrusion coating apparatus disclosed in Japanese Patent No. 46186, Japanese Patent Laid-Open No. 60-238179, and Japanese Patent Laid-Open No. 2-265672; No. 2, JP-A-2-17971, JP-A-2-265672, and the like. Thirdly, the upper and lower layers are applied almost simultaneously by an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965. It is a method. In order to prevent a decrease in electromagnetic conversion characteristics of the magnetic recording medium due to agglomeration of magnetic particles, the inside of the coating head is formed by a method as disclosed in Japanese Patent Application Laid-Open Nos. 62-95174 and 1-2236968. It is desirable to apply shear to the coating solution. Furthermore, it is preferable that the viscosity of the coating solution satisfies the numerical range disclosed in JP-A-3-8471.

  After the coating and drying, the magnetic recording medium is usually subjected to a calendar process. As the calendering roll, a heat-resistant plastic roll or metal roll such as epoxy, polyimide, polyamide, polyimide amide or the like can be used. In particular, when a double-sided magnetic layer is used, it is preferable to treat with metal rolls. The treatment temperature is preferably 50 ° C. or higher, more preferably 100 ° C. or higher. The linear pressure is preferably 200 kg / cm (196 kN / m) or more, more preferably 300 kg / cm (294 kN / m) or more.

[Physical properties]
The friction coefficient with respect to the head of the magnetic recording medium of the present invention is preferably 0.5 or less, more preferably 0.3 or less, in the range of temperature -10 ° C to 40 ° C and humidity 0% to 95%. Is preferably in the range of 10 ⁴ to 10 ¹² ohm / sq of the magnetic surface, and the charged position is within −500V to + 500V. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 100 to 2000 kg / mm ² (980 to 19600 MPa) in each in-plane direction, the breaking strength is preferably 10 to 70 kg / mm ² (98 to 686 MPa), and magnetic. The elastic modulus of the recording medium is preferably 100 to 1500 kg / mm ² (980 to 14700 MPa) in each in-plane direction, the residual spread is preferably 0.5% or less, and the thermal shrinkage rate at any temperature of 100 ° C. or less is preferably It is 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less. The glass transition temperature of the magnetic layer (the maximum loss elastic modulus measured at 110 Hz) is preferably 50 ° C. or higher and 120 ° C. or lower, and that of the lower nonmagnetic layer is 0 ° C. to 100 ° C. It is preferable. The loss elastic modulus is preferably in the range of 1 × 10 ³ to 8 × 10 ⁴ N / 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 30% by volume or less, more preferably 20% 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.

  The center surface surface roughness Ra of the magnetic layer measured with an optical interference surface roughness meter HD-2000 manufactured by WYKO is preferably 1.0 to 6.0 nm, and more preferably 5.5 nm or less. The maximum height Rmax of the magnetic layer is 0.5 μm or less, the ten-point average roughness Rz is 0.3 μm or less, the central surface peak height Rp is 0.3 μm or less, the central surface valley depth Rv is 0.3 μm or less, the central surface The area ratio Sr is preferably 20 to 80%, and the average wavelength λa is preferably 5 to 300 μm. The surface protrusions of the magnetic layer can be arbitrarily set in the range of 0.01 to 1 μm in the range of 0 to 2000, and it is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient. These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the powder added to the magnetic layer, the roll surface shape of the calendering process, and the like. The curl is preferably within ± 3 mm.

  In the magnetic recording medium of the present invention, it is easily estimated that 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 is increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

  The magnetic recording medium of the present invention contains cubic boron nitride having an average particle size of 0.01 to 0.10 μm or further hexagonal boron nitride having an average particle size of 0.01 to 0.10 μm as a nonmagnetic powder in the magnetic layer. As a result, particularly in a magnetic recording / reproducing system using an MR head, both head wear reduction and good durability can be achieved. That is, the magnetic recording medium of the present invention is suitable for recording a magnetic signal and reproducing the signal using an MR head.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples. In addition, unless otherwise indicated, the display of "part" in an Example shows a "mass part".

[Example 1]
For each of the following magnetic layer coating solution and nonmagnetic layer coating solution, each component was kneaded with an open kneader, and then an appropriate amount of zirconia beads having a diameter of 0.5 mmφ was added as a dispersion medium to the coating solution and dispersed with a sand mill. Trifunctional low molecular weight polyisocyanate compound is added to the obtained dispersion liquid in 3 parts in the magnetic layer coating liquid and 5 parts in the non-magnetic layer coating liquid, and 40 parts in cyclohexanone is added to each of them to have an average pore diameter of 1 μm. It filtered using the filter and the magnetic layer coating liquid and the nonmagnetic layer coating liquid were prepared.

  The obtained nonmagnetic layer coating solution is placed on a PEN support having a center line average surface roughness of 3 nm with a thickness of 5 μm, and the thickness of the nonmagnetic layer after drying the obtained nonmagnetic layer coating solution is 1.2 μm. After coating and drying, the magnetic layer coating solution is coated thereon so that the thickness of the magnetic layer after drying is 0.07 μm, and the magnetic layer has a magnetic force of 0.3 T while the magnetic layer is still wet. Oriented and dried with a magnet having Subsequently, a back coat layer coating solution was applied and dried on the opposite surface of the support so that the dry thickness was 0.5 μm. After drying, a surface smoothing treatment was performed at a speed of 90 m / min, a linear pressure of 300 kg / cm (294 kN / m), and a temperature of 90 ° C. using a seven-stage calendar composed only of metal rolls. After that, the surface of the magnetic layer is cleaned with a tape cleaning device that slits to 1/2 inch width, feeds the slit product, and attaches the nonwoven fabric and razor blade to the magnetic surface in a device with a winding device. A magnetic tape was prepared.

(Magnetic layer coating solution)
Hexagonal barium ferrite powder 100 parts Plate diameter: 25 nm
Hc: 175 kA / m (2200 Oe)
σs: 50 A · m ² / kg (50 emu / g)
Polyester polyurethane resin 15 parts (UR8200: manufactured by Toyobo, containing sulfonic acid group)
Cubic boron nitride powder 5 parts Average particle size: 0.08 μm
Mohs hardness: 9.3 Shape: cubic to sphere carbon black (average particle size: 0.04 μm) 0.5 part cyclohexanone 100 parts methyl ethyl ketone 100 parts butyl stearate 1 part stearic acid 2 parts

(Non-magnetic layer coating solution)
α-Fe ₂ O ₃ 80 parts Average long axis length: 0.15 μm
Average needle ratio: 7
BET specific surface area: 50 m ² / g
Carbon black 20 parts Average particle size: 0.02 μm
13 parts of vinyl chloride copolymer (MR110, manufactured by Zeon Corporation)
6 parts of polyester polyurethane resin (UR8200: manufactured by Toyobo, containing sulfonic acid group)
Phenylphosphonic acid 5 parts Cyclohexanone 150 parts Methyl ethyl ketone 150 parts Butyl stearate 2 parts Stearic acid 1 part

(Backcoat layer coating solution)
Particulate carbon black 100 parts (BP-800: Cabot Corporation, average particle size 0.02 μm)
Coarse particulate carbon black 10 parts Average particle size 0.1 μm
α-Fe ₂ O ₃ 15 parts Average long axis length: 0.10 μm
Nitrocellulose resin 100 parts Polyurethane resin 30 parts (N2301 made by Nippon Polyurethane)
Methyl ethyl ketone 2500 parts Butyl acetate 300 parts Toluene 500 parts

(Examples 2 to 10)
The magnetic powder contained in the magnetic layer, the non-magnetic powder type and its average particle diameter, magnetic layer thickness, non-magnetic support type, thickness, non-magnetic layer thickness, back layer thickness, except that the contents described in Table 1 were changed. A magnetic tape was obtained by the same production method as in Example 1.
The characteristics of the ferromagnetic metal powder used in Examples 9 and 10 in place of the hexagonal ferrite powder are shown in Table A below.

(Examples 11 to 16)
Add 1 or 1.5 parts of hexagonal boron nitride as non-magnetic powder seed and 3 parts of cubic boron nitride, and add carbon black (average particle size: 0.04 μm) from the magnetic layer formulation for Examples 13-15 A magnetic tape was obtained by the same production method as in Example 3 except for not doing (= 0 part).

(Comparative Example 1)
A magnetic tape was obtained by the same production method as in Example 1, except that the nonmagnetic powder contained in the magnetic layer was changed to α-Al ₂ O ₃ powder (Mohs hardness 9) having an average particle size of 0.11 μm.

(Comparative Examples 2 to 8)
The magnetic powder contained in the magnetic layer, the non-magnetic powder type and its average particle size and magnetic layer thickness, non-magnetic support type, thickness, non-magnetic layer thickness, back layer thickness, except for changing the contents described in Table 1, A magnetic tape was obtained by the same production method as in Example 1. The characteristics of the ferromagnetic metal powder used in Comparative Examples 5 and 6 are shown in Table A.

(Measuring method)
(2) MR head wear evaluation method The MR head is mounted on a linear tester, and the difference between the initial MR head height and the MR head height after 100 hours of driving is measured in an environment of 23 ° C and 50% RH. Then, the relative value was determined by measuring the amount of wear of the MR head, and 1 or less was considered good.

(3) Durability Evaluation Method Under an environment of 23 ° C. and 50% RH, the surface of the magnetic layer of the magnetic tape is sentust or Altic square (a square having a square cross section with a side of 0.5 cm and a length of 2 cm). The magnetic tape was made to reciprocate for 50 m at a length of 3 m / sec under a tension of 100 g at a wrap angle of 12 ° (see Japanese Patent Application Laid-Open No. 2007-26564 for details).
The durability of the magnetic tape is determined by observing the surface of the magnetic tape after the measurement of the above-mentioned Altic wear width with an optical microscope. ) The case where the coating film was not peeled off was marked with ○, the scratch was slightly seen but the coating film was not peeled off, and the case where the coating film itself was peeled off was marked with ×. If it is (triangle | delta), it can be judged that it has practically sufficient durability.

(Note) BaFe: Barium ferrite, MP: Metal powder PEN: Polyethylene naphthalate, PET: Polyethylene terephthalate, PA: Polyaramid

Evaluation Results As shown in Table 1, the magnetic tapes of Examples 1 to 16 using cubic boron nitride having an average particle size in the range of 0.01 to 0.10 μm as the nonmagnetic powder contained in the magnetic layer are The head wear and durability were also good.
In contrast, the magnetic tape of Comparative Example 1 using α-Al ₂ O ₃ as the nonmagnetic powder contained in the magnetic layer had little head wear but deteriorated durability.
In addition, the magnetic tape of Comparative Example 2 using diamond as the nonmagnetic powder contained in the magnetic layer showed durability with no practical problem, but the head wear was significant. This is presumably because diamond is too high in polishing ability for AlTiC constituting the MR head.
Further, when cubic boron nitride and hexagonal boron nitride were included, head wear was further reduced and durability was good. This is presumed to be the effect of providing lubricity by hexagonal boron nitride.
In the magnetic tape of Comparative Example 7 using cubic boron nitride having a particle size outside the range of 0.01 to 0.10 μm as the nonmagnetic powder contained in the magnetic layer, it is possible to achieve both head wear and durability. could not.

  The magnetic recording medium of the present invention is suitable for a magnetic recording / reproducing system using an MR reproducing head.

Claims (3)

  A magnetic recording medium having a magnetic layer comprising a ferromagnetic powder, a binder and a nonmagnetic powder on a nonmagnetic support, wherein the nonmagnetic powder has a cubic nitriding average particle size of 0.01 to 0.10 μm A magnetic recording medium comprising boron powder.   2. The magnetic recording medium according to claim 1, further comprising a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer.   3. The magnetic recording medium according to claim 1, wherein the nonmagnetic powder of the magnetic layer contains hexagonal boron nitride powder having an average particle size of 0.01 to 0.10 [mu] m.