JP2006338795A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which has high surface recording density, high dimensional stability even under high temperature and high humidity and high mechanical strength and whose error rate can be lowered. <P>SOLUTION: In the magnetic recording medium, a water vapor shielding layer and a magnetic layer are provided in this order on at least one surface of a non-magnetic supporting body, both Young's moduli in the longitudinal and width directions of the non-magnetic supporting body are 7 GPa or more, the magnetic layer includes ferromagnetic hexagonal ferrite powder having 5 to 40 nm average plate diameter or ferromagnetic metal powder having 20 to 100 nm average major axis length and a binder and a laminated body comprising the non-magnetic supporting body and the water vapor shielding layer has 0.001 to 0.3 g/m<SP>2</SP>-24hr water vapor permeability. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having a high surface recording density and a low error rate even under high temperature and high humidity.

In recent years, in the field of magnetic tape, with the spread of personal computers, workstations, etc., research on magnetic recording media for recording computer data as external storage media has been actively conducted. In practical application of magnetic recording media for such applications, especially in combination with the downsizing of computers and the increase in information processing capacity, the recording capacity has been improved in order to satisfy the increasing capacity and downsizing of recording devices. Is strongly demanded.
In recent years, a reproducing head having a magnetoresistive (MR) as an operating principle has been proposed and started to be used in a hard disk or the like, and Patent Document 1 (Japanese Patent Laid-Open No. 8-227517) proposes application to a magnetic tape. Yes. MR heads can produce a reproduction output several times that of induction type magnetic heads and do not use induction coils, so that equipment noise such as impedance noise is greatly reduced. It has become possible to obtain an S / N ratio. In other words, if the magnetic recording medium noise that has been hidden behind the conventional equipment noise is reduced, good recording and reproduction can be performed, and the high-density recording characteristics can be dramatically improved.

Conventional magnetic recording media in which a magnetic layer in which iron oxide, Co-modified iron oxide, CrO ₂ and ferromagnetic hexagonal ferrite powder are dispersed in a binder are coated on a nonmagnetic support have been widely used. Yes. Among them, it is known that ferromagnetic metal powders and ferromagnetic hexagonal ferrite powders are excellent in high density recording characteristics as magnetic powders. In order to reduce noise in the magnetic recording medium, it is effective to reduce the size of the particles of the ferromagnetic powder. In recent magnetic materials, ferromagnetic hexagonal ferrite fine powder having a plate diameter of 40 nm or less, average major axis length of 100 nm. The following ferromagnetic metal fine powder is used to increase the effect.

In order to realize a higher recording density and a larger recording capacity, the track width at the time of recording / reproducing of the magnetic recording medium tends to be narrowed. Further, in the field of magnetic tape, the magnetic tape has been made thinner in order to enable high-density recording, and many magnetic tapes having a total thickness of 10 μm or less have appeared. However, when the thickness of the magnetic recording medium is reduced, the magnetic recording medium is easily affected by changes in temperature and humidity during storage and running, and tension.
In other words, the magnetic head moves in the width direction of the magnetic tape during recording / reproduction in a magnetic recording / reproducing system employing a linear recording method, and one of the tracks must be selected. As the track width becomes narrower, the magnetic tape In order to control the relative position between the head and the head, high accuracy is required. Even if the MR ratio and fine particle magnetic material as described above are used to improve the S / N ratio and narrow the track, the magnetic recording medium is deformed and recorded due to fluctuations in the temperature and humidity of the environment in use and the tension in the drive. Therefore, the dimensional stability of the medium is required to be higher than before. A magnetic recording medium corresponding to such high-density recording requires higher dimensional stability and mechanical strength than conventional media in order to maintain stable recording and reproduction.

Patent Document 2 (Japanese Patent Application Laid-Open No. 8-111020) aims to provide a magnetic recording medium that is excellent in durability of a magnetic layer and has good output characteristics even after storage under high temperature and high humidity. Water vapor transmission rate is 15 g / m ² · 24 hr or less, oxygen transmission rate is 2.0 × 10 ^-12 cm ³ / cm ² · sec · cmHg or less, Young's modulus in the width direction is 700 kg / mm ² or more, and film thickness is 7 μm A polyester film for magnetic recording media comprising the following polyethylene-2,6-naphthalenedicarboxylate has been proposed. However, even the smallest water vapor transmission rate described in the example of Patent Document 2 is 6.5 g / m ² · 24 hr, which is insufficient for use in recent high-density magnetic recording media. Moreover, although it is described that the crystallinity (density) of the film is increased as a means for achieving the water vapor transmission rate, this means that the water vapor transmission rate is further lowered from the value described in the examples. Practically impossible. Furthermore, the magnetic recording medium of Patent Document 2 has a disadvantage that it is inferior in mechanical strength.
Patent Document 3 (Japanese Patent Application Laid-Open No. 8-297929) aims to provide a magnetic recording medium having excellent running stability and electromagnetic conversion characteristics even under severe conditions such as repeated running under high humidity. A magnetic layer is provided on at least one surface of a support film made of aromatic polyamide or aromatic polyimide, and the humidity expansion coefficient β and water vapor permeability of the support film are β ≦ 100 × 10 ⁻⁶ (1 / RH%) a magnetic recording medium which satisfies the water vapor transmission rate ≦ 50 a (g / m ² /24hr/0.1mm) has been proposed. However, for use in Patent water vapor transmission rate of the embodiment is used in the example films of Reference 3 is ¹⁰ (g / m 2 ^/24hr/0.1mm) also the most small, recent high-density magnetic recording medium Insufficient. Further, as a means for achieving the water vapor transmission rate, the stretching ratio at the time of film formation is increased. However, it is substantially impossible to lower the water vapor transmission rate further than the value described in the examples. Is possible.

JP-A-8-227517 Japanese Patent Laid-Open No. 8-1111020 JP-A-8-297829

  Accordingly, it is an object of the present invention to provide a magnetic recording medium having a high surface recording density, high dimensional stability even under high temperature and high humidity, a low error rate, and high mechanical strength. It is.

The present invention is as follows.
1) A water vapor blocking layer and a magnetic layer are provided in this order on at least one surface of the nonmagnetic support, and both the longitudinal and width Young's moduli of the nonmagnetic support are 7 GPa or more. Water vapor in a laminate comprising a ferromagnetic hexagonal ferrite powder having an average plate diameter of 5 to 40 nm or a ferromagnetic metal powder having an average major axis length of 20 to 100 nm and a binder, and comprising the nonmagnetic support and a water vapor barrier layer A magnetic recording medium having a transmittance in the range of 0.001 to 0.3 g / m ² · 24 hours.
2) The magnetic recording medium as described in 1) above, wherein the water vapor blocking layer is a layer containing a metal material or a layer containing a resin.
3) The magnetic recording medium as described in 1) above, wherein the water vapor blocking layer comprises at least two layers having a first layer containing a metal material and a second layer containing a resin.
4) The magnetic recording medium as described in 2) or 3) above, wherein the metal material is a metal oxide, and the resin is a polymer compound having a mass average molecular weight of 1,000 to 100,000.
5) The magnetic recording according to any one of 1) to 4) above, wherein a nonmagnetic layer containing a nonmagnetic powder and a binder is provided between the nonmagnetic support and the magnetic layer. Medium.

  According to the present invention, a non-magnetic support is used that uses a fine particle magnetic material compatible with high-density recording, and provides a water-vapor barrier layer between the non-magnetic support and the magnetic layer to significantly suppress the water vapor transmission rate. Since the Young's modulus of the magnetic field is higher than a specific value, it has a high surface recording density, high dimensional stability even under high temperature and high humidity, low error rate, and high mechanical strength. A recording medium can be provided.

Hereinafter, the magnetic recording medium of the present invention will be described in more detail.
I. Nonmagnetic Support As the nonmagnetic support that can be used in the present invention, for example, biaxially stretched polyethylene naphthalate, polyethylene terephthalate, polyamide, polyimide, polyamideimide, aromatic polyamide, polybenzoxazole, etc. are used. can do. Preferred examples include polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). These nonmagnetic supports may be subjected beforehand to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like.
The Young's modulus of the nonmagnetic support of the present invention is 7 GPa or more in both the longitudinal direction and the width direction, preferably 7.5 to 11 GPa, more preferably 7.6 to 10.8 GPa. May be different.
The Young's modulus (longitudinal direction and width direction) of the nonmagnetic support can be adjusted by biaxially stretching an unstretched film and biaxially orienting it. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. Using a sequential biaxial stretching method that first stretches in the longitudinal direction and then in the width direction, the stretching in the longitudinal direction is divided into three or more stages, the longitudinal stretching temperature is 80 to 180 ° C., and the total longitudinal stretching ratio is 3.0 to 6 It is preferably exemplified that it is carried out at a ratio of 0.0 times and a longitudinal stretching speed of 5000 to 50000% / min. As the stretching method in the width direction, a method using a tenter is preferable, the stretching temperature is from the glass transition temperature (Tg) to Tg + 100 ° C. of the film, and the stretching ratio in the width direction is sometimes larger than the longitudinal magnification in the range of 3.2 to 7.0. It is preferable that the stretching speed in the width direction is doubled in the range of 1000 to 20000% / min. Furthermore, you may perform re-longitudinal stretching and re-lateral stretching as needed.
Further, the center surface average roughness (JISB0660-1998, ISO4287-1997) on the magnetic layer coating surface side of the nonmagnetic support that can be used in the present invention is 1.8 to 9 nm at a cutoff value of 0.25 mm, preferably It is preferable that it is the range of 2-8 nm, and the roughness of both surfaces of a support body may differ. The preferred thickness of the nonmagnetic support in the magnetic recording medium of the present invention is 3 to 60 μm.

II. Water vapor blocking layer In the present invention, a water vapor blocking layer is provided on at least one surface of the nonmagnetic support. The water vapor blocking layer referred to in the present invention may be any material as long as it has a function of blocking water vapor, but the water vapor blocking layer is preferably a layer containing a metal material or a layer containing a resin.
When the water vapor barrier layer is a layer containing a metal material, examples of the metal material include metals, metalloids, alloys, oxides and composites thereof. Specific examples include metals such as Al, Cu, Zn, Sn, Ni, Ag, Co, Fe, and Mn, and semimetals such as Si, Ge, As, Sc, and Sb. These metals and metalloid alloys include Fe-Co, Fe-Ni, Co-Ni, Fe-Co-Ni, Fe-Cu, Co-Cu, Co-Au, Co-Y, Co-La, Co. -Pr, Co-Gd, Co-Sm, Co-Pt, Ni-Cu, Mn-Bi, Mn-Sb, Mn-Al, Fe-Cr, Co-Cr, Ni-Cr, Fe-Co-Cr, Ni -Co-Cr etc. are mentioned. Further, oxides of these metals, metalloids and alloys can be easily obtained by introducing oxygen gas at the time of vapor deposition, for example. Examples of the composite of these metals, metalloids and alloys include Fe-Si-O, Si-C, Si-N, Cu-Al-O, Si-N-O, and Si-C-O. It is done.
In the present invention, the layer containing a metal material is a metal oxide, particularly AlO _x (x is greater than 0 and does not exceed 1.5), such as Al ₂ O ₃ , SiO _y ( y is larger than 0 and does not exceed 2). For example, a layer containing SiO ₂ is preferable.
A method for forming a layer containing a metal material is not limited, but a vacuum deposition method is generally used, and a sputtering method, an ion plating method, or the like can also be used.

Further, when the water vapor blocking layer is a layer containing a resin, examples of the resin include polyvinylidene chloride, polytetrafluoroethylene, polyethylene, hydrochloric acid rubber, polyisobutylene, polysulfide (for example, trade name thiocol manufactured by Toray Rethiocol Co., Ltd.), Examples include vulcanized rubber and sulfurized polyethylene. Of these, polyvinylidene chloride is preferable. Polyvinylidene chloride may be a copolymer of monomers such as vinyl chloride.
Moreover, it is preferable that the glass transition temperature of the said resin is 0-120 degreeC, and it is more preferable that it is 10-80 degreeC. If it is 0 degreeC or more, it will not produce a blocking in an end surface, and if it is 120 degrees C or less, the internal stress in a water vapor | steam barrier layer can be relieve | moderated and it is excellent also in adhesive force. About molecular weight, the range of mass average molecular weight 1000-100000 is mentioned, Especially the thing of 5000-50000 is preferable. If the mass average molecular weight is 1000 or more, no blocking or the like occurs at the end face, and if it is 100000 or less, the solubility in an organic solvent is good, and film formation by coating is sufficiently possible.
Examples of the method for forming the resin-containing layer include a method in which these resins are dissolved in an organic solvent and applied as described above. If the resin is a thermoplastic resin, it may be melt coextruded with the resin constituting the support, and the support and the water vapor barrier layer may be formed in one step.

In the present invention, the water vapor blocking layer may be composed of a single layer, but is preferably composed of at least two layers having a first layer containing a metal material and a second layer containing a resin. If it does in this way, the pinhole of the layer containing the metal material formed, for example by vapor deposition can be filled with the layer containing resin, and a water-vapor-permeation rate can be suppressed further.
In this case, it is preferable that the first layer and the second layer are provided in this order on the nonmagnetic support, and the magnetic layer is provided on the second layer.

Further, according to the present invention, the first layer and the second layer are provided in this order on the nonmagnetic support, and the metal oxide is applied as the metal material of the first layer, so that the oxygen concentration in the first layer is reduced. The distribution is preferably large in the vicinity of the interface on the second layer side. More preferably, the oxygen concentration distribution in the first layer is larger in the vicinity of the interface between the nonmagnetic support side and the second layer side than the central portion in the first layer. This is preferable in terms of the rigidity of the magnetic recording medium. The water vapor barrier layer having such an oxygen distribution can be produced by forcibly oxidizing the surface with an oxidizing gas during or after the first layer is formed, depending on the purpose. It can be controlled. The measurement of the oxygen concentration distribution in the first layer can be performed by analyzing the depth direction of the first layer using an Auger electron spectroscopic analyzer.
Here, “the distribution of the oxygen concentration is large” means that the oxygen concentration is relatively higher than other portions, and particularly includes the case where the concentration variation is 10 atomic% or more.

  The thickness of the water vapor barrier layer of the present invention is, for example, 5 to 500 nm, preferably 10 to 200 nm, and more preferably 15 to 100 nm. Although the thickness of the water vapor barrier layer depends on the components and the like, it is preferable that the water vapor barrier layer is thinner for higher capacity as long as the water vapor transmission rate of the present invention can be satisfied and the surface property and physical strength are ensured.

In the present invention, the water vapor permeability of the laminate composed of the nonmagnetic support and the water vapor barrier layer needs to be in the range of 0.001 to 0.3 g / m ² · 24 hours. When the water vapor transmission rate exceeds 0.3 g / m ² · 24 hours, the dimensional stability cannot be secured, and an error rate tends to occur. In addition, it is difficult to achieve a water vapor transmission rate of less than 0.001 g / m ² · 24 hours. The range of the preferable water vapor transmission rate is 0.005 to 0.2 g / m ² · 24 hours, and more preferably 0.01 to 0.1 g / m ² · 24 hours.
The water vapor transmission rate referred to in the present invention is a value measured at 40 ° C. and 90% RH using a water vapor transmission rate measuring device manufactured by MOCON in accordance with JIS K7129.

III. Magnetic layer <ferromagnetic metal powder>
The ferromagnetic metal powder used in the magnetic layer of the magnetic recording medium of the present invention is known to be excellent in high-density magnetic recording characteristics, and a magnetic recording medium having excellent electromagnetic conversion characteristics can be obtained. . The average major axis length of the ferromagnetic metal powder used in the magnetic layer of the magnetic recording medium of the present invention is 20 to 100 nm, preferably 30 to 90 nm, and more preferably 40 to 80 nm. If the average major axis length of the ferromagnetic metal powder is 20 nm or more, it is possible to effectively suppress a decrease in magnetic properties due to thermal fluctuation. Moreover, if the average major axis length is 100 nm or less, a good SN ratio can be obtained while maintaining low noise.
The average major axis length of the ferromagnetic metal powder is obtained by photographing the ferromagnetic metal powder with a transmission electron micrograph, and directly reading the minor axis length and the major axis length of the ferromagnetic metal powder from the photograph and the image analysis device curl. It can be determined from an average of values obtained by using a method of tracing and reading a transmission electron micrograph with ZEISS IBASSI.

The ferromagnetic metal powder used for the magnetic layer in the magnetic recording medium of the present invention is not particularly limited as long as it contains Fe as a main component, but a ferromagnetic alloy powder containing α-Fe as a main component is preferable. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta in addition to the predetermined atoms. , W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B atoms may be included. It is preferable that at least one of Al, Si, Ca, Y, Ba, La, Nd, Co, Ni, and B is included in addition to α-Fe, and it is particularly preferable that Co, Al, and Y are included. More specifically, it is preferable that Co is contained in an amount of 10 to 40 atomic%, Fe is contained in an amount of 2 to 20 atomic%, and Y is contained in an amount of 1 to 15 atomic%.
The ferromagnetic metal powder may be treated in advance with a dispersant, lubricant, surfactant, antistatic agent, etc., which will be described later, before dispersion. The ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The moisture content of the ferromagnetic metal powder is preferably 0.01-2%. It is preferable to optimize the moisture content of the ferromagnetic metal powder depending on the type of the binder. The ferromagnetic metal powder may be surface-treated with Al, Si, P, or an oxide thereof as required. The amount thereof is 0.1 to 10% with respect to the ferromagnetic metal powder. When the surface treatment is performed, the adsorption of a lubricant such as a fatty acid is preferably 100 mg / m ² or less. The pH of the ferromagnetic metal powder is preferably optimized depending on the combination with the binder used. The range is usually from 6 to 12, but preferably from 7 to 11. 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 . These are preferably essentially absent. If the total of each ion is about 300 ppm or less, the characteristics are not affected. The ferromagnetic powder used in the present invention preferably has fewer pores, and its value is 20% by volume or less, and more preferably 5% by volume or less.

The crystallite size of the ferromagnetic metal powder is preferably 8 to 20 nm, more preferably 10 to 18 nm, and further preferably 12 to 16 nm. This crystallite size is an average value obtained by a Scherrer method from a half-value width of a diffraction peak using an X-ray diffractometer (RINT2000 series manufactured by Rigaku Corporation) under the conditions of a radiation source CuKα1, a tube voltage of 50 kV, and a tube current of 300 mA. .
The specific surface area by BET method of the ferromagnetic metal powder (S _BET) is preferably less than 30 m ² / g or more 50 m ² / g, more preferably from 38~48m ² / g. Within this range, both good surface properties and low noise can be achieved.

The ferromagnetic metal powder is preferably an acicular ferromagnetic powder. The average needle-like ratio [arithmetic length of (major axis length / minor axis length)] of the ferromagnetic metal powder is preferably 4 to 12, more preferably 5 to 12. The Hc of the ferromagnetic metal powder is preferably 159.2 to 238.8 kA / m, and more preferably 167.2 to 230.8 kA / m. The saturation magnetic flux density is preferably 150 to 300 mT, and more preferably 160 to 290 mT. The saturation magnetization (σs) is preferably 140 to 170 A · m ² / kg, and more preferably 145 to 160 A · m ² / kg. The SFD (switching field distribution) of the magnetic material itself is preferably small and is preferably 0.8 or less. When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, the magnetization reversal is sharp, the peak shift is small, and it is suitable for high-density digital magnetic recording. 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 α-Fe ₂ O ₃ , and preventing sintering between particles.
As the ferromagnetic metal powder, those obtained by a known production method can be used, and the following methods can be mentioned. 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, a method of obtaining fine powder by evaporation in an inert gas. The ferromagnetic metal powder thus obtained is subjected to a known slow oxidation treatment. A method of reducing the amount of demagnetization by reducing the hydrous iron oxide and iron oxide with a reducing gas such as hydrogen and controlling the partial pressure, temperature and time of the oxygen-containing gas and inert gas to form an oxide film on the surface. preferable.

<Ferromagnetic hexagonal ferrite powder>
The ferromagnetic hexagonal ferrite powder has a hexagonal magnetoplumbite structure, has extremely large uniaxial crystal magnetic anisotropy, and has a very high coercive force (Hc). For this reason, magnetic recording media using ferromagnetic hexagonal ferrite powder have excellent chemical stability, corrosion resistance, and friction resistance, and can reduce magnetic spacing due to the increase in density, thereby realizing a thin film. , Enabling high C / N and resolution. The average plate diameter of the ferromagnetic hexagonal ferrite powder is 5 to 40 nm, preferably 10 to 38 nm, and more preferably 15 to 36 nm. In general, when the track density is increased and reproduction is performed with a magnetoresistive head, it is necessary to reduce noise and to reduce the average plate diameter of the ferromagnetic hexagonal ferrite powder. Also, from the viewpoint of reducing magnetic spacing, it is preferable that the average plate diameter of hexagonal ferrite is as small as possible. However, if the average plate diameter of the ferromagnetic hexagonal ferrite powder is too small, the magnetization becomes unstable due to thermal fluctuation. For this reason, the lower limit of the average plate diameter of the ferromagnetic hexagonal ferrite powder used for the magnetic layer of the magnetic recording medium of the present invention is set to 5 nm. If the average plate diameter is 5 nm or more, there is little influence of thermal fluctuation, and stable magnetization can be obtained. On the other hand, the upper limit of the average plate diameter of the ferromagnetic hexagonal ferrite powder is 40 nm. If the average plate diameter is 40 nm or less, a decrease in electromagnetic conversion characteristics due to an increase in noise can be suppressed, and this is particularly suitable when reproducing with a magnetoresistive (MR) head. The average plate diameter of the ferromagnetic hexagonal ferrite powder is obtained by photographing the ferromagnetic hexagonal ferrite powder with a transmission electron micrograph, and directly reading the plate diameter of the ferromagnetic hexagonal ferrite powder from the photograph and the image analysis device curl. It can be determined from the average value of values measured in combination with the method of tracing and reading a transmission electron micrograph with ZEISS IBASSI.

  Examples of the ferromagnetic hexagonal ferrite powder contained in the magnetic layer of the present invention include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite substitutes, and Co substitutes. More specifically, magnetoplumbite type barium ferrite and strontium ferrite, magnetoplumbite type ferrite whose particle surface is coated with spinel, and magnetoplumbite type barium ferrite and strontium ferrite partially containing a spinel phase, etc. Is mentioned. In addition to predetermined atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg , Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb may be included. In general, elements such as Co—Zn, Co—Ti, Co—Ti—Zr, Co—Ti—Zn, Ni—Ti—Zn, Nb—Zn—Co, Sb—Zn—Co, and Nb—Zn are added. You can use things. Some raw materials and production methods contain specific impurities.

As described above, the ferromagnetic hexagonal ferrite powder has an average plate diameter of 5 to 40 nm, preferably 10 to 38 nm, and more preferably 15 to 36 nm. The average plate thickness is 1 to 30 nm, preferably 2 to 25 nm, more preferably 3 to 20 nm. The average plate ratio {average of (plate diameter / plate thickness)} is 1-15, and preferably 1-7. If the plate-like ratio is 1 to 15, sufficient orientation can be obtained while maintaining high filling properties in the magnetic layer, and noise increase can be suppressed by stacking between particles. Moreover, the specific surface area by BET method within the said particle size range is 10-200 m < ² > / g. This specific surface area is approximately the value calculated from the particle plate diameter and plate thickness.
The distribution of the particle plate diameter and plate thickness of the ferromagnetic hexagonal ferrite powder is generally preferably as narrow as possible. Although it is difficult to quantify the particle plate diameter and plate thickness, it can be compared by randomly measuring 500 particles from a particle TEM photograph. In many cases, the distribution of the particle plate diameter and plate thickness is not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0.1 to 2.0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improvement process. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

The Hc of the ferromagnetic hexagonal ferrite powder can be in the range of 159.2 to 238.8 kA / m, preferably 175.1 to 222.9 kA / m, and more preferably 183.1 to 214. .9 kA / m. However, when the saturation magnetization (σs) of the head exceeds 1.4T, it is preferably 159.2 kA / m or less. Hc can be controlled by the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element, the particle generation reaction conditions, and the like.
The saturation magnetization (σs) of the ferromagnetic hexagonal ferrite powder is 40 to 80 A · m ² / kg. Higher σs is preferable, but tends to be smaller as the particles become smaller. In order to improve σs, it is well known to combine spinel ferrite with magnetoplumbite ferrite and to select the type and amount of elements contained. It is also possible to use W-type hexagonal ferrite. When the magnetic material is dispersed, the surface of the magnetic material particles is also treated with a material suitable for the dispersion medium and the polymer. As the surface treatment agent, inorganic compounds and organic compounds are 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 addition amount is 0.1 to 10% by mass with respect to the mass of the magnetic substance. The pH of the magnetic material 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. Water contained in the magnetic material also affects the dispersion. Although there is an optimum value depending on the dispersion medium and the polymer, 0.01 to 2.0% is usually selected.
Ferromagnetic hexagonal ferrite powder can be made by mixing barium oxide, iron oxide, iron oxide and metal oxide to replace boron oxide as a glass-forming substance so as to have a desired ferrite composition, and then melting and quenching. Glass crystallization method to obtain barium ferrite crystal powder after re-heating treatment after making it amorphous, after neutralizing barium ferrite composition metal salt solution with alkali and removing by-products Hydrothermal reaction method in which barium ferrite crystal powder is obtained by liquid phase heating at 100 or more, followed by washing, drying and pulverization; neutralizing the barium ferrite composition metal salt solution with alkali, removing by-products and drying. There is a coprecipitation method for treating and pulverizing to obtain a barium ferrite crystal powder, but the present invention does not select a production method. The ferromagnetic hexagonal ferrite powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof as necessary as described above. The amount is 0.1 to 10% with respect to the ferromagnetic powder, and the surface treatment is preferable because the adsorption of a lubricant such as a fatty acid is 100 mg / m ² or less. The ferromagnetic hexagonal ferrite powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they do not particularly affect the characteristics.

IV. Nonmagnetic Layer In the magnetic recording medium of the present invention, a nonmagnetic layer containing a nonmagnetic powder and a binder is preferably provided between the nonmagnetic support and the magnetic layer. The nonmagnetic powder that can be used in the nonmagnetic layer may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like.
Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α-alumina, β-alumina having an α conversion of 90 to 100%, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide Titanium carbide or the like is used alone or in combination of two or more. Preferred are α-iron oxide and titanium oxide.
The shape of the nonmagnetic powder may be any of acicular, spherical, polyhedral and plate shapes. The crystallite size of the nonmagnetic powder is preferably 4 nm to 1 μm, and more preferably 40 to 100 nm. A crystallite size in the range of 4 nm to 1 μm is preferred because it does not become difficult to disperse and has a suitable surface roughness. The average particle size of these non-magnetic powders is preferably 5 nm to 2 μm. However, if necessary, non-magnetic powders having different average particle sizes may be combined, or even a single non-magnetic powder may have a wide particle size distribution. It can also have an effect. The average particle size of the particularly preferred nonmagnetic powder is 10 to 200 nm. The range of 5 nm to 2 μm is preferable because the dispersion is good and the surface roughness is suitable.
The specific surface area (S _BET ) of the nonmagnetic powder is 1 to 100 m ² / g, preferably 5 to 70 m ² / g, and more preferably 10 to 65 m ² / g. A specific surface area in the range of 1 to 100 m ² / g is preferred because it has a suitable surface roughness and can be dispersed with a desired amount of binder. The oil absorption using dibutyl phthalate (DBP) is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. When the tap density is in the range of 0.05 to 2 g / ml, there are few particles to be scattered, the operation is easy, and there is a tendency that it is difficult to adhere to the apparatus. The pH of the nonmagnetic powder is preferably 2 to 11, but is particularly preferably between 6 and 9. When the pH is in the range of 2 to 11, the friction coefficient does not increase due to high temperature, high humidity, or liberation of fatty acids. The moisture content of the nonmagnetic powder is 0.1 to 5% by mass, preferably 0.2 to 3% by mass, and more preferably 0.3 to 1.5% by mass. A water content in the range of 0.1 to 5% by mass is preferable because the dispersion is good and the viscosity of the paint after dispersion is stable. The ignition loss is preferably 20% by mass or less, and the ignition loss is preferably small.

When the nonmagnetic powder is an inorganic powder, the Mohs hardness is preferably 4-10. If the Mohs hardness is in the range of 4 to 10, durability can be ensured. The nonmagnetic powder has a stearic acid adsorption amount of 1 to 20 μmol / m ² , more preferably ² to 15 μmol / m ² . The heat of wetting of the nonmagnetic powder into water at 25 ° C. is preferably in the range of 200 to 600 erg / cm ² (200 to 600 mJ / m ² ). Moreover, the solvent which exists in the range of this heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C. is suitably 1 to 10 / 100A. The pH of the isoelectric point in water is preferably between 3 and 9. It is preferable that Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , and ZnO are present on the surface of these nonmagnetic powders by surface treatment. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ , and ZrO ₂ , but more preferred are Al ₂ O ₃ , SiO ₂ , and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface-treated layer co-precipitated according to the purpose may be used, or a method of treating the surface layer with silica after first treating with alumina, or vice versa may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.
Specific examples of nonmagnetic powders used in the nonmagnetic layer of the present invention include, for example, Showa Denko Nanotite, Sumitomo Chemical HIT-100, ZA-G1, Toda Kogyo DPN-250, DPN-250BX, and DPN. -245, DPN-270BX, DPB-550BX, DPN-550RX Titanium oxide made by Ishihara Sangyo TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-55S, TTO-55D, SN-100, MJ-7 , Α-iron oxide E270, E271, E300, STT-4D, STT-30D, STT-30, STT-65C, manufactured by Titanium Industry, MT-100S, MT-100T, MT-150W, MT-500B, T-manufactured by Teika 600B, T-100F, T-500HD, etc. are mentioned. FINEX-25, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 500A, Titanium Industry Y-LOP manufactured and what baked it are mentioned. Particularly preferred nonmagnetic powders are titanium dioxide and α-iron oxide.
Further, an organic powder can be added to the nonmagnetic layer according to the purpose. Examples of such organic powder include acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder, and polyimide resin. Resin powder and polyfluorinated ethylene resin can also be used.

V. Binder The binder used for the magnetic layer and the nonmagnetic layer of the present invention is a conventionally known thermoplastic resin, thermosetting resin, reactive resin, or a mixture thereof. Examples of the thermoplastic resin 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, and vinyl acetal. And polymers or copolymers containing vinyl ether as a constituent unit, polyurethane resins, and various rubber resins.
Examples of 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, and epoxy-polyamide resins. And a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like. The thermoplastic resin, thermosetting resin and reactive resin are all described in detail in “Plastic Handbook” issued by Asakura Shoten.
Further, when an electron beam curable resin is used for the magnetic layer, not only the coating film strength is improved and the durability is improved, but also the surface is smoothed and the electromagnetic conversion characteristics are further improved.
The above resins can be used alone or in combination. Among them, it is preferable to use a polyurethane resin, and further, a cyclic structure such as hydrogenated bisphenol A, a polypropylene oxide adduct of hydrogenated bisphenol A, a polyol having an alkylene oxide chain with a molecular weight of 500 to 5000, and a chain extender. A polyurethane resin in which a polyol having a cyclic structure and a molecular weight of 200 to 500 is reacted with an organic diisocyanate and a hydrophilic polar group is introduced, or an aliphatic dibasic acid such as succinic acid, adipic acid, and sebacic acid; It has a cyclic structure having an alkyl branched side chain such as 2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol. As a chain extender with polyester polyol consisting of no aliphatic diol An aliphatic diol having a branched alkyl side chain having 3 or more carbon atoms, such as ethyl-2-butyl-1,3-propanediol and 2,2-diethyl-1,3-propanediol, and an organic diisocyanate compound Polyurethane resin in which a hydrophilic polar group has been introduced, or a cyclic structure such as dimer diol, a polyol compound having a long-chain alkyl chain, and an organic diisocyanate, and a polyurethane in which a hydrophilic polar group has been introduced It is preferable to use a resin.

The average molecular weight of the polar group-containing polyurethane resin used in the present invention is preferably 5,000 to 100,000, and more preferably 10,000 to 50,000. If the average molecular weight is 5,000 or more, it is preferable because the resulting magnetic coating film is not brittle and the physical strength is not lowered and the durability of the magnetic recording medium is not affected. Further, when the molecular weight is 100,000 or less, the solubility in the solvent does not decrease, and the dispersibility is also good. Further, since the viscosity of the paint at a predetermined concentration does not increase, the workability is good and the handling is easy.
Examples of the polar group contained in the polyurethane resin include —COOM, —SO ₃ M, —OSO ₃ M, —P═O (OM) ₂ , —O—P═O (OM) ₂ (M is a hydrogen atom) Or alkali metal base), —OH, —NR ₂ , —N ⁺ R ₃ (where R is a hydrocarbon group), epoxy group, —SH, —CN, etc., and at least one of these polar groups is shared. Those introduced by polymerization or addition reaction can be used. Moreover, when this polar group-containing polyurethane resin has an OH group, it preferably has a branched OH group from the viewpoint of curability and durability, and preferably has 2 to 40 branched OH groups per molecule. More preferably, it has 3 to 20 molecules per molecule. The amount of such a polar group is 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.
Specific examples of the binder include, for example, VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYES, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC, PKFE, MPS manufactured by Nisshin Chemical Industry. -TA, MPR-TA5, MPR-TAL, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, MPR-TAO, Electrochemical 1000W, DX80, DX81, DX82, DX83, 100FD, Nippon Zeon MR -104, MR-105, MR110, MR100, MR555, 400X-110A, Nippon Polyurethane Nipponran N2301, N2302, N2304, Dainippon Ink Pandex T-5105, T-R3080, T-5201, Burnock D-400, D 210-80, Crisbon 6109, 7209, Toyobo's Byron UR8200, UR8300, UR8700, RV530, RV280, Daiichi Seika's Daiferamin 4020, 5020, 5100, 5300, 9020, 9022, 7020, Mitsubishi Kasei MX5004, Sanyo Kasei Sampler SP-150, Asahi Kasei Saran F310, F210 etc. can be mentioned.

  The amount of the binder used in the magnetic layer or nonmagnetic layer of the present invention is 5 to 50% by mass with respect to the mass of the ferromagnetic powder (ferromagnetic metal powder or ferromagnetic hexagonal ferrite powder) or nonmagnetic powder. The range is preferably 10 to 30% by mass. When a polyurethane resin is used in the magnetic layer, it is preferable to use a combination of 2 to 20% by mass with respect to the ferromagnetic powder and 2 to 20% by mass of the polyisocyanate. If this occurs, it is possible to use only polyurethane or only polyurethane and isocyanate. When using a vinyl chloride resin as the other resin, it is preferably in the range of 5 to 30% by mass. In the present invention, when polyurethane is used, the glass transition temperature is −50 to 150 ° C., preferably 0 to 100 ° C., the breaking elongation is 100 to 2000%, the breaking stress is 0.49 to 98 MPa, and the yield point is 0.49 to 98 MPa is preferred.

  A preferred magnetic recording medium in the present invention comprises a nonmagnetic layer and at least one magnetic layer. Therefore, the amount of the binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin in the binder, the molecular weight of each resin forming the magnetic layer, the polar group amount, or the resin described above It is of course possible to change the physical characteristics and the like between the non-magnetic layer and each magnetic layer as required, and rather it should be optimized for each layer, and a known technique relating to a multilayer magnetic layer can be applied. For example, when changing the amount of binder in each layer, it is effective to increase the amount of binder in the magnetic layer in order to reduce scratches on the surface of the magnetic layer. The amount of binder in the magnetic layer can be increased to provide flexibility.

  Examples of the polyisocyanate usable in the present invention include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triol. Examples thereof include isocyanates such as phenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates generated by condensation of isocyanates. 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, Sumika Bayer's Death Module L, Death Module IL, Death Module N, Death Module HL, etc. are available alone or in combination of two or more using the difference in curing reactivity Each layer can be used.

VI. Other Additives Additives can be added to the magnetic layer in the present invention as necessary. Examples of the additive include an abrasive, a lubricant, a dispersant, an antifungal agent, an antistatic agent, an antioxidant, a solvent, and carbon black.
Examples of these additives include molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone having a polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, Aromatic ring-containing organic phosphonic acids such as polyolefin, polyglycol, polyphenyl ether, and phenylphosphonic acid, and alkali metal salts thereof, alkylphosphonic acids such as octylphosphonic acid, and alkali metal salts thereof, and aromatic phosphoric acids such as phenyl phosphate Esters and alkali metal salts thereof, alkyl phosphates such as octyl phosphate and alkali metal salts thereof, alkyl sulfonic acid esters and alkali metal salts thereof, fluorine-containing alkyl sulfates and alkali metal salts thereof, lauric acid and the like Monobasic fatty acids which may contain or be branched with an unsaturated bond having 10 to 24 carbon atoms and their metal salts, or monobasic acids which may contain or be branched with an unsaturated bond having 10 to 24 carbon atoms Fatty acid and 1-6 hexahydric alcohol which may contain or be branched including an unsaturated bond having 2 to 22 carbon atoms, alkoxy alcohol or alkylene oxide which may contain or be branched an unsaturated bond having 12 to 22 carbon atoms A mono-fatty acid ester, di-fatty acid ester or polyvalent fatty acid ester, a fatty acid amide having 2 to 22 carbon atoms, an aliphatic amine having 8 to 22 carbon atoms, or the like, which is composed of any one of monoalkyl ethers of a polymer can be used. In addition to the above hydrocarbon groups, alkyl groups, aryl groups, and aralkyl groups substituted with nitro groups and groups other than hydrocarbon groups such as halogen-containing hydrocarbons such as F, Cl, Br, CF ₃ , CCl ₃ , and CBr ₃ You may have something. In addition, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocyclics, phosphonium or sulfoniums, etc. Amphoteric interfaces such as cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, and sulfate ester groups, amino acids, aminosulfonic acids, sulfuric or phosphate esters of aminoalcohols, and alkylbetaines An activator or the like can also be used.
These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.). These additives are not necessarily pure and may contain impurities such as isomers, unreacted products, side reaction products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably 30% by mass or less, more preferably 10% by mass or less. Specific examples of these additives include, for example, Nippon Oil & Fats: NAA-102, castor oil hardened fatty acid, NAA-42, cationic SA, Naimine L-201, Nonion E-208, Anon BF, Anon LG, Takemoto Fats and Oils Manufactured by: FAL-205, FAL-123, Shin Nippon Chemical Co., Ltd .: NJ Lube OL, Shin-Etsu Chemical: TA-3, Lion: Armido P, Lion: Duomin TDO, Nisshin Oilio: BA-41G, Sanyo Chemical : Profan 2012E, New Pole PE61, Ionette MS-400, etc.

Further, the magnetic layer and the nonmagnetic layer in the present invention can be mixed with carbon black to lower the surface electrical resistance and obtain a desired micro Vickers hardness. Micro Vickers Hardness is usually 25~60kg ^/ mm 2 (245~588MPa), preferably in order to adjust the head ^contact, a 30~50kg / mm 2 (294~490MPa), thin film hardness meter (manufactured by NEC Corporation HMA -400), a diamond triangular pyramid needle with a ridge angle of 80 degrees and a tip radius of 0.1 μm can be used for the tip of the indenter. Examples of carbon black that can be used in the magnetic layer and nonmagnetic layer include furnace for rubber, thermal for rubber, black for color, and acetylene black.
Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle size is 5 to 300 nm, pH is 2 to 10, moisture content is 0.1 to 10%, tap density is 0.1 to 1 g / ml is preferred. Specific examples of carbon blacks that can be used in the present invention include Cabot's BLACKPEARLS 2000, 1300, 1000, 900, 905, 800, 700, VULCAN XC-72, Asahi Carbon # 80, # 60, # 55. # 50, # 35, Mitsubishi Chemical # 3050B, # 3150B, # 3250B, # 3750B, # 3950B, # 2400B, # 2300, # 1000, # 970B, # 950, # 900, # 850B, # 650B, # 650B 30, # 40, # 10B, MA-600, CONDUCTEX SC made by Columbian Carbon, RAVEN8800, 8000, 7000, 5750, 5250, 3500, 2100, 2000, 1800, 1500, 1255, 1250, 150, 50, 40, 15, RAVEN-M -P, include Ketchen Black International made Ketchen black EC and the like.
Carbon black may be surface-treated with a dispersant, or may be used after being grafted with a resin, or may be obtained by graphitizing a part of the surface. Carbon black may be dispersed with a binder in advance before being added to the magnetic coating. These carbon blacks can be used alone or in combination. When using carbon black, it is preferable to use 0.1-30 mass% with respect to the mass of a magnetic body. Carbon black has the functions of preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the magnetic layer and the nonmagnetic layer, and are based on the above-described characteristics such as particle size, oil absorption, conductivity, pH, etc. Of course, it is possible to use it properly according to the purpose, but rather it should be optimized in each layer. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

  Known organic solvents can be used in the present invention. The organic solvent used in the present invention is an arbitrary ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methyl Alcohols such as cyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene, Aromatic hydrocarbons such as cresol and chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chloride Ruhidorin, chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The organic solvent used in the present invention is preferably the same in the magnetic layer and the nonmagnetic layer. The amount added may be changed. Use non-magnetic layers with high surface tension (cyclohexanone, dioxane, etc.) to increase coating stability. Specifically, the arithmetic average value of the magnetic layer solvent composition should not be lower than the arithmetic average value of the non-magnetic layer solvent composition. Is essential. In order to improve dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that 50% or more of a solvent having a dielectric constant of 15 or more is included in the solvent composition. Moreover, it is preferable that a solubility parameter is 8-11.

  These additives used in the present invention can be selectively used in the magnetic layer and the nonmagnetic layer according to need. For example, of course, the dispersant is not limited to the example shown here, but the dispersant has a property of adsorbing or bonding with a polar group, and in the magnetic layer, mainly on the surface of the ferromagnetic powder and in the nonmagnetic layer. Then, it is presumed that the organophosphorus compound adsorbed or bonded mainly to the surface of the nonmagnetic powder with the polar group, for example, is difficult to desorb from the surface of the metal or metal compound once adsorbed. Therefore, the surface of the ferromagnetic powder (ferromagnetic metal powder and ferromagnetic hexagonal ferrite powder) or nonmagnetic powder of the present invention is covered with an alkyl group, an aromatic group, etc. The affinity of the powder or nonmagnetic powder for the binder resin component is improved, and the dispersion stability of the ferromagnetic powder or nonmagnetic powder is also improved. In addition, since the lubricant exists in a free state, fatty acids with different melting points are used in the nonmagnetic layer and magnetic layer to control the bleeding to the surface, and leaching to the surface using esters with different boiling points and polarities. It is conceivable to improve the stability of coating by controlling the amount of the surfactant, to improve the lubrication effect by increasing the additive amount of the lubricant in the nonmagnetic layer. All or part of the additives used in the present invention may be added in any step during the production of the coating liquid for the magnetic layer or nonmagnetic layer. For example, when mixing with a ferromagnetic powder before the kneading step, when adding at a kneading step with a ferromagnetic powder, a binder and a solvent, when adding at a dispersing step, when adding after dispersing, when adding just before coating, etc. There is.

VII. Backcoat layer, easy adhesion layer Generally, magnetic tape for computer data recording is strongly required to have repeated running characteristics as compared with video tape and audio tape. In order to maintain such high running durability, a backcoat layer can be provided on the surface of the nonmagnetic support opposite to the surface on which the nonmagnetic layer and the magnetic layer are provided. In the coating material for the backcoat layer, an abrasive, an antistatic agent, and a binder are dispersed in an organic solvent. Various inorganic pigments and carbon black can be used as the particulate component. Moreover, as a binder, resin, such as a nitrocellulose, a phenoxy resin, a vinyl chloride resin, a polyurethane, can be used individually or in mixture, for example.
The nonmagnetic support of the present invention may be provided with an easy-adhesion layer in order to improve the adhesion with the water vapor barrier layer and / or the backcoat layer. Examples of the easy-adhesion layer include solvent-soluble materials such as the following substances. Polyester resin, polyamide resin, polyamideimide resin, polyurethane resin, vinyl chloride resin, vinylidene chloride resin, phenol resin, epoxy resin, urea resin, melamine resin, formaldehyde resin, silicone resin, starch, modified starch compound, alginic acid compound, casein , Gelatin, pullulan, dextran, chitin, chitosan, rubber latex, gum arabic, funori, natural gum, dextrin, modified cellulose resin, polyvinyl alcohol resin, polyethylene oxide, polyacrylic acid resin, polyvinyl pyrrolidone, polyethylene imine, polyvinyl ether , Polymaleic acid copolymer, polyacrylamide, alkyd resin, etc. The easy-adhesion layer is not particularly limited as long as it has a thickness of 0.01 to 3.0 μm. Preferably 0.02～2.0Myuemu, more preferably from 0.05～1.5Myuemu. About the glass transition temperature of resin used by the said easily bonding layer, it is preferable that it is 30-120 degreeC, and it is more preferable that it is 40-80 degreeC. If it is 0 degreeC or more, it will not block at an end surface, and if it is 120 degreeC or less, the internal stress in an easily bonding layer can be relieve | moderated and it is excellent also in adhesive force.

VIII. Layer Configuration The magnetic recording medium of the present invention is provided with at least two coating films, that is, a nonmagnetic layer and a magnetic layer on the nonmagnetic layer, on at least one surface of the nonmagnetic support. Preferably, the magnetic layer may have two or more layers as necessary. In addition, a back coat layer is provided on the opposite surface of the nonmagnetic support as necessary. In the magnetic recording medium of the present invention, a lubricant coating, various coatings for protecting the magnetic layer, and the like may be provided on the magnetic layer as necessary. In addition, an undercoat layer (easy adhesion layer) may be provided between the nonmagnetic support and the nonmagnetic layer for the purpose of improving the adhesion between the coating film and the nonmagnetic support.
In the magnetic recording medium of the present invention, the nonmagnetic layer and the magnetic layer can be provided on both sides of the nonmagnetic support. With respect to the nonmagnetic layer (lower layer) and the magnetic layer (upper layer), the upper magnetic layer can be provided after the lower layer is applied, whether the lower layer is wet or dried. From the viewpoint of production yield, simultaneous or sequential wet coating is preferable, but in the case of a disk shape, it can be sufficiently used even after drying. In the multi-layer structure of the present invention, the upper layer / lower layer can be simultaneously formed by simultaneous or sequential wet coating, so that surface treatment processes such as a calendar process can be effectively used, and the surface roughness of the upper magnetic layer can be improved even with an ultra-thin layer. .
Regarding the thickness structure of the magnetic recording medium used in the present invention, the preferred thickness of the nonmagnetic support is 3 to 80 μm. The non-magnetic support of the magnetic tape has a thickness in the range of 3.5 to 7.5 μm, preferably 3 to 7 μm. When an undercoat layer is provided between the nonmagnetic support and the nonmagnetic layer or magnetic layer, the thickness of the undercoat layer is 0.01 to 0.8 μm, preferably 0.02 to 0.6 μm. The thickness of the backcoat layer provided on the surface opposite to the surface on which the nonmagnetic layer and the magnetic layer of the nonmagnetic support are provided is 0.1 to 1.0 μm, preferably 0.2 to 0. .8 μm.
The thickness of the magnetic layer is optimized according to the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used, but is generally 10 to 100 nm, preferably 20 to 80 nm, and more preferably. Is 30-80 nm. Further, the thickness variation rate of the magnetic layer is preferably within ± 50%, and more preferably within ± 40%. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.
The thickness of the nonmagnetic layer of the present invention is 0.02 to 3.0 μm, preferably 0.05 to 2.5 μm, and more preferably 0.1 to 2.0 μm. The non-magnetic layer of the magnetic recording medium of the present invention exhibits its effect if it is substantially non-magnetic. For example, even if it contains a small amount of magnetic material as an impurity or intentionally, This shows the effect of the invention and can be regarded as substantially the same configuration as the magnetic recording medium of the invention. “Substantially the same” means that the residual magnetic flux density of the nonmagnetic layer is 10 mT (100 G) or less or the coercive force is 7.96 kA / m (100 Oe) or less, preferably the residual magnetic flux density and the coercive force. It means not having.

IX. Physical Properties The saturation magnetic flux density of the magnetic layer of the magnetic recording medium used in the present invention is 100 to 300 mT. The Hc of the magnetic layer is 143.3 to 318.4 kA / m, preferably 159.2 to 278.6 kA / m. The coercive force distribution is preferably narrow, and SFD and SFDr are 0.6 or less, more preferably 0.2 or less.
The friction coefficient with respect to the head of the magnetic recording medium used in the present invention is 0.5 or less, preferably 0.3 or less in the range of temperature -10 to 40 ° C. and humidity 0 to 95%. The surface resistivity is preferably 10 ⁴ to 10 ¹² Ω / sq of the magnetic surface, and the charging position is preferably within −500 V to +500 V. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 0.98 to 19.6 GPa in each in-plane direction, the breaking strength is preferably 98 to 686 MPa, and the elastic modulus of the magnetic recording medium is in-plane. Preferably in the direction of 0.98 to 14.7 GPa, the residual spread is preferably 0.5% or less, and the thermal shrinkage rate at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5%. Hereinafter, it is most preferably 0.2% or less.
The glass transition temperature of the magnetic layer (maximum point of loss elastic modulus measured by dynamic viscoelasticity measured at 110 Hz) is preferably 50 to 180 ° C, and that of the nonmagnetic layer is preferably 0 to 180 ° C. The loss elastic modulus is preferably in the range of 1 × 10 ⁷ to 8 × 10 ⁸ Pa, 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. For example, in the case of a disk medium in which repeated use is important, a larger void ratio is often preferable for running durability.
The maximum height SR _max of the magnetic layer is 0.5 μm or less, the ten-point average roughness SRz is 0.3 μm or less, the center plane peak height SRp is 0.3 μm or less, and the center plane valley depth SRv is 0.3 μm or less. The center surface area ratio SSr is preferably 20 to 80%, and the average wavelength Sλa is preferably 5 to 300 μm. These can be easily controlled by controlling the surface properties with the filler of the support or the roll surface shape of the calender treatment. The curl is preferably within ± 3 mm.
The physical characteristics of the nonmagnetic layer and the magnetic layer in the magnetic recording medium of the present invention can be changed between the nonmagnetic layer and the magnetic layer according to the purpose. For example, the elastic modulus of the magnetic layer can be increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer can be made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

X. Manufacturing Method The step of manufacturing the magnetic layer coating liquid for the magnetic recording medium used in the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided as necessary before and after these steps. Each process may be divided into two or more stages. All raw materials such as hexagonal ferrite ferromagnetic powder or ferromagnetic metal powder, non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, solvent, etc. used in the present invention are at the beginning or middle of any process. It may be added at 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 material having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, glass beads can be used to disperse the magnetic layer solution and the nonmagnetic layer solution. Such glass beads are preferably 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 method for manufacturing a magnetic recording medium of the present invention, for example, the magnetic layer coating liquid is formed on the surface of a nonmagnetic support under running so as to have a predetermined film thickness. Here, a plurality of magnetic layer coating solutions may be applied sequentially or simultaneously, and a nonmagnetic layer coating solution and a magnetic layer coating solution may be applied sequentially or simultaneously. The coating machine for applying the magnetic layer coating liquid or the nonmagnetic layer coating liquid includes air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure A coat, a kiss coat, a cast coat, a spray coat, a spin coat, etc. can be used. As for these, for example, “Latest Coating Technology” (May 31, 1983) issued by General Technology Center Co., Ltd. can be referred to.
In the case of a magnetic tape, the magnetic layer coating liquid coating layer is formed by subjecting the ferromagnetic powder contained in the magnetic layer coating liquid coating layer to a magnetic field orientation process in the longitudinal direction using a cobalt magnet or a solenoid. In the case of a disk, a sufficiently isotropic orientation may be obtained even without orientation without using an orientation device, but known random such as alternately arranging cobalt magnets obliquely and applying an alternating magnetic field with a solenoid. It is preferable to use an alignment device. In the case of a ferromagnetic metal powder, the isotropic orientation is generally preferably in-plane two-dimensional random, but can also be three-dimensional random with a vertical component. In the case of a ferromagnetic hexagonal ferrite powder, in general, it tends to be three-dimensional random in the plane and in the vertical direction, but it can also be two-dimensional random in the plane. Further, isotropic magnetic characteristics can be imparted in the circumferential direction by using a well-known method such as a different pole facing magnet and making the vertical orientation. In particular, when performing high density recording, vertical alignment is preferable. Moreover, circumferential orientation can also be achieved using spin coating.
It is preferable that the drying position of the coating film can be controlled by controlling the temperature, air volume, and coating speed of the drying air, the coating speed is preferably 20 m / min to 1000 m / min, and the temperature of the drying air is preferably 60 ° C. or higher. Also, moderate pre-drying can be performed before entering the magnet zone.
After being dried, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing process, for example, a super calendar roll or the like is used. By performing the surface smoothing treatment, voids generated by removing the solvent during drying disappear and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can. As the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyamideimide or the like is used. Moreover, it can also process with a metal roll. The magnetic recording medium of the present invention preferably has a surface having extremely excellent smoothness. As the method, for example, as described above, a magnetic layer formed by selecting a specific ferromagnetic powder and a binder is subjected to the calendar treatment. As calendering conditions, the temperature of the calendar roll is in the range of 60 to 100 ° C., preferably in the range of 70 to 100 ° C., particularly preferably in the range of 80 to 100 ° C., and the pressure is 100 to 500 kg / cm (98 to 490 kN). / M), preferably 200 to 450 kg / cm (196 to 441 kN / m), particularly preferably 300 to 400 kg / cm (294 to 392 kN / m). Is preferably carried out by
As heat shrinkage reduction means, there are a method of heat-treating in the form of a web while handling at low tension, and a method of heat-treating in a form in which tapes are laminated in a bulk or cassette (thermo-treatment method), both of which can be used. . From the viewpoint of supplying a high-output and low-noise magnetic recording medium, the thermo treatment method is preferable.
The obtained magnetic recording medium can be used after being cut into a desired size using a cutting machine or the like.

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

(Example 1-1)
1. Preparation of coating solution for water vapor barrier layer (second layer) Vinylidene chloride / vinyl chloride = 92/8 copolymer resin 15 parts methyl ethyl ketone / cyclohexanone = 8/2 mixed solvent 100 parts Dissolve the above copolymer resin with water vapor A coating liquid for a barrier layer (second layer) was obtained.

2. Preparation of coating liquid for magnetic layer 100 parts of ferromagnetic acicular metal powder Composition: Fe / Co / Al / Y = 68/20/7/5 (at%), surface treatment layer: Al ₂ O ₃ , Y ₂ O ₃ , Crystallite size: 125 mm, average major axis length: 45 nm, average needle ratio: 5, S _BET : 42 m ² / g, coercive force (Hc): 180 kA / m, saturation magnetization (σs): 135 A · m ² / kg
Polyurethane resin 12 parts Branched side chain-containing polyester polyol / diphenylmethane diisocyanate, hydrophilic polar group: —SO ₃ Na = 70 eq / ton-containing phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size 0.1 μm) 2 parts Carbon black (average particle size 20 nm) 2 parts cyclohexanone 110 parts methyl ethyl ketone 100 parts toluene 100 parts butyl stearate 2 parts stearic acid 1 part

3. Preparation of coating liquid for nonmagnetic layer 85 parts nonmagnetic inorganic powder, α-iron oxide, surface treatment layer: Al ₂ O ₃ , SiO ₂ , average major axis diameter: 0.15 μm, average needle ratio: 7, S _BET : 50 m ² / g, DBP oil absorption: 33 ml / 100 g, pH 8
Carbon black 20 parts S _BET : 250 m ² / g, DBP oil absorption: 120 ml / 100 g, pH: 8, volatile content: 1.5%
Polyurethane resin 12 parts Branched side chain-containing polyester polyol / diphenylmethane diisocyanate, hydrophilic polar group: —SO ₃ Na = 70 eq / ton-containing acrylic resin 6 parts Benzyl methacrylate / diacetone acrylamide, hydrophilic polar group: —SO ₃ Na = 60 eq / ton-containing phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size 0.2 μm) 1 part cyclohexanone 140 parts methyl ethyl ketone 170 parts butyl stearate 2 parts stearic acid 1 part

  For each of the magnetic layer (upper layer) coating liquid and the non-magnetic layer (lower layer) coating liquid, each component was kneaded with an open kneader for 60 minutes and then dispersed with a sand mill for 120 minutes. To the obtained dispersion, 6 parts of a trifunctional low molecular weight polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane) was added and stirred for 20 minutes, followed by filtration using a filter having an average pore size of 1 μm, A non-magnetic paint was prepared.

Using a vacuum deposition apparatus on both sides of a polyethylene naphthalate (PEN) film support having a thickness of 5 μm, a surface roughness of 3 nm on the magnetic layer forming surface side, and a surface roughness of 8 nm on the back surface side, a maximum incident angle of 60 °, and a film traveling speed An Al ₂ O ₃ water vapor barrier layer (first layer) having a thickness of 40 nm and an electron gun power of 16 kW was formed by vapor deposition at 1.5 m / min.

Furthermore, the coating liquid for the water vapor barrier layer (second layer) is applied onto the Al ₂ O ₃ water vapor barrier layer (first layer) on the magnetic layer forming surface side so that the thickness after drying becomes 0.3 μm. After drying, the above non-magnetic paint is then applied so that the thickness after drying is 1.8 μm, and immediately thereafter, the magnetic paint is applied simultaneously in a multilayer so that the thickness after drying is 0.1 μm. did. At this time, magnetic orientation was performed with a 300 mT magnet while both layers were still wet, and after drying, the temperature was 90 ° C., the speed was 100 m / min, and the linear pressure was 300 kg using a seven-stage calendar composed of only metal rolls. / Cm (294 kN / m), heat treatment was performed at 70 ° C. for 48 hours, and slitting to a 1/2 inch width was performed to produce a magnetic tape.

(Examples 1-2 and 1-3)
A magnetic tape was produced in the same manner as in Example 1-1 except that the presence or absence of the first layer and the second layer in the water vapor barrier layer and the formation surface were changed as shown in Table 1.

(Comparative Examples 1-1 to 4)
Example 1 except that the type of the nonmagnetic support, the average major axis length of the ferromagnetic metal powder, the presence or absence of the first and second layers in the water vapor barrier layer, and the formation surface were changed as shown in Table 1. A magnetic tape was produced in the same manner as in No. 1.

(Examples 2-1 to 3)
Preparation of coating liquid for magnetic layer Ferromagnetic plate-shaped hexagonal ferrite powder 100 parts Composition (molar ratio): Ba / Fe / Co / Zn = 1/9 / 0.2 / 0.8, average plate diameter: 25 nm, average Plate ratio: 3, S _BET : 50 m ² / g, coercive force (Hc): 191 kA / m, saturation magnetization (σs): 60 A · m ² / kg
12 parts polyurethane resin Branched side chain-containing polyester polyol / diphenylmethane diisocyanate,
Hydrophilic polar group: —SO ₃ Na = 70 eq / ton-containing phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle diameter 0.15 μm) 2 parts carbon black (average particle diameter 20 nm) 2 parts cyclohexanone 110 parts methyl ethyl ketone 100 Part toluene 100 parts butyl stearate 2 parts stearic acid 1 part

  A magnetic paint was prepared in the same manner as in Example 1-1 using the magnetic layer coating liquid. Moreover, the magnetic tape was produced by the method similar to Example 1-1 except having changed the presence or absence of the 1st layer in the water vapor | steam barrier layer and the 2nd layer, and the formation surface as shown in Table 2. In addition, the same thing as Example 1-1 was used for the coating liquid for nonmagnetic layers.

(Comparative Examples 2-1 to 4)
Example 2 except that the type of the nonmagnetic support, the average plate diameter of the ferromagnetic hexagonal ferrite powder, the presence or absence of the first and second layers in the water vapor barrier layer, and the formation surface were changed as shown in Table 2. A magnetic tape was produced in the same manner as in -1.

(Example 3-1)
Preparation of coating liquid for magnetic layer Ferromagnetic plate-shaped hexagonal ferrite powder 100 parts Composition (molar ratio): Ba / Fe / Co / Zn = 1/9 / 0.2 / 0.8, average plate diameter: 25 nm, average Plate ratio: 3, S _BET : 50 m ² / g, coercive force (Hc): 191 kA / m, saturation magnetization (σs): 60 A · m ² / kg
Polyurethane resin 12 parts Branched side chain-containing polyester polyol / diphenylmethane diisocyanate, hydrophilic polar group: —SO ₃ Na = 70 eq / ton-containing phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size 0.15 μm) 2 parts Carbon black (average particle size 20 nm) 2 parts cyclohexanone 110 parts methyl ethyl ketone 100 parts toluene 100 parts butyl stearate 2 parts stearic acid 1 part

A magnetic paint was prepared in the same manner as in Example 1-1 using the magnetic layer coating liquid.
Using a vacuum deposition device on both sides of a polyethylene naphthalate (PEN) film support with a thickness of 30 μm and a surface roughness of 2 nm on the magnetic layer forming surface, a maximum incident angle of 60 °, a film traveling speed of 1.5 m / min, an electron gun An Al ₂ O ₃ water vapor barrier layer (first layer) having a power of 16 kW and a thickness of 40 nm was formed by vapor deposition.
On the obtained polyethylene naphthalate (PEN) support, the water vapor barrier layer (second layer) coating solution was applied so that the thickness after drying was 0.3 μm, dried, and then Example 1-1. A similar non-magnetic coating was applied so that the thickness after drying was 1.8 μm, and immediately thereafter, the above-mentioned magnetic coating was applied simultaneously so that the thickness after drying was 0.2 μm. While the layer is still wet, it passes through two magnetic field strength AC magnetic field generators with a frequency of 50 Hz, a magnetic field strength of 25 mT, and a frequency of 50 Hz and 12 mT. , Processed at a linear pressure of 300 kg / cm (294 kN / m), heat-treated at 70 ° C. for 48 hours, punched to 1.8 mm and surface-polished, then the CLIK-DIS with the liner installed inside It placed in a cartridge, adding a predetermined mechanical parts to give a flexible disk.

(Examples 3-2 and 3)
A flexible disk was produced in the same manner as in Example 3-1, except that the presence or absence of the first layer and the second layer in the water vapor barrier layer and the formation surface were changed as shown in Table 3.

(Comparative Examples 3-1 to 4)
Example 3 except that the type of nonmagnetic support, the average plate diameter of the ferromagnetic hexagonal ferrite powder, the presence or absence of the first layer and the second layer in the water vapor barrier layer, and the formation surface were changed as shown in Table 3. A flexible disk was produced in the same manner as in -1.

<Measurement method>
1. Measurement of water vapor transmission rate A water vapor transmission rate measuring device manufactured by MOCON in accordance with JIS K7129 was used, and measurement was performed at 40 ° C. and 90% RH.
2. Measurement of surface roughness (Ra) (support)
Measurement was performed with an optical roughness meter (HD-2000 manufactured by WYKO) at a cutoff value of 0.25 mm, and an arithmetic average roughness corresponding to Ra described in JISB0660-1998 and ISO4287-1997 was determined.
3. Measurement of error rate (initial, under high humidity and high temperature) Recording signal was recorded at 23 ° C. and 50% RH by 8-10 conversion PR1 equalization system for magnetic tape and (2,7) RLL modulation system for flexible disk. The measurement was carried out in each environment of ℃, 50% RH (initial), 40 ℃, 80% RH (high humidity and high temperature).
A result is combined with Tables 1-3 and shown.

From the above results, in the magnetic recording medium of the present invention, the water vapor blocking layer and the magnetic layer are provided in this order on at least one surface of the nonmagnetic support, and both the longitudinal and width Young's moduli of the nonmagnetic support are both. 7 GPa or more, and the magnetic layer includes a ferromagnetic hexagonal ferrite powder having an average plate diameter of 5 to 40 nm or a ferromagnetic metal powder having an average major axis length of 20 to 100 nm and a binder, and the nonmagnetic support. And the water vapor permeability of the laminate comprising the water vapor barrier layer is in the range of 0.001 to 0.3 g / m ² · 24 hours, so that excellent magnetic recording with a low error rate even under high temperature and high humidity compared to the comparative example It can be seen that a medium is obtained.

Claims (5)

A water vapor blocking layer and a magnetic layer are provided in this order on at least one surface of the nonmagnetic support. Both the Young's modulus in the longitudinal direction and the width direction of the nonmagnetic support are 7 GPa or more, and the magnetic layer is an average plate. Water vapor permeability of a laminate comprising a ferromagnetic hexagonal ferrite powder having a diameter of 5 to 40 nm or a ferromagnetic metal powder having an average major axis length of 20 to 100 nm and a binder, and comprising the nonmagnetic support and a water vapor barrier layer Is in the range of 0.001 to 0.3 g / m ² · 24 hours.   The magnetic recording medium according to claim 1, wherein the water vapor blocking layer is a layer containing a metal material or a layer containing a resin.   The magnetic recording medium according to claim 1, wherein the water vapor blocking layer includes at least two layers including a first layer containing a metal material and a second layer containing a resin.   The magnetic recording medium according to claim 2, wherein the metal material is a metal oxide, and the resin is a polymer compound having a mass average molecular weight of 1000 to 100,000.   The magnetic recording medium according to claim 1, wherein a nonmagnetic layer containing a nonmagnetic powder and a binder is provided between the nonmagnetic support and the magnetic layer.