JP2007294083A - Magnetic recording medium - Google Patents

Abstract

GMR that suppresses fluctuations in thickness of magnetic layer and consequently fluctuations in output and obtains high S / N
To provide a magnetic recording medium suitable for a head.
In a magnetic recording medium provided with at least one magnetic layer in which a ferromagnetic powder is dispersed in a binder on a nonmagnetic support, the average thickness δ of the magnetic layer is 10 to 100 nm,
In addition, the depth profile of the element that exists only in the magnetic layer among the elements constituting the ferromagnetic powder is measured by TOF-SIMS, and the standard deviation σ _d when the differential curve of the depth profile curve is fitted with a normal distribution is A magnetic recording medium having a thickness of 5 to 50 nm in terms of a coating layer of the magnetic recording medium.
[Selection figure] None

Description

The present invention relates to a magnetic recording medium that exhibits excellent electromagnetic conversion characteristics during high-density recording.

Magnetic recording technology enables other recordings such as the ability to repeatedly use media, the ease of digitizing signals, the construction of a system in combination with peripheral devices, and the simple modification of signals. Since it has excellent features not found in the system, it has been widely used in various fields including video and computer applications.

In order to meet the demands for downsizing equipment, improving the quality of recording and playback signals, extending the recording time, and increasing the recording capacity, the recording density, reliability, and durability of the recording medium are further increased. There has always been a desire for improvement.

For example, practical application of digital recording system that realizes improved sound quality and image quality, high-definition TV
In order to respond to the development of a recording system that supports the recording system, a magnetic recording medium that can record and reproduce short wavelength signals and has excellent reliability and durability even when the relative speed between the head and the medium increases, compared to conventional systems. Is now required. In addition, it is desired that a large-capacity digital recording medium be developed in order to store an increasing amount of data for computer use. Even in the field of magnetic disks, the capacity of data to be handled is increasing rapidly, and it is desired to increase the capacity of flexible disks (FD). A high-capacity disk using a ferromagnetic metal fine powder excellent in high-density recording characteristics has been put into practical use with a high-density FD of 100 MB or more, but a system with a larger capacity and a higher transfer speed is required.

In order to achieve a high recording density of a magnetic recording medium, a shortening of the recording signal wavelength and a narrowing of the track width of the reproducing head have been strongly advanced. When the length of the signal recording area becomes comparable to the size of the magnetic material used, a clear magnetization transition state cannot be created, and recording becomes virtually impossible. For this reason, it is necessary to develop a magnetic material having a sufficiently small particle size with respect to the shortest wavelength to be used, and the finer magnetic material has been directed for many years.

The magnetic tape used in the digital signal recording system has a relatively thick single layer ferromagnetic powder, binder, and polishing on one side of a nonmagnetic support with a thickness of 2.0 to 3.0 μm. A magnetic layer containing an agent is provided, and a back layer is provided on the other side in order to prevent winding disturbance and to maintain good running durability. However, the relatively thick single layer structure magnetic layer as described above has a problem of self-demagnetization during the recording process and a thickness loss problem that the output decreases during the reproduction process.

In order to improve the reduction in reproduction output due to the loss of thickness of the magnetic layer, it is known to make the magnetic layer thin, and the non-lower layer formed by dispersing inorganic powder on the nonmagnetic support and dispersing in the binder. There is disclosed a magnetic recording medium provided with an upper magnetic layer having a thickness of 1.0 μm or less formed by dispersing ferromagnetic powder in a binder while the magnetic layer and the nonmagnetic layer are in a wet state (for example, Patent Documents). (See 1)
.

In recent years, means for transmitting terabyte-class information at a high speed have been remarkably developed, and images and data transfer with enormous information have become possible, while advanced techniques for recording, reproducing and storing them have been required. It has come to be. However, with the improvement of the technical level, both the recording / reproducing apparatus and the magnetic recording medium are required to have a higher recording capacity.
Regarding magnetic tape, there are various uses such as audio tape, video tape, computer tape, etc. Especially in the field of data backup tape, with the increase in capacity of hard disk to be backed up, several 10 to 800 GB per volume. Those with recording capacity have been commercialized.
In the future, a large-capacity backup tape exceeding 1 TB has been proposed, and its high recording capacity is indispensable.

As a means to increase the recording capacity, the approach from the magnetic tape manufacturing side, high recording such as fine particles of magnetic powder and high density filling of them in the coating film, smoothing of the coating film, thinning of the magnetic layer, etc. Densification techniques have been proposed.
On the other hand, in recent years, a reproducing head having an operating principle of magnetoresistance (MR) has been proposed and started to be used. In Patent Document 2 below, in a magnetic recording medium in which a substantially nonmagnetic lower layer and a magnetic layer in which a hexagonal ferrite powder is dispersed in a binder are provided in this order on a support, The magnetic porosity is 15 to 30% by volume, the magnetic layer thickness variation rate (σ / δ) (σ: standard deviation of magnetic layer thickness, δ: magnetic layer thickness) is 30% or less, and the magnetic layer A magnetic recording medium having a surface center plane average surface roughness Ra of 0.5 to 4 nm has been proposed.

By the way, in order to further increase the recording capacity, a higher recording density is required. Therefore, at present, a giant magnetoresistive effect reproducing head having higher sensitivity than an anisotropic magnetoresistive effect reproducing head (so-called AMR head). (So-called GMR head) has also been proposed, but the magnetic recording medium described in Patent Document 2 has a problem that sufficient electromagnetic conversion characteristics cannot be obtained by the GMR head.
In the invention of Patent Document 2, the thickness of the magnetic layer is described up to a minimum of 50 nm, but in the examples, 150 nm is the minimum, which is insufficient for further high-density recording. In addition, since the magnetic layer thickness variation rate is 12% in the example, the standard deviation σ of the magnetic layer thickness is 18 nm as a minimum, which cannot be said to be sufficiently small.
In addition, the magnetic layer thickness variation rate (σ / δ) in the document 2 is shown in paragraphs (0009) and (0010).
As described above, it is obtained from a cross-sectional TEM (transmission electron microscope) image of an ultrathin section of a magnetic recording medium. The information on the thickness of the magnetic layer obtained from the TEM image is obtained by averaging the information in the thickness direction of the slice. Was not considered.
If the distribution of the magnetic material in the thickness direction of the magnetic layer is not uniform, there arises a problem that output fluctuation becomes large when reproducing with a GMR head.
The distribution of the magnetic material in the thickness direction of the magnetic layer is insufficient for a GMR head sensitive to the distribution and needs to be specified.

JP-A-8-306032 JP 2002-304716 A

Therefore, an object of the present invention is to suppress the fluctuation in the thickness of the magnetic layer, and hence the output fluctuation, and to achieve a high S
An object of the present invention is to provide a magnetic recording medium suitable for a GMR head capable of obtaining / N.

The present invention is as follows.
1) In a magnetic recording medium in which at least one magnetic layer formed by dispersing ferromagnetic powder in a binder on a nonmagnetic support is provided.
The magnetic layer has an average thickness δ of 10 to 100 nm,
In addition, the depth profile of the element that exists only in the magnetic layer among the elements constituting the ferromagnetic powder is measured by TOF-SIMS, and the standard deviation σ _d when the differential curve of the depth profile curve is fitted with a normal distribution is A magnetic recording medium having a thickness of 5 to 50 nm in terms of a coating layer of the magnetic recording medium.
2) The magnetic recording medium as described in 1) above, wherein the ferromagnetic powder is a hexagonal ferrite powder.
3) The magnetic recording medium as described in 1) or 2) above, wherein the standard deviation σ _d is 5 to 20 nm in terms of a coating layer of the magnetic recording medium.

According to the present invention, the distribution of the magnetic material in the depth direction of the magnetic layer, particularly at the interface can be made uniform, and the output fluctuation and electromagnetic conversion characteristics can be remarkably improved. In addition, it is possible to provide a high-capacity magnetic recording medium that achieves an improvement in surface recording density required by the market and is suitable for recording / reproducing using a GMR head as a reproducing head.

In the present invention, as a result of examining the above problems, the average thickness δ of the magnetic layer and the TOF-SIMS
The standard deviation σ _d (hereinafter also referred to as “σ _d ”, “standard deviation σ _d of the magnetic distribution in the thickness direction at the interface”) when the differential curve of the depth profile curve measured in step 1 was fitted with a normal distribution was identified. It is important that the distribution of the magnetic material in the depth direction of the magnetic layer, particularly at the interface, can be made uniform, and the output fluctuation and electromagnetic conversion characteristics can be remarkably improved.

Examples of means for achieving the average thickness δ of the magnetic layer and the standard deviation σ _d of the magnetic material distribution in the thickness direction in the present invention include the following.
a) Use of a support having excellent surface smoothness b) Use of a nonmagnetic layer having excellent surface smoothness After the nonmagnetic layer is provided on the support and before forming the magnetic layer, the temperature, processing time, etc. The temperature, pressure, speed, and temperature of the calender roll before the thermo process
For example, a calendar process appropriately setting the material, surface property, roll configuration and the like may be performed.
c) An undercoat layer (smoothing layer) is formed on the support using a polymer or a radiation curable compound,
Form on the nonmagnetic layer.
d) Use of Back Layer with Excellent Surface Smoothness Use of Powder with Fine Particles and Good Dispersion in Coating Solution for Forming Back Layer (also called Back Solution) e) Temperature and pressure of calender roll after formation of magnetic layer and back layer, Apply calendar processing with appropriate settings for speed, material, surface properties, roll configuration, etc.
f) Applying the magnetic coating solution using a pump without a pulsating flow when forming the magnetic layer.

In the present invention, δ and σ _d mean those defined in the examples.
δ is 10 to 100 nm, preferably 20 to 90 nm, more preferably 25 to 85 nm,
Most preferably, it is 30-80 nm. σ _d is 5 to 50 nm, preferably 5 to 40 nm,
More preferably, it is 5-30 nm, Most preferably, it is 5-20 nm.

Next, each component constituting the magnetic recording medium of the present invention will be described.
[Non-magnetic support]
Nonmagnetic supports used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulosic acetate, polycarbonate, polyamide, polyimide, polyamideimide, and polysulfone. , Known films such as polyaramid, aromatic polyamide, and polybenzoxazole can be used. It is preferable to use a high-strength support such as polyethylene naphthalate or polyamide. If necessary, a laminated type support as disclosed in JP-A-3-224127 can be used to change the surface roughness of the magnetic surface and the nonmagnetic support surface. These supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like. It is also possible to apply an aluminum or glass substrate as the support of the present invention.

Of these, a polyester support (hereinafter simply referred to as polyester) is preferred. Such a polyester is a polyester composed of a dicarboxylic acid and a diol, such as polyethylene terephthalate and polyethylene naphthalate.
The main constituent dicarboxylic acid components include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylethanedicarboxylic acid,
Examples include cyclohexane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl thioether dicarboxylic acid, diphenyl ketone dicarboxylic acid, and phenylindane dicarboxylic acid.
Examples of the diol component include ethylene glycol, propylene glycol, tetramethylene glycol, cyclohexanedimethanol, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyethoxyphenyl) propane, bis ( 4-
Hydroxyphenyl) sulfone, bisphenol full orange hydroxyethyl ether, diethylene glycol, neopentyl glycol, hydroquinone, cyclohexanediol and the like.
Among the polyesters having these as main constituents, terephthalic acid and / or 2,6-naphthalenedicarboxylic acid as a dicarboxylic acid component and ethylene glycol as a diol component from the viewpoint of transparency, mechanical strength, dimensional stability, etc. And / or a polyester mainly composed of 1,4-cyclohexanedimethanol is preferred.
Among them, a polyester mainly composed of polyethylene terephthalate or polyethylene-2,6-naphthalate, a copolymer polyester composed of terephthalic acid, 2,6-naphthalenedicarboxylic acid and ethylene glycol, and two or more kinds of these polyesters A polyester having a mixture as a main constituent is preferred. Particularly preferred is a polyester having polyethylene-2,6-naphthalate as a main constituent.
The polyester used in the present invention may be biaxially stretched or a laminate of two or more layers.

The polyester may be further copolymerized with other copolymerization components, or may be mixed with other polyesters. Examples of these include the dicarboxylic acid components and diol components mentioned above, or polyesters composed thereof.
In the polyester used in the present invention, an aromatic dicarboxylic acid having a sulfonate group or an ester-forming derivative thereof, a dicarboxylic acid having a polyoxyalkylene group or an ester-forming derivative thereof, in order to make it difficult for delamination during film formation.
A diol having a polyoxyalkylene group may be copolymerized.
Among them, in terms of polymerization reactivity of polyester and transparency of the film, 5-sodium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 4-sodium sulfophthalic acid, 4-
Sodium sulfo-2,6-naphthalenedicarboxylic acid and compounds obtained by replacing these sodium with other metals (for example, potassium, lithium, etc.), ammonium salts, phosphonium salts, etc., or ester-forming derivatives thereof, polyethylene glycol, polytetramethylene glycol Polyethylene glycol-polypropylene glycol copolymers and compounds converted to carboxyl groups by oxidizing the hydroxy groups at both ends thereof are preferred.
The proportion of copolymerization for this purpose is preferably 0.1 to 10 mol% based on the dicarboxylic acid constituting the polyester.
For the purpose of improving heat resistance, a bisphenol compound, a compound having a naphthalene ring or a cyclohexane ring can be copolymerized. As these copolymerization ratios,
1-20 mol% is preferable on the basis of the dicarboxylic acid which comprises polyester.

In the present invention, the method for synthesizing the polyester is not particularly limited, and can be produced according to a conventionally known polyester production method. For example, a direct esterification method in which a dicarboxylic acid component is directly esterified with a diol component. First, a dialkyl ester is used as a dicarboxylic acid component, this is transesterified with the diol component, and this is heated under reduced pressure. A transesterification method of polymerizing by removing excess diol component can be used. At this time, if necessary, a transesterification catalyst or a polymerization reaction catalyst can be used, or a heat-resistant stabilizer can be added.
In addition, anti-coloring agents, antioxidants, crystal nucleating agents, slipping agents, stabilizers, anti-blocking agents, UV absorbers, viscosity modifiers, antifoaming and clearing agents, antistatic agents, and pH adjustments during each synthesis Agent,
You may add 1 type, or 2 or more types of various additives, such as dye, a pigment, and a reaction terminator.

Further, a filler may be added to the polyester. Examples of the filler include inorganic powders such as spherical silica, colloidal silica, titanium oxide, and alumina, and organic fillers such as crosslinked polystyrene and silicone resin.
Further, in order to increase the rigidity of the support, these materials can be highly stretched, or a metal, semimetal, or oxide layer thereof can be provided on the surface.

In the present invention, the thickness of the polyester as the nonmagnetic support is preferably 3 to 80 μm.
More preferably, it is 3-50 micrometers, Most preferably, it is 3-10 micrometers. The center surface average roughness (Ra) of the support surface is 4 nm or less, more preferably 2 nm or less. This Ra was measured with HD2000 manufactured by WYKO.
Further, the Young's modulus in the longitudinal direction and the width direction of the nonmagnetic support is preferably 6.0 GPa or more, and more preferably 7.0 GPa or more.

The magnetic recording medium of the present invention is provided with a magnetic layer containing ferromagnetic powder and a binder on at least one surface of the nonmagnetic support, and substantially between the nonmagnetic support and the magnetic layer. It is preferable to provide a nonmagnetic layer (also referred to as a lower layer or a nonmagnetic lower layer) that is nonmagnetic in nature.

[Magnetic layer]
As the ferromagnetic powder contained in the magnetic layer, preferably has a volume is 1000～20000Nm ^3, further preferably 2000~8000nm ^3. By setting it within this range, it is possible to effectively suppress a decrease in magnetic characteristics due to thermal fluctuations, and to obtain good C / N (S / N) while maintaining low noise. The ferromagnetic powder is not particularly limited, but ferromagnetic metal powder, hexagonal ferrite powder or iron nitride powder is preferable.
The volume of the acicular powder is obtained from the major axis length and minor axis length assuming that the shape is a cylinder.
In the case of plate-like powder, the volume is determined from the plate diameter and axial length (plate thickness) assuming that the shape is a prism (hexagonal prism in the case of hexagonal ferrite powder).
In the case of iron nitride-based powder, the volume is obtained assuming that the shape is a sphere.
As for the size of the magnetic material, an appropriate amount of the magnetic layer is peeled off. N- to 30-70 mg of peeled magnetic layer
Butylamine is added, sealed in a glass tube, set in a pyrolyzer, and heated at 140 ° C. for about 1 day. After cooling, the contents are taken out from the glass tube and centrifuged to separate the liquid and solids.
The separated solid is washed with acetone to obtain a powder sample for TEM. This sample was photographed with a Hitachi transmission electron microscope H-9000, and the particles were photographed at a photographing magnification of 100,000. The total magnification was 5
A particle photograph is obtained by printing on photographic paper so as to have a magnification of 00000 times. Select the target magnetic material from the particle photograph, trace the outline of the powder with a digitizer, and image analysis software KS made by Carl Zeiss
Measure particle size at -400. Measure the size of 500 particles.
In the present specification, the size of powder such as a magnetic material (hereinafter referred to as “powder size”) is as follows: Larger than the maximum major axis)
Or the like, it is represented by the length of the long axis constituting the powder, that is, the length of the long axis. (Smaller than the maximum major axis), it is represented by the maximum major axis of the plate surface or bottom surface. (3) The shape of the powder is spherical, polyhedral, unspecified, etc. If the axis cannot be specified, it is represented by the equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.
The average powder size of the powder is an arithmetic average of the above powder sizes, and is obtained by carrying out the measurement as described above for 500 primary particles. Primary particles refer to an independent powder without aggregation.
The average acicular ratio of the powder is determined by measuring the length of the minor axis of the powder in the above measurement, that is, the minor axis length, and calculating the arithmetic average of the values of (major axis length / minor axis length) of each powder. Point to. Here, the minor axis length is the definition of the powder size in the case of (1), the length of the minor axis constituting the powder, and in the case of (2),
In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.
When the shape of the powder is specific, for example, in the case of the definition (1) of the powder size, the average powder size is referred to as an average major axis length, and in the case of the definition (2), the average powder size Is called the average plate diameter, and the arithmetic average of (maximum major axis / thickness to height) is called the average plate ratio. In the case of definition (3), the average powder size is referred to as an average diameter (also referred to as an average particle diameter or an average particle diameter). In powder size measurement, the standard deviation / average value expressed as a percentage is defined as the coefficient of variation.

<Ferromagnetic metal powder>
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 (including an alloy), but is ferromagnetic with α-Fe as a main component. Alloy powder is preferred. These ferromagnetic powders include Al, Si, S, other than predetermined atoms.
Sc, Ca, 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,
It may contain atoms such as Mn, Zn, Ni, Sr, and B. Al, Si, Ca, Y,
It is preferable that at least one of 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, Co is Fe.
It is preferable that 10 to 40 atomic%, Al is 2 to 20 atomic%, and Y is 1 to 15 atomic%.

The ferromagnetic metal powder may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent or the like, which will be described later. 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 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 sum of each ion is about 300 ppm or less, there is little influence on the characteristics. The ferromagnetic metal powder used in the present invention preferably has fewer vacancies, and its value is 20% by volume or less, more preferably 5% by volume or less.

The average major axis length of the ferromagnetic metal powder is preferably 10 to 100 nm, more preferably 20 to 70 nm, and particularly preferably 30 to 60 nm.
The crystallite size of the ferromagnetic metal powder is preferably 70 to 180 mm, more preferably 80 to 140 mm, and particularly preferably 90 to 130 mm.
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 50 kV, and a tube current 300 mA. .

The specific surface area (S _BET ) of the ferromagnetic metal powder by the BET method is preferably 45 to 120 m ² / g or more, and more preferably 50 to 100 m ² / g. 45m noise increases is less than ² / g, 120m ² / g by weight, the surface properties obtained hardly undesirable. Within this range, both good surface properties and low noise can be achieved.
If necessary, the ferromagnetic powder may be surface-treated to form Al, Si, P, or an oxide thereof. The amount thereof 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.

As for the shape of the ferromagnetic metal powder, if the particle volume shown above is satisfied, it is acicular, granular,
Although it may be either rice grain or plate, it is particularly preferable to use acicular ferromagnetic powder. In the case of acicular ferromagnetic metal powder, the average acicular ratio is preferably 4 to 12, more preferably 5
~ 8. The coercive force (Hc) of the ferromagnetic metal powder is preferably 159.2 to 278.5 k.
A / m (2000 to 3500 Oe), more preferably 167.1 to 238.7 k.
A / m (2100 to 3000 Oe). The saturation magnetic flux density is preferably 150 to
300 mT (1500 to 3000 G), more preferably 160 to 290 mT. The saturation magnetization (σs) is preferably 90 to 140 A · m ² / kg (90 to 140 e).
mu / g), more preferably 100 to 120 A · m ² / kg. The SFD (switching field distribution) of the magnetic material itself is preferably small, and is preferably 0.6 or less. When the SFD is 0.6 or less, the electromagnetic conversion characteristics are good, the output is high, the magnetization reversal is sharp and the peak shift is small, which is suitable for high-density digital magnetic recording. In order to reduce the Hc distribution, there are methods such as improving the goethite particle size distribution in the ferromagnetic metal powder, using monodispersed αFe 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 using iron or other reducing gas 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 powder is obtained 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>
Examples of the ferromagnetic hexagonal ferrite powder include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and their substitutes such as Co. 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. Other than the 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, Nb, etc. may be included. Generally, Co—Zn, Co—Ti
, Co-Ti-Zr, Co-Ti-Zn, Ni-Ti-Zn, Nb-Zn-Co, Sb-
A material to which an element such as Zn—Co or Nb—Zn is added can be used. Some raw materials and production methods contain specific impurities. Other preferable atoms and the content thereof are the same as those of the ferromagnetic metal powder.

The particle size of the hexagonal ferrite powder is preferably a size satisfying the above volume, but the average plate diameter is 10 to 50 nm, preferably 15 to 40 nm, and 20 to 30 n.
m is more preferable.
The average plate ratio is 1 to 15, and preferably 1 to 7. Average plate ratio is 1
If it is 15, sufficient orientation can be obtained while maintaining high filling properties in the magnetic layer, and noise increase due to stacking between particles can be suppressed. Further, the specific surface area (S _BET ) by the BET method within the above particle size range is preferably 40 m ² / g or more, and 40 to ²
More preferably 00m is ² / g, and most preferably 60~100m ² / g.

The distribution of the particle plate diameter and plate thickness of the hexagonal ferrite powder is generally preferably as narrow as possible. Particle plate diameter
Quantifying the plate thickness 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 1.0. 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 coercive force (Hc) of the hexagonal ferrite powder is 143.3 to 318.5 kA / m (180
0 to 4000 Oe), preferably 159.2 to 238.9 k.
A / m (2000 to 3000 Oe). More preferably 191.0-214.9k
A / m (2200 to 2800 Oe).
The coercive force (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 hexagonal ferrite powder is 30 to 80 A · m ² / kg (emu / g).
It is. Higher saturation magnetization (σs) is preferable, but tends to be smaller as the particles become finer. In order to improve the saturation magnetization (σs), it is well known to combine spinel ferrite with magnetoplumbite ferrite, and to select the type and amount of contained elements. 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. Dispersion medium,
Although there is an optimum value depending on the polymer, 0.01 to 2.0% is usually selected.

The hexagonal ferrite powder is manufactured by mixing (1) barium oxide / iron oxide / metal oxide that replaces iron oxide and boron oxide as a glass-forming substance so as to have a desired ferrite composition, and then melting and quenching. A glass crystallization method for obtaining a barium ferrite crystal powder after reheating treatment after being reheated, and (2) neutralizing barium ferrite composition metal salt solution with alkali to produce by-products After removing the liquid, heating it in liquid phase at 100 ° C or higher, washing, drying,
Hydrothermal reaction method for pulverizing to obtain barium ferrite crystal powder, (3) neutralizing barium ferrite composition metal salt solution with alkali, removing by-products, drying and treating at 1100 ° C or lower,
Although there is a coprecipitation method for pulverizing to obtain barium ferrite crystal powder, the present invention does not select a production method. The hexagonal ferrite powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof as required. The amount thereof 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 powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they do not particularly affect the characteristics.

[Iron nitride magnetic particles]
The average particle diameter of the Fe ₁₆ N ₂ phase in iron nitride magnetic particles, when the layer on the surface of the Fe ₁₆ N ₂ particles are formed, and a Fe ₁₆ N ₂ particles themselves without the relevant layer.

The magnetic particles of the present invention preferably contain at least the Fe ₁₆ N ₂ phase, but do not contain other iron nitride phases. This is because the magnetocrystalline anisotropy of iron nitride (Fe ₄ N or Fe ₃ N phase) is 1 × 10 ⁵ er.
This is because the Fe ₁₆ N ₂ phase has a high magnetocrystalline anisotropy of 2 to 7 × 10 ⁶ erg / cc, whereas it is about g / cc. Thereby, a high coercive force can be maintained even when the particles are made fine. This high magnetocrystalline anisotropy results from the crystal structure of the Fe ₁₆ N ₂ phase. The crystal structure is
It is a body-centered tetragonal crystal in which N atoms regularly enter the positions of Fe octahedral interstitial lattices, and the strain when N atoms enter the lattice is considered to be the cause of the generation of high magnetocrystalline anisotropy. The easy axis of magnetization of the Fe ₁₆ N ₂ phase is the C axis extended by nitriding.

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

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

The particle size of the Fe ₁₆ N ₂ phase, which is a magnetic material, is 9 to 11 nm. This is because as the particle size becomes smaller, the influence of thermal fluctuation becomes larger, and it becomes superparamagnetic and becomes unsuitable for a magnetic recording medium. Also, because of the magnetic viscosity, the coercive force at the time of high-speed recording with a head increases, making it difficult to record. On the other hand, if the particle size is large, the saturation magnetization cannot be reduced, so that the coercive force during recording becomes too high, making it difficult to record. Further, when the particle size is large, the particle noise when the magnetic recording medium is obtained becomes high. The particle size distribution is preferably monodisperse. This is because, in general, monodispersion reduces the medium noise. The variation coefficient of the particle size is 15% or less (preferably 2 to 15%), more preferably 10% or less (preferably 2 to 10%).

The iron nitride magnetic powder containing Fe ₁₆ N ₂ as a main phase preferably has a surface covered with an oxide film. This is because the fine particles Fe ₁₆ N ₂ are easily oxidized and require handling in a nitrogen atmosphere.

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

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

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

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

Magnetic properties of iron nitride-based magnetic particles containing Fe ₁₆ N ₂ as the main phase include their coercive force (Hc).
Is preferably 99.6 to 318.4 kA / m (1,000 to 4,000 Oe), more preferably 159.2 to 278.6 kA / m (2000 to 3500 Oe). More preferably, it is 197.5-237 kA / m (2500-3000 Oe). This is because, if Hc is low, for example, in the case of in-plane recording, it is likely to be affected by the adjacent recording bit and may not be suitable for high recording density, and if it is too high, it may be difficult to record. It is.

Saturation magnetization ^{80~160Am 2 / kg (80~160emu / g} ) is preferred, 80
120 Am ² / kg (80 to 120 emu / g) is more preferable. This is because if the signal is too low, the signal may be weakened. If the signal is too high, for example, in the case of in-plane recording, the adjacent recording bit is likely to be affected, and the recording density is not suitable. As a squareness ratio, 0.6-0.
9 is preferred.

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

As described above, the average particle size of the iron nitride-based powder is 30 nm or less, preferably 5 to 25 n.
m, more preferably 10 to 20 nm.

A known technique can be applied to the method for producing the iron nitride magnetic particles, for example, WO2003 / 0.
79332 can be referred to.

The magnetic particles produced by the above production method can be suitably used for the magnetic layer of the magnetic recording medium. Examples of the magnetic recording medium include magnetic tapes such as video tapes and computer tapes; magnetic disks such as floppy (registered trademark) disks and hard disks.

[Binder]
Binder, lubricant, dispersant for magnetic layer, nonmagnetic layer, and back layer of magnetic recording medium of the present invention,
Additives, solvents, dispersion methods and other known techniques can be appropriately applied to each other. In particular, known techniques relating to the amount and type of binder, the additive, and the amount and type of dispersant can be applied.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to
150 ° C., number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000
000, and the degree of polymerization is about 50 to 1000.

Examples 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 acetate. There are polymers or copolymers containing polyurethane, vinyl ether, etc. as structural units, 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-polyamides. Resin, polyester resin and isocyanate prepolymer, polyester polyol
And a mixture of polyurethane and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like. These resins are described in detail in “Plastic Handbook” published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. These examples and their production methods are described in detail in JP-A No. 62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer,
Examples thereof include a combination of at least one selected from vinyl chloride, vinyl acetate, maleic anhydride copolymer and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known structures 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, - OP =
O (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), —OH, —NR
₂ , It is preferable to use one in which at least one polar group selected from —N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, —SH, —CN, etc. is introduced by copolymerization or addition reaction. The amount of such polar groups is 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 manufactured by Dow Chemical Company,
VYHH, VMCH, VAGF, VAGD, VROH, VYES, VYNC, VMCC,
XYHL, XYSG, PKHH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industry, M
PR-TA, MPR-TA5, MPR-TAL, MPR-TSN, MPR-TMF, MP
R-TS, MPR-TM, MPR-TAO, manufactured by Denki Kagaku 1000W, DX80, DX8
1, DX82, DX83, 100FD, Nippon Zeon MR-104, MR-105, M
R110, MR100, MR555, 400X-110A, Nippon polyurethane N2301, N2302, N2304, Dainippon Ink, Pandex T-5105
, T-R3080, T-5201, Barnock D-400, D-210-80, Crisbon 6109, 7209, Byron UR8200, UR8300, UR-870 manufactured by Toyobo Co., Ltd.
0, RV530, RV280, manufactured by Dainichi Seika Co., Ltd., Daiferamin 4020, 5020, 51
00,5300,9020,9022,7020, Mitsubishi Chemical Co., Ltd., MX5004, Sanyo Chemical Co., Ltd. sampler SP-150, Asahi Kasei Co., Ltd. Saran F310, F210, etc. are mentioned.

The binder used in the nonmagnetic layer and magnetic layer of the present invention is 5% of the nonmagnetic powder or magnetic powder.
It is used in the range of ˜50 mass%, preferably in the range of 10 to 30 mass%. When using a vinyl chloride resin, it is preferable to use 5-30% by weight, when using a polyurethane resin, 2-20% by weight, and polyisocyanate in a range of 2-20% by weight. 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 −50 to 150 ° C., preferably 0 ° C. to 100 ° C.,
Breaking elongation is 100 to 2000%, breaking stress is 0.05 to 10 kg / mm ² (0.49 to 9
8 MPa) and the yield point is preferably 0.05 to 10 kg / mm ² (0.49 to 98 MPa).

Examples of the polyisocyanate used in the present invention include tolylene diisocyanate and 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 with polyalcohols, and polyisocyanates formed by condensation of isocyanates. -G etc. 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 Co., Ltd., Takenate D-102, Takenet D-110N
, Takenet D-200, Takenet D-202, manufactured by Sumitomo Bayer, Death Module L
, Death module IL, Death module N, Death module HL, etc., and these can be used in each layer alone or in combination of two or more using the difference in curing reactivity.

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 / dispersion aid, 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, fluorinated graphite, silicone oil, silicone having a polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, Polyolefin, polyglycol, polyphenyl ether, phenylphosphonic acid, benzylphosphonic acid, phenethylphosphonic acid, α-methylbenzylphosphonic acid, 1-methyl-1-phenethylphosphonic acid, diphenylmethylphosphonic acid, biphenylphosphonic acid, benzylphenylphosphonic acid , Α-cumylphosphonic acid, toluylphosphonic acid, xylylphosphonic acid, ethylphenylphosphonic acid, cumenylphosphonic acid, propylphenylphosphonic acid, butylphenylphosphonic acid, heptylph Aromatic ring-containing organic phosphonic acids such as enylphosphonic acid, octylphenylphosphonic acid, nonylphenylphosphonic acid and alkali metal salts thereof, octylphosphonic acid, 2-ethylhexylphosphonic acid,
Alkylphosphonic acids such as isooctylphosphonic acid, isononylphosphonic acid, isodecylphosphonic acid, isoundecylphosphonic acid, isododecylphosphonic acid, isohexadecylphosphonic acid, isooctadecylphosphonic acid, isoeicosylphosphonic acid, and alkalis thereof Metal salt, phenyl phosphate, benzyl phosphate, phenethyl phosphate, α-methylbenzyl phosphate,
1-methyl-1-phenethyl phosphate, diphenylmethyl phosphate, biphenyl phosphate, benzylphenyl phosphate, α-cumyl phosphate, toluyl phosphate, xylyl phosphate, ethylphenyl phosphate, cumenyl phosphate, propyl phosphate Aromatic phosphates such as phenyl, butylphenyl phosphate, heptylphenyl phosphate, octylphenyl phosphate, nonylphenyl phosphate and alkali metal salts thereof, octyl phosphate, 2-ethylhexyl phosphate, isooctyl phosphate, phosphoric acid Isononyl, isodecyl phosphate, isoundecyl phosphate, isododecyl phosphate, isohexadecyl phosphate, isooctadecyl phosphate, isoeicosyl phosphate, etc., phosphoric acid alkyl esters and alkali metal salts thereof, alkyl sulfonic acid esters and alkali metal salts thereof, Fluorine content Alkyl sulfate ester and alkali metal salt thereof, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, erucic acid, etc. Monobasic fatty acids and their metal salts, which may contain or be unsaturated, or butyl stearate, octyl stearate, amyl stearate, isooctyl stearate,
C10-2 such as octyl myristate, butyl laurate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan tristearate
A monobasic fatty acid which may contain or be branched by 4 unsaturated bonds, a 1 to 6 valent alcohol which may be branched or contain an unsaturated bond having 2 to 22 carbon atoms, Mono-fatty acid ester, di-fatty acid ester or multi-fatty acid ester, fatty acid having 2 to 22 carbon atoms, comprising any one of an alkoxy alcohol which may contain an unsaturated bond or may be branched, or a monoalkyl ether of an alkylene oxide polymer Amides and aliphatic amines having 8 to 22 carbon atoms can be used. In addition to the above hydrocarbon groups, nitro groups and F, Cl, Br
, CF ₃ , CCl ₃ , CBr _{3 and} other halogen-containing hydrocarbon groups such as a hydrocarbon group may be substituted with an alkyl group, an aryl group, or an aralkyl group.

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.).

The lubricants, antistatic agents, and the like are not necessarily pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, and oxides in addition to the main components. These impurities are 30% by mass
The following is preferable, and more preferably 10% by mass or less.

Specific examples of these additives include, for example, NAF-102, castor oil hardened fatty acid, NAA-42, cation SA, Naimine L-201, and nonion E-208 manufactured by NOF Corporation.
, Anon BF, Anon LG, Takemoto Yushi Co., Ltd .: FAL-205, FAL-123, Shin Nippon Chemical Co., Ltd .: NJ Lube OL, Shin-Etsu Chemical Co., Ltd .: TA-3, Lion Corp .: Armide P, Lion Corp .: Duomin TDO, manufactured by Nisshin Oilio Co., Ltd .: BA-41G, manufactured by Sanyo Chemical Co., Ltd .: Profan 2012E, New Pole PE61, Ionette MS-400, and the like.

In addition, carbon black can be added to the magnetic layer in the present invention as necessary. Examples of carbon black that can be used in the magnetic layer include rubber furnace, rubber thermal, color black, and acetylene black. Specific surface area is 5-5
00 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle size is 5 to 300 nm,
The pH is preferably 2 to 10, the water content is preferably 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / ml.

As a specific example of carbon black used in the present invention, Blac manufactured by Cabot Corporation
KPEARLS 2000, 1300, 1000, 900, 905, 800, 700, V
ULCAN XC-72, Asahi Carbon # 80, # 60, # 55, # 50, # 35, Mitsubishi Chemical # 2400B, # 2300, # 900, # 1000, # 30, # 40, # 10
B, CONDUCTEX SC, RAVEN150, 50, 4 by Columbian Carbon
0, 15, RAVEN-MT-P, and Ketjen Black EC manufactured by Ketjen Black International. 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, 0.1 to 30% by mass based on the mass of the magnetic material
It is preferable to use in. 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, 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, and the like. Of course, it is possible to use it properly according to the purpose, but rather it should be optimized in each layer. 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.

[Abrasive]
As the abrasive used in the present invention, α-alumina, β-alumina having an α conversion rate of 90% or more,
Silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond,
Known materials having a Mohs hardness of 6 or more, such as silicon nitride, silicon carbide titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. Moreover, you may use the composite_body | complex (what surface-treated the abrasive | polishing agent with the other abrasive | polishing agent) of these abrasive | polishing agents. These abrasives may contain compounds or elements other than the main component, but the effect is not affected if the main component is 90% or more. The particle size of these abrasives is preferably 0.01-2 μm,
In particular, in order to enhance electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as necessary, or to obtain the same effect by widening the particle size distribution even with a single abrasive. Tap density is 0.3-2
g / cc, water content is preferably 0.1 to 5%, pH is 2 to 11, and specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, a dice shape, and a plate shape, but those having a corner in a part of the shape are preferable because of high polishing properties. Specifically, AKP-1 manufactured by Sumitomo Chemical Co., Ltd.
2, AKP-15, AKP-20, AKP-30, AKP-50, HIT-20, HIT
-30, HIT-55, HIT-60, HIT-70, HIT-80, HIT-100,
Reynolds, ERC-DBM, HP-DBM, HPS-DBM, Fujimi Abrasives,
WA10000, Uemura Kogyo Co., Ltd., UB20, Nippon Chemical Industry Co., Ltd., G-5, Chromex U
2, Chromex U1, Toda Kogyo, TF100, TF140, Ibiden, Beta Random Ultra Fine, Showa Mining, B-3, and the like. These abrasives can be added to the nonmagnetic layer as required. By adding to the nonmagnetic layer, the surface shape can be controlled, and the protruding state of the abrasive can be controlled. The particle size and amount of the abrasive added to these magnetic and nonmagnetic layers should of course be set to optimum values.

Known organic solvents can be used in the present invention. The organic solvent used in the present invention may be any 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, ethyl Nkuroruhidorin, chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane.

These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are 3
It is preferably 0% 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 solvents (cyclohexanone, dioxane, etc.) to increase coating stability. Specifically, the arithmetic average value of the upper layer solvent composition may not fall below the arithmetic average value of the nonmagnetic layer solvent composition. It is essential. In order to improve 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 dispersants, lubricants, and surfactants used in the present invention can be properly used in the magnetic layer and further in the nonmagnetic layer described later, as needed. For example, of course, the dispersant is not limited to the example shown here, but the dispersant has a property of adsorbing or binding with a polar group, and in the magnetic layer, mainly on the surface of the ferromagnetic metal powder and nonmagnetic. In the layer, it is presumed that the organic phosphorus compound adsorbed or bonded mainly to the surface of the non-magnetic powder with the above-mentioned polar group, for example, is difficult to desorb from the surface of metal or metal compound. Therefore, the surface of the ferromagnetic metal powder or non-magnetic powder of the present invention is in a state of being covered with an alkyl group, an aromatic group, etc.
The affinity of the ferromagnetic metal powder or nonmagnetic powder for the binder component is improved, and the dispersion stability of the ferromagnetic metal 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 non-magnetic layer and the magnetic layer, and bleeding is controlled on the surface using esters with different boiling points and polarities. It is conceivable 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 non-magnetic layer. All or part of the additives used in the present invention may be added in any step during the production of the coating solution for the magnetic layer or nonmagnetic layer. For example, when mixing with a ferromagnetic powder before the kneading step, adding at a kneading step with a ferromagnetic powder, a binder and a solvent, adding at a dispersing step, adding after dispersing, adding just before coating, etc. There is.

[Nonmagnetic layer]
Next, detailed contents regarding the nonmagnetic layer will be described. The magnetic recording medium of the present invention can have a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support. 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, and metal sulfides.

Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α-alumina having an α conversion of 90 to 100%,
β-alumina, 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 and the like are used alone or in combination of two or more. Preferable are α-iron oxide and titanium oxide.

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

The specific surface area of the nonmagnetic powder is a 1~150m ² / g, preferably 20~120m ² /
g, more preferably 50 to 100 m ² / g. Specific surface area of 1 to 150 m ² /
If it exists in the range of g, since it has a suitable surface roughness and can be disperse | distributed with the desired amount of binders, it is preferable. The oil absorption using dibutyl phthalate (DBP) is 5 to 100 ml / 100 g,
Preferably it is 10-80 ml / 100g, More preferably, it is 20-60 ml / 100g. 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 the pH 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 water content of the nonmagnetic powder is 0.1 to 5% by mass, preferably 0.2 to
It is 3 mass%, More preferably, it is 0.3-1.5 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. Ignition loss is
The content is preferably 20% by mass or less, and preferably has a small loss on ignition.

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 μmo.
l / m ² . The heat of wetting of nonmagnetic powder into water at 25 ° C. is 200 to 600 erg / cm.
² (200 to 600 mJ / m ² ) is preferable. 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 1 to 10
A piece / 100cm is suitable. The pH of the isoelectric point in water is preferably between 3 and 9. The surface of these non-magnetic powders is subjected to a surface treatment, whereby Al ₂ O ₃ , SiO ₂ ,
_{TiO 2, ZrO 2, SnO 2} , Sb 2 O 3, it is preferred that ZnO is present. 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 the nonmagnetic powder 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, D
PN-250BX, DPN-245, DPN-270BX, DPB-550BX, DPN
-550RX, manufactured 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, ST manufactured by Titanium Industry
T-30, STT-65C, Teica MT-100S, MT-100T, MT-150W
, MT-500B, T-600B, T-100F, T-500HD, and the like. Sakai Chemical FINEX-25, BF-1, BF-10, BF-20, ST-M, D made by Dowa Mining
EFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 500A, Titanium Industry Y-LOP, and those fired. Particularly preferred nonmagnetic powders are titanium dioxide and α-iron oxide.

Carbon black can be mixed in the nonmagnetic layer together with nonmagnetic powder to lower the surface electrical resistance, reduce the light transmittance, and obtain a desired micro Vickers hardness. The micro Vickers hardness of the nonmagnetic layer is usually 25-60 kg / mm ² (245-588 MPa),
Preferably, 30 to 50 kg / mm ² (294 to 490 MP) for adjusting the head contact.
a), and can be measured by using a thin film hardness tester (HMA-400 manufactured by NEC Corporation) with a diamond triangular pyramid needle having a ridge angle of 80 degrees and a tip radius of 0.1 μm at the tip of the indenter. For details, refer to Realize Co., Ltd. The light transmittance is generally 90
It has been standardized that the absorption of infrared rays of about 0 nm is 3% or less, for example, 0.8% or less for a VHS magnetic tape. For this purpose, rubber furnace, rubber thermal, color black, acetylene black and the like can be used.

The specific surface area of carbon black used for the nonmagnetic layer of the present invention is 100 to 500 m ² / g.
, Preferably 150 to 400 m ² / g, DBP oil absorption 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g. The particle size of carbon black is 5-80nm
The thickness is preferably 10 to 50 nm, more preferably 10 to 40 nm. Carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

Specific examples of carbon black that can be used in the nonmagnetic layer of the present invention include BLACKPEARLS 2000, 1300, 1000, 900, 800, manufactured by Cabot Corporation.
880, 700, VULCAN XC-72, Mitsubishi Chemical Corporation # 3050B, # 3150B
, # 3250B, # 3750B, # 3950B, # 950, # 650B, # 970B, #
850B, MA-600, Columbian Corporation's CONDUCTEX SC, RAVE
N8800, 8000, 7000, 5750, 5250, 3500, 2100, 2000
1800, 1500, 1255, 1250, and Ketjen Black EC manufactured by Ketjen Black International.

Carbon black may be surface-treated with a dispersant, or may be grafted with a resin, or may be obtained by graphitizing a part of the surface. Further, carbon black may be dispersed in advance with a binder before it is added to the paint. These carbon blacks do not exceed 50% by mass with respect to the inorganic powder, and 40% of the total mass of the nonmagnetic layer.
Can be used within the range not exceeding. These carbon blacks can be used alone or in combination. The carbon black that can be used in the nonmagnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

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

As the binder, lubricant, dispersant, additive, solvent, dispersion method and the like of the nonmagnetic layer, those of the magnetic layer can be applied. In particular, known techniques relating to the magnetic layer can be applied to the amount of binder, type, additive, and amount of dispersant added, and type.

The magnetic recording medium of the present invention may be provided with an undercoat layer. By providing the undercoat layer, the adhesive force between the support and the magnetic layer or the nonmagnetic layer can be improved. As the undercoat layer, a solvent-soluble polyester resin is used.

[Layer structure]
The thickness structure of the magnetic recording medium used in the present invention is such that the thickness of the nonmagnetic support is 3 as described above.
It is ˜80 μm, more preferably 3 to 50 μm, particularly preferably 3 to 10 μm. Further, when an undercoat layer is provided between the nonmagnetic support and the nonmagnetic layer or the magnetic layer, the thickness of the undercoat layer is
The thickness is 0.01 to 0.8 μm, preferably 0.02 to 0.6 μm.
The undercoat layer (smoothing layer) is formed, for example, by applying a coating solution containing a polymer to the surface of a nonmagnetic support and drying, or a compound having a radiation-curable functional group in the molecule (radiation-curable compound) It can be formed by applying a coating solution containing, and then irradiating with radiation to cure the coating solution.
The molecular weight of the radiation curable compound is preferably in the range of 200 to 2,000. When the molecular weight is within this range, the molecular weight is relatively low, so that the coating film is easy to flow in the calendar process, has high moldability, and a smooth coating film can be formed.
Preferred as the radiation curable compound is a bifunctional acrylate compound having a molecular weight of 200 to 2000, and more preferred are bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, and these alkylene oxide adducts. Acid and methacrylic acid are added.

The radiation curable compound used in the present invention may be used in combination with a polymer-type binder.
As the binder used in combination, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. When ultraviolet rays are used as radiation, it is preferable to use a polymerization initiator in combination. As the polymerization initiator, known radical photopolymerization initiators, cationic photopolymerization initiators, photoamine generators, and the like can be used.
The radiation curable compound can also be used for the nonmagnetic layer.

The thickness of the magnetic layer is optimized by the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used. The thickness variation rate (σ / δ) of the magnetic layer is preferably 20% or less, more preferably 15% or less.
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 0.1 to 3.0 μm, preferably 0.3 to 2.0 μm, and more preferably 0.5 to 1.5 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. Note that substantially the same means that the residual magnetic flux density of the nonmagnetic layer is 10 mT or less or the coercive force is 7.96 kA / m (10
0 Oe) or less, preferably means having no residual magnetic flux density and coercive force.

[Back layer]
In the magnetic recording medium of the present invention, a back layer is preferably provided on the other surface of the nonmagnetic support. The back layer preferably contains carbon black and inorganic powder. For the binder and various additives, the formulation of the magnetic layer and the nonmagnetic layer is applied. Back layer thickness is 0.9μm
The following is preferable, and 0.1 to 0.7 μm is more preferable.

[Production method]
The process for producing the magnetic layer paint, nonmagnetic layer paint or back layer paint used in the present invention comprises at least a kneading step, a dispersion step, and a mixing step provided before and after these steps. . 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 middle of any step. In addition, individual raw materials may be added in two or more steps. For example, polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, a conventional known manufacturing technique can be used as a partial process. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Also,
Glass beads can be used to disperse the magnetic layer paint, nonmagnetic layer paint, or back layer paint. 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 producing a magnetic recording medium of the present invention, for example, a magnetic layer is applied to the surface of a nonmagnetic support under running so that the magnetic layer has a predetermined thickness. Here, a plurality of magnetic layer coating materials may be applied sequentially or simultaneously, and a nonmagnetic layer coating material and a magnetic layer coating material may be applied sequentially or simultaneously. Examples of coating machines for applying the magnetic layer coating or nonmagnetic layer coating include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating 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 layer may be subjected to magnetic field orientation treatment using a cobalt magnet or a solenoid on the ferromagnetic powder contained in the magnetic layer coating layer. In the case of a disk, a sufficiently isotropic orientation may be obtained even without non-orientation without using an orientation device, but known random methods 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. Further, isotropic magnetic characteristics can be imparted in the circumferential direction by using a well-known method such as a different-pole counter 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.

The coating raw material thus obtained is once taken up by a take-up roll, and then unwound from the take-up roll and subjected to a calendar process.
For the calendar process, for example, a super calendar roll or the like is used. The calendering improves the surface smoothness and eliminates the voids generated by the removal of the solvent during drying and improves the filling rate of the ferromagnetic powder in the magnetic layer. Obtainable. According to the smoothness of the surface of the coating raw material,
It is preferable to carry out while changing the calendar processing conditions.

In general, the gloss value of the coating raw material decreases from the core side of the winding roll toward the outside, and the quality may vary in the longitudinal direction. It is known that the gloss value has a correlation (proportional relationship) with the surface roughness Ra. Therefore, in the calendar processing step, if the calendar processing conditions, for example, the calendar roll pressure is kept constant without being changed, no measures are taken for the difference in smoothness in the longitudinal direction caused by the winding of the coating raw material. As a result, the final product also varies in quality in the longitudinal direction.
Therefore, it is preferable to change the calendering conditions, for example, the calender roll pressure, in the calendering process to offset the difference in smoothness in the longitudinal direction caused by the winding of the coating raw material. Specifically, it is preferable to reduce the pressure of the calendar roll from the core side of the coating raw material unwound from the winding roll toward the outside. According to the study by the present inventors, it has been found that when the pressure of the calender roll is lowered, the gloss value is lowered (smoothness is lowered). As a result, the difference in smoothness in the longitudinal direction caused by the winding of the coating raw material is offset, and a final product having no variation in quality in the longitudinal direction is obtained.

In addition, although the example which changes the pressure of a calendar roll was demonstrated above, it can carry out by controlling a calendar roll temperature, a calendar roll speed, and a calendar roll tension besides this. In consideration of the properties of the coating type medium, it is preferable to control the calender roll pressure and the calender roll temperature. By reducing the calender roll pressure or the calender roll temperature, the surface smoothness of the final product is lowered. Conversely, increasing the calender roll pressure or the calender roll temperature increases the surface smoothness of the final product.

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

As the calender 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 an extremely smooth surface as described above. As the calendering conditions employed for that purpose, the temperature of the calender roll is in the range of 60 to 100 ° C., preferably in the range of 70 to 100 ° C., particularly preferably in the range of 80 to 100.
The pressure is in the range of 100 to 500 kg / cm (98 to 490 kN / m), preferably in the range of 200 to 450 kg / cm (196 to 441 kN / m), particularly preferably in the range of 300 to 400 kg. / Cm (294 to 392 kN / m).

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

[Physical properties]
The saturation magnetic flux density of the magnetic layer of the magnetic recording medium used in the present invention is preferably 100 to 400 mT. The coercive force (Hc) of the magnetic layer is 143.2 to 318.3 kA / m (1800 to 4).
000 Oe) is preferred, and 159.2 to 278.5 kA / m (2000 to 3500 Oe).
Is more preferable. The coercive force distribution is preferably narrow, and SFD and SFDr are 0.6 or less,
More preferably, it is 0.3 or less.

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

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

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 1
0 mg / m ² or less. The porosity of the coating layer is preferably 40 for both the nonmagnetic layer and the magnetic layer.
It is not more than volume%, more preferably not more than 30 volume%. 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 a disk medium in which repetitive use is important, the running durability is often preferable when the porosity is large.

The ten-point average roughness Rz of the magnetic layer is preferably 30 nm or less. This can be easily controlled by controlling the surface properties with the filler of the support or the surface shape of the calendar roll. The curl is preferably within ± 3 mm.

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

As a reproducing method in the magnetic recording medium of the present invention, it is preferable to reproduce an AMR head, preferably a GMR head, on a signal magnetically recorded at a maximum linear recording density of 200 KFC I or more.
The distance between the shields (sh-sh) is, for example, 0.08 μm to 0.18 μm, and the reproduction track width is, for example, 0.5 μm to 3.5 μm.

When the magnetic recording medium of the present invention is a tape-shaped magnetic recording medium, a GMR head is used as a reproducing head, so that even a signal recorded in a high frequency region can be reproduced at a high S / N with less output fluctuations than in the past. Is possible. Therefore, the magnetic recording medium of the present invention is most suitable as a magnetic tape for computer data recording for higher density recording and a disk-shaped magnetic recording medium.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to the following example.
In addition, the display of "part" in an Example shows "mass part".

Example 1
<Material for upper magnetic coating>
Hexagonal barium ferrite powder 100 parts Hc: 2000 Oe (160 kA / m), average plate diameter: 20 nm, average plate ratio: 3
BET specific surface area: 80 m ² / g, σs: 50 emu / g (50 A · m ² / kg)
Sulfonic acid group-containing polyurethane resin 18 parts Diamond powder (average particle size: 50 nm) 1 part Silicon carbide powder (average particle diameter: 30 nm) 1 part Cyclohexanone 150 parts Methyl ethyl ketone 150 parts Butyl stearate 2 parts Stearic acid 1 part

Preparation of coating for nonmagnetic layer Iron oxide powder (average major axis length: 80 nm) 80 parts carbon black (average particle size: 25 nm) 20 parts vinyl chloride copolymer resin 10 parts sulfonic acid group-containing polyurethane resin 5 parts phenylphosphonic acid 2 Parts methyl ethyl ketone 130 parts cyclohexanone 100 parts stearic acid 1 part butyl stearate 1.5 parts

<Undercoat paint material>
The following components were mixed and stirred to prepare an undercoat layer paint.
Dimethylol tricyclodecane diacrylate 100 parts methyl ethyl ketone 100 parts

About each of the said upper layer magnetic coating material and a nonmagnetic lower layer coating material, after kneading each component for 60 minutes with an open kneader, it disperse | distributed for 600 minutes with the sand mill. To each of the obtained dispersions, 6 parts of a trifunctional low molecular weight polyisocyanate compound (Nihon Polyurethane Coronate 3041) was added and stirred for 20 minutes, followed by filtration using a filter having an average pore size of 1 μm. A magnetic paint and a non-magnetic undercoat were prepared. Further, the surface roughness Ra on the magnetic layer coating side is 1.mu.m so that the thickness after drying the nonmagnetic lower layer coating material is 1.5 .mu.m.
4 nm, coated on a PEN support having a surface roughness Ra of 2.0 nm on the back layer coating side and applied at 100 ° C.
After having been dried, the film was wound up to prepare a lower layer coating raw material. Next, the lower layer coating material is made into a seven-stage calendar (
After a mirror surface treatment at a temperature of 100 ° C., a linear pressure of 300 kg / cm (294 kN / m), and a treatment speed of 50 m / min), a thermo treatment was performed at 70 ° C. for 36 hours. The undercoat layer coating thus obtained was applied onto the original lower layer coating so that the dry thickness was 0.5 μm, dried at 100 ° C., and irradiated with an electron beam having an acceleration voltage of 100 kV and an irradiation dose of 5 Mrad. After that, the upper magnetic coating material was wet-on-dried so that the thickness after drying was 100 nm, and dried at 100 ° C.
Next, on the surface opposite to the surface on which the nonmagnetic underlayer and magnetic layer of the nonmagnetic support are formed, a back layer coating is applied so that the thickness of the back layer after drying and calendering is 0.5 μm. Applied and dried. For the back layer paint, the following back layer paint components were stored in a bead mill with a residence time of 4
After dispersing for 5 minutes, 8.5 parts of polyisocyanate was added, and the mixture was stirred and filtered.
<Back layer paint component>
Carbon black (average particle size: 25 nm) 40.5 parts carbon black (average particle size: 370 nm) 0.5 parts barium sulfate 4.05 parts nitrocellulose 28 parts polyurethane resin (SO ₃ Na group-containing) ... 20 parts cyclohexanone ... 100 parts toluene ... 100 parts methyl ethyl ketone ... 100 parts The magnetic sheet thus obtained was subjected to a seven-stage calendar (temperature 100 ° C, linear pressure). 300 kg / c
m (294 kN / m), treatment speed of 80 m / min), and a thermo treatment was performed at 70 ° C. for 48 hours. Then, it cut | judged to the 1/2 inch width | variety and produced the magnetic tape.

(Example 2)
The composition of the nonmagnetic lower layer coating material was changed as follows, and each component was kneaded with an open kneader for 60 minutes, and then dispersed with a sand mill for 600 minutes. The obtained dispersion was filtered using a filter having an average pore diameter of 1 μm to prepare a nonmagnetic lower layer coating material for Example 2.
Further, the thickness after drying the non-magnetic lower layer coating is 1.5 μm, the surface roughness Ra on the magnetic layer application side is 1.4 nm, and the surface roughness Ra on the back layer application side is 1.5 μm. After coating on a 2.0 nm PEN support and drying at 100 ° C., it was wound up to prepare a lower layer coating original fabric. Next, the lower layer coating raw material is made into a seven-stage calendar (temperature 100 ° C., linear pressure 300 kg / cm (294 kN / m
) After mirroring at a processing speed of 50 m / min), an acceleration voltage of 100 kV and an irradiation dose of 5 Mr
The electron beam of ad was irradiated. Furthermore, the dry thickness of the undercoat paint is 0.5 μm on the lower layer coating
After being irradiated with an electron beam with an acceleration voltage of 100 kV and an irradiation dose of 5 Mrad, the magnetic coating material is wet-on-dried so that the thickness after drying is 50 nm, and then 100 ° C. And dried. Subsequent processes produced the magnetic tape of Example 2 with the manufacturing method similar to Example 1. FIG.
<Materials for nonmagnetic underlayer paint>
Iron oxide powder (average major axis length: 80 nm) 80 parts carbon black (average particle size: 25 nm) 20 parts electron beam curable vinyl chloride copolymer resin 10 parts electron beam curable polyurethane resin 5 parts phenylphosphonic acid 2 parts methyl ethyl ketone 130 Part cyclohexanone 130 parts stearic acid 1 part butyl stearate 1.5 parts

(Example 3)
The thickness of the undercoat layer paint after drying is 0.5 μm, the thickness is 5 μm, the surface roughness Ra on the magnetic layer application side is 1.4 nm, and the surface roughness Ra on the back layer application side is 2 .0nm PE
After coating on an N support and drying at 100 ° C., and irradiating an electron beam with an acceleration voltage of 100 kV and an irradiation dose of 5 Mrad, the magnetic paint was wet-on-dried so that the thickness after drying was 30 nm. And dried.
Subsequent processes produced the magnetic tape of Example 3 with the manufacturing method similar to Example 1. FIG.

Example 4
The thickness after drying the upper magnetic coating is 80 nm, the surface roughness Ra on the magnetic layer application side is 1.4 nm, and the surface roughness Ra on the back layer application side is 2.0 nm. It was coated on a PEN support and dried at 100 ° C.
Subsequent processes produced the magnetic tape of Example 4 with the manufacturing method similar to Example 1. FIG.

(Comparative Example 1)
The thickness of the same nonmagnetic lower layer paint as in Example 1 above after drying is 1.5 μm, the thickness is 5 μm, the surface roughness Ra on the magnetic layer application side is 1.4 nm, and the surface on the back layer application side After coating on a PEN support having a roughness Ra of 2.0 nm and drying at 100 ° C., winding was performed to prepare a lower layer coating raw material. Next, the lower layer coating raw material was subjected to a thermo treatment at 70 ° C. for 36 hours. On the lower layer coating raw material thus obtained, the upper magnetic coating material was wet-on-dried so that the thickness after drying was 100 nm, and dried at 100 ° C. Subsequent processes produced the magnetic tape of the comparative example 1 with the manufacturing method similar to Example 1. FIG.

(Comparative Example 2)
The thickness of the same nonmagnetic lower layer paint as in Example 1 above after drying is 1.5 μm, the thickness is 5 μm, the surface roughness Ra on the magnetic layer application side is 1.4 nm, and the surface on the back layer application side After coating on a PEN support having a roughness Ra of 2.0 nm and drying at 100 ° C., winding was performed to prepare a lower layer coating raw material. Next, the lower layer coating raw material was subjected to a thermo treatment at 70 ° C. for 36 hours. On the lower layer coating raw material thus obtained, the upper magnetic coating material was wet-on-dried so that the thickness after drying was 150 nm and dried at 100 ° C. Subsequent processes produced the magnetic tape of the comparative example 1 with the manufacturing method similar to Example 1. FIG.

(Comparative Example 3)
The same nonmagnetic lower layer paint as in Example 1 was dried so that the thickness after drying was 1.5 μm, the surface roughness Ra on the magnetic layer application side was 1.4 nm, and the surface on the back layer application side Roughness Ra was applied onto a PEN support having a thickness of 2.0 nm, and a magnetic coating was applied on the PEN support so that the thickness after drying was 100 nm and dried at 100 ° C. Subsequent processes produced the magnetic tape of the comparative example 3 with the manufacturing method similar to Example 1. FIG.

(Comparative Example 4)
The thickness of the same nonmagnetic lower layer paint as in Example 1 above after drying is 1.5 μm, the thickness is 5 μm, the surface roughness Ra on the magnetic layer application side is 1.4 nm, and the surface on the back layer application side After coating on a PEN support having a roughness Ra of 2.0 nm and drying at 100 ° C., winding was performed to prepare a lower layer coating raw material. Next, the lower layer coating raw material was mirror-finished with a seven-stage calender (temperature 100 ° C., linear pressure 300 kg / cm (294 kN / m), processing speed 50 m / min). The magnetic coating material was wet-on-dry coated on the lower layer coating raw material thus obtained so that the thickness after drying was 50 nm, and dried at 100 ° C. Subsequent processes produced the magnetic tape of the comparative example 4 with the manufacturing method similar to Example 1. FIG.

(Comparative Example 5)
The thickness after drying the same nonmagnetic coating material as in Example 1 is 1.5 μm, the surface roughness Ra on the magnetic layer application side is 0.5 nm, and the surface roughness on the back layer application side is 0.5 nm. After coating on a PEN support having a thickness Ra of 2.0 nm, a magnetic paint was wet-on-dried to a thickness of 30 nm after drying, and dried at 100 ° C. Subsequent steps were carried out in the same manner as in Example 1 to produce a magnetic tape of Comparative Example 5.

  The obtained samples were measured and evaluated as follows, and the results are shown in Table 1.

〔Measuring method〕
(Measurement of average thickness δ of magnetic layer and standard deviation σ of the thickness)
The average thickness δ and standard deviation σ of the magnetic layer were obtained as follows (1) and (2).
(1) Acquisition of cross-sectional image of magnetic tape An ultra-microtome method using an embedding block cuts out an ultra-thin section (section thickness, about 80 nm to 100 nm) parallel to the longitudinal direction of the tape. Transmission electron microscope (HITA
Using a CHI TEM H-9000), a photograph of the cross section of the magnetic tape in the sliced ultrathin section was continuously obtained in the longitudinal direction of the tape with a magnification of 100,000 times and a magnetic layer / nonmagnetic layer interface as the center.
Images are taken for ˜30 μm to obtain a continuous cross-sectional image of the magnetic tape.
(2) From the obtained continuous photograph, the magnetic layer surface and the magnetic layer / nonmagnetic layer interface line are visually drawn to trim the magnetic layer. Next, the trimmed magnetic layer line is captured by a scanner, and the width of the magnetic layer surface and the magnetic layer / nonmagnetic layer interface is image-processed to calculate the average thickness δ and the standard deviation σ of the magnetic layer. For image processing, “KS Imaging Sy” by Carl Zeiss
stems Ver. 3 ″ was used, and the magnetic layer thickness width of about 2100 points was measured every 12.5 nm in the longitudinal direction of the magnetic layer.
Scale correction at the time of image capture from the scanner and image analysis was performed using a line with an actual size of 2 cm.

(Measurement of standard deviation σ _d [nm] of magnetic material distribution in thickness direction at interface)
The standard deviation σ _d [nm] of the magnetic material distribution in the thickness direction at the interface is the following (3), (4)
And (5).
(3) Acquisition of magnetic body constituent element depth profile of magnetic tape The depth profile of the element which comprises a magnetic body is measured by TOF-SIMS by ION-TOF. In this example, the depth profile of Ba was measured.
Sputtering was performed in the depth direction with O ₂ sputtering (2 keV, 125 nA, sputtering area was 225 μm square), and ionization was performed with Bi ions (25 keV, 1 pA, 10 kHz) to detect secondary ions (posi). The measurement area is 50 μm square.
Sputtering was performed at 512 cycles at intervals of 1.638 [sec], and sputtering was performed sufficiently long until the depth profile curve of the constituent elements of the magnetic layer became flat (FIG. 1).
(4) Calculation of Sputter Rate of Magnetic Tape The horizontal axis in the depth profile (FIG. 1) acquired under the above conditions, that is, the sputter rate is calculated by the following formula 1.
In this embodiment / comparative example measurement, the sputtering rate is 0.47 [nm / sec].
Formula 1: Sputtering rate [nm / sec] = {Sputtering depth ^* (Altitude difference between sputter region surface after depth profile measurement and initial surface not sputtered) [nm]} / {Sputtering time [sec]}
* The sputter depth was calculated using an atomic force microscope “SPA500” manufactured by Seiko Instruments Inc.
The horizontal axis [sec] of the depth profile was multiplied by a sputtering rate of 0.47 [nm / sec], and the horizontal axis was converted to a sputter depth [nm] value (FIG. 2).
(5) Standard deviation σ _d [nm of magnetic material distribution in the thickness direction at the interface from the depth profile
] The profile curve base line (where the intensity profile becomes flat) is drawn, and the profile from the minimum to the maximum intensity is normalized. From the intensity decrease profile of the constituent elements, a portion corresponding to 16% to 84% when the maximum intensity is 100% is cut out.
Fitting the differential curve of the cut out intensity decrease curve with a normal distribution (Gauss function) (
The standard deviation σ _d [nm] of the differential curve was calculated. For Gaussian function approximation, peak analysis software “Origin-pro.7.5” was used, and the following equation 2 was used as the Gaussian function.
Formula 2: y = y0 + [A / (2σ _d × √ (π / 2))] × (exp {(− 2 (x−x0) ²
/ (2σ _d ) ² )})
y0 = baseline offset A = total area between curve and baseline x0 = peak center (average)
σ _d = standard deviation of magnetic distribution in the thickness direction at the interface

(Measurement of electromagnetic conversion characteristics)
The electromagnetic conversion characteristics were performed using a drum tester (relative speed 2 m / sec).
Bs = 1.6T Gap Length 0.2 μm write head, linear recording density 200 kFCI
The GMR head (reproduction track width (Tw) 1.5 μm, sh-sh = 0.
16 μm).
The SNR was obtained by measuring the ratio of the output of 200 kFCI and the integrated noise of 0 to 400 kFCI. The measured value of Comparative Example 1 was set to 0 dB.
The output fluctuation rate was expressed as a value obtained by sampling 2000 pulses of a recording / reproducing signal of 33.3 kFCI, obtaining an absolute value distribution of peaks, dividing the standard deviation by an average value, and multiplying by 100. 15% or less is considered good.

In Example 1, the lower layer coating raw material is calendered and then thermoprocessed to reduce the lower layer voids and harden, and further, an undercoat layer is provided thereon to cure the electron beam and fill the lower layer surface voids. It suppresses the body from being buried in the lower layer. Therefore, the standard deviation σ _d of the magnetic material distribution in the thickness direction at the interface was small, and a favorable output fluctuation rate and SNR were obtained.
In Example 2, the lower layer coating raw material is calendered and then cured by electron beam irradiation to reduce the lower layer voids, and further, an undercoat layer is provided thereon to cure the electron beam curing to fill the lower layer surface voids. The magnetic material is suppressed from being buried in the lower layer. Therefore, the standard deviation σ _d of the magnetic material distribution in the thickness direction at the interface was small, and a favorable output fluctuation rate and SNR were obtained.
In Example 3, the surface roughness of the support is masked and further smoothed by directly providing an undercoat layer on the support and performing an electron beam irradiation treatment. Therefore, the standard deviation σ _d of the magnetic material distribution in the thickness direction at the interface was small, and a favorable output fluctuation rate and SNR were obtained.
In Example 4, by providing the magnetic layer directly on the smooth support, the standard deviation σ _d of the magnetic material distribution in the thickness direction at the interface was small, and a favorable output fluctuation rate and SNR were obtained.
In Comparative Example 1, since the lower layer is not calendered, the gap on the lower layer surface is large, the magnetic material is buried in the lower layer, and the standard deviation σ _d of the magnetic material distribution in the thickness direction at the interface increases. This is an example in which the fluctuation rate and SNR are deteriorated.
In Comparative Example 2, since the lower layer was not calendered, the gap on the lower layer surface was large, the magnetic material was buried in the lower layer, the standard deviation σ _d of the magnetic material distribution in the thickness direction at the interface was large, and the magnetic This is an example in which the output fluctuation rate and the SNR are deteriorated because the layer thickness δ exceeds 100 nm.
Since Comparative Example 3 is applied wet-on-wet, the nonmagnetic lower layer powder and the magnetic material are mixed at the interface, and the standard deviation σ _d of the magnetic material distribution in the thickness direction at the interface increases,
This is an example in which the output fluctuation rate and SNR are deteriorated.
In Comparative Example 4, the lower layer was calendered in advance to reduce voids on the lower layer surface, but since the curing process was not performed, the surface of the lower layer was roughened when the magnetic layer coating was applied on the lower layer, resulting in a thickness at the interface. The standard deviation σ _d of the magnetic distribution in the direction increases, and the output fluctuation rate and SNR
Is an example of deterioration.
In Comparative Example 5, since no magnetic layer coating was applied and the magnetic layer coating was applied wet-on-dry, the surface of the lower layer was roughened when the magnetic layer coating was applied on the lower layer, and the magnetic material distribution in the thickness direction at the interface This is an example in which the standard deviation σ _d increases and the output fluctuation rate and SNR deteriorate.
As described above, the standard deviation σ of the magnetic material distribution in the thickness direction at the interface obtained by using the depth profile method of TOF-SIMS rather than the standard deviation σ of the thickness of the magnetic layer obtained from TEM observation of the ultrathin slice. _It can be seen that _d is a characteristic that shows the output fluctuation more accurately. In the TEM image of an ultrathin slice, the interface between the magnetic layer and the nonmagnetic lower layer is averaged, whereas in the TOF-SIMS depth profile, the distribution in the thickness direction of the magnetic powder at the interface is accurate. This is because it can be measured.
That is, as in Examples 1 to 4, the magnetic layer has an average thickness of 10 to 100 nm, and TO
By controlling the magnetic material distribution σ _d in the thickness direction at the interface obtained using the depth profile method of F-SIMS to 5 to 50 nm, output fluctuation was suppressed, and good electromagnetic conversion characteristics were obtained.

2 shows a depth profile curve of a magnetic layer constituent element Ba used for measuring σ _d . FIG. 1 shows a depth profile curve obtained by multiplying the horizontal axis [sec] of the depth profile in FIG. 1 by a sputtering rate [nm / sec] and converting the horizontal axis to a sputter depth [nm] value and its differential curve.

Claims (3)

In a magnetic recording medium provided with at least one magnetic layer formed by dispersing ferromagnetic powder in a binder on a nonmagnetic support,
The magnetic layer has an average thickness δ of 10 to 100 nm,
In addition, the depth profile of the element that exists only in the magnetic layer among the elements constituting the ferromagnetic powder is measured by TOF-SIMS, and the standard deviation σ _d when the differential curve of the depth profile curve is fitted with a normal distribution is A magnetic recording medium having a thickness of 5 to 50 nm in terms of a coating layer of the magnetic recording medium.   The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is a hexagonal ferrite powder. The magnetic recording medium according to claim 1, wherein the standard deviation σ _d is 5 to 20 nm in terms of a coating layer of the magnetic recording medium.

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