JP2000251248A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a storage medium assuring good short-wavelength output and S/N, small distortion of magnetization and small noise level by maintaining, to the value in the particular range, the variation coefficient of average grain size and grain size of the non-magnetic powder that is included in the non- magnetic layer on the carrier together with a binder. SOLUTION: An average grain size of non-magnetic powder is set to 20 to 200 m and variation coefficient of such gain size is controlled to 2 to 30%. As the non-magnetic powder, α-alumina having α-conversion coefficient of 90% or more, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, hematite (α-iron oxide), goethite (oxy-iron dydroxide), corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, boron nitride, zinc oxide, calcium carbide, calcium sulfuric acid and barium sulfuric acid are used discretely or in combination. In regard to the magnetic storage medium, non-magnetic layer is provided on the carrier and the magnetic layer including a binder and a ferro-magnetic powder is provided thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk, and more particularly to a magnetic recording medium having a magnetic layer formed by applying a magnetic paint mainly composed of a ferromagnetic metal powder and a binder on a support. The present invention relates to a magnetic recording medium having excellent output and C / N in a short wavelength region in relation to a magnetic recording medium of a type.

[0002]

2. Description of the Related Art Magnetic recording technology requires that a medium can be used repeatedly, signals can be easily digitized, and a system can be constructed by combining with peripheral devices.
Because it has excellent features not found in other recording methods such as easy signal correction, video, audio,
It has been widely used in various fields including computer applications.

In order to respond to demands for downsizing equipment, improving the quality of recording / reproducing signals, extending recording time, increasing recording capacity, etc., the recording medium has a recording density, reliability and durability. It has always been desired to further improve.

[0004] For example, in audio and video applications, in order to cope with the practical use of a digital recording system for realizing an improvement in sound quality and image quality, and the development of a recording system compatible with a high-definition TV, a conventional system is required. A magnetic recording medium capable of recording and reproducing short-wavelength signals and having excellent reliability and durability even when the relative speed between the head and the medium is increased has been required. It is also desired that a large-capacity digital recording medium be developed in order to store an increasing amount of data for computer use.

[0005] In order to increase the recording density of a coating type magnetic recording medium, iron or an alloy magnetic powder mainly composed of iron is used instead of the magnetic iron oxide powder conventionally used.
Improving the magnetic properties of the magnetic layer by improving the magnetic material, such as miniaturization of the magnetic powder, and improving the filling property and orientation, improving the dispersibility of the ferromagnetic powder, and improving the surface properties of the magnetic layer. Various methods have been studied and proposed from the viewpoint of the above.

For example, a method of using a ferromagnetic metal powder or a hexagonal ferrite as a ferromagnetic powder in order to enhance magnetic properties is disclosed in JP-A-58-122623 and JP-A-61-7.
No. 4137, Japanese Patent Publication No. 62-49656, Japanese Patent Publication No. 60-50323, US Pat.
No. 4,666,770 and US Pat. No. 4,543,198.

Japanese Patent Publication No. 1-18961 discloses a metal magnetic powder having a major axis diameter of 0.05 to 0.2 μm and an axial ratio of 4 to 8,
It discloses a ferromagnetic powder having a specific surface area of 30 to 55 m ² / g, a coercive force of 1300 Oe or more, and a saturation magnetization of 120 emu / g or more, and provides a fine metal powder having a small specific surface area. Further, JP-A-60-11300 and JP-A-60-21307 disclose a ferromagnetic powder,
In particular, a method for producing fine α-iron oxyhydroxide needles suitable for ferromagnetic metal powders is disclosed.
~ 0.25 μm, Goitite with an axial ratio of 6-8 to Hc14
50-1600 Oersted, saturation magnetization (σs) 142
It discloses that 強 磁性 155 emu / g of ferromagnetic metal powder is produced. Japanese Patent Application Laid-Open No. 9-91684 discloses that ferromagnetic metal particles whose average major axis length is 0.05 μm to 0.12 μm and whose acicular ratio is 8 or more are 5.0% or less of the entire ferromagnetic metal particles. Alternatively, it has been proposed that ferromagnetic metal particles having a needle ratio of crystallites constituting the pre-ferromagnetic metal particles of 4 or more use 17.0% or less of the whole of the ferromagnetic metal particles.

Further, Japanese Patent Application Laid-Open Nos. Hei 6-340426, Hei 7-109122, Hei 7-109122
JP-A-9-261939 discloses monodisperse spindle-type hematite particles using hematite nuclei, iron hydroxide, and specific ions, and extremely fine ferromagnetic powder obtained by reducing the hematite particles. Is disclosed.

In order to enhance the dispersibility of the ferromagnetic powder, various surfactants (for example, JP-A-52-15660) are used.
No. 6, JP-A-53-15803, JP-A-53-15803
-116114. ) Or various reactive coupling agents (for example,
No. 9-59608, JP-A-56-58135, and JP-B-62-28489. ) Has been proposed.

Japanese Patent Application Laid-Open No. 1-239819 discloses a magnetic powder in which a boron compound, an aluminum compound or an aluminum compound and a silicon compound are sequentially coated on the surface of magnetic iron oxide particles, and the magnetic properties and dispersibility are disclosed. To improve. Further, Japanese Patent Application Laid-Open No. 7-22224 discloses that the content of Group 1a element in the periodic table is 0.05% by weight or less, and 0.1 to 30 atom% with respect to the total amount of the metal element, if necessary. Aluminum, and 0.1 to 10 atomic% of a rare earth element with respect to the total amount of metal elements, and the residual amount of Group 2a element of the periodic table is 0.1% by weight.
The following ferromagnetic metal powder is disclosed, and it is stated that a high-density magnetic recording medium having good storage stability and magnetic properties can be obtained.

Further, in order to improve the surface properties of the magnetic layer,
There has been proposed a method of improving the surface forming treatment method of a magnetic layer after coating and drying (for example, disclosed in Japanese Patent Publication No. 60-47725).

In order to achieve a high recording density of a magnetic recording medium, the use of shorter wavelength signals has been strongly promoted.
If the length of the signal recording area is comparable to the size of the magnetic material used, a clear magnetization transition state cannot be created, and recording becomes substantially impossible. For this reason, it is necessary to develop a magnetic substance having a sufficiently small particle size with respect to the shortest wavelength used, and miniaturization of the magnetic substance has been pursued for many years.

The magnetic recording metal powder has an acicular particle shape and imparts shape anisotropy to obtain a desired coercive force. It is well known to those skilled in the art that for high-density recording, it is necessary to reduce the surface roughness of a medium obtained by reducing the size of a ferromagnetic metal powder. However, in the metal powder for magnetic recording, the acicular ratio decreases with miniaturization, and a desired coercive force cannot be obtained. Recently, a DVC system for digitizing and recording a video signal has been proposed, and a high-performance ME tape and a high-performance MP tape are used.

For example, the present applicant has previously proposed a ferromagnetic metal powder suitable for a DVC system and a magnetic recording medium using the same (JP-A-7-326035). The present invention provides a magnetic layer having a coercive force of 2000 to 3000 Oersted,
An object of the present invention is to provide a magnetic recording medium which is controlled to have a thickness of 0.05 to 0.3 μm and a surface roughness of 1 to 3 nm, and has a specific reversal magnetization component ratio.

In recent years, a very smooth surface has been desired in order to reduce the spacing loss with the head for higher density and higher output. For this reason, even in a magnetic recording medium having at least two layers in which a non-magnetic layer and a magnetic layer are provided on a support, the lower non-magnetic layer which does not directly appear on the surface has as good a dispersibility as possible, There is an increasing need for smooth surface properties when applied. The present applicant has disclosed in Japanese Unexamined Patent Application Publication No.
As proposed in JP-A-718, a non-magnetic inorganic powder having a surface layer coated with an inorganic oxide is used to improve dispersibility, and the thickness of the support, the Young's modulus, and the thickness of the non-magnetic layer are reduced. Although the specification discloses that the surface roughness of the upper magnetic layer is 1 to 5.3 nm, it is still insufficient. It is also considered that the powder used for the lower layer may be made finer in order to smooth the magnetic surface, and the surface property of the lower non-magnetic layer may be secured, so that the surface property of the magnetic layer may be secured. However, when such fine particles are used, there is a problem that the fine particles are liable to agglomerate, and consequently deteriorate the surface properties of the lower layer and, consequently, deteriorate the surface properties of the magnetic layer. This problem is accompanied by a problem that it is difficult to control the interface between the magnetic layer and the lower layer due to poor dispersibility of the lower layer, the interface is disturbed, and a uniform magnetic layer cannot be obtained. That is, when the thickness of the magnetic layer is reduced, the dispersibility of the lower non-magnetic layer further contributes to the surface property when the layers are simultaneously overlaid. There's a problem.

The present invention is a series of the above-mentioned application and aims to provide means for improving the uniformity of performance and quality of a magnetic recording medium. Further, the development of a system equipped with a magnetoresistive (MR) head further excellent in high-density recording / reproducing characteristics has progressed, and the system has been introduced to the market. The magnetization disturbance is small, the noise is small, and S /
There is a demand for a magnetic recording medium having a good N and suitable for an MR head.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has a short wavelength output and a low S output.
It is an object of the present invention to provide a magnetic recording medium that can be applied to a high-density digital recording system having a good S / N ratio and a magnetic recording medium with small disturbance of magnetization, small noise, and good S / N. The magnetic recording medium of the present invention is preferably used for a system equipped with a magnetoresistive (MR) head.

[0018]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium comprising a non-magnetic layer containing a binder and a non-magnetic powder provided on a support, and a magnetic layer containing a binder and a ferromagnetic powder provided thereon. In the recording medium, the nonmagnetic powder has an average powder size (x) of 20 to 200 nm and a coefficient of variation (cv) of the powder size of 2 to 30%. Is done. Preferred embodiments of the present invention are as follows. 1. The dry thickness of the magnetic layer is 0.0
1 to 0.5 μm, and the surface roughness of the magnetic layer is 3D-M
A magnetic recording medium having a center plane average surface roughness of 3.0 nm or less as measured by an IRAU method. 2. The ferromagnetic powder is a ferromagnetic metal powder, and the ferromagnetic metal powder has an average major axis length of 30 to 120 nm, an average acicular ratio of 3.0 to 10.0, and a variation in acicular ratio. Coefficient is 5
30% of the magnetic recording medium. 3. A magnetic recording medium, wherein the ferromagnetic powder is a hexagonal ferrite powder having an average plate diameter of 50 nm or less.

The present inventors have conducted intensive studies on the nonmagnetic layer and the magnetic layer. As a result, the average particle size of the nonmagnetic powder contained in the nonmagnetic layer was 20 to 200 nm, and the variation coefficient of the powder size was 2 to 30%. , The magnetic layer can be made thinner and its surface properties can be improved.
It has been found that a magnetic recording medium which can be applied to a high-density digital recording system having excellent characteristics can be obtained.

In the present invention, the powder size of the non-magnetic powder is determined from a high-resolution transmission electron micrograph.
That is, the powder size is such that the shape of the powder is needle-like, spindle-like,
In the case of columnar shape (however, the height is larger than the maximum major axis of the bottom surface), etc., it indicates the length of the major axis constituting the powder, that is, the major axis length, and the shape of the powder is plate-like or columnar (thickness Height is smaller than the maximum major axis of the plate surface or bottom), refers to the maximum major axis of the plate surface or bottom, the shape of the powder is spherical,
In the case of a polyhedral shape, an unspecified shape, or the like, and when the major axis of the powder cannot be specified from the shape, it refers to a circle equivalent diameter. Here, the circle equivalent diameter is obtained by a circle projection method. The average powder size (x) of the nonmagnetic powder is an arithmetic average of the above powder sizes, and is obtained by performing the above-described measurement on about 500 powders. The coefficient of variation (cv) of the powder size is a value (%) obtained by dividing the standard deviation (σ) of the measured powder size by the average powder size and multiplying by 100, and cv (%) = 100 × It is determined from σ / x. Further, the average needle ratio of the nonmagnetic powder, the length of the short axis of the powder in the above measurement, that is, the short axis length is measured,
It indicates the arithmetic average of the value of (long axis length / short axis length) of each powder. Here, the minor axis length, in the case of the definition of the powder size, the length of the minor axis constituting the powder, in the same case,
In the case of thickness to height, there is no distinction between the major axis and the minor axis, so that (major axis length / minor axis length) is regarded as 1 for convenience. In the measurement of the powder size, the shapes of the powders may be the same or different. In other words, in the present invention, the nonmagnetic layer can contain one or more types of nonmagnetic powder. In the present invention, the non-magnetic layer must contain the above-mentioned specific non-magnetic powder. However, if desired, a non-magnetic powder having a powder size other than the above-mentioned non-magnetic powder may be used. It may be contained in 50% by weight or less of the whole magnetic powder. Further, in this specification, the definition of the powder size (including the average powder size, the variation coefficient, and the average needle ratio) of powders (ferromagnetic powder, abrasive, carbon black, etc.) other than the above nonmagnetic powder is also defined. It is basically the same as the above nonmagnetic powder. When the shape of the powder is specific, for example, in the case of the definition of the powder size, the average powder size is referred to as the average major axis length, and in the case of the same definition, the average powder size is referred to as the average plate diameter. , (Maximum major axis /
The arithmetic average of thickness to height) is referred to as an average plate ratio. In the case of the same definition, the average powder size is called the average particle diameter.

In the present invention, the average powder size of the non-magnetic powder is preferably 20 to 180 nm, more preferably 30 to 170 nm, and the coefficient of variation of the powder size is preferably 2 to 28%, Preferably 2 to 25
%, So that the thickness of the magnetic layer can be reduced and the surface roughness of the magnetic recording medium can be reduced. The thickness of the magnetic layer is preferably in the range of 0.01 to 0.5 μm, more preferably 0.01 to 0.35 μm, and the surface roughness of the magnetic layer is 3 to 3 μm in the center plane average surface roughness by the MIRAU method. 0.0 nm or less, and more preferably 1.5 to 2.6 nm. If the average powder size of the non-magnetic powder is less than 20 nm, it is difficult to disperse the paint when preparing it, and it is easy to agglomerate even when applied, and it is difficult to reduce the surface roughness of the magnetic recording medium. If the average powder size of the nonmagnetic powder exceeds 200 nm, the surface roughness of the magnetic recording medium increases, noise increases, and it is not possible to obtain excellent S / N.

The variation coefficient of the powder size of the nonmagnetic powder is 30.
%, The surface roughness tends to be large, and particularly, in the dry thickness of the magnetic layer of 0.01 to 0.5 μm, the thinner it is, the more difficult it is to reduce the surface roughness, and the more the coarse protrusions are liable to be generated. In addition, the disturbance of magnetization increases, noise increases, and it is impossible to obtain excellent S / N.

The material of the non-magnetic powder is not particularly limited whether it is an inorganic substance or an organic substance, but preferably contains at least an inorganic compound. In the present invention, the method of controlling the powder size and distribution of the nonmagnetic powder for obtaining the nonmagnetic powder satisfying x and cv is not particularly limited, and any method can be used. A method is illustrated. Method of separating nucleation and growth of powder generated by oxide synthesis reaction as much as possible. Control factors of nucleation and growth of generated powder, such as temperature, pressure, precursor generation when obtaining oxide powder from liquid phase system. A method in which the pH control and the alkali addition rate in the neutralization reaction are made as uniform as possible. A method of growing and using core particles having a good size, internal structure and crystallinity. It is desirable that the core particles have a small size. For example, by using core particles of 1 nm to 10 nm and growing them to a desired powder size of 20 to 200 nm, the powder size distribution is sharp and the variation coefficient is small. A method for synthesizing non-magnetic powder. Non-magnetic powder is subjected to multi-step processing more precisely by specific gravity separation, sieving, water classification, centrifugation, etc., and the powder size distribution is sharpened by removing large and small powders, And a method of reducing the coefficient of variation.
Further, for example, there is a method of dissolving with an acid in a method of removing a powder having a large size or a powder having a small size. A method of heat-treating the product to further homogenize its size and crystal structure. The non-magnetic powder used in the present invention can be obtained by controlling the powder size and its distribution by individually or in combination of the above. Note that the above control method is not limited to non-magnetic powder, but is similarly applied to ferromagnetic powder and other desired powder.

The layer structure of the magnetic recording medium of the present invention basically comprises a support and a magnetic layer and a non-magnetic layer containing the non-magnetic powder used in the present invention provided on the support. Is not particularly limited as long as it is provided on one side or both sides of the support surface. The positional relationship between the non-magnetic layer and the magnetic layer is basically arbitrary, but it is preferable that the non-magnetic layer be provided between the magnetic layer and the support. The magnetic layer may be a single layer or may be composed of two or more layers. In the latter case, the layers may be provided adjacent to each other depending on the purpose, with layers other than the magnetic layer interposed therebetween. A known layer configuration can be adopted. In the present invention, the thickness of the magnetic layer means the thickness of the uppermost magnetic layer in the case of a multilayer. As in the case of the magnetic layer, the non-magnetic layer can be provided with two or more non-magnetic layers containing the non-magnetic powder used in the present invention. Can also be provided at the position. Examples of the magnetic layer composed of multiple layers include a ferromagnetic powder selected from ferromagnetic iron oxide, ferromagnetic cobalt-modified iron oxide, CrO ₂ powder, hexagonal ferrite powder, and various ferromagnetic metal powders in a binder. And a combination of magnetic layers dispersed in each other. In this case, even if the ferromagnetic powders are of the same type, magnetic layers containing ferromagnetic powders having different element compositions, powder sizes, etc. can be combined. In the present invention, a magnetic recording medium in which a nonmagnetic layer is provided between a magnetic layer containing a ferromagnetic metal powder or a hexagonal ferrite powder and a support is preferable. In the positional relationship of the layers having such a layer configuration, the magnetic layer is also referred to as an upper layer, and the nonmagnetic layer is referred to as a lower layer.

As the non-magnetic powder used for the non-magnetic layer,
Various compounds can be exemplified as those composed of inorganic compounds. For example, α-alumina, β-alumina, γ-alumina having an α conversion of 90% or more, silicon carbide, chromium oxide, cerium oxide, hematite (α-iron oxide), goethite (iron oxyhydroxide), corundum, nitrided Silicon, titanium carbide, titanium oxide, silicon dioxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate and the like are used alone or in combination. As for hematite and goethite, hematite and goethite, which are intermediate raw materials of ferromagnetic metal powders prepared by a magnetic iron oxide and iron oxide reduction method, are also preferable. The non-magnetic powder used may be surface-treated in order to increase the interaction with the binder used and improve the dispersibility. Examples of the material used for the surface treatment include compounds containing elements such as Si, Al, Al, and Si. By treating with these compounds, at least silica, alumina, and a layer of silica-alumina are formed on the surface of the nonmagnetic powder. Alternatively, the surface of the nonmagnetic powder may be treated with a coupling agent such as a silane coupling agent or a titanium coupling agent. Tap density 0.3-2g / cc, water content 0.1
Preferably, the pH is 2 to 11, and the specific surface area (S _BET ) by the BET method is 5 to 100 m ² / g.

The ferromagnetic powder of the present invention comprises a ferromagnetic metal powder,
And hexagonal ferrite powder are preferred. The saturation magnetization of the ferromagnetic metal powder is usually from 120 to 170 emu / g, preferably from 135 to 170 emu / g. Immediately after the reduction, treatment with a compound described in JP-A-61-52327 or JP-A-7-94310 or a coupling agent having various substituents, followed by slow oxidation can also reduce the saturation magnetization of the ferromagnetic metal powder. It is effective because it can be increased. The coercive force of the ferromagnetic metal powder is 1700 to 3000 Oersted, preferably 1800 to 2800 Oersted.

The ferromagnetic metal powder used in the magnetic layer of the present invention is preferably a ferromagnetic alloy powder containing α-Fe as a main component. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, Ti, V, Cr, Cu,
Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, B
a, Ta, W, Re, Au, Hg, Pb, Bi, La,
Ce, Pr, Nd, P, Co, Mn, Zn, Ni, S
It may contain atoms such as r and B. In particular, Al,
Preferably, at least one of Si, Ca, Y, Ba, La, Nd, Co, Ni, and B is contained in addition to α-Fe,
More preferably, it contains at least one of Co, Y, and Al. The content of Co is 0 at.
Atomic% or less, more preferably 15 atomic% or more and 35 atomic% or less, more preferably 20 atomic% or more and 35 atomic% or less.
Atomic% or less. Y content is 1.5 atomic% or more and 12
Atomic% or less, more preferably 3 atomic% or more and 10 atomic% or less, more preferably 4 atomic% or more and 9 atomic%.
It is as follows. Al is preferably from 1.5 to 20 at%, more preferably from 3 to 20 at%, and still more preferably from 4 to 16 at%. These ferromagnetic metal powders have a dispersant, which will be described later,
The treatment with a lubricant, a surfactant, an antistatic agent or the like may be performed before dispersion. To be more specific,
4-14090, JP-B-45-18372, JP-B-47-22062, JP-B-47-22513, JP-B-46-28466, JP-B-46-38755, JP-B-47-4286, JP-B-47-4286, -12422, JP-B-47-17284, JP-B-47-18509,
JP-B-47-18573, JP-B-39-10307
No., JP-B-46-39639, U.S. Pat.
No. 15, No. 3031341, No. 3,100,194, No. 3,224,005, No. 3,389,014.

The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. A ferromagnetic metal powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, reducing iron oxide with a reducing gas such as hydrogen to reduce Fe or F
a method of obtaining e-Co powder or the like, 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; In a low-pressure inert gas to obtain a powder. The ferromagnetic metal powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and drying. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

[0029] The ferromagnetic metal powder in the magnetic layer of the present invention S _BET
40 to 80 m ² / g, preferably 45 to 80 m ² / g
70 m ² / g. If it is less than 40 m ² / g, the noise is high, and if it is more than 80 m ² / g, the surface properties tend to be difficult to obtain, which may be undesirable. The ferromagnetic metal powder of the magnetic layer of the present invention preferably has a crystallite size of 80 to 1.
80 °, more preferably 100 to 180 °, particularly preferably 110 to 175 °. The average major axis length of the ferromagnetic metal powder is preferably 30 to 120 nm, more preferably 30 to 100 nm. The average acicular ratio of the ferromagnetic metal powder is preferably 3.0 to 10.0, more preferably 3.0 to 9.0, and the coefficient of variation of the acicular ratio is preferably 5 to 30%, more preferably 5 to 28%.

It is desirable that the water content of the ferromagnetic metal powder be 0.01 to 2% by weight. It is desirable to optimize the water content depending on the type of the binder described below. The tap density of the ferromagnetic metal powder is desirably 0.2 to 0.8 g / cc. 0.
If it is more than 8 g / cc, the powder is not gradually oxidized when gradually oxidized, so that it may be difficult to handle the powder safely, or the magnetization of the obtained tape may decrease with time. If the tap density is 0.2 g / cc or less, dispersion may be insufficient. It is preferable that the pH of the ferromagnetic metal powder be optimized depending on the combination with the binder used. The range is usually from 4 to 12, preferably from 6 to 10. Ferromagnetic metal powder as required
The surface treatment may be performed with Al, Si, P, or an oxide thereof. The amount present on the surface is 0.1 to 20% by weight based on the ferromagnetic metal powder after the treatment,
Adsorption of lubricants such as fatty acids is 100m after surface treatment
g / m ² or less, which is preferable. The ferromagnetic metal powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr in some cases. It is preferable that these inorganic ions are essentially absent, but if they are 200 ppm or less, they do not particularly affect the properties. The ferromagnetic metal powder used in the present invention preferably has a small number of vacancies.
0 vol% or less, more preferably 5 vol% or less.
The shape may be any of a needle shape, a rice grain shape, and a spindle shape. SFD (switching-
The field distribution is preferably small, and is preferably 0.8 or less. It is preferable to reduce the distribution of Hc in the ferromagnetic metal powder. When the SFD is 0.8 or less,
It has good electromagnetic conversion characteristics, high output, sharp magnetization reversal, and low peak shift, and is suitable for high-density digital magnetic recording. In order to reduce the distribution of Hc, there are methods of improving the particle size distribution of goethite and preventing sintering in the ferromagnetic metal powder.

As the hexagonal ferrite powder, there are various substitution products of barium ferrite, strontium ferrite, lead ferrite, and calcium ferrite, and Co substitution products. Of these, barium ferrite is preferable. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite in which the powder surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite further containing a part of spinel phase. And
Other than predetermined atoms, Al, Si, S, Sc, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, B, Ge, and Nb. Generally, Co-Zn, Co-Ti, Co
-Ti-Zr, Co-Ti-Zn, Ni-Ti-Zn,
A substance to which an element such as Nb-Zn-Co, Sb-Zn-Co, or Nb-Zn is added can be used. Some raw materials and production methods contain specific impurities. The average plate diameter of the hexagonal ferrite powder is preferably 50 nm or less, more preferably 40 nm or less, and particularly preferably 10 to 35 nm.

In particular, to increase the track density,
When playing back with a pad, the average plate diameter should be
It is preferably 50 nm or less. Arithmetic flatness of sheet ratio (sheet diameter / sheet thickness)
The average plate-like ratio is preferably 1 to 15, more preferably 1 to 8.
Preferred. If the average plate ratio is small, the filling property in the magnetic layer
It is preferable that sufficient orientation cannot be obtained.
is there. If it is larger than 15, the stacking between powders will cause
Noise may increase. S in this powder size range
_BETIs usually 10 to 200 m ^Two/ G. S_BETIs roughly
It is signified by an arithmetic calculation value based on the plate diameter and plate thickness of the powder. powder
In general, the narrower the distribution of the plate diameter and plate thickness, the better. Digitization is
Difficult and the distribution is often not normal
However, the variation coefficient of the powder size (plate diameter or plate thickness) is 10 to
200%. To sharpen the powder size distribution
Make the powder production reaction system as uniform as possible and
Powder that has undergone the same distribution improvement treatment as the non-magnetic powder described above.
It has also been done. For example, ultra fine powder in acid solution
There is also known a method of selectively dissolving the compound. Hexagonal
Coercive force (Hc) measured on ferrite powder is 500-5
You can create up to about 000 Oersteds. Hc is higher
Is advantageous for high-density recording, but limited by the capabilities of the recording head
Is done. Hc is the powder size (plate diameter / plate thickness),
Depends on type and amount, substitution site of element, reaction conditions for powder formation, etc.
Control. Saturation magnetization (σs) is 40 emu / g to 80 emu
/ g. The higher the σs, the better, but the finer the powder
Tends to be smaller. Magnet plan to improve σs
Combining spinel ferrite with bite ferrite
And the selection of the type and amount of contained elements are well known.
You. It is also possible to use W-type hexagonal ferrite
is there. Before dispersing hexagonal ferrite powder in binder
Beforehand, use a surface treatment agent that matches the dispersion solvent and binder beforehand.
The surface has also been treated. As a surface treatment agent
In this case, an inorganic compound or an organic compound is used. Main compounds
As oxides or hydroxides of Si, Al, P, etc.,
Various silane coupling agents, various titanium coupling agents
And the like are typical examples. These compounds
It can also be used when dispersing hexagonal ferrite powder.
Wear. The amount to be present on the particle surface by the surface treatment is
0.1 to 10 for hexagonal ferrite powder before treatment
% By weight. Dispersion of pH of hexagonal ferrite powder
is important. Normally, a dispersion solvent and binding at about pH 4 to 12
There is an optimum value depending on the agent, but the chemical stability and storage stability of the medium
From about pH 6 to 11 are selected. Hexagonal ferrite
The moisture contained in the powder also affects the dispersion, dispersing solvent, binding
There is an optimum value depending on the agent, but usually the moisture is
0.01 to 2.0% by weight is selected. Hexagonal ferrite
Barium oxide, iron oxide, and iron
Substituting metal oxides and boron oxide as a glass-forming substance
Etc. after mixing to obtain the desired ferrite composition
And then quenched to an amorphous body, and then reheated,
Washing and grinding to obtain barium ferrite crystal powder
Crystallization method, barium ferrite composition metal salt solution
Neutralize with Lucari, remove by-products
After washing in a liquid phase, washing, drying and pulverizing,
Hydrothermal reaction method to obtain crystal powder, barium ferrite group
The metal salt solution was neutralized with alkali to remove by-products
After drying, processing at 1100 ° C or lower, pulverizing
Although there is a coprecipitation method for obtaining ferrite crystal powder, the present invention
We do not choose the law.

The coercive force (Hc) of the magnetic layer of the present invention is usually 1800 to 3500 Oe, preferably 1900 to 3000 Oe, and more preferably 2200 to 3000 Oe. (Bm) is usually 3500 to 7000 Gauss (G), preferably 3900 to 7000G. H
If c and Bm are smaller than the lower limits, a short-wavelength output may not be sufficiently obtained, and if they are larger than the upper limits, the head used for recording saturates, and it is difficult to secure the output. May be.

As the binder for the magnetic layer and the non-magnetic layer in the magnetic recording medium of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof can be used. As a thermoplastic resin, the glass transition temperature is -100 to 15
0 ° C., number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and degree of polymerization of about 50 to 10
It is about 00.

As such a binder, vinyl chloride,
Polymers containing vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc. as constituent units Alternatively, there are copolymers, polyurethane resins, and various rubber resins.

The thermosetting resin or the reactive resin includes a phenol resin, an epoxy resin, a polyurethane curing resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, and an epoxy-polyamide resin. , A mixture of a polyester resin and an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, and a mixture of a polyurethane and a polyisocyanate.

In the above-mentioned binder, a better ferromagnetic powder
In order to obtain the dispersion effect and the durability of the magnetic layer,
-COOM, -SO_ThreeM, -OSO_ThreeM, -P = O (O
M) _Two, -OP = O (OM)_Two, (M is water
Element atom or alkali metal base), -OH, -N
R_Two, -N⁺R_Three(R is a hydrocarbon group), epoxy group, S
At least one or more poles selected from H, CN, etc.
Uses those with a functional group introduced by copolymerization or addition reaction
Is preferred. The amount of such polar groups is 10^-1-10
^-8Mol / g, preferably 10^-2-10^-6Mol / g
It is.

The binder used in the magnetic recording medium of the present invention is used in an amount of 5 to 50% by weight, preferably 10 to 30% by weight, based on the ferromagnetic powder. It is preferable to use 5 to 100% by weight when using a vinyl chloride-based resin, 0 to 100% by weight when using a polyurethane resin, and 2 to 100% by weight of polyisocyanate in combination.

The filling degree of the ferromagnetic powder in the magnetic layer can be calculated from the saturation magnetization (σs) and Bm (maximum magnetic flux density) of the used ferromagnetic powder, and becomes (Bm / 4πσs). Is preferably at least 1.7 g / cc, more preferably at least 1.9 g / cc, most preferably at least 2.1 g / cc.

In the present invention, when polyurethane is used, the glass transition temperature is -50 to 100 ° C., and the elongation at break is 1
00-2000%, breaking stress 0.05-10 kg / c
m ² and the yield point are preferably 0.05 to 10 kg / cm ² .

Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene-isocyanate.
1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, isocyanates such as triphenylmethane triisocyanate,
Products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL,
Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takenate D-102, Takenate D-102, Takenate D-110N, Takenate D
-200, Takenate D-202, manufactured by Sumitomo Bayer,
There are death module L, death module IL, death module N, death module HL, etc. These can be used alone or in combination of two or more by utilizing the difference in curing reactivity.

The magnetic layer and / or the non-magnetic layer of the magnetic recording medium of the present invention usually contains various components such as a lubricant, an abrasive, a dispersant, an antistatic agent, a plasticizer, a fungicide, and the like. A material having the function of (1) is contained according to the purpose.

As the lubricant, dialkylpolysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxypolysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkylmonoalkoxypolysiloxane (alkyl has 1 carbon atom)
Silicon oil such as -5, alkoxy has 1-4 carbon atoms, phenylpolysiloxane, fluoroalkylpolysiloxane (alkyl has 1-5 carbon atoms); conductive fine powder such as graphite; molybdenum disulfide, Inorganic powders such as tungsten sulfide; fine powders of plastics such as polyethylene, polypropylene, polyethylene-vinyl chloride copolymer and polytetrafluoroethylene; α-olefin polymers; saturated fatty acids which are solid at room temperature (10 to 2 carbon atoms)
2); an unsaturated aliphatic hydrocarbon liquid at room temperature (a compound in which an n-olefin double bond is bonded to a terminal carbon, having about 20 carbon atoms); a monobasic fatty acid having 12 to 20 carbon atoms and 3 carbon atoms Fatty acid esters, fluorocarbons and the like consisting of up to 12 monohydric alcohols can be used.

Of the above, saturated fatty acids and fatty acid esters are preferred, and both are more preferred. Ethanol, butanol, phenol, benzyl alcohol,
-Methyl butyl alcohol, 2-hexyldecyl alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, monoalcohols such as s-butyl alcohol, ethylene glycol, diethylene glycol,
Examples include polyhydric alcohols such as neopentyl glycol, glycerin, and sorbitan derivatives. Similarly, fatty acids include acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachinic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, and palmitoleic acid And the like or a mixture thereof.

Specific examples of the fatty acid ester include butyl stearate, s-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, and 2-hexyldecyl. Stearate, butyl palmitate, 2-ethylhexyl myristate,
Mixtures of butyl stearate and butyl palmitate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, dipropylene glycol monobutyl ether esterified with stearic acid, diethylene glycol dipalmitate, and hexamethylene diol myristic acid And various ester compounds such as glycerin oleate.

Furthermore, in order to reduce the hydrolysis of fatty acid esters which often occur when the magnetic recording medium is used under high humidity, the fatty acids and alcohols as raw materials are branched / straight chain, isomer structures such as cis / trans and the like, and branch positions. A choice is made. These lubricants are added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

The following compounds can also be used as the lubricant. That is, silicon oil, graphite, molybdenum disulfide, boron nitride, graphite fluoride, fluorinated alcohol, polyolefin, polyglycol, alkyl phosphate, tungsten disulfide, and the like.

The abrasive used for the magnetic layer of the present invention includes α alumina, γ alumina, and generally used materials.
Fused alumina, corundum, artificial corundum, silicon carbide, chromium oxide (Cr ₂ O ₃ ), diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), αFe ₂ O _{3 and the} like are used. These abrasives have a Mohs hardness of 6 or more. Specific examples include AKP-10, AKP-12, and AKP- manufactured by Sumitomo Chemical Co., Ltd.
15, AKP-20, AKP-30, AKP-50, A
KP-1520, AKP-1500, HIT-50, H
IT60A, HIT70, HIT80, HIT-10
0, Nihon Kagaku Kogyo Co., Ltd., G5, G7, S-1, chromium oxide K, Uemura Kogyo UB40B, Fujimi Abrasive Co., Ltd. WA
8000, WA10000, Toda Kogyo TF100,
TF140, TF180, and the like. Those having an average powder size of 0.05 to 3 μm are effective,
Preferably it is 0.05 to 1.0 μm.

The total amount of these abrasives is 1 to 20 parts by weight, preferably 1 to 15 parts by weight, based on 100 parts by weight of the magnetic material. If the amount is less than 1 part by weight, sufficient durability tends not to be obtained, and if it is more than 20 parts by weight, the surface properties and the degree of filling tend to deteriorate. These abrasives may be added to the magnetic paint after dispersion treatment with a binder in advance.

The magnetic layer of the magnetic recording medium of the present invention may contain conductive particles as an antistatic agent in addition to the nonmagnetic powder. However, in a magnetic recording medium in which a nonmagnetic layer is provided between the support and the magnetic layer, in order to maximize the saturation magnetic flux density of the upper layer, the addition to the upper layer should be reduced as much as possible, and the coating layer other than the upper layer Is preferably added. It is particularly preferable to add carbon black as an antistatic agent in terms of reducing the surface electric resistance of the entire medium. As the carbon black that can be used in the present invention, furnace for rubber, thermal for rubber, black for color, conductive carbon black, acetylene black and the like can be used. S _BET is 5-500 m ² / g, D
The BP oil absorption is 10 to 1500 ml / 100 g, the average particle diameter is 5 to 300 nm, the pH is 2 to 10, and the water content is 0.1.
Preferably, the tap density is 0.1 to 1 g / cc. Specific examples of the carbon black used in the present invention include BLACKPEARLS manufactured by Cabot Corporation.
2000, 1300, 1000, 900, 800, 7
00, VULCAN XC-72, manufactured by Asahi Carbon Co., #
80, # 60, # 55, # 50, # 35, manufactured by Mitsubishi Chemical Corporation, # 3950B, # 2700, # 2650, # 260
0, # 2400B, # 2300, # 900, # 100
0, # 95, # 30, # 40, # 10B, MA230,
MA220, MA77, manufactured by Columbia Carbon Co., CO
NDUTEXT SC, RAVEN 150, 50, 4
0, 15, Ketchen Black E manufactured by Lion Aguso
C, Ketjen Black ECDJ-500, Ketjen Black ECDJ-600 and the like. Carbon black may be surface-treated with a dispersing agent or the like, carbon black may be oxidized, or grafted with a resin, or may be used in which a part of the surface is graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. When carbon black is used for the magnetic layer, the amount is preferably 0.1 to 30% by weight based on the magnetic material. 3-20% by weight based on the inorganic non-magnetic powder (however, the non-magnetic powder does not include carbon black) in the non-magnetic layer
It is preferable to include them.

In general, carbon black not only acts as an antistatic agent, but also has a function of reducing a friction coefficient, imparting a light-shielding property, and improving a film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount, and combination, and are selectively used depending on the purpose based on the above-mentioned properties such as powder size, oil absorption, conductivity, and pH. It is of course possible. Carbon black that can be used can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

The magnetic recording medium of the present invention comprises two or more coating layers formed on a support. The coating means may be a sequential coating method (wet-on-dry method) or a simultaneous coating method (wet-on-dry method). (On-wet method), but the latter is particularly excellent because the latter can produce an ultra-thin magnetic layer. As a specific method of the simultaneous application method, that is, the wet-on-wet method,

(1) First, a lower layer is applied by a gravure coating, roll coating, blade coating, or extrusion coating device which is generally used for a magnetic paint, and while the layer is still wet, for example, -46186, JP-A-60-238179 and JP-A-2-2-2
No. 65672, a method of applying an upper layer by a support pressure-type extrusion coating device,

(2) A coating head having two built-in coating liquid passage slits as disclosed in JP-A-63-88080, JP-A-2-17971 and JP-A-2-265672. A method of applying the lower layer coating solution and the upper layer coating solution almost simultaneously,

(3) A method in which an upper layer and a lower layer are coated almost simultaneously by an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

In the case of coating by a wet-on-wet method, the flow characteristics of the coating solution for the magnetic layer and the coating solution for the non-magnetic layer should be as close as possible so that the interface between the coated magnetic layer and the non-magnetic layer will not be disturbed. A magnetic layer having a uniform thickness and a small thickness variation can be obtained. Since the flow characteristics of the coating solution strongly depend on the combination of the powder and the binder in the coating solution, it is particularly important to pay attention to the selection of the nonmagnetic powder used for the nonmagnetic layer.

The thickness of the support of the magnetic recording medium is usually
1 to 100 μm, preferably 3 to 20 μm when used as a tape, and 40 to 80 μm when used as a flexible disk, and the nonmagnetic layer provided on the support is usually 0.5 to 10 μm, preferably 0.5-3
μm.

Further, layers other than the magnetic layer and the non-magnetic layer can be formed according to the purpose. For example,
An undercoat layer for improving adhesion may be provided between the support and the lower layer. This thickness is usually 0.01 to 2 μm,
Preferably it is 0.05 to 0.5 μm. Further, a back layer may be provided on the side of the support opposite to the magnetic layer side.
This thickness is usually 0.1 to 2 μm, preferably 0.3 to
1.0 μm. Known undercoat layers and back layers can be used. In the case of a disk-shaped magnetic recording medium, the above-mentioned layer configuration can be provided on one side or both sides.

The support used in the present invention is not particularly limited, and those commonly used can be used.
Examples of the material forming the support include films of various synthetic resins such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, polyimide, polysulfone, and polyethersulfone, and aluminum foil and stainless steel. A metal foil such as a foil can be used.

In order to effectively achieve the object of the present invention, the surface roughness of the support should be not more than 0.03 μm, preferably 0.02 μm in terms of center plane average surface roughness (Ra) (cutoff value 0.25 mm). The thickness is more preferably 0.01 μm or less. Further, it is preferable that these supports not only have a small center plane average surface roughness but also have no coarse protrusions of 1 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include oxides and carbonates of Ca, Si, Ti and the like, and organic resin fine powders of an acrylic resin and the like. The F-5 value of the support used in the present invention in the web running direction is preferably 5 to 50 kg / mm ² , and the F-5 value in the web width direction is preferably 5 to 50 kg / mm ² .
The five values are preferably 3 to 30 kg / mm ² , and the F-5 value in the web longitudinal direction is generally higher than the F-5 value in the web width direction, but it is particularly necessary to increase the strength in the width direction. When there is, it is not the case.

The heat shrinkage of the support in the web running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage at 80 ° C. for 30 minutes is 30%. Preferably it is 1% or less, more preferably 0.1%.
5% or less. Breaking strength is 5-100Kg in both directions
/ Mm ² and an elastic modulus of 100 to 2000 kg / mm ² are desirable.

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 and tetrahydrofuran, methanol,
Alcohols such as ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate,
Esters such as glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane,
Glycol ethers, such as benzene, toluene, xylene, cresol, chlorobenzene, aromatic hydrocarbons such as, methylene chloride, ethylene chloride,
Carbon tetrachloride, chloroform, ethylene chlorohydrin,
Chlorinated hydrocarbons such as dichlorobenzene, N, N-dimethylformamide, hexane and the like can be used.
These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 1% or less.
0% or less. The kind and amount of the organic solvent used in the present invention may be changed between the magnetic layer and the non-magnetic layer if necessary. Use a highly volatile solvent for the non-magnetic layer to improve surface properties, and use a solvent with a high surface tension (cyclohexanone, dioxane, etc.) for the non-magnetic layer to improve coating stability.
Examples include raising the degree of filling using a solvent having a high solubility parameter for the magnetic layer, but it is a matter of course that the present invention is not limited to these examples.

The magnetic recording medium of the present invention is prepared by kneading and dispersing a nonmagnetic powder or a ferromagnetic powder with a binder and, if necessary, other additives together with an organic solvent, and coating the nonmagnetic paint and the magnetic paint on a support. And optionally oriented and dried.

The step of producing the magnetic paint of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. Non-magnetic powder, ferromagnetic powder, binder, carbon black, abrasive, antistatic agent used in the present invention,
All raw materials such as a lubricant and a solvent may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example,
Polyurethane may be added separately in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion.

For kneading and dispersing the non-magnetic paint and the magnetic paint, various kneaders are used. For example, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand grinder, Segvar (Szegvar)
i), an attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper, a kneader, a high-speed mixer, a homogenizer, an ultrasonic disperser and the like can be used.

In order to achieve the object of the present invention, it is a matter of course that a conventional known manufacturing technique can be used as a part of the process. However, in the kneading step, a strong kneading force such as a continuous kneader or a pressure kneader is used. It is preferable to use one that has When using a continuous kneader or a pressure kneader, all or a part of the ferromagnetic powder and the binder (however, preferably 30% by weight or more of the total binder) and the ferromagnetic powder 1
The kneading treatment is performed in the range of 15 to 500 parts by weight with respect to 00 parts by weight. The details of these kneading processes are described in
106338 and JP-A-64-79274. In the present invention, Japanese Patent Application Laid-Open No.
By using the simultaneous multilayer coating method as shown in No. 3, production can be performed more efficiently.

The residual solvent contained in the magnetic layer of the magnetic recording medium of the present invention is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less, and the residual solvent contained in the magnetic layer is contained in the non-magnetic layer. It is preferable that the amount is smaller than the contained residual solvent.

The porosity of the magnetic layer is preferably 30% by volume or less, more preferably 10% by volume for both the lower and upper layers.
It is as follows. The porosity of the non-magnetic layer is preferably larger than the porosity of the magnetic layer, but may be small as long as the porosity of the non-magnetic layer is 5% by volume or more.

Although the magnetic recording medium of the present invention can have a lower layer and an upper layer, it is easily presumed that these physical properties can be changed between the lower layer and the upper layer according to the purpose. For example, the elastic modulus of the upper layer is increased to improve running durability, and at the same time, the elastic modulus of the lower layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

According to such a method, the magnetic layer coated on the support is subjected to a treatment for orienting the ferromagnetic metal powder in the layer if necessary, and then the formed magnetic layer is dried. If necessary, the magnetic recording medium of the present invention is manufactured by performing a surface smoothing process or cutting into a desired shape. The composition for the upper layer or the composition for the lower layer is dispersed together with a solvent, and the obtained coating solution is coated on a support, and orientation dried to obtain a magnetic recording medium.

The elastic modulus of the magnetic layer at an elongation of 0.5% is desirably 100 to 2000 kg in both the web coating direction and the width direction.
/ Mm ² , and the breaking strength is desirably 1 to 30 kg / c.
m ² , the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kg / mm ^{2 in} both the web coating direction and the width direction, the residual elongation is preferably 0.5% or less, and the thermal shrinkage at any temperature of 100 ° C. or less is desirable. Is 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.

The magnetic recording medium of the present invention may be a tape for video use or audio use, or a floppy disk or magnetic disk for data use.
This is particularly effective for a medium for digital recording in which the loss of a signal due to the occurrence of dropout is fatal.
Furthermore, by making the lower layer a non-magnetic layer and making the thickness of the magnetic layer on the lower layer 0.5 μm or less, a high-density, large-capacity magnetic recording medium with high electromagnetic conversion characteristics, excellent overwrite characteristics, Obtainable.

[0073]

EXAMPLES The novel features of the present invention will be specifically described in the following examples, but the present invention is not limited to these examples. In addition, “parts” means parts by weight unless otherwise specified.

Using the ferromagnetic metal powder or barium ferrite powder shown in Table 1 or Table 2, a magnetic tape or magnetic disk was prepared as follows.

[0075]

[Table 1]

[0076]

[Table 2]

(Magnetic Tape) Example 1 Ferromagnetic metal powder having an average major axis length of 10
3 nm, average needle ratio 6.1, needle coefficient of variation 28
%, Hc is 2420 Oersted, σs is 154 emu
The following magnetic layer composition and non-magnetic layer composition were prepared in order to prepare a multi-layered magnetic tape using a ferromagnetic metal powder having the characteristics shown in MP in Table 1 in Table 1. (Composition of magnetic layer) Ferromagnetic metal powder (MP shown in Table 1) 100 parts Binder 13 parts of vinyl chloride polymer (-SO ₃ Na group: 1 × 10 ^-4 eq / g contained, polymerization degree: 300) Polyester polyurethane resin 5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 (molar ratio), containing -SO ₃ Na group: 1 × 10 ^-4 eq / g) α-alumina (average Particle size: 0.13 μm) 5.0 parts Carbon black (average particle size: 40 nm) 1.0 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 200 parts

(Composition of Nonmagnetic Layer) Hematite a (described in Table 3) 80 parts Carbon black 20 parts (average particle diameter: 17 nm, DBP oil absorption 80 ml / 100 g, S _BET : 240 m ² / g, pH 7.5) Binder 12 parts of vinyl chloride polymer (-SO ₃ Na group: containing 1 × 10 ^-4 eq / g, degree of polymerization: 300) Polyester polyurethane resin 5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2. 6/1 (molar ratio), -SO ₃ Na group: 1 × 10 ^-4 eq / g) butyl stearate 1 part Stearic acid 2.5 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 200 parts 200 parts of the above magnetic layer After kneading each of the composition and the composition of the nonmagnetic layer with a kneader, they were dispersed using a sand grinder. The polyisocyanate was added to the resulting dispersion in an amount of 5 parts for the non-magnetic layer coating solution and 6 parts for the magnetic layer coating solution.
Further, 20 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone 1: 1 was added to each coating solution, and the mixture was filtered using a filter having an average pore diameter of 1 μm to prepare a coating solution for a nonmagnetic layer and a magnetic layer.

The obtained non-magnetic layer coating solution was applied so that the thickness after drying became 1.5 μm, and immediately thereafter, while the non-magnetic layer was still wet, the magnetic layer was Simultaneous multi-layer coating was performed on a 7 μm-thick polyethylene terephthalate support so that the thickness became 0.15 μm, and while both layers were still in a wet state, they were passed through an alignment device and longitudinally oriented. The orientation magnet at this time is a rare earth magnet (with a surface magnetic flux of 50).
(00 gauss), and then passed through a solenoid magnet (magnetic flux density of 5000 gauss), dried until the orientation was not restored in the solenoid, and the magnetic layer was dried and wound up. Thereafter, calendering was performed at a roll temperature of 90 ° C. using a seven-stage calender composed of metal rolls to obtain a web-shaped magnetic recording medium, which was slit to an 8 mm width to prepare a sample of an 8 mm video tape. .

Examples 2 to 10 MP was used as a ferromagnetic metal powder, and hematites b to g and goethites a to c having the properties shown in Table 3 were used as nonmagnetic powders as shown in Table 4. Except for the above, a multilayer tape was prepared in the same manner as in Example 1.

Comparative Examples 1 to 3
The multilayer tape was prepared in the same manner as in Example 1 except that the nonmagnetic powder having the characteristics described in Hematites h to j was used.

Comparative Example 4 The same as Example 1 except that MP in Table 1 was used as the ferromagnetic metal powder, and a nonmagnetic powder having the properties described in Hematite h in Table 3 was used as the nonmagnetic powder. To produce a multilayer tape.

Table 4 shows the magnetic properties, surface roughness of the magnetic layer, 1/2 Tb output, C / N, and still durability measured using a drum tester of the obtained sample. Show.

The magnetic properties were measured in parallel with the orientation direction using a vibrating sample magnetometer (manufactured by Toei Kogyo) with an external magnetic field of 5 kOe. The relative speed of the TSS head (Sendust head for 8 mm video from Sony; head gap 0.2 μm, track width 1.4 μm, saturation magnetic flux density 1.1 Tesla) is 10.2 m / s. , 1 / 2Tb (λ = 0.5 μm), the optimum current is obtained, and this output is measured.
/ 2Tb output. C / N was measured under the same conditions 1
A noise level 1 MHz away from the frequency of / 2Tb was averaged and calculated. Super DC tape for 8 mm video made by Fuji Photo Film was used as a standard for the electromagnetic conversion characteristics. Still durability is FUJIX made by Fuji Photo Film
Playback was performed in still mode using an 8.8 mm video cassette. 23 ° C 50% RH, 5 ° C 20% RH, 40 ° C80
% RH was measured in three environments. A case where all three environments were successfully reproduced for 30 minutes or more was evaluated as ○, and a case where at least one of the three environments was less than 15 minutes and was not reproduced successfully was evaluated as ×.

The surface roughness of the magnetic layer was measured using a light interference three-dimensional roughness meter “TOPO-3D” manufactured by WYKO (US, Arizona).
Was used to measure a 250 μm square sample area. In calculating the measured values, corrections such as tilt correction, spherical correction, and cylindrical correction were performed in accordance with JIS-B601, and the center plane average surface roughness (Ra) was used as the value of the surface roughness. The results are shown in Table 4.

[0086]

[Table 3]

In Table 3, x is the average major axis length, σ is the standard deviation of the major axis length, and cv is the coefficient of variation of the major axis length.

[0088]

[Table 4]

In Table 4, "Actual-" indicates an example, and "Ratio-" indicates a comparative example (the same applies hereinafter). Table 4 shows that the examples of the present invention have still durability and that the magnetic layer is smooth, have a short wavelength output, and are excellent in C / N as compared with the comparative example.

(Magnetic Disk) A magnetic disk was prepared as follows using the magnetic materials shown in Tables 1 and 2 and the nonmagnetic powder shown in Table 3. Example 11 <Preparation of paint> Magnetic layer coating solution X Barium ferrite powder: BaF 100 parts Vinyl chloride resin: MR110 (manufactured by Zeon Corporation) 12 parts Polyurethane resin: UR8200 (manufactured by Toyobo Co., Ltd.) 3 parts Abrasive: HIT55 (Sumitomo) Chemical Co.) 10 parts Carbon black: # 50 (Asahi Carbon Co.) 5 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts Nonmagnetic layer Coating liquid Non-magnetic powder: Hematite a (described in Table 3) 80 parts Carbon black 20 parts Conductex SC-U (manufactured by Columbian Carbon Co.) MR110 12 parts UR8200 5 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexade Stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts

Each of the above two coating solutions was kneaded with a kneader and dispersed using a sand mill. To the resulting dispersion, 10 parts of the polyisocyanate was added to the coating solution for the non-magnetic layer and 10 parts to the coating solution for the magnetic layer, and 40 parts of butyl acetate was added to each.
Then, the mixture was filtered using a filter having an average pore size of 1 to prepare a coating solution for the non-magnetic layer and a coating solution for the magnetic layer.

The obtained non-magnetic layer coating solution was applied to a thickness of 62 μm so that the thickness after drying was 1.5 μm, and immediately thereafter, the thickness of the magnetic layer was 0.2 μm thereon. A multilayer coating is performed simultaneously on a polyethylene terephthalate support having a center plane average surface roughness of 0.01 μm, and while both layers are still in a wet state, a frequency of 50 Hz, a magnetic field strength of 250 Gauss and a frequency of 50 Hz and 120 Gauss are applied. After passing through an AC magnetic field generator having a magnetic field strength, performing random orientation treatment and drying, the temperature is 90 ° C. and the linear pressure is 30 with a seven-stage calendar.
After processing at 0 Kg / cm, and 3.7 inch punching and surface polishing, a 3.7 inch cartridge (zip-dis manufactured by Iomega, USA) with a liner installed inside
k cartridge), add predetermined mechanical parts,
A 3.7 inch floppy disk was obtained.

Examples 12 to 14, Comparative Example 5 Non-magnetic powders listed in Table 5 (specifically described in Table 3)
A 3.7-inch floppy disk was obtained in the same manner as in Example 11, except that the above was replaced. Examples 15 to 17, Comparative Example 6 The magnetic layer coating solution X of Example 11 was changed to the following magnetic layer coating solution Y, and the nonmagnetic powder was changed to that shown in Table 5 (specifically described in Table 3). Except having changed, similarly to Example 11
A 3.7 inch floppy disk was obtained.

Magnetic layer coating liquid Y Ferromagnetic metal powder: MP: described in Table 1 100 parts MR110 (manufactured by Zeon Corporation) 12 parts UR8200 (manufactured by Toyobo) 3 parts HIT55 (manufactured by Sumitomo Chemical) 10 parts # 50 (Asahi) Carbon Co.) 5 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts

Each sample of the floppy disk was measured by the following evaluation method. Magnetic properties (Hc): Vibrating sample magnetometer (Toei Kogyo Co., Ltd.)
Was measured at Hm 10 kOe. Surface roughness (Ra) of magnetic layer: same as in Example 1

Measurement of S / N: Disk test apparatus manufactured by Kokusai Denshi Kogyo (formerly Tokyo Engineering) and SK60
After recording at a recording wavelength of 90 kfci at a radius of 24.6 mm using a metal-in-gap head having a gap length of 0.3 μm using a 6B type evaluation apparatus, the reproduction output of the head amplifier was measured by an oscilloscope 7 manufactured by Tektronix.
It was measured with Model 633. After DC erasure of the disk whose reproduction output was measured, the reproduction output (noise) was measured with a TR4171 type spectroanalyzer manufactured by Advantest. S / N ratio = -20lo
g (noise / reproduction output), and a relative value was used as a standard of electromagnetic conversion characteristics using a Zip100MB disk manufactured by Fuji Photo Film Co., Ltd.

[0097] Durability: Floppy disk drive (ZIP100 manufactured by Iomega, USA: 2968 revolutions)
rpm), the head is fixed at a position with a radius of 38 mm, recording is performed at a recording density of 34 kfci, and then the signal is reproduced.
The output was set to 100%. Thereafter, the reproduction output at the time of running for 1000 hours in a thermocycle environment in which the following thermocycle flow was defined as one cycle was compared with the output before the flow.

[0098]

[0099]

[Table 5] Table 5 shows that the examples of the present invention have durability, have a smooth magnetic layer, and are excellent in short wavelength output and C / N as compared with the comparative examples.

[0100]

According to the present invention, as the nonmagnetic powder contained in the nonmagnetic layer, the average powder size is reduced to 20 to 200 nm, and the coefficient of variation of the powder size is adjusted to 2 to 30%. Ensuring the smoothness and durability of the layer,
Noise can be reduced, and a magnetic recording medium with excellent S / N can be provided. Further, it is possible to provide a magnetic recording medium excellent in MR head suitability.

Claims (4)

[Claims] 1. A magnetic recording medium comprising: a non-magnetic layer containing a binder and a non-magnetic powder on a support; and a magnetic layer containing a binder and a ferromagnetic powder on the non-magnetic layer. A magnetic recording medium having a powder size (x) of 20 to 200 nm and a powder size variation coefficient (cv) of 2 to 30%. 2. The dry thickness of the magnetic layer is from 0.01 to 0.1.
5 μm and the surface roughness of the magnetic layer is 3D-MIRAU
2. The magnetic recording medium according to claim 1, wherein a center plane average surface roughness by a method is 3.0 nm or less. 3. The ferromagnetic powder is a ferromagnetic metal powder, and the ferromagnetic metal powder has an average major axis length of 30 to 120 n.
3. The magnetic recording medium according to claim 1, wherein m is an average acicular ratio of 3.0 to 10.0, and a variation coefficient of the acicular ratio is 5 to 30%. 4. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is a hexagonal ferrite powder having an average plate diameter of 50 nm or less.