JP3473874B2 - Magnetic recording media - Google Patents

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 and, more particularly, to a coating type in which a magnetic coating mainly composed of a ferromagnetic metal powder and a binder is coated on a non-magnetic support to form a magnetic layer. The present invention relates to a magnetic recording medium excellent in sensitivity and S / N in a short wavelength region in relation to the magnetic recording medium.

[0002]

2. Description of the Related Art In magnetic recording technology, a medium can be repeatedly used, signals can be easily digitized, and a system can be constructed by combining with peripheral equipment.
Since it has excellent features not found in other recording methods, such as the ability to easily modify signals,
It has been widely used in various fields including computer applications.

In order to meet the demands for downsizing of equipment, improvement of quality of recording / reproducing signal, lengthening of recording, increase of recording capacity, etc., a recording medium has recording density, reliability and durability. It has always been desired to further improve.

For example, in audio and video applications, in order to cope with the practical use of a digital recording method for improving the sound quality and image quality and the development of a recording method compatible with high-definition TV, it is more important than the conventional system. A magnetic recording medium capable of recording and reproducing a short wavelength signal and having excellent reliability and durability even when the relative speed between the head and the medium is increased has been demanded. 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 applications.

In order to achieve high-density recording of a coating type magnetic recording medium, iron or an alloy magnetic powder mainly composed of iron is used in place of the magnetic iron oxide powder conventionally used,
Improving the magnetic properties of the magnetic layer by improving the magnetic substance such as miniaturization of the magnetic powder and improving its packing and orientation, improving the dispersibility of the ferromagnetic powder, and enhancing the surface property of the magnetic layer. From the viewpoint of the above, various methods have been studied and proposed.

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.
4137, Japanese Patent Publication No. 62-49656, Japanese Patent Publication No. 60-50323, US462953, U
S46666770, US4543198, etc. are disclosed.

JP-A-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,
Specific surface area of 30-55 m ² / g, coercive force of 1300 Oe
As mentioned above, the ferromagnetic powder having a saturation magnetization of 120 emu / g or more is disclosed, and the fine metal powder having a small specific surface area is provided. Further, JP-A-60-11300 and JP-A-60-21307 disclose a method for producing fine α-iron oxyhydroxide needle crystals suitable for ferromagnetic powder, particularly ferromagnetic metal powder. However, in the latter case, the major axis length is 0.12 to 0.2.
Hc1450-1 from Goethite with 5 μm and axial ratio 6-8
It is disclosed that a ferromagnetic metal powder of 600, σ _S 142-155 emu / g is produced.

Further, in JP-A-6-340426 and JP-A-7-109122, hematite nucleus crystals, iron hydroxide, monodisperse spindle type hematite particles using specific ions, and the hematite particles are reduced. The extremely fine ferromagnetic powder obtained is disclosed.

Further, in order to enhance the dispersibility of the ferromagnetic powder, various surfactants (for example, Japanese Patent Laid-Open No. 52-15660).
6, JP-A-53-15803, JP-A-53-15
It is disclosed in Japanese Patent Laid-Open No. 116114. ) Or various reactive coupling agents (see, for example, JP-A-4
9-59608, JP-A-56-58135, JP-B-62-28489 and the like. ) Is proposed.

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

Further, in order to improve the surface property of the magnetic layer,
A method (for example, disclosed in Japanese Patent Publication No. 60-44725) of improving the surface forming treatment method of the magnetic layer after coating and drying has been proposed.

In the metal powder for magnetic recording, the particle shape is needle-like and imparts shape anisotropy to obtain the target coercive force. It is well known to those skilled in the art that it is necessary to refine the ferromagnetic metal powder to reduce the surface roughness of the resulting medium for high density recording. However, the acicular ratio of the metal powder for magnetic recording decreases with miniaturization, and the 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. Since the coercive force of the MP tape used for DVC is 2000 Oe or more, a ferromagnetic metal powder having a large coercive force and a fine particle size distribution is required. Further, since the recording method overwrites the signal, it is desired that the overwrite characteristic is good.

The present applicant has previously proposed a ferromagnetic metal powder suitable for a DVC system and a magnetic recording medium using the same (Japanese Patent Application No. 6-139683). This invention uses a magnetic layer having a coercive force of 2000 to 3000 Oe and a thickness of 0.05 to
The present invention provides a magnetic recording medium in which the surface roughness is controlled to 0.3 μm and the surface roughness is controlled to 1 to 3 nm, and a specific reversal magnetization component ratio is defined.

The present invention is a series of the above-mentioned applications, and further aims to provide means for improving the uniformity of performance and quality of magnetic recording media.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and provides a high density digital recording system having a short wavelength output and a good S / N and excellent overwrite characteristics. It is an object of the present invention to provide a magnetic recording medium that can be applied.

[0016]

An object of the present invention is to provide a magnetic recording medium in which a magnetic layer containing at least a ferromagnetic metal powder is provided on a non-magnetic support, and the coercive force of the magnetic layer is 2000 to 3000 Oe. Bm of the magnetic layer is 3800-
5500 gauss, the average major axis length of the ferromagnetic metal particles is 0.04 to 0.10 μm, the average acicular ratio of the ferromagnetic metal particles is 3.0 to 8.0, and the ferromagnetic A magnetic recording medium characterized in that the average number of crystallites constituting the metal particles is 1.0 to 2.0, and the average acicular ratio of crystallites is 2.0 to 5.0, and the nonmagnetic support. This can be achieved by the above-described magnetic recording medium characterized in that an undercoat layer mainly containing an inorganic non-magnetic powder and a binder is provided between the body and the magnetic layer.

In the present invention, the "ferromagnetic metal particle" means a particle that constitutes the maximum outer shape of the particle. The average major axis length of the ferromagnetic metal particles indicates the average of the major axis lengths of the particles, and the average minor axis length indicates the average of the minor axis lengths of the particles. The average acicular ratio refers to a value obtained by dividing the average major axis length by the average minor axis length. The crystallite of the ferromagnetic metal particle means each crystal of the metal particles constituting the ferromagnetic metal particle.

That is, the present inventor has variously studied a method for producing a fine-particle ferromagnetic metal powder, and even if the ferromagnetic metal particles, which have been difficult to achieve a high coercive force in the past, are small and have a low acicular ratio, By focusing on the crystallites that compose the metal particles and controlling the crystallites, we achieved higher Hc and improved Hc distribution. In the conventional manufacturing method, the morphology control of the starting material is insufficient, and when the ferromagnetic metal powder is used, the number and shape of the crystallites constituting the ferromagnetic metal powder are not controlled. Hc
I think that the improvement of distribution was insufficient. According to the present invention, a starting material having a uniform particle size is subjected to a sintering prevention treatment and is reduced from a metal oxide (eg FeO) to a metal (eg F).
The present invention was achieved by controlling the number of nucleation in e). Monodisperse goethite or monodisperse hematite can be used as the starting material. The average major axis length of the starting material is 0.0
It is preferably 4 to 0.15 μm and the acicular ratio is 3 to 10. When using a raw material having an average major axis length of 0.04 μm or less, Hc,
It is difficult to set σs to the target range. It is difficult to control the number of crystallites to 1.0 to 2.0 using a raw material of 0.15 μm or more, and the Hc distribution deteriorates. When the acicular ratio is greater than 10, it is difficult to control the number of crystallites to 1.0 to 2.0, and when the acicular ratio is less than 3, the coercive force of the ferromagnetic metal powder is small and high. It cannot be used as a medium for density recording.

In the ferromagnetic metal powder used in the present invention, the means for controlling the above-mentioned ferromagnetic metal particles and crystallites is not particularly limited, but specific examples include the following methods and. Mainly to specify the elemental composition inside the ferromagnetic metal powder. Especially in the case of a ferromagnetic metal powder mainly composed of Fe, F
Identify the trace elements that interact with e. As the trace element, Mg, Co, Ni, Cu, Mn and the like are preferable. It is preferable that the trace elements are added after surface treatment during and / or after the production of goethite or hematite. In the method of reducing an oxide of a ferromagnetic metal element to a ferromagnetic metal powder, pretreatment before reduction, for example, dehydration conditions such as goethite, annealing conditions and the reduction conditions,
For example, select temperature, reducing gas, reducing treatment time, etc.

Specifically, the respective conditions for treating the trace element-containing goethite obtained above are as follows. The dehydration conditions are 250 to 400 under a nitrogen atmosphere.
C., preferably 300 to 400.degree. C. for 0.5 to 2 hours, preferably 0.5 to 1 hour. The annealing conditions are 500 to 800 ° C., preferably 550 to 700 ° C., and 1 to 5 hours, preferably 2 in a nitrogen atmosphere.
It may be performed for 3 hours.

The reducing condition is hydrogen / CO (volume ratio)
= 1/9 to 5/5, preferably 1/9 to 4/6, and a temperature of 350 to 450 ° C, preferably 375 to 425 ° C,
The reduction treatment may be performed for 0.3 to 3 hours, preferably 1 to 2 hours, and then the atmosphere may be replaced with nitrogen, followed by reduction treatment with pure hydrogen at the above temperature for 3 to 5 hours. The end of reduction is determined by measuring the water content in the wastewater gas with a dew point meter.

As the method for producing the above-mentioned ferromagnetic metal powder, a known method, for example, the methods described in JP-A-7-109122 and JP-A-6-340426 can be applied. The ferromagnetic metal element of the ferromagnetic metal powder is not particularly limited, but those containing Fe, Ni or Co as the main component (75% or more) are preferable. Co is σ
It is particularly preferable because s can be increased and a dense and thin oxide film can be formed. Co content is 5 to Fe
40 atomic% is preferable, and 10 to 30 atomic% is more preferable. As described above, it is preferable that a part of Co is doped in the raw material, then a necessary amount is deposited on the surface, added to the raw material, and reduced to alloy.

The above-mentioned ferromagnetic metal powder that can be used in the present invention contains Al, Si, S, Ti, V, Cr, Cu, Y, and M in a weight ratio of 20% by weight or less in addition to predetermined metal atoms.
o, Rh, Pd, Ag, Sn, Sb, Te, Ba, S
r, W, Au, Pb, Bi, La, Ce, Pr, Nd,
It preferably contains atoms such as P, Mn, Zn, Sr, B, and Ca. In addition to controlling the shape of the starting material, these elements are effective in preventing sintering between particles, promoting reduction, and controlling the shape of the reduced ferromagnetic metal powder and the unevenness of the particle surface.

The monodisperse goethite or monodisperse hematite is finally reduced to a metal.
Annealing with ₂ O ₃ is useful for reducing the number of crystals. Fe from αFe ₂ O ₃
When reducing to ₃ O ₄ or FeO, various reducing gases can be used instead of pure hydrogen as described above. When generating metal nuclei from metal oxides, and then crystallites, it is necessary to remove the water generated by reduction to the outside of the system in a short time or control the amount of water generated by reduction. . Such water control can be performed by controlling the partial pressure of the reducing gas or by controlling the amount of reducing gas.

As is well known, the ferromagnetic metal powder is gradually oxidized to form an oxide film on the particle surface in order to be chemically stable. The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. When carbon dioxide gas is contained in the gas used during the gradual oxidation, it is adsorbed at the basic points on the surface of the ferromagnetic metal powder, and thus carbon dioxide gas may be contained.

The average major axis length of the ferromagnetic metal particles used in the present invention is 0.04 to 0.10 μm, more preferably 0.0.
5 to 0.09 μm, the acicular ratio is 3.0 to 8.0, more preferably 4.0 to 7.0, and the number of crystallites constituting the ferromagnetic metal particles (that is, the number of crystallites). Is 1.0 to
The acicular ratio of the crystallites is controlled to 2.0, preferably 1.0 to 1.5, and 2.0 to 5.0, preferably 2.5 to 4.0.

That is, in the present invention, the "ferromagnetic metal particle" means a particle which constitutes the maximum outer shape of the particle due to the size and morphology of the starting material. The largest outer shape that constitutes the particle is taken as the average major axis length and the average acicular ratio of the ferromagnetic metal particle. The crystallite means each crystal of the metal particles constituting the ferromagnetic metal particles. The particles forming the outer shape of the metal particles, that is, the ferromagnetic metal particles are not necessarily composed of one crystal, but are composed of a plurality of crystals. When a particle photograph is taken with a high-resolution transmission electron microscope, the particles that make up the largest outer shape of the particle are called ferromagnetic metal particles. It is a crystallite.

Conventionally, metal magnetic powders have been manufactured using goethite (α-FeOOH) or hematite (α-Fe ₂ O ₃ ) as a starting material. It was great. That is, the average major axis length of the ferromagnetic metal particles was about 0.2 to 0.3 μm.
At the same time as deoxidation and reduction to metal, the outer shape of the particle contracted, and conventional metal particles obtained polycrystalline faint crystals as shown in FIG. Moreover, the crystallites had different sizes and shapes. The number of crystallites is 4-1
There were 0 or more. In the present invention, the outer shape of the particles due to the size and morphology of the starting material is made small (average major axis length 0.04 to 0.10 μm), and the conventional polycrystal state is as close as possible to a single crystal as shown in FIG. State,
Aiming for a dense crystal structure. In order to define such a peculiar structure of the ferromagnetic metal powder of the present invention, the average major axis length of the ferromagnetic metal particles is 0.04 to 0.10 μm and the average acicular ratio is 3.0 to 8.0. The average number of crystallites is 1.0 to 2.
0, the average acicular ratio of the crystallites was 2.0 to 5.0. The present invention is particularly applicable to ferromagnetic metal particles having an average major axis length of 0.04 to 0.
10 μm, finer than ever before, with an average number of crystallites of 1.0
It is clearly distinguished from the conventional metal magnetic powder in that it has a crystal close to a single crystal of ˜2.0. Within such a range, the dense, needle-like ferromagnetic metal particles close to a single crystal, which is the object of the present invention, can be obtained.

When the major axis length of the ferromagnetic metal particles is smaller than 0.04 μm, not only the desired coercive force cannot be obtained, but also
It is difficult to disperse when a magnetic paint is prepared, and the effect of orientation does not easily appear even if the magnetic field is oriented. Further, it becomes difficult to secure high saturation magnetization required for high density recording due to the influence of the oxide film formed for stabilization. The major axis length of the ferromagnetic metal particles is larger than 0.10 μm and the average number of crystallites is 1.0 to
Hc when the needle ratio of the crystallite is 2.0 to 5.0
The distribution is greatly deteriorated (particularly, the component of Hc3000Oe or more is increased), which is not preferable in the overwrite characteristic, and the surface roughness of the magnetic recording medium is increased.

The acicular ratio distribution of crystallites is 80
% Or more of particles preferably have an acicular ratio of 2.0 to 5.0, and ideally 100% is in this range.
It is preferable because the distribution is narrowed. Considering analysis accuracy, it is preferable that 85 to 95% is included in the acicular ratio of 2.0 to 5.0. It was observed that when many crystallites had a large acicular ratio, there were many high coercive force components.

The coercive force Hc of the magnetic layer of the present invention is 2000.
~ 3000 Oe, preferably 2100-2800 Oe,
More preferably, it is 2200 to 2500 Oe, and Bm (maximum magnetic flux density) of the magnetic layer is 3800 to 5500 gauss (G), preferably 4000 to 5500G. H
If c and Bm are smaller than the lower limit value, a short wavelength output cannot be sufficiently obtained, and if they are larger than the upper limit value, the head used for recording is saturated and the output cannot be secured.

The saturation magnetization of the ferromagnetic metal fine powder of the present invention is usually 125 emu / g or more, preferably 130 emu / g.
g to 165 emu / g, more preferably 135 to 15
It is 0 emu / g. Immediately after reduction, JP-A-61-2232
It is also effective to perform gradual oxidation after treating with the compound or the coupling agent having various substituents described in JP-A No. 7, since the saturation magnetization of the ferromagnetic metal powder can be increased. The coercive force of the ferromagnetic metal powder is usually 1700 to 3000 Oe (Oersted), preferably 1800 to 2500 Oe, and particularly preferably 2000 to 2300 Oe. By setting the number of crystallites constituting the ferromagnetic metal particles to 1.0 to 2.0, the magnetization reversal mode becomes close to the simultaneous rotation mode, and the fine particles and the high coercive force ferromagnetic metal powder as in the present invention can be obtained. The inventor estimates that it was obtained.

In the present invention, a particle photograph was taken with a high resolution transmission electron microscope, and the number of crystallites was determined from the average major axis length of the ferromagnetic metal particles and the lattice image of the ferromagnetic metal particles. About 20
Such measurement was carried out for 0 particles and the average was obtained. The acicular ratio of the crystallite was calculated by (length / width) by tracing the outline of each crystallite of the photographed high-resolution electron microscope with an image analyzer to obtain the average length and width.

Further, the ferromagnetic metal powder may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before the dispersion. Specifically, JP-B-44-14090, JP-B-45-18372, JP-B-47-22062, and JP-B-47-22
513, JP-B-46-28466, JP-B-46-38755, JP-B-47-4286, JP-B-47-12422, and JP-B-47-17.
No. 284, Japanese Patent Publication No. 47-18509, Japanese Patent Publication No. 47-18573, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 48-39639, and US Patent No. 3026.
No. 215, No. 3031341, No. 3100194,
No. 3242005 and No. 3389014.

The water content of the ferromagnetic metal powder is preferably 0.01 to 2% by weight. It is desirable to optimize the water content depending on the type of binder described below.

The tap density of the ferromagnetic metal powder is 0.2 to
0.8 g / cc is desirable. If it is greater than 0.8 g / cc, the powder is not gradually oxidized uniformly when gradually oxidized, and thus it is difficult to safely handle the powder, or the magnetization of the obtained tape decreases with time. When the tap density is 0.2 g / cc or less, the dispersion tends to be insufficient.

The binder resin of the magnetic layer in the magnetic recording medium of the present invention may be a conventionally known thermoplastic resin, thermosetting resin, reactive resin or a mixture thereof. As a thermoplastic resin, the glass transition temperature is -1.
00 to 150 ° C, number average molecular weight of 1000 to 20000
0, preferably 10,000 to 100,000, and the degree of polymerization is about 50 to 1,000.

Examples of such binder resins include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester,
Styrene, butadiene, ethylene, vinyl butyral,
There are polymers or copolymers containing vinyl acetal, vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins.

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

In order to obtain more excellent dispersion effect of the ferromagnetic powder and durability of the magnetic layer in the above binder resin, COOM, SO ₃ M, OSO ₃ M, P = O (OM) is added as necessary.
₂ , OP = O (OM) ₂ , (wherein M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R
It is preferable to use one in which at least one polar group selected from ₃ (R is a hydrocarbon group), an epoxy group, SH, CN, etc. is introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

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

The filling degree of the ferromagnetic metal powder in the magnetic layer can be calculated from the maximum saturation magnetization σs and Bm of the used ferromagnetic metal powder (Bm / 4πσs), which is desirable in the present invention. Is 1.7 g / cc or more, more preferably 1.9 g / cc or more, and most preferably 2.1 g / cc or more.

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

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

In the magnetic layer of the magnetic recording medium of the present invention, various functions such as a lubricant, an abrasive, a dispersant, an antistatic agent, a dispersant, a plasticizer and an antifungal agent are usually included. The material to have is contained according to the purpose.

The lubricant used in the magnetic layer of the present invention is a dialkyl polysiloxane (where alkyl is 1 to 1 carbon atoms).
5), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms, alkoxy has 1 to 4 carbon atoms), phenyl polysiloxane, fluoro Silicon oil such as alkyl polysiloxane (where alkyl is 1 to 5 carbon atoms); Conductive fine powder such as graphite; Inorganic powder such as molybdenum disulfide and tungsten disulfide; Polyethylene, polypropylene, polyethylene vinyl chloride copolymer, poly Plastic fine powder of tetrafluoroethylene or the like; α-olefin polymer; saturated fatty acid that is solid at room temperature (carbon number 10 to 22); unsaturated aliphatic hydrocarbon that is liquid at room temperature (carbon with n-olefin double bond at the end) Compound having about 20 carbon atoms; a monobasic fatty acid having 12 to 20 carbon atoms Fatty acid esters consisting of 3 to 12 monovalent alcohol prime, fluorocarbons and the like can be used.

Among the above, saturated fatty acids and fatty acid esters are preferable, and it is more preferable to use both in combination. Alcohols used as raw materials for fatty acid esters include ethanol, butanol, phenol, benzyl alcohol, and 2
-Methylbutyl 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, as fatty acids, acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachidic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, palmitoleic acid. And aliphatic carboxylic acids or mixtures 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, 2-hexyl decyl. Stearate, butyl palmitate, 2-ethylhexyl myristate,
Mixture of butyl stearate and butyl palmitate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, ester of dipropylene glycol monobutyl ether with stearic acid, diethylene glycol dipalmitate, hexamethylene diol myristic acid Examples thereof include various ester compounds such as those which are esterified to form diesters and glycerin oleate.

Further, in order to reduce the hydrolysis of fatty acid ester that often occurs when the magnetic recording medium is used under high humidity, branched / straight chain, cis / trans and other isomer structures of branched fatty acids and alcohols as raw materials, and branched positions are used. Is made. These lubricants are added in the range of 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder.

The following compounds may be used as the lubricant. That is, silicone oil, graphite, molybdenum disulfide, boron nitride, fluorinated graphite, fluoroalcohol, polyolefin, polyglycol, alkyl phosphate, tungsten disulfide and the like.

The abrasives used in the magnetic layer of the present invention are generally used materials such as α, γ alumina, fused alumina, corundum, artificial corundum, silicon carbide, chromium oxide (Cr ₂ O ₃ ), diamond and artificial. Diamond, garnet, emery (main components: corundum and magnetite), αFe ₂ O _3, etc. are used. These abrasives have a Mohs hardness of 6 or more. Specific examples include AKP-10, AKP-12, AKP-15, manufactured by Sumitomo Chemical Co., Ltd.
20AKP-30, AKP-50, AKP-1520,
AKP-1500, HIT-50, HIT60A, HI
T70, HIT80, HIT-100, Nippon Kagaku Kogyo KK, G5, G7, S-1, chromium oxide K, Uemura Kogyo UB40B, Fujimi Abrasives WA8000, WA10
000, Toda Kogyo TF100, TF140, TF1
80 etc. can be raised. Average particle size is 0.05-3 μm
Is effective, and is preferably 0.05-
It is 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 it is less than 1 part by weight, sufficient durability cannot be obtained, and if it is more than 20 parts by weight, the surface property and filling degree are deteriorated. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.

The magnetic layer of the magnetic recording medium of the present invention may contain conductive particles as an antistatic agent in addition to the non-magnetic powder. However, in order to maximize the saturation magnetic flux density of the uppermost layer, it is preferable to add as little as possible to the uppermost layer and to add it to a coating layer other than the uppermost layer. As the antistatic agent, it is particularly preferable to add carbon black in order to reduce the surface electric resistance of the entire medium. The carbon black that can be used in the present invention may be a furnace for rubber, thermal for rubber, black for color, conductive carbon black, acetylene black and the like. Specific surface area 5 to 500 m ² / g, DBP oil absorption 10 to 1500 ml / 100 g, particle size 5 mμ
~ 300 mμ, PH 2-10, water content 0.1-10
%, And the tap density is preferably 0.1 to 1 g / cc. Specific examples of carbon black used in the present invention include BLACKPEARLS 200 manufactured by Cabot Corporation.
0, 1300, 1000, 900, 800, 700, V
ULCAN XC-72, Asahi Carbon Co., Ltd., # 80, #
60, # 55, # 50, # 35, manufactured by Mitsubishi Kasei Kogyo, #
3950B, # 3250B, # 2700, # 2650,
# 2600, # 2400B, # 2300, # 900, #
1000, # 95, # 30, # 40, # 10B, MA2
30, MA220, MA77, manufactured by Columbia Carbon Co., CONDUCTEX SC, RAVEN 150,
50, 40, 15, Ketjen Black EC, Ketjen Black ECDJ-500, and Ketjen Black ECDJ-600 manufactured by Lion Aguzo. The carbon black may be surface-treated with a dispersant or the like, the carbon black may be oxidized, a resin may be grafted, or a part of the surface may be graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. When carbon black is used in the magnetic layer, the amount based on the magnetic material is preferably 0.1 to 30% by weight. Further, when a non-magnetic layer is provided, it is preferably contained in the inorganic non-magnetic powder in an amount of 3 to 20% by weight.

Generally, carbon black functions not only as an antistatic agent, but also for reducing the coefficient of friction, imparting light-shielding properties, improving film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention may be used in different types, amounts, and combinations depending on the purpose based on the various characteristics shown above such as particle size, oil absorption, electric conductivity, and pH. Of course it is possible. The carbon black that can be used can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

In the case of forming a non-magnetic layer between the magnetic layer and the non-magnetic support of the magnetic recording medium of the present invention,
The lower layer) is a layer in which an inorganic non-magnetic powder is mainly dispersed in a binder resin. Various types of inorganic non-magnetic powder can be used for the non-magnetic layer. For example, α-alumina, β-alumina having an α conversion rate of 90% or more,
γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate alone Or used in combination. The particle size of these inorganic non-magnetic powders is preferably 0.01 to 2μ, but if necessary, inorganic non-magnetic powders having different particle sizes may be combined, or a single inorganic non-magnetic powder may be used to broaden the particle size distribution. It can also be effective. The inorganic non-magnetic powder used may be surface-treated in order to increase the interaction with the binder resin used and improve the dispersibility. The surface-treated product may be treated with an inorganic substance such as silica, alumina or silica-alumina, or may be treated with a coupling agent. Tap density is 0.3-2g / c
c, water content is 0.1 to 5% by weight, pH is 2 to 11, and specific surface area is preferably 5 to 100 m ² / g. The inorganic non-magnetic powder may be needle-shaped, spherical, dice-shaped, or plate-shaped. Specific examples of the inorganic non-magnetic powder used in the present invention include AKP-20 and AKP manufactured by Sumitomo Chemical Co., Ltd.
-30, AKP-50, HIT-50, Nippon Kagaku Kogyo KK, G5, G7, S-1, Toda Kogyo TF-10.
0, TF-120, TF-140, TT0 made by Ishihara Sangyo Co., Ltd.
55 series, ET300W, TTT3 manufactured by Titanium Industry Co., Ltd.
0, needle-like hematite particles and the like, which are intermediate raw materials for magnetic iron oxide and ferromagnetic metal powder prepared by the iron oxide reduction method.

The layer structure of the magnetic recording medium of the present invention is basically not limited as long as it has at least the above magnetic layer or further the above nonmagnetic layer on the nonmagnetic support.
A magnetic layer or a non-magnetic layer having another structure can be provided. For example, when a ferromagnetic layer is formed instead of the non-magnetic layer, the ferromagnetic material may be iron oxide ferromagnetic material, cobalt modified iron oxide ferromagnetic material, CrO ₂ , hexagonal ferrite, various metal ferromagnetic materials. Various materials having a body dispersed in a resin can be used. These ferromagnetic layers are also called lower layers.

Forming two or more coating layers on a non-magnetic support is also effective in producing a magnetic recording medium having a high recording density, and the simultaneous coating method produces an ultrathin magnetic layer. It is especially excellent because it can be done. As a specific method of the wet-on-wet method as the simultaneous application method,

(1) First, the lower layer is coated by a gravure coating, roll coating, blade coating, and extrusion coating device which are generally used for magnetic paints, and while the layer is still in a wet state, for example, Japanese Patent Publication No. 1 -46186, JP-A-60-238179 and JP-A-2-2
Japanese Patent Publication No. 65672 discloses a method for coating an upper layer by a non-magnetic support pressure type extrusion coating apparatus,

(2) By a coating head having two slits for passing a coating liquid 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 of coating the upper layer and the lower layer almost at the same time by using the extrusion coating apparatus with a backup roll disclosed in Japanese Patent Laid-Open No. 2-174965.

When applying by the wet-on-wet method, the flow characteristics of the coating liquid for the magnetic layer and the coating liquid 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. It is possible to obtain a magnetic layer having a uniform thickness and less variation in thickness. Since the flow characteristics of the coating liquid strongly depend on the combination of the powder particles and the binder resin in the coating liquid,
In particular, it is necessary to pay attention to the selection of the non-magnetic powder used for the non-magnetic layer.

The non-magnetic support of the present magnetic recording medium is usually
1 to 100 μm, preferably 3 to 20 μm, and the thickness of the nonmagnetic layer is 0.5 to 10 μm, preferably 1 to 4 μm. When a magnetic layer is provided on the non-magnetic layer, the thickness of the magnetic layer is usually 0.05 to 3.0 μm, preferably 0.0
5 to 2.0 μm, and when the magnetic layer is provided alone without providing the non-magnetic layer, the thickness of the magnetic layer is usually 0.05 to
The thickness is 5.0 μm, preferably 1.5 to 2.5 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 non-magnetic support and the lower layer. This thickness is 0.01 to 2 μm, preferably 0.1.
05-0.5 μm. Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm
m. Known undercoat layers and back coat layers can be used. In the case of a disk-shaped magnetic recording medium, the above layer constitution can be provided on one side or both sides.

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

In order to effectively achieve the object of the present invention, the surface roughness of the non-magnetic support is 0.03 μm or less, preferably 0.02 μm, in terms of center line average surface roughness Ra (cutoff value 0.25 mm). Hereafter, it is more preferably 0.01 μm or less. Further, it is preferable that these non-magnetic supports not only have a small center line average surface roughness but also that they have no coarse protrusions of 1 μm or more. The shape of the surface roughness can be freely controlled by the size and amount of the filler added to the non-magnetic support, if necessary. Examples of these fillers include oxides and carbonates of Ca, Si, Ti and the like, and fine organic resin powders of acrylic and the like. The F-5 value in the web running direction of the non-magnetic support used in the present invention is preferably 5 to 50 Kg / mm ² ,
The F-5 value in the web width direction is preferably 3 to 30 Kg / m.
m ² and the F-5 value in the longitudinal direction of the web is generally higher than the F-5 value in the web width direction, but this is not the case especially when the strength in the width direction needs to be increased.

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. It is preferably 1% or less, more preferably 0.
It is 5% or less. Breaking strength is 5-100 kg in both directions
/ Mm ² , and the elastic modulus is preferably 100 to 2000 Kg / mm ² .

The organic solvent used in the present invention is 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. , Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, and other glycol ethers, benzene, etc. Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chlorine Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components. The content of these impurities is preferably 30% or less, more preferably 10% or less. If necessary, the type and amount of the organic solvent used in the present invention may be changed between the magnetic layer and the non-magnetic layer. A solvent with a high solubility parameter for the magnetic layer that uses a solvent with high volatility for the non-magnetic layer to improve the surface properties, uses a solvent with high surface tension (cyclohexanone, dioxane, etc.) for the non-magnetic layer, and improves coating stability Examples of such methods include increasing the filling degree by using, but it goes without saying that the present invention is not limited to these examples.

The magnetic recording medium of the present invention is kneaded and dispersed in an organic solvent together with the above-mentioned ferromagnetic metal powder, a binder resin, and other additives if necessary, and a magnetic coating material is applied onto a non-magnetic support. It is obtained by orienting and drying if necessary.

The process for producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes, if necessary. Each process may be divided into two or more stages. Ferromagnetic metal powder, binder, carbon black, abrasive, antistatic agent, lubricant used in the present invention,
All raw materials such as solvents may be added at the beginning or in the middle of any step. In addition, individual raw materials may be divided and added in two or more steps. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion.

Various kneading machines are used for kneading and dispersing the magnetic paint. For example, two-roll mill, three-roll mill, ball mill, pebble mill, tron mill, sand grinder, Szegvari, attritor, high speed impeller disperser, high speed stone mill, high speed impact mill, disper, kneader, high speed mixer, homogenizer, ultra A sonic disperser or the like can be used.

In order to achieve the object of the present invention, it is needless to say that the conventional known manufacturing techniques can be used as a part of the steps, but in the kneading step, strong kneading such as continuous kneader or pressure kneader is used. It is preferable to use one that has strength. When a continuous kneader or a pressure kneader is used, all or part of the ferromagnetic metal powder and the binder (however, 30% or more of the total binder is preferable) and 15 to 500 parts by weight based on 100 parts by weight of the ferromagnetic metal powder. The kneading is performed within the range. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-64-79274.
It is described in Japanese Patent Publication No. In the present invention, JP-A-62-2
By using the simultaneous multi-layer coating method as shown in 12933, it is possible to produce 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 preferably less than the residual solvent contained.

The porosity of the magnetic layer in both the lower layer and the upper layer is preferably 30% by volume or less, more preferably 10% by volume.
It is the following. The porosity of the nonmagnetic layer is preferably larger than that of the magnetic layer, but may be small as long as the porosity of the nonmagnetic layer is 5% by volume or more.

The magnetic recording medium of the present invention can have a lower layer and an upper layer, but it is easily presumed that the physical properties of the lower layer and the upper layer can be changed 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.

By such a method, the magnetic layer coated on the support is optionally subjected to a treatment for orienting the ferromagnetic metal powder in the layer, and then the formed magnetic layer is dried. If necessary, the surface is smoothed or cut into a desired shape to manufacture the magnetic recording medium of the present invention. The above 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 non-magnetic support and oriented and dried to obtain a magnetic recording medium.

The elastic modulus of the magnetic layer at 0.5% elongation is preferably 100 to 2000 kg in both the web coating direction and the width direction.
/ Mm ² , 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 application direction and the width direction, the residual spread is preferably 0.5% or less, and the heat shrinkage rate 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, audio use or the like, or a floppy disk or magnetic disk for data recording.
It is particularly effective for a medium for digital recording in which the loss of a signal due to the occurrence of drop-out is fatal.
Further, by making the lower layer a non-magnetic layer and setting the thickness of the uppermost layer to 1 μm or less, it is possible to obtain a high-density and large-capacity magnetic recording medium having high electromagnetic conversion characteristics and excellent overwrite characteristics.

[0077]

【Example】

The novel features of the present invention will be specifically described in the following examples, but the present invention is not limited thereto.

Production Example 1 Production Examples 1-1 to 5 (Production of Ferromagnetic Metal Powder) In a 150 l tank equipped with a stirrer, 35 mol of 1.7 mol / l sodium carbonate and 2.0 mol / l were added.
To a mixed solution of 15 liters of sodium hydroxide, 0.4 liter of an aqueous solution of 0.5 mol / l of sodium phosphate was added, and while bubbling nitrogen, bubbling nitrogen in another tank dissolved ferrous sulfate and cobalt sulfate. 40 l of an aqueous solution (Fe ²⁺ concentration: 1.35 mol / l, Co concentration: 0.15 mol / l) was added and mixed. After stirring for 10 minutes, the temperature of the suspension was adjusted to 25 ° C., and a precipitate containing ferrous iron was produced.
Air was introduced instead of nitrogen to oxidize the precipitate to generate goethite nuclei. When the Fe ²⁺ concentration in the suspension reached 0.75 mol / l, the air oxidation was discontinued and replaced with nitrogen, the suspension temperature was heated to 40 ° C. and maintained for 2 hours, then sodium aluminate was added. 1 liter of 1.1 mol / l aqueous solution was added. After that, nitrogen was changed to air and the oxidation reaction proceeded to produce spindle-shaped goethite. The obtained particles were filtered and washed with water. A part of it was dried and a transmission electron micrograph was taken to determine the average particle size. The average major axis length was 0.12μ.
m, and the average acicular ratio was 8. The specific surface area was 115 m ² / g after dehydration by heating at 120 ° C. for 30 minutes in nitrogen.

The obtained goethite was made into a 2% slurry in water and stirred so that each addition amount of Co and / or Mg shown in Table 1 (showing atomic% relative to 100 atomic% of iron) and / or aqueous solution of cobalt sulfate and / or Alternatively, an aqueous magnesium chloride solution was added and neutralized with an aqueous sodium hydroxide solution to deposit a cobalt compound and / or a magnesium compound on the particle surface. The slurry was filtered and made into a 2% water slurry again, and an aluminum sulfate aqueous solution was added (Table 1
Shows the atomic% of Al to 100 atomic% of iron). After adding aluminum sulfate and stirring for 20 minutes, a sodium hydroxide aqueous solution was added to neutralize the slurry. After washing with filtered water, a 2% slurry was prepared, an yttrium nitrate aqueous solution was added (atomic% of Y to iron is shown in Table 1), and the pH was adjusted to 8.5 with an aqueous sodium hydroxide solution. It was filtered, washed with water to form a 5% water slurry, and heated at 130 ° C. for 1 hour. After that, the cake obtained by filtering and washing with water was passed through a molding machine and then dried to obtain a spindle-shaped goethite that was subjected to a sintering prevention treatment.

The spindle-type goethite thus obtained was placed in a static reduction furnace, heated in nitrogen at 350 ° C. for 20 minutes for dehydration treatment, and then heated at 600 ° C. for 2 hours to enhance the crystallinity of hematite. The temperature is 450 ° C. and the gas is nitrogen to hydrogen: C
The gas was changed to O = 30: 70 and reduced for 1 hour. After substituting with nitrogen, it was changed to pure hydrogen and reduced for 5 hours. After switching to nitrogen and cooling to room temperature, change the mixing ratio of air and nitrogen to change the oxygen concentration to 0.5% and gradually oxidize at 50 ° C or lower while monitoring the temperature of the metal powder, and when the heat generation subsides, the oxygen concentration is set to 1%. It was gradually oxidized for 10 hours. Then, the distilled water was vaporized so that the water content was 1% of the metal powder, and the distilled water was transported with air to regulate the humidity and stabilize.

The magnetic characteristics of the obtained ferromagnetic metal powder were measured with a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) in an external magnetic field of 10 KOe. A high-resolution transmission electron micrograph of the obtained ferromagnetic metal powder was taken to determine the average major axis length (μm) and average acicular ratio of the ferromagnetic metal particles, and the average number of crystallites and the average acicular ratio.
In addition, dehydration was carried out in nitrogen at 250 ° C. for 30 minutes, and the specific surface area (S _BET ) was measured with Cantersob (manufactured by Canterchrome Co.) and shown in Table 1. [Manufacturing Example 2] Manufacturing Examples 2-1 to 2 A spindle-type goethite that was subjected to a sintering prevention treatment through the same steps as in Manufacturing Example 1 using the elements described in Table 1 was placed in a stationary reduction furnace. Then, the mixture was heated in nitrogen at 350 ° C. for 60 minutes to perform dehydration treatment, the temperature was adjusted to 450 ° C., and the gas was changed from nitrogen to pure hydrogen for reduction for 6 hours. After this, the same treatment as in Production Example 1 was performed. The obtained ferromagnetic metal powder was evaluated in the same manner as in Production Example 1, and the results are shown in Table 1.

[0083]

[Table 1]

[Manufacturing Example 3] Manufacturing Examples 3-1 to 2 When the Fe ²⁺ concentration in the suspension was 0.75 mol / l after the nucleation was generated at 25 ° C. in Manufacturing Example 1. The air oxidation was discontinued and replaced with nitrogen, sodium aluminate was added, and the temperature of the suspension was heated to 50 ° C. to perform air oxidation to produce goethite. The average major axis length of Goethite is 0.20μ
m, the average acicular ratio was 14, and the specific surface area was 130 m ² / g. Thereafter, using the elements shown in Table 2, the additional elements were used in the same manner as in Production Example 1, then treated with a sintering inhibitor, washed with filtered water, passed through a molding machine and dried. After that, reduction and gradual oxidation were performed in the same manner as in Production Example 1. The obtained ferromagnetic metal powder was evaluated in the same manner as in Production Example 1 and shown in Table 2.

[0085]

[Table 2]

Example 1 Production of Magnetic Recording Medium (Examples 1-1 to 5 and Comparative Example 1-1)
~ 4) Production Examples 1-1 to 5, Production Examples 2-1 to 2 and Production Example 3
The following magnetic layer composition and non-magnetic layer composition were prepared in order to prepare a multi-layered magnetic tape using the ferromagnetic metal powders obtained in Nos. 1-2. In the following prescription,
All indications of "part" indicate "part by weight". (Set of product of the magnetic layer) ferromagnetic metal powder (Table 3 described) 100 parts binder resin of vinyl chloride copolymer 12 parts (-SO ₃ Na groups and containing 1 × 10 ^-4 eq / g polymerization degree: 300 Polyester polyurethane 5 parts of the resin (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 (molar ratio), - SO ₃ Na group containing 1 × 10 ^-4 eq / g) alpha-alumina (average particle diameter 0 .13 μm) 5.0 parts carbon black (average particle size 40 nm) 1.0 part Butyl stearate 1 part Stearic acid 2 parts Mixed solvent of methyl ethyl ketone and cyclohexanone 1: 1 200 parts (composition of non-magnetic layer) Needle-like hematite 80 parts (specific surface area by the BET method: 55m ² / g average major axis length 0.12 .mu.m, acicular ratio 8 pH 7.5 aluminized Al / Fe 6.5at%) Carb Black 20 parts (average primary particle diameter 17 nm, DBP及油amount 80 ml / 100 g surface area by BET method 240m ² / g pH7.5) binder resin of vinyl chloride copolymer 12 parts (-SO ₃ Na group of 1 × 10 ^{- 4} eq / g content Degree of polymerization 300) Polyester polyurethane resin 7 parts (basic skeleton: 1,4-BD / phthalic acid / HMDI = 2/2/1 (molar ratio) Molecular weight: 10200 Hydroxyl group: 0.23 × 10 ⁻³ eq / g containing -SO ₃ Na group: 1 × 10 ^-4 eq / g containing) butyl stearate 1 part stearic acid 2.5 parts Methyl ethyl ketone and cyclohexanone 1: 1 magnetic layer composition of the mixed solvent 200 parts the above and non Each of the magnetic layer compositions was kneaded with a kneader and then dispersed using a sand grinder. 5 parts of the coating solution for sexual layer, is added 6 parts of the magnetic layer coating liquid, more ethyl ketone and cyclohexanone 1:
20 parts of 1 mixed solvent was added, and filtration was performed using a filter having an average pore size of 1 μm to prepare coating solutions for the non-magnetic layer and the magnetic layer.

The obtained coating liquid for the non-magnetic layer was coated so that the thickness after drying was 1.8 μm, and immediately thereafter, while the coating layer for the non-magnetic layer was still in a wet state, Then, wet simultaneous multilayer coating was performed on a polyethylene terephthalate support having a thickness of 7 μm so that the magnetic layer had a thickness of 0.15 μm, and while both layers were still in a wet state, they were passed through an aligning device for longitudinal alignment. At this time, the orienting magnet is passed through a rare earth magnet (surface magnetic flux: 5000 gauss) and then through a solenoid magnet (magnetic flux density: 5000 gauss), and dried until the orientation does not return in the solenoid, and further the magnetic layer is dried. I wound up. After that, calendering was performed with a 7-stage calender made of metal rolls at a roll temperature of 90 ° C. to obtain a web-shaped magnetic recording medium, which was slit into a width of 8 mm to prepare an 8 mm video tape sample. Table 3 shows the magnetic characteristics of the obtained sample measured by a vibrating sample magnetometer, the high Hc component, the surface roughness, the output of 1/2 Tb measured using a drum tester, the C / N, and the overwrite characteristics. Fuji DC film Super DC tape was used as the standard for electromagnetic conversion characteristics.

The overwrite characteristic was measured by the following method. Using a drum tester, the relative speed of the TSS head (head gap 0.2 μm, track width 14 μm, saturation magnetic flux density 1.1 Tesla) was 10.2 m / sec,
The optimum recording current is determined from the input / output characteristics of 1/2 Tb (λ = 0.5 μm), and this current is 1/90 Tb (λ = 22.5 μm).
The overwrite characteristic was measured from the erasing rate of 1/90 Tb when the signal of m) was recorded and overwriting was performed at 1/2 Tb.

The magnetic characteristics were measured in parallel with the orientation direction using an oscillating sample magnetometer (manufactured by Toei Industry Co., Ltd.) with an external magnetic field of 5 kOe. In addition, SQ shows a squareness ratio. The high Hc component was measured by the following method. Set the orientation of the measurement sample of the magnetic recording medium in the same direction as the magnetic field in a vibrating sample magnetometer manufactured by Toei Industry Co., Ltd., apply -10 kOe and DC saturate, then return the magnetic field to zero and remanent magnetization ( -Mrmax) is measured. After applying a magnetic field of 3000 Oe in the opposite direction, returning the magnetic field to zero and measuring the residual magnetization Mr, applying 10 kOe and performing DC saturation in the opposite direction, and setting the magnetic field to zero, the residual magnetization Mrmax
To measure. It was calculated by the following formula from the obtained residual magnetization.

High Hc component (%) = 100 × (Mrmax−Mr) /
(Mrmax-(-Mrmax)) The magnitude of the magnetic field applied in the opposite direction can be set arbitrarily,
From the viewpoint of detection sensitivity, 3000 Oe is adopted in the present application. The high Hc component represents a component that causes magnetization reversal at a set applied magnetic field or more. The surface roughness was measured by using a light interference three-dimensional roughness meter "TOPO-3D" manufactured by WYKO (US Arizona) to measure a sample area of 250 μm square. In calculating the measurement value, corrections such as inclination correction, spherical correction, and cylindrical correction were performed according to JIS-B601, and the center surface average roughness RaI was used as the surface roughness value.

[0091]

[Table 3]

[Production Example 4] [Preparation of nuclear crystals] 2M FeC was placed in a sealable 2 liter glass container.
l ₃ was added 5.94N NaOH aqueous 500ml aqueous solution 500ml with stirring for 5 minutes, stirring after completion of the addition a further 20 minutes, it was sealed container completely. It was put in an oven preheated to 100 ° C. and kept for 48 hours. After 48 hours, the mixture was rapidly cooled with running water, the reaction solution was separated and centrifuged at 15000 rpm for 15 minutes in a centrifugal separator, and the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. Thus, the washing with water was repeated three times using the centrifuge. The precipitate of hematite particles (average particle size of about 0.1 μm) that had been washed with water was dried. Distilled water (5 ml) was added to 50 g of the dry powder, and the mixture was crushed for 10 minutes by a raikai machine. It was washed in a beaker using 500 ml of distilled water, divided into 100 ml, and put in 200 ml mayonnaise bottle containing steel beads and dispersed for 10 hours. The dispersion was collected and the mayonnaise bottle was washed with distilled water to collect the dispersion. Distilled water was added to bring the total volume to 1200 ml, and the mixture was ultrasonically dispersed for another 30 minutes.

This dispersion was collected and centrifuged at 10,000 rpm for 30 minutes to take out a supernatant liquid in which ultrafine particle hematite (average particle size: 70Å) was dispersed to obtain a nuclear crystal liquid. The iron concentration in the nucleating solution was 2000 ppm. [Crystallite size control of monodisperse spindle hematite] 180 ml of 1 mol / l ferric nitrate was placed in a reaction vessel equipped with a stirrer,
Cool and bring the temperature of the solution to 5 ° C. With stirring, 180 ml of 2.4 mol / l sodium hydroxide solution are added over 5 minutes. After the addition, stirring was further continued for 5 minutes, 180 ml of the nuclear crystal solution was added, and the mixture was stirred for 10 minutes. The obtained liquid is 6
Collect 0 ml each, and use 0.048 M / l Na as morphological control ions.
After adding 10 ml of H ₂ PO _{4 and} 10 ml of H ₂ O, the mixture was kept in an oven preheated to 100 ° C. for 48 hours. Quench with running water and centrifuge reaction solution at 18000 rpm
After centrifugation for 15 minutes, the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. Thus, the washing with water was repeated three times using the centrifuge. Next, 1 M aqueous ammonia was added and redispersed, and the mixture was centrifuged and the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. Thus, the washing with water was repeated three times using the centrifuge. When a part of the product was taken out and the dried particles were observed with a transmission electron microscope, the average major axis length was 0.07 μm, the acicular ratio (major axis / minor axis) was 4.5, and the major axis length variation (minor axis length ΑFe ₂ O ₃ with an excellent particle size distribution was obtained with a standard deviation / average major axis length of 6%.

The obtained monodisperse spindle hematite was dispersed in distilled water so that the concentration of hematite was 2%, cobalt sulfate was made to be 100 atomic% of Fe in Co, and Co
Was added so as to be 5 atom%, and they were mixed with sufficient stirring. The pH of this suspension was adjusted to 8.0 while monitoring the pH while stirring the suspension to adjust the pH to 8.0, and a Co compound was deposited on the surface of the hematite. Further, sodium aluminate was added to this suspension while stirring so that Fe in hematite was 100 atom% and Al was 8 atom%, and diluted sulfuric acid was added to adjust pH to 6.5. Neodymium nitrate solution was added to this suspension while stirring so that Fe in hematite was 100 atomic% and Nd was 5 atomic%, and sodium hydroxide solution was added to adjust the pH to 7.
It was set to 8. The suspension was filtered and washed with distilled water to remove impurities. The obtained surface-treated spindle-type hematite was passed through a molding plate having a diameter of 3 mm, molded into a cylindrical shape, and dried.

Of surface-treated monodisperse spindle type hematite
500 g was placed in a static reduction furnace and annealed in nitrogen at 500 ° C. for 1 hour. Next, the temperature was set to 425 ° C., the gas was changed from nitrogen to a gas of hydrogen: CO = 30: 70, and reduction was carried out for 1 hour. After substituting with nitrogen, it was changed to pure hydrogen and reduced for 5 hours. After switching to nitrogen and cooling to room temperature, change the mixing ratio of air and nitrogen to 0.5% oxygen concentration and gradually oxidize so as not to exceed 50 ° C while monitoring the temperature of the metal powder,
When the exotherm subsided, the oxygen concentration was adjusted to 1% and the mixture was gradually oxidized for 10 hours. Then, the distilled water was vaporized so that the water content was 1% of the metal powder, and the distilled water was transported with air to regulate the humidity and stabilize. [Production Example 5] The hematite obtained in Production Example 4 was dispersed in distilled water so that the hematite concentration was 2%, and Fe in the hematite was adjusted to 100 atom% and Al was stirred to be 8 atom%. Sodium aluminate was added to the suspension, and diluted sulfuric acid was added to adjust the pH to 6.5. Neodymium nitrate solution was added to this suspension while stirring so that Fe in hematite was 100 atomic% and Nd was 5 atomic%, and sodium hydroxide solution was added to adjust pH to 7.8.
And The suspension was filtered and washed with distilled water to remove impurities. The obtained surface-treated spindle-type hematite was passed through a molding plate having a diameter of 3 mm, molded into a cylindrical shape, and dried.

By firing under the same conditions as in Production Example 4, a ferromagnetic metal powder was obtained. The magnetic characteristics of the ferromagnetic metal powders of Production Examples 4 and 5 were measured with a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) in an external magnetic field of 10 KOe. A high-resolution transmission electron micrograph of the obtained ferromagnetic metal powder is taken, and the average major axis length (μm) of the ferromagnetic metal particles is taken.
The average number of crystallites and the average acicular ratio were calculated. In addition, dehydration was carried out in nitrogen at 250 ° C. for 30 minutes, and the specific surface area was measured with Cantersob (manufactured by Canterchrome).
It was shown to.

[0097]

[Table 4]

Example 2 Using the ferromagnetic metal powders obtained in Production Examples 4 and 5, tape was formed under the following conditions, and the magnetic characteristics and electromagnetic conversion characteristics were measured. (Upper layer composition) the ferromagnetic metal powder (Table 5) 100 parts of the binder resin of vinyl chloride copolymer 14 parts (-SO ₃ Na groups and containing 1 × 10 ^-4 eq / g polymerization degree: 300) Polyester polyurethane resin 4 part (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 (molar ratio) -SO ₃ Na group containing 1 × 10 ^-4 eq / g) alpha-alumina (average particle size 0.1 [mu] m) 3.5 parts carbon black (average particle size 100 nm) 0.5 part butyl stearate 1 part stearic acid 2 parts mixed solvent of methyl ethyl ketone and cyclohexanone 1: 1 200 parts (composition for non-magnetic layer) spherical titanium oxide 80 parts (average particles) systems 0.025 .mu.m, the surface area 60m ² /g,pH6.5 by alumina-treated BET method) carbon black 20 parts (average primary particle 16 nm, DBP及油amount 80 ml / 100 g BET method surface area of 250 meters ² / g pH 8.0 by) the binder resin a vinyl chloride - vinyl acetate - vinyl alcohol copolymer 10 parts ^{_{(-N + (CH 3) 3}} Cl - polarity Group containing 5 × 10 −6 eq / g Monomer composition ratio 86: 13: 1 Degree of polymerization 400) Polyester polyurethane resin 8 parts (basic skeleton: 1,4-BD / phthalic acid / HMDI = 2/2/1 (molar ratio) ) Molecular weight: 10200 Hydroxyl group: 0.23 × 10 ⁻³ eq / g content —SO ₃ Na group: 1 × 10 ⁻⁴ eq / g content) Butyl stearate 1 part Stearic acid 2.5 parts Methyl ethyl ketone and cyclohexanone 1: 1 Mixed solvent 200 parts The above-mentioned non-magnetic layer composition and magnetic layer composition were kneaded with a kneader, and then dispersed using a sand grinder. . To the obtained dispersion, 5 parts of polyisocyanate was added to the coating liquid for the non-magnetic layer, 6 parts to the coating liquid for the magnetic layer, and methyl ethyl ketone and cyclohexanone 1:
20 parts of 1 mixed solvent was added and the mixture was filtered using a filter having an average pore size of 1 μm to prepare coating solutions for forming a non-magnetic layer and for forming a magnetic layer.

The obtained coating liquid for the non-magnetic layer was coated so that the thickness after drying was 2 μm, and immediately thereafter, while the non-magnetic coating layer was still in a wet state, the magnetic layer was formed thereon. When a simultaneous simultaneous multi-layer coating is performed on a polyethylene terephthalate support having a thickness of 7 μm so that the thickness is 0.15 μm and both layers are still in a wet state, a rare earth magnet (surface magnetic flux of 5000 gauss is applied). ) And a solenoid electromagnet (surface magnetic flux of 5000 gauss), magnetic field orientation of the ferromagnetic metal powder was performed and dried. Then, a seven-stage calender composed of metal rolls was calendered at a roll temperature of 90 ° C. to obtain a web-shaped magnetic recording medium, which was slit into a width of 8 mm to prepare a sample of 8 mm video tape. The obtained sample was evaluated in the same manner as in Example 1 and shown in Table 5. Fuji DC film Super DC tape was used as the standard for electromagnetic conversion characteristics.

[0100]

[Table 5]

Example 3 A magnetic recording medium having a single magnetic layer was manufactured as follows. A magnetic recording medium prepared in the same manner as in Example 1 except that the ferromagnetic metal powder of Production Example 1-2 was used to coat the nonmagnetic support in a thickness of 1.5 μm in the magnetic layer composition of Example 1. Example 3-1, produced in the same manner as in Example 2 except that the magnetic layer composition of Example 2 was coated with the ferromagnetic metal powder of Production Example 4 on a non-magnetic support to a thickness of 1.5 μm. Table 3 shows the results of evaluation made in the same manner as in Example 1 with the magnetic recording medium as Example 3-2.

[0102]

[Table 6]

[0103]

The average major axis length of the ferromagnetic metal particles is 0.04.
Even if the particle size is as small as 0.10 μm, which is unprecedented, the average number of crystallites forming ferromagnetic metal particles is controlled by controlling the number of nuclei of metal when the particle sizes of the starting materials are well aligned and the nuclei of metal are generated. By setting the acicular ratio to 0 to 2.0 and setting the acicular ratio to 2.0 to 5.0, a ferromagnetic metal powder having a high coercive force and an excellent coercive force distribution can be prepared, and the ferromagnetic metal powder By using the metal powder, it is possible to provide a magnetic recording medium having excellent short-wavelength output and C / N and excellent overwrite characteristics.

[Brief description of drawings]

FIG. 1 is a diagram for explaining ferromagnetic metal particles used in the present invention.

FIG. 2 is a diagram for explaining conventional ferromagnetic metal particles.

[Explanation of symbols]

1 Ferromagnetic metal particles 2 crystallites

Claims (4)

(57) [Claims] 1. A magnetic recording medium in which a magnetic layer containing at least a ferromagnetic metal powder is provided on a non-magnetic support, and the magnetic layer has a coercive force of 2000 to 3000 Oe and a Bm of 3800 to 5500 gauss. And the average major axis length of the ferromagnetic metal particles is 0.04 to 0.10 μm,
The average acicular ratio of the ferromagnetic metal particles is 3.0 to 8.0, the average number of crystallites constituting the ferromagnetic metal particles is 1.0 to 2.0, and the average acicular ratio of crystallites. Is 2.0 to 5.0
A magnetic recording medium characterized by: 2. The ferromagnetic metal powder contains iron and Co, has a coercive force of 1800 to 2500 Oe and a σs of 130 to 16.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has an emu / g of 5 emu / g. 3. The magnetic recording medium according to claim 1, wherein a nonmagnetic layer mainly containing an inorganic nonmagnetic powder and a binder is provided between the nonmagnetic support and the magnetic layer. 4. The ferromagnetic metal powder contains iron and Co, has a coercive force of 1800 to 2500 Oe, and σs of 130 to 16
The magnetic recording medium according to claim 3, wherein the magnetic recording medium is 5 emu / g.