JPH08185624A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To provide a coating type magnetic recording medium capable of maintaining its electromagnetic transducing characteristics, etc., without causing deterioration even in the case of storage at high temp. and humidity over a long period of time. CONSTITUTION: A magnetic layer contg. metallic magnetic powder is formed on a nonmagnetic substrate. The concn. of Na ions eluted from 1g of the magnetic layer into water is 200ppm and the concn. ratio of Na ions to K ions eluted is 1-4.

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, and more particularly to a coating type magnetic recording medium capable of maintaining the electromagnetic conversion characteristics and the like without deteriorating even when stored under high temperature and high humidity for a long time.

[0002]

2. Description of the Related Art In recent years, with the spread of large-capacity recording devices,
There has been a demand for higher density magnetic recording, and as a magnetic recording medium suitable for such a demand, high coercive force and S
It is required that the FD (coercive force distribution) is small and that the saturation magnetization is large.

For this reason, particularly in a magnetic recording medium such as 8 mm video or DAT, the coercive force is high and the saturation magnetization is large.
Fe metal magnetic powder containing iron as a main component is used for the magnetic layer. The magnetic recording medium is also required to withstand good long-term storage while obtaining good recording characteristics.
Various Fe metal magnetic powders in which rare earth elements, Al, Si, Co and the like are further added to Fe have been proposed to realize these requirements (JP-A-58-60504 and JP-A-56).
-35705, etc.).

In particular, recently, a technique for improving the recording characteristics and the long-term storage stability by incorporating Co in the metal magnetic powder in an amount larger than that of the conventional one has attracted attention and has been studied.
Development is underway. As such an example, for example, in Japanese Patent Laid-Open No. 1-257309, Co is added to Fe in an amount of 6
A metal magnetic powder for a magnetic recording medium containing at least wt% is described, and it is disclosed that a larger saturation magnetization can be maintained and storage characteristics can be improved. In addition, JP-A-6-
In JP 36265, a rare earth element is added to Fe in an amount of 1 to
10 wt%, Al and / or Si 0.5 to 5.0
A magnetic recording medium having a magnetic layer using a metal magnetic powder containing 6 wt% and 6 wt% of Co is disclosed, and it is disclosed that magnetic characteristics such as coercive force and magnetization amount are improved by this.

By the way, in order to add Co or the like to the magnetic metal powder, a method of reducing iron oxyhydroxide or iron oxide containing Co is generally used. It is known that iron oxide can be obtained by the following method. (1) An alkaline aqueous solution is added to a mixed aqueous solution of a ferrous salt and a cobaltous salt, and ferrous hydroxide and cobaltous cobalt are coprecipitated in a colloidal form, and an oxidizing gas such as air is blown in, Co-containing iron oxyhydroxide (Co-containing goethite)
Furthermore, a method of producing Co-containing iron oxide. (2) A method of suspending iron oxyhydroxide or iron oxide in a Co-containing aqueous solution and growing an oxide layer containing Co on the surface by the above oxidation reaction. (3) A method of suspending iron oxyhydroxide or iron oxide in a Co-containing aqueous solution and adding an alkaline aqueous solution to precipitate cobalt hydroxide.

As another method, a method for adhering cobalt hydroxide onto the surface of goethite (Japanese Patent Publication No. 58-
55203), a method of treating the surface of the magnetic powder with a Co chelate compound (JP-A-60-175215).
Etc. have been proposed.

More recently, attempts have been made to improve high magnetic properties and flow properties by examining the shape of "acicular" magnetic powder. The term "needle-shaped" as used herein means not only those in which the major axis diameter of the metal magnetic powder is substantially the same throughout the entire length of the axis, but the diameter gradually narrows toward the major axis end and the major axis end It is a broad concept that includes things that are relatively sharp (generally called spindle-shaped) to things where the long axis ends are hemispherical or nearly flat. More specifically, (X / k) ⁿ +
It is a shape made by rotating X and Y satisfying the formula of Y ⁿ = 1 around the X axis, and in the above formula, the possible value of n is 1
<N <100, preferably 1.2 ≦ n ≦ 20, more preferably 1.5 ≦ n ≦ 10. Note that k represents a so-called axial ratio (ratio of major axis diameter / minor axis diameter), preferably 3
It is -10. Flow characteristics can be improved by making such a "needle-like" magnetic powder shape such that the diameter is gradually narrowed toward the major axis end and the major axis end is relatively sharp. .

In the present specification, hereinafter, the shape of the magnetic powder is "acicular", unless otherwise specified, and is used in the meaning according to the above definition.

Further, in order to improve the performance of the magnetic layer,
The ferrous salt is neutralized with an alkaline aqueous solution such as NaOH to obtain Fe.
A method of neutralizing FeCO ₃ with an alkali carbonate such as Na ₂ CO ₃ instead of (OH) ₂ to produce Co-containing iron oxyhydroxide via this is proposed and put into practical use. . By this method, the Co content is increased, the saturation magnetization (σs) and the coercive force (Hc) are remarkably improved,
It has a surface without pores and branches, and by using this, a high performance magnetic tape can be obtained.

However, the Co-containing Fe metal magnetic powder obtained by dehydrating, heat-treating, and reducing the Co-containing iron oxyhydroxide obtained as described above easily takes in soluble ions such as sodium ions from the outside. When a magnetic recording medium is produced using such Fe metal magnetic powder having an increased amount of soluble ions, the initial characteristics are excellent, but soluble ions are deposited as an insolubilized salt during storage under high temperature and high humidity. There is a product dropout (D
There is a problem that it is easy to cause (O) and output reduction. Regarding this phenomenon, it is considered that the elution of sodium ions contained in the magnetic powder into water is considered to trigger the precipitation of calcium ions, barium ions, etc. contained in the magnetic recording medium as insoluble fatty acid salts. Have already been shown by the present applicants (Japanese Patent Application No. 5-
303441).

Therefore, as one of the countermeasures against the above problems, it is possible to reduce the amount of soluble ions contained in the metal magnetic powder or the magnetic recording medium, especially the amount of sodium ions. As a conventional technique for reducing the amount of soluble ions, the amount of calcium ions in the magnetic powder is set to 0.003% by weight or less in advance (Japanese Patent Publication No. 60-20807), or the amount of water-soluble calcium in the magnetic powder is adjusted. 100 pp
It has been proposed that the thickness be m or less (Japanese Patent Laid-Open No. 4-146519). Other than these, for example, JP-A-60
JP-A-150228 describes a magnetic recording medium in which the amount of water-soluble metal ions eluted from the surface of a magnetic layer mainly composed of a ferromagnetic alloy powder and a binder is 10 ppm / m ² · 100 ml or less. Japanese Patent Publication No. 100402 describes a magnetic recording medium using a ferromagnetic metal powder obtained by washing with water and heat reduction after heat treatment.

However, in any of the conventional methods, it has been difficult to simultaneously satisfy both of the requirements that the characteristics of the magnetic powder and the magnetic recording medium are maintained without being impaired and the soluble ions are reduced. For example, Japanese Patent Publication Sho 60
In JP-A-20807 and JP-A-4-146519, the water-soluble calcium content in the magnetic powder becomes too low, and the precipitation of the insolubilized calcium salt can be prevented, but the magnetic powder aggregates to disperse. However, there is a problem in that the magnetic properties are deteriorated, resulting in deterioration of magnetic properties. Further, in the case of JP-A-60-150228,
In order to reduce the amount of water-soluble metal ions from the magnetic layer to the above-mentioned predetermined amount or less, among the water-soluble metal ions, the content of sodium ions and calcium ions in the magnetic layer, which is considered to be the main factor for the generation of DO in particular, Is suppressed to at least the above-mentioned elution amount, so that the amount of these soluble ions contained in the magnetic layer component becomes too low and agglomeration may occur, leading to a decrease in dispersibility of the magnetic coating material. Further, since the film thickness dependency is not specified, it does not match the actual situation such as thinning of the medium. Also in JP-A-58-100402, when the iron oxide is heat-treated and then washed with distilled water, it is washed with distilled water until the ionization degree of the filtrate does not change. The content of the soluble ions in (1) may be excessively reduced, and similarly, the dispersibility may be reduced.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is a coating type magnetic that can maintain the electromagnetic conversion characteristics and the like without deteriorating even when stored for a long time under high temperature and high humidity. The purpose is to provide a recording medium.

[0014]

To achieve the above object, according to the present invention, there is provided a magnetic recording medium comprising a magnetic layer containing a metal magnetic powder on a non-magnetic support, said magnetic layer comprising: Provided is a magnetic recording medium characterized in that the concentration of sodium ions eluted from 1 g into water is 200 ppm or less, and the sodium / potassium ion ratio (elution concentration ratio) is 1 to 4.

Here, the magnetic layer in the present invention includes not only the magnetic layer but also so-called lower layers such as a non-magnetic layer and an underlayer which can affect the amount of soluble ions in the magnetic layer. The influence on the amount of soluble ions in the magnetic layer may be, for example, the mutual movement of soluble ions between the magnetic layer and the magnetic layer such as the magnetic layer-nonmagnetic layer, resulting in the storage characteristics of the magnetic layer. To have a bad influence on the temperature, and to deteriorate the stability over time.

The metallic magnetic powder of the present invention is a metallic magnetic powder containing Fe as a main component and 6 to 40 wt% of Co with respect to Fe, which is eluted from 1 g of the metallic magnetic powder into water. Sodium ion concentration is 40
It is preferably 0 ppm or less and a sodium / potassium ion ratio (elution concentration ratio) of 100 or less.

The present invention will be described in detail below.

The magnetic recording medium according to the present invention comprises a magnetic layer containing a metallic magnetic powder provided on a non-magnetic support, and the concentration of sodium ions eluted from the magnetic layer 1g into water is 200 ppm or less. It is preferably 100 ppm or less. Here, “the concentration of sodium ions eluted from the magnetic layer 1 g into water is 200 ppm or less” means that when the magnetic layer is contacted with water, the concentration of sodium ions released from the magnetic layer 1 g into the water is 200 ppm or less. Specifically, when this magnetic layer is stored under high temperature and high humidity for a long period of time and moisture or the like adheres to the magnetic layer, sodium ions eluted from the magnetic layer 1g into the moisture are It means that the concentration is 200 ppm or less. Further, in the present invention, the sodium / potassium ion ratio (elution concentration ratio) eluted from the magnetic layer 1g into water is 1 to 4.
When both the concentration of sodium ions eluted and the ratio of sodium / potassium ions (elution concentration ratio) are within the above ranges, the magnetic properties and surface properties are excellent (that is, the dispersibility is good), and the storage properties are excellent. The effect is obtained, and if at least one of the sodium ion elution concentration and the sodium / potassium ion ratio (elution concentration ratio) is out of the above range, the above effect cannot be obtained. For example, if the sodium ion concentration exceeds 200 ppm, an insoluble salt will be deposited on the tape surface, which will cause an increase in dropout, a decrease in output, and the like. further,
If the sodium / potassium ion ratio exceeds 4, the dispersibility will not be a problem, but the storage characteristics will deteriorate, and if it is less than 1, the dispersibility will decrease, and conversely, the elution potassium ions will increase too much and the storage characteristics will decrease. To do. Further, potassium has the only higher ionization tendency than sodium, is easily released as an ion, and is also suitable as a measure of the degree of washing with water.

As described above, the magnetic layer in the invention of the present application includes not only the magnetic layer but also so-called lower layers such as a non-magnetic layer and an underlayer which can affect the amount of soluble ions in the magnetic layer. Therefore, when the lower layer such as a non-magnetic layer or an underlayer is provided, the soluble ion elution concentration from the “magnetic layer 1 g” is the soluble ion elution concentration from 1 g of the lower layer and the magnetic layer. means.

The concentration of sodium ions and potassium ions eluted from 1 g of the magnetic layer into water can be measured by a known method. For example, 1 g of the magnetic layer component is added to 10 ml of pure water, and this is added at a temperature of 60 ° C. After holding for 1 week, the supernatant can be taken and analyzed by the atomic absorption method for measurement. The sodium / potassium ion ratio can be calculated from the concentration of each ion eluted measured by the atomic absorption method.

In the magnetic recording medium of the present invention, Fe is the main component of the metal magnetic powder, and the content of Fe is 6-4.
A metal magnetic powder containing 0 wt% of Co, wherein the concentration of sodium ions eluted from 1 g of the metal magnetic powder into water is 400 ppm or less, and the sodium / potassium ion ratio (elution concentration ratio) is 100 or less. Such a thing is used suitably. By using the Fe magnetic powder having both the sodium ion elution concentration and the sodium / potassium ion ratio (elution concentration ratio) within the above ranges, the above-mentioned action of the magnetic layer in the magnetic recording medium of the present invention,
The effect can be exerted more effectively.

The metallic magnetic powder containing Fe as a main component is
Fe for maintaining excellent magnetic properties and thinning the magnetic layer
With respect to Co is 6-40 wt%, preferably 10-40
wt%, more preferably 20-40 wt%. The concentration of sodium ions eluted from 1 g of the Fe metal magnetic powder into water is 400 ppm or less, preferably 300 ppm or less, more preferably 200 pp.
m or less. Here, “the concentration of sodium ions eluted from 1 g of Fe metal magnetic powder into water is 400 ppm or less” means that when the Fe metal magnetic powder is contacted with water such as water or an aqueous solution, sodium ions in the water are This means that the liberation is 400 ppm or less. Specifically, when the magnetic layer component is prepared by dispersing the Fe metal magnetic powder with a binder, an organic solvent, etc., 1 g of the Fe metal magnetic powder is added to the magnetic layer. It shows that the sodium ions eluted into the component may have a concentration of 400 ppm or less. This eluted sodium ion concentration is 4
If it exceeds 00 ppm, insoluble salts such as NaCl and fatty acid salts are deposited on the surface of the tape, which causes increase in dropout and decrease in output. Furthermore, the sodium / potassium ion ratio (elution concentration ratio) eluted from 1 g of the Fe metal magnetic powder into water is 100 or less, preferably 60 or less. This sodium / potassium ion ratio is 100
If it exceeds, there is a high possibility that more insoluble salt will be deposited on the surface of the tape, resulting in deterioration of storage characteristics.

The degree of agglomeration of the magnetic powder may be measured by measuring the transmittance of the magnetic powder with a sieve, and the sieve opening 1190 has a transmittance of 70% or more, preferably 82% or more.

The concentration of sodium ions and potassium ions eluted from 1 g of Fe metal magnetic powder into water can be measured by a known method, for example, 20 m of pure water.
1 g of metallic magnetic powder was added to 1 liter, and this was added at 1
After holding for a time, ultrasonic dispersion is performed for 1 hour, and after filtration, the filtrate can be analyzed and measured by an atomic absorption method. Further, the sodium / potassium ion ratio (elution concentration ratio) can be calculated from each ion elution concentration measured by an atomic absorption method.

One of the preferable methods for producing the Fe metal magnetic powder as described above is to add FeCO ₃ to a Co-added ferrous salt solution to form an alkali metal-free alkali carbonate to produce FeCO ₃ , which is then oxygen-containing. This is a method of contacting with a gas to form iron oxyhydroxide, dehydrating, heat treating, and then reducing to obtain Fe metal magnetic powder.

Here, as the ferrous salt, FeCl ₂ , Fe
SO ₄ , Fe (NO ₃ ) _{2 and the} like can be mentioned. Among them, Fe
Cl ₂ and FeSO ₄ are preferably used. Further, as alkali carbonate containing no alkali metal, (NH ₄ ) ₂ C
O ₃ , NH ₄ HCO ₃ , NH ₄ HCO ₃ · NH ₄ CO ₂
NH _{2 and the} like can be mentioned.

First, Co is added to the ferrous salt solution,
Specifically, Co compounds such as cobalt sulfate and cobalt chloride are used, and these Co compounds are dissolved in a ferrous salt solution and mixed with stirring.

Next, alkali carbonate containing no alkali metal is added thereto. Neutralizing the ferrous salt with this alkali carbonate that does not contain alkali metal can prevent the incorporation of alkali metal ions (sodium ion, potassium ion, etc.) into the magnetic metal powder from the outside. It is possible to reduce the content of soluble ions in the Fe metal magnetic powder obtained as a result. In addition, by adding an alkaline aqueous solution such as NaOH to the ferrous salt solution, Fe
Instead of (OH) ₂ , add alkali carbonate and add F
By making eCO ₃ and blowing an oxidizing gas into it to produce iron oxyhydroxide (= goethite; FeOOH), the finally obtained magnetic powder has a low content of soluble alkali metal and has a needle-like shape. . That is, the obtained magnetic powder has high magnetic properties, is a fine particle with a short major axis length, has a sharp particle size distribution, and has few pores on the surface.
Therefore, the magnetic layer can be thinned, and a high-performance magnetic medium can be manufactured. The amount of alkali carbonate containing no alkali metal added is preferably about 1 to 10 times the molar equivalent of the ferrous salt solution.

In this way, a slurry of iron oxyhydroxide is obtained. This slurry is filtered and washed with water, then dispersed again in distilled water to obtain a slurry again.

Here, Ni salt or Ca as a crystal control agent is used.
Salt, Ba salt, Sr salt, etc., Periodic Table 2A group salt, Cr salt, Z
An n-salt or the like may coexist, and the particle shape (axial ratio) and the like can be controlled by appropriately selecting and using such a salt. As the Ni salt, a chloride such as nickel chloride is preferable, and Ca salt, Ba salt, Sr salt, Cr
As the salt, Zn salt and the like, chlorides such as calcium chloride, barium chloride, strontium chloride, chromium chloride and zinc chloride are preferable.

Further, additional components such as a sintering inhibitor may be added. By adding these components, it is possible to prevent sintering at the time of reduction in a later step. Examples of the sintering inhibitor include Al, Si and rare earth elements. As an introduction method, after preparing a slurry of iron oxyhydroxide containing Co, an aqueous solution containing an Al compound, a Si compound, etc., and an aqueous solution containing a compound of a rare earth element are added to the slurry and stirred. Preferably mixed, but A
It is also possible to prepare an aqueous solution containing all of the 1 compound, the Si compound, the compound of the rare earth element, etc., and add this. Moreover, you may add to a ferrous salt solution simultaneously with Co. As the Al compound, sodium aluminate, sodium metaaluminate or the like, and as the Si compound, sodium silicate or the like,
Each is illustrated. Further, as rare earth elements, Nd, S
m, Gd, Dy, La, Y, and the like. Examples of compounds of these rare earth elements include chlorides such as neodymium chloride, samarium chloride, gadolinium chloride, dysprosium chloride, lanthanum chloride, and yttrium chloride, neodymium nitrate, dadolinium nitrate, and the like. And the like.

The Co-containing iron oxyhydroxide thus obtained is filtered, washed with water, filtered again, dried in a drier and dehydrated.

Then, this is placed in a nitrogen atmosphere at 400-70.
Heat treatment is performed at a temperature of 0 ° C.

After the heat treatment, reduction is carried out, but it is preferable to carry out the reduction while heating in a reducing atmosphere. Generally, the reducing atmosphere is preferably a hydrogen gas atmosphere, and the flow rate of the hydrogen gas can be appropriately selected. The heating temperature is about 300 to 600 ° C.

Another preferable method for producing the above Fe metal magnetic powder is to add FeCO ₃ to a Co-added ferrous salt solution to produce FeCO ₃ , which is then brought into contact with an oxygen-containing gas to form oxywater. This is a method of obtaining Fe metal magnetic powder by making iron oxide, dehydrating it, and then subjecting it to either water washing-heat treatment or heat treatment-water washing, followed by reduction.

This production method is carried out by adding "alkali carbonate" to the ferrous salt solution for neutralization, and after the dehydration step,
Although it differs from the first manufacturing method in that a water washing step is provided before or after the heat treatment step, it can be performed in the same manner as the first method in other points.

Here, "alkali carbonate" means (NH
_{4) 2} CO in addition to Na ₂ CO ₃ in _3, K ₂ CO _3, Na
HCO ₃ , KHCO _{3 and the} like can be mentioned, especially Na ₂ CO
₃ is preferably used. The amount of alkali carbonate added is
It is preferable that the molar equivalent to the ferrous salt solution is about 2 to 10 times.

Further, after the dehydration step, a water washing step is provided either before or after the heat treatment step, whereby the soluble ions contained in the iron oxyhydroxide are washed out to reduce the content thereof, and sodium ions The ratio of potassium ions is adjusted within a predetermined range. In particular,
Finally, the concentration of sodium ions eluted from 1 g of the magnetic metal powder into water is 400 ppm or less, and the sodium / potassium ion ratio (elution concentration ratio) is 100 or less. Wash with water while adjusting the order and type of water used. Fe
Sodium ion concentration, sodium / potassium ion ratio (elution concentration ratio) eluted from 1 g of metallic magnetic powder into water
Can be measured by a known method as described in the first preferred manufacturing method above.

The water used in the washing step may be any water as long as it does not contain a large amount of soluble ions, and distilled water, tap water, deionized water, ground water or the like can be used.

In the Co-containing Fe metal magnetic powder thus obtained, it is considered that Co exists inside the powder or both inside the powder and on the surface of the powder. In addition, the additive components other than Co are mainly present near the surface of the magnetic powder, and remain in the form of the added compound, or in the form of oxides or hydroxides, or even form alloys or the like. It is believed that These additive elements may be a mixture of these states. This can be confirmed by ESCA or the like.

The magnetic metal powder used in the present invention preferably has a "needle-like" shape, and the major axis has an average value of 0.05 to.
0.2 μm, the minor axis is 0.006 to 0.1 μm on average, and the axial ratio is preferably 3 to 10 on average. These can be confirmed by a TEM photograph or the like. This magnetic metal powder has a coercive force (Hc) of 1500 to 2500.
Oe, saturation magnetization (σs) is 120 to 160 emu /
g, the specific surface area according to the BET method is preferably about 40 to 80 m ² / g. Further, the metal magnetic powder may have an oxide film on the surface, and a magnetic recording medium using the metal magnetic powder having such an oxide film is caused by a decrease in the amount of magnetization due to the external environment such as temperature and humidity. It is advantageous for characteristic deterioration.

The magnetic recording medium according to the present invention preferably comprises a magnetic layer containing the above Fe metal magnetic powder provided on a non-magnetic support, and the magnetic layer is conventionally and conventionally used. It can be prepared by the method described above and coated on a non-magnetic support. For example, a binder, a lubricant, an additive for exhibiting an antistatic effect, a dispersing effect, a plasticizing effect, etc., an inorganic powder, carbon black, a non-ferromagnetic organic powder, etc. are added to the Fe metal magnetic powder. Is mixed and dispersed in an organic solvent to prepare a high-concentration magnetic layer component, and then this high-concentration magnetic layer component is further diluted with a solvent to prepare a magnetic layer component (magnetic paint). Apply to.

In the preparation of the magnetic layer components, a premix, for example, a kneader or the like is used to knead at a high solid or high concentration, or the materials are mixed with a high-speed stirrer and then diluted or left as they are. Dispersion is performed using a media stirring type mill such as a grinder mill. In the dispersion, conventionally, as a dispersion medium, SiO ₂ ,
Although soft glass beads obtained by adding Na ₂ O and K ₂ O to CaO, MgO, Al ₂ O _3, etc. are used, when these soft glass beads are used, alkali metal ions (particularly sodium ions) contained therein are used. Was eluted from the beads into the magnetic layer component, which increased the soluble ion content in the magnetic layer component, resulting in accelerating precipitation of insolubilized calcium salt when stored for a long time under high temperature and high humidity.

In the present invention, the Fe metal magnetic powder obtained by the above manufacturing method is preferably dispersed using a dispersion medium containing no alkali metal to prepare the magnetic layer component. By using a dispersion medium that does not contain an alkali metal, sodium ions are not eluted or increased in the magnetic layer components in the dispersion step, and precipitates can be prevented.

Dispersion media containing no alkali metal
For example, soft glass beads are made alkali-free
Thing; SiO₂ , CaO, MgO, Al₂ O₃ , ZrO
₂ , B₂ O₃ Glass beads made of, TiO, etc .; Z
rO₂ Y₂ O₃ , ZrO₂ MgO, Al₂ O₃ , (Zr
O₂ , SiO₂ ), (ZrO₂ , SiO₂ , Al₂ O
₃ ) TiO₂ Bea made of SiAlON, etc.
B; Iron alloy, for example, metal alloy such as SUS304, 306
, Etc. Among these, especially alkali metals
Ceramic beads that are free of abrasion and have good wear resistance are preferred.
Yes.

The amount of the dispersion medium to be introduced into the disperser is the shape of the disperser (horizontal type, vertical type, pin type, disk type, gap type or screen type), the number of revolutions of the main shaft, and the coating material of the object to be dispersed. It greatly depends on the viscosity and flow rate. Therefore, it is preferable to determine the amount of the dispersion medium to be added in consideration of not only dispersibility but also manufacturing conditions. The particle size of the dispersion medium is preferably about 0.2 to 2 mm, more preferably 0.5 to 1.5 mm, and if the coating material requires high dispersion, small diameter beads are preferable. As for the bead type, ceramic beads having a specific gravity (3 to 6) larger than that of glass beads are preferable.

As the binder used in the magnetic layer component (magnetic paint), a thermoplastic resin, a thermosetting or reactive resin, an electron beam sensitive modified resin, or the like is used. These may be used alone or in combination of two or more, and the combination thereof is appropriately selected and used according to the characteristics of the magnetic recording medium and the process conditions. The thermoplastic resin has a softening temperature of 150 ° C. or lower, an average molecular weight of 5,000 to 200,000, and a polymerization degree of 5.
It is preferably about 0 to 2,000. Thermosetting resin,
As the reactive resin and the electron beam sensitive modified resin, those having the same average molecular weight and degree of polymerization as those described above are used, and coating, drying,
By heating and / or electron beam irradiation after calendering, the molecular weight becomes infinite due to reactions such as condensation and addition.

Among these, a combination of a vinyl chloride copolymer and a polyurethane resin is most preferably used among the thermoplastic resins.

The vinyl chloride copolymer preferably has a vinyl chloride content of 60 to 95 wt%, particularly 60 to 90 wt%, and an average degree of polymerization of about 100 to 500. Specifically, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer, vinyl chloride-vinyl acetate-
Maleic acid, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid, vinyl chloride-vinyl acetate-hydroxyalkyl (meth) acrylate, vinyl chloride-vinyl acetate-hydroxyalkyl (meth) acrylate-maleic acid, vinyl chloride-vinyl acetate- Vinyl alcohol-glycidyl (meth) acrylate, vinyl chloride-hydroxyalkyl (meth) acrylate-glycidyl (meth) acrylate, vinyl chloride-vinyl acetate-vinyl alcohol-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) ) Copolymers of acrylate-allyl glycidyl ether, vinyl chloride-vinyl acetate-vinyl alcohol-allyl glycidyl ether, and the like. Particularly, a copolymer of vinyl chloride and an epoxy (glycidyl) group-containing monomer is preferable.

The vinyl chloride copolymer preferably contains a sulfuric acid group and / or a sulfo group as a polar group (hereinafter referred to as "S-containing polar group"). The S-containing polar group, for example -SO ₄ Y, -SO ₃ Y (provided that, Y is, H or an alkali metal), and the like, -SO ₄ K Among these, -SO ₃ K (Y = Potassium) is particularly preferred. These may contain either one, or may contain both, and when both are contained, the ratio is arbitrary.

These S-containing polar groups are preferably contained in the molecule as S atoms in an amount of 0.01 to 10 wt%, particularly 0.1 to 5 wt%. Further, as the polar group, if necessary,
Other S-containing polar _{groups, -OPO 2 Y, -PO 3 Y} , -C
OOY (Y is H or an alkali metal), an amino group (-
_{NR 2), - NR 3 Cl} (R is, H, methyl, ethyl)
Etc. can also be contained. Among them, the amino group may not be used in combination with S and may be various ones, but a dialkylamino group (preferably alkyl having 1 to 10 carbon atoms) is particularly preferable. Such an amino group is usually obtained by amine modification, and a vinyl chloride / alkylcarboxylic acid vinyl ester copolymer is dispersed or dissolved in an organic solvent such as alcohol, and the amine compound (aliphatic amine, alicyclic group) is contained therein. (A primary, secondary, or tertiary amine such as amine, alkanolamine, or alkoxyalkylamine) and an epoxy group-containing compound for facilitating the saponification reaction, to carry out the saponification reaction. The vinyl unit having the amino group obtained in the above is 0.05 to 5 wt%, and an ammonium base may be consequently contained.

The resin skeleton to which the S-containing polar group is bonded is a vinyl chloride resin, and vinyl chloride, a monomer having an epoxy group, and, if necessary, other monomers copolymerizable therewith, S such as potassium persulfate and ammonium persulfate
It can be obtained by polymerization in the presence of a radical generator having a strong acid radical containing The amount of these radical generators used is usually 0.3 to 9.0 wt%, preferably 1.0 to 5.0 wt% with respect to the monomer, and since many of them are water-soluble in polymerization. , Emulsion polymerization, suspension polymerization using alcohol such as methanol as a polymerization medium, and solution polymerization using ketones as a solvent are preferable. At this time, in addition to the radical generator having a strong acid radical containing S, it is also possible to use a radical generator usually used for polymerization of vinyl chloride. Further, the radical generator having a strong acid radical containing S,
You may combine reducing agents, such as sodium formaldehyde sulfoxylate, sodium sulfite, and sodium thiosulfate.

Examples of the monomer having an epoxy group include glycidyl ethers of unsaturated alcohols such as (meth) allyl glycidyl ether and glycidyl (meth).
Glycidyl esters of (meth) acrylic acid such as acrylate, glycidyl-p-vinyl benzoate, methyl glycidyl itaconate, glycidyl ethyl malate,
Examples include glycidyl esters of unsaturated acids such as glycidyl vinyl sulfonate and glycidyl (meth) allyl sulfonate, butadiene monooxide, vinyl cyclohexene monooxide, and epoxide olefins such as 2-methyl-5,6-epoxyhexene. It is used within the range where the amount of epoxy groups in the copolymer is 0.5 wt% or more.

In addition to vinyl chloride and a monomer having an epoxy group, examples of other monomers which can be optionally used include vinyl acetate, carboxylic acid vinyl esters such as vinyl propionate, methyl vinyl ether and isobutyl. Vinyl ether, vinyl ether such as cetyl vinyl ether, vinylidene chloride, vinylidene fluoride, etc.
Diethyl maleate, butylbenzyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate, methyl (meth) acrylate, ethyl (meth) acrylate, lauryl (meth) acrylate, (meth) acrylic acid-2 -Unsaturated carboxylic acid esters such as hydroxypropyl, olefins such as ethylene and propylene, (meth)
Examples thereof include unsaturated nitriles such as acrylonitrile.

The polyurethane resin used in combination with the above-mentioned vinyl chloride resin is particularly effective in that it has good abrasion resistance and adhesiveness to a support, and has a polar group, a hydroxyl group or the like in its side chain. They may be present, and those containing a polar group containing sulfur (S) or phosphorus (P) are particularly preferable.

Polyurethane resin is a general term for resins obtained by reacting a hydroxyl group-containing resin such as polyester polyol and / or polyether polyol with a polyisocyanate-containing compound, and the synthetic raw materials detailed below are number average molecular weight compounds. Polymerized to about 500 to 200,000, and its Q value (weight average molecular weight / number average molecular weight) is about 1.5 to 4.

This polyurethane resin has a glass transition temperature Tg of −20 ° C. ≦ Tg ≦ 80 in the binder used.
At least two types that differ in the range of ° C are contained so that the total amount is 10 to 90 wt% of the total binder, and by containing these plural polyurethane resins, running stability under high temperature environment Is preferable in that the balance between the magnetic properties, the calendar processability, and the electromagnetic conversion characteristics can be obtained.

Further, a vinyl chloride copolymer and S and /
Alternatively, the P-containing polar group-containing polyurethane resin is preferably mixed and used so that the weight mixing ratio is 10:90 to 90:10. In addition to these resins,
Various known resins may be contained in the range of 20 wt% or less of the whole.

Of the above-mentioned raw materials for polyurethane resin, as the hydroxyl group-containing resin, polyethylene glycol, polybutylene glycol, polypropylene glycol and other polyalkylene glycols, bisphenol A and other alkylene oxide adducts, various glycols and hydroxyl groups are used as molecules. Examples thereof include polyester polyols having chain ends.

As the carboxylic acid component of the polyester polyol, terephthalic acid, isophthalic acid, orthophthalic acid, aromatic dicarboxylic acid such as 1,5-naphthalic acid, p-oxybenzoic acid, p- (hydroxyethoxy) are used.
Aromatic carboxylic acids such as benzoic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, fatty acid dicarboxylic acids such as dodecanedicarboxylic acid, fumaric acid, maleic acid,
Examples thereof include saturate fatty acids such as itaconic acid, tetrahydrophthalic acid and hexahydrophthalic acid, and alicyclic dicarboxylic acids, tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid and pyromellitic acid.

As the glycol component of the polyester polyol, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, Ethylene oxide adducts such as diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, bisphenol A and propylene oxide adduct, ethylene oxide of hydrogenated bisphenol A And propylene oxide adducts, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination.

Other polyester polyols include lactone-based polyester diol chains obtained by ring-opening polymerization of lactones such as caprolactone.

Of the above-mentioned polyurethane resin raw materials, polyisocyanates include tolylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, naphthalene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, diisocyanate methylcyclohexane, diisocyanate. Examples thereof include diisocyanate compounds such as cyclohexylmethane, dimethoxybiphenylene diisocyanate and diisocyanate diphenyl ether, and triisocyanate compounds such as trimer of tolylene diisocyanate and trimer of hexamethylene diisocyanate in an amount of 7 mol% or less of all isocyanate groups.

As polar groups that can be contained in the polyurethane resin, for example, --SO ₃ M (sulfonic acid group) and --SO ₄ M (sulfuric acid group) as S-containing groups, and = PO ₃ M as P-containing polar groups. (Phosphonic acid group), = PO ₂ M (phosphinic acid group), = POM (phosphinous acid group), -P = O (O
M ₁ ) (OM ₂ ), -OP = O (OM ₁ ) (OM ₂ ),
_{-COOM, -NR 3 X, -NR 2} , -OH, epoxy group, -SH, it is preferable to use those introduced by copolymerization or addition reaction at least one polar group selected from -CN and the like ( Here, M, M ₁ and M ₂ are H and L
_{i, Na, K, -NR 3} , shows a -NHR _2; R represents an alkyl group or H; X is a halogen atom).
Na is particularly preferable as M. These polar groups may be present in the main chain of the skeletal resin or in the branches thereof, and are contained in the molecule as atoms in an amount of 0.01 to 10 wt%, and particularly 0.02 to 3 wt%. Is preferred.

These polyurethane resins are prepared by reacting a specific polar group-containing compound and / or a raw material containing a raw material resin reacted with the specific polar group-containing compound in a solvent or in the absence of a solvent by a known method. Is obtained by

Examples of the thermoplastic resin include, in addition to the above-mentioned vinyl chloride copolymer and polyurethane resin, (meth) acrylic resin, polyester resin, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, nitrocellulose. , Styrene-butadiene copolymer, polyvinyl alcohol resin, acetal resin, epoxy resin, phenoxy resin, polyether resin, polyfunctional polyethers such as polycaprolactone, polyamide resin, polyimide resin, phenol resin, polybutadiene elastomer , Chlorinated rubber, acrylic rubber, isoprene rubber, epoxy modified rubber and the like.

Examples of the thermosetting resin include polycondensation phenol resin, epoxy resin, polyurethane curable resin, urea resin, butyral resin, polymeric resin, melanin resin, alkyd resin, silicone resin, acrylic reaction resin, polyamide resin, Epoxy-polyamide resin, saturated polyester resin, urea formaldehyde resin and the like can be mentioned.

Among the above resins, those having a hydroxyl group at the terminal and / or the side chain are preferable as the reactive resin because crosslinking using a polyisocyanate and electron beam crosslinking modification can be easily utilized. Furthermore, polar groups such as —COOH, —SO ₃ M, —OSO ₃ M, and —O are added to the terminals and side chains.
_{PO 3 X, -PO 3 X,} -PO 2 X, -N + R 3 Cl
^- , -NR ₂ and other acidic polar groups, basic polar groups and the like may be contained, and these are suitable for improving dispersibility. These may be used alone or in combination of two or more.

Various polyisocyanates can be used as the crosslinking agent for curing the above resin. Among them, one or more kinds of tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate and the like and a plurality of hydroxyl groups such as trimethylol propane are used. It is preferable to use a cross-linking agent modified to have one or an isocyanurate-type cross-linking agent in which 3 molecules of the diisocyanate compound are bound. The cross-linking agent is preferably blended in a ratio of 1 to 50 parts by weight with respect to 100 parts by weight of the resin, and the cross-linking agent three-dimensionally bonds with hydroxyl groups contained in the resin to improve the durability of the coating layer. it can. The cross-linking agent is specifically Coronate L, HL, 3041 manufactured by Nippon Polyurethane Industry Co., Ltd., 24A-100, TPI-100, BF manufactured by Asahi Kasei Corporation.
-Death modules L and N manufactured by Goodrich are listed.

Generally, in order to cure such a reactive or thermosetting resin, heating in a heating oven at 50 to 80 ° C. for 6 to 100 hours or at a low speed of 8
It is run in an oven at 0 to 120 ° C.

Further, according to the method known to the above copolymer,
It is also possible to use those which have undergone electron beam sensitive modification by introducing a (meth) acrylic double bond. Here, the acrylic double bond means a (meth) acryloyl group which is a residue of (meth) acrylic acid, a (meth) acrylic acid ester, and a (meth) acrylic acid amide.

In order to carry out this electron beam sensitive modification, urethane modification in which a reaction product (adduct) of tolylene diisocyanate (TDI) and 2-hydroxyethyl (meth) acrylate (2-HEMA) is reacted with a resin, or ethylene is used. 1 or more unsaturated unsaturated double bonds and 1 isocyanate group
An improved urethane modification in which a monomer (2-isocyanate ethyl (meth) acrylate or the like) having one in one molecule and no urethane bond in the molecule is reacted with a resin,
Furthermore, a method of reacting a resin having a hydroxyl group or a carboxylic acid group with a compound having a (meth) acrylic group and a carboxylic acid anhydride or a dicarboxylic acid for ester modification is well known. The urethane modification is preferable because it does not become brittle even if the content ratio of the vinyl chloride resin is increased and a coating film excellent in dispersibility and surface property can be obtained.

The content of the electron beam-sensitive group is 1 to 40 mol%, preferably 10 to 30 mol% in the hydroxyl group component in view of stability during production, electron beam curability and the like. In the case of a polymer, the electron beam curable resin having excellent dispersibility and curability can be obtained by reacting the monomer so that the number of functional groups per molecule is 1 to 20, preferably 2 to 10. When these electron beam sensitive modified resins are used, 1 to 50 wt% of a conventionally known polyfunctional acrylate may be mixed and used in order to improve the crosslinking rate.

When the electron beam sensitive modified resin is used as a binder, an electron beam is used as a radiation source at the time of curing, from the viewpoint of controlling the absorbed dose, introducing it into the manufacturing process line, and shielding ionizing radiation. Advantageously, and / or using UV light. In the case of electron beam, accelerating voltage 100KV-750KV, preferably 150-300K
It is convenient to use an electron beam accelerator of V to irradiate the absorbed dose to 20 to 200 kilograys. When electron beam cross-linking is performed, N ₂ and H having an oxygen concentration of 1% or less are used.
It is important to irradiate an electron beam in an atmosphere of an inert gas such as e, CO ₂ or the like, in order to prevent O ₃ or the like generated by radiation irradiation from trapping radicals. On the other hand, when ultraviolet rays are used, a conventionally known photopolymerization sensitizer is added to the binder containing the electron beam curable resin, and the irradiation thereof is performed using a xenon discharge tube, a hydrogen discharge tube, or the like. An ultraviolet light bulb or the like may be used.

As a matter of course, the binder used in the present invention preferably has a small amount of soluble ions. Further, this binder was added to 5 parts by weight of 100 parts by weight of Fe metal magnetic powder.
˜50 parts by weight.

The organic solvent is not particularly limited, but is appropriately selected in consideration of the solubility and compatibility of the binder and the drying efficiency. For example, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, toluene, aromatic hydrocarbons such as xylene, ethyl acetate, esters such as butyl acetate, alcohols such as isopropanol, butanol, dioxane, tethydrofuran, dimethyl. A diluent or solvent such as formamide, hexane or chlorine-substituted hydrocarbons is used as a single solvent or a mixed solvent of these at arbitrary ratios.

These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposition products, oxides and water in addition to the main components. Its content in the organic solvent is preferably 5 wt% or less, more preferably 3 wt% or less. A large amount of impurities adversely affects the dispersibility of the magnetic powder, the storage stability of the paint, the curing characteristics of the magnetic layer, the storage characteristics of the medium, and the like.

These organic solvents are used in an amount of 10 to 10000 wt% with respect to the total amount of the binder so that the viscosity of the paint is 5 to 100 cp at a shear rate of 3000 sec ^-1 by a cone plate type or double cylinder type viscometer at the coating stage.
%, Especially 100-5000 wt%.
As a usage ratio with respect to the total amount of the magnetic coating material, the solid content (nonvolatile content) concentration is 5 to 45 wt%, preferably 10 to 35 w.
It is preferable to use it so as to be about t%. However, to determine the solvent type, mixing ratio, and usage amount, the type of pigment used in the paint, the specific surface area, the particle size, the magnetic amount of magnetic powder, the pigment volume or weight filling degree, and further The viscosity may be adjusted within the above-mentioned range in consideration of the dilution stability of the paint.

The organic solvent addition operation is preferably carried out stepwise in each step of the production of the magnetic paint, and the flow rate is regulated so that the solvent is added sequentially while stirring in the tank, or is gradually mixed with the paint by piping. It is preferable to carry out operations such as the above, and it is more preferable to carry out filtration and / or dispersion treatment at the time of adding or diluting an organic solvent, if possible. By carrying out these operations, the stability and aggregates of the magnetic paint, This is because it is possible to suppress the generation of foreign matter.

Of course, the organic solvent used in the present invention preferably has a small amount of soluble ions.

As the lubricant, various known lubricants can be used, but it is particularly preferable to use a fatty acid and / or a fatty acid ester, which has 12 to 24 carbon atoms.
A monobasic fatty acid (which may contain an unsaturated bond or may be branched) and a monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) Fatty acid and 2 to 22 carbon atoms (may contain an unsaturated bond,
It may be branched) monovalent, bivalent, trivalent, tetravalent,
Mono-fatty acid ester, di-fatty acid ester, tri-fatty acid ester, a mixture thereof, or a combination of two or more thereof, which is composed of any one of cyclic or polysaccharide reducing alcohols such as pentavalent and hexavalent alcohols, sorbitan and sorbitol Good.

Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid as monobasic fatty acids. For esters, butyl myristate, butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl. Examples thereof include stearate, octyl stearate, isooctyl stearate, amyl stearate, butoxyethyl stearate.

The effect of these fatty acids and / or fatty acid esters as lubricants and dispersants appears when the ferromagnetic fine powder is added in a total amount of 0.1 wt% or more, and the content is increased. Although the effect becomes remarkable, when the above total amount exceeds 20 wt%, it is not retained in the magnetic layer and is ejected onto the surface of the coating film, which adversely affects the magnetic head and reduces the output. . Therefore, the content of fatty acid and / or fatty acid ester in the magnetic layer is 0.1 to 20 wt%, more preferably 1 to 1 as the total amount of the ferromagnetic fine powder.
It is 5 wt%, most preferably 1 to 12 wt%.

In addition to the magnetic layer, this lubricant is preferably contained in a back coat layer, an underlayer, etc. In particular, when the magnetic layer is thin, the lubricant is contained in the underlayer to improve the still durability. It is effective because it can be done. Further, when there is a back coat layer, a large amount of lubricant can be contained on the back coat layer side to improve the surface lubricity by transfer to the surface of the magnetic layer.

These fatty acids and / or fatty acid esters are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposition products and oxides in addition to the main component. . These impurities are preferably 40% or less, more preferably 20% or less.

Further, all or a part of the fatty acids, fatty acid esters, additives and the like used may be added at any step in the production of the coating material for forming the magnetic recording medium.
For example, when mixed with the pigment powder before the kneading step, when added in the kneading step with the pigment powder, the binder and the solvent, when added in the dispersion step, when added after the dispersion, when added immediately before coating, in the solvent There is a method such as applying a diluted or dispersed solution onto a previously applied layer.

It is of course preferable that the lubricant used in the present invention has a small amount of soluble ions.

In the magnetic paint, a lubricating effect,
Additives for exhibiting an antistatic effect, a dispersing effect, a plasticizing effect and the like are contained. For example, silicone oils,
Fluorine oil, fluorine-containing hydrocarbon group-containing alcohols, fatty acids, esters, ethers, paraffins, and the above-mentioned monobasic fatty acid metals (Li, Na, K, Ca, B)
a, Cu, Pb, etc.) salts, alcohols for producing the fatty acid ester, alkoxy alcohols, fatty acid ester of polyethylene oxide-added monoalkyl ether,
Aliphatic or cyclic amines, fatty acid amides, quaternary ammonium salts, polyolefins, polyglycols,
Nonionic surfactants such as polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, alkylene oxides, glycerins, glycidols, and alkylphenol ethylene oxide adducts,
Cationic surfactants such as phosphonium or sulfonium and alkali metal salts thereof, anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group and alkali metal salts thereof,
Amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of aminoalcohols, amphoteric surfactants such as alkylbetaine type and the like can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.).

The total content of these additives is 10 wt% or less, especially 0.01 to 5 wt% of the magnetic powder.
In the absence of magnetic powder, 0.0 to binder
It can be used in the range of 05 to 50 wt%.

As a matter of course, it is preferable that these additives used in the present invention have a small amount of soluble ions.

Further, the magnetic paint may contain an inorganic compound. Examples of the inorganic powder that can be used include inorganic powders such as metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Specifically, α-alumina, β-alumina, γ
-Alumina, θ-alumina, δ-alumina, dichromium trioxide, α-iron oxide, γ-iron oxide, goethite, SiO
₂ , ZnO, TiO ₂ , ZrO ₂ , SnO ₂ , silicon nitride, boron nitride, silicon carbide, titanium carbide, molybdenum carbide, boron carbide, tungsten carbide, calcium carbonate,
Barium carbonate, strontium carbonate, magnesium carbonate, barium sulfate, zinc sulfide, molybdenum disulfide, tungsten disulfide, artificial diamond and the like are used alone or in combination. These inorganic compounds are used in a weight ratio of 0.1 to 20 wt% with respect to the magnetic powder. Further, these inorganic compounds may be appropriately combined and used according to the required characteristics of the magnetic layer.

The shape, size, etc. of the particles of these inorganic powders may be set arbitrarily, but the particle shape is preferably spherical, granular or polyhedral, and the particle size is preferably 0.01.
.About.0.7 .mu.m, and these may be appropriately selected from the balance of durability required for the medium and head wear and output at the shortest recording wavelength, if necessary, and may be a single system or a mixed system, or may be used alone. It is also possible to select the particle size distribution and the like.

The above-mentioned inorganic compound does not necessarily have to be 100% pure, and the effect does not decrease if the main component is 70% or more.

Further, these inorganic compounds need to have a small amount of water-soluble alkali metal, alkaline earth metal, chlorine, sulfuric acid, nitric acid, etc. ions, and a large amount thereof will lead to storage characteristics when used as a medium. Adversely affect. Further, these inorganic compounds may be added at the same time as kneading or dispersing with the magnetic powder, or may be added in advance with a binder and added at the time of dispersing the magnetic coating material.

Further, carbon black may be contained in the magnetic paint. Furnace carbon black, thermal carbon black,
Acetylene black or the like can be used. The particle size and the like of these carbon blacks may be set arbitrarily, but may be appropriately selected from the electrical resistance and friction characteristics required for the medium and the output balance (surface roughness) at the shortest recording wavelength. However, a mixed system may be used, and the particle size distribution and the like can be selected independently. The average particle size of these carbon blacks is 10 to 400 nm, preferably 20 to 400 nm.
350 nm, more specifically, 20 to 40 nm is preferable when the electromagnetic conversion characteristics are considered preferentially, and when the frictional characteristics are emphasized, the particle size is as large as possible in the electromagnetic conversion characteristics in the range of 40 to 350 nm. Is preferably used. When selecting carbon black, it is necessary to consider not only the particle size but also the BET value and the DBP value.
Since the ET value and the DBP value are closely related to each other, it is not possible to make them independent numerical values. Therefore, these three factors are required characteristics of the medium and dispersion characteristics in the paint,
It is necessary to select it experimentally depending on the flow characteristics.

These carbon blacks are used in a weight ratio of 10 to 500 wt% with respect to the binder or 0.1 to 20 wt% with respect to the magnetic powder. It is necessary to select experimentally according to the dispersion characteristics and flow characteristics. These carbon blacks may be appropriately combined and used according to the required characteristics of the magnetic layer, the back coat layer, the underlayer and the like.
Further, these carbon blacks may be added simultaneously at the time of kneading or dispersing with the magnetic powder, or may be dispersed with a binder in advance and added at the time of dispersing the magnetic coating material. Further, these carbon blacks may be surface-treated with a lubricant, a dispersant, or the like, or a part of the surface thereof may be graphitized. The carbon black that can be used in the present invention can be referred to, for example, in "Carbon Black Handbook" (edited by Carbon Black Association).

When the carbon black is used in the present invention, it is naturally preferable that the amount of soluble ions is small.

Further, the magnetic paint may contain a non-ferromagnetic organic powder. As the non-ferromagnetic organic powder used, acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, phthalocyanine pigment, azo pigment, polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide system Resin powder, fluorohydrocarbon resin powder, divinylbenzene resin powder and the like can be mentioned. The non-ferromagnetic organic powder has a weight ratio of 0.1 to 20 w with respect to the binder.
Used in the range of t%.

When the non-ferromagnetic organic powder is used in the present invention, it is naturally preferable that the amount of soluble ions is small.

As a non-magnetic support coated with such a magnetic paint, polyethylene terephthalate (PE
T), polyesters such as polyethylene naphthalate (PEN), known films such as polyolefins, polyamide, polyimide, polyamide imide, polysulfone cellulose triacetate, and polycarbonate can be used, and preferably PET, PEN, aromatic Polyamide, more preferably PET or P
It is a composite film obtained by multi-layer coextrusion according to 2 to 3 types of EN or an aromatic polyamide, and when these films are used, it is easy to obtain a balance of electromagnetic conversion characteristics, durability, friction characteristics, film strength, and productivity.

To these non-magnetic supports, inorganic compounds such as oxides and carbonates of Al, Ca, Si and Ti, organic compounds such as fine particles of acrylic resin, etc. may be added as fillers. Preferably, it is possible to freely control the surface property by controlling the amount and the size, and it is possible to control the electromagnetic conversion characteristics, durability, friction characteristics and the like.

Further, these nonmagnetic supports may be previously subjected to corona discharge treatment, plasma discharge and / or polymerization treatment, easy adhesive coating treatment, dust removal treatment, relaxation treatment by heat and / or humidity control, and the like. .

The center line surface roughness of these non-magnetic supports must be 0.03 μm or less, preferably 0.02 μm or less, and more preferably 0.01 μm or less. These non-magnetic supports are required. It is preferable that not only the center line average surface roughness is small, but also there is no coarse protrusion of 0.5 μm or more.

The so-called F-5 value in the tape running direction and the tape width direction of the non-magnetic support is preferably 5.
It is generally about 50 Kg / mm ² , and the F-5 value in the tape longitudinal direction is generally higher than the F-5 value in the tape width direction, but especially the strength in the width direction is increased like a consumer DVT tape. It may be necessary. The heat shrinkage rate of the non-magnetic support in the tape 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 rate at 80 ° C. for 30 minutes is preferably. Is less than 1%,
More preferably, it is 0.5% or less.

The breaking strength of the non-magnetic support is preferably 5 to 100 kg / mm ^{2 in} both directions, and the elastic modulus is 10
0 to 2000 kg / mm ² is preferable.

In the present invention, the form of the non-magnetic support is not particularly limited, and may be in the form of tape, film, sheet, card, disk, drum or the like, and the thickness of the non-magnetic support is also applicable. The optimum one is selected accordingly.

As one aspect of the present invention, at least one lower layer is provided between the non-magnetic support and the magnetic layer. The lower layer includes so-called underlayer, non-magnetic layer and the like. In the lower layer, in addition to the magnetic powder or the non-magnetic powder, the binder, the lubricant, the abrasive used in the formation of the magnetic layer,
It can be formed by appropriately adding additive components such as an antistatic agent and a dispersant, kneading and dispersing in an organic solvent. In the present invention, when such a lower layer is provided, the total soluble sodium ion elution concentration from the lower layer and the upper magnetic layer when the lower layer contacts water is 200 ppm or less, and sodium / potassium ion. It is assumed that the ratio is 1 to 4.

The magnetic powder used in this lower layer is
Examples thereof include iron oxide magnetic powder, ferromagnetic metal powder, plate-shaped hexagonal ferrite, and chromium dioxide.

As the non-magnetic powder contained in this lower layer,
The above-mentioned inorganic compound may be used, and its shape may be any, but it is preferably acicular. When the powder having a needle shape is used, the surface smoothness of the lower layer can be improved, and the surface smoothness of the magnetic layer laminated thereon can also be improved. The powder has an average major axis diameter of less than 0.3 μm, preferably less than 0.20 μm and an average minor axis diameter of less than 0.05 μm, preferably less than 0.03 μm. The axial ratio of powder is usually 2
It is -15, preferably 3-10. The axial ratio as used herein refers to the ratio of the average major axis diameter to the average minor axis diameter (average major axis diameter / average minor axis diameter). BET of non-magnetic powder
The specific surface area by the method is about 10 to 250 m ² / g,
It is preferably 20 to 150 m ² / g.

It is also preferable that the non-magnetic powder is surface-treated with a Si compound and / or an Al compound. By passing through the surface treatment step, the amount of soluble ions is reduced, and when the surface-treated non-magnetic powder is used, the surface condition of the upper layer which is the magnetic layer can be improved. As the content of Si and / or Al,
0.1 to 10% by weight of both Si and Al with respect to the non-magnetic powder
It is preferred that This lower layer has a dry film thickness of 0.3 to
It is coated on the non-magnetic support so as to have a thickness of about 3.0 μm.

A magnetic layer having a dry film thickness of 0.0 is formed on the lower layer.
It is applied so as to have a thickness of about 8 to 1.0 μm. Further, a known back coat layer may be appropriately provided on the surface (back surface) of the non-magnetic support on which the magnetic layer is not provided, for the purpose of improving the running property of the magnetic recording medium, preventing charging and preventing transfer. preferable. It is preferable that the amount of soluble ions in the back coat layer is also equal to or less than that of the magnetic layer.

Next, the manufacturing process of the magnetic recording medium of the present invention will be described.

First, the step of producing the magnetic coating material for 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, if necessary.

Each step may be divided into two or more stages, and the raw material may be divided and added in two or more steps.

Various kneading machines can be used for kneading the magnetic paint. Examples of this kneader include a two-roll mill, a three-roll mill, an open kneader, a continuous twin-screw kneader, a continuous single-screw kneader, a pressure kneader, and a planetary mixer; a high-speed impeller is a high-speed impeller. Dispersers, high speed stone mills, dispersers, high speed mixers, homogenizers and the like;
As a media agitation mill, ball mill, pepper mill,
Examples include a Kobol mill, a sand grinder, a pin type mill, an ultra fine mill, an attritor and a basket mill.

When a continuous kneader or a pressure kneader is used, all or part of the ferromagnetic powder and the binder (however, 30 wt% or more of the total binder is preferable) and 15 to 500 wt% with respect to 100 wt% of the ferromagnetic powder. It is kneaded within the range.

Further, it is desirable to use a dispersion medium having a high specific gravity in dispersing the paint that can be used in each step, and the above-mentioned ceramic medium such as zirconia is suitable.

The coating material is applied onto the long, film-like non-magnetic support drawn out from the unwinding roll by various known coating means such as gravure coating, reverse roll coating and extrusion nozzle coating.

Generally, before coating with a coating material, the non-magnetic support is subjected to wet cleaning using water, a solvent, etc. for the purpose of cleaning and surface adjustment, and dry cleaning using a non-woven fabric or ultrafine fiber fabric as a wiper. , Is treated by various known means such as non-contact cleaning using compressed air, vacuum, ionized air, etc., for the purpose of improving the adhesion of the coating material to the non-magnetic support and the coating surface, etc. Various known non-contact surface treatments such as electric discharge, ultraviolet ray irradiation, and electron beam irradiation are often performed.

Further, an undercoating agent such as a water-based undercoating agent, an emulsion-based undercoating agent and a solvent-based undercoating agent may be applied together with the above-mentioned surface treatment or alone for the purpose of improving the adhesiveness, etc. Instead of just the undercoat, a paint in which a non-ferromagnetic inorganic pigment or organic pigment is dispersed in a binder may be applied as the undercoat layer, or may be used in combination with the above surface treatment.

Generally, the magnetic layer is formed by coating alone,
It is possible to provide two or more layers in order to have more advanced functions. In that case, a magnetic layer or a non-ferromagnetic layer is formed by a known method such as a wet-on-dry method or a wet-on-wet method. You can do it.

After such a coating step, various treatments such as smoothing of the wet film surface of the magnetic coating material formed on the non-magnetic support and regulation of the coating film are usually carried out as the next step. As the smoothing means, a known method such as contacting with a film or bar of resin, metal or ceramics, a non-contact method such as a magnetic field by a permanent magnet or an electromagnet, a vibration by an ultrasonic wave or the like can be used. They can be used alone or in combination.

After the magnetic layer is formed, it is necessary to apply a magnetic field to orient the magnetic particles in the layer. The orientation direction is the longitudinal direction or the vertical direction with respect to the running direction of the medium. The magnetic field may be oblique, and a magnetic field may be applied in a predetermined direction of 1000 G or more by a permanent magnet such as a ferrite magnet or a rare earth magnet, an electromagnet, a solenoid or the like in order to orient in a predetermined direction, or a plurality of these magnetic field generation means may be used in combination. It is also preferable to perform an appropriate drying step before orientation so that the orientation after drying becomes the highest, or to perform orientation and drying at the same time. In this case, the magnetic powder naturally oriented by coating may be made as non-oriented as possible by a permanent magnet, electromagnet, solenoid or the like.

The magnetic coating material which has been subjected to the post-coating treatment in this manner is usually subjected to known drying and evaporation means such as hot air, far infrared rays, an electric heater, a vacuum device, etc. provided inside a drying furnace or the like. Alternatively, it is dried and fixed by a known curing device such as an ultraviolet lamp or a radiation irradiation device.

The drying temperature is in the range of room temperature to about 300 ° C., and may be appropriately selected depending on the heat resistance of the non-magnetic support, the solvent species, the concentration, and the like, and a temperature gradient may be provided in the drying furnace. As the gas atmosphere in the drying furnace, general air or inert gas may be used.

When drying with an ultraviolet lamp or a radiation irradiating device, a curing reaction occurs, so in consideration of post-processing, it is better to use other drying means as much as possible.

Irradiation of ultraviolet rays or radiation with the solvent still contained may cause ignition or smoke.
Also in this case, it is preferable to use other drying means together as much as possible.

After drying the magnetic layer in this way, if necessary, calendering is carried out as a surface smoothing treatment. As a calendering roll, heat resistance of epoxy, polyester, nylon, polyimide, polyamide, polyimide amide, etc. can be used. Plastic rolls (carbon,
A metal or other inorganic compound may be kneaded) and a combination of metal rolls (combination of 3 to 7 stages), or metal rolls may be used for treatment.
The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, and the linear pressure is preferably 200.
kg / cm, more preferably 300 kg / cm or more, and the speed is in the range of 20 m / min to 700 m / min.
After the calendar treatment, in order to accelerate the curing of the magnetic layer, the back coat layer and the non-magnetic layer, a heat curing treatment at 40 ° C. to 80 ° C. and / or an electron beam irradiation treatment may be performed.
Then, the magnetic recording medium is formed into a predetermined shape and further subjected to secondary processing.

Thereafter, if necessary, burnishing or blade processing is performed for slitting.

[0130]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but it goes without saying that the scope of the present invention is not limited thereby.

The characteristics of the metal magnetic powder sample and the magnetic recording medium in this example were evaluated according to the following criteria.

[Characteristic evaluation of metal magnetic powder] [Solution of sodium ion and potassium ion] Pure water 2
0 ml was placed in a Pyrex beaker, 1 g of the sample was added thereto, and the beaker was sealed. After maintaining this at a temperature of 80 ° C. for 1 hour, ultrasonic dispersion was carried out for 1 hour, then the sample was filtered, and the filtrate was analyzed by an atomic absorption method according to a conventional method to obtain 1 g of each sample.
The sodium ion and potassium ion elution concentrations from water to water were measured.

[Sodium / potassium ion ratio] The ratio was determined from the above measurement.

[Alkali Metal Ion Ratio] Using the filtrate in which the elution amounts of sodium and potassium ions were measured, the elution amounts of calcium ions and magnesium ions were determined by ICP. The ratio of the total elution concentration of (Na ⁺ and K ⁺ ) to the total elution concentration of (Na ⁺ , K ⁺ , Ca ²⁺ and Mg ²⁺ ) is taken as the alkali metal ion ratio.

[Coercive Force Hc, Saturation Magnetization σs] Using a VSM manufactured by Toei Industry Co., Ltd., magnetic measurement was performed with an applied magnetic field of 10 KOe to measure coercive force (Hc) and saturation magnetization (σs).

[Stability with Time] Change in saturation magnetization after storage for 7 days in a dry environment at a temperature of 60 ° C. {Δσs =
[(After storage σs-before storage σs) / before storage σs] × 100
(%)} Was measured.

[Magnetic Powder Permeability] A sample of 50 g was put in a cylindrical basket (a wire mesh with a sieve opening of 1190), the basket was rotated at a rotation speed of 700 rpm to crush the sample, and the transmittance of the basket from the sieve was measured. I asked.

[Characteristic Evaluation of Magnetic Recording Medium] [Dispersion Gloss] GLDSS METER GM-3D (Murakami Color Research Laboratory) was used and measured at an incident angle of 60 ° C.

[Viscosity at Dispersion] Shear rate 3000 of the coating material after being dispersed for 30 minutes by a sand mill and after being dispersed for 3 hours.
The apparent viscosity of ^-1 / sec was measured with a cone-plate type viscometer (cone angle: 0.5 degree).

[Magnetic Characteristics] Using VSM manufactured by Toei Industry Co., Ltd., magnetic measurement was performed with an applied magnetic field of 10 KOe to measure coercive force (Hc) and squareness ratio Br / Bm.

[Electromagnetic conversion characteristics] The following characteristics were measured using a Hi-8 deck (EVS-900 manufactured by Sony Corporation).

[0142] · 7M-OUT: 7MH was measured a recording signal playback output of the wavelength of the _Z. Ref at this time is TDK-r
ef was performed by a tape (only Example 4 5MH _Z).

Y-S / N: A video signal of 50% luminance level was recorded / reproduced and measured with a video noise meter. At this time, ref was performed with a TDK-ref tape.

C-OUT: The reproduction output of the chroma signal was measured.

C-S / N: 100% chroma signal was superposed on a video signal of 50% luminance level and recorded, and AM component was measured by a video noise meter.

[Soluble Ion Properties] (1) Sodium Ion and Potassium Ion Elution Concentration In a polypropylene container containing 10 ml of pure water, the magnetic layer of the sample tape was completely immersed in an amount of 1 g. Placed and sealed. This was placed in a constant temperature bath at a temperature of 60 ° C. and kept for 1 week. Then, the supernatant was taken and the elution concentration of sodium ion and potassium ion from 1 g of each magnetic tape to water was measured by an atomic absorption method by a usual method. (2) Sodium ion / potassium ion ratio The ratio was determined by the above measurement.

[Increase in Storage DO, Deterioration of Electromagnetic Conversion Characteristics] The produced magnetic tape was stored in a cassette state for 5 days in an environment of a temperature of 50 ° C. and 80% RH. Recording and reproduction were performed before storage, and reproduction and recording and reproduction were performed at the same place after storage, and dropout and 7 MHz output were measured.

For the dropout, the same EVS-900 (manufactured by Sony Corporation) as the deck whose electromagnetic conversion characteristics were measured was used, and 10 μsec / −16 dB and 3 μsec / −10 d were used.
B was measured. The measurement time was 10 minutes, and the average value of 6 measurements was obtained. For the deterioration of electromagnetic conversion characteristics, the output difference of the electromagnetic conversion characteristics before and after storage was calculated.

[Clog Occurrence Rate] 60% at 0 ° C. and 20 ° C.
After recording the full length of each magnetic tape 108m of RH and 40 ° C. 80% RH, and repeating the full length of 50 times, the decrease in RF output of 3 dB or more for 1 minute or more under each environment was taken as a clogging, The number of the samples was counted, and the ratio with respect to all the measured samples was obtained as the occurrence rate.

(Example 1-1) FeCl ₂ .4H ₂ O
1000 g (5.0 mol) was dissolved in 10 liters of H ₂ O kept at 45 ° C., and cobalt chloride (Co
Cl ₂ ) was dissolved and stirred and mixed so that the amount of Co was 20.0% by weight with respect to Fe. To this solution, (NH ₄ ) ₂
865 g (9.0 mol) of CO _{3 was} added to 10 liters of H
A 45 ° C. aqueous solution dissolved in ₂ O was gradually added while stirring to form a suspension, and after completion, the mixture was stirred and mixed for 60 minutes.

While maintaining the temperature of this suspension at 45 ° C.,
The stirring was continued for 6 hours while blowing air at a flow rate of 10 l / min. Thereafter, the mixture was allowed to cool to room temperature and filtered, the residue was washed with water, and dried at 60 ° C. for 24 hours to obtain needle-shaped iron oxyhydroxide.

100 g of the obtained iron oxyhydroxide was put into 6 liters of H ₂ O and mixed with stirring, and yttrium chloride (YCl ₃ .6H ₂ O) was added thereto in an amount of Y of 8.0 with respect to Fe. Add 1 liter of an aqueous solution dissolved so as to have a weight% and mix with stirring.
An aqueous OH solution was added and mixed with stirring. Next, aluminum chloride (AlCl ₃ ) was added in an amount of 7.0% by weight relative to Fe.
1 liter of an aqueous solution dissolved so that the pH was 8 was added, and further, an aqueous NaOH solution was added so that the pH became 8.
After sufficiently stirring this, it was filtered off, the residue was washed with water, and then dried.

The iron oxyhydroxide thus obtained was heat-treated at 600 ° C. for 1 hour in a nitrogen atmosphere.

Next, 50 g of this was sampled and the temperature was 480 ° C.
Reduction was performed at a hydrogen flow rate of 1 liter / min for 6 hours.
Then, after cooling it to room temperature, air is gradually poured into nitrogen gas to form a slow oxidation film on the surface of the magnetic powder,
A metallic magnetic powder was obtained. Magnetic powder sample No. Set to 1.

The obtained magnetic powder sample No. 1 is TEM
From the photograph, the average major axis length (L) = 0.13 μm, the axial ratio (L
w) = 7. The magnetic powder sample No. The Co amount, Al amount, and Y amount in 1 were confirmed by ICP emission analysis. Further, from the results of ESCA and the like, it was found that Al and Y were mainly present on the powder surface.

(Examples 1-2, 1-3, 1-7) Magnetic powder sample No. 1, except that the cobalt chloride content was adjusted so that the Co content was 30, 40, and 50% by weight relative to Fe, respectively. 2, 3 and 7 were obtained.

Comparative Example 1-4 FeCl ₂ .4H ₂ O
1000 g (5.0 mol) was dissolved in 10 liters of H ₂ O kept at 45 ° C., and cobalt chloride (Co
Cl ₂ ) was dissolved and stirred and mixed so that the amount of Co was 20.0% by weight with respect to Fe. To this solution, Na ₂ CO ₃
930 g (8.8 mol) and NaOH 50 g (1.2
5 mol) dissolved in 10 liters of H ₂ O at 45 ° C
While gradually adding the aqueous solution of (1), the mixture was stirred to form a suspension, and after completion, the mixture was stirred for 60 minutes.

While maintaining the temperature of this suspension at 45 ° C.,
The stirring was continued for 6 hours while blowing air at a flow rate of 10 l / min. Thereafter, the mixture was allowed to cool to room temperature, filtered, and the residue was washed with water and dried at 60 ° C. for 24 hours to obtain acicular iron oxyhydroxide, which was then treated in the same manner as in Example 1-1 to prepare a comparative magnetic powder sample No. ． Got 4.

(Comparative Examples 1-5 and 1-6) Comparative magnetic powder sample No. 4, cobalt chloride (CoCl ₂ ) was added to C
The above comparative magnetic powder sample N except that the addition amounts were adjusted so that the amounts of o were 30 and 40% by weight with respect to Fe, respectively
o. Comparative Magnetic Powder Sample No. 5 and 6 were obtained.

Comparative Example 1-8 Comparative magnetic powder sample No.
4, K ₂ C instead of 930 g of Na ₂ CO ₃
The above comparative magnetic powder sample No. ₃ was used except that 1,210 g of O ₃ was used. Comparative Magnetic Powder Sample No. Got 8.

The above magnetic powder sample No. 1-3 and 7,
And comparative magnetic powder sample No. 4-6 and 8 were used to evaluate the properties of the metallic magnetic powder according to the above criteria. The results are shown in Tables 1 and 2.

Production of Magnetic Recording Medium The magnetic powder sample No. 1-3 and 7, and comparative magnetic powder sample No. Using 4 to 6 and 8, a magnetic recording medium (magnetic tape) was produced.

That is, after a part or all of the following magnetic layer composition was kneaded with each of the above-mentioned metal magnetic powder samples by a kneader, ceramic beads (ZrO _{2) were used} as a dispersion medium.
-Y ₂ O ₃ 99 parts by weight or more and SiO ₂ 0.04 parts by weight or less) were dispersed, mixed and diluted with a sand mill to prepare each magnetic coating material.

3.3 parts by weight of a curing agent (Coronate L; manufactured by Nippon Polyurethane Industry Co., Ltd.) was mixed and added to each of the obtained magnetic paints, and the surface roughness (Ra) was adjusted so that the dry thickness was 2.5 μm. On polyethylene terephthalate having a thickness of 12 nm (thickness: 7.5 μm), followed by orientation treatment, drying, and calendar treatment. Further, a back coat having the following composition was applied on the opposite side of the magnetic layer so as to have a dry thickness of 0.5 μm, and heat-cured after calendering.

The thus-prepared original fabric was cut into a magnetic tape having a width of 8 mm. (Magnetic layer composition) Metal magnetic powder 100.0 parts by weight Vinyl chloride copolymer 8.3 (MR-110; manufactured by Nippon Zeon Co., Ltd.) Polyester polyurethane 8.3 (UR8700; manufactured by Toyobo Co., Ltd.) α-alumina (HIT60A; manufactured by Sumitomo Chemical Co., Ltd.) 8.0 (containing 10 ppm of soluble sodium ion) (containing 2 ppm of soluble potassium ion) stearic acid 1.0 butyl stearate 1.0 methyl ethyl ketone 111.0 toluene 111.0 cyclohexanone 74. 0 (Backcoat layer composition) Carbon black-180.0 (Sc Ultra: Colombian Carbon Co., Ltd.) (Average particle size 21 nm, BET220 m ² / g) (Soluble sodium ion 17 ppm contained) (Soluble potassium ion 9 ppm contained) Carbon Black-2 1.0 ( MT-CI: manufactured by Colombian Carbon Co., Ltd. (average particle size 350 nm, BET 8 m ² / g) (containing soluble sodium ion 46 ppm) (soluble potassium ion 27 ppm contained) α-iron oxide (manufactured by Toda Kogyo Co., Ltd. 100ED) 1. 0 (Average particle size 0.1 μm) Vinyl chloride copolymer A 40.0 (MPR-TA, manufactured by Nisshin Chemical Industry Co., Ltd.) (vinyl chloride-vinyl acetate-vinyl alcohol copolymer, average degree of polymerization 420) Chloride Vinyl Copolymer B 25.0 (manufactured by Nissin Chemical Industry Co., Ltd., MPR-ANO (L)) (vinyl chloride-vinyl acetate-vinyl alcohol copolymer, nitrogen atom 390 ppm content, average degree of polymerization 340) Polyester polyurethane 35 .0 (TS9555: manufactured by Toyobo (Ltd.)) (-SO ₃ Na content, a number average molecular weight 40000) Methyl ethyl ketone 700.0 toluene 4 00.0 Cyclohexanone 300.0 Using this magnetic tape, each property was evaluated according to the above criteria. The results are shown in Tables 1 and 2.

[0166]

[Table 1]

[0167]

[Table 2] (Example _{2-1) FeCl 2 · 4H 2 O} 1000g
10 liters of H (5.0 mol) kept at 45 ° C
This was dissolved in ₂ O, and cobalt chloride (CoCl ₂ ) was dissolved in this so that the amount of Co was 25.0% by weight with respect to Fe, and the mixture was stirred and mixed. To this solution, 930 g of Na ₂ CO ₃
(8.8 mol) and NaOH 50 g (1.25 mol)
Was gradually added to an aqueous solution of 45 ° C. dissolved in 10 liters of H ₂ O and stirred to form a suspension, which was further stirred and mixed for 60 minutes.

While maintaining the temperature of this suspension at 45 ° C.,
The stirring was continued for 6 hours while blowing air at a flow rate of 10 l / min. Thereafter, the mixture was allowed to cool to room temperature and filtered, the residue was washed with water, and dried at 60 ° C. for 24 hours to obtain needle-shaped iron oxyhydroxide.

100 g of the obtained iron oxyhydroxide was put into 6 liters of H ₂ O and mixed with stirring, and neodymium chloride (NdCl ₃ .6H ₂ O) was added thereto in an amount of 10.0 with respect to Fe. An aqueous solution of 1 liter dissolved so as to have a weight% was added and mixed with stirring, and further, an aqueous NaOH solution was added to adjust pH to 8 and mixed with stirring. Next, sodium silicate (Na ₂ SiO ₃ ) was added to the Fe content of 2.
0 wt%, sodium aluminate (Na ₃ AlO ₃ ) was dissolved in 1 liter of an aqueous solution so that the amount of Al was 4.0 wt% with respect to Fe, and a NaOH aqueous solution was further added to adjust the pH to 8. Was added. This was thoroughly stirred, filtered and dried at 120 ° C.

Further, this residue was washed with tap water kept at 45 ° C. until the Na / K ion ratio of the filtrate became constant, and then dried again at 120 ° C. This sample is designated as G-1.

The iron oxyhydroxide (Sample G-1) thus obtained was heat-treated at 600 ° C. for 1 hour in a nitrogen atmosphere to obtain α-iron oxide.

Next, 50 g of this was sampled and the temperature was 480 ° C.
Reduction was performed at a hydrogen flow rate of 1 liter / min for 6 hours.
Then, after cooling to room temperature, air was gradually poured into nitrogen gas to form a slow-oxidation film on the surface of the magnetic powder to obtain a metal magnetic powder sample. Magnetic powder sample No. Set to 9.

(Example 2-2) Magnetic powder sample No. In the water washing of No. 9, distilled water was used instead of tap water (Sample G-
2) After that, reduction and oxidation treatments were performed in the same manner as above to obtain magnetic powder sample N0.10.

(Example 2-3) In Example 2-1
Sample G-1 was heat-treated at 300 ° C. for 1 hour in a nitrogen atmosphere to obtain α-iron oxide. The α-iron oxide was washed with tap water kept at 45 ° C. until the Na / K ion ratio of the filtrate became constant, and then dried again at 120 ° C. (Sample α-1).

After that, the magnetic powder sample No. In the same manner as in No. 9, magnetic powder sample No. I got 11.

(Example 2-4) Magnetic powder sample No. 11
In washing with water, magnetic powder sample N was obtained in the same manner as above except that distilled water was used instead of tap water (sample α-2).
We obtained 0.12.

(Example 2-5) Magnetic powder sample No. 11
A magnetic powder sample N0.13 was obtained in the same manner as described above, except that the heat treatment temperature in the nitrogen atmosphere of 300 ° C. was changed to 600 ° C. (Sample α-3).

(Example 2-6) Magnetic powder sample No. 11
At a heat treatment temperature of 300 ° C. in a nitrogen atmosphere of 60 ° C.
A magnetic powder sample N0.14 was obtained in the same manner as above, except that the temperature was changed to 0 ° C. and the washing was performed using distilled water instead of tap water (Sample α-4).

(Example 2-7) Magnetic powder sample No. 11
A magnetic powder sample N0.15 was obtained in the same manner as described above except that the heat treatment temperature of 300 ° C. in the nitrogen atmosphere was changed to 900 ° C. (Sample α-5).

(Example 2-8) Magnetic powder sample No. 11
At a heat treatment temperature of 300 ° C. in a nitrogen atmosphere at 90 ° C.
A magnetic powder sample N0.14 was obtained in the same manner as above, except that the temperature was changed to 0 ° C. and the washing was performed using distilled water instead of tap water (Sample α-6).

(Comparative Example 2-9) Sample α-3 (Example 2-
50 g of α-iron oxide (No. 5) was collected and reduced to magnetite at a temperature of 480 ° C. and a hydrogen flow rate of 1 liter / min. Then, after cooling to room temperature, it is washed with tap water kept at 45 ° C. until the Na / K ion ratio of the filtrate does not change, dried and then dried at a temperature of 480 ° C. and a hydrogen flow rate of 1 liter / mi.
n, and then air is gradually poured into nitrogen gas to form a slow-oxidation film. 17
I got

(Comparative Examples 2-10 and 11) 50 g of sample α-3 (α-iron oxide in Example 2-5) was sampled and reduced at a temperature of 480 ° C. and a hydrogen flow rate of 1 liter / min. Then, after cooling to room temperature, air is gradually poured into nitrogen gas to form a slow oxidation film on the surface of the magnetic powder. 19 (Comparative Example 2-11) was obtained.

Further, this comparative magnetic powder No. 19 to 45
The filtrate was washed with tap water kept at 0 ° C until the Na / K ion ratio of the filtrate remained unchanged, and dried at 120 ° C to obtain a comparative magnetic powder sample N0.18 (Comparative Example 2-10).

The above magnetic powder sample No. 9 to 16, Comparative Magnetic Powder Sample No. Using 17 to 19, a magnetic recording medium (magnetic tape) was manufactured in the same manner as in Example 1. Using this magnetic tape, each characteristic was evaluated in accordance with the above criteria. The results are shown in Tables 3 and 4.

[0185]

[Table 3]

[0186]

[Table 4] (Example 3-1) FeCl ₂ .4H ₂ O 1000 g
10 liters of H (5.0 mol) kept at 45 ° C
This was dissolved in ₂ O, and cobalt chloride (CoCl ₂ ) was dissolved in this so that the Co content was 10.0 wt% with respect to Fe, and the mixture was stirred and mixed. 1000g of NaOH in this solution
An aqueous solution of (25.0 mol) dissolved in 10 liters of H ₂ O at 45 ° C. was gradually added while stirring to obtain a suspension, which was further stirred and mixed for 60 minutes.

While maintaining the temperature of the suspension at 45 ° C., 10
The stirring was continued for 6 hours while blowing air at a flow rate of 1 / min. Thereafter, the mixture was allowed to cool to room temperature and filtered, the residue was washed with water, and dried at 60 ° C. for 24 hours to obtain needle-shaped iron oxyhydroxide.

100 g of the obtained iron oxyhydroxide was put into 6 liters of H ₂ O and mixed with stirring, and neodymium chloride (NdCl ₃ .6H ₂ O) was added thereto in an amount of 5.0 with respect to Fe. 1 liter of an aqueous solution dissolved so as to have a weight% was added, and the mixture was stirred and mixed.
An aOH aqueous solution was added and mixed with stirring. Next, sodium silicate (Na ₂ SiO ₃ ) was added to the Si content of 2.0 with respect to Fe.
Wt%, sodium aluminate (Na ₃ AlO ₃ ) A
An aqueous solution of 1 liter dissolved so that the amount of 1 was 3.0% by weight with respect to Fe was added, and further an aqueous solution of NaOH was added so that the pH became 8. After stirring this well,
It was filtered off and dried at 120 ° C.

Further, this residue was washed with tap water kept at 45 ° C. until the Na / K ion ratio of the filtrate became constant, and then dried at 120 ° C. again. This sample is designated as G-3.

The iron oxyhydroxide (Sample G-3) thus obtained was heat-treated in a nitrogen atmosphere at 600 ° C. for 1 hour to obtain α-iron oxide.

Next, 50 g of this was sampled, and the temperature was 480 ° C.
Reduction was performed at a hydrogen flow rate of 1 liter / min for 6 hours.
Then, after cooling to room temperature, air was gradually poured into nitrogen gas to form a slow-oxidation film on the surface of the magnetic powder to obtain a metal magnetic powder sample. Magnetic powder sample No. 20.

(Example 3-2) Magnetic powder sample No. 20
In washing with water, distilled water was used instead of tap water (Sample G
-4), and thereafter, reduction and oxidation treatments are performed in the same manner as above,
A magnetic powder sample N0.21 was obtained.

(Example 3-3) In Example 3-1,
Sample G-3 was heat-treated in a nitrogen atmosphere at 300 ° C. for 1 hour to obtain α-iron oxide. The α-iron oxide was washed with tap water kept at 45 ° C. until the Na / K ion ratio of the filtrate became constant, and then dried again at 120 ° C. (Sample α-7).

After that, the magnetic powder sample No. In the same manner as No. 20, magnetic powder sample No. I got 22.

(Example 3-4) Magnetic powder sample No. 22
In the washing with water, magnetic powder sample N was obtained in the same manner as above except that distilled water was used instead of tap water (Sample α-8).
0.23 was obtained. (Example 3-5) Magnetic powder sample No. The heat treatment temperature of 300 ° C. in the nitrogen atmosphere of No. 22 was changed to 600 ° C. (Sample α
Magnetic powder sample N0.
I got 24.

(Example 3-6) Magnetic powder sample No. 22
At a heat treatment temperature of 300 ° C. in a nitrogen atmosphere of 60 ° C.
A magnetic powder sample N0.25 was obtained in the same manner as above, except that the temperature was changed to 0 ° C. and distilled water was used instead of tap water for washing (sample α-10).

Comparative Example 3-7 Sample α-7 (Example 3-)
50 g of α-iron oxide (3) was collected and reduced to magnetite at a temperature of 480 ° C. and a hydrogen flow rate of 1 liter / min. Then, after cooling to room temperature, it is washed with tap water kept at 45 ° C. until the Na / K ion ratio of the filtrate does not change, dried and then dried at a temperature of 480 ° C. and a hydrogen flow rate of 1 liter / mi.
n, and then air is gradually poured into nitrogen gas to form a slow-oxidation film. 26
I got

(Comparative Examples 3-8 and 9) 50 g of a sample α-7 (α-iron oxide of Example 3-3) was sampled at a temperature of 480 ° C.
Reduction was performed at a hydrogen flow rate of 1 liter / min. Then, after cooling to room temperature, air is gradually poured into nitrogen gas to form a slow oxidation film on the surface of the magnetic powder. 28 (Comparative Example 3-9) was obtained.

Further, this comparative magnetic powder No. 28 to 45
The filtrate was washed with tap water kept at 0 ° C until the Na / K ion ratio of the filtrate did not change, and dried at 120 ° C to obtain a comparative magnetic powder sample N0.27 (Comparative Example 3-8).

The above magnetic powder sample No. 20 to 25, comparative magnetic powder sample No. Using 26 to 28, a magnetic recording medium (magnetic tape) was produced in the same manner as in Example 1. Using this magnetic tape, each characteristic was evaluated in accordance with the above criteria. The results are shown in Tables 5 and 6.

[0201]

[Table 5]

[0202]

[Table 6] (Examples 4-1 and 4-2) Magnetic powder sample No. 10, 1
4, the magnetic powder sample No. 4 was obtained in the same manner as in the above cases, except that the Co content was changed from 25% to 7% with respect to Fe. 29 and 30 were obtained.

(Comparative Example 4-3) Comparative magnetic powder sample No.
19, the comparative magnetic powder sample N was prepared in the same manner as described above except that the Co content was changed from 25% to 7% with respect to Fe.
o. I got 31.

The above magnetic powder sample No. 29, 30, comparative magnetic powder sample No. A magnetic recording medium (magnetic tape) was produced in the same manner as in Example 1 using No. 31. However, when making the magnetic paint, it was dispersed with a sand mill after stirring with a high speed mixer instead of a kneader. The magnetic layer thickness is 2.
The thickness was changed from 5 μm to 1.5 μm.

Using this magnetic tape, each characteristic was evaluated in accordance with the above criteria (provided that the output of electromagnetic conversion characteristics was 5 MHz). The results are shown in Table 7.

[0206]

[Table 7] (Example 5-1) Magnetic powder sample No. Example 1 using ceramic beads (99 parts by weight or more of ZrO _{2 and} less than 0.04 parts by weight of SiO ₂ ) as a dispersion medium.
Single layer magnetic recording medium (magnetic tape)
Was produced.

(Example 5-2) Magnetic powder sample No. No. 1 was used, and hard glass beads (SiO ₂
72 parts by weight, CaO 17 parts by weight, MgO 18 parts by weight, A
A single-layer magnetic recording medium (magnetic tape) was produced in the same manner as in Example 1 using 13 parts by weight of 1 ₂ O _{3, 3} parts by weight of ZrO _{2, and} 1 part by weight of TiO.

(Comparative Example 5-3) Comparative magnetic powder sample No.
19 and ceramic beads (Z
rO ₂ 99 parts by weight or more, SiO ₂ less than 0.04 parts by weight)
A single-layer magnetic recording medium (magnetic tape) was manufactured using the same as in Example 1.

(Example 5-4) Magnetic powder sample No. Thirteen
Using hard glass beads (SiO 2) as a dispersion medium.
₂ 72 parts by weight, CaO 17 parts by weight, MgO 18 parts by weight,
A single-layer magnetic recording medium (magnetic tape) was produced in the same manner as in Example 1 using 13 parts by weight of Al ₂ O _{3, 3} parts by weight of ZrO _{2, and} 1 part by weight of TiO.

(Comparative Example 5-5) Magnetic powder sample No. 9 and ceramic beads (ZrO ₂
A single-layer magnetic recording medium (magnetic tape) was produced in the same manner as in Example 1 using 99 parts by weight or more and less than 0.04 parts by weight of SiO ₂ .

Using the above magnetic tapes, the respective characteristics were evaluated according to the above criteria. Table 8 shows the results.

[0212]

[Table 8] (Example 6-1) Magnetic powder sample No. 3, and magnetic beads (ZrO ₂ 99 parts by weight or more, SiO ₂ less than 0.04 parts by weight) were used as a dispersion medium to prepare a magnetic layer component (magnetic paint) having the following composition.

Further, the following non-magnetic lower layer coating material (dispersion medium: ceramic beads ZrO ₂ 99 parts by weight or more,
SiO ₂ (less than 0.04 parts by weight), and using the above magnetic paint and two extrusion nozzles, a magnetic layer thickness of 0.2 μm,
A non-magnetic lower layer was applied by a wet-on-wet method so as to have a thickness of 2.0 μm (dry thickness), followed by orientation, drying and calendering, and then a magnetic tape was produced.

(Example 6-2) Magnetic powder sample No. 3 was used as a dispersion medium for hard glass beads (SiO ₂
72 parts by weight, CaO 17 parts by weight, MgO 18 parts by weight, A
13 parts by weight of 1 ₂ O _{3, 3} parts by weight of ZrO _{2, and} 1 part by weight of TiO) were used to prepare a magnetic layer component (magnetic paint) having the following composition.

Further, in the same manner as in Example 6-1, after producing the non-magnetic lower layer coating material shown below, wet-on was performed so that the magnetic layer thickness was 0.2 μm and the non-magnetic lower layer thickness was 2.0 μm (dry thickness). A magnetic tape was produced after applying by a wet method and then performing orientation, drying and calendering.

(Comparative Example 6-3) Comparative magnetic powder sample No.
6 and ceramic beads (Zr
Using at least 99 parts by weight of O _{2 and} less than 0.04 parts by weight of SiO ₂ , a magnetic layer component (magnetic paint) having the following composition was prepared.

Further, in the same manner as in Example 6-1, the following non-magnetic lower layer coating material was prepared and then wet-on was performed so that the magnetic layer thickness was 0.2 μm and the non-magnetic lower layer thickness was 2.0 μm (dry thickness). A magnetic tape was produced after applying by a wet method and then performing orientation, drying and calendering.

(Example 6-4) Comparative magnetic sample No. 6, magnetic powder sample No. 6 was obtained in the same manner as above, except that a washing step with distilled water was added after drying before α-oxidation. Three
2 was obtained. Using this sample, as a dispersion medium, ceramic beads (ZrO ₂ 99 parts by weight or more, SiO ₂ 0.0
Using less than 4 parts by weight), a magnetic layer component (magnetic paint) having the following composition was prepared.

Further, in the same manner as in Example 6-1, the following non-magnetic lower layer coating material was prepared and then wet-on so that the magnetic layer thickness was 0.2 μm and the non-magnetic lower layer thickness was 2.0 μm (dry thickness). A magnetic tape was produced after applying by a wet method and then performing orientation, drying and calendering.

(Example 6-5) Similarly, comparative magnetic sample N
o. 6, magnetic powder sample No. 6 was obtained in the same manner as above, except that a washing step with tap water was added after α-formation.
I got 33. Using this sample, ceramic beads (99 parts by weight or more of ZrO ₂ , SiO ₂ 0.
(Less than 04 parts by weight) was used to prepare a magnetic layer component (magnetic paint) having the following composition.

Further, in the same manner as in Example 6-1, after producing the non-magnetic lower layer coating material shown below, wet-on was performed so that the magnetic layer thickness was 0.2 μm and the non-magnetic lower layer thickness was 2.0 μm (dry thickness). A magnetic tape was produced after applying by a wet method and then performing orientation, drying and calendering.

(Example 6-6) Magnetic powder sample No. 20
Using, the magnetic tape was produced in the same manner as in Example 6-1.

(Example 6-7) Magnetic powder sample No. 28
Using, the magnetic tape was produced in the same manner as in Example 6-1. However, in the magnetic paint, both the vinyl chloride copolymer and the polyester polyurethane were changed from 8.3 parts by weight to 20 parts by weight.

(Example 6-8) Magnetic powder sample No. 28
Using, the magnetic tape was produced in the same manner as in Example 6-1. However, 10 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the non-magnetic lower layer coating material immediately before coating. (Magnetic layer composition) Metal magnetic powder 100.0 parts by weight Vinyl chloride copolymer 8.3 (MR-110; manufactured by Nippon Zeon Co., Ltd.) Polyester polyurethane 8.3 (UR8700; manufactured by Toyobo Co., Ltd.) α-alumina (HIT60A; manufactured by Sumitomo Chemical Co., Ltd.) 5.0 (containing 10 ppm of soluble sodium ion) stearic acid 1.0 butyl stearate 1.0 methyl ethyl ketone 111.0 toluene 111.0 cyclohexanone 74.0 (non-magnetic layer composition) Needle-shaped α-iron oxide powder (long axis length 0.15 μm, BET53m ² / g, containing 70 ppm of Na ion) 100.0 parts by weight Vinyl chloride copolymer 8.3 (MR-110; manufactured by Nippon Zeon Co., Ltd.) ) Polyester polyurethane 4.2 (UR8700; manufactured by Toyobo Co., Ltd.) Polyester polyurethane 4.2 ( UR8200; manufactured by Toyobo Co., Ltd. α-alumina (HIT60A; manufactured by Sumitomo Chemical Co., Ltd.) 5.0 stearic acid 1.0 butyl stearate 1.0 methyl ethyl ketone 88.0 toluene 88.0 cyclohexanone 60.0 Using the magnetic tapes obtained as described above, each characteristic was evaluated according to the above criteria. The results are shown in Table 9,
It shows in Table 10. In the table, the amount of soluble ions in the magnetic recording medium was measured for both the magnetic layer and the nonmagnetic layer.

[0225]

[Table 9]

[0226]

[Table 10]

[0227]

As described in detail above, according to the present invention, in a magnetic recording medium having a magnetic layer containing a magnetic metal powder provided on a non-magnetic support, sodium eluted from 1 g of the magnetic layer into water. Ion concentration is 200ppm or less and sodium / potassium ion ratio (elution concentration ratio)
To provide a magnetic recording medium capable of forming a magnetic layer without lowering dispersibility and maintaining high electromagnetic conversion characteristics before storage even under high temperature and high humidity storage. There is an effect that can be.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Yutaka Takahashi 1-13-1, Nihonbashi, Chuo-ku, Tokyo TDC Corporation (72) Inventor Ryosuke Isobe 1 Sakura-cho, Hino-shi, Tokyo Konica Stock Company

Claims (6)

[Claims] 1. A magnetic recording medium comprising a magnetic layer containing a magnetic metal powder provided on a non-magnetic support, wherein the concentration of sodium ions eluted from 1 g of the magnetic layer into water is 20.
A magnetic recording medium, which is 0 ppm or less and has a sodium / potassium ion ratio (elution concentration ratio) of 1 to 4. 2. The metal magnetic powder contains iron (Fe) as a main component and contains 6 to 40 wt% of cobalt (C) with respect to Fe.
a metal magnetic powder containing o), wherein the concentration of sodium ions eluted from 1 g of the metal magnetic powder into water is 40
The magnetic recording medium according to claim 1, which is 0 ppm or less and has a sodium / potassium ion ratio (elution concentration ratio) of 100 or less. 3. The metallic magnetic powder is produced by adding an alkali carbonate-free alkali carbonate to a Co-added ferrous salt solution to produce FeCO ₃ , which is then contacted with an oxygen-containing gas to form iron oxyhydroxide. 3. The magnetic recording medium according to claim 1, which is obtained by dehydration, heat treatment, and reduction. 4. The metallic magnetic powder is produced by adding alkali carbonate to a ferrous salt solution containing Co to produce FeCO ₃ , which is then contacted with an oxygen-containing gas to form iron oxyhydroxide, and then dehydrated. And then water washing-heat treatment or heat treatment-
The magnetic recording medium according to claim 1 or 2, which is obtained by reducing after any treatment with water. 5. The magnetic layer is formed by adding an alkali metal-free alkali carbonate to a Co-added ferrous salt solution to form F.
The metal magnetic powder obtained by generating eCO ₃ , contacting it with an oxygen-containing gas to form iron oxyhydroxide, dehydrating it, then heat treating it and then reducing it is dispersed in a dispersion medium containing no alkali metal. Claim 1 obtained by
4. The magnetic recording medium according to any one of 3 to 3. 6. The magnetic layer, wherein FeCO ₃ is produced by adding an alkali carbonate to a Co-added ferrous salt solution, and the FeCO ₃ is contacted with an oxygen-containing gas to form iron oxyhydroxide,
The metal magnetic powder obtained by dehydration, and then treatment with water-heat treatment or heat treatment-water washing, and reduction, is obtained by dispersing with a dispersion medium containing no alkali metal. 2. The magnetic recording medium according to any one of 2 and 4.