JPS631003A - Magnetic powder - Google Patents

Abstract

PURPOSE:To improve properties of dispersion, packing and orientation, by setting the specific surface of magnetic powder by a BET method to be a specified value or above, and by setting the concentration on the surface of a particle of the powder to be within specified limits. CONSTITUTION:It is preferable that the specific surface of magnetic powder by a BET method is 60 m<2>/g or above and that the Concentration of hydroxyl on the surface of a particle thereof is within the limits of 2-10 pieces/nm<2>. As to the magnetic powder whose specific surface by the BET method is smaller than 60 m<2>/g, it is impossible to diminish sufficiently the noise of a magnetic recording medium obtained by using this powder and also to make the surface smoothness of a magnetic layer excellent sufficiently. Moreover, if hydroxyl on the surface of a particle has too lower concentration than two pieces/nm<2>, it can not be combined firmly enough with the functional group of resin of a binder. If the concentration is too higher than 10 pieces/nm<2> to the contrary, the hydroxyl has an undesirable effect on the properties of dispersion, packing and orientation of the magnetic powder. By setting the specific surface by the BET method and the concentration on the surface of a particle to be the aforesaid values; accordingly, excellent properties of dispersion, packing, etc. can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic powder suitable for use in magnetic recording media, and more particularly to the aforementioned magnetic powder that has excellent dispersibility, filling properties, and orientation.

[Conventional technology]

Generally, magnetic powder is mixed and dispersed with a binder component, an organic solvent, and other necessary components to cleave the magnetic paint.
For magnetic recording media made by coating and drying this on a substrate such as a polyester film, it is preferable that the magnetic powder is well dispersed, filled, and further oriented in the magnetic layer. The better the dispersibility, filling properties and orientation of the material, the better the electromagnetic properties and the durability.

For this reason, various attempts have been made to improve the dispersibility, filling properties, and orientation of magnetic powder used in magnetic recording media. to have a relatively large amount of hydroxyl groups,
By creating a strong bond with the functional group of the binder resin,
Efforts have been made to improve the dispersibility, filling properties, and orientation of magnetic powders.

(Problems to be Solved by the Invention) However, when using a conventionally commonly used magnetic powder with a specific surface area of 50 m/g or less by the 13ET method, the higher the hydroxyl group concentration on the powder particle surface, the more the dispersibility becomes , the filling properties and orientation are improved, and the hydroxyl group b1 degree is too high, which does not adversely affect the properties, filling properties and orientation of the magnetic powder, but it improves the electromagnetic properties. Therefore, using a fine amount of magnetic powder, this ?Ii
The concentration of hydroxyl groups on the surface of powder particles was determined by
If the specific surface area measured by the ET method is equal to that of a magnetic powder of 50 m/g or less, the concentration per unit volume of hydroxyl groups present on the surface of the fine powder particles will be too high (too high, and the dispersibility, filling properties, and orientation of the magnetic powder will be reduced). This tendency becomes more pronounced as the magnetic powder is made into finer particles, and when the particles have a specific surface area of 60 m2/g or more by the BET method, the dispersibility, filling property, and orientation of the magnetic powder are impaired. The magnetic recording medium obtained using this method has disadvantages in that the electromagnetic properties are rather deteriorated and the durability is also deteriorated.

[Means for solving problems]

This invention was made as a result of various studies to solve these problems, and the specific surface area according to the BET method was 60.
The hydroxyl group concentration on the particle surface of magnetic powder of m/g or more is 2 to 1.
0 (solid/nm), the dispersibility, filling properties, and orientation of the fine magnetic powder can be sufficiently improved, and the electromagnetic properties and durability of the magnetic recording medium obtained using the fine magnetic powder can be sufficiently improved. This is to ensure that the performance is sufficiently improved.

The magnetic powder in the present invention preferably has a specific surface area of 60 nr/g or more by the BET method, and a concentration of hydroxyl groups on the particle surface in the range of 2 to 10 pieces/nm. If the surface area is smaller than 60 m/g, it will not be possible to sufficiently reduce the noise of the magnetic recording medium obtained by using it, or the surface smoothness of the magnetic layer will be sufficiently smooth, resulting in poor electromagnetic properties. cannot be improved sufficiently. In addition, if the concentration of hydroxyl groups on the particle surface is lower than 2 hydroxyl groups/nl, it will not be possible to form a sufficiently strong bond with the functional groups of the binder fat, and on the other hand, if it is higher than 10 hydroxyl groups/nl, However, too many hydroxyl groups have an unfavorable effect on the dispersibility, filling properties, and orientation of the magnetic powder, and in either case, the dispersibility, filling properties, and orientation of the magnetic powder cannot be sufficiently improved. Therefore, it is preferable that the specific surface area measured by the BET method is 60 m/g or more, and the concentration of hydroxyl groups on the particle surface is within the range of 2 to 10 pieces/nl, and the concentration of hydroxyl groups on the particle surface is further within the range of 3 to 10 pieces/nl. Within the range of 91 hard/nl, 3 to 71
Solid/nr+? It is more preferable to keep it within the range of .

As described above, the concentration of hydroxyl groups on the particle surface of magnetic powder having a specific surface area of 60 i/g or more by the ET method is determined by the fact that hydrophilic compounds and hydrophobic compounds are deposited on the particle surface of this type of fine magnetic powder. By adjusting the amount of these hydrophilic compounds and hydrophobic compounds,
The concentration of hydroxyl groups on the particle surface is adjusted within the range of 2 to 10 (solid/nm).

In this way, the concentration of hydroxyl groups on the particle surface of magnetic powder is
Examples of hydrophilic compounds that adhere to the particle surface of the magnetic powder to improve the condition include cobalt oxide, nickel oxide,
Examples include calcium oxide, aluminum oxide, chromium oxide, zinc oxide, titanium oxide, and other inorganic oxides. These hydrophilic compounds can be attached to the particle surface by dissolving water-soluble compounds such as cobalt sulfate, nickel nitrate, calcium chloride, aluminum sulfate, chromium chloride, zinc chloride, and titanium chloride in water. After dividing the magnetic powder, these hydrophilic compounds are applied to the surface of the magnetic powder particles by adding alkali or acid, and then this is heated at a temperature of 100 to 1000°C. Cobalt oxide, nickel oxide,
Hydrophilic compounds such as calcium oxide, aluminum oxide, chromium oxide, zinc oxide, and titanium oxide are deposited on the surface of the magnetic powder particles. At this time, if the magnetic powder is iron oxide magnetic powder or metal magnetic powder obtained by heating reduction of iron oxyhydroxide or iron oxide or oxidizing it after reduction, these powders are processed at the stage of iron oxyhydroxide or iron oxide. The hydrophilic compound can also be easily deposited on the surface of the particles of the magnetic powder by depositing a hydrate of the hydrophilic compound and then reducing them by heating or oxidizing them after reduction.

Examples of the hydrophobic compound that adheres to the surface of the magnetic powder particles include hydrophobic silica, hydrocarbons, and surfactants. The adhesion of these hydrophobic compounds to the particle surface can be achieved, for example, by adding silicon compounds such as sulfur and lithium orthosilicate, sodium metasilicate, potassium metasilicate, and water glasses of various compositions to an alkaline aqueous solution.
After dispersing the magnetic powder in this solution, it is neutralized by blowing carbon dioxide gas or adding acid to form a hydrate of these hydrophobic compounds on the particle surface of the magnetic powder. This is then heated at a temperature of 100 to 1000° C. to make it hydrophobic, so that hydrophobic silicon oxide is deposited on the surface of the magnetic powder particles. On this occasion,
Magnetic powder heat-reduces iron oxyhydroxide or iron oxide,
Alternatively, in the case of iron oxide magnetic powder or metal magnetic powder obtained by oxidation after reduction, hydrates of these hydrophobic compounds are deposited at the iron oxyhydroxide or iron oxide stage, and then this is After heating at a temperature of 100 to 1000°C to make them hydrophobic, they are subjected to thermal reduction or reduction 1&
A hydrophobic compound is easily adhered to the particle surface of the magnetic powder by oxidation. It is also possible to make the surface of the magnetic powder obtained by thermal reduction or oxidation after reduction hydrophobic by coating it with a hydrophobic hydrocarbon or a surfactant, but inorganic materials are more effective. preferable.

The hydrophilic compound and the hydrophobic compound may be attached to the surface of the magnetic powder particles depending on the hydroxyl group concentration on the surface of the magnetic powder particle to which they are attached. , or both may be applied at the same time. The concentration of hydroxyl groups on the surface of the magnetic powder particles is adjusted by the amount of these hydrophilic compounds and hydrophobic compounds deposited, and when the hydrophilic compounds are deposited, the concentration of hydroxyl groups on the surface of the magnetic powder particles increases. When a hydrophobic compound is deposited, the concentration of hydroxyl groups on the surface of the magnetic powder particles decreases.

In this way, a hydrophilic compound, a hydrophobic compound, etc. are coated on the surface of the powder particles of magnetic powder, and the specific surface area is 6 by the BET method with the concentration of hydroxyl groups on the particle surface being within the range of 2 to 10 pieces/nl. On? The magnetic powder having a weight of more than / g is not particularly limited, but examples include Fe, metal magnetic powder containing mainly Fe and various metals added, and C.

, metal magnetic powder such as Ni, or alloy magnetic powder thereof, r-Fe203 powder, Fe3O4 powder, r-Fe
Intermediate iron oxide powder of 203 and Fe3O4, Co-containing rFe
Suitable examples include 2O3 powder, CO-containing Fe3O4 powder, barium ferrite magnetic powder, and barium ferrite magnetic powder added with various metals.

As described above, the specific surface area measured by the BET method is 60 m/g or more, and the concentration of hydroxyl groups on the particle surface is 2 to 10 pieces/n.
Magnetic powder within the range of An improved magnetic recording medium is obtained.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 20 g of goethite powder with an average major axis of 0.25 μm and an axial ratio (major axis/minor axis) of 15/1 was dispersed in an IN NaOH aqueous solution 21, and 25 mj of 0.5 mol/l aluminum sulfate was added to this. was added and carbon dioxide gas was blown into the powder while sufficiently dispersing it, thereby depositing alumina hydrate on the surface of the goethite powder. Next, this was thoroughly washed, dried, and fired in air at 300°C. Next, 20 g of Matai I powder was added to the alumina coating after firing in 11 lN-Na.
It was dispersed in an OH aqueous solution, 10 ml of 1 mol/l sodium orthosilicate was added, and the mixture was stirred. After stirring thoroughly, add this 1
Carbon dioxide gas was blown into the suspension to neutralize it to a pH of 10 or less to form a two-layer coating of alumina hydrate and silicic acid hydrate on the surface of the hematite powder particles. Then 700℃
The silicic acid hydrate was hydrophobized by heating at a temperature of 2 hours.

Next, the Hemaqui powder, which has alumina hydrate and a hydrophobized silica film formed on the particle surface, was heated in a hydrogen stream.
The particles were thermally reduced at 500° C. for 4 hours to obtain metal iron magnetic powder having an alumina coating and a hydrophobicized silica coating on the particle surface. This metallic iron magnetic powder has a coercive force of 1600
Elstent', saturation magnetization is 120 emu/g,
The specific surface area by BET method was 65 g/g. In addition, the amount of alumina deposited is 5% by weight in terms of the atomic W weight ratio of Al/Fe, and the deposited amount of hydrophobized silica is 0.8% by weight in terms of the Si/Fe atomic weight ratio. %Met. Furthermore, the concentration of hydroxyl groups on the particle surface is 6/nlT?
Met. Using the metal iron magnetic powder thus obtained, 100 parts by weight of metal iron magnetic powder VAGH
(Manufactured by U, C, C, vinyl chloride 10-vinyl acetate-vinyl alcohol copolymer) Bandesox T-5201 (Dai 6, manufactured by Nippon Ink Chemical Co., Ltd., polyurethane) Myristic acid 5 JIS-5
00 (manufactured by Asahi Denka Co., Ltd., power 1〃〃-Bon black) Methyl isobutyl ketone 85/1-luene 85'' was placed in a 3j!'gi steel cracked ball mill,
This was rotated for 72 hours to ensure good dispersion to prepare a magnetic paste. Then, add 4 toluene to this magnetic paste.
0 parts by weight and Coronate Japan Polyurethane Industry Association,
A magnetic paint was prepared by further adding 2 parts by weight of a trifunctional low molecular weight isocyanate compound. Apply this magnetic paint to a thickness of 1
It was coated on a 2 μm polyester film to a dry coating thickness of 4 μm, dried, mirror-finished, and then cut into 1/2 inch width to produce a magnetic tape.

Example 2 Average major axis 0.05 μm, plate ratio (major axis/minor axis) 3/l,
Retention cuff 50 oersted, saturation magnetization 55 emu/g
, 100 g of barium ferrite powder with a specific surface area of 61 m/g by the BET method was added to an I N -N a OH aqueous solution 2β
It was suspended and dispersed well. Next, add 1 mol/! ! Sodium orthosilicate 3Q Qmj! In addition,
Aerate carbon dioxide gas while stirring well to bring the pH of the solution to 9.
I made it below. After washing with water and drying, this was heat-treated in air at 700°C for 2 hours to make the silicic acid hydrate on the surface hydrophobic. The barium ferrite thus obtained has a coercive force of 750 e and a saturation magnetization of 52 e.
mu/g, and the specific surface area by the BET method was 60 m/g, and the amount of hydrophobized silica deposited was 3.2% by weight in ff1 (l ratio) of Si/barium ferrite. The hydroxyl group concentration was 611 N/nn? Then, a magnetic tape was produced in the same manner as in Example 1 using the barium ferrite powder thus obtained.

Comparative Example 1 A coercive force of 1580 oersted and a saturation magnetization of 122 e were prepared in the same manner as in Example 1, except that the hydrophobic treatment of the silicic acid hydrate coated on the surface was omitted.
mu/g, specific surface area by BET method is 66 m
/ g, the amount of alumina deposited is 5% by weight in atomic weight ratio of AI/Fe, and the amount of deposited silicic acid hydrate is Si / g.
A metal iron magnetic powder with an atomic weight ratio of Fe of 0.8% by weight and a hydroxyl group concentration on the particle surface of 12/nm,
I made magnetic tape.

Comparative Example 2 In Example 2, the wave tube treatment on the surface of barium ferrite powder particles of hydrated silicic acid and the hydrophobization treatment of hydrated silicic acid were omitted, and the composition of the magnetic paint used in Example 2 was omitted. In place of the magnetic powder, a material with a coercive force of 750 oersted, a saturation magnetization of 55 emu/g, a specific surface area of 61 m/g by the BET method, and a hydroxyl group concentration on the particle surface of 1
A magnetic tape was produced in the same manner as in Example 2 except that barium ferrite powder of 1/nm was used.

Comparative Example 3 In Example 1, instead of the goethite powder with an average major axis of 0.25 μm and an axial ratio (major axis/minor axis) of 15/1, Dekui 1 powder with an average major diameter of 0.55 μm and an axial ratio of 15/1 was used. The same procedure was used as in Example 1 except that the coercive force was 1020 oersted, the saturation magnetization was 136 emu/g, and B
The specific surface area measured by the ET method is 35 rrr/g, the amount of alumina deposited is 5% by weight in atomic weight ratio of A I / Fe, and the deposited amount of hydrophobized silica is S i / F
The atomic weight ratio of e is 0.8% by weight, and the concentration of hydroxyl groups on the particle surface is 7/n rr? We obtained metallic iron magnetic powder and made magnetic tape.

Comparative Example 4 In Example 2, the average major axis was 0.05 μm, the plate ratio (major axis/minor axis) was 3/1, the coercive cuff was 50 oersted, the saturation magnetization amount was 55 emu/g, and the specific surface area by BET method was 61 r+? /g of barium ferrite powder instead of
The same procedure as in Example 2 was used except that barium ferrite having an average major axis of 0.2 μm, a plate ratio of 3/1, a coercive force of 370 oersted, a saturation magnetization of 57 emu/g, and a specific surface area of 29 m/g by the BET method was used. The coercive force is 395 oersted, the saturation magnetization is 56 emu/g, the specific surface area by BET method is 28 m/g, and the amount of hydrophobic silica deposited is 0.8 in the weight ratio of Si/barium ferrite. Barium ferrite powder with a weight percent and a hydroxyl group concentration on the particle surface of 6/nm was obtained, and a magnetic tape was made.

Regarding the magnetic tapes obtained in each example and comparative example,
The squareness ratio, residual magnetic flux density, durability, and surface smoothness of the magnetic layer were investigated. The squareness ratio was measured in Example 1. For Comparative Examples 1 and 3, the squareness ratio in the horizontal direction was measured, and for Comparative Examples 1 and 3, the squareness ratio in the horizontal direction was measured.
For Comparative Examples 2 and 4, the squareness ratio in the vertical direction was measured. Furthermore, durability was determined by measuring the time until the output decreased by 3 dB when still images were reproduced using a commercially available VTR in a constant temperature room at -5°C. Furthermore, the surface smoothness was measured using a stylus-type roughness meter at a stylus speed of 0.06 cm.
The surface roughness (C, L, A,) of the magnetic layer was measured under the conditions of 0.08 mm cutoff and 0.08 mm cutoff, and the relative value calculated according to the formula below based on Example 1 was used to determine the quality of the surface smoothness. judged.

Table 1 below shows the results.

〔Effect of the invention〕

As is clear from Table 1 above, the magnetic tapes obtained using the magnetic powders obtained in Examples 1 and 2 (Examples 1 and 2) were all similar to those obtained in Comparative Examples 1 to 4. Compared to the magnetic tapes obtained using magnetic powder (Comparative Examples No. 4 to 4), the squareness ratio and residual magnetic flux density are higher, the durability is better, and the surface smoothness is also better. The magnetic powder obtained by the invention has excellent dispersibility, filling property, and orientation. As a result of the improved dispersibility, filling property, and orientation of the magnetic powder, if this magnetic powder is used, electromagnetic It can be seen that a magnetic recording medium with further improved physical characteristics and durability can be obtained.

Claims (1)

[Claims] 1. The specific surface area by BET method is 60 m^2/g or more,
and the concentration of hydroxyl groups on the powder particle surface is 2 to 10 pieces/nm^
Magnetic powder characterized by being within the range of 2.