JPH02250902A - Acicular crystallized iron alloy magnetic particle powder for magnetic record - Google Patents

Abstract

PURPOSE:To manufacture the subject magnetic particle powder improving wetting and releasing in binder by containing B, Co, Al and Ni near surfaces of acicular crystallized goethite particles. CONSTITUTION:The surfaces of the acicular crystallized goethite particles having uniform particle size and mixing no dendrite particles, are coated with B compound (KBO2, etc.), Co compound (CoSO4, etc.), Al compound [Al(SO4)3, etc.] and/or Ni compound (NiSO4, etc.). Successively, this is heated and treated at about 300-600 deg.C to make the particles coated with the respective oxide of B, Co, Al and/or Ni, and further, this is heated and reduced at about 300-500 deg.C to obtain the acicular crystallized iron alloy magnetic particle powder containing B, Co, Al and/or Ni near the surfaces of the particles. By this method, the particle powder having coercive force and saturation magnetization and excellent oxidation stability, S.F.D. and wetting and releasing into the binder particularly containing resin having acidic functional group, is obtd. and suitable to the high density record and high output.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a high coercive force and a large saturation magnetization, and has excellent oxidation stability and S, F, and D, and furthermore, a binder, In particular, it is an object of the present invention to provide acicular iron alloy magnetic particles which have good dispersibility due to their excellent wetting to and loosening of binders containing resins having acidic functional groups.

[Conventional technology]

In recent years, as magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for higher performance magnetic recording media such as magnetic tapes and magnetic disks. That is, high-density recording, high output characteristics, and especially improved frequency characteristics are required. The characteristics of magnetic particles suitable for satisfying the above requirements for magnetic recording media are that they have high coercive force and large saturation magnetization.

In recent years, magnetic particles suitable for high output and high density recording,
That is, the development of magnetic particles having high coercive force and large saturation magnetization is active, and as magnetic particles having such characteristics, acicular goethite particles or acicular hematite particles are prepared in a reducing gas. Acicular iron alloy magnetic particles obtained by thermal reduction are known and have been put into practical use.

The coercive force of acicular iron alloy magnetic particles depends on the particle shape, especially the axial ratio (long axis: short axis), and the larger the axial ratio (long axis: short axis), the higher the coercive force. Moreover, the saturation magnetization tends to increase as the reduction temperature increases and the reduction progresses.

As the reduction progresses, the saturation magnetization improves, but on the other hand,
Since the shape of the particles is distorted and the coercive force decreases, there is an inverse correlation between the two, so there is a strong demand for acicular iron alloy magnetic particles that have both a high coercive force and a large saturation magnetization.

As mentioned above, the acicular iron alloy magnetic particles have a high coercive force and large saturation magnetization, but the acicular iron alloy magnetic particles used for magnetic recording media have a 1μ-
Because they are very fine particles, their surface activity is very high, and when they are taken out into the air after reduction, they rapidly react with oxygen in the air, causing heat generation and ignition, making them extremely unstable. At the same time, since the oxidation reaction turns into an oxide, the magnetic properties, especially the saturation magnetization, are significantly reduced, making it difficult to obtain the desired acicular iron alloy magnetic particles having a large saturation magnetization. Therefore, it is strongly required to have excellent oxidation stability.

In recent years, there has been an unstoppable demand for improved properties of acicular iron alloy magnetic particles, and in addition to having the above-mentioned high coercive force and large saturation magnetization, and excellent oxidation stability, Furthermore, S, F, D, (Switching F
There is a strong demand for excellent yield distribution. This fact is
No. 6821, ``Figure 1 is a diagram showing the relationship between S, F, D, and recording/reproducing output measured for the above magnetic disk....S, P, D, and recording/reproducing output. As is clear from Figure 1, the relationship between the outputs is a straight line, and it can be seen that by using ferromagnetic powder with small S, F, and D, the recording and reproducing output increases.In other words, the recording and reproducing output increases. In order to achieve high output, it is preferable that S, F, and D are smaller.
,D, is required. ” as stated.

By the way, resins with OH groups that have been widely used as resins for magnetic recording media require the presence of a large amount of dispersant in order to disperse the magnetic particles in the binder. It has been pointed out that the dispersant remaining in the coating affects surface properties such as viscosity of the coating film, and problems such as poor operation during use due to changes in environmental temperature, etc. have been pointed out. Therefore, in recent years, there has been a trend to reduce the amount of dispersant mixed in the binder as much as possible, and various studies have been conducted on the type of resin, the surface properties of the magnetic particles, etc. As the resin, instead of the above-mentioned resin having an OH group, Coon group, 5O
Resins with 4Na groups are being used, and for magnetic particle powder, binders containing resins with acidic functional groups such as C0OH groups and SoaNa groups are used to improve dispersibility in the binder. There is a strong demand for improvement in wetting and loosening with.

In the past, various attempts have been made to improve the properties of acicular iron alloy magnetic particles. For example, acicular goethite particles and acicular hematite particles, which are the starting materials, are pretreated with cobalt compounds. A method of heating and reducing after coating with
B-55203), a method in which starting material particles are coated with a boron compound in advance and then thermally reduced (JP-A-54-
57459, JP 54-42832, JP 58-48611, JP 58-46607
No. 1, JP-A-59-32881, JP-A-59-
5603, JP 61-174304, JP 61-186410, JP 59-3288
No. 1) and the starting materials are a water-soluble boron compound and AI,
A method of coating with a water-soluble salt of Cr, Ge, or Nd and then heating and reducing it (Japanese Unexamined Patent Publication No. 186410/1983) is known.

[Problem to be solved by the invention]

It has high coercive force and large saturation magnetization, and has excellent oxidation stability and S, F, and D, and also has a binder,
In particular, acicular iron alloy magnetic particles, which have good dispersibility due to good wetting and loosening in binders containing resins with acidic functional groups, are currently in the greatest demand. , the present inventor has already found that it has high coercive force and large saturation magnetization, and also has oxidation stability and S, F, D,
Acicular iron alloy magnetic particles with excellent properties have been obtained (Japanese Patent Application No. 118585).

That is, the acicular iron alloy magnetic particle powder contains boron and cobalt near the particle surface, and contains S, F, and D.
is 0.50 or less, acicular iron alloy magnetic particles,
Acicular hematite is obtained by coating the particle surface of acicular goethite particles with a boron compound and a cobalt compound, and then heat-treating the particles in a temperature range of 300 to 600°C to coat them with boron oxide and cobalt oxide. The particles are obtained by thermally reducing the acicular hematite particles.

Therefore, the technical object of the present invention is to improve the wetting and loosening of the above-mentioned acicular iron alloy magnetic particles in a binder, particularly in a binder containing a resin having an acidic functional group.

[Means to solve problems]

The present inventor has found that it has high coercive force and large saturation magnetization, and has excellent oxidation stability and s, p, and o, and furthermore,
The present invention was achieved as a result of various studies on a method for obtaining acicular iron alloy magnetic particles that have excellent wetting and peeling properties in binders, especially binders containing resins with acidic functional groups. It is.

That is, the present invention is an acicular iron alloy magnetic particle powder for magnetic recording comprising acicular iron alloy magnetic particles containing boron, cobalt, aluminum or nickel, or the preceding metal near the particle surface.

[For production]

First, the most important point in the present invention is that the particle surface of the acicular goethite particles is coated with a boron compound, a cobalt compound, an aluminum compound or a nickel compound, or both compounds, and then heated in a temperature range of 300 to 600°C. Processing to obtain acicular hematite particles coated with boron oxide and cobalt oxide and aluminum oxide or nickel oxide or the gastric oxide, and then 300 to 500 acicular hematite particles When the heat reduction is carried out in the temperature range of ``C'', it is possible to obtain acicular iron alloy magnetic particles containing boron and cobalt and aluminum or nickel or the preceding metal near the particle surface. The acicular iron alloy magnetic particle powder containing boron and cobalt and aluminum or nickel or the pre-metal in the vicinity of the surface has high coercive force and large saturation magnetization, and also has oxidation stability and S, F and D are excellent, and the dispersibility is also good due to the excellent wetting and loosening of binders, especially binders containing resins with acidic functional groups. .

In the present invention, the acicular iron alloy magnetic particle powder containing aluminum near the particle surface has a large amount of resin adsorption, as shown in the examples below, It can be seen that the wetting into the resin-containing binder is excellent.

In the present invention, the acicular iron alloy magnetic particles containing nickel near the particle surface have excellent initial dispersion as shown in the examples below, and therefore are suitable for use in resins, especially acidic functional groups. It can be seen that the dissolution into the binder containing the resin is excellent.

The acicular iron alloy magnetic particles of the present invention containing aluminum or nickel or the pre-metal near the particle surface have excellent gloss as shown in the Examples below, and are therefore suitable for resins, especially It has excellent dispersibility due to its excellent wetting and loosening properties in a binder containing a resin having an acidic functional group.

Next, various conditions for implementing the present invention will be described.

The acicular iron alloy magnetic particle powder of the present invention containing boron and cobalt and aluminum or nickel or the pre-metal in the vicinity of the particle surface has a structure in which the particle surface of the acicular goethite particles is combined with a boron compound, a cobalt compound and aluminum. compound or nickel compound or both compounds, and then heat treated in a temperature range of 300 to 600°C to coat with boron oxide and cobalt oxide and aluminum oxide or nickel oxide or the stomach oxide. It can be obtained by obtaining acicular hematite particles containing acicular crystals, and then reducing the acicular hematite particles by heating at a temperature range of 300 to 500°C.

The acicular goethite particles of the present invention are obtained by mixing a well-known ferrous salt aqueous solution and an equivalent or more alkaline solution, and preparing a suspension containing ferrous hydroxide particles at 80°C at a pH of 11 or higher. A method for carrying out an oxidation reaction by passing an oxygen-containing gas through the following temperature; and a method for carrying out an oxidation reaction by passing an oxygen-containing gas through a suspension containing FeC0ff obtained by reacting an aqueous ferrous salt solution with an alkali carbonate. Particles with long sleeves of 0.1 to 0.4 μm and an axial ratio (long axis: short axis) of 5:1 to 20:1 can be used. In the above goethite production reaction, Co5Ni, Zn, AI, which are usually added to improve the characteristics of the target acicular iron alloy magnetic particle powder, are
Metal ions such as Mn1Cu may also be present.

In order for the acicular iron alloy magnetic particles to have a preferable SJ, D, especially 0.47 or less, the particle size obtained by the latter method must be uniform, and the acicular iron alloy particles must be acicular with no dendritic particles mixed therein. Crystalline goethite particles may be used as starting material particles. In particular, particles with a uniform particle size and a major axis diameter of 0.18 to 0.3 μ- without dendritic particles mixed, and an axial ratio (
When acicular goethite particles with a large (major axis: minor axis) ratio of 10:1 or more are used as starting material particles,
Acicular iron alloy magnetic particles having more preferable S, F, and D values, especially 0.44 or less, can be obtained.

As the boron compound in the present invention, KBO□, H3B
O,, HBO□, B, 05, etc. can be used.

Coating of the acicular goethite particles with a boron compound can be carried out by mixing and stirring an aqueous solution containing boron and the acicular goethite particles, followed by heating and drying. The amount of boron compound coated is 1.5 to Fe in terms of B.
It is 10 mol%. If it is less than 1.5 mol%, sintering of particles and particles will occur, making it impossible to obtain acicular iron alloy magnetic particles having a high coercive force. 10
If the amount exceeds mol%, the progress of the reduction reaction is hindered, making it difficult to obtain acicular iron alloy magnetic particles.

As the cobalt compound in the present invention, cobalt sulfate, cobalt nitrate, cobalt acetate, cobalt chloride, cobalt hydroxide, etc. can be used. Coating of the acicular goethite particles with a cobalt compound is carried out by mixing and stirring an aqueous solution containing cobalt and the acicular goethite particles, or, if necessary, neutralizing with an alkaline aqueous solution, and then drying the mixture door-to-door. I can do it. The amount of the cobalt compound coated is 1.5 to 10 mol % based on Fe in terms of Co. When the content is 1.5 mol% or less, the saturation magnetization is 130 emu/g or less, S, F, and D are 0.50 or more, and it is difficult to obtain the acicular iron alloy magnetic particles that are the object of the present invention. Even if the amount is 10 mol % or more, it is possible to obtain the acicular iron alloy magnetic particles which are the object of the present invention, but there is no point in containing more than necessary.

As the aluminum compound in the present invention, aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum hydroxide, sodium aluminate, alumina sol, etc. can be used. Coating of the acicular goethite particles with an aluminum compound can be carried out by mixing and stirring an aqueous solution containing aluminum and the acicular goethite particles, or by neutralizing with an alkaline aqueous solution if necessary, and then drying the mixture. can. The amount of coating with the aluminum compound is 1.0 to 10°0 in terms of AI to Fe.
It is mole%. When the amount is 1.0 mol% or less, the wetting to the resin is insufficient, so the improvement in the amount of resin adsorption, which is the objective of the present invention, is not sufficient.When the amount is 10.0 mol% or more, the present invention Although the desired resin adsorption amount is improved, since the progress of reduction is hindered, it is difficult to obtain the desired acicular iron alloy magnetic particles having high coercive force and large saturation magnetization. It also takes a long time. When considering resin adsorption amount, coercive force and saturation magnetization, 1.0~
5.0 mol% is preferred.

As the nickel compound in the present invention, nickel sulfate, nickel nitrate, nickel chloride, nickel hydroxide, etc. can be used. The acicular goethite particles are coated with a nickel compound after mixing and stirring the nickel-containing aqueous solution and the acicular goethite particles, or if necessary,
This can be carried out by neutralizing with an alkaline aqueous solution, then separating in an oven and drying. The amount of coating with the nickel compound is 0.3 to 10.0 mol % based on Fe in terms of Ni.

If the amount is 0.3 mol% or less, the effect of lowering the reduction temperature cannot be obtained, and the separation of particles is still not sufficient, so the initial dispersion, which is the objective of the present invention, is not sufficiently improved.10.
When the amount is 0 mol% or more, the crystal magnetic anisotropy decreases, making it difficult to obtain acicular iron alloy magnetic particles having a high coercive force, and the saturation magnetization tends to decrease.

The particle surface of the acicular goethite particles in the present invention may be coated with a boron compound, a cobalt compound, an aluminum compound or a nickel compound, or both compounds in any order or at the same time.

The heating and firing temperature in the present invention is 300 to 600°C. If the temperature is below 300°C, it is difficult to increase the density of the particles, so the shape of the particles cannot be maintained during heating in the subsequent reduction process, and the coercive force of the acicular iron alloy magnetic particles decreases. Also, S, F, and D are reduced to 0.5
It cannot be:

The reason why S, F, and D are not improved is that if the firing temperature is 300°C or lower, recrystallization becomes insufficient, and the shape anisotropy due to the shape distribution of the particles after reduction is reduced. It is thought that this causes non-uniformity of crystal anisotropy due to uniformity and structural distribution of Fe, B, and Co. If the temperature is 600°C or higher, sintering occurs between the particles and between the particles, causing the particles to lose their shape.

The heating reduction temperature in the present invention is 300 to 500°C. If the temperature is 300° C. or lower, the reduction reaction is insufficient and it is impossible to obtain acicular iron alloy magnetic particles having large saturation magnetization. If the temperature is 500° C. or higher, sintering occurs between particles and particles, and the shape of the particles is distorted, so that the coercive force of the acicular iron alloy magnetic particles decreases.

The acicular iron alloy magnetic particle powder obtained in the present invention is
Long axis 0.1-0.4 pm, axial ratio (long axis: short axis) 5:
It is in the range of 1 to 15:1.

The acicular iron alloy magnetic particles powder after thermal reduction in the present invention can be obtained by a well-known method, for example, by immersing the powder in an organic solvent such as toluene, and after replacing the atmosphere after reduction with an inert gas. It can be taken out into the air by gradually increasing the oxygen content in it and finally slowly oxidizing it with air.

〔Example〕

Next, the present invention will be explained with reference to Examples and Reference Examples.

In addition, the long axis and axial ratio (long axis: short axis) of particles in the following Examples and Comparative Examples are shown as average values of numerical values measured from electron micrographs. The magnetic properties of the acicular iron alloy magnetic particles were measured using a vibrating sample magnetic force diameter VSM-33-15J (manufactured by Tofu Kogyo ■) and applying an external magnetic field of up to 10 KOe.The oxidation stability was measured at a temperature of 60 °C, relative humidity 90%
Saturation magnetization reduction rate (%) after being left for 7 days in the atmosphere of
It was shown in S, F, and D were measured using a sheet-like sample piece with a square shape of 0.85 obtained by the following method.
The differential circuit of the magnetic measuring instrument was used to obtain a differential curve of coercive force, the value was measured at the half value of this curve, and this value was determined by dividing the value by the coercive force at the peak value of the curve.

The sheet-like sample piece was prepared by placing the following ingredients in a 100 cc polyethylene bottle in the proportions shown below, then mixing and dispersing the mixture in a Red Devil for 8 hours, then applying the prepared magnetic paint onto a 25 μ-thick polyethylene terephthalate film using an applicator. The sample was coated to a thickness of 50 .mu.m using the following method, and then dried in a Gauss magnetic field for 3 to 5 days.

3■■φ Steel ball 800 parts by weight Iron alloy magnetic particle powder 100 parts by weight Polyurethane resin having sodium sulfonate group
20 parts by weight Cyclohexanone 83.3 parts by weight Methyl ethyl ketone 83.3 parts by weight Toluene 83.3 parts by weight 20g of crystalline iron alloy magnetic particle powder, 56g of resin liquid, and 120g of 3mmφ stainless steel pole were placed in a 100mj2 polyethylene bottle and dispersed for 60 minutes using a paint conditioner.The resulting paint was centrifuged, and the resin concentration of the supernatant liquid was determined. It is expressed as the difference from the weight when measured as non-volatile matter.

Adjustment of resin liquid Resin solid content 3.57%MEK
32.14% toluene
32.14% Anon
32.14% dispersibility is obtained by placing 15 g of acicular iron alloy magnetic particles, 50 g of the resin solution treated below, and 120 g of a stainless steel pole with 3 ends and 1 φ in a 100+ sl polyethylene bottle, and dispersing with paint conditioner for a specified period of time. , to promote the paint after dispersion? It is expressed as the glossiness of a coating film obtained by applying it onto a film using an applicator. The dispersion time until the gloss saturation was set as 100%, and the gloss at that time was shown as a measure of dispersibility, and the gloss when the dispersion time was 50% was shown as a measure of initial dispersion.

Resin Liquid Resin EK Toluene The glossiness of the cyclohexane coating film is the value measured with a gloss meter manufactured by Nippon Denshoku Kogyo Co., Ltd. with an incident angle of 601. The value when 89.0% is expressed as a percentage.

Surface coating of acicular goethite particle powder> Examples 1 to 1
9 Reference Examples 1 to 6; Example 1 100 g of acicular goethite particles with a long-sleeved 0.21 μm edge and an axial ratio (long axis: short axis) of 12:1 were suspended in 12 water.

I (JOs 10.0g (corresponds to 10.Owtχ for acicular goethite particles) to the above suspension.
Co(CI(ffcoθ)8 ・4HvO13,0g
(corresponds to 13, Owtχ for acicular goethite particles) Al(N(h)3・9)1t0 12g (corresponds to 12 wH for acicular goethite particles)
was added and stirred for 10 minutes. The pH of the suspension at this time was 4.4. Next, after adjusting the pH of the suspension to 9.3 by adding N)140H, the acicular α-Fe0011 particles were separated and dried to obtain acicular crystals coated with boron, cobalt, and aluminum. α-FeOOH particles were obtained.

Examples 2 to 19, Reference Examples 1 to 6 The type of acicular goethite particles, the type and amount of boron compound, the type and amount of cobalt compound, and the type and amount of aluminum compound or nickel compound or both compounds were varied. Acicular crystal α-PeOOH particles coated with various compounds were obtained in the same manner as in Example 1 except for the following changes.

The main manufacturing conditions and characteristics at this time are shown in Tables 1 and 2.

<Production of acicular hematite particles> Examples 20 to 38 Reference Examples 7 to 12; Example 20 50 g of acicular goethite particles coated with boron, cobalt, and aluminum obtained in Example 1 were A heat treatment was performed in air at 400° C. to obtain acicular hematite particles coated with boron oxide, cobalt oxide, and aluminum oxide.

As a result of electron microscopy observation, the particle powder had an average length of 0.19 μm and an axial ratio (long axis:short axis) of 11:1.

Examples 21 to 38, Reference Examples 7 to 12 Acicular hematite particles were obtained in the same manner as in Example 1, except that the temperature in the heating and firing step was varied.

The main manufacturing conditions and characteristics at this time are shown in Tables 3 and 4.

<Production of acicular iron alloy magnetic particles> Examples 39 to 57 Reference Examples 13 to 18; Example 39 Acicular crystals coated with boron oxide, cobalt oxide, and aluminum oxide obtained in Example 20 20 g of crystalline hematite particles were reduced in a hydrogen stream at 420°C for 6 hours to obtain acicular crystalline iron alloy magnetic particles.

A stable oxide film was applied to the surface of the obtained acicular iron alloy magnetic particles to prevent rapid oxidation when taken out into the air. As a result of fluorescent X-ray analysis, the obtained acicular iron alloy magnetic particles contained B at 4.7 mol% relative to Fe, Co at 4.5 mol% relative to Fe, and AI at 2.6 mol% relative to Pa. It contains mol%, and as a result of electron microscopic observation, the long axis is 0.15 μ plow, and the axial ratio (long axis: short axis) is 7.
:1. As for the magnetic properties, the coercive force He is 15400e.
, saturation magnetization ets was 133 emu/g, oxidation stability was 8.0%, and S, F, and D were 0.42.

Further, the resin adsorption amount was 1.4, and the dispersibility was 110 when the dispersion time was 50%, and 120 when the gloss was 100%.

Examples 40 to 57, Reference Examples 13 to 18 Acicular crystal iron alloy magnetic particles were produced in the same manner as in Example 39, except that the type of acicular hematite particles and the temperature in the heat reduction step were varied. Obtained.

The main manufacturing conditions and characteristics at this time are shown in Tables 5 and 6.

Table [Effects of the Invention] The acicular iron alloy magnetic particles according to the present invention have a high coercive force and a large saturation magnetization, as shown in the above examples,
In addition, it has excellent oxidation stability and S, F, and D, and has excellent dispersibility due to its excellent wetting and peeling to binders, especially binders containing resins with acidic functional groups. Since the powder particles have good properties, they are suitable as magnetic particles for high-density recording and high-output applications, which are currently most in demand.

Claims (3)

[Claims] (1) An acicular iron alloy magnetic particle powder for magnetic recording comprising acicular iron alloy magnetic particles containing boron, cobalt, and aluminum near the particle surface. (2) Acicular iron alloy magnetic particle powder for magnetic recording, comprising acicular iron alloy magnetic particles containing boron, cobalt, and nickel near the particle surface. (3) Acicular iron alloy magnetic particle powder for magnetic recording, comprising acicular iron alloy magnetic particles containing boron and cobalt and aluminum and nickel near the particle surface.