JPH043902A - Needle-like magnetic iron oxide powder for magnetic recording and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain the high saturation susceptibility, squareness, and degree of orientation by including phosphorus, aluminum and boron. CONSTITUTION:A needle-like magnetic iron oxide powder for magnetic recording consisting of needle-like magnetic iron oxide particles including phosphorus, aluminum and boron is obtained. Namely, in a water suspension including a needle-like goethite powder of 3.0-10.0wt.%, aqueous solutions of ammonium salt of phosphoric acid of 0.5-1.5wt.% to goethite in term of P2O5, aluminum acetate of 0.5-1.0wt.%, and boric acid or boric acid ammonium of 5.0-10.0wt.%, are added and sufficiently stirred and mixed. After that, a water solution of acetic acid is added to modulate for obtaining pH5.0-7.0. Next, the needle-like goethite particles are separated from the aqueous suspension by filtering and are dried, after which a heating dehydration and reduction are effected by an ordinary method, resulting in needle-like magnetite particles.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is highly sinter-proof and has a high saturation magnetization value.
The present invention also relates to an acicular magnetic iron oxide particle powder that provides a high squareness ratio and a high degree of orientation, and a method for producing the same.

[Prior Art] In recent years, as magnetic recording/reproducing equipment and the like have become smaller and lighter, there has been an increasing demand for higher performance and higher recording density for recording media such as magnetic tapes and magnetic disks.

This is true, for example, in ``synthesis and properties of magnetic fine particles.''
(■Development of magnetic materials and high dispersion technology of magnetic particles published by the General Technology Center (1981), pages 1 to 14), page 7 states, ``Recently, due to demands for higher recording density, 7-Fe
tch particles are gradually becoming smaller (for example, the BET surface area has increased from 20 rrrf/g to 30 rrr/g, and then to 40 n?/g..."). In recent years, there has been an unstoppable demand for finer particles, such as 50r+(/g, 60rrr/g, etc.).

That is, by making the particles finer, they are attempting to meet the demands for higher performance and higher recording density by obtaining a high saturation magnetization value, a high squareness ratio, and a high degree of orientation.

However, since magnetic iron oxide particles are manufactured by subjecting goethite particles to heat treatments of dehydration, reduction, and oxidation, as stated on page 8 of the above-mentioned document, "...in the heat treatment process, the mother salt α
It is necessary to keep the acicular form of -Fe00H intact. ...As the heating temperature rises, the acicularity naturally collapses and the material approaches a spherical shape. At the same time, sintering between particles occurs, resulting in aggregates and poor dispersibility. This is a general change in particle morphology associated with thermal decomposition, and studies have been conducted to control particle morphology using additives in order to eliminate pores without destroying the acicularity... As described in ``, the acicularity collapses due to heat treatment, and as the particle size progresses, the particle morphology becomes more likely to collapse.

Therefore, it becomes difficult to achieve high recording density, and various attempts have been made to maintain the particle morphology.

In particular, a method of retaining the particle form by coating the surface of goethite particles with silicon, phosphorus, aluminum, boron, etc. as a shape-retaining component and subjecting the particles to a heat treatment is well known. For example, JP-A-54-57
459, JP 56-114833, JP 1-26164, JP 63-67705, JP 64-84601, JP 1-239
Examples include prior art disclosed in various publications such as Japanese Patent Application Laid-open No. 817 and Japanese Patent Application Laid-Open No. 62-156201.

[Problems to be Solved by the Invention] Acicular magnetic iron oxide particles having a high saturation magnetization value, a high squareness ratio, and a high degree of orientation are currently required in quantity. In the above-mentioned known methods, it has not been possible to obtain acicular magnetic iron oxide particles having all of these properties.In other words, as a result of numerous experiments conducted by the present inventor, Although it is possible to prevent sintering to a high degree with the technical means of coating the surface of goethite particles with both phosphorus and boron as shown in Japanese Patent No. 57459, the squareness ratio is insufficient.

Also, the above-mentioned Japanese Patent Application Publication No. 56-114833, Japanese Patent Publication No. 1
In technical means such as coating the particle surface of goethite particles with both phosphorus and aluminum as shown in Japanese Patent Application Laid-open No. 26164 and Japanese Patent Application Laid-Open No. 63-67705,
Although a high squareness ratio can be obtained, the saturation magnetization value and degree of orientation are insufficient.

In addition, a high saturation magnetization value and a high squareness ratio can be obtained by technical means such as coating the particle surface of goethite particles with aluminum and boron, as shown in the above-mentioned Japanese Patent Application Laid-Open No. 64-84601. The degree of orientation is insufficient.

In addition, even if the technical means of coating the particle surface of goethite particles with aluminum, silicon, and phosphorus as shown in the above-mentioned Japanese Patent Application Laid-Open No. 1-239817, strong alkaline salt compounds such as sodium salts If a strong acid salt compound such as sulfate or sulfate is used, the liquid phase sintering will be promoted by the strong alkali salt or strong acid salt on the particle surface, making it impossible to fully utilize the effect as a shape-retaining component. It is not possible to obtain acicular magnetic iron oxide particles having a magnetization value, a high squareness ratio, and a high degree of orientation.

Furthermore, even if the technical means includes phosphorus, aluminum, and boron as shape-retaining components as shown in the above-mentioned Japanese Patent Application Laid-open No. 62-156201, strong alkali salt compounds or strong acid salt compounds may be used as described above. If you use
For the above reasons, acicular magnetic iron oxide particles having all three effects cannot be obtained.

Furthermore, in the case of adhesion modification treatment with zinc borate as a boron compound, the acicular goethite particles are subjected to dehydration, reduction, and oxidation heat treatments at temperatures below 700°C to form acicular magnetic iron oxide particles. Since zinc is not ferrite, it is not possible to obtain a high saturation magnetization value, but rather leads to a decrease in the saturation magnetization value. Incidentally, the present inventor has obtained the knowledge from numerous experiments that the inclusion of zinc makes the particle powder hard and the dispersibility becomes poor when the particle powder is used as a magnetic coating material.

As described above, a technical means for obtaining acicular magnetic iron oxide particles having a high saturation magnetization value, a high squareness ratio, and a high degree of orientation has not been established. Therefore,
There is a strong need to establish the technical means to do so.

(Means for solving 1!!t) The present inventor has arrived at the present invention as a result of various studies regarding the above-mentioned technical problems.

That is, the present invention provides acicular magnetic iron oxide particles for magnetic recording and acicular geekite particles comprising acicular magnetic iron oxide particles containing phosphorus, aluminum, and boron at a weight of 3.0 to 10.0%. % of an ammonium salt of phosphoric acid in an amount of 0.5 to 1.5% by weight in terms of P2O based on the goethite.
5-1.0% by weight aluminum acetate and 5.0-10% by weight.
After adding 0% by weight of boric acid or ammonium borate in the form of an aqueous solution and stirring and mixing thoroughly, an acetic acid aqueous solution was added to adjust p)Is, o to 7.0, and then the The acicular goethite particles are filtered out from the aqueous suspension, dried, heated, dehydrated and reduced by a conventional method to form acicular magnetite particles, and if necessary, further oxidized to form acicular maghemite particles. This is a method for producing acicular magnetic iron oxide particle powder for magnetic recording, which is made of acicular magnetic iron oxide particles containing phosphorus, aluminum, and boron.

[For production]

The most important point in the present invention is that the acicular goethite particles are dispersed in water to a concentration of 3.0 to 10. An aqueous suspension with an amount of Ofi%, followed by a 0%
．． 5-1.5% by weight of ammonium salt of phosphoric acid and 0.5
~1.0 wt% aluminum acetate and 5.0-10.0
After adding % by weight of boric acid or ammonium borate each in the form of an aqueous solution and stirring and mixing thoroughly, an acetic acid aqueous solution is added to adjust the pH to 5.0 to 7.0.

Next, the acicular goethite particles are separated from the aqueous suspension and heat-treated in a temperature range of 500 to 700'C, so that the particle surface becomes composed of phosphorous oxide, aluminum hydrated oxide, and boron oxide. Obtain coated acicular hematite particles. Cough needle-shaped hematite particles at 270-400°C
When the temperature is reduced by heating in a temperature range of 100 to 100%, acicular magnetite particle powder consisting of acicular magnetite particles containing phosphorus, aluminum, and boron is obtained.

Further, when oxidized by heating in a temperature range of 200 to 300°C, acicular maghemite particle powder consisting of acicular maghemite particles containing phosphorus, aluminum, and boron is obtained.

The obtained acicular magnetic iron oxide particles containing phosphorus, aluminum, and boron have a high saturation magnetization value, and a high squareness ratio and high degree of orientation can be obtained.

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

The acicular goethite particle powder in the present invention is prepared by mixing a well-known ferrous salt aqueous solution with an equivalent or more alkaline aqueous solution and preparing a suspension containing ferrous hydroxide particles at a pH of 11 or higher and a temperature of 80°C or lower. It can be obtained by a method of performing an oxidation reaction by passing oxygen-containing gas at a temperature of 0.2
~0.5μI, axial ratio (long axis diameter/short axis diameter) 5-20.
BET specific surface area 50-12011 (7 g of particles can be used.

In the goethite production reaction described above, metal ions such as Ni, AI, Mn, and Cu, which are usually added, may be present in order to improve the characteristics of the target acicular magnetic iron oxide particle powder.

The ammonium salt of phosphoric acid in the present invention includes (N
l(4)iPOa , NH4H2PO,, (NH-)a
Pzo7, (N)1. ) HPHO, etc. can be used. The amount of ammonium salt of phosphoric acid added to the aqueous suspension of acicular goethite particles is P relative to goethite.
It is 0.5 to 15% by weight in terms of 2O. If 0.5% by weight is ungrooved, a sufficient sintering prevention effect cannot be obtained. 1.
If it exceeds 5% by weight, a high saturation magnetization value cannot be obtained. However, when using an ammonium salt of phosphoric acid, ammonium ions are volatile and do not remain in the oxide, promoting liquid phase sintering. Because they don't. If a salt other than ammonium salt, such as a sodium salt or a potassium salt, is used, liquid phase sintering will be promoted and a sufficient sintering prevention effect will not be obtained.

In the present invention, the amount of aluminum acetate added to the aqueous suspension of acicular goethite particles is 0 relative to goethite.
．． It is 5 to 1.0% by weight. If it is less than 0.5% by weight, a high squareness ratio cannot be obtained. If it exceeds 1.0% by weight, a high saturation magnetization value cannot be obtained.

Note that aluminum acetate is used because acetate ions are volatile and do not remain in the oxide, so they do not promote liquid phase sintering. If sulfates, nitrates, chlorides, etc. other than acetates are used, liquid phase sintering will be promoted and a sufficient sintering prevention effect will not be obtained.

Boric acid or ammonium borate in the present invention includes LBO+, HBOz, (NH4)to・B2O2
etc. can be used. The amount of boric acid or ammonium borate added to the aqueous suspension of acicular goethite particles is 5.0 to 10.0!1% based on goethite. If it is less than 5.0 ftI%, a high degree of orientation cannot be obtained, and if it exceeds 10.0% by weight, the reduction reaction from hematite to magtite will be slow and there will be no economic or industrial advantage.

Note that if a boron compound such as a non-volatile sodium salt, potassium salt, or lithium salt is used, liquid phase sintering will be promoted and a sufficient sintering prevention effect will not be obtained.

In the present invention, the ammonium salt of phosphoric acid, aluminum acetate, boric acid, or ammonium borate compounds are added in the form of an aqueous solution in order to uniformly coat the surface of the acicular goethite particles. .

In the present invention, the order of addition of the ammonium salt of phosphoric acid, aluminum acetate, boric acid, or ammonium borate in the form of an aqueous solution to the aqueous suspension of acicular goethite particles may be in either order or simultaneously. It may be.

In the present invention, in order to precipitate phosphate and aluminum hydroxide on the surface of the acicular goethite particles, an acetic acid aqueous solution is added to adjust the pH to 5.0 to 7.0.

When the pH is less than 5.0, aluminum hydroxide is difficult to precipitate. If the pH exceeds 7.0, phosphates will be difficult to precipitate.

In addition, boric acid or ammonium borate exists in the state of ions dissolved in the aqueous suspension in the aqueous suspension,
By filtering and drying, it is contained as a borate on the surface of the acicular geekite particles.

Acetic acid is used in the present invention because it is volatile and does not promote liquid phase sintering. When using sulfuric acid, nitric acid, hydrochloric acid, etc. other than acetic acid, liquid phase sintering is promoted and a sufficient sintering prevention effect cannot be obtained.

The acicular magnetic iron oxide particles obtained in the present invention have a major axis diameter of 0.2 to 0.5 μs+ and an axial ratio (major axis diameter/minor axis diameter).
5 to 20, BET specific surface area is 50 to 120 rrr/g, and phosphorus oxide is 0 in terms of P2O with respect to magnetic iron oxide.
．． 5-1.5% by weight of aluminum hydrated oxide as Al0
It contains 0.1 to 0.3% by weight in terms of (OH), and 0.2 to 1.5% by weight in terms of B aro 3 of boron oxide.

〔Example〕

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

In addition, the major axis diameter of the particles in the following examples and comparative examples,
The axial ratio (major axis diameter/minor axis diameter) was expressed as the average value of numerical values measured from electron micrographs. The magnetic properties of the acicular magnetic iron oxide particles are determined by the "vibrating sample magnetometer ν5M-35-15J".
(manufactured by Toei Kogyo ■), and an external magnetic field of up to 10 KOe was applied for measurement. The specific surface area was measured by the BET method.

<Surface treatment of acicular goethite particles> Examples 1 to 4, Comparative Examples 1 to 6; Example 1 Major axis diameter 0.2 μm, axial ratio (major axis diameter/minor axis diameter) 7, BET
2. 100 g of acicular goethite particle powder with a specific surface area of 105.2 rrr/g. It was suspended in OL water.

15 g/l of (NH4)4P20.10 in the above suspension
0m (P2O for 'y'-tight, converted to 0.
This corresponds to 87% by weight.

), 5g/jl! (CH*C00)Jl 1ooII
! (Equivalent to 0.5% by weight relative to goethite.)
70g #2 of H,B0100m (equivalent to 7% by weight based on goethite) was added and stirred for 30 minutes.

The pH of the suspension at this time was 8.5.

Next, 1. After adjusting the pH of the suspension to 6.0 by adding ON CH3CO0H, the acicular goethite particles were filtered out.
After drying, acicular goethite particles whose surfaces were coated with phosphate, aluminum hydroxide, and borate were obtained.

Examples 2 to 4, Comparative Examples 1 to 6 Types of acicular goethite particles, types and amounts of phosphorus compounds, types and amounts of aluminum compounds, types and amounts of boron compounds, and acid for adjusting the pH of the suspension. Acicular goethite particles were obtained in the same manner as in Example 1, except that the types were varied.

Table 1 shows the main manufacturing conditions and characteristics at this time.

<Manufacture of acicular magnetic iron oxide particles> Examples 5 to 8, Comparative Examples 7 to 12; Example 5 The surfaces of the particles obtained in Example 1 were coated with phosphate, aluminum hydroxide, and borate. 100 g of acicular goethite particles powder was heat-treated at 620°C in air,
Acicular hematite particles whose particle surfaces were coated with phosphorous oxide, aluminum hydrated oxide, and boron oxide were obtained.

Next, 80 g of the obtained acicular hematite particles were mixed in 4.
01, and while driving and rotating, H2 gas was aerated at a rate of 1.51 per minute until the reduction temperature was 3.
The mixture was reduced at 00'C for 4 hours to obtain acicular magnetite particle powder.

As a result of electron microscopy observation, the obtained acicular magnetite particles had an average long sleeve diameter of 0.18 μm and an axial ratio (long axis diameter/
The short axis diameter) was 6, and the BET specific surface area was 55 nf/g. In addition, as a result of magnetic measurement, the coercive force was 3400e, the saturation magnetization value was 75e+wu/g, and the results obtained in the same manner as the magnetic sheet sample piece described later were that the coercive force was 3250e, the squareness ratio was 0.80, and the orientation It was 2.55 degrees.

Further, 80 g of the obtained acicular magnetite particles were oxidized in air at 250'C to obtain acicular maghemite particles.

The obtained acicular maghemite particle powder contained pzo, WA summer, 0.89% by weight, Al0(OH)lII! Calculated to 0.
Contains 10% by weight, B20, 0.88% in terms of B20, and as a result of electron microscopy observation, the average major axis diameter is 0.18
μm, axial ratio (long axis diameter/short axis diameter) 6, BET specific surface area 55
rrf/g.

Further, as a result of magnetic measurement, the coercive force was 3300e and the saturation magnetization value was 70 emu/g.

Examples 6 to 8, Comparative Examples 7 to 12 Using the acicular goethite particles obtained in Examples 2 to 4 and Comparative Examples 1 to 6, the same treatment as in Example 5 was performed to obtain acicular maghemite particles. I got it.

Table 2 shows the initial characteristics at this time.

<Manufacture of magnetic sheet> Using the acicular maghemite particle powders obtained in Examples 5 to 8 and Comparative Examples 7 to 12, the following ingredients were placed in a 100 cc polybottle in the following proportions, and then heated in a Lendodevil for 8 hours. The magnetic paint prepared by mixing and dispersing was applied to a thickness of 25 μm.
- onto a polyethylene terephthalate film to a thickness of 50 μm (D) using an applicator, and then
Sheet specimens were obtained by drying in a magnetic field of 5 K Gauss.

31 μmφ steel ball 80 Cap 1 part Magnetic iron oxide particle powder 100 Polyurethane resin having sodium sulfonate group 20 Cyclohexanone 833 〃Methyl ethyl ketone 83.3 〃Toluene
83.3 Table 2 shows the coercive force, squareness ratio, and orientation properties measured for each of the obtained sheet sample pieces.

[Effects of the Invention] As shown in the above examples, the acicular magnetic iron oxide particles according to the present invention are particles that have a high saturation magnetization value and can obtain a high squareness ratio and a high degree of orientation. Since it is a powder, it is suitable as a particle powder for high-density recording, which is currently required in large quantities.

Claims (2)

[Claims] 1. An acicular magnetic iron oxide particle powder for magnetic recording comprising acicular magnetic iron oxide particles containing phosphorus, aluminum, and boron. 2. 3.0 to 10.0% by weight of acicular goethite particle powder
The aqueous suspension containing P_2O_
0.5 to 1.5% by weight of ammonium salt of phosphoric acid and 0.5 to 1.0% by weight of aluminum acetate and 5.0
After adding ~10.0% by weight of boric acid or ammonium borate each in the form of an aqueous solution and stirring and mixing thoroughly, an acetic acid aqueous solution was added to adjust the pH to 5.0 to 7.0,
Next, the acicular goethite particles are filtered from the aqueous suspension, dried, and heated and dehydrated and reduced by a conventional method to obtain acicular magnetite particles, or further oxidized as necessary to obtain acicular maghemite particles. A method for producing acicular magnetic iron oxide particle powder for magnetic recording, comprising acicular magnetic iron oxide particles containing phosphorus, aluminum, and boron, characterized by the following.