JPS5884407A - Manufacture of magnetic fine grain - Google Patents

Abstract

PURPOSE:To form ferromagnetic gamma-ferric oxide particles with excellent dispersi- bility and high magnetic coersive force by a method wherein a coating process is performed on the surface of the particles of gamma-ferric oxyhydroxide using a specific compound, and the above is transformed into gamma-ferric oxide. CONSTITUTION:The surface of the particles of the gamma-ferric oxyhydroxide is coated by the silane compound indicated by the formula [where, R indicates the functional atom which was selected from a chloric atom, an amino group, a mercaptan group and the like, or an alkyl group or vinyl group of carbon numbers of 1-10 having the group, R<1> and R<2> indicate a chloric atom, a hydroxyl group, an alkoxy group of carbon numbers of 1-10 and the like respectively, and y indicates an integral number of 0, 1 or 2.]. The quantity of silane coupling agent used for the above coating differs depending on the type of material used, but generally speaking, 0.05-2.0wt% is used based on the wt% of gamma-ferric oxyhydroxide. The particles of the gamma-ferric oxyhydroxide having a coated layer on the surface obtained as above, are turned into alpha-ferric hydroxide by heating them up at 500-650 deg.C in an air or nitrogenous atmosphere, and then the above is transformed into ferromagnetic gamma-ferric hydroxide by performing reduction and oxidation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnetic fine particles, and particularly to a method for producing ferromagnetic γ-ferric oxide particles that have good dispersibility and exhibit a high coercive force.

r-oxidized secondary material used as a magnetic material for magnetic recording
Iron (γ-Fe2O3) is usually converted into α-oxyhydroxide secondary
Iron (α-F e OOH), γ-ferric oxyhydroxide (
Using acicular ferric oxyhydroxide fine particles such as γ-F e OOH) as a starting material, it maintains its acicular shape while maintaining its acicular shape. - It is produced by heating dehydration → reduction → oxidation or reduction → oxidation. The acicular r-ferric oxide fine particles obtained in this way are mixed with a binder resin and made into a paint, which is then applied onto a substrate such as tape or Dinuku card, and is often used to improve recording and playback characteristics. Therefore, the squareness ratio of the Hinuterishi 7 curve was increased by applying porcelain distribution treatment in the recording direction, and
It is widely used as a magnetic medium for magnetic recording.

What determines the quality of these magnetic coatings and films is not only the magnetic properties of the magnetic material, but also the dispersibility of the magnetic material in the magnetic paint, and the residual magnetic flux density and squareness ratio of the coating film. , affects the magnetic material content, film thinness, surface smoothness, etc.

By the way, r-ferric oxyhydroxide generally has less branching than α-ferric oxyhydroxide, and γ-ferric oxide prepared from it has good dispersibility in paints. However, in particular, γ-ferric oxide obtained by heating and dehydrating γ-ferric oxyhydroxide shows good dispersibility in magnetic coatings.
is known (Industrial Chemistry Magazine Vol. 72, No. 7, p. 1461)
. However, such γ-ferric oxide particles have dehydration holes and the size of the secondary particles is extremely small, so even though they are acicular, they have poor square hysteresis characteristics and extremely low coercive force. low, making it unsuitable for magnetic recording.

As a solution to this problem, a method of growing primary particles by reducing and oxidizing r-ferric oxyhydroxide has been put into practical use, but it still does not show sufficient coercive force, and further improvements are desired. .

′-゛On the other hand, the method of heating iron oxyhydroxide to form α-ferric oxide, and then reducing and oxidizing it to produce r-ferric oxide, when iron oxyhydroxide is α-type, Increase coercive force
It is known that it is effective in making the system (JSPS Transactions 73/2, Vol. 56-C, No. 2). However, this method is known to have no effect at all when the iron oxyhydroxide is in the r-type (Bullet
in of the Chemical 5ociet
y of Japan Volume 50 (6) Volume 1685-16
36 pages (1977).

Therefore, conventionally, γ-ferric oxide has been produced by directly reducing and oxidizing γ-iron oxyhydroxide. However, the coercive force of r-ferric oxide obtained by this direct method was also not satisfactory.

In view of this situation, the present inventors have conducted various studies and found that even if the particle surface of r-ferric oxyhydroxide is coated with a specific compound, γ can be reduced by the method described above.
- It was discovered that the magnetic fine particles obtained can be transformed into ferric oxide, have good dispersibility, and exhibit high coercive force, and have completed the present invention.

That is, the gist of the present invention is that in producing ferromagnetic γ-ferric oxide from γ-ferric oxyhydroxide, the surface of the r-ferric oxyhydroxide particles is treated with a silane coupling agent. Thereafter, this is heated to form α-ferric oxide, and then reduced and oxidized to transform into ferromagnetic γ-ferric oxide.

The γ-ferric oxyhydroxide used as a starting material in the method of the present invention can be produced by various methods.
In particular, it is preferable to use γ-ferric oxyhydroxide produced by wet oxidation of a ferrous chloride solution. γ-oxyhydroxide secondary
It is desirable that the iron particles usually have a needle-like shape with a length of 0.3 to 2.0 μm and a length-to-width ratio of 6 or more.

The compound to be coated on the surface of the particles of γ-ferric oxyhydroxide has the following general formula: %Formula%(1)C In the formula, R is a chlorine atom, an amino group, an aminoalkyl group,
C1-C10 alkyl group or vinyl group having at least one functional atom or group selected from ureido group, glycidoxy group, epoxycyclohexyl group, acryloyloxy group, methacryloyloxy group, mercapto group, and vinyl group , R and R2 are each a chlorine atom, a hydroxyl group, an alkoxy group having 1 to 10 carbon atoms, an alkoxy-substituted alkoxy group having 2 to 15 carbon atoms, and a 2 to 4 carbon atoms
an atom or group selected from hydroxyalkyloxy groups and acyloxy groups having 2 to 15 carbon atoms, y is 0.1
Or indicates an integer of 2. ] Examples include silane compounds represented by the following. In the silane compound [■], k is a functional alkyl group, and preferable examples include β-aminoethyl group, r-aminopropyl group, N-(
β-aminoethyl)-γ-aminopropyl group, r-ureidopropyl group, γ-glycidoxypropyl group, β-
(8,4-epoxycyclohexyl)ethyl group, γ-acryloyloxypropyl group, γ-methacryloyloxypropyl group, γ-mercaptopropyl group, β-kuroethyl group, γ-chloropropyl group, γ-vinylglobyl group, etc. be. Further, R may be a vinyl group.

Specific examples of the silane compound CI) that are preferably used are as follows: γ-aminoderobyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ- ureidopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, β-(8,4-epoxycyclohexyl)ethyltrimethylsilane, γ-methacryloyloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ -chloropropyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrichlorosilane, vinyltriacetoxysilane, etc.

Although the amount of the silane coupling agent to be coated depends on the type thereof, it is generally 0.05 to 2.0% by weight based on the weight of γ-ferric oxyhydroxide. If the coating amount is less than this lower limit, a satisfactory coating effect cannot be obtained. Furthermore, if the amount of coating is greater than this upper limit, the coercive force decreases, although the cause is not clear.

The coating treatment may be carried out by a conventional method. Usually, a method is adopted in which particles of 1-ferric oxyhydroxide are dispersed in an aqueous solution having an appropriate concentration of the silane coupling agent to be coated, and then the particles are removed.

The thus obtained particles of r-ferric oxyhydroxide having a coating layer on the surface are heated to form α-ferric oxide,
Next, it is reduced and oxidized to transform it into ferromagnetic r-ferric monoxide.This heating method converts r-ferric oxyhydroxide into α-ferric oxide in an air or nitrogen atmosphere. This may be done by heating at ~650°C.

Reduction and oxidation themselves may be carried out by conventional methods.

For example, in a reducing atmosphere (
For example, reduction is carried out by heating to 800 to 430°C in an oxidizing atmosphere (for example, a hydrogen stream).
K m) Middle Te 230-280'CK7xJj! Oxidation may be performed using Ft.

The magnetic r-ferric monoxide thus obtained has good dispersibility and exhibits high coercive force, so it can be used as an excellent magnetic recording medium.

The present invention will be specifically described below with reference to Examples. Tasoshi % indicates weight %.

Example 1 Fe 2+ /OH=1 in ferrous chloride solution in advance
Alkali is added so that the molar ratio becomes (molar ratio), and oxidation is started. Oxidation is continued until divalent iron ions are no longer detected without adding an alkali so that the pH does not fall below 6. Acicular fine particles of γ-ferric oxyhydroxide produced in this way (long axis summary: 1.5 μm, uniaxial ratio approximately 20)
'e After dispersing in an aqueous solution of γ-glycidoxypropyltrimethoxysilane, the coating amount of γ-glycidoxypropyltrimethoxysilane was 0.05. 0.
2.0.5. Coated γ-ferric oxyhydroxide particles were prepared that were 1.0° 1.5 and 2.0%. These particles were heated at 600°C in a stream of air for 1 hour to obtain α-oxidized secondary
After transformation to iron, di-γ-ferric oxide was obtained by reduction (heating at 340 °C for 1 hour in a hydrogen stream) and oxidation (heating at 250 °C for 1 hour in an air stream). Ta. Obtained γ−
The magnetic properties of the ferric oxide particles are shown in Table 1.

Note that the coercive force was measured by the Gaussmeter method using a Hall element. The filling rate was 0.2.

Table 1 Example 2 The temperature during transformation to α-ferric oxide was 850″C140
0℃, 450℃, 500℃, 600℃ and 700℃
Magnetic γ-ferric oxide was prepared by repeating the same procedure as in Example 1 except that the amount of silane cutting agent coated was 0.5%. The coercive force is shown in Table 2.

Table 2 Comparative Example 1 The γ-ferric oxyhydroxide synthesized in Example 1 was directly reduced and oxidized under the same reduction and oxidation conditions as in Example 1 without being coated with a silane coupling agent, and then γ-oxidized. When ferric iron was prepared, the coercive force was 8860e.

Patent applicant: Daikin Industries, Ltd.

Claims (1)

[Claims] 16 In producing ferromagnetic γ-ferric oxide from γ-ferric oxyhydroxide, the surface of the γ-ferric oxyhydroxide particles is coated with a silane coupling agent. Thereafter, this is heated to form α-ferric oxide, and then reduced and oxidized to transform into ferromagnetic γ-ferric oxide. Ferric oxyhydroxide has a length of 0.8
2.0μ and a length-to-width ratio of 6 or more. 8. Heating at 500-650℃, reduction at 300-430℃
and oxidation at 280 to 280°C. 4. The manufacturing method according to claim 1, wherein the coating amount of the silane coupling agent is 0.05 to 2.0% by weight based on the weight of the r-ferric oxyhydroxide.