JPS58192308A - Manufacture of acicular alpha-feooh for magnetic recording material - Google Patents

Abstract

PURPOSE:To improve acicularity, particle size distribution and so forth, by obtaining acicular alpha-FeOOH in such a manner that an aqueous ferrous salt solution is partially neutralized and oxidized to form alpha-FeOOH core crystals, which are then grown on oxidation. CONSTITUTION:First, an aqueous ferrous salt solution is partially neutralized with an alkali and oxidized to form a part of the Fe content in the solution into alpha-FeOOH core crystals. The solution having completed the core crystal forming reaction is an aqueous ferrous salt solution having the alpha-FeOOH core crystals suspending therein. The core crystals are grown on oxidation by adding an alkali in the presence of phosphorus acid or phosphite to obtain a desired alpha- FeOOH. Thus, the obtained alpha-FeOOH is corpuscular and therefore has a sharp particle size distribution, with less branching, and has an axial ratio of 10- 18. Accordingly, it is made possible to improve acicularity, particle size distribution and so forth.

Description

[Detailed Description of the Invention] In recent years, in response to higher density and higher quality magnetic recording, ferromagnetic iron oxide for magnetic recording materials has been developed with smaller particles (fine particles) and acicularity (axis ratio). The present invention satisfies these demands, and particularly the acicular α as a precursor for obtaining ferromagnetic iron oxide with smaller particles. -Regarding a method for producing FeOOH.

Conventionally, regarding the correlation between fine grain size and quality, it has been reported that fine grain size can increase the number of particles in a recording medium and improve the S/N ratio [Journal, On.

Audio, engineering, noise
rna/ of Audio Engine@ering
Soci@ty) Vol, 20p98-99 (197
2) ), the S/N ratio can be improved by reducing the volume of individual particles CIEEE) Lance action, on, magnetics (IE E E Tran)
saction on Magnetica).

Vol, Malr, 17Nα6P3032-3034
rx9st)) etc. are known. however,
There are various problems associated with finer particles.1 For example: ■ Decrease in acicularity (c-axis ratio) due to decrease in major axis length, ■ Decrease in heat resistance during heat treatment process, ■ Inability to achieve high growth rate per unit volume. In addition, if the growth rate is set high to reduce the yield from an industrial standpoint, branching and the generation of new nuclei will increase, so improvements cannot be made. Hope
? j is there.

The inventors of the present invention conducted 17 studies in order to obtain a product A with good acicularity and a small particle size distribution while aiming at making the particles finer.
We focused on adding a phosphoric acid compound during the growth of nuclei, but the acicularity (axial ratio) decreased, the particle size distribution broadened due to the generation of new b nuclei, branching occurred, and a sufficient growth rate could not be achieved. However, after further consideration, we found that phosphorous acid, which had never been used before, was used in the formation of nuclei (2), which was completely different from the phosphoric acid compounds used in the past. It has an effect that cannot be obtained by adding conventional phosphoric acid compounds.
For example, while trying to make tli twins, suppressing the decrease in acicularity (axial ratio), suppressing the occurrence of branching and nucleation, improving heat resistance, increasing the growth rate, and improving the yield due to C2. We have completed the present invention by discovering that this can be achieved.

That is, the present invention': J84 partially oxidizes a-FeloJi salt bath solution to generate a-FeloJi nuclei crystals, and then oxidizes the vaginal fluid with an alkali in the presence of phosphorous acid or its salt. Acicular a-FeOOH for magnetic brass material, characterized in that acicular α-FeOOH is produced by growing the nucleus crystals through neutralization and oxidation.
This is a method for producing Fe0Of.

Examples of the fIc1 iron salt solution to be used include ferrous salt solutions of mineral acids such as % ferrous sulfate, ferrous nitrate, and γ1 iron chloride, with fx1 iron sulfate being preferred industrially. Examples of the alkali include sodium hydroxide, potassium hydroxide, sodium oxide, calcium carbonate, and ammonia. Examples include phosphoric acid, alkali metal salts and ammonium salts thereof, and any substance that acts as a sulfur ion may be used.

As the oxidizing agent, air, oxygen, other oxidizing agents, etc. can be used, but air is preferable.

The second method of the present invention is to first partially neutralize the ferrous salt solution with an alkali and oxidize it to remove 20% of the solution from a-F.
e00) (. At this time, the general 3 uue □ iron salt solution. Fe □ 1 x gt/l ~ 100 g/l, and the amount of alkali added is 5~100 g/l to reduce Fe ions in the mother liquor 25
g/1% nitrogen or the amount necessary to precipitate 10 to 15 g/l. If the concentration of the generated nuclei crystals is too low than the above range, the production efficiency will decrease, making it unsuitable for industrial (economical) implementation, and also resulting in an undesirable bur-like shape.
On the other hand, if the temperature is too high, the viscosity of the mother liquor will increase, a uniform oxidation reaction will occur, the particle size distribution will become less sharp, and the γ-Fe that will be induced from this will increase.
leads to a decrease in magnetic properties.

In this nucleation stage, the reaction temperature is usually 30 to 55°C, preferably 35 to 50°C. If this temperature is too low than the above range, the reaction time will be long and the particle size distribution will not be sharp, while if it is too high, it will be unsuitable as a nucleus crystal for obtaining smaller particles, and granular magnetite will be produced. It becomes easier. The pH is usually kept between 3 and 8. In this nucleation, it is better to keep the neutralization precipitation rate below t-70X in order to prevent the contamination of r-FeOOH.''Also, in this reaction, it is better to carry out the oxidation rapidly at C2, and the reaction temperature is t( From the above, the time cannot be specified, but it is usually 10 to 100 minutes, preferably 10 to 60 minutes.

In this nucleation step, birophosphoric acid, acidic birophosphoric acid, birophosphoric acid such as an alkali metal salt or ammonium salt thereof, or its Ca may be used, and in this case, the reaction temperature is set to 55 to 70°C. (It is preferable because it can be removed,
The amount added is 0.05 to 0.8 weight x in terms of p, preferably 0.1 to 0.5 x, based on the normally produced 6-FeOOH nucleus crystal precipitate. It's JiX. If the amount of p is too small than the above range, it will be difficult to obtain the desired nucleus crystals, while if it is too large, the acicular particles of the nucleus particles will become too fine. It is desirable that it be about 50 to 90 myg.

The fc liquid after the above-mentioned nucleation crystal formation reaction O is formed by -F”eOOH
It is an iron salt bath solution with suspended crystals, and then it is oxidized while adding sulfuric acid or other salts, causing the growth of crystals. 1-FljOOH is obtained.

At this stage of nuclei crystal growth, phosphorous acid or its salt may be added to the alkali in advance as a mixture L7, or may be added separately.
The amount of this sulfurous acid or its salt added is normally -
FeOOH total 1 standard p conversion amount 0.03 to 1.5 weight 2
%6, preferably ij O,05-0,51r'i'y
If the amount of p in t・ru is too small than the above range, the desired effect will not be obtained. The zero reactor degree that increases and lowers the saturation magnetization (dS) is usually 35-80'
0, preferably Fi 50-70°C. If this temperature is too low than the above range, the reaction time will be long and economical.
If the gap is too high (-4), granular magnetite will be mixed in and the acicularity (axial ratio) will be lowered.The pH is normally maintained between 3 and 6. [In order to obtain fine particles, particles with a narrow particle size distribution width, and particles with low branching force, it is desirable to adjust the flow rate from 5 to 15 g/l/hour. -F・OOH nucleus crystals can be generated by adjusting the strength of the ferrite and the amount of nuclei crystals produced, by replenishing iron salt after the generation of the nuclei crystals, and then carrying out the growth reaction, or by appropriately stopping the growth reaction. The growth rate based on the weight of the nucleus is 1.
5 to t5, preferably 2 to 3. If this magnification is too lower than the above range, the particles will not be large enough, and the desired acicular section -FeoOH will not be obtained.
If it is too high, the particle size will become smaller (and the number of particle branches will increase by 4h. In this process, the generated α-F e00
H12) BE; 'I' ratio table [Mi product, f + l is 45
It is preferable to adjust the amount to 70 myg.

The α-FeOOH obtained by the 1 method is pleasing because it has a % fine particle distribution, has a sharp particle distribution, has little branching, and has an axial ratio of 10-18. Magnetic iron oxide, cobalt-covered magnetic wrinkled wheat, and magnetic tape made from these have excellent magnetic properties!'[!J''''''';5.
Section 1-1 i'eoOH is obtained as a-Fe0OH powder through t-filtration with electricity, washing with water, drying and pulverization. r-Faxon can be obtained from this a-FeOO)1 powder by a conventional method. That is, first, it is dehydrated in air at a temperature of 300 to 700°C, and then the dehydrated product is heated to a temperature of 300 to 500°C and reduced with water or hydrogen containing water vapor to form Fes.
Obtain Oa, and then heat the peso4 at 200-400°C.
By oxidizing with oxygen or air at a temperature of 1-
It can be Fe1O@.

The present invention will be explained below with reference to Examples and Comparative Examples.

Example (1) Nucleic crystal formation reaction (A) 1.25 mo/l FeSo was added to an aqueous solution 201 in a reactor equipped with an air blowing tube and a stirrer, and the temperature was raised to 45°C. NaOH aqueous solution ff1 (
2.141 (concentrated WIL 5 mol/l) was added under stirring (precipitate pelsg/j), air was blown into this at a rate of 100 to 6017 hours, and the mixture was allowed to react for 35 minutes to form '-Fe00.
H nuclear crystals were obtained for 7'h, and the specific surface area of this nuclear crystal was determined by the BPINT method to be #'172T11''/g.

(2) Nucleic crystal formation reaction (B) -1.25 Tsuru/l OFe504 aqueous solution 207 was put in a reactor equipped with an air blowing tube and a stirrer, and 6G'C1-
While increasing the temperature and maintaining this temperature, the nucleus crystal zone -p@oOH
Birophosphoric acid corresponding to 0.2% of p by weight and an aqueous NaOH solution (conc. f 5 %/l) 1141 were added under stirring (Precipitate #Fe15 g/7) and 10
0-60! Air was blown into the solution at a rate of 1/hour, and the reaction was carried out for 40 minutes to obtain 1-peoou nucleus crystals. The specific surface area of this nucleus crystal by BET method was #i76wl/g.

(3) Nucleic crystal growth reaction After the completion of the nucleation crystal formation reaction, the liquid is heated and maintained at 60°C, and a predetermined amount of phosphorous acid or phosphoric acid compound is added or not, and air is added at a rate of about 6001 AFF. While blowing in NaOH aqueous solution 1 [(1! [5 mol/l)] was gradually added so as to keep the OpH of 1 reaction solution between 3.5 and 5.5, so that the nucleus crystals reached a predetermined ratio (based on weight). They were allowed to react until they grew.

Using the two IL-Fe00Hs obtained in the above reaction, the axial ratio (L/W) by the usual method and the specific surface area (S a) by the BET method were measured, and the particle size distribution (L/i, ) was determined by the following method. was measured, and the results in Table 11 were obtained.

Measurement method of particle size distribution (7L/j) A well-dispersed α-FeOOHt sample was used, and the long axis particle diameter of more than 3,000 particles was read using an electron microscope. Standard deviation, /L(p
) and determine the particle size distribution according to the formula below.

Particle size distribution =, /L/L Table 1 As is clear from the above results, - in the present invention section is for suppressing the decrease in acicularity (axial ratio), suppressing the occurrence of branching and nucleation. ! 1IIf: While measuring, it can be seen that even at high length magnifications, the grain size is reduced.

Each of the samples obtained in the above examples and comparative flR examples
(For pull, F2M, after washing with water, use the usual method) Dehydration (in air, 600℃), Reduction (in water containing water vapor)
00℃) and reoxidation (280℃ in air) b%γ-F
Got etos. For each γ-Fe□0, BE
The specific surface area (SG) was measured by the T method, and the coercive force (He) was measured by the usual method.
Regarding Fe, O, and the like, the mixture was adjusted according to the following proportions and kneaded in a ball mill to produce a magnetic coating material.

(11r −F e= Os powder 100 coulometric parts (2) Soybean lecithin 1.6 “(
3) Surfactant 4" (4) Vinyl acetate vinyl chloride copolymer resin 1O15" (5)
Dioctyl 7 tallate 4
“(6) Methyl ethyl keto 7 84
“(Katoruene 93”)
Next, each magnetic coating material was applied to a polyester film by a conventional method, oriented, and dried to produce a magnetic recording medium having a magnetic am of about 7 μm. The coercive force ('He), saturation magnetization (13m), squareness ratio (Br78m), and switching field distribution (SFD) of these magnetic recording bodies were measured by conventional methods, and the results shown in Table 82 were obtained.

As is clear from the above results, in the H, tape evaluation of this plant, HC, Br78m, Br, OR
, SFD are both excellent, so the acicularity (
It can be seen that the particle size distribution, branching, etc. have been improved.

Applicant: Ishihara Sangyo Co., Ltd.

Claims (1)

[Claims] Partially neutralize and obfuscate the irises iron salt aqueous solution to generate t-p OOH nucleus crystals, and then neutralize and oxidize the vaginal fluid with an alkali in the presence of phosphorous acid or its salt. #A method for producing acicular a-F.OOH for magnetic recording materials, which involves growing nucleus crystals and producing acicular α-F.OOH.