JPH011207A - Method for producing α-Fe00H for magnetic recording materials - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to α, which is a starting material for producing magnetic powder for magnetic recording, particularly ferromagnetic powder suitable for audio tapes, video tapes, and floppy disks. -Fe
The present invention relates to a method for producing OOII particles, which has a relatively small axial ratio (major axis/minor axis), no dendritic particles, and a good particle size distribution.

[Technical background of the invention and its problems]

In recent years, there has been an increasing demand for higher recording density and higher performance for magnetic recording media such as audio, video, and floppy disks.

The requirements include suppressing the decrease in output due to shortening the recording wavelength (high-density recording), and improving the SZN ratio and recording sensitivity by increasing the output and reducing noise.

For this reason, efforts are being made to reduce output loss during short wavelength recording by improving coercive force (Ilc) and residual magnetic flux density (Br), improving SFD, thinning the layer, and smoothing the surface of magnetic coatings. There is a need.

The residual magnetic flux density (Br) depends on the magnetic powder's properties, orientation, and high-density phototransferization into the magnetic coating.
However, increasing the filling property means increasing the number of magnetic powder particles in the unit volume of the coating, which also leads to a reduction in noise. good.

α-FeO, which is the starting material for magnetic powder, meets the above requirements.
The desired properties of the OH particles are as follows.

As α-FeOOH particle powder, it is better to have a small particle size (, no dendritic particles (, uniform particle size), magnetic powder obtained from this powder has improved dispersibility, orientation, filling property, etc.
It improves FD and also makes the coating surface highly smooth.

hR magnetic powder with a smaller axis ratio (major axis/minor axis) has a higher bulk density, less oil absorption, improved filling ability, and better dispersibility (thinner coating and smoother surface). Therefore, the starting material α-FeOOH
The smaller the axial ratio of the particles, the better.

Incidentally, at present, as a starting material for magnetic powder, acicular α-FeOOH is obtained mainly by reacting an aqueous solution of a ferrous salt with Na011 and oxidizing the ferrous salt. In the reaction for producing the above needle-like α-FeOOII, the pH
There are an alkaline method in which the product is generated in an alkaline range of 11 or more, and an acidic method in which the product is produced in a weakly acidic region. however,
α-F e OOH obtained by these methods is
Dendritic particles are mixed and the particle size is not uniform. For these improvements, modifiers such as phosphoric acid or its salts and silicon compounds are added to the ferrous salt aqueous solution, but the axial ratio (major axis/minor axis) is 1071 or more in the alkaline method. Even in the acid method, it is around 1071.

As a method for reducing the axial ratio, for example, in the acid method, there is a method in which orthophosphoric acid is present at the time of nucleic crystal formation.
In this case, it is necessary to add a large amount of orthophosphoric acid,
The resulting axial ratio is about 671 to 871, and if it is attempted to further reduce the axial ratio, it is necessary to add a larger amount. However, addition of a large amount of orthophosphoric acid is not preferable because it increases the magnetizing component and lowers the saturation magnetization (δ,) of the n-type powder.

On the other hand, there is a method of neutralizing and oxidizing a ferrous salt using an alkali carbonate such as NazCO3 to generate spindle-shaped α-FeOOH having an axial ratio (major axis/minor axis) of 371 or less.

However, the recording medium using the 6ff powder derived from this is advantageous when utilizing the magnetic flux component in the direction perpendicular to the coating surface when the gap l of the magnetic head is narrowed. In a system that utilizes the horizontal component of (Coercive force (Ilc
) is also low, which is not preferable.

[Purpose of the invention]

The purpose of the present invention is to use α-FeOOH, which is a starting material for magnetic powder suitable for use in magnetic recording media that has high output, low noise, and excellent high-density recording characteristics, as a material containing fine and dendritic particles. The particle size distribution is narrow, and the axial ratio (long axis/
The goal is to manufacture products with a short axis of about 471 to 771.

[Summary of the invention]

In producing α-FeOOH by an acidic method, the present invention uses ammonia as a neutralizing agent in the presence of a specific amount of phosphorous compound as a modifier, and reacts in the presence of a ferrous ion concentration of a certain amount or more. It was found that when using a caustic alkali such as NaOII, which has been mainly used in the past, the axial ratio of the α-FeOOH produced is lower and the particle size distribution is better. Furthermore, as a result of various tests S4, it was found that α-Fe0 is useful as a raw material for magnetic powder for high-density magnetic recording media while suppressing the addition of a crystallizing agent to a small amount.
This was completed after discovering that 01 could be obtained.

That is, the present invention partially neutralizes and oxidizes an aqueous ferrous salt solution in the presence of a small amount of phosphoric acid or its salt to generate α-FeOOH nucleus crystals, and then neutralizes cough fluid with a neutralizing agent. In the method of producing α-FeOOII particles by oxidizing the phosphoric acid and growing the nucleus crystals, the amount of the phosphoric acid or its salt is determined by the amount of α produced.
-0.05 in P equivalent amount for FeOO11 nuclear crystal precipitate
~0.6% by weight, ammonia is used as the neutralizing agent, and the amount of dissolved Fe in the solution at the end of the generation of the α-FeOOH nucleus crystal precipitate is 1.6% by weight per 1L of Fe in the nucleus crystal. 7
This is a method for producing α-FeOOH for magnetic recording materials, which is characterized by making the amount more than double.

The ferrous salts used include ferrous sulfate, ferrous nitrate,
Examples include ferrous salt solutions of mineral acids such as ferrous chloride, and ferrous sulfate is preferred industrially. As the neutralizing agent, ammonia can be used, for example, as an Nl+4011 aqueous solution or N113 gas. Neutralizing agent is Na Off
With alkali metal hydroxides such as KOtl, the axial ratio (major axis/minor axis) of the obtained α-Fe001 becomes too large, the particle size distribution becomes wider than that of ammonia, and
On the other hand, carbonates with alkali combined pressure such as Na2CO, K2CO3, etc. are not preferred because the axial ratio becomes too small. As the phosphoric acid or its salt, orthophosphoric acid or its salt, or polyphosphoric acid such as hexametaphosphoric acid or pyrophosphoric acid or its salt is used. As an oxidizing agent, air,
Although oxygen, other oxidizing agents, etc. can be used, air is preferred.

In the present invention, first, a ferrous salt aqueous solution is partially neutralized with ammonia and oxidized to convert a part of the Fe content in the solution into α-Fe.
To form OOH nucleus crystals, phosphoric acid or its salt is made to exist in the ferrous salt aqueous solution or in the liquid in which green rust is generated after addition of ammonia. Fe in ferrous salt aqueous solution? The degree of a is usually 30 to 100 g/j2, and the amount of phosphoric acid or its salt to be added is determined by the amount of α-FeO produced.
The amount in terms of P is 0.05 to 0.6% by weight, preferably 0.1 to 0.5% by weight, based on the OH nuclear crystal precipitate. This P
If the amount is too small than the above range, dendritic particles may be present or sufficient refinement may not be achieved. On the other hand, if it is too large, it becomes too fine and the magnetizing property increases, making it undesirable as α-FeOOH for magnetic recording materials.

Addition of ammonia in partial neutralization adds 5 to 25 g of dissolved Fe ions in the ferrous salt aqueous solution! Preferably 1
This is the amount necessary to precipitate 0 to 20 g/l. If the concentration of the generated nuclei crystals is too low than the above range, α-FeOOH with an undesirable burr-like shape will be generated, while if it is too high, the viscosity of the slurry will increase, hindering a uniform oxidation reaction, and making the particle size non-uniform. .

At the end of the α-FeOOH nucleation reaction, the dissolved Fe ions in the nucleus precipitate slurry have a weight ratio of 1.7 times or more, preferably about 2 to 10 times, relative to Fe in the nucleus crystals. If the dissolved Fe ions are below the above ratio, the particle size distribution will be wide, the axial ratio will also be large, and refinement will be insufficient. This appears to be because dissolved Fe ions have a moderating effect on nucleation, and it appears that adjusting the ratio to the above range can reduce the amount of phosphoric acid or its salt added.

In this nucleation stage, the reaction temperature may be any temperature at which α-FeOOH is produced, and is usually carried out at a temperature of 40 to 70°C. Further, this generation reaction time is relatively short, for example, 10
It is best to adjust the time to about 100 minutes; if it is too long, the particle size and axial ratio will increase, and the particle size distribution will also become wider, which is not preferable.

The liquid after the above-mentioned nucleation crystal generation reaction is a ferrous salt solution in which α-FeOOII nucleus crystals are suspended. Usually no remains. In the method of the present invention, the material is then oxidized while adding ammonia to grow nucleus crystals, thereby obtaining desired α-FeOOH particles. This reaction also does not contain magnetite, etc., as in the case of nucleation, and α-FeOO
It can be carried out at a temperature and pH at which H is generated, and the temperature is usually 4.
It is preferable to oxidize while adding ammonia so that the temperature is 0°C or higher and pl+ is maintained at a substantially constant value of 3 to 6.

In this growth reaction, the concentration of the mother liquor and the amount of nucleus crystals produced are adjusted in advance, or ferrous salt is supplied after nucleation to achieve growth.
By appropriately selecting the ratio (magnification) of the weight of α-FeOOIl produced after growth to the weight of
Grow to FeOOH. This growth rate is 1.2 to 3.
It is best to select within the range of 5, and the target α-Fe00
It may be determined from the above range depending on the size of H, the size of the nucleus crystal, and the growth reaction conditions. If this magnification is too large than the above range, the particle size distribution will become wider, which is not preferable.

α-FeOOH obtained by the present invention has no dendritic particles, and Na01, which is conventionally mainly used as a neutralizing agent, has no dendritic particles.
By using ammonia instead of No. 1 caustic alkali or alkali carbonate, the addition of a small amount of phosphoric acid or its salt can result in a small axial ratio and a good particle size distribution. Recording media such as magnetic tapes manufactured from magnetic powders such as cobalt-coated iron oxide have good magnetic properties. In order to maintain the shape of the α-FeOOH particles and prevent interparticle sintering, phosphoric acid, its salt,
It is desirable to treat silicon compounds and the like.

Example 1 A reactor equipped with an air blowing tube and a stirrer was charged with 1.25 liters of water.
Pour ferrous sulfate aqueous solution 21 of mol/1 (70 g/jD of Fe, raise the temperature to 50°C, and while maintaining this temperature, convert sodium pyrophosphate into α-FeO in terms of P.
0.2% by weight based on the OH nucleus precipitate and N114. O
0.21 equivalent of 5 mol/l aqueous ammonia was added. Air is blown into this to cause an oxidation reaction.α
-Fe00H nucleus crystal precipitate was generated. (α-FeOO
Fefil dissolved in the solution at the end of generation of H nucleus crystal precipitate
was 3.67 times as large as Fei in the nuclear crystal. ) The obtained nuclear crystals were observed with an electron microscope to determine the axial ratio (L/
W) was determined, and the BET specific slope surface area G) using N2 gas was also measured.

After the completion of the nucleation crystal formation reaction, the ammonia water was gradually added while blowing air while maintaining the temperature at 50°C, and the reaction was continued until the nucleation crystals grew twice (by weight). The axial ratio (L/W) and specific surface area (SG) of the obtained α-FeOOH were measured in the same manner as in the case of the nucleus crystal, and the results shown in Table 1 were obtained.

Example 2 In Example 1, the amount of sodium pyrophosphate added was
Converted to 0.4% by weight based on α-FeOOH nucleus precipitate
The results shown in Table 1 were obtained by carrying out the same procedure except for using the same method.

Example 3 The same procedure as in Example 1 was carried out except that 0.2% orthophosphoric acid was added to the α-FeOOH nucleus precipitate as calculated by PEA in place of sodium pyrophosphate, and the results shown in Table 1 were obtained. Ta.

Comparative Example 1 The same procedure as in Example 1 was carried out except that an aqueous Na0II solution (5 mol/Z) was used instead of aqueous ammonia as the neutralizing agent, and the results shown in Table 1 were obtained.

Comparative Example 2 The same procedure as in Example 2 was carried out except that an aqueous Na'OII solution (5 mol/6) was used instead of aqueous ammonia as the neutralizing agent, and the results shown in Table 1 were obtained.

Comparative Example 3 The same procedure as in Example 3 was repeated except that an aqueous solution of Na011 (5 mol/liter) was used instead of aqueous ammonia as the neutralizing agent, and the results shown in Table 1 were obtained.

After the α-FeOOH particles obtained in Example 1 and Comparative Example 1 were washed with water, orthophosphoric acid was added to α-FeOOH.
After adhering 0.6% by weight (in terms of P) to the total amount of water, it was dehydrated and heated at 680° C. in air. Thereafter, it was reduced in hydrogen containing water vapor at 400°C and reoxidized in air at 280°C to obtain γ-F+g03. For each γ-Fe203 sample, the axial ratio (
L/W) and specific surface area (SG) were determined, and coercive force (llc) was also measured by a conventional method.

Further, for each γ-pez 03, a formulation was adjusted according to the following formulation ratio and dispersed in a paint shaker to produce a magnetic paint.

(llr-FezO 1100 parts by weight (2) Soybean lecithin 1.64 (3)
Surfactant 4...(4) Vinyl acetate vinyl chloride copolymer resin 10.5 (5) Dioctyl phthalate 4 (6) Methyl ethyl ketone 84 (7) Toluene
93 Next, each magnetic coating material was coated and oriented on a polyester film by a conventional method, and then dried to produce a magnetic recording medium having a magnetic coating film with a thickness of about 10 μm. The coercive force (llc), saturation magnetization (Bm), remanent magnetization (Br), squareness ratio (Br/8m), and inverted 6 field distribution (SFD) of these magnetic recording media were measured using conventional methods and are shown in Table 2. I got the result.

〔Effect of the invention〕

According to the present invention, α-FeOOH having a relatively small axial ratio, no dendritic particles mixed therein, and a good particle size distribution can be produced stably using relatively simple means.

Further, the α-FeOOH obtained by the present invention has good dispersibility and orientation in a magnetic recording medium, and can be easily induced into a highly packed magnetic powder, with high output and It is extremely useful as a raw material for magnetic powder for low noise, high magnetic recording density media.

1. Indication of the case Patent Application No. 156239 of 1988 2. Title of the invention Method for producing α-Fe00H for magnetic recording materials 3. Person making the amendment Relationship with the case Patent applicant 4. Subject of amendmentゝ\/'°゛5. Contents of amendment (1) The scope of claims is amended as shown in Attachment (1).

(2) “Saturation magnetization (δs) J” on page 4, line 17 of the specification
is corrected as [saturation magnetization (σs) J].

(3) Change “4/1~7/l” to “4/1” on page 5, line 16.
/1~8/1''.

(4) Delete "with a neutralizing agent" on page 6, line 12.

(5) On page 6, line 16, "said" is corrected to "said."

(6) In the bottom line of page 13, there is a line that says ``Similarly, the results shown in Table 1 were obtained.'' Next, add the following comparative example on a new line.

[Comparative Example 4 In Example 3, Fe in the ferrous sulfate aqueous solution (the original concentration was set to 0.67 mol/1 (Fe37.5 g/jl), and the neutralization with aqueous ammonia before the oxidation reaction was adjusted to 0.4 equivalent (α
-The same procedure as in Example 3 was carried out except that the amount of Fe dissolved in the solution was 1.5 times the amount of F4 in the nucleus crystals at the end of the generation of the Fe00H nuclei crystal precipitate. I got the results in the table. (7) Table 1 on page 14 of the same document is attached (2
).

Attachment (1) [Claims] "A ferrous salt aqueous solution is partially neutralized and oxidized in the presence of phosphoric acid or its salt to generate α-Fe00H nucleus crystals, and then the liquid α-F is oxidized to grow the nucleus crystal.
e00) In the method for producing 1 particle, the amount of the phosphoric acid or its salt is 0.05 to 0.6% by weight in terms of P based on the α-Fe00H nucleus precipitate to be produced, and Using ammonia as the agent, the amount of dissolved Fe in the cough fluid at the end of the generation of α-Fe00H nuclei crystal precipitates is
A method for producing α-Fe00t for magnetic recording materials, characterized in that the amount of α-Fe00t is 1°7 times or more the amount of e.
” Attachment (2)

Claims (1)

[Claims] A ferrous salt aqueous solution is partially neutralized and oxidized in the presence of phosphoric acid or its salt to generate α-FeOOH nucleus crystals, and then the solution is neutralized with a neutralizing agent and oxidized to generate the nuclei crystals. In the method for producing α-FeOOH particles by growing phosphoric acid or its salt, the amount of the phosphoric acid or its salt is 0.05 to 0.6% by weight in terms of P based on the α-FeOOH nucleus precipitate produced. ,
Using ammonia as the neutralizing agent and α-FeOOH
α-FeOOH for magnetic recording materials, characterized in that the amount of Fe dissolved in the liquid at the end of the generation of the nuclei crystal precipitate is 1.7 times or more the amount of Fe in the nuclei crystals. Production method.