JP3132536B2 - Manufacturing method of magnetic particle powder for magnetic recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing magnetic particles having excellent dispersibility and suitable as magnetic particles for high-density recording.

[0001]

2. Description of the Related Art In recent years, as the size and weight of magnetic recording and reproducing devices and the like have been reduced, higher performance and higher recording density have been required for magnetic recording media such as magnetic tapes and magnetic disks.

[0002] In order to improve the performance and recording density of a magnetic recording medium, it is necessary to improve the residual magnetic flux density Br. The residual magnetic flux density Br of the magnetic recording medium depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property.

[0003] Various attempts have been made to improve the dispersibility of magnetic particle powders.
JP, JP-A-57-56904, JP-A-58-56904
60506, JP-A-58-161725,
JP-A-59-23505, JP-A-60-2175
No. 29, JP-A-61-63921 and JP-A-62-89226, the particle surface of a magnetic particle powder is modified by coating the particle surface with a Si compound or an Al compound. There are ways to quality.

Further, for example, Japanese Patent Application Laid-Open No. 63-161522
As described in the publication, a film made of a Si compound is formed on the particle surface of the magnetic particle powder, a film made of an Al compound is formed thereon, and a film made of a Si compound is further formed thereon. Magnetic powder.

[0005]

The magnetic particle powder having excellent dispersibility is the most demanded at present, but it cannot be said that any of the above-mentioned known methods still has excellent dispersibility. It is difficult.

The reason why particles having excellent dispersibility have not yet been obtained in the known method is, for example, “magnetic paint from the viewpoint of a magnetic recording material researcher” (powder powder metallurgy “No. 7”).
Of the Annual Ferrite Summer Seminar "(1972)
It is generally difficult to obtain a high degree of dispersion even with ordinary non-magnetic pigments. On the other hand, in the case of magnetic powders, magnetic interaction between particles is very difficult. This makes the phenomenon even more complicated.
As described in “‥”, the magnetic particle powder forms an aggregate by an interaction due to magnetism, and thus is caused to be coated on the surface as the aggregate.

[0007] In particular, in the case of hexagonal ferrite particles having an easy axis of magnetization in the direction perpendicular to the plate surface, the particles are strongly aggregated by the interaction due to magnetism, and the aggregated particles are merely obtained by mechanical treatment alone. Is difficult to separate into individual particles.

Further, regarding the dispersibility of the magnetic particle powder,
For example, “Elucidation of Dispersion and Aggregation and Applied Technology” (1992), published by Techno System Co., Ltd., p. , To prepare a stably dispersed magnetic paint.
Using it, a uniform coating thin film is formed on a substrate. Therefore, the performance as a recording medium largely depends on the dispersion stability. ‥‥ ”,
How to disperse the magnetic particle powder in the polymer resin, and many studies have been made on improving the dispersibility for that purpose.

On the other hand, regarding the evaluation of dispersibility, for example,
"Elucidation of dispersion / aggregation and applied technology", pp. 94-96, "‥‥ Many natural and synthetic polymers are adsorbed on the surface of colloid particles to form a thick adsorption layer. (1) Molecular weight of polymer (M)
In general, the following relationship (applicant: note: Equation 2 below) is established between and the saturated adsorption amount (As).

(Equation 2) Here, K ₁ and α are constants peculiar to the system, particularly α is called a molecular weight-dependent parameter, and depends on the structure of the adsorption layer.
To change. When ‥‥ α = 1, the polymer is adsorbed at the molecular end, and As is proportional to the molecular weight (M). In this system, the polymer forms a thickest adsorbed layer formed on the particle surface, so that it exhibits a strong steric repulsion effect and more effectively contributes to the stability of the dispersion system. As described in “‥‥”, it can be represented by a molecular weight-dependent parameter α (hereinafter, represented by α).

[0010] α of the magnetic particle powder obtained so far
Were measured, and the above-mentioned JP-A-55-83207, JP-A-57-56904, and JP-A-58-60
506, JP-A-58-161725, JP-A-59-23505, JP-A-60-217529
JP-A-61-63921 and JP-A-61-63921
When the surface of the magnetic particle powder is coated with a Si compound or an Al compound by a known method such as -89226, α is about 0.40 to 0.45, and these coating treatments are not performed. Α of the magnetic particle powder is 0.28 ~
It was found to be about 0.34.

Also, when the surface of the magnetic particle powder is coated with a Si compound and an Al compound by the method described in the above-mentioned JP-A-63-161522, α is 0.40 to 0.40.
It was about 0.45.

Therefore, the present invention relates to α, which is more excellent in dispersibility.
It is an object of the present invention to provide a coating treatment technique of Si or Al capable of obtaining a magnetic particle powder having a large particle diameter.

[0013]

The above technical object can be achieved by the following method of the present invention.

That is, according to the present invention, an aqueous alkali solution is added to an aqueous suspension containing magnetic particles to form a suspension having a pH of 10 or more, and an aqueous solution containing Al or an aqueous solution containing Si or an aqueous solution containing Al and Si is added to the suspension. Is added, and while stirring, the pH value of this solution is adjusted to near neutral to rapidly precipitate Al or Si or both hydroxides, and then the magnetic particles in the solution are hydroxylated. A mixture of magnetic particles and hydroxide obtained by filtering with a material, washing and drying the mixture, and then subjecting the mixture to a compaction pulverization process using an edge runner. From the operation of adding an alkaline aqueous solution to the aqueous suspension containing the particle powder to make the suspension have a pH value of 10 or more, to the operation of compacting and pulverizing the mixture with an edge runner. The number 1 (in the following formula by repeating at least twice, As is the saturation adsorption amount, K ₁
Is a system-specific constant, M is the molecular weight of the polymer, and α is the molecular weight dependent
Parameters. ) Molecular weight dependent parameters α is not more than 0.50 in, A on the particle surfaces of the magnetic particles
A method for producing magnetic particle powder for magnetic recording, comprising obtaining magnetic particles having an oxide or hydroxide containing l or Si or both.

(Equation 1)

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

The magnetic particles according to the present invention include magnetic iron oxide particles such as maghemite particles, magnetite particles, and a beltlide compound particle which is an intermediate oxide between maghemite and magnetite. Hexagonal ferrite particles such as particle powder containing a different metal such as Co or particle powder obtained by coating Co on these magnetic iron oxide particles, metal magnetic particle powder containing iron as a main component, and plate-like Ba ferrite fine particles Any of powder and the like can be used.

In the present invention, an aqueous alkali solution is added to an aqueous suspension containing magnetic particles to adjust the pH to 10 or more, and then an aqueous compound solution containing Al, an aqueous compound solution containing Si, or a mixed aqueous solution of both compounds is added. This is for dispersing the magnetic particles in a state where the respective compounds are not precipitated as hydroxides, so that the added compounds and the magnetic particles are uniformly mixed.

As the alkaline aqueous solution for adjusting the pH to 10 or more, an aqueous solution of sodium hydroxide, potassium hydroxide, aqueous ammonia or the like can be used.

As the aqueous solution containing Al, an aqueous solution of an alkali aluminate such as sodium aluminate or potassium aluminate, or an aluminum salt such as aluminum sulfate, aluminum chloride or aluminum nitrate can be used.

The amount of the above-mentioned compound containing Al per addition is 0.01 to 5.0 in terms of Al with respect to the magnetic particle powder.
0% by weight. If the amount is less than 0.01% by weight, the effects of the present invention cannot be obtained. When the content exceeds 5.0% by weight, the desired effects of the present invention can be obtained, but the saturation magnetization is decreased by the increase of Al-containing oxides or hydroxides which are not involved in magnetism, which is not preferable. When considering the dispersibility and saturation magnetization of the magnetic particle powder, the content is preferably 0.05 to 3.0% by weight.

As the aqueous solution containing Si, an aqueous solution of sodium silicate, potassium silicate, colloidal silica, No. 3 water glass or the like can be used.

The addition amount of the above-mentioned compound containing Si is 0.01 to 0.01 in terms of SiO ₂ with respect to the magnetic particle powder.
5.0% by weight. If less than 0.01% by weight,
The effect of the present invention cannot be obtained. When the content exceeds 5.0% by weight, the desired effect of the present invention can be obtained, but the saturation magnetization is decreased by an increase in oxides or hydroxides containing Si which are not involved in magnetism, which is not preferable. When considering the dispersibility and saturation magnetization of the magnetic particle powder, 0.1 to 2.0
% By weight is preferred.

The amount of the aqueous solution containing both Al and Si per addition is determined in terms of Al in terms of Al with respect to the magnetic iron oxide particles.
The total amount in terms of O ₂ is 0.01 to 5.0% by weight, preferably 0.05 to 3.0% by weight.

In the present invention, the operation of compacting and pulverizing the mixture comprising the magnetic particles and the hydroxide with an edge runner at least twice, preferably 2 to 3 times.
It may be repeated five times. If the number of times exceeds 5, the effect can be obtained, but the effect tends to be saturated, and it is not industrial. The total amount of the Al-containing compound and the Si-containing compound is 0.01 to 10.0% by weight in terms of Al and SiO2 with respect to the magnetic iron oxide particles.
Preferably, it is 0.05 to 5.0% by weight.

The purpose of using the compound containing Al or the compound containing Si as an aqueous solution is to mix them sufficiently and uniformly in a magnetic particle suspension having a pH of 10 or more. It can be added and dissolved and mixed sufficiently in the suspension.

In the present invention, an aqueous solution containing Al or Si is added to a magnetic particle suspension having a pH of 10 or more, and the pH is rapidly adjusted to near neutral (pH 6.5 to 8.5) with stirring. Thus, almost all of Al and Si are rapidly precipitated as hydroxides to form a mixture of magnetic particles and hydroxide.

[0027] The time for quick settling is in the range of 1 to 10 minutes. When the time exceeds 10 minutes, each of the hydroxides may be formed in a layer on the surface of the magnetic particles. Therefore, after quick settling, it is quickly separated by filtration. It may take less than 1 minute, but it takes about 1 minute to precipitate as the above-mentioned hydroxides and to mix them sufficiently.

As the acid for adjusting the pH, sulfuric acid, hydrochloric acid, acetic acid, nitric acid and the like can be used.

The mixture comprising the magnetic particles and the hydroxide may be separated by filtration, washed with water, and dried in a conventional manner.

As the edge runner used in the compaction crushing treatment in the present invention, "Sandmill" manufactured by Matsumoto Casting Iron Works Co., Ltd. and "Mix Mahler" manufactured by Shinto Kogyo Co., Ltd. can be used.

The line weight of the edge runner is 15 to 80 kg
/ Cm, more preferably 30 to 60 kg / cm. If it is less than 15 kg / cm, the shearing force due to the grinding is too weak, so that the mechanochemical effect cannot be obtained,
Al or Si oxide or hydroxide on the particle surface
Fine particles cannot be fixed sufficiently. 80kg /
cm, the shearing force due to grinding is too strong,
There is a risk of destroying the particles themselves. The processing time is 15 to 120 minutes, preferably 30 to 60 minutes.
Minutes.

[0032]

According to the present invention, the magnetic particles for magnetic recording are composed of magnetic particles having α of 0.5 or more in which an oxide or hydroxide containing Al or Si or both of them is fixed on the particle surface. A powder is obtained.

More specifically, α of the magnetic particle powder composed of hexagonal ferrite particles is about 0.50 to 0.70,
Α of the magnetic particle powder composed of adhered magnetic iron oxide particles has a value of 0.5.
Α of magnetic particle powder comprising magnetic iron oxide particles of maghemite particles, magnetite particles and belt oxide compound particles which are intermediate oxides of maghemite and magnetite is about 0.55 to 0.70. It is.

The present inventor has disclosed in Japanese Patent Application Laid-Open No. 55-83207.
JP, JP-A-57-56904, JP-A-58-56904
60506, JP-A-58-161725,
JP-A-59-23505, JP-A-60-2175
No. 29, JP-A-61-63921 and JP-A-62-89226, the α of magnetic particle powder obtained by coating the surface of a magnetic particle powder with a Si compound or an Al compound by a known method is known. Is 0.40-0.
The reason for the low value of about 45 is that the hydroxide of the compound is deposited over a relatively long time to coat the Si compound or the Al compound on the particle surface of the magnetic particles over a relatively long time, so that the magnetic compound is uniformly coated. It was considered that the polymer had few adsorption points on the particle surface of the magnetic particles when dispersed in a molecular resin.

The α of the magnetic particle powder obtained by coating the surface of the magnetic particle powder with a Si compound and an Al compound by the method described in JP-A-63-161522 is as low as about 0.40 to 0.45. The reason is that in order to coat the surface of the magnetic particles with the Si compound or Al compound, the hydroxide of the compound was deposited over a relatively long time and uniformly coated, so that the polymer It was considered that the number of polymer adsorption points on the surface of the magnetic particles was small when dispersed.

Accordingly, a method for increasing the thickness of the polymer adsorption layer by increasing the number of polymer adsorption points on the surface of the magnetic particles as much as possible was studied.

For this purpose, it was considered necessary to adsorb as many as possible ultrafine particles of oxides or hydroxides of Al or Si on the particle surfaces of the magnetic particles and to chemically adsorb them.

Therefore, ultrafine particles of Al or Si hydroxide are uniformly precipitated and mixed in a suspension containing the magnetic particles, and the mixture is compacted to obtain a mechanochemical effect. Al or Si
Of the magnetic particles could be increased to 0.50 or more. This is thought to be the result of increasing the number of polymer adsorption points on the particle surface.

The effect can be further improved by repeating the rapid precipitation and compaction treatment of hydroxides of Al and / or Si or both on the magnetic particles in the present invention at least twice. The reason is that it is possible to secure the more Al or ultrafine particles oxides or hydroxides of Si on the particle surfaces of the magnetic particles, Al or
Alternatively, the fixation of ultrafine particles of Si oxide or hydroxide can be more firmly ensured . It is considered that the adsorption point of the polymer on the particle surface of the magnetic particle powder can be increased , and a higher α value can be obtained.

Further, since the mixture comprising the magnetic particles and the hydroxide is present together by interaction, it is separated by filtration.
Washing and drying can be performed as usual, and there is no particular deterioration in workability.

Incidentally, a case in which a dispersant is added to the iron oxide magnetic powder slurry disclosed in JP-A-55-157216 to give a mechanical shearing force, and JP-A-2-188.
In the case of dry mixing in which a silane coupling agent disclosed in JP-A-429-429 is added, the effect of the present invention cannot be obtained.

[0042]

Next, the present invention will be described with reference to examples and comparative examples. Average particle size of magnetic particle powder (for needle-shaped particles
Is the average major axis diameter, and in the case of plate-like particles, the plate surface diameter) is the electron microscope
Mirror photo (× 30,000) in vertical and horizontal directions
About 350 particles shown in the photo magnified 4 times
Then, the particle diameter was measured, and the average value was shown. Magnetic
When the conductive particles are acicular particles, the axial ratio is the average major axis diameter and the average
In the case of plate-like particles, the ratio with the minor axis diameter is the plate-like ratio.
It was determined by calculating the ratio of the lengths. Magnetic particle powder
Each Al content and the amount of SiO ₂ is adhered to the surface
Is "X-ray fluorescence spectrometer 3063M" (Rigaku Corporation)
(Manufactured by K.K. Co., Ltd.) and use "Keiko X"
It was measured in accordance with "General rules for line analysis".

The evaluation of the dispersibility in the present invention is based on the following equation.
And the value of α is determined by the binder ( number
Urethane resin having an average molecular weight of 15,000, number average molecular weight 2
8000 urethane resin, 42000 number average molecular weight
(Rethane resin ), the saturation adsorption amount (As) of each binder to the magnetic particle powder is measured by a conventional method, and the obtained As and M are plotted in a log-log table to obtain a linear relationship. The value of α was determined from the slope of the straight line.

The magnetic properties of the magnetic particle powder were determined by using a vibration sample magnetometer VSM-3S-15 (manufactured by Toei Industry Co., Ltd.) with an external magnetic field of 10 KOe (provided that magnetic iron oxide particles were used). Is a value measured under 5 KOe), and various characteristics of the magnetic tape are as follows when the external magnetic field is 10 KOe (however, when using a magnetic iron oxide particle coated with Co and a magnetic iron oxide particle, 5 KOe).
KOe).

The gloss of the surface of the coating film is determined by a gloss meter.
"UGV-5D" (manufactured by Suga Test Instruments Co., Ltd.) with an incident angle of 45
It is a value measured in ° and the value when the standard plate gloss is set to 86.3% is shown in%.

The surface roughness Ra is expressed as “Surfcom-57”.
5A "(manufactured by Tokyo Seimitsu Co., Ltd.) was used to measure the center line average roughness of the coating film.

<Surface Treatment of Magnetic Particle Powder> Examples 1 to 7, Comparative Examples 1 to 5; Example 1 A particle diameter of 0.05 μm, a plate ratio of 5.0, and a coercive force of 7
After using Co and Ti substitution type plate-like Ba ferrite particles of 36 Oe and mixing and stirring 6 kg of the particles in water,
0.1 mol / l NaOH aqueous solution was added to adjust the pH to 1.
A mixed suspension of 1.4 was obtained. After stirring and mixing the mixed suspension, 2,200 ml of a 0.5 mol / l aqueous sodium aluminate solution (0.5 w
t%. ) Was added and stirred and mixed. Then, the suspension was stirred with 0.1 mol / l of HC
The pH was adjusted to 7.0 by addition of 1 aqueous solution. The required time at that time was 8 minutes. Immediately, the particles were separated by filtration, washed with water, and dried to obtain magnetic particle powder.

5 kg of the obtained magnetic particle powder was put into an edge runner “MPUV-2” (manufactured by Matsumoto Cast Iron Works) and compacted with a linear load of 60 kg / cm for 60 minutes. The particle diameter of the obtained magnetic particle powder is 0.05μ.
m, the plate ratio is 5.0, the coercive force is 736 Oe, α
Was 0.59.

Further, 4.5 kg of the obtained magnetic particle powder was again mixed and stirred with water, and then 0.1 mol / l of NaO
An aqueous H solution was added to obtain a mixed suspension having a pH of 10.8.
After stirring and mixing the above mixed suspension, 77.9 g of No. 3 water glass (0.5 w in terms of SiO ₂ with respect to the magnetic particle powder) was used.
t%. ) Was added and stirred and mixed. Then, the suspension was stirred with 0.1 mol / l of HC
The pH was adjusted to 6.5 by addition of 1 aqueous solution. The required time at that time was 6 minutes. Immediately, magnetic particles were obtained by filtration, washing and drying by a conventional method.

4 kg of the obtained magnetic particle powder was put into an edge runner “MPUV-2 type” (manufactured by Matsumoto Cast Iron Works) and compacted and pulverized at a linear load of 60 kg / cm for 60 minutes. The particle diameter of the obtained magnetic particle powder is 0.05μ.
m, the amount of fixed Al is 0.49% by weight, and the amount of fixed SiO ₂ is
1.00% by weight, plate ratio is 5.0, coercive force is 7
42 Oe, saturation magnetization value is 57.8 emu / g, α is 0.
65.

Examples 2 to 7, Comparative Examples 1 to 6 Types of magnetic particle powder, types and amounts of compounds to be added,
Magnetic particle powder was obtained in the same manner as in Example 1 except that the time required for addition and stirring, the linear load and time of the consolidation treatment, and the number of repetitions were changed.

Tables 1 to 4 show main production conditions and various characteristics of the obtained magnetic particle powder in each example.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

<Manufacture of Magnetic Tape> Reference Examples 1 to 13 Reference Example 1 The magnetic particle powder obtained in Example 1 was first mixed with a binder resin and a solvent to obtain a solid content. The mixture was kneaded at a rate of 76% by weight using a plastmill for 30 minutes.
Thereafter, a predetermined amount of the kneaded material was taken out, added to a glass bottle together with an abrasive, carbon black, glass beads and a solvent, and mixed and dispersed for 6 hours with a paint conditioner.

Thereafter, a lubricant and a curing agent were added, and the mixture was further mixed and dispersed for 15 minutes. The composition of the resulting magnetic coating is as follows. Magnetic particle powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10 parts by weight Polyurethane resin having sodium sulfonate group 10 parts by weight Abrasive 10 parts by weight Carbon black 3 parts by weight Lubricant 2.5 parts by weight Parts Curing agent 5 parts by weight Cyclohexanone 52.5 parts by weight Methyl ethyl ketone 130.5 parts by weight Toluene 78.3 parts by weight

The obtained magnetic paint was applied on a 14 μm-thick polyethylene terephthalate film to a thickness of 15 μm using an applicator, and then oriented in a magnetic field of 5 KOe, followed by drying to obtain a sheet sample piece. Was. After calendering the obtained sheet sample piece, a curing reaction was performed at 60 ° C. for 24 hours, and a 0.5-inch width slit was obtained to obtain a magnetic tape. The Hc of the obtained magnetic tape was 786 Oe, the squareness ratio was 0.85, and the gloss was 191.
% And surface roughness Ra were 5.6 nm.

Reference Examples 2 to 13 Magnetic tapes were obtained in the same manner as in Reference Example 1 except that the types of the obtained magnetic particles were changed in various ways.

Table 5 shows various characteristics in each of the reference examples.

[0062]

[Table 5]

[0063]

The magnetic particle powder according to the present invention is excellent in dispersibility as shown in the above-mentioned examples, and is therefore suitable as a magnetic particle powder for high-density recording.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01F 1/11

Claims (1)

(57) [Claims] 1. An aqueous alkali solution is added to an aqueous suspension containing magnetic particles to form a suspension having a pH of 10 or more, and an aqueous solution containing Al or an aqueous solution containing Si or Al is added to the suspension.
A mixed aqueous solution containing Si and Si was added, and while stirring, the pH value of this solution was adjusted to near neutral to rapidly precipitate Al or Si or both hydroxides. A method for producing a magnetic particle powder, comprising filtering the mixture with a hydroxide to obtain a mixture of magnetic particles and a hydroxide, washing and drying the mixture, and subjecting the mixture to compaction and crushing with an edge runner. From the operation of adding an aqueous alkaline solution to the aqueous suspension containing the magnetic particle powder to make a suspension having a pH value of 10 or more from the suspension to the operation of compacting and pulverizing the mixture with an edge runner, By repeating at least twice or more, the following equation 1 (where As is the saturated adsorption amount, K ₁ is a constant specific to the system,
M is the molecular weight of the polymer, α is the molecular weight dependent parameter
You. A) having a molecular weight-dependent parameter α of 0.50 or more and obtaining magnetic particles in which oxides or hydroxides containing Al or Si or both are fixed to the surface of the magnetic particles. Manufacturing method of magnetic particle powder. (Equation 1)