JPS63226008A - Magnetic powder with improved dispersibility - Google Patents

Abstract

PURPOSE:To obtain the magnetic powder having improved dispersibility by a method wherein at least a kind of the hydroxide of Cu, Ag, Al, Sn, Nb, Ta, Sb, Cr and Ni is contained in the surface of the title magnetic powder. CONSTITUTION:The quantity of the hydroxide contained in the surface of magnetic powder is generally 0.01-20 pts. wt. against the magnetic powder of 100 pts. wt., desirably 0.05-5 pts. wt. When the quantity of hydroxide exceeds 20 pts. wt., magnetic flocculation is hardly generated, and it is effective in the improvement of dispersibility. However, as the hydroxide is a non-magnetic substance and the magnetic characteristics such as coercive force and the like of magnetic powder are deteriorated, the use of the hydroxide in excess of 20 pts. wt. is not desirable. The viscosity of the magnetic coating material, in which said magnetic powder is used, is low when compared with the case where the magnetic powder containing no metal hydroxide. From the above- mentioned fact, it can be realized that said magnetic powder has the improved dispersibility in organic binder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic powders having improved dispersibility in various organic binders.

In recent years, there has been a demand for increasingly higher performance in magnetic recording media, and along with this, magnetic powders with high coercive force and magnetic powders with high filling properties are required as magnetic materials.

γ-Fe, which is commonly used as a recording element for magnetic recording media
, O, and cobalt-containing iron oxide have hydrophilic surfaces, so when they are kneaded with various organic binders to prepare magnetic paints, they are difficult to wet with the binder.
Moreover, due to its own magnetic property, particles tend to coagulate magnetically, making it difficult to disperse them uniformly in the binder.

As a countermeasure against this, a method of loosening the agglomerates using mechanical dispersion means (JP-A-50-22297, JP-A-55-15
7216, Japanese Unexamined Patent Publication No. 56-10903) has been attempted. However, this method does not provide a fundamental solution since aggregation begins when the mechanical dispersion operation is stopped. Furthermore, a method of coating the particle surface of magnetic powder with a surfactant or the like that is compatible with an organic binder before preparing a magnetic paint (Tokyo Publication No. 5)
3-19120, JP-A-54-37297, JP-A-53
-141196, JP-A-54-82354, JP-A-54
-85397) and a method of adding a surfactant as a dispersant during the preparation of magnetic paint (Japanese Patent Laid-Open Nos. 55-151068 and 1982-151069) have been attempted.

Methods for coating the surface of particles with surfactant include immersion treatment in aqueous or non-aqueous systems, or direct spraying on the powder, but in this case, the coated surfactant is desorbed during kneading with the organic binder. There are problems with resin selectivity, such as problems with resin selectivity, such as problems such as the effect not being sustained due to urethane resins, and even if the dispersibility with vinyl acetate and vinyl chloride resins is improved, the effect is small with urethane resins.

Furthermore, if a large amount of surfactant is added during the preparation of a magnetic coating material in order to improve the wettability of the magnetic powder in the organic binder, there are disadvantages such as a decrease in the strength of the tape, bleeding, and powder falling off.

As a result of various studies to improve these drawbacks, the inventors of the present invention discovered that Cu, Ag, etc.
1Al, Ti, Zr, Sn, V, Nb+Ta+Sb,
The present invention was completed based on the discovery that dispersibility in an organic binder during the preparation of a magnetic coating material can be improved by containing at least one of the hydroxides of Cr, Mo, W, and Ni.

That is, the present invention has Cu, Ag, ^l on its surface.

A magnetic powder having improved dispersibility characterized by containing at least one of the hydroxides of Sn, Nb, Ta, Sb, Cr and Ni.

Examples of the magnetic powder containing metal hydroxide on the surface of the present invention include 7-Pesos, magnetite, and γ-Fez.
Examples include a bertholed compound which is an intermediate oxide between 03 and magnetite, the above-mentioned magnetic powder containing Co, ferrite, and ferromagnetic chromium oxide.

γ-Fetus, magnetite, or bertolide compounds are prepared by dehydrating acicular hydrated iron oxide using a conventional method.
Those obtained by appropriately combining operations such as reduction and reoxidation can be used. Regarding cobalt-containing magnetic iron oxide, for example, Japanese Patent Publication No. 57-37532, Japanese Patent Publication No. 4B-44
040, JP-A-54-13997, JP-A-54-106
895, as known from Japanese Patent Publication No. 53-100197,
Magnetic iron oxide powder such as 7-Fez03 is coated with cobalt or a metal compound such as cobalt and iron as a nucleus crystal, and dried or heat-treated, or, for example,
As known from Japanese Patent Publication No. 41-6538, Japanese Patent Publication No. 49-4264, and Japanese Patent Publication No. 48-101599, a solid solution containing cobalt can be used.

The term hydroxide here is a general term for hydrated hydroxide, hydrated oxide, or hydrated oxyhydroxide, which is an intermediate between these, and in a strict sense, the negative component is a hydroxyl group. Although not limited to certain compounds, the amount of hydroxide contained on the surface of the magnetic powder is generally 100% of the magnetic powder.
The amount is 0.01 to 20 parts by weight, preferably 0.05 to 5 parts by weight. The amount of hydroxide is 20il
If it exceeds 1 part, it may cause magnetic agglomeration. Although it is effective in improving dispersibility, since hydroxide is a non-magnetic substance, the magnetic properties such as coercive force of the magnetic powder will decrease. Undesirable.

There are no particular limitations on the method for containing metal hydroxide on the surface of the magnetic powder, but it is important that the metal hydroxide precipitates uniformly on the surface of the magnetic powder. The effectiveness decreases when mixed with powder.

In other words, when processing by neutralizing metal salts with acid or alkali in a slurry of magnetic powder, or by hydrolyzing metal salts in a slurry, the slurry must be thoroughly stirred to ensure a good dispersion state of the magnetic powder. Furthermore, it is effective to allow the neutralization reaction and hydrolysis reaction to proceed as gradually as possible in order to ensure uniform content. For this purpose, the slurry temperature, pH
It is necessary to adjust the concentration and the rate of addition of the metal salt solution and alkaline solution to the slurry as appropriate. The same thing can be said even when the neutralization method and the hydrolysis method are used together. The atmosphere at which the hydroxide is contained may be oxidizing, inert, or reducing (the effect of the present invention does not particularly differ depending on the difference in the metal valence of the hydroxide.

The magnetic tape obtained using the magnetic powder of the present invention has a higher squareness ratio (Br78m) and orientation (O
R) has improved.

Furthermore, the viscosity of the magnetic paint using the magnetic powder of the present invention is lower than that of the magnetic paint using the magnetic powder that does not contain metal hydroxide. These results indicate that the magnetic powder of the present invention has improved dispersibility in an organic binder.

It is not necessarily clear why the dispersibility in an organic binder is improved when using the magnetic powder of the present invention, but (1) coating with a metal hydroxide improves the magnetism of the magnetic powder in an organic binder. (2) The affinity between the magnetic powder and the organic binder increases, resulting in better wetting. (3) The metal hydroxide coated in the organic binder is less likely to separate from the magnetic powder, improving the dispersion effect. It is assumed that it is easy to sustain.

Next, examples of the present invention will be described.

Example 1 Acicular 7 FezO:+ (coercive force 11c: 360 oersted, saturation magnetization: 73eIIlu/g, average major axis length about 0.4 μm, acicular ratio 10:1) 200 g
Disperse it in about 21 g of water to make a slurry, I Fez
Adjust the slurry concentration to Oz l OOt,/l.

Transfer 500 d of this slurry to a fourth flask, raise the temperature to 60°C while stirring, and then ^jl! Concentration 4.17
g#! ni m! ! 60 mfl of an aqueous solution of 10 g of NaA
dropwise into the slurry for 30 minutes at a rate of 2-7 minutes. Furthermore, 120 ml of 0.1 N Na011 aqueous solution was added dropwise at a rate of 2 d/min for 1 hour to neutralize to pH 7, and 1-Fe,
0. The surface of the sample is uniformly coated with NaAlO□. After aging for 1 hour, filter and wash using a Buchner funnel. 10
Dry for one day and night at 0°C, coarsely crush in a mortar, and then crush for 2 minutes in a crusher.

Using the magnetic powder thus obtained, a magnetic paint was prepared with the following composition, and this paint was applied onto a polyester film, oriented at an orientation strength of 1000 Gauss, and dried to produce a magnetic tape.

Magnetic powder 100 Parts by weight Dioctyl phthalate 4 Soybean lecithin 1.6 Surfactant (special phosphoric acid ester 4 Mol type nonionic anion activator) Toluene 100 Methyl ethyl ketone 100 Comparative example 1 In Example 1, 7 Fezes 100g/
The slurry, which has been adjusted to a concentration of 1, is immediately filtered through a Buchner funnel without being subjected to coating treatment. 1 of this magnetic powder
The mixture was dried at 00° C. for one day and night, crushed in a mortar, and then crushed for 2 minutes in a crusher to produce a magnetic tape in the same manner as in Example 1.

Reference Example 1 Acicular 7-Fe, 0. (Coercive force 11c: 360 oersted, saturation magnetization: 73e+++u/g, average major axis length approximately 0.4μ, needle-like ratio 10:1) 200g
Dispersed in about 22% water to make a slurry, γ-Fear
s 100g/, j! Adjust the slurry concentration to Transfer 500 d of this slurry into four Lof flasks, raise the temperature to 60°C while stirring, and add 2 60 d of an aqueous solution of voso, ・n1lzO whose v6 degree was adjusted to 4.17 g/f.
Drop into the slurry for 30 minutes at a rate of m1/min. 0 more
．． 120 d of 1N Na011 aqueous solution was added dropwise at a rate of 2 rxl 1 minute for 1 hour to neutralize to p117, y, -Fc4
0. VO5O4·nll□0 is uniformly coated on the surface. After aging for 1 hour, filter and wash using a Buchner funnel. Dry at 100℃ for 1 day and night, crush in a mortar, and then crush with a crusher for 2 days.
Grind for a minute.

Using the thus obtained magnetic powder, a magnetic tape was prepared in the same manner as in Example 1 above.

Reference example 2 Same as reference example I, v6 degree 16.67 g/l
D. Except for changing the N a OIt concentration to 0.4 normal.
A magnetic tape was prepared in the same manner as in Reference Example 1 above.

Reference Example 3 In Reference Example 1, Na1WO4'nllgo was used instead of VOSO4・nllgo, II(/! aqueous solution was used instead of Na011 aqueous solution, and the W concentration was 4.17 g#
! A magnetic tape was prepared in the same manner as in Reference Example 1, except that the HCI concentration was set to 0.1N.

Reference Example 4 In Reference Example 3, w:lIA degree was 16.67 g/
A magnetic tape was prepared in the same manner as in Reference Example 1, except that the C2 concentration was set to 0.4N.

Reference Example 5 In Reference Example 1, instead of VOSO4・n1lzO, (Nlla) Jo? o! 4 * nlIzO1Mo concentration to 4.11 g/l, 0.1N 11N after adding treatment liquid
A magnetic tape was prepared in the same manner as in Reference Example 1, except that the pH was adjusted to 2 using an O3 aqueous solution.

Reference Example 6 Magnetic powder acicular γ-Feze obtained in the same manner as Reference Example 1
Slurry 500d of s 100g/H! Transfer 4 portions of the mixture into a round flask, and heat to 60°C while stirring.

In this slurry, (NI+4) zZrO(COx)
Zr dissolved in z? Q degree 4.17g//! aqueous solution of 60
ml dropwise for 1 hour at a rate of 1-7 minutes. After stirring uniformly for 30 minutes, the temperature was raised to 90°C and stirred for 1 hour.
The surface of Pez02 was coated with hydrated Zr oxyhydroxide. The above-mentioned Reference Example 1 was prepared using the magnetic powder thus obtained.
A magnetic tape was created using the same method.

Reference Example 7 In Reference Example 6, (N114) 22rO(Co, )
! TrCla was used instead of TrCla, and the Ti concentration was 4.17.
A magnetic tape was prepared in the same manner as in Reference Example 1 except that the ratio was changed to g/l.

Reference Example 8 In Reference Example 6, (NII4) zZrO(COi)
N114ν0. instead of z. Using, ■ concentration 2.0
A magnetic tape was prepared in the same manner as in Reference Example 1 except that the concentration was changed to 8 g/l.

The squareness ratio (Or/am) and orientation (OR
) are shown in Table 1.

Table 1 Characteristics of Magnetic Tape As is clear from Table 1, the squareness ratio and orientation values of the magnetic tapes prepared using the magnetic powder of the present invention (Example) and the magnetic powder obtained in the Reference Example are Although there are differences in degree depending on the type of metal element contained on the surface, the amount contained, and the method of inclusion, all are improved compared to the case of using magnetic powder that does not contain metal hydroxide (Comparative Example 1). ing.

This shows that the magnetic powder of the present invention has improved dispersibility in the organic binder.

Next, the viscosity of the magnetic paints obtained in Reference Example and Comparative Example 1 was measured using an E-type viscometer (cone plate type manufactured by Tokyo Keiki Co., Ltd.), and the results are shown in Table 2.

Table 2 Viscosity of magnetic paint (c-p) Example 2 Acicular r Fears (BET specific surface area 31rrf/g
, needle ratio 10:1) was dispersed in 22 water to make a slurry, an aqueous solution of cobalt sulfate and ferrous sulfate was added in a non-oxidizing atmosphere, and then an aqueous NaOH solution was added dropwise to form γ-Feg03 particles. Cobalt and iron were deposited on the surface. The deposited amount was 5% by weight of Co atoms and 10% by weight of Fe atoms relative to iron in r-Fe, O, and iron. This adhered slurry was filtered and washed with water, and the wet cake was placed in an autoclave, replaced with N2, sealed, and heated to 130°C.
The mixture was heat-treated in the presence of steam for 6 hours. The cobalt-containing magnetic iron oxide wet cake thus obtained was dispersed in water to form a 150 g/l slurry, blown with N2 gas, and heated to 60°C. This slurry was stirred and mixed with an aqueous solution of NaOII and SnClI in a non-oxidizing atmosphere.
z ・nH2O was added dropwise over 1 hour while maintaining the pH at 8.5, and then stirred and aged for 1 hour to uniformly coat the particle surface with 0.7% by weight of SnCl and ・n11.0 as Sn. Treated 0 then filtered and washed with water 60
The magnetic powder of the present invention was obtained by drying at ℃ for 8 hours.

Example 3 In Example 2, 5nCf, ·n! A 5 bcz hydrochloric acid aqueous solution was used instead of a 1.0 aqueous solution, and this and Na
Example 2 except that the aqueous solution of 011 was added dropwise while maintaining the pH at 1.5, and the coating amount was 0.7% by weight as sb.
Magnetic powder was obtained in the same manner as above.

Example 4 The same procedure as in Example 2 was carried out, except that an aqueous solution of CuSO4.511□0 was used instead of the SnCl z-nll□0ll method, and 0.7% by weight of Cu was coated in an air atmosphere. A magnetic powder was obtained.

Example 5 In Example 2, an aqueous solution of NiSO4.71hO was used instead of an aqueous solution of SnC1□nil□0, and magnetic properties were obtained in the same manner as in Example 2, except that 0.7% by weight of Ni was coated in an air atmosphere. A powder was obtained.

Reference example 9 Acicular r FezO5 (BET specific surface area 31%/g
, needle ratio 10:1) Disperse 200 g in 22 water to make a slurry, add an aqueous solution of cobalt sulfate and ferrous sulfate in a non-oxidizing atmosphere, then drop an aqueous NaOH solution to obtain γ-Fe, Cobalt and iron were deposited on the surface of the 03 particles. The adhesion amount is C to iron in γ-Fe2O3.
The content of o atoms was 5% by weight, and the content of Fe atoms was 10% by weight. The deposited slurry was filtered and washed with water, and the wet cake was repulped and dispersed in water to form a slurry of 150 g/Il, which was heated to 60° C. by blowing N2 gas. This slurry was stirred in a non-oxidizing atmosphere, and an aqueous solution of Na 011 and VOSO4.nHzO were added dropwise over 1 hour while maintaining the pH at 7.5, and then continued to be stirred for 1 hour to mature, so that the particles were uniformly coated on the surface of the particles. VO (Oll) z・nll□0
Cover. The coating amount is 0.8 weight percent as V based on the cobalt-containing magnetic iron oxide powder. After aging, the wet cake was filtered and washed with water, and the wet cake was placed in an autoclave with water in a separate container, Nzf exchanged, sealed, and incubated at 130°C for 6 hours.
Heat treated in the presence of steam for 0 and then 8 at 60 °C
After drying for several hours, a magnetic powder was obtained.

Reference example i.

Cobalt and iron were deposited on the surfaces of γ-Fe and O in the same manner as in Reference Example 9. This adhering slurry is filtered and washed with water.
This wet cake was heat-treated in an autoclave in the same manner as in Reference Example 9 at 130° C. for 6 hours in the presence of steam. The wet cake of cobalt-containing magnetic iron oxide thus obtained was dispersed in water to make a 150 g/l slurry, and V was uniformly applied to the particle surface by the same method as in Reference Example 9.
O(011), 0.8% by weight, where n1lzO is V
The coated powder was then filtered, washed with water, and dried at 60° C. for 8 hours to obtain magnetic powder.

Reference Example 11 In Reference Example 10, an alkaline aqueous solution of NazMoOn was used instead of the VO5O4/n1lzO aqueous solution, and this and a sulfuric acid aqueous solution were dropped in an air atmosphere while maintaining the temperature at 2118.5, and the coating amount was 0.7 weight as MO. Magnetic powder was obtained in the same manner as in Reference Example 10, except that the magnetic powder was bound by %.

Reference Example 12 Magnetic powder was obtained in the same manner as in Reference Example 11, except that an alkaline aqueous solution of Na2WO4 was used instead of the alkaline aqueous solution of Na2MoO4.

Comparative Example 2 In Reference Example 9, the cobalt and iron were coated, filtered and washed with water, and the wet cake was placed in an autoclave with water in a separate container without being subjected to coating treatment, and the same procedure as in Reference Example 9 was carried out. A magnetic powder was obtained.

Regarding the magnetic powders obtained in Examples 2 to 5, Comparative Example 2, and Reference Examples 9 to 12, the saturation magnetization (σ, )
After measuring, a magnetic paint was prepared according to the blending ratio shown below, and this paint was applied onto a polyester film using the usual method, oriented and dried to create a magnetic tape having a magnetic coating film of about 6 μm. .

Magnetic powder 24 parts by weight Polyurethane resin 5 Vinyl chloride vinyl acetate copolymer 1.2 Dispersant
0.5〃Mixed solvent Toluene/Ml! K
69.3' The squareness ratio (Br/Bad), orientation (OR), and switching field distribution (SFD) of each of the magnetic tapes obtained were measured using conventional methods, and the results are shown in Table 3.

Table 3 Reference Example 13 Using the magnetic powder obtained in Reference Example 9, a magnetic tape with a binder composition mainly composed of chloride-vinyl-acetate-vinyl alcohol copolymer was prepared in the same manner as in Example 1. ratio(
Or/Bm), orientation (OR), etc. were measured, and the results are shown in Table 4.

Comparative Example 3 Using the magnetic powder obtained in Comparative Example 2, a magnetic tape having a binder composition mainly composed of chloride-vinyl-acetate-vinyl alcohol copolymer was prepared in the same manner as in Example 1, and the squareness ratio (
Br70w), orientation (OR), etc. were measured, and the results are shown in Table 4.

Table 4 As is clear from Table 3, even when cobalt-containing iron oxide is used, there are differences in degree depending on the type of metal contained on the surface, but when no metal hydroxide is contained (comparison It can be seen that the values of Br/Bm+, OR, etc. are improved compared to Example).

For reference, Table 4 shows the magnetic properties when the binder composition was changed.

Claims (1)

[Claims] On its surface, Cu, Ag, Al, Sn, Nb, Ta,
A magnetic powder having improved dispersibility characterized by containing at least one of Sb, Cr and Ni hydroxides.