JPS62294101A - Ferromagnetic metal powder - 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 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to ferromagnetic metal powder as a magnetic material in a magnetic recording medium suitable for high-density recording.

[Prior art]

Ferromagnetic metal iron powder, which is used as a magnetic material for magnetic recording, has been widely used as a material for magnetic recording media in recent years because of its high coercive force and excellent recording density due to large saturation magnetization.

Ferromagnetic metal powder as a magnetic material was first put to practical use as a material for audio magnetic tape, and currently 8 mm VT.
It has been put into practical use as a tape material for R.

Acicular ferromagnetic metal powder, mainly composed of iron, is used because of its excellent magnetic potential due to its sufficiently high Hc and σ, but fine particles with a long axis of 1μ or less are usually used. be done.

The characteristics that these ferromagnetic powders must have include excellent dispersibility when used as a magnetic coating, orientation in a coating film, and filling properties, as well as excellent oxidation stability in air. It has been requested to improve trustworthiness.

Conventionally, known methods for ensuring this kind of stability include (1) a method of providing an oxidized layer on the surface layer of the iron powder, and (2) a method of forming a special organic layer on the stone surface of the iron powder.

Among these, in particular, in the method (2) of forming a film with an organic substance, a low molecular weight organic substance with strong surfactant characteristics, such as silicone, is deposited.
8, No. 53-76958, etc., have recently attracted attention.

C Problems to be Solved by the Present Invention] The method of depositing a Si-containing organic substance as described above to form a film on the surface of a ferromagnetic metal powder containing iron as a main component is practical and effective. Many cases have been reported.

However, in the case of the method of forming an organic layer film, it is not enough to simply consider oxidation stability; in other words, it must be possible to actually coat the tape base and easily form a videotape. It won't happen. In this sense, it is necessary to maintain satisfactory properties in terms of affinity with the binder resin for media and even dispersibility in coating, taking into consideration the later conversion into paint. It must be done. In other words, it not only provides oxidation stability against air, but also maintains its dispersibility and original characteristics as a magnetic recording medium under the conditions of actual use.
Furthermore, it is desirable to have something that improves its properties.

In addition, considering the ease of the actual treatment method, it is desirable that the treatment can be carried out at room temperature and in the atmosphere, rather than under special conditions such as high-temperature treatment with a pressurizer or treatment in an inert gas.

Silane coupling agents such as chlorosilanes and alkoxysilanes are conventionally known as Si-containing compounds that can modify the surface of inorganic materials such as iron powder. However, although these silane coupling agents have a strong inherent property of chemically bonding organic materials and P3-free materials, they cannot be used alone to treat materials with very large surface areas such as iron particles. , and the effect of improving the oxidation stability of easily oxidized particles cannot be said to be sufficient.

[Means for solving problems]

In treating the iron powder with organic substances, the present inventors considered operability and searched for organic substances that can be easily treated at room temperature without special conditions such as pressurization or reduced pressure, and are effective. As a result of extensive research, we discovered that ferromagnetic metal powder, mainly composed of iron, obtained by coating with an alkylsilyl isocyanate compound has excellent oxidation stability and is effective in dispersing in paints. Completed the invention.

That is, the present invention provides a silyl isocyanate compound represented by: This is a ferromagnetic metal powder for magnetic recording, characterized in that the surface of the ferromagnetic metal powder is coated with a silyl isocyanate compound having a vinyl group or a phenyl group.

The silyl isocyanate compounds used in the present invention include methylsilyl triisocyanate, dimethylsilyl diisocyanate, trimethylsilyl monoisocyanate, ethylsilyl triisocyanate, diethylsilyl diisocyanate, triethylsilyl monoisocyanate, propylsilyl triisocyanate, dipropylsilyl diisocyanate, tripropyl Preferred examples include silyl monoisocyanate, vinylsilyl isocyanate, and phenyldylyl triisocyanate.

The silyl isocyanate compound used in the present invention is easily available commercially, and can be selected from, for example, the Orgatex-5i series (silicon-functional silyl isocyanate) manufactured by Matsumoto Seiyaku ■.

In the present invention, if the amount of silyl isocyanate added to iron is less than 0.5'' in terms of weight ratio, the effect will be low, and it is desirable to add 1% or more.If the amount is 4% or more, no further increase in effect will be observed. Therefore, preferably 1% or more,
More preferably, it is added in an amount of 2 to 3%.

In the present invention, the above-mentioned silyl isocyanate compound is dissolved in a suitable solvent such as methyl ethyl ketone (
MEK) : ) The iron powder to be treated is impregnated with a solution dissolved in a solution of J renin (TOL) = 1:1, and the solvent is scattered on the surface of the iron powder by a very convenient method of scattering at room temperature. It is possible to form a film that provides oxidation stability and also has siloxane bonds that are effective in improving the dispersibility of magnetic paints.

The reason for this can be considered as follows.

Silyl isocyanate has moderate hydrolyzability, and it is thought that even when operated at room temperature as in the present invention, it is hydrolyzed and condensed by moisture in the air or moisture on the surface of the iron powder, forming a film with strong siloxane bonds. It will be done. Furthermore, since silyl isocyanate undergoes an addition reaction with an active hydrogen compound, it is also thought that it undergoes an addition reaction with hydroxide on the surface of iron, resulting in a film strongly bonded on the surface of iron. In reality, one or both of these effects may be present.

Note that alkoxysilanes are known as silane compounds that produce siloxane bonds through hydrolytic condensation, but the hydrolysis reaction of alkoxysilanes makes it difficult to obtain siloxane bonds by the procedure of the present invention, and alkoxysilanes Silanes and their silanol groups have little to no reactivity with hydroxides on iron surfaces, and there is no possibility of them forming strong bonds with iron surfaces like silylisocyanate. In other words, the object of the present invention cannot be achieved.

In addition, the ferromagnetic metal powder mainly composed of iron used in the present invention is
The method disclosed by the present inventors (e.g.,
1) No. 4833, No. 57-96504, No. 57-10
No. 6527, No. 57-106526, No. 57-1) 3
202, No. 58-48612, etc.) In other words, a shape-retaining component is applied to the surface layer of acicular iron oxyhydroxide powder, and after passing through a washing and drying process, it is subjected to calcining and gas phase catalytic reduction reaction. It can be manufactured by

[Effect]

The effects of the ferromagnetic metal powder coated with the silyl isocyanate compound obtained according to the present invention are summarized as follows.

■) Improved stability against air and humidity 2) Improved dispersibility when forming paints 3) Improved orientation when forming coatings, that is, improved stability against rust that metallic iron powder inherently has, and The effects include improved dispersibility under the conditions of dispersion, that is, during the preparation of magnetic paint, and improved properties after the final recording medium is formed.

〔Example〕

Hereinafter, the effects of the present invention will be explained in detail using Examples and Comparative Examples.

<Manufacture of raw magnetic powder> Iron oxyhydroxide powder containing P and St was synthesized by the method described in JP-A-57-106527 and JP-A-57-96504, and then by the method described in JP-A-58-48612. After undergoing adhesion modification, drying, calcining, and pulverization steps, the iron powder was reduced to reduced iron powder by a gas phase catalytic reduction reaction using H2 gas, and then subjected to gradual oxidation treatment to obtain a sample iron powder. Specific surface area and magnetic properties of the obtained iron powder (sample vibrating magnetometer VSM-1 [
The measurement results in [) are SA'b8.0ffl/g, Hc
15500 e-, σ5120 etnu/g.

<Treatment of silyl isocyanate of iron powder> Using 7 volumes of 1:1 of methyl ethyl ketone (ME) and toluene (TOL) of the silyl isocyanate described below, create a MEK/TOL solution of the silyl isocyanate, and then 100 parts of iron was impregnated into the solution, mixed until sufficiently homogeneous, then the solvent was spattered in the air at room temperature, and air-dried until there was no weight loss. The silyl isocyanate used is as follows.

Example-I 2χ treatment of iron with CHsSi(NGO)s (methylsilyl triisocyanate) Example-2 (CI(i) zs+ (NCO) z (
Example of 2z treatment of dimethylsilyl diisocyanate) on iron - 3CH2・CI5 i (NCO) ) phenyldylyl triisocyanate) to iron with 2χ treatment example-5C1), CH31 (NGO) s to iron with 0.5χ treatment example-6Cl1z=C)ISi (N
Table 1 shows the properties of the silyl isocyanate-treated iron powder obtained in the above example.

Deterioration Acceleration Test of Treated Iron Powder> A portion of the treated iron powder was taken and subjected to an aging acceleration experiment for 4 days in an environment of 60° C. and 80% relative temperature. Among the magnetic properties of iron powder, the deterioration rate of σ5 (la sum to 6n) was particularly evaluated.

The results of the deterioration test of the iron powder coated with silyl isocyanate of Examples 1 to 6 show sufficiently high properties compared to the untreated material.

These results are shown in Table-1.

<Painting/coating and property evaluation of the treated iron powder> 30g of the treated iron powder was collected and the inner volume was 5501 with the following materials.
1) and mixed and dispersed for 3 hours using an Asada Tekko type paint conditioner to create a magnetic paint. α-alumina beads with a diameter of 2 m/m were used as the dispersion medium.

Made by UCC (USA) Salt-vinyl acetate poly? -VAGH: 3g Polyurethane NL-2448 manufactured by Mitsui Toatsu Chemical Co., Ltd.: 3g Solvent EK 42g Toluene 42g Usually, when creating magnetic paint, other dispersants are used, but in order to noticeably observe the treatment effect, Only binder resin was used.

Thereafter, the dispersion media was separated and coated onto a polyester film using an applicator in a precision coater equipped with magnetic tape to a coating thickness of 4 to 5 μm.

After that, calender roll treatment is performed, and further 81) II
It was cut into I width to make a magnetic tape.

At the time of coating, orientation treatment was performed using a permanent magnet at 2500 Gauss.

Table 1 shows the results of measuring the characteristics of the magnetic tape using νSM.

[Comparative example]

Comparative Example 1 The same iron powder as used in the example was mixed with 10 parts of a solvent per 100 parts of iron powder without adding a silyl isocyanate compound.
Comparative Example 1 was obtained by adding and mixing 0 part (M[K:TOL・1:1) and further performing a similar deterioration acceleration test on the powder, which was then made into a paint tape.

The accelerated deterioration test result of this iron powder is σS 90.2emu
/g, and the deterioration rate was 22.6%, and the characteristics of the magnetic tape were Br1630 and Br/8mO,65, which were very low values compared to the examples in which silyl isocyanate treatment was performed.

These results are compared and summarized in Table-1.

Comparative Example 2 The same iron powder as used in the example was used at 2% for 1 loss of CHZ/CH31 (OCL) among alkoxysilanes.
Comparative Example 2 was obtained by carrying out the same treatment using the iron powder, and the results of the deterioration acceleration test of the iron powder obtained and the results of making it into a paint tape.

The accelerated deterioration test result of this iron powder is σs93.7emu
/g deterioration rate was 19.2Vo, and the characteristics of the magnetic tape were 8r1890.8r/Bs O,70.

Although an improvement is seen compared to Comparative Example 1, the characteristics are not very sufficient compared to Examples.

〔effect〕

As is clear from the results of Examples and Comparative Examples, the effects of the present invention can be summarized as follows. That is, acicular iron oxyhydroxide powder is subjected to deposition modification, calcined, reduced, and air-dried to obtain a ferromagnetic metallic iron powder whose main component is iron, which is then coated with a silyl isocyanate compound. This has improved stability against air and humidity, and has a significant effect in suppressing deterioration. Conventionally, magnetic recording metal powder was commercialized by impregnating it with a solvent such as toluene, but the user Due to the ease of handling, there has been a demand for commercialization of dry powder. It can be seen that, in conjunction with these requirements, the silyl isocyanate-treated ferromagnetic metal powder of the present invention is a ferromagnetic metal powder for magnetic recording that has significantly improved stability as a dry powder.

Furthermore, the silyl isocyanate-coated iron powder of the present invention has improved dispersibility in magnetic paints that are actually used, so it can improve the residual magnetic flux density and orientation when made into a magnetic tape. It was confirmed as an effect.

Claims (2)

[Claims] (1) Formula (1) R_nSi(NCO)_4_-_n (1) (In the formula, n represents an integer of 1 to 3) The surface of the ferromagnetic metal powder mainly composed of iron is A ferromagnetic metal powder for magnetic recording, characterized by being coated. (2) The ferromagnetic metal powder for magnetic recording according to claim 1, wherein R is an alkyl group, a vinyl group, or a phenyl group.