JPH01255605A - Method for treating surface of ferromagnetic iron powder and magnetic record medium - Google Patents

Abstract

PURPOSE:To manufacture ferromagnetic iron powder displaying excellent dispersibility, etc., in magnetic coating by pretreating the ferromagnetic iron powder containing iron in main part manufactured by dry reduction method with oxygen and steam, treating with polyurethane resin in organic solvent and specifying each content of denaturant in the organic solvent and moisture. CONSTITUTION:The ferromagnetic iron powder (agglomeration of acicular fine particle having <=about 1mum length) containing iron as main composition manufactured by dry type reduction method is oxidized on the surface thereof under atmosphere of gas containing oxygen to execute oxidization containing about 50-150g of O2/kg of the iron powder. Successively, after bringing it into contact with gas mixing steam having 0.01-10.0% partial pressure of the steam at <=100 deg.C, it is treated with the organic solvent (benzene, etc.) containing the polyurethane resin so as to come to contain <=0.1wt.% denaturant in the organic solvent and <=1.5wt.% moisture in the ferromagnetic iron powder. By this method, the ferromagnetic iron powder displaying excellent dispersibility, orientatability and stability in the magnetic coating, is obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for surface treatment of ferromagnetic iron powder used as magnetic powder for magnetic recording media, and a magnetic layer containing the ferromagnetic iron powder subjected to the surface treatment. The present invention relates to a magnetic recording medium having a magnetic recording medium.

(Prior Art) A coated magnetic recording medium is usually one in which a magnetic paint consisting of magnetic powder, a binder, an abrasive, a lubricant, and an organic solvent is coated on a substrate such as a polyester film.

In addition, ferromagnetic iron powder has high coercive force and saturation magnetization, so its use as magnetic powder for high-density magnetic recording media is expanding.Furthermore, in the direction of higher density, finer magnetic powder and high specific surface area are required. has been done.

However, when the ferromagnetic iron powder is fine and has a high specific surface area, problems arise in terms of the dispersibility of the iron powder when preparing a magnetic coating material and its stability in a recording medium.

One way to solve this problem is to coat the surface of ferromagnetic iron powder with surfactants and coupling agents.

It is being considered that it can be modified with polymeric compounds. That is, Japanese Patent Application Laid-Open No. 61-201702 discloses that when ferromagnetic iron powder is oxidized in an organic solvent, the organic solvent modification products generated on the surface of the iron powder are reduced, and then the iron powder is coated with a polyurethane resin. A method for improving the oxidation resistance 9 dispersibility of iron powder is disclosed. However, the iron powder obtained by this method still has problems in terms of dispersibility and orientation, and furthermore, the corrosion resistance test results of magnetic tapes made using it showed a decrease in surface gloss. be.

(Problems to be Solved by the Invention) The object of the present invention is to
The object of the present invention is to provide a surface treatment method for obtaining ferromagnetic iron powder with excellent dispersibility, orientation, and stability, and a magnetic recording medium using the ferromagnetic iron powder subjected to the surface treatment method.

(Means for Solving the Problems) The inventors of the present invention conducted intensive studies to solve the above problems and found that ferromagnetic iron powder was mixed with oxygen in advance.

The inventors have discovered that ferromagnetic iron powder with excellent magnetic properties can be obtained by treating it with water vapor and then treating it with a polyurethane resin in an organic solvent, leading to the completion of the present invention. That is, in the present invention, ferromagnetic iron powder containing iron as a main component produced by a dry reduction method is subjected to surface oxidation in a gas atmosphere containing oxygen, then subjected to steam treatment, and then treated with an organic solvent containing polyurethane resin. , the organic solvent modification content of ferromagnetic iron powder is 0.1% by weight or less, and the water content is 165%.
The present invention provides a method for surface treatment of ferromagnetic iron powder, characterized in that the surface treatment amount is less than % by weight, and a magnetic recording medium having a magnetic layer containing ferromagnetic iron powder subjected to the treatment method.

The details will be explained below.

The ferromagnetic iron powder used in the treatment method of the present invention is an aggregate of acicular fine particles having a length of 1 μm or less, and has a shape such as a powder, a granulated product, or a crushed product. The main component of this ferromagnetic iron powder is iron, but other components include cobalt and nickel.

Chromium, phosphorus, aluminum, titanium, silicon.

It is also possible to use zirconium, calcium, magnesium, zinc, etc. added as appropriate.

In addition, this ferromagnetic iron powder can be obtained by dry reduction of hydrated iron oxide, etc., but in particular, after treating the surface of α-iron oxyhydroxide with an anti-sintering agent etc., it is dehydrated and calcined. It is preferable to use ferric oxide and then dry reduction using hydrogen gas. Furthermore, there is a risk of ignition if ferromagnetic iron powder is taken out into the air immediately after reduction.
It is preferable to handle in an inert gas atmosphere.

Next, the surface of the obtained ferromagnetic iron powder is oxidized in an oxygen-containing gas atmosphere to impart corrosion resistance and weather resistance.

Conventional methods can be used for surface oxidation in the gas phase, but ferromagnetic It is preferable to perform oxidation in an amount of 50 to 150 g as 02 per 1.0 kg of iron powder.

Further, it is more preferable to carry out the oxidation reaction by changing the temperature in four steps, since excellent corrosion resistance and weather resistance can be imparted. When performing a reaction by changing the temperature in four stages, the first stage reaction is 50 to 150 °C, and the second stage reaction is 0 °C.
~40℃, 3 stages [J reaction is performed at 45~70°C, and the fourth stage reaction is performed at a temperature of 0~40℃, and the oxygen concentration is 0.05 in the first to third stage reactions. The amount of oxidation in the first stage reaction is 20 as 02 per 1°Q kg of ferromagnetic iron powder. ~1
00 g, and the reaction in the second stage stops when the oxidation stops or reaches a constant oxidation rate (usually 2 to 8 hours), and the amount of oxidation in the third stage is 5 to 5 times the amount of oxidation in the first stage reaction.
It is preferable that the fourth stage reaction is carried out for 1 to 5 hours to further suppress the ignitability of the ferromagnetic iron powder.

After that, the surface-oxidized ferromagnetic iron powder is brought into contact with steam and subjected to steam treatment, but this steam treatment only destroys the surface active parts remaining in the ferromagnetic iron powder, so it can be carried out in a short time. can. Further, the steam treatment is preferably carried out at a temperature of 100°C or lower; if the temperature exceeds 100°C, there is a risk that the corrosion resistance of the ferromagnetic iron powder imparted by surface oxidation may deteriorate.

An example of a steam treatment method is to bring ferromagnetic iron powder into contact with an inert gas or a mixture of steam and oxygen-containing inert gas, and the steam content of the gas used at this time is pressure 0.01~10
．． 096 is preferable. Water vapor partial pressure is 0.01
If it is less than %, it will take a long time for the treatment effect to appear.
This is because if it exceeds 10.0%, the magnetic properties and weather resistance of the ferromagnetic iron powder may deteriorate.

As the reaction apparatus used in the process from surface oxidation to steam, a fixed bed type, a fluidized bed type, a one-rotation kiln type, etc. are used.

The steam-treated ferromagnetic iron powder is treated with polyurethane resin in an organic solvent.

The polyurethane resin used in the present invention includes:
Generally, polyurethane binders used in the preparation of magnetic paints are preferred; No. 62-10129, No. G2-4347Q, No. G
No. 2-179521, No. 5G-137522, No. 57
Polyurethane resins disclosed in Japanese Patent No. 113420, No. 57-60152, etc. can also be used.

Further, the organic solvent may be any solvent as long as it dissolves the polyurethane resin used, and aromatic hydrocarbons such as benzene, toluene, and xylene, ketones such as methyl ethyl ketone and cyclohexanone, and esters such as butyl acetate can be used. .

When ferromagnetic iron powder is treated in an organic solvent, the active surface remaining on the surface of the ferromagnetic iron powder oxidizes the organic solvent used.
Oxidative modification products of organic solvents are produced.

The modified product contaminates the surface of the ferromagnetic iron powder and causes a decrease in the dispersibility and orientation of the iron powder in the magnetic paint. Therefore, it is necessary to adjust the modified organic solvent contained in the ferromagnetic iron powder after surface treatment to 0.1% by weight or less based on the dry iron powder. Furthermore, if the moisture content of the ferromagnetic iron powder after surface treatment exceeds 1.5% by weight, the dispersibility and corrosion resistance of the iron powder in the magnetic paint may deteriorate.

Organic solvent modification product contained in ferromagnetic iron powder after treatment.

In order to adjust the water content, it is sufficient to prevent excessive water vapor from adhering during the steam treatment in the present invention, and to select an organic solvent with a low water content as an organic solvent. The ferromagnetic iron powder can be washed with an organic solvent.

Furthermore, the magnetic recording medium of the present invention uses a magnetic coating material as a support, which is prepared by kneading and dispersing a composition consisting of ferromagnetic iron powder subjected to the above surface treatment method, a binder, a solvent, and other components added as necessary. Apply on top.

It has a magnetic layer formed by drying, and can be obtained from iron powder by known means.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these in any way.

Example I Ni, A, Q, Si each 5.5% by weight relative to Fe, 3
．． A granulated product of acicular ferric oxide containing 8% by weight and 0.3% by weight was subjected to fluid reduction in a hydrogen stream at 450° C. for 8 hours to obtain ferromagnetic iron powder.

Thereafter, the obtained ferromagnetic iron powder was heated at 70° in a nitrogen gas stream.
After cooling to C, surface oxidation was performed. Moreover, the surface oxidation was performed in a fluidized reactor while changing the temperature in four stages. The first stage reaction was carried out by supplying nitrogen gas containing 0.2% by volume of oxygen into the reactor at a flow rate of 1 kg of ferromagnetic iron powder and 3 Nm/hour, and the amount of oxidation was 02 per 1.0kg
When the weight reached 70g, the supply of oxygen was stopped.

Next, after cooling to 25°C in a nitrogen gas stream, nitrogen gas containing 0.2 volumes of oxygen was supplied at the same flow rate as in the first stage reaction, and the second stage reaction was carried out, so that the oxygen consumption remained almost constant. The reaction was completed 3 to 5 hours after the reaction.

After the second stage reaction was completed, the temperature was raised to 60° C. at a rate of 20° C./hour while nitrogen gas containing 0.2% by volume of oxygen was continuously supplied into the reactor to carry out the third stage reaction. The amount of oxidation at this time is 1. 12g as 02 per Okg
And so. After the completion of the third stage reaction, the supply of oxygen was stopped, the temperature was cooled to 25°C in a nitrogen stream, and the oxygen was added again by 0.2 volume (96°C).
A fourth stage reaction was carried out by supplying nitrogen gas containing nitrogen. In the fourth stage reaction, the oxygen concentration in the oxygen-containing nitrogen gas was gradually increased, and after 1 hour, the oxygen concentration was reduced to 2% by volume.
The reaction was further continued for 1 hour and then terminated.

Next, the surface-oxidized ferromagnetic iron powder was brought into contact with nitrogen gas having a temperature of 30° C. and a water vapor partial pressure of 1.0%, and was subjected to steam treatment for 1 hour. The moisture content of ferromagnetic iron powder after steam treatment is 0 as a result of M1 constant with Karl Fischer moisture 81.
．． It was 5% by weight.

After steam treatment, the ferromagnetic iron powder is suspended in a methyl ethyl ketone solution containing a linear polyester type polyurethane resin,
Polyurethane resin was applied to the surface of iron powder. At this time, the adhesion m of polyurethane is 2.0% by weight based on the ferromagnetic iron powder.
Met. In addition, the water content of the ferromagnetic iron powder after removing the organic solvent was 0.3% by weight, and the content of the methyl ethyl ketone modified product was extracted using dichloromethane, concentrated, and determined by gas chromatography. 0.1% by weight
It was below.

100 parts by weight of the surface-treated ferromagnetic iron powder obtained above, 25 parts by weight of PVC vinegar picopolymer, 1 part by weight of lecithin, and 160 ml of methyl ethyl ketone. Cyclohexanone 1
The mixture was charged into a sand grinder containing 60 ml of glass beads, and dispersed in one portion for 6 hours to produce an oriented sheet.

In order to evaluate the magnetic properties of the obtained oriented sheet,
Coercive force (lie), residual magnetic flux density (Br), squareness ratio (R
s) was measured using a vibrating sample magnetometer.

In addition, the oriented sheet was placed in air at 60°C and 90% relative humidity. After being left for a period of A, the corrosion resistance was evaluated based on the rate of decrease in residual magnetic flux density (ΔBr) and gloss.

These results are shown in Table 1.

Comparative Example 1 Ferromagnetic iron powder similar to that used in Example 1 was cooled to 70° C. in a nitrogen gas stream, and then surface oxidized. Surface oxidation is performed in a fluidized reactor, and nitrogen gas containing 0.2% oxygen by volume is introduced into the reactor at a rate of 3Nm per 1.0kg of ferromagnetic iron powder.
The ferromagnetic iron powder was supplied at a flow rate of /hour until the oxidation amount reached 7 og at 0.02 kg per 1.0 kg of ferromagnetic iron powder.

The surface-oxidized ferromagnetic iron powder was cooled, immersed in toluene, air-dried, and then surface-treated in methyl ethyl ketone in the same manner as in Example 1 using linear polyester polyurethane as a surface treatment substance.

It can be seen from Table 1 that the content of the organic solvent modified product in the ferromagnetic iron powder after surface treatment is extremely high.

Furthermore, an oriented sheet was prepared using the ferromagnetic iron powder in the same manner as in Example 1, and evaluated.

The results are shown in Table 1.

Comparative Example 2 The surface treatment of ferromagnetic iron powder was carried out in the same manner as in Example 1, except that the steam treatment was carried out in a nitrogen gas atmosphere at 30° C. with a steam partial pressure of 1.0%, and an oriented sheet was formed. We created and evaluated it.

The results are shown in Table 1. From Table 1, it can be seen that the amount of water contained in the obtained ferromagnetic iron powder was large, and the properties of the oriented sheet obtained therefrom were also deteriorated compared to those of the examples. - Comparative Example 3 Ferromagnetic iron powder was surface-treated in the same manner as in Example 1, except that no steam treatment was performed, and an oriented sheet was prepared and evaluated.

The results are shown in Table 1.

Example 2 To 1000 parts by weight of the surface-treated ferromagnetic iron powder obtained in Example 1, binders, additives, and solvents were added in the following proportions,
Kneading and dispersion was performed to obtain a magnetic paint.

PVC/Acid Picopolymer 150 parts by weight Polyurethane resin 100 parts by weight Carbon black 10 parts by weight Lubricant
40 parts by weight chromium oxide, aluminum oxide
30 parts by weight Methyl ethyl ketone 1000 parts by weight Cyclohexanone 1000 parts by weight Toluene 1000 parts by weight Next, an isocyanate compound was added as a curing agent to the obtained magnetic paint, and after stirring, it was applied to one side of a 14 μm thick polyethylene terephthalate film. After orientation and drying, the surface was smoothed by calendering, cured by heating, and cut into a width of 8 mm to obtain a videotape, that is, a magnetic recording medium.

The magnetic properties of the obtained medium are Hc 14000c, B
It was r3000G, Rs O, 82.

(Effects of the Invention) As mentioned above, the ferromagnetic iron powder subjected to the surface treatment of the present invention has excellent dispersibility in magnetic paint.

It shows orientation and stability. Therefore, a magnetic recording medium produced using a magnetic paint obtained from this ferromagnetic iron powder has excellent magnetic properties and excellent corrosion resistance.

Claims (2)

[Claims] (1) After oxidizing the surface of ferromagnetic iron powder whose main component is iron produced by a dry reduction method in an oxygen-containing gas atmosphere, it is treated with steam, and then treated with an organic solvent containing polyurethane resin to strengthen it. The organic solvent modification content of magnetic iron powder is reduced to 0.1
1. A method for surface treatment of ferromagnetic iron powder, characterized in that the water content is 1.5% by weight or less. (2) A magnetic recording medium having a magnetic layer containing ferromagnetic iron powder subjected to the treatment method according to claim 1.