JPH0258727A - Magnetic metal powder for short wavelength magnetic recording medium and magnetic recording medium formed by using this powder - Google Patents

Abstract

PURPOSE:To increase the output of the recording medium and to lower the noises thereof by using the magnetic powder having <10 axial ratio and >=35m<2>/g specific surface area as the magnetic metal powder of the magnetic specific surface area essentially consisting of Fe. CONSTITUTION:The magnetic metal powder for the magnetic recording medium essentially consisting of the Fe has <10 axial ratio, more preferably <8 and further preferably <5 axial ratio and >=35m<2>/g specific surface area, more preferably 45 to 95m<2>/g specific surface ratio. The magnetic recording medium formed by using this magnetic powder is lowered in the noises in a short wavelength region and is increased in the number of particles per unit of the magnetic layer, by which the C/N is improved. There is an effect of improving C/N particularly at >=5MHz carrier wave signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a ferromagnetic metal powder for high-density magnetic recording, and more specifically, to a ferromagnetic metal powder for high-density magnetic recording. The present invention relates to a metal magnetic powder for magnetic recording media containing Fe as a main component and a magnetic recording medium using the same.

[Background of the invention and prior art]

Acicular iron-based powder is well known as a metal magnetic powder for high-density magnetic recording. The production process is as follows: 2. Usually, an equivalent or more aqueous alkali solution is added to an aqueous ferrous salt solution to form a solution containing ferrous hydroxide, and an oxidizing gas is blown into the solution. The most common method is to generate iron oxyhydroxide, heat and dehydrate the obtained iron oxyhydroxide to form hematite, and then reduce it with H2 gas or the like.

The characteristics of the ferromagnetic metal powder obtained by this method are largely due to the particle shape and two-particle size distribution of iron oxyhydroxide, which is the starting material.

Conventionally, in order to reduce the output power and noise of magnetic recording media, it is necessary to improve Hc (coercive force) and Br/8m (squareness ratio) and Br (residual magnetic flux density). It was generally considered that a magnetic material with an axial ratio of 10 or more and a good tJ-like property is desirable. Such acicular magnetic powder with a large axial ratio was produced by sufficiently acicularizing the starting material, iron oxyhydroxide.

It is no exaggeration to say that the characteristics of conventional iron-based magnetic powders using iron oxyhydroxide as a starting material are expressed by increasing the axial ratio.

[Problem that the invention seeks to solve]

In recent years, as magnetic recording equipment has become longer recording time and has become smaller and lighter, there has been an increasing demand for higher performance and higher density magnetic recording media. has become necessary. However, conventional magnetic recording media using magnetic powder with a large axial ratio and good acicular shape are not necessarily suitable for short recording wavelengths, and in particular, the noise is large at short recording wavelengths of 1 μm or less. and a high C/N ratio (Carri
It has been found that it is difficult to obtain the ratio of carrier wave signal to noise. The present invention aims to solve these problems of conventional materials.

[Means to solve problems]

The present invention provides a metal magnetic powder for magnetic recording media containing Fe as a main component, wherein the magnetic powder has an axial ratio of less than 10, preferably 8 or less, more preferably 5 or less, and has an axial ratio of 35 m'' or less.
The present invention provides a metal magnetic powder for use in short wavelength magnetic recording media, which is characterized by having a specific surface area of 45 to 95 m''/g or more, preferably 45 to 95 m''/g.

In other words, the present inventors conducted various tests and studies aimed at solving the above problem, and found that when producing iron-based metal magnetic powder using conventional iron oxyhydroxide as a starting material, the production of iron oxyhydroxide When manufacturing a fine powder with a large specific surface area by adopting manufacturing conditions that reduce the axial ratio, which is different from conventional manufacturing conditions, magnetic recording media using this magnetic powder have lower noise in the short wavelength region and a magnetic layer with a lower noise level. It has been found that the C/N ratio can be improved by increasing the number of particles per unit volume. A magnetic recording medium using this magnetic powder is particularly suitable for tangential wave signals such as 5
It was also found that there is an effect on C/N at frequencies above MHz.

Therefore, the present invention also has the following aspects. In a magnetic recording medium in which a metal magnetic powder containing Fe as a main component is contained on a support, the magnetic powder has an axial ratio of less than 10, preferably 8 or less, more preferably 5 or less, and 35 m''/g or more, Preferably it has a specific surface area of 45-95 m''1g.

The present invention provides a magnetic recording medium in which noise is reduced in a short wavelength region which is particularly effective for C/N in a constant wave signal of 5 MHz or higher. This magnetic recording medium may be manufactured by coating the magnetic powder in the form of a paint on a resin film or disk support and magnetically orienting the powder according to a well-known procedure.

EXAMPLES The content of the present invention will be specifically explained below by listing typical examples of the present invention and comparing them with comparative examples.

〔Example〕

In the conventional general method of exposing ferrous salt to excess alkali and oxidizing the resulting ferrous hydroxide with air to produce iron oxyhydroxide, the alkali equivalent, oxidation temperature, oxidation rate, etc. Various iron oxyhydroxides a to i having different axial ratios and specific surface areas were obtained by changing the iron oxyhydroxides a to i. The obtained iron oxyhydroxide a = 4 was heated and dehydrated to form hematite, and then reduced in a Hz air flow at a temperature of 450°C to obtain ferromagnetic metal powder N.

A-1 was obtained.

These ferromagnetic metal powder No., the axial ratio of A-1 and B
Table 1 shows the ET values and their magnetic properties. The axial ratios in Table 1 were obtained by measuring the average major axis length (l) and average minor axis length (d) of 1000 particles using electron micrographs.

It was determined as the axial ratio -1/d. Hc is coercive force, BET is specific surface area, and σ8 is saturation magnetization.

In addition, for each ferromagnetic metal powder No. A to I, α-F
When the X-ray particle size was calculated from the X-ray diffraction peak of the (110) plane of e, it was found that the larger the BET value, the smaller the X-ray particle size.

Furthermore, each of the ferromagnetic metal powders No., A to ■ in Table 2 was made into a magnetic paint by a known method, coated on a polyester film, subjected to orientation treatment in a magnetic field, dried, and calendered to a size of 8 mm. I cut it up and made magnetic tape. Table 2 shows the C/N ratios of these tapes. The C/N ratio is a carrier wave signal of 7 Hz (recording wavelength = 0.5 μm) using an 8 mm deck.
It was measured with Table 2 also shows the characteristics of each magnetic tape.

Figure 1 shows the axial ratio and BET of each metal magnetic powder in Table 1 and 1
The relationship with the C/N ratio of the magnetic tape using each magnetic powder in Table 2 is plotted. The C/N ratio is commercially available 8.
It is expressed as a relative value (d B '') based on the highest value among the millimeter VTR tapes.

Table 1 (Characteristics of magnetic powder) Table 2 (Characteristics of magnetic tape) The following is clear from these results.

The magnetic powders No., A-No., and F are examples of the present invention with an axial ratio of less than 10 and a BET of 35 m 2 /g or more, and No.
, G and H are comparative examples where the BET is 35 m 2 / g or more but the axial ratio is 10 or more, and No. I is a comparative example where the axial ratio is 1
This is a comparative example in which the BET is less than 0 but less than 35 m 2 /g.

The magnetic powders of Comparative Examples No. 1, G, and H, which have an axial ratio of 10 or more and a large specific surface area, have a high coercive force HC and other good magnetic properties. However, although the magnetic recording medium using this has good coercive force and squareness ratio, the C/N ratio at short wavelengths (tangential wave signal near MHz) is as low as 0 and -1.0.

On the other hand, the magnetic recording media using the magnetic powders of Invention Examples Nos. and A to F, which have an axial ratio of less than 10 and have a large specific surface area, all have a C/N ratio higher than 0, and other The magnetic properties are also generally good.

On the other hand, comparative example No. has a small specific surface area even when the axial ratio is less than 10.
, I has a small C/N ratio of -0.5.

Therefore, it is not possible to increase the C/N ratio by decreasing only the axial ratio, and to improve the C/N ratio, it is necessary to decrease the axial ratio and simultaneously increase the specific surface area.

As shown in Figure 1, this relationship shows that if the axial ratio is less than 10 and the BET (specific surface area) is 35 m''/g or more, C
/N ratio can be made higher than 0. Preferably, the axial ratio is 8 or less and the BET is in the range of 45 to 95 m''/g, and more preferably the axial ratio is 5 or less and the BET is 50 to 8.
It can be seen that within the range of 0 m2/g, the 2-layer C/N ratio is improved. And No., which showed a particularly high C/N ratio,
As seen from the results in Tables 1 and 2, A, No., and B have good magnetic properties other than the C/N ratio.

On the other hand, if the BET becomes too high, the saturation magnetization σ.

Since R becomes small and sufficient r cannot be obtained, the output decreases, making it difficult to obtain an effect in terms of C/N. Therefore, BE
The higher the T, the better. However, there is an appropriate upper limit for improving the C/N ratio, and it is preferably 95 m''/g or less, preferably 80 m''/g or less.

In this way, the present invention has discovered that on the short wavelength side, it is more effective to decrease the C/N ratio by decreasing the axial ratio, contrary to the direction conventionally thought (however, if the specific surface area is (need to be appropriately large) This made it possible to achieve higher performance of the magnetic recording medium.

Although the above examples show pure α-Fe metal powder using iron oxyhydroxide as a starting material, Fe-based materials containing known elements that are advantageous for improving magnetic properties and manufacturing magnetic recording media may also be used. However, as long as the axial ratio and specific surface area are within the range specified by the present invention, the effect of the present invention of improving the C/N ratio can be exhibited. In addition to the magnetic tape example described above, a magnetic disk was also prototyped and tested in the same way, and similar to the magnetic tape, it was able to achieve a high C/N ratio on the short wavelength side. Since the magnetic powder according to the present invention has a high C/N ratio, it is particularly suitable for short wavelength magnetic recording media, but it also has magnetic properties similar to conventional ones even on the long wavelength side.

[Brief explanation of the drawing]

Figure 1 shows the axial ratio and BET value of the magnetic powder A-1 of Example, and the C/
It is a relationship diagram of N ratio.

Claims (3)

[Claims] (1) In metal magnetic powder for magnetic recording media whose main component is Fe, the magnetic powder has an axial ratio of less than 10 and an axial ratio of 35 m^2/
1. A metal magnetic powder for use in short wavelength magnetic recording media, characterized by having a specific surface area of 100 g or more. (2) In a magnetic recording medium in which a metal magnetic powder containing Fe as a main component is contained on a support, the magnetic powder has an axial ratio of less than 10 and a specific surface area of 35 m^2/g or more, and the recording wavelength is A magnetic recording medium with a diameter of 1 μm or less. (3) The magnetic recording medium according to claim 2, wherein the magnetic powder has a specific surface area of 45 to 95 m^2/g, and the magnetic powder is oriented on the support.