JPH0715745B2 - Magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is directed to AO · n {(Fe ₁ -xMx) ₂ O ₃ } (where A is Ba or Ba and Sr and M is Zn). And Ti or Zn, Co and
Ti, n = 6.5 to 11.0, x = 0.05 to 0.25)
A magnetic recording medium coated with a resin composition containing a plate-like magnetoplumbite-type ferrite fine particle powder containing a or Ba and Sr, wherein the change in coercive force in the temperature range of 20 to 90 ° C. of the magnetic recording medium. In the range of -2.0 Oe / ° C to +2.0 Oe / ° C.

[Conventional technology]

In recent years, as the recording and reproducing devices for video and audio have been recorded for a long time and have been made smaller and lighter, there is an increasing need for higher performance of magnetic recording media such as magnetic tapes and magnetic disks. In particular, high density recording of magnetic recording media is required.

Magnetic recording media are generally manufactured by applying a resin composition containing magnetic particle powder onto a substrate.

The conventional recording method is acicular γ-Fe ₂ O ₃ particle powder, Co
Recording is generally performed by orienting acicular magnetic particle powder such as adhered acicular γ-Fe ₂ O ₃ particle powder in the in-plane longitudinal direction of the magnetic recording medium and utilizing residual magnetization in that direction. Met. In order to increase the recording density, it is necessary to shorten the recording wavelength, but in the case of the above recording method, it is necessary to shorten the major axis of the acicular magnetic particles as the recording becomes shorter wavelength. As a result, the influence of the demagnetizing field between the elements increases, and as a result, the reproduction output decreases, which is disadvantageous for high-density recording.

Therefore, in recent years, as a recording method for high-density recording, a so-called perpendicular magnetic recording method has been proposed in which recording is performed by utilizing residual magnetization in the direction perpendicular to the surface of the magnetic recording medium, and is being put into practical use. is there.

In the case of the perpendicular magnetic recording method, the magnetic particle powder is arranged in the direction perpendicular to the surface of the magnetic recording medium, and the different magnetic poles are adjacent to each other. The influence of the demagnetizing field between each other is unlikely to occur, and the particles adjacent to each other reinforce each other's magnetization, so that the decrease in output is small and it is suitable for high-density recording.

As described above, the perpendicular magnetic recording medium capable of high-density recording is the most demanded at present, and as such a magnetic recording medium, for example, as described in JP-A-55-86103. A magnetic recording medium in which a resin composition containing a plate-shaped magnetoplumbite ferrite particle powder containing Ba is coated on a substrate (hereinafter, simply referred to as a medium coated with the plate-shaped magnetoplumbite ferrite particle powder. )It has been known.

Recently, research and development for practical use of a medium coated with plate-shaped magnetoplumbite-type ferrite particle powder have been actively conducted, and it is possible to improve electromagnetic conversion characteristics and durability that are normally required for the medium. In addition, magnetic (in particular, coercive force) stability against temperature (hereinafter, simply referred to as temperature stability) is strongly demanded.

The reason is that magnetic recording is performed by magnetizing the magnetic recording medium by a magnetic field generated by the magnetic head. However, the magnetic field of the magnetic head and the magnetization component of the magnetic recording medium are used at room temperature so that optimum recording can be performed. This is because even if a certain coercive force value is adjusted, optimum recording cannot be performed if the coercive force value of the magnetic recording medium fluctuates due to temperature rise due to environmental changes.

By the way, various characteristics such as electromagnetic conversion characteristics of the magnetic recording medium are
It is closely related to the characteristics of the magnetic particle powder used,
The properties of the magnetoplumbite-type ferrite particle powder containing are generally 0.01 to 0.3 μm in average diameter and excellent in dispersibility, that the coercive force can be controlled in the range of 300 to 2000 Oe, and the magnetization value is as large as possible. Is required. It is necessary to control the coercive force within the range of 300 to 2000 Oe in order to enable recording with a magnetic head made of ferrite which is widely used at present.

[Problems to be solved by the invention]

A magnetic recording medium capable of high-density recording is currently most demanded, and as a medium satisfying such characteristics, there is a medium coated with a plate-like magnetoplumbite type ferrite fine particle powder. , Ba or Ba and Sr
Due to the characteristics of the plate-like magnetoplumbite-type ferrite fine particle powder containing, the coercive force tended to increase as the temperature increased, and the temperature stability was poor.

This phenomenon is described in the "Metal" published by Agne Co., Ltd. (1986) June issue, "The coercive force of barium ferrite increases with increasing temperature ..." on page 10 and "Page 12". The temperature changes of coercive force and saturation magnetization of the magnetic recording medium are determined by the magnetic powder used, and it was confirmed that the coercive force and saturation magnetization of the barium ferrite medium have the same characteristics as the temperature characteristics of the magnetic powder shown in FIG. "."

As mentioned above, the temperature stability of the magnetic recording medium is
It depends on the temperature stability of the plate-like magnetoplumbite type ferrite particle powder containing Ba.
As described in Japanese Patent Laid-Open No. 2003-2003, it has been attempted to improve the temperature stability of plate-like magnetoplumbite ferrite particle powder containing Ba or Ba and Sr.

The method described in Japanese Patent Laid-Open No. 61-152003 uses Co (II) -Ti.
(IV), etc., plate-like magnetoplumbite-type ferrite particle powder containing Ba containing an element for reducing coercive force is heat-treated at 300 to 700 ° C. in a reducing atmosphere. As a result, the coercive force is more than double the value before the heat treatment, and it is difficult to control the coercive force to an appropriate value. Therefore, when a medium is manufactured using the plate-like magnetoplumbite-type ferrite particle powder containing Ba, the coercive force of the medium is improved, and recording with a conventional ferrite magnetic head becomes difficult.

Therefore, there is a strong demand for establishment of a method for obtaining a medium coated with a plate-like magnetoplumbite-type ferrite fine particle powder having an appropriate coercive force and excellent temperature stability.

[Means for solving problems]

The present inventor has various coercive forces, and as a result of various studies to obtain a medium coated with a plate-like magnetoplumbite ferrite fine particle powder having excellent temperature stability,
The present invention has been reached.

That is, according to the present invention, AO · n {(Fe _1- xMx) ₂ O ₃ } is formed on the substrate.
(However, A is Ba or Ba and Sr, M is Zn and Ti or Zn, Co
And Ti, n = 6.5 to 11.0, x = 0.05 to 0.25), or a magnetic recording medium coated with a resin composition containing a plate-like magnetoplumbite ferrite fine particle powder containing Ba or Ba and Sr. Then, the change of the coercive force in the temperature range of 20 to 90 ° C. of the magnetic recording medium is −2.0 Oe / ° C. to +2.0 Oe /
It is a magnetic recording medium in the range of ° C.

[Action]

First, in the present invention, the most important point is that AO.
n {(Fe _1- xMx) ₂ O ₃ } (where A is Ba or Ba and Sr, M
Is Zn and Ti or Zn, Co and Ti, n = 6.5 to 11.0, x = 0.0
It is a fact that the magnetic recording medium coated with the resin composition containing the plate-like magnetoplumbite ferrite fine particle powder containing Ba or Ba and Sr having a composition of 5 to 0.25) has excellent temperature stability.

That is, in the magnetic recording medium according to the present invention, the change in coercive force in the temperature range of 20 to 90 ° C. is within the range of −2.0 Oe / ° C. to +2.0 Oe / ° C.

In particular, in the case of a medium coated with a plate-like magnetoplumbite ferrite fine particle powder containing Ba having a specific composition further containing Co in addition to Zn and Ti, the change in coercive force in the temperature range of 20 to 90 ° C. , 0 Oe / ° C to +2.0 Oe / ° C.

In the present invention, the reason why the magnetic recording medium excellent in temperature stability is obtained is that the temperature stability is excellent because the plate-like magnetoplumbite ferrite particle powder containing Ba to be used has a specific composition. Especially.

That is, the plate-like magnetoplumbite ferrite fine particle powder containing Ba or Ba and Sr in the present invention is 20 to 120 ° C.
The change of coercive force in the temperature range of -2.0 Oe / ℃ ~
Within the range of +2.0 Oe / ℃.

In particular, when the plate-shaped magnetoplumbite-type ferrite fine particle powder having the specific composition according to the present invention further contains Co in addition to Zn and Ti, the change in the coercive force in the temperature range of 20 to 120 ° C. is 0 Oe. Within the range of / ° C to +2.0 Oe / ° C.

The reason why the plate-like magnetoplumbite-type ferrite particle powder containing Ba having a specific composition in the present invention is excellent in temperature stability is not yet clear, but the inventor, as shown in Comparative Examples below, In {(Fe _1- xMx) ₂ O ₃ },
In the case of a plate-like magnetoplumbite-type ferrite fine particle powder containing Ba having a composition other than the range of n = 6.5 to 11.0,
In the case of plate-like magnetoplumbite-type ferrite fine particle powder containing 6.5 to 11.0 Ba in which a part of Fe (III) in ferrite is substituted with either Zn or Ti, temperature stability is improved. Since an excellent plate-like magnetoplumbite-type ferrite fine particle powder containing Ba cannot be obtained, a magnetoplumbite-type ferrite fine particle powder having a specific composition with Zn and Ti in which a part of Fe (III) in ferrite is replaced is obtained. We believe this is due to a synergistic effect with.

Next, various conditions for carrying out the present invention will be described.

The plate-like magnetoplumbite-type ferrite fine particle powder containing Ba or Ba and Sr in the present invention is AO · n {(Fe _1- xM
x) ₂ O ₃ }, n = 6.5 to 11.0 and x = 0.05 to 0.25.

When n is less than 6.5, the change in coercive force in the temperature range of 20 to 120 ° C exceeds +2.0 Oe / ° C.

When n exceeds 11.0, a non-magnetic phase or a spinel ferrite phase is mixed and the magnetization value decreases.

When x is less than 0.05, the change in coercive force in the temperature range of 20 to 120 ° C exceeds +2.0 Oe.

When x exceeds 0.25, a non-magnetic phase or a spinel ferrite phase is mixed and the magnetization value is lowered.

The plate-like magnetoplumbite-type ferrite fine particle powder containing Ba or Ba and Sr in the present invention includes barium carbonate and the like.
Ba raw material (if necessary, part of the Ba raw material may be replaced with Sr raw material such as strontium carbonate) and hematite,
Fe raw materials such as magnetite, maghemite, and goethite, and Zn as substitute elements such as zinc oxide, zinc carbonate, and zinc hydroxide.
Material, Ti material and cobalt carbonate and titanium oxide, cobalt hydroxide, basic cobalt carbonate _{(2CoCO 3 · 3Co (OH)} 2
・ H ₂ O) and other Co raw materials are mixed in a specific blending ratio, then heated and baked in the temperature range of 750 to 950 ° C. in the presence of a flux, and then crushed and water, acid or the like is used. It can be obtained by washing in a conventional manner.

As the flux in the present invention, for example, an alkali metal,
One or more kinds of alkaline earth metal halides and sulfates and silicates can be used.

The existing amount of the flux is 15 to 100% by weight based on the iron raw material.

If it is less than 15% by weight, the ferrite-forming reaction is insufficient, unreacted substances remain, and the particle size distribution of the produced particles is widened, which is not preferable.

Even when it exceeds 100% by weight, the plate-like magnetoplumbite type ferrite fine particle powder containing Ba or Ba and Sr according to the present invention can be obtained, but it is meaningless to make it exist more than necessary.

When the heating and firing temperature is lower than 750 ° C., the ferrite formation reaction is insufficient and unreacted substances remain.

If it exceeds 950 ° C, sintering occurs between the particles and between the particles, which is not preferable as the magnetic particle powder for magnetic recording.

The magnetic recording medium according to the present invention is formed on a substrate by a conventional method.
Alternatively, it can be obtained by applying a resin composition containing a plate-like magnetoplumbite-type ferrite fine particle powder containing Ba and Sr.

A dispersant, a lubricant, an abrasive, an antistatic agent and the like which are usually used may be added to the above resin composition.

As the substrate material in the present invention, polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, polyimide, polysulfone and other synthetic resin films and aluminum, stainless steel and the like which are currently widely used in the production of magnetic recording media are used. Metal or foil plates and various papers can be used.

As the resin in the present invention, a vinyl derivative such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate maleate urethane elastomer, butadiene acrylonitrile copolymer, polyvinyl butyral, and nitrocellulose which are currently widely used in the production of magnetic recording media. A synthetic rubber resin such as polyester resin or polybutadiene, an epoxy resin, a polyamide resin, a polyisocyanate polymer, an electron beam curable acrylic urethane resin, or a mixture thereof can be used.

〔Example〕

 Next, the present invention will be described with reference to Examples and Comparative Examples.

In addition, the average diameter of the particles in the following Examples and Comparative Examples is a value measured by an electron micrograph.

The magnetic properties of the magnetoplumbite-type ferrite fine particle powder containing Ba or Ba and Sr are described in “Vibration Sample Magnetometer
VSM-3S-15 "(manufactured by Toei Industry Co., Ltd.) under an external magnetic field of 10KOe. The characteristics of the magnetic recording medium are 10KOe perpendicular to the surface of the magnetic recording medium. Is a value measured by applying an external magnetic field. The temperature stability of the plate-like magnetoplumbite-type ferrite fine particle powder containing Ba or Ba and Sr and the magnetic recording medium is the difference between the coercive force value at 20 ° C and the coercive force value at 90 ° C between 90 ° C and 20 ° C. The value divided by the temperature difference (70 ° C) is shown in Oe / ° C.

<Production of tabular magnetoplumbite ferrite fine particles containing Ba or Ba and Sr> Examples 1 to 7, Comparative Examples 1 and 2; Example 1 Barium carbonate 195 g, magnetite 1070 g, zinc oxide 131.8
g and titanium oxide 116.2g and NaCl 250g and Na ₄ Si as flux
250 g of O ₄ was mixed and placed in an alumina crucible and heated and baked at 800 ° C. for 1.5 hours in an electric furnace. Then, the heated and baked product is pulverized and washed by a conventional method to remove the flux,
After that, it was dried to obtain brownish brown particle powder.

The obtained ferromagnetic brown powder has an average diameter of 0.07 μm, as is clear from the electron micrograph (× 100,000) shown in FIG. 1. The results of fluorescent X-ray analysis and X-ray diffraction show that BaO · 8.19.
Was magnetoplumbite ferrite fine particles having a composition of _{{(Fe 0.818 Zn 0.096 Ti 0.0860} ) 2 O 3}.

The magnetic properties of this _BaO.8.19 {(Fe _0.818 Zn _0.096 Ti _0.0860 ) ₂ O ₃ } fine particle powder are coercive force Hc530Oe and magnetization value 53.4emu / g.
And the temperature stability was -1.3 Oe / ° C.

Examples 2 to 7, Comparative Examples 1 and 2 Fe raw material type and amount, Ba or Ba and Sr raw material type and amount, Zn raw material type and amount, Ti raw material type and amount, fluxing agent type and amount, and Ba or Ba in the same manner as in Example 1 except that the heating and firing temperature and the heating and firing time were variously changed.
A plate-like magnetoplumbite-type ferrite fine particle powder containing Sr was obtained.

The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2.

<Manufacture of Magnetic Recording Medium> Examples 8 to 14, Comparative Examples 3 to 4; Example 8 100 parts by weight of magnetoplumbite ferrite fine particle powder containing Ba obtained in Example 1, VAGH (vinyl chloride-vinyl acetate) -Vinyl alcohol copolymer) (manufactured by UCC, USA) 14 parts by weight, myristic acid 1 part by weight, toluene 30 parts by weight, methyl ethyl ketone 30 parts by weight, Al ₂ O ₃ powder 1 part by weight and carbon black 2 parts by weight in a kneader. After kneading for 90 minutes, the kneaded product was diluted by adding 45 parts by weight of toluene and 45 parts by weight of methyl ethyl ketone, and then mixed and dispersed by a sand grinder for 3 hours.

To the above-mentioned mixed dispersion, 140 parts by weight of a methyl ethyl ketone solution containing 14 parts by weight of a solid content of a polyurethane resin (product name: Nipolan 2304, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added.
After mixing for 0 minutes, 3 parts by weight of Coronate L (trifunctional low-molecular weight isocyanate compound, manufactured by Nippon Polyurethane Industry Co., Ltd.) was mixed with the excess product to prepare a magnetic coating material.

The above magnetic paint is applied onto a 12 μm thick polyester base film and then dried to obtain a film thickness of 4 μm.
After forming the magnetic layer of m, calendering was performed, and then the tape was cut into 3.81 mm width.

The magnetic characteristics of the above magnetic tape are: coercive force 570 Oe, saturation magnetic flux density Bm 1340 Gauss, residual magnetic flux density Br 427 Gauus, square B
The r / Bm was 0.319 and the temperature stability was -1.4 Oe / ° C.

Examples 9 to 14 and Comparative Examples 3 to 4 Magnetic recording media were obtained in the same manner as in Example 8 except that the type of the magnetoplumbite ferrite fine particle powder containing Ba or Ba and Sr used was variously changed.

Table 3 shows various characteristics of the obtained magnetic recording medium.

(Effect of the invention) The magnetic recording medium according to the present invention has, as shown in the above-mentioned Examples, a plate-like magnetoplumbite ferrite fine particle powder containing Ba or Ba and Sr to be used, which has an appropriate coercive force,
In addition, due to its excellent temperature stability, it has an appropriate coercive force and is excellent in temperature stability, especially 20-
The change in coercive force within the temperature range of 90 ° C is -2.0 Oe / ° C ~
Since it is in the range of +2.0 Oe / ° C, it is most suitable as a magnetic recording medium for high density recording, which is currently most demanded.

[Brief description of drawings]

FIG. 1 is an electron micrograph (× 100, of the magnetoplumbite-type ferrite fine particle powder containing Ba obtained in Example 1).
000).

Claims (1)

[Claims] 1. AO.n {(Fe ₁ -xMx) ₂ O ₃ } (where A is Ba or Ba and Sr, M is Zn and Ti or Zn, Co and
Ti, n = 6.5 to 11.0, x = 0.05 to 0.25)
A magnetic recording medium coated with a resin composition containing a plate-like magnetoplumbite-type ferrite fine particle powder containing a or Ba and Sr, wherein the change in coercive force in the temperature range of 20 to 90 ° C. of the magnetic recording medium. Is a magnetic recording medium having a range of −2.0 Oe / ° C. to +2.0 Oe / ° C.