JPH10269557A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently improve corrosion resistance by specifying the pH of a magnetic recording medium mainly contain MnBi magnetic powder in a magnetic layer to alkalinity of a specific value or above. SOLUTION: The pH of the magnetic recording medium mainly contg. the MnBi magnetic powder in the magnetic layer is specified to the alkalinity of >=7. If the pH in the system of the magnetic recording medium is made alkaline of >=7 in such a manner, a passive phase of an Mn system is formed on the surface of the MnBi magnetic powder and the corrosion resistance of the MnBi magnetic powder is improved. The magnetic recording medium having the corrosion resistance of a practicable use level at which the deterioration of saturation magnetization is extremely little in spite of long-term preservation at and under a high temp. and high humidity is obtd. Nonmagnetic inorg. powder having a particle size of <=10 μm is preferably incorporated into the magnetic layer. Further, the inorg. powder is preferably inorg. powder of pH >=7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium using a MnBi alloy magnetic powder as a recording element, and more particularly to a magnetic recording medium having a practical level of corrosion resistance and excellent corrosion resistance.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as video tapes, floppy disks, credit cards, prepaid cards, and the like because of easy recording and reproduction. However, since recording and reproduction are easy, there are many accidents and crimes such as erroneous deletion or intentional rewriting of credit cards and the like. Especially credit cards,
Crimes that rewrite data such as prepaid cards and misuse them have occurred frequently, and have become a major social problem.

In order to prevent this, a magnetic recording medium using MnBi magnetic powder has been proposed which has the characteristic that once recorded, it is not easily erased at room temperature. (JP-B-57-38962, JP-B-54-
No. 33725, JP-B-52-46801, JP-B-59
No. 31764, Japanese Patent Publication No. 54-19244, Japanese Patent Publication No. 5
7-38963)

However, this MnBi magnetic powder has a problem that its magnetic properties deteriorate due to corrosion and deterioration due to moisture and oxygen. Therefore, various anticorrosives have been added to the magnetic layer so far. Improvement of corrosion resistance has been carried out by forming a corrosion prevention coating on the particle surface. (Japanese Patent Publication No. 60-57127)

[0005]

However, in these conventional methods, practically satisfactory corrosion resistance has not yet been obtained, and a magnetic recording medium using MnBi magnetic powder having a practical level of corrosion resistance has not yet been obtained. Absent.

The present invention has been made as a result of various studies in view of the current situation. The present invention is to make a magnetic recording medium containing MnBi magnetic powder as a main component in a magnetic layer alkaline at pH 7 or more, or to use a MnBi magnetic powder. A non-magnetic inorganic powder having a particle size of 10 μm or less is contained in a main magnetic layer, or a magnetic recording medium containing MnBi magnetic powder as a main component in a magnetic layer is made alkaline at a pH of 7 or more. By including a nonmagnetic inorganic powder having a particle size of 10 μm or less in the magnetic layer mainly composed of powder, the corrosion resistance of the magnetic recording medium is sufficiently improved, and a magnetic recording medium having a practical level of corrosion resistance can be obtained. It was made.

[0007]

According to the magnetic recording medium of the present invention, the pH of a magnetic recording medium containing MnBi magnetic powder as a main component in a magnetic layer is adjusted to 7 or more to make it alkaline.

[0008] The magnetic recording medium of the present invention has MnB
Particle size of 10μ in magnetic layer mainly composed of i-magnetic powder
m or less of non-magnetic inorganic powder.

Further, the magnetic recording medium according to the present invention has Mn
The pH of the magnetic recording medium containing Bi magnetic powder as the main component in the magnetic layer is made alkaline at 7 or more, and the magnetic layer contains nonmagnetic inorganic powder having a particle size of 10 μm or less.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a magnetic recording medium containing MnBi magnetic powder as a main component in a magnetic layer has a pH
Is 7 or more, and the pH of the magnetic recording medium is made alkaline at pH 7 or more.
A Mn-based non-conductive phase is formed on the surface of the MnBi magnetic powder to improve the corrosion resistance of the MnBi magnetic powder, and a practical level of corrosion resistance with very little deterioration of saturation magnetization even when stored for a long time at high temperature and high humidity. Is obtained.

This is because, as shown in FIG. 1, when the MnBi magnetic powder is immersed in water having a pH of less than 7, the amount of magnetization is greatly reduced, but when immersed in alkaline water having a pH of 7 or more. Is due to the fact that the decrease in the amount of magnetization is extremely low, which is considered to be due to the formation of a non-conducting phase in alkaline water having Mn of pH 7 or more. This is because if the inside is made alkaline at pH 7 or more, a Mn-based non-conductive phase is formed on the surface of the MnBi magnetic powder.

In order to make a magnetic recording medium containing such a MnBi magnetic powder as a main component in a magnetic layer alkaline at a pH of 7 or more, a hydrotalcite compound, an alkaline compound or the like is contained in the magnetic layer containing a MnBi magnetic powder as a main component. The method is performed by, for example, including an inorganic powder or the like, and is also performed by a method of being left in an atmosphere of an alkaline gas such as ammonia gas.

In the present invention, the magnetic recording medium containing MnBi magnetic powder as a main component in the magnetic layer is made of MnBi.
Particle size of 10μ in magnetic layer mainly composed of i-magnetic powder
m or less, and if the magnetic layer contains a non-magnetic inorganic powder having a particle size of 10 μm or less, a dense magnetic layer is formed, and this dense magnetic layer is formed. MnBi magnetic powder is confined in the layer,
The corrosion resistance of the magnetic layer is sufficiently improved, and a magnetic recording medium having a practical level of corrosion resistance with very little deterioration of saturation magnetization even when stored at high temperature and high humidity for a long time is obtained.

On the other hand, when the particle size is 10
When not containing a non-magnetic inorganic powder of μm or less, generally MnBi magnetic powder is synthesized by pulverizing the MnBi ingot in a dry or wet method, the shape is not constant,
Poor coating properties when forming the magnetic layer, voids are generated in the magnetic layer, and a dense magnetic layer is not formed. As a result, MnB
The i-magnetic powder cannot be confined in the dense magnetic layer, and the corrosion resistance deteriorates.

The nonmagnetic inorganic powder to be contained in such a magnetic layer mainly composed of MnBi magnetic powder preferably has a particle size of 10 μm or less, more preferably 5 μm or less. If the amount is less than 1% by weight with respect to the MnBi magnetic powder, the desired effect cannot be obtained. If the amount is more than 40% by weight, the magnetic properties are lowered and the required properties cannot be obtained. It is preferred that

As such inorganic powder, TiO ₂ ,
Oxide powders such as Al ₂ O ₃ , SiO ₂ and Fe ₂ O ₃ are preferably used, and powders having a uniform shape such as a sphere or a needle are preferably used.

In particular, when the inorganic powder is an inorganic powder having a pH of 7 or more, the pH of a magnetic recording medium containing MnBi magnetic powder as a main component in a magnetic layer can be made alkaline at a pH of 7 or more. When the inside of the system of the magnetic recording medium is made alkaline at pH 7 or more using the above inorganic powder, a Mn-based non-conductive phase is formed on the surface of the MnBi magnetic powder, thereby improving the corrosion resistance of the MnBi magnetic powder. A dense magnetic layer is formed, the MnBi magnetic powder is confined in the dense magnetic layer, the corrosion resistance of the magnetic layer is further improved, and the saturation magnetization is deteriorated even when stored at high temperature and high humidity for a long time. , A magnetic recording medium having a practical level of corrosion resistance is obtained.

Further, it is preferable that the base film, the top coat layer and the intermediate layer are also made alkaline.

The MnBi alloy magnetic powder used in the present invention is obtained by converting Mn and Bi into a MnBi ingot by a powder metallurgy method, an arc furnace, a high-frequency melting furnace, a melting quenching method or the like, and pulverizing the MnBi ingot. And may be made without grinding.

For example, when producing a MnBi ingot by powder metallurgy, first, Mn powder and Bi powder of 100 to 300 mesh are sufficiently mixed in an inert atmosphere. The ratio of Mn to Bi is from 45:55 to 6 in molar ratio.
0:40, Mn powder as raw material, B
As the i-powder, a powder that has been pulverized in advance may be used, or a lump such as a flake or a shot may be pulverized into fine powder for use. The mixing was performed using an automatic mortar,
It can be performed by any means such as Lumil.

The raw material after mixing is formed into a molded body by using a pressure press, whereby the sintering reaction is promoted and a uniform MnBi ingot is produced. The pressure at this time is preferably 1 to 8 t / cm ^{2. If} the pressing force is low, uniformity of the MnBi ingot cannot be obtained, and if the pressing force is too high, the pressing device becomes expensive. The properties of the MnBi ingot do not improve.

The obtained molded body is sealed in a glass container or a metal container. The inside of the container is placed in a vacuum or an inert gas atmosphere to prevent oxidation during the heat treatment, and then placed in an electric furnace at 260 to 270 ° C. for 2 hours. Heat treatment is performed for ~ 15 days. If the temperature of this heat treatment is low, the heat treatment takes time,
Further, the amount of magnetization of the obtained MnBi ingot also becomes low. Conversely, if the heat treatment temperature is too high, Bi melts, and a uniform MnBi ingot cannot be obtained.

The MnBi ingot thus produced is taken out and coarsely pulverized by an automatic mortar in an inert gas atmosphere to reduce the particle size to 100 to 500 μm, and then subjected to ball mill, planetary ball mill, or the like. Fine particles are obtained by wet pulverization or dry pulverization using a jet mill or the like. As a liquid in the case of wet pulverization, a solvent containing no water such as toluene is used, and in the case of dry pulverization, an inert gas atmosphere is used. Average particle size after grinding is about
0.05 to 10 μm, and can be controlled by pulverization conditions. If the particle size is smaller than 0.05 μm, the saturation magnetization of the finally obtained magnetic powder decreases, and
If it exceeds μm, the surface smoothness of the magnetic recording medium using the finally obtained magnetic powder is reduced, and sufficient recording cannot be performed.

By the above steps, the saturation magnetization becomes 30 emu /
g and MnBi magnetic powder having a coercive force of 3000 to 14000 Oersted.

A magnetic recording medium containing such a MnBi magnetic powder as a main component in a magnetic layer, having an alkaline pH of 7 or more, and containing a nonmagnetic inorganic powder having a particle size of 10 μm or less in the magnetic layer. Is prepared in accordance with a conventional method. For example, a magnetic coating material is prepared by mixing and dispersing a MnBi magnetic powder with an inorganic powder having a pH of 7 or more and a binder resin, an organic solvent, and the like, and forming the magnetic coating material on a substrate. It is produced by coating and drying. It is preferable that after applying the magnetic paint on the substrate, a magnetic field is applied in parallel to the surface of the magnetic layer to perform magnetic field orientation.

Here, as the binder resin, any resin generally used for magnetic recording media is used, for example, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, cellulose resin Resins, polyurethane resins, isocyanate compounds, radiation-curable resins and the like are used.

As the organic solvent, solvents suitable for dissolving the binder resin used, such as cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, benzene, toluene, xylene, tetrahydrofuran and dioxane, are particularly limited. Used alone or in combination of two or more.

The magnetic paint may optionally contain various additives commonly used, for example, dispersants, lubricants, antistatic agents and the like.

[0029]

Next, an embodiment of the present invention will be described. Example 1 Mn flake (manufactured by Furuuchi Chemical Co .; purity 99.9%) Bi
After crushing the shot (Furuuchi Chemical Co .; purity 99.9%) using a mortar and sieving 100 mesh,
30.2 parts by weight of Mn and 94.0 parts by weight of Bi were weighed and thoroughly mixed using a mortar.

Next, this was subjected to 4 t /
It was molded into a cylinder having a diameter of 6 mm x 6 mm in diameter at a pressure of ² cm2, and the molded body was vacuum-sealed in a Pyrex glass tube and heat-treated at 265 ° C for 10 days in an electric furnace to obtain Mn.
A Bi ingot was produced.

Next, the obtained MnBi ingot is roughly pulverized using a mortar in an inert atmosphere using a glove box, and further pulverized in toluene using a planetary ball mill at 200 rpm for 2 hours. did. The MnBi magnetic powder thus obtained has an average particle size of about 3 μm, and the magnetic properties measured using a VSM indicate that the coercive force is 98%.
00 Oersted, the saturation magnetization was 48.6 emu / g, and the maximum applied magnetic field was 16 kOersted.

Using the MnBi magnetic powder obtained as described above, MnBi alloy magnetic powder 70 parts by weight Polyurethane resin (manufactured by Dainippon Ink and Chemicals, T-52 15 @ 50) Alkamizer (Kyowa Chemical Industry Co., Ltd.) Hydrotal 10 site compound, pH: 9.0) A composition of cyclohexanone 75% toluene 75% is sufficiently kneaded and dispersed in a ball mill, and then a polyfunctional polyisocyanate compound (Nippon Polyurethane Industry Co., Ltd.) Co., Ltd., 5 parts by weight was added to prepare a magnetic paint.

This magnetic paint is applied on a 30 μm-thick polyester film so that the thickness after drying becomes 10 μm, and dried while applying a longitudinal orientation magnetic field of 1000 Oe to form a magnetic layer. Thus, a magnetic recording medium was manufactured.

Example 2 In the composition of the magnetic paint in Example 1, the amount of the alkamizer was changed from 10 parts by weight to 5 parts by weight, and Al ₂ O ₃ (particle size: 1 μm, pH: 6.5) was newly added. A magnetic coating material was prepared in the same manner as in Example 1 except that 5 parts by weight was added, to prepare a magnetic recording medium.

Example 3 In the composition of the magnetic coating material in Example 1, the amount of the MnBi magnetic powder was changed from 70 parts by weight to 55 parts by weight, and the amount of the alkamizer was changed from 10 parts by weight to 5 parts by weight.
Parts by weight, and Al ₂ O ₃ (particle size: 1 μm, p
H: 6.5) was prepared in the same manner as in Example 1 except that 5 parts by weight of H) was added to prepare a magnetic recording medium.

Example 4 In the composition of the magnetic paint in Example 2, Al ₂ O ₃
A magnetic coating medium was prepared in the same manner as in Example 2 except that the same amount of TiO ₂ (particle size: 1 μm, pH: 5) was used in place of the above.

Example 5 In the composition of the magnetic paint in Example 2, Al ₂ O ₃
Instead of α-Fe ₂ O ₃ (particle size: 3 μm, pH: 9.5)
Was used in the same manner as in Example 2 except that the same amount was used to prepare a magnetic recording medium.

Example 6 In the composition of the magnetic coating material in Example 1, α-Fe ₂ O ₃ (particle size: 3 μm, pH: 9.
A magnetic coating medium was prepared in the same manner as in Example 1 except that 5) was used in the same amount to prepare a magnetic recording medium.

Comparative Example 1 In the composition of the magnetic paint in Example 1, the amount of MnBi magnetic powder used was changed from 70 parts by weight to 80 parts by weight.
A magnetic coating material was prepared and a magnetic recording medium was prepared in the same manner as in Example 1 except that the alkamiser was omitted.

Comparative Example 2 In the composition of the magnetic paint in Example 1, the amount of MnBi magnetic powder used was changed from 70 parts by weight to 56 parts by weight.
A magnetic coating material was prepared and a magnetic recording medium was prepared in the same manner as in Example 1 except that the alkamiser was omitted.

Comparative Example 3 In the composition of the magnetic paint in Example 2, the amount of MnBi magnetic powder used was changed from 70 parts by weight to 40 parts by weight.
Al ₂ O ₃ (particle size: 1 μm, pH: 6.5)
A magnetic coating material was prepared in the same manner as in Example 2 except that the weight was changed from 35 parts by weight to 35 parts by weight, to prepare a magnetic recording medium.

With respect to the magnetic recording media obtained in each of the examples and comparative examples, the coercive force, the amount of magnetization, and the pH were measured, and the corrosion resistance was tested. The measurement of pH is 15 μm thickness x 3 inch width.
A magnetic recording medium of length h × 1 m is cut into pieces of about 1 cm × 1 cm, put into a quartz flask containing 100 g of H ₂ O, and placed on a hot plate and boiled for 5 minutes. After cooling to room temperature, the solution in the flask was taken out, and the pH of the solution was measured with a pH meter. In addition, the corrosion resistance test was conducted at 60 ° C. for the obtained magnetic recording medium.
The deterioration rate of the amount of magnetization after being left for one week in a high-temperature, high-humidity tank of 90% RH was calculated and examined. Table 1 below shows the results.

[0043]

Further, the samples of Examples 1, 3, 5 and Comparative Example 1 were examined for changes in the amount of magnetization when kept in an atmosphere at a temperature of 60 ° C. and a relative humidity of 90% for one week. FIG. 2 shows the results as a relationship between the number of days left and the deterioration rate of the magnetization amount. Δ represents Example 1, Δ represents Example 3, ▲ represents Example 5, and ● represents Comparative Example 1. The sample is shown.

[0045]

As is clear from Table 1 and FIG. 2, the magnetic recording medium obtained by the present invention (Examples 1 to 6)
Is smaller than the magnetic recording media obtained in Comparative Examples 1 to 3,
In any case, the rate of deterioration of the amount of magnetization is small. Therefore, the magnetic recording medium using the MnBi alloy magnetic powder obtained according to the present invention has very little deterioration of the amount of magnetization even when kept at high temperature and high humidity, and has excellent corrosion resistance. It can be seen that they have

[Brief description of the drawings]

FIG. 1 is a graph showing the change in water resistance of MnBi magnetic powder depending on the pH of water and the relationship between the pH and the rate of deterioration of the amount of magnetization.

FIG. 2 is a graph showing the relationship between the number of days left and the rate of deterioration of the amount of magnetization showing the change in the amount of magnetization of a magnetic recording medium using MnBi magnetic powder in a high-temperature and high-humidity bath.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoru Fukiage 1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd.

Claims (3)

[Claims] An alkaline magnetic recording medium containing MnBi magnetic powder as a main component in a magnetic layer and having a pH of 7 or more. 2. A magnetic recording medium wherein a nonmagnetic inorganic powder having a particle size of 10 μm or less is contained in a magnetic layer mainly composed of MnBi magnetic powder. 3. The magnetic recording medium according to claim 2, wherein the inorganic powder is an alkaline inorganic powder having a pH of 7 or more.