JPH0798857A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the affinity of metallic magnetic powder to a binder and to produce a magnetic recording medium excellent in dispersibility by adsorbing CO or CO2 on the surface of the magnetic powder. CONSTITUTION:A process in which granules of metallic magnetic powder are crushed and fresh interfaces appear, that is, a pulverizing, mixing or kneading process in which shearing force acts on the granules is carried out in an atmosphere of CO and/or CO2. For example, CO2 is substd. for the air in a continuous kneader 10 by introducing CO2 from a gas introducing hole 21 and then kneading is carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called coating type magnetic recording medium manufacturing method.

[0002]

2. Description of the Related Art In the field of magnetic recording, particularly in VTRs (video recorders) and the like, higher density recording is required to achieve high image quality. With this increase in density, iron or a metal material mainly composed of iron has come to be used in place of the iron oxide-based material that has been conventionally used as magnetic powder for magnetic recording media and the like. As the range of applications of this magnetic metal powder (ferromagnetic alloy fine particles) mainly composed of iron expands, the demand for this material is becoming more and more advanced.

[0003] The main requirements are to achieve high saturation magnetization in order to obtain high output, to achieve high coercive force in order to reduce self-demagnetization characteristics, and to achieve high magnetic energy. Etc. At present, the saturation magnetization is 150 Am ² / k due to the progress of fine magnetic powder production technology.
Materials that reach g or coercive force of 160 kA / m have also been proposed.

On the other hand, in order to realize high C / N characteristics,
The particle size of the ferromagnetic alloy fine particles is actively promoted, and the specific surface area measured by the BET method is 50 m ²
/ G and the length of the major axis of the needle-shaped particles is less than 200 nm.

However, when an attempt is made to increase the energy, the cohesive force increases as the magnetic interaction increases, so that the dispersibility tends to decrease. Further, when the atomization is promoted, the surface energy increases, so that the dispersibility is inevitably lowered. When the dispersibility is reduced, the magnetic properties of the magnetic powder cannot be fully exhibited.

[0006] Many attempts have been made to overcome such a decrease in dispersibility, and as a typical method therefor, for example, a mechanical dispersion means such as a hammer mill is used to forcibly form agglomerates. There is a way to destroy it. However, it is difficult to put into practical use because excessive impact easily causes breakage of needle-shaped particles. Also, the use of low molecular weight dispersants and surfactants is a fairly effective means and is being utilized, but there is a so-called compatibility problem with binders and lubricants, and satisfactory ones have always been obtained. Not really.

Further, the disperser has been improved, and progress has been made in the kneading process such that a kneader is used and a ball mill, a sand mill or a sand grinder is used in the dispersing process. However, since an excessive dispersion force causes damage to the particle shape, it is difficult to obtain a sufficient dispersion effect without damaging the particle shape.

[0008]

Further, as a means for improving the dispersibility, carbon monoxide, carbon dioxide or ammonia is previously adsorbed on the magnetic powder, and the adsorption characteristics of the binder or the additive on the magnetic powder. It is also possible to consider a method of controlling. This treatment improves the dispersibility because the acidity of the surface of the magnetic powder is changed and the affinity with the binder is increased.

However, the magnetic metal powder is usually formed into a certain shape, for example, a granule, a pellet, a cylinder or a sand, for the convenience of the manufacturing process. Even if the above-mentioned adsorption treatment is performed on such a granulated body, the inside of the aggregate cannot be completely treated. That is, the new interface that appears when the granules are disintegrated remains untreated, and this portion hinders further improvement of dispersibility.

Therefore, the present invention has been proposed in view of the above conventional circumstances, and in particular, it adsorbs carbon monoxide and / or carbon dioxide on the metal magnetic powder granulated and formed into granules or sand. In doing so, it is an object of the present invention to provide a method for producing a magnetic recording medium capable of improving the dispersibility by sufficiently performing the adsorption treatment of the above gas even on the individual primary particles inside the aggregate.

[0011]

The present invention has been proposed to achieve the above object. The first invention of the present application relates to a method for producing a magnetic recording medium, wherein a magnetic coating mainly composed of a metal magnetic powder and a binder is applied on a non-magnetic support to form a magnetic layer. It is characterized by crushing under a carbon (CO) and / or carbon dioxide (CO ₂ ) atmosphere.

In the first invention of the present application, the metal magnetic powder is pulverized in advance in a carbon monoxide and / or carbon dioxide atmosphere, and then in a carbon monoxide and / or carbon dioxide atmosphere at a temperature of 30 to 100 ° C. It is characterized by holding. Further, the amount of H ₂ O adsorbed on the metal magnetic powder is 5.0 to 30.0 mol / m ² .

The second invention of the present application is a method of manufacturing a magnetic recording medium, wherein a magnetic coating material comprising a metallic magnetic powder and a binder as a main component is applied onto a non-magnetic support to form a magnetic layer,
At least one of the step of mixing the metallic magnetic powder and the binder, and the step of kneading are CO and / or C
It is characterized in that it is performed in an O ₂ atmosphere. Further, in the second invention of the present application, the metallic magnetic powder is previously CO
And / or crushing under a CO ₂ atmosphere.

The coating type magnetic recording medium is prepared by mixing and dispersing magnetic powder, a binder and various additives with an organic solvent to prepare a magnetic coating material, coating the magnetic coating material on a non-magnetic support and drying it. It is made.

Here, the magnetic powder is once made into a granular or sandy magnetic powder granule due to the convenience of the manufacturing process, and the magnetic powder granule is subjected to pulverization treatment such as consolidation treatment to obtain a powder. It is used for the preparation of this magnetic paint.

In the present invention, CO and CO are added to such a magnetic powder.
And / or CO₂Can be effectively absorbed and stored in the magnetic paint.
Granules of magnetic metal powder are disintegrated to improve dispersibility
And a new interface appears, shear force acts on the granules
Step, ie, step of crushing magnetic powder granules, magnetic powder
Mixing powder and binder, solvent for magnetic powder and binder
CO and / or CO in the step of adding and kneading₂ Atmosphere
I will do it under the hood. This allows the magnetic powder agglomerates
CO and / or CO up to individual primary particles of the part ₂Is adsorbed
And the dispersibility of the magnetic powder in the binder is dramatically improved.
Will be.

In addition to the above steps, magnetic powder granules
Was pulverized, and the magnetic powder obtained by further pulverizing the
And / or CO₂ In an atmosphere of 30 to 100 ° C
Magnetic powder including new interface that appeared by crushing when kept heat
Fully dense CO, CO ₂Will be absorbed,
It exhibits high dispersibility in magnetic paints. this
Holds the magnetic powder in an atmosphere at a temperature of 30 ° C. or higher
And CO, CO₂The Chemical Adsorption of Pt on Magnetic Powder?
Thought to be However, the temperature of the magnetic powder should exceed 100 ° C.
If the magnetic field is kept in a viscous atmosphere, the magnetic characteristics may deteriorate.
The upper limit of the temperature of the holding atmosphere is 100 ° C.

Further, H of the magnetic powder granules before pulverization is further added.
_{If the} amount of ₂ O adsorbed is adjusted to 5.0 mol / m ² or more, the adsorption of CO and CO ₂ on the magnetic powder will proceed more efficiently. However, when the H ₂ O adsorption amount of the magnetic powder exceeds 30.0 mol / m ² , on the contrary, the dispersibility of the magnetic powder in the binder deteriorates. This is presumably because excessive H ₂ O hinders the adsorption of the magnetic powder and the binder. Therefore, H of the magnetic powder granules before pulverization
It is desirable to adjust the amount of ₂ O adsorbed in the range of 5.0 to 30.0 mol / m ² .

In order to adjust the H ₂ O adsorption amount of the magnetic powder granulated material, for example, the magnetic powder granulated material whose H ₂ O adsorption amount should be adjusted is spread in a pan in a glow box in which N _{2 is} replaced, and the temperature is adjusted. The mixture is heated to about 40 ° C., N ₂ gas containing water vapor is flown into the glow box and left to stand. At this time,
The amount of H ₂ O adsorbed on the magnetic powder granules is controlled by the water vapor content of the N ₂ gas and the standing time during which the magnetic powder granules are left in the glow box. As a result, H ₂ O is adsorbed on the magnetic powder granules.

The CO and / or CO ₂ adsorption treatment and the H ₂ O adsorption amount adjustment treatment can be incorporated into a part of the ordinary magnetic recording medium manufacturing process, or can be performed separately. is there. Even if it is incorporated into an existing manufacturing process, it can be dealt with by slightly modifying the process. However, when these treatments are performed separately, it is desirable to move the magnetic powder between the existing process and the existing process by sealing the magnetic powder with an inert gas.

In this way CO and / or CO₂adsorption
As the magnetic powder granules to be treated, oxide magnetic powder
Although it may be the final granule,
The effect of the present invention is remarkably exhibited in this case. Oxide magnetic powder
For example, γ-Fe ₂ O₃ , Co-containing γ-Fe
₂ O₃ , Fe₃ O_Four , Co-containing Fe₃ O_Four , Co deposition F
e₃ O_Four , CrO₂ Etc. As metal magnetic powder
For example, ferromagnetic metal materials such as Fe, Co and Ni, and Fe-
Co, Fe-Ni, Fe-Co-Ni, Co-Ni, F
e-Mn-Zn, Fe-Ni-Zn, Fe-Co-Ni
-Cr, Fe-Co-Ni-P, Fe-Co-B, Fe
Fe, Co, N such as -Co-Cr-B and Fe-Co-V
Ferromagnetic gold made of various ferromagnetic alloy materials whose main component is i
Examples of the metal particles include Al, for the purpose of improving various characteristics,
Sources of Si, Ti, Cr, Mn, Cu, Zn, Mg, P, etc.
Element may be added. In addition, such as barium ferrite
Hexagonal ferrite and iron nitride can also be used.

Further, even if these magnetic powder granules are pretreated with one or more gases of carbon monoxide, carbon dioxide and ammonia at the stage of granulation, such treatment is not performed at all. Any of them may be omitted, and the same effect can be obtained in any case. For example, when a magnetic powder granulated product which has been subjected to these treatments in advance is used, the above C
The O and / or CO ₂ adsorption treatment will act on the new interface that appears in the crushing or consolidation process, and when untreated magnetic powder granules are used they are not exposed at the granule stage. This is because it acts on both the surface and the new interface that appeared in the consolidation process.

As the resin binder and the organic solvent which compose the magnetic paint together with the magnetic powder, any conventionally known ones can be used without any limitation.

For example, as the binder, a polymer such as vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, acrylonitrile, or a combination of two or more of them. Examples thereof include copolymers, polyurethane resins, polyester resins and epoxy resins. Alternatively, a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam irradiation curable resin having a specific use method may be used in combination. Also, in order to improve the dispersibility of magnetic powder, -SO
₃ M, -OSO ₃ M, -COOM, -PO (OM) ₂
(M is an alkali metal atom such as Na or an alkyl group) and the like may contain a polar group.

As the solvent for the above magnetic paint, acetone,
Methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and other ketones, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate, monoethyl ether, and other ester systems, glycol dimethyl ether, glycol monoethyl ether, dioxane, and other glycol ethers, benzene , Aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane and heptane,
Examples thereof include chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene.

Further, in the above magnetic layer, in addition to the above-mentioned binder and ferromagnetic powder, an additive such as a dispersant, a lubricant, an abrasive,
Antistatic agents, rust inhibitors, etc. may be added. Further, as the non-magnetic support to which the magnetic paint is applied, polyesters, polyolefins, celluloses, vinyl resins,
A polymer substrate formed of a polymer material typified by polyimides or polycarbonates, a metal substrate made of an aluminum alloy or a titanium alloy, a ceramic substrate made of aluminum glass, a glass substrate, or the like. The shape is not limited at all, and may be any shape such as a tape shape, a sheet shape, and a drum shape.

Further, a back coat layer, a top coat layer or the like may be formed on the magnetic recording medium, if necessary. In this case, the film forming conditions for the back coat layer, the top coat layer and the like are not particularly limited as long as they are the methods usually applied to the manufacturing method of this type of magnetic recording medium.

[0028]

[Function] Granules of metallic magnetic powder are disintegrated and a new interface appears.
A process in which a shearing force acts on the granules, that is, magnetic powder
Process of pulverizing powdered granules, mixing magnetic powder and binder
Step of adding solvent to magnetic powder and binder and kneading
Is CO and / or CO₂Aggregates when done under atmosphere
CO and / or CO up to individual primary particles inside ₂ Sucks
To wear.

When CO and / or CO ₂ is adsorbed on the surface of the metal magnetic powder, the acidity of the surface of the metal magnetic powder is increased and the affinity with the binder is increased, so that the dispersibility is improved. .

The magnetic powder granules are CO and / or C
After pulverizing in an atmosphere of O ₂ , the magnetic powder obtained by pulverizing is further pulverized in an atmosphere of CO and / or CO ₂ at a temperature of 3
When kept at 0 to 100 ° C., CO and / or CO ₂ is sufficiently and densely adsorbed on the entire surface of the magnetic powder including a new interface appearing by pulverization, and a high degree of dispersibility in the magnetic paint is exhibited. This is considered to be because when the magnetic powder is held in the atmosphere of the above temperature range, chemisorption of CO and CO _{2 to} the magnetic powder is promoted.

Further, H of the magnetic powder granules before pulverization₂O sucking
Wear amount is 5.0 to 30.0 mol / m ²Adjust to the range of
When placed, CO, CO to the magnetic powder₂Adsorption is more efficient
Progresses faster, and further to the binder of magnetic powder
Dispersibility is improved.

[0032]

EXAMPLES The present invention will be described below with reference to specific examples, but the present invention is not limited to the following examples.

Experiment 1 In this experiment, in the step of pulverizing the metallic magnetic powder, C
The effect of adsorbing O and / or CO ₂ is shown.

First, a commercially available magnetic powder A for magnetic recording was prepared. Regarding this magnetic powder A, the saturation magnetization (Bs), squareness ratio (Rs), and coercive force (Hc) were examined as magnetic characteristics,
Specific surface area, acicular ratio, and carbon content were investigated as powder characteristics. The results are shown in Table 1.

[0035]

[Table 1]

However, the magnetic characteristics were measured with a sample vibrating magnetometer (Toei Industry Co., Ltd.), and the specific surface area was measured with the BET one-point method (Shimadzu Corporation). As the acicular ratio, an average value of 100 points randomly selected by observation with a transmission electron microscope was adopted. A CHN analyzer (manufactured by Perkin Elmer) was used to measure the carbon content. Since almost no carbon was detected, it can be determined that CO and CO ₂ were not adsorbed on the magnetic powder A.

CO ₂ was adsorbed on the magnetic powder A in the following manner. First, a glove box whose inside was replaced with CO ₂ was prepared, and 200 g of the magnetic powder A was compacted (crushed) in the agate mortar. The granules were sufficiently broken by the grinding treatment for about 5 minutes. As it is left for about 1 hour while maintaining the CO ₂ atmosphere, it was allowed to adsorb CO ₂ in newly emerged surface by grinding processing. Magnetic powder B was obtained by performing the treatment in this manner. This magnetic powder B was sealed in a container after replacing the inside of the glove box with nitrogen.

Further, the magnetic powder A was replaced with C instead of CO _2.
A magnetic powder C was prepared in the same manner as the magnetic powder B except that it was treated with O. Magnetic powder D was prepared by simply leaving magnetic powder A in a glove box replaced with CO ₂ for 1 hour. Subsequently, the magnetic powder D was pulverized in the same manner as the magnetic powder B was prepared to obtain the magnetic powder E. The magnetic properties and powder properties of each magnetic powder are as shown in Table 1.

In any magnetic powder, CO ₂ or CO
It can be seen that the adsorption of

Then, the above-mentioned magnetic powder B was kneaded and dispersed together with the following materials to form a paint, which was coated on a PET (polyethylene terephthalate) film to prepare a magnetic recording medium. This was used as a sample of Example 1-1.

<Magnetic coating composition> 100 parts by weight of magnetic powder B Vinyl chloride-vinyl acetate copolymer (VAGH manufactured by UCC) 10 parts by weight Polyurethane (N-5033 manufactured by Nippon Polyurethane Company) 10 parts by weight Carbon 3 parts by weight Al ₂ O ₃ 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

Similarly, a magnetic coating material was prepared by using the above-mentioned magnetic powder C to prepare a magnetic recording medium.
Two samples were obtained. Further, a sample of Example 1-3 was obtained in the same manner as in Example 1-1, except that the magnetic powder E was used. A sample of Comparative Example 1-1 was obtained in the same manner as in Example 1-1, except that the magnetic coating material was prepared using the magnetic powder A. Furthermore, Example 1-except that the magnetic paint D was used
A sample of Comparative Example 1-2 was obtained in the same manner as in 1.

With respect to the sample obtained as described above, the dispersibility of the magnetic layer was evaluated as glossiness with a gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd.). The incident angle of light rays is 4
The gloss is 5 degrees, and the gloss of a standard plate with a standard surface is 10
It was expressed as a relative value as 0% (according to JIS Z-8741). Moreover, the magnetic characteristics were measured by a sample vibrating magnetometer. The results of these measurements are shown in Table 2.

[0044]

[Table 2]

From Table 2, in the samples of Examples 1-1 to 1-3, high Rs and high gloss were realized, and C
It is understood that the magnetic recording medium having excellent dispersibility can be obtained by pulverizing the magnetic powder in the O ₂ or CO atmosphere. In the sample of Comparative Example 1-2, since the magnetic powder D in which CO ₂ is adsorbed on the surface of the magnetic powder aggregate is used, as compared with the sample of Comparative Example 1-1 using the magnetic powder A, Although the dispersibility is improved, the dispersibility is inferior as compared with the samples of Examples 1-1 to 1-3 using the magnetic powders B, C, and E in which CO ₂ is adsorbed to the primary particles. I understand.

Experiment 2 Next, this experiment shows the effect of adsorbing CO and / or CO ₂ in the step of mixing the magnetic metal powder with the binder.

First, magnetic powder A (the magnetic properties and powder properties are as shown in Table 1) was prepared and mixed with a binder and a solvent in the following composition. <Magnetic coating composition> 100 parts by weight of magnetic powder A Vinyl chloride-vinyl acetate copolymer (VAGH manufactured by UCC) 10 parts by weight Polyurethane (N-5033 manufactured by Nippon Polyurethane Company) 10 parts by weight Carbon 3 parts by weight Al ₂ O ₃ 2 Parts by weight methyl ethyl ketone 27 parts by weight cyclohexanone 27 parts by weight

The entire amount of the above materials was placed in a stirring container,
The inside of the stirring tank was sufficiently replaced with CO ₂ . The oxygen concentration at this time was 0.5%. Since the composition is set to a high concentration of 70% solid content, sufficient shearing force is required to uniformly mix the binder and the alloy powder, and the rotation speed of the stirring blade is set to 30 rpm, and 20 Stir for minutes. During stirring, CO by continuing to flow a small amount of CO ₂ in the tank
_Two concentrations were maintained.

As a result of stirring, the magnetic powder A was uniformly mixed with the binder.
When mixed, all granules are broken into secondary agglomerate fine powder.
It was At this time, the new interface that appeared during crushing was
CO ₂ CO by touching₂ Are adsorbed.

Then, the mixture is kneaded by a continuous kneading device according to a conventional method, and then mixed with another stirring device (disperser).
Diluted and dissolved in methyl ethyl ketone until the solid content became 35%, and further dispersed in a sand mill for 3 hours to prepare a coating material. Then, this magnetic coating material was applied onto a PET film to prepare a magnetic recording medium, whereby a sample of Example 2-1 was obtained.

A magnetic recording medium was prepared in the same manner as in Example 2-1 except that the inside of the stirring tank was replaced with CO ₂ instead of CO 2 to obtain a sample of Example 2-2. A sample of Example 2-3 was obtained in the same manner as in Example 2-1, except that the magnetic powder B (the magnetic characteristics and the powder characteristics are shown in Table 1) was used instead of the magnetic powder A. Further, a sample of Example 2-4 was prepared in the same manner as in Example 2-1, except that the magnetic powder D (the magnetic characteristics and the powder characteristics are shown in Table 1) was used.

A magnetic recording medium was prepared in the same manner as in Example 2-1 except that the inside of the stirring tank was replaced with nitrogen instead of CO ₂ to obtain a sample of Comparative Example 2-1. Further, a sample of Comparative Example 2-2 was obtained in the same manner as in Example 2-1, except that the magnetic powder B was used and the inside of the stirring tank was replaced with nitrogen. A sample of Comparative Example 2-3 was obtained in the same manner as in Example 2-1, except that the magnetic powder D was used and the inside of the stirring tank was replaced with nitrogen.

With respect to the sample obtained as described above, the dispersibility and magnetic characteristics of the magnetic layer were examined in the same manner as in Experiment 1. The results are shown in Table 3.

[0054]

[Table 3]

From Table 3, in the samples of Examples 2-1 to 2-4, high Rs and glossiness were realized, and C
It can be seen that a magnetic recording medium having excellent dispersibility can be obtained by mixing the magnetic powder and the binder in an O ₂ or CO atmosphere. In particular, in Example 2-2, since the magnetic powder B which had already been CO ₂ adsorbed in the pulverizing step was used, CO ₂ (or CO) treatment was performed only in the mixing step (Example 2- 1,2-
It can be seen that the dispersibility is improved as compared with 2).

Experiment 3 In this experiment, in the step of kneading the materials of the magnetic paint,
The effect of adsorbing CO and / or CO ₂ is shown.

First, magnetic powder A (the magnetic properties and powder properties are as shown in Table 1) was prepared and mixed with a binder and a solvent in the following composition. <Magnetic coating composition> 100 parts by weight of magnetic powder A Vinyl chloride-vinyl acetate copolymer (VAGH manufactured by UCC) 10 parts by weight Polyurethane (N-5033 manufactured by Nippon Polyurethane Company) 10 parts by weight Carbon 3 parts by weight Al ₂ O ₃ 2 Parts by weight methyl ethyl ketone 27 parts by weight cyclohexanone 27 parts by weight

Then, the above magnetic paint after mixing was kneaded using a kneading device. The kneading device used at this time may be a batch type or a continuous type, but in view of productivity, the continuous type is advantageous, and the one shown in FIG. 1 is used here. did.

The continuous kneading apparatus 10 shown in FIG. 1 is supplied with a magnetic paint component (magnetic powder, binder, etc.) 16 through a charging port 14 and a screw supply pipe 15, and is a paddle as a kneading member schematically shown by a broken line. 17 is attached to a rotary shaft 25 and is rotationally driven by a motor (not shown) to perform kneading under the action of a high shearing force.

The charging port 14 is sealed after the magnetic paint component 16 is carried in, CO ₂ is forcibly injected from the gas introducing port 21, and the oxygen concentration meter 30 is measured at the gas discharging port 22.
The replacement operation is carried out until the oxygen concentration reaches 0.5%. After the replacement of the inlet 14 is completed, the gas outlet 22 is closed and CO ₂
The flow rate is reduced, the gas outlet 23 on the downstream side of the kneading device 10 is opened, and the inside of the kneading device 10 is replaced with CO ₂ . By starting the kneading at the stage when the oxygen concentration measured at the outlet of the gas outlet 23 reaches 0.5%, the kneading can be performed while maintaining the CO ₂ atmosphere. It is desirable to maintain the atmosphere by continuing to flow a small amount of the gas during the kneading operation.

Thereafter, the kneading paste 26 was diluted and dissolved in methyl ethyl ketone for 2 hours with a stirring device (disperser) until the solid content became 35%, and further dispersed with a sand mill for 3 hours to prepare a coating material. This coating material was applied onto a PET film to prepare a magnetic recording medium, and a sample of Example 3-1 was obtained.

Further, a magnetic recording medium was prepared in the same manner as in Example 3-1 except that the inside of the kneading device 10 was replaced with CO instead of CO ₂ , and a sample of Example 3-2 was obtained.
A sample of Example 3-3 was prepared in the same manner as in Example 3-1, except that the magnetic powder B (the magnetic characteristics and the powder characteristics are shown in Table 1) was used instead of the magnetic powder A. did. A sample of Example 3-4 was obtained in the same manner as in Example 3-1, except that the magnetic powder D (the magnetic characteristics and the powder characteristics are shown in Table 1) was used.

Further, a magnetic recording medium was prepared in the same manner as in Example 3-1 except that the mixing step was carried out in a CO ₂ atmosphere in the same manner as in Example 2-1.
Five samples were obtained. Magnetic powder B is used, and the mixing step is
A sample of Example 3-6 was obtained in the same manner as in Example 3-1, except that it was performed in an O ₂ atmosphere.

Further, a magnetic recording medium was prepared in the same manner as in Example 3-1 except that the inside of the kneading device 10 was replaced with nitrogen instead of CO ₂ , and a sample of Comparative Example 3-1 was obtained. A sample of Comparative Example 3-2 was prepared in the same manner as in Example 3-1 except that the magnetic powder B was used and the inside of the kneading device 10 was replaced with nitrogen instead of CO ₂ . A sample of Comparative Example 3-3 was prepared in the same manner as in Example 3-1, except that the magnetic powder D was used and the inside of the kneading device 10 was replaced with nitrogen instead of CO ₂ .

A magnetic recording medium was prepared in the same manner as in Example 3-1 except that the mixing step was carried out in a CO ₂ atmosphere and the inside of the kneading device 10 was replaced with nitrogen instead of CO ₂ , and Comparative Example 3- 4 samples were obtained. A sample of Comparative Example 3-5 was prepared in the same manner as in Example 3-1, except that the magnetic powder B was used, the mixing step was performed in a CO ₂ atmosphere, and the kneading device 10 was replaced with nitrogen instead of CO _2. Obtained.

The samples prepared as described above were evaluated for dispersibility and magnetic properties in the same manner as in Experiment 1, and the results are shown in Table 4.

[0067]

[Table 4]

From Table 4, in the samples of Examples 3-1 to 3-6, high Rs and glossiness were realized, and C
By carrying out the kneading step in an O ₂ or CO atmosphere,
It can be seen that a magnetic recording medium having excellent dispersibility can be obtained.

In particular, the sample of Example 3-3 uses the magnetic powder B, that is, the pulverizing step is also performed in a CO ₂ atmosphere, so that the surface of the magnetic powder is sufficiently CO _2.
Have been adsorbed and have excellent dispersibility. Similarly, since the sample of Example 3-4 uses the magnetic powder D, it is slightly dispersed as compared with the samples of Examples 3-1 and 3-2 using the magnetic powder A not treated with CO _2. The nature is improving.

In addition, for Example 3-5, the crushing step
Then CO₂ Untreated, but mixed with binder
At CO₂ Since it is processed, only the kneading process
CO ₂ Sumps of Examples 3-1 and 3-2 that are performing treatment
Dispersibility is better than that of Furthermore, Example 3-6
In C, in all of the crushing process, mixing process, and kneading process, C
O₂ Since it is processed, the sample with the highest dispersibility
It became Le.

Experiment 4 In this experiment, after the magnetic powder granules were crushed in a CO and / or CO ₂ atmosphere to obtain magnetic powder, the magnetic powder was subjected to C
The effect of leaving it in the atmosphere of O and / or CO _{2 at} a temperature of 30 to 100 ° C. is shown.

First, magnetic powder A (the magnetic properties and powder properties are as shown in Table 1) was prepared, and the pH and H ₂ O adsorption amount were measured.

The pH was measured by adding 5 g of magnetic powder A to pure water 10
It was poured into 0 ml (pH 5.5), ultrasonically vibrated and stirred for 1 hour in a state where the atmosphere was shut off, and the pH of this water was measured by a pH measuring device (manufactured by Toa Denpa Kogyo KK). As a result, the magnetic powder A had a pH of 9.5 and an H ₂ O adsorption amount of 1.14% by weight (11.9 μm / mm ² ).

The magnetic powder A was subjected to various treatments as described below to prepare magnetic powders F to M.

(1) Preparation of Magnetic Powder F First, a glove box whose inside was replaced with CO ₂ was prepared, and 200 g of the magnetic powder A was compacted (crushed) in an agate mortar. The granules were sufficiently broken by the grinding treatment for about 5 minutes.

Then, the magnetic powder in the glove box is removed.
Heat it to a temperature of 40 ° C with a heater and use it as it is for carbon dioxide.
It was left in the atmosphere for about 2 hours. This makes the magnetic powder
Is the CO on the interface newly appeared by the consolidation treatment.₂Sucks
To wear. In this way CO ₂Magnetism with adsorption treatment
Let the powder be magnetic powder F.

Then, the inside of the glow box was replaced with nitrogen, the obtained magnetic powder F was sealed in a container in this nitrogen atmosphere, and a small amount thereof was sampled to measure the magnetic characteristics and the powder characteristics. The results are shown in Table 5.

As shown in Table 5, the magnetic powder A has a carbon content of 0.01% by weight, while the magnetic powder F has a carbon content of 0.13% by weight. From this, it was confirmed that CO ₂ was certainly adsorbed to the magnetic powder by the CO ₂ adsorption treatment. The magnetic powder A has a pH of 9.5, whereas the magnetic powder F has a pH of 8.4. The magnetic powder F has an increased number of acidic points on the surface due to CO ₂ adsorption. It is supposed that Also,
The magnetic characteristics, the powder characteristics, and the primary particle diameter shape are not different between the magnetic powder F and the magnetic powder A, suggesting that CO ₂ was adsorbed without damaging these characteristics.

(2) Preparation of magnetic powder G When the magnetic powder A was crushed in a glove box substituted with CO ₂ and the obtained magnetic powder was heated and held, the holding temperature was 70 ° C. The CO ₂ adsorption treatment was performed in the same manner as in the case of preparing the powder F. The magnetic powder obtained by performing the CO ₂ adsorption treatment in this manner is referred to as magnetic powder G. The magnetic characteristics and powder characteristics of the magnetic powder G are as shown in Table 5.

(3) Preparation of Magnetic Powder H When the magnetic powder A was crushed in a glove box substituted with CO ₂ and the obtained magnetic powder was heated and held, the holding temperature was 90 ° C. The CO ₂ adsorption treatment was performed in the same manner as in the case of preparing the powder F. The magnetic powder obtained by performing the CO ₂ adsorption treatment in this manner is referred to as magnetic powder H. The magnetic properties and powder properties of the magnetic powder H are as shown in Table 5.

(4) Preparation of Magnetic Powder I When the magnetic powder A was crushed in a glove box substituted with CO ₂ and the obtained magnetic powder was heated and held, the holding temperature was 20 ° C. The CO ₂ adsorption treatment was performed in the same manner as in the case of preparing the powder F. The magnetic powder obtained by performing the CO ₂ adsorption treatment in this manner is referred to as magnetic powder I. The magnetic characteristics and powder characteristics of the magnetic powder I are as shown in Table 5.

(5) Preparation of Magnetic Powder J When the magnetic powder A was crushed in a glove box substituted with CO ₂ and the obtained magnetic powder was heated and held, the holding temperature was set to 120 ° C. The CO ₂ adsorption treatment was performed in the same manner as in the case of preparing the powder F. The magnetic powder obtained by performing the CO ₂ adsorption treatment in this manner is referred to as magnetic powder J. The magnetic characteristics and powder characteristics of the magnetic powder J are shown in Table 5.

[0083]

[Table 5]

(6) Preparation of Magnetic Powder K and Magnetic Powder L CO ₂ adsorption treatment was carried out in a granular state by heating and holding the magnetic powder A in a glove box substituted with carbon dioxide at a temperature of 40 ° C. for about 2 hours. It was CO in this granular state
_{2 The} magnetic powder obtained by applying the adsorption treatment to the magnetic powder K
And Table 6 shows the magnetic characteristics and powder characteristics of this magnetic powder K.

[0085]

[Table 6]

The magnetic powder K was subjected to a compaction treatment in a CO ₂ atmosphere and heating and holding in the same manner as in the preparation of the magnetic powder F. The magnetic powder thus obtained is referred to as magnetic powder L. The magnetic characteristics and powder characteristics of the magnetic powder L are shown in Table 7.

[0087]

[Table 7]

(7) Preparation of magnetic powder M Magnetic powder A was crushed in a glove box and the temperature was 40 ° C.
In when heated holding a glove box CO ₂
A CO adsorption treatment was performed in the same manner as in the preparation of the magnetic powder F, except that a CO atmosphere was used instead of. The magnetic powder obtained by performing the CO adsorption treatment in this manner is referred to as magnetic powder M. The magnetic characteristics and powder characteristics of the magnetic powder M are as shown in Table 8.

[0089]

[Table 8]

Magnetic powders F to
The magnetic powder M and the magnetic powder A are kneaded and dispersed together with the following materials to form a paint, which is applied on a PET film to form a magnetic recording medium (Examples 4-1 to 4-5 and Comparative Example 4).
-1-Comparative example 4-4) were produced. The magnetic powder used in each sample medium is as shown in Table 9.

<Magnetic coating composition> 100 parts by weight of magnetic powder Vinyl chloride-vinyl acetate copolymer (VAGH manufactured by UCC) 10 parts by weight Polyurethane (N-5033 manufactured by Nippon Polyurethane Co., Ltd.) 10 parts by weight Carbon 3 parts by weight Al ₂ O ₃ 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

Then, the dispersibility and magnetic characteristics of the magnetic layer of the produced magnetic recording medium were examined in the same manner as in Experiment 1. The results are shown in Table 9 together with the types of magnetic powder used. FIG. 2 shows the relationship between the holding temperature, the gloss 45, and the saturation magnetization when the magnetic powder is heated and held in a CO ₂ atmosphere.

[0093]

[Table 9]

First, referring to FIG. 2 together with Table 9, the gloss 45 ° becomes larger as the temperature at which the magnetic powder is heated and held in a CO ₂ atmosphere becomes higher. By setting this temperature to 30 ° C. or higher, It can be seen that the value is extremely high, about 200% or more. From this, it is understood that it is effective to perform the consolidation treatment of the magnetic powder in a CO ₂ atmosphere and then heat and hold the magnetic powder in a CO ₂ atmosphere to improve the dispersibility of the magnetic powder.

However, the saturation magnetization tends to decrease as the temperature at which the magnetic powder is heated and held in a CO ₂ atmosphere becomes higher, and when the temperature exceeds 100 ° C., the decrease change becomes particularly rapid. As a result, the magnetic properties such as saturation magnetic flux density and coercive force are deteriorated. From this, it was found that a suitable temperature for heating and holding the magnetic powder in a CO ₂ atmosphere is 30 ° C. to 100 ° C. in order to improve the dispersibility without deteriorating the magnetic properties.

As can be seen from the results of Examples 4-4 and 4-5, even when the magnetic powder was subjected to consolidation treatment in a CO atmosphere, CO ₂ was further preliminarily obtained in the form of granules.
Even when using the magnetic powder that has been subjected to the adsorption treatment, heating and holding it in a CO and / or CO ₂ atmosphere is also effective for improving the dispersibility.

[0097] In Experiment 5 In this experiment, after the magnetic powder granular material compacted treated with CO and / or CO ₂ atmosphere, CO and / or CO ₂ atmosphere, in the case of heating and holding at a temperature 40 ° C., pre magnetic The effect of adjusting the H ₂ O adsorption amount of the powder granules is shown.

First, the magnetic powder A (the magnetic characteristics and the powder characteristics are as shown in Table 1) was subjected to various treatments as follows to prepare the magnetic powder N to the magnetic powder Q.

(1) Preparation of Magnetic Powder N The amount of H ₂ O adsorbed on the magnetic powder A was adjusted as follows. First, a glove box whose inside is replaced with N ₂ is prepared, the container containing the magnetic powder A is opened in an N ₂ atmosphere, and the magnetic powder A is spread on a stainless steel pan placed in the container. It was Then, magnetic powder A is heated with a heater.
Was heated and maintained at a temperature of 40 ° C., and in that state, it was left for about 4 hours while flowing dry N ₂ gas into the glove box.
Table 10 shows the magnetic characteristics and powder characteristics of the magnetic powder at this time.

The magnetic powder whose H ₂ O adsorption amount was adjusted in this manner was subjected to consolidation treatment and heating retention in a CO ₂ atmosphere in the same manner as in the preparation of the magnetic powder F. The magnetic powder thus obtained is referred to as magnetic powder N. The magnetic properties and powder properties of the magnetic powder N are as shown in Table 11.

(2) Preparation of Magnetic Powder O The N ₂ containing water vapor was caused to flow into the glove box by passing through the trap in which pure water was stored, and the standing time in the N ₂ inflow atmosphere was set. The H ₂ O adsorption amount of the magnetic powder was adjusted in the same manner as in the preparation of the magnetic powder N except that the time was about 2 hours. Table 10 shows the magnetic properties and powder properties of the magnetic powder after the H ₂ O adsorption treatment.

The magnetic powder whose H ₂ O adsorption amount was adjusted in this manner was subjected to consolidation treatment and heating and holding in a CO ₂ atmosphere in the same manner as the magnetic powder F was prepared. The magnetic powder thus obtained is referred to as magnetic powder O. The magnetic characteristics and powder characteristics of the magnetic powder O are as shown in Table 11.

(3) Preparation of Magnetic Powder P The H ₂ O adsorption amount of the magnetic powder was adjusted in the same manner as the preparation of the magnetic powder N except that the standing time in the N ₂ inflowing atmosphere was set to about 10 hours. did. Table 10 shows the magnetic properties and powder properties of the magnetic powder after the H ₂ O adsorption treatment.

The magnetic powder whose H ₂ O adsorption amount was adjusted in this way was subjected to consolidation treatment and heating and holding in a CO ₂ atmosphere in the same manner as in preparing the magnetic powder F. The magnetic powder thus obtained is referred to as magnetic powder P. The magnetic properties and powder properties of the magnetic powder P are as shown in Table 11.

[0105] (4) The except that the standing time of about 10 hours under N ₂ flow into the atmosphere together with the inclusion of water vapor in N ₂ flowing into the preparation glove box of the magnetic powder Q is preparing a magnetic powder N The amount of H ₂ O adsorbed on the magnetic powder was adjusted in the same manner as in. Table 10 shows the magnetic properties and powder properties of the magnetic powder after the H ₂ O adsorption treatment.

The magnetic powder whose H ₂ O adsorption amount was adjusted in this way was subjected to consolidation treatment and heating and holding in a CO ₂ atmosphere in the same manner as in the preparation of the magnetic powder F. The magnetic powder thus obtained is referred to as magnetic powder Q. The magnetic properties and powder properties of the magnetic powder Q are as shown in Table 11.

[0107]

[Table 10]

[0108]

[Table 11]

The magnetic powder N ~ prepared as described above
The magnetic powder Q was kneaded and dispersed together with the following materials to form a paint, which was applied on a PET film to form a magnetic recording medium (Examples 5-1 and 5-2 and Comparative examples 5-1 and 5-
2) was produced. The magnetic powder used in each sample medium is as shown in Table 12.

<Magnetic coating composition> Magnetic powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer (VAGH manufactured by UCC) 10 parts by weight Polyurethane (N-5033 manufactured by Nippon Polyurethane Company) 10 parts by weight Carbon 3 parts by weight Al ₂ O ₃ 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

Then, with respect to the magnetic recording medium thus prepared, the dispersibility and magnetic characteristics of the magnetic layer were examined in the same manner as in Experiment 1. The results are shown in Table 12 together with the types of magnetic powder used. Also, the amount of H ₂ O adsorbed on the magnetic powder (however, the amount of H ₂ O adsorbed after heating and holding in a CO ₂ atmosphere)
The relationship between the gloss and the gloss 45 is shown in FIG.

[0112]

[Table 12]

Looking at FIG. 3 together with Table 12, the gloss 45
The value of ° changes depending on the amount of H ₂ O adsorbed on the magnetic powder, and shows an increasing change until the amount of H ₂ O adsorbed on the magnetic powder reaches ²⁰ μmol / m ² , and a decreasing change at ²⁰ μmol / m ^2. become.

From the above, when the CO ₂ adsorption treatment is performed on the magnetic powder, the dispersibility of the magnetic powder depends on the H ₂ O of the magnetic powder.
It can be seen that the adsorption amount can be further improved by setting the adsorption amount within the optimum range, that is, 5 to 30 μmol / m ² .

[0115]

As is apparent from the above description, the present invention is applied to carry out the steps of pulverizing the magnetic metal powder, mixing with the binder, and kneading in a CO and / or CO ₂ atmosphere. Then, the above gas is adsorbed on the surface of the metal magnetic powder, and it becomes possible to manufacture a magnetic recording medium having excellent dispersibility.

The magnetic powder granules were treated with CO and / or C
After pulverizing in an atmosphere of O ₂ , the magnetic powder obtained by pulverizing is further pulverized in an atmosphere of CO and / or CO ₂ at a temperature of 3
When kept at 0 to 100 ° C., the H ₂ O adsorption amount of the magnetic powder granules before pulverization is further increased to 5.0 to 30.0 mol / m ^2.
If it is adjusted to be within the range, the dispersibility of the magnetic powder in the binder can be further improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing a configuration example of a continuous kneading apparatus used in the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a holding temperature, a gloss 45, and saturation magnetization when the magnetic powder is heated and held in a CO ₂ atmosphere.

FIG. 3 is a characteristic diagram showing the relationship between the amount of H ₂ O adsorbed on the magnetic powder and the gloss 45.

[Explanation of symbols]

 10 ... Biaxial continuous kneading device 15 ... Screw feeder 16 ... Magnetic paint component 20 ... Consolidation kneading part 21 ... Gas inlet 22, 23 ... Gas outlet 24 ...・ Paddle 25 ・ ・ ・ Rotating shaft 30 ・ ・ ・ Oxygen concentration meter

Claims (5)

[Claims] 1. A method for producing a magnetic recording medium, comprising forming a magnetic layer by coating a magnetic coating material containing a metallic magnetic powder and a binder as a main component on a non-magnetic support. And / or a method for producing a magnetic recording medium, which comprises pulverizing in a carbon dioxide atmosphere. 2. The metal magnetic powder is previously crushed in a carbon monoxide and / or carbon dioxide atmosphere, and then held at a temperature of 30 to 100 ° C. in a carbon monoxide and / or carbon dioxide atmosphere. The method for manufacturing a magnetic recording medium according to claim 1. 3. The H ₂ O adsorption amount of the metal magnetic powder is
The magnetic recording medium manufacturing method according to claim 1, wherein the magnetic recording medium is 5.0 to 30.0 mol / m ² . 4. A method of manufacturing a magnetic recording medium, comprising forming a magnetic layer by coating a magnetic coating material mainly composed of metallic magnetic powder and a binder on a non-magnetic support, and mixing the metallic magnetic powder and the binder. , At least one of the steps of kneading, carbon monoxide and / or
Alternatively, a method of manufacturing a magnetic recording medium, which is performed in a carbon dioxide atmosphere. 5. The method for producing a magnetic recording medium according to claim 4, wherein the magnetic metal powder is previously pulverized in an atmosphere of carbon monoxide and / or carbon dioxide.