JPH03248329A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersion degree of magnetic power by uniformly dispersing the magnetic power with a binder resin, solvent, etc., in a vacuum atmosphere, further mixing and dispersing them with a sand grinder mill to prepare a magnetic coating material, applying this coating material on a substrate and drying. CONSTITUTION:The magnetic powder is preliminarily dispersed in a binder resin, solvent and other required components in a vacuum atmosphere. Then these materials are further mixed and dispersed with a sand grinder mill to prepare the magnetic coating material, which is then applied on a substrate and dried to form the magnetic layer. Namely, by performing preliminary dispersion in a vacuum atmosphere, dispersion efficiency in the next process with using a sand grinder mill can be improved. By this method, the binder resin is well absorbed to the surface of the particles and the coating material thus prepared has fine magnetic powder in a good dispersion state. Thereby, dispersibility of the magnetic powder in the magnetic layer is improved, and excellent electric characteristics can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a magnetic recording medium, and more specifically to a magnetic recording medium having a magnetic layer with good dispersibility of magnetic powder and excellent electrical properties. Relating to a manufacturing method.

[Conventional technology]

Magnetic recording media are usually made by mixing and scattering magnetic powder with a binder resin, a solvent, and other necessary ingredients, then applying a magnetic paint onto a substrate such as polyester finomum and drying it. /, good dispersibility of magnetic powder and excellent electrical properties are required. Therefore, in order to disperse the magnetic powder A used in the binder resin as uniformly as possible, the magnetic paint is usually conditioned using the following four steps.

That is, the first step is kneading with a kneader. In this step, the magnetic powder is put into a kneader together with a binder resin suspension, a solvent, and other necessary additives.
The mixture is kneaded under an N2 gas atmosphere. After kneading for a predetermined period of time, a small amount of binder resin solution or solvent is usually added to lower the solids concentration at its best to a coating viscosity of 50%, and the mixture is transferred to the next step. In this kneading process, the magnetic paint in a paste state is subjected to shearing force at the clearance between the rotating blade in the kneader and the inner wall of the Negoo, and the magnetic powder is loosened by this shearing force to perform the initial preliminary dispersion.

The second process is a premix process using a high-speed impeller disperser. In this process, the magnetic paint kneaded by a kneader is further mixed and dispersed to a state with no uneven solid content concentration, and then sanded. Preliminary dispersion is performed to reduce the solids concentration required in the grinder mill dispersion process to a coating viscosity of 36%. Through this preliminary dispersion, the highly concentrated magnetic paint with a solid content concentration of 50% is transferred from the kneader to a tank equipped with a high-speed impeller agitator, and the inside of the kneader is washed several times with a solvent and then transferred. The magnetic paint is stirred by a high-speed impeller stirrer, and the solid content concentration is estimated to be 50 to 2.
A magnetic paint with a large solid content concentration unevenness of 0% becomes a state with no solid content concentration unevenness, and a solvent is further added to the paint with a solid content concentration of 36% required in the subsequent dispersion process in a sand grinder mill. reduced to viscosity. At this stage, the aggregate particle size of the magnetic powder becomes 50 to 20 μm or less.

The third step is a dispersion step using a sand grinder mill. In this step, the magnetic paint pre-dispersed in the premix step using the high-speed impeller disperser is continuously supplied from the sand grinder mill supply port, and is passed through the sand grinder mill. In the mill, the magnetic powder is loosened while the magnetic paint is continuously passed through a beaded shear flow. Then, it is continuously discharged from the sand grinder mill outlet. In this dispersion process using a sand grinder mill, a grinding shear force acts between the beads under a bead laminar shear flow, and aggregate particles of 50 to 20 μm or less in the magnetic paint are caught in the gaps between the beads, which are estimated to be 10 μm or less. is 1
It is loosened to the next particle level.

The fourth step is the coating and dispensing step, in which other necessary components such as a crosslinking agent are added to the magnetic paint in which the magnetic powder is dispersed down to the primary particle level using a sand grinder mill.
It is filtered by a filter and dispensed into the magnetic paint supply line of the coating machine.

[Problem to be solved by the invention]

However, when the current dispersion process, which sequentially performs the above four steps, is reviewed from the viewpoint of promoting and strengthening the adsorption of the binder resin, which is the key to high dispersion, and increasing the shear force applied to the magnetic powder aggregates, It has been found that there are the following two problems. That is, in (1) the kneading step using a kneader, the N2 gas adsorbed on the surface of the magnetic powder is first replaced by a solvent, and then adsorbed and replaced by a binder resin. However, among these sequential substitutions, solvent substitution is difficult and has poor reproducibility, so the sequential substitution with solvent and binder resin is incomplete, and the magnetic powder is This has a very large effect on the dispersion and reduces the degree of dispersion of the magnetic powder.

(2) Furthermore, since the premix process is carried out under atmospheric pressure, as the magnetic paint is stirred by a high-speed impeller stirrer, air gets mixed into the magnetic paint and remains as bubbles. Therefore, in the dispersion process using a sand grinder mill, the air bubbles mixed into the magnetic paint are captured between the beads and dispersed in the same way as the aggregated particles in the magnetic paint, and the shear force of the beads is reduced by this. This is reduced by the dispersion of air bubbles.Then, when air bubbles are further trapped between the beads, the grinding shear force applied to the magnetic paint by a quake absorber is alleviated.Thus, in the conventional premix process, Air bubbles are mixed into the magnetic paint, reducing the dispersion efficiency in the subsequent sand grinder mill, and as a result,
The degree of dispersion of the magnetic powder decreases.

Therefore, in the current dispersion process, the promotion and strengthening of binder resin adsorption, which is the key to high dispersion, is insufficient, and the shear force applied to the magnetic powder aggregates is not sufficiently increased, so it is still difficult to spread the magnetic powder uniformly. In particular, magnetic powders with small particle diameters, large specific surface areas, and large cohesive forces, such as metal magnetic powders, cannot be dispersed in the surface of the metal magnetic powders. , ensure dispersion stabilization due to steric hindrance of the adsorption binder resin, and in the case of magnetic powders that cannot be highly dispersed without applying high shear force to the surface of the agglomerated metal magnetic powder to thoroughly loosen it, the magnetic powder must be sufficiently loosened. , it is difficult to make it fine and disperse it uniformly.

[Means for Solving the Problems] The present invention has been made as a result of various studies in view of the current situation, and is based on the following: magnetic powder is mixed with a binder resin, a solvent, and other necessary components in a kneader and a high-speed impeller dispersion machine. The magnetic powder is sufficiently uniformly dispersed by performing preliminary dispersion using a sand grinder or the like in a vacuum atmosphere, and then the magnetic paint prepared by mixing and dispersing with a sand grinder mill is applied onto the substrate and dried. The electrical characteristics of the resulting magnetic recording medium are further improved.

In this invention, the kneading process using a kneader and the preliminary dispersion in the premixing process using a high-speed impeller disperser are preferably performed in a vacuum atmosphere.If the kneading process using a kneader is performed in a vacuum atmosphere, N2 The gas is removed in advance under vacuum, and the magnetic powder is kneaded with the binder resin, solvent and other necessary components under vacuum, thus promoting solvent displacement and binder resin adsorption onto the magnetic powder surface. Therefore, the steric hindrance effect accompanying the adsorption of the binder resin is enhanced, and the degree of dispersion of the magnetic powder is further improved.

Furthermore, if the premixing process using a high-speed impeller disperser is performed in a vacuum atmosphere, air bubbles will not be mixed into the magnetic coating material, and the air bubbles that have already been mixed in will be deflated and removed. However, the dispersion efficiency in the next step, the sand grinder mill, is dramatically improved, and the degree of dispersion of the magnetic powder is further improved.

In the case of a kneading process using a kneader, the degree of vacuum in such preliminary dispersion is determined mainly by the vapor pressure of a solvent such as cyclohexanone or toluene, and should be 160 torr or less at a temperature of about 30°C. is preferable; if it exceeds 160 Torr, the desired effect cannot be obtained. In addition, in the case of a premix process using a high-speed impeller disperser, if the ultimate vacuum level, which is determined by the vapor pressure of the solvent, exceeds 110) at a temperature of about 30°C, the desired effect will not be achieved. Therefore, it is preferable to reduce the temperature to 110 torr or less at a temperature of about 30°C.

In addition, it is most preferable that both the kneading process using a kneader and the premixing process using a high-speed impeller disperser be carried out under a vacuum atmosphere, but only one of these processes may be carried out under a vacuum atmosphere. In this case, the degree of dispersion of the magnetic powder is also dramatically improved.

If preliminary dispersion is performed in a vacuum atmosphere in this way, the dispersion efficiency in the next step, the sand grinder 1' under mill, will be dramatically improved, and the binder resin will be well adsorbed on the particle surface and thoroughly dispersed. A magnetic paint containing fine magnetic powder is prepared, and when the magnetic paint thus obtained is applied onto a substrate and dried, the dispersibility of the magnetic powder in the magnetic layer is further improved, and the electrical properties are improved. A magnetic recording medium with even better properties can be obtained.

Examples of the magnetic powder used in this invention include F
Metal magnetic powder such as e powder, CO powder, Fe-Ni powder, 7-Fe2O, powder, Fe3O4 powder, 7-Fe,
Intermediate oxide powder of O, powder and Fe, O, powder, CrO□
Powder, Co-containing T-Fe2O, powder, Co-containing Fe,
Any of the magnetic powders commonly used in the past, such as 04 powder, are suitable for use, but among them, magnetic powders that are fine and difficult to disperse, such as those with a BET specific surface area of 30
%/g or more and the above-mentioned oxide magnetic powders whose BET specific surface area is 40 po/g or more have dramatically improved dispersion.

In addition, as the binder resin, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, cellulose resin,
Any conventionally commonly used resins can be used, such as polyurethane resins, polyester resins, isocyanate compounds, and acrylic resins.

Furthermore, as a solvent, for example, cyclohexanone,
Ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, hydrocarbon solvents such as hexane and heptane, dimethyl formamide, etc. An organic solvent selected from acid amide solvents, sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydrofuran and dioxane, or a mixture of two or more thereof, or water is used.

〔Example] Next, embodiments of the invention will be described.

Example 1 <Kneading process using two to two goo> DM-98 (manufactured by Dowa Mining Co., Ltd., 40.0 parts by weight metal magnetic powder, BET specific surface area 56±2 M/g) AO3-48 (manufactured by Sumima Kagaku Kogyo 3.2) Tarox R-110-7 (manufactured by Titanium Kogyo Co., Ltd., red iron) Mogul L (manufactured by Cavont Co., Ltd., 0.8〃carbon black) MS-500 (manufactured by Asahi Carbon Co., Ltd. 0.4〃carbon) Black) Zinc stearate (Seido Kagaku 0.2〃manufactured by Kogyo Co., Ltd.) MRIIO-H (Nippon Zeon 17.4〃manufactured by Kogyo Co., Ltd.)
PVC resin solution, solid content 25.0% by weight, cyclohexanone 37.5% by weight, toluene 37.5%) Cyclohexanone 1,5〃Toluene
D. 5. The above composition was put into a 1202 Nigu with a vacuum specification of 10 torr and which had been purged with N2 in advance, and was evacuated using a vacuum pump with an evacuation speed of 25,012/win to reach an ultimate vacuum level of 6 at about 30°C.
After setting it to 0 torr, rotate the kneader blade to 4 or
The mixture was kneaded by rotating at pm for 3 hours.

Next, the 1201 kneader was purged with N2 to return the pressure inside the kneader to atmospheric pressure, and then UR8310 (manufactured by Toyobo Co., Ltd.; polyurethane solution, cyclohexanone/toluene/solid content 35.Q/35.0/30. 0% by weight) to 6.8
By adding part by weight, the kneaded composition in the kneader was changed from a powder state to a paste state, and this paste state was further kneaded by rotating a blade at a rotational speed of 40 rpm for 5.5 hours. After kneading, 17.8 parts by weight of cyclohexanone and 17.8 parts by weight of toluene and 21.4 parts by weight of methyl ethyl ketone were added to make the magnetic paint into a low viscosity paste state, and the volume for the premix process was transferred from the kneader using a pump. The liquid was sent to the 1902 stirring tank.

<Premix process> The capacity for the premix process where magnetic paint is transferred is 19
0! The stirring tank is evacuated with a vacuum pump at a speed of 25012
/win, and after evacuation to an ultimate vacuum of 110 Torr, vacuum stirring was performed for 6 hours at a rotational speed of 1500 rpm using an 8-inch diameter impeller stirrer.

After the premix process, the inside of the stirring tank was evacuated to an ultimate vacuum of 110 torr using a vacuum pump at a pumping speed of 2501/min, and 7.0 parts by weight of cyclohexanone and 7.0 parts by weight of toluene were added to the tank, and the tank was heated to a diameter of 8.
Using an inch impeller agitator, rotation speed 110 Or
pm for 1 hour to let down the paint viscosity suitable for dispersion in a sand grinder mill.

After the letdown, the magnetic paint was dispersed using a sand grinder mill, and 0.8 parts by weight of myristic acid, 0.6 parts by weight of butyl stearate, and 0.6 parts by weight of Coronate L were added to the magnetic paint that had been dispersed using the sand grinder mill.
(Trifunctional low molecular weight isocyanate compound manufactured by Nippon Polyurethane Co., Ltd.) Cyclohexanone 5.0 and toluene 5.0 were added and mixed and dispersed for 1 hour to prepare a magnetic paint. This magnetic paint was applied to a polyester film with a thickness of 7.5 μm to a dry thickness of 3.3 μm.
The magnetic powder was coated so as to have a thickness of .mu.m, the magnetic powder was oriented in the longitudinal direction using an orientation magnet, and calendering was performed to form a magnetic layer.

Next, on the back side of the polyester film on which the magnetic layer was formed, the following paint for a back coat layer was applied to a thickness of 0.8 μm after drying, and dried to form a bank coat layer. Thereafter, it was cut into 8-pan wide pieces to create Hi8 8III11 video tapes.

Paint for back coat layer Mogal Shiki Cabot Co., Ltd., 60.0 parts by weight carbon black) Sepacarb MT-CI (Colo 7.5 Colo 7.5, Inbia Chemil Luss Co., carbon black) Calflex D (Suehiro Lime 30.0 parts made by Co., Ltd.) , calcium carbonate) TF-100 (manufactured by Toda Kogyo Co., Ltd., 2.5 red iron) HA-103 (manufactured by Asahi Kasei Co., Ltd., 204.6) Nitrocellulose solution, solid content 16% by weight, cyclohexanone 42% by weight, toluene 42% by weight ) N2309 (Nippon Boliureta 184.1 〃
(manufactured by Tan Kogyo Co., Ltd., polyurethane solution, solid content 20% by weight, cyclohexanone 40% by weight, toluene 40% by weight) Coronate Shikoku Nippon Polyurethane 16.4 (manufactured by Tan Kogyo Co., Ltd., isocyanate compound, solid content 75% by weight, ethyl acetate 25 weight%) %) Cyclohexanone 253.7 〃Toluene 253.7 〃Example 2 Example 2 Except that in the kneading step using a kneader in Example 1, the kneading was not performed under a vacuum atmosphere but under atmospheric pressure. A magnetic paint was prepared in the same manner as in 1, and a HiB 8111II+ videotape was made.

Example 3 In the premix step and the letdown after the premix step in Example 1, the premix step and the letdown after the premix step were not carried out in a vacuum atmosphere, but were carried out under atmospheric pressure. A magnetic coating material was prepared in the same manner as in Example 1, and an 8m videotape for HiB was made.

Comparative Example 1 In the kneading process using a kneader in Example 1, the premix process, and the letdown after the premix process, the kneading process using the kneader, the premix process, and the letdown after the premix process were performed in a vacuum atmosphere. A magnetic paint was prepared in the same manner as in Example 1, except that the test was carried out under atmospheric pressure, and a Hi8 8-kaku videotape was made.

The degree of dispersion of the magnetic paint obtained in each Example and Comparative Example was examined by a filtration test using a filter. In the filtration test, magnetic paint was applied from the filter at a filtration rate of 2.5 kg/min using Nihon Rotro delta type filter V-600 (filtration accuracy 0.6 μm) and filter V-300 (filtration accuracy 0.3 μm). The filter supply pressure of the magnetic paint required for filtration and discharge was measured and evaluated.

In addition, the video tapes obtained in each of the Examples and Comparative Examples were incorporated into an 8 mm video cassette for Hi8 to produce an 8-mm video cassette for HiS, and recorded in Hi8 mode using this 8-mm video cassette recorder for HiS. RF ratio output chroma output when playing, Y-S/N,
C-S/N was measured and expressed as a relative value to a reference 8 cabinet video cassette tape. Furthermore, still durability at a low temperature of -5°C was measured. Still durability is determined when the playback output is 6dB compared to the recording and playback output at the start of the test.
The time required for the temperature to decrease to

Tables 1 and 2 below are the results.

Table 1 Table 2 [Effects of the Invention] As is clear from Table 1 above, the magnetic paints obtained by the present invention (Examples 1 to 3) are different from the conventional magnetic paints (Comparative Examples 1 to 3).
), the filter supply pressure is lower when any of the filters is used, which shows that according to the present invention, a magnetic paint with much improved dispersibility of magnetic powder can be obtained.

Furthermore, as is clear from Table 2 above, the HiB 8-video tapes (Example Works to 3) obtained according to the present invention are more effective than the conventional HiB 8-video tapes (Comparative Example 1). RF specific output chroma output, Y-3/N, C-3/N are high, and still durability under low temperature is good.
It can be seen that according to the manufacturing method of the present invention, the dispersibility of the magnetic powder is sufficiently improved, and a magnetic recording medium with significantly superior electrical properties can be obtained.

Claims (1)

[Claims] 1. Magnetic powder is predispersed together with a binder resin, a solvent, and other necessary components in a vacuum atmosphere, and then mixed and dispersed in a sand grinder mill to prepare a magnetic paint. Method 2 for producing a magnetic recording medium characterized by coating a paint onto a substrate and drying it to form a magnetic layer.Preliminary dispersion is first performed in a vacuum atmosphere using a kneader, and then a high speed impeller disperser is used. 3. A method for manufacturing a magnetic recording medium according to claim 1, wherein the preliminary dispersion is first carried out under atmospheric pressure using a kneader, and then under a vacuum atmosphere using a high-speed impeller disperser. 4. A method for producing a magnetic recording medium according to claim 1, wherein the preliminary dispersion is first carried out in a vacuum atmosphere using a kneader, and then in a vacuum atmosphere using a high-speed impeller disperser. Manufacturing method 5, claims 1 to 4, wherein the magnetic powder is a metal magnetic powder.
6. A method for manufacturing a magnetic recording medium according to claim 5, wherein the magnetic powder is a metal magnetic powder having a BET specific surface area of 30 m^2/g or more. 7. A method for manufacturing a magnetic recording medium according to claim 5, wherein the magnetic powder is an oxide magnetic powder. A method for producing a magnetic recording medium according to claims 1 to 4, wherein the magnetic powder is an oxide magnetic powder having a BET specific surface area of 40 m^2/g or more.