JP4450543B2 - Method for manufacturing magnetic recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a low-noise and high-density coating type magnetic recording medium.
[0002]
[Prior art]
In order to increase the density of magnetic recording media, in the case of tape-like media, in general, the tape length is increased (the tape thickness is reduced) to increase the volume recording density, or the track width is reduced to reduce the area. Techniques to increase recording density have been used in many systems.
[0003]
As a result, as the tape thickness is reduced, insufficient edge strength of the tape has become a problem, and it has become unavoidable to use a support made of an expensive material having higher strength than conventional products. Also, servo technology has been developed to cope with the narrow track width adopted in recent years, but this technology is particularly difficult in a linear system, and the development cost is enormous.
[0004]
In addition to the above method, there is a method for increasing the linear recording density as a method for increasing the density, but the decrease in C / N (carrier output / noise ratio) due to the shorter wavelength recording is remarkable, and the adoption of this method is postponed. It was done.
[0005]
[Sections to be solved by the invention]
By the way, as a technique for increasing the density, recently, an increasing number of systems adopt a high-sensitivity MR head as a reproducing head. In this case, the magnetic recording medium is required to reduce the medium noise and make the magnetic layer extremely thin. As a technique for reducing the medium noise, it is conceivable to use a magnetic material having a fine particle and a uniform distribution, and uniformly dispersing the magnetic material during the preparation.
[0006]
However, in the conventional liquid preparation method, the initial contact between the magnetic substance and the binder is performed by a kneader or the like. At this time, the agglomerated magnetic powder and high-concentration binder solution are mixed while applying a high shearing force. Therefore, when a fine magnetic material is used, the wettability of the magnetic material decreases, There are problems that the dispersibility is lowered and the aggregation of the magnetic material formed by kneading cannot be crushed even after dispersion. Further, there is a problem that the aggregation of the magnetic material not only causes noise, but also causes defects such as streaks in the coating of an extremely thin magnetic layer.
[0007]
An object of the present invention is to solve the above-described conventional problems and to provide a low-noise high-density coating type magnetic recording medium.
[0008]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides a method of manufacturing a magnetic recording medium in which a magnetic coating material containing a ferromagnetic powder and a binder is coated on a nonmagnetic support, wherein the magnetic coating material comprises:Average primary particle volume is 10,000 nm ³ IsA liquid A composed of a ferromagnetic powder and a solvent and a solution B of the binder are applied. The liquid A is preliminarily dispersed by applying ultrasonic waves, and then the liquid A and the solution B are ultrasonically applied. There is provided a method of manufacturing a magnetic recording medium, characterized in that mixing is performed immediately before and after that, dispersion processing is performed by application of ultrasonic waves.
[0009]
  According to the present invention, a ferromagnetic powder and a solvent are used.Pre-ultrasonic dispersion treatmentLiquid A and binder solution B are applied by applying ultrasonic waves.dispersionTherefore, the agglomerated particles of the ferromagnetic powder can be crushed and the agglomeration of the ferromagnetic powder can be prevented, so that a ferromagnetic powder solution can be obtained in which the binder is uniformly adsorbed. As a result, a magnetic paint suitable for a low-noise, high-density coating type magnetic recording medium can be obtained.
[0010]
That is, the surface area of the magnetic material increases as the magnetic material becomes finer. For this reason, the ferromagnetic powder is more likely to be in an aggregated state when the raw material is produced. This aggregation of the magnetic material is in the form of air, but since the surface area of the magnetic material is large, it is difficult to degas instantly upon initial contact with the binder solution, and the surface of the magnetic material is sufficiently wetted. It will be in a state that is not made.
[0011]
Generally, there is a technique to increase the wettability when contacting the solution by agglomeration such as compaction, but if it is compacted with fine particle magnetic material, it is difficult to disintegrate even in the subsequent dispersion treatment of the magnetic paint. There is a problem of forming aggregates.
[0012]
If the method for preparing a magnetic coating of the present invention is used, both the agglomeration of ferromagnetic powder and the uniform mixing of the ferromagnetic powder and the binder can be performed simultaneously by ultrasonic cavitation. It can be made small and the binder is uniformly adsorbed on the surface of the magnetic material. As a result, it is possible to produce a magnetic coating material that has few clumps after dispersion treatment and is magnetically free of magnetic materials.
[0013]
In the present invention, it is preferable that the ultrasonic wave is applied within 1 second after the liquid A and the solution B are mixed. This is because the above effect can be achieved more efficiently by applying ultrasonic waves within a predetermined time after the liquid A and the solution B are mixed.
[0014]
In addition, it is preferable that the time until the ultrasonic wave is applied after mixing the liquid A and the solution B is within 5 seconds at the minimum. This is because when the liquid A and the solution B are mixed for a long time, the binder may be adsorbed on the surface of the aggregate of the ferromagnetic powder, and it is necessary to prevent this.
[0015]
In the present invention, before the liquid A and the solution B are mixed, it is preferable that the liquid A is subjected to a dispersion treatment by applying ultrasonic waves. As described above, if the liquid A is preliminarily dispersed before mixing the liquid A and the solution B, the effect of the present invention can be more reliably exhibited.
[0016]
In the present invention, the mixing of the liquid A and the solution B by application of ultrasonic waves is preferably performed by a flow type ultrasonic disperser. Thus, according to the flow type ultrasonic disperser, the effect of the present invention can be exhibited more reliably.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of a magnetic paint manufacturing apparatus 10 used in a method for manufacturing a magnetic recording medium according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of a magnetic paint manufacturing apparatus 10, and FIG. 2 is a detailed cross-sectional view of an ultrasonic disperser 40 used in the ultrasonic dispersion system 16.
[0018]
The apparatus 10 for manufacturing a magnetic paint is composed of an A liquid supply system 12, a B liquid supply system 14, an ultrasonic dispersion system 16, a sand mill dispersion system 18, and a magnetic coating liquid preparation system 20 from upstream. The A liquid supply system 12 and the B liquid supply system 14 are provided in parallel, and are piped so as to merge immediately before the ultrasonic dispersion system 16.
[0019]
The A liquid supply system 12 for supplying the liquid A and the B liquid supply system 14 for supplying the solution B are each composed of a liquid tank and a liquid supply means. That is, the A liquid supply system 12 includes a liquid tank 21, a stirrer 22 having a tip disposed in the liquid tank 21, a liquid supply pipe 23 from the liquid tank 21, and a liquid supply pump 24. Similarly, the B liquid supply system 14 includes a liquid tank 25, a stirrer 26 having a tip disposed in the liquid tank 25, a liquid supply pipe 27 from the liquid tank 25, and a liquid supply pump 28.
[0020]
As the various constituent members used in the A liquid supply system 12 and the B liquid supply system 14, various known members can be used. However, it is preferable to employ a material that does not cause contamination and does not cause corrosion due to the liquid property of magnetic coating material for magnetic recording media.
[0021]
In the ultrasonic dispersion system 16, three flow type ultrasonic dispersion machines 40, 60 and 62 are provided in series. For these three units, devices of the same specification are adopted. These ultrasonic dispersers 40, 60 and 62 are configured such that liquid is supplied from the lower surface of the apparatus and liquid is discharged from the side surface of the apparatus. Thus, by providing three ultrasonic dispersers 40, 60 and 62 in series, the aggregated particles of the ferromagnetic powder can be reliably crushed and the ferromagnetic powder and the binder can be mixed uniformly. Become.
[0022]
In FIG. 2, the liquid tank 42 of the ultrasonic disperser 40 is a cylindrical container, and the straight part (liquid supply part) 32 of the inverted Y-shaped pipe 30 is connected to the lower end part. And piping 38 (liquid discharge part) is connected to one place of the side part upper part. The inverted Y-shaped pipe 30 has a bifurcated tip, and the pipe 34 made of the liquid A and the pipe 36 made of the solution B merge to form a straight part 32.
[0023]
By adopting such an inverted Y-type piping configuration, after the liquid A and the solution B are mixed, they flow into the liquid tank 42 of the ultrasonic disperser 40 and are applied with ultrasonic waves within a predetermined time. Therefore, if the same action can be achieved, the same function can be obtained even if the inverted Y-type pipe 30 is replaced with an inverted T-type or horizontal T-type pipe.
[0024]
The upper end of the liquid tank 42 of the ultrasonic disperser 40 is closed by a flange 50 of a vibrator 44 described later to form a sealed container. A cylindrical vibrator 44 is disposed inside the liquid tank 42 so that ultrasonic waves can be applied to the liquid passing through the liquid tank 42. The flange 50 is formed integrally with the vibrator 44.
[0025]
A converter 46 is fixed to the upper end portion of the vibrator 44, and power is supplied to the converter 46 from a power supply 48. Therefore, when the ultrasonic disperser 40 is activated, ultrasonic vibration is excited by the converter 46, and ultrasonic waves are applied to the liquid tank 42 by the vibrator 44.
[0026]
In the ultrasonic disperser 40 having this configuration, the distance between the lower end of the vibrator 44 and the bottom surface of the liquid tank 42 is 3 mm. In the ultrasonic disperser 40 having this configuration, the portion where the ultrasonic waves are effectively applied is the hemispherical zone 52 (hatched portion in FIG. 2) below the lower end of the vibrator 44, and in other zones. The effect of ultrasonic waves is far inferior to that of zone 52.
[0027]
As described above, the ultrasonic dispersers 60 and 62 are successively arranged downstream of the ultrasonic disperser 40. Since the ultrasonic dispersers 60 and 62 have the same configuration as the ultrasonic disperser 40 as described above, description thereof is omitted. However, the pipes connected to the upstream sides of the respective ultrasonic dispersers 60 and 62 are different from the ultrasonic disperser 40 in that they are straight pipes.
[0028]
As the flow type ultrasonic dispersers 40, 60 and 62 described above, for example, a flow type ultrasonic disperser manufactured by Nippon Seiki Seisakusho, trade name: US-1200TCVP can be used. The specifications of this apparatus are a frequency of 20 KHz, a MAX amplitude of 30 μm, a rated output of 1200 W, a distance between the irradiation unit and the holder of 3 mm, and the like.
[0029]
Further, the inner diameters of the pipes on the entry and exit sides of the ultrasonic dispersers 40, 60 and 62 are 14 mm, and the straight part of the inverted Y-type pipe 30 (from the mixing part of the liquid A and the solution B to the inlet of the liquid tank 42). The pipe volume is 3cm^ThreeIt is.
[0030]
In FIG. 1, a sand mill dispersion system 18 disposed downstream of the ultrasonic dispersion system 16 includes a liquid tank 70, a stirrer 72 having a tip disposed in the liquid tank 70, and a liquid supply pipe 74 from the liquid tank 70. A liquid feed pump 76, a sand mill disperser 78, and a return pipe 80 from the sand mill disperser 78 to the liquid tank 70 are configured.
[0031]
In the sand mill dispersion system 18, the liquid flowing in from the ultrasonic dispersion system 16 is repeatedly circulated by the sand mill dispersion machine 78 and a part thereof is supplied to the downstream magnetic coating liquid preparation system 20. ing.
[0032]
This sand mill dispersion system 18 is intended to further disperse the ferromagnetic powder of the liquid mixture of the liquid A and the solution B, and various known members can be used as the various constituent members used for this. However, it is preferable to employ a material that does not cause contamination and does not cause corrosion due to the liquid property of magnetic coating material for magnetic recording media.
[0033]
The magnetic coating liquid preparation system 20 disposed downstream of the sand mill dispersion system 18 includes a liquid tank 82, a stirrer 84 having a tip disposed in the liquid tank 82, a liquid supply pipe 86 from the liquid tank 82, and a filter 88. And a pipe 90 from the filter 88. Further, in the liquid tank 82, a C liquid made of a lubricant and a solvent and a D liquid which is an additive solution (made of carbon black and an abrasive) are newly added.
[0034]
In this magnetic coating liquid preparation system 20, the magnetic paint is finally prepared, and after passing through the filter 88, foreign matters are removed and supplied as a magnetic paint to the coating process.
[0035]
Hereinafter, the production of the magnetic paint using the magnetic paint production apparatus 10 will be described. Various materials can be used as the ferromagnetic powder used in the present invention. When the ferromagnetic powder is hexagonal ferrite, the ferromagnetic powder having a plate diameter of 35 nm or less and a plate ratio of 2 or more is used. Is a ferromagnetic metal powder, those having a major axis length of 60 nm or less and an axial ratio of 2 or more can be preferably used. As the particle size of this ferromagnetic powder, the average primary particle volume is 10000 nm.^ThreeThe following can be preferably used.
[0036]
In the liquid A, the solvent in which the ferromagnetic powder is immersed is preferably a solution containing cyclohexanone. The content of cyclohexanone is preferably 30 to 100% by weight of the total amount of solvent. As a solution other than cyclohexanone, it is preferable to use methyl ethyl ketone, toluene, butyl acetate or the like.
[0037]
A further effect can be obtained by subjecting the liquid A composed of the ferromagnetic powder and the solvent to a dispersion treatment by applying ultrasonic waves before the treatment with the magnetic coating material manufacturing apparatus 10. The dispersion processing by applying ultrasonic waves may be either a batch processing mode or a flow processing mode. That is, more cavities (cavities) generated by ultrasonic dispersion treatment are applied to ferromagnetic powder immersed in a solvent, and the liquid concentration, frequency in ultrasonic dispersion, irradiation area, number of circulations, etc. You only have to set it.
[0038]
The liquid concentration of the liquid A is preferably 5 to 80% by weight, more preferably 10 to 50% by weight, and still more preferably 25 to 50% by weight. The upper limit of the liquid concentration is defined from the ease of penetration, and the lower limit of the liquid concentration is defined by the efficiency of ultrasonic dispersion.
[0039]
The conditions when the ultrasonic dispersion treatment of the liquid A before the treatment by the magnetic coating material production apparatus 10 is performed in a batch treatment will be described. The ultrasonic frequency is preferably 15 to 1000 KHz. A high frequency is preferable in terms of the number of generated cavities, and a low frequency is preferable in terms of the bursting force of the generated cavities. From this point, the coagulated magnetic material can be crushed more effectively by using ultrasonic dispersion treatment of different frequencies together.
[0040]
When ultrasonic dispersion processing is performed at a single frequency, the magnetic material can be crushed by applying a predetermined time (power consumption) at a frequency of 20 to 40 KHz. When the frequency 20 KHz and 40 kHz are compared, 40 kHz is preferable in that the room for expanding the ultrasonic irradiation area is large and the number of ruptures of cavities generated in the liquid is large. As a batch type ultrasonic disperser having a frequency of 40 kHz, various commercially available ultrasonic cleaners can be used. A manufacturer etc. are not specifically limited.
[0041]
In addition, when performing the ultrasonic dispersion treatment, put the liquid A before treatment in a glass or plastic sealed container having a diameter smaller than the ultrasonic irradiation area and place it on the ultrasonic irradiation section. Is preferred. In addition, when the processing liquid A is put in a container having a diameter larger than the ultrasonic irradiation area, it is more preferable to stir with a stirrer.
[0042]
The conditions when the ultrasonic dispersion treatment of the liquid A before the treatment by the magnetic paint manufacturing apparatus 10 is performed by the flow (circulation) treatment will be described. The frequency of a commercially available ultrasonic disperser for flow treatment is generally around 20 kHz. Therefore, it is preferable to secure the number of ruptures of the cavities in the liquid by ensuring the number of circulations of the liquid A and promote the crushing of the aggregated magnetic material. Further, it is preferable to treat with a high liquid amount as a countermeasure against sedimentation of the magnetic substance.
[0043]
As an ultrasonic disperser, for example, a flow type ultrasonic disperser manufactured by Nippon Seiki Seisakusho, trade name: US-1200TCVP can be used. Since the specification of this apparatus has already been described, it will be omitted. This ultrasonic disperser is more preferable in that the ultrasonic irradiation zone is circular with a diameter of 50 mm, and a large irradiation area can be secured.
[0044]
In the B liquid supply system 14 of FIG. 1, the concentration of the solution B of the binder is preferably 10 Pa · s (100 P) or less, more preferably 1 Pa · s (10 P) or less in terms of liquid viscosity. And 0.1 Pa · s (1 P) or less is most preferable.
[0045]
When mixing the solution B and the solution A, the binder ratio of the solution B to the magnetic substance is preferably 0.5 to 30 parts by weight, more preferably 2 to 15 parts by weight with respect to 100 parts by weight. More preferred. Further, from the viewpoint of securing the film strength, ensuring the dispersibility, and the like, it is preferable to add the necessary binder in the middle of the dispersion progress because the dispersion efficiency can be increased.
[0046]
The processing speed of the magnetic paint by the magnetic paint manufacturing apparatus 10 varies depending on the size of the apparatus, the concentration of each liquid, the composition of each liquid, etc., but for example, at the entrance of the ultrasonic dispersion system 16 of the magnetic paint manufacturing apparatus 10. In the corresponding reverse Y-shaped pipe 30, the liquid A and the solution B can be mixed at a flow rate of 500 g / min. In this case, if the inverted Y-shaped pipe 30 is the configuration described above (the straight pipe volume is 3 cm).^Three) After mixing the liquid A and the solution B, ultrasonic waves are applied after 0.18 to 0.32 seconds (mixed liquid specific gravity 1 to 1.8 g / cc) has elapsed.
[0047]
Various known manufacturing methods can be used to manufacture a magnetic recording medium using a magnetic coating obtained by the magnetic coating manufacturing apparatus 10. For example, as an application means for the magnetic paint, a roller coating method, a dip coating method, a fountain coating method, etc. can be employed in the application system, and an air knife coating method, a blade coating method, a bar coating method, etc. can be employed in the metering system. In addition, an extrusion coating method, a slide bead coating method, a curtain coating method, and the like can be adopted as the application system and the weighing system in charge of the same part.
[0048]
The thickness of the magnetic layer of the magnetic recording medium to be produced is preferably 0.02 to 3 μm, more preferably 0.02 to 0.2 μm as a dry film. Further, it is preferable to have a layer structure in which a nonmagnetic layer mainly composed of a nonmagnetic powder and a binder is provided between the magnetic layer and the nonmagnetic support. In particular, in the configuration in which the magnetic layer is a thin layer, it is possible to reduce coating stripes by crushing the agglomerated magnetic material, so it is only necessary to improve the media performance by suppressing the C / N drop in the short wavelength region. There is also an advantage that productivity can be improved.
[0049]
As mentioned above, although the example of embodiment of the manufacturing method of the magnetic-recording medium based on this invention was demonstrated, this invention is not limited to the example of the said embodiment, Various aspects can be taken.
[0050]
For example, in the example of the present embodiment, a configuration in which three flow-type ultrasonic dispersers 40, 60, and 62 are provided in series is adopted, but only one ultrasonic disperser having a higher output is installed. A form may be sufficient and an ultrasonic disperser with small output may be provided in series.
[0051]
Also, as described above, various means that exhibit the same action, such as an inverted T-shaped pipe, can be employed instead of the inverted Y-shaped pipe 30.
[0052]
【Example】
Next, examples of the present invention will be described in comparison with comparative examples. In the following examples, “parts” means “parts by weight”.
[0053]
Each of the following examples employs a layer structure in which a nonmagnetic intermediate layer mainly composed of a nonmagnetic powder and a binder is provided between a magnetic layer and a nonmagnetic support.
[0054]
And Example 1 which is an embodiment of the present invention is an ultrasonic application of a liquid A composed of ferromagnetic powder and a solvent and a binder solution B in the magnetic paint manufacturing apparatus 10 having the configuration shown in FIG. This is an example of using a magnetic paint that has been mixed and then subjected to a dispersion treatment.
[0055]
In contrast, Example 2, which is a comparative example, uses barium ferrite having a plate diameter of 26 nm and a plate ratio of 3 as the ferromagnetic powder, and brings the ferromagnetic powder and the binder solution into contact with an open kneader when preparing the magnetic liquid. This is an example of using a magnetic paint that has been kneaded to produce a liquid and then subjected to a dispersion treatment.
[0056]
Example 3, which is a comparative example, differs from Example 1 (Example) in that it does not undergo prior ultrasonic dispersion mixing and flow type ultrasonic dispersion treatment, and is combined with a liquid A composed of a ferromagnetic powder and a solvent. This is an example in which a magnetic coating material is used which is stirred and mixed with a solution B of the agent at a peripheral speed of 18 m / sec for 30 minutes using a dissolver type stirrer.
[0057]
Hereinafter, with respect to each configuration of Examples 1 to 3, common parts are collectively described, and different parts are individually described.
[0058]
(1) Configuration of non-magnetic intermediate layer (common to Examples 1 to 3)
Nonmagnetic powder α-Fe₂O_Three                        80 copies
Average long axis length 0.1μm
Specific surface area by BET method 48m²/ G
pH 8, Fe₂O_ThreeContent 90% or more
DBP oil absorption 27-38ml / 100g
Surface treatment agent Al₂O_Three
20 parts of carbon black
Average primary particle size 16μm
DBP oil absorption 80ml / 100g
pH 8.0
Specific surface area by BET method 250m²/ G
Volatiles 1.5%
8 parts of vinyl chloride copolymer
MR-110 manufactured by Nippon Zeon
Polyester polyurethane resin 4 parts
Neopentyl glycol / Caprolactone polyol / MDI
= 0.9 / 2.6 / 1
SO_ThreeNa group 1 × 10 −4 eq / g contained Tg 65 ° C.
Phenylphosphonic acid 3 parts
Butyl stearate 1 part
1 part of stearic acid
150 parts of methyl ethyl ketone
100 parts of cyclohexanone
The coating material for the nonmagnetic intermediate layer is prepared by kneading each component except stearic acid and butyl stearate with an open kneader, and then using a horizontal circulation type pin type sand mill disperser (2L type) with small diameter zirconia beads (diameter 0.5 mm). ) Was packed at a bead filling rate of 80%, and the dispersion was performed such that the peripheral speed of the pin tip was 12 m / sec, the flow rate was 0.5 kg / min, and the dispersion residence time was 60 minutes.
[0059]
Add 3 parts of polyisocyanate to the dispersed liquid, add 1 part each of stearic acid and butyl stearate, add a solution dissolved in methyl ethyl ketone and cyclohexanone (methyl ethyl ketone: cyclohexanone = 36 parts: 24 parts), stir and solidify A nonmagnetic coating solution having a partial concentration of 28% and a solvent ratio of methyl ethyl ketone: cyclohexanone = 6: 4 was prepared. This nonmagnetic coating solution was filtered and adjusted using a filter having an average pore size of 1 μm.
[0060]
(2) Configuration of magnetic layer (showing magnetic liquid and additive solution; others are omitted)
a) Additive paste liquid (additive solution) (common to Examples 1 to 3)
α-alumina (particle size 0.18 μm) 4.5 parts
Carbon black (particle size 0.10μm) 0.5 part
MR110 0.45 parts
9.2 parts of cyclohexanone
The additive paste liquid had a ratio of carbon black: alumina: MR110: cyclohexanone = 5: 45: 4.5: 50.5, and this paste liquid was separated from the magnetic liquid by a flow-type ultrasonic disperser (1200 W, frequency 2 passes were performed at a flow rate of 300 g / min using 20 KHz, a diameter of the irradiated portion surface of 50 mm, an interval between the irradiated portion and the holder of 3 mm, and an amplitude of 30 μm.
[0061]
b) Magnetic liquid (differing between Examples 1 to 3)
[Example 1]
100 parts of ferromagnetic powder
Plate diameter 26nm, plate ratio 3, average primary particle volume 3805nm^Three
SBET 60m²/ G, pH 7.9
Hc187856A / m (2360 Oe)
σs 49A ・ m²/ Kg
True specific gravity 5.1g / ml, apparent specific gravity 0.7g / ml
MR110 10 parts
20 parts of methyl ethyl ketone
170 parts of cyclohexanone
Preparation of the magnetic coating liquid of the example was performed by blending the liquid A in a ratio of ferromagnetic powder: cyclohexanone = 100 parts: 150 parts. As a pre-stirring, 100 g of liquid A (mixed liquid) is put into a cylindrical container (inner diameter is flat, thickness is 2 mm, material is glass, height is 100 mm, with lid), and an ultrasonic cleaner made by BRANSON, Model No .: BRANSONIC 220 (specifications: 125 W, diameter of irradiation surface: 50 mm, two oscillating parts, frequency: 40 KHz), and a cylindrical container containing the above-mentioned mixed solution was disposed and treated while water was applied.
[0062]
A cylindrical container was placed right above the oscillation part of the ultrasonic cleaner, and ultrasonic treatment was performed within 1 minute after the solvent immersion (after mixing). The ultrasonic treatment time was 30 minutes. Then, it put in the liquid tank 21 of the A liquid supply system 12 of the magnetic paint manufacturing apparatus 10 shown in FIG.
[0063]
Separately, as a solution B, a binder solution of MR110: cyclohexanone: methyl ethyl ketone = 10: 20: 20 (liquid solid content concentration 20%) prepared by a dissolver type stirrer was used as the magnetic paint manufacturing apparatus 10 B shown in FIG. It put in the liquid tank 25 of the liquid supply system 14, was stirred with the stirrer 26, and was made to wait.
[0064]
The mixing of the liquid A and the solution B was performed by applying ultrasonic waves after the liquid A and the solution B were merged by the inverted Y-type pipe 30. In the ultrasonic dispersion system 16, the flow type ultrasonic dispersion machines manufactured by Nippon Seiki Seisakusho Co., Ltd., trade name: US-1200TCVP (specifications omitted) were used as the flow type ultrasonic dispersion machines 40, 60 and 62.
[0065]
The inflow amounts of the liquid A and the solution B into the reverse Y-shaped pipe 30 were mixed at a flow rate of 500 g / min. The mixed liquid coming out of the ultrasonic disperser 40 was further passed through the ultrasonic dispersers 60 and 62 connected in series.
[0066]
Thereafter, in the sand mill dispersion system 18, this mixed solution was processed by a composition type circulation type (2L type) pin type sand mill dispersion machine 78. The processing conditions are as follows: small diameter zirconia beads (diameter 0.5 mm) are packed at a bead filling rate of 80%, the peripheral speed of the pin tip is 10 m / sec, the flow rate is 0.5 kg / min, and the dispersion residence time is 30 minutes. And distributed.
[0067]
[Example 2]
As a comparative example, barium ferrite having a plate diameter of 26 nm and a plate ratio of 3 was used as the ferromagnetic powder, and the liquid was prepared by bringing the magnetic powder and the binder solution into contact with an open kneader when kneading the magnetic liquid. Above, distributed processing was performed. The mixing ratio of the ferromagnetic powder is the same as in Example 1.
[0068]
More specifically, ferromagnetic powder, binder, methyl ethyl ketone, and cyclohexanone are kneaded with an open kneader, and then filled with small diameter zirconia beads (diameter 0.5 mm) into a horizontal circulation type pin type sand mill disperser (2L type). The dispersion process was performed so that the pin tip peripheral speed was 10 m / sec, the flow rate was 0.5 kg / min, and the dispersion residence time was 30 minutes.
[0069]
[Example 3]
As a comparative example, a prior ultrasonic dispersion mixing and a flow type ultrasonic dispersion treatment were not performed, but a liquid A composed of a ferromagnetic powder and a solvent and a binder solution B were mixed at a peripheral speed of 18 m using a dissolver type stirrer. The mixture was stirred and mixed at a rate of 30 minutes per second for dispersion treatment. The mixing ratio of the ferromagnetic powder is the same as in Example 1.
[0070]
Next, in the magnetic coating liquid preparation system 20 shown in FIG. 1, a process for preparing a magnetic coating material by mixing the magnetic liquids of Examples 1 to 3 and the additive paste liquid described above will be described.
[0071]
The magnetic coating solution and additive paste solution are placed in the liquid bath 82 of the magnetic coating solution preparation system 20 and mixed and stirred by a stirrer 84. Further, 0.5 part of stearic acid and 1.5 parts of butyl stearate are mixed with 50 parts of methyl ethyl ketone. A liquid dissolved in 30 parts of cyclohexanone was added and stirred to prepare a magnetic coating (magnetic coating). The magnetic coating solution was filtered and adjusted using a filter 88 having an average pore size of 1 μm.
[0072]
A magnetic tape as a magnetic recording medium was manufactured by the following process. As a non-magnetic support, the thickness of the AFM roughness spectrum is 5.2 μm and the roughness component intensity at a wavelength of 4.3 μm is 0.03 nm.²Polyester naphthalate was used.
[0073]
On this support, the nonmagnetic layer coating solution is dried to a thickness of 1.5 μm, and immediately thereafter, the magnetic layer is dried to a thickness of 0.1 μm. Simultaneous multilayer coating was performed. While both the non-magnetic layer and the magnetic layer are still in a wet state, they are oriented and dried by a cobalt magnet having a magnetic force of 3000 G and a solenoid having a magnetic force of 1500 G, and then the seven steps composed of only a metal roll. The magnetic tape was manufactured by carrying out a slitting process to a width of 6.35 mm using a calender apparatus under conditions of a temperature of 85 ° C., a linear pressure of 350 kg / cm, and a speed of 50 m / min.
[0074]
The magnetic tapes of Examples 1 to 3 were evaluated in the following two items. That is, the number of bumps and the cluster size.
[0075]
The number of spots was evaluated by counting the number of spot-like aggregated spots per predetermined area with an optical microscope. The total number of 8 visual fields in a 500 times visual field was taken as the number of irregularities. In addition, the area for 8 fields of view with 500 times field of view is 0.1768 mm.²It corresponds to.
[0076]
In Example 1 (Example of the present invention), the number of protrusions was zero. On the other hand, in Examples 2 and 3, which are comparative examples, the numbers of irregularities were 140 and 0, respectively.
[0077]
The cluster size was measured by MFM (magnetic force microscope). In Example 1 (an example of the present invention), the cluster size is 5800 nm.²Met. On the other hand, in Examples 2 and 3 which are comparative examples, the cluster size is 29000 nm, respectively.²10,000 nm²Met.
[0078]
As described above, when the Example of the present invention is compared with the Comparative Example, Example 1 (Example of the present invention) has a spot-like shape when the surface of the magnetic layer is observed with an optical microscope as compared with Example 2 (Comparative Example). It can be seen that the number of aggregated particles is small and the size of the magnetized cluster by MFM is also small, and the effect of the present invention can be confirmed.
[0079]
Although Example 3 (Comparative Example) has a smaller number of bumps than Example 2 (Comparative Example) and the magnetization cluster size by MFM is small, it is clearly inferior to the Example of the present invention. I understand.
[0080]
【The invention's effect】
As described above, according to the present invention, the liquid A composed of the ferromagnetic powder and the solvent and the solution B of the binder can be mixed by applying ultrasonic waves, so that the aggregated particles of the ferromagnetic powder can be crushed. At the same time, since the aggregation of the ferromagnetic powder can be prevented, a ferromagnetic powder solution in which the adsorption of the binder becomes uniform can be obtained. As a result, a magnetic paint suitable for a low-noise, high-density coating type magnetic recording medium can be obtained.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a magnetic paint manufacturing apparatus used in an embodiment of the present invention.
FIG. 2 is a detailed sectional view of an ultrasonic disperser used in an ultrasonic dispersion system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Manufacturing apparatus of magnetic coating material, 12 ... A liquid supply system, 14 ... B liquid supply system, 16 ... Ultrasonic dispersion system, 18 ... Sand mill dispersion system, 20 ... Magnetic coating liquid preparation system

Claims (2)

In a method for producing a magnetic recording medium, wherein a magnetic coating material containing a ferromagnetic powder and a binder is coated on a nonmagnetic support,
The magnetic paint includes a liquid A composed of a ferromagnetic powder having an average primary particle volume of 10,000 nm ³ or less and a solvent, and a solution B of the binder,
The liquid A is preliminarily subjected to a dispersion treatment by applying ultrasonic waves, and then the liquid A and the solution B are mixed immediately before the application of ultrasonic waves, and then the dispersion treatment by applying ultrasonic waves is performed. A method of manufacturing a magnetic recording medium.   2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the liquid mixture of the liquid A and the solution B is subjected to a dispersion process by applying ultrasonic waves, and then a sand mill dispersion process is performed.

Images