JPH05210843A - Production of magnetic coating material for magnetic recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] When ultrasonically dispersing a magnetic paint treatment liquid for a magnetic recording medium, the bubbles generated by cavitation are efficiently treated to stably and strongly disperse the ultrasonic particles. To do. [Structure] The output of the ultrasonic oscillation circuit that excites the ultrasonic oscillator is periodically changed (strengthened) at a certain level or more as shown by the solid line in FIG. The bubbles adhering to the end faces (which are hard to disappear due to the high viscosity of the paint) are efficiently removed during the period when the oscillation output is decreasing. As a result, resonance deviation of the vibrator and fluctuation of load (due to magnetic paint) are eliminated, ultrasonic energy is stably and efficiently transmitted into the magnetic paint, and strong dispersion processing is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a magnetic paint for forming a magnetic film in a magnetic film manufacturing process of a magnetic recording medium having a magnetic film arranged on a non-magnetic substrate or a base film, and more particularly, The present invention relates to a method for producing a magnetic paint for a magnetic recording medium, in which a magnetic paint is ultrasonically treated to obtain a high-dispersion magnetic recording medium suitable for high-density recording.

[0002]

2. Description of the Related Art Conventionally, when a magnetic recording medium such as a magnetic disk or a magnetic tape is manufactured, for example, JP-A-56-10 is used.
No. 0871, a magnetic powder is kneaded together with a non-magnetic reinforcing agent, an additive, a binder, etc. under high shear stress and uniformly dispersed, and then on a non-magnetic substrate or a base film. It is known that a coating film is formed by coating the magnetic powder on the magnetic powder and aligning the easy axes of magnetization of the magnetic powder by magnetic field orientation. However, in order to respond to higher recording density than ever before, miniaturization of magnetic powder, high content of magnetic powder,
The thinning of the coating film has become a necessary issue, and the existing dispersion technology has been insufficient. As a method for solving these problems, for example, as described in JP-A-58-133635, conventional kneading is performed to disperse the mixture to some extent, and then ultrasonic energy is added to the magnetic coating material. Further, as a method of performing strong dispersion by giving a strong shear stress to separate individual particles, or a method of utilizing ultrasonic energy, see, for example, JP-A-61-
As described in Japanese Patent No. 248230, there is one in which ultrasonic treatment and filtration are simultaneously performed.

[0003]

The above-mentioned prior art is an effective means for releasing the agglomeration of the magnetic paint to disperse the magnetic paint, but it occurs when ultrasonic waves are actually applied to the magnetic paint. There is no mention of how to solve the problem,
It turns out that there is a problem in practice. That is, in general, a magnetic coating material has a volatile organic solvent as a solvent and contains several kinds of binders, so that it has a higher viscosity than an aqueous solution during ultrasonic treatment, and as a result, a large amount of bubbles due to small cavitation occurs. It occurs and remains forever, hindering dispersion. Moreover, the generated bubbles have an adverse effect on the ultrasonic wave oscillator and the resonance reaction does not occur, which inhibits the oscillation. Also, the bubbles adhere to the oscillator, and the vibration energy is not transmitted from the oscillator to the magnetic paint. There was a problem. In the future, in performing high-power ultrasonic treatment for achieving high dispersion, a technique for solving these problems will become more important.

Therefore, an object of the present invention is to solve the above problems and to rapidly eliminate the bubbles generated by cavitation or remove the bubbles adhering to the vibrator in the dispersion process of the magnetic paint. An object of the present invention is to provide a method for producing a magnetic coating material for a magnetic recording medium, which is stable and is capable of ultrasonic dispersion treatment suitable for high output treatment.

[0005]

In order to achieve the above object, the present invention is a method for producing a magnetic paint for a magnetic recording medium, wherein the magnitude of the oscillation output is regularly changed in the magnetic paint (for example, in a cycle). Dispersion is performed by applying ultrasonic energy.

As a means for generating such ultrasonic energy, an ultrasonic wave oscillating circuit and a waveform generating circuit for controlling the oscillation output of this ultrasonic wave oscillating circuit can be provided in the ultrasonic wave generating section.

Further, according to the magnitude of the oscillation output controlled as described above, when the magnitude of the oscillation output is reduced, the amount of the magnetic paint processed per unit time is also reduced so that the flow rate ( It is possible to provide a means for synchronizing and controlling the flow velocity).

[0008]

The operation based on the above configuration will be described. In general, it is known that when ultrasonic treatment is applied to a magnetic paint, it is possible to re-disperse a part that is not completely dispersed by the kneading in the previous step or a part that has been once dispersed and then re-aggregated. In the case of an aqueous solution, the viscosity is extremely low, and the bubbles become large as they bond with each other and disappear rapidly and disappear, so that stable cavitation can be continuously generated. On the other hand, in the case of a magnetic paint, unlike an aqueous solution, the viscosity is extremely high, so that bubbles due to cavitation generated during ultrasonic treatment are generated in a small amount and in a large amount, and remain forever. Originally, ultrasonic waves are stably generated by the interaction between the vibrator and the solution to be processed.If a large amount of bubbles are left indefinitely, the bubbles stay around the vibrator and the amplitude of the vibration increases. It fluctuates and dispersion does not proceed as expected. From this point of view, how to successfully treat the foam is important in order to stably improve the dispersion level.

According to the present invention, the magnitude (amplitude) of the ultrasonic oscillation output is regularly (periodically) changed within a certain level or more to make it stronger and stronger, thereby vibrating (exciting) strongly. By vibrating weakly in a certain cycle between the times, it is possible to efficiently remove bubbles that have accumulated or adhered around the vibrator. As a result, the vibrator and the magnetic paint that functions as its load are matched, misalignment is prevented, and ultrasonic energy can be stably and efficiently transferred from the vibrator to the magnetic paint.

In general, ultrasonic dispersion is considered to be a weighted average for the processing amount of the dispersion level processed for each strength. Therefore, if the oscillation output is reduced for a short period of time within a certain level or more, there is no problem as a whole.

Further, in the present invention, the oscillation output is specifically controlled by superimposing the signal of the waveform generating circuit on the analog input of the oscillation circuit.

Further, as in the present invention, by controlling the amount of the magnetic paint to be processed per unit time according to the oscillation output, the ultrasonic output is sent to the ultrasonic wave oscillating unit while the oscillation output is lowered and the bubbles are eliminated. By controlling the amount according to the degree, the cumulative (integrated) dose of ultrasonic energy received per unit flow rate is always constant, and it is considered that the dispersion level according to this dose can be obtained. There will be no problem with the variation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The following compositions were kneaded using a kneader and a ball mill. Magnetic powder [Fe ₂ O ₃ ] 860 parts by weight α-Al ₂ O ₃ powder (reinforcing agent) 97 parts by weight Epoxy resin 210 parts by weight Phenol resin 210 parts by weight Polyvinyl butyral resin 60 parts by weight Cyclohexanone 2600 parts by weight Isophorone 1300 parts by weight Dioxane 400 parts by weight FIG. 1 shows an ultrasonic treatment apparatus for magnetic paint used in this example. In FIG. 1, 1 is an ultrasonic transducer, 2 is a transmission rod, 3
Is an ultrasonic cell, 4 is a pipe (supply pipe) for magnetic paint, 5 is a pressure vessel, 6 is a pressure gas supply device such as N ₂ , and 7 is an ultrasonic wave generation unit including an ultrasonic wave oscillation circuit 8 and a waveform generation circuit 9. 1
0 is a magnetic paint (before ultrasonic treatment), 11 is a magnetic paint treatment liquid (during ultrasonic treatment), 12 is a magnetic paint discharge pipe (after ultrasonic treatment), and 15 is an amplitude detector of the vibrator 1. , 16 are amplitude indicators.

The magnetic paint obtained by the above kneading is filtered, stabilized and stored for 6 hours, and then stored in the pressure vessel 5 of the apparatus as shown in FIG. The degree of the effect of ultrasonic dispersion is determined by the flow rate per unit time of the magnetic paint 10 flowing in the ultrasonic cell 3, the temperature, the oscillation output and frequency of ultrasonic waves, and the processing pas.
s depends on the number of times. The number of passes is the total number of treatments in the case where the magnetic coating material that has been subjected to ultrasonic treatment once is circulated and subjected to ultrasonic treatment many times. The processing conditions in this embodiment are
It is as follows. Total processing amount (liter) 6.5 L Oscillation frequency 20 KHz Processing liquid temperature 23 ° C. Processing flow rate (flow velocity) Pass times shown in FIG. 5 Once Oscillation output Shown in FIG.

In the apparatus shown in FIG. 1, the magnetic coating material 10 stored in the pressure vessel 5 is controlled by the N ₂ gas supply apparatus 6 to the pressure vessel 5 so that the processing flow rate is synchronized with the oscillation output as shown in FIG. The supplied N ₂ gas is supplied. The magnetic paint 10 pressure-fed through the pipe 4 enters the ultrasonic cell 3 and receives ultrasonic waves. At this time, the vibration is applied to the vibrator 1 by the ultrasonic wave generation section 7 including the ultrasonic wave oscillation circuit 8 and the waveform generation circuit 9 in which the output is changed (decreased by some percentage) in the cycle of 30 seconds shown in FIG. It is excited and transmitted to the magnetic paint 10 via the transmission rod 2. This oscillator is 600W, 20K
The vibration width of HZ is about 20 μm. Further, as described above, since the actual vibration is determined by the interaction between the vibrator 1 and the treatment liquid 11 containing the bubble 14, the amplitude is constantly displayed by the amplitude detector 15 using the piezoelectric element method. It was decided to monitor via a total of 16. Then, the magnetic coating material 11 thus treated is dropped on a high-speed rotating aluminum substrate (disk) whose surface has been cleaned in advance and spin-coated, and a magnetic field orientation treatment is carried out immediately after coating, followed by heat curing. A magnetic film having a thickness of 0.4 μ to 0.6 μ was formed. Next, the magnetic film is polished to a final film thickness of 0.3.
A magnetic disk of μ to 0.5 μ was prepared.

First, in comparison with the case of the aqueous solution 18, the generation of bubbles in the ultrasonic cell 3 when the magnetic coating material is subjected to ultrasonic treatment is compared with that of FIG. 2 (in the case of an aqueous solution) and FIG. Case). In general, as shown in FIG.
When ultrasonic vibration is applied to the aqueous solution 18 flowing in through the pipe 17, countless bubbles 19 due to cavitation are directed from the tip of the transmission rod 2 (just below the end face) to the bottom face of the ultrasonic cell 3.
Is generated and emitted like a jet by the energy of sound waves, and stirring is performed around the transmission plate 2,
Since the aqueous solution has low viscosity, the bubbles 19 disappear promptly after being generated, and as a result, it is possible to continuously perform stable processing without adversely affecting the vibrator 1. On the other hand, in the case of magnetic paint, its viscosity is large, and as shown in FIG. 3, when ultrasonic vibration is applied to the magnetic paint 11 flowing in through the pipe 4, it is generated from the tip of the transmission rod 2 (just below the end face). The amount of bubbles 14 formed is much larger than that of the aqueous solution 18 and the particle size thereof is small. Further, since the bubbles 14 are convected in the ultrasonic cell 3 forever and do not disappear, the load applied to the transmission rod 2 largely fluctuates with a tendency to largely fluctuate, resulting in poor tuning of the oscillation frequency or vibration energy. Therefore, it is difficult to perform stable treatment without being transmitted to the magnetic paint. This phenomenon has not been a serious problem in the processing of low oscillation output, but it is expected that it will become a serious problem in the future when high oscillation output is realized. As described above, it is considered that the reason for this is that the magnetic paint is a volatile organic solvent having a viscosity unlike an aqueous solution, which is a great influence.

In view of this, in the present embodiment, as shown by the solid line in FIG. 4, the average oscillation output remains substantially the same as the condition of the conventional example (dotted line in FIG. 1), for example, in a cycle of 30 seconds. For example, the oscillation output is reduced from 450 W to 300 W in 3 seconds and then returned in the next 3 seconds so that the oscillation output is reduced by a required amount in a certain period at a constant cycle. In this way, while the oscillation output is decreasing, the bubbles that have been generated and are attached to the transmission rod 2 disappear or are reduced, so that the load applied to the transmission rod 2 does not fluctuate, and the vibrator does not change. Vibration is stabilized, and the vibration energy is efficiently transmitted to the magnetic paint treatment liquid. Further, in this embodiment, as shown by the solid line in FIG. 5, the average flow rate remains almost the same as the condition of the conventional example (dotted line in FIG. 1), and the oscillating output of the ultrasonic wave generator 7 decreases, that is, In synchronization with the change (decrease) in the ultrasonic energy output of the vibrator 1, the flow velocity of the magnetic paint (the flow rate of the magnetic paint flowing in from the pipe 4 and flowing out from the discharge pipe 12 per unit time) is changed (decreased). To control. This control is performed by the N supplied from the gas supply device 6.
₂ By adjusting the gas. As a result, the cumulative irradiation amount of the ultrasonic energy received by the magnetic paint in the ultrasonic cell 3 becomes substantially constant regardless of the flow velocity, so that the ultrasonic dispersion effect on the magnetic paint becomes substantially constant. From these facts, when the processing is carried out under the processing conditions shown in FIGS. 4 and 5 of the present embodiment, the variation σ of the amplitude of the ultrasonic transducer during the processing is as shown in FIG. It is stable up to about 1/7 compared with. As a result, the ratio of the paint viscosity after treatment divided by the paint viscosity before treatment [hereinafter referred to as "ultrasonic viscosity change"]. ] Has improved as shown in FIG. As a result of evaluating the magnetic disk prototyped in this way, the electrical characteristics were almost the same as those of the conventional method, but the number of errors (the number of errors generated per surface of the magnetic disk when recording and reproducing data)
As shown in FIG. 8, the variation is about half that of the conventional method, and the effect is recognized.

In the above embodiment, the ultrasonic oscillation output waveform (ultrasonic vibration energy output amplitude) has a triangular wave shape.
Not limited to this, an arbitrary waveform such as a sine waveform can be used, which is important. Further, in the above embodiment, the output is changed only in a part of one cycle, but the waveform may be such that it constantly increases or decreases over the entire cycle.

According to the manufacturing method and the manufacturing apparatus of the magnetic paint of the above-mentioned embodiment, by applying ultrasonic energy to the magnetic paint, the oscillation output of which changes regularly (the strength is increased and decreased at a certain level or more), Efficient removal of bubbles by cavitation can reduce variations in the effect of ultrasonic dispersion, and stable and powerful dispersion processing can be performed.

Further, according to this manufacturing apparatus, by providing the ultrasonic wave oscillating section with the waveform generating circuit, it is possible to apply ultrasonic wave energy whose oscillation output changes regularly to the magnetic paint.

Further, according to this manufacturing apparatus, the function of controlling the amount of the magnetic coating material to be processed per unit time according to the controlled oscillation output is provided, so that a stable dispersion effect can be obtained. ..

[0022]

As described in detail above, according to the present invention, in the process of treating the magnetic paint for the magnetic film of the magnetic recording medium, the ultrasonic wave whose amplitude of oscillation output changes regularly with respect to the magnetic paint. Since energy is applied, bubbles generated by cavitation can be quickly eliminated, or bubbles attached to the vibrator can be quickly removed. As a result, the amplitude of ultrasonic vibration is stabilized, the ultrasonic vibration energy can be stably and efficiently transmitted from the vibrator to the magnetic paint, and the dispersion level of the magnetic paint can be uniformly increased. There is an effect that a magnetic recording medium having a high rate can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of a magnetic paint manufacturing apparatus used in one embodiment of the present invention.

FIG. 2 is a schematic explanatory diagram of a bubble generation state when ultrasonic waves are applied to an aqueous solution.

FIG. 3 is a schematic explanatory diagram of a bubble generation state when ultrasonic waves are applied to the magnetic paint.

FIG. 4 is an explanatory diagram comparing conditions of constant oscillation output according to a conventional method with conditions of regularly changed oscillation output according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram comparing a condition of a constant processing flow rate according to a conventional method and a condition of a processing flow rate according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram showing amplitude variations of the ultrasonic transducer according to the embodiment of the present invention.

FIG. 7 is an explanatory diagram showing changes in ultrasonic viscosity before and after ultrasonic treatment of a magnetic paint according to an example of the present invention.

FIG. 8 is an explanatory diagram showing the number of errors in one embodiment of the present invention.

[Explanation of symbols]

1 Ultrasonic Transducer 2 Transmission Rod 3 Ultrasonic Cell 4 Piping (Pre-treatment Magnetic Paint Supply Pipe) 5 Pressure Vessel 6 N ₂ Gas Supply Device 7 Ultrasonic Generator 8 Ultrasonic Transmitter Circuit 9 Waveform Generator 10 Pre-Magnetic Paint 11 Magnetic paint during processing 12 Discharge pipe (for magnetic paint after processing) 14 Foam (in magnetic paint) 15 Amplitude detector 16 Amplitude indicator 17 Piping (supply pipe for pretreatment aqueous solution) 18 Water solution for treatment 19 Foam (aqueous solution) Inside) 20 discharge pipe (after treatment of aqueous solution)

Claims (1)

[Claims] 1. A magnetic material for a magnetic recording medium, characterized in that, in the step of manufacturing a magnetic film for a magnetic recording medium, ultrasonic energy whose magnitude of oscillation output changes regularly is applied to a magnetic paint for producing the magnetic film. Paint manufacturing method.