JPH01319131A - Method for applying magnetic coating compound - Google Patents

Abstract

PURPOSE:To apply even the magnetic coating compd. which is degraded in flowability thinly and uniformly on a substrate by impressing >=50Hz vibrations to a substrate disk under rotation. CONSTITUTION:The substrate disk 4 is fixed to a revolving shaft 5 and is rotated at a specified speed by a motor 6 via a transmission mechanism 7. The rotating speed of the disk 4 is increased and the dropping coating compd. is shaken out so that the thin coated film remains on the substrate when the dropping of the prescribed amt. of the coating compd. onto the disk 4 ends. The shaft 5 is connected to a vibration generator 8 and the vibrations of >=50Hz frequency are impressed to the disk 4 under rotation during the entire stage of the application of the magnetic coating compd. or in a part of the stage. The apparent viscosity of the magnetic coating compd. contg. magnetic powder having high coercive force at a high concn. can be lowered by lowering the yield value of said coating compd. in this way and, therefore, the thin and uniform coating of the magnetic coated film is possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic disk manufacturing process, and is particularly suitable for forming a thin and uniform coating film when applying magnetic paint onto a substrate. This invention relates to a method for applying magnetic paint.

[Conventional technology]

BACKGROUND ART In recent years, the capacity of external magnetic storage devices such as computers has been rapidly increasing, and there is a demand for increasing the recording density of coated magnetic disks. Improving recording density means increasing the number of recorded bits per unit area of a magnetic disk, and for this purpose, materials for magnetic coatings and.

Improvements have been made in the method of its preparation. The coated magnetic disk that is the object of the present invention is a magnetic paint that contains magnetic powder, a binder resin for fixing it in a coating film, a solvent, and a filler powder such as alumina to improve the strength of the coating film. is applied thinly onto a disk-shaped substrate to form a magnetic coating. In order to improve the recording density of such coated magnetic disks, the magnetic paint or coating film is required to have the following characteristics improved. In other words, magnetic powder.

It is necessary to use a material with higher holding power, and the coating film needs to be formed thinner and more uniform by increasing the ratio of magnetic powder to the binder resin, that is, the magnetic powder content in the coating film. . Therefore, a magnetic paint prepared to form such a coating is required to contain a higher concentration of magnetic powder having a higher coercive force.

Conventionally, it has been common to use a spin coating method to apply magnetic paint onto a substrate. That is, first, paint is deposited on the substrate, and then this is rotated at high speed, and the excess paint is shaken off from the substrate by centrifugal force, thereby forming a thin and uniform coating film on the substrate. With this method,
Whether or not the desired thin and uniform coating film can be formed on the substrate is greatly influenced by the fluidity of the magnetic paint used.

In order to successfully achieve this objective, it is generally desirable that the magnetic paint has low viscosity and properties as close as possible to Newtonian fluids.

[Problem to be solved by the invention]

When preparing magnetic paint containing a higher concentration of high-coercivity magnetic powder in order to manufacture magnetic disks compatible with higher recording densities, the viscosity of the paint increases significantly and it also becomes strongly pseudoplastic. . When a paint with such properties is applied using the conventional spin coating method, the fluidity of the paint is poor, so no matter how fast the board is rotated, the paint does not flow well on the board. ! 11WA film thickness becomes too large, or a film with wavy undulations is formed.
It was a layer to form a uniform coating film.

The purpose of the present invention is to provide a method of coating a coating film suitable for high recording density by coating a magnetic coating thinly and uniformly on a substrate even with a magnetic coating material having reduced fluidity by containing a high concentration of magnetic powder with high coercivity. It is about providing.

[Means to solve the problem]

The above object is achieved by applying vibrations of 50 Hz or more to the rotating substrate disk during the process of applying magnetic paint onto the substrate disk using a spinner.

[Effect]

An example of a coating apparatus to which the magnetic coating method of the present invention is applied is shown in FIG. A constant amount is dropped onto the disk 4 at a constant speed. The substrate disk 4 is rotated around a rotating shaft 5,
It is rotated by a motor 6 via a transmission mechanism 7 at a constant speed.

When a predetermined amount of paint has been dropped onto the substrate disk 4, the rotation speed of the substrate disk is increased, and the dropped paint is shaken off, leaving a thin coating film on the substrate.

The rotating shaft 5 is connected to a vibration generator 18, which applies vibrations with a frequency of 50 Hz or more to the substrate disk rotating five times during all or some steps of the magnetic paint application operation.

9 in the figure is a spin coating device.

〔Example〕

<Example 1> Magnetic powder mainly composed of γ-iron oxide 70wt%, filler powder (alumina particles) 3.2wt%, binder resin mainly composed of epoxy resin 15.2wt%, solvent 11.6%
The mixture at a wt% ratio was filled into a kneader and kneaded for about 4 hours to obtain a kneaded product. Kneaded mixture 11
．． 6 wt%, solvent 15 wt%, and diameter approximately Low
After filling a cylindrical alumina container with alumina balls at a ratio of 73.4 wt% and rotating this at 60 revolutions per minute for about 100 hours, 1.8 wt% of the initially filled kneaded mixture was filled.
Twice the weight of solvent and 19.3% by weight of curing agent were added and further mixed by rotation for 24 hours. The magnetic paint thus prepared was taken out and filtered through a filter paper with an opening of 2 μm.

The flow characteristics of the obtained magnetic paint were measured using a rotational viscometer, and the results are shown in A of FIG. As is clear from these results, the magnetic paint has a relatively large yield value and exhibits strong pseudoplastic flow characteristics. This indicates that the magnetic particles in the paint aggregate with each other due to their own magnetic force, forming a crosslinked structure within the paint. The flow characteristics shown here become more pronounced when the coercive force of the magnetic powder in the paint increases or when the concentration of the magnetic powder increases. In other words, the yield value becomes thicker (and the pseudoplasticity becomes stronger). This is because the larger the coercive force of the particles and the higher the particle concentration, the more cohesiveness increases and the easier it is to form a crosslinked structure. be.

Next, a vibration generator was connected to the sample container of the measurement section of the rotational viscometer, and the flow characteristics were measured while applying vibration to the sample. The amplitude and frequency of the applied vibration are each 0.1
m and 100 hertz.

The flow curve thus measured is shown in FIG. 2B.

It can be seen that by applying vibration, the yield value is significantly reduced and the apparent viscosity of the paint is also significantly reduced. That is, by applying vibration, the fluidity of the paint was improved by a factor of 11, making it easier to flow. In particular, since the yield value is significantly reduced, the improvement in fluidity in the low shear rate region is remarkable. By applying vibration in this way,
The reason why the magnetic paint flows easily is thought to be because the above-mentioned aggregation of the magnetic particles and the resulting crosslinked structure are constantly destroyed by vibration. As soon as the application of vibration is stopped, the flow characteristics return to those shown at A in FIG. This is because the magnetic particles in the paint are minute, and even though the paint itself is stationary, the particles within it are constantly moving due to Brownian motion and repeatedly collide with other particles.
This is thought to be because a crosslinked structure is immediately formed.

In this way, it was revealed from this example that by applying vibration to the magnetic paint, the fluidity of the paint was greatly improved.

<Example 2> Using the magnetic paint prepared in Example 1, changes in fluidity of the paint in response to vibration application were examined in more detail. The results are shown in Figure 3, where the shear rate is 31 as the viscosity of the paint.
The apparent viscosity at g" is shown. The larger the amplitude of the applied vibration, the greater the rate of decrease in viscosity in the low frequency range, but when the frequency exceeds about 50 Hz, the influence of amplitude and frequency almost disappears, and the viscosity is almost constant. It becomes constant.

When we measured the viscosity of the same magnetic paint by connecting an ultrasonic oscillator to the sample container of the viscometer instead of the vibration generator, we found that it showed the same viscosity as the steady-state value shown in Figure 3. .

<Example 3> The magnetic paint prepared in Example 1 was applied onto an aluminum substrate disk using an apparatus having the configuration shown in FIG. The substrate used was an 8'/a' aluminum disk. First, the board is rotated at a rotation speed of about 20 Orpm, and after placing magnetic paint on the board, the board is rotated at a rotation speed of about 150 Orpm.
A coating film was formed by rotating at m. 1500rp
The following three conditions were changed while rotating at m.

That is, (1) No vibration is applied. (2) Vibration with an amplitude of 0.3 m and a frequency of 25 hertz is applied in the direction of the substrate rotation axis. (3) Vibration with an amplitude of 0.3 m and a frequency of 70 hertz is applied in the direction of the substrate rotation axis. After the magnetic powder in the coating film formed was subjected to an orientation treatment, the coating film was dried, and the binder resin was subjected to a heat curing treatment. The results of measuring the film thickness and surface roughness of these coating films are shown in FIG. The surface of the film formed under the conditions (1) was clearly wavy even when visually observed, and its flatness and uniformity were extremely poor. It can be seen from (2) and (3) that as the applied vibration intensity increases, the smoothness of the formed coating film improves and the film thickness becomes thinner. still,
In the coating films formed under the conditions (2) and (3), unlike those formed under the conditions (1), no wavy surface roughness was observed by visual observation, and a --like coating film was formed. The electromagnetic properties of a coating film are in a highly proportional relationship with the coating thickness and surface roughness, and the electromagnetic properties of films formed under the conditions (1), (2), and (3) improve in this order.

In the process of applying a thin film of paint by rotating a substrate disk at high speed, the paint on the substrate becomes thinner over time, and the flow rate of the paint on the substrate also slows down. In other words, the shear rate applied to the paint on the substrate decreases, but as is clear from Figure 2, the paint has a large yield value under non-vibration conditions, so the apparent viscosity of the paint dramatically increases during the thinning process. It is thought that it will become larger. On the other hand, by applying vibration, the yield value of the paint becomes so small that it almost disappears, so it is thought that the apparent viscosity of the paint does not increase that much even in the process of thinning the paint. For this reason, when coating without applying vibration, as the paint on the substrate becomes thinner, its apparent viscosity increases rapidly, and once it reaches a certain thickness, it stops flowing, but when applying vibration, In some cases, there is little change in the fluidity of the paint, and therefore it is thought that it can be applied more thinly. For the same reason, it is thought that applying vibration also smoothes the surface of the coating film.

As is clear from the results shown in FIG. 3, results similar to those of this example were obtained when the frequency was kept constant and the amplitude was varied.

In this example, vibration was applied in the direction of the rotation axis of the substrate disk, but as is clear from the above explanation of the mechanism by which the apparent viscosity of the magnetic paint decreases due to the application of vibration, this effect does not change in the direction of the applied vibration. It's completely unrelated. Therefore, the exact same effect as in the example can be obtained by vibrating the substrate disk in the horizontal direction, and the same effect can also be obtained by not rotating the substrate disk uniformly but by giving a vibration factor to the rotation itself. The following effects are obtained, and this example does not limit the scope of the present invention in any way.

〔Effect of the invention〕

According to the present invention, it is possible to reduce the yield value and the apparent viscosity of a magnetic paint containing a high concentration of high-coercivity magnetic powder, thereby making it possible to form a thin and uniform magnetic paint film.
Can be applied smoothly.

Coated magnetic disks with high recording density can be easily formed.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an apparatus to which the coating method of an embodiment of the present invention is applied, Fig. 2 is a flow characteristic diagram of magnetic paint, and Fig. 3 is a characteristic diagram showing changes in apparent viscosity of magnetic paint due to application of vibration. ,
The fourth @ is a diagram showing the relationship between the film thickness and surface roughness of the coating film prepared in the example and the applied vibration frequency. 1...Tank, 2...Pump, 3...Nozzle, 4
... Substrate disk, 5 ... Rotating shaft, 6 ... Motor, 7 ... Rotation transmission Figure 1 and Figure 2 Cθ! ,! (S-ri Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. A method for applying magnetic paint, comprising: applying vibrations of 50 hertz or more to the rotating substrate disk in the step of applying the magnetic paint onto the substrate disk using a spinner.