JPS6363265B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating method and apparatus for manufacturing magnetic disks. Conventionally, as disclosed in U.S. Pat. No. 3,198,657, magnetic disks have been manufactured by dripping magnetic paint containing magnetic powder on the first surface (upper surface) of the disk while rotating it. This was then done by increasing the number of revolutions of the disk and shaking off the excess paint by centrifugal force to form a coating film, which was then dried and hardened to form a magnetic layer. To form a magnetic layer on the second surface (lower surface) of the disk using this method, first form the magnetic layer on the first surface as described above, then turn the disk over and repeat the same method. Needs to be repeated. If magnetic paint is applied to the second side before drying the coating on the first side, the rotation of the disc at that time will make the coating on the first side thinner, allowing the magnetic layer to have the desired thickness. can't get it. Furthermore, if the second surface is coated even after the first surface has dried but before it has hardened, the atmosphere will be filled with vapor due to the evaporation of the solvent in the paint. Adversely affects the surface coating. Therefore, after the coating on the first side has been cured as described above, it is necessary to form a coating on the second side. As a result, the coating film on the first surface is heated twice during curing. Furthermore, the amount of radiant heat received during curing of the coating varies depending on whether one side of the disc is made of metal with no coating applied or whether a coating has already been formed. Therefore, there is a slight difference in performance between the magnetic layers on both sides of the magnetic disk manufactured by the above method. Such a difference is caused by the fact that when the magnetic layer is thick,
Almost negligible. However, it is necessary to reduce the thickness of the magnetic layer of a high-density magnetic disk to about 1 to 3 μm or less. In such cases, the difference in performance between the two surfaces causes various problems. Naturally, work efficiency is also poor. In order to solve this problem or to improve work efficiency, the disk should be placed vertically or 10
For example, it is possible to hold the paint at an angle of ~30 degrees, apply paint to both sides at the same time, dry it, and harden it.
60732, JP-A-48-63709, etc. When forming a coating film by such a method, a problem arises in that when excess paint is shaken off by centrifugal force, the paint shaken upward falls onto the disk due to backflow or back dripping. In order to prevent such paint from splashing back, it has been proposed to provide a casing near the outer edge of the disc to prevent back dripping, and to collect the splashed paint in the casing. However, the direction in which the paint is scattered changes somewhat depending on complicated factors such as the rotational speed of the disc, the amount of excess paint, the viscosity of the paint, and the temperature. Therefore, even a single droplet will bounce off the inlet of the casing and if it falls onto the disc, that part will become defective. It is difficult to improve the structure of the casing so that this does not occur in all cases, and the incidence of defective products increases accordingly. An object of the present invention is to provide an improved magnetic disk coating method and coating apparatus. Another object of the present invention is to provide a magnetic disk coating method and coating apparatus that can simultaneously form a coating film on both sides of the disk and reduce the incidence of defective products. The method of the present invention is a magnetic disc coating method in which magnetic paint is applied while the disc is held horizontally and the disc is rotated, and the thickness of the coating film is adjusted while the disc is rotated. The paint is applied to both sides of the disc almost simultaneously, and the disc is rotated to adjust the thickness of the paint film by arranging shielding plates above and below at least the portion of the disc where the paint film is formed. It is characterized by The present invention will be explained below with reference to the drawings. FIG. 1 is a sectional front view of an embodiment of the coating apparatus of the present invention. A disc 2 is mounted on a rotatable support base 1.
(aluminum plate, inner diameter 170 mm, outer diameter 356 mm, thickness 2 mm) is fixed by the lid 3. The paint is sprayed onto the disc 2 from the tips of the supply pipes 4a and 4b.
5 is an upper shielding plate, 6 is a collection plate, 7 is a lower shielding plate, and 8 is a bottom plate. Upper shield plate 5 as shown
can also serve as the lid of the device. If paint is applied to both sides of the disk at the same time without providing the shielding plates 5 and 7, the properties of the coating films formed on both sides will be different. This is thought to be due to the following reason. Paint is applied to both sides of the disc,
When the excess paint is shaken off by the rotation of the disk,
The shaken-off paint hits the collection plate 6 and accumulates on the bottom plate 8. Since the coating film on the lower surface of the disc comes into contact with the vapor of the solvent that has evaporated from the paint on the bottom plate 8, it becomes difficult for the solvent to evaporate from the coating film. On the other hand, since the paint film on the top surface of the disk comes into contact with air that does not contain solvent, the solvent in it evaporates easily, and therefore the viscosity of the paint film (the viscosity of the paint being applied) is lower than that on the bottom surface. It gets expensive. Due to this difference in viscosity, the coating formed on the top surface is thicker than that on the bottom surface. Since the thickness of the coating film on both sides is different in this way, the electrical characteristics etc. will be different. This difference in film thickness between both surfaces is more pronounced in the inner circumferential portion than in the outer circumferential portion. This is because the air near the surface of the disk during high-speed rotation rotates in the same way as the disk rotates, and the centrifugal force causes the airflow to proceed from the center to the outer circumference. It is presumed that this is because the contacting air contains a certain amount of solvent vapor that has evaporated in the inner peripheral portion. If a magnetic disk with an inner periphery film thickness of about 1 μm is manufactured without providing a shielding plate, the film thicknesses on both sides of the inner periphery will differ by more than 50%. The present invention solves these problems by providing shielding plates above and below the disk and rotating the disk (secondary rotation) to adjust the film thickness. Rotation of the disc when applying paint (primary rotation)
Although it is preferable that a shielding plate be provided in this case, there is no problem even if there is no shielding plate. During application, the paint applied to the underside of the disc
It is preferable to prevent it from falling onto the lower shielding plate. To do this, rotate the disc at a speed of 5 to 700 rpm.
Preferably 30~300rpm, more preferably 30~
It is necessary to apply while rotating at 150 rpm (primary rotation). The centrifugal force caused by the rotation of the disk causes the paint adhered to the disk to flow toward the outer periphery of the disk, so that the paint does not accumulate in one place and fall.
Also, if it is rotated too fast, the paint sprayed on the lower surface will bounce off, which is undesirable. Even if the amount of paint ejected from the supply pipe is too large, the paint will fall onto the shield plate below. It is preferable to adjust the ejection pressure so that the excess paint is shaken off in the outer circumferential direction by centrifugal force and reaches the collection plate, but does not fall onto the shielding plate below. In addition, the position of the collection plate is 30 mm from the outer peripheral edge of the disc and lower shielding plate.
It is preferable that the distance be at least mm, more preferably at least 50 mm. This is to prevent paint that hits the collection plate from rebounding and reaching the disc or shield plate. The supply pipe moves back and forth in the diametrical direction of the disk as indicated by the arrows in FIG. 1, so that the ejected paint adheres to the entire surface of the disk. However, a more preferred method is to move the tip of the supply tube horizontally in a semicircular manner centered on a point at the base of the supply tube. The nozzle at the tip of the supply pipe is 45 to 90 mm to the disk.
The angle is determined so that the paint is projected at an angle of 60 to 80 degrees. In particular, it is preferable that the paint be ejected in the direction of rotation of the disc. The distance from the disk to the upper shielding plate and the distance from the lower shielding plate do not have to be exactly the same, but may be different within a certain range. This range is the distance from the disk to the upper shielding plate (first
The ratio (V 1 /V ₂ ) of the distance to the lower shielding plate ( _{V 1 in} FIG. 1) to V ₂ in the figure is preferably in the range of 1.2 to 2.0. Since the space below the disk and the space above the bottom plate are not completely separated, some solvent vapor evaporated from the paint on the bottom plate enters the space below the disk, resulting in V ₁ / The preferred values of V ₂ are not centered around 1.0 but extend toward larger values. FIG. 2 is a cross-sectional view of another embodiment of the invention. Holes are provided at or near the center of the upper and lower shielding plates and the bottom plate to allow approximately the same amount of air to enter from the outside. The air entering from the outside may contain vapors of the same type of solvent as the paint solvent. In this way, it is sufficient that the upper and lower shielding plates are at least above and below the portion of the disk to which the solvent is to be applied. The coating film is formed as follows, for example. First, the disk 2 is fixed to the support stand 1 with the lid 3, and if necessary, both sides of the disk are washed with a solvent. This involves installing a separate set of supply pipes that are almost the same as the paint application supply pipes, and placing them in a position where movement of the paint application supply pipes cannot be prevented. Shake out the solvent by rotating. The disk is further rotated to create an air current that evaporates the solvent that has accumulated on the lower shield plate. Therefore, in this case, it is preferable to use the apparatus shown in FIG. 2 while introducing air. Next, the disk is rotated at a rotation speed of 5 to 700 rpm, preferably 30 to 300 rpm, more preferably 30 to 150 rpm (primary rotation), and the supply pipe is rotated horizontally and semicircularly over the disk once or twice. While moving above, paint is ejected from the nozzle and sprayed on both sides of the disc at the same time. The rotation causes the paint to
Excess paint spreads over almost the entire surface of the disc,
It is shaken off from the top of the disk by centrifugal force due to rotation.
Next, in order to make the coating film to the prescribed thickness, the rotation speed of the disc is increased to 200 to 3000 rpm and rotated (secondary rotation), and excess paint is shaken off from the top of the disc.
Although the rotation speed of the primary rotation and the rotation speed of the secondary rotation may be the same, it is preferable to increase the rotation speed of the secondary rotation. Furthermore, even if the paint does not spread to some parts of the disc during the primary rotation, it will be sufficiently distributed over the entire surface during the secondary rotation. Magnetic paints in which magnetic powder is dispersed are known from the specifications of the above-mentioned patents and others, and these known paints are used. For example, a binder made of epoxy resin, phenolic resin, and polyvinyl butyral is dissolved in an organic solvent, magnetic powder is dispersed, and if necessary, a reinforcing agent such as alumina is further dispersed to form a magnetic paint. Other polymeric compounds used as the binder include polyester resins, vinyl chloride resins, polyurethanes, polyurethane forming agents, acrylate copolymers, methacrylate copolymers, and mixtures thereof. If necessary, the magnetic paint is further diluted with organic solvents such as tetrahydrofuran, toluene, methyl ethyl ketone, cyclohexanone, dioxane or mixtures thereof to adjust the desired viscosity. Preferred viscosity is approximately 50-480 cp
(20℃), more preferable viscosity is 100~350cp (same)
It is. After the coating is formed on both sides of the disc, magnetic field orientation is performed if necessary. This may be done by magnetic field orientation while the disk remains attached to the support, or by magnetic field orientation after being moved to another position. The disc is then dried and heat cured as usual.
Drying and/or heat curing can also be carried out during magnetic field orientation. Examples of the present invention will be shown below. Using the coating apparatus shown in FIG. 1, the following experiments were carried out by varying the height of the shield plate and setting the ratio of V ₁ /V ₂ as shown in Table 1. Further, V ₃ was maintained at a constant gap. Note that the nozzle of the supply pipe was tilted at an angle of 75 degrees from the horizontal plane so that the paint was jetted approximately in the direction of rotation. The paint consists of 700 parts by weight of magnetic powder, 70 parts by weight of polyvinyl butyral, 120 parts by weight of phenol resin, 120 parts by weight of epoxy resin, and a mixed solvent of cyclohexanone, isophorone, and dioxane with a viscosity of 250 cp.
I used the one from While rotating the disk at 100 rpm, paint is applied to both sides of the disk while being jetted from the feed tube at a rate of 50 c.c./min per feed tube. Then rotate
Rotate at 1200 rpm for 20 seconds to create a film thickness of approximately 1 μm on the inner periphery (film thickness after curing). Table 1 shows the difference in film thickness between both sides of the inner periphery after drying and curing. Note that the inner periphery is a position with a radius of 100 mm, and as described above, there is a large difference in film thickness at the inner periphery. For example, even if the film thickness difference at the inner circumference is 0.15 μm, the difference at the outer circumference (at a radius of 170 mm) is 0.06 μm. Furthermore, when no shielding plate was provided, the difference in film thickness was 0.5 μm or more. The film thickness is
Measurement was performed using a line film thickness meter SST-155 (manufactured by Dai-ni Seikosha).

【table】

[Table] Table 2 shows the results of a similar experiment using the coating apparatus shown in FIG.

【table】

【table】 [Brief explanation of drawings]

1 and 2 are sectional views of one embodiment of the present invention, respectively. 1... Support stand, 2... Disk, 3... Lid, 4a
and 4b... supply pipe, 5... upper shielding plate, 6...
...Collection plate, 7... Lower shielding plate, 8... Bottom plate.

Claims (1)

[Scope of Claims] 1. A magnetic disc coating method in which magnetic paint is applied while the disc is held horizontally and the disc is rotated, and the film thickness is adjusted while the disc is rotated, Magnetic paint is applied almost simultaneously to both sides of the same disc, shielding plates are placed above and below at least the portion of the disc where the coating film is formed, and the distance from the disc to the lower shielding plate is of,
1.2 for the distance from the disc to the upper shield
A magnetic disk coating method characterized by adjusting the thickness of the coating film by rotating the disk while maintaining the thickness within a range of ~2.0 times. 2. The coating method according to claim 1, wherein the disc is rotated at a rotation speed of 200 to 3000 rpm for adjusting the thickness of the coating film. 3. The rotation of the disc for adjusting the thickness of the coating film is carried out while introducing substantially the same amount of air from the center or near the center of the upper and lower shielding plates, as claimed in claim 1 or 2. Application method as described in section. 4. The rotation of the disc for adjusting the thickness of the coating film is performed by introducing approximately the same amount of air containing vapor of the same type of solvent as the solvent of the magnetic paint from the center or near the center of the upper and lower shielding plates. The coating method according to claim 1 or 2, wherein the coating method is carried out while 5. A support for horizontally holding the disc to be coated with magnetic paint, a device for rotating the support together with the disc, and a device for spraying the magnetic paint almost simultaneously onto the upper and lower surfaces of the disc. a supply tube for magnetic paint which is movable so as to be positioned in the vicinity of the upper and lower surfaces of the same disk when desired; and at least above and below the position of said disk where the magnetic paint is to be applied, respectively. The lower shielding plate shall be arranged so that the distance from the above-mentioned circular plate is maintained within a range of 1.2 to 2.0 times the distance from the upper shielding plate to the above-mentioned circular plate. A magnetic disc coating device featuring: 6. The coating device according to claim 5, wherein the tip of the supply pipe is arranged so that the direction of ejection of the magnetic paint forms an angle of 45 degrees to 90 degrees with respect to the disc. 7. The coating device according to claim 5 or 6, wherein the upper and lower shielding plates each have a hole at or near the center thereof through which substantially the same amount of gas can flow.