JPH03181036A - Film forming method for information recording medium - Google Patents

Abstract

PURPOSE:To enable formation of protective film having uniform film thickness and no build-up on the circumferential edge by coating the recording medium layer of the disk substrate with a protective film resin by screen printing method, and then drying and curing the resin. CONSTITUTION:A single-plate structure disk 11 comprising a disk substrate 14 of polycarbonate resin with a center hole 12 and a recording medium layer 14 formed on the one side of the substrate. This disk is set under a screen 15 and coated with a UV-curing type coating liquid 17 through the mesh 15a of the screen with a sliding plate 16. The coating liquid applied is dried to volatilize the diluent, irradiated with UV ray to cure the protective film 18. By this method, a protective film having uniform film thickness can be formed and the amt. of the coating material can be minimized to realize low production cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a film on an information carrier that allows information to be recorded, reproduced and erased at high density and in a large capacity using a laser beam or the like.

Conventional technology A disk in which an information medium layer is formed, such as an unrecorded recording medium layer on one side of a disk-shaped transparent substrate, or a reflective layer formed on uneven pits on which predetermined information signals have been recorded. Using a substrate, a disk with a protective plate pasted with an adhesive to protect the information medium layer, or two disk substrates with an information medium layer formed thereon to increase recording capacity, can be used to transfer information to each other. Optical discs have been put into practical use in which information is recorded and reproduced from the disc substrate side using laser light using double-sided discs that are bonded together with an adhesive so that the medium layers face each other. Furthermore, disks that allow repeated recording and erasing by reversibly changing the optical density of the recording medium layer are being put into practical use. In disks that are bonded together using an adhesive, the quality of the adhesive may cause various problems, such as the inclusion of air bubbles, or oxidative deterioration of the recording medium layer due to the release of acid. Furthermore, when double-sided discs are subjected to two-stage curing of ultraviolet curing and anaerobic curing or heat curing, strain occurs in the boundary areas, that is, the innermost and outermost areas of the recording medium layer, when the adhesive is cured. However, due to this strain, peeling easily occurs from the boundary area, resulting in a lack of reliability. For this reason,
It has been considered to form a film on the surface of the recording medium layer to protect it.As a method for forming this protective film, the fifth conventional method is
As shown in FIG. 6, the center hole 1 is rotated at low speed while the disk 3 fixed to the rotating shaft 2 is inserted into the dispenser 4.
is moved from the center of the disk toward the outer periphery to apply a coating liquid, and then the disk 3 is rotated at high speed to remove excess coating liquid and then cured to form a protective coating 5 as shown in FIG. The main method used was the so-called spin coating method.

Problems to be Solved by the Invention However, in the method of forming a protective film using the conventional spin coating method explained in FIGS. It has the disadvantage that it becomes thicker as it increases, and that a bulge occurs at the outer peripheral edge. Further, after the coating liquid is sufficiently applied to the surface of the recording medium layer of the disk 3, the excess coating liquid is removed by high-speed rotation, but this removed coating liquid cannot be reused.

The usage efficiency of the coating liquid was poor.

In addition, as mentioned above, there is a difference in the thickness of the protective coating 5 between the center and the outer periphery of the disk 3, and a swell (approximately 3 to 5 times the predetermined film thickness) at the outer periphery occurs, resulting in optically poor performance. Since the film cannot be thick enough to cover the entire surface of the recording medium layer, there is a problem in that it affects recording, reproduction or erasing. In addition, the coating liquid usage efficiency is 20%.
There was a problem that it was undesirable when mass production was taken into consideration because the degree of loss was low and there was a lot of loss.

The present invention solves these problems by making it possible to form a protective film with a uniform thickness over the entire information carrier, and to reduce costs by keeping the amount of coating material used to the minimum necessary. The purpose is to

Means for Solving the Problem In order to solve this problem, the present invention provides a method of coating a disk substrate having a recording medium layer on one side with a protective coating resin by screen printing on an area covering at least the entire surface of the recording medium layer. and then cured.

Function: With this configuration, it is possible to form a protective coating on the information carrier that has a uniform thickness and has no bulges at the outer peripheral edge. Furthermore, since only the necessary amount of coating liquid is used, materials can be significantly reduced.

EXAMPLES The following five examples of the present invention will be described based on the drawings.

First, the first embodiment shown in FIGS. 1 to 3 will be described. Reference numeral 11 has a single-plate structure in which a recording medium layer 14 is formed on one side of a disk substrate 13 made of polycarbonate resin and having a center hole 12. It is a disk, which is set on the lower side of the screen 15 so that the mesh part 1 of the screen 15
An ultraviolet curable coating liquid 17 is applied by the second sliding plate 16 of 5a. More specifically, the mesh portion 15a of the screen 15 is formed in a size matching the outer diameter of the disk 11, and is set so that the lower surface of the mesh portion 15a is in contact with the upper surface of the recording medium layer 14. By sliding the cutting plate 16 on the mesh portion 15a and spreading the coating liquid 17, the coating liquid 7 seeped out from the mesh portion 15a is applied to the entire upper surface of the recording medium layer 14, as shown in FIG. Thus, a layer of protective coating 18 is formed. after that,
The protective coating I8 is cured by volatilizing and drying the diluent of the coating liquid 17 and irradiating it with ultraviolet rays. In addition to the ultraviolet curable materials, thermosetting materials can also be used. When a coating liquid made of a resin material is applied and coated using the screen printing method, air bubbles are trapped.

Or, there were concerns about the smoothness of the surface, but
It was possible to solve the problem of bubble entrainment by adding an antifoaming agent and adjusting the viscosity of the coating liquid. Regarding the surface smoothness, a surface roughness RmaxO of 04 μm could be achieved by optimizing the coating conditions, and the film thickness at this time was 18 to 20 μm.

In this way, even with coating by screen printing method, it is possible to obtain sufficient surface properties and film thickness as a protective film for the recording medium layer, and the film thickness is 15 μm or more.
It suffices if it is formed in a range of 30 μm.

By the way, in the first embodiment, the disk substrate 13
The upper recording medium layer 14 has an inner diameter larger than the inner diameter of the center hole 12 of the disk substrate 13 and an outer diameter smaller than the outer diameter of the disk substrate 13. However, as shown in FIG. The protective coating 18 can be similarly formed on the disk 11 having the recording medium layer 14 formed so as to be aligned with the disk substrate 13. Further, in the above embodiments, a disk having a single-plate structure has been described, but a protective film can be similarly formed on a disk in which a disk substrate and a protective substrate are bonded together. Further, the present invention can also be applied to a double-sided disk made by bonding two disk substrates together. Furthermore, even for recordable/erasable disks in which a first dielectric layer, a recording medium layer, a second dielectric layer, and a reflective layer are sequentially formed on a disk substrate, a protective film is similarly formed on the surface of the reflective layer. It is possible.

Effects of the Invention As described above, according to the present invention, the protective coating resin is coated on the recording medium layer of the disk substrate using a screen printing method, dried and cured, so that the film thickness is uniform.
Moreover, it is possible to form a protective coating without any bulges on the outer peripheral edge. Furthermore, since the materials used can be kept to the minimum necessary limit, the materials can be significantly reduced compared to the spin coating method, and costs can be reduced.

[Brief explanation of drawings]

1 to 3 show a first embodiment of the present invention, FIG. 1 is a perspective view showing a coating state, FIG. 2 is a sectional view of FIG. 1,
FIG. 3 is a sectional view of an information carrier, FIG. 4 is a sectional view of an information carrier in another embodiment of the present invention, FIGS. 5 to 7 show a conventional example, and FIG. 5 shows a state of film formation. FIG. 6 is a sectional view, FIG. 6 is a perspective view, and FIG. 7 is a plan view of the information carrier. 11... Disk, 13... Disk board, 14...
...Recording medium layer, 15...Screen, 15a...
Mesh portion, 16... Shaving board, 17... Coating liquid, 18... Protective coating.

Claims (1)

[Claims] 1. A method for forming a film on an information carrier, which comprises coating a disk substrate having a recording medium layer on one surface with a protective coating resin by screen printing on an area covering at least the entire surface of the recording medium layer, and then curing the protective coating resin. .