JPH0715765B2 - Method for manufacturing information recording medium - Google Patents

Description

The present invention relates to a method for manufacturing a disc-shaped information recording medium, and more particularly to a method for manufacturing an optical disc having a protective coating on its surface.

[Prior Art] In manufacturing an information recording medium of a system for writing or reading information by using light rays, such as an optical disc, for example, a video disc or a compact disc,
A method of forming a flat disk-shaped substrate with a hard transparent material, forming a thin film such as a recording material or a light-reflecting material on the information recording surface, and further forming a protective film on it is used, Various kinds of printing are further applied on the protective film as required to complete the product.

The protective coating provided on the information recording surface is required to prevent deterioration of the information recording surface due to moisture or oxygen in the air and to withstand external force such as friction and impact.
It is required that there be no pinholes and the film strength be high.
However, when such a protective coating is thick, there is a problem that the disc may be distorted due to a difference in expansion coefficient between the protective coating and the substrate. Therefore, the protective coating must be thin and uniform. As such a protective film, an ultraviolet curable paint is selected because it can be rapidly cured at room temperature, and in order to apply it uniformly and thinly, the flat disk substrate is rotated at high speed and the paint is applied to the surface of the disc. A so-called spin coating method was used.

Problems to be Solved In the conventional method of forming a protective film as described above, the disk substrate is transferred to a spin coater after being coated with, for example, a vapor deposition film of aluminum on the information recording surface, and shielded from the outside. Thickness 6 after being mounted on the rotating disk in a dust-free environment
A procedure has been adopted in which an ultraviolet curable coating film having a thickness of ˜8 μm is formed, followed by irradiation with ultraviolet rays to cure the protective film, and then taking out from the spin coater. However, this method has a problem that although a protective film having a property to be leaked can be obtained, the operating efficiency of the spin coater is low and the productivity cannot be improved.

Therefore, an object of the present invention is to provide a method for providing a protective film having excellent properties on an information recording medium with high accuracy and high efficiency.

[Structure of Invention]

Means for Solving the Problems The present inventor has investigated various improving means in place of forming a protective film by a conventional spin coating method in order to enhance the manufacturing efficiency of an information recording medium, and surprisingly, the conventional uniform It has been found that the object of the present invention can be achieved by improving the screen printing method, which was considered to be unable to form a uniform film.

That is, in the method for producing an information recording medium of the present invention, in forming a protective coating on the information recording surface of a flat disk-shaped substrate, a mesh screen of 350 to 500 mesh is passed through the information recording surface held horizontally. It is characterized in that an ultraviolet curable coating material having a viscosity of 220 to 250 centipoise is applied so as to have an average thickness of 10 ± 3 μm, and an ultraviolet irradiation treatment is carried out after a holding time of at least 2 seconds has elapsed.

The mesh screen used in the method of the present invention is, for example, a mesh formed by weaving polyester filaments as warp and weft, and has a mesh number of 350 to 500 per inch. If the number of meshes is small, the coating film becomes thick and the smoothness becomes insufficient, and if the number of meshes is too large, the coating film becomes thin and pinholes are likely to occur.

The UV-curable coating used as a coating is, for example, 30 to 50 parts by weight of an oligomer, 20 to 70 parts by weight of a mixture of polyfunctional or monofunctional monomers, and 0.5 to 10 parts by weight of a photopolymerization initiator. It may be appropriately colored with a dye or a pigment. In some cases, a solvent and the like may be contained, but the viscosity needs to be in the range of 220 to 250 centipoise at the use temperature, and more preferably 230 to 240 centipoise.

The coating thickness of such a pigment needs to be 10 ± 3 μm, and when it is too thick, the curing speed due to UV irradiation decreases, unevenness in the dryness is likely to occur, and the disc warps. Lead to an outbreak. If the coating thickness is too thin, the number of pinholes will rapidly increase. Therefore, the coating thickness is 8
It is particularly desirable to be in the range of up to 10 μm. To control the coating thickness in this way, for example, set the screen tension to 8-10 kg / cm and make the screen surface about 5-8 mm from the coating surface.
Fix the screen frame away from each other, and apply a rubber squeegee with a Shore hardness of about 70 at an angle of 70 °,
For example, at a pressure of 2.5 to 3 kg / cm, a paint having a viscosity of 230 to 240 centipoise can be applied, for example, at a speed of 10 cm per second while squeezing from above the screen, which gives a coating film having an average thickness of about 9 μm.

The coating thus obtained is cured by exposure to UV radiation after at least 2 seconds. At this time, if the holding time is shorter than 2 seconds, the occurrence of pinholes increases, but if it is too long, the work efficiency decreases, so the holding time from application to ultraviolet irradiation is preferably 4 seconds or less.

Operation The protective coating formed on the information recording surface by the method of the present invention has a uniform and relatively smooth surface and has excellent properties without pinholes.

〔The invention's effect〕

The method for producing an information recording medium of the present invention, instead of applying a protective coating by the spin coating method in the conventional production method,
A protective film is applied by squeeze coating using a screen, and then the film is cured by irradiation with ultraviolet rays. Therefore, the coating and the curing of the coating can be performed by different apparatuses, and the holding time necessary for smoothing the coating can be passed while moving the coating substrate from the coating apparatus to the curing apparatus. It was possible to change the work into a flow work, eliminate the idle time between processes, and significantly improve the operation rate of the device.

By such an improved method, an information recording medium having a protective film having properties which are not inferior to the products of the conventional methods can be produced with high efficiency and economically.

Claims (1)

[Claims] 1. When forming a protective coating on the information recording surface of a flat disc-shaped substrate, the surface of the information recording surface is held horizontally.
Viscosity 220-250 through mesh screen of 0-500 mesh
Centipoise UV curable paint with an average thickness of 10 ± 3 μm
And a UV irradiation treatment after a holding time of at least 2 seconds has elapsed.