JPH06162578A - Forming method of protective film for optical disk - Google Patents

Abstract

PURPOSE:To provide a forming method of a protective film for an optical disk such as digital audiodisk and videodisk to obtain an optical disk having improved physical accuracy such as warpage of the disk, reduced inner stress of the substrate and small double refraction. CONSTITUTION:A UV-curing resin 3 to form a protective film is dropped annularly on a disk substrate 1 having a center hole 4 and an annular recessed part 5. A printing press pad which transmits UV rays is pressed to the upper side of the UV curing resin 3, while the substrate is irradiated with UV rays to cure the UV-curing resin 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a protective film on an optical disc such as a digital audio disc and a video disc.

[0002]

2. Description of the Related Art At present, an optical disc such as a CD (compact disc) has information pits. For example, a transparent substrate such as PMMA (polymethylmethacrylate) or PC (polycarbonate) has a metal such as aluminum on the side where the information pits are engraved. A reflective film or a recording layer is formed by a vacuum film forming method, and an ultraviolet curable resin or the like is used in an amount of 5 to 10 μm in order to prevent oxidation of the reflective film or the recording layer or prevent scratches from the outside. A protective film having a certain thickness is formed.

A substrate having information pits is formed by compression molding using a stamper having irregularities in which the information pits are reversed, or injection molding, or by using an ultraviolet curing resin on a transparent flat plate such as plastic or glass. By the so-called 2P method or the like for transferring the unevenness of the stamper.

On the other hand, the protective film is generally formed by a spin coating method in which an ultraviolet curable resin dropped on a substrate is applied by a centrifugal type spin coater. In addition, as a method for forming this protective film, a purple film that is generally used as a protective film material is used.

Since the external-curing resin is shrunk when it is cured, the substrate is bent in the opposite direction in advance when it is formed, a protective film is applied, and when the resin is cured, the resin shrinks, resulting in a flat disk. There is also a way to get it.

Further, as a method of forming a protective film which does not use the spin coating, there is also a method of applying an ultraviolet curable resin by pad printing (see JP-A-64-64147).

[0007]

However, in the method of forming the protective film by the above-mentioned spin coating method, after the resin is dropped, the substrate is rotated for several seconds and uniformly coated, and then the coating is continued for several to several tens of seconds. Since the protective film is formed by irradiating with ultraviolet rays, it cannot be said that the method is suitable for mass production when considering the production cycle.

Further, in the method in which the substrate is preliminarily warped in the opposite direction, the degree of warpage of the substrate must be adjusted according to the degree of shrinkage of the resin, so that the physical properties of the protective film material should be adjusted. Since the molding conditions must be changed, it becomes difficult to control the molding conditions. Further, by making the substrate flat by the force of contraction of the resin, the internal stress of the substrate increases and the birefringence which is one of the important optical characteristics of the optical disc substrate becomes large. is there.

Furthermore, in the method of applying the UV-curable resin by pad printing, although the problem of production efficiency is improved, the problem associated with resin shrinkage has not been solved.

The present invention solves the above-mentioned problems associated with resin shrinkage, improves the physical accuracy of the warp of the disc, reduces the internal stress of the substrate, and reduces the birefringence of the optical disc. An object of the present invention is to provide a method for forming a protective film for an optical disc, which is suitable for high density.

[0011]

The present invention has been made in view of the above problems and has the following configuration. That is, 1) dropping a UV curable resin for forming a protective film on a substrate,
A method for forming a protective film for an optical disk, characterized in that the ultraviolet-curable resin is pressure-bonded from above by a pressure-bonding means, and the ultraviolet-curable resin is cured by irradiation of ultraviolet rays to form a protective film.

2) In the method of forming a protective film for an optical disc according to claim 1, the pressure-bonding means is a flat plate that transmits ultraviolet rays, and the side of the flat plate that is pressure-bonded to the ultraviolet-curing resin is transparent to the ultraviolet rays and the ultraviolet-curing resin is used. A method for forming a protective film for an optical disk, which is characterized in that a film having a good detachability with respect to is laminated.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a view of the substrate viewed from above, and FIG. 1B is a side view thereof. A PC (polycarbonate) substrate 1 has a central hole 4 in its central portion and an annular recess 5 in its outer peripheral portion. Information pits are transferred to the upper surface side of this PC substrate 1 and aluminum is formed by a vacuum film forming method. The reflection film 2 is formed to a thickness of about 1000 angstroms.

Then, the ultraviolet curable resin 3 is dropped concentrically on the reflective film 2 and is pressure-bonded thereto from above by a printing pressure-bonding pad 6 having the structure shown in FIG. The UV-curable resin 3 is a series of acrylic or methacrylic compounds, for example, a photo-curable oligomer such as epoxy acrylate, urethane acrylate, polyester acrylate, etc., and merimetylol propane as a reactive diluent if necessary. Add photo-curable monomers such as tri (meth) acrylate, neopentyl glycol di (meth) acrylate, ethylene glycol di (meth) acrylate, and generate radicals such as benzoin ethyl ether and diacetylbenzoin as photopolymerization initiators. The agent is added.

The press-bonding pad 6 is made of, for example, quartz glass, soda lime glass, or silicon rubber, and is attached to the surface of a flat plate 6a formed of a material that transmits ultraviolet rays.
It has a structure in which a film 6c made of polyethylene terephthalate, polypropylene, PMMA, or the like, which transmits ultraviolet rays through b and has a good adhesive property with respect to the ultraviolet curable resin 3 is laminated.

FIG. 3 is a view showing a state in which the printing pressure bonding pad 6 presses the ultraviolet curable resin 3 from above, whereby the ultraviolet curable resin 3 is extended in a circle on the substrate 1. In this state, ultraviolet rays are irradiated from the direction of the arrow, whereby the ultraviolet curable resin 3 is cured to form a protective film of about 6 μm,
For example, an optical disc for a digital audio disc is formed. Then, the pressing force at this time is suitably 0.8 to 1.7 kg / cm ² according to the experimental results of the present inventor.

When the warp angle of the optical disk thus formed was measured, the change in the warp angle after formation of the protective film was an average of +0.01 deg. (The number of samples = 10) and the average when formed by the spin coating method + 0.17d
eg. The change in the warp angle was significantly smaller than that of (the number of samples = 10).

On the other hand, when a protective film was formed with a pressing force of 0.1 kg / cm, the change in the warp angle at this time was not significantly different from that by the spin coating method. Moreover, when a protective film was formed at a pressure of 3.0 kg / cm,
The substrate is deformed.

Further, when the change of the birefringence of the substrate 1 before and after the formation of the protective film of the optical disk according to the present embodiment was measured, the average value of the birefringence at the radius of 55 nm (double pass) was 38 nm before the protective film was formed, After forming the film, there was almost no difference from 39 nm. On the other hand, when a protective film was formed with the same film thickness by the spin coat method and the birefringence was measured in the same manner, it was 38 nm before the formation (average value in double pass at radius 55 nm), but after formation, It increased to 48 nm.

Further, when the protective film was formed by using a polycarbonate flat plate 6a which does not transmit ultraviolet rays as the material of the printing press-bonding pad 6, the ultraviolet curing resin 3 was not cured.

The protective film forming method of this embodiment can be applied not only to forming a protective film on an optical disk but also to printing on a label or the like.

[0022]

According to the method of the present invention, since the change in the warp angle of the substrate before and after the formation of the protective film can be almost ignored, the process of warping the substrate in the opposite direction is unnecessary in the molding process, and the control of the forming conditions is eliminated. Becomes significantly easier. Further, since an increase in internal stress of the substrate after forming the protective film can be prevented, an increase in birefringence can be prevented, and a protective film forming method suitable for increasing the density of the optical disc can be provided.

[Brief description of drawings]

FIG. 1A is a diagram showing a forming process according to the present invention and is a schematic top view of a substrate 1 seen from above. (B) is a side view thereof.

FIG. 2 is a schematic side view of the printing press pad 6.

FIG. 3 is a diagram showing a state in which the printing pressure bonding pad 6 presses the ultraviolet curable resin 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 PC (polycarbonate) substrate 2 Reflective film 3 UV curable resin 4 Central hole 5 Annular recess 6 Printing pressure bonding pad 6a Flat plate 6b Adhesive 6c Film

Claims (2)

[Claims] 1. An ultraviolet curable resin for forming a protective film is dropped on a substrate, and the ultraviolet curable resin is pressure-bonded from above by a pressure bonding means, and the ultraviolet curable resin is cured by irradiation of ultraviolet rays to form a protective film. A method for forming a protective film for an optical disc, comprising: 2. The method for forming a protective film for an optical disc according to claim 1, wherein the pressure bonding means is a flat plate that transmits ultraviolet rays.
A method for forming a protective film for an optical disk, characterized in that the flat plate is laminated with a film which transmits ultraviolet rays and has good adhesiveness to the ultraviolet curable resin, on the side which is pressed against the ultraviolet curable resin.