JPH07110965A - Manufacture of optical disk - Google Patents

Abstract

PURPOSE:To form an optical disk whose flatness has been increased by a method wherein a disk substrate is supported by an elastic body and an adhesive is hardened. CONSTITUTION:Tracking grooves, protective layers, recording layers and the like are formed respectively on two glass substrates 1 whose inside diameter, outside diameter and thickness are set respectively at prescribed values, the substrates are coated with a UV-curing acrylic resin, ultraviolet rays are irradiated, the resin is hardened, and organic protective layers are formed. Then, the whole formation face of the organic protective layer on one side is coated with a UV-curing and thermosetting adhesive, the substrate on the other side is overlapped, the substrate is irradiated with ultraviolet rays, the adhesive at the outermost circumferential part and the innermost circumferential part other than a region for the recording layer is hardened, and the substrates are fixed temporarily. Then, the inner circumferential part is supported by a rigid body 2, four parts at the outer circumferential part are supported elastically by springs 3, the substrates are heated for a required time and at a prescribed temperature, and the adhesive is hardened. Thereby, an optical disk in which the bend of the substrates 1 is prevented in their heating operation and whose flatness has been increased can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical disk, and more particularly to a method for laminating double-sided disks.

[0002]

2. Description of the Related Art Generally, an optical disk has a recording layer, an inorganic protective layer, an organic protective layer, etc. formed on a substrate made of glass or a thermoplastic resin such as polycarbonate in which guide grooves are formed. After that, the two sheets are bonded to each other with the recording layer facing inward. As the adhesive for bonding, polyolefin-based, epoxy-based, acrylic-based, etc. typified by hot melt adhesives are used.

[0003]

By the way, in the case of using an adhesive which is cured by heating or leaving it in the step of adhering an optical disk, the curing state is uniform in order to prevent the adhesive from becoming thicker downward due to gravity. Therefore, it is desirable to keep it horizontal without the influence of gravity. However, in such a horizontal state, bending occurs due to the weight (self-weight) of the substrate itself, and when the adhesive is cured in this state, the bending is fixed as it is, and the disk has poor flatness. There was a problem. A disc with poor flatness adversely affects the tracking performance during recording and reproduction. Further, there is a problem that the thickness of the adhesive layer tends to be non-uniform, and the thin film portion tends to cause corrosion deterioration of the recording film due to infiltration of moisture from the outside, thereby lowering the reliability of the disk.

[0004]

In order to solve the above problems, the inventors of the present invention have conducted intensive studies and found that when the adhesive between two substrates is cured by heating or leaving the substrate horizontal, In this state, by supporting the substrate from below with an elastic body, the deflection due to the weight of the substrate is canceled and the adhesive is cured while maintaining the planarity of the substrate, so an optical disc with excellent planarity is manufactured. The inventors have discovered what is possible and have completed the present invention.

Therefore, in the first aspect of the present invention, "two substrates having at least one recording layer formed thereon are bonded together by using a curable adhesive which is cured by heating or standing. In the method of manufacturing an optical disk capable of recording or reproducing from the above, when the substrate is heated or left in a horizontal state, by supporting the substrate from below by an elastic body, the deflection due to the own weight of the substrate can be canceled. 2. A method for manufacturing an optical disk, characterized in that the adhesive is cured while maintaining the flatness of the substrate. Secondly, "the elastic body is a resin." The method for manufacturing an optical disk according to claim 1, and thirdly, the method for manufacturing an optical disk according to claim 1, characterized in that the support is a liquid. , Wherein the elastic member is a gas, there is provided a manufacturing method "of the optical disk according to claim 1.

[0006]

When the substrate is supported by the elastic body, when the inner peripheral portion is supported by the rigid body, the outer peripheral portion is supported by the elastic body (see FIG. 1), and when the outer peripheral portion is supported by the rigid body. It is convenient and desirable to support the inner peripheral portion with an elastic body (see FIG. 2).
Here, the principle of canceling the bending due to its own weight when the outer peripheral portion of the substrate is supported by a rigid body and the inner peripheral portion is supported by a metal spring that is an elastic body will be described.

The deflection w ₁ (the amount by which the inner peripheral portion lowers with respect to the outer peripheral portion) when an annular plate (doughnut shape) having an inner diameter a, outer diameter b, thickness h, and specific gravity p ₀ is supported by the outer peripheral portion is It is represented by a formula.

[0008]

[Equation 1]

Here, E is an elastic coefficient, and λ is a coefficient determined by the inner / outer peripheral ratio of the circular plate and the support type. The deflection w ₂ that occurs when a concentrated load P is applied to the inner peripheral portion of this circular plate is expressed by the following equation.

[0010]

[Equation 2]

Therefore, the condition for canceling the bending due to its own weight when it is supported by the outer peripheral portion by exerting a force to push it up to the inner peripheral portion is that w ₁ = w ₂ is established, and therefore (1), (2 From the expression,

[0012]

[Equation 3]

Is required. That is, it is only necessary to design the spring so as to generate such a force and push up the inner peripheral portion using the spring. As the elastic body, one or several metal springs or rubbers are suitable, but plastics and elastomers such as urethane resin and silicon resin having high elasticity can also be used.

Further, it is also possible to support the entire surface with a material such as liquid or gas that can be supported by static pressure without supporting the inner circumference or the outer circumference. In the case of a fluid such as liquid or gas, it is preferable to use it by confining it in a thin rubber or the like. Furthermore, the present invention is effective in adhering the protective substrate not only to a disc that can be recorded or reproduced from both sides but also to a disc that can be recorded or reproduced from only one side.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0016]

[Example 1] First, inner diameter 60 mm, outer diameter 304.8 mm, thickness
A layer with tracking grooves formed on each of two 1.2 mm glass substrates with a photopolymer (2
P), and silicon nitride as a protective layer with a thickness of 700Å, TbFeCo as a recording layer with a thickness of 500Å, and silicon nitride as a protective layer with a thickness of 700Å. After forming a film and further applying an ultraviolet curable acrylic resin by a spin coat method,
An organic protective layer cured by irradiation with ultraviolet rays was formed to a thickness of 5 μm. Next, by coating the entire surface of one organic protective layer forming surface with an ultraviolet / heat combined curable adhesive by a spin coat method, superposing the other substrate and irradiating with ultraviolet rays,
TbFeCo, which does not transmit ultraviolet rays, was temporarily fixed by curing the adhesive on the outermost and innermost portions outside the recording layer formation region.

After that, as shown in FIG. 1, the inner peripheral portion is supported by a rigid body, and the outer peripheral portion is pushed up by 4 springs from below, and is heated at 100 ° C. for 12 hours while the deflection due to its own weight is cancelled. The agent was cured to prepare a disc that can be recorded or reproduced on both sides.

[0018]

[Embodiment 2] Still another embodiment of the present invention will be described. As shown in FIG. 2, the outer circumference of the disk temporarily fixed by ultraviolet irradiation in the same procedure as in Example 1 is supported by a rigid body, and the four inner circumferences are pushed up by springs from the bottom to cancel the bending due to its own weight. In this state, heating was performed at 100 ° C for 12 hours to cure the adhesive, and a disc capable of recording or reproducing from both sides was produced.

[0019]

Comparative Example 1 For comparison, a conventional bonding method as shown in FIG. 3, that is, a disk capable of recording or reproducing from both sides was prepared by curing the adhesive while only the inner peripheral portion was supported by a rigid body.

[0020]

COMPARATIVE EXAMPLE 2 For comparison, a conventional bonding method as shown in FIG. 4, that is, a disk capable of recording or reproducing from both sides was prepared by curing the adhesive with only the outer peripheral portion supported by a rigid body. [Measurement] Example 1, Example 2, Comparative Example 1, and Comparative Example 2
Prepare 5 discs each prepared by the method described above, and use a mechanical property tester (LM110 made by Ono Sokki Co., Ltd.) to measure the difference in the height of the substrate surface at a radius of 90 mm and a position of 150 mm over the entire circumference on both sides of these discs. The maximum value was investigated and shown in Table 1.

As is clear from Table 1, the warpage of the disk surface of Examples 1 and 2 is significantly smaller than that of Comparative Examples 1 and 2.

[0022]

[Table 1]

[0023]

As described above, according to the present invention,
Not only was it possible to easily manufacture a disc with excellent flatness, the manufacturing defect rate could be significantly reduced, but also the tracking characteristics were improved, so the recording and reproducing signal quality was improved. Further, the thickness of the adhesive layer can be made more uniform, and therefore, the corrosion deterioration of the recording layer caused by the easy penetration of moisture due to the thin adhesive layer in the peripheral portion is less likely to occur.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing another embodiment of the present invention.

FIG. 3 is a conceptual diagram showing an example of a conventional method.

FIG. 4 is a conceptual diagram showing another example of a conventional method.

[Explanation of symbols]

 1 ... Disk substrate 2 ... Rigid body 3 ... Spring

Claims (4)

[Claims] 1. An optical disc capable of recording or reproducing from both sides is produced by laminating two substrates, each having at least one recording layer formed thereon, with a curable adhesive that is cured by heating or leaving it alone. In the method described above, when the substrate is heated or left in a horizontal state, by supporting the substrate from below by an elastic body, the deflection due to the weight of the substrate is canceled and the planarity of the substrate is maintained. A method for manufacturing an optical disc, comprising curing the adhesive. 2. The method of manufacturing an optical disk according to claim 1, wherein the elastic body is a resin. 3. The method of manufacturing an optical disc according to claim 1, wherein the support is a liquid. 4. The method of manufacturing an optical disc according to claim 1, wherein the elastic body is gas.