JPH06180863A - Production of optical disk - Google Patents

Abstract

PURPOSE:To prevent warpage of laminated protective layers of an optical disk substrate and to make uniform thickness of an adhesive by vertically disposing two substrates each having an org. protective layer in a manner that these protective layers face to each other with the adhesive and pressing the center area of the substrates during the adhesive is thermally hardened. CONSTITUTION:Two substrates 1, each having a recording layer 2 and an org. protective layer 3 are vertically disposed in a manner that the layers 3 face to each other with an adhesive 4. During the adhesive 4 is thermally hardened, the center area of the vertically disposed members is pressed on both sides to adhere the substrates 1. Thereby, warpage of the protective layers 3 is prevented and production of a defective disk which badly influences tracking is prevented. Moreover, thickness of the adhesive is made uniform on the whole surface so that balance of the disk during rotation is improved, and intrusion of moisture is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc manufacturing method. More specifically, the present invention relates to a method for manufacturing a highly reliable bonded double-sided optical disc that does not warp.

[0002]

2. Description of the Related Art In general, an optical disc, which has been attracting attention as a high-density and high-capacity information recording medium, has a recording layer provided on a thermoplastic resin such as polycarbonate having a guide groove or a glass substrate. Then, after arranging an inorganic protective layer if necessary, an organic protective layer is formed, and two of the obtained disk substrates are horizontally opposed to each other, and a hot-melt adhesive, epoxy-based or acrylic-based adhesive is bonded. It is manufactured by laminating with a chemical.

As the organic protective layer in this conventional optical disk, an ultraviolet curable acrylic liquid resin is generally used because it is easy to process, but the ultraviolet curable resin is generally harder than a thermosetting resin or the like. In this case, the shrinkage rate is large, and in particular, the ultraviolet-curable acrylic resin has a drawback that the shrinkage rate is large in comparison with other ultraviolet-curable resins such as epoxy resins. Therefore, in the conventional optical disk, there is a problem that after the formation of the organic protective layer, the contraction of the protective layer causes a warp on the surface on which the organic protective layer is formed. Such warpage that occurs during bonding brings about a variation in the height of the recording film of the optical disc, which adversely affects the tracking performance during recording and reproduction. In addition, the thickness of the adhesive layer sandwiched between the substrates becomes non-uniform over the entire surface of the disk due to the occurrence of the warp, so the balance during disk rotation tends to be lost, and the thin adhesive layer may cause Corrosion deterioration of the recording film is apt to occur due to infiltration of water from the inside. As a result, there is a problem that the reliability of the disk is lowered.

Therefore, the present invention solves the above-mentioned drawbacks of the prior art and suppresses the conventional warpage of a double-sided optical disk manufactured by laminating, tracking performance, balance during rotation, and water content. It is an object of the present invention to provide an improved method capable of manufacturing a highly reliable optical disk that does not cause any inconvenience in terms of penetration.

[0005]

In order to solve the above-mentioned problems, the present invention has two substrates, a recording layer and a substrate on which an organic protective layer is formed, opposed to each other in the organic protective layer to form an adhesive. In the method of manufacturing a double-sided optical disc by stacking the substrates via the adhesive and curing the adhesive, the substrates are stacked upright when the adhesive is cured, and the vicinity of the center of the substrate is externally pressed. A manufacturing method is provided.

[0006]

According to the present invention, the substrate is erected vertically when the adhesive is cured in the laminating step in the double-sided optical disc manufacturing,
In order to correct the warpage that occurs when the organic protective layer is formed, the adhesive is cured while externally applying pressure to the vicinity of the center of the substrate. As a result, it is possible to suppress the occurrence of warpage during the bonding of the optical disk substrates and prevent the generation of a defective disk that adversely affects the tracking. In addition, since the thickness of the adhesive layer can be made uniform over the entire surface of the substrate, the balance during rotation of the disk becomes good, moisture intrusion from the outside can be suppressed, and a highly reliable disk can be obtained.

The method of the present invention will be described in more detail with reference to the drawings. FIG. 1 is a side sectional view illustrating the state of the optical disk substrate at the time of laminating and curing for explaining the method of the present invention. A recording layer portion (2) consisting of 2p groove / recording layer / inorganic protective layer is provided on the substrate (1), and an organic protective layer (3) is formed on the recording layer portion (2). Two substrates (1) having 3) are made to face each other in the organic protective layer (3) and are bonded to each other via an adhesive (4).

In this case, the substrate (1) having the organic protective layer (3) formed thereon has a concave warp due to the contraction of the organic protective layer (3) as shown in FIG. Therefore, when the adhesive (4) is applied and then overlapped and heated or left to cure the adhesive, the substrate (1) is erected vertically as shown in the drawing, and the vicinity of the center of the substrate is externally pressed in the direction of the arrow in the drawing. The reason why the substrate is laid vertically is to reduce the bending due to its own weight. However, if the bending due to its own weight can be reduced, the substrate does not necessarily need to be erected vertically in a strict sense.

The substrate (1) accompanying the contraction of the organic protective layer (3) due to the pressure as described above when the adhesive (4) is cured.
The occurrence of the warp of is effectively suppressed. Less than,
The method of the present invention will be further described by way of Examples.

[0010]

EXAMPLES Examples 1 to 3 A groove (2P) for a tracking group is formed (thickness 50 μm) on each of two glass substrates (inner diameter 60 mm, outer diameter 150 mm, thickness 1.2 mm). SiN film is 700 Å as an inorganic protective layer and TbFeC as a recording layer.
o film is 500Å, and SiN film is 7 as an inorganic protective layer.
A film was formed by the 00Å sputtering method. Next, an ultraviolet-curable acrylic resin as an organic protective layer was applied onto each of the inorganic protective layers by spin coating and irradiated with ultraviolet rays to form an organic protective layer having a thickness of 5 μm. The obtained substrate had a warp in the concave portion on the side of the organic protective layer.

Next, an ultraviolet / heat combined curable adhesive is applied to the entire surface of the thus obtained substrate on which the organic protective layer is formed by a screen printing method, and the other substrate is placed on the surface of the organic protective layer. The layers were overlapped and irradiated with ultraviolet rays to cure the adhesives on the outermost peripheral portion and the innermost peripheral portion for temporary fixing. After this, the temporarily bonded bonded substrates are erected vertically on a stand as shown in FIG.
A pressure sensitive adhesive was cured by heating at a temperature of 100 ° C. for 10 hours while applying pressure from the outside to the inside by springs at each point to manufacture a double-sided optical disk.

Three disks thus obtained were prepared, and the difference in height between the surfaces of the substrates at a radius of 90 mm and a radius of 150 mm on both surfaces of the disks was evaluated over the entire circumference. Table 1 shows the maximum value of each disk surface. As is clear from Table 1 which shows the difference in the height of the substrate surface together with the result of the comparative example to be described later, in this example, the disk was erected vertically at the time of heating and the adhesive was cured while pressing the vicinity of the center of the substrate. Then, as compared with the comparative example in which the disk is leveled at the time of heat curing and the adhesive is hardened, the occurrence of warpage of the disk surface can be effectively suppressed.

Comparative Examples 1 to 3 In Examples 1 to 3, the disk substrate was placed vertically on a Teflon plate without standing vertically, and was heated at 100 ° C. for 10 hours without applying pressure. The adhesive was cured. Thus, a double-sided optical disc was manufactured. Then, as in Examples 1 to 3, the warp of the disk surface was evaluated. The results are also shown in Table 1.

It was confirmed that the warpage was large as compared with Examples 1 to 3.

[0015]

[Table 1]

[0016]

As described above, according to the present invention, when the adhesive is cured, the substrate is erected vertically and the central portion of the substrate is pressed from the outside, so that a disk having a warp much smaller than the conventional one can be manufactured. Therefore, it is possible to prevent the generation of a defective disk that adversely affects the tracking. Further, since the thickness of the adhesive layer can be made uniform over the entire surface, a good balance can be obtained when the disc is rotated, and a highly reliable optical disc can be obtained in which there is no portion where moisture easily enters from the outside. Furthermore, the allowable range of the initial warp caused by the glass substrate itself is widened, and inexpensive glass can be used.

[Brief description of drawings]

FIG. 1 is a side sectional view exemplifying a state in which a disk substrate is erected vertically and pressure is applied to cure an adhesive.

[Explanation of symbols]

 1 substrate 2 recording layer section 3 organic protective layer 4 adhesive

Claims (1)

[Claims] 1. A double-sided optical disk is manufactured by making two recording layers and a substrate having an organic protective layer formed thereon face each other in an organic protective layer, superposing them with an adhesive, and curing the adhesive. The method of manufacturing an optical disc according to the above method, characterized in that when the adhesive is cured, the stacked substrates are erected vertically and the central region of the substrates is externally pressed.