JPS63206926A - Optical disk - Google Patents

Abstract

PURPOSE:To obtain an optical disk which obviates transfer of air bubbles and has low moisture permeability and high reliability by using an adhesive agent having D70-D78 Shore hardness as an adhesive agent for sticking substrates. CONSTITUTION:The optical disk substrates 11, 11' which consist of an epoxy resin, acrylic resin or ester base resin, etc., and have guide grooves are stuck to each other by the adhesive agent 13 consisting of an epoxy resin or the like which is slightly softer than the hardness of the guide grooves and has D70-D78 Shore hardness. The transfer of air bubbles is thereby prevented and since the molecules have fairly high rigidity, the moisture permeability is low and the reliability to the extent that said moisture permeability is of no problem in practicable use is assured.

Description

[Detailed description of the invention] Industrial applications The present invention records information using light such as laser light.

This relates to optical disks (including magneto-optical disks) used in data file devices that perform playback, etc.

BACKGROUND OF THE INVENTION In recent years, optical disks have been developed as high-density, large-capacity memories. The structure of optical discs can be roughly divided into two types. One is a transparent disc with a guide groove on which a thin film layer such as a protective film and a magnetic film is formed, and the other is simply coated with resin etc. The substrates or a substrate with a thin film layer formed thereon and a transparent disk are bonded together using resin.
Or, it is a type in which the periphery is bonded with an air gap (for example, JP-A-55-48837, JP-A-57-66539, JP-A-58-155545).
Publication No.).

The former structure is seen in compact discs and the like.

The present invention relates to the latter.

Conventionally, epoxy resin or silicone resin is applied as a bonding adhesive onto a substrate on which thin film layers such as protective films and magnetic films have been formed, and another substrate is bonded on top of that, and the resin is cured by raising the temperature. Alternatively, in the case where one side is a transparent disk, a method has often been used in which a photocurable resin is applied and bonded, and then ultraviolet rays are irradiated from the transparent disk side to harden the resin. In the case of the air gap type, a metal ring is fitted around the periphery and this is fixed with adhesive.

Problems to be Solved by the Invention However, when a hard resin such as an epoxy resin or a photocurable resin is used as a bonding adhesive, air bubbles mixed in the resin may cause damage to the transparent disk during long-term use. was transferred to the guide groove, causing an error (decrease in C/N ratio). By improving the bonding method, the inclusion of air bubbles can be largely prevented, but if both sides have magnetic films (reflective films), it is impossible to check whether bubbles are present at all. Further, when a soft resin such as silicone resin is used, there is a problem in that the magnetic film etc. are deteriorated in terms of reliability (particularly moisture resistance) due to its high moisture permeability.

In addition, the air gap type required a lot of man-hours and was inferior in reliability.

The transfer of air bubbles in a hard adhesive such as an epoxy resin is thought to be caused by the difference in hardness between the resin forming the guide groove and the adhesive. It is also affected by the size and position of the bubbles.

If the hardness of the adhesive is softer than the hardness of the resin forming the guide groove, no bubble transfer will occur.

However, on the other hand, soft resins have the disadvantage that their molecular chains are less mobile and have greater moisture permeability.

In view of the above-mentioned problems, the present invention provides an optical disc that is free from bubble transfer, has low moisture permeability, and is highly reliable.

Means for Solving the Problems The present invention provides an optical disc having a guide groove made of epoxy resin, acrylic resin, etc., characterized in that an adhesive having a Shore hardness of D70 to D78 is used as a bonding adhesive. It is.

Function As a bonding adhesive, the hardness must be softer than the resin forming the guide groove, in order to avoid transfer of air bubbles. On the other hand, a certain degree of hardness is required for low moisture transferability. The guide groove is formed of an epoxy resin, an acrylic resin, or an ester resin such as epoxy resin or epoxy acrylate, and its hardness is Ds.

The hardness of epoxy resin used as a conventional bonding adhesive is about Dss, and the hardness of silicone resin is about A80. Most commercially available adhesives have a Shore hardness of Dso or higher or Deo or lower. For this reason, when laminated with epoxy resin or photocurable resin, bubbles are transferred, and when silicone resin is used, there is a problem with moisture resistance, but guide grooves made of epoxy resin, acrylic resin, ester resin, etc. When bonding optical disk substrates with an adhesive such as epoxy resin with a shore hardness of D70 to D78, which is slightly softer than the hardness of the guide groove, it is possible to prevent the transfer of air bubbles, and at the same time, the rigidity of the molecules is maintained. Therefore, it was found that the moisture permeability was small and reliability could be ensured to the extent that it would not cause any problems in practical use.

EXAMPLE An example of the present invention will be described below with reference to the drawings. No. 11 is a sectional view of a completed disk substrate according to an embodiment of the present invention. 11.1 in Figure 1
1' is a transparent disk having a guide groove, 12 and 12' are thin film layers such as a protective film and a magnetic film, and 13 is a material with a Shore hardness of D70.
This is a laminating adhesive from D78. Transparent disk 11.1
Glass was used as 1', and guide grooves were transferred and formed thereon from a stamper using a photocurable resin made of epoxy acrylate.

Next, in a sputtering device, Si02 was used as the first protective film, TbFeCo was used as the magnetic film, and S102 was used as the second protective film.
The thin film layers 12 and 12' were formed. A low-viscosity epoxy resin (DB6561 manufactured by Diabond Industries) was applied as a bonding adhesive 13 to the center of the substrate thus prepared.
) Go weight part mixed with 20 weight parts of flexible epoxy resin (MG150 manufactured by Japan Bellnox) was applied in a ring shape, and another board was laminated on top of that and fixed to prevent the resin from shifting. was thermally cured at 80''C to produce an optical disc.The shore hardness of the photocurable resin for forming guide grooves and the bonding adhesive in this example were Dao and D74, respectively.
Met.

The optical disc produced in this way has 80'C8o%R.
As a result of conducting a moisture resistance test with H, no abnormality was observed even after 1000 hours. Table 1 shows the results of the moisture resistance test for the samples laminated using a conventional adhesive and the samples of this example.

Table 1: With conventional silicone adhesives, the magnetic film deteriorated, and with epoxy adhesives, bubbles were transferred to the guide grooves within several hundred hours. Transfer of air bubbles to the guide groove causes an error and C7N
This resulted in a decrease in the ratio.

Figure 2 shows the Shore hardness of the bonding adhesive and 80'C80%.
The relationship between the deterioration time of the optical disc at RH and the second
The table shows the Shore hardness and bubble transferability of the laminating adhesive. As the proportion of flexible epoxy resin increases, the Shore hardness decreases and the deterioration time becomes shorter.

Table 2 As a guideline for a 10-year guarantee at room temperature, 10 at 80°C and 8°
Based on 00 hours, the Shore hardness is D70.
More than that was necessary. On the other hand, for no bubble transfer, D
I also found out that I have to get up to 78.

In particular, as a bonding adhesive, a mixture of a bisphenol A type or novolac type epoxy resin and a flexible resin such as an aliphatic type epoxy resin is excellent in terms of adhesion to the underlying second protective layer and moisture resistance.

Effects of the Invention As described above, according to the present invention, when bonding optical disk substrates having guide grooves made of epoxy resin, acrylic resin, ester resin, etc., the Shore hardness, which is slightly softer than the guide grooves, is from D70 to D78. glue(
In particular, by laminating with an epoxy resin, it is possible to obtain an optical disk with low transparency and high reliability such as moisture resistance, and without deterioration of C7N ratio due to bubble transfer.

Furthermore, in the conventional bonding method, precise control was required to avoid the inclusion of bubbles during bonding, and it was also necessary to inspect for the presence or absence of bubbles. However, with optical discs that have magnetic films (reflective films) formed on both sides, it is almost impossible to check for the presence of air bubbles inside, and even if inspection was possible, those with air bubbles would become defective, leading to a decrease in yield. However, the structure of the present invention has the advantage that the inclusion of air bubbles during lamination can be ignored, there is no decrease in yield, and the work is simple.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an optical disc in an embodiment of the present invention, and Fig. 2 shows the Shore hardness of the bonding adhesive and the 80°C80
FIG. 2 is a characteristic diagram showing the deterioration time of an optical disc at 1RH. 11.11'...--Transparent disk having guide groove, 1
2゜12'...Thin film layer such as a protective film and magnetic film, 13...Adhesive for bonding.

Claims (1)

[Claims] An adhesive for bonding a substrate on which a thin film layer such as a protective film and a magnetic film is formed on a transparent disk having a guide groove made of epoxy resin, acrylic resin, or ester resin has a Shore hardness of D70 to D78. An optical disc characterized by certain things.