JPH0785501A - Optical recording medium - Google Patents

Abstract

PURPOSE:To allow an org. protective layer to adhere to a synthetic resin substrate and to enhance the durability of a medium by disposing a magnetic film and the org. protective layer coating the magnetic film on the substrate and heating a part of the substrate near the edge with ultrasonic waves. CONSTITUTION:An org. protective layer coating a magnetic film disposed on a substrate is melt-stuck to the substrate by heating the entire circumferential edge of the substrate with ultrasonic waves to obtain the objective optical recording medium. The adhesion of the protective layer to the substrate can be considerably enhanced and the penetration of moisture and gas can be prevented. The melt sticking is carried out by allowing a horn having about 0.1-1mm width and a shape corresponding to the circumference of the substrate to adhere to the protective layer and applying ultrasonic waves.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of optical recording and reproduction.

[0002]

2. Description of the Related Art Optical recording media are widely used as external storage devices for computers as large-capacity portable recording media. Optical recording media can be broadly classified into three types: ROM type in which information is written as pits on the substrate, write-once type in which the user can write only once, and rewritable type in which the user can freely record and erase information. Be divided.

An injection molded polycarbonate resin is usually used for the substrate of the medium, and thin films such as a reflective layer and a recording layer are formed on the polycarbonate resin by sputtering or the like. In any of the types, it is important to ensure the reliability of the medium, and particularly in the writable type, preventing the corrosion of the recording film is a major issue. For this reason, except for the air sandwich type used for the perforation type write-once medium, the recording film is covered with an organic protective layer made of a curable resin that is cured by ultraviolet rays, heat, temperature, etc. Is normal.

Here, the recording film includes all recording layers, protective layers, reflective layers, and the like, which are inorganic thin films formed by sputtering or the like. Spin coating is often used for coating the organic protective layer. The thickness of the protective layer is several μm,
After coating, it is cured by UV curing, heat curing, humidity curing, or the like.

In order to sufficiently obtain the protective effect of the organic protective layer, it is important that the protective layer and the recording film (substrate) have a strong adhesive property and that moisture and gas do not enter.
Therefore, the inner peripheral edge portion and the outer peripheral edge portion of the substrate are defined as regions where the recording film is not provided, and the organic protective layer and the substrate are directly contacted with each other at this portion, and the substrate is slightly chemically changed by the components of the organic protective layer. The adhesion between the substrate and the organic protective layer was ensured by dissolution or the like.

[0006]

However, in such a chemical adhesion method, the adhesion is weak and the recording film is often corroded under high temperature and high humidity. In addition, since the adhesion between the substrate and the organic protective layer changes depending on the chemical activity of each, the adhesive force changes depending on the water absorption state of the substrate surface, the oxidation state, or the chemical state of the protective layer side. It was necessary to carry out very strict control in order to carry out stable production.

Further, in recent years, the influence of the birefringence of a polycarbonate substrate on a reproduced signal has become a problem, and in order to solve this problem, an amorphous polyolefin-based substrate has been studied. In this case, the innate nature of the amorphous polyolefin, which is inactive, makes the adhesion to the organic protective layer extremely weak, which makes it difficult to secure the reliability of the medium.

[0008]

The present invention improves the adhesion between a substrate and an organic protective layer by using ultrasonic heating,
High reliability of the medium is obtained. The gist of the present invention is
A recording film and an organic protective layer covering the recording film are provided on a synthetic resin substrate, and the substrate and the organic protective layer are brought into close contact with each other by subjecting the vicinity of the edge of the substrate to ultrasonic heat treatment. It exists in an optical recording medium.

The present invention will be described in more detail below. As the substrate used in the present invention, it is possible to use a polycarbonate resin, a polymethacrylate resin or the like which has been widely used in optical recording media. In particular, it has a remarkable effect on an amorphous polyolefin resin. Examples of the amorphous polyolefin resin include norbornene-based, dicyclopentadiene-based, hydrogenated polystyrene and the like,
For example, ZEONEX (trade name) (Nippon Zeon Co., Ltd.)
Made), APO (trade name) (Mitsui Petrochemical Co., Ltd.), A
RTON (trade name) (manufactured by Japan Synthetic Rubber Co., Ltd.) and the like can be mentioned.

Amorphous polyolefin resins have low adhesion to the organic protective layer, and the corrosion of the recording film for this purpose has been a major problem. However, ultrasonic fusion causes great adhesion to the organic protective layer. Can be improved. Further, as a problem of ultrasonic fusion, it is considered that strain is generated around the fusion portion and birefringence is increased by the photoelastic effect. Since the refraction is small, the photoelastic coefficient is small and birefringence is unlikely to occur.

The combination of an amorphous polyolefin substrate and ultrasonic welding is very preferable in that it can satisfy all of low birefringence, low water absorption and high reliability. However, as a matter of course, the effect of improving the reliability can be obtained even when it is used other than the amorphous polyolefin resin. The substrate can be manufactured by injection molding a resin into a mold (stamper) including pits, grooves and the like. It is also possible to use molding methods other than injection molding.

A recording film is provided on the substrate. The recording film is
For example, in the case of a magneto-optical recording medium, a protective layer made of a dielectric material, a magnetic layer made of an alloy of a rare earth metal and a transition metal, a heat insulating layer made of a dielectric material, a reflective layer made of a metal having a high reflectance, and the like are usually provided by sputtering deposition. As the layer structure, a structure in which no reflective layer is provided, a structure in which a magnetic layer is formed in multiple layers, or the like may be used, but the effect of the present invention is not different.

As a method for producing the recording film, electron beam evaporation, CVD and the like can be cited in addition to sputtering. Besides the magneto-optical recording medium, a phase change medium or an organic dye medium may be used. Further, the present invention can be used to protect the metal of the reflective layer even in the case of a read-only medium in which the pits of the substrate contain information.

In this case, the recording film means the metal of the reflective layer.
Among them, it is possible to obtain a great effect by using the magneto-optical recording medium in which the magnetic layer is very easily corroded. The thickness of the recording film is usually about 10 nm to 1000 nm. When the recording film is provided all over the substrate to the edge,
When the ultrasonic heat treatment is performed, the recording film is divided into islands as the surface of the substrate melts, and the substrate and the organic protective layer are in direct contact with each other, so that a protective effect is obtained.

Although such a structure may be employed, since corrosion may occur along the recording film divided into islands, when the recording film is provided, the recording film may be formed on the inner circumference and / or the outer circumference. It is preferable to form a nonexistent region and subject this part to ultrasonic heat treatment. In particular, it is preferable that there is a region where the recording film does not exist on both the inner circumference and the outer circumference of the substrate.

The region where the recording film does not exist can be obtained by covering the substrate with a mask at the time of manufacturing. After the production of the recording film, an organic protective layer which completely covers the recording film is provided. The organic protective layer is made of, for example, an epoxy-based resin, a urethane-based resin, an acrylic resin, or the like and is usually applied by spin coating, but it may be applied by another method.

The organic protective layer is, for example, an ultraviolet curable resin, a thermosetting resin or the like, and it is preferable to cure the organic protective layer after coating. If the film thickness of the organic protective layer is too large, problems such as distortion of the substrate and insufficient curing inside occur. Therefore, the thickness is preferably 50 μm or less. The particularly preferable film thickness of the organic protective film is 1 μm or more and 20 μm or less.

The organic protective layer and the substrate are ultrasonically heat-treated and fused, and the ultrasonic heat-treatment is performed over the entire circumference of the edge portion of the substrate. This makes it possible to dramatically improve the adhesion between the organic protective layer and the substrate and prevent the ingress of water and gas. To perform ultrasonic fusion, for example, a horn having a width of about 0.1 to 1 mm and having a shape matching the circumference of the substrate may be brought into close contact with the organic protective layer and ultrasonic waves may be applied.

In this case, since the organic protective layer is thin,
It can be fused almost in the shape of a horn. Since the fused portion is somewhat distorted, it is preferable to be separated by 0.1 mm or more from the recording area. It is also important to adjust the power of ultrasonic waves so that the organic protective layer is not completely melted and destroyed.

In ultrasonic fusing, it is possible to apply ultrasonic waves from the substrate side, but since the substrate usually has a thickness of about 1 mm, in this case the ultrasonic waves are concentrated at the fusing point of the substrate. It is preferable to form a rim having a width of about 0.1 to 1 mm. In this case, the width of the horn used can be made slightly wider. Ultrasonic fusion adheres to a certain extent even if they are different substances, but naturally, if they are the same substance, the adhesion becomes stronger by mixing with each other.

Therefore, at the time of fusion bonding, a sheet of the same material as the substrate is provided on the organic protective layer, and ultrasonic waves are applied from above the sheet to ultrasonically fuse the sheet together with the organic protective layer to the substrate. That is also a preferable form. The thickness of the sheet is preferably about 10 to 200 μm. Conventionally, a technique of ultrasonically welding a hub to a substrate is known. In this case, the hub and the substrate are directly fused, but it is also possible to form the organic protective layer up to the hub fusion portion and fuse the hub and the organic protective film on the inner periphery at the same time.

At this time, if the hub is tilted, a problem occurs in recording and reproduction, so it is important to apply the organic protective layer to a uniform thickness. The ultrasonic heat treatment of the organic protective layer is preferably performed on both the inner circumference and the outer circumference, but it is also possible to perform only one of them. Further, it is also possible to make two optical disks that have been subjected to ultrasonic heating face to face with each other and bond them, and use both sides.

[0023]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 As a substrate, a disk-shaped substrate made of ZEONEX resin (trade name) (manufactured by Zeon Corporation) having a thickness of 1.2 mm and a diameter of 86 mm was used. The recording track has a radius of 22.6 mm to 41 mm.

An 80 nm protective layer made of oxidized Ta, a 25 nm recording layer made of TbFeCo, a 30 nm protective layer made of Si nitride, and a 50 nm reflective layer made of Al were sequentially formed on this substrate by sputtering. At this time, a mask is provided on the inner and outer circumferences, and the radius is 41.5 mm.
No recording film was formed on the outer side and the inner side of 22 mm.

Thereafter, spin coating is used to form SD-17, which is an acrylic ultraviolet curing resin, as an organic protective layer.
(Trade name) (manufactured by Dainippon Ink and Chemicals, Inc.) was applied to 5 μm. The coating was performed on the outer peripheral portion with a radius of 20 mm. Then, it was put in an ultraviolet curing device and cured. Organic protection is performed by contacting a horn consisting of two concentric circles with a radius of 21 mm and a radius of 42 mm and a width of 0.2 mm from the top of the organic protective layer, and generating ultrasonic waves with a frequency of 20 kHz and 300 W for 0.1 seconds. Ultrasonic fusion of the layers and the substrate was performed.

The obtained medium was measured at a wavelength of 780 nm, NA0.
55 evaluation machine, linear velocity 5.7 m / s, frequency 3.
Measure the innermost and outermost C / N ratios of the recording area at 7MHz, and then measure 2000 at 85 ° C and 85% RH.
A time acceleration test was performed, and the change in error rate before and after that was measured. The results are shown in Table 1. Example 2 Up to the organic protective layer was prepared in the same manner as in Example 1, and the same material as that of the substrate was formed thereon, and the inner diameter was 20 mm and the outer diameter was 43 mm.
The sheet of m was placed and ultrasonic fusion was performed in the same manner as in Example 1. The evaluation results are shown in Table 1.

Example 3 Polycarbonate was used as the substrate, and the same procedure as in Example 1 was followed. The evaluation results are shown in Table 1. Example 4 The same procedure as in Example 1 was carried out except that the outer periphery of the organic protective layer was applied from a radius of 9 mm, and a hub in which a metal was embedded in ZEONEX resin was ultrasonically fused with the organic protective layer at a radius of 10 mm, Ultrasonic welding was applied to the outer periphery in the same manner as in Example 1. The evaluation results are shown in Table 1.

Comparative Example 1 Up to the organic protective layer was prepared in the same manner as in Example 1, but ultrasonic fusion was not performed. The evaluation results are shown in Table 1. Comparative Example 2 A substrate was made of polycarbonate, and thereafter the same procedure as in Comparative Example 1 was performed. The evaluation results are shown in Table 1.

[0029]

[Table 1]

The C / N ratio was slightly deteriorated due to an increase in birefringence at the outermost circumference as compared with the case where ultrasonic welding was performed on a polycarbonate substrate (Example 3), but it was not so large. For others, C / N by ultrasonic welding
No deterioration of the ratio was observed. In the example, there was almost no change in the error rate before and after acceleration, whereas in the comparative example, the error rate increased. Particularly in Comparative Example 1, the deterioration was severe.

[0031]

By using the present invention, the adhesion between the substrate and the protective film can be easily improved, and the durability of the medium can be dramatically improved.

Claims (5)

[Claims] 1. A synthetic resin substrate is provided with a recording film and an organic protective layer covering the recording film, and ultrasonic heat treatment is applied to the vicinity of the end of the substrate to bring the substrate and the organic protective layer into close contact with each other. An optical recording medium characterized by the above. 2. The light according to claim 1, wherein a recording film does not exist in a region where the substrate and the organic protective layer are brought into close contact with each other by the ultrasonic heat treatment, and the substrate and the organic protective layer are in direct contact with each other. recoding media. 3. The substrate is a disc-shaped one having an opening in the center, and a hub in which a metal is embedded in a resin is fused to the substrate by ultrasonic heating at the inner peripheral edge together with the organic protective layer. The optical recording medium according to claim 1 or 2, characterized in that. 4. The optical recording medium according to claim 1, wherein the organic protective layer is covered with a sheet made of the same material as that of the substrate and subjected to ultrasonic heat treatment for integration. . 5. The optical recording medium according to claim 1, wherein the substrate is made of an amorphous polyolefin resin.