JPS62298040A - Information recording medium - Google Patents

Abstract

PURPOSE:To suppress the increase of double refraction when temp. and humidity change and to obtain an optical disk having high reliability in recording characteristics by adhering a hub having a projection fitting to the central hole of the optical disk and the optical disk at the central hole part. CONSTITUTION:The central hole 6 of the optical disk 5 and the hub 1c provided with a step to the projection are fixed by an adhesive agent 2. The adhesive agent is merely required to be partially stuck thereto as far as thorough fixing is accomplished. Epoxy and urethane adhesive agents which shrink less on curing and yield high adhesive strength are particularly adequate for the adhesive agent. Ester and amide adhesive agents which are highly resistant to heat and yield high adhesive strength are more preferred when a hot-melt adhesive agent is to be used. The hub is made of plastics, metals, ceramics, etc. A polycarbonate, polymethyl methacrylate and composite resin composed of a modified polystyrene and polycarbonate are recommended for the hub.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to an information recording medium having a novel structure. More specifically, the present invention relates to information recording that can be used in an optical information recording and reproducing apparatus and that suppresses increases in birefringence when the temperature and humidity of the environment changes and has excellent reliability in terms of recording characteristics.

Conventional technology In recent years, the amount of information handled in offices and homes has been increasing dramatically, and information recording media and information that can record large amounts of information at high density and store and reproduce information over long periods of time are needed. A recording/reproducing device is desired.

Conventionally, contact-type magnetic recording systems have been mainly used to record and reproduce information, but recently optical disk devices that record and reproduce information in a non-contact manner using laser light have been developed and are being put into practical use.

Up to now, two types of clamping methods for optical discs in drive devices have been proposed: a mechanical chuck method and a magnetic chuck method, but the magnetic chunk method is advantageous for the following reasons.

That is, the structure of an optical disk is roughly divided into three types: a single-plate structure, an air sandwich structure, and a full-surface contact structure, and the thickness of the information recording carrier differs depending on each structure. Single-disc structures are used for playback-only CDs and CD-ROMs, and there is no problem as the thickness is standardized, but optical discs on which users can record information can be either single-sided or double-sided recording formats. Also, due to differences in information recording formats, i.e.
The structure differs between cases involving physical changes such as openings and void formation and cases without physical changes such as magnetism and phase change. The former has an air sandwich structure, and the latter has a full-coverage structure, and because they have different thicknesses,
While the mechanical method has the disadvantage that it is not compatible with the mounting and removal of optical discs into and from the drive device, the magnetic chuck method does not have this drawback.

By the way, in the magnetic chuck method, it is necessary to fix hubs for attaching the optical disc to the drive device on both sides of the disc.

A method for fixing the hub is to surface-bond the hub to the inner circumferential portion of the optical disk using an adhesive.

FIG. 2 is a cross-sectional view of an information recording medium with a hub fixed in this way, and shows an adhesive layer 2 on the inner circumference of the optical disk 5.
The hub 3 is shown surface-bonded with adhesive through the hub 3. 4
6 is the center hole of the hub, and 6 is the center hole of the disk.

However, with this method, since the optical disc has a wide adhesive surface from the center hole to the vicinity of the area where information is recorded, distortion may occur due to the difference in the materials of the hub and the optical disc when the temperature and humidity of the environment changes. If the optical disc substrate material is a material that has high birefringence from the beginning, such as polycarbonate (PC), the birefringence will further increase, causing the CiN ratio to drop by 1 degree in information recording and reproducing characteristics. This is particularly true for magneto-optical disks that utilize the magnetic Kerr effect.

Problems to be Solved by the Invention The present invention aims to solve these problems and provide an information recording medium that suppresses the increase in birefringence when the temperature and humidity of the environment changes and has excellent reliability in terms of recording characteristics. It is something to do.

Means for Solving the Problems In order to achieve the above object, the inventors of the present invention have conducted extensive research, and as a result, the present inventors have developed a method that utilizes the center hole of the disk substrate without adhesively fixing the hub to the disk substrate surface. It was discovered that the object could be achieved by adhering and fixing the material, and based on this knowledge, the present invention was accomplished.

That is, in the present invention, when attaching two hubs to the upper and lower surfaces of an optical disc substrate, each knob is provided with a protrusion corresponding to the center hole of the substrate, and the protrusion is fitted into the center hole. To provide an information recording medium characterized in that a hub is bonded and fixed via an adhesive layer between the outer surface of the projection and the inner surface of the center hole and between the upper surfaces of the opposing knob projections. It is something.

Examples of the adhesive layer used in the present invention include reactive adhesives such as resoldial, cyanoacrylate, epoxy, urethane, and UV-curable acrylate, and hot melt adhesives such as E~'A, synthetic rubber, polyester, and polyamide. General purpose resins such as polyethylene, polypropylene, polycarbonate, polymethyl methacrylate, polyester, and polyamide can be used.

Among the reactive adhesives, epoxy-based and urethane-based adhesives are particularly suitable because they have excellent adhesive strength and have low curing shrinkage.

In addition, to bond the hub using hot melt adhesives and general-purpose resins, you can use them in a heated state, or apply ultrasonic waves or high-frequency waves as a heat source to melt the resin that has been filled in advance. There is a method of gluing
Compared to methods using reactive adhesives, this method is extremely advantageous in terms of process because the adhesion and curing process can be completed in a short time.

As the hot melt adhesive, polyester and polyamide adhesives are preferable because they have high heat resistance and excellent adhesive strength. Specifically, Harpwick A-3200, A-4
000 (manufactured by Asahi Kasei Corporation), Meltron E-80
Polyester resins such as 2 (manufactured by Diabond Industries Co., Ltd., Macromel) 6238 to 6240 (Henke
Polyamide resins such as Meltron 8-703T (manufactured by Diabond Kogyo Co., Ltd.), Evergrip P^-70 Near 6 (A, C, 1, manufactured by Japan Limlted), and the like can be mentioned.

Although resins such as polyethylene, polypropylene, polycarbonate, and polymethyl methacrylate can also be used, polycarbonate and polymethyl methacrylate, which are the same type as the optical disc substrate material and have relatively good heat resistance, are particularly preferred.

When actually using the above-mentioned hot-melt resin and resins such as polycarbonate and polymethyl methacrylate as adhesives, it is also possible to use a liquid that has been heated and melted in advance in a sheet or granular pond. It is advantageous to use a ring-shaped resin made by punching out the resin and apply ultrasonic waves or high frequency waves to bond it, as it is easier to handle and has higher work efficiency.

When using ultrasonic waves or high frequency waves for bonding, applying pressure when applying each energy wave allows the molten resin to penetrate into the fine details and allows the film thickness of the adhesive resin to be adjusted. In addition to improving the adhesive strength, it is also possible to improve the surface accuracy of the hub with respect to the optical disk surface. Adhesive resin film thickness is 10 to 3000
A range of μ shoulder is preferable, and the maximum adhesive strength can be obtained at a film thickness of 30 to 200 μ.

This effect of pressure can also be seen when reactive adhesives are used.

Plastic, metal, ceramic, etc. can be used for the material of the hub, but if a magnetic chuck method is used to clamp the optical disc to the drive device, strong materials such as Fe, Ni, Co, Mn, etc. can be used. Since magnetic metals and alloys are often used, 5tlS-403, 5OS-416, which has excellent corrosion resistance,
SUS430. Ni or the like is suitable.

The hub used in the present invention needs to be provided with a protrusion large enough to fit into the center hole of the optical disk, but there are no particular limitations other than this.

The size of this hub is determined by the size of the turntable of the normally used drive device.

The shape of the protrusion of the hub is preferably stepped or sloped in order to improve the adhesive strength between the optical disc and the hub. 3A, 1B, and 1C are cross-sectional views of examples of hubs with different shapes of protrusions used in the present invention, and 1a has a protrusion with the most basic structure.
1b indicates a protrusion having an inclined structure, and 1c indicates a protrusion having a stepped structure.

Furthermore, in order to increase the adhesive strength, it is desirable to physically treat the adhesive surface of the hub with a file or sandpaper, or to perform a treatment such as etching.

There are no particular restrictions on the material of the optical disc substrate, and any material selected from commonly used resins such as polyethylene, polypropylene, polystyrene, polycarbonate, polymethyl methacrylate, powder resins thereof, or glass may be used. Polycarbonate and polymethyl have low birefringence, excellent mechanical suitability (warpage, surface runout, etc.) under high temperature and high humidity conditions, and are less likely to break if the optical disc is dropped. A powdered resin of polycarbonate F and methacrylate and modified polystyrene is suitable.

The structure of optical disks is broadly classified into three types: single-plate, air-sand inch, and fully-contact structures. Although the present invention can be applied to any structure, due to the mechanical properties of optical disks under high temperature and high humidity, symmetric structures are not possible. Air sandwich and full-surface contact structures are desirable. Additionally, in order to improve the adhesive strength between the hub and the optical disc, it is more desirable to increase the effective adhesive area at the center hole of the optical disc and to perform surface treatment (machining) for the purpose of anchoring the adhesive. .

Next, the information recording medium of the present invention will be described with reference to the accompanying drawings. FIG. The knob 1c and the optical disc substrate 5 are bonded together via the adhesive layer 2, and the hub 1c is fixed in the center hole 6 of the optical disc. This adhesive layer 2 does not necessarily have to be provided over the entire surface of the outer surface of the protrusion, the inner surface of the substrate center hole, or the upper surface of each protrusion, and may be provided only partially as long as the fixation is complete.

Effects of the Invention According to the present invention, by bonding an optical disc to a hub having a protrusion large enough to fit into the center hole of the optical disc at the center hole of the optical disc, changes in the temperature and humidity of the environment can be avoided. This suppresses the increase in birefringence during the recording process, making it possible to obtain an optical disc with excellent reliability in terms of recording characteristics.

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples.Comparative Examples Grooves (depth: 700λ, width: 0.5mm) were formed in advance by injection molding.
1.2u thick PC board (outer diameter 130z, v, inner diameter 1s, vz) with 65μ shoulder, pitch 1.6μl) and 5t
Hub made of lS-416 (outer diameter 32xz, inner diameter 15x
z, thickness 2.1jz) was adhered to the inner circumference of the disk using an epoxy adhesive while aligning the center to prepare a sample (Figure 2).

The birefringence of this sample at a radius of 30JJI was measured and was 35.6zz (double pass).

Next, this sample was subjected to a thermal cycle test (+60℃-
-40℃ for 14 days), the birefringence at the point measured before the cycle test was measured again, and the result was 50.4n[0
(double pass). From this, it can be seen that the structure in which the hub is surface-bonded to the inner circumferential surface of the disk results in an increase in birefringence.

Example 1 A PC molded board from the same lot as the PC board used in the comparative example and a hub having a convex portion sized to fit the center hole of the disk were bonded together with the adhesive used in the comparative example at the center hole of the disk. A sample was prepared by bonding using the same epoxy adhesive while aligning the center (Fig. 1).

The birefringence of this sample at a radius of 30zx was measured and was 35.2 um (double pass). After completing the same cooling and heating cycle test as in the comparative example, the birefringence of this sample was re-measured and found to be 36. Since this is OnI[l (double pass), it can be seen that by fixing the hub at the center hole of the disk, the increase in birefringence when the temperature and humidity of the environment changes can be suppressed.

Example 2 A PC board from the same lot as the PC board used in the comparative example was sandwiched between a hub having a convex portion sized to fit the disc center hole, and ultrasonic waves were applied while applying pressure to the ring that had been inserted in advance. hot melt) 84 fat sheet (2 in Figure 1)
) was melted to adhere the hub and disk (Figure 1).

The birefringence of this sample at a radius of 30zz is the initial value of 34
, 4um (double pass), and the birefringence after the same cooling and heating cycle test as the comparative example was 34.0+on (double pass) at the same location measured before the cycle test.
No increase in birefringence was observed. 4 Example 3 On a PC board from the same lot as the PC board used in the comparative example,
300λ of SiO was formed using the resistance heating method, and ternary co-evaporation of Sb, Te, and Ge was performed on it.
s, Tea, zs, (:eo, <o film with a composition ratio of 33
After forming to a thickness of 0.0 mm, sb was applied to 200 A, and finally SiO was formed to a thickness of 300.

After bonding two of these vapor-deposited veneers together with adhesive to create a disk with a fully adhesive structure, a hub having a convex portion sized to fit the disk center hole was hot-melted using ultrasonic waves in the same manner as in Example 2. An optical disk bonded with resin was fabricated (Figure 1).

This optical disc was put on an evaluation device and the rotation speed was 1800 rpm.
m, recording frequency 3.7MHz, radius 30z C near shoulder
As a result of measuring the 7N ratio, it was 59dB (BW=30KHz)
was gotten.

Next, after completing the same thermal cycle test as in the comparative example, this optical disk was evaluated again under the same conditions. As a result, the archival characteristics remained unchanged at 59clB (Bll = 30Ktlz), and the shelf characteristics were also 60clB (BW = 30KHz).
It was found that there was no effect on the characteristics at all.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an example of an information recording medium of the present invention, FIG. 2 is a sectional view of an example of an information recording medium in which a hub is fixed by a method different from that of the present invention, and FIG. 3 is 1a, 1b, and 1c. 2A and 2B are cross-sectional views of examples of hubs with different shapes of protrusions used in the present invention, respectively. In the figure, reference numeral 2 is an adhesive layer, 3 is a hub, 4 is an adhesive surface, 5 is a center hole of the hub, 6 is a disk substrate, and 7 is a center hole of the disk.

Claims (1)

[Claims] 1. When attaching two hubs to the upper and lower surfaces of an optical disk substrate, each hub is provided with a protrusion corresponding to the center hole of the substrate, the protrusion is fitted into the center hole, and the protrusion is inserted into the center hole. An information recording medium characterized in that a hub is bonded and fixed via an adhesive layer between the outer surface of the center hole and the inner surface of the center hole and between the upper surfaces of the opposing hub protrusions. 2 Claim 1 in which the adhesive layer is a reactive adhesive layer
The information recording medium described in section. 3. The information recording medium according to claim 1, wherein the adhesive layer is a hot melt adhesive layer.