JP2000331380A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of the signal characteristics of a high density optical disk using a sheet. SOLUTION: A reflecting film 2 is formed on the signal side of a substrate 1 with a formed information signal, a transmissive sheet 6 which is thinner than the substrate 1 is stuck on the reflecting film 2 with a transmissive adhesive 5 to constitute the objective optical information recording medium and a protective layer 7 is disposed on the surface of the transmissive sheet 6 to obtain the objective optical information recording medium 10. The protective layer 7 preferably comprises a UV-curing resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium (hereinafter, referred to as an optical disk), and more particularly to an optical information recording medium capable of increasing the recording density by reducing the thickness of a reading surface on which laser light is incident. .

[0002]

2. Description of the Related Art In recent years, optical discs have been developed for high density, large capacity and small size. Higher density can be achieved by shortening the wavelength of laser light or increasing the numerical aperture of the objective lens for irradiating light during recording and reproduction of the optical pickup to reduce the spot diameter of recording and reproduction light. is there. In this case, it is necessary to reduce the thickness on the incident surface side (light passing surface) of the optical disk. For example, the thickness of the CD on the incident surface side is about 1.2 mm, while the DVD having a recording capacity of 6 to 8 times that of the CD is about 0.6 mm.

Recently, there has been a demand for an optical disk capable of providing a large recording capacity of 15 GB or more per disk of the same size as a CD or a DVD. If it is 3 mm, it becomes 15 GB. When the thickness of the substrate on the incident surface side is about 0.1 mm, the recording capacity is 20 GB. As a method for manufacturing a disk having such a high recording capacity, a method shown in FIG. 1 has been proposed.

That is, a substrate 1 containing information signals is prepared by an injection molding method using a polycarbonate resin, and a substrate 1 on which a reflection film (not shown) of aluminum or the like is formed on the information signals by sputtering or the like is placed on a turntable 3 on the information table. After mounting the substrate 1 on a turntable 3 by vacuum suction with the signal surface facing up, an ultraviolet-curable adhesive 5 is dropped on the reflective film while the turntable 3 is rotated at a low speed. The rotation of the turntable 3 and the supply of the ultraviolet curable adhesive 5 are stopped in a state where the curable adhesive 5 has spread around the reflective film in an appropriate amount (see FIG. 1A).

[0005] Next, a polycarbonate sheet 6 (hereinafter, referred to as a sheet 6) processed to the same size as the substrate 1 is placed on the substrate 1 on which an ultraviolet-curable adhesive 5 is applied. The turntable 3 is rotated at a high speed in a state where the ultraviolet-curable adhesive 5 is stretched to an appropriate size by the weight of the sheet 6 to remove excess ultraviolet-curable adhesive 5 and bubbles. Thus, the substrate 1 and the sheet 6 are integrally bonded via the ultraviolet-curable adhesive 5 (see FIG. 1B).

Then, the rotation of the turntable 3 is stopped,
The substrate 1 and the sheet 6 integrated via the UV-curable adhesive 5 are moved under a separate UV irradiation device 9 as shown in FIG. 1C, and irradiated with UV light from the sheet 6 side. The ultraviolet curing adhesive 5 is solidified. Thus, a high-density optical disk can be manufactured in which the reflection film, the solidified ultraviolet-curable adhesive 5 and the sheet 6 are sequentially laminated on the information signal surface of the substrate 1. The total thickness of the sheet 6 and the solidified UV-curable adhesive 5 is a thickness suitable for the desired capacity, and the laser beam is incident on the sheet 6 from the sheet 6 side during reproduction.

[0007]

The high-density optical disk as described above uses the sheet 6 on the incident surface side. The sheet 6 has (1) small thickness unevenness and (2) excellent optical characteristics. This is because there is an advantage such as there is. However, on the other hand, since the sheet 6 is soft and processed by a calender roll or the like, there is a disadvantage that fine indentations are easily formed. Similarly, it is expected that the surface of the sheet 6 will be damaged due to the manufacturing process of the high-density optical disk or the handling of the user. The high-density optical disk manufactured by using the sheet 6 having the indentation or the scratches has a disadvantage that the signal characteristics are poor and the noise component is particularly large, so that the C / N is deteriorated and the jitter is also deteriorated. The sheet 6 also has a disadvantage that the adhesive property is poor because the release agent is contained for the reason of the manufacturing process.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and as a first invention, a reflection film 2 is formed on a signal surface of a substrate 1 on which an information signal is formed. In the optical information recording medium 10 in which a transparent sheet 6 thinner than the substrate 1 is provided on the reflective film 2 by a transparent adhesive 5, a protective layer 7 is formed on the surface of the transparent sheet 6. A second aspect of the present invention is the optical information recording medium 10 provided with a protective layer 7 made of an ultraviolet curable resin.
According to a third aspect of the present invention, in the optical information recording medium described above, an outer diameter of the transparent sheet 6 is smaller than an outer diameter of the substrate 1, and the transparent sheet 6 is covered with the protective layer 7 at an outer peripheral portion. An optical information recording medium according to claim 1 is provided.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described below in detail. In this embodiment, a read-only type (ROM type) in which a metal reflective film is provided on an information signal surface of a substrate will be described. However, the present invention is not limited to this type. It is also applicable to magneto-optical disks.

Also, as described in the prior art,
The thickness of a 15 GB capacity substrate is about 0.3 mm, which is difficult to form by conventional injection molding. On the other hand, considering the total thickness of high-density optical discs,
It is estimated to be 1.2 mm which is the same as VD. Therefore, as one form of the next-generation high-density optical disk, for example, if it is assumed that the thickness of the transparent sheet is 0.3 mm, a substrate containing an information signal having a thickness of 0.9 mm is formed by injection molding or the like. A method is considered in which a reflective film is formed on the information signal surface, a transmissive sheet is attached thereon with a transmissive adhesive, and a light incident surface is formed from the transmissive sheet side.

[0011] Further densification has progressed, and the permeable sheet has a thickness of 0.1%.
At 1 mm, the substrate on which information signals are formed is 1.1 mm. That is, the thickness of the transparent sheet is smaller than that of the substrate containing the information signal. In this embodiment, for example,
An example using a 0.2 mm transmissive sheet will be described. However, the thickness on the incident surface side is a problem determined by the laser wavelength and the capacity determined by the numerical aperture of the objective lens, and is not limited to this.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for eliminating indentations and scratches on a sheet according to the present invention will be described. The indentations and scratches have fine irregularities, so the recesses are filled and the projections are made of a material thicker than their height. Cover the entire sheet. As a method of satisfying both in one step, for example, an ultraviolet curable resin is suitable. In particular, when a low-viscosity UV-curable resin is used, the fine concave portions are filled, and then the unnecessary UV-curable resin is removed by appropriate rotation, and the convex portions are formed of a thicker UV-curable resin layer. Can be solved by uniformly coating the entire surface of the sheet. Thereafter, the sheet is irradiated with ultraviolet rays to solidify the ultraviolet curable resin on the upper surface of the sheet. The UV-curable resin has a viscosity of 150
00 mPa · s or less, more preferably 5000 mPa · s
s or less is desirable.

Further, since the sheet is on the side of the reproduction light incident surface, it is desirable to use a UV-curable resin having a refractive index substantially equal to that of the sheet. Further, in order to prevent scratches in handling by the user, when the ultraviolet-curable resin after curing is harder than the sheet, the effect of preventing scratches is obtained. If an antistatic agent is contained in this UV-curable resin component, a dust-preventing effect can be obtained.

On the other hand, even if there is an indentation on the surface of the sheet on the substrate side, since the substrate and the sheet are bonded together, the same effect can be obtained by using a low-viscosity ultraviolet curable adhesive as described above. Indentation of the sheet is eliminated. still,
The UV-curable resin and UV-curable adhesive used here are both made of the same components,
For example, UV curable adhesives are developed mainly for adhesive strength, and UV curable resins are mainly developed for hardness as a protective layer.

In the high-density optical disk 10 of the present invention, as shown in FIGS. 2 and 3, a reflection film 2 is formed on an information signal surface of a substrate 1 containing an information signal. The transparent sheet 6 having a reduced thickness is attached to the reflective film 2 using an ultraviolet-curable adhesive 5, and further, an ultraviolet-curable resin 7 is applied to the surface of the transparent sheet 6. At this time, the outer diameter of the substrate 1 and the outer diameter of the transparent sheet 6 may be the same as shown in FIG. 3, but the outer diameter of the transparent sheet 6 is made smaller than the outer diameter of the substrate 1 as shown in FIG. By making it smaller,
The ultraviolet curable resin 7 wraps the transparent sheet 6 at the outer periphery and is further adhered to the ultraviolet curable adhesive 5. Since the UV-curable resin 7 and the UV-curable adhesive 5 have similar components, they have strong adhesive strength. Therefore, the peeling of the permeable sheet can be improved by the configuration shown in FIG.

Next, a specific embodiment of the present invention will be described with reference to the explanatory view showing the manufacturing process of FIG. 1 described above. FIG. 2 and FIG. 3 are schematic diagrams showing the configuration of the high-density optical disk 10 according to the present invention formed in the above-described manufacturing process.

First, a substrate 1 containing an information signal having an outer diameter of 120 mm, an inner diameter of 15 mm, and a thickness of 1 mm is prepared by injection molding using an optical disk grade polycarbonate resin, and an aluminum reflective film 2 is formed on the information signal surface by sputtering. The film is formed with a thickness of 60 nm. The substrate 1 is placed with the information signal surface facing upward and a center pin 4 provided at the center of the turntable 3 shown in FIG. 1 as a guide, and the substrate 1 is fixed on the turntable 3 by vacuum suction (not shown).

Next, the turntable 3 is rotated at a low speed (60 rpm).
pm), a UV curable adhesive 5 is dropped from a nozzle (not shown) onto a reflective film (not shown), and a suitable amount of the UV curable adhesive 5 is spread around the reflective film. Rotation and UV curable adhesive 5
Is stopped (see FIG. 1A).

A transparent sheet 6 (in the embodiment, a polycarbonate sheet is used) cut in advance from a roll-shaped sheet having a thickness of 0.2 mm to an outer diameter of 119 mm and an inner diameter of 15 mm in a separate step is placed on an ultraviolet-curable adhesive 5 by a center pin. 4
The turntable 3 is rotated at a high speed (5000 rpm) in a state where the ultraviolet-curable adhesive 5 is stretched to an appropriate size by the weight of the sheet 6, and the excess ultraviolet-curable adhesive 5 Remove air bubbles. (Figure 1
(B)).

After that, the rotation of the turntable 3 is stopped,
The integrated substrate 1 and the transparent sheet 6 are moved to the turntable 8 of the ultraviolet irradiation device 9 via the ultraviolet curing adhesive 5 and irradiated with ultraviolet light from the transparent sheet 6 side while being rotated at a low speed. The curable adhesive 5 is solidified.
Thereafter, the integrated substrate 1 and the permeable sheet 6 are placed on the turntable 3 again with the permeable sheet 6 face up, and the substrate 1 is fixed on the turntable 3 by vacuum suction (not shown). 3 at low speed (60 rpm
m), the ultraviolet curable resin 7 is dropped onto the transparent sheet 6 from a nozzle (not shown) while rotating the turntable 3 in a state where the ultraviolet curable resin 7 spreads an appropriate amount around the transparent sheet 6. The supply of the ultraviolet curing resin 7 is stopped. After stretching the ultraviolet curable resin 7, the turntable 3 is rotated at a high speed (4000 rpm in the embodiment) to remove unnecessary ultraviolet curable resin 7.

Thereafter, the turntable 3 is stopped, and the substrate 1 and the transparent sheet 6 and the ultraviolet-curable resin 7 on the transparent sheet 6 which are integrated via the ultraviolet-curable adhesive 5 are again irradiated with the ultraviolet irradiation device 9. Move to turntable 8,
The ultraviolet-curable resin 7 on the transparent sheet 6 is solidified by irradiating it with ultraviolet light while rotating at a low speed (60 rpm). This makes it possible to form a protective layer of the ultraviolet-curable resin 7 having a uniform thickness on the transparent sheet 6 and at the same time eliminate indentations of the transparent sheet 6.

The high-density optical disk 10 thus obtained
As shown in FIG. 2, on the information signal surface of the substrate 1 on which the information signal is formed, a reflection film 2, a solidified ultraviolet-curable adhesive 5, a transparent sheet 6, and a solidified ultraviolet-curable resin 7, as shown in FIG.
Are sequentially laminated. As a result of examining the signal characteristics of this high-density optical disc 10, C / N 41 dB was obtained.
As described above, it was good with the jitter of 10% or less. on the other hand,
The signal characteristics of a high-density optical disk manufactured from a sheet with an indentation when no countermeasures against indentation were taken were as follows: C / N 26 dB
Below, it was a bad value with a jitter of 15% or more.

In this embodiment, a high-density optical disk of a type in which a transparent sheet is provided on a substrate on which information signals are formed has been described. To form an inverted information signal on the surface of the transmissive sheet, and form a reflective film on it, and attach it to the substrate with the information signal side inside, and the incident surface of the reproduction light from the transparent sheet side Needless to say, the present invention can be applied to all optical disks having a transparent sheet surface as an incident surface.

[0024]

As described in detail above, according to the optical information recording medium of the present invention, indentations existing in the transparent sheet and scratches generated in the manufacturing process of the high-density optical disk can be eliminated. A high-density optical disk having good characteristics can be obtained. Further, by using an ultraviolet-curable resin harder than the transparent sheet, an effect of preventing damage due to handling by the user can be obtained. Further, by including an antistatic agent in the ultraviolet-curable resin, dust can be prevented and a high-density optical disk with stable signal characteristics can be obtained. Further, by making the diameter of the transparent sheet smaller than the outer diameter of the substrate, the transparent sheet is covered with the ultraviolet curable resin, and furthermore, the ultraviolet curable adhesive and the ultraviolet curable resin are bonded on the outer peripheral portion, so that the transparency is improved. The sheet is less likely to peel.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a manufacturing process of a high-density optical disk according to the present invention.

FIG. 2 is a schematic diagram showing a configuration of a high-density optical disk according to the present invention.

FIG. 3 is a schematic diagram showing a configuration of a high-density optical disk according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Reflective film 3, 8 Turntable 4 Center pin 5 UV curable adhesive 6 Transparent sheet 7 UV curable resin (protective layer) 9 UV irradiation device

Claims (3)

[Claims] 1. A reflective film is formed on a signal surface of a substrate on which an information signal is formed, and a transparent sheet thinner than the substrate is provided on the reflective film by a transparent adhesive. An optical information recording medium, wherein a protective layer is provided on a surface of the transparent sheet. 2. The optical information recording medium according to claim 1, wherein said protective layer is made of an ultraviolet curable resin. 3. The transparent sheet according to claim 1, wherein an outer diameter of the transparent sheet is smaller than an outer diameter of the substrate, and the transparent sheet is covered by the protective layer at an outer peripheral portion.
The optical information recording medium according to the above.