JPH09274736A - Optical disk and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the tact time in an ultraviolet rays irradiation process for hardening an adhesive and simultaneously to prevent thermal deformation of a substrate in a stuck disk of a double-face structure constituted by sticking a first single plate-disk, on which a recording layer is formed, to a second single plate-disk, on which the recording layer is formed, with an ultraviolet- curing type adhesive. SOLUTION: At least either one, the first single plate-disk 3 or the second single plate-disk 6, is kept to have a transmissivity of >=0.2% to ultraviolet rays and a reflectance of >=30% to a reproducing light irradiated from the transparent substrate side. The transmissivity to ultraviolet rays of the single plate-disk and the reflectance to the reproducing light are controlled by varying the film thickness of the recording layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called laminated structure in which a first veneer disc having a recording layer and a second veneer disc having a recording layer are pasted together. Optical disk and its manufacturing method.

[0002]

2. Description of the Related Art Optical disks for recording and reproducing information by irradiating a laser beam include magneto-optical disks, various write-once optical disks, digital audio disks (so-called compact disks), and optical video disks (so-called laser disks). Has been put to practical use.

[0003] Among them, compact disks and laser disks are read-only (Read Only Memory).
(y: ROM) type optical disk. In these optical discs, pits corresponding to information signals are formed in a concavo-convex shape on a transparent substrate with a depth of about の of the reproduction light wavelength, and an Al reflective layer having a thickness of 50 nm or more is formed thereon. The film is formed. In such an optical disc, an information signal is reproduced by detecting a change in reflectance caused by optical interference generated in the pit.

On the other hand, write-once optical disks and magneto-optical disks are RAMs on which arbitrary information can be written by a user.
(Random Access Memory) type optical disc.

[0005] That is, a write-once optical disc is an optical disc on which writing can be performed only once by a user, and a write-once recording layer in which optical characteristics are changed or irregularities are formed by irradiation of a laser beam is formed on a transparent substrate. It is composed. For this recording layer, for example, a GeSbTe phase change material that exhibits a crystalline state in the initial state and changes its phase to an amorphous state when irradiated with laser light is used. In this recording layer, a recording pit is formed by changing the phase of a minute area in accordance with the information signal, and the information signal is detected by detecting a change in the reflectance between the amorphous portion corresponding to the pit and the other crystal area. Will be played.

The magneto-optical disk is a rewritable optical disk in which information can be repeatedly written and erased by a user, and a magneto-optical effect (eg, Kerr effect) such as a TbFeCo amorphous alloy thin film is formed on a transparent substrate. A perpendicular magnetization film having is formed and formed. In this magneto-optical disk, recording pits are formed by magnetizing the minute regions of the perpendicularly magnetized film upward or downward in response to an information signal. The information signal is reproduced by utilizing the fact that the rotation angle θk (Kerr rotation angle) of the linearly polarized light in the reflected light differs depending on the magnetization direction of the perpendicular magnetization film.

In such a magneto-optical disk and the above-described write-once optical disk, both sides of the recording layer are sandwiched between transparent dielectric layers for the purpose of preventing the recording layer from being oxidized and increasing the signal modulation degree due to multiple interference. Further, in many cases, a four-layer structure in which an Al reflective layer is laminated thereon is adopted. As the dielectric layer, the silicon layer and ZnS-SiO ₂ mixed film nitride or the like is used.

Recently, studies on using such an optical disk for digital video recording have been actively conducted, and a digital video disk (DVD) has been developed as such an optical disk.

This DVD has a diameter of 120 mm, which is the same as a CD, and records video information equivalent to one movie, so that it can be reproduced with image quality comparable to that of a current television.

In order to record such video information on an optical disk, a recording capacity of, for example, 6 to 8 times that of a CD is required. Therefore, in the DVD, the laser wavelength is shortened to 630 to 680 nm as compared to 780 nm in the CD, and the numerical aperture NA of the objective lens is set to 0.45 in the CD.
By increasing the recording pitch to 0.52 or 0.6, the track pitch and the shortest recording mark length of the pit are reduced, and the recording density is increased.

However, the increase in the numerical aperture NA of the objective lens reduces the allowable amount of warpage of the disk substrate. For this reason, in the case of DVD, the thickness of the substrate is set to 1.
By reducing the thickness to 0.6 mm with respect to 2 mm, the distance that the laser beam passes through the disk substrate is shortened to compensate for the allowable amount of warpage (Nikkei Electronics February 27, 1995 No. 630). ). Then, in order to compensate for the decrease in the disc strength due to the further thinning of the substrate, a so-called bonding structure is adopted in which the substrate is further bonded to the surface of the substrate on which the recording layer is formed.

As the optical disk having such a bonded structure (hereinafter referred to as a bonded disk), a double-sided type in which a recording layer is formed on both of two substrates to be bonded, and one substrate only A single-sided type in which a recording layer is formed has been proposed. As the recording layer of these laminated discs, both the ROM type recording layer and the RAM type recording layer used in the above-mentioned single plate structure can be adopted, and the combination of the recording layers in the case of the double-sided type is as follows. ROM-ROM, ROM-RAM, RAM-RA
There is M.

[0013]

By the way, in the bonded disk, as an adhesive for bonding the substrates to each other, generally, a hot-melt adhesive, an ultraviolet curable adhesive, a thermosetting adhesive or a double-sided adhesive is used. Sheets or the like are used.

However, in the case of DVD, it is desirable to use an ultraviolet-curable adhesive having relatively high strength, because the substrate is thin and strength is required to be secured.

However, in the case of a double-sided bonded disk, in particular, it is difficult to use an ultraviolet curable adhesive as an adhesive for bonding.

That is, in order to perform double-sided bonding using an ultraviolet-curable adhesive, two single-disks (first single-disk, second single-disk) having a recording layer formed on a transparent substrate are used. Of the first veneer disk, and an ultraviolet-curable adhesive is applied to the surface of the first veneer disk on which the recording layer is formed, and the side of the second veneer disk on which the recording layer is formed. Apply a UV-curable adhesive to the surface. Then, the first veneer disk and the second veneer disk are bonded together with the ultraviolet curable adhesives facing each other,
Irradiate ultraviolet rays from both sides of the disc. by this,
The ultraviolet-curable adhesive is cured, and the first single-disk and the second single-disk are fixed in a bonded state.

In this double-sided type optical disc, since the recording layer is formed on both the first single-plate disc and the second single-plate disc, the ultraviolet rays emitted from both sides of the disc will not be irradiated. Also, the ultraviolet curable adhesive is irradiated through the recording layer. At this time,
When an Al reflective layer having a thickness of 50 nm or more is formed as the recording layer, most of the ultraviolet rays are reflected or absorbed by this reflective layer, and the amount of ultraviolet light actually given to the ultraviolet curable adhesive is greater than the amount of emitted light. Also becomes smaller. Therefore, it takes a long time to cure. Further, the substrate directly irradiated with the ultraviolet rays is irradiated with the ultraviolet rays at a very large integrated irradiation amount until the resin is cured, which causes a problem of thermal deformation.

Therefore, the present invention has been proposed in view of such conventional circumstances, and when an ultraviolet curable adhesive is used as the bonding adhesive, the tact time in the ultraviolet irradiation step is shortened. In addition, it is an object of the present invention to provide an optical disc having a bonded structure in which thermal deformation of the substrate is prevented and a manufacturing method thereof.

[0019]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies, and as a result, in a double-sided type bonded disc, by controlling the optical characteristics of the recording layer, We have come to the knowledge that it is possible to use an ultraviolet curable adhesive as a bonding adhesive.

The optical disc of the present invention has been proposed on the basis of such knowledge, and a first single disc having at least one recording layer formed on a transparent substrate and a transparent substrate on the first single disc. A second single-disc having at least one recording layer formed thereon, the recording layers facing each other,
It is made by pasting together with an ultraviolet curing adhesive.
At least one of the single plate disc and the second single plate disc has a transmittance of ultraviolet rays of 0.2% or more and a reflectance of reproduction light emitted from the transparent substrate side of 30% or more. It is a thing.

The optical disk manufacturing method of the present invention comprises:
The first single-disc disk having at least one recording layer formed on the transparent substrate, and the second single-disc disc having at least one recording layer formed on the transparent substrate When facing each other and adhering with a UV-curable adhesive, at least one of the first veneer disc and the second veneer disc is irradiated from the transparent substrate side with an ultraviolet transmittance of 0.2% or more. 30% reflectance of playback light
The above is characterized.

In the bonded disc, at least one of the single discs has an ultraviolet transmittance of 0.2.
% Or more, when irradiating ultraviolet rays from both sides of the bonded disks to cure the ultraviolet curable adhesive, the irradiated ultraviolet rays are efficiently transmitted through the adhesive in the single plate disk whose optical characteristics are regulated. Is irradiated. For this reason, the integrated irradiation light amount irradiated to the disc can be suppressed to a small level,
As a result, the takt time in the ultraviolet irradiation step is shortened, and thermal deformation of the substrate is suppressed.

Further, since this single plate disc has a reflectance of 30% or more for reproducing light, a sufficient reproducing output can be obtained.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 shows a first embodiment of the optical disc of the present invention.

This optical disk comprises a first single plate disk 3 having a recording layer 2 formed on a transparent substrate 1 and a second single plate disk 6 having a recording layer 5 formed on a transparent substrate 4.
Is an optical disc in which the recording layer sides are opposed to each other and adhered by an ultraviolet curable adhesive 7, that is, a double-sided type adhered disc. In each of the single-disk discs of this optical disc, the information signal recorded in the recording layers 2 and 5 is reproduced by irradiating the laser beams from the transparent substrates 1 and 4 side and condensing them on the recording layers 2 and 5. .

In this optical disc, the transparent substrates 1, 4
Any material can be used as the material as long as it is a substrate material usually used for optical discs, and plastic materials such as acrylic resin, polycarbonate resin, polyolefin resin, epoxy resin, and glass are also used. Of these plastic materials, polycarbonate is preferable because it has excellent moldability, low water absorption, and dimensional stability.

Incidentally, various signals are formed on the transparent substrates 1 and 4 by the concavo-convex shapes 8 and 9 as required. As a method for forming the unevenness, an injection molding method using a stamper is used when a plastic material is used for the substrate, and 2P (Photo-Polymeme) is used when a glass plate is used.
Rization) method is used. The thickness of the transparent substrate is, for example, 0.
It is set to about 6 mm.

The recording layers 2 and 5 formed on the transparent substrates 1 and 4 may be read-only (ROM) type recording layers or RAM type recording layers in which arbitrary information can be written by the user. .

In the read-only type, a concavo-convex pattern is formed on the substrate in correspondence with the information signal, and Al or Au is formed on the concavo-convex pattern.
A metal reflection layer mainly composed of, for example, is formed. The metal reflection layer may be composed of Al or Au alone, or may be formed by adding Ti for preventing corrosion to these metals.

The RAM type recording layer is a write-once type or a write-once type that can be written only once by the user.
There is a rewritable type that can be repeatedly erased.

In the write-once type, a low melting point metal thin film, GeSbTe
A phase change film such as a film, a film containing an organic dye, or the like is formed as a recording layer.

In the rewritable type, TbFeCo
A perpendicular magnetization film having magneto-optical characteristics (Kerr effect or Faraday effect) such as an amorphous alloy thin film is formed as a recording layer.

In these RAM types, in addition to the recording layer, a dielectric layer or a reflective layer is provided for the purpose of increasing the reflectance or the degree of signal modulation and protecting the recording layer. You may make it form the recording part of a multilayer structure which consists of a body layer, a recording layer, a 2nd dielectric material layer, and a reflective layer.

As the dielectric layer, an oxide, a nitride or the like can be used. For example, a thin film made of silicon nitride or aluminum nitride, or a ZnS-SiO ₂ mixed film is used.

The reflective layer is preferably composed of a film having a high reflectance that reflects 70% or more of the laser light at the boundary with the second dielectric layer, and is a metal reflective film mainly composed of Al, Au, or the like. Layers are preferred. In addition, this metal reflection layer is made of A
1 and Au may be used alone, or these metals may be added with Ti for corrosion prevention.

The recording layer, the reflective layer, and the dielectric layer are formed by a so-called vapor phase plating technique such as vapor deposition or sputtering.

As a combination of the recording layers 2 and 5, for example, both the first single plate disk 3 and the second single plate disk 6 are ROM type, or the first single plate disk 3 and the second single plate disk are both. One of 6 is a ROM type and the other is R
A combination such as an AM type may be used.

The optical disc comprises a first single plate disc 3 having such a recording layer 2 formed thereon, a second single plate disc 6 having a recording layer 4 formed thereon, and recording layers 2 and 5 formed thereon. The opposite sides are made to face each other, and they are bonded together by an ultraviolet curable adhesive 7.

The UV-curable adhesive 7 serves as a protective film for bonding the first single-disk 3 and the second single-disk 6 together and for protecting the recording layers 2 and 5 from moisture in the external environment. It also has a role. Therefore, as the ultraviolet curable adhesive 7, an acrylic ultraviolet curable adhesive having excellent waterproof property is preferable.

The above is the basic structure of the double-sided bonded disc.
At least one of the single plate disk 3 and the second single plate disk 6 has a transmittance of ultraviolet rays of 0.2% or more and a reflectance of reproducing light emitted from the substrate side of 30% or more.

First, the ultraviolet ray transmittance of the single plate disk is regulated to 0.2% or more in order to efficiently irradiate the adhesive agent with the ultraviolet rays irradiated from both sides of the disk through the single plate disk. By doing so, the cumulative irradiation amount (time × light amount / area) of the ultraviolet rays with which the disk is irradiated is kept small.

That is, in order to bond the first single plate disk and the second single plate disk together, the surface of the first single plate disk on which the recording layer is formed and the second single plate disk An ultraviolet curable adhesive is applied to the surface on which the recording layer is formed. As the coating method, a spin coating method, a silk screen method or the like is used. Then, the first veneer disk and the second veneer disk are bonded together with the ultraviolet curable adhesives facing each other, and ultraviolet rays are irradiated from both sides of the bonded disks. At this time, the ultraviolet rays pass through the substrate and the recording layer and are applied to the ultraviolet curable adhesive to cure the adhesive. As a result, the first veneer disc and the second veneer disc are fixed in a bonded state.

Here, when the transmittance of the single plate disk with respect to ultraviolet rays is less than 0.2%, among the ultraviolet rays irradiated on the disk, it passes through the single disk and is actually converted into an ultraviolet curable adhesive. The amount of light emitted is very small. Therefore, in order to cure the adhesive, it is necessary to irradiate the disk with ultraviolet rays at a large cumulative dose, specifically, at a cumulative dose exceeding 5000 mJ / cm ² . In this case, it takes a lot of time to cure,
Further, when a plastic substrate such as polycarbonate is used, the substrate is thermally deformed. In the present invention, in order to avoid such an inconvenience, the ultraviolet ray transmittance of the single disk is regulated to 0.2% or more.

On the other hand, the reason why the reflectance of the single plate discs 3 and 6 with respect to the reproduction light is restricted to 30% or more is to ensure that a sufficient reproduction output can be obtained from the single plate discs 3 and 6.

The reflectance of the single plate discs 3 and 6 with respect to the reproducing light is the same as that of the CD in terms of compatibility with the CD.
It is preferably 0% or more. Further, in order to obtain a practical tact time in the step of irradiating ultraviolet rays, it is desirable that the cumulative irradiation amount of ultraviolet rays is 2000 mJ / cm ² or less. To cure the adhesive at such a cumulative irradiation amount, a single plate disk is used. It is desirable that the transmittance of the ultraviolet ray to 0.5% or more.

In order to increase the ultraviolet ray transmittance of the single-disks 3 and 6, the ultraviolet rays are mainly reflected and absorbed in the recording layer 2.
Since it occurs in 5, it is effective to reduce the film thickness of the recording layers 2 and 5.

For example, in a ROM-type single-plate disk having an Al reflection layer or a reflection layer formed by adding a small amount of Ti or the like to Al, the transmittance of ultraviolet rays can be reduced by setting the thickness of the reflection layer to 40 nm or less. It becomes 0.2% or more. However, if the film thickness of the reflective layer is less than 5 nm, it is 3
A reflectance of 0% or more cannot be obtained. Therefore, it is appropriate that these reflective layers have a thickness of 5 to 40 nm. The thickness of the reflective layer is preferably 20 to 35 nm in order to obtain the same reflectance of 70% or more as that of CD and to suppress the integrated irradiation amount of ultraviolet rays to 2000 mJ / cm ² or less.

On the other hand, in the RAM type single plate disk, a dielectric layer and a reflective layer are provided in addition to the recording layer as described above.
In some cases, a multi-layered recording unit is formed. In such a multilayer structure, it is difficult to increase the transmittance for ultraviolet rays by controlling the film thickness. Therefore, it is better to limit the optical characteristics of the ROM type single plate disc to a predetermined range in the bonded disc in which the ROM type single plate disc and the RAM type single plate disc are combined.

Next, FIG. 2 shows a second embodiment of the optical disc of the present invention.

In this optical disk, a first single disk 14 having two recording layers 12 and 13 formed on a transparent substrate 11 and two recording layers 16 and 17 formed on a transparent substrate 15 are formed. The second single plate disk 18 formed by the recording layer 1
3 and 17 are made to face each other and are bonded by an ultraviolet curable adhesive 19. The first veneer disk 14 and the second veneer disk 18 are made up of the transparent substrates 11, 1
5, first recording layers 12 and 16 are formed on the first recording layer 12, and ultraviolet curable resin intermediate layers 20 and 21 are formed on the first recording layers 12 and 16.
The second recording layers 13 and 17 are formed via the. In the first single plate disc 14 of this optical disc, by irradiating the laser beam from the transparent substrate 11 side and condensing the laser beam on the first recording layer 12, the information signals recorded on the first recording layer 12 are independently produced. Is played. Further, by irradiating the transparent substrate side 11 with a laser beam, transmitting the laser beam through the first recording layer 12, and further focusing the laser beam on the second recording layer 13, the information signal recorded on the second recording layer 13 is recorded. Played independently. In addition, also in the second single plate disk 18, the transparent substrate 15
By irradiating the first recording layer 16 with laser light from the side, the information signals recorded in the first recording layer 16 are independently reproduced. In addition, by irradiating the laser beam from the transparent substrate side 15 to allow the laser beam to pass through the first recording layer 16 and to focus the laser beam on the second recording layer 17, the information signal recorded in the second recording layer 17 is generated. Played independently.

In this optical disc, the transparent substrate 11,
As the material of 15 and the materials of the first recording layers 12 and 16 and the second recording layers 13 and 17, any of those exemplified for the optical disc of the first embodiment can be used. However, as the first recording layers 12 and 16, the second recording layers 13 and 1
In order to irradiate 7 with laser light, it is necessary to select a material that can transmit the laser light for reproduction to some extent.

First recording layers 12 and 16 and second recording layer 1
3, an ultraviolet curable resin intermediate layer 20 formed between 3,
21 is a first recording layer 12, 16 and a second recording layer 13,
It is a layer for optically separating 17 and, for example, 2P
It is formed to a thickness of 30 to 50 μm by the method.

In this optical disc, especially, the first disc
At least one of the single plate disk 14 and the second single plate disk 18 has a transmittance of 0.2% or more of ultraviolet light irradiated from the substrate side and a reflectance of 30% or more of reproducing light.

Therefore, when irradiating ultraviolet rays from both sides of the bonded disks to cure the ultraviolet curable adhesive, the irradiated ultraviolet rays are efficiently transmitted to the adhesive in the single plate disk whose optical characteristics are regulated. Is irradiated. Therefore, the integrated irradiation light amount applied to the disc is suppressed to a small value, which shortens the tact time in the ultraviolet irradiation step and suppresses the thermal deformation of the substrate.

Further, since this single plate disc has a reflectance of 30% or more for reproducing light, a sufficient reproducing output can be obtained.

In this case as well, in order to obtain compatibility with CD and further reduce the takt time in the ultraviolet irradiation step, the transmittance of the single plate disk for ultraviolet rays is 0.
It is desirable that the reflectance for reproducing light is 5% or more and 70% or more.

The transmittance of the single plate disks 14 and 18 with respect to ultraviolet rays and the reflectance with respect to reproducing light are controlled by changing the film thickness of the first recording layers 12 and 16 and the second recording layers 13 and 17. be able to.

[0059]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments to which the present invention is applied will be described based on experimental results.

First, the following preliminary experiment was conducted in order to obtain a single disk having appropriate optical characteristics.

The film thickness of the Al reflection layer and the transmittance of ultraviolet rays were measured.
討 polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company, Inc. optical grade tradename Iupilon H-4000 series) by injection molding, to produce a transparent substrate having a thickness of 0.6mm which pits uneven shape is formed on one surface. Then, various single plate disks were produced by forming an Al reflective layer by RF (high frequency) sputtering on the surface of the transparent substrate on which the pits were formed. The thickness of this Al reflective layer was changed within the range of 5 to 50 nm. The single plate disk thus produced was irradiated with ultraviolet rays from the substrate side, and its transmittance was measured.

FIG. 3 shows the relationship between the film thickness of the Al reflecting layer and the ultraviolet ray transmittance of the single plate disk. The ultraviolet transmittance is the transmittance at a peak wavelength of 365 nm of the ultraviolet lamp and is expressed in logarithm.

As can be seen from FIG. 3, the ultraviolet ray transmittance of the single plate disk linearly decreases as the film thickness of the Al reflection layer increases. From this, it was found that the ultraviolet ray transmittance of the single plate disk can be controlled by changing the film thickness of the Al reflective layer.

Film Thickness of Al Reflecting Layer and Required for Curing Resin
Examination of integrated irradiation dose of ultraviolet rays A single plate disk was prepared in the same manner as in the above-mentioned examination example, and Al
An ultraviolet curable adhesive was applied on the reflective layer. Then, the adhesive was cured by irradiating ultraviolet rays from the substrate side.
At this time, the adhesive was prevented from being directly irradiated with ultraviolet rays.

Then, the cured adhesive was extracted and the gel fraction was measured. As a result, the gel fraction of the adhesive is 90%
Therefore, the gel fraction was not further increased even if the ultraviolet ray was further irradiated. From this, it was found that this ultraviolet-curable adhesive can be considered to be completely cured when the gel fraction reached 90%.

Next, various single plate disks were prepared by changing the film thickness of the Al reflection layer, and an ultraviolet curable adhesive was applied on the Al reflection layer. Then, the adhesive was cured by irradiating it with ultraviolet rays from the substrate side, and the minimum integrated irradiation dose of ultraviolet rays required for the gel fraction of the adhesive to reach 90% was examined.

FIG. 4 shows the relationship between the film thickness of the Al reflective layer and the minimum integrated irradiation dose of ultraviolet rays required for the gel fraction to reach 90%. The cumulative irradiation amount of ultraviolet rays is the cumulative irradiation amount of ultraviolet rays measured on the surface of the substrate, and is shown in logarithm.

As can be seen from FIG. 4, the gel fraction is 90%.
The minimum integrated irradiation dose required to become linearly increases as the film thickness of the Al reflective layer increases.

Here, the polycarbonate transparent substrate is
When the integrated irradiation dose of ultraviolet rays exceeds 5000 mJ / cm ² , thermal deformation occurs. Looking at Figure 4, the gel fraction is 90%
The minimum integrated dose required to achieve is 5000 mJ / cm
The film thickness of the Al reflective layer is 40 nm, which can be suppressed to ² or less.
In the following cases. From FIG. 3, it can be seen that when the thickness of the Al reflective layer is 40 nm or less, the transmittance of the single plate disk for ultraviolet rays is 0.2% or more.

From this fact, in order to suppress the thermal deformation of the substrate while sufficiently curing the resin, the thickness of the Al reflection layer should be 4
It was found that it is necessary to set the thickness to 0 nm or less and to set the transmittance of the single plate disk to the ultraviolet ray to 0.2% or more. In order to obtain a practical tact time in the step of irradiating ultraviolet rays, it is desirable that the cumulative irradiation amount of ultraviolet rays is suppressed to 2000 mJ / cm ² or less, and therefore the thickness of the Al reflection layer is set to 35 nm or less. Is more preferable.

Examination of reflectance of Al reflection layer and reproduction light Various sample disks in which the thickness of the Al reflection layer was changed were irradiated with laser light of 630 nm or 680 nm (reproduction wavelength used for DVD) from the substrate side. The reflectance in the case of doing was calculated. FIG. 5 shows the relationship between the film thickness of the Al reflective layer and the reflectance calculated. The reflectance is a value that includes both the reflection on the recording layer and the reflection on the substrate.

As can be seen from FIG. 5, the reflectance at 630 nm and the reflectance at 680 nm show almost the same change, and both reflectances decrease as the film thickness of the Al reflective layer becomes thinner. Here, the reflectivity of a magneto-optical disk or a phase-change type disk which has already been put to practical use is 20 to
The signal reproduction is possible if the optical disc has a reflectance of about 20 to 30%. As shown in FIG. 5, the reflectance of 30% or more is obtained when the thickness of the Al reflective layer is 5 nm or more.

From this, it was found that the film thickness of the Al reflection layer must be 5 nm or more in order to enable signal reproduction as an optical disk. In order to obtain compatibility with CD, it is desirable that the reflectance is 70% or more, which is the same as CD, and therefore the thickness of the Al reflective layer is 70%.
It is more preferably 20 nm or more where the above reflectance can be obtained.

Example 1 Next, the film thickness within the optimum range in the above study example, 5 to 40 n
Then, an Al reflective layer was formed with m to prepare a bonded disk.

By injection-molding a polycarbonate resin, a pit of uneven shape is formed on one surface to a thickness of 0.6 m.
m transparent substrates were produced. Then, an Al reflective layer is formed on the surface of the transparent substrate on which the pits are formed by RF sputtering to form two single plate disks (first single plate disk, second single plate disk). Was produced. The thickness of this Al reflective layer is in the range of 5 to 40 nm.

Then, an ultraviolet curable adhesive is applied to each of the surfaces of the first transparent substrate and the second transparent substrate on which the recording layer is formed by spin coating to a thickness of 30 μm, and the adhesive Were made to face each other and bonded. Then, the adhesive was cured by irradiating ultraviolet rays from both sides of the disc to prepare a bonded disc. At this time, the integrated irradiation dose of ultraviolet rays was 5000 mJ / cm ² or less, and the adhesive could be sufficiently cured with this irradiation dose.

The laminated disc thus produced was subjected to signal reproduction with laser light of 630 nm and 680 nm. As a result, a sufficient reproduction signal could be obtained.

As described above, the characteristics of the bonded disk having the combination of ROM-ROM were evaluated.
Similar results are obtained for bonded discs with a combination of ROM.

[0079]

As is apparent from the above description, according to the present invention, a first single-disc having a transparent substrate on which at least one recording layer is formed, and at least one layer on the transparent substrate. An optical disk in which a recording layer is formed on a second single plate disk, and the recording layers are opposed to each other and bonded by an ultraviolet curable adhesive. At least one of them has a transmittance of ultraviolet rays of 0.2% or more and a reflectance of reproducing light emitted from the transparent substrate side of 30% or more, so that the ultraviolet curing of the adhesive can be performed while ensuring a sufficient reproducing output. In the process, the tact time can be shortened and the substrate can be prevented from thermal deformation.

Therefore, according to the present invention, it becomes possible to use the ultraviolet curable adhesive in such a double-sided bonded disk, which can greatly contribute to the improvement of the reliability of the bonded disk.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one configuration example of an optical disc to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view showing another configuration example of the optical disc to which the present invention is applied.

FIG. 3 is a characteristic diagram showing the relationship between the film thickness of an Al reflective layer and the transmittance of a single plate disk for ultraviolet rays.

FIG. 4 is a characteristic diagram showing a relationship between a film thickness of an Al reflective layer and an integrated irradiation amount of ultraviolet rays required for curing an ultraviolet curable adhesive.

FIG. 5 shows the thickness of the Al reflection layer and 630 of a single plate disc.
It is a characteristic view which shows the relationship of the reflectance with respect to the laser beam of nm or 680 nm.

[Explanation of symbols]

1, 4, 11, 15 transparent substrate, 2, 5 recording layer, 3,
14 First Single-Plate Disk, 6,18 Second Single-Plate Disk, 7,19 UV-Curing Adhesive, 12,16 First Recording Layer, 13,17 Second Recording Layer, 20,21
UV curable resin intermediate layer

Claims (3)

[Claims] 1. A first veneer disc having a transparent substrate on which at least one recording layer is formed, and a second veneer disc having at least one recording layer on a transparent substrate. However, the recording layers are made to face each other and are adhered together by an ultraviolet curable adhesive. At least one of the first single plate disk and the second single plate disk has an ultraviolet transmittance of 0.2% or more and is transparent. An optical disc having a reflectance of 30% or more for reproducing light emitted from the substrate side. 2. A metal reflection layer mainly composed of Al having a thickness of 5 to 40 nm, wherein at least one of the recording layer formed on the first single plate disc and the recording layer formed on the second single plate disc. The optical disc according to claim 1, wherein 3. A first veneer disc having at least one recording layer formed on a transparent substrate, and a second veneer disc having at least one recording layer formed on a transparent substrate. When the recording layers are made to face each other and are bonded by an ultraviolet curable adhesive, at least one of the first single plate disk and the second single plate disk has a UV transmittance of 0.2% or more and a transparent substrate. A method of manufacturing an optical disk, wherein the reflectance of reproduction light emitted from the side is 30% or more.