JPH103695A - Multi-layer optical disk and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable regenerative signal without being affected by bi- refringence of a highpolymer sheet by laminating two sheets of highpolymer sheets between recording layers so that the prolonging directions are orthogonally intersected with each other. SOLUTION: The highpolymer sheets 3, 4 and adhesive layers 6, 7, 8 become an intermediate layer optically separating the recording layers 2, 5. In this multi-layer optical disk, the highpolymer sheets 3, 4 are laminated so that the prolonging directions are orthogonally intersected with each other. In the multi- layer optical disk having such a intermediate layer, the stable regenerative signal is obtained e.g. even when a signal is reproduced using rotation of a plane of polarization with hardly being affected by the bi-refringence of the intermediate layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multilayer optical disk having two or more recording layers formed on a transparent substrate and a method for manufacturing the same.

[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] These optical discs are basically constituted by forming a recording layer on a transparent substrate, and the recording layer is selected according to the use of the optical disc.

[0004] For example, in a compact disk or a laser disk which is a read-only type, an uneven pattern corresponding to an information signal is formed on a transparent substrate, and a metal reflective layer made of Al, Au, or the like is formed on the uneven pattern. Is formed as a recording layer.

In a write-once optical disk or a magneto-optical disk, guide grooves and address pits are formed on a transparent substrate, and a recording layer is formed thereon. In the write-once type, a low melting point metal thin film, a phase change film, a film containing an organic dye, or the like is used as the recording layer. In a magneto-optical disk, a recording magnetic layer having a magneto-optical effect such as a Kerr effect or a Faraday effect, for example, a perpendicular magnetization film made of a rare earth-transition metal amorphous alloy such as a Tb-Fe-Co alloy is used.

[0006] As an optical disk, a single-layer optical disk having only one recording layer has become widespread. Recently, for the purpose of increasing the recording capacity, an optical disk having a multilayer configuration having two or more recording layers has been developed. Is being developed. As such an optical disk, a laminated type optical disk in which a number of recording layers are stacked with an intermediate layer interposed therebetween, and two substrates on which the recording layers are respectively formed, are arranged such that the sides on which the recording layers are formed are opposed to each other. And a bonded type optical disk bonded through an intermediate layer. Among these, a digital video disk has been proposed as a bonding type optical disk which can obtain a recording capacity of about 3.7 Gbytes on one side.

[0007]

By the way, in such a multilayer optical disc, an intermediate layer interposed between the recording layers is for optically separating the recording layers from each other.
For example, a polymer sheet made of polycarbonate or the like is used.

However, the polymer sheet is usually pulled in a certain direction in a sheet forming step at the time of production, and the molecular chains are stretched, so that uniaxial birefringence due to this remains.

When such a polymer sheet is used as it is in the intermediate layer of an optical disk, the amount of reflected light and the plane of polarization of the polarized light fluctuate due to the birefringence. When playing,
This birefringence greatly affects the reproduced signal.

At present, a sheet having a relatively small amount of birefringence is used in consideration of such an influence on a reproduced signal. However, in this case, the material of the sheet is limited, and the birefringence cannot be completely suppressed, and further study is required.

Accordingly, the present invention has been proposed in view of such conventional circumstances, and provides a multilayer optical disk capable of reducing the amount of birefringence of an intermediate layer and obtaining a good reproduction signal, and a method of manufacturing the same. The purpose is to:

[0012]

Means for Solving the Problems To achieve the above object, a multilayer optical disk of the present invention is a multilayer optical disk having a plurality of recording layers laminated on a transparent substrate with an intermediate layer interposed therebetween. The intermediate layer is formed by laminating two polymer sheets so that the stretching directions are orthogonal to each other.

Further, in the method for manufacturing a multilayer optical disk according to the present invention, after forming a first recording layer on a transparent substrate, a first polymer sheet is bonded onto the recording layer, A second polymer sheet is bonded on the first polymer sheet so that the stretching direction is orthogonal to the first polymer sheet, and a second recording layer is formed thereon. It is.

When two polymer sheets are laminated so that the stretching directions are orthogonal to each other, the polymer sheets cancel each other's birefringence, and the combined birefringence of the two polymer sheets is close to zero. Can be lowered to Therefore, such a 2
In a multilayer optical disk having two polymer sheets as an intermediate layer,
A good reproduced signal can be obtained even when the signal is reproduced using, for example, the rotation of the polarization plane, without being substantially affected by the birefringence of the intermediate layer.

[0015]

Embodiments of the present invention will be described below.

FIG. 1 shows an example of the multilayer optical disk of the present invention.

This multi-layer optical disc has a first recording layer 2, a first polymer sheet 3, a second polymer sheet 4, a second recording layer 5, The protective layer 9 is formed by laminating in this order. Here, adhesive layers 6, 7, 8 made of an ultraviolet curable resin are provided between the first recording layer 2, the first polymer sheet 3, the second polymer sheet 4, and the second recording layer 5. The adhesive layer 8 between the second polymer sheet 4 and the second recording layer 5 is formed with a concavo-convex pattern by a photopolymer method (2P).

In this multi-layer optical disc, for example, a laser beam is irradiated from the transparent substrate 1 side and focused on the first recording layer 2, whereby the information signal recorded on the first recording layer 2 is reproduced. Further, a laser beam is irradiated from the transparent substrate 1 side, and the first recording layer 2, the adhesive layer 6, the first polymer sheet 3, the adhesive layer 7, the second polymer sheet 4, and the adhesive layer 8 are irradiated. Let through,
By condensing the light on the second recording layer 5, the information signal recorded on the second recording layer 5 is reproduced.

As the transparent substrate 1, an acrylic resin,
In addition to a plastic substrate made of a polycarbonate resin, a polyolefin resin, an epoxy resin or the like, a glass substrate or the like is used. The transparent substrate 1 has an uneven pattern corresponding to information signals or address information and guide grooves on the surface on which the recording layer is formed. This uneven pattern
Plastic substrates are formed by injection molding, etc.
The glass substrate is formed by a photopolymer method (2P method).

The recording layers 2 and 5 may be read-only recording layers or recordable recording layers on which arbitrary information can be written by a user.

In the reproduction-only type, a concave / convex pattern is formed on the transparent substrate 1 or the adhesive layer 8 corresponding to the information signal, and a metal reflective layer mainly composed of Al, Au, or the like is formed thereon.
Alternatively, a semi-transparent film made of a Si-N dielectric or the like is formed as a recording layer. The metal reflection layer may be composed of Al or Au alone.
i may be added. Further, in the case of the first recording layer 2 on the incident side of the laser beam, it is necessary to transmit the laser beam to the second recording layer 5, so that the metal reflection layer or the semi-reflective layer having a relatively small thickness is used. It is desirable to use a transparent film.

The recording layer of the recordable type includes a write-once type in which the user can write once, and a rewritable type in which writing and erasing can be repeatedly performed. These recordable recording layers are formed on the transparent substrate 1 or the adhesive layer 8 on which the concave and convex patterns corresponding to the guide grooves and the address information are formed.

In the write-once type, a low melting point metal thin film, Ge-Sb-
A phase change film such as a Te film, a film containing an organic dye, or the like is formed as a recording layer. In the rewritable type, Tb-
A perpendicular magnetization film having magneto-optical characteristics (Kerr effect or Faraday effect), such as an Fe—Co amorphous alloy thin film, is formed as a recording layer.

The first polymer sheet 3, the second polymer sheet 4, and the adhesive layers 6, 7, 8 optically separate the first recording layer 2 and the second recording layer 5. This multilayer optical disk has two polymer sheets 3 and 4 laminated so that the stretching directions are orthogonal to each other.

That is, the polymer sheet is pulled in a certain direction when the polymer sheet is formed into a sheet at the time of production, and the molecular chains are stretched. For this reason, as shown in FIG.
And the refractive index (no) in a direction orthogonal to the stretching direction have different values. That is,
Birefringence has occurred. The birefringence b is given by b =
It is represented by d × Δn.

Here, when two polymer sheets are laminated so that the stretching directions are orthogonal to each other, the birefringences are offset each other, and the combined birefringence of the two polymer sheets is:
The thickness of the first polymer sheet is d ₁ , the difference in refractive index is Δn ₁ , the thickness of the second polymer sheet is d ₂ , and the difference in refractive index ne−
Assuming that no is Δn ₂ , b = d ₁ × Δn ₁ −d ₂ × Δn ₂ . Usually, there is almost no unevenness in the thickness of the sheet (generally d
₁ = d ₂ ), and the same refractive index difference ne-no (approximately Δn ₁ = Δ
n ₂ ), the combined birefringence b of the two polymer sheets is close to zero.

Therefore, in a multilayer optical disk in which the intermediate layer is formed by laminating the two polymer sheets 3 and 4 such that the stretching directions are orthogonal to each other, the intermediate layer is almost unaffected by the birefringence of the intermediate layer. For example, even when the signal is reproduced using the rotation of the polarization plane, a stable reproduced signal can be obtained. Further, according to this, since the birefringence of each polymer sheet does not become a problem, an appropriate polymer sheet can be freely selected in consideration of other characteristics.

As the first polymer sheet 3 and the second polymer sheet 4, sheets made of polycarbonate, polyarylate, polyethersulfone, polyethylene terephthalate, polyolefin and the like are used.
This sheet may be formed into a sheet by uniaxial stretching, or may be formed into a sheet by biaxial stretching. The appropriate thickness of the sheet is determined from the viewpoint of optically separating the recording layers and spherical aberration. That is, in this multi-layer optical disc, the total thickness of the two polymer sheets 3, 4 and the adhesive layers 6, 7, 8 corresponds to the thickness of the intermediate layer. Cannot be separated optically. As a result, crosstalk from an adjacent recording layer becomes a problem. Also, when the thickness of the intermediate layer increases,
When reading the uppermost recording layer and the lowermost recording layer with a single lens, spherical aberration cannot be ignored. The thickness of the intermediate layer optimized from such a point differs depending on the wavelength λ of the optical system used and the numerical aperture NA of the objective lens. For example, the DVD standard (wavelength λ: 635 nm, lens numerical aperture NA: 0.52) is in the range of 40 to 70 μm.
Therefore, it is desirable that the thicknesses of the polymer sheets 3 and 4 are set to be in this range together with the thicknesses of the adhesive layers 6, 7, and 8. For example, a polycarbonate sheet having a thickness of 10 to 200 μm is commercially available.

In this multi-layer optical disc, a protective layer 9 is formed on the second recording layer 5, and this protective layer 9 is formed by connecting the first recording layer 2 and the second recording layer 5 to the external environment. It is additionally provided to protect the device from moisture and impact. The protective layer 9 is formed, for example, by applying and curing an ultraviolet curable resin.

Although an example of the multilayer optical disk has been described above, the recording layers of the multilayer optical disk are not limited to two layers, and may be further laminated.

Also in this case, when two polymer sheets are laminated between the recording layers so that the stretching directions are orthogonal to each other, the influence of the birefringence of the intermediate layer is hardly exerted, and the stability of each recording layer is reduced. A reproduced signal is obtained.

Next, the manufacturing process of this multilayer optical disc will be described.
This will be described with reference to FIGS. In order to manufacture a multilayer optical disk, first, a single-plate disk 17 having a first recording layer formed on a transparent substrate, a first polymer sheet and a second polymer sheet are laminated via an adhesive layer. Each of the polymer sheet laminates 19 is manufactured.

In order to manufacture the single-plate disk 17, a transparent substrate having a concave and convex pattern corresponding to the first recording layer is prepared. The formation of the concavo-convex pattern is performed by an injection molding method or the like when plastic is used as a substrate material, and by a 2P method when a glass substrate is used. Then, a first recording layer is formed on the uneven pattern of the transparent substrate by sputtering or the like.

On the other hand, as shown in FIG. 3, a Ni stamper 1 having a reverse pattern of the concavo-convex pattern corresponding to the second recording layer was formed in order to produce the polymer sheet laminate 19.
1 is prepared, and an ultraviolet curable resin 1 is placed on the stamper 11.
2 is applied in a circular shape, for example, and a second polymer sheet 13 punched in a disk shape is placed thereon. continue,
An ultraviolet curable resin 14 is placed on the second polymer sheet 13.
Is applied, and a first polymer sheet 15 punched in a disk shape is placed on the first polymer sheet 15 so that the stretching direction is orthogonal to the second polymer sheet 13. When stacking the first polymer sheet 15 and the second polymer sheet 13,
A mark indicating the stretching direction may be provided in advance on both sheets 13 and 15, and the superposition may be performed based on the mark.

Subsequently, an ultraviolet curable resin 16 is applied on the second polymer sheet 15 of the laminated body 19 produced in this manner, and the single-disc disk 1 previously produced on this is cured.
The side on which the first recording layer 7 is formed is overlapped. Then, as shown in FIG. 4, the transparent substrate of the single-plate disk 17 is pressed against, for example, a pressure roller 18 to press the ultraviolet curable resin 12 applied between the respective layers.
14 and 16 are uniformly and thinly stretched and irradiated with ultraviolet rays as shown in FIG.
6 is cured. Note that the pressure bonding may be performed by a flat plate press, instead of using a pressure roller. Further, it may be arranged to be pressed with a hemispherical or conical rubber or the like from directly above.

Thereafter, as shown in FIG. 6, the stamper 11 under the second polymer sheet 13 is peeled off, and the second polymer sheet 13 is peeled off from the ultraviolet curable resin 12 by a sputtering method or the like. Is formed. Through the above steps, a two-layer optical disc is manufactured.

In the case of further laminating a recording layer, the second recording layer and a laminate of a polymer sheet produced in the same manner as described above are overlaid with an ultraviolet curable resin, and pressed. UV irradiation, stamper peeling, and formation of a recording layer are sequentially performed. Further, by repeating this step, a further multilayered recording layer is formed.

When an optical disk was actually manufactured according to this manufacturing process, the birefringence of the two polymer sheets was reduced to 1/10 or less of the birefringence of one sheet. A good reproduction signal can be obtained. The configuration of the manufactured optical disk is as follows.

Transparent substrate: Injection molded substrate made of polycarbonate having a thickness of 0.6 mm First recording layer: Si—N translucent film Second recording layer: Al reflective film First polymer sheet, second high layer Molecular sheet: thickness 50μ
The polycarbonate sheet (birefringence: 20 nm) is a laminated type multilayer optical disc. The present invention relates to a laminated type multi-layer optical disc formed by laminating two transparent substrates on each of which a recording layer is formed. It can also be applied to optical discs.

That is, this multilayer optical disk has a first transparent substrate 2 on which a concavo-convex pattern is formed as shown in FIG.
1 and a second recording layer 24 on a second transparent substrate 23 on which an uneven pattern is formed.
Are formed, and the first transparent substrate 21 and the second transparent substrate 23 are attached to each other with the recording layers 22 and 24 facing each other and a first polymer sheet 25 and a second polymer sheet 26 interposed therebetween. It is configured. Note that the first recording layer 22,
Adhesive layers 27, 28, and 29 made of an ultraviolet curable resin are interposed between the first polymer sheet 25, the second polymer sheet 26, and the second recording layer 24, respectively.

Here, in this multilayer optical disk, two polymer sheets 25 and 26 are laminated so that the stretching directions are orthogonal to each other. Also in this case, two polymer sheets 2
Since the birefringences 5 and 26 cancel each other, the combined birefringence of the two polymer sheets 25 and 26 can be suppressed to almost zero. Therefore, in this multilayer optical disc,
A stable reproduction signal is obtained without being substantially affected by the birefringence of the intermediate layer.

In this multilayer optical disk, the transparent substrates 21, 23, the recording layers 22, 24, and the polymer sheet 2
As the layers 5 and 26, any of those exemplified as a multilayer optical disk of a laminated type can be used.

The recording layers 22 and 24 formed on the first transparent substrate 21 and the second transparent substrate 23 are not limited to one layer.
It may be a multilayer. Also in this case, when two polymer sheets are laminated between the recording layers so that the stretching directions are orthogonal to each other, there is almost no influence of the birefringence of the intermediate layer,
A stable reproduction signal can be obtained from each recording layer.

The manufacturing process of such a laminated type optical disc will be described with reference to FIGS.

In order to manufacture a multilayer optical disk, first, a first transparent substrate 30 having an uneven pattern corresponding to the first recording layer and a second transparent substrate having an uneven pattern corresponding to the second recording layer Prepare 36. And this first
Each of the transparent substrate 30 and the second transparent substrate 36,
A first recording layer and a second recording layer are formed by a sputtering method or the like.

Then, as shown in FIG. 8, an ultraviolet curable resin 31 is applied on the first recording layer formed on the first transparent substrate 30, and then the first polymer sheet 32 is placed thereon. Then, after an ultraviolet curable resin 33 is applied on the first polymer sheet 32, the second polymer sheet 34 is placed. At this time, the stretching directions of the first polymer sheet 32 and the second polymer sheet 34 are orthogonal to each other. Next, an ultraviolet curable resin 35 is applied on the second polymer sheet 34, and a second transparent substrate 36
The second recording layer formed in the above is overlaid.

Then, as shown in FIG. 9, the transparent substrate 36 is pressed against, for example, a pressure roller 37 to spread the ultraviolet curing resins 31, 33, 35 applied between the respective layers uniformly and thinly. After that, as shown in FIG. 10, the ultraviolet curable resin is cured by irradiating ultraviolet rays. Through the above steps, a laminated type multilayer optical disc is manufactured.

Here, when a plurality of recording layers are formed on the first transparent substrate and the second transparent substrate, a plurality of recording layers are formed on the transparent substrate in accordance with the above-mentioned multilayer optical disc of the laminated type. What is necessary is just to laminate | stack and form via two polymer sheets.

When an optical disk was actually manufactured in accordance with this process, the birefringence of the two polymer sheets was reduced to 1/10 or less of the birefringence of one sheet. A reproduced signal can be obtained.

The configuration of the manufactured optical disk is as follows.

First transparent substrate, second transparent substrate: injection molded substrate made of polycarbonate having a thickness of 0.6 mm First recording layer: semi-transparent Si—N film Second recording layer: Al reflective film First Polymer sheet, second polymer sheet: thickness 25μ
m polycarbonate sheet

[0052]

As is clear from the above description, in the multilayer optical disc of the present invention, two polymer sheets are laminated between the recording layers so that the stretching directions are orthogonal to each other. A stable reproduction signal can be obtained without being affected by the birefringence of the sheet, for example, even when the signal is reproduced by rotating the polarization plane.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part showing an example of a multilayer optical disc to which the present invention is applied.

FIG. 2 is a schematic diagram for explaining birefringence of a polymer sheet.

FIG. 3 is a schematic view illustrating a method of manufacturing a laminated optical disk in the order of steps, and illustrating a step of laminating a laminated body of polymer sheets and a single-plate disk.

FIG. 4 is a schematic view showing a pressure bonding step using a roll.

FIG. 5 is a schematic view showing an ultraviolet irradiation step.

FIG. 6 is a schematic view showing a stamper peeling step.

FIG. 7 is a schematic sectional view of a main part showing another example of a multilayer optical disc to which the present invention is applied.

FIG. 8 shows a method of manufacturing a bonding type optical disk in the order of steps, and illustrates a bonding step of a first transparent substrate, a first polymer sheet, a second polymer sheet, and a second transparent substrate. FIG.

FIG. 9 is a schematic view showing a pressure bonding step using a roll.

FIG. 10 is a schematic view showing an ultraviolet irradiation step.

[Explanation of symbols]

1 21,23 transparent substrate, 2,22 first recording layer,
5,24 second recording layer, 3,25 first polymer sheet, 4,26 second polymer sheet

Claims (2)

[Claims] 1. A multilayer optical disc having a plurality of recording layers laminated on a transparent substrate via an intermediate layer, wherein the intermediate layer is formed by laminating two polymer sheets so that stretching directions are orthogonal to each other. A multilayer optical disc characterized by being formed by: 2. After forming a first recording layer on a transparent substrate, a first polymer sheet is adhered on the recording layer, and a second polymer sheet is further formed on the first polymer sheet. A method for manufacturing a multilayer optical disk, comprising: bonding a polymer sheet to a first polymer sheet so that a stretching direction is orthogonal to each other, and forming a second recording layer thereon.