JP2001273680A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk having no deterioration of signal characteristics but high quality by keeping the increase of birefringence in a light transmission layer to a minimum. SOLUTION: This optical disk 10 has a reflection film 3, an addhesive layer 8 and a resin film layer 6 thinner in thickness than a substrate 2 laminated in this order on the substrate 2 having an information signal 1 of an uneven or grooved shape so that the signal 1 on the substrate 2 can be reproduced through the layers 6 and 8. The layer 8 has 100 μm or thinner thickness and the multiplication product of the photoelastic constant, the elastic modulus and the thickness of the resin film of the layer 6 is -0.2 to 0.2 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density optical disk, and more particularly to an optical disk for reading a signal through a resin film and an adhesive.

[0002]

2. Description of the Related Art In recent years, in the field of information recording, researches on optical information recording systems have been conducted in various places. This optical information recording system is capable of non-contact recording and reproduction, achieving a recording density that is at least an order of magnitude higher than the magnetic recording system, and can be used in read-only, write-once, and rewritable memory formats. It has many advantages such as being able to cope with it, and a wide range of applications from industrial use to consumer use is considered as a method that enables realization of inexpensive large-capacity files. Among them, digital audio disks, optical video disks, and the like, which are optical disks corresponding to a read-only memory type, are widely used.

In the optical disk such as the above digital audio disk, a reflective film made of a metal thin film such as an aluminum film is formed on an optical disk substrate which is a transparent substrate on which an uneven pattern such as pits or grooves indicating information signals is formed. Further, a protective film for preventing corrosion and damage of the reflective film is formed on the reflective film. When reproducing information from such an optical disk, the uneven pattern is irradiated with reproduction light such as laser light from the optical disk substrate side, and the information is detected by the difference between the reflectance of the incident light and the return light. Then, when manufacturing such an optical disk, first, an optical disk substrate having the above-mentioned concavo-convex pattern is formed by a method such as injection molding, and a reflective film made of the metal thin film is formed thereon by a method such as evaporation.
Further, an ultraviolet-curable resin or the like is applied thereon to form the protective film.

Recently, higher recording density has been demanded, and in order to cope with this, the numerical aperture (hereinafter, referred to as NA) of an objective lens for irradiating reproduction light of an optical pickup is increased. It has been proposed to reduce the spot diameter of the reproduction light. For example, while the NA of an objective lens of a digital audio disc that has been used so far is 0.45, an optical video that has recently attracted attention because it has a recording capacity of 6 to 8 times that of a digital audio disc. Disk (for example, Digital
Versatile Disc (hereinafter referred to as DVD)
The NA of the objective lens is about 0.60.

When the NA of the objective lens is increased as described above, it is necessary to reduce the thickness of the substrate of the optical disk through which the reproduction light is irradiated and through which the reproduction light passes. This is because the allowable amount of the angle (tilt angle) at which the disk surface deviates from the perpendicular to the optical axis of the optical pickup becomes small, and this tilt angle is easily affected by aberration and birefringence due to the thickness of the substrate. That's why. Therefore, the thickness of the substrate is reduced to minimize the tilt angle. For example, in the above-mentioned digital audio disk, the thickness of the substrate is about 1.2 mm, whereas the optical video disk which has a recording capacity 6 to 8 times that of a digital audio disk such as a DVD, for example. In
The thickness of the substrate is about 0.6 mm.

However, it is expected that higher recording density will be required in the future, and it will be necessary to further reduce the thickness of the substrate. Therefore, for example, irregularities are formed on one main surface of the substrate to form an information recording layer, a reflective film is provided thereon, and a light transmitting layer, which is a thin film that transmits light, is provided thereon. There has been proposed an optical recording medium which reproduces information in an information recording layer by irradiating a reproducing light from the optical recording medium. In this case, it is possible to cope with a high NA of the objective lens by reducing the thickness of the light transmission layer.

However, when the light transmitting layer is made thinner in this way, it becomes difficult to form the light transmitting layer by injection molding using a thermoplastic resin, which is a common technique in the production of optical disks. For example, it is almost impossible at present to form a 0.1 mm light transmitting layer with small birefringence and good transparency.

A method of forming the light transmitting layer with an ultraviolet-curable resin is disclosed in Japanese Patent Application Laid-Open No. Hei 8-235638. However, it is difficult to form a light transmitting layer having a uniform thickness. It is difficult to perform playback stably. To solve such a problem, a resin film having a thickness of about 0.1 mm is applied by pressure bonding with a roller using an adhesive or by a spin coating method using an ultraviolet-curing adhesive to form a light transmitting layer. Is disclosed in JP-A-10-2836.
No. 83, for example.

[0009]

Incidentally, one of the important characteristics of the optical disc is the birefringence of the light transmitting layer through which the reproduction light passes. Birefringence is a phenomenon in which light incident on an anisotropic material is split into two light waves having vibration directions perpendicular to each other. Since these two light waves travel at different speeds,
When coming out of the sample, an optical path difference (phase difference) occurs.
If this optical path difference becomes large, it adversely affects the reproduction signal characteristics. Therefore, the birefringence of the light transmitting layer must be minimized. To cope with such a problem, countermeasures such as improvement of the molding technique of the substrate and improvement of the material of the substrate have been taken, and the same countermeasure has been taken for the bonded optical disk.

However, in the case of an optical disk having a light transmitting layer formed by attaching a thin resin film with an adhesive as described above, there is a problem that the birefringence of the film increases during the step of attaching the film or during reproduction. Was. In other words, for example, in a method of applying a film by roller pressing, a stress distortion occurs partially in a film surface due to a variation in pressure from a roller or a variation in the thickness of an adhesive, and the birefringence is caused by the signal distortion due to the stress distortion. In particular, it increases to a level that affects the fluctuation of the reproduction signal output during one round.

On the other hand, in a method of attaching a film by a spin coating method using an ultraviolet-curable adhesive, the amount of ultraviolet light is increased to increase the curing speed of the adhesive, When curing is performed with air bubbles involved, curing distortion occurs in the adhesive layer.
In addition, since the optical disk is rotated at a high speed during reproduction, distortion of the adhesive layer also occurs due to centrifugal force.
When distortion occurs in the adhesive layer as described above, since the film is in direct contact with the adhesive layer, the distortion of the adhesive layer also causes distortion in the film and increases birefringence.

Further, when used under conditions of high temperature and high humidity (for example, in a car in the middle of summer), the light transmitting layer is made of resin, so that it naturally becomes soft, and as a result, the amount of distortion increases, and the birefringence also increases. There was also a problem in terms of reliability. The present invention has been made in view of the above problems, to increase the curing speed of the adhesive, in the unlikely event that dust or air bubbles are involved, and also minimize the increase in birefringence even during high-speed rotation, It is an object of the present invention to provide a high-quality optical disk without deterioration of signal characteristics.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a reflection film 3, an adhesive layer 8, and a substrate are provided on a substrate 2 having an information signal 1 having an uneven shape or a groove shape. In an optical disc 10 for laminating a resin film layer 6 having a thickness smaller than 2 in this order and reproducing the information signal 1 on the substrate 2 through the resin film layer 6 and the adhesive layer 8,
The thickness of the adhesive layer 8 is 100 μm or less, and
This problem has been solved by providing the optical disc 10 in which the multiplied value of the photoelastic constant, the tensile elastic modulus and the thickness of the resin film of the resin film layer 6 is in the range of -0.2 to 0.2 mm.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The advantages of such a solution will be described in detail below. That is, the present inventors have conducted intensive studies on the above problems, and as a result, have found that the photoelastic constant, the tensile elastic modulus, and the thickness of the resin film used as the light transmitting layer have a large effect. . Even when a homogeneous isotropic transparent object generates internal stress, it becomes optically anisotropic and temporarily exhibits birefringence.This phenomenon is known as a photoelastic phenomenon. ) Is a proportionality constant between the internal stress and the birefringence as shown by the equation. Δn = C · σ (1) where Δn: birefringence C: photoelastic constant σ: internal stress The optical path difference is a problem in the reproduction of the optical disk, and the optical path difference is expressed by equation (2). Is done. R = Δ
n · d = C · σ · d (2) where R: optical path difference Δn: birefringence d: optical path length C:
Photoelastic constant σ: internal stress

[0015] The photoelastic phenomenon is a phenomenon that is caused by the occurrence of strain when stress is applied and the molecular orientation caused by the strain. It is known that the cause of the birefringence of the optical disk substrate is also the molecular orientation. I have. Therefore, also in the conventional resin film for the light transmitting layer, the birefringence of the light transmitting layer is reduced by using a material having a small photoelastic constant or controlling the molecular orientation by molding conditions. However, the photoelastic constant has temperature dependency, and when the temperature rises and the material becomes soft, the photoelastic constant also increases. This is because when the material becomes softer, the amount of strain when stress is applied increases, and as a result, the molecular orientation also increases. Therefore, as a material for the light transmitting layer of the optical disk which is also expected to be used under severe conditions such as high temperature and high humidity, the usage conditions of the optical disk cannot be satisfied even if only the photoelastic constant is considered.

Therefore, the present inventors paid attention to the tensile elastic modulus of the plastic film together with the photoelastic constant. The tensile modulus represents the mechanical strength of a material, and has a temperature dependence completely opposite to the photoelastic constant that decreases with increasing temperature. The value obtained by multiplying the photoelastic constant and the tensile elastic modulus negates the temperature dependence of each other, so that it becomes a new physical property value without temperature dependence, and this physical property value is kept within a certain range. In this case, an increase in birefringence can be suppressed even under high temperature and high humidity environmental conditions. An optical path difference between the two separated lights directly causes a problem in the reproduction of the optical disk. The optical path difference is proportional to the optical path length, that is, the film thickness, as can be seen from the equation (2). Therefore, if the value obtained by multiplying the physical property value obtained by multiplying the above-described photoelastic constant and the tensile elastic modulus by the film thickness is kept within a certain range, it is possible to provide an optical disc with very high quality and high reliability. I found it.

It has also been found that the above-mentioned problem is closely related to the thickness of the adhesive for bonding a thin resin film. Since the distortion generated in the resin film is caused by the distortion generated in the adhesive, when the thickness of the adhesive is small, the influence of the distortion generated in the adhesive layer is less likely to be exerted on the resin film. . Conversely, if the thickness is large, the effect on the resin film will be large,
In that case, the influence of the birefringence of the adhesive layer itself becomes larger than that of the resin film, and the above physical property values cannot be applied. Therefore, the present invention has solved the above-mentioned problem which occurs in an optical disc which is a light transmitting layer by laminating a thin resin film via an adhesive, by constituting the invention as described in the claims.

The optical disk of the present invention can be applied to any type of optical disk, such as a read-only type, a write-once type, and a recordable type. In the case of the read-only type, a reflective layer made of a metal layer is formed on the pit side of the substrate on which the information signal having a concave-convex shape called a pit is formed by a sputtering method or the like, and the reflective layer surface and the resin film are bonded with an adhesive. It is produced by sticking together.

In the case of the write-once type, a reflective layer made of a metal layer is formed on a substrate on which a guide groove and a pit for information for reproduction only in some cases are formed. The recording layer is formed by spin coating or the like, and the recording layer surface is bonded to a resin film via an adhesive.

In the case of the recordable type, a reflective layer, a second dielectric layer, a recording layer, and a first dielectric layer are formed on a substrate on which guide grooves and, in some cases, signals such as embossed pits for address signals are formed. The layers are sequentially formed by a sputtering method or the like. Then, it is manufactured by bonding the first dielectric layer surface and the resin film via an adhesive.

A reflective layer composed of a metal layer is formed on any of the above types of optical discs. The material of the reflective layer may be a metal such as Au, Al, Ag, Pt, Pd, Ni, Cu, a metal alloy, or a metal. Compounds and the like are used.

Examples of the material of the recording layer made of an organic dye of the write-once type include a cyanine dye, a merocyanine dye, an azomethine dye, an azo dye, a phthalocyanine dye which exhibit an absorption spectrum capable of absorbing a laser used for recording information. A metal complex having a dye structure as a ligand is used.

As the material of the first and second dielectric layers in the recordable type, metal oxides, nitrides, and sulfides such as ZnS—SiO ₂ , ZnS, SiO ₂ , and Ta ₂
O ₅ , Si ₃ N ₄ , AlN, Al ₂ O ₃ , AlSiON, Z
A simple substance such as rO ₂ or TiO ₂ or a mixture thereof is used. As a material for the recording layer, a phase change material utilizing a change in reflectance or a change in refractive index between amorphous and crystal, for example, a Ge-Sb-Te system or an Ag-In-Te-Sb system is used.

The type of the resin film is not particularly specified, and may be made of, for example, light having a reproduction wavelength of an optical disk such as polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polystyrene, poly-α-methylstyrene, and triacetyl cellulose. Any material can be used as long as it is transparent.

The magnitude of the photoelastic constant largely depends on the molecular structure of the material, and preferably has a molecularly isotropic structure. However, the photoelastic constant is preferably positive (for example, polycarbonate or polyethylene terephthalate). ) And negative (for example, polymethyl methacrylate or poly-α-methylstyrene), which can be controlled by appropriately blending them. Although the magnitude of the tensile modulus is also affected by the molecular structure, it is also possible to increase the strength by performing a stretching treatment after molding. Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0026]

Embodiment 1 As shown in FIG. 1, for example, a polycarbonate substrate 2 having a diameter of 120 mm and a thickness of 0.9 mm on which a pit group 1 of EFM signals having a shortest pit length of 0.4 μm and a track pitch of 0.74 μm is formed. Is formed by injection molding, and a reflective film 3 of aluminum is formed on the pit group 1 to a thickness of about 600 ° by a sputtering method. The pits were formed with a Kr laser beam having a wavelength of 413 nm. Then, the optical disk substrate on which the reflective film 3 is formed is mounted on a turntable 4 of a spin coater with the reflective film 3 facing up (FIG. 1A). An ultraviolet-curable adhesive 5 is applied thereon (FIG. 1b).

Next, a doughnut-shaped light transmitting layer resin film 6 having an outer diameter of 119 mm, an inner diameter of 30 mm, and a thickness of 300 μm, which is slightly smaller than the previously prepared polycarbonate substrate 2, is applied. Place on adhesive 5 (FIG. 1c). After that, turntable 4
Is rotated at a high speed, and excess adhesive 7 is shaken off to form an adhesive layer 8 between the reflective film 3 and the resin film 6 (FIG. 1d).

Thereafter, the adhesive layer 8 is cured by irradiating ultraviolet rays 9 from the resin film 6 side, thereby producing a read-only optical disk 10 (FIG. 1e). The thickness of the cured adhesive layer 8 was set to 5 μm by controlling the rotation speed of the turntable.

At this time, when an optical disk 10 made of a plastic film for a light transmitting layer having various photoelastic constants, tensile elastic moduli, and thicknesses is used, when reproduction light is incident from the resin film side and a signal is read. The fluctuation of the reproduction signal amplitude during one round during reproduction is measured at a wavelength of 670 nm and a numerical aperture NA of 0.7.
Was measured using a laser pickup. The tensile modulus was measured in accordance with the test method ASTM-D638, and the photoelastic constant was measured with an ellipsometer to a thickness of 100 μm.
Calculated from birefringence measurement by a load change at a wavelength of 633 nm using a m.

FIG. 2 shows the optimum range of the resin film. The horizontal axis represents the value of photoelastic constant × tensile modulus × thickness,
The vertical axis shows the maximum value / minimum value of the amplitude of the reproduced signal during one round. As is clear from this figure, the photoelastic constant, the tensile modulus and the thickness were both measured at 23 ° C. as a normal ambient temperature and at 80 ° C. where the temperature condition was stricter than the upper limit of the current standard value of this kind of optical disc. It can be seen that good signal characteristics can be obtained by setting the multiplied value in the range of -0.2 to 0.2 mm. That is,
Even under such a condition having a temperature difference, if the multiplied value of the photoelastic constant, the tensile elastic modulus and the thickness of the resin film is set in the above range, environmental degradation is small, in other words,
Thus, a high-quality and highly reliable optical disk having no temperature dependency can be obtained.

[0031]

Examples 2 to 5 In Examples 2 to 5, only the thickness of the adhesive layer was set to 20 μm, 40 μm, 70 μm, and 100 μm, and the results of evaluation by the same method as in Example 1 were shown in FIGS. Show. It can be seen that good signal characteristics can be obtained for any film thickness by setting the multiplication value of the photoelastic constant, the tensile modulus and the thickness in the range of -0.2 to 0.2 mm.

[0032]

Comparative Examples 1 to 3 In Comparative Examples 1 to 3, only the thickness of the adhesive layer was set to 120 μm, 150 μm, and 200 μm, and the results were evaluated by the same method as in Example 1 except for the results shown in FIGS.
Shown in It can be seen that the fluctuation of the reproduction signal amplitude is large irrespective of the photoelastic constant, the tensile elastic modulus and the product of the thickness. That is, it is understood that the thickness of the adhesive layer must be 100 μm or less.

[0033]

Embodiment 6 A polycarbonate substrate having a diameter of 120 mm and a thickness of 1.1 mm on which a pit group of an EFM signal having a shortest pit length of 0.254 μm and a track pitch of 0.6 μm is formed, an outer diameter of 119 mm, an inner diameter of 30 mm, and a thickness of 100
An optical disk was produced in the same manner as in Example 1 using a μm resin film. The pits were formed by an Ar laser beam having a wavelength of 351 nm. When the relationship between the characteristic value and the jitter value was examined using a laser pickup having a wavelength of 413 nm and a lens NA of 0.8, the product of the photoelastic constant, the tensile elastic modulus and the thickness was determined to be -0.0. Good signal characteristics could be obtained by setting the range of 2 to 0.2 mm.

[0034]

Comparative Example 4 In Example 6, the thickness of the adhesive layer was set to 120
The results were evaluated by the same method as in Example 6 with μm, 150 μm, and 200 μm. As a result, the fluctuation of the reproduction signal amplitude became large irrespective of the value obtained by multiplying the photoelastic constant, the tensile elastic modulus and the thickness.

[0035]

Embodiment 7 A polycarbonate substrate having a diameter of 120 mm and a thickness of 1.1 mm on which pit groups of EFM signals having a shortest pit length of 0.19 μm and a track pitch of 0.36 μm are formed, an outer diameter of 119 mm, an inner diameter of 30 mm, and a thickness of 100
An optical disk was produced in the same manner as in Example 1 using a μm resin film. The pits are formed at a wavelength of 266.
The measurement was performed by using a YAG fourth harmonic laser light of nm. When the relationship between the characteristic value and the jitter value was examined using a laser pickup having a wavelength of 413 nm and a lens NA of 0.8, the value obtained by multiplying the photoelastic constant, the tensile elastic modulus, and the thickness was − By setting the thickness in the range of 0.2 to 0.2 mm, good signal characteristics could be obtained.

[0036]

Comparative Example 5 In Example 7, the thickness of the adhesive layer was changed to 120.
The results were evaluated by the same method as in Example 7 with μm, 150 μm, and 200 μm. As a result, the fluctuation of the reproduction signal amplitude became large regardless of the value obtained by multiplying the photoelastic constant, the tensile elastic modulus and the thickness.

[0037]

Example 8 A polycarbonate substrate having a diameter of 120 mm and a thickness of 0.9 mm in which a guide groove having a track pitch of 0.36 μm is formed is prepared by injection molding, and a Au reflection layer is formed on the guide groove by about 600 ° by sputtering. The organic dye metal complex represented by Chemical Formula 1 was formed as a recording layer on the reflective layer by spin coating.

[0038]

Embedded image

Then, a resin write-once optical disk was manufactured by bonding resin films in the same manner as in Example 1. The EFM signal was recorded using a laser pickup having a wavelength of 413 nm and a lens NA of 0.8, and the jitter value of the reproduced signal was examined. As in Example 1, the value obtained by multiplying the photoelastic constant by the tensile elastic modulus and the thickness was obtained. From -0.2 to
By setting the distance in the range of 0.2 mm, good signal characteristics could be obtained.

[0040]

Comparative Example 6 In Example 8, the thickness of the adhesive layer was changed to 120.
The results were evaluated in the same manner as in Example 8 with μm, 150 μm, and 200 μm. As a result, the fluctuation of the reproduction signal amplitude became large regardless of the value obtained by multiplying the photoelastic constant, the tensile elastic modulus and the thickness.

[0041]

Embodiment 9 A polycarbonate substrate having a diameter of 120 mm and a thickness of 0.9 mm in which a guide groove having a track pitch of 0.36 μm is formed by injection molding, and a reflective layer of Al—Ti is formed on the guide groove by sputtering. 150
nm, a second dielectric layer (ZnS—SiO ₂ ) and a phase change recording layer (composition: Ag0.0) on the reflective layer.
5-In0.05-Te0.30-Sb0.60) , was the first dielectric layer (ZnS-SiO ₂₎ were sequentially formed by sputtering. Each film thickness is 20n of the second dielectric layer.
m, the phase change recording layer was 23 nm, and the first dielectric layer was 50 nm. Then, a recordable optical disk was manufactured by bonding a resin film in the same manner as in Example 1. The EFM signal was recorded using a laser pickup having a wavelength of 413 nm and a lens NA of 0.8, and the jitter value of the reproduced signal was examined. As in Example 1, the value obtained by multiplying the photoelastic constant by the tensile elastic modulus and the thickness was obtained. From -0.2 to
By setting the distance in the range of 0.2 mm, good signal characteristics could be obtained.

[0042]

Comparative Example 7 In Example 9, the thickness of the adhesive layer was set to 120
The results were evaluated by the same method as in Example 9 with μm, 150 μm, and 200 μm. As a result, the fluctuation of the reproduction signal amplitude became large regardless of the value obtained by multiplying the photoelastic constant, the tensile elastic modulus and the thickness.

In the embodiment of the present invention, an example in which a UV resin is used as an adhesive has been described. However, the present invention is not limited to this. For example, a two-part epoxy adhesive may be used. Or any transparent material that can be used as an adhesive and a light-transmitting layer, such as an anaerobic adhesive, a primer-curable adhesive, a cyanoacrylate-based adhesive, or a plastic sheet coated with an adhesive on both sides. This is clear from the gist of the present invention.

[0044]

As described above, according to the present invention, a reflective film, a reflective film,
An adhesive layer, a resin film layer having a thickness smaller than that of the substrate are laminated in this order, and in an optical disc for reproducing an information signal on the substrate through the resin film layer and the adhesive layer, the thickness of the adhesive layer is 100 μm or less. And by setting the multiplication value of the photoelastic constant, the tensile elastic modulus, and the thickness of the resin film of the resin film layer in the range of −0.2 to 0.2 mm, severe operating environment conditions such as high temperature and high humidity Also, it is possible to provide a high quality and high reliability optical disc having excellent reproduction signal characteristics.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a manufacturing process of an optical disc according to the present invention.

FIG. 2 is a diagram showing a relationship between a photoelastic constant, a tensile elastic modulus, and a product of a thickness of a resin film and a maximum value / minimum value of an amplitude of a reproduced signal during one round in an optical disc according to the present invention. It is explanatory drawing of an example.

FIG. 3 is a diagram showing another relationship between the multiplied value of the photoelastic constant, the tensile elastic modulus, and the thickness of the resin film and the maximum value / minimum value of the amplitude of the reproduced signal during one round in the optical disc according to the present invention. It is explanatory drawing of an Example.

FIG. 4 is a diagram showing another relationship between the photoelastic constant, the tensile elastic modulus, and the product of the thickness of the resin film and the maximum value / minimum value of the amplitude of the reproduced signal during one round in the optical disc according to the present invention. It is explanatory drawing of an Example.

FIG. 5 is a diagram showing another relationship between the photoelastic constant, the tensile elastic modulus, and the product of the thickness of the resin film and the maximum / minimum value of the amplitude of the reproduced signal during one round in the optical disc according to the present invention. It is explanatory drawing of an Example.

FIG. 6 is a diagram showing another relationship between the photoelastic constant of the resin film, the product of the tensile elastic modulus and the thickness, and the maximum value / minimum value of the amplitude of the reproduced signal during one round in the optical disc according to the present invention. It is explanatory drawing of an Example.

FIG. 7 is an explanatory diagram of a comparative example showing a relationship between a photoelastic constant, a tensile elastic modulus, and a multiplied value of a thickness of a resin film, and a maximum value / minimum value of an amplitude of a reproduced signal during one round.

FIG. 8 is an explanatory diagram of another comparative example showing a relationship between a photoelastic constant, a tensile elastic modulus, and a multiplied value of a thickness of a resin film, and a maximum value / minimum value of amplitude of a reproduced signal during one round. .

FIG. 9 is an explanatory diagram of another comparative example showing a relationship between a photoelastic constant, a tensile elastic modulus, and a multiplied value of a thickness of a resin film, and a maximum value / minimum value of an amplitude of a reproduced signal during one round. .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Information signal 2 Substrate 3 Reflective film 6 Resin film layer 8 Adhesive layer 10 Optical disk

Claims (1)

[Claims] 1. A reflective film, an adhesive layer, and a resin film layer having a thickness smaller than that of the substrate are laminated in this order on a substrate having an information signal in an uneven shape or a groove shape, and the resin film layer and the adhesive layer are passed through the resin film layer and the adhesive layer. In an optical disc for reproducing information signals on a substrate, the thickness of the adhesive layer is 100 μm or less, and the product of the photoelastic constant, tensile modulus and thickness of the resin film of the resin film layer is −0. 0.2 to 0.2
An optical disc characterized by being in the range of mm.