JPH11144325A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the high quality lamination type optical disk in which the increase in double refraction is minimized and no deterioration in the signal characteristics is observed even when the hardening speed of an adhesive is accelerated or dust and air bubbles are trapped or in a high speed rotation. SOLUTION: One information signal surface L1 and a reflection film 2 are formed on one surface of a substrate 1B. Moreover, the other information signal surface L0 and a semitransparent film 3 are formed on one surface of a transparent substrate 1A. Then, the substrates 1A and 1B are laminated together through adhesive 4 so that the surfaces L0 and L1 are made mutually opposite to each other. Thus, the one side two layer reproducing type optical disk is realized in which the information signals recorded on the surfaces L0 and L1 are read from the transparent substrate side. In order to reduce the internal stress of the adhesive 4 generated during the laminating, the numerical value, which is defined by multiplying the photoelastic constant of the adhesive 4 and the film thickness together, is set to less than 2.0×10<-4> mm<3> /kg within the operating temperature range of the disk. Thus, the increase in double refraction is minimized even when the hardening speed of the adhesive 4 is accelerated or dust and air bubbles are inadvertently trapped or in a high speed rotation operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an optical disk having at least two recording medium layers.

[0002]

2. Description of the Related Art Conventionally, information is recorded on a transparent substrate such as an unrecorded recording medium layer on one surface of a disk-shaped transparent substrate, or a reflective layer formed on uneven pits in which a predetermined information signal is recorded in advance. 2. Description of the Related Art A bonded optical disk has been put to practical use by using a disk substrate having a medium layer formed thereon and bonding the recording medium layers via an adhesive so that the surfaces of the recording medium layers face each other. In this optical disk, information is recorded and reproduced by laser light from both sides or one side of the disk.

FIG. 15 shows an example of the structure of a conventional bonded optical disk. As shown in the figure, a substrate 22 made of a transparent resin such as polycarbonate or polymethyl methacrylate on which information signals 21 are imprinted in an uneven manner.
Substrates having a reflective layer 23 made of aluminum or the like thereon and, if necessary, having a protective layer 24 made of an ultraviolet curable resin or the like are bonded together via an adhesive 25 such that the protective layers 24 face each other. ing. As the adhesive 25, for example, an ultraviolet curable resin (hereinafter, referred to as a UV resin)
Is used. In addition, in addition to this, a single-sided recording / reproducing type in which an information signal or a reflection layer is not formed on one substrate 22A as shown in FIG. 16 or a reflection layer having a reflectance of 15 to 30% as shown in FIG. By making the semi-transparent layer 26 of a degree, a single-sided dual-layer reproduction type optical disc capable of reading both signals by laser light from one side, or FIG.
8, a double-sided double-layered optical disk in which an information signal 21 </ b> A having another information signal 21 </ b> A laminated on the substrate 22 on which the information signal 21 is engraved is attached to face each other. and so on.

[0004] In this case, the surface of the information signal 21 of the first layer on the outer side is coated with a translucent layer 26. In addition, as an optical disc of a two-layer reproduction type, as shown in FIG. 19, a semi-transparent film 29 is formed on a substrate 28 on which an information signal 21 is imprinted, and another layer is formed by an intermediate film 30. There is also an optical disc having a structure in which an information signal 21A is stacked and a reflective layer 31 and a protective film 32 are formed thereon. In the illustrated example, the back surface of the reflective film or the translucent film is shown as flat, but in practice, this portion is naturally formed along the uneven marking of the information signal. FIG.
5 to 19, c is a center hole.

[0005]

One of the important characteristics of an optical disk is birefringence generated on the disk substrate. 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, an optical path difference (phase difference) occurs when coming out of the sample. When the optical path difference is increased, the jitter value of the reproduced signal is increased, which adversely affects the signal characteristics. The jitter value is one of the important indicators to know the performance of the signal recorded on the optical disk, and indicates the degree of variation of the reproduced signal.The smaller the value, the higher the quality of the optical disk. it can. In other words, an optical disc having a small jitter value has a margin (margin) against the disc tilt or the warpage of the disc caused by a change in temperature and humidity when used in a drive or when clamped on a spindle. That is, stable reproduction can be performed.

On the other hand, if the jitter value is originally large, the jitter value further increases due to a change in the use environment, and accordingly, it becomes difficult to separate the pits (separation of the reproduction signal) by the pickup, and in some cases, the C1 error increases. In severe cases, the reproduction of the optical disk itself becomes impossible. Birefringence is one factor that affects the jitter value, and the birefringence of the disk substrate 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 substrate.

[0007] In the case of a two-layer reproduction type optical disk as shown in FIGS. 17 to 19, since the laser beam passes through the adhesive 25 and the intermediate film 30, not only the substrate but also an adhesive made of UV resin, for example. Also, the birefringence of the intermediate film has an adverse effect. Since the thickness of the adhesive or the intermediate film is as thin as 50 to 60 μm, it is often considered that the influence of the birefringence on the signal characteristics is not so large. When bubbles are involved, the curing strain that causes an increase in birefringence partially increases, and the birefringence increases to a level that affects signal characteristics. In addition, since the optical disk is rotated at a high speed during use, the adhesive and the intermediate film are distorted due to centrifugal force and cause an increase in birefringence. In addition to this, the increase in birefringence due to stress distortion due to clamping and stress distortion due to warpage cannot be ignored. However, at present, no measures have been taken against these problems.

Accordingly, the present invention has been made in view of the above-mentioned problems, and is intended to increase the curing speed of the adhesive, to prevent the adhesive or interlayer film from entrapping dust or bubbles, It is an object of the present invention to provide a high-quality bonded optical disk which minimizes an increase in birefringence even during rotation and does not deteriorate signal characteristics.

[0009]

The present inventors have made intensive studies on the above problems and found that the thickness of the adhesive film and the photoelastic constant of the material used as the adhesive, for example, the ultraviolet curable resin, are greatly affected. This has led to the present invention. That is, the invention defined in claim 1 is a substrate in which one information signal surface is formed on one surface and a reflective film is formed thereon, and the other information signal surface is formed on one surface and translucent on the other surface. The transparent substrate on which the film was formed was bonded via an adhesive such that the one and the other information signal surfaces faced each other, and were recorded on the one and the other information signal surfaces from the transparent substrate side, respectively. In an optical disc of a single-sided dual-layer reproduction type for reading an information signal, in order to reduce the internal stress of the adhesive generated at the time of bonding, the photoelastic constant of the adhesive is multiplied by the film thickness of the adhesive. The combined numerical value is set so as to be approximately 2.0 × 10 ⁻⁴ mm ³ / kg or less within the operating temperature range of the optical disk. As a result, it is possible to suppress the jitter during reproduction and improve the reproduction characteristics.

According to a second aspect of the present invention, one information signal surface is formed on one surface, and a translucent film is formed thereon.
Two transparent substrates on each of which a transparent intermediate film and a reflective film on which the other information signal surface is formed on the semi-transparent film are bonded together via an adhesive such that the reflective films face each other,
In an optical disc of a double-sided dual-layer reproduction type that reads information signals recorded on each information recording surface from the other surface side of both transparent substrates, the internal stress of the intermediate film generated when laminating each intermediate film is reduced. Therefore, a value obtained by multiplying the photoelastic constant of the intermediate film by the film thickness of the intermediate film is approximately 3.0 × 10 within the operating temperature range of the optical disk.
^-4 mm ³ / kg or less. Further, by setting the Young's modulus of the adhesive to 150 kg / mm ² or less within the operating temperature range of the optical disc, it is possible to obtain better reproduction characteristics.

According to the invention defined in claim 4, one information signal surface is formed on one surface of a transparent substrate, a translucent film is formed thereon, and the other information signal surface is formed on this translucent film. A transparent intermediate film and a reflective film are laminated, a protective film is provided on the reflective film, and a single-sided two-layer reproducing type for reading information signals recorded on the one and the other information signal surfaces from the transparent substrate side. In the optical disc, a value obtained by multiplying the photoelastic constant of the intermediate film by the film thickness of the intermediate film in order to reduce the internal stress of the intermediate film generated when stacking the intermediate film is determined by using the optical disc. Within the temperature range, it should be approximately 4.0 × 10 ⁻⁴ mm ³ / kg or less. In addition, as the adhesive or the intermediate film, a commonly used UV resin can be used. However, the present invention is not limited to this, and a transparent material that transmits laser light may be used. The relationship between the molecular structure of the adhesive or the interlayer and the photoelastic constant includes, for example, those having a molecular isotropic structure. Specifically, neopentyl glycol di (meth) acrylate, ethylene Glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate. Neopentyl glycol-modified trimethylolpropane di (meth) acrylate can be exemplified.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical disk according to the present invention will be described below in detail with reference to the accompanying drawings. The inventor of the present invention has achieved the present invention by finding that the thickness of the adhesive layer and the intermediate film and the photoelastic constant of the material constituting these layers have a great influence on the recording / reproducing characteristics. That is, even if a homogeneous isotropic transparent object generates internal stress, it becomes optically anisotropic and temporarily exhibits birefringence. This phenomenon is known as a photoelastic phenomenon. It turned out to be having an adverse effect. This photoelastic phenomenon is expressed by the following equation. R = Δn · d = C · σ · d (1) where R is an optical path difference, Δn is birefringence, d is an optical path length, C is a photoelastic constant, and σ is an internal stress.

[0013] That is, curing distortion generated when the adhesive layer or the intermediate film is cured by UV, stress concentration generated in the vicinity thereof due to mixing of bubbles or dust, or distortion of the adhesive layer or the intermediate film due to centrifugal force during high-speed rotation. Increase in the internal stress .sigma. Caused an increase in the optical path difference R, and as a result, adversely affected the signal characteristics. Therefore, from equation (1), if the photoelastic constant C and the optical path length (that is, the thickness of the adhesive layer and the intermediate film) d of the material used as the adhesive layer and the intermediate film are reduced, the optical path difference R can be reduced. Therefore, the influence of the internal stress can be reduced. Specifically, the value of the product (hereinafter referred to as a characteristic value) of the photoelastic constant C of the material used as the adhesive layer or the intermediate film and the film thickness (optical path length d) is referred to as a bonding type optical disc of various forms. And the optimum range was determined. Hereinafter, the optimum range according to the form of each optical disc will be described.
In each of the embodiments described below, if information can be read from both sides of the disc, the substrates on both sides must be transparent. Need not be transparent.

<First Embodiment> FIG. 1 is a schematic enlarged sectional view showing an optical disk according to a first embodiment of the present invention. In FIG. 1, reference numerals 1A and 1B denote transparent substrates made of, for example, polycarbonate.
0 and L1 are engraved. One substrate, for example, substrate 1
On the surface side of the information signal L0 of A, for example, the reflectance is 15 to 3
A translucent film 3 made of a metal film of about 0% is formed, and a reflection film 2 made of a metal film of, for example, aluminum is formed on the other substrate 1B on the side of the information signal L1. The two substrates 1A and 1B are bonded together with an adhesive layer made of, for example, UV resin as an adhesive layer with the signal surfaces facing each other, thereby forming a single-sided, dual-layer playback type optical disc 10. I have.

As a specific manufacturing method of the optical disk 10, first, the EFM information signals L0 and L1 having the shortest pit length (3T) of 0.4 μm and the track pitch of 0.74 μm.
Are formed by injection molding, and a reflective film 2 of aluminum is formed on the information signal L1 surface of the substrate 1B to a thickness of about 700 mm by a sputtering method. , The other substrate 1
A translucent gold film 3 was formed to a thickness of about 150 ° on the information signal L0 surface of A. Then, several kinds of UV resins A, B, C, D and D having different photoelastic constants as shown in Table 1 are used as the adhesive 4.
E and F were prepared, and the substrates were adhered to each other by a spin coating method using the film thickness as a parameter, to produce a single-sided, dual-layer reproduction type optical disc 10. In addition, specifically,
Resin A is neopentyl glycol diacrylate, F is EO-modified bisphenol A diacrylate,
E was obtained by blending A and F in appropriate proportions.

[0016]

[Table 1]

Table 1 also shows the results of a second embodiment and a third embodiment described later. Here, a method for measuring the photoelastic constant of the UV resin will be described. A measuring device as shown in FIG. 14 was assembled. This measuring apparatus has an optical system in which a He-Ne laser source 35 that emits a measuring laser beam, a polarizer 36, a quarter-wave plate 37, an analyzer 38, and a photodiode 39 are sequentially arranged. Polarizer 3
A test piece 40 is inserted between the sixth and quarter-wave plates 37, and a load is applied thereto. At this time, the detected value obtained by the photodiode 39 is amplified by the amplifier 41 and
Displays the value. Using this apparatus, the test piece 40
Was subjected to a tensile stress, the value of birefringence with respect to the stress was plotted from equation (1), and the photoelastic constant was determined from the slope.
Since the photoelastic constant changes with temperature, all measurements were performed at room temperature (23 ° C.). The test piece 40 was manufactured by pouring a UV resin into a mold made of a PET film having a thickness of about 200 μm, and using a metal halide lamp.
By irradiating 500 mj / cm ² of ultraviolet light, a strip-shaped test piece having a thickness (film thickness) of 200 to 250 μm and a length of 2.5 mm × 30 mm was prepared.

Next, a method for evaluating the signal characteristics of the optical disk will be described. Each of the produced optical discs is reproduced using a laser pickup having a wavelength of 670 nm and a numerical aperture of NA 0.6, the reproduced output is analyzed by a time interval analyzer, and a signal corresponding to each pit of the frequency characteristic curve is obtained. Was determined from the distribution. That is, for only the signal reproduced from 3T, 10 ⁵
Sampling is performed, and the occurrence frequency distribution with respect to time is obtained.
This is a value normalized by dividing the standard deviation of the time axis fluctuation of this distribution by the time corresponding to 1T. If this value exceeds 15%, the pit separation margin at the time of reproduction decreases, which is not practical.
When the jitter exceeds 17%, the C1 error increases,
Continuous reproduction may be difficult. The jitter value is a numerical value obtained by combining various disk characteristics, that is, a numerical value including all factors such as disk warpage, substrate birefringence, reflective film characteristics, and signal pit shape. In the examples, all the disk manufacturing conditions other than the adhesive were the same, the same lot of substrates were used, the film forming conditions were all the same, and the warpage angle was also minimized when measuring the jitter. The measurement was performed while adjusting the tilt. In the case of such bottom jitter, it is desired that the required disk characteristic is 10% or less.

Table 1 above shows the jitter values during reproduction of the information signal L1 under each condition. FIG. 4 shows the relationship between the characteristic value and the jitter value by plotting the jitter value of the first embodiment in Table 1. As is clear from the graph shown in FIG. 4, the jitter value for the characteristic value higher than 2.0 × 10 ⁻⁴ mm ³ / kg was 9.7 to 10.1%, but the characteristic value 2 When the value is less than or equal to 0.0 × 10 ⁻⁴ mm ³ / kg, the jitter value of the reproduced information signal L1 is sharply reduced from 9.4% to 5.4%, resulting in excellent reproduction characteristics. It was confirmed that an optical disk could be provided. In particular, the characteristic value is 2.0 × 10 ⁻⁴ mm ³ / kg or less, and the jitter value for 2.0 to 4.0 × 10 ⁻⁵ mm ³ / kg is 5.9 to 6.5%, which is much higher. Because it ’s small
The jitter margin can be further increased. As described above, as a required characteristic for the optical disk, it is desired that the jitter value is 10% or less. From this point, almost all of the aspects of the first embodiment in Table 1 pass, but the jitter value in the actual optical disk is reduced. If it is set to around 10%, the reproduction characteristics generally deteriorate due to various factors.
Therefore, the inflection point where the jitter value is 10% or less and the jitter value sharply decreases is set as the upper limit of the characteristic value. In the graph shown in FIG. 4, this inflection point is 2.0 × 10 ⁻⁴ mm ³ / kg, so this inflection point is set as the upper limit.

As a modification of the first embodiment, a single-sided, dual-layer reproduction type optical disk on which an EFM information signal L1 having a shortest pit length of 0.254 μm and a track pitch of 0.6 μm is recorded is described in the first embodiment. It was produced by the same method as in the above. Then, the wavelength is 413 nm, and the NA of the lens is 0.6.
The relationship between the characteristic value and the jitter value was examined using the laser pickup of Example 1. As in Example 1, the characteristic value was set to 2.0 ×
The information signal L1 can be obtained by setting it to 10 ^-4 mm ³ / kg or less.
It was confirmed that the jitter value of the optical disk rapidly decreased, and an optical disk having excellent reproduction characteristics could be provided. In particular, the jitter value for the characteristic value of 2.0 to 4.0 × 10 ⁻⁵ mm ³ / kg is much lower, and the jitter margin can be further increased.

<Second Embodiment> Next, a second embodiment of the present invention will be described. FIG. 2 is a schematic enlarged sectional view showing an optical disc according to a second embodiment of the present invention. In FIG. 2, 5
Reference numerals A and 5B denote transparent substrates, and information signals L0 and L0 are engraved on one surface of each substrate. Each substrate 5A, 5
On the surface side of the B information signals L0, L0, translucent films 6, 6 each formed of a metal film having a reflectivity of about 15 to 30% are formed, and a transparent intermediate film made of, for example, a UV resin is formed on the surface thereof. 7 are formed, and the information signals L1 and L1 of the second layer having irregularities are formed on this surface. Further, reflection films 8, 8 made of a metal film such as aluminum are formed on the surface side of each of the information signals L1, L1. The two substrates 5A, 5B thus formed are bonded together with an adhesive 9 made of, for example, a UV resin, with the surfaces on the information signal L1, L1 side facing each other. The optical disk 20 of the mold is formed.

As a specific method of manufacturing the optical disk 20, first, 0.6 mm thick polycarbonate substrates 5A and 5B on which the information signal L0 is formed are manufactured by injection molding, and a gold translucent surface is formed on the information signal L0 surface. About 150 膜 of membrane 6
Was formed to a thickness of Then, on the translucent film 6, UV
Another information signal L1 was formed by a 2P molding method using an intermediate film 7 made of resin, and an aluminum reflective film 8 was formed thereon to a thickness of about 700 °. Then, the two substrates 5A and 5B are bonded to each other by a spin coating method via an adhesive 9 so that the aluminum reflection films 8 face each other, and a double-sided double-layer reproduction type optical disc as shown in FIG. 20 were produced.

At this time, when the resin A, B, C, D, E, and F shown in Table 1 were used as the intermediate film 7 and the film thickness was used as a parameter, the jitter value of the information signal L1 was calculated. The measurement was performed in the same manner as in the first example. The results of the second example are shown in Table 1 and FIG. As is clear from FIG. 5 in which the results of Table 1 are plotted, the inflection point at which the jitter value sharply decreases appears at a point where the characteristic value is approximately 3.0 × 10 ⁻⁴ mm ³ / kg. Characteristic value 3.0 × 10 ^-4 mm ³ / kg
The jitter value for the upper characteristic value is 9.8% to 9.9.
%, The jitter value is 5.6 to 8.6% for a characteristic having a characteristic value of less than 3.0 × 10 ⁻⁴ mm ³ / kg. Therefore, it was confirmed that an optical disk having good reproduction characteristics could be obtained by setting the characteristic value to 3.0 × 10 ⁻⁴ mm ³ / kg or less. In particular, the characteristic value is 3.0 × 10 ⁻⁴ m
m ³ / kg or less, and 2.0 to 5.5 × 10 ⁻⁵ mm
^{Since the} jitter value for ³ / kg is about 5.6%, which is much smaller, the jitter margin can be further increased. Here, as a modification of the second embodiment, the case where the Young's modulus of the adhesive 9 was changed was examined.

FIG. 6 shows a change in jitter of the information signal L1 when the Young's modulus of the adhesive 9 is changed in the second embodiment. In this case, the case where the UV resins A and C in Table 1 were used as the interlayer resin for the intermediate film 7 was examined.
At this time, the intermediate film 7 is formed to a thickness of 55 μm, and the adhesive 9
Was 50 μm in thickness. As is apparent from FIG. 6, it is obvious that the jitter value is not more than 10%, in particular,
When the Young's modulus is smaller than 150 kg / mm ² , the jitter value sharply decreases, indicating an inflection point. Resin C
In the case of, the jitter value for a Young's modulus of about 170 kg / mm ^{2 is} about 7.1%, but the Young's modulus is about 13%.
The jitter value for 0 kg / mm ² is greatly reduced to approximately 6.3%. Similarly, in the case of resin A, the jitter value is approximately 6.
It is greatly reduced from 6% to approximately 5.8%. Therefore, it was confirmed that by setting the Young's modulus of the adhesive 9 to 150 kg / mm ² or less, more excellent reproduction characteristics could be obtained. In particular, both resins A and C have a Young's modulus of 15
The jitter value for each value of 0 kg / mm ² or less and about 50 kg / mm ² or less is about 5.5 to 5.3% and about 5.9 to 5.8%, so the jitter value is much smaller. Is obtained, and the jitter margin can be further increased.

<Third Embodiment> Next, a third embodiment of the present invention will be described. FIG. 3 is a schematic enlarged sectional view showing an optical disc according to a third embodiment of the present invention. In FIG. 3, 17
Is a transparent substrate that is slightly thicker than in the previous embodiment, and has an information signal L0 engraved on one surface thereof. On this information signal L0, for example, a translucent film 11 made of a metal film having a reflectivity of about 15 to 30% is formed, and on the surface thereof, a transparent intermediate film 12 made of, for example, a UV resin is formed. An information signal L1 of the second layer having a concavo-convex shape is formed on the surface. Further, a reflection film 13 made of a metal film such as aluminum is formed on the surface side of the information signal L1. Then, a protective film 14 made of, for example, a UV resin is formed on the reflective film 13, thereby forming an optical disk 19 of a single-sided, dual-layer reproduction type.

As a specific manufacturing method of the optical disk 19, first, a polycarbonate substrate 17 having a thickness of 1.2 mm on which the information signal L0 is formed is manufactured by injection molding, and a gold translucent film 11 is formed on the information signal L0 surface. Was formed into a film having a thickness of about 150 mm. Then, on the translucent film 11, UV
Another information signal L1 is formed by a 2P molding method using an intermediate film 12 made of a resin, an aluminum reflective film 13 is formed thereon to a thickness of about 700 mm, and a protective film 14 is formed thereon as an SD film. -17 (manufactured by Dainippon Ink and Chemicals, Inc.) was formed to a thickness of about 8 μm by spin coating to produce an optical disc 19 of a single-sided, dual-layer reproduction type.

At this time, the resins A, B, C, D, E, and F shown in Table 1 were used as the intermediate film 12 and the jitter value of the information signal L1 when the film was manufactured using the film thickness as a parameter was determined. The measurement was performed in the same manner as in the first example. The results are shown in Table 1 and FIG. As is clear from FIG. 7 in which the results in Table 1 are plotted, the jitter value for the characteristic value higher than 4.0 × 10 ⁻⁴ mm ³ / kg is 9.8% to 9.9%.
However, the jitter value for a characteristic having a characteristic value of less than 4.0 × 10 ⁻⁴ mm ³ / kg is 5.2 to 9.0%. The inflection point at which the jitter value sharply decreases is represented by a point where the characteristic value is approximately 4.0 × 10 ⁻⁴ mm ³ / kg. Therefore, it was confirmed that an optical disk having good reproduction characteristics could be obtained by setting the characteristic value to 4.0 × 10 ⁻⁴ mm ³ / kg or less. In particular, the characteristic value is 4.0 × 10 ⁻⁴ mm ³ / k
g or less, and 2.0 to 5.5 × 10 ⁻⁵ mm ³ / kg
, The jitter value is much smaller at 5.2 to 5.5%, so that the jitter margin can be further increased.

In the present embodiment, only an example of a two-layer reproduction type is shown, but the present invention is not limited to this, and a three-layer or four-layer structure may be used. That is, FIGS.
As shown in (1), the first to fourth reflection layers 50, 51, 52, and 53, and the transparent first intermediate film 54 and the second reflection layer 50, whose reflectivities are gradually increased stepwise from the laser light incident side.
It may have a structure including the intermediate film 55 (the first reflection layer 50).
<Reflectance of second reflective layer 51 <third reflective layer 52
<The reflectance of the fourth reflective layer 53).
In other words, it can be said that the transmittance of the first to third reflective layers 50 to 52 is sequentially reduced stepwise. It is sufficient that the sum of the characteristic values of the respective intermediate films falls within the range of the characteristic value (3.0 × 10 ⁻⁴ mm ³ / kg) or less in the optical disk of the second embodiment. Regarding the thickness of the substrates, in the case of a bonded disk, the two substrates do not necessarily have to have the same thickness, and the substrates 58, 59 and the substrates having different thicknesses as shown in FIGS. 63, 64
A structure in which they are bonded to each other may be used. Incidentally, reference numeral 60 denotes a transflective film, 61 denotes a reflective film, and 62 denotes a protective film. Also, FIG.
C in FIGS. 3 and 8 to 13 indicates a center hole. Further, the material of the intermediate films 7, 12, 54, and 55 is also described in this embodiment as an example in which a UV resin is used. However, it is needless to say that the material is not limited to this.
A transparent material that can be used as an intermediate film, such as a liquid epoxy adhesive, anaerobic adhesive, primer-curable adhesive, cyanoacrylate adhesive, or an adhesive applied to both sides of a plastic sheet What is good is clear from the gist of the present invention.

[0029]

As described above, according to the optical disk of the present invention, the following excellent functions and effects can be exhibited. By setting a value obtained by multiplying a photoelastic constant of a material used for an adhesive layer or an intermediate film of a multi-layer reproduction type optical disk and its film thickness in a predetermined range, a high quality optical disk having excellent reproduction signal characteristics is provided. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged sectional view showing an optical disc according to a first embodiment of the present invention.

FIG. 2 is a schematic enlarged sectional view showing an optical disc according to a second embodiment of the present invention.

FIG. 3 is a schematic enlarged sectional view showing an optical disc according to a third embodiment of the present invention.

FIG. 4 is a graph in which values of the first example shown in Table 1 are plotted.

FIG. 5 is a graph in which values of the second example shown in Table 1 are plotted.

FIG. 6 is a graph showing a relationship between a Young's modulus of an adhesive and a jitter value in a modification of the second embodiment.

FIG. 7 is a graph in which values of the third example shown in Table 1 are plotted.

FIG. 8 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 9 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 10 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 11 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 12 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 13 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 14 is a configuration diagram showing an apparatus for measuring a photoelastic constant of an ultraviolet curable resin.

[Explanation of symbols]

1A, 1B, 5A, 5B, 17 ... substrate, 2, 8, 13 ...
Reflective film, 3 translucent film, 4, 6, 9 adhesive, 7, 12
... intermediate film, 10, 19, 20 ... optical disk, 14 ... protective film, L0, L1 ... information signal.

[Procedure amendment]

[Submission date] January 30, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a schematic enlarged sectional view showing an optical disc according to a first embodiment of the present invention.

FIG. 2 is a schematic enlarged sectional view showing an optical disc according to a second embodiment of the present invention.

FIG. 3 is a schematic enlarged sectional view showing an optical disc according to a third embodiment of the present invention.

FIG. 4 is a graph in which values of the first example shown in Table 1 are plotted.

FIG. 5 is a graph in which values of the second example shown in Table 1 are plotted.

FIG. 6 is a graph showing a relationship between a Young's modulus of an adhesive and a jitter value in a modification of the second embodiment.

FIG. 7 is a graph in which values of the third example shown in Table 1 are plotted.

FIG. 8 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 9 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 10 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 11 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 12 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 13 is a schematic enlarged sectional view of an optical disc according to another modification of the present invention.

FIG. 14 is a configuration diagram showing an apparatus for measuring a photoelastic constant of an ultraviolet curable resin.

FIG. 15 is a diagram showing the structure of a conventional optical disc.

FIG. 16 is a diagram showing a structure of a conventional optical disc.

FIG. 17 is a diagram showing a structure of a conventional optical disc.

FIG. 18 is a diagram showing a structure of a conventional optical disc.

FIG. 19 is a diagram showing the structure of a conventional optical disc.

[Description of Signs] 1A, 1B, 5A, 5B, 17 ... substrate, 2, 8, 13 ...
Reflective film, 3 translucent film, 4, 6, 9 adhesive, 7, 12
... intermediate film, 10, 19, 20 ... optical disk, 14 ... protective film, L0, L1 ... information signal.

Claims (4)

[Claims] 1. A substrate in which one information signal surface is formed on one surface and a reflective film is formed thereon, and a transparent substrate in which the other information signal surface is formed on one surface and a translucent film is formed thereon. A substrate is bonded via an adhesive such that the one and the other information signal surfaces face each other, and a single-sided substrate for reading information signals recorded on the one and the other information signal surfaces from the transparent substrate side, respectively. In a layer-reproducing optical disk, a numerical value obtained by multiplying the photoelastic constant of the adhesive by the film thickness of the adhesive to reduce the internal stress of the adhesive generated at the time of the bonding is as described above. An optical disk characterized by being at most 2.0 × 10 ⁻⁴ mm ³ / kg or less within the operating temperature range of the optical disk. 2. An information signal surface is formed on one side, a translucent film is formed thereon, and a transparent intermediate film having the other information signal surface formed thereon and a reflective film are laminated on the translucent film. Two transparent substrates are bonded together via an adhesive so that the reflection films face each other, and a double-sided double layer for reading information signals recorded on each information recording surface from the other side of both transparent substrates. In a reproduction type optical disk, a numerical value obtained by multiplying the photoelastic constant of the intermediate film by the film thickness of the intermediate film to reduce the internal stress of the intermediate film generated when the respective intermediate films are stacked is An optical disc characterized by being at most about 3.0 × 10 ⁻⁴ mm ³ / kg within the operating temperature range of the optical disc. 3. The optical disk according to claim 2, wherein the adhesive has a Young's modulus of 150 kg / mm ² or less within a use temperature range of the optical disk. 4. A transparent intermediate film in which one information signal surface is formed on one surface of a transparent substrate, a semi-transparent film is formed thereon, and the other information signal surface is formed on the semi-transparent film. A film is laminated, a protective film is provided on the reflective film, and in a single-sided dual-layer reproduction type optical disc which reads information signals recorded on the one and other information signal surfaces from the transparent substrate side, the intermediate film is The value obtained by multiplying the photoelastic constant of the intermediate film by the film thickness of the intermediate film in order to reduce the internal stress of the intermediate film generated during the lamination is approximately within the operating temperature range of the optical disk. An optical disk characterized by being at most 0 × 10 ⁻⁴ mm ³ / kg.