JP2003233930A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium capable of realizing a high recording capacity. <P>SOLUTION: The optical recording medium having an information signal portion and a light transmission layer on the surface of a laser beam incident side is provided with a substrate on the surface of which the information signal portion is formed by injection molding, a first recording layer being formed on the information signal portion, and a sheet 43 made of polycarbonate, on surface of which an information pit or a guide groove is formed by extrusion or casting, a second recording layer being formed thereon. The surface of the second recording layer side of the sheet 43 is stuck through an ultraviolet cured resin 60 to the first recording layer of the substrate, and the optical recording layer is constituted of the sheet 43 and the ultraviolet cured resin 60. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical recording medium.

[0002]

2. Description of the Related Art As a next-generation optical disk medium, an optical disk medium capable of recording / reproducing for NTSC 4 hours on one side has been proposed. This has a function as a new recording medium replacing the current VTR (Video Tape Recorder) by enabling recording and reproducing for about 4 hours as a home video disk recorder.

A CD is used as such a recording medium.
By selecting the same shape and size as the (Compact Disc), it is possible to make the product easy for users who are familiar with the ease and usability of CDs.

Further, by utilizing the access speed which is the greatest feature of the disc form, it is not only a compact and simple recorder but also a product incorporating various functions such as instant recording, reproduction, trick play and editing. Can be realized.

In order to realize the above products, it is required to have a recording capacity of, for example, 8 GB or more.

[0006]

[Problems to be Solved by the Invention]
No optical recording medium having a recording capacity of 8 GB or more was present in a disc having the same diameter size as a CD and having a single information signal layer only on one main surface.

The already proposed DVD (Digital Vers
atile Disc), the irradiation laser light wavelength λ = 0.65 μ in the area of the information signal section, that is, in the area of the radius of 24 to 58 (mm) from the center of the disk.
m, the numerical aperture of the lens N.V. A. = 0.6, the recording capacity is 4.7 GB. In order to achieve a larger capacity than the above DVD without changing the signal format such as ECC or modulation method, for example, in order to achieve 8 GB or more, it is necessary to satisfy the following [Equation 1].

## EQU1 ## 4.7 × (0.65 / 0.60 × NA. /
λ) ² ≧ 8

From the above equation, N. A. It is necessary to satisfy /λ≧1.20. Therefore, the wavelength λ of the irradiation laser beam is shortened, or the numerical aperture N. A.
It is necessary to either increase the value of.

To satisfy the above condition, for example, N. A.
In order to increase the value, it is necessary to reduce the thickness of the light transmission layer formed on the reproduction laser light irradiation surface side on the information signal of the optical disc. This is because the allowable amount of the angle (tilt angle) at which the disc surface deviates from the vertical with respect to the optical axis of the optical pickup becomes small, and this tilt angle is easily affected by the aberration due to the thickness of the light transmission layer. Is.

In order to manufacture a high-density optical recording medium as described above, it is also necessary to reduce the thickness unevenness (Δt) of the light transmitting layer for the same reason.

In view of the above, in the present invention, in particular, the numerical aperture N. A. It is possible to provide a high-capacity optical recording medium having a capacity of, for example, 8 GB or more.

[0012]

According to the present invention, there is provided a method for producing an optical recording medium having an information signal section and a light transmitting layer on a surface on which a laser beam is incident. In the present invention, a substrate on which this information signal portion is formed by injection molding and the first recording layer is formed on this information signal portion, and an information pit or guide on one surface side by extrusion molding or casting method. A sheet made of polycarbonate on which a groove is formed and a second recording layer is formed on the groove, and the second recording of the sheet is performed on the first recording layer of the substrate via the ultraviolet curable resin. The surfaces on the layer side are bonded together, and the light transmitting layer is formed by this sheet and the ultraviolet curable resin.

According to the optical recording medium of the present invention, the numerical aperture N. A. It is possible to deal with the case where the value is increased, and an optical recording medium having a large capacity of 8 GB or more can be obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, examples of specific embodiments of the present invention will be described in detail with reference to the drawings.
Note that, in the present embodiment, an example in which the optical disc is applied to reproduce the signal by irradiating laser light by passing through the light transmission layer on the substrate having the information signal portion will be described. The present invention is not limited to the examples shown below.

Generally, the disk skew margin Θ, the wavelength λ of the laser light of the recording / reproducing optical system, the numerical aperture of the lens N.V. A. , And the laser irradiation surface side of the optical recording medium, and the thickness t of the light transmission layer formed on the information signal has a correlation. The relationship between these parameters and Θ is based on the example of a compact disc (CD) whose playability has been sufficiently proven in practice, and is described in JP-A-3-0971.
No. 34 publication. According to this, | Θ | ≦ 8
It may be 4.115 ° (λ / NA. ³ / t), which is also applicable to the optical recording medium of the present invention.

Here, considering the concrete limit value of the skew margin Θ in the case of actually mass-producing disks,
It is reasonable to set it to 4 °. This is because, in consideration of mass production, if the size is made smaller than this, the yield will decrease and the cost will increase. Regarding existing recording media, the CD is 0.6 ° and the DVD is 0.4 °.

Therefore, with the skew margin Θ = 0.4 °, the wavelength of the laser light is shortened and the N. A. Calculating how much the thickness of the light transmitting layer should be set according to
N. A. Is the N.V. of the result formula of [Equation 1] above. A. / Λ ≧ 1.
From 20, it is required to be 0.78 or more. That is, it is derived that t ≦ 288 μm.

Further, the laser light has a shorter wavelength, and λ = 0.
When it becomes about 4 μm, regarding the numerical aperture of the lens,
N. A. Assuming that ≧ 0.78, the thickness t of the light transmission layer is t = 177 μm. In this case, the maximum thickness of the entire disc is about 1.38 mm, considering that manufacturing equipment such as a CD having a substrate thickness of 1.2 mm is used.

Further, in consideration of the magnetic field modulation of MO, the thickness t of the light transmission layer is required to be further reduced. For example, if the thickness t is set to 30 μm or less, recording / reproduction in MO becomes easy.

On the other hand, the lower limit of the thickness t of the light transmitting layer is determined by the protective function of the light transmitting layer that protects the recording film or the reflecting film, and is 10 μm in consideration of the reliability and the impact of the second group lens described later. The above is desirable.

In order to increase the recording density as described above, N. A. It is essential to increase the value of / λ. In this case, for example, to achieve a storage capacity of 8 GB,
At least N. A. Is 0.7 or more and the wavelength λ of the laser is 0.68 μm or less. Further, as described above, the thickness and the skew of the light transmitting layer have the above-mentioned relationship, but the thickness of the light transmitting layer is 10 to 17 in consideration of the fact that it corresponds to the red laser to the blue laser.
A setting of 7 μm is appropriate.

In order to achieve a recording capacity of 8 GB in the optical recording medium, it is necessary to adjust the track pitch P and the linear density d of the recording signal. The conditions are:
It is necessary to satisfy the following [Equation 2].

(2) (0.74 / P) × (0.267 / d) × 4.
7 ≧ 8 That is, d ≦ 0.1161 / P (μm / bit) should be satisfied.

When the track pitch P = 0.56 μm,
The linear density d ≦ 0.206 μm / bit, which is D
Based on VD ROM (Read Only Memory),
Advances in signal processing technology for recording and reproduction (specifically, PRML
, And the reduction of ECC redundancy),
Further, the linear density is expected to increase by about 15%, and the track pitch P can be increased accordingly. Therefore, the track pitch P can be set to about 0.64 μm at the maximum.

Further, in the high density recording medium, the track pitch fluctuation ΔP also has a strict tolerance. If the recording and reproducing parameters of CD and DVD are diverted as they are, D
VD track pitch 0.74μm, tolerance ± 0.03
Therefore, the following [Formula 3] is obtained.

[Expression 3] | ΔP | ≦ 0.03P / 0.74 = 0.04P Therefore, if the track pitch P = 0.56, then |
ΔP | ≦ 0.023 μm.

Further, the thickness unevenness Δt of the light transmission layer is required to have higher precision.

When the thickness t of the light transmitting layer deviates from the design center of the reproducing objective lens, the aberration amount given to the spot by the thickness error is the numerical aperture N.V. of the lens. A. It is inversely proportional to the fourth power of, and is also proportional to the wavelength λ of the laser light. Therefore, high N.V. A. In order to achieve high density recording by reducing the wavelength or shortening the wavelength, the amount (unevenness Δt of the thickness of the light transmitting layer) is more severely limited. As a concrete system example, regarding CD, N. A. = 0.45 has been put into practical use, and the error standard of the thickness of the light transmission layer is ± 100.
μm. Regarding DVD, N. A. = 0.6
Has been put into practical use, and the error standard of the thickness of the light transmission layer is ± 3
It is said to be 0 μm. Here, when the allowable amount of the thickness of the light transmitting layer in CD is ± 100 μm as a reference, the following [Equation 4] is obtained.

Δt = ± (0.45 / NA.) ⁴ × (λ / 0.78) × 100 = ± 5.26 × (λ / NA. ⁴ ) μm (NA is , Numerical aperture)

Here, with respect to the center of the thickness of the light transmitting layer of 100 μm, the wavelength of 0.68 μm, N. A. FIG. 1 shows the result of an experiment conducted on the relationship between the thickness error of the light transmission layer and the jitter value at 0.875. From FIG. 1, for example, the jitter standard of 8% when there is no perturbation such as skew in DVD
It can be seen that it is about ± 7 μm.
The numerical value derived from the above equation is ± 6 μm, and a good signal can be obtained from a disk medium satisfying this standard.

Therefore, as the density is increased, the unevenness Δt allowed in the thickness of the light transmitting layer is as shown in the following [Equation 5].

[Expression 5] | Δt | ≦ 5.26 × (λ / NA. ⁴ ) μm

Further, the thickness unevenness (Δt) of the above-mentioned light transmitting layer.
Is assumed to be uniform on the surface of the disk irradiated with the recording / reproducing laser beam, and aberration can be corrected by shifting the focus point. However, if there is unevenness in the thickness of the light transmission layer in this area (in the spot), it cannot be corrected by adjusting the focus point. It is necessary to keep this amount within ± 3λ / 100 with respect to the thickness center value.

Further, the eccentricity E is 50 μm for DVD.
On the other hand, E ≦ 50 × P / 0.74 = 67.57P (μm).

From the above, the conditions necessary for the optical recording medium to achieve the high density of the storage capacity of 8 GB are summarized as follows. The recording / reproducing optical system has λ ≦ 0.68 μm and N. A. /Λ≧1.20, and at least in the formation region of the information signal portion, the film thickness t of the light transmission layer is 10 to 177 μm, and the light transmission layer thickness unevenness | Δt | ≦ 5.26 (λ / N ．
A. ⁴ ) (μm) Track pitch P ≦ 0.64 μm Tolerance | ΔP | ≦ 0.04 Pμm Linear density d ≦ 0.1161 / P (μm / bit) Disk skew Θ ≦ 84.115 × (λ / NA.
³ / t) Eccentricity E ≦ 67.57P (μm) Surface roughness | Ra | ≦ 3λ / 100 (in spot irradiation area)

In order to manufacture an optical recording medium, first,
A substrate is manufactured by an injection molding method using a transfer stamper that realizes the pitch and pitch unevenness that meet the specifications required for the optical recording medium as described above, and at the same time, fine irregularities that form an information signal are formed. Since such a high-precision stamper with less pitch unevenness is difficult to achieve with the conventional structure in which the feeding is performed by the screw, it is manufactured by the master exposure apparatus having the feeding structure by the linear motor. Furthermore, the optical system will be covered with a cover for eliminating fluctuations of air, and a vibration damping material will be installed between the laser and the exposure device in order to remove the vibration of the cooling water of the exposure laser.

A reflective film, a recording film, or both are formed on the information signal surface of the substrate. In the optical recording medium manufactured according to the present invention, since signal recording or reproduction is performed by irradiating a laser beam from the light transmitting layer side formed on the reflective film or recording film, formation of these reflective film or recording film in advance. It is necessary to form the pits on the substrate in consideration of the deformation of the signal shape due to the film.

For example, in the case of a ROM having a capacity of 10 GB, the asymmetry of the signal pits when viewed from the substrate side is 25.
%, The asymmetry when viewed from the side opposite to the substrate is 10%. That is, in the present invention, since the signal is reproduced by irradiating the laser beam from the side opposite to the substrate side, for example, asymmetry 10% when viewed from the light irradiation side.
In order to form such pits, it is necessary to make the pit shape formed on the substrate 25% asymmetric.

Similarly, regarding the guide groove formed on the recording disk, the groove duty changes in the recording film, for example, in the case of groove recording (recording / reproducing to a concave portion when viewed from the recording / reproducing surface), the groove becomes narrow. Therefore, it is necessary to take measures such as widening the shape of the stamper in advance.
For example, in the case of land / groove recording, in order to obtain a land / groove width duty of 50% when viewed from the light irradiation side, it is preferable to set it to 55 to 65% when viewed from the substrate side.

It is desirable that the substrate has a rigidity of at least 0.6 mm in the case where the disc is formed of a single plate, because it requires a certain degree of rigidity. Similarly, in the case of a structure in which two substrates are bonded together, it is preferable that the size of one substrate is 0.3 mm or more, which is half that.

After the substrate is manufactured by injection molding as described above, as shown in FIG. 2, a recording film or a reflective film is formed on the information signal portion 11 of the substrate 10. For example, when the target optical disk is a ROM, a reflective film such as Al is formed to a film thickness of 20 to 60 nm.

When forming an information recording film on the information signal section 11, for example, when manufacturing a phase change type optical recording medium, for example, an Al film, a ZnS—SiO ₂ film, a Ge film, etc.
SbTe film, is formed by sequentially stacking a ZnS-SiO ₂ film.

When the target optical disk is a magneto-optical disk, for example, an Al film, SiN film, TbF, etc.
An eCo film and a SiN film are sequentially stacked to form a film.

When the target optical disk is a write-once disk, the Au film or Al film is sputtered, and then a cyanine or phthalocyanine organic dye film is applied by spin coating and dried. To film.

In the example shown in FIG. 2, the recording / reproducing laser beam L is emitted from the main surface side opposite to the substrate 10 side through the recording / reproducing objective lens L.

Next, as shown in FIG. 3, a light transmitting layer 12 is further formed thereon with an ultraviolet curable resin. That is,
The light transmitting layer 1 is formed by dropping a liquid ultraviolet curable resin on the film formation surface on the information signal portion of the optical disc having any structure formed as described above and further rotating and stretching it.
Form 2. The viscosity of the UV curable resin is 30
It is preferably 0 cps or more and 3000 cps or less.
For example, when an ultraviolet curable resin having a viscosity of 5800 cps at 25 ° C. is applied, after dropping the ultraviolet curable resin on the substrate 10, the substrate 10 is rotated at 2000 rpm for 11 seconds to finally obtain about 100 μm. The light transmission layer 12 can be formed.

Here, when the light transmitting layer 12 is formed, if an ultraviolet curable resin is dropped onto the inner peripheral portion of the substrate 10, for example, at a position with a radius of 25 mm, and is rotationally stretched, the centrifugal force and the viscous resistance will cause a relationship. There is a difference between the inner and outer circumferences in the thickness of the light transmitting layer 12. This amount becomes 30 μm or more, and there is a possibility that the thickness range of the light transmission layer 12 as described above cannot be satisfied.

In order to avoid such a difference between the inner and outer circumferences of the light transmitting layer 12, it is effective to drop the ultraviolet curable resin with the center hole 13 of the substrate 10 filled with some means. . For example, a polycarbonate sheet having a thickness of 0.1 mm is processed into a circle having a diameter Φ of 30 mm,
After adhering to the center of the substrate 10, an ultraviolet curable resin may be dropped from the center, rotationally stretched, irradiated with ultraviolet rays to cure the ultraviolet curable resin, and then the center hole may be punched out. According to this process, the difference between the inner and outer circumferences, that is, the waviness of the light transmission layer 12 is 10 μmp-p (peak
It was possible to obtain a reduced light transmission layer within two peaks, the same below).

When forming the light transmitting layer 12, it is possible that the diameter of the disk protrudes to the outer circumference of the disk. Therefore, the diameter of the disk is 120 with respect to the diameter of the CD (120 mm).
It is desirable to set mm + 5 mm as the maximum value.

Further, as shown in FIG. 4, for example, the thickness 10
The light transmitting layer 12 may be formed by adhering a 0 μm polycarbonate sheet 14 with an ultraviolet curable resin 15 interposed therebetween. In this case, the sum of the thickness unevenness of the sheet 14 and the thickness unevenness of the ultraviolet curable resin 15 for adhesion is 10 μm.
It may be mp-p or less. For example, a sheet 14 processed to have the same diameter as the substrate 10 is placed on the substrate 10 via an ultraviolet curable resin 15 for adhesion, and rotationally stretched, so that the sheet 14 becomes a weight of the ultraviolet curable resin 15. As a result, an ultrathin UV-curable resin layer is formed, and the total thickness unevenness can be 10 μm or less, that is, the difference between the maximum value and the minimum value of the UV-curable resin layer can be 10 μm or less. .

Further, the above-mentioned method of manufacturing the optical recording medium is
First recording layer 1 formed on substrate 10 as shown in FIG.
The present invention can also be applied to the case of manufacturing an optical recording medium having a multi-layer structure in which the second recording layer 18 is formed on the intermediate layer 16 via the intermediate layer 16.

Skew is likely to occur in the above-described optical discs, but in order to reduce the skew, as shown in FIG. 6, the light transmission layer 1 is provided on the substrate 10.
It is effective to apply an ultraviolet curable resin as the skew correction member 19 on the surface side opposite to the 2 formation surface side. In this case, the skew correction member 19 may be coated with the same material as the light transmission layer 12, or a material having a higher curing shrinkage than the ultraviolet curable resin which is the material of the light transmission layer 12 may be applied thinly. Good.

In order to record / reproduce the high density recording optical disc as described above, a high N.D. A. A pickup having the objective lens of is required. In this case, the distance between the objective lens and the disc surface (hereinafter referred to as W.
D. Say. ) Is preferred to conventional distances. However, if the distance between the objective lens and the disc surface is shortened, the objective lens may collide with the disc surface and damage the disc surface.

In order to prevent this, as shown in FIG. 7, a surface hard coat (pencil hardness H or more) is formed on the light transmitting layer 12.
It is effective to apply 20. Further, when the thickness of the light transmitting layer 12 is thin, signal reproduction failure is likely to occur when dust is attached, so that the material of the hard coat 20 is preferably one having an antistatic function. Due to this prevention of electrostatic charge, it is possible to prevent dust from adsorbing to the surface of the optical disc, and it is possible to effectively avoid signal defects.

Further, in the optical disc manufactured by the above method, when the wavelength of the measurement light is 780 nm, the in-plane birefringence amount of the light transmission layer is 15 nm or less on average in the reciprocating direction, and the fluctuation within the circumference is 15 nm p-p. Preferably there is.

In the optical disc manufactured by the above method, a recording / reproducing experiment was conducted in the case where the light transmitting layer was formed using a polycarbonate sheet having a thickness of 100 μm and the information recording layer was a phase change film. It was In this case, a linear density of 0.21 μm / bit and a jitter of 8% were obtained. Further, the amount of birefringence of such an optical disk was measured. The measurement result is shown in FIG. In FIG. 23, the horizontal axis represents the radial position (mm), and the vertical axis represents the birefringence amount (nm). In FIG. 23, the distribution is displayed as vertical line segments, and the horizontal line segment position that crosses each line segment is the average value. This birefringence amount is 15 nm or less on average in a round trip,
The intra-circumferential fluctuation could be 15 nmp-p or less.

Further, in the optical disc manufactured by the above method, the light transmission layer 12 is formed by applying a liquid photo-curable resin on the information recording section 11, rotating and stretching, and then photo-curing. The same recording / reproducing experiment was conducted when the information recording layer was a phase change film. In this case, a linear density of 0.21 μm / bit and a jitter of 7% were obtained. Further, the amount of birefringence of such an optical disk was measured. The measurement result is shown in FIG. In FIG. 24, the horizontal axis represents the radial position (mm), and the vertical axis represents the birefringence amount (nm). In FIG. 24, the distribution is displayed by vertical line segments, and the horizontal line segment position that crosses each line segment is the average value. This birefringence amount can be further reduced as compared with the case where the light transmitting layer is formed of a polycarbonate sheet, and the average is 5 nm or less in the reciprocation, and the fluctuation within the circumference is 5 nm p-p.
Could be:

Thus, the optical disk manufactured by the above method has an in-plane birefringence amount of 10 that of a conventional CD or DVD.
It can be seen that it has stable and excellent characteristics even when compared with 0 nm.

In addition, in the optical recording medium manufactured by the above method, the surface on which various recording films are formed may be subjected to silane treatment. By performing the silane treatment, the adhesion between the ultraviolet curable resin used when forming the light transmission layer 12 and various recording films can be improved.

Further, in the optical recording medium produced by the above method, an antireflection film may be formed on the surface of the light transmitting layer 12 by a method such as sputtering. The refractive index N of this antireflection film is preferably lower than the refractive index of the light transmission layer 12, and the thickness of this antireflection film is set when the wavelength of the light for recording and reproduction is λ. And (λ / 3) / n (nm) or less, preferably (λ
It is desirable to set it to about / 4) / n (nm).

As in the optical recording medium manufactured by the above method, the numerical aperture N. A. In order to deal with the high value, the incident angle of the recording / reproducing laser beam also becomes large, so that the reflection of light on the surface of the light transmitting layer 12 cannot be ignored. For example, N. A. = 0.45
In the case of, the incident angle of the recording / reproducing light is 26.7 °, N.
A. = 0.6, it becomes 36.9 °.

Here, N. A. = 0.8, the incident angle of the recording / reproducing light becomes 53.1 °, and the influence of the light reflection becomes large. That is, it has been confirmed that the reflectance of light on the surface of the light transmission layer 12 depends on the incident angle of the laser beam for recording and reproduction, and when the refractive index of the light transmission layer 12 is 1.52, for example. , The surface reflectance of the s-polarized component exceeds 15%. (See page 168 of "Laser and Optics Guide" published by Kinomeles Griot Co., Ltd.) In this case, a problem of loss of light amount occurs and the effective N.V. A. Bring about a decline. In order to avoid such a problem, it is effective to form an antireflection film on the surface of the light transmission layer 12.

The material of the antireflection film has an optical refractive index of 1. 2 when the refractive index of the light transmitting layer 12 is 1.52.
It is known that it is ideal to use about 23 (Kyoritsu Shuppan Optical Technology Series 11 Optical thin film
(See page 28). However, industrially, for example, MgF ₂ is used. The refractive index n of MgF ₂ is 1.38. If the wavelength of the laser beam for recording and reproduction is 650 nm, M
The thickness of the antireflection film made of gF ₂ is (λ / 4) / n
By substituting each numerical value into the formula (nm), about 120
It can be seen that it is preferable to form it to a thickness of nm.

By the way, the amount of light reflected on the surface of the light transmission layer 12 varies from 0 to (λ / 4) / n depending on the thickness of the antireflection film.
When decreasing in the range of (nm), (λ / 4) / n
It has been confirmed that the value becomes the minimum when (nm). On the other hand, the thickness of the antireflection film is (λ / 4) / n (nm)
When the value exceeds, the amount of light reflection increases, and (λ / 2) / n (n
It has also been confirmed that it becomes the maximum when m). From this, it was confirmed that the thickness of the antireflection film should be practically (λ / 3) / n (nm) or less in consideration of the film forming technology in industry.

When the antireflection film is formed on the surface of the light transmission layer 12 as described above, a single layer of MgF ₂ (λ / is used as an antireflection film on the light transmission layer 12 having a refractive index of 1.52, for example).
4) / n (nm), when a recording / reproducing laser beam of 550 nm is used, when the incident angle of the recording / reproducing laser beam is about 60 °, 50% It is possible to prevent the above reduction in the amount of light (see page 174 of "Laser and Optics Guide", published by Kinomeles Griot Co., Ltd.).

In the method of manufacturing the optical recording medium described above, not only the disc having the single plate structure but also the two substrates 51 and 52 having a half thickness of the substrate 10 finally obtained as shown in FIG.
It can also be applied to the case where two sheets are stuck together to produce an optical recording medium having a so-called double-sided structure having information signal recording portions on both sides. In this case, on the substrates 51 and 52 having a thickness of 0.6 mm,
The thickness of the disc is (0.6 + 0.17) × 2 + because the light transmission layer 12 having a maximum size of 170 μm is formed and bonded.
(Adhesive layer thickness) becomes 0.06mm
Then, the thickness of the disk is 1.60 mm. Further, as shown in FIG. 9, the present invention can also be applied to the case of producing an optical recording medium having a so-called double-sided structure having an information signal recording surface and a light transmitting layer 12 on both surfaces of one substrate 50.

Next, a specific application example of the method for producing an optical recording medium of the present invention will be described. As shown in FIG. 10, for example, 100 μ manufactured by extrusion molding or casting method.
An m-thick polycarbonate sheet 40 is prepared, placed on a stamper 41 heated to a temperature higher than the glass transition point of the sheet 40, and pressure is applied to a roller 42 to press them. The pressure in this case can be set to 280 Kgf, for example.

By this operation, as shown in FIG. 11, information pits or guide grooves of the stamper 41 can be transferred onto the sheet 40. And after cooling it,
By peeling the sheet 40 from the stamper 41, for example, a thin plate substrate 43 having a film thickness of 100 μm can be obtained.

Subsequently, similarly to the manufacturing process as described above, a recording film and a reflective film are formed, whereby the desired thin optical recording medium can be finally manufactured.

Further, by using the thin plate substrate 43 shown in FIG. 11, it is possible to manufacture an optical recording medium having a multilayer structure.

First, as shown in FIG. 12, the stamper 1
A liquid ultraviolet curable resin 60 is dropped on 41, and the thin plate substrate 43 shown in FIG. 11 is placed with the recording layer side in contact with the liquid ultraviolet curable resin 60.

In this way, as shown in FIG. 13, the liquid UV curable resin is rotated by rotating the stamper 141 on which the thin plate substrates are superposed while being arranged on the rotary base 61 through the liquid photocurable resin. 60 is stretched to the required thickness,
For example, the thickness is set to 20 μm, and thereafter, as shown in FIG. 14, ultraviolet rays are irradiated from the thin plate 43 side by the lamp 62 to cure the liquid ultraviolet curable resin 60.

As shown in FIG. 15, a thin plate substrate 43 and a photo-cured UV-curable resin 6 having a thickness of, for example, 20 μm are used.
0 is separated from the stamper 141 as a unit.

As described above, various recording films are formed by depositing a metal thin film of, for example, a Si compound or Al or Au on the fine irregularities transferred to the ultraviolet curable resin 60 by the stamper 141. be able to.

Further, by repeating the steps described with reference to FIGS. 12 to 15, an optical disc having three or more layers can be manufactured.

As shown in FIG. 16, the substrate 10 obtained by injection molding, for example, is bonded to the recording film obtained as described above via an ultraviolet curable resin at an interval of, for example, 20 μm. It is possible to manufacture an optical disc with high efficiency.

Further, as shown in FIG. 17, a highly reflective film 70 of, for example, Al or Au is formed on the finally obtained recording film, and a protective film 71 is further formed to form a multilayer structure. A thin optical disc can be manufactured. In this case, when the number of recording layers is N, the thickness of the optical disc finally obtained is the thickness of the thin plate substrate 43, for example, 100.
μm and N times the thickness of the ultraviolet curable resin layer between each layer,
The sum of the thicknesses of the high reflection film 70 and the protective film 71, for example, 5 μm. That is, for example, when the thickness of the ultraviolet curable resin layer between each layer is 20 μm and the thickness of the high reflection film 70 and the protective film 71 is 5 μm, when an optical disc having a four-layer structure is manufactured, the entire optical disc is Has a thickness of 185 μm. However, since the optical disc obtained in this way has a very low rigidity, a flexible thick optical disc is flattened by bonding a thick plate having rigidity to the thin plate substrate 43 side to support it or rotating at high speed during recording and reproduction. It is necessary to take measures such as recording and reproducing by utilizing this.

The numerical value of 20 μm in the example of the thickness between the recording layers described above is determined by the number of layers of the finally obtained optical disc and the movable distance of the lens of the pickup for recording / reproducing this optical disc. For example, when the movable distance of the lenses, that is, the distance between the second group lenses is 50 μm, as shown in FIG.
And 50 may be adhered to each other via an ultraviolet curable resin at intervals of 50 μm. Further, in the case of manufacturing an optical disc having a three-layer structure as shown in FIG.
And the recording layer may be formed at intervals of 25 μm.

In addition, in the above-described method of manufacturing an optical recording medium of the present invention, in addition to the optical disk having the above-described structure, FIG.
As shown in FIG. 0, a thin substrate 43 and a disc-shaped substrate 50 having a thickness of 1.1 mm, for example, formed by injection molding.
And are bonded together via an ultraviolet curable resin and pressure bonded,
You may make it adhere | attach by irradiating an ultraviolet-ray from this board | substrate side.

Further, in the present invention, as shown in FIG. 21, a substrate 50 on which fine irregularities for forming recording layers are transferred by injection molding and a thin substrate 43 are interposed via an ultraviolet curable resin. Laminated board and crimped, thin board 43
It is also possible to irradiate ultraviolet rays from the side and bond them, and finally obtain an optical disc having a four-layer structure.

Next, the depth of pits or grooves formed on the substrate will be described. In the following, the refractive index n of the light transmitting layer is used. The depth of the pit or groove that gives the most modulation is (λ / 4) / n, and the ROM or the like is set to this depth.

In the groove recording or the land recording, when an attempt is made to obtain a tracking error signal by push-pull, the push-pull signal becomes maximum when the depth of the pit or land is (λ / 8) / n.

Furthermore, in land / groove recording,
The groove depth should take into consideration the characteristics of the servo signal as well as the characteristics of crosstalk and cross erase. Experimentally, the crosstalk has a minimum value of (λ / 6) / n to (λ / 3) / n. It has been confirmed that deeper cross erase has less effect. Also, considering the groove inclination,
In order to satisfy both characteristics, (3λ / 8) / n is optimum. The optical recording medium for high density recording manufactured by the manufacturing method of the present invention can be applied within the above depth range.

Next, high N.V. A. An embodiment of recording / reproducing for realizing the above will be described. FIG. 22 shows the configuration of the optical disc and the recording / reproducing lens.

The second lens 32 is arranged between the first lens 31 and the optical disk 21. With this two-group lens configuration, the N.V. A. Can be 0.7 or more, and the first surface 32a of the second lens 32 and the optical disk 2 can be
The distance (WD) from the surface of No. 1 can be narrowed. In addition, it is desirable that the first surface 31a, the second surface 31b, the third surface 32a, and the fourth surface 32b of the first lens 31 and the second lens 32 each have an aspherical shape.

By using this second group lens, it becomes possible to perform high-density recording / reproduction of the above-mentioned optical disc.

[0083]

According to the optical recording medium of the present invention, the thickness of the light transmitting layer can be reduced to form a multilayer structure.
In particular, the numerical aperture N.V. of the objective lens of the recording / reproducing optical system. A. It is suitable for high values, and a large-capacity optical recording medium of, for example, 8 GB or more was obtained.

[Brief description of drawings]

FIG. 1 shows a relationship of changes in a jitter value due to a thickness error of a light transmission layer.

FIG. 2 is a schematic cross-sectional view of an optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 3B is a schematic sectional view of an optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 4 is a schematic cross-sectional view of an optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 5 is a schematic cross-sectional view of an optical disc as an example of an embodiment of an optical recording medium of the present invention.

FIG. 6 is a schematic cross-sectional view of an optical disc as an example of an embodiment of an optical recording medium of the present invention.

FIG. 7 shows a schematic cross-sectional view of an optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 8 is a schematic cross-sectional view of an optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 9 is a schematic sectional view of an optical disc as an example of an embodiment of an optical recording medium of the present invention.

FIG. 10 is a manufacturing process diagram of an optical disc as an example of an embodiment of an optical recording medium of the present invention.

FIG. 11 is a schematic cross-sectional view of a thin plate substrate that constitutes a multilayer optical disc of an example of an embodiment of the optical recording medium of the present invention.

FIG. 12 is a diagram showing a manufacturing process of a multilayer optical disc as an example of an embodiment of an optical recording medium of the present invention.

FIG. 13 is a diagram showing a process of manufacturing a multilayer optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 14 is a diagram showing a manufacturing process of a multilayer optical disc as an example of an embodiment of an optical recording medium of the present invention.

FIG. 15 is a diagram showing a process of manufacturing an optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 16 is a schematic sectional view of an optical disc as an example of an embodiment of an optical recording medium of the present invention.

FIG. 17 is a schematic sectional view of an optical disc as an example of an embodiment of an optical recording medium of the present invention.

FIG. 18 shows a schematic cross-sectional view of an optical disc having a two-layer structure as an example of an embodiment of the optical recording medium of the present invention.

FIG. 19 is a schematic sectional view of an optical disc having a three-layer structure as an example of an embodiment of the optical recording medium of the present invention.

FIG. 20 is a schematic sectional view of an optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 21 is a schematic sectional view of an optical disc as an example of an embodiment of the optical recording medium of the present invention.

FIG. 22 is a configuration diagram of a second group lens used in an optical system for recording or reproducing on or from the optical disc of the embodiment of the optical recording medium of the present invention.

FIG. 23 shows the measurement results of the birefringence amount of the light transmitting layer of the optical disc of the embodiment of the optical recording medium of the present invention.

FIG. 24 shows the measurement results of the birefringence amount of the light transmitting layer of the optical disc of the embodiment of the optical recording medium of the present invention.

[Explanation of symbols]

10, 50, 51, 52 substrate, 11 information signal section, 1
2 Seems to float, 13 Center hole, 14 sheet, 1
5 UV curable resin, 16 intermediate layer, 17 first recording layer, 18 second recording layer, 19 skew correction member, 2
0 hard coat, 21 optical disk, 31 first lens, 32 second lens, 40 sheet, 41, 14
1 stamper, 42 roller, 43 thin board, 6
0 Liquid UV curable resin, 61 rotating base, 62 lamps, 70 highly reflective film, 71 protective film

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yukatsu Nakaoki             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Masahiko Kaneko             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F term (reference) 5D029 JB21 KA07 KB02 RA08

Claims (2)

[Claims] 1. An optical recording medium having an information signal portion and a light transmitting layer on a surface on which laser light is incident, the information signal portion being formed on the surface by injection molding, and the information A substrate on which the first recording layer is formed on the signal portion, and information pits or guide grooves are formed on one surface side by extrusion molding or casting, and a second recording layer is formed on top of this.
And a sheet made of polycarbonate having a recording layer formed thereon, wherein the second recording layer side surface of the sheet is laminated on the first recording layer of the substrate via an ultraviolet curable resin, An optical recording medium, wherein the light transmitting layer is formed by the sheet and the ultraviolet curable resin. 2. An ultraviolet curable resin having a third recording layer formed thereon, wherein the third recording layer and the first and second recording layers have predetermined intervals, respectively, and the substrate and the substrate. The optical recording medium according to claim 1, wherein the optical recording medium is provided so as to be sandwiched between the sheet and the sheet.