JP4618352B2 - Method for manufacturing optical recording medium - Google Patents

Description

The present invention relates to a method for manufacturing an optical recording medium.

  As a next generation optical disk medium, an optical disk medium capable of NTSC 4 hour recording / reproduction on one side has been proposed. This provides a function as a new recording medium to replace the current VTR (Video Tape Recorder) by enabling recording and reproduction for about 4 hours as a home video disk recorder.

  In addition, by selecting the same shape and size as a CD (Compact Disc) as such a recording medium, it is possible to obtain a product that does not feel uncomfortable for users who are familiar with the convenience and usability of the CD.

  Furthermore, using the speed of access as the biggest feature of the disk format, it is possible to realize not only a compact and simple recorder, but also a product that incorporates various functions such as instant recording, playback, trick play, and editing. .

  In order to realize such a product, it has been required to have a recording capacity of, for example, 8 GB or more.

  However, conventionally, an optical recording medium having a recording capacity of 8 GB or more has not existed in a medium having the same diameter as a CD and having a single information signal layer only on one main surface.

In the already proposed DVD (Digital Versatile Disc), the irradiation laser light wavelength λ = 0.65 μm in the area of the information signal portion, that is, in the range of radius 24 to 58 (mm) from the center of the disc. , The numerical aperture of the lens A. The recording capacity is 4.7 GB under the condition of = 0.6. In order to increase the capacity further than the DVD without changing the signal format such as ECC or modulation method, for example, in order to realize 8 GB or more, it is necessary to satisfy the following [Equation 1].
[Equation 1]
4.7 × (0.65 / 0.60 × NA / λ) ² ≧ 8

  From the above equation, N.I. A. It is necessary to satisfy /λ≧1.20. Therefore, the wavelength λ of the irradiation laser light is shortened or the numerical aperture of the lens N.P. A. Either of the conditions to increase the value of is required.

  In order to satisfy the above conditions, N.I. A. In order to increase the thickness of the optical transmission layer, it is necessary to reduce the thickness of the light transmission layer formed on the information signal of the optical disc and on the reproduction laser light irradiation surface side. This is because the allowable amount of the angle (tilt angle) at which the disc surface deviates from the perpendicular to the optical axis of the optical pickup is small, and this tilt angle is easily affected by aberration due to the thickness of the light transmission layer. It is.

  Further, in order to produce a high-density optical recording medium as described above, it is necessary to reduce the thickness unevenness (Δt) of the light transmission layer for the same reason.

In view of the above, in the present invention, in particular, the numerical aperture N.I. A. The present invention provides a method for manufacturing an optical recording medium having a large capacity of, for example, 8 GB or more.

The present invention is a method for producing an optical recording medium comprising at least two or more information signal portions and a light transmission layer on a surface on which laser light is incident,
Forming a first information signal portion on the surface of the substrate by injection molding, filled and forming a first reflective film on the substrate, the center hole of the substrate on the first reflective film state, dropped ultraviolet-curing resin from the center, contacting the stamper via the ultraviolet curing resin, rotates drawing, the second information in which information pits or guide grooves of the stamper has been transferred by curing Yes forming a UV-curable resin layer having a signal portion, and forming a second reflective film on the ultraviolet curing resin layer, and forming a protective layer on the second reflective film, the and to Turkey and features.
Note that the first information signal portion a second information signal section, that kick set to a distance corresponding to the movable range of the number of layers and the pickup lens of the information signal portions are preferred.

According to the above configuration , the light transmission layer can be thinned to have a multilayer structure.

  As described above, according to the present invention, since the thickness of the light transmission layer can be reduced to have a multilayer structure, the numerical aperture N.sub. A. For example, an optical recording medium having a large capacity of 8 GB or more can be obtained.

  Hereinafter, examples of specific embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, an example will be described in which the present invention is applied to an optical disc that reproduces a signal by irradiating a laser beam by passing through a light transmission layer on a substrate having an information signal portion. The present invention is not limited to the examples shown below.

In general, the disk skew margin Θ, the wavelength λ of the laser beam of the recording / reproducing optical system, the numerical aperture of the lens A. , And the laser irradiation surface side of the optical recording medium, which is correlated with the thickness t of the light transmission layer formed on the information signal. The relationship between these parameters and Θ is shown in Japanese Patent Laid-Open No. 3-097134 on the basis of an example of a compact disc (CD) whose playability has been demonstrated in practice. According to this, it is sufficient that | Θ | ≦ 84.115 ° (λ / NA ³ / t), and this can also be applied to the optical recording medium of the present invention.

  Here, considering a specific limit value of the skew margin Θ when the disk is actually mass-produced, it is appropriate to set it to 0.4 °. This is because when mass production is considered, if the size is smaller than this, the yield decreases and the cost increases. The existing recording medium is also 0.6 ° for CD and 0.4 ° for DVD.

  Therefore, the skew margin Θ = 0.4 °, the laser light has a shorter wavelength, and the higher N.V. A. Assuming that the thickness of the light transmission layer should be set by the conversion, the wavelength λ of the laser beam is λ = 0.65 μm. A. Is N. of the result formula of the above [Equation 1]. A. From /λ≧1.20, 0.78 or more is required. That is, it is derived that t ≦ 288 μm.

  When the wavelength of the laser light is shortened to about λ = 0.4 μm, the numerical aperture of the lens is N.P. A. Assuming that ≧ 0.78, the thickness t of the light transmission layer is t = 177 μm. In this case, considering that a manufacturing facility such as a CD having a substrate thickness of 1.2 mm is used, the maximum thickness of the entire disk is about 1.38 mm.

  In consideration of the magnetic field modulation of the MO, it is required to further reduce the thickness t of the light transmission layer. For example, by forming the light transmission layer to be 30 μm or less, recording / reproduction with the MO becomes easy.

  On the other hand, the lower limit of the thickness t of the light transmission layer is determined by the protection function of the light transmission layer for protecting the recording film or the reflection film, and is 10 μm or more in consideration of the reliability and the impact of the collision of the second lens group described later. It is desirable.

  In order to increase the recording density as described above, N.I. A. It is essential to increase the value of / λ. In this case, for example, in order to achieve 8 GB as the storage capacity, at least N.D. A. Is 0.7 or more and the wavelength λ of the laser is 0.68 μm or less. In addition, as described above, there is the above-described relationship between the thickness of the light transmission layer and the skew, but considering the correspondence from the red laser to the blue laser, the thickness of the light transmission layer is 10 to 177 μm. It is appropriate to set.

In an optical recording medium, in order to achieve a recording capacity of 8 GB, it is necessary to adjust the track pitch P and the linear density d of the recording signal. As the condition, it is necessary to satisfy the following [Equation 2].
[Equation 2]
(0.74 / P) × (0.267 / d) × 4.7 ≧ 8
That is, d ≦ 0.1161 / P (μm / bit) may be satisfied.

  When the track pitch P = 0.56 μm, the linear density d ≦ 0.206 μm / bit, which is based on DVD ROM (Read Only Memory), and advances in signal processing technology for recording and reproduction (specifically In consideration of the application of PRML and the reduction of ECC redundancy, the line 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 a high-density recording medium, the tolerance for the track pitch fluctuation ΔP becomes severe. If the recording / reproducing parameters of CD and DVD are used as they are, the following [Equation 3] is obtained from the track pitch 0.74 μm and tolerance ± 0.03 on DVD.
[Equation 3]
| ΔP | ≦ 0.03P / 0.74 = 0.04P
Therefore, when the track pitch P = 0.56, | ΔP | ≦ 0.023 μm.

  Furthermore, higher accuracy is required also for the thickness unevenness Δt of the light transmission layer.

When the thickness t of the light transmission layer deviates from the design center of the reproduction objective lens, the aberration amount given to the spot by the thickness error is the numerical aperture of the lens. A. Is inversely proportional to the fourth power of and is proportional to the wavelength λ of the laser beam. Therefore, high N.I. A. In the case of achieving high-density recording by reducing the wavelength or shortening the wavelength, the amount (light transmission layer thickness unevenness Δt) is more strictly limited. As a specific system example, N.D. A. = 0.45 has been put into practical use, and the error standard of the thickness of the light transmission layer is ± 100 μm. As for DVD, N.I. A. = 0.6 is put into practical use, and the error standard of the thickness of the light transmission layer is ± 30 μm. Here, when the allowable amount of the light transmitting layer in the CD is ± 100 μm as a reference, the following [Equation 4] is obtained.
[Equation 4]
Δt = ± (0.45 / NA) ⁴ × (λ / 0.78) × 100
= ± 5.26 × (λ / NA ⁴ ) μm (NA is the numerical aperture)

  Here, with respect to the center of the light transmission layer thickness of 100 μm, the wavelength is 0.68 μm, N.P. 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, it can be seen that, for example, in the DVD, when the jitter reference is 8% when there is no perturbation such as skew, 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, the unevenness Δt allowed for the light transmission layer thickness as the density increases is expressed by the following [Equation 5].
[Equation 5]
| Δt | ≦ 5.26 × (λ / NA ⁴ ) μm

  Further, the above-described uneven thickness (Δt) of the light transmission layer is assumed to be uniform within the disk surface irradiated with the recording / reproducing laser beam, and the aberration can be corrected by shifting the focus point. However, if there is unevenness in the thickness of the light transmission layer in this region (in the spot), it cannot be corrected by adjusting the focus point. This amount needs to be suppressed to ± 3λ / 100 or less with respect to the thickness center value.

Furthermore, with respect to eccentricity E, for DVD 50μm,
E ≦ 50 × P / 0.74 = 67.57 P (μm).

From the above, the conditions necessary for the optical recording medium for achieving the high density of the storage capacity 8 GB are summarized as follows.
When the recording / reproducing optical system is λ ≦ 0.68 μm and A. /Λ≧1.20, and at least in the formation region of the information signal portion,
Light transmission layer thickness t = 10 to 177 μm
Light transmission layer thickness unevenness | Δt | ≦ 5.26 (λ / NA ⁴ ) (μm)
Track pitch P ≦ 0.64μm
Tolerance | ΔP | ≦ 0.04Pμm
Linear density d ≦ 0.1161 / P (μm / bit)
Disk skew Θ ≦ 84.115 × (λ / NA ³ / t)
Eccentric E ≦ 67.57P (μm)
Surface roughness | Ra | ≦ 3λ / 100 (in the 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 a pitch and pitch unevenness satisfying the specifications necessary for the optical recording medium as described above. Fine irregularities constituting the signal are formed. Such a high-precision stamper with little pitch unevenness is difficult to achieve with a conventional structure in which the feed is performed with a screw, and is thus manufactured with a master exposure apparatus having a feed structure with a linear motor. Furthermore, the optical system is covered with a cover for eliminating air fluctuations, and a vibration isolating material is installed between the laser and the exposure apparatus in order to eliminate 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 produced according to the present invention, signal recording and reproduction are performed by irradiating a laser beam from the reflective film or the light transmitting layer formed on the recording film. It is necessary to form 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, if 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, a signal is reproduced by irradiating a laser beam from the side opposite to the substrate side. For example, in order to form a pit having an asymmetry of 10% when viewed from the light irradiation side, it is formed on the substrate. It is necessary to set the pit shape to be asymmetry 25%.

  Similarly, with respect to the guide groove formed on the recording disk, the groove becomes narrower when the groove duty is changed by the recording film, for example, in the case of groove recording (recording / reproducing into the recess as viewed from the recording / reproducing surface), the stamper It is necessary to take measures such as widening the shape in advance. For example, in the case of land / groove recording, in order to obtain a land and 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.

  The substrate is preferably 0.6 mm or more because a certain level of rigidity is required when the disk is formed of a single plate. Similarly, in the case of a structure in which two sheets are bonded together, it is preferable that one substrate is half or more, which is 0.3 mm or more.

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

When forming an information recording film on the information signal portion 11, for example, when producing a phase change type optical recording medium, for example, an Al film, a ZnS—SiO ₂ film, a GeSbTe film, and a ZnS—SiO ₂ film are sequentially laminated. To form a film.

  When the target optical disk is a magneto-optical disk, for example, an Al film, a SiN film, a TbFeCo film, and a SiN film are sequentially stacked.

  When the target optical disk is a write-once disk, the film is formed by sputtering an Au film or an Al film, and then applying a cyanine or phthalocyanine organic dye film by spin coating and drying.

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

  Next, as shown in FIG. 3, the light transmission layer 12 is further formed thereon with an ultraviolet curable resin. That is, the light transmissive layer 12 is formed by dropping a liquid ultraviolet curable resin on the film formation surface on the information signal portion of the optical disk having any structure formed as described above, and further rotating and stretching. The viscosity of the ultraviolet curable resin is preferably from 300 cps to 3000 cps. 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, and finally about 100 μm. The light transmissive layer 12 can be formed.

  Here, when the light transmission layer 12 is formed, when an ultraviolet curable resin is dropped on the inner peripheral portion of the substrate 10, for example, at a position of a radius of 25 mm, and rotated and stretched, the light transmission layer is obtained from the relationship between centrifugal force and viscosity resistance. An inner / outer circumference difference occurs in the thickness of 12. This amount is 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 peripheries of the light transmission layer 12, it is effective to perform the UV curable resin dripping while the center hole 13 of the substrate 10 is filled with some means. For example, a polycarbonate sheet having a thickness of 0.1 mm is processed into a circular shape having a diameter Φ of 30 mm and bonded to the center of the substrate 10. It is conceivable that the ultraviolet curable resin is cured by irradiating and then the center hole is punched out. According to this process, it was possible to obtain a light transmission layer in which the difference between the inner and outer circumferences, that is, the waviness of the light transmission layer 12 was reduced within 10 μmp-p (peak to peak, the same applies hereinafter).

  Since the light transmission layer 12 may be formed to protrude to the outer periphery of the disk, it is desirable that the disk diameter has a maximum value of 120 mm + 5 mm on the basis of the diameter of a CD or the like (120 mm).

  As shown in FIG. 4, for example, the light transmission layer 12 may be formed by adhering a polycarbonate sheet 14 having a thickness of 100 μm via an ultraviolet curable resin 15. In this case, the sum of the unevenness of the thickness of the sheet 14 and the unevenness of the thickness of the ultraviolet curable resin 15 for bonding may be 10 μmp-p or less. For example, the sheet 14 processed to have the same diameter as the substrate 10 is placed on the substrate 10 via the UV curable resin 15 for bonding and rotated and stretched, so that the sheet 14 becomes a weight of the UV curable resin 15. And an ultra-thin 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-described method for manufacturing an optical recording medium has a multilayer structure in which the second recording layer 18 is formed on the first recording layer 17 formed on the substrate 10 via the intermediate layer 16 as shown in FIG. This can also be applied to the production of the optical recording medium.

  In addition, the optical disk having each of the above-described structures is likely to cause skew, but in order to reduce the skew, as shown in FIG. 6, the surface side opposite to the light transmission layer 12 forming surface side on the substrate 10 In addition, it is effective to apply an ultraviolet curable resin as the skew correction member 19. 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 that is the material of the light transmission layer 12 is thinly applied. Also good.

  In addition, in order to record / reproduce the above-described high-density recording optical disk, a high N.D. A. A pickup having the objective lens is required. In this case, it is desirable to make the distance between the objective lens and the disk surface (hereinafter referred to as WD) shorter than the conventional distance. However, if the distance between the objective lens and the disk surface is shortened, the objective lens may collide with the disk surface and damage the disk surface.

  In order to prevent this, it is effective to apply a surface hard coat (pencil hardness H or higher) 20 on the light transmission layer 12 as shown in FIG. Further, if the thickness of the light transmission layer 12 is reduced, a signal reproduction failure is likely to be caused when dust is attached. Therefore, a material having an antistatic function is preferable as the material of the hard coat 20. This antistatic can prevent dust from adhering to the surface of the optical disk, and can effectively avoid signal failure.

  Further, in the optical disk 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 nmp-p on average in the round trip and 15 nmp-p on the circumference. preferable.

  In the optical disk manufactured by the above-described method, a recording / reproducing experiment was performed when the light transmission layer was formed using a polycarbonate sheet having a thickness of 100 μm, for example, and the information recording layer was a phase change film. In this case, a jitter of 8% was obtained at a linear density of 0.21 μm / bit. Further, the birefringence amount of such an optical disk was measured. The measurement results are shown in FIG. In FIG. 23, the horizontal axis indicates the radial position (mm), and the vertical axis indicates the birefringence amount (nm). In FIG. 23, the distribution is displayed as vertical line segments, and the position of the horizontal line segment crossing each line segment is an average value. The amount of birefringence was 15 nm or less on average in the round trip, and the fluctuation in the circumference could be 15 nmp-p or less.

  Further, in the optical disk manufactured by the above-described method, the light transmission layer 12 is formed by applying a liquid photocurable resin on the information recording unit 11, rotating and then photocuring, and information recording. A similar recording / reproducing experiment was conducted when the layer was a phase change film. In this case, a jitter of 7% was obtained at a linear density of 0.21 μm / bit. Further, the birefringence amount of such an optical disk was measured. The measurement results are shown in FIG. In FIG. 24, the horizontal axis indicates the radial position (mm), and the vertical axis indicates the birefringence amount (nm). In FIG. 24, the distribution is displayed as vertical line segments, and the horizontal line segment positions crossing each line segment are average values. The amount of birefringence can be further reduced as compared with the case where the light transmission layer is formed of a polycarbonate sheet, and the average of the reciprocation is 5 nm or less, and the variation in the circumference can be 5 nmp-p or less.

  Thus, it can be seen that the optical disc manufactured by the above-described method has stable and excellent characteristics even when compared with the conventional CD or DVD having an in-plane birefringence of 100 nm.

  Moreover, in the optical recording medium produced by the above-mentioned method, the surface on which various recording films are formed may be subjected to silane treatment. By performing the silane treatment, it is possible to improve the adhesion between the ultraviolet curable resin used when forming the light transmission layer 12 and various recording films.

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

  Like the optical recording medium produced by the above method, the numerical aperture of the lens A. If the height corresponds to a high value, the incident angle of the recording / reproducing laser beam also increases, so that the reflection of light on the surface of the light transmission layer 12 cannot be ignored. For example, N.I. A. = 0.45, the incident angle of the recording / reproducing light is 26.7 °, N.P. A. In the case of = 0.6, the angle is 36.9 °.

  Here, N.I. A. In the case of = 0.8, the incident angle of the recording / reproducing light becomes 53.1 °, and the influence of light reflection becomes large. That is, it has been confirmed that the light reflectance at the surface of the light transmission layer 12 depends on the incident angle of the recording / reproducing laser beam, 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%. (Refer to page 168 of “Laser and Optics Guide” published by Kinomeres Grio Co., Ltd.) 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.

It is known that it is ideal to use an optical material having a refractive index of about 1.23 as the material of the antireflection film when the refractive index of the light transmission layer 12 is 1.52. (See page 28 of Kyoritsu Publishing Optical Technology Series 11 Optical thin film). However, industrially, for example, MgF ₂ is used. The refractive index n of MgF ₂ is 1.38. When the wavelength of the laser beam for recording / reproducing is 650 nm, the thickness of the antireflection film made of MgF ₂ is about 120 nm by substituting each numerical value into the formula of (λ / 4) / n (nm). It can be seen that it is preferable to form it.

  By the way, the amount of reflection of light on the surface of the light transmission layer 12 is (λ / 4) / n when the thickness of the antireflection film is decreased from 0 to (λ / 4) / n (nm). It has been confirmed that the minimum is (nm). On the other hand, when the thickness of the antireflection film exceeds (λ / 4) / n (nm), the amount of reflected light increases, and may be maximized when (λ / 2) / n (nm). It has been confirmed. From this, it was confirmed that the thickness of the antireflection film should be not more than (λ / 3) / n (nm) practically in consideration of the film forming technique industrially.

As described above, when the antireflection film is formed on the surface of the light transmission layer 12, for example, a single layer of MgF ₂ as an antireflection film on the light transmission layer 12 having a refractive index of 1.52 (λ / 4) / n ( When the laser beam for recording / reproducing is 550 nm, the amount of light is reduced by 50% or more until the incident angle of the laser beam for recording / reproducing is about 60 °. (See page 174 of “Laser and Optics Guide” published by Kinomeres Grio Co., Ltd.).

  The optical recording medium manufacturing method described above is not only a single-plate disc, but also two substrates 51 and 52 that are half the thickness of the finally obtained substrate 10 as shown in FIG. In addition, the present invention can also be applied to the case where a so-called double-sided optical recording medium having information signal recording portions on both sides is produced. In this case, since the light transmission layer 12 having a maximum thickness of 170 μm is formed and bonded to the substrates 51 and 52 having a thickness of 0.6 mm, the thickness of the disk is (0.6 + 0.17) × 2 + (thickness of the adhesive layer). When the thickness of the adhesive layer is 0.06 mm, the disc thickness is 1.60 mm. Further, as shown in FIG. 9, the present invention can be applied to a case where an optical recording medium having a so-called double-sided structure in which an information signal recording surface and a light transmission layer 12 are provided on both surfaces of a single 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, a polycarbonate sheet 40 having a thickness of, for example, 100 μm made by extrusion molding or casting method is prepared, and placed on a stamper 41 heated to a temperature higher than the glass transition point of the sheet 40. In addition, pressure is applied to the roller 42 to press-bond them. The pressure in this case can be set to 280 Kgf, for example.

  By this operation, the information pits or guide grooves of the stamper 41 can be transferred onto the sheet 40 as shown in FIG. And after cooling this, the sheet | seat 40 is peeled from the stamper 41, and the thin board | substrate 43 with a film thickness of 100 micrometers is obtained, for example.

  Subsequently, similarly to the manufacturing process as described above, a target thin optical recording medium can be finally produced by forming a recording film and a reflective film.

  In addition, an optical recording medium having a multilayer structure can be manufactured using the thin plate substrate 43 shown in FIG.

  First, as shown in FIG. 12, the liquid ultraviolet curable resin 60 is dropped on the stamper 141, 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 60 is stretched by rotating the stamper 141 on which the thin plate substrates are stacked while being arranged on the rotating base 61 through the liquid photocurable resin. Then, the required thickness, for example, 20 μm is set, and thereafter, the ultraviolet ray is irradiated from the thin plate substrate 43 side by the lamp 62 as shown in FIG.

  As shown in FIG. 15, the thin plate substrate 43 and the photocured ultraviolet curable resin 60 having a thickness of, for example, 20 μm are integrally peeled off from the stamper 141.

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

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

  On the recording film obtained as described above, as shown in FIG. 16, a substrate 10 obtained by, for example, injection molding is bonded with an ultraviolet curable resin at an interval of, for example, 20 μm, thereby providing a highly rigid optical disc. Can be produced.

  Further, as shown in FIG. 17, a thin optical disk having a multilayer structure is formed by forming a highly reflective film 70 of, for example, Al or Au on the finally obtained recording film and further forming a protective film 71. Can be produced. In this case, when the number of recording layers is N, the thickness of the finally obtained optical disk is as follows: the thickness of the thin plate substrate 43, for example, 100 μm, and the thickness N times that of the ultraviolet curable resin layer between the layers. The thickness of the high reflection film 70 and the protective film 71 is, for example, the sum of 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 disk having a four-layer structure is manufactured, Becomes a thickness of 185 μm. However, since the optical disk obtained in this way is very low in rigidity, a flexible optical disk is flattened by attaching a thick plate having rigidity to the thin substrate 43 side, or by high-speed rotation during recording and reproduction. Therefore, it is necessary to devise such as recording and reproduction using the above.

  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 optical disk finally obtained and the movable distance of the pickup lens for recording / reproducing the optical disk. For example, when the movable distance of the lens, that is, the distance between the two group lenses is 50 μm, the substrate 10 and the thin plate substrate 43 may be bonded via an ultraviolet curable resin at an interval of 50 μm as shown in FIG. Further, when a three-layered optical disk is manufactured as shown in FIG. 19, a recording layer may be formed between the thin plate substrate 43 and the substrate 10 with an interval of 25 μm.

  Further, in the method for manufacturing an optical recording medium of the present invention described above, in addition to the optical disk having the structure described above, as shown in FIG. 20, a thin plate substrate 43 and a thickness of, for example, 1.1 mm made by injection molding are used. The disk-shaped substrate 50 may be bonded and bonded via an ultraviolet curable resin and bonded by irradiating ultraviolet rays from the substrate side.

  Further, in the present invention, as shown in FIG. 21, a substrate 50 on which fine irregularities forming recording layers on both sides are transferred by injection molding and a thin substrate 43 are bonded together via an ultraviolet curable resin. The optical disc may be bonded and irradiated with ultraviolet rays from the thin plate substrate 43 side to finally form an optical disc having a four-layer structure.

  Next, the depth of pits or grooves formed on the substrate will be described. Hereinafter, the refractive index n of the light transmission layer is used. The depth of the pit or groove that can obtain the maximum degree of modulation is (λ / 4) / n, and the ROM or the like is set to this depth.

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

  Further, in the land / groove recording, the groove depth should consider the characteristics of the crosstalk and the cross erase as well as the characteristics of the servo signal. Experimentally, the crosstalk is (λ / 6) / n to (λ / 3) It has been confirmed that / n is minimized and that the cross erase has a less influence when it is deeper. In addition, (3λ / 8) / n is optimum when both characteristics are satisfied in consideration of the groove inclination and the like. The optical recording medium for high-density recording produced by the production method of the present invention can be applied within the above depth range.

  High N. A. A description will be given of an example of recording / reproducing that realizes the above. FIG. 22 shows the configuration of an optical disc and a recording / reproducing lens.

  A second lens 32 is disposed between the first lens 31 and the optical disc 21. By adopting this two-group lens configuration, N.I. A. Can be made 0.7 or more, and the distance (WD) between the first surface 32a of the second lens 32 and the surface of the optical disc 21 can be reduced. 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 are preferably aspherical.

  By using this two-group lens, it is possible to perform high-density recording / reproduction of the optical disk described above.

The relationship of the change of the jitter value by the thickness error of a light transmissive layer is shown. 1 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. B 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. 1 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. 1 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. 1 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. 1 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. 1 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. 1 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. The manufacturing process figure of the optical disk of the example of embodiment of the optical recording medium of this invention is shown. 1 is a schematic cross-sectional view of a thin plate substrate constituting a multilayer optical disc as an example of an embodiment of the optical recording medium of the present invention. The manufacturing process figure of the multilayer optical disk of the example of embodiment of the optical recording medium of this invention is shown. The manufacturing process figure of the multilayer optical disk of the example of embodiment of the optical recording medium of this invention is shown. The manufacturing process figure of the multilayer optical disk of the example of embodiment of the optical recording medium of this invention is shown. The manufacturing process figure of the optical disk of the example of embodiment of the optical recording medium of this invention is shown. 1 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. 1 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. 1 is a schematic sectional view of an optical disc having a two-layer structure as an example of an embodiment of an optical recording medium of the present invention. 1 is a schematic sectional view of an optical disk having a three-layer structure as an example of an embodiment of the optical recording medium of the present invention. 1 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. 1 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. 2 shows a configuration diagram of a two-group lens used in an optical system for recording or reproducing with respect to an optical disc of an example of an embodiment of the optical recording medium of the present invention. The measurement result of the birefringence amount of the light transmission layer of the optical disk of the example of the embodiment of the optical recording medium of the present invention is shown. The measurement result of the birefringence amount of the light transmission layer of the optical disk of the example of the embodiment of the optical recording medium of the present invention is shown.

Explanation of symbols

  10, 50, 51, 52 Substrate, 11 Information signal portion, 12 Light transmission layer, 13 Center hole, 14 Sheet, 15 UV curable resin, 16 Intermediate layer, 17 First recording layer, 18 Second recording layer, 19 skew correction member, 20 hard coat, 21 optical disc, 31 first lens, 32 second lens, 40 sheet, 41, 141 stamper, 42 roller, 43 thin plate substrate, 60 liquid ultraviolet curable resin, 61 rotating base 62 lamps, 70 highly reflective films, 71 protective films

Claims (2)

A method of manufacturing an optical recording medium comprising at least two information signal portions and a light transmission layer on a surface on which laser light is incident,
Forming a first information signal portion on the surface of the substrate by injection molding,
Forming a first reflective film on the substrate;
In a state where the central hole of the substrate is filled on the first reflective film, an ultraviolet curable resin is dropped from the center, a stamper is brought into contact with the ultraviolet curable resin, and the film is rotationally stretched and cured. forming an ultraviolet-curing resin layer having a second information signal portion information pits or guide grooves of the stamper have been transferred,
Forming a second reflective film on the ultraviolet curable resin layer;
Forming a protective layer on the second reflective film;
A method for producing an optical recording medium comprising : The first information signal portion and the second information signal section, the method of manufacturing an optical recording medium according to claim 1, Ru provided in intervals corresponding to the movable range of the number of layers and the pickup lens of said information signal portion .

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