JP7468521B2 - Optical recording media - Google Patents

Description

The present disclosure relates to optical recording media.

Optical recording media are generally said to have higher storage reliability due to their recording and playback principles compared to hard disk drives (HDDs) and flash memories. For this reason, in recent years, there has been a growing demand for optical recording media as archival media. Optical recording media are generally required to have a smooth surface.

In optical recording media, a hard coat layer is widely used to protect the surface of the medium. When a hard coat layer is used, the smoothness of the medium surface is easily impaired, so techniques for forming a smooth hard coat layer are being investigated. For example, Patent Document 1 discloses an optical recording medium formed with a hard coat layer that has excellent durability such as scratch resistance, dust resistance, and stain resistance, and also has excellent surface smoothness when coated.

JP 2009-96927 A

However, optical recording media with smooth surfaces have the problem that when multiple optical recording media are stacked, the optical recording media tend to stick together.

The objective of the present disclosure is to provide an optical recording medium that can prevent the optical recording media from sticking together when multiple optical recording media are stacked.

In order to solve the above-mentioned problems, a first optical recording medium according to the present disclosure comprises an optical recording medium body having a first side and a second side, and a first uneven structure layer provided on the first side, the first uneven structure layer includes a plurality of first structures provided at a pitch equal to or less than the wavelength of light for recording or reproducing an information signal, the area ratio of the convex portions of the first uneven structure layer is 20 % or less, and light is irradiated from the first side.
A second optical recording medium according to the present disclosure comprises an optical recording medium body having a first surface and a second surface, and a first uneven structure layer provided on the first surface, the first uneven structure layer including a plurality of first structures provided at a pitch equal to or less than the wavelength of light for recording or reproducing an information signal, the first structures having a shape similar to the concave or convex portions used for recording signals in the optical recording medium, the area ratio of the convex portions of the first uneven structure layer being 80% or less, and light being irradiated from the first surface side.

Fig. 1A is a perspective view showing an example of the appearance of an optical recording medium according to a first embodiment of the present disclosure, and Fig. 1B is a cross-sectional view showing an example of the configuration of the optical recording medium according to the first embodiment of the present disclosure. FIG. 2 is a cross-sectional view showing an example of the configuration of each information signal layer shown in FIG. FIG. 3 is a plan view showing an example of an arrangement of a plurality of structures. FIG. 4 is a cross-sectional view showing an example of the configuration of an optical recording medium according to the second embodiment of the present disclosure. FIG. 5 is a cross-sectional view showing an example of the configuration of an optical recording medium according to a modified example. Fig. 6A is an SEM image of the relief structure of the optical disk of Example 1. Fig. 6B is an SEM image of the relief structure of the optical disk of Example 2. Fig. 6C is an SEM image of the relief structure of the optical disk of Comparative Example 2. FIG. 7 is a graph showing the frequency distribution of the concave-convex structure of the optical disk in Example 1. In FIG. FIG. 8 is a schematic diagram for explaining a method for measuring the adhesion force. 9A and 9B are graphs showing the relationship between the area ratio of the protrusions and the adhesion force and the sliding force, respectively. Fig. 10A is a graph showing the evaluation results of the signal characteristics of the optical disc of Example 3. Fig. 10B is a graph showing the evaluation results of the signal characteristics of the optical disc of Example 4. Fig. 10C is a graph showing the evaluation results of the signal characteristics of the optical disc of Comparative Example 3.

The embodiments of the present disclosure will be described in the following order.
1 First embodiment 1.1 Structure of optical recording medium 1.2 Manufacturing method of optical recording medium 1.3 Effect 2 Second embodiment 2.1 Structure of optical recording medium 2.2 Manufacturing method of optical recording medium 2.3 Effect 3 Modification

<1 First embodiment>
[1.1 Configuration of optical recording medium]
As shown in FIG. 1A, the optical recording medium 1 according to the first embodiment of the present disclosure has a disk shape with an opening (hereinafter referred to as a "center hole") in the center. The shape of the optical recording medium 1 is not limited to this example, and it can be, for example, a card shape. The optical recording medium 1 is a so-called multi-layer write-once optical recording medium (for example, AD (Archival Disc)), and includes an optical recording medium body 2, a first concave-convex structure layer 3, and a second concave-convex structure layer 4, as shown in FIG. 1B. The optical recording medium 1 is an optical recording medium of a type in which data is recorded on both groove tracks and land tracks (hereinafter referred to as a "land/groove recording type").

(Optical recording medium body)
The optical recording medium body 2 includes a first disk 10, a second disk 20, and a bonding layer 30. The first disk 10 has a configuration in which an information signal layer L0, a spacer layer S1, an information signal layer L1, ..., a spacer layer Sn, an information signal layer Ln, and a light transmission layer 12 as a cover layer are laminated in this order on one main surface of a substrate 11. The second disk 20 has a configuration in which an information signal layer L0, a spacer layer S1, an information signal layer L1, ..., a spacer layer Sm, an information signal layer Lm, and a light transmission layer 22 as a cover layer are laminated in this order on one main surface of a substrate 21. However, n and m are each independently an integer of 2 or more, and from the viewpoint of improving the recording capacity, they are preferably an integer of 3 or more, more preferably an integer of 4 or more, and even more preferably an integer of 5 or more. In the following description, when the information signal layers L0 to Ln and L0 to Lm are not particularly distinguished, they are referred to as an information signal layer L.

The optical recording medium body 2 has light irradiation surfaces on both sides onto which laser light for recording or reproducing information signals is irradiated. More specifically, it has a first light irradiation surface C1 onto which laser light for recording or reproducing information signals of the first disc 10 is irradiated, and a second light irradiation surface C2 onto which laser light for recording or reproducing information signals of the second disc 20 is irradiated.

In the first disc 10, the information signal layer L0 is located at the innermost position based on the first light irradiation surface C1, with the information signal layers L1 to Ln located in front of it. For this reason, the information signal layers L1 to Ln are configured to be able to transmit the laser light used for recording or playback. On the other hand, in the second disc 20, the information signal layer L0 is located at the innermost position based on the second light irradiation surface C2, with the information signal layers L1 to Lm located in front of it. For this reason, the information signal layers L1 to Lm are configured to be able to transmit the laser light used for recording or playback.

In the optical recording medium 1, the information signal of the first disc 10 is recorded or reproduced as follows. That is, the information signal of the first disc 10 is recorded or reproduced by irradiating each information signal layer L0 to Ln included in the first disc 10 with laser light from the first light irradiation surface C1 on the light transmission layer 12 side. For example, the information signal is recorded or reproduced by irradiating each information signal layer L0 to Ln included in the first disc 10 from the light transmission layer 12 side with laser light having a wavelength in the range of 350 nm to 415 nm using an objective lens with a numerical aperture in the range of 0.84 to 0.95, and collecting the laser light.

On the other hand, the information signal of the second disc 20 is recorded or reproduced as follows. That is, the information signal of the second disc 20 is recorded or reproduced by irradiating each information signal layer L0 to Lm included in the second disc 20 with laser light from the second light irradiation surface C2 on the light transmission layer 22 side. For example, the information signal is recorded or reproduced by focusing laser light having a wavelength in the range of 350 nm to 415 nm with an objective lens having a numerical aperture in the range of 0.84 to 0.95, and irradiating each information signal layer L0 to Lm included in the second disc 20 from the light transmission layer 22 side.

Below, we will explain in sequence the substrates 11, 21, bonding layer 30, information signal layers L0-Ln, L0-Lm, spacer layers S1-Sn, S1-Sm and light transmitting layers 12, 22 that constitute the optical recording medium body 2.

(substrate)
The substrates 11 and 21 are, for example, disk-shaped with a center hole in the center. One main surface of the substrates 11 and 21 is, for example, an uneven surface, and the information signal layer L0 is formed on the uneven surface. Hereinafter, the concave portions of the uneven surface are referred to as lands Ld, and the convex portions are referred to as grooves Gv.

The land Ld and groove Gv may have various shapes, such as a spiral shape, a concentric circle shape, etc. The land Ld and/or groove Gv may be wobbled (meandered) to stabilize the linear velocity, add address information, etc.

The spiral directions of the first disk 10 and the second disk 20 may be reversed. In this case, simultaneous recording and playback of the optical recording medium (double-sided disk) 1 formed by bonding the first disk 10 and the second disk 20 together is possible, so the data transfer speed during recording and playback can be increased by approximately two times.

The outer diameter (diameter) of the substrates 11 and 21 is selected to be, for example, 120 mm. The inner diameter (diameter) of the substrates 11 and 21 is selected to be, for example, 15 mm. The thickness of the substrate 11 is selected in consideration of rigidity, and is preferably 0.3 mm or more and 0.545 mm or less, more preferably 0.445 mm or more and 0.545 mm or less.

The material for the substrates 11 and 21 may be, for example, a plastic material or glass, and from the viewpoint of moldability, it is preferable to use a plastic material. The plastic material may be, for example, a polycarbonate-based resin, a polyolefin-based resin, or an acrylic-based resin, and from the viewpoint of cost, it is preferable to use a polycarbonate-based resin.

(Laminating layer)
The bonding layer 30 is provided between the first disk 10 and the second disk 20. The first disk 10 and the second disk 20 are bonded together by the bonding layer 30. More specifically, the surface of the first disk 10 facing the substrate 11 and the surface of the second disk substrate facing the substrate 21 are bonded together with the light transmitting layers 12 and 22 facing the front surfaces.

The bonding layer 30 is made of a cured ultraviolet curing resin. The thickness of the bonding layer 30 is, for example, 0.01 mm or more and 0.22 mm or less. The ultraviolet curing resin is, for example, a radical polymerization type ultraviolet curing resin.

(Information Signal Layer)
The information signal layer L has a concave track (hereinafter referred to as a "land track") and a convex track (hereinafter referred to as a "groove track"). The optical recording medium 1 according to the first embodiment is configured so that information signals can be recorded on both the land track and the groove track. From the viewpoint of high recording density, the track pitch Tp between the land track and the groove track is preferably 0.225 μm or less, and more preferably less than 0.225 μm. The lower limit of the track pitch Tp is not particularly limited, but is, for example, 0.12 μm or more.

As shown in FIG. 2, the information signal layers L0 to Ln include an inorganic recording layer (hereinafter simply referred to as a "recording layer") 13 having an upper surface (first main surface) and a lower surface (second main surface), a protective layer 14 provided adjacent to the upper surface of the recording layer 13, and a protective layer 15 provided adjacent to the lower surface of the recording layer 13. This configuration can improve the durability of the recording layer 13. Here, the upper surface refers to the main surface of the two main surfaces of the recording layer 13 that is irradiated with laser light for recording or reproducing information signals, and the lower surface refers to the main surface opposite to the side irradiated with the above-mentioned laser light, that is, the main surface on the substrate 11 side. The configuration of the information signal layers L0 to Lm can be the same as that of the information signal layers L0 to Ln, so a description thereof will be omitted.

(Recording Layer)
The recording layer 13 is configured to be capable of recording an information signal by irradiation with a laser beam. Specifically, the recording layer 13 is configured to be capable of forming a recording mark by irradiation with a laser beam. The recording layer 13 is an inorganic recording layer and contains a metal oxide as a main component as an inorganic recording material. The metal oxide is, for example, an inorganic recording material containing manganese oxide (MnO-based material), an inorganic recording material containing palladium oxide (PdO-based material), an inorganic recording material containing copper oxide (CuO-based material), or an inorganic recording material containing silver oxide (AgO-based material).

In addition to manganese oxide, the MnO-based material preferably further contains one or both of tungsten oxide and molybdenum oxide, and zirconium oxide. The MnO-based material may further contain one or both of nickel oxide and magnesium oxide, together with or without these oxides other than manganese oxide.

In addition to palladium oxide, the PdO-based material preferably further contains tungsten oxide and copper oxide, and more preferably further contains tungsten oxide, copper oxide and zinc oxide.

The thickness of the recording layer 13 is preferably in the range of 25 nm to 60 nm, more preferably 30 nm to 50 nm. When the thickness of the recording layer 13 is 25 nm or more, it is possible to obtain excellent signal characteristics. On the other hand, when the thickness of the recording layer 13 is 60 nm or less, a wide recording power margin can be ensured.

(Protective Layer)
The protective layers 14 and 15 function as oxygen barrier layers. This can improve the durability of the recording layer 13. The protective layers 14 and 15 also function to suppress the escape of oxygen from the recording layer 13. This can suppress changes in the film quality of the recording layer 13 (detected mainly as a decrease in reflectance), and ensure a film quality that is preferable for the recording layer 13. The protective layers 14 and 15 also function to improve the recording characteristics.

The protective layers 14 and 15 include a dielectric. The dielectric includes at least one selected from the group consisting of, for example, oxide, nitride, sulfide, carbide, and fluoride. The materials of the protective layers 14 and 15 may be the same or different from each other. The oxide may be, for example, an oxide of one or more elements selected from the group consisting of In, Zn, Sn, Al, Si, Ge, Ti, Ga, Ta, Nb, Hf, Zr, Cr, Bi, and Mg. The nitride may be, for example, a nitride of one or more elements selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Nb, Mo, Ti, Nb, Mo, Ti, W, Ta, and Zn, preferably a nitride of one or more elements selected from the group consisting of Si, Ge, and Ti. The sulfide may be, for example, Zn sulfide. Examples of the carbides include carbides of one or more elements selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Ti, Zr, Ta, and W, preferably carbides of one or more elements selected from the group consisting of Si, Ti, and W. Examples of the fluorides include fluorides of one or more elements selected from the group consisting of Si, Al, Mg, Ca, and La. Specific examples of these mixtures include ZnS- _{SiO2 , SiO2} - _{In2O3 - ZrO2 (} SIZ ₎ , SiO2- _Cr2O3 - _ZrO2 (SCZ), In2O3- _{SnO2 (} ITO), _{In2O3 - CeO2} (ICO), In2O3- _{Ga2O3 (IGO), In2O3-Ga2O3-ZnO (IGZO), Sn2O3-Ta2O5 ( TTO ) , TiO2 - SiO2 , Al2O3 - ZnO , and Al2O3 - BaO} .

The thickness of the protective layer 15 is preferably in the range of 2 nm to 30 nm. If the thickness of the protective layer 15 is 2 nm or more, a good barrier effect can be obtained. On the other hand, if the thickness of the protective layer 15 is 30 nm or less, a decrease in the recording power margin can be suppressed.

The thickness of the protective layer 14 is preferably in the range of 2 nm to 50 nm. If the thickness of the protective layer 14 is 2 nm or more, a good barrier effect can be obtained. On the other hand, if the thickness of the protective layer 14 is 50 nm or less, a decrease in the recording power margin can be suppressed.

(Spacer Layer)
The spacer layers S1-Sn, S1-Sm have the role of separating the information signal layers L0-Ln, L0-Lm by a sufficient distance physically and optically, and have an uneven surface on their surface. The uneven surface forms, for example, concentric or spiral lands Ld and grooves Gv. The thickness of the spacer layers S1-Sn, S1-Sm is preferably 9 μm or more and 50 μm or less. The material of the spacer layers S1-Sn, S1-Sm is not particularly limited, but it is preferable to use an ultraviolet-curable acrylic resin. In addition, since the spacer layers S1-Sn, S1-Sm become the optical path of the laser light for recording and reproducing data in the inner layers, it is preferable that they have sufficiently high optical transparency.

(Light transmitting layer)
The light-transmitting layers 12 and 22 are resin layers formed by curing a photosensitive resin such as an ultraviolet-curing resin. Examples of the ultraviolet-curing resin include an ultraviolet-curing acrylic resin. The light-transmitting layers 12 and 22 may be formed of a light-transmitting sheet having a circular ring shape and an adhesive layer for bonding the light-transmitting sheet to the information signal layers Ln and Lm. The light-transmitting sheet is preferably made of a material that has low absorption capacity for the laser light used for recording and reproduction, and more specifically, is preferably made of a material with a transmittance of 90% or more. Examples of the material for the light-transmitting sheet include polycarbonate resin or polyolefin resin (e.g., Zeonex (registered trademark)). Examples of the material for the adhesive layer include an ultraviolet-curing resin or a pressure-sensitive adhesive (PSA: Pressure Sensitive Adhesive).

The thickness of the light-transmitting layers 12, 22 is preferably selected from the range of 10 μm to 177 μm, for example, 57 μm. By combining such thin light-transmitting layers 12, 22 with an objective lens with a high NA (numerical aperture), for example, about 0.85, high-density recording can be achieved.

(First and second concave-convex structure layers)
The first and second uneven structure layers 3 and 4 provide scratch resistance to the first and second light irradiation surfaces C1 and C2, respectively. The first and second uneven structure layers 3 and 4 also provide the first and second light irradiation surfaces C1 and C2 with a reflection suppression function that suppresses reflection of a laser beam for recording or reproducing an information signal. The first uneven structure layer 3 is provided on the first light irradiation surface C1 of the optical recording medium body 2. The second uneven structure layer 4 is provided on the second light irradiation surface C2 of the optical recording medium body 2.

The first and second uneven structure layers 3 and 4 may be made of, for example, acrylic resin, silicone resin, fluorine resin, or organic-inorganic hybrid resin. The first and second uneven structure layers 3 and 4 may contain a fine powder of metal oxide particles such as silica particles to improve mechanical strength.

The upper limit of the area ratio R of the convex portions in the first and second uneven structure layers 3 and 4 is 80% or less, preferably 60% or less, more preferably 50% or less, even more preferably 40% or less, and particularly preferably 20% or less, from the viewpoint of suppressing the adhesion between the overlapped optical recording media 1. On the other hand, the lower limit of the area ratio R is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more, from the viewpoint of improving the reflection suppression effect. Here, the convex portion refers to the convex portion itself when the first and second uneven structure layers 3 and 4 have a convex structure, and refers to a portion without a concave structure that is considered as a convex portion based on the concave portion when the first and second uneven structure layers 3 and 4 have a concave structure. Specifically, the area ratio R of the convex portions in the first and second uneven structure layers 3 and 4 means the ratio of the area Sb of the convex portion formation region to the area Sa of the uneven structure formation region (= (Sb/Sa) × 100). The method for measuring the area ratio R will be described in the examples.

The first uneven structure layer 3 is a hard coat layer having a fine uneven structure (moth-eye structure) on the surface. Specifically, the first uneven structure layer 3 includes a base layer 3A and a plurality of structures 3B. The base layer 3A and the plurality of structures 3B may be made of the same material or different materials. Since the second uneven structure layer 4 has the same structure as the first uneven structure layer 3, the description of the structure of the second uneven structure layer 4 is omitted.

The base layer 3A is the main body of the hard coat layer and is provided on the first light irradiation surface C1. The multiple structures 3B are provided on the base layer 3A. The structures 3B are so-called moth-eye structures (sub-wavelength structures) and have a convex shape with respect to the first light irradiation surface C1. The structures 3B may have a shape similar to a concave or convex portion (e.g., a pit) used for recording an information signal in a read-only optical recording medium. In this case, a master for forming a substrate of a read-only optical recording medium can be used as a master (mold) for forming the first concave-convex structure layer 3 (i.e., the multiple structures 3B). Therefore, the process of separately preparing a master for forming the first concave-convex structure layer 3 can be omitted.

A plurality of structures 3B are arranged, for example, in a plurality of rows on the surface of the first light irradiation surface C1. The rows are, for example, linear, concentric, or curved. Two or more of these shapes may be combined. An example of the curved shape is a periodic or non-periodic meandering curve. Specific examples of such curved shapes include, but are not limited to, sine waves, triangular waves, and other waveforms.

The arrangement of the multiple structures 3B on the first light irradiation surface C1 may be either a regular arrangement or an irregular arrangement. As a regular arrangement, a lattice arrangement such as a square lattice, a quasi-square lattice, a hexagonal lattice, or a quasi-hexagonal lattice is preferable. Note that FIG. 3 shows an example in which the multiple structures 3B are arranged in a hexagonal lattice. Here, the square lattice refers to a square lattice. The quasi-square lattice refers to a distorted square lattice. The hexagonal lattice refers to a regular hexagonal lattice. The quasi-hexagonal lattice refers to a distorted hexagonal lattice.

Specific shapes of the structure 3B include, for example, a cone shape, a column shape, a needle shape, a hemisphere shape, a semi-ellipsoid shape, a polygonal shape, etc., but are not limited to these shapes, and other shapes may be adopted. Examples of cone shapes include, for example, a cone shape with a pointed apex, a cone shape with a flat apex (so-called frustum shape), and a cone shape with a convex or concave curved surface at the apex, but are not limited to these shapes. Examples of cone shapes with a convex curved surface at the apex include, for example, a quadratic curved surface such as a paraboloid. In addition, the cone surface of the cone shape may be curved concavely or convexly.

All of the multiple structures 3B provided on the first light irradiation surface C1 may have the same size, shape, and height, or the multiple structures 3B may include structures having different sizes, shapes, or heights. Also, the multiple structures 3B may include structures that are connected by overlapping their lower parts.

As shown in FIG. 3, the multiple structures 3B are arranged at pitches P1, P2 that are equal to or less than the wavelength of the laser light for recording or reproducing the information signal (e.g., 350 nm or less). The absolute value H of the height of the structures 3B is set, for example, within the range of 40 nm to 450 nm, but is not limited to this. Here, pitch P1 refers to the pitch of the structures 3B in the inter-row direction D1. Also, pitch P2 refers to the pitch of the structures 3B in the row direction (row extension direction) D2.

The aspect ratio of the structure 3B is preferably 1 or more. This is because an aspect ratio of 1 or more provides excellent reflection suppression function and transmission characteristics. The upper limit of the aspect ratio of the structure 3B is preferably 2 or less, more preferably 1.46 or less. This is because an aspect ratio of 2 or less makes it possible to easily peel off the master from the first concave-convex structure layer 3 when forming the first concave-convex structure layer 3. Here, the aspect ratio of the structure 3B means the aspect ratio R1 of the structure 3B in the inter-row direction D1 and the aspect ratio R2 of the structure 3B in the row direction (row extension direction) D2. The aspect ratio R1 of structure 3B in the inter-row direction D1 means the ratio (H/W1) of the height H of structure 3B to the width W1 of structure 3B in the inter-row direction D1, and the aspect ratio R2 of structure 3B in the column direction (extension direction of the columns) D2 means the ratio (H/W2) of the height H of structure 3B to the width W2 of structure 3B in the column direction (extension direction of the columns) D2.

[1.2 Manufacturing method of optical recording medium]
Next, an example of a method for manufacturing the optical recording medium 1 according to the first embodiment of the present disclosure will be described.

(First Disc Manufacturing Process)
First, the first disk 10 is produced as follows.

(Substrate molding process)
First, the substrate 11 is formed with a concave-convex surface formed on one main surface thereof. The substrate 11 can be formed by, for example, an injection molding method or a photopolymerization method (2P method: Photo Polymerization).

(Formation process of information signal layer)
Next, the protective layer 15, the recording layer 13, and the protective layer 14 are laminated in this order on the substrate 11 by, for example, sputtering, thereby forming the information signal layer L0.

(Spacer Layer Forming Process)
Next, for example, by spin coating, an ultraviolet curing resin is uniformly applied onto the information signal layer L0. After that, the concave-convex pattern of the stamper is pressed against the ultraviolet curing resin uniformly applied onto the information signal layer L0, and the ultraviolet curing resin is irradiated with ultraviolet light to cure, and then the stamper is peeled off. As a result, the concave-convex pattern of the stamper is transferred to the ultraviolet curing resin, and a spacer layer S1 provided with, for example, lands Ld and grooves Gv is formed on the information signal layer L0.

(Step of forming information signal layer and step of forming spacer layer)
Next, in the same manner as in the above-mentioned “information signal layer forming process” and “spacer layer forming process”, an information signal layer L1, a spacer layer S2, an information signal layer L3, ..., a spacer layer Sn, and an information signal layer Ln are laminated in this order on the spacer layer S1.

(Light transmitting layer forming process)
Next, a photosensitive resin such as an ultraviolet curing resin (UV resin) is spin-coated on the information signal layer Ln by, for example, a spin coating method, and then the photosensitive resin is irradiated with light such as ultraviolet light to cure it, thereby forming a light transmission layer 12 on the information signal layer Ln.

(Step of forming first concave-convex structure layer)
Next, the first uneven structure layer 3 is formed on the first light irradiation surface C1 of the optical recording medium body 2 by UV nanoimprinting. Specifically, an ultraviolet curing resin is applied to the first light irradiation surface C1 of the optical recording medium body 2 by spin coating, and a master (mold) is pressed against the ultraviolet curing resin, and then the ultraviolet curing resin is irradiated with ultraviolet light to harden the ultraviolet curing resin. After hardening, the master is released from the ultraviolet curing resin. This forms the first uneven structure layer 3. In this manner, the first disc 10 is produced.

(Second Disc Manufacturing Process)
The "second disk manufacturing process" is similar to the above-mentioned "first disk manufacturing process", so a description thereof will be omitted.

(Laminating process)
Next, an ultraviolet curing resin as an adhesive is spread between the first and second disks 10 and 20 produced as described above, for example, by spin coating as follows. First, an ultraviolet curing resin is applied in a ring shape along the periphery of the center hole on the main surface opposite the second light irradiation surface C2 of both main surfaces of the second disk 20. Next, the first disk 10 is pressed against the second disk 20 via the ultraviolet curing resin so that the main surface opposite the first light irradiation surface C1 of both main surfaces of the first disk 10 faces the main surface opposite the second light irradiation surface C2 of both main surfaces of the second disk 20.

Next, the first and second disks 10, 20 are rotated to spread the UV-curable resin between the first and second disks 10, 20 in the radial direction of the first and second disks 10, 20. At this time, the thickness of the UV-curable resin is adjusted to a predetermined thickness by the rotation speed. This allows the UV-curable resin to spread between the first and second disks 10, 20 from the inner periphery to the outer periphery of the first and second disks 10, 20. As a result, an optical recording medium body 2 having an uncured lamination layer 30 is obtained.

In the above-mentioned UV-curable resin stretching process, it is preferable to irradiate the outer periphery of the first and second disks 10 and 20 with UV light to temporarily harden the UV-curable resin stretched to the outer periphery. This makes it possible to prevent openings from occurring in the outer periphery of the first and second disks 10 and 20.

Next, ultraviolet light is applied from an ultraviolet lamp to both sides of the optical recording medium body 2 to harden the lamination layer 30. This results in the desired optical recording medium 1.

[1.3 Effects]
The optical recording medium 1 according to the first embodiment described above has first and second concave-convex structure layers 3 and 4 on the first and second light irradiation surfaces C1 and C2, respectively. This makes it possible to reduce the contact area of the overlapped optical recording media 1 when a plurality of optical recording media 1 are overlapped. This makes it possible to prevent the overlapped optical recording media 1 from sticking to each other. In addition, the sliding force of the overlapped optical recording media 1 can be reduced.

The first and second uneven structure layers 3 and 4 are composed of structures arranged at a pitch equal to or less than the wavelength of the laser light for recording or reproducing information signals (e.g., 350 nm or less). This makes it possible to reduce the amount of reflected light compared to a flat light irradiation surface.

In a method of forming the first and second uneven structure layers on the first and second light irradiation surfaces of the optical recording medium body, respectively, using an ultraviolet curing resin to which fine particles such as nanoparticles are added, it is difficult to control the uneven shape. If the uneven shape of the first and second uneven structure layers cannot be controlled, optical interference is caused in areas with large uneven shapes, and signal quality deteriorates. In contrast, in the manufacturing method of the optical recording medium 1 according to the first embodiment, the uneven shape of the master is transferred to the ultraviolet curing resin to form the first and second uneven structure layers 3 and 4 on the first and second light irradiation surfaces C1 and C2 of the optical recording medium 1, respectively, so that it is easy to control the uneven shapes of the first and second uneven structure layers 3 and 4. Therefore, it is possible to stably reduce interlayer interference over the entire surface of the optical recording medium 1.

<2. Second embodiment>
[2.1 Configuration of optical recording medium]
4, an optical recording medium 101 according to the second embodiment of the present disclosure is a so-called multi-layer write-once optical recording medium, and includes an optical recording medium body 102 and a first uneven structure layer 3. Note that in the second embodiment, the same parts as in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

The optical recording medium body 102 has a configuration in which an information signal layer L0, a spacer layer S1, an information signal layer L1, ..., a spacer layer Sn, an information signal layer Ln, and a light transmitting layer 12 which is a cover layer are laminated in this order on one main surface of the substrate 11A.

The optical recording medium 101 has a light irradiation surface C on one side, onto which light for recording or reproducing an information signal is irradiated. The information signal layer L0 is located at the innermost position based on the light irradiation surface C, and the information signal layers L1 to Ln are located in front of it. For this reason, the information signal layers L1 to Ln are configured to be transparent to the laser light used for recording or reproduction.

In the optical recording medium 101 according to the second embodiment, information signals are recorded or reproduced by irradiating each information signal layer L0 to Ln with laser light from the light irradiation surface C on the light transmission layer 12 side. For example, information signals are recorded or reproduced by focusing laser light having a wavelength in the range of 400 nm to 415 nm with an objective lens having a numerical aperture in the range of 0.84 to 0.86, and irradiating each information signal layer L0 to Ln from the light transmission layer 12 side. An example of such an optical recording medium 101 is a multi-layer Blu-ray Disc (BD: Blu-ray (registered trademark) Disc).

The optical recording medium 101 is typically an optical recording medium using a groove recording method, but may also be an optical recording medium using a land/groove recording method or the like.

The diameter of the substrate 11A is selected to be, for example, 120 mm. The thickness of the substrate 11A is selected in consideration of rigidity, and is preferably selected to be 0.3 mm or more and 1.3 mm or less, more preferably 0.6 mm or more and 1.3 mm or less, for example 1.1 mm. The diameter of the center hole is selected to be, for example, 15 mm. The material of the substrate 11A is the same as that of the substrate 11 in the first embodiment described above.

[2.2 Manufacturing method of optical recording medium]
An example of a method for manufacturing the optical recording medium 101 according to the second embodiment of the present disclosure will be described.

First, the optical recording medium body 102 is produced in the same manner as in the "first disc production process" in the first embodiment described above. Next, the first uneven structure layer 3 is formed on the light irradiation surface C of the optical recording medium body 102 by UV nanoimprinting. This results in the desired optical recording medium 101.

[2.3 Effects]
The optical recording medium 101 according to the second embodiment described above can provide the same effects as those of the first embodiment. For example, by reducing the amount of reflected light compared to a flat light irradiation surface, it becomes possible to provide four or more information signal layers L within the thickness (100 μm) of the light transmission layer 12 of the BD standard.

<3 Modification>
In the above-mentioned first and second embodiments, the information signal layer L is described as having a recording layer 13, a protective layer 14 provided adjacent to the upper surface of the recording layer 13, and a protective layer 15 provided adjacent to the lower surface of the recording layer 13, but the configuration of the information signal layer L is not limited to this. For example, a protective layer may be provided only on either the upper surface or the lower surface of the recording layer 13. Also, the information signal layer L may be composed of only the single recording layer 13. By adopting such a simple configuration, it is possible to reduce the cost of the optical recording medium 1, 101 and improve its productivity. This effect becomes more prominent as the number of layers of the information signal layer L increases.

In the above-mentioned first and second embodiments, the case where all the multiple information signal layers L have the same layer structure (three-layer structure) has been described, but the layer structure may be changed according to the characteristics (e.g. optical characteristics, durability, etc.) required for each information signal layer L. However, from the viewpoint of productivity, it is preferable that all the information signal layers L have the same layer structure.

The optical recording medium to which the present disclosure can be applied is not limited to those having the configurations in the first and second embodiments. For example, the present disclosure can be applied to an optical recording medium (e.g., a CD (Compact Disc)) having a configuration in which multiple information signal layers and a protective layer are stacked in this order on a substrate, and information signals are recorded or reproduced by irradiating the multiple information signal layers with laser light from the substrate side, or an optical recording medium (e.g., a DVD (Digital Versatile Disc)) having a configuration in which multiple information signal layers are provided between two substrates, and information signals are recorded or reproduced by irradiating the multiple information signal layers with laser light from at least one of the substrates.

In the first embodiment described above, the first and second disks 10, 20 each have multiple information signal layers L, but the first and second disks 10, 20 each may have a single information signal layer L.

In the above-mentioned second embodiment, a case has been described in which the optical recording medium 101 has multiple information signal layers L, but the optical recording medium 101 may also have a single information signal layer L.

In the first embodiment described above, a case where a concave-convex structure layer is provided on both the first light irradiation surface C1 and the second light irradiation surface C2 of the optical recording medium body 2 has been described, but a concave-convex structure layer may be provided on either the first light irradiation surface C1 or the second light irradiation surface C2 of the optical recording medium body 2. However, in order to make the reflectance and transmittance of the first light irradiation surface C1 and the second light irradiation surface C2 the same, it is preferable that a concave-convex structure layer is provided on both the first light irradiation surface C1 and the second light irradiation surface C2 of the optical recording medium body 2 as in the first embodiment described above.

In the first embodiment described above, the structure 3B has a convex shape with respect to the first light irradiation surface C1, but as shown in FIG. 5, the structure 3C may have a concave shape with respect to the first light irradiation surface C1. In this case, the absolute value of the depth D of the concave structure 3C can be treated in the same way as the absolute value of the height H of the convex structure 3B in the first embodiment. Similarly, in the second embodiment described above, the structure 3B may have a concave shape with respect to the light irradiation surface C.

In the first and second embodiments described above, the recording layer 13 is an inorganic recording layer, but the recording layer 13 may also be an organic recording layer.

In the first and second embodiments described above, the optical recording medium 1, 101 is described as being of a write-once type, but the optical recording medium 1, 101 may also be of a read-only type or a rewritable type.

In the second embodiment described above, the optical recording medium 101 has a configuration in which an information signal can be recorded or reproduced from only one side, but the optical recording medium 101 may have a configuration in which an information signal can be recorded or reproduced from both sides. In this case, a plurality of information signal layers L and a light transmission layer 12 are provided on both sides of the substrate 11A. In addition, a concavo-convex structure layer may be provided on both sides.

In the above-mentioned first and second embodiments, a case has been described in which the first uneven structure layer 3 is a hard coat layer having a base layer 3A and a plurality of structures 3B, but the first uneven structure layer 3 may not have a base layer 3A and may be composed only of a plurality of structures 3B.

In the first and second embodiments, the first and second uneven structure layers 3, 4 (specifically, the structures 3B, 3C contained in the first and second uneven structure layers 3, 4) may be made to have information. For example, the first and second uneven structure layers 3, 4 may be made to have information by thinning out the moth eye or BD pits, or the CD pits themselves. Examples of information to be provided in the first and second uneven structure layers 3, 4 include disc-specific information such as that provided in the BCA (Burst Cutting Area) or two-dimensional barcode, encryption information for preventing piracy or copying, and security information such as watermarks.

The above information may be detected using an optical system for detecting signals from the information signal layer L, or an optical system using a light source with a different wavelength. In addition, images of the first and second uneven structure layers 3 and 4 may be obtained using an image sensor or the like, and then the information may be detected by image recognition of the images.

In the first embodiment, one of the first light irradiation surface C1 and the second light irradiation surface C2 may have a concave-convex structure layer, while the other may be a surface (smooth surface) without a concave-convex structure layer. In this case, it is possible to distinguish the front and back of the optical recording medium 1 based on the presence or absence of the concave-convex structure layer. The specifications (e.g., structure) of the first concave-convex structure layer 3 of the first light irradiation surface C1 and the second concave-convex structure layer 4 of the second light irradiation surface C2 may be different. In this case, it is possible to distinguish the front and back of the optical recording medium 1 based on the difference in specifications between the first concave-convex structure layer 3 and the second concave-convex structure layer 4. Similarly, in the above-mentioned second embodiment, concave-convex structure layers with different specifications may be provided on the light irradiation surface C and the back surface opposite thereto.

To distinguish between the front and back of the optical recording medium 1, an optical system or image recognition may be used, as in the case of detecting the information of the first and second uneven structure layers 3 and 4.

In the first embodiment described above, a case has been described in which the first and second uneven structure layers 3, 4 are formed on the first and second light irradiation surfaces C1, C2 of the first and second discs 10, 20, respectively, before the bonding process. However, it is also possible to form the first and second uneven structure layers 3, 4 on the first and second light irradiation surfaces C1, C2 of the optical recording medium body 2, respectively, after the bonding process.

The present disclosure will be explained in detail below using examples, but the present disclosure is not limited to these examples.

The embodiments of the present disclosure will be described in the following order.
i Examples and Comparative Examples in which adhesion and sliding strength were evaluated
ii. Examples and Comparative Examples Evaluating the Influence of the Concave-Convex Structure on Signal Characteristics

<i. Examples and Comparative Examples Evaluating Adhesive Strength and Slip Strength>
An optical disk having a fine uneven structure formed on the light irradiated surface was produced as described below, and the adhesive force and sliding force were evaluated.

[Example 1]
A fine uneven structure (moth-eye structure) consisting of concave structures was formed on both light irradiation surfaces (both signal surfaces) of an optical disc body (the specifications are the same as those of a BD-DSD with a recording capacity of 200 GB, except for the uneven structure formed by UV nanoimprinting). At this time, the pitches P1, P2 of the structures, the widths W1, W2 of the structures, and the depth D of the structures (see FIG. 5) were set to the values shown in Table 1. The pitches P1 and P2 were set to be equal to or less than the wavelength of the laser light for recording or reproducing the information signal. As a result of the above, the desired optical disc was obtained.

[Example 2]
BD2T pits (2T pits on a triple-layer 100 GB ULTRA HD Blu-ray (registered trademark) disc arranged at a specified interval) were formed as fine concave-convex structures. At this time, the pitches P1, P2 of the concave-convex structure, the widths W1, W2 of the structure, and the height H of the structure (see FIG. 3) were set to the values shown in Table 1. The pitches P1 and P2 were set to be equal to or less than the wavelength of the laser light for recording or reproducing an information signal. Except for the above, an optical disc was obtained in the same manner as in Example 1.

[Comparative Example 1]
The optical disk of Comparative Example 1 was an optical disk having no fine uneven structure formed on either light irradiation surface (either signal surface) of an optical disk body (BD-DSD, recording capacity 200 GB).

[Comparative Example 2]
CD pits (pits used in CD-ROM substrates) were formed as fine concave-convex structures, and the pitches P1 and P2 of the concave-convex structures, widths W1 and W2 of the structures, and height H of the structures (see FIG. 3) were set to the values shown in Table 1. The pitches P1 and P2 were set to be larger than the wavelength of the laser light for recording or reproducing information signals. An optical disk was obtained in the same manner as in Example 1, except for the above.

(Protruding Area Ratio)
First, an SEM image of the light irradiation surface (signal surface) of the optical disk obtained as described above was obtained. Figures 6A, 6B, and 6C show SEM images of the concave-convex structures of Examples 1, 2, and Comparative Example 2, respectively. Next, contrast data for each pixel was obtained from the obtained SEM images, and a frequency distribution was created. Figure 7 shows the frequency distribution of the concave-convex structure of the optical disk of Example 1. Next, the low contrast (concave) group and the high contrast group (convex) group were each fitted (Gaussian fitting) with an optimal function (Gaussian function), and the intersection point P of the fitting function was obtained. The integral value of the raw data of the group with a pixel contrast lower than the intersection point P was taken as the area of the concave, and the integral value of the raw data of the group with a pixel contrast higher than the intersection point P was taken as the area of the convex. Next, the ratio of the area of the convex to the sum of the areas of the concave and convex was obtained, and this ratio was taken as the area ratio R [%] of the convex on the light irradiation surface (signal surface) of the optical disk.

(Reflectance)
The reflectance of the light irradiation surface (signal surface) of the optical disk obtained as described above was simply measured using a Pulstec evaluation machine (ODU-1000, wavelength λ=405 nm, objective lens NA=0.85) as follows. First, the expander position was adjusted so that the spherical aberration was optimal near the L2 layer. Next, the objective lens was searched in the optical axis direction to obtain the sum signal of the reflected return light from the optical disk. Since the peak that first appears in the obtained sum signal corresponds to the surface of the optical disk, the voltage value of that peak was obtained. Next, the reflectance of the light irradiation surface of the optical disk was calculated using the obtained voltage value of the surface, based on the reflectance of the L2 layer (voltage value of the sum signal) obtained in advance by applying focus servo. The reflectance based on the voltage value of the surface is slightly different because the spherical aberration is optimal for the L2 layer, but since the same conditions are used in all of the above examples and comparative examples, there is no problem in relative comparison.

(adhesive strength)
Fig. 8 is a schematic diagram for explaining the method of measuring the sticking force. First, two optical disks obtained as described above were prepared, and they were stacked on the measurement table so that the light irradiation surface (signal surface) was the upper surface and partly overlapped. Next, a load of 30 to 40 kg was applied to the two stacked optical disks, and then the load was released. Next, while applying a load of 290 g to the two stacked optical disks, the upper optical disk was pulled by a force gauge in a direction horizontal to the surface of the measurement table, and the tensile force at which the optical disk started to move was measured, and the maximum value of this tensile force was taken as the sticking force. Fig. 9A shows the relationship between the area ratio of the convex portion and the sticking force.

(Sliding Force)
First, two optical disks were stacked on the measurement table in the same manner as in the evaluation of the sticking force described above. Next, a load of 290 g was applied to the two stacked optical disks, and the upper optical disk was pulled by a force gauge in a direction parallel to the surface of the measurement table to measure the tensile force, and the maximum value of this tensile force was taken as the sliding force. Figure 9B shows the relationship between the area ratio of the convex parts and the sliding force.

The configurations of the concave-convex structures of the optical disks in Examples 1 and 2 and Comparative Examples 1 and 2 and the evaluation results thereof are shown.

9A, 9B and Table 1 reveal the following.
In the optical discs having a fine uneven structure formed on the light irradiation surface (signal surface) (Examples 1 and 2, Comparative Example 2), the adhesion force and slippage force are reduced compared to the optical disc having a smooth light irradiation surface (signal surface) (Comparative Example 1).
In the optical discs (Examples 1 and 2) in which a plurality of structures are provided on the light irradiation surface (signal surface) at a pitch equal to or less than the wavelength of the laser light for recording or reproducing the information signal, the sticking force and sliding force are reduced compared to the optical disc (Comparative Example 2) in which a plurality of structures are provided on the light irradiation surface (signal surface) at a pitch larger than the wavelength of the laser light for recording or reproducing the information signal.

In optical discs (Examples 1 and 2) in which a plurality of structures are provided on the light irradiation surface (signal surface) at a pitch equal to or less than the wavelength of the laser light for recording or reproducing information signals, the reflectance is reduced compared to an optical disc (Comparative Example 1) in which the light irradiation surface (signal surface) is smooth. On the other hand, in an optical disc (Comparative Example 2) in which a plurality of structures are provided on the light irradiation surface (signal surface) at a pitch greater than the wavelength of the laser light for recording or reproducing information signals, the reflectance may be increased depending on the state of diffraction on the light irradiation surface (signal surface) compared to an optical disc (Comparative Example 1) in which the light irradiation surface (signal surface) is smooth.

<ii. Examples and Comparative Examples Evaluating the Influence of the Concave-Convex Structure on Signal Characteristics>
An optical disk having a fine uneven structure formed on the light irradiation surface (signal surface) was produced as described below, and the effect of the uneven structure on the signal characteristics was evaluated.

[Example 3]
By UV nanoimprinting, a fine uneven structure (moth-eye structure) similar to that in Example 1 was formed on both light irradiation surfaces (both signal surfaces) of an optical disk body (same specifications as AD, 300 GB recording capacity, except for the uneven structure formation by UV nanoimprinting). As a result, the desired optical disk was obtained.

[Example 4]
An optical disk was obtained in the same manner as in Example 3, except that a fine uneven structure (2T pits on a triple-layer 100 GB disk of BD2T pits (ULTRA HD Blu-ray (registered trademark)) arranged at a predetermined interval) similar to that in Example 2 was formed on both light irradiation surfaces (both signal surfaces) of an optical disk body (AD, recording capacity 300 GB).

[Comparative Example 3]
An optical disk of Comparative Example 3 was prepared by leaving the optical disk body (AD, recording capacity 300 GB) without forming a fine uneven structure on both light irradiation surfaces (both signal surfaces).

(Signal characteristics)
The signal characteristics of the optical disks of Examples 3 and 4 and Comparative Example 3 obtained as described above were evaluated as follows. Using a drive capable of recording and reproducing an AD with a recording capacity of 300 GB, the optical disk was reproduced at 64 RUB (Recording Unit Block) intervals of 0.1 mm. The maximum value Max, minimum value Min, and average value Ave of the SER (Symbol Error Rate) during 64 RUB reproduction were obtained over the entire surface at intervals of 0.1 mm, and the average values of the maximum value Max, minimum value Min, and average value Ave were obtained. The results are shown in Figures 10A, 10B, and 10C. From these evaluation results, it was found that the SER did not deteriorate even if a fine uneven structure (moth-eye structure and BD pits) was provided on the light irradiation surface (signal surface) of an AD with a recording capacity of 300 GB.

In addition, using a drive capable of recording and playing back 300GB ADs, the optical disc was played back at 0.1mm intervals of 64 RUBs, and the i-MLSE (Integrated-Maximum Likelihood Sequence Error) was evaluated. The evaluation results showed that even if a fine uneven structure (moth-eye structure and BD pits) is provided on the light irradiation surface (signal surface) of a 300GB AD, the i-MLSE does not deteriorate.

[Examples 5 and 6, Comparative Example 4]
Optical disks were obtained in the same manner as in Examples 3 and 4 and Comparative Example 4, except that an AD having a recording capacity of 500 GB was used as the optical disk body.

[Examples 7 and 8, Comparative Example 5]
Optical disks were obtained in the same manner as in Examples 1 and 2 and Comparative Example 1.

(Signal characteristics)
The signal characteristics of the optical discs of Examples 5 to 8 and Comparative Examples 4 and 5 obtained as described above were evaluated in the same manner as the signal characteristics of the optical discs of Examples 3, 4, and Comparative Example 3. As a result, it was found that the signal characteristics (SER, i-MLSE) did not deteriorate even when a fine uneven structure (moth-eye structure and BD pits) was provided on the light irradiation surface (signal surface) of an AD with a recording capacity of 500 GB and a BD-DSD with a recording capacity of 200 GB.

Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments, and various modifications based on the technical ideas of the present disclosure are possible.

The configurations, methods, processes, shapes, materials, and numerical values, etc. described in the above-described embodiments are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values, etc. may be used as necessary.

The configurations, methods, processes, shapes, materials, numerical values, etc. of the above-described embodiments may be combined with each other without departing from the spirit of this disclosure.

In the numerical ranges described in stages in the above embodiments, the upper or lower limit value of a numerical range of a certain stage may be replaced by the upper or lower limit value of a numerical range of another stage.

Unless otherwise specified, the materials exemplified in the above embodiments may be used alone or in combination of two or more.

The present disclosure may also employ the following configuration.
(1)
an optical recording medium body having a first surface and a second surface;
a first uneven structure layer provided on the first surface,
the first relief structure layer includes a plurality of first structures provided at a pitch equal to or smaller than the wavelength of light for recording or reproducing an information signal;
an area ratio of the convex portions of the first concave-convex structure layer is 80% or less;
The optical recording medium is irradiated with the light from the first surface side.
(2)
2. The optical recording medium according to claim 1, wherein the area ratio of the convex portions of the first concave-convex structure layer is 50% or less.
(3)
3. The optical recording medium according to claim 2, wherein the area ratio of the convex portions of the first concave-convex structure layer is 20% or less.
(4)
The optical recording medium according to any one of (1) to (3), wherein the first relief structure layer is a hard coat layer.
(5)
The optical recording medium according to any one of (1) to (4), wherein the first structures have a shape similar to a recess or protrusion used for recording a signal in the optical recording medium.
(6)
Further comprising a second relief structure layer provided on the second surface,
the second relief structure layer includes a plurality of second structures provided at a pitch equal to or less than the wavelength of the light,
The optical recording medium according to any one of (1) to (5), wherein the light is irradiated from the second surface side.
(7)
The optical recording medium body includes:
A first disk;
a second disk;
The first disk and the second disk are
A substrate;
an information signal layer provided on the substrate;
a cover layer covering the information signal layer,
7. The optical recording medium according to any one of (1) to (6), wherein a surface of the first disk facing the substrate and a surface of the second disk facing the substrate are bonded together.
(8)
The optical recording medium body includes:
A substrate;
an information signal layer provided on the substrate;
a cover layer covering the information signal layer,
The optical recording medium according to any one of (1) to (6), wherein the first surface is a surface on the cover layer side.

Reference Signs List 1, 101 Optical recording medium 2, 102 Optical recording medium body 3 First concave-convex structure layer 4 Second concave-convex structure layer 3A Base layer 3B, 3C Structure 10 First disk 20 Second disk 30 Laminating layer 11, 11A, 21 Substrate 12, 22 Light transmitting layer 13 Recording layer 14, 15 Protective layer L0 to Ln, L0 to Lm Information signal layer S1 to Sn, S1 to Sm Spacer layer C Light irradiation surface C1 First light irradiation surface C2 Second light irradiation surface Gv Groove Ld Land Tp Track pitch

Claims (7)

an optical recording medium body having a first surface and a second surface;
a first uneven structure layer provided on the first surface,
the first relief structure layer includes a plurality of first structures provided at a pitch equal to or smaller than the wavelength of light for recording or reproducing an information signal;
The area ratio of the convex portions of the first concave-convex structure layer is 20 % or less,
The optical recording medium is irradiated with the light from the first surface side. an optical recording medium body having a first surface and a second surface;
a first uneven structure layer provided on the first surface,
the first concave-convex structure layer includes a plurality of first structures provided at a pitch equal to or smaller than the wavelength of light for recording or reproducing an information signal , the first structures having a shape similar to a concave or convex portion used for recording a signal in an optical recording medium,
an area ratio of the convex portions of the first concave-convex structure layer is 80% or less;
The optical recording medium is irradiated with the light from the first surface side. 3. The optical recording medium according to claim 2 , wherein the area ratio of the convex portions of the first concave-convex structure layer is 50% or less. 4. The optical recording medium according to claim 1 , wherein the first relief structure layer is a hard coat layer. Further comprising a second relief structure layer provided on the second surface,
the second relief structure layer includes a plurality of second structures provided at a pitch equal to or less than the wavelength of the light,
5. The optical recording medium according to claim 1, wherein the light is irradiated from the second surface side. The optical recording medium body includes:
A first disk;
a second disk;
The first disk and the second disk are
A substrate;
an information signal layer provided on the substrate;
a cover layer covering the information signal layer,
6. The optical recording medium according to claim 1, wherein a surface of the first disk facing the substrate and a surface of the second disk facing the substrate are bonded together. The optical recording medium body includes:
A substrate;
an information signal layer provided on the substrate;
a cover layer covering the information signal layer,
5. The optical recording medium according to claim 1 , wherein the first surface is a surface on the cover layer side.

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