Optical recording medium

Abstract

This optical recording medium is provided with a plurality of information signal layers. Each of the plurality of information signal layers is provided with a recording layer having a first surface facing the light irradiation surface and a second surface on the opposite side of the first surface, a first dielectric layer provided on the first surface side, and a second dielectric layer provided on the second surface side. The second dielectric layer provided in the innermost information signal layer when viewed from the light irradiation surface contains indium oxide and tin oxide. The recording layer provided in the innermost information signal layer when viewed from the light irradiation surface contains oxides of metal MA, metal MB, metal MD, and metal ME. Metal MA is at least one selected from the group consisting of Mn and Ni, metal MB is at least one selected from the group consisting of W, Mo, Zr, and Ta, metal MD is at least one selected from the group consisting of Cu and Ag, and metal ME is Nb. The contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a1 / (b1 + e1) ≤ 0.41 (where a1 is the atomic ratio [atomic%] of metal MA with respect to the total amount of metal MA, metal MB, metal MD, and metal ME, b1 is the atomic ratio [atomic%] of metal MB with respect to the total amount of metal MA, metal MB, metal MD, and metal ME, e1 is the atomic ratio [atomic%] of metal ME with respect to the total amount of metal MA, metal MB, metal MD, and metal ME, and the atomic ratio e1 of metal ME with respect to the total amount of metal MA, metal MB, metal MD, and metal ME is 5 atomic% or more and 18 atomic% or less).

Description

Technical Field

[0001] The present disclosure relates to an optical recording medium. Background Art

[0002] In recent years, in order to increase the recording capacity of an optical recording medium, a technique of increasing the number of information signal layers has been widely adopted. In a multilayer optical recording medium, various materials of a recording layer included in an information signal layer have been studied in order to improve medium characteristics.

[0003] For example, PTL 1 discloses that by providing a recording layer having the following composition as an information signal layer located innermost when viewed from the light-irradiated surface (hereinafter may be referred to as "innermost information signal layer"), both the reproduction durability (thermal durability) and reflectivity of the innermost information signal layer can be achieved simultaneously. The recording layer includes a recording layer containing oxides of metal MA, oxides of metal MB, oxides of metal MC, oxides of metal MD, and oxides of metal ME, and metal MA is at least one selected from the group consisting of Mn and Ni, metal MB is at least one selected from the group consisting of W, Mo, Zr, and Ta, metal MC is Zn, metal MD is at least one selected from the group consisting of Cu and Ag, and metal ME is Nb. Further, the contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a / (b + e) ≤ 0.71 (where, a: atomic ratio [atomic%] of metal MA with respect to the total amount of metal MA, metal MB, metal MC, metal MD, and metal ME, b: atomic ratio [atomic%] of metal MB with respect to the total amount of metal MA, metal MB, metal MC, metal MD, and metal ME, e: atomic ratio [atomic%] of metal ME with respect to the total amount of metal MA, metal MB, metal MC, metal MD, and metal ME). Further, the atomic ratio e of metal ME is 5 atomic% or more and 30 atomic% or less.

[0004] [Citation List]

[0005] [Patent Document]

[0006] [PTL 1]

[0007] WO 2019 / 172081 Summary of the Invention

[0008] [Problems to be Solved by the Invention]

[0009] However, in the multilayer optical recording medium described in PTL 1, film peeling may occur depending on the storage environment, and the storage reliability may be reduced.

[0010] An object of the present disclosure is to provide an optical recording medium that can minimize a reduction in storage reliability and can achieve both the reproduction durability (thermal durability) and reflectivity of the innermost information signal layer at the same time.

[0011] [Solution to the Problem]

[0012] To solve the above problems, the present disclosure provides an optical recording medium including

[0013] a plurality of information signal layers,

[0014] wherein the plurality of information signal layers include

[0015] a recording layer having a first surface facing the light irradiation surface and a second surface on the opposite side of the first surface,

[0016] a first dielectric layer provided on the first surface side, and

[0017] a second dielectric layer provided on the second surface side,

[0018] wherein the second dielectric layer provided in the innermost information signal layer when viewed from the light irradiation surface contains indium oxide and tin oxide,

[0019] wherein the recording layer provided in the innermost information signal layer when viewed from the light irradiation surface contains oxides of metal MA, oxides of metal MB, oxides of metal MD, and oxides of metal ME,

[0020] wherein metal MA is at least one selected from the group consisting of Mn and Ni,

[0021] wherein metal MB is at least one selected from the group consisting of W, Mo, Zr, and Ta,

[0022] wherein metal MD is at least one selected from the group consisting of Cu and Ag,

[0023] wherein metal ME is Nb,

[0024] wherein the contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a 1 / (b 1 + e 1 ) ≤ 0.41 (where, a 1 : atomic ratio [atom%] of metal MA to the total amount of metal MA, metal MB, metal MD, and metal ME, b 1 : atomic ratio [atom%] of metal MB to the total amount of metal MA, metal MB, metal MD, and metal ME, e 1: The atomic ratio of metal ME with respect to the total amount of metals MA, MB, MD, and ME (atomic %), and

[0025] wherein, the atomic ratio e of metal ME with respect to the total amount of metals MA, MB, MD, and ME 1 is 5 atomic % or more and 18 atomic % or less.

[0026] In the present disclosure, it is preferable to provide a plurality of information signal layers on a substrate, and a covering layer is provided on the information signal layers. The thickness of the covering layer is not particularly limited, but since an objective lens with a high numerical aperture (NA) is used in a high-density optical recording medium, it is preferable to use a thin light-transmissive layer such as a sheet or a coating as the covering layer, and information signals are recorded and reproduced by irradiating light from the light-transmissive layer side. In this case, a substrate with opacity can also be employed. Depending on the format of the optical recording medium, the incident surface of the light used for recording or reproducing information signals is appropriately provided on at least one of the surface on the covering layer side and the surface on the substrate side.

[0027] In the present disclosure, the optical recording medium preferably has a structure including a first disk and a second disk. The first disk and the second disk may include a substrate having a first surface and a second surface, a plurality of information signal layers provided on the first surface side of the substrate, and a covering layer provided on the plurality of information signal layers. A spacer layer may be provided between the respective information signal layers. The second surface of the substrate included in the first disk and the second surface of the substrate included in the second disk may be bonded to each other.

[0028] In the present disclosure, the optical recording medium preferably has a structure including a substrate, a plurality of information signal layers provided on the substrate, and a covering layer provided on the plurality of information signal layers. A spacer layer may be provided between the respective information signal layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Figure 1 is a cross-sectional view showing an example of a structure of an optical recording medium according to a first embodiment of the present disclosure.

[0030] Figure 2 Figure 2 is showing Figure 1 a schematic cross-sectional view of an example of a structure of each of the information signal layers shown.

[0031] Figure 3 Figure 3 is a cross-sectional view showing an example of a structure of an optical recording medium according to a second embodiment of the present disclosure. DETAILED DESCRIPTION

[0032] Embodiments of the present disclosure will be described in the following order.​​​​​​

[0033] 1 First Embodiment

[0034] 1.1 Overview

[0035] 1.2 Structure of the Optical Recording Medium

[0036] 1.3 Manufacturing Method of the Optical Recording Medium

[0037] 1.4 Effects

[0038] 2 Second Embodiment

[0039] 2.1 Structure of the Optical Recording Medium

[0040] 2.2 Manufacturing Method of the Optical Recording Medium

[0041] 2.3 Effects

[0042] <1 First Embodiment>

[0043] [1.1 Overview]

[0044] The inventors have conducted extensive research on the cause of film peeling in the multilayer optical recording medium described in PTL 1. As a result, the inventors have found the following. That is, film peeling is caused by the type of material of the dielectric layer provided on the substrate side of the innermost information signal layer, and when a dielectric layer containing indium oxide and tin oxide is used as the dielectric layer, the occurrence of film peeling is minimized.

[0045] In addition, as described above, PTL 1 discloses that the contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a / (b + e) ≤ 0.71, and the atomic ratio e of metal ME is 5 atomic % or more and 30 atomic % or less. However, the inventors have conducted extensive research on the characteristics of an optical recording medium in which the dielectric layer provided on the substrate side of the innermost information signal layer contains indium oxide and tin oxide, and have found that it is difficult to simultaneously achieve both the reproduction durability (thermal durability) and the reflectance of the innermost information signal layer within the numerical ranges of a / (b + e) and the atomic ratio e of metal ME described in PTL 1, and it is impossible to ensure the power margin of the innermost information signal layer.

[0046] Therefore, in order to solve the above problems in an optical recording medium in which the dielectric layer provided on the substrate side of the innermost information signal layer contains indium oxide and tin oxide, the inventors conducted additional extensive research. As a result, they found that in an optical recording medium in which the dielectric layer provided on the substrate side of the innermost information signal layer contains indium oxide and tin oxide, by making the contents of metal MA, metal MB, and metal ME satisfy 0.30 ≤ a / (b + e) ≤ 0.41, and making the atomic ratio e of metal ME be 5 atomic % or more and 18 atomic % or less, both the reproduction durability (thermal durability) and the reflectivity of the innermost information signal layer can be achieved simultaneously, and the power margin of the innermost information signal layer can be ensured. Hereinafter, an optical recording medium having such a configuration will be described.

[0047] [1.2 Structure of the optical recording medium]

[0048] As Figure 1 shown, the optical recording medium 1 according to the first embodiment of the present disclosure is a so-called multi-layer write-once optical recording medium (e.g., an archive disc (AD)), and includes a first disc 10, a second disc 20, and an adhesive layer 30 provided between the first disc 10 and the second disc 20. The optical recording medium 1 is an optical recording medium of a type that records data on both a groove track and a land track (hereinafter referred to as "land / groove recording type"), and has a disc shape with an opening (hereinafter referred to as "center hole") provided at the center. Here, the shape of the optical recording medium 1 is not limited to the disc shape, and may be any other shape.

[0049] The first disc 10 has a structure 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-transmissive layer 12 as a cover layer are laminated in this order on one main surface of a substrate 11. The second disc 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-transmissive layer 22 as a cover layer are laminated in this order on one main surface of a substrate 21. Here, n and m each independently represent an integer of 2 or more, and from the viewpoint of improving the recording capacity, they are preferably an integer of 3 or more. Here, in the following description, in a case where the information signal layers L0 to Ln and L0 to Lm are not particularly distinguished, they will be referred to as the information signal layer L.

[0050] The optical recording medium 1 has light irradiation surfaces on both sides, and a laser beam for recording or reproducing an information signal is irradiated onto the light irradiation surfaces. More specifically, the optical recording medium 1 has a first light irradiation surface C1 onto which a laser beam for recording or reproducing an information signal in the first disk 10 is irradiated, and a second light irradiation surface C2 onto which a laser beam for recording or reproducing an information signal in the second disk 20 is irradiated.

[0051] In the first disk 10, the information signal layer L0 is located innermost with respect to the first light irradiation surface C1, and the information signal layers L1 to Ln are located above it. Therefore, the information signal layers L1 to Ln have a structure in which a laser beam for recording or reproducing can be transmitted therethrough. On the other hand, in the second disk 20, the information signal layer L0 is located innermost with respect to the second light irradiation surface C2, and the information signal layers L1 to Lm are located above it. Therefore, the information signal layers L1 to Lm have a structure in which a laser beam for recording or reproducing can be transmitted therethrough. Here, although not shown, the optical recording medium 1 may further include a hard coat on the surfaces of the light transmission layers 12 and 22 (i.e., the first light irradiation surface C1 and the second light irradiation surface C2).

[0052] In the optical recording medium 1, the information signal in the first disk 10 is recorded or reproduced as follows. That is, the information signal in the first disk 10 is recorded or reproduced by irradiating a laser beam from the first light irradiation surface C1 on the light transmission layer 12 side onto each of the information signal layers L0 to Ln included in the first disk 10. For example, by condensing a laser beam having a wavelength range of 350 nm or more and 410 nm or less with an objective lens having a numerical aperture in the range of 0.84 or more and 0.86 or less, and irradiating it from the light transmission layer 12 side onto each of the information signal layers L0 to Ln included in the first disk 10, the information signal is recorded or reproduced.

[0053] On the other hand, the information signal in the second disk 20 is recorded or reproduced as follows. That is, the information signal in the second disk 20 is recorded or reproduced by irradiating a laser beam from the second light irradiation surface C2 on the light transmission layer 22 side onto each of the information signal layers L0 to Lm included in the second disk 20. For example, by condensing a laser beam having a wavelength range of 350 nm or more and 410 nm or less with an objective lens having a numerical aperture in the range of 0.84 or more and 0.86 or less, and irradiating it from the light transmission layer 22 side onto each of the information signal layers L0 to Lm included in the second disk 20, the information signal is recorded or reproduced.

[0054] Hereinafter, the substrates 11 and 21, the adhesive layer 30, the information signal layers L0 to Ln and L0 to Lm, the spacer layers S1 to Sn and S1 to Sm, and the light transmission layers 12 and 22 constituting the optical recording medium 1 will be described in sequence.

[0055] (Substrate)

[0056] The substrates 11 and 21 have, for example, a disc shape with a central hole provided in the center. One main surface of the substrates 11 and 21 is, for example, an uneven surface, and an information signal layer L0 is formed on the uneven surface. Hereinafter, in the uneven surface, the concave portion will be referred to as the shore portion Ld, and the convex portion will be referred to as the groove Gv.

[0057] Examples of the shapes of the shore portion Ld and the groove Gv include various shapes such as a spiral shape and a concentric circle shape. In addition, in order to stabilize the linear velocity, add address information, etc., the shore portion Ld and / or the groove Gv can be made to oscillate (meander).

[0058] Here, the spiral directions of the first disc 10 and the second disc 20 can be opposite to each other. In this case, since an optical recording medium (double-sided disc) 1 in which the first disc 10 and the second disc 20 are bonded to each other can be recorded and reproduced simultaneously, the data transfer speed during recording and reproduction can be increased by about 2 times.

[0059] The outer diameters (diameters) of the substrates 11 and 21 are selected to be, for example, 120 mm. The inner diameters (diameters) of the substrates 11 and 21 are 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.

[0060] As the materials of the substrates 11 and 21, for example, a plastic material or glass can be used, and from the viewpoint of plasticity, a plastic material is preferably used. As the plastic material, for example, a polycarbonate resin, a polyolefin resin, an acrylic resin, etc. can be used, and from the viewpoint of cost, a polycarbonate resin is preferably used.

[0061] (Adhesive layer)

[0062] The adhesive layer 30 is composed of a cured ultraviolet-curable resin. Through the adhesive layer 30, the first disc 10 and the second disc 20 are bonded to each other. More specifically, the substrate 11 of the first disc 10 and the substrate 21 of the second disc substrate are bonded to each other such that the light transmission layers 12 and 22 are respectively located on the surface sides.

[0063] The thickness of the adhesive layer 30 is, for example, 0.01 mm or more and 0.22 mm or less. The ultraviolet-curable resin is, for example, a radical polymerization ultraviolet-curable resin.

[0064] (Information signal layer)

[0065] The information signal layer L includes concave tracks (hereinafter referred to as "land tracks") and convex tracks (hereinafter referred to as "groove tracks"). The optical recording medium 1 according to the present embodiment has a structure in which information signals can be recorded in both the land tracks and the groove tracks. From the perspective of obtaining a high recording density, the track pitch Tp between the land tracks and the groove tracks is preferably 0.225 nm or less.

[0066] As Figure 2 shown, the information signal layers L0 to Ln include an inorganic recording layer (hereinafter simply referred to as "recording layer") 41 having a first surface and a second surface, a dielectric layer (first dielectric layer) 42 disposed adjacent to the recording layer 41 on the first surface side of the recording layer 41, and a dielectric layer (second dielectric layer) 43 disposed adjacent to the recording layer 41 on the second surface side of the recording layer 41. With this structure, the durability of the recording layer 41 can be improved. Here, the first surface is the surface of the two main surfaces of the recording layer 41 that faces the first light irradiation surface C1 (i.e., the surface on the side where the laser beam for recording or reproducing information signals is irradiated), and the second surface is the surface on the opposite side of the above-mentioned first surface (i.e., the surface on the opposite side of the substrate 11). Here, since the information signal layers L0 to Lm can have the same structure as the information signal layers L0 to Ln, the description thereof will be omitted.

[0067] When the number of layers of the information signal layer L of the first disk 10 and the second disk 20 is 3, from the perspective of ensuring a good recording signal, the reflectivity of the information signal layer L0 is preferably 3.0% or more and 4.5% or less, and more preferably 3.5% or more and 4.5% or less.

[0068] When the number of layers of the information signal layer L of the first disk 10 and the second disk 20 is 3, the lower limit value of the optimum recording power of the information signal layer L0 at a recording speed of 10x and a reproduction speed of 10x is preferably 58 mw or more, and more preferably 67 mw or more. From the perspective of the upper limit value of the recording Pw in existing civilian drives, the upper limit value of the optimum recording power of the information signal layer L0 at a recording speed of 10x and a reproduction speed of 10x is preferably 75 mw or less. Here, the 1x speed as the reference for the 10x recording / reproduction speed is 3.5 m / s.

[0069] (Recording layer)

[0070] The recording layer 41 provided in the information signal layer L0 contains oxides of metal MA, oxides of metal MB, oxides of metal MD, and oxides of metal ME as main components. The recording layer 41 included in the information signal layer L0 may further contain oxides of metal MC. Metal MA is at least one selected from the group consisting of Mn and Ni. Metal MB is at least one selected from the group consisting of W, Mo, Zr, and Ta. Metal MC is Zn. Metal MD is at least one selected from the group consisting of Cu and Ag. Metal ME is Nb.

[0071] Here, "containing oxides of metal MA, oxides of metal MB, oxides of metal MD, and oxides of metal ME as main components" means that the total content of the above four oxides in the recording layer 41 is 50 atomic % or more. Here, from the viewpoint of improving the characteristics of the optical recording medium 1, the total content of the above four oxides in the recording layer 41 is preferably 60 atomic % or more, more preferably 75 atomic % or more, and still more preferably 90 atomic % or more.

[0072] The contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a 1 / (b 1 +e 1 ) ≤ 0.41 (where, a 1 : atomic ratio [atomic %] of metal MA to the total amount of metal MA, metal MB, metal MD, and metal ME, b 1 : atomic ratio [atomic %] of metal MB to the total amount of metal MA, metal MB, metal MD, and metal ME, e 1 : atomic ratio [atomic %] of metal ME to the total amount of metal MA, metal MB, metal MD, and metal ME). Further, the atomic ratio e of metal ME to the total amount of metal MA, metal MB, metal MD, and metal ME 1 is in the range of 5 atomic % or more and 18 atomic % or less.

[0073] As described above, by making the contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a 1 / (b 1 +e 1 ) ≤ 0.41, and the atomic ratio e of metal ME is 1 in the range of 5 atomic % or more and 18 atomic % or less, the following effects can be obtained. That is, in the case where the dielectric layer 43 of the information signal layer L0 contains a mixture of indium oxide and tin oxide (In 2 O 3 -SnO 2In the optical recording medium 1 including (ITO), both the reproduction durability (thermal durability) and the reflectivity of the innermost information signal layer L0 can be achieved simultaneously. In addition, the power margin of the innermost information signal layer L0 can be ensured.

[0074] When the recording layer 41 included in the information signal layer L0 further contains an oxide of metal MC, the contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a 2 / (b 2 +e 2 ) ≤ 0.41 (where a 2 : the atomic ratio [atomic%] of metal MA to the total amount of metal MA, metal MB, metal MC, metal MD, and metal ME), b 2 : the atomic ratio [atomic%] of metal MB to the total amount of metal MA, metal MB, metal MC, metal MD, and metal ME, and e 2 : the atomic ratio [atomic%] of metal ME to the total amount of metal MA, metal MB, metal MC, metal MD, and metal ME. In addition, the atomic ratio e of metal ME to the total amount of metal MA, metal MB, metal MC, metal MD, and metal ME 2 is in the range of 5 atomic% or more and 18 atomic% or less.

[0075] When the recording layer 41 included in the information signal layer L0 further contains an oxide of metal MC, as described above, by making the contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a 2 / (b 2 +e 2 ) ≤ 0.41, and the atomic ratio e of metal ME 2 is in the range of 5 atomic% or more and 18 atomic% or less, the following effects can be obtained. That is, in the optical recording medium 1 in which the dielectric layer 43 of the information signal layer L0 contains a mixture of indium oxide and tin oxide (In 2 O 3 -SnO 2 (ITO)), both the reproduction durability (thermal durability) and the reflectivity of the innermost information signal layer L0 can be achieved simultaneously. In addition, the power margin of the innermost information signal layer L0 can be ensured.

[0076] The atomic ratio a of metal MA to the total amount of metal MA, metal MB, metal MD, and metal ME 1 is, for example, 11 atomic% or more and 30 atomic% or less. The atomic ratio b of metal MB to the total amount of metal MA, metal MB, metal MD, and metal ME 1For example, it is 31 atomic % or more and 54 atomic % or less. The atomic ratio d of the metal MD with respect to the total amount of the metals MA, MB, MD, and ME 1 For example, it is 14 atomic % or more and 25 atomic % or less.

[0077] When the recording layer 41 provided in the information signal layer L0 further contains an oxide of the metal MC, the atomic ratio a of the metal MA with respect to the total amount of the metals MA, MB, MC, MD, and ME 2 For example, it is 11 atomic % or more and 30 atomic % or less. The atomic ratio b of the metal MB with respect to the total amount of the metals MA, MB, MC, MD, and ME 2 For example, it is 31 atomic % or more and 54 atomic % or less. The atomic ratio c of the metal MC with respect to the total amount of the metals MA, MB, MC, MD, and ME 2 For example, it is more than 0 atomic % and 10 atomic % or less. The atomic ratio d of the metal MD with respect to the total amount of the metals MA, MB, MC, MD, and ME 2 For example, it is 14 atomic % or more and 25 atomic % or less.

[0078] The recording layer 41 of each of the information signal layers L1 to Ln other than the information signal layer L0 contains, for example, oxides of the metals MA, MB, MD, and ME as main components. The atomic ratios of the metals MA, MB, MD, and ME are appropriately selected according to the characteristics required for each information signal layer L.

[0079] The recording layer 41 of each of the information signal layers L1 to Ln other than the information signal layer L0 may further contain an oxide of the metal MC. In this case, the atomic ratios of the metals MA, MB, MC, MD, and ME are appropriately selected according to the characteristics required for each information signal layer L.

[0080] The thickness of the recording layer 41 is preferably in the range of 25 nm or more and 60 nm or less, and more preferably in the range of 30 nm or more and 50 nm or less. When the thickness of the recording layer 41 is 25 nm or more, excellent signal characteristics can be obtained. On the other hand, when the thickness of the recording layer 41 is 60 nm or less, a wide recording power margin can be ensured.

[0081] (Dielectric layer)

[0082] The dielectric layers 42 and 43 function as an oxygen barrier layer. Thereby, the durability of the recording layer 41 can be improved. In addition, the dielectric layers 42 and 43 function to minimize the escape of oxygen in the recording layer 41. Thereby, the change in the film quality of the recording layer 41 (mainly detected as a decrease in reflectivity) can be minimized, and better film quality of the recording layer 41 can be ensured. In addition, the dielectric layers 42 and 43 also function to improve the recording characteristics. It is considered that when this function is achieved, the thermal diffusion of the laser beam incident on the dielectric layers 42 and 43 is appropriately controlled, the excessive change in the shape in the recording portion is minimized, the extrusion deformation of the changed shape caused by the excessive decomposition of the Mn oxide is minimized, and the shape change during recording can be good.

[0083] The dielectric layer 43 provided in the information signal layer L0 contains a mixture of indium oxide and tin oxide (In 2 O 3 -SnO 2 (ITO)). By making the dielectric layer 43 provided in the information signal layer L0 contain a mixture of indium oxide and tin oxide, the occurrence of film peeling at the interfaces between the information signal layers L0 to Ln and the spacer layers S1 to Sn, the interfaces between the information signal layer Ln and the light transmissive layer 22, etc. can be minimized.

[0084] The dielectric layer 42 provided in the information signal layers L0 to Ln and the dielectric layer 43 provided in the information signal layers L1 to Ln contain at least one selected from the group consisting of, for example, oxides, nitrides, sulfides, carbides, and fluorides. Two or more dielectric layers 42 within the information signal layers L0 to Ln may contain the same dielectric material, or may contain different dielectric materials. Two or more dielectric layers 43 within the information signal layers L0 to Ln may contain the same dielectric material, or may contain different dielectric materials. The dielectric layers 42 and 43 provided on the two sides of the information signal layers L0 to Ln may contain the same dielectric material as each other, or may contain different dielectric materials from each other.

[0085] Examples of the oxide include oxides 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. Examples of the nitride include nitrides 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, and preferably include nitrides of one or more elements selected from the group consisting of Si, Ge, and Ti. Examples of the sulfide include sulfide of Zn. Examples of the carbide include carbides of one or more elements selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Ti, Zr, Ta, and W, and preferably include carbides of one or more elements selected from the group consisting of Si, Ti, and W. Examples of the fluoride include fluorides of one or more elements selected from the group consisting of Si, Al, Mg, Ca, and La.

[0086] The dielectric layer 42 of the information signal layers L0 to Ln and the dielectric layer 43 of the information signal layers L1 to Ln may contain, for example, a mixture of the above materials. Specific examples of the mixture include a mixture of zinc sulfide and silicon oxide (ZnS-SiO 2 ), a mixture of silicon oxide, indium oxide, and zirconium oxide (SiO 2 -In 2 O 3 -ZrO 2 (SIZ)), a mixture of silicon oxide, chromium oxide, and zirconium oxide (SiO 2 -Cr 2 O 3 -ZrO 2 (SCZ)), a mixture of indium oxide and tin oxide (In 2 O 3 -SnO 2 (ITO)), a mixture of indium oxide and cerium oxide (In 2 O 3 -CeO 2 (ICO)), a mixture of indium oxide and gallium oxide (In 2 O 3 -Ga 2 O 3 (IGO)), a mixture of indium oxide, gallium oxide, and zinc oxide (In 2 O 3 -Ga 2 O 3 -ZnO(IGZO)), a mixture of tin oxide and tantalum oxide (Sn 2 O 3 -Ta 2 O5(TTO)), a mixture of titanium oxide and silicon oxide (TiO2 -SiO 2 ), a mixture of aluminum oxide and zinc oxide (Al 2 O 3 -ZnO), a mixture of aluminum oxide and barium oxide (Al 2 O 3 -BaO), or a mixture of zinc oxide, tin oxide and zirconia (ZnO-SnO 2 -ZrO 2 ), etc.

[0087] From the viewpoint of improving the reproduction durability, the dielectric layer 42 provided in the information signal layers L0 to Ln preferably contains a mixture of silicon oxide, indium oxide and zirconia (SiO 2 -In 2 O 3 -ZrO 2 ).

[0088] From the viewpoint of improving the reproduction durability, preferably, the dielectric layer 43 provided in the information signal layers L1 to Ln contains a mixture of zinc oxide, tin oxide and zirconia (ZnO-SnO 2 -ZrO 2 ), and more preferably, both the dielectric layer 42 and the dielectric layer 43 provided in the information signal layers L1 to Ln contain a mixture of zinc oxide, tin oxide and zirconia.

[0089] The thickness of the dielectric layer 43 is preferably in the range of 2 nm or more and 30 nm or less. When the thickness of the dielectric layer 43 is 2 nm or more, the reduction of the barrier effect can be minimized. On the other hand, when the thickness of the dielectric layer 43 is 30 nm or less, the reduction (deterioration) of the recording power margin can be minimized.

[0090] The thickness of the dielectric layer 42 is preferably in the range of 2 nm or more and 50 nm or less. When the thickness of the dielectric layer 42 is 2 nm or more, the reduction of the barrier effect can be minimized. On the other hand, when the thickness of the dielectric layer 42 is 50 nm or less, the reduction (deterioration) of the recording power margin can be minimized.

[0091] (Spacer layer)

[0092] The spacer layers S1 to Sn and S1 to Sm each have the function of physically and optically sufficiently separating the information signal layers L0 to Ln, L0 to Lm from each other, and their surfaces are provided with uneven surfaces. On this uneven surface, for example, concentric or spiral banks Ld and grooves Gv are formed. The thickness of the spacer layers S1 to Sn and S1 to Sm is preferably 9 μm or more and 50 μm or less. The material of the spacer layers S1 to Sn and S1 to Sm is not particularly limited, and an ultraviolet curable acrylic resin is preferably used. In addition, since the spacer layers S1 to Sn and S1 to Sm serve as the optical paths of the laser beams for recording and reproducing data in the inner layer, they preferably have a sufficiently high light transmittance.

[0093] (Light transmission layer)

[0094] The light transmission layers 12 and 22 are, for example, resin layers obtained by curing a photosensitive resin such as an ultraviolet curable resin. Examples of the material of this resin layer include ultraviolet curable acrylic resins. In addition, the light transmission layers 12 and 22 may be composed of a light transmissive sheet having an annular shape and an adhesive layer for bonding the light transmissive sheet to the information signal layers Ln and Lm. The light transmissive sheet is preferably formed of a material having a low absorption ability for the laser beam used for recording and reproducing, and specifically, is preferably formed of a material having a transmittance of 90% or more. Regarding the material of the light transmissive sheet, for example, polycarbonate resin or polyolefin resin (e.g., ZEONEX (registered trademark)) etc. can be used. Regarding the material of the adhesive layer, for example, ultraviolet curable resin or pressure sensitive adhesive (PSA) can be used.

[0095] The thickness of the light transmission layers 12 and 22 is preferably selected from the range of 10 μm or more and 177 μm or less, and is, for example, selected to be 57 μm. By combining such thin light transmission layers 12 and 22 with, for example, an objective lens having a high NA of about 0.85, high density recording can be achieved.

[0096] (Hard coat)

[0097] The hard coat is used to impart scratch resistance etc. to the first light irradiation surface C1 and the second light irradiation surface C2. Regarding the material of the hard coat, for example, acrylic resin, silicone resin, fluororesin or organic-inorganic hybrid resin etc. can be used. In order to improve the mechanical strength, the hard coat may contain fine powder of silica gel.

[0098] In the optical recording medium 1 having the above structure, when a laser beam is irradiated onto the recording layer 41, the Mn oxide is heated by the laser beam and decomposes to release oxygen, and the state of the portion irradiated with the laser beam is changed. Thereby, information signals can be irreversibly recorded.

[0099] [1.3 Method for Manufacturing Optical Recording Medium]

[0100] 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.

[0101] (Manufacturing Process of First Disc)

[0102] The first disc 10 is manufactured as follows.

[0103] (Molding Process of Substrate)

[0104] First, the substrate 11 is molded, and the substrate 11 has an uneven surface formed on one main surface. Regarding the molding method of the substrate 11, for example, an injection molding (injection molding) method or a photopolymerization method (2P method: Photo Polymerization) can be used.

[0105] (Film Formation Process of Information Signal Layer)

[0106] Next, for example, by a sputtering method, the information signal layer L0 is formed by sequentially laminating a dielectric layer 43, a recording layer 41, and a dielectric layer 42 on the substrate 11. Hereinafter, the film formation processes of the dielectric layer 43, the recording layer 41, and the dielectric layer 42 will be described in detail.

[0107] (Film Formation Process of Dielectric Layer)

[0108] First, the substrate 11 is transported into a vacuum chamber containing a target for forming the dielectric layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure. Then, while introducing a process gas such as Ar gas or O 2 gas into the vacuum chamber, the target is sputtered to form the dielectric layer 43 on the substrate 11.

[0109] (Film Formation Process of Recording Layer)

[0110] Next, the substrate 11 is transported into a vacuum chamber containing a target for forming the recording layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure. Then, while introducing a process gas such as Ar gas or O 2 gas into the vacuum chamber, the target is sputtered to form the recording layer 41 on the dielectric layer 43.

[0111] Here, regarding the target for forming the recording layer, a target having the same composition as the recording layer 41 provided in the information signal layer L0 can be used, or a target having a composition different from the composition of the recording layer 41 provided in the information signal layer L0 can be used. When using the latter target as the target for forming the recording layer, the recording layer 41 can be formed by reactive sputtering with oxygen.

[0112] As a target for forming the recording layer, a target containing metals MA, MB, MD, and ME is used. Here, metals MA, MB, and ME satisfy 0.30 ≤ a 1 / (b 1 +e 1 ) ≤ 0.41, and the atomic ratio e of metal ME to the total amount of metals MA, MB, MD, and ME 1 is 5 atomic % or more and 18 atomic % or less. The target for forming the recording layer may be a metal oxide target or an alloy target.

[0113] When the recording layer 41 included in the information signal layer L0 further contains an oxide of metal MC, as a target for forming the recording layer, a target containing metals MA, MB, MC, MD, and ME is used. Here, metals MA, MB, and ME satisfy 0.30 ≤ a 2 / (b 2 +e 2 ) ≤ 0.41, and the atomic ratio e of metal ME to the total amount of metals MA, MB, MC, MD, and ME 2 is 5 atomic % or more and 18 atomic % or less.

[0114] (Film formation process of the dielectric layer)

[0115] Next, the substrate 11 is transported into a vacuum chamber containing a target for forming the dielectric layer, and the vacuum chamber is evacuated to a predetermined pressure. Then, while introducing a process gas such as Ar gas or O 2 gas into the vacuum chamber, the target is sputtered to form the dielectric layer 42 on the recording layer 41.

[0116] Thereby, the information signal layer L0 is formed on the substrate 11.

[0117] (Formation process of the spacer layer)

[0118] Next, for example, an ultraviolet curable resin is uniformly coated on the information signal layer L0 by spin coating. Then, the concavo-convex pattern of the stamper is pressed against the ultraviolet curable resin uniformly coated on the information signal layer L0, the ultraviolet curable resin is irradiated with ultraviolet light and cured, and then the stamper is peeled off. Thereby, the concavo-convex pattern of the stamper is transferred to the ultraviolet curable resin, and for example, a spacer layer S1 provided with a land portion Ld and a groove Gv is formed on the information signal layer L0.

[0119] (Film formation process of the information signal layer and formation process of the spacer layer)

[0120] Next, in the same manner as the above-described "film formation process of the information signal layer" and "formation process of the spacer layer", the information signal layer L1, spacer layer S2, information signal layer L3, …, spacer layer Sn, and information signal layer Ln are laminated in this order on the spacer layer S1.

[0121] Here, as the target for forming the recording layer, a target having the same composition as the recording layer 41 provided in each of the information signal layers L1 to Ln, or a target having a composition different from that of the recording layer 41 provided in each of the information signal layers L1 to Ln can be used. As the target for forming the recording layer, for example, a target containing metals MA, MB, MD, and ME is used. If necessary, the target may further contain metal MC. The target for forming the recording layer may be a metal oxide target or an alloy target.

[0122] (Formation process of the light transmission layer)

[0123] Next, for example, by spin coating, a photosensitive resin such as an ultraviolet curable resin (UV resin) is spin coated on the information signal layer Ln, and then light such as ultraviolet light is irradiated onto the photosensitive resin and curing is performed. Thereby, the light transmission layer 12 is formed on the information signal layer Ln. Thereby, the first disc 10 is manufactured.

[0124] (Manufacturing process of the second disc)

[0125] Since the "manufacturing process of the second disc" is the same as the above-described "manufacturing process of the first disc", the description thereof will be omitted.

[0126] (Bonding process)

[0127] Next, as described below, for example, by spin coating, an ultraviolet curable resin as an adhesive is extended between the first disc 10 and the second disc 20 manufactured as described above. First, on the main surface of the second disc 20 on the side opposite to the second light irradiation surface C2 among the two main surfaces, an ultraviolet curable resin is coated in a ring shape along the outer peripheral edge of the center hole. Next, with the ultraviolet curable resin between the two, the first disc 10 is pressed against the second disc 20 such that the main surface of the first disc 10 on the side opposite to the first light irradiation surface C1 among the two main surfaces faces the main surface of the second disc 20 on the side opposite to the second light irradiation surface C2.

[0128] Next, rotate the first disk 10 and the second disk 20, and between the first disk 10 and the second disk 20, extend an ultraviolet curable resin in the radial direction of the first disk 10 and the second disk 20. Thus, between the first disk 10 and the second disk 20, the ultraviolet curable resin diffuses from the inner peripheral portions of the first disk 10 and the second disk 20 to the outer peripheral portions. In this case, according to the rotation speed, adjust the thickness of the ultraviolet curable resin to a predetermined thickness. Thus, an optical recording medium 1 having an adhesive layer 30 in an uncured state is obtained.

[0129] Here, during the extension of the above-described ultraviolet curable resin, it is preferable to irradiate ultraviolet light to the outer peripheral portions of the first disk 10 and the second disk 20 and temporarily cure the ultraviolet curable resin extended to the outer peripheral portions. Thus, an opening can be prevented from occurring in the outer peripheral portions of the first disk 10 and the second disk 20.

[0130] Next, irradiate ultraviolet light from both sides of the optical recording medium 1 using an ultraviolet lamp to cure the adhesive layer 30. Thus, a desired optical recording medium 1 is obtained.

[0131] [1.4 Effects]

[0132] The above-described optical recording medium 1 according to the first embodiment includes a plurality of information signal layers L0 to Ln. The dielectric layer 43 provided in the innermost information signal layer L0 when viewed from the first light irradiation surface C1 and the second light irradiation surface C2 contains a mixture of indium oxide and tin oxide. The recording layer 41 provided in the innermost information signal layer L0 among the plurality of information signal layers L0 to Ln contains oxides of metal MA, oxides of metal MB, oxides of metal MD, and oxides of metal ME when viewed from the first light irradiation surface C1 and the second light irradiation surface C2. Metal MA is at least one selected from the group consisting of Mn and Ni, metal MB is at least one selected from the group consisting of W, Mo, Zr, and Ta, metal MD is at least one selected from the group consisting of Cu and Ag, and metal ME is Nb. Further, the contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a 1 / (b 1 +e 1 ) ≤ 0.41, and the atomic ratio e of metal ME with respect to the total amount of metal MA, metal MB, metal MD, and metal ME 1 is 5 atomic % or more and 18 atomic % or less. Thus, the reduction in storage reliability can be minimized, and both the reproduction durability (thermal durability) and reflectivity of the innermost information signal layer L0 can be achieved simultaneously. Further, a power margin of the innermost information signal layer L0 can be ensured.

[0133] <2 Second Embodiment>

[0134] [2.1 Structure of the optical recording medium]

[0135] As shown in Figure 3 , the optical recording medium 1A according to the second embodiment of the present disclosure is a so-called multi-layer once-writable optical recording medium, and has the following structure: Among them, the information signal layer L0, the spacer layer S1, the information signal layer L1, …, the spacer layer Sn, the information signal layer Ln, and the light-transmissive layer 12 as a cover layer are laminated in this order on one main surface of the substrate 11. Here, in the second embodiment, the same reference numerals will be used to denote the same parts as those in the first embodiment, and their descriptions will be omitted.

[0136] The optical recording medium 1A has a light irradiation surface C on one side, and the light for recording or reproducing the information signal is irradiated onto the light irradiation surface C. The information signal layer L0 is located on the innermost side with respect to the light irradiation surface C, and the information signal layers L1 to Ln are located above it. Therefore, the information signal layers L1 to Ln have a structure that can transmit the laser beam for recording or reproducing.

[0137] In the optical recording medium 1A according to this second embodiment, the information signal is recorded or reproduced by irradiating the laser beam from the light irradiation surface C on the side of the light-transmissive layer 12 to the information signal layers L0 to Ln. For example, by condensing a laser beam having a wavelength range of 400 nm or more and 410 nm or less with an objective lens having a numerical aperture in the range of 0.84 or more and 0.86 or less, and irradiating it from the side of the light-transmissive layer 12 to each of the information signal layers L0 to Ln, the information signal is recorded or reproduced. Examples of such an optical recording medium 1A include multi-layer Blu-ray Discs (BD: Blu-ray (registered trademark) Discs).

[0138] The optical recording medium 1A is typically an optical recording medium of the groove recording type, but may also be an optical recording medium of the land / groove recording type or the like.

[0139] The diameter of the substrate 11A is selected to be, for example, 120 mm. The thickness of the substrate 11 is selected in consideration of rigidity, and is preferably 0.3 mm or more and 1.3 mm or less, and more preferably 0.6 mm or more and 1.3 mm or less, and is selected to be, for example, 1.1 mm. In addition, 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 above first embodiment.

[0140] When the number of layers in the information signal layer L is 3 layers, from the perspective of ensuring a good recording signal, the reflectivity of the information signal layer L0 is preferably 3.0% or more and 4.5% or less, and more preferably 3.5% or more and 4.5% or less.

[0141] From the perspective of ensuring the durability of repeated reproduction, the lower limit of the optimum recording power of the information signal layer L0 at a recording speed of 4x and a reproduction speed of 4x is preferably 26 mw or more, and more preferably 30 mw or more. From the perspective of the upper limit of the recording Pw in existing consumer drives, the upper limit of the optimum recording power of the information signal layer L0 at a recording speed of 4x and a reproduction speed of 4x is preferably 38 mw or less. Here, the speed of 1x as the reference for the 4x recording / reproduction speed is 3.9 m / s.

[0142] [2.2 Method for manufacturing an optical recording medium]

[0143] The method for manufacturing the optical recording medium 1A according to the second embodiment of the present disclosure is the same as the "manufacturing process of the first disc" in the above first embodiment.

[0144] [2.3 Effects]

[0145] In the optical recording medium 1A according to the second embodiment described above, similar to the optical recording medium 1 according to the first embodiment, it is possible to minimize the reduction in storage reliability, and it is possible to achieve both the reproduction durability (thermal durability) and the reflectivity of the innermost information signal layer simultaneously. In addition, it is possible to ensure the power margin of the innermost information signal layer L0.

[0146] [Examples]

[0147] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples.

[0148] Hereinafter, the three information signal layers of the optical recording medium will be referred to as the "L0 layer", the "L1 layer", and the "L2 layer" in order from the substrate to the laser beam irradiation surface. In addition, "upward" refers to the direction from the substrate toward the laser beam irradiation surface, and "downward" refers to the direction from the laser beam irradiation surface toward the substrate.

[0149] The examples of the present disclosure will be described in the following order.

[0150] i Research on the materials of the first and second dielectric layers

[0151] ii Research on the composition of the recording layer provided in the L0 layer

[0152]

[0153] [Examples 1-1 to 1-3, and Comparative Examples 1-1 and 1-2]

[0154] First, a polycarbonate substrate with a thickness of 1.1 mm is formed by injection molding. Here, one main surface of the polycarbonate substrate is an uneven surface composed of banks and grooves. In addition, the track pitch Tp between the banks and the grooves is 0.225 nm. Next, by sputtering, a second dielectric layer, a recording layer, and a first dielectric layer are sequentially stacked on the uneven surface of the polycarbonate substrate, thereby forming the L0 layer.

[0155] The specific structure of the L0 layer is as follows.

[0156] First dielectric layer (upper side)

[0157] Material: Dielectric material shown in Table 1

[0158] Thickness: 10 nm

[0159] Recording layer

[0160] Material: Oxides containing metals MA(=Mn), MB(=W), MC(=Zn), MD(=Cu), and ME(=Nb) (where a = 20 atomic%, b = 38 atomic%, c = 10 atomic%, d = 14 atomic%, e = 18 atomic%, a / (b + e) = 0.36)

[0161] Thickness: 33 nm

[0162] Second dielectric layer (lower side)

[0163] Material: Dielectric material shown in Table 1

[0164] Thickness: 10 nm

[0165] Next, by spin coating, an ultraviolet curable resin is uniformly coated on the L0 layer. The uneven pattern of the stamper is pressed against the ultraviolet curable resin coated on the L0 layer, ultraviolet light is irradiated onto the ultraviolet curable resin to perform curing, and then the stamper is peeled off. Thus, a spacer layer with an uneven surface composed of banks and grooves and a thickness of 25 μm is formed. Here, the track pitch Tp between the banks and the grooves is set to 0.225 nm. Next, by sputtering, a second dielectric layer, a recording layer, and a first dielectric layer are sequentially stacked on the uneven surface of the above spacer layer, thereby forming the L1 layer.

[0166] The specific structure of the L1 layer is as follows.

[0167] First dielectric layer (upper side)

[0168] Material: Dielectric material shown in Table 1

[0169] Thickness: 15 nm

[0170] Recording layer

[0171] Material: (Mn-W-Zn-Cu-Ag)-O

[0172] Thickness: 33 nm

[0173] Second dielectric layer (lower side)

[0174] Material: Dielectric material shown in Table 1

[0175] Thickness: 17 nm

[0176] Here, "(Mn-W-Zn-Cu-Ag)-O" represents an oxide containing Mn, W, Zn, Cu, and Ag.

[0177] Next, by spin coating, the ultraviolet curable resin is uniformly coated on the L1 layer. The concave and convex pattern of the stamper is pressed against the ultraviolet curable resin coated on the L1 layer, ultraviolet light is irradiated onto the ultraviolet curable resin, curing is performed, and then the stamper is peeled off. Thus, a spacer layer with a concave and convex surface composed of a land portion and a groove and a thickness of 18 μm is formed. Here, the track pitch Tp between the land portion and the groove is set to 0.225 nm. Next, by sputtering, the second dielectric layer, the recording layer, and the first dielectric layer are sequentially stacked on the concave and convex surface of the above spacer layer, thereby forming the L2 layer.

[0178] The specific structure of the L2 layer is as follows.

[0179] First dielectric layer (upper side)

[0180] Material: Dielectric material shown in Table 1

[0181] Thickness: 17 nm

[0182] Recording layer

[0183] Material: (Mn-W-Zn-Cu-Ag)-O

[0184] Thickness: 33 nm

[0185] Second dielectric layer (lower side)

[0186] Material: Dielectric material shown in Table 1

[0187] Thickness: 17 nm

[0188] Next, by spin coating, the ultraviolet curable resin is uniformly coated on the L2 layer, ultraviolet light is irradiated onto the ultraviolet curable resin, and curing is performed, thereby forming a light transmission layer with a thickness of 57 μm. Thus, a three-layer optical recording medium of the desired land / groove recording type is obtained.

[0189] (Evaluation of storage reliability)

[0190] First, the obtained optical recording medium was subjected to an accelerated test (temperature: 80 °C, humidity: 85% RH, storage time: 400 hours), and then it was visually observed to confirm whether film peeling occurred in the optical recording medium. The results are shown in Table 1. In addition, for the optical recording media in which film peeling was confirmed to exist, the interface where film peeling occurred was confirmed by compositional analysis. The results confirmed that film peeling occurred at the interfaces between the L0 layer and the spacer layer, between the L1 layer and the spacer layer, and between the L2 layer and the cover layer.

[0191] Table 1 shows the structures and evaluation results of the optical recording media of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2.

[0192] [Table 1]

[0193]

[0194] The compositional ratios of the dielectric materials (SIZ, ZnO-SnO 2 -ZrO 2 , ITO) shown in Table 1 are as follows.

[0195] SIZ: SiO 2 (15)In 2 O 3 (50)ZrO 2 (35) (where the unit of the values in the parentheses is mol%).

[0196] ZnO-SnO 2 -ZrO 2 : ZnO(40)SnO 2 (40)ZrO 2 (20) (where the unit of the values in the parentheses is mol%).

[0197] ITO: In 2 O 3 (90)SnO 2 (10) (where the unit of the values in the parentheses is wt%).

[0198] The following can be seen from Table 1.

[0199] In the optical recording media (Examples 13 to 15) in which the second dielectric layer in the L0 layer is composed of ITO, no film peeling of the optical recording medium occurred. On the other hand, in the optical recording media (Comparative Examples 7 and 8) in which the second dielectric layer in the L0 layer is composed of ZnO-SnO 2 -ZrO 2 or SIZ, film peeling of the optical recording medium occurred.

[0200] <Study on the composition of the recording layer provided in the L0 layer>

[0201] [Examples 2-1 to 2-4 and 2-10, and Comparative Examples 2-2, 2-3, 2-5 and 2-6]

[0202] First, a polycarbonate substrate with a thickness of 1.1 mm is formed by injection molding. Here, one main surface of the polycarbonate substrate is an uneven surface composed of land portions and grooves. In addition, the track pitch Tp between the land portions and the grooves is 0.225 nm. Next, by sputtering, a second dielectric layer, a recording layer, and a first dielectric layer are sequentially stacked on the uneven surface of the polycarbonate substrate, thereby forming the L0 layer.

[0203] The specific structure of the L0 layer is as follows.

[0204] First dielectric layer (upper side)

[0205] Material: SIZ

[0206] Thickness: 10 nm

[0207] Recording layer

[0208] Material: Oxides containing metals MA, MB, MC, MD, and ME shown in Table 2 (oxide of metal MA, oxide of metal MB, oxide of metal MC, oxide of metal MD, and oxide of metal ME)

[0209] Thickness: 33 nm

[0210] Second dielectric layer (lower side)

[0211] Material: ITO

[0212] Thickness: 10 nm

[0213] Next, by spin coating, an ultraviolet curable resin is uniformly coated on the L0 layer. The uneven pattern of the stamper is pressed against the ultraviolet curable resin coated on the L0 layer, ultraviolet light is irradiated on the ultraviolet curable resin to perform curing, and then the stamper is peeled off. Thus, a spacer layer with an uneven surface composed of land portions and grooves and a thickness of 25 μm is formed. Here, the track pitch Tp between the land portions and the grooves is set to 0.225 nm. Next, by sputtering, a second dielectric layer, a recording layer, and a first dielectric layer are sequentially stacked on the uneven surface of the above spacer layer, thereby forming the L1 layer.

[0214] The specific structure of the L1 layer is as follows.

[0215] First dielectric layer (upper side)

[0216] Material: SIZ

[0217] Thickness: 15 nm

[0218] Recording layer

[0219] Material: (Mn-W-Zn-Cu-Ag)-O

[0220] Thickness: 33 nm

[0221] Second dielectric layer (lower side)

[0222] Material: SIZ

[0223] Thickness: 17 nm

[0224] Next, by spin coating, the ultraviolet curable resin is uniformly coated on the L1 layer. The concave and convex pattern of the stamper is pressed against the ultraviolet curable resin coated on the L1 layer, ultraviolet light is irradiated to the ultraviolet curable resin, curing is performed, and then the stamper is peeled off. Thus, a spacer layer having a concave and convex surface composed of a shore portion and a groove and a thickness of 18 μm is formed. Here, the track pitch Tp between the shore portion and the groove is set to 0.225 nm. Next, by sputtering, the second dielectric layer, the recording layer, and the first dielectric layer are sequentially stacked on the concave and convex surface of the above spacer layer, so that the L2 layer is formed.

[0225] The specific structure of the L2 layer is as follows.

[0226] First dielectric layer (upper side)

[0227] Material: SIZ

[0228] Thickness: 17 nm

[0229] Recording layer

[0230] Material: (Mn-W-Zn-Cu-Ag)-O

[0231] Thickness: 33 nm

[0232] Second dielectric layer (lower side)

[0233] Material: SIZ

[0234] Thickness: 17 nm

[0235] Next, by spin coating, the ultraviolet curable resin is uniformly coated on the L2 layer, ultraviolet light is irradiated to the ultraviolet curable resin, and curing is performed, thereby forming a light transmission layer having a thickness of 57 μm. Thus, a three-layer optical recording medium of the desired shore / groove recording type is obtained.

[0236] [Examples 2-5 to 2-9, and Comparative Example 2-4]

[0237] An optical recording medium was obtained in the same manner as in Example 1-1, except that the recording layer in the L0 layer was formed of oxides containing metals MA, MB, MD, and ME shown in Table 2 (oxide of metal MA, oxide of metal MB, oxide of metal MD, and oxide of metal ME).

[0238] [Comparative Example 2-1]

[0239] An optical recording medium was obtained in the same manner as in Example 1-1, except that the recording layer in the L0 layer was formed of oxides containing metals MA, MB, MC, and MD shown in Table 2 (oxide of metal MA, oxide of metal MB, oxide of metal MC, and oxide of metal MD).

[0240] (Evaluation of Reflectivity)

[0241] First, the reflectivity R of the L0 layer of the optical recording medium obtained as described above was measured in the unrecorded portion of the groove using a BD standard evaluation machine. Next, the measured reflectivity R was evaluated according to the following criteria. The results are shown in Table 2.

[0242] Reflectivity R is very good: 3.5% ≤ R ≤ 4.5%

[0243] Reflectivity R is good: 3.0% ≤ R < 3.5%

[0244] Reflectivity R is very poor: 3.0% < R

[0245] Here, in Table 2, the symbols "◎", "○", and "×" represent "very good reflectivity", "good reflectivity", and "very poor reflectivity", respectively, as the evaluation results.

[0246] As described above, when the reflectivity is in the range of 3.5% ≤ R ≤ 4.5% and the reflectivity is very good, a good recording signal is obtained at a linear density higher than the AD1 standard, which is a linear density higher than the BDXL standard. When the reflectivity is in the range of 3.0% ≤ R < 3.5% and the reflectivity is good, a good recording signal is obtained at a linear density higher than the BDXL standard. When the reflectivity is in the range of 3.0% < R and the reflectivity is very poor, it is difficult to obtain a good recording signal at a linear density higher than the BDXL standard.

[0247] (Evaluation of Reproduction Durability)

[0248] First, for the L0 layer of the optical recording medium obtained as described above, a signal was recorded in the grooves of 10 tracks using a BD standard evaluation machine. Next, the signal recorded in the grooves was reproduced to obtain i-MLSE (reproduction characteristics), and the recording power (optimal recording power) P at which i-MLSE is the minimum WO was defined as the recording sensitivity PWO . Here, recording and reproduction are performed according to the BDXL standard. Specifically, the recording speed is set to 4x, the reproduction speed is set to 4x, and the recording density is set to 32GB. Next, based on the obtained recording sensitivity P WO , the reproduction durability is evaluated according to the following criteria. The results are shown in Table 2.

[0249] The reproduction durability is very good: 30mW ≤ P WO

[0250] The reproduction durability is good: 26mW ≤ P WO < 30mW

[0251] The reproduction durability is very poor: P WO < 26mW

[0252] Here, in the evaluation column of the reproduction durability in Table 2, the symbols "◎", "○", and "×" represent "very good reproduction durability", "good reproduction durability", and "very poor reproduction durability", respectively, as the evaluation results.

[0253] In the evaluation of the reproduction durability, the reproduction durability can be evaluated based on the recording sensitivity because there is a correlation between the recording sensitivity (recording power) and the reproduction durability (thermal durability), and there is a relationship of improving the reproduction durability by reducing the sensitivity of the recording layer.

[0254] In the evaluation of the reproduction durability, "very good reproduction durability" specifically means that even after 1 million reproductions, the bottom characteristics hardly deteriorate. "Good reproduction durability" specifically means that even after 1 million reproductions, reproduction is still possible. "Very poor reproduction durability" specifically means that after 1 million reproductions, reproduction becomes difficult.

[0255] (Evaluation of power margin)

[0256] First, for the L0 layer of the optical recording medium obtained as described above, signals are recorded in the grooves of 10 tracks using a BD standard evaluation machine. Next, the signals recorded in the grooves are reproduced to obtain i-MLSE (reproduction characteristics), and the lower side of the recording power where i-MLSE exceeds 13% is set as Pwl, and the upper side is set as Pwh. Here, recording and reproduction are performed according to the BDXL standard. Specifically, the recording speed is set to 4x, the reproduction speed is set to 4x, and the recording density is set to 32GB. Next, the obtained recording powers Pwl and Pwh and the optimum recording power P WO are substituted into the following formula to obtain the power margin PM for SER.

[0257] PM [%] = ((Pwh - Pwl) / P WO ) × 100

[0258] Next, evaluate the power margin PM of the L0 layer of the optical recording medium according to the following criteria.

[0259] The power margin PM is very good: 25% ≤ PM

[0260] The power margin PM is good: 20% ≤ PM < 25%

[0261] The power margin PM is very poor: PM < 20%

[0262] Here, in the power margin evaluation column in Table 2, the symbols "◎", "○", and "×" represent "very good power margin", "good power margin", and "very poor power margin", respectively, as the evaluation results.

[0263] Here, when the power margin PM is 20% or more, stable recording characteristics can be maintained even if the laser power during recording varies with the drive model.

[0264] (Comprehensive evaluation)

[0265] Using the evaluation results of the reflectivity, reproduction durability, and power margin described above, comprehensively evaluate the optical recording medium according to the following criteria.

[0266] The comprehensive characteristics are very good: the reflectivity, reproduction durability, and power margin are all very good

[0267] The comprehensive characteristics are good: none of the reflectivity, reproduction durability, and power margin is very poor, and at least one of these characteristics is good

[0268] The comprehensive characteristics are very poor: at least one of the reflectivity, reproduction durability, and power margin is very poor

[0269] Here, in the comprehensive evaluation column in Table 2, the symbols "◎", "○", and "×" represent "very good comprehensive characteristics", "good comprehensive characteristics", and "very poor comprehensive characteristics", respectively, as the evaluation results.

[0270] Table 2 shows the structures and evaluation results of the optical recording media of Examples 2-1 to 2-11 and Comparative Examples 2-1 to 2-6.

[0271] [Table 2]

[0272]

[0273] In Table 2, "at%", "P WO (4×)", "PM(4×)" are as follows.

[0274] at%: atomic% (atomic percent)

[0275] R: Reflectivity of the L0 layer

[0276] P WO (4×): Recording sensitivity (optimal recording power) during recording and reproduction at 4x speed

[0277] PM(4×): Recording power margin during recording and reproduction at 4x speed

[0278] The following can be seen from Table 2.

[0279] In an optical recording medium in which the second dielectric layer (the dielectric layer on the substrate side) in the L0 layer is made of ITO, the contents of metal MA, metal MB, and metal ME satisfy the relationship of 0.30 ≤ a / (b + e) ≤ 0.41, and the atomic ratio e of metal ME is 5 atomic percent or more and 18 atomic percent or less. Thus, both the reproduction durability (thermal durability) and the reflectivity of the L0 layer can be achieved simultaneously. In addition, the power margin of the L0 layer can be ensured.

[0280] [Example of modification]

[0281] Although the first and second embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above first and second embodiments, and various modifications can be made based on the technical concept of the present disclosure.

[0282] For example, the structures, methods, processes, shapes, materials, numerical values, etc. illustrated in the above first and second embodiments are only examples, and different structures, methods, processes, shapes, materials, numerical values, etc. can be used as needed.

[0283] In addition, in the numerical ranges described in stages in the above first and second embodiments, the upper limit value or the lower limit value of a certain stage's numerical range can be replaced by the upper limit value or the lower limit value of another stage's numerical range.

[0284] In addition, unless otherwise specified, the materials illustrated in the above first and second embodiments can be used alone, or two or more of them can be used in combination.

[0285] In addition, the chemical formulas of the compounds (for example, stoichiometric compounds) illustrated in the above first and second embodiments are representative, and if they are common names of the same compound, the described valence is not limited. For example, non-stoichiometric compounds can be used.

[0286] In addition, in the first and second embodiments, the recording layers 41 of the information signal layers L1 to Ln other than the information signal layer L0 may have the same composition as the recording layer 41 of the information signal layer L0.

[0287] In addition, in the first and second embodiments, the recording layers 41 of the information signal layers L1 to Ln may be known recording layers containing Mn oxide or known recording layers containing Pd oxide. However, in order to reduce the cost of the optical recording media 1 and 1A, it is preferable that the recording layer 41 does not contain the noble metal Pd.

[0288] In addition, in the first and second embodiments described above, the information signal layer L has been described as having a structure including a recording layer 41, a dielectric layer 42 adjacently provided to the first surface of the recording layer 41, and a dielectric layer 43 adjacently provided to the second surface of the recording layer 41. However, the structure of the information signal layer L is not limited thereto. For example, a dielectric layer may be provided only on either the first surface or the second surface of the recording layer 41. In addition, the information signal layer L may be composed of only a single-layer recording layer 41. With such a simple structure, the cost of the optical recording media 1 and 1A can be reduced, and their productivity can be improved. This effect becomes more significant as the number of layers of the information signal layer L of the medium increases.

[0289] In addition, in the first and second embodiments described above, examples of forming the layers of the optical recording media 1 and 1A by a sputtering method have been described. However, the film-forming method is not limited thereto, and other film-forming methods may be used. As other film-forming methods, for example, a chemical vapor deposition (CVD) method (a technique for depositing a thin film from a gas phase using a chemical reaction), such as thermal CVD, plasma CVD, and optical CVD, etc., can be used, and a physical vapor deposition (PVD) method (a technique for forming a thin film by condensing physically vaporized materials on a substrate in a vacuum), such as vacuum vapor deposition, plasma-assisted vapor deposition, sputtering, ion plating, etc., can be used.

[0290] In addition, in the first and second embodiments described above, the case where all the multilayer information signal layers L have the same layer structure (three-layer structure) has been described. However, the layer structure may be changed according to the characteristics required for each information signal layer L (for example, optical characteristics and durability, etc.). However, from the perspective of productivity, it is preferable that all the information signal layers L have the same layer structure.

[0291] In addition, the optical recording medium to which the present disclosure can be applied is not limited to the optical recording medium having the configurations in the first and second embodiments. For example, the present disclosure can be applied to an optical recording medium having a configuration in which a plurality of information signal layers and a protective layer are laminated on a substrate in this order, and information signals are recorded or reproduced by irradiating a laser beam from the substrate side to the plurality of information signal layers (e.g., CD (Compact Disc)), or an optical recording medium having a configuration in which a plurality of information signal layers are provided between two substrates, and information signals are recorded or reproduced by irradiating a laser beam from at least one substrate side to the plurality of information signal layers (e.g., DVD (Digital Versatile Disc)).

[0292] In addition, the following configuration can also be adopted in the present disclosure. (1)

[0294] An optical recording medium, comprising

[0295] a plurality of information signal layers,

[0296] wherein the plurality of information signal layers include

[0297] a recording layer having a first surface facing the light irradiation surface and a second surface on the side opposite to the first surface,

[0298] a first dielectric layer provided on the first surface side, and

[0299] a second dielectric layer provided on the second surface side,

[0300] wherein the second dielectric layer provided in the information signal layer located innermost when viewed from the light irradiation surface contains indium oxide and tin oxide,

[0301] wherein the recording layer provided in the information signal layer located innermost when viewed from the light irradiation surface contains oxides of metal MA, oxides of metal MB, oxides of metal MD, and oxides of metal ME,

[0302] wherein metal MA is at least one selected from the group consisting of Mn and Ni,

[0303] wherein metal MB is at least one selected from the group consisting of W, Mo, Zr, and Ta,

[0304] wherein metal MD is at least one selected from the group consisting of Cu and Ag,

[0305] wherein metal ME is Nb,

[0306] wherein the contents of metal MA, metal MB, and metal ME satisfy 0.30 ≤ a 1 / (b 1 +e 1)≤0.41 (where a 1 : atomic ratio [atomic%] of metal MA with respect to the total amount of metals MA, MB, MD, and ME, b 1 : atomic ratio [atomic%] of metal MB with respect to the total amount of metals MA, MB, MD, and ME, e 1 : atomic ratio [atomic%] of metal ME with respect to the total amount of metals MA, MB, MD, and ME), and

[0307] where the atomic ratio e of metal ME with respect to the total amount of metals MA, MB, MD, and ME 1 is 5 atomic% or more and 18 atomic% or less. (2)

[0309] The optical recording medium according to (1),

[0310] where the second dielectric layer provided in the outermost information signal layer when viewed from the light irradiation surface contains zinc oxide, tin oxide, and zirconium oxide. (3)

[0312] The optical recording medium according to (1) or (2),

[0313] where the first dielectric layer provided in the plurality of information signal layers contains a mixture of silicon oxide, indium oxide, and zirconium oxide. (4)

[0315] The optical recording medium according to any one of (1) to (3),

[0316] where the atomic ratio of metal MA with respect to the total amount of metals MA, MB, MD, and ME is, for example, 11 atomic% or more and 30 atomic% or less,

[0317] where the atomic ratio of metal MB with respect to the total amount of metals MA, MB, MD, and ME is, for example, 31 atomic% or more and 54 atomic% or less, and

[0318] where the atomic ratio of metal MD with respect to the total amount of metals MA, MB, MD, and ME is, for example, 14 atomic% or more and 25 atomic% or less. (5)

[0320] The optical recording medium according to any one of (1) to (3),

[0321] where the recording layer provided in the innermost information signal layer when viewed from the light irradiation surface further contains an oxide of metal MC,

[0322] Among them, the metal MC is Zn,

[0323] Among them, the contents of the metal MA, the metal MB, and the metal ME satisfy the relationship of 0.30 ≤ a 2 / (b 2 +e 2 ) ≤ 0.41 (where a 2 : atomic ratio [atomic%] of the metal MA relative to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME, b 2 : atomic ratio [atomic%] of the metal MB relative to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME, e 2 : atomic ratio [atomic%] of the metal ME relative to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME, and

[0324] Among them, the atomic ratio e of the metal ME relative to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME 2 is 5 atomic% or more and 18 atomic% or less. (6)

[0326] The optical recording medium according to (5),

[0327] Among them, the atomic ratio of the metal MA relative to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME is, for example, 11 atomic% or more and 30 atomic% or less,

[0328] Among them, the atomic ratio of the metal MB relative to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME is, for example, 31 atomic% or more and 54 atomic% or less,

[0329] Among them, the atomic ratio of the metal MC relative to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME is, for example, greater than 0 atomic% and 10 atomic% or less, and

[0330] Among them, the atomic ratio of the metal MD relative to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME is, for example, 14 atomic% or more and 25 atomic% or less. (7)

[0332] The optical recording medium according to any one of (1) to (6),

[0333] Among them, the reflectance of the innermost information signal layer when viewed from the light irradiation surface is 3.0% or more and 4.5% or less. (8)

[0335] The optical recording medium according to any one of (1) to (7), comprising:

[0336] A first disk; and

[0337] A second disk,

[0338] wherein the second surface of the substrate included in the first disk and the second surface of the substrate included in the second disk are bonded to each other.

[0339] A substrate having a first surface and a second surface,

[0340] A plurality of information signal layers provided on the first surface side of the substrate, and

[0341] A cover layer provided on the plurality of information signal layers,

[0342] wherein the second surface of the substrate included in the first disk and the second surface of the substrate included in the second disk are bonded to each other. (9)

[0344] The optical recording medium according to (8),

[0345] wherein the optimum recording power of the innermost information signal layer when viewed from the light irradiation surface is 58 mW or more. (10)

[0347] The optical recording medium according to any one of (1) to (7), comprising

[0348] A substrate;

[0349] A plurality of information signal layers provided on the substrate, and

[0350] A cover layer provided on the plurality of information signal layers. (11)

[0352] The optical recording medium according to (10),

[0353] wherein the optimum recording power of the innermost information signal layer when viewed from the light irradiation surface is 26 mW or more.

[0354] [Reference Mark List]

[0355] 1, 1A Optical recording medium

[0356] 10 First disk

[0357] 20 Second disk

[0358] 30 Adhesive layer

[0359] 11, 11A, 21 Substrate

[0360] 12, 22 Light-transmissive layer

[0361] 41 Recording layer

[0362] 42 Dielectric layer (first dielectric layer)

[0363] 43 Dielectric layer (second dielectric layer)

[0364] L0 to Ln, L0 to Lm Information signal layer

[0365] S1 to Sn, S1 to Sm Spacer layer

[0366] C Light-irradiation surface

[0367] C1 First light-irradiation surface

[0368] C2 Second light-irradiation surface

[0369] Gv Groove

[0370] Ld Shore

[0371] Tp Pitch

Claims

1. An optical recording medium, comprising: a plurality of information signal layers, wherein the plurality of information signal layers include a recording layer having a first surface facing the light irradiation surface and a second surface on the opposite side of the first surface, a first dielectric layer provided on the first surface side, and a second dielectric layer provided on the second surface side, wherein the second dielectric layer provided in the information signal layer located innermost when viewed from the light irradiation surface contains indium oxide and tin oxide, wherein the recording layer provided in the information signal layer located innermost when viewed from the light irradiation surface contains oxides of metal MA, oxides of metal MB, oxides of metal MD, and oxides of metal ME, wherein the metal MA is at least one selected from the group consisting of Mn and Ni, wherein the metal MB is at least one selected from the group consisting of W, Mo, Zr, and Ta, wherein the metal MD is at least one selected from the group consisting of Cu and Ag, wherein the metal ME is Nb, Among them, the contents of the metal MA, the metal MB, and the metal ME satisfy the relationship of 0.30 ≤ a 1 / (b 1 +e 1 ) ≤ 0.41, where a 1 : the atomic ratio [atomic%] of the metal MA to the total amount of the metal MA, the metal MB, the metal MD, and the metal ME, b 1 : the atomic ratio [atomic%] of the metal MB to the total amount of the metal MA, the metal MB, the metal MD, and the metal ME, e 1 : the atomic ratio [atomic%] of the metal ME to the total amount of the metal MA, the metal MB, the metal MD, and the metal ME, and wherein an atomic ratio e of the metal ME relative to the total amount of the metals MA, MB, MD, and ME 1 is not less than 5 atomic % and not greater than 18 atomic %.

2. The optical recording medium according to claim 1, wherein, the second dielectric layer provided in the information signal layer located outside the innermost when viewed from the light irradiation surface contains zinc oxide, tin oxide, and zirconium oxide.

3. The optical recording medium according to claim 1, wherein, the first dielectric layer provided in the plurality of information signal layers contains a mixture of silicon oxide, indium oxide, and zirconium oxide.

4. The optical recording medium according to claim 1, wherein, the atomic ratio of the metal MA to the total amount of the metal MA, the metal MB, the metal MD, and the metal ME is not less than 11 atomic % and not more than 30 atomic %, wherein the atomic ratio of the metal MB to the total amount of the metal MA, the metal MB, the metal MD, and the metal ME is not less than 31 atomic % and not more than 54 atomic %, and wherein the atomic ratio of the metal MD to the total amount of the metal MA, the metal MB, the metal MD, and the metal ME is not less than 14 atomic % and not more than 25 atomic %.

5. The optical recording medium according to claim 1, wherein, the recording layer provided in the information signal layer located innermost when viewed from the light irradiation surface further contains an oxide of metal MC, wherein the metal MC is Zn, Among them, the contents of the metal MA, the metal MB, and the metal ME satisfy the relationship of 0.30 ≤ a 2 / (b 2 +e 2 ) ≤ 0.41, where a 2 : the atomic ratio [atomic%] of the metal MA to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME, b 2 : the atomic ratio [atomic%] of the metal MB to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME, e 2 : the atomic ratio [atomic%] of the metal ME to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME, and wherein an atomic ratio e of the metal ME with respect to the total amount of the metals MA, MB, MC, MD, and ME 2 is not less than 5 atomic % and not more than 18 atomic %.

6. The optical recording medium according to claim 5, wherein, the atomic ratio of the metal MA to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME is not less than 11 atomic % and not more than 30 atomic %, wherein the atomic ratio of the metal MB to the total amount of the metal MA, the metal MB, the metal MC, the metal MD, and the metal ME is not less than 31 atomic % and not more than 54 atomic %, Wherein, the atomic ratio of the metal MC relative to the total amount of the metals MA, MB, MC, MD, and ME is greater than 0 atomic % and not greater than 10 atomic %, and wherein, the atomic ratio of the metal MD relative to the total amount of the metals MA, MB, MC, MD, and ME is not less than 14 atomic % and not greater than 25 atomic %.

7. The optical recording medium according to claim 1, wherein, the reflectance of the innermost information signal layer when viewed from the light irradiation surface is not less than 3.0% and not greater than 4.5%.

8. The optical recording medium according to claim 1, comprising: a first disc; and a second disc, wherein, the first disc and the second disc comprise a substrate having a first surface and a second surface, the plurality of information signal layers provided on the first surface side of the substrate, and a cover layer provided on the plurality of information signal layers, wherein, the second surface of the substrate included in the first disc is adhesively bonded to the second surface of the substrate included in the second disc.

9. The optical recording medium according to claim 8, wherein, the optimum recording power of the innermost information signal layer when viewed from the light irradiation surface is not less than 58 mW.

10. The optical recording medium according to claim 1, comprising a substrate; the plurality of information signal layers provided on the substrate, and a cover layer provided on the plurality of information signal layers.

11. The optical recording medium according to claim 10, wherein, the optimum recording power of the innermost information signal layer when viewed from the light irradiation surface is not less than 26 mW.

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