JP4541192B2 - Write-once optical recording medium - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a write once read many (WORM) optical recording medium, and a write once type optical recording medium capable of performing high density recording with high reliability even at a red laser wavelength or less, particularly at a blue laser wavelength region or less. The present invention relates to a recording medium.

As write-once type optical recording media capable of high-density recording even below the blue laser wavelength, the present inventors have disclosed in Japanese Patent Application Nos. 2004-066122 and 2004-064452, the oxidation of metal or metalloid oxides, especially bismuth. The usefulness of a recording layer containing a material as a main component is proposed (hereinafter, the above application is called in-house prior art). The in-house prior art has been confirmed to have very excellent recording / reproduction characteristics and reliability (reproduction stability, storage stability, etc.).
In addition, as a write-once type optical recording medium using a metal or metalloid oxide as a recording layer, Patent Documents 1 and 2 propose highly reliable TeOx-Pd recording films. In these documents, the composition ratio of the TeOx-Pd recording film is changed in the film thickness direction to improve reliability such as storage stability. In addition, the recording layer made of TeOx-Pd is described in Non-Patent Documents 1 and 2, but there is no description other than the control of the degree of oxidation as a method for improving reliability.

In addition, regarding a material containing a bismuth oxide similar to the present invention, Patent Document 3 describes in “General formula A _x (M _m O _n ) _y (Fe ₂ O ₃ ) _z , various oxides of A, Amorphous ferromagnetic oxide in which various elements of M and various ratios of x, y, and z are defined. ”Is disclosed in Patent Document 4 as“ General formula (Bi ₂ O ₃ ) _x (M _m O _n ) _y (Fe ₂ O ₃ ) _z MmOn oxide, metal oxide containing 50% or more of an amorphous phase in which the ratios of x, y, and z are defined, and a method for producing the same are disclosed in Patent Document 5 as “general formula (B ₂ O ₃ ) _x (Bi ₂ O ₃ ) _1-x is an amorphous compound, the range of the composition x, a rapid cooling method. ”Is disclosed in Patent Document 6 as“ (Bi ₂ O ₃ ) _1-x ( Fe ₂ O _{3) x} (where, bismuth has a 0.90 ≧ x> 0) having a composition - iron-based amorphous compound material ". , It has been disclosed, respectively.
However, these technologies are related to translucent and ferromagnetic amorphous oxide materials, and are used for magneto-optical recording media, functional elements that control light by magnetism, magneto-optical sensors, transparent conductive films, piezoelectrics. Such as a membrane. In addition, these other companies' prior arts are mainly patents relating to materials and manufacturing methods, and there is no mention of application to write-once type optical recording media.

JP-A-6-150366 Japanese Patent Publication No. 6-93300 JP 61-101450 A JP 61-101448 A JP 59-8618 A JP 59-73438 A “Proceedings of The 14th Symposium on PCOS2002” PP. 23-28 "Emotional Technical Report" VOL. 28, NO. 43, PP. 5-8

In the prior art, the elements added to the recording layer are Al, Cr, Mn, Sc, In, Ru, Rh, Co, Fe, Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, There is a description of one or more selected from Hf, Sn, Pb, Mo, V, and Nb, and these additive elements provide excellent recording / reproduction characteristics and reliability (reproduction stability, storage stability, etc.). It has been confirmed that it has.
However, as a result of intensive studies, in addition to the additive element (corresponding to the element X in the present invention), an additive element having excellent recording / reproduction characteristics and reliability (reproduction stability, storage stability, etc.) exists. Has become clear. Conversely, in-house prior art has found a preferable additive element that can be added in addition to bismuth and oxygen, but has not yet clarified the physical properties required as the additive element.
Therefore, in the present invention, the main component of the constituent element is bismuth, and the recording layer containing bismuth oxide can sufficiently ensure recording / reproduction characteristics and reliability. The object is to search for elements and physical properties and to provide a write-once optical recording medium having excellent characteristics.

The above-described problems are solved by the following inventions 1) to 9 ).
1) It has a recording layer in which the main component of the constituent elements is bismuth and contains bismuth oxide, and the recording layer further includes B, P, Ga, As, Se, Pd, Ag, Sb, Te, W, Re Additional element characterized by containing one or more elements X selected from Os, Ir, Pt, Au, Hg, Tl, and Cd, and the atomic ratio of the total amount of element X to bismuth being 1.25 or less Type optical recording medium.
2) The recordable optical recording medium according to 1), wherein the element X is B, P, Ga, Se, Pd, Ag, Sb, Te, W, Pt, or Au.
3 ) A write-once optical recording medium having a structure in which the recording layer, the overcoat layer, and the reflective layer described in 1) or 2) are sequentially laminated on a substrate.
4 ) A write-once optical recording medium having a structure in which a recording layer, an overcoat layer, and a reflective layer described in 1) or 2) are sequentially laminated on a substrate.
5 ) It has a structure in which a recording layer and a cover layer described in 1) or 2) are sequentially laminated on a substrate, and recording / reproduction is performed from the cover layer side. Write-once optical recording medium.
6 ) The recording layer, the undercoat layer, and the cover layer described in 1) or 2) are sequentially laminated on the substrate, and recording / reproduction is performed from the cover layer side. Write-once type optical recording medium characterized by the above.
7 ) The write-once optical recording medium according to any one of 3) to 6) , wherein the undercoat layer and / or the overcoat layer contains ZnS and / or SiO ₂ as main components.
8 ) The write-once type optical recording medium according to any one of 3) to 6) , wherein the undercoat layer and / or the overcoat layer comprises an organic material.
9 ) The recordable optical recording medium according to any one of 1) to 8 ), wherein recording and reproduction can be performed with a laser beam of 450 nm or less.

Hereinafter, the present invention will be described in detail.
The recording layer of the recordable optical recording medium of the present invention is characterized in that the main component of the constituent elements is bismuth and contains bismuth oxide. Bismuth may be contained in any state such as metal bismuth, bismuth alloy, bismuth oxide, bismuth sulfide, bismuth nitride, bismuth fluoride, etc., but bismuth oxide (one of bismuth oxide) is always used Must be contained. By including bismuth oxide in the recording layer, the thermal conductivity of the recording layer can be lowered, the sensitivity and the jitter can be reduced, and the complex refractive index imaginary part of the recording layer is reduced. Therefore, a recording layer having excellent transparency can be obtained, and multilayering is facilitated.
Furthermore, the present invention is characterized in that an element X other than bismuth is added to the recording layer in order to improve the recording / reproducing characteristics.
Bismuth and element X are preferably present in an oxidized state, for example, from the viewpoint of stability improvement and thermal conductivity, but need not be completely oxidized. That is, when the recording layer of the present invention is composed of three elements of bismuth, element X, and oxygen, bismuth, bismuth oxide, element X, and oxide of element X may be included.

As a method of mixing bismuth (metallic bismuth) and bismuth oxide in the recording layer (method of causing the bismuth element to exist in the recording in different states), for example, the following methods (a) to (c) are considered. It is done.
(A) Sputtering method using bismuth oxide target (b) Sputtering method using bismuth target and bismuth oxide target (co-sputtering method)
(C) In the method of (a) in which sputtering is performed while introducing oxygen using a bismuth target, bismuth in the target is in a completely oxidized state, but depending on sputtering conditions such as the degree of vacuum and sputtering power, This utilizes the phenomenon that oxygen is easily lost.

One of the reasons why the element X is added to the recording layer containing bismuth as the main component element and containing bismuth oxide is to make it easy to form a fine mark by lowering the thermal conductivity. The thermal conductivity is a value due to phonon scattering, so when the particle size or crystal size is small, when the number of atoms constituting the material is large, or when the atomic weight difference between the constituent atoms is large, etc. , Thermal conductivity can be lowered. Therefore, by adding the element X to the recording layer whose main component is bismuth and containing bismuth oxide, the thermal conductivity can be controlled and the high density recording characteristics can be improved.
Furthermore, in a recording layer whose main component is bismuth and contains bismuth oxide, bismuth oxide and bismuth are crystallized by recording. The size of the crystals and crystal grains is controlled by element X. it can. Therefore, the size of the crystal and crystal grains in the recording portion can be controlled by the element X, and recording / reproduction characteristics such as jitter can be greatly improved. This is another reason for adding the element X to the recording layer.

From the viewpoint of thermal conductivity, there are almost no conditions imposed on the element X that can be added to the recording layer other than simple conditions such as the stability of the raw materials and the difficulty of production. However, it has been found that the reliability (reproduction stability and storage stability) of the recording layer varies greatly depending on the element X, and regarding the reliability, it has been found that conditions imposed on the element X clearly exist. .
That is, the present inventors have found that the following conditions (I) to (II) are effective as a result of intensive studies on the necessary requirements for the element X added to the recording layer.
(I) Element having Pauling's electronegativity of 1.80 or more (II) Pauling's electronegativity of 1.65 or more, and standard oxide enthalpy ΔH _f ⁰ of −1000 (kJ / mol) or more By using the element X that satisfies these (I) to (II), a write-once type optical recording medium having good recording / reproduction characteristics such as jitter and high reliability can be realized. .

Hereinafter, the necessary conditions (I) to (II) will be described in detail.
The main cause of the decrease in the reliability of the recording layer containing bismuth oxide as the main component element is the progress of oxidation or the change in oxidation state (change in valence, etc.). Since the progress of the oxidation and the change of the oxidation state may cause a decrease in reliability, Pauling's electronegativity and the standard generation enthalpy ΔH _f ^{0 of the} oxide are important as the physical property values of the element X.
In order to sufficiently increase the reliability, first, it is preferable to select an element having a Pauling electronegativity of 1.80 or more as the element X. This is because an element having a high Pauling electronegativity is unlikely to oxidize, and an element having a Pauling electronegativity of 1.80 or more is effective in order to ensure sufficient reliability. It depends. Further, as long as the Pauling electronegativity is 1.80 or more, the oxide standard generation enthalpy ΔH _f ⁰ may take any value.
As the element X having Pauling electronegativity of 1.80 or more, B, Si, P, Fe, Co, Ni, Cu, Ga, Ge, As, Se, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Sb, Te, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Po, At can be mentioned.

Here, the electronegativity will be briefly described.
Electronegativity is a measure of how much an atom present in a molecule attracts an electron to itself. The method of determining the value of electronegativity includes Pauling's electronegativity, Mulliken's electronegativity, Allred-Rocho's electronegativity, etc., but in the present invention, Pauling's electronegativity is used as element X. Judge the appropriateness of the.
Pauling's electronegativity is that the binding energy E (AB) of the molecule AB is larger than the average of the binding energies of the molecules AA and BB [E (AA) and E (BB) respectively], and this difference is different for each atom. It is defined as the square of the difference in electronegativity (χ _A , χ _B ). That is, the following equation (1) is obtained.
E (AB) − [E (AA) + E (BB)] / 2 = 96.48 (χ _A −χ) ² (1)
In Pauling's electronegativity, since the value of electronegativity was determined using an electron volt, a conversion coefficient of 96.48 (1 eV = 96.48 kJmol ⁻¹ ) is included in the equation.
Since the electronegativity varies depending on the valence of the element of interest in the molecule, the present invention places the following restrictions in determining the Pauling electronegativity of each element.
That is, Group 1 element is monovalent, Group 2 element is bivalent, Group 3 element is trivalent, Group 4 to Group 10 element is divalent, Group 11 element is monovalent, Group 12 element is divalent, Group 13 element Is the trivalent value, group 14 is tetravalent, group 15 is trivalent, group 16 is bivalent, group 17 is monovalent, group 18 is monovalent, and group 18 is zero. The Pauling electronegativity of the element.

The Pauling electronegativity of the elements having the Pauling electronegativity of 1.80 or more as defined in the present invention is B (2.04), Si (1.90), and P (2), respectively. .19), Fe (1.83), Co (1.88), Ni (1.91), Cu (1.90), Ga (1.81), Ge (2.01), As (2. 18), Se (2.55), Mo (2.16), Tc (1.90), Ru (2.20), Rh (2.28), Pd (2.20), Ag (1.93). ), Sn (1.96), Sb (2.05), Te (2.10), W (2.36), Re (1.90), Os (2.20), Ir (2.20) , Pt (2.28), Au (2.54), Hg (2.00), Tl (2.04), Pb (2.33), Po (2.00), At (2 20). Among these, when elements not found in the company's prior art are enumerated, the element X provided in the present invention is B (2.04), P (2.19), Ga (1.81), As ( 2.18), Se (2.55), Tc (1.90), Pd (2.20), Ag (1.93), Sb (2.05), Te (2.10), W (2 .36), Re (1.90), Os (2.20), Ir (2.20), Pt (2.28), Au (2.54), Hg (2.00), Tl (2. 04), Po (2.00), and At (2.20).
A plurality of these elements can be added to the recording layer whose main component is bismuth and contains bismuth oxide.

Further, even if Pauling's electronegativity is less than 1.80, Pauling's electronegativity is 1.65 or more, and the standard generation enthalpy ΔH _f ⁰ of the oxide of the element is −1000 (kJ / mol) or more. It has been found that a certain element can ensure sufficient reliability. The reason why this condition is effective is that even when the Pauling electronegativity is somewhat small, if the standard generation enthalpy ΔH _f ⁰ of the oxide is a large value, it is difficult to form an oxide.
In determining Pauling's electronegativity, the valence was fixed by each group, but the same conditions are imposed when determining the standard generation enthalpy ΔH _f ⁰ .
That is, Group 1 element is monovalent, Group 2 element is bivalent, Group 3 element is trivalent, Group 4 to Group 10 element is divalent, Group 11 element is monovalent, Group 12 element is divalent, Group 13 element Is trivalent, group 14 element is tetravalent, group 15 element is trivalent, group 16 element is divalent, group 17 element is monovalent valence, and the value of the oxide of the element _Let the standard enthalpy of generation be ΔH _f ⁰ . However, in the case of transition metals, oxides are formed with various valences, so the standard enthalpy of formation ΔH _f ⁰ of the oxide cannot be easily determined (the higher the valence of the elements forming the oxide, the higher the valence). In general, the standard generation enthalpy ΔH _f ⁰ of the oxide becomes smaller).
That is, in the case of a transition metal, since there are various valences for forming an oxide, it is considered that an oxide is easily formed, and it is not a preferable element X in the present invention.

For example, since V (vanadium) is divalent, the standard formation enthalpy ΔH _f ⁰ of the oxide of V becomes the standard formation enthalpy ΔH _f ⁰ value of VO = −431 (kJmol ⁻¹ ), It corresponds to condition (II). However, V easily forms oxides such as V ₂ O ₃ (trivalent), V ₂ O ₄ (tetravalent), and V ₂ O ₅ (pentavalent) in addition to VO (divalent). The standard formation enthalpies ΔH _f ^{0 of} these oxides are V ₂ O ₃ (−1218 kJmol ⁻¹ ), V ₂ O ₄ (−1424 kJmol ⁻¹ ), and V ₂ O ₅ (−1550 kJmol ⁻¹ ), respectively. These values do not correspond to the condition (II) for the element X of the present invention. In other words, assuming that V forms only an oxide with V being almost divalent, V corresponds to the conditions (I) and (II) for the element X of the present invention, but V is an oxide other than divalent. Forming easily, these oxides are easy to oxidize (more stable) and are therefore excluded from the preferred element X of the present invention.
This exclusion is specified in the description “excluding transition metals” in the condition (II) for the element X of the present invention.

Here, the standard generation enthalpy ΔH _f ⁰ will be briefly described.
Generally, a chemical reaction is represented by the following chemical reaction formula (2).
H ₂ (gas) + (1/2) O ₂ (gas) = H ₂ O (liquid) (2)
The left side is called the original system, and the right side is called the generating system. The coefficient attached to the numerator is called the stoichiometric number.
The heat that enters and exits the chemical reaction of the system at a certain temperature is called reaction heat, and the reaction heat under constant pressure conditions is called constant pressure reaction heat.
Since the heat of reaction measured under general experimental conditions is mostly constant pressure, generally constant pressure heat of reaction is often used. The constant pressure reaction heat is equal to the enthalpy difference “ΔH” between the production system and the original system.
Those having ΔH> 0 are referred to as endothermic reactions, and those having ΔH <0 are referred to as exothermic reactions.
The reaction heat when a compound is generated from a single element of its constituent elements is called generation heat or generation enthalpy, and the standard reaction heat is generated when one mole of a compound in a standard state is generated from a single element of a component element in the standard state. This is called enthalpy. The standard state is the most stable physical state at a specified temperature (usually 298 K) under a pressure of 0.1 MPa (≈1 atm), and its standard generation enthalpy is denoted by ΔH _f ⁰ . It also promises that each unit has zero enthalpy in the standard state.
Therefore, it can be said that the smaller the standard generation enthalpy of an oxide of an element is, the more stable the oxide is and the easier it is to oxidize.
The detailed value of the standard generation enthalpy is described in detail, for example, in “5th Edition Electrochemical Handbook, edited by the Electrochemical Society (Maruzen)”.

By the way, since the standard generation enthalpy ΔH _f ⁰ differs depending on the valence of the element of interest to form the oxide, in the present invention, in determining the standard generation enthalpy ΔH _f ⁰ of the oxide of each element, Add the above restrictions.
Examples of elements having Pauling electronegativity of 1.65 or more and oxide standard generation enthalpy ΔH _f ⁰ of −1000 (kJ / mol) or more include Zn, Cd, and In. The Pauling electronegativity according to the prescription of the present invention is Zn (1.65), Cd (1.69), and In (1.78), respectively, and the standard generation enthalpy ΔH _f ⁰ according to the prescription of the present invention. Are Zn (−348 kJmol ⁻¹ ), Cd (−258 kJmol ⁻¹ ), and In (−925 kJmol ⁻¹ ), respectively. Among these, the element that has not been found in the company's prior art, that is, the element X provided in the present invention is Cd.
The atomic ratio of the total amount of the element X with respect to the bismuth is 1.25 or less.
Since the recording layer of the present invention is based on the principle that the main component of the constituent element is bismuth and contains bismuth oxide, when the atomic ratio of the total amount of the element X to bismuth exceeds 1.25, This is because the recording / reproducing characteristics may not be obtained.

In the write-once type optical recording medium of the present invention, it is preferable that recording / reproduction is performed with a laser beam of 680 nm or less. Unlike the dye, the recording layer of the present invention has an appropriate absorption coefficient and a high refractive index in a wide range, so that it can be recorded and reproduced with a laser beam having a red laser wavelength of 680 nm or less, and has good recording and reproduction characteristics. High reliability can be realized. Among them, the most preferable is to perform recording / reproduction with a laser beam having a wavelength of 450 nm or less. This is because the main component of the constituent elements is bismuth and the recording layer containing bismuth oxide has a complex refractive index particularly suitable as a write-once type optical recording medium in a wavelength region of 450 nm or less.
The write-once optical recording medium of the present invention preferably has the following configuration, but is not limited thereto.
(A) Substrate / Recording layer / Overcoat layer / Reflective layer (b) Substrate / Undercoat layer / Recording layer / Overcoat layer / Reflective layer (c) Substrate / Reflective layer / Overcoat layer / Recording layer / Cover layer ( d) Substrate / Reflective layer / Overcoat layer / Recording layer / Undercoat layer / Cover layer Further, the substrate may be multilayered based on the above structure. For example, when two layers are formed on the basis of the structure of (a), a structure of substrate / recording layer / overcoat layer / reflective layer (semi-transparent layer) / adhesive layer / recording layer / overcoat layer / reflective layer / substrate It can be.

For the undercoat layer and the overcoat layer, simple oxides such as B ₂ O ₅ , Sm ₂ O ₃ , Ce ₂ O ₃ , Al ₂ O ₃ , MgO, BeO, ZrO ₂ , UO ₂ , ThO ₂ are oxidized. _{objects; SiO 2, 2MgO · SiO 2} , MgO · SiO 2, CaO · SiO 3, ZrO 2 · SiO 2, 3Al 2 O 3 · 2SiO 2, 2MgO · 2Al 2 O 3 · 5SiO 2, Li 2 O · Al 2 Silicate oxides such as O ₃ .4SiO ₂ ; Al ₂ TiO ₅ , MgAl ₂ O ₄ , Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , BaTiO ₃ , LiNbO ₃ , PZT [Pb (Zr, Ti ) O ₃ ], PLZT [(Pb, La) (Zr, Ti) O 3], double oxide oxides such as ferrite; nitride non-oxides such as Si ₃ N ₄ , AlN, BN, TiN ; SiC B ₄ C, TiC, non-oxide carbide system such as _WC; LaB _6, TiB _2, non-oxide borides system such as ZrB _2; ZnS, CdS, non-oxide sulfide-based, such as MoS _2; Silicide-based non-oxides such as MoSi ₂ ; carbon-based non-oxides such as amorphous carbon, graphite, and diamond can be used.

Moreover, it is also possible to use organic materials, such as a pigment | dye and resin, for an undercoat layer and an overcoat layer.
The dyes include polymethine, naphthalocyanine, phthalocyanine, squarylium, croconium, pyrylium, naphthoquinone, anthraquinone (indanthrene), xanthene, triphenylmethane, azulene, tetrahydrocholine, phenanthrene , Triphenothiazine, azo, and formazan dyes, and metal complex compounds thereof.
As the resin, polyvinyl alcohol, polyvinyl pyrrolidone, nitrocellulose, cellulose acetate, ketone resin, acrylic resin, polystyrene resin, urethane resin, polyvinyl butyral, polycarbonate, polyolefin and the like can be used, and these can be used alone or in combination of two or more. Can be used.

The organic material layer can be formed by ordinary means such as vapor deposition, sputtering, CVD, and solvent coating. When using a coating method, the above organic material or the like can be dissolved in an organic solvent, and a conventional coating method such as spraying, roller coating, dipping, or spin coating can be used.
As the organic solvent to be used, alcohols such as methanol, ethanol and isopropanol; ketones such as acetone, methyl ethyl ketone and cyclohexanone; amides such as N, N-dimethylacetamide and N, N-dimethylformamide; sulfoxide such as dimethyl sulfoxide Ethers such as tetrahydrofuran, dioxane, diethyl ether and ethylene glycol monomethyl ether; esters such as methyl acetate and ethyl acetate; aliphatic halogenated carbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride and trichloroethane; Aromatics such as benzene, xylene, monochlorobenzene and dichlorobenzene; cellosolves such as methoxyethanol and ethoxyethanol; hexane, pentane, Cyclohexane, and hydrocarbons such as methylcyclohexane.

For the reflection layer, a light reflective material having a high reflectance with respect to the laser beam is used.
Examples of such a light reflective material include metals such as Al, Al—Ti, Al—In, Al—Nb, Au, Ag, and Cu, metalloids, and alloys thereof. These substances may be used alone or in combination of two or more.
When the reflective layer is formed of an alloy, it can be produced by a sputtering method using the alloy as a target material. In addition to this, a chip-on-target method (for example, forming a film by placing a Cu chip on an Ag target), It can also be produced by co-sputtering (for example, using an Ag target and a Cu target).
It is also possible to form a multilayer film by alternately stacking a low refractive index layer and a high refractive index layer with a material other than metal, and use it as a reflective layer.
Examples of the method for forming the reflective layer include sputtering, ion plating, chemical vapor deposition, and vacuum vapor deposition. A preferable film thickness of the reflective layer is 5 to 300 nm.

As a material of the substrate, there are special restrictions as long as it has excellent thermal and mechanical properties, and has excellent light transmission characteristics when recording / reproducing is performed from the substrate side (through the substrate). Absent.
Specific examples include polycarbonate, polymethyl methacrylate, amorphous polyolefin, cellulose acetate, polyethylene terephthalate and the like, and polycarbonate and amorphous polyolefin are preferred.
The thickness of the substrate varies depending on the application and is not particularly limited.

The material of the protective layer formed on the reflective layer, the light transmissive layer, etc. is not particularly limited as long as it protects the reflective layer, the light transmissive layer, etc. from external force. Examples of the organic material include a thermoplastic resin, a thermosetting resin, an electron beam curable resin, and a UV curable resin. Examples of the inorganic _{materials, SiO 2, Si 3 N 4} , MgF 2, SnO 2 and the like.
Thermoplastic resins and thermosetting resins can be formed by applying a coating solution dissolved in a suitable solvent and drying. The ultraviolet curable resin can be formed by applying a coating solution as it is or dissolved in an appropriate solvent and irradiating it with ultraviolet rays to be cured.
As the ultraviolet curable resin, for example, acrylate resins such as urethane acrylate, epoxy acrylate, and polyester acrylate can be used.
These materials may be used alone or in combination, and may be used as a multilayer film as well as a single layer.
As a method for forming the protective layer, a coating method such as a spin coating method and a casting method, a sputtering method, a chemical vapor deposition method and the like are used as in the case of the recording layer. Among these, a spin coating method is preferable.
The thickness of the protective layer is generally in the range of 0.1 to 100 μm, but is preferably 3 to 30 μm in the present invention.
Further, a substrate may be further bonded to the reflective layer or the light transmissive layer surface, or two optical recording media may be bonded to each other with the reflective layer or the light transmissive layer surface facing each other.
An ultraviolet curable resin layer, an inorganic layer, or the like may be formed on the mirror surface side of the substrate in order to protect the surface and prevent the adhesion of dust and the like.

The light transmission layer (cover layer) is required when using a lens with a high NA in order to increase the density. For example, when the NA is increased, it is necessary to reduce the thickness of the portion through which the reproduction light is transmitted. This is due to the angle at which the disk surface deviates from the optical axis of the optical pickup as the NA increases (so-called tilt angle, proportional to the square of the product of the reciprocal of the wavelength of the light source and the numerical aperture of the objective lens). This is because the allowable amount of generated aberration is reduced, and this tilt angle is easily affected by the aberration due to the thickness of the substrate. Therefore, the thickness of the substrate is reduced to minimize the influence of aberration on the tilt angle.
Therefore, for example, an unevenness is formed on the substrate to form a recording layer, a reflective layer is provided thereon, and a light-transmitting light transmitting layer (cover layer) that is a layer that transmits light is further provided thereon, An optical recording medium that reproduces information on the recording layer by irradiating the reproducing light from the light transmitting layer side, a reflective layer is provided on the substrate, a recording layer is provided thereon, and further has light transparency. There has been proposed an optical recording medium in which a light transmission layer is provided and information on the recording layer is reproduced by irradiating the reproducing light from the cover layer side. In this way, the NA of the objective lens can be increased by reducing the thickness of the light transmission layer. That is, it is possible to further increase the recording density by providing a thin light transmission layer and recording / reproducing data from the light transmission layer side.
Such a light transmission layer is generally formed of a polycarbonate sheet or an ultraviolet curable resin. Further, the light transmission layer referred to in the present invention may include a layer for adhering the light transmission layer.

  According to the present invention, a medium using an additive element that has not been found in the company's prior art, the main component of the constituent element is bismuth, and has a recording layer containing bismuth oxide, which is excellent A write-once optical recording medium having recording / reproduction characteristics and reliability can be provided.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples.

(Examples 1-18)
Polyolefin substrate (manufactured by ZEON Corporation, ZEONOR) / The constitutional element is bismuth and the constitution of recording layer / heat insulating layer / reflective layer containing bismuth oxide is selected. A write-once optical recording medium was created.
For the recording layer, a sputtering target was prepared based on a raw material in which Bi ₂ O ₃ and an oxide of the element X shown in Table 1 were mixed in a range of 2: 1 to 5: 1, and the film thickness was about 7 nm using this sputtering target. It formed into a film so that it might become.
The Pauling electronegativity of the element X added to the recording layer and the standard generation enthalpy ΔH _f ⁰ of the oxide of the element X are shown in Table 1 (however, all values are values based on the provisions of the present invention). In addition, when the electronegativity of Pauling is 1.80 or more, the standard generation enthalpy ΔH _f ⁰ of the oxide of the element X is not important, and some elements do not indicate ΔH _f ⁰ ). As described above, in the present invention, the valence is fixed for each group, and the Pauling electronegativity of the element X and the standard generation enthalpy ΔH _f ⁰ of the oxide of the element X are obtained. The valence of each element is shown in Table 1.
“Type” in Table 1 represents that “A” is an element X corresponding to the provision (I) of the present invention, and “B” is an element X corresponding to the provision (II) of the present invention.
The heat insulating _{layer, ZnS-SiO 2 (ZnS:} SiO 2 = 85: 15 mol%) was used to the film thickness 15 nm.
A silver alloy was used for the reflective layer, and its film thickness was 100 nm.
The polyolefin substrate has a track pitch of 0.437 (μm) and a thickness of 0.6 mm.

Recording was performed on these write-once type optical recording media under the following recording / reproducing conditions using an optical disk evaluation apparatus DDU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd. .
As a result, as shown in Table 1, very good recording / reproducing characteristics (jitter) were realized.
<Recording and playback conditions>
・ Modulation method: 1-7 modulation
Recording linear density: shortest mark length (2T) = 0.204 (μm)
Recording linear velocity: 6.6 (m / s)
・ Waveform equalization: Limit equalizer
・ Reproduction power: 0.5 (mW)
Next, these write-once optical recording media were allowed to stand for 100 hours under conditions of 80 ° C. and 85% RH, and the amount of change in jitter was measured. The jitter change amount is a value calculated by (jitter after storage test) − (initial jitter). The results are shown in Table 1.
As is apparent from Table 1, it was confirmed that the element satisfying the requirement (I) for the element X of the present invention had a good initial jitter value and little jitter deterioration due to a storage test.
It was also confirmed that the oxide standard generation enthalpy ΔH _f ⁰ may take any value as long as the requirement (I) is satisfied.
In addition, it was confirmed that the element satisfying the requirement (II) for the element X of the present invention also has a good initial jitter value and little jitter deterioration due to a storage test.

上記実施例では記録再生波長を４０５ｎｍとしたが、記録層の膜厚を約１０〜２０ｎｍに変え、断熱層の膜厚を１５〜１２０ｎｍの範囲で調整することにより、６６０ｎｍのレーザでも良好な記録（ジッタ９％以下）が実現できた。なお、この実験では基板のトラックピッチを０．７４（μｍ）とし、記録再生条件は、ＤＶＤ＋Ｒに準拠した。また、上記実施例と同様の保存試験によるジッタの増加量は、ほぼ表１と同じ結果となった。

In the above embodiment, the recording / reproducing wavelength is set to 405 nm. However, by changing the thickness of the recording layer to about 10 to 20 nm and adjusting the thickness of the heat insulating layer in the range of 15 to 120 nm, good recording can be performed even with a 660 nm laser. (Jitter 9% or less) was realized. In this experiment, the track pitch of the substrate was 0.74 (μm), and the recording / reproducing conditions were based on DVD + R. Further, the amount of increase in jitter by the same storage test as in the above example was almost the same as in Table 1.

(Comparative example)
The same as in Example 1 except that a recording layer made of bismuth formed by sputtering using a metal bismuth target is used in place of the recording layer containing bismuth as a main component element and containing bismuth oxide. Thus, write-once type optical recording media were prepared and evaluated.
As a result of analyzing the recording layer by X-ray photoelectron spectroscopy (XPS), bismuth oxide was not detected except at the interface between the substrate and the recording layer and the recording layer and the ZnS-SiO ₂ interface. . Therefore, it was confirmed that the recording layer of this comparative example was a recording layer containing no bismuth oxide.
As a result of measuring the recording / reproducing characteristics, the initial jitter exceeded 15%, and jitter measurement was impossible after the storage test.
From this result, it was confirmed that the recording layer contains not only bismuth as a main component but also bismuth oxide.

上記光記録媒体に対し、パルステック工業（株）製の光ディスク評価装置ＤＤＵ−１０００（波長：４０５ｎｍ、ＮＡ：０．６５）を用いて、ＨＤ ＤＶＤ−Ｒに準拠した記録再生条件で、評価を行なった。
その結果、記録パワーが５．８ｍＷでＰＲＳＮＲ ２２という良好な値が得られ、良好な記録再生特性を実現することができた。 (Example 19)
On a polycarbonate substrate having a guide groove (groove depth of 50 nm, track pitch of 0.40 μm), a ZnS—SiO ₂ layer (undercoat layer) having a thickness of 65 nm and a BiPdO layer (recording layer) having a thickness of 15 nm are formed by sputtering. Were sequentially laminated. The atomic ratio of Bi and Pd is about Bi: Pd = 3: 1.
Next, an organic material layer (overcoat layer) composed of a dye represented by the following [Chemical Formula 1] is formed on the recording layer by an average coating thickness of about 30 nm by a spin coating method, and a film thickness of 150 nm is formed thereon by a sputtering method. A write-once optical recording medium of the present invention was produced by forming a reflective layer of Ag and further providing a protective layer made of an ultraviolet curable resin with a film thickness of about 5 μm by spin coating.
The dye of [Chemical Formula 1] is a material used for conventional DVD ± R, and is a material that hardly absorbs in the blue laser region.

Using the optical disk evaluation device DDU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd., the above optical recording medium was evaluated under the recording and reproduction conditions compliant with HD DVD-R. I did it.
As a result, a good value of PRSNR 22 was obtained at a recording power of 5.8 mW, and good recording / reproducing characteristics could be realized.

(Example 20)
On a polycarbonate substrate having a guide groove (groove depth 20 nm, track pitch 0.32 μm), a 100 nm-thick Ag reflection layer, a 16 nm-thickness ZnS-SiO ₂ layer (overcoat layer), and a film are formed by sputtering. A 7 nm thick BiPdO layer (recording layer) was sequentially laminated. The atomic ratio of Bi and Pd is about Bi: Pd = 3: 1.
Next, a cover layer (thickness: 0.1 mm) made of resin was adhered to produce a write-once type optical recording medium of the present invention.
The optical recording medium was evaluated using an optical disk evaluation apparatus (wavelength: 405 nm, NA: 0.85) manufactured by Pulse Tech Industry Co., Ltd. under recording / reproducing conditions based on BD-R.
As a result, a good jitter value of 6.0% was obtained at a recording power of 7.0 mW, and good recording / reproducing characteristics could be realized.

(Example 21)
A write-once optical recording medium of the present invention was prepared and evaluated in the same manner as in Example 19 except that the recording layer was a BiBO layer. The atomic ratio of Bi and B is about Bi: B = 2: 1.
As a result, it was confirmed that a good value of PRSNR 23 was obtained at a recording power of 5.6 mW, and good recording / reproducing characteristics could be realized.

(Example 22)
A write-once optical recording medium of the present invention was prepared and evaluated in the same manner as in Example 20 except that the recording layer was a BiBO layer. The atomic ratio of Bi and B is about Bi: B = 2: 1.
As a result, a good jitter value of 5.9% was obtained at a recording power of 6.7 mW, and good recording / reproducing characteristics could be realized.

(Example 23)
On a polycarbonate substrate having guide grooves (groove depth 50 nm, track pitch 0.32 μm), an Ag reflective layer having a film thickness of 100 nm is formed by sputtering, and an organic material layer comprising a dye represented by [Chemical Formula 1] (Overcoat layer) is formed by spin coating with an average film thickness of about 30 nm, and then a 15 nm thick BiBO layer (recording layer) and a 60 nm thick ZnS-SiO ₂ layer (undercoat layer) are formed thereon by sputtering. ) Were sequentially laminated. The atomic ratio of Bi and B is about Bi: B = 2: 1.
Next, a cover layer made of a transparent resin and having a thickness of 100 nm was adhered to produce a write-once type optical recording medium of the present invention.
The optical recording medium was evaluated using an optical disk evaluation apparatus (wavelength: 405 nm, NA: 0.85) manufactured by Pulse Tech Industry Co., Ltd. under recording / reproducing conditions based on BD-R.
As a result, a good jitter value of 6.5% was obtained at a recording power of 4.8 mW, and good recording / reproducing characteristics could be realized.

(Example 24)
On a polycarbonate substrate having a guide groove (groove depth 40 nm, track pitch 0.74 μm), a BiBO layer (recording layer) having a thickness of 15 nm and a ZnS-SiO ₂ layer (overcoat layer) having a thickness of 40 nm are formed by sputtering. ) Were sequentially laminated. The atomic ratio of Bi and B is about Bi: B = 2: 1.
Subsequently, a write-once optical recording medium of the present invention was prepared by providing an Ag reflection layer having a thickness of 100 nm and a protective layer having a thickness of about 5 μm made of an ultraviolet curable resin by sputtering.
The optical recording medium was evaluated using an optical disk evaluation apparatus DDU-1000 (wavelength: 660 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd. under recording and reproducing conditions compliant with DVD + R.
As a result, values of recording power of 12.0 mW and jitter of 7.2% were obtained, and good recording / reproducing characteristics could be realized.

(Example 25)
A write-once optical recording medium of the present invention was prepared and evaluated in the same manner as in Example 24 except that Sb was added to the recording layer. The atomic ratio of Bi and Sb is about Bi: Sb = 4: 1.
As a result, values of recording power 10.0 mW and jitter 7.6% were obtained, and good recording / reproducing characteristics could be realized.

(Example 26)
On a polycarbonate substrate having a guide groove (groove depth 20 nm, track pitch 0.437 μm), a 5 nm thick BiPdO layer (recording layer) and a 15 nm thick ZnS-SiO ₂ layer (overcoat layer) are sequentially sputtered. Laminated. Next, an Ag reflective layer having a thickness of 100 nm is formed thereon by sputtering, and a protective layer made of an ultraviolet curable resin and having a thickness of about 5 μm is provided by spin coating. It was created.
In this example, jitter was measured by changing the atomic number ratio of the total amount of Pd to bismuth in the recording layer. The recording / reproducing conditions are the same as those in Examples 1-18.
As a result, as shown in FIG. 1, it was confirmed that good jitter was obtained in a range where the atomic ratio of the total amount of Pd to bismuth was 1.25 or less (the dotted line in FIG. 1 is 1.25). . Further, it was confirmed that the same tendency was found even with the elements of the present invention other than Pd.

The figure which shows the measurement result of Example 26.

Claims (9)

It has a recording layer in which the main component of the constituent elements is bismuth and contains bismuth oxide, and the recording layer further includes B, P, Ga, As, Se, Pd, Ag, Sb, Te, W, Re, Os. Write-once light characterized by containing one or more elements X selected from Ir, Pt, Au, Hg, Tl, and Cd, and the atomic ratio of the total amount of elements X to bismuth is 1.25 or less recoding media.   2. The write-once type optical recording medium according to claim 1, wherein the element X is B, P, Ga, Se, Pd, Ag, Sb, Te, W, Pt, or Au. A write-once type optical recording medium comprising a structure in which the recording layer according to claim 1 or 2 , an overcoat layer, and a reflective layer are sequentially laminated on a substrate. 3. A write-once type optical recording medium having a structure in which an undercoat layer, the recording layer according to claim 1 or 2 , an overcoat layer, and a reflective layer are sequentially laminated on a substrate. A write-once type characterized by having a structure in which a reflective layer, an overcoat layer, a recording layer according to claim 1 or 2 and a cover layer are sequentially laminated on a substrate, and recording and reproduction are performed from the cover layer side. Optical recording medium. 3. A structure in which a reflective layer, an overcoat layer, a recording layer according to claim 1 or 2 , an undercoat layer, and a cover layer are sequentially laminated on a substrate, and recording and reproduction are performed from the cover layer side. A write-once optical recording medium. Subbing layer, and / or the upper coating layer is, write-once optical recording medium according to any one of claims 3-6, characterized in that the main component ZnS, and / or SiO _2. The write-once type optical recording medium according to claim 3 , wherein the undercoat layer and / or the overcoat layer is made of an organic material. Write-once optical recording medium according to any one of claims 1-8, characterized in that the following laser beam 450nm can record reproducing.

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