JP2009170065A - Method of manufacturing multilayer optical recording medium, and multilayer optical recording medium obtained by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method which reduces cost of a multilayer optical recording medium equipped with a plurality of rewritable information recording layers, and to provide the multilayer optical recording medium at low cost which is manufactured by the method and excellent in signal quality. <P>SOLUTION: The multilayer optical recording medium which is equipped with a plurality of rewritable information recording layers on the substrate, and which performs recording and/or playback with light irradiation from a cover layer side disposed opposite to the substrate, is manufactured by the manufacturing method including steps of: applying and filling UV-curable resin containing a photo-polymerization initiator having an absorption coefficient in a wavelength region of the ultraviolet ray irradiation between a substrate having an information recording layer formed thereon and a stamper having a guide groove formed thereon; curing the resin with ultraviolet ray irradiation from the substrate side; forming an intermediate layer by releasing the stamper from the cured resin; stacking other information recording layer on the intermediate layer; and stacking a cover layer on the other information recording layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical recording medium and a manufacturing technique thereof, and more specifically, a manufacturing method that enables cost reduction of a multilayer optical recording medium having a plurality of additionally recordable information recording layers, and a multilayer optical recording medium obtained thereby About.

  First, in Patent Documents 1 to 3, the present applicant has a metal or semi-metal oxide, particularly bismuth oxide as a main component, as a write-once type optical recording medium capable of recording / reproducing even at a short wavelength of blue laser wavelength or less. It proposes that the recording layer is useful. Further, in Patent Document 4, the main component of the constituent element is bismuth and a recording layer containing bismuth oxide, and the recording layer further includes B, P, Ga, As, Se, Tc, Pd, Ag, Disclosed is a write-once optical recording medium comprising one or more elements X selected from Sb, Te, W, Re, Os, Ir, Pt, Au, Hg, Tl, Po, At, and Cd. ing.

On the other hand, as an optical disk system of the blue laser generation, a Blu-ray disc standard using a 405 nm blue laser and an optical system with a numerical aperture NA = 0.85 has been proposed, and commercialization has already started. This standard is designed to irradiate recording / reproducing light through a cover layer set to a thickness of about 0.1 mm, not from the conventional substrate side, in order to ensure a tilt margin in a high NA optical system. ing.
However, when the cover layer thickness is about 0.1 mm, if this is molded by an injection molding method such as polycarbonate as before, sufficient mechanical strength, plate thickness distribution, in-plane uniformity of optical characteristics, etc. A new problem arises that cannot be secured.

In order to cope with this problem, a reflective layer, a first dielectric layer, a recording layer, and a second dielectric layer are formed on a substrate made of polycarbonate or the like to form an information recording layer, and a cover layer is formed thereon (with the substrate and Has been proposed (see Patent Document 5, for example).
In such a method, a substrate having a pregroove is first injection-molded using a stamper, and then the reflective layer, the first dielectric layer, the recording layer, the first layer are formed on the surface of the substrate on which the pregroove is formed by a sputtering method or the like. Two dielectric layers are formed in this order. Then, a cover layer is formed on the surface of the second dielectric layer by spin coating an ultraviolet curable resin or bonding a film sheet.

  On the other hand, as a method for obtaining a cover layer with high film thickness uniformity, a method of applying an ultraviolet curable resin to the surface of the disk base plate by spin coating after closing the center hole of the disk base plate (see, for example, Patent Document 6). Alternatively, heat energy is applied concentrically to the rotation center of the substrate, a temperature distribution is applied, the viscosity of the photo-curing resin (ultraviolet-curing resin) is changed in the radial direction, and the photo-curing resin is spin coated on the substrate. A method (for example, refer to Patent Document 7) has been proposed.

  In the optical recording medium manufactured as described above, since the recording / reproducing laser is incident from the opposite side of the substrate, the thickness of the substrate can be sufficiently increased. Also, since optical properties such as transmittance and birefringence are not required for the substrate, it is only necessary to perform substrate molding focusing only on transferability and the mechanical properties of the medium. If such an optical recording medium is used, the substrate It is possible to use an NA optical recording medium head while sufficiently ensuring the mechanical strength.

For example, a multilayer optical recording medium having a plurality of information recording layers is manufactured by the process shown in FIG. 1 according to a conventional method. FIG. 1 is a schematic process diagram showing process steps in a conventional manufacturing method of a multilayer optical recording medium having a two-layer structure.
In the method for producing a multilayer recording medium, usually, the same polycarbonate as the substrate is used as a stamper (translucent stamper) in terms of cost and ease of injection molding. For this reason, in the step (1) of FIG. 1, a releaseable ultraviolet curable resin (peelable resin 4) that is difficult to adhere to polycarbonate is applied in advance to the polycarbonate translucent stamper 3, while the first information recording layer 2 is applied. An ultraviolet curable resin (intermediate resin 5) having good adhesiveness is applied on the substrate 1 on which is formed, and after curing in the step (2), it is easy to release the translucent stamper in a subsequent step. The method is taken.

That is, the translucent stamper coated with the above-described releaseable UV curable resin and the substrate coated with the UV curable resin having good adhesiveness are brought into close contact so that bubbles do not enter the resin (for example, in a vacuum), As shown in step (2) of FIG. 1, the resin is cured by irradiating ultraviolet rays from the translucent stamper side. Next, the translucent stamper is peeled off [step (3) in FIG. 1] to form an intermediate layer having the guide groove transferred on the surface. Next, after forming the second information recording layer 6 (step (4) in FIG. 1)], a cover layer 7 is formed in the same manner as the single-layer optical recording medium, and step (5) in FIG. A two-layer optical recording medium as shown in FIG.
Further, in order to obtain a multilayer optical recording medium, an adhesive ultraviolet curable resin is applied on the second information recording layer shown in step (4) of FIG. 1, and steps (1) to (4) of FIG. This process may be repeated.

However, the above conventional multilayer optical recording medium manufacturing method has the following cost problems.
In other words, a translucent stamper made of polycarbonate changes the peelability of the surface when reused, making it difficult to peel off, and electrostatically adsorbs minute dust generated during peeling to eliminate defects in the transfer groove. Because of the increase, etc., it is usually discarded without being recycled. For this reason, translucent stampers are required as many as the number of layers to be stacked, which causes an increase in cost. Due to such a decrease in yield and an increase in cost, the bit unit price of multilayer optical media cannot be lowered to a value that can appeal to users against that of single layer media, which has also contributed to the lack of widespread use of multilayer optical media. .

On the other hand, with regard to the UV curable adhesive for bonding DVD, by using a photopolymerization initiator having a relatively large absorption coefficient in a long wavelength region exceeding about 400 nm, the internal curability is increased and a highly reliable adhesive structure is obtained. It is described that it is obtained (see, for example, Patent Documents 8 to 10).
However, each of these bonded recording media has a structure in which recording and / or reproduction is performed from each substrate surface side. Recording and / or recording from the cover layer side such as the multilayer optical recording medium described in FIG. Or, the structure is different from that of a recording medium for reproduction. Note that a multilayer optical recording medium provided with a plurality of recordable information recording layers targeted by the present invention also performs recording and / or reproduction from the cover layer side.

Further, in the conventional technology such as DVD, when the adhesive layer (interlayer resin) made of ultraviolet curable resin is cured, ultraviolet irradiation is performed from the recording and / or reproducing side (substrate side). The transmittance of the information recording layer on the light irradiation side is usually about 50%, and the ultraviolet curable resin is cured relatively easily.
However, in the Blu-ray disc standard, recording / reproduction of the first information recording layer is performed from the cover layer side through the second information recording layer (layer close to the recording / reproduction light irradiation side: transmittance of about 50%). Done. Therefore, the layer configuration required for the recording / reproduction characteristics of the first information recording layer, that is, the layer configuration having sufficient reflectivity because it is the deepest side when recording / reproducing from the cover layer side, and Therefore, the light transmittance from the substrate side is less than a few percent, and the intermediate layer resin is cured by using the conventional technique (ultraviolet irradiation from the substrate side) that is performed on a DVD or the like. Have difficulty.
In the conventional multilayer optical recording medium described with reference to FIG. 1, ultraviolet rays are irradiated from the stamper side when the intermediate layer is formed by curing the ultraviolet curable resin. For this reason, there is an advantage that the ultraviolet curable resin is cured without intervening layers other than the stamper, but there is a problem of the cost increase described above.

JP 2003-48375 A JP 2005-161831 A JP 2005-108396 A JP 2006-247897 A Japanese Patent No. 3241560 Japanese Patent Application Laid-Open No. 11-213459 JP 2007-226911 A JP 2001-49198 A Japanese Patent Application Laid-Open No. 10-120982 Japanese Patent Laid-Open No. 10-8018 Japanese Patent Laid-Open No. 9-169956

The inventors of the present invention have made it possible to write on a translucent substrate in a recordable multilayer optical recording medium (for example, an optical recording medium capable of complying with the Blu-ray disc standard) designed to irradiate recording / reproducing light through a cover layer. However, the production method of laminating media on the surface has been intensively studied. However, reduction in yield and increase in cost due to problems such as peelability and recyclability of the translucent stamper have been issues to be solved.
In other words, it is necessary to produce a multilayer optical recording medium having a plurality of additionally recordable information recording layers without using a translucent stamper (for example, made of polycarbonate). In providing, it is necessary to cure the ultraviolet curable resin to form an intermediate layer. When the intermediate layer is formed, light irradiation is performed through the information recording layer formed on the substrate in the configuration targeted by the present invention. However, when the information recording layer formed on the substrate is recorded / reproduced from the cover layer side, it is the deepest side as described above, so that it has a layer structure with sufficient reflectivity, and its transmittance is several%. It is about ˜20%, and the difficulty in curing the intermediate layer is higher.
The present invention has been made in view of the above circumstances, and a manufacturing method capable of reducing the cost of a multilayer optical recording medium having a plurality of additionally recordable information recording layers, and the cost and signal quality produced thereby. An object of the present invention is to provide a multilayer optical recording medium excellent in the above.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by the inventions described in the following [1] to [10], and have reached the present invention. Hereinafter, the present invention will be specifically described.

[1]: The above-mentioned problem is a multilayer structure comprising a plurality of information recording layers that can be additionally recorded on a substrate, and having a multilayer structure in which recording and / or reproduction is performed by light irradiation from a cover layer side disposed to face the substrate. An optical recording medium manufacturing method comprising:
At least a step of applying and filling an ultraviolet curable resin between the substrate on which the information recording layer is formed and the stamper on which the guide groove is formed, a step of curing the ultraviolet curable resin, and the cured ultraviolet curing A step of releasing the stamper from the resin to form an intermediate layer in which guide grooves are transferred to the surface of the cured resin, a step of laminating another information recording layer on the intermediate layer, and a step of forming the intermediate layer on the other information recording layer. Laminating a cover layer,
The step of curing the ultraviolet curable resin is performed by making ultraviolet rays incident from the substrate side, and the ultraviolet curable resin contains a photopolymerization initiator having an absorption coefficient in an irradiation wavelength range of incident ultraviolet rays. This is solved by a method for manufacturing a multilayer optical recording medium.

  [2]: The method for producing a multilayer optical recording medium according to [1] above, wherein the photopolymerization initiator has a maximum extinction coefficient at a wavelength of 400 nm to 450 nm of greater than 10 (ml / g · cm). To do.

  [3]: In the method for producing a multilayer optical recording medium according to [1] or [2], the photopolymerization initiator is phenylglyoxylic acid methyl ester, bis (2,4,6-trimethylbenzoyl). -Phenylphosphine oxide, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1,2-dimethylamino-2- (4-methyl-benzyl) -1- (4-morpholine- It is at least one selected from 4-yl-phenyl) -butan-1-one and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide.

  [4]: In the method for producing a multilayer optical recording medium according to any one of [1] to [3], the ultraviolet curable resin contains at least a radical polymerizable acrylate oligomer and / or a (meth) acrylate monomer. It is characterized by.

  [5]: In the method for manufacturing a multilayer optical recording medium according to any one of [1] to [4], the plurality of information recording layers includes a first information recording layer and a second information on a substrate. The light transmission from the substrate side at a wavelength of 365 nm of the composite layer in which the recording layers are sequentially provided and the first information recording layer is formed on the substrate is 6 to 18%. Features.

  [6]: The method for producing a multilayer optical recording medium according to any one of [1] to [5], wherein the plurality of information recording layers have a multilayer film structure including recording layers.

  [7]: In the method for manufacturing a multilayer optical recording medium according to any one of [1] to [6], the plurality of information recording layers are respectively a reflective layer, a first dielectric layer, It is characterized by a multilayer film structure comprising a recording layer and a second dielectric layer.

  [8]: The method for producing a multilayer optical recording medium according to [6] or [7], wherein the recording layer contains bismuth oxide as a main component.

  [9]: The method for producing a multilayer optical recording medium according to any one of [6] to [8], wherein the main component of the recording layer is made of Bi, Ge, and O.

  [10] The above problem is solved by a multilayer optical recording medium manufactured by the method for manufacturing a multilayer optical recording medium according to any one of [1] to [9].

According to the method for manufacturing a multilayer optical recording medium according to the present invention, when an intermediate layer is provided between the substrate on which the information recording layer is formed and the stamper on which the guide groove is formed, ultraviolet rays are incident from the substrate side, It is formed by curing an ultraviolet curable resin containing a photopolymerization initiator having an absorption coefficient with respect to the irradiation wavelength of the incident ultraviolet rays. For this reason, the stamper does not need to be a transparent material, and a stamper (for example, Ni stamper) made of a material excellent in releasability and recyclability can be selected. As a result, it is possible to improve the yield and reduce the cost, which is difficult in the manufacturing method using the conventional translucent stamper. As a result, it is possible to provide a multilayer optical recording medium with low cost and excellent signal quality.
The multilayer optical recording medium according to the present invention includes a plurality of recordable information recording layers, and can perform recording and / or reproduction by light irradiation from the cover layer side disposed to face the substrate. A high-density and large-capacity blue laser generation optical disc system (for example, Blu-ray disc standard) can also be supported. In addition, the bit unit price of the multilayer optical recording medium can be reduced by the above manufacturing method.

As described above, the method for producing a multilayer optical recording medium according to the present invention includes a plurality of information recording layers that can be additionally recorded on a substrate, and is recorded and / or irradiated by light irradiation from the side of the cover layer disposed to face the substrate. A method for producing a multilayer optical recording medium having a multilayer structure for reproduction,
At least a step of applying and filling an ultraviolet curable resin between the substrate on which the information recording layer is formed and the stamper on which the guide groove is formed, a step of curing the ultraviolet curable resin, and the cured ultraviolet curing A step of releasing the stamper from the resin to form an intermediate layer in which guide grooves are transferred to the surface of the cured resin, a step of laminating another information recording layer on the intermediate layer, and a step of forming the intermediate layer on the other information recording layer. Laminating a cover layer,
The step of curing the ultraviolet curable resin is performed by making ultraviolet rays incident from the substrate side, and the ultraviolet curable resin contains a photopolymerization initiator having an absorption coefficient with respect to the irradiation wavelength of the incident ultraviolet rays. It is characterized by this.
Here, the maximum extinction coefficient of the photopolymerization initiator at a wavelength of 400 nm to 450 nm is preferably larger than 10 (ml / g · cm).
Moreover, it is preferable that the plurality of information recording layers have a multilayer structure including a recording layer.
As the multilayer film configuration, for example, in order from the substrate side, a reflective layer, a first dielectric layer (hereinafter, sometimes referred to as “upper protective layer”), a recording layer, a second dielectric layer (hereinafter, referred to as “upper protective layer”). And may be referred to as “lower protective layer”).

The method for producing a multilayer optical recording medium of the present invention will be described by taking as an example the case where the information recording layer has a two-layer structure. FIG. 2 shows a multilayer light having a two-layer structure according to the present invention in which a first information recording layer (first information recording layer) and a second information recording layer (second information recording layer) are sequentially provided on a substrate. It is a schematic process drawing which shows the process sequence of a recording medium.
In the manufacturing method according to the present invention, when the intermediate layer 5 is formed using the ultraviolet curable resin, ultraviolet rays are incident on the substrate 1 side on which the first information recording layer 2 is formed in the step (2) of FIG. Cure the cured resin. For this reason, it is not necessary to use a translucent stamper required in the prior art (for example, see FIG. 1), such as a polycarbonate stamper, as the stamper 8.
That is, in the present invention, for example, a Ni stamper used for injection molding of a substrate can be used. If Ni stampers are used, the releasability between Ni and UV curable resin is good, so the stamper can be used repeatedly, and it is possible to suppress the yield reduction and cost increase as with translucent stampers. It becomes.

In the present invention, two information recording layers each having a two-layer structure in which a first information recording layer (first information recording layer) and a second information recording layer (second information recording layer) are provided in this order on a substrate are provided. A preferred form of the method for producing a multilayer optical recording medium having layers is sometimes referred to as a composite layer (hereinafter referred to as “optical recording medium intermediate”) or “intermediate” in which a first information recording layer is formed on a substrate. The light transmittance from the substrate side at a wavelength of 365 nm is preferably 6 to 18%.
The optical recording medium intermediate having the first information recording layer formed on the substrate is, for example, the first before applying the intermediate layer resin (ultraviolet curable resin) 5 in the step (1) of FIG. A substrate 1 on which an information recording layer 2 is formed.

As described above, the information recording layer of the present invention has a multilayer structure, and the first information recording layer usually includes a highly reflective metal film made of an Ag alloy or the like. The transmittance is less than a few percent.
The reason for this is that, as shown in step (5) of FIG. 2, recording / reproduction of the first information recording layer is performed by the second information recording layer 6 provided on the first information recording layer 2 (light transmittance is 50). As a result, the reflectance at the time of reproduction is reduced to at least 1/4 or less, so that the first information recording layer has a layer structure with a high reflectance.

  Therefore, as in the optical recording medium of the present invention, the composite layer (intermediate) in which the first information recording layer is formed on the substrate has a preferable light transmittance (6 to 18%) from the substrate side. Therefore, it is necessary to reduce the thickness of the reflective layer, and in order to maintain the balance of recording / reproducing characteristics, it is necessary to design the layer configuration of the first and second information recording layers and to develop the recording layer material.

Hereinafter, the intermediate configuration of the present invention in which the above intermediate has a preferable light transmittance is referred to as a “partial transmission structure”.
FIG. 3 shows an example of the light transmission spectrum of the polycarbonate substrate and the transmission spectrum in the partial transmission structure when the thickness of the reflection layer (Ag reflection film) constituting the first information recording layer having the multilayer structure is changed. . As shown in FIG. 3, it can be seen that the transmittance of the partially transmissive structure decreases as the Ag film thickness increases.

FIG. 4 shows an example of an emission spectrum of a typical high-pressure mercury lamp, an absorption spectrum of a photopolymerization initiator contained in an ultraviolet curable resin, and a transmission spectrum of a partially transmissive structure having a transmittance of 15% at a wavelength of 365 nm. The absorption spectrum of the polymerization initiator shown in FIG. 4 is that of 1-hydroxy-cyclohexyl-phenyl ketone.
As shown in FIG. 4, the wavelength at which the photopolymerization initiator can be photoexcited increases in sensitivity from the vicinity of 400 nm toward the short wavelength direction (higher energy), but conversely, the transmittance of the partially transmissive structure is: It becomes low over 300 nm by absorption of the polycarbonate substrate and the first information recording layer.
Accordingly, the wavelength range acting on the curing of the ultraviolet curable resin is the range of A shown in FIG. 4, and when a high-pressure mercury lamp is used as the light source, the emission line spectrum at a wavelength of 365 nm mainly contributes to the curing reaction. Become. This is the reason why attention is paid to the transmittance at a wavelength of 365 nm in the present invention.

In the present invention, as described above, the transmittance of the partially transmissive structure at a wavelength of 365 nm is preferably 6 to 18%.
That is, when the transmittance is lower than 6%, it becomes difficult to cure the intermediate layer resin (ultraviolet curable resin) by irradiation with ultraviolet rays from the substrate side as shown in the step (2) of FIG. Or, as confirmed in reliability tests, etc., the curing becomes insufficient and unreacted substances are released from the intermediate layer film, causing irregular defects, or eroding the information recording layer to cause errors and jitter. It may cause a rise. On the other hand, if the UV irradiation time is lengthened, the resin curing failure can be reduced to some extent, but a resin film cured for a long time with low strength generally has a low crosslinking density and low reliability. Moreover, the temperature of the substrate and the apparatus increases due to the long-term irradiation with ultraviolet rays, which deteriorates the mechanical properties of the medium, which is not preferable. On the other hand, when the transmittance is higher than 18%, the reflectance from the first information recording layer is lowered, the recording sensitivity is deteriorated, and it becomes difficult to adjust the overall signal balance.

As described above, as a preferred embodiment of the method for producing an optical recording medium according to the present invention, the photopolymerization initiator contained in the ultraviolet curable resin desirably has a maximum extinction coefficient at a wavelength of 400 nm to 450 nm.
FIG. 5 illustrates an absorption spectrum when the photopolymerization initiator (1-hydroxy-cyclohexyl-phenyl ketone) shown in FIG. 4 is replaced with bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide. Is.
Since bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide preferably used in the present invention has absorption (= photoexcitation sensitivity) up to a wavelength of around 435 nm, it can be used as a photopolymerization initiator. Since it can efficiently absorb ultraviolet rays in the wavelength range B shown in FIG. 5 and accelerate the curing reaction of the ultraviolet curable resin, it can be suitably used for forming an intermediate layer.
That is, when a high-pressure mercury lamp is used, the emission line energy of wavelengths 405 nm and 435 nm can also be used. When irradiating ultraviolet rays through a partial transmission structure composed of a composite layer, an intermediate layer having good curability even at low illuminance Can be obtained. Further, since excessive ultraviolet irradiation is not required for curing the ultraviolet curable resin, an optical recording medium excellent in mechanical characteristics and groove signal can be obtained.

  The critical value of the preferred absorption characteristics is precisely defined by the difference in the type (spectral characteristics) and intensity of the light source used, the type and composition of the UV curable resin (acrylate oligomer / monomer, etc.), the concentration of the photopolymerization initiator, etc. Although the absorption characteristics of the photopolymerization initiator exhibit the characteristics as shown in FIGS. 4 and 5, the maximum extinction coefficient at a wavelength of 400 nm to 450 nm is 10 ( larger than (ml / g · cm). More preferably, the photopolymerization initiator having a maximum extinction coefficient larger than 100 (ml / g · cm) in the wavelength range, and most preferably the maximum extinction coefficient larger than 150 (ml / g · cm) in the wavelength range. A photoinitiator can be mentioned.

  Particularly suitable photopolymerization initiators include, for example, phenylglyoxylic acid methyl ester (absorption coefficient at 405 nm: 24 ml / g · cm), bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (900 ml). / g · cm), 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 (280 ml / g · cm), 2-dimethylamino-2- (4-methyl-benzyl) ) -1- (4-Morpholin-4-yl-phenyl) -butan-1-one (280 ml / g · cm), 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (165 ml / g · cm) ).

Said photoinitiator may be used independently and may be blended with another photoinitiator as needed.
Examples of the photopolymerization initiator that may be used by blending include 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, and 2,2-dimethoxy- 1,2-diphenylethane-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1- {4 -[4- (2-hydroxy-2-methyl-propionyl) -benzyl] -phenyl} -2-methyl-propan-1-one, 2-methyl- [4- (methylthio) phenyl] -2-morpholino-1 -Propanone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diisopropylthioxanthone, isopropylthioxanthone, etc. It is possible.

  As described above, as a preferred form of the optical recording medium in the present invention, the information recording layer has a multilayer structure (for example, [reflective layer]-[first dielectric layer]-[recording layer]-[second dielectric). Layer]), and an information recording layer formed of a multilayer film includes a write-once type multilayer optical recording medium including a recording layer containing bismuth oxide as a main component.

  The bismuth oxide in the recording layer mainly composed of bismuth oxide includes B, Ga, Pd, Ag, Sb, Te, W, Pt, Au, Al, Cr, Mn, In, Co, Fe, Cu, Ni, Zn It is desirable to include at least one element (element X) selected from Li, Si, Ge, Zr, Ti, Hf, Sn, Mo, V, and Nb.

Usually, it is preferable that bismuth oxide accounts for about 50 to 95 mol% of the entire recording layer material.
Bismuth oxide and element X do not need to be completely oxidized, and the recording layer may be configured in an oxygen deficient state with respect to the stoichiometric composition. The stoichiometric composition here refers to a composition possessed by a compound that exists stably at normal temperature and normal pressure. For example, oxides such as Bi ₂ O ₃ , B ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , and In ₂ O ₃ can be said to have a stoichiometric composition. The oxygen deficiency state with less oxygen than the stoichiometric composition is BiOx in the case of x <1.5, that is, BiO _1.48 . In the case of a stoichiometric composition without oxygen deficiency, BiO _1.5 is obtained.

  When the recording layer is made only of bismuth oxide, it is not practical because deterioration due to reproduction light occurs remarkably or archival jitter increases in storage reliability. Therefore, the addition of at least one element X described above can improve the thermal conductivity, absorption characteristics, recording sensitivity, stability of the recording mark with respect to reproducing light and temperature, and the like.

For example, with respect to recording sensitivity, when the additive element X is Ge, Sn, Li, or the like having an oxide generation enthalpy equivalent to Bi, these oxides release oxygen after sputtering to form a single element in the recording film. Since it is easy to exist, the light absorption rate is improved, and the sensitivity can be improved.
Elements such as Li, Na, Mg, K, Ca, and P have the property of being easily vitrified by coexisting with bismuth oxide. Although the mechanism is not clear, a metastable glass state may be associated with increased sensitivity. In addition, elements that are relatively difficult to oxidize, such as Cu, Ag, and Pd, exist as metals themselves, and are considered to improve sensitivity. Since La-based elements are more easily oxidized than Bi, Bi is likely to exist as a single metal, and is considered to be involved in improving sensitivity.

Another more preferable form is a multilayer optical recording medium having an information recording layer in which the main component of the recording layer is made of Bi, Ge, and O.
The recording layer to which Ge is added increases the light absorption and improves the sensitivity, and exhibits good characteristics particularly in high linear velocity recording. Although the mechanism is not clear, it is believed that the addition of Ge suppresses Bi oxidation and facilitates precipitation of Bi metal, thereby increasing light absorption and improving sensitivity. In addition, when Ge is used as an additive element, sensitivity is improved and a recording power margin is widened, so that stable recording / reproduction is possible.
Desirable Ge content is 0.01 <= Ge / (Bi + Ge) <= 0.1 by atomic ratio. When Ge / (Bi + Ge) is smaller than 0.01, a sufficient Ge addition effect cannot be obtained. On the other hand, if Ge / (Bi + Ge) is larger than 0.1, the recording jitter becomes high on the contrary, which is not preferable.

In particular, if the recording layer is made of Bi, Ge, and O, light absorption is large (extinction coefficient is large), and generally a moderate reflectance is obtained when sandwiched by a dielectric (dielectric protective film) with small light absorption. can get. Therefore, the multilayer optical recording medium of the present invention is preferably applied to the recording layer constituting the first information recording layer on the back side during recording / reproduction as shown in FIG.
In addition, it is considered that the thermal conductivity is increased because Bi metal is easily deposited. As a result, an effect of improving the thermal conductivity can be obtained in the first information recording layer in which the cooling ability is lowered by reducing the thickness of the reflective film and in the second information recording layer in which the cooling ability is similarly lowered by the semi-transmissive structure. An optical recording medium with low crosstalk and low jitter can be obtained.

The perspective view of FIG. 6 shows an example in which a plurality of information recording layers of the multilayer optical recording medium according to the present invention has a two-layer structure and each information recording layer has a multilayer structure.
In FIG. 6, the light incident surface for recording / reproducing is on the lower side (cover layer side) of the drawing. In FIG. 6, a first information recording layer 12 and a second information recording layer 14 made of a multilayer film are formed in this order on the substrate 11 (lower in the figure) with the intermediate layer 13 interposed therebetween, and the cover layer 15 is interposed therebetween. Recording / playback.
Each information recording layer includes, from the substrate side, a reflective layer, an upper protective layer (first dielectric layer), a recording layer containing bismuth oxide, a lower protective layer (second dielectric layer), and the like. For this, a known sputtering method or the like is used. That is, the first information recording layer 12 includes a reflective layer 12a, an upper protective layer 12b, a recording layer 12c containing bismuth oxide, and a lower protective layer 12d. The second information recording layer includes the reflective layer 14a and the upper protective layer 14b. , A recording layer 14c containing bismuth oxide, and a lower protective layer 14d.
The substrate is manufactured by injection molding using a resin such as polycarbonate, acrylic resin, or polyolefin, and has a spiral groove on the information recording layer lamination side. As the substrate material, for example, a polycarbonate having a translucency suitable for the partial transmission structure and having a proven record in CDs and DVDs is preferably selected.

In FIG. 6, the intermediate layer is formed using an ultraviolet curable resin containing a photopolymerization initiator. As a preferred form, at least a radical polymerizable acrylate oligomer and / or a (meth) acrylate monomer,
An ultraviolet curable resin containing a photopolymerization initiator is used, and as shown in step (2) of FIG. 2, the first information recording layer is formed and then cured by light irradiation from the substrate side. As described above, the photopolymerization initiator preferably contains a photopolymerization initiator having a maximum extinction coefficient of greater than 10 (ml / g · cm) at a wavelength of 400 nm to 450 nm.

  The ultraviolet curable resin contains at least a radical polymerizable acrylate oligomer and / or a (meth) acrylate monomer. Examples of the radical polymerizable acrylate oligomer include urethane (meth) acrylate, epoxy (meth) acrylate, and polyester acrylate. Are mentioned as preferred.

The urethane (meth) acrylate is obtained, for example, by reacting a polyol compound, a polyisocyanate compound, and a hydroxyl group-containing (meth) acrylate compound.
Specific polyol compounds used in the reaction of the urethane (meth) acrylate include polyether polyols, polyester polyols, polycarbonate polyols, polycaprolactone polyols, aliphatic hydrocarbons having two or more hydroxyl groups in the molecule, molecules Examples thereof include alicyclic hydrocarbons having two or more hydroxyl groups, unsaturated hydrocarbons having two or more hydroxyl groups in the molecule, and the like. These polyols can be used alone or in combination of two or more.

  Examples of the polyether polyol include aliphatic polyether polyols, alicyclic polyether polyols, and aromatic polyether polyols. Here, as the aliphatic polyether polyol, for example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, pentaerythritol, dipentaerythritol, trimethylolpropane, And trimethylolpropane ethylene oxide addition triol, trimethylolpropane propylene oxide addition triol, trimethylolpropane ethylene oxide and propylene oxide addition triol, pentaerythritol ethylene oxide addition tetraol, dipentaerythritol ethylene oxide addition hexaol, etc. Polyhydric alcohols such as alkylene oxide addition polyols Alternatively polyether polyols such as two or more ion-polymerizable cyclic compounds obtained by ring-opening polymerization.

Examples of the alicyclic polyether polyol include hydrogenated bisphenol A alkylene oxide addition diol, hydrogenated bisphenol F alkylene oxide addition diol, 1,4-cyclohexanediol alkylene oxide addition diol, and the like.
As the aromatic polyether polyol, for example, alkylene oxide addition diol of bisphenol A, alkylene oxide addition diol of bisphenol F, alkylene oxide addition diol of hydroquinone, alkylene oxide addition diol of naphthohydroquinone, alkylene oxide addition diol of anthrahydroquinone Etc.

A commercially available product can be used as the polyether polyol. For example, as an aliphatic polyether polyol, PTMG650, PTMG1000, PTMG2000 (manufactured by Mitsubishi Chemical Corporation), PPG1000, EXCENOL1020, EXCENOL2020, EXCENOL3020, EXCENOL4020 (above, manufactured by Asahi Glass Co., Ltd.), PEG1000, Unisafe DC1100, Unisafe DC1100 DC1800, Unisafe DCB1100, Unisafe DCB1800 (Nippon Yushi Co., Ltd.), PPTG1000, PPTG2000, PPTG4000, PTG400, PTG650, PTG2000, PTG3000, PTGL1000, PTGL2000 (above, Hodogaya Chemical Co., Ltd.), Z- 3001-4, Z-3001-5, PBG2000, PBG2000B Medicine Co., Ltd.), TMP30, PNT4 glycol, EDA
P4, EDA P8 (above, Nippon Emulsifier Co., Ltd.), Quadrol (Asahi Denka Co., Ltd.), etc. are mentioned. In addition, examples of the aromatic polyether polyol include Uniol DA400, DA700, DA1000, DB400 (manufactured by NOF Corporation) and the like.

Moreover, what is obtained by making a polyhydric alcohol and a polybasic acid react as said polyester polyol is mentioned.
Here, as the polyhydric alcohol, for example, ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6- Hexanediol, 1,7-heptanediol, 1,8-octanediol, neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,2-bis (hydroxyethyl) cyclohexane, 2,2 -Ethylene of diethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, glycerin, trimethylolpropane, trimethylolpropane Oxide adducts, propylene oxide adducts of trimethylol propane, the adduct of ethylene oxide and propylene oxide trimethylolpropane, sorbitol, pentaerythritol, dipentaerythritol, alkylene oxide addition polyol, and the like.
Examples of the polybasic acid include phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, adipic acid, and sebacic acid.

  A commercial item can be used as said polyester polyol. For example, Kurapol P1010, Kurapol P2010, PMIPA, PKA-A, PKA-A2, PNA-2000 (above, manufactured by Kuraray Co., Ltd.) and the like can be used.

  Moreover, as said polycarbonate polyol, the polycarbonate diol shown by following General formula (1) is mentioned, for example.

[In the formula (1), R ¹ represents an alkylene group having 2 to 20 carbon atoms, a (poly) ethylene glycol residue, a (poly) propylene glycol residue, a (poly) tetramethylene glycol residue; It is an integer of 30. ]

Specific examples of R ¹ include 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, Diols such as 8-octanediol, 1,9-nonanediol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, etc. Excluded residues are mentioned.

A commercially available product can be used as the polycarbonate polyol. For example, DN-980, DN-981, DN-982, DN-983 (manufactured by Nippon Polyurethane Industry Co., Ltd.), PC-8000 (manufactured by PPG), PNOC1000, PNOC2000, PMC100, PMC2000 (and (Made by Kuraray), Plaxel CD-205, CD-208, CD-210, CD-220, CD-205PL, CD-208PL, CD-210PL, CD-220PL, CD-205HL, CD-208HL, CD-210HL, CD-220HL, CD-210T, CD-221T (above, manufactured by Daicel Chemical Industries, Ltd.) and the like can be used.

Examples of the polycaprolactone polyol include ε-caprolactone such as ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1,2-polybutylene glycol, 1,6-hexanediol, Examples thereof include polycaprolactone diols obtained by addition reaction with diols such as neopentyl glycol, 1,4-cyclohexanedimethanol and 1,4-butanediol.
A commercially available product can be used as the polycaprolactone polyol. As such a commercially available product, for example, Plaxel 205, 205AL, 212, 212AL, 220, 220AL (manufactured by Daicel Chemical Industries, Ltd.) can be used.

  Examples of the aliphatic hydrocarbon having two or more hydroxyl groups in the molecule include ethylene glycol, propylene glycol, tetramethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1, 7-heptanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol, 2,2-diethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-methyl -1,8-octanediol, hydroxy-terminated hydrogenated polybutadiene, glycerin, trimethylolpropane, pentaerythritol, sorbitol and the like.

Examples of alicyclic hydrocarbons having two or more hydroxyl groups in the molecule include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,2-bis (hydroxyethyl) cyclohexane, and dicyclopentadiene. Examples thereof include a dimethylol compound and tricyclodecane dimethanol.
Examples of the unsaturated hydrocarbon having two or more hydroxyl groups in the molecule include hydroxy-terminated polybutadiene and hydroxy-terminated polyisoprene.

Furthermore, examples of polyols other than the above include β-methyl-δ-valerolactone diol, castor oil-modified diol, terminal diol compound of polydimethylsiloxane, polydimethylsiloxane carbitol-modified diol, and the like.
The preferred average molecular weight of these polyol compounds is 50 to 15000, particularly preferably 100 to 8000.

The polyisocyanate compound is preferably a diisocyanate compound.
For example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylphenylene diisocyanate, 4,4'-biphenylene diisocyanate, 1,6-hexane diisocyanate, isophorone diisocyanate 2,2,4-trimethylhexamethylene diisocyanate, bis (2-isocyanatoethyl) fumarate, 6-isopropyl-1,3-phenyl diisocyanate, 4-diphenylpropyl Examples include lopan diisocyanate, lysine diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, and tetramethylxylylene diisocyanate.
Among these, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate and the like are particularly preferable. These diisocyanates can be used alone or in combination of two or more.

  Moreover, the said hydroxyl-containing (meth) acrylate is a (meth) acrylate which has a hydroxyl group in an ester residue, for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl ( (Meth) acrylate, 2-hydroxy-3-phenyloxypropyl (meth) acrylate, 1,4-butanediol mono (meth) acrylate, 2-hydroxyalkyl (meth) acryloyl phosphate, 4-hydroxycyclohexyl (meth) acrylate, 1 , 6-hexanediol mono (meth) acrylate, neopentyl glycol mono (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolethane di (meth) acrylate, pentaerythritol tri Meth) acrylate, dipentaerythritol penta (meth) acrylate or represented by the following general formula (2) (meth) acrylate, and the like.

[In formula (2), R ² represents a hydrogen atom or a methyl radical, n is 1 to 15, preferably an integer of 1-4. ]

Furthermore, the compound obtained by addition reaction of glycidyl group containing compounds, such as alkyl glycidyl ether, allyl glycidyl ether, and glycidyl (meth) acrylate, and (meth) acrylic acid can also be mentioned.
Of these, hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate are particularly preferable.

Although the synthesis | combining method of urethane (meth) acrylate suitable for the ultraviolet curable resin used for this invention is not restrict | limited in particular, For example, it carries out according to the method of the following (i)-(iii).
(I) A method in which a polyisocyanate and a hydroxyl group-containing (meth) acrylate are reacted and then reacted in the order of polyol.
(Ii) A method in which a polyol, a polyisocyanate, and a hydroxyl group-containing (meth) acrylate are charged together and reacted.
(Iii) A method of reacting a polyol and a polyisocyanate and then reacting a hydroxyl group-containing (meth) acrylate.

In the synthesis of the urethane (meth) acrylate, usually, copper naphthenate, cobalt naphthenate, zinc naphthenate, di-n-butyltin dilaurate, triethylamine, 1,4-diazabicyclo [2.2.2] octane, 1, The reaction is preferably performed using 0.01 to 1 part by weight of a urethanization catalyst such as 4-diaza-2-methylbicyclo [2.2.2] octane with respect to 100 parts by weight of the total amount of the reactants. The reaction temperature in this reaction is usually 0 to 90 ° C, preferably 10 to 80 ° C.
Moreover, the preferable number average molecular weights of urethane (meth) acrylate are 400-40000, and it is especially preferable that it is 600-20000.

  Among the radical polymerizable oligomers suitable for the ultraviolet curable resin used in the present invention, examples of the epoxy (meth) acrylate include those obtained by reacting a glycidyl ether type epoxy compound with (meth) acrylic acid.

  Examples of the glycidyl ether type epoxy compound include diglycidyl ether of bisphenol A or its alkylene oxide adduct, diglycidyl ether of bisphenol F or its alkylene oxide adduct, diglycidyl ether of hydrogenated bisphenol A or its alkylene oxide adduct, Diglycidyl ether of hydrogenated bisphenol F or its alkylene oxide adduct, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, cyclohexanedimethanol Diglycidyl ether, polypropylene glycol diglycidyl ether, etc. Rukoto can.

  The epoxy (meth) acrylate suitable for the ultraviolet curable resin used in the present invention is, for example, 0.9 to 1.5 mol of (meth) acrylic acid with respect to 1 equivalent of the epoxy group of the glycidyl ether type epoxy compound. The reaction is preferably carried out at a ratio of 0.95 to 1.1 mol. In this case, the reaction temperature is preferably 80 to 120 ° C., and the reaction time is about 10 to 35 hours.

  In order to accelerate the reaction, for example, a catalyst such as triphenylphosphine, TAP (2,4,6-tris (dimethylaminomethyl) phenol), triethanolamine, tetraethylammonium chloride is preferably used. In addition, a polymerization inhibitor (for example, paramethoxyphenol, methylhydroquinone, etc.) can be used to prevent polymerization during the reaction.

  The molecular weight of the epoxy (meth) acrylate is preferably 400 to 10,000. Epoxy (meth) acrylates can be used alone or in combination of two or more. When the epoxy (meth) acrylate is contained as a component of the ultraviolet curable resin, the content is usually 1 to 30% by weight, preferably 5 to 20% by weight.

Examples of the epoxy (meth) acrylate suitable for the ultraviolet curable resin used in the present invention include bisphenol A type epoxy (meth) acrylate and phenol novolac type epoxy (meth) acrylate.
Examples of the bisphenol-type epoxy resin used in the acrylate include bisphenol A-type epoxy resins such as Epicoat 828, Epicoat 1001, Epicoat 1004, etc. (all are trade names of Yuka Shell Epoxy), Epicoat 4001P, Epicoat 4002P, and Epicoat. Bisphenol F type epoxy resin such as 4003P (all are trade names of Yuka Shell Epoxy Co., Ltd.) and the like.

Among the radically polymerizable oligomers suitable for the ultraviolet curable resin used in the present invention, as the polyester acrylate, for example, a reaction product of a polyester polyol obtained by a reaction between a polyhydric alcohol and a polybasic acid and (meth) acrylic acid Is mentioned.
Examples of the polyhydric alcohol used here include neopentyl glycol, ethylene glycol, propylene glycol, 1,6-hexanediol, and trimethylolpropane. Examples of the polybasic acid include succinic acid, phthalic acid, hexahydrophthalic anhydride, adipic acid, azelaic acid, tetrahydrophthalic anhydride, and the like.

  Examples of the reactive diluent composed of a (meth) acrylate monomer suitable for the photocurable resin used in the present invention include (meth) acrylate compounds having at least one (meth) acryloyl group in one molecule. As these components, any of a monofunctional compound having only one (meth) acryloyl group and a polyfunctional compound having two or more may be used, and they may be used in combination at an appropriate ratio.

As the monofunctional compound, hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate are used from the viewpoint of improving the moisture and heat resistance of the optical disc. Preferably used.
Other monofunctional compounds include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, amyl (meth) acrylate, isobutyl (meth) ) Acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (Meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (Meth) acrylate, octadecyl (meth) acrylate, stearyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, Phenoxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, methoxyethylene glycol mono (meth) acrylate, ethoxyethyl (meth) acrylate, ethoxyethoxyethyl (meth) acrylate, methoxypolyethylene glycol (Meth) acrylate, methoxypolypropylene glycol (meth) acrylate, dicyclo Antadienyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, tricyclodecanyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, Dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, 7-amino-3,7-dimethyloctyl (meth) acrylate, (meth) acryloylmorpholine, 2- (meth) acryloyloxyethylphthalic acid, 2- ( (Meth) acryloyloxyethyl hexahydrophthalic acid, 2- (meth) acryloyloxypropylphthalic acid, 2- (meth) acryloyloxypropyltetrahydrophthalic acid, 2- (meth) acryloyloxy Cypropylhexahydrophthalic acid, 2- (meth) acryloyloxyethyl succinic acid, trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate, hexafluoropropyl (meth) acrylate, octafluoropentyl (meth) acrylate, Heptadecafluorodecyl (meth) acrylate, mono [2- (meth) acryloyloxyethyl] phosphate, mono [2- (meth) acryloyloxyethyl] diphenyl phosphate, mono [2- (meth) acryloyloxypropyl] phosphate, etc. Can be mentioned.

As these commercially available products, Aronix M101, M102, M110, M111, M113, M114, M117, M120, M152, M154, M5300, M5400, M5500, M5600 (above, manufactured by Toagosei Co., Ltd.), KAYARAD
TC-110S, R-128H, R629, R644 (manufactured by Nippon Kayaku Co., Ltd.), IPAA, AIB, SBAA, TBA, IAAA, HEXA, CHA, NOAA, IOAA, INAA, LA, TDA, MSAA, CAA , HDAA, LTA, STA, ISAA-1, ODAA, NDAA, IBXA, ADAA, TCDA, 2-MTA, DMA, Biscote # 150, # 150D, # 155, # 158, # 160, # 190, # 190D, # 192, # 193, # 220, # 320, # 2311HP, # 2000, # 2100, # 2150, # 2180, MTG (manufactured by Osaka Organic Chemical Industry Co., Ltd.), NK ester M-20G, M-40G, M-90G, M-230G, CB-1, SA, S, AMP-10G, AMP-20G, AMP-6 G, AMP-90G, A-SA, NLA (above, manufactured by Shin-Nakamura Chemical Co., Ltd.), ACMO (manufactured by Kojin Co., Ltd.), light acrylate IA-A, LA, SA, BO- A, EC-A, MTG-A, DPM-A, PO-A, P-200A, THF-A, IB-XA, HOA-MS, HOA-MPL, HOA-MPE, HOA-HH, IO-A, BZ-A, NP-EA, NP-10EA, HOB-A, FA-108, epoxy ester M-600A, light ester PM (above, manufactured by Kyoeisha Chemical Co., Ltd.), FA-511, FA-512A, FA-513A (manufactured by Hitachi Chemical Co., Ltd.), AR-100, MR-100, MR-200, MR-260 (manufactured by Daihachi Chemical Co., Ltd.), JAMP-100, JAMP-514, JPA-514 (above, castle Chemical Co., Ltd.), and the like.

  Examples of the polyfunctional compound include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, and 1,6-hexanediol di (meth) acrylate. 1,9-nonanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol di (Meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, hydroxypivalic acid neopen Diglycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate , Dipentaerythritol hexa (meth) acrylate, trimethylolpropane trioxyethyl (meth) acrylate, trimethylolpropane polyoxyethyl (meth) acrylate, trimethylolpropane trioxypropyl (meth) acrylate, trimethylolpropane polyoxyethyl ( (Meth) acrylate, tris (2-hydroxyethyl) isocyanurate di (meth) acrylate, tris (2-hydroxy) Cyl) isocyanurate tri (meth) acrylate, ethylene oxide-added bisphenol A di (meth) acrylate, ethylene oxide-added bisphenol F di (meth) acrylate, propylene oxide-added bisphenol A di (meth) acrylate, propylene oxide-added bisphenol F di (meth) Acrylate, tricyclodecane dimethanol di (meth) acrylate, bisphenol A diepoxy di (meth) acrylate, bisphenol F diepoxy di (meth) acrylate, bis [2- (meth) acryloyloxyethyl] phosphate, bis [2- (meth) acryloyl (E) polyfunctional (meth) acrylates such as oxypropyl] phosphate and tris [2- (meth) acryloyloxyethyl] phosphate The

As these commercial products, SA-1002, SA-2006, SA-2007, SA-4100,
SA-5001, SA-6000, SA-7600, SA-8000, SA-9000 (manufactured by Mitsubishi Chemical Corporation), Biscote # 195, # 195D, # 214HP, # 215, # 215D, # 230, # 230D, # 260, # 295, # 295D, # 300, # 310HP, # 310HG, # 312, # 335HP, # 335D, # 360, GPT, # 400, V # 540, # 700, GPT (Osaka Organic) Chemical Industry Co., Ltd.), KAYARADMANDA, R-526, NPGDA, PEG400DA, R-167, HX-220, HX-620, R-551, R-712, R-604, R-684, GPO-303, TMPTA, THE-330, TPA-320, TPA-330, PET-30, RP-1040, T-142 0, DPHA, D-310, D-330, DPCA-20, DPCA-30, DPCA-60, DPCA-120 (manufactured by Nippon Kayaku Co., Ltd.), Aronix M-210, M-208, M- 215, M-220, M-225, M-233, M-240, M-245, M-260, M-270, M-305, M-309, M-310, M-315, M-320, M-350, M-360, M-400, M-408, M-450 (above, manufactured by Toagosei Co., Ltd.), SR-212, SR-213, SR-355 (above, manufactured by Sartomer), SP -1506, SP-1507, SP-1509, SP-1519-1, SP-1563, SP-2500, VR60, VR77, VR90 (above, Showa Polymer Co., Ltd.), light ester P-2M (above, Mutual prosperity Chemical Co., Ltd.), Viscoat 3PA (manufactured by Osaka Organic Chemical Industry (Ltd.)), EB-169, EB-179, EB-3603, R-DX63182 (or, Daicel UCB Co., and the like, Ltd.) and the like.
Of the reactive diluents, it is particularly preferable to use a combination of the aforementioned hydroxyalkyl (meth) acrylate and polyfunctional (meth) acrylate.

As described above, the information recording layer of the present invention preferably has a multilayer structure. Examples of the multilayer film configuration include a configuration including a reflective layer, a first dielectric layer (upper protective layer), a recording layer, and a second dielectric layer (lower protective layer) in this order from the substrate side.
The material of the first dielectric layer (upper protective layer) and the second dielectric layer (lower protective layer) is a high-melting-point material having high transparency such as metal, semiconductor oxide, sulfide, nitride, and carbide. Can be used.
_{Specifically, SiOx, ZnO, SnO 2,} Al 2 O 3, TiO 2, In 2 O 3, MgO, ZrO 2, Ta oxides such _{2 O 5, Si 3 N 4} , AlN, TiN, BN, Examples include nitrides such as ZrN, sulfides such as ZnS and TaS ₄ , carbides such as SiC, TaC, B ₄ C, WC, TiC, and ZrC, and forms of a single layer or a mixture or a multilayer structure including two or more layers Can be used.

The optimum material for the dielectric layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. Among these, a mixed film with SiO ₂ containing 60 to 90 mol% of ZnS is preferable because there is no crystallization of the film itself, chemical change with the recording layer, and film deformation under a high temperature environment.
The upper protective layer has a function of suppressing the reaction between the recording layer and the reflective layer and appropriately controlling the thermal conductivity to the reflective film, and the preferred film thickness is 5 to 30 nm.
The lower protective layer affects the reflectance of each information recording layer by the optical interference effect, and the preferred film thickness is 5 to 100 nm. In particular, the lower protective layer of the second information recording layer has a function of preventing moisture and oxygen from permeating from the cover layer side and suppressing excessive thermal deformation of the cover layer. The film thickness is 25 to 100 nm.

  As the material of the reflective layer, a material having a sufficiently high reflectance at the wavelength of the reproduction light, for example, a metal such as Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Pd, alone or in an alloy is used. Can be used. Among them, Au, Al, and Ag are suitable as a material for the reflective layer because of their high reflectivity and good thermal conductivity. Further, an alloy containing the above metal as a main component and containing other elements may be used. Examples of other elements include Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Mention may be made of metals and metalloids such as Zn, Cd, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi.

  In particular, as the reflective layer of the first information recording layer, it is desirable to use an Ag alloy having good reflectance and transmittance, that is, low absorption with respect to the recording / reproducing wavelength of 405 nm. In the case where the reflective layer is an Ag alloy, the film thickness is preferably 25 to 45 nm in order to cure the intermediate layer by irradiating ultraviolet rays from the substrate side.

An Ag alloy can also be used for the reflective layer of the second information recording layer. However, when the upper protective layer is made of a mixed film of ZnS and SiO ₂ , the reflective film deteriorates due to the sulfurization reaction. A barrier layer must be provided between the upper protective layers, resulting in a complicated layer structure. In order to avoid this, it is possible to form a laminated film of the upper protective layer and a film having a different refractive index and extinction coefficient and use it as a reflective layer.

As described above, a material mainly composed of bismuth oxide is preferably used for the recording layer. More preferably, a material whose main component is Bi, Ge and O is used. Such a recording layer is formed by, for example, a co-sputtering method including a Bi ₂ O ₃ target and a GeO ₂ target, or a sputtering method using a target in which Bi ₂ O ₃ and GeO ₂ are integrally formed.
At this time, in order to create a state where Bi is oxygen deficient with respect to the stoichiometric composition, the target is sintered in a reducing atmosphere to be in an oxygen deficient state, or a film formation rate or The film formation conditions such as sputtering pressure may be adjusted to adjust the amount of oxygen vacancies, or reactive sputtering may be performed by adding a reducing gas such as hydrogen to the sputtering atmosphere. A desirable recording layer thickness is 5 to 30 nm.

The photocurable resin used for the cover layer includes a radical polymerizable oligomer made of urethane acrylate, epoxy acrylate and / or polyester acrylate, a reactive diluent made of (meth) acrylate monomer, a photopolymerization initiator, and the like. An ultraviolet curable resin may be formed by a known method.
A more specific configuration example of the multilayer optical recording medium in which the information recording layer in the present invention shown in FIG. 6 has a two-layer structure is shown in the perspective view of FIG.
In FIG. 7, a first information recording layer 12 and a second information recording layer 14 made of a multilayer film are formed in this order on the substrate 11 (lower in the figure) with the intermediate layer 13 interposed therebetween, and the cover layer 15 is interposed therebetween. Recording / playback. Further, each of the constituent layers of the first information recording layer 12 shown in FIG. 6 (reflection layer 12a, upper protective layer 12b, recording layer 12c containing bismuth oxide, lower protective layer 12d), and second information recording layer 14 The constituent layers (the reflective layer 14a, the upper protective layer 14b, the recording layer 14c containing bismuth oxide, and the lower protective layer 14d) can be configured using, for example, the materials shown in FIG.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In Examples and Table 1, parts are parts by weight unless otherwise specified.

Example 1
First, on a polycarbonate substrate having a thickness of 1.1 mm and a diameter of 120 mm having a guide groove with a groove depth of 20 nm and a track pitch of 0.32 μm, each layer is sequentially formed by sputtering using targets of the following compositions. The first information recording layer having a multilayer structure was used.
[Each component layer and target]
(1) Reflective layer: Ag-0.5 wt% Bi (film thickness 30 nm)
(2) Barrier layer: Si ₃ N ₄ (film thickness 5 nm)
(3) Upper protective layer (first dielectric layer): ZnS-20 mol% SiO ₂ (film thickness 15 nm)
(4) Recording layer Bi ₂ O ₃ -30 mol% GeO ₂ (film thickness 10 nm)
(5) Lower protective layer (second dielectric layer): ZnS-20 mol% SiO ₂ (film thickness 65 nm)

Next, in accordance with the process of FIG. 2, an ultraviolet curable resin (intermediate part) having the composition of Example 1 shown in Table 1 below (acrylate and polymerization initiator: (each part by weight)) is formed on the Ni stamper and the first information recording layer. Layer resin) was applied by spin coating to a total thickness of 25 μm to form a resin film [step (1) in FIG. 2]. Next, the Ni stamper and the resin film formed on the first information recording layer are brought into close contact with each other in a vacuum and then released into the atmosphere, and the substrate side is used by using a UV lamp HP-6 manufactured by Fusion UV System. To 400 mW / cm ² , ultraviolet rays were applied for 5 seconds to cure the intermediate layer resin [step (2) in FIG. 2]. At this time, the light transmittance from the substrate side at 365 nm of the composite layer (optical recording medium intermediate) in which the first information recording layer was formed on the substrate was 15.4%.

Next, the Ni stamper was peeled off [step (3) in FIG. 2], and each layer was sequentially formed by sputtering using targets having the following compositions to form a second information recording layer having a multilayer structure [ Step (4) in FIG.
[Each component layer and target]
(1) Reflective layer: Nb ₂ O ₅ (film thickness 40 nm)
(2) Upper protective layer (first dielectric layer): ZnS-20 mol% SiO ₂ (film thickness 35 nm)
(3) Recording layer Bi ₂ O ₃ -30 mol% GeO ₂ (film thickness 10 nm)
(4) Lower protective layer (second dielectric layer): ZnS-20 mol% SiO ₂ (film thickness 50 nm)

Next, 75 μm of a cover layer resin FS6306 made by Mitsubishi Rayon was applied on the second information recording layer, and 400 mW / cm ² from the cover layer side using a UV lamp HP-6 made by Fusion UV System, as described above. The cover layer resin was cured by irradiating with ultraviolet rays under conditions of 2.5 seconds to provide a cover layer.
By the above manufacturing method, a two-layer write-once optical recording medium having a thickness of about 1.2 mm, that is, a write-once optical recording medium compatible with the so-called Blu-ray disc standard was produced.

[Evaluation]
The write-once Blu-ray disc standard (BD-R) is used for the write-once optical recording medium produced above using an optical disc evaluation apparatus ODU-1000 (wavelength: 405 nm, NA: 0.85) manufactured by Pulstec Industrial. Recording was performed under 1 × and 4 × recording conditions in accordance with Version 1.2). The results are also shown in Table 1 below.
As shown in Table 1, at 1 × speed, the bottom jitter (value at the recording power at which the jitter is lowest) of each of the first information recording layer and the second information recording layer is 6.0% (jitter standard = 7% or less) ) And 7.3% (jitter standard = 8.5% or less), even at 4 × speed, 5.9% and 7.0% were good respectively.
FIG. 8 shows a power margin at the time of quadruple speed recording.
The power margin is the range of the recording power where the jitter is below the standard value. If the recording power margin is wide when the laser power fluctuates for some reason, recording and playback can be performed normally. A larger (wide) margin is preferable. As shown in FIG. 8, it is 12.2 to 14.7 mW in the first information recording layer on the back side with respect to the recording / reproducing light irradiation, and 13.0 to 15.4 mW in the second information recording layer on the near side. A good two-layer medium with a power margin of about 2 mW was obtained.

(Example 2)
A similar two-layer recordable optical recording medium was produced in the same manner as in Example 1 except that Bi ₂ O ₃ used for the recording layer target in Example 1 was changed to Bi _28.5 B _14.3 O _57.1 .
Using this medium as an optical disk evaluation apparatus ODU-1000 (wavelength: 405 nm, NA: 0.85) manufactured by Pulstec Industrial Co., Ltd., the 1 × speed conforming to the write-once Blu-ray disk standard (BD-R Version 1.2) and Recording was performed under 4 × speed recording conditions.
As a result of the evaluation, the bottom jitter of the first information recording layer and the second information recording layer was good at 6.5% and 7.2% at 1 × speed, respectively. At 4 × speed, the recording jitter exceeded 10% and did not satisfy the standard.

(Example 3)
A similar two-layer write-once optical recording medium was prepared in the same manner as in Example 1 except that Bi ₂ O ₃ used for the recording layer target was changed to Bi _26.9 B _12.3 Zn _2.0 O _58.8 in Example 1.
Recording was performed on this medium under the recording conditions of 1 × speed and 4 × speed in accordance with the write-once Blu-ray disc standard (BD-R Version 1.2) using an optical disc evaluation apparatus ODU-1000 manufactured by Pulstec Industrial.
As a result of the evaluation, the bottom jitter of the first information recording layer and the second information recording layer was good at 6.0% and 7.5% at 1 × speed, respectively. At 4 × speed, the recording jitter exceeded 10% and did not satisfy the standard.

Example 4
A similar two-layer write-once optical recording medium was prepared in the same manner as in Example 1 except that Bi ₂ O ₃ used for the recording layer target in Example 1 was changed to Bi _26.3 B _12.1 Sn _2.0 O _59.6 .
Recording was performed on this medium under the recording conditions of 1 × speed and 4 × speed in accordance with the write-once Blu-ray disc standard (BD-R Version 1.2) using an optical disc evaluation apparatus ODU-1000 manufactured by Pulstec Industrial.
As a result of the evaluation, the bottom jitter of the first information recording layer and the second information recording layer was good at 6.0% and 7.5% at 1 × speed, respectively. At 4 × speed, the recording jitter exceeded 9% and did not satisfy the standard.

(Example 5)
A two-layer write-once optical recording medium was manufactured in the same manner as in Example 1 except that the reflective film thickness of the first information recording layer was changed to 40 nm. In the case of this optical recording medium, the light transmittance from the substrate side at a wavelength of 365 nm of the composite layer (optical recording medium intermediate) in which the first information recording layer was formed on the substrate was 6%.
Next, when an optical disc evaluation apparatus ODU-1000 manufactured by Pulstec Industrial Co., Ltd. was used for this medium and the signal waveform in an unrecorded state was observed, defects were observed. This is because, since the curability of the intermediate layer resin is insufficient, a defect occurs in the groove shape due to outgas from the resin or the like when the second information recording layer is sputtered.
Therefore, the ultraviolet irradiation condition from the substrate side in the two-layer write-once type optical recording medium having the reflection film thickness of the first information recording layer changed to 40 nm is 400 mW / cm ² for 5 seconds, 6 seconds, 7 seconds respectively. When the unrecorded signal was confirmed in the same manner by changing the time between seconds and 8 seconds, it was found that no defect occurred when the irradiation time was 7 seconds or longer.
When recording was performed on this medium under 1 × and 4 × recording conditions, the bottom jitter of the first information recording layer and the second information recording layer was 6.2% and 7.8% at 1 × speed, respectively. . Note that the jitter of the second information recording layer was close to 8.5% of the standard at 6.0% and 8.4% at 4 × speed, respectively. It was not possible to secure a power margin at the time of quadruple speed recording.
From the evaluation results, it is determined that 6% of the light transmittance from the substrate side of the composite layer (optical recording medium intermediate) at the wavelength of 365 nm is close to the limit. Jitter deteriorates because the amount of ultraviolet irradiation when the intermediate layer is cured is large, so that the recording medium is heated and a thermal stress is applied to the interface with the Ni stamper, so that the groove shape of the intermediate layer is easily deformed when the stamper is released. This is probably because of this.
That is, when the light transmittance is less than 6% (when the thickness of the reflective film is greater than 40 nm), it becomes difficult to cure the intermediate layer by transmitting ultraviolet light to the intermediate of the optical recording medium. A sufficient cooling time is set when releasing the mold or a new cooling mechanism is required, which is not preferable from the viewpoint of increasing the cost of the medium.

(Example 6)
A two-layer write-once optical recording medium was manufactured in the same manner as in Example 1 except that the reflective film thickness of the first information recording layer was changed to 25 nm. In the case of this optical recording medium, the light transmittance from the substrate side at a wavelength of 365 nm of the composite layer (optical recording medium intermediate) in which the first information recording layer is formed on the substrate was 18%.
Next, when recording was performed on this medium using the optical disk evaluation apparatus ODU-1000 manufactured by Pulstec Industrial under the recording conditions of 1 × speed and 4 × speed, the bottom jitter of the first information recording layer and the second information recording layer was recorded. Were 6.5% and 7.3% at 1 × speed, respectively. Incidentally, at 4 × speed, they were 6.9% and 7.2%, respectively, and the jitter of the first information recording layer was close to 7.0% of the standard. In particular, it was difficult to secure a power margin at the time of quadruple speed recording.
From the evaluation results, it is determined that the light transmittance from the substrate side of the composite layer (optical recording medium intermediate) at the wavelength of 365 nm is close to the limit of 18%. Jitter deteriorates because the thickness of the reflective film, which also functions as a heat dissipation function, has become thin, and heat during recording of the first information recording layer is excessively transferred in the direction of the track or between the tracks. This is because interfering interference and crosstalk between adjacent tracks (a phenomenon in which a mark is formed so as to protrude from a track and a signal leaks when the adjacent track is reproduced).
That is, when the light transmittance is larger than 18% (when the reflection film thickness is thinner than 25 nm), good recording characteristics cannot be obtained.

(Examples 7 to 10, Comparative Examples 1 to 3)
A similar two-layer write-once type optical recording medium was prepared in the same manner as in Example 1 except that the type and composition of the photopolymerization initiator were changed as shown in Table 1 below.
For each write-once type optical recording medium produced, 1 × speed and 4 × speed conforming to the write-once Blu-ray disc standard (BD-R Version 1.2) using an optical disc evaluation apparatus ODU-1000 manufactured by Pulstec Industrial Co., Ltd. Recording was performed under the recording conditions. The results are also shown in Table 1 below.
Since the recording media of Examples 7 to 10 contain a photopolymerization initiator having a maximum extinction coefficient of greater than 10 (ml / g · cm) at a wavelength of 400 nm to 450 nm as in Example 1, the intermediate layer has good curing. There is a bottom jitter that is sufficiently low with respect to the above evaluation standards.
On the other hand, since the optical recording media of Comparative Examples 2 to 4 do not contain a photopolymerization initiator having a maximum absorption coefficient greater than 10 (ml / g · cm) at wavelengths of 400 nm to 450 nm, the intermediate layer is cured. Insufficient performance resulted in defects as shown in FIG. 9 in an unrecorded state, and the recording jitter could not satisfy the standard.

  By the manufacturing method capable of reducing the cost of the present invention, a recordable multilayer optical recording medium designed to irradiate the recording / reproducing light through the cover layer, for example, a low-cost and signal quality capable of complying with the Blu-ray disc standard. An excellent optical recording medium can be provided.

It is a schematic process drawing which shows the process sequence in the conventional manufacturing method of the multilayer optical recording medium which consists of a two-layer structure. It is a schematic process drawing which shows the process sequence in the multilayer optical recording medium which consists of a two-layer structure in this invention. It is a figure which shows each transmission spectrum in the partial transmission structure at the time of changing the film thickness of the polycarbonate substrate and the reflection layer (Ag reflection film) which comprises the 1st information recording layer. It is a figure which shows the emission spectrum of a high pressure mercury lamp, the absorption spectrum of a photoinitiator, and the transmission spectrum of the partial transmission structure which has the transmittance | permeability of 15% in wavelength 365nm. It is a figure which shows the absorption spectrum at the time of replacing the photoinitiator of FIG. 4 with bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide. 1 is a perspective view showing an example in which a plurality of information recording layers of a multilayer optical recording medium in the present invention has a two-layer structure and each information recording layer has a multilayer film configuration. It is a perspective view which shows the more concrete structural example of the multilayer optical recording medium in which the information recording layer in this invention is a 2 layer structure. It is a figure which shows the power margin at the time of quadruple speed recording obtained in evaluation of the write-once type optical recording medium produced in Example 1 of this invention. It is the figure which observed the signal waveform in the unrecorded state of the optical recording medium produced in Comparative Examples 1-3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 First information recording layer 3 Translucent stamper 4 Peelable resin 5 Intermediate resin 6 Second information recording layer 7 Cover layer 8 Stamper 11 Substrate 11
12 First information recording layer 12a Reflective layer 12b Upper protective layer 12c Recording layer 12d containing bismuth oxide Lower protective layer 13 Intermediate layer 14 Second information recording layer 14a Reflective layer 14b Upper protective layer 14c Recording layer 14d containing bismuth oxide Lower protection layer

Claims (10)

A method for producing a multilayer optical recording medium comprising a multilayer structure comprising a plurality of information recording layers that can be additionally recorded on a substrate, and performing recording and / or reproduction by light irradiation from a cover layer side facing the substrate. And
At least a step of applying and filling an ultraviolet curable resin between the substrate on which the information recording layer is formed and the stamper on which the guide groove is formed, a step of curing the ultraviolet curable resin, and the cured ultraviolet curing A step of releasing the stamper from the resin to form an intermediate layer in which guide grooves are transferred to the surface of the cured resin, a step of laminating another information recording layer on the intermediate layer, and a step of forming the intermediate layer on the other information recording layer. Laminating a cover layer,
The step of curing the ultraviolet curable resin is performed by making ultraviolet rays incident from the substrate side, and the ultraviolet curable resin contains a photopolymerization initiator having an absorption coefficient in an irradiation wavelength range of incident ultraviolet rays. A method for producing a multilayer optical recording medium.   2. The method for producing a multilayer optical recording medium according to claim 1, wherein a maximum extinction coefficient of the photopolymerization initiator at a wavelength of 400 nm to 450 nm is larger than 10 (ml / g · cm).   The photopolymerization initiator is phenylglyoxylic acid methyl ester, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl)- Butanone-1,2-dimethylamino-2- (4-methyl-benzyl) -1- (4-morpholin-4-yl-phenyl) -butan-1-one, 2,4,6-trimethylbenzoyl-diphenyl- The method for producing a multilayer optical recording medium according to claim 1, wherein the method is at least one selected from phosphine oxide.   4. The method for producing a multilayer optical recording medium according to claim 1, wherein the ultraviolet curable resin contains at least a radical polymerizable acrylate oligomer and / or a (meth) acrylate monomer.   The plurality of information recording layers have a two-layer structure in which a first information recording layer and a second information recording layer are sequentially provided on a substrate, and the first information recording layer is formed on the substrate. 5. The method of manufacturing a multilayer optical recording medium according to claim 1, wherein the composite layer has a light transmittance of 6 to 18% from the substrate side at a wavelength of 365 nm.   6. The method for producing a multilayer optical recording medium according to claim 1, wherein the plurality of information recording layers have a multilayer structure including a recording layer.   The plurality of information recording layers each have a multilayer structure including a reflective layer, a first dielectric layer, a recording layer, and a second dielectric layer in order from the substrate side. A method for producing a multilayer optical recording medium according to claim 1.   The method for producing a multilayer optical recording medium according to claim 6, wherein the recording layer contains bismuth oxide as a main component.   9. The method for producing a multilayer optical recording medium according to claim 6, wherein the main component of the recording layer is made of Bi, Ge, and O.   A multilayer optical recording medium manufactured by the multilayer optical recording medium manufacturing method according to claim 1.