Title of Invention | MULTILAYER OPTICAL RECORDING MEDIUM AND OPTICAL RECORDING METHOD |
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Abstract | The present invention discloses a multilayer optical recording medium comprising at least multiple information layers (1, 2); wherein the multiple information layers comprise at least a phase change recording layer (12, 22) capable of recording information by laser irradiation, and a reflection layer (14, 24), wherein each information layer (1) other than an innermost information layer (2) as seen from a side of the laser irradiation comprises a lower protection layer (11), the phase change recording layer (12), an upper protection layer (13), the reflection layer (14) and an optical transmission layer (15) in this order as seen from the side of the laser irradiation, the upper protection layer and the optical transmission layer in each information layer other than the innermost one as seen from the side of the laser irradiation are composed of a material containing an Sn oxide, and a thickness of the upper protection layer in each information layer other than the innermost one as seen from the side of the laser irradiation is 2 nm to 15 nm, characterized in that the upper protection layer in each information layer other than the innermost one as seen from the side of the laser irradiation contains 50 mol% to 90 mol% Sn oxide. |
Full Text | DESCRIPTION MULTILAYER OPTICAL RECORDING MEDIUM AND OPTICAL RECORDING METHOD Technical Field The present invention relates to a multilayer optical medium (hereinafter, also sometimes referred to as "multilayer phase change information recording medium", "multilayer phase change optical recording medium", "multilayer optical disc" and a "multilayer phase change optical disc) capable of recording the information by causing optical change in a recording layer material by irradiation of laser light and having, multiple recording layers containing a phase change recording layer capable of rewriting the information, and an optical recording method in the optical recording medium. Background Art In phase change optical discs (phase change optical recording media) such as CD-RW, generally a basic constitution is made by providing a recording layer composed of a phase change material on a plastic substrate and thereon forming a reflection layer which enhances an optical absorption ratio of the recording layer and has a thermal diffusion effect, and the information is recorded and replayed by irradiating the laser light from a substrate side. Phase change recording materials exhibit the phase change between a crystalline state and an amorphous state by heating with laser light irradiation followed by cooling. When rapidly cooled after rapid heating, they become amorphous whereas when slowly cooled, they are crystallized. The phase change recording medium practically applies this nature to record and replay of the information. Additionally, for the purpose of blocking oxidation, transpiration and deformation of the recording layer which occur by heating with light irradiation, typically a lower protection layer is provided between the substrate and the recording layer, and an upper protection layer is provided between the recording layer and the reflection layer. These protection layers have regulation functions of optical properties of the optical recording medium, and the lower protection layer also combines with the function to prevent the substrate from softening due to the heat when recorded in the recording layer. In recent years, along with the increase of information amounts covered by computers, signal recording capacities of rewritable type discs such as DVD-RAM, DVD-RW and DVD+RW have been increased, and density growth of signal information has been advanced. The recording capacity of current CD is about 650 MB, that of DVD is about 4.7 GB, and it is forecasted that the density growth of the recording is highly required in the future. Along with the increase of the information amounts, it appears to also require enhancement of a recording speed. At present, as the rewritable DVD disc, those capable of recording 8 times faster in a monolayer have been developed and practically applied. As methods to increase the recording density using such a phase change optical recording medium, for example, shortening the laser wavelength used to a blue color area, or enlarging a numeric aperture NA of an objective lens used for pickup which performs record and replay to reduce a spot size of the laser light irradiated to the optical recording medium has been proposed, researched, developed and almost come into practical use. As the method to increase the recording capacity by improving the optical recording medium itself, various types of dual layer phase change optical recording media made by overlapping two information layers composed of at least the recording layer and the reflection layer at one side of the substrate and adhering these information layers with ultraviolet ray-curable resins have been proposed. A separation layer (sometimes referred to as an intermediate layer) which is an adhered portion between these information layers has the function to optically separate two information layers, and made up of a material which does not absorb the laser light as possible because it is necessary that the laser light used for the record and replay attains abundantly as possible to the information layer at an inner side. There are still many problems for this dual layer phase change optical recording medium. For example, if the laser light is not sufficiently transmitted through the information layer (first information layer) at a front side as seen from the side of laser light irradiation, the information can not be recorded in the recording layer of the information layer (second information layer) at the inner side and can not be replayed. Thus, the reflection layer which constitutes the first information layer must be an ultrathin translucent reflection layer. To replay, a high reflectance ratio as possible is required. However, in the optical recording medium having two layers or more of the recording layers and the reflection layers, their optical absorption and optical transmission affect, and the reflectance ratio of the optical recording medium itself becomes low. Recording in the phase change optical recording medium is performed by irradiating the laser light for a very short time to the phase change material in the recording layer followed by rapid cooling to change the crystal to the amorphous and form a mark. Thus, in the case of the translucent reflection layer with a very thin thickness of about 10 nm, a radiator effect become excessively small compared with the optical recording medium having the monolayer. Therefore, it becomes difficult to form amorphous marks when recorded in the recording layer of the first information layer. As a result, a modulation degree is hardly assured. In Patent Document 1, the technology in which materials selected from A1N, Al203, Si3N4, SiO2, Ta2O5, TaO, ZrO2, ZnO, TiO2, SiC and composite materials thereof are used for a transparent heat release layer (sometimes referred to as an optical transmission layer), and ZnS_SiO2 is used for a transparent dielectric layer (sometimes referred to as a protection layer) has been disclosed, but no special effect of Sn oxide is described. In Patent Document 2, a multilayer phase change information recording medium in which a thermal diffusion layer (sometimes referred to as an optical transmission layer) contains tin oxide as a major component and at least antimony oxide has been disclosed, but it is not described that the upper protection layer and the thermal diffusion layer, or the lower protection layer and the upper protection layer and the thermal diffusion layer are composed of Sn oxide. The effect in the blue color laser wavelength area at 405 nm is emphasized, and is different from the present invention. Furthermore in Patent Document 3, a multilayer phase change information recording medium in which the thermal diffusion layer contains ITO (indium oxide-tin oxide) as the major component and at least one of Al and Ga has been disclosed, but it is not described that the upper protection layer and the thermal diffusion layer, or the lower protection layer and the upper protection layer and the thermal diffusion layer are composed of Sn oxide. The effect in the blue color laser wavelength area at 405 nm is emphasized, only the special effect of using ITO for the thermal diffusion layer is described, and this is different from the present invention in constitution. Patent Document!.: Japanese Patent Application Laid-Open (JP-A) No. 2002-298433 Patent Document 2'- JP-A No. 2004-47038 Patent Document 3: JP-A No. 2004-47034 Disclosure of Invention The present invention aims at providing a multilayer optical recording medium where a sufficient heat release effect is obtainable even when a thickness of a reflection layer in each information layer other than the innermost information layer as seen from a side of laser light irradiation is ultrathin, a modulation degree is increased to enhance recording performance as well as recording sensitivity in each information layer, storage stability is also excellent and further a light transmittance in each information layer is made high, to enhance the recording sensitivity of the innermost information layer as seen from the side of laser irradiation, and an optical recording method in the multilayer optical recording medium. Means for solving the ahove prohlems are as follows. That is: A multilayer optical recording medium including at least multiple information layers; wherein the multiple information layers comprise at least a phase change recording layer capable of recording information by laser irradiation, and a reflection layer, wherein each information layer other than an innermost information layer as seen from a side of the laser irradiation comprises a lower protection layer, the phase change recording layer, an upper protection layer, the reflection layer and an optical transmission layer, the upper protection layer and the optical transmission layer in each information layer other than the innermost one as seen from the side of the laser irradiation are composed of a material containing an Sn oxide, and a thickness of the upper protection layer in each information layer other than the innermost one as seen from the side of the laser irradiation is 2 nm to 15 nm. The multilayer optical recording medium according to , wherein the upper protection layer in each information layer other than the innermost one as seen from the side of the laser irradiation contains Sn oxide at 50 mol% to 90 mol%. The multilayer optical recording medium according to any one of to , wherein a thickness of the optical transmission layer in each information layer other than the innermost one as seen from the side of the laser irradiation is 51 nm to 250 nm. The multilayer optical recording medium according to any one of to , wherein the reflection layer in each information layer other than the innermost one as seen from the side of the laser irradiation contains Cu as a major component. The multilayer optical recording medium according to , wherein the reflection layer in each information layer other than the innermost one as seen from the side of the laser irradiation further contains at least one metal element selected from Mo, Ta, Nb, Cr, Zr, Ni, Ge and Au at a ratio of 5% by mass or less. The multilayer optical recording medium according to any one of to , wherein the lower protection layer in each information layer other than the innermost one as seen from the side of the laser irradiation is composed of an Sn oxide-containing material. The multilayer optical recording medium according to any one of to , wherein the lower protection layer in each information layer other than the innermost one as seen from the side of the laser irradiation is composed of a dual layer laminate structure and at least one layer of two layers is composed of the Sn oxide-containing material. The multilayer optical recording medium according to any one of to , having a first substrate, a first information layer, an intermediate layer, a second information layer and a second substrate in this order as seen from the side of the laser irradiation, which is a dual layer optical recording medium wherein the first information layer has a first lower protection layer, a first phase change recording layer, a first upper protection layer, a first reflection layer and a first optical transmission layer in this order as seen from the side of the laser irradiation, and the second information layer has a second lower protection layer, a second phase change recording layer, a second upper protection layer, a second reflection layer and a second optical transmission layer in this order as seen from the side of the laser irradiation. An optical recording method for the multilayer optical recording medium according to any one of to , including1 irradiating repeatedly pulses modulated by two values of a recording power and a bias power on the recording layer in each information layer other than the innermost one as seen from the side of the laser irradiation, and setting an interval Tr between upstrokes of a top pulse and a last pulse in the range of the following formula^ (n-1.5)T |
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00993-kolnp-2008-correspondence others.pdf
00993-kolnp-2008-description complete.pdf
00993-kolnp-2008-international publication.pdf
00993-kolnp-2008-international search report.pdf
00993-kolnp-2008-pct priority document notification.pdf
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993-KOLNP-2008-(09-04-2013)-CORRESPONDENCE.pdf
993-KOLNP-2008-(09-04-2013)-FORM 3.pdf
993-KOLNP-2008-CORRESPONDENCE 1.1.pdf
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993-kolnp-2008-EXAMINATION REPORT.pdf
993-kolnp-2008-FORM 18-1.1.pdf
993-kolnp-2008-GRANTED-ABSTRACT.pdf
993-kolnp-2008-GRANTED-CLAIMS.pdf
993-kolnp-2008-GRANTED-DESCRIPTION (COMPLETE).pdf
993-kolnp-2008-GRANTED-DRAWINGS.pdf
993-kolnp-2008-GRANTED-FORM 1.pdf
993-kolnp-2008-GRANTED-FORM 2.pdf
993-kolnp-2008-GRANTED-FORM 3.pdf
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993-kolnp-2008-GRANTED-SPECIFICATION-COMPLETE.pdf
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993-kolnp-2008-INTERNATIONAL SEARCH REPORT & OTHERS.pdf
993-kolnp-2008-PETITION UNDER RULE 137.pdf
993-kolnp-2008-REPLY TO EXAMINATION REPORT.pdf
993-kolnp-2008-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf
Patent Number | 263008 | ||||||||||||||||
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Indian Patent Application Number | 993/KOLNP/2008 | ||||||||||||||||
PG Journal Number | 41/2014 | ||||||||||||||||
Publication Date | 10-Oct-2014 | ||||||||||||||||
Grant Date | 29-Sep-2014 | ||||||||||||||||
Date of Filing | 06-Mar-2008 | ||||||||||||||||
Name of Patentee | RICOH COMPANY, LTD. | ||||||||||||||||
Applicant Address | 3-6, NAKAMAGOME 1-CHOME, OHTA-KU TOKYO | ||||||||||||||||
Inventors:
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PCT International Classification Number | G11B 7/24,G11B 7/257 | ||||||||||||||||
PCT International Application Number | PCT/JP2006/317707 | ||||||||||||||||
PCT International Filing date | 2006-08-31 | ||||||||||||||||
PCT Conventions:
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