JPWO2005031726A1 - Phase change optical disk - Google Patents

Abstract

The present invention provides a phase change optical disc that can provide reliable recording and reproduction and durability even when a biodegradable resin is used. According to the present invention, a lower dielectric protective film (2), a phase change recording layer (3), an upper dielectric protective film (4), and a metal reflective film (5) are formed on a substrate (1) made of a biodegradable resin. In the phase change optical disk in which the protective film (6) is laminated, the lower dielectric protective layer (2) on the substrate (1) side is formed of a material having low thermal conductivity, and the upper dielectric protective film (4 ) Is made of a material having higher thermal conductivity than the lower dielectric protective layer (2).

Description

  The present invention relates to a phase change optical disk using a reversible phase change between an amorphous phase and a crystalline phase, and more particularly to a phase change optical disk with a low environmental load.

  As phase-change optical disks, rewritable optical disks, for example, CD-RW (Compact Disc-rewable) and DVD-RW (Digital Versatile Disc-rewable) having a larger capacity than CD-RW have been put into practical use.

  FIG. 8 is a schematic cross-sectional view showing the structure of a conventional phase change optical disc 100. As shown in the figure, in the phase change optical disc, a lower dielectric protective film 102, a recording layer 103, an upper dielectric protective film 104, a metal reflective film 105, and a protective film 106 are laminated on a substrate 101.

In a phase change optical disk as a CD-RW, the substrate 101 is made of a polycarbonate transparent substrate having a thickness of 1.2 mm, and the lower and upper dielectric protective films 102 and 104 are made of ZnS and SiO ₂ . In general, the recording layer 103 is made of an AgInSbTe or GeSbTe phase change layer, the reflective film 105 is made of an Al alloy, and the protective layer is made of a UV curable resin. Each layer is provided with a thickness of about 40 to 80 nm for the lower dielectric protective film 102, 10 to 40 nm for the upper dielectric protective film 104, 10 to 40 nm for the recording layer 103, and 20 to 40 nm for the reflective film 105. ing.

  A tracking groove 107 is formed on the polycarbonate substrate 101 by an injection molding method, and lands 108 are formed between the grooves 107.

As described above, in the conventional structure of the phase change optical disk, the recording layer 103 is sandwiched between the dielectric protective films 102 and 104, and the thermal conductivity of SiO ₂ used at room temperature is used. Is as low as 6.8 W / m · K (Watts / meter · kelvin).

The thermal conductivity of SiO ₂ —ZnS dielectric that has been generally used in phase change optical disks is about 7 to 13 W / m · K. For this reason, the heat generated in the recording layer 103 is stored in the recording layer 103 and then gradually transferred to the dielectric layers 102 and 104 and dissipated to both the substrate 101 and the reflective layer 105.

  On the other hand, the above-mentioned DVD-RW optical disc has a structure in which two substrates having a thickness of 0.6 m are bonded, and two single-plate type discs are bonded to increase the recording capacity. There are a bonded structure type in which information recording layers are provided on both sides, and a type in which a dummy substrate is bonded to a substrate in which an information recording layer is formed on a transparent substrate such as a polycarbonate resin. However, in recent years, the demand for higher density recording media has become stronger, and an optical disk is often used in a bonded structure type, including when a transparent substrate is bonded.

  Hot-melt adhesives, UV curable adhesives, and the like are used for bonding optical disks, and spin coating, roll coating, screen printing, and the like are employed as methods for applying these adhesives. .

  By the way, in the optical disk described above, when it becomes unnecessary, since a polycarbonate resin is used as a substrate, it must be disposed of by incineration or landfilling, and there is a problem with waste disposal. It is desirable to take some measures from environmental problems.

In view of such a problem, an optical disc using a biodegradable resin that is a base material that can be decomposed in nature on the substrate of the optical disc has been proposed (for example, see Patent Document 1).
JP 2000-11448 A

However, in a disc using a biodegradable resin, the glass transition temperature of the biodegradable resin is as low as 60 ° C. For this reason, in the optical disk having a structure in which heat is transmitted to the above-described substrate, there is a problem that the substrate is deformed to cause a problem in recording and reproduction, and the durability is remarkably lowered.

  Accordingly, an object of the present invention is to provide a phase change optical disc that can obtain reliable recording / reproduction and durability even when a biodegradable resin is used.

  The phase change optical disc of the present invention includes a substrate made of a biodegradable resin, a first protective layer provided on the substrate, a phase change recording layer provided on the first protective layer, In the phase change optical disc including the second protective layer provided on the recording layer, the first protective layer on the substrate side is made of a material having low thermal conductivity, and the second protective layer is It is formed of a material having higher thermal conductivity than the first protective layer.

  The second protective layer may have a thermal conductivity of 100 W / m · K or more.

  The second protective layer may be composed of a metal reflective layer having high thermal conductivity and high reflectivity.

    Further, the phase change optical disc of the present invention is a phase change optical disc in which at least one of the substrates made of biodegradable resin having a recording layer is bonded, and the first protective layer is provided on at least one of the substrates. A phase change recording layer provided on the first protective layer, and a second protective layer provided on the recording layer, the first protective layer on the substrate side being a heat The second protective layer is formed of a material having a lower thermal conductivity, and the second protective layer is formed of a material having a higher thermal conductivity than the first protective layer.

  The second protective layer may have a thermal conductivity of 100 W / m · K or more.

  The second protective layer may be composed of a metal reflective layer having high thermal conductivity and high reflectivity.

    The base material may be bonded with an adhesive layer containing a biodegradable adhesive as a main component, and the adhesive layer may contain a degrading bacterium.

  The present invention makes it difficult to transmit a temperature rise due to laser light during recording to the substrate, and even when a substrate made of a biodegradable resin is used, deformation of the substrate due to repeated recording can be prevented.

1 is a schematic cross-sectional view showing the structure of a phase change optical disc according to a first embodiment of the present invention. It is a schematic sectional drawing which shows the structure of the phase change type optical disc concerning 2nd Embodiment of this invention. It is a schematic diagram showing a temperature distribution state in increments of 30 ° C. when the thermal conductivity of the dielectric during simulation is 10 W / m · K. FIG. 5 is a characteristic diagram showing the relationship between the thermal conductivity of the dielectric layer on the back side of the recording layer and temperature. It is typical sectional drawing which shows the optical disk concerning 3rd Embodiment of this invention. It is typical sectional drawing which is typical sectional drawing which shows the optical disk concerning 4th Embodiment of this invention. It is typical sectional drawing which is typical sectional drawing which shows the optical disk concerning 5th Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the conventional phase change type optical disk.

Explanation of symbols

1 Substrate 2 Lower dielectric protective film (first protective layer)
3 Phase change recording layer 4 Upper dielectric protective film (second protective layer)
5 Metal reflective film 6 Protective film 7 Groove 8 Land

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the structure of a phase change optical disc 1A according to the first embodiment of the present invention.

  The phase change type optical disc 1A according to the first embodiment is a CD-RW type disc, can record data, and can be rewritten. The structure is such that a lower dielectric protective film (first protective layer) 2 having a thickness of 40 to 80 nm, a phase change recording layer 3 having a thickness of 10 to 40 nm, and a substrate 1 made of a biodegradable resin, The upper dielectric protective film (second protective layer) 4 having a thickness of 10 to 40 nm, which has a higher thermal conductivity than the side dielectric protective film 2, the metal reflective film 5 having a thickness of 20 to 40 nm, and the protective film 6 are arranged in this order. It is formed by stacking. A tracking groove 7 is formed on the substrate 1 by an injection molding method, and lands 8 are formed between the grooves 7.

  The substrate 1 is a so-called injection-molded resin substrate formed integrally with a biodegradable resin that is a base material that can be decomposed in nature in consideration of the environment and the like.

  Resins that are degraded in nature are biodegradable resins that are degraded by microorganisms and resins that are degraded by moisture, ultraviolet rays, etc., and as biodegradable resins that also have transparency, for example, those extracted from corn Typical examples are resins made from lactic acid, such as “Lacty (trade name)” manufactured by Toyota Motor Corporation, “Lacia (trade name)” manufactured by Mitsui Chemicals, and “Terramac (trade name)” manufactured by Unitika. There is. The thickness of the substrate 1 is about 0.5 to 2.0 mm. Note that the CD-RW type optical disk in this embodiment has a substrate thickness of 1.2 mm. The wavelength of the laser used for recording / reproduction is 780 nm, and the track pitch is 1.6 μm.

The recording layer 3 is made of an AgInSbTe or GeSbTe phase change layer, and the metal reflective film 5 is toxic to the human body among materials that are naturally decomposed into oxygen, water, etc. and / or materials that exist in nature. Do not use any substances that are present or require special attention during disposal. Substances that are toxic here refer to substances that clearly cause carcinogenicity or poisoning to the human body, and in particular, be careful of substances that set certain standard values for soil contamination, water quality standards, disposal, etc. It is desirable that it be a required substance and not be used as a material. For example, a single layer film or multilayer film of aluminum or iron or an alloy thereof is used. The film thickness of the aluminum thin film is 40 nm. Further, when iron is used, the reflectance is low. Therefore, a multilayer film in which a thin film of silicon oxide (SiO ₂ ) and a thin film of silicon are stacked on an iron thin film may be used. For example, the film thickness of an iron thin film is 150 nm, silicon oxide is 100 nm, and silicon is 45 nm. The protective layer 6 can be formed, for example, by spin coating a biodegradable resin and then curing the coating film.

  In the present invention, as described above, a material having low thermal conductivity is laminated on the lower dielectric protective film 2 on the substrate 1 side, and a material having high thermal conductivity is formed on the upper dielectric protective film 4 on the protective layer 6 side. Thus, heat transfer to the substrate 1 side is reduced.

  Here, the film thickness of the lower dielectric protective film 2 is 60 nm, the film thickness of the recording layer 3 is 20 nm, the film thickness of the upper dielectric protective film 4 is 40 nm, and the film thickness of the reflective layer 5 is 20 nm. The thermal conductivity of 2 and 4 was set to 10 W / m · K, and the temperature distribution under the lower dielectric protective film 2 side when the recording layer 3 reached the recording temperature was simulated.

    FIG. 3 is a schematic diagram illustrating a temperature distribution state in increments of 30 ° C. when the thermal conductivity of the dielectric during simulation is 10 W / m · K.

  At this time, the high temperature portion is 120 ° C., and the heat distortion temperature of general polycarbonate is 124 ° C. Therefore, there is no problem if the material of the substrate 1 is polycarbonate in this state. However, it can be seen that the substrate 1 made of biodegradable resin exceeds the glass transition temperature 60 ° C. of the biodegradable resin. Therefore, the temperature of the high temperature portion was plotted by changing the thermal conductivity of the upper dielectric protective film 4 behind the recording layer 3 (as viewed from the side irradiated with the laser beam).

    FIG. 4 is a characteristic diagram showing the relationship between the thermal conductivity of the upper dielectric protective film 4 on the back side of the recording layer 3 and the temperature. It can be seen that as the thermal conductivity is increased, the thermal conductivity is 100 W / m · K, which is 60 ° C. and lower than the heat distortion temperature. Therefore, it is desirable that the upper dielectric protective film 4 in contact with the rear side of the recording layer 3 has a thermal conductivity of 100 W / m · K or more.

Therefore, as the first embodiment of the present invention, the lower dielectric protective film 2 is made of SiO ₂ (thermal conductivity = 6.8 W / m · K), SiO ₂ —ZnS (7 to 13 W / m · K), A low thermal conductivity material having a thermal conductivity of 10 W / m · K or less, such as TiO ₂ (9 W / m · K) or Al ₂ O ₃ (2.6 W / m · K), is used. Thereby, the heat insulation effect to the board | substrate 1 can be acquired. A recording layer 3 is formed on the lower dielectric protective film 2, and an upper dielectric protective film 4 having a high thermal conductivity is formed. Specific materials for the upper dielectric protective film 4 are AlN (150 W / m · K) and pure SiN (100 W / m · K or more). Thereby, the temperature rise of the substrate 1 can be suppressed and the deformation of the substrate 1 can be prevented.

  As described above, the phase change optical disc of the present invention makes it difficult to transmit the temperature rise caused by laser light during recording to the substrate, and even when a substrate made of biodegradable resin is used, the substrate is repeatedly deformed by repeated recording. Can be prevented. And at the time of disposal, since the disk is made up of materials that are mostly decomposed in nature, an environmentally friendly optical disk can be provided. However, in the above-described embodiment, the material of the material of the phase change recording layer 3 includes a substance that is highly toxic and has a caution when discarded. However, even if the weight of the material of the phase change recording layer 3 is large, it is about 0.0015 g. On the other hand, the weight of the substrate 1 alone is about 15 to 16 g. In this case, the content ratio of the phase change recording layer 3 with respect to the weight of the entire disk is about 0.00974%. From this ratio, almost all materials can be decomposed in nature, so that an environmentally friendly disc can be provided as compared with a conventional optical disc whose substrate is polycarbonate.

  Next, an optical disc 1B according to a second embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same part as 1st Embodiment, and the description is omitted here in order to avoid duplication of description.

  In the second embodiment, a direct reflection layer 5a is formed instead of the upper dielectric protective film 4 in the first embodiment. The reflective layer 5a has a heat dissipation function and becomes a reflective heat dissipation layer. Materials used for the reflective layer 5a (reflective heat dissipation layer) are Al (235 W / m · K), Cu (401 W / m · K), Au (318 W / m · K), Ag (428 W / m · K), It is a material with extremely high thermal conductivity such as SiC (500 W / m · K). At this time, the reflective layer 5a (reflective heat dissipation layer) has a high heat dissipation function, and at the same time, a reflectivity of 65% or more is necessary to obtain an optimum reproduction signal. Therefore, after forming Al with high reflectivity, it is also possible to form a material with higher thermal conductivity and adjust the reflectivity with the film thickness of Al. Further, a thin dielectric layer having a thickness of about 10 nm may be provided on the recording layer 3, and a material that functions as both a reflective layer and a heat dissipation layer may be further formed thereon as the reflection heat dissipation layer.

  Next explained is the third embodiment of the invention. In the third embodiment, a DVD-RW disc is used as a phase change type optical disc. FIG. 5 is a schematic cross-sectional view for explaining the structure of a DVD-RW type phase change optical disc 1C according to a third embodiment of the present invention.

    Similarly to the first and second embodiments, the phase change optical disc 1C shown in the third embodiment is also provided with a lower dielectric protective film having a thickness of 40 to 80 nm on the disc-shaped light-transmitting substrate 1. 2. Phase change recording layer 3 having a film thickness of 10 to 40 nm, upper dielectric protective film 4 having a film thickness of 10 to 40 nm having a higher thermal conductivity than the lower dielectric protective film 2, and metal reflection having a film thickness of 20 to 40 nm. A film 5 and a protective film 6 are laminated in this order. A tracking groove 7 is formed on the substrate 1 by an injection molding method, and lands 8 are formed between the grooves 7.

    As described above, in the present invention, a material having low thermal conductivity is laminated on the lower dielectric protective film 2 on the substrate 1 side, and a material having high thermal conductivity is formed on the upper dielectric protective film 4 on the protective layer 6 side. In addition, heat transfer to the substrate 1 side is reduced.

  The substrate 1 is a so-called injection-molded resin substrate formed integrally with a biodegradable resin that is a base material that can be decomposed in nature in consideration of the environment and the like.

  The resin substrate 10 is bonded to the protective film 6 by the adhesive layer 44. A printed layer (not shown) is provided on the resin substrate 10. The substrate 10 is also a so-called injection-molded resin substrate integrally formed of a biodegradable resin that is a base material that can be decomposed in nature in consideration of the environment and the like.

  This phase change type optical disc is, for example, a single-sided recording type DVD-RW disc in which a substrate 10 having a thickness of about 0.6 mm and a substrate 10 having a thickness of about 0.6 mm are bonded together. It is a dummy substrate that does not affect recording / reproduction. Although the thickness of the substrate is about 0.6 mm, the thickness of the substrates 1 and 10 is slightly different depending on the refractive index of the resin used. That is, the thickness of the substrate varies depending on the refractive index of the resin used. When polycarbonate is used as the resin, the thickness of the substrate is 0.6 mm, and the compatibility is ensured by making it equal to the product of the refractive index (1.58) of the polycarbonate and the thickness of the substrate. Because. Since the biodegradable resin is smaller than the refractive index of polycarbonate, the thickness of the substrates 1 and 10 is preferably about 2% thicker than 0.6 mm. Note that the thickness of the DVD-RW type optical disk in this example after bonding was 1.2 mm. The wavelength of the laser used for recording / reproduction is 650 nm, and the track pitch is 0.74 μm.

  The substrates 1 and 10, the lower dielectric protective film 2, the phase change recording layer 3, the upper dielectric protective film 4, the reflective film 5, and the protective film 6 are made of the same material as in the first embodiment described above. Is done. The description of the same configuration is omitted here in order to avoid duplication of description.

  As described above, the phase change optical disc of the present invention makes it difficult to transmit the temperature rise caused by laser light during recording to the substrate, and even when a substrate made of biodegradable resin is used, the substrate is repeatedly deformed by repeated recording. Can be prevented.

    In the bonded optical disk described above, as the adhesive layer 44, a hot-melt adhesive, an ultraviolet curable adhesive, or the like can be used. In some cases, it is preferable to use an adhesive that can reduce the soil. For this reason, a biodegradable adhesive may be used as the adhesive layer 44. As the biodegradable adhesive, lactic acid resin can be used in addition to adhesives such as glue, gelatin, starch and the like. For example, when glue is used, a glue solution may be formed and coated on the protective film 6 by spin coating or the like, and then the protective film 6 and the substrate 10 may be opposed to each other.

  By configuring as described above, most materials can be reduced to the soil, and it is possible to provide a simple disposal means with less environmental load.

    In addition, when the adhesive layer 44 made of the above-described biodegradable adhesive material contains decomposed bacteria, soil reduction is further promoted during disposal. For example, lactic acid bacteria or yeasts may be used as the degrading bacteria.

    Note that, according to the above-described third embodiment, the substrates 1 and 10 and the adhesive layer 44 to be bonded together can be composed of only a complete biodegradable resin. For this reason, when the disc is inserted into the biodegradation accelerator for a while, the adhesive layer 44 is immediately decomposed and the two substrates are easily peeled off. Moreover, it will become easy to peel off, if the decomposition promotion microbe is put into the contact bonding layer. If comprised in this way, an appropriate disposal can also be easily performed, such as scraping off the harmful | toxic part which the one-sided dummy board | substrate peels off easily and remaining in the board | substrate of the remaining part.

  Next explained is the fourth embodiment of the invention. The fourth embodiment has a configuration applied to a double-sided recording DVD-RW type. FIG. 6 is a schematic cross-sectional view for explaining the structure of an optical disc 1D according to the fourth embodiment of the present invention.

      An optical disc 1D of the fourth embodiment is a double-sided recording type DVD-RW type disc, and this optical disc has a pair of recording areas in which pits or grooves representing information are formed on the main surface by fine irregularities. Translucent substrate 1, 1, a pair of translucent substrates 1, 1, a lower dielectric protective film 2 having a thickness of 40 to 80 nm, a phase change recording layer 3 having a thickness of 10 to 40 nm, and a lower layer An upper dielectric protective film 4 having a film thickness of 10 to 40 nm, a metal reflective film 5 having a film thickness of 20 to 40 nm, and a protective film 6 having a higher thermal conductivity than the side dielectric protective film 2 are laminated in this order. Yes. And it is comprised from the contact bonding layer 44 which makes a pair of board | substrates 1 and 1 mutually oppose with the protective films 6 and 6.

  These substrate 1, lower dielectric protective film 2, phase change recording layer 3, upper dielectric protective film 4, reflective film 5, and protective film 6 are made of the same material as in the first embodiment described above. . The description of the same configuration is omitted here in order to avoid duplication of description.

    In the bonded optical disk according to the fourth embodiment described above, a hot-melt adhesive or an ultraviolet curable adhesive can be used as the adhesive layer 44, but the substrate can be reduced to the soil. When an environmentally friendly substrate is used, it is preferable to use an adhesive that can reduce the soil. For this reason, a biodegradable adhesive may be used as the adhesive layer 44. As the biodegradable adhesive, lactic acid resin can be used in addition to adhesives such as glue, gelatin, starch and the like. For example, when glue is used, a glue solution is formed and coated on the protective film 6 by spin coating or the like, and then the protective films 6 are opposed to each other and bonded. With such a configuration, it is possible to perform recording on both sides via the double-sided substrate 1, and the capacity of one disc is increased, improving the convenience for the user.

  By configuring as described above, most materials can be reduced to the soil, and it is possible to provide a simple disposal means with less environmental load.

    In addition, when the adhesive layer 44 made of the above-described biodegradable adhesive material contains decomposed bacteria, soil reduction is further promoted during disposal. For example, lactic acid bacteria or yeasts may be used as the degrading bacteria.

  When the biodegradable adhesive material contains the degrading bacteria as they are, the adhesive layer 44 and the like may be decomposed due to a change with time even though they are not discarded. Therefore, FIG. 7 shows an optical disk with improved durability. FIG. 7 is a schematic cross-sectional view that is a schematic cross-sectional view showing an optical disc 1E according to a fifth embodiment of the present invention. Note that portions having the same configuration as in FIG. 5 are denoted by the same reference numerals, and description thereof is omitted here in order to avoid duplication of description.

    In the optical disc 1E shown in FIG. 7, in the third embodiment shown in FIG. 5, the adhesive layer 44 is mainly composed of a biodegradable adhesive, and the degrading bacteria are contained in the biodegradable adhesive layer. The encapsulated microcapsule 41 is mixed. For this reason, unless the microcapsule 41 is destroyed, degradation by degrading bacteria is not performed, and durability is improved. When discarded, the capsule wall of the microcapsule 41 is damaged by bending the optical disk such as by bending, thereby promoting soil reduction.

    What is necessary is just to form the microcapsule 41 to mix, for example by gelatin-coating lactic acid bacteria.

    In the embodiment shown in FIG. 7 described above, one recording area is provided on one side. However, the present invention can also be applied to the fourth embodiment, and is not limited to this, and there are a plurality of recording areas including two recording layers on one side. The present invention can also be applied to those having the recording layer. Further, in the disk 1D of FIG. 6, the case where the DVD-RWs are bonded together is shown. However, the laminate is not limited to the DVD-RW, but may be the CD-RW shown in the first and second embodiments, and one of them is pasted by the CD-RW as in the first and second embodiments. A DVD-RW, which is the dummy substrate portion shown in the third and fourth embodiments, may be bonded. Further, one of them may be a CD-RW or a DVD-RW and the one to be bonded may be a read-only ROM medium (DVD-ROM, CD-ROM, etc.). As a result, it is possible to provide an optical disk with less environmental load, one side being a reproduction medium and the other side being a write-once medium.

  The present invention is not limited to the materials and film configurations disclosed in the above embodiments, and the heat generated in the recording layer by the laser beam affects the substrate made of biodegradable resin via the dielectric layer. In order to prevent this, it has dielectric materials with different thermal conductivity above and below the recording layer, and has a dielectric layer or metal film with high thermal conductivity on the opposite side of the substrate, or a layer made of these laminated films, and heat is applied to the substrate. Any structure that conducts efficiently to the opposite side may be used.

  Not only the above-mentioned DVD-RW standard optical disc but also a next-generation DVD standard HD DVD standard having a substrate thickness of 0.6 mm is bonded to a thickness of 1.2 mm, a laser wavelength of 405 nm, a track pitch of 0. The present invention can be applied to a disk having a structure of 34 μm.

The present invention is also applicable to a Blu-ray (Blu-ray is a registered trademark) type medium in which a biodegradable substrate is used, a cover layer of 0.1 mm is formed on the recording layer, and recording / reproduction is performed from the cover layer side. It is possible to adapt the substrate material, the conditions of the dielectric formed with the recording layer interposed therebetween, and the bonding material.

Claims (8)

A substrate made of a biodegradable resin, a first protective layer provided on the substrate, a phase change recording layer provided on the first protective layer, and a first protective layer provided on the recording layer In the phase change type optical disc comprising the two protective layers, the first protective layer on the substrate side is formed of a material having low thermal conductivity, and the second protective layer has a thermal conductivity higher than that of the first protective layer. A phase change type optical disc characterized by being made of a high material. The phase change optical disk according to claim 1, wherein the second protective layer has a thermal conductivity of 100 W / m · K or more. 2. The phase change optical disk according to claim 1, wherein the second protective layer is a metal reflective layer having high thermal conductivity and high reflectivity. In a phase change optical disc in which two substrates made of biodegradable resin each having a recording layer are bonded together, at least one substrate is provided with a first protective layer and the first protective layer. And a second protective layer provided on the recording layer, wherein the first protective layer on the substrate side is formed of a material having low thermal conductivity, The phase change type optical disc, wherein the protective layer 2 is formed of a material having higher thermal conductivity than the first protective layer. The phase change optical disc according to claim 4, wherein the thermal conductivity of the second protective layer is 100 W / m · K or more. 5. The phase change optical disk according to claim 4, wherein the second protective layer is a metal reflective layer having high thermal conductivity and high reflectivity. 7. The phase change optical disk according to claim 4, wherein the base material is bonded with an adhesive layer containing a biodegradable adhesive as a main component. 8. The phase change optical disk according to claim 7, wherein the adhesive layer contains decomposing bacteria.

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