JP2008310959A - Information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording medium capable of securing a sufficient tilt margin and mechanical strength even when recording density is heightened. <P>SOLUTION: The information recording medium is provided with a substrate (13), first and second recording surfaces which are provided on both surfaces of the substrate and where embossed pits (2) are provided, first and second reflection films (3) provided on the surfaces of the first and the second recording surfaces and first and second protective films (4) provided on the surfaces of the first and the second reflection films, wherein recorded data are reproduced based on light intensity change of reflected light of an optical beam emitted from the protective film sides. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an information recording medium, and more particularly to an information recording medium for surface recording and reproduction.

  In an ordinary optical disk such as a CD or CD-ROM, an emboss pit corresponding to recording data is formed on one surface of a 1.2 mm thick transparent substrate, and a reflective film made of Al or the like is further formed thereon. ing. Information recorded on such a CD is reproduced by irradiating a focused beam from the transparent substrate side opposite to the surface provided with the reflective film.

  In DVD and DVD-ROM discs with higher recording density, a fine embossed pit is formed on one side of a 0.6 mm thick transparent substrate, compared to the case of CD. The reflective film which consists of is formed. The reproduction of information recorded on the recording surface of the disc is performed by irradiating a focused beam from the transparent substrate side opposite to the surface on which the reflective film is formed, as in the case of CD.

  As a material for the substrate having a thickness of 0.6 mm, PC (polycarbonate) which is a transparent resin material is generally used. The 0.6 mm PC board does not have sufficient mechanical properties, and the board is warped as it is. Therefore, the two 0.6 mm PC boards are bonded so that the recording surface is inside, and the total thickness is 1.2 mm. As a disc, the mechanical properties are secured.

  The reason why the substrate thickness of the DVD disk is 0.6 mm is to secure a tilt margin. If the track pitch and pit density are further reduced, the disc tilt, so-called tilt margin, decreases. By reducing the substrate thickness from 1.2 mm to 0.6 mm, a tilt margin can be secured, but a decrease in mechanical strength is inevitable.

Therefore, in order to secure the mechanical strength by thinning the substrate, it has been proposed to secure the mechanical strength by increasing the thickness of the central portion of the disk (see, for example, Patent Document 1). However, in order to ensure mechanical strength, the limit of the substrate thickness of the signal recording area is 0.6 mm. Further, although it has been reported that the thickness of the transparent substrate is 0.1 mm to 0.6 mm (see, for example, Patent Document 2), the thickness of the protective substrate holding the recording film, the thickness of the reflective film, etc. Was not mentioned and was a problem in implementation.
JP-A-9-204686 JP-A-9-204688

  In order to further increase the recording density and to increase the capacity in the future, it is effective from the viewpoint of the tilt margin to further reduce the thickness of the substrate. Even if two sheets are bonded together, it becomes difficult to ensure mechanical strength.

  In addition, when the substrates are bonded together, an adhesive or the like is required, and the manufacturing process becomes complicated.

  Accordingly, an object of the present invention is to provide an information recording medium capable of ensuring a sufficient tilt margin and mechanical strength even when the recording density is further increased.

  An information recording medium according to an aspect of the present invention includes a substrate, first and second recording surfaces provided on both surfaces of the substrate and provided with embossed pits, and the first and second recording surfaces. The first and second reflective films provided on the surface of the first and second protective films, and the first and second protective films provided on the surfaces of the first and second reflective films, and irradiation from the protective film side The recorded data is reproduced based on the light intensity change of the reflected light of the light beam.

  An information recording medium according to another aspect of the present invention includes a substrate provided with guide grooves on both surfaces, first and second reflective films provided on both surfaces of the substrate, and the first, Comprising first and second recording films provided on the surface of the second reflective film, and first and second protective films provided on the surfaces of the first and second recording films, The recording data is reproduced based on the change in the light intensity of the reflected light of the light beam emitted from the protective film side.

  According to the present invention, there is provided an information recording medium capable of ensuring a sufficient tilt margin and mechanical strength even when the recording density is increased.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
FIG. 1 is a cross-sectional view schematically showing an example of the optical disk of this embodiment.

  In the optical disk shown in the figure, a recording surface having embossed pits 2 corresponding to recording data is provided on one surface of a 1.2 mm thick disk substrate 1. A reflective film 3 is formed on the recording surface provided with such embossed pits 2, and a protective film 4 is further overcoated thereon.

  Reading of recorded data recorded on the disc is performed by converging the light beam 5 with the objective lens 6 and entering from the protective film 4 side as shown in the figure, and changing the light intensity of the reflected light from the reflective film 3 as an emboss pit. This is performed by detecting as recorded data.

  In a conventional optical disk, a light beam is incident not from the protective film side but from the transparent substrate side, and emboss data formed on the surface opposite to the light incident surface of the substrate is read. Therefore, securing the tilt margin is limited by the thickness of the substrate. On the other hand, in the optical disk structure as shown in FIG. 1, since the reproduction is performed from the embossed surface of the substrate surface, the thickness of the protective film 4 corresponds to the conventional substrate thickness.

  In the optical disk of the present invention, the distance from the embossed surface (recording surface) to the surface on the protective film 4 side is defined to be smaller than the thickness of the substrate 1, so the film thickness of the protective film is smaller than the substrate thickness. Therefore, it becomes difficult to be limited by the tilt margin due to the substrate thickness, and it is easy to increase the recording density.

  The reflective film 3 can be produced by forming a reflective film material by vacuum deposition or sputtering.

  The protective film 4 disposed on the reflective film 3 can be formed of, for example, a conventional ultraviolet curable resin. The protective layer 4 is formed, for example, by applying an ultraviolet curable resin to the surface of the reflective film 3 by spin coating to form a resin film, and irradiating it with ultraviolet rays to cure it. The thickness of the overcoat protective film 4 is practically in the range of several μm to several mm, preferably 0.6 mm or less, and more preferably in the range of 0.0001 to 0.1 mm. Further, it is desired that the film thickness does not cause optical interference with the reflective film 3.

  The material of the protective film 4 is not limited to the ultraviolet curable resin, and is not particularly limited as long as it is an environmentally and thermally stable material that transmits a light beam used for reproduction. It may be configured. For example, the protective film 4 can also be formed by a vacuum evaporation method, a sputtering method, or the like using SiO2, SiO, AlN, Al2O3, ZrO2, TiO2, Ta2O3, ZnS, Si, Ge, or a mixed material thereof.

  If the reflection film 3 itself is a stable film, the protective film 4 can be omitted.

  The 1.2 mm-thick disc substrate 1 used for the optical disc of the present embodiment can be manufactured by an injection molding method employed in the production of conventional CDs and DVDs. For example, by setting a master disk on which information is recorded in advance on one mold side of an injection molding machine, and setting the space between the two molds so that the substrate thickness after completion is 1.2 mm, A 1.2 mm thick disk substrate 1 is produced.

  Here, FIG. 2 schematically shows an example of a mold for producing the 1.2 mm-thick disk substrate 1 having a recording surface on one side by an injection molding method.

  First, assuming that the recording surface of the disk is the A surface, a stamper for the A surface is produced by conventional mastering, and the center hole 8 is accurately formed in the center of the stamper 7 for the A surface. A protrusion 10 having a hole diameter accuracy corresponding to the center hole 8 of the A-side stamper 7 is provided at the center of one surface of the mold 9.

  The A-side stamper 7 is placed on one side of the injection-molding die 9 so that the recording surface is on the inside, and the center hole 8 of the A-side stamper is disposed on the protrusion 10 provided on the die 9. To do. By fitting the center hole 8 of the stamper into the protrusion 10, the A-side stamper 7 can be aligned.

  The mold 11 is disposed so as to be opposed to the A-side stamper 7 of the mold 9, and the resin which is heated and melted is filled between these through the resin inlet 12. Next, the A-side stamper 7 and the mold 11 are brought close to each other, and the distance between the A-side stamper 7 and the mold 11 is set to a predetermined distance. Specifically, after the resin is cooled and cured, the distance between the A-side stamper surface 7 and the mold surface 11 is set so that the resulting substrate 1 has a thickness of 1.2 mm.

  Through the above steps, a 1.2 mm thick disk substrate 1 having a recording surface formed on one side can be formed by one injection molding.

  In the conventional optical disc, since the recording information is reproduced by entering the light beam from the substrate side, the substrate needs to transmit the wavelength of the light beam used for reproduction. In order to regenerate, the substrate is not necessarily transparent. Since the light beam is irradiated from the protective film side in this way, the birefringence of the substrate does not become a problem. Therefore, the substrate material is not particularly limited as long as it is a material excellent in environmental resistance, heat resistance, and processability. For example, a cheaper material such as an ABS resin, a polyethylene resin, or a polystyrene resin may be used. Is possible.

  A reflective film is formed on the recording surface of the 1.2 mm-thick disk substrate 1 by sputtering or vacuum evaporation. The graph of FIG. 3 shows the relationship between the thickness of the reflective film and the reflectance.

  Here, a reflective film is formed of an Al-based alloy film, and the wavelength of the irradiated light beam is 650 nm. In such a condition, the graph of FIG. 3 shows that when the film thickness is about 14 nm, the reflectance is 45%, and when the film thickness is 40 nm, the reflectance is almost saturated. Since the reflectance shown in this graph includes surface reflection from the surface of the protective film 4, the reflectance on the surface of the reflection film is a value excluding surface reflection. Specifically, since the reflectance when the thickness of the reflective film is zero corresponds to the surface reflection of the protective film 4, in the case shown in the graph of FIG. 3, the value excluding that amount (about 5%) is excluded. Becomes the reflectance of the reflective film.

  FIG. 4 shows the light wavelength dependency of the thickness of the reflective film when the reflectance is 45% and the saturation state is reached. The reflective film was made of an Al-based alloy film, and the wavelength of the light beam was 400 to 800 nm.

  In the graph of FIG. 4, the straight line a is the film thickness at which the reflectance is 45%, and the straight line b is the film thickness when the reflectance is in a saturated state. As shown in this graph, the optical wavelength dependency is small at an optical wavelength of 400 nm to 800 nm, and within this wavelength range, the reflective film thickness at which the reflectivity is 45% is 13 to 14 nm, and the film thickness is at the saturated reflectance. Was approximately 40 nm.

  In the DVD-ROM standard, the reflectivity is defined as 45 to 85%. Therefore, in order to maintain the reproduction compatibility with the DVD-ROM, the reflectivity of the reflective film of the optical disc of the present invention is set to 45% or more. It is required to do. For this purpose, the graph of FIG. 3 shows that the film thickness of the reflectance needs to be 14 nm or more. Furthermore, in order to obtain a constant reflectance by suppressing fluctuations in the thickness of the reflective film, it is desirable for manufacturing to set the film thickness at which the reflectance is saturated. For that purpose, it is preferable that the film thickness of the reflectance is 40 nm or more.

  In addition, since the reflective film made of such an Al-based alloy film has a small light wavelength dependency, it can be used for the future reproduction using green and blue light beams with the above-described film thickness setting. .

(Example 2)
FIG. 5 is a cross-sectional view schematically showing an example of the optical disk of this embodiment.

  In the illustrated optical disk, a recording surface is provided with embossed pits 2 corresponding to recording data on both the front and back surfaces of a 1.2 mm thick disk substrate 13. A reflective film 3 is formed on each recording surface provided with such embossed pits 2 on both sides, and a protective film 4 is further overcoated thereon.

  As shown in the figure, the recorded data recorded on the disk is read out by converging the light beam 5 with the objective lens 6 and entering from both sides of the protective film 4 and changing the light intensity of the reflected light from the reflective film 3. Is detected as embossed pit recording data. Since the optical disk of the present embodiment has recording surfaces on both sides, it can be reproduced from both surfaces, and it is possible to simply secure a recording capacity twice that of a single surface.

  Here, FIG. 6 schematically shows an example of a mold for producing the 1.2 mm-thick disc substrate 13 having recording surfaces on both sides used in the optical disc of this embodiment by an injection molding method.

  First, assuming that one side of the disk is the A side and the other side is the B side, the A-side stamper 7a and the B-side stamper 7b are respectively produced by conventional mastering, and the A-side stamper 7a is formed at the center. The center hole 8 is formed with high accuracy. Similarly, the center hole 14 is formed in the stamper 7b on the B surface.

  A projection 16 having a hole diameter accuracy corresponding to the center hole 8 of the A-side stamper 7a is provided at the center of one surface of the mold 9, and the B-side is provided at the center of one surface of the mold 15. A protrusion 17 having a hole diameter accuracy corresponding to the center hole 14 of the stamper 7b is provided. By providing the protrusions 16 and 17, the center hole 8 of the A-side stamper 7a and the center hole 14 of the B-side stamper 7b can be aligned.

  An A-side stamper 7 a is installed on one side of an injection mold 9 so that the recording surface is on the inside, and a center hole 8 of the A-side stamper is disposed on the protrusion 16 of the mold 9. A B-side stamper 7 b is also installed on the other opposing mold 15 so that the recording surface is on the inside, and the center hole 14 of the B-side stamper is disposed in the protrusion 17 of the mold 15. Thus, with the center holes 8 and 14 of the stamper fitted into the protrusions 16 and 17, respectively, the center hole 8 of the A-side stamper 7a and the center hole 14 of the B-side stamper 7b are made to coincide.

  Next, the recording surface of the A-side stamper 7a and the recording surface of the B-side stamper 7b are arranged to face each other, and a resin that is heated and melted is filled between them through the resin inlet 12.

Thereafter, the A-side stamper 7a or B-side stamper 7b of the mold is pushed out, and the distance between the A-side stamper 7a and the B-side stamper 7b of the mold is set to a predetermined interval. Specifically, the distance between the A-side stamper surface 7a and the B-side stamper surface 7b of the mold is set so that the thickness of the substrate formed after the resin is cooled and cured is 1.2 mm.

  Through the above steps, the 1.2 mm-thick disk substrate 13 having recording surfaces formed on both sides can be formed by one injection molding.

  In forming the reflective film 3 on the recording surface thus formed, for example, a method of forming the reflective film material by vacuum deposition or sputtering is used. A reflective film can be simultaneously formed on two recording surfaces by disposing an evaporation source or a sputtering target material on both sides of the disk so as to face each other and performing opposite evaporation or opposite sputtering. Alternatively, one of the recording surfaces can be masked with a mask material, and a reflective film can be sequentially formed on each side.

  The overcoat of the protective film 4 is formed by masking one of the reflective films 3 with a mask material, sequentially spin-coating one side at a time, applying a UV curable resin to form a resin film, and then curing it in a UV furnace. It can be formed easily. Alternatively, the overcoat protective film 4 may be simultaneously formed on the two reflective films 3. In this case, first, a jig is devised to support and rotate the disk, and spin coating is simultaneously applied onto the reflective film from both sides of the disk to apply a UV curable resin to form a resin film. Next, the disk is passed through a UV furnace in which a UV lamp is installed opposite to be cured. Through these steps, the overcoat protective film 4 can be formed simultaneously on the two reflective films.

(Example 3)
FIG. 7 is a cross-sectional view schematically showing an example of the optical disk of this embodiment.

  In the optical disk shown in the figure, a recording surface having embossed pits 2 corresponding to recording data is provided on one surface of a 1.2 mm thick disk substrate 1. On the recording surface provided with such embossed pits 2, a reflective film 3 is formed, and a first protective film 4 and a second protective film 18 are sequentially overcoated thereon.

  The recording data recorded on the disk is read out by collecting the light beam 5 with the objective lens 6 and entering from the protective film 18 side as shown in the figure, and the light intensity change of the reflected light from the reflective film 3 is embossed pits. This is performed by detecting as recorded data.

  The 1.2 mm thick disk substrate 1, the embossed pit 2, the reflective film 3 and the protective film 4 for constituting the optical disk of the present embodiment can be the same as those of the optical disk of the above-described first embodiment.

  The protective film 18 disposed on the protective film 4 can be formed of, for example, a conventional ultraviolet curable resin. The protective film 18 is formed, for example, by applying an ultraviolet curable resin to the surface of the protective film 4 by spin coating to form a resin film, and irradiating it with ultraviolet rays to cure it. The film thickness of this overcoat protective film 18 is practically in the range of several μm to several mm, and is preferably 0.6 mm or less. Considering the film thickness distribution of the ultraviolet curable resin in the spin coating method, the film thickness of the overcoat protective layer 18 is preferably 0.0001 to 0.1 mm in practice. Further, it is desired that the film thickness does not cause optical interference with the reflective film 3.

  The material of the protective film 18 is not limited to the ultraviolet curable resin as described above. The material is not particularly limited as long as it is an environmentally and thermally stable material that transmits a light beam used for reproduction, and may be made of a dielectric material. For example, it can be formed by a vacuum evaporation method, a sputtering method, or the like using SiO2, SiO, AlN, Al2O3, ZrO2, TiO2, Ta2O3, ZnS, Si, Ge, or a mixed material thereof.

  Moreover, the protective film 18 should just be a transparent material with respect to the wavelength of the light to be used, and is not limited to the material and formation method mentioned above. For example, a film or plate made of a transparent resin material having a thickness of 0.0001 mm to 0.6 mm can also be used. Such a resin film or the like can be adhered onto the protective film 4 by placing it on the protective film 4 when spin-coating the protective film 4 and curing it by UV irradiation in a UV furnace.

  However, the refractive index n2 of the protective film 18 at the wavelength of the light beam used for reproduction needs to be a material smaller than or equal to the refractive index n1 of the protective film 4 at the wavelength of the light beam used for reproduction. . When the optical refractive index of the protective film 18 is larger than the optical refractive index of the protective film 4 (n2> n1), the light reflection at the interface between the protective film 18 and the protective film 4 becomes large and the signal from the recording surface is lowered. In addition, the light efficiency is reduced.

  Therefore, when an optical disk having a structure in which two protective films as shown in FIG. 7 are laminated, the protective film 18 has an optical refractive index n2 smaller than or equal to the optical refractive index n1 of the protective film 4. It is necessary to use a transparent material.

  In the optical disk of the present embodiment, the protective film 18 is further disposed on the protective film 4, so that it is possible to increase the mechanical strength of the disk surface and to prevent scratches in handling the disk. became.

Example 4
FIG. 8 is a cross-sectional view schematically showing an example of the optical disk of this embodiment.

  In the optical disk shown in the figure, recording surfaces having embossed pits 2 and 22 corresponding to recording data are provided on both the front and back surfaces of a 1.2 mm thick disk substrate 13, respectively. On the recording surface provided with the embossed pits 2, the reflective film 3, the first protective film 4, and the second protective film 18 are sequentially formed, and the other recording surface provided with the embossed pits 22. A reflective film 23, a first protective film 24, and a second protective film 19 are sequentially formed thereon.

  In the third embodiment, the recording surface is provided on only one side of the disk substrate. However, in this embodiment, the configuration is the same as that described above except that the recording surface is provided on both sides of the disk substrate. Therefore, the 1.2 mm-thick double-sided disk substrate 13 for constituting the optical disk of this embodiment can be the same as that of the above-described embodiment 2, and the embossed pit 2, the reflective film 3, the protective film 4 and the like are This can be the same as in the first embodiment.

  The second protective films 18 and 19 disposed on the first protective films 4 and 24 can be formed of, for example, a conventional ultraviolet curable resin. Such protective films 18 and 19 are formed, for example, by applying an ultraviolet curable resin to the surface of the protective films 4 and 24 by spin coating to form a resin film, and then irradiating the film with ultraviolet rays to cure it. Is done.

  When the second protective films 18 and 19 are formed on each side, one side of the first protective film is masked with a mask material, and each side is sequentially spin-coated and a UV curable resin is applied. After the film is formed, it can be easily formed by curing it in a UV furnace. Or you may form a 2nd protective film simultaneously on the 1st protective film of both surfaces. In this case, first, the jig is devised to support and rotate the disk, and simultaneously spin-coated from both sides of the disk to apply a UV curable resin to form a resin film. Next, the disk is passed through a UV furnace in which a UV lamp is installed opposite to be cured. Through these steps, the second overcoat protective films 18 and 19 can be simultaneously formed on the first protective films 4 and 24 on both sides.

  The film thickness of the overcoat protective films 18 and 19 is practically in the range of several μm to several mm, and is preferably 0.6 mm or less. Considering the film thickness distribution of the ultraviolet curable resin in the spin coating method, the film thickness of the overcoat protective layers 18 and 19 is preferably 0.0001 to 0.1 mm in practice. Moreover, it is preferable that it is a film thickness which does not produce optical interference with the reflecting films 3 and 23.

  The material of the protective films 18 and 19 is not limited to the ultraviolet curable resin as described above. The material is not particularly limited as long as it is an environmentally and thermally stable material that transmits a light beam used for reproduction, and may be made of a dielectric material. For example, it can be formed by a vacuum evaporation method or a sputtering method using SiO2, SiO, AlN, Al2O3, ZrO2, TiO2, Ta2O3, ZnS, Si, Ge or a mixed material thereof.

  In the case where the second protective films 18 and 19 are simultaneously formed on both surfaces using such a material, an evaporation source or a sputtering target material may be arranged oppositely on both sides of the disk and facing evaporation or facing sputtering may be performed. Alternatively, one surface can be sequentially formed by masking one surface with a mask material.

  Moreover, the protective films 18 and 19 should just be a material transparent with respect to the wavelength of the light used, and are not limited to the material and formation method mentioned above. For example, a film or plate made of a transparent resin material having a thickness of 0.0001 mm to 0.6 mm can also be used. Such a resin film or the like can be adhered onto the protective films 4 and 24 by being placed on the protective film when the protective films 4 and 24 are spin-coated and cured by UV irradiation in a UV furnace.

  When the protective films 18 and 19 are formed by pasting such a resin film or the like, first, one surface of the reflective film is masked with a mask material, and a UV curable resin is sequentially applied to each surface to form a resin film. To do. Next, the protective films 18 and 19 are placed thereon and spin-coated. Finally, it can be easily formed by curing in a UV furnace. Alternatively, the protective films 18 and 19 may be formed simultaneously. In this case, first, the jig is devised to support the disk, and UV curable resin is applied to both sides, and the protective films 18 and 19 are placed on both sides and the spin coat is rotated. Next, the protective film 18 and 19 are simultaneously formed on both surfaces by passing the disk through a UV furnace provided with a UV lamp facing the disk.

  The protective films 18 and 19 on both sides of the disk are made to have a thickness corresponding to the working distance of the light beam, and the two protective films have the same thickness on the upper and lower surfaces of the disk, so that both sides of the disk have the same working distance. Can be played.

  However, the refractive index n2 of the second protective films 18 and 19 at the wavelength of the light beam used for reproduction is different from the refractive index n1 of the first protective films 4 and 24 at the wavelength of the light beam used for reproduction, respectively. It must be a small or equal material. For example, when the light refractive index of the protective film 18 is larger than the refractive index of the protective film 4 (n2> n1), light reflection at the interface between the protective film 18 and the protective film 4 becomes large, and a signal from the recording surface is generated. The light efficiency is lowered. Also between the protective film 19 and the protective film 24, when the optical refractive index of the protective film 19 is larger than the refractive index of the protective film 24, the same inconvenience occurs.

  Therefore, in the case of an optical disc having a structure in which two protective films as shown in FIG. 8 are laminated, the second protective films 18 and 19 have an optical refractive index n2 of the first protective films 4 and 24. It is necessary to use a transparent material that is smaller than or equal to the optical refractive index n1 of each.

  The optical disk of this embodiment has a configuration in which second protective films 18 and 19 are further provided on both surfaces of the first protective films 4 and 24, respectively. In the above-described third embodiment, the recording surface is formed on only one surface. However, in this embodiment, the recording surface is further provided on the other surface of the disk so that the recording surface is double-sided.

  By adopting such a double-sided specification, it is possible to easily double the recording capacity of the disc.

  Further, since protective films 18 and 19 are further provided on both sides of the protective films 4 and 24 on both sides, it is possible to increase the mechanical strength of both sides of the disk and to prevent scratches on the handling of the disk. It became.

(Example 5)
In Example 4 described above, the film thicknesses of the second protective films 18 and 19 on both sides of the disk are the same, but the film thicknesses of the protective films 18 and 19 provided on the upper and lower surfaces of the disk are different. It is also possible.

  For example, in the optical disk shown in FIG. 8, when the thickness of one protective film 18 is 0.0001 to 0.6 mm and the thickness of the other protective film 19 is 0.6 mm, the following is performed. Benefits are gained. That is, the surface on the protective film 18 side is used as a recording / reproducing surface for an optical head with a short working distance, and the surface on the protective film 19 side is used as a recording / reproducing surface for an optical head compatible with the conventional DVD specifications. It becomes possible.

(Example 6)
In Example 5 described above, the thicknesses of the second protective films 18 and 19 on both sides of the disk are different from each other. In this case, the thickness of the entire disk can be adjusted by adjusting the thickness of the substrate 12. Can be set to 1.2 mm.

  For example, in the optical disk shown in FIG. 8, when the thickness of one protective film 18 is 0.1 mm and the thickness of the other protective film 19 is 0.6 mm, the thickness of the disk substrate 13 is 0. When the thickness is 0.5 mm, the thickness of the entire disk is 1.2 mm. As a result, a disc thickness equivalent to that of a conventional CD or DVD disc can be realized, and compatibility in handling the disc can be maintained.

(Example 7)
FIG. 9 is a cross-sectional view schematically showing an example of the optical disk of this embodiment.

  In the illustrated optical disk, a guide groove 26 for tracking the light beam 5 is formed on one surface of a 1.2 mm-thick disk substrate 25, on which a reflective film 27, a lower protective film 28, a recording film 29, and an upper film are formed. A protective film 30 is sequentially formed, and a protective film 4 is further overcoated thereon.

  As shown in the figure, the recording data recorded on the disk is read out by converging the light beam 5 with the objective lens 6 and entering from the protective film 4 side, and the light intensity change of the reflected light from the recording film 29 due to the recording mark. Is detected as recording data.

  The optical disk substrate 25 can be made of a stable material with little change with time. Examples of materials that can be used include acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate resins, epoxy resins, styrene resins, glass, metals such as Al, alloys, and ceramics. Group tracks, land tracks, preformat marks, and the like are formed on the optical disk substrate 25 made of such materials according to the recording format.

  The reflective film 27 has the effect of optically enhancing the optical change of the recording film 29 formed thereon via the lower protective film 28 to increase the reproduction signal, and the cooling effect of the recording film 29. Yes. The reflective film 27 can be formed of a metal film such as Au, Al, Cu, Ni—Cr, or an alloy containing these as a main component by a vacuum deposition method, a sputtering method, or the like. The thickness of the reflective film 27 is practically several nm to several μm.

  The recording film 29 is composed of a phase change film whose crystal structure changes depending on the irradiation condition of the light beam. Such phase change materials include chalcogenide amorphous semiconductor materials such as GeTe, TeSe, GeSbSe, TeOx, InSe, and GeSbTe, and compound semiconductors such as InSb, GaSb, and InSbTe. A material etc. can be used.

  The recording film 29 can be formed by using a material such as that described above by vacuum vapor deposition or sputtering. The film thickness of the recording film 29 is practically several nm to several μm.

  The lower protective film 28 and the upper protective film 30 are disposed above and below the recording film 29 so as to prevent the recording film 29 from scattering or having holes due to the irradiation of the recording beam. have. It also has a function of controlling heat diffusion of heating and cooling of the recording film 29 during recording. The lower protective film 28 and the upper protective film 30 are formed by, for example, vacuum deposition or sputtering using SiO2, SiO, AlN, Al2O3, ZrO2, TiO2, Ta2O3, ZnS, Si, Ge, or a mixed material thereof. can do. The film thickness of the lower protective film 28 and the upper protective film 30 is practically several nm to several μm.

  The overcoat protective film 4 on the upper protective film 30 is disposed to prevent scratches, dust and the like when handling the phase change optical disk, and is usually formed of an ultraviolet curable resin or the like. The protective film 4 can be formed by, for example, applying an ultraviolet curable resin to the surface of the upper protective film 30 by spin coating and irradiating and curing the ultraviolet light. The film thickness of the overcoat protective film 4 is preferably 0.6 mm or less in a practical range of several μm to several mm. Considering the film thickness distribution of the ultraviolet curable resin in the spin coating method, it is practically preferable that the film thickness of the overcoat protective film 4 is 0.0001 to 0.1 mm. Furthermore, it is desired that the film thickness does not cause optical interference with the reflective film 27.

  Although the four-layer configuration has been described as an example of the phase configuration of the phase change recording film, each layer can be multi-layered according to the required performance.

(Example 8)
FIG. 10 is a cross-sectional view schematically showing an example of the optical disk of this example.

  In the illustrated optical disk, one surface of the disk has the same configuration as that shown in FIG. That is, a tracking guide groove 26 for the light beam 5 is formed on one surface of the 1.2 mm thick disk substrate 31, and a reflective film 27, a lower protective film 28, a recording film 29, and an upper protective film 30 are formed thereon. A film is sequentially formed, and a protective film 4 is overcoated thereon.

  As shown in the figure, the recording data recorded on the disk is read out by converging the light beam 5 with the objective lens 6 and entering from the protective film 4 side, and the light intensity change of the reflected light from the recording film 29 due to the recording mark. Is detected as recording data.

  The other side of the disk has the following configuration. That is, a guide groove 34 for tracking the light beam 32 is formed on the surface of the 1.2 mm-thick disk substrate 31, and a reflective film 35, a lower protective film 36, a recording film 37, and an upper protective film 38 are formed thereon. Further, a protective film 39 is overcoated thereon.

  As shown in the figure, the recording data recorded on the disc is read out by converging the light beam 32 with the objective lens 33 and entering from the protective film 39 side, and the light intensity change of the reflected light from the recording film 37 due to the recording mark. Is detected as optical recording data.

  The material of the disk substrate and the characteristics of each film for constituting the optical disk of the present example are the same as those described in Example 7 above. In forming the reflective film, the recording film, and the protective films on both surfaces, the same method as in the case of Example 4 can be applied.

  The overcoat protective films 4 and 39 on the upper protective films 30 and 38 are disposed in order to prevent scratches and dust when handling the phase change optical disk. It is formed. The protective films 4 and 39 can be formed, for example, by applying an ultraviolet curable resin to the surfaces of the upper protective films 30 and 38 by spin coating and irradiating and curing the ultraviolet rays. The thickness of the protective films 4 and 39 is practically in the range of several μm to several mm, and is preferably 0.6 mm or less. Considering the film thickness distribution of the ultraviolet curable resin in the spin coating method, it is practically preferable that the film thickness of the overcoat protective films 4 and 39 is 0.0001 to 0.1 mm. Furthermore, it is desirable that the film thickness does not cause optical interference with the reflective films 27 and 35.

  Although the four-layer configuration has been described as an example of the phase configuration of the phase change recording film, each layer can be multi-layered according to the required performance.

Example 9
In the optical disk having the structure shown in FIG. 9 as described in the above-described seventh embodiment, a protective film is further provided on the protective film 4, and as shown in FIG. 7 as described in the above-described third embodiment. It can also be set as the same structure as a thing.

  By disposing the protective film 18 on the protective film 4, it is possible to increase the mechanical strength of the disk surface and to prevent scratches and the like in handling the disk.

  In this case, as described above, the refractive index n2 of the protective film 18 at the wavelength of the light beam used for reproduction is less than or equal to the refractive index n1 of the protective film 4 at the wavelength of the light beam used for reproduction. It is necessary to be. When the optical refractive index of the protective film 18 is larger than the optical refractive index of the protective film 4 (n2> n1), the light reflection at the interface between the protective film 18 and the protective film 4 becomes large and the signal from the recording surface is lowered. In addition, the light efficiency is reduced.

  Therefore, in the case of an optical disk having a structure in which two protective films are laminated, the protective film 18 is made of a transparent material whose optical refractive index n2 is smaller than or equal to the optical refractive index n1 of the protective film 4. is required.

(Example 10)
In the optical disk having the structure shown in FIG. 10 as described in the above-described eighth embodiment, a protective film is further provided on the protective films 4 and 39, and as shown in FIG. A configuration similar to that shown may be used.

  By disposing the protective films 18 and 19 on both surfaces of the protective films 4 and 39 on both sides, it is possible to increase the mechanical strength of both sides of the disk and to prevent scratches and the like in handling the disk.

  In this case, as already described, the refractive index n2 of the second protective films 18 and 19 at the wavelength of the light beam used for reproduction is equal to the first protective film 4 at the wavelength of the light beam used for reproduction. The material must be smaller than or equal to the refractive index n1 of 24. For example, when the light refractive index of the protective film 18 is larger than the refractive index of the protective film 4 (n2> n1), light reflection at the interface between the protective film 18 and the protective film 4 becomes large, and a signal from the recording surface is generated. The light efficiency is lowered. Also between the protective film 19 and the protective film 24, when the optical refractive index of the protective film 19 is larger than the refractive index of the protective film 24, the same inconvenience occurs.

  Therefore, in the case of an optical disc having a structure in which two protective films are laminated, the second protective films 18 and 19 have an optical refractive index n2 that is greater than an optical refractive index n1 of the first protective films 4 and 24, respectively. It is necessary to use a small, equal or transparent material.

(Example 11)
In the optical disks described in the first to tenth embodiments, all the surfaces of the surface of the disk that are irradiated with the light beam and used for recording and reproducing information are smooth surfaces. If the surface of the disk is smooth, even if there is dust, it is difficult to adhere, and the effect of preventing dust from being attached can be obtained. If the surface of the disk is smooth, an effect of preventing the objective lens from contacting the disk can be obtained.

  The protective films 4, 24, 39 on the surface of the optical disk shown in each drawing have an uneven surface formed by recording embossing or tracking grooves on the inner side, that is, the inner side of the disk. On the other hand, the outer surface of the disk can be smoothed without reflecting the inner uneven surface by forming such a thick protective film.

  The unevenness of the recording surface of the disk substrate is large before and after λ / (8n) (n is the optical refractive index of the surface protective film at the light wavelength) with respect to the wavelength λ of the light beam used for reproduction. Is formed. The distance from the recording surface of the disk substrate to the surface irradiated with the light beam (irradiated surface) is generally 10 times or more from the viewpoint of smoothing the surface. Therefore, the distance from the recording surface of the disk substrate to the surface irradiated with the light beam is preferably 5λ / (4n) or more.

  Further, in order to reduce the light diffraction phenomenon on the surface irradiated with the light beam (irradiated surface), the surface roughness of the irradiated surface is required to be smaller than λ / (8n). The surface roughness of the irradiated surface is desirably λ / (16n) or less, which is 1/2 or less of λ / (8n).

  According to the method of the present invention, a substrate having recording surfaces on both sides can be easily manufactured, and bonding of the substrates becomes unnecessary, so that the manufacturing process of the disc is simplified. Further, since a material such as an adhesive for bonding is not required, a large-capacity disk can be manufactured at a lower cost.

  Furthermore, in the information recording medium of the present invention, it is possible to ensure mechanical strength even if the surface protective film is thinner than the conventional 0.6 mm, and its industrial value is tremendous.

Sectional drawing which represents typically an example of the information recording medium of this invention. FIG. 2 is a schematic diagram schematically showing a mold for manufacturing a disk substrate used in the information recording medium shown in FIG. 1. The graph which represents the relationship between the film thickness of a reflecting film, and a reflectance. The graph showing the optical wavelength dependence of the film thickness of a reflecting film. Sectional drawing which represents typically the other example of the information recording medium of this invention. FIG. 6 is a schematic diagram schematically showing a mold for manufacturing a disk substrate used in the information recording medium shown in FIG. 5. Sectional drawing which represents typically the other example of the information recording medium of this invention. Sectional drawing which represents typically the other example of the information recording medium of this invention. Sectional drawing which represents typically the other example of the information recording medium of this invention. Sectional drawing which represents typically the other example of the information recording medium of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Single-sided optical disk substrate; 2,22 ... Embossed pit; 3,23 ... Reflective film 4,24 ... Protective film; 5,20 ... Light beam; 6,21 ... Objective lens 7 ... Stamper; 7b ... B-side stamper 8,14 ... Center hole; 9,11,15 ... Mold; 10,16,17 ... Protrusions 12 ... Resin inlet; 13 ... Double-sided optical disk substrate; 18,19 ... Second protective film 25 ... single-sided optical disk substrate; 26, 34 ... tracking guide groove 27, 35 ... reflective film; 28, 36 ... lower protective film; 29, 37 ... recording film 30, 38 ... upper protective film; ... light beam 33 ... objective lens; 39 ... overcoat protective film.

Claims (8)

A substrate,
First and second recording surfaces provided on both surfaces of the substrate and provided with embossed pits;
First and second reflective films provided on the surfaces of the first and second recording surfaces;
And first and second protective films provided on the surfaces of the first and second reflective films,
An information recording medium, wherein recorded data is reproduced based on a change in light intensity of reflected light of a light beam emitted from the protective film side. A substrate with guide grooves on both surfaces,
First and second reflective films provided on both surfaces of the substrate;
First and second recording films provided on the surfaces of the first and second reflective films;
First and second protective films provided on the surfaces of the first and second recording films,
An information recording medium, wherein recorded data is reproduced based on a change in light intensity of reflected light of a light beam emitted from the protective film side.   The information recording medium according to claim 1 or 2, wherein the first and second protective films are formed of a UV curable resin by a spin coating method.   3. The information recording medium according to claim 1, wherein the thickness of the first and second protective films is in the range of 0.0001 mm to 0.1 mm.   3. The information recording medium according to claim 1, wherein the first and second protective films are made of a film-like or plate-like transparent resin material.   3. The information recording medium according to claim 1, wherein third and fourth protective films are further provided on the surfaces of the first and second protective films.   The information recording medium according to claim 6, wherein the thickness of the third and fourth protective films is 0.6 mm or less.   7. The information recording medium according to claim 6, wherein the optical refractive indexes of the third and fourth protective films are smaller than or equal to the optical refractive indexes of the first and second protective films.

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