JP2007199125A - Method of manufacturing optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the method of manufacturing an optical recording medium capable of attaining a uniform thickness even when the recording layer is thick. <P>SOLUTION: The method of manufacturing the optical recording medium having a recording layer of performing three-dimensional recording comprises processes of preparing a solution obtained by dissolving a refractive index modifying material and a binder into a solvent, preparing solid material obtained by reducing the concentration of a solvent up to a prescribed concentration from the solution, preparing powder by crushing the solid material, packing the powder into the mold of a recording layer, and heating and pressing the powder to mold the recording layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an optical recording medium having a recording layer for recording three-dimensionally by recording a plurality of data in a region extending in the thickness direction.

  Examples of high-capacity optical recording media currently in use or under consideration include digital versatile discs (DVD), Blu-ray discs, and high definition DVDs (HD DVD). It is done. However, the capacity of these media is considered to be about 100 GB at the maximum, and data represented by holographic memory and multilayer optical memory is recorded three-dimensionally as a high capacity optical recording medium having a capacity larger than this. Optical recording media that perform (volume recording) have been studied. Also, a two-photon absorption medium has been studied as a high capacity optical recording medium.

  An optical recording medium that performs volume recording such as a holographic memory or a multilayer optical memory records a plurality of data not only in the in-plane direction of the recording layer but also in a region extending in the thickness direction of the recording layer. Since recording is performed, the capacity can be increased. In the holographic memory, multiplex recording is performed many times at the same place in the surface by various multiplexing methods. In a multilayer optical memory, a recording bit is formed in each of the multilayer recording layers at the same place in the plane. In addition, the two-photon absorption medium can obtain an effect equal to or better than that of using a short wavelength laser by using a long wavelength laser. A large capacity can be expected by using a two-photon absorption medium as an optical recording medium for volume recording.

  In an optical recording medium for volume recording, in order to increase the capacity, as the recording layer becomes thicker, the travel of incident light through the recording layer tends to become longer. In the holographic memory, it is possible to increase the capacity by uniformly recording the interference fringes over the entire thickness of the recording layer. Even in a multi-layer optical memory, the capacity can be increased by forming recording bits uniformly over the entire thickness of the recording layer.

A method for forming a recording layer has been proposed (see, for example, Patent Document 1), but a method for manufacturing an optical recording medium capable of forming a thick recording layer has not been proposed.
JP-A-6-43634 (paragraph 0060 to paragraph 0062)

  In the conventional method for producing an optical recording medium, when the recording layer is made thicker in order to increase the capacity, a recording layer having a uniform thickness may not be obtained.

  Accordingly, an object of the present invention is to provide a method for manufacturing an optical recording medium capable of realizing a uniform thickness even if the recording layer is thick.

  In order to solve the above problems, an optical recording medium manufacturing method of the present invention is a method for manufacturing an optical recording medium having a recording layer for three-dimensional recording, wherein a solution in which a refractive index modulation material and a binder are dissolved in a solvent is used. To produce a solid having a solvent concentration reduced to a predetermined concentration from this solution, to produce a powder obtained by pulverizing the solid, filling the powder into a recording layer mold, and heating and pressing the powder. And forming into a recording layer. Since the molding is carried out from a solid material that has been solidified by reducing the concentration of the solvent, a recording layer having a uniform thickness can be molded as the shrinkage of the recording layer during molding is small. In addition, since it is molded from a solid material, a thick recording layer can be molded without flowing like a solution. The predetermined concentration is preferably 5% by mass or less, whereby the solution can be solidified. It is preferable that the heating and pressurization is performed in a reduced-pressure atmosphere, whereby bubbles generated during molding can be removed. The refractive index modulation material preferably contains a polymerizable monomer that undergoes a polymerization reaction in the recording of optical information, and preferably contains a refractive index modulation dye that undergoes a coloring reaction or a decoloring reaction. By these things, a hologram can be recorded on an optical recording medium. Furthermore, it is preferable to further dissolve the sensitizing dye in the solvent when forming the solution. Thus, a sensitive hologram can be recorded on the optical recording medium. Further, the refractive index modulation material preferably contains a refractive index modulation dye that performs multiphoton absorption in recording optical information, whereby the optical recording medium can be used as a two-photon absorption medium.

  As described above, according to the present invention, it is possible to provide an optical recording medium manufacturing method capable of realizing a uniform thickness even when the recording layer is thick.

  Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the embodiment, an optical recording medium that performs volume recording such that three-dimensional recording is performed by recording a plurality of data in a region extending in the thickness direction of the recording layer will be described. Specifically, holography ( A holographic memory that records optical information using interference will be described. The present invention can also be applied to multilayer optical memories and two-photon absorption media.

  The holographic memory according to the embodiment of the present invention has a recording layer. Further, if necessary, a light transmissive substrate may be provided above and below the recording layer.

  As is well known, optical information as data is multiplexed and recorded as interference fringes by irradiating the recording layer with reference light and recording light, as is well known. As the multiplexing method, a shift multiplexing method, an angle multiplexing method, a wavelength multiplexing method, a phase code multiplexing method, a polytopic multiplexing method, or a multiplexing method based on a combination thereof can be used. In the case of the angle multiplexing method, the incident angle of the reference light is changed for each recording light of each optical information to be multiplexed recorded. Specifically, first, the reference light set at a predetermined incident angle is adjusted to the recording light of the optical information, and the recording light and the reference light are irradiated to the recording portion of the recording layer, whereby interference fringes are formed on the recording layer. Is formed.

  When interference fringes are recorded on the recording layer, the recording layer material changes along the brightness and darkness of the interference fringes in the recording layer, and recording is performed by causing a difference in refractive index and transmittance. Examples of recording layer materials that are currently under consideration include photopolymer materials, refractive index modulation dye-type materials, silver halides, dichromated gelatin, photorefractive materials, and photochromic materials.

  Photopolymer materials are attracting attention and are being developed because of their high diffraction efficiency, low noise, and good storage stability if they are completely fixed after recording. A typical photopolymer material contains a binder, a polymerizable monomer, a sensitizing dye, a polymerization initiator, and the like.

  Binders and polymerizable monomers having different refractive indexes are used. During recording, bright and dark portions of interference fringes are formed in the recording layer. In the bright part of the interference fringes, the sensitizing dye excites and emits electrons, the emitted electrons move to the polymerization initiator, the polymerization initiator generates radicals, and the radicals move to the polymerizable monomer and polymerize. The polymerization reaction of the reactive monomer is carried out. As a result, in the bright part of the interference fringes, the polymerizable monomer that is polymerized from the adjacent dark part is collected, and the polymerizable monomer becomes rich, and in the dark part of the interference fringe, the binder is removed in correspondence with the binder. Becomes richer. Interference fringes are recorded by generating different refractive indexes due to these mono-rich and binder-rich in the bright and dark portions of the interference fringes. As a result, the optical information is recorded in the recording layer as stripes expressed as different refractive indexes and light transmittances.

  Next, the incident angle of the reference light is changed, and the reference light is adjusted to the recording light of other optical information. Then, an interference fringe is formed at the same location as the recording location where one optical information is recorded, so that other optical information is recorded in an overlapping manner. Hereinafter, a plurality of pieces of optical information are recorded in one recording location of the recording layer by combining reference light having different incident angles for each recording light of other optical information to be multiplexed. Thus, since the angle selectivity of the incident angle is increased by generating the interference fringes in the thickness direction, the recording layer performs multiplex recording using the angle selectivity.

  Then, when the multiplex recording of the predetermined optical information in one recording location is completed, the recording layer moves to another recording location in the recording layer by a stop and go method. Other recording locations and one recording location may or may not partially overlap. The positioned recording light and reference light multiplex-record a plurality of pieces of optical information at other recording locations in the same manner as multiplex recording at one recording location.

  When the recording of the predetermined optical information on the recording layer is completed, the polymerizable monomer that has not been used for recording the optical information is fixed by being exposed to the whole surface with a laser or a white light source, or by heat treatment.

  As is well known, the hologram as optical information recorded in the recording layer is read out as reproduction light generated by irradiating the recording light with reproduction illumination light. Then, each of the plurality of pieces of optical information multiplexed and recorded at each recording location is read by irradiating the reproduction illumination light set at the incident angle of the reference light when each piece of optical information is recorded.

  The recording layer is a layer on which optical information is recorded by being irradiated with light, and has a thickness of 200 μm or more, preferably 0.2 to 2.5 mm, more preferably 0.5 to 2.5 mm. By setting the thickness to 200 μm or more, it is possible to satisfy the number of multiplex recordings required when a holographic memory is commercialized. Moreover, by setting it as 0.5 mm or more, it can satisfy | fill the SN ratio required in the case of commercialization about the SN ratio of the optical information reproduced | regenerated. Moreover, by making it 2.5 mm or less, the material which does not contribute to the recording of optical information can be reduced, and the cost can be reduced at the time of commercialization.

  The polymerizable monomer is not particularly limited as long as it has a polymerizable group, and examples thereof include a radical polymerizable monomer, a cationic polymerizable monomer, and a combination of these polymerizable monomers. Specifically, an epoxy group, Examples thereof include compounds containing a polymerizable group such as an ethylenically unsaturated group. The polymerizable monomer only needs to contain one or more of these polymerizable groups in the molecule, and the polymerizable monomer containing two or more polymerizable groups in the molecule may have different polymerizable groups. And the same thing may be used.

  The sensitizing dye is not particularly limited as long as it has absorption at the recording wavelength of the recording light (reference light), but preferably has a low absorbance, that is, a light absorption coefficient ε, at the recording wavelength. Specific examples of the sensitizing dye include cyan, merocyanine, phthalocyanine, azo, azomethine, indoaniline, xanthene, coumarin, polymethine, diallylethene, fulgidofluorane, anthraquinone, Well-known organic pigments such as styryl are exemplified. In addition to these, a complex dye may be used as the sensitizing dye.

  Examples of the polymerization initiator include a radical generator, a cation generator, and an acid generator.

  Examples of the binder include chlorinated polyethylene, polymethyl methacrylate, copolymers of methyl methacrylate and other (meth) acrylic acid alkyl esters, copolymers of vinyl chloride and acrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl formal, Examples thereof include polyvinyl butyral, polyvinyl pyrrolidone, ethyl cellulose, acetyl cellulose, and polycarbonate. The refractive index of the binder preferably has a large difference from the refractive index of the polymerized polymer (polymer). However, in a combination in which the difference in refractive index is too large, the compatibility between the binder and the polymerizable monomer is lowered, and as a result, light scattering may increase, so a binder with an appropriate refractive index is required. .

  In addition, the recording layer may be a recording layer of this type of optical recording medium such as a sensitizer, an optical brightener, an ultraviolet absorber, a heat stabilizer, a chain transfer agent, a plasticizer, and a colorant. What is commonly used for formation may be included.

  Photopolymer material is a material that records interference fringes by the refractive index difference between polymer and binder formed by polymerizing a polymerizable monomer, and is polymerizable in a urethane matrix formed by the crosslinking reaction of polyol and curing agent by heat. There is a monomer. When forming a recording layer using a photopolymer material, a method in which a solution in which the photopolymer material is dissolved in a solvent is formed by spin coating or a solution is injected into a substrate is generally used. ing. In these methods, volume shrinkage occurs during the thermal polymerization of the crosslinking reaction by heat between the polyol and the curing agent, and as the film thickness of the recording layer is increased, the film thickness may not be uniform.

  As a material other than the photopolymer material of the recording layer material currently being studied, there is a dye-type material for refractive index modulation. The dye-type material for refractive index modulation causes a coloring reaction or a decoloring reaction of the refractive index modulation dye in the bright part of the interference fringe, and a physical property value such as a refractive index difference or a transmittance difference with respect to the dark part of the interference fringe. Cause the difference. The refractive index modulating dye-type material has a binder, a sensitizing dye, a refractive index modulating dye, and an acid generator. Similar to the photopolymer, when the interference fringes are generated, the sensitizing dye is excited and electrons are emitted in the bright part of the interference fringes. The emitted electrons move to the acid generator, and acid is generated from the acid generator. With this acid, the refractive index modulating dye is decolored by a decoloring reaction, and the refractive index changes. Alternatively, the refractive index modulating dye is colored by a color development reaction, and the refractive index changes. In the case of a color development reaction, the refractive index modulation dye may be particularly referred to as a dye precursor.

  The recording layer contains a sensitizing dye and a refractive index modulating dye. The sensitizing dye and the refractive index modulating dye are not particularly limited as long as they have absorption at the recording wavelength of the recording light and the reference light, but the absorbance of the sensitizing dye itself at the recording wavelength, that is, the light absorption coefficient ε is low. Those are preferred. As the sensitizing dye, the same sensitizing dye contained in the photopolymer material can be used.

  A dye-type material for refractive index modulation is a material that contains a dye in a binder and records interference fringes by changing the refractive index due to color development or decoloration of the dye in the light-exposed area. A modulation dye is contained. When forming a recording layer with a refractive index modulating dye-type material, a solution in which a refractive index modulating dye-type material is dissolved in a solvent is formed by spin coating, or the solution is injected into a substrate. This method is generally used. In these methods, when the solution is made thicker than 100 μm, a uniform surface cannot be obtained, and it is difficult to increase the thickness beyond this.

  In addition, examples of the material of the recording layer currently under consideration include silver halide, dichromated gelatin, photorefractive material, and photochromic material.

  Although silver halide has high sensitivity and relatively high resolution, it has a problem that it requires wet processing and is complicated, has a large scattering, and is inferior in light resistance. Therefore, there is much room for improvement as a memory application.

  Bichromated gelatin has the characteristics of high diffraction efficiency and low noise, but has low sensitivity and poor recording storage stability, so there is room for improvement in memory applications.

  Photorefractive materials have the feature of being rewritable, but they require a high voltage application during recording and have poor record retention, so there is room for improvement in memory applications.

  Photochromic materials also have the feature of being rewritable, but they have room for improvement as memory applications because of their extremely low sensitivity and poor record retention.

  Therefore, recording layer materials such as silver halide, dichromated gelatin, photorefractive material, photochromic material, photopolymer material, and refractive index modulation dye-type material may be combined. For example, by combining a refractive index-modulating dye-type material that causes a coloring reaction or a decoloring reaction and a photopolymer material that causes a polymerization reaction, it becomes possible to fix the refractive index-modulating dye-type material, Since the refractive index difference can be easily obtained, the suitability of the recording layer as a material can be obtained synergistically. In addition, even when a photorefractive material and a photopolymer material are combined, it is possible to fix to a photorefractive material as well, and a refractive index difference can be easily obtained. Can be obtained synergistically. Suitable as a material for the recording layer. The recording layer may be formed of a thermopolymerizable resin composition (thermosetting resin composition) according to the recording method.

  The recording layer may be one using a two-photon absorption material. As this two-photon absorption material, a material composed of only the first compound which itself undergoes some chemical or physical change by performing two-photon or multiphoton absorption can be used. In this case, the first compound functions as a polymerizable monomer or a refractive index modulating dye. As the two-photon absorbing material, a material comprising a two-photon or multiphoton absorbing compound and a second compound in which some chemical or physical change is induced by the two-photon or multiphoton absorption can be used. . In this case, the two-photon or multiphoton absorption compound functions as a sensitizing dye, and the second compound functions as a polymerizable monomer or a refractive index modulation dye. In addition to the two-photon or multi-photon absorbing compound and the second compound that induces chemical and physical changes induced by the two-photon or multi-photon absorption of the two-photon or multi-photon absorbing compound, these records are further recorded. It is possible to use a substance containing a third compound that plays a role of adjusting the mechanism. Examples of these two-photon absorption materials include those described in JP-A No. 2002-172864.

  Further, the optical recording medium may include a light transmissive substrate above and below the recording layer in order to hold and protect the recording layer. The thickness of the light transmissive substrate may be about 0.05 to 1.2 mm. Examples of the material for the light transmissive substrate include inorganic substances such as glass, polycarbonate, triacetyl cellulose, cycloolefin polymer, polyethylene terephthalate, polyphenylene sulfide, acrylic resin, methacrylic resin, polystyrene resin, vinyl chloride resin, epoxy resin, and polyester. Examples of the resin include resins and amorphous polyolefins. Of these, glass, polycarbonate, and triacetyl cellulose are preferable because of their low birefringence. Note that the light-transmitting substrate may be formed of the same material or different materials. The surface of the light transmissive substrate may be provided with an antireflection coating, an oxygen permeation prevention coating, a moisture permeation prevention coating, a UV cut coating, or the like as necessary.

  A method for manufacturing a holographic memory according to an embodiment of the present invention includes a dissolution step of generating a solution in which a refractive index modulation material and a binder are dissolved in a solvent in the method for manufacturing a holographic memory having a recording layer, and the solution A concentration step for producing a solid material in which the concentration of the solvent is reduced to a predetermined concentration, a pulverization step for producing a powder obtained by pulverizing the solid material, a filling step for filling the powder into a recording layer mold, and a powder And a molding step of molding the recording layer by heating and pressing. As a result, a recording layer can be formed, and a powdered solid is molded into the recording layer. Therefore, unlike when a solution is molded, it is easy to maintain the molded shape, and a uniform film thickness. In addition, a thick recording layer can be formed.

  First, when a recording layer is formed using a photopolymer material in the dissolving step, a binder, a polymerizable monomer, a polymerization inhibitor, a sensitizing dye, a polymerization initiator, and the like are dissolved in a solvent. As the solvent, methyl ethyl ketone (MEK), tetrafluoropropanol (TFP), cyclohexanone, methylene chloride, or the like can be used. Further, when forming a recording layer using a refractive index modulation dye-type material, a binder, a refractive index modulation dye, an acid generator, a sensitizing dye, and the like are dissolved in a solvent. As the solvent, MEK, TFP, cyclohexanone, methylene chloride, or the like can be used.

  Next, in the concentration step, it is desirable to reduce the concentration of the solvent to the solution to 5% by mass or less. Furthermore, you may reduce to 0 mass%. As a result, the concentration of the solid content of the photopolymer material or the refractive index modulation dye-type material exceeds 95% by mass, and the solution is solidified into a solid. If it is a solid substance, the external shape can be maintained without flowing like a solution. In order to reduce the concentration of the solvent, the solution may be dried.

  Since the solution is solidified in the concentration step, pulverization in the pulverization step becomes possible. The powder is pulverized into a shape (size, particle size) corresponding to the shape of the mold so that the recording layer can be easily filled in the filling process.

  In the filling step, an amount of powder corresponding to the film thickness of the recording layer to be produced is filled.

  In the molding process, it is desirable that the heating and pressurization be performed in a reduced pressure atmosphere. More preferably, the atmosphere is a vacuum. By reducing the atmosphere or reducing the atmosphere, it is possible to prevent bubbles from being formed in the recording layer. The heating temperature is preferably not higher than the boiling point of the photopolymer material or the refractive index modulating dye-type material. This can prevent segregation of the liquefied or vaporized photopolymer material and the refractive index modulating dye-type material. Moreover, 100 degreeC or more is preferable in order to soften a solid substance, to improve fluidity | liquidity and to make it easy to shape | mold. Further, servo pits may be formed on the recording layer in the molding process. This eliminates the need for a separate pit formation process.

  After the molding process, the recording layer is further processed into a desired shape. For example, when processing into a disk shape having a diameter of 12 cm, excess portions such as burrs and protrusions formed during the molding process are cut. The recording layer thus formed is bonded to a light-transmitting substrate such as polycarbonate. If necessary, the light transmissive substrate may be provided with a reflective layer, servo pits, and a scratch-resistant hard coat layer.

  According to the embodiment, it is possible to provide an optical recording medium manufacturing method capable of realizing a uniform thickness even when the recording layer is thick. In the embodiments, the optical recording medium for recording optical information using holography (interference) has been described. However, the present invention is not limited to this, and a multilayer optical memory or a two-photon absorption medium may be used. Good.

  Next, the optical recording medium of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

<Manufacture of optical recording media>
Example 1
In Example 1, an optical recording medium was manufactured using a photopolymer material. First, in order to produce a recording layer, a solution was prepared. Each material of binder, monomer, polymerization initiator, sensitizing dye, and MEK as a solvent shown in Table 1 was weighed so as to have a mass ratio shown in Table 1. Weighing was performed under a red light.

  In addition, PMMA in Table 1 is polymethyl methacrylate (manufactured by Aldrich, Mw: 996000).

  And each raw material was thrown into the brown eggplant type flask under a red light, and the solution was obtained by stirring with a stirrer for 3 hours. The dissolution process is thus completed.

  Next, in the concentration step, a solid material was produced from this solution in which the concentration of the solvent relative to the solution was reduced to 5% by mass. As a result, the solid content concentration of the photopolymer material was 95% by mass, and the solution was solidified into a solid. If it is a solid substance, the external shape can be maintained without flowing like a solution. In order to reduce the concentration of the solvent, for example, the solution may be dried at 40 ° C. for about 10 hours, and if it is difficult to dry, additional drying may be performed with a vacuum dryer.

  Next, in the pulverization step, the solid matter was pulverized to produce a powder. The powder was pulverized so that the maximum width of the powder was equal to or less than the thickness of the recording layer to be produced.

  In the filling step, an amount of powder corresponding to the film thickness of the recording layer to be produced was filled.

In the molding step, the powder is heated and pressed in an atmosphere reduced to about 10 hPa to form a recording layer. The heating temperature can be set to 100 to 200 ° C., but was set to 120 ° C. in this experiment. Pressure applied can be set to ^{2 × 10 3 hPa~1 × 10 5} hPa , but in this experiment was set at 2 × ¹⁰ 3 hPa. The heating and pressing time was 3 minutes. As a result, it is possible to generate a uniform recording layer in which the bubbles are driven out without segregation of the liquefied or vaporized photopolymer material. In addition, since the powdered solid is molded into the recording layer, unlike the case of molding the solution, it is easy to maintain the molded shape, and the film has a uniform film thickness according to the mold. The recording layer can be formed.

  After the molding process, extra parts such as burrs and bulges formed in the molding process were cut in order to process the disk shape with a diameter of 12 cm. The recording layer thus formed was bonded to a light-transmitting substrate such as polycarbonate to complete an optical recording medium.

(Comparative Example 1)
In Comparative Example 1, a photopolymer solution was prepared in the same manner as in Example 1 and concentrated so that the solid content concentration was 90%. Even 90% was apparently solid and could be crushed. The pulverization was performed in the same manner as in Example 1 so that the maximum width of the powder would be equal to or less than the film thickness of the recording layer to be produced.
In the filling step, an amount of powder corresponding to the film thickness of the recording layer to be produced was filled.
In the molding step, the heating temperature is set to 120 ° C., the pressurization is set to 2 × 10 ³ hPa, and the heating and pressurization time is 3 minutes in the atmosphere reduced to about 10 hPa as in the first embodiment. It was. As a result, bubbles were scattered in the recording layer. In the range of heating temperature and time at which a uniform film can be formed, air bubbles must be eliminated, so that a recording layer could not be formed.

(Example 2)
In Example 2, the binder of Example 1 was changed to PC (polycarbonate) and the solvent was changed to methylene chloride.

And each raw material was thrown into the brown eggplant type flask under the red lamp, and it implemented similarly to Example 1 until the filling process. In the molding step, the powder is heated and pressed in an atmosphere reduced to about 10 hPa to form a recording layer. The heating temperature can be set to 100 to 200 ° C., but was set to 140 ° C. in this experiment. Although the pressure to pressurize can be set to 2 × 10 ³ hPa to 1 × 10 ⁵ hPa, it is set to 5 × 10 ³ hPa in this experiment. The heating and pressing time was 3 minutes. As a result, it is possible to generate a material-uniform recording layer in which bubbles are driven out without segregation of the liquefied or vaporized photopolymer material. In addition, since the powdered solid is molded into the recording layer, unlike the case of molding the solution, it is easy to maintain the molded shape, and the film has a uniform film thickness according to the mold. The recording layer can be formed.
After the molding process, extra parts such as burrs and bulges formed in the molding process were cut in order to process the disk shape with a diameter of 12 cm. The recording layer thus formed was bonded to a light-transmitting substrate such as polycarbonate to complete an optical recording medium.

(Example 3)
In Example 3, an optical recording medium was manufactured using a refractive index modulation dye-type material. First, in order to produce a recording layer, a solution was prepared. The binder, sensitizing dye, refractive index modulation dye, acid generator, and donor material shown in Table 3 were weighed so that the mass ratio shown in Table 3 was obtained. Weighing was performed under a red light.

In Table 3, compound a is a compound represented by chemical formula (a), and compound b is a compound represented by chemical formula (b).

  The optical recording medium was manufactured in the same manner as in Example 1 until the optical recording medium was completed through the subsequent dissolution process, concentration process, pulverization process, filling process, and molding process.

<Measurement of recording layer thickness>
The thicknesses of the recording layers of Example 1, Example 2, and Example 3 were measured at 8 points in the disk surface. And the average value of the measured thickness of 8 points | pieces was computed. Further, the uniformity was calculated by dividing the difference between the maximum value and the minimum value of the eight measured values by the average value. A DIGITAL MICROMETER made by Sony was used for measuring the thickness of the recording layer. The thickness of the recording layer was calculated by subtracting the thickness of the light-transmitting substrate from the total thickness of the measured optical recording medium. The average thickness of the recording layer of Example 1 was 202 μm with respect to the target value of 200 μm. The uniformity was 0.7%. The average thickness of the recording layer of Example 2 was 503 μm with respect to the target value of 500 μm. The uniformity was 0.4%. The average value of the thickness of the recording layer of Example 3 was 998 μm with respect to the target value of 1000 μm. The uniformity was 0.5%. According to the manufacturing method of the optical recording medium according to Example 1, Example 2 and Example 3, sufficient uniformity is obtained in the optical recording medium of Example 1, Example 2 and Example 3. Even if the recording layer is as thick as 200 μm or more, it is considered that an optical recording medium having a uniform thickness in the thickness direction can be produced in a wide range in the disk in-plane level.

<Measurement of diffraction efficiency of optical recording medium>
Optical information was recorded / reproduced on each of the manufactured optical recording media of Example 1 and Example 2. Then, the diffraction efficiency η during recording / reproduction was measured by the diffraction efficiency measuring apparatus M shown in FIG.

  The YAG laser light (wavelength: 532 nm) irradiated from the YAG laser source 31 is irradiated on the surface S1 of the optical recording medium OM as the recording light L1 through the objective lens 32, the lens 33, the beam splitter 34, and the mirror 35. It was. At this time, the incident angle of the recording light L1 with respect to the surface S1 of the optical recording medium OM was set to 15 degrees, and the spot diameter was set to 5 mmφ. Then, the light separated by the beam splitter 34 was combined with the recording light L1 through the mirror 35 as the reference light L3. As a result, optical information was hologram-recorded by forming interference fringes in the recording layer of the optical recording medium OM. In this diffraction efficiency measuring apparatus M, optical information was multiplexed and recorded on the recording layer of the optical recording medium OM by schedule recording. With this schedule recording, the same diffraction efficiency η can be obtained during multiplexing.

For each of such multiplexed optical information, the He-Ne laser beam L2 having a wavelength of 633 nm is optically recorded from the He-Ne laser source 38 via the mirror 39 and the mirror 40 at the time of recording and reproduction. The incident light was incident on the back surface S2 of the medium OM at an incident angle of about 18 degrees Bragg. And the change of the diffraction efficiency (eta) with respect to the exposure amount at this time was observed. In order to calculate the diffraction efficiency η, the light quantity of the diffracted light (reproduced light) of the He—Ne laser was measured by the power meter 41 provided on the surface S1 side of the optical recording medium OM. The diffraction efficiency η is calculated by the formula (1) based on the incident light amount of the He—Ne laser incident on the back surface S2 of the optical recording medium OM (the light amount emitted from the He—Ne laser source 38) and the measured light amount of the diffracted light. Calculated.
Diffraction efficiency η (%) = diffracted light quantity / incident light quantity × 100 (1)

  The diffraction efficiency η during recording and reproduction of the optical recording medium of Example 1 was 70% or more, respectively. The diffraction efficiency η during recording and reproduction of the optical recording medium of Example 2 was 70% or more, respectively. The diffraction efficiency η during recording and reproduction of the optical recording medium of Example 3 was 70% or more, respectively. According to the manufacturing methods of the optical recording media according to Example 1, Example 2 and Example 3, sufficient diffraction efficiency η is obtained in the optical recording media of Example 1, Example 2 and Example 3. Even if the recording layer is as thick as 200 μm or more, it is considered that an optical recording medium having a uniform thickness in the thickness direction and a uniform material can be produced even in a narrow spot diameter level range.

It is a schematic diagram of a diffraction efficiency measuring apparatus.

Explanation of symbols

  OM optical recording medium

Claims (7)

In a method for manufacturing an optical recording medium having a recording layer for three-dimensional recording,
Create a solution in which the refractive index modulation material and binder are dissolved in a solvent,
Producing a solid matter in which the concentration of the solvent is reduced to a predetermined concentration from the solution,
Producing a powder obtained by pulverizing the solid,
Filling the powder in a mold,
A method for producing an optical recording medium, comprising heating and pressing the filled powder to form the recording layer.   2. The method of manufacturing an optical recording medium according to claim 1, wherein the predetermined concentration is 5% by mass or less.   3. The method of manufacturing an optical recording medium according to claim 1, wherein the heating and pressurizing is performed in a reduced pressure atmosphere.   The method for producing an optical recording medium according to claim 1, wherein the refractive index modulation material includes a polymerizable monomer that undergoes a polymerization reaction in optical information recording.   5. The optical recording medium according to claim 1, wherein the refractive index modulation material includes a refractive index modulation dye that performs a coloring reaction or a decoloring reaction in recording optical information. Manufacturing method.   6. The method for producing an optical recording medium according to claim 1, wherein a sensitizing dye is further dissolved in the solvent when the solution is produced.   6. The method of manufacturing an optical recording medium according to claim 1, wherein the refractive index modulation material includes a refractive index modulation dye that performs multiphoton absorption in recording optical information. .

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