Recording medium, information recording method, and information reading method

Abstract

A recording medium (100) in one aspect of the present disclosure includes a recording layer (10) including a polymer P. The polymer P contains a group G having a non-linear light absorption property, and has a glass transition temperature of 200 DEG C or more. The information recording method according to one aspect of the present disclosure includes: preparing a light source that emits light having a wavelength of 390 nm or more and 420 nm or less; and a recording layer (10) that concentrates the light from the light source and irradiates the light onto a recording medium (100).

Description

Technical Field

[0001] The present disclosure relates to a recording medium, a method for recording information, and a method for reading information. Background Art

[0002] As a technology for increasing the recording capacity of an optical information recording medium, three-dimensional recording of information in a multilayer body is known. In the field of three-dimensional recording, in order to increase the recording density, a finer light focusing point must be achieved. From the perspective of the diffraction limit of the focused laser, in order to achieve a finer light focusing point, a laser with a short wavelength is used. As such a laser, a laser with a central wavelength of 405 nm, which is the specification of a Blu-ray (registered trademark) disc, can be cited. In this way, an optical recording medium using a laser with a central wavelength of 405 nm is known.

[0003] The recording medium includes, for example, a recording layer containing a pigment. Pigments that may be used in the recording medium are exemplified in Patent Document 1 and Non-Patent Document 1. In particular, Patent Document 1 discloses an optical information recording material in which a nonlinear light absorbing pigment such as pyrene is dispersed in a resin. In Patent Document 1, an optical recording medium including a recording layer formed of an optical information recording material is capable of holographic recording.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6448042

[0007] Non-patent literature

[0008] Non-patent document 1: Harry L. Anderson et al., "Two-Photon Absorption and the Design of Two-Photon Dyes", Angew. Chem. Int. 2009 edition, Vol. 48, pp. 3244-3266. Summary of the invention

[0009] Problems to be solved by the invention

[0010] New recording media using nonlinear light absorbing materials are needed.

[0011] Means for solving problems

[0012] A recording medium in one aspect of the present disclosure includes a recording layer including a polymer including a group having nonlinear light absorption characteristics and having a glass transition temperature of 200° C. or higher.

[0013] Effects of the Invention

[0014] The present disclosure provides a novel recording medium using a nonlinear light absorbing material. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional view showing a schematic structure of a recording medium according to one embodiment of the present disclosure.

[0016] Figure 2A It is a flowchart related to the method of recording information using the recording medium according to one embodiment of the present disclosure.

[0017] Figure 2B This is a flowchart related to a method of reading information using a recording medium according to an embodiment of the present disclosure.

[0018] Figure 3 It is a graph showing the recording and reproducing characteristics of the recording media of the embodiment and the comparative example. DETAILED DESCRIPTION

[0019] (Insights that form the basis of this disclosure)

[0020] In a recording medium including a plurality of recording layers, when the single-photon absorption of light used for recording or reading information is large in each recording layer, the intensity of light decreases as the light passes through each recording layer. In this case, in a recording layer arranged at a position far from the light source, there is a tendency that the sensitivity of recording and reading is greatly reduced. Therefore, a recording layer with a small single-photon absorption for light used for recording or reading information is required. In this specification, reading of information is sometimes referred to as reproduction of information. Single-photon absorption is sometimes referred to as linear light absorption.

[0021] In order to further increase the number of recording layers in a recording medium, it is necessary to reduce the linear light absorption of each recording layer so as to minimize the influence of recording layers other than the recording layer to be recorded or reproduced. In order to reduce the linear light absorption of each recording layer, research has been conducted on a recording layer containing a pigment having almost no linear light absorption band for light used for recording or reproduction and having a nonlinear optical effect.

[0022] It should be noted that the so-called nonlinear optical effect means that when a strong light such as a laser is irradiated on a substance, an optical phenomenon that is proportional to the square of the electric field of the irradiated light or a higher order than the square is generated in the substance. As optical phenomena, absorption, reflection, scattering, luminescence, etc. can be listed. As a secondary nonlinear optical effect proportional to the square of the electric field of the irradiated light, second harmonic generation (SHG), Pockels effect, parametric effect, etc. can be listed. As a third-order nonlinear optical effect proportional to the cube of the electric field of the irradiated light, multiphoton absorption such as two-photon absorption, third harmonic generation (THG), Carr effect, etc. can be listed. In particular, with respect to a recording medium including a plurality of recording layers, multiphoton absorption such as two-photon absorption can be utilized. In this specification, multiphoton absorption such as two-photon absorption is sometimes referred to as nonlinear light absorption. Sometimes a material capable of nonlinear light absorption is referred to as a nonlinear light absorption material. Furthermore, nonlinear light absorption is sometimes referred to as nonlinear absorption.

[0023] So far, inorganic materials that can easily prepare single crystals have been developed as nonlinear optical materials. On the other hand, in recent years, the development of nonlinear optical materials formed by organic materials has been expected. Compared with inorganic materials, organic materials not only have a high degree of design freedom, but also have large nonlinear optical constants. Furthermore, for organic materials, nonlinear response is performed at high speed.

[0024] For compounds constituting organic materials, the closer the wavelength used to make electrons transition from the ground state to the lowest singlet excited state is to the excitation wavelength of multiphoton absorption, the more the multiphoton absorption characteristics of the organic material are improved, for example, there is a tendency to achieve a large two-photon absorption cross-sectional area. With respect to recording media, light having the same wavelength as the excitation wavelength of multiphoton absorption is usually used for recording or reproduction. Based on this design guideline, various compounds are synthesized. In this specification, in a compound, the transition of an electron from the ground state to the lowest singlet excited state is sometimes referred to as an S0-S1 transition. It should be noted that the two-photon absorption cross-sectional area is an indicator of the efficiency of two-photon absorption. The unit of the two-photon absorption cross-sectional area is GM (10 - 50 cm 4 ·s·molecule -1 Photon -1 ).

[0025] (Overview of one aspect of the present disclosure)

[0026] A first aspect of the present disclosure relates to a recording medium including a recording layer containing a polymer including a group having nonlinear light absorption characteristics and having a glass transition temperature of 200° C. or higher.

[0027] According to the first aspect, a new recording medium using a nonlinear light absorbing material can be provided.

[0028] In a second aspect of the present disclosure, for example, according to the recording medium pertaining to the first aspect, the transmittance of light having a wavelength of 405 nm in the recording layer may be 95% or more.

[0029] In a third aspect of the present disclosure, for example, according to the recording medium pertaining to the first or second aspect, the refractive index of the recording layer may be 1.65 or more.

[0030] The recording media according to the second to third aspects tend to have good recording and reproducing characteristics.

[0031] In a fourth aspect of the present disclosure, for example, according to the recording medium pertaining to any one of the first to third aspects, the polymer may have at least one selected from a carbazole skeleton and a naphthalene skeleton in a side chain.

[0032] The polymer described in the fourth embodiment easily increases the refractive index and glass transition temperature while maintaining the transmittance of light with a wavelength in the range of 390 nm to 420 nm. The polymer has appropriate solubility in solvents and is therefore easily applicable to a coating method for preparing a recording layer by applying a coating liquid.

[0033] In a fifth aspect of the present disclosure, for example, according to the recording medium pertaining to any one of the first to fourth aspects, the polymer may include at least one selected from a structural unit derived from styrenes and a structural unit derived from stilbenes.

[0034] The polymer described in the fifth embodiment is easy to adjust the transmittance, refractive index and glass transition temperature of light with a wavelength in the range of 390nm to 420nm to high values. The polymer also has the following tendency: it has appropriate solubility in solvents. Furthermore, it is easy to introduce a group having nonlinear light absorption characteristics into the structural unit derived from styrene or stilbene.

[0035] In the sixth aspect of the present disclosure, for example, according to the recording medium involved in any one of the first to fifth aspects, the polymer may contain at least one selected from the structural unit A represented by the following formula (1), the structural unit B represented by the following formula (2), and the structural unit C represented by the following formula (3).

[0036] [Chemical formula number 1]

[0037]

[0038]

[0039] In the formula (1), R1 to R8 independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I, at least one selected from R4 to R8 contains a group having nonlinear light absorption characteristics,

[0040] In the formula (2), R9 to R 16 independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I, and are other groups other than groups having nonlinear light absorption properties,

[0041] In the formula (3), R 17 To R 27 Each of the atoms is independently selected from the group consisting of H, B, C, N, O, F, Si, P, S, Cl, Br and I.

[0042] The polymer described in the sixth embodiment can easily adjust the light transmittance, refractive index and glass transition temperature to high values. The structural unit A imparts nonlinear light absorption characteristics to the polymer.

[0043] In a seventh aspect of the present disclosure, for example, according to the recording medium of the sixth aspect, in the polymer, the number x of the structural units A, the number y of the structural units B, and the number z of the structural units C may satisfy 0.35≤z / (x+y+z).

[0044] According to the polymer described in the seventh aspect, it is easy to adjust the refractive index of the recording layer to 1.65 or more.

[0045] In the eighth aspect of the present disclosure, for example, according to the recording medium involved in the sixth or seventh aspect, in the polymer, the number x of the structural units A, the number y of the structural units B, and the number z of the structural units C may satisfy 0.07≤x / (x+y+z)≤0.65.

[0046] According to the polymer described in the eighth embodiment, it is easy to adjust the refractive index of the recording layer to 1.65 or more. Furthermore, the polymer has the following tendency: it has an appropriate nonlinear light absorption amount. Therefore, the recording medium having the polymer has a tendency to show good recording sensitivity.

[0047] In a ninth aspect of the present disclosure, for example, according to the recording medium of any one of the sixth to eighth aspects, in the formula (1), at least one selected from R4 to R8 is represented by the following formula (4).

[0048] -LR A (4)

[0049] In the formula (4), L is a linking group containing at least one atom selected from C, N, O and S, and R A It is a group having a pyrene skeleton.

[0050] The polymer involved in the ninth embodiment adjusts the light transmittance, refractive index and glass transition temperature to high values ​​and easily achieves good nonlinear light absorption. The polymer also has the following tendency: it has appropriate solubility in solvents. The recording layer having the polymer tends to show good recording and reproducing characteristics and good thermal stability.

[0051] The information recording method according to the tenth aspect of the present disclosure includes: preparing a light source that emits light having a wavelength of 390 nm to 420 nm; and focusing the light from the light source and irradiating the light to the recording layer in the recording medium according to any one of the first to ninth aspects.

[0052] According to the tenth aspect, information can be recorded on the recording medium at a high recording density.

[0053] The information reading method involved in the eleventh scheme of the present disclosure is, for example, a method for reading information recorded using the recording method involved in the tenth scheme, and the reading method includes: irradiating light to the recording layer in the recording medium to thereby measure the optical properties of the recording layer; and reading information from the recording layer.

[0054] According to the eleventh aspect, information can be easily read from the recording medium.

[0055] The composition according to the twelfth aspect of the present disclosure has a polymer including at least one selected from the group consisting of a structural unit A represented by the following formula (1), a structural unit B represented by the following formula (2), and a structural unit C represented by the following formula (3).

[0056] [Chemical formula number 2]

[0057]

[0058]

[0059] In the formula (1), R1 to R8 independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I, at least one selected from R4 to R8 contains a group having nonlinear light absorption characteristics,

[0060] In the formula (2), R9 to R 16independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I, and are other groups other than groups having nonlinear light absorption properties,

[0061] In the formula (3), R 17 To R 27 Each of the atoms is independently selected from the group consisting of H, B, C, N, O, F, Si, P, S, Cl, Br and I.

[0062] According to the twelfth aspect, a novel composition suitable for a material of a recording layer of a recording medium can be provided.

[0063] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0064] (Implementation Method)

[0065] Figure 1 1 is a cross-sectional view showing a schematic structure of a recording medium 100 according to an embodiment of the present disclosure. Figure 1 As shown, the recording medium 100 includes a recording layer 10. The recording layer 10 includes a polymer P. The polymer P includes a group G having a nonlinear light absorption characteristic and has a glass transition temperature of 200°C or more.

[0066] The recording medium 100 may include a plurality of recording layers 10. The plurality of recording layers 10 are arranged, for example, in the thickness direction of the recording medium 100. In the recording medium 100, the number of recording layers 10 is not particularly limited, and is, for example, 2 or more and 1000 or less. The recording medium 100 including the plurality of recording layers 10 functions as a three-dimensional optical storage. A specific example of the recording medium 100 is a three-dimensional optical disc.

[0067] The recording medium 100 further includes, for example, a dielectric layer 20 located between the two recording layers 10. In this specification, the dielectric layer 20 is sometimes referred to as an intermediate layer. The recording medium 100 may include a plurality of dielectric layers 20. In the recording medium 100, the plurality of recording layers 10 and the plurality of dielectric layers 20 may be arranged alternately. In other words, the plurality of recording layers 10 and the plurality of dielectric layers 20 may be alternately stacked. As an example, the plurality of recording layers 10 are each arranged between the two dielectric layers 20 and are directly connected to each of the two dielectric layers 20. In the recording medium 100, the number of the dielectric layers 20 is not particularly limited, and is, for example, greater than 3 and less than 1001. The dielectric layer 20 can function as a dielectric layer, for example.

[0068] [Record layer]

[0069] As described above, the recording layer 10 contains a polymer P. The polymer P contains a group G having nonlinear light absorption characteristics. As an example, the polymer P has the above-mentioned group G in the side chain. Whether the group contained in the polymer P has nonlinear light absorption characteristics can be judged by the following method. First, a compound having the same structure as the group contained in the polymer P is prepared. For the compound, the light absorption characteristics are measured to determine whether it has nonlinear light absorption characteristics. In the case where the compound has nonlinear light absorption characteristics, it can be judged that the group contained in the polymer P also has nonlinear light absorption characteristics. Furthermore, in the case where the polymer P itself has nonlinear light absorption characteristics, it can also be judged that the polymer P contains the group G having nonlinear light absorption characteristics.

[0070] Since the polymer P contains the group G having nonlinear light absorption characteristics, the polymer P functions as a nonlinear light absorbing material. In the recording layer 10 using the nonlinear light absorbing material, the linear light absorption at the recording and reproducing wavelength is small, and there is a tendency to have good recording sensitivity. In the recording layer 10, if the linear light absorption at the recording and reproducing wavelength is small, it is not easy to affect other adjacent recording layers 10 when the recording or reproducing process of the recording medium 100 is performed. In this way, the recording layer 10 containing the polymer P is suitable for the recording medium 100 having a multilayer structure.

[0071] As the group G having nonlinear light absorption characteristics, for example, a group containing at least one selected from a carbon-carbon double bond, a carbon-carbon triple bond and an aromatic ring can be cited. As specific examples of the group G, a group having a pyrene skeleton, a group having a diphenylacetylene skeleton, a group having a stiff-stilbene skeleton, etc. can be cited.

[0072] Specifically, the polymer P contains a structural unit A having the above-mentioned group G. Examples of the structural unit A include a structural unit A1 derived from styrenes and having a group G, a structural unit A2 derived from stilbenes and having a group G, and the like. In this specification, the structural unit A1 is sometimes referred to as a structural unit A1 derived from styrenes. The structural unit A2 is sometimes referred to as a structural unit A2 derived from stilbenes. For example, the polymer P contains at least one structural unit A selected from the structural unit A1 derived from styrenes and the structural unit A2 derived from stilbenes. The polymer P may contain a structural unit A1 derived from styrenes.

[0073] The structural unit A is represented by, for example, the following formula (1).

[0074] [Chemical formula number 3]

[0075]

[0076] In formula (1), R1 to R8 independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I. At least one selected from R4 to R8 contains a group G having nonlinear light absorption characteristics.

[0077] R1 to R8 may be independently a hydrogen atom, a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a group containing an oxygen atom, a group containing a nitrogen atom, a group containing a sulfur atom, a group containing a silicon atom, a group containing a phosphorus atom, or a group containing a boron atom. At least one selected from R4 to R8 may be a group obtained by substituting a group G having nonlinear light absorption characteristics with a hydrocarbon group, a halogenated hydrocarbon group, a group containing an oxygen atom, a group containing a nitrogen atom, a group containing a sulfur atom, a group containing a silicon atom, a group containing a phosphorus atom, or a group containing a boron atom.

[0078] Examples of the halogen atom include F, Cl, Br, and I. In this specification, a halogen atom may be referred to as a halogen group.

[0079] The number of carbon atoms in the hydrocarbon group is not particularly limited, and may be, for example, 1 to 10, 1 to 8, or 1 to 5. The hydrocarbon group may be linear, branched, or cyclic.

[0080] As the hydrocarbon group, an aliphatic saturated hydrocarbon group, an alicyclic hydrocarbon group, an aliphatic unsaturated hydrocarbon group, etc. can be listed. The aliphatic saturated hydrocarbon group can be an alkyl group. As the aliphatic saturated hydrocarbon group, -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CH(CH3)CH2CH3, -C(CH3)3, -CH2CH(CH3)2, -(CH2)3CH3, -(CH2)4CH3, -C(CH2CH3)(CH3)2, -CH2C(CH3)3, -(CH2)5CH3, -(CH2)6CH3, -(CH2)7CH3, -(CH2)8CH3, -(CH2)9CH3, etc. can be listed. As the alicyclic hydrocarbon group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, etc. can be listed. Examples of the aliphatic unsaturated hydrocarbon group include -CH=CH2, -C≡CH, -C≡CCH3, -C(CH3)=CH2, -CH=CHCH3, and -CH2CH=CH2.

[0081] The so-called halogenated hydrocarbon group means a group in which at least one hydrogen atom contained in the hydrocarbon group is replaced by a halogen atom. The halogenated hydrocarbon group may be a group in which all hydrogen atoms contained in the hydrocarbon group are replaced by halogen atoms. Examples of the halogenated hydrocarbon group include halogenated alkyl groups and halogenated alkenyl groups.

[0082] Examples of the halogenated alkyl group include -CF3, -CH2F, -CH2Br, -CH2Cl, -CH2I, and -CH2CF3. Examples of the halogenated alkenyl group include -CH=CHCF3.

[0083] The group containing an oxygen atom is, for example, a substituent having at least one selected from a hydroxyl group, a carboxyl group, an aldehyde group, an ether group, an acyl group, and an ester group.

[0084] Examples of the substituent having a hydroxyl group include the hydroxyl group itself and a hydrocarbon group having a hydroxyl group. Examples of the hydrocarbon group having a hydroxyl group include -CH2OH, -CH(OH)CH3, -CH2CH(OH)CH3, -CH2C(OH)(CH3)2, and the like.

[0085] Examples of the substituent having a carboxyl group include a carboxyl group itself and a hydrocarbon group having a carboxyl group. Examples of the hydrocarbon group having a carboxyl group include -CH2CH2COOH, -C(COOH)(CH3)2, and the like.

[0086] Examples of the substituent having an aldehyde group include an aldehyde group itself and a hydrocarbon group having an aldehyde group. Examples of the hydrocarbon group having an aldehyde group include -CH=CHCHO and the like.

[0087] As a substituent having an ether group, for example, an alkoxy group, a halogenated alkoxy group, an alkenyloxy group, an ethylene oxide group, and a hydrocarbon group having at least one of these functional groups can be listed. At least one hydrogen atom contained in the alkoxy group can be substituted by a group containing at least one atom selected from N, O, P and S. As an alkoxy group, a methoxy group, an ethoxy group, a 2-methoxyethoxy group, a butoxy group, a 2-methylbutoxy group, a 2-methoxybutoxy group, a 4-ethylthiobutoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a nonyloxy group, a decyloxy group, etc. can be listed. As a halogenated alkoxy group, -OCHF2, -OCH2F, -OCH2Cl, etc. can be listed. As an alkenyloxy group, -OCH=CH2, etc. can be listed. As a hydrocarbon group having a functional group such as an alkoxy group, -CH2OCH3, -C(OCH3)3, 2-methoxybutyl group, 6-methoxyhexyl group, etc. can be listed.

[0088] Examples of the substituent having an acyl group include an acyl group itself and a hydrocarbon group having an acyl group. Examples of the acyl group include -COCH3 and the like. Examples of the hydrocarbon group having an acyl group include -CH=CHCOCH3 and the like.

[0089] As the substituent having an ester group, for example, an alkoxycarbonyl group, an acyloxy group, and a hydrocarbon group having at least one of these functional groups can be cited. As the alkoxycarbonyl group, -COOCH3, -COO(CH2)3CH3, -COO(CH2)7CH3, etc. can be cited. As the acyloxy group, -OCOCH3, etc. can be cited. As the hydrocarbon group having a functional group such as an acyloxy group, -CH2OCOCH3, etc. can be cited.

[0090] The group containing a nitrogen atom is, for example, a substituent having at least one selected from an amino group, an imino group, a cyano group, an amide group, a carbamate group, a nitro group, a cyanamide group, an isocyanate group, and an oxime group.

[0091] As a substituent having an amino group, for example, a primary amino group, a secondary amino group, a tertiary amino group, and a hydrocarbon group having at least one of these functional groups can be listed. As a tertiary amino group, -N(CH3)2 can be listed. As a hydrocarbon group having a functional group such as a primary amino group, -CH2NH2, -CH2N(CH3)2, -(CH2)4N(CH3)2, etc. can be listed.

[0092] Examples of the substituent having an imino group include the imino group itself and a hydrocarbon group having an imino group. Examples of the imino group include -N=CCl2 and the like.

[0093] Examples of the substituent having a cyano group include a cyano group itself and a hydrocarbon group having a cyano group. Examples of the hydrocarbon group having a cyano group include -CH2CN, -CH=CHCN, and the like.

[0094] As a substituent having an amide group, for example, an amide group itself and a hydrocarbon group having an amide group can be listed. As an amide group, -CONH2, -NHCHO, -NHCOCH3, -NHCOCF3, -NHCOCH2Cl, -NHCOCH(CH3)2, etc. can be listed. As a hydrocarbon group having an amide group, -CH2CONH2, -CH2NHCOCH3, etc. can be listed.

[0095] Examples of the substituent having a carbamate group include a carbamate group itself and a hydrocarbon group having a carbamate group. Examples of the carbamate group include -NHCOOCH3, -NHCOOCH2CH3, and -NHCO2(CH2)3CH3.

[0096] Examples of the substituent having a nitro group include the nitro group itself and a hydrocarbon group having a nitro group. Examples of the hydrocarbon group having a nitro group include -C(NO2)(CH3)2 and the like.

[0097] Examples of the substituent having a cyanamide group include a cyanamide group itself and a hydrocarbon group having a cyanamide group. The cyanamide group is represented by -NHCN.

[0098] Examples of the substituent having an isocyanate group include an isocyanate group itself and a hydrocarbon group having an isocyanate group. The isocyanate group is represented by -N=C=O.

[0099] Examples of the substituent having an oxime group include an oxime group itself and a hydrocarbon group having an oxime group. The oxime group is represented by -CH=NOH.

[0100] The group containing a sulfur atom is, for example, a substituent having at least one selected from a thiol group, a thioether group, a sulfinyl group, a sulfonyl group, a sulfinyl group, a sulfonic acid group, an acylthio group, a sulfinamide group, a sulfonamide group, a thioamide group, a thiourea group and a thiocyanate group.

[0101] Examples of the substituent having a thiol group include a thiol group itself and a hydrocarbon group having a thiol group. A thiol group is represented by -SH.

[0102] As a substituent having a thioether group, for example, an alkylthio group, an alkyldisulfide group, an alkenylthio group, an alkynylthio group, a thiirane group, and a hydrocarbon group having at least one of these functional groups can be listed. At least one hydrogen atom contained in the alkylthio group can be substituted by a halogen group. As an alkylthio group, -SCH3, -S(CH2)F, -SCH(CH3)2, -SCH2CH3, etc. can be listed. As an alkyldisulfide group, -SSCH3, etc. can be listed. As an alkenylthio group, -SCH=CH2, -SCH2CH=CH2, etc. can be listed. As an alkynylthio group, -SC≡CH, etc. can be listed. As a hydrocarbon group having a functional group such as an alkylthio group, -CH2SCF3, etc. can be listed.

[0103] Examples of the substituent having a sulfinyl group include a sulfinyl group itself and a hydrocarbon group having a sulfinyl group. Examples of the sulfinyl group include -SOCH3 and the like.

[0104] As the substituent having a sulfonyl group, for example, a sulfonyl group itself and a hydrocarbon group having a sulfonyl group can be listed. As the sulfonyl group, -SO2CH3 can be listed. As the hydrocarbon group having a sulfonyl group, -CH2SO2CH3, -CH2SO2CH2CH3, etc. can be listed.

[0105] Examples of the substituent having a sulfinyl group include a sulfinyl group itself and a hydrocarbon group having a sulfinyl group.

[0106] Examples of the substituent having a sulfonic acid group include a sulfonic acid group itself and a hydrocarbon group having a sulfonic acid group.

[0107] Examples of the substituent having an acylthio group include an acylthio group itself and a hydrocarbon group having an acylthio group. Examples of the acylthio group include -SCOCH3 and the like.

[0108] Examples of the substituent having a sulfinamide group include a sulfinamide group itself and a hydrocarbon group having a sulfinamide group. Examples of the sulfinamide group include -SN(CH3)2 and the like.

[0109] Examples of the substituent having a sulfonamide group include the sulfonamide group itself and a hydrocarbon group having a sulfonamide group. Examples of the sulfonamide group include -SO2NH2, -NHSO2CH3, and the like.

[0110] Examples of the substituent having a thioamide group include a thioamide group itself and a hydrocarbon group having a thioamide group. Examples of the thioamide group include -NHCSCH3 and the like.

[0111] Examples of the substituent having a thiourea group include a thiourea group itself and a hydrocarbon group having a thiourea group. Examples of the thiourea group include -NHCSNHCH2CH3 and the like.

[0112] Examples of the substituent having a thiocyanate group include a thiocyanate group itself and a hydrocarbon group having a thiocyanate group. Examples of the hydrocarbon group having a thiocyanate group include -CH2SCN and the like.

[0113] The group containing a silicon atom is, for example, a substituent having at least one selected from a silyl group and a siloxy group.

[0114] As a substituent having a silyl group, a silyl group itself and a hydrocarbon group having a silyl group can be listed. As a silyl group, -Si(CH3)3, -SiH(CH3)2, -Si(OCH3)3, -Si(OCH2CH3)3, -SiCH3(OCH3)2, -Si(CH3)2OCH3, -Si(N(CH3)2)3, -SiF(CH3)2, -Si(OSi(CH3)3)3, -Si(CH3)2OSi(CH3)3, etc. can be listed. As a hydrocarbon group having a silyl group, -(CH2)2Si(CH3)3, etc. can be listed.

[0115] Examples of the substituent having a silyloxy group include the silyloxy group itself and a hydrocarbon group having a silyloxy group. Examples of the hydrocarbon group having a silyloxy group include -CH2OSi(CH3)3 and the like.

[0116] The group containing a phosphorus atom is, for example, a substituent having at least one selected from a phosphine group and a phosphono group.

[0117] As a substituent having a phosphino group, for example, a phosphino group itself and a hydrocarbon group having a phosphino group can be listed. As a phosphino group, -PH2, -P(CH3)2, -P(CH2CH3)2, -P(C(CH3)3)2, -P(CH(CH3)2)2, etc. can be listed.

[0118] Examples of the substituent having a phosphonyl group include a phosphonyl group itself and a hydrocarbon group having a phosphonyl group. Examples of the hydrocarbon group having a phosphonyl group include -CH2PO(OCH2CH3)2 and the like.

[0119] The group containing a boron atom is, for example, a substituent having a boronic acid group. Examples of the substituent having a boronic acid group include a boronic acid group itself and a hydrocarbon group having a boronic acid group.

[0120] When the group G having nonlinear light absorption characteristics is bonded to the benzene ring adjacent to R4 to R8 in at least one selected from R4 to R8, the conjugated system of the group G is sometimes extended and its electronic state changes. Therefore, a linking group such as an alkylene group may be provided between the group G and the benzene ring adjacent to R4 to R8.

[0121] In formula (1), at least one selected from R4 to R8 can be represented by the following formula (4).

[0122] -LR A (4)

[0123] In formula (4), L is a linking group containing at least one atom selected from C, N, O and S. For example, L does not contain a bond that affects the conjugated system, such as a carbon-carbon double bond. L may contain an ether group or may be -CH2-O-CH2-. L may be an alkylene group.

[0124] R A For example, the group G having nonlinear light absorption characteristics may be a group having a pyrene skeleton. A It can be represented by the following formula (4A).

[0125] [Chemical formula number 4]

[0126]

[0127] In formula (4A), R 28 To R 37 Each of the atoms R comprises independently at least one atom selected from the group consisting of H, B, C, N, O, F, Si, P, S, Cl, Br and I. 28 To R 37 One of them is bonded to L of the above formula (4). L of formula (4) is in R 28 To R 37 At one position in the pyrene ring, it can be directly bonded to the pyrene ring represented by the formula (4A).

[0128] R 28 To R 37They may be independently hydrogen atoms, halogen atoms, hydrocarbon groups, halogenated hydrocarbon groups, groups containing oxygen atoms, groups containing nitrogen atoms, groups containing sulfur atoms, groups containing silicon atoms, groups containing phosphorus atoms, or groups containing boron atoms. As these groups, those groups described above for R1 to R8 may be cited.

[0129] Specific examples of the structural unit A include structural unit A-1 represented by the following formula (A-1).

[0130] [Chemical formula number 5]

[0131]

[0132] The content of the structural unit A in the polymer P is, for example, 5 mol% or more, 7 mol% or more, 10 mol% or more, 15 mol% or more, or 20 mol% or more. The upper limit of the content of the structural unit A is not particularly limited, and is, for example, 65 mol%.

[0133] The polymer P may further include other structural units other than the above-mentioned structural unit A. As other structural units, there can be listed structural units B1 derived from styrenes and not having the above-mentioned group G, structural units B2 derived from stilbenes and not having the group G, etc. In this specification, structural unit B1 is sometimes referred to as structural unit B1 derived from styrenes. Structural unit B2 is sometimes referred to as structural unit B2 derived from stilbenes. For example, the polymer P includes at least one structural unit B selected from structural units B1 derived from styrenes and structural units B2 derived from stilbenes. The polymer P may include structural unit B1 derived from styrenes.

[0134] The structural unit B is represented by, for example, the following formula (2).

[0135] [Chemical formula number 6]

[0136]

[0137] In formula (2), R9 to R 16 They independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I, and are other groups other than the group G having nonlinear light absorption characteristics.

[0138] R9 to R 16 They may be independently hydrogen atoms, halogen atoms, hydrocarbon groups, halogenated hydrocarbon groups, groups containing oxygen atoms, groups containing nitrogen atoms, groups containing sulfur atoms, groups containing silicon atoms, groups containing phosphorus atoms, or groups containing boron atoms. As these groups, those groups described above for R1 to R8 may be cited.

[0139] Selected from R 12 To R 16 At least one of the above may contain a leaving group or a polar functional group that can be used in a nucleophilic substitution reaction. As the leaving group, a halogen group or the like can be listed. As the polar functional group, a hydroxyl group, an amino group, a thiol group or the like can be listed.

[0140] Specific examples of the structural unit B include structural units B-1 represented by the following formula (B-1) to structural units B-8 represented by the following formula (B-8).

[0141] [Chemical formula number 7]

[0142]

[0143] The content of the structural unit B in the polymer P is not particularly limited, and is, for example, 70 mol% or less, 60 mol% or less, 50 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, or 10 mol% or less. The lower limit of the content of the structural unit B is not particularly limited, and is, for example, 1 mol%.

[0144] The polymer P may have at least one selected from a carbazole skeleton and a naphthalene skeleton in the side chain. In other words, the polymer P may contain a structural unit C having at least one selected from a carbazole skeleton and a naphthalene skeleton in the side chain as other structural units other than the structural unit A. Furthermore, in the polymer P, the carbazole skeleton or the naphthalene skeleton may be contained in the main chain. However, the polymer P containing the carbazole skeleton or the naphthalene skeleton in the main chain sometimes shows single-photon absorption characteristics to light with a wavelength in the range of 390nm to 420nm.

[0145] The structural unit C is represented by, for example, the following formula (3).

[0146] [Chemical formula number 8]

[0147]

[0148] In formula (3), R 17 To R 27 Each of the atoms is independently selected from the group consisting of H, B, C, N, O, F, Si, P, S, Cl, Br and I.

[0149] R 17 To R 27They may be independently hydrogen atoms, halogen atoms, hydrocarbon groups, halogenated hydrocarbon groups, groups containing oxygen atoms, groups containing nitrogen atoms, groups containing sulfur atoms, groups containing silicon atoms, groups containing phosphorus atoms, or groups containing boron atoms. As these groups, those groups described above for R1 to R8 may be cited.

[0150] Specific examples of the structural unit C include structural units C-1 represented by the following formula (C-1) to structural units C-17 represented by the following formula (C-17).

[0151] [Chemical formula number 9]

[0152]

[0153]

[0154] The content of the structural unit C in the polymer P is not particularly limited, and may be, for example, 10 mol% or more, 35 mol% or more, 50 mol% or more, 70 mol% or more, or 90 mol% or more. The upper limit of the content of the structural unit C is not particularly limited, and may be, for example, 95 mol%.

[0155] The polymer P includes, for example, at least one selected from the structural unit A represented by the formula (1), the structural unit B represented by the formula (2), and the structural unit C represented by the formula (3). The polymer P may include the structural units A to C. As an example, the polymer P may be a random copolymer represented by the following formula (5).

[0156] [Chemical formula number 10]

[0157]

[0158] In formula (5), R1 to R 27 The same groups as those described above for formula (1), formula (2) and formula (3). x, y and z are independently any integers.

[0159] In the polymer P, the number x of the structural units A, the number y of the structural units B, and the number z of the structural units C may satisfy 0.35≤z / (x+y+z), and may satisfy 0.07≤x / (x+y+z)≤0.65.

[0160] As mentioned above, polymer P is typically a random copolymer. However, polymer P may be a block copolymer, a graft copolymer, or the like.

[0161] Specific examples of the polymer P include a random copolymer P1 represented by the following formula (P1).

[0162] [Chemical formula number 11]

[0163]

[0164] In formula (P1), x, y and z are independently any integers.

[0165] As described above, the glass transition temperature of the polymer P is 200°C or higher. The polymer P having such a high glass transition temperature is thermally stable. The recording layer 10 including the polymer P has a tendency to suppress changes in the shape of the recording mark formed by irradiation with light. That is, according to the polymer P, there is a tendency to improve the stability of the shape of the recording mark. On the other hand, if the glass transition temperature of the polymer P is too high, the recording sensitivity of the recording layer 10 is sometimes reduced. Therefore, from the viewpoint of balancing thermal stability and recording sensitivity, the glass transition temperature of the polymer P is, for example, 200°C or higher and 300°C or lower. The glass transition temperature of the polymer P may be 200°C or higher and 250°C or lower.

[0166] The glass transition temperature of polymer P can be determined by the following method. First, thermogravimetric-differential thermal (TG-DTA) measurement is performed on polymer P under the following conditions to prepare a DTA curve. The glass transition temperature can be determined from the inflection point of heat capacity in the DTA curve.

[0167] ·Measurement conditions

[0168] Atmosphere: Nitrogen atmosphere

[0169] Measuring range: 25℃ to 400℃

[0170] Heating speed: 15℃ / min

[0171] When the weight average molecular weight of the polymer P is large to a certain extent, there is a tendency that the recording layer 10 can be easily formed. On the other hand, if the weight average molecular weight of the polymer P is too large, the solubility of the polymer P decreases, and it is sometimes difficult to form the recording layer 10 by a coating method. Therefore, the weight average molecular weight of the polymer P can be 4000 or more and 100000 or less. The weight average molecular weight of the polymer P can be 4000 or more and 50000 or less.

[0172] As for polymer P, for example, the transmittance, refractive index and glass transition temperature of the light with wavelength in the range of 390nm to 420nm are high. In particular, the polymer P having a carbazole skeleton or a naphthalene skeleton in the side chain is easy to adjust the transmittance, refractive index and glass transition temperature to be high. However, there is a tendency that it is difficult to bond the group G with nonlinear light absorption characteristics for the carbazole skeleton or the naphthalene skeleton. Therefore, in the case of synthesizing polymer P, as a precursor polymer, a copolymer of vinyl carbazole and styrene, a copolymer of vinyl carbazole and stilbene, a copolymer of naphthalene and styrene, a copolymer of naphthalene and stilbene, etc. can be utilized. In these copolymers, by introducing a group G with nonlinear light absorption characteristics in the structural unit from styrene or stilbene, polymer P can be synthesized simply. Styrene and stilbene can not only easily bond with the group G with nonlinear light absorption characteristics, but also moderately have reactivity for copolymerization. The polymer P including a structural unit derived from styrenes or stilbenes has excellent transmittance of light having a wavelength in the range of 390 nm to 420 nm, and tends to have a high refractive index and a high glass transition temperature.

[0173] There is no particular limitation on the synthesis method of polymer P. Polymer P can be synthesized by reacting a nonlinear light absorbing pigment to a precursor polymer. Polymer P can be synthesized by preparing a monomer containing a group G having nonlinear light absorption characteristics in advance and polymerizing a monomer group containing the monomer. As a reaction for bonding a precursor polymer to a nonlinear light absorbing pigment, a nucleophilic substitution reaction in which a leaving group reacts with a polar functional group, a cross-coupling reaction using a transition metal catalyst, etc. can be utilized. As a leaving group, a halogen group, etc. can be listed. As a polar functional group, a hydroxyl group, an amino group, a thiol group, etc. can be listed. As an example, polymer P can be synthesized by reacting a precursor polymer containing a structural unit from styrene or stilbene and having a leaving group with a nonlinear light absorbing pigment with a polar functional group. Polymer P can also be synthesized by reacting a precursor polymer containing a structural unit from styrene or stilbene and having a polar functional group with a nonlinear light absorbing pigment with a leaving group.

[0174] An example of a method for synthesizing the random copolymer P1 is described below. First, vinyl carbazole and 4-chloromethylstyrene are copolymerized using a free radical initiator to synthesize a precursor polymer. This reaction is represented by the following reaction formula.

[0175] [Chemical formula number 12]

[0176]

[0177] There is a tendency that, in the above-mentioned precursor polymer, the more the number z of the structural unit derived from vinyl carbazole is, the higher the refractive index and glass transition temperature are, and the lower the solubility in the solvent is. Therefore, the composition of the precursor polymer can be appropriately adjusted according to the target refractive index, glass transition temperature and solubility. The composition of the precursor polymer can be controlled, for example, by the ratio of the feed amount of vinyl carbazole and 4-chloromethylstyrene.

[0178] Secondly, the precursor polymer is reacted with a pyrene derivative, i.e., 1-hydroxymethylpyrene, which functions as a nonlinear light absorbing pigment. For this reaction, a base can be used as required. Thus, the chlorine atom of the structural unit from 4-chloromethylstyrene is replaced by the polar functional group, i.e., the hydroxyl group, in the nonlinear light absorbing pigment, to obtain a random copolymer P1.

[0179] [Chemical formula number 13]

[0180]

[0181] The random copolymer P1 is soluble in solvents such as chlorobenzene and THF. Therefore, the recording layer 10 can be easily produced by preparing a coating solution containing the random copolymer P1 and forming a film by spin coating or the like.

[0182] The recording layer 10 contains, for example, a polymer P as a main component. The so-called "main component" means a component that is contained in the largest amount by weight in the recording layer 10. The recording layer 10 is, for example, substantially formed of the polymer P. "Substantially formed of..." means that other components that change the essential characteristics of the material mentioned are excluded. However, the recording layer 10 may contain impurities in addition to the polymer P.

[0183] The recording layer 10 is a thin film having a thickness of, for example, 1 nm or more and 100 μm or less. However, the thickness of the recording layer 10 may exceed 100 μm.

[0184] The transmittance of the recording layer 10 at a wavelength of 405 nm is, for example, 90% or more, 95% or more, or 99% or more. The higher the transmittance at a wavelength of 405 nm, the smaller the linear light absorption of the recording layer 10 at this wavelength, and the better the recording sensitivity.

[0185] The above transmittance can be measured by using the recording layer 10 itself as a measurement sample and adopting a method specified in JIS K0115:2004. Specifically, first, light having a wavelength of 405 nm is irradiated to the recording layer 10. The irradiation of light is performed in a manner that the light travels in the thickness direction of the recording layer 10. As a light source, a light source that irradiates light with a photon density that hardly causes nonlinear light absorption by the polymer P is used. Next, the absorbance A of the recording layer 10 at a wavelength of 405 nm is read from the light that has passed through the recording layer 10. Based on the absorbance A, the transmittance T of the light of a wavelength of 405 nm in the recording layer 10 can be calculated according to the following formula (I).

[0186] Transmittance T = 10 (-A) (I)

[0187] It should be noted that in the above measurement, when the recording layer 10 is a thin film, the absorbance A may not be accurately measured due to interference of the film. In this case, the transmittance can be calculated by measuring the extinction coefficient using an ellipsometer. The material of the recording layer 10 can be dissolved in an appropriate solvent, and the transmittance can be calculated using the absorbance value measured in the state of the solution.

[0188] The refractive index of the recording layer 10 may be greater than 1.65, greater than 1.68, or greater than 1.70. The higher the refractive index of the recording layer 10, the easier it is to increase the difference in refractive index with the adjacent dielectric layer 20. When the difference in refractive index between the recording layer 10 and the dielectric layer 20 is large, the reflectivity of light at the interface between the recording layer 10 and the dielectric layer 20 increases. When the reflectivity of light at the above-mentioned interface is high, there is a tendency that a good reproduced signal can be obtained from the recording medium 100. There is no particular limitation on the upper limit of the refractive index of the recording layer 10, and for example, it is 1.90. In this specification, the refractive index of the recording layer 10 is a value for light of a wavelength of 405 nm, and can be measured using an ellipsometer.

[0189] The above-mentioned group G with nonlinear light absorption characteristics has small linear light absorption at the recording and reproducing wavelength, and can have an appropriate nonlinear light absorption amount. For example, when a laser with a wavelength of 405nm is used for recording and reproducing, the two-photon absorption cross-sectional area of ​​the group G with nonlinear light absorption characteristics can exceed 1GM, can be more than 10GM, can be more than 20GM, can be more than 100GM. There is no particular limitation on the upper limit of the two-photon absorption cross-sectional area, for example, it is 1000GM. The two-photon absorption cross-sectional area can be measured by using a compound having the same structure as the group G with nonlinear light absorption characteristics as a measurement sample, for example, using the Z scanning method described in J.Opt.Soc.Am.B, 2003, Volume 20, Page 529. The Z scanning method is widely used as a method for measuring nonlinear optical constants. In the Z scanning method, the measurement sample is moved along the irradiation direction of the beam near the focus of the laser beam. At this time, the change in the amount of light of the light transmitted through the measurement sample is recorded. In the Z scanning method, the power density of the incident light changes according to the position of the measurement sample. Therefore, when the measurement sample performs nonlinear light absorption, if the measurement sample is located near the focus of the laser beam, the amount of transmitted light attenuates. The two-photon absorption cross-sectional area can be calculated by fitting the change in the amount of transmitted light to the theoretical curve predicted by the intensity of the incident light, the thickness of the measurement sample, the concentration of the compound in the measurement sample, etc. As an example, the two-photon absorption cross-sectional area of ​​pyrene derivatives is about 50GM to 300GM.

[0190] The two-photon absorption cross-sectional area may be a calculated value based on computational chemistry. Several methods for estimating the two-photon absorption cross-sectional area based on computational chemistry have been proposed. For example, based on the quadratic nonlinear response theory described in J. Chem. Theory Comput. 2018, Vol. 14, p. 807, the calculated value of the two-photon absorption cross-sectional area can be calculated.

[0191] The group G having nonlinear light absorption characteristics can utilize the nonlinear light absorption phenomenon caused by excited state absorption.

[0192] Furthermore, with regard to existing recording layer, usually, nonlinear light absorption pigment as low molecular compound is dispersed in resin. Through such formation, nonlinear light absorption pigment sometimes diffuses from recording layer to other layers such as dielectric layer. And then, when making recording medium, when utilizing coating method that dielectric layer is made on recording layer, pigment sometimes also dissolves from recording layer. Dissolving of pigment is particularly remarkable when the molecular weight of pigment is little.

[0193] In the present embodiment, as far as the recording layer 10 is concerned, the polymer P contains a group G having nonlinear light absorption characteristics. The polymer P has a tendency to be difficult to diffuse from the recording layer 10 to the dielectric layer 20, etc. That is, in the present embodiment, the diffusion of the polymer P that functions as a nonlinear light absorption material is suppressed. As a result, for example, there is a tendency that the stability of the intensity of the reflected light at the interface between the recording layer 10 and the dielectric layer 20 is improved. Therefore, as far as the recording medium 100 is concerned, the performance of recording and reading information is high, and the performance can be easily maintained. In the present embodiment, even in the case where the dielectric layer 20 is made on the recording layer 10 by a coating method, there is a tendency that the polymer P is difficult to dissolve. Therefore, in the present embodiment, a simple coating process is adopted to make the recording medium 100 with a multilayer structure.

[0194] [Dielectric layer]

[0195] The dielectric layer 20 is made of a material having a suitable refractive index difference with the recording layer 10 and having a high light transmittance at the recording and reading wavelength. The interlayer distance between the recording layers 10 can be appropriately adjusted by adjusting the thickness of the dielectric layer 20 .

[0196] The difference in refractive index between the recording layer 10 and the dielectric layer 20 is, for example, about 0.2. When the refractive index of the recording layer 10 is represented by n1 and the refractive index of the dielectric layer 20 is represented by n2, it is known that the reflectivity at the interface between the recording layer 10 and the dielectric layer 20 is ((n2-n1) / (n2+n1)) 2 That is, when the refractive index of the recording layer 10 is 1.65 and the refractive index of the dielectric layer 20 is 1.45, the reflectivity of the interface between these layers is about 0.004.

[0197] The dielectric layer 20 includes, for example, a polymer material. Generally, the refractive index of the polymer material used in the dielectric layer 20 is about 1.4 to 1.6, and particularly about 1.45 to 1.5. Therefore, when the refractive index of the recording layer 10 is higher than 1.65, it is easy to adjust the refractive index difference with the dielectric layer 20 to about 0.1 to 0.2. By adjusting the refractive index difference between the recording layer 10 and the dielectric layer 20 to the above range, the intensity of the reflected light at the interface can be increased, and good reproduction characteristics can be obtained.

[0198] Examples of the material of the dielectric layer 20 include cellulose acetate, acrylic resin, and methacrylic resin.

[0199] The thickness of the dielectric layer 20 is not particularly limited, and is, for example, 5 nm or more and 100 μm or less. However, the thickness of the dielectric layer 20 may exceed 100 μm.

[0200] [Method for producing recording medium]

[0201] The recording medium 100 can be produced, for example, by the following method: First, a resin material containing a polymer P is mixed with a solvent to produce a coating solution. The coating solution is applied to a substrate by spin coating or the like, and the obtained coating film is dried to produce a thin film recording layer 10.

[0202] Next, the dielectric layer 20 is formed on the recording layer 10. When the dielectric layer 20 includes a resin material, first, the resin material is mixed with a solvent to prepare a coating liquid. The coating liquid is applied to the recording layer 10 by a spin coating method or the like, and the obtained coating film is dried to prepare the dielectric layer 20. In addition, the coating liquid may include a photosensitive monomer, etc., and the dielectric layer 20 may be prepared by polymerizing the monomer by light or heat. The dielectric layer 20 may be prepared by pre-preparing a thin film that functions as the dielectric layer 20 and bonding the thin film to the recording layer 10. The recording medium 100 may be obtained by alternately preparing a plurality of recording layers 10 and a plurality of dielectric layers 20 as needed.

[0203] [How to use the recording medium]

[0204] The recording medium 100 of this embodiment uses light having a wavelength in a short wavelength range, for example. As an example, the recording medium 100 uses light having a wavelength of 390 nm or more and 420 nm or less. The light used in the recording medium 100 has a high photon density near its focus, for example. The power density near the focus of the light used in the recording medium 100 is, for example, 0.1 W / cm 2 Above and 1.0×10 20 W / cm 2 The power density near the focus of the light can be 1.0W / cm 2 Above, can be 1.0×10 2 W / cm 2 Above, can be 1.0×10 5 W / cm 2 As the light source used in the recording medium 100 , for example, a femtosecond laser such as a titanium sapphire laser or a pulse laser having a pulse width of picoseconds to nanoseconds such as a semiconductor laser can be used.

[0205] Next, a method of recording information using the recording medium 100 will be described. Figure 2AThis is a flowchart related to a method for recording information using a recording medium 100. First, in step S11, a light source that emits light with a wavelength of more than 390nm and less than 420nm is prepared. As the light source, for example, a femtosecond laser such as a titanium sapphire laser or a pulse laser such as a semiconductor laser with a pulse width of picoseconds to nanoseconds can be used. Secondly, in step S12, the light from the light source is focused by a lens or the like, and irradiated onto the recording layer 10 in the recording medium 100. In detail, the light from the light source is focused by a lens or the like, and irradiated onto the recording area in the recording medium 100. There is no particular restriction on the NA (numerical aperture) of the lens used for light focusing. As an example, a lens with an NA in the range of more than 0.8 and less than 0.9 can be used. The power density near the focus of the light is, for example, 0.1W / cm 2 Above and 1.0×10 20 W / cm 2 The power density near the focus of the light can be 1.0W / cm 2 Above, can be 1.0×10 2 W / cm 2 Above, can be 1.0×10 5 W / cm 2 In this specification, the recording area refers to a site that exists in the recording layer 10 and can record information by irradiating light.

[0206] In the above-mentioned recording area irradiated with light, physical changes or chemical changes occur, thereby changing the optical characteristics of the recording area. For example, the intensity of light reflected in the recording area, the reflectivity of light in the recording area, the absorptivity of light in the recording area, the refractive index of light in the recording area, the intensity of fluorescent light emitted from the recording area, the wavelength of fluorescent light, etc. change. As an example, the intensity of light reflected in the recording area or the intensity of fluorescent light emitted from the recording area decreases. As a result, information can be recorded in the recording layer 10, more specifically, in the recording area (step S13).

[0207] Next, a method of reading information using the recording medium 100 will be described. Figure 2BThis is a flowchart related to a method for reading information using a recording medium 100. First, in step S21, the recording layer 10 in the recording medium 100 is irradiated with light. Specifically, the recording area in the recording medium 100 is irradiated with light. The light used in step S21 may be the same as or different from the light used to record information in the recording medium 100. Next, in step S22, the optical properties of the recording layer 10 are measured. Specifically, the optical properties of the recording area are measured. In step S22, for example, as the optical properties of the recording area, the intensity of light reflected in the recording area or the intensity of fluorescent light emitted from the recording area is measured. In step S22, as the optical properties of the recording area, the reflectivity of light in the recording area, the absorptivity of light in the recording area, the refractive index of light in the recording area, the wavelength of fluorescent light emitted from the recording area, etc. can be measured. Next, in step S23, information is read from the recording layer 10, specifically, from the recording area.

[0208] In the information reading method, the recording area where information is recorded can be found by the following method. First, light is irradiated to a specific area of ​​the recording medium. The light may be the same as or different from the light used to record information on the recording medium. Secondly, the optical characteristics of the area irradiated with light are measured. As optical characteristics, for example, the intensity of light reflected in the area, the reflectivity of light in the area, the absorptivity of light in the area, the refractive index of light in the area, the intensity of fluorescent light emitted from the area, the wavelength of fluorescent light emitted from the area, etc. can be listed. Based on the measured optical characteristics, it is determined whether the area irradiated with light is a recording area. For example, when the intensity of light reflected in the area is below a specific value, it is determined that the area is a recording area. On the other hand, when the intensity of light reflected in the area exceeds a specific value, it is determined that the area is not a recording area. In addition, the method for determining whether the area irradiated with light is a recording area is not limited to the above method. For example, when the intensity of light reflected in the area exceeds a specific value, it can be determined that the area is a recording area. In addition, when the intensity of light reflected in the area is below a specific value, it can be determined that the area is not a recording area. When it is determined that the area is not a recording area, the same operation is performed on other areas of the recording medium. In this way, the recording area can be found.

[0209] The information recording method and reading method using the recording medium 100 can be performed using a known recording device. The recording device includes, for example, a light source for irradiating light to a recording area in the recording medium 100, a measuring device for measuring optical characteristics of the recording area, and a controller for controlling the light source and the measuring device.

[0210] Example

[0211] Hereinafter, the present disclosure will be described in more detail using examples. It should be noted that the following examples are just examples, and the present disclosure is not limited to the following examples.

[0212] First, as materials for the recording layer, the following compounds A to F were prepared. Note that compounds A to E are all random copolymers.

[0213] [Chemical formula number 14]

[0214]

[0215]

[0216] [Chemical formula number 15]

[0217]

[0218]

[0219] [Synthesis of Compounds A and D]

[0220] Compounds A and D were synthesized according to the method described in Macromolecules 2006, 39, 3140-3146, as shown in the following reaction formula. 1 Identification by H-NMR.

[0221] [Chemical formula number 16]

[0222]

[0223] [Synthesis of Compound B]

[0224] First, 1-hydroxymethylpyrene (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in tetrahydrofuran (THF, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and an excess of potassium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and a small amount of N,N-dimethylformamide (DMF, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added, and the mixture was heated to reflux at 80°C for 1 hour under a nitrogen atmosphere. A THF solution of compound A was further added thereto, and the mixture was heated to reflux at 80°C for 48 hours while stirring. The weight of the added compound A was 0.5 times the weight of 1-hydroxymethylpyrene. Secondly, a white precipitate was obtained by adding the reaction solution cooled to room temperature to a large amount of methanol. The obtained solid was recovered by filtration and a washing operation was performed. In the washing operation, ethanol, water and diethyl ether were used in sequence as washing liquids. Compound B was obtained by vacuum drying the solid. Compound B is used 1 Identification by H-NMR.

[0225] [Chemical formula number 17]

[0226]

[0227] [Synthesis of Compound C]

[0228] Compound C was synthesized in the same manner as Compound B, except that the weight of Compound A added was changed to the same value as the weight of 1-hydroxymethylpyrene. 1 Identification by H-NMR.

[0229] [Synthesis of Compound E]

[0230] Compound E was synthesized in the same manner as Compound B, except that Compound D was used instead of Compound A and the weight of Compound D added was changed to the same value as the weight of 1-hydroxymethylpyrene. 1 Identification by H-NMR.

[0231] [Synthesis of Compound F]

[0232] Compound F was synthesized by the same method as Compound A except that N-vinylcarbazole was not used. 1 Identification by H-NMR.

[0233] <Production of recording media>

[0234] [Example 1]

[0235] First, a glass substrate of 20 mm square and 1 mm thickness was prepared. A solution containing compound B was applied by spin coating on the glass substrate. The solution contained chlorobenzene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a solvent. In the solution, the weight ratio of compound B relative to chlorobenzene was 5% by mass. Spin coating was performed under the conditions of 3000 rpm and 30 seconds. Next, a recording layer was prepared by drying the obtained coating film at 80° C. for 30 minutes. Thus, the recording medium of Example 1 was obtained.

[0236] [Example 2]

[0237] A recording medium of Example 2 was prepared in the same manner as in Example 1 except that Compound C was used instead of Compound B.

[0238] [Example 3]

[0239] A recording medium of Example 3 was prepared in the same manner as in Example 1 except that Compound E was used instead of Compound B.

[0240] [Comparative Example 1]

[0241] A recording medium of Comparative Example 1 was prepared in the same manner as in Example 1, except that Compound A was used instead of Compound B and 20% by mass of 1-hydroxymethylpyrene was further added to the solution relative to Compound A. In the recording layer of Comparative Example 1, 1-hydroxymethylpyrene as a nonlinear light absorbing pigment was dispersed in Compound A.

[0242] [Comparative Example 2]

[0243] A recording medium of Comparative Example 2 was prepared in the same manner as in Example 1, except that Compound D was used instead of Compound B and 16% by mass of 1-hydroxymethylpyrene relative to Compound D was further added to the solution. In the recording layer of Comparative Example 2, 1-hydroxymethylpyrene as a nonlinear light absorbing pigment was dispersed in Compound D.

[0244] [Comparative Example 3]

[0245] A recording medium of Comparative Example 3 was prepared in the same manner as in Example 1 except that Compound F was used instead of Compound B.

[0246] <Characteristics Evaluation>

[0247] (1) Evaluation of the transmittance of the recording layer at a wavelength of 405 nm

[0248] For the embodiments and comparative examples, the transmittance of light of wavelength 405 nm in the recording layer was evaluated by the above-mentioned method. Specifically, first, the linear light absorption characteristics of the recording layer were evaluated using a spectrophotometer and an ellipsometer. In the measurement using the spectrophotometer, the baseline was corrected using the measured value obtained when only the glass was measured. The transmittance at a wavelength of 405 nm was calculated from the obtained spectrum. In the recording media of the embodiments and comparative examples, the transmittance of light of wavelength 405 nm in the recording layer was 95% or more.

[0249] In Examples 1 to 3 and Comparative Examples 1 and 2, the recording layer material was dissolved in chlorobenzene to prepare a solution, and the solution was measured using a spectrophotometer. The results showed that the maximum absorption wavelength of linear light absorption was 350 nm in all cases, and there was no absorption band of linear light absorption at a wavelength of 405 nm.

[0250] (2) Evaluation of refractive index

[0251] For the embodiments and comparative examples, the refractive index of the recording layer was evaluated using an ellipsometer. Specifically, the refractive index at a wavelength of 405 nm was read from the spectrum obtained by the measurement. In addition, in Comparative Example 3, the refractive index of the recording layer was as low as 1.63. Therefore, for Comparative Example 3, the following evaluation of recording and reproducing characteristics and evaluation of solvent resistance were not performed.

[0252] As shown in Table 1, in Examples 1 to 3, the refractive index of the recording layer is 1.65 or more. For these recording layers, for example, when a dielectric layer is made on the recording layer, it is easy to greatly adjust the difference in refractive index with the dielectric layer. By greatly adjusting the difference in refractive index, the reflectivity of light at the interface between the recording layer and the dielectric layer can be increased. Thus, it is estimated that a good reproduced signal is obtained from the recording medium.

[0253] (3) Evaluation of glass transition temperature

[0254] The glass transition temperature (Tg) of compounds A to E was evaluated. Specifically, thermogravimetric-differential thermal (TG-DTA) measurement was performed under the following conditions using powdered test samples of compounds A to E. Tg was determined from the inflection point of heat capacity in the DTA curve.

[0255] ·Measurement conditions

[0256] Atmosphere: Nitrogen atmosphere

[0257] Measuring range: 25℃ to 400℃

[0258] Heating speed: 15℃ / min

[0259] As can be seen from Table 1, the glass transition temperatures of the compounds used in Examples 1 to 3 all exceed 200° C. The recording layer containing these compounds is thermally stable, and it is presumed that the shape change of the recording mark formed by light irradiation can be suppressed.

[0260] (4) Evaluation of recording and reproducing characteristics

[0261] [Record operation]

[0262] First, a recording operation was performed on the recording medium of the embodiment and the comparative example. Specifically, the recording medium was irradiated with pulse light having a central wavelength of 405 nm, a peak power of 100 mW, and a repetition frequency of 100 kHz through a lens of NA 0.85. At this time, the recording medium was irradiated with the pulse light while being parallel moved at a speed of 10 μm / second. The pulse width of the pulse light was adjusted between 10 nanoseconds and 1000 nanoseconds.

[0263] [Replay operation]

[0264] Next, a reproducing operation was performed on the recording medium on which the recording operation was performed. Specifically, light having a central wavelength of 405 nm, a peak power of 3 mW, a pulse width of 200 nanoseconds, and a repetition frequency of 100 Hz was irradiated through a lens of NA0.85 in a manner that crossed the recording line of the recording layer, and the intensity of the reflected light signal was obtained. Based on the measurement results, the change rate of the reflected light signal intensity of the portion where the recording operation was performed relative to the reflected light signal intensity of the portion where the recording operation was not performed was calculated. Figure 3 Graphs showing the recording and reproducing characteristics of the recording media of the embodiment and the comparative example. The vertical axis of the graph represents the calculated rate of change, and the horizontal axis represents the average energy of the light irradiation during the recording operation.

[0265] [Evaluation of recording and reproducing characteristics]

[0266] Secondly, from Figure 3 The change rate of the reflected light amount when the average irradiation energy is 0.03 mW is read from the graph, and this change rate is assumed to be the change rate of the reflected light amount when the reproduction light is irradiated. Furthermore, the change rate of the reflected light amount when the average irradiation energy is 0.12 mW is read from the above graph, and this change rate is assumed to be the change rate of the reflected light amount when the recording light is irradiated. These change rates and their differences are shown in Table 2.

[0267] As can be seen from Table 2, in Examples 1 to 3 and Comparative Examples 1 and 2, the change rate of the reflected light amount when the reproduction light was irradiated was 0%, and no significant change in the reflected light amount was found. Furthermore, in Examples 1 and 2 and Comparative Examples 1 and 2, the change rate of the reflected light amount when the recording light was irradiated was more than 0%, and a change was found in the reflected light amount. From this result, it can be seen that in Examples 1 and 2 and Comparative Examples 1 and 2, by using light with an average irradiation energy of 0.03 mW as the reproduction light and light with an average irradiation energy of 0.12 mW as the recording light, the recording and reproducing operation of the recording medium can be performed.

[0268] On the other hand, in Example 3, the change rate of the reflected light amount when the irradiation average energy was 0.12 mW was 0%, and no significant change in the reflected light amount was found. From this result, it can be seen that in the recording medium of Example 3, when light with an irradiation average energy of 0.12 mW is used as recording light, recording and reproducing operations cannot be performed. Figure 3 As can be seen from the graph, by using light with an average irradiation energy of 0.21 mW or more as recording light, it is possible to perform recording and reproducing operations on the recording medium of Example 3.

[0269] (5) Evaluation of solvent resistance

[0270] For the embodiments and comparative examples, the solvent resistance of the recording layer was evaluated by the following method. First, 1 mL of solvent was dripped onto the recording layer and spin coating was performed. As the solvent, diacetone alcohol was used, which was assumed to be a solvent for the coating solution used to make the dielectric layer. The spin coating was performed at 3000 rpm and 30 seconds. Before and after the dripping of the solvent, the absorption spectrum of the recording layer was measured. The measurement of the absorption spectrum was performed by the same method as (1) above. The light absorbance at the maximum absorption wavelength of 350 nm of the nonlinear light absorbing pigment or the group having nonlinear light absorption was read from the obtained spectrum, and the reduction rate of the light absorbance before and after the dripping of the solvent was calculated. The results are shown in Table 3.

[0271] As shown in Table 3, in Comparative Examples 1 and 2 in which the nonlinear light absorbing pigment is dispersed in the polymer binder, the pigment is eluted from the recording layer due to the dripping of the solvent, and the light absorption at the maximum absorption wavelength of the pigment is reduced by 50% to 100%. On the other hand, when the compound B, C or E corresponding to the polymer P containing a group having nonlinear light absorbing characteristics is used in the recording layer, the change in the absorbance at the maximum absorption wavelength before and after the dripping of the solvent is greatly suppressed. This result shows that the solvent resistance of the recording layer is improved by using the polymer P containing a group having nonlinear light absorbing characteristics, and the dissolution of the pigment from the recording layer is suppressed.

[0272] Table 1

[0273]

[0274] Table 2

[0275]

[0276] Table 3

[0277]

[0278] Industrial Applicability

[0279] The recording medium disclosed herein can be used in applications such as three-dimensional optical storage.

[0280] Description of Reference Numerals

[0281] 10 Recording Layer

[0282] 20 Dielectric layer

[0283] 100 Recording medium.

Claims

1. A recording medium comprising a recording layer comprising a polymer containing a group having nonlinear light absorption characteristics and having a glass transition temperature of 200°C or higher.

2. The recording medium according to claim 1, wherein The transmittance of light of a wavelength of 405 nm in the recording layer is 95% or more.

3. The recording medium according to claim 1, wherein The refractive index of the recording layer is greater than or equal to 1.

65.

4. The recording medium according to claim 1, wherein The polymer has at least one selected from a carbazole skeleton and a naphthalene skeleton in a side chain.

5. The recording medium according to claim 1, wherein The polymer includes at least one selected from a structural unit derived from styrenes and a structural unit derived from stilbenes.

6. The recording medium according to claim 1, wherein The polymer comprises at least one selected from the group consisting of a structural unit A represented by the following formula (1), a structural unit B represented by the following formula (2), and a structural unit C represented by the following formula (3), [Chemical formula number 1] In the formula (1), R1 to R8 independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I, at least one selected from R4 to R8 contains a group having nonlinear light absorption characteristics, In the formula (2), R9 to R 16 independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I, and are other groups other than groups having nonlinear light absorption properties, In the formula (3), R 17 To R 27 Each of the atoms is independently selected from the group consisting of H, B, C, N, O, F, Si, P, S, Cl, Br and I.

7. The recording medium according to claim 6, wherein In the polymer, the number x of the structural units A, the number y of the structural units B, and the number z of the structural units C satisfy 0.35≤z / (x+y+z).

8. The recording medium according to claim 6, wherein In the polymer, the number x of the structural units A, the number y of the structural units B, and the number z of the structural units C satisfy 0.07≤x / (x+y+z)≤0.

65.

9. The recording medium according to claim 6, wherein In the formula (1), at least one selected from R4 to R8 is represented by the following formula (4): -L-R A (4) In the formula (4), L is a linking group containing at least one atom selected from C, N, O and S, and R A It is a group having a pyrene skeleton.

10. A method for recording information, comprising: preparing a light source that emits light having a wavelength of 390 nm or more and 420 nm or less; and concentrating the light from the light source and irradiating the light to the recording layer in the recording medium according to any one of claims 1 to 9.

11. A method for reading information, which is a method for reading information recorded by the recording method according to claim 10, the reading method comprising: measuring optical properties of the recording layer by irradiating the recording layer in the recording medium with light; and reading information from the recording layer.

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