Recording medium, method for recording information, method for reading information, and composition for preparing a recording layer

Abstract

The recording medium according to one embodiment of the present disclosure is provided with a recording layer. The recording layer includes: an aliphatic polymer; and a multiphoton absorption compound that has a multiphoton absorption property and that includes at least one selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond. When the thickness of the recording layer is 100 μm, the transmittance of the recording layer in the thickness direction for light having a wavelength of 405 nm is 80% or more.

Description

[Technical Field]

[0001] The present disclosure relates to a recording medium, a method for recording information, a method for reading information, and a composition for making a recording layer. [Background technology]

[0002] Three-dimensional recording, which records information on a multilayer structure, is known as a technology for increasing the recording capacity of optical information recording media. In the field of three-dimensional recording, it is necessary to achieve a finer focused spot in order to improve recording density. In view of the diffraction limit of focused laser light, a laser beam having a short wavelength is used to achieve a finer focused spot. An example of this laser beam is a laser beam having a central wavelength of 405 nm, which is the standard for Blu-ray (registered trademark) discs. Thus, optical information recording media using a laser beam having a central wavelength of 405 nm are known.

[0003] Examples of technologies related to three-dimensional recording include optical information recording media in which photosensitive materials, dyes, etc. are dispersed in a resin, optical information recording media in which cavities or uneven shapes that function as recording marks are arranged in a three-dimensional direction, and optical information recording media in which two light beams interfere to form a diffraction grating and form a tiny hologram inside. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-58283 [Patent Document 2] Patent No. 5929109 [Patent Document 3] Patent No. 6154898 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-261928 Summary of the Invention [Problem to be solved by the invention]

[0005] It is desired to suppress an increase in one-photon absorption of light having a wavelength in the short wavelength region in the recording layer of a recording medium. [Means for solving the problem]

[0006] In one aspect of the present disclosure, a recording medium includes: It has at least one recording layer. The at least one recording layer contains an aliphatic polymer and a multi-photon absorption compound that contains at least one selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond and has multi-photon absorption properties. When the thickness of the at least one recording layer is 100 μm, the transmittance of the at least one recording layer in the thickness direction for light with a wavelength of 405 nm is 80% or more. [Effects of the Invention]

[0007] The present disclosure provides a recording medium having a recording layer in which an increase in one-photon absorption for light having a wavelength in the short wavelength region is suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a recording medium according to an embodiment of the present disclosure. [Figure 2A] FIG. 2A is a flowchart illustrating a method for recording information using a recording medium according to an embodiment of the present disclosure. [Figure 2B] FIG. 2B is a flowchart illustrating a method for reading information using a recording medium according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a graph showing the 1H-NMR spectrum of compound K. [Figure 4] FIG. 4 is a graph showing the 1H-NMR spectrum of compound L. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Findings that formed the basis of this disclosure) Patent Document 1 discloses the production of an optical recording resin layer by heating a mixture of an epoxy compound and a curing agent to polymerize and harden it. Patent Document 1 also discloses the recording of information on an optical recording medium having one optical recording resin layer using a laser beam having a wavelength of 405 nm.

[0010] Patent Document 2 discloses a method for producing a recording layer by heating and curing a mixture of an ethynylbenzophenone compound exhibiting a nonlinear optical absorption effect, an epoxy compound, and a curing agent. In Patent Document 2, the epoxy compound has an aromatic ring. Patent Document 2 also discloses recording information on an optical information recording medium with one recording layer using a laser beam having a wavelength of 405 nm.

[0011] Patent Document 3 discloses a recording layer containing a dye-bound polymer compound in which a polymer compound and a one-photon absorbing dye are bound to each other. Patent Document 3 also discloses recording information on an optical information recording medium having multiple recording layers.

[0012] Patent Document 4 discloses an optical recording resin material in which a photopolymerizable monomer and a photoinitiator are dispersed in an epoxy resin. In Patent Document 4, the optical recording medium having a recording layer made of the optical recording resin material is capable of holographic recording.

[0013] The recording layer of the recording medium is, for example, a thin film made from a resin material in which a photosensitive material, dye molecules, etc. are dispersed. This thin film can be produced, for example, by the following method. First, a resin material containing a polymer is mixed with a solvent to produce a coating liquid. This coating liquid is applied to a substrate by a method such as spin coating, and the resulting coating film is dried to produce a thin film.

[0014] The recording layer of the recording medium may be a thin film prepared by applying a coating liquid in which a photosensitive material, dye molecules, etc. are dispersed in a monomer for forming a resin, and polymerizing the monomer contained in the resulting coating film. In this method for preparing a thin film, the material containing the monomer further contains a curing agent. The polymerization of the monomer is carried out by photopolymerization or thermal polymerization. The photosensitive material or dye molecules used to prepare this thin film may have a polymerizable functional group.

[0015] In a recording medium with multiple recording layers, if the one-photon absorption of light used to record or read information is large in each recording layer, the intensity of the light decreases as the light passes through each recording layer. In this case, the recording and read sensitivity tends to decrease significantly in recording layers located farther from the light source. Therefore, there is a demand for a recording layer that has low one-photon absorption for the light used to record or read information. In this specification, reading information is sometimes referred to as reproducing information. One-photon absorption is sometimes referred to as linear absorption.

[0016] In order to further increase the number of recording layers in a recording medium, it is necessary to reduce the linear absorption per recording layer and minimize the influence of recording layers other than the recording layer on which recording or reproduction is to be performed. In order to reduce the linear absorption per recording layer, recording layers containing dyes that have almost no linear absorption band for the light used for recording or reproduction and that have a nonlinear optical effect are being studied.

[0017] The nonlinear optical effect refers to the occurrence of an optical phenomenon proportional to the square or higher order of the electric field of the irradiated light when the material is irradiated with intense light such as laser light. Examples of optical phenomena include absorption, reflection, scattering, and light emission. Examples of second-order nonlinear optical effects proportional to the square of the electric field of the irradiated light include second harmonic generation (SHG), the Pockels effect, and the parametric effect. Examples of third-order nonlinear optical effects proportional to the cube of the electric field of the irradiated light include multiphoton absorption such as two-photon absorption, third harmonic generation (THG), and the Kerr effect. Multiphoton absorption such as two-photon absorption can be particularly useful in recording media with multiple recording layers. In this specification, multiphoton absorption such as two-photon absorption is sometimes referred to as nonlinear absorption. Materials capable of nonlinear absorption are sometimes referred to as nonlinear optical materials.

[0018] To date, inorganic materials that can be easily prepared as single crystals have been developed as nonlinear optical materials. Meanwhile, in recent years, there has been a growing expectation for the development of nonlinear optical materials made from organic materials. Compared to inorganic materials, organic materials not only have a high degree of design freedom but also have large nonlinear optical constants. Furthermore, organic materials exhibit high-speed nonlinear response.

[0019] For compounds constituting an organic material, the closer the wavelength for transitioning electrons from the ground state to the lowest singlet excited state is to the excitation wavelength of multi-photon absorption, the better the multi-photon absorption characteristics of the organic material will be, and for example, the more likely it is that a large two-photon absorption cross section can be achieved. In recording media, light having the same wavelength as the excitation wavelength of multi-photon absorption is usually used for recording or reproduction. Various compounds have been synthesized based on this design principle. In this specification, the transition of electrons from the ground state to the lowest singlet excited state in a compound may be referred to as an S0-S1 transition. The two-photon absorption cross section is an index showing the efficiency of two-photon absorption. The unit of the two-photon absorption cross section is GM(10 -50 cm 4 ·s·molecule -1 photon -1 )

[0020] However, according to the studies of the present inventors, when a multiphoton absorption compound is used in a recording layer, the linear absorption of the compound tends to increase at the excitation wavelength of multiphoton absorption. In particular, when the excitation wavelength of multiphoton absorption is located in the short wavelength region, the linear absorption at the excitation wavelength of multiphoton absorption tends to increase significantly. Furthermore, when the multiphoton absorption compound contains at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond, the linear absorption at the excitation wavelength of multiphoton absorption also tends to increase significantly. As a result of extensive studies, the present inventors have newly discovered that the increase in linear absorption in a multiphoton absorption compound is due to a change in the electronic state of the multiphoton absorption compound caused by an interaction between the polymer contained in the recording layer and the multiphoton absorption compound, alteration or decomposition of the multiphoton absorption compound resulting from the process of curing the monomer, and a reaction between the multiphoton absorption compound and the monomer when the monomer is cured. In particular, the inventors have found that even a slight change in the electronic state of a multiphoton absorption compound tends to cause tailing of the absorption band of the S0-S1 transition in the compound, resulting in an increase in linear absorption at the excitation wavelength of the multiphoton absorption.

[0021] Based on their newly discovered findings, the present inventors have conducted further research and discovered that a combination of a multiphoton absorption compound and an aliphatic polymer can suppress tailing of the absorption band of the S0-S1 transition in the multiphoton absorption compound and deterioration of the multiphoton absorption compound, leading to the completion of the recording medium of the present disclosure. Specifically, the present inventors have discovered that a combination of a multiphoton absorption compound and an aliphatic polymer can realize a recording layer in which an increase in one-photon absorption for light having a wavelength in the short wavelength range is suppressed. In this specification, the short wavelength range refers to a wavelength range including 405 nm, for example, a wavelength range of 390 nm to 420 nm.

[0022] (Summary of one aspect of the present disclosure) The recording medium according to the first aspect of the present disclosure includes: It has at least one recording layer. The at least one recording layer is an aliphatic polymer; and a multiphoton absorption compound that contains at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond and has multiphoton absorption properties. When the thickness of the at least one recording layer is 100 μm, the transmittance of the at least one recording layer in the thickness direction for light with a wavelength of 405 nm is 80% or more.

[0023] According to the first aspect, changes in the electronic state of the multiphoton absorption compound are suppressed in the recording layer, and therefore, an increase in one-photon absorption for light having a wavelength in the short wavelength range is suppressed in the recording layer.

[0024] In a second aspect of the present disclosure, for example, in the recording medium according to the first aspect, in the at least one recording layer, the total content of the aliphatic polymer and the content of the multiphoton absorption compound may be 95 wt % or more.

[0025] In a third aspect of the present disclosure, for example, in the recording medium according to the first or second aspect, the aliphatic polymer may contain a structural unit derived from an aliphatic monomer, and the aliphatic monomer may contain at least one selected from the group consisting of an acrylic group, a methacrylic group, an epoxy group, an oxetanyl group, and a vinyl group.

[0026] In a fourth aspect of the present disclosure, for example, in the recording medium according to the third aspect, the aliphatic monomer may contain at least one selected from the group consisting of an acrylic group, a methacrylic group, and an epoxy group.

[0027] In a fifth aspect of the present disclosure, for example, in the recording medium according to the third aspect, the aliphatic monomer may contain at least one selected from the group consisting of compound A represented by the following formula (A), compound B represented by the following formula (B), compound C represented by the following formula (C), compound D represented by the following formula (D), compound E represented by the following formula (E), compound F represented by the following formula (F), and compound G represented by the following formula (G). [ka] In the formula (A), R 1 is a hydrogen atom or a methyl group, and R 2 is an aliphatic group. In the formula (B), R 3 and R 5 are each independently a hydrogen atom or a methyl group, and R 4 is an aliphatic group. In the formula (C), R 6 is a hydrogen atom or a methyl group, and R 7 is an aliphatic group, and R 8 is a hydrogen atom or an aliphatic group. In the formula (D), R 9 is a hydrogen atom or a methyl group, and R 10 is an aliphatic group, and R 11 is a hydrogen atom or an aliphatic group. In the formula (E), R 12 and R 14 are each independently a hydrogen atom or an aliphatic group, and R 13 is an aliphatic group. In the formula (F), R 15 and R 17 are each independently a hydrogen atom or an aliphatic group, and R 16 is an aliphatic group. In the formula (G), R 18 and R 20 are each independently a hydrogen atom or an aliphatic group, and R 19 is an aliphatic group.

[0028] In a sixth aspect of the present disclosure, for example, in the recording medium according to the fifth aspect, the compound A may include at least one selected from the group consisting of a compound A1 represented by the following formula (A1) and a compound A2 represented by the following formula (A2): [ka] In the formula (A1), n ​​is an integer of 0 or more and 11 or less.

[0029] In a seventh aspect of the present disclosure, for example, in the recording medium according to the fifth or sixth aspect, the compound B may contain a compound B1 represented by the following formula (B1). [ka] In the formula (B1), m is an integer of 1 or more and 4 or less.

[0030] In an eighth aspect of the present disclosure, for example, in a recording medium according to any one of the fifth to seventh aspects, the compound E may include at least one selected from the group consisting of a compound E1 represented by the following formula (E1), a compound E2 represented by the following formula (E2), and a compound E3 represented by the following formula (E3): [ka] In the formula (E1), x is an integer of 1 or more and 12 or less. In the formula (E3), y is an integer of 1 or more and 11 or less.

[0031] In a ninth aspect of the present disclosure, for example, in the recording medium according to any one of the first to eighth aspects, the multiphoton absorption compound may contain an aromatic ring.

[0032] According to the second to ninth aspects, an increase in one-photon absorption of light having a wavelength in the short wavelength region is suppressed in the recording layer.

[0033] In a tenth aspect of the present disclosure, for example, the recording medium according to any one of the first to ninth aspects may further comprise a plurality of dielectric layers, and the at least one recording layer may include a plurality of recording layers, and the plurality of recording layers and the plurality of dielectric layers may be arranged alternately.

[0034] According to the tenth aspect, the recording medium has a large recording capacity because it has a plurality of recording layers.

[0035] In an eleventh aspect of the present disclosure, for example, the recording medium according to any one of the first to tenth aspects may record information using light having a wavelength of 390 nm or more and 420 nm or less.

[0036] According to the eleventh aspect, the recording medium can record information at a high recording density.

[0037] An information recording method according to a twelfth aspect of the present disclosure includes: providing a light source that emits light having a wavelength of 390 nm or more and 420 nm or less; and irradiating the light from the light source onto the at least one recording layer of the recording medium according to any one of the first to eleventh aspects.

[0038] According to the twelfth aspect, information can be recorded on the recording medium at a high recording density.

[0039] A method for reading information according to a thirteenth aspect of the present disclosure is, for example, a method for reading information recorded by the recording method according to the twelfth aspect, The reading method includes: measuring optical characteristics of the at least one recording layer by irradiating the at least one recording layer with light; and reading information from the at least one recording layer.

[0040] According to the thirteenth aspect, information can be easily read out.

[0041] The composition according to the fourteenth aspect of the present disclosure comprises: A composition for producing a recording layer having a transmittance of 80% or more in the thickness direction of light with a wavelength of 405 nm when the recording layer has a thickness of 100 μm, an aliphatic monomer; a multiphoton absorption compound containing at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond; Includes:

[0042] According to the fourteenth aspect, in a recording layer formed from the composition, changes in the electronic state of the multiphoton absorption compound are suppressed, and therefore, an increase in one-photon absorption for light having a wavelength in the short wavelength region is suppressed in the recording layer.

[0043] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0044] <Embodiment> Fig. 1 is a cross-sectional view showing a schematic configuration of a recording medium 100 according to an embodiment of the present disclosure. As shown in Fig. 1, the recording medium 100 includes a recording layer 10. The recording layer 10 contains an aliphatic polymer and a multiphoton absorption compound containing at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond. When the thickness of the recording layer 10 is 100 µm, the transmittance of the recording layer 10 in the thickness direction for light with a wavelength of 405 nm is 80% or more.

[0045] The recording medium 100 may include multiple recording layers 10. The multiple recording layers 10 are arranged, for example, in the thickness direction of the recording medium 100. The number of the multiple recording layers 10 in the recording medium 100 is not particularly limited and may be, for example, 2 or more and 1000 or less. The recording medium 100 including multiple recording layers 10 functions as a three-dimensional optical memory. A specific example of the recording medium 100 is a three-dimensional optical disc.

[0046] The recording medium 100 may further include a plurality of dielectric layers 20. In the recording medium 100, a plurality of recording layers 10 and a plurality of dielectric layers 20 may be arranged alternately. In other words, a plurality of recording layers 10 and a plurality of dielectric layers 20 may be stacked alternately. As an example, each of the plurality of recording layers 10 is disposed between two dielectric layers 20 and is in direct contact with each of the two dielectric layers 20. In the recording medium 100, the number of the plurality of dielectric layers 20 is not particularly limited and is, for example, 3 or more and 1001 or less.

[0047] [Recording layer] As described above, the recording layer 10 contains an aliphatic polymer. In this specification, an aliphatic polymer refers to a polymer containing 10 wt% or less of an aromatic ring. The aromatic ring content in the aliphatic polymer may be 5 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.1 wt% or less, or 0.01 wt% or less. The aliphatic polymer may be substantially free of aromatic rings. Aromatic rings include not only those composed of carbon atoms but also heteroaromatic rings containing heteroatoms such as oxygen atoms, nitrogen atoms, and sulfur atoms. Examples of aromatic rings include benzene rings, naphthalene rings, anthracene rings, phenanthrene rings, furan rings, pyrrole rings, pyridine rings, and thiophene rings.

[0048] An aliphatic polymer includes, for example, a structural unit derived from an aliphatic monomer. An aliphatic monomer refers to a monomer that has a polymerizable functional group and does not contain an aromatic ring. As an example, an aliphatic polymer is a polymer of an aliphatic monomer. This polymer may be synthesized by thermal polymerization of an aliphatic monomer or by photopolymerization of an aliphatic monomer. However, the aliphatic polymer may also be a cured product obtained by reacting an aliphatic monomer with a curing agent. The aliphatic polymer may further include, in addition to the structural unit derived from the aliphatic monomer, a structural unit derived from a polymerization initiator, a structural unit derived from a curing agent, etc.

[0049] (aliphatic monomer) Aliphatic monomers are composed of atoms such as hydrogen, boron, carbon, nitrogen, oxygen, fluorine, silicon, phosphorus, and sulfur. The number of polymerizable functional groups contained in the aliphatic monomer may be one or more, or may be two or more. The upper limit of the number of polymerizable functional groups is not particularly limited and is, for example, 10. The aliphatic monomer may contain, for example, at least one polymerizable functional group selected from the group consisting of a (meth)acrylic group, an epoxy group, an oxetanyl group, and a vinyl group. The aliphatic monomer may contain, as the polymerizable functional group, at least one group selected from the group consisting of a (meth)acrylic group and an epoxy group. In this specification, a (meth)acrylic group refers to at least one group selected from the group consisting of an acrylic group and a methacrylic group. The aliphatic monomer may have a methylene group adjacent to the vinyl group. In other words, the aliphatic monomer may contain an allyl group. Note that when the aliphatic monomer has two or more radically polymerizable functional groups such as a (meth)acrylic group or a vinyl group, the aliphatic monomer can function as a crosslinking agent.

[0050] The aliphatic monomer includes, for example, at least one selected from the group consisting of compound A represented by the following formula (A), compound B represented by the following formula (B), compound C represented by the following formula (C), compound D represented by the following formula (D), compound E represented by the following formula (E), compound F represented by the following formula (F), and compound G represented by the following formula (G). [ka]

[0051] In formula (A), R 1 is a hydrogen atom or a methyl group, and may be a hydrogen atom. Compound A has, for example, one (meth)acrylic group. Compound A may or may not contain a polymerizable functional group other than the (meth)acrylic group.

[0052] In formula (A), R 2 is an aliphatic group. An aliphatic group means a group that does not contain an aromatic ring. R 2Examples of the aliphatic group include alkyl groups. The alkyl groups may be linear, branched, or cyclic. The number of carbon atoms in the alkyl group is not particularly limited and may be, for example, 1 to 20, or 1 to 15. At least one hydrogen atom contained in the alkyl group may be substituted with a group containing at least one atom selected from the group consisting of N, O, P, and S. Examples of the alkyl group include methyl, ethyl, propyl, butyl, 2-methylbutyl, pentyl, hexyl, 2,3-dimethylhexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, cyclohexyl, 2-methoxybutyl, and 6-methoxyhexyl.

[0053] The compound A may contain at least one selected from the group consisting of a compound A1 represented by the following formula (A1) and a compound A2 represented by the following formula (A2). [ka]

[0054] In formula (A1), n ​​is an integer of 0 or more and 11 or less. Specific examples of compound A1 include compound a1 represented by formula (a1) below and compound a2 represented by formula (a2) below. [ka]

[0055] In formula (B), R 3 and R 5 are each independently a hydrogen atom or a methyl group. 3 and R 5 may each be a methyl group.

[0056] In formula (B), R 4 is an aliphatic group. 4is a divalent aliphatic group. 4 R may have a functional group containing an oxygen atom, such as an ether group, an ester group, or a hydroxyl group. 4 In the formula, the number of functional groups containing an oxygen atom is not particularly limited, and may be, for example, 1 or more and 10 or less, or may be 1 or more and 5 or less. 4 may not have a functional group containing an oxygen atom.

[0057] R 4 may contain an alkylene group in addition to or instead of the above functional group. The alkylene group may be linear, branched, or cyclic. The number of carbon atoms in the alkylene group is not particularly limited and may be, for example, 1 to 10, or 1 to 5. At least one hydrogen atom contained in the alkylene group may be substituted with a group containing at least one atom selected from the group consisting of N, O, P, and S. R 4 Examples of the alkylene group in R include a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, and a pentane-1,5-diyl group. 4 may contain a polyoxyalkylene group such as a polyoxymethylene group or a polyoxyethylene group.

[0058] Compound B has, for example, two (meth)acrylic groups. 4 may further contain a (meth)acrylic group. In this case, the number of (meth)acrylic groups in compound B is not particularly limited and is, for example, 3 or more and 10 or less. Compound B may or may not contain a polymerizable functional group other than a (meth)acrylic group.

[0059] Compound B may include compound B1 represented by the following formula (B1): Other examples of compound B include compound B2 represented by the following formula (B2) and compound B3 represented by the following formula (B3): [ka]

[0060] In formula (B1), m is an integer of 1 or more and 4 or less. In formula (B2), s is an integer of 1 or more and 10 or less. In formula (B3), t is an integer of 1 or more and 10 or less. Specific examples of compound B1 include compound b1 represented by the following formula (b1). Specific examples of compound B2 include compound b2 represented by the following formula (b2). Specific examples of compound B3 include compound b3 represented by the following formula (b3). [ka]

[0061] In formula (C), R 6 is a hydrogen atom or a methyl group. 7 is an aliphatic group. 7 Examples of the aliphatic group include R 4 Examples include the following.

[0062] In formula (C), R 8 is a hydrogen atom or an aliphatic group, and may be a hydrogen atom. 8 Examples of the aliphatic group include R 2 In formula (C), R 7 and R 8 may be bonded to each other to form a ring structure.

[0063] Compound C has, for example, one (meth)acrylic group and one epoxy group, provided that in compound C, R 7 may further contain at least one selected from the group consisting of a (meth)acrylic group and an epoxy group. In this case, the number of (meth)acrylic groups and the number of epoxy groups in compound C are not particularly limited, and are, for example, from 3 to 10. Compound C may or may not contain a polymerizable functional group other than a (meth)acrylic group and an epoxy group.

[0064] Specific examples of compound C include compound C1 represented by the following formula (C1), compound C2 represented by the following formula (C2), and compound C3 represented by the following formula (C3). [ka]

[0065] In formula (D), R 9 is a hydrogen atom or a methyl group, and may be a hydrogen atom. 10 is an aliphatic group. 10 Examples of the aliphatic group include R 4 Examples include the following.

[0066] In formula (D), R 11 is a hydrogen atom or an aliphatic group, and may be an aliphatic group. 11 Examples of the aliphatic group include R 2 In formula (D), R 10 and R 11 may be bonded to each other to form a ring structure.

[0067] Compound D has, for example, one (meth)acrylic group and one oxetanyl group, provided that in compound D, R 10 may further contain at least one selected from the group consisting of a (meth)acrylic group and an oxetanyl group. In this case, the number of (meth)acrylic groups and the number of oxetanyl groups in compound D are not particularly limited, and are, for example, from 3 to 10. Compound D may or may not contain a polymerizable functional group other than a (meth)acrylic group and an oxetanyl group.

[0068] Specific examples of the compound D include a compound D1 represented by the following formula (D1). [ka]

[0069] In formula (E), R 12 and R 14 are each independently a hydrogen atom or an aliphatic group. 12 and R 14 Examples of the aliphatic group include R 2 Examples include the following.

[0070] In formula (E), R 13 is an aliphatic group. 13 Examples of the aliphatic group include R 4 In formula (E), R 12 and R 13 may be bonded to each other to form a ring structure. 13 and R 14 may be bonded to each other to form a ring structure.

[0071] Compound E has, for example, two epoxy groups. 13 may further contain an epoxy group. In this case, the number of epoxy groups in compound E is not particularly limited and is, for example, 3 or more and 10 or less. Compound E may or may not contain a polymerizable functional group other than an epoxy group.

[0072] The compound E may include at least one selected from the group consisting of a compound E1 represented by the following formula (E1), a compound E2 represented by the following formula (E2), and a compound E3 represented by the following formula (E3). [ka]

[0073] In formula (E1), x is an integer of 1 or more and 12 or less. x may be an integer of 1 or more and 5 or less. Specific examples of compound E1 include compound e1 represented by the following formula (e1) and compound e2 represented by the following formula (e2). [ka]

[0074] In formula (E3), y is an integer of 1 or more and 11 or less. y may be an integer of 1 or more and 5 or less. Specific examples of compound E3 include compound e3 represented by the following formula (e3). [ka]

[0075] Other examples of compound E include compound E4 represented by the following formula (E4), compound E5 represented by the following formula (E5), compound E6 represented by the following formula (E6), compound E7 represented by the following formula (E7), compound E8 represented by the following formula (E8), compound E9 represented by the following formula (E9), compound E10 represented by the following formula (E10), compound E11 represented by the following formula (E11), compound E12 represented by the following formula (E12), compound E13 represented by the following formula (E13), compound E14 represented by the following formula (E14), and compound E15 represented by the following formula (E15). [ka]

[0076] In formula (F), R 15 and R 17 are each independently a hydrogen atom or an aliphatic group. 15 and R 17 Examples of the aliphatic group include R 2 Examples include the following.

[0077] In formula (F), R 16 is an aliphatic group. 16 Examples of the aliphatic group include R 4 In formula (F), R 15 and R 16 may be bonded to each other to form a ring structure. 16 and R 17 may be bonded to each other to form a ring structure.

[0078] Compound F has, for example, one epoxy group and one oxetanyl group, provided that in compound F, R 16 may further contain at least one selected from the group consisting of an epoxy group and an oxetanyl group. In this case, the number of epoxy groups and the number of oxetanyl groups in compound F are not particularly limited, and are, for example, from 3 to 10. Compound F may or may not contain a polymerizable functional group other than an epoxy group and an oxetanyl group.

[0079] In formula (G), R 18 and R 20 are each independently a hydrogen atom or an aliphatic group. 18 and R 20 Examples of the aliphatic group include R 2 Examples include the following.

[0080] In formula (G), R 19 is an aliphatic group. 19 Examples of the aliphatic group include R 4 In formula (G), R 18 and R 19 may be bonded to each other to form a ring structure. 19 and R 20 may be bonded to each other to form a ring structure.

[0081] Compound G, for example, has two oxetanyl groups. 19 may further contain an oxetanyl group. In this case, the number of oxetanyl groups in compound G is not particularly limited and is, for example, 3 or more and 10 or less. Compound G may or may not contain a polymerizable functional group other than the oxetanyl group.

[0082] Specific examples of the compound G include compound G1 represented by the following formula (G1). [ka]

[0083] The exemplified aliphatic monomers may be used alone or in combination of two or more.In addition, the aliphatic monomer is not limited to the above-mentioned, as long as it is a monomer that has a polymerizable functional group and does not contain an aromatic ring.The aliphatic monomer may be, for example, a monomer for forming polyester, a monomer for forming polyamide, or a monomer for forming polycarbonate.

[0084] In the aliphatic polymer, the content of constitutional units derived from aliphatic monomers is, for example, 30 wt% or more, or may be 50 wt% or more, 70 wt% or more, 90 wt% or more, 95 wt% or more, or 99 wt% or more. The aliphatic polymer may be composed essentially of constitutional units derived from aliphatic monomers.

[0085] (Polymerization initiator) As described above, the aliphatic polymer may further contain a structural unit derived from a polymerization initiator. The polymerization initiator can be appropriately selected depending on the type of aliphatic monomer used to synthesize the aliphatic polymer. The polymerization initiator may or may not contain an aromatic ring.

[0086] Aliphatic monomers having a (meth)acrylic group as a polymerizable functional group can be photopolymerized, for example. When synthesizing an aliphatic polymer using this aliphatic monomer, a known photopolymerization initiator can be used as the polymerization initiator. Examples of photopolymerization initiators include carbonyl compounds, phosphine oxide compounds, acylphosphine oxide compounds, azo compounds, azide compounds, organic peroxides, organic tin compounds, organic borates, onium salts, alkylarylborates, iron arene complexes, bisimidazole derivatives, titanocene compounds, triazine compounds, iodonium salts, diaryliodonium salts, organic thiol compounds, and halogenated hydrocarbon derivatives. The photopolymerization initiator may be a carbonyl compound such as 1-hydroxycyclohexyl phenyl ketone. The exemplified photopolymerization initiators may be used alone or in combination of two or more. The weight of the photopolymerization initiator used when synthesizing the aliphatic polymer is not particularly limited, and may be, for example, 0.1 parts by mass or more and 20 parts by mass or less, or may be 0.1 parts by mass or more and 10 parts by mass or less, or may be 0.1 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the aliphatic monomer.

[0087] When synthesizing an aliphatic polymer using an aliphatic monomer having an epoxy group as a polymerizable functional group, a cationic polymerization initiator, an anionic polymerization initiator, or the like can be used as the polymerization initiator. As the polymerization initiator, amines, mercaptans, acid anhydrides, carboxylic acids, imidazoles, or the like may be used. The exemplified polymerization initiators may be used alone or in combination of two or more. The weight of the polymerization initiator used when synthesizing the aliphatic polymer is not particularly limited, and may be, for example, 0.05 to 10 parts by mass, 0.1 to 5 parts by mass, or 0.1 to 2 parts by mass, per 100 parts by mass of the aliphatic monomer.

[0088] (hardening agent) As described above, the aliphatic polymer may further contain structural units derived from a curing agent. The curing agent can be appropriately selected depending on the type of aliphatic monomer used to synthesize the aliphatic polymer. The curing agent may or may not contain an aromatic ring.

[0089] When synthesizing an aliphatic polymer using an aliphatic monomer having an epoxy group as a polymerizable functional group, a compound having a functional group reactive with an epoxy group can be used as a curing agent. In this compound, the number of functional groups reactive with an epoxy group is, for example, one or more, and may be two or more. Examples of this compound include acid anhydrides, carboxylic acids, amines, hydrazides, polymercaptans, and polyols. The curing agent may also be an acid anhydride such as cis-1,2-cyclohexanecarboxylic anhydride. The exemplified curing agents may be used alone or in combination of two or more.

[0090] In the aliphatic polymer, the content of structural units derived from the curing agent is not particularly limited, and may be, for example, 70 wt% or less, 50 wt% or less, 30 wt% or less, or 10 wt% or less.

[0091] (Other ingredients) The aliphatic polymer may further contain structural units derived from components other than the aliphatic monomer, polymerization initiator, and curing agent. Examples of such components include a crosslinking agent different from the aliphatic monomer. The crosslinking agent may have two or more polymerizable functional groups. Examples of the polymerizable functional group contained in the crosslinking agent include radically polymerizable functional groups such as (meth)acrylic groups and vinyl groups. Crosslinking agents containing radically polymerizable functional groups are suitable for crosslinking aliphatic monomers containing one (meth)acrylic group. The crosslinking agent may have a methylene group or a phenyl group adjacent to the vinyl group. That is, the crosslinking agent may contain an allyl group or a styryl group. The crosslinking agents may be used alone or in combination of two or more.

[0092] (Physical properties of aliphatic polymers) The aliphatic polymer may hardly absorb light having a wavelength in the short wavelength range, particularly, the aliphatic polymer may hardly absorb light having a wavelength of 405 nm.

[0093] The recording layer 10 contains, for example, an aliphatic polymer as a main component. "Main component" means the component that is contained in the recording layer 10 in the largest amount by weight. The content of the aliphatic polymer in the recording layer 10 is, for example, 50 wt% or more, or may be 70 wt% or more, or may be 90 wt% or more. There is no particular upper limit to the content of the aliphatic polymer, and it is, for example, 98 wt%.

[0094] (multiphoton absorption compound) As described above, the recording layer 10 includes a multiphoton absorption compound. In this specification, a multiphoton absorption compound refers to a compound having multiphoton absorption properties. A multiphoton absorption compound is sometimes called a nonlinear absorption dye. A multiphoton absorption compound is typically a two-photon absorption compound having two-photon absorption properties. A multiphoton absorption compound exhibits multiphoton absorption properties for light having a wavelength in the short wavelength range, for example. As an example, a multiphoton absorption compound exhibits multiphoton absorption properties for light having a wavelength of 405 nm.

[0095] As described above, the multiphoton absorption compound contains at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond. Furthermore, the multiphoton absorption compound may contain an aromatic ring. The aromatic ring contained in the multiphoton absorption compound may be composed of carbon atoms, or may be a heteroaromatic ring containing a heteroatom such as an oxygen atom, a nitrogen atom, or a sulfur atom. Examples of aromatic rings contained in the multiphoton absorption compound include a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a furan ring, a pyrrole ring, a pyridine ring, and a thiophene ring. The multiphoton absorption compound may contain a benzene ring as the aromatic ring. The number of aromatic rings contained in the multiphoton absorption compound is not particularly limited and may be, for example, 2 or more, 3 or more, or 5 or more. The upper limit of the number of aromatic rings is not particularly limited and is, for example, 15. In the multiphoton absorption compound, a plurality of aromatic rings may be linked by at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond. The plurality of aromatic rings contained in the multiphoton absorption compound may be the same as or different from each other.

[0096] The multiphoton absorption compound is represented by, for example, the following formula (1). [ka]

[0097] In formula (1), R 21 From R 26 are each independently a hydrogen atom (where R 21 From R 26 are hydrogen atoms), or a substituent containing at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond. 21 From R 26At least one selected from the group consisting of may be an arylethynyl group or an arylbutadienyl group. Specific examples of the compound represented by formula (1) include compound H represented by formula (H) below, compound I represented by formula (I) below, and compound J represented by formula (J) below. [ka]

[0098] The compound represented by formula (1) may be represented by the following formula (2): [ka]

[0099] In equation (2), R 27 From R 53 R each independently contain at least one atom selected from the group consisting of H, C, N, O, F, P, S, Cl, I and Br. 27 From R 53 may each independently be a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group, an unsaturated hydrocarbon group, a hydroxyl group, a carboxyl group, an alkoxycarbonyl group, an acyl group, an amide group, a nitrile group, an alkoxy group, an acyloxy group, a thiol group, an alkylthio group, a sulfonic acid group, an acylthio group, an alkylsulfonyl group, a sulfonamide group, a primary amino group, a secondary amino group, a tertiary amino group, or a nitro group.

[0100] Examples of halogen atoms include F, Cl, Br, and I. In this specification, halogen atoms may be referred to as halogen groups.

[0101] The number of carbon atoms in the alkyl group is not particularly limited and may be, for example, 1 to 20. The number of carbon atoms in the alkyl group may be 1 to 10 or 1 to 5. The alkyl group may be linear, branched, or cyclic. At least one hydrogen atom contained in the alkyl group may be substituted with a group containing at least one atom selected from the group consisting of N, O, P, and S. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a 2-methylbutyl group, a pentyl group, a hexyl group, a 2,3-dimethylhexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a 2-methoxybutyl group, and a 6-methoxyhexyl group.

[0102] The halogenated alkyl group refers to a group in which at least one hydrogen atom contained in an alkyl group is substituted with a halogen atom. The halogenated alkyl group may be a group in which all hydrogen atoms contained in the alkyl group are substituted with halogen atoms. Examples of the alkyl group include those mentioned above. A specific example of the halogenated alkyl group is -CF3.

[0103] The unsaturated hydrocarbon group contains an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond. The number of unsaturated bonds contained in the unsaturated hydrocarbon group is, for example, 1 to 5. The number of carbon atoms in the unsaturated hydrocarbon group is not particularly limited and is, for example, 2 to 20, or may be 2 to 10, or may be 2 to 5. The unsaturated hydrocarbon group may be linear, branched, or cyclic. At least one hydrogen atom contained in the unsaturated hydrocarbon group may be substituted with a group containing at least one atom selected from the group consisting of N, O, P, and S. Examples of unsaturated hydrocarbon groups include a vinyl group and an ethynyl group.

[0104] A hydroxyl group is represented by -OH. A carboxyl group is represented by -COOH. An alkoxycarbonyl group is represented by -COOR. a The acyl group is represented by -COR b The amide group is represented by -CONR c R d A nitrile group is represented by -CN. An alkoxy group is represented by -OR. e The acyloxy group is represented by -OCOR f A thiol group is represented by -SH. An alkylthio group is represented by -SR. g The sulfonic acid group is represented by -SO3H. The acylthio group is represented by -SCOR h The alkylsulfonyl group is represented by -SO2R i The sulfonamide group is represented by -SO2NR j R k A primary amino group is represented by -NH2. A secondary amino group is represented by -NHR l The tertiary amino group is represented by -NR m R n The nitro group is represented by -NO2. R a From R n are each independently an alkyl group. Examples of the alkyl group include those mentioned above. However, the R c and R d , and R of the sulfonamide group j and R k may be, independently of each other, a hydrogen atom.

[0105] Specific examples of alkoxycarbonyl groups are -COOCH3, -COO(CH2)3CH3, and -COO(CH2)7CH3. Specific examples of acyl groups are -COCH3. Specific examples of amido groups are -CONH2. Specific examples of alkoxy groups are methoxy, ethoxy, 2-methoxyethoxy, butoxy, 2-methylbutoxy, 2-methoxybutoxy, 4-ethylthiobutoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, tridecyloxy, tetradecyloxy, pentadecyloxy, hexadecyloxy, heptadecyloxy, octadecyloxy, nonadecyloxy, and eicosyloxy. Specific examples of acyloxy groups are -OCOCH3. A specific example of an acylthio group is -SCOCH3. A specific example of an alkylsulfonyl group is -SO2CH3. A specific example of a sulfonamide group is -SO2NH2. A specific example of a tertiary amino group is -N(CH3)2.

[0106] The compound represented by formula (2) may be represented by the following formula (3): [ka]

[0107] In formula (3), multiple Zs are the same as each other. 39 , R 44 and R 49 In formula (3), multiple Z's may be -C(CH3)3. That is, specific examples of the compound represented by formula (3) include compound K represented by the following formula (K): [ka]

[0108] Furthermore, the compound represented by formula (1) may be represented by the following formula (4): [ka]

[0109] In equation (4), R 54 From R 80 R each independently contain at least one atom selected from the group consisting of H, C, N, O, F, P, S, Cl, I and Br. 54 From R 80 may each independently be a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group, an unsaturated hydrocarbon group, a hydroxyl group, a carboxyl group, an alkoxycarbonyl group, an acyl group, an amide group, a nitrile group, an alkoxy group, an acyloxy group, a thiol group, an alkylthio group, a sulfonic acid group, an acylthio group, an alkylsulfonyl group, a sulfonamide group, a primary amino group, a secondary amino group, a tertiary amino group, or a nitro group. Examples of these substituents include R in formula (2). 27 From R 53 The above-mentioned examples are included.

[0110] The compound represented by formula (4) may be represented by the following formula (5): [ka]

[0111] In formula (5), multiple Zs are the same as each other. 66 , R 71 and R 76 In formula (5), the multiple Z's may be halogen atoms, alkyl groups, halogenated alkyl groups, unsaturated hydrocarbon groups, hydroxyl groups, carboxyl groups, alkoxycarbonyl groups, acyl groups, amide groups, acyloxy groups, thiol groups, alkylthio groups, sulfonic acid groups, acylthio groups, alkylsulfonyl groups, sulfonamide groups, primary amino groups, or secondary amino groups. Specific examples of the multiple Z's include -COO(CH2)3CH3. That is, specific examples of the compound represented by formula (5) include compound L represented by the following formula (L). [ka]

[0112] The recording layer 10 contains, for example, as a multiphoton absorption compound, at least one selected from the group consisting of compounds H to L. The recording layer 10 may contain at least one selected from the group consisting of compound H and compounds J to L, or may contain compound L.

[0113] (Physical properties of multiphoton absorption compounds) The two-photon absorption cross-section of the multiphoton absorption compound for light having a wavelength of 405 nm may be 1 GM or more, 10 GM or more, 100 GM or more, 1000 GM or more, 10,000 GM or more, or 20,000 GM or more. The upper limit of the two-photon absorption cross-section of the multiphoton absorption compound is not particularly limited, and is, for example, 150,000 GM. The two-photon absorption cross-section can be measured, for example, by the Z-scan method described in J. Opt. Soc. Am. B, 2003, Vol. 20, p. 529. The Z-scan method is widely used as a method for measuring nonlinear optical constants. In the Z-scan method, a measurement sample is moved along the irradiation direction of a laser beam near the focal point where the beam is focused. The change in the amount of light transmitted through the measurement sample is recorded. In the Z-scan method, the power density of the incident light changes depending on the position of the measurement sample. Therefore, if the sample undergoes nonlinear absorption, the amount of transmitted light will be attenuated when the sample is located near the focus of the laser beam.The two-photon absorption cross section can be calculated by fitting the change in the amount of transmitted light to a theoretical curve predicted from the intensity of the incident light, the thickness of the sample, and the concentration of the multiphoton absorbing compound in the sample.

[0114] The molar extinction coefficient ε of the multiphoton absorption compound for light having a wavelength of 405 nm may be 2000 L / (mol·cm) or less, 1000 L / (mol·cm) or less, 100 L / (mol·cm) or less, 50 L / (mol·cm) or less, or 10 L / (mol·cm) or less. The lower limit of the molar extinction coefficient ε of the multiphoton absorption compound is not particularly limited and is, for example, 0.01 L / (mol·cm). The molar extinction coefficient ε can be measured, for example, by a method conforming to the provisions of Japanese Industrial Standards (JIS) K0115:2004. The molar extinction coefficient ε is measured using a light source that irradiates light with a photon density that causes almost no multiphoton absorption by the multiphoton absorption compound.

[0115] When a multiphoton absorption compound undergoes two-photon absorption, the multiphoton absorption compound absorbs approximately twice the energy of light irradiated onto the multiphoton absorption compound. The wavelength of light having approximately twice the energy of light having a wavelength of 405 nm is, for example, 200 nm. That is, when a multiphoton absorption compound is irradiated with light having a wavelength around 200 nm, one-photon absorption may occur in the multiphoton absorption compound. Furthermore, one-photon absorption may occur in the multiphoton absorption compound for light having a wavelength close to the wavelength range in which two-photon absorption occurs.

[0116] The content of the multiphoton absorption compound in the recording layer 10 is, for example, less than 50 wt%, and may be 30 wt% or less, or 10 wt% or less. The lower limit of the content of the multiphoton absorption compound is not particularly limited, and is, for example, 2 wt%.

[0117] In the recording layer 10, the total content of the aliphatic polymer and the multiphoton absorption compound is, for example, 80 wt% or more, or may be 90 wt% or more, 95 wt% or more, 97 wt% or more, or even 99 wt% or more. The recording layer 10 consists essentially of only the aliphatic polymer and the multiphoton absorption compound. "Consisting essentially of" means excluding other components that alter the essential characteristics of the referenced material. However, the recording layer 10 may contain impurities in addition to the aliphatic polymer and the multiphoton absorption compound.

[0118] (Method for producing recording layer) The recording layer 10 can be produced, for example, by the following method. First, a coating liquid containing an aliphatic monomer and a multiphoton absorption compound is prepared. This coating liquid corresponds to a composition for producing the recording layer 10 of the recording medium 100. That is, the composition for producing the recording layer 10 of the recording medium 100 contains an aliphatic monomer and a multiphoton absorption compound containing at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond.

[0119] The coating liquid may further contain a polymerization initiator, a curing agent, a curing accelerator, a crosslinking agent, etc. as needed. The polymerization initiator, curing agent, and crosslinking agent may be those described above. Examples of the curing accelerator include tertiary amines such as 2,4,6-tris(dimethylaminomethyl)phenol. Tertiary amines are suitable for accelerating the curing reaction of aliphatic monomers containing an epoxy group.

[0120] Next, the coating liquid is applied to a substrate to form a coating film. Examples of the substrate include a glass substrate. The coating liquid may be applied directly onto the dielectric layer 20, rather than onto the substrate. As an example, the coating film may be formed by filling the space formed between two substrates with the coating liquid. Next, energy such as thermal energy or light energy is applied to the coating film. When the aliphatic monomer contained in the coating film has an epoxy group, thermal energy may be applied to the coating film. For example, thermal energy can be applied to the coating film by heating the coating film at a temperature of 70°C or higher for one hour or more. When the aliphatic monomer contained in the coating film has a (meth)acrylic group, vinyl group, or the like, light energy may be applied to the coating film. The light energy may be, for example, light having a wavelength of 365 nm at 20 mW / cm. 2 The coating film can be given energy by irradiating the coating film with a power density of 1000 W. By giving energy to the coating film, the polymerization reaction or curing reaction of the aliphatic monomer contained in the coating film progresses. In this way, the recording layer 10 can be produced.

[0121] When preparing the recording layer 10, photopolymerization of an aliphatic monomer containing a photopolymerizable functional group such as a (meth)acrylic group or a vinyl group may result in a reaction between the aliphatic monomer and a multiphoton-absorbing compound having a carbon-carbon triple bond. The reaction between the multiphoton-absorbing compound and the aliphatic monomer may slightly alter the multiphoton-absorbing compound. Therefore, when preparing an aliphatic polymer using an aliphatic monomer containing a photopolymerizable functional group, the coating film may not contain a multiphoton-absorbing compound having a carbon-carbon triple bond. In other words, when the recording layer 10 contains an aliphatic polymer having a structural unit derived from an aliphatic monomer containing a photopolymerizable functional group, the recording layer 10 may not contain a multiphoton-absorbing compound having a carbon-carbon triple bond.

[0122] (Physical properties of recording layer) The recording layer 10 is a thin film having a thickness of, for example, 1 nm to 100 μm, although the thickness of the recording layer 10 may be greater than 100 μm.

[0123] As described above, the recording layer 10 has a transmittance of 80% or more in the thickness direction for light with a wavelength of 405 nm when the thickness of the recording layer 10 is 100 μm. This transmittance may be 84% or more, 90% or more, 95% or more, or 99% or more.

[0124] The transmittance can be measured using the recording layer 10 itself as a measurement sample according to a method stipulated in JIS K0115:2004. Specifically, first, the recording layer 10 is irradiated with light having a wavelength of 405 nm. The light irradiation is performed so that the light travels in the thickness direction of the recording layer 10. The light source used is one that irradiates light with a photon density that causes almost no multiphoton absorption by the multiphoton absorption compound. 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. The transmittance T of the recording layer 10 at a wavelength of 405 nm can be calculated based on the absorbance A using the following formula (I): Transmittance T=10 (-A) (I)

[0125] Next, the obtained transmittance T is converted into a value when the thickness of the recording layer 10 is 100 μm. More specifically, based on the transmittance T and the actual thickness t (μm) of the recording layer 10, the transmittance when the thickness of the recording layer 10 is 100 μm can be calculated using the following formula (II). Transmittance per 100 μm thickness = T (100 / t) (II)

[0126] In the recording layer 10 of this embodiment, there is almost no interaction between the aliphatic polymer and the multiphoton absorption compound. Therefore, in the recording layer 10, there is almost no change in the electronic state of the multiphoton absorption compound. Furthermore, there is almost no deterioration of the multiphoton absorption compound due to the polymerization reaction or curing reaction of the aliphatic monomer. Therefore, in the recording layer 10, an increase in linear absorption at the excitation wavelength of multiphoton absorption is suppressed. In particular, in the recording layer 10, an increase in single-photon absorption for light having a wavelength in the short wavelength range is suppressed.

[0127] The suppression of the increase in single-photon absorption in the recording layer 10 can be evaluated by the molar absorption coefficient ε of the multiphoton absorption compound contained in the recording layer 10 with respect to light having a wavelength of 405 nm. The molar absorption coefficient ε can be determined by the following method. First, a measurement sample is prepared having the same composition and shape as the recording layer 10, except that the concentration of the multiphoton absorption compound is 0.1 mmol / L to 10 mmol / L and the thickness is 0.5 mm to 1 mm. Note that if the concentration of the multiphoton absorption compound in the recording layer 10 is 0.1 mmol / L to 10 mmol / L and the thickness of the recording layer 10 is 0.5 mm to 1 mm, the recording layer 10 itself may be used as the measurement sample. Next, the measurement sample is irradiated with light having a wavelength of 405 nm. The light irradiation is performed so that the light travels in the thickness direction of the measurement sample. A light source that irradiates light with a photon density that causes almost no multiphoton absorption by the multiphoton absorption compound is used. Next, the absorbance A1 of the measurement sample at a wavelength of 405 nm is read from the light transmitted through the measurement sample. Based on the absorbance A1, the concentration C (mol / L) of the multiphoton absorption compound in the measurement sample, and the thickness t1 (cm) of the measurement sample, the molar absorption coefficient (L / (mol cm)) is calculated using the following formula (III). The calculated molar absorption coefficient can be regarded as the molar absorption coefficient ε of the multiphoton absorption compound contained in recording layer 10 for light having a wavelength of 405 nm. Molar extinction coefficient = absorbance A1 / (concentration C × thickness t1) (III)

[0128] For example, when the recording layer 10 contains compound H as the multiphoton absorption compound, the molar absorption coefficient ε of compound H may be 50 L / (mol cm) or less, 40 L / (mol cm) or less, or 30 L / (mol cm) or less. The lower limit of the molar absorption coefficient ε of compound H is not particularly limited and is, for example, 1 L / (mol cm).

[0129] When the recording layer 10 contains compound I as the multiphoton absorption compound, the molar absorption coefficient ε of compound I may be 200 L / (mol cm) or less, 100 L / (mol cm) or less, or 50 L / (mol cm) or less. The lower limit of the molar absorption coefficient ε of compound I is not particularly limited and is, for example, 10 L / (mol cm).

[0130] When the recording layer 10 contains compound J as a multiphoton absorption compound, the molar absorption coefficient ε of compound J may be 1000 L / (mol cm) or less, 500 L / (mol cm) or less, or 200 L / (mol cm) or less. The lower limit of the molar absorption coefficient ε of compound J is not particularly limited and is, for example, 100 L / (mol cm).

[0131] When the recording layer 10 contains compound K as the multiphoton absorption compound, the molar absorption coefficient ε of compound K may be 2000 L / (mol cm) or less, 1700 L / (mol cm) or less, or 1600 L / (mol cm) or less. The lower limit of the molar absorption coefficient ε of compound K is not particularly limited and is, for example, 1000 L / (mol cm).

[0132] When the recording layer 10 contains compound L as a multiphoton absorption compound, the molar absorption coefficient ε of compound L may be 200 L / (mol cm) or less, 100 L / (mol cm) or less, or 60 L / (mol cm) or less. The lower limit of the molar absorption coefficient ε of compound L is not particularly limited and is, for example, 15 L / (mol cm).

[0133] [Dielectric layer] The dielectric layer 20 has an appropriately adjusted reflectance and absorptance for light used to record or read information. Examples of materials for the dielectric layer 20 include oxides such as ZrO2, HfO2, ZnO, SiO2, SnO2, Cr2O3, TiO2, In2O3, Ga2O3, Y2O3, CeO2, and DyO2, sulfides such as ZnS and CdS, and mixtures thereof. Examples of mixtures include ZrO2-SiO2, ZrO2-SiO2-Cr2O3, ZrO2-SiO2-Ga2O3, HfO2-SiO2-Cr2O3, ZrO2-SiO2-In2O3, and ZnS-SiO2. The dielectric layer 20 may also be made of an organic material. Examples of organic materials include thermoplastic resins, thermosetting resins, ultraviolet-curable resins, electron-beam-curable resins, and adhesives. Examples of ultraviolet curable resins include urethane resins, acrylic resins, urethane acrylate resins, epoxy resins, fluorine-based polymers such as perfluoropolyether, silicone-based polymers such as polydimethylsiloxane, and mixtures of photopolymerization initiators.

[0134] The thickness of the dielectric layer 20 is not particularly limited, and may be, for example, 5 nm or more and 100 μm or less, or 5 nm or more and 80 nm or less.

[0135] [Other Layers] The recording medium 100 may further include layers other than the recording layer 10 and the dielectric layer 20. Examples of such layers include an adhesive layer and a reflective layer. The adhesive layer is disposed, for example, between the recording layer 10 and the dielectric layer 20. The adhesive layer can easily bond the recording layer 10 and the dielectric layer 20. The reflective layer is, for example, a thin film of an Ag alloy containing Ag as a main component. The reflective layer is disposed, for example, between the recording layer 10 and the dielectric layer 20 or between the recording layer 10 and the adhesive layer.

[0136] [How to use the recording medium] In this embodiment, light having a wavelength in the short wavelength range is used to record information on the recording medium 100. As an example, light having a wavelength of 390 nm or more and 420 nm or less is used to record information on the recording medium 100. The light used in the recording medium 100 has a high photon density near its focal point, for example. The power density near the focal point of the light used in the recording medium 100 is, for example, 0.1 W / cm. 2 Over 1.0 x 10 20 W / cm 2 The power density near the focal point of this light is 1.0 W / cm 2 It may be 1.0 x 10 or more. 2 W / cm 2 It may be 1.0 x 10 or more. 5 W / cm 2 The light source used in the recording medium 100 may be, for example, a femtosecond laser such as a titanium sapphire laser, or a pulsed laser such as a semiconductor laser having a pulse width of picoseconds to nanoseconds.

[0137] Next, a method for recording information using the recording medium 100 will be described. FIG. 2A is a flowchart illustrating the method for recording information using the recording medium 100. First, in step S11, a light source that emits light having a wavelength of 390 nm or more and 420 nm or less is prepared. As the light source, for example, a femtosecond laser such as a titanium sapphire laser, or a pulsed laser having a pulse width of picoseconds to nanoseconds such as a semiconductor laser can be used. Next, in step S12, the light from the light source is focused using a lens or the like and irradiated onto the recording layer 10 of the recording medium 100. In detail, the light from the light source is focused using a lens or the like and irradiated onto the recording region of the recording medium 100. The power density near the focus of this light is, for example, 0.1 W / cm 2 Over 1.0 x 10 20 W / cm 2 The power density near the focal point of this light is 1.0 W / cm 2 It may be 1.0 x 10 or more. 2 W / cm 2 It may be 1.0 x 10 or more.5 W / cm 2 In this specification, the recording area means a spot that exists in the recording layer 10 and that can record information when irradiated with light.

[0138] In the recording area irradiated with the light, a physical or chemical change occurs, which changes the optical characteristics of the recording area. For example, the intensity of light reflected by the recording area, the reflectance of light in the recording area, the absorptance 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. For example, the intensity of light reflected by the recording area or the intensity of fluorescent light emitted from the recording area decreases. This allows information to be recorded in the recording layer 10, specifically in the recording area (step S13).

[0139] Next, a method for reading information using the recording medium 100 will be described. FIG. 2B is a flowchart illustrating a method for reading information using the recording medium 100. First, in step S21, light is irradiated onto the recording layer 10 of the recording medium 100. Specifically, light is irradiated onto the recording area of ​​the recording medium 100. The light used in step S21 may be the same as or different from the light used to record information on the recording medium 100. Next, in step S22, the optical characteristics of the recording layer 10 are measured. Specifically, the optical characteristics of the recording area are measured. In step S22, for example, the intensity of light reflected from the recording area or the intensity of fluorescent light emitted from the recording area may be measured as the optical characteristics of the recording area. In step S22, the reflectance of light in the recording area, the absorbance 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. may be measured as the optical characteristics of the recording area. Next, in step S23, information is read from the recording layer 10, specifically, the recording area.

[0140] In the information reading method, the recording area where information is recorded can be found by the following method. First, light is irradiated onto a specific area of ​​the recording medium. This light may be the same as or different from the light used to record information on the recording medium. Next, the optical characteristics of the area irradiated with light are measured. Examples of optical characteristics include the intensity of light reflected from the area, the reflectance of light in the area, the absorbance of light in the area, the refractive index of light in the area, the intensity of fluorescent light emitted from the area, and the wavelength of fluorescent light emitted from the area. Whether or not the area irradiated with light is a recording area is determined based on the measured optical characteristics. For example, if the intensity of light reflected from the area is equal to or less than a specific value, the area is determined to be a recording area. On the other hand, if the intensity of light reflected from the area is greater than a specific value, the area is determined to be not a recording area. Note that the method for determining whether or not the area irradiated with light is a recording area is not limited to the above method. For example, if the intensity of light reflected from the area is greater than a specific value, the area may be determined to be a recording area. Alternatively, if the intensity of light reflected from the area is equal to or less than a specific value, the area may be determined to be a non-recorded area. If it is determined to be a non-recorded area, the same operation is performed on other areas of the recording medium. This allows the search for a recorded area.

[0141] The information recording and reading methods using the recording medium 100 can be performed by, for example, a known recording device. The recording device includes, for example, a light source that irradiates light onto the recording area of ​​the recording medium 100, a measuring device that measures the optical characteristics of the recording area, and a controller that controls the light source and the measuring device. [Example]

[0142] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are merely illustrative and the present disclosure is not limited to the following examples.

[0143] <Multiphoton absorption compounds> First, the above-mentioned compounds H to L were prepared as multiphoton absorption compounds. Commercially available products (manufactured by Sigma-Aldrich) were used as compounds H and I. Compounds J to L were synthesized by the following method.

[0144] [Synthesis of Compound J] Compound J was synthesized in accordance with the method described in K. Kondo et al., J. Chem. Soc., Chem. Commun. 1995, pp. 55-56, and W. Tao et al., J. Org. Chem. 1990, Vol. 55, pp. 63-69.

[0145] [Synthesis of Compound K] First, 1,3,5-tris(4-formylphenyl)benzene (manufactured by Tokyo Chemical Industry Co., Ltd.) and 4-tert-butylaniline (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in ethanol. The resulting solution was heated under reflux for 12 hours while stirring. A solid was filtered from the reaction solution and washed with ethanol. The solid was dried in a vacuum to obtain compound K. Compound K was obtained by the following procedure. 1 The compound K was identified by H-NMR. 1 1 is a graph showing the H-NMR spectrum of compound K. 1 The 1 H-NMR spectrum was as follows: 1 H-NMR(600MHz, CHLOROFORM-D) δ1.36 (s, 27H), 7.23 (d, J=9.0Hz, 6H), 7.44 (d, J=8.4Hz, 6H), 7.83 (d, J=8.4Hz, 6H), 7.91 (s, 3H), 8.04 (d, J=8.4Hz, 6H), 8.56 (s,3H).

[0146] [Synthesis of Compound L] 1,3,5-Tris[4'-(ethynyl)phenyl]benzene (manufactured by BLD PHARMATECH) and methyl 4-iodobenzoate (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in triethylamine. To the resulting solution, catalytic amounts of triphenylphosphine (manufactured by Tokyo Chemical Industry Co., Ltd.), bis(triphenylphosphine)palladium(II) dichloride (manufactured by Tokyo Chemical Industry Co., Ltd.), and copper(I) iodide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were further added. This solution was then stirred at room temperature for 16 hours. The resulting reaction solution was neutralized with hydrochloric acid. The reaction solution was then extracted with ethyl acetate. Magnesium sulfate was added to the resulting extract, and the extract was dehydrated. The magnesium sulfate was then filtered off from the extract. The resulting filtrate was concentrated using a rotary evaporator. The resulting concentrate was purified by silica gel column chromatography. The purified product was then dissolved in a mixture of tetrahydrofuran and methanol (v / v = 1:1). Aqueous sodium hydroxide solution was added to the resulting solution, and the mixture was heated to reflux overnight while stirring. After the reaction in the solution was completed, dilute hydrochloric acid was added to the solution. This acidified the solution, and a solid precipitated. The solid was washed with pure water to obtain the precursor of compound L.

[0147] Next, a suspension was prepared by adding butanol solvent to the precursor of compound L. Next, thionyl chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the suspension, and the mixture was heated and refluxed overnight while stirring. A white solid was filtered from the resulting reaction solution and washed with methanol. The resulting solid was subjected to an extraction treatment using chloroform. Magnesium sulfate was added to the resulting extract, and the extract was dehydrated. Next, magnesium sulfate was filtered off from the extract. The resulting filtrate was concentrated using a rotary evaporator. The resulting concentrate was purified by silica gel column chromatography to obtain compound L. Compound L was obtained as follows: 1 The compound L was identified by H-NMR. 1 1 is a graph showing the H-NMR spectrum of Compound L. 1 The 1 H-NMR spectrum was as follows: 1H-NMR (600MHz, CHLOROFORM-D) δ8.05 (d, J=9.0Hz, 6H), 7.83 (s, 3H), 7.73 (d, J=8.3Hz, 6H), 7.68 (d, J=8.3Hz, 6H), 7.62 (d, J=8.3Hz, 6H), 4.35 (t, J=6.5Hz, 6H),1.75-1.80 (m, 6H), 1.50 (td, J=14.8, 7.3Hz, 6H), 1.00 (t, J=7.6Hz, 9H).

[0148] (Example A1) First, the following materials were mixed by stirring to prepare a uniformly mixed resin precursor (i). Aliphatic monomer: 1,7-octadiene diepoxide (compound e1, manufactured by Tokyo Chemical Industry Co., Ltd.) 5,000 parts by mass Curing agent: cis-1,2-cyclohexanecarboxylic anhydride (Tokyo Chemical Industry Co., Ltd.) 5420 parts by mass Curing accelerator: 2,4,6-tris(dimethylaminomethyl)phenol (Kanto Chemical Co., Ltd.) 50 parts by mass

[0149] Next, the following materials were mixed by stirring to obtain a uniformly mixed coating liquid: The concentration of the multiphoton absorption compound in the coating liquid was 10.0 mmol / L. Resin precursor: Resin precursor (i) 5 mL Multiphoton absorption compound: Compound H 10.3 mg

[0150] Next, two glass substrates were prepared. The dimensions of these glass substrates were 20 mm length, 20 mm width, and 1 mm thickness. Next, the two glass substrates were placed opposite each other with a space between them using a spacer. A 1 mm thick glass substrate was used as the spacer. Next, the mixture was filled into the space formed between the two glass substrates to form a coating film. Next, the coating film was heated at 90°C for 7 hours. This allowed the reaction between the aliphatic monomer and the curing agent to proceed, resulting in the recording layer of Example A1.

[0151] (Example A2) The recording layer of Example A2 was obtained in the same manner as in Example A1, except that resin precursor (ii) was used instead of resin precursor (i). Resin precursor (ii) was prepared by mixing the following materials uniformly by stirring. Aliphatic monomer: 8,000 parts by mass of 1,2-cyclohexanedicarboxylate diglycidyl (compound E2, manufactured by Tokyo Chemical Industry Co., Ltd.) Hardener: cis-1,2-cyclohexanecarboxylic anhydride 4330 parts by mass Curing accelerator: 2,4,6-tris(dimethylaminomethyl)phenol 80 parts by mass

[0152] (Example A3) The recording layer of Example A3 was obtained in the same manner as in Example A1, except that 10 mL of resin precursor (iii) was used instead of resin precursor (i) and the coating film was heated at 90°C for 18 hours. Resin precursor (iii) was prepared by uniformly mixing the following materials by stirring. The number-average molecular weight of the polyethylene glycol diglycidyl ether was 500. The concentration of the multiphoton absorption compound in the coating solution was 5.0 mmol / L. Aliphatic monomer: polyethylene glycol diglycidyl ether (compound E3, manufactured by Sigma-Aldrich) 10,000 parts by mass Hardener: cis-1,2-cyclohexanecarboxylic anhydride 3080 parts by mass Curing accelerator: 2,4,6-tris(dimethylaminomethyl)phenol 100 parts by mass

[0153] (Example A4) The recording layer of Example A4 was obtained in the same manner as in Example A1, except that 10 mL of resin precursor (iv) was used instead of resin precursor (i), and the coating film was irradiated with light from a light-emitting diode (LED) without heating to cause the polymerization reaction of the aliphatic monomer. The wavelength of the light irradiated to the coating film was 365 nm. The power density of the light irradiated to the coating film was 50 mW / cm. 2 Resin precursor (iv) was prepared by uniformly mixing the following materials with stirring. Aliphatic monomer: dodecyl acrylate (compound a1, manufactured by Tokyo Chemical Industry Co., Ltd.) 9000 parts by mass Aliphatic monomer: 1,6-hexanediol diacrylate (compound B3, manufactured by Tokyo Chemical Industry Co., Ltd.) 900 parts by mass Polymerization initiator: 1-hydroxycyclohexyl phenyl ketone (Tokyo Chemical Industry Co., Ltd.) 90 parts by mass

[0154] (Example A5) The recording layer of Example A5 was obtained in the same manner as in Example A4, except that 25 mL of resin precursor (v) was used instead of resin precursor (iv). Resin precursor (v) was prepared by uniformly mixing the following materials by stirring. The concentration of the multiphoton absorption compound in the coating solution was 2.0 mmol / L. Aliphatic monomer: octyl acrylate (compound a2, manufactured by Tokyo Chemical Industry Co., Ltd.) 9000 parts by mass Aliphatic monomer: 1,6-hexanediol diacrylate (compound B3) 900 parts by mass Polymerization initiator: 1-hydroxycyclohexyl phenyl ketone 90 parts by mass

[0155] (Example A6) The recording layer of Example A6 was obtained in the same manner as in Example A4, except that 25 mL of resin precursor (vi) was used instead of resin precursor (iv). Resin precursor (vi) was prepared by uniformly mixing the following materials by stirring. Aliphatic monomer: cyclohexyl acrylate (compound A2, manufactured by Tokyo Chemical Industry Co., Ltd.) 9000 parts by mass Aliphatic monomer: 1,6-hexanediol diacrylate (compound B3) 900 parts by mass Polymerization initiator: 1-hydroxycyclohexyl phenyl ketone 90 parts by mass

[0156] (Example A7) The recording layer of Example A7 was obtained in the same manner as in Example A4, except that 10 mL of resin precursor (vii) was used instead of resin precursor (iv). Resin precursor (vii) was prepared by uniformly mixing the following materials by stirring. Aliphatic monomer: tetraethylene glycol dimethacrylate (compound b1, manufactured by Sigma-Aldrich) 9750 parts by mass Polymerization initiator: 250 parts by mass of 1-hydroxycyclohexyl phenyl ketone

[0157] (Comparative Example A1) The recording layer of Comparative Example A1 was obtained in the same manner as in Example A4, except that 10 mL of resin precursor (viii) was used instead of resin precursor (iv). Resin precursor (viii) was prepared by uniformly mixing the following materials by stirring. The recording layer of Comparative Example A1 contained an aromatic polymer with an aromatic ring content significantly exceeding 10 wt%. Aromatic monomer: 2-phenoxyethyl acrylate (Tokyo Chemical Industry Co., Ltd.) 9000 parts by mass Aliphatic monomer: 1,6-hexanediol diacrylate (compound B3) 900 parts by mass Polymerization initiator: 1-hydroxycyclohexyl phenyl ketone 90 parts by mass

[0158] (Comparative example A2) The recording layer of Comparative Example A2 was obtained in the same manner as in Example A4, except that 10 mL of resin precursor (ix) was used instead of resin precursor (iv). Resin precursor (ix) was prepared by uniformly mixing the following materials by stirring. The recording layer of Comparative Example A2 contained an aromatic polymer with an aromatic ring content significantly exceeding 10 wt%. Aromatic monomer: benzyl acrylate (Tokyo Chemical Industry Co., Ltd.) 9000 parts by mass Aliphatic monomer: 1,6-hexanediol diacrylate (compound B3) 900 parts by mass Polymerization initiator: 1-hydroxycyclohexyl phenyl ketone 90 parts by mass

[0159] (Comparative example A3) The recording layer of Comparative Example A3 was obtained in the same manner as in Example A1, except that resin precursor (x) was used instead of resin precursor (i) and the coating film was heated at 90°C for 10 hours. Resin precursor (x) was prepared by uniformly mixing the following materials by stirring. The recording layer of Comparative Example A3 contained an aromatic polymer with an aromatic ring content significantly exceeding 10 wt%. Aromatic monomer: 9,900 parts by mass of 1,6-bis(2,3-epoxypropoxy)naphthalene (HP-4032D manufactured by DIC Corporation) Curing accelerator: 2,4,6-tris(dimethylaminomethyl)phenol 100 parts by mass

[0160] [Measurement of molar extinction coefficient ε] The molar absorption coefficients ε of the multiphoton absorption compounds contained in the recording layers of Examples A1 to A7 and Comparative Examples A1 to A3 with respect to light having a wavelength of 405 nm were determined by the method described above. The results are shown in Table 1.

[0161] [Transmittance measurement] The transmittance of the recording layers of Examples A1 to A7 in the thickness direction at a thickness of 100 μm for light with a wavelength of 405 nm was determined by the method described above. The results are shown in Table 1.

[0162] [Table 1]

[0163] Example B1 The recording layer of Example B1 was obtained in the same manner as in Example A1, except that 19.5 mg of compound K was used as the multiphoton absorption compound and 5 mL of resin precursor (i) was used. The concentration of the multiphoton absorption compound in the coating liquid was 5.0 mmol / L.

[0164] (Example B2) The recording layer of Example B2 was obtained in the same manner as in Example A2, except that 19.5 mg of compound K was used as the multiphoton absorption compound and 5 mL of resin precursor (ii) was used.

[0165] (Example B3) The recording layer of Example B3 was obtained in the same manner as in Example A4, except that 1.2 mg of compound K was used as the multiphoton absorption compound and 10 mL of resin precursor (iv) was used. The concentration of the multiphoton absorption compound in the coating liquid was 0.15 mmol / L.

[0166] (Example B4) The recording layer of Example B4 was obtained in the same manner as in Example A5, except that 3.1 mg of compound K was used as the multiphoton absorption compound and 25 mL of resin precursor (v) was used. The concentration of the multiphoton absorption compound in the coating liquid was 0.16 mmol / L.

[0167] (Example B5) The recording layer of Example B5 was obtained in the same manner as in Example A6, except that 3.1 mg of compound K was used as the multiphoton absorption compound and 25 mL of resin precursor (vi) was used.

[0168] (Example B6) The recording layer of Example B6 was obtained in the same manner as in Example A7, except that 1.2 mg of compound K was used as the multiphoton absorption compound and 10 mL of resin precursor (vii) was used.

[0169] (Comparative Example B1) The recording layer of Comparative Example B1 was obtained in the same manner as in Comparative Example A1, except that 1.2 mg of compound K was used as the multiphoton absorption compound and 10 mL of resin precursor (viii) was used.

[0170] (Comparative example B2) The recording layer of Comparative Example B2 was obtained in the same manner as in Comparative Example A2, except that 1.2 mg of compound K was used as the multiphoton absorption compound and 10 mL of resin precursor (ix) was used.

[0171] (Comparative Example B3) The recording layer of Comparative Example B3 was obtained in the same manner as in Comparative Example A3, except that 19.5 mg of compound K was used as the multiphoton absorption compound and 5 mL of resin precursor (x) was used.

[0172] [Measurement of molar extinction coefficient ε] The molar absorption coefficients ε of the multiphoton absorption compounds contained in the recording layers of Examples B1 to B6 and Comparative Examples B1 to B3 were measured for light having a wavelength of 405 nm by the method described above. The results are shown in Table 2.

[0173] [Transmittance measurement] The transmittance of the recording layers of Examples B1 to B6 in the thickness direction for light with a wavelength of 405 nm when the thickness was 100 μm was determined by the method described above. The results are shown in Table 2.

[0174] [Table 2]

[0175] Example C1 The recording layer of Example C1 was obtained in the same manner as in Example A1, except that 6.9 mg of compound I was used as the multiphoton absorption compound and 5 mL of resin precursor (i) was used. The concentration of the multiphoton absorption compound in the coating liquid was 5.0 mmol / L.

[0176] (Example C2) The recording layer of Example C2 was obtained in the same manner as in Example A2, except that 13.9 mg of compound I was used as the multiphoton absorption compound and 5 mL of resin precursor (ii) was used. The concentration of the multiphoton absorption compound in the coating liquid was 10.0 mmol / L.

[0177] (Example C3) The recording layer of Example C3 was obtained in the same manner as in Example A3, except that 13.9 mg of compound I was used as the multiphoton absorption compound and 10 mL of resin precursor (iii) was used. The concentration of the multiphoton absorption compound in the coating liquid was 5.0 mmol / L.

[0178] (Comparative Example C1) The recording layer of Comparative Example C1 was obtained in the same manner as in Comparative Example A1, except that 6.9 mg of Compound I was used as the multiphoton absorption compound and 5 mL of resin precursor (viii) was used.

[0179] (Comparative Example C2) The recording layer of Comparative Example C2 was obtained in the same manner as in Comparative Example A2, except that 6.9 mg of Compound I was used as the multiphoton absorption compound and 5 mL of the resin precursor (ix) was used.

[0180] (Comparative Example C3) The recording layer of Comparative Example C3 was obtained in the same manner as in Comparative Example A3, except that 13.9 mg of Compound I was used as the multiphoton absorption compound and 5 mL of the resin precursor (x) was used.

[0181] [Measurement of molar extinction coefficient ε] The molar absorption coefficients ε of the multiphoton absorption compounds contained in the recording layers of Examples C1 to C3 and Comparative Examples C1 to C3 were measured for light having a wavelength of 405 nm by the method described above. The results are shown in Table 3.

[0182] [Transmittance measurement] The transmittance of the recording layers of Examples C1 to C3 in the thickness direction at a thickness of 100 μm was determined by the method described above for light with a wavelength of 405 nm. The results are shown in Table 3.

[0183] [Table 3]

[0184] Example D1 The recording layer of Example D1 was obtained in the same manner as in Example A1, except that 7.2 mg of compound L was used as the multiphoton absorption compound and 5 mL of resin precursor (i) was used. The concentration of the multiphoton absorption compound in the coating liquid was 1.6 mmol / L.

[0185] (Example D2) The recording layer of Example D2 was obtained in the same manner as in Example A2, except that 7.2 mg of compound L was used as the multiphoton absorption compound and 5 mL of resin precursor (ii) was used.

[0186] (Example D3) The recording layer of Example D3 was obtained in the same manner as in Example A1, except that 7.2 mg of compound L was used as the multiphoton absorption compound and 5 mL of resin precursor (xi) was used instead of resin precursor (i). Resin precursor (xi) was prepared by uniformly mixing the following materials by stirring. Aliphatic monomer: 1,5-hexadiene diepoxide (compound e2, manufactured by Tokyo Chemical Industry Co., Ltd.) 5,000 parts by mass Hardener: cis-1,2-cyclohexanecarboxylic anhydride 6750 parts by mass Curing accelerator: 2,4,6-tris(dimethylaminomethyl)phenol 50 parts by mass

[0187] (Comparative Example D1) The recording layer of Comparative Example D1 was obtained in the same manner as in Comparative Example A1, except that 9.0 mg of compound L was used as the multiphoton absorption compound and 5 mL of resin precursor (viii) was used. The concentration of the multiphoton absorption compound in the coating liquid was 2.0 mmol / L.

[0188] (Comparative example D2) The recording layer of Comparative Example D2 was obtained in the same manner as in Comparative Example A2, except that 4.5 mg of compound L was used as the multiphoton absorption compound and 5 mL of resin precursor (ix) was used. The concentration of the multiphoton absorption compound in the coating liquid was 1.0 mmol / L.

[0189] (Comparative Example D3) The recording layer of Comparative Example C3 was obtained in the same manner as in Comparative Example A3, except that 36.0 mg of compound L was used as the multiphoton absorption compound and 5 mL of resin precursor (x) was used. The concentration of the multiphoton absorption compound in the coating liquid was 7.9 mmol / L.

[0190] [Measurement of molar extinction coefficient ε] The molar absorption coefficients ε of the multiphoton absorption compounds contained in the recording layers of Examples D1 to D3 and Comparative Examples D1 to D3 were measured for light having a wavelength of 405 nm by the method described above. The results are shown in Table 4.

[0191] [Transmittance measurement] The transmittance of the recording layers of Examples D1 to D3 in the thickness direction at a thickness of 100 μm for light with a wavelength of 405 nm was determined by the method described above. The results are shown in Table 4.

[0192] [Table 4]

[0193] Example E1 The recording layer of Example E1 was obtained in the same manner as in Example A1, except that 4.7 mg of compound J was used as the multiphoton absorption compound and 5 mL of resin precursor (i) was used. The concentration of the multiphoton absorption compound in the coating liquid was 2.0 mmol / L.

[0194] (Comparative Example E1) The recording layer of Comparative Example E1 was obtained in the same manner as in Comparative Example A3, except that 4.7 mg of compound J was used as the multiphoton absorption compound and 5 mL of resin precursor (x) was used.

[0195] [Measurement of molar extinction coefficient ε] The molar absorption coefficients ε of the multiphoton absorption compounds contained in the recording layers of Example E1 and Comparative Example E1 with respect to light having a wavelength of 405 nm were measured by the method described above. The results are shown in Table 5.

[0196] [Transmittance measurement] The transmittance of the recording layer of Example E1 in the thickness direction for light with a wavelength of 405 nm when the thickness was 100 μm was determined by the method described above. The results are shown in Table 5.

[0197] [Table 5]

[0198] As can be seen from Tables 1 to 5, when the type of multiphoton absorption compound was the same, the molar absorption coefficient of the multiphoton absorption compound for light having a wavelength of 405 nm was smaller in the recording layer of the example containing an aliphatic polymer than in the recording layer of the comparative example containing an aromatic polymer. From this result, it can be said that in the recording layer containing an aliphatic polymer and a multiphoton absorption compound, an increase in one-photon absorption for light having a wavelength in the short wavelength range is suppressed.

[0199] In the comparative example recording layer containing an aromatic polymer, an interaction between the aromatic polymer and the multiphoton absorption compound is presumed to have occurred, causing a change in the electronic state of the multiphoton absorption compound. In particular, since all of the multiphoton absorption compounds contained in the comparative example recording layer contain at least one selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond, and also contain an aromatic ring, it is presumed that they have a strong interaction with the aromatic polymer. In the comparative example recording layer, it is presumed that the absorption band of the S0-S1 transition in the multiphoton absorption compound tails to the long wavelength region due to a change in the electronic state of the compound. In the comparative example recording layer, it is presumed that the molar extinction coefficient ε is significantly increased because part of the wavelength region where one-photon absorption occurs overlaps with 405 nm. [Industrial Applicability]

[0200] The recording medium of the present disclosure can be used as a three-dimensional optical memory having multiple recording layers. In the recording layer of the recording medium of the present disclosure, an increase in one-photon absorption of light used for recording or reading information is suppressed. Therefore, the recording medium of the present disclosure can realize a three-dimensional optical memory having a greater number of recording layers than conventional ones. [Explanation of symbols]

[0201] 10 Recording Layer 20 dielectric layer 100 Recording Media

Claims

1. at least one recording layer; The at least one recording layer is an aliphatic polymer; a multiphoton absorption compound containing at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond, and having multiphoton absorption properties; when the thickness of the at least one recording layer is 100 μm, the transmittance of the at least one recording layer in the thickness direction for light having a wavelength of 405 nm is 80% or more, Information is recorded using light having a wavelength of 390 nm or more and 420 nm or less. Recording medium.

2. The recording medium described in claim 1, wherein the multi-photon absorption compound excludes a non-resonant polymer two-photon absorption compound.

3. in the at least one recording layer, the total content of the aliphatic polymer and the multiphoton absorption compound is 95 wt % or more; The recording medium according to claim 1 .

4. The aliphatic polymer contains constitutional units derived from aliphatic monomers, The aliphatic monomer contains at least one selected from the group consisting of an acrylic group, a methacrylic group, an epoxy group, an oxetanyl group, and a vinyl group. The recording medium according to claim 1 .

5. The aliphatic monomer contains at least one selected from the group consisting of an acrylic group, a methacrylic group, and an epoxy group. The recording medium according to claim 4.

6. The aliphatic monomer includes at least one selected from the group consisting of a compound A represented by the following formula (A), a compound B represented by the following formula (B), a compound C represented by the following formula (C), a compound D represented by the following formula (D), a compound E represented by the following formula (E), a compound F represented by the following formula (F), and a compound G represented by the following formula (G): The recording medium according to claim 4. 【Chemistry 1】 In the formula (A), R 1 is a hydrogen atom or a methyl group, and R 2 is an aliphatic group, In the formula (B), R 3 and R 5 are each independently a hydrogen atom or a methyl group, and R 4 is an aliphatic group, In the formula (C), R 6 is a hydrogen atom or a methyl group, and R 7 is an aliphatic group, and R 8 is a hydrogen atom or an aliphatic group, In the formula (D), R 9 is a hydrogen atom or a methyl group, and R 10 is an aliphatic group, and R 11 is a hydrogen atom or an aliphatic group, In the formula (E), R 12 and R 14 are each independently a hydrogen atom or an aliphatic group, and R 13 is an aliphatic group, In the formula (F), R 15 and R 17 are each independently a hydrogen atom or an aliphatic group, and R 16 is an aliphatic group, In the formula (G), R 18 and R 20 are each independently a hydrogen atom or an aliphatic group, and R 19 is an aliphatic group.

7. The compound A includes at least one selected from the group consisting of a compound A1 represented by the following formula (A1) and a compound A2 represented by the following formula (A2): The recording medium according to claim 6. 【Chemistry 2】 In the formula (A1), n ​​is an integer of 0 or more and 11 or less.

8. The compound B includes a compound B1 represented by the following formula (B1): The recording medium according to claim 6. 【Transformation 3】 In the formula (B1), m is an integer of 1 or more and 4 or less.

9. The compound E includes at least one selected from the group consisting of a compound E1 represented by the following formula (E1), a compound E2 represented by the following formula (E2), and a compound E3 represented by the following formula (E3): The recording medium according to claim 6. 【Chemistry 4】 In the formula (E1), x represents an integer of 1 or more and 12 or less, In the formula (E3), y is an integer of 1 or more and 11 or less.

10. The multiphoton absorption compound includes an aromatic ring. The recording medium according to claim 1 .

11. Further comprising a plurality of dielectric layers; the at least one recording layer includes a plurality of recording layers; the plurality of recording layers and the plurality of dielectric layers are arranged alternately; The recording medium according to claim 1 .

12. providing a light source that emits light having a wavelength of 390 nm or more and 420 nm or less; and irradiating the light from the light source onto the at least one recording layer of the recording medium according to any one of claims 1 to 11. How information is recorded.

13. A method for reading information recorded by the recording method according to claim 12, comprising: The reading method includes: measuring optical characteristics of the at least one recording layer by irradiating the at least one recording layer with light; reading information from the at least one recording layer. How to read the information.

14. A composition for producing a recording layer having a transmittance of 80% or more in the thickness direction for light having a wavelength of 405 nm when the composition has a thickness of 100 μm, and in which information is recorded using light having a wavelength of 390 nm or more and 420 nm or less, an aliphatic monomer; a multiphoton absorption compound containing at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond, and having multiphoton absorption properties; Including, composition.

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