Recording medium, information recording method, and information reading method

Abstract

A recording medium (100) according to one aspect of the present disclosure includes a first dielectric layer (20A), a second dielectric layer (20B), and a recording layer (10). The recording layer (10) has a recording region in which information is recorded by irradiation with light. The reflectance of the light in the recording region where the information is recorded is higher than the reflectance of the light in the recording region before the information is recorded. The thickness D (nm) of the recording layer (10), the refractive index n1 of the recording layer (10), the refractive index n2 of the first dielectric layer (20A), and the refractive index n3 of the second dielectric layer (20B) satisfy relational expressions (1) to (3). (1.33-0.15 n1) {405 (m + 1 / 2) / (2n1)} < D < = (1.33-0.15 n1) {405 (m + 1) / (2n1)} (1) n1 > n2 (2) n1 > n3 (3). In formula (1), m is an integer from 0 to 4.

Description

Technical Field

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

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

[0003] Patent document 1 discloses a recording medium in which the interface between resin layers is used as a reflection surface. In the recording medium of patent document 1, it is not necessary to provide a reflection film separately. Patent document 2 discloses a recording medium in which information is recorded by irradiating a recording layer with recording light to change its refractive index. In patent document 2, the recording layer has a pigment and a polymer binder. Patent document 3 discloses a recording medium using recording light and reproducing light having different wavelengths.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 4890507

[0007] Patent Document 2: Japanese Patent No. 5357114

[0008] Patent Document 3: Japanese Patent No. 4712798

[0009] Patent Document 4: Japanese Patent No. 5553723 Summary of the invention

[0010] Problems to be solved by the invention

[0011] There is a need for a new type of recording medium suitable for recording and reading information.

[0012] Means for solving problems

[0013] A recording medium in one embodiment of the present disclosure includes: a first dielectric layer, a second dielectric layer, and a recording layer having a recording area for recording information by irradiating light and located between the first dielectric layer and the second dielectric layer, the recording layer contains a pigment material, the transmittance of light of a wavelength of 405 nm in the recording layer is 95% or more, the reflectivity of light in the recording area where information is recorded is higher than the reflectivity of light in the recording area before information is recorded, the thickness D (nm) of the recording layer, the refractive index n of the recording layer for light of a wavelength of 405 nm 1 , the refractive index n of the first dielectric layer for light of wavelength 405 nm 2 and the refractive index n of the second dielectric layer for light of wavelength 405 nm 3 The following relational expressions (1) to (3) are satisfied.

[0014] (1.33-0.15n 1 ){405(m+1 / 2) / (2n 1 )}<D≤(1.33-0.15n 1 ){405(m+1) / (2n 1 )} (1)

[0015] n 1 >n 2 (2)

[0016] n 1 >n 3 (3)

[0017] In the formula (1), m is an integer of 0 to 4.

[0018] Effects of the Invention

[0019] The present disclosure provides a novel recording medium suitable for recording and reading information. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a cross-sectional view showing a schematic structure of a recording medium according to one embodiment of the present disclosure.

[0021] Figure 2 is a graph for explaining the relational expression (1).

[0022] Figure 3A It is a flowchart related to the method of recording information using the recording medium according to one embodiment of the present disclosure.

[0023] Figure 3B This is a flowchart related to a method of reading information using a recording medium according to an embodiment of the present disclosure.

[0024] Figure 4 It is a cross-sectional view schematically showing the structure of a recording medium according to a modification.

[0025] Figure 5 is the number of the compound B used in the examples. 1 H-NMR spectrum.

[0026] Fig. 6A This is an optical microscope image showing a recording mark formed in the recording layer of the recording medium of Example 4.

[0027] Figure 6B Graph showing a reproduced signal of a recording mark formed in a recording layer of a recording medium according to Example 4.

[0028] Figure 6C This is a graph showing the degree of modulation of a recording mark formed in the recording layer of the recording medium of Example 4.

[0029] Figure 7 This is a graph showing the relationship between the average energy of irradiation with recording light and the amount of deformation of a concave recording mark for the recording medium of Example 2. DETAILED DESCRIPTION

[0030] (Insights that form the basis of this disclosure)

[0031] [Characteristics of the recording layer and dielectric layer]

[0032] In a multilayer optical recording medium in which a plurality of recording layers and a plurality of dielectric layers are alternately stacked, if the absorption of light at each layer and the reflection of light at the interface of each layer are large, there is a tendency that the light reaching the recording layer located farther from the light source, that is, the inner layer, is attenuated. If the light is attenuated, the recording sensitivity at the inner layer is reduced. Therefore, it is preferable that the recording sensitivity of the recording layer itself is good in each recording layer, the linear light absorption at the recording and reproducing wavelength is small, the refractive index difference with the dielectric layer is appropriately set so as to adjust the light reflectance to an appropriate value, and the stability of the shape of the recording mark is high. From the viewpoint of reducing the linear light absorption of the recording layer and improving the recording sensitivity, it is preferable to use a pigment material with large nonlinear light absorption. For a multilayer recording medium, there is a tendency that the more recording layers there are, the greater the capacity. Therefore, it is advantageous that the thickness of the recording layer is thin. Similarly, for each dielectric layer, it is preferable that the transmittance of light at the recording and reproducing wavelength is high, the refractive index difference with the recording layer is appropriately set, and the thickness is thin to the extent that crosstalk does not occur.

[0033] [Nonlinear optical materials]

[0034] In a recording medium including a plurality of recording layers, when the single-photon absorption of light used for recording or reading information is large at each recording layer, the intensity of light decreases as the light passes through each recording layer. In this case, in a recording layer arranged at a position far from the light source, there is a tendency that the sensitivity of recording and reading is greatly reduced. Therefore, a recording layer with a small single-photon absorption for light used for recording or reading information is required. In this specification, reading of information is sometimes referred to as reproduction of information. Single-photon absorption is sometimes referred to as linear light absorption.

[0035] In order to further increase the number of recording layers in the recording medium, it is necessary to reduce the linear light absorption of each recording layer, and it is necessary to minimize the influence of other recording layers other than the recording layer to be recorded or reproduced. However, if the linear light absorption of the recording layer is reduced, the amount of light required for recording the required recording layer increases. Therefore, if the linear light absorption of the recording layer is excessively reduced, it is difficult to record in the recording layer using a generally available light source. In this way, it is necessary to appropriately adjust the balance between the recording sensitivity of the recording layer and the amount of light used to reach the inner layer. Therefore, research has been conducted on recording layers that include pigments having nonlinear optical effects, particularly pigments that can perform nonlinear light absorption.

[0036] It should be noted that the nonlinear optical effect means an optical phenomenon that is generated in a substance when a strong light such as a laser is irradiated on the substance and is proportional to the square of the electric field of the irradiated light or a higher order than the square. As optical phenomena, absorption, reflection, scattering, luminescence, etc. can be cited. As a second-order nonlinear optical effect proportional to the square of the electric field of the irradiated light, second harmonic generation (SHG), Pockels effect, parametric effect, etc. can be cited. As a third-order nonlinear optical effect proportional to the cube of the electric field of the irradiated light, multiphoton absorption such as two-photon absorption, third harmonic generation (THG), Kerr effect, etc. can be cited. In particular, with respect to a recording medium including a plurality of recording layers, multiphoton absorption such as two-photon absorption can be utilized. In this specification, multiphoton absorption such as two-photon absorption is sometimes referred to as nonlinear light absorption. Sometimes a material capable of nonlinear light absorption is referred to as a nonlinear light absorption material. Furthermore, nonlinear light absorption is sometimes referred to as nonlinear absorption.

[0037] So far, inorganic materials that can easily prepare single crystals have been developed as nonlinear optical materials. On the other hand, in recent years, it is expected that nonlinear optical materials composed of organic materials will be developed. Compared with inorganic materials, organic materials not only have high design freedom, but also have large nonlinear optical constants. Furthermore, for organic materials, nonlinear response is performed at high speed.

[0038] Among organic nonlinear optical materials, two-photon absorption materials are particularly noteworthy. The so-called two-photon absorption refers to the phenomenon that a compound absorbs two photons almost simultaneously and transitions to an excited state. As two-photon absorption, simultaneous two-photon absorption and step-by-step two-photon absorption are known. Simultaneous two-photon absorption is sometimes also called non-resonant two-photon absorption. Simultaneous two-photon absorption means two-photon absorption in a wavelength range where there is no absorption band of a single photon. Step-by-step two-photon absorption is sometimes also called resonant two-photon absorption. In step-by-step two-photon absorption, a compound absorbs the first photon and then further absorbs the second photon, thereby transitioning to a higher-order excited state. In step-by-step two-photon absorption, a compound absorbs two photons one by one.

[0039] In simultaneous two-photon absorption, the amount of light absorbed by the compound is generally proportional to the square of the intensity of the irradiated light, showing nonlinear characteristics. The amount of light absorbed by the compound can be used as an indicator of the efficiency of two-photon absorption. In the case where the amount of light absorbed by the compound shows nonlinear characteristics, for example, the absorption of light achieved by the compound can occur only near the focus of a laser with a high electric field intensity. That is, in a sample containing a two-photon absorption material, the compound can be excited only at a desired position. In this way, the compound that produces simultaneous two-photon absorption brings extremely high spatial resolution, so the application in the recording layer of a three-dimensional optical memory, a photocurable resin composition for optical shaping, and the like is studied. In the case where the two-photon absorption material also has fluorescence characteristics, the two-photon absorption material can also be applied to fluorescent pigment materials used in two-photon fluorescence microscopes, etc. If the two-photon absorption material is used in a three-dimensional optical memory, it is also possible to adopt a method of reading the ON / OFF state of the recording layer based on the change in fluorescence from the two-photon absorption material. In current optical memories, a method of reading the ON / OFF state of a recording layer based on changes in the reflectivity and absorptivity of light in a two-photon absorption material is adopted. However, when this method is applied to a three-dimensional optical memory, the two-photon absorption efficiency of existing two-photon absorption materials is low compared to the single-photon absorption efficiency, so crosstalk may occur based on other recording layers different from the recording layer whose ON / OFF state is to be read.

[0040] For two-photon absorption materials, the two-photon absorption cross-sectional area (GM value) is used as an indicator of the efficiency of two-photon absorption. The unit of two-photon absorption cross-sectional area is GM (10 -50 cm 4 ·s·molecule -1 Photon -1 ). So far, a large number of organic two-photon absorption materials with large two-photon absorption cross-sections have been proposed.

[0041] As a light source, for example, a femtosecond laser such as a titanium sapphire laser or a pulse laser such as a semiconductor laser having a pulse width of picoseconds to nanoseconds can be used. From the viewpoint of being small, highly versatile, and having stable operation, semiconductor lasers are suitable for industrial use. When a laser having a pulse width of picoseconds to nanoseconds or more is used, and light with a photon density increased by focusing with a lens is irradiated onto an organic nonlinear optical material, the electron undergoes single-photon excitation or two-photon excitation at the femtosecond level, and relaxes to the lowest excited state in hundreds of femtoseconds to picoseconds. Even at the moment when the electron relaxes to the lowest excited state, pulse irradiation is being performed. Therefore, sometimes excitation from the lowest excited state to a higher excited state occurs. This phenomenon is called excited state absorption (ESA). Then, as long as the pulse irradiation continues, excited state absorption and relaxation to the lowest excited state are repeated. This relaxation is a very fast process that is completed at the latest in picoseconds, except for special cases such as azulene, and is a radiation-free inactivation. That is, deactivation occurs not by emitting light such as fluorescence or phosphorescence, but by generating heat. In this way, when a nonlinear light absorbing material is locally excited using a laser with a pulse width of picoseconds to nanoseconds or more, heat can be generated locally when the nonlinear light absorbing material further absorbs excited states. This makes it possible to utilize the nonlinear light absorbing material as a heat source for locally deteriorating the recording medium, and even to perform three-dimensional recording.

[0042] [Recording mechanism]

[0043] As a method for recording information on a recording medium, for example, a method for deforming a recording layer or a lower substrate by irradiation with recording light, a method for changing optical properties such as light absorptivity and refractive index in the recording layer, and a combination thereof can be cited. It is believed that the deformation of the recording layer is caused by the pigment contained in the recording layer absorbing light and generating heat, thereby deforming the surrounding resin. For example, in Patent Document 4, a recording medium for recording information by forming a convex shape at the interface between the recording layer and the intermediate layer is disclosed. The thermal stability of the formed convex shape depends on the glass transition temperature of the resin.

[0044] The recording medium generally has a recording area. The so-called recording area refers to a point in the recording layer where information can be recorded by irradiating light. In this specification, the recording area where information is recorded is sometimes referred to as a recording portion, and the recording area before the information is recorded is referred to as an unrecorded portion. The recorded portion and the unrecorded portion can be detected by changes in reflectivity when irradiated with reproduction light, differences in fluorescence characteristics, etc. The change in reflectivity is caused, for example, by differences in shape, light absorption, refractive index, etc. between the recorded portion and the unrecorded portion.

[0045] The recording method using the change of reflectivity can be roughly divided into two types: LTH (Low To High) type and HTL (High To Low) type. In the case of LTH type, the reflectivity of light in the recording area increases by recording. In the case of HTL type, the reflectivity of light in the recording area decreases by recording. In a multilayer recording medium, from the viewpoint of recording sensitivity at the inner layer, it is preferred that the intensity of light reaching the inner layer is large. Therefore, it is preferred that the recording layer has a high transmittance. From the viewpoint of ensuring recording sensitivity, the unrecorded portion in the recording layer also needs to show a certain degree of linear light absorption. Therefore, it is preferred that the reflectivity of light at the unrecorded portion is low within a range where there is no problem in controlling the focus, etc. Furthermore, compared with HTL type recording, LTH type recording may be able to adjust the signal amplitude to be large. The signal amplitude is proportional to the difference between the reflectivity at the unrecorded portion and the reflectivity at the recorded portion. Considering the above, LTH type recording with low reflectivity at the unrecorded portion is suitable for multilayer recording media.

[0046] (Reflection of light and phase of light)

[0047] Generally, when light is incident on a medium with a different refractive index, light reflection occurs. As the way of light incidence, consider the way of light incident from a medium with a low refractive index to a medium with a high refractive index, and the way of light incident from a medium with a high refractive index to a medium with a low refractive index. In the way of light incident on a medium with a high refractive index, fixed-end reflection occurs, and the phase of the light in the reflected light only deviates by π. In the way of light incident on a medium with a low refractive index, free-end reflection occurs, and the phase of the light in the reflected light does not deviate. In addition, it is known that light has the properties of waves, so if two lights coincide with the same phase, they reinforce each other, and if they coincide with opposite phases, they weaken each other.

[0048] The inventors have conducted intensive research and have newly discovered that by focusing on the relationship between the refractive indexes of the recording layer and the dielectric layer and designing the thickness of the recording layer according to the refractive index of the recording layer, LTH-type recording and reproduction using interference of reflected light can be performed. Based on this knowledge, a high-capacity recording medium capable of performing recording and reproduction operations with a simple device configuration can be realized.

[0049] (Overview of one aspect of the present disclosure)

[0050] A first aspect of the present disclosure relates to a recording medium comprising: a first dielectric layer, a second dielectric layer, and a recording layer having a recording area where information is recorded by irradiating light and located between the first dielectric layer and the second dielectric layer, the recording layer containing a pigment material, the transmittance of light of a wavelength of 405 nm in the recording layer being 95% or more, the reflectance of light in the recording area where information is recorded being higher than the reflectance of light in the recording area before information is recorded, the thickness D (nm) of the recording layer, the refractive index n of the recording layer for light of a wavelength of 405 nm 1 , the refractive index n of the first dielectric layer for light of wavelength 405 nm 2 and the refractive index n of the second dielectric layer for light of wavelength 405 nm 3 The following relational expressions (1) to (3) are satisfied.

[0051] (1.33-0.15n 1 ){405(m+1 / 2) / (2n 1 )}<D≤(1.33-0.15n 1 ){405(m+1) / (2n 1 )} (1)

[0052] n 1 >n 2 (2)

[0053] n 1 >n 3 (3)

[0054] In the formula (1), m is an integer of 0 to 4.

[0055] According to the first aspect, a new recording medium suitable for recording and reading information can be provided. In this recording medium, LTH type recording and reproduction can be performed, and there is a tendency that a large reproduced signal can be obtained by a reproduction operation.

[0056] In a second aspect of the present disclosure, for example, according to the recording medium involved in the first aspect, the refractive index n 1 With the refractive index n 2 The difference can be greater than 0.2, and the refractive index n 1 With the refractive index n 3 The difference can be greater than 0.2.

[0057] According to the second aspect, even when a small semiconductor laser is used, interference occurs with the reflected light, and there is a tendency that a sufficient amount of reflected light can be ensured. Therefore, a smaller recording medium can be easily realized.

[0058] In a third aspect of the present disclosure, for example, according to the recording medium involved in the first or second aspect, the refractive index n 1 It can be 1.65 or more.

[0059] According to the third embodiment, it is easy to adjust the refractive index difference between the recording layer and the first dielectric layer and the second dielectric layer to be large. As a result, the range of material selection for the first dielectric layer and the second dielectric layer is expanded. For example, when the first dielectric layer and the second dielectric layer are manufactured, materials that can be used in a coating process can be selected. According to the coating process, there is a tendency that the recording medium can be manufactured simply.

[0060] In a fourth aspect of the present disclosure, for example, in the recording medium according to any one of the first to third aspects, in the recording layer, a concave recording mark can be formed by irradiating the recording light.

[0061] According to the fourth aspect, the reflectance of light in the recording portion can be adjusted using the deformation amount of the recording mark. Therefore, a highly reliable recording medium can be realized.

[0062] In a fifth aspect of the present disclosure, for example, in the recording medium according to any one of the first to fourth aspects, the pigment material may include a polymer P1, and the polymer P1 may include a group having a nonlinear light absorption property.

[0063] In a sixth aspect of the present disclosure, for example, in the recording medium according to the fifth aspect, the polymer P1 may have a structural unit derived from vinyl carbazoles.

[0064] In a seventh aspect of the present disclosure, for example, in the recording medium according to any one of the first to sixth aspects, the recording layer may further contain a polymer P2.

[0065] In an eighth aspect of the present disclosure, for example, in the recording medium according to the seventh aspect, the polymer P2 may have a structural unit derived from vinyl carbazoles.

[0066] According to the fifth to eighth embodiments, the refractive index of the recording layer can be easily increased while maintaining the transmittance of light with a wavelength of 390 nm to 410 nm. The polymer P1 or P2 having a structural unit derived from vinyl carbazole also tends to have a high glass transition temperature. The polymer P1 or P2 also tends to have appropriate solubility in solvents, so the recording layer can be easily prepared by coating film formation.

[0067] The ninth aspect of the present disclosure relates to a method for recording information, comprising: preparing a light source that emits light having a wavelength of 390 nm to 410 nm; and focusing the light from the light source and irradiating the light to the recording layer in the recording medium according to any one of the first to eighth aspects.

[0068] According to the ninth aspect, information can be recorded on the recording medium at a high recording density.

[0069] The tenth scheme of the present disclosure involves a method for reading information, for example, a method for reading information recorded using the recording method involved in the ninth scheme, and the reading method includes: irradiating light to the recording layer in the recording medium to thereby measure the optical properties of the recording layer; and reading information from the recording layer.

[0070] In an eleventh aspect of the present disclosure, for example, according to the information reading method pertaining to the tenth aspect, the optical characteristic may be the intensity of light reflected by the recording layer.

[0071] According to the tenth or eleventh aspect, information can be easily read from the recording medium.

[0072] The following describes embodiments of the present disclosure with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0073] (Implementation Method)

[0074] Figure 1 1 is a cross-sectional view showing a schematic structure of a recording medium 100 according to an embodiment of the present disclosure. Figure 1 As shown, the recording medium 100 includes a recording layer 10, a first dielectric layer 20A and a second dielectric layer 20B. The recording layer 10 is located between the first dielectric layer 20A and the second dielectric layer 20B, for example, directly in contact with the first dielectric layer 20A and the second dielectric layer 20B. As an example, when the recording medium 100 is set in a recording device, the first dielectric layer 20A is located closer to the light source side of the recording device than the second dielectric layer 20B. In this specification, the first dielectric layer 20A and the second dielectric layer 20B are sometimes referred to as the dielectric layer 20.

[0075] The recording layer 10 includes a pigment material and has a recording area. As described above, the recording area is a point where information can be recorded by irradiating light. The light irradiated to the recording area has a wavelength of, for example, a short wavelength range. In this specification, the short wavelength range means a wavelength range including 405nm, for example, a wavelength range of more than 390nm and less than 420nm. In the recording layer 10, the reflectivity of light in the recording area where information is recorded is higher than the reflectivity of light in the recording area before recording information. In other words, in the recording layer 10, in the recording area, the reflectivity of light rises by recording information.

[0076] The transmittance of the light of wavelength 405 nm in the recording layer 10 is 95% or more. Furthermore, in the recording medium 100, the thickness D (nm) of the recording layer 10, the refractive index n of the recording layer 10 for the light of wavelength 405 nm, 1 , the refractive index n of the first dielectric layer 20A for light of wavelength 405 nm 2 and the refractive index n of the second dielectric layer 20B for light of wavelength 405 nm 3 The following relational expressions (1) to (3) are satisfied.

[0077] (1.33-0.15n 1 ){405(m+1 / 2) / (2n 1 )}<D≤(1.33-0.15n 1 ){405(m+1)

[0078] / (2n 1 )} (1)

[0079] n 1 >n 2 (2)

[0080] n 1 >n 3 (3)

[0081] In formula (1), m is an integer of 0 to 4. In the present specification, the transmittance of light of wavelength 405 nm in the recording layer 10, the thickness D of the recording layer 10, and the refractive index n of the recording layer 10 are 1 Specifically, it is a value for the recording layer 10 before information is recorded.

[0082] In the recording medium 100, when light is incident from the first dielectric layer 20A side, the light travels in the first dielectric layer 20A. A portion of the light is reflected at the interface 30A between the first dielectric layer 20A and the recording layer 10. Light incident from the first dielectric layer 20A to the recording layer 10 travels in the recording layer 10. A portion of the light is reflected at the interface 30B between the recording layer 10 and the second dielectric layer 20B.

[0083] As described above, when light is incident from a medium with a low refractive index to a medium with a high refractive index, fixed-end reflection occurs, and the phase of the light in the reflected light is deviated by only π. When light is incident from a medium with a high refractive index to a medium with a low refractive index, free-end reflection occurs, and the phase of the light in the reflected light is not deviated. Therefore, in the recording medium 100 in which the above-mentioned relational expressions (2) and (3) are satisfied, when light is incident from the first dielectric layer 20A side, the reflection at the interface 30A is equivalent to the fixed-end reflection, and the reflection at the interface 30B is equivalent to the free-end reflection.

[0084] The reflected light A from the interface 30A and the reflected light B from the interface 30B overlap at a position closer to the light source than the recording layer 10 and interfere with each other. When the wavelength of the light incident on the recording medium 100 is 405 nm, the thickness D of the recording layer 10 is (1.33-0.15 nm). 1 ){405(m+1 / 2) / (2n 1 )}, the reflected light A and B overlap in the same phase, and their intensity tends to increase the most. On the other hand, the thickness D of the recording layer 10 is (1.33-0.15n 1 ){405(m+1) / (2n 1 )}, the reflected light A and B overlap in opposite phases, and their intensities tend to be the smallest. These phenomena are based on the results of simulation and experiment verification in a light focusing system with NA 0.85.

[0085] Figure 2 is a graph for explaining the relational expression (1). Figure 2 The graph shows the refractive index n of the recording layer 10. 1 An example of the relationship between the thickness D of the recording layer 10 and the reflectivity when light with a wavelength of 405 nm and a wavelength of 1.65 enters the recording medium 100. Figure 2 It can be seen that the curve graph showing the relationship between thickness D and reflectivity has a wave shape, with multiple maximum points and multiple minimum points. The thickness D corresponding to the multiple maximum points is equivalent to (1.33-0.15n 1 ){405(m+1 / 2) / (2n 1 )}. The thickness D corresponding to the multiple minimum points is equivalent to (1.33-0.15n 1 ){405(m+1) / (2n 1 )}.exist Figure 2 In the curve diagram, the range that satisfies the relational expression (1) is represented by a solid line, and the range that does not satisfy the relational expression (1) is represented by a dotted line.

[0086] Depend on Figure 2 As can be seen from the curve graph, when the relationship (1) is satisfied, when information is recorded in the recording area, if the thickness in the recording area decreases, there is a tendency for the reflectivity of the light from the recording area to increase. Therefore, the recording area can form a concave recording mark when the recording light is irradiated. In other words, in the recording layer 10, a concave recording mark can be formed by irradiating the recording light. In this specification, the recording mark means a mark formed when information is recorded in the recording area, and the mark functions as a recording portion.

[0087] The thickness D (nm) of the recording layer 10 can be (1.33-0.15nm) as long as it satisfies the relation (1). 1 ){405(m+0.53) / (2n1 )} or more, can be (1.33-0.15n 1 ){405(m+0.55) / (2n 1 )} or more. The thickness D (nm) can be (1.33-0.15n 1 ){405(m+0.8) / (2n 1 )} or less, can be (1.33-0.15n 1 ){405(m+0.7) / (2n 1 )}the following.

[0088] Furthermore, regarding the above-mentioned relational expression (1), it is assumed that light with a wavelength of 405 nm is incident on the surface of the recording layer 10 in the thickness direction of the recording layer 10. However, when light is irradiated to the recording medium 100, the light is usually focused by a lens or the like. Therefore, even when light is irradiated in the thickness direction of the recording layer 10, a portion of the light enters the recording layer 10 at an angle. In relational expression (1), (1.33-0.15n 1 ) is a correction coefficient derived using the characteristic matrix method in order to adjust the influence caused by the above-mentioned incident angle. Specifically, the correction coefficient is derived using the following method. First, for a plane wave with an incident angle θ, the Maxwell equation is solved under the boundary conditions of the multilayer film to find the reflectivity for each angle θ. For the reflectivity, the total reflectivity is derived from the value of the weighted integral of the incident light intensity on the objective lens. The total reflectivity is plotted for the film thickness of the recording layer 10. The refractive index of the recording layer 10 is changed to produce the same curve. As a result, the value of the film thickness corresponding to the maximum point and the value of the film thickness corresponding to the minimum point depend on the refractive index n of the recording layer 10. 1 Based on this dependence, the above-mentioned correction coefficient is derived.

[0089] If the above relations (2) and (3) do not hold, n 1 <n 2 and n 1 <n 3 When the free end reflection occurs at the interface 30A, the fixed end reflection occurs at the interface 30B. Even in this case, the thickness D of the recording layer 10 is (1.33-0.15n 1 ){405(m+1 / 2) / (2n 1 )}, the reflected light A from the interface 30A and the reflected light B from the interface 30B overlap in the same phase, and their intensities tend to increase the most. On the other hand, when the thickness D of the recording layer 10 is (1.33-0.15n 1 ){405(m+1) / (2n 1 )}, the reflected light A and B overlap with opposite phases, and their intensity tends to be minimized.

[0090] In the case where fixed end reflection occurs at both interfaces 30A and 30B or in the case where free end reflection occurs at both interfaces 30A and 30B, the thickness D of the recording layer 10 is (1.33-0.15n 1 ){405(m+1 / 2) / (2n 1 )}, the reflected light A and B overlap in opposite phases, and their intensity tends to be the smallest. On the other hand, the thickness D of the recording layer 10 is (1.33-0.15n 1 ){405(m+1) / (2n 1 )}, the reflected lights A and B overlap with the same phase and tend to have their intensities increased the most.

[0091] [Record layer]

[0092] As mentioned above, recording layer 10 includes pigment material. Pigment material may include polymer P1. Polymer P1, for example, includes group G with nonlinear light absorption characteristics. Group G typically has nonlinear light absorption characteristics for light with a wavelength in the short wavelength range. As an example, polymer P1 has the above-mentioned group G in the side chain.

[0093] Whether the group contained in polymer P1 has nonlinear light absorption characteristics can be judged by the following method. First, prepare a compound having the same structure as the group contained in polymer P1. For the compound, measure the light absorption characteristics to determine whether it has nonlinear light absorption characteristics. In the case where the compound has nonlinear light absorption characteristics, it can be judged that the group contained in polymer P1 also has nonlinear light absorption characteristics. In addition, in the case where polymer P1 itself has nonlinear light absorption characteristics, it can also be judged that polymer P1 contains a group G having nonlinear light absorption characteristics.

[0094] As the group G having nonlinear light absorption characteristics, for example, a group containing at least one selected from a carbon-carbon double bond, a carbon-carbon triple bond and an aromatic ring can be cited. As specific examples of the group G, a group having a pyrene skeleton, a group having a diphenylacetylene skeleton, a group having a stiff-stilbene skeleton, etc. can be cited.

[0095] The polymer P1 specifically includes a structural unit A having the above-mentioned group G. Examples of the structural unit A include a structural unit A1 derived from styrenes and having a group G, a structural unit A2 derived from stilbenes and having a group G, and the like. In this specification, the structural unit A1 is sometimes referred to as a structural unit A1 derived from styrenes. The structural unit A2 is sometimes referred to as a structural unit A2 derived from stilbenes. For example, the polymer P1 includes at least one structural unit A selected from the structural unit A1 derived from styrenes and the structural unit A2 derived from stilbenes. The polymer P1 may include a structural unit A1 derived from styrenes.

[0096] The structural unit A is represented by, for example, the following formula (1).

[0097] [Chemical formula number 1]

[0098]

[0099] In formula (1), R 1 To R 8 Each of the atoms selected from R 4 To R 8 At least one of them contains a group G having nonlinear light absorption characteristics.

[0100] R 1 To R 8 Each of the above R is independently a hydrogen atom, a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a group containing an oxygen atom, a group containing a nitrogen atom, a group containing a sulfur atom, a group containing a silicon atom, a group containing a phosphorus atom, or a group containing a boron atom. 4 To R 8 At least one of the groups may be a group substituted by a group G having nonlinear light absorption characteristics in a hydrocarbon group, a halogenated hydrocarbon group, a group containing an oxygen atom, a group containing a nitrogen atom, a group containing a sulfur atom, a group containing a silicon atom, a group containing a phosphorus atom, or a group containing a boron atom.

[0101] Examples of the halogen atom include F, Cl, Br, and I. In this specification, a halogen atom may be referred to as a halogen group.

[0102] The number of carbon atoms in the hydrocarbon group is not particularly limited, and may be, for example, 1 to 10, 1 to 8, or 1 to 5. The hydrocarbon group may be linear, branched, or cyclic.

[0103] Examples of the hydrocarbon group include aliphatic saturated hydrocarbon groups, alicyclic hydrocarbon groups, aliphatic unsaturated hydrocarbon groups, etc. The aliphatic saturated hydrocarbon group may be an alkyl group. Examples of the aliphatic saturated hydrocarbon group include -CH 3、-CH 2 CH 3 、-CH 2 CH 2 CH 3 、-CH(CH 3 ) 2 、-CH(CH 3 )CH 2 CH 3 、-C(CH 3 ) 3 、-CH 2 CH(CH 3 ) 2 、-(CH 2 ) 3 CH 3 、-(CH 2 ) 4 CH 3 、-C(CH 2 CH 3 )(CH 3 ) 2 、-CH 2 C(CH 3 ) 3 、-(CH 2 ) 5 CH 3 、-(CH 2 ) 6 CH 3 、-(CH 2 ) 7 CH 3 、-(CH 2 ) 8 CH 3 、-(CH 2 ) 9 CH 3 Examples of the alicyclic hydrocarbon group include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Examples of the aliphatic unsaturated hydrocarbon group include -CH=CH 2 、-C≡CH、-C≡CCH 3 、-C(CH 3 )=CH 2 、-CH=CHCH 3 、-CH 2 CH=CH 2 wait.

[0104] The so-called halogenated hydrocarbon group means a group in which at least one hydrogen atom contained in the hydrocarbon group is replaced by a halogen atom. The halogenated hydrocarbon group may be a group in which all hydrogen atoms contained in the hydrocarbon group are replaced by halogen atoms. Examples of the halogenated hydrocarbon group include halogenated alkyl groups and halogenated alkenyl groups.

[0105] Examples of the halogenated alkyl group include -CF 3 、-CH 2 F, -CH 2 Br, -CH 2 Cl, -CH 2 I. -CH 2 CF 3 Examples of the halogenated alkenyl group include -CH=CHCF 3 wait.

[0106] The group containing an oxygen atom is, for example, a substituent having at least one selected from a hydroxyl group, a carboxyl group, an aldehyde group, an ether group, an acyl group, and an ester group.

[0107] Examples of the substituent having a hydroxyl group include a hydroxyl group itself and a hydrocarbon group having a hydroxyl group. Examples of the hydrocarbon group having a hydroxyl group include -CH 2 OH, -CH(OH)CH 3 、-CH 2 CH(OH)CH 3 、-CH 2 C(OH)(CH 3 ) 2 wait.

[0108] Examples of the substituent having a carboxyl group include the carboxyl group itself and a hydrocarbon group having a carboxyl group. Examples of the hydrocarbon group having a carboxyl group include -CH 2 CH 2 COOH, -C(COOH)(CH 3 ) 2 wait.

[0109] Examples of the substituent having an aldehyde group include an aldehyde group itself and a hydrocarbon group having an aldehyde group. Examples of the hydrocarbon group having an aldehyde group include -CH=CHCHO and the like.

[0110] As the substituent having an ether group, for example, an alkoxy group, a halogenated alkoxy group, an alkenyloxy group, an ethylene oxide group, and a hydrocarbon group having at least one of these functional groups can be cited. At least one hydrogen atom contained in the alkoxy group can be substituted by a group containing at least one atom selected from N, O, P and S. As the alkoxy group, a methoxy group, an ethoxy group, a 2-methoxyethoxy group, a butoxy group, a 2-methylbutoxy group, a 2-methoxybutoxy group, a 4-ethylthiobutoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a nonyloxy group, a decyloxy group, etc. can be cited. As the halogenated alkoxy group, -OCHF can be cited. 2 、-OCH 2 F, -OCH 2 Cl, etc. Examples of the alkenyloxy group include -OCH=CH 2Examples of hydrocarbon groups having a functional group such as an alkoxy group include -CH 2 OCH 3 、-C(OCH 3 ) 3 , 2-methoxybutyl, 6-methoxyhexyl, etc.

[0111] Examples of the substituent having an acyl group include an acyl group itself and a hydrocarbon group having an acyl group. Examples of the acyl group include -COCH 3 Examples of the hydrocarbon group having an acyl group include -CH=CHCOCH 3 wait.

[0112] Examples of the substituent having an ester group include an alkoxycarbonyl group, an acyloxy group, and a hydrocarbon group having at least one of these functional groups. Examples of the alkoxycarbonyl group include -COOCH 3 、-COO(CH 2 ) 3 CH 3 、-COO(CH 2 ) 7 CH 3 As the acyloxy group, -OCOCH 3 Examples of the hydrocarbon group having a functional group such as an acyloxy group include -CH 2 OCOCH 3 wait.

[0113] The group containing a nitrogen atom is, for example, a substituent having at least one selected from an amino group, an imino group, a cyano group, an amide group, a carbamate group, a nitro group, a cyanamide group, an isocyanate group, and an oxime group.

[0114] Examples of the substituent having an amino group include a primary amino group, a secondary amino group, a tertiary amino group, and a hydrocarbon group having at least one of these functional groups. Examples of the tertiary amino group include -N(CH 3 ) 2 Examples of the hydrocarbon group having a functional group such as a primary amino group include -CH 2 NH 2 、-CH 2 N(CH 3 ) 2 、-(CH 2 ) 4 N(CH 3 ) 2 wait.

[0115] Examples of the substituent having an imino group include the imino group itself and a hydrocarbon group having an imino group. Examples of the imino group include -N=CCl 2 wait.

[0116] Examples of the substituent having a cyano group include a cyano group itself and a hydrocarbon group having a cyano group. Examples of the hydrocarbon group having a cyano group include -CH 2 CN, -CH=CHCN, etc.

[0117] Examples of the substituent having an amide group include an amide group itself and a hydrocarbon group having an amide group. Examples of the amide group include -CONH 2 、-NHCHO、-NHCOCH 3 , -NHCOCF 3 、-NHCOCH 2 Cl, -NHCOCH(CH 3 ) 2 As the hydrocarbon group having an amide group, -CH 2 CONH 2 、-CH 2 NHCOCH 3 wait.

[0118] Examples of the substituent having a carbamate group include a carbamate group itself and a hydrocarbon group having a carbamate group. Examples of the carbamate group include -NHCOOCH 3 、-NHCOOCH 2 CH 3 、-NHCO 2 (CH 2 ) 3 CH 3 wait.

[0119] Examples of the substituent having a nitro group include the nitro group itself and a hydrocarbon group having a nitro group. Examples of the hydrocarbon group having a nitro group include -C(NO 2 )(CH 3 ) 2 wait.

[0120] Examples of the substituent having a cyanamide group include a cyanamide group itself and a hydrocarbon group having a cyanamide group. The cyanamide group is represented by -NHCN.

[0121] Examples of the substituent having an isocyanate group include an isocyanate group itself and a hydrocarbon group having an isocyanate group. The isocyanate group is represented by -N=C=O.

[0122] Examples of the substituent having an oxime group include an oxime group itself and a hydrocarbon group having an oxime group. The oxime group is represented by -CH=NOH.

[0123] The group containing a sulfur atom is, for example, a substituent having at least one selected from a thiol group, a thioether group, a sulfinyl group, a sulfonyl group, a sulfinyl group, a sulfonic acid group, an acylthio group, a sulfenamide group, a sulfonamide group, a thioamide group, a thiocarbamate group and a thiocyanate group.

[0124] Examples of the substituent having a thiol group include a thiol group itself and a hydrocarbon group having a thiol group. The thiol group is represented by -SH.

[0125] Examples of the substituent having a thioether group include an alkylthio group, an alkyldisulfide group, an alkenylthio group, an alkynylthio group, a thiirane group, and a hydrocarbon group having at least one of these functional groups. At least one hydrogen atom contained in the alkylthio group may be substituted with a halogen group. Examples of the alkylthio group include -SCH 3 、-S(CH 2 )F, -SCH(CH 3 ) 2 、-SCH 2 CH 3 As the alkyl disulfide group, -SSCH 3 Examples of the alkenylthio group include -SCH=CH 2 、-SCH 2 CH=CH 2 Examples of the alkynylthio group include -SC≡CH and the like. Examples of the hydrocarbon group having a functional group such as an alkylthio group include -CH 2 SCF 3 wait.

[0126] Examples of the substituent having a sulfinyl group include a sulfinyl group itself and a hydrocarbon group having a sulfinyl group. Examples of the sulfinyl group include -SOCH 3 wait.

[0127] Examples of the substituent having a sulfonyl group include a sulfonyl group itself and a hydrocarbon group having a sulfonyl group. Examples of the sulfonyl group include -SO 2 CH 3 Examples of the hydrocarbon group having a sulfonyl group include -CH 2 SO 2 CH 3 、-CH 2 SO 2 CH 2 CH 3 wait.

[0128] Examples of the substituent having a sulfinyl group include a sulfinyl group itself and a hydrocarbon group having a sulfinyl group.

[0129] Examples of the substituent having a sulfonic acid group include a sulfonic acid group itself and a hydrocarbon group having a sulfonic acid group.

[0130] Examples of the substituent having an acylthio group include an acylthio group itself and a hydrocarbon group having an acylthio group. Examples of the acylthio group include -SCOCH 3 wait.

[0131] Examples of the substituent having a sulfenamide group include the sulfenamide group itself and a hydrocarbon group having a sulfenamide group. Examples of the sulfenamide group include -SN(CH 3 ) 2 wait.

[0132] Examples of the substituent having a sulfonamide group include the sulfonamide group itself and a hydrocarbon group having a sulfonamide group. Examples of the sulfonamide group include -SO 2 NH 2 、-NHSO 2 CH 3 wait.

[0133] Examples of the substituent having a thioamide group include a thioamide group itself and a hydrocarbon group having a thioamide group. Examples of the thioamide group include -NHCSCH 3 wait.

[0134] Examples of the substituent having a thiolcarbamate group include a thiolcarbamate group itself and a hydrocarbon group having a thiolcarbamate group. Examples of the thiolcarbamate group include -NHCSNHCH 2 CH 3 wait.

[0135] Examples of the substituent having a thiocyanate group include the thiocyanate group itself and a hydrocarbon group having a thiocyanate group. Examples of the hydrocarbon group having a thiocyanate group include -CH 2 SCN, etc.

[0136] The group containing a silicon atom is, for example, a substituent having at least one selected from a silyl group and a siloxy group.

[0137] Examples of the substituent having a silyl group include the silyl group itself and a hydrocarbon group having a silyl group. Examples of the silyl group include -Si(CH 3 ) 3 、-SiH(CH 3 ) 2 、-Si(OCH 3 ) 3 、-Si(OCH 2 CH 3 ) 3 、-SiCH 3 (OCH 3 ) 2 、-Si(CH3 ) 2 OCH 3 、-Si(N(CH 3 ) 2 ) 3 、-SiF(CH 3 ) 2 、-Si(OSi(CH 3 ) 3 ) 3 、-Si(CH 3 ) 2 OSi(CH 3 ) 3 Examples of the hydrocarbon group having a silyl group include -(CH 2 ) 2 Si(CH 3 ) 3 wait.

[0138] Examples of the substituent having a silyloxy group include the silyloxy group itself and a hydrocarbon group having a silyloxy group. Examples of the hydrocarbon group having a silyloxy group include -CH 2 OSi(CH 3 ) 3 wait.

[0139] The group containing a phosphorus atom is, for example, a substituent having at least one selected from a phosphine group and a phosphono group.

[0140] As a substituent having a phosphine group, for example, a phosphine group itself and a hydrocarbon group having a phosphine group can be listed. As a phosphine group, -PH 2 、-P(CH 3 ) 2 、-P(CH 2 CH 3 ) 2 、-P(C(CH 3 ) 3 ) 2 、-P(CH(CH 3 ) 2 ) 2 wait.

[0141] Examples of the substituent having a phosphonyl group include the phosphonyl group itself and a hydrocarbon group having a phosphonyl group. Examples of the hydrocarbon group having a phosphonyl group include -CH 2 PO(OCH 2 CH 3 ) 2 wait.

[0142] The group containing a boron atom is, for example, a substituent having a boronic acid group. Examples of the substituent having a boronic acid group include a boronic acid group itself and a hydrocarbon group having a boronic acid group.

[0143] In formula (1), R 4 To R 8 At least one of can be represented by the following formula (4).

[0144] -LR A (4)

[0145] In formula (4), L is a linking group containing at least one atom selected from C, N, O and S. L does not contain bonds that affect the conjugated system, such as carbon-carbon double bonds. L may contain an ether group, which may be -CH 2 -O-CH 2 -. L may be an alkylene group.

[0146] R A For example, the group G having nonlinear light absorption characteristics may be a group having a pyrene skeleton. A It can be represented by the following formula (4A).

[0147] [Chemical formula number 2]

[0148]

[0149] In formula (4A), R 28 To R 37 Each of the atoms independently contains at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I. 28 To R 37 One of them is bonded to L of the above formula (4). L of formula (4) is in R 28 To R 37 At one of the positions in , it can be directly bonded to the pyrene ring represented by the formula (4A).

[0150] R 28 To R 37 They may be independently a hydrogen atom, a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a group containing an oxygen atom, a group containing a nitrogen atom, a group containing a sulfur atom, a group containing a silicon atom, a group containing a phosphorus atom, or a group containing a boron atom. Examples of these groups include 1 To R 8 Those groups described above.

[0151] Specific examples of the structural unit A include structural unit A-1 represented by the following formula (A-1).

[0152] [Chemical formula number 3]

[0153]

[0154] The content of structural unit A in polymer P1 is, for example, 5 mol% or more, 7 mol% or more, 10 mol% or more, 15 mol% or more, or 20 mol% or more. The upper limit of the content of structural unit A is not particularly limited, and is, for example, 65 mol%.

[0155] Polymer P1 may further include other structural units other than the above-mentioned structural unit A. As other structural units, structural unit B1 derived from styrenes and not having the above-mentioned group G, structural unit B2 derived from stilbenes and not having the group G, etc. can be listed. In this specification, structural unit B1 is sometimes referred to as structural unit B1 derived from styrenes. Structural unit B2 is sometimes referred to as structural unit B2 derived from stilbenes. Polymer P1, for example, includes at least one structural unit B selected from structural unit B1 derived from styrenes and structural unit B2 derived from stilbenes. Polymer P1 may include structural unit B1 derived from styrenes.

[0156] The structural unit B is represented by, for example, the following formula (2).

[0157] [Chemical formula number 4]

[0158]

[0159] In formula (2), R 9 To R 16 Other groups other than the group G that independently contain at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, Br and I and have nonlinear light absorption characteristics.

[0160] R 9 To R 16 They may be independently a hydrogen atom, a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a group containing an oxygen atom, a group containing a nitrogen atom, a group containing a sulfur atom, a group containing a silicon atom, a group containing a phosphorus atom, or a group containing a boron atom. Examples of these groups include 1 To R 8 Those groups described above.

[0161] Selected from R 12 To R 16 At least one of the above may contain a leaving group or a polar functional group that can be used in a nucleophilic substitution reaction. Examples of the leaving group include halogen groups, etc. Examples of the polar functional group include hydroxyl groups, amino groups, thiol groups, etc.

[0162] Specific examples of the structural unit B include structural units B-1 represented by the following formula (B-1) to structural units B-8 represented by the following formula (B-8).

[0163] [Chemical formula number 5]

[0164]

[0165] The content of the structural unit B in the polymer P1 is not particularly limited, and is, for example, 70 mol% or less, 60 mol% or less, 50 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, or 10 mol% or less. The lower limit of the content of the structural unit B is not particularly limited, and is, for example, 1 mol%.

[0166] The polymer P1 may have at least one selected from a carbazole skeleton and a naphthalene skeleton in the side chain. In other words, the polymer P1 may contain a structural unit C having at least one selected from a carbazole skeleton and a naphthalene skeleton in the side chain as other structural units other than the structural unit A. The polymer P1 may have a structural unit derived from vinyl carbazole as the structural unit C. Furthermore, in the polymer P1, a carbazole skeleton or a naphthalene skeleton may be contained in the main chain. However, the polymer P1 containing a carbazole skeleton or a naphthalene skeleton in the main chain sometimes shows single-photon absorption characteristics for light with a wavelength in the range of 390nm to 410nm.

[0167] The structural unit C is represented by, for example, the following formula (3).

[0168] [Chemical formula number 6]

[0169]

[0170] In formula (3), R 17 To R 27 Each of the atoms is independently selected from the group consisting of H, B, C, N, O, F, Si, P, S, Cl, Br and I.

[0171] R 17 To R 27 They may be independently a hydrogen atom, a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a group containing an oxygen atom, a group containing a nitrogen atom, a group containing a sulfur atom, a group containing a silicon atom, a group containing a phosphorus atom, or a group containing a boron atom. Examples of these groups include 1 To R 8 Those groups described above.

[0172] Specific examples of the structural unit C include structural units C-1 represented by the following formula (C-1) to structural units C-17 represented by the following formula (C-17).

[0173] [Chemical formula number 7]

[0174]

[0175]

[0176] The content of the structural unit C in the polymer P1 is not particularly limited, and may be, for example, 10 mol% or more, 35 mol% or more, 50 mol% or more, 70 mol% or more, or 90 mol% or more. The upper limit of the content of the structural unit C is not particularly limited, and may be, for example, 95 mol%.

[0177] The polymer P1 includes, for example, the structural unit A represented by the above formula (1), and at least one selected from the structural unit B represented by the formula (2) and the structural unit C represented by the formula (3). The polymer P may include the structural units A to C. As an example, the polymer P1 may be a random copolymer represented by the following formula (5).

[0178] [Chemical formula number 8]

[0179]

[0180] In formula (5), R 1 To R 27 The same as described for formula (1), formula (2) and formula (3). x, y and z are independent of each other and are arbitrary integers.

[0181] In polymer P1, the number x of structural units A, the number y of structural units B, and the number z of structural units C may satisfy 0.35≤z / (x+y+z), and may satisfy 0.07≤x / (x+y+z)≤0.65.

[0182] As mentioned above, polymer P1 is typically a random copolymer. However, polymer P1 may be a block copolymer, a graft copolymer, or the like.

[0183] Specific examples of the polymer P1 include a random copolymer P1-1 represented by the following formula (P1-1).

[0184] [Chemical formula number 9]

[0185]

[0186] In formula (P1-1), x, y and z are independently any integers. Specific examples of x:y:z in formula (P1-1) are 7:3:90, 20:45:35 and the like.

[0187] There is no particular limitation on the synthesis method of polymer P1. Polymer P1 can be synthesized by reacting a nonlinear light absorbing pigment with a precursor polymer. Polymer P1 can be synthesized by preparing a monomer with a group G having nonlinear light absorption characteristics in advance and polymerizing a monomer group containing the monomer. As a reaction for bonding a precursor polymer to a nonlinear light absorbing pigment, a nucleophilic substitution reaction in which a leaving group reacts with a polar functional group, a cross-coupling reaction using a transition metal catalyst, etc. can be used. As a leaving group, a halogen group, etc. can be listed. As a polar functional group, a hydroxyl group, an amino group, a thiol group, etc. can be listed. As an example, a precursor polymer containing a structural unit from styrene or stilbene and having a leaving group and a nonlinear light absorbing pigment having a polar functional group can be used to synthesize polymer P1. Polymer P1 can also be synthesized by reacting a precursor polymer containing a structural unit from styrene or stilbene and having a polar functional group and a nonlinear light absorbing pigment having a leaving group.

[0188] The pigment material may contain an organic compound E having light absorption properties instead of the polymer P1, or may contain an organic compound E having light absorption properties together with the polymer P1. The organic compound E is, for example, a low molecular weight compound having a molecular weight of 1,000 or less.

[0189] The organic compound E may have a linear light absorption characteristic or a nonlinear light absorption characteristic for light having a wavelength in a short wavelength range. The organic compound E may utilize a nonlinear light absorption phenomenon caused by excited state absorption. For the recording layer 10, the nonlinear light absorption of the organic compound E may be large from the viewpoint of maintaining the transmittance of light at a high value and improving the recording sensitivity.

[0190] The organic compound E contains at least one selected from a carbon-carbon double bond, a carbon-nitrogen double bond and a carbon-carbon triple bond. The organic compound E may further contain an aromatic ring. The aromatic ring contained in the organic compound E may be composed of carbon atoms, or may be a heteroaromatic ring containing heteroatoms such as oxygen atoms, nitrogen atoms, and sulfur atoms. As the aromatic ring contained in the organic compound E, for example, a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a furan ring, a pyrrole ring, a pyridine ring, a thiophene ring, etc. can be listed. The organic compound E may contain a benzene ring as an aromatic ring. There is no particular limitation on the number of aromatic rings contained in the organic compound E, for example, it is 2 or more, it may be 3 or more, it may be 5 or more. There is no particular limitation on the upper limit of the number of aromatic rings, for example, 15. In the organic compound E, multiple aromatic rings may be connected by at least one bond selected from a carbon-carbon double bond, a carbon-nitrogen double bond and a carbon-carbon triple bond. The multiple aromatic rings contained in the organic compound E may be the same as or different from each other.

[0191] Specific examples of the organic compound E include compound E1 represented by the following formula (E1).

[0192] [Chemical formula number 10]

[0193]

[0194] Other examples of the organic compound E include compound E2 represented by the following formula (E2), compound E3 represented by the following formula (E3), etc. These compounds E2 and E3 tend to show large nonlinear light absorption for light having a wavelength in a short wavelength range.

[0195] [Chemical formula number 11]

[0196]

[0197] The pigment material may contain one polymer P1 or one organic compound E, or may contain two or more polymers P1 or two or more organic compounds E, as long as the transmittance of light of a wavelength of 405 nm in the recording layer 10 is adjusted to 95% or more.

[0198] The pigment material has a small linear light absorption at the recording and reproducing wavelength, and may have an appropriate amount of nonlinear light absorption. For example, when a laser with a wavelength of 405nm is used for recording and reproducing, the two-photon absorption cross-sectional area of ​​the pigment material may be greater than 1GM, may be more than 10GM, may be more than 20GM, or may be more than 100GM. There is no particular limitation on the upper limit of the two-photon absorption cross-sectional area, for example, 1000GM. The two-photon absorption cross-sectional area can be measured by the Z scanning method described in, for example, J.Opt.Soc.Am.B, 2003, Vol.20, page 529. The Z scanning method is widely used as a method for measuring nonlinear optical constants. In the Z scanning method, the measurement sample is moved along the irradiation direction of the beam near the focus of the laser beam. At this time, the change in the amount of light transmitted through the measurement sample is recorded. In the Z scanning method, the power density of the incident light changes according to the position of the measurement sample. Therefore, in the case where the measurement sample undergoes nonlinear light absorption, if the measurement sample is located near the focus of the laser beam, the amount of light transmitted by the light is attenuated. The two-photon absorption cross-sectional area can be calculated by fitting the theoretical curve predicted by the intensity of incident light, the thickness of the measurement sample, the concentration of the compound in the measurement sample, etc. to the change in the amount of transmitted light. As an example, the two-photon absorption cross-sectional area of ​​pyrene derivatives is about 50GM to 300GM.

[0199] The two-photon absorption cross-sectional area may be a calculated value obtained from computational chemistry. Several methods for estimating the two-photon absorption cross-sectional area from computational chemistry have been proposed. For example, based on the quadratic nonlinear response theory described in J. Chem. Theory Comput. 2018, Vol. 14, p. 807, the calculated value of the two-photon absorption cross-sectional area can be calculated.

[0200] The recording layer 10 may further include a polymer P2 different from the polymer P1. As an example, the recording layer 10 may include the polymer P2 and the organic compound E. In this case, the organic compound E may be dispersed in a matrix including the polymer P2.

[0201] The polymer P2, for example, contains the structural unit C described above for the polymer P1. In the polymer P2, as the structural unit C, there may be a structural unit derived from the vinyl carbazole class, or there may be a structural unit derived from the vinyl naphthalene class. Furthermore, in the polymer P2, a carbazole skeleton or a naphthalene skeleton may be contained in the main chain. However, the polymer P2 containing a carbazole skeleton or a naphthalene skeleton in the main chain sometimes shows single-photon absorption characteristics for light with a wavelength in the range of 390nm to 410nm.

[0202] The polymer P2 may not contain the structural unit C and may be a polycarbonate.

[0203] For polymers P1 and P2, for example, the transmittance, refractive index, and glass transition temperature of light with a wavelength in the range of 390nm to 410nm are high. The glass transition temperature of polymers P1 and P2 is, for example, above 200°C. Polymers P1 and P2 having a high glass transition temperature to this extent are thermally stable. For the recording layer 10 containing the polymer P1 or P2, there is a tendency to suppress the change in the shape of the recording mark formed by the irradiation of light. That is, according to polymers P1 and P2, there is a tendency to improve the stability of the shape of the recording mark. On the other hand, if the glass transition temperature of polymers P1 and P2 is too high, the recording sensitivity of the recording layer 10 is sometimes reduced. Therefore, from the viewpoint of taking into account both thermal stability and recording sensitivity, the glass transition temperature of polymers P1 and P2 is, for example, above 200°C and below 300°C. The glass transition temperature of polymers P1 and P2 can be above 200°C and below 250°C.

[0204] The glass transition temperature of polymers P1 and P2 can be determined by the following method. First, for polymers P1 and P2, thermogravimetric-differential thermal (TG-DTA) measurement is performed under the following conditions to prepare a DTA curve. The glass transition temperature can be determined from the inflection point of the heat capacity in the DTA curve.

[0205] ·Measurement conditions

[0206] Atmosphere: Nitrogen atmosphere

[0207] Measuring range: 25℃ to 400℃

[0208] Heating speed: 15℃ / min

[0209] When the weight average molecular weight of polymers P1 and P2 is large to a certain extent, there is a tendency that the recording layer 10 can be easily formed into a film. On the other hand, if the weight average molecular weight of polymers P1 and P2 is too large, the solubility of the polymers is reduced, and it is sometimes difficult to form the recording layer 10 by a coating method. Therefore, the weight average molecular weight of polymers P1 and P2 can be 4000 or more and 100000 or less. The weight average molecular weight of polymers P1 and P2 can be 4000 or more and 50000 or less.

[0210] The recording layer 10 is, for example, a thin film having a thickness of more than 1 nm and less than 1 μm. However, the thickness of the recording layer 10 may be less than 490 nm, and may sometimes be greater than 1 μm. If the thickness of the recording layer 10 is greater than 1 μm, it tends to be difficult to obtain the effect of interference between the reflected light A from the interface 30A and the reflected light B from the interface 30B. This is believed to be caused by irradiating the recording medium 100 with concentrated light. When using concentrated light, a difference in optical path length occurs depending on the angle of incidence, so it is necessary to add the components of light incident from various angles. It is believed that if the thickness of the recording layer 10 exceeds about 1 μm, the difference in optical path length caused by the angle of incidence increases, making it difficult to obtain the effect of interference.

[0211] As described above, the transmittance of light of a wavelength of 405 nm in the recording layer 10 is 95% or more, may be 97% or more, or may be 99% or more.

[0212] The transmittance mentioned above can be measured by using the recording layer 10 itself as a measurement sample and by a method specified in JIS K0115: 2004. Specifically, first, light having a wavelength of 405 nm is irradiated to the recording layer 10. The irradiation of light is performed in a manner that the light travels in the thickness direction of the recording layer 10. As a light source, a light source that irradiates light with a photon density that hardly causes nonlinear light absorption in the recording layer 10 is used. Next, the absorbance A of the recording layer 10 with respect to a wavelength of 405 nm is read from the light that has passed through the recording layer 10. Based on the absorbance A, the transmittance T of the light of a wavelength of 405 nm in the recording layer 10 can be calculated according to the following formula (I).

[0213] Transmittance T = 10 (-A) (I)

[0214] In the above measurement, when the recording layer 10 is a thin film, the absorbance A may not be accurately measured due to interference of the film. In this case, the transmittance can be calculated by measuring the extinction coefficient using an ellipsometer. The material of the recording layer 10 can be dissolved in an appropriate solvent, and the transmittance can be calculated using the absorbance value measured in the solution state.

[0215] The refractive index n of the recording layer 10 is 1The refractive index n of the recording layer 10 may be 1.65 or more, 1.68 or more, or 1.70 or more. 1 The upper limit of is not particularly limited, and is, for example, 1.90. The refractive index of the recording layer 10 can be measured using an ellipsometer. The refractive index n of the first dielectric layer 20A is 2 and the refractive index n of the second dielectric layer 20B 3 It can also be measured using an ellipsometer.

[0216] The refractive index n of the recording layer 10 is 1 The higher the refractive index n of the adjacent dielectric layer 20 is, the easier it is to adjust the difference in refractive index with the adjacent dielectric layer 20 to be large. For example, when the difference in refractive index between the recording layer 10 and the first dielectric layer 20A is large, the intensity of the reflected light from the interface 30A tends to increase. When the difference in refractive index between the recording layer 10 and the second dielectric layer 20B is large, the intensity of the reflected light from the interface 30B tends to increase. As a result, there is a tendency to obtain a good reproduced signal from the recording medium 100. As an example, the refractive index n of the recording layer 10 is large. 1 The refractive index n of the first dielectric layer 20A is 2 The difference between n and n can be 0.2 or more. 1 The refractive index n of the second dielectric layer 20B is 3 The difference can be 0.2 or more. In this case, the interference effect of the reflected light A from the interface 30A and the reflected light B from the interface 30B is fully obtained. Thus, using a small semiconductor laser with a central wavelength of 405nm, it is possible to achieve LTH type recording and reproduction. As a small semiconductor laser, for example, an optical pickup utilized for recording and reproduction of an existing Blu-ray (registered trademark) disc can be used.

[0217] [Dielectric layer]

[0218] The first dielectric layer 20A and the second dielectric layer 20B may have the same or different thicknesses and compositions. For example, the refractive index difference between the dielectric layer 20 and the recording layer 10 can be adjusted to an appropriate value, and a material having a high light transmittance at a recording and reproducing wavelength can be used. In addition, when the recording medium 100 includes a plurality of recording layers 10, the interlayer distance between the recording layers 10 can be appropriately adjusted by adjusting the thickness of the dielectric layer 20.

[0219] As described above, the difference in refractive index between the recording layer 10 and the dielectric layer 20 is, for example, about 0.2 or more. When the refractive index of the recording layer 10 is represented by n1 and the refractive index of the dielectric layer 20 is represented by n2, it is known that the reflectivity at the interface between the recording layer 10 and the dielectric layer 20 is ((n2-n1) / (n2+n1)) 2That is, when the refractive index of the recording layer 10 is 1.65 and the refractive index of the dielectric layer 20 is 1.45, the reflectivity of the interface between these layers is about 0.004.

[0220] The dielectric layer 20 includes, for example, a polymer material. Generally, the refractive index of the polymer material used for the dielectric layer 20 is about 1.4 to 1.6, and particularly about 1.45 to 1.5. Therefore, in the case where the refractive index of the recording layer 10 is higher than 1.65, it is easy to adjust the refractive index difference with the dielectric layer 20 to about 0.1 to 0.2 or more. By adjusting the refractive index difference between the recording layer 10 and the dielectric layer 20 to the above range, the intensity of the reflected light at the interface can be increased, and good focusing servo characteristics can be obtained.

[0221] Examples of the material of the dielectric layer 20 include cellulose acetate, acrylic resin, and methacrylic resin.

[0222] The thickness of the dielectric layer 20 is not particularly limited, and is, for example, 5 nm or more and 100 μm or less. However, the thickness of the dielectric layer 20 may be greater than 100 μm.

[0223] [Method for producing recording medium]

[0224] The recording medium 100 can be produced, for example, by the following method: First, the material of the recording layer 10 is mixed with a solvent to produce a coating solution, and the coating solution is applied to a substrate by spin coating or the like, and the obtained coating film is dried to produce a thin film recording layer 10.

[0225] Next, a dielectric layer 20 is formed on the recording layer 10. When the dielectric layer 20 includes a resin material, first, the resin material is mixed with a solvent to prepare a coating liquid. The coating liquid is applied to the recording layer 10 by a spin coating method or the like, and the obtained coating film is dried to prepare the dielectric layer 20. In addition, the coating liquid may include a photosensitive monomer, etc., and the monomer may be polymerized by light or heat to prepare the dielectric layer 20. A thin film that functions as the dielectric layer 20 may also be prepared in advance, and the thin film may be attached to the recording layer 10 to prepare the dielectric layer 20. As needed, a plurality of recording layers 10 and a plurality of dielectric layers 20 may be prepared alternately to obtain the recording medium 100.

[0226] [How to use the recording medium]

[0227] The recording medium 100 of this embodiment uses light having a wavelength in a short wavelength range, for example. As an example, the recording medium 100 uses light having a wavelength of 390 nm or more and 410 nm or less. The light used in the recording medium 100 has, for example, a high photon density near its focus. The power density near the focus of the light used in the recording medium 100 is, for example, 0.1 W / cm 2 Above and 1.0×10 20 W / cm 2 The power density near the focal point of the light can be 1.0 W / cm 2 Above, can be 1.0×10 2 W / cm 2 Above, can be 1.0×10 5 W / cm 2 As the light source used in the recording medium 100 , for example, a femtosecond laser such as a titanium sapphire laser or a pulse laser having a pulse width of picoseconds to nanoseconds such as a semiconductor laser can be used.

[0228] Next, a method of recording information using the recording medium 100 will be described. Figure 3A This is a flowchart related to a method for recording information using a recording medium 100. First, in step S11, a light source that emits light with a wavelength of more than 390nm and less than 410nm is prepared. As the light source, for example, a femtosecond laser such as a titanium sapphire laser or a pulse laser such as a semiconductor laser with a pulse width of picoseconds to nanoseconds can be used. Secondly, in step S12, the light from the light source is focused by a lens or the like, and irradiated onto the recording layer 10 in the recording medium 100. Specifically, the light from the light source is focused by a lens or the like, and irradiated onto the recording area in the recording medium 100. There is no particular restriction on the NA (numerical aperture) of the lens used for light focusing. As an example, a lens with an NA in the range of more than 0.8 and less than 0.9 can be used. The power density near the focus of the light is, for example, 0.1W / cm 2 Above and 1.0×10 20 W / cm 2 The power density near the focal point of the light can be 1.0 W / cm 2 Above, can be 1.0×10 2 W / cm 2 Above, can be 1.0×10 5 W / cm 2 above.

[0229] In the recording area irradiated with the above-mentioned light, a physical change or a chemical change occurs. As an example, a concave recording mark is formed in the recording area. The depth of the concave recording mark is not particularly limited, for example, it is greater than 1nm and less than 100nm. By causing physical or chemical changes, the optical properties of the recording area change. For example, the intensity of light reflected in the recording area, the reflectivity of light in the recording area, the absorptivity of light in the recording area, the refractive index of light in the recording area, the intensity of fluorescent light emitted from the recording area, the wavelength of fluorescent light, etc. change. As an example, the intensity of light reflected in the recording area increases. In other words, the reflectivity of light in the recording area increases. Thus, information can be recorded in the recording layer 10, specifically in the recording area (step S13).

[0230] Next, a method of reading information using the recording medium 100 will be described. Figure 3B 1 is a flowchart related to a method for reading information using a recording medium 100. First, in step S21, the recording layer 10 in the recording medium 100 is irradiated with light. Specifically, the recording area in the recording medium 100 is irradiated with light. The light used in step S21 may be the same as or different from the light used to record information in the recording medium 100. For example, the wavelength of the reproduction light used in step S21 may be the same as the wavelength of the recording light used in step S12. Next, in step S22, the optical properties of the recording layer 10 are measured. Specifically, the optical properties of the recording area are measured. In step S22, for example, as the optical properties of the recording area, the intensity of light reflected in the recording area or the intensity of fluorescent light emitted from the recording area is measured. In step S22, as the optical properties of the recording area, the reflectivity of light in the recording area, the absorptivity of light in the recording area, the refractive index of light in the recording area, the wavelength of fluorescent light emitted from the recording area, etc. can be measured. Next, in step S23, information is read from the recording layer 10, specifically, from the recording area.

[0231] In the information reading method, the recording area, i.e., the recording part, where the information is recorded can be found by the following method. First, light is irradiated to a specific area of ​​the recording medium. The light may be the same as or different from the light used to record the information on the recording medium. Secondly, the optical properties of the area irradiated with light are measured. As optical properties, for example, the intensity of light reflected in the area, the reflectivity of light in the area, the absorptivity of light in the area, the refractive index of light in the area, the intensity of fluorescent light emitted from the area, the wavelength of fluorescent light emitted from the area, etc. can be listed. Based on the measured optical properties, it is determined whether the area irradiated with light is a recording part. For example, when the intensity of light reflected in the area is greater than a specific value, it can be determined that the area is a recording part. In addition, when the intensity of light reflected in the area is less than a specific value, it can be determined that the area is not a recording part. When it is determined that it is not a recording part, the same operation is performed on other areas of the recording medium. In this way, the recording part can be found.

[0232] The recording method and reading method of information using the recording medium 100 can be performed, for example, using a known recording device. The recording device, for example, includes a light source for irradiating light to a recording area in the recording medium 100, a measuring device for measuring the optical characteristics of the recording area, and a controller for controlling the light source and the measuring device. In this embodiment, the wavelengths of the recording light and the reproducing light irradiated to the recording medium 100 can be the same. In this case, the recording device can use one light source to perform the recording operation and the reproducing operation of the recording medium 100. The recording device, for example, does not have a plurality of light sources but has a simple structure.

[0233] (Variation Example)

[0234] Figure 4 1 is a cross-sectional view showing a schematic structure of a recording medium 110 according to a modified example. Figure 4 As shown, the recording medium 110 includes a plurality of recording layers 10 and a plurality of dielectric layers 20. Except for this, the structure of the recording medium 110 according to the modification is the same as that of the above-mentioned recording medium 100. Therefore, the same reference numerals are given to the common elements in the above-mentioned recording medium 100 and the recording medium 110 according to the modification, and the description thereof is sometimes omitted.

[0235] The plurality of recording layers 10 are arranged in parallel, for example, in the thickness direction of the recording medium 110. In the recording medium 110, the number of the recording layers 10 is not particularly limited, and is, for example, 2 or more and 1000 or less. The compositions of the plurality of recording layers 10 may be the same as or different from each other. The recording medium 110 including the plurality of recording layers 10 functions as a three-dimensional optical storage. A specific example of the recording medium 110 is a three-dimensional optical disc.

[0236] In the recording medium 110, for example, the transmittance of light having a wavelength of 405 nm is 95% or more for each of the plurality of recording layers 10. In such a recording medium 110, the intensity of light reaching the recording layer 10 located farther from the light source, that is, the inner layer, is less likely to decrease.

[0237] In the recording medium 110, the plurality of recording layers 10 and the plurality of dielectric layers 20 are arranged alternately, for example. In other words, the plurality of recording layers 10 and the plurality of dielectric layers 20 are alternately stacked. As an example, the plurality of recording layers 10 are respectively arranged between two dielectric layers 20 and are in direct contact with the two dielectric layers 20. In the recording medium 110, the number of dielectric layers 20 is not particularly limited, and is, for example, 3 or more and 1001 or less. The composition and thickness of the plurality of dielectric layers 20 may be the same as or different from each other.

[0238] In the recording medium 110, when the dielectric layer 20 closest to the upper surface of the specific recording layer 10 among the plurality of dielectric layers 20 is regarded as the first dielectric layer 20A, and the dielectric layer 20 closest to the lower surface of the recording layer 10 is regarded as the second dielectric layer 20B, the thickness D (nm) of the recording layer 10, the refractive index n of the recording layer 10 1 , the refractive index n of the first dielectric layer 20A 2 and the refractive index n of the second dielectric layer 20B 3 The above-mentioned relational expressions (1) to (3) are satisfied. In the recording medium 110, for example, the above-mentioned condition is satisfied for each recording layer 10. As long as the condition is satisfied, the thicknesses of the plurality of recording layers 10 may be the same as or different from each other. For each recording layer 10 of the recording medium 110, when the above-mentioned condition is satisfied, since the thickness of each recording layer 10 is relatively small, the number of recording layers 10 is large, and a recording medium 110 with a large recording capacity can be easily manufactured.

[0239] Example

[0240] The present disclosure will be described in more detail below using examples. Note that the following examples are just examples, and the present disclosure is not limited to the following examples.

[0241] First, the following compound A (manufactured by Tokyo Chemical Industry Co., Ltd.), compound B, and compound C (manufactured by Sigma-Aldrich Corporation) were prepared as dye materials for the recording layer. Compounds A to C correspond to the above-mentioned compounds E1 to E3, respectively.

[0242] [Chemical formula number 12]

[0243]

[0244]

[0245] [Synthesis of Compound B]

[0246] First, 541 mg (3.3 mmol) of 1,3,5-tri(4-formylphenyl)benzene (manufactured by Tokyo Chemical Industry Co., Ltd.) and 16 mg (0.13 mmol) of 4-methoxyphenol (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in 20 mL of dichloromethane. A 5 mL solution of 1199 mg (10 mmol) of 4-aminostyrene (manufactured by Tokyo Chemical Industry Co., Ltd.) prepared separately was added at room temperature and stirred for 4 hours. A yellow solid was obtained by distilling off the solvent from the reaction solution. The obtained solid was washed with ethanol. Then, recrystallization was performed using ethanol and acetone to obtain compound B. Compound B was prepared by 1 Identification by H-NMR. Figure 5 To represent compound B 1 H-NMR spectrum of compound B 1 The H-NMR spectrum is as follows.

[0247] 1 H-NMR (600 MHz, chloroform-D) δ 5.26 (d, J = 10.8 Hz, 3H), 5.78 (d, J = 18.0 Hz, 3H), 6.75 (dd, J = 10.8, 18.0 Hz, 3H), 7.25 (d, J = 13.8 Hz, 6H), 7.48 (d, J = 9.0 Hz, 6H), 8.57 (s, 3H), 8.64 (s, 3H).

[0248] Furthermore, the following compounds D and E were prepared as dye materials for the recording layer. Compounds D and E correspond to the above-mentioned random copolymer P1-1.

[0249] [Chemical formula number 13]

[0250]

[0251] [Synthesis of Compounds D and E]

[0252] First, the precursors F and G of compounds D and E were synthesized. Precursors F and G were synthesized according to the method described in Macromolecules 2006, 39, 3140-3146 as shown in the following reaction formula. 1 Identification by H-NMR.

[0253] [Chemical formula number 14]

[0254]

[0255] [Synthesis of Compound D]

[0256] First, 1-hydroxymethylpyrene (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in tetrahydrofuran (THF, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), an excess of potassium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and a small amount of N,N-dimethylformamide (DMF, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added, and heated to reflux at 80°C for 1 hour under a nitrogen atmosphere. A THF solution of precursor F was further added thereto, and the mixture was heated to reflux at 80°C for 48 hours while stirring. The weight of the added precursor F was the same as the weight of 1-hydroxymethylpyrene. Secondly, a white precipitate was obtained by adding the reaction solution cooled to room temperature to a large amount of methanol. The obtained solid was recovered by filtration and a washing operation was performed. In the washing operation, ethanol, water and diethyl ether were used in sequence as washing liquids. Compound D was obtained by vacuum drying the solid. Compound D is used 1 Identification by H-NMR.

[0257] [Chemical formula number 15]

[0258]

[0259] [Synthesis of Compound E]

[0260] Compound E was synthesized by the same method as compound D except that precursor G was used instead of precursor F. 1 Identification by H-NMR.

[0261] [Chemical formula number 16]

[0262]

[0263] Furthermore, as materials for the recording layer, polyvinyl carbazole (manufactured by Sigma-Aldrich, molecular weight 25,000 to 50,000) and polymethyl methacrylate (PMMA: manufactured by Sigma-Aldrich, molecular weight 120,000 or less) were prepared.

[0264] <Production of recording media>

[0265] [Example 1]

[0266] First, compound A and polyvinyl carbazole are measured and dissolved in chlorobenzene. The amount of compound A is 0.9 mass parts relative to 99.1 mass parts of polyvinyl carbazole. The concentration of the solute in the obtained solution is about 3wt%. Secondly, the obtained solution is applied to a glass substrate by spin coating. The glass substrate is 20 mm square and 1 cm thick. Spin coating is carried out at 3000 rpm for 30 seconds. Secondly, the obtained coating film is dried at 80°C for 30 minutes to prepare a recording layer. Thus, the recording medium of Example 1 is obtained.

[0267] [Example 2]

[0268] The recording medium of Example 2 was prepared in the same manner as in Example 1, except that Compound B was used instead of Compound A, the amount of Compound B was changed to 5 parts by mass relative to 95 parts by mass of polyvinylcarbazole, and the concentration of the solute in the chlorobenzene solution was changed to about 5 wt %.

[0269] [Example 3]

[0270] The recording medium of Example 3 was prepared in the same manner as in Example 1, except that Compound C was used instead of Compound A, the amount of Compound C was changed to 20 parts by mass relative to 80 parts by mass of polyvinylcarbazole, and the concentration of the solute in the chlorobenzene solution was changed to about 5 wt %.

[0271] [Example 4]

[0272] First, compound D was dissolved in chlorobenzene. The concentration of compound D in the obtained solution was about 5wt%. Next, the obtained solution was applied to a glass substrate by spin coating. The glass substrate was 20 mm square and 1 cm thick. Spin coating was performed at 3000 rpm for 30 seconds. Next, the obtained coating film was dried at 80° C. for 30 minutes to prepare a recording layer. Thus, a recording medium of Example 4 was obtained.

[0273] [Example 5]

[0274] A recording medium of Example 5 was prepared in the same manner as in Example 4 except that Compound E was used instead of Compound D.

[0275] [Comparative Example 1]

[0276] A recording medium of Comparative Example 1 was prepared in the same manner as in Example 1 except that the amount of chlorobenzene added was adjusted so that the concentration of the solute in the chlorobenzene solution was about 5 wt %.

[0277] [Comparative Example 2]

[0278] A recording medium of Comparative Example 2 was prepared in the same manner as in Example 2 except that the amount of chlorobenzene added was adjusted so that the concentration of the solute in the chlorobenzene solution was about 7 wt %.

[0279] [Comparative Example 3]

[0280] First, compound A and PMMA were measured and dissolved in chloroform. The compound A was 3.1 parts by mass relative to 96.9 parts by mass of PMMA. The concentration of the solute in the obtained solution was about 4wt%. Secondly, the obtained solution was applied to a glass substrate by spin coating. The glass substrate was 20 mm square and 1 cm thick. Spin coating was performed at 3000 rpm for 30 seconds. Next, the obtained coating film was dried at 80°C for 30 minutes to prepare a recording layer. Thus, a recording medium of Comparative Example 3 was obtained.

[0281] The recording media of Examples and Comparative Examples are all laminates of a glass substrate and a recording layer. In these recording media, the air layer in contact with the recording layer is regarded as the first dielectric layer, and the glass substrate is regarded as the second dielectric layer.

[0282] <Characteristics Evaluation>

[0283] (1) Evaluation of the transmittance of light at a wavelength of 405 nm in the recording layer

[0284] For the embodiments and comparative examples, the transmittance of light with a wavelength of 405 nm in the recording layer was evaluated using the above method. Specifically, first, the linear light absorption characteristics of the recording layer were evaluated using a spectrophotometer and an ellipsometer. In the measurement using the spectrophotometer, the baseline was corrected using the measured value obtained when only the glass was measured. The transmittance at a wavelength of 405 nm was calculated from the obtained spectrum. In the recording media of the embodiments and comparative examples, the transmittance of light with a wavelength of 405 nm in the recording layer was 95% or more.

[0285] Next, compounds B to E were dissolved in chlorobenzene to prepare solutions, and the solutions were measured using a spectrophotometer. The results showed that the maximum absorption wavelength of linear light absorption was around 350 nm in all cases, and there was no absorption band of linear light absorption at a wavelength of 405 nm.

[0286] Next, compound A was dissolved in chlorobenzene to prepare a solution, and the solution was measured using a spectrophotometer. As a result, the maximum absorption wavelength of linear light absorption was around 440nm to 460nm. A portion of the absorption band of this linear light absorption overlapped with the wavelength of 405nm. From this result, it can be seen that when compound A is used to prepare a recording layer, in order to adjust the transmittance of light with a wavelength of 405nm in the recording layer to more than 95%, it is necessary to appropriately adjust the amount of compound A, the thickness of the recording layer, etc.

[0287] (2) Evaluation of recording layer thickness and refractive index

[0288] For the examples and comparative examples, the thickness D and the refractive index n of the recording layer were evaluated using an ellipsometer. 1Specifically, the refractive index n at a wavelength of 405 nm is read from the spectrum obtained by measurement. 1 . Then, calculate the refractive index n 1 The refractive index n of the air layer as the first dielectric layer is 2 The difference and refractive index n 1 The refractive index n of the glass substrate as the second dielectric layer 3 Furthermore, the refractive index n of the air layer for light with a wavelength of 405 nm is 2 is 1. The refractive index n of the glass substrate for light with a wavelength of 405 nm is 3 It is 1.47.

[0289] (3) Evaluation of recording and reproducing characteristics

[0290] <Dynamic evaluation>

[0291] Using the recording media of Examples 1, 2, 4 and 5 and Comparative Examples 1 and 3 as samples, the recording and reproducing characteristics were evaluated by the following operation.

[0292] [Record operation]

[0293] First, the sample was irradiated with pulse light of a central wavelength of 405nm, a peak power of 100mW, and a repetition frequency of 100kHz through a lens with an NA of 0.85. The pulse light was irradiated from the recording layer side, not from the glass substrate, so as to be focused on the recording layer on the glass substrate. At this time, the pulse light was irradiated while the sample was parallel moved at a speed of 10μm / second. The pulse width of the pulse light was adjusted between 10 nanoseconds and 1000 nanoseconds.

[0294] Fig. 6A FIG. 4 is an optical microscope image showing a recording mark formed in the recording layer of the recording medium of Example 4. Fig. 6A It can be seen that recording marks are formed in the form of recording lines in the recording layer by the recording operation.

[0295] [Replay operation]

[0296] Next, the sample that had been recorded was regenerated. Specifically, the sample was irradiated with light of a central wavelength of 405 nm, a peak power of 3 mW, a pulse width of 200 nanoseconds, and a repetition frequency of 100 Hz through a lens with an NA of 0.85 in a manner that cross-cut the recording line of the recording layer, and the reflected light signal intensity at the unrecorded part and the recorded part was obtained. At this time, the sample was irradiated with pulsed light while being parallel moved at a speed of 10 μm / second. Fig. 6A , the irradiation direction of light in the reproduction operation, that is, the reproduction direction is shown.

[0297] Figure 6BGraph showing the reproduced signal of the recording mark formed in the recording layer of the recording medium of Example 4. Figure 6B It was confirmed that the amount of reflected light increased at the position of the recording mark through the above-mentioned reproduction operation.

[0298] <Static evaluation>

[0299] The recording and reproducing characteristics were evaluated by the following operation using the recording media of Example 3 and Comparative Example 2 as samples. The following operation was performed while the samples were kept stationary.

[0300] [Reproduction operation before recording]

[0301] First, the sample was irradiated with pulsed light having a central wavelength of 405 nm, a peak power of 3 mW, a pulse width of 200 nanoseconds, and a repetition frequency of 100 Hz through a lens having an NA of 0.85. The light was focused on the recording layer on the glass substrate rather than from the glass substrate. Thus, the reflected light signal intensity of the unrecorded portion was obtained.

[0302] [Record operation]

[0303] Next, the sample was irradiated with a single pulse of pulse light with a central wavelength of 405 nm and a peak power of 100 mW through a lens with an NA of 0.85, and a recording operation was performed. The pulse width of the pulse light was adjusted between 10 nanoseconds and 5 milliseconds. The pulse light was focused on the recording layer on the glass substrate, not from the glass substrate.

[0304] [Replay operation]

[0305] Secondly, the samples that had been recorded were replayed. Specifically, at the location where the recording operation was performed, pulsed light with a central wavelength of 405 nm, a peak power of 3 mW, a pulse width of 200 nanoseconds, and a repetition frequency of 100 Hz was irradiated through a lens with an NA of 0.85, and the reflected light signal intensity at the recording portion was obtained.

[0306] The degree of modulation was calculated based on the following formula from the results of the above-mentioned dynamic evaluation and static evaluation.

[0307] Modulation degree = (reflected light signal intensity at the recorded portion - reflected light signal intensity at the unrecorded portion) / (reflected light signal intensity at the unrecorded portion)

[0308] Furthermore, a graph was prepared in which the vertical axis represents the modulation degree and the horizontal axis represents the average irradiation energy (mW) during the recording operation. Figure 6C Graph showing the modulation degree of recording marks formed on the recording layer of the recording medium of Example 4. The irradiation average energy was calculated using the following formula.

[0309] Average irradiation energy = (peak power) × (pulse width) × (repetition frequency)

[0310] Depend on Figure 6C It can be seen that in the recording medium of Example 4, recording operation can be performed using light with an average irradiation energy exceeding 0.1 mW. In other words, recording characteristics with a threshold value are obtained. Furthermore, by adjusting the average irradiation energy, a recording operation that matches the desired modulation degree can be performed.

[0311] [Evaluation of recording and reproducing characteristics]

[0312] As can be seen from Table 1 described later, the recording medium of the embodiment confirmed the recording and reproducing characteristics of the LTH type. That is, in the recording medium of the embodiment, the reflectivity of light in the recording area increases by the recording operation. On the other hand, in the recording medium of the comparative example, the recording and reproducing characteristics of the HTL type were confirmed. That is, in the recording medium of the comparative example, the reflectivity of light in the recording area decreases by the recording operation. From these results, especially the results of the embodiment 1 and the comparative example 1, it can be seen that the thickness of the recording layer affects the recording and reproducing characteristics of the recording medium. In addition, the recording media of the embodiment 1 and the comparative example 1 have the same structure as each other except that the thickness of the recording layer is different.

[0313] Next, the cross section of the recording portion of the recording medium of Example 2 after the above-mentioned dynamic evaluation was observed using a scanning electron microscope (SEM). As a result, a concave recording mark was formed in the recording portion. The depth of the recording mark is proportional to the irradiation energy of the light irradiated during the recording operation. Figure 7 Graph showing the relationship between the average energy of recording light irradiation and the deformation amount of a concave recording mark for the recording medium of Example 2. The deformation amount of a recording mark means the depth of the recording mark.

[0314] Depend on Figure 7 It can be seen that, for the recording medium of Example 2, the greater the irradiation energy of the irradiated light during the recording operation, the greater the deformation amount of the recording mark. It is estimated that the greater the light absorption generated by the pigment material, that is, the larger the linear light absorption and the nonlinear light absorption, Figure 7 The slope of the graph increases.

[0315] Next, for the recording medium produced in Example 2, a stripping film (made by Teraoka Seisakusho, film masking tape 605#50) was arranged on the recording layer to prepare a sample. For this sample, the recording operation of the above-mentioned static evaluation was performed. Next, the stripping film was stripped from the sample, and the recording portion was observed using an atomic force microscope (AFM). As a result, a concave recording mark was formed in the recording portion.

[0316] Furthermore, for the recording medium produced in Example 2, a cover layer of cellulose acetate was arranged on the recording layer to prepare a sample. The cover layer was produced by a coating method. The above-mentioned recording operation of the static evaluation was performed on this sample. Next, the cross section of the sample was observed by SEM. As a result, a concave recording mark was formed in the recording portion. From these results, it is inferred that under the evaluation conditions of the above-mentioned recording and reproducing characteristics, the recording process is performed by the same mechanism regardless of the type of dielectric layer used. In addition, it is inferred that this mechanism is performed in the same manner in both the dynamic evaluation and the static evaluation.

[0317] As can be seen from Table 1 described later, in the recording medium of the embodiment, the thickness of the recording layer satisfies the above-mentioned relational expression (1). Therefore, in the embodiment, it is estimated that the thickness at the recording portion is reduced by the recording operation, so that the phase difference between the reflected light from the interface between the recording layer and the air layer and the reflected light from the interface between the recording layer and the glass substrate is reduced. Therefore, it is estimated that in the recording medium of the embodiment, the reproduced signal from the recording portion is detected more strongly than that from the unrecorded portion.

[0318] As can be seen from Table 1 described later, in the recording medium of the comparative example, the thickness of the recording layer does not satisfy the above-mentioned relational expression (1). Therefore, in the comparative example, it is estimated that the thickness at the recording portion decreases by the recording operation, so that the phase difference between the reflected light from the interface between the recording layer and the air layer and the reflected light from the interface between the recording layer and the glass substrate increases. Therefore, it is estimated that in the recording medium of the comparative example, the reproduced signal from the recording portion is detected weakly compared with the unrecorded portion.

[0319] In Comparative Example 3, since the difference in refractive index between the recording layer and the glass substrate is small, the amount of light reflected from the interface between them is small.

[0320] Table 1

[0321]

[0322] (*1) Refractive index of the recording layer n 1 The refractive index of the layer with air is n 2 difference

[0323] (*2) Refractive index of the recording layer n 1 Refractive index n of glass substrate 3 difference

[0324] (*3)○: Relation (1) holds true

[0325] ×: Relationship (1) does not hold

[0326] Industrial Applicability

[0327] The recording medium disclosed herein can be used in applications such as three-dimensional optical storage.

[0328] Description of Reference Numerals

[0329] 10 recording layers:

[0330] 20A first dielectric layer

[0331] 20B Second dielectric layer

[0332] 100, 110 recording medium.

Claims

1. A recording medium comprising: a first dielectric layer, a second dielectric layer, and a recording layer having a recording region where information is recorded by irradiating light and located between the first dielectric layer and the second dielectric layer, The recording layer contains a pigment material, The transmittance of light with a wavelength of 405 nm in the recording layer is 95% or more, The reflectivity of light in the recording area where information is recorded is higher than the reflectivity of light in the recording area before information is recorded. The thickness D (nm) of the recording layer, the refractive index n1 of the recording layer for light of wavelength 405 nm, the refractive index n2 of the first dielectric layer for light of wavelength 405 nm, and the refractive index n3 of the second dielectric layer for light of wavelength 405 nm satisfy the following relations (1) to (3), (1.33-0.15n1){405(m+1 / 2) / (2n1)}<D≤(1.33-0.15n1){405(m+1) / (2n1)}(1) n1>n2 (2) n1>n3 (3) In the formula (1), m is an integer of 0 to 4.

2. The recording medium according to claim 1, wherein The difference between the refractive index n1 and the refractive index n2 is greater than 0.2, and the difference between the refractive index n1 and the refractive index n3 is greater than 0.

2.

3. The recording medium according to claim 1, wherein The refractive index n1 is greater than or equal to 1.

65.

4. The recording medium according to claim 1, wherein In the recording layer, a concave recording mark is formed by irradiating the recording layer with recording light.

5. The recording medium according to claim 1, wherein The pigment material includes a polymer P1, and the polymer P1 includes a group having nonlinear light absorption characteristics.

6. The recording medium according to claim 5, wherein The polymer P1 has structural units from the class of vinylcarbazoles.

7. The recording medium according to claim 1, wherein The recording layer further comprises a polymer P2.

8. The recording medium according to claim 7, wherein The polymer P2 has structural units from the class of vinylcarbazoles.

9. A method for recording information, comprising: preparing a light source that emits light having a wavelength of 390 nm or more and 410 nm or less; and collecting the light from the light source and irradiating the light to the recording layer in the recording medium according to any one of claims 1 to 8.

10. A method for reading information, which is a method for reading information recorded by the recording method according to claim 9, the reading method comprising: measuring optical properties of the recording layer by irradiating the recording layer in the recording medium with light; and reading information from the recording layer.

11. The reading method according to claim 10, wherein: The optical characteristic is the intensity of light reflected by the recording layer.

Images