JP2012203968A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information recording medium allowing an interface of a recording layer to be deformed to record information, in which recording and reproducing light can be delivered and returned to and from the deep recording layer and a good S/N ratio is obtained.SOLUTION: An optical information recording medium 10 includes a first intermediate layer 15A and a second intermediate layer 15B, each of which has a different refractive index, interposed between adjacent recording layers 14. The first intermediate layer 15A and the second intermediate layer 15B are alternately disposed. A difference between a refractive index nof the recording layer 14 and a refractive index nof the second intermediate layer 15B is 0.01 or less. A thickness d of the first intermediate layer 15A satisfies the following equation: where λ represents a wavelength of reading light emitted during reproduction, n≒n=n, and nrepresents a refractive index of the first intermediate layer 15A.

Description

  The present invention relates to an optical information recording medium comprising a plurality of recording layers.

  In order to record information in multiple layers on an optical information recording medium, a method for causing an optical change in a recording material in the optical information recording medium using a multiphoton absorption reaction such as two-photon absorption has been studied (for example, patents). Reference 1). When the multiphoton absorption reaction is used, since there is no linear absorption with respect to the recording light, the recording light can reach a deep layer as viewed from the recording light irradiation side. However, the multiphoton absorption reaction has a problem that the sensitivity is very poor because the reaction efficiency is very poor.

Japanese Patent No. 4546986

  Under the background described above, the present inventor, while studying a high-sensitivity optical information recording medium, can record by relatively high sensitivity by accidentally deforming the interface of the recording layer. I discovered that. However, when recording information by causing deformation at the interface of the recording layer, the reflectivity at the interface causing the deformation needs to be moderately large. Due to selection limitations, the difference in refractive index between the recording layer and the intermediate layer adjacent to the recording layer cannot be made very large, so that there is a possibility that a sufficient S / N ratio cannot be obtained.

  In addition, when recording information using deformation of the interface of the recording layer, it is desirable that the interface on the other side of the recording layer (the interface on the side not used for recording) should have a low reflectance. Since it is desirable that the difference in refractive index between the layer and the adjacent intermediate layer is small, it is difficult to set the difference in refractive index between the recording layer and the intermediate layer provided between the recording layers.

  Therefore, the present invention can sufficiently transfer recording / reproducing light (light used during recording and reproduction) to a deep recording layer in an optical information recording medium that records information by causing deformation at the interface of the recording layer. At the same time, an object is to obtain a good S / N ratio.

In order to solve the above-described problems, the present invention provides an optical information recording medium comprising a plurality of recording layers, wherein a first intermediate layer and a second intermediate layer having different refractive indexes are provided between adjacent recording layers. together is, the a first intermediate layer and the second intermediate layer, are alternately arranged, wherein the refractive index n ₀ of the recording layer, the refractive index n ₂ of the second intermediate layer, the difference is 0.01 The thickness d of the first intermediate layer is as follows: λ is the wavelength of the readout light irradiated during reproduction, n ₀ ≈n ₂ = n, and the refractive index of the first intermediate layer is n ₁ .
And information is recorded by deformation of the interface between the recording layer and the first intermediate layer by irradiation of recording light. Note that n ₀ ≈n ₂ = n is the same even if the difference between n ₀ and n ₂ is slightly different within a range of 0.01 or less, and these are treated as the same value in the formula in order to simplify the formula. It means n. When specific values of n ₀ and n ₂ are slightly different, n is an intermediate value (average) between n ₀ and n ₂ .

According to such an optical information recording medium, the first intermediate layer is adjacent to one interface of the recording layer, and the second intermediate layer is adjacent to the other interface. Then, the refractive index n ₀ of the recording layer and the refractive index n ₂ of the second intermediate layer, the difference is 0.01 or less, i.e., since it is substantially identical, substantially at the interface of the recording layer and the second intermediate layer Reflection does not occur. Thereby, it is easy to make recording / reproducing light go back and forth to a deep recording layer. On the other hand, the first intermediate layer and the second intermediate layer have different refractive indexes, and the recording layer and the first intermediate layer also have different refractive indexes. The first intermediate layer satisfies the above formula (1), and when irradiated with reading light during reproduction, the reflected light reflected at the interface between the first intermediate layer and the recording layer, and the first intermediate layer and the first intermediate layer The reflected light reflected at the interface of the two intermediate layers strengthens each other, and the reflectance viewed from the two interfaces is substantially increased. As a result, the S / N ratio can be increased at the time of reproducing information recorded by deformation of the interface between the first intermediate layer and the recording light.

In the optical information recording medium described above, the thickness d of the first intermediate layer is:
It is desirable to satisfy.

  By satisfying this equation (2), the reflected light reflected at the interface between the first intermediate layer and the recording layer and the reflected light reflected at the interface between the first intermediate layer and the second intermediate layer are most efficiently produced. In addition, even if there is a manufacturing error in the thickness d, the error in the reflectance is small, so that a high S / N ratio can be realized.

  In the optical information recording medium described above, the recording layer may include a polymer binder and a dye dispersed in the polymer binder.

  In this case, the dye may include a multiphoton absorption compound. By using a multiphoton absorbing compound as the dye, the recording light can reach a deep layer, which is advantageous for multilayering of the recording layer.

  The thickness of the recording layer can be 50 nm or more. By setting the recording layer to 50 nm or more, it becomes easy to cause a convex deformation from the recording layer to the first intermediate layer at the interface between the recording layer and the first intermediate layer.

  The thickness of the second intermediate layer may be 5 μm or more to prevent interlayer crosstalk.

  According to the present invention, in an optical information recording medium for recording information by causing deformation at an interface of a recording layer, recording / reproducing light can be transmitted and received to a deep recording layer, and a good S / N ratio can be obtained. Can

It is sectional drawing of a multilayer optical information recording medium. It is a figure which shows the recording spot formed at the time of recording. It is a figure explaining the time of reproduction | regeneration. It is figure (a)-(c) explaining the formation process of a concave shape. It is a graph which shows an example of the relationship between the film thickness of a 2nd intermediate | middle layer, and the reflectance seen in the whole upper and lower interface of a 2nd intermediate | middle layer. It is a graph which shows an example of the relationship of the reflectance and S / N ratio seen in the whole upper and lower interface of a 2nd intermediate | middle layer. It is the table | surface which put together the experimental result. It is an atomic force microscope image of a recording spot. It is an optical microscope image of a recording spot. It is a graph which shows the relationship between the height of a recording spot, and a modulation degree.

Next, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the optical information recording medium 10 includes a substrate 11, a plurality of recording layers 14, a plurality of intermediate layers 15 (first intermediate layer 15A and second intermediate layer 15B), and a cover layer 16. Prepare. In the present embodiment, the interface between the recording layer 14 and the first intermediate layer 15A is referred to as a “front interface 18”, and the interface between the recording layer 14 and the second intermediate layer 15B is referred to as a “back interface 19”. The interface between the first intermediate layer 15A and the second intermediate layer 15B is referred to as an “intermediate interface 20”.

  The substrate 11 is a support for supporting the recording layer 14 and the like, and is made of, for example, a polycarbonate disk. The material and thickness of the substrate 11 are not particularly limited. The substrate 11 is provided with a guide groove 11A for use in tracking servo.

  The recording layer 14 is a layer made of a photosensitive material on which information is optically recorded. In the present embodiment, the recording layer 14 includes a polymer binder and a dye dispersed in the polymer binder. When the recording layer 14 is irradiated with recording light, the polymer binder is deformed by the heat generated by the dye absorbing the recording light, and a convex shape toward the first intermediate layer 15A is formed at the front interface 18. Information is recorded. More specifically, as will be described later, a convex shape is formed such that the center is directed from the recording layer 14 toward the first intermediate layer 15A, and the periphery of the convex shape is a concave shape directed toward the recording layer 14 from the first intermediate layer 15A. (With reference to the recording layer 14) is formed.

  For this reason, the recording layer 14 is formed to be relatively thick, and one recording layer 14 is formed to have a thickness of 50 nm to 5 μm, preferably 100 nm to 3 μm, more preferably 200 nm to 2 μm. When the thickness is smaller than 50 nm, the front interface 18 is deformed into a concave shape with reference to the recording layer 14. However, when the thickness is 50 nm or more, the center of the recorded portion is convex. Deform. The upper limit of the thickness of the recording layer 14 is not particularly limited, but the thickness of the recording layer 14 is preferably 5 μm or less in order to increase the number of recording layers 14 as much as possible. However, in the present invention, the thickness of the recording layer 14 may be less than 50 nm.

  The recording layer 14 is provided, for example, about 2 to 100 layers. In order to increase the storage capacity of the optical information recording medium 10, it is desirable that the number of the recording layers 14 be large, for example, 10 layers or more. Further, the refractive index of the recording layer 14 may or may not change before and after recording.

  The recording layer 14 preferably has an absorptance (one-photon absorptance) for recording light of 5% or less per layer. Further, the absorptance is more preferably 2% or less, and further preferably 1% or less. For example, on condition that the intensity of the recording light reaching the innermost recording layer 14 is 50% or more of the intensity of the irradiated recording light, in order to realize the 30 recording layers, the recording layer 1 This is because the absorption rate per layer needs to be 2% or less, and in order to realize 50 recording layers, the absorption rate per recording layer needs to be 1% or less. Further, if the absorption rate is high, it is difficult to form a convex shape on the front interface 18 by heating the recording layer 14 too much.

  A method for forming the recording layer 14 is not particularly limited, but the recording layer 14 can be formed by spin-coating a liquid in which a dye material and a polymer binder are dissolved in a solvent. As the solvent at this time, dichloromethane, chloroform, methyl ethyl ketone (MEK), acetone, methyl isobutyl ketone (MIBK), toluene, hexane, or the like can be used.

  Polymer binders used for the recording layer 14 include polyvinyl acetate (PVAc), polymethyl methacrylate (PMMA), polyethyl methacrylate, polybutyl methacrylate, polybenzyl methacrylate, polyisobutyl methacrylate, polycyclohexyl methacrylate, polycarbonate (PC), Polystyrene (PS), polyvinyl chloride (PVC), polyvinyl alcohol (PVA), and the like can be used.

  As the dye that absorbs the recording light used in the recording layer 14, for example, a dye that has been conventionally used as a heat mode recording material can be used. For example, phthalocyanine compounds, azo compounds, azo metal complex compounds, and methine dyes (cyanine compounds, oxonol compounds, styryl dyes, merocyanine dyes) can be used. In order to minimize the influence on the adjacent recording layer at the time of recording / reproducing in a recording medium having a multi-layered recording layer, it is desirable to include a multiphoton absorbing dye as the dye that absorbs the recording light. The photon absorbing dye is preferably, for example, a two-photon absorbing compound that does not have a linear absorption band at the wavelength of the readout light.

  The two-photon absorption compound is not particularly limited as long as it does not have a linear absorption band at the wavelength of readout light, and examples thereof include compounds having a structure represented by the following general formula (1).

(In the general formula (1), X and Y each represent a substituent having a Hammett's sigma para value (σp value) of zero or more, which may be the same or different, and n represents an integer of 1 to 4. R represents a substituent, which may be the same or different, and m represents an integer of 0 to 4.)

  In the general formula (1), X and Y are those having a positive σp value in the Hammett formula, so-called electron-withdrawing groups, and preferably, for example, a trifluoromethyl group, a heterocyclic group, a halogen atom, a cyano group Nitro group, alkylsulfonyl group, arylsulfonyl group, sulfamoyl group, carbamoyl group, acyl group, acyloxy group, alkoxycarbonyl group, etc., more preferably trifluoromethyl group, cyano group, acyl group, acyloxy group, Or an alkoxycarbonyl group, and most preferably a cyano group or a benzoyl group. Among these substituents, an alkylsulfonyl group, an arylsulfonyl group, a sulfamoyl group, a carbamoyl group, an acyl group, an acyloxy group, and an alkoxycarbonyl group are further added for various purposes in addition to imparting solubility to a solvent. It may have a substituent, and preferred examples of the substituent include an alkyl group, an alkoxy group, an alkoxyalkyl group, and an aryloxy group.

n represents an integer of 1 or more and 4 or less, more preferably 2 or 3, and most preferably 2. As n becomes 5 or more, linear absorption comes out on the longer wavelength side, and non-resonant two-photon absorption recording using recording light in a wavelength region shorter than 700 nm becomes impossible.
R represents a substituent, and the substituent is not particularly limited, and specific examples include an alkyl group, an alkoxy group, an alkoxyalkyl group, and an aryloxy group. m represents an integer of 0 or more and 4 or less.

  Although it does not specifically limit as a specific example of the compound which has a structure represented by General formula (1), The compound of the following chemical structural formula D-1 to D-21 can be used.

  The intermediate layer 15 is provided between the plurality of recording layers 14, in other words, adjacent to the top and bottom of each recording layer 14. The intermediate layer 15 is provided in order to provide a predetermined amount of space between the recording layers 14 so that interlayer crosstalk (mixing of signals between adjacent recording layers 14) does not occur between the plurality of recording layers 14. Yes.

  One (one layer) intermediate layer 15 includes a first intermediate layer 15A and a second intermediate layer 15B adjacent to the upper side of the first intermediate layer 15A. Accordingly, the first intermediate layer 15A is adjacent to the recording layer 14 on the upper side, which is one side in the incident direction of the recording light, and the second intermediate layer 15B is different from the one side described above with respect to the recording layer 14. Adjacent to the opposite lower side.

  The first intermediate layer 15A and the second intermediate layer 15B are made of a material that does not change due to laser irradiation during recording and reproduction. Further, the first intermediate layer 15A and the second intermediate layer 15B have a recording light, a reading light, and a reading light in order to minimize the loss of the recording light, the reading light, and the reproducing light (light including a reproduction signal generated by irradiation of the reading light). It is desirable to be made of a transparent resin for light and reproduction light. The term “transparent” as used herein means that the total absorption rate of the first intermediate layer 15A and the absorption rate of the second intermediate layer 15B is 1% or less.

The first intermediate layer 15A is provided adjacent to the upper side (near side) of the recording layer 14 as viewed from the recording light irradiation side (upper side in FIG. 1), and has a refractive index different from the refractive index of the recording layer 14. is doing. Thereby, at the interface (front interface 18) between the recording layer 14 and the first intermediate layer 15A, the recording light and the reading light are reflected due to the sudden change of the refractive index. As will be described later, since the first intermediate layer 15A is thin, the reflection by the front interface 18 and the reflection by the intermediate interface 20 interfere and strengthen each other, and the reflected light reflected by these two interfaces is combined. The reflectance as a whole is increased.
The difference between the refractive index n ₁ of the first intermediate layer 15A and the refractive index n ₀ of the recording layer 14 is that the refractive index of the second intermediate layer 15B is n ₂ , the thickness of the first intermediate layer 15A is d, and the reading light It is desirable that the overall reflectance R obtained by the following formula (3) is adjusted to satisfy 0.001 <R <0.04, where λ is the wavelength.

  When the reflectance R is greater than 0.001, the amount of reflected light combining the front interface 18 and the intermediate interface 20 can be increased, and the S / N ratio can be increased during information reproduction. Further, since the reflectance R is smaller than 0.04, the amount of reflected light including the front interface 18 and the intermediate interface 20 is suppressed to an appropriate level, and the recording / reproducing light is greatly attenuated during recording and reproduction. It is possible to reach the deep recording layer 14 without any problems. Thereby, it is possible to increase the capacity by providing a large number of recording layers 14.

In the present embodiment, the first intermediate layer 15 </ b> A is softer than the recording layer 14. Specifically, for example, the first intermediate layer 15 </ b> A has a glass transition temperature lower than the glass transition temperature of the recording layer 14. As another example, the recording layer 14 may be a solid layer, and the first intermediate layer 15A may be an adhesive layer. Such a configuration can be realized by appropriately selecting a polymer binder (resin) that can be used as the material of the recording layer 14 and a resin that can be used as the material of the first intermediate layer 15A.
As described above, the first intermediate layer 15A is configured to be softer than the recording layer 14, so that when the recording layer 14 is heated and expanded by the recording light, the first intermediate layer 15A is easily deformed, and the front interface 18 deformations can be easily caused.

The second intermediate layer 15B is provided adjacent to the lower side (back side) of the recording layer 14 as viewed from the recording light irradiation side, and has a refractive index that is substantially the same as the refractive index of the recording layer 14. Yes. That is, the first intermediate layer 15A and the second intermediate layer 15B have different refractive indexes.
In the present embodiment, information (recording spot M) is recorded by utilizing deformation at the front interface 18, so the back interface 19 does not contribute to information reproduction. Therefore, it is desirable that the back side interface 19 does not reflect the recording / reproducing light, and the refractive index of the recording layer 14 and the refractive index of the second intermediate layer 15B are substantially the same. Specifically, in this specification, the substantially same refractive index means a case where the difference in refractive index is 0.01 or less, preferably 0.002 or less, more preferably 0.001 or less, most preferably. Means 0. As a result, reflection due to a sudden change in the refractive index does not occur at the back side interface 19, and the recording / reproducing light can be transmitted without being reflected.

  In order to reduce the difference between the refractive index of the recording layer 14 and the refractive index of the second intermediate layer 15B, preferably 0, it is preferable to adjust the composition of materials used for the recording layer 14 and the second intermediate layer 15B. Specifically, since a dye such as a two-photon absorption compound is mixed in the polymer binder in the material of the recording layer 14, the refractive index of the dye or the polymer binder is appropriately selected, and the blending ratio of each is selected. By changing the refractive index, the refractive index can be arbitrarily adjusted. In addition, even if the polymer binder has a similar basic structure, the refractive index changes when the degree of polymerization is different, so a polymer binder with a different degree of polymerization can be used, or the degree of polymerization of the polymer binder can be adjusted. By doing so, the refractive index can be adjusted. Furthermore, it is also possible to adjust by blending a plurality of polymer binders. It is also possible to adjust the refractive index by adding a refractive index adjusting agent (such as inorganic fine particles).

  When adjusting the refractive index of the second intermediate layer 15B, the refractive index can be adjusted by adjusting the degree of polymerization of a polymer material such as a resin that can be used as the material of the second intermediate layer 15B. It is also possible to adjust the refractive index by arbitrarily blending materials that can be used as the intermediate layer 15 or to adjust the refractive index by adding a refractive index adjusting agent (such as inorganic fine particles).

In this embodiment, as an example, the refractive index n ₀ of the recording layer 14 is 1.55, the refractive index n ₁ of the first intermediate layer 15A is 1.45, and the refractive index n of the second intermediate layer 15B. ₂ is 1.55.

  In the present embodiment, the second intermediate layer 15 </ b> B can have a hardness equivalent to that of the recording layer 14 or a configuration harder than the recording layer 14. Specifically, for example, the second intermediate layer 15B can have a glass transition temperature equal to or higher than the glass transition temperature of the recording layer 14. Such a configuration can be realized by appropriately selecting a resin that can be used as the material of the recording layer 14 and a resin that can be used as the material of the second intermediate layer 15B. In the present invention, the second intermediate layer 15B may be softer than the recording layer 14.

  As will be described later, the thickness of the second intermediate layer 15B is 5 μm from the viewpoint that the first intermediate layer 15A is very thin, substantially determines the thickness of the entire intermediate layer 15, and prevents the above-described interlayer crosstalk. That's it. As an example, the thickness of the second intermediate layer 15B is 10 μm in the present embodiment. Further, in order to increase the number of recording layers 14, the thickness of the second intermediate layer 15B is preferably 20 μm or less.

The thickness of the first intermediate layer 15A is set so that the reflected light reflected by the front interface 18 and the reflected light reflected by the intermediate interface 20 interfere and strengthen each other. Specifically, the reflectance R ′ at the front interface 18 when there is no influence of this interference is n ₀ ≈n ₂ = n,
R ′ = (n ₁ −n) ² / (n ₁ + n) ²
It is. On the other hand, when the reflected light reflected by the front interface 18 and the reflected light reflected by the intermediate interface 20 interfere with each other, the total reflectance R of these reflected lights combined with the value expressed by the equation (3) is Become.

  When the inequality R ′ <R is solved for the thickness d of the first intermediate layer 15A, the above equation (1) is obtained.

That is, when this formula (1) is satisfied, the reflected light reflected by the front interface 18 and the reflected light reflected by the intermediate interface 20 interfere and strengthen each other, so that the refractive indexes of the recording layer 14 and the first intermediate layer 15A are increased. Even when the difference is not so large, the reflectance R can be increased to obtain a good S / N ratio. Based on the formula (3), the change in the reflectance R depending on the thickness d in the case of the optical information recording medium 10 of the present embodiment is shown in FIG. When the refractive indexes n ₀ , n ₁ , and n ₂ are set as described above and the wavelength λ of the readout light is 405 nm, as shown in FIG. 5, the reflectance R is the largest when d is around 70 nm (69.8 nm). 0.44%. The range of the thickness d in which the reflectance R is larger than that in the case where interference is not used is 23.3 nm <d <116.4 nm.

  As shown in FIG. 5, the reflectivity R changes very gradually with respect to the change in the thickness d in the vicinity of the peak (d = 70 nm), and therefore the thickness d is preferably in the vicinity of this peak. Therefore, it is desirable that the thickness d satisfies the above-described formula (2) in consideration of an error of 5% at the time of manufacturing.

Under specific conditions in the present embodiment, the above formula (2) satisfies 66.3 nm ≦ d ≦ 73.3 nm. At this time, the variation of the reflectance R is only 0.0024%, and a very stable reflectance can be obtained.
For example, when the noise as the reflectance variation is 0.01%, which is larger than 0.0024%, for a signal with a modulation degree of 40%, the S / N ratio is as shown in FIG. At a rate of 0.44%, a sufficient S / N ratio of 34 dB is obtained.

  The refractive index and thickness conditions of the first intermediate layer 15A have been described with reference to the wavelength λ of the reading light in consideration of reflection during reproduction. However, the recording light is also transmitted to the recording layer 14 (front side) during recording. Since it is desirable that there is sufficient reflected light to focus on the interface 18), it is desirable that the above condition (Equation (1) or Equation (2)) is also satisfied for the wavelength of the recording light.

  The cover layer 16 is a layer provided to protect the recording layer 14 and the intermediate layer 15 (the first intermediate layer 15A and the second intermediate layer 15B), and is made of a material that can transmit recording / reproducing light. The cover layer 16 is provided with an appropriate thickness of several tens of μm to several mm. As an example, the thickness of the cover layer 16 is 50 μm.

A method for recording / reproducing information on the optical information recording medium 10 as described above will be described.
When recording information on a desired recording layer 14, as shown in FIG. 2, the recording layer 14 is irradiated with laser light (recording light RB) whose output is modulated in accordance with the information to be recorded. When the recording layer 14 has a multiphoton absorption compound as a recording dye, a pulsed laser beam capable of increasing the peak power may be used as this laser beam. The position of the focal point of the recording light RB is not particularly limited, but can be in the vicinity of the front interface 18, in the vicinity of the back interface 19, or between the front interface 18 and the back interface 19.

  When the recording light RB is irradiated, as shown in FIG. 2, a recording spot M is formed in which the center of the portion irradiated with the recording light RB has a convex shape from the recording layer 14 toward the first intermediate layer 15A. Specifically, the recording spot M has a convex portion M1 at the center and a ring-shaped concave portion M2 around the convex portion M1 toward the recording layer. The distance from the front side interface 18 (the front side interface 18 before deformation) of the deepest portion of the recess M2 is smaller than the distance from the front side interface 18 (the front side interface 18 before deformation) of the apex of the convex part M1. That is, the recording spot M as a whole can be said to be approximately convex. The principle of forming the recording spot M having a convex shape at the center is not clear. However, the principle of forming a concave shape in a recording method in which the center of the irradiation spot has a concave shape is also known. It is inferred from the comparison with

  First, when considering the case of a concave shape, J.A. Appl. According to Phys 62 (3), 1 August 1987, when the recording material is irradiated with the recording light, the recording material (recording layer 14) expands due to the temperature rise of the recording material as shown in FIG. The part shows the heated range). And as shown in FIG.4 (b), the expanded part flows out around by surface tension. Thereafter, when the temperature decreases, as shown in FIG. 4C, the expanded recording material contracts, and the portion that flows out around the irradiated portion is higher than the reference surface (the upper surface of the recording layer 14). The recording material remains at the position and becomes convex, but the central portion becomes lower than the reference surface due to outflow of the material and becomes concave.

  On the other hand, in the optical information recording medium of this embodiment, when the recording light RB is irradiated, the recording layer 14 is thermally expanded, and the recording layer 14 protrudes as shown in FIG. However, in the present embodiment, since the recording layer 14 is relatively thick, the viscosity in the vicinity of the surface of the recording layer 14 is not as low as in the prior art, and the outflow of FIG. 4B does not occur. Therefore, when the expanded portion contracts due to a decrease in temperature, the shape changes from the shape of FIG. 4A to the shape of FIG. 2, leaving a convex portion M1 at the center and a concave portion M2 around the convex portion M1. It is thought that you can.

  When the recording spot M formed in this way is irradiated with the reading light OB with a continuous wave laser as shown in FIG. 3, there is a difference between the refractive index of the recording layer 14 and the refractive index of the first intermediate layer 15A. The reading light OB is reflected by the surface of the recording spot M. At this time, as described above, since the reflected light reflected by the front interface 18 and the reflected light reflected by the intermediate interface 20 interfere and strengthen each other, the difference in refractive index between the recording layer 14 and the first intermediate layer 15A is increased. Even if it is not possible to obtain a large amount, it is possible to obtain reflected light (reproduced light SB) having an intensity required for reproduction. As a result, a difference occurs between the intensity of the reflected light around the recording spot M and the intensity of the reflected light at the recording spot M, so that the recording spot M can be detected by this modulation. For such optical detection, it is desirable that the convex portion M1 protrudes about 1 to 300 nm with respect to the interface before deformation (the front interface 18).

  In the present embodiment, since the recording spot M is formed with the concave portion M2 around the convex portion M1, when the reading light OB for reading the recording spot M is applied to the recording spot M, only the convex portion M1 is present. Compared to the case, the intensity distribution of the reflected light from the recording spot M is considered to change abruptly according to the distance from the center of the convex portion M1, and can be read with a high degree of modulation.

  When erasing information recorded on the recording layer 14, the fluidity of the polymer binder is improved by heating the recording layer 14 to a temperature near the glass transition temperature of the polymer binder, preferably higher than the glass transition temperature. Then, the information recorded in the recording layer 14 can be erased by returning to the original plane without the deformation of the front interface 18 due to the surface tension. By erasing information in this way, re-recording (repeated recording) on the recording layer 14 is possible. At the time of this heating, a method of irradiating a continuous wave laser so as to focus on the recording layer 14 can be used. By heating with a continuous wave laser, it is possible to erase information in a continuous region in the recording layer 14 without unevenness. As this continuous wave laser, a laser used for reproducing information may be used, or another laser may be used. In any case, it is desirable to use a laser that emits light having a wavelength capable of one-photon absorption.

  When erasing information by heating the recording layer 14, the information recorded in all the recording layers 14 is heated by heating the entire optical information recording medium 10 to a temperature higher than the glass transition temperature of the polymer binder. Can be erased at once. As a result, regardless of the type of dye that the recording layer 14 has, the entire information of the optical information recording medium can be easily erased and initialized. In addition, information can be easily deleted when the optical information recording medium is discarded.

  As described above, in the optical information recording medium 10 of the present embodiment, information can be recorded by forming the recording spot M having a convex shape from the recording layer 14 toward the first intermediate layer 15A on the front interface 18. . In order to form this recording spot M, it is not necessary to give high fluidity to the recording layer 14 as in the case of forming a concave shape, so that recording can be performed with high sensitivity accordingly.

  In the optical information recording medium 10 of the present embodiment, the difference in refractive index between the recording layer 14 and the second intermediate layer 15B on both sides of the back side interface 19 not involved in information reproduction is substantially eliminated. As a result, the reflection of the recording / reproducing light at the back side interface 19 can be eliminated, and the recording light RB and the reading light OB can reach the deep recording layer 14, and the number of recording layers 14 can be increased. In addition, since the reflected light reflected by the front interface 18 and the reflected light reflected by the intermediate interface 20 interfere and strengthen each other, the difference in refractive index between the recording layer 14 and the first intermediate layer 15A cannot be made large. However, it is possible to obtain reflected light (reproduced light SB) having an intensity necessary for reproduction. Thereby, the S / N ratio at the time of reproduction | regeneration can be improved.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be appropriately modified and implemented.
For example, in the above-described embodiment, the front interface 18 is deformed so as to be convex from the recording layer 14 toward the first intermediate layer 15A by the irradiation of the recording light RB. You may comprise. In FIG. 2, only the front interface 18 side of the recording layer 14 is shown to be deformed, but at the same time, the back interface 19 between the recording layer 14 and the second intermediate layer 15B is also deformed. It doesn't matter.

  The layer configuration of the optical information recording medium 10 is not limited to the order shown in FIG. 1, and the recording layer 14, the first intermediate layer 15A, and the second intermediate layer 15B are viewed from the incident side of the recording light RB. The order may be reversed. That is, as viewed from the incident side of the recording light RB, the recording layer 14, the first intermediate layer 15A, the second intermediate layer 15B, the recording layer 14, the first intermediate layer 15A, and the second intermediate layer 15B in this order. A configuration in which layers are repeatedly arranged may be used.

  Next, an experiment for confirming that recording can be performed on an optical information recording medium by causing a convex deformation in the recording layer, and an experiment for performing a test for erasing the convex shape will be described. As described above, in the present invention, the recording layer does not necessarily have a convex shape.

1. Recording Material In the examples, a recording material in which a dye was dispersed in a polymer binder was used.

(1) Polymer binder As the polymer binder, polyvinyl acetate (manufactured by Across, Mw: 101600) or polymethyl methacrylate (manufactured by SIGMA-ALDRICH) was used.

(2) Dye As the dye, one or both of a phthalocyanine-based one-photon absorption dye shown in C-1 below and a two-photon absorption dye shown in C-2 were used.

2. Recording Layer Formation Method A coating solution was prepared by stirring and dissolving a dye and a polymer binder in a solvent (described later), and a film was formed on a glass substrate by spin coating. The film thickness was 1 μm. The refractive index of the glass substrate is 1.53.

3. Method for Thermal Analysis of Materials Using the following methods, the glass transition temperature of the polymer binder and the melting point / decomposition point of the dye were confirmed.
Analytical method: TG-DTA (thermogravimetric / differential thermal analysis) measurement Device: TG-DTA6300 (manufactured by Seiko Instruments Inc.)
Temperature increase rate: 10 ° C / min
Measurement temperature range: 25 ° C-600 ° C
Measurement atmosphere: Nitrogen (N ₂ ) atmosphere

The following temperatures were adopted as the glass transition temperature, melting point, and decomposition point (or vaporization temperature).
(1) Glass transition temperature The endothermic reaction peak temperature of the polymer binder without weight reduction was defined as the glass transition temperature.
(2) Melting point The temperature obtained by extrapolating the peak start temperature of the endothermic reaction of the dye without weight reduction was taken as the melting point.
(3) Decomposition point (or vaporization temperature)
The temperature at which the weight was reduced by 10% relative to that before decomposition was taken as the decomposition point (or vaporization temperature). When there were multiple decomposition points, the comparison was made at the lowest temperature.

The results of this thermal analysis are as shown in the table below.

4). Recording / reproduction test / evaluation method Recording light (pulse laser: wavelength 522 nm, repetition frequency 3 GHz, pulse width 500 fsec, average power Pa = 5 to 50 mW, peak power Pp = 3 to 33 W) is irradiated to the recording layer at a peak power of 10 W. did. Then, with respect to the recording layer, the focal position of the recording light is moved by 0.4 μm in the range of 4 μm in the optical axis direction (that is, 11 points in the depth direction), and 4 at each depth position (focal position). A dot recording (ie, recording at a total of 44 locations) was tested.
The recording conditions were adjusted such that the recording time was between 5 μs and 5 ms. Then, recording time [μs] capable of recording 12 recording spots (3 at adjacent focal positions and 4 at each focal position) was obtained as data.
Further, some examples were observed with an atomic force microscope (AFM) and an optical microscope. The observation conditions at this time are as follows.

Atomic force microscope device Nanosearch microscope OLS-3500 (Olympus)
Observation conditions Dynamic mode, scanning range 10μm, scanning speed 1Hz
Use of high aspect ratio probe AR5-NCHR-20 (Nanoworld) Optical microscope Device ECLIPSE LV150 (Nikon)
Observation conditions Objective lens 100x, dark field observation

Further, a continuous wave laser (CW laser) having a wavelength of 405 nm was used as reproduction light, a recording spot was irradiated with a power of 0.5 mW, and the amount of reflected light was read.
The degree of modulation was defined by the following equation and calculated from the experimental results.
Modulation depth =
{(Reflected light amount of unirradiated portion) − (Reflected light amount of irradiated portion)} / (Reflected light amount of unirradiated portion)

5. Conditions for each example and comparative example The conditions for each example and comparative example were as described below.

[Example 1]
Solvent Methyl ethyl ketone (MEK) 7g
Dye C-1 compound 15mg
Polymer binder Polyvinyl acetate (PVAc) 500mg

[Example 2]
The dye was changed to the following for Example 1, and the others were the same as Example 1.
Dye C-2 compound 72mg

[Example 3]
For Example 1, the following two compounds were used as dyes, and the others were the same as Example 1.
Dye C-1 compound 15mg
C-2 compound 72mg

[Example 4]
In contrast to Example 2, the polymer binder was changed to the following, and the others were the same as Example 2.
Polymer binder Polymethyl methacrylate (PMMA) 500mg

[Comparative Example 1]
For Example 2, a recording layer consisting of only a C-2 compound (two-photon absorbing dye) was prepared without using a polymer binder.

[Comparative Example 2]
In contrast to Example 2, the polymer binder was changed to the following, and the others were the same as Example 2.
Polymer binder Polybisphenol A carbonate 500mg
(Mig: 29000, manufactured by SIGMA-ALDRICH)

6). Results FIG. 7 summarizes the configuration and recording time of each example and comparative example.

As shown in FIG. 7, in Examples 1 to 4, the glass transition temperature of the polymer binder is lower than the melting point or decomposition point of the dye. In each of Examples 1 to 4, a recording spot could be formed.
FIG. 8 shows a three-dimensional display of the result of measuring the shape of the recording spot recorded in Example 2 by AFM, and FIG. 9 shows an image obtained by observing the recording spot recorded in Example 2 with an optical microscope. As shown in FIG. 8, the recording spot had a convex part at the center and a concave part around it. Further, as shown in FIG. 9, since the recording spot can be clearly confirmed in the observation with the optical microscope, it was confirmed that the optical reading can be performed satisfactorily.
In Example 2, the recording test was performed without the intermediate layer. However, the same recording test was performed after forming the intermediate layer by applying an adhesive on the recording layer. Then, when the intermediate layer was peeled off and observed with an atomic force microscope, the same convex recording spot could be observed. The glass transition temperature of the intermediate layer (adhesive) used at this time is −53 ° C.

  In addition, FIG. 10 shows the relationship between the degree of modulation measured by measuring the height from the upper surface of the recording layer before deformation for a plurality of recording spots. As shown in FIG. 10, it was found that the higher the recording spot height, the greater the modulation degree. In order to ensure a modulation degree of 0.1, the height of the convex shape of the recording spot is preferably 10 nm or more, and in order to ensure 0.2, the height of the convex shape is 25 nm or more. I found it desirable. Note that the recording spot of the optical microscope image in FIG. 9 has the focal position shifted from the top to the bottom, and the variation in the height of the recording spot is also caused by the deviation of the focal position. As can be seen from the image in FIG. 9, the height of the convex portion is higher in the recording spot that is focused on the recording layer, and a larger modulation degree is obtained. Conversely, the recording spot that is out of focus from the recording layer is convex. The height of the part was low, and a small modulation degree was obtained.

  In Examples 1 to 3 using polyvinyl acetate as the polymer binder, when only the two-photon absorption dye (C-2) is used as the dye (Example 2), it takes 90 μsec to form the recording spot. However, when only the one-photon absorbing dye (C-1) was used (Example 1), it took only 15 μsec to form the recording spot. Further, when both the one-photon absorbing dye (C-1) and the two-photon absorbing dye (C-2) were used, a recording spot could be formed in 5 μsec. That is, the recording with the highest sensitivity was possible by using both the one-photon absorbing dye and the two-photon absorbing dye.

  In Example 4, since a polymer binder having a high glass transition temperature was used, it took longer to form a recording spot than in Examples 1 to 3, but recording was possible in a short time of 450 μsec.

  In Comparative Example 1, there was no polymer binder, and recording spots could not be formed under the condition of an absorption rate as small as 1.8%.

  In Comparative Example 2, the glass transition point of the polymer binder was higher than the melting point of the dye, and a recording spot could not be formed with recording light having a peak power of 10 W.

  As described above, according to the optical information recording medium of the example, it was confirmed that recording with high sensitivity was possible. By the way, a report of a research aimed at enabling recording even when the recording layer has a low absorptivity using a one-photon absorption dye that decomposes upon irradiation with laser light (Yuki Suzuki et al., “The static recording and readout of the twenty -recording layers containing organic dye materials ", ISO'09 Technical Digest, P.202 (release number Tu-PP-09)), a recording medium having 20 recording layers is recorded per recording layer. When the light absorption rate is 16% or less and recording is performed with a semiconductor laser of 2.8 mW and 405 nm, the first layer can be recorded with an exposure time of 8 ms to 4000 ms. In the above example, it was confirmed that recording was possible with high sensitivity even when compared with this report.

[Delete Record]
Examples 1 to 3 (medium using polyvinyl acetate as a polymer binder) on which recording spots were recorded were heated in an oven at 80 ° C. for 1 hour. In addition, Example 4 in which the recording spot was recorded (medium using polymethyl methacrylate as a polymer binder) was heated in an oven at 120 ° C. for 1 hour. As a result, the recording spot disappeared in any optical information recording medium. That is, it was confirmed that the recording can be erased.

DESCRIPTION OF SYMBOLS 1 Recording layer 10 Optical information recording medium 11 Substrate 14 Recording layer 15 Intermediate layer 15A 1st intermediate layer 15B 2nd intermediate layer 16 Cover layer 18 Front side interface 19 Back side interface 20 Intermediate interface M Recording spot OB Reading light RB Recording light SB Playback light

Claims (6)

An optical information recording medium comprising a plurality of recording layers,
A first intermediate layer and a second intermediate layer having different refractive indexes are provided between adjacent recording layers, and the first intermediate layer and the second intermediate layer are alternately arranged.
The refractive index n ₀ of the recording layer, the second refractive index n ₂ of the intermediate layer, the difference is 0.01 or less,
The thickness d of the first intermediate layer is set such that the wavelength of the readout light irradiated during reproduction is λ, n ₀ ≈n ₂ = n, and the refractive index of the first intermediate layer is n ₁ .
The filling,
An optical information recording medium, wherein information is recorded by deformation of an interface between the recording layer and the first intermediate layer by irradiation of recording light. The thickness d of the first intermediate layer is:
The optical information recording medium according to claim 1, wherein:   The optical information recording medium according to claim 1, wherein the recording layer includes a polymer binder and a dye dispersed in the polymer binder.   The optical information recording medium according to claim 3, wherein the dye contains a multiphoton absorption compound.   The optical information recording medium according to claim 3 or 4, wherein the recording layer has a thickness of 50 nm or more.   6. The optical information recording medium according to claim 1, wherein the thickness of the second intermediate layer is 5 μm or more.