JP2011048865A - Optical recording medium - Google Patents

Abstract

【Task】
Even if multiple recording layers are laminated, the attenuation of the laser beam used for recording and reproduction can be suppressed, and even though the light absorption of each recording layer is very small, the recording layer can be changed sufficiently to secure the reproduction signal. Provided is a recording layer for a multilayer optical recording medium that can be raised.
[Solution]
In an optical recording medium recorded and reproduced at a wavelength of 600 nm or less, when the recording layer of the optical recording medium has Ar as the absorbance at the recording and reproduction wavelength, and Ai as the maximum absorbance of the absorption band at 700 to 2000 nm An optical recording medium comprising a dye <A> satisfying the relationship of “Ar> 0 and Ai> 0”, and the thickness of the recording layer being 100 nm or less.
[Selection figure] None

Description

  The present invention relates to an optical recording medium that is recorded and reproduced at a wavelength of 600 nm or less, and more particularly to an optical recording medium having three or more recording layers.

  In recent years, optical recording using laser light has been actively developed because it can store and reproduce high-density information recording. Recently, in order to respond to the demand for higher recording density, production of a double-layer recording medium with a short recording wavelength and doubled recording capacity has been studied, and a double-layer digital versatile disk (DVD-R) has been developed. It is popular. At present, the development of multi-layers of about 2 to 6 layers of Blu-ray Disc (BD-R) is being studied. However, in this method, there is a limit to the recording density, and it is considered that the maximum is about 100 GB.

  This is because when recording layers are stacked by a conventional method such as DVD-R or BD-R, an interval of several tens of μm between adjacent recording layers is necessary, and the number of stacked layers is naturally limited. Furthermore, the absorption of the irradiated laser beam energy causes the recording layer at that location to undergo thermal deformation or change such as decomposition, evaporation, dissolution, etc. This is because when recording is performed, due to the absorption of the recording layer, every time the number of recording layers passes, a considerable amount of light energy is lost by the absorption of each layer, and the recording sensitivity and the amount of reflected light may be significantly impaired.

In view of this, it has been studied to adopt an optical change method based on a photon mode reaction in the recording method instead of the thermal deformation and change method (heat mode recording).
That is, a focused laser beam is irradiated to cause a photon mode reaction such as bond photocleavage or photoisomerization. As a result, a change in emission intensity and a change in absorption spectrum (hereinafter referred to as optical change or optically detectable change) in the reaction part (recording part) are read out as information by light such as laser light. is there.

  However, it is known that in the photon mode reaction, when linear absorption wavelength is used, optical recording is performed linearly with respect to the irradiation light intensity, and there is no threshold value for the intensity of the recording irradiation light. It has been. The threshold property means that optical recording is not performed until the irradiation light intensity reaches a certain value or the recording speed is extremely slow, which is a very desirable requirement for optical recording. This is because when the recording part is formed in the photon mode having no threshold value, irradiation with light for reading information with light causes the same optical change as that during recording to be accumulated. This is because as the information is repeatedly read, the contrast of the optical change between the recorded portion and the unrecorded portion decreases, and eventually the information may not be read.

In order to avoid this problem, it has been proposed that non-resonant multi- (two) photon excitation recording can be performed by a pulsed laser having a giga W / cm ² or higher power using a femtosecond laser ( Patent Document 1, Non-Patent Document 1).
However, the wavelength range in which such non-resonant multi- (2) photon absorption can be effectively used for recording is mainly infrared. Therefore, the merit of high density recording cannot be expected with respect to the recording density of the current blue laser. In addition, the development of such a laser having a huge power requires a high-voltage power supply and special noise reduction equipment, and is currently only used for research and pharmaceutical development.

WO2007034616

Applied. Optics, 45, 33, (2006), p8424.

  In order to achieve further higher density in Blu-ray discs and next-generation ultra-high density optical recording media, at least shorter recordings are required to be localized in three dimensions. . This is because, if the recording light is condensed by the objective lens, the distance that can be condensed is determined by the limitation of the working distance of the objective lens, and there is an upper limit on the total film thickness of the multilayer recording layer. In a Blu-ray disc, an objective lens having a numerical aperture of 0.85 is used and light is collected through a cover layer having a predetermined optical path difference, so that the upper limit of the thickness of the recording medium is approximately several hundred μm to 400 μm. .

Therefore, (a) reducing the film thickness per recording layer as much as possible prevents the loss of recording energy associated with the passage of a plurality of recording layers to the minimum and increases the recording sensitivity as much as possible. It is also preferable for the purpose of earning the total number of records.
Further, (b) by making the interval between the recording layers as narrow as possible, it becomes possible to further increase the total number of recording layers, and the total film thickness can be reduced even with the same number of recording layers. By changing to an objective lens having a large numerical aperture, it is possible to achieve a higher recording density.

  However, in order to satisfy the above (a) and (b), it is necessary to increase the dye concentration in the recording layer as compared with the conventional recording medium so as to obtain a sufficient degree of recording modulation. On the other hand, as described above, when the recording layers are stacked in multiple layers, the laser light must pass through the plurality of recording layers to write data, and the reproduction light sufficient to read the data must return. -The transmittance at the reproduction wavelength needs to be sufficiently secured. However, if the amount of the dye used in the recording layer of the conventional recording medium is reduced in order to satisfy this condition, recording / reproduction becomes difficult even with a single layer.

For reference, in the configuration in which the inventors have a recording layer between the intermediate adhesive layer (refractive index n = 1.58) and the substrate, recording is performed using the refractive index n and the extinction coefficient k of the recording layer as parameters. The results of calculating absorption, reflectance, and transmittance with respect to the film thickness of the layer are shown in FIGS. The recording / reproducing wavelength was assumed to be 405 nm.
As shown in FIG. 1, in order to ensure a wide selection of recording dyes and to make the absorbance 8% or less (corresponding to absorption 16.8% or less) which is the preferred range of the present invention, the recording layer thickness is It turns out that it is so preferable that it is small. Further, FIG. 2 shows that it is preferable that the refractive index n of the recording layer is larger than that of the intermediate adhesive layer in order to ensure the reflectance of the recording layer. However, as can be seen from FIG. 3, when the refractive index of the recording layer is excessively high, the amount of transmitted light is reduced due to interference. Therefore, in an optical recording medium suitable for multilayer recording that is recorded and reproduced at a wavelength of 600 nm or less, which is the aim of the present invention, there is a limit to the reflectance that can be secured for securing the transmittance. It is suggested that effective signal amplification during recording and proper reproduction light intensity and noise reduction during reproduction are necessary to compensate for this point and obtain a sufficient degree of recording modulation. The

  The present invention has been made in view of the above circumstances, and the film thickness per recording layer is 100 nm or less, while ensuring the transmittance at the recording / reproducing wavelength of each recording layer, and An object of the present invention is to provide an optical recording medium capable of obtaining a sufficient recording modulation degree.

  As a result of intensive studies on the above problems, the present inventors have determined that the maximum absorbance of the absorption band having 700 to 2000 nm in an optical recording medium recorded and reproduced at a wavelength of 600 nm or less, where the absorbance at the recording and reproduction wavelength is Ar. When Ai is used, the recording layer uses a dye <A> that satisfies the relationship of “Ar> 0 and Ai> 0”, thereby solving the above problems, and further by generating photoacid generator <B> and acid. It has been found that the effect can be increased by using a color change agent <C> that changes in color and tone.

In the present invention, the absorption band means that the absorbance is 0.001 or more in a continuous wavelength region exceeding 40 nm, and usually has a half-value width of 25 nm or more (absorption is an absorption peak). It means an absorption change having a half-value wavelength range).
That is, the gist of the present invention is as follows.

[1]
In an optical recording medium recorded and reproduced at a wavelength of 600 nm or less, when the recording layer of the optical recording medium has Ar as the absorbance at the recording and reproduction wavelength, and Ai as the maximum absorbance of the absorption band at 700 to 2000 nm An optical recording medium comprising a dye <A> satisfying the relationship of “Ar> 0 and Ai> 0”, and the thickness of the recording layer being 100 nm or less.

[2]
The optical recording medium according to [1], wherein the optical recording medium recorded and reproduced at a wavelength of 600 nm or less has a recording layer thickness of 60 nm or less.
[3]
The optical recording medium according to [1] or [2], wherein the dye <A> further satisfies a relationship of “Ar ≦ Ai”.

[4]
Furthermore, the recording layer of the optical recording medium contains a photoacid generator <B>, and the dye <A> is a sensitizing dye of the photoacid generator <B> [1] to [1] The optical recording medium according to any one of [3].
[5]
The light according to any one of [1] to [4], wherein the recording layer of the optical recording medium further contains a color changing agent <C> whose color and color tone are changed by the generation of an acid. recoding media.

[6]
[1] to [5], wherein the transmittance at the recording and reproducing wavelengths per recording layer of the optical recording medium is 80% or more before and after recording, and three or more recording layers are laminated. ] The optical recording medium of any one of.
[7]
The absorbance occupancy of each component <A><B><C> in the recording layer of the optical recording medium at the recording and reproducing wavelength is 50% to 100% of the dye <A> in the pre-recording state, and photoacid generation The optical recording medium according to any one of [1] to [6], wherein the agent <B> is 0 to 30% and the color change agent <C> is 0 to 30%.

  According to the present invention, even when the recording layers are laminated, it is possible to suppress the attenuation of the laser beam used for recording and reproduction, and the recording is sufficient to secure the reproduction signal even though the light absorption for each recording layer is very small. It is possible to provide a recording layer for a multilayer optical recording medium capable of causing a layer change.

In the configuration having the recording layer between the intermediate adhesive layer (n = 1.58) and the substrate, the result of calculating the absorption with respect to the film thickness of the recording layer using the refractive index n and the extinction coefficient k of the recording layer as parameters. Show. The result of calculating the reflectance with respect to the film thickness of the recording layer using the refractive index n and the extinction coefficient k of the recording layer as parameters in the configuration having the recording layer between the intermediate adhesive layer (n = 1.58) and the substrate. Indicates. The result of calculating the transmittance with respect to the film thickness of the recording layer using the refractive index n and the extinction coefficient k of the recording layer as parameters in the configuration having the recording layer between the intermediate adhesive layer (n = 1.58) and the substrate. Indicates. The SEM observation result of the recording part (5T) and the non-recording part of the medium (disc A) of Example 4 is shown. The reproduction | regeneration result of the 20 layer laminated medium of Example 14 is shown.

  Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention does not exceed the gist thereof. These contents are not specified.

[I. Optical recording medium]
The optical recording medium of the present invention has a recording layer suitable as an optical recording medium for recording / reproducing at a wavelength of 600 nm or less, particularly a multilayer optical recording medium having a plurality of recording layers. That is, the recording layer of the optical recording medium of the present invention has a relationship of “Ar> 0 and Ai> 0, where Ar is the absorbance at the recording and reproducing wavelengths and Ai is the maximum absorbance of the absorption band at 700 to 2000 nm. And a film thickness of the recording layer is 100 nm or less.

I-1: Layer Configuration If the optical recording medium of the present invention is combined with the Blu-ray Disc configuration, a substrate or a dummy substrate (having a guide groove is preferable for stable focus and stable recording light irradiation position control. 1) or more layers selected from a reflective layer, a translucent film, and a wavelength selection layer are laminated on the recording layer, and a recording layer directly thereon or via an intervening layer, and further a protective layer and An intermediate adhesive layer is provided. Further, as the outermost layer of the laminated surface, a cover sheet is usually applied thereon as a surface protective layer via a cover layer or an adhesive layer.
When the optical recording medium of the present invention has a multilayer structure, a multilayer structure is formed by repeatedly laminating units of “intervening layer (optional) / recording layer / (protective layer and / or intermediate adhesive layer)”. .

The present invention is very effective in a multilayer structure in which each layer is divided into a protective layer and / or an intermediate adhesive layer.
The present invention also relates to a volume type light comprising a substrate, a reflective layer or a translucent film, or a wavelength selection layer thereon, a recording layer having a thickness of several hundred μm or more, a cover layer or a cover sheet. The present invention can also be applied to a recording medium.

I-2: Recording layer I-2-1: Dye <A>
The recording layer of the optical recording medium of the present invention satisfies the relationship of “Ar> 0 and Ai> 0”, where Ar is the absorbance at the recording and reproducing wavelengths, and Ai is the maximum absorbance of the absorption band at 700 to 2000 nm. Contains dye <A>. The compound having Ar and the compound having Ai are not necessarily the same, and may be a combination of two or more dyes having absorption in the wavelength range. However, based on the mechanism of the effect of the present invention inferred later, it is preferable that the compound having Ar and the compound having Ai are physically close to each other. In this sense, Ai and Ar are included in the same compound. A recording layer containing a dye having a colorant is preferred. Further, the dye <A> preferably satisfies Ar ≦ Ai, more preferably Ar ≦ Ai / 2, and particularly preferably Ar ≦ Ai / 3. In addition, if Ai is excessively large with respect to Ar, the recording layer may be deteriorated due to heat storage, and therefore Ai / 100 ≦ Ar.
Ar must not be 0.

  As long as the above correlation is satisfied, the absolute values of Ar and Ai are not particularly limited, but the multi-layered optical recording medium, which is the object of the present invention, includes the power that can be emitted from the laser used for recording and the time of reproduction. Depending on the noise reduction method, there is a possibility that the allowable range of the value is somewhat widened. However, Ar is preferably 0.001 or more, more preferably 0.003 or more, usually 0.08 or less, preferably 0.05. Hereinafter, it is more preferably 0.02 or less. If Ar is excessively small, it is difficult to cause a sufficient change to be reproduced in the recording layer. Conversely, if Ar is excessively large, recording light and reproducing light cannot be transmitted across a plurality of recording layers. Ai is preferably 0.01 or more, more preferably 0.03 or more, usually 1.5 or less, preferably 1.0 or less. If Ai is too small, light-to-heat conversion cannot be performed efficiently and recording cannot be performed. Conversely, if Ai is too large, the recording layer may be deteriorated due to heat storage. In the present invention, the absorption Ar at the recording light wavelength is merely the absorption edge of linear absorption. In that respect, it is different from the two-photon absorption which is said in the volume type optical recording medium.

  The light source used for recording and reproduction may be the same or different, but the same is preferable because the drive can be made compact and the cost can be reduced. The wavelength is not particularly limited as long as it is shorter than 600 nm, but a blue-violet to red wavelength (about 350 nm to 600 nm) is often used. For high-density recording, it is preferable to use a wavelength region of 350 nm to 530 nm, particularly 350 nm to 450 nm. . Details of the light source used for recording and reproduction will be described in detail in the section of the recording method.

The dye <A> used in the recording layer of the present invention has an absorption band in at least a part of the 700 to 2000 nm region that is out of the wavelength used for recording and reproduction, and preferably the maximum absorbance in that region is used for recording and reproduction. It is greater than the absorbance at the wavelength.
In a state where a plurality of recording layers are laminated, if it is attempted to sufficiently secure light used for recording and reproduction to the inner layer, it is necessary to increase the transmittance per recording layer as the number of layers increases. If the film thickness of the recording layer is simply reduced or the content ratio of the dye is lowered, the photothermal conversion efficiency deteriorates and the film changes before and after recording, or even if it changes, the film is too thin. In other words, the signal may not be recognized as a signal that can be read sufficiently. However, in the optical recording medium of the present invention, by using the dye <A> in the recording layer, light can be efficiently converted into heat even when light absorption during recording and reproduction is extremely small, and a sufficient film can be obtained. Change, that is, a sufficient degree of modulation can be obtained. The recording layer of the optical recording medium of the present invention is not necessarily clear about the mechanism that can efficiently convert light into heat, but even if it absorbs a small amount of light energy, it can be efficiently converted into heat energy without waste. Think.

The present inventors consider that there are at least, for example, the following three mechanisms that can efficiently convert recording light into heat.
(1) Since there is absorption in the near-infrared region, the heat generated by the absorption by recording, that is, the infrared ray is absorbed, so that the diffusion of heat may be suppressed.
(2) Further, various vibrations are excited from near-infrared excitation, and there is a possibility that the excited state may shift to a reaction that cannot be exceeded due to an energy barrier with recording light energy.
(3) Further, in the case where the dye <A> has a tendency to be decomposed by near-infrared excitation, the recording light energy of less than 600 nm shifts to the near-infrared excitation level without energy loss due to intramolecular conversion. In some cases, there is a possibility of causing a decomposition reaction that is difficult to occur with recording light.

In particular, it is presumed that the mechanism of (3) is further added to the possibilities of (1) and (2) in the system in which the effect of the present invention is expressed by the dye <A> alone.
The dye <A> may satisfy the relationship of “Ar> 0 and Ai> 0, where Ar is the absorbance at the recording and reproducing wavelength and Ai is the maximum absorbance of the absorption band at 700 to 2000 nm. Although not limited at all, for example, macrocyclic compounds having absorption in the visible to near infrared region such as phthalocyanine and naphthalocyanine, polymethine dyes such as cyanine dyes, anthraquinone dyes, azulene dyes, and organic metals such as dithiol nickel complexes And compound dyes.

Note that the dye <A> is more effective in increasing detection sensitivity when it is a dye that emits light in the vicinity of the reproduction light wavelength.
Further, the dye <A> is used together with the photoacid generator <B> and the dye <C> whose color or color tone is changed by the generation of acid, and has an effect as a sensitizing dye of the photoacid generator <B>. Therefore, the film change before and after recording can be remarkably improved, which is preferable when pursuing multilayering.
In sensitizing the photoacid generator <B>, a cyanine dye is particularly effective.

I-2-2: Photoacid generator <B>
The photoacid generator <B> used in the recording layer of the optical recording medium of the present invention is not particularly limited as long as it is a compound that generates an acid directly or via a sensitizer upon receiving laser light during recording, For example, halogen-containing compounds such as halogen-substituted alkanes and halomethylated s-triazine derivatives, onium salts, and sulfone compounds are preferred.
Here, among the halogen-containing compounds, examples of the halogen-substituted alkane include dichloromethane, trichloromethane, 1,2-dichloroethane, 1,2-dibromoethane, and the like.

  Among the halogen-containing compounds, examples of the halomethylated s-triazine derivative include 2,4,6-tris (monochloromethyl) -s-triazine, 2,4,6-tris (dichloromethyl) -s-triazine, 2,4,6-tris (trichloromethyl) -s-triazine, 2-methyl-4,6-bis (trichloromethyl) -s-triazine, 2-n-propyl-4,6-bis (trichloromethyl)- s-triazine, 2- (α, α, β-trichloroethyl) -4,6-bis (trichloromethyl) -s-triazine, 2-phenyl-4,6-bis (trichloromethyl) -s-triazine, 2 -(P-methoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (3,4-epoxyphenyl) -4,6-bis (trichloromethyl) -S-triazine, 2- (p-chlorophenyl) -4,6-bis (trichloromethyl) -s-triazine, 2- [1- (p-methoxyphenyl) -2,4-butadienyl] -4,6- Bis (trichloromethyl) -s-triazine, 2-styryl-4,6-bis (trichloromethyl) -s-triazine, 2- (p-methoxystyryl) -4,6-bis (trichloromethyl) -s-triazine 2- (p-methoxy-m-hydroxystyryl) -4,6-bis (trichloromethyl) -s-triazine, 2- (pi-propyloxystyryl) -4,6-bis (trichloromethyl)- s-triazine, 2- (p-tolyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (p-methoxynaphthyl) -4,6-bis (trichloromethyl) ) -S-triazine, 2- (p-ethoxynaphthyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (p-ethoxycarbonylnaphthyl) -4,6-bis (trichloromethyl) -s -Triazine, 2-phenylthio-4,6-bis (trichloromethyl) -s-triazine, 2-benzylthio-4,6-bis (trichloromethyl) -s-triazine, 2,4,6-tris (dibromomethyl) -S-triazine, 2,4,6-tris (tribromomethyl) -s-triazine, 2-methyl-4,6-bis (tribromomethyl) -s-triazine, 2-methoxy-4,6-bis (Tribromomethyl) -s-triazine and the like. Among them, bis (trihalomethyl) -s-triazine which may have a substituent is preferable, and bis (trichloromethyl) -s-triazine which may have a substituent is particularly preferable. Methyl-4,6-bis (trichloromethyl) -s-triazine, 2-phenyl-4,6-bis (trichloromethyl) -s-triazine, 2- (p-methoxyphenyl) -4,6-bis (trichloro) Methyl) -s-triazine, 2- (3,4-epoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine, 2- [1- (p-methoxyphenyl) -2,4-butadienyl] -4,6-bis (trichloromethyl) -s-triazine, 2- (p-methoxystyryl) -4,6-bis (trichloromethyl) -s-triazine, 2- (p-methoxy-m Hydroxy) -4,6-bis (trichloromethyl) -s-triazine, 2- (p-i- propyloxy) -4,6-bis (trichloromethyl) -s-triazine.

  Examples of the onium salts include ammonium salts such as tetramethylammonium bromide and tetraethylammonium bromide, diphenyliodonium hexafluoroarsenate, diphenyliodonium tetrafluoroborate, diphenyliodonium p-toluenesulfonate, diphenyliodonium camphorsulfonate, dicyclohexyliodonium hexahydrate. Iodonium salts such as fluoroarsenate, dicyclohexyliodonium tetrafluoroborate, dicyclohexyliodonium p-toluenesulfonate, dicyclohexyliodonium camphorsulfonate, triphenylsulfonium hexafluoroarsenate, triphenylsulfonium tetrafluoroborate, triphenylsulfone Um p- toluenesulfonate, triphenylsulfonium camphorsulfonate, tri-cyclohexyl hexafluoroarsenate, tri-cyclohexyl sulfonium tetrafluoroborate, tri-cyclohexyl sulfonium p- toluenesulfonate, sulfonium salts such as tri-cyclohexyl sulfonium camphorsulfonate, and the like.

  Examples of the sulfone compounds include bis (phenylsulfonyl) methane, bis (p-hydroxyphenylsulfonyl) methane, bis (p-methoxyphenylsulfonyl) methane, bis (α-naphthylsulfonyl) methane, and bis (β- Bis (sulfonyl) methane compounds such as naphthylsulfonyl) methane, bis (cyclohexylsulfonyl) methane, bis (t-butylsulfonyl) methane, phenylsulfonyl (cyclohexylsulfonyl) methane, phenylcarbonyl (phenylsulfonyl) methane, naphthylcarbonyl (phenylsulfonyl) ) Methane, phenylcarbonyl (naphthylsulfonyl) methane, cyclohexylcarbonyl (phenylsulfonyl) methane, t-butylcarbonyl (phenylsulfonyl) methane, phenylcal Carbonyl (sulfonyl) methane compounds such as bonyl (cyclohexylsulfonyl) methane, phenylcarbonyl (t-butylcarbonyl) methane, bis (phenylsulfonyl) diazomethane, bis (p-hydroxyphenylsulfonyl) diazomethane, bis (p-methoxyphenylsulfonyl) Diazomethane, bis (α-naphthylsulfonyl) diazomethane, bis (β-naphthylsulfonyl) diazomethane, bis (cyclohexylsulfonyl) diazomethane, bis (t-butylsulfonyl) diazomethane, phenylsulfonyl (cyclohexylsulfonyl) diazomethane, bis (sulfonyl) diazomethane compounds , Phenylcarbonyl (phenylsulfonyl) diazomethane, naphthylcarbonyl (phenylsulfonyl) diazomethane, phenyl Carbonyl (sulfonyl) diazomethane compounds such as carbonyl (naphthylsulfonyl) diazomethane, cyclohexylcarbonyl (phenylsulfonyl) diazomethane, t-butylcarbonyl (phenylsulfonyl) diazomethane, phenylcarbonyl (cyclohexylsulfonyl) diazomethane, phenylcarbonyl (t-butylcarbonyl) diazomethane Etc.

  The photoacid generator <B> may absorb light at the wavelength of light used for recording and reproduction, but at least as a multilayer optical recording medium for which the absorption per recording layer should be minimized, a photoacid generator Rather than lowering the transmittance of the recording layer by absorbing the generator, if the transmittance of the recording layer is lowered by the same amount, the photoacid generator can be sensitized and transmitted by absorbing the dye <A> If the rate is lowered, a larger change in the recording layer can be expected as a result of the photoreaction.

Similarly, from the viewpoint of suppressing the absorption per recording layer as much as possible and ensuring light transmittance in multiple layers, the acid generator <B> decomposes after recording, or changes in absorption with respect to recording / reproducing light. It is preferable that it does not occur.
Furthermore, in the present invention, since the absorption of the photoacid generator <B> is directly excited by recording / reproducing light, the absorption maximum of the photoacid generator <B> is shorter than the wavelength of the recording light. Are preferred. By selecting such a photoacid generator <B>, it is possible to cause nonlinearity in acid generation despite recording at the linear absorption edge.

I-2-3: Discoloring agent <C>
The color change agent <C> used in the recording layer of the optical recording medium of the present invention is not particularly limited as long as the color and tone change before and after generation of acid or free radicals by the photoacid generator <B>. Here, “the color or the color tone changes” includes both a change from colorless to colored color tone and a change from colored to colorless or different colored color tone. Preferred color changing agents are those which form a salt with an acid to change the color tone.

  For example, as examples of the color changing agent that changes from colored to colorless or different colored tones, Victoria Pure Blue BOH [made by Hodogaya Chemical Co., Ltd.], Oil Blue # 603 [made by Orient Chemical Industry Co., Ltd.], Patent Pure Blue [Sumitomo Sangoku] Manufactured by Chemical Co., Ltd.], crystal violet, brilliant green, ethyl violet, methyl violet, methyl green, erythrosin B, basic fuchsin, malachite green, oil red, m-cresol purple, rhodamine B, auramin, 4-p-diethylaminophenyliminonaphthoquinone Triphenylmethane, diphenylmethane, oxazine, xanthene, iminonaphthoquinone, azomethine, or anthracite represented by cyano-p-diethylaminophenylacetanilide Down system of dye and the like.

  On the other hand, examples of the color changing agent that changes from colorless to colored include leuco dyes and, for example, triphenylamine, diphenylamine, o-chloroaniline, 1,2,3-triphenylguanidine, naphthylamine, diaminodiphenylmethane, p, p'-bis. -Dimethylaminodiphenylamine, 1,2-dianilinoethylene, p, p ', p "-tris-dimethylaminotriphenylmethane, p, p'-bis-dimethylaminodiphenylmethylimine, p, p', p"- Primary or secondary represented by triamino-o-methyltriphenylmethane, p, p-bis-dimethylaminodiphenyl-4-anilinonaphthylmethane, p, p ′, p ″ -triaminotriphenylmethane Examples include arylamine dyes.

For example, in an optical recording medium, the solubility in a specific organic solvent considered to be capable of forming a high-quality recording layer and the wavelength range in which color change occurs tend to be preferable in the present invention, and therefore triphenyl is particularly preferable. Methane and diphenylmethane dyes are effectively used, and triphenylmethane dyes are more preferable.
The color change agent <C> of the present invention may absorb light at the wavelength of light used for recording or reproduction in either state before or after recording, but it is preferably as small as possible and more preferably not. However, in the vicinity of the wavelength of light used for recording and reproduction, it is preferable that the fluctuation in absorption is as large as possible before and after recording. Accordingly, it is possible to ensure a remarkable change in the refractive index before and after recording while minimizing the shielding of recording and reproduction light.

I-2-4: <A><B><C> blending ratio <A><B><C> is 1 to 100% by weight, preferably 3 to 90% by weight, based on the total of <C><B> is 0 to 90% by weight, preferably 10 to 80% by weight, and <C> is 0 to 80% by weight, preferably 5 to 50% by weight. If <A> is too small, recording in multiple layers becomes difficult. Also, if the amount of <B> or <C> is excessively large, the recording layer becomes too thick, the reflectance deteriorates, sufficient solubility cannot be ensured, and problems such as precipitation appear in the recording layer may occur. There is sex.

I-2-5: <A><B><C> Absorbance Occupancy at Recording and Reproduction Wavelength of Each Component Absorbance Occupancy at each recording and reproduction wavelength of the recording layer of the present invention is recorded In the previous state, the dye <A> is preferably 50 to 100%, the photoacid generator <B> is preferably 0 to 30%, and the color changing agent <C> is preferably 0 to 30%, particularly preferably the dye <A A> is 80 to 100%, photoacid generator <B> is 0 to 20%, and color changing agent <C> is 0 to 20% before recording. If the occupation ratio of the absorbance of the dye <A> is excessively small, it is difficult to ensure a sufficient film change before and after recording while suppressing the transmittance.

Here, the absorbance occupancy is the sum of absorbances derived from <A>, <B>, and <C> 3 components from absorbances of <A>, <B>, and <C> in the recording layer. Say percentage.
I-2-6: Other components The change in the film before and after recording of the recording layer in the present invention refers to the change in the temperature of the recording layer due to the photothermal conversion of the dye <A> described above. Decomposition and vaporization, and promotion of various chemical reactions including changes in refractive index due to changes in the color and tone of the color change agent <C> caused by the acid generated by the photoacid generator <B>, and As a result of combining them, remarkable modulation can be obtained in spite of maintaining a high transmittance. Therefore, in addition to the dye <A>, photoacid generator <B>, and color change agent <C>, the recording layer of the present invention causes some chemical, physical, or optical change due to heat or acid. It is also effective to add components that can be used. The amount used in the case where a component capable of causing some chemical, physical, or optical change with heat or acid is used, with respect to the total amount of the recording layer materials <A> to <C>. Usually 1 to 500% by weight, preferably 5 to 200% by weight.

In addition to the above components, the recording layer of the present invention may contain a dye as a quencher for improving the temporal stability (temperature, humidity, light stability) of the dye <A>.
As the quencher, a singlet oxygen quencher is generally used. The amount used when an anti-fading agent such as a singlet quencher is used is usually 0.1 to 50% by weight, preferably 1 to 30% by weight, based on the recording layer material. More preferably, it is 5 to 25% by weight.

In addition, various components can be added as required to improve film formability such as suppression of crystallization of the dye component and other needs within the range not impairing the effects of the present invention. For example, a binder (binder) made of a low-polymer material, a polysynthetic monomer, a thermal crosslinking agent, a polymerization inhibitor, an antioxidant, a surfactant, a refractive index control agent, a dielectric, and the like can be given.
Examples of the binder include organic polymers such as cellulose derivatives, natural polymer substances, hydrocarbon resins, vinyl resins, acrylic resins, polyvinyl alcohol, epoxy resins, polyvinyl pyrrolidone, and melamine resins. Examples of the thermoplastic resin include polyethylene, polyvinyl chloride, polystyrene, polypropylene, polymethyl methacrylate, and polycarbonate. More specifically, polystyrene, polyethylene, polyvinyl chloride, polyester, polyamide, fluororesin, polybutadiene, polyisoprene, hydrogenated polybutadiene, ethylene / propylene copolymer rubber, polyvinyl chloride, polyether, polyester, fluororubber, natural Common materials such as a thermoplastic elastomer having thermal expansion properties such as rubber and amorphous polyethylene can be used.

When using additives such as a binder, the amount used is usually 5 to 500% by weight, preferably 10 to 200% by weight, based on the total amount of the recording layer materials <A> to <C>.
Note that the addition of a binder (binder) or a thermal cross-linking agent has a favorable effect when laminated in multiple layers. For example, preferable effects such as infiltration of the recording layer into the adhesive layer, maintenance of the interface, and storage stability can be seen.

I-2-7: Formation of recording layer The recording layer of the optical recording medium of the present invention is prepared by dissolving the recording layer components in an appropriate solvent to prepare a recording layer coating solution. A reflective layer is formed and then formed by coating and drying.
Examples of the coating method include a spray method, a spin coat method, a dip method, a roll coat method, a blade coat method, a doctor blade method, and an ink jet method. In particular, in a recording medium on a disk, the spin coat method is a film. It is preferable because the thickness uniformity can be ensured and the defect density can be reduced. Moreover, it is also preferable that the pigment is dispersed in a thin sheet or coated on another sheet by the above method and produced together with the adhesive layer.

When the optical recording medium of the present invention has a multilayer structure, a multilayer structure is formed by repeatedly laminating units composed of “intervening layer (optional) / recording layer / (protective layer and / or adhesive layer)”.
The solid content concentration of the recording layer coating liquid is usually in the range of 0.01 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, more preferably 0.1 wt% to 4 wt%. Weight%. The film thickness of the recording layer is controlled by adjusting the solid content concentration and application conditions, for example, by adjusting the rotational speed in the case of the spin coating method. In addition, this solid content density | concentration shall be the range which can implement | achieve the following film thickness ranges.

  The film thickness per recording layer is preferably as thin as possible as long as the recording signal amplitude and interlayer crosstalk can be sufficiently suppressed so as not to hinder reproduction. The recording layer of the optical recording medium of the present invention is usually 100 nm or less, preferably 60 nm or less, more preferably 40 nm or less, and particularly preferably 20 nm or less. Moreover, it is 1 nm or more normally, Preferably it is 2 nm or less. When exceeding this range, it may be difficult to form a low-absorption recording layer suitable for constituting the multilayer of the present invention.

However, this film thickness range depends on the number of recording layers, the power range in which a recording / reproducing laser can be emitted, and the noise reduction processing capability. The refractive index and the optical constant of the recording layer are combined to determine an appropriate range.
The film thickness of the recording layer is evaluated by a method of measuring the step between the recording layer coating surface and the substrate exposed surface, a method of measuring the absorption spectrum of the coating film, and evaluating from the correlation between the absorption intensity and the film thickness, etc. It is possible. In the case of multi-layer laminated media, after cutting the medium (disk), the cross section is taken out by ion etching or the like, and the cross section is observed by SEM, the disk small piece is embedded in resin, and the thin piece is cut out in the cross section direction. A method of TEM observation is also effective.

The applied recording layer is usually dried and annealed by a drying method using an IR oven, a convection oven or the like. Moreover, you may combine the reduced pressure drying method of drying in a decompression chamber, without raising temperature.
The conditions for drying and annealing can be appropriately selected according to the type of solvent component, the performance of the dryer used, and the like. The drying time is usually selected in the range of 10 minutes to 2 hours at a temperature of 40 ° C. to 130 ° C., preferably 60 ° C. to 110 ° C., depending on the type of solvent component and the performance of the dryer used. The temperature is selected in the range of 15 minutes to 1 hour.

  Examples of the solvent for the recording layer coating solution include alcohols such as ethanol, n-propanol, isopropanol, n-butanol and diacetone alcohol; fluorinated hydrocarbon solvents such as tetrafluoropropanol (TFP) and octafluoropentanol (OFP). Glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and propylene glycol monomethyl ether; esters such as butyl acetate, ethyl lactate and cellosolve acetate; chlorinated hydrocarbons such as dichloromethane and chloroform; hydrocarbons such as dimethylcyclohexane Ethers such as tetrahydrofuran, ethyl ether and dioxane; ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; These solvents can be appropriately selected in consideration of the solubility of the main component dye material to be dissolved and the boiling point suitable for the coating method, and a mixture of two or more can be used. Further, when an organic material is used as the substrate material on which the recording layer is applied, the smaller the amount of toluene, cyclohexane, or chloroform, the more preferable it is because the problem of distorting the substrate surface can be avoided.

I-3: Substrate When a dummy substrate is used, a substrate in which a focus or tracking position control layer such as a guide groove or a pit is laminated thereon is required. In addition, although a conventionally well-known material can be used suitably for the material of a dummy board | substrate, it is desirable to provide shape stability so that an information recording medium may have a certain amount of rigidity. That is, it is preferable that the mechanical stability is high and the rigidity is large.

  Examples of such materials include acrylic resins, methacrylic resins, polycarbonate resins, polyolefin resins (particularly amorphous polyolefins), polyester resins, polystyrene resins, epoxy resins, and the like, glass, metals, and the like. be able to. Any of these materials may be used alone, or two or more of these materials may be used in any combination and ratio. Among these, polycarbonate resin is preferable as the substrate material from the viewpoints of high productivity such as moldability, cost, low hygroscopicity, and shape stability.

The thickness of the substrate is preferably in the range of usually 0.1 mm or more and usually 1.2 mm or less.
The substrate is provided with a guide groove for tracking (hereinafter also referred to as a groove or a groove) or irregularities representing information such as an address signal, etc., so that compatibility with DVD-R and Blu-ray discs can be obtained. It is preferable that However, in the multi-layer structure, each recording layer does not necessarily require a groove.

In order to ensure the high recording density of the present invention, the groove track pitch is 100 nm to 500 nm, more preferably 100 nm to 400 nm.
The depth of the groove is preferably 20 nm to 60 nm.
The groove width is preferably 50 nm to 250 nm, preferably 0.3 to 0.8 times the track pitch, and more preferably 0.4 to 0.6 times. However, the narrower the groove width, the greater the difficulty of molding.

I-4: Reflective layer, translucent film, wavelength selective layer Providing any of the reflective layer, translucent film, wavelength selective layer on the substrate is a viewpoint of ensuring compatibility with the current BD Therefore, it is preferable. When this layer is a reflective layer, servo information such as grooves and address pits is provided.
The wavelength selective layer is often laminated on the surface of the reflective layer opposite to the substrate.

Below, a reflection layer, a semi-transparent film | membrane, and a wavelength selection layer are demonstrated concretely.
(Reflective layer):
A commonly used sputter layer. The reflective layer is required to have a certain reflectance or more with respect to the laser beam used for recording and reproduction, and a conventionally known material can be appropriately used. As a material of the reflective layer, it is preferable to use an alloy mainly composed of Ag or Al having a high reflectance and a high thermal conductivity.

  The material of the reflective layer suitable for the present invention will be described more specifically. Pure Ag, or Ag, Ti, V, Ta, Nb, W, Co, Cr, Si, Ge, Sn, Sc, Hf, Pd, Rh And an Ag alloy containing at least one element selected from the group consisting of Au, Pt, Mg, Zr, Mo, Cu, Nd, Bi, and Mn. When importance is attached to stability over time, it is preferable to use one or more of Ti, Mg, Au, Cu, Nd, Bi, or Pd as an additive component.

  As another preferable example of the material of the reflective layer, Al is at least one selected from the group consisting of Ta, Ti, Co, Cr, Si, Sc, Hf, Pd, Pt, Mg, Zr, Mo, and Mn. An Al alloy containing a seed element can be given. These can be used in consideration of durability, reflectance, volume resistivity, film formation speed, and the like. It is preferable to specify a preferable range of the film thickness from 1 nm to 100 nm in combination with a desired reflectance, the wavelength of incident light, the number of stacked layers, and the like.

(Translucent film, wavelength selective layer):
Translucent films and wavelength selective layers are not necessarily required for the purposes of the present invention. However, the semi-transparent film and the wavelength selection layer are effective layers for identifying each layer more stably when recording / reproducing each layer constituting the multilayer, or for reflecting the servo light more efficiently. As an alternative, it can be provided in place of the reflective layer or for selecting only the servo light for reproduction.

As the translucent film, a composition that can be used for the reflective layer and the protective layer described below can be used. The optimum composition of the translucent film is determined by the type of elements to be mixed and the mixing ratio so that desired reflectance and transmittance can be ensured.
As the wavelength selection layer, a dielectric multilayer film, a dye film having a very high reflectance of the wavelength of recording light, or the like is used.

In addition, between the reflective layer, the semitransparent film, the wavelength selection layer, and the recording layer described above, the following II-2-5. A protective layer such as a dielectric thin film, which is the same as the protective layer provided between the recording layer and the recording layer or between the recording layer and the cover layer, may be provided. This protective layer also includes what is generally known as a barrier layer.
It is preferable to specify a preferable range of the film thickness from 1 nm to 100 nm in combination with a desired reflectance, a wavelength of incident light, a recording layer, the number of stacked layers, and the like.
I-5: Intervening Layer Although an intervening layer is not necessarily required for the purpose of the present invention, it is effective to provide an intervening layer between the recording layer and the recording layer on the back side when viewed from the incident side. . The intervening layer may have a function of an adhesive layer (intermediate adhesive layer) for multilayer lamination. In addition to having optical transparency with respect to the laser beam used for recording and reproduction, grooves and pits may be formed by unevenness.

Examples of the material for the intervening layer include resin materials such as thermoplastic resins, thermosetting resins, electron beam curable resins, and ultraviolet curable resins (including delayed curable resins). Any of these materials may be used alone, or two or more of these materials may be used in any combination and ratio. Moreover, the layer etc. which mixed the pigment | dye with said resin material may be sufficient.
This intervening layer is provided mainly for the purpose of securing the reflected light amount (return light amount) of each recording layer. Therefore, the refractive index of this layer is preferably as high as possible, but the refractive index difference from the refractive index of the recording layer preferably does not exceed 0.4. An excessively large refractive index difference between the intervening layer and the recording layer is not preferable because return light from the recording layer and the intervening layer interferes and it is difficult to detect a good recording signal intensity (amplitude).

The thickness of the intervening layer is preferably 5 μm to 10 μm or more, and is usually 100 μm or less, preferably 70 μm or less. In particular, in the case of functioning as an adhesive layer, for the purpose of the present invention, since the thinner one is preferable, it is preferably several tens of μm or less.
I-6: Protective layer, barrier layer The protective layer or barrier layer is provided at the interface between the recording layer and the cover layer, the interface between the recording layer and the recording layer, etc., and prevents mutual diffusion and adjustment of optical characteristics. Etc.

The film thickness of the protective layer or barrier layer is usually 1 nm or more, preferably 3 nm or more, and usually 50 nm or less, preferably 15 nm or less.
For example, oxides such as Sc, Y, Ce, La, Ti, Zr, Hf, V, Nb, Ta, Zn, Al, Cr, In, Si, Ge, Sn, Sb, and Te; Ti, Zr, Hf , V, Nb, Ta, Cr, Mo, W, Zn, B, Al, Ga, In, Si, Ge, Sn, Sb, Pb, and other nitrides; Ti, Zr, Hf, V, Nb, Ta, And carbides such as Cr, Mo, W, Zn, B, Al, Ga, In, and Si. Furthermore, a mixture of these oxides, nitrides and carbides can be mentioned. As dielectric materials, sulfides such as Zn, Y, Cd, Ga, In, Si, Ge, Sn, Pb, Sb and Bi, selenides or tellurides, fluorides such as Mg and Ca, or Mention may be made of these mixtures. The composition of this layer is preferably a composition that absorbs recording light and reproducing light close to 100%.

Further, the optimum composition of this layer can be selected according to the chemical characteristics of the components of the recording layer and the layer laminated thereon.
When this protective layer or barrier layer is provided at the interface between the recording layer and the recording layer, that is, when this protective layer or barrier layer is provided between the recording layer and the adhesive layer when viewed from the incident side, The effect of ensuring the reflected light amount (return light amount) of each recording layer can be expected. In that case, when the refractive index difference between the protective layer or the barrier layer and the recording layer exceeds 0.4, the return light from this layer and the recording layer interferes, and the transmitted light to the inner recording layer There is a possibility that it cannot be secured. Further, it is not preferable because good recording signal intensity (amplitude) tends to be difficult to detect.

I-7: Surface protective layer (cover layer, cover sheet), adhesive layer (cover sheet adhesive layer, intermediate adhesive layer for multilayer lamination)
The surface protective layer is provided for the purpose of protecting the disk from contamination, scratches, impact, moisture, and the like and for the purpose of adjusting the concentration of recording light and reproduction light. Accordingly, it is preferable that the recording light and the reproduction light have less absorption. Further, a material having a reasonably low moisture absorption rate and moisture permeability is preferable. Any of these materials may be used alone, or two or more of these materials may be used in any combination and ratio.

The thickness is preferably 0.01 mm to 0.2 mm, 0.05 mm to 0.1 mm.
The surface protective layer is provided as a cover layer formed by spin-coating an ultraviolet curable resin, a thermosetting resin, or the like, or as a cover sheet with an adhesive layer adhered to a disk surface including a recording layer. It is possible. The plastic used as the sheet material is polycarbonate, polyolefin, acrylic, cellulose triacetate, polyethylene terephthalate, or the like.

For the adhesion of the cover sheet, light, radiation curing, thermosetting resin, or pressure sensitive adhesive is used.
As the pressure-sensitive adhesive, pressure sensitive adhesives made of acrylic, methacrylate, rubber, silicon, and urethane polymers can be used.
For example, after the photocurable resin constituting the adhesive layer is dissolved in an appropriate solvent to prepare a coating solution, this coating solution is applied onto the recording layer or the interface layer (protective layer, barrier layer, intervening layer, etc.). Then, a coating film is formed, and a polycarbonate sheet is overlaid on the coating film.

Thereafter, the coating liquid is further stretched and developed by rotating the medium in a superposed state as necessary, and then cured by irradiating ultraviolet rays with a UV lamp. Alternatively, a pressure-sensitive adhesive is applied in advance to the sheet, the sheet is overlaid on the recording layer or the interface layer, and then pressed and pressed with an appropriate pressure.
The pressure-sensitive adhesive is preferably an acrylic or methacrylate polymer pressure-sensitive adhesive from the viewpoint of transparency and durability.

  More specifically, 2-ethylhexyl acrylate, n-butyl acrylate, iso-octyl acrylate and the like are used as main component monomers, and these main component monomers are used as acrylic acid, methacrylic acid, acrylamide derivatives, maleic acid, hydroxyl ethyl acrylate, A polar monomer such as glycidyl acrylate is copolymerized. As the solvent for the acrylic polymer, ethyl acetate, butyl acetate, toluene, methyl ethyl ketone, cyclohexane and the like are used. The pressure-sensitive adhesive preferably further contains a polyisocyanate-based crosslinking agent.

  The pressure-sensitive adhesive is made of the above-mentioned material. A predetermined amount is uniformly applied to the surface of the cover layer sheet material in contact with the recording layer side, and the solvent is dried. If it has, it is cured by applying pressure to the surface) with a laminating roller. When the cover layer sheet material coated with the pressure-sensitive adhesive is bonded to the surface of the optical recording medium on which the recording layer is formed, it is preferably bonded in a vacuum so as not to entrain air and form bubbles.

Also, after applying the above-mentioned pressure-sensitive adhesive on the release film and drying the solvent, the cover layer sheet is bonded together, and the release film is peeled off to integrate the cover layer sheet and the pressure-sensitive adhesive layer, and then optical recording. You may paste together with a medium.
When the optical recording medium of the present invention has an intermediate adhesive layer for multilayer lamination, the same material and method as those for the cover sheet adhesive layer described above can be used as the intermediate adhesive layer. In this case, the thickness of the intermediate adhesive layer is preferably several tens of μm or less because, in the object of the present invention, the thinner one is preferable in order to obtain the number of layers. Further, the lower limit of the film thickness of the intermediate adhesive layer is usually several μm or more. If this intermediate adhesive layer is too thin, the crosstalk between the recording layers may increase and the quality of the reproduced signal may be reduced.

  The optical recording medium of the present invention has a total film thickness of 100 μm or more excluding the reflective layer, the wavelength selection layer, and the semitransparent film in order to ensure a preferable capability as a recording capacity. Preferably there is. Furthermore, it is preferably 400 μm or less so as not to exceed the depth of focus of the laser head (recording / reproducing laser pickup). If the total thickness of the recording layer and other layers, excluding the reflective layer, wavelength selection layer and translucent film of the optical recording medium, is excessively thick, there is a risk that a sufficient amount of return light cannot be secured for reproduction. .

[Performance of optical recording medium of the present invention]
<Transmissivity>
The transmittance of the recording layer of the optical recording medium of the present invention is naturally limited by the number of recording layers to be laminated and the intensity of light used for recording and reproduction, but the transmittance of recording and reproducing wavelengths per recording layer. Is preferably over 80%, more preferably 95% or more, and particularly preferably 97% or more. Here, the transmittance refers to the rate at which the recording / reproducing wavelength light incident on the recording layer (one layer) passes through the recording layer, and can be obtained by measuring the recording layer with a spectrophotometer. In the case of a multilayer laminated medium, after estimating the film thickness of each layer by a method such as cross-sectional observation by SEM or TEM, measuring the amount of transmitted light in a multilayer state excluding the reflective layer, etc. It is possible to determine the transmittance.

<Absorbance>
The optical recording medium of the present invention has an absorbance (OD value) at the recording wavelength and / or reproduction wavelength with respect to the total film thickness of the recording layer and other layers, excluding the reflective layer, wavelength selection layer, and translucent film. The sum is preferably 0.7 or less. When the sum of the OD values at the recording wavelength and / or reproducing wavelength of the total thickness of the recording layer and other layers excluding the reflective layer, wavelength selection layer and translucent film of the optical recording medium is excessively large, reproduction is performed. Therefore, there is a risk that a sufficient amount of return light cannot be secured.

Further, when the product of the extinction coefficient k at the recording / reproducing light wavelength of each recording layer and the film thickness of each recording layer is less than 5 × 10 ⁻³ μm, the absorption of each recording layer is less than 10% or less. Therefore, it is preferable. More preferably, it is 3 × 10 ⁻³ μm or less, further preferably 2 × 10 ⁻³ μm or less, and especially 6 to 7 × 10 ⁻⁴ μm or less. If it exceeds these ranges, the amount of recording / reproducing light absorbed every time it passes through the recording layer increases, and there is a possibility that recording / reproducing of the recording layer from the incident side to the back cannot be performed satisfactorily. In particular, when the product of the extinction coefficient k at the recording / reproducing light wavelength of each recording layer and the film thickness of each recording layer is 2 × 10 ⁻³ μm or less, the absorption of each recording layer is 5% or less, Even in a multilayer recording layer of 10 layers or more, it is easy to secure an appropriate amount of light in all layers.

Here, the absorbance (OD value) is generally called an optical density and is defined by the following mathematical formula.
OD (optical density) = − log ₁₀ (I / I ₀ )
= -Αd / log _e (10)
= − (4πkd / λ) / log (10); λ = wavelength of light In the above equation, d is the film thickness, I is the transmitted light amount, I ₀ is the incident light amount, and k is the extinction coefficient (imaginary part of the complex refractive index). , Α represents an absorption coefficient.

  In the present invention, Ar and Ai information can be obtained by measuring a reflection spectrum with a spectroscope or a microspectrometer when there is no printed layer on the label surface in the case of a disc. The absorption spectrum of the dye layer obtained by cutting the disk, exposing the recording layer surface, solvent extraction of the dye layer, dissolving the solid in an appropriate solvent and spin-coating on a transparent substrate is obtained. It is possible to obtain information on Ar and Ai by measuring or the like.

<Modulation degree>
The degree of modulation means the ratio of the signal amplitude (change in reflectance with respect to the unrecorded portion) of the recording portion reproduced corresponding to the recording pulse length, and is expressed by the following equation.
Modulation factor = (upper envelope voltage value−lower envelope voltage value) / upper envelope voltage value × 100
[II. Recording / reproducing method of optical recording medium]
The light sources used for recording and reproduction of the optical recording medium of the present invention may be the same or different, but the same is preferable because the drive can be made compact and the cost can be reduced. The wavelength is not particularly limited as long as it is shorter than 600 nm, but a blue-violet to red wavelength (about 350 nm to 600 nm) is often used. For high-density recording, it is preferable to use a wavelength region of 350 nm to 530 nm, particularly 350 nm to 450 nm. .

The recording of the optical recording medium of the present invention is performed according to I. The optical recording medium described in 1 is usually performed by irradiating the recording layer with laser light focused to about 0.4 to 0.6 μm with an objective lens having a numerical aperture of 0.85 or more.
Typical examples of such laser light include blue laser light having center wavelengths of 405 nm and 410 nm, and blue-green high-power semiconductor laser light having a center wavelength of 515 nm. Other than these, (a) a semiconductor laser beam capable of continuous oscillation having a fundamental oscillation wavelength of 740 to 960 nm, or (b) a solid-state laser beam capable of continuous oscillation having a fundamental oscillation wavelength of 740 to 960 nm that is excited by the semiconductor laser beam. The light etc. which are obtained by wavelength-converting either by a 2nd harmonic generation element (SHG) are also mentioned.

The SHG may be any piezo element that lacks reflection symmetry, but KDP (KH ₂ PO ₄ ), ADP (NH ₄ H ₂ PO ₄ ), BNN (Ba ₂ NaNb ₅ O ₁₅ ), KN (KNbO ₃ ), LBO (LiB ₃ O ₅ ), a compound semiconductor, and the like are preferable. As a specific example of the second harmonic, in the case of a semiconductor laser having a fundamental oscillation wavelength of 860 nm, a wavelength 430 nm of its harmonic wave, and in the case of a solid-state laser excited by a semiconductor laser, a Cr-doped LiSrAlF6 crystal (basic oscillation wavelength of 860 nm). ) Wavelength of 430 nm and the like. However, since solid-state lasers have various problems in practical use, in the present invention, a medium capable of recording without using such a solid-state laser is considered.

Among these, since higher density recording is preferable in the present invention, it is particularly preferable to use a semiconductor laser having a wavelength of less than 410 nm, more preferably 405 nm or less, that is, a blue laser beam having a central wavelength of about 405 nm.
On the other hand, when reproducing the information recorded on the recording layer, the recording layer is irradiated with a laser beam having lower energy (usually from the same direction as during recording). In the recording layer, information is reproduced by reading the difference between the reflectance of the portion where the optical characteristics change (that is, the portion where information is recorded) and the reflectance of the portion where the change does not occur. It is.

EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to a following example, unless the summary is exceeded.
The components of the recording layer used in the following examples and comparative examples are as follows.

As the photoacid generator, an acid-base indicator that does not increase in absorption by recording / reproducing light was selected.
<Discoloring agent-1>
Victoria Pure Blue BOH (Hodogaya Chemical Co., Ltd.)
<Measurement of Absorbance A: <A><B><C> Evaluation of each component monolayer>
0.08 g of each component of the recording layer was weighed, 9.92 g of tetrafluoropropanol (TFP) was added to the dye, and 9.92 g of diacetone alcohol was added to the photoacid generator and the color change agent. The solution was stirred and dissolved to obtain a 0.8 wt% tetrafluoropropanol solution (coating solution) or diacetone alcohol solution (coating solution) of each component. Since Dye-5 was insoluble in a 0.8 wt% solution, it was carried out with a 0.4 wt% solution.

  These were filtered through a 0.2 μm filter, and then applied onto a polycarbonate substrate on which no guide groove was formed, using a spin coater. The conditions of the spin coating method are as follows. That is, 0.5 g of a diacetone alcohol solution of each component was supplied in the vicinity of the innermost circumference of the disk in an annular shape, the disk was first moved at 580 rpm for 1.5 seconds, spread at 1500 rpm for 10 seconds, and then shaken off at 3000 rpm for 25 seconds. Further, the diacetone alcohol solution was additionally rotated at 2000 rpm for 55 seconds until the coated surface was stabilized. After the application, the solvent was evaporated and removed by holding the disk in an environment of 75 ° C. for 30 minutes.

  Absorbance was measured in the wavelength range of 250 to 2000 nm using the uncoated polycarbonate substrate as a ref for the obtained samples for measuring absorbance. Absorbance (Ar) and maximum absorption wavelength at 406 nm for each, and maximum absorbance (Ai) and dye <A> in the absorption band in the range of 700 to 2000 nm for the dye, or whether it functions as a sensitizer The results are shown in Table 1. In addition, the baseline in the measurement of absorbance was measured by placing an uncoated polycarbonate substrate on the reference side and the sample side, and measuring the absorbance, and using this as the baseline, the absorbance of the sample was measured as described above.

[Examples 1 to 9, Comparative Example 1]
<Create disk A>
On a polycarbonate resin substrate (disk) on which a guide groove having a track pitch of 0.32 μm, a groove width of about 0.18 μm and a groove depth of about 45 nm is formed, an Ag _98.1 Nd _0.9 Cu _1.0 alloy target (composition is In each case, atomic%) was sputtered to form a reflective layer having a thickness of about 50 nm to 70 nm. Further thereon, recording layer coating solutions -1 to 10 which were mixed and dissolved with the composition shown in Table 2 and filtered through a 0.2 μm filter were formed by spin coating.

The conditions of the spin coating method are as follows. That is, 0.5 g of the recording layer coating solution shown in Table 2 was annularly supplied to the vicinity of the innermost periphery of the disk, and the disk was first moved at 580 rpm for 1.5 seconds, then spread at 1500 rpm for 10 seconds, and shaken off at 3000 rpm for 25 seconds. The coating was performed. The diacetone alcohol solution was further rotated at 2000 rpm for 55 seconds until the coated surface was stabilized. Further, after application, the disk was kept in an environment of 75 ° C. for 30 minutes to evaporate and remove (dry) the solvent.
A cover sheet was applied to the surface of the recording layer thus obtained and adhered and bonded together to obtain Disc A.

<Recording / playback evaluation>
Evaluation of recording / reproduction of a disk is performed using a pulse having an optical system having a recording / reproduction light wavelength λ = 406 nm, NA (numerical aperture) = 0.85, and a focused beam spot diameter of about 0.42 μm (a point where the intensity becomes 1 / e ^ 2). The measurement was performed using an ODU1000 tester manufactured by Tech. The disc was rotated at a linear velocity of 4.9 m / s and the recording power was 9.5 mW. For reproduction, the linear velocity was 4.9 m / s and the reproduction power was 0.30 mW. A mark modulation signal (1-7PP) was used for recording. The reference clock period T was 15.15 ns (channel clock frequency 66 MHz), and the modulation degree was measured for 2T, 5T, and 10T. The results are shown in Table-2. At this time, “x” was described for those in which no change was observed before and after recording.

Regarding the disc A, the components of the recording layer diffused into the adhesive layer of the directly attached cover sheet and the performance gradually deteriorated.
<Measurement B of Absorbance>
<Absorbance measurement A> Samples for measuring absorbance of the recording layer coating solutions 1 to 10 were prepared in the same manner except that the coating solution used was changed to the recording layer coating solutions 1 to 10 in Table-2. The absorbance at 406 nm was measured. The results are shown in Table-2.

<Measurement of transmittance>
The transmittance was measured for each sample of the above <Measurement of Absorbance B> (absorbance was converted to transmittance). The results are shown in Table-2.
<<A><B><C> Calculation of Absorbance Occupancy Ratio of Each Component>
Based on the absorbance value (described in Table-1) in each component monolayer obtained in the measurement A of absorbance and the blending ratio of each component (described in Table-2), <A><B><C> After determining the absorbance of the components, it was determined as a ratio (%) to the total absorbance of the three components. The results are shown in Table-2.

In Examples 1 to 9 in which the recording layer contains the dye <A>, the absorbance at 406 nm is 8
%, And the transmittance at 406 nm was maintained at 80% or more, and a recording modulation degree was obtained at least in any of 2T, 5T, and 10T. Further, in Examples 3 to 9 in which the photoacid generator <B> and the color changing agent <C> were used in combination, the recording modulation degree was obtained while maintaining the transmittance at 406 nm of 95% or more.

On the other hand, in Comparative Example 1 in which the recording layer does not contain the dye <A>, a medium was prepared and evaluated under the condition that the absorbance at 406 nm was 8% or less and the transmittance at 406 nm was 80% or more. The degree was not obtained.
In addition, although all evaluation was performed only about the state before recording, since the acid generator used in Examples 3-9 and Comparative Example 1 has a property that absorption does not increase with recording / reproducing light, it is also after recording. It is considered that the transmittance is equivalent or higher.

<SEM observation>
The sample recorded in Example 4 was subjected to gold vapor deposition after peeling off the cover sheet, and SEM (S4500 manufactured by Hitachi, Ltd.) observation of the recording part (5T) and the non-recording part was performed. The SEM observation conditions are an acceleration voltage of 15 kV and a magnification of 50,000 times. The SEM photograph is shown in FIG.
From this result, it was confirmed that there was a hole in the recording layer or a place where it could easily move to the adhesive layer at the time of peeling, and not only the refractive index changed due to the change in color and tone of the color changing agent, but also generation of heat and acid. It was found that changes other than the photon mode, i.e., shape changes, were also caused.

[Examples 10 to 12, Comparative Examples 2 to 5]
<Create Disc B>
Instead of “Recording layer coating solutions-1 to 10 mixed and dissolved in the composition of Table-2 and filtered through a 0.2 μm filter”, the mixed solution was dissolved in the composition of Table-3 and filtered through a 0.2 μm filter. Except for using the recording layer coating solutions 11, 12, 3, 13 to 16 ”, ITO (In ₂ O ₃ —SnO ₂ ) was formed on the surface of the recording layer obtained in the same manner as the disc A production procedure. A target was sputtered to form an interface layer having a thickness of about 16 nm. Further, a cover sheet was weighted thereon and stuck together to obtain a disk B.

<Measurement of film thickness>
After washing and drying, the recording layer coating solution-12.3 used in Examples 11 and 12 was applied to a glass substrate ("AN100" manufactured by Asahi Glass Co., Ltd.) subjected to UV ozone treatment (1000 mj / cm ² with a low-pressure mercury lamp) for 1 minute. Spin coated. The spin coating was performed by supplying 0.2 g of the recording layer coating solution to the center of the substrate, initially moving the substrate at 500 rpm for 5 seconds, and then shaking it off at 1000 rpm for 2 minutes.

A portion where the substrate was exposed was made by scraping off a part of the coated surface of the obtained sample, and a step between the coated surface and the substrate surface was measured using a micromap manufactured by Ryoka System.
Further, for this sample, the absorption spectrum of the coating film was measured to obtain a correlation between the film thickness of each recording layer and the absorption spectrum.
Based on this, when the film thickness was calculated from the absorption spectra of Examples 11 and 12, Example 11 was about 35 nm and Example 12 was about 24 nm.
In addition, it is considered that the film thicknesses of the other examples will be equal or less as judged from the solid content concentration of the recording layer and the absorbance.

<Recording / playback evaluation>
The recording / reproduction evaluation was performed in the same manner as in Example 1 above, and the results are shown in Table-3. Incidentally, with respect to the disc B, there is no problem of component diffusion as in the disc A, so that a stable result was obtained even when evaluation was performed over time.

<Measurement B of Absorbance>
Absorbance was measured in the same manner as in Example 1 above, and the results are shown in Table 3.

In Examples 10 to 12 in which the recording layer contains the dye <A>, 5T and 10T recording modulation degrees were obtained while maintaining an absorbance of about 1% at 406 nm and a transmittance of 95% or more at 406 nm. Further, in Examples 11 and 12 in which the photoacid generator <B> and the color changing agent <C> were used in combination, a recording modulation degree was obtained even at 2T.

On the other hand, in Comparative Examples 2 to 5 in which the recording layer did not contain the dye <A>, the medium was prepared and evaluated under the conditions that the absorbance at 406 nm was 8% or less and the transmittance at 406 nm was 90% or more. The recording modulation degree was not obtained.
Although the evaluation was performed only for the pre-recording state, the acid generator used in Examples 11 and 12 has a property that absorption does not increase with recording / reproducing light. Is considered to have a rate.

[Example 14]
Dye 2 (0.5 wt.% Vs. solvent) used in Example 2 and the following structure A (0.5 wt.% Vs. solvent) were dissolved in diacetone alcohol to form a spin coat recording layer. The recording layer was peeled by bringing it into contact with an intermediate adhesive layer for multilayer lamination, which was applied on the film with a film thickness of about 10 μm, and laminated on the surface of the intermediate adhesive layer for multilayer lamination. This lamination process was repeated 20 times to produce an optical recording medium based on a slide glass in which 20 recording layers were laminated.

  The spin coating conditions were the same as in Example 1, and when the absorption spectrum in one recording layer was measured, the absorbance (Ar) at 405 nm was 0.027, and Ai was 0.125 near 730 nm. . The transmittance was approximately 93%. A confocal optical system (an optical system having a beam expander, beam splitter, galvanometer mirror, and objective lens sequence on the optical path ahead of the laser exit) mounted with a 405 nm semiconductor laser on this 20-layer medium. A semiconductor laser with a wavelength of 405 nm was irradiated through the working oil, and the focus was swept to the substrate in 1 μm steps to reproduce 20 layers one by one (corresponding to NA = 1.3).

As a result, the integration was performed 50 times in the plane, and as shown in FIG. 1, the interface of 20 layers could be reproduced well, and the first layer to 20 layers could be reproduced stably. When the first layer and the fifth layer were recorded, when the fifth layer was recorded with the same recording power as the first layer, the signal intensity was about 1/3 of the first layer. This sample has a structure in which no reflective layer is provided.
As described above, according to the present invention, a recording layer for an optical recording medium in a state in which high transmittance at a recording / reproducing wavelength is maintained is secured, and thereby a multilayer optical recording medium in which recording layers are stacked in multiple layers can be designed. became.

  The optical recording medium of the present invention is suitably used for various media related to optical recording, in particular, for applications such as multilayer optical recording media in which recording layers are laminated.

Claims (7)

  In an optical recording medium recorded and reproduced at a wavelength of 600 nm or less, when the recording layer of the optical recording medium has Ar as the absorbance at the recording and reproduction wavelength, and Ai as the maximum absorbance of the absorption band at 700 to 2000 nm An optical recording medium comprising a dye <A> satisfying the relationship of “Ar> 0 and Ai> 0”, and the thickness of the recording layer being 100 nm or less.   The optical recording medium according to claim 1, wherein the optical recording medium recorded and reproduced at a wavelength of 600 nm or less has a recording layer thickness of 60 nm or less.   The optical recording medium according to claim 1, wherein the dye <A> further satisfies the relationship “Ar ≦ Ai”.   Furthermore, the recording layer of the optical recording medium contains a photoacid generator <B>, and the dye <A> is a sensitizing dye of the photoacid generator <B>. 4. The optical recording medium according to any one of items 3.   The optical recording medium according to any one of claims 1 to 4, wherein the recording layer of the optical recording medium further contains a color change agent <C> whose color and color tone are changed by the generation of an acid. .   Transmittance at recording and reproducing wavelengths per recording layer of the optical recording medium is 80% or more before and after recording, and three or more recording layers are laminated. The optical recording medium according to any one of the above.   The absorbance occupancy of each component <A> <B> <C> in the recording layer of the optical recording medium at the recording and reproducing wavelength is 50% to 100% of the dye <A> in the pre-recording state, and photoacid generation The optical recording medium according to any one of claims 1 to 6, wherein the agent <B> is 0 to 30%, and the color change agent <C> is 0 to 30%.