JPH052768A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obviate the use of an energy transfer preventive layer by forming recording layers consisting of a two-layered structure in such a manner that a 1st recording film has a fluorescent wavelength region which emits light to a longer wavelength side by absorbing light in its absorption wavelength region and a 2nd recording film has an absorption wavelength region without overlapping on the fluorescent wavelength region. CONSTITUTION:The recording film 31 formed on a substrate 10 has the 1st absorption wavelength region DELTAlambdaA and has the fluorescent wavelength region DELTA a which absorbs the light cast thereto and emits the light to the longer wavelength side than the wavelength region DELTAlambdaA on lowering of the absorption peak. The recording film 33 has the 2nd absorption wavelength region DELTAlambdaB which does not overlap on the above- mentioned wavelength region DELTAa. This recording film 33 absorbs the light cast to the wavelength DELTAlambdaB and also emits the light to the longer wavelength side than the wavelength region DELTAlambdaB on lowering of the absorption peak. The adjacent absorption wavelength regions and the fluorescent wavelength regions are so formed as not to overlap on each other in such a manner, by which the need for forming the energy preventive layer is eliminated. Dyes of a cyanine system, merocyanine system, etc., are used for the recording films 31, 33.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium having a multi-layered recording layer, particularly a multi-layered recording layer formed by laminating different kinds of recording films.

[0002]

2. Description of the Related Art In recent years, various dye films have been developed as recording films for optical recording media. Such a dye film is formed on a substrate by, for example, spin coating, and a semiconductor laser beam of a predetermined wavelength is focused on the dye film and converted into heat energy to change the properties of the dye film. Recording is performed by changing. Then, reproduction is performed depending on the difference in the amount of reflected light or the amount of transmitted light with respect to the unrecorded portion. However, the recording density of the conventional optical recording medium is limited to 10 ⁸ bits / cm ² due to the diffraction limit of the accessing light,
Development of an optical recording medium capable of coping with high density recording in an advanced information society is demanded.

As one means for achieving high density of the optical recording medium, there is a method of enabling recording in the vertical direction of the optical recording medium to increase the recording density per unit volume. This is an optical recording medium in which recording films such as dyes of different kinds capable of separating absorption wavelengths from each other are laminated and recording / reproducing (wavelength multiplexed optical recording) is performed by a laser beam having an absorption peak wavelength of a desired recording film. It is possible to record in the vertical direction.

However, when recording is carried out by irradiating light in the absorption wavelength range of a desired dye film on a recording film formed by directly laminating different dye films which can separate absorption wavelengths from each other as described above. However, there is a problem that wavelength-multiplexed optical recording cannot be performed. That is, another dye film having an absorption wavelength on the longer wavelength side than the desired dye film may be recorded. This is presumably because energy transfer (charge, heat transfer, or energy transfer due to molecular vibration, electron orbit resonance, fluorescence, etc.) occurs between the dye films, and the applicant of the present application interferes with each other. A proposal has already been made to provide an energy transfer prevention layer between recording films (Japanese Patent Application No. 2-127553).

[0005]

However, by providing the above-mentioned energy transfer prevention layer, there is an inconvenience that extra cost such as film formation is required and the structure of the medium itself becomes complicated. Therefore, there is a strong demand for avoiding the use of the energy transfer prevention layer if possible.

The present invention was devised in view of the above-mentioned circumstances, and by selecting the type and stacking order of recording films, the use of the energy transfer prevention layer can be eliminated or at least minimized. The purpose is to keep the number of.

[0007]

In order to achieve the above object, the present invention is a recording layer having a two-layer structure formed by directly laminating a first recording film and a second recording film on a substrate. In the optical recording medium having, the first recording film has a first absorption wavelength band, absorbs light irradiated in this absorption wavelength band, and is longer wavelength side than the first absorption wavelength band. The second recording film is configured to have a second absorption wavelength range that does not overlap with the first fluorescence wavelength range.

Further, in an optical recording medium having a recording layer having a multi-layered structure formed by laminating at least three recording layers, the three or more recording layers have an absorption wavelength range and an absorption wavelength range. Each of the recording films having three or more layers has a respective absorption wavelength region and another recording film, which has a fluorescence wavelength region which absorbs the irradiated light and emits light on a longer wavelength side than the absorption wavelength region. It is configured to be optimally arranged so as to minimize direct overlap with the fluorescence wavelength region generated from

[0009]

When the optical recording medium is irradiated with light in the absorption wavelength range of a desired dye film among different dye films forming the recording film formed on the substrate, only the absorption peak of the dye film is selected. The number of records is reduced. At this time, the energy transfer between the dye films can be minimized by eliminating or using the conventional energy transfer prevention layer by selecting the type of recording film and the stacking order. it can.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of an optical recording medium of the present invention. In FIG. 1, an optical recording medium 1 is placed on a substrate 10,
The recording layer 30 is formed by stacking a plurality of recording films.

First, in the medium of the present invention, the recording layer 30
An example will be described in which the recording medium is formed of two layers of recording films 31 and 33. First recording film 3 formed on the substrate 10
1 has a first absorption wavelength range ΔλA as shown in the simplified phenomenon explanatory view of FIG. 2, absorbs light (recording light) irradiated in this absorption wavelength range ΔλA, and With a decrease (recording state), it has a property of emitting light on the longer wavelength side than the first absorption wavelength region ΔλA. To emit light, let the first fluorescence wavelength range be Δa as shown in the figure.

The second recording film 33 has a second absorption wavelength region ΔλB which does not overlap with the first fluorescence wavelength region Δa.
This recording film 33 also absorbs the light (recording light) irradiated in the absorption wavelength range ΔλB, lowers the absorption peak (recording state), and has a wavelength longer than the second absorption wavelength range ΔλB (first wavelength). It has the property of emitting light in the second fluorescence wavelength region ΔB).

Since the first and second recording films 31 and 33 are set so that the absorption wavelength region and the fluorescence wavelength region of the adjacent recording films do not overlap with each other in this manner, the energy prevention layer which has been conventionally required. Need not be formed.

Specific substances constituting the first and second recording films 31 and 33 are dyes, particularly cyanine type, merocyanine type, squarylium type, spiropyran type, phthalocyanine type, naphthalocyanine type, fulgide type, diarylethene type. And the like are suitable.

Such first and second recording films 31,
33 is preferably formed by a so-called LB film forming method, but a known method such as spin coating may be used. The recording film 31 formed in this way,
The film thickness of 33 is about 25 Å to 4000 Å.

Next, the present invention will be described with reference to an example in which the recording film of the optical recording medium 1 shown in FIG. 1 is formed as an LB film. Here, the LB film (Langmuir-Blodgett film) is formed by adsorbing a monomolecular film on the water surface onto a substrate, and is a uniform thin film having a molecular order thickness and a controlled molecular arrangement. Therefore, the thickness of the dye film formed on the substrate by using the dye is about 1/10 of the thickness of the dye film formed on the substrate by the conventional spin coating or the like. Therefore, even if different kinds of dye films are laminated on the substrate, the whole laminated dye film is within the focal depth of the laser beam, and the focusing control of the laser beam becomes easy. Further, while the absorption spectrum of the dye film formed on the substrate by spin coating or the like shows broad absorption, by forming a dye film of cyanine, merocyanine, spiropyran, squarylium or the like as the LB film, the so-called In some cases, a J-aggregate is formed, and the peak of the absorption spectrum shifts to the long wavelength side and becomes steep. Annealing may be appropriately performed after the LB film is formed.

The LB film forming method will be described with reference to FIG. In FIG. 3, the LB film forming apparatus 50 includes a water tank 51 for holding a lower layer liquid, and a solvent in which a dye is dissolved is dropped on the lower layer liquid. The dropped solvent spreads on the lower layer liquid and volatilizes, and the dye molecules quickly spread to the air-water interface,
The hydrophilic groups are arranged in the lower layer liquid so that the hydrophobic groups are exposed to the atmosphere to form a monomolecular film. Next, the barrier 52 is moved to the right in the figure to apply a predetermined membrane pressure to the monomolecular film to maintain the so-called aggregated film state. In this state, by vertically moving the substrate 60 vertically across the liquid surface, a dye LB film of one molecular layer or multiple molecular layers is formed on the substrate 60. As the lower layer liquid, pH-adjusted distilled water is used. In addition, as the solvent, a solvent such as benzene and chloroform, which is incompatible with water and is volatile, is used. In this solvent, a long-chain saturated hydrocarbon as a film forming aid together with a dye,
Long-chain fatty acids and their derivatives may be added.
The membrane pressure control of the above-mentioned monomolecular film is based on the π-A curve obtained from the change of the membrane pressure (π) on the air-water interface accompanying the compression by the barrier 52 and the area (A) obtained from the position of the barrier 52. Can be done based on. At the same time, it is also possible to confirm that the J-aggregate was formed from the shift of the absorption peak by measuring the spectral characteristics of the dye.

As the substrate 10, a substrate having a smooth surface and a sufficiently clean interface can be used. For example, a substrate made of metal, glass, organic polymer material, silicon or the like is used. You can

Next, regarding a medium having three or more recording films, an example of having three recording films will be described with reference to FIGS.
Description will be given with reference to 0. Three-layer recording film 32, 34, 3
Reference numeral 6 has an absorption wavelength region and a fluorescence wavelength region which absorbs light irradiated in this absorption wavelength region and emits light on a longer wavelength side than the absorption wavelength region. , Are optimally arranged so as to minimize the direct overlap between the respective absorption wavelength ranges and the fluorescence wavelength ranges generated from other recording films.

The structure will be described in more detail below. First, the symbols used below will be explained. (1) A, B, C ... The materials constituting the respective recording films are shown.

However, λA <λB <λC, where λ
A, λB and λC are the maximum absorption wavelengths of the materials A, B and C, respectively. (2) ΔλX ... Absorption wavelength range of arbitrary material X Δx: Defined by fluorescence wavelength range of arbitrary material X

Under this definition, the three-layer recording film A,
Considering the stacking order of B and C, fluorescence always appears on the longer wavelength side than the absorption wavelength, so ΔλA and Δb, ΔλA and Δc, and Δ
The overlap of λB and Δc can be ignored, and Δa and ΔλB,
Only the overlap of Δa and ΔλC and Δb and ΔλC need be considered.

The possible cases of overlap are shown in Table 1 below.

[0024]

[Table 1]

In Table 1, in the case of (I), no matter how the stacking order is selected, the interference between the recording films cannot be avoided, and an energy prevention layer (two layers in total) is required between the recording films. Become.

In case (II), the interference pattern between the recording films is as shown in the schematic view of FIG. 5, and the stacking order and the number of necessary energy prevention layers (indicated by *) (n) are shown. Considering the following: -Stacking order (1) ABC → AB * C Therefore, n = 1 (2) ACB → A * C * B Therefore, n = 2 (3) BAC → BA * C Therefore, n = 1 Therefore ( The stacking order of 1) and (3) is according to the present invention.

In the case of (III) case, the interference pattern between the recording films is as shown in the schematic view of FIG. 6, and the stacking order and the number of necessary energy prevention layers (indicated by *) (n) Considering the following: (1) ABC → A * B * C Therefore, n = 2 (2) ACB → AC * B Therefore, n = 1 (3) BAC → B * AC Therefore, n = 1 Therefore ( The stacking order of 2) and (3) is according to the present invention.

In the case of (IV) case, the interference pattern between the recording films is as shown in the schematic view of FIG. 7, and the stacking order and the number of necessary energy prevention layers (indicated by *) (n) Considering the following: (1) ABC → A * BC Therefore, n = 1 (2) ACB → A * CB Therefore, n = 1 (3) BAC → B * A * C Therefore, n = 2 Therefore ( The stacking order of 1) and (2) is according to the present invention.

In case (V), the interference pattern between the recording films is as shown in the schematic view of FIG. 8, and the stacking order and the number of necessary energy prevention layers (indicated by *) (n) Considering the following: -Stacking order (1) ABC → AB * C Therefore, n = 1 (2) ACB → AC * B Therefore, n = 1 (3) BAC → BAC Therefore, n = 0 Therefore (3) Stacking The order is according to the invention.

In the case of (VI) case, the interference pattern between the recording films is as shown in the schematic view of FIG. 9, and the stacking order and the number of necessary energy prevention layers (indicated by *) (n) Considering the following: ・ Layering order (1) ABC → ABC Therefore, n = 0 (2) ACB → A * CB Therefore, n = 1 (3) BAC → BA * C Therefore, n = 1 Therefore (1) The order is according to the invention.

In the case of (VII) case, the interference pattern between the recording films is as shown in the schematic view of FIG. 10, and the stacking order and the required energy prevention layer (*
(Displayed with), the stacking order: (1) ABC → A * BC Therefore, n = 1 (2) ACB → ACB Therefore, n = 0 (3) BAC → B * AC Therefore, n = 1 Therefore, the stacking order of (2) is according to the present invention.

In case (VIII), no matter how the stacking order is selected, there is no interference between the recording films, and the energy prevention layer is unnecessary.

The energy transfer prevention layer provided as necessary is, for example, saturated hydrocarbon such as octadecane, higher fatty acid such as stearic acid and palmitic acid, higher alcohol such as hexadecyl alcohol and octadecyl alcohol, stearylamine and the like. Of the amine and at least one higher fatty acid ester such as methyl stearate. The thickness of such an energy transfer prevention layer is 25 angstroms or more,
It is preferably 50 angstroms or more. The energy transfer prevention layer may be formed by a conventionally known method such as spin coating, or may be formed as an LB film as described later.

Of the three or more layers of recording film, the thickness of the recording film which is interposed and can be said to also serve to prevent energy transfer needs to be 100 angstroms or more. It should be noted that in the above-mentioned embodiment, the description has been given by taking the recording film of three layers as an example, but it is needless to say that the idea of the present invention can be similarly applied to the case of four layers, five layers or more.

Next, the present invention will be described in more detail with reference to experimental examples. (Experimental example) The dye (absorption wavelength range: 360 to 480 nm, fluorescence wavelength range: 450 to 560 nm) represented by the following structural formula (1) was used as the first recording film and the following structural formula ( 2) Dye (absorption wavelength range: 580)
.About.850 nm), and a dye film was formed as an LB film to prepare an optical recording medium having the structure shown in FIG.

[0036]

[Chemical 1]

[0037]

[Chemical 2]

The LB film forming apparatus shown in FIG. 3 was used as the LB film forming apparatus, and the LB film forming conditions were as follows. -Base plate: glass substrate (hydrophobic surface treated) -Solvent: Chloroform-Dye concentration ... 2 mmol / l (solvent) -Lower layer liquid: Distilled water (pH = 6.8, water temperature = 15 ° C) -Barrier transfer Speed: 20 mm / min-Substrate elevation speed: 5 mm / min-Film forming conditions for the first and second recording films: -Film forming aid: stearic acid (dye: stearic acid = 1: 2) molar ratio-membrane pressure …
25 dyne / The thickness of the first and second recording films formed as described above was about 100 Å. This sample was irradiated with light having an absorption peak wavelength (450 nm) of the first recording film for 1000 seconds from the second recording film side, and writing was performed on the first recording film. It was confirmed that there is no effect and recording without crossing is possible.

[0039]

As described above in detail, in the multilayer type optical recording medium capable of multi-layer recording, the conventional energy transfer prevention layer can be used by optimally selecting the kind of recording film and the stacking order as in the present invention. It is possible to eliminate or use only a minimum number.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an optical recording medium (two layers of recording film) of the present invention.

FIG. 2 is a graph showing the relationship between the wavelength of the recording film and the absorbance.

FIG. 3 is a perspective view showing an example of an LB film forming apparatus.

FIG. 4 is a schematic sectional view of an optical recording medium (3 layers of recording film) of the present invention.

FIG. 5 is a graph showing an overlapping pattern of absorption wavelength regions and fluorescence wavelength regions in the case of three recording film layers.

FIG. 6 is a graph showing an overlapping pattern of absorption wavelength regions and fluorescence wavelength regions in the case of three recording film layers.

FIG. 7 is a graph showing an overlapping pattern of absorption wavelength regions and fluorescence wavelength regions in the case of three recording film layers.

FIG. 8 is a graph showing an overlapping pattern of absorption wavelength regions and fluorescence wavelength regions in the case of three recording film layers.

FIG. 9 is a graph showing an overlapping pattern of absorption wavelength regions and fluorescence wavelength regions in the case of three recording film layers.

FIG. 10 is a graph showing an overlapping pattern of absorption wavelength regions and fluorescence wavelength regions in the case of three recording film layers.

[Explanation of symbols]

1 ... Optical recording medium 10 ... Substrate 30 ... Recording layer 31, 32, 33, 34, 36 ... Recording film 50 ... LB film forming apparatus

Claims (3)

[Claims] 1. An optical recording medium having a two-layered recording layer formed by directly laminating a first recording film and a second recording film on a substrate, wherein the first recording film is a first recording film. It has a first absorption wavelength range, absorbs light irradiated in this absorption wavelength range, and is provided with a first fluorescence wavelength range that emits light to a longer wavelength side than the first absorption wavelength range, An optical recording medium, wherein the second recording film has a second absorption wavelength range that does not overlap with the first fluorescence wavelength range. 2. An optical recording medium having a multi-layered recording layer formed by laminating at least three or more recording films, wherein the three or more recording films have an absorption wavelength range and an absorption wavelength range. Each of the recording films having three or more layers has a respective absorption wavelength region and another recording film, which has a fluorescence wavelength region which absorbs the irradiated light and emits light on a longer wavelength side than the absorption wavelength region. An optical recording medium, which is optimally arranged so as to minimize direct overlap with the fluorescence wavelength region generated from the optical recording medium. 3. The optical recording medium according to claim 1, wherein the recording film is an LB film of a dye forming a J-aggregate.