JPH11250496A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the thickness of a recording layer itself by partly or wholly forming a non-recording layer comprising a material in which optical information is not recorded by recording light between layers of two or more recording layers. SOLUTION: The medium contains not only a recording layer or nonrecording layer, but structural elements such as substrate, protective film, light reflection film and other films. The recording layer consists of a material which constitutes the matrix and contains a photoreactive component for information recording. The material to constitute the matrix has specified lighttransmitting property, and may be a polymer material or inorg. material such as glass. Since the nonrecording layer is present between recording layers, the widening of the recording region in the perpendicular direction to the recording layer surface is prevented. Therefore, even when the recording layer is controlled to the thickness of the wavelength order of the irradiation light, the cross talk can be decreased, which means that the thickness of recording layer itself can be decreased. Thus, the interlayer distance of recording layers including the nonrecording layer can be decreased.

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,
More specifically, the present invention relates to reduction of so-called crosstalk in a multilayer optical recording medium, and furthermore, to higher density of recorded information.

[0002]

2. Description of the Related Art In recent years, multilayer optical recording media have been proposed for the purpose of increasing the density of recorded information in optical recording media.

For example, Y. Kawata et. Al., Appl. Opt.,
35 (1996) 2466-, a technique for performing multilayer optical recording on a photopolymer material having a photopolymerizable reactive photoreactive component was reported. Satoshi Kawata published in "Oplus E, August 1996". The paper "Multilayer optical recording using photorefractive material" introduces a method of recording information in multiple layers inside a photorefractive crystal.

[0004]

However, in multilayer optical recording media using these various materials, there has been a problem of crosstalk in recording between layers. In particular, the problem is remarkable in a photopolymer material having the above-mentioned photopolymerizable reactive photoreactive component.

In general, it is conceivable to increase the interlayer distance between recording layers as a countermeasure against such crosstalk. In this case, however, the recording density is directly reduced, and light used for reading and writing of recording is absorbed in the middle. Therefore, the number of recording layers could not be increased.

Accordingly, an object of the present invention is to provide an optical recording medium that can effectively prevent crosstalk while keeping the interlayer distance between recording layers as small as possible.

[0007]

Means for Solving the Problems (Structure of the First Invention) The structure of the first invention (the invention according to claim 1) for solving the above-mentioned problems is a light having two or more recording layers. An optical recording medium, wherein a non-recording layer made of a material on which optical information is not recorded by recording light is interposed in part or all of the layers of the two or more recording layers.

(Structure of the Second Invention) The structure of the second invention of the present application (the invention described in claim 2) for solving the above problems is as follows.
An optical recording medium having two or more recording layers,
Some or all of the recording layers of the layer or more is a recording layer in which optical information is recorded by recording light of different wavelengths from each other,
An optical recording medium.

[0009]

Operation and effect of the present invention (operation and effect of the first invention) When optical recording is performed in multiple layers, the irradiation light for recording is focused and focused on a specific recording layer. In the direction, the area can be narrowed to a narrow area on the order of the wavelength of the irradiation light. This causes crosstalk and causes the interlayer distance to be increased in the prior art.

However, in the first aspect, since the non-recording layer is interposed between the recording layers, the expansion of the recording area in the direction perpendicular to the recording layer surface is blocked. Therefore, even if the recording layer is restricted to a thickness on the order of the wavelength of irradiation light, crosstalk can be reduced. As a result, the thickness of the recording layer itself can be reduced, and the interlayer distance of the recording layer including the non-recording layer can be reduced.

(Function / Effect of Second Invention) In the second invention, when optical information is recorded on a certain recording layer by recording light of a specific wavelength, the optical information is not recorded by the recording light of that wavelength. The present invention not only exerts the same operation and effect as the non-recording layer in the first invention, but also uses itself as one recording layer, so that the problem of the invention can be more effectively solved.

[0012]

Next, embodiments of the first invention and the second invention will be described.

[Optical Recording Medium] The optical recording medium according to the first and second aspects of the present invention includes, in addition to the recording layer and the non-recording layer, components such as a substrate, a protective film, a light reflection film, and other film bodies. It can optionally be included. The recording medium can be used for various known uses as a recording medium for optical information, for example, a recording medium for a computer, a recording medium for music / video, and the like. By selecting a photoreactive component that responds to recording light and a recording form of information, the recording medium can be used as a read-only recording medium, a recording medium that can be written only once, or a recording medium that can be repeatedly read and written.

Normally, in information recording by light, the areal density in the recording layer is limited by the light condensing limit, but by using the optical recording media of the first invention and the second invention, the recording density is substantially increased by increasing the number of recording layers. It is possible to increase the recording density.

[Constituent Material of Recording Layer] The recording layer in the optical recording medium according to the first and second aspects of the present invention contains a material constituting a matrix containing a photoreactive component for recording information.

The material constituting the matrix preferably has a certain translucency, but may be a polymer material or an inorganic material such as glass. Although the kind of such a polymer material is not limited, a urethane group (—O—CO—NH— group) and a urea group (—NH—
Those containing a CO-NH- group, -NH-CO-N <group) or an amide group (-CO-NH- group) further have a ring structure such as a phenylene group in the main chain of the polymer. Things are
Particularly preferred is heat resistance.

Such a polymer material may be of any molecular weight and degree of polymerization as long as it can be formed into a predetermined recording medium shape, and the polymerization form may be any of linear, branched, ladder, star, etc. It may be in the form of The polymer may be a homopolymer or a copolymer. The form of the copolymer in the copolymer is also not limited, and may be a block copolymer, a random copolymer, a graft copolymer, or any other suitable one.

The photoreactive component may be chemically bonded to the material constituting the matrix as a main chain component or a side chain component by a covalent bond, an ionic bond, or the like, or may be simply dispersed. May be. The type of the photoreactive component is not limited. For example, an azo group, a CＣC group, a C
= N group or the like, which may cause a photoisomerization reaction, or a photopolymerizable material, a photochromic material, or any other known photoreactive component may be used.

In view of the above, specific examples of the polymer material containing a photoreactive component, which are particularly preferable, are described below. In addition to those described in Examples, the following Chemical Formulas 1 to 4
And those having a polymer structure shown below. In these specific examples, -X represents a nitro group, cyano group, trifluoromethyl group, aldehyde group or carboxyl group, -Y- represents -N = N-, -CH = N- or -CH = CH-, -R
-Represents a phenylene group, an oligomethylene group, a polymethylene group or a cyclohexane group, respectively.

[0020]

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[0021]

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[0022]

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[0023]

Embedded image In the second invention, the recording layers on which optical information is recorded by recording light of mutually different wavelengths may be configured with the same matrix and photoreactive component, or the matrix and / or photoreactive component may be composed of the same matrix and / or photoreactive component. It may be different.

[Constituent material of non-recording layer] The constituent material of the non-recording layer has a certain translucency and a photo-reactive component (at least a component which reacts to recording light used in the optical recording medium). There is no limitation as long as it does not include. The same material as the material constituting the matrix of the recording layer or a different material may be used.

[Information Recording on Recording Layer] In the first and second aspects of the present invention, there is no limitation on the form of recording information on the recording layer. And the anisotropy of absorbance may be different, and the recording layers of the same optical recording medium may have different recording modes.

The wavelength of light used for recording and detecting information on the optical recording medium, that is, for writing and reading information is not limited, but practically, ultraviolet light, visible light, and near-infrared light are preferable.

[Multilayer Structure of Optical Recording Medium] It is sufficient that the optical recording medium of the first invention and the second invention has at least two or more recording layers.

In the first invention, the best mode is the case where a non-recording layer is interposed between all the two or more recording layers. However, it is not always necessary to do so. Even in the case of intervening, the effect of the invention is ensured as long as it is present, and therefore, it corresponds to the first invention.

In the second invention, the best mode is when all the recording layers are recorded by recording light of different wavelengths, but it is not always necessary to do so, and only some of the recording layers have different wavelengths. Even in the case where the information is recorded by light, the effects of the invention can be ensured as long as it is recorded, and thus the invention corresponds to the second invention. The case where a part of the recording layer recorded by the recording light beams having different wavelengths coexist is included in the second invention.

Although the thicknesses of the recording layer and the non-recording layer in the first and second inventions are not limited, it is more preferable that the thickness of the recording layer is substantially equal to the wavelength of light used for reading and writing. The thickness of the non-recording layer is appropriately selected according to the optical system used for reading and writing, but is typically, for example, about 3 to 50 μm.

In the first invention, when reading recorded information in a light transmission type arrangement, it is preferable that the difference in refractive index between the recording layer and the non-recording layer is small in terms of reduction of scattering loss. When reading recorded information in a reflective arrangement, it is preferable that the refractive index difference between the recording layer and the non-recording layer be large in that a special reflective film can be eliminated.

In the optical recording medium of the first invention, apart from the non-recording layer, which is different from the recording layer in that it does not contain a photoreactive component, two or more adjacent recording media are used in the first and second inventions. It is possible that the recording layers may be of the same constituent material, and therefore these recording layers may be physically recorded in multiple layers on a single optical recording medium material, or may be originally formed separately. The optical recording medium unit may be bonded to a thin optical recording medium unit after being separately recorded.

In the second invention, recording and reading can be performed at an arbitrary wavelength, but it is preferable from the viewpoint of efficiency to write at a wavelength where the absorption of each material is large.

[0034]

Next, an embodiment of the present invention will be described.

( Synthesis of Photoreactive Component ) 2-Methyl-4-
Nitroaniline (30.43 g) was added to water (300 mL) and hydrochloric acid (36).
% Aqueous solution (180 mL) and cooled to 3 ° C. Into it, 15.20 g of sodium nitrite dissolved in 100 mL of water was added. The obtained solution was kept at 3 ° C and stirred for 1 hour.

Further, m-tolyldiethanolamine (39.05 g) was added to water (300 mL) and hydrochloric acid (36% aqueous solution 3).
A solution dissolved in a mixed solution with 0 mL was gradually added over 60 minutes, and then reacted by stirring at 3 ° C. for 150 minutes.

The reaction mixture was neutralized with 141.6 g of potassium hydroxide dissolved in 700 mL of water, and the crude composition was filtered off, washed with water and dried. Repeat the recrystallization purification three times,
4-N, N-bis (2-hydroxyethyl) amino-2,2′-dimethyl-4′-nitroazobenzene represented by “Chemical Formula 5” was obtained (yield; 62%, melting point: 169 °).
C).

[0038]

Embedded image ( Synthesis of Polymer Containing Photoreactive Component ) 2.000 g of the compound of the above “Formula 5” and 2.095 g of 4,4′-diphenylmethane diisocyanate were added to 50 mL of N-methyl-2.
-Dissolved in pyrrolidone, reacted at room temperature with stirring for 15 minutes, and further reacted at 100 ° C with stirring for 60 minutes. After cooling the solution to 50 ° C, 20 mL of N
Trans-2, dissolved in -methyl-2-pyrrolidone
0.319 g of 5-dimethylpiperazine was added and reacted by stirring for 5 hours. The mixture was further heated to 115 ° C. under reduced pressure, and 52 mL of N-methyl-2-pyrrolidone was gradually distilled off over 150 minutes.

The obtained reaction mixture was diluted with 180 mL of pyridine and filtered through a 0.1 μm filter.
The polymer was poured into ethanol and the precipitated polymer was separated by filtration. The obtained polymer was purified twice by a reprecipitation method to obtain a polymer represented by the following formula (yield: 92%, glass transition temperature: 141 ° C, 30% in N-methyl-2-pyrrolidone).
(Intrinsic viscosity at ° C; 0.69 dL / g, absorption maximum wavelength; 475 nm).

[0040]

Embedded image ( Preparation of Recording Medium ) The polymer of Chemical Formula 6 was dissolved in pyridine to prepare a 6.5 wt% solution (hereinafter, “Solution A”).
). On the other hand, polyvinyl alcohol (made by Wako Pure Chemical
162-16325) was dissolved in 3 mL of water (hereinafter, referred to as "solution B").

Solution A was placed on a slide glass at a rotational speed of 1,
Spin coating under the condition of 000 rpm,
Vacuum drying was performed for 0 hour to produce a recording layer having a thickness of about 1 μm. Furthermore, the solution B was spin-coated on the condition of the number of revolutions of 1,500 rpm, and dried under vacuum at 100 ° C. for 24 hours. Further, the steps of spin coating and drying of the above solution B were repeated three times to form a non-recording layer having a thickness of about 8 μm on the recording material layer.

By repeating the above steps, an optical recording medium in which recording layers and non-recording layers were alternately laminated was produced.

( Multilayer Recording of Information ) Each recording layer of the recording medium is irradiated with a condensing spot of an argon laser having a wavelength of 514 nm. At this time, bit data is separately recorded on each recording layer by adjusting the focal length. did. The irradiation light intensity was 400 μW, and the irradiation time was 1/64 second. Observation with a CCD camera using a microscope optical system with white illumination revealed bit data in each recording layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Riki Egami 154-100 Wago-cho, Hamamatsu City, Shizuoka Prefecture (72) Inventor Hirohiro Sugihara 5-15-15 Uejima, Hamamatsu City, Shizuoka Prefecture (72) Inventor Naomichi Okamoto Hamamatsu, Shizuoka Prefecture 2578 No. Masuraku-cho

Claims (2)

[Claims] 1. An optical recording medium having two or more recording layers, wherein a part or all of the layers between the two or more recording layers is made of a non-recording material made of a material on which optical information is not recorded by recording light. An optical recording medium having a recording layer interposed. 2. An optical recording medium having two or more recording layers, wherein a part or all of the two or more recording layers are
An optical recording medium comprising a recording layer on which optical information is recorded by recording light of different wavelengths.