JPH076406A - Optical information recording medium and recording / erasing method - Google Patents

Abstract

(57) [Abstract] [Purpose] An optical information recording medium in an organic optical information recording medium, which has higher sensitivity and a larger wavelength margin than the conventional write-once CD recording medium, and which is capable of writing and erasing information. To provide. [Constitution] An optical information recording medium in which a substrate is directly or undercoated, a light absorbing layer made of an organic dye, a light interference layer, a light reflecting layer, and optionally a protective layer are sequentially laminated,
The interference layer is formed of a polymer blend capable of causing a state change between a compatible state and a phase separated state due to a temperature change. The reflectance of this medium is preferably 70% or more, and the extinction coefficient of the complex refractive index of the light absorption layer is preferably 0.3 or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium using a dye or the like (hereinafter sometimes abbreviated as an optical recording medium).
In particular, the present invention relates to an optical recording medium excellent in durability and storage stability. The present invention also relates to a recording / erasing method using the above optical recording medium.

[0002]

2. Description of the Related Art Recently, a write-once type optical recording medium in which a recording function is added to a compact disc (CD) has been actively developed. Japanese Patent Laid-Open No. 2-87339 discloses that a signal level satisfies the JIS CD standard by laminating a light absorbing layer and a light reflecting layer on a substrate and limiting the birefringence of the light absorbing layer. ing. However, such optical characteristics can be obtained only at the absorption edge of the organic dye, but at the absorption edge, the change of the absorbance with respect to the wavelength is large, and the wavelength dependency of its reflectance sensitivity is also large, and the wavelength margin (λ = 77).
(0 to 830 nm) is also insufficient, and it has been extremely difficult to select a material that can achieve both optical characteristics and reliability.

In order to improve this point, JP-A-2-87
In JP 339, a light-absorbing layer and a light-reflecting layer are laminated on a substrate as a write-once CD recording medium, and the birefringence n of the light-absorbing layer is n ≧ 1.8 and the extinction coefficient k is 0.01 ≦. k ≦ 0.3
It has been proposed to obtain a high reflectance by limiting the above. This is because the optical interference layer is provided between the light absorption layer and the light reflection layer to enable high reflectance, there is no limitation on the optical characteristics of the light absorption layer, and the material selection and the wavelength margin are also eliminated. Has been greatly improved. However, the medium described in the publication also belongs to the so-called write-once type, and erasing and rewriting were impossible.

[0004]

In view of the above problems, the present invention is an optical information recording medium which has higher sensitivity and a larger wavelength margin than the conventional write-once type CD recording medium, and which can be erased and rewritten. And a recording / erasing method using the same.

[0005]

In order to achieve the above object, according to the present invention, a light absorbing layer made of an organic dye is provided on a substrate directly or through an undercoat layer, and a light interference layer is formed on the light absorbing layer. A light-reflecting layer is provided, and a protective layer is further provided on the light-reflecting layer, if necessary. In the optical information recording medium configured to obtain, there is provided an optical information recording medium comprising a polymer blend in which the optical interference layer can change states of a compatible state and a phase separated state due to a temperature change. Further, according to the present invention, there is provided an optical information recording medium having the above structure, wherein the reflectance of the medium is 70% or more. Further, according to the present invention, there is provided an optical information recording medium having the above-mentioned structure, in which the extinction coefficient of the complex refractive index of the light absorbing layer is 0.3 or more. Further, according to the present invention, there is provided an optical information recording medium having the above-mentioned constitution, wherein the polymer blend is an upper critical eutectic temperature type polymer blend or a lower critical eutectic temperature type polymer blend. Further, according to the present invention, there is provided an optical information recording medium having the above-mentioned constitution, wherein a light absorbing substance is contained in the polymer blend. Furthermore, according to the present invention, using the above-mentioned optical information recording medium, a polymer blend in which a laser beam modulated in an informational state is irradiated to cause a state change of a compatible state and a phase separated state due to a temperature change, A recording / erasing method is provided in which after the temperature is raised again to the cloud point or higher, the original state is restored by cooling and erasing.

The optical information recording medium of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the structure of the optical information recording medium of the present invention. A light absorbing layer 2 made of an organic dye, a light interference layer (polymer blend layer) 3, a light reflecting layer 4, and a necessary layer are provided on a substrate 1. The protective layer 5 is provided according to the above. in this case,
An undercoat layer may be provided between the substrate 1 and the light absorption layer 2.
For comparison, a conventional general write-once CD recording medium is shown in FIG.
However, this conventional medium does not have an optical interference layer (polymer blend layer).

Next, required characteristics of each layer and examples of materials constituting the layer will be described. <Substrate> A necessary characteristic of the substrate is that it should be transparent to the laser light used only when recording / reproducing is performed from the substrate side, but it is not necessary to be transparent when recording / reproducing is performed from the recording layer side. As the substrate material, for example, polyester, acrylic resin, polyamide, polycarbonate, polyolefin, phenol resin, epoxy resin, plastic such as polyimide, glass, ceramic or metal can be used. Note that a tracking guide groove or guide pit for tracking, and a preformat such as an address signal may be formed on the back surface of the substrate.

<Undercoating layer> The undercoating layer comprises a) improved adhesion, b) barrier against water or gas, c) improved storage stability of the recording layer, d) improved reflectance, and e) solvent. It is used for the purpose of protecting the substrate from, f) forming guide grooves, guide pits, pre-formats, etc. For the purpose of a), polymer materials such as ionomer resins, polyamide resins, vinyl resins, natural resins, natural polymers, silicones, various polymer substances such as liquid rubber, and silane coupling agents are used. For the purposes of b) and c), other than the above polymeric materials, inorganic compounds such as SiO ₂ , MgF ₂ , SiO, TiO ₂ , Zn can be used.
Semi-metals such as O, TiN, SiN, or Zn, Cu, N
Metals such as i, Cr, Ge, Se, Au, Ag and Al can be used. For the purpose of d), a metal such as Al or Ag or an organic thin film having a metallic luster such as a methine dye or a xanthene dye can be used, and for the purposes of e) and f). An ultraviolet curable resin, a thermosetting resin, a thermoplastic resin or the like can be used as the resin. The thickness of the undercoat layer is 0.01 to 30 μm, preferably 0.05 to 10 μm.

<Light Absorbing Layer> For the light absorbing layer, a material containing an organic dye having an absorptivity in the laser light wavelength range used for recording as a main component can be used. Specific examples of materials include polymethine dyes, naphthalocyanine dyes, phthalocyanine dyes, squarylium dyes, croconium dyes, pyrylium dyes, naphthoquinone dyes, anthraquinone (indanthrene) dyes, xanthene dyes, triphenylmethane dyes,
Examples thereof include azulene-based dyes, tetrahydrocholine-based dyes, phenanthrene-based dyes, triphenothiazine-based dyes, and metal complex compounds. The above dyes may be used alone or in combination of two or more. Further, in the dye, a metal or a metal compound such as In, Te, Bi, Al or S is added.
It is also possible to use e, TeO ₂ , SnO, As, Cd, etc. in the form of dispersion mixing or lamination. Furthermore, various materials such as ionomer resins, polyamide resins, vinyl resins, natural polymers, silicones, liquid rubbers, or silane coupling agents may be dispersed and mixed in the dye, and used. Alternatively, it may be used together with a stabilizer (for example, a transition metal complex), a dispersant, a flame retardant, a lubricant, an antistatic agent, a surfactant, a plasticizer and the like for the purpose of improving the characteristics. The thickness of the light absorption layer is 100Å ~
3000 Å, preferably 500 Å to 2000 Å are suitable.

The light absorption layer is formed by vapor deposition, sputtering,
It can be done by conventional means such as CVD or solvent spraying. When the spraying method is used, it is carried out by dissolving the dye or the like in an organic solvent and applying it by a conventional coating method such as spray coating, roller coating, dipping or spinner coating. As the organic solvent, generally, alcohols such as methanol, ethanol and isopropanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, amides such as N, N-dimethylacetamide and N, N-dimethylformamide, sulfoxides such as dimethyl sulfoxide. , Ethers such as tetrahydrofuran, dioxane, diethyl ether, ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride and trichloroethane, or benzene , Xylene,
Aromatic compounds such as monochlorobenzene and dichlorobenzene can be used.

<Light-Reflecting Layer> The light-reflecting layer is made of a metal, a semimetal, or the like, which has a high reflectance and is hardly corroded.
Specific materials include Au, Ag, Cu, Al, Cr,
Examples thereof include Ni and Al, and Au and Al are preferable. These metals and semi-metals may be used alone or 2
It may be an alloy of more than one kind. As a film forming method, vapor deposition,
Sputtering etc. are mentioned, and the film thickness is 50 to 3
It is 000Å, preferably 100 to 1000Å.

<Protective Layer> The protective layer is intended to protect the light absorbing layer and the light reflecting layer from scratches, dust, dirt, etc., to improve the storage stability of the light absorbing layer and the light reflecting layer, and to improve the reflectance. Used as. A substrate hard coat layer may be provided for the same purpose instead of or together with the protective layer. For these purposes, the materials shown for the undercoat layer can be used. Further, as the inorganic material, SiO,
SiO _2, etc. can also be used, and as the organic material, polymethyl acrylate, polycarbonate, epoxy resin,
Polystyrene, polyester, vinyl resin, cellulose, aliphatic hydrocarbon resin, aromatic hydrocarbon resin, natural rubber, styrene butadiene resin, chloroprene rubber, wax, alkyd resin, dry sleeve, heat-softening resin such as rosin Etc. can be used. Among the above materials, the ultraviolet curable resin having excellent productivity is preferable for the protective film or the hard coat layer on the substrate surface. The thickness of the protective layer or the substrate surface hard coat layer is 0.01 to
30 μm, preferably 0.05 to 10 μm is suitable.

In the present invention, a stabilizer, a dispersant, a flame retardant, a lubricant, an antistatic agent is used for the undercoat layer, the protective layer, and the substrate surface hard coat layer as in the case of the light absorbing layer.
A surfactant, a plasticizer, etc. can be contained.

<Optical interference layer> For the optical interference layer, a polymer blend capable of causing a state change between a compatible state and a phase separated state due to a temperature change is used. However, a combination of a polymer and a monomer may exhibit similar behavior, and such a combination is also included in the polymer blend of the present invention. There are two types of polymer blends, one is a lower-limit critical solution temperature type that has a transparent compatible state at room temperature and undergoes phase separation at a temperature higher than the cloud point and becomes cloudy. There is an upper-limit critical solution temperature type that becomes transparent at the above high temperatures and becomes transparent.

FIG. 3 shows an example of a phase diagram of a lower critical eutectic temperature type polymer blend, in which the horizontal axis represents the volume fraction of one polymer in the polymer blend and the vertical axis represents the temperature. Each point is the cloud point for that composition. The region below the cloud point shows a transparent compatible state, and the region above the cloud point shows a clouded phase separation state. Further, at a temperature lower than Tc in the figure, the polymer blend is uniformly mixed with any composition, so this Tc is referred to as a lower critical solution temperature. The phase diagram of the upper critical eutectic temperature type polymer blend has an upward convex curve, and the upper critical eutectic temperature is similarly determined.

The cloud point of the polymer blend varies depending on the kind of the polymer, its composition, and in the case of the amorphous polymer, the molecular weight distribution and the molecular weight, but it is 60 to 400.
It is preferably in the range of 80 ° C, particularly preferably 80 to
It is in the range of 300 ° C.

The thickness of the light interference layer is set so that a high reflectance is obtained by the multiple reflection interference effect at the interface between the substrate and the light absorption layer and the front and back interfaces of the light interference layer.

A material having a light absorbing ability at the recording laser wavelength can be added to the light interference layer for the purpose of improving sensitivity. The same material as the light absorbing material is used as the material.

Examples of the lower critical solution temperature type polymer blends are as follows. a) Combination of amorphous polymer and amorphous polymer: polystyrene and polyvinyl methyl ether, styrene / acrylonitrile copolymer and poly-ε-caprolactone, styrene / acrylonitrile copolymer and polymethyl methacrylate, polyvinyl nitrate and polymethyl Acrylic rate,
Ethylene / vinyl acetate copolymer and chlorinated rubber, poly-ε
-Caplacton and polycarbonate (bisphenol A
Type), p-chlorostyrene / o-chlorostyrene copolymerization and poly (2,6-dimethyl-1,4-phenylene oxide), polycarbonate (bisphenol A type) and ethylene oxide block copolymer, butylene terephthalate / tetrahydrofuran block Copolymer and polyvinyl chloride, thermoplastic polyurethane (poly-ε-caprolactone soft block) and polyvinyl chloride. b) Combination of crystalline polymer and amorphous polymer: polyvinylidene fluoride and polymethyl acrylate, polyvinylidene fluoride and polyethyl acrylate, polyvinylidene fluoride and polymethyl methacrylate, polyvinylidene fluoride and polyethyl methacrylate, polyvinylidene fluoride and polyvinylmethyl. Ketone. c) Combination of crystalline polymer and crystalline polymer: polyethylene oxide and trioxane, poly-ε-caprolactone and trioxane.

Examples of upper critical solution temperature polymer blends include combinations of amorphous polymers such as polystyrene and polyisoprene, polystyrene and polyisobutene, polypropylene oxide and polybutadiene, and polyisobutene and polydimethylsiloxane. In addition, these polymers can be appropriately copolymerized with other monomers within a range showing the lower limit or the upper limit critical solution temperature.

Next, the operating principle of the present invention will be described. The optical recording medium of the present invention has a structure in which a light interference layer is provided between the light absorption layer and the light reflection layer, and has high reflection due to the multiple interference effect of the front and back interfaces of the substrate, the light absorption layer and the light interference layer. You can get a rate. Therefore, a light absorbing material (complex refractive index n
≧ 1.8, 0.01 ≦ materials not in the range of extinction coefficient k ≦ 0.3), the selection range of the light absorbing material is widened, and the light absorbing material has excellent reliability and recording sensitivity. Can be selected.

Further, by forming the optical interference layer from a polymer blend capable of causing a state change between a compatible state and a phase separated state depending on temperature, the information-modulated laser beam is irradiated to re-form the polymer blend. It is returned to the original state and erased by cooling after raising the temperature above the cloud point. Of course, rewriting is possible.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 On a polymethylmethacrylate plate having a thickness of 1.2 μm,
A photo-absorbing layer was formed by providing 500 μl of a dye of the following structural formula (I) by a vacuum deposition method on a substrate on which a guide groove having a depth of 700 μm, a half width of 0.8 μm, and a track pitch of 1.6 μm was formed with a photopolymer of 50 μm. And Then, as a polymer blend, a lower critical solution temperature type polymer blend of a combination of polyvinylidene fluoride and polymethylmethacrylate was used, and the dimethylacetamide solution was spinner coated to form an optical interference layer of about 2000 liters. Further, Au was vacuum-deposited at about 1000Å to provide a light reflection layer thereon, and the optical recording medium according to the present invention was obtained.

[Chemical 1]

Example 2 An optical recording medium of Example 2 was prepared in the same manner as in Example 1 except that a toluene solution of a polymer blend of a combination of polystyrene and polyvinyl methyl ether was used for forming the light interference layer.

Example 3 In Example 1, a mixture of a polymer blend of a combination of polystyrene and polyvinyl methyl ether and a cyanine dye of the following structural formula (II) was used for forming the light interference layer (mixing weight ratio: polymer blend / dye = 10 / An optical recording medium of Example 3 was prepared in the same manner as in Example 1 except that the toluene solution of 1) was used.

[Chemical 2]

Example 4 An optical recording medium of Example 4 was prepared in the same manner as in Example 1 except that VO-naphthalocyanine was used as the light absorbing material of the light absorbing layer.

Comparative Example 1 An optical recording medium of Comparative Example 1 was prepared in the same manner as in Example 1 except that the optical interference layer was not provided.

The reflectance (λ = 780 nm) of these optical recording media through the substrate was measured with a spectrophotometer. Also,
Linear velocity: 1.3 m / sec, recording laser power: 6 m
W, reproducing laser power: 0.5 mW (λ = 780 n
m), the EMF signal is recorded / reproduced, and JI
It was investigated whether or not a signal satisfying the S CD standard was obtained. For erasing, leave in an oven at 100 ° C for 3 minutes,
Then, the recording characteristics were examined by re-recording and reproducing under the above conditions.
The results are shown in Table 1.

[0030]

[Table 1]

[0031]

ADVANTAGES OF THE INVENTION According to the present invention, by adding a polymer composition capable of causing a change in a compatible state and a phase-separated state due to a change in temperature as a light interference layer to form a medium structure having an increased reflectance, a conventional postscript is added. It becomes possible to use a light-absorbing material that could not be used for the write-once type CD recording medium, and a write-once type CD recording medium with high sensitivity and high reliability can be provided. Further, it becomes possible to use a known highly reliable light absorbing material as a conventional organic write-once CD recording medium as a rewritable CD recording medium capable of writing and erasing.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a configuration of an optical information recording medium of the present invention.

FIG. 2 is a cross-sectional view schematically showing the structure of a conventional write-once CD optical information recording medium.

FIG. 3 is a phase diagram of a lower critical solution temperature type polymer blend used in the present invention.

[Explanation of symbols]

 1 substrate 2 light absorption layer 3 light interference layer (polymer blend layer) 4 light reflection layer 5 protection layer

Claims (6)

[Claims] 1. A light absorbing layer made of an organic dye is provided on a substrate directly or through an undercoat layer, a light interference layer and a light reflecting layer are provided thereon, and a protective layer is further provided thereon as necessary. In an optical information recording medium configured to obtain the reflectance of the medium by utilizing the light reflection interference effect at the interface between the substrate and the light absorption layer and the front and back interfaces of the light interference layer, the light interference layer is An optical information recording medium comprising a polymer blend capable of undergoing a change in a compatible state and a phase separated state due to a temperature change. 2. The optical information recording medium according to claim 1, wherein the reflectance of the medium is 70% or more. 3. The optical information recording medium according to claim 1, wherein the extinction coefficient of the complex refractive index of the light absorption layer is 0.3 or more. 4. The optical information recording medium according to claim 1, wherein the polymer blend is an upper critical eutectic temperature type polymer blend or a lower critical eutectic temperature type polymer blend. . 5. The optical information recording medium according to claim 1, wherein a light absorbing substance is contained in the polymer blend. 6. An optical information recording medium according to any one of claims 1 to 5 is used to irradiate a laser beam modulated informationally to cause a change in a compatible state and a phase separated state due to a temperature change. The recording / erasing method is characterized in that the polymer blend is heated to the cloud point or higher again, and then gradually cooled to the original state to be erased.