OPTICAL RECORDING MEDIUM

Abstract: An optical recording medium having a recording layer provided on a substrate, said recording layer comprising an organic thin film containing at least one diazulenium salt compound represented by the formula [I], [II] or [III], and a recording method using it.

Description: This invention relates to an optical recording medium on which information can be written by means of a laser beam, for example a semiconductor laser beam. It also relates to a recording method and a reading method in which the aforesaid optical recording medium is used. The optical recording medium may be incorporated into an optical disc or an optical card. Generally speaking, an optical recording medium such as an optical disc or optical card can record information at high density by formation of small pits having for example diameters of about 1 µm. These pits when present on a thin recording layer provided on a substrate having spiral, circular or linear grooves can be detected optically. Information may be written onto the recording layer by scanning over the surface of the recording layer a converged laser beam so that the recording layer absorbs energy from the laser and forms optically detectable pits. For example, in the heat mode recording system, the recording layer absorbs heat energy and can form small concave pits as a result of local evaporation or melting. In a different heat mode recording system, absorption of laser energy irradiated onto the recording medium results in local formation of pits which have optically detectable density differences. A known medium for recording and reproducing information in the above mentioned manner comprises a substrate, a metal reflective layer and a recording layer containing a dye. The optical recording medium is formed so that the laser beam incident on the dye-containing recording layer can reach the metal reflective layer, and the reflected light can be easily detected. In this case, the metal reflective layer is present to increase the amount of reflected light which is insufficient when only the recording layer is present. However, the presence of a metal reflective layer increases the complexity of the optical recording medium, and also increases its cost. The use of a high reflectance organic dye thin film as the recording layer can solve the above problems. For example an azulene type dye as disclosed in US patent 4548886 when used in the recording layer exhibits great absorption of light from the laser beam, provides a light absorbent reflective film, and exhibits a metallic lustre (reflectance: 10-50%). The resulting organic recording medium both permits laser recording and reflective reading. Where a semiconductor laser having an oscillation wavelength of 700 to 800 nm is used as the laser light source, it is possible to miniaturise and reduce the cost of the device. Patent specification EP-A-0264198 which is relevant only under Article 54 (3) EPC discloses an optical recording medium exhibiting good storage stability in which the recording layer contains an organic dye and a metal chelate compound. As specific example, an azulenium salt compound having an azulene ring to which a divalent organic residue is attached is disclosed. An object of the present invention is to provide an optical recording medium having an organic thin film which exhibits high sensitivity and is also stable to heat and light, which exhibits high absorption and is highly reflective in the wavelength of oscillation of the laser beam, and particularly which exhibits an absorption band on the longer wavelength side. More specifically, according to one aspect of the present invention, there is provided an optical recording medium having a recording layer provided on a substrate, said recording layer comprising an organic thin film containing at least one diazulenium. salt compound represented by the formula [I], [II] or [III] shown below. wherein R₁ - R₇ and R₁' - R₇' each represent hydrogen atom, a halogen atom or monovalent organic residue, or at least one combination of the combinations of R₁ and R₂, R₂ and R₃, R₃ and R₄, R₄ and R₅, R₅ and R₆, R₆ and R₇, R₁' and R₂', R₂' and R₃', R₃' and R₄', R₄' and R₅', R₅' and R₆', R₆' and R₇' may form a substituted or an unsubstituted fused ring; A represents a monovalent organic residue conjugated with the diazulenium salt nucleus and z ⊖ represents an anion residue. According another aspect of the present invention, there is provided a recording method comprising using an optical recording medium having a recording layer provided on a substrate, said recording layer comprising an organic thin film containing at least one diazulenium salt compound represented by the formula [I], [II] or [III] shown above and performing recording by irradiating a semiconductor laser on said recording layer. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1, Fig. 2, Fig. 3 and Fig. 4 each represent a sectional view showing an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION In the diazulenium salt compounds represented by the formulae [I], [II] and [III] contained in the recording layer in the present invention, R₁ - R₇ and R₁' - R₇' each represent a hydrogen atom, a halogen atom (chlorine, bromine, iodine atom) or monovalent organic residue. Such monovalent organic residue can be selected from a wide scope of compounds, particularly there may be included alkyl groups (methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-amyl, n-hexyl, n-octyl, 2-ethylhexyl, t-octyl, etc.), alkoxy groups (methoxy, ethoxy, propoxy, butoxy, etc.), substituted or unsubstituted aryl groups (phenyl, tolyl, xylyl, ethylphenyl, methoxyphenyl, ethoxyphenyl, chlorophenyl, nitrophenyl, dimethylaminophenyl, α-naphthyl, β-naphthyl, etc.) substituted or unsubstituted aralkyl groups (benzyl, 2-phenylethyl, 2-phenyl-1-methylethyl, bromobenzyl, 2-bromophenylethyl, methylbenzyl, methoxybenzyl, nitrobenzyl), acyl groups (acetyl, propionyl, butylyl, valeryl, benzoyl, toluoyl, naphthoyl, phthaloyl, furoyl, etc.), substituted or unsubstituted amino groups (amino, dimethylamino, diethylamino, dipropylamino, acetylamino, benzoylamino, etc.), substituted or unsubstituted styryl groups (styryl, dimethylaminostyryl, diethylaminostyryl, dipropylaminostyryl, methoxystyryl, ethoxystyryl, methylstyryl, etc.), nitro groups, hydroxy groups, carboxyl groups, cyano groups or substituted or unsubstituted arylazo groups (phenylazo, α-naphthylazo, β-naphthylazo, dimethylaminophenylazo, chlorophenylazo, nitrophenylazo, methoxyphenylazo, tolylazo, etc.). Of the combinations of R₁ and R₂, R₂ and R₃, R₃ and R₄, R₄ and R₅, R₅ and R₆, R₆ and R₇, R₁' and R₂', R₂' and R₃', R₃' and R₄', R₄' and R₅', R₅' and R₆', R₆' and R₇', at least one combination may also form a substituted or unsubstituted fused ring. The fused ring may be a 5-, 6- or 7-membered fused ring, including aromatic rings (benzene, naphthalene, chlorobenzene, bromobenzene, methylbenzene, ethylbenzene, methoxybenzene, ethoxybenzene, etc.), heterocylic rings (furan ring, benzofuran ring, pyrrole ring, thiophene ring, pyridine ring, quinoline ring, thiazole ring, etc.), aliphatic rings (dimethylene, trimethylene, tetramethylene, etc.). Z ⊖ represents an anion residue. R₁ - R₇ and R₁' - R₇' may either the same or different. A represents a monovalent organic residue. Specific examples of azulenium salts containing such A may include those represented by the following formulae (1) - (11). In the formulae, Q ⊕ represents diazulenium salt nucleus shown below, and the right side excluding Q ⊕ represents A. In the formula, R₁ - R₇ and R₁' - R₇' have the same definitions as defined above. In the formula, R₁ - R₇ and R₁' - R₇' have the same definitions as defined above. In the formula, R₁'' - R₇'' have the same definitions as R₁ - R₇ defined above. Z ⊖ represents an anion residue, for example, anions such as chloride ion, bromide ion, iodide ion, perchlorate ion, nitrate ion, benzene sulfonate ion, p-toluenesulfonate ion, methyl sulfate ion, ethyl sulfate ion, propyl sulfate ion, tetrafluoroborate ion, tetraphenylborate ion, hexafluorophosphate ion, benzene sulfinate ion, acetate ion, trifluoroacetate ion, propionacetate ion, benzoate ion, oxalate ion, succinate ion, malonate ion, oleinate ion, stearate ion, citrate ion, monohydrogen diphosphate ion, dihydrogen monophosphate ion, pentachlorostannate ion, chlorosulfonate ion, fluorosulfonate ion, trifluoromethanesulfonate ion, hexafluoroarsenate ion, hexafluoroantimonate ion, molybdenate ion, tungstate ion, titanate ion, zirconate ion, etc R₈ and R₉ each represent hydrogen atom, a halogen atom, nitro group, cyano group, an alkyl group (methyl, ethyl, propyl, butyl, etc.) or an aryl group (phenyl, tolyl, xylyl, etc.) and n represents 0, 1 or 2. In the formula, R₁ - R₇ and R₁' - R₇' have the same definitions as defined above, and the diazulenium salt nucleus represented by Q ⊕ and the diazulene salt nucleus on the right side in the formula (4) may be either symmetric or asymmetric. R₈, R₉ and Z ⊖ have the same definitions as defined above, and n represents 0, 1 or 2. In the formula, R₁ - R₇, R₁' - R₇', R₁'' - R₇'' and Z ⊖ have the same definitions as defined above. The azulemium salt nucleus represented by Q ⊕ and the diazulene salt nucleus on the right side in the formula (6) may be either symmetric or asymmetric. In the formula, R₁ - R₇, R₁' - R₇', R₈ and Z ⊖ have the same definitions as defined above. The azulemium salt nucleus represented by Q ⊕ and the diazulene salt nucleus on the right side in the formula (7) may be either symmetric or asymmetric. D represents a divalent hydrocarbon group (for example, -CH₂-CH₂-, -CH₂-CH₂-CH₂-, -CH=CH-, etc.) for forming a substituted or unsubstituted 5- or 6-membered ring, and may be also fused to these 5- or 6-membered benzene ring, naphthalene ring, etc. n and m represent 1; 2 or 3. In the formulae (8), (9), X₁ represents a group of non-metal atoms necessary for completing a nitrogen containing heterocyclic ring such as pyridine, thiazole, benzothiazole, naphthothiazole, oxazole, benzooxazole, naphthooxazole, imidazole. benzimidazole naphthoimidazole, 2-quinoline, 4-quinoline, isoquinoline or indole, and such heterocyclic group may be substituted with halogen atoms (chlorine, bromine, iodine atoms), alkyl groups (methyl, ethyl, propyl, butyl, etc.), aryl groups (phenyl, tolyl, xylyl, etc.), and others. R10 represents an alkyl group (methyl, ethyl, propyl, butyl, etc.), a substituted alkyl group (2-hydroxyethyl, 2-methoxyethyl, 2-ethoxyethyl, 3-hydroxypropyl, 3-methoxypropyl, 3-ethoxypropyl, 3-chloropropyl, 3-bromopropyl, 3-carboxypropyl, etc.), a cyclic alkyl group (cyclohexyl, cyclopropyl), allyl, aralkyl groups (benzyl, 2-phenylethyl, 3-phenylpropyl, 4-phenylbutyl, α-naphthylmethyl, β-naphthylmethyl), a substituted aralkyl group (methylbenzyl, ethylbenzyl, dimethylbenzyl, trimethylbenzyl, chlorobenzyl, bromobenzyl, etc.), an aryl group (phenyl, tolyl, xylyl, α-naphthyl, β-naphthyl) or a substituted aryl group (chlorophenyl, dichlorophenyl, trichlorophenyl, ethylphenyl, methoxyphenyl, dimethoxyphenyl, aminophenyl, nitrophenyl, hydroxyphenyl, etc.). m represents 0, 1 or 2, and R₈, R₉, R₁₁ and Z ⊕ have the same definitions as defined above. In the formula, R₁₀ represents a substituted or unsubstituted aryl group (phenyl, tolyl, xylyl, biphenyl, α-naphthyl, β-naphthyl, anthralyl, pyrenyl, methoxyphenyl, dimethoxyphenyl, trimethoxyphenyl, ethoxyphenyl, diethoxyphenyl, chlorophenyl, dichlorophenyl, trichlorophenyl, bromophenyl, dibromophenyl, tribromophenyl, ethylphenyl, diethylphenyl, nitrophenyl, aminophenyl, dimethylaminophenyl, diethylaminophenyl, dibenzylaminophenyl, dipropylaminophenyl, morpholinophenyl, piperidinylphenyl, pyperadinophenyl, diphenylaminophenyl, acetylaminophenyl, benzoylaminophenyl, acetylphenyl, benzoylphenyl, cyanophenyl, etc.). Z ⊖ has the same definition as defined above. m represents 0, 1 or 2. In the formula, R₁₃ represents a monovalent heterocyclic group derived from a heterocyclic ring such as furan, thiophene, benzofuran, thionaphthene, dibenzofuran, carbazole, phenothiazine, phenoxazine, pyridine, etc., Z ⊖ has the same definition as defined above. m represents 0, 1 or 2. In the formula, R₁₄ represents an alkyl group (methyl, ethyl, propyl, butyl, etc.) or a substituted or unsubstituted aryl group (phenyl, tolyl, xylyl, biphenyl, ethylphenyl, chlorophenyl, methoxyphenyl, ethoxyphenyl, nitrophenyl, aminophenyl, dimethylaminophenyl, diethylaminophenyl, acetylaminophenyl, α-naphthyl, β-naphthyl, anthralyl, pyrenyl, etc.). R₁₂ and Z ⊖ have the same definitions as defined above. m represents 0, 1 or 2. In the formula, X₂ represents a group of atoms necessary for completing pyran, thiapyran, selenapyran, benzopyran, benzothiapyran, benzoselenapyran, naphthopyran, naphtothiapyran or naphthoselenapyran which may be also substituted. ℓ is 0 or 1. Y represents a sulfur atom, an oxygen atom or selenium atom. R₁₄ and R₁₅ each represent hydrogen atom (methyl, ethyl, propyl, butyl, etc.), an alkoxy group (methoxy, ethoxy, propoxy, butoxy, etc.), a substituted or unsubstituted aryl group (phenyl, tolyl, xylyl, chlorophenyl, biphenyl, methoxyphenyl, etc.), a substituted or unsubstituted styryl group (styryl, p-,methylstyryl, o-chlorostyryl, p-methoxystyryl, etc.), a substituted or unsubstituted 4-phenyl-1,3-butadienyl group (4-phenyl-1,3-butadienyl, 4-(p-methylphenyl)-1,3-butadienyl, etc.) or a substituted or unsubstituted heterocyclic group (quinolyl, pyridyl, carbazolyl, furyl, etc.). R₈, R₉, m and Z ⊖ have the same definitions as defined above. In the following, specific examples of the diazulenium salt compound used in the present invention are enumerated below. Exemplary compounds represented by the above formula (1) - Exemplary compounds represented by the above formula (2) Exemplary compounds represented by the above formula (3) Exemplary compounds represented by the above formula (4)- Exemplary compounds represented by the above formula (5) - Exemplary compounds represented by the formula (6)- Exemplary compounds represented by the above formula (7) - Exemplary compounds represented by the above formulas (8) and (9) - Exemplary compounds represented by the above formula (10)- Exemplary compounds represented by the above formula (11) - Exemplary compounds represented by the above formula (12) Exemplary compounds represented by the above formula (13) Such dyes have not only good solubility in organic solvents but also exhibit absorption peaks with large coefficient of absorption in the near-infrared region, whereby good characteristics for optical recording medium can be obtained. To describe now about the synthetic method of the diazulenium compound to be used in the present invention, the compounds represented by the formulae (1) and (2) can be readily obtained by allowing 1,1-azulenylmethane compounds to react with a squalic acid or a croconic acid in a suitable solvent. The compound represented by the formula (3) can be obtained by allowing 1,1-azulenylmethane compound to react with 1-formylazulene compound, 3-azulene-1'-prophenealdehyde compound or 3-azulene-1'-pentadienealdehyde compound in a suitable solvent in the presence of a strong acid. The compound represented by the formula (4) is obtained by mixing 1,1-azulenylmethane compound with orthoacetals, orthoesters, malondialdehydes or glutacondialdehydes in a suitable solvent in the presence of a strong acid. The compound represented by the formula (5) is obtained by heating 1,1-azulenylmethane compound and glyoxal in a suitable solvent in the presence of a strong acid. The compound represented by the formula (6) is obtained by heating 1,1-bis-[1-azulenyl]-ethane compound and 1,3-diformylazulene compound in a suitable solvent in the presence of a strong acid. The compound represented by the formula (7) is obtained by allowing 1,1-azulenylmethane compound to react with cyclopentanes or cyclohexanes in a suitable solvent in the presence of a strong acid. The compound represented by the formula (8) is obtained by allowing 1,1-bis-[1-azulenyl]-ethane to react with a compound represented by the following formula (14) in a suitable solvent in the presence of a strong acid. In the formula, X₁, R₈, R₉, R₁₀ and m, n have the same definitions as defined above. When m = 0, it can be obtained by allowing a compound represented by the following formula (15) to react with a compound represented by the following formula (16) by use of a suitable solvent. In the formula, R₁ - R₇ and R₁' - R₇' have the same definitions as defined above. In the formula, X₁, R₁₀, Z⁻ and n have the same definitions as defined above. When m = 1 or 2, the compound represented by the formula (9) is obtained by allowing 1,1-bis[1-azulenyl]-ethane to react with a compound represented by the following formula (17) in a suitable solvent in the presence of a strong acid. In the formula, X₁, A, R₈, R₉, R₁₀, R₁₁ and m, n have the same definitions as defined above. When m = 0, it can be obtained by allowing a compound represented by the above formula (15) to react with a compound represented by the following formula (18) in a suitable solvent. In the formula, X₁, A, R₁₀, R₁₁, Z ⊖ and n have the same definitions as defined above. The compounds represented by the formula (10), (11) or (12) are obtained by mixing 1,1-azulenylmethane or 1,1-bis[1-azulenyl]-ethane with corresponding aldehyde compounds in a suitable solvent in the presence of a strong acid. The compound represented by the formula (13), when m = 1 or 2, is obtained by allowing 1,1-bis[1-azulenyl]-ethane to react with a compound represented by the following formula (19) in a suitable solvent in the presence of a strong acid. In the formula, X₂, Y, R₈, R₉, R₁₄, R₁₅, m and 1 have the same definitions as defined above. When m = 0, it can be obtained by allowing a compound represented by the above formula (15) to react with a compound represented by the following formula (20) in a suitable solvent. In the formula, X₂, Z ⊖ , R₁₄, R₁₅, and ℓ have the same definitions as defined above. As the reaction solvent to be used, there may be employed alcohols such as ethanol, butanol, benzyl alcohol, etc.; nitriles such as acetonitrile, propionitrile, etc.; organic carboxylic acids such as acetic acid; acid anhydrides such as acetic anhydride; alicyclic ethers such as dioxane, tetrahydrofuran, etc. and others. Also, butanol, benzyl alcohol, etc. can be also mixed with an aromatic hydrocarbon such as benzene. The temperature during the reaction can be selected from the range of 0 °C to the boiling point. The optical recording medium of the present invention can be made to have a structure as shown in Fig. 1. The optical recording medium shown in the same figure can be formed by providing a recording layer 2 which is an organic thin film containing a compound represented by the above formula [I], [II] or [III] on a substrate 1. Such recording layer 2 can be formed by vacuum vapor deposition of a compound represented by the above formula [I], [II] or [III] or coating of a coating solution containing such compound dissolved or dispersed in an organic solvent. Also, in forming recording layer 2, two or more kinds of the compounds represented by the above formula [I], [II] or [III] can be used in combination, and further other dyes than the compounds of the above formula [I], [II] or [III] may be dispersed by mixing or laminated on the layer comprising the compound represented by the above formula [I], [II] or [III]. Examples of such other dyes may include diazulene type, azulene type, polymethine type, pyrylium type, squalium type, croconium type, triphenylmethane type, xanthene type, anthraquinone type, cyanine type, phthalocyanine type, dioxazine type, tetrahydrocholine type, triphenothiazine type, phenanthrene type, metal chelate complex type dyes or metal and metal compound such as Al, Te, Bi, Sn, In, Se, SnO, TeO₂, As, Cd, etc. Also, the compound represented by the above formula [I], [II] or [III] may be also contained as dispersed or dissolved in a binder. Examples of the binder may include cellulose esters such as nitrocellulose, cellulose phosphate, cellulose sulfate, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose myristate, cellulose palmitate, cellulose acetate propionate, cellulose acetate butyrate, etc.; cellulose ethers such as methyl cellulose, ethyl cellulose, propyl cellulose, butyl cellulose, etc.; vinyl resins such as polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, polyvinyl pyrrolidone, etc.; copolymer resins such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, etc.; acrylic resins such as polymethyl methacrylte, polymethyl acrylate, polybutyl acrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyacrylonitrile, etc.; polyesters such as polyethylene terephthalate, etc.; polyallylate resins such as poly(4,4'-isopropylidenediphenylene-co-1,4-cyclohexylenedimethylenecarbonate), poly(ethylenedioxy-3,3'-phenylenethiocarbonate), poly(4,4'-isopropylidenediphenylenecarbonate-co-terephthalate), poly(4,4'-isopropylidenediphenylenecarbonate), poly(4,4'-sec-butylidenediphenylenecarbonate), poly(4,4'-isopropylidenediphenylenecarbonate-block-oxyethylene), etc.; or polyamides, polyimides, epoxy resins, phenol resins, polyolefins such as polyethylene, polypropylene, chlorinated polyethylene, etc.; and so on. Also, in the recording layer 2, surfactants, antistatic agents, stabilizers, dispersing agents, flame retardants, lubricants, plasticizers, etc. may be contained. Particularly, when an aminium salt compound or diimmonium salt compound as disclosed in Japanese Patent Laid-Open Application No. 60-236131 is incorporated in the recording layer in addition to the diazulenium salt compound as described above, recording and reproducing characteristics and storage stability can be further improved. The aminium salt compound and the diimmonium salt compound to be used in the present invention are represented by the following formulae [IV], [V], respectively. In the formulae [IV], [V], R₁₆ represents hydrogen atom or an alkyl group (e.g. methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, t-butyl, n-amino, t-amyl, n-hexyl, n-octyl, t-octyl and C₉₋₁₂ alkyl groups, etc.), and further other alkyl groups, for example, a substituted alkyl group (e.g. 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-acetoxyethyl, carboxymethyl, 2-carboxyethyl, 3-carboxypropyl, 2-sulfoethyl, 3-sulfopropyl, 4-sulfobutyl, 3-sulfatepropyl, 4-sulfatebutyl, N-(methylsulfonyl)-carbamylmethyl, 3-(acetylsulfamyl)propyl, 4-(acetylsulfamyl)butyl, etc.), a cyclic alkyl group (e.g. cyclohexyl, etc.), an alkenyl group (vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, dodecynyl, prenyl, etc.), an aralkyl group (e.g. benzyl, phenetyl, α-naphthylmethyl, β-naphthylmethyl, etc.), a substituted aralkyl group (e.g. carboxybenzyl, sulfobenzyl, hydroxybenzyl, etc.). A₂ represents or X ⊖ represents an anion. These aminium salt compounds and diimmonium salt compounds can be synthesized according to the synthetic methods disclosed in U.S. Patent Nos. 3,484,467 and 3,637,769. In the following, representative examples of the aminium salt compounds represented by the above formula [IV] are enumerated. In the following, representative examples of the diimmonium salt compounds represented by the above formula [V] are enumerated. When the aminium salt compound of the above formula [IV] or the diimmonium salt compound of the formula [V] is added, the amount added may be 1 to 60 % by weight, preferably 5 to 40 % by weight based on the total solid components as the standard in the recording layer 2 . The organic solvent capable of being used during coating of the recording layer 2, which may differ depending on whether a dispersed state or dissolved state is formed, may generally include alcohols such as methanol, ethanol, isopropanol, diacetone alcohol, etc.; ketones such as acetone, methyl ethyl, ketone, cyclohexanone, etc.; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, etc.; sulfoxides such as dimethylsulfoxide; ethers such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, etc.; esters such as methyl acetate, ethyl acetate, butyl acetate, etc.; aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, trichloroethylene, etc.; aromatics such as benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, etc.; or aliphatic hydrocarbons such as n-hexane, cyclohexane, ligroin, etc. For coating, there may be employed such methods as dip coating, spray coating, spinner coating, bead coating, Myer bar coating, blade coating, roller coating, curtain coating, etc. The recording layer 2 may have a dry film thickness of 5 nm (50 Å) to 100 µm, preferably 200 Å to 1 µm. As the substrate 1, there can be employed plastics such as polyester, acrylic resin, polycarbonate resin, polyolefin resin, phenol resin, epoxy resin, polyamide, polyimide and so forth, glass or metals. Also, the present invention can be made to have a constitution provided with a subbing layer 3 and/or a protective layer 4, as shown in Fig. 2 to Fig. 4. The subbing layer is provided for the purpose of (a) improvement of adhesiveness, (b) as the barrier against water or gas, (c) improvement of storage stability of the recording layer, (d) improvement of reflectance, (e) protection of substrate from the solvent, (f) formation of pregroove and so forth. For the purpose of (a), various materials such as polymeric materials, for example, ionomer resin, amide type resin, vinyl type resin, natural polymer, silicone, liquid rubber, etc. or silane coupling agents and other various materials can be used; for the purposes of (b) and (c), in addition to the above polymeric materials, inorganic compounds such as SiO2, MgF₂, SiO, TiO₂, ZnO, TiN, SiN, etc., metals or semi-metals such as Zn, Cu, S, Ni, Cr, Ge, Se, Cd, Ag, Al, etc. can be used; for the purpose of (d), metals such as Al, Ag, etc. or organic thin films having metallic luster such as diazulene dye, methine dye, etc. can be used; and for the purposes of (e) and (f), UV-ray curable resins, thermosetting resins, thermoplastic resins, etc. can be used. The subbing layer may have a film thickness of 5 nm (50Å) to 100µm, preferably 20 nm (200 Å) to 30 µm. On the other hand, the protective layer is provided for the purpose of protecting from flaw, dust, contamination, etc., improving storage stability of the recording layer and improving reflectance, and the same material as for the subbing layer can be used for the material. The protective layer should have a film thickness of 5 nm (50 Å) or more, preferably 30 µm or more. In the subbing layer and/or the protective layer, the compound of the above formula [I], [II] and/or [III] of the present invention may be also contained. Also, in the subbing layer and the protective layer, stabilizers, dispersing agents, flame retardants, lubricants, antistatic agents, surfactants, plasticizers and so forth may be also incorporated, and the compound of the above formula [IV] and/or [V] may be also contained. Further, as another constitution of the optical recording medium according to the present invention, it can be also made the so-called air sandwich structure in which two sheets of the recording medium with a constitution shown in Fig. 1 to Fig. 4 are used (or only as one sheet thereof is a substrate) and the recording layer 2 composed of an organic thin film is arranged inner side thereof and sealed through a spacer, or alternatively it can be made the so-called closely adhered structure (plastered structure) in which they are adhered through a protective layer 4 without use of a spacer. The optical recording medium of the present invention can be recorded also by irradiation of a gas laser such as argon laser (oscillated wavelength: 488 nm), helium-neon laser (oscillated wavelength: 633 nm), helium-cadmium laser (oscillated wavelength: 442 nm) and so forth. Also, recording is possible by irradiation of a light with 1/2 wavelength of the laser beam by use of SHG element and the like but preferably the recording method by irradiation of a laser beam having oscillated wavelength in the near-infrared or infrared region such as a laser having a wavelength of 650 nm or more, particularly gallium-aluminium-arsenic semiconductor laser (oscillated wavelength: 830 nm) and the forth is suitable. Also, for reading, the laser as described above can be used. In this case, writing and reading can be done with a laser with the same wavelength, or they can be done with lasers of different wavelengths. As described above, by use of the optical recording medium according to the present invention, an optical recording medium having an organic thin film, which has high sensitivity and is also stable to heat and light, can be obtained. Examples The present invention is described in detail below by referring to Examples, but the present invention is not limited thereto. Example 1 An epoxy-acrylate type UV-ray curable resin layer of a thickness of 50 µm was formed on a polymethyl methacrylate (hereinafter abbreviated as PMMA) substrate of 130 mm in diameter and 1.2 mm in thickness, and a pregroove of 70 nm (700 Å) in depth was provided by use of the 2P method (photo-polymer method). After a solution of 2 parts by weight of the above compound No. (17) dissolved in 98 parts by weight of dichloroethane was applied thereon, the coating was dried to obtain an organic thin film recording layer of 80 nm (800 Å). The thus prepared optical recording medium was mounted on a turn table, and with the turn table being rotated by a motor at 1800 rpm, an information was written on the organic thin film recording layer with a spot size of 1.5 µm in diameter, a recording power of 6 mW and a recording frequency of 2 MHz by use of an oscillated wavelength of 830 nm from the substrate side, and reproduced with a reading power of 0.8 mW, and the reproduced waveform was subjected to spectral analysis (scanning filter band width: 30 kHz) to measure a C/N ratio (carrier/noise ratio). Next, the C/N ratio after the portion of the same recording medium recorded under the above measuring conditions was read repeatedly for 10⁵ times was measured. Further, the transmittance (T (%): measured at 830 nm) and C/N ratio were measured after the environmental storage stability test was performed by leaving the same recording medium prepared under the above conditions to stand under the conditions of 60 °C, 95 %RH for 2000 hours. Also, the transmittance (T (%): measured at 830 nm) and C/N ratio were measured after the light-resistant stability test was performed by irradiating a xenon lamp light of 1000 W/m2 (300 - 900 nm) on the same recording medium for 70 hours. Examples 2 - 15 Recording media were prepared according to the same method as in Example 1 by changing the compound No. (17) used in Example 1 to the respective compounds shown in Table 2, to prepare optical recording media of Examples 2 - 15, respectively. The optical recording media of the above Examples 2 - 15 were measured according to the same methods as in Example 1. Examples 16, 17 Each of the following compounds No. (73) and (74) and the above compound No. (17) at a weight ratio of 1 : 1 were mixed with dichloroethane, the mixture was applied according to the same method as in Example 1 to provide a recording layer which was an organic thin film with a dry film thickness of 75nm (750 A) and prepare an optical recording media of Examples 16, 17, respectively. The optical recording media of Examples 16, 17 thus prepared were subjected to the same measurements according to the same methods as in Example 1. Comparative Example 1 An optical recording medium was prepared and measured according to the same methods as in Example 16 except for omitting the compound No. (17) used in Example 16. The above results are shown in Table 1. Example 18 A mixture obtained by mixing 2 parts by weight of the above compound No. (2) and 1 part by weight of a nitrocellulose resin (OH-less Lacquer, produced by Daiseru Kagaku K.K.) in 97 parts by weight of methyl ethyl ketone was applied by the spinner coating method on a PMMA substrate of 130 mm in diameter and 1.2 mm in thickness provided with a pregroove to obtain an organic thin film recording layer with a dry film thickness of 100 nm (1000 Å). The optical recording medium thus prepared was subjected to measurement according to the same methods as in Example 1. Examples 19 - 25 By changing the compound No. (2) used in Example 18 to the above compounds No. (16), (26), (31), (36), (44), (53) and (66) respectively, recording media were prepared according to the same method as in Example 18 to prepare optical recording media of Examples 19 - 25, respectively. The optical recording media of the above Examples 19 - 25 were measured according to the same method as in Example 18. Examples 26, 27 The above compounds No. (1) and No. (22) in amounts of 500 mg were placed in a molybdenum boat for vapor deposition, and after evacuated to 1 x 10⁻⁶ mmHg, vapor deposition was effected on a PMMA substrate of 130 mm in diameter and 1.2 mm in thickness. An organic thin film recording layer of 95nm 950 Å was formed while controlling the heater so that the pressure within the vacuum chamber was not elevated to 10⁻⁵ mmHg or higher during vapor deposition, to prepare optical recording media of Examples 26, 27, respectively. The optical recording media thus prepared were measured according to the same methods as in Example 1. The above results are shown in Table 2. Example 28 On a substrate of a polycarbonate (hereinafter abbreviated as PC) of wallet size with a thickness of 0.4 mm, a pregroove was provided by the hot press method and a solution of the above compound No. (26) mixed in 96 parts by weight of diacetone alcohol was applied by the bar coating method, followed by drying to obtain an organic thin film recording layer of 90 nm (900 Å). Further, on the recording layer through an ethylene-vinyl acetate dry film, a PC substrate of wallet size with a thickness of 0.3 mm was provided by the hot roll method to prepare an optical recording medium of Example 28 having a closely adhered structure. The optical recording medium of Example 28 thus prepared was mounted on a stage driven in the X-Y direction, and information was written on the organic thin film recording layer from the side of the PC substrate with a thickness of 0.4 mm by use of a semiconductor layer of an oscillated wavelength of 830 nm in the Y-axis direction with a spot size of 30 µm in diameter, a recording power of 4.0 mW, and a recording pulse of 80 µsec, and reproduced with a reading power of 0.4 mW, and its contrast ratio ((A - B)/A: A → intensity at the unrecorded portion, B → signal intensity at the recorded portion) was measured. Further, the same recording medium prepared under the above conditions was subjected to the environmental storage stability test and light-resistant stability test under the same conditions as in Example 1, and transmittance and the contrast ratio thereafter were measured. The results are shown in Table 3. Example 29 On a PMMA substrate of 130 mm in diameter and 1.2 mm in thickness, an epoxy-acrylate type UV-ray curable resin layer was provided to a thickness of 50 µm, and a pregroove of 70 nm (700 Å) in depth was provided by use of the 2P method (photo-polymer method). After a solution of the above diazulenium salt compound No. (17) and the above aminium salt compound No. A-9 at a weight ratio of 80 : 20 dissolved in 1,2-dichloroethane was applied thereon by the spinner coating method, the coating was dried to obtain an organic thin film recording layer of 85 nm (850 Å). The thus prepared optical recording medium was mounted on a turn table, and with the turn table being rotated by a motor at 1800 rpm, an information was written on the organic thin film recording layer with a spot size of 1.5 µm in diameter, a recording power of 6 mW and a recording frequency of 2 MHz by use of a semiconductor laser of an oscillated wavelength of 830 nm from the substrate side, and reproduced with a reading power of -1.0 mW, and the reproduced waveform was subjected to spectral analysis (scanning filter band width: 30 kHz) to measure a C/N ratio (carrier/noise ratio). Next, the C/N ratio after the portion of the same recording medium recorded under the above measuring conditions was read repeatedly for 10⁶ times was measured. Further, the reflectance (R (%): measured at 830 nm) and C/N ratio were measured after the environmental storage stability test was performed by leaving the same recording medium prepared under the above conditions to stand under the conditions of 60 °C, 90 %RH for 3000 hours. Also, the reflectance (R (%): measured at 830 nm) and C/N ratio were measured after the light-resistant stability test was performed by irradiating a xenon lamp light of 1000 W/m² (300 - 900 nm) on the same recording medium for 100 hours. Examples 30 - 36 By changing the diazulenium salt compound (AZ) and the aminium salt compound (A) used in Example 29 to the combinations shown below in Table 4, recording media were prepared according to the same method as in Example 29 to provide optical recording media of Examples 30 - 36, respectively. The optical recording media of the above Examples 30 - 36 were measured according to the same methods as in Example 1. Examples 37 - 40 A mixture of 4 parts by weight of a mixture according to the combination of the diazulenium salt compound (AZ) and the aminium salt compound (A) shown below in Table 5 and 1 part by weight of a nitrocellulose resin (OH-less Lacquer, produced by Daiseru Kagaku K.K.) mixed in 95 parts by weight of methyl ethyl ketone was applied by the spinner coating method on a polycarbonate substrate of 130 mm in diameter and 1.2 mm in thickness provided with a pregroove to obtain an organic thin film recording layer with a dry film thickness of 95 nm (950 Å). The optical recording medium thus prepared was measured according to the same methods as in Example 29. Example Diazulenium Compound (AZ) Aminium Salt Compound (A) Weight Ratio (AZ:A) 37 (16) A-11 70:30 38 (18) A-4 75:25 39 (27) A-13 85:15 40 (34) A-18 80:20 The above results are shown in Table 6. Examples 41 - 44 On a substrate of a polycarbonate (hereinafter abbreviated as PC) of wallet size with a thickness of 0.4 mm, a pregroove was provided by the hot press method and a solution of the azulenium salt compound and the aminium salt compound shown below in Table 7 mixed in diacetone alcohol was applied by the bar coating method, followed by drying to obtain an organic thin film recording layer of 85 nm (850 Å). Further, on the recording layer through an ethylene-vinyl acetate dry film, a PC substrate of wallet size with a thickness of 0.3 mm was provided by the hot roll method to prepare optical recording media having a closely adhered structure. The optical recording media of Examples 41 - 44 thus prepared were mounted on a stage driven in the X-Y direction, and information was written on the organic thin film recording layer from the side of the PC substrate with a thickness of 0.4 mm by use of a semiconductor laser of an oscillated wavelength of 830 nm in the Y-axis direction with a spot size of 30 µm in diameter, a recording power of 4.0 mW, and a recording pulse of 80 µsec, and reproduced with a reading power of 0.4 mW, and its contrast ratio ((A - B)/A: A → intensity at the unrecorded portion, B → signal intensity at the recorded portion) was measured. Further, the same recording media prepared under the above conditions were subjected to the environmental storage stability test and light-resistant stability test under the same conditions as in Example 29, and reflectance and the contrast ratio thereafter were measured. The results are shown in Table 8. Examples 45 - 51 Recording media were prepared by the same method as in Example 1 according to the combinations shown in Table 9 by changing the aminium salt compound used in Example 1 to the diimmonium salt compound, to prepare optical recording media of Examples 45 - 51, respectively. The above optical recording media of the above Examples 45 - 51 were measured according to the same method as in Example 1. Examples 52 - 55 Recording media were prepared by the same method as in Example 1 according to the combinations shown in Table 10 by changing the aminium salt compound (A) used in Example 37 to the diimmonium salt compound (D) to obtain optical recording media of Examples 52 - 55, respectively. The above optical recording media of the above Examples 52 - 55 were measured according to the same method as in Example 1. The above results are shown in Table 11. Examples 56 - 59 Recording media were prepared by the same method as in Example 41 according to the combinations shown in Table 12 by changing the aminium salt compound (A) used in Example 41 to the diimmonium salt compound (I) to obtain optical recording media of Examples 56 - 59, respectively. The optical recording media of the above Examples 56 - 59 were measured according to the same methods as in Example 1. The results are shown in Table 13.

Claims: An optical recording medium having a recording layer provided on a substrate, said recording layer comprising an organic thin film containing at least one diazulenium salt compound represented by the formula [I], [II] or [III] shown below: wherein R₁ - R₇ and R₁' - R₇' each represent hydrogen atom, a halogen atom or monovalent organic residue, or at least one combination of the combinations of R₁ and R₂, R₂ and R₃, R₃ and R₄, R₄ and R₅, R₅ and R₆, R₆ and R₇, R₁' and R₂', R₂' and R₃', R₃' and R₄', R₄' and R₅', R₅' and R₆', R₆' and R₇' may form a substituted or an unsubstituted fused ring; A represents a monovalent organic residue conjugated with the diazulenium salt nucleus and z o represents an anion residue. An optical recording medium according to Claim 1, wherein said recording layer contains at least one of aninium salt compounds or diimmonium salt compounds. An optical recording medium according to Claim 2, wherein said aminium salt compound is represented by the formula [IV] shown below: wherein R₁₆ represents hydrogen atom or an alkyl group, A₂ represents and X ⊖ represents an anion. An optical recording medium according to Claim 2, wherein said diimmonium salt compound is represented by the formula [V] shown below: wherein R₁₆ and X ⊖ are the same as defined above. An optical recording medium according to any preceding Claim, wherein said organic thin film has a dry film thickness of 50 Å to 100 µm. An optical recording medium according to Claim 5, wherein said organic thin film has a dry film thickness of 200 Å to 1 µm. An optical recording medium according to any of claims 2-6, wherein the amount of said aminium salt compound or said diimmonium salt compound is 1 to 60% by weight based on the total solid components as the standard in said recording layer. An optical recording medium according to Claim 7, wherein the amount of said aminium salt compound or said diimmonium salt compound is 5 to 40% by weight based on the total solid components as the standard in said recording layer. An optical recording medium according to any preceding claim, wherein the diazulenium salt compound is a compound as defined by any of formulae (1)-(13) in the description. An optical recording medium according to any of claims 1-8, wherein the diazulenium salt compound is any of compounds (1) to (58) mentioned in the description. An optical recording medium according to claim 3, wherein the aminium salt is any of compounds A-1 to A-27. An optical recording medium according to claim 4, wherein the diimmonium salt is any of compounds I-1 to I-23. A recording method, which comprises recording by irradiating using a semiconductor laser the recording layer of an optical recording medium according to any preceding claim. A reading method which comprises irradiating by using a semiconductor laser the recording layer of a recording medium according to any of claims 1-12 and receiving light reflected from the layer.

Inventors: OGUCHI, YOSHIHIRO, SANTOH, TSUYOSHI
Applicants: CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: G11B7
IPC codes: C09B23