Optical recording medium

Abstract: The present invnetion provides an optical recording medium having on a substrate a recording layer containing an organic coloring matter and a record-assisting layer which is formed out of an elastic polymer cured by a radical reaction. So that radicals generated in the record-assisting layer may be inactivated, a radical scavenger is given to the recording layer, or a radical-scavenging layer is provided between the recording layer and the record-assisting layer.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an optical recording medium for optically recording and reproducing information. Related Background Art Magnetic materials are generally used for conventional recording mediums such as credit cards, floppy disks, and the like. These recording mediums are advantageous in that writing and reading of information can readily be performed, but have problems that the recorded matters can readily be altered and high density recording is not achievable. As means of solving such problems and treating a variety of information efficiently, optical information recording methods were proposed which utilize an optical recording medium, and various proposals therefor have been made regarding the recording mediums, recording-reproducing systems, recording-reproducing apparatuses, and the like. The optical recording mediums for optical recording and reproduction of information includes those which comprise silver particles dispersed in a gelatin matrix. Furthermore, a heat-mode recording medium was disclosed in which recording is conducted by projecting a spot-like energy beam such as a laser beam onto the recording layer thereof to change the state of portions of the recording layer. Such a recording medium does not require a developing treatment, allowing direct reading after writing (called a DRAW medium), and enabling high-density recording and additional recording, and is considered to be promising as recording mediums for disks and cards. Organic coloring matters which change their properties by receiving a relatively long wavelength of light are studied comprehensively for use in optical disks and optical cards, because the organic coloring matters are nontoxic and capable of being formed into a film by a coating method at a lower production cost. Generally, optical disks have an air gap structure in which a void space is formed at the upper portion of the recording layer to raise recording sensitivity. The formation of the void space in the upper portion of the recording medium facilitates the change of the state of the recording layer to achieve high sensitivity. The optical cards, however, are frequently carried and used in the same manner as in cash cards and credit cards. Therefore, strength against distortion caused by various external forces is necessary. In addition, there is a desire of making the medium thin. Such facts dontra-indicate the use of an air-gap structure, instead contact-layer structures are generally employed. Optical disks are preferably of the minimum thickness in view of carriage and storage. In order to minimise their thickness, optical disks are also desired to have a contact-layer structure. However, the optical disks having a contact-layer structure disadvantageously exhibit lower recording sensitivity in comparison with the ones having the hollow structure. On the other hand, the formation of a layer of an elastic rubber polymer such as urethane rubber, silicone rubber, and fluororubber on the recording layer was disclosed to improve the recording sensitivity, for example, in Japanese Patent Publication No.63-42333, and Japanese Patent Application Laid-Open Nos. 58-125248 and 58-203095. Further, formation of a thermoplastic soft layer of such material as a styrene-butadiene copolymer, a nylon resin, and a polyvinylbutyral resin was disclosed in Japanese Utility Model Application Laid-Open No. 63-2223 to improve the recording sensitivity. As mentioned above, a record-assisting layer provided on the recording layer is known to improve the recording sensitivity. The material for constituting the record-assisting layer is desired to be capable of forming a film by a coating method on the recording layer without dissolving the recording layer. In the case where the recording layer contains an organic coloring matter, the preferred material for the record-assisting layer includes curable rubber type polymer which exhibits rubber elasticity after curing: for example, silicone rubber, diene type liquid rubber, and the like. The curable rubber polymers are classified into a room-temperature-curable type, a heat-curable type, and a UV- or electron-ray-curable type. Of these types, the UV- or electron-ray curable type of rubber can be cured in an extremely short time of from several seconds to several minutes, and exhibits significantly high productivity. The UV- or electron-ray curable type of rubber polymer undergoes generally the cure reaction in a radical chain reaction caused by a radical formed by irradiation of a UV ray or an electron ray. Therefore, such problem is involved that a part of the radicals generated in the cure reaction will react with the organic coloring matter in the recording layer to deteriorate the recording layer. US Patent No 4315269 discloses an optical recording medium having a light reflective layer, a layer of material containing a highly light absorbent organic dye overlying the light reflective layer, and an overcoat about 0.05-1 mm thick comprising a silicon resin. JP-A-62-28291 discloses an optical recording medium having a thin film of which the main component is an organic dye containing 0.01-30% by weight of an amine composition. The disclosure of GB-A-2155811 is similar. The present invention provides an optical recording medium having the features set out in claim 1 of the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of an example of an optical recording medium of the present invention. Fig. 2 is a side view of another example of an optical recording medium of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT The recording medium of the present invention comprises on a substrate a recording layer, a record-assisting layer and, optionally, a protecting layer, in this order from the substrate. The optical record-assisting layer in the recording medium of the present invention is composed of an elastic polymer which may be cured by irradiation with a UV ray or an electron ray. The optical recording medium also contains a radical scavenger which scavenges the radicals generated on curing the polymerizable component to prevent deterioration of the recording layer from being caused by the radicals. The present invention is described below with reference to the drawings. The optical recording medium of the present invention comprises, as illustrated in Fig 1, a substrate 2, a recording medium 3, a record-assisting layer 4, and optionally a protecting layer 5. The record-assisting layer 4 is formed out of a high-molecular compound having rubber elasticity (hereinafter referred to as an elastic polymer), providing the recording medium with the contact-layer structure. The elastic polymer may be formed by curing a polymerizable component with a UV ray or an electron ray. The term "polymerizable component" herein means a compound which gives a polymer by polymerization or crosslinking. The elastic polymer employed for forming the record-assisting layer 4 includes, for example, silicone rubbers which are curable according to the mechanisms shown by the formulas (1) to (3). (wherein "n" is an integer) Further, the elastic polymer employed for forming the record-assisting layer 4 may include diene type liquid rubbers having a vinyl group in the molecular chain or at the end thereof, for example, as shown in the formula (4). wherein x + y = 1; R and R' are independently a group such as -COOH, OH, or -CH=CH 2 ; and ℓ and m are each an integer. The formulas (1) to (4) exemplify the elastic polymers used for forming the record-assisting layer 4. The record-assisting layer 4 has preferably a hardness after cure in the range of from 2 to 70, more preferably from 3 to 60 according to JIS-K 6301 (or ASTM D2240), while the preferred polymerization degree or molecular weight cannot readily be shown. The radical polymerization initiator, which is employed optionally in curing the polymerizable component, includes usual radical polymerization initiators such as acetophenones, e.g., dichloroacetophenone, trichloroacetopheneone, dialkoxyacetophenone, etc; benzophenone, Michler's ketone, benzylbenzoyl, benzoin ether, benzyldimetylketal, benzoyl benzoate, α-acyloxime esters, and the like. The polymerization initiator is used preferably in an amount of from 5/1000 to 5/100 by weight of the polymerizable component The recording layer 3 contains an organic coloring matter and a radical scavenger. The organic coloring matter includes cyanines, merocyanines, polymethines, phthalocyanines, naphthalocyanines, tetrahydrocholines, dioxazines, pyryliums, azulenes, anthraquinones, and the like. Of these organic coloring matters, cyanines, merocyanines, polymethines, azulenes, phthalocyanines, and naphthalocyanines are highly effective in maintaining the recording sensivity of the recording layer 3 in combination with the record-assisting layer 4 composed of an elastic polymer. The effective radical scavenger, which reacts readily with a radical to inhibit the progress of a radical chain reaction, includes phenols, quinones, amines, and the like. The phenols includes 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2'-methylene-bis-(4-methyl-6-t-butylphenol), 2,2'-methylene-bis-(4-ethyl-6-t-butylphenol), 4,4'-thiobis-(3-methyl-6-t-butylphenol), 4,4'-butylidene-bis-(3-methyl-6-t-butylphenol), 1,1,3-tris-(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionate]methane, bis-[3,3'-bis-(4'-hydroxy-3'-t-butylphenyl)butyric acid] glycol ester, tocopherol, and the like. The quinones include hydroquinone, hydroquinone monomethyl ether, hydroxyhydroquinone, p-benzoquinone, and the like. The amines include N,N-diphenyl-p-phenylenediamine, N,N-di-β-naphthyl-p-phenylenediamine, phenyl-isopropyl-p-phenylenediamine, N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine, and hindered amines. Of these compounds, particularly preferred are phenols as the radical scavenger in view of the low interaction thereof with the organic coloring matter forming the recording layer. The radical scavenger, however, is not limited to these compounds in the present invention. The organic coloring matter is contained preferably in an amount of from 60 to 99.95 %, more preferably from 70 to 99.0 % by weight based on the recording layer 3. (hereinafter the percentage is based on weight). The radical scavenger is contained preferably in a weight ratio to the organic coloring matter of from 5/10000 to 40/100, more preferably from 1/1000 to 30/100. If the content of the radical scavenger is less than 5/10000, the radical scavenging effect is low, while if the content is higher than 40/100, it causes lower reflectance, lower recording sensitivity, or retardation of curing of the record-assisting layer. The radical scavenging compound is distributed at a higher concentration at the side of the record-assisting layer 4 than at the side of the substrate 2 in the recording layer 3 to scavenge radicals effectively.. Such a nonuniform distribution of the concentration decreases the required amount of the radical scavenging compound, thereby preventing the decrease of the reflectivity of the recording layer 3. With the nonuniform concentration distribution of the radical scavenging compound, the content thereof is preferably in a ratio of from 5/10000 to 20/100, more preferably from 5/10000 to 10/100 by weight to the organic coloring matter. Furthermore, the nonuniform concentration distribution of the radical scavenging compound strengthens the contact bonding of the recording layer 3 to the record-assisting layer 4 in the case where the radical scavenging compound has a group like an -OH group, an -NH 2 group, or a C=O group. In one method of giving the nonuniform concentration distribution of the radical scavenging compound, the record-assisting layer 4 is applied on the recording layer 3 and then the recording layer 3 is heated from the side of the substrate 2 at a temperature of from 70 to 140°C prior to the curing. Thereby, the radical-scavenging compound migrates to the side of the record-assisting layer by heating because the radical-scavenging compound is more sublimable than the organic coloring matter. The recording layer 3 may contain optionally a stabilizing agent. This stabilizing agent includes metal chelate compound, particularly those which have a central metal such as Zn, Cu, Ni, Cr, Co, Mn, Pd, and Zr, and a multidentate ligand such as tetradentate ligands, e.g, N 4 , N 2 O 2 , N 2 S 2 O 4 , O 2 S 2 , and O 4 , etc. or their combinations; aromatic amines and diamines; nitrogen-containing aromatic compounds and onium salts thereof such as aminium salts, diimmonium salts, pyridinium salts, imidazolinium salts, and quinolium salts. Pyrylium salts which are salts of oxygen-containing aromatic compound are also useful. The stabilizing agent may be used singly or in combination of two or more thereof. The stabilizing agent is contained preferably in a ratio of from 1/100 to 50/100, more preferably from 10/100 to 40/100 by weight to the organic coloring matter. The optical recording medium described above contains a radical-scavenging compound in the recording layer 3. In another embodiment, the radical-scavenging compound is not contained in the recording layer 3, and instead, a scavenging layer 1 which contains the radical-scavenging compound is provided between the recording layer 3 and the record-assisting layer 4 as illustrated in Fig. 2. The scavenging layer 1, which may be formed exclusively out of a radical-scavenging compound, is preferably composed of the radical-scavenging compound and a binder. In this case, the radical-scavenging compound is contained preferably in an amount of from 0;05 to 10 %, more preferably from 0.1 to 5 % in the scavenging layer 1. The binder to be contained in the scavenging layer 1 includes polymethyl methacrylates, polystyrenes, polyesters, polyurethanes, ethylenevinyl chloride copolymers, polyvinylidene chlorides, polyvinyl chlorides, polybutadienes, polyacetals, polyamides, polyimides, polyamidoimides, polyethylenes, polyethylene terephthalates, polycarbonates, polysulfones, polyvinyl alcohols, polyvinyl ethers, polyvinylbutyrals, polybutylene terephthalates, polypropylenes, nitrcelluloses, cellulose acetates, ethylcelluloses, polyvinyl acetates, ethylene-vinyl acetate copolymers, and vinyl chloride-vinyl acetate copolymers, and combinations of two or more thereof. In the case where the scavenging layer 1 is provided as illustrated in Fig. 2, the recording layer 3 may either contain or not contain a radical-scavenging compound. When the recording layer 3 in Fig. 2 contains a radical-scavenging compound, the recording layer 3 may be the same as the one described with reference to Fig. 1. The absence of the radical-scavenging compound in the recording layer 3 is preferred to avoid the fall of the reflectance of the recording layer. When the recording layer 3 does not contain a radical-scavenging compound, the content of the organic coloring matter in the recording layer 3 is preferably in the range of from 60 to 100 %,more preferably from 70 to 100 %. The recording layer 3 and the scavenging layer 1 provided separately may have either distinct interface or no distinct interface. When the interface between the recording layer 3 and the scavenging layer 1 is not distinct, the components of the two layers are intermingled around the interface. The substrate 2 is preferably made of a light-transmissive material, including acrylic resins, polycarbonate resins, epoxy resins, polyolefin resins, polystyrene resins, and the like. The substrate 2 may have grooves for tracking (not shown in the drawing) on the surface. The protecting substrate 5, which is optionally provided, may be made of the same material as the substrate 2, the material including acrylic resins, polycarbonate resins, epoxy resins, polyolefin resins, and the like. The substrate 2 has a thickness preferably in the range of from 0.2 mm to 1.5 mm. The recording layer 3 has a thickness preferably in the range of from 500 to 2000 Å, more preferably from 700 to 1700 Å whether it contains a radical-scavenging compound or not. The scavenging layer 1 has a thickness preferably in the range of from 50 to 1500 Å, more preferably from 100 to 1000 Å. The record-assisting layer 4 has a thickness preferably in the range of from 3 to 50 µm, more preferably from 5 to 25 µm. The protecting substrate 5 has a thickness preferably in the range of from 50 µm to 1 mm. In the optical recording medium of the present invention, the recording layer 3 and the scavenging layer 1 may be formed by dissolving or dispersing the aforementioned materials respectively in a solvent and applying sequentially the solutions or dispersions onto the substrate 2. The solvent for dissolving the materials of the recording layer 3, such as an organic coloring matter and a stabilizing agent, is desired not to attack the substrate 2. Preferred solvents therefor include diacetone alcohol, cellosolve, 1-methoxy-2-propanol, and the like, and mixtures thereof with a small amount of a halogenated solvent. The solvent for dissolving the material of the scavenging layer 1 is desired not to dissolve the recording layer 3, but may slightly dissolve exclusively the surface of the recording layer 3. The solvent for the material of the scavenging layer 1 includes alcohols such as ethanol, isopropyl alcohol, amyl alcohol; cellosolves such as methylcellosolve and ethylcellosolve; n-hexane, benzene, xylene, and the like, depending on the material for the recording layer 3. The recording layer 3 may also be formed by vapor deposition. The record-assisting layer 4 may be formed by applying the aforementioned polymerizable component and optionally a polymerization initiator onto the recording layer 3 or the scavenging layer 1 in a desired thickness and subsequently exposing it to, for example, ultraviolet light irradiation. The source of the ultraviolet light is preferably a high-pressure mercury lamp, a metal halide lamp, and the like. The protecting substrate 5 which is optionally provided may be formed by lamination of a film of the aforementioned material. The present invention is described more specifically with reference to Examples below. Examples 1 to 11 A UV-curable resin (STM401, made by Dainippon Ink and Chemicals Inc.) was filled between an extrusion-molded polycarbonate base plate of 0.4 mm thick and a stamper having predetermined grooves, and was cured by irradiation of a UV ray to provide a substrate having grooves of 3 µm in breadth, 12 µm in pitch, and 3000 Å in depth (according to a so-called 2P process). On the groove face of this substrate, a solution in dichloroethane of the organic coloring matter and the radical-scavenging compound shown in Table 1 was applied by bar coating to provide a recording layer of 1000 Å thick. The concentration of a mixture of the organic coloring matter and the radical-scavenging compound was 2.0 %, the mixing ratio thereof being shown in Table 1. On the recording layer thus provided, the UV-curable silicone rubber was applied in a thickness of 10 µm by roll coating, and subsequently the applied UV-curable silicone rubber was cured by irradiation of an ultraviolet ray from a high-pressure mercury lamp (160 W/cm) from a distance of 15 cm for 30 seconds in a nitrogen atmosphere to form a record-assisting layer. Further onto the record-assisting layer, a polycarbonate film of 0.3 mm thick was bonded with an ethylene-vinyl acetate copolymer type of hot-melt adhesive (Hirodine 7580, made by Hirodine Kogyo K.K.) by means of a roll laminator at a bonding temperature of 120°C to provide a protective substrate. The resulting medium was cut into card-shaped pieces of 85.7 mm in length and 54.0 mm in breadth, thus providing optical cards of the optical recording medium of the present invention. The organic coloring matters [I], [II], and [III] in Table 1 are represented by the formulas below. Examples 12 to 17 The substrate employed was the same as the one employed in Example 1. The organic coloring matter [I], [II], or [III], the radical-scavenging compound, and the stabilizing agent having the structure of the formula [IV] or [V] below were dissolved in dichloroethane, and the resulting solution was applied onto the face of the grooves of the substrate by bar coating to provide a recording layer of 1000 Å thick. The concentration of a mixture of the organic coloring matter, the radical-scavenging compound, and the stabilizing agent in the dichloroethane solution was 2.0 %. The mixing ratios of the radical-scavenging compound and the stabilizing agent to the organic coloring matter are shown in Table 2. On the recording layer thus formed, a record-assisting layer was formed out of a UV-curable silicone rubber shown in Table 2 in the same manner as in Example 1. Further on this record-assisting layer, the same protecting substrate as in Example 1 was provided. Finally the resulting recording medium was cut into pieces in the same manner as in Example 1 to prepare optical cards of the present invention. Example 18 to 23 Onto the face of the grooves of the same substrate as employed in Example 1, the organic coloring matter [I], [II], or [III], the radical-scavenging compound, and the stabilizing agent of the formula [IV] or [V] described above were applied in the combination and the blending ratios as shown in Table 3 in the same manner as in Example 12, thus forming a recording layer of 1000 Å thick. On the resulting recording layer, the UV-curable silicone rubber shown in Table 3 was applied. The silicone rubber was heated from the substrate side at 90°C for 2 minutes prior to the curing by UV ray irradiation. Subsequently in the same manner as in Example 1, the silicone rubber was cured to form a protecting substrate, and further the resulting recording medium was cut into card-shaped pieces, thereby providing optical cards of the present invention. Examples 24 to 29 The substrate employed was the same as the one employed in Example 1. The aforementioned organic coloring matter [I], [II], or [III], and the aforementioned stabilizing agent of the formula [IV] or [V] were dissolved in dichloroethane in the combination and the ratio shown in Table 4, and the solution was applied onto the face of the grooves of the substrate, by bar coating to provide a recording layer of 1000 Å thick. The concentration of a mixture of the organic coloring matter and the stabilizing agent in the dichloroethane solution was 2.0 %. Then, the radical-scavenging compound shown in Table 4 was dissolved or dispersed in xylene at a concentration of 5.0 % , and was applied onto the above recording layer to provide a scavenging layer of 300 Å thick. On the scavenging layer thus formed, a record-assisting layer was formed from a UV-curable silicone rubber shown in Table 4 in the same manner as in Example 1. Further on this record-assisting layer, the same protecting substrate as in Example 1 was provided. Finally the resulting recording medium was cut into pieces in the same manner as in Example 1 to prepare optical cards of the present invention. Examples 30 to 32 Onto the face of the grooves of the same substrate as the one employed in Example 1, the organic coloring matter [I], [II], or [III], and the stabilizing agent of the formula [IV] or [V] described above were applied in the combination and the blending ratios as shown in Table 5 in the same manner as in Example 24, thus forming a recording layer of 1000 Å thick. Then, the radical-scavenging compound and the binder was dissolved or dispersed in xylene in the combination and the blending ratio shown in Table 5, and was applied onto the above recording layer to provide a scavenging layer of 1000 Å thick. The concentration of a mixture of the radical-scavenging compound and the binder in the xylene solution was 5.0 %. On the scavenging layer thus formed, a record-assisting layer was formed out of a UV-curable silicone rubber shown in Table 5 in the same manner as in Example 1. Further on this record-assisting layer, the same protecting substrate as the one in Example 1 was provided. Finally the resulting recording medium was cut into pieces in the same manner as in Example 1 to prepare optical cards of the present invention. Comparative Examples 1 to 3 The same substrate was employed as the one employed in Example 1. Onto the face of the grooves the organic coloring matter [I], [II], or [III] and the stabilizing agent [IV] or [V] as mentioned above were applied in the combination and the mixing ratio shown in Table 6 in the same manner as in Example 1 to provide a recording layer of 1000 Å thick. This recording layer contained no radical-scavenging compound. Onto the recording layer thus formed, a record-assisting layer of the UV-curable silicone rubber shown in Table 6 was provided in the same manner as in Example 1. The UV-curable silicone rubbers shown in Table 6 are curable by a radical chain reaction. Further thereon, the same protecting substrate as the one in Example 1 was provided. Finally the resulting recording medium was cut in the same manner as in Example 1 to prepare optical cards. Comparative Examples 4 to 8 The substrate employed was the same as the one employed in Example 43. Onto the face of the grooves, the organic coloring matter [I], [VI], or [VII] as mentioned above was applied in the same manner as in Example 33 to provide a recording layer of 1000 Å thick. This recording layer contained no radical-scavenging compound. Onto the recording layer thus formed, a record-assisting layer of the UV-curable silicone rubber shown in Table 7 was provided in the same manner as in Example 1. The UV-curable silicone rubbers shown in Table 9 are curable by a radical chain reaction. Further thereon, the same protecting substrate as the one in Example 1 was provided. Finally the resulting recording medium was cut to prepare optical disks of 86 mm in diameter. Comparative Example Organic coloring matter Record-assisting layer 4 [I] TUV6001 (made by Toshiba Silicone K.K.) 5 [VI] TFC6020 (made by Toshiba Silicone K.K.) 6 [VI] X-31-734 (made by Shin-Etsu Silicone K.K.) 7 [VII] TFC7770 (made by Toshiba Silicone K.K.) 8 [VII] X-31-775 (made by Shin-Etsu Silicone K.K.) The optical cards of Examples 1 to 32, the optical cards of Comparative Examples 1 to 3, and the optical disks of Comparative Examples 4 to 8 were subjected to measurement of the reflectance at the wavelength of 830 nm by introducing light from the side of the substrate by means of a spectrophotometer U-3400 made by Hitachi, Ltd. The measured reflectances are shown in Tables 8 to 11. The optical cards of Examples 1 to 32 and Comparative Examples 1 to 3 were tested for recording and reproduction at a feed rate of 0.06 m/sec by use of a semiconductor laser at a wavelength of 830 nm. The recording was conducted at a recording power of 3.5 mW and pulse width of 50 µsec, and the reproduction was conducted with a reproduction power of 0.2 mW. The record-reproduction contrast was calculated from the equation [A] below. The obtained values of the record-reproduction contrast are shown in Table 8 and Table 9. Record-reproduction contrast = [(Reflectance of non-recorded portion) - (Reflectance of recorded portion)] / (Reflectance of non-recorded portion) The optical disks of Comparative Examples 4 to 8 were tested for recording and reproduction at a rotation rate of 1800 rpm at a wavelength of 830 nm with a semiconductor laser, and the values of C/N were measured. The recording was conducted at a recording power of 8.0 mW at a recording frequency of 3 MHz, and the reproduction was conducted at a reproduction power of 0.5 mW. The obtained C/N values are shown in Table 10 and Table 11. Comparative Example Reflectance (%) Record-Reproduction contrast 1 13.2 0.35 2 20.7 0.42 3 17.9 0.38 Comparative Example Reflectance (%) C/N 4 12.1 21.9 5 16.2 27.1 6 15.4 26.4 7 19.9 22.2 8 21.3 24.3 As is understood from the description above, in the recording medium of an close-adhesion structure having a record-assisting layer, the recording sensitivity of a recording layer of an optical recording medium is maintained high by incorporating a radical-scavenging compound The optical recording medium has high recording sensitivity, particularly in the case where a scavenging layer containing a radical-scavenging compound is provided between the recording layer and the record-assisting layer. Further, the optical recording medium has high recording sensitivity in the case where the radical-scavenging compound in the recording layer is contained in a higher concentration at the record-assisting layer side in the recording layer.

Claims: An optical recording medium comprising: (a) a substrate; (b) a recording layer containing an organic colouring matter; (c) a record-assisting layer formed out of an elastic polymer; and (d) a radical scavenging compound which is (i) contained in the recording layer and distributed so that it is at a higher concentration at the side of the record-assisting layer than at the side of the substrate and/or (ii) being contained in a scavenging layer between the recording layer and the record-assisting layer. The medium of claim 1, wherein the substrate is of an acrylic resin, a polycarbonate resin, an epoxy resin, a polyolefin resin or a polystyrene resin. The medium of claim 2, wherein the substrate is 0.2-1.5mm thick. The medium of any of claims 1-3, which is in the form of a card. The medium of any of claims 1-3, which is in the form of a disk. The medium of any preceding claim, wherein the organic colouring matter is a cyanine, merocyanine, polymethine, azulene, phthalocyanine, or naphthalocyanine. The medium of any preceding claim, wherein the organic colouring matter is contained in an amount of 60-100% by weight based on the recording layer and wherein the recording layer does not contain a radical scavenging compound. The medium of claim 7, wherein the organic colour matter is contained in an amount of 70-99.95% by weight based on the recording layer. The medium of any preceding claim, wherein the recording layer has a thickness of 50-200nm. The medium of claim 9, wherein the recording layer has a thickness of 70-170nm. The medium of any preceding claim, wherein there is present a scavenging layer of thickness 5-150nm. The medium of claim 11, wherein there is present a scavenging layer of thickness 10-100nm. The medium of any preceding claim, wherein there is present a scavenging layer formed exclusively of a radical-scavenging compound. The medium of any of claims 1-12, wherein there is present a scavenging layer formed of a radical scavenging compound and a binder. The medium of any preceding claim, wherein the radical-scavenging compound is selected from the group consisting of phenol compounds, quinone compounds and amino compounds. The medium of claim 15, wherein the radical scavenging compound is selected from: (a) hydroquinone, (b) p-methoxyphenol, (c) hydroxyhydroquinone, (d) p-benzoquinone, (e) 2,6-di-t-butyl-p-cresol, (f) butylated hydroxyanisole, (g) 2,6-di-t-butyl-4-ethylphenol, (h) stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl) proprionate, (i) 2,2'-methylene-bis-(4-methyl-6-t-butylphenol), (j) 2,2'-methylene-bis-(4-ethyl-6-t-butylphenol), (k) 4,4'-thiobis-(3-methyl-6-t-butylphenol), (l) 4,4'-butylidene-bis-(3-methyl-6-t-butylphenol), (m) 1,1,3-tris-(2-methy l-4-hydroxy-5-t-butylphenyl)butane; (n) 1,3,5-trimetyl-2,4,6-tris(3,5-di-t-butyl-4'-hydroxybenzyl)benzene, (o) tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionate]methane, (p) bis-[3,3'-bis-(4'-hydroxy-3'-t-butylphenyl)butyric acid] glycol ester, and (q) tocopherol. The medium of claim 15, wherein the radical scavenging compound is selected from hydroquinone, hydroquinone monomethyl ether, hydroxyhydroquinone, and p-benzoquinone. The medium of claim 15, wherein the radical scavenging compound is selected from N,N-diphenyl-p-phenylenediamine, N,N-di-β-naphthyl-p-phenylenediamine, phenyl-isopropyl-p-phenylenediamine, and N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine. The medium of any preceding claim, wherein the radical scavenger is contained in a weight ratio to the organic colouring matter of 5:10,000 to 20:100. The medium of any preceding claim, wherein the radical scavenger is contained in a weight ratio to the organic colouring matter of 5:10,000 to 10:100. The medium of any preceding claim, wherein the elastic polymer is silicone rubber. The medium of any of claims 1-21, wherein the elastic polymer is a diene type rubber. Optically recording information on a medium as claimed in any of claims 1-22. Optically reproducing information that has been recorded on the medium as claimed in any of claims 1-22. A medium as claimed in any of claims 1-22 bearing optically recorded information.

Inventors: SANTOH TSUYOSHI, TAMURA MIKI, SANTOH, TSUYOSHI, TAMURA, MIKI, SANTOH, TSUYOSHI, C/O CANON KABUSHIKI KAISHA, TAMURA, MIKI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G11B7
IPC codes: G11B7