Optical recording medium and disc cartridge

Abstract

An optical recording medium is provided which has a substrate and a signal recording layer provided on the substrate and in which an information signal is recorded in the form of microscopic pits. A light beam is focused on the signal recording layer and some change of the light beam carried by a return light from the signal recording layer is detected to read the information signal recorded on the signal recording layer. The optical recording medium has a diameter of 65 mm or less and a thickness of 0.4 to 0.7 mm. An information signal recording area extends outwardly from a radial position of 12.5 mm or less from the center of the medium. The ratio in area between the information signal recording area and non-signal recording area is 3.4 or more. The storage capacity of this medium is 2 gigabytes or more. The optical recording medium has formed at the center thereof a center hole around which an annular table-abutment convexing to one side of the medium is formed. A magnetic-clamping hub is installed in the center hole and thus the medium is magnetically clamped to a rotation driving mechanism of an optical recording and/or reproducing apparatus. The compactness and high density of recording of the optical recording medium will contribute greatly to a further compact structure of a recording and/or reproducing apparatus in which the medium is to be used.

We claim as our invention:  
     
         1 . An optical read/write recording medium comprising: 
 a disc having a diameter of 65 mm or less and a thickness between and including 0.4 mm and 0.7 mm, the disc further having a center; and    a recording area for recording an information signal on the disc, the recording area extending outwardly 12.5 mm or less from the center of the disc, a ratio in diametrical length between the recording area and a non-recording area on the disc being 3.4 or more, said recording area having an information signal storage capacity of at least 2 Gigabytes.    
     
     
         2 . The optical read/write recording medium according to  claim 1 , wherein said recording area further comprises tracks having a pitch between and including 0.3 μm and 0.55 μm for recording an information signal represented as pits in said tracks, said pits having a length between and including 0.1 μm/bit and 0.22 μm/bit.  
     
     
         3 . The optical read/write recording medium according to  claim 1 , further comprising: 
 a center hole formed at the center of the disc;    an annular table-abutment formed around the center hole and being convex to one side of the disc; and    a magnetic-clamping hub fixed to the annular table-abutment.    
     
     
         4 . The optical read/write recording medium according to  claim 3 . wherein the annular table-abutment is convex by 0.4 mm to 0.7 mm and has an outside diameter of about 14 mm and inside diameter of about 8 mm.  
     
     
         5 . An optical read/write recording medium comprising: 
 a disc having a diameter between 38 mm and 52 mm and a thickness between and including 0.4 mm to 0.7 mm, said disc having a center; and    a recording area on the disc extending outwardly 12.5 mm or less from the center of the disc, said recording area having an information signal storage capacity of at least 1 Gigabyte.    
     
     
         6 . The optical read/write recording medium according to  claim 5 , wherein the recording area further comprises tracks having a pitch between and including 0.3 μm and 0.55 μm for recording an information signal represented as pits in the tracks, the pits having a length between and including 0.1 μm/bit and 0.22 μm/bit.  
     
     
         7 . The optical read/write recording medium according to  claim 5 . further comprising: 
 a center hole formed at the center of the disc;    an annular table-abutment formed around the center hole and being convex to one side of the disc; and    a magnetic-clamping hub fixed to the annular table-abutment.    
     
     
         8 . The optical read/write recording medium according to  claim 7 , wherein the table-abutment is formed to a same size as that of a second table-abutment formed for a second optical recording medium comprising: 
 a disc having a diameter of 65 mm or less and a thickness between and including 0.4 mm and 0.7 mm, the disc having a center; and    a recording area for recording an information signal on the disc, the recording area extending outwardly 12.5 mm or less from the center of the disc, a ratio in diametrical length between the recording area and a non-recording area on the disc being 3.4 or more, said recording area having an information signal storage capacity of at least 2 Gigabytes.    
     
     
         9 . A read-only optical recording medium simulated to a read/write recording medium, the read/write recording medium having a disc with a diameter of 65 mm or less and a thickness between and including 0.4 mm and 0.7 mm, a recording area on the disc extending outwardly 12.5 mm or less from a center of the disc, the recording area having a storage capacity of at least 2 Gigabytes and a ratio in diametrical length between the recording area and a non-recording area of the disc being 3.4 or more, the read-only optical recording medium comprising: 
 a substrate formed to a disc shape having a thickness between and including 0.4 mm and 0.6 mm by injecting a resin into a mold having formed thereon a pit pattern on a recording track in which a smallest pit length and a recording track pitch are about 1.4 times larger than a pit length and a track pitch on the read/write recording medium;    a fist information recording layer formed on the pit pattern on the substrate;    a light-transparent sheet between and including 0.05 mm and 0.1 mm in thickness and having on one side thereof a pit pattern formed by thermally stamping a pit-pattern stamper; and    a second information recording layer formed on the pit-pattern side of the light-transparent sheet, wherein the pit pattern on the substrate and pit pattern on the light-transparent sheet join each other with a transparent resin between them, the transparent resin between the substrate and light-transparent sheet having a length between and including 20 μm and 35 μm.    
     
     
         10 . The read-only optical recording medium according to  claim 9 , wherein the first information recording layer is translucent for optically reading a recorded information signal from the substrate side.  
     
     
         11 . The read-only optical recording medium according to  claim 9 , further comprising: 
 a center hole formed at the center of the substrate;    an annular table-abutment formed around the center hole and being convex to one side of the substrate; and    a magnetic-clamping hub fixed to the annular table-abutment.    
     
     
         12 . The read-only optical recording medium according to  claim 11 , wherein the annular table-abutment in convex by 0.4 mm to 0.7 mm and has an outside diameter of about 14 mm and inside diameter of about 8 mm.  
     
     
         13 . A read-only optical recording medium simulated to a read-write recording medium, the read-write recording medium including a disc having a diameter between 38 mm and 52 mm and a thickness between and including 0.4 mm and 0.7 mm, a recording area on the disc extending outwardly 12.5 mm or less from a center of the disc, the recording area having an information signal storage capacity of at least 1 GB, the read-only optical recording medium comprising: 
 a substrate formed to a disc shape having a thickness between and including 0.4 mm and 0.6 mm by injecting a resin in a mold having formed thereon a pit pattern on a recording track in which a smallest pit length and a recording track pitch are about 1.4 times larger than a pit length and a track length on the read-write recording medium;    a fist information recording layer formed on the pit pattern on the substrate;    a light-transparent sheet between and including 0.05 mm and 0.1 mm in thickness and having on one side thereof a pit pattern formed by thermally stamping a pit-pattern stamper; and    a second information recording layer formed on the pit-pattern side of the light-transparent sheet, wherein the pit pattern on the substrate and pit pattern on the light-transparent sheet join each other with a transparent resin between them, the transparent resin between the substrate and light-transparent sheet having a length between and including 20 μm and 35 μm.    
     
     
         14 . The read-only optical recording medium according to  claim 13 , wherein the first information recording layer is translucent for optically reading a recorded information signal from the substrate side.  
     
     
         15 . The read-only optical recording medium according to  claim 13 , 
 a center hole formed at the center of the substrate;    an annular table-abutment formed around the center hole and being convex to one side of the substrate; and    a magnetic-clamping hub fixed to the annular table-abutment.    
     
     
         16 . The read-only optical recording medium according to  claim 13 , wherein the annular table-abutment is convex by 0.4 mm to 0.7 mm and has an outside diameter of about 14 mm and inside diameter of about 8 mm.  
     
     
         17 . A disc cartridge in which a read-write recording medium is encased, the read-write recording medium including a disc having a diameter of 65 mm or less and a thickness between and including 0.4 mm and 0.7 mm, a recording area on the disc extending outwardly 12.5 mm or less from a center of the disc, the recording area having a storage capacity of at least 2 Gigabytes, a ratio in diametrical length between the recording area and a non-recording area of the disc being 3.4 or more, the disc cartridge comprising: 
 a cartridge having a rectangular shape and including a first side having length between and including 52 mm and 70 mm, and a second side, perpendicular to the first side, having a length between and including 52 mm and 75 mm, the cartridge having a thickness between and including 3 mm and 6 mm; and    at least one opening formed in a side of the cartridge parallel to the read/write recording medium, the opening being a writing and reading access opening through which a radially extending portion of the recording medium is exposed to a light beam from an optical pickup and through which the magnetic-clamping hub is exposed, the opening further being formed deviated to one lateral side from a middle point of a front side of the cartridge.    
     
     
         18 . The disc cartridge according to  claim 17 , further comprising: 
 a shutter member slidably mounted along one lateral side of the cartridge for opening and closing at least the writing access opening and reading access opening formed in the cartridge.    
     
     
         19 . A disc cartridge having a read-write recording medium is encased therein, the read-write recording medium including a disc having a diameter between 38 mm and 52 mm and a thickness between and including 0.4 mm and 0.7 mm, a recording area on the disc extending outwardly 12.5 mm or less from a center of the disc, the recording area having a storage capacity of at least 1 Gigabyte, the disc cartridge comprising: 
 a cartridge having a rectangular shape and including a first side having a length between and including 41 mm and 57 mm and a second side, perpendicular to the first side, having a length between and including 41 mm and 62 mm, the cartridge having a thickness between and including 3 mm and 6 mm; and    at least an opening formed in a side of the cartridge parallel to the read-write recording medium, the opening being a writing and/or reading access opening through which a radially extending portion of the recording medium is exposed to a light beam from an optical pickup and through which the magnetic-clamping hub is exposed, the opening further being formed deviated to one lateral side from a middle point of a front side of the cartridge.    
     
     
         20 . The disc cartridge according to  claim 19 , further comprising: 
 a shutter member slidably mounted along one lateral side of the cartridge for opening and closing at least the writing access opening and reading access opening formed in the cartridge.    
     
     
         21 . A disc cartridge having a read-only optical recording medium encased therein, the read-only optical recording medium including a disc having a diameter of 65 mm or less and a thickness between and including 0.4 mm and 0.7 mm, a recording area on the disc extending outwardly 12.5 mm or less from a center of the disc, the recording area having a storage capacity of at least 2 Gigabytes, a ratio in diametrical length between the recording area and a non-recording area of the disc being 3.4 or more, the disc cartridge comprising: 
 a cartridge of a rectangular shape including a first side having a length between and including 52 mm and 70 mm and a second side, perpendicular to the first side, having a length between and including 52 mm and 75 mm, the cartridge having a thickness between and including 3 mm and 6 mm; and    at least one opening formed in a side of the cartridge parallel to the read-only recording medium, the opening being a writing and reading access opening through which a radially extending portion of the recording medium is exposed to a light beam from an optical pickup through which the magnetic-clamping hub is exposed, the opening further being formed deviated to one lateral side from a middle point of a front side the cartridge.    
     
     
         22 . The disc cartridge according to  claim 21 , further comprising: 
 a shutter member slidably mounted along one lateral side of the cartridge for opening and closing at least the writing access opening and reading access opening formed in the cartridge.    
     
     
         23 . A disc cartridge having a read-only optical recording medium encased therein, the read-only optical recording medium including a disc having a diameter of between 38 mm and 52 mm and a thickness between and including 0.4 mm and 0.7 mm, a recording area on the disc extending outwardly 12.5 mm or less from a center of the read-only optical recording medium, the recording area having a storage capacity of at least 1 Gigabyte of an information signal as a pit pattern, the disc cartridge comprising: 
 a cartridge of a rectangular shape including a first side having a length between and including 41 mm and 52 mm and a second side, perpendicular to the first side, having a second length between and including 41 mm and 62 mm, the cartridge having a thickness between and including 3 mm and 6 mm; and    at least an opening formed in a side parallel to the read-write recording medium, the opening being a writing and/or reading access opening through which a radially extending portion of the optical disc is exposed to a light beam from an optical pickup and through which the magnetic-clamping hub is exposed, the opening being formed deviated to one lateral side from a middle point of a front side of the cartridge.    
     
     
         24 . The disc cartridge according to  claim 23 , further comprising: 
 a shutter member slidably mounted along one lateral side of the cartridge for opening and closing at least the writing access opening and reading access opening formed in the cartridge.