Multilayered optical information-recording media and process for manufacture thereof

Abstract

This invention provides an optical disk effective in both precision and productivity, and to a process for the manufacture thereof. The optical disk allows reading of the information recorded on each information-recording surface of the two or more information-recording surfaces by varying the focal position of a playback laser beam incident on and passing through said light transmitting substrate; and the optical disk is provided with a transparent layer that is laminated onto the light transmitting substrate and is constituted of a thermoplastic resin sheet of uniform thickness and the transparent layer has an information-recording surface other than the surface of said light transmitting substrate formed thereon.

1 . An optical information-recording medium that has at least two or more information-recording surfaces in the thickness direction of a light transmitting substrate and that allows reading of the information recorded on each information-recording surface of the two or more information-recording surfaces by varying the focal position of playback laser beam incident on and passing through said light transmitting substrate comprising: 
 a transparent layer that is laminated onto said light transmitting substrate and is constituted of a thermoplastic resin sheet of uniform thickness; wherein an information-recording surface other than the surface of said light transmittins substrate is formed on said transparent layer.    
     
     
         2 . An optical information-recording medium as set forth in  claim 1 , wherein the thermoplastic resin sheet which constitutes said transparent layer is a thermoplastic resin sheet with a double-pass birefringence of not more than ±50 nm and a uniform film thickness in the range of about 20 μm to about 100 μm.  
     
     
         3 . An optical information-recording medium as set forth in  claim 1 , wherein the thermoplatic resin sheet which constitutes said transparent layer is an acrylic resin, polycarbonate resin, or amorphous polyolefin.  
     
     
         4 . A process for the manufacture of an optical information-recording medium that has at least two or more information-recording surfaces in the thickness direction of a light transmittin substrate and that allows reading of the information recorded on each information-recording surface of the two or more information-recording surfaces by varying the focal position of a playback laser beam incident on and passing through said light transmitting substrate comprising: 
 a first step in which a thermoplastic resin sheet of uniform thickness is positioned between said light transmitting substrate and a stamper having a crenulated pattern formed thereon corresponding to pits or guide grooves; and    a second step in which said light transmitting substrate and said stamper are heated, followed by pressing the light transmitting substrate and stamper against said thermoplastic sheet, thereby transferring the crenulated pattern formed on said stamper to the surface of said thermoplastic resin sheet and forming an information-recording surface on a surface other than that of said light transmitting substrate.    
     
     
         5 . A process for the manufacture of an optical information-recording medium as set forth in  claim 4 , wherein 
 in said first step, a thermoplastic resin sheet with a light reflecting material coated to one of the surfaces is positioned with the surface to which the light reflecting material is coated to face said stamper side; and    in said second stepm, an information-recording surface is formed on the surface of the sheet to which the light reflecting material is coated.    
     
     
         6 . A process for the manufacture of an opticl information-recording medium as set forth in  claim 4 , wherein 
 the themoplastic resin used in said first step is thermoplastic resin sheet with a double pass birefringence of not more than ±50 nm and has a uniform film thicikness in the range of about 20 μm to about 100 μm.    
     
     
         7 . A process for the manufacture of an optical information-recording medium as set forth in  claim 4 , wherein 
 the thermoplastic resin used in said first step is an acrylilc resin, polycarbonate resin, or amorphous polyolefin.