Optical recording medium

Abstract

An optical recording medium comprising at least a land and a groove where information-recording/reproducing is carried out by a flying type optical head. The optical recording medium keep the flying height of the flying optical head constant in the entire region of the recording/reproducing area, and is provided with at least one characteristic among the following characteristics: RP which is dependent on land and groove parameters and the flying height satisfied the relationship of H>Rp 01.H; centerline means roughness Ra is in the range of 0.2 nm Ra 2.0 nm, and the layer thickness of a liquid lubricant layer satisfies the relation of ΔRp≦λ/16NA which is dependent on the effective numerical aperature, laser wavelength and surface parameters is satisfied where all parameters in the formula are defined in the specification; and the height of a header area is different from the height of a land portion.

1 . In an optical recording medium wherein at least a reflective layer, a recording layer, a dielectric layer and a solid lubricant layer are formed on a substrate in this order and information-recording/reproducing is carried out by a flying optical head, the optical recording medium being characterized in that a centerline mean roughness Ra of a land and/or a groove formed in the recording medium is in a range of 0.2 nm≦Ra≦2.0 nm.  
   
   
       2 . The optical recording medium according to  claim 1 , wherein a liquid lubricant layer having a layer thickness t is formed on the solid lubricant layer in the relation of t≦2Ra.  
   
   
       3 . The optical recording medium according to  claim 2 , wherein in analyzing by a distributive analysis method of a fragment ion peak of a liquid lubricant with use of TOF-SIMS, an agglomerated state of the lubricant forming the liquid lubricant layer on the outermost surface is 10 μm or less in diameter.  
   
   
       4 . The optical recording medium according to  claim 3 , wherein an optical recording layer and the solid lubricant layer are formed on the substrate, and a layer composed of a perfluoropolyether derivative is formed as the liquid lubricant layer on the surface of the solid lubricant layer in a layer thickness of not less than 0.3 nm but less than 2.0 nm.  
   
   
       5 . The optical recording medium according to  claim 4 , wherein in a structure comprising a land and a groove, which takes part in recording/reproducing, the depth of the groove as a guide groove is 20 nm or more but not more than 150 nm after the formation of the solid lubricant layer.  
   
   
       6 . The optical recording medium according to  claim 5 , wherein the solid lubricant layer is a diamond-like carbon layer or a SiO 2  layer.  
   
   
       7 . The optical recording medium according to  claim 5 , wherein the solid lubricant layer comprises a ultraviolet-ray-curable resinous composition.  
   
   
       8 . The optical recording medium according to  claim 2 , wherein at least the reflective layer, an optical recording layer, the solid lubricant layer and the liquid lubricant layer having a layer thickness t 1  which comprises a perfluoropolyether derivative are formed on the substrate, and t 2 /t 1 >0.6 where t2 indicates the layer thickness of the lubricant layer after having been immersed in a solvent of the perfluoropolyether derivative.  
   
   
       9 . The optical recording medium according to  claim 8 , wherein the weight average molecular weight of the perfluoropolyether derivative is 1000-10000.  
   
   
       10 . The optical recording medium according to  claim 2 , wherein the contact angle of water to the front surface of the liquid lubricant layer is 70° or more.  
   
   
       11 . The optical recording medium according to  claim 2 , wherein the liquid lubricant layer is a layer comprising a perfluoropolyether derivative, a fluorine type polymer having at least one fluorine atom in the monomer structure, or a compatibilized product thereof.