Patent ID: 6862740

Claim:
An optical information recording medium comprising at least first and second recording layers, and a protective layer including a plurality of layers, wherein when first to kth layers (k≧2) in the plurality of layers in the protective layer between a surface of the optical information recording medium and the first recording layer are specified as a first protective layer, and first to mth layers (m>k) in the plurality of layers in the protective layer between the surface of the optical information recording medium and the second recording layer are specified as a second protective layer, when i is an integer satisfying 1≦i≦m; the refractive index of the ith layer in the protective layer at a wavelength of 405 nm is n i ; and the thickness of the ith layer is d i , when (a-1) a combined refractive index n of one layer which is substantially equivalent to the first protective layer and substituted for the first protective layer is specified as n=((n 1 d 1 +n 2 d 2 + . . . +n k d k )/(d 1 /n 1 +d 2 /n 2 + . . . d k /n k )) 0.5 ; (b−1) a combined thickness d of said one layer is specified as d=((n 1 d 1 +n 2 d 2 + . . . +n k d k )×(d 1 /n 1 +d 2 /n 2 + . . . +d k /n k )) 0.5 ; and (c-1) an expression f(n): f(n)=−105.8n 3 +551.5n 2 −936.9n+605.2 is specified as a design criterion relating to the thickness of the first protective layers; and when (a-2) a combined refractive index n of one layer which is substantially equivalent to the second protective layer and substituted for the second protective layer is specified as n=((n 1 d 1 +n 2 d 2 + . . . +n m d m )/(d 1 /n 1 +d 2 /n 2 + . . . +d m /n m )) 0.5 ; (b-2) a combined thickness d of said one layer is specified as d=((n 1 d l +n 2 d 2 + . . . +n m d m )×(d 1 /n 1 +d 2 /n 2 + . . . +d m /n m )) 0.5 ; and (c-2) an expression g(n): g(n)=−138.7n 3 +723.7n 2 −1228.7n+796.0 is specified as a design criterion relating to the thickness of the second protective layers, the refractive index n i of the ith layer and the combined refractive index n of the first and second protective layers is equal to or larger than 1.45 and equal to or smaller than 1.65, a difference d−f(n) between the combined thickness d of the first protective layer and the design criterion expression f(n) is equal to or larger than −10 μm, and a difference d−g(n) between the combined thickness d of the second protective layer and the design criterion expression g(n) is equal to or smaller than 10 μm.