Optical recording element

DETAILED DESCRIPTION OF THE INVENTION A.
Light-Absorptive Material The light absorptive materials which are suitable as the active layer of the invention are film-forming polymers having chromophoric groups as part of the polymer molecule, that is, polymeric dyes.
Thus, these materials differ substantially from the prior art optical disk materials in that, in this case, the chromophoric moieties are an integral part of the film-forming polymer--either as part of the polymer chain or pendent thereto--and not merely a dispersion of a dye compound or pigment in an organic medium.
The following terms are used herein in accordance with the definitions given in Hackh's Chemical Dictionary, 4th Edition, McGraw-Hill Book Company, NY (1969): "Auxochrome" is a radical that intensifies the color of a chromophore or develops a color from a chromogen.
"Bathochrome" is an organic radical which displaces the absorption spectrum of an organic molecule toward the red.
"Chromogen" is a structural arrangement of atoms in many colored organic substances, e.
g.
, --N.
dbd.
N--.
"Thermal Diffusion Length" (l) is defined in U.
S.
Pat.
No.
4,222,071 by the relationship l=.
sqroot.
k.
UPSILON.
, in which k is the thermal diffusivity of the layer material and .
UPSILON.
is the exposure time.
A thin layer of low thermal diffusion length, i.
e.
, having a diffusion length less than the diameter of focussed area of the recording beam, provides a highly sensitive recording medium.
As used herein, the term "film-forming" means that the polymeric dye is solid or semi-solid at room temperature and is capable of being formed into a coherent film by conventional coating or extrusion methods.
Polymers having chromophoric groups as part of the polymer molecules, i.
e.
, polymeric dyes, can be made directly by both free radical and condensation polymerization techniques or they can be made by post-polymerization reaction of copolymers having pendent functional groups with reactive chromophoric materials in accordance with processes which are well known in the polymerization art