Decolorizable imaging system

DETAILED DESCRIPTION OF THE INVENTION There are a minimum of four components to the present invention.
The four required components are the dye, acid, the nitrate salt, and the polymeric binder.
THE BINDER Any polymeric binder may be used in the practice of the present invention.
The pH of the resin has been found to affect only the speed of the discolorizing effect.
If the speed is not important, any resin may be used.
Organic polymeric resins, preferably thermoplastic although thermoset resins may be used, are generally preferred.
Where speed is more important, either the more acidic resins should be used or an acid should be added to the system to decrease the pH and increase the rate of decolorizing.
Such resins as polyvinyl acetals, polyesters, polyvinyl resins, polyvinylpyrolidone, polyesters, polycarbonates, polyamides, polyvinyl butyral, polyacrylates, cellulose esters, copolymers and blends of these classes of resins, and others have been used with particular success.
Natural polymeric materials such as gelatin and gum arabic may also be used.
Where the proportions and activities of dyes and nitrate ion require a particular developing time and temperature, the resin should be able to withstand those conditions.
Generally it is preferred that the polymer not decompose or lose its structural integrity at 200.
degree.
F.
(93.
degree.
C.
) for 30 seconds, and more preferred that it not decompose or lose its structural integrity at 260.
degree.
F.
(127.
degree.
C.
) for 30 seconds and most preferred that it withstand 290.
degree.
F.
(144.
degree.
C.
) for 60 seconds.
By far, the most preferred resin comprises polyvinylidene chloride (PVDC).
Binders comprising at least 30% PVDC are more stable than other binder systems.
It is more preferred to have at least 50 to 70% PVDC and most preferred to have more than 85% or more than 90% PVDC as the binder.
Beyond these minimal requirements, there is no criticality in the selection of a binder.
In fact, even transparency and translucency are not required, although they are desirable