Ultraviolet protective overcoat for application to heat sensitive record materials

DETAILED DESCRIPTION AND EXAMPLES OF PREFERRED EMBODIMENT The preferred overcoating compositions of the present invention are not only resisant to the photodegradative effects of ultraviolet radiation but also provide excellent protection from physical abrasion and various degratory substances such as cleaners and detergents used to clean shelf labels, product labels, shipping labels and other applications where direct thermal printing has been or may be employed.
In addition to protecting the record material from the effects of ultraviolet radiation, physical abrasion and certain chemicals, the preferred overcoating compositions of the present invention further serve to prevent unnecessary abrasion or wear of the thermal printing heads, thereby prolonging the life of such thermal heads.
This effect is particularly important in applications where the underlying record material contains photoreactive chemicals of the metalic salt/color former type and/or certain phosphorescent materials which are known to be extremely abrasive to the thermal heads.
One known mechanism by which abrasion and/or other damage to the thermal heads occurs is due to the release of sodium and chloride ions as a product of the chemical reaction occuring in certain leuco dye/color former and metalic salt/color former chemical systems.
The improved overcoating compositions of the present invention are capable of preventing such sodium and/or chloride ions from coming in contact with the thermal head, thereby preventing such sodium and chloride ions from injuring the thermal head.
Cosmetically, the preferred overcoating compositions of the present invention, when applied to thermally sensitive record materials, form a high luster coating which is particularly smooth and enhances the appearance of the thermally sensitive record material.
The application of the preferred overcoatings of the present invention also improves the dimensional stability of the thermally sensitive record material because the overcoating material itself forms an independent, dimensionally stable sheet and thereby adds to the stability of the substrate to which it is applied