Photosensitive material employing encapsulated radiation sensitive composition and process for improving sensitivity by sequestering oxygen

DETAILED DESCRIPTION The present invention provides a process for imaging using a photosensitive material employing an encapsulated radiation sensitive composition which undergoes a viscosity change upon exposure whereby improved photographic properties are provided.
In particular, the present invention is directed to improving the sensitivity of the aforementioned material by subjecting it to a non-imaging exposure in the form of a pre-exposure or a co-exposure which reacts the oxygen in the capsules and converts it to a noninhibiting form.
Thus, the present invention provides a process for imaging with capsulated imaging materials which comprises uniformly exposing the material to a first radiation which reacts the oxygen in the capsules, image-wise exposing the material to a second radiation which controls the formation of images, and rupturing the capsules such that they image-wise release their contents.
It has been found that the presence of oxygen in the capsules containing the radiation sensitive composition reduces the sensitivity of the composition.
Typically, the radiation sensitive compositions used in the aforementioned imaging materials contain a photoinitiator.
The photoinitiator generates a radical upon exposure to actinic radiation which initiates well known photochemistry that alters the viscosity of the internal phase and controls its release from the capsules.
When oxygen is present in the capsules, the radicals frequently react with the oxygen faster than they react with the monomers or polymers making up the radiation sensitive composition.
Thus, the imaging photochemistry is inhibited until the oxygen is depleted.
The sensitivity of the material is also less because the total exposure required to form images is equal to the sum of the exposure involved in forming radicals which react with oxygen in the capsules and the exposure involved in forming radicals which participate in the imaging photochemistry.
In accordance with the present invention a pre-exposure of a co-exposure is used to generate radicals which react with the oxygen present in the capsules and thereby prevent it from inhibiting the imaging photochemistry during the imaging exposure