The present invention relates to an improved transfer imaging system of the type in which a layer of microcapsules having a photosensitive internal phase is provided on a support and image-wise exposed to actinic radiation. 
U.S. Pat.  No.  4,399,209 to The Mead Corporation describes a transfer imaging system in which an imaging sheet comprising a support which carries a layer of photosensitive microcapsules containing a color-forming agent is image-wise exposed to actinic radiation, assembled with a developer sheet, and subjected to a uniform rupturing force.  This causes the microcapsules to rupture in the unexposed areas and image-wise release the color-forming agent which migrates to the developer sheet and reacts with the developer to form an image. 
In some applications, due to the high viscosity of the internal phase of the microcapsules used in the aforementioned transfer imaging systems, the images that are obtained develop slowly and have low density.  While one solution to this problem would be to add a diluent to the internal phase of the microcapsules to reduce its viscosity, in many instances, the addition of the diluent reduces the film speed of the system.  Accordingly, this does not represent an effective solution to the problem.