|
The photopolymers discussed here utilize a photo-initiated crosslinking mechanism to
detackify the imaged regions. The latent image can be rendered visible by applying micron-sized
pigmented toner particles to the tacky non-imaged areas of the photopolymer. Because the toner
contains a solid plasticizer, it serves as a latent ink particle; heating activates the delayed tack
state, characterized by prolonged adhesiveness. The creation of a liquid ink enables the rendered
image to be printed onto a paper substrate. Photopolymer components, migrating into the melted
toner layer, preferentially adsorb to the polymer/air interface after printing to paper, thus
influencing the delayed tack adhesive state, during which excess plasticizer crystallizes.
We examine competitive adsorption phenomena at the polymer solution/air interface, via a
model four-component system, containing two oligomeric surfactant molecules from the film,
both characterized by ethylene-oxide linkages, but distinguished by the fact that one, is linear,
while2 the second, is composed of three branches. The concentrations of these long-chain
constituents are varied in an otherwise constant bulk polymer solution of triphenylphosphate and
the toner polymer simulating typical compositions in the actual melted toner layer. We apply two
techniques of surface analysis, SIMS and ESCA (XPS), in order to reveal the identity of the
adsorbing film species. Although both molecules are capable of a surface excess, the structure
imposed upon the interfacial region is clearly different, depending on the excess surfactant at the
surface. This difference is explained by assuming that the linear molecule lies flat on the surface
while the branched oligomer adsorbs vertically. Specific SIMS/ESCA signals exhibit spectral
intensities that are nonilnearly proportional to the bulk oligomer concentration; from the shapes
of the adsorption isotherms, we deduce that the single chain surfactant is displaced at the surface
by the branched oligomer.
|
