Details:
Summary:
Several new insights into the working mechanisms of latex coalescence/latex fusion thermal printing plate technology (commonly also referred to as "Thermofuse" plate technology) have afforded a boost in its pre-press and press performance, as well as a further increase in its versatility. This now allows the design of plate constructions that better fit the needs of both the general-purpose thermal printing plate market ([mildly] alkaline processing) and those printers who require plates that allow for a more convenient processing, either off-press (so-called "gum processing", also referred to as "chemistry-free" processing or simply "clean-out washing") or on-press (so-called "on-press processing"). The chemical concepts that allow for a proper balance between plate sensitivity, clean-out of the non-image areas during processing and on-press robustness are highlighted, as well as the new chemical concepts that allow to create a clear image contrast upon exposure (required in on-press processing applications). It is shown for example that in order to be able to increase sensitivity by use of small thermoplastic particles with an average particle diameter less than 40 nm, the surface of these particles has to be sufficiently covered with the appropriate anionic IR dyes and/or other anionic "dummy dyes" in order to allow for a solid clean-out performance. The adsorbed amount, without the counter ion taken into account, should be more than respectively 0.80 mg per m2 (on-press processing or gum processing) or 0.65 mg per m2 ([mildly] alkaline processing) of the total surface of the thermoplastic particles present in the coating. In order to create the required visual contrast between the image and non-image areas upon exposure, so-called thermochromic IR-dyes have been designed that form products strongly absorbing in the visual part of the spectrum after exposure to IR light (830 nm) of sufficient energy density (> 100 mJ/cm2). The paper will close with a tentative look at the promises that Thermofuse technology still might hold in the future.