Overview
Many of today's award winning photopolymer platemakers and printers continue to embrace solvent washout technology for both conventional and digital photopolymer plates. Primary reasons include superior print results and print consistency resulting from gauge uniformity, equalized plate surface energy, more repeatable dot generation, and the ability to select from more photopolymer plate materials.
Several advancements have been made in recent years regarding solvent platemaking total-system solutions, which include improved in-line plate processors, high speed dryer technology, new low odor solvents and air cleaners. The result today is solvent washout photopolymer plates that do not require lengthy dry times nor have the VOC levels or odors once common with solvent platemaking not long ago. It is no longer uncommon to experience processing times of 60 to 70 minutes in making solvent polymer plates. In addition, the new high speed white light dryers have often resulted in more consistent plates with better plate drape. The development of better in-line plate processors in combination with low odor solvents, proper room ventilation and proper air cleaners have often resulted in less odors than even thermal systems.
Optimizing Solvent Usage
While the print benefits are clear regarding solvent washed photopolymer plates, the methods used to optimize the solvent usage is sometimes overlooked. Newer in-line washout systems are equipped with features that monitor viscosity of the washout solution and then correlate this viscosity to the amount of suspended solids held within the used solution. As the percentage of solids rises, the effectiveness of the washout is affected. Allowing solid percentage to rise over the manufacturer's recommended level can result in extended washout times and polymer residue build-up within the processor. Newer processors allow the individual to program the equipment to return the solvent to the spent solvent drum or in-line distillation unit once the solids reach a predetermined optimized level.
There are still hundreds of older processors, both in-line and rotary, that are perfectly capable of washing out a quality plate, but the suspended solids are at an unknown level. A calibration curve can be developed in a simple MS Excel database that allows the user to link viscosity using a #2 DIN cup and a stop watch. Determining what level of solid percentage begins to lengthen the washout time and/or affect the cleanliness of the processor, will both optimize the productivity and plate quality of the processor. If you do not feel the need to know the percentage of suspended solids in the dirty solvent, simply understanding at what viscosity the washout is negatively impacted could prove valuable. Optimization of the washout solution will also result in less downtime or maintenance resulting from polymer build-up or un-scheduled clean-ups. Often, the washout solution can maintain effectiveness up to levels that would induce housekeeping issues inside the plate processor.
If the user is utilizing an outside source to reclaim their solvent washout solution, understanding level of percentage of suspended solids in a dirty return solvent drum or tote can also prove useful in understanding how much should be required to make up the difference once the drum has been distilled. If you are interested in understanding more about controlling the level of suspended solids in your plate processor you can contact Tim Reece, APR's Director of Diagnostic and Technical Services Group, at [email protected] or 1-800-445-4017.