How important is proper registration in your manufacturing process? I'm guessing it's one of those factors right at the top of the list along with controlling color and accurate converting. In this post, we will take a brief look into dimensional stability as it relates to flexo plates, and how this factor can effect productivity in the pressroom.
What is dimensional stability? BusinessDictionary.com defines it as the "ability of a material to maintain it's essential or original dimensions while being used for its intended purpose." (BusinessDictionary.com) In terms of printing plates, this means the ability for the plate material to maintain its original dimensions throughout the platemaking and printing processes. Sounds simple enough, and most plates perform this task relatively well when steps are taken to ensure it. When dimensional stability is compromised, a multitude of complications can arise: poor registration from plate to plate, from plate to die, and changes in overall plate gauge resulting in impression or dot gain issues. In this post, we'll review what steps can be taken to promote a dimensionally stable platemaking process.
Solvent-Processed Plates:
Solvent plates present a unique characteristic: they absorb the processing solvent into the photopolymer material. This absorption of solvent causes the plate to become larger in all dimensions after processing. The result is usually 1-2 hour drying times for solvent plates to release the absorbed solvent and return to their target gauge (this ends up being a bit thicker than their indicated gauge). This is why optimizing the drying step is so critical to making quality solvent plates. Related plate QC step: measure dried plates with a micrometer to ensure drying is complete before post-exposure.
Thermally-processed Plates:
These plates are processed by heating the plate surface to melt away the uncured photopolymer, which is then collected by a wicking sheet. This process applies heat and pressure to the plate surface, while the back of the plate is cooled by the processor's chill drum. While thermal plates offer operator convenience and quick turnaround time, the thermal expansion and pressure applied can come into play and interfere with dimensional stability. Since there is no absorption of solvent or drying step to optimize, the operator is left with little control over this phenomenon.
Aqueous Plates:
Aqueous, or water-processed photopolymer plates combine the speed of thermally-processed plates with the quality of solvent-processed plates. This unique washout process uses a 4% surfactant solution in water to essentially scrub away the uncured photopolymer. Cured plate material absorbs no water, therefore the plate does not swell during processing, resulting in an average drying time of 5-10 minutes (to remove surface water). This combination of low temperature processing conditions (maximum temperature occurs during the drying step: 60C /140F) and lack of processing fluid absorption into the plate make aqueous photopolymer plates extremely dimensionally stable.
What can you do to ensure dimensional stability in your platemaking process? No matter what platemaking method you're using today, consistency throughout processing steps and implementing simple QC checkpoints can greatly improve accuracy and reduce errors. A quality micrometer is one of the most important tools for any plate room. Operators should check every plate for overall gauge (proper and complete drying - solvent), floor height or relief depth (proper washout and back exposure - all plate types), and consistency across both the floor and print surfaces (drying or processing problems - all plate types). In addition to measuring plates, operators can improve consistency even further by documenting platemaking procedures and sharing information across shifts.
If you have any questions regarding platemaking, quality control, or flexo supplies, contact us here.