Even in the best circumstances—new and gearless high speed presses, highly trained and attentive pressmen, atmospherically controlled environments, great ink suppliers, etc.—print issues still occur. And while there are plenty of possible causes, many of those issues could be related to ineffective viscosity measurement and control.
Here are the 10 most common symptoms associated with inadequate viscosity control.
Color Changes/Variations During Pressrun
Ink formulations are as important to printing as recipes are to cooking: A wrong ingredient added, or over or undercooking a dish, can turn an evening of fine dining into a gastronomical nightmare. The same holds for inks. An ink supplier provides an ink with the correct “recipe” to ensure the color is correct for the selected print job.
[perfectpullquote align=”right” cite=”” link=”” color=”#00ffff” class=”” size=””]Today, press operators carry a lot more responsibility than they did in the past.
Since color is dependent on viscosity, and viscosity helps maintain the ink “recipe,” measuring and maintaining the fluid viscosity throughout the pressrun is crucial to ensuring consistent color.
By manually controlling or “spot checking” during the run, the recipe will change due to evaporation, contamination and intermittent solvent dosing, and not allow for true viscosity/color control.
Excessive Ink Usage During Pressrun
Let’s be honest: Today, press operators carry a lot more responsibility than they did in the past. Advancements in press technology require that, in addition to being technically intelligent, operators possess time management, organizational habits and multitasking skills in order to successfully run print jobs. It bears some mention that these skill sets vary from operator to operator and from shift to shift.
Today’s press operator has many concerns for which he/she is responsible, only one of which is checking the ink viscosity. The time required to perform other critical tasks may take away from the time necessary to ensure the ink viscosity is consistent.
This sporadic ink checking and the time lapse between viscosity adjustments could result in substantial solvent evaporation. During that time period, the ink viscosity may increase, causing more to be applied to the substrate, resulting in increased usage and less impressions per volume.
Excessive Solvent/Amine/Extender Usage During Pressrun
Correctly “controlling” ink viscosity manually takes a lot of experience, a fair amount of guesswork and time. Manually adding makeup solvent (or extender in water based inks) raises the possibility of adding too much or too little solvent or amine, which may take multiple tries to get “right.”
[perfectpullquote align=”right” cite=”” link=”” color=”#00ffff” class=”” size=””]Once it’s apparent the usual tricks won’t work, it’s back to lost time, lost production and lost resources. Margins, which are already tight, begin to shrink even more.
This haphazard approach will certainly affect, among other things, ink yield, dirty or weak print (see the next point) and ink color. Additionally, since these additives are poured and not consistently metered in, there is limited control on the amount used, resulting in increased, inefficient solvent usage.
Dirty Print or Ink Smearing
If the ink viscosity is not adequately managed throughout a pressrun, it rises and falls due to solvent evaporation, ink usage, environmental contaminants, and fresh ink replacement. Depending on how high or low the viscosity is during the run, the ink may adhere to or build up on the plate, impression roll or substrate, outside of the impression area, resulting in dirty print or smearing in non image areas.
Once this occurs, the risk for job rejection is increased. Additionally, manpower and press time required to either bring the viscosity back into spec, or to clean the deck(s), is wasted.