Even in the best circumstances, (new gearless high speed presses, highly trained and attentive pressmen, atmospherically controlled environments, great ink suppliers, etc.), you can still have print issues.
Many of those issues may be related to ineffective viscosity measurement and control.
Here are the 10 most common symptoms associated with inadequate viscosity control:
1. Color changes or variations during a press run: Since color is dependent on viscosity, measuring and maintaining the fluid viscosity throughout the press run is crucial to ensuring consistent color. Manually controlling or “spot checking” during the run does not allow for true viscosity/color control.
2. Excessive ink usage during a press run: With manual viscosity monitoring, the ink can have large swings in viscosity due to the many other functions the operator is responsible for. This results in only occasional checking and adjusting of the ink. As solvent evaporates, ink viscosity rises and more ink is applied to the substrate.
3. Excessive solvent, amine, or extender usage during a press run: With manual control in place, the possibility of adding too much solvent or amine when dosing is increased. This haphazard approach will certainly affect the ink color. Additionally, since these additives are poured in, not metered in, there is limited control on the amount used.
4. Dirty print or ink smearing: If the ink viscosity is not adequately maintained throughout a press run, the ink viscosity rises and falls due to solvent evaporation and replacement. The ink may adhere to or buildup on the plate, impression roller or substrate outside of the impression area. This may cause dirty print or smearing in non-image areas.
5. Anilox roller cells plug up: This causes print related problems such as deformed dots, dirty print, or other imperfections. This is often due to improperly maintained viscosity. Improperly maintained or inadequately mixed inks can result in ink solids trapped in the anilox cell creating print imperfections. Additionally, ink viscosity directly affects the transfer of ink from the anilox roll to the plate. This changes the volume of ink applied to the substrate and therefore the color and intensity of the image. This is the reason that many printers use different anilox rolls at different times of the day or year.
6. Job rejections due to print related issues: For most companies, "Brand" is one of their most important marketing tools. Anything associated with it comes under greater scrutiny and expectations for a higher quality print job become the norm. If the color associated with the brand is not correct or if there are any print related imperfections, there is a higher chance for a job to be rejected. Often, these rejections or customer returns can be traced back to inconsistent ink viscosity.
7. Excessive clean up time due to ink related issues: If you have housekeeping issues around the ink pail and throughout the press, you may have a viscosity related problem. Ink management, including viscosity control and mixing, can aid in ensuring fewer issues with ink slinging. Commonly, this slinging is the result of either thin ink or buildup due to out-of-range viscosity.
8. Press stoppage during a run to address cleaning related issues: Proper ink management can reduce the number of times it is necessary to stop a press during a run to clean plates, rolls or other press areas due to ink buildup or slinging.
9. Adhesion or flaking issues: When manually maintaining ink viscosity, there is a risk of adding too much or too little solvent to bring the viscosity back into spec. Further, if different solvent blends are used for different inks, the chance for adding the wrong solvent exists, which can result in contaminating the ink and causing additional problems.
10. Inks not drying or drying too quickly: When manually measuring and controlling ink viscosity, there is always the possibility that the ink-to-solvent ratio may not be correct for the volume of ink applied. This can result in the ink drying either too quickly or not quickly enough. Variation in ink drying time can lead to a variety of print related issues including inconsistent color, bleeding, smearing, and flaking. Each of these may cost valuable time, labor and lost income due to rejections.
Ink viscosity is one of the most crucial elements of any printing process. If you are experiencing any of these symptoms, ink viscosity may be the first and easiest place to start your investigation.
EDITOR'S NOTE: This post was originally published in March 2016, but due to its popularity and relevance, we're sharing it again for anyone who may not have seen it.
Download our FREE Viscosity Conversion Table to facilitate accurate conversion among Shell and Zahn Cup seconds, centipoises, SSU, SSF, and other viscosity units.