At Harper, we have researched dirty printing in the highlights and found it occurs when the printing dot is smaller than the anilox cell. As shown in the following picture, a condition we call "dot dipping" occurs when the highlight dot size is smaller than the anilox cell. In this case, the printing dot actually enters the anilox cell and picks up excessive ink, resulting in dirty print.
Follow one of these two solutions to avoid dot dipping:
- Reduce the dot size, or plate screen count, being used.
- Increase the line count of the anilox roll in order to reduce the anilox cell opening.
Remember, the goal is to prevent the smallest dot on a printing plate from dipping into the anilox cell during contact. Go to the SHarper System™ section of this site for more details.
View different dot sizes in relation to anilox cell sizes. Please keep in mind, Harper holds the copyright to these illustrations and must approve any reproductions. For permission, please e-mail Harper Technical Services.
Specify Anilox to Avoid Dirty Printing in the Quarter-Tones
Dirty printing in the quarter-tones (25% - 35%) is the second condition you’ll want to avoid when specifying process printing rolls.
Thick ink films are the primary cause of this condition. To maintain a smooth, thin ink film, use an anilox volume that carries a smaller amount of ink. Through research, we have determined that the best anilox volume for process printing is typically less than 2.0 BCMs.
A volume less than 2.0 BCMs delivers an ink film thickness comparable to gravure and offset printing. Keep in mind, thinner ink films require stronger inks in many cases. However, thinner ink films will drastically improve quality and reduce ink consumption. The reduction in ink consumption will offset the additional cost you may have to pay for higher quality ink.
For more information on dirty printing and how to avoid it, go to Echocel ET2000™ product information.
Inks and Process Printing
In 1990, most inks were not strong enough to achieve desired densities with anilox volume less than 2.0 BCMs. Today, this is no longer the case. Almost every ink company has chemistries capable of achieving good color density with extremely low anilox volumes.
However, these inks do cost more because the amount of pigment added, the primary color component in ink, must be increased to get the extra strength. Pigments in raw form range from $50.00 – $95.00 per pound (USD).
With higher strength inks and extremely low anilox roll volumes, you will get excellent mileage from your inks. If you are currently running process printing with anilox volumes higher than 2.0 BCMs, you can calculate your consumption reduction. Simply divide your current anilox volume into your reduced anilox volumes.
Example: 1.8 BCM / 3.5 BCM = .51 (or 51%) This equals a 49% reduction in ink usage.
Obtaining a Specific Recommendation
If you have a particular job or set of conditions you would like us to address, please email Harper Technical Service or call us at 704-588-3371. If you would like to comment on this page, please do so. Thank you!
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