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Using Prepress as a Foundation for Total Quality Management

(February 2003) posted on Mon Mar 03, 2003

Want to streamline the accuracy, efficiency, and profitability of the screen-printing process? Start by loading quality control into your prepress procedures in order to eliminate variables further downstream in production.

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By Mark A. Coudray

To illustrate how we can reduce your overall cost to print a job by changing the way we work in prepress, we begin by looking at press setup, the first step past screenmaking. Accurate color-to-color alignment can be improved through the use of digital templating, pin registration, and image trapping. Underlying costs of film assembly are also reduced at the same time. A typical, traditional setup can range from 6-20 min per color (or more on larger presses). However, with a correctly designed process stream, setup times can be reduced to 30 sec-2 min per color, and sometimes less.


The goal of setup reduction is to minimize press adjustments solely to the level of image positioning and alignment. Squeegee angle, pressure, and speed, as well as screen off-contact and peel settings can remain constant. And by employing on-press pin registration, we can comfortably position images within ±0.002 in., largely eliminating the need to adjust micro registration.


<P>The savings and efficiencies continue when it comes time to print. Run-up and color development can be reduced to less than 10 sheets for graphics printing and less than six pieces for textile printers. This is accomplished by adhering to strict file preparation and separation parameters and using consistent screen tensions, emulsion thicknesses, open-area percentages, moir&eacute; controls, and dot-gain reduction strategies.


Prepress is used to control primary and secondary moir&eacute; generation, dot gain, and gray-balance stability. If uncontrolled, all of these require press adjustment, leading directly to nonbillable work for our operations. The only adjustment necessary beyond image fit should be bringing the ink film up to the specified density level. Tone and color transition are determined by prepress and will automatically fall in line through effective use of linearization.


Total ink consumption is also controlled by how the separations are produced, using a combination of black generation and total ink limit. By understanding the relationship between chromatic and achromatic gray balance, UCA, UCR, and GCR, we can reduce the amount of ink we use to less than 50% of the amount required in an uncontrolled workflow. For large-format graphics printers, this can save tens of thousands of dollars a year in materials.



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