Abstract

The screen printing process has been the least understood and studied versus other imaging methods in the graphic arts industry. As equipment configurations improve and a continuous technological development and need for high quality output persists, this fascinating process becomes increasingly popular in several end-use applications. Such as in packaging, labeling, durable graphic films printing and even short run large format halftone graphics. There is a serious need for further deep scientific analysis of the process and its variables. One of the poorly investigated sides of the four color screen printing is the effect that ink placement has to the final color appearance of a halftone print. Several known factors can influence the color result of a screen printed image. Limitations inherent to screen printing allow for a smaller color gamut reproduction compared to other methods, but colors are reproduced vividly due to a uniform and high ink film thickness. The screen - equivalent to a printing plate - consists of a stretched porous fabric mounted on a carrier frame that is coated with a light sensitive emulsion (stencil) and subsequently exposed and hardened at the non image areas. The ink will flow through the screen mesh openings when pressure and hydraulic forces are applied by a squeegee blade system. The ink system can be cured or dried by various methods depending on its chemistry and composition. For the specific system investigated, UV curing units expose the wet ink film to high energy radiation for full polymerization. The different types of equipment configurations in screen printing are designed for various processing speeds, base material formats, ink systems of specific drying and curing characteristics and also for various end use applications. This study utilized a Kammann web screen printer with five color stations and UV curing capability for roll to roll one-pass multi color printing. This type of screen printing press is used for applications such as promotional labelling with high precision type and halftone reproduction. A popular film substrate is the polyolefin construction that delivers printability, water resistance, color strength and good process characteristics through roll to roll printing presses. The polyolefin material used for this study was supplied by Fasson Films and is constructed to give a consistent ink film deposit under the set parameters without any penetration, absorption or permeation of the ink system. The samples printed from the total graphics system were produced under the same conditions using in a period of a full working day the press, screens, ink systems and substrate, but only varying the order of the printed process colors yellow (Y), cyan (C) or process blue, magenta (M) or process red and black (K). The importance of ink sequence is determined by creating these prints under the same arrangement and evaluating the color result as it relates to the sequence followed. The purpose of this study was to determine the effect of the ink sequence to the final color appearance of fully dried /cured ink film as expressed by its hue and saturation characteristics. The ink sequence is treated as the sole variable and all other parameters remain constant. An image was designed specifically for this process containing solids, tints and an actual halftone icon. Data was collected by a densitometer and a spectrophotometer from the individual color patches. The representative sampling consists of selected prints throughout each ink sequence run and the measured mean values of all color patches are recorded, plotted, graphed and statistically analyzed. The Hexagon GATF diagram was used to show changes from run to run, densitometric data was also graphed for comparison critique and the CIE*L*a*b* color coordinates allowed mapping of the prints for comparison analysis and color difference [delta]E* study. The data is statistically analyzed and validated versus the null hypothesis using a single factor analysis of variance (ANOVA) and Scheffe comparisons. The final visual evaluation under standard lighting conditions per ASTM standards helps to support the results and conclusion. Experience from the field supports that the ink sequence affects the final color result assuming that all other system components remain equal. This study shows that the sequences' compared color is different and the ink sequence is a critical factor that should be analyzed further for the screen printing industry in order to help maintain color consistency and control. The hypotheses are supported by the study's results. The ink sequence influences the color's hue and saturation in four color halftone screen printing having distinct differences for every sequence that was produced during the printing run. The UV ink systems used, adhere and transfer better to the substrate instead of the ink layers. The placement of black is important for color control and trapping. If black is printed first down then the other inks trap well and a clean image is produced; if black is last, trapping is poor and consequently the color and image appearance. The target guide Nucleus Pattern Sequence Originator was ideal for color measurements and evaluation in screen printing; it is recommended for similar future research work. Densitometry and use of Hexagon diagrams is not very effective in screen printing. The use of colorimetry can show any color changes more accurately. It was also shown that the midtones are influenced the most form the change in ink sequence; especially important for trapping. Finally, two ( 2) of the ink sequences showed good results as concluded by the final evaluation. The MCYK delivered the best output in data and KMCY printed closest to the original proof.

Library of Congress Subject Headings

Color printing; Screen process printing; Printing ink

Publication Date

3-1-1993

Document Type

Thesis

Department, Program, or Center

School of Print Media (CIAS)

Advisor

Hoff, Sam

Advisor/Committee Member

Layne, Chuck

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: TT273 .B684 1993

Campus

RIT – Main Campus

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