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FLEXO Magazine : November 2011
Packaging printers face these critical issues on a daily basis. Adopting a color quality control process is the perfect way to remedy them. YOUR INK Is your ink the right color? How can you tell? Any pressroom manager can tell you that different batches of ink will have slightly and sometimes substantially different color character- istics. The ink color you print today will not necessarily be the same color you print next month. The challenge is to deter- mine whether the color of the ink you are receiving from your supplier falls within an acceptable range of your customer ’s specified colors and tolerances. Color variance is often not discovered until the end of the pressrun; with multiple buckets of ink and many rolls of sub- strate wasted. How can you avoid this pitfall? Manage your ink procurement process by following these steps: 1. Work with your customer/brand owner to define what color values are required and specify the acceptable tolerances in the color balance. 2. Request an ink drawdown on the actual material you are going to print on from your ink supplier. 3. Ask your ink supplier to document how close the batch of ink is to the specified color (∆E) along with the actual color values (L*ab). 4. Use a spectrodensitometer to measure the color of the ink drawdown to verify that it is within the customer- stated color specification and tolerance. 5. Use a spectrodensitometer to measure the pressrun at regular intervals to make sure color accuracy is still consistent with customer tolerances. Swapping in a new bucket of ink may cause unintended color variation. Catching it early can make a major difference in the success of the pressrun, as well as the cost. Just by following these ink guidelines, you can control ink color variations that ultimately lead to costly remakes and wasted materials on press. YOUR SUBSTRATE How will the color of the substrate affect the color of your printed job? It is not only about whether your ink color is ac- curate, at the right viscosity or the correct pH. The materials you are printing on can, and will, substantially influence the accuracy of the color being printed. Since inks are not 100 percent opaque, the color and texture of the substrate will show through the ink being laid down on press, and cause a sometimes substantial color variation. Us- ing a spectrodensitometer to measure the print materials will help ensure that you are getting consistent color between rolls. It will also help you better predict the impact the color of your print material will have on the end result of the printed piece. YOUR COLOR What’s the difference between checking density and mea- suring color in pressroom color measurement? “Density is a great metric of tracking and controlling fluctuations on a printing press, but it’s not a good indicator of how the color correlates to the human eye. Colorimetry is proven to communicate color and provide tolerancing that closely associates with our eyes.” —Dan Reid, RPimaging Densitometers measure density. A density measurement is the amount of light reflected from the printed material. A higher density reading means a darker surface that absorbs more light than it reflects. When adding extender or water to an ink bucket to adjust the density, you are effectively “ water- ing down” the colorants in that ink, thereby making it a lighter surface that absorbs less light than it reflects. A density reading does not tell you whether the color matches your customer’s specification and is within their tol- erances. So while you may achieve your target density, your visual color may be incorrect. Spectrophotometers measure color. The best method to ensure accurate color is to use a spectrodensitometer to mea- sure the color. A spectrodensitometer is an excellent tool for qualifying whether the color being printed is accurate. If it’s not, a spectrodensitometer will quantify how far off the color is from what the customer-specified. And at the end of the pressrun, isn’t it all about printing the correct color and satisfying the customer? So, check density, but be sure to measure color. YOUR TRENDING Are you maintaining consistent color press-to-press, shift- to-shift and plant-to-plant? The press is the most complicated and mechanical part of the process, and because of this it is the part of our manufacturing system that deserves the most attention. In most plants, press conditions are constantly chang- ing. If it is not the season and the weather, then it is wear and tear on machines and the differences in operators. And with the presses being the most expensive pieces of equipment in the plant, as well as the key moneymakers, it should not come as a surprise to find out that the press deserves a lot of attention.” —Ron Ellis, Certified G7 expert and co-chair of the GRACoL Committee One of the main challenges that package printers face is how to check and maintain consistent color between different shifts, presses, and often times, between different print facili- ties that are printing the same customer job. There are three Standardized color control trending software will track the performance of a specific job and indicate how well the pressrun performed across shifts, presses and different facilities. www.flexography.org november 2011 FLEXO 29 FLX_November11.indd 29 11/8/11 3:53 PM