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FLEXO Magazine : June2010
Technologies & Techniques www.flexography.org june 2010 FLeXO 59 Troubleshooting Guide: Ink Drying Issues By john signet Dirty printing caused by ink drying too quickly. All art courtesy ACTegA WiT inc. ink tracking, a common side effect of ink not drying fast enough. DryInG Too FasT When ink is drying too fast, you may first notice ragged edges on type and images or poor coverage. This problem generally pertains to water-based inks. To resolve this issue, examine the printing plate to see if there is a build up of ink on the plate. Dried ink on the plate will not trans- fer to the substrate creating dirty print and poor coverage. To resolve this, first, check the airflow around the press. Many times fans, open doors and windows create unneces- sary airflow around the ink pan and rollers. Next check for proper balance between unit dryers. If airflow and dryers ap- pear to be in order, you will need to check the pH of your ink. If you find the pH to be below 8.5, check with your ink supplier for the proper additive that will raise the pH above 8.5. For most water-based inks the preferred pH level is 9.0 and 10.0. Afterward, you can slow the dry rate with small additions of 2 percent to 3 percent propylene glycol. DryInG Too slowly If ink is drying too slowly you will notice that it is picking-off or transferring to the press rollers or tracking on the print im- age. Two things to check are ink viscosity and airflow between stations. Check your airflow and dryer settings, if these are in balance and working properly the next thing to check is ink viscosity. Ink viscosity is important because if it gets too high, your ink may not dry adequately. Check with your ink supplier for the proper viscosity specifi- cation for the ink system that you’re running; plus, learn what are the correct additives and amounts needed to reduce the ink viscosity. A simple formula to help in reducing viscosity and in drying is to add small amounts of a blend of water and isopropyl alcohol (IPA). Start wit a 70/30 blend of water and IPA. If that is not sufficient, you can continue up to a max of 50/50. Finally, an increase in the airflow between press sta- tions may also help with the dry rate of the ink. ABOUT THE AUTHOR: John Signet is director of marketing at ACTEGA WIT Inc. He has more than 20 years of experi- ence in flexo inks and coatings. He serves on the board of the Phoenix Challenge Foundation and the Graphic Arts and Im- aging Technology Advisory Committee for Central Piedmont Community College in Charlotte, NC. He can be reached at firstname.lastname@example.org. FLX_June2010_mech.indd 59 6/10/10 9:39 AM