Author Mike Thibault (Vice President of Technical Services for leading Canadian pressroom chemical manufacturer Unigraph International), has been at the forefront of solving printing quality issues and reducing downtime in pressrooms across North America for over 33 years.
Here, he presents practical solutions for 10 of the most common – and frustrating – problems xcncountered by today’s press operators.
- Gloss and Chemical Ghosting
(Sheetfed only. This is when the printed image from the first side of a printed sheet can be seen in reverse on the second side printed.)
- Problem: Oxidizing Ink. Solution: Run heavier ink coverage on side first. This avoids lighter coverage burning into facing, unprinted surface.
- Problem: Ink drying too quickly. Solution: Avoid the addition of drying accelerants to inks and fountain solution.
- Mechanical Ghosting (Repeat of image pattern in solids)
- Problem: Poor ink distribution. Solution: Ensure that ink train distributor rollers are set to full oscillation. Allow ink form rollers #2 and #3 to oscillate to help break up ghosting. Do not let #4 oscillate, as this will usually cause more problems.
- Problem: Ink too transparent. Solution: Add small amount of silver or opaque white to ink. Ask ink manufacturer for more opaque ink.
- Dot Gain
- Problem: Blankets packed incorrectly. Solution: Check with a packing gauge. Compressible blankets require about .006” (.15mm) between plate/blanket and blanket/paper to obtain optimal print. Assure that back pressure is set properly.
- Problem: Plate imaging incorrect. Solution: Check exposure element on the plate to assure imaging is correct.
- Multicolour Ink Trapping (Wet, multicolour printing.)
- Problem: Colour sequence incorrect. Solution: Lighter ink coverage should be printed first. Switching cyan, magenta sequence is sometimes necessary.
- Problem: Poor ink/water balance. Solution: Too much water and/or ink will create poor trapping. Establish good ink/water balance. Tack-graded inks may also be considered for better trapping.
- Emulsification
- Problem: Poor ink/water balance. Solution: Start with minimum amounts of ink and water to obtain desired colour. Check front edge of the plate for an even scum line.
- Problem: Poor compatibility between ink and fountain solution. Solution: Ink too soft or too tacky, not allowing controlled emulsion. Consult your ink manufacturer.
- Picture Framing
- Problem: Plate exposure or processing incorrect. Solution: Use deletion fluid or hone in on small area of the plate where picture framing is occurring. If this then stays clean, plate exposure or processing needs to be altered. Consult your plate supplier.
- Problem: Hickey removal system (Vario or Delta) being used. This always runs a little dirtier due to the speed reduction of the dampening form roller on the plate. Solution: Turn the system off if not needed for the job that is being printed.
- Plate Wearing (Metal)
- Problem: Incorrect packing of plate and/or blanket (Incorrect surface speeds of the cylinders in relation to each other will cause premature plate wear.) Solution: Check manufacturer’s packing specs. Use packing gauge to confirm correct packing in relation to the bearers and adjust as necessary.
- Problem: Poor roller settings. Solution: Ensure that the rollers are not being driven by the plate. Normally, the setting to the distributor is slightly heavier than to the plate. Set to manufacturer’s specs.
- Chalking/Powdering
- Problem: Ink not formulated properly for substrate being printed on. Solution: Consult your ink manufacturer. Addition of driers to ink or fountain solution may help.
- Problem: pH of paper or fountain solution is too acidic. Solution: Change to a more neutral or alkaline paper. Remix fountain solution to a pH between 4.5 and 5.
- Ink/Water Balance
- Problem: Poor inking and/or dampening roller settings. Solution: Check and reset rollers to manufacturer’s specs.
- Problem: Small window to work in – either running dry or washing out
(This is caused by contamination in the ink train or fountain solution or both.) Solution: Wash rollers and treat with a high quality water-miscible deglazer as directed. Clean and flush dampening system with a system flush as directed.
- Glazing of Rollers
- Problem: Glazing is caused by many different things including ink residue left in the rollers, gum and residue chemistry picked up from the plates, calcium etc. picked up from the surface of stock, by-products from the fountain solution, and so on. Solution: The best way to combat this is with regular treatment (recommended weekly) of the rollers with a high quality water-miscible deglazer. Ensure that the form rollers are locked or shimmed properly to prevent sideways movement.