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| Problem: | Printed Sheets show color variation from sheet to sheet during the run. Ink film densities are very unstable. |
| Causes: | Low ink level in the fountain Improper roller setting Ink Emulsification Ink backing away from the "fountain" roller Roller Stripping Contaminated ink fountain – dust, grit, etc. |
| Solutions: | Keep ink fountain full to maintain head pressure Reset rollers Decrease water or add heavy body varnish Agitate ink in the fountain or increase ink flow Deglaze the rollers Remove ink, clean fountain, replace with fresh ink |
Ink Drying on the Rollers
| Problem: | Ink is drying on the press rollers |
| Causes: | Excessive Drier in the Ink Light – Take off of ink Roller Pressure is too great, thus creating too much heat Fast drying varnishes in the ink |
| Solutions: | Add Anti-oxidant to retard the drying Reduce ink strength to carry more ink Adjust rollers to minimum pressure necessary to properly transfer ink Add Alkyd varnish to the ink (increases flow –holdout) |
Print Mottling
| Problem: | Print Density is Uneven |
| Causes: | Too much impression Too much ink being carried Low viscosity ink may look mottled on papers with uneven holdout On some stocks, transparent inks will show more mottle |
| Solutions: | Check Blanket Impression and plate to blanket pressure Run a stronger ink to permit a thinner film Higher viscosity ink will have less absorption and reduce mottle Use a more Opaque ink |
Excessive Plate Wear
| Problem: | Image areas of the plate begin to disappear |
| Causes: | Ink too strong for long runs Fountain Solution is too Acidic Plate to Blanket packing is too high Ink may have a poor grind Plate exposure may be too short or too long Abrasive paper particles Ink emulsification and poor transfer mistaken for plate wear The form roller is too tight against the plate |
| Solutions: | Reduce ink strength and carry more ink Increase fountain solution pH Check plate and blanket packing Check Ink Grind Change to a new and properly developed plate Change paper if possible See remedy for ink emulsification Check form roller setting |
Ink Trapping
| Problem: | Poor Trap or Overlay between the colors during process printing (wet trapping) |
| Causes: | Not enough tack difference between colors Second down color is stronger than the first down color Too much water and ink combination Improper ink film thickness on the rollers Paper has too much holdout |
| Solutions: | Increase the tack and viscosity of the first down color Strengthen the first down color or weaken the second down color Reduce the amount of water and/or ink Try a more quick-setting ink |
Welcome to our technical tips department. Please continue to visit on a regular basis as we add to this knowledge base.
12/16/04 - Basic Ink & Drying Information for UV Finishing