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PAPER TROUBLE-SHOOTING CHART FOR OFFSET PRESSMEN
TROUBLE TERM CAUSE POSSIBLE CURE
Wrinkles starting back from the center of the sheet and running to the back edge.
Back Edge Wrinkle
Sheet is badly out of moisture balance and is crowded into a wrinkle.
Sometimes infra-red lamps directed on sides of pile will help. Tighten blanket. Reduce impression cylinder pressure. Keep piles covered between printings if the pressroom is not fully air-conditioned. Keep piles away from windows. Be sure paper is cut square; check alignment of jogger.
Paper goes out and causes misregister between colors or between front and back-up.
Between Printings Stretch
Piles of paper awaiting a second pass through a press can pick up or lose moisture at edges.
Sheet has straight gripper and goes into guides satisfactorily, but distortion and misregister occurs on some sheets. A troublesome curl develops across the back of the sheet, preventing good jogging.
Distortion
Side of sheet rubs the stop. Jogger is not squarely aligned.
Tail Hook
Paper and particularly coated paper, adheres strongly to the blanket. As it is peeled off, a curl is developed. The paper surface is too weak to resist the tack of the ink being used. This is an extreme condition of the above. The ink is too tacky or the stock too weak.
Use a hard, non-tacky blanket, soften the ink and reduce impression cylinder pressure to a minimum. Do same as above and if that does not work use a paper with higher pick strength. Same as above. When you can go no further with ink and pressure, different paper must be used. This is a mill fault and paper should be returned. Try another blanket.
Small areas of coating or paper surface rises and forms blisters in solids. Flecks of paper or coating lift off the sheet and adhere to blanket.
Blister
Pick
A whiting deposit builds-up on the blanket and wears the plate. Frequent stops for cleaning are required. Ink on coated paper offsets in delivery and in the finishing operations. Ink on uncoated paper offsets to the sheet above in the delivery and in the finishing operations.
Blanket Scum
The coating lacks moisture resistance. It softens and adheres to the blankets.
Offsetting (coated)
An ink with very low penetrating power or too little setting characteristics will cause offset. Some uncoated papers have such low absorbing qualities that the ink sets before the vehicle absorbed. Friction will build up static in dry paper. The sheets will cling together and cause trouble. Ink vehicle has been absorbed by paper, leaving pigment in chalky condition on top of sheet. Gum adheres to surface of lacquer. Image is worn off plate.
Add body reducer or more driers. Use spray.
Offsetting (uncoated)
Soften the ink slightly with "o" or "oo" varnish so that faster penetration takes place. Allow more drying time. Use a good static neutralizer and ground the press.
Sheets cling together in feeder and delivery making feeding and jogging very difficult. Ink not rub-proof after drying. Will offset or scuff in some binding operations. Part of image on plate does not take ink.
Static
Chalking
Use a stiffer ink or a less absorbent paper or a faster drying agent. Remake plate. Readjust rollers and pressure. Lower blanket.
Blinding
This document is courtesy of Unisource WorldWide, Inc www.unisourcelink.com
PAPER TROUBLE-SHOOTING CHART FOR OFFSET PRESSMEN
TROUBLE TERM CAUSE
(Continued)
POSSIBLE CURE
Ink does not dry flat. Some areas dull and others shiny.
Mottling
Paper not of same porosity all over sheet. Driers not evenly distributed in ink. The pigment is fugitive or a poor vehicle was used. Too much compound or extruder or acid. First color has crystallized. The surface has dried tight from a cobalt type of dryer. Paper not glossy. Paper absorbs too much vehicle.
Work driers in more thoroughly. Try another paper.
Ink changes hue or lightens under exposure to light.
Fading
Use a light-fast ink. Use less compound, extender and acid.
One color does not adhere properly on a previously printed color.
Trapping
Use a paste drier without cobalt on all colors that are to be overprinted. Use a high gloss paper especially suited to gloss ink printing. Adjust ink to set before too much absorption takes place. Change layout. Change ink. Use less water.
Gloss inks dry dull.
No Gloss
Indistinct image patterns appear in solids.
Ghosting
Poor layout of sheet. Emulsified ink. Too much water being run on plate. First color ink transfers to second color blanket and sensitizes second color plate. Too much water and too much acid used on plate. High humidity of paper and atmosphere. Dirty or dry dampeners or parts of dampeners not touching plate. Plate poorly desensitized. Incorrect fountain solution. Ink greasy or soupy. Running too much ink. Dirty dampeners. Ink and water forming an emulsion.
Second plate on a two-color press scums over first color area.
Second Color Pick-Up Slow Drying
Use better desensitized plates. Run blankets lower.
Ink requires excessive length of time to dry.
Use better plates so that less water and acid are necessary.
Radial band of ink appearing on non-printing areas. Areas of non-printing surface taking ink.
Catch-Up
Re-cover dampeners and re-set them. Correct plate and solution. Stiffen ink. Use stronger and less ink. Clean dampeners.
Scumming
Light tint appearing all over sheet. Can be washed off with sponge.
Tinting
Run less water on plate. Use a more water resistant ink. Try a different paper. Same as above.
Gray and weak printing with granular look. Shadow dots and reverse letters fill up.
Graininess
Ink is waterlogged and in a caked condition. Over pressure or blanket too high.
Slur
Reduce pressure. Remove some packing from under blanket and put it under plate. Run less water on plate. Try another paper. Long varnish in ink.
Ink piles on blanket and rollers.
Piling
Too much water in ink. Coating of paper unsuited for offset. Ink too short.