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    Difficulties encountered in offset printing

The following difficulties encountered in printing mainly originate in the paper in conjunction with the climate and the printing ink. Since paper and cardboard are natural materials changing their dimensions in accordance with changes in climate utmost efforts should be made to keep the climate as constant as possible. The optimum climate is in the range between 20 and 25 degrees Celsius and a relative humidity of 55 to 60%. In order to avoid troubles due to wrong climatic conditions we recommend: start multi colour jobs that shall be printed in a single colour press with a stretching run, i.e. an idle pass of paper through the machine with printing and damaging unit being switched on. Please note that in a single colour press with standard dampening this stretching run will result in an increase of the relative batch humidity of 3 to 4%.

Symptoms Causes Corrective Measure
Wrinkles in paper Paper not matured

Variations in humidity during transport and in store

Gripper adjustment
Use after 30 days of manufacture

Condition the paper


Check Gripper adjustment
Difficulties in register Paper size variations through moisture
Pick - up and moisture loss
Condition paper
Paper buckles in the inking area resulting in register difficulties Large print area and paper with low grammage Use appropriate paper and less concentrated ink
Sheet tail curls The printed sheet curls at the tail due to strong ink and a small break angle at the blanket Do not use concentrated ink
Enlarge the blank area
Sheets stick together Sheets stick together at the printed areas in the second pass Frequently aerate the sheets 
Use only small piles
Replace emulsified Printing ink
Increase the quantity of powder
Paper repels ink The ink is repelled by the paper Change the paper or varnish it
Paper structure shows through in the printing subject Spots in the printed area on the wire side of the paper Print printed area twice
Use less concentrated ink in the first pass
Troubles in paper transport due to static electricity Wrong climatic conditions
Air humidity is too low
Air condition the paper and the shop
Ink accumulates Ink accumulates on the blanket Use sized paper of better quality
Add print oil
Paper sheets cockle in the pile Air is too dry
Paper piles are dry at the edges
Condition the paper
Paper sheets are wavy Air is too humid Condition the paper
       
 

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