Dirt is a term used in the printing field, which refers to the appearance of oil stain in printed matter.Fouling in letterpress, intaglio and perforated plates is mostly caused by improper operation and page contamination.Fouling in lithography can be divided into oil and floating.
Fouling refers to the phenomenon that the blank of printed matter is polluted by ink.Fouling in letterpress, intaglio and perforated plates, mostlyoperationImproper, polluting the layout.Fouling in lithography can be divided into oil stain and floating stain[1]。
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Clean the layout, pay attention to the operation, and then correct it.
Greasy dirt
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For the lithographic layout, the image and text are hydrophilic, and the blank is hydrophilic. Wet the blank with water first;Then apply ink to make the image and text stained with ink, and the blank area will be rejected due to water.When the layout is in direct or indirect contact with the paper, the ink image and text are transferred to the paper as printed matter.If the ink contains more fatty acids or polar substances, has excessive adhesion to the page, slightly insufficient wetting water in the blank, or the hydrophilic layer is unstable and damaged, the ink particles will become lipophilic.When continuing to print, ink staining gradually increased and expanded, finally making the printed matterblankThe occurrence of ink stains at the position is called oil dirt.
In the process of printing, if the amount of ink on the page is too large or the amount of water on the page is too small, it is also easy to cause oil dirt.Scrub the layout, remove ink stains, and apply hydrophilic glue;Add thick and low polarity inking oil to the ink;Strengthening the wetting capacity of wetting water and increasing the dosage can correct[2]。
Floating dirt
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Another situation is that the ink is too thin and water resistance is poor;The excessive wetting water and too high acidity make the ink emulsified seriously and become particles mixed with the wetting water, so that the blank of the printed matter is completely stained with a layer of light ink, which is called floating dirt.
Scrub the layout, and add thick and water resistant inking oil into the ink;Reducing the amount of wetting water and reducing acidity and surface activity can correct[3]。
