(a) The back of the dirty
The ink printed on the substrate adheres to the back of another sheet, causing smudging. To prevent back-scratching, a dusting device is generally installed at the delivery section of the printing press so that fine-grained calcium carbonate is dispersed between printed sheets. In addition, accelerating the drying of the ink, reducing the height of the printed sheet, and placing a good ink-absorbing paper between the printed sheets suppress the pick-up phenomenon.
(b) Printout of ink
Offset of ink refers to the phenomenon that the front side of the printed sheet can be seen on the back side. To prevent the ink from passing through, you can choose a tight paper printing, can also increase the viscosity of the ink, and appropriately reduce the printing pressure.
(iii) Flying ink
The tiny droplets of ink, scattered in the air, are called "flying ink", also called fogging, and are the most common failures of high-speed rotary letterpress printers. To slow down the "flying ink" phenomenon, we can increase the humidity in the printing shop and use conductive inks such as water-based inks.
(d) Static electricity
In the printing process, the paper is not easy to separate, the paper on the delivery table is uneven, or the paper on the delivery table is skewed and overprinting is not allowed, etc., which may be caused by static electricity. To eliminate static electricity from printing, a static eliminator is generally installed on the printing press to ionize the air around the printing press so that positive and negative electrostatic charges on the paper are neutralized. It is also possible to spray an appropriate amount of mist around the press or behind the impression cylinder to eliminate static electricity on the paper. In addition, increasing the humidity in the printing shop is conducive to the elimination of static electricity.
Fifth, the quality requirements of letterpress print
Product quality means that the product is suitable for a certain purpose and can meet people's needs. The use of printed matter is various, the variety is different, and the printing methods are different. According to the process and equipment of letterpress printing, the quality of printed matter should meet the following requirements
(1) Dimensional Requirements The allowable error for fine product open size is 0.5mm, and the general product is 1.0mm.
(2)Pressure, ink printing pressure, ink uniformity. Text imprinting, fine products are clear and complete, and general products have no obvious lack of strokes.
(3) The degree of evenness of printed pages requires that the web uniformity of fine products be greater than 15/16, and the web uniformity of general products should be greater than 14/16.
(4) In the set-printing pages, the front and back pages of the pages are accurate, and the overprint error fine product is less than 1.5mm, and the general product is less than 2.5mm.
(5) The appearance of fine products, printed pages clean, unblemished version, nails, dirty marks, flawless pen breaks. General products, printed pages clean, no obvious paste, imprints, dirty marks, no obvious lack of strokes.
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