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In letterpress printing, the common faults are: dirty back, ink through printing, flying ink, static electricity, etc. These faults affect the printing quality, and corresponding measures must be taken to eliminate them.
(1) The ink printed on the back of the substrate is rubbed on the back, which sticks to the back of another printed sheet, causing smudging. In order to prevent the back side from being smudged, a powder spraying device is generally installed in the paper receiving department of the printing press to disperse fine particles of calcium carbonate between the printed sheets. In addition, accelerating the drying of the ink, reducing the height of the stack of printed sheets, and placing paper with good ink absorption between the printed sheets can suppress the smearing phenomenon.
(2) Ink-through printing Ink-through printing refers to the phenomenon that the front imprint can be seen on the back of the printed sheet. To prevent the through printing of ink, you can choose paper with high tightness to print, or you can increase the viscosity of the ink and reduce the printing pressure appropriately.
(3) The tiny droplets of flying ink ink, which are scattered in the air, are called "flying ink", also known as the mist of ink, which is the most common failure of high-speed rotary letterpress printing machines. To slow down the "flying ink" phenomenon, you can increase the humidity of the printing workshop, so that the device has conductive ink such as water-based ink.
(4) During the electrostatic printing process, the paper is not easy to separate, the paper on the delivery table is unevenly received, or the paper on the delivery table is skewed and the overprint is not accurate, etc., may be caused by static electricity. To eliminate printing static electricity, a static eliminator is generally installed on the printing machine to ionize the air near the printing machine, thereby neutralizing the positive and negative static electricity on the paper. You can also spray an appropriate amount of water mist in the vicinity of the printing machine or the upper back of the impression cylinder to eliminate static electricity on the paper. In addition, increasing the humidity in the printing workshop is conducive to the elimination of static electricity.
(5) The quality requirements of relief printing products The product quality refers to the products that are used for a certain purpose and can meet the characteristics that people must need. Printed materials have many uses, different varieties, and different printing methods. According to the technology and equipment of letterpress printing, the quality of the printing should meet the following requirements (1) Size requirements. The tolerance of the fine product format size is 0.5mm. The general products are 1.0mm.
(2) Pressure, ink color printing web pressure, ink color average. Text imprints, fine products are clear and complete, and general products have no obvious missing strokes.
(3) The average format of printed book pages requires that the average format of fine products should be greater than 15/16, and that of general products should be greater than 14/16.
(4) In the page of the page printing, the positive and negative overprints of each page are correct. The precision of the overprint error is less than 1.5mm, and the general product is less than 2.5mm.
(5) Fine-looking products, neatly printed pages, no paste, nail shadows, dirty marks, and missing pens. For general products, the printed book pages are neat, without obvious paste, nail marks, dirty marks, and no obvious lack of pens and strokes.
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