Analysis on the Causes of Dirty Prints and Countermeasures
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The ink printed on the surface of the paper, under the action of paper stacking gravity or moving friction between papers, or relative movement with other objects in contact with it, produces dirt on the back of the top sheet of paper, mainly with dirt, sputum Dirty, dirty, sticky and other forms. Some adjacent two prints adhere to each other through the sticky layer of the ink layer during the drying process.
1. The cause of dirty prints
(1) The surface of the paper is flat and smooth, and the ink cannot be dried quickly.
(2) The amount of ink is too large, causing the printed ink layer to be too thick and not easy to dry.
(3) The ink is too thin and the viscosity is too small.
(4) The ink itself has poor drying properties.
(5) The operator does not properly control the ink and water balance, causing the ink to emulsifie.
(6) The accumulation of printed matter is too high, and gravity imprinting works.
(7) The paper has not dried out and moved.
(8) The surface of the impression cylinder is dirty and transferred to the back of the print.
(9) The transfer roller is dirty.
(10) There are shredded paper inside the machine and it is printed when printed.
(11) When the maintenance is carried out, the oil eye of each part is too much butter and is thrown out during printing.
(12) If the semi-finished product is not dry, it will be printed if the printing or the finished product is not dry.
2. Upper dirt generated by the folding process
The web offset press needs to be folded after printing, and the folding machine part is also prone to dirty prints. The main reasons are as follows:
(1) Mistake in paper path: The printed matter is in contact with the parts of the printing machine (not the paper-feeding roller), causing friction.
(2) Too much ink on the paper feed roller.
(3) There is ink on the surface of the folding machine.
(4) The folding machine has one fold and two folds of paper on the surface of the paper conveying roller.
(5) Too much ink is accumulated on the platen roller and paper guide roller.
(6) There is too much ink on some parts inside the folding machine, and the printed matter is encountered when folding.
(7) Inside the folder, there are shredded paper hanging on the part, and the printed matter is hit when the page is folded.
(8) Folding machine with paper conveying belt, because the bearing of the fixed paper conveying belt is inflexible or stuck, the friction between the belt and the printed matter is generated, and the belt does not turn or the time does not turn when the belt rotates.
(9) When the printed matter is not completely dry, if the operator of the code page touches the graphic of the printed matter, fingerprint printing is easy to occur.
(10) The main reason for the adhesion is that the printed matter is too thick and the placement time is too long. The ink oxidizes the conjunctiva between the papers to release a large amount of heat, which promotes the thoroughness of the drying, and finally forms a page to be uncovered and forms a "cake" shape.
3. Exclusion method
(1) Adding and drying the paper towel holder, according to a certain amount, separate the printed materials layer by layer with special wooden boards to increase the contact between the printed matter and the air to promote drying.
(2) Use fast drying ink.
(3) Use a proper amount of powder spray to spray a layer of powder on the surface of each print without affecting the post-process to prevent sticking.
(4) Control the balance of ink and water, and adhere to the dry operation of water dry.
(5) If necessary, add an appropriate amount of desiccant to the ink to speed up the drying.
(6) After the printed matter has been printed for a period of time, it should be loosened to allow air to enter and speed up the drying.
(7) According to the different jobs, choose different types of printing presses. For example, if you want to print a large amount of ink, you should choose a printing machine with a drying device.
(8) Do not move unfinished and semi-finished products.