The ink printed on the surface of the paper, under the action of the accumulation of gravity of the paper or the moving friction between the paper, or relative movement with other objects in contact, produces dirty marks on the back of the top sheet of paper, mainly smeared, rub Dirty, dirty, sticky and other forms. Some adjacent two printed materials will stick to each other during the drying process through the stickiness of the graphic ink layer.
1. Causes of dirt on 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 ink layer of the printed matter 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 is poorly dry.
(5) The operator did not control the water-ink balance correctly, causing the ink to emulsify.
(6) The accumulation of printed matter is too high, gravity imprinting works.
(7) The paper is not dry enough and is moved and rubbed.
(8) The surface of the impression cylinder is dirty and transferred to the back of the printed matter.
(9) The transfer roller is dirty.
(10) There is shredded paper inside the machine, and the printed matter is encountered during printing.
(11) Too much grease is added to each part of the oil eye during maintenance, and it is thrown out during printing.
(12) The semi-finished products are printed before they are dried or the finished products are bound before they are dried.
2. Fouling caused by folding process
The web offset press needs to be folded after printing, and the part of the folding machine is also prone to dirt on the printed matter. The main reasons are as follows:
(1) Wrong paper path: The printed matter is in contact with the parts of the printing machine (non-paper feed roller), causing friction.
(2) Too much ink has accumulated on the feed roller.
(3) There is ink accumulation on the surface of the triangle plate of the folder.
(4) There is ink accumulation on the surface of the one-fold and two-fold paper transfer roller parts of the folding machine.
(5) Too much ink has accumulated on the platen roller and paper guide roller.
(6) Too much ink accumulates on some parts inside the folding machine, and the printed matter is encountered when folding.
(7) Inside the folding machine, shredded paper hangs on the parts. When folding, it hits the running printed matter.
(8) For the folding machine with paper transfer belt, due to the inflexible rotation or jamming of the bearing that fixes the paper transfer belt, friction occurs between the belt and the printed matter, and the belt does not rotate or does not rotate when rotating.
(9) When the printed matter is not completely dry, if the operator of the code page touches the graphic of the printed matter, it is easy to produce fingerprint prints.
(10) The main cause of adhesion is that the accumulation of printed matter is too thick, the placement time is too long, the ink oxidizes the conjunctiva between the paper to release a large amount of heat, which promotes complete drying, and finally forms the page and the page cannot be uncovered, forming a "pie" shape.
3. Exclusion method
(1) Add drying racks, according to a certain amount, use special wooden boards to separate the printed products layer by layer, increase the contact between the printed products and the air, and promote drying.
(2) Use quick-drying ink.
(3) Use powder in an appropriate amount, and spray a layer of powdery material on the surface of each printed product without affecting the subsequent process to prevent sticking.
(4) Control the balance of water and ink, and insist on the operation of water and ink drying.
(5) If necessary, add an appropriate amount of desiccant to the ink to accelerate the drying speed.
(6) After the printed matter is printed for a period of time, it should be loosened to allow air to enter and accelerate the drying speed.
(7) According to the different jobs, choose different types of printing machines. For example, the printing machine with a large amount of ink should choose a printing machine with a drying device.
(8) Do not move unfinished products and semi-finished products.
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