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[China Glass Network] In the printing process, a single fault caused by a single material is rare. Most faults are caused by many factors, but some factors are the main cause of faults. The proportion of faults caused by inks in offset printing is relatively large, mainly in the following aspects:
First, sticky and dirty on the back
Since the ink dries too slowly, the ink is too soft, too thin, and the amount of ink is too large, the ink on a printed piece of ink is stuck to the back of the upper sheet of paper. Most of this phenomenon occurs in the solid (or dark) portion of the ink on the print. Sticking, pasting, and lumping (commonly known as sticking together) is a more serious phenomenon of sticking back. This refers to the case where a printed pile of printed matter is stuck together. The second side of the embossed viscous means that it is printed on the second side immediately after being printed on the front side, and the result is sticky in the printing.
At present, to solve the problem of dirty on the back of the printed matter, the following measures are generally adopted:
(1) Using a fast drying ink, an infrared dryer is used for a web offset press.
(2) Use dusting to prevent back dirt.
(3) Use a cool shelf to reduce the height of the stack.
(4) Printing on rough paper by increasing the printing pressure and reducing the amount of ink.
(5) Control the pH value and amount of the dampening solution to prevent ink emulsification.
(6) Adjust the temperature and humidity of the workshop and rearrange the printing color sequence.
(7) The field area of ​​the graphic is too large, and the ventilation is enhanced after printing.
(8) Adjust the amount of desiccant.
(9) A method of using an anti-sticking agent or a viscous liner.
Second, ink crystallization (vitrification)
The so-called "ink crystallization" means that the printing interval of the two-color ink is improperly controlled, and the first printing ink has been dried before the one-color ink is overprinted. Since the dry-solid ink layer is very low in viscosity and wetted by the ink, it is difficult for the next color ink to adhere thereto.
Generally, this phenomenon occurs in the ink overprinting of a monochrome offset printing machine. In order not to cause ink crystallization failure, the ink layer of the first printing must generally have the following conditions:
(1) Maintaining a certain wettability, it can be wetted by the ink printed on the back.
(2) Maintain a certain viscosity, and the adhesion of the ink after printing is greater than the cohesion of the ink after printing.
(3) Control the amount of desiccant (dry oil) used.
If there is a printing process failure of "ink crystallization", the surface of the ink can be rubbed with a fine gauze to make the surface of the ink film rough, and the capillary adsorption force is increased to improve the ink overprinting effect. For "ink crystallization" prints with large printing size and large batch size, it is better to overprint the viscous oil with high viscosity on the surface of the ink, and use its strong adsorption to adhere to the dry ink layer, and then use it. As a medium, the post-printing ink adheres well.
Treatment method: Because the number of prints is large, it is necessary to cover the oil once and then print. Remember to make plans for the next print.
Third, the ink plate caused by the ink factor
(1) The viscosity of the ink is too large to cause the plate to produce a pattern. The viscosity of the ink is too large, in addition to making the transfer difficult, it will also break the condition of the intermediate layer of the ink layer, so that the remaining ink layer of the plate is insufficient, and the pattern is partially exposed and worn to cause the pattern.
Treatment: Add some de-adhesive to reduce the viscosity of the ink, but do not increase the fluidity of the ink too much.
(2) The viscosity of the ink is too small, so that the printing plate paste, the ink with small viscosity is easy to be emulsified, causing the floating, the ink can not be transferred normally, and the pigment particles are gradually accumulated on the ink roller, the printing plate and the blanket. When the pigment particles are deposited to a certain thickness on the printing plate, the paste is caused, and sometimes the plate is caused by insufficient remaining ink layer on the printing plate.
Treatment method: Add some No. 0 varnish.
(3) Excessive fluidity of the ink causes the dot to expand and deform. The fluidity of the ink is insufficient to cause the printing plate to produce a pattern. If the ink is too fluid, the ink layer is easy to spread, the footprint geometrical size is enlarged, the dot cannot be correctly copied, and the ink fluidity is insufficient. Often spread unevenly, causing the printing plate to be insufficiently inked.
Treatment method: Different varnishes can be selected according to ink fluidity.
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