In the printing process, a single failure caused by a single material is rare, and most failures are caused by a variety of factors. It is just that a certain factor is the main cause of the failure. The proportion of ink-induced failures in offset printing is relatively large, mainly in the following areas:
A sticky and dirty back
Because the ink is drying too slowly, the ink is too soft, too thin, and the amount of ink to be supplied is too large, the ink on a printed sheet is smeared on the back of the upper sheet. Most of this occurs in the larger solid (or dark) portion of the ink on the print. Sticking, sticking, and sticking (commonly referred to as sticking together) is the most serious phenomenon of sticky backs. This refers to the situation where printed piles of printed matter are stuck together. The second side of imprinting and sticking is that the first side is printed on the second side immediately after it is printed. As a result, there are stickies in the printing. This situation is mainly caused by the following factors:
(1) Paper with a rough printed surface requires a large amount of ink.
(2) Print double-sided glossy paper.
(3) The ink volume is large at the sites where printing is performed or where the density is high.
(4) When printing with oxidatively drying ink on poorly absorbent paper.
(5) The amount of ink desiccant is too much, it is easy to oxidize heat in the paper stack, cause the ink to stick and make the paper stick together.
(6) Ink emulsification causes stickiness.
At present, the following measures are generally adopted to solve the problem of sticky back of prints:
(1) Use fast-drying inks, infrared dryers for web offset presses.
(2) Use dusting to prevent sticky back.
(3) Use a cool stand to reduce the stack height.
(4) Printing on rough paper by increasing the printing pressure and reducing the amount of ink.
(5) Control the pH and amount of dampening solution to prevent ink emulsification.
(6) Adjust the workshop temperature and humidity and rearrange the printing color sequence.
(7) The area of ​​the graphic text is too large and the ventilation is strengthened after printing.
(8) Adjust the amount of desiccant.
(9) Use a non-adhesive agent or a sticking liner.
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In recent years, printing companies in many regions of the country have printed inks that are dry and have not returned to the film after they have been printed. However, after the printing process or the finished product is delivered to the user for a period of time, the ink film feels. Non-smooth, refers to the severe phenomenon of sticking when sticking or sticking or packing. The reproduction of this phenomenon is actually due to the fact that the softening point of the ink binder of the packaging printing product is too low. Of course, when the ink is diluted, the ink is mistakenly added with too much slow-drying solvent or the appearance of dampness due to inhalation of moisture.
Treatment method (1) Strictly choose the ink type produced by the regular manufacturer and with technical parameters.
(2) Surface treatment should be performed on substrates that are stained with oils, waxes, etc. during printing.
(3) Select the ink with higher softening point in the ink system.
(4) In the dry printing, the ink of one color is printed after the ink of one color is about to dry.
(5) Strictly control the temperature and humidity of the printing shop.
[Case 2-9]
A certain factory in the south processed a batch of wine boxes, which had a relatively large area on the ground. The surface was sticky and stained on the back for several days after printing. After the investigation, it was found that this phenomenon occurred not only in a printing factory. Many printers have similar situations.
[case analysis]
This is related to the local temperature and humidity. Under normal circumstances, if the temperature is low and the humidity is high, the finished or semi-finished products after printing must be ventilated to avoid the above failures.
[Case 2-10]
A factory uses J2205 type machine, 157g/m2 paper to print off the portrait, when the yellow, magenta two-color printing and then printing sky blue, black, found that the first two color bonding is serious, the color of the edge of the stick is difficult to tear open.
[Case Analysis]: There are two possible reasons for this phenomenon. One is that the yellow and magenta inks are heavier, and the other is larger. The second is that ink emulsification is more serious. This should not only pay attention to the amount of wetting fluid, but more importantly, the semi-finished products printed on the surface of the ink should be shaken after the film is formed, that is, after the semi-finished product is shaken, it is piled on another paper table.
Two ink crystallization (vitrification)
The so-called "ink crystallization" refers to the improper control of the printing interval between the two inks. The ink that has been printed first has been dried and solidified before it is overprinted. Due to the low viscosity of the dried ink layer and the low wettability of the ink, it is difficult for the next color ink to adhere thereto.
Generally, this phenomenon occurs in the ink overprint of a monochrome offset printing press. In order to prevent ink crystallization failure, the ink layer that is printed first generally must have the following conditions:
(1) Maintaining a certain degree of wettability, it can be wetted and adhered by the ink after printing.
(2) Maintaining a certain degree of tackiness, and 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 problem with the “ink crystallization†printing process, fine gauze can be used to rub the surface of the ink on the printed product to roughen the surface of the ink film and increase the capillary suction force to improve the ink overprinting effect. For large-format, large-volume "ink crystallization" prints, it is best to superimpose high-viscosity ink on the surface of the ink first, use its strong adsorption, adhere to the dry ink layer, and then use it For the media, the post-printing ink adheres well.
[Case 2-11]:
A factory uses a monochrome offset press to print 100,000 flower calendars. Its pattern is a red peony, the paper is 128g/m2 double copper, and the ink is a quick-drying light. When the yellow and the magenta were printed, when sky blue was overprinted, many blue inks were found to be difficult to adhere to.
[case analysis]:
This is a typical phenomenon of "ink crystallization". The reason for this phenomenon is that the paper used is poor in ink absorption, the second is the use of quick-drying light, and the third is the amount of white paper that is put on. Therefore, in view of this situation, special attention should be paid to the proper control of the amount of white paper to be discharged by the single-color offset printing press, and to change the color sequence appropriately.
Treatment method: Because of the large number of prints, it was necessary to cover the oil once before printing. Remember that you must plan well when you next print.
Three ink factors caused by the flower version
(1) The viscosity of the ink is too large, so that the layout produces a flower pattern. Ink viscosity is too large, in addition to making the printing difficult, but also will break the middle of the ink layer fracture conditions, so that the layout of the remaining ink layer is insufficient, due to the graphics part of the exposed wear caused by the flower version.
Treatment method: Add a certain amount of release agent, reduce the viscosity of the ink, but do not let the ink flow increase too much.
(2) The viscosity of the ink is so small that the paste of the printing plate and the ink of low viscosity are easily emulsified, resulting in floating of the ink and the ink cannot be transferred normally, so that the pigment particles are accumulated on the ink roller, printing plate, and blanket. When the pigment particles accumulate on the plate to a certain thickness, it will cause a paste plate, sometimes due to the lack of residual ink layer on the plate.
Treatment method: Add some No. 0 varnish ink properly.
(3) Insufficient ink fluidity causes the dots to expand and deform. The lack of ink fluidity causes the printing plate to produce flower patterns. When the ink fluidity is too large, the ink layer spreads easily, the geometric dimensions of the printing mark are enlarged, the dots cannot be correctly reproduced, and the ink flowability is insufficient. Often spread unevenly, resulting in lack of ink printing plate version.
Treatment method: According to the ink fluidity can choose different varnish.
Source: Ke Yin Network