How to solve the problem of paper sticky rubber in offset printing
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In the offset printing process, the paper sticky rubber means that the surface fiber material of the paper is adhered to the surface of the blanket by the ink during printing. Paper-adhesive rubber generally appears in the case of printing full-page and large amount of ink, especially when printing coated paper, when the printed ink layer is relatively thick, and the amount of ink is large, the paper sticks to the rubber. occur. It affects the reproduction of printed products and the integrity of the dots, making printing impossible, and printing inks and wastes cause waste. If it is found to be untimely, the blanket will be embossed or the paper adhered to the surface of the blanket will be transferred to the ink roller through the plate cylinder, so that the print adheres to the paper scum, causing the printing to be interrupted. The improper adjustment of the paper feeding mechanism of the offset printing machine is one of the causes of the paper sticky rubber, and the other aspects are as follows.
1. The bite force of the impression cylinder biting paper is not enough
In offset printing, especially printing thick and high-grade coated paper, cloth paper, offset paper, etc., encountering a large area of the ground, a large amount of ink, the ink layer is required to be full and thick, paper adhesive rubber is easy to occur, the main reason is the biting paper of the impression cylinder Caused by insufficient bite force.
Solution: The bite force of the impression cylinder is not enough, which will cause the printing overprinting problem to be inaccurate. Increase the biting force of the impression cylinder to bite the paper, and bite the bite of the paper to make the bite of each bite. The force is uniform. If the overall biting force is still insufficient, the strength of the two side springs can be increased; if the paper sticking rubber is caused by the bite or the pressure pad is too smooth, it can be solved by attaching a fine gauze to the tooth pad to make the biting paper pad rough. In order to bite the paper, the bite force of the biting paper is not enough, causing the paper to stick to the rubber.
2. The timing of the transfer of the paper and the picking teeth of the drum is incorrect.
During the offset printing process, the paper is bitten from the oscillating paper, and the paper is passed to the paper to complete the printing process, and then transferred to the paper receiving teeth. There must be a certain transfer time between them to ensure the accuracy of the overprint and the paper transfer process. Continuity, at this time, if the handover time between the roller bite and the receiving jaw is too short, the handover time is too early, too late or incorrect, the paper will be lost in an instant, causing the paper to stick to the rubber.
Solution: Adjust the position of the opening plate of the paper-feeding teeth and the paper-biting teeth, and do not bite the paper to break the mouth. The transfer time of the two is controlled within the range of 3 to 6 mm.
3. The paper bite bite too light
When the paper picks up and bites the paper, the back end of the paper does not leave the drum, and the paper will still be in a rolling state. If the biting force of the paper picking teeth is small, it is impossible to bite and bite the paper. The back end of the paper is easily adhered to the surface of the blanket, which also causes the paper to stick to the blanket.
Solution: The bite force of the paper-carrying teeth depends on the four springs on the shaft of the paper-receiving teeth. If the bite force of the overall paper-carrying teeth is too light, the four springs can be pressed at the same time to increase the bite. Force, then adjust the bite force of each bite, use 60g/m2 kraft paper to reach into the teeth, pull the test out, so that the bite force in the middle and both ends of the tooth row is uniform, if the bite paper or the tooth pad is too smooth, the paper sticks the rubber You can remove the gauze or tape on the pad to remove the fault.
4. The pressure between the blanket cylinder and the impression cylinder is too large.
In the offset printing process, too much pressure on the printing will cause the paper to stick to the blanket. Even if the bite force of the roller biting paper and the receiving tooth is increased when the fault occurs, this phenomenon occurs frequently, especially in the printing ink layer. Thick, paper-like smooth coated paper is more common. At this time, the frictional pull force generated by the excessive printing pressure is greater than the bite force of the bite. This paper causes the paper to stick the blanket and make the paper on the blanket. The surface layer adheres very firmly, and it is very difficult to peel off the paper by hand, which is why it is caused by this reason.
Solution: The entire offset printing process is to solve the contradiction between ink and paper. To transfer the ink image coated on the printing plate to a certain amount of ink, then it must be transferred in the graphic and text process. Apply a certain amount of pressure. People often say that "no pressure is not a print" fully illustrates the importance of printing pressure.
Since printing pressure is so important, is it that the greater the pressure, the better? That is of course not. In general, the appropriateness of printing pressure is often manifested by the printing quality of printed products. The printing pressure should be based on the premise that the printed product has a strong dot, a clear picture, a bright color and a light shade, and the smaller the better, the better.
In order to avoid the paper sticky rubber caused by the printing pressure is too large, the printing dot is clear and complete, the minimum pressure should be used, and the neutral and soft lining materials should be selected.
5. The receiving bite axis positioning is not correct
Under normal circumstances, the offset printing machine is positioned correctly before the factory, and the positioning of the receiving teeth is basically correct. However, there is a certain error in the processing of the receiving head of the receiving head. During the process of adjusting the receiving and gnashing teeth, the position of each of the receiving teeth and the dental pad is not consistent. When it is connected with the nip of the impression cylinder, it reflects that the distance between the receiving teeth and the front edge of the impression cylinder is inconsistent. If the distance is too large, it will cause the paper to bite and the paper will not bite or the paper will be too little.
Solution: For the incorrect positioning of the delivery tray, it should be solved by replacing the new shaft cover. For improperly adjusted delivery, the teeth should be readjusted so that each row of pads is in the same parallel. on-line.
6. Paper viscosity rubber caused by the viscosity of the ink
Offset y, m, c, Bk four-color common ink, the viscosity of which is Bk>c>m>y, the viscosity of black ink is large, and the viscosity of yellow ink is the smallest, so when offset printing darker color ink, due to high viscosity It is prone to failure of the paper sticky rubber.
Solution: 1 In order to make the ink have good printing adaptability, it is often necessary to add some auxiliary materials according to the requirements of the printing to adjust the viscosity of the ink. 6# varnish can be added, 6# varnish is a kind of oily fluid substance with a certain viscosity and a yellowish color obtained by heating and refining dry vegetable oil. 6# varnish can play two roles. :a, that is, it plays a role in dilution in the ink; b, plays a role in reducing the viscosity of the ink. When the 6# varnish is added to the ink, the viscosity and concentration of the ink are lowered, and the fluidity of the ink is increased. Brushability enhances the printability of the ink.
2 Add a detackifier to the ink. The detackifier is a mixture of wax pastes and is an auxiliary material for adjusting the viscosity of the ink. Without increasing the fluidity of the ink, the viscosity of the ink can be lowered to shorten the filament of the ink.
In summary, the failure of the paper adhesive rubber is caused by a variety of factors. In the work, the problem of paper-adhesive rubber is encountered. It is necessary to comprehensively analyze and treat differently. In addition to the failure of paper-feeding, paper-receiving and paper-feeding in offset printing machines, the poor printability of raw paper and ink is also one of the reasons.