In the offset printing process, paper sticky rubber means that the surface layer of fiber material in the printing is adhered to the surface of the blanket by ink. Paper sticky rubber generally appears when printing full-page solids and with a large amount of ink, especially when printing on coated paper. When the ink layer of the printed product is relatively thick and the amount of ink is large, the phenomenon of paper sticking to rubber is easy. occur. It affects the reproduction of graphics and texts of printed products and the integrity of the dots, making printing impossible, and the ink stains on the printed products causing waste products. If it is not found in time, the blanket will be dented or the paper adhering to the blanket surface will be transferred to the ink roller through the plate cylinder to make the printed matter adhere to the paper dust and ink residue, causing the printing to be interrupted. Improper adjustment of the paper delivery mechanism of the offset press is one of the causes of the sticky rubber of the paper, and there are the following aspects.
1. The bite force of the impression cylinder to bite the paper is not enough
In offset printing, especially thicker high-grade coated paper, textured paper, offset paper, etc., encountering a large solid area, large amount of ink, the ink layer needs to be full and thick, and paper sticking rubber is easy to occur, mainly due to the bite of the impression cylinder Caused by insufficient teeth bite.
Solution: Insufficient bite force of the platen of the impression cylinder will cause the problem of inaccurate printing overprint. Increase the bite force of the platen of the impression cylinder. The bite force of the platen tooth can make the bite of each bite bite. The force is uniform. If the overall bite force is still insufficient, the strength of the springs on both sides can be increased; if the paper sticky rubber caused by the tooth bite or pressure pad is too smooth, it can be solved by sticking fine gauze on the tooth pad to make the paper bite pad rough , Before it can bite the paper, to prevent the bite of the paper from biting, and cause the paper to stick to the rubber.
2. The delivery time of the roller's clenching teeth and the receiving teeth is incorrect
During the offset printing process, from swinging the paper teeth to bite the paper, to the roller teeth to complete the printing process, and then to the paper collection teeth, there must be a certain handover time between them to ensure the accuracy of the overprint and the paper transfer process Continuity. At this time, if the transfer time between the roller teeth and the delivery teeth is too short, the transfer time is too early, too late or incorrect, it will lose control of the paper in an instant, causing the paper to stick to the rubber.
Solution: Adjust the position of the splint at the junction of the paper-collecting teeth and the roller teeth, and control the delivery time of the two within the range of 3 ~ 6mm based on the principle of not biting and tearing the paper.
3. Too little biting force for paper collection
When the delivery bite bites the paper, the rear end of the paper does not leave the roller, and the paper will still be in a rolling state at this time. If the receiving bite bite force is small, it is impossible to bite the paper tightly. The rear 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 collection teeth depends on the elasticity of the four support springs on the paper collection teeth. If the bite force of the overall paper collection teeth is too light, the four support springs can be pressed at the same time to increase their bite. Force, then adjust the bite force of each bite, use 60g /? Kraft paper to extend into the bite, pull out the test to make the bite force on the middle and both ends of the row of teeth uniform, if the tooth bite or pad is too smooth, the paper sticks , You can stick the fine gauze or adhesive tape on the bite pad to stick to the bite pad to eliminate the fault.
4. Excessive pressure between the rubber cylinder and the impression cylinder
In the offset printing process, excessive printing pressure will cause the paper to stick to the blanket. Even if the bite force of the roller bite and take-up teeth is increased when the fault occurs, this phenomenon occurs from time to time, especially in the printing ink layer. Thick, smoother coated paper is more common. At this time, the frictional pulling force caused by excessive printing pressure is greater than the bite force of the bite. The paper sticking to the blanket caused by this reason makes the paper on the blanket The surface layer adheres very firmly, and it is very laborious to peel off the paper by hand, which means that this is caused.
Solution: The entire offset printing process is to resolve the contradiction between ink and paper. To transfer the ink and text coated with a certain thickness on the printing plate to the printed paper, then the graphic and text transfer process A certain amount of pressure is applied. It is often said that "there is no printing without pressure" fully illustrates the importance of printing pressure.
Since printing pressure is so important, is this pressure the better? Of course not. Generally speaking, the appropriateness of printing pressure is often expressed by the printing quality of the printed matter. The printing pressure should be based on the premise that the printed product has strong dots, clear graphics, bright colors and shades, and the smaller the application, the better.
In order to avoid the paper sticky rubber caused by excessive printing pressure and make the printing dots clear and complete, the minimum pressure should be used, and neutral and soft lining materials should be used.
5. Incorrect positioning of the take-up grit shaft
Under normal circumstances, the offset printing machine's positioning of the gear-grinding shaft is basically correct before leaving the factory. However, there will inevitably be some errors in the processing of the head of the shaft of the paper-receiving row. In the process of adjusting the paper collection teeth, the position of each row of paper collection teeth and the dental pads cannot be kept consistent. When it intersects with the platen teeth of the impression cylinder, it reflects the inconsistent distance between the collection teeth and the front edge of the impression cylinder. If the distance is too large, it will cause the paper to catch the teeth or the paper will not bite too much, and the paper will stick to the rubber.
Solution: For the incorrectly positioned paper-receiving tooth row, it should be solved by replacing the new shaft head cover and repositioning. For improperly adjusted paper-receiving teeth and dental pads, readjustment should be made so that each row of dental pads is in the same parallel on-line.
6. Paper sticky rubber caused by high viscosity of ink
The commonly used four-color inks of y, m, c, and Bk for offset printing are in the order of Bk> c> m> y. The viscosity of black ink is large, and the viscosity of yellow ink is the smallest. , Prone to the failure of paper stick rubber.
Solution: ①In order to make the ink have good printing suitability, it is often necessary to add some auxiliary materials according to the requirements of the printed matter to adjust the viscosity of the ink when adjusting the ink. 6 # Ink Adjusting Oil can be added. 6 # Ink Adjusting Oil is a kind of yellowish oily fluid substance with a certain viscosity obtained by heating and refining dry vegetable oil. 6 # Ink Adjusting Oil can play two roles ： A. It plays the role of dilution in the ink; b. It plays the role of reducing the viscosity of the ink. When the 6 # ink is added to the ink, it reduces the viscosity and concentration of the ink and increases the fluidity of the ink. Brushability enhances the printability of the ink.
â‘¡ Add debonding agent to the ink. The detackifier is a mixture of wax pastes and an auxiliary material for adjusting the viscosity of the ink. Without increasing the fluidity of the ink, it can reduce the viscosity of the ink and make the filament of the ink shorter.
To sum up, the failure of paper stick rubber is caused by many factors. When encountering the problem of sticking to rubber in work, comprehensive analysis and differential treatment are required. In addition to the faults in paper feeding, paper collection and paper transmission of offset presses, poor printability of raw paper and ink is also one of the reasons.
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