Quick elimination of wrinkle in carbon free paper

"Padding method" can quickly eliminate the wrinkle fault of carbon free paper printing

carbon free copy paper, also known as pressure-sensitive recording paper, is a commonly used printing material for multi copy reports, bills, computer terminals and so on. It is convenient and fast to use, and is deeply welcomed by users. It is widely used in aviation, postal service, telecommunications, commerce and other service industries. Because the carbon free paper is light and thin, and its stiffness is relatively poor, when the moisture content of the base paper is not properly controlled, the paper edge is prone to curl or wave deformation after unpacking. In this way, when the offset press is used for printing, the edge of the paper is easy to wrinkle, which not only does the printing quality of the product not meet the user's requirements, but also causes certain obstacles to the normal printing of the machine

1 Analysis of printing wrinkling fault

our company used J2205 split two-color offset printing machine to print the top couplet and Zoomlion carbon free paper (large four-way open 59.5 44.3cm specification), but when the Yellow bottom couplet printed to 45g was carbon free on the basis of repeatedly soliciting the opinions of relevant departments, enterprises, industry experts and scholars, Both sides of the paper are frequently used in domestic experiments and even become indispensable equipment. The machine is cheap and often has wrinkling faults, resulting in the quality defects of form layout deformation and missing pen and stroke of text. It also affects the accuracy of nested products and does not meet the quality requirements of use. After this problem occurred, although the operator successively reduced the printing pressure, checked the flatness and tightness evenness of the blanket, and repeatedly adjusted the pressure of the paper teeth of the drum, it was of no help, and the printing wrinkle still could not be eliminated. The semi-finished base paper after cutting can not be returned or replaced. The customer is in a hurry to demand the goods. The situation is difficult. I don't know what to do. In this regard, through on-site observation and inspection, the author found that the carbon free paper is prone to wrinkling after printing, and the edges are curled and deformed. In addition, the left and right corners of the paper do not correspond to the roller teeth. In this way, with the rapid rotation of the roller during the printing process, both sides of the paper fall back because they are not bitten by the teeth, so that the left and right sides of the paper do not keep a straight line and synchronous rolling with the middle paper edge. Therefore, During embossing, it is easy to make the uneven paper surface produce several fold marks towards the two sides of the trailing tip through the extrusion of the roller. After analyzing the causes, the author immediately came up with an idea to solve the problem. Add cardboard liners to the left and right sides of the printing sheet, and use the elasticity of the blanket to tighten the paper surface through the liner cardboard strips to eliminate printing wrinkles

2. The so-called padding method is to pad and paste two cardboard strips with appropriate thickness and width on the appropriate position of the impression cylinder corresponding to both sides of the printing sheet. In view of the fact that the specification of the printing sheet is 44.3 59.5cm, in order to eliminate the problem of printing wrinkle quality, the author pasted a piece of white board paper with appropriate width and thickness on both sides of the printing sheet (the direction of the specification of 59.5cm), so as to tighten the paper surface in the stamping process, thus avoiding the wrinkle of the printing sheet faster and better, not only realizing the normal production, but also ensuring the product quality. The specific method is as follows: take a 250g thick white board, cut out two pieces of cardboard with a width of 5mm and a length of 430mm respectively, then use 5430mm double-sided adhesive tape to stick them on one side of the two cardboard respectively, remove a layer of wax paper on the surface, and then put a large fourfold paper on the cardboard, let the paper enter the embossing cylinder to bite the teeth according to the normal printing positioning of the machine, and jog the machine to the appropriate position, Paste the two strips of cardboard one by one on both sides of the impression cylinder and corresponding to the left and right sides of the printing sheet. When pasting, it is required that a section of the edge of the two 430mm long strips of cardboard should be about 13mm away from the corresponding edge of the biting paper of the printing sheet, that is, the long edge of the two strips of cardboard can be aligned with the trailing tip end of the printing sheet. In this way, the paper surface on the left and right sides of the printing sheet contacts the surface of the two strips of cardboard first, Subsequently, the hard cardboard strips force the rubber blanket to sink, so that the loose paper surface is tightened in the tensile deformation, that is, when the machine is in the embossing state, it first presses on the left and right edges of the paper, and then plays the role of tensioning the paper surface, so as to better eliminate the wrinkling phenomenon of paper printing. It is worth mentioning here that for the thin paper with uneven printing surface, the cardboard strips are used to pad the two sides of the embossing cylinder (corresponding to the two sides of the printing sheet). The good blanket should be replaced with the old one, so as not to press out two traces of the good blanket, resulting in two lighter traces when printing the flat or field version. In addition, after the printing of this batch of paper with poor flatness is completed, the two strips of cardboard on the embossing cylinder shall be torn off, and the residual glue on the cylinder shall be cleaned with gasoline to avoid the depression and deformation of the good blanket. If the wave deformation at the edge of the paper is particularly severe, the thickness of the pasted cardboard strip can be increased (for example, a layer of whiteboard can be pasted), and then the corresponding area and thickness of the backing paper on the back of the blanket corresponding to the cardboard strip can be cut off. In this way, the hanging state on both sides of the blanket can be used to form more expansion space during stamping, so that the tension range obtained during stamping can be further increased. The printing sheet is not easy to crack, and the damage to the blanket is also light, which can play a good role in eliminating the wrinkling of paper printing

3 Technical tips for reducing or preventing printing wrinkling

the production process practice shows that uneven printing sheets are the main cause of printing wrinkling. However, poor machines can also easily cause printing wrinkling. For example, there are defects in the structural characteristics, position and pressure of the paper teeth, as well as the characteristics of the lining, the flatness of the drum and the printing pressure, which will also cause the wrinkling of the printed tissue paper. Therefore, from the technical point of view of preventing printing wrinkling, when the printing sheet is held by the paper teeth for imprinting, there should be no slight slip or deformation after the pressure of the printing sheet. In particular, if the two paper corners at the edge of the paper bite move backward, it is very easy to produce printing wrinkling failure. Therefore, the paper corners at the left and right (width) sides of the printing sheet should correspond to the paper teeth when printing, Especially for thin printing paper, if the printing sheet is not bitten by the paper teeth, the probability of printing wrinkling is even higher. Secondly, during the positioning of the printing sheet, the paper teeth should bite more paper edges as much as possible, and the pressure of each tooth should be adjusted enough and kept uniform. Third, the lining shall be kept flat and compact to minimize the coefficient of compression deformation. Fourth, under the premise of maintaining the appropriate clarity of the printing page, the printing shall be carried out under the light printing pressure as far as possible. Through the control of these technical measures, the printing wrinkling fault can be minimized and avoided

after the reasonable adjustment of the machine, the thin paper with severe deformation of the printing paper still has the wrinkle fault, so the only way is to use cardboard strips to paste both sides of the embossing cylinder to tighten the paper in the embossing process and achieve the purpose of eliminating the printing wrinkle. Although this practice is suspected of violating the printing three level theory, the successful practice has shown that this method is feasible and practical. This is because the blanket is very elastic, and the two cardboard strips that are slightly higher than the surface of the embossing cylinder force the partially loose paper surface to be tensioned to both sides through embossing, which does not cause too much adverse impact on the printing pressure, page registration and ink layer transfer. Since the author established this method more than 10 years ago, the small offset printing test was successful, and then the printing wrinkling fault of J2108B split monochrome Offset printing machine was tested. The same good solution effect was achieved, which greatly reduced the waste of paper and improved the qualified rate of products. This time, our company used J2205 split two-color offset printing machine to print carbon free paper. After obvious wrinkling fault first appeared, the author applied this solution to quickly eliminate the wrinkling fault of paper printing, and also achieved good results in eliminating the wrinkling fault of carbon free paper printing. The effect is quite satisfactory