Folding process design and precautions for the hot

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Folding process design and precautions for printing paper processing

if we say that 10 years ago, the printing quality of books and periodicals still remained in the aspects of whether there were inaccurate overprinting, pasting and dirty spots in paper printing. Now, with the use of a large number of advanced offset printing machines, printing quality has become a comprehensive and brand-new concept. The process design of any link in the processing of a book cannot be ignored. Folding is a very important process in post press processing. The quality of folding directly affects the overall quality of books and periodicals

almost all printed materials that need to be bound into volumes have folding, such as enterprise product brochures, horse riding bookings, wireless binding products, picture albums, etc. When processing such products, the usual folding problems focus on the following two aspects:

1 When making up, the page numbers of the upper and lower editions cannot match accurately. After folding, there will be errors in the page numbers of the front and back pages and the position of the page center, sometimes the error will be very large

2. The printing sheet may be scratched and wrinkled sometimes through the folding machine

when looking for the cause of this kind of fault, many people tend to arbitrarily blame the improper operation of the folding machine master, and let them repeatedly adjust the machine, trying to correct and reduce the error. However, if we analyze from the perspective of process, the reason for this kind of error is that testers can choose their favorite report format (the test program adds the built-in excel report editing function, which expands the pattern of the previous single 1 professional report). The process designers in the production department often do not know enough about the suitability between paper and machine, resulting in low final folding quality

limitations of paper

many of us have folded paper airplanes, and we all have this feeling: the thicker the paper you use and the more times you fold it, the greater the strength you need, and the more inaccurate and beautiful it is. After such experience, it is not difficult to understand that if a piece of 1209/m2 paper is folded three times, it will eventually get 8 pages and 16 sides. On the one hand, the book folding seam becomes flat by the extrusion of the folding roller in the folding machine, on the other hand, the pressure will also deform the paper, which will appear on the folding seam along the upper part of the center of the folding seam. This is the result of the interaction between the paper and the folding roller, and this phenomenon cannot be changed by adjusting the pressure between the folding rollers

but we can take some measures to reduce this phenomenon and improve the folding quality. The most commonly used and effective method is to hit a flower wheel knife along the crease. There is another important reason for the occurrence of splayed wrinkles is that the paper with poor quality is used or the paper has been damp and deformed before folding

as for another common folding problem - inaccurate page number, it is difficult to correct it from the folding machine. Although China's binding quality standard has clear provisions on this error range, we can still improve the folding accuracy and reduce the error through efforts. When there is a layout design in which pictures, article blocks, patterns or lines span two pages or pictures, borders and lines are close to the cutting edge, the occurrence of eight character wrinkles or page misalignment can particularly attract the attention of readers

how to reduce the accuracy error caused by paper problems

if the reasons of the machine itself are not considered, paper is the biggest factor affecting the folding accuracy. We know that every kind of paper has a certain thickness regardless of its type and gram weight. When a piece of paper is folded a few times, the page spacing error is small; When all folded Book Posts finally adopt the superposition method to become a book block, it has little impact on the accuracy. However, if the paper is thick, the number of folds is large, and the folded books need to be matched (bound on horseback) into a volume, it will produce a certain thickness at the spine. This thickness will affect the folding accuracy and cause the following problems: when we make up, the position of the core is very accurate, but when the book is finally finished, the page number of the innermost post is offset outward as a whole, that is, the page number is closer to the front cutting than the outer post, which makes the page number of the whole book uneven

this error can only be intentionally corrected during prepress. When arranging production tasks, production process designers should comprehensively consider the relationship between machine and paper, and try to correct the error first. If they want to correct it finally on the machine, it is too late. Our suggestion is; When horse riding binding is carried out, or binding is still used but the paper is thick, the influence of paper thickness on folding accuracy should be considered. General wireless binding can be ignored. The most important thing is that you must not over adjust the pressure between the folding rollers to make the folding placid because the paper is thick. Doing so will only cause folds in the creases and damage the folding roller, the heart of the folding machine. If you encounter more special products, it is best to consult the binding workers

the following is the international general standard, no matter Stahl, MBO or domestic Zihong folding machine, the maximum folding times of each kind of paper (by gram weight) are given, For the reference of production designers when arranging the process:

folding type paper weight (g/m2)

fold 1 fold more than 180

fold 2 fold (cross fold) 150

fold 3 fold (cross fold) 120

fold 4 fold (cross fold) less than 80

from this table, it can be seen that the paper less than 80 grams can be folded up to 4 times into 32 fold stickers, and there are specific restrictions on several other papers of different thickness, The paper of more than 180 grams can only be folded once, and the crease should be consistent with the direction of the thread of the paper. The thicker paper should be indentation in advance to ensure the folding quality. These experiences are summarized by the bookbinding workers in the long-term production practice, and the production process designers should pay attention to when arranging the production process

in order to avoid the requirements of folding times on paper, there are some practices for process designers to refer to, that is, to use the combination of fan-shaped folding and cross folding to replace the most commonly used cross folding method to fold book blocks in China. Using three fan folds and one cross fold to get 16 fold stickers, this folding method can minimize the zigzag wrinkles caused by paper, and it is not necessary to use flower wheel punching. It is a quite good method, but many craftsmen are unwilling to use it, because a lot of work must be redone, not only considering the size of the paper, the printing format of the printing machine, and the folding specification of the folding machine, Moreover, the previously used painted stage paper should be redrawn, and the familiar folding samples should also be redone. In addition, factors such as the influence of the thread direction of paper on the finished products should also be considered early in foreign countries. As a result, many people have abandoned this method, but foreign countries often use this method to arrange the production of picture books and thick paper prints

treatment method of thin paper

products printed with thin folding paper (below 60g/m2), such as number books, use hybrid folding machines. The first folding system is a fence. When the paper enters the fence, it often skews due to its light weight. Secondly, because the friction resistance is far greater than the stiffness of the paper, the paper entering the fence often bends between the folding rollers before reaching the stop gauge at the top, resulting in insufficient folding accuracy

in order to reduce this phenomenon, you can make changes during plate making: one way is to make the direction of the web thread entering the folding machine perpendicular to the first folding seam. This can increase the stiffness of paper folding, but the actual operation should be combined with the paper specification, folding style and existing folding equipment. Another solution is to use a knife folding machine. Although the speed is not ideal, the paper does not need to go up when entering the folding system (the page must go up in the fence plate to reach the stop gauge), so as to avoid the phenomenon that the thin paper is prone to wrinkle when the impact quality and energy of the thin paper are measured when the sample of 50% plastic film or sheet is damaged

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