Folding process design and precautions for printing paper processing

If we say that the quality of books and periodicals printed 10 years ago is still in terms of whether there is inaccurate overprinting, pasting and dirty spots on the page printing. Nowadays, with the use of a large number of advanced offset presses, the printing quality is a comprehensive , 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, and the quality of folding directly affects the overall quality of books and periodicals.

Almost all prints that need to be booked have folding links, such as corporate product brochures, saddle stitched books, wireless perfect binding products, picture albums, etc. For processing such products, the usual folding problems focus on the following two aspects:
1. When imposition, the page numbers of the upper and lower versions can not exactly match. After folding, there will be errors in the page numbers of the front and back pages and the position of the center of the page, and sometimes the errors will be very large;
2. The printed sheet passes through the folding machine, and sometimes it may be scratched, and sometimes "8" wrinkle marks appear.
When looking for the causes of such failures, many people often arbitrarily blame the improper operation of the folding machine master, and let them repeatedly adjust the machine to try to correct and reduce errors. However, if we analyze from the process point of view, the cause of this type of error is often due to the insufficient understanding of the suitability between the paper and the machine by the process designer of the production department, resulting in poor final folding quality.

Paper restrictions

Many of us have folded paper airplanes before, and we all have the feeling that the thicker the paper you use and the more times you fold it, the greater the effort you need, and it is not accurate or beautiful. After having such experience, it is not difficult to understand that if a sheet of 1209 / m2 is folded three times, 8 pages and 16 sides are finally obtained. On the one hand, the signature crease is flattened by the squeezing of the folding roller in the folding machine, on the other hand, the pressure will also deform the paper, and the "eight" will appear along the upper center of the crease on the crease. Wrinkle, which is the result of the interaction between the paper and the folding roller, cannot be changed by adjusting the pressure between the folding rollers.

But we can take some methods to reduce the occurrence of this phenomenon to improve the quality of folding. The most common and most effective method is to make a flower wheel cutter along the crease. Another important reason for the "eight" wrinkle is the use of poor quality paper or the paper has been dampened and deformed before folding.

For another common folding problem, the one-page code set is inaccurate. It is more difficult to correct from the folding machine. Although China's binding quality standards have clear provisions on this error range, we can still work hard to improve the folding accuracy and reduce errors. When there is a layout design in which pictures, article blocks, patterns or lines span two pages or pictures, frames and lines are closer to the cutting edge, the appearance of wrinkles or page number misalignment can particularly attract readers' attention.

How to reduce accuracy errors caused by paper problems

If you do not consider the reason of the machine itself, paper is the biggest factor affecting the folding accuracy. We know that each type of paper has a certain thickness regardless of the type and weight. When the number of folding of a piece of paper is not large, the error of page number spacing is not large; when all folded signatures finally use the stacking method to become a book core Time, it has little effect on accuracy. However, if the paper is thicker and has more folds, and the folded signatures need to be matched (horseback binding) into a book, a certain thickness will be produced at the spine. This thickness will affect the folding accuracy, and will cause the following problems: when we make the layout, the core position is very accurate, but when the book is finalized, the page number of the innermost post is offset outwards, that is, the page number is cut from the front mouth The location is closer to the outer post, which makes the page number of the whole book uneven. [next]

This error can only be corrected intentionally during prepress imposition. When the production process designer arranges the production task, he should consider the relationship between the machine and the paper comprehensively, correct the error as far as possible, and it is too late to correct it on the machine. Our suggestion is: when doing saddle stitch binding, or still use offset binding but the paper is thicker, we must consider the effect of paper thickness on folding accuracy. General wireless binding can be ignored. The most important thing is that it must not be because of the thick paper, and excessively adjust the pressure between the folding rollers to make the folds flat. This will only cause wrinkles in the creases and damage the folding machine's heart-the folding roller. If you encounter more special products, it is best to consult the binding workers.

The following international standards are given. Whether it is STAHL, MBO or the domestic Zihong folding machine, the maximum number of times each paper (by gram weight) can be folded is provided for production designers to refer to when arranging the process:
Folding paper weight (g / m2)
Fold 1 fold 180 or more fold 2 fold (Cross-fold) 150
Fold 3 fold (cross cross fold) 120
Fold 4 folds (cross cross fold) below 80

It can be seen from this table that paper under 80 grams can be folded up to 4 times into 32-sided folds. There are specific restrictions on several other papers with different thicknesses, while papers over 180 grams can only be folded once, and the fold seam should be the same. The direction of the thread of the paper is the same, and the thickest paper should be indented in advance to ensure the folding quality. These experiences are summed up by the majority of bookbinding workers in the process of long-term production practice, and the production process designer should pay attention to when arranging the production process.

In order to avoid the requirement of folding times on paper, there are some methods for process designers to refer to, that is, to use fan-shaped folding and cross-folding to replace the most common cross-folding method in China to fold the book block. Using 3 fan-shaped folds and 1 cross-fold to obtain 16-sided folds, this folding method can minimize the buckle caused by the paper, and does not need to use the flower wheel to punch, which is a very good method , But many craftsmen are reluctant to use it, because a lot of work must be redone, not only to consider the size of the paper, the printing format of the printing press, the folding specifications of the folding machine, but also the commonly used previously drawn plate paper To redraw, familiar folds must also be redone. In addition, the influence of the direction of the paper thread on the finished product should also be considered. In this way, many people have abandoned this method, but foreign countries often use this method to arrange the production of albums and thick paper prints.

Tissue paper processing method

Products printed on tissue paper (60g / m2 or less), such as telephone directories, etc., use a hybrid folding machine. The first folding system is a fence. When the paper enters the fence, it is often skewed due to lightness. Second, Because the frictional resistance is far greater than the stiffness of the paper, the paper that enters the fence often has not reached the top stop, and it has been bent between the folding rollers, resulting in insufficient folding accuracy.

To reduce the occurrence of this phenomenon, changes can be made during plate making: One method is to make the direction of the sheet thread entering the folding machine be perpendicular to the first folding crease. This can increase the stiffness of paper folding, but the actual operation should be combined with paper specifications, folding styles and existing folding equipment. Another solution is to use a knife-type folding machine, although the speed is not ideal, but the paper does not need to go up when entering the folding system, (the sheets must go up in the fence plate to reach the stop), thus avoiding the thin paper It is easy to produce wrinkles.

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