If we say that the print quality of books and publications 10 years ago was still limited in terms of overprinting, pasting, and dirty spots in paper printing, and now, with the introduction of a large number of advanced offset presses, the printing quality has become a comprehensive one. New concept. Any process in a book's processing process cannot be ignored. Folding is a very important process in post-press processing. The quality of folding affects the overall quality of the book directly.
Almost all printed materials that need to be booked have hinged links, such as corporate product brochures, horseback books, wireless binding products, and albums. When processing such products, the usual folding problems are concentrated in the following two aspects:
1. When imposition, the page numbers of the upper and lower versions cannot be accurately matched. After folding, there will be errors in the page number of the front and rear pages and the position of the layout, sometimes the error will be large;
2. Sheets pass through a folding machine, which can sometimes be scratched and sometimes appear as "Eight" wrinkles.
When looking for the causes of such failures, many people often arbitrarily blamed them on the improper operation of the folding machine master and allowed them to repeatedly adjust the machines in an attempt to correct and reduce errors. However, if we analyze from the point of view of the process, the reason for this kind of error is often concentrated in the lack of understanding of the paper and the machine between the process designers of the production department, which results in the low quality of the final folding.
Paper restrictions
Many of our county counties have folded paper planes and they have the same feeling: When you use thicker paper and fold more times, the more effort you need, the more you can't fold it. After having such experience, it is not difficult to understand that if a 1209/m2 paper is folded 3 times, it will eventually get 8 pages and 16 surfaces. On the one hand, the signature folds become flat against the pressure of the folding roller in the folding machine. On the other hand, the pressure causes the paper to be deformed, and the “eight†appears on the center of the fold. Wrinkles, which are the result of the interaction of the paper and the folding rollers, cannot be changed by adjusting the pressure between the folding rollers.
However, we can take some measures to reduce the occurrence of this phenomenon to improve the quality of folding. The most common and effective method is to use a knurling wheel cutter along the crease. Another important reason for the occurrence of the "eight" wrinkling is that the paper with poor quality or the paper before the folding has been deformed by moisture.
For another common folding problem, one page is inaccurate, and it is difficult to start correcting it from a folding machine. Although China's binding quality standards have clear provisions on this error range, we can still work hard to improve the accuracy of folding and reduce errors. When the picture, article block, pattern, or line appears across two pages or the layout of the picture, border, and line is closer to the edge of the crop, the appearance of wrinkles or misalignment of page numbers can particularly arouse the reader's attention.
How to reduce the accuracy error caused by paper problems
If you do not consider the reasons for the machine itself, paper is the biggest factor affecting the accuracy of folding. We know that each type of paper has a certain thickness regardless of type or weight. When the number of times a single sheet of paper is folded is small, the page-to-page distance error is not large; when all folded signatures are finally stacked, it becomes a book core. At the same time, it has little effect on accuracy. However, if the paper is thick and the number of folds is greater, and the folded signatures need to be nested (bookbinding) into a book, they will have a certain thickness at the spine. This thickness will affect the accuracy of the folding, and will cause the following problems: When we make up, the position of the core is spelled correctly, but when the book is finally written, the page number of the innermost frame is shifted outwards, ie, the page number is cut off from the front mouth. At the distance from the outer posts, the pages of the entire book are missing.
This error can only be intentionally corrected during prepress imposition. When the production process designer arranges production tasks, he should comprehensively and comprehensively consider the relationship between the machine and the paper, correct the error as far as possible, and it will be too late to correct it on the machine. Our suggestion is that when saddle-stapling is done, or when the glue is still used but the paper is thick, consider the effect of the paper thickness on the accuracy of the folding. General glue binding can be ignored. The most important thing is that we must not over-adjust the pressure between the folding rollers to make the folds flat because of the thick paper. This will only cause creases to crease and damage the folding machine's heart-folding roller. If you encounter more special products, it is best to consult the binding workers.
The internationally-available standards are given below. Whether it is STAHL, MBO or domestic purple macro folding machines, the maximum number of times each type of paper (by gram weight) can be folded is for reference by the production designer when arranging the process:
Fold Type Paper Weight (g/m2)
Discount 1 off 180 or more
20% off (cross fold) 150
Discount 3 fold (cross fold) 120
40% off (cross fold) 80 or less
From this table, it can be seen that papers under 80 g are folded up to 32 times in a maximum of 32 folds. There are specific limits for papers of several different thicknesses, and papers over 180 g can only be folded once, and the creases should be The direction of the cocoon of the paper is the same, and thicker paper should be pre-indented to ensure the quality of the fold. These experiences are summarized by the vast number of binding workers in the long-term production practice. The production process designers should pay attention to the production process.
In order to avoid the number of folds on the paper, there are some methods for the process designer to refer to, that is, use the fan-fold and crisscross fold in place of the most commonly used cross-folding folding book. The use of 3 fan-folds and 1 cross-folds gives 16-sided folds. This folding method can minimize the wrinkles caused by the paper, and it is not a good method to use the flower wheel to make holes. However, many craftsmen are reluctant to use it. The reason is that a lot of work must be reworked, not only considering the size of the paper, the printing press of the printing press, the folding specification of the folding machine, but also the previously used well-prepared printing paper. If you want to redraw, you must do it again. In addition, factors such as the influence of the paper's silk direction on the finished product must also be taken into consideration. As a result, many people gave up this method, but foreign countries often use this method to arrange the production of albums and thick paper prints.
Thin paper processing method
For products printed with folded paper (below 60g/m2), such as phonebooks, etc., using a hybrid folding machine, the first folding system is a fence. When the paper enters the fence, it is often skewed due to lightness. Secondly, Because the frictional resistance is much greater than the stiffness of the paper, the paper that enters the fence has not reached the top gauge in many cases, and it has been bent between the folding rollers, resulting in insufficient folding accuracy.
In order to reduce the occurrence of this phenomenon, it can be changed at the time of plate making: One way is to make the sheet fed into the folder to be perpendicular to the first folding seam. This can increase the stiffness of the paper folding, but the actual operation should be combined with paper specifications, folding styles and existing folding equipment. Another solution is to use a blade folding machine, although the speed is not ideal, but the paper does not need to go up when entering the folding system, (pages in the fence must be up to reach the gauge), thus avoiding the thin paper It is easy to produce wrinkles.