At present, the printing of books and periodicals is a key business of many printing companies. It is related to the operation and development of enterprises, and the market competition launched by them is fierce. The quality of products does not become a weapon for enterprises to win. This article only introduces some experience in the quality control of offset offset printing press products.
Paper hanging and humidity conditioning
Papers for books and magazines are mainly offset paper, and are generally allocated directly from the paper mill by the publishing house. Due to poor printability of offset paper, printing directly on the machine can seriously affect the overlay accuracy of the product, and even wrinkle, ghosting, ink instability, inconsistent failure. Therefore, in addition to a few excellent quality offset papers, ordinary offset paper must be fully aired before printing to conduct proper humidity control. This can be used to blow away the paper ash and paper dust contained in the paper to reduce cleaning. The number of pauses in the blanket and Federer's delivery of paper can also make the moisture content of the paper in the printing process basically stable and reduce the paper deformation. These pre-printing preparations will undoubtedly have positive significance for improving the quality of book products.
Printing process quality control
The printing of books and periodicals has its own characteristics and must be targeted for process adjustment. In summary, its characteristics are reflected in two aspects.
1. Large batches of products, large number of posts, and more books and periodicals generally have larger prints and more pages, especially textbooks for primary and secondary schools. Therefore, it is necessary to use more brains and considerate production arrangements. Mainly to grasp the following points.
(1) Equipment Arrangement Which books a book is printed on by which machines, which specific machine to print which posts, must be assigned in accordance with the performance of the machine and the degree of difficulty of each post, to prevent a post by a number of different types of machines Printing, causing ink inconsistencies and other issues. The cover of the book is usually printed on a better machine.
(2) Use and preservation of printing plates For long-lived printing, it is necessary to pay attention to the protection of printing plates to improve the printing plate's resistance to printing force, and to avoid frequent changes in the printing process resulting in ink color changes. For businesses that need to be printed, the printed plates should be sealed after printing, and the original printing plates should be used as far as printing is concerned.
(3) Printing color sequence arrangement Due to the limitation of the quality of the used paper, the printing color sequence arrangement of offset paper and coated paper is different. First, offset paper is not as smooth as coated paper, and has strong surface absorption. It absorbs moisture easily during the printing process. Moreover, offset paper needs more printing pressure than coated paper, and it is prone to warp deformation. The text and some important patterns in printed products Inevitably there will be ghosting and overprinting.
For this reason, we generally use C, M, Y, K or M, C, K, and Y color printing sequences so that even if we encounter poor paper, the text will not appear ghost image, and the Y color will be placed at the end. One group is mainly for the purpose of not affecting the color rendering effect of the color pattern. As for the C version before the M version, it depends on whether the color version has a large area of flat screen. If the flat screen is more, it should be placed in the latter color group to make its outlets clear and to reduce network distortion. Of course, under special circumstances, it can be adjusted again. The purpose is to ensure that the writing is clear and the patterns are vivid and real. Of course, it is best to use a uniform color sequence in a book to prevent the colors of the machines from being in the same order, and the final ink color of the printed products is inconsistent.
(4) The unity of the ink in a special place should pay special attention to the uniform color of the same color block and cross-page picture in the book product. Otherwise, after the book is bound into a book, the ink color of two adjacent pages will be different, which will affect the product quality.
(5) Each machine must have a uniform ink signature for each machine. Excessively deep or shallow samples are not conducive to the control of ink and ink-water balance. Taking into account the strong ink absorption of offset paper, the density of the ink after drying will drop by about 0.10, so it can be slightly darker than the original when printing, to prevent the ink from drying out and lighten the color.
2. Paper surface is rough, paper is loose, and paper is more
Compared with the copper plate, the offset plate has poor printability and often brings many difficulties in printing. However, if handled properly, it can still solve this problem better.
(1) Increase printing pressure appropriately
Compared with coated paper, the printing pressure of offset printing is increased by about 0.1mm on the basis of the original setting. When the printing surface is low-strength, easy-to-pull and blanket-offset paper, printing pressure of about 0.05mm can be increased, the degree of brushing will be reduced, the imprinting will be more real, and the number of cleaning blankets may also be reduced. Although the increase in printing pressure will cause unnecessary increase in network points, but for the general books and products, it is not the main factor affecting the quality, it is important to grasp the stability and consistency of the color ink products.
(2) According to product conditions, ink viscosity should be properly adjusted to increase its fluidity. Ink is too sticky, too hard is not conducive to accurate transmission, affect the stability of the ink, and easy to pull the paper.
(3) Reasonably determine the number of clean blankets, neither too hard nor too lazy. After each cleaning, it is necessary to put 20 or so ink-jet papers and randomly extract them to prevent mixing with genuine products.
There are many factors that affect the stability of the quality of books and periodicals. In the actual work, we must not only pay attention to the daily routine work such as the traditional Sanping Sanqin, ink and water balance control, normal paper feeding by Feida, and accurate paper transfer, but also analyze and make specific adjustments according to the characteristics of each printed product. Trying to overcome various unfavorable factors and strive to improve product quality.
Reprinted from "Printing Technology" by Mo Guoxin
