Analysis on the key points of screen hanging techn

2022-08-02
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Analysis on the key points of the hanging process for the printing of commonly used books and periodicals (Part 2)

④ setting of the total amount of ink

the printing characteristics of the paper and the production speed of the printing machine determine that the total amount of ink in the image cannot be too high, which must be adjusted in place during prepress production. In Photoshop, a professional image processing software, appropriate printability control and adjustment can be carried out, as shown in Figure 1. According to the actual production comparison, the corresponding adjustment parameters are as follows:

⑴ the total ink volume of paper printing is generally controlled at 240% ~ 260%

⑵ the total ink volume of coated paper printing is generally controlled at 280% ~ 350%

⑶ the total ink volume of offset paper printing is generally controlled at 290% ~ 340%

⑷ the total ink volume of light coated paper printing is generally controlled at 280% ~ 300%

⑷ the total ink volume of light paper printing is generally controlled at 300% ~ 340%

the setting of this value is determined by the production process and actual printing conditions of each unit, and depends on the dot enlargement rate during printing. If the dot enlargement rate is too large (≥ 20%), it is necessary to reduce the value. Otherwise, the dark tone part is easy to die, and the medium dark tone level is seriously lost; If the dot enlargement is basically normal (≤ 10%), the value can be appropriately increased to ensure that the dark tone part is full of color, fully represent the level of the dark tone area, and facilitate the reproduction of the whole tone. In addition, the appropriate ink shall be selected according to different papers and printing machines

5 proficiency in printing technology

advanced printing equipment is controlled by operators who master the relevant printing technology. Pre press, printing and post press processing should be considered as a whole. If the operation is improper, even if the number of high lines is added (250 ~ 300lpi CTP version), it may not be able to print high-quality batch products. Only by formulating strict color management system and standardizing operation can we meet the requirements of the printing market. The following author lists some examples:

① a customer was attracted by CTP's advanced plate making technology, and was required to review whether the product could be tightened at the joint of the oil circuit system according to the different contents of the experiment (regular products, with 65g light coated paper printed on both sides in four colors, 16 product promotion leaflets, 1 print sheet, 200000 copies) using 250lpi CTP plate printing. Due to the lack of experience when CTP was just used, when printing to 50000 ~ 60000 printing, the plate was seriously ground, the dark tone paste plate and the highlight point were lost, so the CTP plate could only be re printed. A total of 3 overprint plates were printed. The printing effect was not better than that of PS plate printing with 2400dpi/175lpi film. After analysis, the paper surface is rough and not smooth enough. At the same time, the CTP version hangs too high, resulting in a bit of printing resistance. In the future, the CTP version of 2400dip/175lpi will be printed again on the same kind of paper. The phenomenon of too fast plate grinding will disappear. At the same time, the printing effect is very good, and the customer is satisfied

② a captain operates a Heidelberg CP2000 four-color machine, which was manufactured in 2002, to print plastic products for construction and industrial supporting facilities (automobiles, communications, computers, household appliances, wires and cables, etc.) in China. The annual amount of plastic used is even more amazing, and the picture album cover with high quality requirements. The materials are 2400dpi/175lpi CTP printing plate, imported 200g/m2 double copper paper and Japanese four-color ink. Due to the tight production cycle, CP2000 is arranged for temporary insertion printing. During proofreading and sample checking, it was found that the highlight part of the printed matter was seriously lost, and the dark tone was generally not full. After increasing the pressure, it was still not resolved. Check that the relevant printing parameters were normal. When the captain was puzzled, the author checked the work records of the machine and found that the machine had continuously printed color pages of teaching materials for more than 50 days, the blanket had not been replaced, and many parts had been indented. At that time, only the rubber reducing agent was used for coating, and the elasticity of the rubber blanket has become poor. After being reminded to replace the new blanket, the problem was solved and the cover was successfully printed

③ for a cover product, the customer provides electronic documents and digital samples, which are printed in four colors (with large field black) + large field gold and silver ink spot colors, and the author's unit is entrusted to print. Due to the negligence of prepress work, there was no effective printing suitability treatment, and problems were encountered during printing: Although the corresponding ink volume was increased, the black, gold and silver ink color still did not meet the requirements, and the ink color was flat and not full enough. If the ink volume was increased again, the bottom would be sticky and dirty, and the plate would be pasted. The film could only be readjusted and printed again, so as to achieve the effect required by the customer. The specific adjustment is as follows: black field plus green 50%, gold field plus yellow 50%, magenta 20%, green 20%, silver field plus black 15%, and a small amount of bright paste is added to black, gold and silver inks to improve the gloss of the printed image

④ light weight printing paper is also called "light weight paper". Its paper color conforms to the international trend of environmental protection that the whiteness of paper is not higher than 84 degrees. The original color is used to make people more comfortable when reading. Books and periodicals printed on light weight paper are not easy to turn yellow. The paper is 20% thicker than offset paper of the same weight, which is quite luxurious and high-grade. At present, it is mostly used in books, teaching materials and high-end magazines. As it is a new paper material, we failed to master its printability when we first printed. During four-color printing, 175lpi is too high, the highlight is dimmed, the dark tone is grayed, and it is easy to paste the plate. The whole page is extremely dim. Therefore, 150lpi is hung instead, and the image is moderately contrasted, sharpened and saturated. Printing with ink with good fluidity has significantly improved the printing effect, and the printing task is completed according to the contract

source: PRINT world author: Huang Ge

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