Experience in quality management of pre printing o

2022-08-07
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Experience in prepress output quality management

although CTP technology is becoming more and more mature, the laser Imagesetter still maintains its strength in production. In the printed publications such as commodity packaging, books, magazines and picture albums, there are still quite a few that need to go through the process of prepress design and production, output Phototypesetting films, and finally print the finished products. The quality of phototypesetting film is directly related to the quality of the final printed product, which shows that there are still many areas to be studied and explored in the traditional process. Next, the author will talk about the experience of prepress output quality management from the perspective of process management

original quality

from the perspective of total quality management, the quality of phototypesetting film should be controlled from the original, because the quality of the original determines the quality of phototypesetting film, so the original must be carefully checked

1. Check whether the surface of the original is scratched or dirty, whether the text and lines are complete, and whether there are missing pens and broken paintings

2. Check whether the screen is biased. Under the natural light or the standard light source close to the sunlight, observe whether the white, gray, black and other achromatic parts on the reflection manuscript are interfered by other colors

3. Check whether the main colors are accurate. Generally speaking, the color of the reflection draft (such as photos) will be slightly exaggerated than the color of the actual scene, for example, it is more bright than the original color. The reflection manuscript with the characters as the main body should be based on the ruddy complexion of the face

4. Check whether the contrast is moderate. The contrast of a reflection includes brightness contrast, color contrast and contrast balance. The brightness difference is moderate, and there will be rich transitional color levels between the high-key parts and the dark parts; If the color contrast is moderate, the color concentration of the draft will be large, and it has a strong three-dimensional feeling; If the contrast is well balanced, the color reproduction of the same color in high-key parts and dark parts will be very consistent

output document quality

main inspection items for documents requiring phototypesetting output:

1 Check whether the overprint line, color code and various printing and cutting lines are set up completely. The overprint line should be four-color nested black (C100, M100, Y100, k100). If there is no overprint line, the output four-color or multi-color phototypesetting film is equivalent to a pile of waste products

2. Check the image color mode. When the laser Imagesetter outputs color separations, all color images are in CMYK color mode. Therefore, before output, carefully check whether the color mode of the linked image is correct through the linked image table. If the color mode of the color image is RGB or lab mode, the mode conversion shall be carried out in the image processing software, otherwise when the color separation film is output, only the black version will have an image, or the color separation condition is not ideal, or even cannot be output; In case of black-and-white image, the image mode shall be grayscale or binary mode

3. Check whether the resolution of the image used meets the printing requirements. It is necessary to ensure that the scanned images, photos and other lattice images have appropriate resolution, which is necessary to ensure the quality of output Phototypesetting films

the resolution of printed image is generally set to be 1.5 ~ 2 times of the number of dots and lines. The setting standards for the resolution of some common publications are as follows: the scanning resolution used by newspapers is 125 ~ 170dpi, because the number of dots and lines used for newspaper printing is 85 ~ 133 lines/inch; The scanning resolution of periodicals and publicity materials is 300dpi, because the number of dots and lines used for printing is 133 lines/inch or 150 lines/inch; The scanning resolution of high-quality albums is 350 ~ 400DPI, because most of the beautifully printed albums use 175 ~ 200 lines/inch. It is better not to use the downloaded images, because the resolution of these images is generally only 72dpi, and some are even lower. No matter how they are processed, the output effect will not be good

4. Interpret preview results through rip. Rip explains that the preview is consistent with the result that the average annual growth rate of the final release exceeds 24%. Through preview, check whether the image linked to the file is correct, whether the image interpretation is intact (if the image is copied incorrectly, rip interpretation will be wrong), whether the image color is consistent with the original, whether the text is garbled, whether each element of the file is misaligned, whether the black version is overprinted, etc. This is the final inspection before output, so you must be careful to avoid quality problems

operation of the imagesetter

after the imagesetter is started, its working state can generally be seen in the graphical interface of the control software of the output workstation. Items to be checked:

1 Whether the setting of the laser Imagesetter matches the system equipment and operates normally. To ensure the stability of laser energy, the laser head should be tested and calibrated regularly

2. Whether the concentration and temperature of the tablet processor are normal. The developing and fixing parameter values shall be set according to the performance of the Phototypesetting tablets and the solution, and the test shall be carried out regularly with the test strip and the ladder. At the same time, the daily cleaning and maintenance of the tablet punching machine shall be done to prevent the sediment from making the Phototypesetting tablets dirty

3. Whether the performance of phototypesetting tablets and liquid medicine is stable. In order to ensure the stability of phototypesetting film quality, variable factors should be minimized in the use of raw materials, so that the use of raw materials is relatively fixed

4. The phototypesetting film is easily scratched by foreign matters during the operation and transmission of the equipment. The transmission parts shall be cleaned and wiped regularly. Once the parts are damaged, they shall be replaced in time

output film quality

in case of oil leakage, the quality of output film shall be checked when changing seals. As the last process of film production, enough attention shall be paid to it to truly supplement and stop leakage

1. Check the fitting accuracy. Generally speaking, the nesting error of four-color or multi-color films continuously output is very small. If a live part needs to be supplemented with one color or two-color versions, and the films of other colors were output one day, two days or more ago, the nesting accuracy of each color film should be carefully checked. If the nesting error is very large, all color versions of films should be continuously output. Of course, this should be determined according to the service time and working stability of the imagesetter. Even if the nesting error of some imagesetters' continuous output of four-color films is very large, it should be considered to repair or update the machine

2. Check the imprinting relationship of each color plate against the original or proof. Sometimes, due to personnel operation or machine failure, layout elements may be lost or misplaced. For books, periodicals and publications, the best inspection method is to attach the film to the original or proofing draft, and errors and omissions will be clearly visible. Of course, in this process, we should pay attention to avoid the scratch of the film, which will affect the print quality

3. Check whether the film is dirty. Film smudging is a common problem in the output process. Generally speaking, the water washing tank should be cleaned before starting the machine every day without any broken or inverted rod. Before water injection, the water purification equipment with external water supply switch should be turned on to prevent the sediment deposited in the pipeline from being brought into the water washing tank, scratched or attached to the film, affecting the film quality. After the work, the water washing tank shall be emptied and cleaned carefully

4. Check the line angle of each color output film. In order to avoid collision, in theory, the difference between the four colors should be 22.5 °. In actual production, the four-color printing usually adopts 15 °, 45 °, 75 ° and 90 °. Among them, the yellow version is weak in visual stimulation comparison and Research on aluminum based composite materials, and the visual sense is poor, so it is generally set at 90 °. Since human vision is most sensitive to 45 °, the main tone version of the original is generally set to 45 °, and the specific setting should be determined according to the print design. The line angle can be checked with a magnifying glass or measured with a line angle measuring tool. Except for the special requirements of customers, the general line angle setting should not be changed at will to avoid unnecessary losses

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