Despite the growing maturity of CTP technology, the laser imagesetter still maintains its strength in production. In printed publications such as product packaging, books and periodicals, there are still a considerable number of processes that need to be designed and produced before printing, output phototypes, and finally print the finished product. The quality of the phototypes will directly affect the quality of the final printed products, which shows that there are still many areas in the traditional process that need to be studied and explored. The author will talk about the experience of pre-press output quality management from the perspective of process management.
Original quality
From the perspective of total quality management, controlling the quality of phototypes should start with the manuscript. Because the quality of the manuscript determines the quality of the phototypes, the manuscript must be carefully checked.
1. Check whether the surface of the original is scratched, dirty, whether the text and lines are complete, and whether there are missing pens and broken pictures.
2. Check if the picture is discolored. Under natural light or a standard light source close to daylight, observe whether the achromatic parts such as white, gray, and black on the reflective manuscript interfere with other colors.
3. Check whether the main colors are accurate. In general, the colors of reflective drafts (such as photos) will be slightly more exaggerated than the actual scene colors, such as more vivid than the original colors. Reflective drafts with people as the main body should be based on the facial complexion.
4. Check if the contrast is moderate. The contrast of the reflection draft includes brightness difference, color contrast and contrast balance. Moderate brightness difference, there will be rich transitional color levels between high-key parts and dark-tone parts; moderate color contrast, the reflection color density is large, and has a strong three-dimensional sense; good contrast balance, the same color in high-key parts The color reproduction of the dark tone part will be very consistent.
Output document quality
The main inspection items for the documents that need to be typeset output:
1. Check if the register line, color mark and various printing and cutting lines are set up completely. The registration line should be black with four colors (C100, M100, Y100, K100). If there is no registration line, the output of four-color or multi-color phototypes is equivalent to a pile of waste products.
2. Check the image color mode. When the laser imagesetter outputs color separation films, all color images are in CMYK color mode. Therefore, you should carefully check whether the color mode of the linked image is correct through the linked image table before output. If the color mode of the color image is RGB or Lab mode, the mode conversion should be performed in the image processing software, otherwise there will be an image on the black version only when outputting the color separation film, or the color separation situation is not ideal, and even it cannot be output; if it is black and white Image, image mode should be grayscale or binary mode.
3. Check whether the resolution of the used image meets the printing requirements. Make sure that the scanned images, photos and other dot matrix images have the proper resolution, which is necessary to ensure the quality of the output photos.
The resolution of the print image is generally set to 1.5 to 2 times the number of dot lines. The resolution of some common publications is set as follows: the scanning resolution used by newspapers is 125 to 170dpi, because the number of dot lines for newspaper printing is 85 to 133 lines / inch; the scanning resolution of journals, magazines and promotional materials is 300dpi, because the number of dots for printing is 133 lines / inch or 150 lines / inch; the scanning resolution of high-quality picture books is 350 ～ 400dpi, because The number of dot lines used in most exquisitely printed albums is 175-200 lines / inch. It is best not to use the pictures downloaded online, because the resolution of these pictures is generally only 72dpi, and some are even lower. No matter how they are processed, the output will not be good.
4. Interpret preview results through RIP. The RIP interpretation preview is consistent with the final release result. By previewing the comparison manuscript or proof, check whether the image of the file link is correct, the image interpretation is intact (if the image is copied incorrectly, the RIP interpretation will be wrong), and the image color Consistent with the original, whether the text is garbled, whether the elements of the document are misaligned, whether the black version is overprinted, etc. This is the final check before output, so be careful to avoid quality problems.
Phototypesetter operation
After the imagesetter is started, its working status can generally be seen in the graphical interface of the control software of the output workstation. Items to be checked:
1. Whether the settings of the laser imagesetter match the system equipment and operate normally. To ensure the stability of laser energy, the laser head should be tested and corrected regularly.
2. Whether the concentration and temperature of the filming machine are normal. The development and fixing parameter values ​​should be set according to the performance of the photographic film and the chemical solution. The test strips and ladders should be used for regular testing. At the same time, the daily cleaning and maintenance work of the punching machine should be done to prevent the sediment from making the photographic film dirty.
3. Whether the performance of photosetter and liquid medicine is stable. In order to ensure the stability of the quality of phototypes, the use of raw materials should minimize the variable factors to achieve a relatively fixed use of raw materials.
4. Phototype plates are susceptible to being scratched by foreign objects during the operation and transmission of the equipment. The transmission components should be cleaned and wiped regularly, and replaced if they are damaged.
Output film quality
Check the quality of the output film, as the last process of the film, to really play a role in making up for the leak, it should pay enough attention to it.
1. Check the fitting accuracy. Generally speaking, the registration error of continuous output four-color or multi-color film is very small, if a job needs to complement one-color or two-color version, and the other color film is one day, two days or more For output, you should carefully check the registration accuracy of each color film. If the registration error is large, you should continuously output all color versions of the film. Of course, this should be based on the use time and working stability of the imagesetter. Some imagesetters have a large registration error even if they continuously output four-color film. At this time, you should consider repairing or updating the machine.
2. Check the imprint relationship of each color version against the original or proof. Sometimes, due to personnel operation or machine failure, the layout elements may be lost or misplaced. For books and publications, the best way to check is to attach the film to the original or proofs, if there are errors or omissions will be clearly visible. Of course, in this process, we must pay attention to avoid scratching the film, affecting the quality of printing.
3. Check whether the film is dirty. Dirty film is a common problem in the output process. In general, the water washing tank should be cleaned before starting up every day, and the water purification equipment of the external water supply switch should be turned on before water injection, so as to prevent the sediment deposited in the pipeline from being brought into the water washing tank, scratching or attaching to the film Film quality. After the work is completed, the water washing tank should be emptied and carefully cleaned.
4. Check the network cable angle of each color output film. In order to avoid hitting the net, in theory, the difference between the four colors should be 22.5 °. In actual production, the four-color printing usually uses 15 °, 45 °, 75 ° and 90 °. Among them, the yellow version has weaker visual stimulation and poorer visual perception, so it is generally set to 90 °. Since human vision is most sensitive to 45 °, the main color version of the original is generally set to 45 °, and the specific setting should be based on the design of the printed product. The angle of the network line can be checked through the magnifying glass to the angle of the network line of each color version of the film, or it can be measured with a network angle measurement tool. In addition to the special requirements of customers, the general network cable angle setting should not be changed at will, so as to avoid unnecessary losses.
5. Check the solid density of the output film. Check the solid density of the film through the transmission densitometer, which is generally required to be above 3.5, preferably around 4.2. If the density is too high, the phenomenon of paste will occur; if the density is too low, the ink color will be lighter and look unrealistic for the printed products with text and solid layout. At this time, we must consider replacing the fixing solution or cleaning the laser head to ensure the stability of the output film quality.
In summary, the pre-press output process is carefully and accurately checked, and corresponding measures are taken to control it, which can not only improve the quality of phototypes, but also improve the production efficiency.
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