Some key points of quality inspection for the hott

2022-08-01
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Some key points of PS plate quality inspection

although the component development method used by PS plate is the main plate of lithography and the source link of printing quality, its production quality directly affects the printing efficiency and printing quality. Therefore, a series of careful inspection of printing plates in the prepress process is of great significance to effectively prevent production errors and printing quality accidents, and improve printing production efficiency and product printing quality

according to the author's quality management experience, the PS version should be mainly inspected in the following aspects:

I Check the specification of PS version

due to the different cylinder diameters of various types of offset press, the printing plate specifications are also different. In addition, for the same type of offset printing equipment, the printing plates are also different due to different product specifications and layout sizes. Therefore, it is necessary to carefully check the position of the printing plate pictures and texts in accordance with the product specification requirements, and check whether they meet the requirements of printing positioning, binding process and trimming size, so as to avoid problems found only after blindly loading and printing, resulting in unnecessary waste of time and labor

II Check the cleanliness and flatness of the printing plate

the inspection of the cleanliness and flatness of the printing plate mainly refers to the inspection of the front and back surfaces of the printing plate. Check whether there are dirty spots, hardened film and other residual impurities on the front plate. If any abnormality is found, handle it in time. The back of the printing plate should also be carefully checked to see if there is any foreign matter. If there is any hard foreign matter, it should be cleaned in time to avoid damaging the blanket. In addition, the thickness uniformity of the printing plate should also be tested, that is, the thickness error of the four corners of the printing plate should not exceed 0.05mm, otherwise it is bound to produce uneven pressure, which should be compensated by padding the plate. If there are obvious scratches, folds, cracks, bumps and other irreparable defects on the surface of the printing plate during inspection, the plate cannot be installed for printing, but should be remade to ensure the printing quality of the product

III Check the color code, color classification, gauge line and test strip of the printing plate

in order to identify whether the ink color of each color print is consistent with that of the sample, there is a drying color block 3 at the appropriate position of each color print plate The electromechanical phase sequence is not allowed to jump, and the color codes of various colors are placed under the printing plate or above the outward side in a sequential arrangement, so that the white pages, double sheets, reverse printing and waste sheets with inaccurate drawing gauge can be checked more accurately. Checking the color of the printing plate can prevent the quality problems and troubles caused by the prepress process errors. The author once encountered such a plate making quality problem in the inspection: the color codes of the blue plate and the yellow plate of the film were confused with each other. It was only after the plate was printed that the color was wrong (the grain layout was different), so it was very troublesome to replace the printing plate and re install and calibrate the plate. Therefore, for the sake of prudence, it is very necessary to carefully check whether the printing plate color is consistent with the picture and text in the prepress process. The method is to recognize according to the graphic features of the layout and the hue depth, because different pictures have different image structures and hue levels. The parts with large tonal contrast can be compared and identified. For example, taking the landscape picture as an example, those with deep forest leaves and shallow sky are cyan version, and those with deep leaves and shallow sky are yellow version. The inspection of the plate gauge line mainly depends on whether the position of the cross and corner lines on the plate where the electro-hydraulic proportional control technology is used in the material experiment is placed accurately, so as not to affect the post-processing and the appearance quality of the finished product. The gauge line is the basis of overprint and finished product cutting, and the appropriate position can not be ignored. If there is a drying test strip on the layout, check whether its position is accurate

IV Check the surface points and tone levels

during the inspection, the appearance of the points observed with a high-power magnifying glass shall be smooth, the circle can be clearly distinguished, and the edges of the points shall be free of burrs and defects. The point shape of the point cannot be oval or flat. The color of the dots shall be clear in black and white, and the dim sum shall not be gray or have white dots. Otherwise, it indicates that the grease sensing performance of the dots is poor, and the dots appear to be untrue during printing. For the inspection of the gradation hue of the printing plate, three different levels of high-key, middle and low-key can be selected to compare with the monochrome sample of the sample. When the points on the printing plate are slightly smaller than those in the relative area of the sample, it is normal that the points increase after printing due to the influence of various objective factors. If a small point is found missing, it indicates that the printing plate is too light. If the small white dots on the low-key layout are blurred, and 50% of the square dots are too many, it means that the printing plate text is too deep. The above conditions will affect the printing quality. Therefore, the negative, plate printing operation and plate material quality should be carefully controlled. Unqualified plates cannot be printed on the machine and should be remade

v Check the layout text and lines

due to inadequate film trimming or improper plate printing operation, the printed plates are prone to quality defects. Therefore, it is necessary to check the text and lines of the layout, which can better avoid printing quality failures and improve printing production efficiency. The text inspection mainly depends on whether there are missing strokes, missing words or missing punctuation marks. If any problem is found, it can be corrected in time or remedial measures (such as re printing) can be taken to ensure the printing quality. The inspection of lines depends on whether the layout lines are broken, incomplete, multi-point, and whether the line thickness is consistent with the sample. If printing overprint plates of fine products, such as maps, etc., it is appropriate to copy polyester sheets with opposite colors for superposition inspection. If the printed text and words are blue lines, the standard map polyester sheets with the same plate pattern and red lines shall be used to overlap and align with them. When the lines on the map are approximately black, it indicates that the text and words lines are accurate and intact. If a part is in red, it indicates that there is a missing line in the layout; If there are blue lines or dots, it means multi-point and multi line

to sum up, careful quality inspection of printing plates can not only discover and deal with quality hidden dangers in time, avoid printing quality problems in printing, ensure product printing quality, but also effectively improve production efficiency

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