Quality inspection and control of color restoratio

2022-06-23
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Inspection and control of color restoration quality of electric engraving intaglio

inspection and control of color restoration quality of electric engraving intaglio

in the printing industry, after long-term practice, people have realized that only in the whole printing reproduction process, through data management, can quantitative control of printing quality meet the needs of the rapid development of current printing technology. At present, the testing elements of control printing and plate making (plate printing) - signal strips, test strips and control strips have been widely used in offset printing, that is, in raw cotton samples and formal printing, color codes or control strips are printed on the remaining white areas, and the field density, point increase rate, neutral gray, tone, printing uniformity, resolution, clarity, etc. of four-color printing are scientifically and quantitatively controlled through testing instruments and charts. The method of feeding back data from printing to plate making is adopted, and a series of best data are selected as the basis for process implementation and quality management through a large number of measured data accumulated by engineers. This plays an important role in the management and control of offset color

however, in gravure color printing, especially in electric engraving gravure printing, there is no continuous and perfect quantitative control system in the whole process from plate making to printing. In most cases, operators compare the color originals and gravure samples of plate making manufacturers with the printing plants, and rely on subjective visual evaluation to evaluate the color restoration of printing plates. There are many disadvantages in this way. First, there is a big difference in the process between the gravure pre proofing of the plate making factory and the official printing of the printing factory. As far as the current proofing technology is concerned, it is still difficult to simulate the official printing effect, and the color restoration quality, which is difficult to be determined by printing samples alone, still needs to be determined after printing on the machine; Second, there is a big difference between the proofing conditions of the plate making factory and the printing conditions of the printing factory. It may take a long time for printing debugging to catch up with or approach the proofing effect of the gravure printing of the plate making factory, resulting in a large waste of printing materials; Third, for color tone restoration, quantity analysis cannot be done, and point increase cannot be detected; Fourth, during the printing process, it is unable to track and detect the surface wear of the printing plate, the change of point value, and the amount of ink transfer on the printing plate; Fifthly, the consistency of printing effect cannot be effectively controlled and managed for series printing plates and reproduction and reprint plates. Therefore, gravure printing should also be the same as offset color control. Test blocks or test strips should be placed at the remaining white areas of printing, for example, directly below the mark line or other places, without affecting the printing pattern and printing alignment, so as to detect and control the color restoration in the whole process of plate making and printing. This paper attempts to put forward the suggestion of adding test strips to standardize and standardize the detection and control of color restoration of electric engraving intaglio, and hopes to discuss with colleagues of intaglio printing and plate making factories

in fact, at present, a very strict quality control system has been established in gravure plate making and printing plants. However, most printing plants are not very clear about the plate making process of the plate making plant, and the plate making plant also lacks the necessary understanding and understanding of the printing process of the printing plant. Therefore, the color detection and control of gravure color printing is a common research topic of the plate making factory and the printing factory. The restoration control of color printing runs through the whole plate making and printing process. Both parties should strengthen mutual understanding and cooperation to ensure the continuity of color control from plate making to printing. It is not only necessary to connect the whole process of plate making to printing through gravure proofing. The gravure proofing must carry the necessary color control information

I. determination and control of printing characteristic curve

after the engraving values of the line, type and electronic engraving of the printing plate are determined, the ink content of each ladder of the gray ladder on the printing plate has been determined. In other words, under certain printing conditions, the printing characteristics of the plate cylinder are determined at the same time. We know that on the mathematical plane coordinate system, any two points can determine a straight line, that is, to determine a curve, at least three points are required. Therefore, when we measure the printing characteristic curve, considering that we can not place more test blocks or color codes on the printing plate cylinder, we usually place 4-5 steps of the ladder to measure the density value of each step on the ladder, so that we can approximately know and describe the printing characteristic curve of the printing plate. For example, 5 steps, such as 5%, 25%, 50%, 75% and 100% can be set on each color plate cylinder

the printing plant and the plate making plant can work out the printing density for official printing at these five places and the density value range for proofing by the proofing machine. It is very important to work out the engraving process at the printing point of the plate making plant. The engraving process parameters must be based on the actual printing effect of the printing plant and meet the requirements of the printing characteristics of the printing plant. The engraving process parameters of the electric engraving machine can only be determined after repeated calibration with the printing samples of the printing plant. In other words, the tone restoration of color is based on the final results of the printing plant. In the process of printing and proofing, by detecting the density value of each step of the ladder and comparing it with the standard value, you can know whether the printing characteristics of the printing plate are normal as the number of times of use increases, and you can also judge whether the printing and plate making Proofing of the printing plate are qualified, whether the color separation of the Electrical Division is accurate, whether the conversion of gravure printing is matched, etc

II. Measurement of the point value of the ladder

whether the engraving of the ladder on the printing plate is normal can directly reflect whether the color tone restoration is normal. Only when the point value engraving of each ladder slows down to normal can the correct color tone restoration be guaranteed under certain printing conditions. The engraving operators and quality management personnel of the plate making factory can determine whether the engraving value of the printing plate point is normal by detecting the point value of each level of the ladder. Because the engraving characteristics of the engraving head of the electric engraving machine can be described by a linear curve, it is possible to determine the engraving characteristic curve of the engraving head of the electric engraving machine as long as the engraving values of 2 points are defined. Therefore, in the process of electronic engraving and plate making, you can test the high light and dark point values in advance. After these two values are determined, you can determine the engraving characteristics of the engraving head of the electric engraving machine. However, the engraving value of the engraving head of the electric engraving machine will become smaller, the ink content will be reduced, and the gradient restore will deviate. With a ladder, you can monitor the wear of the engraving needle. For example, Nanhai plate making center found that the magenta version was not well transferred and the sample sheet was biased when making concave samples in a wall calendar plate making process. However, the trial engraving values of the magenta version were all normal. After checking the points of the flat part, it was found that the engraving needle was worn

if there is a ladder in the imported version, it is easy to find the abrasion of the engraving needle by checking the point engraving value of the middle step of the ladder. Most printing plants in Switzerland are not equipped with point measuring devices, which can not detect the point engraving of the printing plate, track and observe the surface condition of the printing plate during the printing process, and quantitatively analyze the changes of points due to wear. Therefore, in order to control the restoration of color gradients, printing plants should be equipped with not only densitometers, but also point measuring instruments. Using densitometer and point measuring instrument, we can control and test the quality of printing plate. Through the data analysis of the printing materials and ladder printing data of the printing plant, the engraving process of the engraving plate in the plate making plant can be calibrated repeatedly, and the best electro engraving process parameters can be selected

to study the action of material friction and wear 1. Generally, a series of parameters such as the friction and wear characteristics of the friction pair need to be measured with the help of a friction and wear testing machine. 3. Determination of small points in the highlight area

determination of small points in the highlight area of various color plates is the focus of plate making. Human vision is the most sensitive to the medium and high profile of the image, which can also be reflected in the printing characteristic curve. Whether the small dot value of the highlight area is properly formulated directly affects the restoration of the medium and high tone level. If the highlight value is set to be low, some pixels of the image highlight will be lost during printing. Although increasing the ink concentration can improve it, it is easy to make the dark tone density too large and produce color deviation. If the highlight value is set too high, it is also easy to cause the image tone change, resulting in the loss of dark tone levels. Therefore, the small dot value in the highlight area should be well matched with the dark tone dot value to avoid the problem of high and low tone in printing. 5% of the dot value in the 5-step ladder ruler can detect whether the high light dot engraving value is normal. In the official printing of the printing plant, if the highlight transfer is found to be abnormal, first use the point measuring instrument to check whether the highlight point value of the printing plate is normal

IV. standardization of gravure printing samples

the specification of the increased value of proofing points is very important, because it directly affects the quality of samples, and is closely related to the firmness of points, the clarity of layers and the fluctuation of neutral gray. For example, if the printing point is increased by 10%, the darkening point of the color plate is 100%-10%=90%. If the printing point is increased by 20%, the darkening point of each color plate can only be extended to 80%. The more the printing point is increased, the more the darkening points of each color plate will be compressed, and the darkening merging will be more serious. In addition, in the printing process, as long as the color balance relationship of the three primary colors is determined after the first color is printed, and then the density of the overprinted color does not match the density of the previous color, the neutral gray will fluctuate, and the printed matter can output these data through the RS232 port at the same time, which will produce color deviation. Therefore, in proofing and printing, it is necessary to clearly specify the ink concentration and the density value of dark tone. Of course, the ink hue used by the plate making factory and the printing factory must be the same or very close, and the substrate must also be the same. In short, the printing conditions should be as close as possible

it is not enough for color control to simply control the primary color tone restoration. If the printing position of the printing plate permits, a neutral gray test unit and a two-color and three-color overprint unit for detecting the color overprint effect should be added to the test block to improve the control of color restoration

in a word, the color restoration of gravure plate making can be ensured through the measurement and control of the density and points of the 5-step ladder, as well as the control of neutral and overprint. After the platemaking quality is stable, the 5-step ladder can be reduced to 3-step ladder, such as 20%, 50% and 100%. By monitoring the density and point value of the 3-step ladder, you can also control the version quality and gravure sample. The reserved position can save other test blocks and add more reference information and control information to the printing

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