On the quality control of color newspaper printing

2022-08-24
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On the control of color newspaper printing quality

release date: Source: China paper

in the process of color newspaper printing, there are many factors that affect the quality of color newspaper, mainly including the restoration of picture color and level, ink color, layout, registration, ink balance and the condition of equipment. In actual production, we mainly control from the following five aspects. Today, China paper takes you into the color newspaper control of packaging and printing, and introduces the relevant contents in detail

first, whether the color and hierarchy of color newspaper pictures are well restored

the restoration of color and hierarchy of pictures is mainly related to the two processes of scanning and printing. When scanning, first classify the originals (including fax pictures, photos and secondary originals). Scan the fax picture and the original picture with the appropriate number of lines after the aligned scanner lens. When processing the scanned picture, pay attention to four points: ① ensure that the highlight part of the picture is continuous; ② Ensure that the dark part of the picture is not at the same level; ③ Try to ensure that the intermediate tone has rich levels and moderate brightness; ④ When removing the background color, make sure that the four colors of the dark part of the picture are not more than 260% - 280% after superposition. For the secondary original, in order to prevent the "moire" phenomenon in the printing process, the scanner lens should be properly virtualized before scanning or the scanned image of the secondary original should be properly decontaminated after scanning, the scanning accuracy should be increased or the angle rotation should be less than 15 °, and a certain point should be focused and blurred. In these processes, the scanner adjusts the R, G and B parameters of each picture according to his own experience and the conditions of the printing equipment of his newspaper

the production of newspaper eyebrows, take Xinhua as an example. Xinhua has 16 color newspapers a, B, C and D every day, and there is a standard color bar superimposed by four colors at the bottom of each page. The production of color bar includes two aspects: ① 100% point mainly tests hue and density; ② 30%, 50% and 70% points are mainly used to measure the increase rate of printing points. We produce this standard color bar for the following three purposes

1. Theoretically, as long as the printer adjusts the color bar of the day to close to the standard color bar, the ink volume of each color of the photo on the color bar is basically in place

2. When adjusting the exposure time and developer concentration, the printer can determine the exposure time and developer concentration according to the 3% - 4% point alignment of the highlight part in the color bar

3. The scanner can compare the effect of the picture above the color bar with the original according to the sample report of the printer when adjusting the color bar to close to the standard color on the same day, and reflect on whether there is any need for further improvement in processing the R, G, B parameters of the picture, which can provide empirical data for scanning similar pictures in the future

II. Whether the ink color of the text part of the color newspaper is uniform and the layout is flat

in order to ensure the ink color of the text part of the color newspaper is uniform and the layout is flat, we require the operators to start from the following three aspects:

1 Ensure that the text is clear and the density is uniform when the film is exposed

in the actual production process, due to the change of exposure time or the difference of sensitivity of different batches of films, the characters on the exposed films are broken and the density is uneven. At this time, the staff need to take measures in time, or re produce the film, or take other remedial measures to ensure the quality of the film

2. During plate making, ensure that the text of PS plate is clear, the density is uniform and the layout is flat after exposure and development

in the production process, in order to make a qualified PS version, the staff usually take the following steps: ① select a qualified table paper to ensure that the surface of the table paper is free of scratches and dust; ② Wipe all the table paper with anhydrous alcohol before using it; ③ Check all films for quality problems; ④ When printing, make sure there is no other sundries in the table paper room; ⑤ When printing, make sure to inhale well and expose properly; ⑥ Ensure that the developer is in good working condition and that there is no sundries attached to the rubber stick of the developer. When printing, the PS version made is unqualified due to poor suction of the printing machine or dirt adsorbed on the table paper

3. In the printing process, in order to make the layout of color newspaper flat, ink color uniform and text clear, printing operators are usually required to start from the following aspects

① ensure that the cylinder pressure of the printing machine is moderate. In general, during round printing, the printing pressure between the rubber cylinders of high-speed imported machines is 0.25-0.3mm, the printing pressure between the rubber cylinder and the plate cylinder is 0.15-0.2mm, and the drum runout is allowed to be 0.01-0.03mm. If the printing pressure of the drum is too large, the strokes of the printed words become thicker. If the drum beats too much, it is easy to cause the layout to be scratched and the words to appear ghosting. At the same time, there will be uneven paper feeding during printing

② adjust the pressure between the rubber rollers of the printing machine. Adjusting the pressure between the rubber rollers is very important to ensure the uniformity of the color ink of the printed newspaper. First, adjust the gap between the ink core roll and the corrugated roll (the standard of this gap is different for different models). In the actual production process, the quality of this gap adjustment is directly related to the whole ink transfer process; Next, adjust the pressure between the corrugated roller and the ink transfer glue, as well as between the ink transfer glue and the ink string glue (under normal circumstances, the large rubber roller with a diameter of more than 120mm is stamped at 7-8mm, and the rubber roller with a diameter of 80-95mm is stamped at 5-6mm); Finally, adjust the pressure between the inner and outer glue and the plate cylinder (usually the impression of the inner glue on the plate is 1mm smaller than that of the outer glue on the plate)

③ ensure good performance of rubber blanket. The flatness and good resilience of the blanket are very important to ensure the flatness of the layout of the color newspaper and the point restoration of the picture. When using the blanket in the production process, we should pay attention to the following points

a, several indicators of new blanket: thickness, hardness, surface flatness and surface resilience of blanket. At present, there are many brands of blanket in the market. Even for the same brand, it is difficult to guarantee the specified technical indicators for the blanket provided due to different places of origin and price differences. For example, the thickness is not enough, the length cannot meet the specified size requirements, the resilience is not good, and the surface is uneven, which directly affects the printing quality of newspapers

b, alternate use. When the new blanket is printed on the machine, its resilience gradually weakens with the passage of time. If each machine prepares two sets of blanket to be used alternately on a regular basis in the production process, it can not only improve the printing quality of color newspapers, but also improve the service life of the blanket

c. Rubber blanket is selected according to the model and machine condition. At present, the model structure used for newspaper printing mainly includes Y type and B-B type, because y type is two rubber rollers pressing one rubber roller, while B-B type structure is two rubber rollers pressing each other. Therefore, when choosing blanket, we should consider that the hardness of blanket is different. Generally, the blanket used by Y-type structure machine should be harder, which can effectively reduce the possibility of 2-3 version blooming. In addition, if the drum jump of the machine is large during long-term use, we should try to choose blanket with high hardness when choosing blanket, which can also reduce the degree of layout blooming

④ adjust the ink layer of the ink core to ensure good performance of all ink keys. At present, most of the printing machines used by newspapers are modern rotary machines imported from abroad. The adjustment of ink volume is completed by centrally controlling all the ink keys of the machine on the console, and the adjustment of ink layer is the most important step. In order to enable the operator to effectively control the ink volume of all pages on the console, the operator must first strictly and carefully adjust the original ink layer of the ink core roller to the specified data, And when adjusting, ensure that the ink layer of the ink core roller is adjusted evenly. The ink layer thickness setting is usually determined according to the thickness of the wrinkle roll and the gap between the wrinkle roll and the ink core roll: for the coarse wrinkle roll, the ink layer thickness setting is 0.08-0.1mm more than the gap between the wrinkle roll and the ink core roll; For the fine grain roller, the ink layer thickness is set to be 0.03-0.05mm more than the gap between the roller and the ink core roller

⑤ overall quality of operators. The technical content, heart and practical experience of operators are human factors that affect the quality of color newspaper printing. Operators with technical and practical experience can accurately and timely grasp each process. At the same time, when there are problems in the quality of color newspaper, they can timely and effectively find out the problems and solve them. In addition, in the printing process, we should cultivate the working heart of operators, carefully adjust the ink color of each page, and make the ink color of each page uniform 8 It can control and maintain the experimental force, deformation, displacement and other rates, and the ink volume is moderate. At the same time, it can always control the ink balance in the printing process

III. whether the registration of color newspaper meets the specified accuracy requirements

there are many factors affecting the registration accuracy of color newspaper: ① whether the sent film itself can be registered; ② Whether the registration accuracy can be guaranteed when making up; ③ Whether punching, printing, bending and loading are accurate and in place; ④ Whether the main paper guiding roller of the printing machine is horizontal and whether the surface of the paper guiding roller in the middle of the printing sheet is cleaned in time; ⑤ Whether the pressure of the blanket on both sides of the double width printing machine is balanced; ⑥ The gap between the two rubber sheets is large (be careful not to touch the small active pointer, which will also affect the accuracy of upper and lower registration; ⑦ whether the paper itself has rewinding phenomenon in the printing process; ⑧ the fan-shaped expansion of the paper in the printing process affects the registration accuracy of color newspapers, etc. Considering the above factors, we require that the registration accuracy error of the assembled film is less than 0.02mm, and the registration accuracy of the finally printed newspaper is guaranteed to be about 1 line, no more than 2 lines at most, Newspapers with more than 2 lines will be treated as waste newspapers

IV. whether the water ink balance of color newspaper reaches the best state in the printing process

it is very important to maintain the best water ink balance state in the printing process of color newspaper. When the water ink balance is well controlled, the color newspaper can be printed with bright colors and good gloss, and it is easy to print the most beautiful color newspaper with the least amount of water and ink; On the contrary, if this problem is ignored, the unlimited expansion of ink in the printing process will bring hazards such as large-scale emulsification of ink, wet and sticky hands of newspapers, graying headlines and darkening photos

there are generally two consequences of the destruction of the ink balance: one is that the layout is dirty; First, the water volume is too large. We all know the harm of dirty newspapers. Here we mainly talk about the harm of too much water

the surface phenomenon of excessive water volume is that the printed newspapers are gray and the graphics and texts are Matt. In fact, the harm of excessive ink is also reflected in the following aspects:

① water will enter the ink bucket along the ink transfer roller and the ink string roller, causing a wide range of ink emulsification

② it will wet the printing sheet and affect the quality of the newspaper

③ it will make the printed newspaper headlines gray and the photos dark

④ make the viscosity of the ink drop sharply, produce floating dirt or make the ink block roll into the bucket, and then flow back to the water tank. For a long time, there are coagulant ink particles in the water, no matter compared with the north, Shanghai, Guangzhou and Shenzhen tank

⑤ a large amount of acidic water vapor will be produced, which will corrode the machine

v. the impact of equipment maintenance on the quality of color newspaper printing

the best water ink balance should be achieved in printing

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