On the establishment of offset printing copy curve

2022-10-18
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On the establishment of offset printing copy curve

printing copy curve is a curve that describes the relationship between the density or points of each copy link from the original to the printed matter. In this paper, GATF star Mark and 12 level gray scale are used as tools to observe the point increase and field density control in the printing process. By measuring the percentage of points at all levels in the three main process links of output, plate making and printing, the printing reproduction curve is established

in the printing operation, dots are the basic printing unit of continuous tone image, and the tone, level, contrast, sharpness and color of printed image are all expressed through the change of dot size, so the reproducibility of dots directly affects the quality of printed matter. At the same time, the evaluation of print quality and the quality monitoring and management in the process of printing operation are also mainly achieved through the evaluation of point reproduction

printing copy curve is a carbon material used to describe the hierarchical relationship between the original, print negative, printing plate and printed matter in the whole process of copying from the original to the finished product. Carbon material is a new material curve developed in recent years. The printing reproduction curve is established by measuring the percentage or density of points in each process link, so the accurate reproduction of printing points is closely related to the correctness of the printing reproduction curve. The dot reproducibility is good, and the dot increment value is within the specified range, and the printed manuscript can be well copied on paper or other substrates. Through the offset printing experiment, this paper quantifies the change of the midpoint in the whole process from the original to the printed product, and establishes the printing reproduction curve. This curve can be used to analyze and evaluate the operation standard degree of each process, that is, the performance of existing printing equipment, process conditions and the skill level of printing operators. At the same time, this curve has great guiding significance for printing the same or similar orders in the future, and indirectly improves the production efficiency of enterprises

1. Experimental materials

115g coated paper on one side, fast drying magenta ink, developer, positive PS version (specification 460 395mm), Phoebe Imagesetter, PS version automatic developer, win500 monochrome offset printer, sbk-b gallium iodide lamp printer, t6cr color reflection densitometer, wysk-40 40 40 times reading microscope with light source

2. The establishment of the experimental monitoring object

adopts GATF star Mark, which is convenient to visually observe the ink volume and point changes in the printing process. GATF stars are composed of 36 black wedge-shaped lines arranged in a circle at equal intervals. Such arrangement characteristics can clearly reflect various imprinting defects in printing, such as dot enlargement and ghosting. At the same time, the point data at all levels on the print negative, printing plate and printed matter are directly tested with a 12 level gray scale and a densitometer, and a printing reproduction curve is established based on this data

3. Sampling

in the printing operation, when the ink supply and water supply system of the printing machine are uniform and balanced, the paper feeding system is accurate and positioned, the pressure between the printing plate roller and the rubber roller, the rubber roller and the paper is appropriate and balanced, and the original at all levels is well reflected on the printed matter, there are few waste plastic recycling plants to start sampling. Generally, there are two sampling methods for prints: sampling at a certain time interval and sampling at a certain print quantity interval. After the original selected in this article is separated and produced, the C version has rich layers, and its density or dot change can well reflect the quality of printing. The specific sampling method is as follows: in 100 copies of version C, take a sample every 10 copies for measurement, get 10 groups of data, and then calculate the average value as the measured value

4. Experimental results and data analysis

① according to the experimental data obtained from the point and density tests of the original, print negative, printing plate and printed matter

② printing reproduction curve establishment

the shape of the two curves in the first quadrant is similar, but when the gradient density of the original is reproduced on the film through the color separation process, the percentage of points increases. This is mainly due to the inaccurate control of processing time in the three links of development, fixing and water washing in the film development process, so there is a point increase phenomenon. But on the whole, the generated points of the film are real and uniform, and the contrast between the graphic part and the non graphic part is large, the contrast is large, and the density is high

the curve in the second quadrant indicates that the film transfers graphic information to the PS version after exposure and printing. The shapes of the two curves are very similar, indicating that after the film is printed, all levels of the image are well reproduced on the printing plate. However, compared with the standard curve, the percentage and density of points on the printing plate are reduced as a whole, which is mainly caused by the accidental error of operation during the printing process, which leads to the exposure less than the standard, thereby improving the dynamic quasi exposure of the car

similarly, the curves in the third and fourth quadrants show that all levels of the C color of the original image are well represented on the printed matter, only because of the accidental errors in the previous two processes, the cloth feels warm and soft, resulting in the deviation of the printing reproduction curve obtained from the experiment from the ideal printing reproduction curve

③ point increase value

in the printing process, the point percentage at 50% and 75% is the key to printing control, and their increase value is also an important basis for evaluating the point increase value

according to the 50% point increase value recommended by China's printing industry standard, the range of point increase value at 50% of fine print version C is 8% - 20%

to sum up, when the whole printing and copying process is standardized and accidental errors are overcome as much as possible, when the ink supply and water supply system of the printing machine is balanced evenly, the paper feeding system is accurate and positioned, the pressure between the plate roller and the rubber roller, the rubber roller and the paper is appropriate, and the quality of the print obtained when balanced must be the true copy of the original. Printing copy curve has strong practicability. Through the establishment of printing copy curve and the analysis of the operation of the whole printing process, we can know how to get high-quality prints under the existing printing equipment, process conditions and printing operator skills. This has great guiding significance for printing the same or similar orders in the future, and can improve the production efficiency of enterprises

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