Experimental Analysis of Factors Influencing Color Screen Printing Dot Change (I)

Screen printing is known as "all things except air and water can be printed." It has such a wide range of printability, printing ink thickness, layout soft, and not subject to the limitations of the size, shape, and material of the printed object, which is currently not be replaced by other printing methods. It is also for these reasons that there are a wide variety of screen printing products, ranging from smooth surfaces to rough surfaces, from paper and fabrics to sheet metal and glass. With the advent of high-quality photosensitive adhesives and inks, people hope that screen printing can print things that can only be printed by offset printing in the past. Therefore, many people directly take the color separation sheets of offset printing to print, but the printed results are always inexhaustible. It is not a serious loss of tone, but a serious color cast that produces a moire pattern that is difficult to see. The reason why this phenomenon occurs is that they are not very clear about the factors affecting the change of the screen printing point, and thus cannot be quantitatively controlled. For this reason, this article makes a simple analysis of the factors that affect the change of screen printing dots, such as dot shape, screen number, printing materials, ink, exposure time, and so on, to provide a certain reference for color screen printing tone reproduction.

1 Effect of Dot Shape on Dot Change

First of all, using Coreldraw8 as a test tool for gray-scale testing - gray scale ladder, its tone range is 5% -100%. The production line uses 40lpi, 60lpi, 80lpi, and 100lpi screen respectively, and the screen angle is 45 degrees. The screen points are selected as circular and square dots. The experimental materials used were coated paper, offset paper, 300 mesh screens, screen printing inks (fluorescent peach, fluorescent yellow, fluorescent blue), offset printing inks (red, sky blue, medium yellow, magenta), loved with X-RITE 528 Selenium densitometers and transmission densitometers measure the percentage of dots. Experiments were performed using the above experimental materials and instruments to obtain experimental data (as shown in the following tables). According to these data, the percentage of dots on the film (F0) was taken as the abscissa, the percentage of dots on the printed matter (Fin) and the percentage of dots. The delta (ΔF) is plotted on the vertical axis (difference between the percentage of the printing dot and the percentage of the film dot), and the dot variation curve is drawn (as shown in FIGS. 1 to 5 ).

Experiment 1 Using the same type of ink, the same number of lines, the same exposure time, and the same substrate, use different dot shapes for printing (silk screen printing ink, 40 lpi, exposure time 40 s, coated paper, square dot, and circular dot).

From the data of Experiment 1 (Table 1) and the dot change curve (Figure 1), it can be seen that the largest expansion points of square dot and round dot dots are 50% and everywhere, respectively, because the square dot points are compared with other dot shapes at 50%. The enlargement factor is the highest, because 50% of the dots are connected at the four corners, and the corners of the dots are likely to cause ink blockage during printing, resulting in an increase in the dot area; the circumference of the circular dot is the smallest among all dots, and its dot gain is relatively large. The coefficient is relatively small, generally under normal circumstances, the dots are connected at 70% of the circumference, but once the dots are connected, the dot enlargement coefficient will become larger, resulting in the dark dots in the printing area being blocked due to the large amount of ink. Finally, the dark part of the image loses its proper level.

Table 1 Percentage of Dots with Different Dot Shapes

F0 square field 807069493625171065 round ground 817068483625171165F Indian side field 908079614431 15744 round ground 8987675339221122 â–³ Fang 1010101286-2-3-2-1 round 19191919171450-4-3



Fig. 1 Dot area variation of different dot shapes

2 Influence of the Number of Network Cables on the Changes of Network Points

Experiment 2 Printing was performed using different screens, the same exposure time, the same substrate, and the same type of ink (40 lpi, 60 lpi, 40 s, square dot, copperplate, offset red ink). The measured data are shown in Table 2.


From the data of Experiment 2 (Table 2) and the dot change curve (Figure 2), it can be seen that the higher the number of screen lines, the larger the dot gain value generated. This shows that the number of color separation lines is sufficient to ensure the clarity of image reproduction. The larger the difference between the number of screen meshes, the more the tone of the image can be kept intact; and the possibility of repeated appearance of the interference pattern is smaller, because 300 mesh screens are used in this experiment, when 100 lpi screening is used. When the color separation film was made, moire had already appeared on the produced printing plate.

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