Experimental Analysis of Factors Affecting the Change of Color Screen Printing Nets
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Screen printing claims that "all items except air and water can be printed." Its printing compatibility is wide, the printing ink layer is thick, the layout is soft, and it is not restricted by the size, shape and material of the printing object. It is irreplaceable by other printing methods. It is for these reasons that screen printing products range from smooth to rough, from paper to fabric to iron and glass, which can be said to be all-encompassing. 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. Therefore, many people directly use offset color separation films to print, but the results of printing are always endless. The intention is that the loss of the tone is serious and the color is severe, which is to produce a moiré that is difficult to see. This phenomenon occurs because they are not very clear about the factors that affect the change of the screen printing point, and thus cannot be quantitatively controlled. To this end, this paper makes a simple analysis of the factors affecting the change of screen printing dot, such as dot shape, screen line number, printing material, ink, exposure time, etc., and provides a reference for color screen printing tone reproduction.
1 Influence of dot shape on dot changes
First, use Coreldraw8 to do the test tool for the tone test - gray scale ladder, the range of the tone is 5% -100%. The hair row is 40lpi, 60lpi, 80lpi, 100lpi, and the screen angle is 45 degrees. The dot points are round dots and square dots. The experimental materials used coated paper, offset paper, 300 mesh screen, screen printing ink (fluorescent peach, fluorescent yellow, fluorescent blue), offset ink (red, sky blue, medium yellow, magenta), love with X-RITE 528 The color reflection density meter and the transmission densitometer measure the dot percentage. Experiment with 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) is plotted on the horizontal axis, and the percentage of dots on the printed matter (F print) and the percentage of dots. The increment (ΔF) is the vertical axis (the difference between the percentage of printed dots and the percentage of film dots), and the dot change curve is drawn (as shown in Figures 1 to 5).
Experiment 1 Using the same ink, the same number of lines, the same exposure time, the same substrate, and printing with different dot shapes (screen printing green ink, 40 lpi, exposure time 40s, coated paper, square dots and round dots).
From the data of Experiment 1 (Table 1) and the change curve of the dot (Fig. 1), it can be seen that the largest expansion of the square dot and the dot dot dot is 50%, because the square dot is compared with other dot at 50%. The expansion factor is the highest, because 50% of the dots are connected at the four corners. When printing, the corners are likely to cause ink clogging and the dot area increases. The circumference of the circular dots is the smallest among all the dots, and its dot is enlarged. The coefficient is small, generally under normal circumstances, the dots are connected around 70%, but once the dots are connected, the dot expansion factor will become larger, and the dots in the dark-adjusted area during printing will be blocked due to excessive ink volume. Finally, the dark part of the image is lost to the level it should.
Table 1 Percentage of dots in different dot shapes
F0 side field 80 70 69 49 36 25 17 10 6 5
Round field 81 70 68 48 36 25 17 11 6 5
F Indian Fact 90 90 79 61 44 31 15 7 4 4
Round field 89 87 67 53 39 22 11 2 2
△F side 10 10 10 12 8 6 -2 -3 -2 -1
Round 19 19 19 19 17 14 5 0 -4 -3
Figure 1 Change in dot area of different dot shapes
2 The effect of the number of network lines on the change of the network
Experiment 2 Printing with different mesh lines, the same exposure time, the same substrate, the same exposure time, the same substrate, and the same ink type (40lpi, 60lpi, 40s, square dots, coated paper, offset red ink), The relevant data are measured as shown in Table 2.
From the data of experiment 2 (Table 2) and the curve of the dot change (Fig. 2), it can be known that the higher the number of screen lines, the higher the value of the dot gain, and the larger the dot gain value, which indicates that the image reproduction is guaranteed. In the case where the difference between the number of color separation lines and the mesh size is larger, the more the tone of the image is completed, and the possibility that the interference pattern is repeated is smaller, because 300 mesh is used in this experiment. In the net, when a 100 lpi screening color separation film is used, a moiré has appeared on the printed plate.
Table 2 Percentage of outlets with different number of network lines