The correct choice of screen in glass screen printing (2)
Today, I will continue to introduce you how to choose the right screen printing mesh for glass.
Reflected in the production of the screen, the photosensitive film is just the opposite. The smaller the through hole of the bright photosensitive film, the larger the through hole of the image is. For the dots in the bright-adjusted area, in order to ensure that printing can be performed, the dots are not lost, and the image is complete in level. It must be ensured that the diameter of the smallest dot of the bright-adjusted area to be printed is not less than three times the diameter of the wire used. Otherwise The dots are blocked by the wire diameter of the screen, causing the lack of dots. For the dots in the dark-adjusted area, in order to ensure that printing is possible, it is also ensured that the diameter of the photosensitive dots at the top of the dark-adjusted area is more than three times that of the wire, if the size of the photosensitive dots in the dark-adjusted area is smaller than that of the wire. Three times the diameter, there are two cases that will cause the lack of photosensitive dots. In one case, the photosensitive dots are located just above the wire mesh and are blocked by the wire. In the other case, the photosensitive dots are located in the mesh. Inside, the wire mesh cable cannot support the photosensitive dots.
For the determination of the minimum dot diameter, for the plate making of the tone screen printing, the minimum photosensitive dot on the screen depends on the image.
1 dark adjustment area, in the actual production, in order to ensure that the minimum photosensitive glue point of the image dark adjustment area is supported by the mesh of the screen, it is necessary to select the appropriate mesh with the mesh diameter for printing. In order to select the correct screen, we need to accurately calculate the diameter of the smallest dot to be printed. For the calculation of the minimum dot diameter, we should based on the number of screen lines and the percentage of image dot area, if we print on glass. The image has a screen line of 75 lines/in (2a5 lines/cn). The tonal range of the image is 20%~80%, which means that the minimum dot area percentage in the brightness area is 20%. We can pass the formula. :d=(L1284t)1/2/L, d is the diameter of the minimum dot to be printed, t is the percentage of the dot area, L is the number of screen lines of the image, and the minimum dot diameter in the image brightness area is calculated to be 0ll7cm. After the diameter of the minimum dot to be printed is determined, in order to ensure that the minimum dot can be printed, the diameter of the minimum dot is not less than three times the diameter of the wire diameter of the wire used, and the wire diameter of the wire mesh used should be no more than 57 mm. In addition, the surface of the glass is a non-absorbent surface, so the dot gain is more serious than paper printing. In fact, the wire diameter of the wire is lower than the theoretical value.
2 Secondly, it is necessary to avoid interference between the dot of the tone image and the wire mesh. Moiré is a potential problem for halftone screen printing. It is generated because the two lines or two objects are constant. The visual result of interference between angle and frequency. When the human eye cannot distinguish the two lines or two objects, only the interference pattern can be seen, and the mesh and the screen can form another form of moiré. The distribution of moiré stripes on the screen can produce patterns that are illegible and significantly different from the original. In the screen printing, it is very difficult to completely eliminate the moire fringe. We can only avoid the appearance of the full moire fringe of the whole image. The high mesh mesh number and the image screening line ratio will be very helpful. The elimination of the fringe, in general, the ratio of the mesh number of the screen to the number of screen lines of the image is 5:1, which greatly improves the moire fringe, for example, when we need to print an image with a line number of 7 lines/inch, At this time, it is necessary to select a mesh with a mesh size of 350 mesh/inch. If the ratio of the mesh number of the mesh to the number of screened lines of the image is lower than 孓5, it will easily lead to the overall tension of the printed image. After 72 hours, two kinds of The screen-pressed screen again measures the tension and suddenly compares the attenuation of the two tensions. The smaller the attenuation, the more stable the tension of the screen is, which is more conducive to the printing, especially for products with higher precision requirements. Be sure to use a wire mesh that maintains a stable tension.