Traditional platemaking using manual methods, that is, through the way of manual engraving template, that is, in the form of the film transparent and not transparent two states, so screen printing is sometimes called template printing.Parts of the substrate with ink are removed, parts of the plate that do not require ink are retained on top, and the template is used as the printing screen frames.
The photosensitive platemaking method is more commonly used in modern times.This plate-making method is first stretched on the screen coated with photosensitive adhesive, the formation of photosensitive film, and then the use of photosensitive materials of light hardening, the positive bottom plate close on the plate, uv exposure, development, wash screen plate.Because the picture and text on the plate is not exposed to light, photosensitive film can be dissolved in water, after washing the plate only screen, forming a transparent part, printing ink, ink on the substrate, get the picture and text.The photosensitive glue on the printing plate is hardened and cannot dissolve in water to form a curing film, which seals the mesh hole and forms a blank part when printing ink cannot pass through.
For line printing products, only different areas on the plate transparent and sealed parts.For halftone and color overprinter plates, the layout is composed of different sizes and areas of photosensitive film dot. Screen printing is done with a positive picture (sometimes with a negative picture). Where the area of photosensitive film is large, the corresponding printing dot area is smaller and the tone is lighter, and vice versa.The darker parts of the printing plate due to more of the film, less ink through the printing, forming the original part of the bright.This is the opposite of offset printing, offset printing plate on the dark part of the ink, the formation of the manuscript of the dark part.
Dot is the basic printing unit that makes up the continuous image.Rich continuous tone manuscript for gradual levels, in the process of printing copy, in addition to the intaglio printing, other printing way due to the plate to substrates on the ink layer thickness is the same, is impossible for us to make the rich continuous changes in gradual levels, therefore, can only be used to change the image in the basic unit of lis area how to represent the level of the continuous variation, which is the dot area coverage per unit area of high and low order indicated level, a gray transition of printing samples and the large screen.It can be seen that the change in gray scale is caused by the different proportion of the size of the dot.In other words, the contrast between these units and the blank part achieves the effect of reproducing the continuous tone.
Dot is the basis of the printing and reproduction process, is the most basic unit of the picture and text, dot in the printing and reproduction to perform the task of hue, lightness and saturation;Is the smallest unit of induction ink, is the basic element of image transfer;In color composition is the organizer of image colors, layers, and Outlines.Screen on the dot is the development of the rinsed film points, these film points prevent ink through, no film in the part of the printing plays the role mentioned above.
Although screen printing dot and other various printing methods dot function is the same, screen plate color printing is also different area rate dot overprint.But the same dot, in the screen screen is screen divided into many smaller points, ink through these small mesh to form a dot.This is different from the dot composition in which the idea above is the most basic unit.
In the printing image processing, according to the different screening methods, it can be divided into am dot and FM dot, as well as mixed screening dot studied in recent years.The amplitude modulation dot is used to represent the image hierarchy with fixed point spacing and varying point size.The frequency modulation dot represents the image hierarchy by the density of points rather than the size of points.Mixed mesh points use both mesh size and mesh density to represent the image hierarchy.At present, in the screen printing process, am dot is widely used, its characteristic parameters mainly include dot area coverage rate, dot Angle, dot line number and dot shape.Screen color printing plate-making, due to the silk wire mesh itself weaving and the relationship between the Angle of the fine mesh, the selection of the dot Angle is of vital importance.Angle choice is not good, will appear moire, affect the image beautiful.The common dot angles are 90%, 15, 45″.75 “.The 45 dot performance is the best, stable and not inflexible: the Angle stability of 15 and 75 is a little bit worse, the Angle of 90° is the most stable, but the visual effect is too inflexible, no aesthetic feeling.
In addition to the relationship between mesh size, the size of the added mesh also determines the image fineness, which is similar to the decomposition rate. The higher the number of dot lines, the more dots can be accommodated in a unit area, the smaller the basic unit of the image, the finer the expression of the subtle level, and the better the reproducibility of the order. Fine print, generally use a higher level of paper printing, should choose the number of business dot to copy. The silk printing, because of the technical level, also is not suitable for reappearance of fine lines, site of the manuscript, also should pay attention to when the plate making, don’t blindly increase the number and cable, silk screen printing is suitable for performance text and line and lively monochromatic complete manuscript, also apply to the performance contrast greatly, level clear color manuscript.