Detailed Prepress Operation - Separation Work Chapter VI

Six, color letterpress color separation operation

Color letterpress is a common method used for decoration and printing. The change of the screen level and color is relatively simple. The printing paper and ink are the same as those of plain printing. However, the dot expansion and layer changes during the process of letterpress printing are large, and they cannot be eliminated. . Therefore, color relief electronic color separation should follow (1) to establish a relief level correction curve, as shown in Figure 6.16, using negative grid point ruler according to standard stable plate making conditions, making relief (A: copper zinc plate; B: resin Version], and printed under controlled printing conditions. Measured at each level of screen points and printed ladder feet at various levels of network data, and the negative graph network as the horizontal axis, the printing network as the vertical axis, depicting the network point level change curve (figure 6.16(a)), with the vertical axis of C negative film as the vertical axis, and the negative Y, M negative film nodes as the horizontal axis, depicting the gray balance curve (Fig. 6.16(b)) according to the variation of relief image and dot layer and its The gray balance curve can be derived from the gradient curve of the original screen-casting chart according to the procedure shown in Figure 6.17.The first quadrant HS in the diagram is the contrast of the original document, and the DE is the hierarchical reproduction curve of the relief copy (by Y, M , C three-color overprint), DC is the reproduction curve of the cyan printing layer. In the second quadrant, using the cyan field density and the Murray Davis formula, the reflection dot density curve of the cyan plate is obtained. The third quadrant is the plus. Network shade with the printing network level In the curve, A is a copper-zinc plate and B is a resin plate, the fifth quadrant is a three-color gray balance curve between a copper zinc plate and a resin plate, and the sixth quadrant is a layered curve of a color plate produced by a color manuscript.(2) Strictly guarantee the consistency of the gray balance and dot gain value of the three primary colors (3) Use electro-dividing positive plots to reverse the negative plate making method.(4) Extreme highlight areas should be controlled at 3-5%, and the finger-index level range should be controlled. Control at 10% -90%, copper zinc plate control at 10% -65%.(5) Toppan plate-making screen line number should be used below 150L/inch square-shaped outlets.



(to be continued)

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