The roller-rolled contact surface (ie, the embossing surface in printing) is approximately flat; the pressure distribution on the embossed surface is generally saddle-shaped. The pressure corresponding to the centroid is the pressure necessary for the printing process, but from the viewpoint of ink transfer, it is not the proper pressure in the printing. In order to determine the appropriate printing pressure (also called working pressure), it is necessary to clarify the relationship between the ink transfer rate and the printing pressure and other factors; to clearly determine the various factors that should be taken into account in determining the appropriate printing pressure; to find a specific method to determine the appropriate printing pressure. .
First, the relationship between ink transfer rate and printing pressure
The ratio of the amount of ink y transferred to the surface of the printing material to the amount x of ink applied to the printing plate is f=y/xÃ—100% called the ink transfer rate; during the printing process, it is always desirable to obtain high ink under certain conditions. The transfer rate, and the size of the ink transfer rate, are related to many factors such as printing pressure, printing speed, printability of paper ink, and the like.
The three-dimensional space diagram in Figure 2-14(a) shows the relationship between ink transfer rate y/x, printing pressure pd, and printing speed Ï…. It can be seen that y/x increases with pd when v is constant. When pd reaches a certain value, y/x is no longer significantly changed; the three-dimensional space diagrams in Figure 2-14(b) and (c) indicate y/x and pd, paper smoothness s, and y/c, respectively. With the relationship between pd and the plastic viscosity of the ink, it can be seen that the change of y/x with pd is similar to the above case when the smoothness or Î· is constant.
Figure 2-14 Relationship between ink transfer rate and printing pressure pd, printing speed v, smoothness s, and ink viscosity
Figure 2-15 Relationship between ink transfer rate f and printing pressure pd
The relationship between the ink transfer rate f and the printing pressure pd in the case where the printing speed and the printing conditions are constant, and the printability such as the paper smoothness and the ink plastic viscosity are constant, is roughly as shown in Fig. 2-15. The AB segment of the f-pd curve rises slowly. Because the printing pressure is too low, the compression of the liner is too small, and the ink cannot fully contact with the paper surface, resulting in incompleteness of the imprinting; the BC segment f is nearly linear with the pd, with f With the increase, the ink color of the printed product gradually improved; by the point C, the ink product with satisfactory ink quality can be obtained. The pc (ie, pt) is the pressure necessary for the printing process; after the point C, the curve is almost straight, ie, printing. The ink transfer rate of the ink with a further increase in pressure remains basically the same; however, if the pressure is too large to the point D of the curve, there will be a serious expansion of the network, and the pressure is too high will bring the previously analyzed "sliding , friction and a series of problems; therefore, the appropriate printing pressure should be between pC and pD, such as pt.
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