The expansion of dots does have an adverse effect on offset printing, so how to control the expansion of dots? We talk about specific operational measures from the following aspects.
1. Master the exposure time of offset printing
Controlling the ratio of exposure time, development time, developer humidity and concentration is one of the ways to reduce the expansion of the dots. Separated four-color film transfers the graphic dots to the printing plate through printing, requiring the dots to expand as little as possible, 3% to 5% dots are not lost, 5% dots are not expanded, 95% -98% dots are not Blurred version, the dots are strong, the particles are round and neat, the dots have no white dots and burrs, and the tone is rich and clear. This requires accurate preparation of the developer of the PS version, according to the proportion of the recipe in the manual. The exposure time is digitally controlled by the gray ladder ruler and the printing signal strip. After the printing plate is exposed, use a 5-10 times magnifying glass to check the ladder and the The signal bar level is lost and the network is expanded.
2. Reasonable choice of lining material and printing pressure
Offset printing is an indirect printing method. It requires an elastic body in the middle of the rubber cylinder to transfer the graphic dots of the printing plate to the surface of the paper. The blanket and its lining are the intermediate media for the transfer of graphics and text. By adjusting the thickness of the offset liner, you can get the best printing pressure, enhance the uniformity of the ink density of the printed product and the clarity of the dots. The printing pressure is obtained by adjusting the thickness of the lining and the center distance of the cylinder. The pressure should be based on the premise that the printed product has strong dots, clear graphics, bright colors and shades, and the smaller the amount of application, the better the control dots expand. Deformation and adjustment of accurate printing pressure are very important. Accurately calculate and measure the thickness of the rubber roller lining with a micrometer in the work, adjust the center distance of the two rollers, and use the minimum printing pressure evenly within the allowable range of the dot expansion.
3. Control water and ink balance to reduce network expansion
Only by controlling the water-ink balance can the quality of printed products be improved. It is recommended to use as little moisture as possible on the premise of not dirty or pasted plates. Ink and ink balance is also a standard to measure the technical level of offset printing operators. Only when the ink and ink balance is reached, the paper has small expansion and deformation, high overprint accuracy, bright colors, and colors and hues can meet the prints of a batch of samples. It is strong. When offset printing, avoid the large dots of water and ink, and the dots of the ink layer spreading outward. Control the small dots of 3% to 5% of the bright tone area not to be lost, and the 5% of the mid tone dots do not expand or stretch, and the dark tone area 95% -97% of the large dots are not confused, the control standard of the ink volume is: the graphic dots are strong and clear, and the color and hue of the printed ink are accurate, and the minimum amount of ink is used.
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