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Oven temperature control
The oven is divided into 3 parts: pre-heating zone, high temperature zone, and cooling zone. In the preheating zone, the surface temperature of the paper is about 80°C; in the high temperature zone, the temperature of the oven reaches 770°C, and the surface temperature of the paper reaches about 120°C; in the cooling zone, cold air is blown to the surface of the paper, and the surface temperature of the paper drops to about 80°C. After cooling rollers, the surface temperature of the paper returns to normal. The oven temperature should be determined according to the length of the oven and the speed of the printing. Under normal circumstances, it is necessary to ensure that the time of the paper in the oven reaches 1 second. The surface temperature of the paper is about 120°C to ensure that the ink film on the print is completely dry. . If these conditions are lower than these conditions, scumming will occur in the cooling and folding sections. If the oven temperature is adjusted too high or the printing speed is too low, the moisture content of the paper will drop rapidly, and it will not be completely smooth even after passing through the flattening roller. Waves appear.
2. Ink film thickness control
In printing, the ink is often printed very thick, thick ink coated by silicone oil, the color of the print is very bright, but the normal temperature can not dry the ink, then need to increase the temperature of the oven, so that the ink film surface quickly dry. However, the internal force of the ink film still exists. After the printing is completed, due to the release of the internal force of the ink film, the surface of the ink film blisters and the print product loses its luster. Therefore, in actual operation, we must control the thickness of the ink film to ensure that the printed product is bright in color and the dots are firm and flat. In pre-press plate making, the non-color structure copying process should be used correctly, and some Y, M, and C color inks should be replaced with black ink. For example, the sum of the dots covered by the four-color solid printing overlays amounts to 400%, and after the bottom color is removed , that is, 260% coverage of the network, the visual effects are basically the same, reducing the amount of color ink, reducing the cost, improve the printability, ink film thickness is significantly reduced, the oven temperature required can be reduced, so that the print Keep it flat.
3. Ink balance control
The purpose of offset printing water is to ensure and maintain the blank part of the printing plate to have hydrophilic and ink resistant properties, and to use the least amount of water to achieve ink-water balance. If the water content of the plate is excessive, that is, the water content in the ink is too much, the ink emulsification is increased. When the paper passes through the oven, the ink film surface is immediately dried, and the moisture inside the ink film is sealed by the ink film and is not easily dried. The imprinting of the imprint on the chill roll and the flaps will cause the oven temperature to increase, but it will cause waves of paper. Therefore, when printing, we must control the balance of water and ink, choose better quality fountain solution and easy-drying thermosetting ink, reduce the amount of fountain solution, reduce the temperature of the oven, and achieve the plain paper after printing.
4. Paper tightness and moisture control
In addition to requiring low oil absorption, strong hydrophobicity, smooth, lint-free, elastic and opaque paper, commercial webs also require better tightness and moderate water content. The soft, fluffy paper is applied to the back surface of the oven. The plastic part will be wrinkled and layered and cannot be printed normally. The moisture content of the paper with high water content is not uniform after evaporation in the oven, and the formed waves cannot be eliminated even if they are placed for a long time. The moisture content of the paper is too low. After forming waves after the oven, the static electricity of the printed matter is relatively large, which can result in inaccurate folding, brittle printing, and difficulty in handling after printing. Under normal circumstances, the water content of the paper is required to be 7% to 10%, the relative humidity of the stored room is maintained at 60% to 70%, and the temperature is controlled at 20 to 25°C.
Source: "Printing Technology"
Solve wave problems from commercial roller prints
Commercial rotation meets the demands of large quantities and various types of low-quantity paper printing with stable quality and high production efficiency. Because the moisture content of the paper changes in the oven, it easily generates waves and bubbles in the ink film. After printing, it needs to be fast. Drying, cooling, and equalizing processes. In the actual production process, to select the right paper, ink, to control the temperature of the oven and the surface temperature of the paper, in order to ensure the flatness of the printed product, in actual operation to consider from the following aspects: