Offset Printing Common Causes and Solutions

Offset printing is the use of the oil and water immiscible principle, so that part of the printing plate graphic is hydrophilic, hydrophobic, and the blank part is hydrophilic and oleophobic to achieve the purpose of printing and copying. Because the surface of the printing plate must accept both ink and water during the printing process, the common problems of offset printing are related to the ink and fountain solution. The main manifestations are the pulling of paper, the color of the printed product becoming lighter, the color of the ink powder, and the adhesion. Drying too slowly, flying ink, paste, heap rubber, heap roller, dirty oil, dirty version and so on. In view of the above phenomenon, most of the exclusion methods need to start from the ink and fountain solution and the related factors.

(1) Pull the paper. The main reason is that the ink viscosity is too high or the paper strength is poor. The elimination method is to add an appropriate amount of ink remover to reduce the viscosity of the ink, use paper with high surface strength, and reduce the speed of the printing press.

(2) The color of printed products becomes lighter. The main reason is that the thixotropy of the ink is too large and the viscosity is too small. The exclusion method is to add a new fluid with a large ink or to add a high viscosity resin varnish.

(3) Pulverization of ink fades. The main reason is the lack of binder in the ink, the viscosity is too small, too slow drying, poor water resistance. Paper is too ink-absorbent and the fountain solution or paper is too acidic. The elimination method is to speed up the ink drying speed, and appropriate amount of red dry oil is added to the ink to reduce the acidity of the fountain solution and reduce the amount of water.

(4) Adhesion. The main reason is that the amount of dusting is too small, the stack is too high, and the ink cures too slowly. The method of elimination is to increase the amount of powder to be sprayed, reduce the thickness of the finished product, select the amount of fast oil, or add polyethylene wax to the ink.

(5) Drying is too slow. The main reason is that the desiccant in the ink is insufficient and the paper or fountain solution is too acidic. The elimination method is to add an appropriate amount of desiccant to the ink and adjust the pH of the fountain solution.

(6) Flying ink. The main reason is that the ink layer is too thick, the viscosity is too small, or the ink roller is not installed properly. The elimination method is to use a better thicker ink, reduce the amount of ink used, check whether the ink roller installation is reasonable to eliminate static electricity, and increase the indoor temperature.

(7) paste version. The main reason is that the ink is too heavy, the content of the powder is too high, the particles are coarse, the viscosity is too small, the water resistance is poor, the ink roller and the ink layer of the printing plate are too thick, and the paper is powdered. The exception is to increase the viscosity of the ink or add new thick ink to adjust or replace the paper.

(8) Heap rubber. The main reason is that the ink is poor in water resistance, less viscous, insufficient in connection materials, poor transfer, or decontamination of paper. The elimination method is to adjust the specific gravity of the ink by adding ink with higher coloring power, improving the water resistance of the ink or replacing the better paper.

(9) Stacker roller. The main reason is that the water resistance of the ink is not good, the viscosity is too large, and the amount of water supplied by the fountain solution is too large. The method of elimination is to add new ink, reduce the amount of fountain solution, or add isopropyl alcohol to the fountain solution to improve the wettability and increase the volatility.

(10) Dirty oil. The main reason is that the water resistance of the ink is poor, the viscosity is not enough, and the oiliness is too strong. The elimination method is to increase the viscosity of the ink, add a small amount of external oil, use a quick-drying bright ink, and add a small amount of light magnesium carbonate to the ink to reduce the oiliness, or try not to use a lake pigment ink.

(11) dirty version. The main reason is that the ink is too soft, the viscosity is small, the water resistance is bad, the acid and gum arabic in the fountain solution are insufficient, and the water glue is not clean. The elimination method is to replace the ink with better elasticity, and add an appropriate amount of arabic resin glue in the fountain solution to increase the acidity of the fountain solution, and add an appropriate amount of isopropyl alcohol to thoroughly clean the wet roller.

(author/Xu Xihong)

Zhong Bao Bao