Precautions when printing gold ink and silver ink

Gold and silver powders are all coarse particles and their transfer performance is also poor. Heap rubber and ink-carrying roller, relatively speaking, silver ink has better stability than gold ink, and printability is better than gold ink. However, both of them are not acid-resistant and easily oxidized, resulting in discoloration of the ink. Due to these characteristics compared with ordinary printing inks, failures are easily caused during the printing process. Therefore, the following points should be noted when printing gold and silver ink.

Gold ink is a printing ink prepared by brewing gold powder. Gold powder usually uses ground copper powder. Silver ink is a printing ink prepared by silver powder and salt, and silver powder is aluminum powder or silver paste after grinding. The fineness specifications of gold and silver powders are expressed in terms of "mesh." General powder is about 1000-1200 mesh; silver powder is about 1000 mesh.

1. Thoroughly clean printing unit before machine to ensure pure ink

When cleaning, it can be cleaned with yellow ink (printed gold ink) and white ink (printed silver ink) 1-2 times before cleaning with a special ink cleaner. After cleaning, be sure to wait for the cleaning agent to completely evaporate before printing. Because gold and silver inks encounter organic solvents such as car washes, gasoline, and kerosene, they react and cause ink discoloration.

2. Adjust the middle roller to separate it from the ink and water system

The intermediate roller is an ink roller connected to the water and ink paths on an alcoho I (alcohol) wetting device (eg Heidelberg 102V). The main role of the intermediate roller is to transfer the fountain solution to the ink circuit system, so that the ink is emulsified as necessary so that the ink balance is quickly reached before printing. Since gold and silver inks contain a large amount of copper powder and aluminum powder, and the particles are coarse, they are not easily soluble in water and are not easily emulsified by water. Therefore, if the intermediate roller does not separate from the ink and water system, many unnecessary Problems, so that printing can not be normal. For example, in the ink distribution process, determined by the characteristics of the alcohol wetting system, the ink is transferred to the water roller through the intermediate roller, so that the water roller is covered with ink, but since the metal ink cannot be emulsified, it cannot be used for water. The roller absorbs moisture, causing the water roller to fail to supply water to the plate. Therefore, when printing gold and silver, the intermediate roller must be separated from the ink and water system.

3. Try to arrange gold and silver ink in the final printing

The stickiness of gold and silver inks is lower than that of four-color overprinting inks. According to the principle of multi-color ink sticking from high to low, in order to avoid the problems of color mixing, reverse printing or overprinting caused by wet-press printing, Put it in the last set of prints.

4. Add desiccant

Due to the poor mobility of gold and silver inks, thin inks or de-stickers are often added to the machine to increase the leveling properties of the ink. Dry oil is added at the same time as additives are added. Golden ink can be added about 1% of the red dry oil; silver ink is generally added from the kerosene and red dry oil, added in about 1.5%; or in the silver ink mixed dry oil, added in the amount of 1% - Between 1.5%.

5. Appropriately increase the alcohol content in fountain solution

Because alcohol is volatile, it can reduce the temperature of the ink roller; it has low surface tension and good wettability, which is conducive to the control of the plate surface moisture.

6. Speed ​​should not be too fast

The speed is generally controlled at 5000-6000 sheets/hour. If the speed is too fast, it will cause the friction between the rollers to increase and generate a large amount of heat, causing the ink to oxidize and discolor.

7. Paper acidity causes discoloration

Paper is often not acidic or alkaline. In particular, papers with a relatively large acidity, when printing gold and silver inks, on the one hand cause ink discoloration, and on the other hand, the drying speed becomes slower.

8. Fountain solution PH can be properly increased

Appropriately increasing the pH of the fountain solution (decreasing the acidity) will facilitate the printing of gold and silver inks, and the print will not fade easily.

9. Consider stacking when making plates

When overprinting gold or silver characters on field blocks, it is necessary to make printed gold and silver characters into stenciled characters, and the stenciled characters must be made smaller, the gold and silver characters must be made larger, or the stencil characters must be overlaid with 40 words. % flat screen, so that in the final printing of gold, silver, gold, silver ink can be printed on all or most of the blank paper, to avoid printing on other ink layers, due to wet pressure caused by printing failure. When overprinting silver or gold on full editions, because gold and silver inks have strong hiding power, they can make small prints on gold and silver editions, and make the first printed words thicker.

10. Correctly adjust printing pressure

Excessive printing pressure will accelerate the friction and cause the ink to accumulate on the roller and the blanket.

11. Printed finished or semi-finished products should not be stacked too much

On the one hand, because the ink film under the pressure of the paper, will produce adhesion. On the other hand, gold and silver inks release heat during the drying process, and under the pressure, the heat is not easily dissipated in time, which will accelerate the oxidative discoloration of gold and silver inks.

Reprinted from: Printed in China