The Causes and Preventive Measures of Discolouration of Offset Printing Gold and Silver Printing

In today's packaging and decorating and other printed matter, in addition to the use of gold (silver) technology, offset printing gold (silver) printing process is still a lot of manufacturers in the selection. The printed gold (silver) has the advantages of delicate and solid imprinting, good metal texture, strong hiding power, high floating force, strong metallic luster, and low cost. Offset printing companies can directly select finished products of gold (silver) offset inks or use copper gold powder (aluminum silver paste) and offset gold oil self-adjusting gold and silver inks in two ways.

First, the basic composition of offset printing ink

Copper powder (aluminum paste) 30%-50%
Offset transfer oil 70%-50%
Mix copper powder (aluminum silver paste) and gold transfer oil into gold silver ink.

Second, the causes of discoloration of India gold and preventive measures

1, the acidity of the paper. Due to improper handling in the pulping and papermaking processes, such as organic acids in the pulp or chlorine left in the afternoon when bleached, the paper will be acidic, and when the alkaline filler and pigment are added, the paper will be alkaline. Paper or acidic, acid paper will inhibit the drying of the imprinted oxidized wax and slow the drying rate; while the alkaline paper is too strong, the alkaline substances in the printing process will continue to be transferred to the fountain solution. Therefore, the original weakly acidic fountain solution is neutralized, which affects the normal pH of the fountain solution, causing discoloration and deterioration of the remaining ink, and it will emulsify the ink and cause turbidity. Therefore, the selected paper has a pH of 7, which means that it is neutral and it can effectively avoid discoloration.

2, note the liquid PH value and ink balance. Using the offset printing of the new oil hydrophobic and non-graphical part of the printing plate graphics and text, the acidity in the printing solution can be used to clean the dirty side of the plate, but the strong acidity can easily cause discoloration of the printing ink. , Loss of metallic luster, resulting in printing plate version, imprinted slow dry, back sticky and other quality problems; and weak acid, printing plate network from the dirty, paste version. Therefore, the general fountain solution PH value is controlled at 5-6 is appropriate. The balance of water and ink is to minimize the amount of water in the plate, so that the amount of emulsification of the ink can be controlled within a minimum range of 25%. Because of the large points, it is easy to cause the Indian ink gold too pale, the gold ink dull, the color is not bright, the gold ink is emulsified, the paper stretching and deformation caused by overprint and other non-greeting quality ills; moisture is too small, easy to make the layout from the dirty Since it is greasy and there are problems such as doubling paste, mastering the ink-and-wash balance is critical. In addition, the intermediate roller must be separated from the ink and water system, and it is also an essential method to avoid it.

3, printing speed. If the printing speed is too high, it will easily cause severe friction between the ink rollers, and the resulting heat will cause the ink to change color. The general experience is that the control should be controlled at 5000 sheets/hour.

4, copper gold powder, aluminum silver paste oxidation. Silver powder and gold powder have the drawback of being easily oxidized and discolored. Therefore, unfinished gold and silver powder must be kept as close to the air as possible, and the storage time should not be too long.

5, the transfer of gold acidity. Silver powder and gold powder are easy to oxidize. Therefore, the gold transfer oil used must be a fast-drying, fast-curing, high-viscosity resin oil with low oxidation and neutrality. To prevent long-term storage, oxidation is preferred. That is, the self-adjusting method can further improve anti-twisting and discoloration.

Reprinted from: Harbin Advertising Network