In commodity packaging and label printing, gold ink is often used to realize the printing of golden pictures and texts, and gives people a feeling of exquisiteness, gorgeousness and nobility. As a special printing method, gold ink printing is slightly different from ordinary ink printing methods in the use of printing raw materials and process operations.
1. Gold ink deployment
Gold ink is made by mixing gold powder, gold oil and a small amount of auxiliary materials. Ordinary color inks are in the form of pastes and stored in tanks. Normally, gold ink is stored in two different containers with gold powder and gold oil. When printing gold ink, press The ratio (usually the ratio of gold powder and gold oil is 1: 1) is mixed with gold ink. At present, there are also gold ink supplies that have been prepared on the market and can be printed directly. However, the printing plant must consider factors such as the amount of ink used in the layout, the printing cycle and the number of products. Because the printing performance of gold ink will change after opening for 1 to 2 hours, and it will also lose the original metallic luster, it is best to use it when printing with gold ink.
2. Gold ink printing process
Gold ink printing generally adopts neutral or neutral hard liner, and the pressure of the inking roller on the printing plate should not be too large, otherwise it will cause the phenomenon of paste.
During printing, when the gold ink layer on the printing plate is transferred to the surface of paper or other substrates, the amount of ink is often insufficient, or even the bottom is exposed. Therefore, in order to make the gold ink reach the saturation state and fully display its unique metallic luster, the secondary printing method is generally adopted. At present, there are basically two secondary printing methods: one is to print fake gold ink as the background color, and then overprint the gold ink; the second is to directly print the gold ink twice. The fake gold ink used in the former method is generally based on two kinds of yellow ink, transparent yellow or medium yellow. If the paper quality is loose and the flatness of the paper is poor, the fake gold ink is mainly yellow, and an appropriate amount of gold ink is added. If the paper is tight and the paper surface is smooth, use transparent yellow plus a small amount of gold ink to make up fake gold ink. When printing, the ink amount of the background color should be as small as possible, based on the principle of no bottom and no seepage. When the background ink is not completely dry, then overprint the gold ink, the ink volume can be slightly larger, so as to reach the saturation state of the gold ink. When using the latter method, it should also be emphasized that it is appropriate to overprint the second pass of gold ink before the first print of the gold ink is not completely dry. This is because the gold powder in the gold ink is a metallic pigment. Dry and reprint, the particles are not easy to stick.
3. Precautions for gold ink printing
(1) Nature of paper
The nature of the paper will have a great impact on the quality of the gold ink printing. The higher the smoothness and the better the tightness of the paper, the better the metallic effect of the printing. Poor. In addition, the pH value of the paper surface is preferably greater than 5.5. Otherwise, when the printed products are stacked and stored, the sulfate contained in the paper will cause the gold powder to change color and black, and even cause the gold powder to corrode and disappear.
(2) Gold ink printing graphics
The graphics on the gold-ink printing layout should not be too thin, otherwise it will easily cause paste and the reflection effect will also be poor.
(3) Wear resistance
The wear resistance of the gold ink layer after printing is an important indicator to measure the quality of gold ink printing. At present, there are two measures to solve the abrasion resistance of gold ink: one is to use gold oil with a slightly higher viscosity to adjust the gold ink, and the other is to use gloss paste to polish after printing.
(4) Discoloration of gold ink
After the gold ink printing product is placed for a period of time, the gold powder will be invaded by sulfur, oxygen, moisture, etc. in the air, making the surface of the imprint darkened or even blackened, affecting the quality of the product. This is what we usually call the problem of discoloration of gold ink, which should be paid attention to during the storage of printed matter.
(5) Overprint of gold ink and other color inks
The gold ink should be printed on the dark ground as much as possible, such as printing gold on red, blue, black, the effect is better, especially when printing gold ink on purple, black, dark blue and other colors, the effect is better.
In addition, it should also try to avoid printing ordinary color ink on gold ink. If you must print ordinary color ink on a large area of ​​gold ink, you should first reduce the viscosity of the ordinary ink, and you must wait until the gold ink is completely dry before printing, otherwise it will cause the gold ink graphics to bloom.
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