Impression of printing gold

Because the gold ink has a unique metallic luster, the printed gold print can give people a feeling of exquisite elegance and richness and richness. Whether it is packaging and decoration, or book printing, through the embellishment of gold ink, will make the product a higher grade, the added value of the product can be further improved, so in recent years, offset printing technology has been more and more widely used. However, gold ink is different from ordinary inks, and its particularity makes printing gold inks difficult. In actual printing, due to various reasons, the quality of printed gold is often unsatisfactory. How to improve it can effectively improve the quality of offset printing. I would like to talk about a few experiences here.

Strive for scientific and reasonable printing process design

1. Gold layout design strives to be reasonable

Process design has an important role in improving the printing quality in printing, and those unreasonable processes are often “time bombs” for printing production and product quality. For Indian gold, reasonable layout and scientific process design are particularly important.

Gold ink is made of gold powder and gold oil. The so-called gold powder, that is, copper-zinc alloy powder, coarse particles, large weight, poor adhesion, poor adsorption capacity, poor transfer performance. Therefore, when designing a gold edition, it is best to use the field and lines as the main subject, and the lines and texts are of a moderate size and should not be too fine or too small to avoid the stencils caused by the use of small, anti-white text or lines. If it is the design of the mesh adjustment, it should try to open the dark tone level, set the highlight part. If it is necessary to print graphics on gold ink, it is possible to directly print on the monochrome ink machine. The multicolor machine is best designed to blank this graphic part on the gold printing plate and achieve it by overprinting.

2. Solve the problem of poor ink gold adsorption Golden ink has a strong hiding power, but poor adsorption capacity. The solution to this problem is to create a background in the area of ​​the gold. This background color not only enhances the attraction of the gold ink, makes the ink layer thick, but also plays a role in foiling the gold ink. Gloss. In general, a clear yellow ink, light yellow ink, or fake gold ink is used as a background color. If you add a small amount of gold ink in the background, you can make the gold more glossy. Printing gold ink on dark ground, such as black or blue, can also achieve better metallic luster effect, but try to avoid printing gold on multi-colored overprinted large areas, which will lead to gold ink printing. Not on or imprinted.

3. Arrange the color sequence rationally In the color sequence arrangement, gold ink should be printed in the last color. Because in the multi-color printing, in order to prevent the reverse printing caused by color mixing or printing defects, must be arranged in accordance with the principle of ink viscosity from high to low, that is, the viscosity of the ink after printing is less than the previous color. The viscosity of the gold ink is relatively low. If the ink is placed in front, the viscosity of the ink of the latter color is greater than that of the gold ink, and the gold ink that has just been printed on the paper is pulled back, making the gold ink layer thinner, tarnished, and fluffy. . For monochrome machines, although it is wet and dry printing, it is not appropriate to put gold in front of it, otherwise it will also cause decoloration, which will reduce the gloss of gold ink. The best time to print gold is when the front color is dry but not completely dry. At this time, the gold ink is most firmly attached.

Pay attention to the choice of paper

In actual production, some manufacturers often choose some cheaper, lower-grade paper for gold printing in order to reduce costs. However, due to the coarse particles of gold ink, the transfer and adhesion are not good. If printed on offset paper, relief paper or whiteboard paper, the rough surface, poor smoothness, and strong absorption will lead to the dispersion of coarser gold powder. No smooth, smooth ink film can be formed on the surface of the paper. Therefore, in order to give full play to the advantages of gold ink and obtain the desired metallic luster, it is necessary to use smooth, strong, smooth paper. For higher demanding commercial prints, high-end packaging and decoration, when printing gold, better quality coated paper, glass cardboard, or white cardboard should be used as far as possible. These papers have smoothness, ink absorption, surface strength, Whiteness, pH, etc. are compatible with the gold printing process, which can make the metallic ink effect of gold ink incisively and vividly.

Pay attention to the prevention of paste version

Offset printing is more prone to paste failures, which is related to the coarse particles, high quality, and high thermal conductivity of gold powder. After the gold ink is transferred to the rubber roller, it will produce higher heat than normal ink after high-speed extrusion friction. Due to the high thermal conductivity of the gold powder, the oil-based binder material mixed with the gold powder increases in the heating temperature, the fluidity increases, the discrete force increases, and the edge portion of the printing plate on the printing plate spreads, and due to the rubber roller and the blanket With the continuous extrusion of the layout, the expansion of the scope of spread, the occurrence of paste version. In order to prevent such paste failures, the following preventive measures can be taken.

(1) It is appropriate to reduce the speed of the vehicle during printing. Usually, when printing on high-speed machines, it is advisable to control the speed below 5,000 sheets/hour.
(2) Appropriately reduce the ink roller, and temporarily remove the ink roller that has little effect on the ink transfer route. This will not only reduce friction, but also reduce the amount of heat generated, thus constraining the temperature increase.
(3) The content of alcohol in the fountain solution should be properly increased. Because alcohol is volatile, it not only accelerates the emission of heat, but also has a cooling effect on the ink roller; and it has a low surface tension and good wettability. Control surface moisture.

Prevent printing ink

The so-called pile of ink is in the printing process, the gold ink on the ink roller is constantly piled up, so that the printing plate graphic part can not get enough ink, the product produces a phenomenon of thin imprints and virtual flowers. Even if the ink fountain is increased, or ink is added to the ink roller, there is not much improvement. This failure of stacking is mainly due to the fact that gold ink is too thick and fluidity is low. If the ink is too thick and the amount of fountain solution is too large, it will result in serious ink emulsification and the phenomenon of heaping ink will be more serious. The solution to this problem is as follows.

(1) Appropriately adjust the proportion of gold transfer ink in gold ink, that is, add proper amount of gold transfer oil or appropriate amount of transfer ink to reduce the viscosity of gold ink and improve its flowability. In fact, if you add 5% to 10% bright light paste (advanced thinner) in gold ink, you can also improve the gold ink's transfer performance.
(2) Be diligent in cleaning rollers, plates, and blankets.

Improve gold gloss

The purpose of printing gold is to use the special metallic luster effect of gold ink to decorate printed matter. However, due to the influence of many factors, the poor glossiness of gold printing has always been a big problem that plagued the offset printing process, in which the quality of gold ink and the gold printing ink Process conditions have a direct effect on the gloss of printed gold.

1. The effect of gold ink quality on the gloss of printed gold

Gold ink is divided into two kinds of self-tuning and finished products. For self-adjusting gold ink, attention should be paid to the choice of gold powder and gold transfer oil. Gold powder is a kind of metal powder and it is easily oxidized. After the oxidation, the color of the gold ink becomes dark and loses its original gloss. Therefore, the quality of the gold powder itself is very important. It is appropriate to control the fineness of the gold powder in the range of 1000 to 1500 mesh. Too fine will make the metallic luster worse; too thick will cause the viscosity of the gold ink to deteriorate, and the adhesion will be reduced to affect the printing effect. In addition, the storage of gold powder should also be noted, storage environment temperature, exposure to a long time will accelerate the oxidation of gold powder, making it dark. In addition, the gold transfer oil also has a great influence on the quality of the gold ink. The good gold transfer oil has low acidity, stable chemical properties, good drying and fixing performance, moderate viscosity, and can form a good and stable suspension after deployment. Printing compatibility, good compatibility with gold powder, will not affect the color of gold powder, can improve the color performance of gold powder. For the deployment of a good finished gold ink, due to its easy to use, stable quality and wider application range.

2. The effect of gold printing process on the gloss of printed gold

The gold printing process has a great influence on the printing effect of gold ink, and special attention should be paid in printing.
(1) Correctly adjust the printing pressure. In order to increase the gloss of the printed gold, the pressure between the rollers may be appropriately increased, and an increase of 0.03 to 0.05 mm is generally appropriate, which is favorable for improving the transferability of the gold ink. The pad of the blanket cylinder is instead neutral or rigid so as to reduce compression deformation and obtain a thick, smooth ink layer.
(2) As for the fountain solution for printing gold, the gold ink is easily oxidized and discolored due to the presence of acidic substances and other impurities, and the glossiness is reduced. Therefore, alcohol fountain solution with small surface tension and good wetting property should be used as far as possible, and The best amount of water is the minimum amount of wetting when printing.
(3) For a large area of ​​printed gold products, the use of a final overprinting method of bright oil not only protects the gold ink, improves its abrasion resistance, but also increases the gloss of the printed gold. Of course, the use of polishing, laminating, etc., after the finishing process can also increase the gold gloss.

Author: Gui Jiao

Reprinted from: Printing Technology