With the development of society and the improvement of living standards, people's requirements for the packaging of goods are getting higher and higher, and gold or silver ink is often printed on fine products such as cigarette packets and wine labels. Gold and silver inks can exhibit metallic luster, giving people a solemn, luxurious, splendid and colorful feeling that cannot be represented by spectral colors. Therefore, gold and silver inks have been widely used in packaging and decoration printing. The use of gold and silver inks on commodity packaging and trademark labels can not only embellish other colors, but also improve the overall product quality. The importance of improving the printing quality of silver ink is self-evident.
First, the composition of gold and silver ink
Like other inks, gold and silver inks are mainly composed of pigments and linking materials. Simply put, gold inks are made of gold powder and gold transfer oil. Silver inks are made of aluminum powder and silver oil. Blended.
We know that pigments are colorants in inks. They give inks a certain color. Pigments in gold and silver inks are made by grinding metal powders, mainly gold powder and silver powder.
The pigment in gold ink is gold powder, which is actually a powder made of copper and zinc alloy. The content of zinc in gold powder is generally about 8% to 30%, among which the zinc content is between 8% and 12%. The color of gold ink is reddish, and it is customarily called red gold. The color of gold ink with a zinc content between 20% and 30% is partial green. It is generally called the green gold, and it is called between the red gold and the green gold. Green gold. In gravure printing, the golden ink used in the deployment of gold ink is generally used for the 800-point gold powder, and the surface of the gold powder particles are mostly coated with a surfactant, and can be better combined with the resin binder.
Silver powder is actually aluminum powder and is composed of 65% aluminum flakes and 35% volatile hydrocarbon solvents. Aluminum pigments have a small specific gravity and are easy to float in liquids. What is used in the gravure silver ink is the floating silver powder that has floating ability in the link material. Silver ink generally uses 400 to 1000 mesh silver powder. If silver ink is printed on a large area, lower mesh silver powder can be used. For example 400 silver powder mod silver ink, after printing has a high metallic luster.
2. The binder material is the liquid component in the ink. On the one hand, it is the carrier of the pigment so that the powdered pigment particles can be uniformly dispersed therein. On the other hand, it also serves as a binder for the pigment. Finally can be fixed on the substrate material surface. The binder material largely determines the viscosity, viscosity, flowability and drying performance of the ink. Therefore, the quality of the binder material directly affects the performance of the ink.
The linking material used in gold and silver inks is a special varnish, which is generally called gold transfer oil or silver regulating oil. The main components are oil, resin, and organic solvent auxiliary materials. The linking material of gravure gold and silver ink should meet the following conditions: 1 Must have enough viscosity to combine well with gold powder or silver powder. 2 The transparency must be high, and it cannot influence the hue of gold and silver ink. 3 The acidity of the transferred oil or silver oil is low, otherwise it will cause chemical reaction of the powder or silver powder. 4 gold transfer oil or silver transfer oil should also have quick-drying and fast fixation, to prevent the back of the gold or silver ink prints appear dirty.
Second, the characteristics of gold and silver ink
1. The fineness of the ink
The better the fineness of the ink, the better the dispersibility of the pigment particles. Compared with the pigments in other inks, the pigment particles of the gold and silver inks are coarser, and it is easy to block the printing cylinders during the gravure printing process. Caverns, resulting in blockages and reduced ink transfer rates. Therefore, when deploying gold and silver inks, it is necessary to select gold powder and silver powder with high fineness and good floatability so as to facilitate uniform deployment and get a good print.
2. The gloss of the ink
The glossiness of gold and silver inks is largely related to the particle size of gold powder or silver powder. In general, the larger the particles, the better the gloss of the ink; conversely, the smaller the particles, the less the gloss of the ink. However, it is worth noting that with the increase of metal pigment particles, the printability of gold and silver inks will also decrease, the transfer performance will be relatively poor, and printing defects such as stencil printing will easily occur.
3. Heat resistance
Compared with the pigments in other inks, the gold powder and the silver powder in the gold and silver ink have the characteristics of high conductivity and high thermal conductivity, and the golden ink has poor heat resistance and is easily discolored when exposed to heat. Therefore, high temperature and heat accumulation should be avoided during use. The silver ink has good light and heat reflection properties, good heat resistance, and is not susceptible to discoloration under high temperature conditions.
4. Chemical instability
Silver ink chemical properties are relatively stable, but the silver ink is not acid-resistant, and can easily react with acidic substances, thus reducing the metallic luster of the imprint. Therefore, neutral auxiliary materials should be used for printing in the printing process. This should be paid special attention. . The chemical nature of gold ink is not stable enough. It will cause chemical changes in different degrees when it comes in contact with acids, alkalis, and sulfides. It will reduce its metallic luster and gold ink will appear black. Second, gold ink is also very easy. Discoloration occurs due to chemical reaction with air and water vapor. Therefore, be sure to seal the container tightly when storing the gold ink.
Third, the design process should pay attention to some issues
According to the type of substrate materials and printing process, reasonable layout design, not only to do a nice appearance, but also fully take into account the characteristics of gold and silver ink and printing process, as far as possible the occurrence of printing failures.
1. In general, gold and silver inks are mainly applied in the field parts or color patches, and it is better not to design them into gold or silver for very small intaglio, yang text and level transitions.
2. When printing gold and silver ink on paper, it is usually necessary to lay down the background ink. For example, when printing silver ink, first lay a light layer of white ink, and then print the silver ink. This can not only improve the gloss of the silver ink layer, but also It also enhances the adhesion of silver ink on paper.
3. If the substrate material is aluminum foil or vacuum aluminized paper, printing transparent yellow on it, can achieve the golden effect; in the plastic film composite printing process, after printing transparent yellow on the OPP plastic film and then composite aluminum foil, print The ink layer can also achieve a golden effect, which can not only save expensive metallic ink, but also achieve the desired effect.
4. The color sequence arrangement of gold and silver ink should be taken into consideration in the process of plate design so that it can ensure the metallic color.
5. If it is a printed product, after printing gold ink and silver ink, UV coating or water-based coating should also be considered, or the print should be coated to prevent the gold ink from oxidizing or discoloring.
Fourth, the printing process should pay attention to the problem
There are many factors that affect the quality of gravure printing products, such as the type of substrate materials, the characteristics of the printing press, the characteristics of the ink, and the ambient temperature and humidity. Therefore, in the gravure printing process must be strictly related to technology, margin, silver ink printing quality.
1. Reasonable Selection of Substrate Material The properties of the substrate material must be compatible with the printing process characteristics of gold and silver ink. Only by selecting the proper substrate material can we highlight the printing effect and metallic luster of gold and silver. It is required that the physical and chemical indexes such as whiteness, evenness, smoothness, surface strength and flatness of the substrate materials be good, the stretching rate should be small, and the ink absorption should be moderate. If the substrate material is poor in flatness, large in stretchability, and poor in solidity, it is difficult to maintain a constant printing pressure, and it is easy to produce print pressure inhomogeneities, poor adhesion of the inked ink layer, and poor quality of the ink. Therefore, if gold and silver inks are to be printed on paper, substrate materials such as coated paper, glass cardboard, and whiteboard paper can be selected, and the metallic luster of gold and silver inks can be highlighted. If the substrate material is a plastic film, the plastic film must be pre-treated between printing, such as corona treatment, to improve the printability of the plastic film and the adhesion of gold and silver ink.
2. The control of the printability of gold and silver inks The control of the performance of gold and silver inks mainly includes the following aspects: 1. The viscosity of the ink. Viscosity is the most important control index in ink application. It directly affects the transfer performance of inks and the quality of prints. Too low viscosity can easily cause the ink to spread. Conversely, if the viscosity is too high, the transfer performance of the ink is relatively poor, and a large area is prone to appear. Some inaccurate ink lines, thin lines and other defects. When large areas of gold and silver ink are printed, the viscosity of the ink can be adjusted slightly lower to ensure that the ink layer after printing is uniform; when printing gold and silver ink on lines with smaller areas, the viscosity of the ink should be slightly higher. 2 ink dryness. The drying speed of the ink should be appropriate, the drying speed of the ink is too fast, and the dry plate is liable to occur, which affects the transfer of the ink. However, the drying speed of the ink cannot be too slow, or else the back stain of the printed matter may occur. The general principle for selecting the ink drying speed is that under the existing conditions of the printing machine, the ink should be sufficiently dry before the next printing group and before rewinding or stacking, but it cannot be dried on the printing plate. During the printing process, appropriate amounts of slow-drying solvents or fast-drying solvents can be added to the gold and silver inks to adjust the drying speed of the gold and silver inks.
In addition, the use of gold and silver ink should also follow the principle of follow-up with the printing, the amount of ink each deployment should not be too much, to avoid the excessive deployment of ink to make the powder in the air exposure time is too long, and the oxygen of the air The water vapor undergoes a chemical reaction and loses its golden luster.
3. Control of the printing press 1 Printing pressure. The appropriate printing pressure should be set according to factors such as the printing method, ink performance, and the ink absorption properties of the substrate material. The printing pressure is too large, the ink spreads, the graphic is easily thickened and widened, and even the stencil is printed; the printing pressure is too small, Insufficient ink may cause inaccurate graphics. In the printing process of gold and silver ink, if it is a large-area solid color patch, the printing pressure can be appropriately increased to make the ink layer even and thick; if it is a small line or text, the printing pressure should be reduced appropriately , Avoid imprint expansion, paste version and other ills. 2 tension control. The tension should be adjusted according to the type of substrate material and its stretching rate. For example, the stretching rate of PE film is relatively large, and the tension value should be small; and for paper or plastic films with low elasticity such as PET, OPP, the tension can be appropriately large. some. In addition, the winding tension should not be too large to prevent back sticking. 3 printing speed. When printing gold ink, the speed of the printing machine cannot be too fast. Otherwise, the heat generated due to friction will continue to accumulate, which will easily cause oxidation and darkening of the gold ink. This will not only affect the gloss of the gold ink, but may also cause the stencil. . 4 drying capacity. The temperature of the drying oven should not be too high, otherwise it will easily cause shrinkage of the substrate material, especially the PE film. Therefore, when setting the temperature of the drying oven, factors such as the printing speed, the printing tension, the type of substrate material, and the size of the printing pattern must be taken into consideration.
In addition, the printing roller of gold and silver ink should be cleaned in time after printing so as to prevent the dry knot from being formed in the net of the roller and cause the clogging of the cell.
4. Control of ambient temperature and humidity The humidity is too high, and the content of water vapor in the air is high, which easily discolors the gold ink, and also affects the moisture content of the paper substrate material, resulting in dimensional deformation, resulting in faults such as overprinting. If the humidity is too low and the air is too dry, static electricity can easily occur. Therefore, the temperature and humidity in the printing room should be kept constant. In general, the relative humidity is controlled between 55% and 60%, and the temperature is controlled between 20~28Â°C.
Five, plastic printing gold, silver common fault
1. Causes of dirty print on the back side: 1The drying speed of the ink is too slow to be completely dried; 2 The printing speed is too fast; 3 The winding tension is too large or the printing stack is too high; 4 The operating environment temperature is too high; The machine has low drying capacity. Solution: 1 add quick-drying solvent, or change the formula of gold, silver oil; 2 reduce the printing speed; 3 reduce the winding tension or printing stack height; 4 reduce the operating environment temperature; 5 increase the air volume and far Infrared light intensity.
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