Gold and silver ink and its printing technology points (below)

Four, gold and silver ink printing process design considerations

When designing a good layout, when considering the types of printing materials and the different printing processes, we must also fully pay attention to the characteristics of gold and silver inks and printability, avoid weaknesses, and make the best use of them.

(1) As the gold and silver powder particles are coarse, the dispersion is not good, and the stencil is easily produced during printing. Therefore, the gold or silver ink is mainly applied to the solid part or the color patch, but for the fine text of the stroke, the thin wire is used. The pattern and the level of transition, it is best not to design gold or silver.
(2) Since the emissivity of the silver ink is very similar to the true color of the paper, silver ink should not be used when designing small area patterns or characters, otherwise it is difficult for the naked eye to distinguish them.
(3) In the process of plate design, the order arrangement of gold, silver ink and other color inks should be taken into account to ensure that the metal color is not covered or weakened.
(4) When printing gold and silver ink on paper, it is usually necessary to first coat the background ink. For example, when printing silver ink, first lay a light layer of white ink, and then print silver ink. This will not only improve the gloss and saturation of the silver ink layer, but also enhance the adhesion of the silver ink to the paper.
(5) If the printing material is aluminum foil or vacuum aluminized paper, printing transparent yellow ink on it can achieve the golden effect; in the plastic film composite printing process, printing transparent yellow on the OPP plastic film and then compounding the aluminum foil, The print ink layer can also achieve a golden effect, which can not only save expensive metallic ink, but also achieve the desired effect. If it is a table printing product, after printing gold ink and silver ink, it is also necessary to consider UV glazing or water-based glazing, or to coat the printed material and other processes to prevent the oxidized discoloration or detachment of the gold ink.

V. Preparation of gold and silver ink before printing

(1) Selection of printing materials The performance of printing materials must be compatible with the printing process characteristics of gold and silver ink. Only by selecting suitable printing materials can the printing effect and metallic luster of gold and silver be highlighted. This requires the printing material to have good whiteness, evenness, smoothness and surface strength, low stretchability, and moderate ink absorption. Otherwise, it is likely to cause quality problems such as non-uniform printing pressure, poor adhesion of the ink layer to the ink, and ink coloring. Therefore, when printing gold and silver ink on paper, substrates such as coated paper, glass cardboard, and whiteboard paper can be selected so as to highlight the metallic luster of gold and silver ink. If the printing material is a plastic film, the plastic film must be surface-pretreated before printing, such as corona treatment, to improve the printability of the plastic film and the adhesion of gold and silver ink on the film.

(2) Requirements for the printing performance of gold and silver ink The requirements for the performance of gold and silver ink mainly include the following aspects: 1 Viscosity of ink is the most important control index in ink applications. It directly affects the transfer performance of ink and the print Quality, low viscosity is likely to cause the ink to spread; conversely, if the viscosity is too high, the transfer performance of the ink is relatively poor, and it is prone to defects such as inconsistent ink and thin line breakage in a large area. 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 the gold or silver ink is printed on lines with smaller area, the viscosity of the ink may be slightly higher. . 2 Drying of Ink The drying speed of the ink must be appropriate. If the drying speed is too fast, it will be prone to dry printing and affect the transfer of the ink. On the contrary, if the drying speed of the ink is too slow, the back of the printed matter will become dirty. The general principle for selecting the ink drying speed is that under the existing conditions of the printing machine, the ink should be sufficiently dried before entering the next printing group and before rewinding or stacking, but it cannot be dried on the printing plate. In the printing process, an appropriate amount of drying inhibitor or drying property may be added to the gold and silver inks to adjust the drying speed of the gold and silver inks according to the specific conditions. 3 The deployment of gold and silver ink The use of gold and silver ink should also follow the principle of printing with the tone, the amount of ink each deployment should not be too much, to avoid the excessive deployment of ink so that the exposure of the powder in the air is too long, and Air oxygen and water vapor react chemically and lose their metallic luster.

(3) adjustment of the printing press 1 printing pressure According to the printing method, the ink properties and the ink absorption properties of the printing material and other factors to set the appropriate printing pressure. Printing pressure is too high, ink spread, the picture is easy to thicken and widen, even paste version; printing pressure is too small, the amount of ink is not enough, the graphic may be inked uneven. 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 print defects such as enlarged prints and stencils. 2 tension control should be based on the type of printing materials and its expansion rate to adjust the tension, such as PE film expansion rate is relatively large, the tension value should be smaller; and for paper or PET, OPP and other low elongation rate plastic film, tension can be appropriate Something bigger. 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 can't be too fast. Otherwise, the heat generated due to the friction will continue to accumulate, it is easy to make the black ink oxidized and darkened, which will not only affect the gloss of the gold ink, but also may cause Cause paste version. 4 Drying capacity Drying oven temperature can not be too high, otherwise it is easy to cause printing materials (especially PE film) shrinkage deformation. Therefore, when setting the temperature of the drying oven, factors such as the printing speed, the printing tension, the type of the printing material, and the size of the printing image area must be comprehensively considered. In addition, gold and silver inks are used for gravure printing. After the printing is completed, the printing roller of gold and silver ink must be cleaned in time to prevent the ink from being dried in the roller holes of the roller, thus causing the clogging of the cells or the decline of the ink transfer capacity.

(4) The control of the environment temperature and humidity is too high. The content of water vapor in the air is large, which easily discolors the gold ink. It also affects the moisture content of the paper, causing its size to distort, resulting in failures such as overprinting. . If the humidity is too low and the air is too dry, it can easily cause static electricity. In addition, if the temperature is too low, the fluidity of the gold-silver ink will be lowered, and if the temperature is too high, the transfer performance of the gold-silver ink will be degraded. Therefore, the temperature and humidity in the printing shop should be kept as constant as possible. In general, the relative humidity is controlled between 55% and 60%, and the temperature is preferably controlled between 20°C and 26°C.

Six, gold and silver ink printing process technical points

Gold and silver inks can be used in offset printing, embossing, gravure printing, and screen printing. However, different printing methods have different technical points in the use of gold and silver inks.

(1) Gold and silver ink offset technology

Gold and silver ink offset printing is a new type of printing technology that has been developed in recent years. It was originally based on field and line printing, and gradually developed into dot printing. In the gold and silver ink offset should pay attention to the following things. 1 The gold and silver inks should be used for cash adjustment. It is generally advisable to control the use of ink in 4 hours, and it is not possible to use too much ink at a time. 2 When printing gold ink, the machine speed is too fast will cause the ink roller temperature to rise, gold ink oxidation black, poor transfer performance and other failures, the general printing speed is controlled at 4000 prints / hour. 3 Because the moisture is too high, the gold and silver inks will emulsify and affect the printing quality. Therefore, the layout moisture should be controlled to a minimum. 4 Because the gold and silver ink particles are relatively coarse, the transfer performance during printing is poor, so the printing pressure must be adjusted, otherwise, the phenomenon such as paste printing is likely to occur. In the case of printing silver ink, after the silver ink is full-printed, before the ink is completely dried, the original plate is air-pressed once again to prevent coarse silver particles from floating on the surface of the print, resulting in false printing, and a problem of the bottom of the plate. 5 Make the ink thick and flat, and at the same time master the dryness of the bottom ink. It is ideal to superimpose metal ink when the bottom ink ink film surface becomes sticky. 6 In the printing color sequence, the gold and silver inks are generally arranged to be printed in the last color, otherwise the metallic luster is easily covered or a color mixing phenomenon occurs.

(2) Highlights of Gold and Silver Ink Embossing Technology

Embossing gold and silver inks are generally used for the printing of commodity packaging, book covers, inserts, and fine samples. Gold and silver ink need to pay attention to the following issues when embossing. 1 When loading, consider the factors such as paper feeding, pressure, and ink, and fix the plate in the frame. 2 In letterpress printing, it is usually required that the ink distributing roller and the ink roller be more than one, so that the ink can be smoothly and evenly transferred to the printing plate. However, in the printing of gold and silver ink, if the speed of the printing press is faster, the more ink rollers, the greater the heat generated when they are rubbed with each other, which will make the ink and metal powder particles in the gold and silver ink dry. On the roller, there is a build-up of remaining ink that affects the transfer of ink. Due to repeated friction with the ink roller, the protective layer on the surface of the powder particles (for example, stearic acid and the like) is destroyed, and the powder is oxidized and discolored. Therefore, gold and silver ink printing requires less uniform roller and ink roller as well. 3 When selecting the ink roller, the ink roller should be soft, flexible and smooth. Before actual printing, it is necessary to reasonably adjust the pressure of the ink roller so that there is good contact between the adjacent ink roller and paper, and light and uniform pressure is needed. The adjustment of the printing pressure should be matched with the speed of the printing press, because the increase of the printing speed will cause the reduction of the contact time between the printing plate and the paper. Only by increasing the printing pressure can the printing plate and the paper contact well and the gold and silver ink transfer smoothly. 4 After the bottom ink is printed, clean the ink roller, ink fountain and transfer roller. For convenience, it is best to use two sets of ink rollers for bottom ink and gold and silver ink printing.

(3) Gold and silver ink gravure printing technology

1 gravure gold and silver ink is mainly used for printing plastic and composite film, because the film is non-absorbent material, its film surface smooth, low surface tension, chemical stability, and antioxidant, and gold and silver ink is Depending on the dryness of the oxidized conjunctiva, in order to improve the adhesion of the gold and silver ink, the plastic film must be subjected to a surface treatment (such as corona discharge) before printing. 2 The composition of the varnish used in plastic gravure gold and silver inks is also different from other linking materials. It is not a volatile dry type linking material, but an oxidative polymerization-based varnish. Drying method, printing speed, environmental conditions and auxiliary consumables must be coordinated. 3 When printing gold and silver ink on the surface of the paper, it is generally necessary to print a light base color to strengthen the metallic luster and strengthen the adhesion of gold and silver ink. However, when printing gold and silver ink on the surface of a plastic film, it is not necessary to first print the background color, and most of them use a certain color block in the graphic to play the above-mentioned role.

(4) Gold and silver ink screen printing technology

When printing gold and silver ink, pay attention to the following issues. 1 Screen printing requires the ink to pass through the screen smoothly. Since the particles of gold and silver powder are relatively large, mesh screens with a slightly lower number of mesh lines (larger meshes) are generally used, and screens of 160 to 250 mesh/inch are generally selected. 2 In order to make the gold and silver ink printing products have good gloss and three-dimensional effect, they should try to print gold and silver on the dark ground. To print gold and silver on white paper, you must use yellow, black or light gray ink to make a bottom, print a thin layer, and then print gold and silver ink. This will make the gold and silver ink thick and improve the color quality of the metal. 3 In order to ensure the purity of gold and silver ink, gold and silver ink printing is usually arranged at the end. In addition to its metallic color, the gold and silver ink is more importantly, it is the surface of the conjunctiva dry, the reflection of light is the surface color. If other colors of ink are printed on it, the effect of gold and silver ink is lost. We must take full advantage of the strong hiding power of gold and silver ink, put it in the best printing, and strengthen the luster and thickness of gold and silver ink. When printing a large area of ​​gold and silver ink or printing on a large area of ​​gold and silver ink, in order to prevent the gold and silver ink from falling off, the ink should be used to adjust. At the same time avoid excessive contact of gold and silver ink with air, resulting in oxidative discoloration. 4 In order to improve the color quality of gold and silver ink, it is necessary to increase the content of gold and silver powder in gold and silver ink, but the increase in the content will reduce the printability of gold and silver ink. Therefore, the following two points must be noted: a. According to gold and silver ink In the ink roller in the transfer of poor performance characteristics, in order to ensure the effective transfer of gold and silver ink, available low hardness scraper, scraping angle should not be too much. b. In order to ensure the transfer performance of gold and silver ink, it is usually necessary to increase the squeegee force, but too much squeegee force will inevitably cause stencil printing. Therefore, a screen with a low number of meshes can be used.

Source: 21st