In packaging printing and some special printing, there are more and more products that use gold and silver inks. It uses the characteristics of gold and silver inks that have flashing metallic color to enhance the effect of packaging and security printing, but since gold and silver inks have Because of its special nature, it is necessary to fully grasp its characteristics in use in order to print exquisite products.
The characteristics of a gold and silver ink
Gold and silver inks are gold powder or silver powder (usually copper, aluminum powder, or copper or aluminum flakes). That is, mechanical and copper particles are used together with stearic acid for grinding, grading and polishing. The resulting scaly metal powder. Powder instead of pigment particles, produces a gold-silver density ink with a high concentration. Gold powder and silver powder must have the characteristic of exhibiting a suspension phenomenon in a liquid medium in order to obtain the unique color-forming property of the metal. The flaky powder has this property, so the gold powder and silver powder must be made into scale-like powder. The characteristics of gold and silver powder are different. In addition to copper, gold powder also contains zinc, silicon and other powders. The amount of zinc (usually 10% to 30%) can produce different colors of gold powder, such as zinc content 8% ~ 12%, color red, commonly known as red gold or red gold; 20% ~ 30%, color Partial blue, commonly known as Qingguang gold or green gold. The zinc content of gold powder in different countries is also different. For example, the British gold powder contains 72.2% copper, 27.28% zinc, 0. 019% aluminum, and 0.12% silicon. The American gold powder contains 88.3% copper. %, Zinc 11.29%, Aluminum 0. O19%, Silicon 0.1O%, The appropriate amount of silicon is added to the gold powder to increase the comminution of the copper-zinc alloy and to overcome the ductility, so that the gold powder generates tiny scales, increasing Glossiness: The chemical properties of gold powder are unstable, and the chemical reaction occurs when acid, alkali, carbonic acid gas and sulfide gas are produced, resulting in the reduction or disappearance of metallic luster. Therefore, in order to improve the oxidation resistance of gold powder surface, gold powder is often added during the production process. A suitable amount of stearic acid forms a protective layer on the exposed gold powder, which is easy to be suspended, has strong covering ability, good stability, good reflection of light and heat, strong heat resistance, and is not easily discolored and is not affected by climate. Strong durability, but silver powder density is small, easy to fly in the air, will explode in the event of Mars; in case of acidic substances will undergo chemical changes, so that metallic luster affected.
The gold and silver inks can be used with the gold and silver powder, the binder, and auxiliary materials. Can also be produced by professional ink factory finished products, ready to use. The connection material of gold and silver ink is a special type of varnish, referred to as gold transfer oil or silver adjustment oil. They are made from specialty resins, dry vegetable oils and a variety of organic solvents that are refined at high temperatures. The most important feature of gold and silver ink printing is that it can show the unique suspension properties and color-forming properties of gold and silver powder after printing, and ensure the stability of quality and no discoloration during storage. Gold and silver powder pigment particles are divided into fine particles and coarse particles. Finer particles can be directly used to make ink, and coarser particles are used only for rubbing (bismuth) gold technology. In general, a light-reflecting surface with a large particle diameter of the powder has a wide color, exhibits a strong coloration property with a metallic color, a small particle diameter of the powder, a narrow light-reflecting surface, and a weak color-forming property exhibiting a metallic color. In addition to the direct use of the corresponding metallic pigments, the gold and silver inks can also be used to manufacture inks. They can also be colored with other colored pigments or blended with transparent colored inks to produce a variety of special gold and silver colors, but such colored gold and silver inks are produced. Less applied. The gold and silver inks formulated from fine metal foils form a layer of stamped metal foil on the surface of the print when the ink is dry. When the metal pigment forms a thin layer on the surface of the print, it will produce a higher gloss of gold or silver ink. If you change the composition of the ink's flakes, the golden ink's color range will vary from reddish gold to gold. Gold and silver ink require a special manufacturing process to form, and generally require a special printing process. These inks are generally less durable than pigment particles but can be protected with a print coating or glaze layer. In general, inks made with powdered metallic pigments have a thickening (thickness) phenomenon on a printing press, and inks prepared with a wet gold-silver paste pigment are preferred.
The brightness of the gold-silver ink printing layer is not only dependent on the color-generating property of the metal powder itself, the suspension of the metal powder, and the diameter and shape of the powder particle, but also the affinity of the gold-modulating oil or the silver-plating oil on the metal powder. The impact of performance factors. Therefore, in order to make the gold and silver inks have good printability, the used varnish must have good adaptability: It has sufficient viscosity, and after it is harmonized with the metal powder, it basically reaches the performance index such as the viscosity and fluidity of the printing ink. If the viscosity of the varnish is too low and there is not enough tension, the metal powder can not be transferred very well. When printing, it will often cause failures such as stacker roller and stacking plate; Good chemical stability, and generally require acid value. Lower; the varnish can be evenly mixed with gold and silver to ensure the stability of the gold and silver powder suspension and good printing performance; the varnish must have good transparency to improve the color performance of the gold and silver powder. To make the metal luster and coloring ability stronger; the varnish must have quick-drying and fast fixing properties, and it should be printed on the substrate quickly and dry to avoid the backside sticking fault.
Second, gold and silver ink screen printing should pay attention to the problem
Gold and silver ink can be used for offset printing, gravure printing, letterpress, screen printing and other printing processes. However, there are differences in technical requirements to be noted in various kinds of printing.
1. Gold and silver ink screen printing technology essentials
In screen printing, gold and silver inks are generally used for packaging decorative printing. In order to enhance the special effects of commodity packaging, various gold and silver characters and patterns are printed on the packaging box. Screen printing gold and silver ink requires a skilled plate-making process and printing process operating techniques. We know that the pigments in gold and silver inks are essentially made up of extremely fine scale-like copper or aluminum metal powders and other auxiliary materials and trace amounts of other elements. The powders are generally o. Ol~o. 5 ITI, light brightness 92% ~ 97%, fineness l 000 mesh. The gold and silver powder reacts with acid and alkali to reduce the luster of the gold and silver powder. The high temperature will also affect the metallic luster. The oxygen in the air will also easily change from the oxidation reaction. The color performance of the shiny material of the gold and silver ink depends on the suspension of the gold powder and the silver powder, that is, the better the suspension, the better the coloration of the gloss. Screen printing gold and silver ink should pay attention to the following technical essentials.
(1) Screen Printing Unlike other printing, it is necessary to consider whether the ink can pass through the screen smoothly. Since gold and silver powders in gold and silver inks are metal particles or flakes, attention should be paid to the size of the gold-silver powder particles when selecting the number of screen meshes. If the diameter of the particles is large, the mesh size is small, and the screen mesh is generally large. 160 ~ 250 mesh screen can be selected.
(2) In order to make the products printed by gold and silver inks have a strong three-dimensional effect and have a good luster, try to arrange the gold and silver in dark, black, dark blue and other dark grounds when designing the originals. Printed on a white paper, it is applied with yellowish black and light gray primer. This not only makes the gold and silver ink thick, but also improves the color quality of the metal. But be aware that the background color cannot be printed too thickly. If it is a fast-drying ink, it is prohibited to add a desiccant. Once it is over-dried, the surface of the ink will crystallize, that is, the surface will be glassy and will not print or appear empty. Therefore, the time interval between the printed background and the printed gold and silver ink cannot be too long.
(3) General gold ink and silver ink are all arranged for final printing. For example, when printing large area gold ink or large area silver ink, or printing on large areas of gold ink layer, in order to prevent the falling of gold and silver powder, adjustment should be made by adjusting the ink and printing large areas of gold and silver ink layers. The gold and silver inks are isolated from the air, reducing the oxidation reaction, ensuring the original color of the metal, and receiving good results. Some products change the color sequence according to their specific requirements.
(4) Since the reflectance of silver ink is very close to the true color of the paper, silver ink is not suitable for small areas of screen printing or writing. Because the area is small and the text strokes are thin, it is difficult for the naked eye to distinguish between them, and thus the silver is lost. the goal of. It is best to print silver on a dark screen as gold, so that the gloss on the screen is consistent with the original metallic luster. At the same time, since the particles of silver powder are coarser than other pigment particles, and its dispersibility is relatively poor, it is easy to produce a paste plate when printing, so it is not easy to print a thin or fine-grained pattern.
(5) Note the content of gold and silver powder and printability. In order to improve the color quality of gold or 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 inevitably reduce the printability; if you want to improve the printability, the less the content of gold and silver powder, the better. . In order to improve the color and printability of gold and silver ink, and to resolve this contradiction in the process of printing gold and silver, we should pay attention to two points. First, according to the poor transferability of gold ink and silver ink in the ink roller, in order to ensure that the gold and silver ink can be effectively transferred, a low hardness scraper can be used, and the scraping angle should not be too large. Second, due to the poor transferability of gold and silver inks, the gold and silver inks cannot be transferred to papers very smoothly. Therefore, it is necessary to increase the pressure, but increasing the pressure will inevitably cause scumming. You can use low mesh screens, such as 120T screen plate.
(6) It is forbidden to add ink or mineral oil to ink. Because gold and silver powders react chemically with varnish and mineral oils, they lose their luster.
(7) Conscientiously adjust the ink and increase the printability. Attention should be paid to adding gold and silver ink when adjusting the ink. Because the gold, silver or oil in the ink is easy to separate from the gold and silver powder, the remaining gold and silver powder will be more. , will seriously affect the transfer of ink. It is best to add less. Increase the number of additions to ensure good delivery.
2. Troubleshooting of common faults in gold and silver ink screen printing: Product imprinting
Main reasons: (1) Insufficient concentration of varnish, high content of penetrating substances, even if the texture of paper is not very loose, it may cause imprinting due to excessive penetration of the binder; (2) Gold and silver ink Gold and silver powders are formulated with a varnish, and the powder and the binder have poor affinity. When transferred to the paper surface, the excessive amount of the binder was separated from gold and silver powder and penetrated into the interior of the paper, resulting in chalking of the print.
Solution: In the printing of gold and silver inks, first print the undercoat ink first, and then use the overprint method to print the gold or silver ink again. On the one hand, the use of undercoat inks reduces the absorption of gold and silver ink binders by the paper. On the other hand, printing gold and silver inks when the undercoat inks are not completely dry can firmly bind the gold and silver inks to the undercoat inks and avoid the chalking of the prints. . In addition, in order to avoid powder failures, the amount of water should be set to a minimum. When printing on high-crepe paper or enamel surfaces, appropriate amount of desiccant should be added to the ink. Before printing with gold or silver ink, the surface of the substrate is usually sealed with a conventional oil-based clear white ink coated with a glue. If chalking has already occurred, an additional layer of ink on the surface of the first layer will often compensate or reduce this phenomenon.
Symptoms: Dark and dull prints
The main reason is that the reconciliation time is too long, and it is oxidized or discolored by acid, alkali, sulfur and other chemical substances, and it is colored with other inks.
Solution: Gold ink is used with the tone, cleaning the ink pump, pipe, ink tank and printing plate on time to prevent cross-coloring. Once it is strung, change it immediately.
Symptoms: Printed text is false, not clear
Main reasons: Due to improper adjustment of printing pressure, too little ink, or uneven local ink volume, the content of the varnish is too much; the surface of the paper is too rough or the background color printing is not ideal.
Solution: The printing pressure and ink volume can be appropriately increased to ensure uniform ink volume; reducing the amount of varnish.
Qi Cheng Screen Printing - Issue 7 of 2006