In packaging printing and some special printing, there are more and more products using gold and silver inks. It uses the characteristics of gold and silver inks that have flashing metallic colors to enhance the effect of packaging and security printing, but since gold and silver inks have their own Because of its special nature, it is necessary to fully grasp its characteristics in use in order to print exquisite products.
First, the characteristics of gold and silver ink
Gold and silver inks are gold powder or silver powder (usually copper, aluminum powder or copper and 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 property of exhibiting a suspension phenomenon in a liquid medium in order to obtain the unique color-forming properties of the metal. The flaky powder has this property, so gold powder and silver powder must be made into scaly 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 of 8% ~ 1 2%, reddish color, commonly known as red light gold or red gold; 20% ~ 30%, The color of partial green, 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% of copper, 27.28% of zinc, 0.019% of aluminum, 0.11% of silicon, 88.3% of copper in the United States, and 11.29% of zinc. 0.019% aluminum and 0.10% silicon. The appropriate amount of silicon is added to the gold powder to improve the comminution of the copper-zinc alloy and to overcome the ductility, so that the gold powder generates a very small flaky shape and increases the gloss. The chemical properties of gold powder are not stable, and chemical reactions occur in the presence of acids, alkalis, carbon dioxide, and sulfide gases, causing the metallic luster to decrease or disappear. Therefore, in order to improve the oxidation resistance of the gold powder surface, gold powder is often added with an appropriate amount of stearic acid during the production process, so that the exposed gold powder forms a protective layer. Silver powder is easy to be suspended, has strong covering ability, good stability, good reflection property to light and heat, strong heat resistance, is not easy to change color, is not affected by weather, and has strong durability. However, the density of silver powder is small, it is easy to fly in the air, and it will explode in the event of Mars. In case of acid, chemical changes will occur and the metallic luster will be 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 display 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 gold. In general, a light-reflecting surface with a large particle diameter of the powder has a wide color, exhibits a strong coloration property of 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 metal 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 are made of fine metal foils. When the ink is dry, these foils form a layer of stamped metal foil on the print surface. 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 better.
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 ink have good printability, the used varnish must have good adaptability: there is enough viscosity, after the metal powder is reconciled, it basically reaches the printing ink viscosity, fluidity and other performance indicators. If the viscosity of the varnish is too low and there is not enough pulling force, the metal powder cannot be transferred very well. When printing, it often causes failures such as stacker roller and stacking plate; good chemical stability, and generally requires 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 quick-fixing properties, and be printed on the substrate quickly and dry to avoid the backside sticky 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 and 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 small scale-like copper or aluminum metal powders and other auxiliary materials and trace amounts of other elements. The powders are usually 0.01-0.5 μm, and the brightness is 92%-97. %, with a fineness of 1 000 mesh. Gold and silver powder reacts with acids and alkalis to reduce the luster of gold and silver powders. High temperatures can also affect metallic luster. Oxygen in the air can also cause oxidation and change color. The luster coloration of gold and silver inks depends on the suspension of gold powder and silver powder. That is, the better the suspension, the better the coloration of luster. 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 and silver powder particle diameters when selecting the number of screen meshes. When the particle diameter is large, the mesh size is small and the mesh mesh is 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, ​​resulting in no printing or empty appearance. 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. Such as screen printing large area of ​​gold ink or large area of ​​silver ink, or printing on a large area of ​​gold ink layer, in order to prevent the fall of gold and silver powder, should be used to adjust the ink adjustment, printing a large area of ​​gold and silver ink, so that The gold and silver inks are isolated from the air, reducing the oxidation reaction, ensuring the original color of the metal, and can receive good results. Some products change the color sequence according to their special requirements.
(4) Since the reflectivity of the silver ink is very similar to the true color of the paper, silver ink is not suitable for the small area pattern or text on the screen. Because the area is small, the strokes of the characters are thin, making it difficult for the naked eye to discern, and thus the printing silver is lost. the goal of. It is best to print silver on a dark screen, just like 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 fine or fine-grained patterns.
(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 the paper smoothly. Therefore, it is necessary to increase the pressure, but increasing the pressure will inevitably result in a paste. You can use a low mesh screen, such as 120 T 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) Carefully adjust the ink and increase the printability. Attention should be paid to the addition of gold and silver inks when adjusting the ink, because the gold, silver or oil in the ink is easily detached from the gold and silver powder, so that the remaining gold and silver powder is increased. , will seriously affect the transfer of ink. It is best to add less. Increase the number of additions to ensure good delivery.
2. Exclusion of common faults in gold and silver ink screen printing
Symptoms: Product imprinting powder
Main reasons: (1) The concentration of the varnish is insufficient, and the content of penetrating substances is relatively large. Even if the texture of the paper is not very loose, too much penetration of the connecting material will cause the imprinted powder to be stained. (2) The gold and silver ink is caused by Gold and silver powder and varnish formulated, the powder and the binder affinity is poor. When transferred to the paper surface, the excess binder was removed from the silver powder to penetrate the interior of the paper, causing 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 reprint the gold or silver ink. On the one hand, the use of the background ink reduces the absorption of the gold and silver ink binders on the paper. On the other hand, printing the gold and silver inks when the ink of the background ink is not completely dry can firmly bind the gold and silver inks to the ink of the background ink and avoid the chalking of the ink. . In addition, to avoid powder failure, the amount of water should be set to a minimum. When printing on high-coated paper or enamel surfaces, an 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, printing another layer of ink on the surface of the first layer will often compensate or reduce this phenomenon.
Symptom: Prints are dull and gray
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 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 the color is strung, replace it immediately.
Symptoms: Printed text is not clear
The main reason: due to improper adjustment of printing pressure, too little ink or uneven local ink, too much ink content; paper surface is too rough or background 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.
Source: Screen Printing
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