The production of colored aluminum foil can be accomplished by aluminum foil printing and coating machines. Forming a color pattern on the surface of the aluminum foil can be achieved in the printing process or in the coating process. The following two methods are described below.
Printing overprint or ink coating to produce colored aluminum foil
Overprinting different colors of aluminum foil in the printing process is one of the most widely used methods for multi-color printing of aluminum foil in pharmaceutical blister packaging. This printing process can print three to four colors. According to actual samples of aluminum foil products printed by the user, a monochrome printing plate roller with different network line angles is used in the process, and the multicolor printing products with the same original gradation and hue are finally obtained in accordance with the printing color sequence.
In the printing of color aluminum foil, the applicability of the ink is the key. At present, there are two main types of inks with better adaptability of the metal aluminum foil. One type is a polyamide ink, and the ink has a good effect on plastics and metals. Adhesion, dispersibility, gloss, abrasion resistance, solvent release. Because of its softness, it is mostly used for plastic film printing, but in the printing of aluminum foil as the base material, the excellent performance of the ink can be expressed, and its heat resistance can also meet the requirements of aluminum foil printing. The other type is a complex aluminum foil ink mainly composed of a vinyl chloride-vinyl acetate copolymer resin/acrylic resin, characterized by its bright color, high concentration, particularly strong adhesion to aluminum foil, and good transparency. In the selection of ink, inks containing toxic ingredients such as heavy bowls are not used.
Color aluminum foil ink deployment
According to the law of three primary colors, accurate ink distribution can be achieved. Since any color can be blended using different proportions of the three primary colors, the hue change of the ink utilizes this rule. If the three primary inks are mixed in equal amounts, they can become black (approximate). The three primary colors inks are mixed in equal amounts and different proportions of white inks are added, so that various shades of light gray ink can be formulated. If the three primary color inks are blended in different proportions, the inter-color or multi-colors of a plurality of different hues can be prepared, but the hues of the three primary colors are biased toward a large proportion of primary color hues. If the two primary inks are mixed in the same amount, they can become standard inter-colors. After mixing the two primary inks in different proportions, they can be mixed into a plurality of different hue inter-colors, but the hue thereof tends to be larger in proportion to the primary color hue. In addition, after the addition of white ink to any color ink, the hue appears brighter. Conversely, after adding black ink, the hue becomes dark. When deploying inks, it is necessary to determine which of the inks should be used to match the hue of the originals. For example, it is necessary to deploy lake blue ink, which can be adjusted by adding visual experience and practical experience. White ink is the main color, and peacock blue is the auxiliary color. If you want to deepen slightly more product blue. If you want to adjust the olive yellow-green ink, you can determine the main white ink, add light yellow and peacock blue and slightly pink. As long as the main color is determined slightly pink. As long as the main color is determined, the other colors are auxiliary colors. Gradually add a small amount of stirring, and then apply a little ink on the aluminum foil, scrape to the thickness of the printed ink, and compare it with the original to see if it is appropriate. When comparing samples, it is necessary to look at the relatively thin and light parts of the ink layer on the surface of the aluminum foil in order to see accurately. When you transfer ink, you must also master a principle that you should use as few inks as possible. If you can use two inks, do not use three inks to adjust the ink so as not to reduce the gloss of the ink. On the one hand, the color tone of the scraping ink is slightly deeper than the original color, so that the printed color sample is relatively accurate. After the sample's ink hue is quasi-precise, it can be batched to adjust the ink according to their respective ink proportions. The operation process of coating the color aluminum foil with ink is:
The ink is weighed on a bench scale, poured into a batching bucket at a certain mass ratio, stirred for a period of time with a stirrer until the ink solution is uniform, and the desired viscosity and color are achieved, and then the ink is placed on the printing or coating machine use. The surface of the inverted aluminum foil can be coated with ink to obtain a colored aluminum foil, but the cost is relatively high. If the surface of the aluminum foil is not clean or has oil stains, the combination ratio of the ink and the aluminum is low, and the ink is likely to be peeled off in large areas, which affects the product quality. The viscosity of the ink should be adjusted properly. In general, the viscosity of the ink in the application is relatively large. When printing, the ink should be diluted to achieve the required viscosity and fluidity. In the adjustment process, several factors must be grasped, namely, the structure of the printing press, the printing speed, and the temperature and humidity in the room. When using the No. 4 viscosity cup to measure the viscosity of the ink, when the printing speed of the machine is between 30-80m/min, the viscosity reading should be between 22-30. When ink is blended, when a large viscosity ink is used with a large amount of diluent, it should be stirred evenly so that the diluent is evenly distributed throughout the ink. Since the temperature and humidity of the indoor environment have an influence on the ink concentration in the printing, it is best to use an ink concentration detection apparatus to determine the amount of the added solvent, and to measure the concentration of the ink at intervals according to changes in temperature and humidity. In the process of gravure printing aluminum foil, if the ink concentration is too low, the color of the printed text pattern will not be bright, and the paste pattern will appear at the texture. However, if the ink concentration is too high, the turtle will appear in the pattern, which not only wastes the ink, but also causes the print surface to be uneven and unattractive.
The use of coating production process to show the color of aluminum foil
In the printing process of aluminum foil, it is necessary to perform the process of applying a protective agent and a binder on the surface of the aluminum foil, and uniformly spread the pigments or dyes of various colors into the protective agent and the binder system so that aluminum foil is used. The protective layer and adhesive layer exhibit different colors, which requires a certain choice of pigment or dye. Since aluminum foil is used for the packaging of medicines, disposable medical products and certain foods, the selected pigment must be harmless to the human body, and be stable in the state of the protective laminate adhesive layer, solvent resistance, migration resistance Good, will not contaminate the packaged drugs, medical supplies or food. In addition, since the medical aluminum foil needs to be heated at a high temperature during coating, printing, and blister packaging, the heat resistance of the pigment is also relatively high. The aluminum foil coating pigment is an organic pigment surface-treated with a high molecular polymer. The principle of applying color to the surface of the aluminum foil is to envelop the pigment particles with the resinous high polymer, so that the pigment particles are in the protective layer and the adhesive layer. A mechanical barrier layer is formed between adjacent pigment particles to prevent the relative binding of the pigment particles during the drying process. The resulting polymer-coated pigment is a kind of coating core with a pigment as a core and a high polymer coating as a shell. The oleophilic layer coated on the outside of the particles absorbs the oily medium to form a solvation layer, which protects the dispersed state of the pigment particles, and the pigment content of the use system can be as high as 40%. The color protective agent and the adhesive formulated with such a pigment have a stable state, a vivid color, a uniform color, a good heat resistance and migration resistance, and an excellent use performance.
Coating amount and coating solution concentration affect uniform color
The number of lines, depth, and shape of the coated mesh affect the amount of coating and can change the color. At present, most aluminum foil printing and coating equipment use an anilox roller coating process, also known as a wire coating method. The anilox roller is composed of a net hole and a net strength. The pit on the roller is usually called a net hole, and the high part is called a net wall or a net wire. The ratio of wall to wall is about 1 to 5. After processing, the anilox roller is coated with a hard chrome with a thickness of 0.015 to 0.02 mm to increase the surface hardness of the anilox roller, and its hardness value is HRC-65. When using this roller for color aluminum foil coating, the working state of the anilox roller is: When the liquid color slurry (or protective agent, adhesive) fills the anilox roller's cell, the anilox roller is driven by the mechanical rotation. When the cell leaves the liquid color slurry surface, the liquid on the smooth surface of the roller is scraped off by a scraper, leaving only the liquid that cannot be scraped in the cell cavity. This liquid color paste is then brought into contact with the surface of the coated aluminum foil substrate. This contact is achieved by the action of a resilient rubber roller. In this way, a part of the liquid color paste in the cell has fluidity, and it will slowly and automatically level on the surface of the aluminum foil so that the original discontinuous liquid becomes a continuous and uniform liquid layer. A portion of the liquid in the anilox roller cell is transferred to the aluminum foil. The anilox roller rotates at the same time. Once it is rotated again, it is immersed again in the liquid color paste. The liquid color paste will fill the cell hole again. . An anilox roller with a small diameter can continuously and uniformly transfer the liquid color slurry to the surface of the aluminum foil without interruption, so that the surface of the aluminum foil can be evenly coated, thereby achieving a uniform surface color. Obviously, if there are fewer network lines per unit area on the anilox roller, the deeper the cells will be, the more liquid color paste will be coated, and the more the surface color of the aluminum foil will be, the deeper the surface color of the aluminum foil will be. Ultra-shallow cell sites, the less liquid color paste is filled, the coating amount becomes smaller, and the surface color becomes lighter.
The concentration and density of the matching liquid color paste affect the coating amount, and thus the surface color of the aluminum foil can be changed. In the process of producing colored aluminum foil, an anilox roller has already been made, the depth of the cell depth and the number of reticulate lines have been fixed, and the shape of the cell site can no longer be changed. When the color paste is formulated under this condition, the required color is related to the concentration and density of the liquid color paste prepared, that is, the higher the concentration, the color develops deeper, and vice versa.
Source: Guangzhou Printing Network