Anodized aluminum hot stamping has unparalleled advantages in improving packaging grade, brand recognition and product anti-counterfeiting. Therefore, it is more and more widely used in the surface decoration of folding cartons. In the past two years, there have been major changes in the materials and printing techniques used for folding cartons. For example, packaging materials such as aluminum foil paper, laser cardboard, and vacuum aluminum-plated transfer paper have been gradually applied. Printing and surface finishing processes such as screen frosting (ice flower, refraction) have also been born. And these have put forward higher requirements for anodized aluminum stamping. This article analyzes the process problems related to anodized aluminum hot stamping encountered by the printing plant in the actual production process, and hopes to provide some reference for the printing plant. 1. Factors affecting the bronzing process 1. Hot stamping temperature All anodized aluminum has its recommended hot stamping temperature, the temperature range is usually around ± 10 ℃. In the production process, increasing the temperature is often the first solution that operators think of when they encounter problems such as hot or poor adhesion. However, excessively increasing the hot stamping temperature is not only not conducive to the solution of the problem, but it may cause the adhesive molecules of the adhesive layer to stick together, causing paste plates, and at the same time causing the overheating of the dyeing layer to cause rainbow patterns and spots to appear. The aluminum will also oxidize at high temperatures and darken the color. 2. Hot stamping pressure The effect of pressure adjustment on the hot stamping of anodized aluminum can not be ignored. The pressure is low, and the hot stamping or the hot stamping pattern are not firmly attached; the high pressure will cause problems such as pasting and thickening of the hot stamping line. 2. New situations and solutions in hot stamping process 1. Hot stamping on laser jammed paper When hot stamping on laser jammed paper, anodized aluminum with high adhesion should be selected. At the same time, when performing large-area hot stamping, attention should be paid to whether bubbles are generated. Unlike ordinary paper, there is no adsorption of gas by the fiber capillary holes during hot stamping, so if the air between the laser cardboard and the anodized aluminum is too late to form bubbles, it can pass through the anodized aluminum. " "Pinhole", in this case, the middle part of the plate should be slightly higher than the surrounding area, so that the air can easily escape; or when ordering the electric engraving version, the center of the hot stamping plate made by the supplier is required to be slightly higher than the surrounding area. 2. Reprint on hot stamping foil In order to better reflect the design effect, some carton adopts hot stamping (usually laser anodized aluminum hot stamping) and then UV printing process. Pay attention to the following issues during the production process. (1) Because the hot stamping plate easily expands when heated, if the accuracy of the overprint of the printed pattern and the hot stamping pattern is high, the surrounding area should be reduced by 0.02 mm when making the hot stamping film before printing. (2) Choose anodized aluminum with a surface tension of (4.0 to 4.6) × 10-4N to ensure good adhesion of the printing ink. (3) Pay attention to the quality of hot stamping during the hot stamping process. If the adhesion of the anodized aluminum is not strong, there will be "flying gold", paste and other phenomena. During the offset printing process, metal powder is easy to accumulate on the blanket, resulting in frequent shutdown and wiping, which affects production efficiency. (4) After printing, the UV ink is printed, but the adhesion is not firm, and it can come off by wiping it by hand. There are two reasons for this phenomenon: ①During the hot stamping process, the wax in the peeling layer of the anodized aluminum is not completely melted and remains on the surface of the anodized aluminum. In this case, the temperature can be increased by 8-10 ° C during hot stamping to completely melt the wax. ② The adhesion of the ink itself is not strong, you can try other types of UV ink. 3. Anodized aluminum stamping on UV varnish Not all UV varnishes can be stamped with anodized aluminum. UV varnish contains acrylic monomers, silicone resin and other components. Among them, the amount of silicone resin determines the gloss, smoothness and abrasion resistance of varnish, and it is also the most important factor affecting the suitability of UV varnish hot stamping. During the UV varnish curing process, the silicone resin migrates to the surface of the varnish film layer, thereby affecting the hot stamping of the anodized aluminum. In order to improve the hot stamping performance of UV varnish, varnish suppliers can partially replace silicone resin with melamine resin, but this also reduces the gloss of UV varnish. When large-area hot stamping is performed on the surface of the UV varnish or water-based varnish film layer, a "steam bubble" phenomenon may occur, that is, anodized aluminum hot stamping is performed when the varnish or ink is not completely dry. Caused by the inability to escape from the stamping pattern. The solution to this problem is to re-dry the printed or glazed print. Of course, the best way is to hot stamp first, and then apply UV varnish. At this time, it is necessary to confirm that the anodized aluminum can be stamped on the varnish. In addition, for some printed products that obtain special texture effects such as UV frosting, refracting light, and ice flowers on the cardboard paper by laser printing, the parts that need to be stamped with anodized aluminum should be hollowed out on the silk screen to avoid electrification Aluminum hot stamping is not possible. The emergence of new materials and new processes has put forward higher requirements for the traditional hot stamping process. The adjustment in anodized aluminum hot stamping is no longer a simple adjustment of the balance point of temperature, pressure and speed (hot stamping time). The problems that may arise in some cases may be the result of the interaction of multiple factors, which requires the operator to learn more about materials and processes while mastering hot stamping skills.
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(5) If the phenomenon that the anodized aluminum powder does not accumulate on the blanket, the ink can be added to reduce the viscosity of the ink, or by changing the printing color sequence to solve.
Influencing factors and problem analysis of bronzing process