In recent years, with the continuous development of the technical level of the printing and packaging industry, the product quality has been continuously improved. Especially in the fiercely competitive tobacco industry, in order to enhance the artistic visual effects of cigarette packs, various processes are constantly being updated, and its design level, printing quality, and post-press processing have also been continuously improved. Among the various post-printing processes of cigarette pack products, the bronzing process is popular with people because of its unique surface finishing effect and is widely used.

Principle and characteristics of bronzing

Hot stamping uses the principle of hot press transfer to transfer the aluminum layer in anodized aluminum to the surface of the substrate to form a special metal effect. Because the main material used for bronzing is anodized aluminum foil, so bronzing is also called anodized aluminum hot stamping. Anodized aluminum foil is usually composed of multiple layers of materials, the substrate is often PE, followed by separation coating, color coating, metal coating (aluminum plating) and glue coating.

The basic process of bronzing is under pressure, that is, in the state where the anodized aluminum is pressed by the hot plate and the substrate, the anodized aluminum is heated to melt the hot-melt silicone resin layer and the glue on it. The viscosity of the silicone resin becomes smaller, and the viscosity of the special heat-sensitive adhesive increases when it is heated and melted, so that the aluminum layer and the anodized aluminum base film are peeled and transferred to the substrate at the same time. As the pressure is removed, the adhesive quickly cools and solidifies, and the aluminum layer is firmly attached to the substrate to complete a hot stamping process.

Bronzing has two main functions: one is surface decoration, which can increase the added value of the product. The combination of bronzing and other processing methods such as embossing and embossing technology can show the strong decorative effect of the product: the second is to give the product a higher anti-counterfeiting performance, such as the use of holographic positioning hot stamping trademark logos.

After bronzing, the pattern is clear, beautiful, colorful and eye-catching, wear-resistant and weather-resistant. At present, the bronzing process on printed tobacco labels accounts for more than 85%. In graphic design, bronzing can play a finishing touch and highlight the design theme. It is especially suitable for the decoration of trademarks and registered names.

The development of bronzing technology

In recent years, with the improvement of the processing level of bronzing materials and bronzing plates and the use of new machinery and equipment, the domestic bronzing process has also received some new developments. High-speed bronzing, three-dimensional bronzing, holographic positioning bronzing and printing after bronzing are widely used in cigarette pack production.

Three-dimensional bronzing: three-dimensional bronzing technology is a combined technology of bronzing technology and concave-convex embossing technology. It uses corrosion or engraving technology to make the bronzing and embossing graphics into a negative and positive concave and convex mold. Achieve the process of hot stamping and bump embossing technology at one time. This process simultaneously completes bronzing and embossing, which reduces the waste products caused by the inaccurate processing procedures and overprinting, and improves production efficiency and product quality.

Because the product effect formed by three-dimensional bronzing is a relief-shaped three-dimensional pattern, it can no longer be printed on, so it must be designed after printing first and then hot. At the same time, due to its high precision and high quality requirements, it is not suitable for cold stamping. Technical production. The three-dimensional bronzing equipment usually has two types: flat flattening and round flattening. The round flattening method is not suitable for three-dimensional bronzing.

The flat pressing flat three-dimensional hot stamping equipment is represented by BOBST equipment, which is developing in the direction of high speed, high precision, and convenient use. It is the main model of three-dimensional hot stamping. Bost hot stamping machine has reached a hot stamping speed of 7,500 sheets / hour, and the accuracy can be kept within 0.1 ~ 4mm, which is one of the most advanced hot stamping machines.

The method of round pressing and round bronzing is usually used for web-line processing. Because the round pressing is a line contact, the bubble phenomenon that may exist in the flat pressing and bronzing can be completely avoided, and the speed is fast and the quality is good. However, because the bronzing version and the bottom die relief are round, the processing is difficult and the cost is high. The heat transfer effect of the circular bronzing version is not very ideal, so it is not widely used. It is often used in some large output and high quality long Edition work, such as cigarette packs, wine bags, health products, etc.

Due to the popular flexible packaging of high-end cigarettes, the original post-press processing technology used on white cardboard has also been transferred to soft paper. The process of soft paper embossing and positioning hot stamping completes hot stamping and embossing in one process. The product has the characteristics of full hot stamping, fine graphics, beautiful appearance, and no embossing and skew. However, this process is difficult, and the precision requirements for hot stamping plates, holographic films, and hot stamping machines are extremely high, and the various operating indicators are very strict. Because of this, it is difficult to be imitated and the degree of anti-counterfeiting is high.

Hologram bronzing: Laser holograms are made according to the principle of laser interference and using spatial frequency coding. Laser holograms are widely used in the field of anti-counterfeiting due to their good color, obvious layers, vivid images, good optical transformation effects, and high information technology content.

The latest optical variable pattern technology has been clearly distinguished from the widely used HOLOGRAM hologram (three-dimensional hologram), and some holograms already have machine recognition functions. The mechanism of holographic hot stamping is that the hot melt adhesive layer and the separation layer on the holographic hot stamping material are heated and melted by the hot stamping die on the hot stamping equipment, and under a certain pressure, the information layer of the hot stamping material is holographic grating The stripe is separated from the PET base material, so that the aluminum foil information layer is bonded to the ironing surface and melted into one body to achieve a perfect combination.

Holographic hot stamping mainly includes ordinary hot stamping and positioning hot stamping. Among them, the special version of hologram positioning hot stamping has frequently appeared on high-end cigarette packs in the past two years. It refers to that the hologram of a specific part of the holographic anti-counterfeiting hot stamping anodized aluminum is accurately stamped on a specific position of the cigarette pack by photoelectric identification on the hot stamping equipment. The hologram positioning technology is very difficult, not only requires printing plants to be equipped with high-performance and high-precision special positioning equipment, but also requires high-quality special positioning hot stamping anodized aluminum, and the production process must be strictly controlled to produce qualified Cigarette products.

Cold bronzing process: Cold bronzing technology is the first new technology achievement in the European and American printing industry in recent years. It is to complete the transfer of anodized aluminum foil under cold pressing. Cold bronzing uses special anodized aluminum, the back of which is not coated with adhesive. The adhesive is directly applied to the location where decoration is needed during printing. During the transfer, under the action of the adhesive, the anodized aluminum adheres to the surface of the printed product.

The cold bronzing process first prints UV ink. After drying, the special UV curing adhesive is printed on the ink surface where gold foil is needed; then the moisture in the adhesive is evaporated through the UV drying device and a thin layer of high-viscosity adhesive is formed. Then, under the action of a pair of metal rollers, the aluminum foil is brought into contact with the adhesive and pressed together. Due to the large adhesive force between the adhesive and the aluminum foil, when discharging, the part where the aluminum foil contacts the adhesive remains on the surface of the printed product and is integrated with the printed product, while the other parts of the aluminum foil are discharged like traditional bronzing. Thus completing the first part of the bronzing technology. Since the aluminum foil pattern transferred on the printed matter floats on the surface of the printed matter, the firmness is poor, so the surface of the printed matter must be polished or coated to protect the aluminum foil pattern.

Compared with the traditional hot stamping process, the cold stamping process is fast and saves energy: the material has a wide range of applications, and cold stamping can be performed on thermal paper and some film materials. The general flexographic printing plate is used to replace the expensive metal plate cylinder, so the production cost and cycle of the bronzing plate are greatly reduced, and the pollution during the corrosion of the metal plate is also reduced.

The cold bronzing process is limited by the conditions of adhesives and metal foils, and also has some disadvantages. For example, the printed products must be glazed or coated after cold bronzing to protect the bronzing patterns, which increases the cost and complexity of the process. The cold foiling process is not suitable for application on shrinkable PVC, PE and other film materials. Due to the poor leveling of the UV adhesive, the surface smoothness after drying is poor, which leads to the poor brightness of the metal foil surface transferred thereon, and the phenomenon of diffuse reflection, which is not as good as the traditional hot stamping process. The key technology of the cold bronzing process is UV adhesives and special anodized aluminum metal foil, which has broad development prospects.

First hot printing process: In order to highlight the specific patterns and logos on cigarette packs, in recent years, some printing houses have introduced a new process of hot stamping anodized aluminum and then printing patterns on the anodized aluminum, which can make the theme of the cigarette pack more Vivid and lively.

Printing first and then printing is a new idea in the industry of cigarette label design and printing. The application of this process has high requirements for anodized aluminum. The key of the process is that the hot stamping of anodized aluminum must be firm. During the printing, the anodized aluminum must not be pulled back by the printing ink. Anti-pulling not only affects the quality of the cigarette pack, but also the anodized aluminum that is pulled back will quickly accumulate on the blanket, ranging from the loss of the image dots to the partial printing of the image. As the machine runs, the anodized aluminum powder also It will be transferred to the ink roller system to accelerate the wear of the ink roller. Therefore, this process should select the appropriate anodized aluminum according to the characteristics of the printing paper to ensure that the anodized aluminum can be firmly attached to the surface of the paper.

In addition to the requirements of accurate bronzing position, smooth and bright surface, balanced and uniform pressure, no blistering, no paste version in production, it also requires that there should be no obvious indentation on the edge of the bronzing pattern. Good adhesion and no obvious scratches and scratches. Everyone knows that the bronzing process is actually a process in which the paper is heated and compressed. For white cards and glass cards, special attention should be paid to the protection of semi-finished products, and various adverse factors of paper deformation should be minimized during the production process, which will greatly help the smooth progress of the post-gilding process and the improvement of product qualification rate.

Micro-embossing process: This process is to use micro-embossing on the aluminum foil paper graphics and text to apply various fine lines. The obtained product has the effect of hot stamping and embossing, and the metal texture is very strong.

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