Because the product effect formed by three-dimensional bronzing is a relief-like three-dimensional pattern, it can no longer be printed on it, so the process design of printing first and then ironing must be adopted, and because of its high precision and high quality requirements, it is not suitable for cold stamping process. Three-dimensional bronzing equipment usually has two types: flat pressing and round pressing, and round pressing is not suitable for three-dimensional bronzing.
Rotary hot stamping is usually used for online processing of web. Because the circular pressing is in line contact, the bubble phenomenon that may exist in flat pressing can be completely avoided, with high speed and good quality. However, because the hot stamping plate and the bottom die relief plate are round, the processing is difficult and the cost is high, and the heat transfer effect of the round hot stamping plate is not very ideal, so it is not used much, and it is mostly used for some long editions with large output and high quality, such as cigarette packs, wine packs and health care products.
Due to the popular soft packaging form of high-grade cigarettes, the mature post-press processing technology used in white cardboard has also been transferred to soft paper. Embossing and positioning ironing of soft paper is a process of combining stamping and embossing. The product has the characteristics of full bronzing, fine graphics and text, beautiful appearance and no embossing skew. However, this process is technically difficult, and the precision requirements for hot stamping plates, holographic films and bronzing machines are particularly high, and all operating indicators are very strict. Because of this, it is difficult to be imitated and has a high degree of anti-counterfeiting. Holographic bronzing: The laser hologram is made by the method of spatial frequency coding according to the principle of laser interference. Laser hologram is widely used in the field of anti-counterfeiting because of its good color, obvious layering, realistic image, good optical conversion effect and high information technology content.
The latest optical variable pattern technology is obviously different from the widely used holograms (three-dimensional holograms), and some holograms have the function of machine recognition. The mechanism of holographic hot stamping is that the hot melt adhesive layer and separation layer on the holographic hot stamping material are heated and melted by the hot stamping die heated on the hot stamping equipment, and the holographic grating stripes of the information layer of the hot stamping material are separated from the PET substrate under a certain pressure, so that the aluminum foil information layer and the hot stamping surface are bonded into a whole to achieve perfect combination.
Holographic hot stamping mainly includes ordinary hot stamping and positioning hot stamping. Among them, special edition holographic positioning hot stamping has frequently appeared on high-grade cigarette cases in recent two years. It means that the hologram of a specific part of the holographic anti-counterfeiting hot stamping anodized is accurately hot stamped on the specific position of the cigarette pack by photoelectric identification on the hot stamping equipment. Holographic positioning ironing technology is very difficult, which requires not only the printing factory to be equipped with high-performance and high-precision special positioning ironing equipment, but also high-quality special positioning bronzing anodized aluminum, and the production process must be strictly controlled to produce qualified cigarette packs. Cold stamping technology: Cold stamping technology is a new technical achievement first applied in the printing industry in Europe and America in recent years. It completes the transfer of electrochemical aluminum foil under cold pressure. Special anodized aluminum is used for cold stamping, and the back is not coated with glue. When printing, the glue is directly coated on the position that needs decoration. During transfer printing, anodic aluminum oxide is attached to the surface of printed matter under the action of adhesive.
The cold stamping process prints UV ink first. After drying, the special UV curing adhesive is printed on the part of the ink surface that needs bronzing; Then the moisture in the adhesive is evaporated by UV drying device to form a thin pressure-sensitive adhesive layer with high viscosity. Then, under the action of a pair of metal rollers, the aluminum foil contacts the adhesive and is pressed into a whole. Because of the strong adhesion between the adhesive and the aluminum foil, when the waste is discharged, the part of the aluminum foil that contacts the adhesive remains on the surface of the printed matter and blends with the printed matter, while the other parts of the aluminum foil are discharged like traditional bronzing, thus completing the first part of the bronzing process. Because the aluminum foil pattern transferred to the printed matter floats on the surface of the printed matter and has poor firmness, it is necessary to polish or cover the surface of the printed matter to protect the aluminum foil pattern.
Compared with the traditional bronzing process, the cold bronzing process is fast and energy-saving: the material has a wide range of applications and can be used for cold bronzing on thermal paper and some film materials. Replacing the expensive metal plate roller with ordinary flexographic plate greatly reduces the production cost and cycle of bronzing plate, and also reduces the pollution in the process of metal plate corrosion.
The cold stamping process is limited by adhesive, metal foil and other conditions, but there are also some shortcomings, such as: after cold stamping, the printed matter must be glazed or covered with film to protect the stamping pattern, which increases the cost and complexity of the process. Cold stamping process is not suitable for PVC, PE and other film materials with shrinkage characteristics. Due to the poor leveling of UV glue and the poor surface finish after drying, the brightness of the metal foil transferred on it is poor, and the diffuse reflection phenomenon appears, and the effect is not as good as that of the traditional hot stamping process. The key technologies of cold stamping process are UV glue and special anodized metal foil, which have broad development prospects.
Hot stamping first and then printing: In recent years, some printing houses have introduced a new process of hot stamping anodized first and then printing patterns on anodized, which can make the theme of cigarette packets more lively.
Printing after ironing is a new idea for cigarette label design and printing industry. The application of this process requires high anodized aluminum, and the key of the process is that anodized aluminum must be hot stamped firmly, and anodized aluminum must never be pulled down by ink during printing. Reverse drawing not only affects the quality of cigarette packets, but also causes anodic aluminum oxide to quickly accumulate on the blanket, resulting in the loss of image dots and the inability to print local images. With the operation of the machine, anodic alumina powder will be transferred to the ink roller system, which will accelerate the wear of the ink roller. Therefore, according to the characteristics of printing paper, this process should choose appropriate anodized to ensure that anodized can firmly adhere to the paper surface.
In production, in addition to the requirements of accurate stamping position, smooth and bright surface, uniform pressure, no foaming, no paste and so on. In addition, it is especially required that there should be no obvious indentation on the edge of stamping pattern, and the adhesion of anodized aluminum on the stamping surface should be good, and there should be no obvious scratches and scratches. As we all know, the bronzing process is actually a process in which paper is heated and pressed. For white cards and glass cards, special attention should be paid to the protection of semi-finished products, and various unfavorable factors of paper deformation should be reduced as much as possible in the production process, which is of great help to the smooth progress of stamping process and the improvement of product qualification rate. Micro-engraving technology: This technology uses micro-engraving board to press all kinds of fine lines on the graphic part of aluminum foil paper, and the products obtained have the effects of bronzing and embossing, and the metal texture is very strong.
Hot stamping quality control
At present, although a variety of new hot stamping processes emerge one after another, the traditional anodized hot stamping technology, as an important process in post-press processing, has not been neglected because of its unique decorative effect and mature process operation, but has received more attention and favor.
The traditional hot-pressed anodic oxidation foil mainly uses heat and pressure to transfer patterns or characters to the surface of hot stamping materials. To complete this process, you need a bronzing machine, a template engraved with special words or patterns, the temperature required for heating, the pressure required for transfer printing and the corresponding time. It should be noted that when hot stamping different materials, it is necessary to choose the appropriate model of anodized and the appropriate temperature, pressure and hot stamping time to achieve the ideal hot stamping effect.
Hot stamping plate: high-quality hot stamping plate is the primary factor to ensure the quality of hot stamping. At present, the production of bronzing plate mainly adopts photographic etching process and electronic engraving technology, and the material is mostly copper plate or zinc plate. Copper plate is fine in material, and its surface smoothness and heat transfer effect are better than zinc plate. The use of high-quality copper plate can improve the gloss and outline clarity of bronzing graphics and texts.
The traditional photo etching technology is simple in process, low in cost and short in service life, and is mainly used for bronzing characters, thick lines and general images. For bronzing plates with fine and uneven graphic thickness, secondary etching or electronic engraving technology is needed. The bronzing plate made by electric carving can show rich and delicate level changes, which greatly expands the performance ability of packaging. This process is beneficial to environmental protection, but the investment of electric engraving equipment is large, and the current engraving depth is not ideal, which is easy to cause bronzing "paste version", but its printing resistance is high, which is suitable for long-version live parts of cigarette packs. Holographic anti-counterfeiting bronzing plate has high technical requirements and long plate-making cycle, and is only used for packaging fixed and mass products.