In recent years, as people have improved the appearance and quality requirements of product packaging, printing technology and packaging technology have made great progress, and post-press processing technology has achieved vigorous development, while hot stamping of aluminum foil is used as post-press. Part of the processing, the changes in the past few years are even greater. The continuous emergence of new technologies, new processes and the combination of multiple technologies has enabled the printed products to achieve good results in terms of glossiness, three-dimensionality, metallic sensation, and anti-counterfeiting performance after hot stamping, especially for the current applications. A wide range of three-dimensional hot stamping technology makes the packaging of goods appear high-end fine, magnificent and full of personality. At present, the technology is mainly used for greeting cards, bookmarks, trademarks, tobacco and wine packaging and various high-grade packaging boxes.
Hot stamping and three-dimensional hot stamping
1. Hot stamping
The bronzing is the use of a certain pressure and temperature, using the stencil installed on the stamping machine, so that the printed matter and the hot stamping press can be pressed together in a short time, and the metal foil or the color pigment foil can be transferred to the quilt according to the graphic requirements of the hot stamping stencil. Hot material surface processing technology. Since hot stamping is based on gold and silver, it is often called bronzing. This technology is an important process for increasing the visual effects and grades of labels, trademarks, cigarette packets, wine bags and various high-end packaging boxes. From the process can be divided into the first hot after printing and printing after the first hot. The first hot stamping is to print the foil on the blank substrate first, and then print the graphic on the surface of the aluminum foil layer, which is mostly used for packaging printing that requires large area hot stamping. The first printing and then the hot is printed on the printed matter, in the hot stamping part of the hot stamp on the desired pattern, this is a widely used technology. From the hot stamping method, it can be divided into hot stamping technology and cold stamping technology. Hot stamping technology is the hot stamping process mentioned above that requires a certain temperature and pressure to complete the transfer of galvanized aluminum foil. The cold stamping technology is a process of transferring an electro-aluminum foil to a surface of a packaged printed matter by applying a UV adhesive on a part where the printed matter needs to be stamped. These two methods have their own characteristics to meet the requirements of different products.
2. Three-dimensional hot stamping
The three-dimensional bronzing technology is a composite technology combining bronzing technology and embossing and embossing technology. It is the use of corrosion or engraving technology to make the bronzing and embossing graphics into a concave and a convex mold with a positive and a negative mold. Embossing technology once completed the process. This process also completes bronzing and embossing at the same time, which reduces the number of waste products that are not allowed to be processed and overprinted, and increases productivity and product quality.
Since the three-dimensional hot stamping is a combination of hot stamping and embossing and embossing technology, the resulting product is a three-dimensional pattern in an embossed shape and cannot be printed on it. Therefore, it is necessary to adopt the process of printing first and then hot, and at the same time, due to its high precision. And high quality requirements, not suitable for cold stamping technology, but more suitable for hot stamping technology.
Three-dimensional hot stamping technology and features
The three-dimensional bronzing technology is quite different from ordinary bronzing. In addition to the three-dimensional pattern that can form an embossed pattern, there are differences in plate making, temperature control, and pressure control.
1. Plate making
(1) Ordinary hot stamping version
The high-quality hot stamping version guarantees the quality of the hot stamping. The ordinary hot stamping version is relatively simple to produce, mainly adopting a photo etching process and an electronic engraving plate making process. Commonly used plates are copper plates or zinc plates. Due to its fine texture, smooth surface, good heat transfer performance, wear resistance, and pressure resistance, the copper plate is currently the mainstream hot stamping plate. The use of high-quality copper plates enhances the gloss and clarity of hot stamping graphics. For some hot stamping products with less hot stamping quantity and low quality requirements, zinc plate can also be used.
Photo etching plate making is a traditional manufacturing method with simple process, low cost, and low precision, and is mainly applicable to images whose characters, bold lines, and quality are not high. The hot stamping plate made by electronic engraving can enrich the delicate image representation level, and can reproduce the fine lines and graphics with uneven thickness, but the relative cost is high.
(2) three-dimensional hot stamping version
The production principle of the three-dimensional hot stamping printing plate is the same as that of the ordinary hot stamping plate, but it is more complicated than the normal printing plate because it needs to form a three-dimensional relief pattern. The hot stamping plate is generally concave, and has a depth and depth change, and the depth is also higher than the ordinary hot stamping. Plates are deeper and more accurate. At present, the copper plate photographic etching method is mainly used in China. This method has the advantages of low cost and simple process, but it is only suitable for flat hot stamping. Due to poor three-dimensional sense, short service life, and resistance to printing force, it is only about 100,000 impressions, so it is commonly used in some packages that do not require high relief effect. On the product.
At present, the brass plate has been widely used in foreign countries. Scanners are used to first scan the pattern to be stamped, store the data in a computer, and then carry out three-dimensional engraving through computer and software control to form a gravure intaglio with a rich three-dimensional pattern. Because it is controlled by a computer, it can form a very fine pattern, and it is more ideal for subtle parts. It can withstand up to 1 million impressions or more, so it is very suitable for making three-dimensional hot stamping with high quality and large quantity. Die intaglio. Of course, due to the need to provide high-end electronic engraving machines, scanners, computers and software, engineering and technical personnel, etc., the production cost is higher than the photographic corrosion method. Because of its complicated production and technical difficulty, it can prevent some counterfeit companies from counterfeiting and have certain anti-counterfeiting functions. Therefore, for some long-lived products with high quality and requiring anti-counterfeiting features, such as cigarette packs, wine bags, health products packaging and greeting cards, etc., it is appropriate to use three-dimensional hot stamping. In the past, such hot stamping plates had to be processed abroad. The cost was high and the delivery was not timely. The design effect was also unsatisfactory. At present, a small number of manufacturers in China have been able to process this hot stamping version, which has effectively reduced the cost. In particular, direct communication between the processing manufacturer and the design personnel can correctly understand the design intent and achieve satisfactory results.
(3) Counters Letterpress
Stereoscopic bronzing is different from ordinary gilding. The ordinary gilding plate is flat and does not require special production. The bottom plate of the three-dimensional bronzing must be a positive mold platelet corresponding to the hot plate, that is, the concave area of â€‹â€‹the hot plate should be on the bottom plate. It is convex, and the height of the bulge corresponds to the depth of the hot plate depression. The method for making the bottom mold relief is the same as the method for making the male mold relief of the embossed stamp. The commonly used materials include plaster and glass fiber. If gypsum is used, it must be completed on the machine. Therefore, the process is more complicated and the replacement of the bottom plate is troublesome, but the cost is low, and it is now commonly used in China. If glass fiber is used, it can be prefabricated according to the model of the hot stamping plate, and the positioning holes can be made with the processed copper plate to facilitate the replacement of the positioning.
The bottom mold relief is to form a three-dimensional relief pattern in order to cooperate with the stamping gravure, which must exactly correspond to the hot stamping version. However, the three-dimensional hot stamping is different from the embossing and embossing. Most of the embossing and embossing do not require heating, and the three-dimensional hot stamping must be heated at high temperature During hot stamping, as the temperature rises, the hot stamping plate expands, but the temperature of the bottom mold stamping remains basically unchanged. This results in a mismatch between the hot stamping plate and the bottom mold relief plate, resulting in a crushing bottom mold. Or can not hot stamping phenomenon. Therefore, when making the bottom mold relief, the expansion rate of the hot stamping plate should be fully taken into account to make an accurate bottom mold relief plate.
2. Three-dimensional hot stamping process requirements
(1) Electrochemical aluminum foil
Electrochemical aluminum foil generally consists of 4 to 5 layers of different materials, such as: base film layer (polyester film), peeling layer, colored layer (silvered aluminum without color layer), aluminized layer, adhesive layer.
The main role of each layer is:
1 The base film layer mainly serves to support other layers.
2 The role of the peeling layer is to separate the electro-aluminum foil layer from the base layer, which determines the transferability of the electro-aluminum layer.
3 The main role of the color layer is to display the color of the aluminum and protect the underlying layer. The common colors are gold, silver, brownish red, light blue, black, red, green, among which gold and silver are the two most commonly used.
4 The role of the aluminized layer is to show metallic luster.
5 The function of the adhesive layer is to act as a bonding hot stamping material.
The adhesive materials that make up the adhesive layer differ in their adhesive properties. In order to adapt to the different surface properties of different stamping materials, different bonding layers are used for the electroformed aluminum, thus constituting different types of electro-aluminum.
Hot stamping speed and quality are mainly affected by the peeling layer and the adhesive layer. If these coatings are not sensitive to heat, the hot stamping speed will be reduced accordingly. In the past, due to the limitation of heat transfer speed, the flat stamping and hot stamping speeds were low, reaching less than 5,000 sheets per hour. However, some of the worldâ€™s leading suppliers of anodized aluminum have produced enough aluminum products to meet the industryâ€™s demand for hot stamping. Printing speed requirements, Swiss Bobst hot stamping machine has achieved a hot stamping speed of 7500 / hour. Because the embossed pattern is formed by three-dimensional hot stamping, the control of temperature, speed, and pressure is different from that of ordinary hot stamping. Therefore, the requirements for hot stamping foils are also different from ordinary stamping foils. When using hot stamping foils, three-dimensional hot stamping should be used. Hot stamping foil, but can not be used as a normal hot stamping foil stamping, otherwise it will produce hot stamping quality is not good or other unexpected phenomenon.
(2) Temperature, pressure, speed
Temperature, pressure and speed are the three major elements of hot stamping technology. Only by controlling the relationship between the three can control the quality of hot stamping. The same applies to three-dimensional stamping. Since the three-dimensional bronzing is a complete bronzing and embossing stamping, the temperature requirements are even higher. The normal bronzing temperature is only 70Â°C to 90Â°C, while the three-dimensional bronzing can be completed at about 150Â°C. If the temperature is too low, the adhesive layer and the peeling layer of the galvanized aluminum may not be fully melted, and the galvanized aluminum foil may not be completely transferred during hot stamping, resulting in that the hot stamp is not on the exposed or exposed bottom. If the temperature is too high, the paper will be deformed too much, the image will be confusing, the writing will be unclear, and even the phenomenon of anodized aluminum will change. At the same time, the hot stamping plate may swell too much due to the high temperature, and it may not be accurate. Mold fit, resulting in bad hot stamping. Therefore, the temperature control is the first of three major factors.
Hot stamping pressure refers to the pressure on the hot stamping layout. In the hot stamping process, the molten anodized aluminum adhesive layer is pressed by pressure to complete the anodized aluminum transfer, so the size and uniformity of the pressure directly affects the quality of the hot stamping. The three-dimensional hot stamping in addition to requiring the transfer of aluminum foil to the print surface, but also with a huge pressure in the hot stamping parts out of the three-dimensional relief pattern, so the pressure is greater than the ordinary hot stamping, which also requires the strength of hot stamping foil to be better, To withstand the pressure of a squeeze. Of course, this does not mean that the greater the pressure, the better. It must be appropriate. The pressure is too large or too small to get a beautiful pattern. Excessive pressure may cause squashing of hot stamping foils, or even crush the bottom molds and prints to be stamped. If the pressure is too low, incomplete transfer of stamping foils or hot stamping may not occur, so that the embossed three-dimensional relief cannot be achieved. Quality requirements. So pressure control is also critical.
The hot stamping speed is actually the contact time between the stamping material and the anodized aluminum, that is, the heating time of the anodized aluminum. Hot stamping speed, short heating time, fast hot stamping temperature drop, resulting in too low temperature, hot stamping fastness will be affected; hot stamping speed, long heating time, hot stamping temperature drop slow, hot stamping fastness, However, if the control is not good, the hot stamping temperature will be too high. Therefore, a suitable hot stamping speed is also a guarantee for obtaining a high-quality hot stamping effect.
3. Three-dimensional hot stamping equipment
Three-dimensional hot stamping equipment is usually flat and round pressure round two, round flat is not suitable for three-dimensional hot stamping.
The flat pressing flat three-dimensional hot stamping equipment is represented by Swiss Bobst equipment. It is developing in the direction of high speed, high precision and easy use. It is the main model of three-dimensional hot stamping. BOBST hot stamping machine has reached a gilding speed of 7,500 sheets/hour, and the accuracy can be maintained within Â±0.1mm. It is one of the most advanced hot stamping machines in the world.
Round calendering methods are commonly used for web in-line processing.
Because the circle rounding is line contact, bubble phenomena that may exist in flat bronzing can be completely avoided, and at the same time, the speed is fast and the quality is good. However, because its hot stamping and counter stamps are all round, the processing is difficult, the cost is high, and the heat transfer effect of the round stamping plate is not very satisfactory. Therefore, it is not widely used, and it is often used in large quantities and high in quality. Edition live, such as cigarette packs, wine bags, health products, etc.
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