Hot stamping process principle and practical operation guide

The bronzing process is a special printing process that does not use ink. The so-called hot stamping refers to the process of hot stamping electroformed aluminum foil to the surface of the substrate under a certain temperature and pressure...

In recent years, China's light industry, packaging and printing industry has developed rapidly. The packaging and decoration of goods has become an important means to promote the circulation of goods. From cigarettes, alcohol, medicines, foods, clothing, cosmetics and other daily life fields, the rapid development of packaging, decoration and printing has been reflected, which has led to increasingly fierce competition in the printing market.

In order to increase the added value and technological content of printed materials, post-press finishing has received more and more attention. Nowadays, despite the development of science and technology, the post-press finishing process continues to innovate, and new cold stamping and holographic positioning hot stamping processes have emerged. However, traditional hot stamping (also known as hot stamping) is an important process in postpress finishing. It has played a unique decorative role in prints and has not been neglected. On the contrary, it still attracts people's attention and preferences. Therefore, it is necessary to continue to discuss the bronzing process.

1 hot stamping

Bronzing is a special printing process that does not use ink. The so-called bronzing is the process of stamping an galvanized aluminum foil onto the surface of a substrate under a certain temperature and pressure.

The graphic display of the electro-aluminum stamping shows a strong metallic luster, which is colorful and dazzling and never fades. In particular, gold and silver anodized aluminum, with its splendid, sophisticated decoration embellished the surface of prints, enhanced the artistic quality of printed products, played a prominent theme of the propaganda effect; its brightness greatly exceeded the printing of gold and silver, so that the product With high-end feel and give people a beautiful enjoyment. At the same time, because of its excellent physical and chemical properties, it has played a role in protecting the printed products. Therefore, the bronzing process is widely used in high-end, exquisite packaging and decoration trademarks, calendars, and covers of books and magazines, etc.; secondly, hot stamping of aluminum foil. The scope is very wide, from general book covers, logo designs, promotional advertisements, plastic products to general merchandise, from paper to leather, cotton cloth, etc.; again, bronzing is a dry processing method that can be packaged and transported immediately after bronzing. . Therefore, bronzing technology is widely used at present, and the scope of application of hot stamping is still expanding.

2 hot stamping process

As the quality of electro-aluminum foil, specifications, model, etc. will affect the quality of hot stamping, therefore, the scientific and rational use of electro-aluminum foil is a prerequisite for improving the quality of bronzing process. In order to use electro-aluminum foil correctly, one must first understand its composition and hot stamping mechanism.

1) Electrochemical aluminum foil composition

The main material for bronzing is galvanized aluminum (also known as gold foil). It is made of a polyester film as a base, coated with an alcohol-soluble dyeing resin layer, vacuum metallized aluminum, and then coated with an adhesive layer. That is, it is composed of a base film layer, an alcohol-soluble dyed resin layer (which can be further divided into a barrier layer and a dyed layer), an aluminum layer, and an adhesive layer.

The base film layer is the carrier film of the other layers of the electro-aluminum foil, and plays a supporting role. The material used for the base film layer is a 12 to 16 μm thick polyester film.

The separation layer can easily separate the tinted layer of the galvanized aluminum foil from the base film layer; the tinted layer is used to show the color of the galvanized aluminum foil, which is composed of a melamine-based resin, a silicone resin, and a dye.

The aluminized layer allows the electro-aluminum foil to exhibit a metallic luster. Aluminum is a good light reflective material. The gaseous aluminum can be uniformly attached to the surface of the dyed layer under vacuum.

The adhesive layer is mainly composed of methacrylate or shellac, which is used to bond the electro-aluminum foil coating to the substrate during hot stamping and to protect the aluminum layer. 2) Hot stamping mechanism

The bronzing process includes:

Hot Stamping Preparation → Plate → Pad → Hot Stamping Process Parameters Determination → Hot Stamping → Signature → Official Stamping.

The process is mainly the use of the principle of heat transfer. Electro-aluminum is contacted with the hot stamping plate and the substrate under the combined pressure, and the hot plate has a certain amount of heat due to the heating of the hot plate. The heated aluminum heats the hot-melt dyed resin layer and the adhesive, and the dyed resin layer is adhered. Reduce, and the special heat-sensitive adhesive has increased viscosity after melting, and the aluminum layer and the aluminum base film are peeled off and transferred to the substrate at the same time. As the pressure is removed, the adhesive rapidly cools and solidifies, and the aluminum layer firmly adheres to the substrate. Finished a hot stamping process.

From the composition of the anodized aluminum and hot stamping mechanism, in order to obtain the ideal hot stamping effect, the galvanized aluminum foil used for hot stamping must meet the following requirements: uniform coloring of the bottom layer, no obvious color difference, color strips and stains; primer coating Uniform, smooth, white, no impurities, no obvious streaks, spots, and oxidation; good gloss; strong firmness; high definition;

3 The main factors affecting the quality of bronzing

The perfect bronzing effect depends on the level of temperature, pressure, and bronzing speed. Therefore, to control the quality of bronzing, proper bronzing temperature, bronzing pressure and bronzing speed should be mastered. This creates good conditions for bronzing so that the quality of bronzing can be guaranteed. 1) Effect of temperature on gilding quality

The temperature has a very important influence on the hot stamping. The temperature must be controlled within the corresponding range, so that the dyed resin layer and the adhesive are moderately melted to ensure the good transfer of the aluminum layer.

If the temperature is too high and the melting is excessive, the electro-aluminum around the stamping graphic will melt and fall off, resulting in stencil printing. At the same time, the high temperature will cause chemical changes in the aluminum-stained resin and the aluminum layer, and the brightness of the stamping product will be reduced and the metallic luster will be lost. Even blots appear as fog or blisters; but if the temperature is too low, melting is not sufficient, it can also cause hot stamping or stamping is not strong, the imprint is not strong, easy to fall off, or lack of pen strokes, imprinted flowers.

In general, the electrothermal temperature should be controlled between 70 ~ 180 °C, hot stamping area is larger, the electrothermal temperature is relatively higher; for small text, lines, hot stamping area is smaller, hot stamping temperature should be lower. At the same time, the suitable stamping temperature is also different for various types of aluminum. 1# is 80-95°C; 8# is 75-95°C; 12# is 75-90°C; 15# is 60-70°C; while pure gold foil is 80-130°C; gold foil, silver foil is 70-120 °C.

Of course, the ideal stamping temperature should be at the lowest and can be printed with clear graphic lines as a criterion, which can only be determined by pressing hot. 2) The effect of pressure on the quality of bronzing

The transfer of the hot stamping of the aluminum layer must be done through pressure. The size of the stamping pressure affects the adhesion of the anodized aluminum. Even if the temperature is right, if the pressure is not enough, it will not be able to transfer the aluminum foil to the substrate well. It will cause problems such as missing prints and stencils. Conversely, if the pressure is too high, the compression deformation of the liner and the substrate will be too large. Imprinting will be thick, even adhesion, paste version. Usually the hot stamping pressure should be adjusted properly to achieve no color change, good adhesion fastness as a guideline.

To adjust the stamping pressure, we must integrate various factors such as printing materials, stamping temperature, speed, and electrochemical aluminum itself. In general, the paper is strong and smooth, the printed ink layer is thick, and the hot stamping temperature is high, the speed is slow, the hot stamping pressure should be smaller, on the contrary, it should be larger. Hot stamping pressure must be uniform, if you find that the local hot stamping is not and spend linen, it is likely that the pressure here is too small, should be placed on a thin layer of paper on the plate, so that the pressure tends to balance.

Hot stamping pads also have a greater effect on pressure. Hard liner can make the prints delicate, suitable for strong, smooth paper, such as coated paper, glass cardboard; and soft liner is the opposite, the print is thick, suitable for large area of ​​the hot stamping, especially the uneven surface , Paper flatness, poor smoothness, rough paper.

At the same time, the installation of hot stamping foil should not be too tight or too loose. When it is too tight, the writing will be cut off; if it is too loose, the writing will be unclear and the stencil will be dirty. 3) Effect of Speed ​​on Bronzing Quality

The hot stamping speed actually reflects the contact time between the substrate and the hot stamping foil during hot stamping and directly affects the fastness of the hot stamping. If the hot stamping speed is too fast, the hot stamping may not be caused or the printing may be printed. If the hot stamping speed is too slow, it will affect the stamping quality and affect the production efficiency.

In addition, the limiting factor of the hot stamping speed is the type and performance of the electro-aluminum itself. Different types and performances have a greater impact on the hot stamping speed. For example, the appropriate hot stamping speeds for various types of galvanized aluminum are different. For example, the suitable hot stamping speed for 8# and 12# galvanized aluminum is 18-30 sheets/minute, and the 15# anodized aluminum is 18-22 sheets/minute. 1# aluminum foil is 40 sheets/minute, suitable for fast hot stamping.