[Post-press Technology] Operation Guide for Hot Stamping Process

1 The basic process of bronzing

The main material of bronzing is anodized aluminum, so bronzing is also called anodized aluminum stamping. Bronzing is to transfer the aluminum layer in anodized aluminum to the surface of the substrate by using the principle of hot-press transfer. The basic process is as follows: First, under the 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 adhesive on it. The viscosity of the silicone resin is reduced, and the viscosity of the special heat-sensitive adhesive is increased after being melted by heat, 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.

The process of hot stamping includes: hot stamping preparation, plate-setting, pad-setting, adjustment of hot stamping process parameters, trial ironing, signing, and formal hot stamping.

2 ways to improve the quality of bronzing

As can be seen from the basic process of bronzing, the three basic elements of bronzing are: temperature, pressure and hot stamping time. In order to obtain the ideal hot stamping effect, the process parameters such as hot stamping temperature, hot stamping pressure and hot stamping speed must be reasonably mastered; in addition, the quality of the raw materials related to hot stamping must also be guaranteed, such as: the suitability of the hot stamping of the substrate , The performance of anodized aluminum materials and the quality of hot stamping plates and so on. If something goes wrong in one link, it will affect the final hot stamping effect.

1) Choose the right substrate

There are many substrates that can be gilded, usually paper, such as: coated paper, whiteboard paper, white cardboard, cloth paper, offset paper, etc. But not all paper bronzing effects are ideal. If the surface is rough and the paper is loose, for example, for book paper, poor offset paper, etc., because the anodized aluminum layer cannot adhere well to its surface, the unique metal The gloss can not be reflected well, and even the hot stamping can not be achieved. Therefore, the hot stamping substrate should be selected from the paper with dense texture, high smoothness and high surface strength, so as to obtain good hot stamping effect, the unique anodized aluminum The gloss is fully reflected.

2) Select the appropriate anodized aluminum model according to the different substrates

The structure of anodized aluminum has 5 layers, namely: polyester film layer, shedding layer, color layer (protective layer), aluminum layer and adhesive layer. There are many types of anodized aluminum, the common ones are No. 1, No. 2, No. 8, No. 12, No. 15 and so on. In addition to gold, there are dozens of colors such as silver, blue, brown-red, green, and scarlet. Choosing anodized aluminum not only needs to choose the appropriate color, but also choose the corresponding model according to the different substrates. Different models have different performances and suitable material ranges. Normally, No. 8 is the most used for hot stamping of paper products, because No. 8 anodized aluminum has moderate adhesion and good gloss. It is more suitable for general printing paper or glazed paper and varnish hot stamping. If you stamp on hard plastic, you should choose other corresponding models, such as 15 # anodized aluminum.

The quality of anodized aluminum is mainly checked by visual inspection and feel, such as checking the color, brightness and trachoma of anodized aluminum. Good quality anodized aluminum requires uniform color, smooth after hot stamping, no trachoma. For the fastness and tightness of the anodized aluminum, you can generally check it by rubbing it by hand or using a transparent tape to test its surface. If the anodized aluminum is not easy to fall off, it means that the fastness and tightness are better. It is more suitable for hot stamping of small text patterns. It is not easy to paste the plate when hot stamping. It can be used for sparse hot stamping. In addition, pay attention to the broken ends of anodized aluminum. The fewer the broken ends, the better.

It is worth noting that the anodized aluminum must be properly stored. It should be stored in a ventilated and dry place. It cannot be mixed with acids, alkalis, alcohols, and other substances. It must be protected from moisture, high temperature, and sun. Otherwise, the anodized aluminum will be shortened. Period of use.

3) Make a hot stamping plate

Hot stamping plates generally include copper plate, zinc plate and resin plate. Relatively speaking, copper plate is the best, zinc plate is moderate, and resin plate is slightly worse. Therefore, for fine hot stamping, copperplate should be used as much as possible. For the hot stamping plate, it is required that the surface is smooth, the graphic lines are clear, the edges are smooth, and there are no pits and burrs. If the surface is slightly uneven or slightly scratched or fluffed, it can be gently wiped with fine charcoal to make it smooth and smooth. The depth of the hot stamping plate should be slightly deeper, at least 0.6mm or more, and the slope is about 70 °, to ensure that the hot stamping graphics are clear, reduce the occurrence of continuous pieces and paste plates, and improve the printing durability.

The design of hot stamped text, lines and patterns is very particular. The picture and text should be as thin and moderate as possible, and reasonable in density and density. If it is too small and too thin, it is easy to miss the pen stroke; if it is too thick and too dense, it is easy to paste.

4) Control the hot stamping temperature

The hot stamping temperature has a great influence on the melting degree of the hot melt silicone resin peeling layer and the adhesive. The hot stamping temperature must not be lower than the lower limit of the temperature resistance range of the anodized aluminum, which is the minimum temperature to ensure the melting of the anodized aluminum adhesive layer. If the temperature is too low and the melting is inadequate, it will cause the hot stamping to fail or the hot stamping will not be strong, making the blots not strong, incomplete, missing pens or strokes or flowers; while the temperature is too high, it will melt too much and cause the adhesion around the blot The anodized aluminum also melts off and produces paste plates. At the same time, the high temperature will also oxidize and polymerize the synthetic resin and dye in the color layer, the blistering or fogging of the blot, and cause the surface of the aluminum layer and the protective layer to oxidize, which reduces the hot stamping products. Brightness or loss of metallic luster

In general, the electric heating temperature should be adjusted between 80 ~ 180 ℃, the larger the hot stamping area, the electric heating temperature is relatively higher; otherwise, it is lower. The specific situation should be determined according to various factors such as the actual temperature of the printing plate, the type of anodized aluminum, and the status of graphics and text. Usually, the most suitable temperature should be found by trial ironing, and the clear graphics and lines should be printed at the lowest temperature As standard.

5) Must reasonably control the stamping pressure

The stamping pressure has a great relationship with the fastness of anodized aluminum. Even if the temperature is appropriate, if the pressure is insufficient, it will not make the anodized aluminum adhere to the substrate, or cause discoloration, blotting, etc .; on the contrary, if the pressure is too high, the compression deformation of the pad and the substrate will be too large, resulting in paste The version or print becomes thicker. Therefore, the stamping pressure should be adjusted carefully.

Main considerations should be taken into account when setting the stamping pressure: properties of anodized aluminum, stamping temperature, stamping speed, substrates, etc. Generally speaking, when the paper is strong and smooth, the printed ink layer is thick, and the hot stamping temperature is high and the vehicle speed is slow, the hot stamping pressure should be smaller; otherwise, it should be larger. In addition, similar to printing, hot stamping liner should also pay attention to, for smooth paper, such as: coated paper, glass cardboard, it is best to use rigid liner paper, so the imprint obtained is clear; on the contrary, for smoothness For poor and rough paper, the liner should be softer, especially if the hot stamping area is large. In addition, the hot stamping pressure must be even. If the local hot stamping is not found or there is numbness during the trial printing, it may be that the pressure here is uneven. You can place a thin paper on the flat plate at this place to make appropriate adjustments.

6) The stamping speed is as constant as possible

The contact time and the hot stamping fastness are proportional under certain conditions, and the hot stamping speed determines the contact time between the anodized aluminum and the substrate. The hot stamping speed is slow, the contact time between the anodized aluminum and the substrate is long, and the bonding is relatively strong, which is conducive to hot stamping; on the contrary, the hot stamping speed is fast, the hot stamping contact time is short, the hot melt silicone resin layer and adhesive of the anodized aluminum Not completely melted, it will cause hot stamping or imprinting. Of course, the stamping speed must also be adapted to the pressure and temperature. If the stamping speed increases, the temperature and pressure should also be increased appropriately.

In addition, the performance of anodized aluminum itself has a greater impact on the speed of hot stamping. Good quality anodized aluminum can achieve rapid hot stamping, which is quite different from domestic anodized aluminum and imported anodized aluminum. Domestic anodized aluminum is usually only suitable for low-speed hot stamping, the speed is about 2000 sheets / h, and the maximum is generally not more than 3000 sheets / h; imported ones can reach 8000 sheets / h or even higher. Regardless of the speed, the important point is that the stamping speed should be kept as stable as possible, and should not be changed easily. Under the premise of stabilizing the hot stamping speed, the hot stamping temperature and pressure should be appropriately adjusted to optimize the hot stamping effect, which can reduce the variable factors, stabilize the operation, and easily control the hot stamping quality.

The above are just a few main factors that affect the quality of bronzing, and these factors are not isolated from each other, they are mutually restrictive. The determination of these factors should be based on the hot stamping suitability of the anodized aluminum and the characteristics of the substrate, the hot stamping plate graphic structure, area and hot stamping speed to determine the best pressure, and finally adjust the appropriate hot stamping temperature. The basic starting point should be hot stamping with as uniform and moderate pressure as possible, low temperature and relatively stable hot stamping speed to achieve clear and clean graphics, smooth and firm, high gloss, no dirty spots, no trachoma Good effect.

3 Other issues that should be noted in hot stamping

The quality of bronzing is affected by many factors, especially because the bronzing is performed after printing, its printing effect, the thickness of the ink layer, the nature of the ink, etc. will directly affect the bronzing effect. Therefore, the following issues should be noted:

1) Hot stamping should be done after the ink has dried. If the ink layer is not completely dry, hot stamping will start. Because the ink is not firmly attached, it is easy to cause the failure of the ink layer, so that the hot stamping cannot be achieved.

2) If hot stamping on the background color, the background ink layer should not be too thick and too thick, try to achieve deep ink thin printing, avoid 3 colors, 4 colors overprinting, so as to avoid the ink adhesion is not strong enough due to the thick ink layer, resulting in Unfavorable phenomena such as hot stamping, blurring, or even pulling off the ink layer. In addition, when stamping a solid background color, the stamping temperature should be appropriately reduced, so that the stamping effect is more ideal.

3) If hot stamping is performed on spot colors on the spot, the amount of ink additives should be controlled when printing spot colors. For example, excessive amount of desiccant will cause the crystallization of the ink layer, which will cause the hot stamping of anodized aluminum; in addition, printing It should be avoided when mixing non-drying oils, such as engine oil, kerosene, slow drying agent and corn flour, so as to avoid the situation of hot stamping. If the hot stamping fails due to the addition of ink additives, use absolute alcohol to wipe the surface of the printed matter, destroy the oil layer or wax, to enhance the adhesion of the anodized aluminum and improve the hot stamping effect.

4) If you are hot stamping on the glazed, filmed printed matter, you should pay attention to choose the corresponding anodized aluminum model.