How to improve the quality of hot stamping process
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At present, due to the continuous development of science and technology, the finishing process of post-press finishing has been continuously updated, and various new processes such as holographic positioning hot stamping and cold stamping have appeared, but traditional bronzing is an important process in post-press processing, in view of its unique luxurious decoration. The effect has not been left out, but has been more concerned and favored by customers. Therefore, how to improve the quality of bronzing is often a problem that people discuss. The operation of some bronzing processes will be explained in several aspects below.
First, the basic process of bronzing
The main material for bronzing is anodized aluminum, so bronzing is also called electro-aluminum hot stamping. Hot stamping is the transfer of the aluminum layer in the anodized aluminum onto the surface of the substrate by the principle of hot pressing.
Basic process:
First, in the state where the combined pressure, that is, the anodized aluminum is pressed by the hot stamping plate and the substrate, the anodized aluminum is heated to melt the hot-melt silicone resin layer and the adhesive, and the melted silicone resin is viscous at this time. Small, while the special heat-sensitive adhesive is heated and melted, and the viscosity is increased, so that the aluminum layer and the electrochemical aluminum base film are peeled off and transferred to the substrate.
As the pressure is removed, the adhesive cools and solidifies rapidly, and the aluminum layer is firmly attached to the substrate to complete a hot stamping process.
Process flow:
Hot stamping preparation - loading version - pad version - adjusting hot stamping process parameters - trial hot - signing - official hot stamping.
Second, 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 bronzing must also be guaranteed, for example: the hot stamping suitability of the substrate. , the performance of electrochemical aluminum materials and the quality of hot stamping plates, etc. If something goes wrong in a certain link, it will affect the final hot stamping effect.
1. Choose the right substrate
There are many substrates that can be bronzing, usually paper, such as coated paper, white paper, white cardboard, textured paper, offset paper, and so on. However, not all paper bronzing effects are ideal. If the surface is rough and the paper is loose, such as for book paper, poor offset paper, etc., because the electrochemical aluminum layer does not adhere well to its surface, the unique metal The gloss is not well reflected, and it can't even be printed.
Therefore, the substrate of hot stamping should use paper with dense texture, high smoothness and high surface strength, so as to obtain a good hot stamping effect and fully reflect the unique electroluminic aluminum luster.
2. Select the appropriate type of anodized aluminum according to the substrate.
The structure of the anodized aluminum has five layers, namely, a polyester film layer, a peeling layer, a color layer (protective layer), an aluminum layer, and a rubber layer. There are many types of electrochemical aluminum, and 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 red.
Choosing anodized aluminum requires not only choosing the right color, but also selecting the appropriate model depending on the substrate. Different models, the performance and the range of materials that are suitable for ironing are also different.
Under normal circumstances, the most used paper products for hot stamping is No. 8, because the 8th galvanic aluminum has moderate adhesion and good gloss, which is more suitable for general printing paper or glazed paper and varnish hot stamping. If hot stamping on hard plastic, you should choose another corresponding model, such as No. 15 anodized aluminum.
The quality of anodized aluminum is mainly determined by visual inspection and hand feeling, such as checking the color, brightness and trachoma of anodized aluminum. Good quality anodized aluminum requires uniform color, smooth and smooth after hot stamping, and no trachoma.
For the fastness and tightness of the anodized aluminum, it can generally be checked by hand rubbing or by using a scotch tape paper to test its surface layer.
If the electrochemical aluminum is not easy to fall off, it indicates that the fastness and tightness are better, and it is more suitable for hot printing of small text patterns. It is not easy to paste when hot stamping; if it is lightly rubbed, the aluminum will fall off, indicating that the tightness is poor, only It can be used for the hot stamping of the image; in addition, pay attention to the broken end of the electrochemical aluminum, the fewer the broken ends, the better.
It is worth noting that the electrochemical aluminum must be kept in a safe place. It should be stored in a ventilated and dry place. It should not be mixed with acid, alkali, alcohol and other substances. It should be protected against moisture, high temperature and sun. Otherwise, the electrochemical aluminum will be shortened. Period of use.
3. Make a hot stamping version
Hot stamping plates generally have copper plate, zinc plate and resin plate. Relatively speaking, the copper plate is the best, the zinc plate is moderate, and the resin plate is slightly worse. Therefore, for fine hot stamping, copper plates should be used whenever possible. For hot stamping plates, the surface is required to be flat, the lines are clear, the edges are smooth, and there are no pitting 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 stencil should be slightly deeper, at least above 0.6mm, and the slope should be around 70° to ensure that the hot stamping is clear, reduce the occurrence of contiguous and paste, and improve the printing durability.
The design of hot stamped text, lines and patterns is very particular. The graphic should be as moderate and moderate as possible, such as too small and too thin, and it is easy to miss the pen; 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 electrochemical temperature range of the electrochemical aluminum, which is the lowest temperature for ensuring the melting of the electrochemical aluminum adhesive layer.
If the temperature is too low, the melting will be insufficient, which will result in poor hot stamping or poor hot stamping, making the imprint unsound, incomplete, lacking pen breaks or smearing;
When the temperature is too high, the melting is excessive, so that the electro-aluminum adhered around the imprint is also melted and detached to produce a paste, and at the same time, the high temperature also oxidizes the synthetic resin and the dye in the color layer, and the blistering or fogging occurs, and causes The surface of the aluminum layer and the protective layer are oxidized to reduce the brightness or loss of metallic luster of the hot stamping product.
In general, the electric heating temperature should be adjusted between 80 and 180 ° C. If the hot stamping area is large, the electric heating temperature is relatively higher; otherwise, it is lower.
The specific situation should be determined according to the actual temperature of the printing plate, the type of electrochemical aluminum, the condition of the graphic and so on. Usually, the most suitable temperature should be found by trial ironing. The temperature should be the lowest and the clear graphic lines can be printed. As standard.
5. To properly control the hot stamping pressure
The stamping pressure has a great relationship with the adhesion of the anodized aluminum. Even if the temperature is right, if the pressure is insufficient, it will not be able to make the anodized aluminum adhere to the substrate, or cause color loss, embossing, etc.; if the pressure is too large, the compression deformation of the liner and the substrate will be too large, resulting in a paste. The plate or blot is thicker. Therefore, the hot stamping pressure should be carefully adjusted.
When setting the stamping pressure, the main considerations should be: the properties of the electrochemical aluminum, the hot stamping temperature, the hot stamping speed, and the substrate. In general, when the paper is strong, the smoothness is high, 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 pads should also be noted, for smooth paper, such as: coated paper, glass cardboard, it is best to use hard liner paper, so that the obtained print is clear; on the contrary, for smoothness For poor, rough paper, the liner is preferably softer, especially if the hot stamping area is large.
Finally, the hot stamping pressure must be uniform. If the partial hot stamping is not produced or the flower is produced during the trial printing, the pressure here may be uneven. You can put a thin paper on the flat plate here and make appropriate adjustments.
6. Hot stamping speed is as constant as possible
The contact time and the hot stamping fastness are proportional to the certain conditions, and the hot stamping speed determines the contact time between the electrochemical aluminum and the substrate.
The hot stamping speed is slow, the contact time between the electrochemical aluminum and the substrate is long, the bonding is firmer, which is beneficial to hot stamping; on the contrary, the hot stamping speed is fast, the hot stamping contact time is short, and the hot-melt silicone resin layer and adhesive of the electrochemical aluminum Not completely melted, it will cause hot stamping or imprinting.
Of course, the hot stamping speed must also be compatible with the pressure and temperature. If the hot stamping speed is increased, the temperature and pressure should be appropriately increased.
In addition, the performance of the electrochemical aluminum itself has a greater impact on the hot stamping speed. A good quality of anodized aluminum can achieve rapid hot stamping. This difference between domestically produced anodized aluminum and imported anodized aluminum is quite large.
Domestically produced anodized aluminum is usually only suitable for low-speed hot stamping, the speed is about 2000 sheets/h, the highest is generally no more than 3000 sheets/h; the imported ones can reach 8000 sheets/h or even higher. But regardless of the speed, the important point is that the hot stamping speed should be as stable as possible and should not be changed easily.
Under the premise of stable hot stamping speed, the hot stamping temperature and pressure should be properly adjusted to optimize the hot stamping effect, which can reduce the variable factors, make the operation stable, and easily control the quality of hot stamping.
The above are just a few of the main factors affecting the quality of bronzing, and these factors are not isolated from each other, and they are mutually restrained.
It is determined that these factors are based on the hot stamping suitability of the anodized aluminum and the characteristics of the substrate, and the optimum pressure is determined by the graphic structure, area and hot stamping speed of the hot stamping plate, and finally the appropriate hot stamping temperature is adjusted.
The basic starting point should be hot stamping with as uniform, moderate pressure as possible, lower temperature and relatively stable hot stamping speed, in order to achieve clear, clean, smooth, high gloss, no dirt, no blisters. Good results.
Third, other issues should be noted in hot stamping
The quality of bronzing is affected by many factors, especially since bronzing is carried out after printing. The printing effect, the thickness of the ink layer, the nature of the ink, etc. will directly affect the hot stamping effect. Therefore, you should pay attention to the following issues:
01. Should be hot stamped after the ink is dry. If the ink layer is not dry yet, the hot stamping is started. Since the ink is not firmly adhered, the failure of the deinking layer is liable to occur, so that the hot stamping is not possible.
02. If the hot ink is printed on the ground color, the ink layer of the bottom color should not be too thick or too thick. Try to make deep ink and thin print to avoid 3 colors and 4 colors overprinting, so as to avoid the ink layer is too thick and the ink adhesion is not strong enough. Hot stamping is not strong, buzzing, and even pulling off the ink layer and other undesirable phenomena. In addition, when hot stamping the ground color, the hot stamping temperature should be appropriately reduced, so that the hot stamping effect is ideal.
03. If hot stamping is done on the spot color in the field, it is necessary to control the amount of ink additive added when printing the spot color. For example, if the amount of desiccant is too much, the ink layer will be crystallized, resulting in the disappearance of the anodized aluminum. In addition, printing When possible, avoid mixing non-drying oils such as engine oil, kerosene, slow-drying agent and corn flour to avoid hot stamping.
If the hot stamping is not caused by the addition of ink auxiliaries, the surface of the printed matter can be wiped with anhydrous alcohol to destroy the oil layer or wax, so as to enhance the adhesion ability of the electrochemical aluminum and improve the hot stamping effect.
04. If hot stamping on glazing and film-printed prints, please pay attention to the corresponding electro-aluminum model.