How to improve the quality of bronzing

Nowadays, despite the development of science and technology, the post-press finishing process continues to innovate, and new cold stamping, holographic positioning, hot stamping and other new processes have emerged, but traditional bronzing is an important process in post-press processing due to its unique decorative effect. It has not been neglected. Instead, it has received more attention and preference from people. Therefore, how to improve the quality of bronzing is often a problem that people have discussed. Here, the author discusses some personal experiences on this issue from several aspects.

1 The basic process of bronzing

The main material for bronzing is galvanized aluminum, so bronzing is also called galvanized aluminum stamping. Hot stamping is the use of the principle of heat transfer to transfer the aluminum layer in anodized aluminum onto the substrate surface. The basic process is as follows: First, under pressure, that is, the aluminum foil is pressed by a hot Plate and the substrate is pressed, the aluminum foil is heated to melt the upper-melting silicone resin layer and the adhesive, which is melted by heat at this time. The viscosity of the silicone resin becomes smaller, and the viscosity of the special heat-sensitive adhesive melts after melting, so that 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 is firmly attached to the substrate, completing a hot stamping process.

The hot stamping process includes: Hot stamping preparation Armored version Brass pad version î ‡ Adjustment of hot stamping process parameters î ‡ Test hot stamping î ‡ Sample stamping î ‡ Formal hot stamping.

2 Ways to Improve the Quality of Bronzing

From the basic process of bronzing can be seen, the three basic elements of bronzing are: temperature, pressure and 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 controlled; in addition, the quality of raw materials related to hot stamping must also be guaranteed, such as the hot stamp adaptability of the substrate. , the performance of electro-aluminum materials, and the quality of hot stamping Plates, etc. If something goes wrong, it will affect the final hot stamping effect.

1) Choose the right substrate

There are many substrates that can be stamped, usually paper, such as coated paper, whiteboard, white cardboard, textured paper, offset paper, and so on. However, not all paper gilding effects are ideal. For example, if the surface is rough and paper with loose paper, such as books and paper, poor offset paper, etc., because the galvanized aluminum layer does not adhere well to its surface, the unique metal Luster can not be reflected well, and even hot stamping is not possible. Therefore, foil-printed substrates should be dense, smooth, and with high surface strength, so as to obtain a good stamping effect. Gloss is fully reflected.

2) According to the different choice of substrates

Electrochemical aluminum structure has 5 layers, namely: polyester film layer, shedding layer, color layer (protective layer), aluminum layer and adhesive layer. Electrochemical aluminum models are more common, there are l, 2, 8, 12, and so on. In addition to gold, there are dozens of colors such as silver, blue, brown-red, green, and red. The choice of anodized aluminum is not only to choose the right color, but also to select the appropriate model according to the different substrates. Different models, its performance and suitable range of materials are also different. Under normal circumstances, the most used paper stamping is No. 8, because No. 8 anodized aluminum adhesive moderate, good gloss, more suitable for general printing paper or coated paper, lacquer stamping. If hot stamping on hard plastic, you should choose other corresponding models, such as 15 aluminum.

The quality of anodized aluminum is mainly determined by visual inspection and feel, such as checking the color, brightness and trachoma of the anodized aluminum. The quality of the good quality of anodized aluminum requires uniform color, bright and clean after hot stamping, no trachoma. The fastness and tightness of anodized aluminum can generally be checked by hand rubbing, or by scotch tape to test the surface layer. If the galvanized 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. When the hot stamping is performed, it is not easy to paste the plate. If you gently rub the galvanized aluminum, it will fall off, indicating that the tightness is poor. Can be used for graphic sparse hot stamping; In addition, we must pay attention to broken aluminum, broken the less the better.

It is worth noting that the electro-aluminum must be properly kept and stored in a ventilated, dry place. It must not be mixed with acids, alkalis, alcohols, etc., and must be protected against moisture, heat, and sun. Otherwise, the electro-aluminum will be shortened. Period of use.

3) Make a hot stamping version

Hot stamping plates generally have copper plates, zinc plates, and resin plates. Relatively speaking, copper plates are the best, zinc plates are moderate, and resin plates are slightly inferior. Therefore, for fine stamping, copper plates should be used as much as possible. For hot stamping, it is required to have a smooth surface, clear lines and lines, smooth edges, no pockmarks and burrs. If the surface is slightly uneven or slightly bruised or fluffed, it can be gently wiped with fine charcoal to make it smooth and smooth. The depth of the stencil printing plate should be slightly deeper, at least above 0.6mm, and the slope should be around 70° to ensure that the hot stamping graphic is clear, contiguous and stencil printing is reduced, and the printing rate is improved.

Hot stamping text, lines and designs are very particular about design. The figures and texts should be as thick and thin as possible, and should be dense and reasonable. If they are too small and too thin, they are prone to lack of strokes. If they are too thick and too dense, they are easy to paste.

4) Control the stamping temperature

The hot stamping temperature has a great influence on the melting degree of the exfoliative layer of the hot-melt silicone resin and the adhesive, and the hot stamping temperature must not be lower than the lower limit of the temperature range of the electro-aluminum, which is the lowest temperature for ensuring the melting of the electro-aluminum adhesive layer. If the temperature is too low and the melting is not sufficient, the hot stamping may not be achieved or the hot stamping may not be firm, so that the imprinting is not sturdy, incomplete, lack of strokes or scratches, and if the temperature is too high, the melting is excessive, resulting in adhesion around the imprints. The galvanized aluminum is also melted and detached to produce a paste plate. At the same time, the high temperature also causes the synthetic resins and dyes in the colored layer to oxidize and polymerize, and the imprinting is blistering or fog-like, and the surface of the aluminum layer and the protective layer is oxidized, so that the hot stamping product is reduced. Brightness or loss of metallic luster. In general, the electrothermal temperature should be adjusted between 80 ~ 180 °C, hot stamping area is larger, the electrothermal 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 anodized aluminum, graphic conditions and other factors. Usually, the most suitable temperature should be determined through the test press, and the clearest graphic lines should be imprinted at the lowest temperature. As standard.

5) To master the stamping pressure

The hot stamping pressure has a great relationship with the adhesion of the aluminum foil. Even if the temperature is appropriate, if the pressure is insufficient, it will not be able to stick the aluminum foil to the substrate, or cause discoloration or blotting; otherwise, if the pressure is too high, the compression and deformation of the liner and the substrate will be too large, resulting in paste Plate or blot becomes thicker. Therefore, the stamping pressure should be carefully adjusted.

Setting the stamping pressure should mainly consider: the nature of the aluminum, hot stamping temperature, hot stamping speed, substrates and so on. Generally speaking, under the condition of strong paper, high smoothness, thick printed ink layer, high stamping temperature and slow speed, the hot stamping pressure should be smaller; otherwise, it should be larger. In addition, similar to printing, hot stamping liners should also be noted that for smooth paper, such as: coated paper, glass cardboard, hard liner paper is preferred, so that the resulting print is relatively clear; on the contrary, for smoothness For poor, rough paper, the liner is preferably softer, especially if the hot stamp area is large. In addition, the hot stamping pressure must be uniform. If the partial hot stamping or spotting is not found during the trial printing, the pressure may be uneven. A thin paper may be placed on the flat plate at the place and the appropriate adjustment may be made.

6) The hot stamping speed is as constant as possible

The contact time and the hot-stamping fastness are proportional to certain conditions, and the hot-stamping speed determines the contact time between the anodized aluminum and the substrate. The slow hot stamping, the long contact time between the aluminum foil and the substrate, the bonding is more solid, which is conducive to hot stamping; on the contrary, the hot stamping speed is fast, the hot stamping contact time is short, the aluminum foil hot melt silicone resin layer and adhesive If it is not completely melted, it will cause hot stamping or blotting. Of course, the hot stamping speed must also be compatible with the pressure and temperature. If the hot stamping speed increases, the temperature and pressure should also be increased.

In addition, the performance of the aluminum itself has a greater impact on the hot stamping speed. A good quality of aluminum can achieve fast hot stamping, which is different from imported aluminum. Domestic aluminum is usually only suitable for low-speed hot stamping, the speed is about 2000 sheets/h, the maximum is generally not more than 3000 sheets/h; the imported can reach 8000 sheets/h, or even higher. However, regardless of speed, it is important to note that the hot stamping speed should be as stable as possible and should not be changed easily. Under the premise of stabilizing the hot stamping speed, the stamping temperature and pressure should be properly adjusted to optimize the hot stamping effect. This can reduce the variable factors, make the operation stable, and control the stamping quality easily.

The above are just a few of the major factors affecting the quality of gilding, and these factors are not isolated from each other and they are mutually restrictive. Determine these factors to be based on the aluminum foil stamping adaptability and the characteristics of the substrate based on the hot stamp plate graphic structure, area and hot stamping speed to determine the best pressure, and finally adjust the appropriate stamping temperature. The basic starting point is to apply hot stamping as uniformly as possible, moderate pressure, low temperature and relatively stable stamping speed in order to achieve a clear, clean, smooth and graphic image with high gloss, no dirt spots, no blisters The good results.

3 Hot stamping should pay attention to other issues

The quality of bronzing is affected by many factors, especially since the bronzing is performed 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, the following issues should be noted:

1) Hot stamping should be done after the ink has dried. If the ink layer has not dried yet, the hot stamping starts. Since the ink is not firmly adhered, the failure of the pull-and-deink layer may occur, so that the hot stamping may not be performed.

2) If the hot stamping on the background, the underlying ink layer can not be too thick, too thick, as far as possible to dark ink thin printing, to avoid 3 color, 4 color overprint, so as to avoid ink layer is too thick, ink adhesion is not solid, resulting in Hot stamping is not strong, hair paste, and even pull off the ink layer and other undesirable phenomena. In addition, the hot stamping temperature should be properly reduced when hot stamping the ground background, so that the hot stamping effect is ideal.

3) If hot stamping is performed on spot colors, it is necessary to control the amount of ink additives when printing spot colors. For example, excessive amount of desiccant can cause crystallization of the ink layer, resulting in failure of hot stamping of the aluminum foil; Should avoid the incorporation of non-dry oils, such as oil, kerosene, slow drying agent and corn flour, etc., in order to avoid hot stamping situation. If the stamping agent is caused by the addition of ink additives, the surface of the printed matter may be wiped with anhydrous alcohol to destroy the oil layer or the wax, so as to enhance the adhesion of the aluminum foil and improve the effect of the stamping.
4) If hot stamping is applied on glazing or laminating prints, the corresponding galvanized aluminum model should be selected.

Author: Gui Jiao party company