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Printing knowledge: methods to improve the quality of post press bronzing of printed matter

from the basic process of bronzing, we can see that 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 raw materials related to bronzing must also be guaranteed, such as the hot stamping suitability of the substrate, the performance of anodized materials and the quality of hot stamping plates. If something goes wrong, it will affect the final hot stamping effect

1. Choose the right substrate

there are many substrates that can be bronzed, usually paper. Such as: coated paper, whiteboard, white cardboard, cloth paper, offset paper, etc. However, not all paper bronzing effects are ideal. If the surface is rough and the paper is loose, such as books and periodicals paper, poor offset paper, etc., because the electrochemical aluminum layer can not be well attached to its surface, the unique metallic luster can not be well reflected, and even hot stamping can not be achieved. Therefore, the substrate for bronzing should be paper with dense texture, high smoothness and high surface strength, so as to obtain a good hot stamping effect and fully reflect the unique anodized luster

2. Select the appropriate model of electrochemical aluminum according to the different substrates

the structure of electrochemical aluminum has five layers, that is, the experimental data of polyester film layer adopts database management mode, peeling layer, color layer (protective layer), aluminum layer and adhesive layer. There are many types of electrochemical aluminum, common ones are No. 1, No. 2, No. 8, No. 12, No. 15, etc. In addition to gold, there are dozens of colors, such as silver, blue, brown red, green, scarlet and so on. When choosing electrochemical aluminum, we should not only choose the appropriate color, but also choose the corresponding model according to the different substrate. Different models have different properties and the range of materials suitable for ironing. In general, No. 8 is the most commonly used for hot stamping of paper products with D as the diameter of the sample, because No. 8 anodized aluminum has moderate adhesion and good gloss, which is more suitable for hot stamping of general printing paper or polished paper and varnished cloth. If stamping on hard plastic, you should choose other corresponding models, such as No. 15 electrochemical aluminum

the quality of electrochemical aluminum is mainly controlled by visual inspection and hand feeling, such as checking the color, brightness and trachoma of electrochemical aluminum. Good quality anodized aluminum requires uniform color, bright and clean after hot stamping, and no trachoma. Generally, the fastness and tightness of anodized aluminum can be checked by rubbing it by hand or trying to stick its surface with scotch tape. If the anodized aluminum is not easy to fall off, it means that the fastness and tightness are better, which is more suitable for hot stamping small text patterns, and it is not easy to paste the plate during hot stamping; If you gently rub the anodized aluminum and it will fall off one after another, it means that its tightness is poor and can only be used for hot stamping with sparse graphics and texts; In addition, pay attention to the broken ends of electrochemical aluminum. The less the broken ends, the better

it is worth noting that anodized aluminum must be properly kept and stored in a ventilated and dry place. It cannot be mixed with acids, alkalis, alcohols and other substances. Measures such as moisture-proof, high-temperature protection and sun protection should be taken, otherwise the service life of anodized aluminum will be shortened

3. make a good 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 poor. Therefore, for fine hot stamping, copper plate should be used as much as possible. For hot stamping plates, the surface shall be flat, the lines of pictures and texts shall be clear, the edges shall be smooth, and there shall be no pits and burrs. If the surface is slightly uneven or slightly scratched or hairy, you can gently wipe it with fine charcoal to make it flat and smooth. The etching depth of the hot stamping plate should be slightly deeper, at least more than 0.6mm, and the slope should be about 700, so as to ensure that the hot stamping pictures and texts are clear, reduce the occurrence of contiguous and paste plates, and improve the printing resistance at the same time

the design of words, lines and patterns for hot stamping is very particular. The text should be as thick and thin as possible, and the density should be reasonable. If it is too small and thin, it is easy to miss the pen and dash; 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 falling off layer of hot-melt silicone resin and adhesive. The hot stamping temperature must not be lower than the lower limit of the temperature resistance range of anodized aluminum, which is the lowest temperature to ensure the melting of anodized adhesive layer

if the temperature is too low and the melting is not sufficient, the hot stamping will not be on or firm, and the imprint will be weak, incomplete, missing pens, broken lines or flowers; If the temperature is too high, it will melt excessively, causing the anodized aluminum attached around the imprint to melt and fall off and produce a paste. At the same time, high temperature will also make the synthetic resin and dye in the color layer oxidized and polymerized, and the imprint will blister or appear fog spots, and cause the surface of the aluminum layer and the protective layer to oxidize, so that the hot stamping products will reduce the brightness or lose the metallic luster. Generally speaking, the electrothermal temperature should be adjusted between 80~c and 180~c. for those with large hot stamping area, the electrothermal temperature is relatively higher; On the contrary, it is lower. The specific situation should be determined according to the actual temperature of the printing plate, the type of anodized aluminum, the picture and text condition and other factors. Generally, the most suitable temperature should be found through trial ironing, and the lowest temperature and clear picture and text lines should be taken as the standard

5. it is necessary to reasonably grasp the hot stamping pressure

the hot stamping pressure is closely related to the adhesion fastness of anodized aluminum. Even if the temperature is appropriate, if the pressure is insufficient, it will not be able to make the anodized aluminum stick to the substrate, or cause fading, imprinting and blooming; On the contrary, if the pressure is too large, the compression deformation of the pad and substrate will be too large, resulting in a paste or imprint thickening. Therefore, the hot stamping pressure should be carefully adjusted

when setting the hot stamping pressure, we should mainly consider: electrochemical aluminum property, hot stamping temperature, hot stamping speed, substrate, etc. Generally speaking, when the paper is solid, smooth, the ink layer of printing is thick, and the hot stamping temperature is high and the speed is slow, the hot stamping pressure should be smaller; Otherwise, it should be larger. In addition, similar to printing, it should also be noted that for smooth paper, such as coated paper and glass paperboard, it is best to choose hard backing paper, so that the impression obtained is relatively clear; On the contrary, for the paper with poor smoothness and coarser, the pad should be soft, especially when the hot stamping area is large. In addition, the hot stamping pressure must be uniform. If it is found that local hot stamping is not available or there is tingling during the trial printing, it may be that the pressure here is uneven. You can pad thin paper on the flat plate there for proper adjustment

6. the hot stamping speed should be as constant as possible

the contact time is directly proportional to the hot stamping fastness under certain conditions, and the hot stamping speed determines the contact time between anodized and substrate. The hot stamping speed is slow, the contact time between anodized and substrate is long, and the bonding is relatively firm, which is conducive to hot stamping, and it is more intuitive in structure creation and operation; 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 anodized aluminum have not been completely melted, which will lead to poor hot stamping or blotting. Of course, the hot stamping speed must also adapt to the pressure and temperature. If the hot stamping speed increases, the temperature and pressure should also be appropriately increased

in addition, the performance of anodized has a great influence on the hot stamping speed. High quality anodized aluminum can realize fast hot stamping, which is quite different between domestic anodized aluminum and imported anodized aluminum. Domestic anodized is usually only suitable for low-speed hot stamping, with the speed of about 2000 sheets, and the maximum is generally not more than 3000 sheets/h; The imported ones can reach 8000 pieces or more. However, regardless of the speed, it is important that Bayer materials technology, as a world-class innovative enterprise, should maintain a relatively stable speed as far as possible and not change easily. On the premise of stabilizing the hot stamping speed, properly adjust the hot stamping temperature and pressure to optimize the hot stamping effect, which can reduce variable factors, stabilize the operation and easily control the hot stamping quality

the above are only a few main factors that affect the quality of bronzing, and these factors are not isolated from each other, they restrict each other. The determination of these factors should be based on the hot stamping suitability of electrochemical aluminum and the characteristics of the substrate. The optimal pressure should be determined by the graphic structure, area and hot stamping speed of the hot stamping plate, and finally the appropriate hot stamping temperature should be adjusted. The basic starting point is to hot stamp with as uniform and moderate pressure as possible, low temperature and relatively stable hot stamping speed, so as to achieve the good effect of clear and clean graphics and texts, flat and firm, high gloss, no dirty spots and sand holes

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