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Silver powder is actually a metal aluminum, also known as aluminum pigment, according to the form can be divided into two types of powder and slurry, according to the performance can be divided into floating, non-leafing and water-dispersible three types, silver particle size and granules The shape is related to the effect of its reflective metallic luster, and the flat silver foil has the best reflective performance. The thickness of a flat silver foil is 0. L-2μm, floating silver powder with a few hundred micrometers in diameter, mixed with a suitable binder to make a silver ink, the reflectivity of the printing ink layer can reach 60% to 90%, and the plastic film gravure printing silver often uses floating Silver powder, after printing, the solvent will volatilize from the ink layer, and the silver ink will form a bright metal film on the plastic film after drying the conjunctiva.
Gold powder and silver powder all have the characteristics of good conductivity, fast heat conduction, heavy weight, coarse particles, poor adhesion and unstable performance of the classics. The intaglio printing cylinder used for gravure gold printing and silver printing, whether it is processing accuracy, flatness, smooth surface and clean, or the degree of web etching and webpage angle, the quality of all aspects should be higher than that of ordinary gravure. In general, the deeper the etching of the printing plate, the thicker the printing ink layer, but the etching too deep will not only affect the drying speed of the ink layer, but also affect the fastness of the ink layer. Therefore, the gold and silver ink layers are not It is better to use thickness instead, but it should be based on the achievement of various quality indicators. The quality index mentioned here mainly refers to the adhesion fastness, flatness, evenness, and brightness of the printing ink layer, and it requires the graphic text to be free from burrs, not to be pasted, and to be free from dirty and anti-sticking. Of course, the corrosion depth of the printing plate should not be too shallow, and the depth of the cell depth is too shallow. The brightness of printed gold or silver will not affect the quality of the product and will not meet the customer's requirements. Under normal circumstances, the depth should not be less than 25μm, and not more than 45μm, and the printing concentration of the printing plate of 30-40μm can be printed. Ideal. The quality requirements of plastic film gravure printing on gold ink and silver ink mainly rest on the aspects of transitivity, fineness, glossiness, and printability, etc. Here, the plastic film gravure is printed on gold. The common faults in silver are analyzed.
The faulty ink layer easily falls off
Plastic film gravure gold printing, silver ink layer is easy to fall off, hand gently rub it off with the film, which is one of the common faults in the printing, analysis of the reasons, mainly the following points:
1) The surface tension of substrate is small. Plastic four-ink gold ink, silver ink and other plastic inks are dried by oxidized conjunctiva. There are strict requirements on the surface tension of the substrate, and the surface tension must meet the standard. For example: "BOPP (biaxially oriented polypropylene) film surface tension value can not be less than 3.8 × 10-2N / m (-2N / m index), PET (polyester) film surface tension value can not be lower 5.2×10-2N/m (-2N/m superscript) The surface tension of PA (nylon) film must not be lower than 5.2 × 10-2N/m (-2N/m superscript), plastic film If it is left for a long time, the surface tension value will decrease and the adhesion of the ink will be affected. Therefore, it is necessary to corona-treat the substrate before gold or silver printing so that the gold and silver ink and the substrate can be produced. Good adsorption, which is used to print gold on plastic films, which has low adhesion fastness and easy to fall off.Corona treatment method is one of the most commonly used methods in printing soft plastics, in order to pass the film surface through high voltage. The shots, named after their uneven surface, produce rough and more favorable to oil And filling an adhesive, thereby improving adhesion.
2) When printing gold or silver, the shedding separation is closely related to the thickness of gold and silver particles. The coarse particles and poor transferability are prone to ink film peeling. In general, the thickness of gold particles is 0.12-1. .75μm, diameter 50-1000μm, high hiding power, the average dosage is about 10g/m2. The unit for measuring the particle size of gold powder and silver powder is called "mesh." The higher the mesh number, the finer the powder of gold powder (silver powder) is, the more favorable it is for transmission. In contrast, the lower the mesh number, the coarser the particles, the lower the ink viscosity, and the poorer in adhesion. It is not easy to deliver. But this does not mean that you must use very fine powder and silver powder. The reflection of light by the ink formulated with fine gold and silver powder may be affected. When printing gold and silver, it is necessary to add a certain amount of gold oil or silver oil to gold ink and silver ink in order to improve the viscosity of the ink. Make it well adhered to the substrate film.
In order to make printing gold and printing silver better, add additives such as gold transfer oil, transparent yellow, etc., but must be based on the actual careful deployment, understand the principles, and do not match the wrong, so as to avoid waste and reduce losses. Ink is printed on the surface and printed on the inside, that is, polyamine resin printing gold oil or chlorinated polypropylene resin composite printing gold oil, careless mixing, will make the resin precipitation, decomposition or expansion , The final ink scrapped, this one must pay attention to. If the reflectance of the printed product is not good, it is recommended to use the corresponding transparent golden color, which is generally not more than 30% of the amount used.
3) It is easy to fall off when printing gold and silver ink, and the adhesion fastness is also related to the temperature and humidity of the printing shop and the speed of the printing machine. Under normal circumstances, the workshop temperature should be controlled at 22-25 °C, and relative humidity should be controlled at 60%-70%. The speed of the printing press is too fast, the ambient humidity is too high, and the drying temperature is low, which may cause the adhesion of gold and silver ink layers to be poor and easy to fall off. Moreover, excessively high speeds will also have a certain influence on the volatilization of solvents, and even cause anti-adhesion. In severe cases, the gold pattern of the first unit has not been introduced into the second unit and it has been removed by the pulling roller.
The color ink is gray
1) Gold powder and silver powder chemically react with themselves. As mentioned above, the chemical properties of gold powder and silver powder are extremely unstable and prone to oxidation. To make the gloss of the printing ink dark, in order to solve this problem, when printing gold, often add some transparent yellow or transparent golden in the gold ink to improve, the gold layer's reflection rate can reach about 95%, basically meet the quality requirements, When used with gold ink, transparent yellow: transparent golden: the mixing ratio of gold powder is generally 2.5:0.5:1 (weight ratio) or 3:1:1, and the effect is good.
2) The ink is too light, too much solvent, making gold. The leveling of the silver ink deteriorates, the viscosity decreases, the adhesion is impaired, and the gloss is dark. The solution is to properly increase the concentration of gold and silver ink, reduce the amount of solvent, so that the leveling of the ink can be improved. When increasing the ink concentration, the ink should be mixed evenly along the pouring direction of the ink.
3) The grids on the plate are too shallow, and the grids are too shallow to meet the requirements, which will reduce the amount of gold and silver inks to be inked, and the gloss of the ink layer will be unsatisfactory. The solution is to cooperate with the plate-making factory to appropriately increase the depth of the cell site and proofing. Compare. Of course, the deeper the better the network, the more likely it is that if the network is too shallow, the color scheme will appear gray and white.
4) Static electricity accumulation. Accumulation of static electricity on the plastic film causes the gloss of the gold and silver ink layers to decrease. The solution is to antistatically process the plastic film.
5) Effect of squeegee pressure. The size of the squeegee pressure, moderate or not, also directly affects the amount of ink applied and gloss. Squeegee pressure is too high, the angle is too high, gold color printing on the case is not ideal, as long as reducing the pressure of the blade, the angle can be reduced to solve, under normal circumstances, the angle of the scraper at 35" is appropriate. Pressure is too small, will scrape It is necessary to pay attention to the quality accidents caused by unclean products.
Thin lines are not clear
1) Ink linking material drying too fast, the ink has not been transferred to the substrate on the dry solid, the solution is to add appropriate in the ink drunk solvent, such as butanol, to be adjusted. Because alcohol solvents can improve the ink transfer performance;
2) The printing speed is too slow. Generally, the printing speed is slower at the time of starting up, and the gold and silver inks are prone to poor transfer, resulting in the inability to print on thin lines. As long as the medium speed and ink transferability are improved, it will naturally be better.
3) When the printing plate is jammed and the printing plate is jammed, darker colors can be printed on it. The lighter colored lines and lines cannot be printed. The so-called blocked version means that the ink is solidified in the cell and cannot be dissolved. It can not be printed on the substrate, the solution is to stop cleaning, our company used sweet potato powder mixed with alcohol solvent cleaning effect is very good.
4) The mixing roller is separated from the printing plate. If the ink mixing roller in the ink tank is separated from the printing plate, it may cause the fine lines to not be printed. Especially when printing gold or silver, it is most likely to occur and attention should be paid. When printing plastic film, the quality of the squeegee is often accompanied by some cutting lines and the web page is deep. Appropriate blowing can reduce knife line production. However, if the blow is too great, sometimes the fine lines will fall out of print and not be printed. The solution is to change the knife or grinding scraper until the thin line is printed on
Finished product after rolling back anti-stick
After printing gold and silver products, the anti-adhesion on the back side of the printed product leads to scrapping of the printed products. This problem often occurs in the color printing and packaging industry, especially when printing gold.
l) The winding tension is too large, the winding is too tight, the solvent in the ink cannot be completely volatilized, and the pressure on the printed product is too large, and it is naturally easy to stick. The solution is to reduce the winding tension and reduce the anti-sticking rate.
2) Gold and silver ink dry slowly. The special nature of gold and silver inks determines their poor affinity, so people in the industry believe that the finished products must be processed and compounded in time; When silver is used, it is necessary to speed up the dry solvent, so that the solvent in the ink is accelerated, and it is completely volatilized. It is also very important to increase the drying temperature. If it is table printing, use toluene:ethyl acetate:isopropanol=5:2:3. If it is printed in India, then toluene: butanone: ethyl ester 6:2:2 or 7:2:1, peers may wish to try, if the printed product is white, there are phenomena such as pan-silk, indicating that the color scheme is too fast. The reproducibility is poor. The solution is to use a slow-drying solvent.
3) Improper control of temperature and humidity in the workshop. Anti-adhesion of printed products, delamination is also related to the temperature and humidity of the workshop, when the humidity is too high, it is prone to anti-adhesion, so the conditions of the enterprise should be installed on the air conditioning on the temperature and humidity of the shop to adjust, so that the printing products to obtain the best The effect of printing gold and silver printing should be selected when the printed gold and silver printed products need to be compounded. Ye Qiang, the assimilation part can make the adhesive that the gold powder (silver powder) does not react well, it is very important to increase the coating amount of the adhesive properly, increase the compound pressure and drying temperature.
4) Different types of inks are mixed for printing, printing gold, silver parts are easy to fall off, anti-adhesion, the product is scrapped, and the sealing knife is prone to delamination or delamination. This is mainly due to the unique nature of gold and silver. The solution is not to be compatible with different types of inks. The solution is to adapt the printability of gold ink to other inks, that is, the surface ink is printed, the ink is printed, and the ink is printed in the ink.
Gold powder ink: printing gold and silver common faults and its treatment
Gold ink is mainly composed of gold powder and binder. The composition of gold powder is metal copper or copper alloy. For example: the ratio of copper to zinc of red gold powder is 92:8, and the ratio of copper to zinc of green gold powder is 70:30. Under the circumstances of schooling, the gold powder granules and the printing ink layer are bright, but the hiding power is not so good and it is not suitable for deployment. Jinmo, for example: “The gold powder used for gravure plastic film printing is an ultra-fine grade powder of approximately 1% to 1000 mesh. Compared with the pigments used for formulating ordinary inks, the gold powder is characterized by strong buoyancy and coarse particles. The dispersibility in the binder and the fixation force on the substrate are relatively poor, and the unique characteristics of the gold powder are also the main reason for the ink layer to be easily peeled off.The gold powder is more sensitive to chemicals, especially the red gold is the most unstable. In addition to copper powder, aluminum powder is commonly used. Aluminum powder is a golden powder formed by oxidation treatment of aluminum silver powder. Its appearance is similar to that of copper powder, but its specific gravity is small and its stability is good. The prepared gold ink can be stored for a long time.