The hottest questions about gravure composite

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Several problems about gravure printing compounding

first, surface printing ink

in gravure printing process, different inks are selected according to whether the post printing processing process is compounded. If you want to compound after printing, whether it is dry compound or extrusion compound, the ink that is wrapped by two layers of film and sandwiched in it is called internal printing ink, or composite ink. On the contrary, non compounding after printing, regardless of which side of the film the ink layer is on, is called surface printing ink. The surface printing ink can be printed on the inside of the transparent film, first in black, blue, red and yellow, and then on the bottom of the white plate, making full use of the reflective characteristics of the film to make the surface of the printed matter brighter. Gravure plastic calendars, which were popular in previous years, and PVC heat shrinkable film labels in recent years are successful examples of using calcium stearate to cover and lubricate the outside. There are also those that print the surface printing ink on the opaque OPP label film to replace the paper labels, such as the bottle stickers of PET bottles such as Coca Cola, Pepsi Cola, sunrise beverage, etc

the fundamental difference between surface printing and inner printing is whether it is composite or not. Because whether the subsequent process is compounded or not, there is a great difference between the main resins that constitute the ink. As far as we know, polyamide is the main resin of surface printing ink, while interior printing ink is different, mainly chlorinated polypropylene and nitrided EVA. The surface printing ink requires wear resistance and good scratch resistance, because it has no protective layer outside, and can only rely on its own binder to ensure that its ink surface is not damaged by external forces. It must have certain heat resistance. At the moment of heat sealing, the ink layer must withstand a high temperature of more than 100 ℃. In addition, because it is impossible to enhance the color by the brightness of the film, surface printing ink must emphasize its gloss. However, polyamide resin has a problem, that is, its solvent residue is too large. As the plastic gravure printing process mainly relies on hot air to dry the ink surface, the drying mechanism is to dry from the outside, from the outside to the inside, and gradually dry through. But because it is dry outside first, it forms a membrane first. Although the formation of this film avoids the ink sticking during the next color group printing, it also prevents the inner solvent from emitting. Therefore, when printing with poly acyl skin ink, in order to make the ink completely dry, the hot air should be turned up appropriately and the speed should not be too fast. Remove the residual solvent as much as possible. Otherwise, we often encounter such situations in daily production. A roll of finished products is printed, packed into the box, and then opened after a period of time. A pungent smell comes to my face, which is the problem of residual odor that often attracts customers' complaints

to solve this problem, we suggest taking the following measures without changing the ink:

1. Appropriately increase the drying temperature, slow down the speed, and make the solvent volatilize fully

2. check the exhaust gas emission system of the gravure press, check the air inlet pressure and air outlet pressure, and refer to the data provided by the printer manufacturer to make the pressure difference as large as possible

sometimes, the heat has been turned on a lot, but the smell is still there. At this time, it is necessary to check the wind pressure. If there is only temperature but no qualified wind pressure, the solvent still cannot volatilize well. Pay attention to check whether the air duct is unblocked. In days with low air pressure, the exhaust system itself cannot meet the process requirements. At this time, check the rationality of the exhaust system. Because the exhaust system of the machine is designed by the manufacturer, but the installation of the equipment in the factory depends on the technical strength of each manufacturer. The installation position of the exhaust chimney and the height of the air inlet and outlet will directly affect the exhaust efficiency. More than 20 years ago, when Shanghai people were making coal stoves, they often covered them with a small chimney nearly 1 meter high. At this time, even if they didn't use a fan to fan, the wind and fire of the coal stoves were booming. This is the result of rational use of differential pressure. The exhaust system should also make rational use of this pressure difference. Of course, the most thorough way is to replace the ink, and replace the polyamide ink with the ink with the minimum solvent residue. Based on our experience, we recommend several inks from Dalian Schmidt ink company (DSPI). DSPI pa-c ink is alcohol soluble ink, and the connecting material is polyethylene butyraldehyde resin, which can be used for gravure printing and flexographic printing. The solvent is a mixture of alcohols, and the ink does not contain ethyl ester. When the ink is used for surface printing, a special wax compound should be added to the ink, which can withstand the high temperature of 110 ℃, and is suitable for paper, plastic and aluminum. The heat sealing OPP and pearlescent film mentioned in Ms. Zhang's letter can be used completely. DSPI's mv-f-ka series inks are made of nitrocellulose, alcohol soluble, surface printing, and high temperature resistant up to 160 ℃. The specific usage of the above ink can be directly inquired by the company

II. Temperature resistance of ink

bopp prints have scald stripes during extrusion and compounding with CPP aluminized film. This is actually a problem of ink temperature resistance. According to our experience, when the extrusion compound is not coated with AC agent, the extruder temperature is controlled at about 240~340 ℃. If AC agent is applied, the extruder temperature will be slightly lower. However, the temperature resistance of AC agent must be above 100 ℃, so the temperature resistance of ink must also be above 100 ℃. The mv-f-ka series inks of DSPI company mentioned above can reach 160 ℃. It is recommended to try them

III. about the "tunnel" phenomenon in the composite process

the commonly referred to "tunnel" phenomenon generally refers to the lateral stripes of the composite product as an innovative energy storage technology, especially at both ends of the material. This kind of wrinkle, with one kind of composite base material flat and the other kind of bulge, forms a "tunnel". The convex part of wrinkles requires that the composite layer is separated and does not stick firmly. There are many such phenomena in the two-layer composite. The bopp/al/pe three-layer composite mentioned in the letter has another composite process and more opportunities. The reasons for this phenomenon are generally the following:

1. The tension of the substrate

the dry composite process is to simply press one of the two rolls of different substrates together by heating rollers after coating them with adhesive. Therefore, the tension of these two different substrates is crucial to the tension relationship of the composite finished product. Generally speaking, the tension of two kinds of base materials is not suitable when compounding, one of which is too large and the other is too small. When compounding, because each film roll is tight, it seems that nothing can be seen. After compounding, the base material with too much tension is bound to shrink, and its shrinkage is significantly larger than that of the base material with low tension, which will cause relative displacement and wrinkles. Take the composite of BOPP and aluminum foil as an example. After BOPP is glued, it is heated in the drying channel. If the unwinding tension is large, it will be pulled tightly, and then heated, it will be stretched and deformed. However, the tension of aluminum foil cannot be as large as that of BOPP, and the elongation is small. Therefore, once the composite is cooled, BOPP shrinks, wrinkles appear, aluminum foil bulges, and transverse "tunnels" appear. Of course, this example is an extreme example. In fact, for another composite substrate, such as vacuum aluminizing film, or PE and CPP film, as long as the unwinding tension of the two substrates does not match well, this situation will occur. There are two solutions. One is to adjust the unwinding tension of the two substrates to make them adapt to each other. The unwinding tension regulating device composed of magnetic powder brake is often installed on the dry-type compound machine, which is designed for this purpose. The second is to reduce the temperature of the drying channel appropriately. Because the substrate with large deformation is dried by the drying channel, the higher the temperature, the greater the elongation of the film, the greater the deformation, and the more severe the shrinkage after cooling. Of course, this method must consider the problem of solvent residue, and the lower the temperature, the better

2. The problem of adhesive force

there are several aspects to this problem. ① Choose suitable adhesives. The solid content of the commonly used polyurethane adhesive main agent is 35% or 50%, and the solid content of the curing agent is 75%. In order to adapt to the high-speed dry composite process, now most of them adopt the practice of high solid content and low viscosity. However, the adhesive with low viscosity is often divided into small amount and low cohesion. The ideal adhesion can be achieved only when it is cured and crosslinked to form a macromolecular structure. When just compounding, the initial viscosity is very small and insufficient. Therefore, when a substrate shrinks, there will be relative displacement between the upper and lower substrates, that is, wrinkles and "tunnels". Therefore, choosing adhesives with high solid content, low viscosity and high initial viscosity is the first choice to solve this problem- Appropriate coating amount. One of the factors affecting the market volume is the corrugation roller used for gluing. The thickness of the corrugation roller line and the depth of the hole directly affect the adhesive dose it can carry. The second is the preparation of glue and the control of glue concentration. Each glue supplier shall have a detailed introduction to the preparation proportion and method. Third, pay attention to the hardness and pressure of the rubber roller, the angle and pressure of the scraper. Generally speaking, for plastic/plastic composite and plastic/aluminum composite, no matter whether the composite is mainly printed in large area or blank without printing, the gluing amount of 2.0~5.0g/m2 is necessary, and the gluing amount cannot be too low. It's too low. It seems to save costs, but it's not solid in practice. On the contrary, all previous efforts have been wasted. Of course, too much glue is unnecessary. Within a certain range, the fastness is directly proportional to the amount of glue applied, but to a certain extent, it is out of proportion

3. The winding tension problem after composite

the winding tension is too small, the winding is not tight, and the composite has relaxation, which provides the possibility of shrinkage for the substrate to be shrunk. This phenomenon is most obvious at both ends of the composite product, and the middle part is often firm, but the exposed parts at both ends wrinkle due to uneven shrinkage. The solution is very simple. Try to tighten it up as much as possible. The winding tension should be large, and the winding should be tight and compacted without relaxation. Even if some of the tension is not hooked and the initial adhesion is insufficient, the possibility of shrinkage of the woven film roll is smaller. When the adhesive is crosslinked and cured during curing, the initial adhesion is greatly improved, and the relative displacement between the composite substrates will lose the living conditions. In this way, wrinkles will not appear

IV. we haven't encountered the problem that the printing ink and sprayed aluminum powder on the aluminized film will fall off after the aluminized film is placed for a period of time. The printing on the aluminized film is usually printed on the non aluminized surface. If the ink printed on the non aluminized surface and the lead powder sprayed on the other side fall off, maybe there is a problem with the stability of the film itself. Sometimes, the antistatic agent in the film leaks out, which may be similar. Since the error cannot be reduced to the minimum, it is difficult to put forward valuable opinions. After BOPP printing, we have sent it into the vacuum chamber to spray aluminum, that is, aluminum is sprayed on the ink surface, and we have never encountered a similar situation. It is suggested that the printing factory check the surface wetting tension on both sides of the film. The aluminum spraying surface should reach a certain surface wetting tension, and the printing surface should also reach a qualified surface wetting tension, so that the fastness of aluminum spraying and printing can be guaranteed

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