Gravure Composite Problems (I)

First, the table printing ink gravure printing process chooses different inks according to the post-printing processing technology whether is compounded. If it is to be compounded after printing, whether it is dry compounding or extrusion compounding, any ink that is sandwiched by two layers of film and sandwiched therein is referred to as a printed ink, or compound ink. Conversely, after printing, it is not compounded, and regardless of which side of the film the ink layer is on, it is called a surface ink. Table printing ink can be printed on the inside of the transparent film, first printing black, blue, red, yellow all colors, and finally use the white version of the bottom, make full use of film reflective characteristics, so that the print surface is brighter. The gravure plastic calendars that were popular in previous years and the PVC heat-shrinkable film labels in recent years are examples of successful use of this process. There are also bottles of PET bottles such as Coca-Cola, Pepsi, and Rising Sun that are printed on opaque OPP labels instead of paper labels.
The fundamental difference between the distinction between printing and printing is that it is compounded or not compounded. Because the follow-up process is compounded or not, the difference is significant for the main resins that make up the ink. According to our understanding, the main resin of table printing ink is polyamide, while the printing ink is different, mainly chlorinated polypropylene and nitrided EVA. Table printing ink requires abrasion resistance and good scratch resistance because it does not have any protective layer outside and can only rely on its own link material to ensure that its ink surface is not damaged by external forces. It must have a certain degree of heat resistance. At the moment of heat sealing, the ink layer must withstand temperatures above 100°C. In addition, due to the inability to add color to the brightness of the film, the table printing ink must emphasize its own gloss. However, polyamide resin has a problem that its solvent residue is too large. Since the plastic gravure process is mainly based on hot air to dry, the hot air blows the ink surface dry. The drying mechanism is dry from the outermost surface and gradually dry from the outside to the inside. However, because it is dry outside, it is first formed into a film. The formation of this film, while avoiding the stickiness of the next color group printing, also prevents the inner layer solvent from being emitted. Therefore, the use of polyester skin ink printing, in order to make the ink thoroughly dry, hot air should be opened more properly, the speed can 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 product is printed, packed into a box, opened again after a period of time, and a pungent odor is rushed on. This is the residual odor problem that often attracts customer complaints. To solve this problem, we propose to take the following measures without changing the ink:
1. Appropriately increase the drying temperature, slow down the vehicle so that the solvent evaporates sufficiently;
2. Check the gravure exhaust system of the gravure printing machine, check the air inlet pressure and outlet air pressure, and refer to the data provided by the printing press manufacturer to make the pressure difference as large as possible.
Sometimes, the heat is already very high, but the odor is still there. At this time, we must check the air pressure. If there is only a temperature and there is no acceptable air pressure, the solvent will not evaporate well. Pay attention to checking whether the air duct is open. In a relatively low-pressure day, the exhaust system itself cannot meet the process requirements. At this time, we must check the rationality of the exhaust system. Because the exhaust system of the machine is designed by the manufacturer, but the equipment is installed in the factory, it depends on the technical strength of each manufacturer. The installation position of the exhaust chimney, the height of the air inlet and air outlet, will directly affect the efficiency of the exhaust air. More than 20 years ago, when Shanghai people were making coal stoves, they often covered a small one-meter-high chimney on coal stoves. At this time, even if they did not use fans to fan the wind, coal-fired stoves were prosperous. This is the result of rational use of differential pressure. The exhaust system should also rationally use this differential pressure. Of course, the most thorough approach is to replace the ink and replace the polyamide ink with an ink that has as little residual solvent as possible. Based on our experience, the reader is recommended to use several inks from Dalian DSM. DSPI's PA-C inks are alcohol-soluble inks, and the connecting material is a polyvinyl butyral resin that can be used for gravure printing as well as for flexo printing. The solvent is a mixture of alcohols and the ink does not contain ethyl esters. When the ink is used for table printing, a special wax compound is added to the ink, which can withstand high temperatures of 110° C. It is suitable for paper, plastic, and aluminum. The heat-sealing OPP and pearlescent film mentioned in Ms. Zhang's letter can be fully used. DSPI's MV-F-KA series ink, the link material is nitrocellulose, alcohol-soluble, surface printing, high temperature up to 160 °C. The specific use of the above ink can be found directly by the company.
Second, the temperature of the ink BOPP prints and CPP aluminum film extrusion process, there are scalding stripes. This is actually an ink temperature problem. According to our experience, the extruder temperature is controlled at about 240-340°C when AC compounding is not applied. If coated with AC agent, the extruder temperature is slightly lower. However, the AC agent must be resistant to temperatures above 100°C. Therefore, the temperature resistance of the ink must also be chosen to be above 100°C. The above-mentioned DSPI's MV-F-KA series ink can reach 160°C. It is recommended to try it. (To be continued)