In the process of plastic gravure printing, knife wire phenomenon often appears. The causes are very complex, involving plate making, ink, scraping knife and environment. So, how to solve this phenomenon? Today, let's take a look at it.
If the ink used in plastic gravure printing is not fine enough, the pigment particles are too large or mixed with particulate impurities, it will lead to the appearance of knife wire. Therefore, we should choose a better quality ink, the pigment particles should be less than 10 μ m, should be added in the ink system filter device, and often check it, so as to avoid the ink impurities coarse particles damage the printing plate and scraper.
2. Doctor blade.
The scraper is an important part of plastic gravure printing. It should be self grinding scraper with compact material and moderate hardness. Generally speaking, a hard blade produces more thread than a soft blade. When the blade of the blade is damaged and there is a gap, it will produce regular left and right ink marks on the substrate. The small gap of the doctor blade can be polished with fine sandpaper until it is smooth. If there is a large gap, it needs to be replaced. Therefore, it is necessary to level the blade when installing it. Before installing the blade, it is also necessary to carefully check whether there is a gap in the blade. After installing the blade, it is necessary to grind it carefully. If there is knife thread phenomenon in the printing process, it is necessary to stop the machine for grinding, and it is strictly forbidden to mix the knife oil into the ink.
3. Printing plate.
The surface finish and hardness of the chromium plating layer on the printing plate will have an important impact on the generation of the cutter wire. The pigment of plastic gravure printing ink is generally dispersed in the binder in the form of particles. In the printing process, when the ink is full of mesh, the excess ink is scraped off by the scraper, and the printing plate surface is constantly rubbed. If the hardness of the chromium plating layer on the printing plate surface is not enough, it is easy to be scratched by coarse-grained ink and produce knife wire. In addition, the machining accuracy and installation accuracy of the drum should be strictly controlled to prevent the eccentricity from exceeding the standard, so as to avoid the impact on the doctor blade and the generation of cutter wire in high-speed printing.
In addition, the temperature, humidity and air cleanliness of the printing workshop will affect the appearance of cutter wire. If the temperature is too high, the solvent volatilization is too fast, the ink drying is too fast, if the humidity is too high, the ink dissolves poorly, the viscosity becomes larger, and the ink scraping is difficult, both of these two situations will easily cause the appearance of knife wire. Therefore, in the printing process, the temperature should be controlled at 18 ~ 23 ℃, and the humidity should be controlled at 50% ~ 60%.
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