How to solve the phenomenon of knife thread in plastic gravure printing
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In the process of plastic gravure printing, there is often a knife phenomenon. The reasons for this are very complicated, involving various aspects such as plate making, ink, squeegee and environment. Now Amway Mall analyzes and discusses it for your reference.
1. Plate aspect
The surface finish and hardness of the chrome plate on the plate will have an important influence on the generation of the wire. The pigment of the ink used for the gravure printing is generally dispersed in the binder in a particulate state. During the printing process, after the ink is filled with the mesh, the excess ink is scraped off by the doctor blade while continuously rubbing the surface of the printing plate. If the chrome plating on the surface of the printing plate is not sufficiently hard, it is easily scratched by the coarse particle ink to produce a knife wire.
On the other hand, if the plate cylinder polishing process is poor at the time of plate making, the layout has fine throwing or the pattern is too deep. During the printing process, the ink will remain there and cannot be scraped off by the doctor blade, and transferred onto the printing material. Will produce irregular, very thin blades. Therefore, special polishing equipment and special polishing sandpaper should be used for polishing.
In addition, the drum processing precision and installation accuracy should be strictly controlled to prevent the eccentricity from exceeding the standard, so as to avoid the impact on the squeegee during high-speed printing to generate the cutter wire.
2. Ink aspect
If the ink used for the gravure printing of plastic is not fine enough, the pigment particles are too large or mixed with particulate impurities, the occurrence of the knife wire will be caused. Therefore, a better quality ink should be selected, and the pigment particles should be less than 10 μm. Filtration devices should be added to the inking system and often inspected to avoid coarse particles in the ink from damaging the plates and the squeegee. If the viscosity of the ink is too large and the drying is too fast, the relative friction between the plate cylinder and the doctor blade will be increased, making it difficult for the doctor blade to scrape off excess ink on the plate to form a wire. Therefore, the viscosity of the ink should be controlled. For inks that are too fast to dry, use a slow drying solvent or dilute the ink.
In addition, if the ink dilution is not standardized, the use of an incompatible solvent causes the pigment in the ink to precipitate, forming large particles, thereby producing a wire. Therefore, a solvent that matches the gravure ink should be selected. If the antistatic performance of the ink is poor, or the lubricating performance is poor, it will also lead to the occurrence of the wire phenomenon. Therefore, it is necessary to strictly control whether the quality indicators of the inspection ink are analyzed.
3. Scraper
The squeegee is an important part of the plastic gravure. It should be made of self-grinding squeegee with tight material and moderate hardness. In general, a hard squeegee produces more knives than a soft squeegee. When the squeegee is damaged by a gap, a regular left and right moving ink trace is produced on the substrate. The fine squeegee gap can be polished to a smooth and smooth surface with fine sandpaper. If there is a large gap, it needs to be replaced. Therefore, it is necessary to level the squeegee when installing the squeegee. Before installing the knives, carefully check whether the squeegee has a gap. After the knives are carefully ground, if there is a knives during the printing process, it must be stopped for grinding, and the grinding oil is strictly prohibited. In the ink.
In addition, in the printing process, the angle and pressure between the squeegee and the printing plate must be mastered to reduce the relative friction of the squeegee to the printing plate. Generally, the angle between the doctor blade and the plate cylinder is 70° to 75°, the inclination is upward, and the blade pressure is controlled between 200 and 400 kPa.
4. Environmental aspects
Temperature, humidity and air cleanliness in the pressroom can affect the appearance of the wire. If the temperature is too high, the solvent evaporates too quickly, and the ink dries too fast; if the humidity is too large, the ink dissolves poorly, the viscosity becomes large, and the ink is difficult to scrape. In both cases, it is easy to cause the appearance of the wire. Therefore, during the printing process, the temperature should be controlled at 18 to 23 ° C, and the humidity should be controlled at 50% to 60%. If there is more dust in the air, the plastic film will generate electrostatic adsorption during printing. These dust will be transferred from the film to the plate cylinder during printing, and will be adhered to the doctor blade when the ink is gathered into the ink. wire. To this end, a static eliminator should be installed and an antistatic screen or antistatic plant belt should be hung over the plastic substrate film. The gravure production environment should be kept as closed as possible, and the air filter should be installed and the dust content should be measured to maintain the cleanliness of the air and avoid the occurrence of the wire.
In short, in the process of plastic gravure printing, there are many reasons for the phenomenon of the wire, and often it is mutually influential. It should be inspected and analyzed from the printing plate, ink, scraper and environment, and excluded one by one.