Reasons and elimination of "knife wire" in plastic printing

In the plastic gravure printing process, the knife wire phenomenon often occurs. The reason for its production is very complex, involving plate making, ink, squeegee and environment, etc. Now it is analyzed and discussed for reference by peers.

1 The surface finish and hardness of the chrome plating layer on the printing plate will have an important influence on the production of the knife wire. The pigments used in plastic gravure inks are generally dispersed in the binder in the form of particles. In the printing process, after the ink is filled with the mesh, the excess ink is scraped off by a doctor blade while constantly rubbing the surface of the printing plate. If the hardness of the chrome plating layer on the plate surface is not enough, it can easily be scratched by the coarse-grained ink to produce a knife wire.

On the other hand, if the plate cylinder is badly polished at the time of plate making, there are fine patterns or too deep imprint on the plate. In the printing process, the ink will remain on it and cannot be scraped off by the doctor blade, and it will be transferred to the printing material. It will produce irregular, thin knives. Therefore, special polishing equipment and special polishing sandpaper should be used for polishing.

In addition, the 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 of the squeegee on the high speed printing.

2 Ink inks used in plastic gravure printing may cause knife threads if the fineness of the ink is not enough, pigment particles are too large, or particles are contaminated. Therefore, a better quality ink should be selected, and its pigment particles should be less than 10 μm. Filtering devices should be added to the inking system, and they should often be inspected to avoid coarse particles of the ink damaging the plate and 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 squeegee may be increased, so that it is difficult for the squeegee to scrape off excess ink on the plate to form a knife wire. Therefore, the viscosity of the ink should be controlled. For the ink that dries too quickly, a slow-drying solvent can be used or the ink can be diluted.

In addition, if the ink is not diluted properly, the use of immiscible solvents will result in the precipitation of pigments in the ink, forming large particles, resulting in the production of knife threads. Therefore, the solvent that matches the gravure ink should be selected. If the antistatic performance of the ink is poor, or the lubrication performance is poor, it will also lead to the occurrence of the knife wire phenomenon, so it should be strictly controlled whether the quality indicators of the test ink are analyzed.
Source of Confidence: Jiangyin Lida Printing & Packaging Machinery Co., Ltd.