The ink dries on the surface of the printing plate. In addition to the use of static elimination agents, it can also be adjusted by physical methods, such as temperature and humidity in the printing workshop. This is also the root cause of the ink ink is not true.
In general, in gravure printing, only 1 / ~ 2/3 of the ink in the printing plate cell is transferred to the surface of the printing material.
Blockage of the printing plate leads to false ink failure
The most commonly used flexible packaging is polyethylene, polypropylene, etc .; abbreviated as: PE, PP, PVC, PS, PVA, PC, PET, CA, NY, etc. The surface of the impression cylinder is made of rubber or polyurethane material. Therefore, it should be noted in actual printing: the viscosity control of the ink is extremely important. If the viscosity is too high, the solvent content in the ink is relatively small, and it is more volatile and the ink is dried on the plate surface, so it is necessary to appropriately reduce the viscosity of the ink; If the drying speed is too fast, it is easy to block the plate. Slow drying agent can be used appropriately to adjust the drying speed of the ink.
The inking failure is related to the surface aging, wear and slip of the impression cylinder:
The ink pigment particles are large or not fully dissolved, the ink storage period is too long to cause deterioration, the solvent balance changes, resulting in reduced solubility of the ink, improper use of different types of ink formulation and chemical reactions. Ink layer coatings or other adhesives are not easy to adhere firmly to the surface of such films. Poor fluidity, reduced ink transfer rate, etc. can cause blockage. Impurities mixed in the ink, such as scraper blades, undissolved ink residues, etc., can also cause blockage. It should be solved by filtering the ink. Now packaging When printing plastic films in color printing factories, most of the printing plates use electronic engraving plates. If the process of plate-making, the inner wall of the net hole may be naturally sheltered due to process and other reasons, chrome plating leaves surface defects or the dot is lost, and the printing is incomplete. . After unwinding the plastic film, it passes between the high-frequency voltage electrode rollers, and the discharge device impacts the plastic film to make the pores appear uneven on the surface. Through the magnifying glass, we can see the original dense, smooth surface becomes smooth Crude, the ink adhesion is enhanced, the affinity and compatibility of the ink layer and the substrate are also increased, and the freckles and poor reproduction of graphics and text also disappear. Most of the composite inks are printed with BOPP film. This type of ink is mainly based on chloropropylene resin. Chloropropylene is dissolved in esters, ketones and aromatic hydrocarbons. Toluene xylene is added, and some esters such as ethyl acetate are added for adjustment; The effect of printing speed: "The speed is too slow, which prolongs the volatilization time of the solvent in the ink, making the ink dry in the mesh easily. For printing plates with dots, this phenomenon is more common, and the ink scraping can be shortened according to the actual situation. The distance between the ink scraping point and the imprinting point of the knife. Add a slow drying agent to the ink or increase the printing speed appropriately. It should be noted that when the downtime is long, it is best to raise the doctor blade to let the plate cylinder Run at low speed in the ink tank to prevent the ink from drying out on the plate surface. Once the blockage phenomenon occurs, the plate should be washed with decontamination powder. If the printing is completed, the plate must be cleaned with a solvent and coated with a blanket of protective oil. , Effectively placed in a dry place to avoid blocking the next printing. If dust or foreign objects adhere to the surface of the impression cylinder, they often appear as grainy freckles in the picture and text, and the open spaces of freckles stick to the foreign objects. The situation is consistent. In addition, if the infrared spectroscopy is used to measure the spark-treated material, it can be found that there are carboxyl groups. If the film made of additives is added during the printing process, the additive department and the bleed out easily form on the film surface. An oily layer. Most of them are non-polar materials, with dense, smooth surfaces and an inert surface.
The function of the squeegee is to scrape the ink away from the mesh, so that the ink in the mesh is clean and evenly printed on the substrate. Because it is under great pressure during printing and is corroded by solvent for a long time, the surface is easily swelled, aging or abraded.
Environmental factors are very important. The temperature of the printing workshop should be 21 ℃ ~ 23 ℃, and the relative temperature should be below 60%. If the ambient temperature is too high and the solvent volatilizes quickly, causing blockage, it should be adapted to add a slow drying agent and speed up the machine. Nylon NY is most susceptible to static electricity during printing, causing freckles to appear on the printed matter.
When plastic film is printed with dot products, the reproducibility of the printed layer is poor, usually with small freckles freckles, mainly due to the shallow cell depth of the dot department, the transferability of the ink is poor, and the ink is easily dried in the cell , It is difficult to truly reflect the tone level of the pattern. Therefore, as long as the surface energy of the substrate is only 738 dynes, its inking condition and adhesion fastness have been significantly improved.
Adverse effects of plastic film surface tension
Poor performance of the ink and the impact of printing plate quality issues. During printing, the pressure of the doctor blade and the angle of the doctor blade are determined according to the depth of the graphic and the ink application of the printed product. The surface energy is relatively low, such as polyethylene is only 2.9 ~ 3.0 × 10-6J / C, the surface energy is low, the transfer rate of the ink is not ideal, the surface is smooth, there is no capillary pores, the ink layer is not easy to fix or the fixation is not strong. After one color is printed, it is easily glued off by the ink of the next color overprint, which makes the pattern and text incomplete and causes defects. If printing a gradation plate, the angle of the doctor blade is extremely important. If the angle is too large and the pressure is too high, it will easily cause printed dots, incomplete printing of text lines, and plate wear. The angle of the doctor blade is too large, and the ink on the plate If the scraping angle is too small, it will affect the depth of the ink layer, which will affect the hiding power of the ink. Generally, it is because the drying speed of the ink is too fast, the viscosity of the ink is high, or the printing speed is slow.
Other factors leading to inaccurate ink:
The fineness and smoothness of the surface of the impression cylinder are closely related to the fault of inking. Most of them can't be printed and are distributed in blocks. The solution is to replace the same type of impression cylinder. Therefore, the surface free energy of the plastic film needs to be improved. The most commonly used method is corona treatment. Cracks or tiny pits appear on the surface, and the pattern department that is in contact with the defect position will not be inked during printing, resulting in incomplete graphics, especially when the printing plate is a layered version, and the depth of the mesh is extremely shallow .
Ink drying on the surface of the printing plate is one of the main reasons for blocking the plate.
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