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In general, in gravure printing, only 1/ to 2/3 of the ink in the substrate of the printing plate is transferred to the surface of the printing material, resulting in the freckles of the printing product:
Plate blocked version caused false ink failure
The most commonly used flexible packaging polyethylene, polypropylene, etc.; abbreviations: PE, PP, PVC, PS, PVA, PC, PET, CA, NY and so on. The surface of the impression cylinder is made of rubber or polyurethane. Therefore, we should pay attention to the actual printing: ink viscosity control is extremely important, if the viscosity is too high, the solvent content of the ink is relatively small, more volatile and the ink dry in the layout, it is necessary to properly reduce the viscosity of the ink; ink Drying too fast, easy to produce blockage, slow drying agent can be properly used to adjust the ink drying speed.
Inaccurate ink inscription is related to aging, wear, and slippage of the surface of the impression cylinder:
Ink pigment particles are large or have not been fully dissolved, the storage period of the ink is too long to cause deterioration, the solvent balance changes, and the ink solubility decreases. Different types of inks are used improperly to cause chemical reactions. Ink layer coatings or other adhesives are not easily bonded on the surface of such films. Poor flowability, reduced ink transfer rate, etc. will all result in blockages. Immersion of impurities in the ink, such as the scraper blade, undissolved ink residue, etc., will also result in blockage, which should be solved by filtering the ink. Most of the printing plates used in the printing of plastic films are electronic engraving plates. If plate-making processes are performed, the inside walls of the cell walls may be eroded due to the process and other reasons, and chrome plating may leave surface defects or network dots missing. Printing may be incomplete. . After the plastic film is unwound, it passes through the high-frequency voltage between the electrode rollers, and discharges the impact of the plastic film on the discharge device, causing the surface to have pores that are uneven. Through the magnifying glass, we can see the original compactness, and the smooth surface becomes smooth. Roughness, increased ink adhesion, increased affinity and compatibility of the ink layer with the substrate, and disappearance of freckles and poor reproduction of images and texts. Among the composite inks, the majority of BOPP films are printed. This type of ink is mainly composed of chlorinated acrylic resin, chloropropane dissolved in esters, ketones, and aromatics. Toluene xylene is the main component, and the addition of sector esters, such as ethyl acetate, etc. The effect of printing speed: “The speed is too slow, prolongs the solvent evaporation time in the ink, so that the ink can be easily dried in the cell. For printing plates with dots, this phenomenon is more common and the ink can be shortened according to the actual situation. The interval between the ink scraping point and the nip point of the knife is to add slow-drying agent to the ink or to appropriately increase the printing speed. It should be noted that when the half-way down time is long, it is better to raise the squeegee and let the plate cylinder Run in low speed in the ink tank to prevent the ink from drying on the plate. Once the plate jamming occurs, use the decontamination powder to wash the plate. If printing is completed, the plate must be scrubbed with solvent and coated with protective oil. ,Effective ventilation drying place, in order to avoid the next printing plate blocking phenomenon.If the surface of the impression roller attached to dust or foreign matter in the graphics often appear as granular freckles, freckles in the open space and foreign objects attached to the sticky In addition, if infrared spectroscopy is used to measure the point-spark treated material, the presence of carboxyl groups can be found, and if the film made by incorporation of additives is added during the printing process, the additive department will easily seep out and form on the surface of the film. A layer of oily layer, mostly non-polar materials, the surface is dense, smooth, is an inert surface.
The role of the squeegee is to scrape off the ink at the cells, clean the ink in the cells, and print them on the substrate. Because the printing is under great pressure, and the solvent is corroded for a long time, the surface is likely to swell, deteriorate or wear out.
The environmental factors are very important. The temperature of the printing shop should be 21°C～23°C, the relative temperature should be less than 60%, the ambient temperature is too high, the solvent volatilizes quickly, and the plate is blocked. The slow drying agent should be added and the machine speed should be increased. Nylon NY is most likely to produce static electricity when printed, causing freckles to appear on printed products.
When the plastic film is printed with a dot product, the reproducibility of the print layer is poor, and small fringe-like freckles usually appear. This is mainly due to the shallow depth of the dot network in the dot printing department, the poor transferability of the ink, and the ink is easily dried in the net It is difficult to truly reflect the tone of the pattern. Therefore, as long as the substrate surface energy as long as 738 dyne, the ink situation and the attachment fastness are significantly improved.
Plastic film surface tension adverse effects
The poor function of ink and the influence of printing plate quality problems. When printing, the pressure of the squeegee and the size of the squeegee angle are determined in detail according to the depth of the printing plate graphic and the ink situation of the printing product. Relatively low surface energy, such as polyethylene is only 2.9 ~ 3.0 × 10-6J / C, the surface energy is low, the ink transfer rate is not ideal, the surface is smooth, there are no pores, the ink layer is not easy to fix or not firmly fixed, the first After one color is printed, it is easily stuck by the ink of the next color overprinting, so that the pattern and the text are incomplete, causing defects. If the printing of the gradation version, the squeegee angle is extremely important, the angle is too large, the pressure is too high, it easily causes the printing product outlets, the text line printing is incomplete, the printing plate is worn, the angle of the squeegee is too large, the ink on the printing plate The scraping is not clean, and the squeegee angle is too small to affect the depth of the ink layer, thereby affecting the hiding power of the ink. Generally, it is caused by the fact that the ink is dried fast, the viscosity of the ink is high, or the printing speed is slow.
Other factors that led to ink misrepresentation:
The fineness of the surface of the embossing cylinder, the smoothness and the inaccuracy of the ink-printing are closely related. Most of them cannot be printed and they 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 the corona treatment method. Surface cracks or tiny pits, the printing department in contact with the location of the defect will not be inked, resulting in graphic defects, especially when the printing plate is a layered version, and the most extreme when the depth of the cell site is extremely shallow .
The drying of ink on the surface of the plate is one of the main reasons for blockage.
Ink unevenness of plastic ink
The ink dries on the surface of the plate. In addition to the use of static eliminators, physical methods can be used to adjust, such as the temperature and humidity in the press room. This is also the root cause of the ink's inaccurate ink.