Common problems and methods of printing
1. Poor adhesion of ink on substrate
1.1 Wetting of ink adhesion mechanism: The adhesion fastness is the result of the interaction between the printing substrate film and the ink binder material. Compatibility: The connection material of the ink and the base material have similar polarities and good compatibility. (Be sure to select the ink that matches the printed matter).
1.2 Reasons for poor adhesion and countermeasures for base material factors.
a. The corona treatment degree on the surface of the substrate is not enough, the required tension is not reached, or the treated substrate surface has a poor storage environment and the storage time is too long, causing the surface tension to decay and fail. Generally, the surface tension of PP and PE ≧ 38mN / m, PET ≧ 50mN / m, NY ≧ 52mN / m. Check the surface tension of each batch of membranes before use.
b. During the processing, most of the base materials are added with certain lubricants, antistatic agents, moisture-proof agents, etc. These additives slowly penetrate into the surface from the film over time, forming a weak interface layer on the surface of the film, affecting the ink Adhesion. Therefore, the film should be used within the validity period, and the surface tension should be checked before use. Available Dyne pen test. Substrate factor The factor of substrate moisture absorption. For example, PA, PVA, PT and other materials are easy to absorb moisture and reduce adhesion. Such substrates should be stored under good conditions (temperature and humidity control) and fully preheated before use. The wrong type of ink is used, and different types of ink are mixed. There are many types of ink for gravure printing, including surface printing and back printing inks. Different materials correspond to different inks. Various special inks must be used correspondingly, otherwise the adhesion fastness is not enough, and the operation process instructions should be checked before production. Ink whitening. Deterioration and whitening of the ink greatly reduce the adhesion. Ink drying is insufficient. Insufficient drying, there are many residual solvents inside, in addition, a certain drying temperature is extremely beneficial to improve the adhesion of some resin binders.
2. Overprint error
Overprint errors are mostly common defects in printing. The phenomenon is that during the multi-color overprint process, each color cannot completely overlap, and there is a certain deviation.
2.1 Personnel quality Because the color registration error exists objectively, it requires employees to have extremely strong work ability. Printing is a meticulous job, which must be done with care, care and responsibility. Self-inspection and self-inspection should be done during work, and observations should be made by multiple parties to find problems in time.
2.2 Equipment factors The accuracy and performance of the entire equipment, the tension control of the overprint, the heating air supply system, the cooperation of the imprinting rubber roller, plate roller, plate shaft, guide roller and other systems, these conditions determine the temperature, pressure, parallelism during overprinting Degree, elongation, winding, etc., and the color registration system itself limits its accuracy. Registered photoelectric devices should be maintained and operated correctly. For example, if the light source of the halogen light source is weak, the optical fiber or halogen bulb should be replaced, and the distance between the reflector and the scanning head is adjusted correctly, generally about 8mm. The increase of the plate roller is not suitable, and it is easy to produce longitudinal color registration inaccuracy, the rubber of the impression roller is deformed, and the elasticity is insufficient. Keep the pressure roller in good condition.
2.3 Operation process The tension setting of the substrate is unreasonable, the tension is too small, the substrate is slack, and the color registration in the vertical and horizontal directions is not accurate; if the tension is too large, the substrate shrinks laterally and the color registration in the vertical direction is unstable, and adjust the tension accordingly. The temperature is not suitable, especially if the temperature of the oven is too high, and the temperature of the cooling roller is too high to deform the film. For a film that is not flat, the temperature of the preheating box should be appropriately increased. The intake and exhaust air flow in the oven is unbalanced, which causes the film to shake in the oven. The anemometer should be used to measure the intake and exhaust air flow and control it. The plate roller is not installed properly. If eccentricity occurs, the ink on the plug must be wiped clean before the plate roller is installed.
3.1 Causes of scraper line marks ① No ink line marks. The main reason is that the ink is mixed with hard inorganic impurities, such as sand, etc. These hard particles are embedded in the blade edge of the scraper and cause line marks. Sometimes such scraper line marks are also dashed lines, and the appearance of such scraper line marks can easily damage the printing and the scraper.
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