1. Poor adhesion of ink on substrate
1.1 Ink adhesion mechanism Wetting:
Adhesion fastness is the result of the forced interaction between the printing substrate film and the ink connection material.
Compatibility:
The polarity of the ink connecting material and the substrate is similar, and the compatibility is good. (Be sure to choose an ink that matches the print).
1.2 Reasons for poor adhesion and related substrate factors:
A. The corona treatment degree of the substrate surface is not enough, and the tension is not reached, or the treated substrate surface is degraded due to poor storage environment and too long storage time, resulting in surface tension attenuation and failure.
General requirements PP, PE surface tension ≧38mN/m, PET≧50mN/m, NY≧52mN/m. The surface tension of each batch of film should be checked before use.
B. Most of the substrates add certain lubricants, antistatic agents, moisture-proof agents, etc., and these additives slowly penetrate from the film to the surface 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 measured before use. Test with a Dyne pen.
Substrate factor:
Substrate moisture absorption factor. 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 was used. Different types of ink were mixed.
There are many kinds of inks for concave printing, including surface printing and inner printing inks, different materials correspond to different inks, and 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:
Ink deterioration, whitening, the adhesion is extremely reduced. The ink is not dry enough. Insufficient drying, internal residual solvent, in addition, a certain drying temperature for some resin joint adhesion is very favorable.
2. Overprint error
Most of the overprinting errors are common defects in printing, the phenomenon is that in the multi*color overprinting process, each color can not completely overlap, there is a certain deviation.
2.1 Personnel factors:
Because the color error is an objective existence, employees are required to have strong working ability. Printing is a meticulous work, we must do hard, careful, responsible. When working, we should do a good job of self*examination, self*examination, multi*party observation, and timely detection of problems.
2.2 Equipment factors:
Accuracy and performance of the entire equipment, overprinting tension control, heating and air supply system, stamping rubber roller, plate roller, plate shaft, guide roller and other systems, these conditions determine the overprinting temperature, pressure, parallelism, elongation, winding, etc., and the color system itself is the limit of its accuracy. The color photoelectric device should be maintained and operated correctly. For example, 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 appropriate, easy to produce longitudinal miscoloration, rubber deformation of the imprinting roller, and insufficient elasticity. Keep the roller in good condition.
2.3 Operation process:
The base material tension setting is unreasonable, the tension is too small, the base material is relaxed, and the vertical and horizontal color registration is not allowed; If the tension is too large, the transverse shrinkage of the substrate and the longitudinal coloring are unstable, and the tension is adjusted accordingly. The temperature is not suitable, especially the oven temperature is too high, the cooling roller temperature is too high to deform the film, and the preheating box temperature should be appropriately increased for the film that is not too smooth. The inlet and exhaust air volume in the oven is not balanced, causing the film to shake in the oven. The inlet and exhaust air volume is measured by anemometer and controlled. Plate roller installation is not suitable, such as eccentricity, before the plate roller installation must scrub the ink on the plug.
3. The cause of scraper line marks:
No ink line marks. Mainly the ink mixed with hard inorganic impurities, such as sand, these hard particles embedded in the blade and caused line marks. Sometimes this type of scraper line marks are also dotted, and the appearance of this scraper line marks is easy to damage the printing and scraper.