Common Problems and Solutions in Curved Surface offset printing

The ink of the curved surface offset printing machine has poor adhesion to the substrate

1.1 Ink Adhesion Mechanism Wetting: The adhesion strength is the result of the intermolecular force interaction between the printing substrate film and the ink binder.

Compatibility: The polarity of the ink's binder is similar to that of the substrate, ensuring good compatibility. Be sure to choose ink that matches the printed matter.

1.2 Causes and Countermeasures of Poor Bonding: Substrate factors.

a. The surface corona treatment of the base material is insufficient, failing to meet the required tension, or the surface tension of the treated base material decreases due to poor storage environment or long storage time, thus resulting in failure.

Generally, the surface tension of PP and PE should be ≥38mN/m, that of PET should be ≥50mN/m, and that of NY should be ≥52mN/m. The surface tension of each batch of film should be checked before use.

During the processing of the base material, certain lubricants, antistatic agents, moisture-proof agents, etc. are added more often. Over time, these additives gradually penetrate from the film to the surface, forming a weak interface layer on the film surface, thereby affecting the adhesion of the ink. Therefore, the film should be used within its validity period and its surface tension should be tested before use. It can be tested with a Danone pen. Substrate factor: The factor of moisture absorption by the substrate. For instance, materials such as PA, PVA, and PT tend to absorb moisture, reducing their adhesion. Such substrates should be stored under good conditions (temperature and humidity control) and fully preheated before use. The wrong ink was used, and different inks were mixed together.

There are many types of inks for curved surface offset printing machines, including surface printing inks and internal printing inks. Different materials require different inks. All kinds of special inks must be used accordingly. Otherwise, the adhesion will not be strong enough. The operation process manual should be checked before production. Ink whitening. The deterioration and whitening of the ink lead to a significant decrease in adhesion. The ink is not dry enough. Insufficient drying will result in a large amount of solvent remaining inside. In addition, a certain drying temperature is extremely beneficial for enhancing the adhesion of certain resin adhesives.


2. Overprinting error

Overprint errors are the most common defects in printing. The phenomenon is that during the multi-color registration process, each color cannot completely overlap and there is a certain deviation.

2.1 Personnel Quality: Due to the objective existence of color registration errors, it is required that employees possess extremely strong working capabilities. Printing is a meticulous job that requires dedication, attention to detail and a sense of responsibility. At work, one should conduct self-examination and self-inspection, observe from multiple perspectives, and promptly identify problems.

2.2 Factors of Curved surface Offset Printing Machine: The precision and performance of the entire equipment, the tension control during registration, the heating and air supply system, the coordination of the impression rubber roller, plate roller, plate shaft, guide roller and other systems, these factors determine the temperature, pressure, parallelism, elongation, winding, etc. during registration. In addition, the color registration system itself further limits its accuracy. The color-matching photoelectric device should be well maintained and operated correctly. For instance, if the light emitted by the halogen light source is weak, the optical fiber or halogen bulb should be replaced. The distance between the mirror and the scanning head should be adjusted correctly, generally around 8mm. If the addition of the printing plate roller is inappropriate, it is easy to cause inaccurate longitudinal color matching, rubber deformation of the impression roller and insufficient elasticity. Keep the pressure roller in good condition.

2.3 The tension of the substrate was set unreasonably during operation. If the tension is too small, the base material will loosen, and the color matching in both the longitudinal and transverse directions will be inaccurate. If the tension is too high, the base material will contract laterally and the longitudinal color matching will be unstable. Adjust the tension accordingly. The temperature is not appropriate, especially the oven temperature is too high and the temperature of the cooling roller is too high, which causes the film to deform. For films that are not very flat, the temperature of the preheating box should be appropriately increased. The imbalance of the intake and exhaust air volumes inside the oven causes the film to shake inside the oven. Anemometers should be used to measure and control the intake and exhaust air volumes. If the printing plate roller is not installed correctly, such as eccentricity, it should not cause instability.