In modern printing, flexo printing and gravure printing are mainly based on rotary printing; in many areas of offset printing, rotary printing is also the most important method. However, the web printing materials used for rotary printing are very likely to cause difficulties in printing due to the absorption of impurities such as dust, which leads to a decrease in the quality of the printed matter and increase the scrap rate.
How to effectively remove dust and other impurities
Since dust and other impurities are attached to the surface of the printing material by electrostatic adsorption, it is first necessary to eliminate the electric charge and cooperate with other corresponding measures in order to completely remove dust and other impurities and achieve the requirements of printing and other processing. After the printing material is treated with static electricity, it can avoid re-adsorption of dust and other impurities.
1, how to eliminate the electrostatic charge
The methods to eliminate electrostatic charges are:
(1) Directly transfer electrons away from printing materials;
(2) transfer electrons by contact with other materials;
(3) Transfer electrons by contact with ions in the surrounding air.
1). Transfer electrons directly from printing materials
In the environment with high humidity, the substrate is directly grounded, and the electrostatic charge on the substrate can disappear, making it no longer retain high charge, and meet the printing process requirements.
2). Transfer electrons by contact with other materials
Charges that have been ionized, similar to conductors tend to discharge from objects charging. In this case, the use of fiber brushes, the use of helium, neon and other low-level elements and radiation generated by the ions in the surrounding air, you can neutralize the electrostatic charge surface of the printing material, but this method is only used for certain special occasions. Under normal circumstances, the direct current or AC high voltage can be used to neutralize the electrostatic charge on the surface of the substrate to eliminate the electrostatic effect.
The commonly used method of eliminating static electricity is to eliminate static electricity by electrostatic sticks. The static bar consists of steel needles with very little distance between them. Place the electrostatic stick over the substrate and neutralize the electrostatic charge with a current generated by a very high ac voltage of 50Hz or 60Hz. Recently, DC pulse currents have also been used to neutralize electrostatic charges. The currents used are high-voltage bipolar pulsed currents. Different transmission frequencies, powers, and polar directions can be selected according to the desired neutralization electrostatic charge intensity and other characteristics.
The use of a constant DC current is also an effective method to control the electrostatic charge with a continuous DC current. This method is particularly suitable for high electrostatic charge and high-speed printing conditions.
Electrostatic generators are another technique that can be used not only to eliminate static electricity, but also to build an electrostatic field. This electrostatic field can be used in more industrial fields, making its production process more efficient.
3). Transfer electrons by contact with ions in the surrounding air
Ionized air can also be used to eliminate the charge. It is achieved by mechanically spraying the ionized air in the working environment on the surface of the printing material. This device is called a charge ionization eliminator. Various shapes of needles or rods can be used as electrodes, and the ionized air stream of strong air is blown toward the surface of the printing material through a nozzle in the shape of a gun mouth.
2, how to remove dust and other impurities
The printing materials have to achieve an acceptable level of printing, not only to eliminate the electrostatic charge on the surface, but also to remove all the dust and other impurities adsorbed on the surface. After the charge is eliminated, the adsorption capacity of the printing material to dust can disappear immediately, and the dust in the surrounding environment can be prevented from being adsorbed again. However, this does not mean that the dust and other impurities that have been adsorbed on the surface have been removed, and therefore other measures must be used in conjunction with it. .
The easiest way is to remove the electrostatic charge and then use a brush to clean it. However, this method can only remove large particles and incomplete removal.
A more effective method is to use an ultrasonic generator to generate a strong compressed air flow. Through the same width as the paper roll web and very close to the nozzle of the paper roll, the compressed air is blown to the surface of the printing material to produce an air knife-like effect to sweep the dust. . Its function is like a vacuum cleaner, dust will not return to the surface of printing materials. Although the nozzles of different brands have different geometrical profiles, they all use their own proprietary technology to make the air flow reach a very high speed. Some nozzles can generate airflow speeds of more than 560 kilometers per hour, which can effectively remove the adherence. Dust particles on the surface of the printing material.
In addition to the above-mentioned method of removing dust particles by a strong compressed air flow, there are still methods for removing particles using a tape, and the apparatus adopted by this method has a simple structure and is easy to install.