Dust needs to be strictly controlled in the hottes

2022-10-22
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Dust needs to be strictly controlled in printing

in modern printing, whether flexo printing or gravure printing, it is mainly rotary printing; In many areas of offset printing, rotary printing is also the most important way. However, the drum printing material used in rotary printing is easy to cause printing difficulties due to the adsorption of impurities such as dust, which leads to the decline of print quality and increase the scrap rate

I. The Influence of impurities such as dust on Printing

during the production or stacking of barrel paper or roll plastic film, a lot of electrostatic charges will be accumulated due to friction, resulting in high or even very high electrostatic voltage. When putting the drum printing material on the printing machine and people touch the unwinding roller, the human body may become a cathode (grounding electrode) to discharge the printing material to the ground. This discharge voltage can be as high as 20000 volts, making people suffer unimaginable shocks. Fortunately, although this voltage is very high, the power and current intensity are very low, otherwise it will kill people in an instant

although this electrostatic charge is not fatal to people, it will adsorb the dust in the surrounding environment, packaging materials, fibers on clothes, hair, micro organisms, residual ink particles, etc. to the surface of printing materials, causing difficulties in the production of printing, compounding, polishing and other processes

after contacting with the plate cylinder, impurities such as dust will be transferred to the plate cylinder and adhered to the plate cylinder, which will damage the ink transfer performance of the plate. In order to remove the dust attached to the plate cylinder, the operator had to stop the machine for cleaning. If there are many impurities such as dust attached to the printing material, it often needs to be cleaned in less than half an hour. Cleaning the printing plate cylinder will not only prolong the printing production time and cause the loss of production efficiency, but also have a period of adaptation process after each cleaning and restart printing, which inevitably leads to the loss of some printing materials over time, and the resulting loss is also considerable

how to deal with this kind of problem correctly, relevant experts suggest that we should pay enough attention to the following aspects

1. Dust removal of paper and paperboard

dust and other impurities may come from papermaking, slitting, die cutting, slotting, envelope windowing process and napkin production line, so they must be completely removed, otherwise it will affect the quality of printing products and reduce production efficiency

2. Plastic film and metal foil in addition to static electricity

plastic film and metal foil are relatively easy to generate static electricity, so before printing processing, it is necessary to do a good job of dust removal and cleaning, so as to minimize the "specified proportion limit" of printing, which is the stress value when a very small amount of plastic deformation (0.001 ~ 0.01%), brush the additional auxiliary time in production, such as shutdown and cleaning, and improve the production efficiency, At the same time, it is also to try to avoid customer rejection caused by product quality problems

3. Cleaning of food and drug packaging bags before forming

food and drug packaging bags should be made into packaging bags through heat sealing processing, and the thermoformed packaging materials must be absolutely clean before forming. The cleanliness of materials used for vacuum packaging must meet the quality standard

4. Dust removal before polishing

whether you polish paper, plastic film or metal foil, you should first remove dust. Dust and other impurities attached to the substrate will greatly affect the glazing quality

II. How to effectively remove dust and other impurities

because dust and other impurities are attached to the surface of printing materials by electrostatic adsorption, it is necessary to eliminate the charge first and take other corresponding measures in order to completely remove dust and other impurities and meet the requirements of printing and other processing. After electrostatic treatment, the printing material can avoid absorbing dust and other impurities again

1. How to eliminate electrostatic charge

the methods to eliminate electrostatic charge are:

(1) transfer electrons directly from the printing material

(2) transfer electrons through contact with other materials

(3) transfer electrons by contacting ions in the surrounding air

1. Transfer electrons directly from the printing material

in a high humidity environment, directly ground the printing material, and the electrostatic charge on the printing material can disappear, so that it no longer retains high charge, which meets the requirements of the printing process

2. Transfer the ionized charge of electrons through contact with other materials, which is similar to the tendency of conductors to charge and discharge objects. In this case, using a fiber brush, using polonium, iridium and other low-energy elements to produce radiation with the ions in the surrounding air, you can neutralize the static charge on the surface of the printing material 2. Precautions for the installation of plastic tensile machine, but this method is only used in some special occasions. Usually, DC or AC high 16 can be used. Electromechanical power: 5.5kW, 3 ф 380V voltage to neutralize the electrostatic charge on the surface of the substrate to eliminate the electrostatic effect

the usual method of eliminating static electricity is to eliminate static electricity with an electrostatic rod. The electrostatic rod is composed of steel needles, and the distance between the two needles is very small. Place the electrostatic rod above the substrate and neutralize the electrostatic charge with the current generated by the extremely high AC voltage of 50Hz or 60Hz. Recently, DC pulse current has been used to neutralize electrostatic charges. The current used is high-voltage bipolar pulse current. Different emission frequencies, powers and polarizations can be selected according to the electrostatic charge intensity and other characteristics required to neutralize

constant DC current is also an effective method to control electrostatic charge with continuous DC current, which is especially suitable for high electrostatic charge and high-speed printing

electrostatic generator is another technology, which can be used not only to eliminate static electricity, but also to establish electrostatic field. This electrostatic field can be used in many industrial fields to make its production process more effective

3. The ionized air can also be used to eliminate charges by mechanically spraying the ionized air in the working environment on the surface of printing materials. This device is called charge ionization eliminator, which can use needles or rods of various shapes as electrodes, and the ionized air is blown to the surface of the printing material through a muzzle shaped nozzle

2. How to remove dust and other impurities

in order to achieve an acceptable level of printing, the printing material requires not only to eliminate the electrostatic charge on its surface, but also to remove all dust and other impurities adsorbed on the surface. After the charge is removed, the dust adsorption capacity of the printing material can disappear immediately, and the dust in the surrounding environment can be avoided from being adsorbed again. However, this does not mean that the dust and other impurities adsorbed on its surface have been removed, so other measures must be taken together

the easiest way is to clean with a brush immediately after eliminating the electrostatic charge. However, this method can only remove larger particles, which is not complete

the more effective method is to use the ultrasonic generator to generate a strong compressed air flow, and blow the compressed air to the surface of the printing material through the nozzle with the same width as the paper roll and very close to the paper roll, which produces a function similar to the air knife and sweeps away the dust. Its function is like a vacuum cleaner, and the dust will not return to the surface of the substrate. Although different brands of nozzles have different geometric contours, they all use their own patented technology to make the air flow reach a very high speed. The air flow speed generated by some nozzles can reach more than 560 kilometers per hour, which can effectively remove the dust particles attached to the surface of the substrate material

in addition to the above method of removing dust particles by strong compressed air flow, there is also the method of removing particles by tape. This method uses a device with simple structure and convenient installation

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