The harm, elimination and utilization of static electricity in printing and packaging

Regarding static electricity, I believe that everyone is not unfamiliar. Static electricity is often generated in our production. Some people disagree with this, thinking that this is only a slight amount of electricity and will not play a role in printing and packaging. The idea of ​​this paralysis is wrong. When a certain amount of static electricity is relative to a certain concentration of flammable gas, the occurrence of fire is unavoidable, so understanding the static electricity is very necessary.

Today we will discuss static electricity.

First, the harm of static electricity

1. Affect product print quality

The first is the surface of the substrate charged, such as paper, polyethylene, polypropylene, cellophane, etc., which will absorb paper dust or a large amount of dust, impurities, etc. that are filled in the air, thereby affecting the transfer of the ink, reducing the ink transfer rate, in the print There are "flowers", acupunctures, or small white spots on the upper hand, or due to mutual repulsion, the winding and slipping are uneven. Electrostatic discharge can also damage the surface coating of materials, affecting the quality of the product.

Followed by the ink charge. This often occurs when the ink is at a lower viscosity, or when the antistatic component of the ink is not enough. If it is discharged on the move, it may appear on the prints "static ink spots", 'looks like the ink's poor fluidity, ink is very uneven, like this often occurs in the level of thin printing Happening. But sometimes it also appears in the white version of the field, and it also shows another phenomenon - exclusion. Originally, white ink was the foundation, but when some text layouts were encountered (most of them were black ink), a gap was formed around these words. The main reason is that the quality of white ink is not good, and then the viscosity is too small. If the charged ink is discharged at the edge of the line on the print, "black whiskers" may appear here. This happens mostly in the field version. In addition, the ink can also be formed as a result of the charged version of the fog, resulting in serious pollution of the printed matter and the printing environment.

Static electricity often also strikes the operator's body, especially the fingers, causing operator misoperation and printing problems that should not occur.

2. Affect production safety

A charged substrate may even cause an air discharge due to an excessively high potential in severe cases, resulting in electric shock or fire. Charged ink may cause the ink, solvent to catch fire, or shock personnel through the ink. Many components in high-speed printing presses generate large amounts of static electricity due to strong friction during high-speed operation. In old-fashioned web rotary presses with imperfectly discharged devices, the voltage at some locations on the machine may sometimes reach as high as 15,000 V at high speeds. The current is also about 100~A. The influence of such a powerful voltage and current on the printing process is intricate and the hazard is quite serious, especially the direct threat to the personal safety of the operator.

Second, the elimination of static electricity

Understand the harm of static electricity, then how can we effectively eliminate it? Here are some effective ways to eliminate static electricity.

1. Grounding

This is the easiest way to eliminate static electricity. That is, the metal conductor is connected to the ground to make it equal to the earth, and the charge leaks through the earth. However, this method has almost no effect on the insulator. If there are two printers adjacent, although they each have a wire grounded, because of the difference in the degree of charge leakage, there is still a potential difference between them, and in order to avoid discharging each other, they must be connected by wires.

2. Control the relative humidity

This is a simple and effective way. The surface resistance decreases as the relative humidity of the air increases. Therefore, by increasing the relative humidity of the air, the conductivity of the surface of the paper can be increased, and the leakage of charge can be accelerated. In the printing shop, the temperature is around 25~C and the relative humidity is about 65%. Therefore, sprinkle some water in the printing environment, if necessary, use an air humidifier, and pay attention to wipe the ground, which can effectively eliminate static electricity.

3. Adjust ink viscosity

Increasing the viscosity of the ink can also effectively reduce (eliminate) static electricity in the ink and improve printing quality.

4. Add antistatic agent or isopropyl alcohol to the ink

It is best to use antistatic agents, because adding more isopropanol will cause the ink to “anti-slag”. Many books introduce that the amount of isopropyl alcohol added is not more than 2%, but according to practice, it must be far more than this amount. Will have effect.

Third, the use of static electricity

The above is about electrostatic hazards. In fact, things have both advantages and disadvantages, and they have two relative aspects. Static electricity also has its place to contribute. Let us list one or two below.

Comparing gravure printing with letterpress printing and lithographic printing, there is more ink left in the print and graphics. Large printing pressure must be applied to transfer the ink in the ink hole to the surface of the printing material. The letterpress printers and lithographic printers have large loads. Despite the high printing pressure, the ink transfer rate is only about 60%. In order to increase the ink transfer rate of gravure printing, an electrostatic ink-absorbing device can be installed on the printing machine, and the printing ink can be sucked onto the substrate by means of electrostatic ink-absorption so that the ink transfer rate can be increased by 20%, and the machine is extended. The longevity of the printed matter has also made the reproduction of the subtle levels of the printed matter abundant, which has greatly improved the quality and grade of printed products.

The impression cylinder of the printing press is conductive. During printing, an electrostatic high-voltage generator is used to generate an electric field between the printing plate and the impression cylinder. The electric field attracts the ink in the printing ink hole of the printing plate onto the substrate by means of electrostatic attraction. This device, due to the presence of a high voltage electric field, can eliminate static electricity on the substrate, and overcome various printing failures caused by the electrostatic charge of the substrate.

IV. Safety precautions in production

Through all of the above, let us understand the harm and use of static electricity, let us understand the hidden dangers of static electricity in the safety of production. When the concentration of volatile organic solvents in the air is high, a strong electrostatic discharge can cause fire. Therefore, in order to prevent fire in the workshop, in addition to paying attention to the elimination of static electricity, another basic precaution is to reduce the concentration of organic solvents, volatiles, and other flammable substances in the air. Here we talk about how to control:

• Be careful not to spill solvents or ink. Be careful not to fill the ink tank or other containers too full.

· Spilled liquids must be cleaned in time. If you need to use organic solvents, you must choose a high fire point cleaning solvent.

• Keep only solvent and ink necessary for production in the work area and pack it in an airtight container. Wipes soaked with organic solvents should also be packed in closed containers.

• All printed parts, dryers, and dust on the floor should be regularly cleaned. Care should be taken to maintain good ventilation during the cleaning process.

The following measures will help prevent sparks from static electricity:

• Insulated shoes (sports shoes, rubber sole shoes) and synthetic fiber rags are prone to sparking and should be disabled. The floor on which people walk cannot be covered with plastic sheeting. Dry ink or other debris will become insulators, which will prevent the body's electrostatic discharge to the earth and should be removed.

• All containers or nozzles that come in and out of ink, solvents should be grounded and preferably interconnected directly.

• If the relative humidity in the operating room is equal to or higher than 50%, the conductivity of the substrate and the cement floor will be increased to reduce the generation of static electricity. The static eliminator must be installed in the correct position and kept clean to have the best effect.

V. Conclusion

Safety issues are particularly important during the printing process of the production process. Many accidents are actually caused by people's careless negligence. When we understand the process of static electricity generation, we can eliminate it from the source. Understand the harm of static electricity, we can cause more attention to it. In addition, the above-mentioned static elimination method also provides a reference for actual operation. It is believed that with sufficient knowledge, people will maintain a good awareness of safety hazards, and safety accidents will stay away from us.