Prevention of electrostatic in paint production

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publisher: ALPTEC

Issue Time: Aug 15,2020

Summary

This article describes the generation and harm of static electricity in paint production.

Prevention of electrostatic in paint production

In recent years, people have done more research on the phenomenon of static electricity, the use of static electricity and the harm of static electricity. As the use of static electricity, the can-making process in the paint industry has adopted the electrostatic spraying process, and other industries have many applications such as electrostatic dust prevention, electrostatic flocking, and electrostatic copying. However, with the development of paint production, people pay more and more attention to the hazards of static electricity. A large number of flammable solvents and organic powders are used in paint production. The existing production sites are crowded and the production equipment is not closed. Once the static electricity generated in the production process accumulates to a certain strength, it will cause many harms. In the past, due to our lack of understanding of the hazards of static electricity, the factors that generate static electricity and the methods of elimination have not been fully grasped, so accidents caused by static electricity in the coating industry, especially fire accidents, continue to occur. We must fully understand the hazards of static electricity, master the safety measures and technologies to eliminate static electricity, and do a good job in the safety of paint production.

Friction can generate static electricity. When two substances continue to rub, one substance transfers electrons to the other substance to be positively charged, and the other substance gets electrons to be negatively charged, generating static electricity. However, the amount of electrostatic charge carried by a substance is not only determined by the generation of static electricity, but also by the dissipation of static electricity. If there are sufficient dissipation conditions, even if the static charge is generated, it cannot be accumulated. The resistivity of a substance is an important factor that determines the dissipation and accumulation of static electricity. It can be seen from experiments that even if a substance with a resistivity between 10⁶-10⁸ ohm·cm accumulates static charges, it can dissipate instantly without causing any harm; substances with a resistivity between 10⁹-10¹⁰ ohm·cm usually have little charge. ; The material with resistivity in 10¹¹-10¹⁵ ohm·cm is easy to be charged with static electricity but not easy to dissipate, so it will accumulate static electricity, which is the key object of anti-static work. When the resistivity is greater than 10¹⁵ ohm·cm the object is not easy to generate static electricity when it is centimeters. But once it is charged with static electricity, it is difficult to eliminate it. Most of the main raw materials used in the paint industry have a resistivity between 10-10 ohms, which is easier to generate and accumulate static charges, as shown in Figure 2-4:

Name	Resistivity ohm·cm	Name	Resistivity ohm·cm
Benzene	1.6*10¹³-10¹⁴	Alkyd resin	10¹¹-10¹³
Toluene	1.110¹²-2.710¹³	Melamine resin	10¹²-10¹⁴
Xylene	2.410¹²-310¹³	Chlorinated rubber	10¹³-10¹⁵
Nitrocellulose	1*10¹³	Gasoline	10¹²-10¹⁴
Phenolic Resin	10¹²-10¹⁴	polyester resin	10¹²-10¹⁵

In the paint production process, the biggest hazards caused by static electricity are explosions and fires. Although the amount of static electricity is not large, because of its high voltage, it is prone to discharge and electrostatic sparks. Therefore, in workplaces with flammable liquids, static sparks may cause fires;

In places with explosive gas mixtures or explosive fiber mixtures, an explosion may be caused by static sparks.

There are the following situations in places prone to static electricity fire accidents during the paint production process.

When using pipes to transport solvents and resins with resistivity in 10¹¹-10¹⁵ ohm·cm, especially when using plastic pipes such as polyethylene, static electricity is more likely to occur. Experiments show that when using polyethylene plastic pipe to transport toluene, the static voltage can be measured as high as 25,000 volts.

For example, a paint factory used a plastic tube to pump toluene from a 53-gallon iron bucket to a storage tank. The first bucket was pumped smoothly. Then, about two-thirds of the second bucket was pumped, an explosion occurred and caused a fire. An operator died. The reason is that when the plastic pipe transports toluene, it rubs with toluene to generate static electricity, and the discharge spark ignites the toluene vapor and causes a fire.

When pouring a solvent with a resistivity of 10⁷-10¹¹ ohm·cm, if the solvent has a strong impact with the container, or the scouring splash will generate static electricity.For example, a paint factory uses an oil tank truck to load and unload the fuel oil for the boiler. The tank truck stops at the entrance of the oil storage tank, inserts the oil drain hose into the oil inlet of the oil storage tank, opens the cut-off door and the upper cover of the tank truck tank, and starts unloading. After working for about a minute, there was a sudden explosion with a loud noise, which caused a fire. The reason is that the position of the oil pipeline is too high, as much as 3 meters from the oil surface, and the oil directly impacts the liquid surface in the tank to generate static electricity. The tank car body, the tank and the oil discharge hose and other oil unloading facilities have no conductive grounding device, and the static charge cannot release, generated electrostatic discharge sparks causing oil vapor deflagration.