January 28, 2020
Causes of electrostatic charging generation
Last week, we covered how static electricity is generated and by consequence electrostatic charging that can be damageable for manufacturers.
Static electricity is due to unbalanced quantity of electrons (-) and protons (+) in a material which can be caused by contact charging or friction charging. In both cases, the main principal is the transfer of the charges (+ or -) or charge separation in other words.
There are various effects that can cause the charge separation to occur.
Static electricity generation causes
There are various causes of electrostatic charging generation:
- the friction phenomenon when the film is wound by the roller,
- the peeling phenomenon such as peeling off the adhesive tape,
- the deformation or damage of the object,
- and the phenomenon related to charged particles.
Industrial production sites generate a lot of static electricity mainly due to repeated friction and peeling in various processes.
Today, we will cover 4 specific causes that can generate electrostatic charging in a production site:
- the triboelectric charging,
- the peeling electrification,
- the induction charging,
- and the polarization.
Triboelectric charging is a charging phenomenon that occurs when the contact surfaces are rubbed between insulators and conductors. The electrostatic charging occurs between the material after being rubbed together.
The charge amount is much larger than the contact charge. This is probably due to friction rubbing the surface irregularities and to the increased rubbed area. In other words, the friction surface is not always exactly at the same place, and in reality its position is slightly shifted. Therefore, the continuous increase of the rubbed area (contact area) will increase the charge.
In addition, it is possible that the contact surface may be renewed because of the deterioration of the surface due to aging during friction. As the temperature rises due to the destruction of the surface material during the friction, it also has a significant effect on the charging phenomenon.
During friction between objects, electrons, ions, and neutral molecules are released from the rubbed surface. This phenomenon is called “tripo mission”, and the electron discharge phenomenon lasts for a long time immediately after friction.
This friction charging phenomenon occurs between different substances, and no charge is generated between exactly the same substances.
Except if the same material has different sizes and the surfaces are charged by friction under different conditions (rough surface vs. smooth surface), which is called asymmetric friction.
As an example, this asymmetric friction can be seing when there are different size ice particles in the clouds causing electrostatic discharge, or lightning, due to friction.
A strong charging phenomenon occurs when the contacting object is peeled (separated). For example, when peeling off an adhesive tape or a protective film from a liquid crystal glass substrate.
This phenomenon is generally called “peeling charging” because it is charged by the peeling (separation) operation.
In this case, the higher the degree of adhesion, the higher the charge density, which generates a large electrostatic charging.
The amount of charge depends on the peeling speed:
- when the peeling speed is low, the amount of charge is small because a small amount of electrostatic discharge occurs continuously;
- when the peeling speed is high, the amount of charge increases because the electrostatic discharge is suppressed.
Induction charging is a phenomenon that occurs only when a substance is a conductor. When a charged material approaches a conductive material, the surface of the conductive material collects a polarity opposite to the charged polarity.
For example, when the charged body of the positive pole (+) approaches the conductor,
the electrons (-) in the conductor move, and the electric charge of the negative pole appears on the surface of the conductor on the charged side. And the positive pole appears on the opposite side.
This is due to the uniformity of the charge collected on the surface of the conductor. This state is called “induction.”
When the conductor is grounded in this state, the charge of the same polarity as the induced charged body is pushed out of the conductor and supplied or absorbed by the ground. And the conductor has only the opposite polarity to the charged body.
When the ground is removed and the two substances are separated, the conductor is charged to the opposite electrode of the charged body.
This is a phenomenon called “induction charging“.
When an insulator is brought closer to a charged substance or a voltage is applied across the electrodes, electrons cannot move because the insulator does not conduct electricity. And the alignement of molecules changes due to electric force.
In other words, one part of the object is charged to the + pole and the other part is charged to the – pole. Therefore, the charged state of the object is almost 0V.
This phenomenon is called “polarization“. In this case, it looks like an induction phenomenon. However, even if it is grounded, there is no movement of electrons and no charge is generated unlike the induction charging phenomenon.
How can IKEUCHI help?
As mentioned at the beginning, all these charging phenomenon can occur in a production site due to the interaction between workers, machines and end products. There is no “natural” way to prevent electrostatic charging to build up except by adding an external solution.
That is why we’ve studied the optimal solution to prevent electrostatic discharge (ESD) by adding humidity in working environment.
Contact one of our engineers to assess the optimal solution to prevent ESD in your production site.
Nina MONCEAUX – IKEUCHI EUROPE B.V.