Static electricity is caused by the following:
- They contact each other and then separate (including friction, traveling over rollers, etc.)
- Heat quickly changed (e.g., material going through an oven)
- High-energy radiation, such as UV, X-rays, and strong electric fields (not very common in the industry)
- Cutting the action (e.g., a slitter or sheet cutter)
- Induction is the process of getting to know someone better (standing in the electric field generated by a static charge)
- Getting in touch and getting apart
A common cause of static in industries where film and paper are being processed is when people contact each other and break apart. In this case, it happens when material unwinds or goes over a roller. An analogy with a plate capacitor can help you understand how this process works: When moving a capacitor’s plates, you use mechanical energy to drive them apart.
This energy is then turned into electricity. An imbalance is caused by a small charge moving from the material to the roller. As the fabric comes off the roller, the voltage gets more extensive, like the plates of a capacitor that separate them.
The size of the voltage that comes out in practice is limited by the break strength of the materials around it, surface conduction, and other factors. You may hear small crackles, or static discharges, as the material comes out of the roller and moves away from it. Static electricity has reached a point where the air around it can’t break it down.
In theory, a static charge can be shown by a simple electric circuit:
- Like a battery, C is like a capacitor. It stores the charge like that. Most of the time, it’s the material’s surface or product.
- In this case, R is the charge relaxation ability of the material or system. This is usually a small amount of current flow. If the material is conductive, the charge will go to the ground and not be a big deal. There’s no way for the cost to get out, so it could be a problem.
- It’s called the Spark. The gap is the point at which voltage can’t build up.
- The charging current is the charge made when a product moves over a roller or something else.
- When the charging current comes through, it charges the capacitor (the product), increasing its voltage V. As the voltage goes up, more current flows through the resistor R. It will come to a point where the charging current is equal to the current that flows through the resistor simultaneously.
- Ohm’s Law comes in: voltage = current x resistance.
- When the product can store a lot of charges, and there is a lot of voltage around, a static problem needs to be solved. There will be a spark, electrostatic repulsion/attraction, or shocks to the people who work on the machine.
The static charge can be positive or negative, but it can’t be both at once. There isn’t usually a lot of difference in the polarity of the cost when you use an AC static eliminator or a passive discharger (brush).
Rapid Change in the Heat
Some materials can make static when they get hot or cold. Pyroelectricity is the term for this. On the other hand, plastic moldings are more likely to get a static charge as they cool down after molding or other heat treatment. Plastic is not electrically stable until it is at least a little bit cold. 40o to 50o C is a good range for electrical stability.
A lot of energy is emitted
Exposure to UV, X-rays or strong electric fields can cause static electricity to build up. This isn’t very common in the workplace, but it can happen. Plastic films that have been treated with Corona to make them easier to print will often have too much static electricity.
Cutting the Action
A static charge will be made when cutting, splitting, and trimming sheets of paper. This might not be a big deal on a single sheet, but when many sheets or components are stacked, the “battery effect” can cause a lot of static electricity.
Wearing insulative shoes, a person who works with static can stand near a process that generates static, then move away and touch an earthed object. They may feel a little tingly but are usually safe. This can be dangerous, not because of the electric shock itself, but because of the uncontrolled “recoil” reaction of the person who is using the machine.
Static electricity has what purpose?
All this is interesting, but what can it be used for? You can’t make toast with a lightning bolt, and you can’t charge your cell phone by rubbing its case on your sweater, either. Initially, you might think that static electricity is one of those exciting but ultimately useless science pieces that have no use in the real world. But you’d be wrong: static electricity is used in much everyday technology.
Laser printers and photocopiers utilize static electricity to make up ink on a drum and then move it to paper, like a copy machine. Static electricity is also used in crop spraying. It helps herbicides stick to the leaves of plants and spread evenly over the leaves. They use a similar trick to make sure paint droplets are attracted to metal car bodies and not the machinery around them.
Electricity from static electricity is used in many power plants and chemical factories to get rid of pollutants in the air (read more in our article on electrostatic smoke precipitators). Static electricity can indeed be wrong, but it’s also good. There are places where it can start fires and explode, and if you’re working with electronic parts, it can be a real pain.
Engineers and chemists have created all kinds of anti-static technologies, from easy wires to clever, slightly conducting paints and coatings, to keep static from building up in important places. We know that someone is trying to find a new way to use static electricity or stop it from doing bad things while you’re reading these words. In this case, static electricity isn’t moving, but it’s always moving!