Many companies experience problems with static plastic film and ask how they can make film anti-static. In view of this recurring request for help, we would like to provide some extra information about this.
What is static electricity?
Static electricity is the name given to the build-up of electrical charge on a surface of a poorly conductive material; electrically charged particles are absorbed or released, but because there is no room for an electrical current in the material, a voltage difference is created in the material itself, but also between the material and surrounding surfaces.
The charge in the material can be positive or negative. Positive charge is caused by a shortage of negatively charged particles (electrons), negative charge is caused by an excess of electrons.
The voltage difference that arises has a number of adverse consequences for you as a user. We will explain these in more detail later in this article.
When does static electricity arise?
Static electricity is a surface phenomenon and occurs as soon as two or more surfaces come into contact with each other and are separated again. This causes some kind of splitting, i.e. a transfer of negative electrons from one surface to another. The height of the charge (the field strength) depends on several factors: the material and its physical and electrical properties, temperature, humidity, pressure and speed of separation. The higher the pressure or the speed of separation, the higher the charge.
This charge can only flow away once contact is made with an otherwise charged surface (voltage difference). This can be metal, water, but also charged (ionized) air.
What makes plastic so vulnerable to the formation of static charge?
Most plastics (including polyethylene) are known for their poor conductivity. They have a high so-called surface resistance. The higher the resistance, the more energy is needed for an electron to get through. If the electron doesn’t have enough energy, it stays put and will only move when it finds a way out that offers less resistance.
There are materials with a much better conductivity. Copper is a good example. Such materials are used in electrical wires to create a good electrical current. Water (moisture) is also a material that conducts well. We can take advantage of this in some cases. We will come back to this later.
Whether a surface prefers to become positive or negative differs per material. Polyethylene typically becomes negatively charged, while air and our skin, for example, become more positively charged during electron exchange. The greater the difference in electrical preference, the easier the exchange of electrons, the faster the static charge will build up. Air currents in the process are therefore often the underestimated cause of the build-up of static charge. In daily life, the static charging of hair (+) while taking off a woolen sweater (-) is a well-known example. In winter this effect will be worse due to the low humidity. After all, water is a good conductor and (dry) air is not.
What is the result of static charge?
In principle, there should be no problems. Two poorly conductive surfaces come into contact with each other, exchange some electrons, get static charge, and separate again. As long as that situation would remain, it wouldn’t be a problem. However, the surfaces will probably come into contact with each other again or with another material.
With static charge, this basically works the same as with magnetism. Surfaces that have the same charge (- or ++) repel each other. Surfaces with different polarity (+/-) attract each other.
If one of the two materials conducts well, the electrical charge will dissipate when touched. When your skin comes into contact with a statically charged surface, it will emit an electric shock. After the shock, the voltage difference is gone and the static charge will be less.
Positively charged film can be seen as a kind of vacuum cleaner because of this attraction. It attracts all kinds of neutral or negatively charged materials with drift around in the environment. Think of dust particles, paper shreds, sawdust, etc..
Because static charge in foil can occur very locally, there can also be a voltage difference in the foil itself. This can be seen, for example, by sticking several successive layers of film on top of each other.
If you want to be sure whether a film has static charge, you can test this by blowing the layers apart. If the layers close again after blowing them open, you are probably dealing with static film. Another way is to gently rub the film with the back of your hand. If the little hairs are attracted by the foil, there is probably (some form of) static. There is also handy measuring equipment available to demonstrate this, so-called “electrostatic field meters”.
Problems caused by static film for you as a user
Static electricity is not only annoying because users of the foil can experience annoying electric shocks, it can also cause the following problems:
- Static film can attract dust or other dirt to the film, which can compromise food safety.
- Adverse consequences during the sealing process because dirt collects at the place where the seal will be applied.
- The film can stick together so it doesn’t open easily
- The film web will behave differently in the machine, or loose bags will not be guided properly in the machine.
- Unsafe situations in environments with flammable or explosive substances; e.g. ink or dust
- In addition, a lot of static electricity shortens the life span of expensive electronics on, for example, your packaging machines.
What factors influence static film?
- Air humidity;
Low humidity reduces conductivity. During the winter months, the air is often dry, which can lead to an increase in static charge.
- Friction in the production process;
Rollers in the machine that have become rough (dirty) or move less smoothly, can cause extra friction which will increase the static electricity.
- Air currents in the production process;
Air is an opposite of electrical charge. Air wants to become + and foil wants to become -.
- Temperature differences;
Temperature differences between production location and a colder storage location can result in static charging of the foil. That is why we always advise our customers to store the foil at the ambient temperature at least 24 hours in advance.
Corona treatment of the foil can affect the static charge.
How do I make supplied static film antistatic?
Removing static electricity by yourself, from film that has already been produced, is complicated. Customers could purchase ionization bars to blow electrical charge on the film during the production process. A simpler solution is to degrade the film. An earth wire can be held against the foil to conduct the electricity to earth by means of a metal object. A last, not exactly elegant way with ready-made bags is to hit a bundle of bags on the ground like a mat beater.
This type of emergency solution is not always effective and would not be necessary if the foil is delivered without tension.
How does KIVO prevent film from being static?
In the production process, we have installed various ionization beams that neutralize any build-up of static electricity in the foil. These beams are frequently maintained to guarantee operation.
In addition, we have nebulizers that ensure that the air humidity in the production location remains at an adequate level, safe and healthy. The correct air humidity ensures that the build-up of static electricity is limited.
In addition, additives can be used. These additives ensure that the surface resistance of the foil is reduced. A lower surface resistance ensures better conductivity of the electrical particles. This ultimately results in lower static training. The electrons need to remain in motion to avoid static charge.
Different types of additives
- Fast-acting antistatics;
Functional 24 hours after production because they migrate quickly to the surface of the film. These anti-statics only work at a certain humidity.
- Permanent anti-statics;
Have less tendency to migrate so that they function less quickly and less well in the short term but are functional for a longer time than the fast-acting anti-statics.
- “Carbon Black” anti-statics;
The advantage of these anti-statics is that it is not dependent on humidity. It does not migrate, it is in the foil and does not move to the surface. This is the best additive to combat static charge. These can be used in environments with an extremely high risk of explosion and fire. One disadvantage of this additive is that it is black in color, so aesthetically not an elegant solution. This additive is therefore only used when there is no other option.
Are these additives food safe?
The additives used within KIVO are food safe. These additives can be added to the recipe for extruding the film as required.
Questions regarding the prevention of static film?
Do you have any questions regarding this article or is static plastic film a problem for you and are you looking for a solution? Please feel free to contact one of our experts, they will be happy to talk to you.