The Antistatic Effect

It may have been some years ago, but can you still remember what happened when you slid down a plastic slide? Your hair flew around, and your synthetic shirt stuck to your skin. The cloth clings because of friction, when electrons are exchanged between the different materials: One becomes positively charged, one becomes negatively charged, and these opposite charges attract. A clingy shirt is the result.

In production processes with non-conductive powders or granules, we have that plastic slide effect too: When small particles are transported through plastic pipes, they may become electrostatically charged due to friction. The result is powders or granules that adhere to the walls of the pipes. Which leads to expensive production downtimes because all facilities need to be cleaned regularly.

To avoid these costs, many producers add an Evonik product called fumed alumina to their powders and granules. Fumed alumina has the ability to neutralize opposing charges so that powders and granules can flow properly without sticking to pipes, mixers, or pumps. This is what we call the antistatic effect.

But at Evonik we take the antistatic effect one step further: In a laser printer the pigment powder has to travel from the negative charged imaging drum to the positive charged piece of paper. For this difficile transfer process, the color pigments need to have a precise charge profile. Guess what’s used to adjust the charge of the toner exactly so that your laser printer can do its job: our fumed alumina products.

The antistatic effect is the stepsister of the free-flow effect that also enhances the production and handling of powders. Instead of fumed alumina, fumed silica is typically used for the free-flow effect. If that is what you are looking for, you will find answers here. 

Electrostatic charge due to triboelectricity occurs everywhere in your production, always ready to cause problems: Electrostatically charged powders and granules adhere to the walls of pipes, mixers, pumps, all sorts of containers, and everywhere else where they are not supposed to stick. But adding less than 0.1 % of our highly pure AEROXIDE® fumed alumina or AEROSIL® fumed silica neutralizes all the charge. Which, for your production, means:

• AEROXIDE® and AEROSIL® fumed silica help to avoid expensive downtimes.
• AEROXIDE® and AEROSIL® fumed silica enhance the processability of powders and granules and increase throughput.
• AEROXIDE® and AEROSIL® fumed silica enable precise dosage of powders.

But what is the science behind this antistatic effect? AEROXIDE® and AEROSIL® particles are much smaller than the particles of your host powder. They are distributed over the surface of your host powder where the tiny particles act as spacer to reduce friction and electrostatic charge. Additionally, fumed alumina has a positive surface charge that “neutralizes” the negative charge that most synthetic host powders tend to pick up when colliding with other particles, pipes, or the paddle of a mixer. And what works for powders works for granules as well.

A more advanced use of the antistatic effect is in laser printer toner. Here it is not only important to get rid of electrostatic charge but to achieve a stable and precise charge characteristic for transferring the pigments from the imaging drum to the paper. To reach the preferred polarity and melt temperature a combination of AEROXIDE® fumed alumina and AEROSIL® fumed silica may be recommended for both, mechanical and chemical toner. The toner surface will take on the characteristics of the silica and/or metal oxide which allows you to control the properties of your toner:

• enhanced powder flow
• minimized image background problems
• reduced sensitivity to relative humidity
• advanced storage and moisture stability
• precise tribo-charging
• easy cleaning of imaging drums

But how can you add the antistatic effect to your product? Simply by mixing. AEROXIDE® mixes well with all sorts of powders or granulates, a ploughshare, paddle, or belt mixer is usually perfectly adequate. So, in most cases no additional equipment is needed.

Our portfolio comprises aluminum oxides, titanium dioxides, and mixed oxides for all kinds of technical applications. All AEROXIDE® and AEROSIL® products are chemically stable so that they have a shelf life of two years or even longer. Just keep them in sealed containers, away from moisture or volatile organic compounds, and you will always have it to hand when you need it.

Precision and efficiency also help nature: Our highly pure metal oxides support you to avoid unnecessary waste in production, storage and usage. Here are some examples:

• Less loss in processing: Your product will not be affected by electrostatic charge, which means that less material will “die” in pipes, mixers, or containers.
• Less loss in storage: Our fumed metal oxides also enhance the storage stability of your products. So, less material has to be dumped due to decay.
• Less loss in usage: AEROXIDE® and AEROSIL® enable a more precise dosage of your product which also helps to prevent unwanted wastage. 

We have more than 70 years of experience in the use of advanced fumed metal oxides: Simply drop our specialists a line at ask-se@evonik.com or press the contact button above. They will get back to you as soon as possible.

Our clients will get help and knowledge from their regional contact and from our application engineers. We are looking forward to hearing from you.