What is Plasma Treatment? A Powerful Surface Treatment Technology!

Plasma Treatment Primes and Prepares Materials For Processing

Plasma treatment, also known as plasma surface treatment, is a process used to clean, activate, prepare and prime surfaces for improving adhesion and wetting of liquids on a material. Plasma treatment can be done using Atmospheric Plasma treatment systems or within a Vacuum Plasma system.

Both Vacuum and Atmospheric Plasma Treatment come in a range of types and sizes, but their performance is usually very similar and normally the reason to choose one version over the other is simply down to the part shape and size or the production process you’re working with.

Many extrusion lines for example work with atmospheric plasma nozzles because they simply bolt on above an existing line, while making a batch process vacuum system work in this environment would be very challenging and not continuously in line.

When using either atmospheric or vacuum plasma treatment technology, the plasma will affect the material surface and only the surface in a way that adds new chemistry, preparing it so that any liquids that can bond to it, will bond to it. A liquid adhesive, coating or printing ink for example will be able to key to the material and form a strong and permanent bond. Even a tape, label or mastic material can be thought of as liquid as it interacts in a similar way – anywhere adhesion is looking to be improved, plasma helps!

This technology is a modern, clean and energy efficient way to prepare a material for other processes and often replaces older processes such as abrasion, chemical etching or primers. A lot of the older techniques might be unrepeatable, costly or use dangerous or hazardous chemicals.

What Is Plasma?

Plasma is an energetic gas and is created by adding energy to a normal gas and is considered the next step in matter from solid, liquid and gas to plasma.

In the normal states of matter, the molecules themselves move apart from each other, but remain intact. For example oxygen will be O₂ in solid, liquid and gas form. As energy is added to a solid, the molecules shake and move away from each other. As they go from liquid to gas the molecules have so much energy that they now bounce all over and only weakly interact with other oxygen molecules.

In a plasma, the O₂ itself gets ripped apart, creating ions, radicals, free electrons and other excited species. These excited bits are plasma and they interact strongly to react with materials or simply transfer energy and create a new and useful surface.

While this sounds complex, it’s something that happens more often than you may realise and especially in space it’s the most common form of matter. The sun and all the stars are forms of plasma. The highly energetic areas of the sky called nebula are plasmas. The northern lights are plasma!

Here in the real world, we also see it all around too but we might not call the examples plasma in every day use. Fire, neon lights and plasma televisions are all examples of energetic plasma systems being used. One of the big plasma sightings in the real world are the Northern Lights which stun with colours of different gas plasma compositions high in the atmosphere, we found this article on them very interesting!

How Does Plasma Treatment Work?

Plasma is created by adding energy to a gas and in most cases for surface treatment the obvious gas to use is air. Some specialist systems or older systems might prefer pure oxygen and in some cases it might be sensible to use argon, nitrogen or other specific chemistry to tailor the process and avoid the use of oxygen entirely.

Tantec Plasma systems all add energy to the gas by using high voltage, which is an efficient and controllable technique that can be scaled from small lab based systems up to large industrial machines. This method creates the plasma using high voltage, but the plasma discharge itself is voltage free so even a powerful machine can treat delicate substrates like PCBs or thin films without causing damage.

Atmospheric Plasma Treatment

A Plasma nozzle contains a vortex of high voltage, high energy air being swirled around and turned into plasma. As it blows out of the end of the nozzle a fine 10mm jet fires out at the part to be treated.

The jet hits the surface and spreads with the force and energy of the compressed air flowing behind and treats a stripe usually around 15mm.

Larger systems can treat up to 150mm and the systems are great for targeted treatment or for installing on moving parts such as extrusion lines or inline printers.

Vacuum Plasma Treatment

Because plasma in a vacuum has had most (but not all) molecules removed, it’s easier to create the energetic gas everywhere without using excessive energy.

Taking the pressure down to around 1/1000th of the air we breath we can make a uniform and stable plasma that will treat any exposed surface in a gentle and repeatable way.

This all over treatment doesn’t care about number of parts in the machine, or whether the part is extra complex like a populated circuit board. The treatment gets everywhere and does its thing!

While we discuss the pure plasma systems here, it’s worth knowing about the similar technology called Corona Treatment which works in a very similar way, however, instead of using the high voltage just to energise the plasma, it goes through the part too.

A common question is what’s the difference between plasma and corona, and it’s true to say that a corona treater is a type of plasma but the key difference is you could touch a plasma (it might be hot so don’t run out to try) but you could never touch a corona because it is high voltage and can often be many thousands of volts.

Is Plasma Cleaning, Treating, Etching or Doing Something Else?

Secondly, especially for softer materials like plastics and rubbers we move on to plasma treatment. Polymers are mostly made of long chains of carbon and hydrogen. The excited molecules in plasma can attack these chains and insert themselves in, adding reactive molecules like oxygen or others present in the gas which break up the surface and add that little bit of extra chemistry that makes a big difference for adhesion.

This new chemistry only effects the top molecular layers of the material so it’s not changing it significantly, but it is giving the interface layer that little jump it needs to interact strongly with adhesives, paints, printing inks and any other liquid that it comes in to contact with.

If we leave our plasma treatment on for a longer period, we will start to break up the material surface and etch away. This might be beneficial for some materials but for many it’s more like overtreatment so knowing what is happening is important.

Once cleaned or treated, the reactivity and available energy for interacting with is a measurable quality of the surface known as Surface Free Energy and is often measured for determining how much treatment has been applied. Some call it dyne level and it can be measured using Dyne Pens and Test Inks or Contact Angle measuring systems.

What Specific Plasma Treatment Systems Are There?

Plasma treatment can be performed in two key methods which are nozzle, atmospheric type systems or vacuum plasma systems.

Vacuum Plasma

Vacuum plasma, also known as low pressure plasma, is one of the most powerful and versatile plasma systems available.

Vacuum Plasma treatment systems come in a range of sizes, shapes and options but the general systems include the vacuum chamber itself that needs to be big enough for parts to fit. There are small lab scale versions and huge industrial versions available.

The chamber is powered by a generator and control system which usually has an interface such as a screen, although it may be controlled by an external computer or system.

The other part of the system is the vacuum pump system which ranges from small simple pumps easy to move around up to large high powered pumps designed to work quickly and day after day.

The Tantec VacuTEC series has a number of standard designs and can also be custom built to meet specific requirements. They’re high performing industrial systems used globally to treat many materials and trusted for demanding industries like automotive and medical device manufacturing.

Atmospheric Plasma

Atmospheric Plasma, also known as open air plasma, plasma discharge, air plasma and cold plasma, is a treatment system that comes in a range of shapes and sizes, from small focused jets to wide plasma curtains.

Nozzle plasmas creating jets of plasma are versatile and easy to integrate into many systems and applications. From users hand holding smaller systems to large rotating head systems in fully automated production lines, there’s a wide range of systems.

All systems are made up of at least two common parts; the nozzle system which might be an individual nozzle, bank of nozzles or rotating head system. The individual nozzles tend to be the most powerful but also the most narrow and the rotating and spinning systems are usually more gentle and spread the plasma over a wider area.

All Plasma Nozzle systems are powered by the PlasmaTEC-X generator series which is a compact modular system. Easy to switch between lines, service and change between projects.

Both forms of plasma treatment have their uses and using one over the other normally comes down to the way production is run, the size of the part and the number of parts to be treated.

When Would you Use One Form Of Plasma Treatment Over Another?

We find that some customers get drawn to one treatment technique over another – perhaps because they’ve heard of it, or used it before elsewhere. But the truth usually is that either technology (or corona treatment) are likely to be successful in treating the material.

The real question is how are you looking to use and integrate the systems?

Inline systems on high speed lines are unlikely to use vacuum plasma because vacuum treatment systems are batch processing. There is the VacuLINE system but even this is batch indexing, certainly difficult to use for something like an extrusion.

Equally, a moulded 3D component such as an automotive interior part requiring 100% ‘A Surface’ treatment, or even the entire part treatment, will struggle with a plasma nozzle. The plasma treatment nozzles are fantastic at area treatment but very difficult to get in to tight areas or large areas. Even a skilled robot programmer will find it tough to get the same speed and distance over the entire part of a large dashboard.

There can be some differences between Atmospheric Plasma Treatment and Vacuum Plasma Treatment and working in the lab to determine surface energy and performance strength is key to understanding any differences.

Where we might see a difference is when we’re trying to really do something specific, like when we use gases or precursor vapours in the treatment. A nozzle works with high pressure air flow and is exposed to the world, so adding something to this flow can be costly and potentially dangerous if not controlled.

Vacuum plasma on the other hand is operating at maybe 1/1000th of normal air pressure, so it only takes a tiny volume of gas or vapour to quickly fill the chamber, which is controlled and can be vented to scrubbers or external extraction. Some customers use acid vapours in these machines which would not be sensible for use with air plasmas.

These examples are quite specific, in reality, air is the most common treatment gas and both systems perform around the same so the question goes back to ‘how do you want to integrate and install your plasma treatment equipment?’

Why Is Plasma Treatment An Effective Preparation Process?

Using Plasma as a pretreatment in manufacturing is becoming more and more common. Traditionally it was reserved for more high end applications while more manual or chemical heavy processes could be used cheaply for standard processing.

With environmental concerns restricting the use of many cleaning or priming chemicals, and product quality being more important that ever restricting the use of manual processes like abrasion, plasma treatment is an automated, repeatable and environmentally friendly technology that solves a number of manufacturing problems.

This technology is also useful across a wide range of materials and often doesn’t need big parameter or machine changes. Both types of plasma are used to clean, treat and activate metals, polymers, glass, ceramics, circuit boards, composites and almost any material that it can help with.

For some applications it can be true that plasma treatment performance isn’t as good as some traditional harsh chemical primers and cleaners and the trade off might mean redesigning or rethinking your materials or processes, however, once understood how and where treatment is useful, you can deploy it again and again.