What is Corona Treatment?

An Introduction to Corona Treatment

Corona treatment, also described as corona discharge, dielectric barrier discharge and corona surface treatment is an established and widely used surface treatment process used for industrial manufacturing around the world.

The technology primes materials for improved adhesion using a high-frequency, high-voltage corona discharge which opens up the surface by changing the chemistry very slightly to give improved wettability and adhesion. It is most commonly used to make sure that print and coatings don’t scratch or rub away from materials, or for adhesives to stick properly to materials such as polypropylene and polyethylene.

Corona treatment is most commonly used for plastics, however it is used on a wide range of materials including glass and metals in particular and while there are many standard systems such as the ever popular web treaters seen on many print lines, there are also hundreds of specific treatment system designs that have been made.

Corona treatment has such a wide variety of designs because it tends to be a more custom and engineered solution for surface treatment. Perhaps not always the most versatile technology, what it can do is surface treatment fast and efficiently with minimal running and maintenance costs and very high uptime.

What Does Corona Do?

The basics of how corona treatment works is fairly simple because all that’s needed is to apply high voltage from a discharge electrode to a ground or counter electrode. The part is placed within the high voltage with a few millimetres air gap and treatment takes place quickly and easily.

The high voltage breaks up air molecules to create energetic and excited ions and radicals that interact with the material to increase surface energy. While there are differences to plasma, the effect is very similar and if you’re interested you can read more about the process itself in our article What Is Plasma?

If you’ve worked with high voltage before then you might immediately know one the biggest challenges is that voltage will always find the easiest path to ground with least resistance. If your corona treatment isn’t manufactured well then short circuits can happen easily and this is especially true for some of the larger systems that can be running at over 30,000 volts.

The parameters of corona treatment are mostly power in watts and voltage in volts. We typically use volts to jump gaps… if the part is thick we need more volts to get through the material. The high voltage doesn’t necessarily give good surface treatment, but it does allow treatment to work.

Voltage jumps gaps while watts deliver the treatment itself. Higher power, more watts, means more treatment.

What Are The Key Advantages Of Corona Treatment?

Corona Treatment systems are really useful tools, we find that our customers tend to use them for some of the following reasons:

1. Corona treatment can treat wide, flat materials consistently, quickly and inline. The most common corona treater is a web treater and you can be treating narrow web at only a few millimetres wide, or a full blown extrusion at several meters. You can also be running at an indexing or crawling speed, or hundreds of meters a minute. The technology is really flexible for this and nothing else comes close.
2. Corona treatment is highly efficient with low running and service costs. It is usually true that a corona treatment system might be a bit more costly to purchase, it might be more engineered and require more consideration to install inline – especially for some of the more complex systems. But once in, there are very few consumables, treatment typical runs at less than 2kw and power is your only consumable.
3. Treatment systems are modular and have minimal downtime. A service for ozone extraction is required over a period, usually yearly, but other than that the key maintenance is to keep the system clean. Running corona systems in dirty environments or with build up of debris isn’t a good idea, but assuming a light clean has taken place weekly – monthly depending on the factory, the machines will keep running for years with minimal interruption.
4. Health and safety of corona treatment is exceptional, especially versus alternatives such as abrasion or chemical primers. There are some safety concerns, such as ozone gas being given off – which can easily and effectively be filtered and returned to the room without issue, or the fact the system is uses high voltage, but keep it guarded and there’s no problems.

For many applications, corona treatment is unrivalled. Obviously there’s a lot of situations where corona treatment isn’t the right tool for the job and cross over with primers, abrasion, flame treatment and plasma treatment are there.

As with any of these technologies, the trick is to use the right tool for the job. If your part is a thin web material requiring treatment over the full width then corona is the one. If it’s a high speed line looking for specific area treatment then corona is likely very sensible.

Alternatively if you’re looking for small runs of complex parts, primers, abrasion and plasma might be a smarter option.

What Can You Treat With Corona Treatment?

Corona treatment is used extensively due to its ability to treat both metal and plastic surfaces; raising the surface energy and improving the characteristics of these materials so that any type of printing or bonding can take place.

It is typically applied to a range of surfaces made from materials such as:

• PVC and Vinyls
• Common polymers such as Polyethylene (PE) and Polypropylene (PP)
• Engineering polymers such as Nylon (PA6, PA66 etc), PEEK, Polyimide (PI) and others
• Foils
• Metallic surfaces including aluminium, gold, titanium and stainless steel
• Paper and board
• PET and other packaging materials

The real restrictions of corona treatment isn’t conductive or non conductive materials, it can be used on any material. The real restriction is in treating a mixture of conductive and non conductive substrates.

A few common examples treating exposed metal tracks on a circuit board, as all the power will go straight to the conductive track. Equally when treating conductive rubbers or composites, the easiest path to ground, which is the path the treatment will take, is often through the conductive elements.

This can give some really nice effects, looking like a sparkler jumping around. However it is not an effective treatment.

The other restriction is in the size and shape of the part. Because treatment flows the path of least resistance to ground, it won’t go through thick plastic if a thinner section is close by. Corona treatment also won’t flow nicely around a sphere from top to bottom for example, it’s more likely to find a track and follow a single run around.

This doesn’t mean that 3D components can’t be treated, but there is a point where it’s not sensible and using a plasma system is the right tool for the job.

For more information on plasma, you might want to read: Blog – What Is Plasma Treatment?

Corona Treatment Running Costs

We balance the system with amps using the following equation derived from Ohms Law:

Power (watts) = Voltage (volts) x Current (amps)

Rearranging the equation to find amps we divide power by voltage so a typical 1,000 watt system at 20,000 volts will only have 0.05 amps of current.

Rearranging this again you will find that when we have the mains incoming, our figures are 240v mains voltage, 1,000 watts power which gives us 4.1 amps so running a corona unit with these settings would be similar to running a domestic dishwasher or microwave.

We look more in depth at this topic in our article How Much Do Plasma and Corona Systems Cost to Run?

How Long Does Corona Treatment Last?

This is one of the most common questions we get asked, and the answer is similar for both plasma and corona treatment. The lifetime of corona treatment will depend on the treated material and the conditions under which it is stored. Typically, it depends on three factors:

• Introduction of contaminants to the surface material such as fingerprints and airborne oils
• The migration of additives such as plasticisers blooming to the surface
• The movement of molecules in softer, non-cross linked materials.

It is possible to test the length of the treatment life if you’re seeking a longer processing window, but typically for most materials it is at least days – if not months or years.

Here is an example graph of three materials, all polyethylene (PE) based and the expected treatment life for them.

Because this is quite a complex topic, with a variety of answers depending on these factors and more, we’ve dedicated an entire blog to it which you can find here: Blog – How Long Does Plasma and Corona Treatment Last?

What Is Corona Treatment – Conclusion

Corona treatment is one of the top tools at our disposal, it’s an effective pretreatment, highly efficient inline and especially useful for a range of materials including thin delicate substrates up to large, heavy duty materials.

While corona treatment tends to find it’s home with flat materials such as web materials, boards, sheets and foams; the engineered version to treat 3D parts such as syringes and bottles are systems unrivalled by many other technologies. One of the trickier sides of corona treatment is that because it’s often more engineered than other systems, there are hundreds of designs. This is good from the point of view that we can really make a machine that suits your specific problem, but it’s hard to showcase every machine type and variation.

Power consumption is low and even though the high voltage tag sounds scary, it’s cheap to run, easy to service and safe for operators to be nearby.

For us, customers probably don’t buy this unit every week – it’s not as popular as plasma treatment, but that tends to be because it’s not as flexible. A plasma nozzle or plasma chamber can be redeployed in moments to treat a completely different part, where as corona treatment may struggle, especially if the parts are 3D.

That aside, if your product is the same year on year, such as those in the medical device market, the efficiencies of corona are so good that it’s a fit and forget type of technology.

In our factory for contract surface treatment, Ebble Manufacturing, we find it’s one of our most popular machines. People send thin non woven medical materials, thick Velcro hook and loop materials for construction products, technical foils for battery manufacturing and everything in between.

Tantec welcome you to visit and see corona treatment first hand! Compare it to the plasma systems and get to know the technology yourself.