Ozone As A Surface Treatment
While everyone has probably heard of ozone, especially when it comes to the planets ozone layer and the problems reported.
Normal oxygen in the air is made of two oxygen molecules (O2) while ozone is made of three oxygen molecules (O3) and especially at land air pressure and temperature is the unstable and reactive cousin of oxygen. In the atmosphere where temperature and pressure are very different, ozone is stable, however in our normal world it is unstable breaks down to create normal oxygen that we can breath.
2 O3 —> 3 O2
Chemistry lesson aside, the point is that ozone is unstable and reactive and wants to go from ozone back to oxygen or something else that’s more stable. This is why it is an excellent surface treatment system, because it will react with a material surface to change the component and at the same time react to be something else.
The material will now have oxygen at the surface in a very similar way to how plasma, corona or flame treatment will prepare a material and similar properties are achieved so we can expect improved adhesion for inks, glues, coatings or other liquid adhering materials.
Because ozone is not stable, it’s not a gas that’s found in the air in significant quantities and it’s not something we can refine but it is something we can generator and create very easily!
How To Generate Ozone
Ozone is a natural bi-product of high voltage which includes Corona Treatment. Usually our key focus is to remove ozone as it is hazardous to health, but if we control how it’s made and where it goes then it can be used for surface treatment.
The Tantec OzoneTEC uses the principal of corona treatment which is to create a high voltage arc within air. The oxygen in the air in such an energetic environment combines to create ozone and then we can blow this gas in to areas where treatment is needed.
While this can be done fairly easily and is actually made in many areas including around high voltage photocopiers, the industrial control and safety of such a machine as well as the volume required makes the machine much more technical than simply applying high voltage in an open environment.
At room temperature ozone can last a number of days so once inside a part, it will have time to work. If ozone is needed to be removed from the part then we also manufacture ozone extraction systems which normally come with corona treaters as they create a lot of ozone as a bi-product.
Why Would You Use Ozone Over Other Surface Treatments?
Ozone generation for surface treatment is much less common than plasma, corona or flame treatment but finds it’s home for components where the surface needing treatment isn’t exposed such as the inside of a bottle or moulding.
Ozone can flow in to areas that traditional surface treatments can’t. This works especially well for products that need internal treatment and the technology has often found great success for treatment products such as rotational mouldings or composites with internal cavities.
In many applications, the key reason for needing improved adhesion and flow properties has been to improve adhesion for liquid polyurethane or other foams being injected into the product to give it strength, rigidity or insulation properties.
Cool boxes with side walls and a lid that want to be lightweight but insulate the food and drinks inside work brilliantly with ozone treatment. The lightweight skin of the box can be made, ozone treatment can take place and then finally the lightweight but strong and insulating foam can be injected in to the cavity to finish the product.
Similar for boat hulls on composite ships which might be looking for insulation or structural integrity. In either case the treatment does two key things.
- Improves wetting of the material which allows the liquid foam to get in to every last bit of the cavity, displacing air readily and leaving no large voids which would be uninsulated and weak compared to the rest.
- Improves adhesion so that in the life of the product the foam does not come loose which could happen with repeated heating and cooling, swelling and contraction of the product.
The principal of ozone treatment and these exact concerns are covered in our product animation for OzoneTEC:
6 Of the Good and Bad Points of Ozone Treatment
This type of treatment is less common than others and for many applications that’s simply because the other techniques are stronger and you choose the right tool for the job. But there are also additional considerations with OzoneTEC treatment and here are the top 6 we have in mind when discussing this type of treatment:
1. Ozone Treatment Can Get Anywhere
Within an enclosed cavity, ozone can flow and dissipate in to areas that other treatments simply can’t and this can give strong treatment in otherwise impossible to treat parts. Rotational mouldings, small tubes and composite manufactured materials are perfect for treatment in this way.
2. Ozone Is Slower Than Most Treatments
Ozone treatment is much slower than plasma or corona treatment and it might take 30+ minutes of exposure to get a similar result. Most people using the technology will add ozone to the cavity being treated for a few minutes and then leave it enclosed for a certain amount of time rather than continuously treating the part for the entire duration.
3. Ozone Is A Hazardous Gas
First and foremost we need to understand that ozone is not something we want to be breathing in, it is hazardous to health and is well understood and published by UK Government in the form of EH38.
Because of this the treatment needs to be in a confined space that can either be extracted to remove the ozone, or left long enough for ozone to return back to safe oxygen which is highly dependent on humidity, temperature and materials in contact but can be a number of days until fully decomposed.
4. Extraction and Removal
Using ozone treatment safely usually means that you will enclose the part within the treatment and you will add just the right amount of ozone to get the job done within the timeframe and not too much that it takes weeks to break down. If you can manage this, which is very feasible, then there’s nothing extra to do.
Others might want a higher concentration to begin with so might treat heavily for longer to get faster cycle times. This might mean that by the time you want to use the part, there is still ozone within the cavity. If this is the case it is likely that you will connect an extraction machine to remove ozone which will go through the extraction unit where it is turned quickly back in to oxygen so it’s safely back in the room.
5. Ozone Can Damage Materials
Ozone is an oxidising gas and when in contact with materials susceptible to oxidation, mild steel for example will quickly rust. Polymer materials and composites are generally resistant enough not to cause problematic damage and only be treated, but it is a consideration.
6. Low Costs and No Consumables
Using ozone treatment generally only needs a standard plug, possibly some compressed air. No other gases, no chemicals and no physical media are needed to make the system work. While available in a few different versions, the key OzoneTEC has a nozzle handle pump style delivery system so it can be inserted in to a part easily. The environment can be made safe and the machine started. Operator training and ongoing machine maintenance are generally very low.
Other Considerations
The main comparison for using ozone in this way for surface treatment is comparing it to similar systems that could do the same treatment; atmospheric and vacuum plasma and corona treatment. It’s likely that the inline treatment of corona or atmospheric plasma are faster and easier to control. Vacuum plasma is likely to be faster and has no safety considerations.
Ozone treatment might still be a strong contender for being the treatment system of choice because it is highly flexible and can treat both internal and external surfaces. While we focus on the fact it can treat internal surfaces because it really is the strong point of the technology, it will treat anything it comes in to contact with. Enclosing a large jog of parts in a room filled with ozone will treat the entire jig easily and would likely be a lot cheaper than a comparative vacuum plasma machine. This type of system would be slower than vacuum plasma but could work well for a manufacturer making large components at low volume, perhaps aerospace or other production industries.
