Most corona treatment problems start with a number nobody wrote down. Operators inherit a treater, dial the power to whatever setting the previous shift used, and never check whether that figure delivers the right dose for the current substrate, width and line speed. Corona treater power is not a preference - it is a derived value, and getting the calculation right is the difference between consistent adhesion and a line that fails three hours into a run. This guide covers the formulas, the units, and the practical limits of corona power in production.
The Core Formula Behind Corona Treater Power
Treatment dose is expressed as watt density: watts per square centimetre per minute of treated surface.
Watt density (W/cm²/min) = Applied power (W) ÷ [ Web width (cm) × Line speed (cm/min) ]
Work in consistent units. If width is given in metres and speed in metres per minute, multiply both by 100 to convert to centimetres.
A worked example: a 1.6 m wide line runs at 250 m/min and the generator applies 24 kW.
- Web width = 160 cm
- Line speed = 25,000 cm/min
- Treated area per minute = 160 × 25,000 = 4,000,000 cm²/min
- Watt density = 24,000 ÷ 4,000,000 = 0.006 W/cm²/min
That number looks tiny because the formula produces watts per square centimetre per minute. It is conventional to multiply by 1,000 and report the result in milliwatts, or to work in W/m²/min for industrial figures. Industry data sheets usually quote watt density in W/cm²/min scaled to a practical range, so always confirm which convention a supplier is using before comparing figures.
The relationship that matters practically: required corona treater power scales linearly with line speed and with web width. Double the speed and you need double the power for the same dose. This is why a treater that works perfectly at 150 m/min fails at 300 m/min even though nothing about the equipment changed.
Working Backwards from Your Substrate
The more useful direction is to start from the substrate and derive the power you need.
- Identify the substrate family and its untreated surface energy.
- Set the dyne target for the downstream process - typically 38 to 42 dynes for polyolefins, 45 to 48 for PET.
- Choose a baseline watt density from the supplier's recommendation or from previous production data for that substrate.
- Multiply by web area per minute using the current width and speed.
- Add a margin - usually 15 to 25 percent - to cover ageing, ambient variation and electrode wear.
- Confirm the generator can deliver it and that the electrode and dielectric can dissipate the resulting heat.
Baseline watt densities for common cases sit in these bands:
| Substrate | Typical dyne target | Baseline watt density | Notes |
|---|---|---|---|
| LDPE / LLDPE film | 38–42 | 6–10 | Full width treatment |
| BOPP film | 38–40 | 5–8 | Slip additives reduce bond |
| PET film | 45–48 | 3–6 | Over-treatment risk |
| Aluminium foil | 42–46 | 6–12 | High roll thermal load |
| Paper / board | 40–44 | 4–8 | Moisture sensitive |
| Metallised film | 44–50 | 3–5 | Protect the metal layer |
| Coated substrate | 40–46 | 3–6 | Reduced duty cycle |
These are starting points. Every line has its own heat balance, dwell geometry and ambient conditions, so treat them as a first estimate and confirm by measurement.
Corona Treater Power Ratings and Generator Headroom
Generators are rated by output power, but the nameplate figure is not what reaches the web. Losses occur in the transformer, the high-voltage cabling and the electrode assembly itself. Expect between 10 and 25 percent of the nameplate rating to be unavailable at the discharge.
Sizing rule: specify a generator at least 30 percent above your calculated production requirement. That headroom covers three real needs. First, product changeovers to heavier watt densities. Second, electrode and dielectric ageing, which raises the voltage needed for the same dose. Third, ambient conditions - high humidity suppresses the discharge, so a line that runs comfortably in winter may struggle in a monsoon season.
Undersizing a generator forces a permanent compromise. Once the corona treater power ceiling is reached, line speed becomes the only variable, and slowing a line to make treatment work is an expensive way to solve an equipment sizing error.
Oversizing carries its own cost. A generator running far below its rated output behaves less predictably in terms of waveform quality, and the extra capacity is capital that sits idle. Aim for a comfortable margin, not a lavish one.
What Limits Corona Treater Power in Practice
You cannot simply keep raising power. Several physical limits intervene.
Dielectric breakdown of the roll covering. Every dielectric has a maximum tolerable watt density. Exceed it and the covering develops conductive tracks, then punctures. Silicone coverings tolerate far less than ceramic. This is the hard ceiling on most installations.
Thermal limits of the substrate. Thin films distort, shrink or block when the web temperature climbs. The treatment zone contributes heat, and so does the discharge itself.
Electrode erosion. Higher power accelerates erosion of the electrode edge, which changes the gap geometry and therefore changes the dose over time. A treater run at 90 percent of its ceiling will need electrode service far more often than one run at 60 percent.
Ozone generation. Ozone output scales with power. More ozone means more extraction capacity, more corrosion of nearby components, and a larger environmental control burden.
Backside treatment. Excessive power on thin films drives the discharge through the web, treating the reverse face. The symptom is blocking on the unwind or unexplained adhesion on the wrong side.
The engineering answer is to maximise dwell time rather than power. A larger roll diameter, a wider treatment footprint or a slower line all increase the time the web spends in the discharge, letting you hit the target dose at lower corona treater power. Lower power means less heat, longer dielectric life and a wider operating window.
Monitoring and Adjusting Corona Treater Power in Production
A calculation set at commissioning is not a set point forever. Build these habits into the line.
Log the dose, not just the power setting. Record width, speed, applied power and calculated watt density at the start of every run. When adhesion drifts, the log shows whether the process changed.
Measure dyne level at three points. Centre, drive side and operator side. Edge values falling below centre values points at electrode or dielectric wear rather than a power shortfall.
Track the trend, not the absolute value. A slow upward creep in the power needed to hold dyne level is the earliest indicator of dielectric ageing.
Recheck after any product change. Substrate, width and speed all feed the calculation. A change in any one of them invalidates the previous set point.
Verify with a bond test. Dyne level is a proxy. Peel or tape tests on finished product confirm that the corona treater power you are applying actually produces the adhesion your customer requires.
Common Mistakes in Corona Treater Power Calculation
- Confusing power with dose. Two lines running the same generator at 20 kW but at different widths and speeds receive completely different treatment levels.
- Forgetting unit conversion. Mixing metres with centimetres or metres per minute with centimetres per minute produces results off by two orders of magnitude.
- No headroom in generator sizing. A generator sized exactly to the current process cannot accommodate changeovers or ageing.
- Chasing dyne level with power alone. If uniformity is the problem, more power makes it worse, not better.
- Ignoring ambient humidity. Seasonal shifts change the effective efficiency of the discharge and therefore the corona treater power required for a given dose.
- Treating the power setting as a fixed recipe. The correct set point moves with speed, width, substrate and electrode condition.
FAQ
Q1: How do I calculate the corona treater power I need?
Multiply your target watt density by the treated area per minute, which is web width times line speed converted to consistent units. Then add 15 to 25 percent margin and confirm the generator rating is at least 30 percent above that figure.
Q2: Why does my treatment fail when I increase line speed?
Speed reduces the dwell time in the discharge, so the same corona treater power delivers a lower dose. Either raise power proportionally or increase the treatment footprint with a larger roll.
Q3: What is a normal watt density for corona treatment?
For polyolefin films on an extrusion coating or printing line, 5 to 12 W/cm²/min covers most cases once scaled to the supplier's convention. PET and metallised films run lower, foils and board often run higher.
Q4: Can I treat too much?
Yes. Over-treatment burns the surface, creates a weak boundary layer, generates excess ozone, accelerates dielectric wear and can cause backside treatment on thin films. More corona treater power is not automatically better.
Q5: How much headroom should I leave in the generator?
At least 30 percent above the calculated production requirement. That absorbs electrode ageing, seasonal humidity variation and future product changes without forcing a line speed reduction.
Q6: Does electrode condition change the power needed?
It does. As the electrode edge rounds and the dielectric wears, the gap effectively changes and more voltage is required for the same dose. A rising power requirement is an early maintenance signal.
Q7: How often should I recalculate the dose?
Recalculate whenever substrate, width or line speed changes, and re-verify the set point quarterly. Run the calculation at the start of every production campaign rather than relying on an inherited setting.
Conclusion
Corona treater power is a derived value. Start with the substrate and the required dyne level, choose a baseline watt density, multiply by the treated area per minute at your actual width and speed, add margin, and confirm the generator and dielectric can carry the load. Then log the result and watch the trend, because the number that works today will drift as electrodes age and seasons change.
Shenzhen Hefeng Jiada Technology supplies corona treaters, plasma treatment machines and contact web cleaning equipment with generators sized for real production duty. Tell us your web width, maximum line speed and substrate mix and our engineers will calculate the corona treater power and electrode configuration your line needs.