Printing Wetting, Ink Adhesion and Film Performance

Corona Treatment Monitoring: Check Corona Surface Treatment and Plasma Treatment Before Printing, Digital Print and Laminate

Corona treatment raises film surface energy so ink, coating and adhesive can wet and bond, but the effect is uneven, fades and can overshoot. Measure water contact angle across the web on every roll, add surface energy when you need it, and catch weak treatment before the substrate reaches the press or laminator.

Who this is for: Blown film and cast film extruders, flexible packaging and label printers, laminators, and any converter that runs corona or atmospheric plasma treaters.

Where it fits: Treater setup, roll release, incoming film inspection, storage checks and root cause work after adhesion failures.

What it does not do: It does not measure ink adhesion or laminate bond strength. Tape, rub and peel tests still decide.

Method

Sessile drop water contact angle at edge, centre and edge; two liquid surface energy when needed

Standard

Follows the water contact angle approach of ASTM D5946 and ISO 15989; supports dyne checks to ASTM D2578 and ISO 8296

Setup

About 2 minutes

Book a 15 minute demo Request a quote

Printed plastic film running over rollers on a printing press

Written by

Gurdeep Singh Saini

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

COO at Droplet Lab

Why corona treatment needs measuring

Above 90°

water contact angle is the guide band for marginal or no treatment on polyolefin film; below 71° is very high treatment.

ASTM D5946-24, section 5.4

33 to 55 mJ/m²

rise in polyethylene surface energy after corona treatment, measured directly with a surface forces apparatus.

Mangipudi, Tirrell and Pocius, Langmuir 11(1):19, 1995

76° to 96°

rise in water contact angle on corona treated polypropylene after washing with water, as loose oxidised material from treatment dissolved away.

Strobel et al., Plasmas and Polymers 8(1):61, 2003

Sources: ASTM D5946-24, Standard test method for corona treated polymer films using water contact angle measurements; Mangipudi V., Tirrell M., Pocius A. V., Direct measurement of the surface energy of corona treated polyethylene using the surface forces apparatus, Langmuir, 1995; Strobel M. et al., A comparison of corona treated and flame treated polypropylene films, Plasmas and Polymers, 2003. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this corona treatment check does and what it does not

A quick reference for treater, print and laminating teams checking fit before reading further.

Evidence Box

Problem this solves

Rolls that pass a dyne check and still fail on press, uneven treatment across the web, and treatment that fades in storage, with no number to track it.

Standards

ASTM D5946 and ISO 15989 measure water contact angle on corona treated film; ASTM D2578 and ISO 8296 use dyne solutions. Both say their number alone is not a complete measure of adhesion.

Peer reviewed method

The Dropometer drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, in Review of Scientific Instruments and Colloids and Surfaces A.

Customer case study

A labels and office products manufacturer measures film surface energy before adhesives, coatings or primers go on, and ordered the same Dropometer for a second lab.

Published research

Peer reviewed studies show treatment raising surface energy, fading over weeks and leaving a water soluble layer when pushed too far.

Honest limit

A good contact angle does not guarantee adhesion. Ink, adhesive, cure and laminating conditions still decide.

Who this is for

What corona treatment question are you trying to answer?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Quality manager

You release treated rolls or accept treated film from a supplier. A water contact angle map on each roll gives a recorded number to release or hold, instead of a dyne pen judgement.

Record hours since treatment with every reading.

Process or treater engineer

You set power, line speed and electrode gap on a corona or plasma treater. Contact angle across the web shows uneven treatment, electrode wear and the effect of each change.

More watt density does not always mean better adhesion.

R&D or ink and adhesive lab

You qualify films, slip packages, inks or adhesives. Surface energy with polar and dispersive parts shows what treatment adds and how fast it fades.

Set gates from your own adhesion results, not a single dyne value.

Fit check

Is this the right check for your corona treatment?

It measures how water and other liquids wet the treated surface. It does not measure bonding.

Good fit if

You run corona or atmospheric plasma treaters on film, foil or paper.

You print, coat or laminate BOPP, polyethylene, polypropylene or PET.

You need to map treatment across the web.

You track treatment decay in storage.

Your customers still ask for dyne levels.

Less relevant if

You need a bond strength or peel value.

Your surface reacts chemically with water.

You need an inline, non contact reading on a moving web.

Your substrate is too rough or porous to hold a drop.

Summary

How contact angle supports corona treatment monitoring

The answer in under a minute.

Measure water contact angle at edge, centre and edge of each treated roll, at a fixed time since treatment. A low angle inside your gate means the surface can wet; a high angle, an uneven map or a rising trend means weak, uneven or fading treatment. Confirm with your ink adhesion, coating or laminate bond test.

The Dropometer contact angle and surface energy kit runs the check. The ASTM D5946 and ISO 15989 page covers the water contact angle method, and a labels manufacturer case study shows film surface energy checked before adhesives and primers. Our Beyond 38 dynes article, surface energy measurement guide and plastics guide explain the background, and the Dropometer and dyne pens comparison covers the two methods side by side.

Expert Quote

Expert perspective on what contact angle measures

“

A contact angle is a thermodynamic property: fix the liquid and the solid and the same angle appears whether the drop sits on a plate or climbs a capillary.

The problem

Why corona treatment is hard to control

Polyethylene and polypropylene film have low surface energy, around 29 to 34 mN/m untreated, so water-based inks and the adhesives used in coating and laminating cannot wet them well. A corona treater passes the web through a discharge between an electrode and a roll. The discharge oxidises the top layer of the plastic and adds polar functional groups, including hydroxyl and carbonyl groups, which raises surface energy and wettability. Atmospheric plasma does the same with more control over the gas. The treatment level depends on power, line speed, electrode width and gap, which treater makers express as watt density. Three things make it hard to control. Treatment is often uneven across the web because of electrode wear, gap or wrinkles. It fades in storage as the surface recovers, faster in some films than others, and amide slip additives that bloom to the surface lower it further. Too much treatment can leave low molecular weight oxidised material that washes off and weakens the bond. Dyne pens give a quick answer, but the standards describe it as a subjective reading of how the liquid behaves, so converters need a number they can map, record and trend.

Ink or coating beads or pulls back on the treated side.

Laminates delaminate or show low bond strength.

One edge of the web prints or bonds worse than the centre.

Rolls pass when fresh and fail after storage.

Dyne pen results differ between operators or shifts.

Troubleshooting

Why corona treatment fails and what to check

Why:

Power is too low for the line speed and width, so too few polar groups are added.

How to detect:

Water contact angle reads high across the whole web. ASTM D5946 treats angles above 90° as marginal or no treatment; our ASTM D5946 page covers the bands.

Corrective action:

Raise power or slow the line, then remeasure the same map.

Why:

Electrode wear, a changed gap, a damaged roll cover or wrinkles treat one part of the web less.

How to detect:

Edge readings differ from the centre, or one lane reads high.

Corrective action:

Inspect the electrode, gap and roll cover, and map more points across the web.

Why:

Treated surfaces recover over days and weeks as polar groups reorient or move away from the surface.

How to detect:

The angle rises on the same roll over storage time.

Corrective action:

Record hours since treatment, shorten storage, or bump treat before you convert the roll.

Why:

Amide slip additives migrate to the surface and lower the energy available for ink and adhesive.

How to detect:

The angle rises faster than on films without slip, and treatment works less well at higher slip levels.

Corrective action:

Review slip level with the film supplier and treat closer to printing or laminating.

Why:

High doses break polymer chains into low molecular weight oxidised material that dissolves in water and weakens the bond.

How to detect:

The angle is low, but rises sharply after a gentle water rinse, and bonds fail at the surface.

Corrective action:

Reduce dose and compare rinsed and unrinsed samples at each setting.

Why:

Drop volume, read time and handling change the reading. Our guide to reproducible contact angle measurement covers fair comparisons.

How to detect:

A reference film reads differently between sessions.

Corrective action:

Fix drop volume and read time, handle film by the edges and measure a reference film each shift.

Not sure why treated rolls still fail on press?

Send passing and failing film, and we will compare them on a call.

Book a 15 minute demo

Lab records

What a corona treatment record contains

Each check produces a record you can file with the roll or lot, beside adhesion and bond results. It can feed into your existing quality records.

Roll

Film type, lot and roll, treated side, and hours since treatment.

Treater settings

Power, line speed, electrode width and watt density at the time of treatment.

Method settings

Liquid, drop volume, read time, temperature and humidity.

Readings

Water contact angle at each zone, with median and spread, and surface energy if reported.

Decision

Release, remeasure or hold, and the adhesion test that confirmed it.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure on corona treated film

Level

Water contact angle on the treated side

Why it matters: It is the primary output of ASTM D5946 and ISO 15989 for treatment level.

How to interpret: ASTM D5946 guide bands: above 90° marginal or none, 85 to 90° low, 78 to 84° medium, 71 to 77° high, below 71° very high. Set your release gate per film and end use from your own correlation with adhesion results.

When it is not enough: ASTM D5946 says contact angle alone is not a complete measure of ink, coating or adhesive adhesion.

Uniformity

Spread across the web

Why it matters: Uneven treatment fails in lanes or at one edge.

How to interpret: Compare edge and centre medians, and watch the spread within each zone.

When it is not enough: Rough or textured film adds spread of its own.

Ageing

Angle against hours since treatment

Why it matters: Treatment fades at different rates on different films.

How to interpret: Repeat the same map at fixed times, such as day 0, 3 and 7, under your storage conditions.

When it is not enough: It does not separate decay from slip additive bloom on its own.

Detail

Surface energy with polar and dispersive parts

Why it matters: Treatment mostly adds the polar part, and that is what decays.

How to interpret: Use water and diiodomethane and compare like with like. A dyne value can be estimated from the D5946 conversion chart for customers who still specify dyne levels.

When it is not enough: Values depend on the model and liquids used.

Validation

Validated measurement approach for corona treated film

How the Dropometer itself has been validated, and how the check fits treatment standards.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

How it fits ASTM D5946 and ISO 15989

ASTM D5946 and the identical ISO 15989 measure water contact angle on corona treated polymer film and give guide bands for treatment level. ASTM D5946 also notes that multiple measurements are needed because treatment varies across a film, and that traditional dyne values come from a subjective reading of test liquid behaviour. The Dropometer measures the angle and records the drop image.

Read the ASTM D5946 page

QC Protocol

How to monitor corona treatment by contact angle

Six steps per roll. Repeat after any treater change and during storage.

1

Lock the method

Fix water quality, drop volume, read time and room conditions, and handle film by the edges only.

2

Check a reference film

Measure a known good film each shift. Our treated versus untreated surfaces experiment shows the difference treatment makes.

3

Sample across the web

Cut samples at edge, centre and edge of the treated side, and note hours since treatment.

4

Measure and map

Place several drops in each zone on fresh spots, and record the median and spread.

5

Decide

Compare with your gate and release, remeasure or hold. Customers who ask for dyne levels can get an estimate; our dyne level glossary entry explains the link.

6

Track decay

Repeat the map on stored rolls at fixed times. Our surface free energy calculator turns two liquid angles into surface energy.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the corona and plasma treatment SOP

A two page SOP you can adapt for your films and treaters, with the method lock, a web map, how to set a gate against your adhesion results, a troubleshooting table and a record sheet.

Contact angle measurement with the Dropometer

Example output

Example corona treatment roll log

Example data only. Your values and gates will differ and must come from your own adhesion results.

How to read this log

Example gate: water contact angle at or below 77° in every zone for this BOPP film and water based ink. Roll 1 passed. Roll 2 had one weak edge, pointing to the electrode. Roll 3 was good when fresh but faded past the gate after storage. Compare your own films with our surface free energy of common polymers reference.

Sessile drop contact angle measurement: DI Water on Nylon, left contact angle 50.1°, right 54.9°

Example corona treatment roll log

Roll	Hours since treatment	Operator edge (°)	Centre (°)	Drive edge (°)	Decision
Untreated	n/a	101	102	101	Reference only
1	2	73	72	74	Release
2	2	74	73	86	Hold; check electrode
3	2	72	73	73	Release
3	336	80	81	80	Hold; bump treat

Example data, not customer data. Corona treated BOPP film; 2 µL water drops read at 2 s; median of 5 drops per zone.

Signal order

The order to check signals on treated film

Check these in order. Each one rules out a cause before you look at the next.

1

Method and reference film

Rules out timing, drop size and handling effects.

2

Treatment level

Shows whether the centre of the web is inside the gate.

3

Web uniformity

Shows edge or lane problems from the treater.

4

Decay and rinse check

Shows fading in storage or loose material from over treatment.

5

Ink and adhesive fit

Confirms the result with the real ink or adhesive. Our ink adhesion on film page and ink beading page cover the next steps.

FAQ

Common questions about corona treatment monitoring

Questions treater, print and laminating teams ask about contact angle and dyne levels.

What does corona treatment do to a film surface?

The discharge oxidises the outer layer of the plastic and adds polar functional groups, including hydroxyl and carbonyl groups. That raises surface energy, so inks, coatings and adhesives can wet and bond. One study measured polyethylene rising from 33 to 55 mJ/m² after treatment. Atmospheric plasma treatment works the same way with more choice of gas.

What contact angle means good corona treatment?

ASTM D5946 gives guide bands for polyolefin film: above 90° marginal or no treatment, 85 to 90° low, 78 to 84° medium, 71 to 77° high and below 71° very high. The right gate depends on your film and end use, so set it from your own adhesion results. Our ASTM D5946 page explains the method.

How do dyne levels relate to contact angle?

Dyne pens and dyne solutions to ASTM D2578 and ISO 8296 find the test liquid that just wets the film. ASTM D5946 includes a chart that estimates wetting tension from the water angle, so you can report both. ASTM D2578 notes that 35 dynes/cm or more has generally been acceptable for flexo on polyethylene film. Our articles on Beyond 38 dynes and the ISO 8296 and 38 dyne guideline go further.

Are dyne pens accurate enough?

They are quick, but ASTM D5946 says traditional values come from a subjective reading of how the test liquid behaves. A contact angle is a measured number with a stored drop image, and it can be mapped across the web and trended. Our Dropometer and dyne pens comparison and ASTM D2578 page cover both methods.

How fast does corona treatment fade?

It depends on the film, dose, additives and storage. Corona treated polypropylene rose 9° in water contact angle over six months in one study, and plasma treated polypropylene film lost over half of its surface energy gain within 30 days in another. Measure your own films at fixed times after treatment and bump treat when needed.

Can a film be over treated?

Yes. High doses break polymer chains into low molecular weight oxidised material that dissolves in water. In one study, rinsing corona treated polypropylene raised the angle from 76° to 96°. The surface looks well treated but the loose layer weakens the bond, so compare rinsed and unrinsed samples when you raise power.

How do I set watt density?

Watt density is treater power divided by electrode width and line speed, and treater makers publish starting values per film. Higher watt density does not raise surface energy in proportion, and too much can over treat. Measure contact angle at each setting and pick the lowest that meets your gate across the web.

Which instrument do we need?

One that measures water contact angle on film at fixed read times, and two liquid surface energy when you need the polar part. The Dropometer does both at the bench, and a labels manufacturer uses it to check film surface energy before adhesives and primers go on.

Business impact

What changes when you measure corona treatment

Typical changes in how teams work. Benchmarks are given only where a published source exists.

Before and with corona treatment checks

Metric	Before Dropometer	With Dropometer	Indicative Benchmark
Roll release	Dyne pen pass or fail	Water contact angle map with a recorded gate	Guide bands from above 90° (none) to below 71° (very high) (ASTM D5946-24)
Web uniformity	Found after printing or laminating	Edge and centre compared on each roll	No published benchmark; track on your own rolls
Stored film	Printed regardless of age	Angle tracked against hours since treatment	Over half of the gain lost in 30 days on plasma treated PP (Seidelmann et al., 2017)
Treater setting	More power when in doubt	Lowest setting that meets the gate, with a rinse check	Angle 76° to 96° after rinsing over treated PP (Strobel et al., 2003)

See the measurement on your own film

Send passing and failing treated film. We will show the comparison on a call.

Book a 15 minute demo

Estimate avoided reprints and scrap from poor treatment

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Instrument cost ($) Each unit is $5,000; default models 1 unit.

Rolls or jobs reprinted, retreated or scrapped for poor treatment per month From your own records. No published benchmark.

Average cost per affected roll or job ($) Your own cost to retreat, reprint or relaminate one affected roll or job.

Events you expect to catch before printing (%) No published benchmark. Use your own records; start low if unsure.

Extra scrap cost per event ($) Film, ink, adhesive and press time lost per event, from your own records.

Other monthly savings ($) Any other monthly saving you can document from your own records.

Result

~0

Monthly savings

~0

Payback period

~0

First year net benefit

Monthly savings = preventable rework cost + preventable scrap cost + other monthly savings.

Limits

What contact angle cannot tell you about corona treatment

Honest limits, so you know when to reach for another test.

It does not measure adhesion or bond strength.

A low angle can hide loose material from over treatment.

Readings change with hours since treatment.

It is a bench check on samples, not an inline reading.

Not valid where the surface reacts with water.

Gates from one film do not transfer to another.

Contact angle shows treatment level, uniformity and decay on the film surface. Ink adhesion, laminate bond strength and coating performance need their own tests on the converted product.

Book a 15 minute demo Request a quote

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items

01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

Contact us to report a correction

Sources

References

1.

Strobel, M., Jones, V., Lyons, C. S., Ulsh, M., Kushner, M. J., Dorai, R., Branch, M. C. A comparison of corona treated and flame treated polypropylene films. Plasmas and Polymers 8(1):61 to 95, 2003. https://cpseg.eecs.umich.edu/pub/articles/pap_8_61_2003.pdf

2.

Mangipudi, V., Tirrell, M., Pocius, A. V. Direct measurement of the surface energy of corona treated polyethylene using the surface forces apparatus. Langmuir 11(1):19 to 23, 1995. https://doi.org/10.1021/la00001a006

3.

Zolek Tryznowska, Z., Cudna, K., Tryznowski, M. Processes 13(10):3190, 2025. https://doi.org/10.3390/pr13103190

4.

Ding, L., Zhang, X., Wang, Y. Study on the behavior of BOPP film treated by corona discharge. Coatings 10(12):1195, 2020. https://doi.org/10.3390/coatings10121195

5.

Lindner, M., Rodler, N., Jesdinszki, M., Schmid, M., Sangerlaub, S. Surface energy of corona treated PP, PE and PET films, its alteration as function of storage time and the effect of various corona dosages on their bond strength after lamination. Journal of Applied Polymer Science 135(11):45842, 2018. https://doi.org/10.1002/app.45842

6.

Suzer, S., Argun, A., Vatansever, O., Aral, O. XPS and water contact angle measurements on aged and corona treated PP. Journal of Applied Polymer Science 74(7):1846 to 1850, 1999. https://repository.bilkent.edu.tr/items/becd1ca4-ed04-4ba8-af64-59a25cc4a998

7.

Seidelmann, L. J. W. et al. Reel to reel atmospheric pressure dielectric barrier discharge (DBD) plasma treatment of polypropylene films. Applied Sciences 7(4):337, 2017.

https://doi.org/10.3390/app7040337

8.

Owens, D. K., Wendt, R. C. Estimation of the surface free energy of polymers. Journal of Applied Polymer Science 13(8):1741 to 1747, 1969.

https://doi.org/10.1002/app.1969.070130815

9.

ASTM D5946-24. Standard test method for corona treated polymer films using water contact angle measurements. See our ASTM D5946 page.

https://store.astm.org/d5946-24.html

10.

ISO 15989:2004. Water contact angle on corona treated polymer films; identical to ASTM D5946.

https://www.iso.org/standard/29046.html

11.

ASTM D2578-23. Standard test method for wetting tension of polyethylene and polypropylene films. See our ASTM D2578 page.

https://store.astm.org/d2578-23.html

12.

ISO 8296:2003. Wetting tension of plastic film and sheeting; equivalent to ASTM D2578. See our ISO 8296 page.

https://www.iso.org/standard/38451.html

13.

Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018.

https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone

14.

Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects.

https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744

15.

Droplet Lab validation papers

16.

Customer publications that cite the Dropometer

17.

Surface energy measurement guide

18.

Surface free energy calculator

Corona Treatment Monitoring: Check Corona Surface Treatment and Plasma Treatment Before Printing, Digital Print and Laminate

Featured Studies & Publications

Why corona treatment needs measuring

Above 90°

33 to 55 mJ/m²

76° to 96°

What this corona treatment check does and what it does not

Evidence Box

What corona treatment question are you trying to answer?

Quality manager

Process or treater engineer

R&D or ink and adhesive lab

Is this the right check for your corona treatment?

Good fit if

Less relevant if

How contact angle supports corona treatment monitoring

Expert perspective on what contact angle measures

Why corona treatment is hard to control

Why corona treatment fails and what to check

Not sure why treated rolls still fail on press?

What a corona treatment record contains

Roll

Treater settings

Method settings

Readings

Decision

Drop images

What to measure on corona treated film

Water contact angle on the treated side

Spread across the web

Angle against hours since treatment

Surface energy with polar and dispersive parts

Validated measurement approach for corona treated film

How to monitor corona treatment by contact angle

Lock the method

Check a reference film

Sample across the web

Measure and map

Decide

Track decay

Download the corona and plasma treatment SOP

Example corona treatment roll log

Example corona treatment roll log

The order to check signals on treated film

Method and reference film

Treatment level

Web uniformity

Decay and rinse check

Ink and adhesive fit

Common questions about corona treatment monitoring

What changes when you measure corona treatment

Before and with corona treatment checks

See the measurement on your own film

Estimate avoided reprints and scrap from poor treatment

Estimate the value of catching weak or faded treatment before printing or laminating.

What contact angle cannot tell you about corona treatment

Standards, evidence and related print workflows

ASTM D5946 and ISO 15989

ISO 8296 and the 38 dyne guideline

Labels manufacturer

Dropometer

Printing wetting and ink adhesion

Ink adhesion on plastic film

Ink beading troubleshooting

Dropometer vs dyne pens

How this page was created

Drafting assistance

Technical review

Verification steps

Updates

Report a correction

References