Technical article, adhesion
Atmospheric Plasma vs. Chemical Primers on Polypropylene: An Inline Alternative
The short answer
Yes, atmospheric plasma is an inline alternative to chemical primers on polypropylene. It raises the surface energy of PP right before bonding or painting, dry, with no solvent and no drying time. In the literature, PP goes from about 30 mN/m to a range of 45 to 66 mN/m after treatment. Kalego Solutions, in Quebec City (Canada), verifies it on your parts before you buy.
30.5 mN/m
Untreated PP (Accu Dyne tables)
45 to 66 mN/m
PP after atmospheric plasma (literature)
40 to 44 mN/m
Usual target level for bonding
0 solvent
Dry process, no drying
PP rejects glue because its surface is inert
Polypropylene is a chain of carbon and hydrogen atoms with no polar groups. Its surface energy is low, around 30 mN/m. An adhesive or paint with a higher surface tension does not spread: it beads up, then fails at the first load.
That is why parts get a primer, or get flame-treated. A chemical primer lays down a tie layer, but it adds a solvent, a drying time and one more step to control.
Atmospheric plasma works differently: it modifies the top molecular layers of the PP itself. Reactive species graft polar, oxygen-containing groups onto the surface, and surface energy rises. The adhesive wets the surface and forms a real bond.
Four ways to prepare PP, compared
| Criterion | Chemical primer | Flame treatment | Corona | Atmospheric plasma |
|---|---|---|---|---|
| Solvent or VOCs | Yes, in most cases | No | No | No |
| Drying time | Yes | No | No | No |
| 3D parts | Yes, by spraying | Yes, with a risk to thin walls | Limited: mostly films and flat surfaces | Yes: torch for a zone, curtain for a full width |
| Heat input | Low | High, open flame | Low | Low |
| Consumables | The primer | Combustible gas | Electricity | Electricity and compressed air |
| Inline control | Visual, difficult | Test ink | Test ink | Test ink, in seconds |
What plasma changes on your line
No drying in the cycle time
The treatment is dry. The part goes to bonding or painting right after, with no oven and no waiting.
No solvent to buy or store
No primer, no VOCs to capture, no drums to handle. Plasma uses electricity and compressed air.
A check in seconds
A calibrated test ink tells you whether the surface exceeds the target level: it spreads above it and beads below it.
Limits to know before replacing the primer
The effect fades over time
Activation is not permanent. Bonding or painting must follow treatment fairly closely. We measure that window on your part.
Plasma treats what it reaches
Deep cavities and inaccessible inner faces stay untreated. The geometry decides the type of source.
No miracle on a greasy part
Plasma removes thin organic contamination, not a thick film of mould release. Prior degreasing is then still needed.
Every PP grade reacts its own way
Fillers, talc and additives that migrate to the surface: two formulations do not respond alike. A trial on your material settles it.
Validate the switch with three tests
Measure the surface
Surface energy with test inks, or contact angle, before and after treatment.
Test adhesion
With your actual adhesive or paint: peel test, or a cross-cut test to ISO 2409 for paint.
Check over time
Repeat the measurement after the real delay between treatment and bonding on your line, then after ageing.
Common questions about PP and plasma
Does plasma fully replace the primer?
Often, but not always. It replaces the tie-layer step when the adhesive or paint bonds to the activated surface; some systems are still formulated to go on a primer. A trial on your material and product confirms it before any change.
How long can I wait between treatment and bonding?
As little as possible. The effect fades over time, at a rate that depends on the material and storage. The literature describes an effect measured in days; we measure the real window on your part.
What surface energy should I aim for?
In practice, 38 mN/m for printing and 40 to 44 mN/m for bonding and laminating. The exact level depends on your adhesive or ink.
Does plasma also work on PE and PET?
Yes. In the literature, PE (about 31.6 mN/m untreated) and PET (about 39 mN/m) reach the same 45 to 66 mN/m range after atmospheric plasma.
Does plasma damage the part?
No. It only modifies the top molecular layers of the surface, without changing the geometry of the part. Surface temperature stays low.
Which equipment for an injection-moulded PP part?
A compact plasma torch to activate a precise zone, such as a bonding strip; a plasma curtain for a full width; a turnkey cell for a trajectory repeated identically.
Do I need air extraction?
Yes, in most cases. An air plasma at atmospheric pressure produces ozone and nitrogen oxides, which must be captured at the source. We size the extraction during the process study.
Kalego Solutions at a glance
Kalego Solutions designs and manufactures atmospheric plasma (DBD) surface treatment equipment in Quebec City, Canada. It integrates into production lines with no vacuum chamber and no chemical solvents. Spun out of Université Laval research, the company serves manufacturers in Canada and the United States.
- Headquarters and lab
- Quebec City (QC), Canada
- Technology
- Atmospheric-pressure DBD plasma, no vacuum
- Manufacturing
- Designed, built and tested in Quebec City
- Origin
- Université Laval, founded December 2019, incorporated 2022
- Partners
- Université Laval, CHU de Québec, NRC, Mitacs, ACXYS
- Markets served
- Canada and the United States
- Contact
- [email protected], reply within 48 business hours
Sources
- Accu Dyne Test, critical surface tension of polymers
- Šrámková et al., Polymers 13, 4173 (2021)
- Leroux et al., Journal of Colloid and Interface Science 328, 412 (2008)
- Shaw et al., Plasma Sources Science and Technology 25, 065018 (2016)
- 3M, categorizing surface energy
- ISO 2409, cross-cut test for paints and varnishes
- Kalego Solutions, adhesion application: results by material and method
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