Surface Energy & Dyne Level Calculator
Check whether an ink, coating or adhesive will wet your plastic, turn contact-angle readings into surface energy, and look up typical dyne levels for common plastics.
Will it wet? Substrate vs. ink, coating or adhesive
A liquid wets a surface only when the surface energy is higher than the liquid's surface tension. The working rule: acceptable adhesion is achieved when the plastic is about 8-10 dyn/cm above the ink, coating or adhesive. Pick your plastic, or enter a dyne level you measured, and what goes on it.
Result · dyn/cm
The surface exceeds the liquid by at least 8 dyn/cm - the 8-10 dyn/cm margin at which acceptable adhesion is normally achieved. Confirm with a trial using your actual ink, coating or adhesive: wetting is necessary, not sufficient.
The liquid may spread, but with less than an 8-10 dyn/cm margin expect crawling, pinholes and weak or inconsistent adhesion. Raise the surface energy with pretreatment.
The liquid's surface tension is higher than the plastic's surface energy, so it beads up instead of spreading - and no drying time, pressure or reformulation changes that arithmetic. Pretreat first.
Target surface energy for this liquid: 42 dyn/cm or higher, measured at the time of printing, coating or bonding.
Contact angle to surface energy (Owens–Wendt)
Dyne solutions tell you pass or fail. Contact angles tell you how much surface energy there is and how much of it is polar - the part pretreatment adds. Water and diiodomethane are the usual pair: water supplies the polar contribution, diiodomethane is essentially non-polar. This calculator uses the Owens-Wendt-Rabel-Kaelble (OWRK) model; record the model with your result.
Result · mN/m
Polarity: 2% of the total is polar.
Untreated polyolefins are almost entirely dispersive, with a polar part near zero. Plasma, flame and corona treatment add polar groups to the surface, which is what raises the polar part.
The equation and the liquid data this calculator uses
Written once for each liquid, this gives two equations in two unknowns — the dispersive (γSᵈ) and polar (γSᵖ) parts of the solid's surface energy. Their sum is the total. Liquid values (mN/m):
| Liquid | Total | Dispersive | Polar |
|---|---|---|---|
| Water | 72.8 | 21.8 | 51 |
| Diiodomethane (methylene iodide) | 50.8 | 50.8 | 0 |
| Formamide | 58 | 39 | 19 |
| Ethylene glycol | 48 | 29 | 19 |
| Glycerol | 63.4 | 37 | 26.4 |
| 1-Bromonaphthalene | 44.4 | 44.4 | 0 |
Surface energy of common plastics
Typical surface energies of untreated plastics, the pretreatments normally used, and how long an oxygen or air plasma treatment typically stays usable. Grade, fillers, additives, mold release and storage all move these numbers - treat them as a starting point for a test plan, not a specification.
| Plastic | Untreated surface energy dyn/cm = mN/m | Prints / bonds untreated? | Usual pretreatment | Treatment stays usable after air / O₂ plasma |
|---|---|---|---|---|
| PTFE and fluoropolymers | 18-20 | No | Pyrosil® or cold gas plasma | Minutes to hours |
| Silicone | about 24 | No | Pyrosil® | Minutes to hours |
| Polypropylene (PP, OPP, BOPP) | 29-31 | No | Flame (moldings), corona (film), atmospheric plasma | Hours to a few days |
| TPO and olefinic TPE | 29-31 | No | Atmospheric or flame plasma | Fast - bond within hours |
| Polyethylene (LDPE, HDPE) | 30-31 | No | Flame (moldings), corona (film), atmospheric plasma | Hours to a few days |
| PBT | about 32 | Treat first | Atmospheric or cold gas plasma | Days to weeks |
| PVC, plasticized (flexible) | 33-38 | Marginal | Plasma, then bond or print promptly | Fast |
| Polystyrene (PS) | 33-38 | Some inks | Flame or plasma | — |
| Acetal (POM) | below 36 | No | Cold gas plasma | — |
| ABS | 35-42 | Often | Clean; flame or electrical plasma for consistency | One to several weeks |
| Acrylic (PMMA) | 38-41 † | Often | Clean; electrical plasma (flame can haze optical surfaces) | One to several weeks |
| PPS | about 38 | No | Atmospheric or cold gas plasma; Pyrosil® for long treat-to-bond windows | Days to weeks |
| PVC, rigid | about 39 | Often | Clean; plasma for demanding jobs | — |
| Nylon (PA 6, PA 66) | 40-46 | Often (dry parts) | Corona, air or atmospheric plasma, flame, cold gas plasma | Days to about two weeks |
| Polyimide | about 40 | Some systems | Plasma | — |
| PEEK | 40-44 † | Marginal | Cold gas plasma or Pyrosil® | Days to weeks |
| Polyester (PET) | 41-44 | Some systems | Corona (film), plasma | One to several weeks |
| Polysulfone (PSU) | about 41 | Often | Clean; plasma | — |
| Polycarbonate (PC) | 42-46 | Often | Clean; electrical plasma (flame can haze optical surfaces) | One to several weeks |
| Modified PPO | about 47 | Often | Clean; plasma | — |
How to measure surface energy
Dyne solutions and pens (ASTM D2578)
Start with a high dyne level - 60 - and draw it across the surface. If the liquid does not break into droplets within two seconds, the surface energy is at least that value. If it beads sooner, repeat with the next lower level until a stripe holds. Never retest the same spot, record the temperature and humidity, measure across the part rather than at one point, and test immediately after pretreatment and again at the point of use. Solutions keep 6-12 months; pens dry out and drift. Test solutions contain 2-ethoxyethanol and formamide, so handle them with care - pregnant workers should not perform the test.
Contact angle
A goniometer measures the angle a drop of liquid makes with the surface - the method to use when a number has to be defended. Use a consistent drop volume of a few microliters, measure quickly, and take several readings. Water alone is a quick treatment check:
| Water contact angle | Surface | Typical of |
|---|---|---|
| Below 30° | Well wetted, hydrophilic | A well-treated surface |
| 30-60° | Moderately wetted | Treated polyolefin, or an untreated polar polymer |
| 60-90° | Poorly wetted | Untreated engineering thermoplastic; marginal for bonding |
| 90-120° | Non-wetting, hydrophobic | Untreated polyolefin |
| Above 120° | Strongly hydrophobic | Fluoropolymer, silicone - or a silicone-contaminated surface |
A good reading is not the whole story
Pretreatment activates whatever is on the surface, contamination included, and a dyne solution will read an activated contaminant quite happily. If the dyne level is good and the bond still fails, look for contamination before raising the treatment level - the adhesion failure troubleshooter walks through it.
Treatment decays - measure at the point of use
Plasma, flame and corona treatment is not permanent: polymer chains reorient and additives migrate to the surface. On a polyolefin most of the loss happens in the first 24 hours, and warm storage speeds it up. The table above gives typical usable windows; to set your own, measure treated parts at 0, 1, 4 and 24 hours and at 3, 7, 14 and 28 days under real storage conditions, then write a maximum treat-to-bond time into the process specification. See how long plasma treatment lasts.
Frequently asked questions
What dyne level do I need for printing or bonding plastic?
As a rule, acceptable adhesion is achieved when the plastic's surface energy is about 8-10 dyn/cm higher than the surface tension of the ink, coating or adhesive. For most inks and adhesives on polyolefins that means 38-44 dyn/cm; UV inkjet inks typically want 42 or more, PET film is treated to 46-52, and structural bonds can need far more - nylon 50-54 dyn/cm, PPS with epoxy at least 48-54. Confirm the figure with a trial using your actual chemistry.
Is dyn/cm the same as mN/m?
Yes. 1 dyn/cm equals 1 mN/m. Dyne levels (dyn/cm) are the traditional unit in printing and converting; mN/m is the SI unit used in contact-angle work.
What is the surface energy of polypropylene?
Untreated polypropylene is about 29-31 dyn/cm (mN/m), almost entirely dispersive. That is below the surface tension of almost every ink and adhesive, which is why PP is flame, corona or plasma treated before printing or bonding.
Are dyne pens as accurate as contact angle measurement?
No. Dyne solutions and pens are fast production checks, but they are a subjective read of whether a film holds for two seconds, and pens age. Contact angle goniometry gives a number you can defend, and with two liquids it separates the polar and dispersive parts of the surface energy.
How long does plasma or corona treatment last?
From minutes to weeks, depending on the polymer, its additives and storage. Typical usable windows after oxygen or air plasma: silicones and fluoropolymers minutes to hours; PP and PE hours to a few days; nylon days to about two weeks; ABS, PC, PET and PMMA one to several weeks. Warm storage and slip additives shorten them. Pyrosil® treatment typically stays usable for weeks to months.
Go deeper
Surface still not accepting ink or adhesive?
Scott Sabreen has solved adhesion problems on plastics for more than 30 years. Describe the part, the material and the process, and he will tell you where to look.
More free tools: Adhesion Failure Troubleshooter · Laser Marking Plastics Chart · All engineering tools
