Dyne Test (Dyne Level)

Dyne Test (Dyne Level)

Key Takeaways

• A dyne test brackets surface energy in 2 dyne/cm steps: the highest calibrated fluid that holds a film for two seconds.
• Untreated polyolefins read 29–31 dyne/cm; inks and adhesives need the surface 7–10 dyne/cm above their surface tension.
• Fluids age, contaminate the part and depend on the operator’s eye: a dyne level is a monitoring number, not a qualification number.
• Specify fluid set, timing, sampling, reader and acceptance level, or two plants will measure one part and disagree.

Dyne Test (Dyne Level)

A dyne test is a wetting test in which calibrated fluids of known surface tension are drawn across a plastic surface to find the highest fluid that holds a continuous film for two seconds; the dyne level is that fluid’s surface tension, taken as the part’s practical surface energy in dyne/cm. One dyne/cm equals one mN/m; the older unit persists on fluid and pen labels.

ASTM D2578 and ISO 8296 standardise the method for polyolefin film; the same fluids and caveats apply to moulded parts. What the test reports is strictly a wetting tension: a proxy for surface energy good enough for process control and not for a dispute.

Fluids, Pens and the Two-Second Criterion

The ASTM D2578 fluids are formamide (about 58 dyne/cm) and 2-ethoxyethanol (roughly 30 dyne/cm) blended in 2 dyne/cm steps from 30 to 56; commercial sets such as Accu-Dyne Test fluids run to 72 dyne/cm and are dyed for visibility. Both solvents are reproductive toxins, so formamide-free fluids exist; they are not interchangeable with the ASTM mixtures, so a specification should name which is in use.

A thin stroke is applied with a fresh cotton applicator or a dyne pen, and the operator watches the film edge:

• Film holds for two seconds — the surface is at or above that value; move up one step on a fresh area.
• Film breaks sooner — the surface is below it; move down one step. The dyne level is the highest fluid that holds; the true figure lies between steps.

Solutions with single-use applicators are the production standard; pens pick up contamination from each surface and lose solvent to evaporation, so they drift.

Typical Dyne Levels by Polymer

Figures are for clean, freshly moulded surfaces. Mould release, slip agents and fingerprints read lower than the polymer beneath, so untreated parts can test 4–6 dyne/cm under handbook values and treated ones can hold a film on activated contamination.

The Margin Rule for Inks and Adhesives

A liquid wets a solid only when its surface tension is below the solid’s surface energy, and wets reliably only with a margin covering the variation in both:

Minimum dyne level ≈ surface tension of the ink or adhesive + 7 to 10 dyne/cm

Build the specification from the supplier’s data sheet, not the row above. The surface energy calculator applies the margin to any liquid and reports whether a resin, untreated or treated, will wet it.

Limitations, and When Contact Angle Is Better

Every limit comes from one place: a person judging a film of a fluid that is itself a variable.

• Operator-dependent. Stroke speed, film thickness and the call on “two seconds” differ between people; agreement within 2 dyne/cm is good, 4 is common.
• Fluids contaminate the surface. Tested areas carry formamide and dye and must not be printed or bonded.
• Fluids and pens age. Evaporation and absorbed moisture raise the fluid’s surface tension so it reads low; a contaminated tip lowers it so it reads high.
• No polar/dispersive breakdown. Two surfaces at 44 dyne/cm can bond differently and the test cannot tell them apart.
• Rough or textured surfaces. Capillary channels hold a film that should break; ridges break one that should hold.

Contact angle goniometry is the better method when the number must be defended: validation, disputes, a bond that fails at an acceptable dyne level, textured or small parts, and separating polar from dispersive components.

Troubleshooting Wrong Readings

The last row is not an error: treated polyolefins lose several dyne/cm within days, and how long plasma treatment lasts depends on the polymer and its additives more than the treater.

Specifying and Verifying a Dyne Level

“Minimum 42 dyne/cm” alone passes at one site and fails at another on the same parts. Five items make it enforceable:

• Fluid set. ASTM D2578, ISO 8296 or a named commercial formulation, with step size and shelf-life rule; never mix formamide-based and formamide-free results.
• Timing convention. Two seconds from the end of the stroke, film unbroken over a stated length (25 mm is typical), fresh applicator and area per fluid.
• Sampling. Parts per lot, positions on each (centre and edge, print and bond faces), and when: at the treater, the point of use, or both.
• Who reads. A trained operator against a reference coupon, with a second reader for any result within one step of the limit.
• Acceptance level. Supplier surface tension plus the margin, as a minimum at the point of use; add a maximum where over-treatment risks a weak boundary layer that wets well and bonds poorly.

Anchor the limit at qualification with contact angle on the same coupons, and revalidate when resin, additives, pretreatment method or ink change.

Related Terms and Reading

• Surface energy
• Contact angle
• Surface energy calculator
• How long does plasma surface treatment last?
• Polymer surface pretreatment methods
• The science of solving plastics adhesion problems

Applying this in production

The Sabreen Group provides independent engineering support for dyne testing, surface energy specification and adhesion troubleshooting. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.

Frequently Asked Questions

What dyne level does a plastic need before printing or bonding?

The surface tension of the ink or adhesive plus 7–10 dyne/cm, from the supplier’s data sheet, not a generic table. That puts most solvent inks at 36–42 dyne/cm, water-based and UV inks at 40–52, and epoxies and polyurethanes at 48–56. Untreated polyolefins at 29–31 dyne/cm miss every one.

Is a dyne pen as reliable as dyne solutions?

No. A pen’s felt tip picks up contamination from every surface it touches and loses its volatile component to evaporation, so it can read high and low within a month. Solutions with a fresh cotton applicator per stroke are the ASTM D2578 method; pens are for a quick go/no-go look.

Why does ink or adhesive fail when the dyne test passes?

Usually one of three: a contaminant activated with the polymer wets the test fluid but not the ink; the polar component the adhesive needs is low, which a dyne fluid cannot detect; or the part was bonded days after testing, after decay. Two-liquid contact angle and retesting at the point of use separate them.

How does a dyne test differ from a contact angle measurement?

A dyne test is a pass/fail judgment by eye, bracketed in 2 dyne/cm steps, that leaves fluid on the part. Contact angle is an instrument measurement of a droplet profile, and with two liquids it separates polar from dispersive energy. Dyne solutions suit shift-by-shift monitoring; contact angle suits validation and disputes.

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