Engineering
Substrate matching guide
Ink adhesion is a surface energy problem before it is an ink problem. This page sets out the thresholds, the pretreatment options and the drying bands for the materials we see most often, and the tests that settle the question on your own product.
Start with the surface, not the ink
A liquid wets a solid when the solid surface energy exceeds the liquid surface tension. In practice the margin needs to be comfortable — a gap of roughly 8 to 10 mN/m is the working rule of thumb, not a few units.
This is why polyolefins are the classic problem. HDPE sits around 28 to 32 mN/m and PP around 26 to 28 mN/m, both below the surface tension of most coding inks. A solvent ink on untreated HDPE can look perfect wet and then flake off under a thumbnail.
Polyester behaves differently: PET measures around 40 to 42 mN/m, which is already above the threshold for a solvent ink. The same ink that fails on HDPE may hold well on a PET bottle, which is why "plastic" is too broad a category for ink selection.
Pretreatment moves the surface energy
Corona discharge and flame treatment raise the surface energy of a polyolefin by oxidising the surface layer. In published figures, corona treatment lifts HDPE from roughly 30 to 38 – 42 mN/m, PP to around 40 – 44 mN/m, and PET to 46 – 55 mN/m.
Two cautions matter more than the numbers. First, treatment decays: a treated bottle loses its dyne level over storage time, so an ink that held in the lab may fail on stock that has sat in a warehouse. Second, primers and coatings can substitute for treatment, but the coating becomes the surface you are printing on — which is why a lacquered metal behaves like the lacquer, not like the metal.
Drying is a line speed question
Drying time only matters in relation to what happens to the product after the printhead. On a porous carton the ink is absorbed within a fraction of a second. On a non-porous plastic or coated metal the carrier has to evaporate, and that takes seconds, not milliseconds.
The practical test is not the drying time on a datasheet but where the first contact happens: the first roller, the first stacker, the first time two printed surfaces touch. We ask for that distance and the line speed, because those two numbers define the drying budget.
Where the budget is too short, the options are to move the printhead, add an air knife or dryer, reduce the ink load, or change the ink system. Changing the cartridge alone rarely fixes a drying problem caused by line layout.
Substrate reference table
The values on this page are published industry ranges and general engineering rules, not measurements of your specific material. Surface energy varies by grade, additive package and surface state, and certification of any coding outcome rests with the party applying the code.
| Material | Surface energy | Recommended ink | Pretreatment | Adhesion difficulty | |
|---|---|---|---|---|---|
| Kraft / paperboard | Kraft / paperboard | Absorbent — surface energy is not the limiting factor | Water-based | Not normally required for this substrate | Straightforward |
| Wood (raw) | Wood (raw) | Absorbent — surface energy is not the limiting factor | Water-based | Not normally required for this substrate | Straightforward |
| Corrugated carton | Corrugated carton | — | Water-based | Not normally required for this substrate | Straightforward |
| Kraft paper | Kraft paper | — | Water-based | Not normally required for this substrate | Straightforward |
| Uncoated label | Uncoated label | — | Water-based | Not normally required for this substrate | Straightforward |
| PP | PP | 26–28 mN/m | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Demanding |
| HDPE / LDPE | HDPE / LDPE | 28–32 mN/m | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Demanding |
| PET | PET | 40–42 mN/m | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Demanding |
| Rigid PVC | Rigid PVC | 38–40 mN/m | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Demanding |
| Coated / lacquered metal | Coated / lacquered metal | 30–38 mN/m | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Workable with care |
| Metallised film | Metallised film | 32–38 mN/m | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Workable with care |
| Glass | Glass | High energy but chemically inert — adhesion depends on the primer | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Workable with care |
| Coated aluminium foil | Coated aluminium foil | — | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Workable with care |
| Metallised BOPP film | Metallised BOPP film | — | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Workable with care |
| Lacquered tinplate | Lacquered tinplate | — | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Workable with care |
| Anodised aluminium | Anodised aluminium | — | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Workable with care |
| Coated steel tube | Coated steel tube | — | Solvent fast-dry | Commonly required — corona, flame or primer (target: 8–10 mN/m above the ink) | Workable with care |
| Follows the carrier substrate | Follows the carrier substrate | Select the carrier substrate first, then apply the covert layer | Covert UV (invisible) | Not normally required for this substrate | Workable with care |
| Pharma carton and label | Pharma carton and label | — | Covert UV (invisible) | Not normally required for this substrate | Workable with care |
| Cosmetic secondary packaging | Cosmetic secondary packaging | — | Covert UV (invisible) | Not normally required for this substrate | Workable with care |
| Premium beverage packaging | Premium beverage packaging | — | Covert UV (invisible) | Not normally required for this substrate | Workable with care |
| Spare-part and warranty labels | Spare-part and warranty labels | — | Covert UV (invisible) | Not normally required for this substrate | Workable with care |
| Document and certificate stock | Document and certificate stock | — | Covert UV (invisible) | Not normally required for this substrate | Workable with care |
How to qualify an ink on your own product
We would rather spend a week on a sample than have you discover at commissioning that the ink will not hold.
Request free printed samples- 01
Print a sample on the actual substrate, at the actual line speed, with the actual coding content. A test on a clean lab coupon is not evidence about your product.
- 02
Tape test: apply a pressure-sensitive tape, press firmly, remove at 90 degrees, and look at how much ink comes away with it.
- 03
Wipe test: apply ethanol or IPA as used in your cleaning process and wipe under consistent pressure. Check for colour transfer and for loss of contrast in the code.
- 04
Rub test: where the surface will be handled or abraded, run a solvent rub and count the double rubs to breakthrough rather than recording a pass or fail.
- 05
Environmental test: for cold chain or condensation exposure, hold the sample under the conditions the product actually sees and re-check readability afterwards.
- 06
Verify readability, not just appearance: scan the code with the equipment you will use at end of line, and confirm the contrast ratio is adequate on the actual colour of the substrate.
Standards and references
Where a figure or a method on this page rests on an outside standard, the standard is named here and linked to the publisher. We do not paraphrase what a standard says — the document itself is the authority.
- ASTM D2578ASTM International
A wetting-tension (dyne) test method for polyethylene and polypropylene film. It measures the state of a treated surface; it does not by itself predict how an ink will hold.
- ASTM D3359ASTM International
A tape test for coating adhesion. The standard states that it was developed on metallic substrates and points to ISO 2409 for non-metallic ones — read it as one input, not a verdict on plastic.
ISO and ASTM documents are sold by the bodies that publish them; the links open each publisher’s own page, where the abstract and scope are public.
Substrate matching tool
Pick the material you print on and what the code has to survive. The recommendation updates immediately.
Questions this guide gets asked most
My print rubs off. Is it the ink or the substrate?
The substrate is the first suspect, not the ink. Surface energy decides whether an ink can wet and bond at all: a water-based ink that performs on carton will not hold on untreated HDPE, and HDPE measures around 28–32 mN/m untreated against 38–42 after corona or flame treatment. Check the surface first, then the ink.
What surface energy does HDPE need before printing?
Roughly 38–42 mN/m after treatment, against 28–32 untreated. These are published industry ranges for the material class, not a measurement of your specific stock, and treatment decays: a treated bottle that has sat in a warehouse can fall back below the threshold. That is why the sample has to be printed on stock that is representative rather than on a freshly treated coupon.
Do I need corona or flame treatment for PET?
Often yes, and it is worth verifying rather than assuming. PET film usually needs treatment to hold a solvent or water-based code, while some coated and metallised surfaces print without it because the coating is what the ink actually bonds to. Measure the surface you are printing on, not the material named on the label.
How do I test adhesion on my own product?
Three tests, in this order: a tape test for how much ink lifts, a wipe test with the ethanol or IPA your cleaning process uses, and a rub test that counts double rubs to breakthrough instead of recording a pass or fail. Print the sample at your line speed with your real code content — a coupon printed in a lab is not evidence about your product.
Send us your substrate — we will send back a printed code
Tell us the material, the line speed and the text you need to print. We will recommend an ink system and put printed samples in the post so you can test them yourself.