Surface preparation before bonding - how is it done?
More than 80 percent of all bonding failures start at the interface, not inside the adhesive. This guide shows how to clean, abrade, prime and activate surfaces with plasma or flame treatment - matched to the material and its surface energy.
View cleaners and primersWhy does the substrate decide bond strength?
An adhesive is only as strong as the interface it bonds to. Adhesion requires the liquid adhesive to fully wet the substrate, and that only happens when the surface energy of the material is higher than the surface tension of the adhesive.
The rule of thumb: the substrate needs at least 38 mN/m, ideally above 40 mN/m, so a droplet spreads out instead of beading up. Metals and glass are high, while non-polar plastics such as PP and PE sit at only 29‑31 mN/m and must be activated first.
- High surface energy: aluminium, steel, glass, many paints - usually easy to bond.
- Low surface energy: PP, PE, POM, PTFE, silicone - activation required.
- Test inks to ISO 8296 read the wettability directly in mN/m.
Cleaning and abrading - what comes in which order?
Every pretreatment starts with degreasing. Release agents, oils, finger grease and dust block any bond, so you clean first with a residue-free solvent such as isopropanol - using clean, lint-free wipes in one direction, never in circles.
Abrading follows. Sanding or blasting enlarges the area and creates a mechanical key. The order matters: clean roughly first, then abrade, then degrease a second time to remove the sanding dust.
When to use plasma, flame treatment or primer?
Non-polar plastics can hardly be improved mechanically, so only chemical or physical activation helps. Plasma, corona and flame treatment build polar groups on the surface and lift the surface energy in seconds from around 30 to over 50 mN/m.
- Atmospheric plasma: non-contact, ideal for PP, PE and inline production.
- Flame treatment: fast large-area activation, common on polyolefin automotive parts.
- Corona: the classic choice for films and webs in roll processes.
- Primers and adhesion promoters: a thin film for glass, PTFE or elastomers.
Primers are applied thin and even and must flash off completely before bonding. Layers that are too thick form a weak boundary instead of an adhesion bridge. The maker's data on flash-off time and film thickness is binding here.
Frequently asked questions
What surface energy does a substrate need for bonding?
As a guide the surface energy should be at least 38 mN/m, better above 40 mN/m. Then the adhesive wets the surface and forms a load-bearing interface. Non-polar plastics sit below this and must be activated.
Is sanding enough for plastics like PP and PE?
No. PP and PE are chemically inert and low-energy. Sanding alone gives no durable bond. Only plasma, flame treatment or a dedicated adhesion promoter creates the polar surface required.
How long does a plasma treatment last?
The raised surface energy decays over time. Depending on material and storage the window ranges from a few hours to several days. Bonding within one to two hours is safest.
Which cleaner is right for degreasing?
Isopropanol is the standard because it evaporates without residue. Acetone works too but is more aggressive on sensitive plastics. Always use lint-free wipes and wipe in one direction.
Preparing the substrate correctly?
We supply cleaners, test inks, abrasive pads, primers and activation technology - matched to your material and the bond strength you need.
Process-reliable
Defined steps from cleaning through to activation.
Measurable wetting
Test inks to ISO 8296 make the energy visible.
Standards-based
Pretreatment following the principles of DIN EN 923.
Expert advice
Our specialists help with material and method.