What is ink adhesion?
Ink adhesion is the bond between a printed ink film and the substrate surface. This bond allows the print to remain attached during handling and use. It depends on interactions at the ink-substrate interface, including wetting, surface chemistry, surface topography, ink properties, surface preparation, and curing or drying conditions.
A brief overview:
- Adhesion concerns bonding between dissimilar materials at an interface, while cohesion concerns attraction between similar molecules within the material.
- Good wetting increases liquid-substrate contact, while contamination or low surface energy can increase the contact angle and reduce wetting.
- On some polymer films, corona treatment can improve surface conditions for print durability with water-based inks.
- Ink adhesion can involve chemical, dispersive, diffusive and mechanical interactions at the material interface.
Mechanisms at the ink-substrate interface
Ink adhesion depends on what happens at the boundary between the ink and the substrate. The mechanisms below describe general forms of attraction and interaction, without assigning one specific mechanism to every ink or material.
Adhesion and cohesion
Adhesion describes bonding between dissimilar materials at an interface, such as a printed film and its substrate. Cohesion describes attraction between similar molecules within one material, such as the internal strength within the ink.
Chemical, dispersive, diffusive and mechanical interactions
Ink adhesion can involve chemical, dispersive, diffusive and mechanical interactions at the material interface. These are recognised general adhesion mechanisms rather than a fixed list that applies in the same way to every material pairing.
Factors affecting ink adhesion
Material and process conditions can change the bond formed by the print. The main considerations include wetting, surface condition, chemistry, topography, ink properties, preparation, and drying and curing.
Wetting, contact angle and surface condition
Wetting describes how a liquid makes contact with a solid surface. Contact angle helps describe that interaction, while surface energy, liquid surface tension and cleanliness affect the area of contact between the liquid and the substrate.
Contamination can reduce contact with the substrate. Low surface energy can increase the contact angle, which is associated with reduced wetting and limits the contact formed before the ink dries or cures.
Ink properties, preparation and drying or curing
Ink properties influence how the print interacts with its substrate. Surface preparation also changes the condition of that boundary, while curing and drying conditions affect the resulting film.
Drying conditions and surface treatment both form part of the print process for water-based ink on polymer surfaces.
When you need ink adhesion
Treat ink adhesion as a material-and-process compatibility question in production labelling systems when print needs to remain attached during handling and use. Assess the actual ink, substrate, surface condition and drying or curing process together rather than relying on one surface property alone.
Ink adhesion and adhesion testing
Production discussions benefit from keeping the property being considered separate from the activity used to assess it. This distinction matters when interpreting separation at a boundary or within the material.
Bond and assessment activity
Ink adhesion describes bonding at the boundary between the print and its substrate. Adhesion testing evaluates the strength or failure behaviour of that bond.
The two terms should therefore remain separate in production discussions. One describes the property of the print, while the other describes how that property is examined. No single test result changes the meaning of the underlying interface bond.
Adhesive and cohesive failure
Test interpretation can distinguish adhesive failure from cohesive failure. Adhesive failure means separation where the ink or applied material meets its substrate.
Cohesive failure means breakdown within that material itself. This distinction helps identify whether separation occurred at the substrate boundary or inside the ink film, without treating both outcomes as the same type of failure.
ALS Identify supplies labelling consumables for ink adhesion
For ink adhesion requirements, ALS Identify supplies inks as part of its labelling consumables range. Contact ALS Identify about your substrate and printing process.
