Identification Systems Technical Information 5.1 Effect of surface energy on bonding properties The surface energy (also known as surface tension) is an important factor in the selection of the right adhesive. Because of their chemical formulation, all surfaces have their own polarity and surface tension. The Flat drops cause of surface tensions is the tendency of • High surface energy liquids to reduce their surface as far as • Good wetting possible, thus to form drops. When a • Good bonding properties surface which is to be marked (substrate) is wetted with an adhesive, in addition to the adhesive formulation and the surface quality (material, roughness, dampness etc.) the surface energy is also a decisive factor in the maximum attainable bonding force of the adhesive. As a basic rule, it can be noted that the Rounded drops surface energy of the adhesive must be less • Low surface energy than the surface energy of the material to • Poor wetting be bonded (substrate). The adhesive should • Weak bonding properties completely wet the substrate and not form any drops. Surface energies of different materials The material combination Material Surface energy [mN/m]* For optimum marking using acrylate-based is the decisive factor adhesive labels, HellermannTyton uses an An acrylate-based adhesive is polar and Polytetrafluor ethylene (PTFE) 18 improved adhesive formulation, which is therefore has a relatively high surface energy. Silicone (Si) 24 coordinated to the most common materials Acrylate-based adhesives achieve optimum Polyvinyl fluoride (PVF) 25 in industry. In most cases it is possible to final bonding on polar substrates (e.g. glass Natural rubber 25 guarantee very good application of these or metals) with a high surface energy. Polypropylene (PP) 29 labels. In borderline cases, a modified Acryl (PMMA) 31 adhesive formulation may be necessary. More critical is the application of labels using Epoxy (EP) 36 acrylate-based adhesives on materials with Polyacetal (POM) 36 low surface energy (apolar substrates) such Talk to us, we’ll be delighted to advise Polystyrol (PS) 38 as, for example, silicone, polyethylene and you. Polyvinyl chloride (PVC) 39 polypropylene. The surface tensions of an Vinylidene chloride (VC) 40 acrylate-based adhesive can be reduced for Polyester (PET) 41 particular applications by the addition of Polyimide (PI) 41 specific additives. However, this step brings Polyarylsulfone (PAS) 41 with it some drawbacks, for example, a Phenolic resin 42 free-flowing adhesive and thus a limited life Polyurethane (PUR) 43 and storage ability of the labels. Polyamide 6 (PA 6) 43 The lower bonding force of low-energy Polycarbonate (PC) 46 surfaces must therefore be taken into Lead (Pb) 450 account of when considering the end use. Aluminium (Al) 840 Copper (Cu) 1100 Chromium (Cr) 2400 Iron (Fe) 2550 *The values stated are non-binding reference values and for guidance purposes only. Date of issue: April 2011 469.