Selecting the proper adhesives for a nameplate, label or membrane switch application requires consideration of environmental, surface, appearance and other performance requirements. Our purpose here is to cover some of the principles of adhesion.
Surface contact is fundamental to adhesive performance. To maximize adhesive contact on a surface:
Adhesion is the molecular force of attraction between unlike materials. The strength of attraction is determined by the surface energy of the material. The higher the surface energy, the greater the molecular attraction. The lower the surface energy, the weaker the attractive forces.
Greater molecular attraction results in increased contact between an adhesive and substrate. In other words, on a high surface energy material, the adhesive can flow (or "wet-out") to assure a stronger bond.
Consider an automobile that has not been waxed for a long time. When water contacts the surface, it spreads in large puddles. The unwaxed car surface exhibits high surface energy - the molecular attraction allows the water to flow.
In comparison, water beads up into small spheres on freshly waxed car. It is an example of low surface energy - the liquid (or adhesive) does not flow out. Surface energy is measured by dynes per centimeter. The dyne level is the actual reading of the critical surface tension.
Modified acrylic and synthetic adhesives with better flow (or "wet-out") characteristics have been developed to adhere to low surface energy substrates. The Surface Energy Chart below compares the relative surface energy of commonly used substrates.
3M™ High Performance Acrylic Adhesive 200MP will not readily adhere to substrates categorized as having "low surface energy." However, 3M™ Adhesives 300, 320, 350, and 300LSE modified acrylics or 700 synthetic rubber adhesives have been designed to adhere to low surface energy plastics, and should be considered for those applications.
This illustration demonstrates the effect of surface energy on adhesive interfacial contact. High surface energy materials draw the adhesive closer for high bond strength.
Applying firm pressure to the bond increases adhesive flow and contact for more secure bonding. Time and temperature will typically further increase contact and adhesion values.
3M offers a wide range of innovative adhesives that can be selected for optimal bond area and anticipated loadings in joint designs.
Through the 3M IATD TSR Program and the 3M IATD Design Solutions Program, 3M also helps customers by conducting design reviews and identifying the best design solutions.