Substrates and Adhesion

Adhesives attach to the surfaces of two substrates, unlike a process that fuses substrates into a unified whole such as welding metal or solvent activation of plastics. In selecting a 3M adhesive or tape, surface condition must be considered: roughness, smoothness, porosity, coated, uncoated, cleanliness, flexibility, size of the part, and surface energy of the part.

Adhesive paste, for example, flows readily into a rough surface for improved effective adhesion. Flexible materials such as paper or thin
gauge metal can be bonded with a thin adhesive transfer tape. Large rigid parts with smooth clean surfaces can be bonded with a variety
of 3M products ranging from double coated foam tapes to two-part structural adhesives. Some plastics have plasticizers which migrate to
the surface and degrade the bond over time, so a plasticizer-resistant adhesive or tape is essential. If the substrate has been powder coat painted, the coating is the bonding surface rather than the substrate, and you would want to consider a 3M tape or adhesive developed specifically for that surface.

Surface energy ranges from high to low. To illustrate the concept of surface energy, think of water on the unwaxed hood of a car. The unwaxed hood has high surface energy and water on the hood flows into puddles. In comparison, a waxed hood has low surface energy
and the water beads up rather than flows out. Similar to water, adhesive on a high surface energy surface flows and “wets out” the surface. “Wetting out” is required to form a strong bond.

As a rule of thumb, the higher the surface energy, the greater the strength of adhesion.

Specially formulated adhesives are available for low surface energy surfaces. The following illustrations and surface rankings give you an
idea of relative surface energy.

Regardless of surface energy, the substrate must be unified, dry, and clean to maximize adhesive contact.

Barnes and Noble. Bow and arrow. Holmes and Watson. All the right combinations. Same as your tough bonding challenge and the 3M TSR.

Using the 3M Technical Service Request (TSR) Program, a 3M representative will work with you on initial testing of an adhesive design solution. One or two best options will be identified then a sample of your substrate is brought to the 3M Laboratories and tested for stress or other factors the product will encounter. The 3M test results will help you select the best design solution for your manufacturing process and customer needs.