Adhesive Education Series: How Do Adhesives Function?

Bostik offers a diverse line of smart adhesives, from webs to M-resins, for a variety of markets stretching from automotive to labeling. Yet while these adhesives and their applications are unique, all of them function in a similar, basic manner:

• Wetting Out: All adhesives must wet out to form a bond, which means they cover a surface to maximize the contact area and the attractive forces between the adhesive and bonding surface. Good wettability of an adhesive is a prerequisite for ensuring good adhesive bonding. Considerable effort has been expended in developing simple tests to assess surface energy/tension prior to bonding.

 

• The extent to which an adhesive wets out on a surface is the determining factor for adhesion.

For adhesives to effectively wet out on a surface, the surface energy of the adhesive must be as low or lower than the surface energy of the substrate to be bonded. If not, then the surface energy of the substrate must be raised. Adhesives.org provides further information on surface energy and wetting out.

• Setting: After “wetting out”, all adhesives must solidify to gain strength, i.e., they lose their heat or carrier.

 

• This is the determining step for cohesion.

While all adhesives set, the manner in which they set is dependent upon their chemistry.
If there is no chemical reaction, adhesives set the following ways:

• By loss of solvent (solvent-based adhesives)
• By loss of water (water-based adhesives)
• By cooling from a melt (polyamides, polyesters, butyls)

If there is a chemical reaction, adhesives set the following ways:

• By reaction with a curing agent (polyurathanes)
• By reaction with light or radiation (acrylates)

And, finally, all adhesives must undergo:

• Balancing Adhesive and Cohesive Forces: All adhesives must balance adhesive and cohesive forces in order to maintain a proper bond.

For over a century, Bostik has perfected its knowledge in the adhesive industry, creating new, innovative ways to use glue to benefit a variety of markets. For more information on how our smart adhesives can help your company, contact a Bostik expert.