Questions and answers in the adhesives and sealants industry.

Question: I recently saw cyanoacrylate adhesives marketed with an accelerator. I always thought these super-glue-type adhesives were instant? Why would they need to be accelerated?

Answer: Cyanoacrylate adhesives are promoted as “instant” adhesives by many suppliers, but on some substrates and under certain conditions they can be less than instant.

These adhesives crosslink via an ionic polymerization and are catalyzed by chemical compounds that are more basic than themselves. Acid vs. base is a relative condition, and to a cyanoacrylate adhesive, water is a base. Cyanoacrylate adhesives normally depend upon atmospheric moisture to supply this critical ingredient to their cure. When very dry conditions occur, or if the substrate in question happens to be acidic relative to the adhesive, cure can be slowed or inhibited. Human tissue is bonded very quickly with these adhesives, not only due to the water content, but also the amino acids present, which are quite basic to the adhesive.

Among the earliest accelerators was common chalk, a natural carbonate. Modern accelerators include a number of organic and inorganic bases, usually supplied in a liquid carrier. When applied to one or more of the surfaces to be bonded, these will accelerate the cure of a cyanoacrylate.

Most manufacturers supply suitable accelerators for their adhesives and can recommend specific combinations for most bonding requirements.

-Bob Smith

Question: We currently use a two-part epoxy adhesive for bonding our parts together, but would like to color the adhesive so the joint is not so visible to our customers. Can we add pigment to this adhesive, and if so, how?

Answer: Generally, adhesive systems, including epoxies can be pigmented or dyed to specific colors. However, it is recommended you contact your adhesive supplier or alternate suppliers to obtain adhesive in a color that is acceptable to your application. Epoxy adhesives are reactive systems. Adding colored materials to them might interfere with the chemistry, change the mix ratios, or otherwise negatively affect your assembly. The chemistry of the epoxy may also change the color of the colorant with time. Suppliers may require certain minimum quantities to supply you a specific color.

-Bob Smith

Question: We manufacture labels using pressure sensitive transfer film we purchase from a supplier. We recently tried to develop a label for use on automotive tires, but the adhesive we use on almost everything failed our customer’s basic testing. What can we do?

Answer: Adhering a pressure sensitive adhesive to automotive tires can be a challenge. The tire-manufacturing process leaves residues on the rubber surface, some of which are mold-release agents. It is not surprising you experienced difficulties. Contact your adhesive film supplier and see if he or she can provide you with an alternative adhesive for this application. Tell your supplier what the problem is. He or she may have a ready alternative.

-Bob Smith