Chemicals used with Adhesives – What are they and what do they do?
Primers, Cleaners, Etchants, Initiators, Activators, Accelerators and Surface Conditioners are all examples of different chemicals that are used in conjunction with some adhesive applications in order to achieve desired results. The requirements of the process will guide the selection of the appropriate chemical. In some cases the substrates must be primed, in other instances the adhesive cure is triggered with an activator. Use products as recommended by the manufacturer for use with the adhesive in your application.
The following summary descriptions will introduce you to the ways that these chemicals can affect the outcome of an adhesive application.
A primer is a surface coating that changes the character of a surface so that an adhesive or coating will adhere to it more effectively. Use of a primer can significantly increase the adhesive’s ability to wet out the surface.
Plastics often require a primer that is quite specific to certain types of plastics. For example, polyolefin primers are designed to increase adhesion to the surface of polyolefin. When used on other materials such as nylon and composites they can actually decrease the adhesion.
A particular adhesive type may also have a specific primer formulated for use. So while one primer will increase the adhesion of cyanoacrylate to the substrate, it will not increase the adhesion of a UV light curable adhesive.
When accelerators are used to speed up the cure time, in most cases there is a tradeoff in the bond strength. When bonding a very porous material with a cyanoacrylate, accelerator applied to the substrate can increase adhesion by causing the cure before the adhesive is fully absorbed by the material.
Anaerobic Surface Conditioner
Anaerobic adhesives cure only in the presence of metal ions. Some metals are more reactive than others. In those cases a surface conditioner designed for anaerobic adhesives will increase the cure speed or allow cure on a non-metal surface. Like accelerators, anaerobic surface conditioners may cause a reduction in bond strength.
Initiators or Activators
Initiators or activators are catalysts. They are used with two component adhesives and cause cure to occur. These are specific to the adhesive so use care in selection.
Most commercially available cleaners sold by adhesive manufacturers are designed to clean up spilled adhesive – not to clean components to be bonded. Standard industrial cleaners and solvents generally do the job.
Cleaning components is easiest when the surface contaminants are known. Simple cleaning will do the trick to remove surface mold releases and plasticizers and allow the adhesive more direct contact with the plastic surface. For example heavily plasticized PVC will have higher surface tension after being wiped down with isopropyl alcohol. Similarly alcohol or acetone will remove many mold releases.
Some plastics respond well to a simple cleaning that eliminates the need for a primer without sacrificing the strength of the bond.
Etchants are acid-based solutions designed to prepare challenging surfaces for bonding. The surface energy of many metal compounds, and some plastics, such as fluoropolymers, will not be increased via either a cleaner or a primer. Etchants can be purchased or the process can be outsourced.
In closing, not every adhesive application requires the use of a chemical to achieve desired results, however the use of one may be just the trick you didn’t know you were looking for! Consult the manufacturer for recommendations for your particular application.
If you need any further help or advice, please contact Permabond.