More adhesive isn’t necessarily better when you want an effective bond or seal. Covering the bond surface is the main requirement. The type of adhesive and the bonding environment have a lot to do with how much is “enough” and how much less or extra will cause adhesive failure.
Adhesive failure is a common issue when using too much adhesive. Following are some examples, probable causes, and suggested solutions.
Problem – Slow cure time.
Cause – Low moisture to adhesive ratio. Cyanoacrylates bond when trace amounts of moisture deactivate the adhesive’s built in stabilizer. Differing amounts of trace moisture are present in the surfaces being bonded, as well as in the air. Cure speed reduces when there is too much adhesive in proportion to the amount of moisture.
Solution – Tests should be made to determine the smallest amount of adhesive to achieve the desired bond. Production consistency can be improved with regulated temperature and humidity controls. (Testing is also a more economical and safer process when making critical bonds.)
Problem – white haze or crust on the finished piece.
Cause – Cyanoacrylates are designed to bond two mating surfaces. The amount of adhesive required is directly related to the size of the surfaces. Excess adhesive squeezed out of the bond area cures very slowly, allowing enough time for the cyanoacrylate to volatilize, cure in the air and fall back to the surface as a white residue.
Solution – Reduce the amount of adhesive used to eliminate squeeze out or use a surface activator / accelerator to cure the squeeze out.
The manufacturer’s technical support staff can help with this issue.
When troubleshooting a bonding problem, the first step is to determine if the problem is cohesive or adhesive in nature. Simply put, you want to figure out if the problem is related to
Too much initiator was used. Because initiators are very thin and water like substances, they are nearly invisible once applied to some surfaces. Overuse of an initiator can reduce the strength of the cured bond.
Use according to the directions on the technical data sheet.
The adhesive bond to one of the surfaces fails. Also known as Interfacial Failure
The tearing apart of an adhesive or sealant as the joint is stressed. The adhesive remains bonded to both surfaces but the adhesive itself cracks or tears down the middle. This occurs if the adhesive (bond) capabilities exceed its cohesive capabilities.
Adhesive unsuited to application – contact manufacturer for recommendation
The material being bonded fails before the adhesive.
In all cases of substrate failure, it is important to first identify the source of the stress that caused the failure. Effective adhesive choices must be suitable for the stresses on each joint as well as the substrate(s).
Stress cracks at or near the bond area may be the result of solvent exposure. Select solvent free adhesives; wipe away excess adhesive before cure.
Delaminated or broken substrates often indicate a need for stronger substrates. In some cases, redesigning the joint may do the trick.
For further help and advice, please contact Permabond.