“We are using UV light-curable adhesive to bond a polycarbonate hub to the passivated stainless steel hypotube. We encountered a leakage issue during our in-process air-leak test. Confirmation of the leak happened at the interface between the adhesive and the hypotube when injected with a colored dye. Prior to dye injection, “delamination” could be seen between the adhesive and hypotube. We tried appying primer on the hypotube, wiping the hypotube with IPA, and using a longer curing time, but none of these steps helped to eliminate the “delamination” issue.
What do you think is the cause of this problem and the solution?”
If contamination has been ruled out, delamination is most likely related to uneven stresses within the adhesive joint. I suggest looking at the adhesive, viscosity, bond gap, and curing process.
Are the adhesive and the viscosity appropriate for this application and given bond gap? UV light-curable adhesives shrink during the curing process and may pull away from the surface they have less adhesion to. The larger the bond gap, the more likely we will see air bubbles or delamination. In such a case I would try an adhesive with lower shrinkage or a filled, higher viscosity adhesive. Suitable products from DYMAX are 1180-M and 1180-M-T-UR, which are the higher viscosity versions for larger bond gaps.
You mentioned you tried a longer curing time; did you also explore curing with different intensities? I would recommend trying a shorter light exposure at a higher intensity and a longer exposure at a lower intensity.
Do you cure the adhesive from the top or from the side? If you cure from the side and use a UV spot lamp equipped with one or two lightguides, there is a risk of introducing uneven stress due to the shrinkage of the adhesive. The areas not directly exposed to the light often exhibit delamination or airbubbles in the bond joint. In such a case I would recommend using a 3- or 4-pole lightguide instead.