Coloured super glue enables automated QA in optical component assembly

The manufacturer’s intended daily volume of components produced was some 10,000, making automated assembly a must, including the application of the adhesive. With uninterrupted flow of the components a critical part of the process, the company approached Advanced Adhesives.

Managing director Graham Crozier says: “A cyanoacrylate (super glue) looked to be the most suitable choice for ensuring a secure assembly, but as it was transparent the camera would be unable to verify that the adhesive had been applied correctly before the component advanced to the next stage of production, the final assembly.

“So a key hurdle we had to overcome was to find a dye or pigment compatible with the cyanoacrylate. Everything we had tested in previous years lowered the shelf life of the adhesive to hours, or at a maximum a day.

“We had also tested a UV pigment on a range of adhesive activators so once applied and evaporated a UV trace was left, such that a witness of the components being activated was left on the surface visible under a low powered UV light. This led to a conversation with the customer and camera manufacturer as to the suitability of a UV trace in the adhesive.”

This had all the makings of a possible solution, but on initial testing the adhesive only lasted over night before solidifying, which would not be suitable in an automated dispensing application.

A great deal of work was carried out on many, many dyes and pigments until a solution was found with a very clever piece of chemistry involving a pigment which not only dispersed into the cyanoacrylate and remained stable within the adhesive without any separation, but also did not then cure the adhesive to a solid in the bottle or tubing for the delivery of the adhesive, and allowed the adhesive technical process in cure and strength to then be unaffected.

“The sample solution we initially made was then oven tested to increase the shelf life to 12 months and then onto 24 months to ensure the pigment was not affecting the adhesive and making it solidify,” says Crozier. “And it worked. It was completely stable and glowed like the proverbial Belisha beacon, enabling the camera able to see the adhesive. It did not diminish any strength of the adhesive or affect the cure speed of the adhesive. And it allowed the adhesive to stay in a liquid state for the whole of the adhesive’s shelf life.

“We like challenges here at Advanced Adhesives and this task certainly was a challenge, but one where we were prepared to go that extra mile for our intended customer –something we do regularly here and for which we have become synonymous for with customers,” Crozier concludes. “Needless to say, the 10,000 components per day are being successfully manufactured with all being now viewed by the camera to ensure the adhesive in place. We have delivered another solution to another happy customer.”