As Mr. McGuire said to Benjamin in the classic movie The Graduate:
“I just want to say one word to you….. Just one word”
“Are you listening?”
“Yes, I am.”
Benjamin would have been wise to take that prescient advice back in 1967. Plastics are used in practically everything these days. They are great; light, strong, flexible, low cost and wonderful.
Until you have to bond them.
To make matters worse, the “best” plastics like polyethylene and polypropylene can be the most difficult to bond. Even polystyrene, polyvinyl chloride (PVC) and acrylics can be problematic.
You can use mechanical fasteners, but they don’t seal, don’t look nice and create localized stress points that lead to substrate failure. Solvent welding can work, but tends to be messy, inconsistent and not very workplace friendly.
Many engineers evaluate surface-to-surface bonding with double sided tapes or liquid adhesives, but the low surface energy characteristics of the plastics can make this difficult. How many times have you tried to use glue or tape to bond a plastic part only to have it fail the instant any type of stress is applied?
You can use primers or surface treatments like flame treatments or corona treatments to improve the bonding strength, but then you are adding time, expense and complexity to your process, which can largely defeat the some of the advantages of using an adhesive.
Given the headaches associated with using adhesive for bonding low surface energy plastics, I was pretty stoked to see the new Loctite 3035 Polyolefin Bonder adhesive:
- Requires no priming or surface treatment
- Has a convenient 1:1 mix ratio
- No special storage requirements
- Fixtures in fifteen minutes
- Cures in 24 hours at room temperature
It might not be the solution for every low surface energy plastic bonding challenge, but it’s great to have another “wrench” in the engineering toolbox.