Bonding polycarbonate without stress cracks
Polycarbonate is impact-resistant and transparent – but sensitive to the wrong adhesive: solvents and some superglues can cause stress cracks that cloud and weaken the component over several days. Using the correct adhesive class reliably prevents this.
To the point
Use UV-curing acrylates, two-component epoxies , or elastic silicones/MS polymers – they do not cause stress cracks. Avoid solvent-based adhesives and highly penetrating superglues on tensioned PCs, and install components with as little stress as possible.
Why polycarbonate cracks
Polycarbonate is prone to environmental stress cracking: Where the material is under mechanical stress and simultaneously exposed to an aggressive medium, fine cracks (crazing) develop and propagate. Solvents from adhesives and the vapors of curing cyanoacrylates have the same effect. This is exacerbated by residual stresses from injection molding or machining. The result is clouding and loss of strength – often only becoming apparent days after bonding.
Which adhesives are safe
| adhesive | Suitable for PC | Products |
|---|---|---|
| UV acrylate | very good, transparent, low-stress | LOCTITE AA 307, AA 3494 |
| 2K epoxy | Good, no severe stress cracks | Araldite 2012 |
| Silicone / MS polymer | good for flexible/sealing joints | Merbenit HM21 |
| cyanoacrylate | only with caution; paid, low-flowering types | LOCTITE 460 |
How to avoid cracks
Choose a solvent-free adhesive, mount the component under low stress, and reduce residual stresses – for heavily machined parts, annealing (stress-relieving annealing) before bonding is helpful. With UV acrylates, ensure that UV light reaches the adhesive. For general substrate selection, see Bonding Plastics; for UV technology, see UV and Light-Curing Adhesives; and for cyanoacrylate limitations, see Cyanoacrylate.
Frequently Asked Questions
Why does my polycarbonate become cloudy after gluing? These are stress cracks caused by solvents or cyanoacrylate fumes on stressed material. Switch to UV acrylate or epoxy.
Is superglue completely out of the question? Use caution and low-blooming types for small, stress-free areas – for visible or stressed bonds, UV acrylate and epoxy are the better choice.
How do I glue transparent PC? With clear UV acrylates that were developed for transparent plastics.
Consultation and samples
Tell us about the component, the load it will be subjected to, and whether the bond will be visible – we'll recommend the stress-free solution and provide a sample. Contact us or write to info@silitech.ch.
