Manufacturers using polycarbonate substrate materials often look to an adhesive for bonding or joining parts. Industrial adhesives offer a low-cost and convenient method of adhering parts. It allows flexibility of choice of substrate e.g. you can bond polycarbonate to other plastics, wood or metal. Other bonding techniques such as ultrasonic welding or solvent welding do not work of dissimilar substrates. Other benefits include minimal equipment outlay (welding equipment can be costly to purchase and run.) And also safer material handling – many workplaces are trying to reduce solvent exposure.
Polycarbonate is a relatively easy surface to bond; it has a reasonably high surface energy for surface wetting of the adhesive. Generally, it doesn’t require any surface preparation and is bondable “As Received”.
Most prefer a clear, non-yellowing adhesive that does not alter the appearance of the polycarbonate – keeping its clarity. There are a number of different industrial adhesive options to consider:
–Cyanoacrylates: These offer a rapid cure and are ideal for small surface areas or for high speed production lines. Opt for an alkoxy-ethyl cyanoacrylate if surface “frosting” (a white powdery residue) is an issue, also these products tend to smell less pungent. Limitations are a 0.5mm gap fill and environmental exposure – if the joint interface is in contact with water for long periods it can degrade the adhesive. Excess cyanoacrylate adhesive can cause stress cracking of polycarbonate so it is important to minimise excess liquid adhesive or cure it with an activator.
–Two-part epoxy: Bonds can be formed with a two part epoxy. Clear products (in thin film) are available. Thick layers of epoxy may yellow slightly over time. Epoxies offer excellent environmental resistance and are available in a variety of cure speeds to suit the user’s requirements. Stress cracking is minimised by thorough mixing in the correct mix ratio so the adhesive cures fully. Faster-set products can also reduce the likelihood of stress cracking.
–Two-part structural acrylics: it is best to opt for a 2 component pre-mix product with a static mixing nozzle to ensure all industrial adhesive is fully reacted to minimise attack on the polycarbonate.
–UV curable adhesives – visible light curing UV-adhesives are an excellent choice for bonding polycarbonate. Due to the UV-stabilisation of most polycarbonate, it is important to select a UV which cures in the 400-420µm wavelength spectrum. These products offer a clear, non-yellowing high strength bond and are a favourite for bonding polycarbonate.
Stress cracking is a common problem for polycarbonate which is particularly vulnerable to volatile chemicals and solvents. Making sure any adhesive you use is properly mixed and cured fully will reduce the chance of this occurring. Additional use care upon assembly, adhesive can lubricate press fit joints allowing the assembler to over engage (for example tubing into a polycarbonate fitting) thus creating hoop stress on the fitting which will become visible overtime.
For more information on bonding polycarbonate with industrial adhesive, please contact us.