The best adhesive for bonding nylon to metal

Bonding nylon (chemically known as Polyamide, or PA for short) with adhesives has traditionally been a challenge. Key characteristics of nylon which make it tough to bond are its hydrophobicity (resistance to wetting) and hygroscopicity (absorption and internal spreading of moisture from the air around it). Both these factors make it harder for an adhesive to effectively bond nylon and ensure a strong, long-lasting bond.

Bonding nylon to metal, however, introduces a new level of challenge. This is because nylon and metals are fundamentally vastly different materials with opposing chemical characteristics. For example, nylon has a medium surface energy, whereas most metals' surface energy is very high. This causes uneven surface wetting. Nylon also has much higher thermal expansion and contraction than metals, meaning that changes in temperature can create stress on the adhesive bond as the nylon swells and shrinks more than the metal.

The same is true with moisture absorption - as mentioned earlier, nylon is almost hungry for moisture and will readily take this up from the air around it. Metals, on the other hand, do not. Under humidity nylon can therefore swell as it takes in moisture, leading to stress and even breaking of adhesive bonds. Bonding nylon to metal therefore requires an adhesive that can effectively handle these imbalances in characteristics and still provide a strong bond.

Bonding nylon to metal: Is surface treatment needed?

Since nylon can be a bit of a 'problem child' for bonding, traditionally it has needed to be surface treated beforehand. Treatments such as plasma and/or flame treatment, as well as corona discharge, can be used to simultaneously raise its surface energy and reduce its hygroscopicity. Improvements in these areas can make bonding nylon to metal easier, as they bring the two substrates closer in chemical alignment.

Another common surface preparation method is to 'dry out' the nylon before bonding. This can be done by putting it in the oven at 60degC for 2+ hours (ideally overnight) and then attempting to bond. Unlike with other substrates, simply abrading or roughening the surface offers minimal bond strength improvement. It can provide very slightly more mechanical interlocking, but not enough to constitute anything meaningful.

Traditional surface treatment, while effective, can be costly, time-consuming and comes with its own set of risks. Corona discharge creates static, which can attract dust and constitutes a health and safety risk. Flame treatment must be done very carefully to ensure an even treatment and avoid fire risks. Chemical etching, another form of surface treatment, must be done in a fume hood because it is a toxic, corrosive and flammable process.

Thankfully, Permabond has developed an adhesive solution for bonding nylon to metal that allows you to avoid surface treatment altogether. TA4550 offers several benefits for bonding nylon to metals. Of great importance is its flexibility, giving it the ability to both handle thermal expansion and contraction as well as any swelling of the nylon due to humidity or moisture in the air. Other adhesives would embrittle and eventually break under such conditions, but not TA4550.

TA4550 has built-in surface adhesion technology that also allows it to overcome nylon's hydrophobicity. This means it can fully wet and key into the nylon, ensuring a strong, durable bond. Lastly, TA4550 excels in bonding metals, other plastics and composites, including bonding dissimilar materials - for example, bonding nylon to metal. This makes it a great all-rounder to have in your toolbox for general use, as well as for nylon to metal bonding.

Why surface preparation (not treatment) still matters

Although TA4550 removes the need for primers or complex pre-treatments, basic cleaning can still help ensure a stronger bond and more lasting, consistent results. Below are Permabond's recommendations for preparing nylon and metals before bonding with adhesives.

For nylon: Wipe with isopropanol to remove oils, grease, or mold release agents.

For metal: Degrease, lightly abrade or grit blast to remove surface oxidation for best results.