Powder Coating and Thermal Breaks in Aluminium Windows - Enemies or Friends?

By Bogdan Grebenyuk, Product Manager at Thermevo
on May 27, 2017
Powder coating aluminium thermal break technology can cause problems with insulation performance, so how does the fenestration industry cope?
While powder coating aluminium window frames is commonly done to achieve a number of finishes which can be extremely architecturally pleasing, polyamides are notoriously difficult to coat with the same degree of success. For a thermal break aluminium window, this constitutes something of a problem because the insulation products aluminium windows are most frequently fitted with today are polyamide isolation strips. Indeed, a typical polyamide isolation profile will not function as intended when it has come into contact with powder coat paint because it is hygroscopic to some degree. In other words, water molecules can diffuse into the material as a result of the powder paint process and become trapped there. This is particularly the case if the polyamide bars coating contains voids that can hydrogen-bond water into a position such that it cannot escape. All too often, the result is that the polyamide thermal break bar - that is supposed to sit within the window frame without touching the internal sides - swells up significantly and remains saturated rendering it useless.

"Utilising advanced polyamide thermal break technology, [allows for]... high thermal performance with the added benefits of large glazed spans and slim sight lines." - Stuart Holt, Commercial Aluminium Manager at Total Glass.

Should Powder Coating Aluminum Window and Door Frames Continue?

With the noted problems of polyamide profile coating mentioned above, window technicians and architectural designers of aluminium-framed façades and atria might be forgiven for thinking that thermal break technology and powder coating are not conducive to one another. However, there should be no compromise between insulating the frames of aluminium windows with the latest thermal technology to hand and achieving the best powder coated finish for the project. Given the many advances there have been in the development of polyamides within the plastics industry in recent years, such as chlorine resistant and reverse osmotic membranes, suitable solutions can be found that mean there is no pay-off between providing a good powder coating and insulation performance.

Developments in Powder Coating Aluminium Thermal Break Technology

Although not exclusively, the aluminium fenestration industry tends to use the most polyamide 66 for the purposes of creating a thermal barrier within window frames. Polyamide 66, also known as Nylon 66, is well-regarded for its low thermal conductivity and its ability to continue to operate well even in extreme sub-zero temperatures. Nevertheless, this particular polymer is also subject to water absorption and it will often swell up when exposed to moisture. Other types of polyamide isolation strips can face problems of bubbles occurring in the powder paint coating when it is applied to the profile after the insulating material has been added. Furthermore, when water is retained after the melting of the powder coating material either in the polymerised covering or in the polyamide surface itself, the result can often be severe blistering. One of the tried and test solutions to these defects has been to use a material such as Nylon 12 in the place of other polyamides. Nylon 12 is among the least problematic polyamides when it comes to the issue of swelling and blistering caused by the hygroscopic ingress of fluids. This material is also noted for its tensile strength its abrasion resistance, but among the common montmorillonite nanocomposite membranes its effectiveness as a water barrier is probably most noteworthy.

A Revolution Powder Coat Paint Technology?

In addition to the type of polyamide thermal break technology window makers can choose from to optimise insulation performance when their products are powder coated, paint manufacturers have also developed novel approaches to the problem. Leading powder coating specialists have spent a great deal of investment to come up with a new line of paints referred to in the fenestration industry as NBPs, or non-blistering polyamides. These elegant coatings are able to minimise the number of potential defects found in thermal breaks by simply allowing the moisture present in a polyamide to be released. Such coatings can be adapted to meet a wide number of colour requirements and can even provide textured finishes, if required – something that has traditionally been the most problematic area for marrying successful powder coatings with thermal performance. As such, there is no reason to consider powder coating to be the enemy of thermal break aluminium windows any longer.
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