Protection of Underwater LEDs featured Image
Protection of Underwater LEDs

Last month, I departed from my usual format – essentially to provide as much information as possible on the subject of resins, their formulations, chemistries, special properties and so forth, to concentrate more on how they are used to solve real world problems. As I mentioned last month, there is a growing interest in LED lighting, which offers a more efficient and longer-life alternative to halogen, incandescent and fluorescent lighting systems for both interior and exterior applications, as well as providing greater freedom of expression in terms of product design and installation. Indeed, it is not too strong a statement to say that LED lighting has become a market phenomenon; expected to grow into a $70 billion industry by 2020, and due to turn its market share from a current 18% to 70% in a little over five years, this is one industry whose needs we cannot ignore!

Last month, I described a couple of applications – (continents apart), which showed how resins are helping lighting manufacturers – specifically LED lighting manufacturers – to overcome the practical and sometimes technically challenging problems that they frequently encounter. Increasingly, they are turning to companies such as Electrolube for help and guidance on which potting and encapsulation resin or thermal management product is right for their project.

So I make no apology for returning to this subject again for this month’s blog! I’d like to give an account of a project we recently undertook for an Australian customer, who had a number of issues to address with the resin encapsulation of a particular LED lighting unit they had designed for swimming pool illumination, and they’ve given us the green light (no pun intended) to talk about it.

There were a couple of pressing problems here that needed some specialist input from our Australasian and UK based technical teams. Firstly, the lighting unit had to be sealed not just against freshwater, but also saltwater – saltwater pools being particularly popular in Australia. These pools are not chlorinated in the usual way and swimmers avoid the unpleasant smell of chlorine and its effects on the eyes and skin. Salt resistance was therefore the first imperative when it came to choosing an appropriate resin for this application.

Apart from being able to tolerate a working temperature range of 5 to 40°C, as well as being flame retardant, the resin colour was another important issue for this project, where a light blue shade was preferred for aesthetic reasons. Our customer had been using an epoxy resin on this application from a different supplier, but due to the highly exothermic reaction associated with epoxies, some slight deformation of the base unit was occurring as a result of the high temperatures generated during resin cure, which was deemed totally unacceptable. So our choice was narrowed down to polyurethane – but which product from our large portfolio of polyurethane resins was going to work for our Australian customer?

Polyurethane resins offer excellent water resistance; indeed, some formulated products are designed specifically for marine applications, such as our UR5041, which has proved very effective in applications where the potted unit is likely to be immersed and continually operating in saltwater. Providing exceptional resistance to seawater, this resin has the added benefit of an exceptionally wide operating temperature range (-60°C to 125°C), so it was certainly one to consider for the Australian job.

Then there’s UR5083, one of our particularly high performing resin systems that has the unique ability to ‘self heal’ if penetrated. This feature is ideal for applications involving the sealing of submerged units or underwater cabling and wiring where connectors or components need to be passed through the resin after application. The resin maintains contact with the potted unit, while sliding off a wire or connector as it is removed and closing up behind it to provide a moisture barrier.

Another contender was our UR5528 polyurethane resin, which features excellent chemical and water resistance. Our customers have used this on many occasions to protect marine electronics, or other applications where moisture ingress is a potential issue.

We finally decided to offer the customer our UR5097 encapsulation and potting compound. The cured polyurethane has great thermal conductivity – an important property as far as LED lighting units are concerned – and it has a wide temperature range. It is also flame retardant to UL94, which was another of our customer’s requirements. As was the case with all the other polyurethane resins we considered, the extremely low water absorption rate of polyurethane was considered the most critical property for this application.

Indeed, UR5097 met all the requirements of this project – with the exception of the colour, that is. Apart from UR5083, which is a light straw colour, our other polyurethane resin contenders for this project were all black as standard, so we had some re-formulation to do in order to meet the customer’s requirement for a light blue. The colour of a batch of the chosen UR5097 resin was duly altered to the desired shade, and we made sure it was right prior to shipping by matching it against a RAL standard.

With the first production batch of material manufactured to the customer’s specification and shipped to Australia, we were confident of a good result. However, during a courtesy visit to the customer by our Australia and New Zealand Manager, Mike Woods, accompanied by yours truly, we discovered that there had been a couple of issues with the material.

Over time, sedimentation had occurred and the product was proving increasingly difficult to reincorporate back into the resin mix. Moreover, there was a slight bleed of resin through the gap between the resin and LED unit. With a bit of lateral thinking the logical solution would be to increase the thixotropic nature of the resin, which would help to slow down the rate of sedimentation to an acceptable level, as well as preventing the resin bleeding so readily through the gap. The polymer used in UR5097 is also highly resistant to the transmission of water even at various pressure differences experienced due to the depth of the water.

A couple of weeks of lab work and testing with a number of different options produced a material that had sufficient thixotropy to slow down the sedimentation and avoid leakage into the gap, while still being easy to mix and pour into the unit. In the end, the actual increase in the mix viscosity of modified resin was only slightly higher than that of the original material.

So there you have it – a job well done, despite the setbacks, and one that met with the full approval of our customer who can rest assured that the chosen resin will continue to protect their lighting products for years to come.