Issue link: https://iconnect007.uberflip.com/i/1475604
60 DESIGN007 MAGAZINE I AUGUST 2022 PolyBD resins generally have exceptional resistance to water, even holding up well against saltwater immersion, but are suscep- tible to attack by organic solvents such as oils and fuels. Resins with a polyether/polyester part A base, however, generally have a bet- ter resistance to organic solvents. But while they offer good water resistance at lower tem- peratures, they typically are not as strong as the polyBD based materials when the condi- tions are both hot and wet. Even within those broad categories there are differences in per- formance, which is why it's best to bring your application and conditions to specialists in the first instance so a resin can be matched with the best combination of properties for your needs. Thermal Conductivity e trend for miniaturisation means high power density devices are increasingly com- mon. ermal dissipation away from hot areas of the device to heat sinks and metal casings is more important than ever. e thermal conductivity of a resin is influ- enced by the type of conductive filler used and even particle size distribution and particle shape, as this will affect the packing of the par- ticles, and thus heat transmission, through the material. ermal conductivities quoted on datasheets are of limited value as different test methods can give different values for the same material. is means that two resins with the same stated TDS value can perform very dif- ferently in-application. Some methods are most accurate when measuring lower thermal conductivity mate- rials, such as the guarded hot plate method, while others such as the laser flash method are particularly strong for testing at high tem- peratures. Several methods (including both already mentioned) rely on precise test sample dimensions, which means the testing is time- consuming and can be influenced by operator technique and precision. We use a modified transient plane source (MTPS) instrument which is a non-destructive technique suitable for liquids, solids, pastes, and powders, and which gives accurate and repeatable measure- ments, even for smaller sample sizes. To achieve the most accurate comparison it is important to test side by side in-application, if possible, to see the real-world heat reduction achieved. is is not just relevant for resins, it also applies when considering thermal inter- face materials. Bio-based Raw Materials Sustainability is becoming ever more of a priority globally, for manufacturers and for us here. We take our ESG targets very seriously and have been devoting a lot of R&D time to the use of bio-based raw materials in our resins, which led to the introduction of our UR5645 resin, a chemically resistant, high temperature bio-based PU. ere is an element of future- proofing in using bio-based resins, as synthetic raw materials derived from crude oil will not be available forever. Results demonstrated by our resin development chemist, Beth Turner, have highlighted that there can be significant technical benefits from transitioning over to bio-based raw materials. e results also show that not all bio-based raw materials are created equally. A lot depends on their origin as some cheaper bio-based fillers did not offer the same performance benefits as other options, and users cannot assume that all resins advertised as using bio-based materials will offer a techni- cal advantage. ere are numerous opportuni- ties for bio-based encapsulation resins for use The trend for miniaturisation means high power density devices are increasingly common.