Transparent polyurethanes
Transparent Polyurethane.htm
Transparent Polyurethanes
UV stability
In general, polyurethanes are produced by means of a reaction between polyols and isocyanates. Some polyols and isocyanates absorb light. In particular, aromatic isocyanates absorb in the UV region.As a result, aromatic polyurethanes that are produced from these isocyanates, will absorb light, and therefor, will not be colourless. Even more, by absorption of UV radiation, they will gradually change their colour over time - a process called yellowing. This may take place in several weeks. Aromatic polyurethanes are found in traditional, filled potting systems. Since traditionally potted devices are hidden away inside equipment, the theoretical problem of discolouration on exposure to UV- or sunlight is academic, but irrelevant to the electronic devices manufacturers.
In translucent applications, such as LED packaging and encapsulation, the casting resin is permanently exposed to UV- or sunlight. In many cases, the casting resin is not just a means of protection – it becomes a part of the design and looks of the device. The efficiency of the LED will also depend on the translucency of the casting resin. Therefor, in these applications, the polyurethanes must be absolutely colourless and fully transparent, in other words, they should not absorb in the UV-VIS region. With these prerequisites, polyurethanes can be obtained that are stable even after exposure to UV – or sunlight for a long time. For outdoor applications it is furthermore relevant that the UV stability also leads to a longer lifetime as regards mechanical failure. Since UV radiation is not absorbed, there is no radiation damage to the polymeric network. Absorption of UV energy leads to an electronically excited state that results in the formation of some radicals. Eventual radical attack of the polymeric network will cause deterioration of the mechanical properties of the product, hereby dramatically shortening its outdoor lifetime.
Intercol's transparent polyurethanes are made up of polyols and isocyanates that do NOT absorb in the UV-VIS region. Our fully transparent polyurethanes, are therefor colourless, fully transparent and UV stable. In other words, discolouration or 'yellowing' is not observed in our transparent polyurethanes, even if they are exposed to artificial- or sunlight for long periods of time. In addition, the mechanical properties of the product are maintained throughout the exposure.
This makes Intercol's transparent polyurethanes ideally suited for outdoor, heavy duty, translucent applications