Polyurethane resins for LED industries that are fully UV-stable and hard-wearing.

Fully transparent polyurethane compounds are attracting attention for use in a variety of LED (Light Emitting Diode) applications. Transparent polyurethanes are good chemical and mechanical resistant. Polyurethanes are usually applied by casting, but are likely to be used in injection and compression mold processes. Otherwise then epoxies polyurethanes are 100% non yellowing and can better withstand cratches.

Download here our Polyurethane potting compound folder (English version, PDF)

Download hier onze Polyurethaan gietharsen (PUR) folder (Dutch/Nederlands, PDF)

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Properties of Polyurethanes

Traditionally polyurethane potting compounds have a long history of application in the manufacturing of electronical devices (transformers, power supplies etc.) . Potting compounds are polyurethanes filled with minerals that provide good electrical insulation and thermal conductivity.

Transparent polyurethanes are available in a large variety of formulations, providing:

• High optical transmittance of light
• Excellent UV-stability (non yellowing).
• A wide range mechinal properties, from flexible to hard, all extremely tough.
• Good flame retardancy possible (up to UL-V0).
• Good adhesion to a variety of substrates
• Advantages against epoxies like more transparency, non yellowing
• Refractive index around 1.50 

More information about Polyurethane potting compounds you can find also at www.gietharsen.nl.

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Applications - Transparent polyurethanes

Transparent polyurethanes can be used in a large number of outdoor en light applications. Both very small single LED applications and large scale projects (multi LEDs, large surfaces as within flooring) are possible. Because polyurethanes are very durable they can be used in hard wearing conditions such as vandalism resistant projects, roadmarks and traffic lights. Transparent polyurethanes offer new possibilities to for LED packaging and encapsulations (e.g. Protective encapsulants, lenses etc.).

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Transparent polyurethane products

• Colors (transparency colors)
• Flame retardancy
• Pot Life (cross linking time)
• Flame retardancy
• Flexibility

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Transparent Polyurethane casting guide

Polyurethanes are produced by mixing two components (polyol + isocyanate). The reaction between polyol and isocyanate, that produces the polyurethane, is sensitive to water and moisture. Therefor all objects and surrounding should be as dry as possible when casting. After the curing time the polyurethane can withstand outdoor applications very well. When mouldings are being used, they should be perfectly smooth, to prevent adhesion of PU to the mould.

A casting guide for polyurethanes in general is available at www.gietharsen.nl

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.

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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.  

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