Greenhouses, winter gardens and roofs of large shopping centers – these are some of the many places where transparent plastics such as polycarbonate (PC), polyester (PET here) and acrylic glazing (PMMA) are nowadays replacing glass since plastics are lightweight, break-resistant and easy to shape. The material has to meet stringent requirements in such cases since it has to withstand UV radiation and other effects of weathering for decades while retaining its mechanical properties and appearance to the greatest extent possible. However, good processability of the plastic is likewise an important aspect for manufacturers of sheets, films and panels. The UV absorber TINUVIN® 1600 has allowed BASF researchers to set new standards in both respects. The filter absorbs more UV radiation than conventional products do, and it is also extraordinarily resistant to light, heat and weathering. The low volatility and good compatibility of the additive with substrates also make the plastic very easy to process.
The light stabilizer is based on an extremely stable chromophore which, like the hydroxy-phenyl-triazine (HPT), for example, in Tinuvin® 1577, belongs to the class of the triazines. Other chromophores in BASF’s product line are the benzotriazoles, benzophenones and cyanoacrylates. The various chromophore classes differ, among other things, in their absorption capacity and absorption range as well as in their inherent light stability. This is why they are suitable for different applications.
The outstanding absorption capacity of TINUVIN® 1600 shows in its very high degree of absorption as well as in its broad absorption curve. In the wavelength range between 290 and 350 nanometers, the absorption degree of TINUVIN® 1600 by far surpasses that of all other UV absorbers currently in use.
Moreover, in comparison to benzotriazoles, triazines fundamentally have a much greater light stability, and their absorption capacity hardly drops over time. The performance value of TINUVIN® 1600 for a 20 micrometer-thick cast film made of PMMA still amounts to more than 80 percent of the original value, even after 20,000 hours of exposure to xenon light. By way of comparison: the absorption capacity of a benzotriazole drops to less than 50 percent of the original value after just 5,000 hours. Last but not least, the additive performs much better than all of the other conventional systems when it comes to retaining optical properties such as color, color deviation and transparency.
Transparent thermoplastics such as PC, PET and PMMA differ in terms of the wavelength ranges in which they react most sensitively to UV radiation. Thanks to its very broad absorption curve, TINUVIN® 1600 can provide very good UV-protection to different polymers. Moreover, this UV absorber is well compatible with various substrates.
When compared to other UV absorbers, TINUVIN® 1600 exhibits very little volatility. At a temperature of 320 degrees Celsius [608 degrees Fahrenheit], the relative weight loss in a dynamic thermogravimetric measurement is less than one percent. This is an important aspect since polycarbonate sheets are normally extruded at temperatures between 250 and 290 degrees Celsius [482 and 554 degrees Fahrenheit]. Moreover, TINUVIN® 1600 stands out for its very high thermal stability as well as low outgassing and plate-out during the extrusion process. This improves not only the productivity of the plant but also the working conditions at the machine. The influence of the UV-absorber on the flow properties of the material (Melt Flow Index, MFI) matches that of other commonly used UV filters.
This extremely high-performance and light-stable UV filter lends itself particularly well for long-term outdoor use for up to 20 years under strong exposure to UV light. It is also well-suited for transparent final applications in the construction sector such as, for instance, PMMA laminated films for window profiles and window films made of PET or PVC. Other applications include cover layers on PC sheets for winter gardens or roofs of soccer stadiums and shopping centers.
For manufacturers of plastic sheets and films, the properties of this UV-absorber translate into higher productivity, less waste and less cleaning effort. The final product is much more durable than standard ones. This also helps BASF customers to tap into new market segments. For example, this UV-absorber could gain a foothold in automotive construction, where there have been ongoing efforts to find a replacement for glass in car windows. However, when it comes to the market of the future in photovoltaic technology, special plastics could forge ahead into as yet unknown performance ranges, thanks to TINUVIN® 1600.
Another example is PC sheets that are co-extruded with TINUVIN® 1600, and sometimes also laminated. In certain applications, this method can replace very costly coating procedures calling for additional processing steps. The UV-protection is very good with both of these methods, but TINUVIN® 1600 performs better here as well. Nevertheless, there is quite a difference between these two methods as far as the costs are concerned.
The market for transparent sheets and films made of PC, PET, PMMA, and SAN is enjoying steady growth. At the same time products are expected to be more and more durable and weather-resistant. BASF is responding to this trend by offering a broad portfolio of light stabilizers for all kinds of plastic applications, ranging from standard technologies such as Tinuvin 360, Uvinul® 3030 and Tinuvin 1577, all the way to UV filters such as TINUVIN® 1600 for very demanding projects. This premium filter is currently the best performing product on the market for plastic light stabilizers.
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