UV Thickness and the case of 50µm (microns)
One of the most common questions we get asked is, is your polycarbonate UV coated, if so, how thick is the coating? Then comes the big finale, the ultimate showdown question – your competitor’s polycarbonate sheets specify 50 microns of UV coating, how thick is yours?
The process of plastic degradation and deterioration due to UV light exposure is the result of a chemical process called photo-oxidation, also known as photo-degradation. Ultra violet rays weaken the chemical bonds within the polycarbonate polymer chain, reduces the molecular weight of the plastic, resulting in loss of strength among other physical properties.
In the case of transparent or translucent polycarbonate sheets, with current polycarbonate co-extrusion technology, the extra UV-cap layer acts as an absorbent which “stabilizes” the UV. As the name suggests, UV Stabilizers absorbs the UV radiation to prevent the initiation of photo oxidation reactions, delaying the degradation process, prolonging the lifespan of polycarbonate sheets.
When it comes to UV coating, word on the street is 50 microns is the best, as if all UV resin are created equal and the thicker the coating the better the weathering resistance.
UV additives, in its original form, is usually a liquid or powder, mixed with polycarbonate resin, which is then dried and made into polycarbonate pellets/resin again. Which means that polycarbonate resin and UV resin blends together perfectly, even when co-extruded. What they don’t tell you is that UV masterbatches come in all kinds of concentrations and cost difference may go as high as 10X difference, though sadly, it cannot be proven by the naked eye. Some manufacturers may say that the thickness is measurable by microscope, but this method has never approved by Covestro or Sabic or any other major polycarbonate resin manufacturers, and never, ever used to determine the weathering capabilities of the polycarbonate sheet.
People might think there is a clear line separating the UV cap layer from the polycarbonate base material. In reality, when looked under a microscope, it looks just like a colored fizzy drink (see bottom photo), and impossible to tell where the purple color stops and the clear color begins. This means that any measurement of the co-extruded coating thickness, even when magnified under a microscope, is wildly inaccurate.
For example, on the photo below, it is obvious that there is no clear parting line between the said UV cap layer and base material, as the intersecting area extremely fuzzy. It’s a mystery how the operator came up with the measurements 42.204μm and 38.865μm.
What’s more, more often than not, customers are never told that the maximum concentration of the co-extruded layer regardless of the type of additives (color pigments, UV, heat reducing material) on polycarbonate is roughly 8%. The coated layer becomes saturated after 8%, which means that any effect of that certain material will remain at 8%, even when the concentration is higher.
The Q-UV ASTM G-154 accelerated weathering test is a well-known test protocol for plastics and is used worldwide as a test that best resembles real world exposure to the elements.
The only reasonable explanation people use simple microscopic measurements instead of performing standard accelerated weathering tests such as the aforementioned Q-UV ASTM G-154 test protocol, is probably due to test being extremely time consuming and costly. For example, a 3000hrs QUV test means that the machines will have to run 3000hrs non-stop, and fees amount to tens of thousands of US dollars.
The Avient (previously Avient) CESA-Light UV & Light Stabilizers Vulcan Polycarbonate sheets use are made into masterbatches with 100% Virgin Covestro PC3113 as base, co-extruded onto our sheets during production, and have passed 3000hrs of accelerated weathering test with flying colors.
There you go, myth busted. Vulcan thrive to provide the best polycarbonate sheets in the category and use the best UV and Light Stabilizers available on the market, no expense spared, in exchange for peace of mind for both the customer and manufacturer.