Passing UV Light with Polycarbonate|
Article - February 7, 2016 By LarsonElectronics.com
Passing UV Light with Polycarbonate
Lenses, covers and sheets handle ultraviolet (UV) light differently. Some are capable of blocking harmful UV bands, while allowing specific wavelengths to pass through. Others rely on film and coatings to improve its UV-blocking properties. Polycarbonate is one of the most common materials that is used for UV protection. Its applications range from mainstream eyewear to fixture covers for industrial lighting products.
Properties of Polycarbonate
Polycarbonate was invented in 1953 and two decades later became popular in the 1970s. The material is a tough thermoplastic (long-chain linear polyesters of carbonic acid and dihydric phenols) that is lightweight and impact resistant. During the manufacturing process, polycarbonate takes on the form of tiny pellets. Using injection molding, the pellets are exposed to high temperatures until they converted into liquid and are ready to be injected into the molding trays. Inside the molds, the material takes on the shape of the sample and is cooled down in the final phase.
Aesthetically, polycarbonate is 20 percent thinner than mainstream plastic and glass lenses. The transparent material is capable of withstanding up to 10 times more impact than glass or plastic. Moreover, it surpasses FDA requirements for impact resistant surfaces by up to 40 times and EN/EU grade for Low Energy Impact Resistance (small particle) standards. This makes polycarbonate ideal for manufacturers that are concerned about compliance with regulations surrounding production. To give you an idea of how strong the material is- it can withstand the impact of a steel ball at speeds up to 160 km/hr without shattering. When it comes to weight, polycarbonate is extremely light and flexible, which is useful for applications that cannot accommodate heavy glass.
The material comes with some minimal drawbacks that individuals should carefully take into consideration. Polycarbonate is not scratch resistant, and can easily be damaged when rubbed against rough surfaces. In order to address this issue, some manufacturers apply a scratch-resistant coating for added durability. It is also prone to more lens reflections, compared to glass or plastic variants. For individuals that use the material for lenses in glasses (eyewear), there is a very low risk of reduced visual clarity in patients with high prescription requirements.
Blocking UV Light
Polycarbonate is highly efficient in blocking UV rays with a 99 percent success rate. Additionally, it can achieve this feat on its own without special coating. By comparison, Trivex lenses also boast 99 percent efficiency against UV bands. However, the material is thicker (up to 10 times) and must undergo cast molding during production. The slow casting process allows Trivex lenses to achieve sharper optics than polycarbonate.
For extra UV protection, stabilizers may be added to the material. Although polycarbonate can resist UV light, long periods of exposure may degrade the natural properties of the surface. In particular, UVA and UVB can damage polycarbonate sheets, but it is essential to note that this process does not happen instantly, especially when coated with UV stabilizers. UVC poses less of a threat to the material because it does not persistently penetrate the Earth’s ozone layer.
When exposed to UV rays, the outer layer of a polycarbonate sheet is compromised (not penetrated). Photo-degradation of the surface causes the polymers’ chain scission to transform; and as its strength decreases on a molecular level, its weight (on a molecular level) also decreases prolifically. The degree of UV coating manufacturers apply to the material varies, depending on where the sheet will be used. In regions with persistent UV exposure, higher levels of UV coating are applied on the material.
Polycarbonate is mostly used as a viable replacement for lenses in the eyewear sector. Due to its impact resistant features, children and athletes may favor the material over fragile lenses. In the industrial lighting industry, it is used to house outdoor fixtures, serving as protection from water, obstruction and debris. In competitive racing, polycarbonate may be incorporated with helmets and car windows. Sheets of the material can also be installed on greenhouses, roofs and soundproof systems (since they can also block out loud noise).
In most cases, polycarbonate is effective in replacing tough glass and polyethylene membranes. For glass replacements, manufacturers create smooth, transparent versions of the material to promote light transmission. Embossed and frosted variants are manufactured for decorations and aesthetics. Polycarbonate can also take on solid and hollow properties. Solid sheets are naturally stronger, heavier and are mostly applied to light manufacturing and residential roofing. Hollow sheets offer robust thermal insulation and are utilized for outdoor growing houses. It is able to achieve such benefits, because it is composed of two walls (minimum). This allows the material to trap air in the hollow pockets of the sheet.