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bl2501-uv-enclosures-a

UV RAYS – THE INVISIBLE THREAT

Prolonged exposure to sunlight can discolour and degrade plastic enclosures. The ultraviolet (UV) rays cause a photochemical reaction, breaking down the polymer bonds. This process is known as photodegradation.

And don’t just assume this is an outdoor issue. Even enclosures used exclusively indoors can still be susceptible to damage from sunlight. More than 50% of UVA rays can still pass through standard window glass.

Even a dependable plastic such as ABS – which is widely used for electronic enclosures – will suffer a series of microcracks, affecting its appearance. The solution is to specify a UV-stable plastic as an alternative material for your enclosures.

HOW UV LIGHT DAMAGES PLASTICS

Ultraviolet light, part of the electromagnetic spectrum, is divided into three types: UVA, UVB, and UVC. When plastics are exposed to UV light, the energy from the UV rays can excite the polymers’ chains, causing them to break down.  Additionally, the presence of oxygen can accelerate this process – leading to faster degradation.

UVA, UVB, and UVC all have different effects on plastics. UVA (320-400 nm) and UVB (280-320 nm) rays can pass through some types of plastic, causing discolouration and brittleness over time. UVC (100-280 nm) is often blocked by most common plastic materials but when it does penetrate, it can cause significant damage due to its higher energy levels.

IMPACT OF UV LIGHT ON PLASTICS

UV light can cause plastics to change colour, often resulting in a yellowing or chalky appearance. This is due to the breakdown of chemical bonds within the plastic, leading to changes in the material’s surface layer.

The breakdown of polymer chains makes the plastic more brittle, causing it to crack or shatter more easily. Also, the surface of the plastic can become rough and less glossy, affecting its aesthetic and functional properties.

Some plastics may show signs of degradation within a few months of continuous exposure, while others may take years. The time it takes for UV light to damage and discolour plastics depends on several factors, including the type of plastic and the intensity of UV exposure.

Environmental conditions can also affect the process. Higher temperatures can accelerate the degradation process by increasing the rate of chemical reactions within the plastic. This can lead to faster breakdown of polymer chains, resulting in quicker discolouration and brittleness.

Humidity can also accelerate the degradation process by introducing moisture into the plastic. This moisture can react with the plastic’s chemical structure, speeding up the breakdown of polymer chains. Additionally, the presence of moisture can facilitate the formation of free radicals, which are highly reactive and can cause further damage to the plastic.

SPECIFY UV-STABLE PLASTICS FOR YOUR ENCLOSURES

Acrylonitrile butadiene styrene (ABS) used to be the go-to plastic for enclosures. It’s a tough and reliable thermoplastic that resists impacts and chemicals, and it has a low melting point so it’s easy to mould. But ABS is vulnerable to UV light – so Acrylonitrile Styrene Acrylate (ASA) was developed as a UV-stable alternative.

ASA copes better with UV rays than ABS due to its composition. ASA replaces the polybutadiene rubber found in ABS with acrylic rubber, which is inherently more UV resistant. This substitution significantly enhances ASA’s UV stability, making it less prone to degradation and discolouration.

ASA retains many of ABS’s desirable properties – such as strength, resilience and ease of manufacturing – while adding superior resistance to UV light. It also withstands heat, rain and temperature fluctuations better, making it a smart choice for protecting outdoor electronics. Furthermore, ASA also has a better flammability rating: UL 94 V-0, compared with UL 94 HB for ABS.

Need a more durable plastic that’s still UV stable? Look for enclosures moulded from an ASA+PC blend. Polycarbonate (PC) is an extremely robust plastic that is used to manufacture riot shields, bullet-proof glass and CDs. Combining it with ASA gives you the best of both worlds.

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