Vinyl Durability Problems
Theory
UV Rays
For outdoor adhesive vinyl films, everything revolves around the sun. (Ha. See what we did there?) The simple reason is this: UV rays. The sun is the primary source of ultraviolet light. Unfortunately for vinyl films, UV rays are deadly. UV rays destroy the polymers in polyvinylchloride (PVC). The results show up in multiple ways. Have you ever seen old vinyl decals that are covered with tiny cracks? That’s the result of polymer breakdown from UV rays. Have you ever seen old-ish vinyl decals that have shrunk slightly since installation? Once again, that’s the result of UV rays breaking down the polymers.
The effect has multiple terms including weathering, fatigue, and the high-falutin term “photodegradation.” No matter what you call it, it has a major impact on outdoor vinyl signs.
PVC Formulation
Vinyl film manufacturers are well aware of the challenge. They have two ways to combat UV degradation. The first method is PVC formulation. Really cheap vinyl is made with monomeric PVC. This stuff doesn’t cost much, and it is highly vulnerable to UV rays. Polymeric PVC, on the other hand, is much more UV resistant. All PVC films from popular brands such as 3M, Orafol, Avery Dennison are made from polymeric PVC. The second method of combatting UV degradation is UV absorber additives. Typically, the higher the film quality, the more UV absorbers that have been added during manufacturing. Based on PVC type and quantity UV absorbers, manufacturers calculate outdoor durability estimates.
However, vinyl film formulation is only one part of the UV durability equation. The other part is the vinyl installation.
Implications
No matter what vinyl film you choose for a client’s sign, UV exposure will significantly impact the sign’s longevity. Let’s think through some environments that have greater or lesser exposure to the sun.
Latitude & Climate
Where do you live? On what part of the globe? Northern Canada? Southern USA? Your latitude determines two components of the UV rays: sun angles and UV index intensity. The further north you go, the less sun rays shine directly overhead. However, southern facing signs will end up with a lot of UV exposure, especially compared to northern facing signs. The closer you get to the equator, the more sun rays shine overhead.
UV index is the intensity of UV radiation. Often used as a measure of sunburn risk, it also indicates the rate of PVC degradation. If your skin is burning, exposed vinyl will degrade. Latitude plays a role here as well. Latitudes closer to the equator typically have higher UV indexes, but - most significantly - have many more days of high UV index than northern latitudes.
One indirect factor of latitude is climate and heat. Heat also degrades PVC, so manufacturers add chemicals to increase PVC’s heat resistance. Obviously, warmer climates will face more PVC degradation than cooler climates. Most vinyl film manufacturers specify climate zones when providing outdoor durability ratings for their films. Hot climates close to the equator face the double whammy of heat AND intense UV radiation.
Orientation
Besides the geographic location of the sign, sign orientation affects UV exposure. Orientation includes vertical, horizontal, and compass directions. As already mentioned in the discussion about geography, vertically oriented south-facing signs in northern latitudes will receive significantly more UV radiation than north-facing ones. Hence, vinyl films on south-facing signs will degrade much more quickly than signs facing other directions. Most building and roadside signs are orientated vertically. This is by far the most popular use of vinyl films. Horizontally oriented signs are going to receive a lot more UV radiation. Vinyl on those surfaces is going to degrade up to 5 times faster than vinyl on vertical surfaces. For surfaces that aren’t strictly horizontal or vertical but are somewhere in between, the closer to horizontal the surface becomes, the more UV radiation it will receive.
You’re probably thinking. Vinyl signage isn’t just on buildings and highway signs. It’s on vehicles too. That brings us to the next factor.
Vehicles
Based on what you know about orientation, which parts of a vehicle are going to receive the most UV rays? That’s right. The horizontal surfaces: hoods, roofs, and trunk lids. On vehicles wraps, those are the precise areas that break down the soonest. A special mention goes to hoods. Not only are they horizontal surfaces that consistently bask in the sun, but they also sit directly above a heater: the engine. Remember, heat is another factor that degrades PVC. So, of the worst parts of a car – the hood, the roof, and the trunk lid – which part is the number one worst? The hood. Most manufacturers list durability for vehicle wrap films with some fine print. If you read the fine print, you’ll see that horizontal surfaces last a fraction of what the vertical durability rating is.
Besides vehicle wraps, partial wraps and decals are popular. Luckily for durability, most decals are installed on largely vertical surfaces: the sides or back. Because vehicles move around, park facing different directions, and move from climate to climate, we can’t draw any blanket conclusions regarding durability for latitude and climate. However, the same principles apply. A hot climate equals lower durability. Consistently parking with one side of the vehicle facing south means that side will get more UV exposure (and greater vinyl degradation) than the others.
One more special mention goes to tanker trailers. We have a blog post that specifically addresses the issues of tanker trailers. However, it can be summarized by UV rays and orientation. The top part of the tank is nearly horizontal - it receives substantial UV rays. The sides receive average rays, and the bottom receives practically none, since it is consistently shadowed. Based on that information, you can deduce which area of the tank graphics fail first.
Printing Effects
The last part of the durability issue is printing. Coloured films, including coloured car wrap, are unaffected. Printing on vinyl changes the chemical make up in the printed areas. This change is not a good thing for durability. As soon as you print, durability decreases. Most printed vinyl gets laminated with a transparent UV protective film. Although this may influence overall durability of the vinyl, it is typically used to extend the life of the ink, keeping the colours vibrant for longer. (UV rays also degrade inks, causing the colours to fade). The more ink used, the more the durability decreases.
Manufacturer Ratings
How do all these factors influence the manufacturer’s outdoor durability rating for vinyl? First, the durability rating is typically based on a set quantity of UV radiation in laboratory settings. The problem is that the lab is much less variable than vinyl film’s natural habitat. The manufacturer ratings are based on unprinted vinyl applied to vertical surfaces in northern climates. Do you see the problem? That’s right. Those conditions are the least harsh of possible conditions. Many manufacturers precede the durability rating with an “up to,” indicating durability may be lower. In many cases, it can be considerably lower. For a worst-case scenario, imagine a heavily printed car wrap film applied to the hood of a truck in Houston, Texas. While the idealized manufacturer durability rating says 8 years, actual durability may be as low as 1 or 2 years.
Summary
· Theory
o PVC is degraded by UV rays
o More sun = shorter lifesapn
o Film manufacturers add UV absorbers to increase outdoor durability
· Implications for Sign Installation
o Latitude and climate
§ Sun angle and direction impacts lifespan of vinyl signage
§ Hot climates degrade vinyl faster than cooler climates
o Orientation
§ Vertical: less direct sun light = slower degradation
§ Horizontal: lots of direct sunlight = faster degradation
§ Compass directions: south-facing signs = faster degradation
o Vehicles
§ Hoods, roofs, and trunk lids get the most UV rays
§ Engine under the hood adds heat to the degradation equation
§ Tanker trailers have high UV areas at the top where the surface is horizontal
o Printing effects
§ More ink = less UV resistance
o Manufacturer durability ratings
§ Durability ratings are based on vertical exposure in northern latitudes
§ Read the fine print for specific climate ratings
§ Worst case scenario
· A heavily printed decal installed on the of a car hood in Houston, Texas
· Manufacturer rating of 8 years = 1-2 years actual durability
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