Signs, like most things, deteriorate due to weathering. As such, this discussion refers to exterior signs only - most interior signs can effectively be considered to be permanent.
Whilst some degradation is caused by pollutants and dirt build up on the surface of the sign, by far the biggest component of the weathering process is caused by UV light from the sun.
The UV light causes two separate issues, the first and most obvious being the fading of pigments (colour), and secondly the breaking down of any plastics (including paints and clear-coats) that have been used in the making of the sign.
Because NZ is relatively close to the South Pole, we have higher levels of exposure to UV light than most other places, and so we see faster fading and break down than might otherwise be expected.
Also, as the amount of UV exposure a sign is exposed to is directly related to how much sunlight it receives, the position of the sign has a large influence on its life. A north facing sign in an exposed position may well receive twice as much sunlight over its life-span than a similar sign facing south in a shady area. For this reason, it is not possible to be very precise in the estimation of expected life spans, and hence why you see large ranges used when discussing such issues.
Generally speaking, exterior signs can be divided into two categories - "temporary" and "permanent".
Temporary signs are used to promote specific events, and are made from low cost materials to keep costs reasonable. Examples include banners, billboards and Corflute signs. No over-lamination is applied to the graphics, and the UV light will quickly start to break down the pigments in the inks and graphics. These types of signs would have a life of around 6 to 12 months without noticeable fading.
The word "permanent" when applied to signs, is something of a misnomer. Harsh UV conditions mean that all outdoor signs have a relatively limited life-span.
Firstly, the substrate that the graphics have been applied to should outlast the graphics by a large margin (assuming the sign company has used a modern, exterior rated product) and so the following discussion focuses on the graphics and films which have been applied to the substrate surface.
The majority of full colour exterior signs are manufactured using one of three methods and materials. (or a combination of the three).
Fully painted signs are very rare these days, as the labour required to produce them makes them uneconomic in most cases. Modern paints can be expected to last from seven to ten years, if chosen and applied correctly.
Computer cut vinyl.
Signs made using this process use a coloured self adhesive PVC film which is cut to shape using a computer controlled plotter and applied to the substrate to form the text and graphics. As the pigment is embedded through the thickness of the film, these graphics are fairly resistant to fading and failure usually comes about through the breakdown of the film itself.
Manufacturers offer several grades of film, ranging from low cost films designed for short term exterior exposure, through to relatively expensive films designed for maximum longevity. These long term films can be as much as ten times as expensive as their short term counterparts, and to the untrained eye look much the same on a new sign.
Unfortunately, this enables unscrupulous "cowboy" sign makers to substitute cheaper, lower grade film whilst claiming similar durability to a properly made sign, with the consequences not being evident until a year or three down the track.
Large format digital printing
Large format digital printing has revolutionised the sign making industry in recent years, allowing full colour images such as photographs and other graphic effects to be reproduced on one-off signs cost effectively. As the technology has advanced, the quality and speed of these processes has increased, while the costs have been driven down. As a result, a large proportion of modern signs are now produced using this process.
A sign which has failed prematurely because the signmaker has used cheap vinyl to cut costs.
A sign manufactured using the computer cut vinyl process should be expected to last from 5 to 7 years in NZ, providing that the sign maker has used the correct (expensive) grade of film. If lower grade films have been used, failure usually occurs in 1 to 3 years, depending on the grade used.
Unfortunately there is a downside, which is outdoor durability. Digital printing deposits a relatively thin (compared to paint or vinyl) layer of ink on to the surface, meaning that the pigment is very susceptible to fading. The life of the ink is extended by covering it with a clear protective film designed to filter UV, but even so, signs produced using this method can only be expected to last 3 to 5 years in New Zealand's harsh conditions.
As the over laminate film is expensive, a false economy can be achieved by leaving it off. Expect a digitally printed sign with no UV protection to display noticeable fading in as little as 12 to 18 months.
Concept Sign and Display Ltd, 111 Nelson St, Petone, Wellington
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