There Is No Simple Answer To This Question. 

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.

Temporary Signs

 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.

Permanent Signs.

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).

1) Paint

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.

 

2) 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.

 

3) Large Format Digital Printing – Using Media

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 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.

 

4) Large Format Digital Printing – Straight to Substrate

An alternative to roll to roll printing is printing directly to substrate which removes the need for media, and associated liners.  This method is therefore more environmentally friendly, particularly as most of these printers utilise inks which do not release any VOCs (volatile organic compounds) into the air.  Printing direct can be done to a wide range of substrates, particularly if white ink is used.

Over-lamination with either a film or a sprayed automotive grade 2 pack clear coat will extend the longevity of the sign similar to that of the roll to roll media.  However, some clear advantages can be achieved if a clear coat vs a film laminate is used.  Automotive grade clear coats offer scratch protection, superior anti-graffiti protection (paint can be easily removed with a proprietary graffiti removal spray, without effecting the clear coat) it won’t de-laminate or get the cloudy effect with aged laminate films.  The clear coat also can be used as a quasi whiteboard.