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May 2016

  Anti-graffiti Coatings
  I grew up as a kid in New Jersey. As a youth I would travel into New York City with my friends and family. In the 1970s and 80s, New York was a scary place - drug dealers, petty crime, graffiti everywhere. It was considered too big and too chaotic to rule. And so there was a lot of lawless behavior back in those days and it was a rather ugly place. In 1990, William Bratton became the head of the NYC Transit Police. He implemented policies that embraced the broken windows theory. The theory which was detailed in a book Fixing Broken Windows1, by George L. Kelling and Catherine M. Coles, posits that there is a link between disorder and crime. If a window remains broken, soon more windows will be broken and the risk of more serious crime ensues. However, if petty crime like vandalism and graffiti is nipped at the bud and removed promptly, order and the rule of law can prevail and lead to a better quality of life, lower crime rate at all levels, greater neighborhood security and a less chaotic urban atmosphere. In 1993, Rudy Giuliani was elected mayor. He made Bratton his police chief and by then the broken windows theory was in full implementation mode. In 1995 Mayor Giuliani set up a multi-agency initiative to combat graffiti in what amounted to the largest anti-graffiti campaign in US history. Subsequent administrations have continued to fight graffiti with equal vigor in NYC.2

Today NYC spends millions of dollars annually on the CleaNYC program which includes a fleet of graffiti removal vans like the one shown below. Teams of workers remove graffiti from public and private property in an effort to make NYC a better place by reducing urban decay and lowering overall crime rates.3

Since graffiti removal has become such a big business in urban areas worldwide, not just in New York City, surface scientists have been busy working on ways to make graffiti more easily removed. In the past, graffiti has been handled reactively. Graffiti is painted over or removed using tedious manual methods. The current trend, however, is to address the issue proactively by coating surfaces in advance that are prone to be targeted by graffiti vandals using special coatings optimized to permit graffiti to be easily removed and cost-effectively removed.

Current anti-graffiti coatings fall into two classes: sacrificial coatings and permanent coatings. A sacrificial coating may consist of a low-cost clear polymer coat made up of acrylates, biopolymers, and waxes. Since these polymers form a weak bond, a worker with a power washer can easily remove graffiti along with the sacrificial layer which would then need to be reapplied afterwards. Commercial sacrificial coating products include Rainguard VandlSystem and Artisan Anti-Graffiti Coating. A gallon costs about $40 USD. Application is about the same process as painting a surface. 

Permanent coatings are more costly to purchase and also more costly to apply but do not require reapplications. These coatings work on the principle of decreasing surface energy and increasing omniphobicity. Fluorine is commonly used since it shows little affinity for electrons of other liquids. Silicon-based coatings rely more on being omniphobic. Increasingly, a method that relies on nanoparticles is being developed. Reactive and nonreactive nanoparticles are formed using the sol-gel method to create ligands that are superhydrophobic as well as others that are oleophobic (repelling oil). They are chemically grafted into silica nanoparticles forming a coating that is omniphobic - it's equally adept at repelling both water and oil (such as spray paint).4

Sherwin-Williams has commercialized a non-sacrificial anti-graffiti paint that is made of a siloxane compound.5 It dries to the touch in an hour. Graffiti can easily be removed from a treated surface using a power washer with cold water.

Rainguard makes a non-sacrificial coating called VandlGuard. At $100 USD / gallon it's not cheap and must be applied as a topcoat to an already painted or treated surface. In some cases, multiple coats are necessary. This product is designed to make graffiti easily removed using VandlClean Super Graffiti Cleaner ($30 for 32 oz. bottle).

Currently, more than one ramé-hart customer is developing anti-graffiti coatings. And with graffiti removal becoming a billion dollar business worldwide, look for exciting developments in anti-graffiti coating technology in the months and years to come. And for those who are developing such coatings, we are here to help you measure the efficacy of your product or method through contact angle and surface energy analysis.

1 See http://www.amazon.com/Fixing-Broken-Windows-Restoring-Communities/dp/0684837382/.
2 See http://cooperator.com/article/the-mayors-anti-graffiti-task-force
3 See http://tinyurl.com/jmn683c
4 For example, Covestro uses this method. See: http://tinyurl.com/jnldgyx.
5 See http://tinyurl.com/j3wvt29

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