Anti Grafitti Coatings

Anti-Graffiti Barriers

As it is not usually possible to prevent graffiti, removal methods must be both efficient and fast. The best method of easing graffiti removal is generally agreed to be the insertion of a barrier between the surface and the defacing material, such as paint spray, crayon or marker pen.

Sacrificial Anti-Graffiti Coatings

Anti-graffiti barriers and coatings fall into three distinct categories. Sacrificial coatings are mostly based on easily removable waxes. After soiling with graffiti, both the wax and graffiti are removed together, sometimes with solvents or more commonly by melting the wax with steam or hot water. The biggest problem with this approach is that the coatings must be replaced after each removal operation, which is time consuming and expensive.

Semi-Permanent Anti-Graffiti Coatings

Semi-permanent coatings are commonly based on acrylics or cross-linking systems, such as epoxy, urethane or polyester. They can be multi-coat systems that possess a moderate degree of resistance to aggressive cleaning chemicals. These coatings will normally withstand a few graffiti-removal operations with strong chemicals, but eventually attack by the removal chemicals makes replacement necessary. Aggressive removers are necessary as the marking media usually has some affinity for the coating and a degree of adhesion or diffusion of the marking media takes place, which tends to increase with time.

Permanent Anti-Graffiti Coatings

Permanent coatings are relatively new and offer an extremely long-life surface from which graffiti, fly-posters and other soiling can be removed repeatedly, using safe and mild agents, without the loss of properties, performance or appearance of the coating itself. Coatings of this type normally have release properties similar to those of non-stick domestic kitchenware. Any soiling can easily be removed using aqueous surfactant/detergent mixtures, or at worst, benign chemical mixtures which have little or no effect on the coating itself, resulting in a truly permanent anti-graffiti coating.

Non-Stick Surfaces

Fluorine-Based Non-Stick Systems

The two elements fluorine and silicon are pre-eminent in the world of non-stick applications. Most people are familiar with non-stick frying pans and baking utensils, which have a polymeric coating resin containing fluorine atoms. One of the most familiar examples of these coatings is Teflon, a PTFE polymer which owes its non-stick characteristics to the high fluorine content of the structure. Unfortunately, fluorine-containing polymeric resins are expensive and extremely difficult to apply, but the degree of non-stick achieved can be extremely high.

Silicon-Based Non-Stick Systems

Silicon atoms, joined to oxygen atoms in long molecular chains, produce silicone molecules with variants called silanes and siloxanes. Resins made from long chains with alternating silicon and oxygen atoms, when dried or suitably cross-linked, can result in non-stick coating systems. The degree of non-stick is nearly as high as that achieved with fluorine-containing coatings, but the price is normally much lower and the case of application on most surfaces is usually improved.

Other Chemically-Active Groups Used in Non-Stick Systems

Some semi-permanent anti-graffiti coatings, even when fully-cured, still have chemically-active groups such as hydroxyls and keto-groups at their surfaces. Sometimes, these groups can act as bonding-sites for graffiti resins, making them quite difficult to remove. So cleaning requires the use of chemicals capable of breaking these bonds. Additionally, mild abrasion is sometimes required in order to supplement the chemical action. This has a deleterious effect upon the coating itself, even after relatively few cleaning cycles.

Disadvantages of Non-Stick Systems

To get around these problems of degradation, largely chemically-inert coatings such as fluorinated resin systems and silicones/siloxanes are popular. These are inherently non-stick, having few or no bonding-sites to which graffiti inks can adhere. Unfortunately, most fluorinated-resin systems also have other problems, such as the need to use unwholesome curing agents or activators (such as isocyanates), and the use of smelly, toxic and flammable solvents for the resin or curing agent.

Epoxy-Modified Siloxane Anti-Graffiti System

One epoxy-modified, siloxane clear coating system recently developed for Urban Hygiene, an anti-graffiti coatings manufacturer, has been undergoing a series of laboratory and in-use tests. The coating has proved that it can overcome some of the existing problems with these types of coatings, many of which are not able to provide a clear finish.

The Systems and Its Properties

The engineered siloxane has a two pack, high-solids system that is virtually solvent-free, has few bonding sites for defacement inks, and has very high resistance to abrasion when fully-cured, so it is extremely resistant to the less aggressive chemicals used to remove graffiti. The single-coat system has a low cost per unit area, and most importantly, can be purged of graffiti with the mildest of environmentally-safe chemicals, retaining its non-stick surface-energy after dozens of cleaning cycles.