Thermoplastic
First developed in the 1950’s, thermoplastic offers a highly durable alternative to other
Road Markings Materials for the UK environment.
Despite trends towards a greener environment traffic volumes are expected to rise, so the
durability of road markings is vital to our network.
Thermoplastic is generally more resistant to weathering and traffic wear, in some instances
lasting up to eight times longer than some other materials. Efficient application methods,
teamed with fast drying times minimises the disruption to traffic, offering a cost effective solution.
Thermoplastic is typically made up of a mixture of:
- Glass Beads - (20-30%)
- Pigment - (8-10%)
- Low Molecular Weight Polythene - (3-5%)
- Hydrocarbon Resin Binder - (12-15%) (Of Which Plastecizer 1-3%)
- Filler Materials - (Remaining %)
Thermoplastic compounds, also known as "hot-melts" are generally manufactured in dry blend form,
once heated to a temperature specified by the manufacturer (approximately 420F) and agitated,
the blend turns to liquid. Even the bag melts down to become part of the mix.
Glass beads within the mix create retro-reflectivity, the pigment supplies the colour
(white pigment is provided by titanium dioxide), the low molecular weight polythene provides flexibility and strength,
the binder is a mixture of plasticizer and resins that hold all the materials together.
(Plastecizer is used to create viscosity to the mixture so that it can be applied to the road surface.)
Filler materials include calcium carbonate, sand and other inert bulking substances.
Resins
Hydrocarbon is the most common polymer used in thermoplastic binder; it is heat stable, adheres well to the road surface,
and is relatively predictable in application. However, it is only recommended in areas where vehicles are unlikely to
be stationary as the material breaks down if it comes into contact with oil.
In inner cities and other areas where oil contamination is more likely, Alkyd polymer based resins are often used,
as they are resistant to petroleum, the downside is they are more heat sensitive and require greater care during application.
Application
Once heated to the correct temperature the thermoplastic becomes viscous and can be applied.
Care must be taken to heat the thermoplastic to the optimum temperature if over heated it
can become discoloured and brittle.
Thermoplastic must be applied to a dry road surface, to ensure good adhesion.
Applied at approximately 5mm, the thermoplastic melts into the upper road surface filling all holes
in porous surfaces, as it cools it firmly adheres to the road surface.
Before the material cools completely, additional glass beads are applied. As the marking wears,
the glass beads within the thermoplastic mix become exposed ensuring consistent retro-reflectivity throughout the life of the line.
Paints
Road Marking paints are used extensively across Europe, while historically in the UK they have been used
for car park markings with limited works on the highway.
However, with the introduction of BSEN 1436 legislation, paint is now an option due some consideration
for the UK market. Of the various paints available on the market methyl methacrylate is one of the paint systems available.
Methyl methacrylate resins are 100% solids product with no solvents, so comply with health and safety requirements.
When mixed with peroxide additives a chemical reaction takes place, this is unaffected by climatic extremes and
produces a highly durable road marking.
They are commonly referred to as "cold plastic" to differentiate with the more traditional thermoplastic materials.
Methyl methacrylate resins have been shown to offer:
- Extended Durability
- Excellent Retro-reflectivity
- High Skid Resistant Values
- High Wet Night Visibility
- Easy To Maintain And Reinstate Markings
Although curing times are perceived to be an issue by some contractors and clients.
|
