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150
International Journal for Traffic and Transport Engineering, 2015, 5(2): 150 - 169
APPLICATION AND CHARACTERISTICS OF WATERBORNE ROAD
MARKING PAINT
Darko Babić1, Tomasz E. Burghardt2, Dario Babić3
1, 3 University of Zagreb, Faculty of Transport and Traffic Sciences, Vukelićeva 4, 10000 Zagreb, Croatia
2 M. Swarovski Gesellshaft m.b.H., Industriestrasse 10, 3300 Amstetten, Austria
Received 21 November 2014; accepted 14 January 2015
Abstract: Horizontal road markings are one of the essential safety features of modern
roadways. All of the utilised systems consist of a pigmentedcoating containing partially
embeddedretroreflective elements such as glass beads. In addition to durability and functionality
of the road marking, ease of application and effect on human health and environment are
primary considerations for their selection. Road marking systems can be divided into plural
component materials that cure due to chemical reaction occurring at the site of application,
thermoplastics that require heat for application, and paints, drying upon evaporation of the
dissolving medium. The focus of this paper is on road marking paints with a special emphasis
on contemporary waterborne materials. Over 100 years old solventborne technology furnishes
paints that afford consistent application properties under a variety of conditions such as
lower temperatures and high humidity. Their environmental and human health impact is
significant and durability quite poor. Modern waterborne paints are based on acrylic resins
and incorporate developed in the 1990s quick-set chemical mechanism for drying. Under
favourable weather conditions, they dry faster as compared to solventborne. However, their
known weakness is risk of washout in case of rain and sluggish development of washout
resistance at marginal application conditions like high humidity and low temperature. Impact
of waterborne paints on human health and environment is very significantly minimised as
compared to other materials. Their durability is significantly higher as compared to solvent-
based paints. Analysis of characteristics of waterborne road marking paints and preliminary
results from their trial application in Croatia are presented herein. Based on the presented
comparison with solventborne materials, after results from test application become available,
intelligent decisions regarding future use of waterborne road marking paints in Croatia and
other countries that have not embraced this technology shall be possible.
Keywords: waterborne road marking paint, road markings, traffic paint, solventborne road
marking paint, retroreflection.
1 Corresponding author: dbabic@fpz.hr
UDC: 656.055DOI: http://dx.doi.org/10.7708/ijtte.2015.5(2).06
1. Introduction
In 2011, 25 726 people died on the roads of
the European Union and 1 115 410 persons
were injured (European Road Statistics,
2013). One of the international efforts is
reduction of these numbers by 50% before
2020 (“Towards a European road safety
area: policy orientations on road safety 2011-
2020”). The corresponding social cost was
approximately 130 billion Euros (European
Commission, 2010).
Horizontal road markings are one of the
safety features on modern roads; their
inf luence on driving safety is especially
151
Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
prominent at night and in adverse
weather conditions (Migletz et al., 1994).
The markings can be defined as a set of
longitudinal and transversal lines, signs and
symbols on the surface of transportation
infrastructure. They represent a fraction of
overall traffic signalisation and cannot be
at present replaced by other means. Studies
shown that generally, the presence of only
centre a nd edge lines ca n reduce all accidents
by 20% (Miller, 1992).
Eff iciency and durability of road markings
are required by both road users and the
road authorities. From the users’ point of
view, road markings provide an optical
path by means of contrast of colour and
luminance with the road surface and it
appears that these properties should
be maximised (Horberr y et al., 2006).
Selection of the type of road marking
materials by road administrators depends
on many factors, including the desired
durability, required visibility, price, and
local considerations. Considerable funds
are allocated to keep the markings at
adequate performance level. Even though
the overall long-term performance and
cost should be balanced, unfortunately,
quite frequently it seems that short-term
expense plays more significant role.2 A
model could be functional contracts, such
as are in place for example in Finland,
where the application company is paid
for maintaining the retroreflectivity and
the choice of materials is in its hands.
Envi ronmental friend liness is also critical:
not only in terms of contents of emissions
of Volatile Organic Compounds (VOC),
but also as an overall impact on our
planet. Green Public Procurement (GPP)
2 In Croatia, public tenders have condition that the
price is the only consideration, according to the “Law
of Public Procurement“, Article 58, Paragraph 1b.
criteria for outdoor paints and varnishes
is extended to road marking materials as
well.3
Assessment of effects of various road
mark ings has not produced definitive results
as to which road markings maximise safety
benefits (Asdrubali et al., 2013). Field of
driver attention is changing depending on
the construction characteristics of the road,
the traffic conditions, and the vehicle speed,
generally decreasing with increase if the
speed and increasing when reducing speed
(Thurston, 2009). Studies showed that with
high visibility markings on outer roads the
drivers tend to increase speed, thus nullifying
the benefits on safety (Retting et al., 2000).
At urban level, things get more complicated
because of factors like pedestrian crossings,
turnabouts, stop signals and also a different
way of dr iving (Ret ting et al., 20 00). It was a lso
demonstrated that removal of all horizontal
markings in low-speed residential areas in a
“shared space” concept lead to i ncreased safety
for all due to dr ivers paying more attention on
surroundings and other road users instead of
following the guiding path (Hamilton-Baillie
and Jones, 2005; Experiment done in town of
Drachten, 2007; Bosley, 2007).
2. The Role of Road Markings
Road ma rkings a re one of the most impor tant
components of traffic signalisation because
of their position in the central area of
drivers’ attention. Their function is to warn
drivers about conditions of the road and its
construction characteristics and to help in
determining lateral or transverse position of
3 GPP for road marking materials is included in
“European Commission Decision establishing the
ecological criteria for the award of the Community
eco-label to outdoor paints and varnishes.“
(2009/543/EC) Official Journal of the European Union, L
181/27; 14.7.2009.
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International Journal for Traffic and Transport Engineering , 2015, 5(2): 150 - 169
their and other vehicles. Important feature
of road markings is their continuity along
the entire length of the road, which is a
significant fact in the process of orientation.
It can be said that road markings are telling
the driver, with a specific language, what to
do and how to behave in certain situations
in traffic. They are especially beneficial in
poor visibility conditions. The main tasks
of road markings are:
• Drawing attention to the situation
around and in the area in front of the
vehicle, which requires special attention
and caution.
• Ensuring traffic management,
particularly at approaches to
intersections.
• Defining the road in its course and
layout.
• Giving drivers clear orientation and safe
guidance by day and night.
• Informing drivers about certain legal
restrictions.
• Helping to regulate traffic flow in an
optimal w ay.
• Helping drivers to safely reach their
destinations.
All drivers interact with environmental
clues during driving. Indeed, driving is a
series of decisions based 90% on visual clues
(Thurston, 20 09). As the overall society age
increases, it becomes increasingly important
that road systems incorporate sufficient
tolerances that cater for deteriorating light
perception and also for the longer time it
takes for the elderly to react to all of these
important visual clues (Zwahlen et a l., 1998;
Eby et al., 2008).
Two important factors describe connection
between driver and road markings:
• A dr iver must be able to see road ma rkings
at a certain distance to perceive, process,
and react to the information that the
pavement marking presents in order to
receive adequate information to safely
guide the vehicle. Since the required
distance increases as the speed of the
vehicle increases, it is often described
as constant preview time.
• “It has been established that for night
time low-beam conditions, a driver
requires a minimum recommended
preview time (comprising both eye
fixation time and driver reaction
time) of 3.65 seconds at 80 km/h, of
oncoming road geometr y to enable safe
negotiation without the driver requiring
to shift attention away from the road,
to look for other clues.“ (Zwahlen et
al., 1998)
The contrast between white (in some
countries also yellow) marking and black
road surface is sufficient at daylight, but at
night retroreflectivity plays more significant
role. Visibility of road markings at night
is accomplished by materials like glass
or ceramic beads, which ref lect the light
from vehicles headlights, as show in Fig. 1
(Migletz et al., 1999). Proper embedment
of the ref lective elements is critical for
retroreflectivity (Grosges, 2008).
A cross-section cut shown in Fig. 2 shows
also anti-skid particles and completely sunk
glass beads.
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Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
Fig. 1.
Retroreflectivity of Glass Beads in Road Marking
Source: Asdrubali et al. (2013)
Fig. 2.
Cross-Section of a Well-Embedded Glass Bead
Source: By Authors
Poor visibility of most markings at night
during rainy conditions is caused by water
blocking retroref lection, as shown in Fig.
3. This deficiency can be alleviated by
utilisation of structured markings and
large glass beads, which do not become
submerged during normal rain conditions.
Retroref lectivity is achieved as long as
the ref lective elements remain properly
embedded – upon their loss or imperfect
embedment, only daytime ref lectivity is
maintained.
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International Journal for Traffic and Transport Engineering , 2015, 5(2): 150 - 169
Fig. 3.
No Retroreflectivity of Glass Beads under Water
Source: Swarco Brochure: Reflective Glass Beads
Retroreflectivity is better if the driver is
sitting lower, because the observation
angle is smaller, as demonstrated in Fig.
4. Observation angle is important because
retroreflective light is returned as a narrow
cone with the inner part of the cone being
most intense. Therefore, the light appears
brighter to a normal car driver sitting lower
and nearer to the headlights, than to a lorry
driver who sits higher above the headlights.
Fig. 4.
Angles of Observation in Different Types of Vehicles
Source: Company 3M Materials
155
Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
3. Materials for Road Markings
The available plethora of road marking
materials is quite di fficult to unambig uously
classif y. Assigning to categories based on
the material type – paint, thermoplastic,
plural component systems, and tape is
rather frequent. Another method is based
on the solvent: Solventborne, waterborne,
and solvent-free. Yet another categorising is
based on their durabilit y, into conventional,
durable, and temporary marking products.
Dividing road markings types based
on their chemistry is also possible and
frequently employed. Types of achieved
retroreflection under rainy weather is yet
another classification method.
Road authorities could also divide the
marking systems based on the initial
or overall expense of application and
maintenance; indeed, some data sources list
durabilit y and relative prices of various road
mark ings (Montebello a nd Schroeder, 20 00).
Even though such information can serve as
general guideline, one must remember that
only side-by-side comparison could provide
reliable scientifically valid information.
(Simultaneously, such compa rison would not
necessarily be fair due to different ty pically
applied film builds and design of different
materials for particular layer thickness.)
No references of such comparisons could
be found. Even homologation in Germany,
run under strictly controlled laboratory
conditions, falls into the dissimilar film
thickness issue. Hence, all comparisons
have to be taken with a grain of salt.
Comprehensive cost-benefit analysis that
would include all of the cradle-to-grave
factors, including also financial and social
costs, is still to be done. Overall, one must
remember that due to various surfaces and
climates, there is never a definite answer
(Gates et al., 2003; Dwyer et al., 2013).
Table 1 shows the summary of the road
marking materials and attempts their
assignment to different categories. Different
classes of materials, with particular attention
paid to paints, are reviewed below.
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International Journal for Traffic and Transport Engineering , 2015, 5(2): 150 - 169
Table 1
Road Marking Systems
Typ e Price(a) Durability Resin Solvent VOC
(g/l)
––– Risks for users –––– Typical applied
thickness Advantages Disadvantages
Health Environmental Transport and
storage
Paint / 1K(b) Moderate High Acrylic Water <50
(1-3%) Minimal Minimal None wet
300-900 µm,
dry
200-600 µm
- High durability.
- Low environmental footprint.
- Safety.
- Quick tack-free time
- Fast drying at proper conditions.
- Adhesion to various surfaces.
- Cost.
- Slow development of water resistance (risk of
washout).
- Application in warm dry weather preferred.
- Requires the use of stainless equipment.
Paint Very low Very low Alkyd or
styrenic Organic 400-600
(20-35%) High
(solve nts) High
(solve nts) Flammable. wet
300-400 µm,
dry
200-250 µm
- Initially inexpensive.
- Easy to apply.
- Easy clean-up.
- May use inexpensive equipment.
- Very low durability.
- Poor UV resistance.
- Rather slow drying.
- High environmental impact.
- Require organometallic driers.
- Solvent harmfulness and odour.
Paint Low Low to
moderate Acrylic Organic 400-600
(20-
35%)
High
(solve nts) High
(solve nts) Flammable. wet
300-400 µm,
dry
200-250 µm
- Initially inexpensive.
- Easy to apply.
- Dry in adverse conditions.
- Easy clean-up.
- May use inexpensive equipment.
- Low durability.
- High environmental impact.
- Solvent harmfulness and odour.
Paint / 2K(c) High High Epoxy or
urethane or
urea, also
modified
Organic 400-600
(25-
35%)
High
(solvent,
epoxy
toxicity)
High (solvent,
toxicity to
aquatic life)
Flammable. wet
300-400 µm,
dry
200-250 µm
- High durability.
- Reasonable cost-performance
balance.
- Very costly.
- Risk of human allergic reaction.
- High environmental impact.
- Solvent odour.
- Poor ultraviolet stability.
- Poor flexibility.
- Slow drying.
2K Very high Very high Epoxy or
urethane or
urea, also
modified
– <50
(0-1%) High
(epo xy
toxicity,
amine
corrosive)
High (toxicity
to aquatic
life)
Flammable. 500-1500 µm - High durability.
- No solvents.
- Super-quick drying.
- Very costly.
- Special heated application equipment needed.
- Corrosive amine for curing.
Coldplastic Very high Very high Mostly
acrylic,
rarely
polyester
– <50
(0-1%) Moderate Mod erate to
high Flammable,
uncontrolled
polymerisation.
Organic
peroxide
1000-3000 µm - Ver y high durability.
- No solvents.
- Quick drying.
- Excellent adhesion to some
surfaces.
- Costly.
- Special application equipment needed.
- Sensitive to moisture and temperature (location-
specific formulations needed).
- Risk of uncontrolled polymerisation.
Tap e (d) Moderate
to
extremely
high(e)
Moderate
to very
high
Mostly
acrylic – <50
(0-1%) None
known None known None 1000-3000 µm - Superior durability.
- Tailoring durability with specific
requirements.
- Ease of application.
- Very high retroreflectivity.
- Ease of removal of temporary
markings.
- Extremely high cost.
- Application surface preparation (poor adhesion can
lead to complete peel-off)
Thermoplastic Very low High A lkyd or
hydrocarbon – <50
(0-1%) Moderate
(heat
during
application,
unpleasant
odour)
Minimal None. 2000-5000 µm - Durability with quite constant
retroreflectivity.
- Low cost.
- Ease of application.
- Requires heat to apply.
- High environmental cost.
- Discolouration from asphalt oils possible.
- Surface preparation flaws may lead to failures.
- Sensitive to air temperature (location-specific
formulations needed).
(a) Relative price estimate of materials and application at typical film build; long-term durability not taken into consideration. (b) Due to irreversibility of the solidification reaction, quick-set waterborne single component
material is somewhat different as compared to the typical paint (vide infra). (c) Two-component solventborne materials are applied like paint. (d) Tape comes in many varieties, including designed for temporary marking; hence,
its price depends on durability.
Source: By Authors
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Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
3.1. Thermoplastic
Thermoplastic road marking materials
were developed and patented in the United
Kingdom by R. S. Clare & Co. Ltd of
Liverpool, England in 1933 (Clare, 2015).
They remain one of the most successful
road marking materials still in use, despite
being an 80 years old technology. It should
be noted that term ‘thermoplastic’ has in
road marking context different meaning
than in chemistry of polymers – these are
merely plastic masses, barely modified by
polymerisation, that require thermal energy
for processing.
Thermoplastic road marking materials are
composed of a solid hydrocarbon or alkyd
resin intermixed with pigments and fillers
as well as glass beads. The resins come
either from natural renewable resources,
plantations of pine trees, or from petroleum
distillates.
Manufacturing of thermoplastic masses
is done at high temperature and then the
materials are either dried and palletised
or pre-formed to the desired shape of
special road markings. Application simply
requires re-heating of the thermoplastic
to about 200 °C to melt it – it can be done
by heated extruding or in case of pre-
formed marking by heating with a torch.
Process of thermoplastic road marking
materials is shown schematically in Fig. 5.
Thermoplastics are used for line markings,
pedestrian crossings, and various signs on
road surface.
RESIN
(ALKYD OR
HYDROCARBON)
PIGMENTS
AND FILLERS,
GLASS BEADS
SOLID
THERMOPLASTIC
MATE RIAL
ADDITIVES
ROAD MARKING
1. heating
2. mixing
3. cool ing
pelletising
cutting to
desired shape
THERMOPLASTIC
PRE-FORM
1. heat ing f or applicat ion
2. cool ing on road s urf ace
Fig. 5.
Process of Thermoplastic Road Marking Materials
Source: By Authors
At application time, additional glass beads
and anti-skid materials are dropped-on
to assure good initial retroreflection and
low surface slip. Proper preparation of the
application surface is critical as imperfect
adhesion may lead to peeling off and
complete loss of material. Thermoplastic
materials are modified for the use in specific
climates and any m ismatches lead to inferior
performance.
Thermoplastic materials are essentially
solvent-free and some of the resins are from
renewable natural resources, but t he need to
heat them t wo times significantly increases
environmental impact.
Typical application thickness of 3 mm
assures long service life, even in highly
used motorways reaching 2-4 years. As
the material wears off, intermixed glass
158
International Journal for Traffic and Transport Engineering , 2015, 5(2): 150 - 169
beads progressively become exposed to the
traffic, which allows for maintaining high
retroreflectivity throughout the usable life.
3.2. Two Component Systems: Epoxy,
Urea, Urethane, and their Modifications
With plural component systems, chemical
reaction that occurs at the application
site assures formation of ver y durable
markings, usable for up to 5 years even on
major roads. In these systems, one of the
components contains solubilised resin,
pigments and fillers and the other the
catalyst. In this context, word ‘catalyst’
denotes merely “component B” and not a
catalyst in chemical meaning of the word.
Component B, in case of epoxy systems
polyamine, is typically not pigmented, but
it can be. General process is as shown in
Fig. 6. Such materials are used mainly for
line markings.
EPOXY RESIN
PIGMENTS
AND FILLERS
EPOXY PAINT
(PART "A")
ADDITIVES,
SOLVENTS
WET FILM ROAD MARKING
applic ation
mixing and
grinding
curing by chemical
react ion
CATAL YST
(PART "B") SOLVENTS (VOC)
Fig. 6.
Generic Epoxy-Based Materials Process
Source: By Authors
Because epoxy resins are very viscous, the
use of solvents is common: VOC content
of such epoxy paints is high and can reach
even 600 g/l. Due to generally sluggish
reaction that might take even hours after
application, pre-mixing in application tank
is at times possible. All epoxy systems are
formulated to obtain easy mix ratios like 1:1
or 1:2. Epoxy systems are not flexible, but
hard and very durable. Typically, they have
high affinity for glass beads, which increases
usable life of the applied road markings.
Their drawback is quite poor resistance to
ultraviolet radiation, which causes yellowing:
Indeed, applied epoxy road ma rkings must be
constantly exposed to traffic to avoid visible
discolouration. They can be successfully
applied at various conditions, in extreme
cases even on slightly moist road surfaces!
More recently developed systems include
multi-functional modified epoxy resins
and can be formulated as solvent-less
systems furnishing drying times as quick
at 5 minutes (Tan, 2011). However, their
application requires heated equipment to
liquefy molasses-like epoxy component and
mixing with the catalyst must be done only
at the nozzle. Properly designed systems
are not only exceptionally durable, but also
hard and f lexible.
The hazards of all epoxy systems are
numerous and start with the epoxy resin
itself, which can initiate allergic reaction,
general human toxicity of the starting
materials for production of the resin,
corrosive properties of the polyamine
component, and either the need for heated
159
Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
equipment or slow drying. European Union
is attempting to limit the use of epoxies
due to human and environmental health
considerations.4 Indeed, epoxy paints are
seldom used in Europe.
Systems based on straight or modified
polyurea or polyurethanes are in general
principles similar to epoxy. Due to high
pricing and human health considerations
(the presence of isocyanates, which are
known to cause allergic sensitisation),
they are even more rarely used.
4 First steps were taken to limit contact of
epoxy materials with foods in Commission
Directive 2002/16/EC (20.02.2002).
As compared
to epoxy, durability of such
systems tends to be better and they are less
sensitive to ultraviolet radiation.
3.3. Coldplastic
Coldplastic is more of a class in itself, even
though it is in a sense a plural component
system. In coldplastics, monomers (most of
the time various acrylates) are mixed with
pigments and fillers and anti-skid materials
and polymerised on the road surface to form
exceptionally durable, hard, well-adhering
mark ing. Schematic process is shown in Fig. 7.
MONOMERS
PIGMENTS
AND FILLERS
MIX FOR
APPLICATION
ADDITIVES
WET FILM ROAD MARKING
applic ation
mixing polymeri sati on
INITIATOR
Fig. 7.
Coldplastic Process
Source: By Authors
To start the polymerisation, small amount
of an initiator is added, which requires high
dosing accuracy and specialised equipment.
Coldplastics are quite sensitive to moisture
and temperature, which mandates the use of
special for mulations and/or an accelerator or
a retarder as needed. When properly applied,
coldplastics dry within 20-30 minutes and
with correctly selected glass beads provide
high retroreflectivity. Coldplastics are
used mainly on high-traffic roads and on
pedestrian crossings (Asdrubali et al.,
2013). They can be extruded at thick layers
or as structured markings for lines and also
applied by hand. The t ypical thick ness is 2-5
mm, which assures long service life.
Amongst major risks associated with
the use of coldplastic, one must list the
monomers, which are f lammable and can
undergo uncontrolled polymerisation.
Another major risk is associated with the
initiator, which requires special labelling
and transportation. Due to these hazards,
coldplastics, despite being versatile, having
minimal environmental impact at the
time of application, and offering excellent
properties, cannot fulfil GPP requirements
for ecologically-friendly product. A mongst
human health considerations, it is quite
interesting that whi le some people report the
odour of acrylic monomers as pleasant and
fruity, to others it is aggressively unpleasant
160
International Journal for Traffic and Transport Engineering , 2015, 5(2): 150 - 169
and ir ritating. Commonly used butyl acr ylate
has the odour detection limit of mere 0.1 ppb
(0.00052 mg/m3). Human nose can detect
butyl acrylate as a level about 1,000 times
lower than the permissible exposure limit!
(National Institute of Health). Hardly ever
used polyester-based materials fall into this
category.
3.4. Road Markings Tapes
These materials are available at several
performance levels and types, both
permanent and temporary. Tapes are
typically applied by rolling onto hot or
primed surfaces, or are at times placed in
specially prepared grooves. High quality
of surface preparation and application
technique are of utmost importance. Glass
beads are incorporated into the material
during factor y manufacturing, wh ich leads to
improved per formance and retroref lectivit ies
of up to 1000 mcd/m2/lx can be achieved.
High-end tapes have a service life longer
than others marking systems.
These s ystems are expensive: In addition to ver y
high cost of the tapes themselves, which can
reach even 60 €/m2, application could cost 5 to
10 times more than application of t hermoplastic
markings.5 Frequently, low-end tapes are used
for tempora ry mark ing due to their relative ease
of application and removal. Most, if not all of
high-performance tapes are covered by patents
assigned to 3M Corporation, which appear to
hamper competitive development (Jones and
Bredahl, 1980).
3.5. Paints
Paint remains the most widely used road
marking material in the world since it
5 Average price in Croatia between 2008 and 2014.
Source: Authors.
was first applied as a centreline in 1911 in
Mich igan, U.S. A. Paint appl ication is done by
simple spraying using high- or low-pressure
equipment; it does not require heating or
special technological ly advanced application
machines. Paint s generally have good affinity
for glass beads, which sometimes are pre-
mixed or more frequently dropped-on or
injected to the wet film.
All paints are composed of the resin
(historically, chlorinated rubber or alkyd
resins were used; more recently styrene-
acrylic, acrylic-al kyd blends or 100% acrylic
are preferred), pigments and fillers, solvents,
and numerous additives.
Partia lly as a par t of the worldwide movement
to limit VOC emissions and to m inimise the
effects on human health and partial ly to seek
improved performance, solventborne paints
are slowly being replaced by waterborne
paints or solvent-less road mark ing materials
(Andrady, 1997; Mouton, 2010).
3.5.1. Solventborne Paints
Contempora ry solventbor ne paints are based
on acrylic resins (rarely styrenic- or alkyd-
acrylic blends) that are dissolved in organic
solvents like esters or ketones. In countries
where it is still permitted, aromatic solvents
are used despite their harmfulness for the
environment and human health hazards
(McMichael, 1988) – that is due to their
lower price, better control of drying, and
generally improved adhesion to asphaltic
and oily surfaces.6 Low surface tension of
6
(a) In Poland up to 2% of aromatic solvents are permitted
per “Warunki Techniczne. Poziome znakowanie dróg. POD-
2006. Seria „I” - Informacje, Instrukcje.” IBDiM, Warszawa,
2007; (b) In the United States, “Federal Specification
TT-P-115F (5.12.1985): Paint, traffic (highway, white and
yellow)” does not limit the use of solvents and indeed, even
xylenes are occasionally used (Source: Authors).
161
Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
solvents permits them to penetrate road
surface crack s, which assures good adhesion
of solventbor ne paints to road surfaces, even
those in poor condition.
After application, evaporation of the solvent
causes the polymer to solidify and thus the
film forms, as a purely physical phenomenon,
as shown schematically in Fig. 8. The solvent
serves its purpose only to make the paint
liquid and then escapes to the atmosphere
as VOC, which in a typical high-solids
solventborne road marking paint reaches
400-500 g/l (~25%). It has been estimated
that in European Union about 35,000
tonnes of VOC are annually emitted from
solventborne road marking paints (“Review
of directive 2004/42/EC.”, 2011).
DRY POLYMER
(RESIN)
ADDITIVES
PIGMENTS
AND FILLERS
PAINT
SOLVENTS
WET FILM
SOLVENTS (VOC)
ROAD MARKING
applic ation
mixing and grinding solvent evaporati on
Fig. 8.
Solventborne Paints Process
Source: By Authors
In-can st ability of solventbor ne paints is most
of the time rather poor (stable formulations
are quite rare in the market due to their high
cost) – settling and thickening occur, but
they can be easily alleviated by the users by
mixing and addition of solvent. Application
is typically done at wet film builds reaching
only 400 µ m; thicker films tend to form sk in
and take ver y long to dry, even at favourable
conditions.
Application of solventborne paints can be
done at air temperatures 5-40 °C and surface
temperat ure below 50 °C. The roadway must
be clean, dry, and the temperature above
dew point. Drying of such paints is strongly
inf luenced by air and surface temperature,
air movement, applied film build, and the
utilised solvent blend. Humidity does not
really affect solventborne paints and it has
been seen that their application is stopped
only when drizzle starts – this is their biggest
advantage.
Solventborne paints are not suitable for
high-volume roadways due to their poor
durability: The expected service life on a
side-line marking is only 6-12 months.
3.5.2. Waterborne Paints
Before waterborne paints are discussed, a
property unique to them must be explained:
washout resistance. The applied waterborne
paint achieves washout when it no longer
is affected by rain, which is later (in some
cases much later) than dr y-through. There is
no standard protocol of measuring washout
resistance time. Laboratory procedure
where paint applied on a panel is exposed
to running water, which is to imitate heavy
rain, is frequently used. However, a method
preferred by the authors is a water droplet
– finger push-and-twist method: A drop
of water is applied to paint surface for 1
minute and then finger with a set pressure
is applied with twisting motion that is to
162
International Journal for Traffic and Transport Engineering , 2015, 5(2): 150 - 169
imitate car tyres moving on the surface –
washout resistance is achieved when the
paint is no longer affected by the action.
Such test can be conveniently performed at
the application site, too. Even though the
method is subjective, it is quite reproducible
with experienced user – for a more scientific
laboratory alternative, one could utilise an
instrument such as Dry Time Tester.
Washout resistance time very strongly
depends on the uti lised binder and additives
and is affected by weather conditions, in
particular humidity. Under normal dry
conditions, there is no need to wait for paint
to achieve washout resistance to open the
road to traffic – this property is absolutely
critical only when there is a risk of rain.
First waterborne road marking paints were
commercialised in the 1980s. Those paints
were quite similar to solventborne coatings
in terms of solvent evaporation causing
drying, but their main solvent was water.
They suffered from sluggish drying and very
slow development of washout resistance;
hence, their use remained quite limited. On
the other hand, very good durability, in-can
stability, and quite low price made them a
good option in certain areas, where they are
still utilised.
The development of quick-set binders by
Morton International in the early 1990s
(Clinnin et al., 1991) recently lead to
the success of waterborne paints in some
markets. Generic process, shown in Fig.
9 from the starting materials to prepare
the binder, is obviously more complex as
compared to solventborne paints. The
presence of carefully selected amine and
high pH assure that the resin, containing
acidic moieties in the backbone, does not
precipitate in aqueous environment. Upon
application, drop of pH occurs as ammonia
evaporates and the polymer irreversibly
solidifies. Hence, dried water-based paint
cannot be re-dissolved in water or even
in most common organic solvents. This
physicochemical change of state is as major
dif ference from solventborne paints as using
water as the medium.
ADDITIVES
PIGMENTS
AND FILLERS
WET FILM
AMMONIA
ROAD MARKING
appli cation
mixing and grinding
drying
(paint achieves dry-through)
MONOMERS
(ACRYLATES;
ACIDS AND ESTERS)
ADDITIVES,
AMMONIA
POLYMERISATION
INITIATORS
RESIN
(AQUEOUS EM ULSION)
WATER
Polymer isat ion
PAINT
DRY FILM
WATER
drying
(pain t ach ieves was hout resis tance)
Fig. 9.
Waterborne Paints Process
Source: By Authors
From the quick-set technology comes a
unique proper ty of waterbor ne road marking
paints – they stop being tacky very quick ly.
Clear distinction between tack-free, dr y-
through, and washout resistance times can
be measured. For the applicator, quick tack-
free time means lesser unsightly overdrive
marks.
163
Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
Application at film builds reaching 900 µm
or more is possible without very significant
slowing in drying (as mentioned above,
solventbor ne paints applied at wet f ilm builds
higher than 400 µm are not practical due
to very dramatic increase of dry-through
time). Application of sandwich systems is
also feasible with waterborne paints.
VOC content of a typical waterborne road
marking paint is less than 50 g/l (~2%),
coming from t he required additives. Properly
designed waterborne paints have shelf life of
about one year – no settli ng or skin for mation
should occur during storage and the paint is
ready to apply as delivered. Minor viscosity
increase is normal and the paints can be
thi nned by the applicators w ith a tiny a mount
of water. Paint has to be protected from frost
and extreme heat, though.7
The same equipment and procedures as are
utilised for application of solventborne paints
can be followed, with two caveats: to avoid
rusting only stainless steel equipment is
allowed and the paint cannot be permitted
to dry in the equipment (which forces
the applicators to maintain clean work
environment).
Waterborne road marki ng paints are repor ted as
compatible wit h a variety of sur faces, including
bituminous and concrete materials. As with
all other materials, they show sensitivity to
freshly applied concrete or asphalt. Waterbor ne
paints generally adhere well to the existing
markings independently on their type, even
to thermoplastic masses, which made them
excellent choice for marking renewal.
7 United States specifications require freeze-thaw
and heat stability (Cf. TT-P-1952E.). In Europe,
there is no freeze-thaw requirement and the heat
stability demands are less strict (Cf. specification EN
1871).
4. Characteristics and Application of
Waterborne Road Marking Paint – General
Considerations
Waterborne road marki ng paint is com monly
used in the United States – not real ly because
of its environmental friendliness as it is a
country where acetone or a f luorinated and
chlorinated aromatic compound are not
considered VOC (sic!), but due to excellent
cost-performance balance.8 In Europe,
waterborne paints are used in Scandinavia,
where solventborne paints are banned, and
also in France, Italy, Spain, and to a limited
extend in a couple lands in Germany. Other
European countries use mostly, if not solely,
paints based on organic solvents.
Amongst the advantages of waterborne
road marking materials one must first list
their environmental friendliness. A cradle-
to-grave Life Cycle Analysis (LCA) was
prepared and presented by Dow, major
manufacturer of the binders for waterborne
paints, where in all of the measured
LCA categories, waterborne paints were
presented as winners (Kheradmand, 2012).
Simultaneously, manufacturer of monomers
for coldplastic, Evonik, presented their LCA
showing advantage of their product (Klein,
2012). The authors herein do not assess
truthfulness of either analysis.
For the contractor applying road markings,
the advantage of using waterborne paint is
the absence of hazardous and f lammable
ingredients, which can lead into lower
transportation and storage costs. However,
a disadvantage is that the paint must
be protected from frost and extreme
temperature. At the application time,
advantages and disadva ntages of waterborne
road marking materials are ambiguous.
8 Per 40 CFR 51.100.
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International Journal for Traffic and Transport Engineering , 2015, 5(2): 150 - 169
Dry ing at favourable conditions can be much
faster as compa red to solventborne materials
(see Table 2 below), but simultaneously at
unfavourable humid conditions or in case of
sudden ra in there is a risk of washout. Hence,
the applicators must be properly trained
and must understand the limitations of the
systems: vide Scandinavia, where rain is
frequent and hot-dry conditions essentially
absent and there are no problems with
waterborne paints.
For the road authorities, advantages of
waterborne paints are numerous: faster
drying at proper conditions means lesser
traffic congestion, higher durability means
lower overall road maintenance cost, and
the environmental friendliness means lower
impact on our and our planet’s health. The
environmental impact should be considered
particularly in cities suffering from high
ground-level ozone. The disadvantage is
slightly higher immediate price tag that must
be paid – even thoug h long-term performa nce
balances the initial cost.
One must remember that there are several
qualities of waterborne paints and it would
be unfair to compare the low-end material
with, for example, coldplastic – especially at
dif ferent applied f ilm builds (Montebel lo and
Schroeder, 20 00). Simi larly, some documents
lists waterborne paints as hav ing no pick-up
times of up to 15 minutes, dry-through of up
to 1 hour – that is all true, but does not fully
apply to modern fast-dry paints.
Durability in the field is t ypically measured
by retroreflectivity. This is affected by the
utilised glass beads, weather conditions at
the application site, application technique,
road surface quality, etc. High durability of
waterborne paints is expected, based on their
chemistr y. Indeed, in a study done by Dow at
an application site in Pennsylvania, U.S.A.,
a high-end waterborne paint applied at 600
µm (900 g/m2) wet film build (about 400
µm dry film) was reported to outperform a
thermoplastic road marking material applied
at 3000 µm (Randazzo, 2013)!
5. Characteristics and Application of
Waterborne Road Marking Paint –
Application in Croatia
Recently, a field application was done on a
heavily travelled two-lane Croatian road to
assess (1) feasibility and ease of applying
waterborne road marking paints in Croatia,
(2) evaluate the paints’ performa nce, and (3)
test various glass beads for retroref lectivity
and its retention under normal use
conditions.
The selected road stretch near Zagreb is
travelled by approximately 8000 vehicles
per day, has two years old asphalt in good
condition, and was marked w ith the standard
solventborne paint commonly utilised in
Croatia. The application work was done
by crew from Chemosignal d.o.o. (Zagreb,
Croatia), under the direction of Faculty of
Transport and Traffic Science, Department
for Traffic Signalization (University of
Zagreb), using two waterborne paints from
Swarco Limburger Lackfabrik GmbH (Diez,
Germany) and drop-on ref lective materials
from M. Swarovski GmbH (Amstetten,
Au s t r ia).
The application crew has never worked with
waterborne paints, but was experienced
with solventborne paints and other road
mark ing materials. After a few adjustments
of the machinery (pressure, nozzle, etc.)
the waterborne paints were applied without
difficulties at target wet film builds 400 µm
and 600 µm. Changes of paint and layer
165
Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
thickness were accomplished effortlessly,
but tuning of the mac hine was necessary each
time. Lesser required coning and absence
of the tyre marks from vehicles driven by
careless and impatient drivers encroaching
on the freshly marked lines were noted.
Accidentally, the crew run out of paint and
that lead to initiation of paint dr ying in the
drum and f low difficulties – immediate
cleaning of the filters solved the problem.
There were no issues with drop-on glass
beads; their embedment was visually good.
(A little curiosity must be noted here: The
utilised small American-made application
machine has a container for glass beads
holding only 49 kg of beads, so two full
bags did not fit!) Side and centre lines were
marked at the standard width of 15 cm; each
system was applied at 500-m stretch.
Drying and washout times shown in Table
2 were achieved in the field. The weather
conditions were perfect: mostly sunny with
mild wind, roadway temperature 30-45 °C
and air temperature 20-28 °C at 40-60%
relative humidity.
Table 2
Drying and Washout Resistance of Various Road Marking Materials during Application near Zagreb
Road marking material Applied wet film
build
Dry-through Washout
resistance
Swarco Limboroute Aqua W13, fast-dry waterborne paint 400 µm 4 min. 8 min.
Swarco Limboroute Aqua W15, high-performance waterborne paint 400 µm 10 min. 22 min.
Swarco Limboroute Aqua W15, high-performance waterborne paint 600 µm 15 min. 36 min.
Two standard solventborne high-solids paints 400 µm 17 min. –
Source: By Authors
While retroreflectivity is used to measure
quality of the road mark ing, durability of
the paints themselves can be assessed in the
laboratory using Taber abrasion, accordi ng to
ASTM C1353 procedure. Fig. 10 illustrates
durability achieved with the road marking
material s that were applied near Zagreb. Poor
performance of the high-solids solventborne
100% acrylic paint is obvious – the repor ted
data represents average of t wo solventborne
paints and duplicate results. The result of
this on the road should be visible after loss
of glass beads, which in addition to providing
retroreflectivity serve to protect the paint.
166
International Journal for Traffic and Transport Engineering , 2015, 5(2): 150 - 169
Standard (high-solid s
solvent borne):
fail at 626 rounds,
9,1% loss
Swarco W15
(high-performance
waterborne) :
fail at 2920 rounds,…
Swarco W13
(fast-dry w aterborne):
fail at 2650 rounds,
16,4% loss
0%
2%
4%
6%
8%
10%
12%
14%
16%
18%
Paint loss
Rounds
PAINT DURABILITY
(Taber abras ion method, without glass beads)
Fig. 10.
Taber Abrasion Testing of Paint Durability (600-µm Drawdowns), Without Glass Beads
Source: By Authors
Initial retroref lectivity, measured two
weeks after application, depended on the
film build and glass beads type and size.
Three months after application, sur prisingly
increased retroreflectivity of waterborne
paints as compared to initial was measured
in some cases. Quite possibly, the time to
develop maximum retroreflectivity may be
longer in case of waterborne paints than is
commonly accepted.9
9 According to German rules described in ZTV M 13,
full development of retroreflectivity occurs in exactly
12 days.
Retroreflectivity was measured using both
dynamic and static test methods. The
dynamic method, using retroreflectometer
installed on a vehicle, is collecting data
all the time (in milliseconds) and delivers
average value every 25 meters. Data
collection is done during normal driving at
speeds up to 130 km/h. Static measurements
are done traditionally, using handheld
retroreflectometer. It is def initely much too
early for conclusions, so only selected data is
provided in Table 3. The initial results meet
our expectations.
167
Babić D. et al. Application and Characteristics of Waterborne Road Marking Paint
Table 3
Dynamic Measurements of Retroreflectivity, Centre Line
Paint Applied wet
film build
Glass beads type
and size range (µm)
Retroreflectivity (mcd/m2/lx) –
Initial 3 months
W15 600 µm Megalux-Beads® 600-1400 423 582
W15 600 µm Swarcolux50 212-1400 379 404
W15 400 µm SolidPlus100 212-850 677 671
W15 400 µm SolidPlus30 300-1000 516 383
W13 600 µm Swarcolux50 212-1400 440 424
W13 400 µm SolidPlus100 212-850 645 442
Solventborne 400 µm Swarcolux50 200-800 538 384
Source: By Authors
6. Conclusions
Waterborne road marking paints appear a
viable alternative to the currently utilised
solventborne paints with possibility to
encroach onto the markets currently
occupied by more dur able systems. Durabil ity
of waterborne paints, measured by Taber
abrasion, is outstanding and significantly
outperforms the compared standard
solventborne materials. The measured
drying and washout resistance times were
excellent under favourable conditions
at application time: waterborne paints
dried significantly faster than comparable
solventborne materials. The caveat is the
risk of washout in case of sudden downpour
and inferior drying at low temperature –
high humid ity conditions. Ad hesion of glass
beads appears enhanced as compared to
solventborne paints, as evidenced by better
retention of retroreflectivity, but the results
from the test applicat ion are too fresh to draw
positive conclusions.
From the point of view of application,
waterborne paints can be applied ef fortlessly
as long as the personnel is appropriately
trained and maintains clean work
environment. During the test application
work in Croatia, the crew was satisfied; they
noticed and praised quick dry ing during the
good weather at the application time.
With the use of waterborne road marking
paints, absence of hazardous, f lammable, and
toxic chemicals and lower emissions benefit
our and our planet’s health. For the road
authorities, the use of waterborne pa ints would
mean somewhat higher i nitial cost that should
be offset by longer usable paint life and lesser
social health costs. In addition, quick drying
under good conditions would permit lesser
road blocking and easing traffic congestion.
Testing of retroref lectivity shall be done
periodically – the initial results reported
herein are meeting and exceeding our
expectations (Babić et al., 2014).
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