Note: Descriptions are shown in the official language in which they were submitted.
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Preformed Thermoplastic Pavement Marking and Method for High Skid
Resistance with Maintained High Retroreflectivity
PRIORITY
The present application is a PCT International conversion of and claims
priority to US
Nonprovisional application 14/506,248, entitled "Preformed Thermoplastic
Pavement
Marking and Method for High Skid Resistance with Maintained High
Retroreflectivity", filed
October 3, 2014, which is a continuation-in-part and claims priority under 35
U.S.C. 120
from U.S. Patent Application No. 12/592,458, entitled "Preformed Thermoplastic
Pavement
Marking and Method Utilizing Large Aggregate for Improved Long Term Skid
Resistance
and Reduced Tire Tracking", filed November 25, 2009 which is a continuation of
10/816,635
entitled, "Pavement Marking Pattern and Method", filed 2 April 2004 and
granted as US
7,645,503 on January 12, 2010. In addition this application hereby expressly
incorporates by
reference, in its entirety, all applications specified above.
FIELD OF THE INVENTION
The disclosure herein pertains to preformed thermoplastic pavement marking
materials
comprising an intermix and drop-on combination of glass beads and anti-skid
aggregate of
selected size and/or size ratio, where the glass beads have an average
diameter within the
range of 1.0 to 1.4mm and aggregate particles having an average size of 70% to
120% of the
glass bead diameter, provided in specified proportions to achieve high skid
resistance of
Class S5 while maintaining high retroreflectivity Class of R5 using non-
clustered regular
glass beads per standard IS EN 1436, and particularly pertains to such markers
as lines,
legends, arrows, indicia, and decorative marking including pavement marking
patterns
utilizing thermoplastic sheeting which utilize an adhesive (sprayable or
otherwise) to
maintain the integrity of the pattern prior to its application to a substrate.
BACKGROUND OF THE INVENTION
Traffic markings convey information to drivers and pedestrians by providing
exposed visible,
reflective, colored and/or tactile surfaces that serve as indicia. In the
past, such a function was
typically accomplished by painting a traffic surface. Modern marking materials
offer
significant advantages over paint such as dramatically increased visibility
and/or reflectance,
improved durability, and temporary removable marking options. Examples of
modern
pavement marking materials are thermoplastic, pavement marking sheet
materials, tapes and
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raised pavement markers.
Preformed and hot applied thermoplastic materials used as pavement markings or
for other
indicia possess many advantages compared to paints and other less durable
markings. These
materials can be used for years and are capable of possessing high reflective
properties with a
retro-reflective luminance (RL) exceeding 500 mcd/m2/1x. However, pavement
marking
materials of a high RL typically have low skid-resistant properties.
Known materials using high friction aggregates on the surface to improve
friction has been
known. The surface applied aggregates provide good initial values, however as
the surface is
worn due to traffic, the skid resistance decreases. After surface layers
containing anti-skid
materials become worn out these aggregate materials loose their effectiveness
and become
slippery because they do not contain high friction particles (of sufficient
size to provide good
skid properties) in the intermix.
Current thermoplastics include small particulate aggregate to improve the skid-
resistant
properties of the markers. However, over time, it has been shown that when
such particulates
are too small, they become worn too quickly and thus do not provide sufficient
skid-
resistance for high traffic areas. Today's thermoplastic materials do not
include properties of
long-term skid resistance with long-term retroreflectivity.
A review of these issues demonstrates the need for thermoplastic products that
maintains high
RL while also providing high skid resistance once the marking product has been
installed on
the road surfacer
DESCRIPTION OF RELEVANT ART
U.S. Patent No. 3,958,891 to Eigenmann, Ludwig, and not assigned, describes an
aggregate
for securing in a layer of material which is used to form a traffic-regulating
indicium, so as to
improve the nighttime visibility characteristics and anti-skid characteristics
of the traffic-
regulating indicium. The aggregate comprises a core body surrounded at least
partially by a
mass of shock-absorbent binder substance and a plurality of elements that
improve either
nighttime visibility or anti-skid properties, or both. The elements are
arranged in and bound
by the binder substance such that the latter substantially fills the
interspaces between at least
the majority of adjacent pairs of the aforementioned elements, some of which
being arranged
adjacent to an external surface of the mass so as to impart a roughened
texture to the external
surface, thereby permitting the aggregate to be firmly secured in the traffic-
regulating
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indicium. The remainder of the elements are distributed among different levels
interiorly of
the mass so that progressive wear of the aggregate and concomitant detachment
of elements
from the aggregate causes exposure of others of the elements, thereby
conveying long-term
durability to the traffic-regulating indicium.
U.S. Patent No. 4,020,211 to Eigermann, Luwig and not assigned describes a new
material
adapted to be laid down and adhesively secured on a road surface to provide a
traffic
regulating sign with the material which has an upper surface exposed to
traffic and provided
with a plurality of sharp tips projecting above the surface for imparting good
non-skid
properties thereto, the new material comprising an upper layer adjacent to the
upper surface,
at least partially embedding hard particles to form sharp tips and consists of
a polymeric resin
having a high molecular cohesion such as a polyamide resin, a polyurethane
resin or a
polyterephthalic resin, thereby adding improved wear resistance properties to
non-skid and
high visibility properties.
U.S Patent No. 5,077,117 to Harper, et al., describes a pavement marking
material
comprising a flexible base sheet that is conformable to an irregular pavement
surface. A
durable, wear-resistant, polymeric top layer is adhered to one surface of the
base sheet. The
top layer is capable of undergoing brittle fracture at a temperature from 0
degrees Centigrade
to 45 degrees Centigrade such that when the base sheet conforms to an
irregular surface the
top layer readily forms ruptures to relieve stress build-up in the top layer
as the regions of the
top layer defined by the ruptures remain adhered to and follow the conformance
of the base
sheet. A plurality of particles are embedded in and protrude from the top
layer. The particles
comprise retroreflective beads and skid-resistant granules. In a preferred
embodiment, the top
layer is characterized by a Young's modulus of from about 50,000 psi to about
300,000 psi,
and a percent elongation at break of from about 4% to about 35%.
U.S. Patent No. 6,217,252 to Tolliver, Howard R, et al., and assigned to 3M,
describes a
method for marking a transportation surface in which the surface is heated to
a temperature
above the ambient temperature and a finely-divided, free flowing, flame-
sprayable, powder
binder material selected from the group consisting of acrylic polymers and
copolymers, olefin
polymers and copolymers having a number average molecular weight greater than
10,000,
urethane polymers and copolymers, curable epoxy resins, ester polymers and
copolymers,
and blends thereof is melted or substantially softened. The molten or softened
binder is then
applied to the surface with a particulate topcoat or particulate filler
selected from the group
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consisting of reflective elements; skid-resistant particles, magnetizable
particles and mixtures
thereof, and finally the applied materials are allowed to cool to form a
marker in which the
binder adheres directly to the surface.
U.S. Patent No. 3,935,365 to Eigenmann, Ludwig, and not assigned, describes a
tape material
-- for securement to primer layers provided on roadway pavements so as to form
traffic-
regulating indicia on the latter. The tape material comprises a first layer
that contains a
polymeric binder having high molecular cohesion and one surface adapted to
face towards a
roadway pavement and another surface adapted to be exposed to traffic, a
plurality of hard
particles having a minimum of about 6 on the Mohs' Hardness Scale, some of
which should
-- have a sharp tip, distributed among various levels of the aforementioned
first layer, and a
second layer adapted to be secured to a primer layer on the roadway pavement
bonded to one
surface of the first layer. The second layer is compatible with the first
layer so that a firm
bond is formed between them. It is also compatible with the primer layer so
that a bond forms
between them when the tape material is placed on the primer layer. This tape
material imparts
-- good anti-ski properties to a traffic-regulating indicium formed therewith
due to the presence
of the tips of the hard particles, which provide gripping areas when exposed.
It is also an
effective skid-resister during wear of the traffic-regulating indicium due to
the distribution of
the hard particles among various levels of the first layer, which enables
fresh hard particles to
become exposed as hard particles next to the latter are removed by wear.
-- U.S. Patent No. 5,053,253 to Haenggi, Robert, et al., and assigned to
Minnesota Mining and
Manufacturing Company, describes a method of producing skid-resistant
substrate marking
sheet in which a base sheet is provided and an upward face of the base sheet
is coated with a
liquid bonding material. A plurality of ceramic skid-resistant spheroids is
embedded in the
liquid bonding material, wherein the ceramic spheroids are characterized by
having rounded
-- surfaces and no substantial points and characterized by Krumbein roundness
of at least 0.8.
The liquid bonding material is then cured to a solid adherent polymeric matrix
coating with
the ceramic skid-resistant spheroids partially embedded, wherein the spheroids
comprise a
fired ceramic made from various raw materials.
U.S. Patent No. 5,094,902 to Haenggi, Robert, et al., and assigned to
Minnesota Mining and
-- Manufacturing Company, describes a skid-resistant, surface marking
material, comprising a
polymer matrix phase having a top surface and a plurality of opaque, skid-
resistant ceramic
spheroids partially embedded in and protruding from the top surface of the
polymer matrix
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phase, wherein said ceramic spheroids have rounded surfaces and no substantial
points, and
wherein said ceramic spheroids have a Krumbein roundness of at least 0.8.
U.S. Patent No. 6,679,650 to Britt, Jerry, et al., and assigned to Ennis Paint
Incorporated,
describes a marked pavement system comprising a pavement surface, a first
marking stripe
adhered to the top of the pavement surface with a thickness of at least about
40 mils to about
110 mils and comprised of a solidified thermoplastic resin composition with a
black pigment,
and a second marking stripe adhered to the surface of the first marking stripe
with a thickness
of at least 40 mils to 750 mils. The second marking stripe should be narrower
than the first
marking stripe and comprised of a solidified thermoplastic resin composition
with a pigment
that visibly contrasts with the first marking stripe, wherein the marked
pavement system is
highly visible during the daylight hours and during periods of rain.
U.S. Patent No. 6,790,880 to Purgett, Mark, et al., and assigned to 3M,
describes a pavement
marking comprising a binder having polyurea groups, wherein the binder is
prepared from a
coating composition comprising one or more aliphatic secondary amines, one or
more
polyisocyanates, and at least about 15 weight percent non-soluble material
based on the
weight of the final dried coating, and reflective elements. The patent also
discloses the
pavement marking wherein the binder is a sprayable, two-part coating
composition.
U.S. Patent No. 6,217,254 to Wallgren et al, and assigned to Flint Trading,
Inc. of North
Carolina, (original assignee Cleanosol AB, of Sweden) provides for a road
marking
comprising reflective material disposed on a first portion and a friction
material disposed on a
second portion of a fixed road marking. These portions can be shaped, to
include strips. The
main features of this disclosure are that there are separate portions
(sections) of reflective and
skid material, shaped portions (preferably strips or patches of variable
shapes). Application
is described as a two-step process and there is no mention of the bead
specifics outside of
mentioning the possibility of a large >0.7 mm bead to improve visibility in
dark or wet
conditions. The best properties achieved herein were a skid resistance of 55
SRT and a RL of
380, correlating to a skid resistance class of S3 and a RL class of R5 as
determined by the
newest edition of IS EN 1436.
U.S. Patent Application No. 2011/0059295 to Greer et al. and assigned to Flint
Trading, Inc
of Thomasville, NC (also herein the applicants) provides for a retroreflective
pavement
marking material composition comprising a base layer composition for
application to a
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pavement substrate and a top layer comprising retroflective glass beads
wherein the beads
range in size from greater than 2 mm to about 5 mm, wherein the base layer and
the top layer
combine to form a single composite film. High index bead clusters are
disclosed and are
provided for with regular glass beads of 1.5 index of refraction (TOR) and a
large diameter
size.
3MTm StamarkTM High Performance Marking Tape A380SD is used an inlay for hot
asphalt
surfaces or an overlay pavement marking for asphalt and concrete surfaces in
highway travel
conditions of free-rolling traffic, and is used to mark lane lines, edge
lines, channeling lines
and gore markings. Abrasion resistant ceramic beads and ceramic skid particles
are applied
in a patterned pile formation and the marking is applied using a pressure
sensitive adhesive.
As stated in the product bulletin, A380 SD fulfils the following classes of EN
1436 in new
conditions relevant to this disclosure: R5 (?300 mcd) and S3 (?55 SRT). A non-
warrantied,
initial value of approximately 550 mcd/m2/1x is provided by 3MTm but is not a
maintained
Class S5 value as provided herein. In order to provide legends and symbols, an
alternate
product in the 3MTm series, L3805D, is recommended, where the disclosed
thermoplastic
pavement markings can provide lines, warnings, legends, road signage and other
forms of
road marking communications.
Great Britain Patent Application No. GB 2429978A to Aubree, Barry Mark, and
assigned to
Barry Mark Aubree, describes a method of producing a thermoplastic road-
marking
composition that comprises mixing an opaque pigment, a translucent particulate
thermoplastic material and reflective glass beads such that when the
thermoplastic material is
subsequently melted to bind the composition and the composition is laid as a
marking, the
glass beads on the visible surface of the markings are not substantially
obscured by the
opaque pigment. The application also presents a thermoplastic road-marking
composition
comprising a mixture of a particulate filler material, a pigment, a
translucent thermoplastic
material and reflective glass beads wherein the pigment clings to the filler
material and the
reflective glass beads are generally clear of the pigment. Accordingly, the
thermoplastic road-
marking immediately has retroreflectivity without the requirement for an
additional operation
of adding glass beads to the surface of the marking and without the need to
let the road-
marking wear before it becomes retroreflective.
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WIPO Patent Application No. W003064771A1 to Hong, Le Hoa, et al., and assigned
to
Avery Dennison Corporation, describes a method for securing a preformed
pavement
marking construction with a top surface and at least one perimeter edge to
pavement with a
relatively flat roadway surface. The method includes adhering the preformed
pavement
marking construction the roadway surface, providing a curable structural
adhesive, and
applying the curable structural adhesive to the at least one perimeter edge
such that the
curable structural adhesive overlaps a portion of the top surface of the
preformed pavement
marking construction at its at least one perimeter edge and a portion of the
roadway surface.
Finally, the curable structural adhesive is cured to form a traffic-bearing
top surface
extending between the roadway surface and the preformed pavement marking
construction.
The disclosed review of the relevant art indicates that a need still exists
for a thermoplastic
pavement marking method using an adhesive (sprayable or otherwise) that
maintains the
integrity of the pattern and a thermoplastic pavement marking composition that
includes
selected size bead/aggregate ratios for high skid resistance with a
corresponding high retro-
reflective luminance (RL) or retroreflectivity.
SUMMARY OF THE INVENTION
The present disclosure describes a preformed thermoplastic pavement marking or
hot melt
applied material with high Class S5 skid resistance and high RL of Class R5
once the
pavement marking has been adhered to road surfaces or other solid substrates.
The need
exists to produce preformed thermoplastic pavement marking materials with both
high skid
resistance and high RL, as the use of higher quantities of drop-on glass beads
increases the
product RI, yet lowers the skid-resistance while a gain in skid-resistance
shows a decline in
RL, making a simultaneous achievement of these high performance
characteristics previously
unattainable. The uniqueness of the present invention lies in maintaining
homogeneous
bead-aggregate compositions throughout the entire preform or hot melt
composition
including the surface and the body, thereby providing longevity to both
reflectivity and skid
resistance without sacrificing any other physical or physio-chemical
properties.
The preformed thermoplastic material of the present invention is comprised of
about 20%
binder and 80% "intermix", where the intermix includes non-organics such as
silica, calcium,
and other inorganic pigments as well as high friction aggregate capable of
passing through
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sieves sizes of about 10 to about 24 together with large beads. The surface
applied anti-skid
materials provide high initial friction properties, while large size aggregate
and large beads in
the intermix provide long term skid resistance and improve initial friction
properties by
creating an appropriately textured surface.
To achieve the desired traction and friction properties it should be
recognized that there is a
difference between slip resistance, which relates to traffic traveling over
the pavement
markers at a slow speed and to pedestrian traffic traveling over the same
pavement marker
surfaces and related to the static COF (coefficient of friction). Skid
resistance relates,
however to traffic traveling over the pavement markers at high speed, and
depends on surface
texture. Skid resistance is more applicable to the type of vehicular traffic.
Most specifically, the preformed or hot applied thermoplastic marking
composition
comprises a planar top surface portion and a planar bottom surface portion
that are coplanar
to each other, wherein the bottom surface portion is directly applied to a
substrate via
application of heat or pressure or both heat and pressure and wherein the top
surface portion
comprises both an intermix with retroreflective beads and aggregate that
exists and is uniform
throughout the thermoplastic composition and a surface drop on composition
also
comprising retroreflective beads and aggregate wherein the size ratio of said
beads to the
aggregate is 0.85:1.50 and the weight ratio of the beads to the aggregate is
0.80:1.60 and /or a
surface area coverage at range of ratios of beads to aggregate of between
2.8:1 to 0.7:,
thereby maintaining uniformity both on the surface and within a body of the
thermoplastic
marking composition thus providing retroreflectivity of greater than or equal
to 300 mcd and
improving long-term skid resistance as measured by an SRV of greater than or
equal to 65.
DESCRIPTION
Common test methods for measuring the effectiveness of these pavement markers
for slip and
skid resistance include ASTM E303, entitled "Standard Test Method for
Measuring Surface
Frictional Properties Using the British Pendulum Tester", which is the most
commonly used
test methodology. The British Pendulum Tester (BPT) is one of the most widely
used
instruments in the measurement of friction characteristics of pavement
surfaces, Skid
Resistant Values (SRV) are determined by the BPT. SRV values from the BPT can
also be
reported as the British Pendulum Number (BPN) or the Pendulum Test Value
(PTV), and the
BPT referred to as the Skid Resistance Test (SRT).
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European Standard IS EN 1436 is a specification that concentrates on driver
need and
governs the required quality of the road marking and performance
characteristics of white
and yellow markings based on luminance, day- and night-time visibility, wet-
night visibility
and skid-resistance in combination with durability. IS EN 1436 has specified
for roads with
extensive traffic an RL of Class R5 of at least 300 mcd/m2/1x and a skid
resistance of Class
S5 of 65 SRV (BPN) as shown for white road markings in Table 1. Yellow marking
specifying criteria are provided in Table 2.
Table 1: Criteria for White Road Markings (IS EN 1436)
:, pli.ti..tolt roNli.dr,,i : Rti ti?-t e.1.401:e5t1 twoi i, .....
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: ...............................................................
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: :::,,.. - ' : 1 x" I, ' 3 " '' %
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.
...........
. i 55 1 EZ :3 IRV
.
Table 2: Criteria for Yellow Road Markings (IS EN 1436)
Retio-Mlectiot) :14/A := 14triflekiAm t...o.M :i LtItniaatlf:e Ski4
RtsMaoce j
=Cia.mi I Vilpm - ClAm i Vall.to 1 Claw \ Vaitom
oas.,..1.õL, Vatt.t!)
- I ---- . RW¨..r."IIIL El NIL , , m
i :al',1,,
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titc:,i :::; Tii1¨"MImitr"12"""Ii""""`
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Road surfaces made from concrete or asphalt have SRT values in the range of 65
to 75, and a
similar skid resistance of the pavement marking and road surface is beneficial
to increasing
driving safety at high speeds necessitating the need for a Class S5 skid
resistance of the
applied thermoplastic pavement marker.
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Known materials have achieved only a combination of Class R5-S3 levels, as
provided by
3M StamarkTM High Performance Pavement Marking Tape A380 and by Wallgren in US
Pat.
6,217,254. The new composition of the present disclosure provides a
combination of the
highest performance classes, generating R5-S5 classification results.
The required materials for the present invention to achieve both the necessary
high
retroreflectivity of Class R5 and equally high skid resistance of Class S5, as
provided in IS
EN 1436 entitled "Road Marking Materials ¨ Performance for Road Users", are
those that
contain a size ratio of bead to aggregate of 0.85:1.50, a weight ratio of bead
to aggregate of
0.80:1.60 or a surface area coverage at range of ratios of beads to aggregate
between 2.8:1 to
0.7:1.
The high friction large aggregates are included in the intermix with a weight
percent content
of up to 45% and the percent of beads are at about 30%. The optimal size of
the large
aggregates to be selected from are about 12 to about 20 grit (about 0.8 to
about 1.7
millimeters depending on size of the large beads used). The present invention
also includes
the use of normally surface applied large aggregate in a range from about 14
to about 20 grit
(about 0.8 mm to about 1.4 mm). Product using small particle aggregate sizes
(approximately
24 grit or less) covered the surface area of the thermoplastic marking sheets
more effectively;
however, these aggregates did not provide the required skid resistant
classification.
It has also been shown that it is possible to use single grit size aggregate
in the intermix. The
use of an intermix of different grit sized aggregates in different proportions
based on the need
for the future use of different materials (larger sizes for thicker and larger
thermoplastic
sheets and smaller aggregates for narrow strips) is also part of the present
disclosure.
The aggregates used are angular particles primarily exhibiting a Mohs hardness
of greater
than 7, including corundum, quartz, calcined bauxite, and others ( trade names
of such
materials include Mulcoa grade 60, AlphaStar0, UltrablastO, and Alodur0 which
provide
hardness ratings in the range of 7 to 9). A portion of the intermix used with
the thermoplastic
road marking includes 16 grit size aggregate also with a hardness in the Mohs
scale reading
of greater than 6. This combination has never been tried before in preformed
or hot melt
applied thermoplastic surface applications, and has resulted in improved
friction.
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Regular soda-lime glass, with a refractive index at about 1.5 and a larger
than lmm average
diameter, is the bead of choice for this application. Glass beads with
gradation according to
AASHTO M247-11 are provided as follows:
= Type 3 (T3) glass beads provide 70% of the beads with a diameter in the
range of 1.0
¨ 1.18 mm and 95% having diameter > 0.85 mm.; overall weighted average
diameter
1.05 mm
= Type 4 (T4) glass beads provide 70% of the beads with a diameter in the
range of 1.18
¨ 1.4 mm and 95% having diameter > 1.0 mm.; overall weighted average
diameter
1.25 mm
= Type 5 (T5) glass beads provide 70% of the beads with a diameter in the
range of 1.4
¨ 1.7 mm and 95% having diameter > 1.18 mm.; overall weighted average
diameter
1.4 mm
The aggregate particle size is to be selected as having an average of 70% to
120% of the glass
bead diameter used. Aggregate particle size is defined and described per
ANSFASTM E-11-
81. In order to achieve this required property, the following must be
maintained for the
selected glass bead type:
= T3 glass bead diameter 1.0¨ 1.18mm, aggregate 0.71 to 1.18 diameter (mesh
size
(grit) 24 to 18)
= T4 glass bead diameter 1.18¨ 1.4mm, aggregate 0.85 to 1.4 diameter (mesh
size (grit)
20 to 14)
= T5 glass bead diameter 1.4¨ 1.7mm, aggregate 1.0 to 1.7 diameter (mesh
size (grit)
18 to 12)
An additional desired result is improved overall skid resistance of the
preformed
thermoplastic markers without any associated loss of retroreflective
luminance.
The aforestated special aggregates also improve the coefficient of sliding
friction (COF) as
determined per the ASTM E274 test. As the COF decreases below a certain level
on the
surrounding asphalt, a small wheel grabs onto the asphalt and if the COF is
reduced on the
pavement marking too much, undesirable skidding will occur. It is desirable
that the COF of
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the preformed or hot melt thermoplastic match or be greater than the road
pavement surface.
The COF, in this case, as measured per ASTM E274 requires using a small cart
pulled behind
a car with a wheel attached to the bottom of the cart that rides at the speed
of the car, thus
touching the pavement surface, which eventually results in locking the wheel,
thereby
allowing for measurement of the force of the cart on the surface.
Therefore, a surprising result found during the course of experimentation and
resulting in an
important embodiment of the present application is that these thermoplastic
marking surfaces
maintain high RL of Class R5 and possess high skid resistance of Class S5,
while marking
surfaces without the special bead/aggregate combination described above have
not achieved
such classifications. In all previously known compositions, high values of
retroreflectivity
A further embodiment of this disclosure is the achievement of these
bead/aggregate
combination thermoplastic marking surfaces maintaining R5-S5 classification
without the use
of special high refractive index glass beads, domes, or ceramic clusters,
providing a more
economical formulation. The refractive index of the selected regular glass
bead is RI =1.5. It
has been possible to achieve a high RL by using a high index glass bead;
however, this type
of glass bead selection has proven to not be durable.
There is also a strong need in the industry to provide a layer of preformed
thermoplastic so
that these marking surfaces are skid resistant and can be used for any
crosswalk material.
There is also a requirement that the skid resistance provides no compromise in
retroreflectivity value (RL). The combination of "large" beads and hard
aggregate using the
defined ideal ratios with respect to the size and weight of beads to aggregate
(such as
corundum) using primarily a homogeneously mixed material, has not been
previously
accomplished.
An additional embodiment and surprising result is that in the past, without
the use of these
specific aggregate/bead combinations, the RL is compromised in the
optimization of skid-
resistance where the thermoplastic pavement marking materials with RL
exceeding 400
mcd/m2/1x, do not usually achieve a BPN value exceeding 40 ¨ 45 (or Class Si).
In the case
of the present disclosure, this is not true and this undesirable result has
been eliminated.
In the present invention, the use of uniform particulate material or blends of
particulate
materials for the aggregate with differing hardness values, providing more
economical
solutions, can be introduced into the intermix during formulation. The
introduction of these
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blends usually occurs prior to extrusion and completion of the thermoplastic
pavement
marking. The aggregates and other particles such as glass beads and the
inorganic choices
stated above can also, however, be dropped on the hot material during
installation and
completely embedded into body of the thermoplastic marking material in that
fashion. The
preformed thermoplastic surface marking product can be applied using pressure
sensitive
adhesives as well as by flame torching.
Another object of the present invention is to provide for long term skid
resistance and
maintained retroreflective luminance through the addition of Type 3 ¨ Type 5
glass beads in
selective combination with certain sized aggregate particles. More
specifically, the ratios to
be maintained to maintain high IZI, and adequate skid resistance requires
surface bead sizes
between T3 and T5 using 16-20 mesh or grit size (here the words mesh size and
grit size are
used interchangeably) corundum. The corresponding intermix requires bead sizes
of between
T3 and T5 with 12-20 mesh or grit sized aggregate. The ideal ratios are
therefore as
follows:
0.85: 1.5 for the size ratio of beads : aggregate; and
0.6-1.6 for the weight ratio of beads: aggregate.
In previous intermix compositions, which do not cover the present disclosure,
intermix beads
are comparatively very small with the drop on beads ¨ which are comparatively
much larger.
This combination is unacceptable when trying to combine high retroreflectivity
with
improved skid resistance for performed thermoplastic or hot melt road markers-
in all these
cases the skid resistance decreases and with increased retroreflectivity.
As stated above, the present invention includes larger grit size aggregate
than is normally
used in similar preformed thermoplastic pavement marking products.
Specifically, the
aggregate should be between 12 and 20 mesh (grit) in size, depending on the
size glass bead
selected, and may be comprised of quartz, corundum, crushed gravel, crushed
granite, or any
combination thereof The aggregate used may also measure 7 or greater on the
Mohs
Hardness Scale. This selection of grit size improves the skid resistance
properties of the
pavement marker in combination with the corresponding size of glass bead
selection and
ensures that the product wears down more slowly, conveying greater durability
and also
longer term skid resistance ¨ often through the end-of-life of the applied
preformed
thermoplastic.
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Other advantages achieved using these working examples include the fact that
when the
surface applied aggregate provides high initial skid resistance using
aggregate in the intermix,
the surface maintains high skid properties during the entire period of use of
the pavement
markings and also provides increasing skid resistance. The drop on beads mixed
together
with aggregate provide an intermix so that the product maintains high RL and
skid resistance
during markings lifespan.
It should be understood that although examples are given it should not be
construed that these
are examples provide the only examples of the invention and that variations of
the present
invention are possible, while adhering to the inventive concept herein
disclosed.
WORKING AND COMPARATIVE EXAMPLES
Test Methodology
European Standard IS EN 1436 specifies that for roads with extensive traffic a
RL class of R5
of at least 300 mcd/m2/1x and a skid resistance class of S5 of at least 65 SRT
(BPN) is
required.
Retroreflectivity of the applied material was tested using retroreflectometer
Delta LTL-X
Friction properties were tested according to ASTM E303.
WORKING EXAMPLE 1:
An example of the hydrocarbon resin composition for the preformed
thermoplastic of the
present invention is provided as follows:
Material composition
Binder:
Escorez 7720 ¨ 8%
C5 hydrocarbon resin ¨ 7%
Escorene EVA MV 02514 3.2%
Refined mineral oil ¨ 1.8%
Fumed silica ¨ 0.3%
Titanium dioxide (Rutile) ¨ 10%
Fillers
Glass beads Type 3 ¨ 30%
Corundum Grit 20 20%
CaCO3- 19.7%
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The material composition has a softening temperature (Ring and Ball) of 112 C
measured
according to ASTM D36-06 entitled "Standard Test Method for Softening Point of
Bitumen
(Ring-and-Ball Apparatus)".
The thermoplastic material composition was extruded using a casting die to
create 125 mil
thick preformed thermoplastic sheets. As the sheets were extruded glass beads
T3 were
dropped onto the melted thermoplastic material. Subsequently at a location
further from the
die exit on the manufacturing line, corundum grit 16 was added to the
thermoplastic and
indented visual heating indicators were applied to the surface.
Composition Type Beads Aggregate Weight Ratio Size
Ratio
Beads:
Beads: Aggregate
Aggregate
Intermix, T3 Corundum, Grit 20
Weight percent 30% 20% 1.5: 1.0 1.22:
1.0
Surface Drop-on, T3 Corundum Grit 16
Lbs. / sq/ft 0.106 0.068 1.56 :1.0 0.88:
1.0
Surface area cover ratio (bead: aggregate) = 2.39 : 1.0
Using a Flint-2000 propane torch, the material composition was applied on
asphalt and tested
using Delta LTL-X retroreflectometer and British Pendulum tester and had the
following
properties:
initial retroreflectivity RL, 344 mcd/m2/1x
skid resistance 65 BPN.
WORKING EXAMPLE 2
An example of alkyd based preformed thermoplastic of the present invention is
provided as
follows:
Material composition
Polyamide Unirez 2633 7.8%
Hard resin Sylvacote 7021 8.5%
Plasticizer DINP 3%
Polyethylene Wax 2%
Fumed silica 0.4%
Titanium dioxide 10%
Glass beads T4 29%
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Corundum Grit 16 24%
CaCO3 15.3%
The material composition has a softening temperature (Ring and Ball) of 118 C
measured
according to ASTM D36-06 entitled "Standard Test Method for Softening Point of
Bitumen
(Ring-and-Ball Apparatus)".
The thermoplastic material composition was extruded using a casting die to
create 90 mil
thick preformed thermoplastic sheets. As the sheets were extruded glass beads
T4 were
dropped onto the melted thermoplastic material. Subsequently at a location
further from the
die exit on the manufacturing line, corundum grit 20 was added to the
thermoplastic and
indented visual heating indicators were applied to the surface.
Composition Type Beads Aggregate Weight Ratio Size
Ratio
Beads:
Beads: Aggregate
Aggregate
Intermix, T4 Corundum, Grit 16
Weight percent 29% 24% 1.21 : 1.0 1.04:
1.0
Surface Drop-on, T4 Corundum Grit 20
Lbs. / sq/ft 0.112 0.090 1.24 :1.0 1.45:
1.0
Surface area cover ratio (bead: aggregate) = 2.22: 1.0
Using a Flint-2000 propane torch, the material composition was applied on
asphalt at a test
deck located on Holden Rd. in Greensboro, NC with average daily traffic (ADT)
of 6500 per
direction. Material was tested using a Delta LTL-X retroreflectometer and a
British
Pendulum tester and exhibited the following properties:
Initial Properties:
RL = 425 mcd/m2/1x; BPN = 71
After two months RL = 480 mcd/m2/1x, BPN = 75
After 12 month RL = 350 mcd/m2/1x; BPN = 66
After 20 moths RL = 320 mcd/m2/1x; BPN = 70
WORKING EXAMPLE 3
Another example of a bead/aggregate drop-on for the preformed thermoplastic of
the present
invention is provided as follows:
Material Composition for Working Example 3
Binder composition
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Polyamide resin Uni-Rez 2633 7.8%
Modified rosin resin Sylvacote 4984¨ 7.1%
Phthalate plasticizer ¨ 2.3%
PE based wax ¨ 1.6%
TiO2¨ 10%
Fillers
Glass beads T5 25%
Corundum grit 14 30%
CaCO3 ¨ 16.2%
Drop-On:
Bead: T5 at 0.102 lb/ft2
Aggregate: Corundum grit 20 at 0.112 lb/ft2
Composition Type Beads Aggregate Weight Ratio Size
Ratio
Beads:
Beads: Aggregate
Aggregate
Intermix, T5 Quartz, Grit 14
Weight percent 25% 30% 0.83 : 1.0 0.98:
1.0
Surface Drop-on, T5 Corundum grit 16
Lbs. / sq/ft 0.102 0.155 0.66:1.0 1.16 :
1.0
Surface area cover ratio (bead: aggregate) = 0.7 : 1.0
Material was extruded, applied and tested similar to the Example 2
Properties: RL = 376 mcd/m2/1x
BPN =69
WORKING EXAMPLE 4
An additional example of a bead/aggregate drop-on for the preformed
thermoplastic of the
present invention is provided as follows:
Material Composition for Working Example 4
Binder composition
Polyamide resin Uni-Rez 2633 8 %
Modified rosin resin Sylvacote 4984 ¨ 7.5%
Phthalate plasticizer ¨ 2.0%
PE based wax ¨ 2.0%
TiO2¨ 10%
Fillers
Glass beads T3 30%
Corundum grit 20 25%
CaCO3¨ 15.5%
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Material was extruded and applied on asphalt similar to the process described
in the Example
2.
Drop-On:
Bead: T4 at 0.092 lb/ft2
Aggregate: Corundum grit 20 at 0.094 lb/ft2
Composition Type Beads Aggregate Weight Ratio Size
Ratio
Beads:
Beads: Aggregate
Aggregate
Intermix, T3 Corundum, Grit 20
Weight percent 30% 25% 1.2: 1.0 1.22:
1.0
Surface Drop-on, T4 Corundum, Grit 20
Lbs. / sq/ft 0.108 0.078 1.4 :1.0 1.45 :
1.0
Surface area cover ratio (bead: aggregate) = 1.52 : 1.0
Properties: RL = 444 mcd/m2/1x
BPN = 73
While the many embodiments of the invention have been disclosed above, many
other
embodiments and variations are possible within the scope of the present
disclosure and in the
appended claims that follow. Accordingly, the details of the embodiments and
examples
provided are not to be construed as limiting. It is to be understood that the
terms used herein
are merely descriptive rather than limiting and that various changes and
numerous
equivalents may be made without departing from the spirit or scope of the
invention as
claimed.
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