Note: Descriptions are shown in the official language in which they were submitted.
68~6
Back~round of the Invention
This invention relates to reflective material and
more particularly to reflective particles, a methoa of making
them ~nd their use in reflective marking.
~ he present invention, while of general application,
is particularly well suited for use on highways to provide
reflective markers such as edge and lane striping, signs, etc.
As is well known, it has become common practice to drop small
glass spheres onto a painted line on a highway while the paint
is still tacky such that the spheres are partially imbedded in
the paint when it has dried. The spheres render the line or
other marker retroreflective and reflect the light from
headlights so that the marker is more visible to the motorist.
In some cases the spheres were imbedded in spherical or
irregularly shaped plastic granules prior to being applied
to the paint in the manner disclosed in U.S. Patents 3,252,376
and 3,254,563, for example, in an effort to further improve
the reflectivity of the marker.
Heretofore, difficulties were encountered in the
manufacture and use of reflective material of the foregoing
type. As an illustration, in many instances the adhesion of
the glass spheres to the paint proved deficient, with the
result ~hat some of the spheres were loosened by traffic or
washed away during rains~orms, 'or example, with a corresponding
deterioration in the reflectivity of the surface. In~a~dition,
the spheres that remained were subjected to severe ~brasion
under heavy traffic conditions and exhibited flattened upper
~26~30~6
surfaces which further impaired the ref}ectivity of the
marker. Furthermore, and this has ~een of special moment
during periods of heavy rain, the reflectivity of even
freshly applied striping or other marking wa~ deficient
in a number of respects.
Summary
One general object of the invention, therefore,
is to provide a new and improved reflective particle for use
in highway and other reflective marking.
Another object of the invention is to provide a
new and improved method of making such a particle.
More specifically, it is an object of ~his invention
to provide a reflective particle that remains in place on a
supporting surface for an extended period of time.
A further object of the invention is to provide a
reflective marker which exhibits uniform and in some cases
improved reflectivity after long periods of use.
Still another object of the invention is to provide
a reflective marker which exhibits good reflectivity when in
a wet or moistened condition.
A still further object of the invention i5 to
provide an improved reflective marker and method of makinq
-the same which are economical snd thoroughly reliable in
operation. _ -
~ 2 ~ ~ 0 ~i
In one illustrative embodiment of the invention,
the reflective marker comprises a multiplicity of uniquely
shaped granules of plastic material. Imbedded in ~t least
the exposed ~urfaces of the granules are a plurality of glass
spheres which protrude through the surfaces to provide the
granules with reflcctive characteristics. For many applications
the granules are dropped or otherwise applied to a painted
substrate with the paint in a tacky condition, but in other
cases the granules may be premixed with paint and then applied
to the substrate in a single operation.
$n accordance with one feature of the invention,
each of the granules is provided with at least one flat face
and is of a shape such that when dropped from a random position
onto a horizontal surface the flat face is disposed in a down-
ward direction. The flat face is imbedded in the layer of
paint to provide optimum adhesion of the granule to the
surface.
In accordance with another feature of the invention,
in certain particularly important embodiments, each granule is
in the shape of a tetrahedron. The tetrahedrons preferably
are of a shape such that when sprinkled from a random
position onto a painted line of a highway, ~or example, one
of the faces of the tetrahedron is disposed downwardly and the
remaining faces meet the downward face at an angle of ~bout
seventy degrees. With this arrangement the resulti~g marker
exhibits high reflectivity with respect to the headlights
of a vehicle particularly under wet conditions.
--3--
- ~68~
In accordance with a further feature of several
advantageous embodiments of the invention, the maximum height
of the plastic granules Pbove the surface lies within the
range of from about 2 millimeters to about 12 millimeters,
and the granules are of at least two distinct sizes. The
larger size granules become flattened by traffic to expose
a greater quantity of the glass spheres imbedded therein,
while the smaller granules retain their tetrahedron shape
for an extended period of time. ~he arrangement is such
that the reflectivity of the marker remains substantially
uniform and in some cases increases during long periods of
use.
In accordance with still another feature of the
invention, in several good arrangements, the granules are
formed by advancing a plastic sheet in a softened conditi~n
over a roller containing a multiplicity of tetrahedron-shaped
indentations to individually mold each granule. The glass
spheres are applied to the sheet prior to the molding operation
by spraying the spheres onto the flat surfaces of the sheet
and in some cases by mixing additional spheres with the plastic
material used to form the sheet. The size and shape of each
individual granule is determined by the configuration of the
indentations in the roller to provide a very precise control
over the reflectivity characteristics of the resulting marker.
The present invention, as well as further~DDjects
and features thereof, will be more iully understood_from the
following description of certain preferred embodiments, when
read with reference to the accompanyiny drawings~
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016
Brief Description of the Drawings
Figure 1 is a substantially enlarged perspective view
of a molded tetrahedron-shaped granule containing glas~ spheres
in accordance with An illustrative embodiment of the invention.
~ igure 2 is a vertical ~ectional view taken along the
line 2-2 in Figure 1.
Figure 3 is an enlarged side elevational view of a
portion of a roadway having a reflective marker which includes
different size granules of the type illustrated in Figure 1.
Figure 4 is a vertical sectional view of the roadway
portion of Figure 3.
Figure 5 is a vertical sectional view similar to
Figure 4 but showing the reflective marker after it has been
subjected to heavy traffic.
Figure 6 is a perspective view with a portion shown
in section of a thermoplastic sheet used in the manufacture of
the granules.
Figure 7 is a perspective view of the thermoplastic
sheet of Figure 6 during the application of glass spheres to
its exposed surfaces.
Figure 8 is a partially schematic front elevational
view of the thermoplastic sheet as it is advanced between
rollers to form the granules.
. Figure 9 is a partially schema~ic side elevational
view of the rollers and associated components illus~ra~ed in
Figure 8.
6 8 ~ ~
Description of Certain Preferred Embodiments
-
Referring to Figures 1 and 2 of the drawinqs, there
is shown a small reflective particle in the form of a plastic
resin granule 20. The granule ~0 has nt least one flat face
22 and ~s of ~ shape such that when dropped from ~ random
position onto a horiæontal surface the face 22 is disposed
in a downward direction, for purposes that will become more
fully ~pparent hereinafter. Advantageously the granule 20
is in the form of a tetrahedron ~nd in addition to the downward
face 22 has additional faces 23, 24 ~nd 25. For granules in
the shape of an equilateral tetrahedron the angle ~ between
the face 2~ and the adjoining faces 23, 24 and 25 is 60.
Particularly good results are achieved with granules h~ving
an angle ~ of at least 60 and preferably about 7~.
Evenly dispersed throughout the granule 20 ~re a
multiplicity of glass beads or spheres 27. Some of the spheres
27 protrude through the faces 22, 23, 24 and 25 of the granule
20 and similarly arc evenly dispersed throughout the surface
area of each face. The spheres 27 are of a type commonly used
in reflective marking and have a diameter in the range of from
about 6.0 microns to about 0.125 inches depending upon the
particular type of reflective marker with which the spheres
are to be used. For best results the spheres 27 should have
an index of refraction of at least about 1.5, and in situations
where particularly good retroreflectivity is desir~ ~he
refractive index of the spheres may be up to ~bout 2~0.
In some cases a reflective coating such ~s a silver may be
applied to the spheres which provides even higher
--6--
-
12~8t)~6
retroreflectiuity for certain applications. The
spheres illustratively may be produced in the manner disclosed
in T.~. ~ood U.S. Patent 2,947,115, for example, and for many
applications they ~re provided with a suitable coupling agent
coating such as the silanes, titanates with vinyl groups,
terminal amines or epoxides. For a more detailed discussion
of representative coatings for the spheres, reference may be
had to James R. Ritter et al ~.S. Patent 3,867,178.
The tetrahedron-shaped granules 20 containing the
glass spheres ~7 may ~e employed as illustrated in Figure 3
to provide a reflective marker on a surface 30 which illustratively
comprises a roadway or highway sign. A layer 31 of traffic
paint or other adherent material is first applied to the surface
30, and while the paint is still tacky the granules 20 are
dropped from a random position and become imbedded in the paint.
Because of their configuration the granules 20 come to rest
on the painted surface with one of their flat faces 22 disposed
in a downward direction irrespective of ~he orientation of the
granules at the time of their release. With this arrangement
the entire area of the face 22 on each granule is in facing
contact with the paint to provide extremely good adhesion
between the granules and the roadway surface. Each individual
granule is imbedded in the layer of paint, and the paint may
exhibit a slight wicking action to further help maintain
the granules in position and prevent ~ny substanti~I quanti~y
of granules from becoming dislodged even under hcaYy traffic
conditions.
~26t3~)16
The size of the plastic granules 20 is carefully
controlled such that their height above the roadway surface 30
ranges between about 2 millimeters and about 12 millimeters. For
granules having a height much below 2 millimeters the quantity of
glass spheres 27 within each granule i5 too small to provide a
satisfactory impr~vement in retroreflecti~e properties,
particularly during rainy conditions, while for granules
above about 12 millimeters in height the surface becomes
too rough and there is unnecessary wastage of the granule
material due to traffic wear, shearing by snow plows, etc.
In addition, the granules within this range advantageously
are divided into two and in some cases three distinct
sizes. As illustrated in Figures 3 and 4I for example, the
granules applied to the surface 20 comprise comparatively
large granules 20a which range in height from about 6 millimeters
to about 12 millimeters, medium-size granules 20b which range
in height from about 4 millimeters to about 6 millimeters, and
small granules 20c which range in height from about 2 millimeters
to about 4 millimeters. In cases in which only two size ranges
are used for the granules, the large granules have a height of
between about 5 millimeters and about 12 millimeters, and the
small granules have a height between about 2 millimeters and
about S millimeters.
Figure 5 is an illustration of the granule-coated
roadway surface 30 after being subjected to abras~on by heavy
traffic. The upper portions of the large granules 20a and the
medium-size granules 20b have been eroded-to provided flat
horizontal surfaces 33, while the upper portions of the small
granules 20c have not been subjected to abrasion and retain their
~26~30~6
original tetrahedron shapes. During the erosion of the
granules 20a and 20b the glass spheres 27 within the interiors
of the granules become exposed and protrude through the upper
surfaces 33 to help retain the optical propertieS of these
l~rger granules. In ~ddition, the reflective angle Q (~igure 2)
remains the same irrespective of the degree vf er~sion and
preferably is approximately 70D to provide an optimum reflective
angle on a highway for the headlights of a vehicle. The arrange-
ment is such that the reflective marker retains good retro-
reflective properties even after being exposed to long periods
of heavy traffic, and there is very little impairment o~ the
retroreflective properties during rainstorms and in other
instances where puddles are formed on the roadway. The flat
surfaces 33 on the larger granules 20a and 20b in many
instances ~re disposed above the puddles, and the glass
spheres protruding therefrom retain much of their retro-
reflective properties.
The material from which the granules 20 are formed
may be selected from a wide variety of ~hermoplastic and
thermosetting resins. Suitable thermoplastic resins include
the polyolefins, polyethylene, polypropylene, polymethyl
methacrylate, acrylonitrile butadiene styrene, etc., while
the thermosetting resins that may be used comprise the
polyesters, urethanes, methyl methacrylate and ~crylonitrile.
Substantially ~ny thermoplastic or thermosetting ~e~in may
be employed ~hat exhibits good wear resist~nce and gives
off a minimum of volatile matter during curing.
~ ~ 6 ~
The polyester resins, for example, in general comprise
unsaturated alkyd resins which are formed by the reaCtiQn of
one or more dicarboxylic acid components and ~ne or more polyhydric
alcohols. Illustrative dicarboxylic acid components include
~aturated anhydrides and adipic and azelaic acids, and the
unsaturated components fumaric acid and maleic acid. The commonly
used dihydric alcohols include glycols o~ ethylene propylene, 1,
3- and 2, 3- butylene, diethylene and dipropylene. The polyester
reaction products are mixed with a nonvolatile unsaturated
monomeric cross-linking agent for the polyester resin such
as a methyl methacrylate. Other unsaturated hydrocarbons that
may be employed as a monomeric agent include styrene, vinyl
toluene, vinyl acetate, ~rtho and para methyl styrene, divinyl
ben~ene, ethyl acrylate and many others. ~he monomeric agent
is of the nature such that it is consumed during the curing
of the resin without forming volatile materials.
Still other illustrative materials that may be
employed to form the granules 20 include the epoxy resins
containing both epoxide and hydroxyl groups and the urethane
resins resulting from reactions between hydroxyl groups and
polyisocyanates. For a more detailed dis~ussion of
representative thermoplastic and thermosetting resins which
are useful as the granule material, reference may be had,
for examole, to De Vries et al U.S. Patents 3,171,827 and
3,254,563.
--10--
o~
The resin ma~erial ~or the granules 20 is obtained
commercially in liquid, powder or pelletized form. The
material is thoroughly mixed with slass spheres having ~
diameter in the range of from about 6.0 microns to about
0.125 inches and nn index of refraction of from about 1.5
to ~bout ~.0 and even higher depending upon the particular
application. For highway striping, for example, the glass
spheres may be produced from conventional soda lime silicate
glass having an index of refraction of about 1.5. For
roadways in areas subjected to heavy precipitation, or
for signs, motion picture screens and other applications
where even better reflectivity is desired, ~he spheres m~y
be fabricated from some of the titanium glasses having
a higher index of refraction, or they may comprise spheres
having varying indices or ~pheres coated with a reflective
material such as silver or aluminum. As an illustration,
good results may be achieved where the spheres located
in the interiorof the granules have an index of refraction
of, say, 1.5, and the exposed spheres on the surfaces of
the granules have an index of refraction of about 1.9.
A suitable pigment is added to the mixture of
resin material and glass spheres to impart reflection to the
xesin as well as color and opacity. For edge striping on a
highway, for example, a white pigment is employed such as
rutile titanium dioxide or anatase titanium dioxid~ or
example. Other pigments that may be used to produce white,
yellow or other colored mixtures include aluminum oxide,
~L26801~i
iron oxide, silicon carbide, antimony oxides, lead oxide,
lead chromates, zinc chromates, cadmium pigments, siennas,
umbers, inorganic or organic reds, chrome yellows, chrome
oranges, chrome greens, etc. The pigments can be oxtended
with suitable natural or manufactured granule ma~erials.
~ he thermosetting resins commonly are available
in liquid form. Upon being mixed with the glass spheres 27
and the pigment, the liquid is spread onto the upper surface
of a flexible rubber sheet or belt which contains a multi-
plicity of tetrahedron-shaped indentations. A suitable
doctor blade may be employed to urge the material into each
indentation. The material is then cured ~t an elevated or
room temperature, and the sheet is flexed to discharge the
individual tetrahedron granules into appropri~te collecting
equipment. Additional spheres may be applied to the surfaces
of the tetrahedrons ~s they are formed, nd one preferred
embodiment uses spheres having a refractive index of about
1.5 in the interiors of the tetrahedrons to provide rigidity
and good wear resist~nce, and surface spheres having a
refractive index of about 1.9 for high retrorefl~ctivity.
The thermoplastic resins, on the other hand, for
the most part are available commercially in powder or
pelleti~ed form. After being mixed with the gl~ss spheres 27
and the pigment, the particulate material is extruded under
heat to form a softened flat sheet which is shownib~ the
reference character 35 in ~igures 6-9. The sheet 35 includes
a multiplicity of the glass spheres 27 substantially
evenly dispersed ~herein. At ~his stage in the manufacturing
-12-
process substantially all of the spheres are imbedded within
the resin material, and the gl~ss i5 not exposed to eny great
extent on the flat opposed surfaces of the sheet.
As best shown in Figure 7, ~he thermoplastic sheet
35 is then advanced between two spray nozzles 37 and 38. The
nozzles 37 and 38 direct additional glass spheres 27 onto the
opposed flat surfaces of the sheet 35 to ~artially imbed the
additional spheres in the still tacky material.
The sheet 35 containing the glass spheres 2~ dis~ersed
therein and on its opposed flat surfaces is advanced through the
nip between ~wo rollers 40 and 41 (Figures 8 and 9). The rollers
40 and 41 are rotated at a constant speed by a suitable drive
mechanism (not shown). The lowermost of these rollers 40 contains
a multiplicity of tetrahedron-shaped indentations ~2 throughout
its cylindrical surface, and the indentations correspond in size
and configuration to the plas~ic granules 20a, 20b and 20c
illustrated in ~igures 3-5. Thus, some of ~he indentations
are of a size equal to or only slightly greater than the large
granules 20a, other indentations are of a size equal to or only
slightly greater than the medium granules 20b, and still other
indentations are of a size equal to or only slightly greater
than the small granules 20c. The indentations ~erve as molds
126~
for the individual granules, and as the sheet 35 passes between
the rollers 40 and 41 the sheet m~terial is urged under pressure
into each indentation to thereby form the granules. The glass
spheres 27 ~re substantially evenly dispersed throughout each
granule with some of the ~pheres protruding through the outer
granule surfaces.
As the thus molded granules 20 leave the nip between
the rollers 40 and 41, the roller 40 is cleaned by scraping
excess resin material from its cylindrical surface through the
use of a doctor blade 45. The excess material is discharged
into a trough 46 so that it may be recycled to form additional
granules,
Upon continued rotation of the roller 40, ~he granules
20 within the indentations 42 drop onto a suitable conveyor 50.
The conveyor 50 collects the granules 20 and transports them to
a suitable bagging machine or other packaging equipment.
The proportion of the glass spheres ~7 within and
on the surfaces of each of the granules 20 should be carefully
controlled to provide optimum reflective properties. ~or
best results ~he finished granule incorporates about 30 percent
to about 60 percent by weight of the spheres. If the weight
of the spheres exceeds ~bout 60 percent of the granule
material the structural integrity of the granules is too poor
to provide a satisfactory product, while with ~ sphere weight
below about 30 percent of the granule material th~ _
reflectivity is so low that the granules are unsuit~ble
~L~680~6
for use as a reflective marker. In ~ases in which the weight of
the spheres within each granule ~nd on its exposed s~rfaces is about
fifty percent the weight of the granule, the gr~nule exhibits
particularly good characteristics when employed for l~ne marking
and other highway striping.
The thus prepared granules 20 are applied to a
roadway or other surface through the use of conventional
delineation equipment. ~he granules Are dropped from a random
position onto the surface, and each granule comes to rest with
one of its flat faces disposed in a downward direction such
that it is imbedded in the paint. The different size granules
20a, 20b and 20c are evenly distributed on the surface, ~nd
when the paint or other film forming material is fully cured
the particles are firmly held in position to provide an
extremely effective reflective marker.
In some embodiments of the invention the reflective
granules 20 may be pre-mixed with liquid paint prior to being
applied to the surface. For highway striping, for example, the
mixture of paint and granules is applied directly to the roadway,
and a large percentage of the granules become oriented with the
faces 22 disposed in a downward direction while the viscosity of
the paint is still relatively low. As the paint dries and
hardens, the granules are maintained in place, and upon being
exposed to traffic the thin layer o pAint adjacen~~the upper
portions of the granules is worn ~ff to provide good reflectivity.
-15-
~L~68016
In order to more thoroughly disclose the nature
of the present invention, the following examples illustrating
the invention are given. It should be understood, howe~er,
that this is done solely by way of example and is intended
neither to delineate the scope of the invention nor limit
the ambit of the appended claims.
Example 1
Methyl methacrylate resin in liquid form is mixed
with a conventional white highway pigment and with glass
spheres manufactured in accordance with the teachings of
T~K. Wood V.S. Patent 2,945,326. The spheres are of soda
lime silicate glass with an index refraction of 1.5, ~nd
they range in diameter from 200 microns to 350 microns.
The spheres are substantially evenly dispersed throughout
the resin in a proportion of about 1 part by weight of
spheres to about 2 parts by weight of the resin material.
Through the use of a doctor blade, the thus
prepared mixture is spread over a flat rubber sheet which
contains a multiplicity of tetrahedron-shaped indentations
in its upper surface. The mixture i5 urged into each of the
,. _
1~680~
indentations and is cured through the application of heat to
form a multiplicity of tetrahedron-shaped granules containing
glass spheres substantially evenly dispersed throughout each
granule with some of ~he spheres protruding through the outer
faces thereof. The indentations in the sheet are of a
size such that approximately one-half of the granules
have a height of 6 millimeters and one-half have a height
of 4.5 millimeters. The granules are removed from the
indentations and placed in bags.
The bags of reflective particles produced in this
example are transported to a roadway, ~nd the particles are
dropped from a random position onto a line of moist white
traffic paint having a thickness of ~pproximately 0.75
millimeters. Each of the particles drops onto the paint
with one of the faces of the particle disposed in a downward
direction such that it is imbedded in the paint. As the
paint dries, the particles are firmly held in position on
the roadway to prcvide an extremely effective reflective
marker. After repeated exposure of the soadway to heavy
traffic, the upper portions of some of the larger reflective
particles are flattened by abrasion, but substantially all
-17-
12680~i
of the particles remain imbedded in the paint, and there is
only a very slight decrease in reflectivity even after extended
periods of use.
Example 2
Acrylonitrile butadiene styrene resin in powder form
is mixed with glass spheres produced in accordance with the
teachings of T.K. Wood et al U.S. Patent 3,279,905. A titanium
glass is used for the spheres to provide an index of refraction
of 1.9, and the diameter of the spheres ranges between about
350 microns and about 630 microns. The resin-sphere mixture
is extruded at an elevated temperature to form a thin tacky
sheet, and additional glass spheres are sprayed onto both of
the flat surfaces of the sheet to partially imbed the additional
spheres therein.
The sheet in a softened condition is then advanced
through the nip between a pair of continuously rotating
rollers of the type illustrated in Figures 8 and 9 of the
drawings. One of the rollers is provided with a multiplicity
of indentations in its cylindrical surface which are each
in the shape of an equilateral tetrahedron. As the sheet
moves between the rollers the sheet material is urged into
these indentations to form a multiplicity of tetrahedron-
shaped thermoplastic granules containing glass spheres
substantially evenly dispersed throughout each granule with
~ome of the spheres protruding through the outer ~rfaces
thereof. The indentations in the roller are of ~wo_diferent
sizes such that approximately 50 percent of ~he tetrnhedron-
shaped granules have a height of 4 millimeters and the
-18-
1~:6801~;
remaining 50 percent have a height of 6 millimeters. The
weight of spheres within each granule is equal to that of
the granule material.
~ he granules are removed from the indentations
in the roller and ~re transported to ~ highway, where they
are dropped from random positions onto a yellow line of
still tacky traffic paint along the center of the highway.
Each granule comes to rest with one of its flat faces disposed
in a downward direction and imbedded in the paint. After the
paint has dried the granules remain in position during periods
of heavy rain and after long use.
Example 3
Polypropylene recin in pelletized form is extruded at
a temperature of 180C to form a thin flat sheet. Glass spheres
having a size of between 50 and 100 mesh U.S. Standard are
sprayed onto the opposite faces of the sheet while the sheet
is maintained in a softened condition at about 120C to about
140C. The spheres are of barium titinate glass with an
index of refraction of 1.9 and are partially imbedded in the
faces of the sheet. The sheet is then advanced in a
softened condition over a roller which cont~ins a
multiplicity of tetrahedron-shaped indentations in its
~ylindrical surface to urge material from the sheet into the
indentations and thereby form a multiplicity of te~r~hedron-
shaped granules containing glass spheres. The indentations
are of equal size to simil~rly produce equal-~ize granules
having a height of 4.5 millimeters. The proportion of spheres
--19--
126~
to the polypropylene resin is about 3 parts by weight of
spheres to about 5 parts of resin.
The tetrahedron-shaped granules are transported to a
highway and dropped onto a line of tacky traffic paint in the
manner descr~bed above. Upon the hardening of the paint the
granules remain in position and exhibit good reflectivity
characteristics.
Exampla 4
In each of the foregoing examples a pigment of the
same color as that used for the highway line is admixed with
the resin material prior to the time the material is extruded.
The resulting granules have a corresponding color and provide
a further improvement in the reflectivity of the line.
Exam~le 5
A thin coating of silver is applied to the glass
spheres in the manner more fully described in British patent
2,115,396. The thus coated spheres are used to produce
plastic granules in the manner set forth in Examples 1-4, and
the granules are dropped from a random position onto the
horizontally disposed painted surface of a highway sign while
the paint is in a tacky condition. The granules remain in
place on the sign for an extended period of time and provide
an even further improvement in the overall reflectivity.
- 20 -
8~ L6
The terms and expressions which have been employed
~re used as terms of description and not of limitation, and there
is no intention in the use of such terms and expressions of
excluding any equivalents of the features shown and described
~r portions thereof, but it is recognized that various
modifications are possible within the scope of the invention
claimed.
