Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02222423 1997-11-26
WO 95'/011675 PCT/US96/07162
ENCASED RETROREFLECTIVE ELEMENTS
AND METHOD FOR MAKTNG
Field of the Invention
The present invention relates to a retroreflective element and a
process for making the same, and in particular, to a retroreflective system
suitable
for pavement marking exhibiting wet retroreflectivity.
Background of the Invention
Pavement markings such as reflective paints and tapes containing
ta~ansparent microspheres are widely used to guide motorists along the
roadways.
Very often pavement markings are retroreflective so that motor vehicle drivers
can
vividly see the markings at nighttime. Retroreflective pavement markings have
the
ability to return a substantial portion of incident light toward the source
from which
the light originated. Light from motor vehicle headlamps is returned toward
the
vehicle to illuminate road features, e.g., the boundaries of the traffic
lanes, for the
motor vehicle driver. However, when the surfaces of such pavement markings
become wet, the exposed microspheres exhibit significantly reduced
r~~troreflectivity. Typical exposed lens retroreflectors depend on an air
interface in
conjunction with a glass lens and a diffuse reflector. Water interrupts this
relationship, resulting in reduced retroreflective brightness when the article
is wet.
Attempts to achieve good retroreflectivity during wet conditions
iziclude raised, rigid pavement markers, pavement markers with embossed
profiles,
and large diameter glass beads. A raised pattern of protuberances on an upper
surface of a base sheet may be used to elevate the optical elements above any
water
or other liquids on the roadway and orient the retroreflective structure more
optimally, thereby enhancing retroreflectivity of the pavement marking under
wet
conditions, such as disclosed in U. S. Patents Nos. 5,227,221, 5,087,148,
4,969,713,
and 4,388,359.
However, these solutions typically suffer from substantial cost
limitations and may provide less than desired performance. Although large
glass
beads or,raised pavement markers can aid in draining water off of the lens,
even a
thin layer of water reduces reflectivity substantially. Additionally, these
types of
pavement markers become more wettable upon degradative exposure to sunlight
and road abrasion, so that this effect becomes more pronounced. Raised markers
used for temporary marking applications tend to scar or damage the road
surface
when removed. In some locations, raised markers are subject to damage from
snow
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CA 02222423 1997-11-26
WO 97/~1675 PCT/US96/07162
plows. Finally, raised markers do not provide adequate lane definition in
daylight
and are generally used in combination with other forms of pavement marking.
Thus, there exists a need for a low-cost retroreflective element for
use on pavement marking and other applications that provides good
retroreflectivity
during wet conditions.
~ummarv of the Invention
The present invention provides a retroreflective element that exhibits
exceptional wet retroreflectivity, and a method of manufacturing the same. The
retroreflective element comprises an assembly of a mufti-sided retroreflector
and a
clear thermoplastic resin. In one embodiment, the thermoplastic is thermally
deformed to create a convex reflective dome that substantially encases the
multi-
sided retroreflector. The dome structure improves retroreflectivity of high
incident
light rays. The mufti-sided retroreflector may be randomly or uniformly
oriented
relative to the convex dome of the retroreflective elements.
In one embodiment, a mufti-sided retroreflector is laminated between
at least two sheets of a clear plastic. The laminate is formed into
retroreflective
elements, e.g., cubes, cylinders, etc., that can provide random orientation of
the
mufti-sided retroreflector when deposited on a substrate or other surface. The
retroreflective elements may be covered with an overcoating, such as a
thermoplastic. The overcoating may create a surface that assists in
retroreflection
of high incident light rays.
The mufti-sided retroreflector may include first and second layers of
transparent microspheres positioned in optical association with opposite sides
of a
reflecting layer, such as a specular, diffuse, or pigmented reflector. In an
alternate
embodiment, the mufti-sided retroreflector may have three or more surfaces
with
retroreflective properties. Enclosed lens retroreflectors, such as embedded
lens or
encapsulated lens microsphere-based retroreflectors or prismatic
retroreflectors,
may be utilized in constructing the present retroreflective elements.
Additionally,
the reflecting layer may either be a specular reflector or a reflecting
pigment.
The present invention is also directed to a wet retroreflective
pavement marking system in which a plurality of the present retroreflective
elements
are adhered to a pavement surface by a variety of techniques. For example, a
pavement marking paint may be used as a bonding material to attach the present
retroreflective elements to a pavement surface. Glass beads may also be added
to
the pavement marking paint to provide additional dry retroreflectivity.
Alternatively, the retroreflective elements may be bonded to a pavement
marking
tape. In yet another embodiment, the present retroreflective elements may be
2
CA 02222423 2005-07-29
60557-5683
thermally laminated between two thermoplastic sheets. The assembly of
thermoplastic sheets and retroreflective element is then bonded to a suitable
substrate prior to attachment to the pavement.
The present invention is also directed to a method of preparing a
retroreflective element which includes forming an assembly of a multi-sided
retroreflector and a clear thermoplastic resin. The method of forming the
assembly
may include laminating the retroreflector between first and second sheets of
clear
thermoplastic resin. The resulting assembly is then divided into a plurality
of pieces
which may be circles, squares, hexagons, or a variety of other shapes. A
plurality of
l0 the resulting retroreflective elements may be thermally or adhesively
bonded to a
pavement surface or a pavement marking tape. Alternatively, the
retroreflective
element may be thermally bonded between an upper and a lower thermoplastic
sheet. In one embodiment, a portion of the thermoplastic resin is thermally
deformed to define a convex dome.that substantially encases the multi-sided
retroreflector.
In an alternate embodiment, the mufti-sided retroreflector.is divided
into a plurality of mufti-sided retroreflectors pieces, which are then mixed
with the
clear thermoplastic resin and extruded to form an extruded retroreflective
member.
The resulting extruded retroreflective member may be divided into a plurality
of
extruded member pieces, which are subsequently thermally deformed to form the
convex dome. If desired, the extruded member pieces may be deposited on a
substrate. The extruded retroreflective member may have a circular cross-
section
or a variety of other shapes suitable for forming the present retroreflective
elements.
The extrusion process may be used to form a retroreflective fiber suitable for
weaving into fabrics or other woven materials.
The present method also includes extruding the mufti-sided
retroreflector generally within the clear thermoplastic resin to form an
extroded
retroreflective member. The mufti-sided retroreflertor may be twisted during
the
extruding process so as to further randomize the orientation of the mufti-
sided
retroreflector within the extruded retroreflective member. The extruded
retroreflective member is then divided into a plurality of extruded member
pieces,
which are thermally deformed to define convex domes.
3
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60557-5683
According to one aspect of the present invention,
there is provided in combination: (a) an adhesive material,
and (b) a plurality of discrete rigid retroreflective
elements each comprising a multi-sided retroreflector and a
clear thermoplastic resin encasing the mufti-sided
retroreflector, the retroreflective elements adhered by the
adhesive material to a surface at random orientations with
respect to each other to provide non-directional
retroreflection.
According to another aspect of the present
invention, there is provided in combination: a) a road
surface; b) a plurality of discrete rigid retroreflective
elements each comprising a mufti-sided retroreflector and a
clear thermoplastic resin encasing the mufti-sided
retroreflector; and c) an adhesive adhering the
retroreflective elements to the road surface at random
orientations with respect to each other to provide
non-directional retroreflection.
According to a further aspect of the present
invention, there is provided a method of providing
retroreflectivity to a surface, comprising the steps of: a)
applying an adhesive to a surface; and b) applying plurality
of discrete rigid retroreflective elements to the surface at
random orientations, each element comprising a mufti-sided
retroreflector and a clear thermoplastic resin encasing the
mufti-sided retroreflector.
Definitions used in this application:
"Mufti-sided retroreflector" means a
retroreflector having retroreflective properties on two or
more sides.
3a
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60557-5683
"Clear thermoplastic resin" means for example
acrylics, polycarbonates, polyurethanes, polyolefins,
polyesters, fluoropolymers, polyvinyl
3b
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WO 97/01675 PCT/US96/07162
chloride or other clear thermoplastic materials resistant to abrasion, salt,
water, oil,
and ultraviolet light, having low color and cost, and having a heat deflection
or
softening temperature greater than the temperatures typically encountered on
roadway surfaces.
"Convex dome" means a regular or irregular shaped surface at least
a portion of which is convex.
"Enclosed-lens retroreflector" as used herein comprise a monolayer
of microspheres having a reflective layer in optical association with the rear
surfaces
thereof, sometimes spaced apart by a spacing layer, and a coves layer in which
the
front surfaces of the microspheres may be embedded.
"Embedded-lens retroreflectors" comprise a monolayer of
microspheres having a reflective layer in optical association with the rear
surface
thereof, spaced apart by a spacing layer, and a cover layer in which the front
surfaces of the microspheres are embedded.
"Encapsulated-lens retroreflectors" as used herein comprise a
monolayer of microspheres with reflective means in association with the rear
surfaces and a cover film disposed to the front surface thereof or a layer of
cube
corner elements with a cover film sealed to the rear surface thereof.
"High incident angle light rays" means light rays of approximately
greater than 80 degrees from vertical, and typically between 86 and 90
degrees,
such as may be generated by headlights on vehicles illuminating a pavement
surface
or vertical barrier parallel to the road surface, for example a Jersey barner.
"Prismatic retroreflectors" are retroreflectors having an array of
cube corner elements with either a sealed air pocket or a specular reflector
as the
reflecting means.
"Wet reflectivity" means a system that retains a substantial portion of
its dry retroreflectivity when wetted.
Brief Description of the Drawings
The invention will be further explained with reference to the
drawings, wherein:
Figure 1 is a cross-section of a portion of a first exemplary multi-
sided retroreflector;
Figure lA is a cross-section of a retroreflector having retroreflective
properties on three sides;
Figure 2 is a cross-section of a portion of a second exemplary multi-
sided retroreflector;
4
CA 02222423 1997-11-26
Figure 3 illustrates an exemplary cylindrical retroreflective
assembly with the retrorellective sheet longitudinally oriented;
Figure 4 illustrates an exemplary square retroreflective assembly;
Figure 5 illustrates an exemplary cylindrical retroreflective
assembly;
Figure 6 illustrates an exemplary die for forming a plurality of the
cylindrical retroreflective assemblies of Figure 3;
Figure 7 illustrates a conventional wire coating extrusion process
for forming an extruded retroreflective member;
Figure 8A is a perspective view of an extruded retroreflective
member;
Figure 8B illustrates an alternate cylindrical, extruded
retroreflective member having randomized mufti-sided retroreflector pieces;
Figure 9 is an alternate embodiment of the extruded retroreflective
member of Figure 8 in which the mufti-sided retroreflector is twisted during
extrusion;
Figure 10 is a cross-sectional view of a retroreflective pavement
marking system in which the retroreflective elements are encased in
thermoplastic
sheets;
Figure I 1 is a cross-sectional view of a retroreflective pavement
marking system in which the retroreflective elements are deposited in pavement
marking part; and
Figure 12 is a cross-sectional view of a retroreflective pavement
marking system in which the present retroreflective elements are attached to a
substrate.
Figure 13 is a cross-sectional view of a retroreflective pavement
marking system in which retroreflective elements are attached to a substrate.
These figures, which are idealized, are not to scale and are
intended to be merely illustrative and nonlimiting.
5
~~rin~~ ~;~tEFr
CA 02222423 1997-11-26
WO 9 i'/011675 PCT/US96/07162
Detailed Description of Illustrative Embodiments
Figure 1 illustrates an exemplary mufti-sided retroreflector 20 of
tile present invention. A first layer of transparent microspheres 22 is held
in a
fixed relationship relative to reflecting layer 26 by a transparent binder
layer 30 to
form an upper retroreflector 25. A second layer of transparent microspheres 24
is held in a fixed relationship relative to reflecting layer 28 by transparent
binder
layer 30 to form a lower retroreflector 27. Transparent space layers 32~are
interposed between the layer of microspheres 22, 24 and the reflecting layers
26,
28, respectively.
An adhesive 33 joins the upper and lower retroreflectors 25, 27 to
farm the mufti-sided retroreflector 20. It will be understood that the upper
and
the lower retroreflectors 25, 27 may alternatively be formed as a unitary
structure. In one embodiment, a transparent film 34 covers the microspheres
22,
24 to form an embedded lens retroreflector 36. In an alternate embodiment, the
mufti-sided retroreflector 20 may operate without the transparent film 34.
Figure 2 is a cross-sectional view of an alternate mufti-sided
retroreflector 20' having an upper layer of microspheres 22 and a lower layer
of
microspheres 24, each fixed in a binder layer 30. The binder layers are
joirned
back-to-back by an adhesive 33. A reflecting layer 40 is deposited on the rear
surface of the microspheres 22, 24. A transparent film 42 is applied to the
multi-
sided retroreflector 20' to create an air gap 41 and encapsulate the
microspheres
22, 24. It will be understood that the mufti-sided retroreflectors 20 and 20'
may
be; combined in a single retroreflective element. The transparent films 34, 42
are
typically between 0.025 to 0.13 mm in thickness, though it will be understood
that the thickness may vary depending upon the particular application. For
e~:ample, where the retroreflectors 20, 20' are to be formed into cubic
structures
(see Figure 4) or where the transparent films 34, 42 are to be thermally
deformed
to create retroreflective elements such as in Figures 10-12, the transparent
films
34, 42 may be 1.0 to 2.0 millimeters (mm) thick.
Figure lA is a sectional view of a mufti-sided retroreflector 20"
wiith three layers of microspheres 22 joined by an adhesive 34. The
microspheres
22 are held in a fixed relationship with the reflecting layer 26 by a
transparent
bender 30. The transparent falm 34 may optionally be attached to the outer
surface of tine microspheres 22. The three sided retroreflector 20" may be
constructed as a unitary structure or by attaching layers of microspheres to a
triangular substrate. It will be understood that the present invention is not
limited
to two or three sided retroreflectors and that more complex, mufti-sided
re~troreflector structures may be used herein.
6
CA 02222423 2005-07-29
60557-5683
Jllustrative examples of a microsphere-type and a cube-corner type
encapsulated lens retroreflector that may be used in the present invention are
disclosed in U.S. Patent No. 4,025,159 to McGrath. An
illustrative example of an embedded lens retroreflector that
S may be used in the present invention is disclosed in U.S.
Patent No. 2,407,680 to Palmquist. A variety of commercially
available retrorellectors products may be used to construct the mufti-sided
retroreflectors 20, 20', 20" of the present invention. Examples of
commercially
available enclosed lens retroreflectors with and without a transparent film
l0 covering include SCOTCI-iLITE Band reflective sheeting products Series 3750
and 4750, respectively, available from Minnesota Mining and Manufacturing
Company ("3M"), St. Paul, Minnesota. An example of a flexible, encapsulated
retroreilector includes SCO?CHLITE Brand reflective sheeting products Series
3810-l available from 3M, St. Paul, Minnesota. Examples of commercially
15 available prismatic retroreilectors include SCOTCHLITE Brand reflective ,
sheeting products Series 3990 and 39706 available from 3M, St. Paul,
Minnesota.
The microspheres 22, 24 are generally less than about Z00
micrometers in diameter and greater than about 25 micrometers in diameter.
20 Preferably, the microspheres are between approximately 60 and 90
micrometers
in diameter. The glass microspheres (also known as beads) 22, 24 are formed of
glass materials having indices of refraction of from about 1.8 to about 2.9,
and
more particularly approximately 1.9 for encapsulated retroreflectors and 2.3
for
enclosed lens retroreflectors. Illustrative examples of suitable specular
reflectors
25 for the reflecting layers 26, 28, 40 include aluminum and silver. It will
be
understood that microspheres having average diameters and indices of
refraction
outside these ranges may be used if desired.
Polyvinyl butyral, polyester, and polyurethane extended polyester
are illustrative examples of materials useful for the binder layer 30. The
30 transparent films 34, 42 and thermoplastic 52 (discussed below) may be
constructed, for example, of aliphatic urethane, ethylene copolymers such as
ethylene acrylic acid, ethylene methacrylic acid or ionically crosslinked
versions
thereof. 1t will be understood that the thermoplastic 52 may contain small
ponions of thermoset or lightly-crosslinked materials. The thermoplastic 52
35 preferably has a refractive index in the range of 1.33 to 1.6 and are at
least 70
percent transparent as measured by ASTM D1003. The thermoplastic 52 and
transparent film 34, 42 are t)Pically selected based on good adhesion
therebetween.
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WO 97/~1675 PCT/LTS96/07162
Figure 3 illustrates a cylindrical retroreflective assembly 50 in
which the mufti-sided retroreflector 20, 20', 20" is laminated in a
cylindrically
shaped clear thermoplastic 52, e.g., having a diameter of about 1 to 5 mm. The
cylindrical retroreflective assembly 50 may then be cut or broken into a
plurality
of pieces of desired dimension. The cylindrical shape of the assembly 50
allows
for random orientation of the mufti-sided retroreflector 20, 20', 20" when
deposited on a substrate (see Figure 13). In one embodiment, the assemblies 50
are deposited on a substrate and thermally deformed to create the convex
retroreflective domes of the present retroreflective elements (see Figures 10-
12).
Figures 4 and 5 illustrate cubic and cylindrical retroreflective
assemblies 60, 62, respectively, in which a mufti-sided retroreflectors 20,
20', 20"
are laminated between a clear thermoplastic 52. The thermoplastic layer resin
52
preferably has a thickness of about 0.25 to 2 mm, and typically most
preferably
about 0.6 to 1.5 mm. The cubic and cylindrical retroreflective assemblies 60,
62
1 S may be formed by stamping or cutting a sheet of retroreflective assembly
material
into a desired shape and size. In one embodiment, the retroreflective
assemblies
60, 62 are deposited on a substrate and thermally deformed to create domed
retroreflective elements 80 (see Figures 10-12).
It has been found that the square retroreflective assembly 60 may
not consistently encase the mufti-sided retroreflectors 20, 20', 20" during
the
thermal deformation process. In particular, corners of the retroreflectors 20,
20',
20" may protrude through the thermoplastic 52, creating points of weakness or
peel points that may compromise the retroreflective elements. The cylindrical
retroreflective assembly 62 provides a more uniform distribution of the
thermoplastic 52 during thermal deformation. However, cutting the cylindrical
retroreflective assemblies 62 from a sheet of retroreflective assembly
material
generates a greater quantity of scrap material. A hexagonal shaped
retroreflective
assembly represents a compromise between consistent encapsulation of the multi-
sided retroreflector 20, 20', 20" and minimum quantity of scrap material.
Figure 6 illustrates an exemplary thermal forming roll 51 having an
upper roll 53 and a lower roll 55 for simultaneously forming multiple
cylindrical
retroreflective assemblies 50 (see Figure 3) containing retroreflectors 20,
20', 20".
Sheets of the thermoplastic 52 are thermally deformed by the rolls 53, 55 to
produce a plurality of the retroreflective assemblies 50. As will be discussed
in
detail below, the plurality of cylindrical retroreflective assemblies 50 are
separated and subsequently divided or cut into a plurality of pieces. These
piece
may be deposited on a substrate (see Figure 13) or thermally deformed to
create
the present retroreflective elements (see Figures 10-12).
8
CA 02222423 1997-11-26
WO 97JO1L675 PCT/US96/07162
Figure 7 is a sectional view of an exemplary wire extrusion system
70, in which a filament 72 may be embedded in the thermoplastic 52 to assist
in
the formation of an extruded retroreflective member 74. In some applications,
tine mufti-sided retroreflector 20, 20', 20" may have suffcient tensile
strength to
a.~sist in forming the extruded retroreflective member 74 without the filament
72.
Figure 8A illustrates the cylindrically enclosed extruded retroreflective
member
74, manufactured using the wire extrusion system 70 of Figure 7. It will be
understood that coating of the filament 72 with the thermoplastic 52 may be
accomplished by either high solids liquid coating or conventional wire coating
thermoplastic extrusion. Additionally, the cross section of the extruded
re:troreflective member 74 may be a variety of shapes, such as square,
triangular,
hE;xagon, etc.
Figure 8B is an alternate embodiment in which the mufti-sided
retroreflectors 20, 20', 20" are broken into a plurality of pieces and
randomly
dispersed into the thermoplastic 52 prior to extrusion of the extruded
retroreflective member 74'. Figure 9 is an alternate embodiment of a
cylindrically
enclosed retroreflector element 74" in which the mufti-sided retroreflector
20, 20',
20" is twisted during the extrusion process. As with the retroreflective
assemblies 50, 60, 62 of Figures 3, 4, and 5, the extruded retroreflective
members
74, 74', 74" preferably are cut or broken into a plurality of pieces as
desired prior
to the thermal deformation process.
In one illustrative embodiment, the extruded retroreflective
members 74, 74', 74" are formed into fine strands having a diameter of
approximately 1 to 5 mm. A flexible or semi-rigid thermoplastic 52 such as
polyester, nylon or vinyl provides the members 74, 74', 74" with sufficient
flexibility to be woven into a fabric, so as to give the fabric
retroreflective
properties.
Figure 10 is a sectional view of a pavement marking system 78
having a plurality of retroreflective elements 80. The layer of thermoplastic
84 is
extrusion coated to a substrate 86 and may contain pigments and other
additives
as desired. auitable substrates include metal foil, or plastics or rubbers
having
low elasticity and high permanent deformation properties. The retroreflective
assemblies 50, 60, 62 and/or extruded retroreflective members 74, 74', 74" are
then deposited on the thermoplastic layer 84 and thermally deformed to create
the
ret~roreflective elements 80. Glass beads 94 may optionally be deposited on
the
thermoplastic layer 84. An overcoat of a transparent thermoplastic 82 may also
be applied to the system 78 in which case glass beads 94 should have an index
of
refraction of about 2.1 or more. The substrate 86 is bonded to a road.pavement
9
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WO 97/01675 PCT/US96/07162
surface 88 by a suitable adhesive 87. A variety of embodiments of substrate 86
and adhesive 87 as are well known in the art may be used in the present
invention.
The thermoplastic sheets 82, 84 are preferably constructed from a
thermoplastics
resin that has good bonding properties with the thermoplastic 52 of the
retroreflective elements 80. The retroreflective elements 80 generally extend
above any water present on the pavement 88 so that high incident light rays
may
be captured by the convex retroreflective domes 90 surrounding the mufti-sided
retroreflectors 20, 20', 20". Water that coats the retroreflective elements 80
does
not inhibit retroreflectivity.
Figure 11 illustrates an alternate pavement marking system 95 in
which the thermally deformed retroreflective elements 80, 80' are deposited
into a
pavement marking paint 92. The convex retroreflective domes 90 of the
retroreflective elements 80 are generally oriented upward due to their shape.
However, it will be understood that random dispersion of the elements 80 may
result in some of the retroreffective elements 80 being oriented upside down
although the spherical retroreflective elements 80' are orientation
independent.
Glass beads 94 may also be deposited in the pavement marking paint 92, as is
conventionally done in the art:
Figure 12 is a sectional view of an alternate pavement marking
system 100, in which the retroreflective elements 80 are bonded to a substrate
102, such as the thermoplastic sheets discussed above. The retroreflective
elements may be thermally bonded directly to the substrate 102 or attached via
a
suitable adhesive. The substrate 102 is then attached to a second substrate
86,
such as metal foil, which is attached to the pavement 88 by an adhesive 87.
Figure 12 also illustrates the operation of present retroreflective
elements 80 with high incident angle light rays A-C. Light ray B strikes the
retroreflective element 80 substantially normal or perpendicular to the
surface
thereof. Consequently, the light may pass through the element 80 without
refracting or striking the mufti-sided retroreflector 20, 20', 20" depending
upon
the orientation and position of the mufti-sided retroreflector. Light ray A
strikes
the surface of the element 80 at a shallow angle and is deflected with very
little
refraction. Light ray C enters the element 80, is refracted toward the mufti-
sided
retroreflector 20, 20', 20" and is reflected back to its source. The area
between
the light rays A and B is the effective aperture of the element 80. The
effective
3 5 aperture will depend upon the shape of the dome 90 and the orientation of
the
mufti-sided retroreflectors 20, 20', 20".
Figure 13 is an alternate embodiment in which the cubic
retroreffective assemblies 60 of Figure 4 and the cylindrical retroreffective
CA 02222423 1997-11-26
WO 97/01675 PCT/US96/07162
assemblies 50 of Figure 3 are attached to a substrate 102 by an adhesive 87.
The
cubic and cylindrical shape of the retroreflective assemblies S0, 60 permit
random
orientation of the mufti-sided retroreflectors 20, 20', 20". A clear
overcoating
104, such as a thermoplastic, may be applied to protect the assemblies 50, .60
and
to enhance retroreflectivity. However; it will be understood that the
cylindrical
retroreflective assemblies 62, as well as other shapes, may be suitable for
this
purpose.
The method of the present invention includes generally encasing
tlhe mufti-sided retroreflector 20, 20', 20" in the clear thermoplastic 52 by
a
variety of techniques (see Figures 3-9). In one embodiment, the mufti-sided
r~etroreflector 20, 20', 20" is laminated between sheets of clear
thermoplastic 52
(see Figures 3-6). The resulting assemblies 50, 60, 62 are then cut or divided
into
a plurality of pieces, such as cylinders, circles, squares, hexagons, or a
variety of
other shapes.
Alternatively, the mufti-sided retroreflector 20, 20', 20" may be
extruded in a clear thermoplastic 52 to form an extruded retroreflective
member
74, 74', 74" (see Figures 7-9). The resulting extruded retroreflective member
74,
74', 74" may be divided into a plurality of extruded member pieces. In an
alternative embodiment, the extruded retroreflective members 74, 74', ~74"
forms
a fiber or filament that may be woven into fabrics or other woven materials.
The assemblies 50, 60, 62 and extruded members 74, 74', 74" may
b~e deposited on substrate (such as a pavement marking tape) or directly to
the
pavement surface and optionally covered with a suitable overcoating.
Alternatively, assemblies 50, 60, 62 and extruded members 74, 74', 74" may be
deposited on a substrate and thermally deformed to define the convex domes 90
of Figures 10-12.
The invention will be further explained by the following illustrative
examples.
Eaamnle 1
A 0.38 mm (0.015 inch) thick sheet of polyethylene acrylic acid
resin sold under the tradename PRI1VIACORTM 5980 (available from E.I, duPont
de Nemours and Company of Wilmington, Delaware) was extruded onto a
0.061mm (0.0024 inches) thick polyethylene terephthalate carrier web (herein
called PET) using common thermoplastic extrusion coating techniques. To make
a thicker sheeting, three layers of the PRIMACORTM were laminated together
using a heated roller at about 121 oC (250oF) (although a thicker layer could
have been extruded initially if desired). A SCOTCHLITE Brand reflective
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sheeting product series 3750 (available from 3M Company, St. Paul, Minnesota)
was primed with MORTON ADCOTE SOT4983 (available from Morton
Chemical Co.), using common gravure coating and drying techniques, with the
ADCOTE solution thinned with 10% Isopropanol to facilitate wetting of the
S 3750. Then the laminated PRIMACOR'~'M 5980 sheeting was hot laminated to
the series 3750 reflective sheeting again using common hot laminating
techniques ,
of a heated roller and a rubber pressure roller. Lamination was done at 138oC
(280oF) and 6.1 meters/min. (20 FPM). After the assembly sheeting was
removed from the heated roller, the web was quickly cooled by passing the hot
assembly sheeting around a series of cold rollers before winding the sheet
into a
roll. Two sheets of the assembly sheet (PRIMACORTM 5980 laminated to series
3750 reflective sheeting) were laminated together at room temperature to form
the mufti-sided retroreflector of Figure 1 by removing the release liner from
the
series 3750 reflective sheeting to expose the pressure sensitive adhesive and
1 S passing the sheets past a rubber pressure roller.
The resulting mufti-sided retroreflector was cut into approximately
2.54 mm (1/10") squares to form a nearly cubic element as shown in Figure 4.
The squares were deposited on a white pigmented polyethylene methacryIic acid
film (20 weight percent TI02 sold under the tradename NUCRELTM 699 also
available from duPont) that was extruded about 0.11 mm (4. S mil) thick onto
0.076 mm (3 mil) thick aluminum foil. The film/foil laminate was preheated to
149oC (300° F) before distributing the enclosed sheeting elements. The
assembly
was placed in a 204oC (400°F) oven for approximately one minute,
allowing the
heat to partially melt, and thus shape the PRIIviACORTM resin to form the
2S circular domes generally illustrated in Figures 10-12. Under these
conditions the
mufti-sided retroreflectors were generally encased in the clear PRIMACORTM
5980 resin, although some of the corners of the mufti-sided retroreflectors
did
protrude out from the resin. Approximately 1.14 mm (0.045 inches) of clear
resin was used on each side of the retroreflector in the example.
Example 2
Retroreflective elements as defined in Example 1 were formed,
except that the resulting enclosed sheeting elements were cut into circular
pieces ~
as illustrated in Figure S. The cylindrical configuration was observed to
minimize
3S the chance for the mufti-sided retroreflector 20, 20', 20°' to
protrude through the
clear thermoplastic resin following thermal deformation, and thereby possibly
cause peel points.
12
CA 02222423 1997-11-26
WO 9'7/01675 PCT/US96/07162
1!:zamnle ~
Small pieces of the mufti-sided retroreflector of Example 1 were
added to a molten mix of clear thermoplastic and the mixture was extruded into
strands as illustrated in Figures 8A, 8B, and 9. The strands were later cut
into
small cylindrical pellets and heated to form the convex retroreflective domes
illlustrated in Figure 10-12.
It will be understood that the exemplary embodiments in no way
liimit the scope of the invention. Other modifications of the invention will
be
apparent to those skilled in the art in view of the foregoing descriptions.
'These
descriptions are intended to provide specific examples of embodiments which
clearly disclose the invention. Accordingly, the invention is not limited to
the
described embodiments or ~to the use of specific elements, dimensions,
materials
o~r configurations contained therein. All alternative modifications and
variations
o~f the present invention which fall within the spirit and broad scope of the
appended claims are covered.
13
