U.S. patent application number 10/039957 was filed with the patent office on 2003-07-03 for matrix element pavement marker and method of making same.
Invention is credited to Borden, Thomas R., Khieu, Sithya S., Tolliver, Howard R..
Application Number | 20030123931 10/039957 |
Document ID | / |
Family ID | 21908291 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030123931 |
Kind Code |
A1 |
Khieu, Sithya S. ; et
al. |
July 3, 2003 |
Matrix element pavement marker and method of making same
Abstract
A method of making a pavement marker including the steps of
forming an array of pavement elements in a predefined pattern
interconnected by a carrier web. A frangible connection is formed
between a plurality of the pavement elements and the carrier web.
After the array of pavement elements is applied to the pavement
surface using an adhesive, a portion of the carrier web surrounding
the pavement elements is removed or allowed to substantially
deteriorate and dissipate, leaving an array of discrete pavement
elements.
Inventors: |
Khieu, Sithya S.; (Eden
Prairie, MN) ; Tolliver, Howard R.; (Woodbury,
MN) ; Borden, Thomas R.; (Oakdale, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
21908291 |
Appl. No.: |
10/039957 |
Filed: |
December 31, 2001 |
Current U.S.
Class: |
404/12 |
Current CPC
Class: |
E01F 9/512 20160201 |
Class at
Publication: |
404/12 |
International
Class: |
E01F 009/06; E01F
009/08 |
Claims
What is claimed is:
1. A method of making a pavement marker comprising the steps of:
forming an array of discrete pavement elements in a predefined
pattern interconnected by a carrier web; and forming a frangible
connection between a plurality of the discrete pavement elements
and the carrier web.
2. The method of claim 1 wherein the step of forming the pavement
elements interconnected by a carrier web comprises the step of
integrally forming the pavement elements and the carrier web.
3. The method of claim 1 wherein the step of forming the pavement
elements interconnected by a carrier web comprises the step of
bonding the pavement elements to the carrier web.
4. The method of claim 1 wherein the step of forming the pavement
elements interconnected by a carrier web comprises the steps of
bonding the carrier web to an upper surface of the array of
pavement elements.
5. The method of claim 1 further comprising the steps of: applying
a pressure sensitive adhesive to a rear surface of the pavement
elements; and applying a release liner over the adhesive.
6. The method of claim 1 wherein the step of forming a frangible
connection comprises the step of at least partially severing the
carrier web around a perimeter of the pavement elements.
7. The method of claim 1 wherein the step of forming a frangible
connection comprises the step of at least partially severing the
carrier web around one or more groups of pavement elements.
8. The method of claim 1 wherein the carrier web is selected from a
group consisting of paper, a liner, a screen, a mat, a film or
nonwoven web of a water-soluble or water-dispersible polymeric
material, and a biodegradable material.
9. The process of claim 1 wherein the pavement elements are
selected from a group consisting of retroreflective lens and single
bead durable pavement elements.
10. A method for applying the array of pavement elements of claim 1
to a pavement surface comprising the steps of: interposing an
adhesive between the pavement elements and the pavement surface;
and engaging the adhesive to the pavement surface under
pressure.
11. The method of claim 10 further comprising the step of removing
a portion of the carrier web between adjacent pavement elements to
yield an array of discrete pavement elements adhered to a pavement
surface.
12. A pavement marking article attachable to a pavement comprising:
an array of discrete pavement elements in a predefined pattern
interconnected by a carrier web; and a frangible connection between
a plurality of the pavement elements and the carrier web.
13. The article of claim 12 wherein the carrier web and the
pavement elements are integrally formed.
14. The article of claim 12 wherein the pavement elements are
bonded to the carrier web.
15. The article of claim 12 wherein the carrier web is bonded to
upper surfaces of the pavement elements.
16. The article of claim 12 further comprising a pressure sensitive
adhesive applied to a rear surface of the pavement elements, and a
release liner extending over the adhesive.
17. The article of claim 12 wherein the frangible connection
comprises slits around a perimeter of the pavement elements.
18. The article of claim 12 wherein the carrier web is selected
from a group consisting of paper, a liner, a screen, a mat, a film
or nonwoven web of a water-soluble or water-dispersible polymeric
material, and a biodegradable material.
19. The article of claim 12 further comprising an adhesive
interposed between the pavement elements and the pavement
surface.
20. A pavement marker comprising: discrete pavement elements having
a pressure sensitive adhesive layer on a bottom surface, the bottom
surfaces being arranged in an array on a release liner; and a
carrier web bonded to an upper portion of the pavement elements
capable of maintaining the spatial orientation of the array of
pavement elements when the release liner is removed.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to a pavement marker
having an array of discrete pavement elements and a method for
making the same, and more particularly, to an array of pavement
elements arranged in a predefined pattern on a frangible and/or
biodegradable carrier web.
BACKGROUND OF THE INVENTION
[0002] Pavement marking sheet material that is economical to
produce and performs well in both daylight and night conditions is
a continuing goal of the pavement marking industry. Night
performance is primarily provided by retroreflection, which may be
defined as a phenomenon in which a large portion of incident light
is returned in substantially the direction from which it
originates. Spherical lens elements, typically tiny glass beads or
microspheres in conjunction with reflective pigments, are well
known for this purpose.
[0003] Flat single layer polymeric sheet material, as well as flat
laminated materials, are known to hold retroreflective elements in
position. The sheet material may be applied to a roadway surface
and serves to both cushion and hold the retroreflective elements.
The efficiency of flat pavement marking materials, however, is
limited for two reasons. First, the array of retroreflective
elements is directed upward, whereas the optimal orientation would
be toward the vehicle headlights, which typically illuminate with
retroreflective beads at an angle slightly above the road surface.
Second, in an upwardly directed fashion, the exposed surfaces of
the retroreflective elements are exposed to maximum abrasive wear
by vehicle tires, thus allowing for the rapid destruction of the
exposed surfaces.
[0004] An alternative approach is to provide a raised pattern of
retroreflective elements on a pavement marking strip. The raised
pattern encourages the run-off of rainwater. Additionally, the
raised pattern provides non-horizontal surfaces for supporting
retroreflective elements. The non-horizontal surfaces tend to
isolate and protect the optical surfaces from abrasive wear by
traffic and provide a more efficient orientation for
retroreflection.
[0005] Pavement marking tapes with retroreflective elements are
disclosed in U.S. Pat. Nos. 5,227,221, 4,988,555, and 4,988,541
(Hedblom). The preformed pavement marking tapes of Hedblom include
a resilient polymeric backing sheet having a plurality of
protrusions. A discontinuous layer of a liquid bead bond is applied
to selected surfaces of the protrusions to retain microspheres at
those locations. The relatively thick backing sheet adds cost to
the pavement marking tape. Additionally, the resiliency of the
backing sheet occasionally limits conformability to rough pavement
surfaces.
[0006] U.S. Pat. No. 4,792,259 (Eigenmann) discloses a method and
apparatus for individually depositing discrete retroreflective
markers onto a road surface. A backing sheet is pulled around a
sharp angle so that the individual retroreflective markers are
sequentially released and deposited onto the roadway surface. The
feed rate of the backing sheet must be closely synchronized with
the movement of the vehicle depositing the retroreflective markers
in order to maintain the proper spacing between the markers. It is
also possible for the individual retroreflective markers to be
overturned or displaced during tamping.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention is directed to a pavement marker
having an array of discrete pavement elements interconnected by a
removable or frangible carrier web that is conformable and that
minimizes unnecessary materials, improves tamping efficiency and
isolates adjacent pavement elements. Various methods of making the
array of pavement elements are also disclosed. The present
invention is also directed to a method of applying the present
array of pavement elements onto a pavement surface.
[0008] The present array of discrete pavement elements uses less
material than conventional pavement marking tapes because the
conformance layer between the raised discrete pavement elements is
substantially eliminated. The tamping efficiency is also improved
by isolating the tamping force on the pavement elements. In
particular, the discrete pavement elements act as force-guides that
direct the tamping forces to create an enhanced bond of marker
material to the pavement surface. Once applied to the pavement, the
array of discrete, pavement elements are not substantially
interconnected, so that the delamination of a single pavement
element does not adversely effect adjacent pavement elements.
[0009] In one embodiment, the method of making the pavement marker
includes forming an array of pavement elements arranged in a
predefined pattern interconnected by a carrier web. A frangible
connection is formed between a plurality of the pavement elements
and the carrier web. In one embodiment, a pressure sensitive
adhesive is applied to rear surfaces of the pavement elements. A
release liner is applied over the adhesive. A frangible connection
is formed between a plurality of the pavement elements and the
carrier web, preferably without cutting through the release liner.
After the array of pavement elements is applied to the pavement
surface, the portion of the carrier web surrounding the pavement
elements is removed, leaving an array of discrete, raised
retroreflective pavement elements.
[0010] The pavement elements may be integrally formed with the
carrier web as a unitary structure. Alternatively, the pavement
elements may be bonded to the carrier web. The step of forming the
frangible connection between the pavement elements and the carrier
web can comprise partially severing the carrier web around a single
pavement element or around groups of the pavement elements.
[0011] The present method may be used with various types of
pavement markers such as retroreflective lenses, raised ridges with
glass microspheres, retroreflective pavement elements, or single
glass bead devices.
[0012] The carrier web may be a material that is frangible,
biodegradable, and/or capable of deteriorating quickly from
abrasion and impact from roadway traffic, such as paper, a liner,
an open scrim, a screen, a mat, or a film or nonwoven web of a
water-soluble or water-dispersible polymeric material. The carrier
web is conformable, typically preferably extensible.
[0013] In an alternate embodiment, the pavement elements are formed
in a predefined pattern on a carrier web. The carrier web has
frangible portions between adjacent pavement elements that is
preferably capable of substantially deteriorating when exposed to
roadway conditions for a short time. In one embodiment, a pressure
sensitive adhesive is applied to the rear surfaces of the pavement
elements and a release liner is applied over the adhesive. The
carrier web serves to maintain the array of pavement elements in a
predetermined configuration until they are applied to a pavement
surface. The carrier web subsequently deteriorates, leaving an
array of discrete pavement elements spaced in substantially the
same configuration as on the carrier web.
[0014] In another embodiment, a carrier web is bonded to upper
portions of an array of pavement elements. The carrier web being
capable of maintaining the spatial orientation of the array of
pavement elements during bonding of bottom surfaces of the pavement
elements to a pavement surface.
[0015] In another embodiment, the pavement elements have a pressure
sensitive adhesive on their bottom surfaces. The adhesive-coated
bottom surfaces of the pavement elements are arranged in an array
on a release liner. A carrier web is bonded to upper portions of
the pavement elements to maintain the spatial orientation of the
array when the release liner is removed. The carrier web may also
be biodegradable, frangible and/or water soluble.
[0016] The present invention is also directed to a method of
applying an array of pavement elements to a pavement surface. An
adhesive, such as a pressure sensitive adhesive, is interposed
between the pavement elements and the pavement surface. The portion
of the carrier web surrounding the pavement elements is removed
from the array. In another embodiment, the array of pavement
elements are formed in a predetermined pattern on a conformable
carrier web.
[0017] In another embodiment, the release liner is removed from the
array of pavement elements. The pressure sensitive adhesive is
engaged with the pavement surface under pressure. The portion of
the carrier web surrounding the pavement elements is removed from
the array.
[0018] The present invention is also directed to a pavement marking
article. An array of pavement elements in a predefined pattern is
interconnected by a carrier web. A frangible connection is located
between a plurality of the pavement elements and the carrier
web.
[0019] In another embodiment, a pressure sensitive adhesive is
located on the rear surfaces of the pavement elements. A release
liner extends over the adhesive. A plurality of slits are provided
for at least partially severing the pavement elements from the
carrier web without cutting through the release liner. The adhesive
may either be pattern coated on the rear surfaces of the pavement
elements or applied to substantially the entire rear surfaces of
the pavement elements and the carrier web.
[0020] As used herein,
[0021] "Conformable" refers to a carrier web that exhibits a low
unload energy of less than 125 grams/centimeter (0.7 pounds/inch)
and an inelastic deformation of greater than about 10%, preferably
greater than 20%, more preferably not less than 30% at 25.degree.
C.
[0022] "Frangible connection" refers to a connection between the
carrier web and pavement elements (or in some embodiments a segment
of the carrier web between a minor portion of the carrier web
attached to a single pavement element and the remaining portion of
the carrier web) that is easily broken or breakable after
application of the pavement elements to the road.
[0023] "Frangible portion" refers to a portion of the carrier web
that is easily broken or breakable, e.g., that is biodegradable,
water-soluble, or otherwise capable of substantially
deteriorating.
[0024] "Substantially deteriorating" refers to degradation and
dissipation of the carrier web when exposed to a variety of
environmental factors, such as abrasion, rain, ultraviolet
radiation, and impact from roadway traffic, such that the carrier
web cannot transfer energy sufficient to remove or delaminate a
pavement element.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0025] FIG. 1 is a cross-sectional view of an illustrative array of
pavement elements according to the present invention.
[0026] FIG. 2 is a cross-sectional view of the array of pavement
elements of FIG. 1 being applied to a pavement surface.
[0027] FIG. 3 is a cross-sectional view of an alternate
illustrative array of pavement elements according to the present
invention.
[0028] FIG. 4 is a cross-sectional view of the array of pavement
elements of FIG. 3 being applied to a pavement surface.
[0029] FIG. 5 is a cross-sectional view of an alternate
illustrative array of pavement elements according to the present
invention.
[0030] FIG. 6 is a cross-sectional view of an alternate
illustrative array of pavement elements having a top-mounted
carrier web according to the present invention.
[0031] FIG. 7 is a cross-sectional view of the array of pavement
elements of FIG. 6 being applied to a pavement surface.
[0032] FIG. 8 is a schematic illustration of an exemplary process
for making raise pavement elements according to the present
invention.
[0033] FIG. 9 is a schematic illustration of an alternate
illustrative process for making pavement elements according to the
present invention.
[0034] FIG. 10 is a schematic illustration of an illustrative
pavement marker according to the present invention.
[0035] These figures, which are idealized, are not to scale and are
intended to be non-limiting.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE
INVENTION
[0036] FIG. 1 is a side sectional view of a pavement marker having
an array 20 of pavement elements according to a first embodiment of
the present invention. The array 20 includes a plurality of
protrusions 24 and an integrally formed carrier web 22. In the
illustrated embodiment, the protrusions 24 have side surfaces to
which are bonded a plurality of retroreflective beads 36 using a
binder that typically contains pigment flakes 32. The carrier web
may be a polymeric film, paper, liner, screen, mat, nonwoven web,
or open scrim that is removable, frangible, biodegradable, and/or
capable of deteriorating quickly from abrasion and impact from
roadway traffic.
[0037] An adhesive 34 is preferably pattern coated to bottom
surfaces 36 of the protrusions 24 without being applied to the
interstitial portions of web 22. The adhesive 34 may alternatively
be coated across the entire surface of the carrier web 22 and the
protrusions 24. A release liner 38 optionally extends across the
adhesive 34 until the array 20 is ready for use. Adhesives known to
be suitable for adhering articles to pavement surfaces include
pressure sensitive adhesives, hot melt adhesives, hot melt pressure
sensitive adhesives, contact bond cement, thermoset adhesives and
two-part epoxy adhesives. Some of these alternate adhesives are
preferably interposed between the pavement elements and pavement
surface (not shown) or are applied to the pavement surface before
bonding, rather than being coated on the array of pavement
elements.
[0038] A frangible connection 40 is formed around the perimeter of
the protrusions 24, typically by die cutting, so that the carrier
web 22 can be removed. The frangible connection 40 preferably has
sufficient strength to releasably connect the protrusions 24 and
carrier web 22 until the array 20 is applied to a pavement surface
42 (see FIG. 2). The frangible connection 40 does not necessarily
need to be around the immediate perimeter of the protrusions 24,
but may be formed some distance from the perimeter of the
protrusion 24. Forming the frangible connection 40 around a
plurality of the protrusions or pavement elements refers to forming
it generally around the perimeter of two or more discrete
protrusions 24, or around groups of protrusions. Top surfaces 26 of
the protrusions 24 may optionally include non-slip particles 30.
The non-slip particles 30 are embedded in the protrusion 24. The
non-slip particles 30 may be attached to the top surface 26 of the
protrusion 24 by binder 32.
[0039] FIG. 2 is a side sectional view of the array 20 of FIG. 1
being applied to a pavement surface 42. The release liner 38 is
removed and the array 20 is tamped to the pavement surface 42. The
protrusions 24 act as force-guides to focus the tamping forces
directly to the interface between the adhesive 34 and the pavement
surface 42. In an embodiment where the adhesive 34 is coated across
the entire surface of the carrier web 22, the protrusions 24
minimize the tamping force applied to the carrier web 22.
[0040] The carrier web 22 that surrounds the pavement elements 44
is then removed or peeled-back from the array 20 by breaking the
frangible connection 40. The adhesive 34 provides an adhesive force
between the protrusions 24 and the pavement surface 42 greater than
the breaking force of the frangible connection 40. The resulting
array of discrete, pavement elements 44 is arranged on the pavement
surface 42 in substantially the same configuration maintained by
the carrier web 22 in the array 20. The discrete pavement elements
44 are not interconnected, so that the delamination of a single
pavement element does not typically adversely affect adjacent
pavement elements.
[0041] FIG. 3 is a side sectional view of an alternate pavement
marker having an array 50 of pavement elements 52 bonded to a
carrier web 54 by any of a variety of suitable methods. An adhesive
56 is applied to the entire lower surface 57 of the carrier web 54
or underneath the pavement elements 52. A release liner 58 is
optionally applied to the adhesive until the array 50 is ready for
use.
[0042] FIG. 4 is a side sectional view of the array 50 of FIG. 3
applied to a pavement surface 42. The release liner 58 is removed
and the array 50 is tamped to the pavement surface 42. The carrier
web 54 defines frangible portions 60 between adjacent pavement
elements 52. The frangible portions 60 are preferably capable of
substantially deteriorating from the impact of roadway traffic. As
illustrated in FIG. 4, the frangible portions 60 progressively
deteriorates, leaving an array of discrete, pavement elements 52
having substantially the same pattern as on the carrier web 54
prior to application to the pavement surface 42. In an alternate
embodiment, a series of slits 62 may optionally be formed around
the perimeter of the pavement elements 52, as discussed above. The
portions of the carrier web 54 surrounding the pavement elements
may be peeled-back or otherwise removed, such as shown in FIG.
2.
[0043] FIG. 5 is an alternate pavement marker having an array 70 of
pavement elements 72, 74 arranged on a carrier web 76. Pavement
element 72 comprises a single bead 78 attached to a housing 80.
Pavement elements 74 comprise an embedded cube corner
retroreflective lens 82 bonded to the carrier web 76, e.g., by an
adhesive 84. The carrier web 76 is coated with an adhesive 86 and
optionally covered by a release liner 88 substantially as shown in
FIG. 3. The frangible portions 90 between the adjacent pavement
elements 72, 74 may either be allowed to deteriorate from the
impact of roadway traffic or can be severed around the perimeter 92
of the pavement elements 72, 74 for removal, as discussed in
connection with FIG. 2. In the embodiment of FIG. 5, the carrier
web 76 is preferably not biodegradable.
[0044] FIG. 6 is a side sectional view of an alternate array 100 of
pavement elements 102 having an adhesive 104 on a bottom surface
106. The bottom surfaces 106 are arranged in an array on a release
liner 108. A carrier web 110 is bonded to portions of the pavement
elements 102, preferably by an adhesive, to maintain the spatial
orientation of the array 100 when the release liner 108 is removed.
In one embodiment, the adhesive used to bond the carrier web 110 to
the pavement elements 102 has a lower peel strength than does
adhesive 104 to the substrate (not shown). In another embodiment,
the carrier web 110 is a biodegradable material, such as paper, or
a water soluble or water dispersible polymeric film or nonwoven
web.
[0045] FIG. 7 is a side sectional view of the array 100 of FIG. 6
bonded to a pavement surface 42. The release liner 108 has been
removed and the array 100 has been tamped to the roadway surface
42. The carrier web 110 may then be removed, leaving an array of
pavement elements 102 on the pavement surface. Alternatively, the
carrier web 110 may be allowed to substantially deteriorate in
place.
[0046] FIG. 8 is a schematic illustration of one embodiment of an
extrusion and embossing method 130 for manufacturing a pavement
marker having an array of pavement elements 132 according to the
present invention. The expression pavement elements refers to both
finished pavement elements or protrusions that can be subsequently
processed to form a pavement element, such as by application of
reflective material. The elastomeric precursor sheeting 134 is
embossed by an embossing roll 136 prior to vulcanization to form
protrusions 144 of specified shapes and dimensions connected by a
portion of the elastomeric sheeting 134 forming a base sheet 145.
An adhesive 138 is applied by a coating roll 140. A liner 142 is
applied to the layer of adhesive 138. Alternatively, the adhesive
138 and liner 142 can be simultaneously laminated to the rear
surface of the embossed sheeting. The protrusions 144 formed on the
embossed sheeting are then subjected to die cutting 146 to form a
frangible connection 148 between the base sheet 145 and the
protrusions 144. The pavement elements 132 can be applied to a
pavement surface generally as illustrated in FIGS. 1 and 2.
[0047] Exemplary materials for forming the precursor sheeting 134
include acrylonitrite-butadiene polymers, millable urethane
polymers, and neoprenes. Extended resins, inorganic fillers, such
as silica, and reinforcements may also be included. Pigment such as
titanium dioxide are preferred in the base sheet to provide a white
diffuse surface to uncoated portions of the base sheet 142 in the
protrusions 138. Lead-free yellow pigments are may also be used.
The present array of pavement elements may be made using a variety
of techniques, such as disclosed in U.S. Pat. Nos. 4,388,359,
4,086,388, and 4,988,541.
[0048] FIG. 9 is a schematic illustration of a cast and cure method
for making a pavement marker in accordance with the present
invention. A polymeric material is extruded through a nozzle 150
from a screw-type extruder 152 to form a bank or tip of molten
material 154 at an orifice between a steel forming drum 156 and a
doctor drum 158. The circumferential surface of the drum 156
includes a series of cavities 160 which are the negative of the
desired protrusions 162. The molten material 154 fills the cavities
160 and is solidified to form a series of protrusions 162 on an
elastomeric web 168. The extruder 152 preferably meters the
quantity of polymeric material. Alternatively, a skiving tool such
as a roller or a doctor blade can be used to scrape excess
polymeric material from the roller 156 before the assembly 166 is
brought into engagement with the roller 156. The polymeric material
is typically a thermoset polymer. The polymeric material may also
include inorganic fillers and reinforcements, such as glass beads,
ceramic particles, micro-particles of glass or ceramic, and/or
glass fiber strands.
[0049] Also entering the nip between the drums 156, 158 is an
assembly 166 including a carrier web 168, an adhesive 170, and a
release liner 172. Upon being drawn into the nip containing the
molten material 154, the carrier web 168 fuses and becomes
inseparably united with the protrusions 162. The forming drum 156
may optionally be heated to facilitate curing of thermoset
materials or cooled to facilitate curing thermoplastic
materials.
[0050] The array 174 of protrusions 162 is then subjected to die
cutting 176 which at least partially severs the web 168 around the
perimeter of the protrusions 162. In one embodiment, the die
cutting step 176 cuts through the carrier web 168, but not through
the adhesive 170 or the liner 172. The pavement elements may be
subject to additional processing, such as the application of
reflective material, either before or after the die cutting
step.
[0051] In an alternate embodiment, the gap defined by the nip
between the drums 156, 158 is increased so that the thin web of the
thermoplastic elastomer composition is formed on the web 168
between the protrusions 162, such as is illustrated in FIGS. 1 and
2. The subsequent die cutting step 176 preferably severs the thin
web and carrier web 168 around the perimeter of the protrusions
162. Alternate methods of forming structured protrusions onto a
carrier web are disclosed in U.S. Pat. Nos. 5,152,917 (Pieper et
al.); U.S. Pat. No. 5,435,816 (Spurgeon et al.); and U.S. Pat. No.
5,500,273 (Holmes et al.).
[0052] In an alternate embodiment, a rotary screen hot-melt pattern
coater is used to coat a pattern corresponding to the pavement
elements. The thermoplastic materials are first heated to a molten
state and delivered to a die. The die coats the molten material not
a screen with a specified pattern and places the materials onto a
first surface of a web or frangible carrier having pressure
sensitive adhesive and release liner on the second surface. The
depth and definition of the pattern can be controlled by the die
slot, speed of the belt, and/or viscosity of the thermoplastic
material. The resulting assembly is then subjected to die cutting
that at least partially severs the carrier web around the perimeter
of the pavement elements. This embodiment of the present invention
can be performed using a rotary screen hot-melt pattern coater
available from May Coating Technologies, Inc. of White Bear Lake,
Minn.
[0053] In yet another embodiment, insert molding in one possible
injection molding technique may be used for forming the pavement
marker in accordance with the present invention. The frangible
carrier web can be inserted into the molds and the pavement
elements can be molded on the top of the carrier web. Once the
assembly is cooled, the pavement elements are ejected from the mold
and the carrier web is indexed forward and the molding process
repeated. Injection molding has the advantage that it is relatively
fast and the technology is widely available. Other processing
techniques applicable for making pavement elements according to the
present invention are disclosed in U.S. Pat. No. 5,201,916 (Berg et
al.), U.S. Pat. No. 5,304,331 (Leonard et al.), and commonly
assigned U.S. Patent application entitled Matrix Element Magnetic
Pavement element and Method of Making Same (Attorney Docket No.
53750USA2A), filed on the same date herewith.
[0054] FIG. 10 illustrates a raised pavement marker 210 having an
exemplary array of pavement elements 212 according to the present
invention. The protrusions 214 typically have a height of about
0.38 millimeters to about 1.6 millimeters (0.015-0.065 inches). The
carrier web 216 typically has a thickness of at least 0.025
millimeters (0.001 inches). The array 210 comprises rows and
columns of protrusions 214 preferably spaced apart by a distance of
about 1.6 millimeters to about 12.7 millimeters (0.063-0.5 inches),
and more preferably spaced apart by about 3 millimeters to about 6
millimeters (0.125-0.25 inches). The spacing of the protrusions 214
in the array 210 will vary depending on the height of the
protrusions and the particular application for which the pavement
elements are to be used. In one embodiment, frangible connection
218 is formed around a group of the protrusions 214, rather than
each of the discrete protrusions 214. Other spacing scenarios can
be used, such as for long line applications disclosed in U.S. Pat.
No. 5,683,746 (Hedblom).
[0055] The pavement elements of the present invention may be coated
with retroreflective beads by a variety of techniques, such as
disclosed in U.S. Pat. No. 4,988,541. Suitable bead bond material
for adhering the beads may be either a thermoplastic or a thermoset
polymeric binder. One such binder is vinyl based thermoplastic
resin, including a white pigment, as described in U.S. Pat. No.
4,117,192. Other suitable bead bond materials include two-part
polyurethane formed by reacting polycaprolactone diols and triols
with derivatives of hexamethylene diisocyanate; epoxy based resins
as described in U.S. Pat. No. 4,248,932, 3,436,359, and 3,580,887;
and blocked polyurethane compositions as described in U.S. Pat. No.
4,530,859. Other suitable bead bond materials are polyurethane
compositions comprising a moisture activated curing agent and a
polyisocyanate prepolymer. The moisture activated curing agent is
preferably an oxalolidene ring, such as described in U.S. Pat. No.
4,381,388.
[0056] Particles such as retroreflective beads suitable for use in
the process include glass beads formed of glass materials having
indices of refraction (n) from about 1.5 to about 2.26, and more
preferably from about 1.5 to about 1.9. As is well known in the
art, glass beads of material having an index of refraction of about
1.5 are less costly and more scratch and chip resistant than glass
beads of material having an index of refraction of from about 1.75
to about 2.26. However, the cheaper, more durable glass beads are
less effective retroreflectors. In one embodiment, the glass beads
may include a silver or other specular reflective metallic or
dielectric coating. The non-embedded portion of the silver coat is
subsequently removed to provide a highly effective retroreflector.
In another embodiment, beads having a hemispheric coating of a
specular reflective metal, such as silver, are applied to the
liquid bead bond layer. Because the beads are randomly oriented
when applied, a fraction of the beads become embedded in a
orientation which is effective for retroreflection. Generally, the
effectively oriented beads have the uncoated surface exposed and
the silver coated surface embedded.
[0057] Preferred retroreflector beads are disclosed in U.S. Pat.
No. 4,564,556 and U.S. Pat. No. 4,758,469. These beads are
described generally as solid, transparent, non-vitreous, ceramic
spheroids comprising at least one crystalline phase comprised of at
least one metal oxide. These beads may also have an amorphous phase
such as silica. The term non-vitreous means that it is not been
derived from a melt or mixture of raw materials brought to liquid
state at high temperature, like glass. These spheroids are very
resistant to scratching and chipping, being quite hard (e.g., above
700 Knoop) and can be made with a relatively high index of
refraction (ranging between 1.4 and 2.6). Examples of the
compositions of these beads are zirconia-alumina-silica and
zirconia-silica.
[0058] The approximate weight of typical ceramic beads with a
density of approximately 4.0 grams per cubic centimeter,
corresponding to flood coatings (i.e., a monolayer of beads over
all surfaces with binder 32) of the entire surface of the
protrusion 24. Levels of bead application for selectively applied
beads range from just greater than 0% to about 100% of flood coat.
Preferred levels, however, are from 15-50% of flood coat, with
about 30% being most preferred. Another consideration is the
relationship of the bead bond layer to the bead size. Unlike flat
pavement marking constructions, beads will retroreflect on the side
surfaces of the protrusions when deeply embedded, as long as a
portion of the bead surface is exposed. Preferably, beads should be
embedded up to approximately 50 to 70% of their diameter in the
liquid bead bond layer for an acceptable compromise between bead
retention in the field and ability to retroreflect light. Retention
of glass beads may also be improved by silane treatment.
[0059] Conformable Carrier Webs
[0060] Conformability of carrier web can be evaluated in several
ways. One simple way is to press a layer or sheet of the material
by hand against a complex, rough or textured surface, such as a
concrete block or asphalt composite pavement, remove, and observe
the degree to which surface roughness and features are replicated
in the layer or sheet. The conformable carrier web of this
invention will conform to complex shapes and rough surfaces.
[0061] Elastic recovery is the tendency of a layer or sheet to
return to its original shape after being deformed. Delayed elastic
recovery can be observed by noting the tendency of the replicated
roughness to disappear over time. A simple test for delayed elastic
recovery is to use a blunt instrument to indent the carrier web.
The ease with which an impression can be made and the permanence of
the impression may be used to form rough comparative judgments
about the conformance properties of the material used to form the
sheet or layer.
[0062] Conformable carrier webs of this invention must be capable
of being deformed under reasonable forces in order to take on the
shape of the road surface irregularities and thereby to allow
formation of a good bond to the road surface. By reasonable forces
is meant that after application of the carrier web to a road
surface and rolling over the applied, flat marking sheet with a
suitable tamping means, the carrier web conforms to the road
surface. In such an application, the tamped carrier web
substantially replicates the surface texture of the road. The
suitable tamping means should not be excessively unwieldy. For
prior art preformed pavement marking tapes, a tamping cart with a
load (total weight about 250 lbs. (115 kg)) has commonly been
employed in the application of marking tapes.
[0063] Another test for conformability is available through the
following sequence of steps: 1. A test strip about 2.54 centimeters
(1 inch) wide and about 10.16 centimeters (4 inches) long is pulled
(i.e., deformed or strained) in a tensile strength apparatus at a
rate of about 30.5 centimeters/minute (12 inches/minute) until it
is strained to about 105% of original sample length (elongation of
about 0.51 centimeters). 2. The pull is reversed and the machine
returned to its starting point at a rate of about 30.5
centimeters/minute, causing a complete release of the tensile
stress in the sample. 3. The strain at which a resisting force is
first observed on the second pull (i.e. when the sample again
becomes taut) is observed. The strain at which resistance is first
observed on the second pull, divided by the first strain is defined
as inelastic deformation (ID). In the present embodiment, strain is
measured as the distance until the sample is taut is divided by the
original elongation of 0.51 centimeters. A perfectly elastic
material would have 0% ID, i.e., it would return to its original
length. Metals approach 90% ID, but yield only at very undesirably
high tensile stresses. Preferably, the force required to achieve 5%
strain (i.e., deformation) in a base sheet (initial thickness
typically about 250 micrometers) is less than 25 lbs. per inch of
sample width (44 Newtons/cm of sample width) and more preferably
less than 10 lbs. per inch (18 NT per cm).
[0064] Unload energy is also a significant factor in determining
the conformability of a carrier web for use in the present
invention. The unload energy is defined as the energy remaining in
the memory portion of an elongated material. Materials with lower
unload energies should be more conformable.
[0065] Conformable composite materials of this invention combine a
low unload energy of less than 1.25 grams/centimeter (0.7
pounds/inch) and an ID of greater than about 10%, preferably
greater than 20%, more preferably not less than 30% at 25.degree.
C.
[0066] Patents and patent applications disclosed herein, including
those disclosed in the background of the invention, are hereby
incorporated by reference in their entirety. It will be apparent to
those skilled in the art that many changes can be made in the
embodiments without departing from the scope of the invention.
Thus, the scope of the present invention should not be limited to
the methods and structures described herein, but only to methods
and structures described by the language of the claims and the
equivalents thereof.
* * * * *