U.S. patent application number 10/039654 was filed with the patent office on 2003-07-03 for matrix element magnetic pavement marker and method of making same.
Invention is credited to Borden, Thomas R., Jacobs, Gregory F., Keech, Robert L., Khieu, Sithya S., Tolliver, Howard R..
Application Number | 20030123930 10/039654 |
Document ID | / |
Family ID | 21906631 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030123930 |
Kind Code |
A1 |
Jacobs, Gregory F. ; et
al. |
July 3, 2003 |
Matrix element magnetic pavement marker and method of making
same
Abstract
A method for making a magnetic pavement marker having an array
of magnetic pavement elements arranged in a predefined pattern
interconnected by a carrier web. After the array of magnetic
pavement elements is applied to the pavement surface, the portion
of the carrier web surrounding the magnetic pavement elements is
removed or allowed to substantially deteriorate and dissipate,
leaving an array of discrete, magnetic pavement elements.
Inventors: |
Jacobs, Gregory F.; (Elmira,
NY) ; Keech, Robert L.; (White Bear Lake, MN)
; 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: |
21906631 |
Appl. No.: |
10/039654 |
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 |
Claims
What is claimed is:
1. A method of making a magnetic pavement marker comprising the
steps of: forming an array of magnetic pavement elements
interconnected by a carrier web; and forming a frangible connection
between the magnetic pavement elements and the carrier web.
2. The method of claim 1 wherein the step of forming the magnetic
pavement elements interconnected by a carrier web comprises the
step of integrally forming the magnetic pavement elements and the
carrier web.
3. The method of claim 1 wherein the step of forming the magnetic
pavement elements interconnected by a carrier web comprises the
step of bonding the magnetic pavement elements to the carrier
web.
4. The method of claim 1 wherein the step of forming the magnetic
pavement elements interconnected by a carrier web comprises the
steps of bonding the carrier web to an upper surface of the
magnetic pavement elements.
5. The method of claim 1 wherein the magnetic pavement elements
comprise magnetic particles distributed in a binder.
6. The method of claim 1 further comprising the step of inducing an
alternating polarity along the array of magnetic pavement
elements.
7. The method of claim 1 further comprising the steps of: applying
a pressure sensitive adhesive to a rear surface of the magnetic
pavement elements; and applying a release liner over the
adhesive.
8. 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 magnetic pavement
elements.
9. The method of claim 1 wherein the carrier web is selected from a
group consisting of a polymeric films, paper, a liner, a screen, a
mat, a nonwoven web, an open scrim, or a film or nonwoven web of a
water-soluble or water-dispersible polymeric material.
10. A method for applying the array of magnetic pavement elements
of claim 1 to a pavement surface comprising the steps of:
interposing an adhesive between the magnetic 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 magnetic pavement
elements to form an array of discrete magnetic pavement elements
adhered to a pavement surface.
12. A method for making a magnetic pavement marker comprising the
steps of forming an array of magnetic pavement elements in a
predefined pattern on a conformable carrier web.
13. The method of claim 12 wherein the conformable carrier web
comprises an extensible carrier web.
14. A method for applying the array of magnetic pavement elements
of claim 12 to a pavement surface comprising the steps of:
interposing an adhesive between the magnetic pavement elements and
the pavement surface; and engaging the adhesive to the pavement
surface under pressure.
15. A magnetic pavement marker attachable to a pavement surface
comprising: an array of magnetic pavement elements interconnected
by a carrier web; and a frangible connection between the magnetic
pavement elements and the carrier web.
16. The article of claim 15 wherein the carrier web and the
magnetic pavement elements are integrally formed.
17. The article of claim 15 wherein the magnetic pavement elements
are bonded to the carrier web.
18. The article of claim 15 wherein the carrier web is bonded to
upper surfaces of the magnetic pavement elements.
19. The article of claim 15 further comprising a pressure sensitive
adhesive applied to a rear surface of the magnetic pavement
elements, and a release liner extending over the adhesive.
20. The article of claim 15 further comprising an adhesive
interposed between the magnetic pavement elements and the pavement
surface.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to magnetic pavement markers
and a method of making the same, and more particularly, to a system
for guiding vehicles and other mobile objects along a roadway,
warehouse floor, and the like.
BACKGROUND OF THE INVENTION
[0002] Safer, more efficient and more accessible transit for
citizens is a high priority. Public service workers, public transit
vehicles and emergency vehicles must have the capability to move
more rapidly and safely on roadways in a variety of weather
conditions.
[0003] Inclement weather and even blinding sunlight or oncoming
traffic light present special problems both for existing travel
systems and for guidance systems that offer lateral vehicle
control. Snowy conditions, fog, heavy rain, blowing dust and smoke
are examples of challenges to vehicle drivers. Snowy weather
presents particularly challenging driving conditions to snowplow
drivers trying to clear lanes in blowing snow or when lane markers
are obstructed by snow. Furthermore, reduced visibility brought by
blowing snow has caused numerous tragic accidents when automobile
drivers have rear-ended snowplows traveling slower than surrounding
traffic. Winter weather will continue to challenge any intelligent
transportation system (ITS) in which vehicles move at faster speeds
and closer together on more crowded roadways.
[0004] In addition to vehicles, other mobile objects such as farm
animals, pets, fire fighters, visually impaired pedestrians, and
the like may also benefit from control and/or guidance systems.
Mobile robots equipped with magnetic sensors may be guided and/or
controlled as they move on their path, for example, along an
industrial assembly line. Perimeter and boundary awareness systems
can be used for pet containment systems. Additionally, games
frequently require defined boundaries, such as foul territory in
baseball and out of bounds in soccer, and it is frequently desired
that toys and sporting equipment emit audible signals when crossing
a designated line.
[0005] Several alternate methods for sensing the lateral position
of a vehicle on a roadway are known. One option involves the use of
visible signs or markings and optical sensors. A system that relies
on optical sensors can be obscured by dirt, ice, or snow, and
visibility can be impaired by fog, blowing snow, blowing dust, and
the like. Furthermore, for night usage, a considerable amount of
energy is expended, either to illuminate the signs or to emit a
beam from the sensor.
[0006] Another approach is the use of radar reflective markers with
a radar ranging system on the vehicle. Both the markers and the
radar detection systems are expensive in comparison with magnetic
systems. In addition, metallic radar reflective markers embedded in
the roadway are likely to have durability and corrosion
problems.
[0007] A magnetic system is not adversely affected by weather
conditions and does not require expensive video or other radio
frequency equipment. A magnetic system's operating costs remain low
since the marker is passive (no power is required to make a
magnetic marker function). Some magnetic markers can last the life
of the roadway (typical roadways have life spans of six to eight
years) and may even be reprogrammed while still a part of the
roadway.
[0008] One magnetic marking system includes a series of magnetic
"nails" embedded in the roadway. Since the field strength decreases
as the cube of the distance from such a dipolar magnetic field
source, the "nails" have to be fairly closely spaced to produce a
useful signal. Material costs would be high if the most powerful
rare earth magnets were used to minimize the size and maximize the
spacing. Boring holes in the roadway and using rigid nails may also
lead to stress concentration and premature pavement failure, which
may be exacerbated by corrosion of nails. The use of simple ferrous
metal spikes would not provide the alternating signal desirable for
effectively separating the position signal from noise.
[0009] Another magnetic marking system employs a magnetic paint to
produce magnetic stripes on the roadway. A sufficiently strong
magnetic signal is difficult to obtain with the typical thickness
of paint layers. If the thickness of the paint is built up to
obtain a good magnetic signal, the paint durability can be reduced.
The paint stripe can be magnetized only after it has dried. A
specially designed magnetizing fixture would have to be driven
along the strip. Since limitations in the magnetic field produced
by such a fixture, the coercivity of the magnetic material would
likely be limited to about 1000 oersteds, making it susceptible to
erasure.
[0010] Some previously known magnetic guidance systems have
employed materials embedded within a roadway, such as disclosed in
U.S. Pat. Nos. 3,609,678 and 3,714,625. The polymer-based magnetic
materials disclosed are resilient and flexible, such as nitrile and
silicone rubber, and plasticized PVC. Resilient refers to
recovering to substantially the original shape after removal of a
deformation force. The '678 patent discloses, in one embodiment, a
polymeric magnetic tape or sheet that is "either inserted edgewise
in a narrow channel or slot or laid flat in a more shallow channel
cut in the roadway." (col. 3, lines 4-6). This patent further
states that magnets may also be embedded within the pavement of the
roadway instead of in an open channel. (col. 3, lines 31-32). A
flux sensor is mounted on a vehicle that travels over the roadway
The sensor can generate an electric signal in response to the
magnetic medium if the magnetic field is sufficiently strong to be
sensed. The '678 patent discloses that the intensity of the
magnetic field at the surface of the roadway should be at least 2
gauss, preferably at least 10 gauss, and more preferably at least
100 gauss, to provide a strong signal even when road conditions are
less than optimal. (col. 4, line 75 through col. 5, line 6).
[0011] Conventional conformable non-magnetic pavement marking sheet
materials are known in the art and typically comprise a polymeric
material, such as one that could be crosslinked to form an
elastomer, but which is not crosslinked in the sheet material and
thereby provides desired viscoelastic properties. Conformable
refers to being capable of being deformed under a loading force and
retaining a substantial part of that deformation after removal of a
loading force. Illustrative examples of conformable non-magnetic
pavement markings include U.S. Pat. No. 4,490,432, U.S. Pat. No.
5,316,406, U.S. Pat. No. 4,069,281, and U.S. Pat. No.
5,194,113.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to a magnetic pavement
marker having an array of magnetic pavement elements interconnected
by a removable or frangible carrier web that is conformable and
that minimizes unnecessary materials, improves tamping efficiency
and isolates adjacent magnetic pavement markers. Various methods of
making the array of magnetic pavement elements are also disclosed.
The present invention is also directed to a method of applying the
present array of magnetic pavement elements onto a pavement
surface.
[0013] The present magnetic pavement marker uses less material than
conventional magnetic pavement markers because the conformance
layer is substantially eliminated. The tamping efficiency is also
improved by isolating the tamping force on the discrete magnetic
pavement elements. In particular, the magnetic pavement elements
act as force concentrators that direct applied tamping forces to
create an enhanced bond of the marker material to the pavement
surface. In one embodiment, the array of discrete, magnetic
pavement elements are substantially not interconnected, so that the
delamination of a single pavement element does not adversely effect
adjacent magnetic pavement elements. In some embodiments, the
carrier web is sufficiently conformable that movement of an
individual magnetic pavement markers does not adversely affect
adjacent magnetic pavement elements.
[0014] In one embodiment the method of making a magnetic pavement
marker includes forming an array of magnetic pavement elements,
typically arranged in a desired predefined pattern, interconnected
by a carrier web. A frangible connection is formed between the
magnetic pavement elements and the carrier web.
[0015] The step of forming the magnetic pavement elements
interconnected by a carrier web can be performed by integrally
forming the magnetic pavement elements and the carrier web, bonding
the magnetic pavement elements to the carrier web, or bonding the
carrier web to an upper surface of the magnetic pavement elements.
The step of forming the frangible connection between the magnetic
pavement elements and the carrier web can comprise partially
severing the carrier web around a single magnetic pavement element
or around groups of the elements.
[0016] In one embodiment, the magnetic pavement elements comprise
magnetic particles distributed in a binder. The particles can be
oriented to product a magnetic field. Additionally, a polarity can
be induced in the magnetic pavement elements. The magnetic pavement
elements can be constructed of conformable polymeric materials or
non-conformable magnetic materials. The magnetic pavement elements
may be a variety of shapes, such as a rope, a sheet, a perforated
article, etc. The shape is dictated largely by the specific use of
the article. The magnetic pavement elements can be selected from a
group consisting of polymer, ceramic, metal and metal alloy
magnets.
[0017] The carrier web can be selected from a group consisting of a
polymeric film, paper, a liner, a screen, a mat, a nonwoven web, an
open scrim, or a film or nonwoven web of a water-soluble or
water-dispersible polymeric material. After the array of magnetic
pavement elements is applied to the pavement surface, the portion
of the carrier web surrounding the magnetic pavement elements is
removed, leaving an array of discrete, magnetic pavement elements.
The carrier web is conformable, typically preferably
extensible.
[0018] In an alternate embodiment, the magnetic pavement markers
includes magnetic pavement elements formed in a predefined pattern
on a carrier web. The carrier web has frangible portions between
adjacent magnetic pavement elements. The frangible portion is
preferably capable of substantially deteriorating when exposed to
roadway conditions for a short time. A pressure sensitive adhesive
can be applied to the rear surfaces of the magnetic pavement
elements and a release liner is applied over the adhesive. The
carrier web serves to maintain the array of magnetic pavement
elements in a predetermined configuration until they are applied to
a pavement surface. The carrier web subsequently deteriorates,
leaving an array of discrete magnetic pavement elements spaced in
substantially the same configuration as on the carrier web.
[0019] In another embodiment, the magnetic pavement elements have a
pressure sensitive adhesive on their bottom surfaces. The
adhesive-coated bottom surfaces of the magnetic pavement elements
are arranged in an array on a release liner. A carrier web is
bonded to top portions of the magnetic pavement elements to
maintain the spatial orientation of the array when the release
liner is removed.
[0020] The present invention is also directed to a method of
applying an array of magnetic pavement elements to a pavement
surface. The release liner is removed from the array of magnetic
pavement elements. An adhesive, such as a pressure sensitive
adhesive, is interposed between the magnetic pavement elements and
the pavement surface. The portion of the carrier web surrounding
the magnetic pavement elements is removed from the array. In
another embodiment, the array of magnetic pavement elements are
formed in a predetermined pattern on a conformable carrier web.
[0021] The present invention is also directed to a magnetic
pavement article. An array of magnetic pavement elements in a
predefined pattern is interconnected by a carrier web. A frangible
connection is located between the magnetic pavement elements and
the carrier web.
[0022] The array of magnetic pavement elements may be magnetized in
a single pattern, but are preferably magnetized in a pattern to
produce a readily-detectable alternating magnetic signal on the
sensor. However, to convey more detailed information, the inventive
articles may be magnetized ("encoded" or "written") in more
complicated patterns, as found in bar codes, credit card strips, or
magnetic tape recordings.
[0023] The magnetic pavement markers are unpowered, meaning that
they do not require an outside power source either to send or
receive a signal. In this regard, the present invention is
distinguishable from powered embedded articles such as those that
are typically used to determine whether a vehicle on a roadway is
stopped at an intersection, such as at a red light. Embedded
sensors of this type are further distinguishable from the present
invention in that the former requires electrical power, whereas the
latter is an unpowered magnetic field source. The unpowered
magnetic pavement marker of the present invention also requires
less installation time and less maintenance, cost nothing to
operate, and may be used in remote locations where a power supply
is not readily available. Thus, the unpowered magnetic pavement
markers of this invention provide several advantages over
conventional embedded powered articles.
[0024] Another embodiment of the invention is a guidance system for
guiding vehicles or mobile objects traveling on a pavement surface.
The guidance system provides information to a vehicle driver or to
another mobile object or system and/or controlling a vehicle or
mobile object. The magnetic pavement elements may be underlaid
beneath an existing traffic-bearing structure or installed on a
pavement surface. The discrete magnetic pavement elements are much
less susceptible to damage by vehicular traffic or a mismatch of
thermodynamic and mechanical properties between the pavement
surface and the discrete magnetic pavement elements. In one
embodiment, the system includes an array of magnetic pavement
elements according to the present invention are bonded to the
pavement surface and a sensor for passing over a array. The sensor
is capable of detecting the magnetic signal of the array of
magnetic pavement elements. The output of the sensor would
optionally be a lateral offset signal. The output of the sensor may
be used to control a vehicle and/or provide information to a driver
via a display unit.
[0025] A method of providing a guidance system for a
traffic-bearing structure is another aspect of the present
invention. The invention may be used in conjunction with the
magnetic guidance of a snow plow. It is important for a snow plow
to be properly located on the traffic-bearing structure, so that
inadvertent damage to curbs, roadside signs, mailboxes, and the
like can be avoided. Because lane markers can be obscured by snow
or ice on a road, a snow plow driver would benefit from having a
magnetic guidance system of the type described, such that the snow
plow remains on the traffic-bearing surface. The present invention
may be particularly beneficial for guiding snow plows in white-out
(intense, blowing snow) conditions when visual guidance is limited.
Other useful applications include an electronic "rumble strip" that
would provide warning to a driver that the vehicle was approaching
the edge of a traffic-bearing structure, or a school zone, bridge
deck, curve in the traffic-bearing structure, or obscure
traffic-bearing structure entrance or exit, and as a component of
an automated highway system in which vehicles are automatically
guided in assigned lanes.
[0026] As used herein,
[0027] "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.
[0028] "Frangible connection" refers to a connection between the
carrier web and magnetic 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 magnetic pavement elements to the road.
[0029] "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.
[0030] "Substantially deteriorating" refers to degradation and
dissipation of the carrier web when exposed to a variety of
environmental factors, such as abrasion, rain and impact from
roadway traffic, to yield an array of discrete pavement
elements.
BRIEF DESCRIPTION OF THE DRAWING
[0031] FIG. 1 is a cross-sectional view of an illustrative array of
magnetic pavement markers according to the present invention.
[0032] FIG. 2 is a cross-sectional view of the array of magnetic
pavement markers of FIG. 1 being applied to a pavement surface.
[0033] FIG. 3 is a cross-sectional view of an alternate
illustrative array of magnetic pavement markers according to the
present invention.
[0034] FIG. 4 is a cross-sectional view of the array of magnetic
pavement markers of FIG. 3 being applied to a pavement surface.
[0035] FIG. 5 is a cross-sectional view of an alternate
illustrative array of magnetic pavement markers having a
top-mounted carrier web according to the present invention.
[0036] FIG. 6 is a cross-sectional view of the array of magnetic
pavement markers of FIG. 5 being applied to a pavement surface.
[0037] FIG. 7 is a cross-sectional view of an array of magnetic
pavement markers of FIG. 5 embedded in the pavement.
[0038] FIG. 8 is a schematic illustration of an exemplary process
for making magnetic pavement markers according to the present
invention.
[0039] FIG. 9 is a schematic illustration of an alternate
illustrative process for making magnetic pavement markers according
to the present invention.
[0040] FIG. 10 is a schematic illustration of an alternate
illustrative process for making magnetic pavement markers according
to the present invention.
[0041] FIG. 11 is a schematic illustration of an illustrative array
of magnetic pavement markers according to the present
invention.
[0042] FIG. 12 is a schematic diagram of an inventive control
and/or guidance system in accordance with the invention.
[0043] These figures, which are idealized, are not to scale and are
intended to be non-limiting.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE
INVENTION
[0044] FIG. 1 is a side sectional view of a magnetic pavement
marker having an array 20 of magnetic pavement elements in
accordance with a first embodiment of the present invention. The
array 20 includes a plurality of magnetic pavement elements 24 and
an integrally formed carrier web 22. In the illustrated embodiment,
the magnetic pavement elements 24 comprise a permanently
magnetizable material 25 dispersed in a binder 27. An adhesive 26
is pattern coated to a bottom surface 28 of the magnetic pavement
elements 24. The adhesive 26 may alternatively be coated across the
entire surface of the carrier web 22 and the magnetic pavement
elements 24 without being applied to the interstitial portions of
web 22. In the embodiment illustrated in FIGS. 1 and 2, the
magnetic pavement elements 24 and the carrier web 22 are formed
from the same material.
[0045] A release liner 30 optionally extends across the adhesive 26
until the array 20 is ready for use, particularly in embodiments
where the adhesive 26 is a pressure sensitive adhesives. Top
surfaces 36 of the magnetic pavement elements 24 that may
optionally include non-slip particles. The non-slip particles may
be embedded in the magnetic pavement elements 24 or adhesively
attached. A frangible connection 32 is formed around a perimeter of
the magnetic pavement elements 24, typically by die cutting, so
that the carrier web 22 can be removed after installation. The
frangible connection 32 preferably has sufficient strength to
releasably connect the magnetic pavement elements 24 and carrier
web 22 until the array 20 is applied to a pavement surface 42 (see
FIG. 2).
[0046] FIG. 2 is a side sectional view of the array 20 of FIG. 1
being applied to a pavement surface 42. The release liner 30 is
removed and the array 20 is tamped to the pavement surface 42. The
magnetic pavement elements 24 act as force concentrators to focus
the tamping forces directly to the interface between the adhesive
26 and the pavement surface 42. In an embodiment where the adhesive
26 is coated across the entire surface of the carrier web 22, the
magnetic pavement elements 24 minimize the tamping force applied to
the carrier web 22.
[0047] The carrier web 22 that surrounds the magnetic pavement
elements 24 is then removed or peeled-back from the array 20 by
breaking the frangible connection 32. The resulting array of
discrete, magnetic pavement elements 24 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
24 are not interconnected by the web 22, so that the delamination
of a single pavement element does not typically adversely affect
adjacent pavement elements. The array 20 has a high degree of
conformance to the surrounding pavement surface 42 and is better
able to accommodate for mismatches of the thermodynamic and
mechanical properties between the pavement surface 42 and the
discrete magnetic pavement elements 24.
[0048] FIG. 3 is a side sectional view of an alternate array 50 of
magnetic pavement elements 52 bonded to a carrier web 54 by a
variety of methods. An adhesive 56 is applied to the entire lower
surface 57 of the carrier web 54 or underneath the magnetic
pavement elements 52. A release liner 58 is then applied to the
adhesive 56 until the array 50 is ready for use. The carrier web 54
is conformable and frangible, preferably extensible. A nonexclusive
list of carrier webs include polymeric films, paper, liners,
screens, mats, nonwoven webs, and open scrims. In the embodiment of
FIGS. 3 and 4, the magnetic pavement elements can be conformable or
non-conformable magnets, including polymeric magnets, ceramic
magnets, metal magnets and metal alloy magnets. The magnetic
pavement elements 52 can optionally have a plurality of
retroreflective beads 55 bonded thereto using an adhesive 59, such
as disclosed in U.S. Pat. No. 4,988,541 (Hedblom).
[0049] 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 when exposed to roadway conditions. As
illustrated in FIG. 4, the frangible portions 60 progressively
deteriorates, leaving an array of discrete, magnetic 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. The portions of
the carrier web 54 surrounding the pavement elements may optionally
be peeled-back or otherwise removed, such as shown in FIG. 2.
[0050] In yet another embodiment, the carrier web 54 is conformable
and extensible. The resulting array 50 of magnetic pavement
elements 52 is arranged on the pavement surface 42 in substantially
the same configuration maintained by the carrier web 54. Although
the pavement elements 52 are interconnected by the portions 63 of
the carrier web 54 (shown in dashed lines), the conformable and/or
extensible carrier web 54 provides a high degree of conformance to
the surrounding pavement surface 42 to accommodate for mismatches
of the thermodynamic and mechanical properties between the pavement
surface 42 and the elements 52.
[0051] FIG. 5 is a side sectional view of an alternate array 100 of
magnetic 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 upper 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 that of the adhesive 104 to bottom surface 106 or
pavement surface 42. In another embodiment, the carrier web 110 is
a biodegradable material, such as paper, or a film or nonwoven web
of a water-soluble or water-dispersible polymeric material. In an
alternate embodiment, the carrier web 110 can be a conformable and
extensible material.
[0052] FIG. 6 is a side sectional view of the array 100 of FIG. 5
bonded to a pavement surface 42. In one embodiment, the release
liner 108 is removed and the array 100 is 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 42.
Alternatively, the carrier web 110 may be allowed to substantially
deteriorate. For the inlayed or underlayed embodiments discussed in
connection with FIG. 7, the carrier web 110 can optionally be a
conformable and/or extensible material.
[0053] FIG. 7 is an alternate embodiment in which magnetic pavement
element 105 is underlaid and magnetic pavement element 107 is
inlaid on an irregular pavement surface 42. The pavement surface 42
is a traffic-bearing structure such as base layer material,
asphalt, gravel, concrete, cement, brick, wood, dirt, and/or clay.
The array of magnetic pavement makers 100 is applied to the
traffic-bearing structure 42 using one of the techniques disclosed
above. FIG. 7 shows the embodiment from FIG. 6 for illustration
purposes only. A pavement surface layer 109 is then applied to
underlay/inlay the magnetic pavement elements 105, 107 within the
pavement surface 42'. Underlaid is defined herein as being
substantially surrounded by traffic-bearing structure material on
all sides. Inlaid is defined herein as being at least partially
surrounded by traffic-bearing structure material.
[0054] Other configurations for magnetic pavement markers are
disclosed in U.S. patent application Ser. No. 08/682,477 entitled
Conformable Magnetic Articles for Use with Traffic Bearing
Surfaces, Methods of Making Same, Systems Including Same, and
Methods of Use and U.S. Pat. No. 5,853,846, entitled Conformable
Magnetic Articles Underlaid Beneath Traffic-Bearing Surfaces.
[0055] 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
magnetic pavement markers and pavement surface 42 before bonding,
rather than being coated on the array of magnetic pavement
elements.
[0056] FIG. 8 is a schematic illustration of one embodiment of an
extrusion and embossing method 130 for manufacturing an array of
magnetic pavement elements 132 according to the present invention.
The expression magnetic pavement markers refers to both finished
magnetic pavement markers or protrusions that can be subsequently
processed to form a magnetic pavement marker, such as by orienting
the magnetic particles 135 dispersed in a binder 137. The precursor
sheeting 134 is the permanently magnetizable material embossed by
an embossing roll 136 to form protrusions 144 of specified shapes
and dimensions connected by a portion of the elastomeric sheeting
134 forming a base sheet 145.
[0057] An adhesive 138 is applied by a coating roll 140. A liner
142 is applied to the layer of adhesive 138. Alternatively, an
assembly having a pressure sensitive adhesive 138 and liner 142 can
be simultaneously laminated to the rear surface of the embossed
magnetic pavement elements 132. 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 magnetic pavement elements 132 can be applied
to a pavement surface generally as illustrated in FIGS. 1 and
2.
[0058] The precursor sheeting 134 can be constructed from a variety
of polymer based magnetic materials, such as disclosed in U.S. Pat.
No. 4,497,722 (Tsuchida et al.) Additional exemplary materials for
forming the precursor sheeting 134 include acrylonitrile-butadiene
polymers, millable urethane polymers, neoprenes, and pavement
marking materials disclosed in U.S. Pat. Nos. 5,194,113 (Lasch et
al.) and 5,127,973 (Sengupta et al.). Extender resins, inorganic
fillers, such as silica, and reinforcements may also be included.
The present array of magnetic pavement markers may be made using a
variety of techniques, such as disclosed in U.S. Pat. Nos.
4,388,359, 4,086,388, 4,988,541, and 5,194,113 (Lasch et al.).
[0059] FIG. 9 is a schematic illustration of an alternate method
130' for manufacturing an array of magnetic pavement elements 132'
according to the present invention. A series of die cuts 148' are
formed in a precursor sheeting 134' of magnetic material by die
cutting roll 136' to form magnetic pavement elements 144'. The
magnetic material can be conformable or non-conformable. The die
cutting roll 136' can be configured to cut a variety of patterns in
the precursor sheeting 134', such as the array illustrated in FIG.
11. An adhesive 138' is applied by a coating roll 140'. A
conformable and/or extensible carrier web 142' is applied to the
layer of adhesive 138'.
[0060] In an embodiment in which the carrier web 142' is
conformable, a portion of the magnetic pavement elements 144' are
removed at station 146' to form an array of magnetic pavement
elements (see FIG. 11). In an embodiment in which the carrier web
142' is extensible, the carrier web 142' can be biaxially stretched
either before or during application to the pavement surface 42 to
form a separation or gap between adjacent magnetic pavement
elements 142'. The magnetic pavement elements can be applied to a
pavement surface as discussed above.
[0061] FIG. 10 is a schematic illustration of a cast and cure
method according to the present invention. A polymeric material
containing permanently magnetizable particles 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 magnetic pavement elements 162. The molten material 154
fills the cavities 160 and is solidified to form a series of
magnetic pavement elements 162 on an extensible carrier 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 may be a thermoplastic
polymer or a polymer that is subsequently cured to be 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.
[0062] Also entering the nip between the drums 156, 158 is an
assembly 166 including a carrier web 168, a pressure sensitive
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 magnetic pavement elements
162. The forming drum 156 may optionally be heated to facilitate
solidification of thermoset materials or cooled to facilitate
curing thermoplastic materials.
[0063] The array 174 of magnetic pavement elements 162 is then
subjected to die cutting 176 which at least partially severs the
web 168 around the perimeter of the magnetic pavement elements 162.
In one embodiment, the die cutting step 176 cuts through the
carrier web 168, and optionally through the pressure sensitive
adhesive 170, but not through the liner 172. The magnetic pavement
elements may be subject to additional processing, such as the
application of reflective material, either before or after the die
cutting step.
[0064] 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 composition is formed on the web 168 between the
magnetic pavement elements 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 magnetic
pavement elements 162. Alternate methods of forming magnetic
pavement markers on a carrier web are disclosed in U.S. Pat. Nos.
5,152,917 (Pieper et al.); 5,435,816 (Spurgeon et al.); and
5,500,273 (Holmes et al.).
[0065] If the material 154 is semi-liquid as it separates from the
drum 156, the desired orientation of the magnetic particles may be
produced by exposure to a permanent magnet or electromagnet 161.
Mechanical working, such as that which occurs during extrusion or
calendering, and/or externally applied fields will also promote
orientation. Orientation enables one to obtain desired magnetic
performance.
[0066] In an alternate embodiment, a rotary screen hot-melt pattern
coater is used to coat a pattern corresponding to the magnetic
pavement elements. The thermoplastic materials are first heated to
a molten state and delivered to a die. The die coats the molten
material on a screen with a specified pattern and places the
materials onto a first surface of a web or frangible carrier having
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
magnetic 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.
[0067] In yet another embodiment, insert molding (injection
molding) techniques may be used for forming the magnetic pavement
elements according to the present invention. The frangible carrier
web can be inserted into the molds and the magnetic pavement
elements can be molded on the top of the carrier web. Once the
assembly is cooled, the magnetic 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 magnetic pavement
markers according to the present invention are disclosed in U.S.
Pat. Nos. 5,201,916 (Berg et al.), 5,304,331 (Leonard et al.), and
commonly assigned U.S. patent application entitled Matrix Element
Pavement Marker and Method of Making Same (Attorney Docket No.
53325USA3A), filed on the same date herewith.
[0068] FIG. 11 illustrates an exemplary array 210 of magnetic
pavement elements 212, 214 on a carrier web 216 in accordance with
the present invention. The array 210 of the present invention may
comprise sections of alternating polarity along its length, as
illustrated by the + sign on the elements 212 and - sign on the
elements 214, separated by a transition zone 213. For typical
magnetic pavement marking applications, the polarity alternates
about every meter. The magnetic pavement elements 212, 214 in the
illustrated embodiment have a height of about 0.25 millimeters to
about 1.0 millimeters (0.010 to 0.040 inches), but less than 3
millimeters (0.118 inches). It will be understood that elements
having other heights may be used if desired.
[0069] The array 210 comprises rows and columns of magnetic
pavement elements 212, 214 preferably spaced apart by a distance of
about 250 micrometers to about 5 millimeters, although spacing
between the magnetic pavement elements can be as close as possible
without interfering with conformabilty of the array. The planar
dimension or width of the magnetic pavement elements is typically
about 3 millimeters to about 10 millimeters, but elements having
other widths may be used in accordance with the invention. The
spacing of the magnetic pavement elements 212, 214 in the array 210
will vary depending on the height of the magnetic pavement elements
and the particular application for which the magnetic pavement
elements are to be used.
[0070] Retroreflective Magnetic Pavement Markers
[0071] The magnetic pavement markers 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.
[0072] 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.
[0073] 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.
[0074] The retroreflector beads preferably have a diameter
compatible with the size, shape, spacing and geometry of the
magnetic pavement markers present upon the base sheet. For the
earlier described base sheet 100, beads of 50-350 micrometers
diameter may be suitably employed. Other factors affecting bead
size are the number of rows of beads desired to be available to
vehicle headlights. At an angle of about 2-3 degrees from the base
sheet 100, only about 380 micrometers of side surface is visible.
Thus, only about 1 row of 300 micrometer beads is visible, or about
2 rows of 225 micrometer beads.
[0075] Binder Materials for Conformable Magnetic Layers
[0076] In one embodiment of the present invention, conformable
magnetic pavement elements are formed by dispersing a plurality of
magnetic particles in a binder. A sufficient amount of magnetic
particles are present to provide a magnetic signal through the
traffic-bearing structure to a sensor. Typically magnetic particles
are non-spherical.
[0077] In some organic binder embodiments, for example when the
organic binder comprises non-crosslinked elastomeric precursors
(see for example U.S. Pat. No. 4,490,432), traditional rubber
processing methods preferably are used to produce the conformable
magnetic layer, such as a heavy duty, batch or continuous, rubber
kneading machine, such as a Banbury mixer or twin screw
extruder.
[0078] "Elastomer precursor" is used herein to describe a polymer
which can be crosslinked, vulcanized, or cured to form an
elastomer. An "elastomer" is a material that can be stretched, to
at least about twice its original dimensions without rupture and
upon release of the stretching force rapidly returns to
substantially its original dimensions. Illustrative examples of
useful elastomer precursors include acrylonitrile-butadiene
polymers, neoprene, polyacrylates, natural rubber, and
styrene-butadiene polymers. Extender resins, preferably halogenated
polymers such as chlorinated paraffins, but also hydrocarbon
resins, polystyrenes or polycyclodienes, are preferably included
with the non-crosslinked elastomer precursor ingredients, and are
miscible with, or form a single phase with, the elastomer precursor
ingredients. The extender resins preferably account for at least 20
weight of the organic components in a conformable layer when using
this binder.
[0079] Useful thermoplastic reinforcing polymers are known in the
pavement marking art (e.g., polyolefins, vinyl copolymers,
polyethers, polyacrylates, styrene-acrylonitrile copolymers,
polyesters, polyurethanes and cellulose derivatives).
[0080] In other embodiments of the invention, the conformance layer
has two primary components: a ductile thermoplastic polymer and a
nonreinforcing magnetic mineral particulate. Preferably, the
thermoplastic polymer is a polyolefin. These binders are described
generally in U.S. Pat. No. 5,194,113.
[0081] Magnetic Particles
[0082] The most likely choice of magnetic material is a composite
of particles of a permanent magnetic material dispersed in a matrix
of an organic binder. Many types of magnetic particles capable of
being remanently magnetized are known to those familiar with the
magnetic materials art.
[0083] The major axis length of such particles (defined as the
maximum length in any direction) suitable for use in this invention
ranges from about 1 millimeter down to about 10 nanometers. The
preferred range is from about 200 micrometers down to about 0.1
micrometer. The saturation magnetization of the magnetic particles
can range from about 10 to about 250 emu/g (electromagnetic
units/gram), and is preferably greater than 50 emu/g. The
coercivity of such particles can range from about 100 to about
20,000 oersteds, more preferably ranging from about 200 to about
5000 oersteds. Particles with coercivities less than about 200
oersteds are too easily accidentally demagnetized, while particles
with coercivities greater than 5000 oersteds require relatively
expensive equipment to magnetize fully.
[0084] One class of high-performance permanent magnet particles are
the rare earth-metal alloy type materials. Examples of the
incorporation of such particles into a polymeric binder include
U.S. Pat. No. 4,497,722, which describes the use of samarium-cobalt
alloy particles, and European Patent Application No. 260,870, which
describes the use of neodymium-iron-boron alloy particles. Such
particles are not the most preferred for this application, because
the alloys are relatively costly; the alloys may experience
excessive corrosion under conditions of prolonged outdoor exposure;
and the coercivity of such alloys is typically greater than 5000
oersteds.
[0085] Many other types of metal or metal-alloy permanent magnet
particles could be used, but are not the most preferred. They
include Alnico (aluminum-nickel-cobalt-iron alloy), iron,
iron-carbon, iron-cobalt, iron-cobalt-chromium,
iron-cobalt-molybdenum, iron-cobalt-vanadium, copper-nickel-iron,
manganese-bismuth, manganese-aluminum, and cobalt-platinum
alloys.
[0086] Other magnetic materials are of the class of stable magnetic
oxide materials known as the magnetic ferrites. One particularly
preferred material is the hexagonal phase of the magnetoplumbite
structure commonly known as barium hexaferrite, which is generally
produced as flat hexagonal platelets. Strontium and lead can
substitute in part or completely for the barium, and many other
elements can partially substitute for the iron. Thus strontium
hexaferrite is also a preferred material. Another class of
preferred materials is the cubic ferrites, which are sometimes
produced as cubic particles, but more often as elongated
needle-like, or acicular, particles. Examples include magnetite
(Fe.sub.3O.sub.4), magnemite or gamma ferric oxide
(gamma-Fe.sub.2O.sub.3), intermediates of these two compounds, and
cobalt-substituted modifications of the two compounds or of their
intermediates. All of these magnetic ferrites are produced in large
quantities at relatively low cost and are stable under conditions
of prolonged outdoor exposure. Their coercivities fall in the most
preferred range of 200 to 5000 oersteds.
[0087] Chromium dioxide is another alternate material which may be
useful as a magnetic particle in the invention due to its low Curie
temperature, which facilitates thermoremanent magnetization
methods.
[0088] The magnetic particles are generally dispersed in the
polymeric matrix at a high loading. The magnetic particles
constitute at least 1 volume percent of the magnetic layer, while
it is difficult to include particles in an amount constituting more
than about 75 volume percent of the material. Preferably, the
magnetic pavement markers have a binder comprising at least 30
volume percent of magnetic particles. A preferred loading range
would be about 30 to 60 volume percent, more preferably from about
45 to about 60 volume percent. To obtain the highest remanent
magnetization, the particles preferably are substantially
domain-size, anisotropic particles, and there preferably is
substantially parallel alignment of preferred magnetic axes of a
sufficient number of the particles so as to make the magnet
material itself anisotropic.
[0089] Ferrites, especially barium, lead, and strontium ferrites,
generally in a roughly plate-like form having preferred magnetic
axes perpendicular to the general planes of the plates, are
preferred as the particulate materials. However, other materials
having permanent magnetic properties, such as iron oxide particles
or such as particles of manganese-bismuth or iron protected against
oxidation, can also be used.
[0090] As is known in the art and referred to above, the
orientation of the magnetic particles may be optimized by
physically orienting (e.g. calendering) the particles.
[0091] For an exemplary array of magnetic pavement elements having
a width of approximately 10 cm, and an average magnetic thickness
layer of about 0.1 cm, the magnetic field is about 10 gauss at the
surface of the article, 5 gauss at a distance of about 5 cm, 2
gauss at a distance of about 10 cm, and 1 gauss at a distance of
about 15 cm. Thus, if the array were underlaid about 10 cm beneath
a traffic-bearing surface, the magnetic field strength at the
traffic-bearing surface would be approximately 2 gauss, which is
believed to be sufficient to be detected by a sensor. Of course,
stronger or weaker magnetic fields may also be produced by the
array of magnetic pavement elements, depending on the materials and
processes used to make the article.
[0092] The array of magnetic pavement markers of the present
invention may be applied to the pavement surface either manually,
or by a machine. The magnetic pavement markers of the present
invention may be installed as part of a pavement surface using any
one of a variety of apparatus, such as a manual dispenser, "behind
a truck" types of dispensers, and "built into a truck" types of
dispensers. For example, U.S. Pat. No. 4,030,958 discloses a
suitable behind a truck type dispenser for applying the articles of
the invention in the form of adhesive-backed tapes to a surface and
U.S. Pat. No. 4,623,280 discloses a manual-tape applicator.
[0093] Guidance Systems
[0094] The invention also provides a system for guiding vehicles or
mobile objects 222 traveling on a roadway 224, through a warehouse,
and the like, general illustrated in FIG. 12. The array of magnetic
pavement markers 226 is applied to the pavement surface 224 as
discussed above. The array of magnetic pavement markers 226 can
then be detected by a sensor system 228 on a vehicle 222 which
drives over the pavement surface 224. A typical sensor system 228
includes a sensor device and a guidance device.
[0095] A number of sensors and transducers are available to convert
the magnetic signal from the magnetic pavement markers of the
invention into an electrical signal suitable for further
processing. Illustrative examples of such sensors include flux-gate
magnetometers, Hall effect sensors, and solid-state
magnetoresistive (MR) sensors.
[0096] A potential problem exists in distinguishing the guidance
signal from magnetic "noise" produced by steel reinforcing bars,
other vehicles, and the like. If the inventive magnetic pavement
markers are magnetized in a regular alternating pattern or in some
"unique" pattern, the magnetic signal will then be periodic with a
frequency proportional to the vehicle's speed. Modern signal
processing techniques can then be used to extract the signal at a
known frequency from the noise.
[0097] Magnetic sensors 228 attached to the vehicle 222 may
determine the field in one, two, or all three directions. The
signal from one sensor or a mathematical combination of two or
three field components may be used to compute a signal that can be
related to lateral distance of a vehicle 222 from the inventive
articles.
[0098] By magnetizing the strip in a more complicated pattern,
additional information can be encoded. For example, information
about the direction and radius of an upcoming curve in the road or
about the slope of an approaching upgrade or downgrade could be
used for feed-forward control of the lateral position and speed of
the vehicle. As part of a vehicle navigation system, location codes
could be given. Illustrative examples of indicating means include
at least one horn, gauge, whistle, electrical stimulation, LCD,
CRT, light, combination of these, and the like. One or more
indicating means may be desired in a particular situation.
[0099] Conformable Carrier Webs
[0100] 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.
[0101] 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.
[0102] 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.
[0103] 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).
[0104] 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.
[0105] 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.
EXAMPLE
[0106] Several strips of 25.4 mm wide (1 inch) and 1.5 millimeters
(0.060 inches) thick Plastiform.TM. magnetic tape with a pressure
sensitive adhesive on one side protected with a release liner
(available from Arnold Engineering Company of Norfolk, Nebr.) were
passed through the gap of a permanent magnet to magnetize the
strips in one direction perpendicularly through the plane of the
strip. Some of the strips were magnetized with the North pole on
the non-adhesive coated side of the strip and some with the North
pole on the adhesive coated side. The strips were then cut
longitudinally to a width of about 12.7 mm (0.5 inch) using
scissors and then again into about 12.7 mm (0.5 inch) square chips
of Plastiform.TM. on adhesive and release liner. The release liner
was removed from the chip and the squares were adhered to a piece
of Reemay 2410 nonwoven scrim (available from Reemay, Inc. located
in Old Hickory, Tenn.) in an array 5 chips wide with a spacing of
about 6.35 mm (0.25 inches) between each square. The array for this
prototype was approximately 10.16 cm (4 inches) in width and about
22.86 cm (9 inches) in length. About 15.24 cm (6 inches) of the
array was arranged so that the North pole of the magnetic chips was
up and the remaining 7.62 centimeter (3 inches) was arranged so
that the North side was down (i.e., toward the scrim). The sheet
was run through a hand laminator to improve the bond between the
pressure sensitive adhesive on the bottom of the magnetic chips and
the scrim to yield an array of magnetic elements interconnected by
a carrier web (i.e., the scrim).
[0107] A 0.127 millimeters (0.005 inches) thick layer of PM-7701
pressure sensitive adhesive (available from Minnesota Mining and
Manufacturing Company) on a release liner (a rubber resin pressure
sensitive adhesive commonly used for pavement marking tape
applications) was laminated to the bottom of the scrim.
[0108] The prototype (or one without the layer of PM7701) could be
useful for underlaying beneath the top surface of a roadway during
its construction to provide a magnetic signal. Also, the array of
magnetic chips could be mounted to the surface of a roadway. The
nonwoven scrim or web provides a convenient low cost carrier for
the magnetic chips. The discrete nature of the chips, rather than a
continuous sheet, allows some movement of the chips relative to one
another to accommodate roughness of the road surface, or, in the
case of an underlay installation, movement during road compaction,
in a way that would not be possible with a continuous sheet of
non-conformable magnetic material. This feature also allows some
movement to accommodate thermal expansion and contraction and
flexural stresses in a road during use.
[0109] In this example, a polymeric Plastifor.TM. magnet was used.
Ceramic, metal or other magnets could also be employed. Other
deformable or conformable carrier webs or scrims could be used as
an alternate to the Reemay scrim. Conformable base sheets used in
pavement marking tape conformance layers could be useful.
[0110] A portion of the conformable mosaic magnetic pavement
marking example prepared above was cut to a size of about 2 by 9
piece array with a magnetic transition such that 4 rows of chips
had magnetic south facing up and 5 rows had magnetic north facing
up from the plane of the sheet. The liner was stripped from the
lower adhesive layer and the adhesive side of the article was
laminated to a piece of asphalt pavement and pressed in place by
hand using a rubber roller. While the individual magnetic pieces
did not significantly conform to the roughness of the asphalt, the
sheet as a whole adapted itself to accommodate the surface
roughness.
[0111] A Magnaprobe (small freely rotating bar magnet suspended in
a gimbal mounting--available from Cochranes of Oxford Ltd.,
Leafield, Oxford OX85NT, England) was passed over the conformable
mosaic magnetic pavement marking attached to the asphalt. The
freely rotating magnet reversed its direction of orientation as it
was passed over the boundary defining the change in direction
(north up/south up) in the magnetic signal in the marking.
[0112] Patents and patent applications cited herein, including
those cited in the Background, are 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 described above
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
thereto.
* * * * *