U.S. patent application number 10/255421 was filed with the patent office on 2003-04-10 for pavement markings comprising synthetic polymeric fibers.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Helland, Randall H., Ng, Chin Yee.
Application Number | 20030069358 10/255421 |
Document ID | / |
Family ID | 26760916 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030069358 |
Kind Code |
A1 |
Helland, Randall H. ; et
al. |
April 10, 2003 |
Pavement markings comprising synthetic polymeric fibers
Abstract
The invention relates to thermoplastic pavement marking
compositions comprising synthetic polymeric fibers.
Inventors: |
Helland, Randall H.; (Lake
Elmo, MN) ; Ng, Chin Yee; (Maplewood, MN) |
Correspondence
Address: |
Attention: Carolyn A. Fischer
Office of Intellectual Property Counsel
3M Innovative Properties Company
P.O. Box 33427
St. Paul
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
26760916 |
Appl. No.: |
10/255421 |
Filed: |
September 26, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10255421 |
Sep 26, 2002 |
|
|
|
10078771 |
Feb 18, 2002 |
|
|
|
60325279 |
Sep 27, 2001 |
|
|
|
Current U.S.
Class: |
525/165 |
Current CPC
Class: |
E01F 9/578 20160201;
C08K 7/08 20130101; Y10T 428/252 20150115; C08L 101/00 20130101;
E01F 9/512 20160201 |
Class at
Publication: |
525/165 |
International
Class: |
C08L 067/02 |
Claims
What is claimed is:
1. A pavement marking composition comprising synthetic polymeric
fibers dispersed within a thermoplastic-based polymeric material,
wherein the synthetic polymeric fibers have a melt point greater
than the polymeric material.
2. The pavement marking sheet of claim 1 wherein the fibers are
randomly dispersed within the polymeric material.
3. The pavement marking composition of claim 1 wherein the
synthetic polymeric fibers have a melt point greater than
400.degree. F.
4. The pavement marking composition of claim 1 wherein the
synthetic polymeric fibers are selected from the group comprising
polyester, polyamide, polypropylene, tetrafluoroethylene and
copolymers thereof.
5. The pavement marking composition of claim 1 wherein said
composition is provided as a sheet having a thickness ranging from
about 0.25 mm to about 5 mm, said sheet having a downweb direction
and crossweb direction.
6. The pavement marking sheet of claim 5 wherein the sheet is
conformable.
8. The pavement marking sheet of claim 5 wherein the downweb
direction and crossweb direction has a tear ratio that ranges from
0.5 to 2 when measured according to ASTM 1938.
9. The pavement marking sheet of claim 5 wherein the downweb
direction and crossweb direction has a tear ratio that ranges from
0.7 to 1.3 when measured according to ASTM 1938.
10. The pavement marking composition of claim 1 wherein the
synthetic polymeric fiber ranges from about 0.2 weight-% to about 2
weight-%.
11. The pavement marking of claim 1 wherein the polymeric material
is selected from the group comprising alkyd thermoplastic and
hydrocarbon thermoplastic.
12. The pavement marking of claim 11 wherein the polymeric material
is a hydrocarbon thermoplastic.
13. The pavement marking of claim 12 wherein the polymeric material
comprises an acid containing copolymer of ethylene.
14. The pavement marking composition of claim 1 wherein the
composition comprises other ingredients selected from the group
comprising reflective elements, extender resins, fillers, and
pigments.
15. The pavement marking of claim 1 wherein the composition
comprises magnetic particles.
16. The pavement marking composition of claim 1 wherein the
synthetic polymeric fibers have a fiber length of at least 6
mm.
17. The pavement marking composition of claim 1 wherein the
synthetic polymeric fibers have a fiber length of at least 10
mm.
18. A method of making a pavement marking comprising: providing a
composition comprising a thermoplastic-based polymeric material and
synthetic polymeric fibers; heating the composition to a
temperature wherein the composition is extrudeable and the
synthetic polymeric fibers are unmelted; and extruding the
composition on a pavement surface.
19. A method of making a pavement marking comprising: dry blending
a thermoplastic polymer and synthetic polymeric fibers; melting and
mixing the blend; and extruding the blend onto a pavement surface
at a temperature less than the melt point of the synthetic
polymeric fibers.
Description
RELATED APPLICATIONS
[0001] This application claims priority from U.S. provisional
patent application serial No. 60/325279 filed Sep. 27, 2001 and
U.S. patent application Ser. No. 10/078771 filed Feb. 18, 2002.
FIELD OF THE INVENTION
[0002] The invention relates to thermoplastic pavement marking
compositions comprising synthetic polymeric fibers.
BACKGROUND OF THE INVENTION
[0003] Pavement markings are typically used to delineate the
boundaries for lanes of traffic on a roadway. The marking may
extend continuously, such as along the outermost boundaries of the
driving lanes, or intermittently, such as between lanes.
[0004] U.S. Pat. No. 4,490,432 relates to a pavement-marking sheet
material which comprises a non-crosslinked elastomeric precursor
such as acrylonitrile-butadiene polymer; a thermoplastic polymer
such as polyethylene which reinforces the sheet material, e.g., by
orientation of the thermoplastic polymer so that the calendered
product exhibits greater strength downweb than crossweb; and a
particulate inorganic filler, which preferably includes
platelet-type fillers such as talc, mica, or magnesium
silicate.
[0005] U.S. Pat. No. 5,194,113 (Lasch et al.) relates to
thermoplastic-based pavement marking sheets. The marking sheets
employ a conformant composite material including: polyolefin a
nonreinforcing mineral particulate; and/or a thermoplastic upper
surface. Preferably, the sheet's thermoplastic upper surface is
embedded with reflective elements and/or skid-resistant particles.
A solventless process of embedding particles in thermoplastic
pavement marking sheets is disclosed. Processes for preparing
marking sheets are also disclosed. Conformant pavement marking
sheets which may be applied in cooler conditions are also
disclosed.
[0006] Thermoplastic pavement marking materials are 100% solids
compounds typically containing a thermoplastic polymeric material,
pigments, filler and glass spheres. Hot-applied thermoplastic is
prepared for road deposition in a melting apparatus where granular
or block material is introduced and heated until the material
liquefies at temperatures in excess of 400.degree. F. (204.degree.
C.). Alkyd thermoplastics tend to be preferred over hydrocarbon
thermoplastic compositions in view of such compositions being oil
impervious. Thermoplastic pavement markings have had limited
commercial success in cold climates due to the tendency of such
markings to shatter from the roadway upon impact with a
snowplow.
SUMMARY OF THE INVENTION
[0007] It has since been discovered that pavement marking sheets
having a greater strength in one direction (e.g. downweb) versus
the other direction (e.g. crossweb) tend to result in reduced
conformability and reduced shear strength. Accordingly, industry
would find advantage in pavement marking compositions that exhibit
a similar downweb and crossweb tear. Further, industry would also
find advantage is thermoplastic pavement markings having improved
cold temperature performance.
[0008] The Applicants have discovered that thermoplastic pavement
markings can be improved by the addition of synthetic polymeric
fibers.
[0009] In one embodiment the invention relates to a pavement
marking composition comprising synthetic polymeric fibers dispersed
within a thermoplastic-based polymeric material. The synthetic
polymeric fibers have a melt point greater than the polymeric
material such that the fibers retain their fiber form.
[0010] In another embodiment the invention relates to a method of
making a pavement marking comprising providing a composition
comprising a thermoplastic-based polymeric material and synthetic
polymeric fibers, heating the composition to a temperature wherein
the composition is extrudeable and the synthetic polymeric fibers
are unmelted; and extruding the composition on a pavement
surface.
[0011] In another embodiment the invention relates to a method of
making a pavement marking comprising dry blending a thermoplastic
polymer and synthetic polymeric fibers, melting and mixing the
blend; and extruding the blend onto a pavement surface at a
temperature less than the melt point of the synthetic polymeric
fibers. In each of these embodiments, the fibers are preferably
randomly dispersed within the polymeric material throughout the
sheet. Preferred polymeric fiber materials typically have a melt
point greater than about 400.degree. F. (204.degree. C.) such as in
the case of polyester, polyamide, polypropylene and
tetrafluoroethylene. In a preferred embodiment the marking
composition is sufficiently conformable such that the downweb
direction and crossweb direction has a tear ratio ranging from
about 0.7 to 1.3 when measured according to ASTM 1938. In another
preferred embodiment that composition exhibits good cold
temperature properties such that the composition does not shatter
into pieces upon impact at cold temperatures. The amount of
synthetic polymeric fibers preferably ranges from about 0.2
weight-% to about 2 weight-%. The composition optionally comprises
other ingredients selected from the group comprising reflective
elements, extender resins, fillers (e.g. magnetic fillers), and
pigments. The synthetic polymeric fibers preferably have a fiber
length of at least 6 mm.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] The pavement marking composition of the invention comprises
synthetic polymeric fibers incorporated into a thermoplastic
polymeric material. The synthetic polymeric fibers may be
thermoplastic or thermosetting. If the synthetic polymeric fibers
are comprised of a thermoplastic material, such material has a melt
point greater than the thermoplastic polymeric material the fibers
are incorporated within. This insures, that the synthetic polymeric
fibers do not substantially melt and thus retain their fiber form.
Thus, the synthetic polymeric fibers are dispersed randomly
three-dimensionally throughout the polymeric material in the
finished marking.
[0013] The composition of the synthetic polymeric fibers is chosen
based on the melt point of the intended thermoplastic-based
polymeric material and/or the intended processing temperature.
Typically, thermoplastic-based polymeric materials have a softening
point or melt point ranging from about 240.degree. F. (116.degree.
C.) to about 450.degree. F. (232.degree. C.). For improved cold
temperature properties, it is surmised to employ synthetic
polymeric fibers that don't fracture at cold temperatures such as
fibers comprised of a material having a low glass transition
temperature (Tg) as measured according to Diffferential Scanning
Calorimetry (DSC). For moderate climates, the Tg of the synthetic
polymer fiber material is preferably less than 30.degree. F.
(-1.degree. C.), for colder climates, the Tg is preferably less
than 0.degree. (-18.degree. C.), for even colder climate the Tg is
preferably less than -20.degree. F. (-29.degree. C.), and more
preferably less than -40.degree. F. (-40.degree. C.).
[0014] Suitable synthetic polymeric fiber materials include such
polymers as polyolefins, vinyl copolymers, polyethers (e.g.
polyamides), polyacrylates (i.e. acrylic polymers),
styrene-acrylonitrile copolymers, polyesters, polyurethanes,
tetrafluoroethylene, and copolymers thereof. The synthetic
polymeric fiber is preferably comprised of polyester,
polypropylene, tetrafluoroethylene, and copolymers thereof.
Although the fiber length may range from about 3 mm to 40 mm, the
synthetic polymeric fibers preferably have a fiber length of at
least 6 mm (6000 microns, 0.24") and more preferably a length of at
least 10 mm.
[0015] The pavement marking composition comprising the synthetic
polymeric fibers within a polymeric material in combination with
other optional ingredients such as retroreflective elements (e.g.
glass beads), filler, pigment, etc. preferably exhibits certain
properties. In one aspect the pavement marking composition is
conformable. The ability of the marker to conform to gross defects,
such as deep cracks or other depressions commonly present on a
pavement surface, can provide a substantial durability advantage
over preformed adhesive tapes. In general, the composition of the
invention has a downweb and crossweb tear strength of at least 2.5
kilograms per square centimeter at 25.degree. C. when measured
according to ASTM 1938. Further, the ratio of the downweb average
tear strength of the pavement marking sheet to crossweb tear
strength preferably ranges from 0.5 to 2 and more preferably ranges
from 0.7 to about 1.3.
[0016] Alternatively or in addition thereto, the pavement marking
exhibits improved cold temperature properties. The cold temperature
properties can be evaluated by extruding the composition into a 4
inch wide (101 mm) strip having a thickness of 1 to 2 mm. The sheet
can then be conditioned at the temperature of interest for 4 hours.
Immediately after removing the sheet from the conditioning chamber
the sheet is struck with a hammer. Poor cold temperature properties
is indicated by the sheet breaking into pieces. Good cold
temperature properties is indicated by the sheet remaining intact
in a single piece, although cracking may be evident. Upon
inspection one can typically see the fibers in the cracks.
[0017] The pavement marking composition generally comprises at
least 0.1 weight-% synthetic polymeric fiber, but no more than
about 20 weight-%. Typically, the amount of synthetic polymeric
fiber is less than 10 weight-%, preferably less than 5 weight-% and
more preferably less than 2 weight-%, and even more preferably
about 1 weight-% or less. The amount of synthetic polymeric fiber
is preferably at least 0.2 weight-% and more preferably at least
about 0.3 weight-%. The amount of polymeric material preferably
ranges from about 10 weight-% to about 85 weight-%. The pavement
marking composition may optionally comprise up to about 75 weight-%
of other ingredients selected from reflective elements (e,g, glass
beads), extender resins, fillers and pigment. Further, in addition
to the synthetic polymeric fibers, the pavement marking composition
may further comprise other fibers such as inorganic fiber or other
synthetic polymeric fibers, provided the presence of such does not
detract from the intended properties. Preferably, the pavement
marking composition is free of glass fibers.
[0018] The thermoplastic polymeric material provides a viscoelastic
character, which permits absorption of the forces and pressures of
wheeled road traffic without creating internal forces that tend to
remove the marking from the roadway. Typically, a hydrocarbon or
alkyd thermoplastic material is employed. Preferred hydrocarbon
thermoplastic materials include acid containing ethylene
copolymers. Representative acid containing ethylene copolymers
include ethylene acrylic acid (EAA) copolymers and ethylene
methacrylic acid (EMAA) copolymers, and mixtures of EAA and EMAA;
as well as ionically cross-linked EMAA. Alternative thermoplastic
materials, although less preferred for the topmost layer, include
ethylene n-butyl acrylate (EnBA), ethylene vinyl acetate (EVA) and
blends thereof, as well as polyolefins. Particularly preferred
thermoplastic materials include EMAA polymer commercially available
from the E. I. Dupont de Nemours and Company (Dupont) of
Wilmington, Del. under the trade designation "NUCREL" and ionically
cross-linked ethylene methacrylic acid (EMAA) ionomers available
from Dupont under the trade designation "Surlyn". Other suitable
thermoplastic materials suitable for thermoplastic pavement
markings as described in U.S. Pat. No. 6,217,252 (Tolliver);
incorporated herein by reference. Although this reference relates
to flame-sprayed pavement markings, the polymeric materials (i.e.
binders) described therein would also be suitable for conventional
thermoplastic-based pavement marking applications methods.
Polymeric materials described therein include acrylic polymers and
copolymers, olefin polymers and copolymers preferably having a
number average molecular weight greater than about 10,000, urethane
polymers and copolymers, curable epoxy resins, ester polymers and
copolymers, and blends thereof. For improved cold temperature
performance, it is surmised that the pavement marking is based on a
thermoplastic material having a low glass transition temperature as
previously described with regard to the fiber material.
[0019] Fillers are generally included in the composition at least
for the purpose of enhancing the visibility of the exposed top
layer. However, fillers also advantageously enhance properties such
as reinforcement, extending, surface hardness, and abrasion
resistance. Platelet fillers, i.e., fillers having a plate-like
shape, such as magnesium silicate, talc, or mica, have been found
to contribute the best abrasion resistance and downweb strength
properties. Also the platelet fillers make the sheet material
harder, which contributes to maintaining a white appearance on the
roadway. In addition, the platelet fillers have a high ratio of
surface area to volume, which enhances their reinforcing ability.
Magnetite particles such as strontium platelet fillers may also be
employed. Such platelets become aligned in a north south
orientation such that high magnetic strength can be achieved for
magnetic lane awareness markings. Such markings are described in
greater detail in copending U.S. patent application Ser. No.
10/039654 filed Dec. 31, 2001; incorporated herein by reference.
Other fillers, such as needle-type or bead-type fillers, may be
employed instead of or in addition to low concentrations of
platelet fillers. The amount of filler included in the sheet
material of the invention varies with the kind of filler used.
Preferably, at least 3 weight-% of platelet fillers are used. With
lower amounts of synthetic polymeric fibers, higher amounts of
filler are typically desired though fillers in an amount of more
than 50 weight-% tend to stiffen the product excessively.
Preferably, the amounts of filler ranges from about 5 and about 20
weight-%.
[0020] Retroreflective elements (e.g. transparent microspheres,
cube-corner particles derived from ground sheeting) or and
skid-resisting particles (e.g. sand particles) are also preferably
included in the pavement marking composition at concentration up to
about 45 weight-% to provide reflectivity at night and to give the
sheet material skid-resisting qualities. Preferably, about 25
weight-% to about 40 weight-% reflective glass beads are dispersed
throughout the thickness of the pavement marking sheet. An exterior
layer of such particles may be provided on the top of the sheet
material, partially embedded in the sheet material and partially
protruding from the sheet material, to provide immediate
reflectivity and skid-resistance; and other particles may be
embedded in the sheet material to become exposed as the sheet
material is worn away. The particles may be held in the partially
protruding position by use of a support film adhered to the sheet
material of the invention, for example, as taught in column 4 of
U.S. Pat. No. 4,988,541; incorporated herein by reference.
[0021] Typically the synthetic polymeric fibers are dry blended
with the polymeric material and other optional ingredients forming
a relatively homogeneous mixture. The mixture can be supplied in
either a granular form or is the form of a block. Various apparatus
are commercially available for receiving such forms. Such apparatus
heat and agitate the thermoplastic composition until melted and
then transfer the melted composition into a screed, ribbon or spray
device wherein it is then shaped into the specified width and
thickness as a line, legend or symbol. When applied on asphaltic
pavement, the thermoplastic marking material typically forms a
sufficient thermal bond via heat fusion. When applied to Portland
concrete cements or on oxidized or aged asphaltic paved surfaces,
application of a primer is recommended in order that a sufficient
mechanical bond is achieved.
[0022] Following application, the marker should be allowed to cool
so that the solidified binder material becomes tack-free. Adequate
adhesion of the marker to the transportation surface can be
evaluated in a variety of ways. Exposure to normal environmental or
traffic conditions for a period of time, e.g., one day or more,
will give the most reliable test results. However, relatively
simple tests such as a boot scuff test or attempting to remove the
marker with a putty knife will often be sufficient to determine
whether marker has adhered adequately to the transportation
surface. In cases where the marker has been applied to asphalt, it
may be necessary to allow the asphalt to cool for several hours or
more before evaluating adhesion. Asphalt can retain significant
heat from the preheating step and may undergo cohesive failure
within the asphalt if marker adhesion is tested too soon after the
marker has been applied.
[0023] Similarly, the composition can be extruded onto a release
paper forming a sheet for the purpose of evaluating properties such
as conformability and cold temperature properties of the pavement
marking composition. Further, the composition may be employed in a
pavement marking tape as a conformance layer, such as described in
U.S. Pat. No. 5,194,113 (Lasch et al.).
[0024] Conformability of a marking can be evaluated in other ways
as well. 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 the
sheet, and observe the degree to which the surface has been
replicated in the sheet. Another assessment of the conformance of a
marking tape may be obtained as follows. First, the force required
to deform the sheet material a suitable amount is measured. Second,
a portion of the induced strain is relieved. Finally, the
retractive force remaining in the material at the reduced strain
level is measured. A specific example of this process would be to
deform a sample to 115% of its original length by stretching the
sample at a strain rate of 0.05 sec.sup.-1 and measuring the stress
at 115% deformation, release the strain at the same rate, allow the
material to return to 110% of its original length, and measure the
retractive force. This measurement may be made using a standard
tensile testing apparatus such as, for example, the servohydraulic
tensile testers available from MTS Systems Corporation of
Minneapolis, Minn. Preferred comformable materials exhibit a force
to deform the sample to 115% of its original length of less than 35
NT per cm width (20 lbs per inch width), and a retractive force at
a subsequent 110% deformation of less than 14 NT per cm width (8
lbs per inch width), although lesser forces are even more
preferred. Other measures of conformability are described in U.S.
Pat. No. 5,194,113, and may also be used in conjunction with the
pavement marking tapes of the present invention to evaluate
conformance of a sheet material to an irregular surface.
[0025] The pavement marking preferably has good abrasion resistance
as may be indicated by a modified Taber abrasion test. The test
uses an H-22 Taber abrader wheel, with a one kilogram weight on the
wheel. The test specimen is held under water, and the abrader wheel
passed over the specimen for 500 cycles. Sheet material of the
invention generally exhibits a loss of no more than about 5 grams
in this test.
[0026] Objects and advantages of the invention are further
illustrated by the following examples, but the particular materials
and amounts thereof recited in the examples, as well as other
conditions and details, should not be construed to unduly limit the
invention. All percentages and ratios herein are by weight unless
otherwise specified.
EXAMPLES
[0027] Table I, as follows, identifies the chemical description,
trade designation, supplier and location for each of the
ingredients employed in the examples.
1TABLE I Chemical Description Trade Designation Supplier Location
Ethylene Acrylic "AC 5120" Allied Signal Morristown, NJ Acid
Copolymer TiO.sub.2-Pigment "TI PURE 960" DuPont Wilmington, DE
Magnetic Filler "UHE-9" Fermag Edison. NJ Industries Polyester
Fiber (1/4") "6-3025-1/4" Mini Fibers Johnson City, (1/2")
"6-3025-1/2" Inc. TN Glass Fiber "731A-16-W-1/4") Owens Corning
Toledo, OH
[0028] Table II as follows sets forth the weight percentage of each
ingredient employed in Comparative Example A, and Examples 1-2.
2TABLE II Comparative Example 1 Example 2 Example A Trade
Designation 81.9 81.9 81.9 "AC 5120" 17.7 17.7 17.7 "TI PURE 960"
0.4 -- -- "6-3025-1/4" -- 0.4 -- "6-3025-1/2" -- -- 0.4
"731A-16-W-1/4"
[0029] The materials were dry blended in gallon jars. The mixture
was heated on a hot plate until the temperature reached 305.degree.
F. (152.degree. C.) and poured into a heated (300.degree.
F./152.degree. C.) extrusion head that delivers the mixture unto
silicone release paper forming a 1-2 mm thick 4"(101 mm) wide
tape.
[0030] For each of the examples the tear strength was evaluated
according to ASTM D1938. Table III, as follows sets forth the test
results:
3 TABLE III Comparative Example 1 Example 2 Example A Down Web
Average 2.49 2.26 3.13 Tear Lb (kg) (5.48) (4.97) (6.89) Cross Web
Average 2.39 2.98 1.89 Tear Lb (kg) (5.26) (6.56) (4.16) Ratio-Down
Web 1.04 0.76 1.65 Tear/Crossweb Tear
[0031] The results show that the ratio of down web tear to crossweb
tear of the synthetic polymeric fiber containing extruded sheet is
considerably closer to 1 than the composition comprising glass
fibers. Further the 1/2" synthetic polymeric fiber contributes a
higher crossweb tear strength, particularly in comparison with the
glass fibers.
[0032] Examples 1 and 2 and Comparative Example A were conditioned
for 4 hours at -40.degree. F. The sample were removed from the
freezer and struck with a hammer. Comparative Example A shattered
into several pieces. Examples 1 and 2 cracked, yet the pieces did
not separate along the crack.
[0033] Prepared in the same manner, Table III as follows sets forth
the weight percentage of each ingredient employed in Comparative
Example B, and Examples 3-5.
4TABLE III Comparative Example 3 Example 4 Example 5 Example B
Trade Designation 39.42 39.26 39.18 39.4 "AC 5120" 17.7 17.7 17.7
"UHE-9" 0.394 0.785 .98 -- "6-3025-1/4"
[0034] The cold temperature properties of these samples were
evaluated in the same manner at -10.degree. F. Comparative Example
B shattered; whereas Examples 3-5 cracked yet remained intact.
* * * * *