Reinforced pavement-marking sheet material

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 tensile strength downweb than crossweb; and a particulate inorganic filler, which preferably includes platelet-type fillers such as talc, mica, or magnesium silicate.

BACKGROUND OF THE INVENTION 
The present invention provides a new pavement-marking sheet material of the 
general type described in U.S. Pat. No. 4,117,192. Such sheet material 
comprises a polymeric material that could be crosslinked to form an 
elastomer, but which is not crosslinked in the sheet material and thereby 
provides desired viscoelastic properties. A blend of this material with 
other polymeric materials and inorganic fillers has been found to provide 
properties that give long-lasting pavement markings--good conformability 
to a roadway surface, abrasion resistance, tensile and tear strength, etc. 
Despite its well established utility, the described sheet material is 
deficient for some uses because asbestos fibers constitute a large 
proportion of the inorganic fillers in the sheet material. Asbestos fibers 
contribute importantly to the desired properties of the sheet material, 
but for toxicity reasons, use of such fibers has been foreclosed under 
many circumstances. 
The new sheet material eliminates asbestos fibers, and does it without 
sacrificing desired properties of the sheet material. To the contrary, 
sheet material of the invention offers superior properties--superior 
abrasion resistance, higher tensile strength and modulus, and improved 
whiteness; and also the composition may be processed into sheet form more 
readily. 
Briefly, these advantages are obtained with a composition that comprises 
100 parts of non-crosslinked elastomer precursor.sup.1 : at least 5 parts 
of a thermoplastic reinforcing polymer which is dispersed in the elastomer 
as a separate phase (i.e., because of insolubility or immiscibility with 
the other polymeric ingredients) and softens at a temperature between 
about 75.degree. C.; and 200.degree. C.; and a particulate inorganic 
filler dispersed in the composition. This composition is processable on 
calendering rolls into a thin sheet material, generally between about 1/4 
and 3 millimeters in thickness. 
FNT .sup.1 "Elastomer-precursor" is used herein to describe a polymer which can 
be crosslinked, vulcanized, or cured to form an elastomer. "Elastomer" is 
used to mean 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. 
The separate-phase nature of the reinforcing polymer is considered 
desirable, in that it is believed that the polymer becomes oriented during 
the calendering operation and reinforces the sheet material. Such a 
reinforcement is indicated by the fact that the tensile strength of the 
sheet material is significantly stronger in the downweb direction (i.e., 
in the direction of calendering) than in the crossweb, or transverse, 
direction. 
Preferably the reinforcing polymer comprises polyolefin, especially 
polyethylene. An extender resin such as halogenated paraffin, which is 
soluble in the non-crosslinked elastomer precursor, is also preferably 
included in the composition. Also, platelet fillers, such as magnesium 
silicate, are preferred. 
An earlier patent, U.S. Pat. No. 4,069,281, teaches a pavement-marking 
sheet material which includes low-molecular-weight polyethylene together 
with regenerated nitrile rubber and chlorobutadiene rubber (neoprene). 
However, when sheet material as described in this patent is made and 
calendered, no orientation or downweb reinforcement is detected. The sheet 
material is as strong in the crossweb direction as it is in the downweb 
direction. Apparently the low-molecular-weight polyethylene does not form 
an oriented reinforcement in the manner of the reinforcing polymer in 
sheet material of the invention. The prior art composition is low in 
tensile and tear strength, especially at elevated temperatures such as may 
be experienced in summer-time application of pavement markings; and it is 
difficult to process the composition in an internal mixer and calender it. 
Also, the sheet material is quite soft, making it more susceptible to dirt 
pick up, and glass microspheres tend to be pushed into the sheet material 
by road traffic, whereupon the microspheres are embedded and reflection is 
reduced. 
DETAILED DESCRIPTION 
Non-crosslinked elastomer precursor is used in pavement-marking sheet 
material of the invention to provide 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. Acrylonitrile-butadiene polymers are especially desirable 
elastomer precursors because they offer a high degree of oil resistance. 
Other useful non-crosslinked elastomer precursors which offer good oil 
resistance include neoprene and polyacrylates. Natural rubber and 
styrene-butadiene polymers may also be used. Extender resins, preferably 
halogenated polymers such as chlorinated paraffins, but also hydrocarbon 
resins or polystyrenes, are preferably included with the non-corsslinked 
elastomer precursor ingredients, and are miscible with, or form a single 
phase with, the elastomer precursor ingredients. The latter preferably 
account for at least 50 weight-percent of the polymeric ingredients in a 
composition of the invention. 
To achieve desired mixing of the thermoplastic reinforcing polymer and the 
other ingredients, the reinforcing polymer should soften at a temperature 
between about 75.degree. C. and 200.degree. C. Useful thermoplastic 
reinforcing polymers include polyolefins, vinyl copolymers, polyethers, 
polyacrylates, styrene-acrylonitrile copolymers, polyesters, polyurethanes 
and cellulose derivatives. Polyolefins act as a plasticizer during the 
mixing operation, and lower the energy required to complete the mixing, 
which is one reason they are preferred. To achieve desired reinforcement, 
the polymer should generally be extrudable as a self-supporting 
stretchable continuous film, which is typified by low-density 
polyethylenes having molecular weights of 75,000-100,000 or more and 
linear low-density polyethylene (i.e., low density polyethylene, which has 
short-chain polymer branching, but having reduced long-chain polymer 
branching) and high-density polyethylenes having molecular weights of 
20,000 or more. 
Another advantage of polyolefins, especially polyethylene, is that they do 
not absorb or otherwise pick up dirt as fast as many other polymers, with 
the result that a pavement-marking composition of the invention can remain 
whiter and cleaner longer than prior-art pavement-marking materials. 
At least 5 parts of thermoplastic reinforcing polymer, but no more than 100 
parts, are generally included for each 100 parts of non-crosslinked 
elastomer precursor in a sheet material of the invention, and preferably 
between about 10 and 50 parts are included. The proportions can be varied 
within the stated ranges depending upon the amount of other ingredients 
included in the composition, especially the amount and kind of fillers 
included. 
Fillers are generally included in the composition at least to color it but 
preferably also to add other 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, are 
preferred, because they have been found to give the best abrasion 
resistance and downweb strength properties. The platelets become oriented 
during the calendering procedure, which contributes especially to the 
abrasion resistance and downweb properties of the sheet product. 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. 
Other fillers, such as needle-type or bead-type fillers, may be included 
instead of or in addition to the platelet fillers, but they are less 
desired because of their lower surface area per unit volume. 
The amount of filler included in sheet material of the invention varies 
with the kind of filler used. Preferably at least 10 parts of platelet 
fillers are used per 100 parts of non-crosslinked elastomer-precursor. 
With lower amounts of thermoplastic reinforcing filler, higher amounts of 
filler are desired, though platelet fillers in an amount more than 150 
parts per 100 parts of elastomer-percursor tend to stiffen the product 
excessively. Best results have been achieved with amounts of platelet 
fillers between about 50 and 100 parts. 
Transparent microspheres and skid-resisting particles are also generally 
included in a sheet marterial of the invention to provide reflectivity at 
night and to give the sheet material skid-resisting qualities. 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 sheet 
material of the invention, for example, as taught in U.S. Pat. No. 
4,117,192. 
After mixing, the ingredients are processed on calendering rolls where they 
form a smooth band and are processed into thin sheets of the desired 
thickness. Generally sheets are formed having a thickness of at least 
about 1/4 millimeter, and preferably at least about 1 millimeter, but 
generally the sheets are less than about 5 millimeters thick, and 
preferrably less than 3 millimeters thick. 
As previously indicated, the calendered sheet material is found to have a 
significantly greater tensile strength downweb than it does crossweb, 
i.e., its downweb tensile strength is at least about 20-25 percent higher 
than its crossweb tensile strength, apparently due to orientation of the 
reinforcing polymer. A high downweb tensile strength is desirable for ease 
of processing and for ease of application, but a lower crossweb tensile 
strength may allow the sheet material to have better conformability to a 
roadway surface. Sheet material of the invention generally has a downweb 
tensile strength of at least 10 kilograms per square centimeter at 
25.degree. C., and preferably at least 25 kilograms per square centimeter 
downweb. 
The sheet material also 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. 
Other ingredients may also be included in sheet material of the invention, 
such as reinforcing fibers, pigments, and various additives. 
Pavement-marking compositions of the invention are especially useful in 
sheets or tapes having an embossed top surface to improve reflectivity and 
other properties. Such an embossed sheeting is described in U.S. Pat. No. 
4,388,359 and other embossed forms of pavement marking sheet material are 
also taught in the art.

The invention will be further illustrated by the following examples. 
EXAMPLE 1 
The ingredients shown in Table I were mixed in an internal mixer, such as a 
Banbury mixer, where they reached a temperature of approximately 
150.degree. C. The material was then cooled and calendered into a sheet 
about one millimeter thick. 
TABLE I 
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Material Parts by Weight 
______________________________________ 
Acrylonitrile-butadiene 
100 
non-crosslinked elastomer precursor 
("Hycar 1022" supplied by 
B. F. Goodrich) 
Chlorinated paraffin 70 
("Chlorowax 70-S" supplied 
by Diamond Shamrock) 
Chlorinated paraffin 5 
("Chlorowax 40") 
Fibers of high-density 
20 
polyethylene having a molecular 
weight ranging between 30,000 and 
150,000 
Titanium dioxide pigment 
130 
Talc platelet filler particles 
100 
averaging 2 micrometers in size and 
having a surface area of 25 square 
meters per gram 
Transparent glass microspheres 
280 
averaging about 100 micrometers in 
diameter and having an index of 
refraction of 1.5 
Spherical silica reinforcing 
20 
filler ("Hisil 233" supplied by 
PPG Industries) 
Stearic acid release agent 
3.5 
Ultramarine Blue 0.5 
Chelator ("Vanstay SC" supplied 
0.5 
by Vanderbilt) 
______________________________________ 
The resulting sheet material was tested for tensile strength, abrasion 
resistance in the test described above, and Shore A hardness. Similar 
measurements were made on a sheet material ("First Prior Art Sheet 
Material" in the table below) as described in the Example in column 4 of 
U.S. Pat. No. 4,069,281, using Hycar 1022 for the "regenerated nitrile 
rubber" and low-density polyethylene having a molecular weight of about 
5000 as the "low-molecular weight" polyethylene, and on sheet material 
having the composition described in U.S. Pat. No. 4,117,192, table 
bridging columns 4 and 5 ("Second Prior Art Sheet Material"). Results are 
presented in Table II. 
TABLE II 
______________________________________ 
First Second Sheet 
Prior Art 
Prior Art 
Material 
Sheet Sheet of the 
Material 
Material Invention 
______________________________________ 
Abrasion loss 1.8 3 0.7 
Tensile strength (kilograms 
per square centimeter) 
Downweb 5.2 18 70 
Crossweb 5.3 12.6 30 
Shore A hardness 
66 88 88 
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EXAMPLES 2 TO 14 
Following the procedures of example 1, a wide variety of pavement-marking 
compositions were prepared in which different classes of polymeric 
materials were chosen as the thermoplastic reinforcing polymer. Table III 
summarizes processing conditions and test properties for these 
pavement-marking compositions of the invention. The column headed Tmax 
gives the maximum temperature that the ingredients reached during mixing. 
TABLE III 
__________________________________________________________________________ 
Thermoplastic Abrasion 
Tensile Strength 
Ex. 
Reinforcing 
Tmax 
Loss kg/cm.sup.2 Hardness 
No. 
Polymer.sup.2 
(.degree.C.) 
(grams) 
Downweb 
Crossweb 
(Shore A) 
__________________________________________________________________________ 
2 Low Density 
150 0.7 52.0 32.0 85 
Polyethylene 
3 Linear Low 
152 0.8 49.8 17.1 80 
Density 
Polyethylene 
4 Vinyl copolymer 
164 0.2 35.6 28.9 78 
5 Vinyl copolymer 
164 0.7 47.6 37.7 83 
(OH functional) 
6 Vinyl copolymer 
167 0.6 38.5 30.4 80 
(COOH functional) 
7 Aromatic 151 1.2 21.6 15.5 75 
polyether 
8 Styrene- 161 1.3 23.9 16.3 76 
acrylonitrile 
copolymer 
9 Acrylic 155 1.5 17.6 13.6 75 
copolymer 
10 Polyester 154 1.4 18.3 14.8 71 
11 Aromatic 180 0.9 13.0 11.0 71 
Polyester 
12 Polyester- 
164 2.0 13.1 10.8 72 
urethane 
13 Polyether- 
154 1.7 17.0 14.3 76 
urethane 
14 Ethyl Cellulose 
168 1.6 13.7 11.5 73 
__________________________________________________________________________ 
.sup.2 The commercial designations and suppliers for polymers used as th 
thermoplastic reinforcing polymer in the examples are: 
2 LD600, Exxon 
3 GRSN 7047, Union Carbide 
4 VYHH, Union Carbide 
5 VAGH, Union Carbide 
6 VMCH, Union Carbide 
7 Phenoxy PKHH, Union Carbide 
8 Lustran 317042, Monsanto 
9 Plexiglas V, Rohm & Haas 
10 Vitel VPE307, Goodyear 
11 Kodar PETG 6763, Eastman 
12 Qthan PS 629, K. J. Quinn 
13 Qthane PE 192, K. J. Quinn 
14 Ethocel MS Natural, American Polymers 
EXAMPLE 15 
Following the procedures of Example 1, the ingredients shown in Table IV 
were processed to form a pavement-marking composition of the invention. In 
this example, the non-crosslinked elastomer precursor comprises a mixture 
of a styrene-butadiene copolymer and natural rubber. The sheet material 
was tested for tensile strength, abrasion resistance as described above, 
and Shore A hardness. Test results are found in Table V. 
TABLE IV 
______________________________________ 
Material Parts by Weight 
______________________________________ 
Styrene-butadiene non-crosslinked 
75 
elastomer precursor (SBR 1502, 
supplied by General Tire) 
Natural rubber (Standard Malaysian 
25 
Rubber SMR #5) 
Chlorinated paraffin (Chlorowax 70) 
70 
Chlorinated paraffin (Chlorowax 40) 
10 
Fibers of high-density polyethylene 
20 
Titanium dioxide pigment 
130 
Talc filler 75 
Glass microspheres 280 
Spherical silica 30 
Stearic acid 3.5 
Ultramarine Blue 0.5 
______________________________________ 
TABLE V 
______________________________________ 
Abrasion loss, grams 
1.9 
Tensile strength (Kg/m.sup.2) 
Downweb 14.3 
Crossweb 5.4 
Shore A hardness 74 
______________________________________