Asbestos-free asphalt roof coating

An asbestos-free asphalt composition is provided of the kind used in roofing applications. A polypropylene carbonate coupling agent is used with high density polyethylene fibers to prevent settling or separation of the components.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to asbestos-free asphalt compositions of 
the type used in roof coatings and specifically to an asphalt composition 
utilizing finely divided polyolefin fibers and a coupling agent to hold 
the fibers in suspension. 
2. Description of the Prior Art 
Asphalt compositions comprising asphalt cutback, asbestos fiber, and 
particulate fillers such as limestone are well known in the roofing 
industry. These compositions are used in caulking and flashing, and as 
roofing cement and waterproofing agents in roofing applications. 
Increasingly stringent government standards regulating the use of asbestos 
have focused attention on the need for a replacement for the asbestos 
component in asphalt compositions. Although various materials can be used 
to thicken asphalt compositions, asbestos fibers provide the strength 
needed in many applications. 
Blending synthetic fibers with asphalt is a concept which has been known 
for some time. For instance, U.S. Pat. No. 3,505,260 to Gene N. Woodruff, 
issued Apr. 7, 1970, entitled "Asphalt-Polyolefin Fiber Blends" discloses 
an asbestos-free asphalt composition containing polyolefin fibers in a 
water based system. U.S. Pat. No. 3,634,293 to Eckhard Bonitz, issued Jan. 
11, 1972, entitled "Compositions Containing Bitumen and an Olefin 
Polymer", teaches the use of olefin polymers with a basic substance and 
sulfur in bituminous compositions. Replacing asbestos with polyolefin 
fibers has posed problems in the past, however, because the polyolefin 
fibers tended to separate or settle out during storage. This problem is 
especially troublesome in roofing applications in which the coating is 
often applied with a spray gun. 
Recent efforts toward asbestos-free asphalt compositions have tended to be 
"fiber-free" in order to avoid the problem of separation of components. 
See e.g. U.S. Pat. No. 4,168,179 to William F. Hesseler, issued Sept. 18, 
1979, entitled "Bituminous Composition" in which high structure carbon 
black is dispersed in asphalt cutback. However, as has been mentioned, 
fibers provide added strength. Fibers provide improved bond strength 
between the asphalt and the underlying surface as well as improved film 
strength in the asphalt layer itself. For these reasons, fiber containing 
asphalt compositions show as much as 30 percent increase in tensile 
strength over asphalt compositions which are fiber-free. Also certain of 
the fiber-free formulations are prohibitively expensive as compared to 
asbestos containing compositions. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an 
asbestos-free asphalt composition in which no separation of the components 
occurs. 
It is also an object of the present invention to provide an asbestos-free 
asphalt composition which contains fibers for added strength. 
Another object of the present invention is to provide an asbestos-free 
asphalt composition which is competitively priced. 
Accordingly, the asbestos-free asphalt composition of the present invention 
comprises asphalt cutback, finely divided polyolefin fibers, and propylene 
carbonate coupling agent. A preferred composition includes: 
asphalt cutback, wherein said cutback comprises approximately 70 weight 
percent asphalt and 30 weight percent solvent for said asphalt; 
approximately 3.5 weight percent calcium carbonate filler based on the 
total composition; 
approximately 2 weight percent finely divided fibers of high density 
polyethylene based on the total composition; and 
approximately 2 weight percent propylene carbonate coupling agent based on 
the total composition. 
A method for producing an asbestos-free asphalt composition is disclosed 
which comprises the steps of: 
simultaneously adding approximately 92.5 weight percent asphalt cutback and 
2 weight percent propylene carbonate coupling agent based on the total 
composition to a mixing vessel; 
slowly mixing the contents of the vessel until they are thoroughly blended; 
adding approximately 2 weight percent high density polyethylene fibers 
based on the total composition and mixing thoroughly; and 
adding approximately 3.5 weight percent calcium carbonate filler based on 
the total composition and mixing thoroughly.

DETAILED DESCRIPTION OF THE INVENTION 
The asbestos-free asphalt compositions of the present invention include 
asphalt cutback, finely divided polyolefin fibers, and propylene carbonate 
coupling agent. The asphalt cutback used in the practice of the invention 
comprises asphalt and a suitable solvent which, when combined with the 
asphalt in the proper proportions, gives a pumpable liquid. Asphalt 
suitable for use in compositions of the present invention can be any of 
the asphalts normally found suitable for roofing purposes including 
natural asphalt, and asphalt obtained as a residue in petroleum or coal 
tar refining which has been air and/or steam blown. Asphalt tested 
according to the procedure outlined in The American Society of Testing 
Materials Standard (ASTM) D-5-73 and characterized by penetrations at 
77.degree. F. (Fahrenheit) between about 5 and about 100 dmm (tenths of a 
millimeter) and having a ring and ball softening point between about 
80.degree. F. and about 240.degree. F. are suitable. The preferred 
material is a catalytically blown asphalt having a penetration at 
77.degree. F. between about 60 to 75 dmm, and a ring and ball softening 
point between about 135.degree. to 150.degree. F. 
The solvent used in preparation of the asphalt cutback is conveniently any 
of the solvents normally used for asphalt cutbacks with naphtha 
300.degree.-360.degree. being preferred. Other suitable solvents include 
Stoddard solvent, mineral spirits, and the like. The asphalt cutback of 
the present invention comprises between about 30 to 80 weight percent 
asphalt and between about 20 to 70 weight percent solvent for said 
asphalt. While the amount of solvent in the asphalt cutback can be broadly 
within the range given above, it will be understood that the amount of 
solvent used in a particular composition will depend, at least in part, 
upon the particular solvent and asphalt used as well as the temperature at 
which the composition of the invention is to be used. If desired, a 
portion of the solvent content of the asphalt cutback can be added during 
blending of the composition of the invention rather than during 
manufacture of the asphalt cutback. 
Polyolefin fibers, particularly finely divided fibers of mono-1-olefins 
having from 2 to 4 carbon atoms per molecule, preferably polymers of 
ethylene or propylene including homopolymers and copolymers, are used in 
the inventive composition. The preferred material is a high density 
polyethylene fiber sold under the trademark FYBREL by Crown Zellerbach 
Company, said material having a melting range from 130.degree. to 
135.degree. C. (Centrigrade), an average fiber length of 0.7 mm 
(millimeters) and an average fiber diameter of approximately 0.035 mm. The 
polyolefin fibers are present in the asbestos-free asphalt composition in 
a range from about 0.5 to 5.0 weight percent, preferably about 1.0 to 3.0 
weight percent with the preferred amount being about 2.0 weight percent 
based on the total composition. Increasing the amount of polyolefin fibers 
present increases the viscosity of the composition. Above about 5.0 weight 
percent polyolefin fibers, the composition becomes too thick to spray. 
The preferred coupling agent is propylene carbonate (4 methyldioxylene-2). 
Propylene carbonate is present in a range from about 0.5 to 6.0 weight 
percent, preferably about 0.5 to 2.5 weight percent, with the preferred 
amount being 2.0 weight percent based on the total composition. At lower 
storage temperatures, about 0.5 weight percent propylene carbonate is 
sufficient to prevent separation of the components. Where storage 
temperatures are expected to range between 100.degree.-150.degree. F., as 
where drums of roof coating are stored in direct sunlight, about 2 weight 
percent propylene carbonate is preferred. Amounts above about 6.0 weight 
percent are unnecessary to prevent separation of the components and are 
limited primarily by economic considerations. 
The asbestos-free asphalt compositions of the present invention can 
optionally contain a particulate filler. Suitable filler materials include 
particulate fillers of the type generally considered suitable for asphalt 
compositions including, for example, calcium carbonate, bentone clay, 
perlite, glass microspheres, sandstone, dust, slate powder, rubber, 
alumina, etc. The preferred particulate filler is calcium carbonate which 
thickens the composition while also acting as a UV inhibitor. The 
particulate filler is present in a range from about 0 to 30 weight 
percent, preferably about 2 to 12 weight percent, with the preferred 
amount being about 3.5 weight percent based on the total composition or it 
may be omitted entirely. 
The invention is best described with reference to the following example 
wherein an asbestos-free asphalt roof coating was prepared by 
simultaneously adding approximately 92.5 weight percent asphalt cutback 
and 2.0 weight percent propylene carbonate to a mixing vessel. The asphalt 
cutback is approximately 70% by weight asphalt and 30% by weight naphtha 
solvent. The contents of the vessel are then mixed slowly until thoroughly 
blended. Approximately 2.0 weight percent high density polyethylene fibers 
are then added and mixed thoroughly. Approximately 3.5 weight percent 
calcium carbonate is added to the composition in the final step and mixed 
thoroughly. It is critical that the above method be carried out in the 
sequence specified. The propylene carbonate must be thoroughly blended 
with the asphalt cutback prior to adding the polyethylene fibers or 
separation of the components will occur. 
EXAMPLE I 
______________________________________ 
Weight % based on 
Component the total composition 
______________________________________ 
asphalt cutback 92.5 
Ca CO.sub.3 3.5 
polyethylene fibers 
2.0 
propylene carbonate 
2.0 
______________________________________ 
The following physical properties of the composition were noted: 
______________________________________ 
penetration 
253 dmm cure time 24 hrs. 
total solids 
67.8% temp. at which 
sagging occurs 
300.degree. F. 
ash 1.72% separation None 
wt/gal 7.6 lbs. 
flash point 
111.degree. F. 
______________________________________ 
Penetration tests were performed using a similar procedure that outlined in 
ASTM D-5-73. The procedure was modified to account for the fact that the 
asphalt compositions of the invention are liquid at room temperature. In 
the standard procedure for testing base asphalts which are solid at room 
temperature, a needle with a gauge attached falls onto a layer of asphalt 
contained in a small pan. The gauge is read after five seconds and 
indicates the penetration of the needle in tenths of a millimeter (dmm). 
In the modified procedure, the specimen is contained in a sample tube 21/2 
inches long and 3/8 inch internal diameter. A plunger 1/4 inch in outside 
diameter and 2 inches long is screwed to the shaft of a grease 
penetrometer. The combined weight of the shaft and plunger is 25 grams. 
The sample tube is mounted on the grease penetrometer in the line of 
travel of the plunger. The sample is tested at 77.degree. F. The plunger 
is allowed to fall into the sample tube. The distance the plunger falls 
into the sample in five seconds is read off the penetrometer gauge. 
Readings are in dmm. Preferred readings for roof coatings are between 
about 198 and 314 dmm. 
The composition was tested for separation or settling by placing a specimen 
in a centrifuge and spinning the same for approximately 10 minutes at 3500 
rpm. The specimen was then visably examined to see if separation or 
settling of the components had occurred. A properly blended composition 
has a rough texture and dull appearance. When separation occurs, the 
asphalt cutback forms a smooth shiny film on the top of the specimen. 
EXAMPLE II 
A composition was prepared using the method described in Example I. 
______________________________________ 
Weight % based on 
Component the total composition 
______________________________________ 
asphalt cutback 82.4 
Ca CO.sub.3 11.5 
polyethylene fibers 
4.5 
propylene carbonate 
1.6 
______________________________________ 
The following physical properties were observed: 
______________________________________ 
penetration 202 dmm flash point 113.degree. F. 
total solids 
76.78% cure time 24 hrs. 
ash 9.56% temp. at which 
sagging occurs 
300.degree. F. 
wt/gal 8.2 separation None 
______________________________________ 
EXAMPLE III 
A composition was prepared using the method described in Example I. 
Additional solvent in the form of mineral spirits was added in the first 
step and bentone clay filler was added in the final step. 
______________________________________ 
Weight % based on 
Component the total composition 
______________________________________ 
asphalt cutback 78 
Ca CO.sub.3 10 
mineral spirits 7.5 
propylene carbonate 
1.5 
polyethylene fiber 2.0 
bentone clay 1.0 
______________________________________ 
The following physical properties were observed: 
______________________________________ 
penetration 
233 dmm flash point 104.degree. F. 
total solids 
68.0 cure time 24 hrs. 
ash 7.81 temp. at which 
sagging occurs 
340.degree. F. 
wt/gal 8.03 separation None 
______________________________________ 
It should be apparent from the foregoing that an improved asbestos-free 
asphalt compositions have been provided in which no separation of the 
components occurs. Although asbestos-free, the compositions contain 
polyolefin fibers for added strength. The polyethylene fibers of the 
present invention cost approximately four times as much as the prior art 
asbestos fiber. However, prior art asbestos containing compositions 
contained approximately 8-10 weight percent asbestos. Because of the 
increased surface area of the high density polyethylene fibers, 
approximately 2 weight percent is sufficient. The improved asbestos-free 
asphalt composition which has been provided can, therefore be produced at 
a price which is competitive with prior art asbestos containing 
compositions. 
While the invention has been shown in only three of its forms, it should be 
apparent to those skilled in the art that it is not thus limited but is 
susceptible to various changes and modifications without departing from 
the spirit thereof.