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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to asphalt compositions and more
particularly to a roofing shingle utilizing a specific asphalt
composition.
2. Description of Prior Art
Most roofing shingles made today are constructed of a base sheet, usually
either rag felt or, more recently, glass fiber mat, saturated with a
bituminous substance, usually asphalt, including a large amount of filler
material such as limestone dust. Roofing shingles of this general type are
made in various different sizes and shapes and utilize asphalt
compositions and base sheets which differ greatly from one another. In
this regard, the various competitors making up the roofing industry are
constantly striving to decrease the manufacturing costs of their shingles
while, at the same time, striving to improve shingle strength,
weatherability and overall general quality. One feature which, in recent
years, has been somewhat overlooked is shingle fire-resistance. For the
most part, this is because many manufacturers already have a
"fire-resistant" asphalt shingle having a "Class A" rating from
Underwriters Laboratories, the highest UL rating for fire resistance that
can be presently obtained.
In order to keep the cost of asphalt shingles at a competitively low level,
most manufacturers use an inexpensive low-viscosity asphalt and relatively
inexpensive filler material such as limestone in manufacturing their
shingles. To improve upon shingle fire-resistance, many manufacturers have
found it necessary to incorporate some type of fire-resistant improving
additive to the asphalt-filler combination. One typical additive is
asbestos and another is ferric chloride (FeCl.sub.3). A major problem in
utilizing asbestos is that it is at least thought to be a hazardous
material and thereby requires expensive equipment to maintain acceptable
air quality standards during manufacture.
A major problem with FeCl.sub.3 is that it is a corrosive material and
FeCl.sub.3 asphalts tend to form troublesome coats and skin during shingle
manufacture. However, without any additive, that is, utilizing an asphalt
composition including only asphalt of the inexpensive and low-viscosity
type typically used and filler material such as limestone, it is difficult
to provide a highly fire-resistant shingle without, for example, utilizing
an expensive base sheet. The major reason for this resides in the
viscosity or flow characteristics of the asphalt used.
More specifically, shingled roofs, unlike built-up roofing decks, lie at a
slope with the horizontal. When the shingles are subjected to a fire, the
asphalt melts and reaches high temperatures rather rapidly. At these
temperatures, without any additive other than the conventional filler, the
asphalt has a low viscosity and flows quite rapidly down the roof slope
and away from the source of fire. In so doing, it carries much of the
filler and base material with it. This, in turn, leaves any hot spots on
the support deck exposed to the air and particularly any breeze or wind.
By utilizing an additive such as asbestos or FeCl.sub.3, the asphalt is
sufficiently viscous such that a protective coating or crust is formed
over the hot spot acting as a shield against the outside air. This
protective coating or crust results from the burned remains of at least a
portion of the combustible ingredients comprising part of the asphalt
composition.
PRIOR ART REFERENCES
U.S. Pat. Nos. 2,489,242 (Slayter et al.), 2,771,387 (Kleist et al.), and
3,332,830 (Tomlinson et al.) are being made of record herein because, it
is believed, they are of general relevance to the subject matter disclosed
herein. However, it is not believed that the subject matter disclosed in
these patents is at all pertinent to the present invention. For example,
Slayter et al. is directed to a particular method and particular apparatus
for making fine glass fibers. As disclosed, these fibers are used as
additives in several different types of products such as, for example,
innertubes for pneumatic tires. As specifically stated, "It has been found
the addition of these very fine fibers to many liquids such as kerosine,
resin solutions, etc., is effective to increase the viscosity of the
liquids to a great extent even when only a very small percentage of fibers
are added. This is due apparently to the extreme fineness and the great
surface area of the fibers." (See column 11, lines 17-24.)
The Kleist et al. patent and the Tomlinson et al. patent both disclose
asphalt-treated glass fiber structures and methods of producing them. The
former patent, in discussing its method, states in column 7, lines 6-11,
"It is desirable sometimes to load the material [the bituminous material]
with inorganic finely divided or powdered fillers such as glass sandings,
clays, slate flour, chalk, micadust, crushed or powdered silica,
diatomaceous earth and the like to reduce flow and tackiness of the
bituminous impregnating composition and to improve its insulating
property." The Tomlinson et al. patent discloses a way of enhancing fire
safeness of its asphalt shingle "by incorporating concentrations of
chopped strands or bundles of fibers of discrete length at the product
edges which are critically exposed when installed on the surface to be
protected." (Column 3, lines 60-63.) It should be noted that these chopped
strands or bundles of fibers are provided in concentrated areas well after
impregnation or saturation of the glass fiber mat which also comprise part
of the Tomlinson et al. shingle.
The present invention is entirely different from and unobvious in view of
the above-discussed patents, as will be seen hereinafter. Applicants of
the present invention have discovered that they can uniformly disperse a
very small amount of glass in the form of glass fiber bundles in molten
asphalt to control its viscosity in an advantageous way. More
specifically, they have found a way to maintain the viscosity of molten
asphalt at a sufficiently low level to readily permit saturation of a base
sheet while, at the same time, causing the viscosity of the asphalt to
increase at elevated temperatures to a level which retards the flow of the
asphalt an amount sufficient to permit formation of the aforedescribed
protective coating or crust. This can be done without using undesirable
additives such as asbestos or FeCl.sub.3.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a fire-resistant asphalt
roofing shingle.
Another object of the present invention is to provide a
viscosity-controlled asphalt composition for saturating a base sheet.
Still another object of the present invention is to provide a method of
making a fire-resistant asphalt-saturated base sheet.
These objects, as well as other objects and features to become apparent
hereinafter, are achieved by the utilization of a particular asphalt
composition made in accordance with the present invention. This
composition is comprised of molten asphalt, which is maintained at a
relatively low saturating or coating temperature, preferably between
approximately 350.degree.F and 450.degree.F, and a mineral filler
material, such as limestone, dispersed throughout the molten asphalt.
In accordance with the present invention, glass fiber bundles of a
preselected type, each bundle comprising a plurality of monofilaments
bonded together, are also dispersed throughout the molten asphalt. These
glass fiber bundles are selected to meet a number of requirements. For
example, with the bundles dispersed throughout the molten asphalt and with
the asphalt being maintained at a relatively low temperature, for example
between 350.degree.F and 450.degree.F, i.e., the asphalt-saturating or
coating temperature, the monofilaments of each bundle should substantially
remain bonded together (unless, of course, the asphalt is severely
agitated) and the viscosity of the molten composition must remain at a
sufficiently low level for saturating or coating the base sheet.
After saturation of the base sheet, let it be assumed that the saturated
base sheet is positioned on a sloped deck and subjected to a source of
fire, reaching a temperature of, for example, 700.degree.F. Under these
conditions, the monofilaments of each bundle should separate and disperse
throughout the asphalt and the viscosity of the composition, specifically
the asphalt, should increase from the saturating level to a level which
retards the flow of the asphalt. More specifically, the flow of the
asphalt should be retarded an amount sufficient to prevent at least some
of the combustible material, for example some of the base sheet and some
of the mineral filler, from flowing away from the source of fire. In this
manner, that portion of the base sheet and filler material will burn, the
residue or ash forming a coating or crust at the source of fire and
preventing the outside air from reaching any hot spots.
By selecting the glass fiber bundles preferably to meet the aforediscussed
requirements, the molten asphalt composition is sufficiently flowable to
readily saturate or coat the base sheet in producing roofing shingles and
yet, when subjected to flame temperatures, is sufficiently viscous to
produce the aforestated protective crust or coating.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS
The present application is directed generally to asphalt roof coverings and
more particularly to an asphalt roofing shingle with improved
fireresistance. The asphalt shingle, which may be of any suitable size or
shape, includes a base or support sheet encased in and saturated by an
asphalt composition, commonly referred to as a filled asphalt coating. The
asphalt saturated base sheet is preferably coated at least on its top
surface with mineral (ceramic coated) granules or other suitable
particulate matter.
As will be seen hereinafter, the asphalt composition includes as its major
constituents asphalt and a mineral filler such as limestone dust. In
accordance with the present invention, the composition includes a very
small amount of glass, in the form of glass fiber bundles, dispersed
throughout the asphaltfiller mixture. In fact, in accordance with a
preferred embodiment of the present invention, the asphalt composition
preferably consists essentially of these three ingredients, i.e., the
asphalt, mineral filler and small percentage of glass fiber bundles.
The base sheet utilized as part of the asphalt shingle of the present
invention may be any one of many which are presently being used for this
purpose. It may, for example, be of the rag felt type or, as more recently
provided, the base sheet may take the form of a glass fiber mat. In any
event, the base sheet could be made by conventional means in a
conventional way and would include the appropriate physical
characteristics necessary in manufacturing the shingle and in providing
the ultimately manufactured shingle with its own appropriate physical
characteristics. One with ordinary skill in the art could reasonably
provide such a base sheet.
The asphalt utilized in the asphalt composition of the present invention
may also be one which is presently being used by the industry. An asphalt
of this type typically has a softening point (R & B) of between, for
example, 190.degree.F and 240.degree.F and a penetration at 77.degree.F
between, for example, 14dmm and 25dmm. In saturating the aforedescribed
base sheet, the asphalt is maintained in a molten state, preferably at a
temperature anywhere between 350.degree.F and 450.degree.F. At this
temperature and without any fillers or additives, the molten asphalt has a
viscosity in Saybolt Furol seconds of between 100 and 300.
The physical properties of the asphalt, as recited herein, are for
exemplary purposes only. Any asphalt which functions in the manner to be
described hereinafter may be utilized and, in fact, may be readily
provided by those skilled in the art. In this regard, the saturating or
coating temperature of the molten asphalt, or the operating temperature as
it is commonly called, will depend in part on the particular asphalt used
and in part on the other ingredients in the overall composition. In any
event, the temperature of the asphalt should be sufficiently high to
readily saturate or coat the base sheet with the asphalt composition and
yet it should not be maintained at a temperature higher than necessary.
This is, of course, because a large amount of energy is required to
maintain the composition in its molten state.
The asphalt composition of the present invention preferably includes
between approximately 40% and 50% asphalt by weight of the total
composition. When less than approximately 40% is provided, the asphalt
does not satisfactorily fulfill its intended purpose, that is, it does not
satisfactorily provide the ultimately produced shingle with adequate
physical characteristics. In addition, it tends to be too viscous at the
preferred saturating temperatures. On the other hand, providing the
composition with more than 50% asphalt is not necessary and, taking into
account cost considerations, is not preferable. In this regard, to
"extend" the asphalt a suitable conventional filler such as, for example,
limestone dust or other mineral filler, is added thereto.
The mineral filler is dispersed throughout the asphalt by conventional
means, for example mechanical agitation, when the asphalt is in its molten
state, preferably at its saturating temperature. Between approximately 45%
and 55% mineral filler, by weight of the total asphalt composition, is
preferably utilized. The exact percentage of mineral filler provided will
be dictated by the amount of asphalt and the amount of glass in the form
of glass fiber bundles which are utilized in the composition, especially
when these are the only ingredients comprising the composition. Of course,
the filler must not be of a type or an amount which will prevent
saturation of the base sheet at reasonable saturating temperatures.
As stated above, in accordance with the present invention, a small
percentage of glass in the form of glass fiber bundles is added to the
asphaltfiller mixture. These glass fiber bundles are dispersed throughout
this mixture or could be dispersed throughout the asphalt prior to the
addition of the filler but, in any case, are added while the asphalt is in
a molten state, preferably at its saturating temperature. In this regard,
the glass may be dispersed in the asphalt by, for example, mechanical
agitation. However, the degree of agitation must be sufficiently low to
prevent the fiber bundles from separating in any substantial degree into
individual monofilaments. The main reason for adding the glass fiber
bundles is to substantially improve fire-resistance of the ultimately
produced shingle without using conventional additives such as previously
discussed asbestos and FeCl.sub.3. The glass fiber bundles are of a
preselected type which, when added to the molten asphalt-filler mixture,
cause the overall asphalt composition to function in a predetermined
manner, which will be discussed directly below.
As stated previously, the asphalt-filler mixture when maintained at the
aforedescribed saturating temperature, for example, between 350.degree.F
and 450.degree.F, will have a sufficiently low viscosity so as to permit
easy saturation of the base sheet. While the addition of the glass fiber
bundles to this mixture will increase the viscosity slightly, the amount
and type of bundles selected must be such that the overall composition, at
the saturating temperature, has a sufficiently low viscosity level to
permit easy saturation of the base sheet.
While the addition of the glass fiber bundles must not appreciably affect
the viscosity of the molten asphalt at the saturating temperature of the
asphalt, it must be of the type and amount which will substantially
increase the viscosity of the overall composition, actually of the asphalt
itself, when the composition is subjected to extremely high temperatures,
for example, temperatures above 700.degree.F.
Let it be assumed, for example, that a shingle or, for that matter, an
asphalt-saturated base sheet, utilizing the asphalt composition of the
present invention, is mounted on a sloped deck at, for example, 5 inches
per foot inclination to the horizontal. Let it further be assumed that the
shingle or saturated base sheet generally is subjected on its top surface
to a source of fire such that the asphalt composition reaches a
temperature of, for example, at least 700.degree.F. Under these
circumstances, the viscosity of the composition, as a result of adding the
fiber bundles, will increase from its low level at the saturating
temperature to a level which retards the flow of the asphalt. The
viscosity will increase an amount sufficient to permit formation of a
fixed coating or crust of the aforedescribed type over the roof deck
adjacent the source of fire. Stating this in the negative, the asphalt
will not be sufficiently flowable so as to carry away rapidly the base
sheet, filler material, granules and added glass fiber from the source of
fire. Rather, the asphalt will be sufficiently viscous so as to hold these
other components of the shingle at the source of fire long enough to burn
and form a crust or coating of the burned remains at the source of fire.
This is accomplished by selecting glass fiber bundles of the type which,
when dispersed throughout the asphalt, will defilamentize, that is,
separate into individual monofilaments and disperse throughout the asphalt
when the latter reaches these high temperatures. It has been found that
this defilamentization of the fiber bundles and resulting dispersion of
the monofilaments cause the viscosity of the asphalt to increase to the
level desired. In this regard, it should be noted that, since
defilamentization does substantially increase the viscosity of the
asphalt, the glass fiber bundles must be of a type which will not
defilamentize to any appreciable degree at the saturating temperature of
the asphalt, i.e., at for example, temperatures below 450.degree.F. In
addition, severe mechanical agitation of the asphalt for initially
dispersing the fiber bundles should be avoided. If the fiber bundles did,
in fact, defilamentize to a large extent at these lower temperatures, the
asphalt composition would be too viscous to saturate the base sheet.
The exact amount of glass fiber additive utilized in the asphalt-filler
mixture will depend in large part on the particular type and amount of
glass fibers used as well as the particular type and amount of asphalt and
filler. However, it is believed that as little as 0.1% or 0.2% and as much
as 3% glass fiber additive, by weight of the total asphalt composition,
may be satisfactory. Below approximately 0.1% there more than likely is
not sufficient glass in the asphalt to substantially increase the
viscosity of the asphalt (at the higher temperatures) to the degree
required to accomplish the foregoing results, even though it may be
completely defilamentized and dispersed. By the same token, when more than
approximately 3% glass additive is provided, the asphalt composition may
be too viscous at the saturating temperatures to saturate the base sheet
and, since 3% or approximately 3% will usually accomplish the desired
results, there is no economical reason to include more. In any event, one
with ordinary skill in the art, in view of the teachings in the present
disclosure, could readily determine the amount of glass to be added for
achieving the desired results.
The exact type of glass fiber which could be used may vary and could also
be readily determined by those skilled in the art in view of the teachings
of the present invention. However, those which have been found to be
acceptable are between approximately 1/8 inch and 1/2 inch in length,
including between 100 and 800 filaments per bundle and having a filament
diameter of, for example, 13 to 18 .mu.. The binder utilized in holding
the monofilaments together must, of course, be one which will continue to
hold the bundles together, to at least a substantial degree, at the
saturating temperature of the asphalt, even though the asphalt is mildly
agitated to disperse the glass bundles. It must also be one which, by
melting, dissolving or in any other such way, allows the fiber bundles to
defilamentize to a large extent at substantially higher asphalt
temperatures, for example, at temperatures in excess of 700.degree.F. A
suitable and actually preferable binder is polyvinyl acetate. However,
other binders may be selected and in view of the teachings set forth
herein, they could be readily selected by those skilled in the art.
Obviously, the degree of defilamentization will depend upon the type and
amount of glass fiber additive utilized. It is only required that there
must be sufficient defilamentization to achieve the aforedescribed desired
results.
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