Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLEXIBLE THERMAL PROTECTIVE COMPOSITIONS
AND COATINGS AND STRUCTURES FORMED WITH THEM
Technical Field
This invention relates to thermal protective compositions which form
chars when exposed to fire or other thermal extremes. The invention is
particularly well suited to use in epoxy resin, intumescent coatings for
substrates and as novel intumescent sheets, but its usefulness is not
limited thereto.
Background Art
Various compositions are known which provide protection against fire
and other thermal extremes, such as temperatures above about 300° C.
Some of the compositions are foamed inorganic passive insulative
compositions which protect merely by their low thermal conductivity and
their thickness as applied. These include, for example, foamed cement
or intumesced silicates. The present invention 'is not concerned with
such systems, but with systems which include a polymeric binder and
which form a char when exposed to fire or hyperthermal conditions. The
char-forming compositions may operate by various modalities. The
compositions may be used in various forms, including thick film (mastic)
coatings, thin film coatings, castings, extrusions, and others. The
compositions may include organic or inorganic binders and various
additives. Upon exposure to heat the compositions slowly lose weight
as portions of the composition are volatilized, and a char is formed which
provides a measure of protection against the transfer of heat energy.
Eventually, the char is consumed by physical erosion and by chemical
processes, primarily oxidation by oxygen in the air and by free radicals
produced by the coating or otherwise in a fire environment, and
protection is lost. The length of time required for a given temperature
rise across a predetermined thickness of the composition, under
specified heat flux, environmental, and temperature conditions, is a
measure of the effectiveness of the composition in providing thermal
protection.
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When subjected to fire or other hyperthermal conditions, different
coatings behave differently.
Ablative coatings swell to less than twice their original thickness.
They provide limited passive thermal protection, but they tend to
produce dense chars having good physical and chemical resistance.
Intumescent coatings swell to produce a char more than five times
the original thickness of the coating. This char provides an insulative
blanket which provides superior thermal efficiency, but at the cost of
some of the physical and chemical properties of the ablative coatings.
The char of the intumescent materials tends to form coarse and irregular
cell structures, cracks, and fissures as it expands, and the char may not
expand uniformly at corners, leaving areas where the char provides far
less protection than the average thermal protection of the underlying
structure. Examples of the intumescent systems include silicate
solutions or ammonium phosphate paints or mastic compositions such
as those disclosed in Nielsen et al., U.S. Patent 2,680,077, Kaplan, U.S.
Patent 3,284,216, Ward et al., U.S. Patent 4,529,467, or Deogon, U.S.
Patent No. 5,591,791.
A third type of char-forming coating is a subliming coating disclosed
in Feldman, U.S. Patent 3,849,178. When subjected to thermal
extremes, these compositions both undergo an endothermic phase
change and expand two to five times their original thickness to form a
continuous porosity matrix. These coatings tend to be tougher than
intumescent coatings. They provide far longer thermal protection than
ablative coatings, frequently.longer than intumescent coatings, in part
because the gasses formed by the endothermic phase change provide
active cooling as they work their way through the open-cell matrix.
These coatings may also have a tendency to crack and form voids and
fissures.
The present invention relates primarily to the Feldman-type subliming
compositions which undergo an endothermic phase change and swell
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two to five times their original thickness. Some aspects of the invention
are also applicable to intumescent char-forming coatings.
Additionally, thermal protective systems have long been formed as
self-supporting shapes formed, for example, by molding or extruding a
protective material similar to, or identical with, the foregoing coating
materials. Such free-standing systems are described, for example, in
Feldman, United States Patent No. 4,493,945. Such systems suffer
from the considerable expense of casting, molding, or extruding the
shapes, and from the fact that the shapes and sizes of each system
must be determined prior to forming the shape.
In both the coating systems and the free-standing systems, it is often
useful to incorporate a mesh of some sort to strengthen the system.
Examples of such mesh are metal mesh and cloth mesh such as
fiberglass or graphite mesh. The mesh may be formed in many known
ways, such as weaving and knitting. The term "mesh" is used broadly
herein to include any perforate material.
Sometimes the materials are first applied to a reinforcing structure
such as a flexible tape or flexible wire mesh, and the combined structure
is applied to the substrate. Examples of this approach are found in
Feldman, U.S. Pat. No. 3,022,190, Pedlow, U.S. Pat. No. 4,018,962,
Peterson et al, U.S. Pat. No. 4,064,359, Castle, U.S. Pat. No. 4,276,332,
and Fryer et al, U.S. Pat. No. 4,292,358. In these last-mentioned
systems, the purpose of the reinforcing structure may be both to
strengthen the resulting composite and to permit its application to a
substrate without directly spraying, troweling or painting the uncured
coating materials onto the substrate. In any of the foregoing methods
and structures, multiple layers are frequently applied to the substrate to
provide additional protection.
Summary of the Invention
In accordance with one aspect of the present invention, generally
stated, a thermal protective composition is provided which when
exposed to flame or thermal extreme exhibits a volume increase through
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the formation of an expanded char, the composition comprising a flexible
epoxy resin, the resin being internally flexibilized with soft resin
segments contributing to the overall flexibility of the resin. The
composition preferably includes a component which volatilizes at fixed
temperatures to absorb and block heat. Preferably, the composition
responds to hyperthermal conditions with a small volume increase of two
to five times its initial thickness to form an open cell matrix.
The internally flexibilized epoxy resins which are useful in the
present invention are widely available. The resins have sufFicient
flexibility that a flat 175 mil (4.5 mm) sheet of the material can be rolled
by hand around a one inch (25.4 mm) pipe at room temperature (23° C).
Internally flexibilized epoxy resins have been known for many years, as
evidenced by Sellers, et al, United States Patent 3,522,210. The
internally flexibilized epoxy resin's soft resin segments are preferably
alkylene or oxyalkylene units. Representative of such resins are a butyl
glycidyl ether-modified bisphenol A diglycidyl ether epoxy resin having
an epoxy equivalent of about 310 to about 390 sold by Ciba Geigy Ltd.
as XB-4122 or PY-4122US. Several similar commercial flexible epoxies
are described in Fretz, United States Patent 4,793,703 and Kitabatake et
al, United States Patent 4,883,830, which gives a generalized formula (I)
for a preferred group of epoxy compounds suitable for use in the present
invention.
The preferred compositions of the invention comprise a part A
including the internally flexibilized epoxy resin and a part B including a
polysulfide, most preferably a polymer of bis-(ethylene oxy)methane
containing disulfide linkages and curable terminal thiol groups. The two
part system of the preferred compositions includes a curing agent. An
amine curing agent is preferred. The preferred compositions also
include gas formers such as polyol spumifics, amine blowing agents,
and phosphate acid producers.
In the presently preferred embodiments, the composition includes
from about 20% to about 65% polysulfide-modified flexible epoxy resin,
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more preferably about 40% to about 60% polysulfide-modified flexible
epoxy resin.
In the preferred embodiments, the composition is in the form of a
sheet of material about two to about thirty millimeters thick, more
preferably about 3-15 mm thick, most preferably about 3-10 mm thick.
Other additives may be included in the composition for their
known properties. Merely by way of example, boron or zinc may be
included in the composition or incorporated in a surface layer. Fillers
may be included for their known properties. Some or all of the additives
of Deogon, U.S. Patent 5,591,791, Feldman et al., U.S. Patent
5,372,846, Feldman et al., U.S. Patent 5,622,774, and Deogan et al.,
U.S. Patent 5,591,791 may be incorporated in the present compositions.
Although not presently preferred, it is also possible to include in
the coatings and structures of the present invention both a lower layer in
accordance with the invention and an upper layer of an ablative fire
protective material. The ablative material may be of a different
composition, but it is preferred that the ablative material includes an
internally flexibilized epoxy resin. The upper layer, in these
embodiments, forms an open cell matrix when exposed to a jet fire to
permit passage of gasses from the lower layer to ambient.
The compositions of the present invention have outstanding
adhesive qualities. They are therefore well adapted to direct application
to a substrate by standard methods such as spraying, troweling, or
rolling.
In accordance with preferred embodiments of the invention, they
can also be formed into sheets by applying them to a surface having a
mold release agent applied to it. Because the cured compositions of the
present invention, unlike conventional epoxy resins, can be wrapped
around a small pipe, having a diameter of 1" (25.4 mm) or less, the
sheets can be wrapped around almost any substrate, particularly
structural substrates. The sheets can therefore be easily adapted to
protecting structures of almost any size or shape. They can be used
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with standoffs, or they can be adhered to the substrate with a contact
cement, or preferably with a thin layer of the uncured composition itself.
When wrapped around a substrate, the sheet is preferably adhered to
the substrate and the ends of the sheet are held to each other by
overlapping and securing with a mechanical fastener as by stapling.
The flexible properties of the sheets also make the sheets
useable by themselves as free standing structural elements. They can,
for example, be bent into substantially rectangular cross sections and
used without little or no underlying structure as cable trays.
The ability of the sheets of the present invention to bend around
relatively sharp corners greatly reduces the labor required to install fire-
protective sheets around columns, beams, cable trays, and other
structural elements. When ordinary fire protective sheets or boards are
bent around corners, they must be scored before they are bent, and the
scored edges filled with additional material. The sheets of the present
invention do not require scoring to be bent around corners and thus
eliminate the need to fill the edges.
The coatings and structures of the present invention may include
a mesh reinforcing layer, preferably embedded in the composition.
Fiberglass and graphite fabrics are presently favored as the mesh,
although flexible ceramic fabrics, metal mesh and other types of mesh
may also be used.
The coatings and structures of the present invention have been
found to provide excellent protection against fire or other thermal
extreme. A flexible sheet having a thickness of 0.175" (4.5 mm)
wrapped around a 1.5" (38.1 mm) solid rod provides over 51 minutes of
protection against a 900° C standard fire (maximum temperature rise to
400° C in a furnace rising to 500° C in five minutes,
700° C in ten
minutes, 800° C in twenty minutes, and 900° in forty-six
minutes).
The foregoing patents are all incorporated herein by reference.
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Brief Description of the Drawings
Figure 1 is a graph showing average furnace temperature and
average sample temperature of a 1.5" (38.1 mm) diameter solid metal
rod protected by a 0.175" (4.5 mm) sheet of the present invention,
wrapped around the rod.
Best Mode for Carr r~ ing Out the Invention
The following detailed description illustrates the invention by way
of example and not by way of limitation. This description will clearly
enable one skilled in the art to make and use the invention, and
describes several embodiments, adaptations, variations, alternatives
and uses of the invention, including what we presently believe is the best
mode of carrying out the invention.
EXAMPLE 1
A composition of the present invention was prepared containing a
two-component epoxy. The composition is formulated to be thermally
activated by flame or thermal extreme; it volatilizes at fixed
temperatures, exhibiting a small volume increase through the formation
of an open cell matrix, and absorbs and blocks heat to protect the
substrate material. The composition included a polyfunctional alcohol, a
1,3,5-triazine-2,4,6-triamine, an internallyflexibilized epoxy resin and a
polymer of bis-(ethylene oxy)methane containing disulfide linkages and
curable terminal thiol groups (a polysulfide). The composition had a
nominal formula as follows:
Weight percent
Melamine 5
Ammonium polyphosphate 25
Pentaerythritol 10
Flexible epoxy resin 30
Polysulfide 20
Glass fibers 5
Catalyst 5
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The composition was spread on a plate (previously coated with a
standard release agent) to a nominal thickness of 0.175" (4.5 mm). A
graphite fabric was pressed into the layer of material before it set. The
layer was allowed to cure at 30° C. for one month.
EXAMPLE 2
A test article was prepared by coating a solid 1.5" (38.1 mm)
diameter metal rod with a contact adhesive. The sheet of EXAMPLE 1
was wrapped around the rod, and the excess was cut off, leaving a small
overlap. The overlap was stapled to the underlying sheet, and the
stapled area was filled with uncured composition of EXAMPLE 1. The
test article was cured for about sixteen hours.
EXAMPLE 3
The test article prepared in accordance with EXAMPLE 2 was
exposed to a simulated fire in accordance with the conditions of ASTM
E-119. The actual conditions are shown in FIGURE 1. The test showed
that the system provided approximately fifty-one minutes of protection
under the conditions of the test.
In view of the above, it will be seen that the several objects and
advantages of the present invention have been achieved and other
advantageous results have been obtained.
As various changes could be made in the above constructions
without departing from the scope of the invention, it is intended that all
matter contained i'n the above description or shown in the accompanying
drawings shall be interpreted as illustrative and not in a limiting sense.
