Note: Descriptions are shown in the official language in which they were submitted.
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1
1077 CAN
FIRE RETARDANT CAVITY FILLED INSULATION PACK
FIELD OF THE INVENTION
This invention relates to bubble-pack thermal insulation materials for use in
framed structures, walls, crawl spaces and the like or wrapping for hot and
cold water
heaters, pipes and the like wherein the bubbles contain a fire retardant
material.
BACKGROUND TO THE INVENTION
Insulation materials are known which comprise a clean, non-toxic, heat barrier
made of aluminum foil bonded to a single or double layer of polyethylene-
formed
bubbles spaced one bubble from another bubble in the so-called "bubble-pack"
arrangement. Such non-foil bubble-packs are used extensively as packaging
material,
whereas the metal foil bubble-pack is used as thermal insulation in wood frame
structures, walls, attics, crawl spaces, basements and the like and as
wrapping for hot
water heaters, hot and cold water pipes, air ducts and the like. The
reflective surface of
the metal, particularly, aluminum foil enhances the thermal insulation of the
air-
containing bubble pack.
Organic polymers, such as polyethylene, are generally considered to be high-
heat-release materials. They can easily initiate or propagate fires because,
on exposure
to heat, they undergo thermal degradation to volatile combustible products. If
the
concentration of the degradation products in the air is within flammability
limits, they
can ignite either spontaneously, if their temperature is large enough, or by
the effect of
an ignition source such as a spark or flame. The ignition of polyethylene can
be delayed
and/or the rate of its combustion decreased by means of fire retardant
materials.
The ultimate aim of fire retardants is to reduce the heat transferred to the
polymer below its limit for self sustained combustion or below the critical
level for
flame stability. This can be achieved by decreasing the rate of chemical
and/or physical
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processes taking place in one or more of the steps of the burning process. One
or a
combination of the following can achieve fire extinguishing:
1. creation of a heat sink by using a compound that decomposes in a highly
endothermic reaction giving non-combustible volatile products, which perform a
blanketing action in the flame, e.g., aluminum or magnesium hydroxide;
2. enhancements of loss of heat and material from the surface of the burning
polymer by melt dripping, e.g., mixture of halogenated compounds with free
radical initiators;
3. flame poisoning by evolution of chemical species that scavenge H and OH
radicals which are the most active in propagating thermo-oxidation in the
flame,
e.g., hydrogen halides, metal halides, phosphorus-containing moieties;
4. limitation of heat and mass transfer across the phase boundary, between
thermal
oxidation and thermal degradation by creation of an insulating charred layer
on
the surface of the burning polymer, e.g., intumescent chart; or
5. modification of the rate of thermal volatilization of the polymer to
decrease the
flammability of the volatile products; which approach strongly depends on the
chemical nature of the polymer.
Fire retardant materials are generally introduced to the polyethylene as
merely
additives or as chemicals that will permanently modify its molecular
structure. The
additive approach is more commonly used because it is more flexible and of
general
application.
Generally, low density polyethylene films of 1 - 12 mil, optionally, with
various
amounts of linear low density polyethylene in admixture when additional
strength is
required, are used for the above applications. The insulating properties of
the bubble
pack primarily arise from the air in the voids. Typically, bubble diameters of
1.25 cm,
0.60 cm and 0.45 cm are present.
Regardless of the application method of fire retardant material(s), a
satisfactory
insulative assembly must have a fire rating of Class A with a flame spread
index lower
than 16, and a smoke development number smaller than 23. Further, the bonding
of the
organic polymer films and their aging characteristics must meet the aforesaid
acceptable
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standards. Yet further, the fabrication methods) of a new fire retardant
system or
assembly should be similar to the existing technology with reasonable and cost
effective
modifications to the existing fabrication system/technology. Still yet
further, other
physical properties of an improved fire standard system must at least meet,
for example,
the standard mechanical properties for duct materials as seen by existing
competitive
products.
Fire retardant polyethylene films, wires and cables containing a fire
retardant
material in admixture with the polyethylene her se are known which satisfy
cost criteria
and vigorous fire retardant technical standards to be commercially acceptable.
However, it has been found that forming a bubble pack comprising such a film
results in
a poor bonding between the cavity-containing layer and the adjacent sealing
layer used
to cover the cavities to form the bubbles. Delamination of these layers,
particularly,
after installation constitutes a significant problem.
Conventional fire retardant additives are usually compounds of small molecular
weights containing phosphorus, antimony, or halogens. The most effective
commercially available fire retardant systems are based on halogen-containing
compounds. However, due to concerns over the environmental effects of such
halogenated compounds, there is an international demand to control the use of
such
halogenated additives.
Some of the most common halogenated agents are methyl bromide, methyl
iodide, bromochlorodifluoromethane, dibromotetrafluoroethane,
dibromodifluoromethane and carbon tetrachloride. These halogenated fire
retarding
materials are usually available commercially in the form of gases or liquids.
Unlike
chlorine and bromine, fluorine reduces the toxicity of the material and
imparts stability
to the compound. However, chlorine and bromine have a higher degree of fire
extinguishing effectiveness and, accordingly, a combination of fluorine and
either
chlorine or bromine is usually chosen to obtain an effective fire-retarding
compounds.
Other commercially available fire retardant materials that do not include
halogens include boric acid and borate based compounds, monoammonium
phosphonate, and urea-potassium bicarbonate.
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Intumescent compounds which limit the heat and mass transfer by creating an
insulating charred layer on the surface of the burning polymer are also
considered fire
retardant materials. A typical intumescent additive is a mixture of ammonium
polyphosphate and pentaerythritol.
S Fire retardant additives are often used with organic polymer/resins.
Typically, a
brominated or chlorinated organic compound is added to the polymer in
admixture with
a metal oxide such as antimony oxide. Halogenated compounds are also sometimes
introduced into the polymer chain by co-polymerization. Low levels i.e. less
than 1%
~V/W are recommended to make adverse effects of halogen-based systems
negligible.
Another common fire retardant additive is diglycidyl ether of bisphenol-A with
Mo03.
Other additives to improve the fire retarding properties of polyethylene
include, for
example, beta-cyclodextrin, magnesium hydroxide and alumina trihydrate, tin
oxide,
zinc hydroxystannate, and chlorosulphonated polyethylene.
A problem found with commercially available fire retardant polyethylene films,
i.e. films comprising a fire retardant dispersed throughout the body of the
film is that the
fire retardant, generally, selected from the oxides of antimony, alumina
trihydrate or
magnesium hydroxide tend to migrate to and leach out of the film surface
during the
service life of the film and this constitutes an unsatisfactory aging
characteristic.
Further, because of the presence of the fire retardant at or adjacent to the
film surface,
heat sealing of multiple films together is also unsatisfactory. The
unfavourable aging
and heat sealing characteristics are a function proportional to the amount of
additive in
the film.
There is, therefore, a need for a thermal insulation system having improved
fire
retardant properties.
SUN>NIARY OF THE INVENTION
Surprisingly, I have found that the fire-retardant assemblies according to the
invention have satisfactorily met the dual requirements of acceptable aging
properties
and bonding strengths, i.e. delamination.
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It is one object of the present invention to provide a thermal insulation
system
for residential and commercial establishments having improved fire retardant
properties.
Accordingly, in one aspect the invention provides an improved bubble pack
comprising a first thermoplastic film having a plurality of portions wherein
each of said
5 portions define a cavity; a second thermoplastic film in sealed engagement
with said
first film to provide a plurality of closed said cavities; the improvement
comprising
wherein said cavities contain a fluid or solid fire retardant material.
The terms "cavity" or "cavities" in this specification include voids,
bubbles or other like closed spaces. The cavities may be formed of any desired
suitable
shapes. For example, semi-cylindrical, oblong or rectangular. However, a
generally,
hemi-spherical shape is preferred.
The bubble pack preferably comprises the cavities being wholly or partially
filled with a fire-retardant solid compound or composition.
The thermoplastic films may be formed of any suitable polymer or copolymer
material. The first and second film may be formed of the same or different
material.
Most preferably, the bubble pack has each of the films formed of a
polyethylene.
The fire retardant material may be a compound or composition comprising one
or more compounds having acceptable fire retardant properties in the form of,
for
example, a gaseous, liquid or gel fluid contained within the cavity; solid in
the form of a
particulate powder or dust within the bubble or coating upon the cavity wall.
The amount of fire retardant material is such as to provide an efficacious
amount
in relation to the amount of plastic and other components present in the
bubble pack.
Thus, the amount of fire retardant material required will depend on the
application of
the assembly, the type and effectiveness of the fire retardant material used,
the final
properties required e.g. flame spread index, slow burning or self
extinguishing, and the
bubble size. The fire retardant is generally present in an amount selected
from 0.1 -
70% W/W, more preferably, 10 - 60% W/W, preferably 20 - 50% W/W in relation to
the thermoplastic film.
Examples of suitable fire retardants of use in the practice of the invention,
include those classes and compounds as hereinbefore described. Preferably, the
fire
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retardant compound is selected from alumina trihydrate ( ATH, hydrated
aluminum
oxide, A1203.3H20), oxides of antimony, decabromodiphenyl oxide and mixtures
of
these compounds, optionally with a dimethyl siloxane fluid (DC200).
Most preferably, the bubble pack further comprises one or more foils, layers,
films, laminates or the like of a suitable metal, for example, aluminum to
enhance
reflection of infra-red radiation and lamination of the first and second films
in the
manufacturing process as hereinafter described.
Thus, a most preferred plastic is polyethylene, particularly a low-density
polyethylene, optionally, in admixture with a linear low density polyethylene
of use as
aforesaid first and second films.
The number, size and layout of the bubbles in the pack according to the
invention may be readily selected, determined and manufactured by the skilled
artisan.
Typically, in a single pack, the bubbles are arrayed in a coplanar off set
arrangement.
Each of the hemi-spherical bubbles may be of any suitable diameter and height
protruding out of the plane of the bonded films. Typically, the bubble has a
diameter
selected from 0.5 cm - 5 cm, preferably 0.8 - 1.5 cm; and a height selected
from 0.2 cm
- 1 cm, preferably 0.4 - 0.6 cm. A preferred bubble pack has an array of about
400
bubbles per 900 cm2.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be better understood, preferred embodiments
will
now be described by way of example only, with reference to the accompanying
drawings, wherein
Fig. 1 is an isometric view of a wall insulation panel comprising a bubble-
pack
assembly according to the prior art;
Fig. 2 is an isometric view of a wall insulation panel comprising a bubble-
pack
assembly according to the invention;
Fig. 3 is a diagrammatic, isometric view, in part, of a bubble pack-forming
apparatus
according to the invention;
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Fig. 4 is a modified version of the apparatus of Fig. 3 having enlarged
diagrammatic
cross-sectional views shown as Figs. 4A and 4B; and wherein the same numerals
denote
like parts.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
With reference to Fig. 1, this shows generally as 10, a prior art double
layer,
bubble-pack insulation assembly. The double layer consists of a pair of bubble
arrays
12, 14 bonded together through an intervening low density polyethylene film
16.
Arrays 12, 14 are formed of a plurality of bubbles or sealed cavities 18, 20,
respectively,
from a 5 mil polyethylene film 22, 24, respectively. Each of films 22, 24 is
bonded to a
reflective aluminum foil 26, 28, respectively.
Assembly 10 has approximately 20, 1 cm diameter, 0.5 cm high bubbles per 30
cm length and breadth within each of films 22, 24.
1 S The aforesaid assembly 10 is made by a double hot roller thermal and
vacuum
forming process for cavity forming and lamination sealing techniques known in
the art,
and has a fire rating of Class A/Class 1, a flame spread index of 16 and a
smoke
development number of 23. However, improvements in these ratings are required
for
new applications such as, for example, thermal insulation for heating and
ventilation
ducts.
Fig. 2 shows the embodiment described with reference to Fig. 1 but wherein
each bubble 18, 20 contains 5% W/W aluminum hydroxide fire-retardant 30
relative to
the amount of low density polyethylene resin.
The aluminum hydroxide fire retardant 30 may be added to cavities 18, 20 by
any suitable manual or automated method. In alternative embodiments,
alternative
retardants may be added by gas or liquid fluid injection or as a poured or
blown
particulate solid insertion method.
The apparatus shown in Fig. 3, generally as 200, has an endless belt conveyer
mold shown generally as 210 with which a film of thermoplastics material 202
operably
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moves in the direction L-R of the arrow under the influence of a sprayer or
dispenser
212, scraper 214, heaters 216 and nip roller 218, further described
hereinbelow.
A pre-heater 220 at a suitable temperature disposed below film 202 softens
film
202 to just below its melt temperature of, for example, 136 - 140°C for
polyethylene.
Mold 210 has an endless belt of segmented aluminum elongate members 222
movable by means of terminal rotating cog and sprocket assemblies (not shown).
Each
of members 222 has portions defining semi-spherical cavities 224 intermittent
along the
width of member 222 and offset to adjacent cavities 222 on adjacent members
222.
Each of cavities 222 has an aperture 226 to provide a suctional force on the
soft film for
the film to be pulled onto the inside cavity surface, by a vacuum pump (not
shown).
Disposed above softened film 202 adjacent the feed end 228 of apparatus 200,
is an
elongated feed conduit sprayer 212 having a plurality of exit apertures 232
which direct
filler material 234 in the form of particulate solid, e.g. powder, or liquid,
gel, emulsion
into each cavity 222. Although the spraying of material 234 may be suitably
1 S mechanically or electronically controlled to dispense material 234 only
wherein a cavity
222 is directly beneath an individual aperture 232, I have found that
sufficient resultant
adhesion between film 202 and covering film 236, subsequently bonded to film
202, as
hereinafter described, can be obtained by means of scraper 214 horizontally,
diagonally
disposed on film 202 to scrape off excess material.
Heater system 216 disposed above cavity-filled film 202 maintains the softness
of film 202 in addition to softening film 236 fed in arrow direction T-B prior
to its
melding and bonding with film 202 under nip roller 218 to form cavity-filled
bubble
pack film 238.
The size, shape and arrangement of the cavities in the film may be as suitably
determined by the skilled person. The temperatures of films 202, 236 as well
as film
throughput rate can be readily selected by the skilled person. Throughput
rates of the
magnitude of SO meters/minute are preferred.
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EXPERIMENTAL
GENERAL
Fire retardant bubble packs were formed consisting of a lower bubbled-
polyethylene film, an upper flat polyethylene film and a fire retardant
chemical placed
in the bubble cavities of the lower film. The pack was formed by hot pressing.
Peel
tests used a modified ASTM D902 method and flame retardant tests were based on
1
ED Method 707.
The samples were subsequently exposed to aging tests simulating twenty years
service.
Similar tests were also performed on heat bonded films having fire retardant
deliberately put between the films prior to hot pressing.
Two polyethylene films of different thickness were used as base films. A
bubble
film with an original thickness of 6 mil, and a plain/flat film with a
thickness of 3 mil
were used. A 1.25 mm thick, aluminum plate/mold having a surface area of 32 cm
x 32
cm was used for the bonding (hot pressing) tests of the polyethylene films. A
rubber-
dimpled plate (0.6 cm thick) was secured on top of the aluminum plate having
dimples
so sized as to support the bubbled polyethylene film supplied. The rubber
provided a
non-stick surface to the polyethylene films during hot pressing.
The hot press consisted of two plates that were independently heated to a
controlled temperature and pressed together by a hydraulic press with the
applied load
measured by a pressure gauge. To calculate the applied pressure, the measured
load is
divided by the surface area of the plate. The temperature of each of the
plates was
measured by a thermocouple. However, for the purpose of these tests, only the
top plate
was heated.
Several tests were made to determine the optimum pressure, time and
temperature for the bonding of the polyethylene films, each of a surface area
of 32 cm x
32 cm. A bubbled 6 mil film was secured in the dimpled plate and a 3 mil film
was
placed on top of it. The weight of the bubbled film was 19.4 g while the
weight of the
flat 3 mil polyethylene film was 5.2 g. A thin Mylar sheet was then placed on
top to
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prevent sticking of the polyethylene to the top hot plate of the hot press.
The top hot
plate of the hot press was then heated the required temperature and lowered
onto the
plate-films arrangements. The required load applied to the films was reached
using the
hydraulic press.
Several time-temperature tests were undertaken. The pressure was kept constant
in all cases at 30 psi. Temperature below 136°C did not produce good
bonding, while
temperatures above 140°C rapidly melted the polyethylene films.
Different
pressing/bonding durations at 138°C were tested at pressing periods of
1 second, 15
seconds, 30 seconds and 60 seconds. Peel tests were used to determine the
effect of the
10 hot-pressing period on the bonding of polyethylene films, using a modified
ASTM
D903 "Standard Test Method for Peel or Stripping Strength of Adhesive Bonds"
to
accommodate specimen size and specifications. Table 1 summarizes the peel
strength
results as a function of press time at 138°C and 30 psi of pressure.
1 S Table 1. Peel strength as a function of pressing time
PRESS TIME (seconds)PEEL STRENGTH (N/m)
1 349.4
711.1
773.5
30 763.3
60 863.2
The results indicated that best bonding results were obtained using 60 seconds
of
hot pressing. The one-second hot pressing produced very poor bonding.
Peel test on the bonded polyethylene were undertaken on two different samples.
Both samples, however, were manufactured from the same type of materials,
i.e., a
bubbled 6 mil and a flat 3 mil polyethylene sheet. The first sample had a peel
strength
of 552.2 N/m, while the second sample did not peel before it broke which
suggests that
its bonding strength is stronger than the tensile strength of its components.
The results presented above indicate that the peel strength of the
manufactured
insulation bonded according to the invention is of good quality and compares
very well
with manufactured prior art products. The bonded insulation was also tested
visually as
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well as by attempting to press the bubbles of the bonded insulation. Visual
inspection
and comparison to manufactured prior art products indicated overall good
bonding. By
pressing on the bubbles of the bonded insulation, the bubbles broke if the
bonding was
good. If the bonding was weak, the air bubbles migrate into the flat space
between the
films. Except when using a one-second hot-pressing period, excellent bonding
occurred
at all other conditions examined.
In summary, best results were obtained with the following condition:
Temperature: 138°C
Pressure: 30 psi
Duration: 60 seconds
Good peeling strength was also obtained when the hot-pressing time was
between 15 and 30 seconds. These conditions and the plain polyethylene samples
obtained from these tests provided a base line for subsequent testing,
comparison and
analysis.
A second arrangement was also examined for bonding. This time, the 6 mil
bubbled polyethylene was bonded to a 1 mil polyethylene film backed by an
aluminum
foil. This arrangement is the preferred arrangement for insulation
applications.
Bonding tests were examined by preparing samples at different hot pressing
durations
while keeping the temperature and pressure constant at 138°C and 30
psi, respectively.
The results of the peel tests are shown in Table 2.
Table 2. Peel strength as a function of pressing time using aluminum-backed
polyethylene
PRESS TIME (seconds) PEEL STRENGTH (N/m)
1 S 734.9
1223.0
60 1127.0
Peel stengths were larger than those prepared, under the same conditions using
similar two polyethylene films but without aluminum backing. This suggests
that the
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aluminum film provides a useful and important role in improving the heat
conduction
throughout the sample and between the hot plate and the polyethylene films.
BONDING OF POLYETHYLENE BUBBLE PACK FILMS CONTAINING FIRE
S RETARDANT CHEMICAL
The purpose of this test was to test the feasibility of bonding of
polyethylene
films filled with chemicals. In these trials, the 32 cm x 32 cm film was
divided into four
different quadrants of 16 cm x 16 cm area with each section being filled with
a different
chemical composition. The combinations prepared were those shown listed in
LIST A.
LIST A
1. Mix #l : Antimony Trioxide - 1 part (by weight) plus decabromodiphenyl
ether
- 2 parts (20g & 3.0g & 1.5g)).
2. Mix #2: Mix #1 plus 14 weight percent dimethylsiloxane (DC200) fluid (50g &
3 .0g & 3.0g & 1. 5g).
3. Mix #3: Mix #1 plus 14~% propylated triphenyl phosphate (Phosflex 41P) (50g
& 3.0g & 3 .0g & 1. 5g & 1. 5g).
4. Mix #4: Mix #1 plus 14% butylated triphenyl phosphate plus triphenyl
phosphate (Fyrquel EHC-S) (25g).
5. Alumina trihydrate (3.25g).
6. Calcium cabonate (3.0g).
7. Vermiculite (3.75g).
8. Phosflex 41P fluid (3.25g).
The figures between brackets show the actual weight of the chemical mix placed
within the 16 cm x 16 cm area of polyethylene film. In some cases, this
effective
weight percent amount was much higher than what is generally recommended by
suppliers for these materials. The results of the fire-retardant tests of
these samples,
therefore, provided an excellent indication of the effectiveness of each of
the selected
fire retardant chemicals in improving the fire retardant properties of
polyethylene films.
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Bonding was undertaken by hot pressing at conditions outlined hereinbefore.
Visual inspection, hand peeling and bursting of bubbles of the prototypes
prepared
indicated all samples with powder chemicals were well-bonded. The only sample
that
appeared to show a weak bonding between the two layers was that containing the
fire
retardant fluid Phosflex 41P. This suggests that during hot pressing some of
the fluid
evaporated from the bubbled areas and condensed onto the flat surfaces between
the
polyethylene films. Since bonding of the polyethylene films required good
contact
between the films, the migration of the fluid to the flat surfaces prevented
the required
contact between the films and, thus, prevented good bonding.
To determine the effect of the dimethylsiloxane fluid used on bonding of the
polyethylene, the fluid was first sprayed onto the bubbled film. The required
amount of
powder material was then applied on top of the sprayed fluid within the
bubbles and on
the flat surfaces. Hot pressing at the conditions indicated above did not
produce a good
bond between the films, even after repeated hot pressing. This suggests that
this method
of application may not be practical in making the bubble pack according to the
invention.
Aluminum backed polyethylene was also bonded to bubbled films with different
retardant chemicals placed within the bubbles. Examples of this system were
examined
for R-value and fire retardant properties and provided the preferred bubbled
pack
according to the invention.
BONDING OF FIRE RETARDING POLYETHYLENE FILMS
Several tests were undertaken to bond prior art fire retardant polyethylene
films.
Films with two different thicknesses were used in the test, namely, 10 mil and
3 mil.
Attempts to bond the two films together at the conditions specified for the
polyethylene
films hereinbefore described for the bubble pack of the invention were not
successful.
Increasing the temperature to 140°C also did not provide the bonding
required although,
this time, there was some very localized but weak bonding formed between the
two
films. A third test was undertaken a plain bubble-film was bonded to the 3-
mil, flat fire-
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14
retardant polyethylene film. The conditions for this test were also similar to
those used
for plain polyethylene films. This test resulted in good bonding between the
two
different films.
As mentioned hereinbefore, fire retarding polyethylene films because they
contain compounds with relatively small molecular weights, migrate and leach
out of
the surface of the polymer during the service life of the polymer material or
upon
heating.
The results of the bonding tests of these films confirmed the inadequate
bonding
of these films.
RESULTS
The following sections provide results for fire tests, peel tests, aging tests
and R-
value measurements.
PRELIMINARY FIRE TESTS
The first experimental screening tests were fire tests on the polyethylene
film
bubble packs containing the compounds identified in LIST A, hereinbefore. In
addition
to these packs, plain polyethylene bubbled films and commercial fire-retardant
polyethylene films were also subjected to the same fire testing and
evaluation. The
materials were exposed to 15 seconds of flame. Burn, ignition, after-burn,
melting,
formation of holes and the size of the holes formed were all parameters
observed during
and after each fire test. When a fire retardant compound was added to the
polyethylene
film, the fire test was undertaken twice. In the first test the flame was
directed towards
the bubble side while in the second test the flame was directed towards the
flat side of
the sample. In all cases the fire-test results from either of the two sides
were similar.
The results on plain/bubbled polyethylene material showed that the material
burned and ignited in less than 10 seconds. The sizes of the holes were
usually larger
than 40 mm. The fire retardant polyethylene films also ignited at 8 - 10
seconds but
their burn rate was slower than that of regular polyethylene materials.
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The results of the preliminary fire tests on polyethylene containing fire
retardant
chemicals are summarized in Table 3 for the chemicals and mixes identified in
LIST A.
In all the tests, the material used was l6cm x 16 cm area and which was
exposed to 15
seconds of flame.
S
Table 3. Summary of Preliminary Fire Tests
MATERIAL WEIGHT OF WEIGHT OBSERVATIONS
CHEMICAL ADDED RATIO
Mix 1 20 g 6.7 Starts to ignite but
no burn,
Some small holes were
formed ~7mm diameter
Mix 2 50 g 16.7 No ignition or burn;
melting
resulted in a 3-cm
diameter
hole.
Mix 3 25 g 6.7 No ignition or burn
or any
holes.
Mix 4 3.25 g 1.1 Starts to ignite but
not burn;
melting resulted in
a 5-cm
hole.
Alumina 3.0 g 1.0 No ignition, 4-cm
hole with
trihydrate smaller holes ( 1
cm) in
bubbles.
Calcium 3.0 g 1.0 Burns easily.
carbonate
Vermiculite 3.75 1.25 Burns and i nites.
Phosflex 41P 3.0 g 1.0 Softened, small holes,
no
fluid burn, oil .
Mix 1 3.0 g 1.0 No ignition or burn,
small
holes ~3 mm
Mix 2 3.0 g 1.0 Melts but no burn;
melt hole
6 cm .
Mix 3 3.0 g 1.0 Melts but no burn;
melt hole
Scm.
These tests clearly indicated that calcium carbonate and vermiculite were not
as
effective in fire retarding as the other chemical/mixes. In addition, mix 4
comprising
10 antimony trioxide, decabromodiphenyl ether, butylated triphenyl phosphate
and
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triphenyl phosphate had one more component than mix 3 but its fire test
results were not
as good.
The results show that polyethylene films having mixes 1, 2 ,3 and alumina
trihydrate had excellent fire retardant characteristics. Further, the
polyethylene bubble
pack according to the invention with any of these four compositions showed
excellent
fire retardant properties and a self extinguishing capability after the flame
was removed.
The effect of using a lighter, i.e. thinner polyethylene bubbled material was
also
examined.
Mix 2 was added to an embodiment consisting of a 4 mil bubbled polyethylene
sheet backed by a 3-mil flat polyethylene film. Fire tests on this combination
showed
that a hole formed after only 10 seconds of exposure to the flame, and the
fire retarding
ability appeared to be reduced compared to the thicker polyethylene film. This
suggests
films have a minimum thickness readily determined by the skilled person for
use in fire
retarding applications. Thus, preferably, a 6 mil thickness should be used as
the
minimum thickness that would provide adequate fire retarding properties.
One of the mains applications for the new fire-retardant polyethylene bubble
pack according to the invention is in the construction industry. For these
applications,
the pack comprises a bubbled polyethylene film backed by a flat polyethylene
film with
aluminum foil backing. Embodiments having this configuration were processed
for
further testing using the four final candidate compounds identified earlier.
The processing conditions outlined hereinbefore were similarly used to prepare
these embodiments. The amount of compound used in each 25 cm x 25 cm section
under test was 6.0g, i.e. 1.5 g for each 12.5 cm x 12.5 cm subsection). The
weight ratio
of the compound to polyethylene was, thus, 0.5.
Fire tests were conducted on samples each containing mixes l, 2, 3 and alumina
trihydrate. For all samples, two tests were conducted. In the first test, the
aluminum
foil was exposed to the test flame, while in the second test, the polyethylene
bubbles
containing each of the compounds were exposed to the test flame for 15
seconds. In
some cases, the sample was exposed to the flame for another 1 S seconds. One
sample
(with mix 1) was exposed to the flame for another 30 seconds period.
CA 02282967 1999-09-17
17
The sample containing mix 1 was exposed to the flame for a total of 60 seconds
(15 + 15 + 30 seconds). The sample containing alumina was exposed for a total
of 30
seconds (15 + 15 seconds). It is clear that excellent fire-retarding
properties were
obtained when the test flame was directed towards the aluminum foil. This
excellent
fire retardant characteristic was also confirmed for samples that contain
mixes 2 and 3.
It appears that the aluminum foil acts as a radiation shield and, because of
its high
thermal conductivity, it also allows for the fast distribution of heat from
the flame
throughout the sample and thus, reduces the concentration of heat to the
exposed area.
This result also suggest that better fire resistance of the bubble pack of the
invention
could be accomplished by increasing the thickness of the aluminum foil.
On the other hand, when polyethylene bubbles are exposed to the test flame,
the
polyethylene film melted and slowly ignited after 15 seconds of flame
exposure. The
fire was self extinguished after 30 seconds from removing the test flame.
The effect of using a relatively large amount of fire retardant chemicals
within
the polyethylene pack system was investigated. Fire tests were undertaken on
bubbled
polyethylene sheets of area 12.5 cm x 12.5 cm, mass = 3 g and containing SO g
of mixes
2 and 3, i.e. mass ratio (chemical/polyethylene) of ~ 17. After 15 seconds of
exposure
to a test flame there were no indication of any burns, ignition and/or holes.
This
suggests that there is some improvement in the fire retarding properties of
polyethylene
with increasing the amount of fire retarding compound present in the voids.
However, a critical mass ratio appears to exist. Using mass ratios above the
critical value appears not to significantly increase the fire retarding
properties. For
mixes 1, 2 and 3, it appears that there were only slight improvements in fire-
retarding
characteristics with increasing the amount of fire retarding chemical above a
ratio of 1.0
(mass ratios examined = 0.5, l, 8, 17). A mass ratio near 1.0, thus, provides
excellent
fire retarding properties to the polyethylene bubble pack of the invention
CA 02282967 1999-09-17
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PEEL TESTS AND AGING EFFECTS
The hereinbefore peel test results on the plain polyethylene material provide
a
benchmark for comparison of the developed fire retardant systems. Peel tests
before
and after aging were undertaken on fire retardant packs of the invention. The
samples
were exposed to and accelerated aging process to simulate aging for twenty
years. For
these tests, aluminum backed polyethylene was used as the flat film.
Conditions used for
bonding of the films were 139°C, 30 psi, and 15 seconds. Four different
compounds
were used: Mix #1 (Antimony Trioxide plus decambromodiphenyl ether); Mix #2 (
Mix
# 1 plus DC 200 fluid); Alumina trihydrate; and Alumina trihydrate plus DC 200
fluid.
A weight ratio of 100% (equal weights of compound and polyethylene) was used
in all
tests. As a reference, a plain specimen was also prepared and tested for peel
strength.
Table 4 summarizes the peel tests results before and after aging.
Table 4. Peel stength for fire retardant rFOIL systems, before and after a~in~
Fire Retardant CompoundPeel Strength (N/m)Peel Strength
After A in N/m
No Fire Retardant 730 776
Mix 1 508 547
Mix 1 + DC 200 468 548
Aluminum trih drate 664 674
Aluminum Trihydrate 545 519
+ DC 200
The results show that the peel strength of the plain prototype is similar to
that
obtained in previous tests (e.g. Table 2) but higher than the peel strength of
the
specimens with fire retardant compounds. This could be attributed to the
existence of
some material between the flat surfaces of the bonded films. The differences
between
the value of the peel strength between the specimens could also attributed to
the
variation in the amounts of material between the flat surfaces from one sample
to the
other. The most significant result is that the peel strength was not reduced
after the
simulated aging process. This confirms that the insertion of the fire
retardant
compounds within the bubbles of the polyethylene does not have any significant
CA 02282967 1999-09-17
19
detrimental effect on the aging characteristics of the fire-retardant bubble
packs of the
invention. This contrast to the existing fire retardant polyethylene films
which exhibit a
deterioration of their bonding strength within a very short period of time,
e.g. 6 months.
THERMAL PROPERTIES
The thermal R-value of the packs was only slightly lowered when the voids
contained fire retardant compounds in the packs according to the present
invention.
Although this disclosure has described and illustrated certain preferred
embodiments of the invention, it is to be understood that the invention is not
restricted
to those particular embodiments. Rather, the invention includes all
embodiments which
are functional or mechanical equivalents of the specific embodiments and
features that
have been described and illustrated.
