Note: Descriptions are shown in the official language in which they were submitted.
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The present invention is concerned with thermal insulation in situ-
ations, for example in building structures, in which it is desired to reduce
the thermal conductivity between spaced apart surfaces having an air space
between them. This may be achieved by filling the air space between such sur-
faces with a material of appropriate thermal conductivity characteristics,
and in the case of building structures of cavity wall construction it is known
to fill the cavity with insulating materials such, for example, as expanded
vermiculite, mineral wool, cellular polystyrene or polyurethane foam.
Expanded polystyrene beads have a cellular structure, and are thus
in principle well adapted to the insulation of cavities. However, their very
low bulk density and free flowing characteristics often make it difficult to
ensure that they are retained in the cavities and do not escape through joins
or faults in the cavity walls. A solution to this problem developed by the
Applicants is to coat the expanded polystyrene beads with a binder of synthet-
ic polymer latex. The presence of this latex binder then hinders flow of
polystyrene beads through any openings in the cavity walls to such an extent
that any flow is stopped before a significant amount of beads has passed
through.
One of the most important applications of cavity insulation is in
the insulation of buildings, because of the substantial savings in energy con-
sumption thereby achieved. In such applications it is important not only to
achieve improved thermal insulation but also to ensure satisfactory fire re-
tardant properties, and although grades of expanded polystyrene beads are com-
mercially available which contain a flame retardant additive, the use of such
beads with a synthetic polymeric latex binder does not always provide a suffi-
ciently high level of fire retardancy. The Applicants have now devised a
method whereby a flame retardant can be introduced with the synthetic poly-
meric latex binder into the cavity, thereby providing good fire retardant
properties in the cavity fill composition. Accordingly the present invention
provides a method of providing a flame
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retardant thermal insulation between a plurality of spaced apart
surfaces having an air-filled cavity between them, which compris-
es introducing into said cavity a mixture containing cellular
particles of expanded polymer, a synthetic polymer latex binder,
and an organic bromine-containing compound conferring flame
retardant properties on the bound polymer particles.
Beads of expanded polystyrene are particularly suitable
for use as the cellular polymer particles in the method of this
invention, but other types of cellular, expanded polymers may
also be used. As is well known cellular polystyrene particles
are conveniently prepared from expandable particles manufactured
in the form of beads or pearls by suspension or emulsion poly-
merisation techniques, the expanding agent such as pentane being
incorporated therein during or after polymerisation. Upon heat-
ing of the expandable pearls or beads, "pre-expansion" occurs,
yielding the cellular polystyrene particles suitable for use in
the method of this invention. Pre-expansion, a well-known step
in the art of cellular polystyrene, comprises steaming the ex-
pandable beads or pearls to give an expansion of some 20 to 30
times their original volume, and during cooling, allowing air to
penetrate into the individual cells to raise the internal pressure
to atmospheric pressure. These expanded cellular polystyrene
particles have a spherical shape, an apparent, packed density
of, e~g. 6-100 g/l and free-flowing properties. For wall cavity
filling the particle size of the beads is suitably in the range
of 1-10 mm, and for this application it is desirable to employ
self-extinguishing grades of polystyrene beads. A number of
additives is known for this purpose, such as brominated or
chlorinated organic compounds.
The synthetic polymer latex used as binder in the method
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of this invention may be any aqueous colloidal suspension of
particles of a polymer obtained by addition polymerisation.
Generally the colloidal suspension is stabilised by the presence
of a suitable surface-active agent, and the most suitable poly-
mers are those obtained by free-radical emulsion polymerisation.
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Thus, suitable latices include those based on, for example, styrene-butadi-
ene copolymers, acrylic copolymers, butadiene-acrylonitrile polymers, vinyl-
idene chloride copolymers, butyl rubber, isoprene or, preferably, polymers
or copolymers of vinyl alkanoates, such as vinyl acetate or vinyl propionate.
A preferred class of latices are based on vinylacetate copolymers, in partic-
ular on copolymers of vinyl acetate with higher vinyl esters such as vinyl
caproate, vinyl laurate and vinyl~,~-dimethyloctanoate. It has been found
that particularly satisfactory results are obtained if the latex is based on
a copolymer of vinyl acetate and a vinyl ester of a carboxylic acid having 6
10 to 16, in particular 8 to 12, carbon atoms per molecule, such copolymers
being available commercially under the Trademark "VeoVa". In the latter type
of copolymers the weight ratio of vinyl acetate to higher vinyl ester may be
from 10:90 to 85:15, preferably from 60:40 to 80:20. The latex may, if de-
sired, contain other additives such as silica fillers, thickening agents, cor-
rosion inhibitors, pigments and water soluble dyes.
The organic bromine-containing compound used as the flame retardant
component in the method of this invention may be any of the compounds of this
type conventionally incorporated into polystyrene beads, for example, bromo-
phenyl alkenyl ethers such as pentabromophenyl allyl ether, brominated cyclo-
alkanes such as hexabromocyclododecane, or organic phosphates such as tris-
(2,3-dibromopropyl)phosphate. If the flame retardant is a solid, it may con-
veniently and efficiently be introduced into the cavity by means of a flow-
able suspension concentrate, which, as such, forms a further feature of this
invention and comprises 10-85%w of the solid flame retardant, 0.5-15%w of dis-
persing agents, 0.1-10%/w of suspending agents such as protective colloids
and thixotropic agents, 0-10%/w of supplementary additives such as flame re-
tardant synergists, for example, antimony oxide, defoamers, corrosion inhib-
itors, stabilisers, penetrants, bacteriostatic preservatives and stickers,
and as carrier, water or an organic liquid in which the flame retardant is
substantially insoluble; certain organic solids or inorganic salts may be
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dissolved in the carrier to assist in preventing sedimentation or as anti-
freeze agents for water, for example, ethylene glycols.
The dispersing agent may be nonionic, such as an ethylene oxide/
propylene oxide copolymer, an ethoxylated alkyl phenol or an ethoxylated long
chain alcohol, or anionic, such as a metal, suitably sodium or calcium, salt
of lignin sulphonic acid, methacrylic acid, or other polyelectrolyte. The
suspending agent may be a water-soluble polymer, such as a polysaccharide or
hydroxyethyl cellulose, or a finely divided inorganic solid, such as benton-
ite, montmorillonite, or other clay powders. The particle size of the flame
retardant should desirably be as small as practicable, suitably with a vol-
ume median diameter below 10 ~m and preferably between 1 and 5 ~m. The pre-
cise nature and proportions of the components incorporated into such a suspen-
sion concentrate will naturally be dependant on the physico-chemical proper-
ties of the selected flamé retardant component, and it will be understood by
those skilled in the art that not every potential dispersing agent will nec-
essarily be sufficiently compatible with every suspending agent and every
flame retardant. In the case of pentabromo phenyl allyl ether, good results
have been obtained using an aqueous suspension concentrate containing a natur-
ally occurring polysaccharide and an ethylene oxide/propylene oxide copolymer.
Advantageously, according to a further feature of this invention,
the cellular particles of expanded polymer are introduced into the cavity by
means of a mixing gun in which streams of particles, latex binder and flame
retardant are combined in the desired ratio and the resulting mixture is de-
livered into the cavity through the gun nozzle. Such a mixing gun suitably
comprises a tube or like device adapted to be connected to a reservoir of par-
ticles, such as a feed hopper, and having inserted therein a main jet through
which air or other gaseous fluid under pressure can be introduced for the pur-
pose of sucking the particles along the tube or the like from the reservoir,
and also one or more supplemental jets through which the binder latex and
flame retardant component are introduced.
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For wall cavity filling the amount of latex is suitably such as to
provide 5-10%, preferably 6-8%w of latex solids, based on the weight of the
polymer particles. The solids content of the latex itself may be 10-20%/w
while the total weight ratio of polymer particles to latex is usually in the
range of 10:1 to 10:10 for these types of applications. The proportion of
flame retardant will normally be between 0.1-10%/w based on the weight of the
polymer particles.
- Although the latex binder and the flame retardant component may, if
desired, be fed separately into the mixing gun ~or even separately into the
cavity), it has been found that the practical operation of the cavity filling
method is significantly simplified if the flame retardant agent, suitably in
the form of a suspension concentrate, is pre-blended with the latex binder,
and the cellular polymer particles are coated with the resultant mixture,
conveniently in the mixing gun. This procedure not only simplifies the design
of the mixing gun by reducing thé number of separate feeds and supplemental
jets, but also makes it possible for the latex/flame retardant mixture to be
formulated at a central location and transported to the individual sites
where the cavity filling is to take place. This procedure thus reduces the
number of separate formulation components required at the site of operation,
and thereby both reduces the demands of logistical organisation and storage
space, and also eliminates the need to provide for independant measurement by
the operator of the quantity of flame retardant. However, it will be appreci-
ated that such a centralised formulation of the latex/flame retardant mixture
is possible only if the resultant mixture has adequate storage stability, the
achievement of which is largely contingent upon the use of a suitable formula-
tion of the flame retardant component. The Applicants have found that the use
of a suspension concentrate of the flame retardant component generally enables
satisfactory storage stability to be obtained when it is admixed with the
latex binder.
After the cavity has been filled by the method of this invention
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the resulting filling is allowed to dry and set. Upon sufficient evaporation
of water the latex polymer will coalesce upon the cellular polystyrene par-
ticles and function as a permanent binding agent. After moistening the poly-
styrene particles by the latex, before setting, the free-flowability of the
particles is somewhat reduced which will prevent the beads from undue spill-
ing.
The setting time of the composition - usually 1/2 to 3 hours -
depends upon a number of factors, such as environmental temperature and rel-
ative humidity, free passage of air, and composition and amount of the latex
employed. Generally the temperatures for setting are in the range of 15-40C.
The minimum film formation temperature may, if desired, be reduced to as low
as 5C by the addition of small amounts of high molecular weight alcohols,
e.g. 1-5%/w on latex. Suitable alcohols for this purpose are polyethylene
glycols, polypropylene glycols and ester-alcohols.
It will be understood that, although the method of this invention
is particularly convenient for the insulation of the cavities in existing
buildings incorporating a cavity wall construction, it is by no means limited
to this application. Thus, blocks or panels used in building construction
are often formed with cavities to reduce their weight, and the method of this
invention may be employed to fill those cavities and increase the thermal
insulation properties of the product. Other applications, including many
outside the field of building, will be apparent to those skilled in the art.
The invention is illustrated in the following Examples.
Example I
Pentabromophenyl allyl ether ~PEPAE) was formulated as a suspension
concentrate (SC) containing, by weight, 65 parts PBPAE, 1.25 parts of the
ethylene oxide/propylene oxide copolymer available under the Trademark
"Pluronic" P.105 and 0.3 parts of the naturally occurring xanthan gum avail-
able under the Trademark "Kelzan" XC. This suspension concentrate was mixed
in varying amounts (shown in Table 1 below) with a latex of a vinylacetate
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copolymer with "VeoVa" 10, a registered Trademark for a vinyl ester of ~
dimethyloctanoic acid in a monomer weight ratio of 70:30, containing 3%wt, of
an anionic emulsifier and having a solids content of 17%wt, and a pH of
4-4.5. This composition was then mixed in a mixing gun with cellular poly-
styrene beads having a diameter of 3-5 mm, a true density of 20 g/l, and in-
corporating 0.6% wt of PBPAE as flame retardant, the mixing ratio being about
60 parts by wt of PBPAE/latex mixture to 500 parts by wt of polystyrene par-
ticles, and the mixture injected at 2SC into a cavity.
After 1 hour the mixture had set in the cavity to an apparent bulk
density of 10 g/l (based on polystyrene), and the flame retardancy of this
filling was then evaluated using both the time of flame to extinguish ~as
defined in the flammability test of BS 3837), and the "oxygen index" deter-
mination as described in Modern Plastics, March 1970, pages 124-130 (also
ASTM D 2863). The precise compositions of the different mixtures evaluated,
and the results of the fire retardancy tests, are set out in Table 1 below.
TABLE 1
Composition ~parts by weight) Flame Retardancy
EPS Beads Latex PEPAE SC Flammability-BS 3837 Oxygen Index-
(incorporated ~time in secs. for ASTM D2863
in latex)flame to extinguish) t% oxygen)
100 12 - - 18
100 12 0.5 11
100 12 1.0 14 22
100 12 1.5 4
100 12 2.0 2 24.5
Example II
The vinyl acetate/"VeoVa" latex described in Example I was mixed
with varying amounts (as shown in Table 2 below) of the liquid flame retard-
ant tris-(2,3-dibromopropyl)phosphate (T23P) and 1%wt (based on T23P) of
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glyceryl monostearate, and the resulting mixture diluted with two volumes of
water. This diluted latex mixture was injected, together with cellular poly-
styrene beads, into a cavity, following the procedure described in Example I;
the procedure being carried out both with PBPAE - containing beads ("F"
grade) and similar beads in which no flame retardant had been incorporated
~"R" grade). Flammability tests were then carried out on the composition
filling the cavity, and the results are shown in Table 2 below:-
TABLE 2
Flammability, in secs. to extinguish
% T23P (BS 3837)
(based on beads) "F" beads "R" beads
1.5 over 20 over 20
2.0 over 20 over 20
2.5 2-3 2-3
5.0 o o
