Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
A MINERAL WOOL PRODUCT
BACKGROUND OF THE INVENTION
The invention relates to a heat-hardened mineral wool
product consisting essentially of mineral wool fibers, in
particular rockwool, and a binder(s) which will harden when
heat-treated.
The expression "mineral wool product" includes most
products made from mineral wool, such as mineral wool rolled
insulating felts, insulating panels, insulating mats, laminar
mats and other shaped bodies, such as insulating tubes for
covering pipes, and virtually any type body which is subject
to pêrmanent or changing thermal stresses (heat). Illustra-
tively, a "mineral wool product" includes a product formed of
mineral wool fibrous material used for heat insulating appli-
cations, such as insulation for ovens, homes, pipes or con-
duits, or the like.
The manufacture of mineral wool products, particularly
mineral wool insulation, is carried out by transforming
silicate melts into fibers. The diameters of the vitreously
solidified mineral fibers range from about l~m to about lO~m
with averages of 4~m to 5~m.
Aqueous solutions of phenol-urea formaldehyde resins have
been found to be practical binders for the manufacture of
mineral wool products/insulation. Such resins, when present
at an early stage of polycondensation, are substantially
soluble in water and, therefore, are highly dispersible when
introduced into the flow of fibers with the result that the
fine mineral fibers are very thinly coated with the resin and
link or bond together substantially at point-contact sites.
The binder content in the insulation is generally less than 8%
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by weight with the remaining 92% by weight being the mineral
wool fibers. Moreover, lubricants are added to enhance
hydrophobic properties and to increase the "touch" or "feel."
Such lubricants can consist of, for example, oil-in-water
emulsions, mineral oils, silicone oils, silicone resins and
modified silicon resins.
Because an aqueous medium is used to disperse the phenol-
formaldehyde resin, the emission of possibly ecologically
injurious organic solvents is avoided, and industrially more
significant, the cooling rate of the fibers is raised to such
an extent that they solidify in a vitreous manner at tempera-
tures so low that pre-hardening of the fiber films or droplets
on the fibers in associated conventional collecting chambers
is prevented. The process requires the individual mineral
fibers to be collected in the collecting chamber after which
they are stratified to a desired thickness and are fed between
a pair of compression belts in a constant flow of fibers to a
conventional hardening oven. It is in the hardening oven that
the manufacture of the insulaticn material is completed with
the thickness and density being determined by the predeter-
mined space between the compression belts and the initial
density/thickness of the fibers sandwiched and/or compressed
therebetween. The heat of the hardening oven irreversibly
hardens the phenol-formaldehyde resin into a pressure-setting
plastic at temperatures of between 250C - 300C.
A substantial deficiency of utilizing organic phenol-urea
formaldehyde resin is that it will decompose at relatively
high temperatures and in the process of decomposing odorous
and possibly health-damaging gasses are generated. The
thermal resistance of the hinder is roughly 250C to 325C
and, therefore, is well below the melting point of the fibers
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which is preferably higher than 1000C with respect to fibers
such as those fused from raw materials, namely, greenstone,
basalt or the like.
Many attempts have been made to replace organic fibers by
inorganic fibers, illustratively water glasses have been tried
as substitutes to bind the fibers. The same is also true for
making solid fibers with clay minerals keing suitable in this
respect. Such fibers can be bound by using the sol-gel
process, for instance with sodium-boron-silicon compounds.
This creates a very brittle binder and very large amounts of
binder are required. As a result, the conventional process/
technology of the mineral wool industry are generally inappli-
cable. Furthermore, insulation made in the latter convention-
al manner lacks desired/mandatory flexibility as, for example,
an initial density range < 200 kg/m3 required in numerous
applications. In other applications elasticity is a mandatory
property but is found wanting n such conventionally manufac-
tured fiber insulation.
It is also known that aluminum metaphosphate in the
binary system Al203-P205 is a re]ati.vely yood vitrifying agent.
Compositions with higher contents of aluminum oxides, for
instance AlPO4, are found unsuitable before they solidify in
crystalline form, they differ substantially in their expansion
coefficients with respect to the expansion coefficients of the
associated binder and mineral wool/glass wool/fiberglass
fibers, and they detach from the latter and fail to achieve
the desired bond.
There are also chain-structured polyphosphates, for
instance sodium polyphosphate, which, however, can only form
water-soluble glasses but even in such cases, there is no
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assurance that a long-lasting bond between the fibers can be
achieved.
_UMMARY OF THE INVENTION
An object of the present invention is to avoid the
disadvantages heretofore noted in the manufacture of a mineral
wool product and, of course, the mineral wool product per se
by producing a mineral wool product possessing requisite
strength properties even when subject to high thermal stress
(high heat) and can be manufactured by a process which will
not generate odorous or health damaging gases.
The object of the present invention is achieved by
utilizing as a binder aluminum metaphosphate Al(PO3)3
dispersed/dissolved in water. In practice, the aluminum
metaphosphate can be prepared as a micro-fine powder which is
dispersed in water and is sprayed in uniform very finely dis-
persed form onto hot mineral wool fibers. Due to the latter,
a substantial aclvantage is achieved in that the mineral wool
product or insulation can be processed or stressed thermally
up to the softening point of the mineral fibers without the
formation of noxious gases.
A further advantage of the invention is an excellent and
long-lasting bond is achieved between the binder and the
mineral fibers. One reason for this advantage is that the
meta-phosphoric acid forms annular molecules of different
sizes. The conventional strength properties are thereby
retained, and the final mineral wool product of the invention
can be processed into rolled insulating felts, insulating
panels, insulating mats, laminar mats, or into any arbitrary
shaped bodies desired for a particular application, such as
cylinders for insulating heating/air conditloning ducts,
liquid conveying pipes or the like.
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Advantageously the proportion of aluminum meta-phosphate
is about 3% to 20% by weight, and is preferably 7% to 12% by
weight relative to the total weight.
The mineral wool product of the invention is preferably
made from mineral fibers, foremost alkali-poor fibers, such as
rock wool.
In ~urther accordance with this invention, a lubricant
such as mineral oil or oil-in-water emulsions is added in a
finely dispersed form during the manufacture of the mineral
wool product.
Preferably, the impregnation of the binder and/or the
lubricant and/or the thickener with the mineral fibers is
achieved by impregnation through conventional impregnating
means or through the utilization of an aerosol or a steam
phase which creates total saturation/impregnation of the
mineral wool product or insulating material.
P.n example of a speciflc ~process for producing a mineral
wool product or insulating material of the present invention
is as follows:
Aluminum meta-phosphate Al(P03)3 is dispersed in water
and modified by the various plastics as earlier defined, and
is sprayed alone or together with lubricants, such as mineral
oils, oil-in-water emulsions in finest form (atomized), etc.
onto the hot mineral fibers. The plastic additives used
jointly with the natural hydration content of the aluminum
meta-phosphate first cause adequate bonding of the binder
films or droplets to the fibers. At the same time the binder
reactivity is retained. This is the basic presumption for the
fibers so impregnated be:ing collected and beiny fed in a known
manner to a hardening oven. The fibers so impregnated are fed
at a predetermined thickness/density as a constant flow of
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fibers between compression belts, as described earlier, into
a hardening oven. The end product is, of course, dependent
upon the space between the compression belts, the dwell time
and the density of the fiber flow, the thickness, the initial
density of the fibers, the fiber orientation, etc. but the end
product can be so regulated to produce a desirably flexible
mineral wool product, particularly adapted for heat insulation
applications. During the latter heating, the moisture and the
proportion of plastic are removed by means of a flow of hot
air between 250C and 500C, preferably between 250C ad
350C. The desired phosphate glass bond is formed both with
the preferably alkali-poor mineral fibers and with each other.
Thus, because of the very similar expansion coefficients of
the phosphate glass and the fiber glass, permanent bonds are
achieved.
Alternatively, the aforementioned prior art problems are
by utilizing as a monoalumlnum phosphate Al(H2PO4)3.
The expression "monoaluminum phosphate" shall be con-
strued herein as being generic. The literature also uses the
general designation of "aluminum hydrogen phosphate" or
"aluminum dihydrogen phosphate." Within the scope of the
invention, the binder used also may be in a special form,
namely, it may be water-dissolved monoaluminum phosphate
trihydrate Al(P03)3.3H20 or an aluminum dihydrogen phosphate
of chemical formula Al(H2PO4)3.3H20.
By thermally treating the fibers impregnated with the de-
scribed binders at a temperature higher than 250C, an acid
triphosphate AlH2P301o is formed and upon further raising the
temperature above 500C, especially to 600~C, the binder is
transformed into a long-chain aluminum polyphosphate and a
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cyclical aluminum tetrametaphosphate. The temperature-
dependent different degree of transformation of the particular
binder is deliberately made use of to achieve, on one hand,
flexible binders low in dust to insulate periodically operated
highly thermally stressed equipment, such as furnaces and the
like. When used in such equipment, the binder in the thermal-
ly highly stressed zones of the equipment will be transformed
irreversibly into water-insoluble polyphosphates or tetrameta-
phosphates. In the outer, thermally less stressed zone of the
equipment, the binder remains reversible. Thereafter, the
mineral wool product with the compound contained in it remains
markedly flexible and elastic on account of the binder.
Another advantage of this reversible state is that the binder
permits, for instance during equipment rests, atmospheric
moisture being absorbed by the mineral wool product, whereby
the dust bonding of the mineral wool product is advantageously
influenced.
Advantageously with respect to other practical applica-
tions, the binder shall already be in the desired transforma-
tion stage in the course of manufacturing the mineral wool
product in that the length of insulating mineral wool is made
to pass through an oven set to the corresponding temperature.
The above discussion regarding the aluminum metaphosphate
also applies to the previously cliscussed group of monoaluminum
phosphates. In this case, as well, the advantage is achieved
that the mineral wool products or insulators can be used
thermally up to the softening point c,f the mineral fibers
without forming, for instance by thermal dissociation of
organic substances, noxious or unpleasantly odorous gases.
Several advantageous implementations of the invention are
discussed below. ~dvantageously a thickener such as
polysaccharides, carbo-oxyl-methyl cellulose, polyvinyl
alcohol or a mixture of phenol-formaldehyde-urea-resin may be
added.
The aluminum meta-phosphate dispersed in water and
modified by the various plastics, or the monoaluminum phos-
phate dissolved in water, is sprayed, alone or together with
lubricants such a mineral oils, oil-in-water emulsions in
finest form, onto the fibers. The plastic additives used
jointly with the natural hydration content of the aluminum
meta-phosphate or the monoaluminum phosphate first cause
adequate bonding of the binder films or droplets to the
fibers. At the same time the binder reactivity is retained.
This is the basic presumption for the fibers so impregnated
being collected and being fed in a known manner to a hardening
oven. Because of the spacing between the compression belts or
rollers and on account of the corresp~nding setting of the
dwell time and the density of fiber flow, the thickness,
initial density, orientation and also the structure of the
mineral-wool product or insulator can be determined.
Both the moisture still present and the proportion of
plastic are removed by means of a flow of hot air between
250C and 500C, preferably between 275C and 350C. The
desired phosphate glass bond is formed both with the prefera-
bly alkali-poor mineral fibers and with each other. Because
of the very similar expansion coefficients of the phosphate
glass and the fiber glass, permanent bonds are achieved.
Although preferred emhodiments of the invention has been
specifically illustrated and described herein, it is to be
understood that minor variations may be made in the apparatus
without departing from the spirit and scope of the invention,
as defined the appended claims.
