Note: Descriptions are shown in the official language in which they were submitted.
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eomposite glazlng p~ l@3
This invention relates to composite glazing panels affording high acoustic
attenuation.
There exists a demand for glazing panels which afford a high degree of
acoustic attenuation, and various types of glazing panel have been proposed to
satisfy that demand. In particular, are known hollow glazing panels, including
gas ~e.g. air) filled panels and evacuated panels, and laminates including those of
which the bonding resin is of a rather pliable nature so that it has a damping
effect. Both hollow and laminated panels may be provided with sheets of
o asymmetric thickness to improve acoustic attenuation at certain frequencies. And
of course it is known to incorporate one or more laminated panes in a hollow
glazing panel. Such panels suffer from certain disadvantages, which render them
unsuitable for use in certain circumstances where it would be desirable to provide
a high degree of acoustic insulation.
s Gas-filled hollow panels have an acoustic attenuation which is in large part
determined by the "thickness" of the gas-fillecl inter-sheet space. For high
attenuation, the inter-sheet spacing must be rather large, and this can present
dif~lculties in manufacture and framing. Merely as an example. such panels are
unsuitable for mounting in thin partition walls because of their thickness. While
evacuated hollow panels can afford a good attenuation with a relatively narrow
inter-sheet space, such evacuation, especially in the case of rather large panels,
tends to dish the vitreous sheets of the panel, and this can present an undesirable
aspect in reflection.
Laminated glazing panels afford an attenuation which, broadly speaking, is
26 dependent on their mass. For high attenuation, a high speci~lc mass (that i9,
mass per unit area) is required. Again, merely as an example, such panels are
unsuitable for mounting in walls where weight considerations are an important
factor.
It is an object of this invention to provide a composite glazing panel which
affords a very high degree of acoustic attenuation in relation to its overall
thickness and specific mass.
According to the invention, there is provided a composite glazing panel
affording high acoustic attenuation, characterised in that such panel comprises
two sheets of vitreous material between which is sandwiched a layer of an aerogel
.~6 which sandwich is bonded together as a monolithic laminate.
The expression "monolithic laminate" is used herein to denote a laminate
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which is bonded together in such a manner that it vibrates in the same manner asa single plate of a material having an elastic modulus which may be calculatetl
from the elastie moduli and thicknesses of the individual strata of the laminate.
Such monolithic laminates may be contrasted with hollow panels and with
5 laminates which are only weakly coupled together so that they behave in vibration
as a box rather than as a plate. Thus in a monolithic laminate there is no "mass-
space-mass" resonance.
Such a composite glazing panel affords a very high degree of acoustic
attenuation in relation to its overall thickness and specific mass.
Such a panel also has the advantage of ensuring that both major faces of
the aerogel layer are protected from atmospheric humidity. Aerogels in general
are highly absorbent of humidity, whereupon they tend to crack and break down
to dust. The edges of such a laminate can readily be protected in a manner
known per se by the use of a moisture resistant sealant such as a silicone-based15 mastic preparation.
It is a further object of this invention to provide a method of
manufacturing such a panel.
Accordingly, the present invention also provides a method of
manufacturing a composite glazing panel affording high acoustic attenuation,
20 characterised in that a layer of an aerogel is sandwiched between two sheets of
vitreous material, and the sandwich is bonded together as a monolithic laminate. This is a very simple method of manufacturing such a panel.
The aerogel used may be an aerogel of alumina, zirconia, stannic oxkle or
tungsten oxide, but it is preferably an aerogel based on silica. In order to form a
26 plate of aerogel for incorporation into such a laminate, a layer of the appropriate
gel in a solvent is spread out on an appropriate moulding plate, and the solvent is
removed from the layer to leave an aerogel plate. In one preferred method. a gelof silica in alcohol as solvent is spread out on a moulding plate which is then
introduced into an autoclave. The autoclave is pressurized, and the gel is
30 optionally flushed with liquid carbon dioxide to displace all or most of the
alcohol solvent. The pressure in the autoclave is increased to a pressure greater
than the critical pressure for the solvent liquid present in the layer (about 80 bar
for alcohol or about 74 bar for carbon dioxide). The temperature in the
autoclave is then increased to above the critical temperature for that solvent
.~5 (about 240C for alcohol or about 31~C for carbon dioxide). In this way it is
possible to remove the solvent from the layer without collapsing the structure of
the silica to form the aerogel, and in fact the structure of the aerogel can contain
up to about 98% voids by volume. The aerogel plate resulting from this process is
then sandwiched between two vitreous sheets, and the sandwich is bonded
together as a monolithic laminate, in order to form a panel accordlng to the
invention.
Panels according to the invention may be opaque, for example they may be
formed as decorative panels which may be coloured by the incorporation of
colouring agents in the aerogel or otherwise, but preferably, said sandwich is
bonded together to form a light-transmitting laminate. If the laminate is light-transmitting, it may be used as a window closure or elsewhere where light
o transmission is an important factor. Depending on the thickness of the aerogel
within the laminate, it may even be transparent.
Care must be taken when bonding a pre-formed layer of an aerogel to a
vitreous sheet. If a solvent based adhesive is used, it is likely that the solvent
could penetrate the aerogel, and this would cause the aerogel matrix to break
down in rnuch the same way as would the absorption of moisture. It is therefore
preferable for the bonding agent to be substantially free from solvent. Thus it is
preferred to use a heat-softenable or f'usible adhesive material. ~erogels are well
able to resist temperatures of the levels required for fusing many heat-softenable
adhesive materials. Such heat-softenable adhesive material could be in the form
20 of a thin sheet or film, but it is advantageous for the adhesive to be in powcler
form since this simplifies handling problems. Such a powcler adhesive can readily
be applied for example by an electro-static spraying technique well known per se.
Fusible silicone resins are especially well adapted to form a highly efficient bond
betweeen silica-based aerogels and vitreous sheets which are also rich in silica.
~6 In especially preferred embodiments of the invention, the or at least one
said aerogel layer is directly bonded to a said vitreous sheet. This avoids any
problems in selecting and applying an intervening layer of adhesive material, and
greatly simplifes manufacture. The easiest way to ensure such direct bonding is
to use a said vitreous sheet as the moulding plate on which the aerogel layer is30 first formed. In this way, the or at least one said aerogel layer is formed directly
on a said vitreous sheet so that it becomes directly bonded thereto. A silica-
based aerogel will readily bond directly to the vitreous silica matrix of e.g. a glass
sheet.
In s(~me preferred embodiments of the invention, said laminate comprises
35 two aeroge:l layers, each directly bonded to a said vitreous sheet. By assembling
two aerogel layers, each directly formed on a said vitreous sheet to form said
laminate, a panel can readily be formed which has a very high degree of acoustic
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attenuation in relation to its thickness and weight.
The acoustic attenuation across a glazing panel according to the invention
is believed to be due in large part to the very great difference in acoustic
impedance as between the aerogel and the vitreous material, due to the very low
s velocity of sound propagation in aerogel. However in order to take full
advantage of this phenomenon, the aerogel layer(s) should not be too thin, and it
is accordingly preferred that the or at least one said layer of aerogel is at least
10 mm in thickness. Increasing the thickness of a said layer of aerogel is also
highly beneficial for thermal insulation should this be desirecl. It is to be noted,
o however, that aerogel layers transmit a significant proportion of light in a diffuse
manner~ and therfore the total thickness of the aerogel in a panel should not betoo great if a high degree of resolution through the panel is considered of
importance.
In order to protect the aerogel fully against possible attack by atmospheric
humidity, it is preferred that the aerogel is hermetically sealed within said
laminate. This can be done in various ways, for example by the use of an
edge sealant of mastic type as aforesaid, optionally in coruunction with a channel
frame for example of extruded aluminium. Preferably, however, the laminate is
hermetically sealed by means of one or more spacer members extending around
the panel and soldered to the vitreous sheets of the laminate. This provides a
very effective and long-lasting protection for the aerogel.
In some preferred embodiments of the invention in which the aerogel is
hermetically sealed within said larninate, the interior of the laminate is evacuatecl.
This is hlghly favourable from the point of vlew of thermal insulation, ancl it can
26 also have a useful beneft in allowing a more certain conservation of the very low
speed of sound propagation in aerogel.
Preferred embodiments of the invention will now be described by way of
example only with reference to the accompanytng diagrammatic drawings in
which:
Figure 1 illustrates a stage in the manufacture of a panel in accordance
with this invention, and
Figures 2 and 3 are respectively cross sections through two embodiments of
panel according to this invention.
A vitreous sheet I of appropriate size and shape has a framing dam 2
3s placed around its periphery (compare Figure I).
The space formed above the sheet 1 and within the dam 2 is then fillecl
with an aerogel-forming solution. As illustrated in Figure I, the sheet I is then
placed within an autoclave 3 having gas inlet 4 and outlet 5 valves, and a heater
shown at 6.
The solution used is an alcogel solution, that is, a solution in alcohol. The
gel-forming solute may be silica alone, or it may have additions of other oxides,
5 for e,~ample of aluminium, tellurium, germanium or other materials so as to confer
special desired properties on the aerogel to be formed.
After the aerogel-forming solution has been poured, and any bubbles have
been removed, the solutic-n is allowed to form a gel and is aged. The alcogel thus
formed is purged with liquid carbon dioxide which replaces the alcohol in the
o alcogel solution. This may be done by repeated rinsing of the gel solution at
about 18-20C at a pressure of about 55 bar. This has the advantage of much
simplifying the next stage of manufacture.
The pressure within the autoclave 3 is then increased to above the critical
pressure of the solvent, 7aS bar for carbon dioxide, and the temperature within the
5 autoclave is then increased to above the critical temperature, 31C for carbondioxide. This stage is simplified by the substitution of carbon dioxide as solvent.
since if the solvent were to remain alcohol, the temperature and pressure required
would be in excess of 240C and 80 bar respectively. Typical practical
temperatures for this stage of the process are about 40C for carbon dioxide and20 about 270C for alcohol as solvent. Carbon dioxide is suitably used as
pressurizing gas, supplied via inlet valve ~1. During drying of the layer, part of
the vapour within the autoclave is allowed to escape via outlet valve 5, and on
completion of drying a layer of aerogel 7 is left directly bonded to the sheet 1.
The layer of aerogel 7 is then sanclwiched between the first sheet 1 and a
26 second vitreous sheet.
Figure 2 shows such a panel in which the aerogel layer 7 is boncled to a
second sheet 8 of glass via an intervening layer of adhesive 9. Such bonding is
effected by electrostatically sprayin~ a layer of powdered silicone resin onto the
aerogel layer 7, assembling the second sheet 8 to the adhesive, and heating the
30 assembly to effect fusion of the resin so that on cooling the sandwich is bonded
together as a laminz~te. The panel is finished off by placing a silicone-based
mastic material 10 into the re-entrant between the aerogel layer 2 and the firstsheet 1 which was left on removal of the framing dam 2 ~Figure 1).
In Figure 3 is shown a second embodiment of panel which is formed by
bonding together two layers 7 of aerogel each formed on and directly bonded to avitreous sheet l. Like the laminate of Figure 2, the laminate of Figure 3 is
bonded together by means of an adhesive layer 9 which is suitably formed in the
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same way.
Each of the vitreous sheets 1 of Figure 3 bears a marginal metallising layer
of copper covered by a layer of solder, these being together shown at 11. These
layers l l were applied before the aerogel layers 7 were formed, and they were
masked by the framing dams 2 during formation of such aerogel layers. After
bonding together of the laminate, metal spacer strips 12 are soldered between the
metallising/solder layers around the margin of the panel so that the aerogel layers
are hermetically sealed from ambient atmosphere. The interior of the panel may
then be evacuated if desired.
o Such panels, whether according to Figure 2 or Figure 3, afford a very high
degree of acoustic attenuation having regard to their overall thickness and their
weight per unit area, and they also afford excellent thermal insulation.
In a variant of the embodiment shown In Figure 3, the spacer strip 12 does
not lead straight between the two vitreous sheets, but rather it is corrugated so as
to lengthen the path of thermal conduction between those sheets around their
margins.
In a further variant panel, either according to Figure 2 or Figure 3. the
sealing material 10 of Figure 2 or the metallising strip 11 and spacer 12 of Figure
3 is or are dispensed with. Instead the two glass sheets are "solderecl" together
by a glass joint.
It will be appreciated that a laminate such as is shown in Figure 2 or 3
may be assembled to one or more further elements to form a panel of more
complex structure if this is desired. In particular, such a more complex panel
may comprise one or more further glass sheets such as 1 bearing a directly
moulded layer 7 of aerogel.
