Note: Descriptions are shown in the official language in which they were submitted.
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Foam boards having improved thermal insulation
propertieS~ and a process ~or the production thereof
The present invention relates to a process for the
production of foam boards having improved thermal insulation
properties. In particular, the present invention relates to
foam boards of this type which have an anisotropy of the type
that the cells a~e compressed in the direction of the board
thickness, and to a process for aftertreating known foam
boards by temporary compression.
Foam boards, fo~ example made of polyolefin foams
or made from polystyrene extruded or particle foam, have long
been employed for thermal and sound insulation.
For sound insulation, in particular impact
(footstep) sound insulation, preference is given to foam
boards which have been elasticized by temporary compression
in the direction of the board thickness.
For example, the use of elasticized EPS (expandable
polystyrene) insulating boards for impact sound insulation in
accordance with DIN 18164, Part 2, Schaumkunststoffe als
Dammstoffe fUr das Bauwesen, is known. Boards of this type
must have adequate resilience. The resilience is characterized
in DIN 18 164, Part 2, by the dynamic rigidity s' (also known
as the impact sound reduction factor) of the insulating layer,
including the air trapped in it.
For structural engineering reasons, impact sound
insulation boards must have very low dynamic rigidity and
relatively restricted deformation under load (difference
between the supplied thickness or nominal thickness and the
thickness under load, expressed as the (dLdB) value in
accordance with DIN 18164, Part 2.
This means that the degree of compression (also
known as the degree of elasticization), and thus the
deformation, of the foam structure can only be modified to a
limited extent.
In the known aftertreatment of foam boards by
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compression (also known as elasticization), foam boards
typically having a density of from 8 to lo kg/m3 are
compressed to a maximum extent of 66% of their original
thickness, and this is maintained for a certain time (usually
less than 60 seconds).
After the pressing is terminated, slight
irreversible deformation of the cell structure remains, all
the cells having an anisotropy such that the ratio between the
long and short axes is from 1.15 to 1.25. The dynamic rigidity
values achieved, for example, in a 25 mm thick foam board made
from polystyrene particle foam are around 10 N/cm3. The (dLdB)
values are from about 1 to 3 mm.
In addition to sound insulation, an important factor
for improving the properties of foam boards is, in particular,
also the thermal insulation.
It is an object of the present invention to improve
the thermal insulation properties of known foam boards by
reducing the thermal conductivity, in particular in the
direction of the board thickness, and in addition to improve
the sound insulation properties.
It has found that, surprisingly, this object is
achieved by a process which comprises compressing conventional
foam boards having a density of from 11 to 40 kg/m3 to a
maximum extent of from 50 to 90% of their original thickness,
maintaining this compression for at least 10 seconds, and
subsequently releasing the compression. The foam boards
obtained by this process have improved thermal insulation
properties. They have cells compressed in the direction of
the board thickness, and an increased density of from 15 to
45 kg/m3. Their anisotropy is such that the ratio between the
long and short axes in the compressed cells being from 1.2 to
1.6, preferably from 1.3 to 1.55, particularly preferably from
1.35 to 1.5.
Conventional foam boards or foam slabs can be
employed in the process according to the invention. In
general, however,
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foam slabs are employed, from which foam boards are
subsequently cut in a suitable size in a conventional and
known manner perpendicular to the elasticization direc-
tion.
This allows the process according to the
invention to be carried out in a very economical manner
in one step for a large number of future foam boards. In
addition, there are no problems caused by edge effects.
The terms foam slab and foam board are therefore
used synonymously-in the description, unless stated
otherwise at the point in question.
The foam boards can comprise closed- or open-cell
polyolefin foam, phenolic resin foam, polystyrene foam or
polyurethane foam. Preference is predom;n~ntly given to
closed-cell foams, in particular made from polystyrene,
polyurethanes and polyolefins.
The foam boards very particularly preferably
comprise polystyrene foam. Preference is given to poly-
styrene particle foam as opposed to extruded polystyrene
foam.
The preferably isotropic foam slabs on which the
foam boards according to the invention are based are
produced in a conventional and known manner.
For example, foam slabs are produced from poly-
styrene particle foam by expanding blowing agent-contain-
ing, expandable polystyrene beads by heating at above
their melting point, for example by means of hot air or
preferably by means of steam. After cooling and if
desired interim storage, the foam particles obtained can
be welded together by re-heating in a mold which does not
seal in a gas-tight manner to give a foam slab.
Suitable expandable polystyrene beads are des-
cribed, for example, in EP-B 106 129, EP-A 383 133 and
DE-A 39 15 602.
Preference is given to expandable polystyrene
beads having a size of from l to 2 mm.
The freshly produced foam boards are preferably
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stored for at least 2 hours and particularly preferably
for at least 6 hours before the process according to the
invention is carried out.
The known foam boards or slabs employed in the
process according to the invention generally have a
density of from 11 to 40 kg/m3.
By comparison, the foam boards or slabs according
to the invention generally have a density of from 15 to
45 kg/m3. Rowever, the effect of the invention is par-
ticularly pronounced at densities above 20 kg/m3. The
density is therefore preferably from 20 to 30 kg/m3.
As a consequence of carrying out the process
according to the invention, the density of the foam slabs
is permanently increased by up to about 50%, based on the
pre-process density.
In the process according to the invention, the
foam slabs are generally compressed in the direction of
a surface perpendicular to a m~x;mllm extent of from 50 to
90%, preferably from 70 to 85%, particularly preferably
from 70 to 80%, of their original thickness. Depending on
the compressive set or properties desired, the foam
boards can be compressed to a m~x;mll~ extent of 90% using
certain programs for the compression rate and subsequent
release and if desired for certain hold times.
In general, the compression is carried out by
moving two plane-parallel metal plates toward one another
at a constant compression rate and without interim hold
times to a ~x;mll~ compression. At the m~x;mllm compres-
sion, the slabs are held for a certain time, but for at
least 10 seconds. The distance between the two metal
plates is then increased again, in general likewise at a
constant release rate.
The compression rate used is generally from 1 to
150 cm/min, preferably from 30 to 95 cm/min, particularly
preferably from 70 to 80 cm/min.
The foam slabs are generally held at the m~; mllm
compression for from 10 to 120 seconds, preferably for
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from 30 to 90 seconds.
The compression can be carried out in a conven-
tional and known manner in presses for EPS. Examples of
suitable presses are marketed by Maschinenfabrik Paul Ott
in 7050 Waiblingen-Neustadt, Germany.
However, it is also possible to carry out the
compression at a rate which varies with time and with
interim hold times of various lengths.
For example, it is possible to first compress the
slabs to less than the m~;mllm compression and to hold
the compression at this value for a certain time.
In addition, it may be advantageous to carry out
the pressing with superimposed vibration (vibration
pressing).
After complete release, the foam slabs after-
treated by the process according to the invention are
generally stored under atmospheric conditions for at
least 5 hours. This enables the foam slabs to relax to
their final dimensions. A storage time of the compressed
slabs of from 1 to 2 days has proven particularly ad-
vantageous.
Foam boards can then be obtained from these foam
slabs by cutting perpendicular to the elasticization
direction in a conventional and known manner. These foam
boards usually have a cross-sectional area of at least 50
cm2 .
The foam boards according to the invention and
the process according to the invention have a number of
advantages. Thus, it is possible for thinner insulating
layers and thus less material to be used during
construction in order to achieve a certain thermal
- resistance (see DIN 4108, Part 2), or for the thermal
resistance for a prespecified insulating material
thickness to be lower than in the case of untreated foam
board.
The board thickness is frequently determined by
the application. It is a considerable advantage of the
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foam boards according to the invention that prespecified
thermal conductivities can be achieved usinq boards of
low density. For example, the thermal conductivity of
foam boards according to the invention in which the
density is 20 kg/m3 is as low as in conventional foam
boards having a density of 28 kg/m3. There is thus a
material saving of from 30 to 50%.
A further surprising advantage is that the
resilience (s') can be set to the low level of less than
or equal to 10 N/cm3 which is necessary for improving the
thermal conductivity, independently of the density and
board thickness in the density range from 15 to 30 kg/m3
which is conventional for thermal insulation boards in
construction applications. The dynamic rigidity in the
direction of the board thickness is usually from 4 to
10 Ntcm3 in accordance with the invention.
Since the long-term compressive stress of, for
example, EPS boards is affected in a linear manner by the
foam density, the small drop in compressive stress caused
by the elasticization can be compensated by correspond-
ingly increased foam densities, even in pressure-affected
applications.
EXAMPLES
In the Examples and Comparative Examples, foam
boards made from polystyrene particle foam were employed.
A 300 K 25 press from Maschinenfabrik Paul Ott in
7050 Waiblingen-Neustadt, Germany, was employed for
compressing the polystyrene particle foam slabs.
The compression was carried out between two
plane-parallel plates at a force of 25 MP and a rate of
75 cm/min. The hold time at m~;ml~m compression was 1
minute in each case. The two plates were then moved away
from one another at a rate of 192 cm/min.
The compressed slabs were stored for 2 days under
atmospheric conditions after release.
The thermal conductivity was determined in
accordance with DIN 52612, Part 1, for the novel foam
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boards aftertreated by compression and for untreated foam
boards.
In addition, the effect of different maximum
compressions was investigated for foam boards having
different densities.
The anisotropy was determined by evaluating foam
sections under an optical microscope. To this end, foam
cells were measured and the anisotropy determined as the
ratio between the long and short axes.
The experimental results are summarized in the
Table.
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