Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
t~O~ B
D E S C R I P T I O N
This invention relates to a plaster foam having a
porous structure, to a process for its preparation and to
its use.
Sound and heat insulating materials play an
important part in the building industry. Heat insulating
materials reduce the thermal energy consumption in
buildings and thus contribute to the protection of the
environment by reducing the emission of fuel smoke. Sound
insulating materials are used for noise abatement and
building and space acoustics.
Heat insulating materials are used in the form of
mats, panels or shaped products of porous and/or fibrous
organic and inorganic materials having a low thermal
conductivity such as coconut fibres, wood fibres, glass
and mineral fibres or cork, aerated concrete or plastics
foams. The sound absorbent building materials used are
mainly absorbent materials of mineral fibres or other open
celled foams which may be provided with a sound transmitt-
ing covering for reasons of design and are fixed to
foundations as non-weight bearing parts, introduced
between structural parts or tied in with weight bearing
constructions.
If a material is to be sound absorbent, it must
have a porous structure. Fibrous materials (e.g. glass
wool or rock wool) or open celled foams have such a
structure. The cells of the material intercommunicate
~open celled structure) so that air can flow through them.
In an absorbent material, sound can be propagated due to
the porous structure and acoustic energy is converted into
thermal energy due to localized losses by friction on the
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fibres or boundaries of the cells.
Mineral fibres require a high expenditure of
energy for melting the glass or basalt used as the
starting materials. The drawn fibres are bonded 'ogether
to produce the required densities and thicknesses and the
adhesives used for this purpose continue to emit into the
environment for a considerable time. On the other hand,
the starting materials are plentifully available and
inexpensive. When fibre mats are finished by cutting or
grinding, they give rise to short fibre sections which get
caught in the clothing and cause itching. They also cause
respiratory disturbances in humans.
Plastic foams are not all ecologically harmless
since numerous foams can only be foamed by
means of fluorochlorohydrocarbons (FCHC) which are said to
play an important part in the destruction of the ozone
layer.
Plaster is a widely used material for the interiors
of buildings and is partly obtained from naturally
occurring substances and partly obtained in such large
quantities from the desulphurisation plants (REA) of power
stations that the entire annual plaster requirement of the
Federal Republic of Germ~ny could be covered from REA plasters alone.
With the continuing efforts to reduce the level of
impurities in the atmosphere, the amount of desulphurisa-
tion plasters available will increase and the need to
dispose of these substances will lead to serious difficul-
ties. There is therefore an urgent need to bring new
plaster products on the market with a wider range of
properties than the plaster conventionally used for
plaster surfaces and plasterboard for floors, walls and
ceilings. Plaster foam is such a product.
Porous plaster parts used as structural units have
hitherto been produced from commercial gypsums with
various aggregates such as aluminium powder or magnesium
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powder by heating the mass to 300C - 800C.
This process results in closed cell plaster foams used
inter alia as heat insulating materials. These plaster
foams have the disadvantage that they are expensive to
produce, apart from containing physiologically harmful
metals and requiring a large amount of energy for their
production.
A foamed plaster product having a large number of
isolated cells intercommunicating by fine channels in the
cell walls is described in US-PS 4 330 589. This foamed
plaster is obtained by foaming up a plaster slurry
containing hydrogen peroxide and a cobalt compound. The
cobalt compounds used are not physiologically harmless and
the production of this plaster requires an additional
drying process at a temperature of 459C for 6 hours.
An open-celled foamed plaster containing car-
bonaceous material and capable of absorbing fluid
materials is described in EP 0 263 975. This material is
intended for use as a filter material and is not envisaged
for acoustic or thermal applications.
An artificial stone containing inter alia foam
plaster is described in DE 3 804 884. This stone is also
suitable for use as thermal insulating material but it has
the disadvantage of requiring a comb~lstion process in a
furnace at a high temperature for its production.
A process for the production of plaster foam and of
structural elements of plaster foam is described in
DE 2 546 181. The materials obtained have a porous
structure and improved heat insulation compared with
ordinary plaster products which have not been foamed.
Their density is in the range of from 0.45 to 0.8 g/cm3.
This known process requires the use of various additives.
The addition of a liquefier for the plaster is a disad-
vantage. The plaster liquefier used is a sulphonic acid-
modified melamine resin, ~hich is relatively expensive.
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The mixture of gypsum and water used in the known processhas a relatively low viscosity and the product is liquid.
It has the disadvantage that it leaks out of holes and
exposed,open areas in the moulds. E~urther, the mixture has
5 a cream time of only 5 minutes, which is rather short for
a manual operation and not sufficient for carrying out the
process.
A foam plaster which is produced like t~e plaster
according to DE 2 546 181 but in addition contains
10 polyvinyl alcohol and boric acid is described in
DE 2 940 785. The boric acid present in this known
plaster is a disadvantage since it is physiologically
harmful; moreover,the preparation of this plaster is
accompanied by the disadvantages mentioned above in
15 connection with DE 2 546 181.
DE-OS 2 250 611 relates to a process for the
production of a lightweight, reinforced structural
material whose compression resistance, tensile strength
and resistance to flexural tension have advantageous
20 values for structural panels. These materials are also
said to have good sound absorption properties and thermal
conductivities. The K-factor given in Example 3 cannot be
fitted into any known system for measuring thermal
conductivity as it contains no physical measuring units.
25 The magnitude given in Example 4 is unknown and cannot be
allocated to any existing units. If the building boards
are placed between reinforcing sheets of paper used as
coverings, the sound absorption properties of the boards
are substantially reduced.
Plaster cornpositions containing plaster ar~ dust of rigid
foam are described in DE 2 716 918. These campositions are used
for producing plaster surfaces, plaster-cardboard panels,
seals, modelling masses and filling masses. Their use for
acoustic and thermal applications is not envisaged.
35 Sealing bodies containing foamed gypsum of
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anhydrite with a porous cell structure for sealing cavities
in mines are ~escribed in Utility Model Application DE 83 13
354.2-U1. These products are not suitable as heat insulating
materials or as sound absorbent materials.
EP-A-0 256 330 relates to a process for the production
of reinforced plaster plates made of plaster~hemihydrate),
optionally reinforcement substances, preferably cellulose
particles such as sawdust, with the admixture of
polyisocyanates. The plates obtained by this known process
are unsuitable as sound absorbent materials or as heat
insulating materials, since they do not have an open-cell
structure.
It is an object of the present invention to provide
sound insulating materials and heat insulating materials
with good thermal insulation or sound absorption proper-
ties. It also relates to a process for the production of
the insulating materials. Their production should not
require high temperatures and they should be able to be
produced without great expenditure of energy. The
insulating materials should not contain any short fibre
sections liable to produce unpleasant reactions such as
itching or respiratory disturbances. The material should
be inexpensive and hygienic.
It is an object of the invention to provide a
process for which gypsum, in particular desulphurisation
gypsum, can be used as raw material.
The object of the invention relates to a plaster foam
with a porous structure, containing a polyurea resulting
from polyisocyanates and a wetting agent, which is
characterized in that it has a specific gravity in the range
of 0.1 to 0.4 g/cm3, is open celled and the polyurea
contained therein is the condensation product of
diphenylmethane-4,4'-diisocyanate prepolymers and water and
has been produced by wetting the plaster with water and
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reacting the plaster paste with diphenylmethane-4,4'-
diisocyanate prepolymers in the presence of a wetting agent.
The invention further relates to a process for the
preparation of the plaster foam, characterized in that
gypsum is moistened with water, diphenylmethane-4,4'-
diisocyanate prepolymer and a wetting agent are added to
the resulting slurry and the composition is thoroughly
mixed, introduced into the required mould and hardened.
The invention further relates to the use of the
plaster foam as sound insulating and/or heat insulating
material.
The gypsum used in the present invention may be any
calcium sulphate modification in a pulverulent form of the
usual degree of fineness which is neutral or slightly acid
in reaction and can be set by water. Ordinary commercial
gypsum qualities having a water-gypsum factor of 0.3 are
preferably used. It is particularly pre~erred to use ~-
gypsum or desulphurisation gypsum. Desulphurisation
gypsums are obtained from flue gas desulphurisation
plants. They consist of moist dihydrate which may,
however, also be obtained in the form of semi-hydrates,
depending on their quantity.
According to the invention, the gypsum is mixed
with diphenylmethane-4,4'-diisocyanate prepolyme~
Diphenylmethane-4,4'-diisocyanate prepolymer has the
special advantage of being free from solvents, providing a
constant NCO content as prepolymer and containing less
than 0.5% of monomers. The product used is preferably one
which has an isocyanate content of from 12 to 20~ by
weight, preferably from 14 to 18% by weight, most
preferably 16% by weight. Such products are available
commercially. They have a viscosity of 10,000 mPa/s +2000
at 20~C.
The diisocyanate prepolymer reacts in known manner
with the water used for preparing the plaster and the
water of crystallisation of the gypsum to form a carbamic
acid derivative which is converted into a primary amine
with elimination of carbon dioxide. The primary amine
reacts with the isocyanate to form a urea derivative or
ureide which may undergo further reaction. In the present
application, the term "polyurea" is to be understood to
include the condensation products obtained from the
diphenylmethane-4,4'-diisocyanate prepolymers and water.
The plaster foam according to the invention has a specific
gravity in the range of from 0.1 to 0.4 g/cm3, preferably
from 0.15 to 0.35 g/cm3, most preferably from 0.2 to 0.3
g/cm3. It is open celled and at least 80% of its cells
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measure from 0.3 to 2 mm. In the plaster foam according
to the invention, preferably as many of the cells as
possible measure from 0O8 to 1.2 mm. The specific gravity
is adjusted by the quantity of diphenylmethane-4,4'-diiso-
cyanate prepolymer used. The greater this quantity, thelower is the specific gravity, and the man of the art can
determine with the aid of simple preliminary tests what
quantity of diisocyanate prepolymer is required for
obtaining a plaster foam having a particular specific
gravity.
The plaster foam according to the invention
contains from 55 to 90% by weight of gypsum, from 45 to
10% by weight of polyurea and from 0.1 to 2.0% by weight
of wetting agent. The plaster foam according to the
invention need not contain any other additives although it
may contain conventional additives in a quantity of from
0.1 to 2% by weight, based on the dry weight of gypsum,
polyurea and wetting agent.
To prepare the plaster foam according to the
invention, the gypsum, preferably ~-gypsum, is moistened
with water . Diphenylmethane-4,4'-diisocyanate prepoly-
mer and a wetting agent are added to the resulting slurry
and the mixture is thoroughly mixed. The mixture
obtained has a cream time of from 10 to 15 minutes. After
it has been mi~ed, the substance is introduced into the
required mould and left to harden. Hardenin~ is carried
out at room temperature for a period from 30 minutes to 2
hours. The material may be removed from the mould when it
has hardened. After-hardening, which may take place
inside or outside the mould, is generally completed within
a period from 8 to 12 hours.
According to the invention, from S0 to 70% by
weight, preferably from 55 to 66% by weight, of gypsum,
from 10 to 25% by weiht, preferably from 15 to 25% by
weight, of water, from 10 to 30~ by weight, preferably
~~
from 15 to 25% by weight, of diphenylmethane-4,4'-
diisocyanate prepolymer and from 0.1 to 2.0% by weight,
preferably from 0.1 to 1% by weight, of wetting agent are
mixed together.
The wetting agents used according to the invention
may be known wetting agents, e.g. commercially available
products such as fatty alcohol sulphonates, quaternary
ammonium compounds or other cationic, non-ionic or anionic
agents. Specific examples of wetting agents include
ethylene oxide/propylene oxide polyglycol, a betaine siloxane
surface active agent, a low molecular weight acrylic
copolymer and an alkyl phenol oxethylate. The latter is
preferred. The wetting agents influence through-hardening and
the process of imparting elasticity. They are used in
quantities of from 0.1 to 2.0% by weight, preferably from
0.5 to 1.0% by weight, most preferably in a quantity of
0.5% by weight. They are used for regulating the pore
size. The higher the proportion of wetting agent present,
the smaller will be the pores.
The plaster foam according to the invention is used
as sound insulating material and/or heat insulating
material. In a preferred method of carrying out the
invention, the plaster slurry obtained is poured into
special moulds and foamed up therein to give rise to
specially formed structural elements. It is particularly
preferred to incorporate the plaster foam according to the
invention in prefabricated room dividing systems or to use
it as acoustic ceilings or acoustic wall elements
(optionally under a finishing facing on the wall or
ceiling). The plaster foam may also be used for the
production of panels, pipes and elements of various
geometrical forms. The plaster foam according to the
invention is suitable for the insertion of dowels or nails
and can be glued. It may also be mechanically finished by
cutting, sawing, milling and brushing.
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This is necessary in particular when the plaster
foam is to be used as sound absorbent material. Since the
plaster foam has a non-cellular skin after completion of
the foaming process, it is necessary to strip off the
surface to open the pores. This may be achieved by means
of any of the mechanical after-treatment processes
mentioned above. If desired, several o~ these processes
may be carried out on the same workpiece. For example, in
the case of panels the surface may be rubbed down by
brushing and the sides may be cut.
The material obtained from the mechanical after-
treatment may be reused. If it is obtained in the form of
relatively large pieces, these may be size reduced and
then ground down. The pulverulent material is then added
to the starting mixture of diphenylmethane-4,4'-diisocyan-
ate prepolymer, gypsum, water and wetting agent. From 5 to
15% by weight, preferably from 8 to 12% by weight, most
preferably 10% by weight of the powder obtained from the
waste may be added to the starting, based on the muxture.
The material may also be lined or covered with film
or foil to increase its mechanical strength and regulate
the resistance to diffusion of water vapour (vapour
barrier). The acoustic properties will not be impaired if
a film of suitable thickness is used and
it may also be used as sandwlch panels. Theprccess according to the invention may be carried out
continuously or discontinuously. In the discontinuous
process, the plaster slurry obtained is poured into
moulds, for example box moulds. To produce sandwich
panels, bottom plates or top plates may be introduced into
the hox mould. The continuous process may be carried out
by, for example, continuously applying the plaster slurry
to a mould in the form of a continuous belt and then
covering the belt with a cover plate. Endless panels are
3~ thereby obtained which may be cut up or sawn up to the
11
ZQ~68
required shapes and sizes.
The plaster produced according to the invention has
the following advantages:
(a) The plaster foam according to the invention has
excellent sound absorption. The degree of sound
absorption for sound incident at rightangles
(measurement according to DIN 52 215) on a sample
body 38 mm in thickness is shown in Table 1 for
various frequencies. The results obtained for a
sample of glass wool of the same thickness are
shown for comparison.
TABLE 1
i
l l Degree of sound absorption
15 ¦ Frequency ¦ Plaster foam Glass wool
... . . . _ _ l .. ... _ . ............ _ . .. . l
¦ 100 Hz ¦ 0.18 ¦ 0.14
¦ 200 Hz ¦ 0.20 ¦ 0.21
¦ 400 Hz ¦ 0.49 ¦ 0.46
20 ¦ 800 Hz ¦ 0.77 ¦ 0.76
¦ 1600 Hz ¦ 0.57 ¦ 0.91
¦ 3200 Hz ¦ 0.65 ¦ 0.89
(b) It has excellent thermal insulation. The ~ value
was 0.045 W/mK. Polystyrene foams and mineral wools
have a thermal conductivity of ,~ - 0.035 W/mK to
0.05 W/mK. The values obtained for the material
accordiny to the invention are thus outstandingly
good.
30 (c) Compared with known building materials, the plaster
foam according to the invention has a substantially
lower specific gravity. The known plaster foams
have a specific gravity of from 0.6 to 0.7 g/cm3.
The plaster foam according to the invention is
therefore easier to handle and in particular to
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process and transport, which is of great practical
importance for its use.
(d) The plaster foam according to the invention can be
dowelled, nailed or glued and may be subjected to
mechanical after-treatment by cutting, sawing,
milling or brushing.
The process according to the invention has the
following advantages:
(a) It is not necessary to use any additives in addition to the
gypsum, the isocyanate and the wetting agent, in
particular no metals are required. There is
therefore no contamination of the environment.
(b) The process according to the invention does not
require the addition of a gypsum liquefier. The
process according to the invention may therefore be
carried out with a gypsum-water slurry of higher
viscosity so that leakage from holes and from the
mould can be prevented.
(c) The cream time is at least 10 minutes in the
process according to the invention, in most cases
15 minutes. This enables the operator to mix the
components thoroughly and introduce the mixture
into the moulds without any risk of premature
hardening.
25 (d) There is no need to use a foaming accelerator. In
the known processes, foaming was accelerated by
means of metal compounds which, as mentioned above,
are physiologically harmful.
(e) In contrast to the known processes, there is no
need to preheat the water used for preparing the
slurry. This means that the process according to
the invention may easily be carried out by small
firms and in small factories since it does not
require complicated apparatus.
35 (f) The process according to the invention does not
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require the addition of foaming agents such as
fluorochlorohydrocarbons as in the known process
disclosed in DE 25 46 181. The use of fluorochloro-
hydrocarbons is damaging to the environment.
(g) The process according to the invention enables the
large surplus of gypsum obtained from desulphuriza-
tion to be disposed of by employing it for the
production of useful building materials.
(h~ The process according to the invention is very cost
effective since it requires neither expensive
apparatus nor a great deal of energy nor a large
work force.
The following Examples serve to illustrate the
lnventlon.
Example 1
66.5 Parts by weight of ~-gypsum are moistened with
16.5 parts by weight of water. 16.5 Parts by weight of
solvent-free diphenylmethane-4,4'-diisocyanate prepolymer
having an NCO content of 16% by weight are added as well
as 0.5% by weight of a non-ionogenic alkyl phenol
oxethylate as wetting agent.
All the compounds are thoroughly mixed together and
poured into the required mould.
The reaction begins after about 10 to 12 minutes
and is completed in about one hour. The product obtained
is a board which has good surface hardness.
Example 2
65 Parts by weight of ~-gypsum are mixed with 21.5
parts by weight of water, 0.4 part by weight of a
commercially available alkyl phenol oxethylate used as
wetting agent and 13.1 parts by weight of solvent-free
diphenylmethane-4,4'-diisocyanate prepolymer having an NCO
content of 16% by weight.
The components are thoroughly mixed and the mixture is
introduced into the required mould.
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168
The reaction begins after 10 to 12 minutes and is
completed in about one hour. The product obtained is a
board which has good surface hardness.
Example 3
The procedure described in Example 1 is employed
and the following components are used:
59.4% by weight cf ~-gypsum,
15.0% by weight of water,
16.0% by weight of diphenylmethane-4,4'-diiso-
cyanate prepolymer having an NC0
content of 16% by weight,
0.4% by weight of cation-active fatty amine salt
as wetting agent and
9.0% by weight of gypsum residue which has
already reacted.
After the components have been mixed, the whole
mixture is intrGduced into a box mould. The reaction
begins after about 10 minutes and is completed in about
one hour.
Example 4
60 Parts by weight of ~-gypsum are mixed with 20
parts by weight of water, 0.5 parts by weight of a
commercially obtainable alkyl phenol oxethylate as wetting
agent, 16 parts by weight of diphenylmethane-4,4l-
diisocyanate prepolymer having an NCO content of 16% hyweight and 4 parts by weight of previously reacted plaster
foam in powder form obtained according to Example 3.
When the components have been mixed, the whole
mixture is introduced into a box mould. The reaction
begins after about 10 minutes and is completed in about
one hour.
The boards and parts produced according to Examples
1, 2, 3 and 4 may be cut and sawn. The skin formed on
their surface in the course of their production may be
removed by milling, which affects the sound absorpticn
20~ 8
properties. The absorption properties may be specially
influenced in accordance with the frequency by covering
the products with various materials. The parts may be
nailed and dowelled.
