PROCEDE DE PRODUCTION DE PIECES MOULEES, HYDROFUGES, EN PLATRE POREUSE

PROCESS FOR PRODUCING WATER-REPELLENT, POROUS PLASTER MOULDED BODIES

Abrégé anglais

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ABSTRACT
A Process for Producing Water-Repellent,
Porous Plaster Molded Bodies
The process for producing water-repellent porous
plaster molded bodies, more specifically, porous plaster
panels, from the components plaster powder, mixing water,
foam and optionally, further common additives by adding
alkylhydropolysiloxanes is effected in that the alkyl-
hydropolysiloxanes are added to the mixing water or par-
tial streams thereof containing common additives, followed
by intense mixing of the mixture in a tube several meters
long using turbulent flow.

Revendications

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C L A I M S:
1. A process for producing water-repellent porous
plaster molded bodies, more specifically, porous plas-
ter panels, from the components plaster powder, mixing
water, foam and optionally, further common additives,
by addition of alkylhydropolysiloxanes, characterized
in that the alkylhydropolysiloxanes are added to the
mixing water or partial streams thereof containing
common additives, followed by intense mixing of the
mixture in a tube several meters long using turbulent
flow.
2. The process accordiny to claim 1, character-
ized in that the alkylhydropolysiloxanes are added to
the partial stream of a pasted paper pulp.
3. The process according to claim 1, character-
ized in that the alkylhydropolysiloxanes are added to
the partial stream containing non-foaming surface-
active substances.
4. The process according to claim 1, character-
ized in that the alkylhydropolysiloxanes are added to
the partial stream containing gelatinated starch.

Description

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A Process for Producina Water-Repellent,
Porous Plaster Molded Bodies
The present invention is directed to a process for
producing water-repellent porous plaster molded bodies,
more specifically, porous plaster panels, from the com-
ponents plaster powder, mixing water, foam and optionally,
further common additives by adding alkylhydropoly-
siloxanes.
From the DE-AS-12,23,287, there is known a process
for producing water-repellent molded bodies and coatings
from inorganic masses setting on addition of water, where-
in, in order to achieve water-repellency, organosilicon
compounds in the form of aqueous emulsions are added to
the inorganic masses prior to molding. In practice, these
pre-produced emulsions have proven worthwhile; however,
they are significantly more expensive than the organo~
silicon compounds in non-emulsified form marketed in the
form of oily suspensions.
From DE-OS 27,40,049, it is known to admix linear
monomethylpolysiloxanes to the plaster powder in the ab-
sence of water and only thereafter to paste this plaster
with water. In practice, this process has not proven bene-
ficial since, on the one hand, a relatively high amount of
monomethylpolysiloxane is required and, on the other hand,
a plaster powder pre-treated in such fashion is consider
ably poorer in further processing.
.
From EP-PS-0,171,018, there is known a process
wherein water-repellent porous plaster molded bodies are

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produced using alkylhydropolysiloxanes by forming a foam
from water, surfactant and polyalkylhydrosiloxane, and
adding this foam to the aqueous plaster paste consisting
of mixing water, plaster powder and optionally further
common additives. This process has proven useful in prac-
tice as long as highly specific parameters are maintained
which, however, are not indicated in the patent specifica-
tion. A substantial drawback of this process is that in
practice, in the production of plaster panels on appropri-
ate large-scale plants metering the mixed plaster paste is
controlled by varying the added amount of foam, among
other. Therefore, the varying amounts of foam likewise
result in variably strong hydrophobizing of the final
product.
It is the object of the present invention to de~
velop a process for producing water-repellent porous plas-
ter molded bodies, more specifically, porous plaster
panels, wherein perfect products are formed from the com-
ponents plaster powder, mixing water, foam and optionally,
further common additives and alkylhydropolysiloxanes,
without the necessity of employing the alkylhydropoly-
siloxanes in the form of pre-produced emulsions or in the
form of a foam immediately generated prior to production.
Thus, the attempt is made to combine the advantages of
continuous metering of the alkylhydropolysiloxanes when
adding emulsions with the substantial lower costs when
adding alkylhydropolysiloxanes to the foam wherein, how-
ever, the drawback must be accepted that dosage of varying
amounts of foam likewise results in varying hydrophobiz-
ing
Now, this object could be attained .in a surpris~
ingly simple fashion by adding the alkylhydropolysiloxanes
to the mixing water or partial streams thereof containing
common additives, followed by intense mixing of the mix-
ture in a tube several meters long using turbulent flow.

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Regarding the state of the art, this result was in
no way predictable. Still, in the EP~PS-0,171,018, column
1, lines 27-39, it is expressly stated that in practice,
it is impossible to disperse the oil, due to its insolu-
bility in water, in the aqueous plaster paste consisting
of mixing water and plaster powder. Although addition of
non-emulsified oils represents the substantially more
economic form, there was no process for uniformly dispers~
ing the oil in the plaster paste.
Large-scale technical experiments in Applicant's
existing production plants have demonstrated that accord-
ing to the invention, it is nonetheless possible to work
with oil and to abandon metering in foam generation. It is
of decisive significance that the alkylhydropolysiloxanes
as an oil are thoroughly mixed with the mixing water in a
tube several meters long using turbulent flow, before they
come in contact with the plaster powder. For such inten-
sive mixing, 2 m of tube are just sufficient. Tube lengths
of from 4 to 6 m have proven excellently useful. While it
is possible to use even longer tubes, the effect herein is
not further improved unless the required amount of water
calls for relatively large tube diameters. Namely, in
order to generate turbulent flow within the tube, the tube
diameter should be 2% of the tube length at maximum. Pre-
ferably, tube diameters having from 0.1 to 1~ of the tube
length are selected. With turbulent flow, a constant time-
averaged velocity profile is formed in flow direction only
after 50 to 100 tube diameters. Then, the Reynolds number
is no longer significant. Vnder such conditions of turbu-
lent flow, water and silicon oil may be processed into an
emulsion which can be processed immediately.
The examinations have led to the result that it is
not only possible to add the alkylhydropolysiloxanes to
the main stream of mixing water but that it is likewise
possible to add the alkylhydropolysiloxanes to the various

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partial streams containing common additives. Proven par-
ticularly useful as the additive to the partial stream has
one containing pasted paper pulp. However, since not all
the porous plaster panels contain paper pulp, the alkyl-
hydropolysiloxanes may also~be added to that partial
stream which does not contain foaming surface-active sub-
stances. Finally, the alkylhydropolysiloxanes may also be
added to that partial stream which contains gelatinated
starch.
As another surprising advantage, it was determined
that according to the invention, the foaming agent con-
sumption may be lowered by about 20% compared to a process
wherein the silicon oil is added to the foam generator.
Examination of the finished plaster panels has led
to the result that the quality of the plaster panels ac-
cording to the invention is in any respect comparable to
products wherein the silicon oil has been supplied to the
foaming plant.
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