Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
1. Fi~l~ of ~he Invention
The present invention relates to a device for protecting
or connecting electrical circuits with a housing which
lncludes at least one opening for receiving at least one cable
including electrical lines and at least one additional opaning
enabling the production of fixed or detachable connections to
connection or control lines via the electrical lines, and
which is filled with an insulating sealing or embedding
compound.
2. Description of the Related Art
A disadvantage in known devices of this type, which can
~ be cable sealing devices, cable branch or splice boxes, cable
end distributors or cable sleeves, and particularly plug-in
connectors, consists in the fact that they can only withstand
higher temperatures to a limited extent. The sealing and
embedding compound is impaired under the influence of high
temperatures such as those occurring in nuclear power stations
and particularly in fires. The compound can dissolve and in
extreme cases can even be liquefied or gasified. The
insulating capacity of the compound is destroyed relatively
quickly under the influence of extreme heat that to which
devices may be subjected.
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It should be mentioned that the use of organically based
duromer backbone polymers as binder matrices for insulating
materials is preferred in the modern electric and electronics
~ndustrv. These duromer materials are preferably produced
~rom epoxy resins and polyurethane resins, amino plastics
and/or phenol plastics. Recently, hybrid systems, e.g. with
isocyanurates, polyimides and other nitrogen-containing
polvmers, have also become known especially for improving
long-term temperature resistance. Epoxy resins continue to be
considered particularly reliable insulating materials, since
they have made possible modern solutions in electrical
; engineering, among others, in electronic and electromagnetic
structural component parts because of their favorable
processing properties and work material characteristics. "
Despite the excellent properties of duromer tool resins,
particularly epoxy resins, they are not capable of providing
solutions to a number of problems involved in sealing and ;
embedding because their organic binder matrices have no long-
term resistance to increased temperatures and in some
instances exhibit considerable shrinkage in spite of their
high proportion of inorganic fillers. Although binder
matrices with higher glass transition temperatures which can
temporarily withstand temperatures of up to approximately
360~C have been developed with the recently known hybrid
systems, e.~ based on epoxy resins and isocyanurates, their
long-term temperature resistance is still limited to roughly
250 to 300~C.
Thus, with respect to binder matrices having a high
insulating resistance in addition to a long-term resistance to
temperatures, there still exists a gap in the temperature
range between 300C and 1500C.
In order to fill this gap, commercial endeavors aimed at
developing such insulating materials with a high temperature
resistance on an inorganic basis. Aluminum oxide, silicon
dioxide, and aluminum silicates were among the raw materials
employed. Nevertheless, a suitable sealing and embedding
compound could not be produced because of the lack of
knowledge concerning the structure`of the binder matrix.
However, other essential factors also had a negative influence
on the final characteristics. Among these factors were:
- impurities in the filler material which e.g. impaired
electrical characteristics;
:~,
- uneven grain distribution in the binding agents and
filler materials leading to disruptions in the spatial
binder matrix structures and a deterioration of
mechanic,l characteristics:
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- very slow hardening processes (up to 30 days at room
temperature) with "more easily water-soluble" binder '
constituents, additional crystallization during the
hardening process, and development of large crystals so
that a homogeneous, resistant binder matrix could not be
developed;
- air-drying sealing and embedding compounds produced, as a
rule, from water glasses with quartz filler and aluminum
oxide filler materials can generally only be hardened at
temperatures up to a maximum of 60C in the presence of
circulating air, since higher temperatures during initial
hardening - due to the increased steam pressure of the
water - lead to damage and formation of cracks, etc. in
the compound so that it is not possible to seal large
spaces or embed in thick layers with these compounds.
However, chemically binding, inorganic sealing and
embadding compounds are also known which are generally based
on phosphates and alXali silicates. The hardening reactions
proceed either in acidic medium as condensation reactions or
as precipitation reactions by adjusting a determined ion
concentration. However, acidic condensation reactions lead,
among other things, to corrosion phenomena in relation to
metallic work materials, as is the case e.g. with zirconium-
magnesium phosphates. Thus, on the whole, inhomogeneous
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binder matrices with fluctuating high-temperature resistance
and insulating resistance are obtained.
But also there remains much to be desired of the
resistance to water, water steam, alkalis and many others.
As a result of these and other characteristics, the
inorganic sealing and embedding compounds known from the prior
art have many weaknesses and can only be used economically and
technically within a very limited spectrum of applications in
spite of a possible static temperature resistance of around
1000C. Often, they are only used at all because the market
offers no alternative possibilities.
However, since the demand for sealing and embedding
compounds which, after hardening, form a binder matrix which
is resistant to high temperatures and has a high insulating
resistance continues to increase in hi-tech electrical and
electronic technology for technical as wPll as economic
reasons, alternative, economical innovations must be
developed.
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8UMMARY OF THE INVEN~ION
TherePore, the primary object of the present invention is
thexe~ore to further develop the device of the above-desaribed
type in such a way that it is capable of withstanding high
temperatures with a sealing and embedding compound based on
inorganic binder matrices with high insulating resistance and
long life. This is because the cable insulating and wire
insulating materials are destroyed at the required high
temperature loads (750C, 3 h, and 1000C, 10 min). Such
temperatures reduce the insulation to a kind of ash with a
very high proportion of glass fibers. But this ash
disintegrates under the slightest mechanical load. For this
reason, it is important that the sealing compound protect the
individual wires located in the cable connection region
against mechanical stresses so as to ensure the operability of
the plug-in connection. In so doing, it must be taken into
account that the devices, e.g. plug-in connectors, must
conform to Ex II d type explosion protection class.
Regulations governing the layout of electrical components
state that parts intended for use may have no "noxious
20 spaces". In this type of application, "noxious spaces" are
defined as spaces in which e.g. gases or mixtures of dust and
air could collect and result in destruction if ignited.
In accordance with the present invention, for ensuring a
high resistance to temperature and accordingly protection
against short-circuiting also at extremely high temperatures,
but with a high insulating resistance the sealing and
embedding compound has a binder matrix having as chief
constituent a hardened mixture of
a) ~ln~ly particulate SiO2 and
b) at least partially water-soluble silicates.
When the silicate-containing binder matrix is built from
a threa-dimensional lattice structure, it ensures outstanding
mechanical stability of the sealing and embedding compound, on
the one hand, and an extremely high resistance to temperature
10 with a high insulating resistance, on the other hand.
? Further, the additives, e.g. filler materials, can be fibers
which are taken up in the binder matrix so as to be
distributed in a finely-dispersed manner.
Devices according to the invention with a compound based
on a silicate-containing binder matrix also allow long-term
resistance to temperatures of more than 1000C. Resistance tQ
temperatures of up to 1500C can be observed. Another ; ;
advantage is that the binder matrix is not flammable.
Moreover, the binding agent has a high resistance to solvents,
-20 grease, oils, fuels of all types as well as to strong caustic
materials and acids. In addition to the extremely great
hardness of the binder matrix, a high flexural strength, e.g.
up to 30 MPa, a high compressive strength, e.g. up to 90 MPa, - -
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a high module of elasticity, and high vibration damping can be
observed.
Further, the binder matrix has a very low thermal
expansion coef~icient (approximately 4 to 9 x 10-6Kl).
Further, extremely low shrinkage and creep characteristics
have been demonstrated which are substantially lower than in
~ynthetic resin-bonded sealing and embedding compounds.
Further, a very high dimensional stability under alternating
temperature loads has been established. Also, the binder
matrix is friendly to the environment so that there are no
disposal-related problems.
Advantages with respect to manufacture consist in the
possibility of low processing temperatures between 10 and
lOO-C, and in that processing is possible without protective
gases or solvents. The only solvent required is water for
forming a paste; part of the water can be built into the
matrix during the cross-linkage reaction and part of the water
escapes during subsequent after-hardening processes. The ;
starting compound can be cast, extruded, injection molded and
pressed so that all conventional processing techniques can be
employed. The hardening process itself, which is reinforced
by thermal energy, can be carried out without pressing
pressures, i.e. no costly apparatuses are needed for producing
the se~ling and embedding compound~.
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DE~CRIP~ION OF THE PREFERRED EMBODIMENTS
In a ~urther development of the invention, the binder
matrlx is produced from the aforementioned mixture of ~inely
p~rtlculate SiO2 and at least partia~ly water-soluble
silicates, which mixture is hardened at increased temperature.
This mixture results in a uniformly constructed binder
matrix which is branched three-dimensionally by
polycondensation and ensures an outstanding quality and
durabilit~ of the sealing and embedding compound. Another
advantage of this step consists in that the starting materials
have a very good wetting ratio, i.e. the additives which are
to be incorporated in the binder matrix, as appropriate, are
built into the binder matrix in a uniform manner.
- Suitable reactive constituents in the production of the
binder matrix according to the invention are amorphous sio2,
possibly Al203, and the undissolved sio2, if any, of the
amorphous water-containing silicic acid. Mixtures of ;~
amorphous sio2 and Al203 are particularly preferred. The
weight ratio of sio2 to Al203 can range from 5 - 98 percent by
weight sio2 to 95 - 2 percent by weight Sio2, preferably 5 - 80
percent by weight to 95 - 20 percent by weight.
SiO2 is preferably present in amorphous, particularly
anhydrous form. This form is also preferred for the finely
particulate mixture of sio2 and Al203, although the Al203 can be
partly in the form of crystals, for example. The SiO2 can also
25 originate from the amorphous, water-containing silicic acid. -
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The finely particulate individual constituents and/or mlxtures
have a particle size S 50 ~m, preferably ~ 40 ~m, particularly
S 10 ~m. The smaller the particle si~es, the denser and more
~t~bl~ the binder matrix according to the invention.
Surprisingly, it has been found that the use of biogenic
silicic acids is indicated for the formation of specific
binder matrices according to the present invention,
particularly to achieve high resistance to temperatures and to
achieve dimensional stability. The biogenic silicic acids
possess amorphous structures and are associated with tridymite
and/or cristobalite with respect to their mineralogical
compositions. The biogenic, amorphous silicic acids are
obtained from carbonated rice husks among others. They have
sintering points of approximately 1500C and melting points of
15 approximately 1600~C. The grain sizes are S 5 mm, preferably
S 3 mm, in particular < 2 mm. The SiO2 contents are 2 90%,
particularly 2 95%. In the sealing and embedding compounds
according to the invention, they have dual functions,
~ predominantly as binders and/or "reinforcing filler
materials".
The oxides can contain impurities such as iron, sodium,
potassium, calcium, and so forth. Insofar as the heavy-metal
impurities are ~ 0.5% and are embedded in the binder matrix in
a dispersed manner, they often do not change the insulating
resistance. The ratio of oxide components, i.e. sio2 and/or
Al2O3, to the water-soluble silicates is 80 to 20 : 5 to 60,
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particularly in a quantitative range of 15 percent by weight
~n relation to the total mixture of the two components. Dusts
from ~igh-temperature smelting processes, filter dust,
~l~ctrostatic filter ash from high-temperature nuclear
reactors, and calcinated, powdered bauxite are particularly
su~table reactive components.
For binder matrices with a particularly high insulating
resistance of 2 1o6n, particularly 2 1o8n~ the use of aluminum
silicate, particularly dehydrated aluminum silicate, is
10 preferred according to the invention. The aluminum silicate ``
may be a kaolinite as Al2O3 2SiO2 H2O and meta-kaolinite `
(dehydrated kaolinite) as Al2O3 2SiO2. The transitional
states can also be used. Meta-kaolinites are preferred since
they possess a greater reactivity.
` 15 As was surprisingly discovered when using hydraulic
binder media such as those described in the following, a
minimum content of meta-kaolinite is required in order to
~` impart a greater stability to the hardened compound.
Such additives are particularly advantageous in reactive -
components which bond hydraulically in the presence of the
existing polycondensating components, so that hybrid systems
` are formed. They include the clinker phases from concrete
production, e.g. alite (C3S), tricalcium aluminate (C3A),
wherein C = calcium oxide, S = silicon dioxide, and A =
aluminum oxide, as well as high-alumina cement, anhydrides,
gypsum, anhydrous alkaline earth, and magnesium oxide.
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Alkali silicates or ammonium silicates which can be usedalone or in mixtures are particularly suitable as water-
~oluble sil~cates which act as hardeners for the oxides of sio2
and A1203. They generally include a surplus of free alkali
and/or ammonium. The molar ratio of alkali or ammonium to
silicon oxide is generally between 1.0 and 5 moles, preferably
between 1.5 and 4 moles sio2 per mole of alkali or ammonium.
Potassium water glass and/or ammonium water glass are
particularly preferred since they impart particularly good,
homogeneous physical characteristics to the structure-forming
matrix and bind the necessary additives in a very favorable
manner. The alkali silicates or ammonium silicates can also
be preparations in àqueous form.
- ~he formation components of silicates, i.e. the
corresponding oxides or hydroxides of the alkali or ammonium
and amorphous, water-containing silicic acids in the form of
dispersed powder, can also be contained in a particularly
advantageous manner instead of silicates. This step has the ~
advantage that these precursors of the silicates have good -
storage properties as solids and can be mixed with water to
form a paste prior to processing. Thus, according to the
invention, reactive single-component systems are obtained,
which are particularly simple to manage.
In a particularly advantageous manner, salts of
fluorosilicic acid can also be used as hardeners, either alone
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or in combination with the aforementioned alkali siliaates.
These include compounds of the general formula
MI2 I siF6]
wherein MI - univalent metal.
Alkali fluorosilicates and alkaline earth fluorosilicates
such as sodium, barium hexafluorosilicates, are mentioned by
way of example. Organic fluorosilicates are also suitable
e.g. bis-(methylammonium)fluorosilicate, bis-
~dibutylammonium)-fluorosilicate, dianilinium fluorosilicate.
The binder matrix according to the invention is formed by `
a hydraulic and/or polycondensation`process. Not only can
one-component and two-component sealing and embedding compound
systems be produced by way of these hardening mechanisms, but
the binding parameters can also be varied within relatively "
broad limits. These parameters include the so-called pot
life, hardening temperatures, green strength, and final -
strength.
Since the water in the polycondensating substances
according to the invention, which form the binder matrix, only
serves as a vehiale or wetting agent, it can be used in hybrid
systems for activating the hydraulically binding substances
forming the binder matrix so as to achieve a faster green
strength.
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The following are particularly suitable additives for
binding in the binder matrix according to the invention:
- filler materi~ls
wollastonite, mica, inorganic sulfates such as barium
~ul~ate, inorganic carbonates such as calcium carbonate,
inorganic oxides such as silicon dioxide (quartz powders)
or the like.
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Strengthening agents in the form of fibers can be added
if necessary for certain uses.
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~ 10 Ex~mples of inorganic fibers are:
: glass fibers, carbon fibers, rock wool, aluminum silicate
fibers and aluminum oxide fibers, ceramic fibers, silicon
carbide fibers, etc. insofar as they do not lower the
insulating resistance.
.
~xamples of organic ~ibers:
phenol fibers, aramide fibers and the like.
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Porous structures are often required for diverse uses of
` sealing and embedding compounds to take over sound-damping and
thermal-insulating functions and/or to reduce the inherent
weight. For this reason, a further development of the present
invention provides to produce self-supporting structural foams
`` by adding expanding agents and/or propellants prior to or
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during the binding process. According to the invention,
par~icularly suitable expanding agents and/or propellants
include peroxide compounds such as hydrogen peroxide,
persul~ates, perborates, percarbonates, organic peroxides such
as dibenzoyl peroxide or compounds which form gases or expand
in contact with water, e.g. carbides, aluminum powder, metal
hydrides, hydrazine derivatives, semicarbazides or the like.
Foams can also be produced during the pot life phase by
introducing gases such as air, nitrogen, and carbon dioxide.
These can be open-cell or closed-cell foams so that a wide
range of applications is covered. But foam-like structures
can also be developed in the binder matrix according to the
invention by adding so-called micro~cavities, such as hollow
micro-glass spheres.
It is also possible to produce pore structures by adding
powder or fibrous materials as pore-forming materials which
evaporate, melt or shrink when hardening.
Moreover, additional filler materials such as pigment,
dyes, thixotropic agents or other additives for regulating
rheological characteristics, wetting or the like can be added
to the sealing and embedding compounds according to the
invention for use in devices of the type mentioned in the
beginning. ~ ;
In order to maintain a low water content or binder/water
ratio when forming a ~aste with the homogeneous starting
components and/or to adjust lower viscosities for casting,
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in~ection molding or extrusion, it has surprisingly been found
that known green-mortar additives for liquefying and/or
pla~ticizing can be added to the mixing water, to the liquid
h~rdener and/or to the pasty compound. Such additives include
lignosulfonates, melamine formaldehyde condensate sulfonates,
naphthalene formaldehyde condensate sulfonates, tensides,
abietic acid derivatives, and certain hydrolyzed proteins.
The additives generally amount to 5% with reference to the
binder weight.
In order to stabilize a high insulating resistance during
and/or in the use of the compounds according to the invention
any existing hygroscopicity can be eliminated by furnishing
hydrophobicity. Nonpolar organic compounds, metallo-organic,
silico-organic and inorganic compounds are suitable for
providing hydrophobicity. The water-repelling agents most
often used include salts of aluminum and zirconium, complex
chromium salts, silanes, silicones, and perfluorinated organic
compounds insofar as no conductivity can develop under
conditions of relative humidity. Silanes and/or silicones are
particulàrly preferred, since they can be at least partially
- integrated in the binder matrix as compounds of the same
family.
But hydrophobicity can also be achieved by increasing the
concentrations of alkaline earth cations in the compound
compositions or by means of subsequent impregnation with
alkaline earth oxides or the like. Calcium compounds which,
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~8~
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among other things, react with the still reactive silicates to
form insoluble calcium silicates are particularly effective
and ~conomical.
Ac¢ording to the invention, the intimate, homogeneous
mixture o the starting components sio2 and water-containing
siliaates and the necessary additives with water is mixed to
form a paste until a deformable consistency is achieved or the
starting components are first processed with water and the `~
necessary additives are then added while forming a flowable,
pasty consistency, and the compound is then hardened after
deformation as required. The hardening compounds can also be
applied on a carrier material of metallic, inorganic or
organic work materials and then harden. Such carrier
materials can be steel, iron, wood, stone, concrete, plastics
such as duroplastics or thermoplastics, or the like.
When producing the compact compound for insulation, the
compound can be degassed by vacuum beforehand. But gas can
also be removed from the pre-formed cast articles or in
coatings by shaking or evacuation.
The water or an aqueous, alXaline medium can be used e.g.
in amounts of 5 to 70 percent by weight, preferably 20 to 50
percent by weight, in relation to the total dry compound.
The compounds which are mixed with water to form a paste
can be processed by casting, extrusion, injection molding and
pressing~
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In the production of compact sealing and embedding
compounds the hardening time is approximately 1 to 2 hours at
~5'C, wherein an exothermic polycondensation is used. This
i5 ~ollowed by after-drying at 20 to 50C until a constant
weight is achieved so as to expel the residual retained water.
If the sealing and emb~dding compounds are to be used at
higher temperatures, they are heated by stages to temperatures
of +80C to 1500C, wherein an after-hardening can be
observed. Generally, for high- temperature applications it is
necessary to heat in stages beyond the operating temperatures
in order to achieve a good resistance to temperature and a
good dimensional stability.
In the absence of additional energy resources for
hardening and for forming the binder matrix according to the
invention, as is the case e.g. in on-site assembly, the
hardening reactions can also be carried out at temperatures >
10C, particularly 15 to 30C, by adding so-called hardening
accelerators. Suitable hardening accelerators are anhydrous
; alkaline earth oxides such as quick lime, aluminum phosphates
and the above-mentioned clinker phases, high-alumina cements,
anhydrides, gypsum and possibly metal hydrides, as has been
discovered according to the invention, insofar as they cause a
reaction heat of 2 500 joules/g when in contact and/or in
solution with water.
In the production of porous sealing and embedding
compounds, the compounds harden at 20C in a maximum time of 2
19
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hours or at 50C in approximately 1 hour. After-hardening can
be effected at ~50 to +100C. If the porous sealing and
embedding compounds are likewise provided for use at high
temperatures, a stepwise heating to temperatures up to 1100C
is also e~fected.
The sealing and embedding compounds can also be furnished
with hydrophobicity if required. Silanes, polydimethoxy
sllanes or the like are suitable for this purpose.
Because of the low processing temperatures, the inorganic
agents according to the invention, provide an extremely wide
range of variations for production of the binder matrix, one
reason being that all of the additives mentioned above, as
well as other additives, can be integrated into the structural
matrix in a simple manner. .
On the basis of the binder matrix according to the
invention, the person skilled in the art is provided with a
binding, inorganically based sealing and embedding compound
intended for devices for protecting and connecting electrical
circuits which is distinguished by the following advantages
and advances, among others:
., .
- ease of processing
- environmental and ecological friendliness `
- uncritical mixture ratios of the 2-component systems
~ . ,
- adjustable pot life and binding times
- ability to process also at temperatures below 0C
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- binding in the presence of water
- non-combustibility
- extremely economical in comparison to sealing and embedding
compounds based on organic polymers.
The properties of the set sealing and embedding compounds
include:
- fast green strength and final strength, e.g. 30 minutes
- non-combustibility, i.e. no development of flue gases
- resistance to solvents, weak and strong alkalis, and
sulfuric acid
- surface hardness according to Mohs adjustable to 3 to 8
- volume weight in compact compounds: 1600 - 3500 kg/m3
in foam compounds : 200 - 1000 kg/m3
- flexural strength: adjustable between 10 - 40 MPa
- compressive strength: adjustable between 20 - 100 MPa
- E-module: 10,000 - 50,000 MPa
- linear thermal expansion: 1 to 8 x 10-6/k-
- high degree of vibration damping
- lower creep behavior in comparison to organic sealing and
embedding compounds
- thermal dimensional stability
- high resistance to ageing
- high insulating resistance of > lOo M n.
21
In the device according to the invention for protecting
and connecting electrical circuits, it follows from the above
that the cavities between the electrical elements and between
the device walls are filled with an insulating, inorganic
~aliny and embedding compound which can be processed in the
presence of water without the water participating in the
hardening reactions. Thus, the mixing water is only a vehicle
as suspending agent and/or dispersing agent for transforming
the solid components of the compound according to the
invention into a processible, liquid aggregate state. The
mixing water is to be removed from the hardened cast articles
- usually by evaporation - after polycondensation (hardening).
While the rheological properties of the sealing and
embedding aompounds according to the aforementioned
compositions are sufficient in simpler construction of the
device to achieve cast articles which are free of bubbles, it
is considerably more difficult to cast complicated or angular
housing constructions to cast cavities so as to be free of
bubbles. Although the rheology of the compounds is partially
improved by increasing the content of mixing water, this makes
sealing and hardening more costly and time-consuming and does
not provide a clean technical solution.
In a further development of the invention, the
; rheological processing characteristics of the sealing and
embedding compounds which are mixed with water can be improved
in a surprising manner with respect to viscosity, flow
22
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behavior and pouring behavior, etc., possibly accompanied by a
~imultaneous reduction in the mixing water requirement, by
add~ng rheology-improving additives to the sealing and
embedding compound which are based on alkali phosphates and/or
~lkali alkyl siliconates and their derivatives which take
effect when mixed with water.
The backbone binding agents mentioned in the beginning
include finely particulate sio2 and/or Al203 and originate from
different sources. These are amorphous inorganic substances
with a particle size of 100 um.
The further improved backbone binding agents belong to
~.~
the inorganic compounds whose practical applications rely to a
great extent on their rheological characteristics which, amo;ng
other things, are related to the following:
- the layer structure
- the plate-shaped and/or spherical configuration
- the negative charges
- the variable structure at the particle edges
- the cation and anion exchange capacity, and
~0 - the capacity to form different aggregates, suspensions and
colloidal dispersions in aqueous systems.
Although the rheological behavior of suspensions or
dispersions of the backbone binding agents according to the
invention can be described in qualitative terms, they have so
23
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far successfully resisted any mathematical treatment.
Surprisingly, it has been found that the alkaline earth ions,
preferably Ca~ ions, have a decisive influence on rheological
characteristics when the backbone binding agents according to
the invention are mixed with water, particularly in the case
of m-kaoline. They influence the peptization and accordingly
determina the required amount of mixing water for achieving
low viscosities and good flow and pouring properties.
Surprisingly, it has now been found that thinner
. .
suspensions and dispersions of the backbone binding agents
according to the invention and water are obtained when alkali
ions, e.g. Na~ ions, are added to the mixing water. A pH of
7.0 is particularly advantageous so that the positive edge
charges and edge (+)/ surface (-) contacts are prevented.
Water glasses etc., which are present according to the
invention in any case, are used for peptization.
However, the supply of or increased concentration (pH) of
alkali ions is not sufficient in itself for increased
` liquefaction, since the negative edge charge density is not
increased simultaneously. Surprisingly, it has been found
that alkali phosphates and/or alkali alkyl siliconates
::
according to the invention are suitable for enhancing the
peptization and increasing the edge charge density so as to ;
achieve thinner-liquid sealing and embedding compounds. The
alkali alkyl siliconates set in the presence of C02, among
others, to form the polyalkyl silicic acids according to the
24
invention, since the latter impart additional hydrophobic
characteristics to the hardened compounds.
These additives of alkali phosphates and/or alkali alkyl
silioonates according to the invention not only liquefy the
~ealing and embedding compounds, but also simultaneously
reduce the requirement of mixing water without thereby
changing the improved rheological properties.
The following alkali phosphates, alkali alkyl siliconates
and their derivatives, as well as mixtures thereof, are
suitable as additives according to the present invention which
improve the rheological properties.
According to the invention, the alkali phosphates are
meta-phosphates, ortho-phosphates and/or polyphosphates. The
: sodium phosphates and/or potassium phosphates, particularly
the sodium polyphosphates and potassium polyphosphates, are
particularly preferred.
; ~he alkali alkyl siliconates contain an alkyl group with
: 1 to 11 carbon atoms, wherein the sodium alkyl siliconates
and/or potassium alkyl siliconates whose alkyl group is a
methyl group, ethyl group, propyl and/or butyl group are
preferred.
Mixtures of both groups of additives are particularly
preferred because
- alkali phosphates bring about the higher li~uefaction
capacity and
- by way of hardening, the alkali alkyl siliconates form
. ~ .
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~.. . . , ~ , -. ;. ,
polyalkyl silicic acids which make the hardened compounds
hydrophobic.
All additives are soluble in water at a pH of 7Ø
The added quantities of the additives according to the
invention can fluctuate within a wide range. The amounts of
these additives contained in the sealing and embedding
compounds mentioned in the beginning are determined by the
liquefaction capacity relative to the compound compositions
and by the required hydrophobicity in the hardened compounds.
In general, the added amounts in relation to the total solids
content of a compound according to the invention are
- 10.0 m-%, particularly 5.0 m-~, for alkali phosphates and
- 50.0 m-%, particularly 25.0 m-~, for alkali alkyl
siliconates.
If the additives are in liquid form, they are added to
the hardener, insofar as the latter is a liquid water glass.
In all other applications, the additives are mixed in with the -~
backbone binding agents homogeneously.
After the addition of mixing water, the sealing and
embedding compounds which are modified by these additives are
stable, pumpable, thin-liquid suspensions or dispersions
having a relatively high solids conten~.
` ` ' :
.,
26
, " ,,," " ~":~",: ,;",,,, "~
~ ~ $ ~ ~ t ~ ,
The additives also convert the polyvalent cations present
in the mixing water, e.g. MgZ', CaZ~, Al3+, into water-soluble
complexes so as to prevent, in addition, a flocculent and
rapid precipitation of backbone binder particles. This
lengthens the processing time since the sealing and embedding
compound formulation remains homogeneous for a longer time.
The invention is not limited by the embodiments described
above which are presented as examples only but can be modified
in various ways within the scope of protection defined by the
appended patent claims.
27
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