Note: Descriptions are shown in the official language in which they were submitted.
1117734
The present invention relates to a hydrophobic precipi-
tated silica and its use as a reinforcing filler in material
which can be hardened to form elastomers.
Fillers are solid substances of usually inorganic ori-
gin and varied composition. Their particles can be fine-grained
to coarse-grained and can have various shapes. Such fillers are
added to a chemicotechnical product in order to improve specific
properties.
The present invention provides a hydrophobic precipi-
10 tated silica which is characterized by the following data:
-BET surface area 110 + 40 sqm/g
average size of the primary
particles as determined by
, EM (Electric Micrograph)
photographs 15 - 22 nm
loss on drying according to
~ DIN 55921 after 2 hours at
j 105C ~2.5%
loss on ignition (relative
to the substance dried for 2
hours at 105C.) according
to DIN 55921 5.5 + 1.5%
pH value (in a 5% aqueous
-methanolic suspension)
according to DIN 53200 7.5 + 1.0
conductivity (in a 4%
aqueous methanolic suspension) ~600_ ~S
bulk density of the non-
ventilated material according
to DIN 53194 130 + 40 g/litre
~D
wettability with water <0.1
carbon content 2.5 t 0.6%
water absorption at 30C
and 30% RH 1.2 + 0.4%
at 30C and 70%RH 1.5 + 0.5~
In a preferred embodiment of the hydrophobic precipi-
tated silica according to the invention the loss on drying can
be from 2.5 to 0.0%. The conductivity of the hydrophobic pre-
cipitated silica according to the invention can be from 50 to
-- 1 --
1~17734
300 ~S and its wettability with water can be from 0 to 0.05.
The present invention also provides a process for
producing the hydrophobic precipitated silica according to the
invention in which a precipitated silica having the following
physico-chemical characteristic data (obtained by separating
said precipitated silica from the precipitated suspension, in-
tensive washing with water and drying the precipitated hydro-
philic silica for a long time):
BET surface area according to DIN 66131 ~60 - 40 sqm/g
average size of the primary particles as
determined by EM photographs 14 - 22 nm
loss on drying according to DIN 55921
after 2 hours at 105C 2.5 - 4.0%
loss on ignition (relative to the
substance dried for 2 hours at 105C) +
according to DIN 55921 3.5 - 1.0%
pH value (in a 5% aqueous suspension)
according to DIN 53200 7.0 - 8.5
conductivity (in a 4% aqueous sus-
pension) <600 ~S
bulk density of the non-ventilated +
substance according to DIN 53194 140 - 40 g/litre
SO content (relative to the sub-
st~nce dried for 2 hours at 105C) ~0.3%
Na O content (relative to the sub-
stance dried for 2 hours at 105C) <0.3%
and a hydrophobic agent are put into an original precipitated
suspension while maintaining an alkaline pH value, the mixture
thus obtained is stirred, separated and dried for a lengthy per-
iod of time and the product thus obtained is tempered for 60 to
180 minutes, preferably for 70 to 130 minutes, at a temperature
of 200 to 400C and ground.
The initial precipitated suspension of the hydrophobic
precipitated silica can be obtained in the following manner:
1 part by volume of water is put into a reactor,
whereupon from 0.15 to 0.25 parts by volume of sodium-tetrasili-
~2
lil7734
.
cate solution ~modulus of SiO2:Na2O = 3.5 and 26% of SiO2) and0.015 to 0.025 part by volume of 96% ~2SO4 are added while
stirring. During the addition an alkaline pl~ value is maintained
in the mixture. On completing the addition of sodium tetrasili-
cate and H2SO4 the pH value of the suspension obtained is in the
weakly alkaline range.
Organo-silicon compounds, which are reacted with the
hydrophilic precipitated silica suspended in the aqueous phase
and which have been used for this kind of reaction heretofore,
~ 10 can be used as hydrophobic agents. Organo-silicon compounds
,~ having the general formula
(R3Si)aZ
are preferred. In this formula R represents identical or differ-
ent monovalent hydrocarbon radicals, which are substituted and/
or polymer if required, a is 1 or 2 and Z represents halogen,
hydrogen or a radical having the formula -OH, -OR, -NRX, -ONR2,
-SR, -OOCR, -O-, -N(X)- or -S-, wherein R always has the above
meaning for R and X represents hydrogen or has the same meaning
as R. Examples of these organo-silicon compounds are hexamethyl
disilizane, trimethyl silane, trimethyl chlorosilane, trimethyl
' ethoxysilane, triorgano-silyl mercaptans such as trimethyl-silyl
mercaptan, triorgano-silyl acylates such as vinyl dimethyl ace-
toxysilane, triorgano-silyl amines such as trimethyl-silyl-iso-
propyl arnine, trimethyl-silyl-ethyl amine, dimethyl-phenyl-silyl-
propyl amine and vinyl dimethyl-silyl-butyl amine, triorgano-
silyl-amino oxy compounds such as diethyl-amino-oxy-trimethyl
silane and diethyl-amino-oxy-dimethyl-phenyl silane as well as
hexamethyl disiloxane, l,3-divinyl-tetramethyl disiloxane, 1,3-
diphenyl-tetramethyl disiloxane and 1,3-diphenyl-hexamethyl di-
silazane.
Further examples of organo-silicon compounds which
within the scope of the invention, can be reacted with hydrophilic
-- 3 --
11~7734
precipitated silica suspended in the aqueous alkaline phase are
dimethyl dichloro-silane, dimethyl diethoxysilane, dimethyl
ethoxy-silane, dimethoxy-silane, diphenyl diethoxy-silane, vinyl-
~; methyl dimethoxy-silane and octamethyl cyclotetrasiloxane and/or
dimethyl polysiloxanes having 2 to 12 siloxane units per molecule
and containing an Si-linked hydroxyl group in each of the term-
inal units.
¦ Mixtures of various organo-silicon compounds can be
reacted with the precipitated silica which is in the form of an
3 lo aqueous original precipitated suspension.
~ In a preferred embodiment of the invention dimethyl
7 dichlorosilane can be used as the hydrophobic agent.
' The organo-silicon compounds, which are reacted with
the hydrophilic precipitated silica in the form of aqueous
alkaline original suspension, are used preferably in amounts of
5 to 30~ by weight, in each case relative to the weight of the
j precipitated silica to be reacted therewith.
The present invention also provides for the use of the
hydrophobic precipitated silica according to the invention as a
reinforcing filler in material which is based on diorgano-poly-
j siloxanes and can be hardened to elastomers. Thus, in a pre-
3 ferred embodiment the hydrophobic precipitated silica according
to the invention can be used in one-component silicone-rubber
joint-sealing compounds.
Furthermore, said hydrophobic precipitated silica can
be used in organo-polysiloxane elastomers, which can be hardened
at room temperature, as for example, preferably in a two-component
silicone molding material.
According to the invention the hydrophobic precipitated
silica can be used in heat-vulcanized diorgano-polysiloxane
elastomers, which, for example, can be used as cable-insulating
material. Any diorgano-polysiloxane, which was or could be used
-- 4
~117734
heretofore as a base for material hardening to organo-polysilox-
ane elastomers at room temperature (RTV), at only slightly ele-
vated temperature (LTV) or at high temperature (EITV) can be
;~ used as diorgano-polysiloxanes. They can be represented, for
example, by the general formula
Z Si(R)-o-[si(R2)o]-xsi(R)-zn
j 3-n 3-n
d
wherein R represents identical or different monovalent hydro-
~ carbon radicals which, if required, are substituted and/or
;;~ . polymer Z represents a hydroxyl group, a hydrolyzable group and/
:' or a hydrolyzable atom or if material which can be hardened at
only slightly elevated temperature is present, then Z represents
~ alkenyl groups, n is 1, 2 or 3 and x represents an integer having
j a value of at least 1.
j Examples of the hydrocarbon radical R are alkyl radi-
i cals such as methyl, ethyl, propyl, butyl, hexyl and octyl radi-
cals; alkenyl radicals such as the vinyl, allyl, ethyl-allyl and
the butadienyl radical; and aryl radicals such as the phenyl and
the tolyl radical.
¦ Examples of substituted hydrocarbon radicals R are
particularly halogenated hydrocarbon radicals such as the
3,3,3-trifluoropropyl radical, the chloro-phenyl radical and the
bromo-tolyl radical; and alkyl-cyanide radicals such as the ~-
ethyl-cyanide radical.
¦ Examples of polymer (also known as "modifying") sub-
stituted and non-substituted hydrocarbon radicals R are poly-
styrene, polyvinyl-acetate, polyacrylate, polymethacrylate and
polyacrylonitrile radicals linked by way of carbon to silicon.
At least the majority of the radicals R preferably con-
sist of methyl groups primarily because they are more readily
1~177;}4
available. The other radicals R which are possibly present are
particulariy vinyl and/or phenyl groups.
Particularly in case of the presence of material which
- is storable if water is excluded but which hardens to elastomers
at room temperature if water is admitted, Z usually represents
hydrolyzable groups. Examples of these groups are amino, amido,
amino-oxy, oxime, alkoxy, alkoxy-alkoxy (for example, CH3OCH2CH2O-),
alkenyl-oxy (for example, H2C=(CH3)-CO), acyl-oxy and phosphate
groups. Primarily because they are more readily available, acyl-
oxy groups, particularly acetoxy groups are preferred as Z. How-
, ever, if Z represents oxime groups like those haviny the formula
-ON=C(CH3)(C2~15), then excellent results are obtained.
Examples of hydrolizable atoms Z are halogen and hydro-
gen atoms.
~ Examples of alkenyl groups are particularly vinyl
`~ groups.
Identical or different Z can be linked to an Si atom.
Mixtures of different diorgano-polysixanes can also be
used.
By rnixing the hydrophobic precipitated silica according
~ to the invention with diorgano-polysiloxanes and if required with
I further substances at room temperature or at only slightly ele-
vated temperature, possibly on adding cross-linking agents,
material which can be hardened to elastomers, particularly to
storable elastomers when water is excluded, or material which
hardens to elastomers at roo~ temperature when water is admitted,
can be produced.
The mixing operation can be carried out in any known
manner, for example, in mechanical mixers.
The fillers used according to the invention are prefer-
3 ably applied in amounts of 5 to 50% by wei~ht, relative to the
total weight of the material which can be hardened to elastomers.
1~177;}~
In the case of HTV organo-poly-siloxane elastomers from 5 to 50
by weight can be applied and in the case of RTV organo-polysil-
oxane elastomers from 5 to 35% preferably 5 to 25~ by weight.
If the diorgano-polysiloxanes containing reactive
,.
terminal units contain Si-linked hydroxyl groups as the only
reactive terminal units, then in order to harden said diorgano-
polysiloxanes in a conventional manner or to convert them into
compounds which are hardened by the moisture contained in the
atmosphere, if required by adding additional water, they must
be reacted in a conventional manner with cross-linking agents,
if required, in the presence of a condensation catalyst. In the
.~ case of HTV diorgano-polysiloxane elastomers organic peroxides,
, as for example, bis-2,4-dichlorobenzoyl peroxide, benzoyl peroxide,dicumyl peroxide, tert. butyl perbenzoate or butyl peracetate,
t can be used as cross-linking agents at corresponding high tempera-
tures.
Organo-siloxanes, the organic substituents of which
consist of methyl, ethyl, phenyl, trifluoromethyl phenyl
[F3CC6H4-] or trimethyl silyl methylene radicals [(CH3)3SiCH2-],
for example, dimethyl, ~iethyl, phenyl-methyl, phenyl-ethyl,
ethyl-methyl, trimethyl-silyl methylene methyl, trimethyl-silyl-
methylene ethyl, trifluoromethyl-phenyl methyl or trifluoromethyl-
phenyl-ethyl-siloxanes or copolymers of these compounds can be
used as heat-vulcanizing organo siloxanes. Moreover, the poly-
mers may contain limited amounts of diphenyl-siloxane, bis-tri-
methyl-silyl-methylene-siloxane, bis-trifluoromethyl-phenyl
siloxane units as well as siloxanes containing units having the
formula RSiol 5 and R3Sioo 5, wherein R represents one of the
above radicals.
Examples of cross-linking agents are particularly
silanes having the general formula
R4 tSiZ't
-- 7
1~177;~
wherein R has the meaning defined hereinbefore, Z represents a
hydrolyzable group and/or a hydrolizable atom and t is 3 or 4.
The above examples of hydrolyzable groups Z and hydrolyzable
atoms Z also apply to the hydrolyzable groups Z' and hydrolyzable
atoms Z' in their entirety.
Examples of silanes having the above formula are
methyl-triacetoxy silanes, isopropyl-triacetoxy silane, isopro-
poxy-triacetoxy silane, vinyl-triacetoxy silane, methyl-tris-
diethyl-amino-oxy silane, methyl-tris(-cyclohexyl-amino) silane,
methyl-tris(-diethyl-phosphato)-silane and methyl-tris(-methyl-
ethyl-ketoximo)silane.
~ Moreover, instead of using silanes having the above
'~ formula or mixtures thereof, it is also possible to use, for
~, example, polysiloxanes containing at least 3 Z' groups or atoms
per molecule and the silicon valencies which are not saturated
by Z' groups or atoms are saturated by siloxane-oxygen atoms
and if required by R groups. The best known examples of the
latter kind of cross-linking agent are the polyethyl silicate
having an SiO2 content of approximately 40~ by weight, hexace-
thoxy disoloxane and methyl-hydrogen polysiloxanes.
~ The best known examples of condensation catalysts are
¦ tin salts of fatty acids such as dibutyl tin dilaurate, dibutyl
tin diacetate and tin-(II)-octoate.
If the only active terminal units present in the dior-
gano polysiloxanes containing reactive terminal units are those
j with alkenyl groups, then thè hardening to elastomers can be
carried out in a conventional manner with organo-polysiloxanes,
which contain on the average at least 3 Si-linked hydrogen atoms
per molecule such as methyl-hydrogen polysiloxanes, in the pre-
sence of catalysts promoting the addition of alkenyl groups to
Si-linked hydrogen such as platinum-(IV)-chloro acid. This
material (LTV) can be hardened at room temperature or at only
1~177;}~
slightly elevated temperature/usually from 50 to 80C).
Finally the hardening by means of polycyclic organo-
polysiloxanes in the presence of equilibrium catalysts, such as
phosphorus nitxile chlorides, is mentioned as a further example.
Of course, the material which can be hardened to elas-
tomers can contain, in addition to diorgano-siloxanes, precipi-
tated silica aceording to the invention, cross-linking agents
and cross-linking catalysts and, if required, fillers which
conventionally are used usually or frequently in materials to be
hardened to elastomers. Examples of these substances are fillers
i having a surface area less than 50 sq m per gram, such as
~1 quartz powder, diatomaceous earth, zirconium silicate and cal-
cium carbonate as well as untreated pyrogenically produced sili-
con dioxide, organic resins such as polyvinyl-chloride powder,
organo-polysiloxane resins, fibrous fillers such as asbestos,
glass fibres and organic fibres, pigments soluble dyes, odorous
substances, corrosion inhibitors, agents which stabilize the
material against the effeet of water, such as acetic anhydride,
agents retarding the hardening such as benzo triazole, plasti-
cizers, sueh as terminal dimethyl polysiloxanes blocked by tri-
methyl-siloxy-groups.
The cited eombination of physico-chemical charaeteris-
tie data of the hydrophobic preeipitated siliea aeeordiny to the
invention results in a highly effective reinforein~ filler be-
cause of the excellent dispersibility of said silica. The equil-
ibrium moisture eontent which is distinctly reduced as compared
with the known precipitated silica results in advantages when
processing, for example, in the no-pressure vulcanization, in
which the vulcaniæates obtained have fewer blisters than those
obtained when using the conventional hydrated precipitated sili-
¦ ca. The low eleetrolyte eontent in combination with the low
moisture eontent results in good eleetrical properties of the
g _
~1177~
vulcanizates. In cold-hardening silicone-rubber sealing com-
pounds the hydrophobic precipitated silica according to the
invention is favourable for the storage properties of the non-
hardened material because of its low water content.
The production, the physico-chemical data and the use
of the hydrophobic precipitated silica according to the invention
are described in greater detail by means of the Examples hereafter.
_ample 1
Production of the Original Precipitated Suspension
10of a Hydrophilic Precipitated Silica for the Subse-
quent Wet Hydrophobic Operation
~, '
50 cu m of water are put into a reactor. 9.2 cu m of
.! sodium tetrasilicate solution and 0.9 cu m of H2SO4 are then
.~added while stirring. During the addition an alkaline pH value
is maintained in the mixture. On completing the addition of
sodium tetrasilicate solution and H2SO4 the pll value of the sus-
pension thus obtained is in the alkaline range.
In order to characterize the hydrophilic precipitated
silica, a portion of the suspension is filtered off, washed
until its electrolyte content is low, whereupon it is dried in
a drying cabinet at 105C until the weight is constant, whereupon
it is ground in a pinned disc mill.
The hydrophilic precipitated silica thus obtained has
the following physico-chemical characteristic data:
BET surface area according to DIN 66131 155 sq m~g
average size of the primary particles as
determined by EM photographs 18 - 20 nm
loss on drying according to DIN 55921
after 2 hours at 105C 3.0
loss on ignition (relative to the
substance dried for 2 hours at 105C)
according to DIN 55921 3.3%
pH value ~in a 5% aqueous suspension)
-- 10 --
1~177;~4
according to DIN 53200 7.7
conductivity (in a 4% aqueous sus-
pension) 240 ~S
3 bulk density of the non-ventilated
material according to DIN 53194 140 g/litre
S2 content (relative to the sub-
stance dried for 2 hours at 105C) 0.22%
Na2O content (relative to the sub-
stance dried for 2 hours at 105C) 0.18
j Determination of the Electrical Conductivity
~ A sample of 4.0 g of silica is heated in a 150-litre
~4
; 10 beaker with 50 g of water completely free from salt, whereupon
the suspension is boiled for one minute while stirring. The
suspension is then transferred to a 100-ml measurin~ flask, cooled
;~ and filled up to the mark with water completely free from salt.
~ After shaking, the cell of the conductivity-measuring device is
'A first rinsed with the suspension to be measured, whereupon it is
filled and the cell is dipped into the suspension. ~rhe electri-
cal conductivity is read on the measuring device and the tempera-
ture of the suspension is determined during the measurement.
Calculation: The electrical conductivity is defined in ~S,
relative to 20C.
' Example 2
Production of a Hydrophobic Precipitated Silica
according to the Invention Obtained by Net Hydro-
phobic Operation
~ 193 g of dimethyl dichlorosilane are added to 10 litres
¦ of an aqueous original precipitated suspension of the precipi-
tated silica according to Example 1, which has a solid concentra-
tion of 57.9 g per litre, while stirring intensively for 30
minutes. During the addition, the pH value of the suspension
is maintained at 8.5. After a subsequent mixing period of 60
minutes the precipitated silica, 25~ of which is covered with
-- 11 --
1~177;}~
dimethyl dichlorosilane, is separated, dried at 105C, tempered
at 350C for 2.0 hours and subsequently dried.
The hydrophobic precipitation silica thus obtained has
the followiny physico-chemical characteristic data:
loss on ignition at 1000C according
to DIN 55921 5.5gO
humidity thereof at 105C according
to DII~ 55921 0.4
f pH value according to DIN 53200 ~.0
BET surface area according to DII~
7 66131 89 sqm/g
~i 10
wettability with water 0.05%
eonduetivity 160 ~S
C eontent 2.2%
water absorption at 30C and 30% RH 1.2~
~ at 30C and 70~ RH 2.0%
?~ bulk density of the non-ventilated
material according to DIN 53194 130 g/litre
t Determination of the Wettability of Hydro-
phobic Silicas with Water
The determination of the hydrophobic silica portions
which are wettable with water is described in the analytical
method hereafter.
Carrying out the Determination
0.2 g of hydrophobic silica and 50 ml of distilled
water are put into a 250-ml separatory funnel and shaken for
1 minute with the aid of a Turbula mixer at maximum speed.
After allowing the wetted portions to settle for a
short time, 45 ml of the suspension are drawn off into an evapor-
ating dish after shaking carefully, whereupon this portion of the
suspension is evaporated on a water bath and then dried at 105C.
Calculation: dry residue _100 _ ~ of portions wettable
weighed-in portion with water
Determination of the Moisture Absorption
In the determination of the moisture absorption the
- 12 -
~.~17734
maximum or time-dependent moisture absorption of silicas is
determined as a function of both the temperature and the rela-
I tive humidity of the air.
i Carrying out the Determination
A silica sample of approximately 2.5 g is weighed into
~, a dry tared weighing glass with an accuracy of 0.1 mg and dried
~ for 2 hours at 105~C. After cooling, the weight is determined
3 on an analytical balance. The open weighing glass with the sam-
ple is then stored in a conditioning cabinet at predetermined
~ 10 temperature and relative humidity of the air. Either a moisture
J absorption-time diagram or the maximum moisture absorption can
~j then be determined.
The determination is usually carried out at:
30C and 30% relative humidity of the air
30~C and 70~ relative humidity of the air
Calculation: g of portion weighed out 100 = % of moisture
g of portion weighed in dried absorption
sample
Example 3
The Use of a Hydrophobic Precipitated Silica
~ according to the Invention in Cold-Hardening
i One-Component Silicone Rubber Compounds
i
In this example the hydrophobic precipitated silica
according to the invention and example 2 is tested as a rein-
forcing filler and thixotropic agent in a one-component sili-
cone-rubber joint-sealing compound (cold-vulcanizing).
In the tests the silica Aerosil 150 of the firm of
Degussa and the commercial product HD~ H 2000 of the firm of
Wacker are tested for comparison in the same silicone-rubber
material. R
HDK H 2000 lS a highly dispersed silica, which is
- 13 -
~1177~4
produced by flame hydrolysis of volatile silicon compounds and
is subsequently rendered hydrophobic by reaction with organo-
silanes. Therefore, on the surface said silica is densely
4 covered with trimethyl silyl groups and had the following
physico-chemical characteristic data:
surface area according to BET 170 + 30 sqm/y
SiO2 content >97% by weight
powder density (non-pressed) approximately 90g/litre
moisture according to DIN 53198
process A (after 2 hours at
. 10 105C) <0.6% by weight
j loss on ignition according to
,j DIN 52911 (2 hours at 1000C) <2.5-o by weight
;`1 pH va]ue according to DIN 53200
j (in a 4% dispersion in water-
methanol = 1:1) 6.7 - 7.7
grit according to Mocker
(DIN 53580) <0.05% by weight
adhering HCQ <0.020% by weight
AQ2O3 <0.05gO by weight
~! F~03 <0.005% by weight
Tio2 <0.003gO by weight
C <3% by weight
Aerosil 150 is a pyrogenically produced silica having
the following physico-chemical characteristic data:
surface area according to BET 150 + 50 sqm/g
average size of the primary
particles 14 nm
loss on drying according to
DIN 53198/A (2 hours at 105C 0.5%
_ loss on ignition according to
DIN 52911 (2 hours at 1000C) 1%
pH value according to DIN 53200
(in a 4% aqueous dispersion) 3.6 - 4.5
SiO2 *) 99.8%
2 3
- 14 ~
1~17734
2 3 0.003
2 0.03
I HCQ 0.025
grit according to Mocker
(DIN 53580) 0.05~
wetting characteristics hydrophobic
*) relative to the substance tempered for 2 hours at 1000C.
I The following formula with acetate hardener is used
; as a basis:
86.4 parts by weight of dimethyl polydisiloxane with
" 10
~ hydroxy terminal groups, viscosity 50,000 cSt.
.~ . 271 parts by weight of dimethyl polysiloxane with
trimethyl-siloxy terminal groups, viscosity 1000 cSt
4.5 parts by weight of methyl-triacetoxy silane
(cross-linking agent)
~ 0.005 parts by weight of dibutyl-tin diacetate plus
j silica to be tested.
The silica is incorporated after adding the cross-
linking agent in a planetary mixer, which can be evacuated.
The joint-sealing compound, which was still pasty,
~ and its vulcanizate, which had been hardened for 7 days in air,
! was then subjected to the following test:
a) extrudability according to ASTM 2452-69
b) stability under load according to the cap
method
c) modulus at 100% elongation according to
DIN 53504
d) tensile strength according to DIN 53504
e) elongation according to DIN 53504
f) tear propagation strength according to
DIN 53515
g) Shore-A hardness according to DIN 53505
The results of these tests have been compiled in
Table I (see below). Compared with the known pyrogenic hydro-
- 15 -
f 1117734
philic silicas Aerosil 150 and the hydrophobic silica HDK H 2000
the following advance in the art is evident:
~ Aerosil 150 (a trademark) can be incorporated in the
-~ one-component sealing compound only up to 8%. A higher degree
of filling result in a material which can be processed only
with difficulty. The level of the mechanical data obtained with
~ a degree of filling of 8% corresponds to the prior art.
3 However, with the silica according to the invention
i used in Example 2, a substantially higher level of the mechani-
10 cal data is obtained at a degree of filling of 20o~ ~Ihese data
satisfy the requirements to be met by high-strength sealing
compounds. The extrudability of the material is fully satisfied
at this degree of filling. The storage life is also good.
However, at a degree of filling of 20%~ the value
level of the mechanical data of the commercial product HDK H 2000
which represents the latest state of the art, is not comparable
to the vulcanizates filled with the precipitated silica
according to the invention. This applies particularly to the
tensile strength and the elongation, both of which are 45~ be-
20 low the corresponding values of the silica according to the
invention. Only on increasing the degree of filling to 25% can
the data for E~DK H 2000 be fully balanced.
Surprisingly enough, it has thus been shown that when
using only 20% of the precipitated silica according to the
invention a property pattern which in some respect is distinctly
better (than 25% of HDK H 2000) can be attained. With the appre-
ciably lower costs of production as compared with pyrogenic
hydrophobic silica, additional uses thus present themselves.
- 16 -
- 1~17734
Table I
Testing of a ~Iydrophobic Precipitated Silica
according to the Invention and Example 2 in
a One-Component Silicone Sealing Compound as
Compared with a Pyrogenic Silica of the Prior
Art
.
silica type storage life stability extrudability
type (%)*) lUoaddr (g/min)
(cap method)
_
Oflica
example
,, 2 20 good good 8.2 after 0 days
~ 8.0 after 28 days
'~ Aerosil
.~ 150 8 good good 8 after 0 days
.~ 8 after 28 days
;.~ HDK H 2000 20 good good 19 after 0 days
22 after 28 days
good good 11 after 0 days
9 after 28 days ,
., silica ~ype modulus 100 tensile elongation I tear Shore-~
type (%)*)(N/mn2) strength (~) propagation hardnes
(N/n)m) li S(t/mm)''h
.
silica
example
2 20 4.6 45 780 16 1 18
Aerosil ,
HDK 8 3.0 10 400 1 2.5 , 20
H 2000 20 5.0 25 430 ¦ 15 24
25 6.0 45 490 1 18 1 32
_ I ,,
*) % by weight, relative to total mixture.
~177;}~
Example 4
Production of a Hydrophobic Precipitated Silica
according to the Invention, Obtained by Wet
Hydrophobic Process
,~
175.6 g of dimethyl dichlorosilane are added to 12
litres of an original precipitation suspension of the precipi-
tated silica according to Example 1 with a solid concentration
of 57.9 g per litre within 30 minutes while stirring intensively
., and while maintaining a pH value of 8.5 in the suspension. After
,~ 10 a subsequent mixing time of 60 minutes, the precipitated silica,
7 20% of which is covered with dimethyl dichlorosilane, is dried
at 105C, tempered for 1.5 hours, whereupon it is ~round. The
precipitated silica obtained has the following physico-chemical
1 characteristic data:
.q
t loss on ignition at 1000C according
to DIN 55921 5.5
humidity thereof at 105C according
to DI~ 55921 0.4%
pH value according to DIN 53200 7.5
BET surface area according to
DIN 66131 94 sqm/g
j wettability with water 0.06
! conductivity 92 ~S
C content 2.1P6
water absorption at 30C and 30% ~i 1.3%
at 30~C and 70% Rll 2.0%
bulk density of the non-ventilated
material according to DIN 53194 137 g/litre
Example 5
Use of a Hydrophobic Precipitated Silica
according to the Invention in Cable Material
Based on Organo Polysiloxanes
In this example, the hydrophobic precipitated silica
according to the invention and Example 4 is incorporated in heat-
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. 11177;~4
vulcanizing silicone rubber as a reinforcing filler and tested
for the electrical volume resistance of the vulcanizates pro-
duced therewith.
s Because of its excellent dielectrical properties, heat-
vulcanizing silicone rubber is also used as high-grade cable-
insulating material. On account of its compactness and favour-
; able dielectrical properties highly active pyrogenic silica is
usually used as a reinforcing filler in this case. It is known
1 that the insulating properties are further improved if the fully
' 10 vulcanized material is subsequently subjected to a lengthy
i tempering process (at least 6 hours) at elevated temperatures
(approximately 200C).
In the tests for this example, the following formula
was used:
100 parts by weight of diemthyl polysiloxane with
i trimethyl-siloxy terminal groups and a content of vinyl groups.
j 40 parts by weight of silica
1.4 parts by weight of 50% bis-2,4-dichloro-benzoyl
peroxide (as a paste in silicone oil).
vulcanization: 7 minutes at 130C.
tempering: 0 or 6 hours at 200C and 80~ relative
humidity of the air.
The results of the tests as compared with Aerosil
200 R ) (a pyrogenic silica of the firm of Degussa) are shown in
Figure 1. As is evident from the curves, with the precipitated
silica according to the invention similarly good resistance
values can be attained as with the pyrogenic silica. Moreover,
it has been surprisingly found that with the silica according
to the invention, the good electrical properties can also be
attained without the costly tempering process mentioned herein-
j before. Apart from the more favourable costs of production,
~ this is a further advantage of the precipitated silica according
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to the invention.
*) Aerosil 200R is a highly dispersed silica produced
by flame hydrolysis of volatile silicon compounds and has the
following physico-chemical characteristic data:
surface area according to BET 200 + 25 sqm/g
average size of the primary
particles 12 mll
j bulk density (DIN 53194) 1700 ml/lOOg
compressed material 1000 ml/lOOg
loss on drying (DIN 53198, process
A) 2 hours at 105C <1.. 5% by weight
loss on ignition (DIN 52911)
~ 2 hours at 1000C ~1.5~ by weight
:' pH value (DIN 53200) in a 4%
aqueous dispersion 3.6 - 4.3
~1 SiO >99.8% by weight
i AQ03 <0.05% by weight
~203 <0.003~ by weight
TiO2 <0.03% by weight
HCQ <0.025~ by weight
grit according to Mocker
(DIN 53580) 0.05% by weight
I
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