Precipitated silicic acid

Details Precipitated silicic acid Precipitated silicic acid

1999-09-03

2001-07-31

Cain, Edward J. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C423S327100, C423S333000, C423S335000, C423S339000

Reexamination Certificate

active

06268424

ABSTRACT:

INTRODUCTION AND BACKGROUND
The present invention relates to precipitated silicic acids (silica), a process for their preparation, and their use in rubber mixtures.
It is known to incorporate precipitated silicas into rubber mixtures (see Wolff, Kautschuk, Gummi, Kunstst. 7 (1988) p.674). Precipitated silicas have to be readily dispersible when used in rubber mixtures. A poor dispersibility is often the reason why precipitated silicas are not used in tire mixtures.
Document WO 95/09128 discloses precipitated silicas that can be used in tires. Their use in tire carcasses is however not mentioned.
On account of the more stringent requirements of the tire industry, even the improved dispersion of this precipitated silicic acid is no longer sufficient for use in tire treads.
WO 96/30304 describes a precipitated silica that can be dispersed in tire treads.
Using the known precipitated silica described in WO 96/30304 it is possible to achieve a reduction in the rolling resistance of the tire by 20-30% compared to tires filled with carbon black. This corresponds to a saving in fuel of ca. 5%.
Different tire constituents contribute in various proportions to the rolling resistance of an automobile tire:
Tread:
50%
Belt.:
20%
Carcase:
10%
Side wall:
10%
Tire bead:
 5%
Inner layer:
 5%
In a truck tire the proportion of the individual tire segments to the rolling resistance differs from the distribution in an automobile tire:
Tread:
30%
Belt:
20%
Carcase:
24%
Side wall:
10%
Tire bead:
16%
This distribution of the proportions contributing to the rolling resistance shows that in automobile tires 50% and in truck tires even up to 70% of the rolling resistance is due to structural parts of the tire carcase. Up to now carbon black has overwhelmingly been used as active filler in tire carcasses.
Some sections of the automobile industry demand that the rolling resistance be reduced by approximately a further 10%. Up to now it has not been possible to achieve his.
An object of the present invention is to achieve a further considerable reduction in the rolling resistance of tires.
Another object of the invention is to achieve a precipitated silica that is easily dispersible in tire carcasses.
Truck tire customers are in addition asking for an increase in the service life of truck tires. Another object of the present invention is to meet this request, combined with a reduction in the amount of heat generated.
SUMMARY OF THE INVENTION
The above and other objects can be achieved by a precipitated silica that is characterized by an Al
2
O
3
content of 0.2 to 5.0 wt. % and a wk coefficient of less than 3.4 as described by the present invention.
The precipitated silica according to the invention can have a BET surface area of 80 to 180 m
2
/g.
The precipitated silica according to the invention can have a CTAB surface area of 80 to 139 m
2
/g.
The precipitated silica according to the invention is characterized by the following physico-chemical data:
BET surface area
80-180 m
2
/g
CTAB surface area
80-139 m
2
/g
BET/CTAB ratio
1.0-0.6
Sears No. (consumption of
5-25 ml
0.1 N NaOH)
DBP (dibutyl phthalate) No.
200-300 ml/100 g
Al
2
O
3
content
<5%
wk coefficient
<3.4
Degraded particles
<1.0 &mgr;m
Non-degradable particles
1.0-100 &mgr;m
The physico-chemical data are determined using the following methods:
BET surface area
Areameter, Fa. Ströhlein,
according to ISO 5794/Annex D
CTAB surface area
At pH 9, according to Jay, Janzen
and Kraus in “Rubber Chemistry and
Technology” 44 (1971) 1287
Sears No.
According to G. W. Sears, Analyst.
Chemistry 12 (1956) 1982
DBP No.
ASTM D 2414-88
wk coefficient
Cilas Granulometer 1064 L (for
description see below)
The precipitated silica according to the invention in a preferred embodiment exhibits the following physico-chemical data:
BET surface area
90-150
m
2
/g
CTAB surface area
80-130
m
2
/g
BET/CTAB ratio
1.0-1.6
Sears No.
5-25
ml
(consumption of
0.1N NaOH)
DBP No.
200-300
ml/100 g
Al
2
O
3
content
<2%
wk coefficient
<3.4
Degraded particles
<1.0
&mgr;m
Non-degradable particles
1.0-30
&mgr;m
The precipitated silica according to the invention in a particularly preferred embodiment exhibits the following physico-chemical data:
BET surface area
90-150
m
2
/g
CTAB surface area
80-130
m
2
/g
BET/CTAB ratio
1.0-1.6
Sears No.
5-25
ml
(consumption of
0.1N NaOH)
DBP No.
200-300
ml/100 g
Al
2
O
3
content
0.2-0.66%
wk coefficient
<3.4
Degraded particles
<1.0
&mgr;m
Non-degradable particles
1.0-30
&mgr;m
The invention also provides a process for the preparation of the precipitated silica with the following physico-chemical parameters:
BET surface area
80-160
m
2
/g
CTAB surface area
80-140
m
2
/g
BET/CTAB ratio
1.0-1.6
Sears No.
5-25
ml
(consumption of
0.1N NaOH)
DBP No.
200-300
ml/100 g
Al
2
O
3
content
0.2-5%
wk coefficient
<3.4
Degraded particles
<1.0
&mgr;m
Non-degradable particles
1.0-100
&mgr;m
which is characterized in that alkali silicate is reacted with mineral acids and aluminum sulfate solution at temperatures of 60-95° C. at a pH of 7.0-11.0 while stirring continuously, the reaction is continued until a solids concentration of 40 g/l-110 g/l is achieved, the pH is adjusted to a value between 3 and 5, and the precipitated silica is filtered off, washed, then dried and optionally ground or granulated.
In a particular modification the addition of water glass, aluminum sulfate solution and sulfuric acid may be discontinued for 30-90 minutes and then continued.
In a preferred embodiment commercially available sodium water glass (modulus 3.2-3.5) may be reacted with sulfuric acid at a pH between 7.5 and 10.5, some of the sodium water glass being added beforehand to adjust the pH in the reaction vessel. The addition of water glass and sulfuric acid is maintained over a period of up to 120 minutes, wherein in a particular modification the addition may be discontinued for 30-90 minutes, following which the reaction mixture may be acidified to pH 3-5, filtered, washed and dried.
In order to achieve a particularly good dispersibility the simultaneous addition of sodium water glass and sulfuric acid preferably takes place over a period of between 40 and 90 minutes. The surface of the silica can be adjusted via the precipitation duration.
Chamber filter presses or membrane filter presses or band filters or rotary filters or automatic membrane filter presses or two of the filters in combination can be used for the filtration.
A pneumatic drier, rack drier, flash drier, spin-flash drier or similar equipment can be used for the drying.
In a further embodiment of the invention liquefied filter cakes can be dried in a spray drier with an atomizer or two-substance nozzle or a single-substance nozzle and/or integrated flow bed.
A roller-type compactor or similar equipment can be used for the granulation.
In a particularly preferred modification the precipitated silicas can be dried by means of a flash drying.
The precipitated silica according to the invention can be modified with organosilanes of the formulae I to III:
[R
1
n
—(RO)
3-n
Si—(Alk)
m
—(Ar)
p
]
q
[B]  (I),
R
1
n
(RO)
3-n
Si-(alkyl)  (II),
or
R
1
n
(RO)
3-n
Si-(alkenyl)  (III),
in which
B denotes —SCN, —SH, —Cl, —NH
2
(when q=1) or —Sx— (when q=2),
R and R
1
denote an alkyl group with 1 to 4 carbon atoms, the phenyl radical, all radicals R and R
1
in each case being the same or having a different meaning,
R denotes a C
1
to C
4
-alkyl group or C
1
to C
4
-alkoxy group,
n denotes 0, 1 or 2,
Alk denotes a divalent linear or branched hydrocarbon radical with 1 to 18 carbon atoms,
m denotes 0 or 1,
Ar denotes an arylene radical with 6 to 12 carbon atoms, preferably with 6 carbon atoms,
p denotes 0 to 1, provided that p and n do not simultaneously denote 0,
x denotes an integer from 2 to 8,
Alkyl denotes a monovalent linear or branched saturated hydrocarbon radical with 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms,
Alkenyl denotes a monovalent linear or branched unsaturated hydrocarbon radical with 2 to 20 car

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