# Patent

## Title
Hydrophobic silica

## Abstract

Methods of making hydrophobic, pyrogenically produced silica having a tamped density, of 55 to 200 g/l. Said silica is produced by hydrophobizing pyrogenically produced silica by reaction with a halogen free silane and then compacting it with means consisting of a roller compactor or a belt filter press. The silica may be used for the production of dispersions.

## Background
REFERENCE TO RELATED APPLICATIONS
This application is a continuation of application Ser. No. 09/740,039 filed Dec. 20, 2000, now abandoned, which claims the benefit of provisional application 60/171,667 filed Dec. 27, 1999, both of which are relied on and incorporated herein by reference.


INTRODUCTION AND BACKGROUND
This invention relates to a hydrophobic, pyrogenically produced silica, to a process for the production thereof and to the use thereof.
It is known to compact hydrophilic, pyrogenically produced silica (EP0 280 851 B1). Disadvantageously, as tamped or bulk density increases, thickening action declines in a linear manner. Dispersibility also falls as density increases. This results in unwanted speckling. Thus, once compacted, a hydrophilic, pyrogenically produced silica may only be used for a limited number of applications.
It is therefore an object of the present invention to avoid the problems of compacted, hydrophobic, pyrogenically produced silica of the past.
SUMMARY OF THE INVENTION
The above and other objects of the present invention can be achieved by developing a hydrophobic, pyrogenically produced silica having a tamped density of 55 to 200 g/l.
The tamped density is preferably from 60 to 200 g/l.
A feature of the present invention is a process for the production of the hydrophobic, pyrogenically produced silica having a bulk density of 55 to 200 g/l, which process is characterised in that pyrogenically produced silica is hydrophobized using known methods and then compacted.
Hydrophobing can preferably be performed by means of halogen-free silanes. The chloride content of the silica can be less than or equal to 100 ppm, preferably from 10 to 100 ppm.
Compaction can be performed by means of a roller compactor. Compaction can preferably be performed by means of a belt filter press according to EP 0 280 851 B1, which reference is relied on and incorporated by reference.
The hydrophobic, pyrogenically produced silica used for purposes of the present invention can be, for example, the silicas known as:

    Aerosil R 812 or Aerosil R 8128, having the group —0—Si (CH3)3 
    Aerosil R 202, Aerosil MS 202, Aerosil MS 202, Aerosil R 106 or Aerosil R 104 having the group






    Aerosil R 805 having the group






These are commercially available products from Degussa Hüls AG.
The hydrophobic, pyrogenic silica according to the invention having a tamped density of 55 to 200 g/l exhibits the following advantages:
Transport costs are distinctly lower as a result of the higher tamped density.
Once dispersed, the silica according to the invention is in the form of relatively small aggregates. In other words, the dispersions are more finely divided because the silica according to the invention is more readily dispersible.
The dispersions produced using the silica according to the invention exhibit a lower Grindometer value.
Both UV transmission transparency and visual transparency of the dispersions are distinctly improved by using the silica according to the invention.
Dispersions containing the silicas according to the invention exhibit distinctly increased stability because the tendency towards settling is distinctly lower.
Another advantage of the silica according to the invention is reduced dusting during incorporation and the distinctly reduced incorporation or wetting time in, for example, liquid systems.
In comparison with hydrophobic, pyrogenic silica of a lower bulk density, the hydrophobicity of the silica according to the invention is unchanged. Thickening action is also unchanged.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be further understood with reference to the following detailed embodiments thereof.


EXAMPLE 1
Various hydrophobic, pyrogenically produced silicas are investigated, wherein different compaction states are compared.
The following definitions apply:













bulk =
pulverulent, unmodified silica


CF =
silica compacted with a Carter filter


VV 60 =
silica compacted to a tamped density of approx. 60 g/l


VV 90 =
silica compacted to a tamped density of approx. 90 g/l









Aerosil grades R 202, US 202, US 204, R 812, R 812S and R 805 are investigated. The results are shown in Table 1.
As evaluated by the Corning Glass methanol wettability method, the degree of compaction has virtually no appreciable influence on hydrophobicity. Viscosity also exhibits no clear systematic dependency upon tamped density. Especially for R 812, dispersibility improves with increasing density. R 812S, which contains more SiOH groups than R 812, exhibits the above phenomenon less markedly.
US 202 and US 204 have very comparable theological properties and are inferior to AEROSIL R 202.
Surprisingly, the compacted variants, in particular of R 812, R 202 and US 202/4, exhibit an incorporation time reduced by up to half. The compacted silicas moreover exhibit reduced dusting.


























444701
444702
444703
444704
444705
444706
444707
444708







AER
AER
AER
AER
AER
AER
AER
AER
444709
444710
444711




202
202
202
202
805
805
805
805
AER812
AER812
AER812


PA
Test method
CF
CF
VV60
VV90
bulk
CF
VV60
VV90
bulk
CF
VV60





0330
Viscosity, epoxy before cure
459
456
382
430
190
181
185
178


0335
Viscosity, epoxy after cure
54.4
54.7
49.4
52.8
42
41.7
39
43


0340
Thickening action








11.7
13.3
11.5


0410
Grind motor value








127
102
92


0420
Methanol wetability


0701
Tamped density
45
50
51
75
44
62
55
68
45
44
50


0920
Agglemerate strength

11
20
18

15
15
20


0930
Hand: |sic|sieve oversize
0
24
4
27
0
36
7
19
0
0


0955
Effectiveness
258
274
203
266
235
260
236
258
166
185
169


0965
Effectiveness(UT)
280
290
226
295
271
281
270
288
197
213
209


0975
Settling(effectiveness)
15
15
15
8
10
15
10
5
13
15
8

























444712
444713
444714
444715
444716











AER
AER
AER
AER
AER
444717
444718
444719
444720
444721
444722
444723




812
812S
812S
812S
812S
US202
US202
US202
US204
US204
US204
US204


PA
Test method
VV90
bulk
CF
VV60
VV90
bulk
CF
VV60
bulk
CF
VV60
VV90





0330
Viscosity, epoxy





350.4
377.6
380.8
379.2
350.4
358.4
368



before cure


0335
Viscosity, epoxy after cure





50.7
45.9
45.3
49.9
47
52.6
50.7


0340
Thickening action
11.1
17.3
17.3
18.2
17


0410
Grind motor value
77
93
110
110
100


0420
Methanol wetability


0701
Tamped density
73
49
50
58
75
39
50
67
44
45
57
71


0920
Agglemerate strength
22



28

10
15


16
23


0930
Hand: |sic|sieve oversize
12
0
0
0
4
0
27
36
0
0
3
20


0955
Effectiveness
159
168
169
187
209
320
304
320
186
193
192
201


0965
Effectiveness(UT)
225
201
200
216
235
336
327
346
223
225
225
230


0975
Settling(effectiveness)
5
8
8
3
0
15
10
3
10
10
10
10









EXAMPLE 2
Investigation of the Influence of Higher Compaction on Applicational Properties

















AE R 812,
AE R 812,




AE R 812,
compacted
compacted



uncom-
RHE
RHE



pacted
UB 3847-2
UB 3847-3



UB 3847-1
(4)
(5)
AE R 812



10 kg
15 kg
20 kg
RHE



sack
sack
sack
specific.





















Tamped density (DIN ISO
g/l
50
87
106
approx.


787/11)




50


Effectiveness, ethanol

184
214
209
216 1)


(0955)


Effectiveness (UT),

218
260
290
236 1)


ethanol (0965)


Settling
vol. %
10
1
1
1)


(effectiveness, high-


speed mixer)









1. Determined on standard sample (UB 3391)

RHE in the above table indicates the Rheinfelden plant located in Germany.
Rheological Testing:


    Polymer: Araldit M (biphenol-1-expoxy resin by Ciba-Geogy, in the form of clear yellow liquid).
    Thixotroping agent: R 202 and R 812 Additive:—












Sample production date: 24 Feb. 1994 Spindle: 5












Storage time
5 rpm
50 rpm




in days
[mPa*s]
(mPa*s)
T.I.













Sample A R 812 10 kg 2-10123












0
16600
4460
3.72




80-85 μ









Sample A R 812 15 kg 1.0/8 min












0
15100
4060
3.72




50-60 μ









Sample AR 812 20 kg 0.6/14 min












0
15100
4020
3.73




50-60 μ










Compaction may amount to a type of predispersion. Accordingly, effectiveness values rise with tamped density, i.e. the particles effectively present in the ethanol dispersion become smaller and the compacted samples exhibit distinctly less settling. Any suitable organic solvent can be used to form the dispersion.
The compacted samples accordingly have a more favourable Grindometer value in Araldit. However, since the larger particles have a decisive influence on thickening action, the property declines slightly on compaction.
It may be seen from the effectiveness values that, while the highly compacted AEROSIL R 812 sample may indeed still be broken up with the Ultra-Turax® mixer(0965), it can no longer be broken up with the high speed mixer (0955). Due to the smaller surface area of AEROSIL R 202 (and to the consequently theoretically improved dispersibility), this phenomenon hardly occurs with AEROSIL R 202. The parenthetical values (0965) and (0955) are the PA numbers in the tables on pages 5 and 6.
As compaction rises, the particles effectively present in an ethanol dispersion thus become smaller and 90° angle scattering rises due to Rayleigh scattering. Total scattering (over all angles), however, falls and the samples become distinctly more transparent on visual inspection, as is also substantiated by the UV transmission spectra.
Compaction has no influence on hydrophobicity, which in each case substantially corresponds to that of the standard sample.
EXAMPLE 3
Investigation of the Influence of Higher Compaction on Applicational Properties.

















AE R 202,
AE R 202,




AE R 812,
compacted
compacted



uncompacted
RHE
RHE



UB 3848-1
UB 3848-2
UB 3848-3



2-02024
2-01024-
2-01024-
AE R 202



10 kg
(2)
(3)
RHE



sack
15 kg sack
20 kg sack
specific.





















Tamped density (DIN ISO 787/11)
g/l
51
93
119
approx. 60 3)


Effectiveness, ethanol (0955)

319
334
336
334 1)


Effectiveness (UT), ethanol (0965)

346
365
373
339 1)


Settling
vol. %
10
5
1


(effectiveness, high-speed mixer)





1) Determined on standard sample (UB 3391)


3) Guide value






The compacted AEROSIL R 202 samples behave in a similar manner to the compacted AEROSIL R 812 samples.
Reference is thus made to Example 2 with regard to the discussion.
The parameter of “effectiveness” reported in the tables herein relates to the high degree of fineness of the particle. This is therefore an indicator of high transparency and good stability of the resulting dispersions.
Further variations and modifications of the foregoing will be apparent to those skilled in the art and are intended to be encompassed by the claims appended hereto.
German priority application filed Dec. 22, 2000 199 61 933.6 is relied on and incorporated herein by reference.

## Claims

1. A process for the production of the finely divided, readily dispersible hydrophobic, pyrogenically produced silica in the form of aggregates having a tamped density of 55 to 200 g/l comprising hydrophobizing pyrogenically produced silica by reaction with a halogen-free silane and then compacting said silica with means consisting of a roller compactor or a belt filter press.