# Patent

## Title
Silicas

## Abstract

Silanised, structurally modified silicas, characterised by groups fixed on the surface, the groups being alkylsilyl (SiCnH2n+1, with n=2-18). They are produced in that pyrogenically produced silicas are treated with the silanising agent and structurally modified. They are used to improve scratch resistance in lacquers.

## Background
INTRODUCTION AND BACKGROUND
The invention relates to silanised, structurally modified, pyrogenically produced silicas, a process for the production thereof and their use.
Silanised silicas are used as thickeners, such as e.g. for water-thinnable lacquers and resins, such as e.g. epoxy resins.
From EP 0 672 731 B1, silanised, pyrogenically produced silicas are known, which are characterised in that the pyrogenically produced silicas are treated with a compound from the group (RO)3SiCnH2n+1, wherein n=10 to 18 and R=short-chained alkyl radicals. For example, the pyrogenically produced silicas have been treated with the compound (CH3O)3SiC16H33 (hexadecyltrimethoxysilane) or with the compound (CH3O)3SiC18H37 (octadecyltrimethoxysilane).
The production of the silanised, pyrogenically produced silicas takes place in that the pyrogenically produced silicas are placed in a mixer, the silicas are sprayed, optionally first with water and then with the compound from the group (RO)3SiCnH2n+1 while mixing intensively, mixed for a further 15 to 30 minutes and then tempered at a temperature of 100 to 160° C. for a period of 1 to 3 hours.
SUMMARY OF THE INVENTION
The invention provides silanised, structurally modified, pyrogenically produced silicas characterised by groups fixed on the surface, the groups being alkylsilyl (SiCnH2n+1, with n=2-18), preferably octylsilyl and/or hexadecylsilyl.
The silica according to the invention can have the following physico-chemical characteristics:













BET-surface area m2/g:
 25-400


Average size of the
  5-50


primary particles nm:


pH value:
  3-10


Carbon content %:
0.1-25


DBP value %:
The DBP value is at least 10% lower than the



DBP value of the corresponding silanised, non-



structurally modified silica. With very marked



structural modification, the structure can be



broken down in such a way that the DBP value



can no longer be determined.









A silica produced by a high-temperature hydrolysis route from SiCl4+H2 and O2 can be used as the pyrogenically produced silica.
In particular, a silica produced by high temperature hydrolysis having the following physico-chemical characteristics can be used:
















TABLE 1







AEROSIL
AEROSIL
AEROSIL
AEROSIL
AEROSIL
AEROSIL
AEROSIL
AEROSIL



90
130
150
200
300
380
OX 50
TT 600

















Behaviour in respect of water
hydrophilic


Appearance
loose white powder
















BET surface area1)
m2/g
90 ± 15
130 ± 25
150 ± 15
200 ± 25
300 ± 30
380 ± 30
50 ± 15
200 ± 50


Average size of the
nm
20
16
14
12
7
7
40
40


primary particles


Tamped density2)


standard material
g/l
ca. 80 
ca. 50 
ca. 50 
ca. 50 
ca. 50 
ca. 50 
ca. 130
ca. 60


compacted material
g/l
—
ca. 120
ca. 120
ca. 120
ca. 120
ca. 120
—
—


(additive “V”)


Loss on drying3)

<1.0
<1.5
<0.59)
<1.5
<1.5
<1.5
<1.5
<2.5


(2 hours at 1000° C.)
%


on leaving supplier's


works


Loss on ignition4)7)
%
<1
<1
<1
<1
<2
<2.5
<1
<2.5


(2 hours at 1000° C.)


pH value5) (in 4%

3.6-4.5
3.6-4.3
3.6-4.3
3.6-4.3
3.6-4.3
3.6-4.3
3.8-4.8
3.6-4.5


aqueous dispersion)


SiO28)
%
>99.8
>99.8
>99.8
>99.8
>99.8
>99.8
>99.8
>99.8


Al2O38)
%
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.08
<0.05


Fe2O38)
%
<0.003
<0.003
<0.003
<0.003
<0.003
<0.003
<0.01
<0.003


TiO28)
%
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03


HCl8)9)
%
<0.025
<0.025
<0.025
<0.025
<0.025
<0.025
<0.025
<0.025


Sieving residue6)
%
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.2
<0.05


(acc. to Mocker,


45 μm)





1)based on DIN 66131


2)based on DIN ISO 787/XI, JIS K 5101/18 (not sieved)


3)based on DIN ISO 787/II, ASTM D 280, JIS K 5101/21


4)based on DIN 55 921, ASTM D 1208, JIS K 5101/23


5)based on DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24


6)based on DIN ISO 787/XVIII, JIS K 5101/20


7)based on the substance dried for 2 hours at 105° C.


8)based on the substance ignited for 2 hours at 1000° C.


9)HCl content is a component of the loss on ignition






Pyrogenic silicas of this type are known. They are described, inter alia, in:
Winnacker-Küchler, Chemische Technologie, volume 3 (1983), 4th edition, page 77 and
Ullmanns Encyklopädie der technischen Chemie, 4th edition (1982), volume 21, page 462.
The pyrogenically produced silicas are treated with a compound from the group (RO)3SiCnH2n+1, wherein n=2 to 18 and R=alkyl, such as e.g. methyl, ethyl or similar.
In particular, the following compounds can be used:

Silane I (CH3O)3SiC16H33 (hexadecyltrimethoxysilane)

Silane II (CH3O)3SiC8H17 (octyltrimethoxysilane)

The silicas according to the invention can be produced in that the pyrogenically produced silicas are placed in a mixer, the silicas are sprayed, optionally first with water and then with the compound (organosilane) from the group (RO)3SiCnH2n+1 while mixing intensively, mixed for a further 15 to 30 minutes and then tempered at a temperature of 100 to 160° C. for a period of 1 to 3 hours, structurally modified and/or optionally post-ground. A further tempering can optionally take place after the structural modification and/or post-grinding.
The structural modification can take place e.g. with a ball mill or a continuously operating ball mill. The post-grinding can take place e.g. using an air-jet mill or pin mill. The tempering can take place batchwise, e.g. in a drying cupboard, or continuously, e.g. in a fluidised bed. The tempering can take place under protective gas, e.g. nitrogen.
The water used can be acidified with an acid, e.g. hydrochloric acid, down to a pH value of 7 to 1.
The organosilane used can be dissolved in a solvent, such as e.g. ethanol.
The tempering can be performed in a protective gas atmosphere, such as e.g. under nitrogen.
The pyrogenically produced silicas according to the invention silanised with silane I have the physico-chemical characteristics listed in Table 2 before structural modification:















TABLE 2





Educt
A 90
A 130
A 150
A 200
A 300
A 380
OX 50
TT 600







Average size of the
20
16
14
12
 7
 7
40
40


primary particles


[nm]


BET surface area
40-90
 60-130
 75-150
100-200
150-300
200-380
20-50
100-250


[m2/g]


Tamped density
 40-140
 40-140
 40-140
 40-140
 40-140
 40-140
 40-140
 40-140


[g/l]


Loss on drying [%]
<2
<2
<2
<2
<2
<2
<2
<2


Loss on ignition
0.1-10 
0.1-10 
0.1-10 
0.5-15 
0.5-20 
0.5-25 
0.1-10 
0.1-20 


[%]


C content [%]
0.1-10 
0.1-10 
0.1-10 
0.5-15 
0.5-20 
0.1-25 
0.1-10 
0.5-20 


pH value
3.5-5.5
3.5-5.5
3.5-5.5
3.5-5.5
3.5-5.5
3.5-5.5
3.5-5.5
3.5-5.5









The silanised, structurally modified, pyrogenically produced silicas according to the invention can be used to improve scratch resistance in lacquers.


DETAILED DESCRIPTION OF INVENTION
Examples
The pyrogenically produced silicas used have the physico-chemical characteristics listed in Table 1.
As organosilanes, the following compound with the general formula (RO)3SiCnH2n+1 is used:

(CH3O)3SiC16H33  (Silane I)

The silica is placed in a mixer and sprayed first with water and then with organosilane, mixing intensively.
When the spraying is complete, stirring is continued for a further 15 to 30 minutes and then the mixture is tempered for 1 to 3 hours at 100 to 160° C. The tempering can also take place under protective gas, e.g. nitrogen.
The individual reaction conditions can be taken from Table 3.
The physico-chemical characteristics of the silanised silicas obtained are listed in Table 4.














TABLE 3












Tem-





Silane
Water
Ethanol
Tem-
pering


Ex-


quantity
quantity
quantity
pering
temper-


am-


(g/100 g
(g/100 g
(g/100 g
period
ature


ple
Aerosil
Silane
Aerosil)
Aerosil)
Aerosil)
(h)
(° C.)






















1
A 300
Silane I
1
0
9
2
120


2
A 200
Silane I
2.5
0
0
2
140


3
A 200
Silane I
20
5
0
2
140


4
A 200
Silane I
10
2.5
0
2
140


5
A 200
Silane I
5
1.25
0
2
140


6
A 200
Silane I
2.5
1.25
0
2
140






















TABLE 4







Tamped

Surface
Loss on
Loss on




density
C content
area
drying
ignition


Example
pH value
(g/l)
(%)
(m2/g)
(%)
(%)





















1
4.3
50
1.3
253
0.4
1.8


2
4.4
49
1.7
176
0.3
2.5


3
4.6
68
10.1
116
0.6
12.7


4
4.5
72
5.7
144
0.6
7.1


5
4.7
52
2.6
167
0.6
3.4


6
4.5
51
1.9
171
0.7
2.5









Production and Physico-Chemical Properties of the Silicas According to the Invention

Production of the Silicas According to the Invention:

The silicas, which can be produced as described in EP 0 672 731, are then structurally modified by mechanical action and possibly post-ground in a mill. A tempering can possibly take place after the structural modification and/or post-grinding.
The structural modification can take place e.g. with a ball mill or a continuously operating ball mill. The post-grinding can take place e.g. using an air-jet mill or pin mill. The tempering can take place batchwise, e.g. in a drying cupboard, or continuously, e.g. in a fluidised bed. The tempering can take place under protective gas, e.g. nitrogen.







TABLE 5







Overview of the production of the comparative silicas and


the silicas according to the invention (Examples)














Post-






grinding





after
Tempering



Surface-fixed
Structural
structural
after


Designation
group
modification
modification
post-grinding





Comparative
Hexadecylsilyl
No
—
—


silica 1


Comparative
Octylsilyl
No
—
—


silica 2


Silicas 1
Hexadecylsilyl
Yes
No
No


Silicas 2
Octylsilyl
Yes
Yes
No


Silicas 3
Hexadecylsilyl
Yes
Yes
Yes


Silicas 4
Octylsilyl
Yes
No
Yes


Silicas 5
Octylsilyl
Yes
Yes
No


Silicas 6
Hexadecylsilyl
Yes
Yes
No


Silicas 7
Hexadecylsilyl
Yes
Yes
No


Silicas 8
Hexadecylsilyl
Yes
No
No


Silicas 9
Octylsilyl
Yes
Yes
No


Silicas 10
Octylsilyl
Yes
No
No


Silicas 11
Octylsilyl
Yes
Yes
No


Silicas 12
Octylsilyl
Yes
No
No
















TABLE 6







Physico-chemical data of the silicas according to the invention (Examples)


and the comparative silicas















Tamped

Loss on


DBP
BET specific



density
Loss on
ignition


adsorption
surface area


Designation
[g/l]
drying [%]
[%]
pH value
C content [%]
[%]
[m2/g]

















Comparative silica 1
57
0.5
1.8
4.6
1.2
302
195


Comparative silica 2
51
0.6
6.8
5.3
5.4
263
175


Silicas 1
137
0.7
1.9
4.9
1.3
217
193


Silicas 2
112
0.7
7.0
5.8
5.5
145
175


Silicas 3
118
0.7
2.3
5.1
1.3
228
176


Silicas 4
163
0.9
6.7
5.3
5.4
134
176


Silicas 5
114
0.5
7.1
6.0
5.4
142
175


Silicas 6
113
1.3
2.2
5.1
1.4
221
193


Silicas 7
123
0.7
2.6
6.0
1.4
208
197


Silicas 9
146
1.1
2.3
5.8
1.4
182
195


Silicas 9
240
0.8
6.7
4.8
5.3
 87
169


Silicas 10
322
0.3
6.9
6.0
5.3
Could not
172








be








determined


Silicas 11
204
0.7
6.4
5.7
5.4
101
173


Silicas 12
276
0.3
6.6
6.6
5.3
Could not
168








be








determined









Application Examples
Example 1
For the investigation of the improvement in scratch resistance, a conventional 2-component polyurethane lacquer was used. The formulation of the lacquer and its production, including application, are summarised below:
Formulation:













Parts



by wt.



















Millbase




Acrylic resin, 50% in xylene/ethylbenzene 3:1
53.3



Butyl acetate 98%
6.7



Xylene
6.7



Silica
5.0



Σ
71.7



Lacquer make-up



Acrylic resin, 50% in xylene/ethylbenzene 3:1
1.1



Xylene
12.2



Ethoxypropyl acetate
1.5



Butyl glycol acetate
1.5



Butyl acetate 98%
—



Aliphatic polyisocyanate, approx. 75% in 1-
17.0



methoxypropyl-2-acetate/xylene 1:1




Σ
105.0


























Binder concentration:
  40%



Silica calculated on the basis of millbase (solids):
18.8%



Silica calculated on the basis of lacquer (total):
 5.0%



Silica calculated on the basis of lacquer (solids):
12.5%










Production and Application of Lacquers

The binder is mixed with the solvents. Then, for the purpose of predispersion, the silica is incorporated into this mixture with the high-speed mixer (disk Ø 45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30 min at 2500 rpm and 60% pump capacity using glass beads (Ø approx. 1 mm). The millbase is tested with a grindometer, 25 μm, according to DIN ISO 1524. It must be smaller than 10 μm.
The conversion of the millbase to lacquer takes place in accordance with the formulation, the components being mixed at 2000 rpm with a vane agitator. The hardener is incorporated in the same way.
After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C.
Scratch Tests:
The metal sheets are abraded with a quartz/water slurry (100 g water+1 g Marlon A 350, 0.25%+5 g Sikron F500) and with a CaCO3/water mixture (100 g water+1 g Marlon A 350, 0.25%+5 g Millicarb BG) using an abrasion and washing resistance tester (Erichsen, brush with hog's bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20° irradiation angle).







TABLE 7







Summary of the properties of the liquid lacquers relevant in terms of lacquer technology,


and of the applied and dried films.



















Reference



Reference



Comparative


without
Comparative

Silica
without



silica 1
Silica 7
Silica 8
silica
silica 2
Silica 9
11
silica



















Grindometer value [μm]
<10
<10
<10
<10
<10
<10
<10
/


Viscosity (millbase) [mPas]


 6 Rpm
409
210
220
/
5670
935
832
/


60 Rpm
407
210
212
/
1260
409
407
/


Viscosity (lacquer + hardener)


[mPas]


 6 rpm
120
80
80
60
446
195
175
55


60 rpm
113
82
82
61
194
146
144
64


Flow
poor
OK
OK
OK
Orange peel
OK
OK
OK



fine cracks



effect







Scratch resistance















20° reflectometer value
81
89.5
89.1
91.3
38
85.5
85.3
91.7


before scratching


Haze before scratching
101
9
12
2
423
18
19
2


Black value My
272
286
286
291
260
283
282
294


40 strokes with Sikron
83.4
88.5
90.7
51.8
/
80.4
84.3
56.1


F 500 residual gloss [%]









The silicas 7+8 and 9+11 according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface owing to their substantially lower rheological efficiency compared with comparative silica 1+2. In addition, the silicas according to the invention display a substantial improvement in scratch resistance of the lacquer surface.
Example 2
In this example the influence of the structural modification was investigated on the basis of a high solids 2-component PU clear lacquer. The formulation of the lacquer and its production, including application and testing, are summarised below:
Formulation:













Parts by



wt.



















Millbase




Acrylic copolymer, mod. with synthetic
61.0



fatty acids, 70% in n-butyl acetate



Butyl acetate 98%
7.3



Methoxypropyl acetate
1.7



Solvesso 100
2.0



Xylene
2.0



Baysilon OL 17, 10% in xylene (silicone
0.7



oil)



Silica
5.0



Σ
79.7



Lacquer make-up (hardener)



Aliphatic polyisocyanate, 90% in n-
22.3



butyl acetate



Butyl acetate 98%
2.0



Solvesso 100
1.0



Σ
105.0


























Binder concentration:
62.8%



Silica calculated on the basis of millbase (solids):
11.7%



Silica calculated on the basis of lacquer (total):
5.0%



Silica calculated on the basis of lacquer (solids):
8.0%










Production and Application of the Lacquers

The binder is mixed with the solvents. Then, for the purpose of predispersion, the silica is incorporated into this mixture with the high-speed mixer (disk Ø 45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30 min at 2500 rpm and 60% pump capacity using glass beads (Ø approx. 1 mm). The millbase is tested with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm.
The conversion of the millbase to lacquer takes place in accordance with the formulation, the components being mixed with a vane agitator at 2000 rpm. The hardener is incorporated in the same way.
After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C.
Scratch Tests:
The metal sheets are abraded with a quartz/water slurry (100 g water+1 g Marlon A 350, 0.25%+5 g Sikron F500) using an abrasion and washing resistance tester (Erichsen, brush with hog's bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20° irradiation angle).







TABLE 8







Summary of the properties of the liquid lacquers


relevant in terms of lacquer technology, and of the applied


and dried films.















Reference



Comparative

Silica
without



silica 1
Silica 7
8
silica















Bulk density [g/l]
50
146
123
/


Grindometer value [μm]
<10
<10
<10
/


Viscosity (millbase)


[mPas]


 6 rpm
767
376
376
205


60 rpm
717
359
361
205


Viscosity (lacquer + hardener)


[mPas]


 6 rpm
459
279
281
120


60 rpm
399
272
274
120


Flow
poor (fine
OK
OK
OK



“cracks”)







Scratch resistance











20° reflectometer
82.3
86.5
86.3
88.2


value before


scratching


Haze before scratching
3
4
4
2


Black value My
275
283
282
292


40 strokes with
63.2
78.2
75.4
30.2


Sikron F 500


residual gloss [%]









The silicas 7+8 according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface owing to their substantially lower rheological efficiency compared with comparative silica 1. In addition, the silicas according to the invention display a substantial improvement in the scratch resistance of the lacquer surface.
Example 3
For the investigation of the improvement of the scratch resistance, a conventional 2-component polyurethane lacquer was used. The formulation of the lacquer and its production, including its application, are summarised below:
Formulation















Parts by wt.



















Millbase




Acrylic copolymer, mod. with
43.4



synthetic fatty acids, 60% solution



Butyl acetate 98%
17.8



Xylene
3.9



Silica
5.0



Σ
70.7



Lacquer make-up



Xylene
11.3



Ethoxypropyl acetate
3.4



Butyl glycol acetate
1.6



Aliphatic polyisocyanate, approx.
18.6



75% in 1-methoxypropyl-2-



acetate/xylene 1:1




Σ
105.0


























Binder concentration:
  40%



Silica calculated on the basis of millbase (solids):
19.2%



Silica calculated on the basis of lacquer (total):
 5.0%



Silica calculated on the basis of lacquer (solids):
12.5%










Production and Application of the Lacquers

The binder is mixed with the solvents. Then, for the purpose of predispersion, the silica is incorporated into this mixture with the high-speed mixer (disk Ø 45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30 min at 2500 rpm and 60% pump capacity using glass beads (Ø approx. 1 mm). The millbase is tested with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm.
The conversion of the millbase to lacquer takes place in accordance with the formulation, the components being mixed with a vane agitator at 2000 rpm. The hardener is incorporated in the same way.
After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C.
Scratch Tests:
The metal sheets are abraded with a quartz/water slurry (100 g water+1 g Marlon A 350, 0.25%+5 g Sikron F500) using an abrasion and washing resistance tester (Erichsen, brush with hog's bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20° irradiation angle).







TABLE 9







Summary of the properties of the liquid lacquers relevant in terms of lacquer technology,


and of the applied and dried films.



















Reference



Reference



Comparative


without
Comparative

Silica
without



silica 1
Silica 7
Silica 8
silica
silica 2
Silica 9
11
silica



















Grindometer value [μm]
<10
<10
<10
/
<10
<10
<10
/


Viscosity (millbase)


[mPas]


 6 rpm
409
210
220
/
5670
935
832
/


60 rpm
407
210
212
/
1260
409
407
/


Viscosity (lacquer + hardener)


[mPas]


 6 rpm
120
80
80
60
446
195
175
55


60 rpm
113
82
82
61
194
146
144
64


Flow
Poor
OK
OK
OK
Orange-peel
OK
OK
OK



fine cracks



effect







Scratch resistance















20° reflectometer
81
89.5
89.1
91.3
38
85.5
85.3
91.7


value before


scratching


Haze before scratching
101
9
12
2
423
18
19
2


40 strokes with Sikron
83.4
88.5
90.7
51.8
/
80.4
84.3
56.1


F 500


Residual gloss [%]









The silicas 7+8 and 9+10 according to the invention can be used in high concentrations without impairing the appearance of the lacquer surface owing to their substantially lower rheological efficiency compared with comparative silica 1 and 2. In addition, the silicas according to the invention display a substantial improvement in the scratch resistance of the lacquer surface.
Example 4
Direct comparison of the silicas according to the invention with a scratch-resistant lacquer according to DE 198 11 790 A1, in which AEROSIL R 972 is used to improve the scratch resistance.















Silicas 2)



Prior art
according to the



1)
invention




















Millbase





Desmophen A 2009/1

190.2



Methoxypropyl acetate:

36.8



Solvesso 100 1:1



Silica

23.0



Σ

250.0



Lacquer make-up



Desmophen A YEP4-55A,
96.0
—



contains AEROSIL R 972



Millbase
—
48.9



Desmophen 2009/1
—
24.9



OL 17, 10% in MPA
—
—



Modaflow 1% in MPA
—
—



MPA:
11.6
33.8



Solvesso 100 1:1



Butyl glycol acetate
10.5
10.5



Byketol OK
7.5
7.5



Byk 141
0.8
0.8



Addition of hardener



Desmodur N 3390
23.6
23.6



Σ
150.0
150.0










Production and Application of the Lacquers














1)
Comparative silica 1 is incorporated into the binder in accordance



with DE 198 11 790 A1 using a jet disperser.


2)
The binder is mixed with the solvents. Then, for the purpose of



predispersion, the silica is incorporated into this mixture with the



high-speed mixer (disk Ø 45 mm) and predispersed for 5 mm at 2000



rpm. The mixture is dispersed in a laboratory pearl mill for 30 min



at 2500 rpm and 60% pump capacity using glass beads (Ø approx. 1



mm). The millbase is tested with a grindometer, 25 μm, according to



DIN ISO 1524. It must be smaller than 10 μm.









The conversion to lacquer of the millbases corresponding to 1) or 2) takes place in accordance with the formulation, the components being mixed at 2000 rpm with a vane agitator. The hardener is incorporated in the same way.
After adjusting the lacquers to spray viscosity in accordance with DIN 53411, the lacquers are applied to black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by spray application (coat thickness about 40-50 μm). After spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C.
Scratch Tests:
The metal sheets are abraded with a CaCO3/water slurry (100 g water+1 g Marlon A 350, 0.25%+5 g Millicarb CaCO3) using an abrasion and washing resistance tester (Erichsen, brush with hog's bristles). The gloss before and 10 min after the abrading is determined with a reflectometer (20° irradiation angle).







TABLE 10







Summary of the properties of the liquid lacquers


relevant in terms of lacquer technology, and of the applied


and dried films.













Prior art
Silica 7
Reference
















Grindometer value
<10
<10
/



[μm]



Viscosity (millbase)



[mPas]



 6 rpm
58
30
30



60 rpm
48
43
40



Surface
Orange
OK
OK




peel



20° reflectometer
88.0
86.5
98.5



value before



scratching



100 strokes with
88.6
96.3
59.6



Millicarb



Residual gloss [%]










It is shown that a substantially better improvement in the residual gloss is achieved after a scratch stressing of the lacquer surface by using the silica according to the invention than with the prior art. In addition, owing to its low rheological efficiency, the silica according to the invention does not cause an orange-peel effect.

## Claims

1. Silanised, structurally modified, pyrogenically produced silicas,
characterised by octylsilyl and/or hexadecylsilyl groups fixed to the surface, wherein structural modification is done by spraying pyrogenically produced silica optionally first with water and then with hexadecyltrimethoxysilane (CH3O)3 SiC16H33 or octyltrimethoxysilane (CH3O)3 SiC8H17, mixing intensively, mixing for a further 15 to 30 minutes and then tempering at a temperature of 100 to 160° C. for a period of 1 to 3 hours, then structurally modifying said silica by subjecting said silica to a ball mill to produce a silica with a DBP value of at least 10% lower than the DBP value of non-structurally modified silica.

2. Process for the production of the silanised, structurally modified, pyrogenically produced silicas according to claim 1,
characterised in that a pyrogenically produced silica is placed in a mixer, the silica is sprayed, optionally first with water and then with the compound from the group (RO)3SiCnH2n+1 while mixing intensively, mixed for a further 15 to 30 minutes and then tempered at a temperature of 100 to 160° C. for a period of 1 to 3 hours, structurally modified by ball milling and/or optionally post-grinding.

3. Process for the production of the silanised, structurally modified, pyrogenically produced silica according to claim 2,
characterised in that an additional tempering of said silica is carried out.

4. Lacquer composition comprising a lacquer vehicle and the silanised, structurally modified, pyrogenically produced silica of claim 1.

5. A lacquer containing the silanised, structurally modified, pyrogenically produced silica of claim 1.

6. A surface having applied thereto a coating produced from the lacquer of claim 5.

7. The surface according to claim 6, which is metal.

8. A silanised, structurally modified, pyrogenically produced silica, said silica having been structurally modified by ball milling,
and
having the following physical chemical properties:














BET surface area
 25-400 m2/g


Average size of primary particles
  5-50 nm


pH value
  3-10


Carbon content
0.1-25%


DBP value in %
at least 10% lower than the DBP



value of a corresponding silianised,



non-structurally modified silica,








wherein the pyrogenically produced silica has been treated with a compound selected from the group consisting of (CH3O)3SiC16H33 and (CH3O)3SiC8H17.

9. A process for the production of the silanised, structurally modified, pyrogenically produced silica according to claim 8, comprising placing the pyrogenically produced silica in a mixer, spraying the silica, optionally first with water, and then spraying with said compound while mixing intensively, mixing for a further 15 to 30 minutes and then tempering at a temperature of 100 to 160° C. for a period of 1 to 3 hours, structurally modifying by ball milling and and/or optionally post-grinding.

10. The process for the production of the silanised, structurally modified, pyrogenically produced silica according to claim 9, further comprising additionally tempering said silica.

11. The process according to claim 10, wherein tempering takes place in a drying cupboard or in a fluidized bed.

12. The process according to claim 11, wherein the tempering takes place under protective gas.

13. The process according to claim 9, further comprising post grinding said silica by using an air-jet mill or pin mill.

14. A lacquer containing the silanised, structurally modified, pyrogenically produced silica of claim 8.