Silanized silicic acids

Abstract

The silanized, pyrogenically prepared silicic acids are prepared by treating pyrogenically prepared silicic acids with an organosilane selected from the group (RO).sub.3 SiC.sub.n H.sub.2n+1, in which n--from 10 to 18 and R stands for an alkyl.

Description

FIELD OF THE INVENTION

The invention relates to silanized silicic acids, the process for preparing them, and their use as a thickening agent.

BACKGROUND OF THE INVENTION

It is known to produce a silanized, pyrogenically made silicic acid by treating the pyrogenically made silicic acid with dimethyldichorosilane (Publish, Examined German Patent Application DE-AS 11 63 784).

Pyrogenically made silicic acids are also known that carry chemically bound --SiC.sub.8 H.sub.17 groups, trimethylsilyl groups, or polydimethylsiloxane groups on their surface (Schriftenreihe Pigmente �Publication Series, "Pigments"! No. 11, page 15, August 1991 Edition).

The subject of the invention is silanized, pyrogenically prepared silicic acids, which are characterized in that the pyrogenically prepared silicic acids are treated with a compound selected from the group (RO).sub.3 SiC.sub.n H.sub.2n+1, where n=from 10 to 18 and R stands for an alkyl, such as methyl, ethyl, or the like.

A silicic acid prepared by high-temperature hydrolytic means from SiCl.sub.4 +H.sub.2 and O.sub.2 can be used as the pyrogenically prepared silicic acid.

In particular, a temperature-hydrolytically prepared silicic acid can be used that has the following physical- chemical specifications:

TABLE 1__________________________________________________________________________ AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL 90 130 150 200 300 380 OX 50 TT__________________________________________________________________________ 600Behavior with respect to water hydrophilicAppearance loose white powderSurface area in accordance with 90 .+-. 15 130 .+-. 25 150 .+-. 15 200 .+-. 25 300 .+-. 30 380 .+-. 30 50 .+-. 15 200 .+-. 50BET.sup.1)m.sup.2 /gMean size of the primary particles, in nm 20 16 14 12 7 7 40 40Stamping density.sup.2) ca. 80 ca. 50 ca. 50 ca. 50 ca. 50 ca. 50 ca. ca. 60Normal goods g/1 -- ca. 120 ca. 120 ca. 120 ca. 120 ca. 120 -- --Compacted goods g/1(Additive "V")Drying loss.sup.3) <1.0 <1.5 <0.5.sup.9) <1.5 <1.5 <1.5 <1.5 <2.5(2 hours at 1000.degree. C.) %Upon leaving manufacturing plantAnnealing loss.sup.4).sup.7) % <1 <1 <1 <1 <2 <2.5 <1 <2.5(2 hours at 1000.degree. C.)pH value.sup.5) (in 4% aqueous dispersion) 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 3.6-4.5SiO.sub.2 .sup.8) % >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 >99.8Al.sub.2 O.sub.3 .sup.8) % <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.08 <0.05Fe.sub.2 O.sub.3 .sup.8) % <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 <0.01 <0.003TiO.sub.2 .sup.8) % <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03HC1.sup.8).sup.9) % <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 <0.025Screen residues.sup.6) <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.2 <0.05(Per Mocker, 45 .mu.m)__________________________________________________________________________ 1) in reliance on DIN 86131 2) in reliance on DIN ISO 787/XI, JIS K 5101/18 (unscreened) 3) in reliance on DIN ISO 787/II, ASTM D 280, JIS K 5101/21 4) in reliance on DIN 55 921, ASTM D 1208, JIS K 5101/23 5) in reliance on DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24 6) in DIN ISO 787/XVIII, JIS K 5101/20 7) referred to the 2 hours at 105.degree. C. of dried substance 8) referred to the 2 hours at 1000.degree. C. of the annealed substance 9) HC1content is a component of the annealing loss

Pyrogenic silicic acids of this kind are known. They are described in the following literature, among other sources:

Winnacker-Kuchler, Chemische Technologie �Chemical Technology!, Vol. 3 (1983), 4th Ed., page 77, and

Ullmanns Encyklopadie der technischen Chemie �Ullmann's Encyclopedia of Industrial Chemistry!, 4th Ed. (1982), Vol. 21, p. 462.

The pyrogenically prepared silicic acids are treated with a compound selected from the group (RO).sub.3 SiC.sub.n H.sub.2n+1, where n=from 10 to 18 and R stands for an alkyl, such as methyl, ethyl, or the like.

In particular, the following compounds can be used:

Silane I: (CH.sub.3 O).sub.3 SiC.sub.16 H.sub.33 (hexadecyltrimethoxysilane)

Silane II: (CH.sub.3 O).sub.3 SiC.sub.18 H.sub.37 (octadecyltrimethoxysilane)

The silicic acids according to the invention can be prepared in that the pyrogenically prepared silicic acids are placed in a mixer, and while being mixed intensively the silicic acids are sprayed, optionally first with water and then with the compound (organosilane) selected from the group (RO).sub.3 SiC.sub.n H.sub.2n+1, mixing is continued for from 15 to 30 minutes, and then temperature stabilization is done at a temperature of from 100.degree. to 160.degree. C. over a period of time from 1 to 3 h.

The water used may be acidified with an acid, such as hydrochloric acid, to a pH value of from 7 to 1.

The organosilane used can be dissolved in a solvent, such as ethanol.

The temperature stabilization can be carried out in a protective gas atmosphere, for instance in nitrogen.

The pyrogenically prepared silicic acids, silanized with silane I, according to the invention have the physical- chemical specifications listed in Table 2:

TABLE 2__________________________________________________________________________E duct A 90 A 130 A 150 A 200 A 300 A 380 OX 50 TT__________________________________________________________________________ 6000Mean size of the primary particles �nm! 20 16 14 12 7 7 40 40Surface area per BET �m.sup.2 /g! 40-90 60-130 75-150 100-200 150-300 200-380 20-50 100-250Stamp density �g/1! 40-140 40-140 40-140 40-140 40-140 40-140 40-140 40-140Drying loss �%! <2 <2 <2 <2 <2 <2 <2 <2Annealing loss �%! 0.1-10 0.1-10 0.1-10 0.5-15 0.5-20 0.5-25 0.1-10 0.5-20Carbon Content �%! 0.1-10 0.1-10 0.1-10 0.5-15 0.5-20 0.5-25 0.1-10 0.5-20pH 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 silicic acids according to the invention can be employed as thickening agents in liquids, such as water- dilutable paints, and resins such as epoxy resins. The silicic acids according to the invention can also be employed in silicon rubber, rubber, cosmetic articles, toner powders, and as agents for improving pourability and also as reinforcing fillers.

EXAMPLES

The pyrogenically prepared silicic acids employed have the physical-chemical specifications listed in table 1.

As organosilanes, the following compounds of the general formula (RO).sub.3 SiC.sub.n H.sub.2n+1 are used:

(Silane I) (CH.sub.3 O).sub.3 SiC.sub.16 H.sub.33

(Silane II) (CH.sub.3 O).sub.3 SiC.sub.18 H.sub.37

The silicic acid is placed in a mixer and sprayed first with water and then with organosilane, while being mixed intensively.

After the spraying has ended, further mixing continues for from 15 to 30 minutes, and then temperature stabilization is done for from 1 to 3 h at 100.degree. to 160.degree. C. The temperature stabilization may also be done in a protective gas, such as nitrogen.

The various reaction conditions may be learned from table 3.

The physical-chemical specifications of the silanized silicic acids obtained are listed in Tables 3-4.

TABLE 3__________________________________________________________________________ Amount of Silane Amount of Water Amound of Ethanol Temp. Stabilization Temp. StabilizationExample Aerosil Silane (g/100 g Aerosil (/100 g Aerosil) (g/100 g Aerosil) Time (h) Temp. (.degree.C.)__________________________________________________________________________1 A200 Silane II 15 0 0 2 1202 A300 Silane I 1 0 9 2 1203 A200 Silane I 2.5 0 0 2 1404 A200 Silane I 20 5 0 2 1405 A200 Silane I 10 2.5 0 2 1406 A200 Silane I 5 1.25 0 2 1407 A200 Silane I 2.5 1.25 0 2 140__________________________________________________________________________ TABLE 4__________________________________________________________________________ Stamp density Carbon content Surface area Drying loss Annealing lossExample Valve (g/1) (%) (m.sup.2 /g) (%) (%)__________________________________________________________________________1 4.8 52 7.9 127 0.5 5.22 4.3 50 1.3 253 0.4 1.83 4.4 49 1.7 176 0.3 2.54 4.6 68 10.1 116 0.6 12.75 4.5 72 5.7 144 0.6 7.16 4.7 52 2.6 167 0.6 3.47 4.5 51 1.9 171 0.7 2.5__________________________________________________________________________

The thickening action was tested for the silicic acids prepared according to the invention. As the model system, a mixture of propanol and water in a ratio of 1:1 was chosen, with 150 g of starting materials and 7.5 g of silicic acid by weight (5 weight %). Dispersion was done for 5 minutes at 2500 rpm with dissolver and measured with a Brookfield RVT viscometer (spindle 4):

______________________________________Example System or silicic acid Viscosity______________________________________ 8 propanol/water 1:1 80 9 Aerosil 200 20010 per example 3 40011 per example 4 1400012 per example 5 980013 per example 6 80014 per example 7 400______________________________________

It can be seen that the silanized silicic acids according to the invention, in terms of thickening, are superior to the untreated starting silicic acid A 200.

Claims

1. Silanized, pyrogenically prepared silicic acids, produced by the process characterized in that the pyrogenically prepared silicic acids are placed in a mixer, and while being mixed the silicic acids are sprayed, optionally first with water and then with the compound (RO).sub.3 SiC.sub.n H.sub.2n+1, where n=from 10 to 18 and R stands for an alkyl, with the proviso that the compound is not stearyltrimethoxysilane, and mixing is continued for from 15 to 30 minutes, and then temperature stabilization is done at a temperature of from 100.degree. to 160.degree. C. over a period of time from 1 to 3 h.

2. Silanized, pyrogenically prepared silicic acids of claim 1, characterized in that the compound is hexadecyltrimethoxysilane.

3. Silanized, pyrogenically prepared silicic acids of claim 1, characterized in that the compound is octadecyltrimethoxysilane.

4. A process for preparing silanized, pyrogenically prepared silicic acids, characterized in that pyrogenically prepared silicic acids are placed in a mixer, and while being mixed the silicic acids are sprayed, optionally first with water and then with the compound (RO).sub.3 SiC.sub.n H.sub.2n+1, mixing is continued for from 15 to 30 minutes, and then temperature stabilization is done at a temperature of from 100.degree. to 160.degree. C. over a period of time from 1 to 3 h.