# Patent

## Title
Clean color shade, yellow-tinged red iron oxide pigments, and a process

## Abstract

This is a continuation of application Ser. No. 08/379,694, filed on Jan. 27, 1995, which was abandoned upon the filing hereof.

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

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, Aug. 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: __________________________________________________________________________ AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL 90   130   150  200   300   380   OX TT __________________________________________________________________________ 600 Behavior with respect to water hydrophilic Appearance         loose white powder Surface area in accordance with 90 .+-. 15 130 .+-. 25 150 .+-. 15 200 .+-. 25 300 .+-. 30 380 .+-. 30 50 200 .+-. 50 BET.sup.1) m.sup.2 /g Mean size of the primary particles, in nm 20   16    14   12    7     7     40   40 Stamping density .sup.2) ca. 80 ca. 50 ca. 50 ca. 50 ca. 50 ca. 50 ca. ca. 60 Normal 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 plant Annealing 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 3.6-4.8 3.6-4.5 SiO.sub.2 .sup.8) % >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 A1.sub.2 O.sub.3 .sup.8) % <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.08 <0.05 Fe.sub.2 O.sub.3 .sup.8) % <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 <0.01 <0.003 TiO.sub.2 .sup.8) % <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 HC1 .sup.8) .sup.9) % <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 Screen residues .sup.6) % <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.2 <0.05 (Per Mocker, 45 .mu.m) __________________________________________________________________________ .sup.1) in reliance on DIN 66131 .sup.2) in reliance on DIN ISO 787/XI, JIS K 5101/18 (unscreened) .sup.3) in reliance on DIN ISO 787/II ASTM D 280, JIS K 5101/23 .sup.4) in reliance on DIN 55 921, ASTM D 1208, JIS K 5101/21 .sup.5) in reliance on DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24 .sup.6) in DIN ISO 787/XVIII, JIS K 5101/20 .sup.7) referred to the 2 hours at 105.degree. C. of dried substance .sup.8) referred to the 2 hours at 1000.degree. C. of the annealed substance .sup.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: (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: (hexadecyltrimethoxysilane) (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: __________________________________________________________________________ E duct            A 90 A 130 A 150 A 200 A 300 A 380 OX TT __________________________________________________________________________ 600 Mean size of the primary particles [nm] 20   16    14    12    7     7     40   40 Surface area per BET [m.sup.2 /g] 40-90 60-130 75-150 100-200 150-300 200-380 20-50 100-250 Stamp density [g/1] 40-140 40-140 40-140 40-140 40-140 40-140 40-140 40-140 Drying loss [%]   <2   <2    <2    <2    <2    <2    <2   <2 Annealing loss [%] 0.1-10 0.1-10 0.1-10 0.5-15 0.5-20 0.5-25 0.1-10 0.5-20 Carbon Content [%] 0.1-10 0.1-10 0.1-10 0.5-15 0.5-20 0.5-25 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 silicic acids according to the invention are not dispersed in a solvent and 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.

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:

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. __________________________________________________________________________ Exam-        Amount of Silane Amount of Water Amount of Ethanol Temp. Stabilization Temp. Stabilization ple Aerosil Silane (g/100 g Aerosil (/100 g Aerosil) (g/100 g Aerosil) Time (h) Temp. (.degree.C.) __________________________________________________________________________ 1   A 200 Silane II 15      0       0        2        120 2   A 300 Silane I 1       0       9        2        120 3   A 200 Silane I 2.5     0       0        2        140 4   A 200 Silane I 20      5       0        2        140 5   A 200 Silane I 10      2.5     0        2        140 6   A 200 Silane I 5       1.25    0        2        140 7   A 200 Silane I 2.5     1.25    0        2        140 __________________________________________________________________________ __________________________________________________________________________ Stamp density Carbon content Surface area Drying loss Annealing loss Example Valve (g/1)  (%)    (m .sup.2 /g) (%)   (%) __________________________________________________________________________ 1   4.8 52     7.9    127   0.5   5.2 2   4.3 50     1.3    253   0.4   1.8 3   4.4 49     1.7    176   0.3   2.5 4   4.6 68     10.1   116   0.6   12.7 5   4.5 72     5.7    144   0.6   7.1 6   4.7 52     2.6    167   0.6   3.4 7   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   200 10           per example 3 400 11           per example 4 14000 12           per example 5 9800 13           per example 6 800 14           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 which are not dispersed in a solvent, 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 stearyltrimethoxy-silane, 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. A process for preparing silanized, pyrogenically prepared silicic acids which are not dispersed in a solvent, 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.