DE1083241B - Process for the production of finely divided silica - Google Patents

Description

GERMAN

The invention relates to a method for stabilizing silica, which is used as a reinforcing filler suitable for rubber and other purposes.

In the patent application C 6515 IVa / 12i is a method proposed for the precipitation of finely divided silica, in which an acidifying agent, such as carbon dioxide, is added at a controlled rate to an aqueous solution of an alkali metal silicate. It it has been found that a gelatinous substance is formed when the acidifying agent is added to the alkali silicate solution is added quickly. The silica produced in this way is not suitable as a rubber reinforcing filler. on the other hand the precipitated product becomes too coarse for use with rubber if the speed at which the Acidifier is added is too low. Often this product is too rough for other purposes.

It has been found that, in order to achieve the properties required for rubber reinforcement, it is essential that the silica be precipitated under conditions in which the precipitated silica has an average final particle size of less than 0.1 microns, preferably about 0.01 to 0.05 μ . It is useful here to relate the particle size and the properties of the filler to its surface, as determined by nitrogen absorption. As a general rule, silica which has a surface area between 50 and 200 m ² / g and an average final particle size of 0.015 to 0.05 microns is suitable as a rubber reinforcing filler. A silica with a surface area between 10 and 15 m ² / g and an average final particle size between 0.05 and 0.1 μ or even 0.2 μ is suitable as a paper filler. The surface preferably emphasized here is one in which the pH of the slurry of the precipitated silica is adjusted to 7, the silica is recovered and dried at about 105 ° C. and the surface of the dry product obtained is measured.

As proposed in patent application C 6515 IVa / 12i, these fillers can be produced in such a way that the acidifying agent of the sodium silicate or similar alkali metal silicate solution with a certain Speed increases.

Even after the silica has been precipitated with the appropriate particle size and surface area, the pH of the silica slurry that makes up the silica is finally obtained, has a significant impact on the surface of the product. So if the Silica is brought to a pn value of 2 after precipitation, the surface area increases considerably, and the filler recovered after filtering and drying such a product is generally as Inferior rubber reinforcement filler.

In the patent application C 14314 IVa / 12i (German method for obtaining
finely divided silica

Addition to patent application C 14314 IVa / 12 i
(Auslegeschrift 1 076 650)

Applicant:

Columbia-Southern Chemical Corporation, Pittsburgh, Pa. (V. St. A.)

Representative:

Dr. W. Beil and A. Hoeppener, lawyers,
Frankfurt / M.-Höchst, Antoniterstr. 36

Claimed priority:
V. St. v. America September 3, 1957

Fred S. Thomhill, Akron, Ohio (V. St. A.),
has been named as the inventor

Auslegeschrift 1 076 650) it has been proposed that silica stabilizes against a changing ρπ value can be by subjecting it to the action of an aqueous medium, the ρπ value of the silica not less than about 5 and the temperature is at least 60 ° C. When the silica on this Has been treated or conditioned by heat, it has a much lower tendency to prove Adding acid even down to a pH of 2 or less will change the surface. Even if at Addition of acid to a silica which has been stabilized as described has a low surface area should take place, this change affects the rubber reinforcing properties of the filler not detrimental and is relatively small compared to the major changes that are taking place, if no heat treatment has taken place.

The time required for this heat treatment depends on the temperature at which it is carried out and some of the temperature at which the silica was previously precipitated. If the If the temperature is low, the treatment time is long, and if it is high, relatively shorter times are sufficient. A heat treatment of the silica at temperatures between 50 and 75 ° C can, for. B. 10 to Require 20 hours or more, while the treatment time is slightly shorter, about 5 hours if the

009 530/491

Claims (1)

3 4 Heat treatment temperature between 70 and amount (less than 0.08 ° / ₀ ), as is usually found in commercial 80 ° C. An effective heat treatment temperature of moderate sodium silicate is present. is 80 to 100 ° C and above, and at such the solution is at a temperature of 73 ± 3 ° C Temperature is a heat treatment time of min- held. 40 ° / _σ CO ₂ -containing carbon dioxide gas (the rest at least 30 minutes to 2 hours is sufficient. 5 in nitrogen and air) is at a gas temperature of It has now been found that at heat treatment 46 to 63 ° C at a rate of 1881 / sec. temperatures above 100 ° C, e.g. B. 120 to 300 ° C, which (measured at a pressure of 760 mm and 0 ° C) in the Heat treatment initiated for considerably less than 30 minutes of solution. The gas is just below one can be. It is-in fact in such a case expedient-Turbo agitator introduced so that a uniform moderate, to a heating time of less than 30 million distribution of the gas is achieved, with the mixture Grooves to decrease, since the particle size of the pebbles is vigorously stirred. The carbon dioxide discharge will acidity increases slightly excessively if the silica continued at the same rate for 4 hours; Longer slurry time more than 30 minutes on one after this time is about 120 to 140% of the theoretical Temperature of more than 120 ° C is heated. So CO _{2 was} introduced. found that the silica was effective against a substantial number of small parts of this slurry Liehe change in the surface in addition of acid to a _pH value of from about 10 minutes to about 2 is Can be stabilized if the silica is in a steam jacket for 4 hours action of an aqueous medium at a pH of 100, 140 and 160 ° C Rohr. The surface no less than S and a temperature greater than any of these products was measured once before the 100 ° C, preferably between 120 and 300 ° C, as long as ao proportions of the treated slurry on a pn is subjected until the surface of the product value of 4 were turned off, and then once, is stabilized for at least half a minute, but not It was found that a heat treatment at 160 ° C longer than about 25 minutes. stabilization against an upper After this treatment, the precipitated change in the area of the silica is obtained, which is the same as that caused by acid, if necessary with acids such as acetic acid, nitric acid - 25 heating for 256 minutes at 100 ° C, acid, hydrochloric acid, sulfuric acid, a similar mineral- A heat treatment lasting 16 minutes at 140 ° C acid or another acid, extracted in order to return a stabilization against a surface change permanent alkali metal oxide (such as Na ₂ O) to be removed. tion the same as it by 128 minutes long This alkali metal oxide or Na ₂ O is obtained in combination heating to 100 ° C, with the silica present and usually provides a 30 A heating to temperatures above 160 ° C, e.g. B. Na ₂ O amount of sodium silicate Na ₂ O (SiO ₂ ) ,,. (where χ 200 ° C, shows essentially the same results. 2 to 4 means), which is not with the silica from A silica produced in this way was stabilized, the chemical combination neutralized or removed by after setting the pn value of the slurry has been. After this treatment, the silicic acid is heated to 160 ° C. for four minutes by suitable means such as settling or filtering. The material stabilized in this way had a surface won. of 145 m ² / g. Another part of the 16 minutes 16O ⁰ C The process described here is particularly advantageous when heated, had a surface area of 177 m ² / g.
Adhesive, since simple means can be used. When incorporated in order to remove the alkali metal oxide or the alkali metal from the silica precipitated in GR-S rubber, these two products resulted in a rubber with a tear-precipitated silica without the strength of 217 kg / cm ² or better,
to adversely affect precipitated filler. In the case of a silica obtained in this way, which is to be stabilized according to the invention, the surface does not increase significantly after various methods of alkali removal. getting produced. A particularly advantageous method The particle size of the silica obtained is suggested in German Auslegeschrift 1 049 834 within the already defined area, the top 45. The filler is after its precipitation and before area size is between about 10 and 200 m ² / g and drying to an anhydrous state in one when a rubber reinforcing filler is produced in aqueous medium at a pn value of about 5 or should be, usually between 70 and 200 m ² / g. more, less than 30 minutes, preferably less than The heat treatment is treated in any suitable way for 20 to 25 minutes, at over 100 ° C, carried out. If the treatment temperature is above 50, - 100 ° C, the silica is in an aqueous Auf- = patent claims: slurry treatment in an autoclave or 1st modification of the process for obtaining fine subjected to another pressure vessel so that the particulate silica according to patent application C14314 action carried out at superatmospheric pressure IVa / 12 i (German Auslegeschrift 1076650), thereby can be. To an excessive reduction of 55 characterized that to stabilize the silica Surface area and increase in particle size to avoid against surface changes for heating the silica, after it has risen to over 100 ° C, is pre- in an aqueous medium with a ρπ value of not preferably above 120 ° C, has been heated, 25 to 30 Mi- less than 5 for at least half a minute ute after the temperature is above 120 ° C for a maximum of 25 minutes a temperature of more has been reached, cooled to below 100 ° C. This is applied 60 as 100 ° C. can be characterized by suitable cooling of the slurry, 2. The method according to claim 1, z. B. by diluting with water, the temperature of which indicates that the heat treatment at a temperature is below 100 ° C. temperature of at least 120 ° C no longer than about _j. 25 minutes is carried out. - ¹³⁶¹³ P ¹⁶¹ 65 3. Method according to claim 1 or 2, characterized in that 181 m ^a sodium silicate solution are in a 227 m ³ indicates that the temperature is between 140 and full tank. This solution contains Na- 300 ° C. trium silicate Na ₂ O (SiOo) ₃ in amounts sufficient to obtain a Na ₂ O concentration of 20.3 g / l. This indicates that the silica an average solution does not contain sodium chloride, except for a smaller particle size of less than 0.1 μ . © 009 530/491 6.60