DE102004021515A1 - Production of hollow micro-spheres from boron silicate comprises use of solution of caustic soda and sodium silicate - Google Patents

Abstract

In a process to make hollow micro-spheres from boron silicate using a solution of Na 2O, SiO 2and B 2O 3, boric acid is mixed with caustic soda to form a solution. This solution is mixed in a pre-determined ratio with sodium silicate solution. The resulting solution is injected via a jet into a spray tower, resulting in the formation of hollow micro-spheres. The ratio of Na 2O, SiO 2and B 2O 3is in the range 1:10; 0.44:1;2.49:0.44, preferably 1:2.1:0.44. The ratio of boric acid to caustic soda is 35.7 Ma-% to H 3BO 3powder to 64.3 Ma-% in 33.33% caustic soda.

Description

The invention relates to a method for producing hollow microspheres of borosilicate by means of a solution of Na ₂ O, SiO ₂ and B ₂ O ₃ according to the preamble of claim 1. Furthermore, the invention relates to hollow microspheres of borosilicate according to the preamble of claim 9 and a solution from Na ₂ O, SiO ₂ and B ₂ O ₃ for the production of hollow microspheres according to the preamble of claim 10.

Out US 5 534 348 Hollow microspheres of borosilicate are known, which are prepared by spray-drying a solution of Na ₂ O, SiO ₂ and B ₂ O ₃ . A method also described in this document provides that, to form this solution, sodium silicate and sodium borate are mixed in water, the resultant solution is spray-dried, then the resultant borosilicate precursor particles are comminuted and then a heating process to form the hollow microspheres a mean diameter below 25 microns and with a density below 0.25 g / cm ^{3 is} performed. In this context, in US 5 534 348 indicated that the desired parameters of the final products - so the hollow microspheres - can only be obtained if predetermined proportions of sodium silicate and sodium borate and Na ₂ O, SiO ₂ and B ₂ O _{3 are} applied.

so produced hollow microspheres need in your initial already existing spherical shape destroyed by the reduction process and by means of an additional He warming up be formed again hollow spherical.

The As a rule, hollow microspheres produced in this way exhibit a relatively high pH, in certain uses of the hollow microspheres thus produced is undesirable due to the associated low hydrolytic stability.

As a result, The present invention is based on the object, a method for the production of hollow microspheres to provide, which the Preparation of hollow microspheres made of borosilicate with a pH value of Range of about 6 - 8 and by an alternative solution composition in a simple way. It is a further object of the invention, such hollow microspheres and one for that required solution to disposal to deliver.

These Task is procedurally by the features of claim 1 and product side solved by the features of claims 9 and 10.

• – Vermischen von Borsäure mit Natronlauge zu einer Natronlauge – Borsäure – Lösung;
• – Vermischen der Natronlauge – Borsäure – Lösung mit einer Natriumsilikatlösung zu der Lösung aus Na₂O, SiO₂ und B₂O₃;
• – Sprühtrocknen der Lösung in einem Sprühturm unter Bildung von Mikrohohlkugeln;
• – Vermischen der Mikrohohlkugeln mit einem sie umhüllendes Aluminiumsilikathydrat zu einem Endgemisch und
• – Erwärmen des Endgemisches auf eine Temperatur von mehr als 300°C über eine Zeit spanne von mehr als 0,1 Sekunden.

An essential point of the invention is that in a process for producing hollow microspheres of borosilicate by means of a solution of Na ₂ O, SiO ₂ and B ₂ O _{3, the} following steps are carried out:

• - Mixing boric acid with sodium hydroxide solution to a sodium hydroxide - boric acid solution;
• - Mixing the sodium hydroxide - boric acid solution with a sodium silicate solution to the solution of Na ₂ O, SiO ₂ and B ₂ O ₃ ;
• Spray-drying the solution in a spray tower to form hollow microspheres;
• - Mixing the hollow microspheres with an enveloping aluminum silicate hydrate to a final mixture and
• - Heating the final mixture to a temperature of more than 300 ° C over a period of time of more than 0.1 seconds.

Thus, an alternative solution preparation for the production of hollow microspheres of borosilicate is obtained in a simple manner. The use of H ₃ BO ₃ as boric acid and NaOH as sodium hydroxide solution also makes it possible to produce the solution cost-effectively. A resulting solution / ratio of Na ₂ O, SiO ₂ and B ₂ O ₃ in a range from 1: 1.0: 0.44 to 1: 2.49: 0.44, preferably from 1: 2.1: 0.44 allows the formation of hollow microspheres by means of the heating process with a temperature above 300 ° C as Nachtemperierungsvorgang. Such hollow microspheres are oleophilic.

It has been found that a Nachtemperierungsvorgang of the hollow microspheres alone is not sufficient to achieve the desired hydrolytic stability of the hollow microspheres. Rather, this is the additional addition of an additive, such as kaolin, talc or calcined kaolin required before the Nachtemperierungsvorgang takes place. Only by such a mixing in of the additive can a noticeable reduction in the pH, for example from 11 to about 7, be achieved during the overnight tempering process. In this case, the determined pH serves as an evaluation variable for the hydrolysis stability. The closer the neutral point with respect to the pH is reached, the higher the hydrolysis stability of the end product.

such Additives are subsequently added preferably with a float or air sifting process of the actual hollow microspheres separated again, for their Further processing, for example in a polymer, no unnecessary additives to have available.

by virtue of the solution composition according to the invention and the sequence of the invention Process steps are hollow microspheres with a mean diameter from 6 to 50 μm available, without that an additional Crushing step - like so far - required is.

The added Aluminum silicate hydrate can be kaolin with a bulk density of 0.01 - 1 g / ml be. Such a kaolin is preferred with the hollow microspheres in a mixing amount ratio from hollow microspheres to kaolin of 1: at least 0.001% by volume mixed.

Further advantageous embodiments emerge from the dependent claims.

advantages and expediencies The invention is related to the following description with the listed Example and to take the drawing.

example

Boric acid (H ₃ BO ₃ ) is dissolved with sodium hydroxide (NaOH). Subsequently, this sodium hydroxide-boric acid solution is mixed with a sodium silicate solution. The solution of Na ₂ O, SiO ₂ and B ₂ O ₃ obtained therefrom has a ratio of 1: 2.1: 0.44, based on Na ₂ O, SiO ₂ and B ₂ O ₃ .

Subsequently, will by means of a spray-drying process in a commercial Spray chamber off this solution formed a plurality of hollow microspheres. These hollow microspheres have the following values as output parameters:

Table 1

One further comminution process does not take place. Instead, become the hollow microspheres are tempered in this spherical shape with their grain size at night.

at This Nachtemperierungsvorgang the hollow microspheres are initially with an aluminum silicate hydrate, such as kaolin, having a bulk density from 0.01 - 1 g / ml dry mixed.

in this connection becomes a mixing ratio from 1 volume fraction of hollow microspheres to at least 0.001 volume fraction used on kaolin. This mixture is sufficiently homogenized and finally at a temperature of more than 300 ° C over a period of at least Heated for 0.1 seconds.

at such a Nachtemperierungsvorgang change the spherical shape, the grain size and the bulk density the hollow microspheres not. As a result of the Nachtemperierungsvorganges Micro hollow balls are obtained in a mixing process show a significantly lower alkaline pH with water as before the Nachtemperierungsvorgang. For example, the Micro hollow spheres before a pH value of 11 and afterwards one PH value of about 7, preferably 6.8.

The following table 2 shows the effects of the application Temperatures during the Nachtemperierungsvorganges on the pH of the hollow microspheres and have their state.

Table 2

at those listed in Table 2 Experimental series were hollow microspheres without the addition of additives, such as Aluminum silicate hydrate used. Table 2 is clearly too It can be seen that although a certain pH - reduction alone by the Nachtemperierungsvorgang can be obtained, but only until to a minimum pH from 10,7. In addition, in the case of hollow microspheres, state changes occur, such as low agglomeration, stronger Agglomeration and sintering conditions on. Consequently, a Nachtemperierungsvorgang alone is not enough off to a desired one hydrolytic stability the hollow microspheres while maintaining the desired Micro hollow sphere - structure to obtain.

Of the Table 3 below shows a series of experiments, in the hollow microspheres with the addition of additives such as kaolin, talc or calcined kaolin, be tempered at a desired temperature PH value to obtain.

Table 3

This Table 3 shows that, depending on the use of various additives and various ratios of hollow microspheres to additives a pH - reduction up to 6.8 is possible.

Advantageous can after the Nachtemperierungsvorgang a separation process of Micro hollow spheres and additive are performed. This can be, for example by floating or by air sifting done.

The Table 4 below shows specification data of the used Additives.

Table 4

1 shows a light micrograph of the hollow microspheres according to the invention and

2 shows a further optical micrograph of the hollow microspheres according to the invention.

The 1 and 2 It can be seen that the outer contours, so the structure of the hollow microspheres after a Nachtemperierungsvorgang performed and after a separation process of the hollow microspheres of a kaolin remain intact.

Of the Table 5 and Table 6 below show test series. which the hydrolysis stability the invention produced Microbubbles in long-term measurements reflects.

Table 5

Table 6

Of the Table 5 clearly shows that a measurement made after 7 days individual listed in Table 3 Micro hollow sphere - compositions as a result, only a minor one Increase of pH value revealed. In addition, it can be observed that the separation process for desired Floating the hollow microspheres has led. According to table 6, the measurement was repeated after 30 days. This table is to see clearly that, especially when using Kaolin as an additive a long-term hydrolysis stability of the hollow microspheres is present, since these have only a slight increase in the pH. Accordingly, the hydrolytic stability of the inventively prepared Hollow microspheres, measured as pH, also over one longer Period are kept stable. The desired structure of the hollow microsphere remains hereby.

Of course you can for the separation of the additive from the hollow microspheres next to the in the Tables indicated floating method any other known Separation method can be used.

All Features disclosed in the application documents are considered to be essential to the invention as long as they are individually or in combination with respect to State of the art are new.

Claims (11)

Process for the preparation of hollow microspheres of borosilicate by means of a solution of Na ₂ O, SiO ₂ and B ₂ O ₃ , characterized by the following steps: - mixing boric acid with sodium hydroxide solution to form a sodium hydroxide-boric acid solution; - Mixing the sodium hydroxide-boric acid solution with a sodium silicate solution to the solution of Na ₂ O, SiO ₂ and B ₂ O ₃ ; Spray-drying the solution in a spray tower to form hollow microspheres; Mixing the hollow microspheres with an aluminum silicate hydrate surrounding them to a final mixture and heating the final mixture to a temperature of more than 300 ° C over a period of more than 0.1 seconds. Method according to claim 1, characterized that the aluminum silicate hydrate kaolin with a bulk density from 0.01 - 1 g / ml. Method according to claim 2, characterized that a mixture amount ratio from hollow microspheres to kaolin of 1: at least 0.001% by volume becomes. Method according to one of the preceding claims, characterized in that the solution ratio of Na ₂ O, SiO ₂ and B ₂ O ₃ in a range of 1: 1.0: 0.44 to 1: 2.49: 0.44 lies. Method according to claim 4, characterized in that that the ratio 1: 2,1: 0,44. Method according to one of the preceding claims, characterized characterized in that the hollow microspheres are heated after the step of heating the Final mixture a pH from about 6 to 8. Method according to one of the preceding claims, characterized characterized in that after the step of heating the final mixture Aluminum silicate hydrate from the hollow microspheres by a floating or wind sifting process is disconnected. Borosilicate hollow microspheres, characterized that the hollow microspheres according to a method according to a of the preceding claims are made. Borosilicate hollow microspheres, characterized the hollow microspheres have a pH of about 6 to 8. Solution of Na ₂ O, SiO ₂ and B ₂ O ₃ for the production of hollow microspheres, characterized in that the solution is formed from a mixture of H ₃ BO ₃ , NaOH and a sodium silicate solution and Na ₂ O, SiO ₂ and B ₂ O. ₃ in a ratio of 1: 1.0: 0.44 to 1: 2.49: 0.44. solution according to claim 10, characterized in that the ratio 1 : 2.1: 0.44 is.