Preparing aerogel-like structured silicic acids

(54) Title: Aerogelated structured silica and process for its preparation and its use as a coating agent in coating agents

Process for the preparation of aerogelic structured silica.

The present invention relates to a process for the preparation of aerogelated structured silica (silicic acids).

By aerogels is meant silica gels with low bulk density (about 20-50 g / l) and high macroporosity (DBP number up to 3.4 mg / l). Due to the contraction effect described by R. 1'er, which, when drying aqueous phase silica gels, causes a breakdown of the pore structure, silicic acid aerogels can only be obtained according to the method described by Kistler in US Patent 2,249,77. £ Co mmo^;For this purpose, silicas are partially dewatered with silicic acid sols with alcohols, after which the aqueous alcove is dried in autoclave by pressure reduction (Single Chip) under supercritical conditions. In this way, particularly fortuitously constructed structures of primary particles are obtained from the silica sol, which has a high volume value in the range of macropores (> 300 Å) at very low apparent density (bulk density).

These materials, which are referred to as aerogels, are used depending on the degree of porosity and bulk density such as fillers, carrier silica, matting agents, thickening agents, etc. The process for preparing these aerogels is due to the required use of organic solvents and the like. autoclave performed supercritical drying very demanding from technical and

7503483-5 economic point of view.

It has been found, according to the invention, that the disadvantages of previously available processes for the preparation of aerogels can be avoided if, instead of the particles of a silica sol, primary particles of pyrogenically produced silica are used and refrain from liquid phase recovery.

, The primary particles of the pyrog one silica exist in layers such as loosely associated particles through the action of electrostatic forces and van der Waalska forces. They form flocks that exhibit high air content and therefore have very high apparent pore volume and correspondingly low acrylic density. A layer of these flocks is best characterized as air dispersion. However, the picks are unstable and disintegrate, unlike the secondary particles in the Kistlerian aerogels, at least mechanical impact to primary particles.

The present invention relates to a process for the preparation of aerogelic, structured silica products, which is characterized by incorporation in air-dispersed pyrogenic silica

5-50% by weight of water under uniform distribution and drying the resulting powdered mixture. Since the volume of silica in the incorporation of water only slightly decreases, it can be assumed that the initially existing association of the primary particles in the air dispersed pyrogenic silica is substantially maintained. By the infiltration with water, a partial dissolution of the surface of silica is probably obtained so that dissolved silica (silicic acid is present). This, on subsequent drying, coalesces the primary particles at their contact points.

Thus, through controlled mixing with water and subsequent drying of a pyrogenic silica, a dispersing substance corresponding to the Kistlerian aerogels with high macropore volume and very low apparent density is formed (bulk density).

It has further been found that the apparent pre-incorporation of the water, which is determined by the packing density of the pyrogenic silicon dioxide in air, which is expressed by the apparent density (bulk density), has a clear influence on the product of the process according to the invention. : the more volume the starting product is, the more volume the final product will be.

It has been discovered that for the preparation of products / products according to the invention / in using 'pyrogenic silica-with a

7S03483-5 bulk density of 10-60 and preferably 15-30 and especially about 20 g / l.

In addition, it has been found advantageous to have well-pyrogenic silica with a large specific surface area and thus low primary particle size. According to a favorable embodiment of the process according to the invention, silica is used on a BET surface between 100 and 480 and in particular 250 to 300 m²/ G.

Full wetting of the primary particles can be achieved already by inarbetting of 5-20 'and especially 7-15% by weight of water under uniform distribution in the silica. Since the incorporated water must then be removed by drying, the lowest possible amount of water is sought for economic reasons. However, the amount required depends to some extent on the nature of the incorporation.

The structure of the structure according to the process according to the invention can be markedly improved if basic reacting compounds such as ammonia, sodium or potassium hydroxide, water-soluble amines, water glasses and the like are added to the water. The added amounts are suitably selected in such a way that a pH value of 7-14, preferably 8-12, and in particular 10-11 is adjusted in the water.

The alkaline substances used act as dissolution agents for silica and increase the macroporosity of products according to the invention.

Instead of alkaline compounds, free silicic acid (silica) or hydrolytic silicic acid and / or alkali-free substances can be added to the water. Thus, free silicic acid, which is prepared, for example, by acidification or ion exchange of silicate solutions or by hydrolytic decomposition of silica compounds, for example of tetramethyl silicate, thus also improves the structure structure. For example, a substance that hydrolytically releases alkali and silicic acid is sodium methyl siliconate.

The uniform distribution of the water in the silicic acid can be achieved by entrapment or incorporation into the silicic acid stirred at temperatures of the silicic acid between 20 and 100 ° C and preferably 40-70 and in particular 5O-6O ° 0.

The blended motion is conveniently obtained by stirring.

A further variant of the method of introducing water involves injecting the water into, for example, a fluid stream of silicic acid flow stream, for example.

Furthermore, it has been found appropriate to carry out the water pollution at moderately elevated temperature. This can be achieved

7503483-5 by preheating either the water to be incorporated or the silicic acid or both components. Thus, the water to be incorporated may have a temperature between 20 and 100, preferably 50 and Ϊ00, and in particular 90 and 100 ° C.

It is also possible to favor the structural build-up by short-term steam treatment of the charged silicic acid in closed rooms. Steam treatment results in a particularly good water distribution. Hereby, it has been found suitable to steam treat the water-laden silicic acid prior to drying in closed vessels, for example 5-60, preferably 10-50 and especially for about 20 minutes at temperatures up to the boiling point of the water, preferably at 50-80 and especially at about 6o ° C.

A further possibility of improving the water distribution involves feeding the water-laden silicic acid, for example with pin or air jet mills.

The material is then dried, presumably fixing the pre-prepared structure with the dissolved surface particles or at the surface with free silicic acid primary particles.

The drying method is of less critical importance. For example, one can dry the prepared mixture of silicic acid and water, which phenomenologically resembles a dry powder, for example in bed, plate, swap, flow or microwave drying devices. However, the water-impregnated silicic acid (silica) can also be milled and dried simultaneously in a steam or air jet mill with the saving of a particular working step.

In a separate drying of the powdery mixture obtained after boiling with water, dry milling with the pin or air jet mill can then be carried out.

The invention also relates to an aerogelous structured silicic acid (silica) having the following material properties:

The BET surface is between 80 and 450 m²/ g

Bulk density between 10 - 6o g / l

DBP numbers between 2.4 and 5.8 average particle size 0.1 - 7 µm most common particle size range 1 - 2 µm pH in 4 # water slurry 6-8.

A further object of the invention is the silica (silicic acid) produced by the process described.

The invention also relates to the use of the described aerogelic structured silica as a matting component.

7503483-5

The invention is further elucidated with exemplary embodiments.

Example 1,

In a solder mixer device, the pyrogen 2 silica was moistened with a bulk density of 25 g / l and a BET surface of 304 m / g with 20 ml of water, which had a pH of 6.8. The baking was carried out at room temperature with stirring. The water was entrapped from a burette for a period of 18 minutes.

• It was obtained in a powder which appeared dry and had a water content of 15.3% by weight. This powder was ground on a counter-rotating pin mill and dried in a laboratory oven at 120 ° C.

A powdery, opalescent powder having a bulk density of 17.8 g / L and a DBP of 2.78 ml / g was obtained.

The activity as a matting agent was tested in a polyurethane coating composition. The results are set forth in Example 9 ·

The resulting product and the starting material were slurried in water and dispersed with ultrasound. A drop of each of these dispersions was dried on a slide, (Aperture). Electron microscopic examination and photography of the samples showed that the product structured according to the invention was in the form of secondary particles mainly in the size range between 1 and 10µιη. However, the starting material is practically complete in the form of primary particles.

With regard to the two electron microscope photographs, the following may be noted.

In Figure 1, with the magnification ratio 1: 5-000, the starting material of Example 1 is shown, which has been ultrasonically dispersed in water and dried. The primary particles are largely separate.

Figure 2 shows in the magnification 1: 5,000 final product according to External Pill 1, which is ultrasonic dispersed in water and dried. Formation of a secondary structure is evident.

Example 2.

In a solder mixer device, 5 liters of a pyrogenic silica (silicic acid) having a bulk density of 19.3 g / l and a BET surface of 189 wf / g with 20 ml of water adjusted to a pH of 11 were moistened. , 3 with sodium hydroxide solution.

The baking was carried out at room temperature under stirring for a period of 20 minutes. The addition of the water was carried out dropwise from a burette.

A powder which appeared dry and had a water content of 11;

Because the powder contained tangible solid ingredients, such as ι

Obviously due to the breakdown of the apparent structure of the pyrogenic silica by local water excess, the powder was ground in a pin mill and dried in a laboratory oven at 120 ° C.

A lucid, opalescent powder was obtained with a bulk density of 17.5 ε / l and a BET surface of 153 m²/ g, a DBP number of 2.6 ml / g, one in water pore volume according to Innes of 1.9 ml / g and a residual water content of 2.6 <$.

The matting action of the material was tested in a polyurethane coating

and composition of Example 9 · j

Example 5. t ' ^! In a drop tube, a silica dioxide-dosed silica was fed through a bulk density of 29 g / l and a BET surface of 297 m / g. ,

In this flowing mass flowing in the downpipe 1.5 parts of silica was injected with 1.5 parts of ammoniacal water with a pH of 10.1. ·

A powder which appeared dry and had a bulk density of 26 g / l and a water content of 12% by weight was obtained.

This powder was dried on a microwave hearth. ,

F

An opalescent leachate powder was obtained with a bulk sealant. _;heat of 25 g / l, a BET surface of 270 m / g and a DBP of 5.1 ml / g.

The matting action of the material was tested in a polyurethane coating composition and set forth in Example 9 ·

Example 4. i

A water-loaded product according to Example 5 was ground to improve the water distribution in a company air jet mill (

Jet-o-mizer of type Λ 0202 at 5.1 ato mill pressure, 5.2 ato injection pressure and an added amount of 8.8 kg per hour. ;

The drying to 5.2 wt% residual water content was carried out in a laboratory oven at 120 ° C. j

A lukewarm, opalescent powder was obtained with a bulk density of 14 g / l, a BET surface of 277 m²/ G, ^efcfc DBP figure of 5.6 ml / g and a water pore volume according to Innes of 2.4 ml / g.

The matting effect of the material was tested in a polyurethane coating composition and is set forth in Example 9 ·} (

Exempel'5. j

A product loaded with 12 wt.% Water according to Example 3 t (ground in a counter-rotating pin mill and Anghe treated in a closed, preheated powder bottle for 20 minutes at and dried io ^! then at 120 ° C in a laboratory oven to a residual moisture content of (wt.% - i

A leachate, opalis, in-one powder was obtained with a bulk density of 16 g / l, a BET surface area. · 264 m²/ g, a DBP of 5.78 ml / g and t

750es water volume according to Innes of 2.4 ml / g.

The matting action of the material was tested in a polyurethane coating composition and set forth in Example 9.

Example 6

A heated, to 70 ° C, heated drop tube was fed through a dosing shell of pyrogenic silica having a bulk density of 54 g / l and a BET surface of 311 m / g. In this fluidized mass stream, 3 parts of warm water of 80 ° C were injected per 10 parts of silica, set with water glass at a pH of 10.4.

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A powder was obtained which appeared dry and had a bulk density of 8o g / l and a moisture content of 1.8.3% by weight. This powder was ground to the air jet mill specified in Example 4 under the conditions specified therein and then dried on a plate dryer with a plate temperature of 127 ° 0 to a residual water content of 4.2 °.

An opalescent liquefied powder having a bulk density of 36 g / l, a BET surface of 26²/ g and a DBF number of 3.2 ml / g.

The matting effect of the material was tested in a polyurethane coating composition and set forth in Example 9 ·

Example 7

A dry product of Example 5 was re-milled in a pin mill.

A slurry powder having a bulk density of 13 g / l and a DBP number of 3.2 ml / g was obtained.

The matting effect of the material was tested in the polyurethane coating composition and set forth in Example 9 ·

Example 8.

The matting effect of the products obtained according to Examples 5 and 7 was compared with the effect of a commercial grade aerogel produced by the Kistlerian process, the comparison being carried out in a black burn-in paint. The degree of gloss according to Lange was determined at a reflection angle of 45 ° and gate value according to Ilegemann.

The following values ​​were determined:

<td>Product</td><td>Gate value; □ i pm -</td><td>reading gloss 45 '</td>

<td>Trade quality aerogel</td><td> 02</td><td> 4,0</td>

<td>Product acc. Example 5</td><td> 38</td><td> 0,2</td>

<td>Product acc. Example 7</td><td> 30</td><td> 3,7</td>

<td>The paint used had</td><td colspan="2">the following composition in parts by weight:</td>

7503483-5

<td></td><td></td><td></td><td> 0</td>

<td> 7</td><td>sotpasta</td><td>Branch 1</td><td></td>

<td> 53</td><td>Ålgital</td><td> 64 75</td><td>in xylene</td>

<td> 12</td><td>Matrenal</td><td>NP 55</td><td>in butanol</td>

<td> 4</td><td>butanol</td><td></td><td></td>

ethyl glycol 16 xylene glycolic butyl ester butyl acetate 85 µ silicone oil OL 10 µ in xylene r

In each particular case, 5 parts by weight of product was incorporated. The incorporation was carried out by stirring for 10 minutes with a wing stirrer at 2,000 rpm. The varnish was sprayed as a layer having a dry thickness of 30 microns on sheet, air dried and incubated for 30 minutes at 180 ° C.

Example 9.

The matting action of the product obtained in Examples 1-7 was tested in a very ordinary matting agent very poorly matte polyurethane coating material which is preferably matte with aerogels. It was quite surprising that, as is evident from the following and graphical representation, a relationship between porosity, expressed in DBP's, and the obtained matting step could be demonstrated. The matting step was measured according to Lange at a reflection angle of 60 ° C

<td colspan="3">(Figure 3). .</td>

<td>product</td><td>60 Residual gloss 60 °</td><td>DBP number (ml / g)</td>

<td>Precursor</td><td></td><td></td>

<td>Example 1</td><td> 15,0</td><td></td>

<td>from ex. 1</td><td> 4,3</td><td>0 Q 2, 1 0</td>

<td> 2</td><td> 5,0</td><td> 2,60</td>

<td>»H -2 S</td><td> 2,8</td><td> 3,10</td>

<td>II II</td><td> 0,7</td><td> 3,60</td>

<td>11 II 5</td><td> 0,5</td><td> 3,78</td>

<td> .. _β</td><td> 1,6</td><td> 3,20</td>

<td>II II γ</td><td> 1,4</td><td> ' 3,20</td>

<td>Trade product</td><td> 1,5</td><td> 3,30</td>

<td>The used one</td><td>the coating pulp had the following</td><td>composition:</td>

<td>Polyurethane coating recipes</td><td></td><td></td>

<td>3.01 parts by weight</td><td>Mi kroli in black</td><td></td>

<td>0, o2 </td><td>Mi krol i tti ^ bl ate t</td><td></td>

<td> 84,0</td><td>30 fy, Irapranil ^ CHl ·. ' in ethyl acetate</td><td></td>

<td> 10-20 </td><td>etylaceteit</td><td></td>

7503463-5

In this mass, 5.62 parts by weight of the product to be tested was incorporated with a spatula and then dispersed for 4 minutes with a Dissolver type device at 2000 rpm.

Then, in each particular case, 4.22 parts by weight of Impraf ix® and Desmodur® L were stirred with a spatula and applied to a carton with a drawbar for the dimension of 500 µm.

After the coating was dried in air, the coating was cured for 50 minutes at, So ° C in a drying cabinet.

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