Method for producing hydrophobic silica mouldings

Abstract

The invention relates to a method for producing hydrophilic silicia moulded bodies, in which i) a mixture containing hydrophilic silicic acid is added at a maximum temperature of 55° C. to hydrophobic means and ii) the mixture obtained in step i) is compacted after a maximum storage time of 30 days to form moulded bodies, iii) during steps ii and iii and until the moulded bodies are used, the temperature is at a maximum of 55° C.

Claims

1. A method for producing mechanically stable hydrophobic silica moldings, comprising: i) coating a mixture containing hydrophilic silica with at least one hydrophobicizing agent at a temperature of not more than 55° C.; and ii) compacting the mixture from step i) after a storage time of not more than 30 days, to create moldings, iii) wherein the temperature is not more than 55° C. during steps i) and ii) and up to use of the moldings, and wherein the moldings produced in step ii) are mechanically stable moldings having a density of from 100 to 400 g/L.

2. The method of claim 1, wherein the moldings are plates or mats.

3. The method of claim 1, wherein the hydrophobicizing agents are reactive organosilanes, organosiloxanes or silicone resins having hydrophobicizing properties, which are liquid at 25° C. and are capable of reacting with Si—OH groups of the silica surface.

4. The method of claim 1, wherein the hydrophobicizing agents are OH-terminated polydimethylsiloxanes having a kinematic viscosity measured at 25° C. of from 5 mm.sup.2/s to 100 mm.sup.2/s.

5. The method of claim 1, wherein the hydrophilic silica is pyrogenic silica, precipitated silics or mixture thereof having a BET surface area in accordance with DIN 66131 in the range from 100 to 500 m.sup.2/g.

6. The method of claim 1, wherein, in step i, the hydrophilic silica is coated with from 0.5% to 20% by weight of hydrophobicizing agent, based on the weight of the total mixture.

7. The method of claim 1, wherein the mixture is stored for not more than 15 days after step i) and before the compaction in step ii).

8. The method of claim 1, wherein the mixture from step i) is deaerated before compaction to a target density.

9. The method of claim 1, wherein residues obtained in the method of claim 1 and/or during the use of moldings are recirculated into the method of claim 1.

10. The method of claim 1, wherein the hydrophobicizing agent in the mixture from step i) has not completely reacted with surface silanol groups of the silica prior to compaction in step ii).

11. The method of claim 1, wherein the moldings are insulation boards.

12. The method of claim 1, wherein the moldings are thermal insulators having a thermal conductivity of 18 to 35 mW/m.Math.K.

13. The method of claim 1, wherein prior to compacting in step ii), an IR opacifier, electrostatic charge—reducing agent, or both of these are added.

14. The method of claim 1, wherein compacting in step ii) takes place within 24 hours of step i).

15. A method for producing hydrophobic silica moldings, comprising: iv) coating a mixture containing hydrophilic silica with at least one hydrophobicizing agent at a temperature of not more than 55° C.; and v) compacting the mixture from step i) after a storage time of not more than 30 days, to create moldings, vi) wherein the temperature is not more than 55° C. during steps i) and ii) and up to use of the moldings, further comprising adding fibers to the mixture before step ii).

16. The method of claim 15, wherein the moldings produced in step ii) are mechanically stable moldings having a density of from 100 to 400 g/L.

17. The method of claim 15, wherein the hydrophobicizing agent in the mixture from step i) has not completely reacted with surface silanol groups of the silica prior to compaction in step ii).

18. The method of claim 15, wherein the moldings are insulation boards.

19. The method of claim 15, wherein prior to compacting in step ii), an IR opacifier, electrostic charge—reducing agent, or both of these are added.

Description

EXAMPLES

(1) In the following examples, all amounts and percentages are by weight, all pressures are 0.10 MPa (abs.) and all temperatures are 20° C., unless indicated otherwise in the particular case.

(2) Density

(3) The density of the plate was calculated from the weight of the plate and the plate volume. The volume of the plate was calculated from the external dimensions of the plate. The density is, unless indicated otherwise, reported in grams per liter (g/1).

(4) Determination of the Thermal Conductivity

(5) In the production of plate-shaped bodies by means of a pressing operation, the thermal conductivity was determined at a temperature of 23° C. by a method based on DIN EN 12667:2001 on an A206 instrument from Hesto on plates having the dimensions 11×11×2 cm.

(6) Qualitative Test for Hydrophobicity

(7) The assessment of the hydrophobicity was carried out two weeks after pressing. For this purpose, pieces having a size of about 5 mm were cut out using a sharp knife. 1 g of these pieces was introduced into 100 ml of water and stored in a closed vessel for 24 hours. The assessment is carried out as follows: + Hydrophobic: the pieces of the plate are barely wettable by water and float completely on the water surface. ∘ Partially hydrophobic: the pieces of the plate are wettable, but mostly float on the water surface. − Not hydrophobic: the pieces of the plate are immediately wettable and sink downward in the water within a few minutes.

(8) Fracture Force

(9) The fracture force, i.e. the force until fracture of the insulation plate occurs, was determined by a method based on DIN 53 423 (3-point bending test). For this purpose, a BTC-FR010TH.A50 instrument from Zwick/Roell was used. The span width between the supports in the measurement is 100 mm, and the dimensions of the plates are 110×110 mm. The thickness of the plates is 20 mm (for precise value, see table). The fracture force is reported in newtons (N).

(10) Determination of the Carbon Content

(11) The determination of the carbon content (C content) of the samples was carried out on a Leco CS 230 analyzer. The analysis was carried out by high-frequency combustion of the sample in a stream of oxygen. Detection was carried out by means of nondispersive infrared detectors.

(12) Sources:

(13) HDK® T30: hydrophilic, pyrogenic silica from Wacker Chemie AG having a BET surface area of 300 m.sup.2/g.

(14) HDX® 830: hydrophobic, pyrogenic silica from Wacker Chemie AG having a BET surface area of 270-320 m.sup.2/g, a density of about 40 g/l and a C content of 1.4-2.6%.

(15) HDE® 8H18: hydrophobic, pyrogenic silica from Wacker Chemie AG having a BET surface area of 170-230 m.sup.2/g, a density of about 50 g/l and a C content of 4-5.2%.

(16) OH-term. PDMS: OH-terminated polydimethylsiloxane from Wacker Chemie AG having a kinematic viscosity in the region of about 35 mm.sup.2/s.

(17) Methyltriethoxysilane: WACKER® SILAN M1-TRIETHOXY from Wacker Chemie AG.

(18) Dimethyldiethoxysilane: WACKER® SILAN M2-DIETHOXY from Wacker Chemie AG.

(19) All further laboratory chemicals were procured from Sigma-Aldrich.

(20) Digested viscose staple fibers having a length of 6 mm and a diameter of 9 μm were used for armoring.

(21) All further laboratory chemicals were procured from customary suppliers.

(22) Production of the Silica-Containing Mixture

(23) Method A

(24) The mixture consisting of silica and additives was intensively stirred at 25° C. for 10 minutes, so that the material was fluidized. The organosiloxane was atomized through a two-fluid nozzle and sprayed onto the fluidized silica. After coating, the fibers were added and the mixture was intensively mixed for a further 2 minutes in a high-speed mixer (4000 rpm). This gave a mixture which was stored at room temperature for a maximum of 3 days before compaction.

(25) Method B

(26) 10% of the mixture to be used, consisting of silica and additives, was intensively stirred at 25° C. for 10 minutes, so that the material was fluidized. The organosiloxane was subsequently added dropwise to the mixture while stirring. In selecting the stirrer and the stirring time, attention was paid to ensuring that very little organosiloxane remained on the vessel walls. This could, for example, be checked by coloring the organosiloxane and by weighing the resulting mixture and if necessary optimized.

(27) After coating, a free-flowing powder (masterbatch) was obtained.

(28) In a larger stirring apparatus, the remaining amount of the mixture consisting of silica and additives was intensively stirred at room temperature. The masterbatch was sprinkled into this mixture while stirring. The fibers were subsequently added with intensive stirring (high-speed mixer, 4000 rpm) and the mixture was intensively mixed for 2 minutes. This gave a mixture which was stored at room temperature for a maximum of 3 days before compaction.

(29) Mixture A:

(30) 800 g of HDK T30

(31) 150 g of OH-terminated polydimethylsiloxane (viscosity 35 mm.sup.2/s)

(32) 50 g of viscose staple fibers

(33) Mixture B:

(34) 800 g of HDK T30

(35) 50 g of silicon carbide

(36) 100 g of OH-terminated polydimethylsiloxane (viscosity 35 mm.sup.2/s) 50 g of viscose staple fibers

(37) Mixture C:

(38) 875 g of HDK T30

(39) 75 g of OH-terminated polydimethylsiloxane (viscosity 35 mm.sup.2/s)

(40) 50 g of viscose staple fibers

Example 1

(41) 60 g of the mixture A, produced by method A, were introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plate displayed good mechanical stability and could be taken undamaged from the mold without problems. After removal from the mold, the thickness was measured (see table 1).

Example 2

(42) 60 g of the mixture A, produced by method B, were introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plate displayed good mechanical stability and could be taken undamaged from the mold without problems. After removal from the mold, the thickness was measured (see table 1).

Example 3

(43) 60 g of the mixture B, produced by method A, were introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plate displayed good mechanical stability and could be taken undamaged from the mold without problems. After removal from the mold, the thickness was measured (see table 1).

Example 4

(44) 85.0 g of hydrophilic silica (HDK T30) were intensively stirred at 25° C. for 10 minutes, so that the material was fluidized. 15.0 g of an OH-terminated polydimethylsiloxane (viscosity 35 mm.sup.2/s) were atomized through a two-fluid nozzle and sprayed onto the mixture. The plate is brittle, less mechanically stable compared to the plates containing fibers (Ex. 1) and has to be handled carefully during removal from the mold and during the analytical studies. A mixture was obtained which was stored at room temperature for a maximum of 3 days before compaction.

Example 5

(45) 60 g of the mixture A, produced by method A, were introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. Subatmospheric pressure was applied via the bottom plate covered with a filter nonwoven, as a result of which the material to be pressed was deaerated and thereby precompacted. The material was subsequently pressed using a punch to a thickness of 2 cm by means of a manual hydraulic press. The plate displayed good mechanical stability and could be taken undamaged from the mold without problems. After removal from the mold, the thickness was measured (see table 1).

Example 6

(46) 60 g of the mixture C, produced by method A, were introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plate displayed good mechanical stability and could be taken undamaged from the mold without problems. After removal from the mold, the thickness was measured (see table 1). The plate displayed a somewhat lower hydrophobicity because of the smaller proportion of hydrophobicizing agent.

Example 7

(47) A freshly produced insulation plate as per example 1 was cut by means of a bandsaw into strips of about 5 mm (offcuts). 80 g of a freshly produced mixture A produced by method A were mixed with 20 g of the offcuts for 3 minutes in a high-speed mixer (4000 rpm). 60 g of this mixture were introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plate displayed good mechanical stability and could be taken undamaged from the mold without problems. After removal from the mold, the thickness was measured (see table 1).

Example 8

(48) In a round-bottom flask, 11 g of dimethyldiethoxysilane, 0.5 g of Ti(OiPr).sub.4 and 10 g of HDK T30 were mixed to form a free-flowing powder. This powder mixture was mixed further for 60 minutes with a further 45 g of HDK T30 in a high-speed mixer (4000 rpm). 3.3 g of viscose staple fibers were subsequently added. The mixing procedure was continued for 2 minutes. The powder mixture was subsequently transferred to a pressing mold having the dimensions 11×11 cm and compacted to a thickness of 2 cm by means of a hydraulic press. The plate displayed good mechanical stability and could be removed undamaged from the mold without problems. The plates were stored at 25° C. for 2 weeks before further analysis.

Example 9

(49) In a round-bottom flask, 6 g of methyltriethoxysilane, 6 g of dimethyldiethoxysilane, 0.5 g of Ti(OiPr).sub.4 and 10 g of HDK T30 were mixed to form a free-flowing powder. This powder mixture was mixed further for 60 minutes with a further 40 g of HDK T30 in a high-speed mixer (4000 rpm). 3.3 g of viscose staple fibers were subsequently added. The mixing procedure was continued for 2 minutes. The powder mixture was subsequently transferred to a pressing mold having the dimensions 11×11 cm and compacted to a thickness of 2 cm by means of a hydraulic press. The plate displayed good mechanical stability and could be removed undamaged from the mold without problems. The plates were stored at 25° C. for 2 weeks before further analysis.

(50) Comparative example 1 (not according to the invention) 60 g of the mixture A, produced by method A, were introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plate was subsequently heated at 125° C. for 60 minutes. The plate displayed good mechanical stability and could be taken undamaged from the mold without problems. After removal from the mold, the thickness was measured (see table 1). The plate displayed, despite the additional heat treatment, a comparable hydrophobicity to example 1 according to the invention in which a subsequent heat treatment was omitted.

(51) Comparative example 2 (not according to the invention) 100 g of the mixture A, produced by method A, were stored at 60° C. for 6 hours. 60 g of this mixture were subsequently introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plates displayed, compared to the examples according to the invention having the same content of hydrophobicizing agent, a significantly lower mechanical stability and could be removed undamaged from the mold only by careful handling. For the analytical tests, only intact plates were used; in order to obtain these, a number of plates were produced as required. After removal from the mold, the thickness was measured (see table 1).

(52) Comparative example 3 (not according to the invention) 800 g of HDK T30 were intensively stirred at 25° C. for 10 minutes, so that the material was fluidized. 150 g of the OH-terminated polydimethylsiloxane (viscosity 35 mm.sup.2/s) were atomized through a two-fluid nozzle and sprayed onto the fluidized silica. After coating, the mixture was stored at 25° C. for 3 months. The stored, coated silica and 50 g of viscose staple fibers were subsequently intensively mixed for 2 minutes in a high-speed mixer (4000 rpm). 60 g of this mixture were subsequently introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plates displayed, compared to the examples according to the invention having the same content of hydrophobicizing agent, a significantly lower mechanical stability and could be removed undamaged from the mold only by careful handling. For the analytical tests, only intact plates were used; in order to obtain these, a number of plates were produced as required. After removal from the mold, the thickness was measured (see table 1).

(53) Comparative example 4 (not according to the invention) 95.0 g of hydrophobic silica (HDK H18) and 5.0 g of viscose staple fibers were intensively mixed at 25° C. for 2 minutes (high-speed mixer, 4000 rpm). 60 g of this mixture were subsequently introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plates displayed, compared to the examples according to the invention, a significantly lower mechanical stability and could be removed undamaged from the mold only by careful handling. For the analytical tests, only intact plates were used; in order to obtain these, a number of plates were produced as required. After removal from the mold, the thickness was measured (see table 1).

(54) Comparative example 5 (not according to the invention) 95.0 g of hydrophobic silica (HDK H30) and 5.0 g of viscose staple fibers were intensively mixed at 25° C. for 2 minutes (high-speed mixer, 4000 rpm). 60 g of this mixture were subsequently introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plates displayed, compared to the examples according to the invention, a significantly lower mechanical stability and could be removed undamaged from the mold only by careful handling. For the analytical tests, only intact plates were used; in order to obtain these, a number of plates were produced as required. After removal from the mold, the thickness was measured (see table 1).

(55) Comparative example 6 (not according to the invention) 95.0 g of hydrophilic silica (HDK T30) and 5.0 g of viscose staple fibers were intensively mixed at 25° C. for 2 minutes (high-speed mixer, 4000 rpm). 60 g of this mixture were subsequently introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. The plate displayed good mechanical stability and could be removed undamaged from the mold without problems. After removal from the mold, the thickness was measured (see table 1). The plate is not hydrophobic.

(56) Comparative example 7 (not according to the invention) 60 g of a hydrophobic HDK (HDK H18) were introduced into a pressing mold having the dimensions 11×11 cm, with care being taken to ensure a uniform bed height. The mixture was subsequently brought to a thickness of 2 cm by means of a manual hydraulic press. After removal from the mold, the thickness was measured (see table). The plate could, despite many attempts, not be removed from the mold undamaged and analyzed because of the low mechanical stability, and so no further analysis apart from the test for hydrophobicity could be carried out. Compared to the example according to the invention without fibers (example 4), the mechanical stability of the pieces obtained must be classified as significantly lower.

(57) TABLE-US-00001 TABLE 1 Analytical data Plate Fracture thickness Density λ value force Hydro- Example [mm] [g/l] [mW/K*m] [N] phobicity 1 20.1 247 23.0 69 + 2 20.4 243 22.5 70 + 3 20.0 248 22.2 68 + 4 20.3 244 21.5 11 + 5 19.9 249 22.8 71 + 6 20.0 248 21.5 79 ∘ 7 20.3 244 22.8 62 + 8 20.8 258 21.1 87 + 9 19.8 242 21.4 68 + Comp. 1* 20.2 245 22.9 68 + Comp. 2* 20.3 244 21.8 48 + Comp. 3* 20.5 242 21.4 52 + Comp. 4* 20.4 243 22.4 41 + Comp. 5* 19.8 250 20.5 55 + Comp. 6* 20.3 244 21.9 93 − Comp. 7* Plates Plates Plates Plates + disin- disin- disin- disin- tegrate tegrate tegrate tegrate *not according to the invention