Method for producing hydrophobic heat insulation material

Abstract

Process for producing a thermally insulating mixture comprising hydrophobic silica, in which a) a pulverulent carrier material selected from the group consisting of precipitated silicas, SiO.sub.2 aerogels, pearlites and mixtures thereof is coated with a liquid silicon compound, where the liquid silicon compound has at least one alkyl group and a boiling point of less than 200° C., and b) the pulverulent carrier material that has thus been coated with the liquid silicon compound is mixed with a composition comprising a pulverulent hydrophilic fumed silica and the mixture is subjected to thermal treatment at more than 40° C. and c) any unreacted silicon compound is subsequently removed from the thermally treated mixture, thus giving the thermally insulating mixture comprising hydrophobic silica.

Claims

1. A process for producing a thermally insulating mixture comprising hydrophobic silica, wherein: a) a pulverulent carrier material selected from the group consisting of precipitated silicas, SiO.sub.2 aerogels, perlites and mixtures thereof is coated with a liquid silicon compound, wherein the liquid silicon compound has at least one alkyl group and a boiling point of less than 200° C. and wherein coating is performed at a temperature of 0-40° C.; b) the pulverulent carrier material that has been coated in step a) with the liquid silicon compound is mixed with a composition comprising a pulverulent hydrophilic fumed silica to form a mixture which is then is subjected to thermal treatment at more than 40° C., thereby forming a thermally treated mixture; and c) any unreacted liquid silicon compound is subsequently removed from the thermally treated mixture obtained in step b), thus giving the thermally insulating mixture comprising hydrophobic silica.

2. The process of claim 1, wherein the liquid silicon compound is present in an amount of 10-300 g per 100 g of pulverulent carrier material employed in step a).

3. The process of claim 1, wherein the pulverulent carrier material coated with the liquid silicon compound is present in an amount of 1-50 g per 100 g of pulverulent hydrophilic fumed silica employed in step b).

4. The process of claim 1, wherein the liquid silicon compound employed in step a) is present in an amount of 1-20 g per 100 g of the sum of the amounts of the pulverulent hydrophilic fumed silica employed in step b) and the pulverulent carrier material employed in step a).

5. The process of claim 1, wherein the pulverulent carrier material has a quotient of DOA absorption/tamped density of 0.005-0.1 l/g, wherein the DOA absorption is reported in g per 100 g of carrier material and the tamped density in g/l.

6. The process of claim 1, wherein the pulverulent carrier material has a DOA absorption of 200-300 g/100 g.

7. The process of claim 1, wherein the pulverulent carrier material has a tamped density of 90-300 g/l.

8. The process of claim 1, wherein the pulverulent hydrophilic fumed silica has a quotient of DOA absorption/tamped density of 0.02-0.1 l/g, wherein the DOA absorption is reported in g per 100 g of silica and the tamped density in g/l.

9. The process of claim 1, wherein the quotient of DOA absorption/tamped density of the pulverulent hydrophilic fumed silica is greater than that of the pulverulent carrier material.

10. The process of claim 1, wherein the pulverulent carrier material has been hydrophobized.

11. The process of claim 1, wherein the pulverulent hydrophilic fumed silica has a DOA absorption of 200-300 g/100 g and a tamped density of 30-70 g/l.

12. The process of claim 1, wherein the liquid silicon compound is selected from the group consisting of CH.sub.3—Si—Cl.sub.3, (CH.sub.3).sub.2—Si—Cl.sub.2, (CH.sub.3).sub.3—Si—Cl, C.sub.2H.sub.5—Si—Cl.sub.3, (C.sub.2H.sub.5).sub.2—Si—Cl.sub.2, (C.sub.2H.sub.5).sub.3—Si—Cl, C.sub.3H.sub.8—Si—Cl.sub.3, CH.sub.3—Si—(OCH.sub.3).sub.3, (CH.sub.3).sub.2—Si—(OCH.sub.3).sub.2, (CH.sub.3).sub.3—Si—OCH.sub.3, C.sub.2H.sub.5—Si—(OCH.sub.3).sub.3, (C.sub.2H.sub.5).sub.2—Si—(OCH.sub.3).sub.2, (C.sub.2H.sub.5).sub.3—Si—OCH.sub.3, C.sub.8H.sub.15—Si—(OC.sub.2H.sub.5).sub.3, C.sub.8H.sub.15—Si—(OCH.sub.3).sub.3, (H.sub.3C).sub.3—Si—NH—Si(CH.sub.3).sub.3 and mixtures thereof.

13. The process of claim 1, wherein the composition comprising the hydrophilic fumed silica comprises an IR opacifier and/or inorganic fibres.

14. The process of claim 13, wherein the silica is present at 60%-90% by weight and the IR opacifier is present at 10%-30% by weight, based on the composition comprising the hydrophilic fumed silica employed in step b).

15. The process of claim 1, wherein the mixture is compacted prior to the thermal treatment.

16. The process of claim 15, wherein the thermal treatment of the mixture is carried out not more than 3 hours after compaction thereof and wherein, between performing compaction and thermal treatment, the mixture is kept at a temperature in the range of 0-40° C.

17. The process of claim 15, wherein the mixture is compacted to a granular material.

18. The process of claim 15, wherein the mixture is compacted to a board.

19. The process of claim 14, wherein the liquid silicon compound used in step a) is (H.sub.3C).sub.3—Si—NH—Si(CH.sub.3).sub.3 and the thermally insulating mixture is compacted to a granular material with a tamped density of 100-400 g/l.

20. A method for making a structure for insulation comprising a) a pulverulent carrier material selected from the group consisting of precipitated silicas, SiO2 aerogels, perlites and mixtures thereof is coated with a liquid silicon compound, wherein the liquid silicon compound has at least one alkyl group and a boiling point of less than 200° C. and wherein coating is performed at a temperature of 0-40° C.; b) the pulverulent carrier material that has been coated in step a) with the liquid silicon compound is mixed with a composition comprising a pulverulent hydrophilic fumed silica to form a mixture which is then is subjected to thermal treatment at more than 40° C., thereby forming a thermally treated mixture; c) any unreacted liquid silicon compound is subsequently removed from the thermally treated mixture obtained in step b), thus giving the thermally insulating mixture comprising hydrophobic silica; and d) compacting the thermally insulating mixture comprising hydrophobic silica into a board.

Description

EXAMPLES

Example 1

(1) 108 g of HMDS (hexamethyldisilazane) are metered gradually into 60 g of SIPERNAT® 50 S while stirring over a period of 45 minutes. This gives rise to a free-flowing powder. At a temperature of 20° C., 9.5 g of this powder are mixed into 50 g of a mixture consisting of 80% by weight of AEROSIL® 300 and 20% by weight of SiC (SILCAR G14 from ESK-SIC), and mixed in at low speed for 5 minutes. The tamped density is about 60 g/l. The mixture thus obtained is introduced into an oven preheated to 150° C. with nitrogen blanketing and gas suction, and kept at this temperature for 2 hours. Thereafter, the oven is switched off and left to cool for 12 hours.

Example 2

(2) 108 g of HMDS are metered gradually into 60 g of SIPERNAT® 50 S while stirring over a period of 45 minutes. This gives rise to a free-flowing powder. At a temperature of 20° C., 9.5 g of this powder are mixed into 50 g of a mixture consisting of 80% by weight of AEROSIL® 300 and 20% by weight of SiC (SILCAR G14 from ESK-SIC), and mixed in by means of a ploughshare mixer for 5 minutes. The tamped density is about 60 g/l.

(3) This mixture is compacted by means of a vacuum compactor roll, Vacupress, to a tamped density of 250 g/l. Within a period of three hours since its production, the mixture thus obtained is introduced into an oven preheated to 150° C. with nitrogen blanketing and gas suction, and kept at this temperature for 2 hours. Thereafter, the oven is switched off and left to cool for 12 hours.

Example 3

(4) 108 g of HMDS are metered gradually into 60 g of SIPERNAT® 50 S while stirring over a period of 45 minutes. This gives rise to a free-flowing powder. At a temperature of 20° C., 9.5 g of this powder are mixed into 50 g of a mixture consisting of 80% by weight of AEROSIL® 300 and 20% by weight of SiC (SILCAR G14 from ESK-SIC), and mixed in by means of a ploughshare mixer for 5 minutes. The tamped density is about 60 WI. The mixture thus obtained is compacted to a board by means of an evacuatable press. The mixture is compacted here at least by a factor of 2 within one minute. Thereafter, the board is decompressed.

(5) Within a period of three hours since its production, the board thus obtained is introduced into an oven preheated to 150° C. with nitrogen blanketing and gas suction, and kept at this temperature for 2 hours. Thereafter, the oven is switched off and left to cool for 12 hours.

(6) The density of the resulting board is 160 WI.

(7) TABLE-US-00001 TABLE Feedstocks - physicochemical values SIPERNAT ® 50 S BET surface area 500 m.sup.2/g DOA absorption 258 g/100 g Tamped density 105 g/l DOA absorption/tamped density 0.025 l/g AEROSIL ® 300 BET surface area 300 m.sup.2/g DOA absorption 235 g/100 g Tamped density 50 g/l DOA absorption/tamped density 0.047 l/g Calculated values g HMDS/100 g SIPERNAT ® 50 S 180 g (SIPERNAT ® 50 S + HMDS)/100 g AEROSIL ® 300 23.8 g HMDS/100 g (SIPERNAT ® 50 S + AEROSIL ® 300) 14

(8) AEROSIL® 300 as the fumed silica and SIPERNAT® 50 S used as the carrier material show comparable DOA absorption. The effect of the carrier material having a tamped density higher by a factor of 2 compared to AEROSIL® 300 is that the proportion by volume of the carrier material in a thermal insulation body or thermal insulation granules is lower by a factor of 2 compared to a thermal insulation body or thermal insulation granules in which the fumed silica functions as carrier material. This is advantageous in relation to total thermal conductivity, since the carrier material by its nature is a poorer insulator than fumed silica. If the fumed silica were to be used as the sole carrier material, the advantageous pore structure thereof would be lost because of the capillary forces, and hence the inherently better thermal insulation will likewise worsen.