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

1-21. (canceled)

22. 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, pearlites 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.; b) the pulverulent carrier material that has 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.

23. The process of claim 22, wherein the proportion of the liquid silicon compound is 10-300 g per 100 g of pulverulent carrier material.

24. The process of claim 22, wherein the proportion of the pulverulent carrier material coated with the liquid silicon compound is 1-50 g per 100 g of pulverulent hydrophilic fumed silica.

25. The process of claim 22, wherein the proportion of liquid silicon compound is 1-20 g per 100 g of (pulverulent hydrophilic fumed silica+pulverulent hydrophilic carrier material).

26. The process of claim 22, wherein the temperature in the coating operation is 0-40 C.

27. The process of claim 22, 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.

28. The process of claim 22, wherein the pulverulent carrier material has a DOA absorption of 200-300 g/100 g.

29. The process of claim 22, wherein the pulverulent carrier material has a tamped density of 90-300 g/l.

30. The process of claim 22, 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.

31. The process of claim 22, wherein the quotient of DOA absorption/tamped density of the pulverulent hydrophilic fumed silica is greater than that of the pulverulent carrier material.

32. The process of claim 22, wherein the pulverulent carrier material has been hydrophobized.

33. The process of claim 22, 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.

34. The process of claim 22, wherein the liquid silicon compound is selected from the group consisting of CH.sub.3SiCl.sub.3, (CH.sub.3).sub.2SiCl.sub.2, (CH.sub.3).sub.3SiCl, C.sub.2H.sub.5SiCl.sub.3, (C.sub.2H.sub.5).sub.2SiCl.sub.2, (C.sub.2H.sub.5).sub.3SiCl, C.sub.3H.sub.8SiCl.sub.3, CH.sub.3Si(OCH.sub.3).sub.3, (CH.sub.3).sub.2Si(OCH.sub.3).sub.2, (CH.sub.3).sub.3SiOCH.sub.3, C.sub.2H.sub.5Si(OCH.sub.3).sub.3, (C.sub.2H.sub.5).sub.2Si(OCH.sub.3).sub.2, (C.sub.2H.sub.5).sub.3SiOCH.sub.3, C.sub.8H.sub.15Si(OC.sub.2H.sub.5).sub.3, C.sub.8H.sub.15Si(OCH.sub.3).sub.3, (H.sub.3C).sub.3SiNHSi(CH.sub.3).sub.3 and mixtures thereof.

35. The process of claim 22, wherein the composition comprising the hydrophilic fumed silica comprises an IR opacifier and/or inorganic fibres.

36. The process of claim 35, wherein the proportion of the silica is 60%-90% by weight and that of the IR opacifier 10%-30% by weight, based on the composition.

37. The process of claim 22, wherein the mixture is compacted prior to the thermal treatment.

38. The process of claim 37, wherein the period between compaction and thermal treatment is not more than 3 hours and wherein the temperature between compaction and thermal treatment is 0-40 C.

39. The process of claim 37, wherein the mixture is compacted to a granular material.

40. The process of claim 37, wherein the mixture is compacted to a board.

41. A thermally insulating board, comprising: a hydrophobized fumed silica and a hydrophobized precipitated silica, wherein the proportion of precipitated silica is 3-15 g per 100 g of hydrophobized fumed silica, and the carbon content is 3%-10% by weight, based on the board.

Description

EXAMPLES

Example 1

[0039] 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

[0040] 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.

[0041] 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

[0042] 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.

[0043] 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.

[0044] The density of the resulting board is 160 WI.

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

[0045] 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.