Method for producing a molded heat-insulating element

Abstract

A process for producing an ammonia-treated hydrophilic thermal insulation molding which includes treating a thermal insulation molding containing hydrophilic silica with ammonia by introducing the thermal insulation molding into a chamber and supplying gaseous ammonia until a pressure difference p of 20 mbar is achieved. A process for producing a thermal insulation molding containing hydrophobic silica which includes treating the ammonia-treated hydrophilic thermal insulation molding with an organosilicon compound.

Claims

1. A process for producing an ammonia-treated hydrophilic thermal insulation molding, comprising treating a thermal insulation molding comprising hydrophilic silica with ammonia, such that the thermal insulation molding is introduced into a chamber and gaseous ammonia is supplied until a pressure difference p of 20 mbar is achieved.

2. The process of claim 1, wherein a pressure in the chamber before introduction of the gaseous ammonia is below atmospheric pressure.

3. The process according to claim 1, wherein the hydrophilic thermal insulation molding comprises up to 5 wt % water.

4. The process of claim 1, further comprising introducing steam into the chamber.

5. The process of claim 1, wherein the hydrophilic thermal insulation molding kept in the chamber for 1 to 100 hours starting from the point at which the gaseous ammonia is added.

6. The process of claim 1, wherein a temperature in the chamber is between 0 C. and 100 C.

7. The process of claim 1, wherein the hydrophilic silica is a fumed silica.

8. A process for producing a thermal insulation molding comprising hydrophobic silica, comprising treating the hydrophilic thermal insulation molding obtained by the process of claim 1 with an organosilicon compound.

9. The process of claim 8, wherein the treatment with the organosilicon compound comprises introducing the hydrophilic thermal insulation molding treated with ammonia into a chamber and introducing a vaporous organosilicon compound into the chamber until a pressure difference p of 20 mbar is achieved.

10. The process of claim 9, wherein the ammonia-treated hydrophilic thermal insulation molding comprises not more than 2 wt % water.

11. The process of claim 9, wherein a pressure in the chamber before introduction of the organosilicon compound is below atmospheric pressure.

12. The process of claim 9, wherein a temperature in the chamber is 20 C. to 300 C.

13. The process of claim 9, wherein the ammonia-treated hydrophilic thermal insulation molding is kept in the chamber for 1 minute to 1 hour starting from the point at which the organosilicon compound is added.

14. A process for producing a thermal insulation molding comprising hydrophobic silica, the process comprising: a) treating a thermal insulation molding comprising hydrophilic fumed silica with ammonia by introducing the molding into a chamber and supplying gaseous ammonia until a pressure difference p of 20 mbar is achieved, b) subsequently treating the thus treated thermal insulation molding with (CH.sub.3).sub.3SiNHSi(CH.sub.3).sub.3 thus forming ammonia, and c) supplying the thus obtained ammonia, optionally with further ammonia, to another chamber in which a thermal insulation molding comprising hydrophilic fumed silica is disposed, wherein ammonia is supplied until a pressure difference p of 20 mbar is achieved.

Description

EXAMPLES

(1) Carried out as per DIN ISO 844:2009 and EN 826:1996. In contrast to the test specifications the present procedure comprises stressing samples to 1 bar and evaluating the compression values. In addition only a single measurement was carried out without acclimatizing the specimens prior to testing.

Example 1a (Comparative Example)

(2) A thermal insulation mixture composed of 76.2 wt % AEROSIL 300 (fumed silica; Evonik Industries; BET surface area 300 m.sup.2/g), 19 wt % silicon carbide (Silcar G14; ESK; d.sub.50=2.73 m) and 5 wt % glass fibres (average fibre diameter about 9 m; length about 6 mm) is pressed into a thermal insulation sheet. The thermal insulation sheet has a density of 149 g/cm.sup.3.

Example 2a (Inventive)

(3) A section of the thermal insulation sheet from example 1a having dimensions of 707020 mm is transferred into a desiccator. The pressure in the desiccator is reduced to 20 mbar. Sufficient vaporous ammonia is then introduced into the desiccator to raise the pressure to 300 mbar. The thermal insulation sheet is then kept in the desiccator for 2 hours. The density is unchanged.

Example 2b (Inventive)

(4) analogous to example 2a. The thermal insulation sheet is kept in the desiccator for 20 hours.

Example 2c (Inventive)

(5) analogous to example 2a, but using the thermal insulation sheet from example 1b instead of 1a. The thermal insulation sheet is kept in the desiccator for 100 hours.

(6) The table shows the compression values for the thermal insulation sheets. It is apparent that the compression values for the thermal insulation sheets produced by the process according to the invention are significantly lower than for untreated sheets. The results also show that, contrary to the teaching of the prior art, previously pressed thermal insulation sheets are hardened by the treatment.

(7) TABLE-US-00001 TABLE Compression under compressive stress Reaction time Compression Example [h] at 1 bar [%] 1a 16.4 2a 2 14.9 2b 20 8.8 2c 100 9.2