THERMAL INSULATING COMPOSITION BASED ON FUMED SILICA GRANULATES, PROCESSES FOR ITS PREPARATION AND USES THEREOF

Abstract

The present invention relates to a thermal insulating composition, containing 5 to 60% by weight of a hydrophobized granular material comprising fumed silica and at least one IR-opacifier, and 40 to 95% by weight of an inorganic and/or an organic binder, whereby the hydrophobized granular material has a content of free hydroxyl groups of no greater than 0.12 mmol/g, as determined by the reaction with lithium aluminium hydride.

Claims

1-15. (canceled)

16. A thermal insulating composition, containing 5 to 60% by weight of a hydrophobized granular material comprising fumed silica and at least one IR-opacifier, and 40 to 95% by weight of an inorganic and/or an organic binder, wherein the hydrophobized granular material has a content of free hydroxyl groups of no greater than 0.12 mmol/g, as determined by reaction with lithium aluminium hydride.

17. The thermal insulating composition of claim 16, wherein the IR-opacifier is selected from the group consisting of: silicon carbide; titanium dioxide; zirconium dioxide; ilmenites; iron titanates; iron oxides; zirconium silicates; manganese oxides; graphites; carbon blacks; and mixtures thereof.

18. The thermal insulating composition of claim 16, wherein the hydrophobized granular material contains from 30% to 95% by weight of fumed silica, and from 5% to 70%, by weight of the IR opacifier.

19. The thermal insulating composition of claim 16, wherein the hydrophobized granular material has a tamped density of 50 to 250 g/L.

20. The thermal insulating composition of claim 16, wherein the hydrophobized granular material has a thermal conductivity of less than 50 mW/(m*K) according to EN 12667:2001, measured in the bed, at a mean measurement temperature of 10° C., a contact pressure of 250 Pa under an air atmosphere and at standard pressure.

21. The thermal insulating composition of claim 16, wherein the hydrophobized granular material has a methanol wettability of 10 to 80% by volume methanol in a methanol/water mixture.

22. The thermal insulating composition of claim 16, wherein the hydrophobized granular material has a numerical median particle size d.sub.50 of greater than 10 μm.

23. The thermal insulating composition of claim 16, wherein the hydrophobized granular material is essentially free of particles smaller than 200 μm.

24. The thermal insulating composition of claim 16, wherein the inorganic binder is selected from the group consisting of: lime; gypsum; cements; and mixtures thereof.

25. The thermal insulating composition of claim 16, wherein the organic binder is selected from the group consisting of: (meth)acrylates; alkyd resins; epoxy resins; gum arabic, casein; vegetable oils; polyurethanes; silicone resins; wax; cellulose glue; and mixtures thereof.

26. The thermal insulating composition of claim 16, wherein the composition has a thermal conductivity of less than 100 mW/(m*K) according to EN 12667:2001, measured at a mean measurement temperature of 10° C., a contact pressure of 250 Pa under an air atmosphere and at standard pressure.

27. The thermal insulating composition of claim 17, wherein the hydrophobized granular material contains from 30% to 95% by weight of fumed silica, and from 5% to 70%, by weight of the IR opacifier.

28. The thermal insulating composition of claim 27, wherein the hydrophobized granular material has a tamped density of 50 to 250 g/L.

29. The thermal insulating composition of claim 27, wherein the hydrophobized granular material has a thermal conductivity of less than 50 mW/(m*K) according to EN 12667:2001, measured in the bed, at a mean measurement temperature of 10° C., a contact pressure of 250 Pa under an air atmosphere and at standard pressure.

30. The thermal insulating composition of claim 29, wherein the hydrophobized granular material has a methanol wettability of 10 to 80% by volume methanol in a methanol/water mixture.

31. The thermal insulating composition of claim 29, wherein the hydrophobized granular material has a numerical median particle size d.sub.50 of greater than 10 μm.

32. A process for producing the thermal insulating composition of claim 16, comprising the following steps: a) mixing a hydrophilic fumed silica with at least one IR-opacifier; b) densifying the mixture obtained in step a) to give a hydrophilic granular material; c) subjecting the hydrophilic granular material produced in step b) to thermal treatment at a temperature of 200 to 1200° C.; d) hydrophobizing the hydrophilic granular material subjected to thermal treatment in step c) with a hydrophobizing agent to obtain a hydrophobized granular material; and e) mixing the hydrophobized granular material produced in step d) with an inorganic and/or an organic binder.

33. The process of claim 32, wherein the hydrophobizing agent used in step d) is selected from the group consisting of halosilanes, alkoxysilanes, silazanes and siloxanes.

34. A process for producing the thermal insulating composition of claim 16, comprising the following steps: a) mixing a hydrophilic fumed silica with at least one IR-opacifier; b) densifying the mixture obtained in step a) to give a hydrophilic granular material; c) treating the hydrophilic granular material produced in step b) with ammonia; d) hydrophobizing the hydrophilic granular material treated with ammonia in step c) with a hydrophobizing agent to obtain a hydrophobized granular material; and e) mixing the hydrophobized granular material produced in step d) with an inorganic and/or an organic binder.

35. The process of claim 34, wherein the hydrophobizing agent used in step d) is selected from the group consisting of halosilanes, alkoxysilanes, silazanes and siloxanes.

Description

EXAMPLES

[0064] Preparation of Silica Granular Material A According to the Invention

[0065] Preparation of hydrophobized silica granular material containing IR-opacifier has been conducted according to PCT/EP2018/051142:

[0066] Mixing

[0067] 1000 F silicon carbide (Carsimet), manufacturer: Keyvest, 20% by weight, and AEROSIL® 300 hydrophilic silica (BET=300 m.sup.2/g, manufacturer: EVONIK Resource Efficiency GmbH), 80% by weight, were mixed by means of a Minox PSM 300 HN/1 MK ploughshare mixer.

[0068] Densification

[0069] The mixture of AEROSIL® 300 with silicon carbide produced above was densified with a Grenzebach densifying roll (Vacupress VP 160/220). The tamped density of the granular material obtained was adjusted via the contact pressure, the roll speed and the reduced pressure applied. The vacuum applied was less than 300 mbar, absolute. The roll speed was 5 rpm, and the pressure was 2000 N. The obtained particles were processed in an oscillating sieve mill with mesh size 3150 μm (manufacturer: FREWITT), in order to establish an upper particle limit and hence remove the particles larger than this upper limit.

[0070] Sintering/Hardening

[0071] The subsequent thermal hardening was effected in an XR 310 chamber kiln from Schröder Industrieöfen GmbH. For this purpose, multiple layers with a bed of height up to 5 cm were subjected to a temperature programme. The temperature ramp was 300 K/h up to the target temperature of 950° C.; the hold time was 3 hours; then the samples were cooled (without active cooling) until removal.

[0072] Hydrophobization

[0073] The final hydrophobization of the thermally hardened granular material was effected at elevated temperatures over the gas phase. For this purpose, hexamethyldisilazane (HMDS) as hydrophobizing agent was evaporated and conducted through by the reduced pressure process in accordance with the process from Example 1 of WO 2013/013714 A1. The specimens were heated to more than 100° C. in a desiccator and then evacuated. Subsequently, gaseous HMDS was admitted into the desiccator until the pressure had risen to 300 mbar. After the sample had been purged with air, it was removed from the desiccator.

[0074] Sieving/Fractionation

[0075] The thermally hardened granular material was fractionated in the desired particle fractions, for example from 200 to 1190 μm or from 1190 to 3150 μm. This was done using a vibrating sieve from Sweco, model LS18S. Granular material A had a tamped density of ca. 190 g/L.

[0076] Preparation of Silica Granular Material B According to the Invention

[0077] AEROSIL® 200 hydrophilic silica (BET=200 m.sup.2/g, manufacturer: EVONIK Resource Efficiency GmbH) was used instead of AEROSIL® 300 for granular material A. Otherwise, the manufacturing procedure for granular material B has been identical to that for granular material A. Granular material B had a tamped density of ca. 165 g/L.

[0078] Preparation of Silica Granular Material C (Comparative Example)

[0079] Mixing

[0080] 1000 F silicon carbide (Carsimet), manufacturer: Keyvest, 20% by weight, and AEROSIL® R 812 hydrophobic silica (produced from hydrophilic Aerosil® 300 with BET=300 m.sup.2/g, hydrophobized with HMDS, manufacturer: EVONIK Resource Efficiency GmbH), 80% by weight, were mixed by means of a Minox PSM 300 HN/1 MK ploughshare mixer.

[0081] Densification

[0082] The mixture of AEROSIL® R 812 with silicon carbide produced as described above was densified with a Grenzebach densifying roll (Vacupress VP 160/220). The tamped density of the granular material obtained was adjusted via the contact pressure, the roll speed and the reduced pressure applied. The vacuum applied was less than 300 mbar, absolute. The roll speed was 5 rpm, and the pressure was 2000 N. The obtained particles were processed in an oscillating sieve mill with mesh size 3150 μm (manufacturer: FREWITT), in order to establish an upper particle limit and hence remove the particles larger than this upper limit.

[0083] Sieving/Fractionation

[0084] The densified granular material was fractionated in the desired particle fractions, for example from 200 to 1190 μm or from 1190 to 3150 μm. This was done using a vibrating sieve from Sweco, model LS18S. Granular material C had a tamped density of ca. 165 g/L.

[0085] Preparation of Silica Granular Material D (Comparative Example)

[0086] Mixing

[0087] 1000 F silicon carbide (Carsimet), manufacturer: Keyvest, 20% by weight, and AEROSIL® R 974 hydrophobic silica (produced from hydrophilic Aerosil® 200 with BET=200 m.sup.2/g, hydrophobized with dimethyldichlorosilane, manufacturer: EVONIK Resource Efficiency GmbH), 80% by weight, were mixed by means of a Minox PSM 300 HN/1 MK ploughshare mixer.

[0088] Densification

[0089] The mixture of AEROSIL® R 974 with silicon carbide produced as described above was densified with a Grenzebach densifying roll (Vacupress VP 160/220). The tamped density of the granular material obtained was adjusted via the contact pressure, the roll speed and the reduced pressure applied. The vacuum applied was less than 300 mbar, absolute. The roll speed was 5 rpm, and the pressure was 2000 N. The obtained particles were processed in an oscillating sieve mill with mesh size 3150 μm (manufacturer: FREWITT), in order to establish an upper particle limit and hence remove the particles larger than this upper limit.

[0090] Sieving/Fractionation

[0091] The densified granular material was fractionated in the desired particle fractions, for example from 200 to 1190 μm or from 1190 to 3150 μm. This was done using a vibrating sieve from Sweco, model LS18S. Granular material D had a tamped density of ca. 230 g/L.

[0092] Determination of OH-Group Density

[0093] The hydroxyl group density was determined by the method published by J. Mathias and G. Wannemacher in Journal of Colloid and Interface Science vol. 125, pages 61-68 (1988) by reaction with lithium aluminium hydride.

[0094] The measured hydroxy group contents of granular materials A-D are summarized in Table 1 below. Using the known surface areas of granular materials, these hydroxyl group values in mmol/g can be converted into the number of OH-groups per nm.sup.2 of surface area (Table 1).

[0095] Preparation of Thermal Insulating Compositions (TIC), Determination of Maximal Loading of Granular Material in TIC.

[0096] Binder (Acronal Eco 6270, manufacturer: BASF, 276 g) was filled into a cylindrical glass vessel with 9.5 cm diameter and stirred with a propeller stirrer at 600 rpm. Granular materials (sieve fraction 200-1190 μm) were gradually added to the stirred binder, and the stirring was continued until a homogeneous mixture has been achieved, i.e. all granular material was incorporated into the mixture with a binder.

[0097] The maximum loading is determined by a gradual adding of the granular material to the binder. The granules are added until a substantial increase of viscosity is observed, which makes the incorporation of further granular material into the polymeric binder matrix impossible and the added granules remain separated from the thermal insulating composition.

[0098] Maximal loadings of granular materials A-D in TICs in % by weight, related to the total weight of wet TIC (not dried, still contains water) with granular material, are summarized in Table 1 below.

[0099] Preparation of Thermal Insulating Compositions (TICs) and Determination of Their Thermal Conductivity.

[0100] Binder (267 g Acronal Eco 6270, manufacturer: BASF) was filled into a cylindrical glass vessel with 9.5 cm diameter and stirred with a propeller stirrer at 600 rpm. Granules (33 g, sieve fraction 200-1190 μm) were gradually added to the stirred binder, and the stirring was continued until a homogeneous mixture has been achieved, i.e. all the granules were incorporated into the mixture with a binder.

[0101] The formulation is filled in a frame to obtain an approximately 1 cm thick wet TIC. The TIC is pre-dried for 48 hours under ambient conditions and for 24 hours at 80° C. in an oven to remove all remaining water of binder. The dry TIC is flattened by a mortising machine to obtain an even surface for the thermal conductivity measurement. The thermal conductivity was measured according to EN 12667:2001 by the method with the hot plate and the heat flow meter instrument. The mean measurement temperature is 10° C. and the contact pressure 250 Pa; the measurement was conducted under air atmosphere at standard pressure.

[0102] Thermal conductivities of granules A-D of dry TICs with a loading level of 11% by weight, related to the total wet weight of TIC with granules, are summarized in Table 1 below.

TABLE-US-00001 TABLE 1 Hydroxyl-group content, BET surface area, number pro surface area, maximal loadings of granular material in TICs and thermal conductivity of TICs. Thermal conductivity of TICs containing Maximal loading of 11 wt. % of granular granular material in material related to OH-groups OH-groups number BET TICs [wt. % related to total weight of wet content pro surface area surface area total weight of wet TIC TIC with granular [mmol OH/g] [number/nm.sup.2] [m.sup.2/g] with granular material] material [mW/(mK)] Granular 0.04 0.158 152 22.2 82 material A Granular 0.09 0.475 114 20.5 89 material B Granular 0.13 0.455 172 15.2 113 material C Granular 0.22 1.027 129 17.5 111 material D

[0103] Granular material A, possessing significantly lower OH-groups content than granular material C (both with comparable BET surface areas of 152 and 172 m.sup.2/g, respectively), shows higher maximal loading of granular material in the respective thermal insulation coating (22.2 vs 15.2% by weight). Granular material B, possessing significantly lower OH-groups content than granular material D (both with comparable BET surface areas of 114 and 129 m.sup.2/g, respectively), in turn shows higher maximal loading of granular material in the respective thermal insulation coating (20.5 vs 17.5% by weight). Both granular materials A and B show significantly lower values of thermal conductivity (82 and 89 mW/(mK), respectively), than granular materials C and D (113 and 111 mW/(mK), respectively) in similar TICs with 11% by weight content of the granules.

[0104] Viscosity Measurement

[0105] A rotational viscometer Brookfield DV2T Extra was used to conduct measurements of the dynamic viscosity of the formulations (mixture of binder and granular material). Spindles and rotational velocity were chosen according to the given viscosity range in the manual.

[0106] General Experiment Description for Measuring Viscosity of Compositions with Granular Materials after Various Storage Times

[0107] Preparation of the Formulations:

[0108] Binder (Acronal Eco 6270, manufacturer: BASF, 276 g) was filled into a cylindrical glass vessel with 9.5 cm diameter and stirred with a propeller stirrer at 600 rpm. Granular materials (24 g, sieve fraction 200-1190 μm) were gradually added to the stirred binder, and the stirring was continued until a homogeneous mixture has been achieved, i.e. all the granular material were incorporated into the mixture with a binder.

[0109] Measurements:

[0110] The dynamic viscosity of all samples was measured immediately after their preparation. The samples were closed with an impermeable lid and additionally sealed with a Parafilm M foil. The thus closed samples were stored at room temperatures (25° C.) without stirring, opened after defined time of storage for a measurement of the dynamic viscosity, as previously described, and closed again for further storage. For three weeks, all samples were measured twice a week to observe their thickening behaviour.

TABLE-US-00002 TABLE 2 Viscosity of TICs with granular materials A and B over the time Granular Storage time [days] Example material 0 4 7 12 15 19 22 Viscosity [Poise] Example 1 A 27 154 209 490  528  595 2112 Example 2 B 26 539 696 667 2864 3136 3872

[0111] The results of the viscosity measurements after various storage time are summarized in Table 2. These results show that the compositions with granular materials A and B are both stable at testing conditions, wherein the granular material A with the higher BET surface area (152 m.sup.2/g vs 114 m.sup.2/g for the granular material B) leads to lower viscosity of TIC than granular material B after the same storage time.