WO2000024799A1 - Insulated bodies - Google Patents

Abstract

Method for making an insulated body such as an appliance cabinet or door comprising the steps of a) mixing an organic polyisocyanate and an isocyanate trimerisation catalyst and optionally a (co)polymer containing at least one isocyanate-reactive group in a suitable solvent, b) injecting this mixture in a body or mould that will give rise to the final insulating body, c) maintaining said mixture in a quiescent state for a sufficiently long period of time to form a polymeric gel, and d) drying the obtained gel.

Description

DESCRIPTION

INSULATED BODIES

The present invention relates to polyisocyanate based aerogel or aerogel-like materials and to methods for making an insulated body thereof.

Aerogels are a unique class of ultra fine cell size, low density, open-celled foams. Aerogels have continuous porosity and their microstructure with pore sizes below the free mean path of air (pore sizes in the nanometer range) is responsible for their unusual thermal properties.

More in depth understanding of the aerogel texture and terminology can be found in the following references: D. Schaefer, "Structure of mesoporous aerogels", MRS Bulletin, April 1994, p. 49-53; R.W. Pekala, D.W. Schaefer, "Structure of organic aerogels. 1. Morphology and Scaling", Macromolecules 1993, 26, p. 5487-5493; M. Foret, A. Chougrani, R. Vacker, J. Pelous, "From colloidal-silica sols to aerogels and xerogels", Journal de Physique IV, Colloque C2, supplement au Journal de Physique III, Volume 2, October 1992, p. 135-139; R.W. Pekala, C.T. Alviso, "Carbon aerogels and xerogels", Mat. Res. Soc. Symp. Proc. Vol. 270, 1992, p. 9; Journal ofNon Crystalline Solids, Vol. 186, June 2 1995, Chapter 1.

Organic aerogels based on polyisocyanate chemistry are described in WO 95/03358, WO 96/36654, WO 96/37539, WO 98/44013 and WO 98/44028.

They are prepared by mixing a polyisocyanate and a catalyst and optionally a polyfunctional isocyanate- reactive compound in a suitable solvent and maintaining said mixture in a quiescent state for a sufficiently long period of time to form a polymeric gel. The gel so formed is then dried.

Aerogels are commonly dried using a supercritical drying process. These processes require high pressures and temperatures when organic solvents are used to form the aerogel. Alternatively lower temperatures but still high pressure equipment can be used if the organic solvents are exchanged for liquefied gasses such as, for instance, CO2 or propane. Alternatively to supercritical drying a conventional drying method can be employed. Other suitable drying techniques are vacuum drainage, vacuum evaporation, convective air drying, freeze drying, microwave or radiofrequency drying or any combination of the above.

Aerogel or aerogel-like materials have been described to make insulated bodies, see, for instance, US 5765379. However one disadvantage of this method is the lack of structural integrity of these highly efficient insulation materials. Especially silica based aerogel or aerogel-like materials are known for their brittle behaviour and lack of shock or impact resistance, be it in powder, granular or monolith form. Conventional closed celled polyurethane foams are known to give structural integrity to an insulating box but do not exhibit the excellent thermal performance reported for aerogel or aerogel-like materials. These foams may also contain blowing agents which have a non-zero ozone depletion potential, present a fire hazard and have volatile organic content contributions. Alternatively open celled foams have been described to make such insulating boxes which are then evacuated to achieve the good thermal performance whilst maintaining the structural integrity of the insulating body. The disadvantage of these open celled foams is the need for extremely low pressures (general below 1 mbar) to achieve the desired thermal performance which imposes severe restrictions on the selection of materials for the inner and outer box material and the evacuation equipment.

The present invention describes the use of aerogel or aerogel-like materials to make insulated bodies in a one-shot approach. This offers the advantage of good thermal insulation values (less than 10 mW/mK) at a pressure below 100 mbar, whilst maintaining structural integrity of the insulation box and not containing blowing agents which may have a negative impact on the environment. The insulated body based on aerogel or aerogel-like materials may be filled with gasses occurring in nature. Examples of such gasses include nitrogen, carbon dioxide, hydrogen, helium, neon, argon, xenon, krypton and radon.

Densities of the aerogel or aerogel-like materials used in the present invention are generally in the range 1 to 1000 kg/m3, more generally in the range 10 to 800 kg/m3 and even more generally in the range 20 to 400 kg/m3 or even 30 to 300 kg/ ^.

The aerogel or aerogel-like materials used in the present invention generally have pore sizes in the range 1 to 300 nm, more generally in the range 5 to 50 nm and even more generally in the range 5 to 25 nm. Surface areas of the aerogel or aerogel-like materials used in the present invention are generally in the range 0.05 to 800 m2/g, more generally in the range 0.2 to 500 m2/g.

Accordingly, the present invention provides a method for making an insulated body comprising the steps of a) mixing an organic polyisocyanate and an isocyanate trimerisation catalyst and optionally a (co)polymer containing at least one isocyanate-reactive group in a suitable solvent, b) injecting this mixture in a body or mould that will give rise to the final insulating body, c) maintaining said mixture in a quiescent state at room temperature or elevated temperature for a sufficiently long period of time to form a polymeric gel, and d) drying the obtained gel.

Polyisocyanates for use in the present invention include aliphatic, cycloaliphatic, araliphatic and aromatic polyisocyanates known in the literature for use generally in the production of polyurethane/polyisocyanurate materials. Of particular importance are aromatic polyisocyanates such as tolylene and diphenylmethane diisocyanate in the well known pure, modified and crude forms, in particular diphenylmethane diisocyanate (MDI) in the form of its 2,4'-, 2,2'- and 4,4'-isomers (pure MDI) and mixtures thereof known in the art as "crude" or polymeric MDI (polymethylene polyphenylene polyisocyanates) having an isocyanate functionality of greater than 2 and the so-called MDI variants (MDI modified by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine or isocyanurate residues).

The polyisocyanate is used in amounts ranging from 0.5 to 30 % by weight, preferably from 1.5 to 20 % by weight and more preferably from 3 to 15 % by weight based on the total reaction mixture. Trimerisation catalysts for use in the present preparation method include any isocyanate trimerisation catalyst known in the art such as quaternary ammonium hydroxides, alkali metal and alkaline earth metal hydroxides, alkoxides and carboxylates, for example potassium acetate and potassium 2-ethylhexoate, certain tertiary amines and non-basic metal carboxylates, for example lead octoate, and symmetrical triazine derivatives. Specific preferred trimerisation catalysts for use in the present method are Polycat 41 available from Abbott Laboratories, and DABCO TMR, TMR-2, TMR-4 and T 45 available from Air Products, and potassium salts such as potassium octoate, potassium hexanoate, potassium 2-ethyl hexanoate and potassium acetate.

Another class of catalysts that can be used in addition to the trimerisation catalysts are the conventionally known catalysts in the polyurethane industry that catalyse the formation of amines, urethane, uretidione and carbodiimide groups. Specific examples include aliphatic and aromatic tertiary amines, for example, N,N- dimethylcyclohexylamine; alkanolamines; organo-metallic compounds, especially tin compounds, for example, dibutyltin dilaurate; trialkylphosphines and dialkylarylphosphines; phospholine oxides. Combinations of the above catalysts may be used as well.

The polyisocyanate/catalyst weight ratio varies between 5 and 1000, preferably between 5 and 500, most preferably between 10 and 200.

The preferred polyisocyanate/catalyst weight ratio depends on the amount of polyisocyanate used, the reaction/cure temperature, the solvent used, additives used.

The solvent to be used in the method according to the present invention should be a solvent for the monomeric (non-reacted) polyisocyanate as well as for the polymeric (reacted) polyisocyanate. The solvent power should be such as to form a homogeneous solution of non-reacted compounds and to dissolve the reaction product or at least prevent flocculation of the reaction product. Solvents with a solubility parameter between 0 and 18 MPa¹^ and a hydrogen bonding parameter H between 0 and 15 MPa'/² are most suitable.

Suitable solvents for use in the method according to the present invention include hydrocarbons, dialkyl ethers, cyclic ethers, ketones, alkyl alkanoates, aliphatic and cycloaliphatic hydrofluorocarbons, hydrochlorofluorocarbons, chlorofluorocarbons, hydrochlorocarbons, halogenated aromatics and fluorine- containing ethers. Mixtures of such compounds can also be used.

Suitable hydrocarbon solvents include lower aliphatic or cyclic hydrocarbons such as ethane, propane, n- butane, isobutane, n-pentane, isopentane, cyclopentane, neopentane, hexane and cyclohexane.

Suitable dialkyl ethers to be used as solvent include compounds having from 2 to 6 carbon atoms. As examples of suitable ethers there may be mentioned dimethyl ether, methyl ethyl ether, diethyl ether, methyl propyl ether, methyl isopropyl ether, ethyl propyl ether, ethyl isopropyl ether, dipropyi ether, propyl isopropyl ether, diisopropyl ether, methyl butyl ether, methyl isobutyl ether, methyl t-butyl ether, ethyl butyl ether, ethyl isobutyl ether and ethyl t-butyl ether.

Suitable cyclic ethers include tetrahydrofuran.

Suitable dialkyl ketones to be used as solvent include acetone, cyclohexanone, methyl t-butyl ketone and methyl ethyl ketone.

Suitable alky] alkanoates which may be used as solvent include methyl formate, methyl acetate, ethyl formate, butylacetate and ethyl acetate.

Suitable hydrofluorocarbons which may be used as solvent include lower hydrofluoroalkanes, for example difluoromethane, 1,2-difluoroethane, 1,1,1,4,4,4-hexafluorobutane, pentafluoroethane, 1,1,1,2- tetrafluoroethane, 1,1,2,2-tetrafluoroethane, pentafluorobutane and its isomers, tetrafluoropropane and its isomers and pentafluoropropane and its isomers. Substantially fluorinated or perfluorinated (cyclo)alkanes having 2 to 10 carbon atoms can also be used.

Suitable hydrochlorofluorocarbons which may be used as solvent include chlorodifluoromethane, 1,1- dichloro-2,2,2-trifluoroethane, 1 , 1 -dichloro- 1 -fluoroethane, 1 -chloro-1 , 1 -difluoroethane, 1 -chloro-2- fluoroethane and 1,1,1 ,2-tetrafluoro-2-chloroethane.

Suitable chlorofluorocarbons which may be used as solvent include trichlorofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane and tetrafluorodichloroethane.

Suitable hydrochlorocarbons which may be used as solvent include 1- and 2-chloropropane and dichloromethane.

Suitable halogenated aromatics include monochlorobenzene and dichlorobenzene.

Suitable fluorine-containing ethers which may be used as solvent include bis-(trifluoromethyl) ether, trifluoromethyl difluoromethyl ether, methyl fluoromethyl ether, methyl trifluoromethyl ether, bis- (difluoromethyl) ether, fluoromethyl difluoromethyl ether, methyl difluoromethyl ether, bis-(fluoromethyl) ether, 2,2,2-trifluoroethyl difluoromethyl ether, pentafluoroethyl trifluoromethyl ether, pentafluoroethyl difluoromethyl ether, 1,1 , 2,2 -tetrafluoroethyl difluoromethyl ether, 1,2,2,2- tetrafluoroethyl fluoromethyl ether, 1 ,2,2-trifluoroethyl difluoromethyl ether, 1,1-difluoroethyl methyl ether, 1,1,1 ,3,3,3-hexafluoroprop- 2-yl fluoromethyl ether.

Preferred solvents for use in the method according to the present invention are dichloromethane, methyl ethyl ketone, acetone, tetrahydrofuran, monochlorobenzene, trichlorofluoromethane (CFC 1 1), chlorodifluoromethane (HCFC 22), l,l,l-trifluoro-2-fluoroethane (HFC 134a), 1,1-dichloro-l-fluoroefhane (HCFC 141b) and mixtures thereof such as HCFC 141b/CFC 11 mixtures, 1,1,1,3,3-pentafluoropropane (HFC 245fa), 1 ,2-difluoroethane (HFC 152), difluoromethane (HFC 32) and 1,1,1,3,3-pentafluorobutane (HFC 365mfc).

Another suitable solvent is liquid carbon dioxide (CO2). Liquid carbon dioxide may be used under various pressures (above 63 bar) and temperatures. Also sub- or supercritical carbon dioxide can be used as a solvent. The solvent power of sub- or supercritical carbon dioxide can be adjusted by adding suitable modifiers such as lower alkanes (C1-C4), methanol, ethanol, acetone, HCFC 22, dichloromethane in levels of 0.1 to 50 % by volume.

In case liquid carbon dioxide is used as solvent it has been shown to be an advantage to use as polyisocyanate in the preparation of the present aerogels a fluorinated isocyanate-ended prepolymer made from a polyisocyanate and a fluorinated isocyanate-reactive compound such as a fluorinated monol or diol. Alternatively sub- or supercritical hydrofluorocarbons may be used as sole solvent or admixed with CO2.

The isocyanate-reactive group present in the (co)polymer is an OH, COOH, NH2 or NHR group, preferably an OH group.

Examples of suitable classes of (co)polymers are polyacrylates, polystyrenics, polyketones, bisphenol A resins, hydrocarbon resins, polyesters, polyaldehyde-keton resins, resols, novolaks, neutral phenolic resins, polymethacrylates, polyacrylonitrile, polyvinylacetate, PET derivatives, polyamides, cellulose, polyethers, modified polyethylene and polypropylene, polybutadienes and alkyd resins.

A particularly preferred class of (co)polymers are those derived from ethylenically unsaturated monomers; preferred are styrene, acrylic acid and acrylic acid ester derivatives such as methylacrylate esters, hydroxyacrylate esters and partially fluorinated acrylate esters.

Another preferred class of (co)polymers are those obtained by condensation of aldehydes (preferably formaldehyde) and/or ketones such as phenolic resins, particularly neutral phenolic resins, polyaldehyde- keton resins, polyketones, novolaks and resols.

Preferably the (co)polymer has an OH value of between 30 and 800 mg KOH g, preferably between 100 and 500 mg KOH g and a glass transition temperature of between -50 and 150°C, preferably between 0 and 80°C. The molecular weight of the (co)polymer is preferably between 500 and 10000, more preferably between 4000 and 6000. The (co)polymer has preferably a melt range of 60 to 160°C. Optimal results are generally obtained when the aromaticity of the (co)polymer is at least 15 %; the aromaticity being calculated as 7200 x number of aromatic moieties in the polymer / number average molecular weight.

Preferred (co)polymers are copolymers of styrene and hydroxyacrylate and optionally also acrylate. Such copolymers are commercially available, for example, Reactol 180, Reactol 255 and Reactol 100 (all available from Lawter International).

Other preferred (co)polymers which are commercially available from Lawter International are K 1717 (a polyketone), Biresol (a bisphenol A resin ), K 2090 (a polyester), K 1717B (an aldehyde-keton resin) and K 1 1 1 1 (a neutral phenolic resin).

The (co)polymers are used preferably in such an amount that the ratio between functional groups in the polyisocyanate (NCO) and in the (co)ρolymer (OH) is between 1:1 and 100:1, preferably between 2:1 and 25: 1. In absence of the (co)polymers the ratio can be defined as infinite.

A solution is made of the polyisocyanate, the (co)polymer, and the solvent. Subsequently the catalyst is added hereto. Alternatively the polyisocyanate and the (co)polymer are dissolved in a marginal part of the solvent; subsequently a solution of the catalyst in the residual amount of solvent is added hereto. Mixing can be done at room temperature or at somewhat higher temperatures.

In case of low boiling solvents (boiling point below room temperature), for example HCFC 22, the solvent containing the catalyst is added to a pressure vessel containing the polyisocyanate and the (co)polymer under its own vapour pressure.

The solids content of the reaction mixture is preferably between 2 and 30 % by weight, more preferably between 4 and 20 % by weight, most preferably between 5 and 15 % by weight.

In the present invention separate stock solutions of polyisocyanate, optionally (co)polymer and catalyst can be prepared in marginal parts of the solvent.

It is also possible to make one stock solution of polyisocyanate and (co)polymer or (co)polymer and catalyst. The latter is particularly useful as it can lead to faster gelation.

These stock solutions are then mixed and poured into the shape or mould which contains the form of the insulated body.

This body may, for instance, be - but is not limited to - a refrigerator cabinet or door made of an inner and outer box or a freezer cabinet or door or a water heater. Another preferred application is the manufacture of insulation panels which can be used in the construction industry for new buildings or for building improvement and/or renovation constructions. Another application could be panels for insulated transportation. Yet another application could be pre-insulated pipes consisting of a metal inner-(transport) pipe and a jacket pipe with a thermal insulation barrier between the two pipes; the aerogel reaction mixture is then injected into the annular cavity between the inner steel pipe and the jacket.

The selection of material for the inner and outer box is depending on the end use envisaged and the solvents employed. Alternatively a solvent different from those listed above may be selected so as to be compatible with the materials of the inner and outer box. Typical materials for inner and/or outer box are metal or metal alloys, aluminium coated or uncoated, polycarbonate, polymefhylacrylate, polyacrylate, polystryrene, acrylonitrile, polyethylene, polypropylene, polyvinylchloride, high impact polystyrene, ABS or any other thermoformed, blow moulded or thermoset plastic. The inner and/or outer box may also be a composite material of any of the above materials.

Depending on the envisaged end use the inner and or outer box may be coated with mould release agents such as, for instance, those based on terpentine or on polyethylene waxes.

The inner and/or outer box may also be coated or surface treated, such as corona treated, in order to increase the adhesion between the aerogel forming material and the inner and/or outer box.

The pouring of the reaction mixture into the mould is done in such a way that the desired stoichiometry of reactants is obtained and that the total cavity is filled prior to the onset of the gelation reaction. This onset can under certain conditions be observed by the formation of a haziness or turbidity in the solution.

In order to avoid entrapment of air in the insulated body or in the gel forming mixture anti-foaming agents may be added to the solution in a concentration of from 0.01 to 10 wt%. Examples of such anti-foaming agents include, for example, polydimethylsiloxane surfactants or surfactants as commonly used by the oil drilling industry.

It is also possible to de-aerate the solvents prior to use by exposing them to a moderate vacuum whilst keeping the solution refrigerated.

The position of the mould should be such that air is able to escape from within the box while the liquids are poured in the cavity formed between the inner and the outer box.

Another method to add the reaction mixture and remove air bubbles from within the gelating mixture is the use of ultrasound waves or application of vibrating plates on which the assembly rests.

The mixture is left standing in the cavity for a certain period of time to form a polymeric gel. This time period varies from 10 seconds to several weeks depending on the system and the targeted void size and density. Reaction mixtures of the present invention containing the (co)polymer form a sol-gel quicker than those not containing said (co)polymer. In general gelation is obtained in less than one hour. Temperatures in the range of from about -50 to about 50°C, preferably from 0 to 45°C may be employed. In the case of low boiling solvents such as HCFC 22 the pressure in the closed vessel is maintained at its saturated vapour pressure and the gelation reaction is carried out at higher temperatures (preferably in the range 30 to 50°C).

A post cure cycle at elevated temperatures can be included. In case the cure temperature is above the boiling point of the solvent selected the whole assembly of inner and outer box containing the sol-gel must be put in a sealed pressure vessel as is the case when solvents with a boiling point below ambient conditions are used (for instance HCFC 22).

In order to shorten the total process time microwave or radio frequency waves can be used to heat the sol- gel. Alternatively the curing can be accelerated by employing conventional heating to a closed, optionally pressurised, container.

In order to further improve the structural integrity and the handling of the final insulated body a reinforcement material can be incorporated in the sol-gel process, preferably in an amount of between 0.05 and 30 % by weight. Examples of suitable reinforcement materials include glass fibre, glass mat, felt, glass wool, carbon fibre, boron fibre, ceramic fibre, rayon fibre, nylon fibre, olefin fibre, alumina fibre, asbestos fibre, zirconia fibre, alumina, clay, mica, silicas, calcium carbonate, talc, zinc oxide, barium sulfates, wood and shell floor, polystyrene.

Alternatively woven fibres or mats can be used at the bottom and/or top of the mould in which the monolith is cast to give structural strength. An example of such a woven fibre is Ty vec (available from Dupont).

Further suitable additives to be used in the process of the present invention and further suitable processing methods are described in WO 95/03358, WO 96/36654, WO 96/37539, WO 98/44013 and WO 98/44028, all incorporated herein by reference.

The aerogel can be used in its pure form or mixed with other additives such as opacifiers, antistatic agents, colorants, pigments, carbon blacks and lubricants.

After formation of the solid sol-gel and possible cure thereof the solvent needs to be removed. This can be done via a supercritical drying route as commonly employed for making aerogels or via conventional drying techniques. For this aspect in the design of the mould or case it is important to foresee a surface as large as possible for evaporation. This can, for instance, be achieved for a refrigerator box by ensuring to leave the back part open and design the inner and outer box assembly such that the box is positioned on the edges with the future back or bottom of the appliance facing upwards. For metal panels this can be done by leaving one of the long sides open and casting on a vertical standing panel rather than in a horizontal situated panel. These are some examples but should not be seen as limiting the invention. The solid assembly can be turned around, for instance, after gelation to be put on a vacuum suction grid which would facilitate the removal of the solvent by, for instance, vacuum drainage and/or vacuum drying. Alternatively the assembly may be heated via radiative heating, convective air heating, radiofrequency heating or microwave heating to evaporate off or to expel the solvent. One preferred way of drying is the combination of vacuum and microwave heating which leads to extremely short drying times. Another possible process is freeze drying or a combination of freeze drying with microwave heating. Following the removal of the solvent the assembly may be optionally evacuated and/or sealed and/or re- filled with natural occurring gasses.

One particular advantage of the present invention over the use of open or closed celled foams as a core material for insulated bodies is the low viscosity of the starting liquids which allow them to flow over and through complex shapes without disturbance of the final structure or the introduction of density fluctuations over the whole assembly. This is particularly useful for refrigerators and freezers where commonly the cooling coils and steering equipment is situated inbetween the inner and outer box hence introducing flow restrictions.

The need for these cooling coils can be advantageous for the solvent removal provided a microporous coil is used while the sol-gel is made and cured. By applying a vacuum on this coil solvent can be drained away from the complex shape more rapidly. After complete solvent removal this coil can then be filled with a gas tight coil of slightly smaller diameter which can be connected to the cooling circuit.

The present invention is illustrated but not limited by the following examples in which the following ingredients were used:

Reactol 180: a (hydroxy)acrylate/styrene copolymer available from Lawter International, having an OH value of 180 mg KOH/g.

SUPRASEC DNR: a polymeric isocyanate available from Huntsman Polyurethanes.

DABCO TMR: a trimerisation catalyst available from Air Products.

Polycat P 41 : a catalyst available from Air Products acetone: Rathburn-glass distilled grade.

VP 70551 : a terpentine-based mould release agent available from KVS Eckert & Woelk.

SUPRASEC is a trademark of Huntsman ICI Chemicals LLC.

EXAMPLE 1

A three dimensionally shaped insulated body was prepared from the following solutions: (i) a hydroxyl functional solution made by dissolving 0.7 kg of Reactol 180 in 5 kg of technical grade acetone, (ii) an isocyanate solution based on 2.14 kg of SUPRASEC DNR in 6 kg of acetone and (iii) a catalyst solution made from 35,7 g of DABCO TMR and 35,7 g of Polycat 41 in 1 kg of acetone.

The mould for the insulated body was made from a polyethylene box of dimensions 0.8 m by 0.4 m by 0.5 m internal diameter in which a second polyethylene box with outer dimensions of 0.75 m by 0.45 m by 0.45 m was fixed in place in such a manner that an open space was left on all sides and at the bottom. The internal volume of this box was approximately 30 1. 7.79 kg of technical grade acetone was added beforehand to the three dimensional polyethylene mould. Prior to the polymerisation process, the catalyst solution (solution iii) was blended into the hydroxyl functional solution (i). The polyol (solution i) and the isocyanate solution (solution ii) were mixed during the filling of the mould . After a cure period of 6 hours at ambient conditions the inner polyethylene box was removed and the remaining sol-gel in the outer polyethylene box was left to stand. The sol-gel was dried by natural convection.

The resulting aerogel had the following characteristics: an average pore size of 274 nm, a specific surface area of 6.84 g/m2 and an average density of 143 ± 5 kg/m^.

The thermal conductivity of this material was 8 mW/mK at a pressure below 20 mbar.

EXAMPLE 2

Mould release agent VP 70551 was used to coat the inner walls of polyethylene bottles. This would make it easier to remove the sol-gel from the recipient and additionally provide smooth edges on the dried specimen.

Two separate solutions were prepared: (i) a hydroxyl functional/catalyst solution by dissolving 6.99 g of

Reactol 180 in 120 g of technical grade acetone; after complete dissolution of the Reactol 180 0.53 g

DABCO TMR and 0.53 g of Polycat 41 were added via a micro syringe; (ii) an isocyanate solution by dissolving 21.25 g of SUPRASEC DNR in 51.55 g of acetone.

Both the polyol and the isocyanate solution were poured into the polyethylene bottle (6 cm diameter, 18 cm length) while ensuring a continuous mixing of both chemical streams. After a cure period of 3 hours at

45°C the sol-gel was first submitted to a vacuum drainage at modest vacuum (±500 mbar) to remove the first excess of acetone. Subsequently the solgel was removed from its recipient and dried by natural evaporation at ambient conditions to obtain the complete dried specimen with a density of 155 kg/m3 and very smooth surface finish. The mould release has eased the removal of the aerogel from the polyethylene bottle.

EXAMPLE 3

A metal mould was made with dimensions of 10 cm width, 20 cm length, 2 cm height. This mould was coated with the VP 70551 mould release agent.

Two separate solutions were prepared: (i) a hydroxyl functional/catalyst solution by dissolving 7.05 g of Reactol 180 in 180 g of technical grade acetone; to this solution 0.271 g of DABCO TMR and 0.271 g of Polycat 41 were added via a micro syringe; (ii) an isocyanate solution by dissolving 21.7 g of SUPRASEC DNR in 30.65 g of acetone.

Both the polyol and the isocyanate solution were poured into the small mould while ensuring a continuous mixing of both chemical streams. After a cure period of 3 hours at 45°C the sol-gel was dried. For this process the mould back cover was replaced by a metal grid connected to a vacuum suction port. The sol-gel was first submitted to a vacuum drainage at modest vacuum (±500 mbar) to remove the first excess of acetone (9%). This drainage was then followed by natural evaporation at ambient conditions to obtain the complete dried specimen. The density of this insulation body was on average 200 ± 8 kg/m^ . The thermal conductivity of the insulation body as a function of pressure is given in Figure 1.

Claims

1. Method for making an insulated body comprising the steps of a) mixing an organic polyisocyanate and an isocyanate trimerisation catalyst and optionally a (co)polymer containing at least one isocyanate- reactive group in a suitable solvent, b) injecting this mixture in a body or mould that will give rise to the final insulating body, c) maintaining said mixture in a quiescent state for a sufficiently long period of time to form a polymeric gel, and d) drying the obtained gel.

2. Method according to claim 1 wherein the organic polyisocyanate is diphenylmethane diisocyanate or polymethylene polyphenylene polyisocyanate.

3. Method according to claim 1 or 2 wherein the organic polyisocyanate is used in an amount of between 0.5 and 30 % by weight based on the total reaction mixture.

4. Method according to any one of the preceding claims wherein the trimerisation catalyst is a potassium salt of a carboxylate.

5. Method according to any one of the preceding claims wherein the polyisocyanate/catalyst weight ratio varies between 5 and 1000.

6. Method according to any one of the preceding claims wherein the solvent is acetone.

7. Method according to any one of the preceding claims wherein the isocyanate-reactive group present in the (co)polymer is an OH group.

8. Method according to claim 7 wherein the (co)polymer is a copolymer of styrene and hydroxyacrylate and optionally also acrylate or a (co)polymer obtained by the condensation of aldehydes and/or ketones.

9. Method according to any one of the preceding claims wherein the (co)polymer is used in such an amount that the ratio between functional groups in the polyisocyanate and in the (co)polymer is between 8: 1 and 100: 1.

10. Method according to any one of the preceding claims wherein the solids content of the reaction mixture is between 2 and 30 % by weight.

1 1. Method according to any one of the preceding claims wherein the insulated body is a refrigerator or a freezer or a water heater.

12. Method according to any one of the preceding claims wherein the mould is first coated with a mould release agent.

13. Method according to claim 12 wherein the mould release agent is a terpentine-based mould release agent.

14. Method according to any one of the preceding claims wherein the drying step d) involves vacuum and/or microwave heating.