GB2286234A - Evacuated insulation panel - Google Patents

Abstract

Evacuated insulation panel such as for a refrigerator comprises a core of open celled organic foamed insulating material enveloped in a vessel of low gas permeability, wherein the core comprises alternate layers of open celled foamed material and infrared blocking interlayers. The infrared blocking interlayers may consist of a plastics substrate coated with or containing an infared blocking substance, such as a polyester vacuum metallised with aluminium, or may simply be a thin metal sheet. The open celled foamed material may comprise open celled rigid polyurethane or urethane-modified polyisocyanurate foam.

Description

DESCRIPTION This invention relates to evacuated insulation panels and in particular to evacuated insulation panels filled with open celled foamed material.

Evacuated insulation panels having a reduced internal pressure are known for various uses including use in refrigeration appliances where they greatly enhance the degree of thermal insulation within the cabinet of the appliance.

Such evacuated insulation panels generally comprise a low thermal conductivity filler material and a vessel formed of a gastight film enveloping said filler, the whole being evacuated to an internal pressure of about 5 mbar or less and then hermetically sealed. Besides insulation the filler has also the function of supporting the skin of the vessel so that it does not collapse when it is evacuated.

Known filler materials for use in such evacuated insulation panels include finely divided inorganic powders such as fumed silica, silica dust, precipitated silica, precipitated silica/fly ash mixtures, alumina, fine perlite and fiberglass. It has also been proposed, in Japanese Patent Application Kokai No. 133870/82, to use organic foamed materials having open cells as the core material in evacuated insulation panels, for example, open celled rigid polyurethane foam (see European Patent Publications Nos 0 498 628 and 0 188 806).

An important feature for such an evacuated insulation panel is the pressure level to which the vessel needs to be evacuated in order to reach an acceptable thermal insulation value. Another important feature is the extent of increase in thermal conductivity with increasing internal pressure. Both of these features are dependent for a great deal on the type of filler used in the evacuated insulation panel.

Therefore evacuated insulation panels filled with open celled foamed materials should have a thermal conductivity as low as possible at pressures of between 1 and 10 mbar. Thermal conductivities should be below 10 mW/mOK at these pressure levels.

It is an object of the present invention to provide evacuated insulation panels filled with open celled foamed materials, especially open celled rigid polyurethane foam, showing improved thermal insulation properties over the known evacuated insulation panels filled with open celled foamed materials.

The present invention provides an evacuated insulation panel comprising a core of open celled organic foamed insulating material enveloped in a vessel of low gas permeability, characterised in that the core comprises alternate layers of open celled foamed material and infrared blocking interlayers.

The evacuated insulation panels of the present invention show substantially improved thermal insulation properties compared to the known evacuated insulation panels of the prior art filled with open celled foamed materials but not containing infrared blocking interlayers.

By infrared blocking interlayers as used herein is meant layers that block (by absorption, scatter or reflection) strongly (at least 50 % on average) electromagnetic radiation in the wavelength range 103 to 10-6 m.

Especially preferred infrared blocking interlayers for use in evacuated insulation panels of the present invention are interlayers blocking on average at least 50 %, preferably at least 75 % and more preferably at least 90 % of electromagnetic radiation in the wavelength range 2 to 50 micron, preferably in the wavelength range 5 to 40 micron, most preferably in the wavelength range 6 to 20 micron.

According to one embodiment of the present invention the infrared blocking interlayers for use in the present evacuated insulation panels consist of a plastics substrate coated with or containing an infrared blocking substance.

Examples of the polymers for the interlayer substrate include polyester, polypropylene, polyethylene (low density or high density), polyacrylonitrile and polyvinylidenechloride. Of these preference is given to polyester, polypropylene and high density polyethylene.

The thickness of these plastic substrates is usually in the order of 10 to 200 micron and preferably 20 to 100 micron.

The infrared blocking substance can be compounded into the bulk of the polymer material or applied as a coating on the plastic substrate.

If applied as a coating the coating thickness will depend on the activity of the infrared blocking substance itself and on the application technique.

Coatings may be applied i.a. by spray coating, printing and in the case of metal coatings by vacuum metallisation, electroless plating or electrolytic plating. An overview of various metallisation techniques is given in "Plastics Engineering Handbook of the Society of the Plastics Industry, Inc.", fourth edition, edited by Joel Frados, Van Nostrand Reinhold Company, pages 742 to 752.

In the case of metal coatings the thickness may vary between 0.1 to 10 micron (for printed metal layers) and 50 to 1000 Angstrom, preferably 50 to 400 Angstrom (for vacuum metallised films).

In the case of non-metallic coatings the coating thickness may vary between 0.1 and 10 micron.

Common metals to be used as infrared blocking substance in the interlayers of the present evacuated insulation panels (usually applied as coatings) include aluminium, gold, silver, copper, bronze, brass, tin and lead. Preference is given to aluminium.

Examples of other suitable infrared blocking substances for use in the interlayers of the present evacuated insulation panels include carbon black, TiO2, iron oxides such as Fe2Q and Fe3O4, CrxFe2x (x = 0.3 to 2), mica, talc, BeO, Awl2 03, Cur303, My203, MnO2, ZrO2, FeTiO3, MgAl2O4, CoAl204, hydrated oxides such as FeO(OH), aluminum silicate, aluminates such as lithium aluminate, borides such as tungsten boride, borates and perborates such as sodium tetraborate, carbides such as boron carbide, carbonates and bicarbonates such as nickel carbonate, silicides such as zirconium silicide, silicates and mixed silicates with alumina etc. such as kaolin clay, titanates such as nickel titanate, zirconates such as strontium zirconate, stannates such as cerium stannate, nitrates such as aluminium nitrate, cerates such as magnesium hexanitratocerate, phosphides such as iron phosphide, phosphates (meta, ortho and pyro) such as monobasic potassium orthophosphate, arsenates and arsenites such as antimony arsenate, antimonates such as lead antimonate, vanadates such as iron orthovanadate, niobates and niobites such as potassium metaniobite, oxides such as titanium dioxide, hydroxides such as aluminium trihydroxide (gibbsite), chlorides such as zirconyl chloride, sulphates and sulphites such as magnesium sulphate, selenides and selenites such as copper selenite, tellurides such as molybdenum telluride, chromates and dichromates such as lithium dichromate, molybdates such as ammonium paramolybdate, tungstates such as magnesium tungstate, fluorides such as titanium trifluoride, fluoroborates such as zinc tetraborate, fluorosilicate such as magnesium hexafluorosilicate, fluoroantimonates such as ammonium fluoroantimonate, fluorotitanates such as calcium fluorotitanate, fluorozirconates such as indium fluorozirconate, fluorotantalates such as potassium fluorotantalate, chlorides such as magnesium chloride, perchlorates such as gallium perchlorate, bromides such as lanthanum bromide, bromates such as zinc bromate, iodides such as zirconium iodide, manganates and permanganates such as lithium manganate, ferrates such as copper ferrate, metal carbides, metal silicides, metal nitrides, metal nitrates (especially cadmium nitrate), metal borders (especially nickel and its alloysi, metal cyanides such as Berlin Blue, metal fibres/flakes and organic dyestuffs such as ultramarine and (metal) phthalocyanlne, Ni bis(dithiolene) complexes, polymethine dyes, heterocyclic cyanine dyes, croconium dyes and minerals of the kaolinite-halloysite series. Especially preferred non-metallic infrared blocking substances are carbon black and titanium dioxide.

According to another embodiment of the present invention the infrared blocking interlayer consists of a thin metal sheet.

The thickness of such a sheet is usually in the order of 1 to 100 micron.

According to another embodiment of the present invention the infrared blocking interlayer is composed of an open celled foamed material filled with an infrared blocking substance or metallised.

Examples of infrared blocking substances to be used in this embodiment are listed above.

The thickness of this type of interlayer is generally in the range 1 to 10 mm.

Especially preferred infrared blocking interlayers to be used in the present evacuated insulation panels are vacuum metallised plastics such as polyester vacuum metallised with aluminium.

The number and spacing of the interlayers to be used in the present evacuated insulation panels will depend on the insulation value of the open celled foamed material itself, on the infrared blocking activity of the interlayer and the thickness of the panel itself.

If several interlayers are used in the present evacuated insulation panel they may be of the same type or of different types.

Also the alternate layers of open celled foamed material may be of the same type or of different types. For example, the nature of the organic material itself may differ or the same organic material may be used but differing in density or cell size or hardness.

The open celled organic foamed material to be used as insulating filler in the evacuated insulation panels of the present invention may be derived from the following materials: polyurethanes, polystyrenes, polyethylenes, acrylics, phenolics (such as phenol formaldehyde), halogenated polymers such as polyvinyl chloride Preference is give to open celled rigid polyurethane and urethane-modified polyisocyanurate foams.

Open celled rigid polyurethane and urethane-modified polyisocyanurate foams are in general prepared by reacting the appropriate organic polyisocyanate and polyfunctional isocyanate-reactive compound in the presence of a cell-opening agent. Examples of formulations for making open celled rigid polyurethane foam are described in European patent publications nos 0 498 628 and 0 188 806.

Suitable organic polyisocyanates for use in the preparation of open celled rigid polyurethane foams include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams, and in particular the aromatic polyisocyanates such as diphenylmethane diisocyanate in the form of its 2,4'-, 2,2'- and 4,4'-isomers and mixtures thereof, the mixtures of diphenylmethane diisocyanates (MDI) and oligomers thereof known in the art as "crude" or polymeric MDI (polymethylene polyphenylene polyisocyanates) having an isocyanate functionality of greater than 2, toluene diisocyanate in the form of its 2,4- and 2,6-isomers and mixtures thereof, 1,5-naphthalene diisocyanate and 1,4-diisocyanatobenzene.

Other organic polyisocyanates which may be mentioned include the aliphatic diisocyanates such as isophorone diisocyanate, 1,6-diisocyanatohexane and 4,4'-diisocyanatodicyclohexylmethane.

Polyfunctional isocyanate-reactive compositions for use in the preparation of open celled rigid polyurethane foams include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams. Of particular importance for the preparation of rigid foams are polyols and polyol mixtures having average hydroxyl numbers of from 300 to 1000, especially from 300 to 700 mg KOH/g, and hydroxyl functionalities of from 2 to 8, especially from 3 to 8. Suitable polyols have been fully described in the prior art and include reaction products of alkylene oxides, for example ethylene oxide and/or propylene oxide, with initiators containing from 2 to 8 active hydrogen atoms per molecule. Suitable initiators include: polyols, for example glycerol, trimethylolpropane, triethanolamine, pentaerythritol, sorbitol and sucrose; polyamines, for example ethylene diamine, tolylene diamine, diaminodiphenylmethane and polymethylene polyphenylene polyamines; and aminoalcohols, for example ethanolamine and diethanolamine; and mixtures of such initiators. Other suitable polymeric polyols include polyesters obtained by the condensation of appropriate proportions of glycols and higher functionality polyols with dicarboxylic or polycarboxylic acids. Still further suitable polymeric polyols include hydroxyl terminated polythioethers, polyamides, polyesteramides, polycarbonates, polyacetals, polyolefins and polysiloxanes. The quantities of the polyisocyanate compositions and the polyfunctional isocyanate-reactive compositions to be reacted will depend upon the nature of the rigid polyurethane or urethane-modified polyisocyanurate foam to be produced and will be readily determined by those skilled in the art.

The preparation of open celled rigid polyurethane foam may be carried out in the presence of any of the blowing agents known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams. Such blowing agents include water or other carbon dioxide-evolving compounds, or inert low boiling compounds having a boiling point of above -700C at atmospheric pressure.

In order to reach low thermal conductivity levels at reduced pressure levels, open celled rigid polyurethane foams having decreased cell sizes (in the range 50 to 150 micron) have been used.

These fine celled open celled rigid polyurethane foams can be obtained by incorporating an inert, insoluble fluorinated compound into the foam-forming mixture.

The term inert as used herein with reference to the inert, insoluble fluorinated compound to be used in the preparation of fine celled open celled rigid polyurethane foam is to be understood as indicating a substantial lack of chemical reactivity with any of the other components used in the foamforming reaction.

The term insoluble as used herein with reference to the inert, insoluble fluorinated compound to be used in the preparation of fine celled open celled rigid polyurethane foam is defined as showing a solubility in either the isocyanate-reactive composition or the polyisocyanate composition with which it is to be blended of less than 500 ppm by weight at 250C and atmospheric pressure.

Inert, insoluble fluorinated compounds for use in the preparation of fine celled open celled rigid polyurethane foam include any of those disclosed in US Patent No. 4,981,879, US Patent No. 5,034,424, US Patent No. 4,972,002, European Patent Applications Nos 0508649 and 0498628.

The term substantially fluorinated as used herein with reference to the inert, insoluble, substantially fluorinated compound to be used in the preparation of fine celled open celled rigid polyurethane foam is to be understood to embrace compounds in which at least 50 % of the hydrogen atoms of the unfluorinated compounds are replaced by fluorine.

Suitable compounds include substantially fluorinated or perfluorinated hydrocarbons, substantially fluorinated or perfluorinated ethers, substantially fluorinated or perfluorinated tertiary amines, substantially fluorinated or perfluorinated amino-ethers and substantially fluorinated or perfluorinated sulphones.

Suitable examples of substantially fluorinated or perfluorinated hydrocarbons are those containing from 1 to 15 carbon atoms, which may be either cyclic or acyclic, either aromatic or aliphatic and either saturated or unsaturated, such as substantially fluorinated and perfluorinated methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, cyclobutane, cyclooctane, cyclohexane, cyclopentane, cycloheptane, norbornadiene, decaline, dimethylcyclobutane, methylcyclohexane, 1-methyldecaline, phenanthrene, dimethylcyclobutane, and isomers thereof. Particular mention may be made of the various isomers of perfluoropentane and perfluorohexane such as perfluoron-pentane and perfluoro-n-hexane.

Suitable examples of substantially fluorinated or perfluorinated ethers are those containing from 3 to 15 carbon atoms, which may be cyclic or acyclic, such as substantially fluorinated or perfluorinated dialkyl ethers and alkyl substituted cyclic ethers. Particular mention may be made of perfluorinated methyl ethyl ether, perfluorinated methyl propyl ether, the perfluorinated alkyltetrahydropyrans such as perfluorinated propyltetrahydropyran, and the perfluorinated alkyltetrahydrofurans such as perfluorinated propyltetrahydrofuran and perfluorinated butyltetrahydrofuran. Additional examples of substantially fluorinated or perfluorinated ethers which are suitable for use in the process of the invention are the commercially available fluorinated polyethers such as Galden HT 100, HT 200, HT 230, HT 250 and HT 270 from Montefluos SpA (Galden is a Trade Mark).

Suitable examples of substantially fluorinated or perfluorinated amines are tertiary amines containing from 3 to 15 carbon atoms, which may be cyclic or acyclic, such as substantially fluorinated or perfluorinated trialkylamines, N-alkylated cyclic amines, tetraalkylhydrazines and trialkylhydroxylamines.

Particular mention may be made of substantially fluorinated or perfluorinated trimethylamine, triethylamine, ethyldimethylamine, methyldiethylamine, tripropylamine, tributylamine, tripentylamine, tetramethylhydrazine, trimethylhydroxylamine, O-ethyl dimethylhydroxylamine, O,O'-bis- (dialkylaminopropylene-glycol, O,O'-b s-(d alkylamino)ethyleneglycol, N methylpyrrolidine and the N-alkylpiperidines such as N-methylpiperidine.

Suitable examples of substantially fluorinated or perfluorinated aminoethers include those having from 3 to 15 carbon atoms, which may be cyclic or acyclic, such as substantially fluorinated or perfluorinated trialkylethanolamines and N-alkylmorpholines. Particular mention may be made of substantially fluorinated or perfluorinated trimethylethanolamines and N (C s alkyl)morpholines such as N-methyl, N-ethyl and N-isopropylmorpholine.

Suitable examples of substantially fluorinated or perfluorinated sulphones include perfluorinated dialkylsulphones having from 2 to 8 carbon atoms such as perfluoro- (dimethylsulphone) and perfluoro-(methyldiethyl-sulphone).

Certain inert, insoluble fluorinated compounds suitable for use in the preparation of fine celled open celled rigid polyurethane foam may themselves act as blowing agents under the conditions pertaining to the foam-forming reaction, particularly where their boiling point is lower than the exotherm temperature achieved by the reaction mixture. For the avoidance of doubt, such materials may, partly or completely, fulfil the function of blowing agent in addition to that of inert, insoluble fluorinated compound.

The amount of the inert, insoluble fluorinated compound to be used in the preparation of fine celled open celled rigid polyurethane foam ranges from 0.05 to 10 , preferably from 0.1 to 5 %, most preferably from 0.6 to 2.3 % by weight based on the total foam-forming composition.

The inert, insoluble fluorinated compound will usually be incorporated in the foam-forming reaction mixture in the form of an emulsion or preferably a microemulsion in one of the major components, that is to say in the isocyanate-reactive component and/or the polyisocyanate component. Such emulsions or microemulsions may be prepared using conventional techniques and suitable emulsifying agents.

Emulsifying agents suitable for preparing stable emulsions or microemulsions of fluorinated liquid compounds in organic polyisocyanates and/or isocyanatereactive compounds include surfactants chosen from the group of nonionic, ionic lanionic or cationic) and amphoteric surfactants. Preferred surfactants are fluoro surfactants and/or alkoxylated alkanes. Particular examples of fluoro surfactants include fluorinated alkyl polyoxyethylene ethanols, fluorinated alkyl alkoxylates and fluorinated alkyl esters. Examples of useful fluorinated surfactants which are commerciaily available are Fluorad FC 430 and FC 431 from 3M, Forafac lll0D, 1157, 1157N and 1199D from Atochem and Fluowet S 3690, OTN and CD from Hoechst.

The amount of emulsifying agent used is between 0.02 and 5 pbw per 100 pbw of foam forming reaction system and between 0.05 and 10 pbw per 100 pbw of polyisocyanate or polyol composition.

In addition to the polyisocyanate and polyfunctional isocyanate-reactive compositions, the inert, insoluble fluorinated compound and the blowing agent, the foam-forming reaction mixture will commonly contain one or more other auxiliaries or additives conventional to formulations for the production of open celled rigid polyurethane and urethane-modified polyisocyanurate foams.

Such optional additives include crosslinking agents, for examples low molecular weight polyols such as triethanolamine, foam-stabilising agents or surfactants, for example siloxane-oxyalkylene copolymers, urethane catalysts, for example tin compounds such as stannous octoate or dibutyltin dilaurate or tertiary amines such as dimethylcyclohexylamine or triethylene diamine, fire retardants, for example halogenated alkyl phosphates such as tris chloropropyl phosphate or alkyl phosphonates, and cell-opening agents such as polymer particles (such as polymer polyols), incompatible liquids such as solvents or polyols, inorganic fillers such as bentonite clays, silica particles (particularly fumed silica), metal flakes and stearates.

A particularly preferred process for the preparation of open celled fine celled rigid polyurethane or urethane-modified polyisocyanurate foam comprises the step of reacting an organic polyisocyanate with an isocyanate-reactive material in the presence of a blowing promotor being an isocyanate-reactive cyclic compound of formula:

wherein Y is O or NR wherein each R independently is a lower alkyl radical of C1-C or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of C.-C6 or (CHr)i-X wherein X is an isocyanate-reactive group which is OH or NE and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of R or R is or comprises an isocyanatereactive group; and in the presence of an inert, insoluble fluorinated compound which is present as the dispersed phase of an emulsion or a microemulsion and in the presence of a metal salt catalyst.

A preferred compound of formula (I) wherein Y is O is an isocyanate-reactive cyclic carbonate which is glycerol carbonate.

Preferred compounds of formula (I) wherein Y is NRl are isocyanate-reactive cyclic ureas of formula:

The isocyanate-reactive cyclic blowing promotor is used in amounts ranging from 0.1 to 99 , preferably from 1 to 60 by weight based on the total isocyanate-reactive material.

Suitable further blowing agents may be used in the said preferred process of the present invention such as water or inert low boiling compounds having a boiling point of above -500C at 1 bar.

The amount of water used as blowing agent may be selected in known manner to provide foams of the desired density, typical amounts being in the range from 0.05 to 5 parts by weight per 100 parts by weight of reactive ingredients, although it may be a particular embodiment of the present invention to incorporate up to 10 % by weight or even up to 20 W by weight of water.

Suitable inert blowing agents include, for example, hydrocarbons, dialkyl ethers, alkyl alkanoates, aliphatic and cycloaliphatic hydrofluorocarbons, hydrochlorofluorocarbons, chlorofluorocarbons and fluorine-containing ethers.

Suitable hydrocarbon blowing agents include lower aliphatic or cyclic hydrocarbons such as n-pentane, isopentane, cyclopentane, neopentane, hexane and cyclohexane.

Preferred metal salt catalysts are those selected among group Ia and group IIa metal salts, more preferably among group Ia and group IIa metal carboxylates.

Particularly suitable catalysts are potassium acetate and potassium ethylhexoate.

The metal salt catalyst is used in amounts ranging from 0.01 to 3 % by weight based on the total reaction system.

Apart from the metal salt catalyst some amine catalyst may be used in this process.

In operating the process for making open celled rigid polyurethane foams, the known one-shot, prepolymer or semi-prepolymer techniques may be used together with conventional mixing methods and the rigid foam may be produced in the form of slabstock, mouldings, cavity fillings, sprayed foam, frothed foam or laminates with other materials such as hardboard, plasterboard, plastics, paper or metal.

To reduce the number of component streams delivered to the final mixing apparatus, most of the additives such as the blowing agent, catalyst, fluorinated compound and optionally others may be premixed with one of the major components of the foam formulation, in general with the isocyanatereactive component.

In manufacturing the evacuated insulation panels of the present invention the core material comprising the multilayered structure of open celled foamed insulating filler material and infrared blocking interlayers is enveloped in a vessel of low thermal conductivity material which has a low permeability to atmospheric gases and the interior thereof is evacuated to a desired pressure level, in general to below 5 mbar (preferably below 1 mbar and most preferably below 0.1 mbar), and then the vessel is hermetically sealed.

The vessel is preferably made of a film material which has a gas permeability as low as possible and which is easily sealed by heat sealing. The gas permeation rate of the vessel directly affects both the occurence of heat leakage and thus the thermal insulation efficiency of the resulting evacuated insulation panel as well as the operating lifetime of the panel.

Materials suitable for the vessel include plastics such as polyester, polyvinylidene chloride, polypropylene and polyvinyl alcohol. Preferably the plastics film is vapor deposited with a metallic film or laminated with a metallic foil providing for higher protection against vacuum leak. The plastic film bag may also include a heat sealed layer made of a polyolefin, such as a polyethylene and a polypropylene, a polyamide, such as nylon 11 and nylon 12, a polyacrylonitrile or a similar synthetic resin.

An air permeable pouch may be used to provide a container for the insulating filler material in order to facilitate further processing.

It is preferred to precondition the insulating filler material and also the infrared blocking interlayers prior to placement in the air permeable pouch or in the gastight envelope.

This preconditioning involves heating and optionally, agitating the filler material in order to remove contaminants from the surface of the filler. The removal of filler contaminants improves inter alia the expected panel life.

Further the removal of contaminants reduces the time required to evacuate the vessel thereby reducing the time and cost associated with the manufacture of an evacuated insulation panel.

Reduced pressures may also be used together with heating and/or agitation.

It is generally necessary to provide within the sealed panels materials to absorb or otherwise interact with gases and vapors that remain due to imperfect evacuation, that permeate the enclosure from the outside atmosphere or evolve from the filler material itself. Such materials are known as getters and may include, for example, a granular form of calcium sulfate which is excellent in removing water vapor, activated carbon to remove organic gases, metals to absorb oxygen and r.itrogen and zeolites to absorb carbon dioxide and nitrogen. Other suitable getter materials are described in US Patents Nos. 4,000,246, 4,444,821, 4,663,551, 4,702,963 and 4,726,974 and in European Patent Publications Nos. 434266 and 181778.

A method of fabricating the evacuated insulation panels of the present invention is as follows.

The open celled foamed filler material layers and infrared blocking interlayers are first preconditioned with heat and optionally agitation, preferably under reduced pressure. Once preconditioned, alternating layers of open celled foamed material and infrared blocking inter layers are placed in the gas barrier envelope. The vessel is placed in an evacuation chamber, evacuated to the desired pressure and sealed. The panels thus provided are relatively rigid and have a thickness of approximately 1 to 5 cm.

Refrigeration appliance is only a single example of a product that can utilise evacuated insulation (Mellinex available from Imperial Chemical Industries) were placed in the same type of gast;ght envelope and evacuated to a pressure of 0.1 mbar. The thermal conductivity value at 100C was 4.4 mW/m K.

This example shows that by using infrared blocking interlayers in evacuated insulation panels filled with open celled foamed material a substantial improvement (20 %) in thermal insulation is obtained.

Example 2 A block of 20 x 20 x 4 cm open celled rigid polyurethane foamed material of density 28 kg/m3 was prepared.

When placed in a gastight envelope and evacuated to a pressure of 0.1 mbar a thermal conductivity value of 4.9 mW/mOK at 100C was obtained.

The same block of open celled rigid polyurethane foamed material was cut into 4 slices of 1 cm thickness each.

These 4 slices together with 3 interlayers of metallised polyester film (Mellinex available from Imperial Chemical Industries) were placed in the same type of gastight envelope and evacuated to a pressure of 0.1 mbar. The thermal conductivity value at 10 C was 4.3 mW/mOK.

This example also shows that by using infrared blocking interlayers in evacuated insulation panels filled with open celled foamed material a substantial improvement (12 t) in thermal insulation is obtained.

Claims (9)

1. Evacuated insulation panel comprising a core of open celled organic foamed insulating material enveloped in a vessel of low gas permeability, characterised in that the core comprises alternate layers of open celled foamed material and infrared blocking interlayers.

2. Evacuated insulation panel according to claim 1 wherein the infrared blocking interlayers consist of a plastics substrate coated with or containing an infrared blocking substance.

3. Evacuated insulation panel according to claim 2 wherein the infrared blocking interlayer is a vacuum metallised plastic.

4. Evacuated insulation panel according to claim 3 wherein the infrared blocking interlayer is a polyester vacuum metallised with aluminium.

5. Evacuated insulation panel according to any one of the preceding claims wherein the open celled organic foamed insulating material comprises open celled rigid polyurethane or urethane-modified polyisocyanurate foam.

6. Evacuated insulation panel according to claim 5 wherein the cells of said foam have average diameters of less than 150 micron.

7. Evacuated insulation panel according to claim 6 wherein the foam preparation is carried out in the presence of an inert, insoluble fluorinated compound.

8. Evacuated insulation panel according to claim 7 wherein the inert, insoluble fluorinated compound is perfluoro-n-pentane or perfluoro-n hexane.

9. Evacuated insulation panel according to claim 7 or 8 wherein the foam preparation is carried out in the presence of a blowing promotor which is an isocyanate-reactive cyclic compound of formula

wherein Y is O or NR: wherein each Rl independently is a lower alkyl radical of C1-C, or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of Cl-Cs or (CH2)n-X wherein X is an isocyanate-reactive group which is OH or NH and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of R1 or R is or comprises an isocyanate-reactive group; and in the presence of a metal salt catalyst.

Evacuated insulation panel according to claim 9 wherein the compound of formula (I) is an isocyanate-reactive cyclic carbonate or an isocyanate-reactive cyclic urea.

Evacuated insulation panel according to claim 9 wherein the metal salt catalyst is a group Ia or group IIa metal carboxylate.