EVACUATED INSULATION PANEL

Abstract: Method for producing an evacuated insulation panel comprising the steps of enveloping an open celled (semi-)rigid insulating foam in a substantially gas impermeable flexible vessel, evacuating the whole and sealing, wherein the panel is compressed during or after evacuation and sealing to a thickness of 10 to 90 % of its initial thickness prior to compression.

Description: DESCRIPTION EVACUATED INSULATION PANELS This invention relates to evacuated insulation panels, a method for the production thereof and their use for thermal insulation purposes. Evacuated insulation panels and methods for their production are known. 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 ithin the cabinet of tne 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 0498628 and 0188806) . WO 97/27986 describes a method to improve the thermal insulation properties of an evacuated insulation panel filled with an open celled rigid insulating foam. This method involves compressing the open celled rigid foam to a thickness of 40 to 90 % of its initial thickness prior to compression, enclosing the compressed foam in a receptacle, evacuating the receptacle to a partial or near total vacuum and hermetically sealing the receptacle. The insulating performance of the foam on a per unit thickness is enhanced by compression of the foam. However evacuated panels compressed according to the method described in WO 97/27986 are not completely flat and the surface of the panels shows a lot of wrinkles. This can lead to air entrapments wnen the panel is foamed- m-place in a refrigerator cabinet. Therefore it is an object of the present invention to provide an evacuated insulation panel comprising an open celled insulating foam having improved thermal insulation properties. It is a further object of the present invention to provide an evacuated insulation panel comprising an open celled insulating foam, said panel having a very flat surface with zero or almost zero wrinkles. According to the present invention an evacuated insulation panel comprising an open celled insulating foam is provided, said panel after its manufacture being compressed to a thickness of 10 to 90 % of its initial thickness prior to compression. Compressed evacuated insulation panels of tne present invention have a lower thermal conductivity than non-compressed panels. Further the panels are near flat and the surface of the panels shows zero or almost no wrinkles. This makes it easier to stick the panels to the sides of the unit to be insulated. The panels also show an improved dimensional stability when heated which is beneficial in the process of encapsulating the panels within insulating foam. During the encapsulation process the panels are subjected to a higher temperature (generally about 80°C) for a short period of time. The evacuated insulation panels of the present invention are made by enveloping an open celled insulating foam in a substantially gas impermeable flexible vessel, evacuating the whole and sealing, whereby the panel is compressed to a thickness of 10 to 90 % of its initial thickness during or after evacuation and sealing. Preferably the compression takes places after evacuation and sealing but it can also take place simultaneously with the evacuation and sealing. The panel is compressed to a thickness of 10 to 90 % of its initial thickness, preferably to a thickness of between 20 and 80 % of its initial thickness, more preferably to a thickness of between 40 and 60 % of its initial thickness, most preferably to about 50 % of its initial thickness. Compression may be accomplished by any means known in the art such as between opposing parallel plates or opposing rolls. Compression may be effected on-line as part of a continuous manufacturing process or may be effected off-line on individual panels. Compression usually takes place at room temperature but any temperature between 10 and 150°C can be used. Preferably the temperature is between 20 and 120 C C, most preferably between 70 and 100°C. Heating while compressing the panels even further improves the surface appearance and flatness. Suitable insulating foams to be used as filler for the evacuated insulation panels of the present invention are open celled organic foamed materials. The foams have an open celled content of at least 70 <, preferably at least 90 %, and most preferably at least 95 I. The foam is preferably as close as possible to complete or 100 % open cells. The foam (prior to compression) preferably has a density of 16 to 250 kg/m 3 and most preferably 25 to 100 kg/m 1 . Density will increase proportionally with the extent of compression. The open celled organic foamed materials to be used as insulating foam may be αerived from the following materials: polyuretnanes, polystyrenes, polyethylenes, acrylics, pnenolics (such as prenol formaldehyde), halogenated polymers such as polyvmylchloride . In this invention most preference is given 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 0498628, 0547515, 0188806 and in PCT Patent Publication No. 95/02620. 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 m particular the aromatic polyisocyanates such as diphenylmethane dusocyanate in the form of its 2,4'-, 2,2'- and 4,4'- lsomers and mixtures thereof, the mixtures of diphenylmethane dusocyanates (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 dusocyanate in the form of its 2,4- and 2,6-ιsomers and mixtures thereof, 1, 5-naphthalene dusocyanate and 1, 4-dιιsocyanatobenzene. Special mention may be made of the so-called MDI variants (diphenylmethane dusocyanate modified by the introduction of urethane, allophanate, urea, biuret, carbodnmide, uretonimine or isocyanurate residues) . Other organic polyisocyanates which may be mentioned include the aliphatic dusocyanates such as isophorone dusocyanate, 1, 6-dιιsocyanatohexane and 4 , 4 ' - dusocyanatodicyclohexylmethane. 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 πgiα 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 ana mcluae 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, tπmethylolpropane, tnethanolamme, pentaerythπtol, sorbitol and sucrose, and polyammes, for example ethylene dia ine, tolylene diamine, diammodiphenylmethane and polymethylene polyphenylene polyammes, and am oalcohols, for example, ethanolamine and diethanola ine, 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 acids. Still further suitable polymeric polyols include hydroxyl terminated polythioethers, polyamides, polyesteramides, polycarbonates, polyacetals, polyolefms 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. Isocyanate indices of from 70 to 140 will typically be used in preparing open celled rigid polyurethane foams but lower indices may be used if desired. Higher indices, for example 150 to 500 or even up to 3000, may be used in conjunction with trimeπsation catalysts to make foams containing isocyanurate linkages. 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 -70°C at atmospheric pressure. 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 % by weight of water. Suitable inert blowing agents include, for example, hydrocarbons, dialkyl ethers, alkyl alkanoates, aliphatic and cycloaliphatic hyαrofluorocarbons, hydrochlorofluorocarbons, chlorofluorocarbons and fluorine-containing ethers. Suitable hydrocarbon blowing agents include lower aliphatic or cyclic hydrocarbons such as n-pentane, isopentane, cyclopentane, neopertane, hexane and cyclohexane. 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) (prior to compression) can be used. These fine celled open celled rigid polyurethane foams can be ootamed by air-nucleation or by incorporating a substantially insoluble organic compound into the foam-forming mixture. Air-nucleation is the use of very finely dispersed gas bubbles (< 10 μm) in one or both foam components prior to mixing of tne foam components and subsequent foam formation. These bubbles enable finer foams to De obtained. The insolubility of the organic liquid the reaction mixture usually arises from the fact that it is insoluble in one or more of the major ingredients of the foam formulation, especially the isocyanate-reactive material and/or the polyisocyanate. Solubility in these materials can be determined by conventional techniques. The term "insoluble" as used herein with respect to the insoluble organic liquid 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 25°C and atmospheric pressure. Examples of insoluble organic liquids include fluormated compounds, especially substantially fluormated or perfluor ated compounds. A substantially fluormated compound as used herein is defined as a compound wherein at least 75 % and preferably at least 90 % and most preferably at least 99 % of the hydrogen atoms have been replaced by fluorine atoms. Insoluble fluormated compounds for use in the preparation of fine celled open celled rigid polyurethane foam include any of those described in US 4981897, US 5034424, US 4972002, EP 0508649, EP 0498628, WO 95/18176. Suitable compounds include substantially fluormated or perfluormated hydrocarbons, substantially fluormated or perfluormateα ethers, substantially fluormated or perfluormated tertiary amines, substantially fluormated or perfluormated ammo-ethers and substantially fluormated or perfluormated sulphones. Suitable examples of substantially fluormated or perfluormated hydrocarbons are those containing from 1 to 15 carbon atoms, which may be either cyclic or acyclic, either aromatic or alipnatic and either saturated or unsaturated, such as substantially fluormated or perfluormated methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, cyclobutane, cyclooctane, cyclohexane, cyclopentane, cycloheptane, norbornadiene, decalme, dimethylcyclobutane, methylcyclohexane, 1- methyldecalme, phenantrene, dimethylcyclohexane, and isomers thereof and perfluoro (cyclo) olefms such as hexafluoropropene dimers and tπmers. Particular mention may be made of the various isomers of perfluoropentane and perfluorohexane ana perfluoro (4-methylpent-2-ene) . Particular examples of substantially fluormated or perfluormated ethers include: perfluorobutyltetrahydrofuran and perfluoropropyltetrahydrofuran. Particular examples of substantially fluormated or perfluormated ammo- ethers include perfluormated alkyl) morpholmes such as N-methyl, N-ethyl and N-isopropylmorpholme . To ensure zero ozone depletion potential, it is preferred to use fluormated compounds containing no other halogen atoms. Certain insoluble organic liquids suitable for use m the preparation of fine celled open celled rigid polyurethane foam may themselves act as blowing agents under the conditions pertaining to the foam-formmg 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 insoluble organic liquid. The amount of the insoluble organic liquid 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 reaction system. The substantially insoluble organic liquid will usually be incorporated in the foam-formmg 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 fluormated liquid compounds in organic polyisocyanates and/or isocyanate-reactive compounds include surfactants chosen from the group of nonionic, ionic (anionic or cationic) and amphoteric surfactants . Preferred surfactants for emulsifying the fluormated liquid compound in the isocyanate-reactive composition are fluoro surfactants, silicone surfactants and/or alkoxylated alkanes. 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 blowing agent and, optionally, the insoluble organic liquid, 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 crosslmkmg agents, for example low molecular weight polyols such as triethanolamine, foam-stabilismg agents or surfactants, for example siloxane-oxyalkylene copolymers, urethane catalysts, for example tin compounds such as stannous octoate or dibutyltm dilaurate, fire retardants, for example halogenated alkyl phosphates such as tπs chloropropyl phosphate or alkyl phosphonates, infrared attenuating agents such as carbon black, and cell-opening agents such as polymer particles (such as polymer polyols), incompatible liquids such as solvents or polyols, inorganic fillers such as bentonite clay, silica particles (particularly fumed silica), metal flakes and stearates. A particularly preferred process for the preparation of open 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: (C wherein Y is 0 or NR 1 wherein each R 1 independently is a lower alkyl radical of or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of or (CH 2 ) m -X wherein X is an isocyanate-reactive group which is OH or NH 2 and m is 0, 1 or 2; and with the proviso that at least one of R 1 or R is or comprises an isocyanate- reactive group. A preferred compound of formula (I) wherein Y is 0 is an isocyanate-reactive cyclic carbonate which is glycerol carbonate. Preferred compounds of formula (I) wherein Y is NR 1 are isocyanate-reactive cyclic ureas of formula: o n .c- H0-CH,-N N-CH,-OH (ID H-C ■ C-H I on OH and CH,-N N-CH, (III) H-C - •C-H OH OH The isocyanate-reactive cyclic blowing promotor is used in amounts ranging from 1 to 99 %, preferably from 1 to 60 % by weight based on the total isocyanate-reactive material. Further details of this process are described in EP 498628, EP 498629, EP 662494, WO 95/02620, WO 96/25455, WO 96/36655 (all incorporated herein by reference) . 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 foams may be produced m the form of slabstock, mouldings, cavity fillings, sprayed foam, frothed foam or laminates with other materials such as hardboard, plasterboard, paper, plastics or metal. General descriptions of the construction of evacuated insulation panels and their use in thermal devices can be found in US Patents Nos 5,066,437, 5,032,439 and 5,076,984 and European Patent Publications Nos 434266, 434225 and 181778, all incorporated herein oy reference as well as the references mentioned therein. Suitable enveloping vessels need to be highly impermeable for gases as 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. Also, they should prevent transmission of heat by conduction or radiation, be easily sealable by heat sealing and, preferably, flexible. Materials suitable for the vessel include plastics such as polyester, polyv ylidene chloride, polypropylene and polyvmyl alcohol. Preferably tne plastics film is vapor deposited with a metallic film or laminated with a metallic foil providing for higher protection against vacuum leak. The plastic bag may also include a thermoplastic heat sealing layer consisting of a thermoplastic resin having a relatively low melting point (lower than 200°C) . Examples of suitable thermoplastics include polyolefms, such as low density polyethylene, high density polyethylene and polypropylene, polyacrylomtrile, polyvmylidenechloride and copolymers thereof, and polyamme, such as nylon 11 and nylon 12, or a similar synthetic resin. For the film deposited on or foil laminated with the plastics film metals can be used such as aluminum, titanium, lead, iron and alloys thereof or tin and its alloys, such as tin alloys with antimony, bismuth and copper or mixtures thereof. Preference is given to a laminate of a thin Al foil. It is preferred to precondition the insulating filler material prior to placement in the gastight envelope. This preconditioning involves heating and, optionally, agitating the filler material preferably under reduced pressure 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. To improve the performance of the evacuated insulation panel, materials are provided within the sealed panels 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 polyurethane foam filler itself. Such materials are known as getters and may include, for example, granulated calcium sulfate or microporous bariumoxide which is excellent in removing water vapor, activated carbon to remove organic gases, metals to absorb oxygen and nitrogen and zeolites to adsorb carbon dioxide and nitrogen. Other suitable getter materials are described in US Patents Nos 4,000,246, 4,444,821, 4,663,551, 4,702,986, 5,191,980, 5,312606, 5,312,607 and 4,726,974, WO 93/25843 and in European Patent Publications Nos 434266 and 181778. Refrigeration appliance is only a single example of a product that can utilise evacuated insulation panels. They can also form part of an insulated building panel. Other environments having a hot side and a cold side could also benefit from the use of the present invention, for example water heaters. The evacuated insulation panels can be easily arranged in the door and walls of a refrigerator. Tney are generally attached by adhesive to the walls of the thermal device to be insulated and then foamed-m-place with a liquid organic material sucn as polyurethane. The polyurethane foam then assists m holding the panels between the walls and also provides additional insulation. The invention is illustrated but not limited by the following examples. EXAMPLE 1 An evacuated insulation panel was made by enveloping an open celled rigid polyurethane foam and a getter in a plastic film laminated with a thin Al foil, evacuating the whole to an internal pressure of 0.05 mbar and sealing the whole. The size of the panel was 274 mm x 247 mm with an initial thickness of 30.4 mm. The initial density of the panel was 45.3 kg/m 3 . The initial thermal conductivity of the panel was 5.6 mW/mK. The panel was compressed in a press at 20°C to a thickness of 20.6 mm corresponding to a density of 66.8 kg/m 3 . Thermal conductivity of this compressed panel was 4.4 mW/mK. The panel was further compressed to a thickness of 15.2 mm corresponding to a density of 90.5 kg/m 3 . Thermal conductivity of this compressed panel was 4.1 mW/mK. The compressed panels were flat and showed almost no wrinkles (see photograph 1) . COMPARATIVE EXAMPLE 2 The open celled rigid polyurethane foam of example 1 was compressed to a thickness of 15.6 mm corresponding to a density of 88.2 kg/m 3 and subsequently enveloped in the same type of film as in example 1 above together with the same getter as in example 1 above, evacuated and sealed. The thermal conductivity of this compressed panel was 4.3 mW/mK. However the surface of this compressed panel was not flat and showed a lot of wrinkles (see photograph 2) . EXAMPLE 3 An evacuated insulation panel was made by enveloping an open celled rigid polyurethane foam and a getter in a plastic film laminated with a thm Al foil, evacuating the whole to an internal pressure of 0.05 mbar and sealing the whole. The initial thickness of the panel was 40 mm with an initial density of 30 kg/m 3 . The initial thermal conductivity of the panel was 8 mW/mK. The appearance of the panel surface was poor to medium. The panel was compressed m a flat bed type press at 20°C to a thickness of 15 mm. Thermal conductivity of this compressed panel was 5.8 mW/mK. The surface of the panel was flat and good. A similar panel was compressed in the same way except for the fact that the compression took place at a temperature of 80°C. Thermal conductivity of this compressed panel was 5.1 mW/mK; the surface was flat and very good, mirror-like. Another similar panel was also compressed in the same way but this time at a temperature of 120 C C. Thermal conductivity of this compressed panel was 4.8 mW/mK; the surface was flat and very good, mirror-like. These results show that compressing the evacuated insulation panels at elevated temperatures further improves the surface appearance of the panels.

Claims: CLAIMS 1. Method for producing an evacuated insulation panel comprising the steps of enveloping an open celled (semi-) rigid insulating foam in a substantially gas impermeable flexible vessel, evacuating the whole and sealing, characterised in that the panel is compressed during or after evacuation and sealing to a tmckness of 10 to 90 % of its initial thickness prior to compression. 2. Method according to claim 1 wherein the panel is compressed to a thickness of 20 to 80 % of its initial thickness. 3. Method according to claim 2 wherein the panel is compressed to a thickness of 40 to 60 % of its initial thickness. 4. Method according to claim 3 wherein the panel is compressed to a thickness of about 50 % of its initial thickness. 5. Method according to anyone of the preceding claims wherein the insulating foam comprises an open celled (semi-) rigid polyurethane or urethane-modified polyisocyanurate foam. 6. Method according to any one of the preceding claims wherein the compression step takes place at a temperature of between 70 and 120°C. 7. Method according to claim 5 wherein said polyurethane foam is prepared by reacting an organic polyisocyanate with an isocyanate- reactive material m the presence of a blowing promotor being an isocyanate-reactive cyclic compound of formula: 0 II (CR 2 ) n CR 2 wherein Y is 0 or NR 1 wherein each R 1 independently is a lower alkyl radical of Cj-Cj or a lower alkyl radical substituted with an isocyanate- reactive group; each R independently is hydrogen, a lower alkyl radical of C_-C 6 or (CH 2 ) B -X wherein X is an isocyanate-reactive group which is OH or NH 2 and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of R 1 or R is or comprises an isocyanate-reactive group. 8. Process according to claim 7 wherein the isocyanate-reactive cyclic blowing promoter is a cyclic urea of formula 0 il -- C _- H0-CH,-N N-CH,-OH -ID or 0 II • C CH 3 - N-CH 3 (III) H-C C-H I I OH OH 9. Evacuated insulation panel obtainable by the method as defined in any one of the preceding claims. 10. Use of an evacuated insulation panel as defined in claim 9 as thermal insulation. 11. Use according to claim 10 in refrigerators, construction panels, heating pipes or tubes, or boilers.

Inventors: STROOBANTS JAN MAURICE, STROOBANTS, JAN, MAURICE
Applicants: ICI PLC, IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1998
Main classification: E04B1
IPC codes: C08G18, E04B1, F16L59