EVACUATED INSULATION PANEL HAVING NON-WRINKLED SURFACES

Abstract: Evacuated insulation panel (10, 20), also referred to as vacuum insulation panel (VIP), comprising: A) a deformable receptacle (14, 24) which has been evacuated to an absolute pressure of about 10 torr or less and hermetically sealed surrounding B) a corestock (12, 22) of one or more porous or open-celled rigid material matrixes having one or more indentations (16, 26) therein which extend in at least one dimension across a surface of a rigid material matrix, wherein the receptacle (14, 24) substantially conforms to the shape of the corestock (12, 22) and the indentations (16, 26) therein and the finished panel (10, 22) has surfaces which are substantially non-wrinkled; and methods of making the panel (10, 20).

Description: EVACUATED INSULATION PANEL HAVING. NON-WRLNKLED SURFACES CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of U. S. Ser. No. 08/993,536 filed December 18, 1997, allowed, which is hereby incorporated by reference. Background of the Invention This invention relates to an improved evacuated insulation panel, also referred to as a vacuum insulation panel (VIP), having a corestock that has indentations therein to provide a finished panel having mechanically and aesthetically desirable, non-wrinkled surfaces. To significantly improve the performance of insulating systems, evacuated or vacuum panel technology is currently being evaluated by industry. The removal of substantial amounts of air or gas in the panels affords the possibility of superior insulating performance. A useful evacuated panel is one employing a panel corestock of a porous or open- celled rigid material matrix, such as a rigid open-cell alkenyl aromatic polymer foam. The open-cell or porous structures of the foam and other rigid material matrixes allow rapid and substantially complete withdrawal of gases from within the material and the panel containing it. The rigid material matrix provides a corestock of substantial mechanical strength and insulating performance. A problem with employing panel corestocks of various porous or open-celled rigid material matrixes, including open-cell alkenyl aromatic polymer foams, is their tendency to shrink upon being evacuated and/or being exposed to elevated temperatures. The shrinking may result in a wrinkled surface appearance for the receptacle or enclosure maintaining a hermetic seal in the panel. It would be desirable to have an evacuated insulation panel with a corestock of a porous or open-celled rigid material matrix, including open-cell alkenyl aromatic polymer foam, the surface or surfaces of which would exhibit an aesthetically desirable, relatively smooth and homogeneous surface substantially free of wrinkles or ridges. Mechanically, for the use of these panels in other articles of manufacture, it would be desirable to produce panels having a substantially flat surface so that the insulating panel can be placed or situated flush or adjacent to flat, smooth surfaces such as the inside of a refrigerator wall. It would also be desirable to be able to reduce the evacuation time in comparison to prior art panels. Summary of the Invention According to the present invention, there is provided an evacuated insulation panel comprising: A) a deformable receptacle which has been evacuated to an absolute pressure of about 10 torr or less and hermetically sealed surrounding B) a corestock of one or more porous or open-celled rigid material matrixes having one or more indentations therein which extend in at least one dimension across a surface of a rigid material matrix, wherein the receptacle substantially conforms to the shape of the corestock and the indentations therein and the finished panel has surfaces which are substantially non-wrinkled. In another embodiment of the present invention, there is provided an evacuated insulation panel comprising: A) a deformable receptacle which has been evacuated to an absolute pressure of about 10 torr or less and hermetically sealed surrounding B) a corestock of one or more porous or open-celled rigid material matrixes, optionally having one or more indentations therein which extend in at least one dimension across a surface of a rigid material matrix, and C) one or more rigid plates having one or more indentations therein, the one or more plates being situated contiguous to a major surface of the corestock, wherein the receptacle substantially conforms to the shape of the corestock and the plate or plates and the indentations therein, and the finished panel has surfaces which are substantially non-wrinkled. In a preferred embodiment of the present invention, there is provided an evacuated insulation panel, the panel comprising a corestock of an open-cell alkenyl aromatic polymer foam and a deformable receptacle, the foam comprising an alkenyl aromatic polymer material comprising greater than 50 weight percent of alkenyl aromatic monomeric units based upon the total weight of the alkenyl aromatic polymer material, the foam having an open cell content of about 70 percent or more, the receptacle being capable of receiving the foam and being hermetically sealed, the foam being situated within the receptacle, the receptacle being hermetically sealed, the open cells of the foam and the interior of the receptacle being evacuated to an absolute pressure of about 10 torr or less, the foam having indentations therein extending in two dimensions across a surface of the foam, the receptacle substantially conforming to the shape of the foam and the indentations therein. In another embodiment of this invention there is provided an evacuated insulation panel, the panel comprising; a) a corestock of an open-cell alkenyl aromatic polymer foam, b) one or more rigid plates, and c) a deformable receptacle, the foam comprising an alkenyl aromatic polymer material comprising greater than 50 weight percent of alkenyl aromatic monomeric units based upon the total weight of the alkenyl aromatic polymer material, the foam having an open-cell content of about 70 percent or more , the plate being situated contiguous to a major surface of the foam, the receptacle being capable of receiving the foam and the plate and being hermetically sealed, the foam and the plate being situated within the receptacle, the receptacle being hermetically sealed, the open-cells of the foam and the interior of the receptacle being evacuated to an absolute pressure of about 10 torr or less, the plate having one or more indentations therein, the receptacle substantially conforming to the shape of the foam and the indentations within the plates. Further according to the present invention, there is a method of making an evacuated insulation panel having a substantially non-wrinkled surface, comprising: a) providing a corestock of one or more porous or open-celled rigid material matrixes; b) indenting one or more surfaces of the matrix wherein the indentations extend in at least one dimension across the surface or surfaces of the matrix; c) providing a deformable receptacle capable of receiving and containing the corestock and placing the corestock therein; d) evacuating the interior of the receptacle to an absolute pressure of 10 torr or less; e) hermetically sealing the receptacle. Further according to a preferred embodiment of the present invention, there is provided a method of making an evacuated insulation panel having a substantially non- wrinkled surface, comprising: a) providing a corestock of an open-cell alkenyl aromatic polymer foam comprising and alkenyl aromatic polymer material, the alkenyl aromatic polymer material comprising greater than 50 weight percent of alkenyl aromatic polymer units based upon the total weight of the alkenyl aromatic polymer material, the foam having about 70 percent or more open cell content; b) indenting one or more surfaces of the foam wherein the indentations extend in two dimensions across the surface or surfaces of the foam; c) providing a deformable receptacle capable of receiving and retaining the foam; d) placing the foam within the receptacle; e) evacuating the open cells of the foam and the interior of the receptacle to an absolute pressure of 10 torr or less; f) hermetically sealing the receptacle to form the panel; g) allowing the foam to shrink and the receptacle to conform substantially within the indentations. Brief Description of the Drawings Figure 1 is a plan view showing an embodiment of an evacuated insulation panel according to the present invention. The panel has a foam corestock defining diagonally- disposed grooves therein traversing continuously across its dimensions. The foam corestock is shown in cutaway at the bottom left of the figure. Figure 2 is a plan view showing an embodiment of an evacuated insulation panel according to the present invention. The panel has a foam corestock (not shown) defining grooves therein in a rectangular grid traversing continuously across its dimensions. Figure 3A is a enlarged, cross-sectional view of the panel of Figure 2 along Line 3A- 3 A. The foam corestock of the panel is shown. Figure 3B is an enlarged, cutaway, cross-sectional view of the panel of Figure 2 from Figure 3A. Figure 4 is a plan view of an evacuated insulation panel not in accordance with the present invention. The panel has a substantially wrinkled surface. A foam corestock is shown in cutaway at the bottom left of the figure. Figure 5A is an enlarged, cross-sectional view of the panel of Figure 4. Figure 5B is an enlarged, cutaway, cross-sectional view of the panel of Figure 4 from Figure 5A. Detailed Description of the Invention The present invention addresses the problem of wrinkling of a surface or surfaces of an evacuated insulation panel having a corestock therein of a porous or open-celled rigid material matrix, such as an open-cell, alkenyl aromatic polymer foam, by providing a corestock having indentations therein. When the corestock shrinks upon evacuation and/or exposure to elevated temperatures, the deformable receptacle or enclosure surrounding the corestock deforms to the shrunken corestock. The indentations provide extra surface area for the receptacle to deform or conform within. Without the indentations, wrinkles would form in the receptacle upon shrinkage of the corestock. The invention significantly improves the aesthetics and physical appearance of the panel. An additional benefit is reduced evacuation time. Preferably one or both of the one or more porous or open-celled rigid material matrixes and the one or more plates have a plurality of indentations. The indentations necessarily extend in at least one dimension across the surface of a material matrix, but preferably the indentations extend in two dimensions across the surface of one or both of the one or more porous or open-celled rigid material matrixes and the one or more plates. In one embodiment, the matrix has indentations therein in a criss-crossing rectangular or diagonal pattern across substantially the entire surface of one or both of the one or more porous or open-celled rigid material matrixes and the one or more plates. In another embodiment, the matrix has indentations therein in a dimple pattern across substantially the entire surface of one or both of the one or more porous or open-celled rigid material matrixes and the one or more plates. Although generally the indentations are about 3.2 millimeters or less in depth and about 3.2 millimeters or less across, they may also be larger for particular corestocks. Indentations in a surface or surfaces of the matrix may take a variety of forms such as dimples, grooves, or troughs. The indentations may take a regular or irregular pattern across a surface. Indentations may traverse or extend across the surface continuously or non- continuously. The indentations extend in two dimensions across a surface or surfaces of the matrix. The indentations preferably extend generally from one edge of the matrix to another. If the indentations are in the form of dimples, they preferably occur at regular intervals across substantially an entire surface or surfaces of the matrix. If the indentations are in the form of grooves or troughs, they preferably criss-cross as they traverse or extend across the surface. Preferably, indentations are provided at an incidence and at a depth such that the deformable receptacle will rest upon the surfaces of the matrix and the indentations within upon shrinkage of the corestock and that the surfaces of the receptacle are substantially free of wrinkles. In other words, the additional corestock surface area provided by the indentations after shrinkage of the corestock preferably approximately corresponds to the total surface area of the corestock anticipated to be lost due to shrinkage. Indentations may be to any depth or width within the corestock but preferably have a depth of about 1/8 inch (3.2 millimeters) or less and a width of about 1/8 inch (3.2 millimeters) or less. Indentations may be impressed into the corestock by any means known in the art such as the following: a) passing the foam through a set of opposing impressing rollers having the desired groove pattern as raised ridges in the rollers; b) impressing with opposing plates having the desired groove pattern as raised ridges in the plates; c) impressing the desired pattern with a series of wires positioned adjacent the corestock; d) cutting the desired pattern into the corestock using knives, saws, routers, or water spray; and e) melting the desired pattern into the corestock with hot wires or other heat source. In the case of a) and b), momentary impression by the raised ridges is usually sufficient to leave permanent indentations, although impression for longer periods of time may be desirable if the corestock is being compressed for other reasons. Figures 1 and 2 show two embodiments of the present invention. In Figure 1, panel 10 comprises a foam 12 and a receptacle 14. Grooves 16 are impressed within foam 12 and traverse it continuously in a diagonal or criss-cross pattern. Grooves 16 extend in two dimensions (length and width) substantially across foam 12. In Figure 2, panel 20 comprises a foam 22 and a receptacle 24. Grooves 26 are impressed within foam 22 and traverse it continuously in a criss-crossing rectangular pattern or grid. Receptacle 24 conforms substantially to the shape of foam 22 and rests substantially within grooves 26 as shown in Figure 3 A and Figure 3B. Grooves 26 extend in two dimensions (length and width) substantially across foam 22. Panels 10 and 20 each have a substantially non- wrinkled appearance. Figure 4 shows a panel 30 not in accordance with the present invention. Panel 30 comprises a foam 32 and a receptacle 34. Receptacle 34 has wrinkles 36 therein. Receptacle 34 does not conform to the shape of foam 32. The raised configuration of wrinkles 36 is shown in Figures 5A and 5B. If a given wrinkle 36 is large enough, it may define an evacuated cavity 38 underneath it above foam 32. This invention may be useful for the manufacture of any vacuum insulation panel which utilizes a corestock which exhibits contraction upon exposure to atmospheric pressure or elevated temperatures while encapsulated within a barrier pouch or receptacle. Examples of suitable corestock materials for use in this invention are polystyrene foam; other open cell thermoplastic foam such as polypropylene, preferably the polypropylene foam described in U.S. patent 5,527,573, which is hereby incorporated by reference; polycarbonate foams; thermoset foams, such as polyurethane foam, epoxy-resin foams, formaldehyde foams, phenolic foams, Isocyanurate foams; or any other polymeric material, either thermoplastic or thermoset, which has an open cell structure allowing removal of air and gas from the cells before encapsulation. Other materials generally useful as corestock materials in the manufacture of vacuum insulation panels which may benefit from the application of this invention are silica or other powder filled panels if the loose powder is sufficiently compressed or bonded in any way to form a unified structure, which is then scored to produce a smooth surface after evacuation. Additionally, this invention can be applied to compressed fiberglass or glass bead panels, if the core is sufficiently solid to allow scoring of the surface, and to aerogel and xerogel filler materials, which exhibit shrinkage upon encapsulation Winton VIP's. Preferred corestock materials are polystyrene and polypropylene foams, with polystyrene foams being especially preferred. Prior to inco oration in an evacuated panel, a foam may, optionally, be compressed to increase insulating capability on a per unit thickness basis as taught in WO 97/27986, which is incorporated herein by reference. This reference teaches that foams are desirably compressed to about 30 to about 90 percent, preferably from about 40 to about 70 percent, and more preferably 50 to about 60 percent of their initial (original) thickness or volume prior to compression. Desired compression levels vary as function of polymer identity, foam physical properties, level of evacuation, and desired insulating performance. Compression to increase insulating capability on a per unit thickness basis may be accomplished by any means known in the art such as between opposing, moveable parallel plates, between a moveable plate and a stationary plate or surface, or opposing rollers or belts. Compression may be applied in one step or in multiple steps in sequence. When compression occurs in multiple steps, it is preferable to allow the foam to relax between compression steps by removing the source of compression. The foam may, optionally, also be compressed to impart dimensional stability. The foam is compressed and simultaneously heated for a period of time sufficient to render the foam dimensionally stable. Such compression and heating to impart dimensional stability is taught in Attorney Docket No. 43401, filed July 14, 1997, which is incorporated herein by reference. Compression to impart dimensional stability must be substantially maintained at a desired level for a period of time. Typically, such compression will be carried out by opposing parallel plates or belts positioned to press together opposing, major surfaces of a foam. The degree of compression required to impart dimensional stability can be as little as about 5 percent to about 10 percent of initial thickness or volume prior to compression. In a preferred process, compression and heating to impart dimensional stability is carried out simultaneously indentation of a surface or surfaces of the foam. The foam is compressed by opposing parallel plates having raised surfaces corresponding to the desired indentation pattern. The foam is heated and compressed simultaneously for a period of time sufficient to impart dimensional stability and indentations to the foam. The time period will depend upon . foam composition and physical properties, extent of compression, and exposure temperature. The period of time may be as little as a few moments, but will typically be about one minute or more. About one to ten minutes is most typical. The heating step is carried out or effected by heating an open -cell alkenyl aromatic polymer foam and maintaining it at a temperature for a time sufficient (in conjunction with the compression step) to impart dimensional stability to the foam. The temperature required will vary according to polymer physical properties and foam composition, but will typically be within about 10°-20°C (less than) of the glass transition temperature. For polystyrene resins of the type commonly employed in foams, typical glass transition temperatures range from about 100°C-110°C. Suitable exposure (heating) temperatures for polystyrene foams will typically range from about 85°C to about 110°C. The temperature profile within the foam may be uniform or non-uniform throughout; the temperature profile may be non- uniform so long as the temperature is at a sufficient level at both the exterior and interior portions of the foam to impart the desired dimensional stability (in conjunction with the compression step). The foam may be evacuated by any means known in the art for withdrawing gases such as with a suction nozzle or by placement in an evacuated chamber. Hermetic sealing of the deformable receptacle typically takes place after the desired level of evacuation has been achieved. To reduce the time required to evacuate, the skin layer of the foam is preferably removed by planing or skiving to obtain maximum open-cell surface exposure area. The foam has an open cell content of about 70 percent or more, preferably about 90 percent or more, and most preferably about 95 percent or more prior to compression according to ASTM D2856-A. The foam is preferably as close as possible to complete or 100 percent open-cell. The open cell content after compression, if any, will be equal to or greater than the open cell content prior to or before compression. The panel and the open cells of the foam are evacuated to a partial vacuum or near total vacuum of subatmospheric absolute pressure. The foam is evacuated to an absolute pressure of about 10 torr or less, more preferably about 1 torr or less, and most preferably about 0.1 torr or less in its open cells. The foam (prior to compression, if any) has a density of about 16 to about 150 kg/m 3 and most preferably about 25 to about 60 kg/m 3 according to ASTM D- 1622-88. Foam density will increase proportionately with compression. The insulation panel may be formed from a foam of any desired size, shape, thickness, or dimension. Panels are most commonly formed from foams which are square or rectangular in width and length. Plank foams and sheet foams are useful. Thicknesses of about 1/8 inch (3.2 millimeters) to about 2 inches (50.8 millimeters) are most common, but thicknesses outside that range are possible. Other possible shapes include L-shaped foams and block- shaped foams useful in corners. The panel most commonly comprises a single layer or piece of foam but may comprise two or more adjacent or stacked layers or pieces. The panel preferably contains an infrared attenuating agent ( IAA) to enhance its insulating performance. The IAA is preferably dispersed in the foam but could be dispersed in one or more film layers attached to the foam or part of the receptacle as a part of a laminate. The IAA is composed of a different substance than the polymer substrate of the foam in which it is incorporated. The IAA may absorb and/or reflect infrared radiation. Useful IAA include particulate flakes of metals such as aluminum, silver, and gold; titanium dioxide; and carbonaceous substances such as carbon black, activated carbon black and graphite. Useful carbon blacks include thermal black, furnace black, acetylene black, and channel black. Preferred IAA are thermal black and graphite. The IAA preferably comprises between about 1.0 and about 25 weight percent and preferably between about 2.0 and about 20 weight percent and most preferably about 3.0 to about 10 weight percent based upon the weight of the polymer material. Various additives may be incorporated in the foam such as inorganic fillers, pigments, antioxidants, acid scavengers, ultraviolet absorbers, flame retardants, processing aids, extrusion aids, and the like. The panel may be used to insulate a surface by applying it to the surface. Such panels are useful in any conventional insulating applications such as roofing, building and construction panels, refrigerators, freezers, controlled temperature rooms, controlled temperature shipping containers and packages, water heaters, refrigerated trucks and rooms, etc. A substantially wrinkle-free insulation panel may be formed as according to the following: a) providing a corestock of an open cell alkenyl aromatic polymer foam comprising an alkenyl aromatic polymer material, b) indenting one or more surfaces of the foam: c) providing a deformable receptacle capable of receiving and retaining the foam; d) placing the foam within the receptacle; e) evacuating the open cells of the foam and the interior of the receptacle; f) hermetically sealing the receptacle to form the panel; and g) allowing the foam to shrink and the receptacle to conform substantially within the indentations. The open cells and the interior of the panel is evacuated to about 10 torr or less, more preferably to about 1 torr or less, and most preferably to about 0.1 torr or less absolute pressure. The receptacle or enclosure of the evacuated panel may be formed of any of those known in the a * rt. One embodiment of an evacuated panel employs a receptacle or enclosure formed of a laminate sheet of three or more layers. The outer layer comprises a scratch resistant material such as a polyester or a nylon. An interior layer or layers comprise a barrier material such as aluminum, polyvinylidine chloride, or polyvinyl alcohol. The barrier material may be in the form of a separately applied foil or film or, in the case of a metal, may be applied by vapor deposition The inner layer comprises a heat seal able material such as polyethylene or ethylene/acrylic acid copolymer. Additional teachings are seen in U.S. Patent No. 5,346,928 and 5,627,219, which is incorporated herein by reference. To further enhance the long-term performance of the vacuum panel, the evacuated interior of the panel may be provided with a "getter" material. The getter material adsorbs gases and/or vapors which seep or permeate into the vacuum panel over time. Conventional getter materials include metal and metal alloys of barium, aluminum, magnesium, calcium, iron, nickel, and vanadium. Teachings to suitable getter materials include but are not limited to those set forth in U.S. Patent Nos. 5,191,980; 5,312,606; 5,312,607; and WO 93/25843, which are incorporated herein by reference. Other types of useful getter materials include conventional desiccants, which are useful for absorbing water vapor or moisture. Such materials are advantageously incorporated into the evacuated insulation panel in the form of a packet having a porous or permeable wrapper or receptacle containing the material therein. Useful materials include silica gel, activated alumina, aluminum-rich zeolites, calcium chloride, calcium oxide, barium oxide, and calcium sulfate. A preferred material is calcium oxide. Open-cell foams of virtually any average cell size can be employed in the present invention, but it is preferable to use a foam with an average cell size as small as possible to minimize foam thermal conductivity. Preferred foams are microcellular and have an average cell size of about 70 micrometers or less, more preferably about 30 micrometers or less, and most preferably about 10 micrometers or less according to ASTM D3576-77. The cell size or pore size (diameter) for the microcellular foams is determined according to ASTM D3576-77 except that measurement is taken from an enlarged photograph obtained by scanning electron microscopy instead of measurement taken directly from the foam. The foam can be formed from any thermoplastic polymer resin which exhibits relatively high modulus and is capable of being blown into a foam. Preferred resins include those exhibiting a modulus of greater than 30,000 pounds per square inch (206,850 kilopascals) according to ASTM D695. Also useful are thermoset polymer foams such as polyurethane foams which exhibit some degree of shrinkage upon evacuation and/or exposure to heat or high temperature. A preferred foam is an extruded alkenyl aromatic polymer foam. Extruded alkenyl aromatic polymer foams are generally prepared by heating a polymer material to form a plasticized or melt polymer material, incorporating therein a blowing agent to form a formable gel, and extruding the gel through a die to form the foam product. Prior to mixing with the blowing agent, the polymer material is heated to a temperature at or above its glass transition temperature or melting point. The blowing agent may be incorporated or mixed into the melt polymer material by any means known in the art such as with an extruder, mixer, blender, or the like. The blowing agent is mixed with the melt polymer material at an elevated pressure sufficient to prevent substantial expansion of the melt polymer material and to generally disperse the blowing agent homogeneously therein. A nucleating agent additive may be blended in the polymer melt or dry blended with the polymer material prior to plasticizing or melting. The formable gel is typically cooled to a lower temperature to optimize or attain desired physical characteristics of the foam. The gel may be cooled in the extruder or other mixing device or in separate coolers. The gel is then extruded or conveyed through a die of desired shape to a zone of reduced or lower pressure to expand to form the foam. The zone of lower pressure is at a pressure lower than that in which the foamable gel is maintained prior to extrusion through the die. The lower pressure may be superatmospheric, subatmospheric (evacuated or vacuum), or atmospheric level. Most preferred microcellular foams are extruded, microcellular alkenyl aromatic polymer foams. They are preferred because it is possible to make such foams to a relatively small average cell size, such as about 70 micrometers or less. Extruded, open-cell microcellular alkenyl aromatic polymer foams having an open cell content of about 70 percent or more and an average cell size of about 70 micrometers or less may be made by the following process: a) heating an alkenyl aromatic polymer material to form a melt polymer material; b) incorporating into the melt polymer material a nucleating agent additive at from about 0.1 to about 5 parts by weight per hundred parts polymer material; c) incorporating into the melt polymer material at an elevated pressure to form a foamable gel a blowing agent of which about 50 mole percent or more and preferably about 70 mole percent or more is selected from the group consisting of lJ-difluoroethane (HFC- 152a), lJJ-trifluoroethane (HFC-143a), 1,1,1,2 -tetrafluoro-ethane (HFC- 134a), chlorodifluoromethane (HCFC-22), carbon dioxide (CO2), and difluoromethane (HFC-32), ethyl chloride, and mixtures of the foregoing based upon the total number of moles of blowing agent, the blowing agent being present at about 0.06 to about 0J7 gram-moles or less and preferably about 0.08 to about 0J2 gram-moles or less per kilogram of polymer material; d) cooling the foamable gel to a foaming temperature sufficient to form a foam having about 70 percent or more open cell content; and e) extruding the formable gel through a die into a region of lower pressure to form the foam. Preferred foaming temperatures will vary from about 1 10°C to about 150°C and preferably about 115°C to about 125°C depending upon foaming-forming compositions and process conditions. Additional teachings to microcellular foams are seen in WO 96/34038, which is incorporated herein by reference. Suitable alkenyl aromatic polymer materials include alkenyl aromatic homopolymers and copolymers of alkenyl aromatic compounds and copolymerizable ethylenically unsaturated comonomers. The alkenyl aromatic polymer material may further include minor proportions of non-alkenyl aromatic polymers. The alkenyl aromatic polymer material may be comprised solely of one or more alkenyl aromatic homopolymers, one or more alkenyl aromatic copolymers, a blend of one or more of each of alkenyl aromatic homopolymers and copolymers, or blends of any of the foregoing with a non-alkenyl aromatic polymer. Regardless of composition, the alkenyl aromatic polymer material comprises greater than 50 and preferably about 70 percent or more by weight alkenyl aromatic monomeric units. Most preferably, the alkenyl aromatic polymer material is comprised entirely of alkenyl aromatic monomeric units. Suitable alkenyl aromatic polymers include those derived from alkenyl aromatic compounds such as styrene, alphamethylstyrene, ethylstyrene, vinyl benzene, vinyl toluene, chlorostyrene, and bromostyrene. A preferred alkenyl aromatic polymer is polystyrene. Minor amounts of monoethylenically unsaturated compounds such as C 2 . 6 alkyl acids and esters, ionomeric derivatives, and C _ 6 dienes may be copolymerized with alkenyl aromatic compounds. Examples of copolymerizable compounds include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, acrylonitrile, maleic anhydride, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, methyl methacrylate, vinyl acetate and butadiene. Preferred foams comprise substantially (i.e., about 90 percent or more, preferably about 95 percent or more by weight and most preferably entirely of polystyrene. It is contemplated that the present invention could be practiced by placing one or more rigid plates having indentations therein at one or more surfaces of a foam within an evacuated insulation panel. The indentations could take the form, pattern, and dimensions as described above for indentations within the foam. The panel could be assembled as described above except that one or more plates are inserted within the deformable receptacle along with the foam. For a typical rectangular or square panel, plates will typically be situated at the two major surfaces of the foam. The plate or plates can be made of any natural or synthetic material, such as for example, metals, wood, plastic, which is chemically inert to the corestock and the receptacle, as long as it has sufficient rigidity to resist deformation during evacuation. Upon evacuation of the panel and shrinkage of the foam, the deformable receptacle will conform to the shape of the foam and rest substantially within the indentations of the plate or plates. The use of plates inside a VIP, or outside a VIP, shields low melting point corestocks from transient heat exposure, such as is experienced during the foaming of polyurethane foam around a VIP during the construction of an appliance. While embodiments of the foam, evacuated insulation panel, and method of the present invention have been shown with regard to specific details, it will be appreciated that depending upon the manufacturing process and the manufacturer's desires, the present invention may be modified by various changes while still being fairly within the scope of the novel teachings and principles herein set forth. Example 1 Open cell polystyrene foam suitable for use in vacuum insulation panels was made per U. S. Patent No. 5,674,915. This foam was compressed to 2.5 cm (1 inch) as taught in WO 97/27986. A series lines were then compressed into the surface of the foam on both sides using the edge of metal spatula which was 0.85 cm (1/3 inch) thick. These lines were permanently depressed into the foam surface by siding the spatula with pressure along the edge of a straight ruler while pushing down with pressure. The resultant depressed lines in the foam were approximately 0J6 cm (1/16 inch) at the top, 0.008 cm (1/32 inch) at the bottom, and 0J6 cm (1/16 inch) deep. These depressions were placed in a diamond pattern with the side of the parallel lines 5J cm (2 inches) apart on both the top and bottom surfaces of the board. Vacuum panels without this pattern exhibited extremely large folds in the film upon evacuation. Vacuum panels with this pattern has significantly reduced to no film folds. Example 2 Foam produced identical to Example 1 was passed through parallel compression rollers which had a raised pattern machined into the surface of the rollers such that depressed lines were pressed into the foam as it passed between the rollers. These ridges on the compression rollers were 0.24 cm (3/32 inch) deep, 0.008 cm (1/32 inch) at the top and 0J6 cm (1/16 inch) at the bottom. The pattern impressed into the foam was a diamond shape with 5J cm (2 inches) between the parallel sides of the diamond. Vacuum insulation panels made with this foam showed significantly less wrinkles on the surface of the panel than foam made without this pattern impressed into the foam. Example 3 An open cell polyurethane foam with a cell size averaging 50 mm was prepared with surface depressions in the same was as Example 1. The sample with the surface grooves has no film wrinkles on either side of the panel while the sample which did not have surface grooves did have surface wrinkles.

Claims: WHAT IS CLAIMED IS: 1. An evacuated insulation panel comprising: A) a deformable receptacle which has been evacuated to an absolute pressure of about 10 torr or less and hermetically sealed surrounding B) a corestock of one or more porous or open-celled rigid material matrixes having one or more indentations therein which extend in at least one dimension across a surface of a rigid material matrix, wherein the receptacle substantially conforms to the shape of the corestock and the indentations therein and the finished panel has surfaces which are substantially non- wrinkled. 2. An evacuated insulation panel comprising: A) a deformable receptacle which has been evacuated to an absolute pressure of about 10 torr or less and hermetically sealed surrounding B) a corestock of one or more porous or open-celled rigid material matrixes, optionally having one or more indentations therein which extend in at least one dimension across a surface of a rigid material matrix, and C) one or more rigid plates having one or more indentations therein, the one or more plates being situated contiguous to a major surface of the corestock, wherein the receptacle substantially conforms to the shape of the corestock and the plate or plates and the indentations therein, and the finished panel has surfaces which are substantially non-wrinkled. 3. The panel of one of Claims 1-2, wherein one or both of the one or more porous or open-celled rigid material matrixes and the one or more plates have a plurality of indentations. 4. The panel of one of Claims 1-3, wherein the indentations extend in two dimensions across the surface of one or both of the one or more porous or open-celled rigid material matrixes and the one or more plates. 5. The panel of Claim 4, wherein the matrix has indentations therein in a crisscrossing rectangular or diagonal pattern across substantially the entire surface of one or both of the one or more porous or open-celled rigid material matrixes and the one or more plates. 6. The panel of one of Claims 1-4, wherein the matrix has indentations therein in a dimple pattern across substantially the entire surface of one or both of the one or more porous or open-celled rigid material matrixes and the one or more plates. 7. The panel of one of the previous Claims, wherein the indentations are about 3.2 millimeters or less in depth and about 3.2 millimeters or less across. 8. An evacuated insulation panel, the panel comprising a corestock of an open- cell alkenyl aromatic polymer foam and a deformable receptacle, the foam comprising an alkenyl aromatic polymer material comprising greater than 50 weight percent of alkenyl aromatic monomeric units based upon the total weight of the alkenyl aromatic polymer material, the foam having an open cell content of about 70 percent or more, the receptacle being capable of receiving the foam and being hermetically sealed, the foam being situated within the receptacle, the receptacle being hermetically sealed, the open cells of the foam and the interior of the receptacle being evacuated to an absolute pressure of about 10 torr or less, the foam having indentations therein extending in two dimensions across a surface of the foam, the receptacle substantially conforming to the shape of the foam and the indentations therein. 9. The panel of Claim 8, wherein the foam has indentations therein in a crisscrossing rectangular or diagonal pattern across substantially the entire surface of the foam. 10. The panel of Claim 8, wherein the foam has indentations therein in a dimple pattern across substantially the entire surface of the foam. 11. The panel of Claim 8, wherein the indentations are about 3J millimeters or less in depth and about 3.2 millimeters or less across. 12. The panel of Claim 8, wherein the foam comprises an alkenyl aromatic polymer material comprising about 70 weight percent or more of alkenyl aromatic monomeric units based upon the total weight of the alkenyl aromatic polymer material, the foam having an open-cell content of about 90 percent or more, the open-cells of the foam and the interior of the receptacle being evacuated to an absolute pressure of about 1 torr or less, the foam having a density of about 16 to about 150 kilograms per cubic centimeter, the foam having an average cell size of about 70 micrometers or less. 13. The panel of Claim 8, wherein the foam comprises an alkenyl aromatic polymer material comprising about 70 weight percent or more of alkenyl aromatic monomeric units based upon the total weight of the alkenyl aromatic polymer material, the alkenyl aromatic polymer material comprising polystyrene, the foam having an open-cell content of about 95 percent or more, the open-cells of the foam and the interior of the receptacle being evacuated to an absolute pressure of about 0.1 torr or less, the foam having a density of about 25 to about 60 kilograms per cubic centimeter, the foam having an average cell size of about 30 micrometers or less. 14. An evacuated insulation panel, the panel comprising; a) a corestock of an open-cell alkenyl aromatic polymer foam, b) one or more rigid plates, and c) a deformable receptacle, the foam comprising an alkenyl aromatic polymer material comprising greater than 50 weight percent of alkenyl aromatic monomeric units based upon the total weight of the alkenyl aromatic polymer material, the foam having an open-cell content of about 70 percent or more , the plate being situated contiguous to a major surface of the foam, the receptacle being capable of receiving the foam and the plate and being hermetically sealed, the foam and the plate being situated within the receptacle, the receptacle being hermetically sealed, the open-cells of the foam and the interior of the receptacle being evacuated to an absolute pressure of about 10 torr or less, the plate having one or more indentations therein, the receptacle substantially conforming to the shape of the foam and the indentations within the plates. 15. The foam of claim 14, wherein the foam has indentations therein in a criss- crossing rectangular or diagonal pattern across substantially the entire surface of the foam, the indentations being about 3.2 millimeters or less in depth and about 3J millimeters or less across. 16. The foam of claim 14, wherein the foam has indentations therein in a dimple pattern across substantially the entire surface of the foam, the indentations being about 3.2 millimeters or less in depth and about 3.2 millimeters or less across. 17. A method of making an evacuated insulation panel having a substantially non- wrinkled surface, comprising: a) providing a corestock of an open-cell alkenyl aromatic polymer foam comprising and alkenyl aromatic polymer material, the alkenyl aromatic polymer material comprising greater than 50 weight percent of alkenyl aromatic polymer units based upon the total weight of the alkenyl aromatic polymer material, the foam having about 70 percent or more open cell content; b) indenting one or more surfaces of the foam wherein the indentations extend in two dimensions across the surface or surfaces of the foam; c) providing a deformable receptacle capable of receiving and retaining the foam; d) placing the foam within the receptacle; e) evacuating the open cells of the foam and the interior of the receptacle to an absolute pressure of 10 torr or less; f) hermetically sealing the receptacle to form the panel: g) allowing the foam to shrink and the receptacle to conform substantially within the indentations. 18. A method of making an evacuated insulation panel having a substantially non- wrinkled surface, comprising: a) providing a corestock of one or more porous or open-celled rigid material matrixes; b) indenting one or more surfaces of the matrix wherein the indentations extend in at least one dimension across the surface or surfaces of the matrix; c) providing a deformable receptacle capable of receiving and containing the corestock and placing the corestock therein; d) evacuating the interior of the receptacle to an absolute pressure of 10 torr or less; e) hermetically sealing the receptacle. 19. The evacuated insulation panel of Claim 1 , Claim 2 or Claim 18, wherein the rigid material matrix of the corestock is an open cell thermoplastic foam, a polycarbonate foam, a thermoset foam, a polyurethane foam, an epoxy-resin foam, a formaldehyde foam, a phenolic foam, an Isocyanurate foam, silica, fiberglass, glass bead, aerogel, or xerogel. 20. The evacuated insulation panel of Claim 19, wherein the rigid material matrix of the corestock is polystrene or polypropylene.

Inventors: MALONE BRUCE A, MALONE, BRUCE, A.
Applicants: DOW CHEMICAL CO, MALONE BRUCE A, MALONE, BRUCE, A., THE DOW CHEMICAL COMPANY
Application year: 1998
Main classification: F25D23
IPC codes: B32B5, F16L59, F25D23