Patent Publication Number: US-2004058119-A1

Title: Vacuum insulated panel and container

Description:
RELATED APPLICATION  
     [0001] This application is a continuation-in-part of application Ser. No. 08/997,126, filed Dec. 23, 1997 and also claims the benefit of provisional patent application Serial No. 60/033,827, filed Dec. 23, 1996. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] In the production of insulated panels or containers, for example, of the general type disclosed in U.S. Pat. No. 3,416,692, No. 5,082,335, No. 5,252,408 and No. 5,273,801, it is known to place a panel of microporous insulation material, such as a rigid foam having extremely small open cells, within an envelope or bag of an air impervious flexible barrier film. A plurality of the open bags are then usually placed within a vacuum chamber which evacuates air from the foam, after which each bag is sealed while in the vacuum chamber. It is also known to evacuate a sealed insulation bag by attaching an evacuation tube to a sealed bag, for example, as disclosed in above-mentioned U.S. Pat. No. 5,252,408.  
       [0003] In the production of vacuum insulation panels such as disclosed in the above-mentioned patents, it is desirable to provide for rapid evacuation of the air from the microporous insulation media, especially from foam material within large panels, and to assure that substantially all of the air is evacuated from the media. It is also desirable to determine that an evacuated panel does not have any leakage before the panel is sealed and to provide for efficiently producing a vacuum insulated box-like container which has minimal panel joints in order to minimize thermal leak paths and provide the container with a maximum R value.  
       SUMMARY OF THE INVENTION  
       [0004] The present invention is directed to an improved vacuum insulated panel and container which have the maximum R value per inch of wall thickness and to an efficient and dependable method of producing such panels and containers. In accordance with preferred embodiments of the invention, a generally flat panel or box-like container is produced by forming parallel spaced grooves within a flat panel of rigid microporous plastics foam having open cells on the order of 150 microns or less. The foam panel is inserted into a partially sealed envelope or bag of gas impervious barrier plastics film material or the foam panels are formed into an open end box which is inserted into a bag of the barrier film material. The bag includes an integrally formed tubular evacuation portion and is sealed around the panel or box of the foam material.  
       [0005] The bag is then evacuated with a computer control evacuation system including a nozzle which is releasably sealed to the tubular evacuation portion of the bag. The grooves provide for rapid evacuation of the foam and for receiving the barrier film material during evacuation. The evacuation system senses the vacuum level within the bag during evacuation and automatically controls a set of valves which may provide for directing an additive gas into the foam after a very low level of the evacuation is attained. The evacuation system also checks or monitors the vacuum to assure a constant vacuum level within the bag before the bag is sealed, and thereby assure the production of high quality vacuum insulation panels or containers. A thin layer of rigid foam is applied in liquid form to the outer surfaces of the vacuum insulated panel and allowed to cure to provide the panel with thermal and mechanical protection as well as a panel with a uniform thickness and a smooth outer surface.  
       [0006] Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0007]FIG. 1 is a perspective view of a vacuum insulated panel produced in accordance with the invention and with the center portion broken away;  
     [0008]FIG. 2 is an exploded perspective view showing the components of the panel in FIG. 1 and the nozzle used for evacuation;  
     [0009]FIG. 3 is a fragmentary plan view of the panel shown in FIG. 1 with a portion shown in section during the evacuation process;  
     [0010]FIG. 4 is a fragmentary plan view of the panel shown in FIG. 3 after the evacuation and sealing operations;  
     [0011]FIG. 5 is a perspective view of a vacuum insulated container constructed in accordance with another embodiment of the invention and with the center portion broken away;  
     [0012]FIG. 6 is an exploded perspective view of the components used to form the container of FIG. 5;  
     [0013] FIGS.  7 - 9  are perspective views illustrating the method of producing the vacuum insulated container shown in FIG. 5;  
     [0014]FIG. 10 is a schematic diagram of the system for evacuating the panel shown in FIG. 1 and the container shown in FIG. 5;  
     [0015]FIG. 11 is a fragmentary section through a vacuum insulated panel constructed in accordance with a modification of the invention;  
     [0016]FIG. 12 is a fragmentary section showing the panel of FIG. 11 after bending.  
     [0017]FIG. 13 is a fragmentary perspective view of a vacuum insulated panel having a thin outer protective layer of rigid foam, and constructed in accordance with a modification of the invention; and  
     [0018]FIG. 14 is an enlarged fragmentary section of the panel, taken generally on the line  14 - 14  of FIG. 13. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0019] A vacuum insulated panel  10  includes a core  12  of filler material in the form of a rigid foam having open cells which are extremely small, for example, on the order of four microns. One source for the microporous foam core  12  is Dow Chemical Company of Midland, Mich. As shown in FIG. 2, the rigid foam core  12  comprises a board or strip or panel having opposite side surfaces  14  in which are cut or formed parallel spaced evacuation passages or grooves  16 . The grooves extend the full length of the core  12  and intersect a common groove  19  formed within an end or edge surface  21  of the core  12 . Laterally extending grooves may also be used to intersect the grooves  16 .  
     [0020] The end groove  19  extends from a recess or cavity  23  which receives a spacer in the form of one or more strips  24  of plastic wire-like mesh which is retained within the cavity  23  by a plastic screen mesh  27  and a series of staples  28  extending into the foam core  12 . Preferably, each of the grooves  16  and  19  has a width of about 0.125 inch and a depth of about 0.200 inch. The foam core  12  is also provided with a slot  32  within an edge surface  33 , and a packet  36  of desiccant or getter material, such as calcium oxide, is inserted into the slot  32  to absorb any residual gas and/or moisture from the foam core.  
     [0021] The vacuum insulated panel  10  also includes a container or enclosure  40  for the rigid foam core  12 , and the enclosure is preferably in the form of a pouch or bag of flexible barrier film material  41  which is impervious to the passage of air and other gases. One form of flexible barrier film material  41 , which has performed satisfactorily, includes a plurality of polyester or MYLAR layers including an inner layer of heat-sealable polyethylene and an outer metalized or aluminum layer which is formed by laminating a metal foil to the film layer or by metal deposition on the layer. Sources of such flexible barrier film material are Fresco in Pennsylvania and DuPont in Delaware.  
     [0022] As shown in FIG. 2, the enclosure or bag  40  may be initially formed by double folding the barrier film material  41  or by using two sheets of the film material and then fusing or sealing together the inner opposing thermoplastic layers of the film material by a series of peripheral heat-seals  43  and  44  along two sides or one end of the bag. When the bag is initially formed, one end  46  of the bag is left open, and the opposite end is provided with an evacuation channel or passage  47  formed by a projecting tubular portion  48  of the bag. The integral tubular portion  48  has marginal heat-seals  51  which extend from the heat-seals  44  and includes a flared outer end portion  54  which forms an enlarged circular mouth for the evacuation passage  47 .  
     [0023] In the production of the vacuum insulated panel  10 , the rigid open cell foam core  12  with the attached spacer screens  24  and  27  and confined desiccant or getter package  36 , is inserted into the opening  46  of the enclosure or bag  40 . The open end portion of the bag  40  is then heat-sealed so that the bag  40  forms a positive air-tight enclosure completely surrounding the rigid foam core  12 .  
     [0024] When it is desired to evacuate or remove all of the air from inside the bag  40 , an evacuation tool  60  (FIG. 2) is used to remove the air within the bag  40  and from the microscopic open pores or cells within the rigid foam core  12 . The metal tool  60  has a tubular outer end portion  62  which is preferably connected by a flexible hose to an evacuation pump through a set of valves, as will be explained later. The opposite end of the tool  40  includes a metal evacuation tube  66  with a flared or flattened tip portion  68  which defines a suction slot. The tool  60  also includes a cylindrical portion  69  having a tapered or rounded nose surface  72  with a circumferential groove receiving a resilient O-ring  74 .  
     [0025] To evacuate the bag or enclosure  40 , the evacuation tube  66  is inserted into the tubular portion  48  of the bag  40  until the inner end of the flared tip portion  68  engages the spacer screen  27 , as shown in FIG. 3. After the tool  60  is inserted, the flared portion  54  of the evacuating tube  48  is pulled onto the rounded or tapered end surface  72  of the tool  60 , as shown in FIG. 3, until the O-ring  74  forms an airtight seal with the film material. A vacuum gel may be coated over the O-ring  74  and within the flared portion  54  to assure an air-tight seal between the tool  60  and the evacuation tube  48 . As the flattened tip portion  68  engages the spacer screen  27 , the tubular portion  48  is caused to bunch and form a bellows-like neck portion. It is also within the scope of the invention to use a nozzle which supports a stack of resilient O-rings for receiving the tubular portion  48 , and a clamping collar is shifted by an actuator axially over the tubular portion  48  and around the O-rings to compress the tubular portion against the O-rings.  
     [0026] The evacuation pump is operated until a vacuum of under 0.1 Torr and preferably about 0.05 Torr is obtained within the bag and the cells of the rigid foam core  12 . After the bag  40  is evacuated, the bag is tested for leaks, and while a vacuum is still being applied, the tool  60  is retracted to the position shown in FIG. 4. The evacuation tube  48  then receives a heat-seal  78  so that the evacuated bag  40  is completely sealed to prevent air from re-entering the evacuated open cells of the foam core  12 . The evacuation tube  48  is then removed by cutting the tube adjacent the heat-seal  78 , after which the heat-sealed peripheral edge portions of the enclosure  40  are folded back and attached by adhesive or tape to the adjacent side surfaces of the panel  10 , as shown in FIG. 1. The folded back peripheral edge portions may also be retained by extruded plastic U-shaped channels.  
     [0027] Referring to FIGS.  5 - 9  which illustrate another embodiment of the invention, a vacuum insulated box-like container  90  is constructed similar to the panel  10  and includes a box-shaped core  92  (FIG. 6) of the open cell microporous rigid foam material. The foam core  92  is formed from flat foam side panels  94  each of which has parallel spaced grooves  96  on its outer surface. The panels are joined together at the corners by dove-tail connections  98  (FIG. 7) or tongue and groove connections, and one end of the core  92  is closed by a bottom panel  102  having a grid of X-Y grooves  96  which intersect the grooves  96  within the sidewall panels  94 . The bottom panel  102  is connected to the sidewall panels by tongue and groove connections  104 , and a rectangular cavity  107  is formed Within the bottom surface of the bottom panel  102 . The cavity  107  receives one or more strips of plastic mesh  108  which are retained by a plastic screen mesh  109  and a set of staples  28 , as described above in connection with FIGS. 2 and 3.  
     [0028] As shown in FIG. 7, the foam box  92  is inserted into the open end of a plastic film envelope or bag  115  which is constructed similar to the envelope or bag  40  described above and of the same flexible barrier film material  41 . The bag  115  also includes an integral tubular portion  48  which is used as described above for evacuating the bag. After the foam core box  92  is inserted into the bag  115  (FIG. 7), the bag  115  is closed on its open end by a heat seal  117  (FIG. 8). The foam core box  92  and bag  115  are then evacuated through the integral evacuation tube  48 , using the method described above and in more detail in connection with FIG. 10.  
     [0029] Referring to FIG. 9, as the bag  115  is being evacuated, the end portion of the bag projecting from the box  92  (FIG. 8) is sucked or pulled down into the open end of the box  92 , and the external flap portions  118  (FIG. 5) of the collapsed bag are folded against the outer surfaces of the evacuated container  90 . If desired, the parallel spaced grooves  96  may also be formed within the inner surfaces of the side panels  94  and bottom panel  102  to provide for more rapid evacuation and to provide for accumulating the barrier film material as it shrinks against the foam core. It is also within the scope of the invention to form or produce two vacuum insulated containers  90  with one container being slightly larger than the other container so that the smaller container interfits into the larger container in opposing relation to form a completely enclosed vacuum insulated container. The open end of the insulated container  90  may also be closed by a vacuum insulated panel  10  which interfits snugly into the open end of the container  90 .  
     [0030] Referring to FIG. 10 which illustrates diagrammatically a system for evacuating a bag  40  or  115  and the foam core within the bag, the tubular portion  48  of the bag is inserted onto the nozzle  60  which is connected to a vacuum pump  120  through a manifold passage  122  connected to a set of valves  124 ,  126  and  128  and through a filter  130 . A vacuum sensor or transducer  132  senses the level of the vacuum within the manifold passage  122  and thus within the bag and nozzle  60 , and a passage including a valve  134  is connected to exhaust the manifold passage  122 . A bottle or tank  136  of compressed gas, such as helium, is connected to the manifold passage  122  through the valve  128 , and all of the valves  124 ,  126 ,  128  and  134  are solenoid actuated valves which are selectively controlled by a controller or computer  140 . A data line  142  connects the vacuum sensor or transducer  132  to the computer  140  so that the solenoid valves may be controlled or actuated in response to the level of vacuum created in the nozzle  60  and the bag by the vacuum pump  120 .  
     [0031] In operation of the evacuation system shown in FIG. 10, the bag is connected to the nozzle  60  while the exhaust valve  134  is open and the valves  124 ,  126  and  128  are closed. The computer  140 , through its operating software, then commences the evacuation process whereby valve  134  is closed and valve  124  is opened to allow the bulk of the evacuation air in the bag and any loose foam particles to flow through the filter  130  to the vacuum pump  120  where air is discharged through an exhaust port  144 . The filter  130  collects any loose foam particles, and the vacuum level is monitored by the transducer  132  which feeds back the vacuum level information to the computer  140 .  
     [0032] After air pressure has been reduced in the bag to the level of several Torr, the air flow is slower so that the flow does not carry significant foam dust particles. The computer  140  then closes the valve  124  and opens the valve  126  to increase the evacuation flow rate by bypassing the restriction of the filter  130 . After a pressure level below one Torr is attained, the computer  140  may, as an option, close the valve  126  and open the valve  128  to admit additive pressurized gas, such as helium, from the tank  136 . This gas is selected either to control the type of residual gas remaining within the bag at the completion of evacuation to provide improved insulation qualities, or to help purge residual gases from the foam core. The valve  128  is then closed by the computer  140 , and valve  126  is reopened to complete evacuation.  
     [0033] The computer  140  is programmed by its software to close periodically all of the valves and allow the resulting vacuum level in the bag and manifold  122  to be sensed by the transducer  132  so that the computer  140  may determine whether a satisfactory final vacuum level has been achieved and that there are no leaks in the bag before the bag is sealed. If the vacuum level has not been achieved, the valve  126  is reopened by the computer for a predetermined time after which the test cycle is repeated. After a satisfactory test result, the valve  126  is opened by the computer, and the operator seals the tubular portion  48 . The keyboard of the computer  140  is then used to enter a signal that the tube  48  on the bag has been sealed. The computer then closes valve  126  and opens valve  134  to flood the manifold  122  and nozzle  60  to atmospheric air pressure. This permits the bag evacuation tube  48  to be easily removed from the nozzle  60  so that the bag for the next panel or container may be connected to the evacuation system.  
     [0034] Referring to FIGS. 11 and 12, it is within the scope of the invention to form closely spaced grooves  16  within opposite sides of the foam panel  14  and to offset the grooves on one side from the grooves on the opposite side. When the foam and bag are evacuated, the film  41  collapses and is pulled into the groove  16 , as shown in FIGS. 1 and 11. The panel  10  may then be curved or bent, as shown in FIG. 12, without tearing or rupturing the foam core panel  14  or the film  41  at the corner.  
     [0035] Referring to FIGS. 13 and 14, a skin or layer  150  of polyurethane foam is applied to the outer surface or exterior of the vacuum insulated panel  10  after the panel is formed. Preferably, the layer has a thickness within the range of 0.060 inch and 0.250 inch. The foam within the layer  150  is preferably closed cell and has a density within a range of 1.0 pound per cubic foot to 4.0 pounds per cubic foot. For example, a density of 1.9 pounds per cubic foot has been found to provide desirable results. The layer  150  is applied in liquid form by a spray or as a laminated coating and may be applied to one or both flat side surfaces of the panel  10  or may surround the panel so that the layer also covers and bonds to folded sealed edge flanges  152  of the impermeable barrier film  41 . As also shown in FIG. 14, the parallel spaced grooves  16  within the core  12  of open-microcell foam material preferably have a depth substantially greater than the width of each groove, for example, a depth of {fraction (3/16)} inch and a width of {fraction (1/16)} inch. The narrow grooves are preferably cut into the foam core  12  with one inch spacing between adjacent grooves  16 . The narrower or thinner grooves  16  result in larger vacuum passages for more rapid evacuation since the barrier film  14  is sucked into the grooves by a lesser extent during the evacuation step. The narrow grooves also minimize the suction force applied to the barrier film bridging the grooves.  
     [0036] As apparent from the drawings and the above description, a vacuum insulated panel constructed in accordance with the invention provides desirable features and advantages. For example, the connected grooves  16  and  19  or  96  within the foam core  12  or  92  are narrow and deep so that the grooves continue to form evacuation passages even after the flexible enclosure film has been partially sucked into the grooves. The grooves also provide for better flow of urethane foam around a panel  10  when the panel is used between walls. Evacuation passages may also be formed internally within a foam core panel by securing together two foam boards with one or both having grooves adjacent the other board. The evacuation passages substantially decrease the time for evacuating the microscopic open cells within the foam material. The grooves also decrease the time for the desiccant pouch  36  to absorb any free moisture in the panel, allow for panel flexing or bending and take up wrinkling slack in the film when the bag is evacuated, as shown in FIGS. 11 and 12.  
     [0037] In addition, the evacuation tool  60  provides for efficiently evacuating the enclosure  40  through the evacuation tube  48  which seals against a resilient O-ring during evacuation. The flattened tip portion  68  also cooperates with the spacer screens  26  and  27  or  108  and  109  to assure that the slot-like suction opening within the tip portion is not blocked by the foam core  12  or  92  and does not become clogged with foam particles during evacuation. The flared tip portion  68  also assures that the evacuation tube  48  remains flat without wrinkles when the tool  60  is retracted in order to obtain an effective heat-seal  78 , as shown in FIG. 4.  
     [0038] The above method of efficiently forming a vacuum insulated panel  10  or container  90  uses relative low cost equipment and provides for flexiblity in that dependable panels or containers of various sizes and configurations may be produced with a substantially high R value per inch of thickness, for example, an R value over 30. Thus a vacuum insulated panel or container produced in accordance with the invention may be made in various shapes and sizes, such as a box, cylinder or three sided corner section, which are highly desirable for use in many applications such as in lining refrigeration or freezer cabinets and appliances, heating appliances, refrigerated containers and coolers and as insulation for a building.  
     [0039] The modification of the vacuum insulated panel shown in FIGS. 13 and 14 and including the exterior foam layer  150 , provides additional advantages. For example, the foam layer  150  positively adheres or bonds to the outer surface of the panel  10  and provides both a mechanical and thermal protection for the barrier film  41  and an open cell foam core  12 . That is, the foam layer  150  helps prevent the barrier film  41  from being punctured and also functions as a desiccant to the barrier film by restricting moisture from contacting the barrier film so that the barrier film&#39;s gas permeation rate remains low, thereby maximizing the life of the vacuum insulated panel  10 . A desiccating additive, such as hydrophillic precipitated silica or calcium oxide, may be added to the polyurethane or other exterior foam insulation material forming the layer  150  to enhance the desiccating properties of the foam coating or layer.  
     [0040] It is also apparent from FIGS. 13 and 14 that the exterior foam skin layer  150  may also be used to provide the panel  10  with a smooth exterior finish or surface and also with a uniform thickness. This is frequently desirable when the foam panel  10  is used in the manufacture of applicances such as refrigerators. The insulating panel is sandwiched between the outer cabinet and the inner liner, and a polyurethane foam is used to fill the gaps between the vacuum insulated panel and the outer cabinet and/or inner liner. The foam layer  150  also provides a thermal delay when used with in situ foaming by preventing the peak transient temperatures generated during the exothermic chemical reaction of the foaming process from being transferred to the barrier film  41  and the core material  12 . Also, while a semi-rigid or rigid polyurethane foam is described above for producing the protective layer  150 , other foam materials, such as polyethylene or polypropylene foams, may be used to form the layer  150  for some applications or uses of the panel  10 .  
     [0041] While the method and forms of vacuum insulation panel and container herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to the precise method and forms described, and that changes may be made therein without departing from the scope and spirit of the invention as defined in the appended claims.