Abstract:
A refrigerator cabinet is provided with a plastic liner, the inside wall of the refrigerator, which is resistant to chemical degradation by fluorocarbons. Freon and Freon substitutes used as blowing agents for foaming the insulation contained between an outer metal cabinet and on the inside wall of the refrigerator can cause blistering, cracking, and sometimes dissolution of materials used to form the plastic liner which is the inside wall of the refrigerator. There is provided a plastic liner which is resistant to those blowing agents and particularly to those blowing agents which are partially halogenated and tend to be more aggressive than Freon. The plastic liner wall maintains impact strength and toughness after exposure to fluorohydrocarbons conventionally employed in refrigerator units for in situ polyurethane foam production.

Description:
This is a continuation-in-part of application Ser. No. 07/758,641 filed Sep. 12, 1991, issued as U.S. Pat. No. 5,221,136. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a refrigerator cabinet appliance, the liner wall of which is resistant to attack by Freon and Freon substitutes. 
     BACKGROUND OF THE INVENTION 
     Typical refrigerator appliance cabinets consist of an outer metal cabinet, an inner plastic liner, typically ABS (acrylonitrile-butadiene-styrene) or HIPS (high impact polystyrene), and an insulating foam core, typically polyurethane foam. Blowing agents for the polyurethane foam are locked into the foam. Freon, a completely halogenated methane, fluorotrichloromethane, is presently employed commercially as the blowing agent. For environmental reasons, implemented by regulations, substitutes for Freon must be found. Proposed substitutes for Freon are halogenated hydrocarbons which contain at least one hydrogen atom. 
     Polyurethane blowing agents, such as Freon (CFC-11) and Freon substitutes, such as 2-fluoro-2,2-dichloroethane and 2,2-dichloro-1,1,1-trifluoroethane (HCFC 141b and HCFC 123, respectively), can cause liner blistering, catastrophic cracks, tiny cracks (crazing), and loss of impact properties (embrittlement), as well as stress whitening and/or dissolution. The blowing agents HCFC 141b and HCFC 123 appear to be more chemically aggressive than Freon (CFC-11) in attacking the liner. It is the common belief that blowing agent attack of the liner occurs on condensation of the blowing agent to liquid, which occurs on cooling. Cooling and condensation of the blowing agent does occur during shipping and storage. Shipping conditions are simulated during fabrication by cycling the appliance cabinet from hot to cold to cause evaporation and condensation of the blowing agent(s). 
     It is proposed to provide a plastic sheet structure to be thermoformed into a refrigeration liner that is resistant to chemical attack. 
     It is an object of the invention to provide a refrigeration appliance liner to be fabricated from a thermoformable, plastic sheet material exhibiting resistance to chemical attack (blistering, cracking, crazing, as mentioned above), by polyurethane foam blown with Freon (CFC-11) or potential Freon substitutes, including HCFC-123 and HCFC-141b, which are mentioned above. 
     It is an object of the invention to provide a refrigeration appliance liner to be fabricated from a thermoformable, plastic sheet material which retains a high level of toughness (impact properties) and strength (tensile properties), even at low temperatures (at 5° F. or less). 
     It is another object of the invention to provide a liner made from a plastic sheet material that maintains processability similar to HIPS or ABS, including favorable extrusion conditions and similar thermoforming behavior. 
     It is another object of the invention to provide a liner made from a plastic sheet containing a layer of a special multi-functional blend that exhibits excellent chemical resistance to Freon or potential Freon substitutes, may additionally function as an adhesive layer between optional layers of HIPS (or ABS) and polyolefin, and finally acts as a compatibilizing agent when regrind plastic sheet scrap is recycled to virgin plastics resin being extruded into the core sheet layer. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a refrigerator appliance is provided with a plastic liner which is substantially chemically inert to Freon and Freon substitutes. A conventional refrigerator appliance cabinet includes an outer metal cabinet, an inner plastic liner comprising ABS (acrylonitrile-butadiene-styrene) or HIPS (high impact polystyrene), and an insulating foam core, typically polyurethane foam. Blowing agent for the polyurethane foam is locked into the foam. 
     The plastic liner serves as the inner plastic wall of the refrigerator. The plastic wall is of variable thickness, as a result of thermoforming during fabrication. However, it is formed of a composite of relatively uniform thickness. 
     In accordance with the invention, the plastic liner comprises a barrier layer, which is substantially chemically inert to completely halogenated and partially halogenated hydrocarbons, e.g., chlorinated and/or fluorinated hydrocarbons used as blowing agents for polyurethane foam formation. In one embodiment of the invention, a core layer of ABS (acrylonitrile-butadiene-styrene) or HIPS (high impact polystyrene), for example by coextrusion or lamination, is affixed to the barrier layer. For visual attractiveness, a glossy patina on the barrier layer or the core layer must be present either due to the inherent properties of the core layer or by providing an independent layer of material which provides high gloss. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing of a refrigerator cabinet. 
     FIG. 2 is a schematic drawing of the plastic liner serving as the inner plastic wall of the refrigerator. 
     FIG. 3 is a fragmentary cross section of the composite forming the plastic liner. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be explained with reference to the appended drawings. 
     The refrigerator appliance of FIG. 1 includes a cabinet and is defined by an outer cabinet metal wall 1, an inner liner wall 2, and a body of foamed-in-place insulation 3 there between. In one popular design, the cabinet may define a freezer space 4 and an above-freezing refrigeration space 5. 
     Inner liner wall 2 is thermoformed into the desired configuration, as shown in FIG. 2. Inner liner wall 2 is a thermoformed product of liner sheet 6, one embodiment of which is illustrated in FIG. 3 as a multi-lamina composite. After being thermoformed into the desired configuration, the inner liner wall 2 is disposed into the outer cabinet wall 1 in a nested, spaced relationship for introduction of the foamed insulation by a conventional foaming-in-place operation. Usually, the outer cabinet wall 1 and the inner liner wall 2 are joined physically by mating of joints. 
     The barrier layer of the invention is substantially chemically inert to halogenated hydrocarbon(s) used as blowing agents in polyurethane foam production. If a core layer is employed, it is disposed on a surface of the core layer. During polyurethane in situ foam production, in one embodiment of the invention, it is the surface of the barrier layer of the composite which is contiguous to and bonds with the foam. However, it is not essential that the barrier layer of the invention be contiguous to the foam. In FIG. 3, the barrier layer is illustrated as numeral 8. 
     The barrier layer comprises 3.5 to 50 percent by weight of a composite which includes a core layer and comprises polymers or copolymers of ethylene or propylene which are selected from the group consisting of polypropylene, low density polyethylene, linear low density polyethylene, high density polyethylene (melt index of 1 to 10 and density of 0.935 to 0.960), high molecular weight high density polyethylene (melt index of 0.05 to 1.0), ethylene vinyl alcohol, certain high impact polystyrenes, nylon 66, and PVC. The barrier layer may comprise one or more lamina of the same or different polymer or copolymer. 
     The barrier layer may contain 0 to 40 weight percent, preferably 4 to 30 weight percent, based upon the weight of the barrier layer material, of a synthetic block copolymer. The synthetic block copolymer rubber can be selected from styrene-butadiene diblock; styrene-ethylene/propylene diblock copolymer; styrene-ethylene/butylene-styrene triblock; styrene-ethylene/butylene-styrene triblock functionalized with maleic anhydride, maleic acid or admixtures thereof, or combinations of any of the above. 
     The liner sheet may be formed of ABS (acrylonitrile-butadiene-styrene) or HIPS (high impact polystyrene) core layer which constitutes the major proportion of the composite. The core layer comprises 50 to 96 weight percent, preferably 55 to 85 weight percent, of the composite. Those core materials are chemically degradable by the completely or partially halogenated hydrocarbon blowing agent used in the polyurethane foam production. Both of these core materials are commercially available. In FIG. 3, the core layer chemically degradable by the fluorinated hydrocarbon is designated as 7. 
     The core layer which is (1) high impact polystyrene or (2) acrylonitrile-butadiene-styrene copolymer contains 5 to 35, preferably 5 to 20, and usually 5 to 15 weight percent rubber, in the form of particles. The rubber is usually polybutadiene and can be a styrene-butadiene copolymer. The rubber particles can have average diameters of at least 2 microns, and preferably at least 5 microns average diameters and generally up to 10 microns. When the rubber particles are 1 micron or less, as described in U.S. Pat. No. 4,513,120, high gloss polystyrene (medium impact) is produced. U.S. Pat. 4,513,120 is herein incorporated by reference. 
     Various alternatives are available for maximizing the adhesion of the core material to the barrier layer. Moreover, these alternatives can improve adhesion of the foam insulation to the barrier material. The core layer may be subjected to corona discharge treatment, or to ultraviolet light exposure, and by methods known in the art. In accordance with one embodiment of the invention, maximizing the adhesion of the barrier layer to the foam and optionally to a core layer appears to be achieved chemically. In a preferred embodiment, the material of the barrier layer contains maleic anhydride, maleic acid, and/or derivatives of maleic acid in an amount ranging from 0.05 to 10 weight percent of the barrier material. Conveniently, this can be achieved by inclusion of styrene-ethylene/butylene-styrene triblock functionalized with maleic anhydride, maleic acid or admixtures thereof; the triblock material is available from Shell Chemical Company as Kraton FG-1901X. 
     In one embodiment of the invention, the composite is formed with a barrier layer disposed on one surface of the core layer with a third layer of medium impact high gloss polystyrene on the exposed surface of the core layer. The third layer of medium impact high gloss polystyrene comprises 0.5 to 8 weight percent of the composite. The third layer is depicted in FIG. 3 as element 9. 
     The composite is formed by coextrusion of the materials of the laminae described above. The composite sheet can then be cut into suitable lengths for thermoforming into any desired configuration, one of which is illustrated by FIG. 2. The resulting liner wall 2 is then assembled with the outer cabinet wall 1 and in situ foaming of the insulation material is performed. The resulting structure exhibits impact strength and substantial elimination of thermal cracking and of blistering. 
     In situ foaming involves admixing an isocyanate with a masterbatch. The masterbatch comprises 60 to 60 percent of a polyol; 0.3 to 1.5 percent of a surfactant; 0.5 to 3.0 percent of a catalyst; 0.4 to 2.5 percent of water; and 12 to 30 percent of the blowing agent. The isocyanates used in appliances include TDI and PMDI. TDI comprises an 80:20 mixture of 2,4- and 2,6- isomers of products produced by dinitration of toluene, catalytic hydrogenation to the diamines, and phosgenation. CF. Kirk Othmer, Encyclopedia of Chemical Technology, Vol. 23, page 581 (Third Edition). PMDI is the reaction product formed by nitration of benzene and reduction to produce aniline; reacting aniline with formaldehyde in the presence of hydrochloric acid to produce a mixture of oligomeric amines, which are phosgenated to yield PMDI. Cf. Kirk Othmer, Encyclopedia of Chemical Technology, Vol. 23, page 581 (Third Edition). The blowing agent can be Freon or Freon substitutes which are partially halogenated lower hydrocarbons of 1 to 5 carbon atom, usually of 2 to 4 carbon atoms; halogenated includes fluorinated and/or chlorinated. By &#34;partially halogenated&#34; is meant that the Freon substitutes of the invention preferably contain at least one hydrogen atom. Illustrative of the partially halogenated lower hydrocarbons are 1,1-dichloro-1-fluoroethane and 2,2-dichloro-1,1,1-trifluoroethane, chlorodifluoromethane (HCFC-22),1,1,1,2-tetrafluoro-2-chloro-ethane (HCFC-124),1,1,1,2-tetrafluoroethane (HFC-134a), and pentafluoroethane (HFC-125). The foams produced contain in their cellular structure residual amounts of the blowing agent. The foam is formed in situ by foaming in a high pressure mixhead equipped to a nozzle for introducing the foam and foaming components into the cavity formed by the nesting of outer metal cabinet 1 and the plastic liner. 
     EXAMPLES 
     Example 1 
     Plastic sheets of composition described in Table 1 were fabricated into test plaques (15&#34;×15&#34;×0.050&#34;) and Brett-type test panels (783/4&#34;×77/8&#34;×0.050&#34;). These test sheets were then positioned as pairs into closed foaming jigs with a 2&#34; space between the sheets. Polyurethane foam chemicals were then introduced into the jigs to fill the space between the plastic sheets, to produce plastic/foam/plastic composite structures. These composite structures were thermally cycled several times between -20° F. and 140° F., to cause condensation and vaporization of liquid blowing agent along the exposed plastic sheet surfaces. 
     Several blowing agents (CFC-11 and HCFC-123) at several levels (9-15 percent) were evaluated in separate tests. CFC-11 is trichlorofluoromethane (CCl 3  F); HCFC-123 is 2,2-dichloro-1,1,1-trichloroethane, HCFC-141b is 1,1-dichloro-1-fluoroethane (CHCl 2  CF 3 ). The thermally cycled composite structures were then tested, as summarized in Table 1, and inspected for signs of chemical attack. 
     
                                           TABLE 1__________________________________________________________________________POLYSTYRENE/POLYOLEFIN BLENDSMIS-ESCR AND PHYSICAL PROPERTIES__________________________________________________________________________         MOBIL         PS7100              BLEND 1                    BLEND 2                           BLEND 3                                 BLEND 4                                        BLEND 5                                              BLEND                                                    BLEND__________________________________________________________________________                                                    7Composition (%)*HIPS/**PS, % 100  80    80     80    80     80    80    80Polyolefin, % 0    10    10     10    10     10    10    10Compatabilizer, %         0    10    10     10    10     10    10    10HIPS/PS, Type 7100 7100  7100   7100  7100   7100  7100Polyolefin, Type   Hilmont                    Aristech                           Himont                                 Mobil  Mobil Himont                                                    Himont              6231  FF-028N                           SA-747M                                 HMA-045                                        MMA-169                                              SA-747M                                                    SA-747M                                        LLDPE Rand                                                    Rand PPCompatibilizer, Type              Homo PP                    Homo PP                           Rand PP                                 HDPE   G1657 50:50 FG1901X              G1657 G1657  G1657 G1657  S-EB-S                                              1657:1901                                                    SEBS/MA              S-EB-S                    S-EB-S S-EB-S                                 S-EB-SMIS-ESCR, 1000 psi (min)Chiffon       63   138   394    125   63     2     600   630COOA          115  441   1186   491   256    4     5963  1708CFC-11        9    7     9      8     6      0     12    14HCFC-123      5    4     14     10    2      0     14    20HCFC-141b     6    8     13     10    6      0     17    18MIS-ESCR, 400 psi (min)CFC-11        22                37                       44HCFC-123      13                65                       69HCFC-141b     23                51                       60Physical Properties:MFI (G), g/10 min         2.9  9.3   6.8    8.2   8.7    12.1  5.8   5.7Vicat, C      103  103   103    101   100    92    101   101Tensile Yield, psi         2500 2200  2500   2100  2100   1600  2600  2800Tensile Fail, psi         3500 2200  2500   2100  2100   1600  2600  2800Tensile Modulus, PSI         182,000              97,000                    109,000                           99,000                                 96,000 58,000                                              112,000                                                    116,000Elongation, % 41   31    41     31    29     28    40    40Izod Impact, ft.lb/in         2.1C 1.0C  1.4C   1.2C  1.1C   1.1C  1.5C  1.6HGardner Impact, in.lb         123  49    95     69    18     6     93    99__________________________________________________________________________         BLEND 8               BLEND 9                     BLEND 10                           BLEND 11                                  BLEND 12                                        BLEND 13                                              BLEND                                                    BLEND__________________________________________________________________________                                                    15Composition (%)HIPS/PS, %    85    80    80    70     60    50    60    60Polyolefin, % 10    10    10    20     30    40    30    30Compatabilizer, %         10    10    10    10     10    10    10    10HIPS/PS, Type 7100  7100  7100  7100   7100  7100  7100  7100Polyolefin, Type         Hilmont               Himont                     OxyChem                           OxyChem                                  OxyChem                                        OxyChem                                              OxyChem                                                    Himont         SA-747M               SA-747M                     L5005 L5005  L5005 L5005 L5005 SA-747M         Rand PP               Rand PP                     HMW-  HMW-   HMW-  HWM-  HWM-  Rand PP                     HDPE  HDPE   HDPE  HDPE  HDPECompatibilizer, Type         G1702 G1702 FG1901X                           FG1901X                                  FG1901X                                        FG1901X                                              G1657 G1657         S-EP  S-EP  SEBS/MA                           SEBS/MA                                  SEBS/MA                                        SEBS/MA                                              S-EB-S                                                    S-EB-SMIS-ESCR, 1000 psi (min)Chiffon       147   90    342   753    1700  2887  37    22COOA          7026  4995CFC-11        7     5     8     13     25    31    3     4HCFC-123      4     3HCFC-141b     5     4MIS-ESCR, 400 psi (min)CFC-11                    41    48     80    130   51    48HCFC-123                  56    74     142   270   93    146HCFC-141b                 48    63     115   218   73    88Physical Properties:MFI (G), g/10 min         2.8   2.7   3.5   2.9    2.2   1.8   3.6   11.1Vicat, C      101   101   100   101    102   103   99    101Tensile Yield, psi         2400  2400  3000  3070   3020  2940  2500  2200Tensile Fail, psi         2400  2400  3000  3070   3020  2940  2500  2040Tensile Modulus, psi         152,000               145,000                     138,000                           130,000                                  124,000                                        118,000                                              106,000                                                    79,000Elongation, % 12    7     50    46     36    33    34    39Izod Impact, ft.lb/in         2.1C  2.1C  2.1C  2.0C   1.8C  1.5H  1.4C  1.0CGardner Impact, in.lb         66    66    121   127    109   55    100   136__________________________________________________________________________         BLEND 16               BLEND 17                     BLEND 18                           BLEND 19                                  BLEND 20                                        BLEND 21                                              BLEND                                                    BLEND__________________________________________________________________________                                                    23Composition (%)HIPS/PS, %    60    60    60    60     50    50    40    40Polyolefin, % 30    30    30    30     40    40    50    50Compatabilizer, %         10    10    10    10     10    10    10    10HIPS/PS, Type 7100  7100  7100  7100   9524  7800  7800  1800Polyolefin, Type         Himont               Chevron                     Chevron                           Chevron                                  OxyChem                                        OxyChem                                              OxyChem                                                    OxyChem         SA-747M               PE5280T                     PE5280T                           PE5272 L5005 L5005 L5005 L5005         Rand PP               PE/EVA                     PE/EVA                           PE/EVA HMW-  HMW-  HMW-  HMW-               8%    8%    4%     HDPE  HDPE  HDPE  HDPECompatibilizer, Type         FG1901X               FG1901X                     G1657 G1657  G1657 G1657 FG1901X                                                    FG1901X         SEBS/MA               SEBS/MA                     S-EB-S                           S-EB-S S-EB-S                                        S-EB-S                                              SEBS/MA                                                    SEBS/MAMIS-ESCR, 1000 psi (min)Chiffon       914   &gt;10000             &gt;1000 &gt;1000 &gt;1000 &gt;1000COOA                (400 psi)          (400 psi)                                        (400 psi)CFC-11        16HCFC-123HCFC-141bMIS-ESCR, 400 psi (min)CFC-11        88    75    68    53     96    88    311   346HCFC-123      230   150   160   126    197   170   642   627HCFC-141b     159   105   103   74     135   108   &gt;1000 495Physical Properties:MFI (G), g/10 min         6.3   4.6   6.1   7.7    1.9   1.7   1.8   1.6Vicat, C      103   88    77    103    104   104   106   109Tensile Yield, psi         2790  2520  2000  1930   2500  2500  2790  3890Tensile Fail, psi         2770  2520  2000  1930   2000  2300  2830  3460Tensile Modulus, PSI         101,000               84,000                     65,000                           61,000 102,000                                        103,000                                              122,000                                                    174,000Elongation, % 36    54    42    42     46    48    82    23Izod Impact, ft.lb/in         1.4C  2.6H  2.1H  1.9H   1.9C  1.7C  1.7C  0.8CGardner Impact, in.lb         154   242   215   240    104   89    67    14__________________________________________________________________________                      BLEND 24                            BLEND 25                                  BLEND 26                                        BLEND 27                                              BLEND                                                    BLEND__________________________________________________________________________                                                    29        Composition (%)        HIPS/PS, %    60    60    60    50    0     20        Polyolefin, % 30    30    30    40    80    65        Compatabilizer, %                      10    10    10    10    20    15        HIPS/PS, Type 1800  1800  7800  7100  7100  7100        Polyolefin, Type                      Mobil Mobil OxyChem                                        Mobil Mobil Mobil                      HYA-301                            HCX-002                                  L5005 HMX-034                                              HMX-034                                                    HMX-034                      HDPE  HDPE  HMW-  HDPE  HDPE  HDPE                                  HDPE        Compatibilizer, Type                      FG1901X                            FG1901X                                  FG1901X                                        FG1901X                                              FG1901X                                                    FG1901X                      SEBS/MA                            SEBS/MA                                  SEBS/MA                                        SEBS/MA                                              SEBS/MA                                                    SEBS/MA        MIS-ESCR, 1000 psi (min)        Chiffon       223   &gt;1000 734   &gt;1000 &gt;1000 &gt;1000        COOA        CFC-11        HCFC-123        HCFC-141b        MIS-ESCR, 400 psi (min)        CFC-11        62    679   83    351   &gt;1000 &gt;1000        HCFC-123      76    523   120   630   &gt;1000 &gt;1000        HCFC-141b     87    496   97    544   &gt;1000 &gt;1000        Physical Properties:        MFI (G), g/10 min                      4.7   9.4   3.7   9.3   9.8   10.8        Vicat, C      106   103   103   105   115   108        Tensile Yield, psi                      5160  4140  2950  2890  1830  2170        Tensile Fail, psi                      5160  4140  2950  2890  1830  2170        Tensile Modulus, psi                      229,000                            192,000                                  151,000                                        126,000                                              58,000                                                    71,000        Elongation, % 5     15    121   18    500   477        Izod Impact, ft.lb/in                      1.1H  0.7H  4.3H  0.6C  13.8  1.4C        Gardner Impact, in.lb                      38    44    207   48    &gt;320  294__________________________________________________________________________ *high impact polystyrene **polystyrene 
    
     Example 2 
     Sheets of several different compositions described in Table 2 invention were exposed to the liquid blowing agents by sealing a glass ball joint to the sheet samples and adding the specific liquid blowing agent being evaluated (CFC-11, HCFC-123, and HCFC-141b). The samples were exposed to the blowing agents for 30 minutes each, then exposed to heat (60° C. for 30 minutes to drive off the blowing agents, and finally inspected for chemical attack. Several sheet samples displayed no signs of chemical attack at all, and most samples showed at least some reduction in chemical attack when compared to sheets of HIPS or ABS. The results are set forth in Table 2. 
     
                       TABLE 2______________________________________LIQUID BLOWING AGENT CONTACT STUDY     CFC-11   HCFC-123   HCFC-141b______________________________________UNMODIFIEDRESINS:Mobil PS7100       Severe     Severe     SevereHIPS        Blistering Blistering BlisteringMobil PS7800       Severe     Severe     SevereMIPS        Blistering Blistering BlisteringMobil PS5350       Severe     Severe     SevereHIPS        Blistering Blistering BlisteringDow 469 HIPS       Severe     Severe     Severe       Blistering Blistering BlisteringMonsanto ABS       Unaffected Cracking   Cracking                  Severe     No Blistering                  BlisteringPS/POLYOLEFINBLENDSCOEX. ON PS7100:CA10        Severe     Severe     Severe(10% Random PP)       Blistering Blistering BlisteringCB30        Moderate   Moderate   Moderate(30% Random PP)       Blistering Blistering BlisteringLB40 (40%   Skin       Skin       SkinHMW-HDPE)   Delamination                  Delamination                             Delamination       Moderate   No Blistering                             No Blistering       BlisteringBASF KR2773 Skin       Slim       Skin(30% HDPE)  Delamination                  Delamination                             Delamination(10% CaCO3 filled)       No         Slight     Slight       Blistering Blistering BlisteringBASF KR2774 Severe     Moderate   Moderate(30% LDPE)  Blistering Blistering BlisteringBARRIER FILMSLAMINATED ONPS7100:Mobil MMA-169       Moderate   Unaffected UnaffectedLLDPE (2 mil)       BlisteringMobil HMA-045       Unaffected Unaffected UnaffectedHDPE(2 mil)Oxy L5005   Unaffected Unaffected UnaffectedHMW-HDPE(2 mil)DuPont EVOH Unaffected Unaffected Unaffected(5 mil)______________________________________ 
    
     Example 3 
     The invention is illustrated by use in a top mount (freezer on top) refrigerator of 15 cu. ft. capacity, with HCFC-123 as the polyurethane blowing agent at an estimated 18 percent level weight. The layers of the composite are described below. 
     
         ______________________________________Pre-Thermoformed Sheet:______________________________________Sheet Total Thickness          202 mil (0.202&#34;)Barrier Layer Thickness          10 mil (0.010&#34;)Core Layer Thickness          190 mil (0.190&#34;)Gloss Layer Thickness          2 mil (0.002&#34;)Barrier Layer Percent          5 percentof Total SheetPre-Thermoformed          77.75 × 46.75 × 0202 inchesSheet DimensionsBarrier Layer Material*Core Layer Material          Mobil ES7100 Refrigeration          Grade HIPSGloss Layer Material          Mobil ES7800 Medium Impact,          High Gloss PS______________________________________ *Barrier Material used had the following:High Density   Mobil HMX-034 HDPEPolyethylene Type          (Melt Flow = 4.0, Density = 0.954)Rubber Type    Shell Chemical Co.,          Kraton FG-1901X          Styrene-Ethylene/Butylene-          Styrene Triblock          (functionalized with 2 percent maleic          anhydride)withPolyethylene Level          80 percentRubber Level   20 percentIrganox 1010 Antioxidant          500 ppm 
    
     The barrier layer material was compounded in a Werner &amp; Pfleiderer ZSK 30/30 mm twin screw extruder at a temperature profile which ranged from 225° F. to 400° F. 
     The composite was formed from a two-layer system including the core layer (ES7100) and the barrier layer, which were coextruded. The gloss layer of medium impact polystyrene (Mobile ES7800) was laminated thereto. The temperature profile for coextrusion is set forth below. 
     
         ______________________________________Coextrusion Temperature Profile:______________________________________ES 7100 ExtruderProfile          (345-380-350-300-390-400)° F.Die              415° F.Melt Temp.       440° F.Barrier Material ExtruderProfile          (275-300-325-330)° F.Die              415° F.Melt Temp.       340° F.______________________________________ 
    
     The thermoformed product assembled in a metal cabinet with subsequent in situ insulation formation was subjected to 12 temperature cycles ranging from -40° F. to +150° F. Polyurethane foam adhesion to the barrier layer was good and better than the adhesion of the barrier layer to the core material. The liner wall exhibited satisfactory impact strength, no signs of cracking during thermal blistering, and de minimus blistering. 
     Example 4 
     A 22 cu. ft. refrigerator, a side-by-side model (configuration of refrigerator and freezer compartments), was fitted with a liner and then insulated with polyurethane foam produced by CFC-11 blowing agent at an estimated 16 weight percent level. The compositions and dimensions of the preformed sheet components are described below. 
     
         ______________________________________Sheet Total Thickness          198 mil (0.198&#34;)Barrier Layer Thickness          6 mil (0.006&#34;)Glue/Compat. Layer          2 mil (0.002&#34;)ThicknessCore Layer Thickness          188 mil (0.188&#34;)Gloss Layer Thickness          2 mil (0.002&#34;)Glue plus Barrier Layers          5 percentPercent of SheetPre-Thermoformed Sheet          78.75 × 36.00 × 0.198 inchesDimensionsBarrier Layer Material*          Mobil HMX-034 HDPEGlue/Compatibilizer          Mobil Developmental LB40Layer**Core Layer Material          Mobil ES7100 Refrigeration          Grade HIPSGloss Layer Material          Mobil ES7800 Medium Impact,          High Gloss PS______________________________________*Barrier Layer Mobil HMX-034 HDPEMaterial Used  (high Density          Polyethylene) (Melt Flow = 4.0,          Density = 0.954).**Glue/Compat. LayerComposition:Polyethylene Type          OxyChem Alathon L5005;          HMW-HDPE          (Melt Flow = 0.055 Cond. F,          Density = 0.95)Rubber Type    Shell Chemical Co.          Kraton FG-1901X;          Styrene-Ethylene/Butylene-Styrene          Triblock (functionalized with 2          percent maleic anhydride)HIPS Type      Mobil ES7100 Refrigeration Grade          (Melt Flow = 2.5).Polyethylene Level          40 percent.Rubber Level   10 percent.HIPS Level     50 percent. 
    
     The glue/compatibilizer layer materials were compounded in a Werner Pfleiderer 30 mm twin screw extruder at a temperature profile ranging from 225° F. to 450° F. The ES7800 gloss layer was laminated to the remaining laminate which were coextruded in a Welex Coextrusion System. 
     The unit(s) were subjected 12 times to a temperature cycle of -40° to 150° F. The unit exhibited satisfactory impact strength and de minimus blistering. 
     Thus, it is apparent that there has been provided in accordance with the invention a refrigerator plastic liner wall that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.