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 the outer metal cabinet and 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 now 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:
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, fluorotrichloro methane, 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 may 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 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, and 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 4 to 50% 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, and preferably does, contain 4 to 30 weight percent of synthetic block copolymer rubber. The synthetic block copolymer rubber can be selected from styrene-butadiene diblock; 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 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 5 microns, and generally of at least 6 microns average diameters and 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. No. 4,513,120 is incorporated by reference herein. 
     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 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 0.1 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 the 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 70 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 applicances 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 hydrocarbon of 1 to 5 carbon atoms, 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 contains at least one hydrogen atom. Illustrative of the partially halogenated lower hydrocarbon 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 
     Examples 1 
     Plastic sheets of composition described in the Table 1 were fabricated into test plaques (15&#34;×15&#34;×0.050&#34;) and Brett-type test panels (783/4&#34;×7 7/8&#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%) were evaluated in separate tests. CFC-11 is trichlorofluoromethane (CCl 3  F): HCFC-123 is 2,2dichloro-1,1,1,-trifluoroethane, HCFC-141b is 1,1-dichloro-1-fluroethane (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__________________________________________________________________________                                                  6Composition (%)HIPS/PS, %    100  80     80     80     80     80      80Polyolefin, % 0    10     10     10     10     10      10Compatibilizer, %         0    10     10     10     10     10      10HIPS/PS, Type 7100 7100   7100   7100          7100    7100Polyolefin, Type   Hilmont                     Aristech                            Himont Mobil  Mobil   Himont              6231   FF-028N                            SA-747M                                   HMA-045                                          MMA-169 SA-747MCompatibilizer, Type              Homo PP                     Homo PP                            Rand PP                                   HDPE   LLDPE   Rand PP              G1657  G1657  G1657  G1657  G1657   50:50              S-EB-S S-EB-S S-EB-S S-EB-S S-EB-S  1657:1901MIS-ESCR, 1000 psi (min)Chiffon       63   138    394    125    63     2       600COOA          115  441    1186   491    256    4       5963CFC-11        9    7      9      8      6      0       12HCFC-123      5    4      14     10     2      0       14HCFC-141b     6    8      13     10     6      0       17MIS-ESCR, 400 psi (min)CFC-11        22                 37HCFC-123      13                 65HCFC-141b     23                 51Physical Properties:MFI (G), g/10 min         2.9  9.3    6.8    8.2    8.7    12.1    5.8Vicat, C      103  103    103    101    100    92      101Tensile Yield, psi         2500 2200   2500   2100   2100   1600    2600Tensile Fail, psi         3500 2200   2500   2100   2100   1600    2600Tensile Modulus, psi         182,000              97,000 109,000                            99,000 96,000 58,000  112,000Elongation, % 41   31     41     31     29     28      40Izod Impact, ft.lb/in         2.1C 1.0C   1.4C   1.2C   1.1C   1.1C    1.5CGardner Impact, in.lb         123  49     95     69     18     6       93__________________________________________________________________________              BLEND 7                     BLEND 8                            BLEND 9                                   BLEND 10                                          BLEND 11                                                  BLEND__________________________________________________________________________                                                  12Composition (%)HIPS/PS, %         80     85     80     80     70      60Polyolefin, %      10     10     10     10     20      30Compatibilizer, %  10     10     10     10     10      10HIPS/PS, Type      7100   7100   7100   7100   7100    7100Polyolefin, Type   Himont Hilmont                            Himont OxyChem                                          OxyChem OxyChem              SA-747M                     SA-747M                            SA-747M                                   L5005  L5005   L5005              Rand PP                     Rand PP                            Rand PP                                   HMW-HDPE                                          HMW-HDPE                                                  HMW-HDPECompatibilizer, Type              FG1901X                     G1702  G1702  FG1901X                                          FG1901X FG1901X              SEBS/MA                     S-EP   S-EP   SEBS/MA                                          SEBS/MA SEBS/MAMIS-ESCR, 1000 psi (min)Chiffon            630    147    90     342    753     1700COOA               1708   7026   4995CFC-11             14     7      5      8      13      25HCFC-123           20     4      3HCFC-141b          18     5      4MIS-ESCR, 400 psi (min)CFC-11             44                   41     48      80HCFC-123           69                   56     74      142HCFC-141b          60                   48     63      115Physical Properties:MFI (G), g/10 min  5.7    2.8    2.7    3.5    2.9     2.2Vicat, C           101    101    101    100    101     102Tensile Yield, psi 2800   2400   2400   3000   3070    3020Tensile Fail, psi  2800   2400   2400   3000   3070    3020Tensile Modulus, psi              116,000                     152,000                            145,000                                   138,000                                          130,000 124,000Elongation, %      40     12     7      50     46      36Izod Impact, ft.lb/in              1.6H   2.1C   2.1C   2.1C   2.0C    1.8CGardner Impact, in.lb              99     66     66     121    127     109__________________________________________________________________________              BLEND 13                     BLEND 14                            BLEND 15                                   BLEND 16                                          BLEND 17                                                  BLEND__________________________________________________________________________                                                  18Composition (%)HIPS/PS, %         50     60     60     60     60      60Polyolefin, %      40     30     30     30     30      30Compatibilizer, %  10     10     10     10     10      10HIPS/PS, Type      7100   7100   7100   7100   7100    7100Polyolefin, Type   OxyChem                     OxyChem                            Himont Himont Chevron Chevron              L5005  L5005  SA-747M                                   SA-747M                                          PE5280T PE5280T              HMW-HDPE                     HMW-HDPE                            Rand PP                                   Rand PP                                          PE/EVA 8%                                                  PE/EVA 8%Compatibilizer, Type              FG1901X                     G1657  G1657  FG1901X                                          FG1901X G1657              SEBS/MA                     S-EB-S S-EB-S SEBS/MA                                          SEBS/MA S-EB-SMIS-ESCR, 1000 psi (min)Chiffon            2887   37     22     914    &gt;10000COOA                                           (400 psi)CFC-11             31     3      4      16HCFC-123HCFC-141bMIS-ESCR, 400 psi (min)CFC-11             130    51     48     88     75      68HCFC-123           270    93     146    230    150     160HCFC-141b          218    73     88     159    105     103Physical Properties:MFI (G), g/10 min  1.8    3.6    11.1   6.3    4.6     6.1Vicat, C           103    99     101    103    88      77Tensile Yield, psi 2940   2500   2200   2790   2520    2000Tensile Fail, psi  2940   2500   2040   2770   2520    2000Tensile Modulus, psi              118,000                     106,000                            79,000 101,000                                          84,000  65,000Elongation, %      33     34     39     36     54      42Izod Impact, ft.lb/in              1.5H   1.4C   1.0C   1.4C   2.6H    2.1HGardner Impact, in.lb              55     100    136    154    242     215__________________________________________________________________________              BLEND 19                     BLEND 20                            BLEND 21                                   BLEND 22                                          BLEND 23                                                  BLEND__________________________________________________________________________                                                  24Composition (%)HIPS/PS, %         60     50     50     40     40      60Polyolefin, %      30     40     40     50     50      30Compatibilizer, %  10     10     10     10     10      10HIPS/PS, Type      7100   9524   7800   7800   1800    1800Polyolefin, Type   Chevron                     OxyChem                            OxyChem                                   OxyChem                                          OxyChem Mobil              PE5272 L5005  L5005  L5005  L5005   HYA-301              PE/EVA 4%                     HMW-HDPE                            HMW-HDPE                                   HMW-HDPE                                          HMW-HDPE                                                  HDPECompatibilizer, Type              G1657  G1657  G1657  FG1901X                                          FG1901X FG1901X              S-EB-S S-EB-S S-EB-S SEBS/MA                                          SEBS/MA SEBS/MAMIS-ESCR, 1000 psi (min)Chiffon                   &gt;1000  &gt;1000  &gt;1000  &gt;1000   223COOA                      (400 psi)                            (400 psi)CFC-11HCFC-123HCFC-141bMIS-ESCR, 400 psi (min)CFC-11             53     96     88     311    346     62HCFC-123           126    197    170    642    627     76HCFC-141b          74     135    108    &gt;1000  495     87Physical Properties:MFI (G), g/10 min  7.7    1.9    1.7    1.8    1.6     4.7Vicat, C           103    104    104    106    109     106Tensile Yield, psi 1930   2500   2500   2790   3890    5160Tensile Fail, psi  1930   2000   2300   2830   3460    5160Tensile Modulus, psi              61,000 102,000                            103,000                                   122,000                                          174,000 229,000Elongation, %      42     46     48     82     23      5Izod Impact, ft.lb/in              1.9H   1.9C   1.7C   1.7C   0.8C    1.1HGardner Impact, in.lb              240    104    89     67     14      38__________________________________________________________________________                     BLEND 25                            BLEND 26                                   BLEND 27                                          BLEND 28                                                  BLEND__________________________________________________________________________                                                  29        Composition (%)        HIPS/PS, %   60     60     50     0       20        Polyolefin, %                     30     30     40     80      65        Compatibilizer, %                     10     10     10     20      15        HIPS/PS, Type                     1800   7800   7100   7100    7100        Polyolefin, Type                     Mobil  OxyChem                                   Mobil  Mobil   Mobil                     HCX-002                            L5005  HMX-034                                          HMX-034 HMX-034                     HDPE   HMW-HDPE                                   HDPE   HDPE    HDPE        Compatibilizer, Type                     FG1901X                            FG1901X                                   FG1901X                                          FG1901X FG1901X                     SEBS/MA                            SEBS/MA                                   SEBS/MA                                          SEBS/MA SEBS/MA        MIS-ESCR, 1000 psi (min)        Chiffon      &gt;1000  734    &gt;1000  &gt;1000   &gt;1000        COOA        CFC-11        HCFC-123        HCFC-141b        MIS-ESCR, 400 psi (min)        CFC-11       679    83     351    &gt;1000   &gt;1000        HCFC-123     523    120    630    &gt;1000   &gt;1000        HCFC-141b    496    97     544    &gt;1000   &gt;1000        Physical Properties:        MFI (G), g/10 min                     9.4    3.7    9.3    9.8     10.8        Vicat, C     103    103    105    115     108        Tensile Yield, psi                     4140   2950   2890   1830    2170        Tensile Fail, psi                     4140   2950   2890   1830    2170        Tensile Modulus, psi                     192,000                            151,000                                   126,000                                          58,000  71,000        Elongation, %                     15     121    18     500     477        Izod Impact, ft.lb/in                     0.7H   4.3H   0.6C   13.8    1.4C        Gardner Impact, in.lb                     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 thirty 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 HIPS       Severe     Severe     Severe       Blistering Blistering BlisteringMobil PS7800 MIPS       Severe     Severe     Severe       Blistering Blistering BlisteringMobil PS5350 HIPS       Severe     Severe     Severe       Blistering Blistering BlisteringDow 469 HIPS       Severe     Severe     Severe       Blistering Blistering BlisteringMonsanto ABS       Unaffected Cracking   Cracking                  Severe     No Blistering                  BlisteringPS/POLYOLEFINBLENDS COEX.ON PS7100:CA10 (10% Ran-       Severe     Severe     Severedom PP)     Blistering Blistering BlisteringCB30 (30% Ran-       Moderate   Moderate   Moderatedom PP)     Blistering Blistering BlisteringLB40 (40% HMW-       Skin       Skin       SkinHDPE)       Delamination                  Delamination                             Delamination       Moderate   No Blistering                             No Blistering       BlisteringBASF KR2773 Skin       Slim       Skin(30% HDPE)  Delamination                  Delamination                             Delamination(10% CaCO.sub.3       No         Slight     Slightfilled)     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 HMW-       Unaffected Unaffected UnaffectedHDPE (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 at 15 ft 3  capacity, with HCFC-123 as the polyurethane blowing agent at an estimated 18% 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 % of            5%Total sheetPre-Thermoformed Sheet            (77.75 × 46.75 ×Dimensions       0.202) inchesBarrier 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 Tri-block            (functionalized with 2%            maleic anhydride)withPolyethylene Level            80%,Rubber Level     20%, andIrganox 1010 Antioxidant            500 ppm 
    
     The barrier layer material was compounded in a Werner &amp; Pfleiderer ZSK30 mm twin screw extruder, at a temperature profile which ranged from 225° 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 (Mobil ES7800) was laminated thereto. The temperature profile for coextrusion is set forth below: 
     
         ______________________________________Coextrusion Temperature Profile:______________________________________ES 7100 Extruder         Profile (345-380-350-300-390-400)° F.         Die 415° F.         Melt Temp 440° F.Barrier Material         Profile (275-300-325-330)° F.Extruder      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 barrier layer to the core material. The liner wall exhibited satisfactory impact strength, no signs of cracking during thermal blistering and de minimis blistering. 
     Example 4 
     A 22 ft 3  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 % 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 Thickness             2 mil (0.002&#34;)Core Layer Thickness             188 mil (0.188&#34;)Gloss Layer Thickness             2 mil (0.002&#34;)Glue + Barrier Layers             5%% of sheetPre-Thermoformed Sheet             (78.75 × 36.00 ×Dimensions        0.198) inchesBarrier Layer Material*             Mobil HMX-034 HDPEGlue/Compatibilizer Layer**             Mobil Developmental LB40Core Layer Material             Mobil ES7100 Refrigeration             Grade HIPSGloss Layer Material             Mobil ES7800 Medium Impact,             High Gloss PS______________________________________*Barrier Layer-Material used             Mobil HMX-034 HDPE             (High Density Polyethylene)             (Melt Flow = 4.0, Density =             0.954)**Glue/Compat Layer Composition: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 Tri-block             (functionalized with 2%             maleic anhydride)HIPS Type         Mobil ES7100 Refrigeration             Grade (Melt Flow = 2.5)Polyethylene Level             40%Rubber Level      10%HIPS Level        50% 
    
     The glue/compatabilizer 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 minimis 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.