Abstract:
A domestic refrigerator or freezer has a food storage compartment delimited by insulated walls and by one or more access doors to the compartment. One or more walls or doors are provided with a metallic film, preferably a metallised polymeric film, capable of enhancing the performance of the refrigerator with regard to energy saving.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a domestic refrigerator of the type comprising a food storage compartment delimited by insulated walls and by one or more access doors to said compartment. 
   The term “refrigerator” refers to any household electrical appliance for food storage, the internal temperature of which appliance is maintained below ambient temperature; said definition includes both conventional refrigerators per se and also upright or chest freezers and the various combinations thereof. 
   2. Description of the Related Art 
   It is a well known requirement in the domestic refrigeration sector to reduce energy consumption, for example by increasing the thermal insulation of the storage compartment. This may involve using thicker insulating walls, with the unwanted result of reducing the usable volume of the food storage compartment, or using insulating materials with a lower coefficient of thermal transmission (for example evacuated insulation panels), with a considerable increase in production costs. 
   The aim of the present invention is to provide a refrigerator of the above-stated type that has low energy consumption while still being simple and economical to manufacture. 
   SUMMARY OF THE INVENTION 
   According to the invention, said aim is achieved by means of the characteristics specified in the attached claims. 
   The applicant has found that using metallic films or metallised polymeric films on the walls of the refrigerator (applied internally, externally or as layers incorporated into the walls) makes it possible to achieve a surprising energy saving in comparison with conventional refrigerators. Such advantages are particularly obvious when a metallic film or metallised polymeric film is used on the wall facing the condenser and are all the more remarkable when it is considered that such a saving is achieved without a substantial increase in the final cost of the product and without any excessive complication of the production process. 
   According to a first embodiment, the metallic film can be constituted by a laminate, for example made of aluminium, bonded to an external or internal wall of the refrigerator. Alternatively, the metallic film can be formed directly on an internal or external surface of the wall or door, for example using a well known method for depositing metallic films on polymer-type substrates. 
   In the second embodiment of the invention, in which a metallised polymeric film is used, the polymeric substrate (of the polyester, polyolefin etc. type) is coated on one side with a thin layer of metal (for example of silver, nickel, chromium, aluminium or indium) of a thickness of preferably between about 0.2 and about 7 microns, more preferably between about 0.5 and about 5 microns. The thickness of the polymeric substrate film is preferable between about 50 and about 120 microns, more preferably between about 70 and about 90 microns. 
   The metallic film or coating can be applied to the substrate film using any known deposition method, for example by means of cathodic sputtering, PVD (physical vapor deposition) or IAD (ion assisted deposition). 
   The function of the metallic film or metallised polymeric film is to reflect some of the thermal radiation into the environment in which the refrigerator is located and, in so doing, to reduce the transmission of heat through the material used for insulation. The film can be applied to any wall of the refrigerator, preferably keeping the metallic part exposed to the source of heat (outwards). The metallic layer of the metallised film can advantageously be provided with a protective layer that enhances its reflective properties together with its resistance to moisture and abrasion. Application can be performed using double-sided adhesive films (suitable for bonding surfaces with low surface energy) or by means of colamination. 
   According to another embodiment, the metallised polymeric film can also be incorporated into the actual structure of the wall or door. For example, excellent results (in terms of energy saving) have been achieved by using the metallised film between the (expanded) insulating material and the cellular coating material of the rear wall of the unit (generally know as “corrugated plastic sheet”). 
   According to a preferred characteristic of the invention, the metallised film is bonded to the rear wall of the refrigerator with the metal layer facing the condenser. In this manner, virtually all the heat irradiated by the condenser is reflected outwards. 
   According to another embodiment of the invention, once the metallised polymeric film has been applied to the external face of a refrigerator wall or door, a shielding sheet, for example made of polymeric material or paperboard, is in turn applied thereto. Energy-saving results can be further improved if the shielding sheet is applied to the metallised polymeric film with interposed spacers, so as to create a gap and associated chimney effect. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages and characteristics of a refrigerator according to the invention will emerge from the following detailed description, which is provided purely by way of non-limiting example, with reference to the attached drawings, in which: 
       FIG. 1  is a cross-sectional view of a schematized figerated appliance according to the invention comprising an insulated wall separating a food storage compartment from a compressor, and 
       FIGS. 2–5  are schematic representations of a vertical section of the insulated wall of the refrigerator according to four embodiments of the invention. 
   

   DETAILED DESCRIPTION 
   With reference to the  FIG. 1 ,  20  designates a refrigerated appliance comprising a cabinet  22  and an access door  24 . The cabinet comprises a top wall  26 , a rear wall  28 , a bottom wall  30 , and an inclined wall  32  extending from the bottom wall  30  to the rear wall  28  and defining a food storage compartment  42 . A condenser assembly  40  is located externally of and adjacent to the inclined wall  32 . A suitably shared enclosure wall  36 , shown in  FIG. 1  as an L-shaped shell, cooperates with the inclined wall  32  to define a condenser assembly compartment  38  in which the condenser assembly  40  is enclosed. In  FIGS. 1–5 ,  10  designates overall one of the cabinet walls  26 – 32  of the food storage compartment  42 , or a wall of the access door  24  constituted by an internal wall  10   a  obtained conventionally by thermoforming of sheets of polymer, by an insulating material  10   b  (for example polyurethane foam) and by an external covering  10   c , likewise of polymeric material of cellular type. The covering  10   c  may be conventionally constituted by an extruded cellular sheet in which an air gap is defined (said sheet is conventionally known as “corrugated plastic sheet”). A metallised polymeric film  12  is bonded to the external covering  10   c , said polymeric film having a layer of polymer  12   a , such as a polyester or a polyolefin, in contact with the covering  10   c  of the wall  10  and a metallic layer  12   b , which may preferably face toward a condenser assembly  40  comprising a condenser  14  of the refrigerator ( FIG. 2 ). As one of skill in the art will recognize the layer of polymer  12   a  maybe a polyester or polyolefin and the metallic layer  12   c  may be a silver, nickel, chromium, aluminum, indium or any mixture thereof. 
   For the sake of clarity, the thicknesses of the film  12  shown in the drawings have deliberately been magnified. It is contemplated that the total thickness of the polymeric film should be in the range of about 50 to about 120 microns and the thickness of the metallic layer should be in the range of about 0.2 to about 7 microns, although other thickness&#39; outside these ranges may also be applicable. 
   In testing carried out by the applicant, which revealed a distinct energy saving compared with identical refrigerators not provided with the metallised film bonded to the rear wall of the refrigerator, the film used was HPR 18 produced and sold by the Southwall company. The film has a polyester substrate and a total thickness of about 80 microns; the metallised layer of the film has a thickness of about 0.5 micron and is preferably, but not limited to being based on silver and indium. Other tests were performed with different types of metallised films, which yielded similar results in terms of energy savings. 
   In the embodiment shown in  FIG. 3 , the metallised film  12  is interposed between the external covering  10   c  (corrugated plastic sheet) and the insulating material  10   b . The film  12  can be applied during the process of forming the insulating material (foaming), in which the polyurethane insulator is injected between the internal wall  10   a  of the refrigerator and the external covering  10   c.    
   In the further embodiment shown in  FIG. 4 , a shielding sheet  16 , for example of polymeric material or paperboard, is applied to the metallised film  12 . The beneficial effect on energy saving is further increased if the shielding sheet is appropriately spaced as shown in  FIG. 5  from the metallised film  12  to define a gap  44 , for example by means of double-sided adhesive elements of a predetermined thickness (not shown) interposed between the shielding sheet  16  and the metallised film  12 .