Abstract:
A refrigerated display case having a transparent insulating glazing unit for displaying cold or frozen products. The glazing unit has an antifrosting absorbent layer that inhibits the formation of visible condensation or frost.

Description:
This application is a Continuation-in-Part of U.S. Ser. No. 09/926,609, Aug. 30, 2002, now U.S. Pat. No. 7,003,920, issued 28 Feb. 2006, the complete disclosure of which is incorporated herein by reference, which is a national stage entry under 35 U.S.C. 371 of International Application No. PCT/FR00/01424, filed 25 May 2000, now abandoned, designating the U.S. This application claims foreign priority under 35 U.S.C. 119 and 365 to French Patent Application No. 99 06586, filed 25 May 1999. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a refrigerated display case, more particularly a self serve merchandiser, having a transparent insulating glazing unit for displaying cold or frozen products, for example, food products, non-food items requiring refrigeration such as, drinking water, beverages, flowers and pharmaceuticals. 
     BACKGROUND OF THE INVENTION 
     When food products kept in a refrigerated self serve merchandiser have to remain visible for the consumers, as is the case in numerous commercial premises at the present time, the refrigerated merchandiser is preferably equipped with transparent glazing unit in order to save energy costs. These refrigerated self serve merchandisers exist in many various forms. When these merchandisers are vertical, then it is the door itself which contains the transparent glazing unit. When these merchandisers are horizontal and constitute chests, then it is the horizontal lid door which contains the transparent glazing unit to allow the contents to be seen. The refrigerated merchandiser is also commonly referred to as a refrigerated display case. 
     In these types of merchandisers, it is necessary that the food products remain easily visible to the customers so that the products can be preselected without opening the merchandiser. 
     However, one of the main problems encountered with these merchandisers is the condensation that builds up on the exterior surface of the glazing unit facing the ambient atmosphere. What happens is that this exterior surface is cooled by the refrigerated environment on the opposite side of the glazing unit. When the temperature of this exterior surface is at a temperature below the dew point, visible condensation occurs in form of droplets, which makes the food products on display barely visible. 
     Another significant problem is the formation of visible condensation, or even frost, on the interior surface of the glazing unit when the door of the display case is opened in order to take the food products out. What happens is that the inside surface of the glazing unit, which is at a very low temperature, often times below 0° C., contacts the ambient atmosphere, which is far more loaded with moisture and at a far higher temperature. The temperature of this interior surface is usually then below the dew point, which causes visible condensation to form on the surface. This condensation can even turn to frost when the temperature of this surface is below 0° C. or 32° F. The presence of condensation or frost makes a visible barrier between the consumers and the food products, and it then takes several minutes or even several tens of minutes, for this condensation or the frost to completely disappear. When the food products are not easily visible, impulse sales are lost and customers open the doors for longer periods of time to select the food products, which causes the refrigeration unit to run longer to maintain the temperature of the goods and generates at the same time more condensation or frost that will require more time to disappear. 
     The use of performing insulating glazing units in refrigerated display cases has been avoided since it exacerbates the problem of condensation or frost forming on the surface of the glazing unit facing the interior of the merchandiser. When the insulation is performing, then the inside surface is cooler and the cooler the surface the greater the problem of condensation or frosting when the door is opened. 
     Heating means are commonly used to reduce the problem of condensation or  0  frost forming on the surface of the glazing unit facing the interior of the merchandiser. See, for example, U.S. Pat. Nos. 5,449,885, 5,852,284, and 6,144,017, which all disclose the use of heating means. However, the use of heating means consumes significant quantities of electricity, first to generate the heat and second to compensate through the refrigeration unit for the heat that is transferred inside the merchandiser. And despite this, depending on the ambient conditions and the power of these heated means, condensation or frost can still occur and the benefit of the heated means is then only to rapidly remove condensation or frost in a short period (generally less than 2 minutes). 
     Furthermore, while the use of insulating glazing units in combination with heating means has been disclosed in these patents, the various functional layers used previously, including the low-emission coatings, disclosed in these patents substantially reduce the light transmission ratios of the glazing units so that additional lighting power is often required inside the merchandiser to compensate and to see the food products on display. This additional lighting generates additional heat, which can increase the temperature of the products on display in the merchandiser and requires additional power consumption by the corresponding refrigeration unit. 
     In light of rising energy costs, there is a great need for an environmentally friendly refrigerated merchandiser having an insulating transparent glazing unit that does not require powerful interior lighting or heating means to avoid visible condensation or frost formation on the exposed surfaces of the glazing unit. 
     SUMMARY OF THE INVENTION 
     An objective of the invention is to provide a refrigerated display case having an insulating glazing unit that inhibits the formation of visible condensation or frosting on both the surface of the glazing unit facing the interior of the display case and the surface of the glazing unit facing the exterior of the display case, without relying on the use of heating means. 
     A further object of the invention is to provide an insulating glazing unit having improved thermal properties for use in a refrigerated display case, which avoids visible formation of condensation or frost, even under difficult conditions of vastly different exterior and interior environments, and the length of time for which it is open for taking out products or restocking, and which performs well in terms of energy saving and allows the products arranged in the display case to be seen clearly and easily. 
     The above objects and other objects are met by a refrigerated display case comprising:
         a refrigerated enclosure constructed and arranged to contain cold or frozen products;   a door constructed and arranged to seal the refrigerated enclosure when in a closed position, the door having a transparent insulating glazing unit comprising at least two glass substrates; and   an antifrosting adsorbent layer disposed on a surface of a glass substrate facing an interior of the refrigerated enclosure and formed from at least one hydrophilic polymer, wherein the transparent insulating glazing unit inhibits the formation of condensation on a surface of the glass substrate in contact with the ambient atmosphere and the antifrosting adsorbent layer inhibits the formation of water crystals on the surface of the glass substrate facing the interior of the refrigerated enclosure when the door is opened.       

     These objects are also obtained by a refrigerated display case comprising:
         a refrigerated enclosure constructed and arranged to contain cold or frozen products;   a door constructed and arranged to seal the refrigerated enclosure when in a closed position, the door having a transparent insulating glazing unit comprising at least two glass substrates; and   an antifrosting adsorbent layer disposed on a surface of a glass substrate facing an interior of the refrigerated enclosure, the antifrosting adsorbent layer being further an absorbent layer which is porous to allow condensation to absorb therein, wherein the transparent insulating glazing unit inhibits the formation of condensation on a surface of the glass substrate in contact with the ambient atmosphere and the antifrosting adsorbent layer inhibits the formation of water crystals on the surface of the glass substrate facing the interior of the refrigerated enclosure when the door is opened.       

     These objects are also met by a transparent insulating glazing unit constructed and arranged for use in a refrigerated display case, the transparent insulating glazing unit comprising:
         at least two glass substrates bound together by a spacer; and   an antifrosting adsorbent layer disposed on an exterior surface of a glass substrate constructed and arranged to contact an interior of a refrigerated display case when the glazing unit is mounted in a door and the door is in a closed position on the display case, the antifrosting adsorbent layer being further an absorbent layer which is porous to allow condensation to absorb therein, wherein the transparent insulating glazing unit inhibits the formation of condensation on a surface of the glass substrate in contact with the ambient atmosphere and the antifrosting adsorbent layer inhibits the formation of water crystals on the surface of the glass substrate facing the interior of the refrigerated enclosure during use on the refrigerated display case.       

     The objects are further obtained by an insulating glazing unit for a door of a refrigerated display case comprising three glass substrates, a first glass substrate having an external surface of which is in contact with an interior of a o refrigerated enclosure when the glazing unit is mounted in the door and the door is in a closed position, a second glass substrate, and a third glass substrate the external surface of which is in contact with the ambient environment when the glazing unit is mounted in the door, the three substrates being separated from one another by a spacer of low thermal conductivity, a low-emission coating being disposed on at least in part on one of the surfaces of the glass substrates, and an antifrosting adsorbent layer for inhibiting the formation of condensation and frost being disposed on at least part of the external surface of the first glass substrate, wherein the thickness of the substrates is between 2 and 5 mm, at least one space between the substrates is filled with at least one rare gas, a thickness of the space between the substrates is at least 4 mm, a spacer for bonding the substrates together has a thermal conductivity of less than 1 W/m.K, the glazing unit has no heating element, the glazing unit has a thermal conductivity coefficient U of less than 1.1 W/m 2 .K, with at least 85% gas filling, and the glazing unit has a light transmission ratio of at least 67% and an external light reflection factor of below 18%. 
     These objects are also obtained by an insulating glazing unit for a door of a refrigerated display case comprising two glass substrates, a first substrate the external surface of which is in contact with an inside of the display case when the glazing unit is mounted in the door and the door is in a closed position, and a second substrate the external surface of which is in contact with the ambient environment, which substrates are separated from one another by a spacer of low thermal conductivity, the space between the substrates being filled with a rare gas, a low-emission coating being deposited at least in part on one of the surfaces of the substrates, and an antifrosting adsorbent layer for inhibiting the formation of condensation and frost being disposed on at least part of a surface of the first glass substrate intended to be in contact with an interior of the refrigerated display case, wherein the thickness of the substrates is from 2 to 5 mm, the space between the substrates is filled with krypton or xenon, the thickness of the layer of krypton or of xenon is at least 8 mm, and the spacer has a thermal conductivity of less than 1 W/m.K, the glazing unit has no heating element, the glazing unit has a thermal conductivity coefficient U of less than 1.15 W/m 2 .K, with at least 85% gas filling, and the glazing unit has a light transmission ratio of at least 75% and an external light reflection factor of below 12%. 
     In the remainder of the description interior and exterior will be used to qualify elements which face towards the inside or, respectively, the outside of the refrigerated cabinet when the door is in the closed position. 
     Internal and external will be used to qualify elements which face towards the inside and, respectively, towards the outside of the insulating glazing unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a view of a refrigerated display according to the present invention; 
         FIG. 2  illustrates a view of three glass panel glazing unit according to the present invention; and 
         FIG. 3  illustrates a view of a two glass panel glazing unit according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be explained with reference to the attached FIG.s without being limited thereto.  FIG. 1  illustrates a view of a refrigerated display case  7  comprising a refrigerated enclosure  8  and a door  9  for sealing the refrigerated enclosure  8  when the door  9  is in a closed position. The door  9  comprises a transparent insulating glazing unit  10   a . The glazing unit  10   a  has an antifrosting adsorbent layer deposited on the surface of the glazing unit  10   a  facing the interior of the refrigerated enclosure  8 . 
     Such a glazing unit, especially when it is an insulating glazing unit, and more particularly a vacuum insulating glazing unit, can be used in a door of a refrigerated enclosure having at least one viewing area consisting, for example, of the said vacuum insulating glazing unit combined with an antifrosting adsorbent layer advantageously deposited on that surface of the said viewing area which is in contact with the refrigerated environment. 
     It has been shown that such a door, comprising the glazing unit according to the invention, makes it possible to prevent the frosting phenomenon, or more  0  precisely to delay it or at the very least limit its appearance. 
     According to a first embodiment, the antifrosting adsorbent layer is deposited directly on the glass substrate, and more specifically on that surface of the vacuum insulating glazing unit which is in contact with the refrigerated environment. This is the surface in contact with the refrigerated environment when the door is in its closed position. Such a layer may be deposited by techniques of the sputtering or coating type, especially of the flow-coating or deep-coating type, the deposition being carried out before or after manufacturing of the vacuum glazing unit. Advantageously, an adhesion primer of the silane type is provided; it is either deposited beforehand on the glass or at the same time as the layer is formed, the silanes being introduced into the composition of the antifrosting adsorbent layer. 
     According to a second embodiment, the antifrosting adsorbent layer is deposited, for example according to one of the abovementioned methods, on a plastic film and the plastic film is itself fastened to the vacuum insulating glazing unit. The plastic film used is advantageously a polycarbonate film preferably having a thickness of less than 3 millimetres; this plastic is especially chosen for its mechanical strength properties. The plastic film is fastened to the glazing in a sealed manner so that no trace of moisture can exist between the glass surface and the plastic film. It may be fastened, for example, by adhesive bonding around the periphery; the air layer possibly existing between the glass and the plastic film must then advantageously not exceed 3 mm. The fastening may also be achieved by means of an aluminium frame combined with a desiccant and an adhesive, similar to that for an insulating glazing unit of conventional construction; advantageously, the air layer between the glass and the plastic film then does not exceed 10 mm. 
     According to an advantageous embodiment of the invention, the antifrosting adsorbent layer comprises at least one hydrophilic polymer. Such a polymer may be non-limitingly chosen from the following polymers: a polyvinylpyrrolidone of the poly(N-vinyl-2-pyrrolidone) or poly(1-vinylpyrrolidone) type, a polyvinylpyridine of the poly(N-vinyl-2-pyridine) type, of the poly(N-vinyl-3-pyridine) type or of the poly(N-vinyl-4-pyridine) type, a polyacrylate of the poly(2-hydroxyethyl acrylate) type, a polyacrylamide of the poly(N′,N-hydroxyacrylamide) type, a polyvinyl acetate, a polyacrylonitrile, a polyvinyl alcohol, a polyacrolein, a polyethylene glycol or a polyoxyethylene. It may also be a copolymer based on two or more of the abovementioned polymers. 
     Preferably, the invention specifies that the layer consists of at least one crosslinked hydrophilic polymer. Crosslinking the polymer makes it possible, in particular, to obtain better cohesion of the layer and thus to prevent any risk of the layer being dissolved by water, over the long or short term. 
     According to a preferred embodiment of the invention, the hydrophilic polymer is combined with an organic or inorganic absorbent material, the said absorbent material preferably being porous. 
     An inorganic absorbent material especially improves the mechanical strength of the layer and more particularly prevents the formation of scratches. The inorganic function is advantageously achieved by depositing a mesoporous material (CPG-MCM 41), such as TiO.sub.2 nanoparticles, or by depositing orthosilicate hydrolysis condensation products, or other silicon derivatives. 
     An organic absorbent material especially allows retention of the hydrophilic polymer; a polyurethane is used, for example. 
     The inventors have thus been able to demonstrate that the presence of a porous layer which includes a hydrophilic polymer on the surface of the glazed area allows water to be adsorbed. This principle prevents the formation of water droplets and thus the formation of a film liable to frost over and affect visibility through the glazed area. The choice of hydrophilic polymer and of the porosity in the case of a porous absorbent material make it possible to control the antifrosting behaviour of the layer. In particular, increasing the porosity allows the rate of water absorption and the water absorptivity, as well as the level of water in microdroplet form, to be controlled. 
     According to a preferred embodiment of the invention, the porosity of the layer is between 0.1 and 1000 cm.sup.3/g. In the case of a polymeric material, it is advantageously between 0.1 and 100 cm 3 /g and preferably less than 20 cm 3 /g. It is preferably between 200 and 1000 cm 3 /g in the case of a mesoporous material. The porosity defines the void volume of the pores per unit mass of the layer. 
     Also preferably, the layer has pores whose mean diameter is between 0.05 and 50 microns, preferably between 0.1 and 20 microns and more preferably between 1 and 15 microns. The shapes of the cavities making up the pores are oval or spherical. 
     Whatever the nature of the antifrosting adsorbent layer and the method of producing the latter, it advantageously has a thickness of less than 100 microns, preferably less than 50 microns and more preferably less than 35 microns and, in some cases, preferably less than 25 microns and more preferably less than 20 microns. 
     Further details and advantageous characteristics of the invention will emerge below from the description of illustrative examples of the invention and of tests carried out. 
     Instead of using the exemplary vacuum insulating glazing unit described above, any other suitable insulating glazing unit may be utilized in combination with the novel antifrosting absorbent layer described herein, such as those shown in  FIGS. 2 and 3 . 
       FIG. 2  illustrates, according to a third embodiment of the invention, an insulating glazing unit  10  filled with gas, with no heating element, and comprising at least one low-emission coating  30  and one anti-frost coating  40 , having a heat transfer coefficient U of less than 1.1 W/m 2 .K and a light transmission ratio of at least 67%. 
     The insulating glazing unit  10  comprises three glass substrates, a first substrate or interior substrate  11 , the external surface  11   a  of which is intended to be in contact with the inside of the cabinet when the door is in the closed position, a second substrate or intermediate substrate  12 , and a third substrate or exterior substrate  13  the external surface  13   a  of which is intended to be in contact with the environment outside the cabinet. The first and third substrates  11  and  13  are preferably made of toughened glass. 
     The surfaces of the substrates are labelled from  1  to  6  and referenced ( 1 ) to ( 6 ) in  FIG. 2  and correspond respectively to the external surface  13   a  (surface  1 ) intended to be in contact with the environment outside the cabinet to the surface  11   a  (surface  6 ) intended to be in contact with the inside of the cabinet when the door is in the closed position. 
     While thicker glass substrates can be utilized if desired, the thickness of each of the glass substrates is ideally between 2 and 5 mm to provide suitable weight and light transmission of the glazing unit, and is preferably 3 or 4 mm. 
     Preferably, the substrates are separated from one another by a spacer  50  having a low thermal conductivity. The spacer can be made up of two separate elements or a single element straddling the intermediate substrate. This spacer preferably has a thermal conductivity coefficient of at most 1 W/m.K (or 1.88 BTU/h.ft.F), preferably below 0.7 W/m.K, and even below 0.4 W/m.K. It is now well known that 0.534 W/m.K corresponds to 1 BTU/h.ft.F. 
     One example of spacer has a basic body made of a thermoplastic, for example of the styrene acrylonitrile (SAN) or polypropylene type, and reinforcing fibres, for example of the glass type, mixed into the thermoplastic, and a metal sheet providing tightness to gases and to water vapour. This metal sheet is bonded onto part of the basic body that is intended to face away from the interior space of the glazing unit. The basic body, which also includes a dehydratant, is deposited at the periphery and in the separating space, between the substrates using butyl. An additional sealing barrier against liquids and vapour, which seals the spacer and is made, for example, of polysulphide, polyurethane or silicone, is arranged on the same side as the metal sheet of the spacer. 
     Such a spacer, which is based on SAN and glass fibres, is known for example by the trade name SWISSPACER® by the company SAINT-GOBAIN GLASS when the metal sheet of the basic body is made of aluminium, and by the name SWISSPACER V® when the metal sheet of the basic body is made of stainless steel, and which in association with a double barrier of polysulphide has a thermal conductivity coefficient of 0.64 W/m.K (or 1.20 BTU/h.ft.F) in the case of SWISSPACER® and 0.25 W/m.K (or 0.47 BTU/h.ft.F) in the case of SWISSPACER V®. 
     It is also possible to mention by way of spacer the spacer described in application WO 01/79644, incorporated herein by reference, which is made of a more or less flat profile section arranged, not within the glazing unit but on the outside, secured to the edges of the substrates. This profile section may be made entirely of stainless steel or of aluminium or of fibre-reinforced plastic, its linear buckling strength being at least 400 N/m. The spacer is for example made of aluminium, 0.5 mm thick, and has a thermal conductivity coefficient of 0.25 W/m.K (or 0.47 BTU/h.ft.F). The spacer comprises a sealing barrier against gases, dust and liquids, and it has at least on the external surface a metallic coating. The metallic coating can be any metallic coating suitable for use as a sealing barrier against gases, dust and liquids. 
     The interior space between the interior substrate  11  and the intermediate substrate  12  comprises an interior layer of gas  14 , and the space between the exterior substrate  13  and the intermediate substrate  12  comprises an exterior layer of gas  15 . The thickness of the layers of gas and composition thereof are selected to provide a desired level of heat transfer coefficient U. For example, when a rare gas is utilized suitable thicknesses have been found to o be from 4 mm for reaching the desired coefficient U to preferably 16 mm for not having a too thick glazing unit and because beyond 16 mm, the coefficient U is not better. When air is used for one of layers of gas, the thickness is preferably at least 10 mm. 
     At least one of the layers of gas preferably comprises a rare gas chosen from argon, krypton or xenon, or even a mix of 2 or more gases from this list with a gas fill level of at least 85%. For a better value of coefficient U, it is preferable to have a gas fill level at least 92%, in particular for krypton or xenon. If desired, when there are more than one gas layers, one of the layers can comprise air. 
     The glazing unit comprises a low-emission coating  30  arranged on at least part of the surface  13   b  of the exterior substrate which faces the interior of the glazing (surface  2 ), and/or another low-emission coating  31  of the same type deposited on at least part of the surface  12   a  of the intermediate substrate which faces the interior substrate  11  (surface  4 ). When just one low-emission coating is provided, it is preferably disposed on the surface of the glazing unit associated to the thickest layer of gas. 
     The low-emission coatings are based on layers of metal and metal oxides, which can be obtained by various methods: by vacuum methods (thermal evaporation, cathode sputtering, magnetron sputtering) or thermal decomposition (CVD) of organo-metallic compounds propelled in liquid, solid or gaseous form by a carrier gas onto the surface of the heated substrate. 
     As a preference, the metallic layers are based on silver, and the layers of metal oxides are based on compounds of zinc, tin, titanium, aluminium, nickel, chromium, antimony (Sb), on nitrides or on a mixture of at least two of these compounds, and possible blocking layers such as a blocking metal or blocking metal alloy, of the Ti type, as a superlayer on the silver. 
     For examples, the following layers can be utilized for which the (TiO 2 ) reference means that it is an optional element:
 
Glass/SnO 2 /(TiO 2 )/ZnO/Ag/Ti ou NiCr ou NiCrO x /ZnO/SnO 2   ou Si 3 N 4 /SnZnO x :Sb ou TiO x  
 
Glass/SnO 2 /TiO 2 /ZnO/Ag/NiCrO x /(TiO 2 )/SnO 2 /SnZnO x :Sb
 
     For further details, particularly regarding alternative forms of embodiments, thicknesses, and quantities of compounds, reference may be made to patent applications FR 2783918 or EP1042247, which are incorporated herein by reference. 
     According to the invention, the type of coating allows a suitable compromise to be reached between the optical quality of the substrate, particularly regarding its light transmission ratio, and its ability to reflect in the infrared. The low-emission coating used in the display case of the invention has an emissivity of 0.3 or below, preferably of 0.05 or below, and a light transmission ratio higher than 75%, preferably higher than 85%. 
     Also, it is possible to use by way of a substrate provided with such a coating, the commercially available product PLANITHERM® FUTUR N by SAINT-GOBAIN GLASS which has, in glass 4 mm thick, an emissivity of 0.04 and a light transmission ratio of 88.4%. 
     Another product which can be used according to the invention is for example PLANITHERM® ULTRA of SAINT-GOBAIN GLASS which has, in glass 4 mm thick, an emissivity of 0.02 and a light transmission ratio of 86.7%. When this glass is used rather than the PLANITHERM® FUTUR N, the U coefficient is better but the glazing provides slightly less light transmission. 
     In addition, at least one anti-reflective coating  32  may be provided on one or several substrates, preferably on surface  1  and/or  3  and/or  5 , and this has the advantage, besides its anti-reflection function, of improving the light transmission ratio of the glazing unit and of making the products in the display case even easier to see. 
     Finally, the glazing unit comprises an antifrosting absorbent layer  40  associated with the external surface  11   a  of the interior substrate  11 . This antifrosting absorbent layer  40  may be a layer deposited directly on the substrate or deposited onto a plastic film secured to the substrate as described above. This antifrosting absorbent layer  40  is described above. 
     In this third embodiment of the invention, several alternative forms may be envisaged according to the desired performance for the heat transfer coefficient U, accompanied by a compromise regarding the bulkiness of the glazing unit, its weight and its optical qualities and cost. 
       FIG. 3  illustrates a fourth embodiment of the invention for which the door  9  (shown in  FIG. 1 ) has an insulating double glazing unit  20  filled with xenon and/or krypton, with no heating element and comprising at least one low-emission coating  30  and one anti-frost coating  40 . This double glazing unit has a heat transfer coefficient U of less than 1.15 W/m 2 .K. 
     The double glazing unit  20  comprises two glass substrates  21  and  22 , similar to those described above, intended respectively to be in contact with the interior environment of the refrigerated cabinet and with the exterior environment. They are spaced apart by a spacer  50  having a low thermal conductivity like the one described in the third embodiment. For example as shown on the  FIG. 3 , the spacer  50  is secured to the edges of the substrates  21  and  22 . 
     The gas layer  23  of xenon and/or krypton between the two substrates is usually between 4 and 16 mm thick, and preferably has a thickness of at least 8 mm. 
     In this fourth embodiments,  FIG. 3  shows the surfaces of the substrates labelled from  41  to  44 , with  41  being the surface exposed to the ambient atmosphere and surface  44  exposed to the interior of the refrigerated display case when the door is closed. A low-emission coating  30  is arranged on at least an interior surface of the glazing unit, on surface  42  and/or on surface  43 . The coating is of the type described in the third embodiment, based on silver and metal oxides. 
     The anti-frost coating  40  is deposited on the external surface  21   a  (also shown as  44 ) of the interior substrate and corresponds to the one described in the third embodiment. 
     An anti-reflective coating  32  may be provided on at least one of the substrates, preferably on surface  41  and/or  43  of the glazing unit. 
     EXAMPLES 
     The invention will now be described with reference to the following non-limiting examples. 
     As described above, a door for a refrigerated sales cabinet was produced. It consisted of a vacuum insulating glazing unit in order to form the viewing area and of a door frame, for example made of metal. This frame may especially support all the mechanical systems of the handle and hinge type, as well as the seals which seal against the walls of the refrigerated enclosure. 
     The insulating glazing unit consists of two glass sheets between which a vacuum has been created. The glass sheets are separated from each other by studs (spacer) distributed over the entire surface of the glazing and are joined together around their periphery by a seal of inorganic adhesive. Such a vacuum insulation glazing unit is, for example, produced according to a technique as described in Patent Application EP 645 516. 
     According to the invention, a polycarbonate film having a thickness of 2 millimetres is fastened to the vacuum insulating glazing unit by means of an adhesive forming a strip with a thickness of 1 millimetre around the periphery of the glazing. Thus, an air cavity is formed between the glazing and the completely sealed polycarbonate film. This complex is produced in such a way that the trapped air is dry. The film is fastened to that side of the vacuum insulating glazing unit which is intended to face the inside of the refrigerated enclosure when the door is in its closed position. 
     Before attaching it, the polycarbonate film is coated with an antifrosting adsorbent layer, this being deposited so as to face the inside of the refrigerated enclosure when the door is in the closed position. The layer thus deposited forms a polymeric porous three-dimensional network based on polyvinylpyrrolidone and polyurethane. 
     Measurements were carried out on the layer in the wet state using transmission electromicroscopy; these measurements allow the thickness of the layer and the size of the pores to be checked. The thickness of the layer is equal to 14.5 microns and the pores have a mean diameter varying from 1 to 8 microns. 
     Tests were carried out on various types of doors. These doors are fitted onto refrigerated sales cabinets within which a temperature of −28° C. is maintained. The cabinets themselves are placed in an atmosphere at a temperature of 25° C. The tests consist in opening the door for a period of 3 minutes and a period of 12 seconds. The 3-minute period simulates the average time needed for this type of cabinet to be stocked up in the morning. The 12-second duration simulates the average time needed for a consumer to take one or more products. 
     The measured results are the times needed for satisfactory visibility through the door to return, that is to say the times needed to remove the condensation and/or frosting. 
     The first door tested, A, has an insulating glazing unit consisting of three glass sheets. The second door tested, B, has a vacuum insulating glazing unit. 
     The third door, C, is that according to the invention that has just been described. 
     The results are given in Table I below: 
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 3-min opening 
                 12-s opening 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 A 
                 8 
                 min 20 s 
                 1 min 15 s 
               
               
                   
                 B 
                 31 
                 min 10 s 
                 1 min 40 s 
               
               
                   
                 C 
                 0 
                 s 
                 0 s 
               
               
                   
                   
               
             
          
         
       
     
     From these results it is clearly apparent that door C, produced according to the invention, prevents the formation of frosting. 
     Another test was carried out under similar conditions. Only the nature of the layer differs in this second example. This second example consisted in depositing a layer consisting only of a hydrophilic polymer; this hydrophilic polymer was based on polyvinylpyrrolidone, having a molecular mass of 1,300,000 g/mol and diluted to 10% by mass in ethanol. The composition thus obtained was then deposited on the glass by flow coating. 
     Tests such as those described above, consisting in opening the door for a period of 12 seconds and for 3 minutes, were carried out. In both cases, there was no sign of any frosting on the viewing area of the door. 
     The presence of the adsorbent layer therefore prevents the formation of frosting when the door is opened under normal operating conditions. Table II below summarizes several exemplary embodiments D to H of triple glazing units which meet the required thermal insulation and non-formation of mist and frost performances without the need to heat the glazing unit. 
     The results in Table II indicate the overall thickness of the glazing unit, the thicknesses of each glass substrate, the position of the low-emission coating(s), the thicknesses of the layers of gas, the type of gas, the corresponding light transmission ratio and external light reflection factor, and the heat transfer coefficient U obtained for the example with respect to the chosen gas and the gas fill level (85% and 92%), together with the global heat transfer coefficients Uw of the doors incorporating such glazing units. 
     For each of these examples: 
     the spacer of low thermal conductivity  50  was made of two distinct elements for each of the two spaces in the glazing unit; that were made of SAN and glass fibres with a stainless steel sheet as described above and marketed under the trade name SWISSPACER V® by the company SAINT-GOBAIN GLASS; the low-emission coatings  30  and  31  were deposited on glass substrates which correspond to the products PLANITHERM® FUTUR N by SAINT-GOBAIN GLASS, except for the example D1 which corresponds to the example D for which one of substrates was replaced by the product PLANITHERM® ULTRA by SAINT-GOBAIN GLASS of which the specificities are described above; the anti-frost coating  40  was deposited directly onto the glass substrate; this is the EVERCLEAR® coating marketed by SAINT-GOBAIN GLASS; the anti-reflective coatings  32  were deposited on glass substrates and correspond to the products Vision-Life Plus® by SAINT-GOBAIN GLASS. 
     The heat transfer coefficient U was calculated at the center of the glazing unit and in accordance with the standards prEN 673 and prEN 410; hence, this calculation was independent of the type of spacer. 
     The global heat transfer coefficient Uw of the door was calculated for glazing units incorporated in an aluminium frame with thermal breaker bridge and incorporated in a PVC frame. These values were calculated according to the standard EN ISO 10077-2 in taking the sizes of the door, the glazing unit, the frame and the type of frame and of spacer into account. 
     The door was 1800 mm×800 mm. The frame had a squared profile of 40 mm×40 mm with a heat transfer coefficient U equal to 2.6 W/m 2 .K for aluminium and 1.8 W/m 2 .K for PVC. The glazing unit was incorporated in the groove of the frame on a 25 mm depth. 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE II 
               
             
             
               
                   
                   
               
               
                   
                 Embodiment 
               
             
          
           
               
                   
                 D 
                 D1 
                 E 
                 E1 
                 E2 
                 F 
                 G 
                 H 
               
               
                   
                   
               
             
          
           
               
                 Overall thickness 
                 29 
                 29 
                 29 
                 29 
                 29 
                 29 
                 35 
                 35 
               
               
                 (mm) 
               
               
                 Thickness of the 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
               
               
                 exterior substrate 
               
               
                 (mm) 
               
               
                 Thickness of the 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
               
               
                 middle substrate 
               
               
                 (mm) 
               
               
                 Thickness of the 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
               
               
                 interior substrate 
               
               
                 (mm) 
               
               
                 Layer surface 1 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 Anti- 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 reflective 
               
               
                 Layer surface 2 
                 Low- 
                 Low- 
                 Low- 
                 Low- 
                 Low- 
                 Low- 
                 Low- 
                 Low- 
               
               
                   
                 emission 
                 emission 
                 emission 
                 emission 
                 emission 
                 emission 
                 emission 
                 emission 
               
               
                 Layer surface 3 
                 — 
                   
                 — 
                 — 
                   
                 — 
                 — 
                 Anti- 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 reflective 
               
               
                 Layer surface 4 
                 Low- 
                 PLANITHERM ® 
                 Low- 
                   
                 Low- 
                 Low- 
                 Low- 
                 Low- 
               
               
                   
                 emission 
                 ULTRA low- 
                 emission 
                   
                 emission 
                 emission 
                 emission 
                 emission 
               
               
                   
                   
                 emission 
               
               
                 Layer surface 5 
                 — 
                 — 
                 — 
                 — 
                   
                 — 
                 — 
                 Anti- 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 reflective 
               
               
                 Layer surface 6 
                 Anti-frost 
                 Anti-frost 
                 Anti-frost 
                 Anti-frost 
                 Anti-frost 
                 Anti-frost 
                 Anti-frost 
                 Anti-frost 
               
               
                 Thickness of the 
                 8 
                 8 
                 8 
                 8 
                 8 
                 8 
                 8 
                 8 
               
               
                 exterior gas layer 
               
               
                 (mm) 
               
               
                 Type of gas in 
                 Argon 
                 Argon 
                 Krypton 
                 Krypton 
                 Krypton 
                 Krypton 
                 Argon 
                 Argon 
               
               
                 exterior layer 
               
               
                 Thickness of interior 
                 10 
                 10 
                 10 
                 10 
                 4 
                 10 
                 16 
                 16 
               
               
                 gas layer (mm) 
               
               
                 Type of gas in 
                 Argon 
                 Argon 
                 Krypton 
                 Krypton 
                 Krypton 
                 Air 
                 Argon 
                 Argon 
               
               
                 interior layer 
               
               
                 Light transmission 
                 71.2 
                 69.9 
                 71.2 
                 72.4 
                 71.2 
                 71.2 
                 71.2 
                 79.8 
               
               
                 ratio (%) 
               
               
                 External light 
                 15.5 
                 16.8 
                 15.5 
                 17.4 
                 15.5 
                 15.5 
                 15.5 
                 7.2 
               
               
                 reflection factor (%) 
               
               
                 Coefficient U with 
                 0.96 
                 0.93 
                 0.69 
                 1.04 
                 0.93 
                 0.90 
                 0.79 
                 0.79 
               
               
                 gas fill level 85% 
               
               
                 (W/m 2  · K) 
               
               
                 Coefficient U with 
                 0.93 
                 0.91 
                 0.64 
                 0.98 
                 0.86 
                 0.86 
                 0.77 
                 0.77 
               
               
                 gas fill level 92% 
               
               
                 (W/m 2  · K) 
               
               
                 Global coefficient 
                 1.16 
                 1.14 
                 0.89 
                 1.21 
                 1.09 
                 1.09 
                 1.01 
                 1.01 
               
               
                 Uw with gas fill level 
               
               
                 92% in aluminium 
               
               
                 frame (W/m 2  · K) 
               
               
                 Global coefficient 
                 1.10 
                 1.08 
                 0.83 
                 1.15 
                 1.04 
                 1.04 
                 0.95 
                 0.95 
               
               
                 Uw with gas fill level 
               
               
                 92% in PVC frame 
               
               
                 (W/m 2  · K) 
               
               
                   
               
             
          
         
       
     
     These glazing units thus had a heat transfer coefficient U of below 1.1 W/m 2 .K with a gas fill level of 85%, and even below 0.80 W/m 2 .K when argon was used with a gas fill level of at least 92% and with a thickness of 16 mm for one of the layers of gas (Examples G and H), and preferably below 0.65 W/m 2 .K with krypton for both layers of gas (Example E). 
     The global heat transfer coefficient Uw of the door in which such glazing units were incorporated thus was below or equal to 1.25 W/m 2 .K with a gas fill level of at least 92%. 
     These glazing units thus make it possible to obtain a light transmission ratio of at least 67% and an external light reflection factor of below 18%. 
     For the example D1, as described above, the use of a low emission glass substrate PLANITHERM® ULTRA provided, compared with the example D, an increasing of thermal insulating performances although the glazing unit in other respects lost a bit in optical quality while retaining nevertheless very reasonably good values. 
     The use of an anti-reflective layer, for example, on surfaces  1 ,  3  and  5  (Example H) results in an overall transmission ratio of 79.8% with a light reflection factor reduced to 7.2%, providing the glazing with excellent optical qualities. 
     The example F using only one layer of krypton may be desired compared to example E if cost is a concern because krypton is an expensive gas. 
     The glazing unit of example F provided good thermal insulating performances even though it only utilized one layer of krypton. 
     Furthermore, this example F shows the case for which if a complete leak of gas should happen for one of the gas layers in a glazing originally made according to E. 
     It is estimated that, over the course of time, the loss of gas can be as much as 1% per year for a glazing unit (standard prEN 1279-3). Hence, after several years, a glazing unit will see a drop in its gas fill level and its thermal insulation performance will therefore also drop. The row showing the coefficient U with a 85% gas fill level simulates in this respect the thermal performance of a glazing originally filled with a 92% gas fill level after at least 7 years. 
     Table III below illustrates three Examples I, J and J of a double glazing unit according to the invention. The heat transfer coefficient U was calculated at the center of the glazing unit and in accordance with the standard prEN 673 and prEN 410; hence, this calculation was independent of the type of spacer. 
     The low-emission coating corresponds to the PLANITHERM® FUTUR N by SAINT-GOBAIN GLASS. The anti-frost coating corresponds to EVERCLEAR® by SAINT-GOBAIN GLASS, and the anti-reflective coating corresponds to Vision-Lite Plus® by SAINT-GOBAIN GLASS. 
     As explained above for triple glazing units, the global heat transfer coefficient Uw of the door in which these double glazing units have been incorporated has been calculated according to the same way with the same sizes and type of spacer and frame. 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE III 
               
             
             
               
                   
                   
               
               
                   
                 Embodiment 
               
             
          
           
               
                   
                 I 
                 J 
                 K 
               
               
                   
                   
               
             
          
           
               
                 Total thickness (mm) 
                 16 
                 16 
                 18 
               
               
                 Thickness of exterior 
                 4 
                 4 
                 4 
               
               
                 substrate (mm) 
               
               
                 Thickness of interior 
                 4 
                 4 
                 4 
               
               
                 substrate (mm) 
               
               
                 Thickness of the gas layer 
                 8 
                 8 
                 10 
               
               
                 (mm) 
               
               
                 Layer surface 1 
                 — 
                 Anti- 
                 — 
               
               
                   
                   
                 reflective 
               
               
                 Layer surface 2 
                 Low-emission 
                 Low- 
                 Low- 
               
               
                   
                   
                 emission 
                 emission 
               
               
                 Layer surface 3 
                 Low-emission 
                 Low- 
                 Low- 
               
               
                   
                   
                 emission 
                 emission 
               
               
                 Layer surface 4 
                 Anti-frost 
                 Anti-frost 
                 Anti-frost 
               
               
                 Layer surface 5 
                 — 
                   
                 — 
               
               
                 Thickness of the gas layer 
                 8 
                 8 
                 10 
               
               
                 (mm) 
               
               
                 Type of gas in exterior layer 
                 Xenon 
                 Xenon 
                 Krypton 
               
               
                 Light transmission ratio (%) 
                 78.4 
                 81.5 
                 78.4 
               
               
                 External light reflection 
                 9.6 
                 6.0 
                 9.6 
               
               
                 factor (%) 
               
               
                 Coefficient U with gas fill 
                 1.12 
                 1.12 
                 1.08 
               
               
                 level of 85% (W/m 2  · K) 
               
               
                 Coefficient U with gas fill 
                 0.99 
                 0.99 
                 1.01 
               
               
                 level of 92% (W/m 2  · K) 
               
               
                 Global coefficient Uw with 
                 1.22 
                 1.22 
                 1.23 
               
               
                 gas fill level of 92% 
               
               
                 (W/m 2  · K) with aluminium 
               
               
                 frame 
               
               
                 Global coefficient Uw with 
                 1.16 
                 1.16 
                 1.18 
               
               
                 gas fill level of 92% 
               
               
                 (W/m 2  · K) with PVC frame 
               
               
                   
               
             
          
         
       
     
     These glazing units, when designed for slim doors have a small overall thickness and, thus, have a heat transfer coefficient U below 1.15 W/m 2 .K for 85% gas filling and below of 1.05 W/m 2 .K for at least 92% gas filling. And the doors present a global heat transfer coefficient Uw below of 1.20 W/m 2 .K for at least 92% gas filling for a PVC frame and below of 1.25 W/m 2 .K for at least 92% gas filling for an aluminium frame. 
     These glazing units, thus, make it possible to obtain a light transmission ratio of at least 75% and an external light reflection factor of below 12%. 
     The light transmission ratio for Examples I and K is 78.4% and advantageously increases to 81.5% when anti-reflective coatings are added, with external light reflection factors of 9.6% and 6.2% respectively. 
     Thus, the glazing units according to the third and fourth embodiments of the invention meet the classes  2 ,  3 ,  4  and  5  of environment given in standard EN441, and summarized in Table IV below, and particularly meet the class  6  when the heat transfer coefficient U is below 0.8 such as with examples E, G and H. 
     
       
         
               
               
               
               
             
           
               
                 TABLE IV 
               
               
                   
               
               
                   
                 Temperature 
                 Relative 
                   
               
               
                 Class of environment 
                 outside the 
                 humidity 
               
               
                 In accordance with 
                 cabinet 
                 outside the 
                 Dew point 
               
               
                 standard EN441 
                 ° C. 
                 cabinet % 
                 ° C. 
               
               
                   
               
             
             
               
                 2 
                 22 
                 65 
                 15.1 
               
               
                 3 
                 25 
                 60 
                 16.7 
               
               
                 4 
                 30 
                 55 
                 20.0 
               
               
                 5 
                 40 
                 40 
                 23.8 
               
               
                 6 
                 27 
                 70 
                 21.1 
               
               
                   
               
             
          
         
       
     
     While the claimed invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one of ordinary skill in the art that various changes and modifications can be made to the claimed invention without departing from the spirit and scope thereof.