THERMAL INSULATION ELEMENTS

Abstract

The invention relates to thermal insulation elements comprising a) a covering layer having a thickness of from 0.2 to 1.0 mm, b) at least one vacuum insulation panel located on a), c) a further thermal insulation material, d) a further covering layer.

Description

The invention relates to thermal insulation elements comprising vacuum insulation panels, refrigeration appliances produced from these thermal insulation elements and a process for producing the thermal insulation elements and also refrigeration appliances produced therefrom.

Refrigeration appliances play an important role in many fields. Refrigeration appliances include, for example, refrigerators, freezer chests, upright freezers, cooling containers or superstructures of refrigerated vehicles. The refrigeration appliances usually comprise a hollow space surrounded by thermal insulation elements within which the material to be cooled being located. The thermal insulation elements usually comprise two covering layers between which a thermal insulation material, usually a rigid polyurethane foam, is located.

There is an ongoing need to reduce the energy consumption of refrigeration appliances. One possible way of achieving this is to reduce the thermal conductivity of the thermal insulation materials used. One possible way of bringing this about is the use of vacuum insulation panels, hereinafter also referred to as VIPs.

Thus, the energy saving potential when using VIPs is about 10-40% compared to conventional, closed-celled rigid polyurethane foams.

Such vacuum insulation units generally comprise a thermally insulating core material, for example open-celled rigid polyurethane (PUR) foam, open-celled extruded polystyrene foam, silica gels, glass fibers, loose beds of polymer particles, pressed milled rigid PUR foam or semirigid PUR foam or perlite, which is packed in a gastight film, evacuated and heat sealed in so as to be airtight.

The use of VIPs in refrigeration appliances is known and has been described many times. Thus, WO 97/36129 describes VIPs which have an edge length of at least 40 cm and can be installed in refrigeration appliances.

EP 434 225 describes VIPs and their installation in refrigeration appliances. Here, the VIP is arranged between the covering layers and surrounded with foam.

WO 99/61503 describes VIPs which are installed in refrigeration appliances. Here, they are fixed to the side facing the interior of the refrigeration appliance by means of an adhesive and the hollow space between the covering layers is then filled with a rigid polyurethane foam system.

A further ongoing requirement is to reduce the usage of materials in the production of refrigeration appliances. The use of VIPs enables, owing to their lower thermal conductivity, a reduction in the thickness of the insulation of the refrigeration appliances to be achieved. In this way, an increase in the interior space and thus the useful volume of the refrigeration appliances is possible at the same dimensions of the refrigeration appliance.

A further saving has been able to be achieved by reducing the thickness of the covering layers. However, this is possible only to a limited extent.

When filling the hollow spaces of refrigeration appliances with rigid polyurethane foam systems, flaws and voids are usually formed. When the thickness of the covering layers is too low, these flaws show up on the outside. This impairs the esthetics of the refrigeration appliances and is regarded as a disadvantage.

It was an object of the present invention to efficiently produce refrigeration appliances which have a low energy consumption and a high quality/defect-free appearance, are simple to produce and can be recycled without problems.

This object was able to be achieved by the thermal insulation elements described in more detail below, by means of which refrigeration appliances can be produced.

The object was able to be achieved by thermal insulation elements comprising

• • a) a covering layer having a thickness of from 0.2 to 1.0 mm,
  • b) at least one vacuum insulation panel located on a),
  • c) a further thermal insulation material,
  • d) a further covering layer.

The covering layer a) can comprise metal, for example, steel sheet. In another embodiment of the thermal insulation elements of the invention, the covering layer a) comprises polymers, in particular thermoplastic polymers. Preference is given to using polystyrene or ABS polymers as polymers. As described, the metal covering layers have a thickness of from 0.2 to 0.5 mm, preferably at least 0.25 mm and in particular 0.3 mm, and not more than 0.4 mm. In the case of polymer, a thickness of 0.7-1.0 mm is preferred.

Preference is given to at least 60%, particularly preferably at least 70% and in particular at least 80%, of the area of the covering layer a) being covered with the vacuum insulation panel. Complete coverage of the covering layer a) is possible, but it is not preferred because a filling of the corners with foam should be undertaken to make the refrigeration appliances produced from the thermal insulation elements stable. In addition, it cannot be ensured that regions in which the vacuum insulation panels abut and form hollow spaces which can also not be filled by the further insulation material c) are formed at the corners or edges in the production of the refrigeration appliances.

The covering layer a) can be covered by a plurality of vacuum insulation panels, but preferably by only one vacuum insulation panel. Here, the vacuum insulation panels preferably have an edge length of at least 40 cm, preferably 60±20 cm×160±40 cm, and a thickness of at least 5 mm and at most 50 mm. The size of the vacuum insulation panels is preferably adapted to the size of the refrigeration appliances and should, as described, be such that at least 60% of the covering layer a) is covered by only one vacuum insulation panel.

The advantage of using only one vacuum insulation panel b) per thermal insulation element is, in particular, that the diffusion of water vapor and the thermal conductivity can be reduced as a result of the gap-free covering of the covering layer a) and any gaps which can occur at the outer skin at the boundary between two vacuum insulation panels are avoided. Due to the size, this embodiment can be used, in particular, when the thermal insulation elements are used for producing refrigerators or freezer chests.

The production of vacuum insulation panels and the materials used for this purpose are known. As core materials, preference is given to using, as described, open-celled rigid polyurethane foams or foamed melamine-formaldehyde condensation products.

A process for producing the foamed melamine-formaldehyde condensation products is, for example, described in EP 220 506.

The foamed melamine-formaldehyde condensation products can comprise up to 50% by weight of other thermoset formers which have been cocondensed. These are preferably condensation products of compounds comprising amine, amide, hydroxyl and/or carboxyl groups with aldehydes, in particular formaldehyde. Preferred thermoset formers are condensation products of substituted melamine, urea, urethanes, aliphatic amines, amino alcohols, phenols and their derivatives with aldehydes. As aldehydes, it is possible to use, in a mixture with or in place of formaldehyde, further aldehydes such as acetaldehyde, benzaldehyde, acrolein, terephthalaldehyde.

Furthermore, the foamed melamine-formaldehyde condensation products can comprise further additives such as organic or inorganic fillers. As additives, it is possible to use fibers, inorganic powders such as metal powders, kaolin, quartz, chalk, further dyes and pigments.

Since the foamed melamine-formaldehyde condensation products have only cell struts and no cell walls, they are very easy to evacuate. Preference is given to using rigid melamine-formaldehyde condensation products.

Foamed melamine-formaldehyde condensation products are known and are marketed, for example, by BASF AG under the trade name Basotect®. They are usually produced by partly dissolving a pulverulent melamine-formaldehyde condensation product in water comprising salts or surfactants, mixing the resulting paste-like intermediate with a blowing agent, preferably in an extruder, and foaming the resulting product by heating, for example in a hot air oven. The foam can subsequently be heat treated in a heat treatment apparatus. Foaming is preferably carried out in a temperature range from 120 to 180° C., and heat treatment is preferably carried out in a temperature range from 200 to 250° C.

Suitable rigid polyurethane foams are described, for example, in EP 1512707. In the production of the open-celled rigid polyurethane foams, water and/or hydrocarbons are preferably used as blowing agents.

In a specific embodiment of the invention, open-celled foams based on isocyanate having a cell size of less than 100 μm are used as core material of the vacuum insulation panels. Such foams can be obtained via aerogels.

In the production of vacuum insulation panels using rigid polyurethane foams, the foam is firstly produced in a manner known per se. The foams obtained are then, if they have not already been produced as moldings having the desired size, are brought to the shape which they have as core of the vacuum insulation panel. This is preferably achieved by sawing to the appropriate board size. The moldings are then packed in the gastight sheathing, preferably the composite film, evacuated and heat sealed so as to be gastight.

It is usual for a getter material to be heat sealed in together with the core material in order to prevent volatile substances which outgas later from impairing the vacuum. Getter materials which can be used are, for example, zeolites, activated carbons, strongly hygroscopic materials.

A film is generally used as sheathing material for the vacuum insulation panels. Preferred films are composite films, in particular multilayer composite films having a vapor-deposited or laminated-on metal layer, for example of aluminum. Suitable films comprise, for example, polyester, polyvinyl chloride, polyolefins such as polyethylene or polypropylene or polyvinyl alcohol.

The use of open-celled rigid polyurethane foams as core material for the vacuum insulation panel is, as described, preferred. The advantages are firstly that the refrigeration appliances produced in this way are completely recyclable since no constituents extraneous to the system are comprised in the refrigeration appliance. Secondly, the boards can be handled more easily than pulverulent materials in the production of the vacuum insulation panels.

The vacuum insulation panels b) can be fixed to the covering layer a) by means of adhesives or adhesive tapes.

As described, the thermal insulation elements of the invention are used predominantly for the production of refrigeration appliances. Refrigeration appliances are, for example, refrigerators, freezer chests, upright freezers, cooling containers or superstructures for refrigerated vehicles. The thermal insulation elements of the invention can be used both as wall elements and as door elements.

The refrigeration appliances can be produced in various ways.

In one embodiment of the production of the refrigeration appliances, the thermal insulation elements are produced separately as flat elements and are then joined to produce the refrigeration appliances. This embodiment is, in particular, preferred in the case of very large refrigeration appliances, for example cooling containers or superstructures for refrigerated vehicles. Here, the covering layers a) and d) can be fixed in place with the desired spacing and the insulation material c) can be introduced. As insulation material c), use is made of, in particular, rigid polyurethane foam whose liquid starting components are introduced into the hollow space where they cure to form the polyurethane and at the same time firmly join the covering layers a) and d) to one another.

It is in principle also possible to produce the thermal insulation elements by the continuous double plate process. For this purpose, the vacuum insulation panels b) are placed on the moving lower covering layer a), the liquid starting components for the rigid polyurethane foam are placed on these and the upper covering layer d) is then applied. The thermal insulation element obtained can then, depending on the length of the vacuum insulation panels b) introduced, be cut between the vacuum insulation panels b).

In the production of refrigerators or freezer chests, preference is given to molding the outer covering layer a) and the inner covering layer d) to form the housing of the appliance and to introduce the liquid starting components of the rigid polyurethane foam used as insulation material into the hollow space between the covering layers. The rigid polyurethane foam firmly joins the covering layer and thus stabilizes the housing.

In one embodiment of refrigerators, insulation elements whose covering layer a) comprises cardboard or polyolefin, e.g. polyethylene or polypropylene, are used for the rear side where aesthetic considerations naturally do not play a dominant role. Otherwise, these thermal insulation elements have the same structure as described above.

In a further embodiment of the production of the refrigeration appliances, it is possible, as described above, for the thermal insulation elements to be produced on a continuous double plate unit and, as described in EP 1 075 634, cut to length, mitered and folded to form the housing of the refrigeration appliance. Care has to be taken here that the vacuum insulation panels b) introduced are not damaged.

The rigid polyurethane foams which are preferably used as insulation material c) are preferably the customary and known compounds as are described, for example, in Kunststoff-Handbuch, Volume 7 “Polyurethane”, 3rd Edition 1993, Carl Hanser Verlag, Munich, Vienna. These compounds are usually produced by reacting polyisocyanates, preferably diphenylmethane diisocyanate and mixtures of diphenylmethane diisocyanate with polyphenylene-polymethylene polyisocyanates, also referred to as crude MDI, with compounds having at least two hydrogen atoms which are reactive toward isocyanate groups. The compounds having at least two hydrogen atoms which are reactive toward isocyanate groups are usually polyether alcohols and/or polyester alcohols, preferably ones having a functionality of at least 3. The polyester alcohols are usually reaction products of polyfunctional carboxylic acids with polyfunctional alcohols. The polyether alcohols are usually reaction products of compounds having at least 3 active hydrogen atoms with alkylene oxides, preferably ethylene oxide and/or propylene oxide. As compounds having at least 3 active hydrogen atoms, use is usually made of polyfunctional alcohols such as glycerol, trimethylolpropane or sugar alcohols, preferably sucrose or sorbitol, aliphatic amines such as ethylenediamine or aromatic amines such as tolylenediamine (TDA) or diphenylmethanediamine (MDA), usually in admixture with its higher homologues.

The reaction usually proceeds in the presence of catalysts, blowing agents and auxiliaries and/or additives. Water is usually used as blowing agent, most often in combination with inert compounds which are liquid at room temperature and vaporize at the reaction temperature of polyurethane formation, known as physical blowing agents. Customary physical blowing agents are alkanes, fluoroalkanes and methyl formate. Among the alkanes, pentanes and in particular cyclopentane have the greatest industrial importance.

In the case of the rigid polyurethane foams used as core material for the vacuum insulation panels, use is in principle made of the same starting materials as for producing the polyurethanes used as insulation materials c). However, water and hydrocarbons, preferably cyclopentane, are predominantly used as blowing agent.

The advantages of the thermal insulation elements of the invention over thermal insulation elements without vacuum insulation panels are the significantly lower thermal conductivity, the lower gas diffusion and the ability to reduce the thickness of the insulation layer and thus save material. The process of the invention surprisingly also makes it possible to reduce the thickness of the carbon layer without this resulting in disadvantages in terms of the aesthetics of the refrigeration appliances, the stability and the use properties. In addition, the residence times in the mold can be reduced by up to 50% as a result of decreasing the thickness of the remaining insulation layer c) when using rigid polyurethane foam as c) in an appropriate design. Furthermore, a more useful space can be made available by reducing the layer thickness at the same external dimensions.

In the production of the thermal insulation elements of the invention, the temperature of the tool or the mold can be reduced down to 23° C.

Claims

1. A thermal insulation element, comprising:

a) a covering layer having a thickness ranging from 0.2 to 1.0 mm,

b) at least one vacuum insulation panel located on a),

c) an additional thermal insulation material,

d) an additional covering layer.

2. The thermal insulation element according to claim 1, wherein the covering layer a) comprises metal.

3. The thermal insulation element according to claim 1, wherein the covering layer a) comprises a polymer.

4. The thermal insulation element according to claim 1, wherein the vacuum insulation panel b) comprises a core of open-celled rigid polyurethane foam which is sheathed by a film, evacuated and closed.

5. The thermal insulation element according to claim 1, wherein the vacuum insulation panel b) is fastened in an adhesive manner to the covering layer a).

6. The thermal insulation element according to claim 1, wherein the vacuum insulation panel b) covers at least 60% of the area of the covering layer a).

7. The thermal insulation element according to claim 1, wherein at least 70% of the area of the covering layer a) is covered by a vacuum insulation panel b).

8. The thermal insulation element according to claim 1, wherein the additional insulation material is a polymer foam.

9. The thermal insulation element according to claim 1, wherein the additional insulation material c) is a rigid polyurethane foam.

10. The thermal insulation element according to claim 1, wherein the vacuum insulation panel b) comprises a core of foamed melamine-formaldehyde condensation product.

11. The thermal insulation element according to claim 1, wherein the additional covering layer d) comprises a metal or a polymer.

12. (canceled)

13. A refrigeration appliance, comprising:

a hollow space which is surrounded by sheet-like thermal insulation elements, wherein at least one of the sheet-like thermal insulation elements is the thermal insulation element according to claim 1.

14. The refrigeration appliance according to claim 13, wherein the thermal insulation elements are arranged so that the covering layer a) forms the outer surface of the refrigeration appliance.

15. A process for producing thermal insulation elements according to claim 1, which comprises:

ai) fixing a vacuum insulation panel b) onto the covering layer a),

bi) fixing the covering layer d),

ci) introducing a liquid rigid polyurethane foam system into the hollow space formed in step bi),

di) curing the rigid polyurethane foam formed in step ci).

16. A method of thermally insulating refrigeration appliances, comprising:

incorporating the thermally insulating element according to claim 1 as a door element or wall element in refrigeration appliances.