GB2289015A

GB2289015A - Flexible barrier film for evacuated insulation panels

Info

Publication number: GB2289015A
Application number: GB9408002A
Authority: GB
Inventors: Anthony Cunningham; Norman Washington Keane
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1994-04-22
Filing date: 1994-04-22
Publication date: 1995-11-08
Also published as: GB9408002D0

Abstract

Multilayer flexible barrier film suitable for use in evacuated insulation panels comprising a tin based metal foil layer and a thermoplastic heat sealing layer wherein the tin comprises at least one of Sb, Bi and Cu. The evacuated insulation panel may comprise first and second substantially gas impermeable panel walls, at least one of which is the multilayer flexible barrier film, the walls being sealably joined to one another along their edges, the space between the walls being evacuated and containing insulating material.

Description

DESCRIPTION This invention relates to evacuated insulation panels and in particular to gas impermeable barrier films for use in such evacuated insulation panels.

Evacuated insulation panels having a reduced internal pressure are known for various uses including use in refrigeration appliances where they greatly enhance the degree of thermal insulation within the cabinet ^. the appliance.

Such evacuated insulation panels generally comprise a low thermal conductivity filler material and a vessel formed of a gas impermeable film enveloping said filler, the whol-e being evacuated to an internal pressure of about 5 mbar or less and then hermetically sealed. Besides insulation the filler has also the function of supporting the skin of the vessel so that it does not collapse when it is evacuated.

The evacuated insulation panels must remain effective for the life of the appliance, generally a period in excess of 20 years.

To do so, the panels must be highly gas impervious, yet must be able to prevent transmission of heat not solely by conduction and radiation through the panels, but also by conduction along the surface of the panels.

Efforts have been made to employ plastic materials for the panel walls.

However, most gases permeate plastic. The permeation rate depends upon the specific gas and specific plastic.

Since very few gases permeate metals, metals have been used as barrier layers on the plastic to reduce their permeation rates.

Therefore multilayered structures of metal foil layers (such as aluminum foil) and plastic material layers have been used as barrier films for evacuated insulation panels. Such barrier films provide superior resistance to permeation by gases and water vapor, largely due to the impermeability of the metal foil layer.

However the high thermal conductivity of aluminum significantly increases the conduction of heat along the edges of the panel. The aluminum foil provides an excellent conduction path and a considerable amount of heat gets conducted from the hot face to the cold face of the panel through the foil.

Some kind of thermal break has to be provided around the perimeter of such an evacuated insulation panel to prevent this edge conduction effect. Such thermal breaks have been constructed in the art by utilising a metal foil having smaller dimensions than the other layers so that the sealed edges do not comprise the metal layer edges (see EP-A-0 437 930 and EP-A-0 196 721) or by utilising a plastic edge strip (see US-P-4,444,EjZ1!.

The use of such thermal breaks leads to more cumbersome manufacturing of the barrier film itself and/or of the evacuated insulation panel.

Instead of aluminum low thermal conductivity metals can be used in order to reduce the edge conduction effect. These metals preferably have a thermal conductivity at IOOC of below 70 mW/mOK. Examples cf such metals include tin, titanium, lead, iron and alloys thereof such as Sta-nless Steel, Mild Steel and tin/lead alloys with a tin/lead weight ratio of between 90:10 and 40:60.

In EP-A-0 184 415 a laminated film including an outer layer of a synthetic resin (such as polyethylene terephthalate), an intermediate layer of a metallic foil (such as aluminum, iron, stainless steel or tin) and an inner layer of a synthetic resin (such as low density or high density polyethylene) is described for use as gas impermeable film for an evacuated insulation panel.

Using pure tin as the metal foil layer leads to difficulties in terms of rollability of the film material.

Since lead has a negative impact on the environment the use of tin/lead foils is to be avoided.

It is an object of the present invention to provide an evacuated insulation panel of improved construction which at least partly mitigates the aforementioned disadvantages.

In accordance with the present invention a multilayer flexible barrier film suitable for use in evacuated insulation panels is provided, said barrier film comprising a tin based metal foil layer and a thermoplastic heat sealing layer characterised in that the tin comprises at least one alloying material selected from the group consisting of antimony, bismuth and copper.

The barrier films of the present invention show extremely low gas and water vapor permeability. They are easily rollable and do not have a negative impact on the environment.

Evacuated insulation panels provided with the barrier films of the present invention do not show an increase in thermal conductivity due to edge conduction of the metal layers and provide excellent insulation performance for 15 to 20 years.

The tin used in the present barrier films can contain. only one of the selected alloying materials or can contain a mixture of several of these alloying materials.

Antimony is the preferred alloying material.

The alloyIng terial is added to the tin In amounts ranging from 0.1 to 10 % by weight. In particular for antimony and copper the preferred range is 0.1 to 5 % by weight. The preferred compcsiticn contains about 2 t by weight of bismuth, copper or antimony, especially 2 W by weight of antimony.

The thickness of the metal foil layer is generally in the range 1 to 150 micron. Preferred thicknesses are in the range 10 to 50 micron, preferably 15 to 40 micron and most preferably 5 to 20 micron.

The heat sealing layer of the present barrier film consists of a thermoplastic resin having a relatively low melting point (lower than 2000C). Examples of suitable thermoplastics include low density polyethylene, high density polyethylene, polypropylene, polyacrylonitrile, polyvinylidenechloride and copolymers thereof.

In the selection of a suitable heat sealing layer aspects such as gas and water vapour permeability and outgassing of the thermoplastic resin may be taken into account. For example polyacrylonitrile has a low permeability for oxygen and carbon dioxide but a high permeability for water vapour, while high density polyethylene has a low permeability for water vapour. Further moisture containing polymers such as polyacrylonitrile show substantial outgassing in the form of water vapour which also increases the internal pressure of the evacuated insulation panel.

The thickness of the heat sealing layer is generally in the range 5 to 200 micron, preferably 50 to 100 micron and most preferably 20 to 50 micron.

The heat sealing layer is applied to the metal foil layer by hot melt coating (extrusion), by dispersion coating or by lamination. The latter is preferred.

A suitable a adhesive is used to secure the heat sealing layer to the metal foil layer. Examples of suitable adhesives include polyurethanes and polyesters.

Preference is given to thermoset adhesives over thermoplastic adhesives because the lack of heat resistance of thermoplastic adhesives retricting the heat sealing range of the laminate. The adhesives can be either solvent or non-solvent based. Polyurethane adhesives are most preferred.

The thickness of the a adhesive layer is generally in the range 1 to 5 micron.

In the selection of a suitable type and thickness of adhesive, permeability and outgassing properties of the adhesive are to be taken into account. lonally a support layer is provided on top of the metal foil layer to protect the metal during transport and handling, especially if the thickness the meta; fs ; layer is less than 2 micron, especially less than 10 Common thermoplastics are used in the construction of this support layer, such as polyethylene terephthalate, polyacrylonitrile and polyethylene. Since the sort layer is provided on the outermost side of the evacuated insulation panel, permeability and outgassing aspects of the thermoplastic are not that important. Preference is given to polyethylene terephthalate.

The thickness of this support layer is between 10 and 50 micron, preferably between 10 and 25 micron. support layer s secured to the metal foil layer with the use of a adhesives as listed above. The thickness of the adhesion layer is generally in the range 1 to 10 micron.

Since all the layers of the present barrier film have the same dimensions the film can be easily manufactured in a continuous roll.

The barrier film according to the present invention is particularly suitable for use in evacuated insulation panels.

Therefore the present invention also provides an evacuated insulation panel comprising a) a first substantially gas impermeable panel wall; b) a second substantially gas impermeable panel wall, said first and said second panel wall sealably joined to each other along the edges of said walls, the space between said sealed panel walls being evacuated; and c) an insulating material disposed within said volume; characterised in that at least one of said first or second panel wall is a a multilayer flexible barrier film comprising a tin based metal foil layer and a thermoplastic heat sealing layer wherein the tin comprises at least one alloying material selected from the group consisting of antimony, bismuth and copper.

At least one cf the panel walls of the evacuated insulation panel is a barrier film according to the present invention. The other panel wall may be a conventional barrier film known in the art such as an aluminum foil - plastic laminate. If the evacuated insulation panel is attached to a secondary metal surface, sa for insulation of a refrigerator cabinet wall, this other panel wall is preferably provided on the side facing the secondary metal wall.

In the construction of evacuated insulation panels according to the present invention the two panel wall films, at least one of which is a barrier film according to the present inention, are sealably joint to each other along the wall edges with the plastic layers of the panel walls facing the interior of the panel.

The evacuated insulation panel may be constructed in the form of a bag or in the form of a tray. The flat side of the tray is then attached to a secondary metal surface.

The evacuable internal volume defined by the sealed edges of the panel walls is filled with an insulation material which not only functions to provide insulation but also to maintain the two panel walls in a spaced apart relationship. Evacuation of the panel is accomplished through a conventional tubulation point which, after evacuation, is heat-sealed.

The insulation material may be in the form of individual sheets of fibrous material such as glass fiber insulation or in the form of microporous powder material such as fumed silica, silica dust, precipitated silica, precipitated silica/fly ash mixtures, alumina, fine perlite or in the form of an organic foamed material having open cells such as open celled rigid polyurethane foam.

Preference is given to open celled rigid polyurethane foam. A preferred formulation for making open celled rigid polyurethane foam is described in European patent publication no. 0 498 628.

An air permeable pouch may be used to provide a container for the insulation material in order to facilitate further processing.

It is preferred to precondition the insulation material prior to placement in the air permeable pouch or in the sealed panel walls.

This preconditioning involves heating and optionally, agitating the insulation material in order to remove contaminants from the surface of the insulation material. The removal of contaminants improves inter alia the expected panel life. Further the removal of contaminants reduces the time required to evacuate the panel thereby reducing the time and cost associated with the manufacture of an evacuated insulation panel.

Reduced pressures may also be used together with heating and/or agitation.

It is generally necessary to provide within the sealed panels materials to absorb or otherwise interact with gases and vapors that remain due to imperfect evacuation, tht permeate the enclosure from the outside atmosphere or evolve from the insulation material or the barrier film tself Such materials are knows as getters and may include, for example, a granular form of calcium sulfate or microporous bariumoxide which is excellent in removing water vapor, activated carbon to remove organic gases, metals ~- - r~ oxygen and nitrogen and zeolites to absorb carbon dioxide and nitrogen. Other suitable getter materials are described in US Patents N@s. @ 000,246, 4,444,821, 4,663,551, 4,702,963 and 4,726,974 and in European Patent Publications Nos. 434266 and 181778.

If polyacrylonitrile is used as the heat sealing layer of the present t barrier film it is particularly preferred to include a dessicant into the sealed panel in order to absorb water vapour outgassing from the polyacrylonitrile.

The panels thus provided are relatively rigid and have a .ess of approximately 1 to 5 cm.

The evacuated insulation panels may be of various dimensions. Panels as large as 40 cm x 40 cm can be easily manufactured.

Refrigeration appliance is only a single example of a product that tan utilise evacuated insulation panels. They can also form part of an insulated milding panel. Other environments having a hot side and a cold slide could also benefit from the use of the present invention.

The rigid evacuated insulation panels can be easily arranged in the door and walls of a refrigerator. They are generally attached by adhesive to the walls of the thermal device to be insulated and then foamed-in-place with a liquid organic material such as polyurethane. The polyurethane foam the assists in holding the panels in place between the walls and also provides additional insulation.

Further descriptions relating to the construction of evacuated insulation panels and their use in thermal devices can be found in US Patents Nos 5,066,437, 5,032,439 and 5,076,984 and European Patent Publications Nos 434266, 434225, 437930 and 181778, all incorporated herein by reterence as well as the references mentioned therein.

Claims

CLAIMS 1. Multilayer flexible barrier film comprising a tin based metal foil layer and a thermoplastic heat sealing layer characterised in that the tin comprises at least one alloying material selected from the group consisting of copper, bismuth and antimony.
Multilayer flexible barrier film according to claim 1 whereIn the amount of alloying material is in the range 0.1 to 10 W by weight.
3. Multilayer flexible barrier film according to claim 2 wherein the amount of alloying material is about 2 e by weight.
4. Multilayer flexible barrier film according to any one of the preceding claims wherein the alloying material is antimony.
5. Multilayer flexible barrier film according to any one of the preceding claims wherein the thickness of the metal layer is in the range 1 to 150 micron.
6. Multilayer flexible barrier film according to any one of the preceding claims wherein the heat sealing layer consists of a thermoplastic resin selected from the group consisting of low density polyethylene, high density polyethylene, polypropylene, polyacrylonitrile and polyvinylidenechloride.
7. Multilayer flexible barrier film according to any one of the preceding claims wherein the thickness of the heat sealing layer is in the range 5 to 200 micron.
8. Multilayer flexible barrier film according to any one of the preceding claims wherein an adhesive layer is provided between the metal foil layer and the heat sealing layer.
9. Multilayer flexible barrier film according to claim 8 wherein said adhesive layer contains polyurethane adhesives and has a thickness in the range 1 to 5 micron.
10. Multilayer flexible barrier film according to any one of the preceding claims wherein a support layer is provided on top of the metal foil layer.
11. Evacuated insulation panel comprising a) a first substantially gas irpermeable panel wall; b) a second substantially gas impermeable panel wall, said first and said second panel wall sealably joined to each other along the edges of said walls, the space between said sealed panel walls being e.-a-~a:e~; and c) an Insulating material disposed within said volume; characterised in that at least one of said first or second Sane wall is a multilayer flexible barrier film as defined in any one of the preceding claims.
12. Evacuated insulation panel according to claim 11 wherein the insulating material is an open celled rigid polyurethane foam.
13. Evacuated insulation panel according to claim 12 wherein the open celled rigid polyurethane foam is prepared by reacting an organic polyisocyanate composition with a polyfunctional isocyanate-reactive composition in the presence of an inert, insoluble fluorinated compound and in the presence of a blowing promotor which is an isocyanate reactive cyclic compound of formula

wherein Y is O or NR wherein each R1 independently is a lower alkyl radical of C1-C6 or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of C1-c. or (CH2)m-X wherein X is an isocyanate-reactive group which is OH or - and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of R: or R is or comprises an isocyanate-reactive group; and in the presence of a metal salt catalyst.
14. Evacuated insulation panel according to any one of claims 11 to 13 wherein a getter material is also provided withIn the sealed panel.