HUP0200652A2 - Vacuum insulation panels - Google Patents

Description

VACUUM INSULATION PANELS

The invention relates to vacuum insulation panels with improved insulation properties, to a gas-tight plastic film suitable for producing such vacuum insulation panels, and to the use of vacuum insulation panels in refrigerating and freezing machines.

Vacuum insulating panels (VIP) are excellent thermal insulation materials that are important in all areas of thermal insulation, but especially in household refrigerators and freezers. The thermal insulation capacity of vacuum insulating panels is usually more than twice that of rigid polyurethane foam. Vacuum insulating panels are usually manufactured by wrapping a microporous carrier material with foil and then sealing it under vacuum. The absolute pressure inside the vacuum insulating panel is usually below 100 Pa, because only such a low pressure provides the necessary thermal insulation. Conventional vacuum insulating panels can be divided into two groups:

Precipitated microporous silica surrounded by a plastic film according to EP 0 436 311 A1 or DE 40 19 870 A1, EP 0 396 961 B1 and EP 0 446 486 A2 or DE 40 08 480, and associated microcellular plastic foam covered with aluminum foil (e.g. US 4,669,632).

The disadvantage of a vacuum insulation panel containing microporous silica precipitated in the core is that it is made from a powdery material and therefore has fluctuating thicknesses and deviations from flat surfaces, which make installation in refrigerators and freezers difficult.

The disadvantage of vacuum insulation panels containing plastic foam inside is that the plastic foam has a low gas, especially water vapor, absorption capacity, therefore, when using this otherwise excellent VIP core material, the gas-tightness of the foil used is very important. Conventional sealing foils made of plastic, such as

95299-1174 To such as those described in EP 0 517 026 A1, do not achieve the required gas barrier effect. In order to bind the diffusing gas and maintain the low pressure in the VIP, it is possible to place gas-absorbing or gas-reactive substances ("getters") in the inner layer, but this measure does not always produce the desired result. Therefore, in order to maintain the vacuum of the VIP, a bonded aluminum foil is preferably used as a completely gas-tight layer. However, the bonded aluminum foil conducts so much heat at the edges that a large part of the insulating performance of the VIP is lost. However, this effect can only be demonstrated by measuring the heat transfer on a complete refrigerator or freezer. The wind effect cannot be determined by measuring the thermal conductivity according to DIN 18164 parts 1 and 2.

Despite the above, the market share of vacuum insulation panels with a plastic foam core is significant because their dimensions can be precisely maintained and they can be processed simply and cost-effectively as sheet metal with a perfectly flat surface. However, the aforementioned disadvantage of heat transfer at the edges of the double-sided aluminum foil hinders the further spread of aluminum foil vacuum insulation panels.

The task of the present invention was to develop a vacuum insulation panel that has the advantages of a panel containing plastic foam as a core (flat surface, ability to be produced in precise dimensions), but eliminates or significantly minimizes the reduction in insulation capacity due to heat transfer at the edges.

According to the invention, the above problem has been solved with a vacuum insulation panel which contains a microporous plate as a core and the cover of the plate is formed by a highly gas-tight plastic film consisting of at least 7 layers in the following order of layers: (1) polyolefin hot melt adhesive layer (I) (2) adhesive or bonding layer (II) (3) gas-tight layer (ΠΙ) (4) adhesive or bonding layer (II) (5) polyolefin layer (IV) (6) adhesive or bonding layer (II) (7) layer (V) consisting essentially of polyester and/or polyamide and/or polypropylene vaporized with aluminum or silicon oxide of the formula SiO _x or with the oxide of a metal belonging to the 2nd or 3rd main group.

The oxygen permeability of the vacuum insulation panel according to the invention is less than 0.01 cm ³ /m ² · day · 10 ⁵ Pa, the water vapor permeability is < 0.02 g/m ² · day, so the durability of the thermal insulation effect of the panel produced according to the invention meets the requirements of practice. The loss of the insulation effect along the edges, as occurs when using associated aluminum foils, is not observed.

As a material for the layer (I) consisting of hot melt adhesive, polyolefin homo- or copolymers can be considered. The following are preferred: linear low-density polyethylene (LLDPE), polybutylene (PB), ethylene vinyl acetate (EVA), high-density polyethylene (HDPE), ionomer (I) and mixtures thereof. According to the invention, a multilayer hot melt adhesive layer produced by coextrusion from the above materials is also conceivable. The thickness of the layer (I) consisting of hot melt adhesive is preferably 20-200 μm, particularly preferably 50-100 μm.

As the adhesive and connecting layer (Π) between the individual layers, commercially available reactive adhesives are preferably used, particularly preferably two-component polyurethane adhesives. However, polyolefin adhesion promoters, preferably polyethylene homopolymer, ethylene ethyl acrylate (EEA) or ethylene methacrylic acid (EMA), can also be used. The thickness of the adhesive or connecting layer (II) is preferably at most 6 μm, particularly preferably 2-6 μm.

The material of the gas barrier layer (III) is preferably essentially polyvinyl alcohol (PVOH), ethylene/vinyl alcohol copolymer (EVOH) and/or polyamide, or a mixture of PA and EVOH, or in the case of a multilayer design, alternating layers of PA and EVOH. The gas barrier layer is preferably stretched in at least one direction and optionally provided with a sealing varnish layer, preferably an acrylic varnish layer. The thickness of the gas barrier layer (III) is preferably 10-120 μm, in the case of a three-layer design it is particularly preferably 10-20 μm.

The polyolefin layer (IV) preferably consists essentially of polyethylene, polypropylene or polyethylene copolymer. This layer is preferably 5-500 μm thick, particularly preferably 50-200 μm thick, according to the invention. It has been found that the relatively thick polyolefin layer (IV) gives the panel a significantly smoother and more uniform surface. This is particularly advantageous if the panel is installed in the refrigerator by gluing. If the panel were to wrinkle, the surface area wetted by the adhesive is usually not large enough for the panel to adhere.

The layer (V) consisting of polyester and/or polyamide and/or polypropylene is preferably vapor-deposited with aluminum, SiO _x silicon oxide or a metal oxide of main group 2 or 3 on the side facing away from the other layers in the usual manner and is optionally provided with a topcoat layer, preferably an acrylic lacquer layer, on the other side. The layer (V) preferably consists essentially of polyester or polypropylene and is vapor-deposited with aluminum, preferably in a layer thickness of 30-80 nm. The thickness of the layer (V) is preferably 10-40 μm, particularly preferably 10-20 μm.

One or more layers of the plastic film consisting of at least 7 layers, which is also the subject of the invention, may be prepared with additives and auxiliaries used in conventional amounts, such as lubricants, anti-blocking agents and antistatic agents.

It has been proven that the combination of the relatively thick polyolefin layer (IV), the gas barrier layer (III), preferably consisting of polyvinyl alcohol, and the steam-cured layer (V) ensures an unexpectedly high tightness. It is also important that the gas barrier layer (III) is located directly below the hot melt adhesive layer and is thus protected from moisture.

According to the invention, panels with a plastic foam core are preferred. The plastic foam may be polyurethane or polystyrene foam. Sheets made from ground and then extruded plastic foam, such as those described in EP 0791155 B1, may also be considered.

According to the invention, microcellular, open-cell foam sheets, in particular sheets made of polyurethane or polystyrene foam, are preferably used as the core layer. According to a further preferred embodiment, the core layer consists of ground closed-cell foam, which has been pressed into a sheet with an optionally suitable binder. This is advantageous because the production of the vacuum insulation panels according to the invention can thus be part of the recycling process of old plastic foam.

During the production of vacuum insulation panels, the microporous sheet, which generally serves as the core layer, is placed in a bag made of the film according to the invention (the polyolefin hot melt adhesive layer (I) forms the inner side of the bag), and the still open side is glued with the hot melt adhesive under vacuum (132 - 0.132 Pa). After the pressure in the vacuum chamber has been equalized, the finished panel can be removed.

The excellent gas barrier properties of the film according to the invention ensure sufficient service life of the panel despite the low absorption capacity of the core layer. If a getter (a gas-reactive or gas-absorbing material) is to be used to extend the service life, this can be quite small. In some cases, it is sufficient to use a small amount of water vapor-binding material. The following can be considered as getters.

Alkali metals and alkaline earth metals are used to bind oxygen and nitrogen from the air, alkaline earth metal oxides are used to bind moisture and carbon dioxide, and commercially available silica gels and molecular sieves are used to bind moisture only. Getters made of such materials, suitably packaged, are commercially available.

According to a special embodiment of the invention, the foil according to the invention forms only one side of the foil bag, the other side is made of a conventional composite foil containing an aluminum barrier layer, which preferably contains an aluminum layer with a thickness of 6-20 pm and a PE layer with a thickness of 50-200 pm. In this embodiment, heat transfer at the edges is also hardly noticeable.

The vacuum insulation panels according to the invention can be widely used as high-performance insulation materials in the construction industry, as technical insulation and, above all, in refrigeration and freezing machines.

In refrigerators and freezers, the vacuum insulation panels according to the invention fill only a part of the volume of the traditional insulation material - these machines are usually insulated with rigid polyurethane foam - thus achieving energy savings of up to 30% without increasing the wall thickness.

Examples

Measurement methods:

The properties of the multilayer film according to the invention were determined using the following methods.

Oxygen, nitrogen and carbon dioxide permeability of the films: according to DIN 53380.

Water vapor permeability of the films: DIN 53122.

Thermal conductivity factor λ: according to DIN 18164 parts 1 and 2.

The determination of the cabinet number (heat transfer through the refrigerator wall) is described in detail in Example 7.

The invention is further illustrated by the following examples.

1. Foils

The outstanding insulating effect of the films according to the invention was demonstrated on the films according to the following example.

a) example

Layer I: polyolefin hot melt adhesive layer of ethylene/vinyl acetate copolymer, 3.5% vinyl acetate, 50 pm Layer II: two-component polyurethane adhesive, 2 pm Tier III: gas barrier layer made of polyvinyl alcohol, stretched in two directions, 12 pm Layer II: two-component polyurethane adhesive, 2 pm Layer IV: polyethylene layer, 120 pm Layer II: two-component polyurethane adhesive, 2 pm Layer V: metallized, bidirectionally stretched polyethylene terephthalate film, 12 pm

example b)

Layer I: polyolefin hot melt adhesive layer of ethylene/vinyl acetate copolymer, 3.5% vinyl acetate, 50 pm Layer II: two-component polyurethane adhesive, 2 pm Tier III: gas barrier layer made of polyvinyl alcohol, stretched in two directions, 12 pm Layer II: two-component polyurethane adhesive, 2 pm Layer IV: polyethylene layer, 120 pm Layer II: two-component polyurethane adhesive, 2 pm Layer V: metallized, bidirectionally stretched polypropylene film, 20 pm

c) example

Layer I: polyolefin hot melt adhesive layer of ethylene/vinyl acetate copolymer, 3.5% vinyl acetate, 50 pm Layer II: two-component polyurethane adhesive, 2 pm Tier III: gas barrier layer made of polyvinyl alcohol, varnished on both sides with PVDC Layer II: two-component polyurethane adhesive, 2 pm

Layer IV: polyethylene layer, 120 pm Layer II: two-component polyurethane adhesive, 2 pm Layer V: metallized, bidirectionally stretched polyethylene terephthalate film, 12 pm

d) example

Layer I: polyolefin hot melt adhesive layer of ethylene/vinyl acetate copolymer, 3.5% vinyl acetate, 50 pm Layer II: two-component polyurethane adhesive, 2 pm Tier III: gas barrier layer made of coextruded PA/EVOH/PA layers Layer II: two-component polyurethane adhesive, 2 pm Layer IV: polyethylene layer, 120 pm Layer II: two-component polyurethane adhesive, 2 pm Layer V: metallized, bidirectionally stretched polyethylene terephthalate film, 12 pm

e) comparative example (Combithen PXX, according to EP 0 517 026 Al)

1st layer: polyolefin layer, 50 pm 2nd layer: two-component polyurethane adhesive, 2 pm 3rd layer: polyvinyl alcohol layer, 12 pm 4th layer: two-component polyurethane adhesive, 2 pm 5th layer: polyolefin layer, 120 pm Layer 6: two-component polyurethane adhesive, 2 pm 7th layer: polyvinyl alcohol layer, 12 pm 8th layer: two-component polyurethane adhesive, 2 pm Layer 9: polyolefin layer, 120 pm Layer 10: two-component polyurethane adhesive, 2 pm

11th layer: expanded polyethylene terephthalate film, 12 μπι

f) comparative example (Aluthen P, Wolff-Walsrode):

1st layer: polyolefin layer, 50 μπι

2nd layer: two-component polyurethane adhesive, 2 μπι

3rd layer: stretched polyethylene terephthalate film, 12 μπι

4th layer: two-component polyurethane adhesive, 2 μm

5th layer aluminum foil, 12 μm

6th layer: two-component polyurethane adhesive, 2 μm

7th layer: stretched polyethylene terephthalate film, 12 μm

The following water vapor, oxygen, nitrogen and carbon dioxide permeability were measured:

Example Permeability [cm ³ /m ² · day · 10 ⁵ Pa]* Water vapor permeability [g/m ² · day]** oh ₂ n _{2 CO2} a) 0.01 <0.01 0.02 0.015 b) 0.01 <0.01 0.03 0.02 c) 0.01 <0.01 0.02 0.015 d) 0.01 <0.01 0.02 0.015 e) comparative p. 0.01 <0.01 0.03 0.1 f) comparative p. immeasurably small immeasurably small

*) 23 °C, 0 % relative humidity **) 23 °C, 85 % relative humidity

2. Description of the foil bag

To make the foil bag, we weld 50x50 cm pieces of foil together on three sides. We made the foil bag from the following materials:

I. symmetrically constructed foil bag made of commercially available aluminum-containing multilayer foil (Aluthen-P, Wolff-Walsrode, example f))

II. semi-metric foil bag made of commercially available metal-free barrier foil (Combithen PXX, Wolff-Walsrode, example e))

III. symmetrically constructed foil bag made of the multilayer foil according to example la)* of the invention

IV. Asymmetrical foil bag made of the multilayer foil according to the invention mentioned in point 2.III. and the aluminum-containing multilayer foil mentioned in point 2.1.

3. The core layer: sheet made from recycled hard foam according to WO 96/14207

1000 g of PUR hard foam powder from a refrigerator dismantling and component recycling plant is mixed evenly with 35 g of water and 100 g of polyisocyanate mixture (diphenylmethane diisocyanates and polyphenyl polymethylene polyisocyanates, Desmodur® VP PU 1520 A 20; Bayer AG) in a Lödige mixer equipped with a 2-component nozzle. The mixture is formed into a 400 x 400 mm shaped body in a mold frame, compacted evenly, and then pressed to 25 mm in a laboratory press at 120 °C at a pressure of 5x10 ⁵ Pa for 8 minutes (using a timer program).

A porous plate of 25 mm thickness is obtained, with a bulk density of 250 kg/m ³ . The plate is kept at 120 °C for about 2 hours to remove all volatile compounds.

4. Production of vacuum insulation panel

The core layers produced according to point 3 are placed in the foil bags produced according to 2.1 - 2.IV., evacuated to a pressure of 16.4 Pa, and then the bags are welded together. After the vacuum chamber is vented, the panel is removed. It was observed that the surface of the panel made with the thick foil according to the invention is significantly smoother than that of the panel made with the thin foil.

The remaining low water vapor permeability can be determined by storing the panel and then measuring the weight gain. The storage period was 1 year, and the result was extrapolated to 15 years, taking into account that the water absorption capacity of the core made of rigid polyurethane foam is 0.5-1% of its own weight, so that the pressure in the panel does not increase at the beginning. The weight gain due to oxygen, nitrogen and carbon dioxide absorption is negligible, as it is in the mg range.

Calculated and measured mass gain due to water vapor/withdrawal

Panel foil (example) Weight gain [g] After 1 year (calculated After 1 year (measured) extrapolation for 15 years 2.1 0 0.2 3 2.II 11.68 5.34 80.1 2. III 1.75 1.63 24.45 2.IV 0.88 0.72 10.8 1

5. Measurement of the thermal conductivity coefficient λ

The heat transfer of vacuum insulation panels manufactured with foils according to 2.1 - 2.IV according to point 4 was measured according to DIN 18164 parts 1 and 2. The heat transfer coefficient of the panels is essentially the same, 9.0 - 9.1 mW/m °K.

6. Installing the panel in the freezer

As shown in the vertical section of Figure 1, panels of dimensions 60 x 50 x 2.5 and 50 x 50 x 2.05 [ (1) reference] made of foils produced according to points 2.1 - 2.IV are glued to the inside of the outer casing (2) before the assembly of a table freezer. An additional panel is placed on the inside of the door and on the inside of the rear wall (not shown in the drawing). The panels thus fill part of the insulation volume. After the installation of the inner casing (3), the remaining insulation volume is filled with PUR foam (4) in the conventional manner.

As shown above, we are installing 4 freezers, the panels inside are made of different foils.

During gluing, panels made with thicker foils, which are preferred according to the invention, were more adhesive than those made with thin foils (e.g. according to 2.1). In the latter, after foaming the remaining volume, there was partially no adhesion between the panel and the outer layer.

7. Measuring the number of cabinets in freezers produced with different panels.

The number of cabinets of the freezers manufactured according to point 6 was measured as follows. The interior of the freezer is heated to a temperature 30-40 °C above the ambient temperature using a controllable electric heater located inside the freezer. After the interior temperature has stabilized (usually after 4 days), the number of cabinets [W/°K] is determined by determining the electric running power and the average temperature difference between the interior and the environment (based on 24 hours). The interior temperature was measured with 6 thermocouples. The following values were obtained.

Panel foil structure Cabinet number fW/°K] 2.1 0.36 2.II 0.30 2.III 0.29 2.IV 0.29

It can be seen that in case 2.1 (aluminum foil attached on both sides) the heat transfer is significantly higher than in the case of plastic foil, even if there is plastic foil on only one side and aluminum foil attached on the other (2.IV).

Claims (11)

Patent claims 1. Vacuum insulation panels containing a microporous sheet as a core and a cover of the sheet consisting of at least 7 layers of plastic film in the following order of layers: (1) polyolefin hot melt adhesive layer (I) (2) adhesive or bonding layer (II) (3) gas barrier layer (III) (4) adhesive or bonding layer (II) (5) polyolefin layer (IV) (6) adhesive or bonding layer (II) (7) layer (V) consisting essentially of polyester and/or polyamide and/or polypropylene vaporized with aluminum or silicon oxide of the formula SiO _x or with an oxide of a metal belonging to main group 2 or 3. Vacuum insulation panels according to claim 1, wherein the polyolefin hot melt adhesive layer (I) is single or multi-layered and consists essentially of a polyolefin homo- or polyolefin copolymer. 3. Vacuum insulation panels according to claim 1 or 2, wherein the adhesive or bonding layer (II) is a two-component polyurethane adhesive or a polyolefin adhesion promoter. Vacuum insulation panels according to any one of claims 1-3, wherein the gas barrier layer (III) consists essentially of polyvinyl alcohol (PVOH), ethylene/vinyl alcohol copolymer (EVOH) and/or polyamide or a mixture of PA and EVOH, and optionally is multilayer. 5. Vacuum insulation panels according to any one of claims 1-4, wherein the polyolefin layer (IV) is essentially polyethylene, polypropylene or polyethylene copolymer and has a thickness preferably of 5-500 µm. 14 : :-·.··..·· • · · · · · · · · · 6. Vacuum insulation panels according to any one of claims 1-6, in which the layer (V) consists essentially of polyester or polypropylene and preferably carries a vapor-deposited aluminum layer with a thickness of 30-80 nm. 7. Vacuum insulation panels according to any one of claims 1-6, in which the core layer is a microcellular, open-pored foam sheet consisting of polyurethane or polystyrene. 8. Vacuum insulation panels according to any one of claims 1-6, in which the core layer is a closed-cell foam material ground, which has been pressed into a sheet, optionally using a suitable binder. 9. Vacuum insulation panels according to any one of claims 1-8, wherein only one side of the core layer covering is formed by a plastic film consisting of at least 7 layers in the following order of layers: (1) polyolefin hot melt adhesive layer (I) (2) adhesive or bonding layer (II) (3) gas barrier layer (ΠΙ) (4) adhesive or bonding layer (II) (5) polyolefin layer (IV) (6) adhesive or bonding layer (II) (7) layer (V) consisting essentially of polyester and/or polyamide and/or polypropylene vaporized with aluminum or silicon oxide of the formula SiO _x or an oxide of a metal belonging to main group 2 or 3, and the other side is formed by a conventional multilayer associated film containing aluminum as a barrier layer. 10. Plastic film for the production of vacuum insulation panels, which film is at least It consists of 7 layers in the following order of layers: (1) polyolefin hot melt adhesive layer (I) (2) adhesive or bonding layer (II) (3) gas barrier layer (III) (4) adhesive or bonding layer (II) (5) polyolefin layer (IV) (6) adhesive or bonding layer (II) (7) layer (V) consisting essentially of polyester and/or polyamide and/or polypropylene vaporized with aluminum or silicon oxide of the formula SiO _x or with an oxide of a metal belonging to main group 2 or 3. 11. Use of vacuum insulation panels according to any one of claims 1-9 for insulating refrigerators and freezers. The authorized person: