NL1005962C1 - Vacuum insulation panel - Google Patents

Abstract

A vacuum insulation panel comprises two parallel external plates (1, 2) which are bonded together around their edges to form a sealed cavity (4) in between, inside which a high vacuum is created. Spacer elements (6) are provided to maintain the correct distance between the two plates. A thermal lining (7a, 7b) comprising several layers of metal foil or metallised film is applied to the inside of the cavity, extending parallel to the plate and covering practically all the cavity surface area. The spacer elements protrude through the cover. Preferably the cover includes several layers of metallised Mylar (RTM : polyester) film.

Description

Short designation: Vacuum insulation panel.

The invention relates to a vacuum insulation panel, comprising two plates, which are placed substantially parallel to each other and which are connected to each other on or near the plate edges in such a way that a closed space is formed between the plates and the edges, in which closed space there is high vacuum and spacers are provided to maintain the distance between the plates.

10 Insulation materials, including insulation panels according to the preamble, are widely used. As application examples, we mention buildings, refrigerators, cooling rooms, refrigerated vehicles, cryogenic installations and installations in which so-called high-temperature superconductors are applied.

Improved insulating materials can help enable temperatures that are desired from a particular target point of view. For example, a comfortable temperature may be desired in a building, and a low temperature may be desired in a refrigerator to prevent premature decay of foodstuffs stored in the refrigerator. In addition, improved insulation materials make it possible to maintain desired temperatures with less energy consumption. As a result, they enable savings in energy costs and also reduce the burden on the environment.

For a good understanding of the manner in which an effective operation of vacuum insulation panels can be obtained, it is important to know that in vacuum insulation panels heat transfer between the two plates can take place in two ways: (1) by heat radiation between the 35 plates, (2) by guiding (a) through the closed space, 1005962 -2- (b) through the edges of the closed space and (c) through the means to maintain the distance between the plates. A third way of heat transfer, namely convection in the enclosed space, is impossible due to the vacuum.

5

A high vacuum also impedes conduction through the enclosed space. We call the pressure in the enclosed space in an insulating panel high-vacuum, if the pressure is such that the average free path length of the 10 gas molecules in the enclosed space is of the same order of magnitude as the largest dimensions of the enclosed space. At pressures below this high-vacuum limit value, the heat conduction of the gas in the enclosed space is significantly lower than at pressures higher than this limit value. This is described, inter alia, in U.S. Patent No. 5,157,893, to inventors D.K. Benson and T.F. Potter, and in the article "Metal-Coated Vacuum Panels as Thermal Insulation" by K.H. Brodt and G.C.J. Bart, published in the Journal of 20 Thermal Insulation and Building Environments, Volume 17, January 1994.

The above application areas of insulating panels usually require a service life of at least ten years. In order to maintain the high vacuum in an insulation panel for such a long period, the construction of such an insulation panel must be highly gas-tight. Furthermore, the material applied within the enclosed space must not or hardly gas out during the lifetime. In some cases, a getter material disposed in the enclosed space can trap particles that are present due to a low degree of outgassing, thus ensuring the high vacuum.

Below we describe the state of the art. We also mention 1005962 -3- panels which are not expressly intended for use under high vacuum, since in some cases a vacuum panel which is not manufactured for high vacuum can still be used effectively under high vacuum.

We distinguish in the prior art (1) insulation panels that are provided with means for shielding heat radiation between the plates, (2) 10 insulation panels that are not provided with such means, and (3) filling materials that can be used in vacuum insulation panels as mentioned in the preamble.

1. Insulation panels provided with means for shielding heat radiation

U.S. Patent No. 5,084,313 in the name of Parenti et al. Discloses an insulating panel comprising an airtight envelope within which there is vacuum and in which a plurality of alternating layers of thin reflective foil and thin insulating foil are provided. These layers are densely packed and arranged substantially perpendicular to the heat flow direction. The walls of the casing are thin and flexible enough to deform during the application of the vacuum and thereby transfer the atmospheric pressure to the foil layers, these layers being pressed tightly together.

In such an insulation panel, heat radiation 30 is shielded by the layers of reflective foil. The insulating foil, on the other hand, is intended to achieve a reduced heat conduction through the insulation panel. By compressing the foil layers, however, the insulating effect of the insulating foil 35 is partly canceled out, as a result of which a considerable heat conduction occurs through the insulating panel. It seems that this drawback is inherent in insulation panels 1005962-4- in which the enclosed space is filled and the casing is compressible.

5 2. Insulation panels without shielding from heat radiation

U.S. Patent 2,989,156, to Brooks et al., Discloses an insulating panel, which includes a vacuum space, which is enclosed between two metal plates, and which vacuum space is filled with perlite powder. Such an insulating panel has the above-mentioned drawback of considerable heat conduction, due to compression of the perlite powder. In addition, such an insulation panel does not provide any shielding from heat radiation.

The same objection applies to US Patent 5,032,439, in the name of Glicksman, which discloses an insulating panel containing a filling of 20 compressed powders with low heat conduction coefficient, and in Patent US 4,486,482, in the name of Kobayashi, and the Patent US 5,601,897, to Vermilion et. al., both of which disclose vacuum insulation panels which have a fiberglass mat as filler material.

The glass fiber mat according to the aforementioned patent US 5,601,897 is provided with a carbon-containing asphalt coating. Such a coating is intended to make the insulation panel suitable for use at elevated temperatures, up to several hundred degrees Celsius. In addition, the carbon in the asphalt coating can be activated to adsorb gassed particles, thus maintaining the vacuum for a long time.

Although the insulation panel is intended for use at high temperatures, at which temperatures heat transfer by heat radiation within the enclosure plays a significant role in 1005QR2-5, no measures have been taken to limit such heat transfer.

U.S. Patent 5,157,893 (WO 91/19867), 5 to Benson and Potter, discloses a vacuum insulation panel comprising two metal plates spaced a short distance apart, and between which a plurality of spherical or other glass or ceramic beads are arranged to provide support and ensure the spacing between the plates when vacuuming the space between the metal plates. The two metal plates are provided with profiling, which gives the plates extra stiffness and thus reduces the number of beads required and thus reduces the number of paths along which heat conduction occurs. In addition, the metal plates are provided with convex protrusions into which the glass beads partially fall, which protrusions are intended to fix the beads and reduce the heat transfer between the metal plates and the beads. The metal plates are also provided with a glass or porcelain coating, to reduce the heat transfer between the metal plates and the beads. The patent US 5,157,893 also discloses a second embodiment of the insulation panel, in which embodiment the beads have been replaced by a material comprising a thin laminated plate with a large number of protuberances, which project transversely in opposite directions from the opposite surfaces of the thin laminated sheet. The thin laminated sheet consists of two thin metal layers, which enclose a third layer, which third layer consists of a material with low heat conductivity. The thin laminated sheet is sandwiched between the two metal sheets that form the insulation panel shell. Patent US 5,157,893 mentions as advantages of the two described embodiments of the insulation panel that they have a very good insulating effect, are durable and have a very small thickness. An additional advantage is mentioned that the insulation panels do not attack the ozone layer, while widely used known insulation panels in which foam materials are used do. In an example of the thin laminated sheet embodiment, the insulation panel has a thickness of 2.5 mm. As further advantages of the insulating panels from US 5,157,893 are mentioned that they are flexible and therefore suitable for many kinds of applications. Despite the measures taken in the insulating panels of US 5,157,893 to reduce the heat conduction in both embodiments, in the embodiment with beads the number of beads per surface area required will be 15, otherwise the metal plates of the casing collapse under the pressure of the surrounding air. In the thin laminated sheet embodiment, the required number of protuberances of the laminated sheet will be large, otherwise the laminated sheet or the metal sheets of the envelope will collapse under the pressure of the surrounding air. Therefore, in both embodiments, the number of paths along which heat conduction occurs is large, and therefore it is likely that the heat transfer by conduction is considerable despite the measures mentioned to limit this conduction.

A second drawback of the insulating panels according to US 5,157,893 is that hardly any measures have been taken to reduce the heat transfer by heat radiation between the metal plates of the casing. Although heat radiation absorbing coatings have been applied to the inside of the envelope, there is no effective shielding of the remaining heat radiation. In the embodiment with a thin laminated plate, this plate itself offers some shielding from the heat radiation. In summary, the total 1005962 -7 heat transfer through the insulating panels according to US 5,157,893, calculated as the sum of the heat transfer by heat conduction and the heat transfer by heat radiation, is significant, despite the measures taken to reduce the heat transfer by these insulating panels. Reduce.

3. Filling materials for vacuum insulation panels German patent DD-215.112-A, in the name of Mueller et al., Discloses a filling material for vacuum insulating materials, which filling material consists of spheres with a low heat conductivity, which spheres are covered with a metal coating on which a second coating is applied which consists of a material with a poor quality

heat conduction. U.S. Pat

4,303,732 in the name of Torobin, discloses small hollow glass spheres, which have a thin metal coating on the inner surface, and which are intended as

20 filler material for insulating solar collectors. The filler materials from patents DD-215,112-A and US

4,303,732 are intended to provide low heat conductivity and good radiation shielding. When these fill materials are used in insulating panels, they will effect a significant amount of heat conduction between the casing plates, unless special constructional measures are taken. Moreover, they will only effectively shield the heat transfer by radiation if several layers of the filling material 30 are present between the plates.

In summary, we state that the known vacuum insulation panels (a) either offer moderate protection against heat transfer by conduction between the two plates, (b) or provide hardly any shielding from heat radiation between the two plates, (c) or provide moderate protection against heat transfer. by 1005962 -8- conductivity between the two plates coupled with moderate shielding from heat radiation. Therefore, none of the known insulation panels offers complete heat insulation. The object of the invention is to reduce this drawback.

5

The object of the invention is to provide a vacuum insulation panel which has a very good heat-insulating effect, has a small thickness, and which is moreover durable. Another object of the invention is to provide a vacuum insulation panel which offers the aforementioned advantages and is suitable for use at both high and low temperatures. Moreover, it is an object of the invention to provide a vacuum insulation panel which offers the aforementioned advantages and which can be produced in large numbers at an acceptable cost.

The invention achieves these objectives by means of an insulating panel according to the preamble, wherein a thermal blanket is arranged in the enclosed space, which thermal blanket consists at least of a number of layers of metal foil or metallized foil, and which thermal blanket extends substantially parallel to the outer plates extends over almost the entire surface of the enclosed space, and through which thermal blanket 25 protrude spacers at considerable mutual distances.

In the thus obtained insulating panel, the heat radiation between the outer plates is effectively shielded over almost the entire surface of the insulating panel by the thermal blanket, and a greatly reduced heat conduction between the outer plates is obtained because only a small number of spacers per surface unit are provided.

Advantageous embodiments of the above-mentioned insulation panel are described in the subclaims, and are aimed at further reducing the heat transfer by heat radiation 1005962-9 and heat conduction between the outer plates.

An advantageous embodiment is obtained if the spacers are formed by cylindrical rods, by pillars with a cross-shaped cross-section, or by pillars with a Y-shaped cross-section, the longitudinal axis of each spacer being oriented substantially perpendicular to the outer plates, and each spacer at least one end is provided with a curved surface. With such spacers, only slight disturbance of the thermal blanket is obtained, and the contact conductivity between the spacers and the outer plates is limited. Moreover, pillars with a cross-shaped cross-section and with a Y-shaped cross-section provide the insulation panel with mechanical stability, because if vacuum prevails in the enclosed space, they will tilt only with great and unusual mechanical load of the insulation panel relative to the outer plates.

Furthermore, an advantageous embodiment is obtained if the thermal blanket comprises a number of layers of wrinkled metal foil. Thus, the contact conductivity between the successive layers of the thermal blanket is reduced, and thus the heat transfer through the thermal blanket. Another way to achieve this effect is obtained by applying a layer of spacer material in the thermal blanket between each two adjacent layers of the metal foil or metallized foil. Moreover, the heat transfer by contact conduction between the thermal blanket and the outer plates is reduced if a layer of spacer material is arranged between each of the outer plates and the thermal blanket. The spacer material can be a spacer material commonly used in space travel.

1005962 -10-

A particularly advantageous embodiment is obtained if the thermal blanket consists of a number of layers of Mylar, wherein a layer of metal has been deposited on each layer of Mylar, and wherein the spacer material consists of a glass fiber mat with activated carbon. The spacer material in this embodiment serves to reduce the contact conductivity and also serves as a so-called getter material. A getter material serves to trap particles in the enclosed space. In the said embodiment, such particles can be evaporated from the Mylar.

In the aforementioned embodiments it is advantageous to provide the two outer plates with an infrared-absorbing coating on the sides facing the closed space.

Furthermore, an advantageous embodiment is obtained if, in one of the aforementioned embodiments, a central plate is arranged in the enclosed space, substantially parallel to the outer plates and substantially equidistant from the outer plates, the spacers being arranged between each of the outer plates and the middle plate in such a way that the spacers on one side of the center plate are offset from the spacers on the opposite side of the center plate, and wherein the thermal blanket consists of two blanket parts, of which two blanket parts are located between an outer plate and the center plate, and the second is located between the other outer plate and the center plate. In addition, it is advantageous if the middle plate is profiled. In addition, it is advantageous to form the middle plate from a poorly conductive material, or from two layers of metal, between which two layers are arranged a layer of poorly conductive material. Finally, it is advantageous to provide the middle plate on the two outer surfaces with a 1005962 -11 infrared radiation absorbing coating.

The heat transfer between the outer plates by contact conduction can be considerably reduced by providing each of the spacers with a poorly conductive coating at the places where it contacts one of the outer plates or with the center plate, and / or providing each of the outer plates with a poorly conductive coating where it comes into contact with the spacers. If a center plate is provided, it is advantageous to also provide it with a poorly conductive coating at the places where it comes into contact with the spacers. In particular, the poorly conductive coating can consist of glass or glass-like material. In the embodiments thus obtained, the contact conductance between a spacer and an outer plate or middle plate always takes place through at least one layer of poorly conductive material, as a result of which the contact conductivity is small.

20

The present invention will be explained below with reference to the drawing. Herein: figure 1a. an enlarged cross-section of an insulation panel according to the invention, figure 1b. an enlarged detail of the insulation panel from figure 1a, and figure 2. a reduced top view of the middle plate of the insulation panel from figure 1.

30

The insulation panel of figure 1 comprises two rectangular outer plates 1,2 of a steel with low heat conductivity, which outer plates are placed parallel to each other at some distance from each other. These outer plates are mutually connected at the edges by four strips 3 of the same steel type. The strips are attached by laser welding along the perimeters of the 1005QR2-12 outer plates, such that a closed space 4 is formed between the outer plates and the strips. In the enclosed space, a center plate 5 is provided parallel to and midway between the outer plates, which is held in place by a number of spacers 6, which are arranged between the middle plate and each of the two outer plates, and which are fixed in place by press the outer plates against the spacers 10 under the influence of the ambient pressure.

In addition, a thermal blanket is arranged in the closed space 4, which is divided into two blanket parts 7a, 7b, of which one blanket part 7a is located on one side of the middle plate between the middle plate and the relevant outer plate, and of which the other blanket part 7b the other side of the middle plate is located between the middle plate and the relevant outer plate, both blankets of which are intersected by the spacers.

The spacers 6 form straight pillars with a cross-shaped cross-section, and are injection-molded from an alloy with a low heat conductivity. The longitudinal axes of the spacers are oriented perpendicular to the outer plates. The spacers have a curved surface at the ends such that the surface near the ends of the four sides of the cross extend further from the spacers than the surface at the center of the cross-shaped cross-section. In addition, each spacer at both ends near the ends of the four sides of the cross-section is covered with a thin glass cover 8. The curvature of the ends of the spacers provides a reduced contact area between the spacers and the outer plates and the center plate, respectively , and the 1005962-13 glass cover increases the thermal contact resistance of the contact surface.

The thermal blanket consists of about forty layers, 5 in each case a layer of reflective foil 9 is alternated with a layer of spacer material 10. The reflective foil consists of Mylar on which a thin gold layer has been evaporated, and the spacer material consists of a glass fiber mat that has been impregnated with activated carbon, which carbon serves as a getter material. The thermal blanket is held in place by the spacers, outer plates and center plate. It is important that the closed space provides sufficient space for the thermal blanket, so that it is not compressed by the outer plates and the middle plate, and thus a good functioning of the thermal blanket is promoted. In the insulation panel according to the example, the distance from the center plate to the outer plate is approximately 4 mm on either side of the center plate. The total thickness of the insulation panel is approximately 11 mm.

The two outer plates and the center plate are provided with a thin glass cover layer 11 at the places where they are touched by spacers. In addition, an infrared radiation-absorbing cover layer 12 is applied to each of the two outer plates on the side facing the closed space. An infrared radiation-absorbing cover layer 13 is provided on both sides of the middle plate.

30

In Figure 2, the reduced center plate 5 of the insulating panel of Figure 1 is shown, into which center plate profile ribs 14 are pressed, which protrude beyond the plane of the center plate, and which provide the center plate with additional stiffness against bending. For clarity, the spacers that rest against the center plate when mounted at the top are also indicated as crosses, and the spacers that rest against the center plate when mounted at the bottom are indicated as dotted crosses.

5

Although the insulation panel in Figure 1 is flat, it goes without saying that versions with curved outer surfaces are also possible. In addition, the spacers can have a cross-section of a different shape, such as an H shape, and the spacers can be made of a material of a different type, such as ceramic. The insulation panel can be provided with fasteners on the outside, with which the panel can be attached to a supporting construction. Furthermore, the insulation panel can be provided on the outside with a coating, for instance to provide the insulation panel with mechanical or acoustic properties that are adapted to the specific purpose of the insulation panel. Finally, one or more of the 20 outer plates can be adapted to make the insulation panel part of a supporting construction.

The insulation panel of figure 1 has a very good heat-insulating effect, in that it combines a low heat conduction between the outer plates and a small heat radiation between the outer plates. In addition, the insulation panel from figure 1 is durable and has only a small thickness. Finally, the insulation panel is suitable for use at both high and low temperatures, and can be produced in large numbers at an acceptable cost.

10059R2

Claims (21)

A vacuum insulation panel, comprising two outer plates (1,2), which are spaced substantially parallel to each other, and which are joined together at or near the edges in such a way that between the outer plates 5 a closed space (4) is formed in which enclosed space is highly vacuum and spacers (6) are provided to maintain the distance between the outer plates, characterized in that a thermal blanket (7a, 7b) is provided in the enclosed space, which thermal blanket comprises at least a number of layers of metal foil or metallized foil (10), and which thermal blanket extends substantially parallel to the outer plates over substantially the entire surface of the enclosed space, and through which thermal blanket protrude at spaced intervals. Vacuum insulation panel according to claim 1, characterized in that the spacers (6) are formed by cylindrical rods, the longitudinal axis of each cylindrical rod being oriented substantially perpendicular to the outer plates, and at least one end of each cylindrical rod has a curved surface. Vacuum insulation panel according to claim 1, characterized in that the spacers (6) are formed by pillars with a cross-shaped cross section, the longitudinal axis of each pillar being directed substantially perpendicular to the outer plates, and at least one of each pillar tip is slightly curved. Vacuum insulating panel according to claim 1, characterized in that the spacers (6) are formed by pillars with a Y-shaped cross-section, the longitudinal axis of each pillar being oriented substantially perpendicular to the outer plates 1005962-16, wherein at least one end of each pillar is slightly curved. Vacuum insulation panel according to any one of claims 1-4, 5, characterized in that the thermal blanket (7a, 7b) comprises a number of layers of wrinkled metal foil. Vacuum insulation panel according to any one of claims 1 to 5, characterized in that a layer of spacer material (10) is arranged in the thermal blanket (7) between every two adjacent layers of the metal foil or metallized foil (9). Vacuum insulation panel according to any one of claims 1-6, 15, characterized in that a layer of spacer material is arranged between each of the outer plates (1,2) and the thermal blanket (7a, 7b). Vacuum insulation panel according to claim 6 or 7, characterized in that the thermal blanket (7a, 7b) consists of a number of layers of Mylar (10), with a layer of metal being vapor-deposited on each layer of Mylar, and wherein the spacer material (10) consists of a glass fiber mat with activated carbon. 25 Vacuum insulation panel according to one or more of claims 1-8, characterized in that the outer plates (1,2) are provided on the side facing the closed space (4) with an infrared radiation-absorbing cover layer (12). Vacuum insulation panel according to one or more of claims 1-9, characterized in that a central plate (5) is arranged in the closed space (4), substantially parallel to the outer plates (1,2) and substantially in the same distances from the outer plates, the spacers (6) being disposed between each of the outer plates and the center plate 1005962-17 so that the spacers are offset on one side of the center plate from the spacers on the opposite side of the center plate , and wherein the thermal blanket consists of two blanket parts (7a, 7b), two blanket parts of which the first is located between an outer plate and the center plate, and the second is located between the other outer plate and the center plate. Vacuum insulation panel according to claim 10, characterized in that the center plate (5) is profiled. Vacuum insulation panel according to claim 10 or 11, characterized in that the center plate (5) is formed from a poorly conductive material. Vacuum insulation panel according to claim 10 or 11, characterized in that the middle plate (5) is formed from two layers of metal, between which two layers are provided a layer of poorly conductive material. A vacuum insulation panel according to any one of claims 10-13, characterized in that the middle plate (5) is provided on the two outer surfaces with an infrared radiation-absorbing cover layer (13). Vacuum insulation panel according to any one of the preceding claims, characterized in that each of the spacers (6) is provided with a poorly conductive coating (8) at the locations where it contacts one of the outer plates (1,2) or with the center plate (5). Vacuum insulation panel according to any one of the preceding claims, characterized in that the two outer plates 35 (1,2) and the optionally present middle plate (5) are provided with a poorly conductive coating (11) at the places where they come into contact with the spacers 1005962 (6). -18- Vacuum insulation panel according to any one of the preceding claims, characterized in that the center plate (5) is provided with a poorly conductive coating (15) at the places where it contacts the spacers (6). Vacuum insulation panel according to any one of claims 10-15-17, characterized in that the poorly conductive cover layer (8,11,15) consists of glass or glass-like material. 19. A vacuum insulation panel according to any one of claims 1-18, characterized in that means are provided on the middle plate or at least one of the outer plates for connecting the insulation panel to a supporting construction. 20. Vacuum insulation panel according to any one of claims 1-19, characterized in that a coating is arranged on the outside of the insulation panel. Vacuum insulation panel according to any one of claims 1-20, characterized in that the middle plate or at least one of the outer plates forms part of a supporting construction. 1005962