EP0368529A1

EP0368529A1 - Panels of thermal insulating material

Info

Publication number: EP0368529A1
Application number: EP89311189A
Authority: EP
Inventors: John Thomas Hughes
Original assignee: Micropore International Ltd
Current assignee: Micropore International Ltd
Priority date: 1988-11-08
Filing date: 1989-10-30
Publication date: 1990-05-16
Also published as: GB8826163D0; GB2228556A; GB8925083D0

Abstract

A panel (10) of thermal insulating material has a layer (12) of compressed microporous insulating material in a tray (14). The tray includes peripheral portions of rigid flanged strip (16) spot-welded together to form a frame. A sheet (22) of self-adhesive aluminium foil is secured to the strip material by the adhesive and forms the base of the tray.

Many different sizes and shapes of tray can be made without any need for a wide variety of component materials. During compression of the insulating material a patterned sheet (34), such as expanded metal, can be placed under the aluminium foil to emboss it, so as to remove creases and provide a neat and attractive finish.

Description

This invention relates to panels of thermal insulating material, and particularly to panels incorporating microporous insulating material.
The term microporous material, as used herein, means a porous material in which the mean pore size is less than the mean free path of an air molecule at normal temperature and pressure. Such materials can form extremely efficient insulators and may be made, for example, from a silica aerogel (a gel in which the liquid phase is replaced with air or other gas without permitting disruption of the structure by capillary forces), from an open lattice material obtained by precipitation from a silica solution under controlled conditions of temperature and pH, or from equivalent open lattice silica structures such as fumed pyrogenic or electro-thermal types (e.g. made by high temperature hydrolysis of a silicon tetrahalide such as silicon tetrachloride) in which the average particle size is less than 100 nanometers.
For practical use as insulators microporous materials are typically mixed with a reinforcing fibre of a ceramic material such as aluminosilicate, and with an opacifier such as titanium dioxide powder to block transmission of infrared radiation through the insulation. In addition the material must be compressed to a density (typically 200 kg/cubic m or more) which is several times higher than its intrinsic density, in order to produce a satisfactory insulator.
Although blocks of such compressed material can be handled and installed in that form, they have little tensile strength, so it is sometimes necessary or desirable to provide additional support or protection for the insulation material. To this end, in one approach, the insulating material is compressed into a shallow, flat tray which has been previously pressed from a metal sheet. This has the problem that manufacture of the tray requires special tooling to produce each required shape and size of tray, with consequent high cost of manufacture, especially for small quantities.
According to one aspect of this invention there is provided a panel of thermal insulating material incorporating a layer of compressed microporous insulating material, characterised in that said layer is disposed in a tray having peripheral portions of relatively rigid material and a membrane of flexible material extending between said peripheral portions and across a face of said layer. The peripheral portions may be made of a material such as metal, plastic or glass fibre, for example in strip form, and may be spot-welded together. The membrane may be a foil, of a metal such as aluminium, and may be secured to the peripheral portions for example by adhesive. The peripheral portions preferably have a base section and a flange, so that the membrane may be secured to these base sections.
According to another aspect of this invention there is provided a method of manufacturing a panel of thermal insulating material, characterised by the steps of securing together pieces of relatively rigid material to form a periphery of a tray, securing a membrane of flexible material to extend between said peripheral pieces and form a base for said tray, and compressing microporous insulating material into said tray. During the compression step the tray may be urged against a member (for example a sheet over part of a press tool) having a surface pattern which is pressed into the membrane; this serves to remove blemishes and provide an attractive appearance.
A panel of thermal insulating material and a method for its manufacture, both in accordance with the invention, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a panel of thermal insulating material;
Figure 2 is a section through the panel of Figure 1 along the line II-II;
Figure 3 is a section through the panel of Figure 1 along the line III-III; and
Figure 4 illustrates the manufacture of the panel of Figure 1.

Referring to Figures 1 to 3, a panel 10 of thermal insulating material comprises a layer of microporous insulating material 12 compressed into a tray 14. The insulating material 12 is a mixture of silica aerogel, ceramic reinforcement fibre and titanium dioxide opacifier, such as that made and sold under the trade mark MICROTHERM by Micropore International Limited.
The periphery of the tray 14 is made of four lengths 16 of flanged galvanised steel strip which have butted flanges 18 and overlapping base sections 20. These base sections are spot-welded together where they overlap to provide the tray with strength and rigidity. A sheet of self-adhesive aluminium foil 22 is secured by its adhesive to the underside of the base sections 20 to form a membrane extending across and providing a base for the tray 14 and closing the aperture framed by the peripheral portions 16. The sheet 22 extends across one face of the layer of insulating material 12. If the sheet 22 has adhesive over its whole surface, the insulating material 12 will stick to the adhesive but this is not essential.
The panel 10 is made by first cutting flanged strip to provide four peripheral portions 16 of the required lengths. Many sizes and shapes of tray can be made from a supply of a single kind of flanged strip by appropriate choice of these lengths, thereby effecting significant economies compared to the use of one-piece trays pressed from sheet material. It is of course also possible to make the portions 16 in other ways, for example by cutting from sheet stock and bending.
The peripheral portions 16 are butted together and their base sections are spot welded where they overlap. Next a sheet 22 of self-adhesive aluminium foil is cut to size and stuck to the underside of the base sections, and the tray 14 thus formed is placed in a press (indicated at 30 in Figure 4). Preferably a lower tool 32 of the press 30 has a raised surface pattern. This can conveniently be provided with a sheet 34 of material having a regular pattern of projections from its surface, for example a sheet of so-called 'expanded metal' having louvre-like perforations separated by ridges of raised material. This sheet 34 is simply placed on the lower press tool 32 under the tray 14.
An appropriate quantity of microporous material mixture 12 is placed in the press tool 30 and an upper tool 36 is brought down to compress the mixture 12 to an appropriate density (typically 200 kg/cubic m or more). Precise details of the pressing operation, such as the dwell time of the press in its closed position, form no part of this invention and are known to those skilled in the art, and therefore need not be discussed here.
The upper tool 36 is raised and the completed panel 10 is extracted. The sheet 34 embosses the sheet 22 of aluminium foil with a pattern complementary to its own surface, thereby removing surface blemishes such as creases and providing a neat and attractive finish.
Despite the very low inherent tensile strength of the compressed microporous material, and the lack of rigidity of aluminium foil and similar membranes, we have found that the panel 10 is surprisingly robust and can withstand handling without damage or deformation.
Various modifications may be made to the invention. For example, the peripheral portions 16 may be made of a non-metallic material such as plastic or glass fibre; the material used need not be completely rigid, but is of course relatively much more rigid than either the insulating material 12 or the sheet 22. The sheet 22 may be made of a material other than aluminium foil. The microporous insulating material may incorporate microporous materials other than silica aerogel, in particular a precipitated silica; and fibres other than ceramic fibre may be used, for example glass fibre.

Claims

1. A panel of thermal insulating material incorporating a layer of compressed microporous insulating material, characterised in that said layer (12) is disposed in a tray (14) having peripheral portions (16) of relatively rigid material and a membrane (22) of flexible material extending between said peripheral portions and across a face of said layer.

2. The panel of claim 1, characterised in that the peripheral portions (16) are made of metal, plastic or glass fibre, for example in strip form.

3. The panel of claim 1 or claim 2, characterised in that the peripheral portions (16) are spot-welded together.

4. The panel of any one of the preceding claims, characterised in that the membrane (22) is a foil.

5. The panel of any one of the preceding claims, characterised in that the membrane (22) is metal, for example aluminium.

6. The panel of any one of the preceding claims, characterised in that the membrane (22) is secured to the peripheral portions (16) by adhesive.

7. The panel of any one of the preceding claims, characterised in that each peripheral portion (16) has a base section (20) and a flange (18).

8. The panel of claim 7, characterised in that the membrane (22) is secured to the base sections (20) of the peripheral portions (16).

9. A method of manufacturing a panel of thermal insulating material, characterised by the steps of:
securing together pieces of relatively rigid material (16) to form a periphery of a tray (14);
securing a membrane (22) of flexible material to extend between said peripheral pieces (16) and form a base for said tray (22); and
compressing microporous insulating material (12) into said tray

10. The method of claim 8, characterised in that during the compression step the tray (14) is urged against a member (34) having a surface pattern which is pressed into the membrane (22).