GB2480230A

GB2480230A - Structural panel

Info

Publication number: GB2480230A
Application number: GB1004801A
Authority: GB
Inventors: Anthony Asbury
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-03-23
Filing date: 2010-03-23
Publication date: 2011-11-16
Also published as: GB201004801D0

Abstract

A honeycomb panel is manufactured by securing across one face of the honeycomb structure 11a first planar panel skin 14 to close one open face of the cells, spreading a foaming adhesive premix such as a polyurethane precursor across a first planar surface of a second panel skin 15, pressing the first planar surface across the second open face of the honeycomb structure and allowing the foaming adhesive to foam and set. A porous membrane or veil 16 may be present between the panel skins and the honeycomb structure. A foaming adhesive may also be present between the first panel skin and the honeycomb structure. The honeycomb may be made of metal, paper or polymeric material. The skins may be of metal or plastics. The panel has improved insulating properties and may be used in buildings, containers, aircraft or furniture.

Description

AN IMPROVED STRUCTURAL PANEL

Field of the Invention

The present invention relates to an improved material for use as part of or as a panel. The material provides both strength and insulating properties to the panel.

In addition a method of manufacture of said materials and panels is disclosed.

Background to the Invention S.. * S **S.

: ** The present invention is particularly concerned with panels of the type which have a honeycomb structure sandwiched between two planar skins. Such panels which : * were first used on a large scale in the manufacture of aircraft, are strong but relatively lightweight. They are therefore ideally suited to uses in which a : product's weight needs to be kept to a minimum. As such they now find use in *:*. many situations such as a building's walls -particularly interior walls -packing cases, boats and trains as well as in engine assemblies and aircraft panels.

A number of methods is known to manufacture the honeycomb. In one method strips of material from which the honeycomb interior is to be made are secured together in a predetermined pattern at a plurality of points along their length.

Once a sufficient number of strips has been so secured, the strips are pulled away from each other: the securing points then causing the strips to form the honeycomb. As the unsupported honeycomb is relatively weak to forces in the plane of the honeycomb, planar boards are bonded to either side of the honeycomb resulting in a strong, stiff panel being created due to the "Inbeam effect" of the honeycomb onto the planar panels in the combined structure. * -2-

Within the industry, a wide variety of materials is used to form the honeycomb itself. The most common material used is aluminium. However, other metals and alloys such as titanium, copper, nickel or steel are known. In addition paper and polymeric materials such as polycarbonates or fibre glass are used where required.

In the case of plastics materials, the honeycomb core is sometimes formed by other, more direct means such as extruding or moulding. For the outer skin of the panel, again a large number of materials can be used to suit the particular application.

It will be appreciated however that the panel structure includes a large number of void spaces within the cells of the honeycomb. Although aiding the lightweight nature of the panel, the voids result in the panels being relatively poor insulators.

The present invention seeks to address the above problems and provide a honeycomb panel having good insulating properties. S... * .

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* : * Summary of the Invention S. *S * . *

* * According to a first aspect of the invention there is provided a method of *.

* 20 manufacturing a honeycomb panel, the method comprising the steps of selecting a honeycomb structure in the structure's expanded forms, securing across one face *:*. of the honeycomb structure a first planar panel skin to close one open face of the cells, selecting a second panel skin and spreading across a first planar surface of the second panel skin a foaming adhesive premix, and pressing said first planar surface across the second, open face of the honeycomb structure, allowing the foaming adhesive to foam and set and thereby secure the second panel skin to the honeycomb.

The panel produced has the lightweight advantages of the honeycomb, but with improved insulating properties due to the foam within the cells of the honeycomb.

Preferably, the foaming adhesive premix comprises a polyurethane resin mixed with water. The polyurethane formed is both a good adhesive and insulating medium. The polyurethane to water ratio is further preferably from 5:1-10:1 by weight, and especially preferably 7:1 by weight.

Alternatively, the polyurethane may be mixed with a chemical curing agent having, under the prevalent conditions, foam-producing properties.

Advantageously the method includes the further step of securing a porous membrane across the second face of the honeycomb. This porous membrane, which is further advantageously thermally bonded to a substrate acts primarily to create a binding interface between a low-energy difficult-to-bond plastic core e.g. polypropylene, and the planar boards. The porous membrane also acts to control * : * * flow of the foaming adhesive into the cells. Yet further advantageously, a porous membrane is secured across the first open face of the honeycomb prior to the placement of the first panel skin.

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L: In a second embodiment of the method, the foaming adhesive composition is spread across the either or both porous membrane or membranes, the panel skin or skins then being pressed onto and secured by the adhesive applied to the or either porous membrane or membranes.

Spreading of the adhesive premix composition is optionally by means of a coarse-toothed trowel, further optionally made of polypropylene.

The premix adhesive composition preferably comprises a moisture activated polyurethane precursor, which is further preferably in liquid form to achieve better mixing.

A panel comprising an outer and an inner panel skin, a honeycomb structure therebetween separating and supporting said panel skins, at least some of the cells containing a foam insulating material.

Brief Description of the Drawings

The invention is now described with reference to the accompanying drawing which shows by way of example only one embodiment of a honeycomb panel. In the drawing: Figure 1 illustrates a panel having a honeycomb structure in the interior.

Detailed Description of the Invention

The panels as described herein are of the type known as honeycomb panels in the industry and in their most general form comprise an outer and an inner skin, separated and secured to a honeycomb structure. The honeycomb structure *..S..

* defines a plurality of voids or free volumes and by itself has limited structural integrity. When bonded to the skins however, a strong lightweight structure is formed which can be used, amongst other things, as panels in buildings, containers, aircraft or furniture.

The shape of the voids, usually referred to as cells is most usually hexagonal, but other shapes such as squares, octagons and circular tubes are known in the art.

The cell walls can be made from, depending on the use, a wide variety of materials such as metals and metal alloys, paper or plastics materials.

In addition to the above, an intermediate porous membrane can be included between a skin and the honeycomb to assist in the bonding process and also change the permeability characteristics of the panel. Such membranes, sometimes referred to as veils are often used with cells made from polypropylene or other similar materials.

As will be appreciated however, the panels can be quite poor thermal insulators allowing heat to be carried easily from one side of the pane to the other. Although air does have some insulating properties it is still relatively poor in this function.

Attempts have been made to improve the insulation properties, for example, by partial evacuation of air from the cells. Nevertheless, this does not completely solve the problem and in addition increases the costs of manufacture both to produce the partial vacuum and also render the cells able to retain the lower pressure.

Another alternative solution is to increase the insulating properties of the skins themselves, by forming the skin of an insulating material or including a layer of such material. The present invention can be used to improve the thermal insulation properties of a panel and can be used either by itself or in conjunction with the insulating skins already known. It will be recognised that in providing thermal insulation, then insulation against other things such as sound may also be improved. *. ..

S Referring to Figure 1, this shows a standard panel, generally referenced 10, from S..

* which one of the skins has been partially removed to show the honeycomb 11 structure within the panel 10. The honeycomb 11 comprises a plurality of . : hexagonal cells 12 each linked to six adjoining cells through a common edge. A void 13 is therefore formed within each cell 12.

The cells 12 are all of the same (approximately) height and so define two planar surfaces to which a skin can be attached: predominantly by means of an adhesive.

A first skin 14 is bonded to one of the planar surfaces and a second skin 15 to the other. The skins 14, 15 are selected according to the panel's use and can be formed of metal, plastics or other suitable material. In the embodiment shown in Figure 1, an intermediate layer 16 is present between the honeycomb 11 and the skin 15.

In order to improve the insulating properties of the panel 10 over prior art panels, the panel 10 can be formed as follows. In a first embodiment of a method, a panel is partially formed by securing a first skin 14 to a honeycomb 11.

A premix comprising a moisture activated foaming adhesive such as a polyurethane precursor is formed and spread across the surface of the second skin 15. The second skin 15 is then pushed onto the honeycomb 11 and then held at pressure, typically from 1-2 kgcm2' with the adhesive bearing face towards the honeycomb 11 until cured. The polyurethane precursor reacts to form the polyurethane, which is formed as a foam material, penetrating into the voids 13 of the cells 12. Moreover as the polyurethane forms it becomes solid and acts to secure the skin 15 to the honeycomb 11. Once the reaction to form the polyurethane has completed, usually after around an hour, skins are bonded to the honeycomb and the foamed polyurethane within the cells acts as an efficient insulator.

In the above, the polyurethane precursor resin is obtained in liquid form for initial ***** * mixing with water. It has been found that in order to give good bonding and -insulation, and also allows sufficient time for the material to be properly spread and the skin positioned, then a ratio of from 5:1-10:1 by weight of polyurethane resin to water can be used. A ratio of around 7:1 has been shown to be especially preferable, giving the user around 10 minutes to carry out the above.

In a preformed embodiment of the above method, both outer faces of the honeycomb become foam-bonded and are pressed simultaneously. This serves to limit the stresses in the laminating planar panels and help create a more structurally-balanced panel.

Mixing of the polyurethane resin with water should be thorough but can be achieved with conventional mixers which are readily commercially available. In order to spread the mixed adhesive/insulator across the skin a spreader such as a coarse-toothed trowel, which can be polypropylene can be used. In large-scale production it may be more appropriate to apply the adhesive mix through a spray head via mixing valves.

In an alternative embodiment of the method, a porous membrane 16 or veil is firstly bonded to a planar sides of the honeycomb 12. The mixed polyurethane premix is then spread across the surface of the membrane 16. The skin 15 is pressed onto the polyurethane premix and the veil 16 which pressure acts to some extent to force the premix through the pores of the veil 16. As the polyurethane is formed the pressing also forces the foaming material into the void 13 of the cells 12. Once the polyurethane has set into a solid foam therefore the resulting panel includes insulating material within the cells. Moreover, the polyurethane also acts to bond the skin 14 to the rest of the panel 10. Yet further additionally, the rigid foam inside the cells enhances the structural stiffness of the panel.

It will of course be understood that the invention is not limited to the specific *..*,. details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention. * * * * S

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Claims

CLAIMS1. A method of manufacturing a honeycomb panel, the method comprising the steps of selecting a honeycomb structure, securing across one face of the honeycomb structure a first planar panel skin to close one open face of the cells, selecting a second panel skin and spreading across a first planar surface of the second panel skin a foaming adhesive premix, and pressing said first planar surface across the second, open face of the honeycomb structure, allowing the foaming adhesive to foam and set and thereby secure the second panel skin to the honeycomb.
2. A method according to Claim 1, wherein tho foaming adhesive premix comprises a polyurethane resin mixed with water.
3. A method according to Claim 2, wherein the polyurethane to water ratio is from 5:1-10:1 by weight. *. ..

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4. A method according to Claim 3, wherein the ratio is from 7:1 by weight.
5. A method according to Claim 1, wherein the polyurethane is mixed with a I...chemical curing agent having, under the prevalent conditions, foam-producing properties.
6. A method according to any preceding Claim, wherein the method includes the further step of securing a porous membrane across the second face of the honeycomb.
7. A method according to Claim 6, wherein the porous membrane is thermally bonded to a substrate prior to the membrane being secured.
8. A method according to Claim 6 or Claim 7, wherein a porous membrane is secured across the first open face of the honeycomb prior to the placement of the first panel skin.
9. A method of manufacturing a honeycomb panel, the method comprising the steps of spreading foaming adhesive composition across a porous membrane secured across a first face of the honeycomb structure a panel skin then being pressed onto and secured by the adhesive applied to the porous membrane.
10. A method according to Claim 9, wherein a second porous membrane is secured across the second open face of the honeyconib structure and a panel skin then being pressed onto and secured by the adhesive applied to the porous membranc.
11. A method according to any preceding Claim, wlierein spreading of the * * 20 adhesive premix composition is by means of a coarse toothed trowel.

* ** *** * *
12. A method according to Claim 11, wherein the trowel is made of * S S * polypropylene.
13. A method according to any preceding Claim, wherein the premix adhesive S...*: * composition comprises a moisture activated polyurethane precursor in liquid form to achieve better mixing.
14. A method according to Claim 13, wherein the precursor is in liquid form to achieve better mixing.
15. A panel comprising an outer and an inner panel skin, a honeycomb structure therebetween separating and supporting said panel skins, at least some of the cells containing a foam insulating material.55.5.5 * . * S..... * . *. *5 5* . * S S I*