GB2294468A

GB2294468A - Electrically conductive composite polymeric material

Info

Publication number: GB2294468A
Application number: GB9521964A
Authority: GB
Inventors: Christopher John Mould
Original assignee: BTR PLC
Current assignee: BTR PLC
Priority date: 1994-10-27
Filing date: 1995-10-26
Publication date: 1996-05-01
Anticipated expiration: 2015-10-26
Also published as: GB9521964D0; WO1996013320A1; GB2294468B

Abstract

An electrically conductive composite material for forming at least a part, such as a header end section (13), of a filter element (10) comprises a body of polymeric material which has moulded therein an array (16) of interconnected filamentary type electrically conductive elements which are in electrically conductive association with one another, the filamentary type elements having free ends and at least some of the said free ends lying exposed at a surface region of the polymeric material. The body may be prepared by positioning the array (16) in a mould, adding liquid polymeric material to the mould to surround the array and allowing the polymeric material to solidify. <IMAGE>

Description

ELECTRICALLY CONDUCTIVE COMPOSITE POLYMERIC MATERIAL This invention relates generally to an electrically conductive composite polymeric material and to an article such as a filter element in which at least a part of the article is required to be electrically conductive to enable a build up of static electricity to be avoided. The invention relates in particular though not exclusively to a material and an article comprising a material which also is compressible.

A filter element for removal of explosible particulate matter such as wood dust from a stream of air commonly comprises a filter medium of an envelope shape. Dust laden air is drawn inwards through the walls of the envelope. Filtered air flows out from the inside of the envelope through an opening in an integrally moulded compressible end section known as a header end.

The header end is sealed to a separator plate which divides a filter housing into a filtered side and an unfiltered side. The separator plate has an opening for each filter element header end to allow filtered air to flow from inside each filter element to the clean side of the separator plate.

To reduce the risk of fire or explosion of the flow of explosible dust or an accumulated dust cake on the filter element it is necessary to ensure that static charge does not build up on the filter element. This may be achieved partly by providing the filter medium with an anti-static coating such as a carbon loaded coating on its outer surface. Means must be provided also for connecting the filter medium or that coating to earth, usually via the frame structure of the filter housing.

If the header end is moulded from non-conductive material a special earthing connection needs to be made between the filter coating and frame structure of the filter housing. A disadvantage of this is that when replacing a filter element it is necessary to re-establish the earth connection. This involves additional maintenance time. Also there is the risk that an operator will fail to make a good connection or check that a good connection has been made.

Consideration has been given to use of an electrically conductive material for the compressible header end. For example materials loaded with carbon particles have been tried. These are found generally not to be satisfactory because they age and decrease in electrical conductivity. Also their initial conductivity often is poor, as also are their mechanical properties.

The present invention seeks to provide an improved article such as a filter element in which the foregoing disadvantages are addressed. It seeks also to provide an improved electrically conductive composite polymeric material, e g a material of a compressible type and method for the manufacture said article or composite material.

In one of its aspects the present invention provides an electrically conductive composite polymeric material comprising a body of polymeric material which has moulded therein an array of interconnected filamentary type electrically conductive elements which are in electrically conductive association with one another, the filamentary type elements having free ends and at least some of said free ends lying exposed at a surface region of the polymeric material.

In another of its aspects the present invention provides a method for the manufacture of an electrically conductive composite polymeric material comprising providing a mould, positioning in the mould an array of interconnected filamentary type electrically conductive elements, adding liquid polymeric material to the mould to surround and embed the conductive material and allowing the liquid polymeric material to solidify.

The polymeric material may be a compressible type material such as one having a hardness which is in the range 60 to 70 Shore A, preferably in the order of 65 Shore A.

An example of a compressible type polymeric material for use in the present invention is polyurethane. Use may be made preferably of a polyurethane which during moulding has a viscosity in the range 3,000 to 4,000 mPas at 25 C.

The polymeric material may be substantially incompressible. An example of such a material for use in the present invention is epoxy resin.

The polymeric material may be shaped for example by moulding or by cutting.

The body of polymeric material may comprise a first region of substantially incompressible polymeric material and a second region of a polymeric material of a compressible type. The filamentary type electrically conductive elements may be provided in only one of said regions or may lie in both of said regions.

The body of polymeric material, or at least one of said regions in the case of a body comprising two or more regions of different polymeric materials, may comprise, at least in part, a section of elongate form. That section preferably has a cross-sectional shape for which the aspect ratio, being the maximum ratio of the dimensions of the cross-section in any two mutually perpendicular directions, is less than 5:1, more preferably less than 3:1.

The method preferably comprises positioning in at least a section of the mould an array of interconnected filamentary type electrically conductive elements which is over size such that end regions of at least some of the filaments inherently tend respectively to bear resiliently against confronting surface areas of the mould.

The array of interconnected filamentary type elements may be in the form of a three dimensional mesh at outer surface regions of which the elements have free ends. Preferably the array of filamentary type elements comprises at least one electrically conductive core strand from which a plurality of filaments extend radially outwardly in a configuration such as that of tinsel.

Preferably the electrically conductive elements extend substantially wholly through a cross-section of the body of polymeric material, or a region thereof in the case of a body comprising two or more regions of different polymeric materials. Thus it is envisaged that the conductive elements are not confined to just a surface region or coating layer, and are not excluded from any specific zone of the body or region. They may lie randomly or be distributed in a substantially uniform manner.

Two or more lengths of tinsel or other arrays of interconnected filamentary type elements may be provided, e.g. to extend substantially side-by-side in which instance preferably those lengths are electrically interconnected.

Examples of suitable electrically conductive materials for the filamentary type elements are metallic materials such as copper, aluminium and stainless steel, and non-metallic materials such as carbon fibre.

Filaments, such as those of tinsel typically may have a length in the order of 10 to 80 mm, a thickness in the order of 0.01 to 0.05 mm and, if of rectangular section, a width between 0.01 and 0.5 mm.

A preferred tinsel filament may have a length in the order of 15 mm and a section of 0.02 mm thick and width between 0.25 and 0.5 mm.

The present invention provides also an article such as a filter element comprising at least in part a body of said composite polymeric material or a composite polymeric material made by said method. That material may be moulded and it may be moulded to form a structural interconnection, preferably a substantially fluid- or air-tight interconnection, with another part of the article. Said another part of the article may be at least in part electrically conductive and arranged in electrical contact with the elements of the body of polymeric material.

Said article may be a filter element comprising a first section of a filter medium which is, or has a surface coating of, electrically conducting material and a second section which comprises an electrically conductive composite polymeric material of the invention and arranged in electrically conductive contact with the filter medium or surface coating thereof.

The second section may be a header end section and preferably is compressible so as to be suitable for forming a substantially fluid-tight seal with the frame structure of a filter housing. Preferably ends of the filamentary type elements are exposed at that surface region of the polymeric material which forms a fluid tight seal. The ends are then able to form an electrical connection with an earthed metal part of the filter housing.

Said second section may be another part, e g a closed tail end section, of the filter element. In that case it may be substantially incompressible. It may be clamped to an electrically conductive structure which is earthed for example via the frame of a filter housing.

An embodiment of the present invention will now be described, by way of example, with reference to the Drawings, in which: Figures 1 and 2 are edge and side face views respectively of a filter element of the invention; Figure 3 is a perspective view of the filter element of Figures 1 and 2; Figure 4 is a side view of a multi-ended metallic insert, and Figure 5 shows in detail an end section of the filter element of Figures 1 to 3; Figure 6 is a top view of another filter element of the invention; Figure 7 is a side view of part of the element of Figure 6; Figure 8 is a detail of part of the element of figures 6 and 7, and Figure 9 is a part section on the line 9-9 of Figure 6 A flat type filter element 10 for the filtration of dust laden air comprises two superimposed layers 11,12 of pleated filter material.Each layer 11,12 has on its outer surface a carbon loaded surface coating to render it electrically conductive. The ends of the corrugated layers are embedded in a moulded header end section 13 and a moulded tail end section 14.

The header end section 13 is of a moulded compressible type polymeric material (in this case a polyurethane resin) adapted for forming a substantially fluid tight seal against a separator plate (not illustrated) which separates contaminated and filtered zones of a filter housing. The header section defines an opening 15 through which filtered air can flow from the space between the pleated layers 1 1,12 through an opening in the separator plate and into the filtered zone of the housing.

The tail end section 14 is also of a moulded polymeric material (in this case of the same material as the header end section, i e polyurethane), but is not compressible. In this case it is substantially incompressible.

The header and tail sections each have moulded therein at least one length of copper tinsel 16 (illustrated in Figure 4). It is found that surprisingly the hair like elements 17 which radiate outwards from the core strand 18 (as shown in Figure 4) remain substantially in that orientation even when moulded into the body of polymeric material and are not forced to lie flat against the core strand.

The tinsel hair elements 17 and length of the core strand 18 are chosen so that in the moulded end sections 13,14 each length of tinsel extends along the whole length of the end section and so that the hair like elements do not stop short of outer surface regions of the moulded material.

The end sections are formed by a moulding operation in which part of the mould shape is defined by the pleated filter medium. A moulded interconnection and bond between the end sections and filter medium results. The tinsel elements are positioned in the mould in the narrow channel formed between apex, i e ridge zones of the filter pleats and confronting mould surfaces. Thus during moulding the free ends of the tinsel hair elements 17 are present at outwardly facing surfaces of the end sections and also those surfaces which form a moulded interface with the filter medium and the stiffness of the elements is sufficient to resist displacement when the mould space is filled with polyurethane. The elements 17 therefore lie in electrical contact with the conductive carbon coatings on the corrugated layers 11,12.

At the header end section 13 exposed tinsel hair elements at the face of the section which seal against the separator plate result in electrical continuity between the carbon coating and separator plate which may be of metal and earthed.

At the tail end section 13 outer surfaces of the moulded end are encased in a stainless steel tray 20. Tinsel hair ends communicate with the tray 20 to provide overall, continuous conductivity with the conductive coating of the pleated filter material.

Instead of or in addition to an earthed connection at the header end section, the tail end section 14 may be clamped in electrical contact with said tray which is connected to earth.

Each end section 13,14 may have two or more sections of copper tinsel embedded therein. Preferably one length of tinsel is folded back on itself to provide a U-shaped configuration of two sections 21,22 as shown by the dashed line of Figure 3 and arranged to lie alongside the respective corrugated layers 11,12.

The filter element 30 of a second embodiment of the invention as shown in Figures 6 to 9 comprises a header section 31 that incorporates lengths of copper tinsel 34 over only a central part 32 of the length of each of the longer side regions 33 of the header section.

At each side region the tinsel is folded back on itself such that two halves of the length of that tinsel lie side-by-side.

Each half length is of a size which in a free condition would more than wholly occupy the cross-section (see figure 9) of the header section.

Thus during manufacture in which the tinsel is inserted in a mould for forming the header section 31, e.g. from moulded polyurethane, tinsel fibre end regions 37 will bear resiliently against confronting mould cavity surfaces (one of which may be defined by the filter medium 36) that form the opposite sides 38,39 of the header sections as shown in Figure 9. Although each half length is arranged to wholly occupy said header cross-section, by laying the tinsel in a doubled form there is achieved a higher degree of conductivity between surface regions.

The other end of the filter medium 36 is moulded into a stainless steel tray 40. Three lengths 41 of tinsel extend transversely across the tray and are embedded in the moulded material (see figure 8), e.g. polyurethane, to provide electrical conductivity between the tray and filter medium.

As evident especially from figure 9, the conductive material 34 is embedded in and extends randomly throughout a body of polymeric material in contrast to being merely a surface coating. Thus even if structure against which the header section may be clamped in use were to cut into and damage a surface region, electrical conductivity would not suffer in the manner that it would if the conductive elements were confined to the surface region.

Claims

CLAIMS:

1. An electrically conductive composite polymeric material suitable for use in a filter element and comprising a body of polymeric material which has moulded therein an array of interconnected filamentary type electrically conductive elements which are in electrically conductive association with one another, the filamentary elements having free ends and at least some of said free ends lying exposed at a surface region of the polymeric material.

2. A composite material in accordance with Claim 1 wherein the polymeric material is of a compressible type.

3. A composite material in accordance with Claim 2 wherein the polymeric material has a hardness in the range 60 to 70 Shore A.

4. A composite material in accordance with any one of the Claims 1 to 3 wherein the polymeric material is polyurethane.

5. A composite material in accordance with Claim 1 wherein the polymeric material is substantially incompressible.

6. A composite material in accordance with Claim 5 wherein the polymeric material is epoxy resin.

10. A composite material in accordance with any one of the preceding Claims wherein the body of polymeric material comprises at least in part a section of elongate form.

11. A composite material in accordance with Claim 10 wherein said section has a cross-sectional shape for which the maximum ratio of the dimensions of the cross-section in any two mutually perpendicular directions is less than 5:1.

12. A composite material in accordance with Claim 11 wherein said ratio is less than 3:1.

13. A composite material in accordance with any one of Claims 10 to 12 wherein the electrically conductive elements extend substantially wholly through said cross-section.

14. A composite material in accordance with any one of Claims 1 to 1 2 wherein the body of polymeric material comprises a first region of substantially incompressible polymeric material and a second region of a polymeric material of a compressible type.

15. A composite material in accordance with Claim 14 wherein the electrically conductive elements lie in only one of the said regions.

16. A composite material in accordance with Claim 14 wherein the electrically conductive elements lie in both of the said regions.

17. A composite material in accordance with any one of Claims 14 to 16 wherein the electrically conductive elements extend substantially wholly through at least one of said regions.

18. A composite material in accordance with one of the preceding claims wherein the array of interconnected filamentary type electrically conductive elements is in the form of a three dimensional mesh having outer surface regions at which the elements have free ends.

19. A composite material in accordance with any one of the Claims 1 to 17 wherein the array of interconnected filamentary type electrically conductive elements comprises at least one electrically core strand from which a plurality of filaments extend radially outwardly.

20. A composite material in accordance with any one of the preceding claims wherein the electrically conductive elements are elements of a metallic material.

21. A composite material in accordance with any one of Claims 1 to 19 wherein the electrically conductive elements are elements of carbon fibre.

22. A composite material in accordance with Claim 1 and substantially as described with reference to and as shown in the Drawings.

23. A method for the manufacture of an electrically conductive composite polymeric material comprising providing a mould, positioning in the mould an array of interconnected filamentary type electrically conductive elements, adding liquid polymeric material to the mould to surround and embed the conductive material and allowing the liquid polymeric material to solidify.

24. A method according to Claim 23 wherein the liquid polymeric material has a viscosity in the range 3,000 to 4,000 mPas at 25 C.

25. A method according to Claim 23 or Claim 24 wherein the mould has a pair of confronting surface areas and end regions of at least some of the filaments bear resiliently against said confronting surfaces.

26. A method according to any one of Claims 23 to 25 applied to the manufacture of a composite material in accordance with any one of Claims 1 to 22.

27. A method for the manufacture of a composite material in accordance with Claim 23 and substantially as hereinbefore described.

28. A filter element comprising at least in part a body of a composite material in accordance with any one of Claims 1 to 23.

29. A filter element in accordance with Claim 28 wherein said body of composite material is moulded and structurally interconnects in a fluid tight manner with another part of the article.

30. A filter element in accordance with Claim 29 wherein said another part of the article is electrically conductive and is in electrical contact with the electrically conductive elements of the body of composite material.

31. A filter element in accordance with Claim 30 wherein said another part comprises a filter medium which has at least a surface of electrically conductive material.

32. A filter element comprising a first section comprising a filter medium which has at least a surface of electrically conductive material and a second section which comprises an electrically conductive composite polymeric material comprising a body of polymeric material which has moulded therein an array of interconnected filamentary type electrically conductive elements which are in electrically conductive association with one another and have free ends which lie exposed at a surface region of the polymeric material, said material of the second section being arranged in electrically conductive contact with material of the first section.

33. A filter element in accordance with Claim 32 wherein said second section is a header end section of the filter element.

34. A filter element in accordance with Claim 32 or Claim 33 wherein said second section is a composite material in accordance with any one of Claims 1 to 23.

35. A filter element in accordance with Claim 28 or Claim 32 and substantially as described with reference to and as shown in the Drawings.