Relating to electrically conducting materials

Abstract

The present invention relates to a composite material (10) comprising a layer of electrically conductive material (12) being provided on both sides with a lightweight fibrous veil (14), each veil (14) being coated on its surface remote from the electrically conductive material layer (12) with a curable thermosetting resin matrix material (16).

Claims

1. A conductive layer comprising a layer of electrically conductive material having provided on both sides a lightweight fibrous veil, each veil being coated on its surface remote from the electrically conductive material layer with a curable thermosetting resin matrix material; wherein the coatings of curable thermosetting resin matrix material on each of the veils have a thickness of from 20 to 150 m.

2. The conductive layer according to claim 1, wherein the curable thermosetting resin matrix material coating each veil also penetrates the veil and contacts the layer of electrically conductive material.

3. The conductive layer according to claim 2, wherein the curable thermosetting resin matrix material coating each veil also penetrates the layer of electrically conductive material.

4. The conductive layer according to claim 3, wherein the veil comprises a lightweight fabric having a weight in the range of from 3 to 30 gsm.

5. The conductive layer according to claim 4, wherein the veil comprises thermoplastic fibres.

6. The conductive layer according to claim 1, wherein the electrically conductive material is metal.

7. The conductive layer according to claim 6, wherein the metal is an expanded metal foil.

8. The conductive layer according to claim 1, wherein the layer of electrically conductive material has a weight per unit area of from 5 to 1000 g/m.sup.2.

9. The conductive layer according to claim 1, wherein the weight of the conductive layer excluding the weight of the layer of electrically conductive material is less than 800 g/m.sup.2.

10. The conductive layer according to claim 1, wherein the coatings of curable thermosetting resin matrix material on each of the veils have a weight of from 10 to 200 g/m.sup.2.

11. The conductive layer according to claim 1, wherein the coatings of curable thermosetting resin matrix material on each of the veils comprise the same material and are of substantially the same thickness.

12. The conductive layer according to claim 1, wherein the curable thermosetting resin matrix material is a thermosetting epoxy resin matrix composition.

13. The conductive layer according to claim 12, wherein the thermosetting epoxy resin matrix composition has a viscosity of at least 50 Pascal seconds at 116 C. after 150 minutes heating.

14. The conductive layer according to claim 12, wherein the thermosetting epoxy resin matrix composition comprises an additive increasing the viscosity of the composition.

15. The conductive layer according to claim 1 which is in the form of a strip having a width of from 2mm to 2m.

16. The conductive layer according to claim 15, wherein the width of the strip varies along its length by no more than 0.2mm.

17. A process of forming a conductive layer, said process comprising: a) providing a layer of electrically conductive material; b) providing a first veil having a layer of curable thermosetting resin matrix material coating a surface of the veil; c) providing a second veil having a layer of curable thermosetting resin matrix material coating a surface of the veil; d) applying the first veil to a first side of the electrically conductive material so that the layer of curable thermosetting resin matrix material coating the surface of the first veil is remote from the electrically conductive material layer; e) applying the second veil to the second side of the electrically conductive material so that the layer of curable thermosetting resin matrix material coating the surface of the second veil is remote from the electrically conductive material layer; and f) pressing the first and second veils together so that the layer of curable thermosetting resin matrix material coating the surface of each veil passes through the veil to contact the layer of electrically conductive material.

18. The cured fibre reinforced composite containing a conductive layer according to claim 1, wherein the curable thermosetting resin matrix material has been cured.

19. The automated lay-up process in which an electrically conductive layer according to claim 18 is incorporated with a tape of prepreg in the automated lay-up process.

Description

(1) The invention will now be clarified by way of example only and with reference to the following Figure and Examples in which:

(2) FIG. 1 shows a diagrammatic cross sectional view of a conductive layer according to an embodiment of the invention; and

(3) FIG. 2 shows a diagrammatic cross sectional view of a conductive layer according to a particularly preferred embodiment of the invention.

(4) In FIG. 1, the conductive layer 10 comprises a central electrically conductive material 12 having provided on both sides a lightweight fibrous veil 14, each veil 14 being coated on its surface remote from the electrically conductive material layer with a curable thermosetting resin matrix material 16.

(5) The veil 14 is polyester of 20 g/m.sup.2. The resin matrix material 16 is M92 resin, as manufactured by Hexcel Corporation, and the electrically conductive material 12 is an expanded copper foil ECF 175 as supplied by Dexmet.

(6) The material is in the shape of a tape having a width of 6.35 mm, which is suitable for lay-up in an AFP process.

(7) In FIG. 2, the conductive layer 20 comprises a central electrically conductive material 22 having provided on both sides a lightweight fibrous veil 24, each veil 24 being coated on its surface remote from the electrically conductive material layer with a curable thermosetting resin matrix material 26. The curable thermosetting resin matrix material 26 also penetrates the veils 24, forming a layer 28 between each veil 24 and the electrically conductive material 22, and also penetrates the electrically conductive material 22.

(8) The veil 24 is polyester of 20 g/m.sup.2. The resin matrix material 26 is M92 resin as manufactured by Hexcel Corporation, and the electrically conductive material 22 is an expanded copper foil ECF 175 as supplied by Dexmet.

(9) The material is in the shape of a tape having a width of 3.2 mm, which is suitable for AFP.

EXAMPLE 1

(10) A conductive layer having a structure corresponding to the structure shown in FIG. 1 was prepared. The conductive layer was an annealed expanded copper foil having an area weight of 175 g/m.sup.2 available from Benmetal. The veils were polyester veils having area weights of 20 g/m.sup.2. The outer resin layer coatings comprised a resin matrix material based on aerospace resin M21, available from Hexcel Corporation, but comprising 1 wt % treated fumed silica and 24.3 wt % hydrous, pulverised and spray dried kaolin clay as filler materials to increase the viscosity. The area weight of the coating layers was 90 g/m.sup.2. The total area weight of the conductive layer was 395 g/m.sup.2. The conductive layer was prepared by providing the veils with one surface coated in the resin and placing one veil on either side of the conductive layer, with the uncoated surface of each veil contacting the conductive layer. The combined layers were then compacted together so that the resin coating each veil passed through the veil to forma layer between the veil and the conductive layer, and also to penetrate the conductive layer. A coating of resin remained on the outer surface of each veil.

EXAMPLE 2

(11) A conductive layer corresponding to the layer of Example 1 was prepared but the conductive layer was replaced by an unannealed expanded copper foil having an area weight of 175 g/m.sup.2, available from Benmetal. In addition, the area weight of the resin coating layer was increased to 120 g/m.sup.2 on each veil, giving a total area weight for the conductive layer of 455 g/m.sup.2.

EXAMPLE 3

(12) A conductive layer corresponding to the layer of Example 1 was prepared but the polyester veils were replaced by carbon veils having area weights of 34 A conductive layer corresponding to the layer of Example 1 was prepared but the conductive layer was replaced by an unannealed expanded copper foil having an area weight of 175 g/m.sup.2, available from Benmetal. In addition, the area weight of the resin coating layer was increased to 120 g/m.sup.2 on each veil, giving a total area weight for the conductive layer of 455 g/m.sup.2, giving a total area weight for the conductive layer of 423 g/m.sup.2.

EXAMPLE 4

(13) A conductive layer corresponding to the layer of Example 1 was prepared but the conductive layer was replaced by an unannealed expanded copper foil having an area weight of 175 g/m.sup.2, available from Benmetal, as used in example 2. The conductive layer had a total area weight of 395 g/m.sup.2.

EXAMPLE 5

(14) A conductive layer corresponding to the layer of Example 4 was prepared, and an additional lightweight veil (area weight 4 g/m.sup.2) was added to each outer resin coating layer, giving a total area weight for the conductive layer of 403 g/m.sup.2.

(15) Each of the materials of Examples 1 to 5 were found to be suitable for use in providing electrical conductive layers in combination with prepregs, having acceptable conductive and surface properties. The materials of Examples 1 and 5 were particularly suitable, having very low surface tack and being dry to touch respectively.

(16) The conductive layers of Examples 1 to 5 were all tested for slitting tolerance by slitting with conventional slitting equipment to form tapes having an average width of 6.35 mm. The average tape widths for tapes prepared from each material were measured by taking 10 measurements for each material using a LaserMike instrument, and the results are shown in Table 1.

(17) As shown in Table 1, each of the materials of Examples 1 to 5 could be successfully slit to provide tapes having average widths of between 6.25 mm and 6.35 mm, and having very low levels of variation in width along their lengths.

(18) TABLE-US-00001 TABLE 1 Individual width measurements (mm) Example 1 Example 2 Example 3 Example 4 Example 5 1 6.306 6.306 6.348 6.260 6.277 2 6.332 6.283 6.322 6.248 6.296 3 6.292 6.306 6.323 6.260 6.272 4 6.318 6.244 6.322 6.269 6.294 5 6.317 6.285 6.341 6.256 6.264 6 6.338 6.279 6.313 6.217 6.248 7 6.250 6.288 6.320 6.238 6.276 8 6.359 6.346 6.398 6.225 6.246 9 6.356 6.302 6.367 6.305 6.324 10 6.306 6.282 6.298 6.263 6.254 Average 6.317 6.292 6.335 6.254 6.275