INTERMEDIATE MATERIAL AND A METHOD OF MANUFACTURING SUCH MATERIAL

Abstract

The invention relates to an intermediate material (132) for the manufacture of composite components, having a prepreg layer (116) and an interleaving layer (120) made up of at least two sections of thermally joined thermoplastic interleaving material sections (120a, 120b). The invention also relates to a method of manufacture of such an intermediate material.

Claims

1. (canceled)

2. (canceled)

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

8. (canceled)

9. (canceled)

10. (canceled)

11. (canceled)

12. A method of manufacturing an intermediate material comprising the steps of: a) providing a length of master prepreg having a first width; b) cutting the master prepreg into a plurality of longitudinal strips of prepreg, each of the strips having a width less than the width of the master prepreg; c) providing a first section of thermoplastic interleaving material, the first section of thermoplastic interleaving material having a length less than the length of each of the strips of prepreg; d) placing a first end of the first section of thermoplastic interleaving material in contact with a first end of one of the strips of prepreg, the first section of thermoplastic interleaving layer having a width the same as or greater than the width of the strip of prepreg; e) bringing the length of the first section of thermoplastic interleaving material gradually into contact with the length of the strip of prepreg; f) before the second end of the first section of thermoplastic interleaving material contacts the strip of prepreg providing a second section of thermoplastic interleaving material having a width the same as or greater than the width of the strip of prepreg, and joining the second end of the first section of thermoplastic interleaving material to a first end of the second section of thermoplastic interleaving material by the application of heat to form a continuous length of thermoplastic interleaving material; g) once the second end of the first section of thermoplastic interleaving material contacts the strip of prepreg bringing the length of the second section of thermoplastic interleaving material gradually into contact with the length of the strip of prepreg; winding the strip of prepreg in contact with the continuous layer of thermoplastic interleaving material such that the interleaving material reduces or eliminates self-contact of the prepreg layer.

13. (canceled)

14. The method according to claim 12, in which the step of applying heat in step f) also comprises applying pressure.

15. The method according to claim 14, in which the step of joining the two sections of thermoplastic interleaving material in step f) comprises the step of overlapping the ends of the two sections such that they are joined by a lap joint.

16. The method according to claim 15, in which the length of overlap is from 20 mm to 50 mm.

17. (canceled)

18. (canceled)

19. (canceled)

20. (canceled)

21. The method according to claim 16, in which the join regions are formed by contact with a heated wire.

22. The method according to claim 21, in which the continuous length of thermoplastic interleaving layer is wider than the strip of prepreg such that it overhangs the strip of prepreg on one or both edges.

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)

30. (canceled)

31. (canceled)

32. The method according to 22, in which the step of applying heat in step f) comprises applying heat using a hand-held heating device.

33. The method according to claim 32, in which the hand-held heating device is a battery powered device.

Description

[0058] An example intermediate material, interleaving layer and manufacturing process will now be described with reference to the accompanying drawings in which:

[0059] FIG. 1A is a schematic side view of an apparatus for, and method of, manufacturing an intermediate material according to the invention in a first stage of operation;

[0060] FIG. 1B is a schematic plan view of the apparatus and process of FIG. 1A;

[0061] FIG. 1C is a schematic side view of the apparatus and process of FIG. 1A in a second stage of operation;

[0062] FIG. 2A is a plan view of a first stage in a second manufacturing process for an interleaving layer;

[0063] FIG. 2B is a plan view of a second stage in the manufacturing process for an interleaving layer of FIG. 2A;

[0064] FIG. 3 is a plan view of a third stage in the manufacturing process for an interleaving layer of FIG. 2A;

[0065] FIG. 4 is a plan view of an alternative third stage in the manufacturing process for an interleaving layer of FIG. 2A; and,

[0066] FIG. 5 is a side view of an apparatus for carrying out the stage of FIG. 4.

[0067] Referring to FIGS. 1A and 1B, an apparatus 100 for carrying out a manufacturing method according to the invention is shown. The apparatus 100 comprises a master roll 102, a cutting assembly 104, a tensioning assembly 106, an interleaving material roll 108 and a spool winder 110.

[0068] The master roll 102 has uncured (or partially cured) master pre-impregnated (prepreg) material 112 wound thereon. The master prepreg material 112 has a width W in the transverse direction T (normal to a longitudinal direction L). The width in this embodiment is 1 m, but the skilled addressee would understand that other widths are possible. The length Lp of master prepreg material 112 stored on the master roll is 1000 m in this embodiment, but is typically in the range of 700 to 1,500 metres. The prepreg material moves in the longitudinal direction L during the process.

[0069] The cutting assembly 104 comprises a plurality of N cutting blades 114 spaced apart in the transverse direction T. Each cutting blade is configured to cut through the thickness of the prepreg material as it moves in the longitudinal direction. The cutting blades 114 are equally spaced such that N+1 strips or tapes 116 of prepreg material having width w are produced where w=W/(N+1).

[0070] Although not shown in FIG. 1 for simplicity, once all of the material 112 on the master roll 102 has been slit, a new master roll essentially identical to the first master roll 102 is arranged for slitting using the cutting assembly 104 to produce a further plurality of tapes essentially identical to the first plurality of tapes 116, and each of the further plurality of tapes are joined to one of the first plurality of tapes 116, so that the length of each of the individual tapes 116 is greater than the length of the prepreg 112 on the master roll 102. The slit tapes may be joined in any convenient manner and the process is preferably continuous, such that the first ends of a new slit tape is joined to the second ends of an original slit tape 116 as soon as it is formed, i.e. before the rest of the further tape is formed by slitting from the master. As many master rolls of prepreg 102 may be joined in this manner as necessary to produce the desired length of rolled intermediate material 132. For example, nine master rolls 102 each of 1,000 m in length may be joined to produce an intermediate material 132 of approximately 9,000 m.

[0071] FIGS. 1B and 1C then show what happens to one of the N+1 tapes 116, although it will be appreciated that in a typical process, all N+1 tapes are simultaneously treated in this manner.

[0072] The tape 116 is passed through the tensioning assembly 106, which comprises a series of rollers 118.

[0073] A first length of interleaving material 120a is provided, wound onto a first interleaving material roll 108a. The interleaving material is typically 3 to 12 mm wider than the tapes of prepreg 116, but crucially is typically supplied in a shorter length than the desired length of intermediate material 132.

[0074] Interleaving material 120a is off-wound from the roll 108a and passes over a roller 122 to an assembly roller 124. At this point, the first end of the interleaving material 120a comes into contact with the prepreg tape 116, and as the prepreg tape 116 and the first section of interleaving material 120a pass over assembly roller 124 they gradually come into planar contact beginning from the first end of the first section of the interleaving material 120a.

[0075] The interleaving material 120 is typically a thermoplastic polymer material, in this case LDPE (low density polyethylene). Such materials are generally provided in lengths in the order of hundreds of metres up to about 2,500 m. Typically, therefore the available lengths of the interleaving material Li will be less than the total length of the strips of prepreg material Lp used in the process, i.e. the length of the tapes of prepreg produced by the joining of lengths of prepreg slit from multiple master rolls or by the slitting of very long lengths of master prepreg. More typically Li<2Lp. It is not unusual for Li to be an order less than Lp, for example Li may be in the order of hundreds of meters up to 2,500 m, with Lp in the order of thousands of metres, such as 9,000 m or more.

[0076] In order to provide a length of interleaving material 120 suitable to layer a substantial length (if not all) of the length of a prepreg tape 116, according to the invention a plurality of lengths of interleaving material 120a, 120b, etc. are joined as part of the process, as described below.

[0077] Before the roll 108a is exhausted (i.e. the interleaving material 120a has been used), a second roll 108b of interleaving material 120b is provided. The second length of interleaving material 120b is joined to the first length 120a at a join 126. A typical join 126 is shown at region A in FIG. 1C. In the present embodiment, the apparatus 100 is stopped to facilitate the join. Further details of how the first length of interleaving material 120a is joined to the second length of interleaving material 120b are given below.

[0078] The wider interleaving material 120 overhangs the prepreg tape 116 on both sides. Because the prepreg is tacky, the assembled prepreg tape 116 and interleaving material 120 form an intermediate material 132. The intermediate material 132 is wound onto the spool winder 110 such that the interleaving material 120 is radially inward of the prepreg tape 116 as it is wound. This prevents the tacky prepreg sticking to itself.

[0079] The resulting reel 110 of intermediate material 132 comprising the layered interleaving material and prepreg can then be passed to an automated fibre placement rig for deposition. It will be understood that after unwinding, the AFP rig will separate the interleaving material before depositing the prepreg.

[0080] FIGS. 2A and 2B show a first way in which the join 126 can be formed. The two sections 120a, 120b are overlapped to form an overlap 128, and heat and pressure is applied to form the join 126 (FIG. 2B) as a lap joint. The overlap is typically in the range of 20 mm to 50 mm in the longitudinal direction.

[0081] FIG. 3 shows a first way in which heat and pressure may be applied to the overlap 128. In this example, equal heat and pressure is applied over the entire overlap 128 to fuse the sections 120a, 120b. The heat and pressure may be applied by a hand-held device, preferably a battery powered hand-held device, having a heating head with a width equal to the width of the join 128 in the longitudinal direction and a length equal to the width of the two sections of interleaving material 120a, 120b.

[0082] FIG. 4 shows a second way in which heat and pressure may be applied to the overlap 128. In this example, equal heat and pressure is applied to three individual longitudinally extending regions 130a, 130b, 130c of the overlap 128 to fuse the sections 120a, 120b. In this embodiment, the heat and pressure may be applied by a small heating element, such as a heated wire, extending in the longitudinal direction, as will be discussed below.

[0083] In each of the embodiments of FIGS. 3 and 4, it will be noted that the lateral edges of the overlap 128 (and therefore the sections 120a, 120b) are sealed. This is advantageous as it ensures that there is less potential for snagging and other such problems which may be caused by loose ends/edges.

[0084] In the embodiments shown in FIGS. 1A, 1B, 1C, 2A, 2B, 3 and 4 the heating to form a join is preferably carried out using a hand-held device, and most preferably a battery powered hand-held device.

[0085] Referring to FIG. 5, an apparatus 200 for joining the two sections 120a, 120b is shown. The apparatus comprises an anvil 202 and a press 204. The press comprises a single heated wire 206. The press 204 can be advanced towards the anvil 202 to apply simultaneous heat and pressure from the wire 206 onto the overlap 128. This creates a first join region 130a. The apparatus 200 is then moved in the transverse direction to form the second join regions 130b, and then moved again to form the third join region 130c (although it will be understood that the three join regions could be formed in any order, or that more join regions could be formed if required). In one embodiment both sides of the device 200 (the press 204 and the anvil 202) may comprise heating elements to thereby heat both sides of the interleaving material. Instead of a wire, the joining apparatus 200 may have heated heads of different shapes and configurations, for example hatching, cross-hatching, or a plurality or matrix of dots etc. This device is preferably a hand-held device, and most preferably a battery powered hand-held device.

[0086] Application of heat to the thermoplastic interleaving material partially melts and tackifies it, so that it joins to the opposing section.

[0087] When using the apparatus 200 in the process of the present invention, the pressure is preferably slowly released after sealing (which in these embodiments takes about 2 seconds). The speed of release depends on a number of factors, but the time and speed at which pressure is released is determined by when the joint is stable. This may be achieved by allowing the joint to cool sufficiently to form, either by stopping heating while the press is still closed or releasing the press slowly so the joint cools before the press and anvil are fully separated.

[0088] Once cool, the interleaving material will not exhibit further tackiness.

[0089] In an example of joining lengths of interleaving material according to the present invention, the respective ends of two strips of 9 mm wide and 50 m thick LDPE (PE Hoods Blue, available from Plasthill B.V.) were overlaid to give an overlap of 25 mm and joined together by the application of heat and pressure using a battery operated hand-held device (Bheema Mini Portable Handy Plastic Bag Sealer Sealing Machine, available from Amazon, UK). This device is small (approximately 110 mm by 45 mm by 25 mm) and lightweight (approximately 58 g), and does not require connection to a separate power source, and is therefore particularly convenient for use in the restricted spaces available on a process line for the manufacture of narrow prepreg tapes with an interleaving material layer. The full melting point of the LDPE is approximately 124 C., but it softens and becomes pliable as it is heated up through 40 C. to 110 C. Thus, the optimum temperature for forming a joint between the strips of LDPE is in the range 70 C. to 110 C., although to fully form the joint it is also necessary to apply pressure. Using pressures in the range that can be conveniently achieved by hand squeezing the device (i.e. from 30N to 400N) joints can be formed in from 2 seconds (using temperatures towards the top of the range) to 8 seconds (using temperatures towards the bottom of the range).

[0090] When using the sealer device, the act of releasing pressure breaks the circuit and the resistive heating of the wire in the device therefore ceases, causing a reduction in its temperature, such that the LDPE polymer sheet cools relatively rapidly, causing the joint to consolidate and allowing the material to be handled easily. The resulting join has a tensile strength within the range of non-joined LDPE as reported by the supplier, in this case greater than 21 MPa in the machine direction.

[0091] Variations fall within the scope of the present invention.