COMPOSITE MATERIAL AND RELATED ARTICLES AND METHODS

Abstract

A reinforcement sheet has a composite layer including fibres and a polymer A and a coating layer including polymer B, each polymer having at least 65 mol % of a repeat unit of formula:

##STR00001##

wherein for each polymer A and B, t1, and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2. A method of forming the reinforcement sheet is also disclosed, in addition to a method for forming an article comprising a laminate of the reinforcement sheets and the article comprising such a laminate. The repeat unit may be ether-ether-ketone.

Claims

1. A reinforcement sheet comprising: a composite layer having first and second faces, the composite layer comprising fibres and a first polymer A, the first polymer having at least 65 mol % of a first repeat unit A′ of formula ##STR00007## wherein t1, and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2; and a coating layer applied to the first face, and defining an interface therebetween, the coating layer comprising a second polymer B, wherein the second polymer comprises at least 65 mol % of a second repeat unit B′ of formula ##STR00008## wherein t1, and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2.

2. A reinforcement sheet according to claim 1 wherein the first polymer A comprises at least 90 mol % of first repeat unit A′, and preferably consists essentially of repeat unit A′.

3. A reinforcement sheet according to claim 1 wherein the first repeat unit A′ and the second repeat unit B′ are the same repeat unit, having common values for t1, w1 and v1.

4. A reinforcement sheet according to claim 3 wherein the first repeat unit A′ and the second repeat unit B′ are both according to the formula:
—O-Ph-O-Ph-CO-Ph- wherein Ph represents a phenylene moiety.

5. A reinforcement sheet according to claim 4 wherein the second polymer B comprises from 0 mol % to 35 mol % of a third repeat unit C′ according to the formula:
—O-Ph-Ph-O-Ph-CO-Ph- wherein Ph represents a phenylene moiety.

6. A reinforcement sheet according to claim 1 wherein the second polymer comprises at least 80 mol % of second repeat unit B′.

7. A reinforcement sheet according to claim 1, wherein the level of crystallinity in the polymeric material A is 20% or more; and the level of crystallinity in the polymeric material B is 20% or more.

8. A reinforcement sheet according to claim 1, wherein the composite layer comprises from 30 to 75% by weight of fibres and from 70 to 25% by weight of the first polymer A.

9. A reinforcement sheet according to claim 1 wherein the coating layer comprises at least 90% by weight of the second polymer B.

10. A reinforcement sheet according to claim 1 wherein the fibres of the composite layer do not extend into the coating layer.

11. A reinforcement sheet according to claim 1 wherein the coating layer has a thickness which varies by +/−2.0 micrometres or less from a mean thickness of the coating layer.

12. A reinforcement sheet according to claim 1 wherein the coating layer has a mean surface roughness Ra of 1.2 micrometres or less.

13. A reinforcement sheet according to claim 1 wherein the first and second faces of the composite layer each have a mean surface roughness Ra of 2.0 micrometres or less measured prior to any application of the coating layer.

14. A reinforcement sheet according to claim 1 comprising a further coating layer deposited on the second face.

15. A reinforcement sheet according to claim 1 wherein the composite layer comprises the fibres as a woven or non-woven textile impregnated with the first polymer A.

16. A method of forming a reinforcement sheet according to claim 1, the method comprising i) providing the composite layer comprising fibres and the first polymer A; and ii) depositing the coating layer comprising the second polymer B onto the respective face of the composite layer.

17. A method according to claim 16 wherein the coating layer is deposited onto the respective face of the composite layer by film depositing the coating layer onto the composite layer with the polymer A of the composite layer in a solidified state.

18. A method according to claim 16 wherein the coating layer is deposited onto the respective face of the composite layer by film depositing the coating layer onto the composite layer with the polymer A of the composite layer in a molten state.

19. A method according to claim 16 wherein the composite layer and the coating layer are each provided as a solid sheets and are pressed together and heated together to bond the coating layer to the respective face of the composite layer to form the reinforcement sheet.

20. A method according to claim 1 wherein the composite layer is provided by impregnation of polymer A as a melt into a woven or non-woven textile of the fibres, with subsequent solidification of the melt to provide the composite layer.

21. A method according to claim 20 wherein the solidification of the melt is arranged to provide a crystallinity of 20% or more for the polymer A.

22. A method according to claim 16 arranged to provide a crystallinity of 20% or more for the polymer B.

23. A method for forming an article comprising a laminate of reinforcement sheets according to claim 1, bonded to a substrate, the method comprising: a) melt-bonding the coating layer of a reinforcement sheet according to any one of claims 1 to 15, to the substrate, to form a topmost bonded reinforcement sheet; b) melt-bonding the coating layer of a further reinforcement sheet, according to any one of claims 1 to 15, to the bonded topmost reinforcement sheet, whereby the further reinforcement sheet becomes the topmost bonded reinforcement sheet; and c) repeating step (b) as required to provide the laminate of reinforcement sheets.

24. An article comprising a laminate of reinforcement sheets according to claim 1.

25. An article according to claim 24 wherein for each reinforcement sheet, each of the first polymer A of the respective composite layer and the second polymer B of the respective coating layer has a crystallinity of 20% or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0110] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

[0111] FIG. 1 shows a cross-sectional view of automated tape laying (ATP); and

[0112] FIG. 2 is a schematic cross sectional representation of an embodiment of a process according to the second aspect of the invention.

[0113] Turning to FIG. 1, a conventional ATP (Automated Tape Placement) for advanced reinforced thermoplastic materials is shown in operation.

[0114] A composite tape 10 comprising fibres and impregnated with thermoplastic polymer is fed into a nip of roller 12, rotating about an axle 13 pasta pre-heater 11 which is used to raise the temperature of the composite tape 10 to a value close to the melting point of the polymer. The nip is formed between the roller 12 and the topmost layer 14 of a laminated substrate 14, 15, 16 and the roller is pressed in the direction P to press the composite tape 10 into the topmost substrate layer 14. Heat is applied to the composite tape 10 in the nip of the roller 12 by a suitable means (such as by means of a hot air jet shown as H in FIG. 1). However, it will be understood that other heating means may be employed, such as laser heating. The roller 12 may also be at an elevated temperature in order to heat the composite tape 10 and substrate 14, 15, 16. A zone 17 in the nip of roller 12 has the polymer in a molten state as a result of the applied heat H, and this leads to melt-bonding of the composite tape 10 to the topmost layer 14 of the substrate 14, 15, 16. The material passing through the nip may be elevated to a temperature slightly lower than the Tm melting temperature for the polymer A in the composite layer, for instance from 5 to 20° C. lower. So, if the melting point of polymer A is 340° C., the nip material may be at 320-335° C. In another embodiment, the composite layer passing through the nip may be elevated to a temperature slightly higher than the Tm melting temperature for the polymer A in the composite layer, for instance from 5 to 20° C. higher. In another embodiment, the composite layer passing through the nip may be elevated to a temperature about the same as the Tm melting temperature for the polymer A in the composite layer, for instance from 5° C. lower to 5° higher. The surfaces of the rollers 23, 24 may be at a lower temperature, such as 10° C. or less, than the melting temperature for polymer A, with the composite layer including polymer A being fed into the nip with a temperature in excess of the Tm value for polymer A, such as 5° C. or more in excess of Tm, for instance 10° C. or more. In such an embodiment, the coating layer(s) may be at ambient temperature when fed into the nip. In this way, melt bonding may be achieved with reduced risk of adhesion of the coating layer to roller surfaces.

[0115] A cooling unit 18 is also provided to assist in solidification of the zone 17 after bonding. As the composite tape is melt-bonded to the substrate, the assembly of preheater 11, axle 13, roller 12 and cooling unit 18 (which are connected to move in unison) moves along the topmost layer 14 of the substrate 14, 15, 16 towards the left side of the Figure, so that the cooling unit 17 passes over the previously molten zone 17, cooling it, and the composite tape 10 is melt bonded to topmost layer 14 in a continuous manner as the roller 12 moves along the substrate. Cooling and solidification of the thermoplastic polymer leads to consolidation of the tape as part of the substrate to which it was applied.

[0116] Turning to FIG. 2, this shows a schematic cross sectional representation of an embodiment of a process according to the second aspect of the invention for forming a reinforcement sheet by applying a coating layer to a composite layer by melt-bonding.

[0117] A composite layer 19 (the formation of which is not shown in detail, but is achieved as already described above) leaves a cooling tunnel 21 where it is cooled and solidified using a cold air flow 22. In an alternative embodiment tunnel 21 is a heating tunnel 21 which ensures that composite layer 19 is molten upon arrival at a pair of rollers 23 and 24. The composite layer is drawn through rollers 23, 24, along with a coating layer 20. The roller 24 is heated and melt-bonds the coating layer 20 to the composite layer, with the rollers 23 and 24 biased together to squeeze the coating layer 20 and composite layer 19 together during the melt-bonding. As an alternative, if the composite layer 19 is molten upon arrival at rollers 23 and 24, one or more of said rollers 23 and 24 may be cooled.

[0118] Also shown are a thickness monitor 25 and a length measuring device 26, monitoring the length of reinforcement sheet delivered to the take-up spool 27. An arrangement of an adjustable pulley 28 and a tensioning pulley 29 allows for control of take-up as the reinforcement sheet 30 is collected on the take-up spool 27.

EXAMPLES

[0119] Reinforcement sheets were formed using the process as set out above in relation to FIG. 2 using either a carbon fibre tape (Example 1) or a glass fibre tape (Example 2) as composite layer and a coating layer of Victrex® APTIV® PEEK of 5-20 micrometre thickness.

[0120] The polymer used as polymer A for the composite layer was Victrex® PEEK 150 obtained from Victrex Manufacturing Ltd, with a Tm of 340° C. and MV of 0.15 (measured at 400° C. and 1000 s.sup.−1 as described above).

[0121] The PEEK used as polymer B in the coating layer coating layer was Victrex® APTIV® PEEK film (1000 series) obtained from Victrex Manufacturing Ltd: Tm 340° C.

[0122] The carbon fibre used was supplied by SGL, Mitsubishi, Toray, Hexcel, or Toho Tenax. Any carbon fibre available from SGL, Mitsubishi, Toray, Hexcel, or Toho Tenax is suitable for use in the present invention.

[0123] The glass fibre used was supplied by AGY or Owens Corning. Any glass fibre available from AGY or Owens Corning is suitable for use in the present invention.

[0124] In detail, referring to FIG. 2, coating layer 20 at ambient temperature was drawn into the nip gap between rollers 23, 24, along with the composite layer 19 (fibre tape). The surfaces of the rollers 23, 24 were maintained at a temperature below the Tg of polymer A and polymer B (i.e. specifically less than 140° C. for both A and B, typically 120° C.). In an alternative embodiment the surfaces of the rollers 23, 24 were maintained at a temperature of 60-90° C. The roller pressure was set at a level greater than 5 N/mm, preferably greater than 50 N/mm, of tape width (e.g. 6 N/mm). The composite tape 19 entered the nip between rollers 23, 24 at a temperature at least 10° C. greater than the melt temperature of polymer A (i.e. greater than 350° C. for PEEK 150G, typically 380° C.). This was also at least 10° C. greater than the melt temperature of polymer B. The line speed is 5-25 metres per minute, typically 10 metres per second.

[0125] The thickness of the coating layer was measured before application using a Hanatek thickness gauge. Mean thickness was 12.48 micrometres, with a minimum of 12.0, a maximum of 13.6 and a standard deviation of 0.28 micrometres. The thickness of the coating layer was also measured before application using XRF (X-Ray fluorescence spectrometry. Mean thickness was 12.48 micrometres, with a minimum of 12.0, a maximum of 13.6 and a standard deviation of 0.28 micrometres. It was found that the mean thickness after application as measured by XRF was 12.43 μm, with a minimum of 11.5, a maximum of 13.9 and a standard deviation of 0.30 μm.

[0126] After application of the coating layer to form the reinforcement sheet, the coating layer thickness was measured in situ using optical microscopy with an Olympus SZx10 optical microscope equipped with a graticule eyepiece calibrated against films of known thickness. A cross-section of the laminated tape was examined and the thickness recorded at multiple points across and along the cross-section, the values obtained were averaged to arrive at the thickness value.

[0127] The mean thickness after application was measured as 12.23 μm, with a minimum of 11.2 μm and a maximum=13.4 μm, with a standard deviation of 0.34 μm.

[0128] Crystallinity Values as Measured by DSC

[0129] 12.5 μm APTIV PEEK coating layer before application: 31.1%

[0130] Complete carbon fibre/PEEK reinforcement sheet including coating layer: 24.6% (Example 1)

[0131] Complete glass fibre/PEEK reinforcement sheet including coating layer: 32.2% (Example 2)

[0132] Coating film after removal from the carbon fibre/PEEK reinforcement sheet: 32.1% (Example 1)

[0133] Coating film after removal from the glass fibre/PEEK reinforcement sheet: 35.6% (Example 2)

[0134] No degradation of the polymer was observed to result from the application of the coating layer. Degradation may be assessed by examination of the DSC trace: if the polymer has degraded, there will be a corresponding shift in the Tc value (crystallisation temperature on cooling form the melt) in the DSC trace, usually to a lower value, depending on the kind of degradation. In these Examples, there was no change in the Tc observed.

[0135] The surface roughness of the reinforcement sheet Examples was measured using a Form Talysurf Intra instrument using the methodology as set out above, in accordance with the standards of measurement as set out in ISO 4288:1966. The surface roughness was measured over 2 areas in 3 segments of the surface, using 4 mm data length with 5 cut-offs, and with the cut-off for Lc set as 0.8 mm and the cut-off for Ls set as 0.0025 mm, and with a bandwidth of 300:1.

[0136] The results were as follows (measured for the coating layer after application to the composite layer):

[0137] Example 1 (carbon fibre) composite layer surface roughness: Ra=1.0379

[0138] Example 1 (carbon fibre) coating layer surface roughness: Ra=0.6004

[0139] Example 2 (glass fibre) composite layer surface roughness: Ra=1.5964

[0140] Example 2 (glass fibre) coating layer surface roughness: Ra=1.0397

[0141] Hence it can be seen that the application of the coating layer leads to a significant reduction in surface roughness.

PEEK/PEDEK EXAMPLES

[0142] A further Example (Example 3) was prepared using the following:

[0143] The polymer used as polymer A for the composite layer was Victrex® PEEK 150G obtained from Victrex Manufacturing Ltd, with a Tm of 340° C. and MV of 0.15 (measured at 400° C. and 1000 s.sup.−1 as described above). The composite layer was a carbon fibre composite tape using any carbon fibre supplied by SGL, Mitsubishi, Toray, Hexcel, or Toho Tenax.

[0144] The polymer B for the coating layer was a melt extruded film of PEEK/PEDEK copolymer, Tm 305° C., MV 0.15 (measured at 400° C. and 1000 s.sup.−1 as described above), with PEEK:PEDEK molar ratio 75:25.

[0145] The PEEK/PEDEK film thickness was again 5-20 μm.

[0146] Crystallinity measurements gave the following results for Example 3:

[0147] PEEK/PEDEK coating layer before application 24.2%

[0148] Sheet: carbon fibre/PEEK composite and bonded coating layer 22.7%

[0149] Coating layer after removal from reinforcement sheet 26.3%

[0150] Surface roughness measurements for Example 3 gave:

[0151] Example 1 (carbon fibre) composite layer surface roughness: Ra=1.0166

[0152] Example 1 (carbon fibre) coating layer surface roughness: Ra=0.4116

[0153] Although a few preferred embodiments have been shown and described as examples, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0154] All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0155] Each feature disclosed in this specification (including any accompanying claims and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0156] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.