Composite materials

Abstract

A curable sheet-like composite material comprising curable resin and at least one layer of structural fibers and comprising an outer backing layer of substantially resin-free material which is gas permeable but is substantially non-permeable with respect to the curable resin at room temperature.

Claims

1. A semipreg having a first surface and a second surface which define the thickness of said semipreg, said semipreg being of sufficient thickness and flexibility to be formable into a roll of semipreg where said first surface and second surface are in contact with each other and wherein said roll of semipreg can be unrolled, said semipreg comprising: a resin rich structural layer comprising a layer of prepreg that comprises structural fibers and prepreg resin, said resin rich structural layer having a first side that comprises said prepreg resin and a second side that also comprises said prepreg resin; a resin free structural layer consisting of dry structural fibers, said resin free structural layer having an inside surface that is in contact with said prepreg resin located at the first side of said resin rich structural layer, said resin free structural layer having an outside surface that forms the first surface of said semipreg; a layer of polymeric fleece that consists of non-woven polymeric fibers, said layer of polymeric fleece having a first side and a second side wherein the first side of said layer of polymeric fleece is in contact with said prepreg resin located at the second side of said resin rich structural layer and wherein the second side of said layer of polymeric fleece does not form the second surface of said semipreg; and a layer of glass fleece that consists of non-woven glass fibers, said layer of glass fleece having an inside surface that is in contact with the second side of said polymeric fleece and an outside surface wherein the outside surface of said layer of glass fleece forms the second surface of said semipreg and wherein said layer of glass fleece is separable during unrolling of said roll of semipreg such that a portion of said layer of glass fleece becomes attached to the first surface of said semipreg.

2. A semipreg according to claim 1 wherein said structural fibers in said resin rich structural layer are unidirectional fibers.

3. A semipreg according to claim 1 wherein said polymeric fibers in said polymeric fleece comprise a phenoxy material.

4. A semipreg according to claim 1 wherein the weight per unit area of said layer of polymeric fleece is from 10 to 100 grams per square meter and wherein the weight per unit area of said layer of glass fleece is from 10 to 100 grams per square meter.

5. A semipreg according to claim 1 wherein the thickness of said layer of polymeric fleece is from 50 to 200 micrometers and wherein the thickness of said layer of glass fleece is from 50 to 200 micrometers.

6. A semipreg according to claim 5 wherein the thickness of said semipreg is from 0.5 mm to 5.0 mm.

7. A semipreg according to claim 6 wherein the weight per unit area of said layer of polymeric fleece is from 15 to 75 grams per square meter and wherein the weight per unit area of said layer of glass fleece is from 15 to 75 grams per square meter.

8. A semipreg according to claim 1 wherein the mean pore size of said layer of polymeric fleece is from 10 to 100 micrometers and wherein the mean pore size of said layer of glass fleece is from 10 to 100 micrometers.

9. A roll of semipreg comprising semipreg according to claim 1 which has been formed into a roll in which the first surface of said semipreg is in contact with the second surface of said semipreg and wherein said prepreg resin has migrated into said resin free structural layer to form a partially impregnated structural layer.

10. A roll of semipreg according to claim 9 wherein said prepreg resin has migrated into said layer of polymeric fleece to form a partially impregnated layer of polymeric fleece.

11. A roll of semipreg according to claim 9 wherein the weight per unit area of said layer of polymeric fleece is from 10 to 100 grams per square meter and wherein the weight per unit area of said layer of glass fleece is from 10 to 100 grams per square meter.

12. A roll of semipreg according to claim 9 wherein the thickness of said semipreg is from 0.5 mm to 5.0 mm.

13. A roll of semipreg according to claim 12 wherein thickness of said layer of polymeric fleece is from 50 to 200 micrometers and wherein the thickness of said layer of glass fleece is from 50 to 200 micrometers.

14. A roll of semipreg according to claim 13 wherein the weight per unit area of said layer of polymeric fleece is from 15 to 75 grams per square meter and wherein the weight per unit area of said layer of glass fleece is from 15 to 75 grams per square meter.

15. A roll of semipreg according to claim 14 wherein the weight per unit area of said layer of glass fleece is from 30 to 50 grams per square meter.

16. A roll of semipreg according to claim 15 wherein said polymeric fibers in said polymeric fleece comprise a phenoxy material.

17. A semipreg according to claim 1 wherein the thickness of said semipreg is from 0.5 mm to 5.0 mm.

18. A semipreg according to claim 1 wherein the structural fibers in said resin rich structural layer are unidirectional fibers.

19. A semipreg according to claim 18 wherein said unidirectional fibers are glass fibers.

20. A semipreg according to claim 1 wherein the dry structural fibers in said resin free structural layer are unidirectional fibers.

Description

(1) The inventions will now be illustrated, by way of example, and with reference to the following figures, in which:

(2) FIG. 1 is a schematic representation of a semipreg known in the art.

(3) FIG. 2 is a schematic representation of a composite material according to the invention.

(4) FIG. 3 is a schematic representation of another composite material according to the invention.

(5) Turning to the figures, FIG. 1 shows a semipreg 10 known in the art comprising a layer of structural fibers 12 arranged in rows and impregnated in a curable epoxy resin 14. The semipreg 10 comprises a second layer of structural fibres 16, also arranged in rows but not impregnated with resin.

(6) When such a semipreg 10 is rolled onto itself, resin 14 can migrate into an adjacent layer of fibres 16. Such migration causes the rolled semipreg layers to fuse together and cannot be unrolled without damaging the structural fibre layers. Thus, a solid backing sheet, e.g. polythene is added before such rolling occurs.

(7) FIG. 2 shows a semipreg 20 according to the invention. The semipreg 20 has all the features of semipreg 10 and the same numbers have been employed where the features are the same.

(8) However, the semipreg also comprises a first backing layer 22 and a second backing layer 24 both arranged on the same outer face of the semipreg.

(9) The first backing layer 22 is a fibrous fleece comprising phenoxy fibres and having a weight per unit area of 25 gsm.

(10) The second backing layer 24 is a fibrous glass fleece and having a weight per unit area of 30 gsm.

(11) When such a semipreg 20 is rolled onto itself, resin 14 is unable to migrate through backing layers 22 and 24 because they are substantially non-permeable with respect to the curable resin 14. Thus adjacent layers of semipreg 20 do not adhere to each other and the roll can be unrolled with a low force and without damage to the structural fibres.

(12) However, inevitably there will be some resin migration into fleeces 22, 24. In this case, as there are two backing layers, provided no resin migrates as far as the interface between the two fleeces 22, 24 then separation can occur easily.

(13) However, even if some resin migrates to the interface between the fleeces 22, 24 a low peel force with no damage to the structural fibres results. This is because the integrity of the glass fleece 24 is low and can therefore separate or split into two layered portions upon unrolling.

EXAMPLES

(14) Formulating Materials: ST-3022 30 gsm non-woven glass fleece from Johns Manville GmbH, Wertheim, Germany. S5030 50 gsm non-woven glass fleece from Johns Manville GmbH, Wertheim, Germany. Grilon MS 25 gsm non-woven phenoxy fleece from EMS-Griltech, Domat/Ems, Switzerland.

(15) Substrate Materials

(16) HexFIT 1000: M9.7G/35%/B310+B310/2G semipreg material from Hexcel GmbH, Neumarkt, Austria.

(17) HexFIT 2000: M9.6-LT/35%/BB630/2G semipreg material from Hexcel GmbH, Neumarkt, Austria.

(18) M9.6-LT, M9.7G resin from Hexcel GmbH, Neumarkt, Austria.

(19) Test Equipment

(20) Instron 5569 test frame using Instron Series IX software, from Instron, High Wycombe, UK.

(21) Backing Layer Characteristics and Fleece Characterisation

(22) This was achieved by means of the Keyence VHX Digital Microscope. Samples of veil were presented to the microscope by mounting them to a blue plastic card in order to help highlight the open areas when viewed on the computer monitor. The microscope was set at 175 magnification with the light output set to maximum and the gain dial set to 3 o'clock. The computer image was saved and represented a total area of 2951002 m.sup.2.

(23) The image was manipulated by means of adjusting sliders on a histogram in order to create a two colour image whereby one colour represents the veil fibres and the other represents the open space. The software is then used to measure the areas of all the individual open spaces. This data is saved to a spreadsheet which can then be used to calculate the total area occupied by open spaces (in order to calculate the % openness) along with the average size of the open areas.

(24) TABLE-US-00001 Fleece % openness Average open size m.sup.2 ST-3022 30gsm 54.25% 3055 S5030 50gsm 22.92% 993 Grilon MS 25gsm 37.92% 3049

(25) Test Method for Antiblocking Behaviour

(26) Double sided pressure sensitive adhesive fabric was used to secure samples of semi-preg to a rigid aluminium substrate and a flexible aluminium foil substrate. These were pressed at ambient temperature at 11 kPa for 2 days using a pneumatic press. The sample panels were then cut into 25 mm strips for testing.

(27) Testing was carried out using an Instron 5569 test frame using Instron Series IX software and a 2 kN load cell. The foil side was peeled off at 180 at a cross head speed of 300 mm/min, with the cross head moving 200 mm. This peeled back 100 mm of the sample. Peel strengths were recorded in units of N/25 mm. Qualitative assessment of fibre tow damage was also recorded.

Example 1Peel Force HexFIT 1000

(28) A semi-preg assembly of the HexFIT 1000 type comprise a resin rich prepreg material attached to one side of a dry fabric usually by means of the inherent tack of the prepreg resin. See FIG. 1.

(29) This example comprises a HexFIT 1000 material constructed from a prepreg consisting of a 310 gsm layer of stitched unidirectional glass fabric impregnated with a 310 gsm layer of M9.6-LT or M9.7G resin (Hexcel proprietary formulated resin systems) and a further layer of dry glass UD fibrous reinforcement attached to either side of the prepreg. The unidirectional fibres in the prepreg run at +45 or +30 to the warp (i.e. 0) direction and the other attached dry fibrous layer possesses the same unidirectional reinforcement fibres running at 45 or 30 to the warp direction. The reinforcement fibres are typically bundled into tows which are held in place by lightweight yarns woven into the tows. The yarns run in the warp (0 C. direction). On to the resin rich side of the semi-preg is assembly is placed a layer of fleece optionally followed by a second fleece. The fleeces are lightly pressed on to the semi-preg in order for them to stay in position. See FIG. 2.

(30) Such an assembly then has the ability to be pressed together without the need for a polythene interleaf. This has been measured using an in-house test method of pressing together two plies of the above material such that the fleece side of the material is in contact with the dry fibre side of the adjacent layer.

(31) The results are shown below in Table 1.

(32) TABLE-US-00002 TABLE 1 Fibre tow Fleece 1 Fleece 2 Peel force N damage None None 57 Yes Grilon 25gsm None 50 Yes Grilon 25gsm Grilon 25gsm 9 No S5030 None 16 Minor S5030 S5030 7 No ST-3022 None 21 Minor ST-3022 ST-3022 3 No Grilon 25gsm S5030 6 No Grilon 25gsm ST-3022 2 No

Example 2Peel Force HexFIT 2000

(33) A standard semi-preg material constructed from a 340 gsm film layer of M9.6-LT resin (Hexcel proprietary formulated resin system) to which a layer of glass UD fibrous reinforcement is attached to either side of the film. One reinforcement layer typically possesses unidirectional fibres running at +45 or +30 to the warp (i.e. 0) direction of the resin film and the other layer possesses the same unidirectional reinforcement fibres running at 45 or 30 to the warp direction. Again, the reinforcement fibres are typically bundled into tows which are held in place by lightweight yarns woven into the tows. The yarns run in the warp (0 C. direction). In examples according to the invention, to one side of the assembly a layer of fleece is attached and optionally also to the other side of the assembly. See FIG. 3.

(34) Such an assembly when pressed together brings together the first fleece of one semipreg with the second fleece of the adjacent layer of semi-preg.

(35) The results are shown below in Table 2.

(36) TABLE-US-00003 TABLE 2 Fibre tow Fleece 1 Fleece 2 Peel force (N) damage None None 38 Yes Grilon 25gsm None 41 Yes Grilon 25gsm Grilon 25gsm 19 No S5030 None 25 No S5030 S5030 15 No ST-3022 None 22 No ST-3022 ST-3022 15 No Grilon 25gsm S5030 17 No Grilon 25gsm ST-3022 15 No

Example 3 Interlaminar Shear Strength (ILSS)

(37) Laminates consisting of 7 plies of HexFIT 2000 materials with backing layers according to the invention including a control with no backing layers, such that the fibres were orientated at +/30 throughout the laminate, were prepared by curing in a vacuum bag assembly for 1 hour at 120 C. Test coupons of appropriate size of nominally 31025 mm were then cut so that the fibre direction remained at +/30 to the length of the test coupon. The coupons were then subjected to ILSS testing according to BS EN 2563.

(38) ILSS results can be summarized in the table 3:

(39) TABLE-US-00004 TABLE 3 Material Antiblocking layers ILSS MPa M9.6-LT/35%/BB630/2G None (control) 45 M9.6-LT/35%/BB630/2G 1 layer of ST-3022 fleece 32 M9.6-LT/35%/BB630/2G 1 layer of ST-3022 fleece and 1 45 layer of Grilon MS fleece M9.6-LT/35%/BB630/2G 2 layers for Grilon MS fleece 54

(40) Therefore, whereas the use of ST-3022 alone reduces the ILSS performance, a combination of ST-3022 and Grilon MS results in a comparable ILSS performance to the control laminate and the use of Grilon MS fleece alone results in improved ILSS performance.

Example 4Interlaminar Shear Strength

(41) A standard semi-preg material constructed from a 340 gsm film layer of M9.6-LT resin (Hexcel proprietary formulated resin system) to which a layer of glass UD fibrous reinforcement is attached to either side of the film. One reinforcement layer typically possesses unidirectional fibres running at +45 or +30 to the warp (i.e. 0) direction of the resin film and the other layer possesses the same unidirectional reinforcement fibres running at 45 or 30 to the warp direction. Again, the reinforcement fibres are typically bundled into tows which are held in place by lightweight yarns woven into the tows. The yarns run in the warp (0 direction.) To one side of the assembly a layer of a fibrous phenoxy layer in the form of Grilon MS fleece is attached and to the other side of the assembly a layer of ST-3022 is attached. The ST-3022 fleece can be substituted with another layer of Grilon MS fleece.

(42) Laminates consisting of 7 plies of HexFIT 2000 materials with antiblocking layers including a control with no antiblocking layers such that the fibres were orientated at +/30 throughout the laminate, were prepared by curing in a vacuum bag assembly for 1 hour at 120 C. Test coupons of appropriate size of nominally 31025 mm were then cut so that the fibre direction remained at +/30 to the length of the test coupon. The coupons were then subjected to ILSS testing according to BS EN 2563.

(43) ILSS results can be summarized in the following table:

(44) TABLE-US-00005 Material Antiblocking layers ILSS MPa M9.6-LT/35%/BB630/2G None (control) 45 M9.6-LT/35%/BB630/2G 1 layer of ST-3022 fleece 32 M9.6-LT/35%/BB630/2G 1 layer of ST-3022 fleece and 1 45 layer of Grilon MS fleece M9.6-LT/35%/BB630/2G 2 layers for Grilon MS fleece 54

(45) Therefore Grilon MS results in improved ILSS performance.

(46) Various additional embodiments of the inventions will now be described below.

(47) In embodiment 1 there is provided a curable sheet-like composite material comprising curable resin and at least one layer of structural fibres and comprising an outer backing layer of substantially resin-free material which is gas permeable but is substantially non-permeable with respect to the curable resin at room temperature.

(48) In embodiment 2 the composite material of embodiment 1 is in the form of a roll.

(49) In embodiment 3 the composite material of embodiments 1 or 2, is sufficiently flexible so as to be able to form a roll with a diameter less than 20 cm, preferably less than 10 cm.

(50) In embodiment 4 the composite material of any one of the preceding embodiments has a thickness of from 0.5 to 5.0 mm, preferably from 1.0 to 4.0 mm.

(51) In embodiment 5 the composite material of any one of the preceding embodiments is free of any removable solid backing sheet.

(52) In embodiment 6 the composite material according to any one of the preceding embodiments is a prepreg or a semipreg, preferably a semipreg.

(53) In embodiment 7 the composite material according to embodiment 6 is a semipreg and includes a layer of curable resin in contact with one or two layers of structural fibres which are not impregnated with resin.

(54) In embodiment 8 the composite material according to embodiment 7, has a curable resin adjacent to one such structural fibre layer.

(55) In embodiment 9 the composite material according to any of the preceding embodiments is suitable for use in forming a structural component.

(56) In embodiment 10, the composite material according to any of the preceding embodiments can form a roll forming a cylinder having a length of greater than 10.0 cm, and at least 1.0 m of rolled material.

(57) In embodiment 11 the composite material according to any of the preceding embodiments comprises two backing layers of substantially resin-free material which are gas permeable but are substantially non-permeable with respect to the curable resin at room temperature.

(58) In embodiment 12, the backing layer is separable or splittable into two layered portions.

(59) In embodiment 13 the composite material is obtainable by the process of rolling a composite material according to embodiment 12 onto itself and subsequently unrolling the rolled material to produce a composite material with both outer faces each comprising a separated or split layer of the backing layer.

(60) In embodiment 14, the composite material of any one of the preceding embodiments wherein the backing layer or layers are fibrous, preferably comprised of random fibres of material, intertwined together in the form of a fleece.

(61) In embodiment 15, the composite material of any of the preceding embodiments, wherein the backing layer comprises a glass fibre fleece, a phenoxy fibre fleece or both are present.

(62) In embodiment 16 the backing layer or layers of any of the preceding embodiments have a density in the range of from 100 to 300 kg.Math.m.sup.3.

(63) In embodiment 17 the composite material according to any one of the preceding embodiments comprises a backing layer or layers having an effective pore size of from 10 to 100 micrometers.

(64) In embodiment 18 the composite material according to any one of the preceding embodiments comprises a backing layer or layers having a weight per unit area of from 10 to 100 grams per square meter.

(65) In embodiment 19 the composite material according to any one of the preceding embodiments comprises a backing layer or layers having a degree of openness of from 10% to 70%, preferably from 15% to 60%.

(66) In embodiment 20, the composite material according to any one of the preceding embodiments comprises a backing layer or layers having a thickness of from 50 to 200 micrometers.

(67) In embodiment 21 there is provided a method of forming a roll of uncured composite material wherein a composite material according to any one of embodiments 1 to 20 is rolled onto itself without the presence of a removable solid backing sheet.

(68) In embodiment 22 there is provided a method of unrolling a roll of uncured composite material according to any one of embodiments 1 to 20 rolled onto itself without the presence of a removable solid sheet, whereby the unrolling is facilitated by the separation or splitting of a backing layer into two layered portions.

(69) According to another embodiment 23 of the invention, there is provided a curable composite material comprising curable resin and at least one layer of structural fibres and comprising a layer of fibrous phenoxy material.

(70) In embodiment 24, the curable composite of embodiment 23 is a prepreg or a semipreg.

(71) In embodiment 25, the curable composite of embodiment 24 is a semipreg and includes a layer of curable resin in contact with one or two layers of structural fibres which are not impregnated with resin, and wherein the fibrous phenoxy material is substantially resin-free.

(72) In embodiment 26, the curable composite of embodiment 24 is a prepreg and wherein the fibrous phenoxy material is substantially impregnated with curable resin.

(73) In embodiment 27, there is provided a curable stack of composite material, the stack comprising a plurality of layers of structural fibres and comprising at least one layer of fibrous phenoxy material.

(74) In embodiment 28, the curable stack according to embodiment 27, wherein prepregs comprising an essentially fibre-free resin layer are part of the composite material stack, and the fibre-free layers form interleaf layers within the stack.

(75) In embodiments 27 or 28, the stack comprises at least half as many fibrous phenoxy layers as there are layers of structural fibres, preferably comprising at least 75% as many fibrous phenoxy layers as there are layers of structural fibres, more preferably comprising approximately the same number of fibrous phenoxy layers as structural fibre layers.

(76) In embodiment 30, in the curable stack according to any one of the preceding embodiments, the fibrous phenoxy material is comprised of random fibres of material, intertwined together in the form of a fleece.

(77) In embodiment 31, in the curable composite or curable stack according to any one of the preceding embodiments, the fibrous phenoxy material has a material density (in a non-resin impregnated form) of from 100 to 300 kg.Math.m.sup.3.

(78) In embodiment 32, in the curable composite or curable stack according to any one of the preceding embodiments, the phenoxy material has an effective pore size of from 10 to 100 micrometers.

(79) In embodiment 33, in the curable composite or curable stack according to any one of the preceding embodiments, the phenoxy material has a degree of openness of from 10% to 70%, preferably from 15% to 60%.

(80) In embodiment 34, in the curable composite or curable stack according to any one of the preceding embodiments, the fibrous phenoxy material (in a non-resin impregnated form) has a weight per unit area of from 10 to 100 grams per square meter.

(81) In embodiment 35, in the curable composite or curable stack according to any one of the preceding embodiments, the fibrous phenoxy material has a thickness of from 50 to 200 micrometers.

(82) In embodiment 36, there is provided a cured composite material obtainable by exposing a composite material or stack according to any one of the preceding embodiments to an elevated temperature, and optionally an elevated pressure, at a temperature and for a duration sufficient to cause curing of the curable resin.

(83) In embodiment 37, the cured composite according to embodiment 36 is in the form of a structural component.