GB2536255A

GB2536255A - Moulding material for composite panels

Info

Publication number: GB2536255A
Application number: GB1504068.6A
Authority: GB
Inventors: Thomas Jones Daniel
Original assignee: Gurit UK Ltd
Current assignee: Gurit UK Ltd
Priority date: 2015-03-10
Filing date: 2015-03-10
Publication date: 2016-09-14
Anticipated expiration: 2035-03-10
Also published as: US20180043637A1; EP3268219B1; EP3268219A1; GB2536255B; US10870240B2; WO2016142479A1; GB201504068D0

Abstract

The present. invention describes a prepreg for the manufacture of fibre reinforced resin matrix composite materials, the prepreg comprising: a surface film comprising a thermosetting resin and a particulate filler material dispersed therein, and a fibrous layer on which the surface film is disposed, the fibrous layer comprising a plurality of non-woven carbon fibres which are substantially randomly oriented, wherein the fibrous layer has interstices between the carbon fibres dimensioned for absorbing at least a portion of the thermosetting resin during a resin infusion step and filtering at least a portion of the particulate filler material in the surface film to remain in the surface film during the resin infusion step. The thermosetting resin may be epoxy, the particulate filler may be talc and the composite panels can be high performance automotive body panel parts.

Description

MoirldingiNaterial for Composite Panels The present invention relates to a prepreg for the manufacture of fibre reinforced resin matrix composite materials. The present invention also relates to a method for preparing the fibre reinforced resin matrix composite material. In particular, the method of the present invention enables the manufacture of body panels, such as automotive body panels, comprising fibre reinforced resin matrix composite materials, where the body panels have a high quality surface finish.

In the field of automotive body panels, a significant weight saving can be achieved by replacing current metallic automotive body panels with composite materials, With lower cost tooling, significant savings can be made in lower volume production runs, High performance body panc.l parts may be manufactured from preimpregnated materials (known as "prepreg") as described in EP 1 322 460 and EP 1 128 958, or from tun-directional prepreg layers. Plies of prepreg can be first assembled offline of the mould to form a preform or laid directly into the mould and cured. For higher production rates and lower cost, the prepreg can he compression moulded as described in EP 2 855 127, EP 2 855 123, EP 2 855 122, EP 2 855 126, EP 2 855 125, EP 2 855:128.

To reduce surface porosity and thereby imlirove the panel finish prior to ting, a variety of prepreg surface resin films are available in the market (see, fin example, Guth SF70, SF80. S.E95PP and SF96, Cytec Surface Master 905 and FM02, OMS Composites E-272 and E-282, and TenCate Advanced Composites 8020 Surface Film), Typically, these resins are of a high viscosity so as to form a barrier of resin at the surface of the mould during the curing step. The resins usually contain a resin film, which is cast on to a consumable release film, and a lightweight carrier fabric. The lightweight carrier is typically applied dry to the cast resin film during manufacture, and is then either partially or fully impregnated during manufacture, or it becomes partially or fully impregnated on the roll when. stored.

The carrier stabilises the resin film and allows the resin film to be cut and handled during part manufacture without excessive stretch or tear, and without poor release of the resin film from the consumable release film. The resins are usually a hot-melt blend of epoxy resins with optional fillers and flow control agents and a latent curing agent. B-Staged or hot-melt resin preferred to solvent cast resins, as solvent cast resins can lead to entrapped solvent causing later paint defects in the surface layer.

In addition to reducing surface porosity, it is necessary to buffer further the paint from the underlying fibre layers in order to achieve Class A automotive finish. on a composite body panel. A repeating pattern from structural fabrics such as woven and multi-axial stitched products is easily noticeable in the final surface. Panels made from uni-directional prepreg can also produce print in the final painted surface especially if there are gaps or distortions in the drape forming the prepreg. The presence of resin rich zones in the fibre gaps can witness through to the surface with the difference in the fibre and resin modulus, thermal expansion and resin shrinkage during cure and then!ater through resin swelling and relaxation events over time and exposure to moisture. This problem is more pronounced in carbon composites where there is a higher differential in the fibre modulus and then-nal expansion of the fibre than the resin.

To eliminate surface porosity, it is know that films weighing as low as 150 gsm can be u and that the higher pressure of autoclave or compression moulding gives a reduced pin-hole surface than the lower pressure of vacuum consolidation using a flexible vacuum bag process. However, to mask the print surface from carbon prepreg layers, current surface films weighing 700 gsm are required as a barrier on the component A-surface to mask woven carbon and multiaxial laminates. One such example film is Gurit SF96 surface film available as SA11-4417 SF96/S/700/1260 mm, 'Mitch is a 700 gsm epoxy prepreg film with a 70 gsm glass carrier. This epoxy prepreg film has a total areal weight of 770 gsm, and is curable from 90°C. A similar product with. the same areal weight is also sold. as 802(1 Surface Film by 'refigure Advanced Composites. Thus, such films add undesirable weight to the composite.

When making a thin laminate, such as a car body panel, the surface layer causes the panel to twist after the de-moulding stage due to the difference in thermal expansion of the surface layer compared to the laminate. To reduce the resin shrinkage, thermal expansion, and to make the surface easier to sand to prepare for painting, the Ciurit SA11-4417 SE96/5/700/1260 311111 resin contains a total of 3540% talc and calcium c 24% by volume, ^nate fillers by w which equates to 20 to To eliminate this problem, a symmetrical laminate be made by repeating the surface layer at the B-surface of the part, However, the inclusion of the surface layer on. the I3-surface adds further weight. An alternative (for example, Gurit CBS(1) is to use a high resin content glass prepreg on the B-Siarface to balance out the expansion and shrinkage of the surfacing resin. An example of a high resin content glass prepreg is Gorit prepreg SA11-4800 ST861-11111E40017289gm/S18, Which is a 400 gam woven glass epoxy prepreg having a resin content of 42% by weight. However, both of the above-mentioned options add weight and cost to the carbon laminate.

It is accordingly an aim of this invention to provide a prepreg stud:acing material that gives a lower cost and lower weight laminate, and overcome at least some of these significant disadvantages.

The present invention provides a prepreg for the manufacture of fibre reinforced resin matrix composite materials, the prepreg comprising a surface film comprising a thermosetting resin and a particulate filler material dispersed therein, and a fibrous layer on which the surface film is disposed, the fibrous layer comprising a plurality of non-woven carbon fibres which are substantially randomly oriented, wherein the fibrous layer has interstices between the carbon fibres dimensioned for absorbing at least a portion of the thermosetting resin during a resin infusion step and filtering at least a portion of the particulate filler material in the surface film to remain in the surface film during the resin infusion step.

The prepreg provides the advantage in that it provides a high quality surface finish by forming a thinner final cured surface resin layer and providing structural stiffness and strength to the laminate. As such, lighter and lower cost symmetrical carbon laminates can be formed that do not respond asymmetrically to applied thermal or mechanical loads, and require reduced pre aration for painting to an A-class finish.

The present invention further provides a method for preparing a fibre reinforced resin composite material, the method comprising the steps of: (i) providing a prepreg comprising surface film comprising a thermosetting resin and a particulate filler material dispersed therein, and a fibrous layer on which the surface film is disposed, the fibrous layer comprising a plurality of non-woven carbon fibres which are substantially randomly oriented, wherein the fibrous layer has interstices between the carbon fibres dimensioned for absorbing at least a portion of the thermosetting resin during a resin. infusion step and filtering at least a portion of the particulate filler material in the surface film to remain in the surface film during the resin on step; (ii) providing a mould; (iii) loading the prepreg into a cavity of the mould such that the surface film is located toward a moulding surface of the mould; and (iv) subjecting the prepreg to a moulding step, the moulding step comprising applying a vacuum to the cavity of the mould and applying a closure load to the mould to generate a pressure in the cavity of the mould to cause at least a portion of the thermosetting resin to infuse into the fibrous layer to impregnate the carbon fibres and to filter at least a portion of the particulate filler material in the surface film to remain in the surface film, The present invention further provides a method for preparing a fibre reinforced resin matrix composite material, the method comprising the steps of: (1) providing a prepreg according to any one of claims -33; 00 providing a heated premould; (in) loading the prepreg into the premould; (iv) optionally subjecting the prepreg to a temperature of from 0 to 150°C andior pressure of from 0.01 to 10 bar so as to increase the rigid. v in the layers of the prepreg and form a preform; (v) providing a mould; (vi) loading the prefom into a cavity of the mould such that the surface film is located toward a moulding surface of the mould; and (vii) subjecting the preform to a moulding step, the moulding step comprising applying a vacuum. to the cavity of the mould and applying a closure load to the mould to generate a pressure in the cavity of the mould to cause at least a portion of the thermosetting resin to infuse into the fibrous layer to impregnate the carbon fibres and to filter at least a portion of the particulate filler material in the surface film to remain in the surface film.

These methods enable a cost effective light weight composite material to be formed that do not respond asymmetrically to applied thermal or mechanical loads, and require reduced preparation for painting to an A-class finish, The present tion further provides a fibre reinforced. resin matrix composite material comprising a surface film comprising a cured thermosetting resin and a particulate filler material dispersed therein, wherein -le surface film has a thickness of at least 100 microns and the particulate filler material comprises at least 2 voi% of the surface film, and a fibrous layer on which the surface film is disposed, the fibrous layer comprising a plurality of non-woven carbon fibres which are substantially randomly oriented, wherein the fibrous layer has interstices filled with the cured thermosetting resin and. a thickness of at least 200 microns.

The composite material provides a high quality surface finish by forming a thinner final cured surface resin layer with a higher solids content which imparts less shrinkage and distortion into the subsequent panel. The particulate filler is filtered and reduces the resin rich zones at the surface of material formed by fibre cross-avers and any needling voids created in stabilising the non-woven material nto a bondable product.

The present invention further provides a vehicle body panel comprising the composite material of the present invention. The vehicle body panel has excellent surface finish, stiffness and strength to weight ratios. The panels require less preparation for painting to an.A-class finish.

Preferred features of the present invention are defined in the respective dependent claims.

As used throughout, by average particle size, it is meant that the mean size as measured using a particle size analyser.

By substantially randomly orientated, it is meant the regular repeating fibre angles are not noticeable as in the case of a unidirectional, woven, or multiaxial fabric, Particle size distributions were measured using a Malvern 3801 Mastersizer particle size analyser.

id-plane, it is meant the middle of the prepreWpreformicomposite material such that the layers either side of the mid-plane are a mirror image of each another. The mid-plane may be defined as the neutral axis, By A-surface, ii is meant the final intended visible cosmetic surface, for example the exterior surface of an automotive hood, or in the case of an separately moulded inner stiffener bonded to that hood the surface seen when the hood is opened to inspect the engine compartment.

By =3-surface, it is meant the usual surthee hidden from. view surface viewed as not having the same cosmetic finish standard if both surfaces are to be seen.

Embodiments of the present invention to the accompanying drawings, in Which: e described by way of example, with e e Figure 1 schematically ustrates a prepreg according to an bodiment of the present invention; Figure 2 schematically illustrates a composite material according to an embodiment of the present invention; Figure 3 schematically illustrates a multilayer prepreg according to another embodiment of the present invention; Figure 4 schematically illustrates a composite material comprising two surface films according to another embodiment of the present invention; Figure 5 schematically illustrates a prepreg comprising an additional layer sandwiched between two opposing fibrous layers according to another embodiment of the present invention; Figure 6 schematically illustrates a prepreg comprising a syntactic layer sandwiched between two opposing fibrous layers according to another embodiment of the present invention; Figure 7 schematically illustrates a composite material comprising a syntactic layer sandwiched between two opposing fibrous layers according to another embodiment of the present invention; Figure 8 schematically illustrates a prepreg comprising a layer comprising unidirectional prepregs sandwiched between two opposing fibrous layers according to another embodiment of the present invention; Figure 9 schematically illustrates a composite material comprising a unidirectional prepreg layer sandwiched between two opposing fibrous layers according to another embodiment of the present invention; is a microscope image showing a cross-section of laminate formed as per Example 1.

Figure 11 is a microscope image showing a cross-section of laminate formed as per Comparative Example 1 Referring to Figure 1, there is shown in schematic limn a prepreg 1 according to an aspect of the present invention, As described hereinafter, the prepreg is utilised to manufacture a reinforced resin matrix composite material, which can he subsequently processed into a vehicle body panel.

The prepreg 1 comprises a surRice film prises a the/ dug resin and particulate filler 3 material dispersed therein.

The surface film riiay have a thickness of from 150 to 600 microns. Optionally, the surface film has a thickness of from 200 to 500 microns. Typically, the surface film has a weight of from 200 to 900 grams per square metre. Optionally, the weight of the surface film is from 300 to 700 grams per square metre, further optionally 400 to 600 grains per square metre.

Dispersed in the surface film is a particulate filer material. The surrace flint typically has a particulate filler material concentration of from 2 to 40 vol%, based on the volume of the surface film, Optionally, surface film has a particulate tiller material concentration of from 2 to 20 vol'?4, based on the volume of the surface film.

The particulate filler material typically comprises and inorganic material. For example, the particulate filler material may comprises Talc, calcium carbonate, silica, alumino-silicate ash, chalk, clay minerals, marble dust, slate powder or silicon carbide. Optionally, the particulate filler may comprise Tale. Optionally, the particulate filler is Talc. Further optionally, the particulate filler is Magi! Star 3504 talc, The particulate filler material may have a weight of from 80 to 400 grams per square metre, and/or an average particle size of from 5 to 30 microns. Optionally, the average particle size of the particulate filler material is from 8 to 20 microns, for example about 12 microns.

Typically, east 98 wt% of the particulate filler passes through a 45 micron sieve, Optionally, the particulate filler material has a particle size distribution of 99 wt% less than 75 microns. 84 wt% less than 30 microns, 68 wfil(0 less than 20 microns and 48 wt% less than 10 microns, The surface film also comprises a thermosetting resin, which may comprise an epoxy, vinyl ester, polyester, erylic, cyanate ester, phenolic, foram or benzoxazine resin. Typically, the thermosetting resin po; resin, Optionally, the thermosetting resin is epoxy, vinyl ester, polyester, acrylic, cyariaec ester,phenolic, firan, or benz.oxazine resin. Further optionally, the thermosetting resin is an epoxy resin.

The surface film is disposed on the fibrous layer 4. The fibrous layer comprises a plur non-woven carbon fibres 5, which are substantially randomly orientated, This is preferred over a powder bound chop strand matt, which has a coarse distribution of fibres. The fibrous layer has interstices between the carbon fibres dimensioned. for absorbing at least a portion of the thermosetting resin during a resin inthsion step and filtering at least a portion of the particulate filler material in the surface film to remain in the surface film during the resin infusion step.

Typically, the fibrous layer may have interstices between the carbon fibres dimensioned fair absorbing at least 25 vol% of the thermosetting resin during a resin infusion step and filtering at least 2 vol%, optionally at least 5 voi%, further optionally at least 10 vol%, of the particulate filler material in the surface film to remain in the surface film;luring the resin infusion step.

The non-woven carbon fibres may be chopped and/or cut fibres. Thus, the fibrous layer may comprise chopped andlor cut fibres. Such chopped and/or cut carbon fibres may have a length of less than 250 mm. Optionally, at least 50 wt% of the fibres have a length of from 10 to 150 mm, optionally from 10 to 50 min and further optionally from 10 to 30 mm.

The carbon fibres may be recycled carbon fibr... (recycled fibre sources), fix example from ELG Carbon Fibre Ltd, SGL Group, and Forniax. The advantage of recycled carbon fibres is that the cost and carbon footprint of the method used to manufacture the fibrous layer is reduced. The fibrous layer may he formed as a ban, optionally here the hats is formed of single or multiple fibre layers.

The fibrous layer may be manufactured by a carding process. Following the carding process, a multiply-layered substantially randomly oriented fibre matt may be formed by a needling process to entangle the fibrous layers and enable it to be subsequently wound and handled in a roll format Thus, the fibrous layer may comprise sub-layers, the sub-layers being optionally interconnected by needling. Stitching of the matt induces print marks into the final surface and a greater surface resin layer is needed to mask the stitching marks and is not preferred. The fibrous layer may therefore optionally comprise needle holes 6, which are formed during the needling. A needling process provides stabilisation but usually induces resin rich zones in cured parts made from alternative processes to this invention. Resin rich zones can also form at the fibre cross ovens on the part surface. in contrast to other manufacturing process such as VARTM, RTM and RTM light, which use low viscosity liquid resin by combining the particulate filled surface resin these resin rich zones in the fibrous layer are filled with a high concentration of particulate which prevents a later read-through of needle and fibre marks into the final painted surface.

The thickness of the fibrous layer may be from 500 microns to 10 mm. Optionally, the thickness of the fibrous layer is from 1 mm to 7.5 nun, for example 4 mm. The fibrous layer may also have a weight of nrearer than 100 grains per square metre, optionally from 100 to 300 grams per square metre and further optionally from ISO to 250 grams per square metre.

The fibrous layer typically has a loft such h fibrous layer is compressed in thickness by at least 30%, typically at least 45%, more typically at least 50% of the uncompressed thickness when subjected to a compressive load of I bar at 3°C2 As shown in Figure 3, the prepreg may comprise more than one of the surface flms 2, typically two surface films, and at least one, typically one, of the fibrous layers 4 to form a multilayer prepreg 7. In the mintilayer prepreg, the at least one fibrous layer is sandwiched between opposing surface films. Optionally, the more than one surface films and the at least one fibrous layer are present such that the prepreg layers are symmetrical with respect to a mid-plane of the prepreg, as shown in Figure 3. In this format the material forms a ready to use moulding material that will not warp or tist when demoulded. or given a subsequent thermal or mechanical lead. The material gives a paintahie finish on both the A-and B-surfaces, As shown in Figure the prepreg may also comprise at least two, typically two, of the fibrous layers 4 and at least one additional layer 8 sandwiched between opposing fibrous layers.

The additional layer may be a fabric ply, the fabric ply typically comprising carbon fibres. Optionally, the fabric ply is multiaxial, woven or non-woven.

Alternatively, the additional layer may comprise a syntactic layer 9, as shown in Figure 6. The syntactic layer typically comprises a resin and hollow microspheres 10 dispersed therein. Optionally', the syntactic layer comprises flow control agents dispersed therein.

Alternatively, the additional layer may comprise sin, optionally wherein the additional layer is a resin layer. The resin may optionally comprises a particulate filler material, the particulate filler material typically comprising the same fillers that are in the surface resin or additional fillers designed to impart further strength, stiffness, toughness, and stiffness such as milled carbon fibre, wollstinate, impact modifiers, rubbers and thermoplastic particles that could migrate into the space not filled by the longer fibres of the fibrous layer or form interleave or phase toughened layers.

Optionally, the additional layer comprises one or more unidirectional prepregs 11, as shown in Figure 8. The one or more unidirectional prepregs each comprise fibres aligned unidirectional.ly, The unidirectional prepregs may be used to provide strength, optionally to provide strength to the prepreg in a single direction.

Typically, the additional layer comprises more than one unidirectional prepreg. Each more than one unidirectional prepregs comprise fibres aligned. unidirectionally. The fibres in each of the more than one unidirectional prcpregs may be aligned in a direction so as to provide greater stiffness and. strength to the laminate. Optionally, the direction of the fibres in each of the more than one unidirectional prepregs are staggered with respect to each other. Thus, the fibre alignment of the more than one prepreg may be staggered with respect to each other. To avoid unwanted tension shear-coupling, a multi-axial, cross ply or quasi-isotropic laminate could be formed using plies of unidirectional prepreg, e:ac' cot g unidi ectional fibres which are aligned at different fibre angles relative to each other.

Typically, the additional layer is positioned in the multilayer prepreg as a central layer such that the combined prepreg layers are symmetrical about the central layer. This avoids unwanted warp or twist responses to thermal or mechanical loads. Such a feature can been seen in the prepregs of Figures 5, 6 and H. The prepreg of the present invention may be shaped to form. a preform. Optionally, the prepreg is subjected to a temperature of from 0 to 150°C andlor a pressure of from 0.01 to 10 bar to term the preform., further ptionally wherein the preform is subsequently cooled.

Optionally, the prepreg is tacked together to form the preform.

Optionally the preform may be partially, fully impregnated, or cooled prior to loading into the mould tool to make the preform more rigid"An advantage of providing a preform prior to the moulding step described hereinbelow instead of laying the prepreg directly into the mould is that the preform can be shaped to the correct size and form is more rigid, can be easily handled into the tool. Thus, the correct resin and fibre ratio and shape can be prepared off-line from the main tool.

Another aspect of the present invention is a method for preparing a fibre reinforced resin matrix composite material from the prepregs of the present invention.

In a t step of the method a prepreg is provided, where the prepreg comprises a surface film comprising a thermosetting resin and a particulate filler material dispersed therein, The surface film is disposed on a fibrous layer. The fibrous layer comprises a plurality of non-woven carbon fibres which arc substantially ranrtrsrctly oriented. The fibrous layer also has interstices between the carbon fibres.

The prepreg may be any prepreg as described her,in. That is, the surface film, thereto resin, particulate filter material and fibrous layer may contain any of the characteristics as described herein in relation to the prepreg of the present invention.

In a second step of multi is provided. The prepreg is then loaded into a cavity of the mould in a third step such that the surface film of the prepreg is located toward a moulding surface of the mould, Typically, the prepreg is loaded into a cavity of the mould such that the surface film is located against a moulding surface of the mould.

In a fourth step, the prepreg is subjected to a moulding step, for example compression moulding or autoclave moulding, so as to cure the prepreg. Optionally, the moulding step is compression moulding. During the moulding step, a vacuum is applied to the cavity of the mould and then a closure load is applied to the mould to generate a pressure in the cavity of the mould. This causes at least a portion of the thermosetting resin to infuse into the fibrous layer to filly or partially impregnate the carbon fibres and to filter at least a portion of the particulate filler material in the surface film to remain in the surface film. The moulding step may be conducted at a pressure from 6 to 100 bar, typically from 6-50 bar, The moulding step may optionally be conducted at a temperature of from 0250°C, typically at a temperature of from I 20-220°C, The interstices in the fibrous layer are dimensioned for absorbing at least a portion of the thermosetting resin during the resin infusion step (i.e. the moulding step). Optionally, during the moulding step the fibrous layer absorbs at least 25 vol% of the thermosetting resin. During the moulding step, the fibrous layer is dimensioned so as to filter at least a portion of the particulate filler material in the surface film to remain in the surface film. Typically fibrous layer filters at least 2 vol%, optionally at least 5 vol%, further optionally at least 30 vol V3F, of the particulate filler material in the surface film to remain in the surface film.

Thus, during the moulding step, at least a portion of thermosetting resin infuses into the fibrous material from the surface film, resulting in full or partial impregnation of the carbon fibres. Typically, the carbon fibres are Godly impregnated by the thermosetting resin.

The fibrous layer in the prepreg may also comprise needle holes. When such needle holes are present, the needle holes are at least partially filled with the filler material during the moulding step. Without the particulate filler the surface would be of insufficient quality as the needle holes would read through into the final painted surface.

During the moulding step the fibrous layer may have a high loft such that when the fibrous layer is a subjected to a compressive load of 1 bar at 18-23°C, the thickness of the fibrous layer is reduced by at least 30%, optionally at least 43%, further optionally at least 50%.

As the fibrous yer has high loftt it absorbs a significant volume of the thermosetting resin during the moulding step. The fibrous layer acts as an effectiye filter to concentrate the particulate filler particles within the thin mosetting resin to form a high solids consistent resin layer between the fibrous layer and the A-Surthce. By providing the prepreg o the present invention with a surface layer comprising a thermosetting resin and particulate filler, it is possible to achieve an A-class finish at lower areal weights than has been achieved before. The prepreg of the present invention overcomes defects seen when such materials have been used in other manufacturing processes to make composite parts. For example, recycled and non-recycled carbon fibres of this form have been used in RTM resin injection processes to make carbon fibre parts. However, defects in the surface are evident from the needling process, which produces holes within the fibrous layer and localised resin and fibre rich zones at the surface and which show through to the painted finish.

The surface film in the prepreg, i.e. prior to the moulding step, typically has a thickness of from 150-600 microns and a particulate filler concentration of from 2 to 40 vol%. After the moulding step, the surface film of the fibre reinforced resin matrix composite material has a thickness of from 25-400 microns and a filler concentration of from 10 to 70 vol%.

Optionally, the prepreg in the first step of the method described hereinabove comprises a plurality of the surface films, typically two surface films, and at least one of the fibrous layer, typically one fibrous layer, to form a multila.yer prepreg, where the at least one fibtous layer is sandwiched between opposing surface films. Typically, the more than one surface flints and the at least one fibrous layer in such a prepreg are present such that the prepreg layers are symmetrical with respect to a mid-plane of the prepreg, When such a prepreg is used in the method described hereinabove, at least a portion of the thermosetting resin from each of the opposing surface films infuses, i.e. migrates, into the at least one (sandwiched) fibrous layer to fully or partially impregnate the carbon fibres during the moulding step, This material format is suitable for moulding of thinner panels as a single moulding material or allowing fewer plies containing thicker fibrous layers to be used as each resin can impregnate a proportion of the fibrous layer.

Further optionally, the prepreg in the first step of the method may comprise at least two of the fibrous Layers, typically two, and further comprises at least one additional layer sandwiched between oppoSing fibrous layers. The additional layer may be a fabric ply, the fabric ply typically comprising carbon fibres, Optionally, the fabric ply is multiaxial, woven or nonwoven, Alternatively, the additional layer may comprise a syntactic layer. The syntactic layer typically comprises a resin and hollow mi.crospheres dispersed therein. During the curing step, at least a portion of such a resin in the syntactic layer inbases into each of the fibrous layers to billy or partially impregnate the carbon fibres. Thus, this results in a. decrease in the density of the syntactic layer, and therelbre a decrease in weight of the resultant composite material Alternatively, the additional layer may comprises a resin, optionally wherein the additional layer is a resin layer. The resin may optionally comprises a particulate filler material, the particulate filler material typically comprising the same fillers that are in the surface resin or additional fillers designed to impart further strength, stiffness, toughness, and stiffness such as milled carbon fibre, wolistinate, impact modifiers, rubbers and thermoplastic particles that could migrate into the space not filled by the longer fibres of the fibrous layer or form interleave or phase toughened layers, Optionally, the additional layer comprises one or more unidirectional prepregs. The one or more unidirectional prepregs each comprise fibres aligned tmidirectionally, The unidirectional prepregs may be used to provide strength, optionally to provide strength to the prepreg in a single direction.

Typically, the additional layer comprises more than one unidirectional prepreg. Each of the more than one unidirectional prepregs comprise fibres aligned unidirectionally. The fibres in each of the more than. one unidirectional prepregs may be aligned in a direction so as to provide greater stiffness and strength to the laminate. Optionally, the direction of the fibres in each of the more than one unidirectional prepregs are staggered with respect to each other. Thus, the fibre alignment of the more than one prepreg may be staggered with respect to each other. To avoid unwanted tension shear-coupling, a multi-axial, cross ply or quasi-isotropic laminate could be formed using plies of unidirectional prepreg, each comprising unidirectional fibres which are aligned at different fibre angles relative to each other, Typically, the additional layer is a central layer of the prepreg, such that the prepreg layers are symmetrical about the central layedmid-plane of the prepreg. 'has, the resulting composite material is also typically symmetrical about the central layer/ naid-piarie oaf the composite material.

In another aspect of the present invention, a method for preparing a fibre reinforced resin matrix composite material is described, where the method comprising the following steps.

In a * first step, a prepreg according to the present hsvertion is provided.. The second and third steps involve providing a heated premould and loading the prepreg into the premould, In a fourth step, the prepreg is optionally subjected to a temperature of from 0 to 150°C and/or a pressure of from 0.01 to 10 bar so as to increase the rigidity of the prepreg layers and form a preform.

The advantage of forming a preform from the o tae moulding step is that the preforms are more rigid, can be cut easily and are easier to transfer.

Subsequently, in fifth and sixth steps, a mould is provided and the preform formed in step (iv) is loaded into a cavity of the mould such that the surfiice film is located toward a moulding surface of the mould. Typically, the surface film is located against the moulding surface of the mould. Finally, in the seventh step, the preform is subjected to a moulding step, for example compression moulding or autoclave moulding. Optionally, the moulding step is compression moulding. During the moulding step, a vacuum is applied to the cavity of the mould and then a closure load is applied to the mould to generate a pressure in the cavity of the mould. This causes at least a portion of the thermosetting resin to infuse, i.e. migrate, into the fibrous layer to fully or partially impregnate the carbon fibres. At the same time, at least a portion of the particulate filler is material is filtered in the surface film to remain in the surface film. The moulding step may be conducted at a pressure of from 6 to 100 bar, typically from 6-50 bar. The moulding step may optionally be conducted at a temperature of from 80-250°C, typically at a temperature of from 120-220°C.

When a prepreg according to the present invention formed into a preform to load into floe mould, the loft of the non-woven fibrous layer is such that a significant volume fraction ofvoid space remains in the unimpregnated fibrous layer during the loading and pre-closing step of the mould. The void passages are maintained even when the thermosetting resin begins to warm and soften during the fourth step. The void passages provide an air escape route that allows any entrapped air with the FelonEA to escape from the preform during a vacuum hold stage, which occurs before the moulding step. Materials having less loft and which are easily impregnated do not provide such efficient degassing of air channels within the ply stack.

The material eliminates the previous problems seen when using the lower tool to form the part A-surface, Another aspect of the present invention is a fibre reinforced resin matrix composite material. Referring to Figure 2, there is shown in schematic form the fibre reinforced resin matrix composite material 12. The fibre reinforced resin matrix composite material may he formed from the prepreg of the present invention using the methods described hereinabove.

The fibre reinforced resin matrix composite material comprises a surface film 13. The surface film comprises a cured thermosetting resin and a particulate filler material 14 dispersed therein.

The surface film has a thickness of at least 100 microns, Optionally, the surface film has a thickness of from 100 to 600 microns, andlor a weight of from 200 to 900 grams per square metre.

The particulate filler material is dispersed in the surface film. The particulate filler material comprises at least 2 voi% of the surface film, i.e. 2 vol% of the surface film is the particulate filler material. Optionally, the particulate filler material comprises at least 5 v01510 of the surface film, i.e. 5 voi% of the surface film is the particulate filler material, Further optionally, the particulate filler material comprises at least 10 vol% of the surface film, i.e. 10 vol% the surface film is the particulate tiller material, The particulate filler material may comprise an inorganic material, .thr example, Talc, calcium carbonate, silica, alumino-silicate ash, chalk, clay minerals, marble dust, slate powder or silicon carbide, Optionally, the particulate filler comprises Talc, Optionally, the pa ier is Tale, Further Ily, the particulate filler is Magi' Star 3504 tale.

The particulate terial may optionally have a weight of from 40 to 400 grams per square metre, andior an average particle size of from 5 to 30 microns, optionally from 8 to 20 microns, for example about 12 microns, Typically, at least 98 wt% of the particulate filter material passes through a. 45 micron Optionally, the particulate filler material has a particle size distribution of 99 wt% less he 75 microns, 84 wit % less than 30 microns, 68 wt% less than 20 microns and 48 wt% less that 10 microns.

The surface film also comprises a cured thermosetting resin, y comprising a cured epoxy, vinyl ester, polyester, acrylic, anate ester, phenolic, furan, or benzoxazine resin.

Optionally, the cured thermosetting resin is a cured epoxy resin. Typically, the cured thermosetting resin comprises a cured epoxy resin. Optionally, the cured thermosettin is a cured epoxy, vinyl ester, polyester, acrylic, cyanate ester, phenolic, fin-am or benzoxazine resin. Further optionally, the cured thermosetting resin is a cured epoxy resin.

The surface film of the composite material is disposed on the fibrous layer 15. The fibrous layer has a thickness of at least' 00 microns, optionally 500 microns to 7 min. The fibrous layer may have a weight of greater than 100 grams per square metre.

The fibrous layer comprises a plurality of non-woven carbon fibres 16, which are substan randomly oriented. This is preferred over a powder bound chop strand matt, which has a coarse distribution of fibres. The fibrous layer has interstices filled with the cured thermosetting resin. Thus, the fibrous layer has interstices between the carbon fibres in Which. a portion of the thermosetting resin is present.

Typically, at least 50 wt% of the fibres having a length of from 10 to 150 mm. Optionally, at least. 50 wt% of the fibres have a length of from 10 to 50 mm, further optionally from 10 to 30 mm. The non-woven carbon fibre may be chopped andior cut fibres, The chopped andlor cut carbon fibres may have a length of less than 250 mm, The carbon fibres may be recycled carbon fibres (recycled fibre sources). The advantage recycled carbon fibres is that the cost and carbon footprint of the method used to manufacture the fibrous layer is reduced.

On curing to form. the composite material, rstice.s between the carbon fibres in the fibrous layer are filled with at least a portion of the thermosetting resin, In addition, if the fibrous layer comprises needle holes 17 from needling, such needle holes at least partial ly filled with the filler material, Thus, the fibrous layer of the composite material may comprise needle holes \yhich are at least partially filled with the filler material.

he composite material may optionally comprise more than one 4 i,e. a plurality) of the surface s (each of which comprises a cured thermosetting resin and a particulate filler dispersed therein) and at least one of the fibrous layers to form a multilayer composite material 18, as shown. in Figure 4. In such a multilayer composite material, the at least one fibrous layer sandwiched between opposing surface films 13. Optionally, the plurality of surface films and the at least one fibrous layer are present such that the composite material layers are symmetrical with respect to a mid-plane of the composite material.

The composite material comprise at. least two of the fibrous layers and at least one additional layer sandwiched between opposing fibrous layers. The additional layer may be a fabric ply, the fabric ply typically comprising carbon fibres. Optionally, the fabric ply is multiaxial, woven or non-woven.

tnatively, the additional layer may comprise a syntactic layer 19, as shown in Figure 7. The syntactic layer typically comprises hollow microspheres 20 dispersed therein. Optionally, the syntactic layer comprises flow control agents dispersed therein. On curing, some, i.e. at least a portion, of the resin in the syntactic layer infuses from the syntactic layer into the fibrous layers. In this instance, the fibrous layer acts as an effective filter to keep the microspheres from migrating through the laminate stack. Thus, the syntactic layer of the composite material consists of a core containing a higher final volume fraction of hollow microspheres, which reduces the density of the syntactic layer.

Thus, a composite material. can be made that is lighter, stronger and stiffer construction, The syntactic layer can also compensate for changes in the moulding cross section and flow to fill the different thickness. This is highly useful for avoiding a significant skin thickness change that may induce surface print. The syntactic can also help self-compensate for any changes in areal weight in the fibrous layers by that would have caused a local hard pressure intensity spot when attempting to compress to a high volume fractions and mark the final painted surface by flowing to fill the lower fibre weight areas and allowing high resin pressure to be maintained for high volume fraction without local crushing of the high fibre gsm zones.

Alternatively, the additional layer may comprises a resin, optionally wherein the additional layer is a resin layer, The resin may optionally comprises a particulate filler material, the particulate * material typically comprising the same fillers that are in the surface resin or additional fillers designed to impart further strength, stiffness, toughness, and stiffness such as milled carbon fibre, wollstinate, impact modifiers, rubbers and thermoplastic particles that could migrate into the space not filled by the longer fibres of the fibrous layer or form interleave or phase toughened layers.

Optionally, the addition aver comrprises one or more unidirectional piepregs 21, as shown in 9. Typically, the additional layer comprises Mere than one unidirectional prepreg, wherein each unidirectional prepreg comprises fibres aligned unidireetionall,y, and wherein the fibre alignments of the more than one prepregs are staggered.

The additional layer may be positioned in the composite material as a central layer such that the composite material layers are symmetrical about the central layer/mid-plane of the composite material, This arrangement can be seen, for example, in Figures 7 and 9. In this regard, as the surface layer is lighter and the non-woven fibrous layer contributes to the structural strength and stiffness of the composite material, some of the composite material can be replaced with the prepreg of the present invention. As such, it is more economic and weight saving to produce a symmetrical laminate where the prepreg is used on both the A-and B-surface of the composite material, and optionally within the composite material, to provide a symmetrical composite material structure, This is an advantage of a material such as the c -glass Cant CBS®, which contains more residual stress from the thicker surfacing layers and can respond to loads asymmetrically.

In another aspect, the present invention relates to a vehicle body panel, optionally an automotive body panel, comprising the composite material.s defined herein above.

The present invention is further illustrated with reference to the following no Examples.

Examples

Guth ST160 prepreg resin film was used to produce different laminate panels. The prepreg resin contains a blend of epoxide functional resins and latent curing agents to provide a Tonset of 38-I44°C and a heat of reaction between 360440 measured using Differential Scanning Calorimetry (TA Instruments Q20 or Mettler Toledo DSC 12e) using a ramp from 25°C to 260°C at I WV/min, In its uncured state, this resin typically has a minimum viscosity of 4 to 12 poise at 113°C, when measured using a TA Instrument AR2000 Rheorneter fitted with disposable 25 ram diameter aluminium plates to run an oscillation experiment from. 30-130"C at 2°C/ruin using a displacement of 1x1.0" rads and a frequency of 1 Hz, When cured at 15 minutes at 155°C ST160 resin would on average give a dry Tg of 160-170°C obtained after press curing a reference laminate containing 200 gsm of woven carbon fibre when testing with a Dynamic Mechanical Analysis (TA Instruments Q800) in dual cantilever mode using a beat ramp from 30°C to 200°C at 3°C/min. applying a frequency of 1 Hz.

To produce the surfacing resin, different loadings of Magil Star 350# tale filler was dispersed into the prepreg resin, The filler had an average particle size of 12 microns and produced to give a particle size distribution (measured using a Malvern 3801 Mastersizer particle size analyser) of 99 wt% less than 75 microns, 84 wt% less than 30 microns, 68 wt% less than 20 microns and 48 w less than 10 microns. Such a talc filler is available by Richard Baker Harrison.

To produce the syntactic prepreg, K20 glass inicrospheres from 3M were dispersed into the prepreg resin to lower the density to 850 pl.

Plies of Cunt 245gsm woven carbon prepreg PA13-6210 SE160,IRC2/15T/1250/42%/POPA and 300gsin multi-axial biax prepreg SA23-6434 ST160/11KC30001.270/51%/S/S POPA were used. to test more structural laminates using the same base ST160 epoxy prepreg resin as the surfacing and syntactic layers. These materials mainly increase the in-plane strength and stiffness, Each part was compression moulded by an isothermal hot in-hot out process with the tool temperature measured to be within 150-160°C. The material was loaded into the hot tool and partially shut to engage a vacuum chamber seal. A vacuum was applied before applying pressure to the material to remove any entrapped air. After a Rill vacuum had been achieved the tool was slowly closed. The load was then increased in a smooth manner to ensure that the had. within 90 seconds of applying the material charge to the hot tool.

The surface quality was visually assessed painting bility, using the iollowing two process: ow surface preparation: (a) clean panel using DuPont Axalta 3608s; (b) abrade with red scotch until surface matt finish was obtained; (c) clean panel using DuPont Axalta 3608s; (d) spray-apply two coats of Dupont DP 5150 primer, allowing 15 minutes flash off period between the first d second coat to give an approximately 100 micron finished coating weight; and (e) Allow 30min from the final coat prior to bat g the paint for 30min at 50°C 2) High surface preparation: (a) clean panel using DuPont Axalta 3608s; (b) Abrade surface with 180grit and ending with 3211 grit abrasive to remove any visible fibre print in the surface (c) Clean with clean compressed air to remove any surface dust (d) Abrade with red scotch until consistent all over matt finish obtained (e) clean panel using DuPont Axalta 3608s; spray-apply two coats of Dupont DP 5150 primer, flowing 15 minutes per pass; (g) flash off period between the first and second coat to give an approximately 100 micron finished coating weight; and (11) Allow 30min from the final coat prior ri baking the paint for 30min at 50°C cure the paint primer and assess the surface finish Flexural rigidity was assessed by testing the flexural properties in roll direction of the prepreg n accordance with ISO 14125 Fibre Reinforced Plastic Composites 3-Point Bend Determination of Flexural Properties. A comparison to steel flexural rigidity was made by comparing the El of the panel, giving the relationship that the same stiffness would be obtained in a first material of modulus E: and thickness t: as that of a second material having a modulus 1112 and thickness t2 if the following equation is met: t3 asstrmed to have a modulus of 200 CPa and a density of 2 -For this purpose, steel pa 7800 k..glra3.

Compaction of the fibrous layer was measured using a Zwick Mechanical Testing machine, Three plies of I 00x100mm dry fibrous material were compressed between two 80mm cylinders. The vertical displacement was first zeroed by closing the cylinders with no material present. The cylinders were then opened and the material placed between, The cylinders were then closed and the point of first contact noted. Further force was applied to measure the thickness of the material stack vs. the applied pressure, The average ply thickness from 5 different test specimens was used.

Three different non-woven fibre materials were used as shown in Table 1, below. Non

Material Desc neamtan-carbon. Mixed fibre 10 1.50mm 196usra Woven needled. multi-layered carbon Mixed fibre 10 to 150min 245gsm Ni Woven needled n

A

-anion I 25rar n

I -

1Ippe chod fibre Thickness r /nun Thickness ( 1 bar /min Compactio 4.1 9% 19% 6.0 82% Exam, A preform was m h d and press-cured. The pretbraconsisted of 3 plies «p epmg material: aining 1. a repreg con a 1 licron so_ payer weig ing 29C 38% pbw (22% by in contact with the fibrous layer of material B. The resin side was ientatowards A-sarface of the tool; a syntactic prepreg yer of 800 gsra; and 1. The same r:a @>,l but with the resa-ide was o & wsurface be tool.

The panel had a measured cured ply thickness of 1.2i? .rum and weight of 1,63 Kg/m2 after the resin bleed-out from processing. The panel had a flexural modulus of 23.2 (Wa and a flexural strength of 437.40 MPa. The panel had the equivalent stiffness of a 0,63 mm steel plate weighing 501 Kg/m2, giving a 67% weight saving.

The panel had a good surface finish. It was prepared for paint using the low surface preparation method and assessed to have an acceptable finish to topcoat for an A-class panel. Figure 10 shows a micrograph of this laminate. The remaining surface film thickness was on average measured to now he 85 microns. With the flow of resin into the fibrous layer it was estimated at the new surface:Maness of 85 microns could now contain up to 51% particulate by volume.

Example 2

A preform was manufactured and press-cured. The Tie Ipreforrrr consisted of 4 plies of prepreg material: 1. a prepreg containing a 282 micron surface re weighing 452 m and containing 38% pbw (22% by vol) particulate filler in contact with the fibrous layer of material B. The resin side was orientated towards the A-surface of the tool; 2. a prepreg formed of from cast films of STI.60 prepreg resin in contact with the fibrous layer of material B to give a prepreg containing 300 gsm resin film containing no particulate filler; 3. the same prepreg as ply 2 4. the same prepreg as ply 1 but \vial the resin side orientated toward the B-surface of the tool.

The panel had a good surface finish. It was prepared for paint using the low surface preparation method and assessed to have an acceptable finish to topcoat for an A-class panel.

Example 3

A. preform was manufactured and press-cured. The preform consisted of plies of prepreg material: 1, a prepreg containing a 282 tricron surface resin layer wei weighing452 gsrir and containing 38% pbw (22% by vol) pat ate filler in contact with the fibrous layer of material B. The resin side was orientated towards the A-surface of the tool; 2. a prepreg formed of from cast lilies of ST160 prepreg resin in contact with the fibrous layer of material B to give a prepreg containing 450 gsrri resin film containing no particulate filler; 3. the same prepreg as ply 2; 4. the same prepreg as ply I but with the resin side orientated toward the B-surface of the tool.

The panel had a good surface finish. It was prepared for paint using the low surface preparation method and assessed to have art acceptable finish to topcoat for an A-class panel, Eton* 4 A preform was manufactured and press-eured. The preform consisted of 3 plies of prepreg material; I. to prepreg containing a 528 micron surface resin layer weighing 688 gsm and containing 15% pbw (8% by vol) particulate filler in contact with the fibrous layer of material A. The rosin side was orientated. towards the A-surface of the tool; 2, one ply of 300gsm biaxial prepreg emit SA23-6436 ST160/Xe300C11270/51%/S/S POPA; the same preg as ply 1 but with the resin side orientated toward the B-surface of the tool.

The panel had a measured cured ply thickness of 1.39 mm and weight of 2,08 Kghnz after the resin bleed-out from processing, The panel had a flexural modulus of 17.11 CPa and a flexural strength of 312.91\4Pa, The panel had the equivalent stiffness of a 0.61 mm steel plate giving a 56.5% weight saving

Example 5

A preform was manufactured and press-cured. The preform consisted of plies of prepreg material: 1. a prepreg containing a 528 micron surface resin layer weighing 688 gsm and containing 15% pbw (8% by vol) particulate filler in contact with the fibrous layer of material C. The resin side was orientated towards the A-surface of the tool; are ply of 300gsm prepreg Gurit SA23-6436 ST160/XC30001270/51%/S/S POPA; the same prepreg as ply 1 but with the resin. side orientated toward the B-surface the tool.

The panel had a good surface finish. It was prepared for paint using the low surface preparation method and assessed to have an acceptable finish to topcoat for an A-class panel The panel had a measured cured ply thickness of 1.51 mm and weight of 2,32 Kg/m2 after the resin bleed-out from processing. The panel had a flexural modulus of 18.3 GI'a and a flexural strength of 267 MPa. The panel had the equivalent stiffness of a 0.68 mm steel plate giving a 56.3% weight saving

Example 6

A preform s manufactured and press-cured. The preform consisted of plies of prepreg materia 1. a prepreg containing a 521# micronsurface resin layer weighing 688 gsrn and containing 15% pbw (8% by veal) particulate filler in contact with the fibrous layer of material A. The resin side was orientated towards the.A-surface of the tool; 2. one ply of 0/90 3K 2x2 twill weave 245gsai carbon prepreg C:iurit SE160/1R.C245T/ 1250/42%/POPA; 3. the same prepreg as ply 1 but with wit:ta the resin side orientated toward the B-surface of the tool.

The panel had a good surface finish, IC uas prepared for paint using the low surface prepare method and assessed to have an acceptable finish to topcoat for an A-class panel.

Example 7

A preform was manufactured and press-cured. The preform prepreg material: 1, a prepreg containing a 528 micron surface resin layer weighing 688 pm and containing 15% Ow (8% by veil) particulate filler in contact with the fibrous layer of material A. The resin side was orientated towards the A-surface of the tool; 2. a prepreg formed of from cast films of ST160 prepreg resin in contact with the fibrous layer of material A to give a prepreg containing 400 gam resin film containing no particulate tiller; t. The same prepreg as ply 1 but with the resin side orientated oward the B urface of the tool.

The panel had a good surface finish. it was prepared for paint using the low surface treatment method and assessed to have an acceptable finish to topcoat for an A-class panel.

The panel had a measured cured ply thickness of l.73 mm and weight of 2.54 Kgirth-after the resin bleed-out from processing, The panel had a flexural modulus of 18,5 GPa and a flexural strength of 313 Iv1Pa. The panel had the equivalent stiffness of a 0,78 DIM steel plate giving a 53.3% weight saving

Comparative Example

A preform was manufactured and press-cured. The preibrra consisted of 3 plies of prepreg material: 1, a prepreg containing a 242 micron surface weighing 290 gam and containing no particulate filler in contact with the fibrous layer of material B. The resin side was orientated towards the A-surface of the tool; a synthetic prepreg layer of 800 gsrn; and the same prepreg, as ply I but with the resin le was orientated icuwmurd tlae B-surface of the tool.

The panel had a measured cured ply thickness of 1.31 mm and weight of 1.70 after the resin bleed-out from processing. The panel had a flexural modulus of 23.6 CiPa and a flexural strength of 440 NIPa. The panel had the equivalent stiffness of a 0.64 rum steel plate weighing 5.14 Kg/m2, giving a 67% weight saving.

The panel had visible pin holes e. it was prepared for paint using the low surface preparation method and assessed to have an unacceptable topcoat finish for an A-class panel, Figure 11 shows a micrograph of this laminate. Ther absence of a surface layer with fibres close to the surface. Small pits can also be seen in the resin surface Comparative Example 2 limit epoxy prepreg CBS® was used with a 0.7 mm core known to matching the flexural rig city of a 0,7 mm steel panel.

The material was cured at 120"C for 30 min using a vacuum bag consolidation on a; teel tool. A lightweight 35 gsm polyester scrim (R114-001 RP35/1310 W3139/1310 PLAIN P.E. 35gsm from Guilt) was first applied to the A surface of the 3E96 to act as an air path to remove any trapped voids between the mould surface and prepreg during care.

* SAI1-4417 5F96/S/700/1260mm = Surface an * SA13-2102 ST86E.C1RC200T/1270/42%/IPA/L. = 200 gsm. woven carbon * SOA0-2448 SY110/00/560g-0.7mmil 270min 0.7 mm thick syntactic core SA11-4800 ST86ITT/RE40017289gm/SIS prepreg -thermal balancing 400gsm glass fibre layer After cure, the weight as 2.38 ICg/mt, 1he equivalent steel weight is 5.46 Kg/m2, giving a 56% weight sav The panel had a good surface finish but with some are print. It was prepared lot paint using the high urface preparation method as the low surface preparation method was not sufficient to prepare the panel for an A-class paint finish. After priming it was and assessed to have an acceptable finish to topcoat for an A-class panel.

Comparative Example. 3 Gurit epoxy prepreg CBS® was used with a 1.0 mm core known to latching the flexural rigidity of a 0.8 min steel panel.

The mater A lightweigh as cured at 120'( min using a vacuum bag consolidation on a steel tool.

gsm polyester scrim (R114-001 RP35/1310 W3139/13] 0 PLAIN P.E, 35gsm from Gurit) was first applied to the A surface of the SF96 to act as an air path to remove any trapped voids between. the mould surface and prepreg during cure.

* SA11-4417 SF96/S/70011260mrai = surfiace film * SA13-2102 ST86EURC200171270/42%/IPAIL -200 gsm woven carbon SOA.0-2442 SY110/001800g-I.Orrimi1 270min-0.7 mm thick syntactic core * SA 1.1.-4800 STR6HTIRE400T/289gm/SIS prepreg After cure, the weight was 2,60 Kg/ant, The equivalent steel weight is 6,24 -, giving a 58% weight saving.

The panel had a good surface finish. but with some fibre print. It was prepared for paint using the high surface preparation method as the low surface preparation method was not sufficient to prepare the panel for an A-class paint finish, After priming it was and assessed to have an acceptable finish to topcoat for an A-class panel

Claims

CILAINIS1. A prepreg for the manufacture of fibre reinforced resin matrix composite matori prepreg comprising: a surface film comprising a thermosetting resin and a particulate filler material dispersed therein; and a fibrous layer on. which. the surface film is disposed, the fibrous layer comprising a plurality of nonwoven carbon fibres which are substantially randomly oriented, wherein the fibrous layer has interstices between the carbon fibres dimensioned. for absorbing at least a portion of the thermosetting resin during a resin infusion step and filtering at least a portion of the particulate filler material in the surface film to remain in the surface film during the resin infusion step.
2. The prepreg according to claim 1, wherein the surface film has a thickness of from 150 to 600 microns, optionally from 200 is 500 microns.
3. The prepreg according to any one of the preceding claims, wherein the surface film has a weight of from 200 to 900 grams per square metre, optionally from 300 to 700 grams per square metre, further optionally from 400 to 600 grams per square metre,
4. The prepreg according to any one of the preceding claims, wherein the particulate material comprises an inorganic material, optionally wherein the particulate filler material comprises Talc, calcium carbonate, silica, aliunine-silicate ash, chalk, clay minerals, marble dust, slate powder or silicon carbide, further optionally wherein the particulate filler is Talc.
5, The prepreg according to any one of the preceding claims, wherein the particulate filler material has a weight of from 80 to 400 grains per square metre.
6, The prepreg according to any one of the preceding claims, wherein the particulate filler material has an average particle size of from 5 to 30 microns, optionally from 8 to 20 microns, further optionally about 12 microns.als the
7. The prepreg according to any one of the preceding claims, wherein at least 98 wt% of the particulate tiller material passes through a 45 micron sieve.
8. The prepreg according to any one of the preceding claims, wherein the particulate filler material has a particle size distribution of 99 wt% less than 75 microns, 84 wt% less than 30 microns, 68 wt% less than 20 microns and 48 wt% less than 10 microns
9. The prepreg, according to any erne of the preceding claims, wherein the surface film has a particulate filler material concentration of from 2 to 40 vol%, optionally from 2 to 20 vo]%, based on the volume of the surface film..
10. The prepreg according o any one of the preceding claims, wherein the thermosetting resin comprises an epoxy resin, 1. The prepreg according to any one of the preceding claims, wherein the fibrous layer has a thickness of from 500 microns to 10 mm, optionally from 1 mm to 7.5 mm.12. The prepreg according to any one of the,preeeding claims, wherein the fibrous layer has a weight of greater than 100 grams per square metre, optionally from 100 to 300 grams per square met; e, fi,mher optionally from 150 to 250 grams per square metre.13. The prepreg according to any one of the preceding claims, wherein the fibrous layer comprises chopped and/or cut fibres.14. The prepreg according to claim 13, wherein the chopped and/or cut fibres have a lengt of less than 250 mm.15. The prepreg according to any one of the preceding claims, wherein the carbon fibres are recycled carbon fibres.16. The prepreg according to any one of the preceding elahns, whey us layer is formed as a hart.17, The prepreg according to claim 1fi, wherein the Batt is formed of s gi tiple fibre layers.18. The prepreg according to any one of the preceding claims, wherein the fibrous layer comprises sub-layers interconnected by needling.19. The prepreg according to any one of the preceding claims, wherein the fibrous layer comprises needle holes.20. The prepreg according to any one of the preceding claims, wherein at least 50 wt% of the fibres have a length of from 10 to 150 ram, optionally from 10 to 50 mm, farther optionally. from 10 to 30 mm.21. The prepreg according to any one of the preceding claims, wherein the fibrous layer has a loft such that the fibrous layer is compressed in thickness by at least 30%, optionally at least 45%, of the uncompressed thickness when subjected to a compressive load of 1 bar at a temperature of 18-23°C.22. The prepreg according to any one of the preceding claims, wherein the fibrous layer has interstices between the carbon fibres dimensioned, for absorbing at least 25 vol% of the thermosetting resin during a resin infusion step and filtering at least 2 vol%, optionally at least 5 vol%, further optionally at least 10 vollK, of the particulate filler material in the surface film to remain in the surface film during the resin i ion step.The prepreg according to any one of the preceding claims,wherein the prepreg comprises a plurality of the surface films and at least one of the fibrous layers to form a multilayer prepreg, wherein the at least one fibrous layer is sandwiched between opposing surface films.24. The prepreg according to claim 23, wherein the plurality of surface films and the at least one fibrous layers are present such that the prepreg layers are symmetrical with. respect to a mid-plane of the prepreg.25. The prepreg according to any one of the preceding claims, wherein the prepreg comprises at least two of the fibrous layers and further comprises at least one additional layer sandwiched between opposing fibrous layers.26. The prepreg according to claim 25, wherein the additional layer is a fabric ply, optionally wherein the fabric ply comprises carbon fibres.27. The prepreg according ac:orming to any one 26, wherein the fabric ply is multiaxial, 28. The prepreg according to claim 25, wherein dditional layer comprises a syntactic layer, optionally wherein the syntactic layer comprises resin and hollow mierospheres dispersed therein.29. The prepreg according, to claim 25, wherein the additional layer co p es a resin.optionally wherein the additional layer is a resin layer.30. The prepreg according to claim 29, wherein the resin comprises a particulate filler material.31. The prepreg according to claim 25 wherein the additionalcomprises one more unidirectional prepregs.32. The prepreg according to claim 3 wherein the additional layer comprises more than one unidirectional prepreg, wherein each unidirectional preprea comprises fibres aligned unidirectionally, and optionally wherein the fibre alignments of the more than one prepregs are staggered with respect to each other.The prepreg according to any one of the claims 25-32, wherein the addition& layer is a central layer of the prepreg, and the prepreg layers are symmetrical about the central layer.34. The prepreg according to any one of claims 1-33, wherein the prepreg is shaped to form a preform.35. The p efbnr, according to claim 34, wherein the prepreg has been subjected to a tem' erature of from U to 150°C and/or a pressure of from 0,01 to 10 bar to form the preform, optionally wherein the preform is subsequently cooled.The preform according to any one i4-35, wherein the prepreg loos been tacked together to form the preform.37. A fibre reinforced resin matrix composite material comprising: a surface film comprising a cured thermosetting resin and a particulate filler material dispersed therein, wherein the surface film has a thickness of at least 100 microns and the particulate filler material comprises at least 2 vol% of the surface film; and a fibrous layer on which the surface film is disposed, the fibrous layer comprising a plurality of non-wovert carbon fibres which are substantially randomly oriented, wherein the fibrous layer has interstices filled with the cured thermosetting resin and a thickness of at least 200 microns.38. The composite material according to claim 37, wherein the surface film has a thickness of from.1100 to 600 microns.The composite: material according to any one of claims 37-38, wherein le surface film has a weight of front 200 to 900 grams per square metre.40. The composite material according to any one of claims 3739, wherein the particulate filler material comprises an inorganic material, optionally Talc, calcium carbonate, silica, alumi.no-silicate ash, chalk, clay minerals, marble dust, slate powder or silicon carbide, further optionally wherein the particulate filler is Talc.41. The composite material according to any one of claims 7-40, wherein the particulate filler material has a weight of from 40 to 400 grams per square metre.42. The composite taterial according to any one of claims 37-41, wherein the particulate filler material has an average particle size of from 5 to 30 microns, optionally from 8 to 20 microns, ibrther optionally about 12 microns.43. The composite material according to any one of claims 2, wherein t least 98 wt% of the particulate tiller material passes through a 45 micron sieve, 44, The composite material according to any one of claims 37-43, wherein the particulate filler material has a particle size distribution of 99 wt% less than 75 microns, 84 wt% less than 30 microns, 68 wt% less than 20 microns and 48 wt% less than 10 microns.45. The composite material according tta axiy one of claims 37-44, wherein the particulate tiller material comprises at least 5 wit% of the surface film, optionally at least 10 void, of the surface film 46. The composite material according to any one of claims 37-45, wherein the cured thermosetting resin comprises a cured epoxy resin.47. The composite material according to any one of clait wherein fibrous layer has a thickness of from 500 microns to 7 mm.48. The composite.3aterial according to any one of claims 37-47, wherein the fibrous layer has a weight of greater than 100 grams per square metre.49. )e composite material according of claims 37-48, wherein the fibrous layer comprises chopped and/or cut fibres.50. The composite material according to claim 49, wherein the chopped and/or cut fibres have a length of less than 250 mm, 51, The composite material according to any one of claims 3 7-50, Wherein the fibres are recycled fibres, 52. The composite material according to any one of cl ne 37-51, wherein the fibrous layer comprises sub-layers interconnected by needling.53. The composite material according to any one of claims 37-52, wherein the fibrous layer comprises needle holes, and wherein the needle holes are at least partially filled with the particulate tiller material.54, The composite material according to any one of claims 37-53, wherein at least 50 wt% of the fibres have a length of from 10 to 150 mm, optionally from 10 to SO inm, further optionally from 10 to 30 min. 55. The composite material according to any one of 37-54, wherein the composite material comprises a plurality of the surface films and at least one of the fibrous layers to form a multilayer composite material, wherein the at least one fibrous layer is sandwiched between opposing surface films.56. .aterial according to claim 55, wherein the plurality of surface films and the at least one fibrous layers are pr such that the composite material layers are symmetrical about a mid-plane of the com.pos 57. The composite material according to any one of claims 37-56, wherein the composite material comprises at least two of the fibrous layers and finther comprising at least one additional layer sandwiched between opposing fibrous layers.58. The composite material ig to claim 57, wherein the additional layer is a fabric ply, optionally wherein the fabric ply comprises carbon fibres.The composite material according to any one of claims 58, wherein the ab ply is multiaxial, woven or non-woven.60. The composite material according to claim 57, wherein the additional layer comprises a syntactic layer, optionally wherein the syntactic layer comprises hollow microspheres dispersed therein.61. The composite material according to claim 57, wherein the additional layer comprises a resin, optionally wherein the additional layer laayer is a resin layer, 62. The composit to cl.airn 61, wherein the resin comprises a particulate filler material.63. The composite material according claim 57, wherein additional layer comprises one or more unidirectional prepregs.64. The composite medal according to claim 63, wherein [he additional layer comprises more than one unidirectional prepreg, wherein each unidirectional prepreg comprises fibres aligned unidirectionally, and optionally wherein the fibre alignments of the more than one prepregs are staggered with respect to each other.65. The composite material accord additional layer is a central layer of the corn are symmetrical about the central layer. any one of the claims 5744, wherein the terial and the composite material. layers 66. A vehicle body panel comprising the composite material as defined in any one of 1 37-65.67, The ody panel according to claim 66, wherein the body panel is an automotive body panel.68. A method for preparing a fibre reinforced resin matrix osite material, the method comprising the steps, of: (i) providing a prepreg comprising: a surface film comprising a thermosetting resin and particulate filler material dispersed therein; and a fibrous layer on which the surface film is disposed, the fibrous layer comprising a plurality of non-woven carbon fibres which are substantially randomly oriented, wherein the fibrous layer has interstices between. the carbon fibres dimensioned for absorbing at least a portion of the therrn.osetting resin during a resin infusion step and filtering at least a portion of the particulate filler material in the surface film to remain in the surface film during the resin infusion step; (ii) providing a mould; (iii) loading the prepreg, into a cavity of the mould such. that the surface film is located toward a moulding surface of the mould; and (iv) subjecting the prepreg to a moulding step, the moulding step comprising applying a vacuum to the cavity of the mould and applying a closure load to the mould to generate a pressure in the cavity of the mould to cause at least a portion of the thermosetting resin to infuse into the fibrous layer to impregnate the carbon fibres and to filter at least a portion of the particulate filler material in the surface film to remain in the surface film.69. The method according to claim 68, wherein the surface film in the prepreg has a thickness of from 150-600 microns and a particulate filler concentration of from 2 to 40 vol%, and wherein after the moulding step the surface film of the fibre reinforced resin matrix composite material has a thickness of from 25-400 microns and a particulate filler concentration of from 10 to 70 vol%, 70, The method according to any one of claims 63-69, wherein during the moulding step the fibrous layer has a loft such that when the fibrous layer is a subjected to a compressive load of 1 bar at 18-23 °C the thickness of the fibrous layer is reduced by 30%, optionally 45%, 71. The method according to any one of claims 6870, wherein step (iii) comprises loading the prepreg into a cavity of the mould such that the surface film is located against a moulding surface of the mould.72. The method according to any one of claims 68-71, wherein during the moulding step the fibrous layer absorbs at least 25 vo[% of the thermosetting resin.73, The method according to any one of claims 68-72, wherein during the moulding step the fibrous layer filters at least 2 vol%, optionally at least 5 vol%, further optionally at least 10 vol% of the particulate filler material in the surface film to remain in the surface film.74. The method according to any one of claims 63-73, wherein the fibrous layer in the prepreg comprises needle holes, and wherein the needle holes are at least partially filled with the particulate filler material during the moulding step.75. The method according to any one of claims 63-74, wherein the prepreg in step (0 comprises a plurality of the surface films and at least one of the fibrous layers to form a multilayer prepreg, wherein the at least one fibrous layer is sandwiched between opposing surface fitnis, and wherein during the moulding step at least a portion of the thermosetting resin from each of the opposing surface films infuses into the at least one fibrous layer to impregnate the carbon fibres.76. The method according to any one of claims 68-75, wherein the prepreg in step (1) comprises at. least two of the fibrous layers and further comprises at least one additional layer sandwiched between opposing fibrous layers, 77. The method according to claim 76, wherein the additional layer s a fill optionally wherein the fabric ply comprises carbon fibres.The method according to any one of claims n the fabric ply is multiaxial, 79. The method according to claim 76, wherein the additional layer comprises a syntactic layer, optionally wherein the syntactic; layer comprises a resin and hollow microspheres dispersed therein.80. The method according to claim 79, wherein during the moulding step at least a portion of thennosetting resin from the syntactic layer infuses into each of the fibrous layers to impregnate the carbon fibres.81. The method according to claim 76, wherein the additional layer comprises a resin, optionally wherein the additional layer is a resin layer.82. The prepreg according to claim 81, w herein t,e resin comprises a particulate filler material, 83. The prepreg according claim 76, wherein the additional Layer comprises one or more unidirectional prepregs.84. The prepreg according to claim 83, wherein the additional layer comprises more than one unidirectional prepreg, wherein each unidirectional prepreg comprises fibres aligned unidirectionally, and optionally wherein the fibre alignments of the more than one prepregs are ered with respect to each other.85. The method according to any one cif claims 7684, wherein the additional layer is a central layer of the composite material and the composite material layers are symmetrical about the central layer.86. A method for preparing a fibre reinforced resin matrix composite material, the method comprising the steps of: (i) providing a prepreg according to any one of claims 1-33; (ii) providing a heated premould; (iii) loading the prepreg into the premould; (iv) optionally subjecting the prepreg to a temperature of from 0 to 150' and/or a pressure of from 0,01 to /0 bar so as to increase the rigidity in the layers of the prepreg and form a preform; (v) providing a mould; (vi) loading the preform into a cavity the mould such that the surface film is located toward a moulding surface of the mould; and (vii) subjecting the preform to a moulding step, the moulding step comprising applying a vacuum to the cavity of the mould. and applying a closure load to the mould to generate a pressure in the cavity of the mould to cause at least a portion of the thermosetting resin to infuse into the fibrous layer to impregnate the carbon fibres and to filter at least a portion of the particulate filler material in the surface film to remain in the surface 87, The method according to any one of claims 68-86, wherein the moulding step is conducted at a pressure of from 6 to 100 bar, optionally from 6 to 50 bar, 88. The method according to any one of claims 68-87, wherein the moulding step is conducted at a temperature of from 80 to 250'C, optionally of from 120 to 220°C.