UD tape with improved processability and its manufacturing method

Abstract

The present invention relates to a method for producing a unidirectional tape, the method comprising the steps of: a) providing an impregnation slurry comprising primary particles, secondary particles, water, optionally an organic carrier medium, optionally an organic compound, and optionally a surface-active compound to provide a unidirectional fiber layer having an average inter-filament distance, wherein the primary particles comprise a first polymer, and the primary particles have a particle size equal to or smaller than the average inter-filament distance, and the secondary particles comprise a second polymer, and the secondary particles have a particle size larger than the average inter-filament distance; b) impregnating the unidirectional fiber layer with the impregnation slurry to form an impregnated unidirectional fiber web comprising an impregnated unidirectional fiber layer and a surface polymer layer, wherein the impregnated unidirectional fiber layer comprises unidirectional fibers and primary particles, preferably consisting only of unidirectional fibers and primary particles, and the surface polymer layer comprises secondary particles; and c) drying the impregnated unidirectional fiber web to obtain a unidirectional tape.

Description

[Technical field]

[0001] The present invention relates to a thermoplastic UD tape with improved processability and a method for producing the same.

[0002] Unidirectional tapes (UD tapes) are fiber-reinforced tapes of various widths that have been known for many years. The unidirectionally aligned reinforcing fibers are typically impregnated with a thermoplastic polymer, and the reinforcing fibers are usually carbon or glass fibers. Using UD tapes, structures can be formed that have advantageous structural properties such as high stiffness and strength as well as being lighter than structures formed with conventional materials. As a result, UD tapes are used in a wide range of industries, including the automotive, aerospace, and home appliance industries, for a variety of applications. Depending on the application, UD tapes may need to meet many criteria, including mechanical performance such as strength and stiffness, size, and weight criteria, as well as excellent processability and formability into complex shapes.

[0003] Subsequent processing of UD tapes typically involves melting the thermoplastic polymers present in the UD tapes to form a coherent laminate or multi-layer laminate. These steps include tacking, tape placement, tape laying, solidifying, and welding. Thus, most steps require the melting and interdiffusion of the thermoplastic polymers present at the interfaces of adjacent UD tapes to form a fully consolidated laminate.

[0004] There is a demand in the art for improved processability of UD tapes, meaning rapid adhesion, solidification properties, thermoforming behavior, and lateral flow for complex shapes. At the same time, UD tapes must have good mechanical properties such as toughness and stiffness. Furthermore, special applications, such as the aerospace sector, additionally require UD tapes to have good electrical and / or thermal conductivity. Certain other applications require UD tapes to have electrical insulating properties.

[0005] Therefore, there is a need in the art to provide UD tapes that have improved processability and at the same time excellent mechanical properties.

[0006] There is also a need in the art to provide UD tapes that have improved processability, good mechanical properties and at the same time good electrical and / or thermal conductivity.

[0007] There is also a need in the art to provide UD tapes that have improved processability, good mechanical properties as well as good electrical insulation.

[0008] It is therefore an object of the present invention to provide a UD tape which has improved processability and at the same time excellent mechanical properties.

[0009] It is a further object of the present invention to provide a UD tape that has rapid adhesion, improved setting characteristics, improved thermoforming behavior, and improved lateral flow for complex shapes, while at the same time having toughness and stiffness.

[0010] A further object of the present invention is to provide a UD tape having improved processability, excellent mechanical properties and at the same time excellent electrical and / or thermal conductivity.

[0011] A further object of the present invention is to provide a UD tape having improved processability, excellent mechanical properties and at the same time insulating properties.

[0012] It is also an object of the present invention to provide a method for producing a UD tape having these properties.

[0013] Surprisingly, it has been found that all of the above objectives can be achieved by a method for producing a UD tape with a polymer layer on top of a unidirectional fibre layer, i.e. a UD tape is produced with a surface polymer layer providing improved processability on a unidirectional fibre layer providing improved mechanical properties.

[0014] Even more surprisingly, it was found that the properties of the UD tape can be tuned in terms of electrical conductivity and / or insulation by functionalizing this surface polymer layer, where functionalization means incorporating non-polymeric components into the surface polymer layer in order to give it specific properties.

[0015] The present invention therefore provides a method for producing a unidirectional tape, the method comprising the steps of: a) providing an impregnation slurry comprising primary particles, secondary particles, water, optionally an organic carrier medium, optionally an organic compound, and optionally a surface active compound to provide a unidirectional fiber layer having an average interfilament distance, (i) the primary particles have a size equal to or smaller than the average interfilament spacing and the secondary particles have a size greater than the average interfilament spacing; and / or (ii) the primary particles have a particle size of 10 to 50 μm and the secondary particles have a particle size of 51 to 500 μm; and b) impregnating the unidirectional fibrous layer with the impregnating slurry to form an impregnated unidirectional fibrous web comprising an impregnated unidirectional fibrous layer and a surface polymer layer, the impregnated unidirectional fiber layer comprises unidirectional fibers and primary particles, preferably consisting of only unidirectional fibers and primary particles, and the surface polymer layer comprises secondary particles; c) drying the impregnated unidirectional fibrous web to obtain a unidirectional tape; Includes.

[0016] The invention further provides a unidirectional tape obtained by the method according to the invention.

[0017] The present invention also has several surprising advantages. The polymer of the surface polymer layer can be similar, identical, or different from the polymer in the unidirectional fiber layer to further optimize the mechanical and / or processing performance of the UP tape by simultaneously tailoring the properties of both the surface polymer layer and the unidirectional fiber layer.

[0018] For example, the surface polymer layer can be tailored to have, for example, an increased lateral flow, thereby resulting in improved processability of the UD tape. At the same time, the mechanical properties of the UD tape can be tailored by selecting suitable fibers and / or suitable polymers for the unidirectional fiber layer.

[0019] Furthermore, the formation of a surface polymer layer increases the polymer content present at the surface of the UD tape, which in turn reduces friction between the layers and between the mold and the composite laminate. Reduced friction improves formability, allowing faster forming and / or the forming of more complex shapes.

[0020] Furthermore, the present invention allows the fine-tuning of the properties of the UD tape by functionalizing this surface polymer layer. Functionalization means the incorporation of components other than polymers into the surface polymer layer in order to give it specific properties. These specific properties can be electrical conductivity or insulation. This functionalization can be easily achieved by the method of the present invention.

[0021] The method for producing a unidirectional tape (UD tape) according to the present invention will be described in more detail below.

[0022] In step a) a layer of unidirectional fibres having an average interfilament distance is provided.

[0023] The unidirectional fiber layer includes a plurality of unidirectional fibers. These unidirectional fibers are generally arranged in one direction. That is, the plurality of fibers are generally arranged parallel to each other. Preferably, at least 75% of the plurality of fibers of the unidirectional fiber layer are aligned in one direction, more preferably at least 80%, even more preferably at least 90%, and most preferably at least 95%. The unidirectional fibers include filaments or are composed of filaments only. The number of filaments forming one fiber may vary. Typically, one unidirectional fiber may be formed from 12,000 or 24,000 filaments. The diameter of the filaments is generally 5 to 7 μm.

[0024] The average interfilament distance between adjacent filaments in the unidirectional fiber layer is preferably 40 to 60 μm, more preferably 45 to 55 μm, more preferably 47 to 52 μm, more preferably 49 to 51 μm, and most preferably 50 μm.

[0025] The average interfilament distance of the unidirectional fiber layer is measured before the unidirectional fiber layer is impregnated. The average interfilament distance of the unidirectional fiber layer can be adjusted, for example, by using a gripping or drawing device commonly used in drawing processes. The gripping or drawing device can be, for example, a rotating mandrel. The gripping or drawing device keeps the unidirectional fibers in tension during the process of the present invention. Thus, the average interfilament distance of the unidirectional fiber layer can be adjusted by changing the tension applied to the fibers by the gripping or drawing device.

[0026] The process of the present invention is preferably carried out as a drawing process.

[0027] The average interfilament distance can be calculated, for example, by optical microscopy, where the interfilament distance is measured at least three times between adjacent filaments of the fibers for at least five fibers, and the average interfilament distance is calculated as the arithmetic mean.

[0028] The unidirectional fiber layer has two opposing surfaces, a first surface and a second surface, and a surface polymer layer is formed on either the first surface or the second surface, or on both the first surface and the second surface.

[0029] The impregnation slurry used in the method of the present invention comprises primary particles, secondary particles, water, optionally a surfactant, optionally an organic support medium, optionally an organic compound, and optionally a surface active compound.

[0030] The impregnation slurry of step a) comprises primary particles and secondary particles, the particle size of the secondary particles being larger than the particle size of the primary particles.

[0031] The primary particles include the first polymer, and preferably consist of only the first polymer. The primary particles either (i) have a particle size equal to or smaller than the average interfilament distance, or (ii) have a particle size of 10 to 50 μm, more preferably 15 to 40 μm, and even more preferably 20 to 30 μm.

[0032] In this way, by appropriately selecting the particle size of the primary particles taking into account the average interfilament distance, the primary particles can be attached, i.e., bonded, between adjacent filaments during impregnation, i.e., the primary particles can penetrate into the impregnated unidirectional fiber layer.

[0033] The secondary particles contain the second polymer, and preferably consist of only the second polymer. The secondary particles either (i) have a particle size larger than the average interfilament distance, or (ii) have a particle size of 51 to 500 μm, more preferably 70 to 400 μm, and even more preferably 100 to 300 μm.

[0034] By appropriately selecting the particle size of the secondary particles in consideration of the average inter-filament distance, the secondary particles are prevented from penetrating between adjacent filaments in the unidirectional fiber layer. The secondary particles remain on the surface of the unidirectional fiber layer. That is, most of the secondary particles are preferably attached only to the surface of the unidirectional fiber layer, i.e., adhere only to the surface.

[0035] The particle size was measured by laser diffraction analysis using a laser diffraction particle size distribution analyzer S3500 available from Microtrac.

[0036] Preferably, the impregnation slurry does not contain primary particles having a particle size larger than the average interfilament distance and / or does not contain secondary particles having a particle size equal to or smaller than the average interfilament distance.

[0037] Preferably, the impregnation slurry does not contain primary particles having a particle size greater than 50 μm, greater than 55 μm, or greater than 60 μm, and / or does not contain secondary particles having a particle size smaller than 51 μm, or smaller than 45 μm, or smaller than 40 μm.

[0038] The primary particles and the secondary particles can be preferably obtained by grinding the first polymer and the second polymer, respectively, and using a sieve to obtain the primary particles and the secondary particles having the desired particle size.

[0039] The weight ratio of the primary particles to the secondary particles in the impregnation slurry in step a) is preferably 90:10 to 70:30, more preferably 85:15 to 75:25, and most preferably 80:20.

[0040] Preferably, the water is deionized water.

[0041] Preferably, the organic support medium comprises an alcohol.

[0042] Preferably, the organic compound comprises an antifoaming agent.

[0043] Preferably, the surface active compound comprises a surfactant. The surfactant is preferably a non-ionic surfactant and / or an anionic surfactant. The non-ionic surfactant preferably comprises polyethylene glycol. The anionic surfactant preferably comprises a sulfate group, a sulfonate group, a phosphate group, or a carboxylate group.

[0044] In step b), the unidirectional fibrous layer is impregnated with an impregnation slurry to form an impregnated unidirectional fibrous web.

[0045] Preferably, step b) is carried out in an impregnation vessel, i.e. a vessel containing the impregnation slurry. The unidirectional fibre layer is impregnated with the impregnation slurry, preferably by moving or drawing the unidirectional fibre layer through the impregnation vessel. The moving or drawing is preferably carried out by a gripping or drawing device, e.g. a rotating mandrel. The gripping or drawing device is usually located downstream of the impregnation vessel or impregnation step b). Preferably, the impregnation slurry is stirred during step b).

[0046] In step b), the unidirectional fiber layer is impregnated with the impregnation slurry to form an impregnated unidirectional fiber web, the impregnated unidirectional fiber web including an impregnated unidirectional fiber layer and a surface polymer layer, the surface polymer layer being adjacent to the impregnated unidirectional fiber layer.

[0047] The impregnated unidirectional fiber layer comprises unidirectional fibers and primary particles, preferably consisting of only unidirectional fibers and primary particles. As mentioned above, the average particle size of the primary particles is equal to or smaller than the average interfilament distance between adjacent filaments in the unidirectional fiber layer. This allows the primary particles to be attached, i.e. adhered, between adjacent filaments in the impregnation step b), i.e. the primary particles can penetrate into the impregnated unidirectional fiber layer.

[0048] The surface polymer layer includes secondary particles. As mentioned above, the particle size of the secondary particles is preferably larger than the average distance between adjacent unidirectional fibers in the unidirectional fiber layer. Unlike the primary particles, the secondary particles cannot penetrate into the unidirectional fiber layer and remain on its surface. That is, the secondary particles only attach to the surface of the unidirectional fiber layer, i.e., they only adhere to the surface. Therefore, the surface polymer layer is formed by the secondary particles and only a small amount, if any, of the primary particles. Therefore, the surface polymer layer can also be indicated as a "polymer-rich layer", or more precisely, a "second polymer-rich layer".

[0049] Preferably, there are no other layers located between the impregnated unidirectional fiber layer and the surface polymer layer.

[0050] The method further comprises, after step b), a step of drying the impregnated unidirectional fibrous web to obtain a unidirectional tape. Drying can be performed in an oven, preferably by an oven comprising an infrared heater. During drying, water and surfactants, if present, evaporate and the primary and secondary particles of the impregnated unidirectional fibrous web are melted.

[0051] The thickness of the surface polymer layer is preferably 1 to 15 μm, more preferably 2 to 10 μm, and most preferably 4 to 6 μm.

[0052] Preferably, the first polymer and / or the second polymer are thermoplastic polymers, more preferably, both the first polymer and the second polymer are thermoplastic polymers.

[0053] Preferably, the thermoplastic polymer is a polymer of one class selected from a list of multiple classes, the list of multiple classes consisting of polyaryletherketone (PAEK)-based polymer materials, polyphenylene sulfide (PPS), polyetherimide (PEI), polyethersulfone (PESU, PES), and polysulfone (PSU); more preferably, the thermoplastic polymer is a polymer of one class selected from a list of multiple classes, the list of multiple classes consisting of polyaryletherketone (PAEK)-based polymer materials or polyetherimide (PEI).

[0054] The polyaryletherketone (PAEK) based polymeric material is one of a plurality of classes of thermoplastic polymers. Preferably, the polyaryletherketone (PAEK) based polymeric material is a polymer of one subclass selected from a list of a plurality of subclasses, the list of the plurality of subclasses being polyetherketone (poly-ether-ketone: PEK), polyetheretherketone (polyether-ether-ketone: PEEK), polyetheretherketoneketone (poly-ether-ether-ketone-ketone: PEEKK), polyetheretherketoneketone (poly-ether-ether-ketone-ketone: PEKK), polyetherketoneetherketoneketone (poly-ether-ketone-ether-ketone: PEE ... Polyaryletherketone (PAEK)-based polymeric materials having reactive (end) groups, copolymers thereof, and mixtures thereof. More preferably, the polyaryletherketone (PAEK)-based polymeric materials are a subclass of polymers selected from a list of a plurality of subclasses, the list of the plurality of subclasses being composed of polyetheretherketoneketone (PEKK), polyetherdiphenyletherketone (PEDEK), polyetheretherketone (PEEEK), polyetherdiphenyletherketone (PEDEK), and copolymers thereof.

[0055] Preferably, the first polymer is of the same class or subclass of polymer as the second polymer, or the first polymer is of a different class or subclass of polymer than the second polymer.

[0056] When the first polymer is of the same class or subclass as the second polymer, only one class of polymer is present in the impregnated unidirectional fiber web or tape. When the first polymer is of the same class or subclass as the second polymer, it is preferred that the first polymer differs from the second polymer in weight average molecular weight, branching, any substituted end groups and / or copolymer composition.

[0057] An advantage of the first polymer being of a class or subclass of polymer other than the second polymer is that the second polymer can be specifically selected to form the surface polymer layer.

[0058] Preferably, the unidirectional fibers are carbon fibers and / or glass fibers and / or quartz, more preferably carbon fibers. The unidirectional fibers are preferably continuous fibers, more preferably continuous carbon fibers.

[0059] Preferably, in step b), an impregnated unidirectional fibrous web is formed comprising an impregnated unidirectional fibrous layer and two surface polymer layers located on either side of the impregnated unidirectional fibrous layer, the two surface polymer layers comprising secondary particles.

[0060] That is, the impregnated unidirectional fiber layer is sandwiched between two surface polymer layers, both of which contain or consist exclusively of secondary particles, with the advantage that both surfaces of the UD tape can be conditioned and / or functionalized as described herein.

[0061] As mentioned above, the surface polymer layer can be functionalized. Functionalization means incorporating further components into the surface polymer layer in order to give it certain properties. These properties are preferably electrically conductive or insulating. In such a case, the surface polymer layer can also be indicated as a "functionalized surface polymer layer". Such functionalization is achieved by adding further components to the secondary particles.

[0062] Preferably, the secondary particles further comprise an electrically conductive component and / or an electrically insulating component.

[0063] Preferably, the conductive component is a metal or a carbon-based component. Preferably, the metal is in the form of particles. The size of the metal particles must be smaller than the size of the secondary particles. Preferably, the metal is copper and / or bronze and / or the carbon-based component is selected from the group consisting of carbon fibers, carbon black, graphene and mixtures thereof. The conductive component is preferably mixed, more preferably melt mixed, with the secondary particles comprising the second polymer, preferably before step a).

[0064] The electrical conductivity of the surface polymer layer is advantageous not only in applications where electrical conductivity is desired, but also in some cases where high electrical conductivity is required in consideration of the possibility of a lightning strike, in which case the electrically conductive surface polymer layer acts as a lightning protection.

[0065] Preferably, the electrically insulating component is a ceramic particle, the size of which should be smaller than the size of the secondary particles.

[0066] Preferably, the unidirectional fiber layer in step b) further comprises one or more conductive wires on the surface of the unidirectional fiber layer, or one or more conductive wires are introduced into the surface polymer layer after step b). Preferably, the conductive wires are copper wires. The one or more conductive wires can be present or laid on one or both sides of the unidirectional fiber layer. Then, from step b) of the method, the processing of the unidirectional fiber layer with the one or more conductive wires begins.

[0067] Alternatively, one or more conductive wires are preferably introduced into the surface polymer layer after step b). One or more conductive wires can be laid on one or both sides of the impregnated unidirectional fibrous layer either after step b) and before step c), or after step c).

[0068] It is also possible after step c) to introduce one or more conductive wires into the surface polymer layer by melting the surface polymer layer, introducing one or more conductive wires into the molten surface polymer layer and solidifying the surface polymer layer, for example by cooling.

[0069] Preferably, the method according to the invention further comprises a step d) of electrostatically depositing tertiary particles on the surface polymer layer, more preferably on both surface polymer layers. This allows the formation of an additional surface polymer layer, which comprises or is composed of tertiary particles, on one or both surface polymer layers of the unidirectional tape. This means that a unidirectional tape with one or two additional surface polymer layers can be obtained. The one or two additional surface layers are preferably the outermost layers of the unidirectional tape. This allows the adaptation and fine-tuning of the surface properties of the UD tape, especially for a specific application.

[0070] Preferably, electrostatic deposition is accomplished by electrospraying, preferably using one or more spray guns.

[0071] Step d) is preferably carried out before or after step c), more preferably after step c). Preferably, after step d), the unidirectional tape with the one or two additional surface polymer layers is dried or solidified.

[0072] The tertiary particles comprise a third polymer, preferably composed only of the third polymer. Preferably, the third polymer is a thermoplastic polymer. The thermoplastic polymer is the same as that described herein above for the first and second polymers. Preferably, the third polymer is a polymer of the same class or subclass as the first and / or second polymer, or the third polymer is a polymer of a class or subclass other than the first and / or second polymer.

[0073] The tertiary particles preferably have a particle size of 10 μm to 500 μm, more preferably 15 to 250 μm, and most preferably 20 to 200 μm. The size of the tertiary particles must be such that they can be electrostatically deposited, more preferably by electrospray. The particle size is measured by laser diffraction analysis as described above.

[0074] The invention also relates to a unidirectional tape obtained by the method according to the invention. All embodiments of the method according to the invention described above are also preferred embodiments of the unidirectional tape obtained by the method according to the invention.

[0075] The present invention also relates to an impregnated unidirectional fibrous web comprising an impregnated unidirectional fibrous layer having an average impregnated filament spacing and a surface polymer layer, The impregnated unidirectional fiber layer comprises unidirectional fibers and primary particles comprising a first polymer, preferably consisting of only unidirectional fibers and primary particles comprising a first polymer, and the surface polymer layer comprises secondary particles comprising a second polymer; i) the primary particles have a particle size equal to or smaller than the average inter-filament spacing and the secondary particles have a particle size greater than the average inter-filament spacing; and / or ii) the primary particles have a particle size of 10 to 50 μm and the secondary particles have a particle size of 51 to 500 μm; Either:

[0076] All embodiments of the inventive method described above, where applicable, are also preferred embodiments of the impregnated unidirectional fibrous web.

[0077] The average interfilament distance between adjacent filaments in the impregnated unidirectional fiber layer is preferably 40 to 60 μm, more preferably 45 to 55 μm, more preferably 47 to 52 μm, more preferably 49 to 51 μm, and most preferably 50 μm.

[0078] After the unidirectional fiber layer is impregnated, the average wetted filament spacing of the impregnated unidirectional fiber layer is measured.

[0079] The average interfilament distance can be calculated, for example, by optical microscopy. The wetted interfilament distance is measured at least three times between adjacent filaments of the fibers for at least five fibers, and the average wetted interfilament distance is calculated as the arithmetic mean.

[0080] Preferably, the first polymer is the same as the second polymer, or the first polymer is different from the second polymer. The first and second polymers are preferably as described above for the method.

[0081] Preferably, the secondary particles further comprise an electrically conductive component, and / or a thermally conductive component, and / or an electrically insulating component.

[0082] Preferably, the surface polymer layer further comprises one or more conductive wires, the more conductive wires being preferably copper wires.

Claims

1. A method for producing a unidirectional tape, comprising the steps of: a) providing an impregnation slurry comprising primary particles, secondary particles, and water to provide a unidirectional fiber layer having an average filament-to-filament distance, the primary particles include a first polymer and the secondary particles include a second polymer; (i) the primary particles have a particle size equal to or smaller than the average interfilament distance, and the secondary particles have a particle size greater than the average interfilament distance; or (ii) the primary particles have a particle size of 10 to 50 μm and the secondary particles have a particle size of 51 to 500 μm; and b) impregnating the unidirectional fibrous layer with the impregnating slurry to form an impregnated unidirectional fibrous web comprising an impregnated unidirectional fibrous layer and a surface polymer layer, the impregnated unidirectional fiber layer includes unidirectional fibers and the primary particles, and the surface polymer layer includes the secondary particles; c) drying the impregnated unidirectional fibrous web to obtain a unidirectional tape; The method includes:

2. The method of claim 1 , wherein the first polymer and / or the second polymer is a thermoplastic polymer.

3. 3. The method of claim 2, wherein the thermoplastic polymer is a class of polymer selected from a list of classes, the list of classes consisting of polyaryletherketone (PAEK) based polymeric materials, polyphenylene sulphide (PPS), polyetherimide (PEI), polyethersulfone (PESU, PES), and polysulfone (PSU).

4. The polyaryletherketone (PAEK)-based polymer material is a polymer of one subclass selected from a list of a plurality of subclasses, the list of the plurality of subclasses being polyetherketone (poly-ether-ketone: PEK), polyetheretherketone (polyether-ether-ketone: PEEK), polyetheretherketoneketone (poly-ether-ether-ketone-ketone: PEEKK), polyetheretherketoneketone (poly-ether-ether-ketone-ketone: PEKK), and polyetherketoneetherketoneketone (poly-ether-ketone-ether-ketone-ketone).

4. The method of claim 3, wherein the polymeric material is selected from the group consisting of polyetheretherketone-etherketone (PEKEKK), poly-ether-ether-ketone-ether-ketone (PEEKEK), poly-ether-ether-ether-ketone (PEEEK), poly-ether-diphenyl-ether-ketone (PEDEK), meta-polyether-ether-ketone (PEmEK), polyaryletherketone (PAEK) based polymeric materials having reactive (end) groups, copolymers thereof, and mixtures thereof.

5. 5. The method of claim 3 or 4, wherein the first polymer is of the same class or subclass as the second polymer, or the first polymer is of a class or subclass other than the second polymer.

6. 6. The method according to claim 1, wherein the unidirectional fibres are carbon fibres and / or glass fibres and / or quartz.

7. Step b) comprises impregnating a unidirectional fibrous layer with the impregnating slurry to form an impregnated unidirectional fibrous web comprising an impregnated unidirectional fibrous layer and two surface polymer layers; the two surface polymer layers being located on either side of the unidirectional fiber layer; The unidirectional fiber layer includes unidirectional fibers and primary particles, The two surface polymer layers include secondary particles; 7. The method according to any one of claims 1 to 6.

8. The method of claim 1 , wherein the secondary particles further comprise an electrically conductive component and / or an electrically insulating component.

9. The method of claim 8 , wherein the electrically conductive component is a metallic and / or carbon-based component and / or the electrically insulating component is a ceramic particle.

10. 10. The method of claim 1, further comprising a step d) of electrostatically depositing tertiary particles onto the surface polymer layer.

11. 11. The method according to claim 1, wherein the unidirectional fiber layer in step b) further comprises one or more conductive wires on the surface of the unidirectional fiber layer or one or more conductive wires are introduced into the surface polymer layer after step b).

12. An impregnated unidirectional fibrous web comprising an impregnated unidirectional fibrous layer having an average impregnated filament spacing and a surface polymer layer, The impregnated unidirectional fiber layer includes unidirectional fibers and primary particles including a first polymer, and the surface polymer layer includes secondary particles including a second polymer; i) the primary particles have a particle size equal to or smaller than the average wetted filament spacing and the secondary particles have a particle size greater than the average wetted filament spacing; or ii) the primary particles have a particle size of 10 to 50 μm and the secondary particles have a particle size of 51 to 500 μm; Either Impregnated unidirectional fibrous web.

13. 13. The impregnated unidirectional fibrous web of claim 12, wherein the first polymer is the same as the second polymer or the first polymer is different from the second polymer.

14. The secondary particles further comprise an electrically conductive component and / or an electrically insulating component, or The surface polymer layer further comprises one or more conductive wires.

14. An impregnated unidirectional fibrous web according to claim 12 or 13.