Manufacturing process of nanofiber membrane reinforced composite and nanofiber membrane for the process

Abstract

A composite material and a method for producing such a composite reinforcement material are disclosed, comprising the steps of: arranging a plurality of layers of reinforcing fibers, impregnating said layers with a resin matrix, laminating said layers of reinforcing fibers by increasing pressure and / or heat, placing an intermediate layer of polymeric nanofibers between said layers of reinforcing fibers, wherein said intermediate layer of polymeric nanofibers, prior to said step of laminating, is interwoven between said layers of reinforcing fibers by laying down a film of polymeric nanofibers adhered to a backing substrate, said film of polymeric nanofibers being obtained by direct electrospinning on a backing substrate by needleless technology, and wherein prior to said step of laminating, a sedimentation prevention property is provided which prevents said film of polymeric nanofibers from prematurely sinking into said resin matrix.

Description

Technical Field

[0001] This invention relates to a manufacturing process for a composite material having a nanofiber membrane, and a nanofiber membrane for use in this process. Background Technology

[0002] Composite materials are typically materials with reinforcing components, usually consisting of high-strength fibers in random or woven form, and a matrix component, such as resin, that holds the reinforcing components in place and protects them from the effects of the external environment.

[0003] Composite materials can be thermoplastic or thermosetting, depending on the matrix composition used. Reinforcing components can take many forms, such as filament bundles, rovings, tows, chopped fibers, nonwovens, woven fabrics, mats, tapes, microspheres, and various nanospheres, while the most commonly used fiber types are carbon / graphite fibers, aramid fibers, and glass fibers.

[0004] To assemble structural components, composite materials are typically laminated, which involves bonding several thin layers together (prepreg or resin impregnated during lamination) and applying pressure and heat to achieve curing or crosslinking.

[0005] One of the most significant problems in composite materials is delamination, which is the evolution of fractures that propagate between one layer and another in a laminated composite.

[0006] Over the years, it has been found that the possibility of effectively binding the layers together by arranging a certain number of microfibers (i.e., fibers with a diameter much smaller than that of the main reinforcing fibers) between one layer of a laminated composite material and acting as a filler and adhesive between the resin matrix and the reinforcing fiber pad is greatly reduced.

[0007] It has also been suggested that nanofibers obtained by electrospinning from nozzles are commonly used.

[0008] For example, U.S. Patent 6265333 describes a process for producing prepreg composite materials, which envisions polymeric microfibers and nanofibers obtained through electrospinning.

[0009] Regarding basic research, there are also some scientific articles involving similar technologies. For example, T. Brugo a, R. Palazzetti, “Influence of Nylon 6,6 Nanofiber Pad Thickness on Mode I-II Fracture Mechanics of UD and Braided Composite Laminates,” published in Composite Structures 154 (2016), pp. 172-178, describes the experimental characterization of carbon fiber and epoxy resin composites interwoven with nylon 6,6 nanofibers.

[0010] However, while these existing technical documents provide general information on potential technologies that can be used to reduce the problem of nanofiber delamination, they do not address the problems encountered in industrial settings to practically reduce these theoretical and empirical concepts.

[0011] In particular, it has been noted that electrospinning technology is almost the ideal method to obtain nanofibers to improve the toughness of composites, but a satisfactory method for introducing nanofibers into composites that is repeatable, fast, and does not have a negative impact on prepreg fabrics is still needed in industrial production environments.

[0012] More information on processing nanofiber membranes is disclosed in US2011 / 259518. Other examples of nanofiber membranes in the field of composite materials are disclosed in US2016 / 010249, GB2568105, CN112810259 and US2015 / 086743. Summary of the Invention

[0013] Therefore, the object of the present invention is to provide a composite material production process in which the introduction of polymer nanofibers to improve the toughness of the product relative to delamination is simple and relatively inexpensive.

[0014] This objective is achieved through the methods and membranes disclosed in the basic clauses of the appended claims.

[0015] The dependent claims disclose specific and advantageous features.

[0016] Specifically, according to the first aspect of this study, a method for manufacturing a composite reinforced material is disclosed, comprising the following steps:

[0017] Arrange multiple layers of reinforcing fibers,

[0018] The layer is impregnated with a resin matrix.

[0019] The reinforcing fiber layers are laminated by increasing pressure and / or heat, with an intermediate layer of polymer nanofibers placed between the reinforcing fiber layers.

[0020] in

[0021] The intermediate layer of the polymer nanofibers, prior to the laying of the second reinforcing fiber layer and the lamination step, is formed by laying a polymer nanofiber film adhered to a backing substrate on the first reinforcing fiber layer, interwoven between the reinforcing fiber layers.

[0022] The polymer nanofiber membrane is obtained by direct electrospinning on a backing substrate using a needle-free technique, and wherein...

[0023] Prior to the lamination step, anti-settling properties are provided to prevent the polymer nanofiber membrane from prematurely settling into the resin matrix.

[0024] Preferably, the polymer film consists of a PA 6 solution and a solvent containing acetic acid and formic acid. The solution may contain about 12% by weight of PA 6.

[0025] According to a preferred embodiment, the resin matrix is ​​a cross-linked thermosetting resin. Furthermore, the composite reinforcing material includes a reinforcing fiber layer made of carbon.

[0026] According to another aspect, the amount of nanofibers adhering to the backing substrate for forming the polymer film is between 1 and 15 g / m². 2 between.

[0027] Preferably, the nanofibers constituting the polymer film have a size of about 100-150 nm.

[0028] According to another preferred aspect, the backing substrate is an easy-peel backing substrate made of double-siliconized paper mesh, which is removed before the second layer of reinforcing fibers is laid and the lamination step is performed.

[0029] Another related aspect is that the anti-settling properties may include treating the polymer nanofiber membrane with an oil-resistant surface treatment prior to the laying step, or treating the resin matrix with a material having low affinity.

[0030] According to another aspect of the invention, a polymer film is provided, which serves as an intermediate layer between reinforcing fiber layers within a composite resin matrix material, the polymer film comprising electrospun nanofibers spun into a film using a needle-free technique, the film being deposited on a continuous backing substrate having an easily peelable surface. Attached Figure Description

[0031] Further features and advantages of the process and membrane according to the invention will in any event become more apparent from the following detailed description of the same preferred embodiments, provided purely by way of non-limiting example and illustrated in the accompanying drawings, wherein:

[0032] Figure 1 This is a schematic diagram of an exemplary membrane production facility according to the present invention; and

[0033] Figure 2A-2D These are SEM views of the membrane according to the present invention at different magnifications. Detailed Implementation

[0034] The composite material is prepared in a manner known per se, for example by weaving a fabric layer of reinforcing fibers, such as carbon fibers, and impregnating the fabric layer with a suitable resin matrix, such as a cross-linked thermosetting resin (e.g., epoxy resin). Resin impregnation can be performed during the manufacturing process of the composite material or at a stage prior to the storage phase, thereby providing a prepreg fabric.

[0035] Components based on reinforcing fibers—hereinafter referred to as mats—can also be constructed in another way, for example, as nonwoven fabric made of cut fibers.

[0036] The starting composite material, whether it consists only of reinforcing fibers or prepreg, is preferably in the form of a continuous pad roller.

[0037] In the preparation of composite material products, two or more layers of reinforcing fiber pads are pressed together and inserted or embedded into the resin matrix.

[0038] Before laminating two layers of composite material, an intermediate component based on nanofibers is inserted between them, preferably by laying the intermediate component on the first layer and then applying the other layer on top of the first layer.

[0039] According to the invention, the intermediate component comprises a nanofiber membrane obtained by electrospinning a polymer, particularly a polymer membrane obtained from continuous electrospinning according to the method specified below. In practice, this yields a continuous, uniform membrane deposited on an easily peelable substrate, which makes the industrial incorporation process efficient, as will be seen later.

[0040] To fabricate nanofiber polymer membranes, a suitable polymer solution must first be prepared. The polymer-solvent pair to be electrolyzed differs from the desired polymer: according to preferred embodiments, a pair of products proven particularly effective for composite applications is polyamide 6 (PA6) – for example, BASF's trade name Ultramid B24N 03 – dissolved in a mixture of acetic acid and formic acid – for example, a product marketed by Carlo Erba Reagents. Another polymer / solvent pair is polyvinylidene fluoride (PVDF) dissolved in dimethylacetamide or dimethylformamide, for example, but other technical polymers with specific properties can be added, such as, but not limited to, polyimide, polyethersulfone, polysulfone, and polydecanoic acid.

[0041] A feasible solution process involves metering the correct amount of the component to be prepared and placing it in a suitable temperature-controlled container, such as a thermostatic container. A precise amount of solvent for preparing the polymer solution is introduced into the container, and the metered polymer is added in granular or powder form. Preferably, the system is capable of directly recovering the solvent used in the raw material tank provided by the manufacturer and keeping it continuously agitated by an internal stirrer. To promote the dissolution of the polymer in the solvent, the contents are stirred by a mixer, and a gentle heating process can also be performed in the mixer to promote dissolution.

[0042] In the preferred embodiments disclosed herein, a PA6 solution of 12% by weight is preferably used. For example, the following ratio is used for 1000g of material:

[0043] -120g PA6 (12% by weight)

[0044] -587 grams of glacial acetic acid (58.7% by weight)

[0045] -293 grams of formic acid (29.3% by weight)

[0046] The ratio of acetic acid to formic acid is 2:1, and this ratio remains constant even when the general concentration of the solution varies. For example, increasing the overall concentration of PA6 can proportionally decrease both acids while maintaining their ratio.

[0047] Once the solution has dissolved completely (clear solution) and the material has been kept at room temperature, the solution can be characterized before electrospinning can be performed.

[0048] Specifically, it is advantageous to perform three different characterizations, which is essential for obtaining stable and repeatable electrospinning processes over time using the techniques suggested here.

[0049] 1) Assess the viscosity (h) of the solution using a rotational viscometer. Generally, the viscosity of polymer solutions ranges from 50 to 10,000 mPa·s. Preferably, solutions with a viscosity range from a minimum of about 120 mPa·s to a maximum of about 900 mPa·s are considered, depending on the concentration of the solution.

[0050] 2) The percentage concentration of the polymer solution is assessed by using heat equilibrium, which provides direct concentration data, or by oven drying. Typically, for polymer solutions, the concentration value ranges from 0.5% to 30% by weight, depending on the type of polymer and the solvent system. Preferably, solutions with a minimum concentration of 8% to a maximum of 25% by weight are envisioned.

[0051] 3) Assess conductivity (e) using a conductivity meter with an immersion probe. The conductivity value must be between 1 and 5000 mS / cm.

[0052] For industrial production optimization, it has been found that using 15-30 kg of solution per production batch is advantageous to avoid aging of the polymer solution and to optimize the dissolution method of the polymer in the solvent.

[0053] The resulting polymer solution is used to prepare nanofiber membranes on various types of easily peelable substrates via continuous electrospinning and needle-free electrospinning techniques.

[0054] Compared to the needle-type system mentioned in US 6265333, needleless electrospinning ensures industrial-grade (in meters) precision. 2 High productivity (in units of / h) and allows for the acquisition of materials with industrial efficiency.

[0055] Membranes produced using this technology, while exhibiting dimensional uniformity compared to other microfiber production techniques (i.e., hydroentangling and meltblown), also boast larger surface areas (due to the nanoscale size of the material) and can be produced even at low weights (at most 1 g / m³). 2 It can also be processed and manufactured during production, even at minimum thickness. These characteristics are crucial for not negatively impacting market requirements for composite materials, such as lightness and overall thickness.

[0056] There are four different macroscopic types of suitable backing substrates for manufacturing nanofiber layers: monofilament fabrics with calibrated mesh, nonwoven fabrics of various types and weights, single / double silicated papers of various weights, and polymer films of various thicknesses and surface finishes (e.g., based on HDPE, LDPE, etc.). For applications related to composite materials, the selection of the material for the electrospun polymer solution is particularly important. It must function solely as a carrier without altering the properties of the product. The optimal choice for such applications is double silicated paper, where the side in contact with the electrospun material has a larger release grade than the opposite side. This process allows for roll formation with sufficient internal tension (avoiding unwinding issues). The choice of silicated paper allows for the application of sufficient tensile stress to maintain complete flatness of the material during the coupling stage on the coating line, thus ensuring perfect adhesion of the nanofiber membrane to the resin used and subsequent removal of the substrate without causing membrane breakage or defects.

[0057] The release grade of the substrate must be precisely adjusted to allow for complete film separation, but also sufficient to ensure that the paper is retained in subsequent stages of cutting into sheets to protect the composite material, especially in fields such as aerospace, where cleaning is a mandatory requirement during the cutting stage.

[0058] Needleless electrospinning technology is based on purely physical principles and does not imply any transformation of the material at the level of chemical bonds. Such transformation occurs in solution, in the stage prior to electrospinning, or in subsequent surface treatments (such as plasma treatment).

[0059] like Figure 1 As shown, needleless electrospinning equipment is based on the absence of needles and static or rotating metal current collectors, but typically includes a pair of steel wires placed above each other at a distance, serving as the anode and cathode of the system. The number of these wire pairs can range from a minimum of one pair in pilot facilities to up to eight pairs in currently sold industrial plants.

[0060] In electrospinning, two conductors cross current through a voltage difference ranging from a minimum of 0 kV to a maximum of 120 kV. A potential difference is required for the spinning process to occur. In fact, the electric field, based on the properties of the polymer solution, causes the latter to be coldly "squeezed out" from the layer deposited on the cathode wire. The polymer solution moves towards the anode wire, where it is attracted. During its flight, the polymer solution thins and dries due to turbulent motion until it impacts the substrate used each time, which acts as a collector and flows a certain distance. Therefore, between the pair of conductors acting as the anode and cathode, there is a virtual plane that intercepts the electric field, along which the substrate moves.

[0061] The distance between the lower conductor (cathode) and the substrate is the working distance of the production line, and it is always shorter than the distance between the anode and the cathode.

[0062] To deposit the polymer solution onto the wire that acts as the cathode, the system is equipped with a deposition tray. The latter has a through-shell through which the cathode wire passes. Inside each shell is a steel device with calibrated feed holes (from 0.5 mm to 0.9 mm) within which the cathode wire resides, preventing contact between the individual metal components. These feed holes are located on the tray as part of the polymer solution feed piping system. The polymer solution, placed in a special container with a controlled atmosphere (to prevent solvent evaporation), is transferred to the feed holes at a set flow rate via one or more pumps controlled by the production line's control panel. Thus, the polymer solution, depending on the opening size of the feed holes, is deposited on the cathode wire in the form of a thin film as a trolley slides along the cathode wire, ranging from a minimum of 50 cm to a maximum of 200 cm depending on its extension on the production line.

[0063] The polymer solution is continuously dispensed regardless of the direction of the tray's back-and-forth sliding.

[0064] The lateral extension of the substrate is on the same order of magnitude as the distance traveled by the bracket. The substrate moves orthogonally to the sliding direction of the trolley at a certain sliding speed.

[0065] In the case of a specific substrate, the upper conductive wire that acts as the anode can be replaced by a conductive pad. The conductive pad rotates while the substrate moves to ensure the roll-to-roll process.

[0066] The entire electrospinning area is located in an area defined as the “electrospinning chamber”, which is in a controlled atmosphere, specifically in controlled relative humidity and temperature.

[0067] The most important parameter that can affect the final properties of the resulting membrane in this electrospinning process is:

[0068] - Concentration of polymer solution

[0069] - Viscosity of the polymer solution

[0070] - Conductivity of polymer solution

[0071] - Distance between electrodes (top and bottom)

[0072] -External electric field

[0073] - Relative humidity in the electrospinning machine room

[0074] -Speed ​​of the deposition cart

[0075] - Diameter of the steel hole installed on the trolley

[0076] - Wire diameter for depositing polymer solution

[0077] -Repetitive system pump

[0078] -Substrate displacement velocity

[0079] -Substrate type

[0080] - Voltage applied to the substrate

[0081] -Indoor air recirculation (inlet-outlet flow rate)

[0082] During the molding process, nanofibers fly between the wires and the collector and randomly deposit onto the substrate, forming a three-dimensional structure whose weight and thickness depend on the substrate's displacement velocity and therefore on the number of fibers deposited on it. When surface-functionalized for specific applications (e.g., air filtration), such a material with a three-dimensional structure weighs approximately 0.1 g / m³. 2 When used to characterize materials that can be defined as “self-supporting”, the weight gradually increases to a maximum of 15 g / m³. 2 That is, it can be processed without support. According to the present invention, the amount of nanofibers deposited on the substrate, for a specific application as a reinforcing interlayer in the composite material, is preferably 3 to 10 g / m², depending on the diameter of the produced nanofibers. 2 between.

[0083] Experimental tests show that approximately 3 g / m of the composite material... 2 The amount of nanofibers is sufficient to significantly improve its performance by approximately 40% compared to composites without nanofibers. When the fiber diameter is approximately 100-150 nm, the weight is approximately 7-8 g / m². 2 The fracture resistance of the composite material is improved by approximately 94%. However, it should be noted that during the composite lamination process, even when the weight limit is reached, such as 8-9 g / m³, the composite material's fracture resistance is improved. 2 The film is completely independent of the weight of the composite resin used, because these specific amounts are still below the error threshold that is typically added to fiber fabrics.

[0084] To achieve optimal performance, defining certain membrane and process parameters is crucial. In particular, to achieve optimal performance, it is essential to:

[0085] - Optimize resin usage related to film thickness

[0086] - Optimize the amount of resin based on the diameter of the nanofibers and the pore size of the membrane.

[0087] The melting temperature of PA6 nanofibers can be greater than 200°C, for example, 220°C, while the melting temperature of polyimide nanofibers can even be greater than 300°C. This makes the resulting films suitable for insertion into high-temperature composite materials used in aerospace, where the high temperatures involved do not allow for the use of toughening additives traditionally used in the automotive industry.

[0088] The nanofiber membranes obtained according to the present invention show that the role of the nanofibers mainly occurs at the interface between the resin and the next layer of fibers (e.g., carbon fibers). The material has a very high surface area and inherent porosity (approximately 80% of the free surface area, such as...). Figure 2A-2D (As shown in SEM images at different magnifications) and the strong oleophilicity of the nanofiber membrane, it was ensured that, under sufficient pressure during subsequent hot lamination, it was completely absorbed by the fluid resin and fixed within it after curing or crosslinking. Subsequent fracture strength tests on the surfaces of different layers in the composite material, i.e., at the weakest points of the material, typically revealed delamination between the composite layers, highlighting the benefits derived from the nanofiber insertion.

[0089] Composite materials loaded with nanofibers have a matrix at the interfaces between carbon fiber layers. This matrix contains not only resin but also these very long fibers with nanometer diameters, resulting from the random but consistent and uniform deposition of the nanofibers during electrospinning using a needle-free technique, ensuring their uniform distribution within the resin itself. During fracture testing (e.g., according to international standard D5528-13), the presence of nanofibers within the resin prevents fracture from propagating uniformly throughout the composite as in standard composites. This effect is likely due to the fracture line encountering a barrier each time it passes through the nanofiber layer incorporated into the resin. The better the intercontinence between the cured or cross-linked resin and the nanofibers, the more complex the fracture path, resulting in greater energy dissipation during fracture and thus slowing its progression. This non-uniform movement of fracture propagation leads to a significant increase in material strength.

[0090] The backing substrate or carrier formed and placed on the electrospun polymer film is easily rolled up, allowing for storage before use. In particular, the electrospun film deposited on a siliconized paper substrate allows for easy release of the material once the coupling stage with the pre-impregnated material and subsequent processing (e.g., cutting) is complete. This does not cause the film itself to break and poses no problem for the final handling of the end customer's parts. Using dual silicon paper immediately and clearly indicates which side of the film is deposited, thus making it immediately apparent which side is used when coupling with an impregnated composite pad (brown silicone paper – white film layer).

[0091] In the industrial process of incorporating nanofibers into composite products, once the reinforcing fiber pad is impregnated with a resin matrix, a backing substrate layer (especially a bisilicone sheet) can be unfolded and laid, with the polymer film facing the composite pad. The adhesion of the polymer film to the resin matrix on the composite pad is slightly higher than the separation force between the film and the backing substrate layer: subsequent continuous removal of the backing substrate layer allows the film to lie perfectly on the composite site material without tearing in the nanostructure of the film, and without decomposing the reinforcing fibers in the composite matrix (which currently still have low viscosity).

[0092] Once the support layer is removed, a composite material can be laminated on top of the first layer equipped with a polymer film, which can also be tightly bonded between the two layers by means of lamination pressure and possible lamination heat (which makes the resin more fluid).

[0093] To optimize the toughening properties of the composite material, according to the present invention, it is important to ensure that the nanofiber membrane layer does not sink into the prepreg at the interface with the other prepreg layer to be laminated therewith, but remains on the surface of the resin material (the resin film of the prepreg-coated composite pad). This potentially critical situation should be avoided, as it may reduce the advantages derived from using an intermediate nanofiber layer.

[0094] Therefore, in the manufacturing method of the present invention, anti-settling properties are advantageously provided to prevent the nanofiber membrane from prematurely settling into the resin matrix. Various anti-settling measures can be considered for this purpose:

[0095] One option is to optimize the final thickness of the nanofiber layer: a greater thickness can prevent sinking or cause only minimal sinking, thereby minimizing performance loss.

[0096] Related embodiments include an oil-resistant surface treatment deposited on a nanofiber material film: the solution can prevent the aforementioned phenomena that occur over time by reducing the ability of resin to wet and incorporate nanofibers.

[0097] In another embodiment, this phenomenon can be prevented by using more oil-resistant polymers (i.e., those with surface energy below 30 mN / m) or polymers with lower intrinsic affinity for resins to fabricate nanofiber membranes, due to the chemical properties of the materials.

[0098] Finally, another viable option is to use an intermediate layer made of a thin, uniform substrate of microfiber material, such as a wet-laid or melt-blown substrate made of a low surface energy polymer (<30 mN / m), attached to the nanofiber membrane layer. The thin layer of microfiber material can act as a mechanical support for the nanofiber membrane, preventing it from sinking into the resin. Furthermore, if chosen properly, this type of substrate can provide further reinforcement to the final composite material and can avoid providing a backing substrate to be removed in subsequent processing steps of the prepreg or composite material.

[0099] To develop new and increasingly industrially efficient materials, treatments designed to alter the reactivity of membrane surfaces are also envisioned. For example, treatments aimed at increasing surface hydrophilicity, or plasma treatments that simultaneously increase surface roughness and generate free radioactivity or reactive chemicals on the surface, could further enhance the adhesion of nanomaterials to resins, thereby further influencing performance improvements.

[0100] As can be understood from the description provided above, the method according to the invention allows for the full realization of the objectives described in the introduction.

[0101] Electrospinning and subsequent deposition of polymer nanofiber membranes on an easily peelable backing substrate enable a highly efficient industrial process. The backing substrate, for example, when made of release paper, can be peeled off during application, or, for example, when made of microfiber materials, can be retained in the composite material. Numerous adjustable parameters available in polymer nanofiber membrane production allow for flexible adjustment of the membrane's consistency and reactivity based on the nature and size of the components present in the composite material.

[0102] It goes without saying that the present invention should not be limited to the specific embodiments described and illustrated, but rather that different variations are possible, all of which are within the scope of those skilled in the art and do not depart from the scope of protection of the invention itself, as fully defined by the following claims.

Claims

1. A method for manufacturing a composite reinforced material, comprising the following steps: Arrange multiple layers of reinforcing fibers, The multilayer reinforcing fibers are impregnated with a resin-based matrix. The multilayer reinforcing fibers are laminated by applying pressure and / or heating, with a polymer nanofiber interlayer placed between the multilayer reinforcing fibers. Its features are, The polymer nanofiber interlayer is interleaved between the reinforcing fiber layers in the following manner: before laying the second layer of reinforcing fibers and performing the lamination step, the polymer nanofiber interlayer attached to the backing substrate is laid on the first layer of reinforcing fibers. After removing the backing substrate, a second layer of reinforcing fibers is laminated on top of the first layer of reinforcing fibers, which has been fitted with a polymer nanofiber interlayer. The polymer nanofiber interlayer is tightly bonded between the first and second reinforcing fibers by means of lamination pressure and possible lamination heat. The polymer nanofiber interlayer is obtained by direct electrospinning on the backing substrate using needle-free technology, and Anti-sinking measures are provided prior to the lamination step to ensure that the polymer nanofiber intermediate layer does not sink into the impregnated first layer of reinforcing fibers, but remains on the surface of the resin-based matrix material at the interface with another impregnated second layer of reinforcing fibers that will be laminated therewith. The anti-sinking measures include treating the polymer nanofiber intermediate layer with an oil-resistant surface before the laying step, or treating it with a material having low affinity for the resin-based matrix.

2. The method according to claim 1, characterized in that, The polymer nanofiber interlayer is obtained from a solution of PA 6 and solvents containing acetic acid and formic acid.

3. The method according to claim 2, characterized in that, The solution contains approximately 12% by weight of PA 6.

4. The method according to claim 1, characterized in that, The resin-based matrix is ​​a cross-linked thermosetting resin.

5. The method according to claim 4, characterized in that, The composite reinforcing material includes a reinforcing fiber layer made of carbon.

6. The method according to claim 1, characterized in that, The amount of nanofibers adhering to the backing substrate for forming the polymer nanofiber interlayer is between 1 and 15 g / m. 2 between.

7. The method according to claim 1, characterized in that, The nanofibers that make up the intermediate layer of the polymer nanofibers have a size of 100-150 nm.

8. The method according to claim 1, characterized in that, The backing substrate is an easy-peel backing substrate made of double-siliconized paper mesh, which is removed before the second layer of reinforcing fibers is laid and the lamination step is performed.

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