Two-component or multi-component fibers used in large composite material parts

Abstract

A bicomponent or multicomponent fiber 3 is used for the manufacture of a composite part, comprising a reinforcing core 1 of a first material and at least one sheath 2 of a thermoplastic or prepolymerized thermosetting second material, the matrix of which consists of the material of said sheath 2, said first material having a degradation temperature, ignition temperature, glass transition temperature, melting temperature or liquidus temperature higher than the melting temperature, flow temperature or softening temperature of said second material, said reinforcing core 1 having a core volume fraction v defined as the volume fraction of the reinforcing core 1 in the bicomponent or multicomponent fiber 3. f with a core volume fraction v f is in the range of 0.3 to 0.8, and along the longitudinal axis Z of the bicomponent or multicomponent fiber, the outer surface 4 of the sheath 2 has a corrugated shape, preferably an irregular corrugated shape.

Description

[Technical Field]

[0001] The present invention relates particularly to two-component or multi-component fibers for producing large composite parts, preforms based on such fibers, methods for producing such fibers, composite parts based on such fibers or preforms, and the use of such fibers for producing composite parts, etc. [Background technology]

[0002] Fiber-reinforced polymer composites are a well-established solution for industries that rely on high structural performance combined with lightweight properties. However, challenges remain in mass production, with many markets still needing to rely on cheaper but less efficient materials, while others must tolerate limited material choices and time-consuming production methods. This problem is even more pronounced when manufacturing large components, such as pipes, tanks, silos, ship hulls or other marine components, aircraft fuselages or wing components, rocket fairings, and turbine blades, including wind turbine blades.

[0003] Typically, large parts in this field are those that are too large to be processed by hydraulic presses (all dimensions exceeding 2m), but also include those that cannot be processed in an autoclave due to size limitations (all dimensions exceeding 10m to 40m).

[0004] For example, current wind turbine rotor designs feature blades longer than 50 meters, and offshore turbine blades exceed 100 meters. Because conventional metal-based designs do not provide the necessary performance, composite materials have become standard in this industry. Nevertheless, while rapid composite fabrication relies primarily on press technology and the use of thermoplastic polymers, current blades can only be manufactured using the time-consuming impregnation and curing of thermosetting resins, making mass production still problematic. Due to the long design life of 20-30 years, structural fatigue is a major concern in wind turbine blades, and material performance limits both structural efficiency and achievable component size.

[0005] Furthermore, most designs can only be realized by manufacturing multiple parts and then joining them using adhesives or mechanical fasteners such as bolts or rivets. This adds more weight to the structure and creates weakened areas where fatigue increases the likelihood of structural failure.

[0006] As more and more wind turbines are built, the disposal of older turbines is becoming an increasing problem. When they reach the end of their lifespan, thermosetting composite materials become waste and can only be incinerated or dumped in landfills.

[0007] Currently, composite components can only be manufactured using thermoplastic matrix polymers with presses or autoclaves because available intermediate materials can only be properly compacted at pressures higher than atmospheric pressure. Therefore, large components require significant capital investment, and the largest components, exceeding approximately 40 meters in length, cannot be manufactured from thermoplastic matrix composites at all. This severely limits the use of thermoplastic composites, which possess properties beneficial to both the design and production of large structures. The current state of technology for producing (wind) turbine blades or composite hulls, or other large composite components from the energy infrastructure, aerospace, or marine sectors, as well as industrial plant components, involves vacuum bagging of bare fiber fabrics combined with a thermosetting resin impregnation process, followed by curing, and often post-curing / tempering. However, for applications with the highest demands on mechanical performance, more expensive processing routes remain necessary, such as processing pre-impregnated fiber fabrics (prepregs) with thermoplastic or thermosetting matrix materials in an autoclave, or using expensive out-of-autoclave (OOA) prepregs (thermosetting materials only).

[0008] Patent Document 1 provides a fibrous material for reinforcing molding materials that exhibits improved dispersibility / mixability and a high reinforcing effect when compounded with hydraulic materials such as mortar and concrete, or various molding materials such as resins and rubber. Disclosed is a resin-impregnated fiber bundle, which is made by impregnating and integrating a thermoplastic resin (B) with a fibrous material (A) selected from organic fibers and inorganic fibers, and having an uneven surface, and is used as a fibrous material for reinforcing molding materials. The molding material is selected from hydraulic materials, synthetic resins, natural resins, synthetic rubbers, natural rubbers, and ceramic materials.

[0009] Patent Document 2 relates to an apparatus for producing at least one pre-impregnated preform from a plurality of dried semi-finished products or dried fabrics impregnated with resin. The apparatus comprises at least one first vacuum chamber and a flexible vacuum foil that clamps the at least one first vacuum chamber. The at least one preform is surrounded by the first vacuum chamber and the vacuum foil. At least one second vacuum chamber is provided, and the vacuum foil separates the at least one first vacuum chamber from the second vacuum chamber. The at least one first vacuum chamber is liquid-tight. The invention also relates to a method for producing at least one pre-impregnated preform using such an apparatus, and to a product obtained from this method. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2011-162905 [Patent Document 2] European Patent Application Publication No. 2481558 [Overview of the Initiative]

[0011] The present invention offers a unique solution to all of the aforementioned problems, particularly for cost-effectively producing large and extra-large thermoplastic or thermosetting composite parts of high mechanical quality in large quantities through a novel and innovative material architecture with a cost-effective and scalable manufacturing route, without investing in presses, autoclaves, or expensive OOA prepregs.

[0012] The present invention includes hybrid two-component fibers and / or multi-component fibers (BCF and / or MCF) having an irregular outer casing, methods for producing such fibers, and the use of such fibers in a vacuum bag molding process for producing composite structures.

[0013] These fibers comprise at least a rigid and tough reinforcing core fiber and a thermoplastic (including thermoplastic elastomer) or prepolymerized thermosetting sheath, the sheath forming the outermost layer of the fiber. "Prepolymerized thermosetting" means that the thermosetting (polymer) material is not yet fully cured and / or polymerized and can still be handled as a fluid at elevated temperatures, while maintaining its intrinsic shape at room temperature.

[0014] The core may consist of an organic material (polymer) or an inorganic material (ceramic, glass, basalt, carbon) that can be fiberized using conventional spinning methods (e.g., melt spinning, wet spinning, gap spinning), or its precursors can be fiberized in the same manner. Mixtures of core fibers, such as carbon and glass, are also possible, i.e., mixtures of different types of hybrid fibers. The sheath may consist of any thermoplastic or prepolymerized thermosetting material having a lower melting point, softening temperature, flow temperature (or glass transition temperature), or liquidus temperature (preferably, if present, all of these temperatures are lower than each of the core temperatures) than the core, and particularly and preferably, the sheath is an amorphous or semi-crystalline thermoplastic polymer. The solid sheath may be non-porous or foamy and may have an open-cell or closed-cell porous structure. Furthermore, the fibers may include one or more intermediate layers of additional material between the core and the sheath to modify the mechanical properties of the core-sheath interface or for functionalization, for example, to make the fibers conductive, magnetic, or to increase structural damping. The core is typically cylindrical with an arbitrary cross-sectional shape, particularly circular or nearly circular. However, core fibers can also have non-circular cross-sections, and therefore can be flat fibers with, for example, rectangular, elliptical, or cocoon-shaped cross-sections. Furthermore, the core can be hollow fibers (e.g., H-glass). The core can have any width, usually less than 20 μm. The cross-sectional shape of the sheath is arbitrary. The thickness or width of the sheath varies along the length of the fiber. This variation can be of any shape and may be periodic or irregular. The core may be completely covered by the sheath, or it may exhibit bare portions where the sheath thickness is zero. On average, the sheath can occupy 20% to 70% of the total volume of the fiber (excluding air and other gases from the total volume).

[0015] More generally, the present invention relates to the following subject: a two-component fiber or a multi-component fiber comprising a reinforcing core made of a first material (or a mixture of the first material) and at least one sheath made of a thermoplastic or prepolymerized thermosetting second material, which is suitable and suitable for the manufacture of composite components, wherein the matrix of the composite component is made of the material of the sheath.

[0016] The underlying concept behind this fiber is that the volume of the sheath is sufficient to produce an essentially airless composite component based on the proposed fiber, where the sheath material forms a matrix and the reinforcing fibers provided by the core are embedded within that matrix.

[0017] For this purpose, the reinforcing core has a core volume fraction defined as the volume fraction of the reinforcing core in a two-component or multi-component fiber, and this core volume fraction is in the range of 0.3 to 0.8, preferably 0.5 to 0.7. The volume fraction defined here is called the fiber volume content (FVG: Faservolumengehalt) according to DIN 16459. If the fiber core is a hollow fiber core, the void space within the core is counted as part of the volume fraction of the reinforcing core.

[0018] The minimum average amount of coating on the outermost sheath of a two-component or multi-component fiber is equal to the volume not occupied by the rest of the fiber, assuming close packing. In particular, for any given application with a desired volume content of the core material (which may be multiple) of the fiber, the average amount of coating on the outermost sheath is equal to the remaining volume content. That is, v f However, this is the desired volume fraction of the core material (which may be multiple) in the material that is ultimately compacted, and v s However, if it is the volume fraction of the outermost sheath among the fibers before compaction, then v s = 1 - v f This is the result. f Typical values ​​are in the range of 0.3 to 0.8. In particular, v in high-performance structural applicationsf Typical values ​​for this value are in the range of 0.5 to 0.7.

[0019] This concept is completely different from Patent Document 1, which is one of the prior art described above. In Patent Document 1, the fibers are not used without a matrix; that is, the fibers are not such that the actual matrix of the final part is provided solely by the fiber coating. It is explicitly stated that the fibers in Patent Document 1 are used with a matrix called a “molding material,” which is selected from hydraulic materials, synthetic resins, natural resins, synthetic rubber, natural rubber, and ceramic materials. In Patent Document 1, it is proposed that the fibers, or more precisely the fiber bundles of Patent Document 1, be mixed with such a matrix, and specifically, in

[0044] , the ratio of fibers is not more than 50 parts by mass per 100 parts by mass of cement. Therefore, in addition to the fiber coating, there is always a matrix present, and the ratio of this matrix is ​​very large. Consequently, the coating in Patent Document 1 is much thinner than that claimed in this invention, and therefore the core volume fraction is significantly higher than the upper limit of 0.8 claimed in this invention. Furthermore, looking at the actual purpose of Patent Document 1, there is no motivation to aim for a small core volume fraction below 0.9 in the intended use of Patent Document 1.

[0020] Furthermore, in certain uses in vacuum forming processes where the core volume fraction exceeds 0.8, voids remain, and the matrix material is insufficient to actually form a truly useful fiber-reinforced material. For the purpose aimed at in Patent Document 1, having a thick sheath is not meaningful, and therefore, those skilled in the art will understand from Patent Document 1 that the core volume fraction is well above 0.9.

[0021] For this type of hybrid fiber material presented in this specification, when the coating provides the entire amount of the matrix material of the final composite, the core volume ratio should be at most 0.8. This is because a higher proportion of fiber cores with a cylindrical or nearly cylindrical geometry leads to voids that impair the properties of the final part for high-density or maximum-density filling. In the case of a completely cylindrical fiber core with equal diameters, the maximum-density filling, i.e., triangular filling, is calculated to occupy a volume fraction of 0.91. That is, by definition, at a higher volume fraction, additional matrix material is required to fill the space between the core materials. However, practical applications further reserve the possibility of stacking fibers in different orientations, i.e., a layer of fibers oriented in one direction can be covered by another layer oriented in a different second direction. This arrangement does not allow triangular filling but maximizes square filling as the maximum-density configuration, in which case the maximum volume fraction is easily calculated to be at most 0.8. Therefore, in order to enable such an arrangement of fibers without leaving empty spaces, the core volume of the two-component or multi-component fibers should be at most 0.8. According to the proposed invention, the first material (core material (possibly plural)) has a degradation temperature, ignition temperature, glass transition temperature, melting temperature, or liquidus temperature (start) (preferably any one of these temperatures, a combination of these temperatures, or all of these temperatures) that is higher than the melting temperature of the outermost thermoplastic or prepolymerized thermosetting second material (in the case of a prepolymerized thermosetting material, the melting temperature is rather often a softening temperature or a flow temperature). It is preferred that all of these temperatures of the second material are lower than any of the temperatures of the first material. This feature is important in that when the second material (sheath material) melts or softens due to a temperature increase and becomes processable, the first material (core material) or its mixture does not lose its mechanical properties, particularly its elastic properties.

[0022] Furthermore, and importantly, the outer surface of the sheath has a wavy shape along the longitudinal axis of the bicomponent or multicomponent fiber. This wave can be regular or irregular. However, due to the production process used, this wavy shape is usually irregular. If these filler fibers already hold in the form of a sheath what is intended to be the matrix material, these filler fibers can be further processed using evacuation and heating to produce a composite part. The wavy outer shape along the longitudinal axis of the fiber promotes increasing the transverse permeability required for evacuation by providing channels between the fibers that are filled nearly parallel. When using such fibers with a non-wavy surface, a high-density filling is obtained that has no or hardly any permeability and channels in a direction essentially perpendicular to the longitudinal direction, i.e., in the transverse direction. The proposed wave creates an intermediate space between the filled fibers, thereby forming air channels in the transverse direction and thus dramatically facilitating the removal of air from what is intended to be the composite part in a vacuum / heat consolidation process. Thus, the proposed wavy fibers make it possible to produce much larger parts that are air-free or essentially air-free, thereby significantly enhancing the mechanical stability of the final composite part.

[0023] Thus, the wave has the characteristic of enabling the formation of such transverse air channels.

[0024] Thus, the main point of the present invention lies in using BCF / MCF, preferably having a variable sheath thickness, to form a composite structure. Thus, the wave on the outer surface of the sheath can be due to a variable sheath thickness along the length of the fiber core, which has a constant diameter along its axis and more generally a constant cross-section. However, the wave can also be due to a wavy core structure, and the layer thickness of the sheath can be constant along the length of the fiber. Also, a combination of these two is possible.

[0025] The variability in the width of the hybrid fibers results in gaps between the fibers, which create open porosity within the structure, i.e., isotropically dispersed air gaps. While fiber filling typically results in gaps extending along the direction of fiber orientation, these irregular coatings also create gaps in the transverse direction of the fibers. This creates flow channels that degas in the thickness direction of the laminate during vacuuming. This is an essential feature for the manufacture of large components where complete degassing through channels along the fiber length alone is impossible. Furthermore, the presented invention ensures proper vacuum distribution and degassing even in the thickest laminates. Since voids impair the mechanical strength and fatigue resistance of the final composite, gaps formed in the form of BCF / MCF need to collapse during consolidation. Therefore, by using a thermoplastic or prepolymerized thermosetting sheath, the gaps are preserved during degassing but collapse during consolidation. Simultaneously, this thermoplastic or prepolymerized thermosetting material becomes the matrix of the composite, i.e., the material that binds the reinforcing fibers that hold the main mechanical loads of the structure. This innovation enables the production of large fiber-reinforced thermoplastic parts, which are inherently unattainable with current consolidation processes for thermoplastic composite preforms that require pressures higher than atmospheric pressure. Therefore, the use of BCF / MCF preforms is the only way to produce large parts without using massive autoclaves or constructing extremely expensive and technically complex presses. BCF / MCF is the only hybrid thermoplastic composite intermediate material that can be completely consolidated under vacuum pressure, especially using the vacuum bag method, thus realizing a cost-effective value chain for large-volume and high-scale parts.

[0026] The combination of BCF / MCF fibers or preforms and vacuum bag molding constitutes the only processing chain that enables the use of thermoplastic matrix materials for manufacturing large-scale parts with virtually no size limitations. This is only possible due to the microstructure of the fibers, which exhibits thickness / width variations in the outermost sheath along the fiber direction, thereby ensuring proper degassing throughout the entire part. Compared to conventional resin impregnation processes, this technology can reduce the total mold occupancy time by more than 30% by replacing the time-consuming impregnation, curing, and post-curing / tempering processes with a single heating and cooling cycle. This significant reduction in cycle time is also an advantage over resin impregnation methods based on novel reactive thermoplastic resins. Furthermore, BCF technology does not require compromises in the polymerization reaction design for a more efficient manufacturing process, as does reactive thermoplastic resins. Therefore, BCF / MCF technology has the potential to shake up the market for large-scale composite manufacturing. BCF / MCF can also be used in conventional thermoplastic composite press-based manufacturing processes, in which case it results in a significant reduction in overall production costs. Currently, efficient press forming, such as stamp forming, relies on expensive pre-consolidated intermediate materials. Pre-consolidation is used to impregnate dry fiber preforms with thermoplastic molten material, but it is a time-consuming and therefore costly process. This process can be performed by the material supplier or the part manufacturer themselves, but so far there has been no way to avoid it. BCF / MCF preforms can be stamp-formed without the pre-consolidation process, and depending on the method used to manufacture them, the entire value chain can be significantly reduced in overall production costs by avoiding the time-consuming and costly impregnation process.

[0027] For example, energy infrastructure, aircraft, ships and boats, industrial plants, and technology infrastructure markets, particularly the wind turbine blade market, can significantly benefit from the added customer value provided by the proposed BCF / MCF preform technology. The total production cost of blades can be drastically reduced by switching from resin impregnation at the current level of technology to vacuum bag molding with BCF / MCF, by reducing mold occupancy time by an estimated 30% or more. This allows for cost savings by reducing the number of expensive molds used for each production process of a given blade design, and opens up the potential to shift offshore blade production to a 24-hour molding cycle, which is not currently possible. This results in more consistent product performance and fewer manufacturing defects, as skilled workers perform the same tasks in every shift, rather than requiring training for every part of the production process. The improvement in production efficiency brought about by BCF makes it possible to increase blade production volume. In light of current market developments, this supports the use of sustainable wind energy as an alternative to fossil fuels. Mold occupancy time can be further reduced by replacing standard adhesive bonding techniques—joining the two halves of the blade shell and joining the shear web to the spar—with simple welding of thermoplastic composite materials. Welding of thermoplastic composites is already established in the aerospace industry, providing cost-effective bonding solutions that enable more structurally efficient blade designs, i.e., longer and therefore more efficient blade designs. Compared to thermosetting resins, thermoplastic materials offer higher toughness and elongation at break, which has the potential to mitigate structural fatigue problems in the shell layers. Here, damage progressing between reinforcing fibers is a central structural design issue (inter-fiber fracture). Here, improving material performance further advances the possibility of more efficient blade designs. Furthermore, material scrap generated by trimming and boring operations after demolding the blade can be reused as core material in another blade or sold for production of short-fiber reinforced parts in other markets.These proposed values ​​will advance the current state of technology in energy infrastructure, aircraft, ships and boats, industrial plants, and technological infrastructure, particularly in the production of wind turbine blades, and break down the structural efficiency barriers imposed on current designs for more cost-effective and sustainable energy sources.

[0028] BCF / MCF preforms offer advantages in various conversion processes that generate complex composite structures. Similar advantages outlined for the wind energy market also apply to the marine industry, where the manufacture of large components such as ship hulls can benefit from the use of welding methods to join layers of thermoplastic composites, traditionally produced using BCF / MCF through vacuum bag forming and heat treatment cycles. The manufacture of medium-sized parts using rapid conversion processes such as rapid stamping in presses can benefit from BCF due to significant material cost reductions, given the high cost of producing preforms (consolidated blanks or so-called organosheets) at the current level of technology used in these methods. A further advantage is the ability to pre-manufacture three-dimensional near-net-shape preforms before moving them to presses, taking advantage of the higher flexibility of BCF preforms at room temperature compared to existing market solutions. These advantages make them attractive for use in the production of automotive body parts, as well as radomes or other antenna covers in the aerospace sector. The 3D printing industry benefits from the simple fact that BCF provides a hybrid intermediate material on a single-filament scale. This opens up possibilities for fused deposition modeling-type processes that convert continuous fiber-reinforced thermoplastic materials to print structural prototypes at high resolution or to print parts much smaller than currently possible.

[0029] The outer surface of the outermost sheath in the two-component or multi-component fiber according to the present invention must exhibit a corrugated shape along the axial direction of the fiber. This corrugation consists of regions where the distance between the surface and the geometric midpoint of the same corrugated cross-section is much larger than in other regions. Hereinafter, regions where the distance between the surface and the midpoint in the cross-section is relatively long will be called peaks, and regions where the distance between the surface and the midpoint in the cross-section is relatively short will be called valleys. The above-described corrugation is characterized by such peaks and valleys and transitional regions between them. The width and / or height of the peaks and valleys may be irregular.

[0030] The various parameters and characteristics relevant here are defined herein as follows:

[0031] Ignition temperature: Defined as the lowest temperature at which combustion of a flammable material can begin, depending on the temperature level and heat flux (energy flow per unit area and unit time). This material can spontaneously ignite even without an external ignition source. The autoignition temperatures of liquids and solids in a high-pressure, oxygen-enriched environment can be determined by ASTM G72 for materials with an ignition temperature of up to 500°C. The corresponding German standard for flammable materials is DIN 54836.

[0032] Degradation temperature: The temperature at which changes occur in the chemical structure that affect (usually worsen) the performance of a material, such as a decrease in strength and ductility, a change in color, or an increase in embrittlement. The degradation temperature can be determined by thermogravimetric analysis, for example, according to ASTM E2550 or DIN EN ISO 11358-1. Here, the mass of the sample decreases due to the formation of volatile products as the temperature rises. The degradation temperature can also be determined using differential thermal analysis or differential scanning calorimetry. In this case, the physical changes affect the characteristic glass transition temperature or melting temperature.

[0033] Softening temperature: The temperature at which a material softens beyond a certain specified degree of softness. Softening occurs due to an increase in the mobility of molecules, crystals, or molecular chains within the material, resulting from an increase in thermal energy within the material. For polymers, this temperature is determined by the Vicat softening method (DIN EN ISO 306), the heat deflection test (ASTM-D648), or the ring-or-ball method (DIN EN 1238 for thermoplastic adhesives or DIN EN 1427 for bituminous). In the case of the Vicat softening temperature, it is defined as the temperature at which a needle with a flat end penetrates a specified depth into the sample under a specific load using a selected uniform rate of temperature rise. For glass, the softening temperature is the point below which the glass behaves as a solid, and is measured by ASTM C338 as the temperature at which the sample elongates at a specified rate due to its own weight. The corresponding ISO standard is DIN ISO 7884-6.

[0034] Liquidus temperature: Defined by ASTM C162 as the maximum temperature at which equilibrium exists between molten glass and its primary phase. It is most commonly used for alloys, glass, or impurities such as minerals. ASTM C829 "Measurement of Liquidus Temperature of Glass by the Gradient Furnace Method".

[0035] Glass transition temperature: For glasses, defined by DIN ISO 7884-8; for polymers, defined by DIN EN ISO 11357-2.

[0036] The thermal properties (melting temperature, glass transition temperature) can be determined by referring to ISO standards 11357-1 / -2 / -3 for pellets.

[0037] More specifically, for amorphous and microcrystalline materials, differential scanning calorimetry (DSC) can be performed at a heating rate of 10 K / min. Heat to a temperature between the extrapolated end temperature of the glass transition temperature (DSC, ISO 11357, heating rate 10 K / min) and the start point of mass loss (TGA, ISO 11358, heating rate 10 K / min). After cooling to below the extrapolated start temperature of the glass transition temperature (DSC, ISO 11357, cooling rate -10 K / min), release the vacuum and demold.

[0038] For semi-crystalline materials, heating can be performed up to a temperature between the extrapolated end temperature of the melting temperature (DSC, ISO 11357, heating rate 10K / min), and the starting point of mass loss (TGA, ISO 11358, heating rate 10K / min) can be used.

[0039] According to a first aspect of the present invention, in order to have a waveform according to the present invention, when measuring a given window over the length of the fiber, the difference between the total width of the peak portion with the widest width and the total width of the trough portion with the narrowest width must be minimized. Considering that the fiber core may have any width or diameter, the relevant measure is not an absolute difference, but rather the relative variation of the total width measured with respect to a given window over the length of the fiber with respect to a constant width that is characteristic of the fiber.

[0040] The method for measuring this quality involves taking microscopic images of the fiber shown in the transverse direction, measuring the distribution of the total cross-sectional width w in the radial direction along the longitudinal axis Z, and interpreting this distribution w(Z) as a wave signal. The relevant measure is to obtain the standard deviation σ of the above signal over a length L (a given window spanning the length of the fiber) that is 5 to 50 times the average width <w> of the fiber, and the minimum value w of the above signal within this measurement window. min This is obtained by normalizing over σ / w. This measure σ / w in this first aspect is obtained by normalizing over σ / w. min This value shall exceed 0.1, preferably exceeding 0.2, or even exceeding 0.3. For an example of how this is actually done, see Figure 11 and the corresponding description.

[0041] Therefore, it is preferable that the above waveform shape is characterized in that the diameter distribution of the outer surface of the sheath along the longitudinal axis Z within a predetermined window has a normalized standard deviation. The normalized standard deviation is obtained by dividing the standard deviation σ by the minimum value w in the diameter distribution within the above predetermined window. min It is defined as the quotient. This normalized standard deviation is preferably at least 0.1, more preferably at least 0.2, or even more preferably 0.3. The above predetermined window is given as a length along the longitudinal axis Z that is 5 to 50 times, preferably 10 to 40 times, and most preferably 25 times the average width <w> of the diameter distribution.

[0042] In other words, the waveform is characterized in that, over a 100-μm longitudinal length window of the bicomponent fiber or multicomponent fiber, the difference in the total fiber width between the maximum width portion and the minimum width portion in the transverse direction within this length window is at least 5 μm, preferably at least 7 μm.

[0043] The waveform can also be characterized by the variation in amplitude in that the reinforcement core has an essentially constant core radius along the longitudinal axis, that is, there is a single core fiber with a circular cross-section. The radius of the outer surface of the sheath shows variations around the average sheath radius along the longitudinal axis, and this variation has a sheath variation amplitude. The relative sheath variation amplitude defined as the quotient of the above sheath variation amplitude divided by the core radius is at least 0.3, preferably greater than 0.3, and most preferably at least 0.35.

[0044] When the core material (which may be plural) has a circular cross-section and the outer periphery of the cross-section has a radius r for the fiber, the average thickness <t> of the outermost sheath follows the following formula.

[0045]

Equation

[0046] Typical values ​​for r are in the range of 1.5 μm to 20 μm. In particular, typical values ​​for r in high-performance structural applications are in the range of 3 μm to 7 μm.

[0047] According to yet another characteristic of the waveform, the waveform shape is characterized by peaks with large radii and troughs with small radii. Over a longitudinal length window of 1 mm, the ratio of the average longitudinal length of the peaks to the average longitudinal length of the troughs is preferably less than 0.9, more preferably less than 0.8. The peaks and troughs are defined by determining the average radius along the length window and drawing an axial line along this average radius. The peaks are variations that deviate from the average radius in the direction of increasing radius, and the troughs are variations that deviate from the average radius in the direction of decreasing radius.

[0048] According to a preferred embodiment, the reinforcing core consists of a single fiber having an essentially circular cross-section, the cross-section being essentially constant along the longitudinal axis. Typically, in this case, the diameter of the fiber is in the range of 2 μm to 40 μm, more preferably in the range of 5 μm to 25 μm, and most preferably in the range of 6 μm to 20 μm.

[0049] The reinforcing core is made of glass fiber or carbon fiber, preferably glass fiber having a round cross-section, and preferably the glass fiber or carbon fiber is provided with a sizing layer (typically a silane-based structure) to improve adhesion with the thermoplastic or thermosetting second material.

[0050] According to a preferred embodiment, the first material is selected from the following group: inorganic materials such as mineral materials, for example, industrial glass (insulating glass (E glass, aluminoborosilicate glass with less than 1% by weight of alkali oxide), A glass (alkali lime glass with little to no boron oxide content), AR glass, electrical resistance / chemical resistance glass (ECR glass, aluminoborosilicate glass with less than 1% by weight of alkali oxide and high acid resistance), C glass (alkali lime glass with a high boron oxide content). Materials include T glass (also known as T glass), D glass (low dielectric constant borosilicate glass), R glass (aluminosilicate glass that does not contain MgO and CaO), S glass (aluminosilicate glass that does not contain CaO and has a high MgO content), M glass), or basalt, kaolin, alkaline earth silicates (combinations of AES, CaO, MgO, and SiO2), refractory ceramic fibers (RCF, aluminosilicate, also known as ASW), polycrystalline wool (PCW, containing more than 70% aluminum oxide), alumina, and silicon carbide. Furthermore, metallic materials (alloy steel; aluminum alloys; copper alloys, platinum alloys, and pure platinum, especially alloys with rhodium); and carbon fibers (polyacrylonitrile-derived fibers (PAN-based fibers), HT, IM, HM, HST, HMS, UHM; intermediate-phase pitch-derived fibers (MPP-based fibers), HT, IM, HM, HST, HMS, UHM, glassy carbon).

[0051] Alternatively, polymer materials including organic materials such as aramid (para-aramid; meth-aramid), polyethylene (PE) (UHMWPE, HMWPE, HDPE, LLDPE, LDPE), polyamide (PA) (PA-6, PA-6.6, PA-11, PA-12), polysulfone (polyethersulfone (PES)), polypropylene (PP), and liquid crystal polymer (LCP) (polyethylene terephthalate copolyester; copolyamide; polyesteramide; aromatic polyester) are selected.

[0052] The thermoplastic second material is preferably selected from the group consisting of polymer materials that contain or do not contain filler particles. The material can be selected from the following group: polymers soluble in trichloromethane, tetrachloromethane, or 1-bromonaphthalene, such as acrylic polymers (acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), polyisobutyl methacrylate (PiBMA), poly-n-butyl methacrylate (PnBMA), polyethyl methacrylate (PEMA), polymethyl methacrylate (PMMA)), cellulose acetate butyrate (CAB), fluorinated ethylene polypropylene (FEP), polyamides (PA) such as polyamide 12 (PA-12), polycarbonates (PC) such as polybutadiene and bisphenol-A polycarbonate, polyimides such as polychlorotrifluoroethylene (PCTFE) and polyetherimide (PEI), polysulfones such as polyethersulfone (PES), UHMWPE, HMWPE, HDPE, LLD Polyethylene (PE), LDPE, etc. (PE), polyethylene terephthalate (PET), polyisobutylene (PiB, butyl rubber), polyisoprene (PiP), polylactic acid (PLA), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polypropylene (PP), atactic PP, isotactic PP, polystyrene (PS), polysulfone (PSU), polyurethane (PU), polyvinyl acetate (PVA), polyvinyl butyral, polyvinyl chloride (PVC), bromine-soluble polymers, acrylic polymers, polyethyl methacrylate (PEMA), polymethyl methacrylate (PMMA), cellulose acetate (CA), cellulose acetate butyrate (CAThB), nitrocellulose (cellulose nitrate), polycarbonate (PC), bisphenol-A polycarbonate, polyphenylene oxide (PPO), polyurethane (PU), polyvinyl acetate (PVA).

[0053] Water-soluble polymers such as sodium polyacrylate, polyethylene glycol, sodium polymethylacrylate, sodium polystyrene sulfonate, dextran, and pullulan are also possible.

[0054] Polymers that can be processed in the molten phase are also possible, and these include all polymers listed as "soluble in trichloromethane, tetrachloromethane, or 1-bromonaphthalene," "soluble in bromine," and "water-soluble," but also cellophane, polyamide (PA), PA-6, PA-6.6, PA-11, polyacrylonitrile, polybutylene terephthalate, polyaryl ether ketone (PAEK), polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK), and polymethacrylonitrile (P This also includes MAN, polyoxymethylene (POM, polyacetal, polymethylene oxide), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVOH), polyvinyl butyral, polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), liquid crystal polymer (LCP), polyethylene terephthalate copolyester, copolyamide, polyesteramide, aromatic polyester, thermoplastic elastomer (TPE), polyamide elastomer (TPA), copolyester elastomer (TPC), olefin elastomer (TPO), styrene elastomer (TPS), polyurethane elastomer (TPU), and crosslinked rubber elastomer.

[0055] The particulate material (the polymer sheath may contain nanoparticles having a primary particle size (TEM) of less than 1 μm as filler material) can be selected from metal particles, iron, copper, graphite powder, carbon nanotubes (CNTs), single-walled carbon nanotubes (SWCNTs), ceramic particles, silicates, alumina, titania, and magnesia.

[0056] The second material of the sheath may further include additives, in particular colorants, processing aids, polymerization-derived residues, rheological modifiers, pigments, conductive additives, impact resistance modifiers, adhesion promoters (e.g., amphiphilic molecules), and flame retardants.

[0057] The second material of the sheath may also be a prepolymerized thermosetting polymer or a mixture of prepolymerized thermosetting polymers (for example, applied to the core fibers and cured to an intermediate state that provides a stable sheath that does not fuse under ambient conditions but fuses under heated conditions). This includes epoxy resins and curing agents, polyurethane resins and curing agents, and silicone resins and curing agents (addition-curing silicones or condensation-curing silicones).

[0058] The second material of the sheath may also be a mixture of thermoplastic polymers, copolymers, blended polymers, prepolymerized thermosetting polymers, or a mixture of thermoplastic and prepolymerized thermosetting polymers.

[0059] To enable optimal processing temperatures in the manufacture of composite material components, the degradation temperature, ignition temperature, glass transition temperature, melting temperature, or liquidus temperature (preferably any of these) of the first material is preferably at least 10°C, preferably at least 20°C, and most preferably at least 50°C higher than the melting temperature, softening temperature, flow temperature, or glass transition temperature of the thermoplastic or prepolymerized thermosetting second material.

[0060] Typically, the reinforcing core is a single fiber, but it can also be a bundle of up to 50 fibers, preferably up to 20 fibers, and more preferably up to 10 fibers.

[0061] The proposed BCF, MCF, and / or combinations thereof can be processed into fabrics and / or three-dimensional preforms, particularly random fiber mats, fleeces, woven fabrics, unidirectional, bidirectional, or multiaxial non-crimped fabrics, and into sewn, braided, knitted, or wound preforms.

[0062] Therefore, according to yet another preferred embodiment, the present invention relates to a preferably tightly packed preform comprising or consisting of the fibers detailed above, preferably having a woven structure, a braided structure, or a nonwoven structure.

[0063] Furthermore, such rovings, yarns, or fabric preforms made from them may contain mixtures of different two-component or multi-component fibers, including mixtures with bare or glued reinforcing fibers. This is similar to the concept of mixed yarns, where bare or glued reinforcing fibers are combined with thermoplastic fibers intended as a shaping material to form a composite matrix. The transverse breathability of rovings, yarns, or fabrics is further increased when two-component or multi-component fibers are mixed with different levels of corrugated outer sheaths, and / or with bare or glued reinforcing fibers, compared to the case of purely cylindrical fiber configurations.

[0064] In short, these fibers can be processed into many types of fiber fabric preforms used to manufacture continuous fiber-reinforced plastics.

[0065] Methods for creating fabric preforms are not limited to weaving, but include plain weave, twill weave, satin weave, and one-way weave (where the weft is a light auxiliary thread used only to hold the warp in place and is not intended as actual reinforcement).

[0066] Non-crimp fabrics (NCF) such as unidirectional (UD) NCF, biaxial NCF, triaxial NCF, and multiaxial NCF layups are possible, where one or more unidirectional layers of yarn or roving are sewn together.

[0067] It is also possible to create assemblies, including pre-forming parts by directly assembling them around a mold, and continuously assembling tubular intermediate materials.

[0068] It is possible to knit fabrics, including crochet, 3D knitting or 3D weaving, nonwoven fabrics, or fleece including oriented fleece, cross-ply fleece, and randomly oriented fleece, which are adapted to produce a three-dimensional near-net shape preform.

[0069] Furthermore, the present invention relates to a method for producing composite components, preferably turbine blades, wind rotor blades, etc., using the fibers detailed above or the preforms just mentioned. The fibers or preforms are each introduced into a mold without additional matrix material, vacuumed, preferably then heated to a temperature at or above the melting temperature of a second thermoplastic material, and compressed while forming the composite component, preferably cooled to a temperature below the crystallization temperature or glass transition temperature of the second thermoplastic material. Thus, such preforms are placed in a mold and covered with a sealed vacuum film or vacuum bag. The mold can be pretreated with a chemical release agent or release film. Before stacking the preforms, a gel coat layer or film can be applied to hold a thermoplastic material having similar functions (scratch resistance, UV protection). Before applying the vacuum film, the preforms can be covered with a release agent (perforated or semipermeable film or fabric) and breathable fleece or similar vacuum distribution aid. To process the material into a rigid structure, the assembly is vacuumed, removing air and any other gases from the preform. At some point during or after the assembly process, a temperature gradient is applied to the mold so that the BCF / MCF sheath temperature reaches the liquidus temperature only after a sufficient vacuum pressure has been achieved. This heating can be performed by heating only the mold, or by heating all the fibers or selected ones therein by resistance heating or induction heating (in the case of conductive and / or ferromagnetic materials). A similar function can be achieved by including a layer of conductive and / or ferromagnetic material, e.g., copper wire or steel wire mesh, within the preform layup. Once the liquidus temperature of the sheath is reached at all points in the preform, heating is stopped, and the mold and layup assembly can be passively or actively cooled to below the solidus temperature of the preform (the solidus temperature is defined as the temperature below which the material becomes completely solid). Until then, the layup is compressed and the preform is compacted by the pressure difference acting on the vacuum bag assembly.After the solidus temperature is reached at all points in the material being processed, the vacuum can be removed, and the fiber-reinforced composite structure can be demolded.

[0070] In a preferred vacuum bag molding process, the sealed layup is typically vacuumed after the bag molding process. This removes any gas present in the preform and simultaneously compacts the material by applying pressure to the layup. The entire structure is then heated in a furnace, autoclave, or heating tent, or using a heating system integrated into the mold and / or the preform or layup itself. If a thermoplastic matrix material is used for the outermost sheath, these will eventually become liquid and fuse together. At this point, heating is stopped, the part is removed from the heating system and left to cool passively, or cooled via an active cooling system implemented in the mold. This cooling causes the thermoplastic matrix to solidify. Once the entire part is solid, the vacuum can be released, the vacuum bag can be opened, and the part can be demolded.

[0071] When using a prepolymerized thermosetting matrix material for the outermost sheath, the viscosity of the resin decreases as the temperature rises, leading to sheath fusion. Over time, the polymerization and crosslinking of the resin are accelerated by the heat, causing the resin to harden. Once the hardening reaction yields a solid part with the desired mechanical properties, the vacuum can be released to cool and demold the part.

[0072] Typical values ​​for vacuum pressure and temperature: Typical vacuum pressures range from 1 mbar to 100 mbar. Vacuum pressures below 50 mbar are particularly desirable. For cost reasons, typical vacuum environments do not reach pressures below 10 mbar within a vacuum bag.

[0073] When processing thermoplastic sheath materials, the typical temperatures for melting and solidifying depend on the exact material being used. The typical processing window is based on the quantifiable thermal properties of the material being used.

[0074] Amorphous and microcrystalline materials: Heat to a temperature between the extrapolated end temperature of the glass transition temperature (DSC, ISO 11357, heating rate 10 K / min) and the start point of mass loss (TGA, ISO 11358, heating rate 10 K / min).

[0075] After cooling to below the extrapolation start temperature of the glass transition temperature (DSC, ISO 11357, cooling rate -10K / min), the vacuum is released and the mold is demolded.

[0076] Semi-crystalline material: Heat to a temperature between the extrapolated end melting temperature (DSC, ISO 11357, heating rate 10 K / min) and the start point of mass loss (TGA, ISO 11358, heating rate 10 K / min).

[0077] After cooling to below the extrapolated start temperature of the crystallization temperature (DSC, ISO 11357, cooling rate is the same as the actual cooling rate during component production) or below the extrapolated start temperature of the glass transition temperature (DSC, ISO 11357, cooling rate is the same as the actual cooling rate during component production), the vacuum is released and the mold is demolded.

[0078] Furthermore, the present invention relates to composite material components, preferably in the form of turbine blades or wind turbine blades, which are manufactured using the aforementioned fibers or preforms, preferably using the methods detailed in the preceding paragraphs.

[0079] Furthermore, the present invention relates to the use of the fibers or preforms described above in detail, for example, in a vacuum forming process for producing composite material parts using the method described in detail above.

[0080] According to further aspects of the proposed invention, a method for producing these BCF / MCF is presented. This method comprises a process that begins with the fibrillation of a material (e.g., glass, basalt, polymer) or precursor material (e.g., polyacrylonitrile (PAN) precursor of carbon fibers) and ends with the recovery of multiple fibers collected in parallel on a bobbin. Between fibrillation and fiber recovery, standard modification or transformation processes (e.g., fiber stretching, stabilization, and carbonization of PAN) can be applied, keeping the individual fibers isolated and processed in parallel throughout. Between these optional processes and the collection of a single fiber, one or more continuous coating methods are used in-line to apply one or more coatings onto the core. The final coating comprises a thermoplastic sheath, which is converted into a composite matrix when the fibers are used in part production. Specific examples already employed include the melt spinning of glass fibers, in-line coating of the fibers with polymer-containing solutions (particularly polycarbonate (PC) or polymethyl methacrylate (PMMA) dissolved in trichloromethane), and in-line drying of the solution on the fibers. The coating can be applied by a kiss roll; that is, the fibers are stretched over a rotating roll that is partially immersed in a tank containing the polymer solution. As the roll rotates, it encloses a thin layer of the solution. The fibers are in contact with the surface of the roll for only a short time, but during this time, the fibers are immersed in the solution film held by the roll, and therefore, upon separation from the roll, the fibers themselves are enclosed in the coating. This mechanism is assisted by the use of grooves on the roll. These grooves are designed to ensure robust coating application, enable faster coating speeds, and keep the fibers separated. These grooves can have any cross-section, but their shape, size, and aspect ratio affect the efficiency of the coating process, i.e., the speed at which the desired coating can be applied. Irregularities in the sheath thickness can be introduced actively or passively through several methods.Specifically, the thickness can be actively etched via serrations extending perpendicular to the fiber direction on the kiss roll, or via an additional set of serrated finishing rolls that etch thickness variations while the sheath solidifies. Alternatively, the surface tension of the coating liquid used can be adjusted to promote or suppress the amplitude of the thickness variation. The rotation speed of the kiss roll can be varied at a high frequency, already resulting in a variable film thickness on the roll itself, as well as varying the relative speed between the core fibers and the roll, thereby affecting the thickness of the film encrusted with the fibers. Finally, as an alternative, the coating liquid can be sprayed onto the fibers to promote droplet formation on the filaments. This last method can be used to coat the entire amount of the desired sheath material, or this method can be used before or after a coating step to coat the same material to a constant thickness. A two-roller system is also possible, for example, to etch the texture. These systems tend to further increase the robustness of the coating process.

[0081] Therefore, more generally speaking, the present invention proposes a method for producing the fibers detailed above, wherein the reinforcing core is coated with the thermoplastic second material described above. The thermoplastic second material is heated to a temperature above its melting point and applied to the surface of the reinforcing core in a continuous process while the sheath cools and solidifies, or A second thermoplastic material is dissolved in a suitable solvent and applied to the surface of the reinforcing core in a continuous process, while the solvent evaporates and a sheath forms.

[0082] When a polymer is dissolved in a solvent, the volume content of the polymer in the solution is v pThe viscosity can be in the range of 2% to 50% by volume, particularly 5% to 25% by volume. The kinematic viscosity η is preferably in the range of 1 mPa·s to 1 Pa·s when measured by rotational flow measurement using a double-walled Couette geometry. The surface tension γ is more preferably in the range of 1 mN / m to 100 mN / m when measured by the pendant drop test method. The preferred processing characteristics of the glass in the bushing when produced in-line are as follows: The temperature inside the bushing is 1000°C to 1600°C when measured using a thermocouple type S welded to the inner surface of the bushing. The preferred viscosity of the glass molten inside the bushing is 10 Pa·s to 500 Pa·s, particularly 50 Pa·s to 100 Pa·s. Other parameters can be selected as follows: The linear fiber stretching rate V is 1 m / s to 100 m / s, particularly 5 m / s to 60 m / s; the kissroll peripheral speed U is 0.05 m / s to 30 m / s, particularly 0.1 m / s to 10 m / s; and the kissroll radius R is 5 mm to 500 mm, particularly 10 mm to 100 mm.

[0083] To generate a waveform, the Kiss Roll can be operated by selecting a combination of fluid properties and process parameters that result in a regime that introduces instability in the free surface flow on the roll, i.e., a high capillary number Ca greater than 0.01 and / or a high Weber number We greater than 1. Furthermore, the Kiss Roll can be driven so that its circumferential speed is adjustable. In other words, the Kiss Roll does not rotate at a constant speed, but its speed follows a periodic signal whose root mean square value is positive. The Kiss Roll may also include circumferential grooves that guide monofilaments or small groups of fibers during the coating stage. These grooves can exhibit a waveform width and / or waveform depth. Preferably, the shape of the waveform satisfies the same or at least similar requirements as those imposed on the waveform shape of the resulting fibers.

[0084] Between the Kissroll coating applicator and the gathering shoe, a pair of finishing rollers exhibiting a corrugated surface can imprint the roller's corrugation onto the fibers. This corrugation can be oriented along the roller axis or at any angle other than 90 degrees; that is, the corrugation does not form parallel grooves extending along the circumference of the roller. When measured along the circumferential direction of the roller, the shape of the corrugation can satisfy the same requirements imposed on the resulting fiber corrugation shape.

[0085] The method used in the production of BCF / MCF is the only proven process capable of continuously producing the desired fibers. This method is easily expandable through parallelization (spinning many fibers in parallel and coating those fibers on the same kiss roll), and is highly cost-effective due to the high throughput during expansion.

[0086] A second thermoplastic material can be applied using a kiss roll, for example, by adapting the relative rotational speed of the kiss roll to the speed of the reinforcing core, or by a corrugated surface that structures the contact area of ​​the kiss roll, or both.

[0087] Further embodiments of the present invention are described in the dependent claims.

[0088] Preferred embodiments of the present invention are described below with reference to the drawings. The drawings are intended to illustrate, but not to limit, current preferred embodiments of the present invention. [Brief explanation of the drawing]

[0089] [Figure 1] Figure 1 is a cross-sectional view through a proposed fiber in a possible example. [Figure 2] Figure 2 is a cross-sectional view through proposed fibers, showing possible examples of two-component fibers (far left) and multi-component fibers. [Figure 3]Figure 3 shows axial cross-sectional views through the proposed fibers in different examples, with the top figure representing a conventional two-component fiber. [Figure 4] Figure 4 is a schematic cross-sectional view through a vacuum forming apparatus. [Figure 5] Figure 5 shows the vacuum forming process from left to right in a cross-section passing through the material. [Figure 6] Figure 6 shows an apparatus for manufacturing fibers and coating them with a sheath downstream. [Figure 7] Figure 7 shows an example of a groove in a kiss roll having an arbitrary cross-section. [Figure 8] Figure 8 shows an example of a kiss roll with three different grooves. [Figure 9] Figure 9 shows an example of an additional finishing roller used to engrave thickness variations in the outermost sheath. [Figure 10] Figure 10 shows a microscopic image illustrating the deformation of the material during the vacuum bag forming process. [Figure 11a] This figure shows the waveform analysis of fiber a) according to the present invention. In this example, the top figure shows a micrograph of fiber a), the figure directly below it shows a black and white conversion of the micrograph, and the bottom figure shows the distribution of the total fiber width as a function of the Z axis, with calculated values ​​for minimum width, maximum width, the difference between minimum width and maximum width, and mean, standard deviation and normalized standard deviation. [Figure 11b] This figure shows the waveform analysis of fiber b) according to the present invention. In this example, the top figure shows a micrograph of fiber b), the figure directly below it shows a black and white conversion of the micrograph, and the bottom figure shows the distribution of the total fiber width as a function of the Z axis, with calculated values ​​for minimum width, maximum width, the difference between the minimum and maximum widths, and the mean, standard deviation, and normalized standard deviation. [Figure 11c]This figure shows the waveform analysis of fiber c) according to the present invention. In this example, the top figure shows a micrograph of fiber c), the figure directly below it shows a black and white conversion of the micrograph, and the bottom figure shows the distribution of the total fiber width as a function of the Z axis, with calculated values ​​for minimum width, maximum width, the difference between the minimum and maximum widths, and the mean, standard deviation and normalized standard deviation. [Modes for carrying out the invention]

[0090] Figure 1 shows 16 different examples of fibers possible according to the present invention in cross-sectional views. As can be seen, the cross-section of the reinforcing core 1 can be circular (top row), rectangular (second row), hexagonal (third row), or irregular (bottom row). On the other hand, it should be noted that the core can also be made of flat fibers such as elliptical, cocoon-shaped, or eyebrow-shaped fibers. Furthermore, the core can be made of hollow fibers. In addition, different types of cores may be mixed in roving, etc.

[0091] Furthermore, the shape of the sheath can vary in the cross-sectional view. As shown in the first column, the shape of the sheath can be circular, but it can also be essentially rectangular as shown in the second column, hexagonal as shown in the third column, or irregular as shown in the rightmost column. The sheath defines the outermost surface 4 of the fiber.

[0092] Figure 2 shows that the proposed fiber can be a two-component fiber consisting of a core 1 and a sheath 2, as shown in the leftmost figure. On the other hand, the proposed fiber can also be a multi-component fiber, as shown in the other figures. Typically, the proposed fiber is a multi-component fiber, especially in the case of glass fibers, as shown in the second figure from the left, in the sense that a so-called adhesive layer 5 is first provided on the outer surface of the core 1 to improve adhesion between the core material and the sheath matrix material, followed only by the sheath 2 which forms the outermost layer of the fiber. Further layers may be present, as shown in the two figures on the right. The rightmost figure shows an example in which the reinforcing core 1 has an adhesive layer 5, followed by two additional layers, and finally surrounded by the sheath 2. These two additional layers can be made from thermoplastic material and can therefore be considered as part of the sheath, as well as melted in the manufacturing process to become the matrix material. However, the two additional layers can also be part of the core and therefore not melted in the manufacturing process of the composite component.

[0093] Figure 3 shows an axial cross-section through the fibers. In each example, the core fibers have a constant diameter along the longitudinal axis. However, it is also possible in principle to create a corrugated core. The top figure shows the situation according to the current state of technology. In this example, the sheath is not corrugated along the longitudinal axis of the fibers, and the sheath is essentially smooth. The problem with these fibers is that when filled into a mold in the transverse direction, the degassing properties are insufficient to enable the manufacture of large composite parts.

[0094] The second example from the top features a regularly fluctuating sheath structure. Such a structure may have the problem that, due to the symmetry of the outer surface, adjacent fibers may become nested and fail to form sufficient degassing channels.

[0095] This is improved in the third example from the top, where the wider sections are sufficiently spaced to avoid nesting without degassing channels.

[0096] The fourth example from the top and the remaining two (bottom) examples exhibit irregular waveform structures, which are usually due to the production process, even if a regular structure is provided by, for example, a kiss roll.

[0097] Figure 4 schematically illustrates a vacuum bag forming layup that converts a proposed fiber or a preform made from the fiber into a compacted laminate in the form of a preformed stack. The preform 26 is positioned on top of the mold 6, and a release film (not shown) may be provided between the mold and the preform. From bottom to top, the preform is followed by a perforated release film 7, then a vacuum distribution medium 8, and finally a vacuum bag 9. The edges are provided with sealing tape 10 to seal the inside of the vacuum bag, and at least one edge is provided with a vent 11 for degassing to apply a vacuum. Typically, the mold and / or vacuum bag are provided with heating means.

[0098] Figure 5 schematically illustrates what happens when a vacuum is applied to such a mold and it is heated. The leftmost figure shows fibers that are arranged essentially parallel to each other but are sufficiently spaced apart due to the wavy shape of the sheath. Between the fibers are left degassing channels 12, indicated by dotted areas. These degassing channels 12 allow for ventilation and thus allow for the removal of air in the transverse direction. When a vacuum is applied, as shown in the second figure from the left, the air schematically indicated by dots in the leftmost figure is removed from these degassing channels 12. Subsequently, as heat is applied while the vacuum is continued, the sheath begins to melt as shown in the second figure from the right, but the transverse degassing channels remain long enough to allow for essentially complete degassing without air being sealed or trapped in the form of bubbles or the like, which would result in weakening. Finally, the matrix 13 completely encloses the reinforcing core 1, forming the composite component 14.

[0099] Figure 6 illustrates the spinning process from fiber formation to winding onto a winder, which includes an in-line Kiss Roll coating that imprints thickness variations on the outermost sheath and optional additional finishing rollers. Molten glass 16 is supplied to a tank 15, and this glass flows through an array of glass fiber extrusion nozzles 17. The freshly extruded glass fibers 18 solidify downstream of these extrusion nozzles 17, and after solidification, are in-line coated with the sheath material using Kiss Rolls 19. The Kiss Rolls 19 are partially immersed in a tank 20 of molten or molten thermoplastic sheath material. In the figure shown on the left, the Kiss Rolls rotate counterclockwise, and the contact surface 24 contacts the fibers passing over the surface of the Kiss Rolls. The rotation also holds the thermoplastic material, which is in a molten state or in the solvent, on its surface, entraining it from the tank 20. The corrugation can be adapted as needed by matching the glass fiber transfer rate to the rotation speed of the Kiss Rolls, i.e., the relative speed between the fibers and the Kiss Roll surface. Downstream of the kiss roll, a pair of finishing rolls 21 can be provided at a location where the thermoplastic material has not yet solidified when a molten thermoplastic material is applied, or at a location where the solvent has not yet evaporated when a solution of the thermoplastic material is applied. This will be further explained below in the context of Figure 9. When glass fibers are extruded as multiple parallel strands, a recovery roll or gathering shoe 23 may be present downstream of the pair of finishing rolls, and finally, the fibers 3 are recovered onto the winder 22.

[0100] Figure 7 schematically shows possible cross-sectional shapes of the groove 25 in the kiss roll for the purposes described in the summary of the present invention.

[0101] Figure 8 schematically shows a kiss roll 19 having three different grooves, which give a corrugated topology on the glass fibers passing through these grooves 25 to coat a second thermoplastic material onto the core fibers.

[0102] Figure 9 shows a possible configuration for generating a corrugated surface on a smooth core fiber using a pair of finishing rolls 21. The sheath is applied using kiss rolls to produce an essentially smooth surface, leading to a situation as shown in 3'. To generate the corrugation, the still wet or still partially soft sheath layer is pressed between a pair of rolls 21 having a corrugated surface topology. The resulting corrugated traces then form the final outer surface of the fiber, thus resulting in a corrugated structure along the longitudinal direction.

[0103] Figure 10 shows, by micrograph, the transition from a composite article filled with glass fibers having a corrugated surface (top left) to a void-free composite article (bottom right) after vacuum and heat treatment. This figure is derived from a specific example detailed below.

[0104] Figure 11 shows micrographs of fibers converted to binary images, where the fibers are shown in white and the surrounding area in black. These binary images were measured with respect to the distribution of fiber width along the longitudinal Z-axis (array of the number of white pixels in each column). This plot shows the resulting signal and the relevant statistical measures in the title. All samples have a normalized standard deviation value σ / w greater than 0.1. min It can be observed that it exhibits this characteristic.

[0105] Section concerning experiments: Examples of manufacturing fibers with corrugated coatings: The fibers shown in the first two samples a) and b) of Figure 11 were produced as follows: Aluminoborosilicate glass beads (SiLibeads, type SL from Sigmund Lindner) were heated to 1240°C in a bushing made of Pt / Rh embedded in refractory material. The bushing was subjected to resistance heating (Joule effect) and contained a single spinning nozzle at its lower end. The molten glass flow exiting the spinning nozzle was pulled downward by crossing a winder and wound onto a cardboard collet (136 mm in diameter) covered with a polytetrafluoroethylene film. Between the spinning nozzle and the winder, a single glass fiber was continuously spun and pulled over a rotating kiss roll (130 mm in diameter), which was partially immersed in a tank containing a polymer solution. A solution containing 11.5% by volume of polycarbonate (Makrolon 3108 from Covestro) was dissolved in trichloromethane (319988 from Sigma-Aldrich).

[0106] To achieve a corrugated coating with an irregular wave pattern along the length of the fiber, spinning and coating parameters were selected such that a) the fluid film accompanying the Kiss Roll exhibits a wave-shaped thickness along the circumference of the Kiss Roll, and b) the fluid film accompanying the fiber exhibits a wave-shaped thickness along the length of the fiber, even if the fluid film on the Kiss Roll exhibits a constant thickness along its circumference when it is drawn from the liquid film on the Kiss Roll. This was achieved by performing both the drawing of the liquid from the tank onto the Kiss Roll and the drawing of the liquid from the Kiss Roll onto the fiber in a flow mode subject to Plateau-Rayleigh instability. As described in AG Gonzalez, JA Diez, R. Gratton, DM Campana, FA Saita, "Instability of a viscous liquid coating a cylindrical fiber," Journal of Fluid Mechanics 651 (2010) 117-143. doi: 10.1017 / S0022112009993788, under the necessary physical conditions, Plateau-Rayleigh instability arises in free surface flows such as dip coatings.

[0107] The conditions necessary to induce a Plateau-Rayleigh instability can be defined by the capillary number Ca, which is obtained by multiplying the extraction rate V by the kinematic viscosity η of the coating fluid and dividing by the surface tension γ of the coating fluid.

[0108]

number

[0109] For Plateau-Rayleigh instability to occur, this dimensionless number must be close to or greater than 1. Depending on the geometry of the substrate from which the liquid is drawn, a value greater than 0.01 may already be sufficient to promote flow instability. The samples shown in Figure 11 were obtained using a roll peripheral speed of 0.3 m / s and fiber speeds of 5.0 m / s (sample a) and 7.9 m / s (sample b), respectively.

[0110] The kinematic viscosity of the polymer solution was determined under ambient conditions using vibration and continuous rotation flow spectroscopy (Anton Paar MCR 502) in a double-walled Couette cell (concentric cylinder, DG 26.7). Amplitude sweeps from 0.01% to 100% at a frequency of 10 rad / s showed constant values, indicating that all measurements remained below the limit for linear viscoelasticity. Frequency sweeps from 1 rad / s to 100 rad / s at 100% amplitude showed a phase shift angle greater than 85°, indicating that the elastic effect is negligible. The flow curve for shear rates from 10 1 / s to 1000 1 / s showed constant values, thus exhibiting the Newtonian behavior of the solution. When a solution containing 11.5 vol% polycarbonate in trichloromethane was measured, the kinematic viscosity was 6.70 mPa·s.

[0111] The surface tension of polymer solutions was determined under ambient conditions using the suspension method performed with a Kruess DSA100 droplet shape analyzer. For each solution tested, at least 30 droplets were generated by extruding through a 1.8 mm outer diameter steel cannula with a flat end. Each generated droplet was imaged 31 times. For a solution containing 11.5 vol% polycarbonate in trichloromethane, the droplet shape analyzer returned a surface tension of 25.8 mN / m.

[0112] Using the above measurements regarding the fluid properties of the solution, along with the capillary numbers shown in the table below, it is possible to confirm that the coated fiber sample was produced.

[0113] [Table 1]

[0114] Example of a vacuum bag molding process: A two-component monofilament sample was produced by spinning aluminoborosilicate glass (SiLibeads, type SL, Sigmund Lindner) at 1240°C and a fiber speed of 4.34 m / s, and then coating the kiss roll with a solution of 21 vol% polymethyl methacrylate (Plexiglas 7N, Evonik) in trichloromethane (Sigma-Aldrich 319988) at a roll peripheral speed of 0.3 m / s and a kiss roll diameter of 130 mm. Measurement of the resulting sample revealed that the core fiber contained 58.1 vol% of the core fiber (glass volume fraction). This was determined using thermogravimetric analysis (temperature profile: rising from ambient temperature to 600°C at 10 K / min, maintaining 600°C for 10 minutes, and then returning to ambient temperature at -60 K / min) on a Perkin Elmer Pyris 1 TGA, with a glass density of 2.59 g / cm³. 3 The polymer density is 1.19 g / cm³. 3 The measurement was performed by converting the mass fraction to the volume fraction using [a specific method / tool].

[0115] The sample was compacted using a vacuum bag process to form a rigid plate. The sample was cut to a length of approximately 6 cm and arranged on an aluminum plate in one direction (so that all fibers were parallel). This plate was pre-treated with a release agent (Loctite Frekote 700-NC) to facilitate demolding after the process. The sample was first covered with a release film (Airtech's Wrightlon 5200, ETFE), then with a breathable fleece (Airtech's Air-weave N4, polyester), and finally with a vacuum film (Airtech's Wrightlon 7400). The purpose of the breathable fleece was to distribute vacuum to the edges of the sample, while the release film prevented the sample from adhering to this breathable fleece, which was on the top surface of this configuration. The vacuum film was sealed to the aluminum plate using sealing tape ("Tacky tape", Airtech's AT 200 Y) to form an airtight vacuum bag assembly. The vacuum port was located next to the sample. A cross-section of this configuration is shown in Figure 4.

[0116] The sealed vacuum bag assembly was evacuated to an absolute pressure of 0.06 bar (relative pressure of -0.94 bar, measured at the vacuum port) and placed in the furnace. The furnace was heated to 200°C (air temperature inside the furnace), and as soon as this temperature was reached, the furnace was turned off and the door was opened to allow the sample to cool. Once the sample had cooled sufficiently to be touched, the vacuum was released, the vacuum bag assembly was opened, and the compacted plate was demolded.

[0117] To analyze the compaction quality of the resulting plates, the plates were cut across the fiber direction and embedded in epoxy resin (Struers SpeciFix-20). The cured samples were polished (using a Struers Abramin lapping disc) and imaged using a digital microscope (Keyence VHX-6000). The micrograph shown on the right in Figure 10 shows a typical cross-section of the compacted plate, demonstrating that high quality was achieved (no voids / air trapped inside are observed). [Explanation of Symbols]

[0118] 1 core 2 sheaths 3 Fibers 4. Outer surface of the fiber 5. Adhesive layer Type 6 7 Release film 8. Vacuum distribution medium (air permeable) 9 Vacuum bags 10 Seal tape 11. Ventilation opening for de-aeration 12 Transverse degassing channels 13 Thermoplastic resin or thermosetting matrix 14 Composite material parts 15. Bath of molten glass 16. Molten glass 17. Glass fiber extrusion nozzle 18 Freshly extruded glass fibers 19 Kiss Roll 20 A tank of melted or molten thermoplastic sheath material 21 Finishing Roll 22 Drum roll, winder 23. Recovery Roll or Gathering Shoe 24 Contact surface of the Kiss Roll channel 25 19 24 groove 26 Preform

Claims

1. A method for manufacturing a composite component, comprising using a two-component fiber or multi-component fiber (3) comprising a reinforcing core (1) made of a first material and at least one sheath (2) made of a thermoplastic or prepolymerized thermosetting second material, or by using a tightly bonded preform made of the two-component fiber or multi-component fiber (3), The first material has a degradation temperature, ignition temperature, glass transition temperature, melting temperature, or liquidus temperature that is higher than the melting temperature, flow temperature, glass transition temperature, liquidus temperature, or softening temperature of the thermoplastic or prepolymerized thermosetting second material. The reinforcing core (1) has a core volume fraction (vf) defined as the volume fraction of the reinforcing core (1) in the two-component fiber or multi-component fiber (3), and the core volume fraction (vf) is in the range of 0.3 to 0.

8. Along the longitudinal axis (Z) of the two-component fiber or multi-component fiber, the outer surface of the sheath (2) has a corrugated shape or an irregular corrugated shape. The aforementioned fibers or the aforementioned preforms are, respectively, It is introduced into the mold without additional matrix material. Vacuum is applied, and the thermoplastic or prepolymerized thermosetting second material is heated to a temperature at or above its melting temperature, flow temperature, or softening temperature. The composite material component is compressed while being formed, and then cooled to a temperature below the crystallization temperature or glass transition temperature of the thermoplastic second material, or The composite component is compressed and cured while the thermosetting second material solidifies, The method involves cooling the area afterward.

2. The method according to claim 1, characterized in that the waveform shape has a normalized standard deviation defined as the width distribution of the outer surface of the sheath (2) along the longitudinal axis (Z) within a predetermined window, which is obtained by dividing the standard deviation (σ) by the minimum value (wmin) in the width distribution within the predetermined window, wherein the normalized standard deviation is at least 0.1, or at least 0.2, or even more than 0.3, and the predetermined window is given as a length along the longitudinal axis (Z) that is 5 to 50 times, or 10 to 40 times, or 25 times the average width (〈w〉) of the width distribution.

3. The method according to claim 1 or 2, characterized in that the waveform is such that, over a 100 μm longitudinal length window of the two-component fiber or multi-component fiber (3), the difference in total fiber width between the maximum width portion and the minimum width portion in the transverse direction within this length window is at least 5 μm.

4. The reinforcing core (1) has a core radius (rf) that is essentially constant along the longitudinal axis (Z), The radius of the outer surface of the sheath (2) shows variation along the longitudinal axis (Z) around the average sheath radius, and the variation has a sheath variation amplitude (A). The relative sheath fluctuation amplitude (a), defined as the sheath fluctuation amplitude (A) divided by the core radius (rf), is at least 0.3 and / or The method according to any one of claims 1 to 3, wherein the waveform shape is characterized by a peak portion with a large radius and a trough portion with a small radius, and the ratio of the average longitudinal length of the peak portion to the average longitudinal length of the trough portion over a longitudinal length window of 1 mm is less than 0.

9.

5. The method according to any one of claims 1 to 4, wherein the reinforcing core (1) consists of a single fiber having an essentially circular cross-section, the cross-section being essentially constant along the longitudinal axis (Z), and the diameter of the fiber being in the range of 2 μm to 40 μm, or 5 μm to 25 μm, or 6 μm to 20 μm.

6. The method according to any one of claims 1 to 5, wherein the reinforcing core (1) is a glass fiber, ceramic fiber, or carbon fiber having a round cross-section, and in the case of the glass fiber or carbon fiber, an adhesive layer is provided to improve adhesion with the thermoplastic or thermosetting second material, and / or the core is further a hollow or solid core.

7. The method according to any one of claims 1 to 6, wherein the thermoplastic or prepolymerized thermosetting second material is selected from the group consisting of polyolefins, polyesters, polyamides, polyurethanes, polysulfones, acrylic polymers, polycarbonates, polyphenylene oxides, phenol-formaldehyde resins, polyurea resins, melamine resins, epoxy resins, polyurethane resins, silicone resins, and combinations or copolymers thereof.

8. The method according to any one of claims 1 to 7, wherein the degradation temperature, ignition temperature, glass transition temperature, melting temperature, or liquidus temperature of the first material is at least 10°C, at least 20°C, or at least 50°C higher than the melting temperature, flow temperature, or softening temperature of the thermoplastic or prepolymerized thermosetting second material.

9. The method according to any one of claims 1 to 8, wherein the reinforcing core (1) is a single fiber, or a bundle of at most 50 fibers, or at most 20 fibers, or at most 10 fibers.

10. A method for producing a two-component fiber or a multi-component fiber (3) comprising a reinforcing core (1) made of a first material and at least one sheath (2) made of a thermoplastic or prepolymerized thermosetting second material, wherein the fiber is for producing a composite component without additional matrix material, and the matrix of the composite component consists of the material of the sheath (2). The first material has a degradation temperature, ignition temperature, glass transition temperature, melting temperature, or liquidus temperature that is higher than the melting temperature, flow temperature, glass transition temperature, liquidus temperature, or softening temperature of the thermoplastic or prepolymerized thermosetting second material. The reinforcing core (1) has a core volume fraction (vf) defined as the volume fraction of the reinforcing core (1) in the two-component fiber or multi-component fiber (3), and the core volume fraction (vf) is in the range of 0.3 to 0.

8. Along the longitudinal axis (Z) of the two-component fiber or multi-component fiber, the outer surface of the sheath (2) has a corrugated shape. The reinforcing core (1) is coated with the second thermoplastic or prepolymerized thermosetting material. The thermoplastic or prepolymerized thermosetting second material is heated to a temperature above its melting point and applied to the surface of the reinforcing core in a continuous process while the sheath is cooled and solidified, or The thermoplastic or prepolymerized thermosetting second material is dissolved in a suitable solvent and applied to the surface of the reinforcing core in a continuous process while the solvent evaporates and the sheath forms. The method wherein the second thermoplastic or prepolymerized thermosetting material is applied using a kiss roll, and the corrugated shape is generated by a corrugated surface that structures the contact area of ​​the kiss roll, or both, by adapting the relative rotational speed of the kiss roll to the speed of the reinforcing core (1).

11. The method according to any one of claims 1 to 9, wherein the composite material component is a component of a large-scale energy infrastructure, aerospace, marine, or industrial plant infrastructure, including large aircraft components, ship hulls, rocket fairings, pipes, tanks, silos, or turbine blades, wind rotor blades.

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