BI- OR MULTICOMPONENT FIBRES FOR LARGE COMPOSITE PARTS

Abstract

Bi— or multicomponent fibre (3) comprising a reinforcing core (1) of a first material and at least one sheath (2) of a second, thermoplastic or pre-polymerized thermoset material, for the manufacturing of composite parts, the matrix of which composite parts consists of the material of said sheath (2), wherein said first material has a degradation temperature, ignition temperature, glass transition temperature, melting temperature or liquidus temperature which is higher than the melting temperature, flowing temperature, r softening temperature of said second, thermoplastic or pre-polymerized thermoset material, wherein said reinforcing core (1) has a core volume fraction (v.sub.f) defined as the volume fraction of the reinforcing core (1) in the bi- or multicomponent fibre (3), which is in the range of 0.3-0.8, and wherein along a longitudinal axis (Z) of the bi- or multicomponent fibre outer surface (4) of the sheath (2) has a corrugated, preferably irregular corrugated shape.

Claims

1-15. (canceled)

16. A bi- or multicomponent fibre comprising a reinforcing core of a first material and at least one sheath of a second, thermoplastic or pre-polymerized thermoset material, for the manufacturing of composite parts, the matrix of which composite parts consists of the material of said sheath, wherein said first material has at least one of a degradation temperature, ignition temperature, glass transition temperature, melting temperature and liquidus temperature which is higher than a melting temperature, flow or glass transition temperature, liquidus temperature or softening temperature of said second, thermoplastic or pre-polymerized thermoset material, wherein said reinforcing core has a core volume fraction of defined as a volume fraction of the reinforcing core in the bi- or multicomponent fibre, which is in the range of 0.3-0.8, and wherein along a longitudinal axis of the bi- or multicomponent fibre the outer surface of the sheath has a corrugated shape.

17. The fibre according to claim 16, wherein said corrugated shape has a width distribution of the outer surface of the sheath along the longitudinal axis in a predetermined window which has a normalised standard deviation, defined as the standard deviation a divided by a minimum value w.sub.min in that width distribution in said predetermined window, of at least 0.1 wherein said predetermined window is given as a length along the longitudinal axis which is 5-50 times a mean width (w) of said diameter distribution.

18. The fibre according to claim 16, wherein the corrugation is characterised in that, over a longitudinal length window of 100 μm of the bi- or multicomponent fibre, the difference in total fibre width in a transverse direction between a widest section and a narrowest section within this length window is at least 5 μm.

19. The fibre according to claim 16, wherein said reinforcing core has a core radius r.sub.f)which is essentially constant along said longitudinal axis wherein the radius of the outer surface of said sheath shows variations along said longitudinal axis around a mean sheath radius, said variations having a sheath variation amplitude, and wherein a relative sheath variation amplitude defined as said sheath variation amplitude divided by said core radius r.sub.f, is at least 0.3, and/or wherein said corrugated shape is characterised by peak sections of large radius and valley sections of small radius, and wherein the mean longitudinal length of peak sections divided by the mean longitudinal length of valley sections, is less than 0.9.

20. The fibre according to claim 16, wherein the reinforcing core consists of a single fibre with an essentially circular cross-section, which cross-section is essentially constant along said longitudinal axis.

21. The fibre according to claim 16, wherein the reinforcing core is a glass fibre, ceramic or carbon fibre, with round cross-section.

22. The fibre according to claim 16, wherein said second, thermoplastic or pre-polymerized thermoset material is selected from the group consisting of: polyolefin, polyester, polyamide, polyurethane, polysulfone, acrylic polymers, polycarbonate, polyphenylene oxides, phenol-formaldehyde resins, polyurea resins, melamine resins, epoxy resins, polyurethane resins, silicone resins, and combinations or copolymers thereof.

23. The fibre according to claim 16, wherein said degradation temperature, ignition temperature, glass transition temperature, melting temperature or liquidus temperature of said first material is at least 10° C. higher than the melting temperature, flowing temperature, or softening temperature of said second, thermoplastic or pre-polymerized thermoset material.

24. The fibre according to claim 16, wherein the reinforcing core is a single fibre or a bundle of at most 50 fibres.

25. An essentially coherent preform consisting of fibres according to claim 16.

26. A method for making a fibre according to claim 16, wherein the reinforcing core is coated with said second, thermoplastic or pre-polymerized thermoset material, in that either the second, thermoplastic or pre-polymerized thermoset material is heated to a temperature above its melting temperature and applied to the surface of the reinforcing core in a continuous process under cooling and solidification of the sheath, or the second, thermoplastic or pre-polymerized thermoset material is dissolved in a suitable solvent and applied to the surface of the reinforcing core in a continuous process under evaporation of the solvent and formation of the sheath.

27. The method according to claim 26, wherein the second, thermoplastic or pre-polymerized thermoset material is applied by using a kiss roll, wherein by way of adapting the relative speed of rotation of the kiss roll to the speed of the reinforcing core, by way of corrugated surface structuring the contact region of the kiss roll, or both, the corrugated shape is generated.

28. A method for making a composite part, by using fibres according to claim 16, wherein the fibres or the preform, respectively, are introduced without additional matrix material into a form, subjected to evacuation and heating up to a temperature at or above the melting temperature, flowing temperature, or softening temperature of the second, thermoplastic or pre-polymerized thermoset material, and compacted and cooled, under formation of said composite part or compacted, cured until solidification of the second, thermoset material and under formation of said composite part, and then cooled.

29. A composite part made using fibres according to claim 16.

30. A method of using fibres according to claim 16 in a vacuum forming process for making a composite part.

31. The fibre according to claim 16, wherein along a longitudinal axis of the bi— or multicomponent fibre the outer surface of the sheath has an irregular corrugated shape.

32. The fibre according to claim 16, wherein said corrugated shape has a width distribution of the outer surface of the sheath along the longitudinal axis in a predetermined window with a normalised standard deviation, defined as the standard deviation a divided by the minimum value w.sub.min in that width distribution in said predetermined window, of at least 0.2, or at least 0.3, wherein said predetermined window is given as a length along the longitudinal axis which is 10-40 times the mean width ((w)) of said diameter distribution.

33. The fibre according to claim 16, wherein said corrugated shape is characterised by peak sections of large radius and valley sections of small radius, and wherein, over a longitudinal length window of 1 mm, the mean longitudinal length of peak sections divided by the mean longitudinal length of valley sections, is less than 0.9.

34. The fibre according to claim 16, wherein the reinforcing core consists of a single fibre with an essentially circular cross-section, which cross-section is essentially constant along said longitudinal axis (Z), wherein the diameter of the fibre is in the range of 2-40 μm or in the range of 5-25 μm, or in the range of 6-20 μm.

35. The fibre according to claim 16, wherein the reinforcing core is a glass fibre or carbon fibre with round cross-section, wherein the glass fibre or carbon fibre is provided with a sizing layer for improving adhesion with said second, thermoplastic or thermoset material and/or wherein further the core is a hollow or solid core.

36. The fibre according to claim 16, wherein said degradation temperature, ignition temperature, glass transition temperature, melting temperature or liquidus temperature of said first material is at least 20° C., or at least 50° C. higher than the melting temperature, flowing temperature, or softening temperature of said second, thermoplastic or pre-polymerized thermoset material.

37. The fibre according to claim 16, wherein the reinforcing core is a single fibre or a bundle of at most 20 fibres, or at most 10 fibres.

38. A preform according to claim 25, wherein the preform is a woven, knitted, or nonwoven structure.

39. The method according to claim 28, wherein the composite part is a large energy infrastructure, aerospace, marine or industrial plant infrastructure part.

40. The method according to claim 28, wherein the composite part is a large aeroplane part, a boat hull, a rocket fairing, a pipe, a tank, a silo, or a turbine blade, wind rotor blade.

41. The composite part according to claim 29 in the form of a large energy infrastructure, aerospace, marine or industrial plant infrastructure part.

42. The composite part according to claim 29, in the form of a large aeroplane part, a boat hull, a rocket fairing, a pipe, a tank, a silo, or a turbine blade, wind rotor blade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

[0090] FIG. 1 shows cross sections through possible examples of the proposed fibres;

[0091] FIG. 2 shows cross sections through possible examples of the proposed fibres as bi-component (leftmost example) and multicomponent fibres;

[0092] FIG. 3 shows axial cuts through different examples of the proposed fibres, the uppermost representation reflecting the prior art bicomponent fibre;

[0093] FIG. 4 shows a schematic cut through a vacuum forming device;

[0094] FIG. 5 shows, from left to right, the vacuum forming process in a cut through the material;

[0095] FIG. 6 shows the device for manufacturing the fibre and the downstream coating with the sheath;

[0096] FIG. 7 shows examples of grooves in the kiss roll with arbitrary cross sections;

[0097] FIG. 8 shows an example of the kiss roll with 3 different grooves;

[0098] FIG. 9 shows an example of additional finishing rollers imprinting the thickness variation in the outermost sheath;

[0099] FIG. 10 shows the transformation of the material in the vacuum bagging process with microscopic images;

[0100] FIG. 11 shows the corrugation analysis of several fibres a)-c) according to the invention, wherein in each case the uppermost illustrations shows a micrograph of the respective fibre, the illustration right below a black and white conversion thereof, and at the bottom the total fibre width distribution as a function of the Z axis together with the calculated values for the minimum width, the maximum width, the difference between these two, as well as for the mean value, the standard deviation and the normalised standard deviation.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0101] FIG. 1 shows, in a cross-sectional representation, 16 different examples of fibres which are possible according to the present invention. As one can see, the cross-section of the reinforcing core 1 can be circular (uppermost line), it can however also be rectangular (second line), hexagonal (third line) or it can have an irregular shape (bottom line). However, it should be noted that the core can also be a flat fibre, for example of oval shape, cocoon shape, eyebrow shape, or the like. Furthermore, the core can be a hollow fibre. Also, it can be a mixture of different types of cores in a roving or the like.

[0102] Also, the shape of the sheath, in a cross-sectional view, can have different forms, as given in the first column, it can be circular, but it can also be essentially rectangular as given in the second column, hexagonal, as given in the third column, or irregular as given in the rightmost column. The sheath is defining the outermost surface 4 of the fibre.

[0103] FIG. 2 illustrates that the proposed fibre can be a bicomponent fibre as illustrated in the leftmost representation, consisting of the core 1 and the sheath 2. However, it can also be a multicomponent fibre as given in the other representations. Typically, it is a multicomponent fibre in the sense that, as illustrated in the second representation from the left, the outer surface of the core 1, in particular in case of a glass fibre, is first provided a so-called sizing layer 5, providing for an improved adhesion between the core material and the sheath matrix material, and only then follows the sheath 2 forming the outermost layer of the fibre. Further layers can be present, as illustrated in the 2 rightmost representations, wherein the rightmost representation illustrates an example with the reinforcing core 1 including a sizing layer 5, then followed by 2 additional layers and finally surrounded by the sheath 2. These 2 additional layers can also be made of thermoplastic material and can therefore be considered part of the sheath and to be molten in the manufacturing process to become matrix material. The 2 additional layers can however also be part of the core, so not to be molten in the manufacturing process of the composite part.

[0104] FIG. 3 illustrates axial cuts through fibres. In each case, the core fibre has a constant diameter along the longitudinal axis. However, it is in principle also possible that the core is provided with corrugations. The uppermost representation illustrates the situation according to the state-of-the-art, in this case the sheath along the longitudinal axis of the fibre is not provided with corrugations, but is essentially smooth. The problem with these fibres is that if packed into the form in a transverse direction the deaeration properties are insufficient to allow for the manufacturing of large composite parts.

[0105] The second example from the top is provided with a regularly oscillating sheath structure. Such structures may have the problem that due to the symmetry of the outer surface adjacent fibres may nest and not generate sufficient deaeration channels.

[0106] This is improved in the third example from the top, where the widening sections are spaced sufficiently so as to avoid nesting without deaeration channels.

[0107] The fourth example from the top and the two remaining (lowermost) examples represent irregular corrugation structures, normally due to the production process even if regular structures are imposed for example by kiss roll, rather irregular structures will be produced.

[0108] FIG. 4 schematically represents a vacuum bagging layup to convert the proposed fibres, or preforms made thereof, in the form of a preformed stack into a consolidated laminate. The preform 26 is located on top of the mould 6, wherein between the mould and the preform that can be provided a release film (not illustrated). From bottom to top, the preform is followed by a perforated release film 7, then by a vacuum distribution medium 8, and finally by the vacuum bag 9. At the edges sealing tapes 10 are provided for sealing the interior of the vacuum bag, and at least one peripheral point there is provided a vent 11 for deaeration, so to apply the vacuum. Typically, the mould and/or the vacuum bag are provided with means for heating.

[0109] FIG. 5 shows schematically what is taking place, if in such a mould vacuum is applied and then heat. The leftmost illustration shows the fibres arranged essentially parallel to each other, but well spaced due to the corrugations of the sheaths. Between the fibres there remain deaeration channels 12 illustrated with dotted areas. These deaeration channels 12 allow venting, so removal of air in a transverse direction. If the vacuum is applied, as represented in the second representation from the left, air schematically illustrated by the dots in the leftmost representation, is removed from those deaeration channels 12. If then heat is applied while continuing the vacuum, the sheath begins to melt as illustrated in the second representation from the right, and there still remain transverse deaeration channels sufficient to allow for essentially complete deaeration with no encapsulations or entrapments of air in the form of weakening bubbles or the like. At the end the matrix 13 fully surrounds the reinforcing cores 1 and the composite part 14 is formed.

[0110] FIG. 6 shows the spinning process from fibre formation to take up on winder including in-line kiss roll coating and optional additional finishing rollers to imprint thickness variation in outermost sheath. In a bath 15 molten glass 16 is provided, and this glass is flowing through an array of glass fibre extrusion nozzles 17. The freshly extruded glass fibre 18 is solidifying downstream of these extrusion nozzles 17 and after solidification is in line coated with the sheath material by way of a kiss roll 19. Kiss roll 19 is immersed partially in bath 20 of dissolved or molten thermoplastic sheath material. In the representation given on the left side the kiss roll rotates in a counter clockwise direction to contact, with the contact surface 24, the fibres passing on the surface of the kiss roll, and due to the rotation the thermoplastic material, either molten or in a solvent, is carried on that surface as entrained from the bath 20. By adapting the transportation speed of the glass fibre relative to the speed of rotation of the kiss roll, i.e. the relative speed of fibre and kiss roll surface, the corrugations can be adapted to the needs. Downstream of the kiss roll, at a position where the thermoplastic material has not yet solidified in case of application of molten thermoplastic material, or at a position where the solvent has not yet fully evaporated in case of application of the solution of thermoplastic material, there can be provided a pair of finishing rolls 21 which shall be explained further below in the context of FIG. 9. In case of extrusion of several parallel strands of glass fibre there can be a collecting roll or gathering shoe 23 downstream of that finishing roll pair, and finally the fibres 3 are collected on the winder 22.

[0111] FIG. 7 schematically illustrates a possible cross-sectional shape of the groove 25 in the kiss roll for the purposes described in the summary of the invention.

[0112] FIG. 8 schematically illustrates a kiss roll 19 with 3 different grooves for imparting a corrugated topology on the glass fibers passing through these grooves 25 for the coating of the second thermoplastic material on the core fibre.

[0113] FIG. 9 illustrates the possibility of using a pair of finishing rolls 21 to generate the corrugated surface on a smooth core fibre. The sheath is applied using the kiss roll in a way generating an essentially smooth surface, leading to the situation as illustrated with 3′. To generate the corrugations the still wet or the still partly soft sheath layer is pressed between the pair of rolls 21 having a corrugated surface topology. This corrugated imprint is then forming the outer surface of the final fibre so leading to the corrugated structure along the longitudinal direction.

[0114] FIG. 10 illustrates with microscopic pictures the transition from the packed glass fibres with corrugated surface (upper left) followed by vacuum and heat treatment and leading to the composite article without any voids of air (lower right). The representations are derived from the specific example detailed below.

[0115] FIG. 11 illustrates micrographs of fibres, which were converted into binary images showing the fibre in white and its surrounding in black. These binary images were measured for the distribution of fibre width along its longitudinal Z axis (array of number of white pixels in every column). The plots show the resulting signals and the relevant statistical measures in the title. It can be seen that all samples exhibit normalized standard deviation values σ/w.sub.min>0.1.

[0116] Experimental Section:

Example for Fabrication of Fibre with Corrugated Coating

[0117] The fibres shown in the first two samples a) and b) of FIG. 11 were produced as follows: Alumino-borosilicate glass marbles (Sigmund Lindner SiLibeads, type SL) were heated to 1240° C. inside a bushing consisting of Pt/Rh and embedded in refractory. The bushing was resistance heated (Joule effect) and contained a single spinning nozzle at its lower end. The stream of molten glass exiting the spinning nozzle was drawn downwards by a traversing winder and wound onto a cardboard collet (diameter 136 mm) covered with a polytetrafluoroethylene film. Between the spinning nozzle and the winder, the continuously spun single glass fibre was drawn over a rotating kiss-roll (diameter 130 mm) which was partially immersed in a bath containing a polymer solution. The solution contained 11.5 vol % polycarbonate (Covestro Makrolon 3108) dissolved in trichloromethane (Sigma-Aldrich 319988).

[0118] In order to realize a corrugated coating with irregular corrugations along the length of the fibre, the spinning and coating parameters were chosen such that a) the fluid film entrained by the kiss-roll would exhibit a corrugated thickness along the circumference of the kiss-roll; and b) the fluid film entrained by the fibre as it was withdrawn from the liquid film on the kiss-roll would exhibit a corrugated thickness along the length of the fibre, even if the fluid film on the kiss-roll would exhibit a constant thickness along its circumference. This was realized by forcing both the withdrawal of liquid from the bath onto the kiss-roll and the withdrawal of liquid from the kiss-roll onto the fibre to operate in a flow regime which is subject to a Plateau-Rayleigh-type instability. Given the necessary physical conditions, such instabilities occur in dip-coating-like free surface flows, as described in A. G. Gonzalez, J. A. Diez, R. Gratton, D. M. Campana, F. A. Saita, Instability of a viscous liquid coating a cylindrical fibre, Journal of Fluid Mechanics 651 (2010) 117-143. doi: 10.1017/S0022112009993788.

[0119] The necessary conditions to force these instabilities can be described by the Capillary number Ca, which is defined as the withdrawal velocity V times to dynamic viscosity n of the coating fluid divided by the surface tension γ of the coating fluid:

[00002]$\mathrm{Ca}\stackrel{\Delta }{=}\frac{V\eta }{\gamma }$

[0120] To make it possible for such instabilities to occur, this dimensionless number needs to be close to unity or larger. Depending on the geometry of the substrate, which is withdrawing the liquid, a value greater than 0.01 may already suffice to promote an instability in the flow. The samples illustrated in FIG. 11 were produced using a peripheral roll velocity of 0.3 m/s and fibre velocities of 5.0 m/s (sample a) and 7.9 m/s (sample b), respectively.

[0121] The dynamic viscosity of the polymer solution was determined at ambient conditions using oscillatory and continuous rotational rheometry (Anton Paar MCR 502) with a double-wall couette measuring cell (concentric cylinders, 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 an amplitude of 100% revealed phase shift angles greater than 85°, indicating that elastic effects are negligible. Flow curves over shear rates of 10 1/s to 1000 1/s revealed constant values, therefore showing Newtonian behaviour of the solution. The solution of 11.5 vol % polycarbonate in trichloromethane was measured to exhibit a dynamic viscosity of 6.70 mPa s.

[0122] The surface tension of the polymer solution was determined at ambient conditions using the pendant drop method performed on a Kruss DSA100 drop shape analyzer. Per solution tested, at least 30 droplets were produced by extrusion through a steel cannula with a flat end and an outer diameter of 1.8 mm. Each droplet produced was imaged 31 times. For the solution of 11.5 vol % polycarbonate in trichloromethane, the drop shape analyzer returned a surface tension of 25.8 mN/m.

[0123] With the above measurements for the fluid properties of the solution, it can be determined that the coated fibre samples were produced using Capillary numbers as given in the following table:

TABLE-US-00001 Capillarity of flow Fibre Capillarity of flow Sample onto the kiss-roll velocity onto the fibre a Ca = 0.078 5.0 m/s Ca = 1.30 b Ca = 0.078 7.9 m/s Ca = 2.05

Example for Vacuum Bagging Process

[0124] A bicomponent monofilament sample was produced by spinning alumino-borosilicate glass (Sigmund Lindner SiLibeads, type SL) at 1240° C. and at a fibre velocity of 4.34 m/s and kiss-roll coating it with a solution of 21 vol % polymethyl methacrylate (Evonik Plexiglas 7N) in trichloromethane (Sigma-Aldrich 319988) at a peripheral roll velocity of 0.3 m/s and a kiss-roll diameter of 130 mm. The resulting sample was measured to contain a core fibre volume fraction (glass volume fraction) of 58.1 vol %. This was measured using thermogravimetric analysis in a Perkin Elmer Pyris 1 TGA (temperature profile: ambient to 600° C. at 10 K/min, dwell at 600° C. for 10 min, then to ambient at −60 K/min) and converting the mass fraction to volume fraction using densities of 2.59 g/cm.sup.3 for the glass and 1.19 g/cm.sup.3 for the polymer.

[0125] The sample was consolidated into a stiff plate using a vacuum bag process. The sample was cut to lengths of ca. 6 cm and placed onto an aluminium plate in a uni-directional fashion (all fibres arranged in parallel). The plate was previously treated with a release agent (Loctite Frekote 700-NC) for easier release after the process. The sample was first covered with a release film (Airtech Wrightlon 5200, ETFE), then with a breather fleece (Airtech Air-weave N4, polyester), and finally with a vacuum film (Airtech Wrightlon 7400). The purpose of the breather fleece was to distribute the vacuum around the periphery of the sample, while the release film hindered the sample from adhering to said breather fleece on the top surface of the arrangement. The vacuum film was sealed to the aluminium plate using sealant tape (“Tacky tape”, Airtech AT 200 Y) to form an airtight vacuum bag assembly. A vacuum port was included next to the sample. A cross-section of this arrangement is depicted in FIG. 4.

[0126] The sealed vacuum bag assembly was evacuated to an absolute pressure of 0.06 bar (−0.94 bar relative pressure, measured at the vacuum port) and placed in an oven. The oven was heated to 200° C. (air temperature in the oven) and as soon as this temperature was reached, the oven was turned off and the door opened to cool the sample. As soon as the sample was cold enough to touch by hand, the vacuum was released and the vacuum bag assembly was opened to release the consolidated plate.

[0127] To analyse the consolidation quality of the resulting plate, it was cut across the fibre direction and embedded in epoxy (Struers SpeciFix-20). The cured specimen was polished (Struers Abramin lapping machine) and imaged under a digital microscope (Keyence VHX-6000). The micrograph illustrated on the right side in FIG. 10 depicts a representative cross-section of the consolidated plate, demonstrating the high quality achieved (no visible voids/air entrapments).

TABLE-US-00002 LIST OF REFERENCE SIGNS 1 core 2 sheath 3 fibre 4 outer surface of the fibre 5 sizing layer 6 mould 7 release film 8 vacuum distribution medium (breather) 9 vacuum bag 10 sealing tape 11 vent for deaeration 12 transverse deaeration channels 13 thermoplastic or thermoset matrix 14 composite part 15 bath of molten glass 16 molten glass 17 glass fibre extrusion nozzles 18 freshly extruded glass fibre 19 kiss roll 20 bath of dissolved or molten thermoplastic sheath material 21 finishing rolls 22 drumroll, winder 23 collecting roll or gathering shoe 24 contact surface of kiss roll 25 groove in 24 of 19 26 preform