WO2019236950A1

WO2019236950A1 - Stitching yarn containing hollow fibers or filaments, and ncf fabric containing such yarn

Info

Publication number: WO2019236950A1
Application number: PCT/US2019/035965
Authority: WO
Inventors: Dominique Ponsolle; Carmelo Luca Restuccia; Andreas NAHR; Pierre-Yves Lahary; Jerome BIKARD
Original assignee: Cytec Industries, Inc.
Priority date: 2018-06-07
Filing date: 2019-06-07
Publication date: 2019-12-12

Abstract

The present disclosure relates to a stitching yarn and non-crimp fabrics containing such yarn. The stitching yarn described herein is a stitching yarn comprising at least one hollow fiber or filament, the at least one hollow fiber or filament comprising one or more hollow voids, typically one hollow void, extending longitudinally through a substantial portion of said fiber or filament. The present disclosure also relates to a fiber preform, composite material, and composite article containing the non-crimp fabric.

Description

STITCHING YARN CONTAINING HOLLOW FIBERS OR FILAMENTS, AND NCF

FABRIC CONTAINING SUCH YARN

Cross Reference to Related Applications

This application claims priority to U.S. Provisional Application No. 62/681 ,752, filed June 7, 2018, the entire contents of which is hereby incorporated by reference.

Field of the Invention

The present invention relates to stitching yarns and NCF fabrics containing such yarns. The present invention further relates to preforms, composite materials, and composite articles containing the NCF fabrics described herein. The preforms, composite materials, and composite articles according to the present disclosure are particularly suited to the production of composite parts for use in many applications, such as in the aviation field as well as in the automobile and naval industries.

Background of the Invention

Noncrimped fabrics (NCF) generally comprise one or more layers of structural fibers, filaments, or yarn, each layer having the fibers, filaments, or yarns oriented in discrete directions. The fibers, filaments, or yarn are also referred to as reinforcement fibers, filaments, or yarn. The layers are typically consolidated by a stitching yarn.

The development of microcracking in a composite part may result, in part, from stress generation in the thermoset resin used in manufacturing the composite part. Such stress generation may arise from thermal contraction/expansion during heating/cooling conditions used in manufacturing or encountered in the environment during use. Further mechanisms that may lead to stress generation and microcracking behavior include, but are not limited to, mismatch of the coefficient of thermal expansion (CTE) of constituent materials, modulus difference and/or lack of bonding compatibility between the resin matrix and stitching thread material. Herein, a new strategy for limiting microcracking behavior of composite articles by reducing stress generation in composite parts by engineering the stitching yarn, particularly through the use of hollow fiber or filaments, used in the formation of the constituent NCF fabric is described.

Summary of the Invention

In a first aspect, the present disclosure relates to a non-crimp fabric comprising at least one layer of unidirectionally oriented multifilament carbon yarns and a stitching yarn interlinking the multifilament carbon yarns, wherein the stitching yarn comprises at least one hollow fiber or filament, the at least one hollow fiber or filament comprising one or more hollow voids, typically one hollow void, extending longitudinally through a substantial portion of said fiber or filament.

In a second aspect, the present disclosure relates to a fiber preform comprising the non-crimp fabric described herein.

In a third aspect, the present disclosure relates to a composite material, comprising:

- a matrix resin, and

- a non-crimp fabric according to the present disclosure.

In a fourth aspect, the present disclosure relates to a composite article obtained by curing the composite material described herein.

In a fifth aspect, the present disclosure relates to a process for making a non-crimp fabric described herein, the process comprising interlinking a plurality of multifilament carbon yarns into a unidirectionally oriented layer with a stitching yarn, wherein the stitching yarn comprises at least one hollow fiber or filament, the at least one hollow fiber or filament comprising one or more hollow voids, typically one hollow void, extending longitudinally through a substantial portion of said fiber or filament.

Brief Description of the Figures FIG. 1 shows the cross-sections of various fibers or filaments comprising one or more hollow voids suitable for use according to the present disclosure - a), b) circular void having various void diameter and wall thickness; c), d), e) multilobal void having various number and shape of lobes; f) triangular void; g) quadrangular void.

Detailed Description

The development of microcracking in a composite part may result, in part, from stress generation in the thermoset resin used in manufacturing the composite part. Such stress generation may arise from thermal contraction/expansion during heating/cooling conditions used in manufacturing or encountered in the environment during use. The present disclosure contemplates a new strategy for limiting microcracking behavior of composite articles by reducing stress generation in such articles by using hollow fiber or filaments to fabricate stitching yarns used in the formation of NCF fabric.

Without wishing to be bound by theory, the use of fibers or filaments having one or more hollow voids in stitching yarns used in the manufacture of NCF fabric is believed to reduce the stress in the filaments of the said stitching yarn and creates an internal space for the filament to expand or contract due to the thermal conditions without inducing microcracking of the resin matrix or debonding from the matrix during the cure of the composite or during standard aircraft operational conditions. This stress reduction mechanism may be controlled by modulating the properties of the fiber or filament containing the one or more hollow voids, for instance, void size, and the chemical and thermomechanical nature and thickness of the material surrounding the void, among others. Such relief of thermal stresses reduces the propensity for microcracking as hollow fiber releases more stress than full fiber inside a resin pocket.

Thus, the present disclosure relates to a non-crimp fabric comprising at least one layer of unidirectionally oriented multifilament carbon yarns and a stitching yarn interlinking the multifilament carbon yarns, wherein the stitching yarn comprises at least one hollow fiber or filament, the at least one hollow fiber or filament comprising one or more hollow voids, typically one hollow void, extending longitudinally through a substantial portion of said fiber or filament.

As used herein, the terms“a”,“an”, or“the” means“one or more” or“at least one” unless otherwise stated.

As used herein, the term“comprises” includes“consists essentially of” and“consists of.” The term“comprising” includes“consisting essentially of and“consisting of.”

The term“non-crimp fabric” or“non-crimped fabric”, sometimes“NCF”, refers to a construct comprising one or more layers of fibers, filaments, or yarns. The fibers, filaments, or yarns in a single layer are arranged such that they are parallel to each other and oriented in a single direction (i.e. , unidirectional). Multiple layers may be stacked so that the fibers, filaments, or yarns of one layer are oriented parallel to the fibers, filaments, or yarns of an adjacent layer or are oriented crosswise to the fibers, filaments, or yarns of an adjacent layer. When the fibers, filaments, or yarns of one layer are oriented crosswise to the fibers, filaments, or yarns of an adjacent layer, the angles between the axis of one layer, the axis being determined by the direction of the fibers, filaments, or yarns in the layer, and that of the axis of the adjacent layer are virtually infinitely adjustable. For example, the angles between adjacent fiber layers may be 0°or 90°, or such angles plus or minus 25°, plus or minus 30°, plus or minus 45°, or plus or minus 60°, the zero-degree direction being determined by methods known to those of ordinary skill in the art. For example, the machine direction may be designated as the 0° direction. Accordingly, the term“multiaxial” refers to an NCF fabric having more than one layer, each layer oriented in various directions. Multiaxial fabrics include biaxial fabrics in which the layers are oriented in two directions and triaxial fabrics in which the layers are oriented in three directions, and so on. Multiaxial non-crimp fabrics can be produced e.g. by means of warp knitting looms or stitch bonding machines.

In an embodiment, the non-crimp fabric comprises one layer of unidirectionally oriented multifilament carbon yarns. In another embodiment, the non-crimp fabric comprises more than one layer of unidirectionally oriented multifilament carbon yarns. In an embodiment, the non-crimp fabric comprises more than one layer of unidirectionally oriented multifilament carbon yarns, which layers are oriented in the same direction. In another embodiment, the non-crimp fabric comprises more than one layer of unidirectionally oriented multifilament carbon yarns, which layers are oriented in different directions.

As used herein, a yarn is a continuous strand of one or more fibers, one or more filaments, or material in a form suitable for use in the production of textiles, sewing, crocheting, knitting, weaving, stitching, etc. Yarns include, for example, (1 ) a plurality of filaments laid or bundled together without applied or intentional twist, sometimes referred to as a zero-twist yarn or a non-twisted yarn; (2) a plurality of filaments laid or bundled together and are either interlaced, have false-twist, or are textured in some manner; (3) a plurality of filaments laid or bundled together with a degree of twist, sometimes referred to as a twisted yarn; (4) a single filament with or without twist, sometimes referred to a monofilament or monofilament yarn. Textured yarns may be filament or spun yarns that have been given noticeably greater volume through physical, chemical, or heat treatments or a combination of these. In some instances a yarn is called a filament yarn or a multifilament yarn, both of which are generally yarns made from a plurality of filaments.

As used herein,“fiber” refers to a material having a high ratio of length to thickness. Fibers may be continuous, in which case such fibers are referred to as filaments, or staple length (i.e. , discrete length).

The unidirectionally oriented multifilament carbon yarns within a single layer of the NCF of the present disclosure are interlinked by a stitching yarn having at least one hollow fiber or filament, the at least one hollow fiber or filament comprising one or more hollow voids, typically one hollow void, extending longitudinally through a substantial portion of said fiber or filament.

The at least one hollow fiber or filament may be characterized by linear mass density, given in units of tex, or more commonly decitex (dtex), and is defined as the mass in grams per 1000 meters of the hollow fiber or filament. In an embodiment, the at least one hollow fiber or filament has a linear density of less than 800 dtex, less than 100 dtex, less than 80 dtex, less than 50 dtex, less than 10 dtex, or less than 5 dtex. In some embodiments, the at least one hollow fiber or filament has a linear density of less than 5 dtex, typically less than 3 dtex, more typically less than 2 dtex.

The hollow fiber or filament comprises an outer surface and one or more inner surfaces, the inner surface or surfaces defining the void or voids extending longitudinally through the hollow fiber or filament. Since each hollow void is defined by a surface surrounding the void inside the fiber or filament, it would be understood that the cross-sectional shape exhibited by the void is defined by the cross-sectional shape of the surface surrounding the void.

The shape of the one or more hollow voids extending longitudinally through a substantial portion of said fiber or filament, as viewed by cross-section, is not particularly limited. The cross-sectional shape exhibited by the one or more hollow voids extending through the length of the fiber or filament may be random and/or irregular, or may have a defined shape, such as circular, triangular, rhomboid, multilobal, or a shape characterized by a mathematical function, such as sinusoidal shape. As used herein, the term“multilobal” refers to a shape having more than one critical point along the boundary of the hollow void. A critical point is defined as being a change in the absolute value of the slope of a line drawn perpendicular to the boundary of the hollow void when the boundary is cut perpendicular to the void axis. In an embodiment, the cross-sectional shape of the one or more hollow voids extending throughout the length of the fiber or filament is circular or substantially circular. In the case where the cross-sectional shape of the one or more hollow voids extending throughout the length of the fiber or filament is circular or substantially circular, the size of the cross-sectional shape of the hollow void may be characterized by a void diameter, which is defined herein as the diameter of the cross-section of the void. Figures 1 a and 1 b show the schematic diagrams of circular or substantially circular cross-sectional shapes of fibers or filaments suitable for use according to the present disclosure. In another embodiment, the cross-sectional shape of the one or more hollow voids extending throughout the length of the fiber or filament is multilobal. Figures 1 c to 1 e show the schematic diagrams of multilobal cross-sectional shapes of fibers or filaments suitable for use according to the present disclosure.

Figures 1f and 1 g show the schematic diagrams of a triangular cross-sectional shape and a quadrangular, such as square, cross-sectional shape, respectively, of fibers or filaments suitable for use according to the present disclosure.

The shape of the outer surface of the one or more fibers or filaments, as viewed by cross-section, is also not particularly limited. The cross-sectional shape exhibited by the outer surface of the one or more fibers or filaments, including polymeric fibers or filaments, may be the same or different from those of the cross-sectional shape exhibited by the hollow void(s). For example, the cross-sectional shape of the outer surface of the one or more fibers or filaments may be random and/or irregular, or may have a defined shape, such as circular, triangular, rhomboid, multilobal, flat elongated shape with rounded ends, or a shape characterized by a mathematical function, such as sinusoidal shape. In an embodiment, the cross-sectional shape of the outer surface of the one or more fibers or filaments, including polymeric fibers or filaments, is circular or substantially circular.

In accordance with the present disclosure, the fibers or filaments comprising the one or more hollow voids may further comprise additional voids that partially or fully extend throughout the length of the fibers or filaments. In an embodiment, the at least one hollow fiber or filament comprises one hollow void extending longitudinally through the entire fiber or filament.

In an embodiment, both the cross-sectional shape of the hollow void extending throughout the length of the fiber or filament and the cross-sectional shape of the outer surface of the fiber or filament are circular or substantially circular. In such an embodiment, the boundary surface of the hollow void defines an internal radius and the outer surface of the fiber or filament defines an external radius. In an embodiment, the external radius is from 2 miti to 200 miti, typically 2 miti to 20 miti, more typically 5 pm to 15 pm.

The size of the one or more hollow voids extending through the length of the fibers or filaments may be characterized by a ratio of cross-sectional area of the void to the cross-sectional area of the surrounding fiber material. The ratio of cross sectional area of the void to that of the surrounding fiber material is greater than 0 and less than 5, typically less than 3, more typically less than 1. In an embodiment, the ratio of cross sectional area of the void to that of the surrounding fiber material is in a range from 0.05 to 1 , typically 0.05 to 0.65.

A person of ordinary skill in the art will understand that the cross-sectional shape of the outer surface and of the inner surface surrounding the one or more voids may be distorted by preparation, for example, by cutting, of the fiber or filament for observation. To avoid the collapse of the filament and deformation of the cross- section to be observed, the filaments are prepared in a manner such that the filaments retain their original shape prior to cutting and observation. Preparation of the filaments may include freezing the filaments using liquid nitrogen or injecting a wax in the hollow section of the filaments and allowing it to solidify prior to cutting the filaments with a very sharp blade, such as a scalpel blade. Then the observation process can be performed using any available instrumentation and methods known to those of ordinary skill in the art, such as SEM microscopy.

The stitching yarn may comprise one or more fibers or filaments, at least one of which contains one or more hollow voids extending longitudinally through a substantial portion of said fiber or filament. Thus, when the stitching yarn is a multifilament yarn, it may be characterized by filament count, which is the number of filaments making up the yarn. The filament count of the stitching yarn is less than or equal to 1.0 times the linear density of the stitching yarn, typically less than or equal to 0.9 times the linear density, more typically less than or equal to 0.8 times the linear density. In some embodiments, the filament count is in the range of 0.1 to 0.8 times the linear density of the yarn, typically 0.1 to 0.6 times the linear density of the yarn, more typically 0.1 to 0.5 times the linear density of the yarn.

The one or more fibers or filaments, including the at least one hollow fiber or filament, of the stitching yarn may be made from any material known to be suitable for use in composite parts. The fibers or filaments, including the at least one hollow fiber or filament, may be organic, typically polymeric, for example, comprising polyamide, copolyamide, polyester, and/or copolyester; or inorganic, for example, comprising carbon, glass, silica, basalt, ceramic, or mixtures thereof.

Suitable polymeric materials include, but are not limited to, polyamides such as aliphatic polyamides (PA), cycloaliphatic polyamides, aromatic polyamides, polyphthalamides (PPA), ether or ester block polyamides (PEBAX, PEBA), polyesters such as polyethyleneterephthalates (PET), polyethylenenaphthalates (PEN) and Polytrimethylene terephthalate (PTT) , polyolefines such as polypropylenes (PP), polyethylenes (PE), thermoplastic polyolefins (TPO) such as Ethylene Propylene Diene (EPDM) and Ethylene Propylene (EPR) rubbers polyphenylene sulfides (PPS), , polyetherimides (PEI), polyimides (PI), polyimides having phenyltrimethylindane structure, polyamidoamides (PAI), polysulfones, polyarylsulfones such as polyethersulfone (PES), polyethersulfone-etherethersulfone (PES:PEES), polyetherethersulfone (PEES), polyketones, polyaryletherketone (PAEK) such as polyetherketone (PEK), polyetheretherketone (PEEK) and polyetherketoneketones (PEKK), polyurethanes, polyether or polyester-b-urethanes, thermoplastic polyurethanes, polycarbonates, polyacetals, polyphenyleneoxides (PPO), polyethers, polyethernitriles, polybenzimidazoles, thermoplastic elastomers, such as Styrene Ethylene Butylene Styrene (SEBS), Styrene Ethylene Propylene Styrene (SEPS) and Styrene Butylene Styrene (SBS) block copolymers and hydrogenated versions thereof, vulcanized thermoplastic elastomers (TPV) such as vulcanized Ethylene Propylene Diene block copolymers; liquid crystal polymers (LCPs), and combinations and copolymers thereof. In an embodiment, the stitching yarn comprises polymeric fibers or filaments comprising polyamide, polyester, polyhydroxyethers, or copolymers thereof. In another embodiment, the stitching yarn comprises polymeric fibers or filaments comprising PA 6, PA 6/6, PA 6T, PA 12, PA 6/10, PA 9T, PA 10/10, PA 10T, PA1 1 , PA 6/12, PA 10/12, or blends or copolymers thereof.

The fibers or filaments, including the at least one hollow fiber or filament, of the stitching yarn may be characterized by the density of the material used to produce the fibers or filaments, including the at least one hollow fiber or filament. In an embodiment, the material used to produce the at least one hollow fiber or filament has a density of from 0.5 to 2.5 g/cm³, typically from 0.8 to 1.8 g/cm³, more typically from 0.9 to 1.5 g/cm³. In another embodiment, the material used to produce the at least one hollow fiber or filament has a density of from 0.9 to 1 .4 g/cm³.

In accordance with the present invention, the linear density of the stitching yarn is in the range of 1 to 800 dtex, typically 1 to 150 dtex, more typically 1 to 60 dtex, even more typically 1 to 40 dtex.

The fibers or filaments of the stitching yarn may be interlaced, also referred to as entangled or intermingled, according to methods known to those of ordinary-skill in the art. For example, yarn filaments may be interlaced by exposing a plurality of filaments to a localized fluid jet, such as an air stream. Interlacing gives rise to points of entanglement, called nodes, which are separated by spaces of unentangled filaments. Thus, the extent of interlacing is typically given as the number of nodes per meter of yarn. The extent of interlacing of the multifilament stitching yarn is less than 25 nodes / meter.

In an embodiment, the non-crimp fabric is multiaxial and comprises more than one layer of unidirectionally oriented multifilament carbon yarns. The layers of a multiaxial NCF fabric can be connected and secured to each other according to methods known to those of ordinary skill in the art, for example, by a plurality of stitching or knitting threads arranged parallel to each other and running parallel to each other and forming stitches. The stitching or knitting threads used to connect and secure the layers of the multiaxial NCF fabric to each other may be the same as or different from the stitching yarn described herein. In an embodiment, the stitching or knitting threads used to connect and secure the layers of the multiaxial NCF fabric to each other is the same as the stitching yarn described herein.

The stitching yarn holds together the unidirectionally oriented multifilament yarns within a single layer of the NCF and/or secures two or more layers in the NCF fabric to one another, and does not provide any structural reinenforcement. Thus, the stitching yarn used according to the present disclosure for interlinking of the unidirectionally oriented multifilament carbon yarns within a single layer of the NCF and/or the consolidation of two or more layers in the NCF fabric is non-structural. In contrast, the unidirectionally oriented multifilament carbon yarns are structural as they provide structural reinforcement in a composite material or article made therefrom.

The stitching yarn used to consolidate the yarns within in a single layer of an NCF fabric and/or connecting and securing a plurality of layers of yarns may be characterized by twist. As used herein, twist refers to the spiral arrangement of the fibers or filaments around the axis of a yarn. The stitching yarn of the present disclosure may or may not contain twist. Twist, when present, is provided as the number of revolutions per unit length, typically revolutions per meter. The stitching yarn described herein has a low amount of twist, typically less than 200 revolutions per meter. In an embodiment, the stitching yarn has a twist of less than 150 r/m, typically less than 100 r/m, more typically less than 50 r/m. In an embodiment, the stitching yarn has no twist.

The tension and its control as applied to the stitching yarn is adjustable and its level is selected based on a combination of several parameters that include, for example, the stitching yarn attributes, stitching pattern, and desired drape, among others. While there is no particularly limitation on the tension applied to the stitching yarn during its insertion into the NCF, the tension typically applied to the stitching yarn is low. The tension and its control on the carbon fibers depends on the quality of the preparation of the carbon tows before laydown and the quality of the preparation after they have been laid down and clamped to the machine conveyor. While there is no particular limitation on the tension on the carbon fibers, a higher tension is typically used.

The non crimp fabric may further comprise one or more layers of a nonwoven veil. For example, the non crimp fabric may comprise a layer of unidirectionally oriented multifilament carbon yarns combined with a layer of a nonwoven veil. Any nonwoven veil known to those of ordinary skill in the art may be used. The layers constituting the NCF fabric, including the one or more layers of nonwoven veil, can be connected and secured to each other according to methods known to those of ordinary skill in the art, for example, by a plurality of stitching or knitting threads. The nonwoven veil layer, when used, advantageously provides improved process performance, such as permeability, as well as mechanical performance, such as impact and delamination resistance. Exemplary nowwoven veils that may be used are described in PCT Publications WO 2017/083631 and WO 2016/003763, which are incorporated by reference.

The interlinking of the unidirectionally oriented multifilament carbon yarns within a single layer of the NCF and/or the consolidation of two or more layers in the NCF fabric may be achieved using various stitch types, stitch width (i.e. , the distance between the points in the weft direction), and stitch lengths (i.e., the distance between the points in the warp direction) known to those of ordinary skill in the art. Suitable stitch patterns include straight stitches, chain stitches, lock stitches, zig-zag stitches, tricot stitches, or a combination thereof. There is no particular limitation to the stitch width and the stitch length that may be used. For example, the stitch width may be in the range of 1 to 20 mm, typically 1 to 10 mm. The stitch length may be in the range of 1 to 20 mm, typically 1 to 10 mm, for instance.

The present disclosure also relates to a fiber preform comprising the non-crimp fabric described herein. The fiber preform comprises at least one layer of the non- crimp fabric. As used herein, the term“preform” refers to a construct in which one or more layers of reinforcement material, such as the NCF fabric described herein, are laid without matrix resin in a mold for further processing, such as infusion or injection of matrix resin, to form a composite material or article.

The fiber preform may further comprise layers of any type of textiles known to those of ordinary skill for manufacturing composite materials. Examples of suitable fabric types or configurations include, but are not limited to: all woven fabrics, examples of which are plain weave, twill weave, sateen weave, spiral weave, and uni-weave fabrics; warp-knitted fabrics; knitted fabrics; braided fabrics; all non-woven fabrics, examples of which include, but are not limited to, nonwoven veils, mat fabrics composed of chopped and/or continuous fiber filaments, felts, and combinations of the aforementioned fabric types.

In an embodiment, the fiber preform may further comprise a non-woven veil. Any non-woven veils known to those of ordinary skill in the art may be used. For example, the veil described in PCT International Publication WO 2017/083631 may be used. A binder component may be distributed on at least one side of the nonwoven veil layer or penetrated through portions of the nonwoven veil, or distributed throughout the non-crimp fabric, including in spaces between the unidirectionally oriented fibers and on portions of the veil. For example, the binders described in PCT International Publication WO 2016/003763, which is incorporated herein by reference, may be used. The binder may be present in an amount less than or equal to 15% by weight or less of the final fabric. Typically, the binder component does not form a continuous film at the surface of the fibrous material.

The present disclosure relates to a process for making an NCF fabric, the process comprising interlinking a plurality of multifilament carbon yarns into a unidirectionally oriented layer with a stitching yarn, wherein the stitching yarn comprises at least one hollow fiber or filament, the at least one hollow fiber or filament comprising one or more hollow voids, typically one hollow void, extending longitudinally through a substantial portion of said fiber or filament. The interlinking of the plurality of multifilament carbon yarns into a unidirectionally oriented layer is achieved using the stitching yarn described herein.

When the NCF fabric comprises more than one layer, the multiple layers may be connected and secured to each other by stitching or knitting according to known methods using a stitching yarn, such as the stitching yarn described herein. When the NCF fabric is multiaxial, the production of such multiaxial NCF is known and makes use of conventional techniques, described, for instance, in the book“Textile Structural Composites, Composite Materials Series Volume 3” by Tsu Wei Chou & Franck K. Ko, ISBN-0-44442992-1 , Elsevier Science Publishers B. V., 1989, Chapter 5, paragraph 3.3.

Composite materials may be made by molding a preform and infusing the preform with a thermosetting resin in a number of liquid-molding processes. Liquid-molding processes that may be used include, without limitation, vacuum-assisted resin transfer molding (VARTM), in which resin is infused into the preform using a vacuum-generated pressure differential. Another method is resin transfer molding (RTM), wherein resin is infused under pressure into the preform in a closed mold. A third method is resin film infusion (RFI), wherein a semi-solid resin is placed underneath or on top of the preform, appropriate tooling is located on the part, the part is bagged and then placed in an autoclave to melt and infuse the resin into the preform.

Thus, the present disclosure also relates to a composite material, comprising:

- a matrix resin, and

- a non-crimp fabric described herein.

The matrix resin for impregnating or infusing the preforms described herein is a curable resin. “Curing” or“cure” in the present disclosure refers to the hardening of a polymeric material by the chemical cross-linking of the polymer chains. The term “curable” in reference to a composition means that the composition is capable of being subjected to conditions which will render the composition to a hardened or thermoset state. The matrix resin is typically a hardenable or thermoset resin containing one or more uncured thermoset resins. Suitable matrix resins include, but are not limited to, epoxy resins, oxetanes, imides (such as polyimide or bismaleimide), vinyl ester resins, cyanate ester resins, isocyanate-modified epoxy resins, phenolic resins, furanic resins, benzoxazines, formaldehyde condensate resins (such as with urea, melamine or phenol), polyesters, acrylics, hybrids, blends and combinations thereof.

Suitable epoxy resins include glycidyl derivatives of aromatic diamine, aromatic mono primary amines, aminophenols, polyhydric phenols, polyhydric alcohols, polycarboxylic acids and non-glycidyl resins produced by peroxidation of olefinic double bonds. Examples of suitable epoxy resins include polyglycidyl ethers of the bisphenols, such as bisphenol A, bisphenol F, bisphenol S, bisphenol K and bisphenol Z; polyglycidyl ethers of cresol and phenol-based novolacs, glycidyl ethers of phenol-aldelyde adducts, glycidyl ethers of aliphatic dials, diglycidyl ether, diethylene glycol diglycidyl ether, aromatic epoxy resins, aliphatic polyglycidylethers, epoxidised olefins, brominated resins, aromatic glycidyl amines, heterocyclic glycidyl imidines and amides, glycidyl ethers, fluorinated epoxy resins, or combinations thereof.

Specific examples are tetraglycidyl derivatives of 4,4'-diaminodiphenylmethane (TGDDM), resorcinol diglycidyl ether, triglycidyl-p-aminophenol, triglycidyl-m- aminophenol, bromobisphenol F diglycidyl ether, tetraglycidyl derivatives of diaminodiphenylmethane, trihydroxyphenyl methane triglycidyl ether, polyglycidylether of phenol-formaldehyde novolac, polyglycidylether of o-cresol novolac or tetraglycidyl ether of tetraphenylethane.

Suitable oxetane compounds, which are compounds that comprise at least one oxetano group per molecule, include compounds such as, for example, 3-ethyl-3[[(3- ethyloxetane-3-yl)methoxy]methyl]oxetane, oxetane-3-methanol, 3,3-bis- (hydroxymethyl) oxetane, 3-butyl-3-methyl oxetane, 3-methyl-3-oxetanemethanol, 3,3-dipropyl oxetane, and 3-ethyl-3-(hydroxymethyl) oxetane. The curable matrix resin may optionally comprise one or more additives such as curing agents, curing catalysts, co-monomers, rheology control agents, tackifiers, inorganic or organic fillers, thermoplastic and/or elastomeric polymers as toughening agents, stabilizers, inhibitors, pigments, dyes, flame retardants, reactive diluents, UV absorbers and other additives well known to those of ordinary skill in the art for modifying the properties of the matrix resin before and/or after curing.

Examples of suitable curing agents include, but are not limited to, aromatic, aliphatic and alicyclic amines, or guanidine derivatives. Suitable aromatic amines include 4,4'-diaminodiphenyl sulphone ( 4,4'-DDS), and 3,3'diaminodiphenyl sulphone (3,3 - DDS), 1 ,3-diaminobenzene, 1 ,4-diaminobenzene, 4,4'-diammodiphenylmethane, benzenediamine(BDA); Suitable aliphatic amines include ethylenediamine (EDA), 4,4'-methylenebis(2,6-diethylaniline) (M-DEA), m-xylenediamine (mXDA), diethylenetriamine (DETA), triethylenetetramine (TETA), trioxatridecanediamine (TTDA), polyoxypropylene diamine, and further homologues, alicyclic amines such as diaminocyclohexane (DACH), isophoronediamine (IPDA), 4,4' diamino dicyclohexyl methane (PACM), bisaminopropylpiperazine (BAPP), N- aminoethylpiperazine (N-AEP); Other suitable curing agents also include anhydrides, typically polycarboxylic anhydrides, such as nadic anhydride, methylnadic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, endomethylene-tetrahydrophtalic anhydride, pyromellitic dianhydride, chloroendic anhydride and trimellitic anhydride.

Still other curing agents are Lewis acid:Lewis base complexes. Suitable Lewis acid:Lewis base complexes include, for example, complexes of: BCI₃:amine complexes, BF₃:amine complexes, such as BF₃:monoethylamine, BF₃:propylamine, BF₃:isopropyl amine, BF₃:benzyl amine, BF₃:chlorobenzyl amine, BF₃:trimethylamine, BF₃:pyridine, BF₃:THF, AICI₃:THF, AICI₃:acetonitrile, and ZnCI₂:THF. Additional curing agents are polyamides, polyamines, amidoamines, polyamidoamines, polycycloaliphatic, polyetheramide, imidazoles, dicyandiamide, substituted ureas and urones, hydrazines and silicones.

Urea based curing agents are the range of materials available under the commercial name DYHARD (marketed by Alzchem), and urea derivatives, such as the ones commercially available as UR200, UR300, UR400, UR600 and UR700. Urone accelerators include, for example, 4,4-methylene diphenylene bis(N,N-dimethyl urea) (available from Onmicure as U52 M).

When present, the total amount of curing agent is in the range of 1 wt % to 60 wt % of the resin composition. Typically, the curing agent is present in the range of 15 wt % to 50 wt %, more typically in the range of 20 wt % to 30 wt %.

Suitable toughening agents may include, but are not limited to, homopolymers or copolymers either alone or in combination of polyamides, copolyamides, polyimides, aramids, polyketones, polyetherimides (PEI), polyetherketones (PEK), polyetherketoneketone (PEKK), polyetheretherketones (PEEK), polyethersulfones (PES), polyetherethersulfones (PEES), polyesters, polyurethanes, polysulphones, polysulphides, polyphenylene oxide (PPO) and modified PPO, polyethylene oxide) (PEO) and polypropylene oxide, polystyrenes, polybutadienes, polyacrylates, polystyrene, polymethacrylates, polyacrylics, polyphenylsulfone, high performance hydrocarbon polymers, liquid crystal polymers, elastomers, segmented elastomers and core-shell particles.

Toughening particles or agents, when present, may be present in the range 0.1 wt % to 30 wt % of the resin composition. In an embodiment, the toughening particles or agents may be present in the range 10 wt % to 25 wt %. In another embodiment, the toughening particles or agents may be present in the range from 0.1 to 10 wt%. Suitable toughening particles or agents include, for example, Virantage VW10200 FRP, VW10300 FP and VW10700 FRP from Solvay, BASF Ultrason E2020 and Sumikaexcel 5003P from Sumitomo Chemicals. The toughening particles or agents may be in the form of particles having a diameter less than or equal to 5 microns, typically less than or equal to 1 micron in diameter. The size of the toughening particles or agents may be selected such that they are not filtered by the fiber reinforcement. Optionally, the composition may also comprise silica-gels, calcium- silicates, silica oxide, phosphates, molybdates, fumed silica, amorphous silica, amorphous fused silica, clays, such as bentonite, organo- clays, aluminium-trihydrates, hollow glass microspheres, hollow polymeric microspheres, microballoons and calcium carbonate.

The composition may also contain conductive particles such as the ones described in PCT International Publications WO 2013/141916, WO 2015/130368 and WO 2016/048885.

The carbon of the multifilament carbon yarns may be in the form of graphite. The carbon may be metallized with discontinuous or continuous metal layers. Graphite fibers which have been found to be especially useful in the invention are those supplied by Solvay under the trade designations T650-35, T650-42 and T300; those supplied by Toray under the trade designation T700, T800 and T1000; and those supplied by Hexcel under the trade designations AS4, AS7, IM7, IM8 and I M 10. The carbon fibers, typically filaments, may be unsized or sized with a material that is compatible with the resin composition.

The mold for resin infusion may be a two-component, closed mold or a vacuum bag sealed, single-sided mold. Following infusion of the matrix resin in the mold, the mold is heated to cure the resin to produce a composite article, which is a finished part.

Thus, the present disclosure relates to a composite article obtained by curing the composite material described hereinabove.

During heating, the resin reacts with itself to form crosslinks in the matrix of the composite material. After an initial period of heating, the resin gels. Upon gelling, the resin no longer flows, but rather behaves as a solid. After gel, the temperature or cure may be ramped up to a final temperature to complete the cure. The final cure temperature depends on the nature and properties of the thermosetting resin chosen. Thus, in an embodiment, the composite material is heated to a first temperature suitable to gel the matrix resin, after which the temperature is ramped up to a second temperature and held for a time at the second temperature to complete the cure.

The at least one hollow fiber or filament used in the stitching yarn typically has a lower stiffness than the cured matrix to allow for deforming when stressed. Typically, the walls of the at least one hollow fiber or filament are solid, preventing uncured resin to enter the hollow section of the filament in the infusion and cure stages.

The NCF fabric, stitching yarn, and the preform, composite material, and composite article made therefrom according to the present disclosure are further illustrated by the following non-limiting examples.

Examples

Unless otherwise stated, all NCF fabrics are manufactured using 2 plies of carbon fiber and areal weight per ply of 196 gsm (grams per square meter). The machine gauge is an E5 and the stitch pattern is a tricot stitch. Stitch density, as used herein, refers to the number of stitches per unit length. In the examples, stitch density is 8 stitches per inch.

Example 1

An untexturized stitching yarn, having a nominal linear density of 44 dtex and filament count of 30, is made from hollow filaments having a measured external diameter of 18.5 pm. The ratio of cross sectional area of the void to that of the surrounding fiber material is about 0.08. The stitching yarn is then used to manufacture an NCF fabric. As a comparative example, an NCF fabric is made in the same manner, except that the stitching yarn comprises only solid filaments with no hollow filaments.

Approximately 3mm thick composite articles are manufactured from the inventive and comparative NCF fabrics by infusing a balanced lay-up of biaxial fabrics with Solvay Prism^® EP2400 and curing the infused preform at 180°C for 2 hours and cooling down the laminates at 3°C/min. The composite panels are subjected to up to 1600 hygrothermal cycles.

Due to a high level of stress, some microcracking is observed in the composite article made from the comparative NCF fabrics while significantly less or no microcracking is observed in the composite article made from the inventive NCF fabric under 100X magnification under bright field light or fluorescent light.

Example 2

A texturized PA 6/6 stitching yarn, having linear density of 60 dtex and filament count of 30, comprising hollow filaments (available from Nylstar) is used to manufacture an NCF fabric.

As a comparative example, an NCF fabric is made in the same manner, except that the stitching yarn comprises only solid filaments with no hollow filaments.

Claims

WHAT IS CLAIMED IS:

1. A non-crimp fabric comprising at least one layer of unidirectionally oriented multifilament carbon yarns and a stitching yarn interlinking the multifilament carbon yarns, wherein the stitching yarn comprises at least one hollow fiber or filament, the at least one hollow fiber or filament comprising one or more hollow voids, typically one hollow void, extending longitudinally through a substantial portion of said fiber or filament.

2. The non-crimp fabric of claim 1 , wherein the at least one hollow fiber or filament has a linear density of less than 800 dtex, less than 100 dtex, less than 80 dtex, less than 50 dtex, less than 10 dtex, or less than 5 dtex.

3. The non-crimp fabric of claim 1 or 2, wherein the cross-sectional shape exhibited by the one or more hollow voids is random and/or irregular, or has a defined shape, typically circular, triangular, rhomboid, multilobal, or a shape characterized by a mathematical function, typically sinusoidal shape.

4. The non-crimp fabric of claim 3, wherein the cross-sectional shape of the one or more hollow voids is circular, substantially circular, or multilobal.

5. The non-crimp fabric of claim 4, wherein the cross-sectional shape of the one or more hollow voids is circular or substantially circular.

6. The non-crimp fabric of any one of claims 1 -5, wherein the cross-sectional shape of the outer surface of the at least one hollow fiber or filament is random and/or irregular, or has a defined shape, typically circular, triangular, rhomboid, multilobal, flat elongated shape with rounded ends, or a shape characterized by a mathematical function, typically sinusoidal shape.

7. The non-crimp fabric of claim 6, wherein the cross-sectional shape of the outer surface of the at least one hollow fiber or filament, is circular or substantially circular.

8. The non-crimp fabric of any one of claims 1 -7, wherein the at least one hollow fiber or filament further comprises additional voids that extend partially or fully throughout the length of said hollow fiber or filament.

9. The non-crimp fabric of any one of claims 1 -8, wherein the at least one hollow fiber or filament comprises one hollow void extending longitudinally through the entire fiber or filament.

10. The non-crimp fabric of claim 9, wherein the cross-sectional shape of the hollow void extending longitudinally through the entire fiber or filament and the cross- sectional shape of the outer surface of the fiber or filament are circular or substantially circular.

11 . The non-crimp fabric of any one of claims 1-10, wherein the external radius of the at least one hollow fiber or filament is from 2 pm to 200 pm, typically 2 pm to 20 pm, more typically 5 pm to 15 pm.

12. The non-crimp fabric of any one of claims 1 -1 1 , wherein the ratio of cross sectional area of the void to that of the surrounding fiber material is greater than 0 and less than 5, typically less than 3, more typically less than 1.

13. The non-crimp fabric of any one of claims 1-12, the ratio of cross sectional area of the void to that of the surrounding fiber material is in a range from 0.05 to 1 , typically 0.05 to 0.65.

14. The non-crimp fabric of any one of claims 1-13, wherein the stitching yarn has a filament count of less than or equal to 1.0 times the linear density of the stitching yarn, typically less than or equal to 0.9 times the linear density, more typically less than or equal to 0.8 times the linear density.

15. The non-crimp fabric of any one of claims 1 -14, wherein the at least one hollow fiber or filament is organic, typically polymeric, for example, comprising polyamide, copolyamide, polyester, and/or copolyester; or inorganic, for example, comprising carbon, glass, silica, basalt, ceramic, or mixtures thereof.

16. The non-crimp fabric of any one of claims 1-15, wherein the linear density of the stitching yarn is in the range of 1 to 800 dtex, typically 1 to 150 dtex, more typically 1 to 60 dtex, even more typically 1 to 40 dtex.

17. The non-crimp fabric of any one of claims 1-16, wherein the filament count of the stitching yarn is in the range of 0.1 to 0.8 times the linear density of the yarn, typically 0.1 to 0.6 times the linear density of the yarn, more typically 0.1 to 0.5 times the linear density of the yarn.

18. The non-crimp fabric of any one of claims 1-17, wherein the stitching yarn has a twist of less than 150 r/m, typically less than 100 r/m, more typically less than 50 r/m.

19. The non-crimp fabric of any one of claims 1-18, wherein the material used to produce the at least one hollow fiber or filament has a density of from 0.5 to 2.5 g/cm³, typically from 0.8 to 1.8 g/cm³, more typically from 0.9 to 1.5 g/cm³.

20. The non-crimp fabric of any one of claims 1-19, wherein the material used to produce the at least one hollow fiber or filament has a density of from 0.9 to 1.4 g/cm³.

21 . The non-crimp fabric of any one of claims 1-20, wherein the stitching yarn has interlacing of less than 25 nodes/meter.

22. The non-crimp fabric of any one of claims 1-21 , wherein the non-crimp fabric is multiaxial and comprises more than one layer of unidirectionally oriented multifilament carbon yarns.

23. The non-crimp fabric of any one of claims 1-22, further comprising a non- woven veil.

24. A fiber preform comprising the non-crimp fabric according to any one of claims 1-23.

25. The fiber preform according to claim 24, further comprising a non-woven veil.

26. A composite material, comprising:

- a matrix resin, and

- a non-crimp fabric according to any one of claim 1 -23.

27. A composite article obtained by curing the composite material according to claim 26.

28. A process for making a non-crimp fabric according to any one of claims 1-23, the process comprising interlinking a plurality of multifilament carbon yarns into a unidirectionally oriented layer with a stitching yarn, wherein the stitching yarn comprises at least one hollow fiber or filament, the at least one hollow fiber or filament comprising one or more hollow voids, typically one hollow void, extending longitudinally through a substantial portion of said fiber or filament.