Method for producing sized and resin coated fibers

Abstract

A method for making a sized and resin-coated fiber tow for use in a fiber-reinforced composite material, comprising the steps of providing fibers and contacting at least a portion of the fibers with a sizing slurry to form a sized and resin-coated fiber tow, the sizing slurry comprising 0.1-25% by weight of a sizing agent and 20-80% by weight of a matrix resin powder in a solvent, based on the total weight of the sizing slurry, and a total solids content of the sizing slurry, including the sizing agent and the matrix resin powder, of greater than 30% by weight. The method further comprises drying the sized and resin-coated fibers at a temperature below the melting point of the matrix resin powder, thereby forming a dried sized and resin-coated fiber, and winding the dried sized and resin-coated fiber onto a spool.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 172,970, filed April 9, 2021, the disclosure of which is incorporated herein by reference in its entirety for all purposes. FIELD OF THEINVENTION

[0002] This disclosure relates generally to sized and resin-coated fibers for use in fiber-reinforced composites, and to methods for making such fiber tows. This disclosure also relates generally to sizing compositions for use in making the sized and resin-coated fibers. [Background technology]

[0003] Fiber-reinforced composites have been developed over the past few decades and are used in many industries to maximize mechanical properties while maintaining or reducing mass by combining reinforcing fibers with thermoplastic or thermoset polymers.

[0004] However, to reduce the overall cost of manufacturing, methods of manufacturing with fewer steps are desired. Summary of the Invention

[0005] One aspect of the invention is a method for producing sized and resin-coated fiber tows for use in fiber reinforced composites. The method includes the steps of providing carbon fibers and contacting at least a portion of the fibers with a sizing slurry to form sized and resin-coated fibers, the sizing slurry including 0.1-25% by weight of a sizing agent and 20-80% by weight of a matrix resin powder in a solvent, such that the total solids content of the sizing slurry including the sizing agent and the matrix resin powder is greater than 30% by weight, wherein the amounts in weight percent are based on the total amount of the sizing slurry. The method also includes drying the sized and resin-coated fibers at a temperature below the melting point of the matrix resin powder, thereby forming a dried sized and resin-coated fiber, and winding the dried sized and resin-coated fiber onto a spool.

[0006] In one embodiment, the method is a continuous process further comprising steps (i)-(iv) prior to the step of contacting at least a portion of the fibers with a sizing slurry: (i) stabilizing the precursor fiber at a temperature in the range of 200-300° C. to form a stabilized precursor fiber; (ii) carbonizing the stabilized precursor fiber at a temperature in the range of 1000-1500°C to form a carbonized fiber; (iii) graphitizing the carbonized fibers at a temperature in the range of 2000 to 3000° C. to form carbon fibers; and (iv) optionally, treating at least a portion of the surface of the carbon fibers.

[0007] In one embodiment, the drying step provides dried sized and resin coated fibers having greater than 21% and less than 80% by weight of size and matrix resin, based on the total weight of the dried sized and resin coated fibers.

[0008] In another embodiment, the contacting step includes providing a sizing slurry comprising a matrix resin powder having an average particle size in the range of 1 to 500 μm.In another embodiment, the contacting step includes providing a sizing slurry comprising a sizing agent comprising at least one of epoxy, phenoxy, polyester, polyamide, polyimide, polypropylene, polyurethane, polyvinyl acetate, vinyl ester, polyvinyl alcohol, ethylene / vinyl alcohol copolymer, silane-grafted polyvinyl alcohol and silane-grafted ethylene / vinyl alcohol copolymer, silane-grafted polyvinyl alcohol, silane-grafted ethylene / vinyl alcohol copolymer, and the like.

[0009] In one aspect, the contacting step includes providing a sizing slurry comprising a matrix resin powder that is a thermoset (co)polymer, a thermoplastic (co)polymer, or alloys and blends thereof. In one embodiment, the contacting step includes providing a sizing slurry comprising a thermoset (co)polymer comprising an epoxy, a vinyl ester polyester, a bismaleimide, a cyanate ester, a polyurethane, or mixtures thereof. In another embodiment, the contacting step includes providing a sizing slurry comprising a thermoplastic (co)polymer comprising a polyethylene, a polypropylene, a polycarbonate, a polyethylene terephthalate, a polybutylene terephthalate, a polyamide-6, a polyamide-66, a polyamide-11, a polyamide-12, a polyamide-46, a polyetherimide, a polyphenylene sulfide, a polysulfone, a polyimide, a polyethersulfone, a polyether-ketone-ketone, a polyether-ether-ketone, or mixtures thereof.

[0010] In one embodiment of the invention, the method further comprises molding the dried sized and resin-coated fibers without impregnation with additional matrix resin.

[0011] In yet another aspect, there is a fiber reinforced composite material produced by the methods as disclosed herein.

[0012] In one embodiment, the sizing slurry comprises 0.1-25% by weight of a sizing agent and 20-80% by weight of a matrix resin powder in a solvent, such that the total solids content of the sizing slurry, including the sizing agent and the matrix resin powder, is greater than 30% by weight, where the amounts in weight percent are based on the total amount of the sizing slurry.

[0013] In another embodiment, there is a sized and resin coated fiber comprising: (i) carbon fibres; (ii) a sizing agent disposed on at least a portion of the fibers; and (iii) a matrix resin disposed on at least a portion of the fibers and attached to the sizing agent; Here, the sized and resin coated fibers have more than 21% and less than 80% by weight of size and matrix resin, based on the total weight of the sized and resin coated fibers.

[0014] In one aspect, there is a continuous method for producing sized and resin coated carbon fiber tows for use in carbon fiber reinforced composites, the method comprising the steps of: a) unwinding a spool of polyacrylonitrile (PAN) fiber; b) stabilizing the PAN fibers at a temperature in the range of 200-300°C to form stabilized PAN fibers; c) carbonizing the stabilized PAN fibers at a temperature in the range of 1000-1500°C to form carbonized fibers; d) graphitizing the carbonized fibers at a temperature in the range of 2000 to 3000°C to form carbon fibers; e) treating at least a portion of the surface of the carbon fibers; f) contacting at least a portion of the fibers with a sizing slurry to form sized and resin-coated fibers, the sizing slurry comprising 0.1-25% by weight of sizing agent and 20-80% by weight of matrix resin powder in a solvent, such that the total solids content of the sizing slurry, including sizing agent and matrix resin powder, is greater than 30% by weight, wherein said amounts in weight percent are based on the total amount of the sizing slurry; g) drying the sized and resin coated carbon fibers at a temperature below the melting point of the resin, thereby forming dried sized and resin coated carbon fibers; and h) Winding the dried sized and resin coated carbon fibers onto a spool.

[0015] In one aspect of this continuous process, the drying step provides dried sized and resin-coated carbon fibers having greater than 21% and less than 80% by weight of size and matrix resin, based on the total weight of the dried sized and resin-coated carbon fibers.

[0016] In another aspect, the continuous process further comprises forming the dried sized and resin coated carbon fibers without impregnating the dried sized and resin coated fibers with additional matrix resin. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 illustrates generally a process for producing sized and resin-coated fibers for use in fiber-reinforced composites, in accordance with an embodiment of the present invention.

[0018] [Diagram 2] FIG. 2 illustrates generally a continuous process for producing sized and resin coated carbon fibers for use in making molded fiber reinforced composite materials in accordance with an embodiment of the present invention.

[0019] [Diagram 3] FIG. 3 illustrates generally another continuous process for producing sized and resin coated carbon fibers for use in fiber reinforced composite materials, in accordance with an embodiment of the present invention.

[0020] [Figure 4] FIG. 4 illustrates a schematic diagram of a process for producing molded carbon fiber reinforced composites directly from sized and resin coated carbon fibers without impregnating the sized and resin coated carbon fibers with additional matrix resin, in accordance with an embodiment of the present invention.

[0021] [Diagram 5] FIG. 5 shows a photograph of a spool of sized and resin coated carbon fiber according to an embodiment of the present invention.

[0022] [Figure 6] FIG. 6 shows a photomicrograph of sized and resin coated carbon fibers according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Carbon fibers are one of the best ways to maximize mechanical properties and weight savings. Carbon fibers are typically classified according to their tensile modulus, for example: - Low elastic modulus (<200GPa) - Standard elastic modulus (~230GPa) - Medium elastic modulus (~300GPa) - High elastic modulus (>350GPa) - Ultra-high elastic modulus (over 600GPa)

[0024] Other fibers, such as basalt, quartz, alumina, silicon carbide, nylon, polyester, polypropylene, aramid, acrylic, etc., can also be used in such a capacity. Many natural fibers, such as hemp, jute, etc., can also be used to make "green" reinforced plastic composites. However, regardless of the type of fiber used as a reinforcement, a size or binder on the fiber is generally required to protect the fiber during the manufacturing process and to enhance the bond between the fiber and the plastic matrix resin.

[0025] Generally, the manufacturing process of fiber reinforced composites involves fiber production, including a sizing step to produce sized fibers, polymer production, and impregnating sheets or fabrics of sized fibers with resin to form intermediate products called prepregs. These prepregs are then molded into the desired shape without the addition of additional resin. The process may include post-molding steps such as, but not limited to, painting, trimming, machining, and bonding. Some processes, such as infusion, may combine the steps of impregnation and molding into one process.

[0026] Fibers often require treatments, commonly referred to as spin finishes, binders or sizes, before they can be used to make fiber-reinforced composites. For textile fibers, the purpose of the spin finish is to impart surface lubricity, antistatic properties, dye affinity, wetting or anti-wetting properties, and abrasion resistance. When textile fibers are used for plastic reinforcement, the spin finish or binder may contain a resin dispersion to enhance compatibility with the plastic being reinforced. For inorganic fibers used for plastic reinforcement, the binder or size provides surface lubricity, antistatic properties, wetting properties, oxidation resistance, abrasion resistance, resin binding properties, and compatibility. This principle also applies to natural fibers of plant origin.

[0027] As used herein, the terms "fiber" and "fibers" include continuous fibers, nanotube(s), microfiber(s), and nanofiber(s).

[0028] Suitable fibers that can be used to form the sized and resin-coated fibers according to the present invention include, but are not limited to, carbon fibers. The carbon fibers can be of any class, type, or grade known in the art. Examples of grades of carbon fibers that can be used to form the sized reinforcing fillers according to the present invention include, but are not limited to, low modulus carbon fibers, standard modulus carbon fibers, medium modulus carbon fibers, high modulus carbon fibers, and ultra-high modulus carbon fibers. The carbon fibers that can be used to form the sized reinforcing fillers according to the present invention can be derived from either polyacrylonitrile (PAN) or pitch.

[0029] In one aspect of the invention, the present disclosure provides a method of making sized and resin coated fiber tows for use in fiber reinforced composites, as shown in Figure 1. The method 100 includes providing a fiber 110, contacting at least a portion of the fiber 110 with a sizing slurry 120 to form a sized and resin coated fiber 130, drying 140 the sized and resin coated fiber 130 at a temperature below the melting point of the matrix resin powder, thereby forming a dried sized and resin coated fiber 150, and winding the dried sized and resin coated fiber 150 onto a spool, bobbin, tow, or roving.

[0030] The step of contacting at least a portion of the fibers 110 with the sizing slurry 120 includes forming the sizing slurry 120 in-situ by adding the matrix resin powder to a sizing composition including a sizing agent and a solvent, and mixing with a slurry agitator to keep the matrix resin powder in suspension and prevent settling of the matrix resin powder. The sizing slurry 120 can include 0.1-25%, or 0.5-20%, or 1-15% by weight of the sizing agent and 20-80%, or 25-75%, or 30-70% by weight of the matrix resin powder in the solvent, based on the total weight of the sizing slurry. The total solids content of the sizing slurry 120, including the sizing agent and the matrix resin powder, is greater than 30%, or greater than 35%, or greater than 40%, or greater than 45%, or greater than 50%, or greater than 55%, by weight, based on the total weight of the sizing slurry. In one embodiment, the matrix resin powder is present in an amount ranging from 30 to 80% by weight, or 35 to 70% by weight, or 40 to 60% by weight, based on the total weight of the sizing slurry. Traditionally, the amount of sizing agent has been less than the matrix resin powder in the sizing slurry because a minimum amount of 30% by weight of matrix resin is required to fill the voids between the cylindrical carbon fiber filaments in the fiber reinforced composite. Any suitable solvent can be used. In one embodiment, the solvent comprises water. In another embodiment, the solvent comprises water and at least one water-miscible solvent, such as ethanol. In one embodiment, the solvent consists of 10% by volume ethanol in water. In yet another embodiment, the solvent consists of water. The solvent can be present in any suitable amount, such as, for example, in the range of 15 to 70% by weight, or 19 to 60% by weight, or 20 to 55% by weight, based on the total weight of the sizing slurry.

[0031] Typically, the sizing agent can be one or more of a compound, an oligomer, and / or a polymer. In general, the sizing agent provides optimal processability / handling of the carbon fibers and enhances compatibility with the matrix resin when forming a carbon fiber reinforced composite material by forming a coating on the carbon fibers. On the other hand, the polymer used as the matrix resin powder in the sizing slurry of the present invention is intended to function as the matrix resin of the carbon fiber reinforced composite material.

[0032] In one embodiment of the invention, the sizing agent comprises at least one of epoxy, phenoxy, polyester, polyamide, polyimide, polypropylene, polyurethane, polyvinyl acetate, vinyl ester, polyvinyl alcohol, ethylene / vinyl alcohol copolymer, silane-grafted polyvinyl alcohol and silane-grafted ethylene / vinyl alcohol copolymer, silane-grafted polyvinyl alcohol, silane-grafted ethylene / vinyl alcohol copolymer, and the like.

[0033] The matrix resin powder according to the present invention can be any suitable thermosetting (co)polymer and / or thermoplastic (co)polymer known in the art. In one embodiment, the matrix resin powder has an average particle size in the range of 1 to 500 μm, or 10 to 300 μm, or 20 to 250 μm.

[0034] Examples of such thermosetting (co)polymers include, but are not limited to, epoxy, vinyl ester polyester, bismaleimide, cyanate ester, polyurethane, or mixtures thereof. Examples of the most commonly used thermosetting matrix resin powders include, but are not limited to, unsaturated polyester, epoxy, vinyl ester, phenolic resin, and thermosetting polyurethane. Exotic resins such as polyimide, bismaleimide (BMI), benzoxazine, and silicone are also used, but have a very low market share due to their high cost. Sizing agents commonly used to size fibers for such matrix resins include polyvinyl acetate, vinyl acetate-ethylene, vinyl ester, epoxy, phenoxy, unsaturated polyester, saturated polyester, and polyurethane.

[0035] Examples of thermoplastic (co)polymers include, but are not limited to, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyamide-6, polyamide-66, polyamide-11, polyamide-12, polyamide-46, polyetherimide, polyphenylene sulfide, polysulfone, polyimide, polyethersulfone, polyether-ketone-ketone, polyether-ether-ketone, or mixtures thereof. In certain embodiments, the matrix resin powder according to the present invention may be a mixture of two or more thermoplastic (co)polymers. For thermoplastic fiber reinforced composites, polyolefins (e.g., polyethylene (PE) and polypropylene (PP)), acrylonitrile-butadiene-styrene (ABS), polyvinyl chloride (PVC), and polystyrene (PS) account for the majority of matrix resin consumption. Among fiber reinforced composites, nylon has the highest volume percentage, followed by thermoplastic polyesters. Conventional sizes used to toughen nylon matrix resins include, but are not limited to, polyurethane dispersions (PUDs), polyamide dispersions, epoxy dispersions, acrylics, maleic anhydride grafted ethylene, etc. Conventional sizes used to toughen thermoplastic polyester matrix resins include, but are not limited to, epoxy dispersions, polyurethane dispersions, and polyester dispersions.

[0036] In addition to the sizing agent (film former) and matrix resin powder, the sizing slurry may include coupling agents and / or processing aids (i.e., lubricants, wetting agents, neutralizing agents, antistatic agents, antioxidants, nucleating agents, crosslinking agents, and any combination thereof). Examples of such coupling agents include, but are not limited to, chromium (III) methacrylate (available as Volan® from Zaclon LLC), silanes, and titanates. Examples of such processing aids include, but are not limited to, lubricants, wetting agents, neutralizing agents, antistatic agents, antioxidants, nucleating agents, crosslinking agents, and any combination thereof. In certain embodiments, the sized and resin-coated fibers according to the present invention may further include cationic lubricants and antistatic agents.

[0037] In one aspect of the invention, there is a continuous process for producing shaped carbon fiber reinforced composites. FIG. 2 shows an overview of a process that combines two sub-processes: a process 255 for producing carbon fibers 250 and a process 265 for directly forming the carbon fibers 250 into a shaped carbon fiber reinforced composite 270. In one embodiment, the two processes 255 and 265 are separate and take place at two different manufacturing locations. In another embodiment, the two processes 255 and 265 are part of one process and take place at one manufacturing location. In one aspect of the invention, as shown in FIG. 2, the method for producing sized and resin coated carbon fiber tows is a continuous process 200. The continuous process 200 includes a step for producing carbon fibers prior to the step of contacting at least a portion of the fibers with a sizing slurry. The continuous process 200 includes unwinding a spool of polyacrylonitrile (PAN) fibers 201 and oxidizing 202 the precursor fibers 201 to form stabilized precursor fibers. The process 200 further includes a carbonization step 204 to form carbon fibers, and a treating / sizing step 209 to form sized and resin coated carbon fibers 250. The carbonization step may include graphitization. As shown in Figure 2, the process may further include molding the sized and resin coated fibers 260 directly from a spool without impregnating the sized and resin coated carbon fibers 250 with additional matrix resin to form a molded fiber reinforced composite product 270.

[0038] In one aspect of the invention, providing the fiber includes producing carbon fiber from precursor fiber, such as PAN. FIG. 3 illustrates another embodiment of the invention, a continuous process 300 for producing sized and resin coated carbon fiber tow. The continuous process 300 includes producing carbon fiber prior to contacting at least a portion of the fiber with a sizing slurry. The continuous process 300 includes unwinding a spool of precursor fiber 301, such as polyacrylonitrile (PAN) fiber, and stabilizing 302 the precursor fiber 301 at a temperature in the range of 200-300° C. to form stabilized precursor fiber 303. The process further includes carbonizing 304 the stabilized precursor fiber 303 at a temperature in the range of 1000-1500° C. to form carbonized fiber 305, graphitizing 306 the carbonized fiber 305 at a temperature in the range of 2000-3000° C. to form carbon fiber 310, and optionally pretreating 308 at least a portion of the surface of the carbon fiber 310.

[0039] After carbonization, the fibers have a surface that does not bond well with epoxies and other materials used in composites. Therefore, to obtain better bonding properties, at least a portion of the fibers is treated by slightly oxidizing its surface. The addition of oxygen atoms to the surface provides good chemical bonding properties and also etches and roughens the surface for good mechanical bonding properties. Oxidation can be achieved by immersing the fibers in various gases, such as air, carbon dioxide, or ozone, or in various liquids, such as sodium hypochlorite or nitric acid. The fibers can also be electrolytically coated by placing the fibers at the positive terminal in a bath filled with various conductive materials. The surface treatment process needs to be carefully controlled to avoid the formation of microscopic surface defects, such as pits, that can cause the fibers to fail.

[0040] The process 300 further includes a treating / sizing step that includes contacting at least a portion of the fibers 310 with a sizing slurry 320 to form a sized and resin-coated fiber 350. The contacting step further includes forming the sizing slurry 320 in-situ by adding a matrix resin powder to a sizing composition that includes a sizing agent and a solvent, and mixing with a slurry agitator to keep the matrix resin powder in suspension and to prevent the matrix resin powder from settling. The sizing slurry 320 includes 0.1-25%, or 0.5-20%, or 1-15% by weight of a sizing agent and 20-80%, or 25-75%, or 30-70% by weight of a matrix resin powder in a solvent, such that the total solids content of the sizing slurry, including the sizing agent and the matrix resin powder, is greater than 30% by weight, to form the sized and resin-coated carbon fiber 350. Here, the above amounts in mass % are based on the total amount of the sizing slurry.

[0041] The process 300 further includes a drying step 340, in which the sized and resin-coated carbon fibers 330 are dried at a temperature below the melting point of the matrix resin, thereby forming dried sized and resin-coated carbon fibers 350. In one embodiment, the drying step 340 provides dried sized and resin-coated carbon fibers 350 having greater than 21% and less than 80%, or greater than 25% and less than 75%, or greater than 30% and less than 70%, by weight of size and matrix resin, based on the total weight of the dried sized and resin-coated carbon fibers.

[0042] In one embodiment of the invention, the method can further include molding the dried sized and resin coated carbon fibers directly from the spool without impregnating the dried sized and resin coated carbon fibers with additional matrix resin, as shown in FIG.

[0043] In another aspect there is a fiber reinforced composite material produced by the method as described above in this disclosure.

[0044] Another embodiment includes a sizing slurry comprising 0.1-25%, or 0.5-20%, or 1-15% by weight of a sizing agent and 20-80%, or 25-75%, or 30-70% by weight of matrix resin powder in a solvent such that (i) the total solids content, including sizing agent and matrix resin powder, of the sizing slurry is greater than 30% by weight, and (ii) the amount of matrix resin powder is greater than the amount of sizing agent, wherein the amounts in weight percent are based on the total amount of the sizing slurry.

[0045] Yet another embodiment is a sized and resin coated fiber comprising carbon fiber, a size disposed on at least a portion of the fiber, and a matrix resin disposed on at least a portion of the fiber and attached to the size, wherein the sized and resin coated fiber has greater than 21% and less than 80%, or greater than 25% and less than 75%, or greater than 30% and less than 70%, by weight of size and matrix resin, based on the total weight of the sized and resin coated fiber.

[0046] In yet another aspect of the present invention, the present disclosure provides articles, such as molded components, formed from the fiber reinforced composite material according to the present invention, including unidirectional reinforced thermoplastic tapes, randomized continuous mats, long chopped mats, pelletized long compounds, and extruded long logs. In one embodiment, there is a component comprising an article as described above in the present disclosure, the component configured for use in one or more of an automobile, a home appliance, and an electronics assembly. Examples of such articles include, but are not limited to, automobile door liners, front end modules, air intake manifolds, bumper beams, motorbike boots, automotive cooling fan blades, air conditioner fan blades, pump housings, automobile body panels, dashboard carriers, multi-blade impellers, liftgates, truck liners, automobile vertical panels, instrument panel carriers, door panel structures, seat structures, underhood components, gas doors, mirror housings, front end carriers, dashboard carriers, door base plates, underbody covers, front under trays, washing machine tubs, airbag housings, business machines, electronics packaging, and hard disk drives. Of course, many other types of products can be formed.

[0047] The following examples are included to illustrate preferred embodiments. Those skilled in the art will appreciate that the techniques disclosed in the examples that follow represent techniques discovered by the inventors to work well in the practice of the products, compositions and methods described in this disclosure, and therefore constitute preferred modes for the practice of the invention. However, those skilled in the art will appreciate in light of this disclosure that many changes can be made in the specific embodiments disclosed and still obtain the same or similar results without departing from the spirit and scope of the disclosure. EXAMPLES

[0048] Materials used

[0049] Polyamide 6 (PA6) spherical resin powder (ORGASOL® 2001) was obtained from Arkema, King of Prussia, Pa. Carbon fiber tow ZOLTEK PX35 was obtained from Zoltek Corporation, Bridgeton, Mo. Hydrosize U6-01 was obtained from Michelman, Cincinnati, Ohio.

[0050] Example 1: Method for producing sizing slurry

[0051] A sizing slurry was prepared by adding 35% by weight of PA6 Orgasol® 2001 to a solution containing 5% Hydrosize U6-01 as a sizing agent and 60% distilled water. The mixture was stirred for about 15 minutes to form the sizing slurry.

[0052] Example 2: Manufacturing method of sized and coated carbon fibers with PA6 resin

[0053] Carbon fiber tow PX35 was sized with the sizing slurry of Example 1 and dried at 150°C for about 5-7 minutes to form sized and PA6 resin coated carbon fibers. After drying, the sized and PA6 resin coated carbon fibers had 500-45% by weight PA6 resin based on the total weight of PA6 resin, carbon fiber, and sizing additive. Figure 4 is a photograph of a spool of sized and PA6 resin coated carbon fibers. Figure 5 is a micrograph of sized and PA6 resin coated carbon fibers.

[0054] Example 3: Manufacturing method of carbon fiber reinforced composite material

[0055] The as-prepared sized and PA6 coated carbon fibers were molded into test panels (2 mm thick, 200 mm wide, 300 mm long) at 250° C. for 60 min without adding additional PA6 resin or other resins.

[0056] When the carbon fibre reinforced composite test panels were tested for interlaminar shear strength (ILSS) according to the ISO 14130 method, the panels exhibited a maximum shear strength of 60 MPa, which is in line with the state of the art.

[0057] It will be apparent to those skilled in the art that various modifications and variations are possible in the practice of this invention without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

1. 1. A method for producing sized and resin coated fiber tows for use in a fiber reinforced composite material, comprising: a) providing carbon fibers; b) contacting at least a portion of the fibers with a sizing slurry to form sized and resin-coated fibers, the sizing slurry comprising 0.1 to 25% by weight of a sizing agent and 20 to 80% by weight of a matrix resin powder in a solvent, such that the total solids content of the sizing slurry, including the sizing agent and the matrix resin powder, is greater than 30% by weight, wherein said amounts in weight percent are based on the total amount of the sizing slurry; c) drying the sized and resin-coated fibers at a temperature below the melting point of the matrix resin powder, thereby forming dried sized and resin-coated fibers; and d) winding the dried sized and resin coated fibers onto a spool.

2. 10. The method of claim 1, wherein the method is a continuous process further comprising steps (i)-(iv) prior to the step of contacting at least a portion of the fibers with the sizing slurry: (i) stabilizing the precursor fiber at a temperature in the range of 200-300° C. to form a stabilized precursor fiber; (ii) carbonizing the stabilized precursor fiber at a temperature in the range of 1000 to 1500° C. to form a carbonized fiber; (iii) graphitizing the carbonized fibers at a temperature in the range of 2000 to 3000° C. to form carbon fibers; and (iv) optionally treating at least a portion of the surface of the carbon fibers.

3. 2. The method of claim 1, wherein the drying step provides the dried sized and resin coated fibers having greater than 21% and less than 80% by weight of size and matrix resin, based on the total weight of the dried sized and resin coated fibers.

4. 10. The method of claim 1, wherein the contacting step includes providing the sizing slurry comprising the matrix resin powder having an average particle size within the range of 1 to 500 μm.

5. 10. The method of claim 1, wherein the contacting step includes providing the sizing slurry comprising the sizing agent comprising at least one of an epoxy, a phenoxy, a polyester, a polyamide, a polyimide, a polypropylene, a polyurethane, a polyvinyl acetate, a vinyl ester, a polyvinyl alcohol, an ethylene / vinyl alcohol copolymer, a silane-grafted polyvinyl alcohol, and a silane-grafted ethylene-vinyl alcohol copolymer, a silane-grafted polyvinyl alcohol, a silane-grafted ethylene / vinyl alcohol copolymer, and the like.

6. 10. The method of claim 1, wherein the contacting step comprises providing the sizing slurry with the matrix resin powder being a thermoset (co)polymer, a thermoplastic (co)polymer, or alloys and blends thereof.

7. 7. The method of claim 6, wherein the contacting step comprises providing the sizing slurry comprising the thermosetting (co)polymer comprising an epoxy, a vinyl ester polyester, a bismaleimide, a cyanate ester, a polyurethane, or a mixture thereof.

8. 7. The method of claim 6, wherein the contacting step comprises providing the sizing slurry comprising the thermoplastic (co)polymer comprising polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyamide-6, polyamide-66, polyamide-11, polyamide-12, polyamide-46, polyetherimide, polyphenylene sulfide, polysulfone, polyimide, polyethersulfone, polyether-ketone-ketone, polyether-ether-ketone, or mixtures thereof.

9. 10. The method of claim 1, further comprising molding the dried sized and resin-coated fibers without impregnating the dried sized and resin-coated fibers with additional matrix resin.

10. A fiber-reinforced composite material produced by the method according to any one of claims 1 to 9.

11. A sizing slurry comprising, in a solvent, 0.1 to 25% by weight of a sizing agent and 20 to 80% by weight of a matrix resin powder, the amounts being based on the total weight of the sizing slurry, such that the total solids content of the sizing slurry, including the sizing agent and the matrix resin powder, exceeds 30% by weight.

12. A sized and resin coated fiber comprising: (i) carbon fibres; (ii) a sizing agent disposed on at least a portion of the fibers; and (iii) a matrix resin disposed on at least a portion of the fibers and attached to the sizing agent; wherein the sized and resin coated fibers have greater than 21% and less than 80% by weight of sizing agent and matrix resin, based on the total weight of the sized and resin coated fibers.

13. A continuous process for producing sized and resin coated carbon fiber tows for use in carbon fiber reinforced composites, comprising the steps of: a) unwinding a spool of polyacrylonitrile (PAN) fiber; b) stabilizing the PAN fibers at a temperature in the range of 200-300° C. to form stabilized PAN fibers; c) carbonizing the stabilized PAN fibers at a temperature in the range of 1000-1500° C. to form carbonized fibers; d) graphitizing the carbonized fibers at a temperature in the range of 2000-3000° C. to form carbon fibers; e) treating at least a portion of the surface of the carbon fibers; f) contacting at least a portion of the fibers with a sizing slurry to form sized and resin coated fibers, the sizing slurry comprising 0.1 to 25% by weight of a sizing agent and 20 to 80% by weight of a matrix resin powder in a solvent, such that the total solids content of the sizing slurry, including the sizing agent and the matrix resin powder, is greater than 30% by weight, said amounts in weight percent being based on the total amount of the sizing slurry; g) drying the sized and resin coated carbon fibers at a temperature below the melting point of the resin, thereby forming dried sized and resin coated carbon fibers; h) winding the dried sized and resin coated carbon fibers onto a spool.

14. 14. The continuous process of claim 13, wherein the drying step provides dried sized and resin-coated fibers having greater than 21% and less than 80% by weight of size and matrix resin, based on the total weight of the dried sized and resin-coated fibers.

15. 14. The continuous process of claim 13, further comprising forming the dried sized and resin coated carbon fibers without impregnating the dried sized and resin coated fibers with additional matrix resin.

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