WO2019195069A1

WO2019195069A1 - Carbon fibers with tuned stiffness

Info

Publication number: WO2019195069A1
Application number: PCT/US2019/024502
Authority: WO
Inventors: Shane POLEN; James R. Priest
Original assignee: Ocv Intellectual Capital, Llc
Priority date: 2018-04-05
Filing date: 2019-03-28
Publication date: 2019-10-10
Also published as: TW202003647A

Abstract

A coated carbon fiber is disclosed that includes a first coating composition disposed on a carbon fiber; and a second coating composition disposed on the carbon fiber. The second coating composition comprises about 0.01 wt.% to about 2.0 wt.% by strand solids of a film former; a processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and optionally, a compatibilizer comprising one or more of a coupling agent or an antistatic agent. The coated carbon fiber has a total solids content of about 0.01 to about 3.0 wt.%, based on the weight of the coated carbon fiber.

Description

CARBON FIBERS WITH TUNED STIFFNESS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and any benefit of U.S. Provisional Patent Application No. 62/653,027, filed April 5, 2018, and U.S. Provisional Patent Application No. 62/799,088, filed January 31, 2019, the contents of which are incorporated herein by reference in their entireties.

BACKGROUND

[0002] Fiber reinforced composite materials consist of fibers embedded in or bonded to a matrix material with distinct interfaces between the materials. Generally, the fibers are the load- carrying members, while the surrounding matrix keeps the fibers in the desired location and orientation, acts as a load transfer medium, and protects the fibers from environmental damage. Common types of fibers in commercial use today include various types of glass, carbon, and synthetic fibers.

[0003] Carbon fibers present processing difficulties in many applications, which may lead to slower and more costly product manufacturing. For instance, carbon fibers tend to be limp, lacking inherent stiffness, which causes difficulty in chopping the fibers. Carbon fibers further have low abrasion resistance and thus readily generate fuzz or broken threads and may release particulate material into the air during downstream processing applications. Additionally, due at least in part to their hydrophobic nature, carbon fibers do not interface or wet (i.e., take and hold an aqueous coating) as easily as other reinforcement fibers, such as glass fibers, in traditional resin matrices. Wetting refers to the ability of the resin to uniformly spread over and bond to the fiber surface.

[0004] Although efforts have been made to improve the stiffness of carbon fibers by applying a surface treatment to the fibers, such as that described in co-pending U.S. provisional application No. 62/482,682, which is fully incorporated herein by reference. However, in certain applications, it has been found that the particular degree of stiffness must be balanced with the level of fiber loft, bundle integrity, and various other fiber properties.

SUMMARY

[0005] In accordance with various aspects of the general inventive concepts, coated carbon fiber is disclosed. The coated carbon fiber includes a first coating composition disposed on a carbon fiber and a second coating composition disposed on the carbon fiber. The second coating composition comprises about 0.01 wt.% to about 2.0 wt.% by strand solids of a film former; a processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and optionally, a compatibilizer comprising one or more of a coupling agent or an antistatic agent. The coated carbon fiber has a total solids content of about 0.01 to about 3.0 wt.%, based on the weight of the coated carbon fiber.

[0006] In some exemplary embodiments, the film former comprises one or more of polyvinylpyrrolidone, polyvinyl acetate, polyurethane, and epoxy. The polyvinylpyrrolidone may have a molecular weight of 1,000,000 to 1,700,000.

[0007] In some exemplary embodiments, the coated carbon fiber comprises a plurality of fiber bundles, wherein each fiber bundle comprises no more than 12,000 carbon filaments, such as no more than 6,000 carbon filaments, and no more than 3,000 filaments.

[0008] In some exemplary embodiments, the coated carbon fiber has a solids content of about 0.05 to about 2.0 wt.%, based on the weight of the coated carbon fiber, such as no greater than about 0.1 to about 1.5 wt.%, based on the weight of the coated carbon fiber.

[0009] In some exemplary embodiments, the compatibilizer comprises a coupling agent, comprising one or more of a silicone-based coupling agent, a titanate coupling agent, or a zirconate coupling agent. In other exemplary embodiments, the compatibilizer comprises an antistatic agent including a quaternary ammonium antistatic agent. The compatibilizer may be present in the coating composition in an amount from about 0.05 wt.% to about 1.0 wt.% solids.

[00010] In some exemplary embodiments, the processing aid comprises one or more of a wax, selected from the group consisting of ethylene bis-stearamide wax (EBS), Fischer- Tropsch wax (ET), oxidized Fischer-Tropsch wax (FTO), stearic acid pitch, polyolefin waxes, alcohol wax, silicone wax, petroleum wax, and chlorinated wax. The processing aid may be included in the coating composition in an amount from about 0.15 wt. % to about 2.7 wt.% solids.

[00011] In some exemplary embodiments, the coated carbon fiber has a stiffness that is at least 30% higher than an otherwise identical carbon fiber that has not been coated with the secondary coating composition.

[00012] In various exemplary embodiments, the coating composition further includes one or more performance additive, selected from the group consisting of silica, nano-silica, silicon carbine, graphene, graphene oxide, graphite, nanoclay, nano-zinc/zinc-oxide, nanoaluminum oxide, core shell rubber, and mixtures thereof. The performance additive may comprise functionalized material, unfunctionalized material, or mixtures thereof. [00013] In accordance with further aspects of the general inventive concepts, a coated carbon fiber is provided that includes a first coating composition disposed thereon and a secondary coating composition disposed thereon. The coated carbon fiber has a coating solids content thereon of no greater than 2.0 % and wherein the coated carbon fiber has a stiffness that is at least 20% higher than an otherwise identical coated carbon fiber that has not been coated with the secondary coating composition.

[00014] In some exemplary embodiments, the secondary coating composition comprises about 0.01 wt.% to about 3.0 wt.% by strand solids of a film former; a processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and optionally, a compatibilizer comprising one or more of a coupling agent or an antistatic agent. The film former may comprise one or more of polyvinylpyrrolidone, polyvinyl acetate, polyurethane, and epoxy. The polyvinylpyrrolidone may have a molecular weight of 1,000,000 to 1,700,000.

[00015] In accordance with further aspects of the general inventive concepts, a stiffened carbon fiber roving is provided that includes a plurality of carbon fiber bundles comprising no greater than 12,000 carbon filaments. The carbon fiber bundles are coated with a coating composition comprising about 0. 1 to about 4.0 wt.% solids of a film former and about 0.1 to about 3.0 wt.% of a processing aid. The stiffened carbon fiber bundle has a stiffness that is at least 20% higher than an otherwise identical carbon fiber bundle that does not include the coating composition.

[00016] In some exemplary embodiments, the carbon fiber bundles comprise no greater than about 6,000 filaments, or no greater than 3,000 filaments.

[00017] In accordance with further aspects of the general inventive concepts, a carbon fiber- reinforced composite is disclosed. The carbon fiber-reinforced composite includes a plurality of chopped carbon fiber bundles, wherein each fiber bundle comprises no more than 12,000 carbon filaments, and polymer resin material. The chopped carbon fiber bundles comprise a first coating composition and a second coating composition disposed thereon. The second coating composition has a solids content of no greater than 2.0 % and the chopped carbon fibers have a stiffness that is at least 20% higher than an otherwise identical chopped fibers that have not been coated with the secondary coating composition. The carbon fiber reinforced composite has a tensile strength between about 100 and about 300 MPa.

[00018] In some exemplary embodiments, the composite has a tensile strength between about 180 MPa and about 220 MPa, a tensile modulus between about 20 GPa and about 40 GPa, a flexural modulus between about 10 GPa and about 50 GPa, and/or a flexural strength between about 250 MPa and about 500 MPa.

[00019] In some exemplary embodiments, the reinforcement comprises a sheet molding compound.

[00020] In accordance with yet further aspects of the general inventive concepts, a sheet molding compound is provided that includes a polymer resin matrix material; and a plurality of coated carbon fiber bundles. The coated carbon fiber bundles comprise a first coating composition and a second coating composition disposed on the carbon fiber bundles. The second coating composition comprises about 0.01 wt.% to about 2.0 wt.% by strand solids of a film former; a processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and optionally, a compatibilizer comprising one or more of a coupling agent or an antistatic agent.

[00021] In some exemplary embodiments, the sheet molding compound has a tensile strength of between about 100 MPa and about 300 MPa, a tensile modulus of between about 20 GPa and about 40 GPa, a flexural modulus of between about 10 GPa and about 50 GPa, and/or a flexural strength of between about 250 MPa and about 500 MPa.

[00022] In accordance with yet further aspects of the general inventive concepts, a coating composition is provided that includes about 0.5 to about 4.0 wt.% solids of a film former comprising one or more of polyvinylpyrrolidone, polyvinyl acetate, polyurethane, and epoxy; about 0.1 to about 3.0 wt.% of the processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and optionally, at least one compatibilizer, wherein the coating composition has a total solids content of less than 5 wt.%.

[00023] In some exemplary embodiments, the composition is an aqueous composition. In other exemplary embodiments, the composition is a nonaqueous composition.

[00024] In some exemplary embodiments, the polyvinylpyrrolidone has a molecular weight of 1,000, 000 to 1,700,000.

[00025] In some exemplary embodiments, the compatibilizer comprises a silicone-based coupling agent, a titanate coupling agent, or a zirconate coupling agent. In other exemplary embodiments, the compatibilizer comprises one or more of gluteric dialdehyde, glycoxal, malondialdehyde, succidi aldehyde, phthaladldehyde. In other exemplary embodiments, the compatibilizer comprises riethylalkyletherammonium sulfate. The compatibilizer may be present in an amount from about 0.01 wt.% to about 1.0 wt.%. In some exemplary embodiments, the processing aid is present in an amount from about 0.15 wt.% to about 2.7 wt.%.

DESCRIPTION OF THE DRAWINGS

[00026] Various aspects of the general inventive concepts will be more readily understood from the description of certain exemplary embodiments provided below and as illustrated in the accompanying drawing.

[00027] Figure 1 illustrates the results of a“drape test” performed on coated carbon multi- end rovings.

DETAILED DESCRIPTION

[00028] While the general inventive concepts are susceptible of embodiment in many different forms, there are shown in the drawings and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the general inventive concepts. Accordingly, the general inventive concepts are not intended to be limited to the specific embodiments illustrated herein.

[00029] Unless otherwise defined, the terms used herein have the same meaning as commonly understood by one of ordinary skill in the art encompassing the general inventive concepts. The terminology used herein is for describing exemplary embodiments of the general inventive concepts only and is not intended to be limiting of the general inventive concepts. As used herein, the singular forms“a,”“an,” and“the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term“about” means within +/- 10% of a value, or more preferably, within +/- 5% of a value, and most preferably within +/- 1% of a value.

[00030] As used herein, the term“wetting” refers to the ability of the resin to bond to and uniformly spread over and bond to the fiber surface. Wetting results from the intermolecular interactions between a liquid and a solid surface.

[00031] As used herein, the term“tow” refers to a large collection of filaments, which are typically formed simultaneously and optionally coated with a sizing composition. A tow is designated by the number of fiber filaments they contain. For example, a l2k tow contains about 12,000 filaments.

[00032] As used herein, the term“roving” means a collection of parallel strands (assembled roving) or parallel continuous filaments (direct roving) assembled without intentional twist. A roving includes both single-end roving and multi -end roving (“MER”). A single-end roving is a single bundle of continuous filaments combined into a discrete strand. A multi -end roving is made up of a plurality of discrete strands, each strand having a plurality of continuous filaments. The phrase“continuous” as used herein in connection with filaments, strands, or rovings, means that the filaments, strands, or rovings generally have a significant length but should not be understood to mean that the length is perpetual or infinite.

[00033] The present invention relates to methods of imparting increased, tunable stiffness to carbon fibers. While the exemplary embodiments shown and described herein are described in the context of carbon fiber tows, the general inventive concepts are not so limited and instead may be applicable to the decomposition of other types of fibers as well, such as graphite fibers and polymer fibers.

[00034] Carbon fibers are generally hydrophobic, conductive fibers that have high tensile strength, high temperature tolerance, and low thermal expansion, and are generally light weight, making them popular in forming reinforced composites. However, carbon fibers may cause processing difficulties, leading to slower and more costly product manufacturing. For instance, conventional carbon fibers typically droop and curve downward due to gravity when held parallel to the ground. Due to this lack of stiffness, the fibers are difficult to chop and utilize in downstream manufacturing processes. Further issues include the tendency for the fibers to break and/or fray during the rubbing, pulling, and spreading motions that occur during processing. Such breaking and fraying may lead to the release of particles into the atmosphere and the formation of“fuzz” on the fibers. In addition to processing difficulties, carbon fibers are hydrophobic and tend to agglomerate, making them harder to wet than hydrophilic glass fibers in traditional matrices.

[00035] Carbon fibers may be turbostratic or graphitic or have a hybrid structure with both turbostratic and graphitic parts present, depending on the precursor used to make the fibers. In turbostratic carbon fibers, the sheets of carbon atoms are haphazardly folded, or crumpled together. Carbon fibers derived from polyacrylonitrile (PAN) are turbostratic, whereas carbon fibers derived from mesophase pitch are graphitic after heat treatment at temperatures exceeding 2,200 °C. In some exemplary embodiments, the carbon fibers of the present invention are derived from PAN.

[00036] In some exemplary embodiments, the carbon fibers of the present invention are coated with a first coating composition, such as a sizing composition, to protect the fibers during handing, improve mechanical properties, and/or promote thermal and hydrolytic stability. A sizing composition may also form surface functional groups to promote improved chemical bonding and homogenous mixing within a polymer matrix. Homogenous mixing of the fibers or“wetting” within a polymer matrix material is a measure of how well the reinforcement material is encapsulated by the polymer matrix. It is desirable to have the carbon fibers completely wet with no dry fibers. Incomplete wetting during this initial processing can adversely affect subsequent processing as well as the surface characteristics of the final composite.

[00037] The sizing composition may be applied to the carbon fibers at any time during the fiber formation process ( e.g ., prior to packaging or storing of the formed fibers) in an amount from about 0.5% to about 5% by weight solids of a fiber, or from about 1.0% to about 2.0% by weight solids of the fiber. Alternatively, the fibers may be coated with the sizing composition after the fibers have been formed (e.g., after the fibers have been packaged or stored). In some exemplary embodiments, the sizing composition is an aqueous-based composition, such as a suspension or emulsion. The sizing composition may comprise at least one film former. The film former holds individual filaments together to aid in the formation of the fibers and protect the filaments from damage caused by abrasion including, but not limited to, inter-filament abrasion. Acceptable film formers include, for example, polyvinyl acetates, polyurethanes, modified polyolefins, polyesters, epoxides, and mixtures thereof. The film former also helps to enhance the bonding characteristics of the carbon fibers with various resin systems. In some exemplary embodiments, the sizing composition helps to compatibilize the carbon fibers with an epoxy, polyurethane, polyester, nylon, phenolic, and/or vinyl ester resin.

[00038] Carbon fibers are frequently supplied in the form of a continuous tow wound onto a reel. Each carbon filament in the tow is a continuous cylinder with a diameter of about 5 pm to about 10 pm. Carbon tows come in a wide variety of sizes, from lk, 3k, 6k, l2k, 24k, 50k, to greater than 50k, etc. The k value indicates the number of individual carbon filaments within the tow. For instance, a l2k tow consists of about 12,000 carbon filaments, while a 50k tow consists of about 50,000 carbon filaments.

[00039] To obtain fine tows (e.g., l2k or smaller), the carbon must either be manufactured as a fine carbon tow or a larger carbon tow must be split to reduce its filament count. Splitting a high carbon tow (e.g, 24k, 50k, or larger) into smaller splits (e.g, less than l2k) facilitates providing better impregnation with resin and better dispersion when the tow is processed.

[00040] In some exemplary embodiments, the carbon fiber tow may be spread to disassociate individual carbon filaments and begin to create a plurality of thinner bundles. The spread carbon fibers may then be pulled under tension to maintain consistent spreading and to further increase the spread between the fibers. For example, a plurality of carbon fibers having widths of about 3/8” to about ½” may be pulled along a variety of rollers under tension to form spreads between about ¾” to about 1 ½ The angles and radius of the rollers should be set to maintain a tension that is not too high, which could pull the spread fibers back together.

[00041] It has been discovered that coating carbon fibers with a surface treatment, such as a secondary coating composition, at any time during the formation or processing of carbon fibers works to increase the stiffness and improve the processability of the fibers. The secondary coating may be applied at the time of carbon fiber formation, such as when PAN is converted to carbon fiber. Alternatively, or additionally, the secondary coating may be applied after the carbon fiber is sized with a sizing composition and at least partially cured. Alternatively, the surface treatment may be applied after carbon fibers are further processed, such as after carbon fibers are spread and/or split into smaller fiber bundles.

[00042] Prior surface treatments included coating compositions, such as those disclosed in WO2017/062734 and WO2018/187532, each fully incorporated herein by reference. Such coating compositions comprised a minimum solids content of about 2.5 wt.% solids, based on the total solids content of the aqueous composition. Once applied to the fibers, the coating composition has a solids content of about 0.1 wt.% to about 5.0 wt.%, or in an amount from about 0.5 wt.% to about 2.0 wt.% active strand solids, or from about 0.5 wt.% to about 1.0 wt.% active strand solids, including all combinations and sub-ranges contained therein.

[00043] However, some applications, such as SMC applications, require reduced stiffness and moisture uptake ability. All SMC systems involve a thickening mechanism, either an alkaline earth system (MgO, CaO or ZnO) or an isocyanate crosslinking mechanism. In both cases, the rate of viscosity increase or“thickening,” is driven by moisture availability. In all cases, consistency and control of moisture is critical for wetting of the fiber with the resin system prior to high viscosity prevents the wetting the fibers properly. High or varying levels of moisture can cause variation or failure of the system to wet the fibers resulting in poor composite performance. Additionally, reducing the fiber loft minimizes the air entrapment in SMC, which results in less defects and bubbling.

[00044] Previous efforts to reduce loft have resulted in poor bundle integrity. It has been unexpectedly discovered that lowering the solids content of the coating composition, while also optionally including a processing aid results in a fiber with a balance between stiffness, moisture uptake, bundle integrity, and loft.

[00045] Accordingly, in some exemplary embodiments, the secondary coating composition comprises less than about 5.0 wt.% solids, or less than about 3.0 wt.% solids, or less than about 2.5 wt.% solids, or less than about 2.0 wt.% solids, or less than about 1.5 wt.% solids, or less than about 1.0 wt.% solids, based on the total solids content of the aqueous composition, including all combinations and sub-ranges contained therein.

[00046] Once applied to the fibers, the secondary coating composition has a solids content of about 0.01 wt.% to about 3.0 wt.%, or in an amount from about 0.05 wt.% to about 2.0 wt.% active strand solids, or from about 0.1 wt.% to about 1.5 wt.% active strand solids, including all combinations and sub-ranges contained therein. In some exemplary embodiments, once applied to the fibers, the secondary coating composition has a solids content of about 1.05 wt.% to about 1.3 wt.%.

[00047] In some exemplary embodiments, the secondary coating composition comprises at least one film former. For example, the coating composition may comprise one or more of polyvinylpyrrolidone (PVP), polyvinylacetate (PVA), polyurethane (PU), and epoxy as a film forming agent.

[00048] Polyvinylpyrrolidone exists in several molecular weight grades characterized by K- value. For example, and not by way of limitation, PVP K-12 has a molecular weight of about 4,000 to about 6,000; PVP K-15 has a molecular weight of about 6,000 to about 15,000; PVP K-30 has a molecular weight of about 40,000 to about 80,000; and PVP K-90 has a molecular weight of about 1,000,000 to about 1,700,000. In some exemplary embodiments, the film former comprises PVP K-90.

[00049] The film former may be present in the coating composition in an amount from about 0.1 wt.% to about 4.0 wt.%, or from about 0.25 wt.% to about 2.75 wt.%, or from about 0.5 wt.% to about 1.75 wt.%, based on the total solids content of the aqueous composition, including all combinations and sub-ranges contained therein.

[00050] Once applied to the fiber strands, the film former may be present in an amount from about 0.01 wt.% to about 2 wt.% by strand solids, or about 0.1 wt.% to about 1.5 by wt.% by strand solids, including all combinations and sub-ranges contained therein.

[00051] In some exemplary embodiments, the coating composition additionally includes a compatibilizer. A compatibilizer may provide a variety of functions synergistically between the film former, the carbon fiber, and a resin interface. In some exemplary embodiments, the compatibilizer comprises a coupling agent, such as a silicone-based coupling agent ( e.g silane coupling agents), a titanate coupling agent, or a zirconate coupling agent. Silane coupling agents are conventionally used in sizing compositions for inorganic substrates having hydroxyl groups than can react with the silanol-containing reactive groups. Although such coupling agents have been traditionally used in sizing compositions for glass fibers, alkali metal oxides and carbonates do not form stable bonds with Si-O. However, it has been surprisingly discovered that utilizing such coupling agents in the present surface treatment composition does in fact function to enhance the adhesion of the film forming polymers to the non-glass (i.e., carbon) fibers and reduce the level of fuzz, or broken fiber filaments, during subsequent processing and splitting. Examples of silane coupling agents, which may be suitable for use in the coating composition, include those characterized by the functional groups acryl, alkyl, amino, epoxy, vinyl, azido, ureido, and isocyanato.

[00052] Suitable silane coupling agents for use in the coating composition include, but are not limited to, g-aminopropyltriethoxysilane (A-1100), n-trimethoxy-silyl-propyl-ethylene- diamine (A-1120), g-methacryloxypropyltrimethoxysilane (A-174), g- glycidoxypropyltrimethoxysilane (A- 187), methyl -trichlorosilane (A- 154), methyl - trimethoxysilane (A-163), g-mercaptopropyl -trim ethoxy-si lane:(A-l 89), bis-(3-

[triethoxysilyl]propyl)tetrasulfane (A-1289), g-chloropropyl-trimethoxy-silane (A-143), vinyl- triethoxy-silane (A-151), vinyl-tris-(2-methoxyethoxy)silane (A-172), vinylmethyldimethoxysilane (A-2171), vinyl-triacetoxy silane (A-188), octyltriethoxysilane (A-137), methyltriethoxysilane (A-162), polyazamide silane (A-1387), and gamma- ureidopropyltrialkoxysilane (A-l 160).

[00053] In some exemplary embodiments, the compatibilizer comprises a mixture of two or more silane coupling agents. For instance, the compatibilizer may include a mixture of aminopropyltriethoxysilane (A-l 100) and one or more of methyl-trimethoxysilane (A-163) and g-methacryloxypropyltrimethoxysilane (A- 174). In some exemplary embodiments, the compatibilizer includes one or more of polyazamide silane (A- 1387) and gamma- ureidopropyltrialkoxysilane (A-l 160).

[00054] In some instances, the compatibilizer includes A-l 100 and A-163 in a ratio of about 1 : 1 to about 3 : 1. In some instances, the compatibilizer includes A-l 100 and A- 174 in a ratio of about 1 : 1 to about 3 : 1.

[00055] In some exemplary embodiments, the compatibilizer comprises an organic dialdehyde. Exemplary dialdehydes include gluteric dialdehyde, glycoxal, malondialdehyde, sued di aldehyde, phthaladldehyde, and the like. In some exemplary embodiments, the organic dialdehyde is gluteric dialdehyde.

[00056] In some exemplary embodiments, the compatibilizer comprises one or more antistatic agents, such as a quaternary ammonium antistatic agent. The quaternary ammonium antistatic agent may comprise triethylalkyletherammonium sulfate, which is a trialkylalkyetherammonium salt with trialkyl groups, 1-3 carbon atoms, alkyl ether group with alkyl group of 4-18 carbon atoms, and ether group of either ethylene oxide or propylene oxide. An example of a triethylalkyletherammonium sulfate is EMERSTAT 6660 A.

[00057] The compatibilizer may be present in the coating composition in an amount from about 0.05 wt.% to about 5.0 wt.% active solids, or in an amount from about 0.1 wt.% to about 1.0 wt.% active solids, or from about 0.2 wt.% to about 0.7 wt.% active solids. In some exemplary embodiments, the compatibilizer is present in the coating composition in an amount from about 0.3 wt.% to about 0.6 wt.% active solids.

[00058] In some exemplary embodiments, the secondary coating composition further includes one or more processing aids, such as one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol. Any type of wax, or a mixture of different waxes, capable of functioning as described herein can be used in the coating composition. In some exemplary embodiments, the wax is one or more of a paraffin wax and a non-paraffin wax. Paraffin waxes typically have melting points below 70 °C and have less than 45 carbon atoms. Non-paraffin waxes typically have melting points above 70 °C and have more than 45 carbon atoms. The non-paraffin wax can be one or more of a natural wax, a modified natural wax, a partial synthetic wax, and a full synthetic wax. Non-limiting examples of suitable partial and fully synthetic waxes include ethylene bis-stearamide wax (EBS), Fischer-Tropsch wax (ET), oxidized Fischer-Tropsch wax (FTO), stearic acid pitch, polyolefin waxes such as polyethylene wax (PE), oxidized polyethylene wax (PEO), polypropylene wax, polypropylene/polyethylene wax, alcohol wax, silicone wax, petroleum waxes such as microcyrsatlline wax, and chlorinated wax. Any suitable mixtures of different waxes can also be used. For example, the wax can include a blend of a Fischer-Tropsch wax and a polyethylene wax.

[00059] In some exemplary embodiments, the wax is a naturally occurring wax can be derived from a plant, animal or mineral. Some examples of natural waxes that may be suitable include plant waxes such as candelilla wax, camauba wax, rice wax, Japan wax and jojoba oil; animal waxes such as beeswax, lanolin and whale wax; and mineral waxes such as montan wax, ozokerite and ceresin.

[00060] In some exemplary embodiments, the processing aid comprises at least ethylene bistearamide (EBS). EBS is a brittle wax -like solid formed from the reaction of an amine with hydroxystearic acid. The formed hydroxystearamide is a high melting point wax -like material that is extremely resistant to acids and alkalis in contrast to natural and synthetic ester waxes.

[00061] In some exemplary embodiments, the processing aid comprises a salt of a fatty acid ester, such as a fatty acid ester derived from a plant or animal. [00062] Alternatively, or in addition, the processing aid may be one or more of a Fischer- Tropsch wax, a polyethylene wax, an oxidized polyethylene wax, and a fatty acid amide. Fatty acid amides are amides produced from the reaction of a fatty acid and an amine. The fatty acid amide can be a monoamide, a substituted amide, a bisamide, a methylol amide, an ester amide, an alkyl urea, and the like. Non-limiting examples of suitable fatty acid amides include oleamide, stearamide, erucamide, behenamide, N-oleylpalmitamide, N-stearylerucamide, ethylene bis-stearamide (EBS), and ethylene bis-oleamide.

[00063] In some exemplary embodiments, the processing aid is included in the coating composition in an amount from about 0.01 wt. % to about 3.0 wt.% solids, based on the total weight of the composition. In some exemplary embodiments, the processing aid is included in an amount from about 0.15 to about 2.7 wt.% solids, or from about 0.25 to about 2.5 wt.% solids, or from about 0.3 to about 2.0 wt.% solids, or from about 0.4 to about 1.5 wt.% solids, or from about 0.5 to about 1.0 wt.% solids, based on the total weight of the coating composition, including any combinations and sub-ranges contained therein.

[00064] Optionally, the secondary coating composition further includes one or more performance additive to further tune and/or improve mechanical properties of the carbon fibers. The performance additives may include silica, nano-silica, silicon carbine, graphene, graphene oxide, graphite, nanoclay, nano-zinc/zinc-oxide, nanoaluminum oxide, and core shell rubber. The performance materials may comprise functionalized material, unfunctionalized material, or a mixture thereof.

[00065] The secondary coating composition may be an aqueous coating composition, such that the balance of the composition is water. In other exemplary embodiments, the composition is non-aqueous, comprising one or more solvents, such as alcohol, or it may include a non- aqueous solvent, comprising a liquid other than water, such as acetone, acetonitrile, dichloromethane ethyl acetate, tetrahyudrofuran, dimethylformamide, and dimethyl sulfoxide.

[00066] In some exemplary embodiments, the secondary coating composition has a pH of less than about 10. In some exemplary embodiments, the secondary coating composition has a pH between about 3 and about 7, or between about 4 and about 6, or between about 4.5 and about 5.5.

[00067] Excess coating composition remaining on the fibers may be removed to at least partially dry the fibers. The fibers may be dried by any method known or practiced in the art.

[00068] In some exemplary embodiments, the coated fibers may be dried, such as by pulling the fibers through a dryer, such as an oven. In some exemplary embodiments, the oven is an infrared or convection oven. The oven may be a non-contact oven, meaning that the carbon fiber tow is pulled through the oven without being contacted by any part of the oven. The oven temperature may be any temperature suitable for properly drying the coating composition on the carbon fibers. In some exemplary embodiments, the oven temperature is from about 230 °F to about 600 °F, or from about 300 °F to about 500 °F.

[00069] Once dried, the surface treated fibers may be wound by a winder to produce a high stiffness fiber package, or the fibers may be immediately utilized in a downstream process, such as for compounding with a thermoplastic composition in a long fiber thermoplastic compression molding process, or chopped for use in a compounding process, such as SMC. In some exemplary embodiments, the tuned stiffness coated fiber tow is utilized to produce a hybrid assembled roving, as described in PCT/US 15/54584, the disclosure of which is incorporated herein by reference.

[00070] In the formation of fiber reinforced composites, prepregs, fabrics, nonwovens, and the like, the polymer resin matrix material may comprise any suitable thermoplastic or thermosetting material, such as polyester resin, vinyl ester resin, phenolic resin, epoxy, polyimide, polyurethane, and/or styrene, and any desired additives such as fillers, pigments, UV stabilizers, catalysts, initiators, inhibitors, mold release agents, viscosity modifiers, and the like. In some exemplary embodiments, the thermosetting material comprises a styrene resin, an unsaturated polyester resin, or a vinyl ester resin. In structural SMC applications, the polymer resin film may comprise a liquid, while in Class A SMC applications, the polymer resin matrix may comprise a paste.

[00071] By reducing the amount of film former and total weight percent of solids in the coating composition, while also incorporating a particular amount of a processing aid, it was discovered that the stiffness of the fibers could be increased over an otherwise identical uncoated fiber, while also achieving a reduced stiffness compared to a fiber coated with the coating compositions disclosed in WO2017/062734 and WO2018/187532 (hereinafter referred to as“Comparative Compositions.” The coating composition disclosed herein provides a balance between an appropriate level of stiffness and fiber loft, bundle integrity, and moisture uptake.

[00072] Accordingly, in some exemplary embodiments, the secondary coating composition imparts an increased stiffness to the carbon fibers over otherwise identical uncoated fibers, while also achieving a stiffness that is less than that achieved by carbon fibers coated with the Comparative Compositions. For example, carbon fibers that have been coated with the subject coating composition demonstrate at least a 20% increase in stiffness, or at least a 30% increase in stiffness, or at least a 40% increase in stiffness, or at least a 50% increase in stiffness, compared to an otherwise identical carbon fiber that has not been coated. Additionally, carbon fibers that have been coated with the subject coating composition demonstrate at least a 5% decrease in stiffness, or at least a 10% decrease in stiffness, or at least a 20% decrease in stiffness, or at least a 25% decrease in stiffness, compared to an otherwise identical carbon fiber coated with the Comparative Compositions. The degree of stiffness imparted to the fibers is tunable (i.e., adjustable property).

[00073] In some exemplary embodiments, the secondary coating composition reduces the loft in carbon fibers that have been chopped, compared to the loft achieved by fibers coated with the Comparative Compositions. Particularly, a carbon fiber tow may be split into a plurality of thinner carbon fiber bundles, each comprising no greater than about 15,000 (15k) carbon filaments. Such split carbon fiber tows tend to increase the density of the chop loft. In some exemplary embodiments, the carbon fiber bundles comprise less than about 12,000 carbon filaments, or less than about 10,000 carbon filaments, or less than about 9,000 carbon filaments, or less than about 8,000 carbon filaments, or less than about 7,000 carbon filaments, or less than about 6,000 carbon filaments, or less than about 5,000 carbon filaments, or less than about 4,000 carbon filaments, or less than about 3,000 carbon filaments, or less than about 2,000 carbon filaments, or less than about 1,000 carbon filaments. In some exemplary embodiments, the carbon fiber tow comprises from about 1,000 to about 12,000 carbon filaments, or from about 2,000 to about 6,000 carbon filaments, or from about 2,000 to about 3,000 carbon filaments. The carbon fiber bundles have a diameter of about 0.5 mm to about 4.0 mm, or about 1.0 mm to about 3.0 mm.

[00074] Additionally, carbon fibers coated with the present secondary coating composition demonstrate reduced water uptake and therefore a lower moisture content. PVP can absorb up to 40% of its weight in atmospheric water. As mentioned above, in some cases, the rate of viscosity increase or“thickening”, is driven by moisture availability. Consistency and control of moisture is critical for wetting of the fiber with a resin system prior to high viscosity prevents the wetting the fibers properly. High or varying levels of moisture can cause variation or failure of the system to wet the fibers resulting in poor composite performance.

[00075] It has been discovered that the addition of a processing aid reduces the moisture uptake by the coated fiber by at least 10%, or at least 15%, or at least 20%, or at least 30%, or at least 40%, or at least 50%.

Table 1 :

[00076] Table 1 illustrates the moisture content of a carbon fiber coated the coating composition of the present application, compared to the Comparative Compositions. As shown in Table 1, adding wax to the Comparative Compositions did slightly reduce the moisture uptake of the coated fiber. However, when the amount of PVP was reduced by 75% and 0.5 wt.% wax was added, the moisture uptake reduced by over 50%, particularly 58%.

[00077] In some exemplary embodiments, the coating composition improves the compatibility of the carbon fibers with a polymeric resin matrix material for composite production. Compatibilizing the carbon fibers with a matrix material allows the carbon fibers to flow and wet properly, forming a substantially homogenous dispersion of carbon fibers within the polymer matrix material. The coating composition also imparts increased cohesion, which allows for improved chopping of the fibers and improved wetting in the consolidation process.

[00078] Moreover, the coating composition improves the ability to process a carbon fiber tow by reducing the development of fuzz, fiber breakage, and/or fiber fraying, over otherwise identical carbon fibers that are only coated with a sizing composition, and over otherwise identical carbon fibers that are coating with the Comparative Compositions. In some exemplary embodiments, the development of fuzz is reduced by at least 25% and in some instances, as much as 130% in carbon fibers coated with the coating composition, compared to otherwise identical fibers coated with the Comparative Compositions. When carbon fibers are chopped for downstream processing, the formation of fuzz works against dispersion of the chopped fibers in a matrix material. Accordingly, by coating the carbon fibers with the coating composition disclosed herein, the formation of fuzz is reduced, which improves fiber dispersion.

[00079] As mentioned above, it has been discovered that the coating composition may be adjusted to“tune” the particular properties achieved by the treated fibers. For example, the coating composition may be adjusted to increase or decrease the level of fiber stiffness and/or the level of loft. Such adjustments include increasing or decreasing the solids content (LOI) of the coating composition, exposing the coated fibers to varying temperatures at varying speeds, adjusting the moisture content of the coated fibers, adjusting the angle of contact points that the fibers encounter, changing the particular type of surface treatment applied to the fibers, and/or combining various types of surface treatments.

[00080] In some exemplary embodiments, the coated carbon fibers are utilized as large, stiff ribbons (at least 24k) in the formation of composite, such as in the formation of wind turbine blades. Due to the use of the secondary coating compositions disclosed herein, the stiff fiber ribbons have a low solids content (0.5 wt.% to 2.0 wt.% solids), which leads to improved composite properties.

[00081] As noted above, the coated reinforcement fibers may then be used in the formation of reinforcement materials, such as reinforced composites, prepregs, fabrics, nonwovens, and the like. In some exemplary embodiments, the coated fibers may be used in sheet molding compound (“SMC”) applications, for forming an SMC material. In an SMC production process, a layer of a polymer film, such as a polyester resin or vinyl ester resin premix, is metered onto a plastic carrier sheet that includes a non-adhering surface. Reinforcing fibers are then deposited onto the polymer film and a second, non-adhering carrier sheet containing a second layer of polymer film is positioned onto the first sheet such that the second polymer film contacts the reinforcing fibers and forms a sandwiched material. This sandwiched material is then kneaded to distribute the polymer resin matrix and fiber bundles throughout the resultant SMC material, which may then be rolled for later use in a molding process.

[00082] In the production of SMC compounds, it is desirable that the carbon material homogeneously contact and mix within the polymeric matrix material. One measure of this homogenous mixing is referred to as wetting, which is a measure of how well the carbon fiber material is encapsulated by the matrix resin material. It is desirable to have the carbon fiber material completely wet with no dry fibers. Incomplete wetting during this initial processing can adversely affect subsequent processing as well as the surface characteristics of the final composite. For example, poor wetting may result in poor molding characteristics of the SMC, resulting in low composite strengths and surface defects in the final molded part. The SMC manufacturing process throughput, such as lines-speeds and productivity, are limited by how well and how quickly the fibers can be completely wet.

[00083] The SMC material may then be stored for 2-5 days to permit the resin to thicken and mature. During this maturation time, the SMC material increases in viscosity within the range of about 15 million centipoise to about 40 million centipoise.

[00084] Once the SMC material has reached the target viscosity the SMC material may be cut and placed into a mold having the desired shape of the final product. The mold is heated to an elevated temperature and closed to increase the pressure. This combination of high heat and high pressure causes the SMC material to flow and fill out the mold. The matrix resin then goes through a period of maturation, where the material continues to increase in viscosity as a form of chemical thickening or gelling. Exemplary molded composite parts formed using the coated carbon fibers may include exterior automotive body parts and structural automotive body parts.

[00085] Including carbon fibers that have been coated with the secondary coatings disclosed herein in SMC material allows the productions of SMC material that is at least 3%, or at least 4% stronger (tensile strength) than an otherwise identical SMC material that includes only carbon fibers coated with the Comparative Composition.

[00086] In some exemplary embodiments, a carbon fiber-reinforced composite material formed in accordance with the present inventive concepts (i.e., SMC material) has a tensile modulus of between about 20 GPa and about 40 GPa, or from about 25 GPa to about 30 GPa including all combinations and sub-ranges contained therein. In other exemplary embodiments, the carbon fiber-reinforced composite material has a tensile modulus from about 26 GPa to about 32 GPa, or from about 27 GPa to about 30 GPa including all combinations and sub ranges contained therein.

[00087] In some exemplary embodiments, a carbon fiber-reinforced composite material formed in accordance with the present inventive concepts (i.e., SMC material) has a tensile strength of between about 100 MPa and about 300 MPa, or from about 130 to about 250 MPa, including all combinations and sub-ranges contained therein. In other exemplary embodiments, the carbon fiber-reinforced composite material has a tensile strength from about 180 MPa to about 220 MPa, or from about 190 MPa to about 208 MPa, including all combinations and sub ranges contained therein.

[00088] In some exemplary embodiments, the resulting SMC material has a flexural modulus of between about 10 GPa to about 50 GPa, including about 15 GPa to about 35 GPa, about 20 GPa to about 30 GPa, and about 24 GPa to about 28 GPa, including all combinations and sub ranges contained therein.

[00089] In some exemplary embodiments, the resulting SMC material has a flexural strength of about 250 MPa to about 500 MPa, including about 300 MPa to about 400 MPa, about 325 MPa to about 385 MPa, and about 350 to about 375 MPa, including all combinations and sub ranges contained therein.

[00090] Having generally described various aspects of the general inventive concepts, a further understanding can be obtained by reference to certain specific examples illustrated below. These examples are provided for purposes of illustration only and are not intended to be limiting unless otherwise specified.

EXAMPLES

[00091] A“drape test” was performed on fibers that were treated with the inventive coating composition and the results are illustrated in Figure 1. The coated roving was then attached to a board and the stiffness was tested based on the level of droop or curvature in the rovings. As illustrated in Figure 1, the coated fibers achieved a balance between a stiff fiber in accordance with the Comparative Compositions (line A) and an uncoated fiber (line B). This balance demonstrates the tunability of the fiber stiffness.

[00092] Although various exemplary embodiments have been described and suggested herein, it should be appreciated that many modifications can be made without departing from the spirit and scope of the general inventive concepts. All such modifications are intended to be included within the scope of the invention, which is to be limited only by the following claims.

[00093] All references to singular characteristics or limitations of the present disclosure shall include the corresponding plural characteristic or limitation, and vice versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made.

[00094] All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.

[00095] The methods may comprise, consist of, or consist essentially of the process steps described herein, as well as any additional or optional process steps described herein or otherwise useful.

[00096] In some embodiments, it may be possible to utilize the various inventive concepts in combination with one another ( e.g ., one or more of the first, second, etc., exemplary embodiments may be utilized in combination with each other). Additionally, any particular element recited as relating to a particularly disclosed embodiment should be interpreted as available for use with all disclosed embodiments, unless incorporation of the particular element would be contradictory to the express terms of the embodiment. Additional advantages and modifications will be readily apparent to those skilled in the art. Therefore, the disclosure, in its broader aspects, is not limited to the specific details presented therein, the representative apparatus, or the illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concepts.

Claims

1. A coated carbon fiber comprising:

a first coating composition disposed on a carbon fiber; and

a second coating composition disposed on the carbon fiber, the second coating composition comprising:

about 0.01 wt.% to about 2.0 wt.% by strand solids of a film former;

a processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and optionally, a compatibilizer comprising one or more of a coupling agent or an antistatic agent;

wherein the coated carbon fiber has a total solids content of about 0.01 to about 3.0 wt.%, based on the weight of the coated carbon fiber.

2. The coated carbon fiber of claim 1, wherein the film former comprises one or more of polyvinylpyrrolidone, polyvinyl acetate, polyurethane, and epoxy.

3. The coated carbon fiber of claim 2, wherein said polyvinylpyrrolidone has a molecular weight of 1,000,000 to 1,700,000.

4. The coated carbon fiber of claim 1 wherein the coated carbon fiber comprises a plurality of fiber bundles, wherein each fiber bundle comprises no more than 12,000 carbon filaments.

5. The coated carbon fiber of claim 1, wherein the coated carbon fiber comprises a plurality of fiber bundles, wherein each fiber bundle comprises no more than 6,000 carbon filaments.

6. The coated carbon fiber of claim 1, wherein said coated carbon fiber comprises a plurality of fiber bundles, wherein each fiber bundle comprises no more than 3,000 carbon filaments.

7. The coated carbon fiber of claim 1, wherein the coated carbon fiber has a solids content of about 0.05 to about 2.0 wt.%, based on the weight of the coated carbon fiber.

8. The coated carbon fiber of claim 1, wherein the coated carbon fiber has a solids content of about 0.1 to about 1.5 wt.%, based on the weight of the coated carbon fiber.

9. The coated carbon fiber of claim 1, wherein the compatibilizer comprises a coupling agent, comprising one or more of a silicone-based coupling agent, a titanate coupling agent, or a zirconate coupling agent.

10. The coated carbon fiber of claim 1, wherein the compatibilizer comprises an antistatic agent including a quaternary ammonium antistatic agent.

11. The coated carbon fiber of claim 1 , wherein the compatibilizer is present in said coating composition in an amount from about 0.05 wt.% to about 1.0 wt.% solids.

12. The coated carbon fiber of claim 1, wherein the processing aid comprises one or more of a wax, selected from the group consisting of ethylene bis-stearamide wax (EBS), Fischer- Tropsch wax (ET), oxidized Fischer-Tropsch wax (FTO), stearic acid pitch, polyolefin waxes, alcohol wax, silicone wax, petroleum wax, and chlorinated wax.

13. The coated carbon fiber of claim 1, wherein the processing aid is included in the coating composition in an amount from about 0.15 wt. % to about 2.7 wt.% solids.

14. The coated carbon fiber of claim 1, wherein the coated carbon fiber has a stiffness that is at least 30% higher than an otherwise identical carbon fiber that has not been coated with the second coating composition.

15. The coated carbon fiber of claim 1, wherein the second coating composition further includes one or more performance additive, selected from the group consisting of silica, nano- silica, silicon carbine, graphene, graphene oxide, graphite, nanoclay, nano-zinc/zinc-oxide, nanoaluminum oxide, core shell rubber, and mixtures thereof.

16. The coating carbon fiber of claim 15, wherein the performance additive comprises functionalized material, unfunctionalized material, or mixtures thereof.

17. The coated carbon fiber of claim 1, wherein said processing aid is included in the second coating composition in an amount from about 0.3 to about 2.0 wt.% solids.

18. A coated carbon fiber comprising

a first coating composition disposed thereon; and

a secondary coating composition disposed thereon, wherein said coated carbon fiber has a coating solids content thereon of no greater than 2.0 % and wherein said coated carbon fiber has a stiffness that is at least 20% higher than an otherwise identical carbon fiber that has not been coated with the secondary coating composition.

19. The coated carbon fiber of claim 18, wherein said secondary coating composition comprises:

about 0.01 wt.% to about 3.0 wt.% by strand solids of a film former;

a processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and

optionally, a compatibilizer comprising one or more of a coupling agent or an antistatic agent.

20. The coated carbon fiber of claim 19, wherein said film former comprises one or more of polyvinylpyrrolidone, polyvinyl acetate, polyurethane, and epoxy.

21. The coated carbon fiber of claim 20, wherein said polyvinylpyrrolidone has a molecular weight of 1,000,000 to 1,700,000.

22. The coated carbon fiber of claim 18, wherein the coated carbon fiber has a stiffness that is at least 30% higher than an otherwise identical carbon fiber that has not been coated with the secondary coating composition.

23. A stiffened carbon fiber roving comprising:

a plurality of carbon fiber bundles comprising no greater than 12,000 carbon filaments, said carbon fiber bundles being coated with a coating composition comprising about 0. 1 to about 4.0 wt.% solids of a film former and about 0.1 to about 3.0 wt.% of a processing aid, wherein said stiffened carbon fiber bundle has a stiffness that is at least 20% higher than an otherwise identical carbon fiber bundle that does not include the coating composition.

24. The stiffened carbon fiber of claim 23, wherein said carbon fiber bundles comprise no greater than about 6,000 filaments.

25. The stiffened carbon fiber of claim 23, wherein said carbon fiber bundles comprise no greater than about 3,000 filaments.

26. A carbon fiber-reinforced composite comprising:

a plurality of chopped carbon fiber bundles, wherein each fiber bundle comprises no more than 12,000 carbon filaments, the chopped carbon fiber bundles comprising a first coating composition and a second coating composition disposed thereon, said second coating composition having a solids content of no greater than 2.0 % and wherein the chopped carbon fibers have a stiffness that is at least 20% higher than an otherwise identical chopped fibers that have not been coated with the second coating composition; and

a polymer resin material, wherein the carbon fiber reinforced composite has a tensile strength between about 100 and about 300 MPa.

27. The carbon fiber-reinforced composite of claim 26, wherein the composite has a tensile strength between about 180 MPa and about 220 MPa.

28. The carbon fiber-reinforced composite of claim 26, wherein the composite has a tensile modulus between about 20 GPa and about 40 GPa.

29. The carbon fiber-reinforced composite of claim 26, wherein the composite has a tensile modulus between about 25 GPa and about 30 GPa.

30. The carbon fiber-reinforced composite of claim 26, wherein the composite has a flexural modulus between about 10 GPa and about 50 GPa.

31. The carbon fiber-reinforced composite of claim 26, wherein the composite has a flexural strength between about 250 MPa and about 500 MPa.

32. The carbon-fiber reinforced composite of claim 26, wherein the composite comprises a sheet molding compound.

33. A sheet molding compound comprising:

a polymer resin matrix material; and

a plurality of coated carbon fiber bundles, said coated carbon fiber bundles comprising: a first coating composition and a second coating composition disposed on said carbon fiber bundles, the second coating composition comprising:

about 0.01 wt.% to about 2.0 wt.% by strand solids of a film former; a processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and

34. The sheet molding compound material of claim 33, wherein said sheet molding compound has a tensile strength of between about 100 MPa and about 300 MPa.

35. The sheet molding compound material of claim 33, wherein the sheet molding compound has a tensile modulus of between about 20 GPa and about 40 GPa.

36. The sheet molding compound material of claim 33, wherein the sheet molding compound has a flexural modulus of between about 10 GPa and about 50 GPa.

37. The sheet molding compound material of claim 33, wherein the sheet molding compound has a flexural strength of between about 250 MPa and about 500 MPa.

38. A coating composition comprising:

about 0.5 to about 4.0 wt.% solids of a film former comprising one or more of polyvinylpyrrolidone, polyvinyl acetate, polyurethane, and epoxy;

about 0.1 to about 3.0 wt.% of the processing aid comprising one or more of a wax, a fatty acid, a fatty acid ester, a fatty acid salt, a fatty acid amide, a polymeric lubricant, and a fatty alcohol; and

optionally, at least one compatibilizer, wherein said coating composition has a total solids content of less than 5 wt.%.

39. The coating composition of claim 38, wherein said composition is an aqueous composition.

40. The coating composition of claim 38, wherein the composition is a nonaqueous composition.

41. The coating composition of claim 38, wherein the polyvinylpyrrolidone has a molecular weight of 1,000,000 to 1,700,000.

42. The coating composition of claim 38, wherein the compatibilizer comprises a silicone- based coupling agent, a titanate coupling agent, or a zirconate coupling agent.

43. The coating composition of claim 38, wherein the compatibilizer comprises one or more of gluteric dialdehyde, glycoxal, malondialdehyde, sued di aldehyde, phthaladldehyde.

44. The coating composition of daim 38, wherein the compatibilizer comprises riethylalkyletherammonium sulfate.

45. The coating composition of daim 38, wherein the compatibilizer is present in an amount from about 0.01 wt.% to about 1.0 wt.%.

46. The coating composition of daim 38, wherein the processing aid comprises one or more of a wax, selected from the group consisting of ethylene bis-stearamide wax (EBS), Fischer- Tropsch wax (ET), oxidized Fischer-Tropsch wax (FTO), stearic acid pitch, polyolefin waxes, alcohol wax, silicone wax, petroleum wax, and chlorinated wax.

47. The coating composition of claim 38, wherein the processing aid is present in an amount from about 0.15 wt.% to about 2.7 wt.%.