Carboxylic acid salts of amine compounds as curing agents

Abstract

Provided herein are sizing compositions, and more particularly, sizing compositions comprising an epoxy resin and a carboxylic acid salt of an amine compound, for use in the treatment of carbon fibers. The amine used to make the carboxylate has a structure of RnXmQ wherein Q is an amine-containing group, X is a polyether group, and R is a linear or branched, saturated or unsaturated aryl or alkyl group, or a combination thereof. M and n are integers greater than or equal to 0. The composition reduces or eliminates light and gloss on the carbon fibers in the finished product. Also provided are carbon fiber reinforced composites and carbon fibers incorporating the sizing composition.

Description

Cross - Reference to Related Applications

[0001] This application claims the benefit and priority of U.S. Provisional Application Serial No. 63 / 380,657, filed Oct. 24, 2022, which is hereby incorporated by reference in its entirety for all purposes. Technical Field

[0002] The present invention generally relates to sizing compositions, and more particularly, to sizing compositions for the treatment of carbon fibers, which comprise an epoxy - containing resin and a carboxylate of an amine compound as a latent epoxy resin curing agent. Background Art

[0003] Carbon fibers have been used in a variety of structural applications and industries due to their desirable properties. For example, carbon fibers can be formed into structural components that combine high strength and high stiffness while being significantly lighter in weight than metal components with equivalent properties. A common method of preparing carbon fibers involves transforming polyacrylonitrile (PAN) precursor fibers in a multi - step process in which the precursor fibers are heated, oxidized, and carbonized to produce fibers that are 90% or more carbon. The resulting carbon fibers can be molded into high - strength composites for structural applications, used in their pure form for electrical and friction applications, or can be further processed for use in adsorbents, filters, or other applications. In particular, composites have been developed in which carbon fibers are used as reinforcing materials in resin, ceramic, or metal matrices.

[0004] At the end of the carbon fiber manufacturing process, a sizing material is typically applied to the carbon fibers. This sizing material (also referred to as a size or just sizing) helps to protect the carbon fiber filaments during subsequent handling, weaving, and processing. The sizing can also provide compatibility with the matrix resins used in the process of preparing composites.

[0005] Typically, in decorative applications of carbon - fiber - based prepregs and woven fabrics, the appearance of these carbon - based materials is of utmost importance and is sometimes more important than strength properties and other composite mechanical characteristics. Herein, the term "decorative application" refers to applications where the appearance of the carbon fibers in the finished product can be observed by the customer. Examples of such applications can be seen in carbon - fiber - based woven fabrics or prepregs used in consumer electronics (such as laptop computer bodies), automotive applications, and sporting goods. The appearance of a variety of visible defects is well - known in the art and is highly undesirable. One such defect is referred to herein as a "stripe" and appears as a distinct difference in the darkness variation at the tow level from one tow to another, which becomes particularly evident in woven fabric items.

[0006] There are several plausible reasons for this change within the material, some of which can be attributed to contamination, variations in the sizing amount on the fibers, etc. Regardless of whether these reasons are natural or unnatural, this change in the appearance of the fibers in the finished product is highly undesirable. These effects are particularly strong in fibers having a bright / smooth appearance due to high luster or gloss on the fibers. Therefore, it is advantageous to eliminate the luster or gloss of the carbon fiber tow in such applications. Additionally, for aesthetic reasons, there are times when it is desirable for the appearance of the fibers or fiber woven products to be as dark and non-glossy as possible.

[0007] Accordingly, there remains a need for an improved sizing composition that can eliminate luster or gloss and improve the uniformity between carbon fiber tows in a composite material. SUMMARY OF THE INVENTION

[0008] It has unexpectedly been found that when a sizing containing an epoxy group is combined with a carboxylate of an amine and cured / dried on carbon fibers at a certain temperature, the decorative appearance of the carbon fibers and composites containing the carbon fibers can be improved.

[0009] An embodiment of the present invention is a sizing composition comprising:

[0010] a resin containing an epoxy group; and

[0011] a carboxylate of an amine, wherein the amine has the following formula

[0012] R n X m Q

[0013] wherein:

[0014] Q is an amine-containing group comprising at least one primary or secondary amine;

[0015] X is a polyether group selected from: poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) or a mixture thereof;

[0016] m is an integer, where m ≥ 0;

[0017] R is an aryl or alkyl group, where each alkyl group can independently be straight-chain or branched, and where each alkyl group can independently be saturated or unsaturated; R contains 0 - 10 heteroatoms; and R is unsubstituted or substituted with 1 - 5 substituents selected from: C 1 -C 12 alkyl, C 1 -C 12 heteroalkyl, C 6 -C 14 aryl, and C 6 -C 14 heteroaryl; and

[0018] n is an integer and n ≥ 0.

[0019] Another embodiment of the present invention is a carbon fiber prepared by drying and curing the composition as described above on its surface.

[0020] Another embodiment of the present invention is a method of treating carbon fibers, the method comprising applying the sizing composition as described above to the carbon fibers to form a coating on the carbon fibers.

[0021] Another embodiment of the present invention is a carbon fiber reinforced composite comprising the carbon fibers as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Depicts the comparison of the grayscale darkness values of control fibers and certain darker experimental fibers at different viewing angles.

[0023] Figure 2 Depicts the different regions within each fiber used to calculate the median grayscale value for comparison. DETAILED DESCRIPTION

[0024] The present invention will now be described more fully hereinafter. These inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Throughout, the same numbers refer to the same elements. As used in the specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. All patents and patent application publications are hereby incorporated by reference in their entirety.

[0025] I. DEFINITIONS

[0026] For the purposes of this application, the following terms shall have the following meanings:

[0027] The terms "sizing material", "sizing agent", "sizing", and "sizing paste" refer to materials applied to carbon fibers for the purposes of: 1) improving the handling, weaving, and / or processing of carbon fibers, and / or 2) improving the compatibility of carbon fibers with the matrix in a composite material.

[0028] The term "fiber" may refer to fibers of finite length or filaments of infinite length.

[0029] The term "precursor fiber" refers to a fiber containing a polymeric material that can be converted into a carbon fiber having a carbon content of about 85% or higher, particularly about 95% or higher by weight, after application of sufficient heat. The precursor fiber can contain both homopolymers and copolymers of acrylonitrile (AN), and can include vinyl copolymers such as methyl acrylate (MA), methacrylic acid (MAA), sodium methallyl sulfonate, itaconic acid (IA), vinyl bromide (VB), isobutyl methacrylate (IBMA), and combinations thereof. In one embodiment, the precursor fiber contains a polyacrylonitrile (PAN) polymer formed primarily from acrylonitrile monomers.

[0030] The term "gray scale" is a digital method of representing the darkness of an object on a scale from 0 (black) to 255 (white). The numbers between these values refer to varying gray scales, where the number closer to 0 is darker and the number closer to 255 is lighter.

[0031] PAN precursor fibers are typically prepared by melt spinning or by solubilizing the precursor polymer in an organic and / or inorganic solvent (such as dimethyl sulfoxide, dimethylformamide, zinc chloride, or sodium thiocyanate solution) to form a spinning solution. For example, the spinning solution can be formed from water, acrylonitrile polymer, and sodium thiocyanate in an exemplary respective weight ratio of about 60:10:30. The solution can then be concentrated by evaporation and filtered to provide the spinning solution. The spinning solution is passed through a spinneret using various spinning processes such as dry, dry / wet, or wet spinning to form polyacrylonitrile precursor fibers. After leaving the spinneret, the spun filaments are washed. In some embodiments, the spun filaments can be stretched in hot water and steam several times their initial length. After washing the fibers, and typically before and / or after the stretching, the fibers are subjected to a finishing step where a spin finish is applied to the fibers to protect the fibers in subsequent processing steps.

[0032] As used herein, the terms "about" and "substantially" mean a deviation (plus / minus) of less than 10%, particularly less than 5%, less than 4%, less than 3%, and less than 2% of the value.

[0001] It should be understood that when a parameter range is provided, all integers within that range, as well as the range itself and its tenths and hundredths, are also provided by the embodiments. For example, "5 - 10%" includes 5%, 6%, 7%, 8%, 9%, and 10%; 5.0%, 5.1%, 5.2%....9.8%, 9.9%, and 10.0%; and 5.00%, 5.01%, 5.02%....9.98%, 9.99%, and 10.00%, and also, for example, 6% - 9%, 8% - 10%, 5.1% - 9.9%, and 5.01% - 9.99%. Similarly, when presenting a list, unless otherwise stated, it should be understood that each individual element of the list, as well as each combination of the components of the list, is a separate embodiment. For example, in multiple embodiments, "1, 2, 3, 4, and 5" encompasses 1; 2; 3; 1 and 2; 3 and 5; 1, 3, and 5; and 1, 2, 4, and 5.

[0033] The "carboxylate" of the term amine refers to a compound produced by reacting a carboxylic acid with an amine-containing compound. As used herein, it means that all primary amines and / or secondary amines present have reacted and been converted to their corresponding carboxylates.

[0034] The term "epoxy group-containing resin" refers to any resin prepared from monomers containing at least one epoxy group. In an embodiment, the epoxy group-containing resin is an epoxy resin.

[0035] An embodiment of the present invention is a sizing composition, the sizing composition comprising:

[0036] An epoxy group-containing resin; and

[0037] The carboxylate of an amine, wherein the amine has the following formula

[0038] R n X m Q

[0039] Wherein:

[0040] Q is an amine-containing group, the amine-containing group comprising at least one primary amine or secondary amine;

[0041] X is a polyether group selected from: poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) or a mixture thereof;

[0042] m is an integer, where m ≥ 0;

[0043] R is an aryl or alkyl group, wherein each alkyl group can independently be straight-chain or branched, and wherein each alkyl group can independently be saturated or unsaturated; R contains 0 - 10 heteroatoms; and R is unsubstituted or substituted with 1 - 5 substituents selected from: C 1 -C 12 alkyl, C1 -C 12 heteroalkyl, C 6 -C 14 aryl and C 6 -C 14 heteroaryl; and

[0044] n is an integer and n ≥ 0.

[0045] In an embodiment, Q is a monoamine. In an embodiment, Q contains multiple amino groups. In an embodiment, Q contains multiple primary or secondary amino groups. In an embodiment, Q contains an epoxy-amine adduct.

[0046] In an embodiment, X contains PPO. In an embodiment, X contains PEO.

[0047] In an embodiment, m ≥ 1, m ≥ 2, or m ≥ 3.

[0048] In an embodiment, X is absent.

[0049] In an embodiment, at least one R is straight-chain. In an embodiment, at least one R is branched-chain. In an embodiment, at least one R is saturated. In an embodiment, at least one R is unsaturated. In an embodiment, R is unsubstituted. In an embodiment, R is substituted.

[0050] In an embodiment, n ≥ 2, or n ≥ 3. In an embodiment, n is 0 - 20. In an embodiment, n is at least, at most, or about 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, or within a range defined by any two of these values.

[0051] In an embodiment, the carboxylate is derived from a monocarboxylic acid. In an embodiment, the carboxylate is derived from a polycarboxylic acid. In an embodiment, the carboxylate is derived from a polycarboxylic acid derivative having at least one free / unmodified acid group.

[0052] An embodiment of the present invention is a carbon fiber, which is prepared by drying and curing the composition as described above on its surface. After the drying and curing, carboxylate may not be present in the coating. An embodiment of the present invention is a carbon fiber reinforced composite, which contains the carbon fiber as described above. In an embodiment, the carbon fiber reinforced composite contains a resin matrix impregnated into the fiber.

[0053] An embodiment of the present invention is a method for preparing a treated carbon fiber, the method comprising the following steps: i) applying the sizing composition as described above to the carbon fiber to form a coated carbon fiber; ii) Dry the coated carbon fibers, and iii) Cure the coated carbon fibers; Thereby forming treated carbon fibers.

[0054] Step i) is typically carried out at room temperature or near room temperature (about 20°C - 25°C), but this is not a requirement. Step i) is also typically carried out by immersing the fibers or a fabric comprising a plurality of fibers in a bath containing the sizing composition. In an embodiment, step i) is carried out for about 5 seconds to about 60 seconds. In an embodiment, step i) is carried out for at least, at most, or about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 seconds, or within a range defined by any two of these values.

[0055] In an embodiment, step ii) is carried out at a temperature between about 100°C and about 190°C. In an embodiment, step ii) is carried out at a temperature of at least, at most, or about 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, or 190°C, or within a range defined by any two of these values.

[0056] In an embodiment, step ii) is carried out for about 15 seconds to about 5 minutes. In an embodiment, step ii) is carried out for at least, at most, or about 15 seconds, 30 seconds, 45 seconds, 1 minute, 1.5 minutes, 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, or 5 minutes, or within a range defined by any two of these values.

[0057] In an embodiment, step iii) is carried out at a temperature between about 100°C and about 190°C. In an embodiment, step iii) is carried out at a temperature of at least, at most, or about 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, or 190°C, or within a range defined by any two of these values. The term "cure" does not require 100% curing and encompasses partial curing.

[0058] In an embodiment, step iii) is carried out for about 15 seconds to about 5 minutes. In an embodiment, step iii) is carried out for at least, at most, or about 15 seconds, 30 seconds, 45 seconds, 1 minute, 1.5 minutes, 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, or 5 minutes, or within a range defined by any two of these values.

[0059] In an embodiment, steps ii) and iii) are carried out in parallel. In an embodiment, steps ii) and iii) are carried out sequentially (e.g., when drying the coated fibers at a temperature below the temperature required for curing). When step i) is carried out by immersing carbon fibers or a fabric comprising a plurality of carbon fibers in a bath comprising a sizing solution, the fibers or fabric are removed from the bath before carrying out steps ii) and iii).

[0060] 1. Epoxy resin

[0061] The epoxy resin used in the sizing composition of the present invention can be any epoxide-containing material known in the art. In an embodiment, the epoxy resin is an epoxy-containing copolymer, such as epoxy methacrylate, epoxy acrylate, epoxy ester, and siloxane epoxy copolymer. In an embodiment, the epoxy-containing copolymer is an epoxy / polyurethane copolymer.

[0062] Examples of suitable epoxy resins include those disclosed in U.S. Patent Nos. 4,409,288 and 6,013,730 and US2013 / 0224470, which are hereby incorporated by reference in their entirety. In an embodiment, the epoxy resin is bisphenol-based. In an embodiment, the epoxy resin is bisphenol A-based. In an embodiment, the epoxy resin is bisphenol F-based. In an embodiment, the epoxy resin is bisphenol S-based. In an embodiment, the epoxy resin is glycidylamine. In an embodiment, the epoxy resin is phenolic resin. In an embodiment, the epoxy resin is aliphatic. In an embodiment, the epoxy resin is halogenated.

[0063] Specific epoxy resins suitable for the present invention include:

[0064] Bisphenol A-based: EPON 828, EPON 825, EPON 826, EPON 830, Epon 834 (Hexion), DER332 (Dow Chemical), Tactix 123, and Tactix138 (Huntsman).

[0065] Bisphenol F-based: Araldite GY 281 / 282 / 285 (Huntsman) and Rutapox0158 (Bakelite).

[0066] Epoxy novolac-based: DEN 431, DEN 428, DEN 439 (Dow Chemical), EPN 1138, and EPN 1139 (Huntsman).

[0067] Glycidylamines: Araldite MY 9512, Araldite MY 721 and Araldite MY 720 (Huntsman).

[0068] Halogenated (brominated): Araldite LT 8049 (Huntsman), DER 542 (Dow Chemical).

[0069] Alicyclic epoxy resins: CY179-1 (Diacel), Araldite 175 (Huntsman) and Epalloy 5000 (Huntsman).

[0070] Examples of compounds having epoxy groups and polyurethane groups include polyurethane-modified epoxy resins. Examples include EPU-78-13S, EPU-6, EPU-11, EPU-15, EPU16A, EPU-16N, EPU-17T-6, EPU-1348 and EPU-1395 (Adeka Corporation) and Hydran CF-025 (DIC Corporation).

[0071] 2. Amines

[0072] The structure of the amine used to prepare the salts of the present invention can be described by the following general formula:

[0073] R n X m Q,

[0074] wherein:

[0075] Q is an amine-containing group having multiple amines or a single amino group. In either case, it is important that there is at least one primary or secondary amine. Non-limiting examples include monoamines, polyamines and polyamidoamines. Q can also be an epoxy-amine adduct. The amine independently or in combination with itself contains R or X groups. Generally, the above formula describes the class of amine-containing compounds known in the art as curing agents for epoxy resins.

[0076] X is a polyether group selected from the following: poly(propylene oxide) (PPO) compounds and poly(ethylene oxide) (PEO) compounds, or mixtures thereof. In an embodiment, X comprises PPO. In an embodiment, X comprises PEO. In an embodiment, X is a blend of PPO and PEO. In an embodiment, each X comprises 2 - 50 propylene oxide and / or ethylene oxide monomer units. In an embodiment, each X comprises 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50 propylene oxide and / or ethylene oxide monomer units. In an embodiment, each X comprises at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50 propylene oxide and / or ethylene oxide monomer units. In an embodiment, each X comprises at most 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48 or 49 propylene oxide and / or ethylene oxide monomer units.

[0077] m is an integer, where m ≥ 0.

[0078] R is a straight-chain or branched-chain, saturated or unsaturated or a combination thereof aryl or alkyl. In an embodiment, the aryl is C 6 -C 14 aryl. In an embodiment, the aryl is selected from phenyl, benzyl, tolyl, xylyl and naphthyl.

[0079] In an embodiment, the alkyl is C 1 -C 24 alkyl. In an embodiment, the alkyl is C 1 、C 2 、C 3 、C 4 、C 5 、C 6 、C 7 、C 8 、C9 , C 10 , C 12 , C 12 , C 13 , C 14 , C 15 , C 16 , C 17 , C 18 , C 19 , C 20 , C 21 , C 22 , C 23 or C 24 alkyl. In an embodiment, the alkyl is at least C 1 , C 2 , C 3 , C 4 , C 5 , C 6 , C 7 , C 8 , C 9 , C 10 , C 12 , C 12 , C 13 , C 14 , C 15 , C 16 , C 17 , C 18 , C 19 , C 20 , C 21 , C 22 or C 23 alkyl. In an embodiment, the alkyl is at most C 2 , C 3 , C 4 , C 5 , C 6 , C 7 , C 8 , C 9 , C 10 , C 12 , C 12 , C 13 , C 14 , C 15 , C 16 , C 17 , C 18 , C 19 , C 20 , C 21 , C 22 , C 23 or C 24 alkyl.

[0080] R may be substituted with 1 - 5 substituents each independently selected from the following: C 1 -C 12 alkyl, C 1 -C 12 heteroalkyl, C 6 -C 14 aryl and C 6 -C 14 heteroaryl. C 1 -C 12 Heteroalkyl includes, for example, C 1 -C 12 alkoxy, C 1 -C 12 alkylamino and C 1 -C 12 haloalkyl.

[0081] R may contain 1 - 10 heteroatoms in its main chain (i.e., alkyl or aryl) and / or substituents. A heteroatom is any atom other than C or H. Non - limiting examples of such heteroatoms are N, O, P, and S. R may also be free of heteroatoms.

[0082] n is an integer and n≥0. If n≥2, each instance of R need not be the same as the other instances of R.

[0083] It should be understood that when m is 0, X does not exist, and when n is 0, R does not exist.

[0084] It should also be understood that R n X m Q is not a structural formula in which at least one R group can be directly bonded to Q, even in the presence of X.

[0085] 3. Carboxylic Acid

[0086] The carboxylic acid used to prepare such carboxylate amines is not limited to any class and can be, for example, a mono - carboxylic acid or a poly - carboxylic acid, substituted or unsubstituted. Derivatives of poly - carboxylic acids can also be used.

[0087] In some embodiments, the carboxylic acid is a mono - carboxylic acid. Examples of mono - carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, caproic acid, etc., or hydroxy - carboxylic acids (such as glycolic acid, lactic acid, etc.). These mono - carboxylic acids can be used alone or as a mixture of two or more of them.

[0088] In one embodiment, the carboxylic acid is a di - carboxylic acid. In the embodiment, the di - carboxylic acid has the following formula: where R 1 either does not exist or is a saturated or unsaturated, straight - chain or branched - chain, aromatic, substituted or unsubstituted hydrocarbon group; Y 1 and Y 2 are independently a group containing nitrogen, oxygen, sulfur or phosphorus, C 1 -C 6 -alkyl, alkoxy and / or phenyl group. X 1 and X 2 are independently hydrogen, a metal, a quaternary amine, an alcohol or a hydrocarbon group having up to 6 carbon atoms, said hydrocarbon group being an alkyl, alkylene or aromatic group, which may be branched or straight-chain and may optionally have one or more heteroatoms selected from nitrogen, oxygen, sulfur and phosphorus.

[0089] Examples of metals for X 1 and X 2 include alkali metals such as lithium, potassium and sodium.

[0090] By way of guidance, some examples of possible embodiments of R 1 are provided below, where R 1 is selected from hydrocarbons having any one or more of the following:

[0091] a saturated, straight-chain or branched alkyl chain substituted with one or more groups containing nitrogen, oxygen, sulfur or phosphorus (examples of such groups include carbonyl, ether, amide, amine, alcohol, etc.);

[0092] an unsaturated, branched or straight-chain alkyl group;

[0093] an unsaturated, branched or straight-chain alkyl group substituted with one or more groups containing nitrogen, oxygen, sulfur or phosphorus (examples of such groups include carbonyl, ether, amide, amine, alcohol, etc.);

[0094] one or more polyethylene glycol or polypropylene glycol groups;

[0095] an aromatic group optionally substituted with one or more alkyl, nitrogen-containing, oxygen-containing, sulfur-containing or phosphorus-containing groups (examples of such groups include carbonyl, ether, amide, amine, alcohol, etc.); and

[0096] one or more of an alkene, alkyne, alcohol, carbonyl, ether, amine, amide, phenyl, benzene, furan, pyridine or pyran group or imidazole group.

[0097] In some embodiments, R 1 may also include combinations of the foregoing exemplary hydrocarbon groups. It should also be recognized that in some embodiments, R 1 may be absent.

[0098] Examples of dicarboxylic acids that can be used in certain embodiments of the present invention include DL-tartaric acid, L-tartaric acid, D-tartaric acid, fumaric acid, methylfumaric acid, oxamic acid, succinic acid, 2-methylsuccinic acid, L-malic acid, DL-malic acid, D-malic acid, aspartic acid, pyruvic acid, muconic acid, oxaloacetic acid, glutamic acid, glycolic acid, iminodiacetic acid, 2,2'-oxydipropionic acid, 3,3'-oxydipropionic acid, 2,2'-[1,2-ethylenediylbis(oxy)]bis-acetic acid, 3,3'-[1,2-ethylenediylbis(oxy)]bis-propionic acid, 3,3'-[oxybis(ethane-2,1-diyl)oxy]dipropionic acid, poly(ethylene glycol) bis-acetic acid, polyethylene glycol bis(carboxymethyl) ether, polyethylene glycol diacid 600, chelidonic acid, pyridine dicarboxylic acid, 2,5-furandicarboxylic acid, isophthalic acid, terephthalic acid, phthalic acid, trimellitic acid, 1,4-benzenediacetic acid, 1,3-benzenediacetic acid, and their derivatives, such as diammonium tartrate, potassium hydrogen tartrate, ammonium hydrogen oxalate, monomethyl fumarate, and monoethyl fumarate, and mixtures thereof.

[0099] In some embodiments, the dicarboxylic acid can comprise keto acids, such as one or more of the following: hydroxypyruvic acid, α-ketoglutaric acid and β-ketoglutaric acid, α-ketoadipic acid, α-oxovaleric acid, levulinic acid, 4-hydroxy-2-oxovaleric acid, and 4-hydroxybenzpyruvic acid.

[0100] 4. Surfactant

[0101] The sizing composition can further include a surfactant. The surfactant is not particularly limited and can be selected from nonionic, anionic, cationic, and amphoteric surfactants known to those skilled in the art. A combination of one or at least two of such emulsifiers can be used.

[0102] Nonionic surfactants include, for example, linear polyoxyalkylene alkyl ethers such as polyoxyethylene hexyl ether, polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, and polyoxyethylene cetyl ether; branched polyoxyalkylene primary alkyl ethers such as polyoxyethylene 2-ethylhexyl ether, polyoxyethylene isocetyl ether, and polyoxyethylene isostearyl ether; branched polyoxyalkylene secondary alkyl ethers such as polyoxyethylene 1-hexylhexyl ether, polyoxyethylene 1-octylhexyl ether, polyoxyethylene 1-hexyl octyl ether, polyoxyethylene 1-pentylheptyl ether, and polyoxyethylene 1-heptylpentyl ether; polyoxyalkylene alkenyl ethers such as polyoxyethylene oleyl ether; polyoxyalkylene alkyl phenyl ethers such as polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, and polyoxyethylene dodecyl phenyl ether; polyoxyalkylene alkyl aryl phenyl ethers such as polyoxyethylene tribenzyl phenyl, polyoxyethylene dibenzyl phenyl ether, and polyoxyethylene benzyl phenyl ether; polyoxyalkylene fatty acid esters such as polyoxyethylene monolaurate, polyoxyethylene monooleate, polyoxyethylene monostearate, polyoxyethylene monomyristate, polyoxyethylene dilaurate, polyoxyethylene dioleate, polyoxyethylene dimyristate, and polyoxyethylene distearate; sorbitan esters such as sorbitan monopalmitate and sorbitan monooleate; polyoxyalkylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monostearate and polyoxyethylene sorbitan monooleate; fatty acid glycerides such as glycerol monostearate, glycerol monolaurate, and glycerol monopalmitate; polyoxyalkylene sorbitol fatty acid esters; sucrose fatty acid esters; polyoxyalkylene castor oil ethers such as polyoxyethylene castor oil ether; polyoxyalkylene hydrogenated castor oil ethers such as polyoxyethylene hydrogenated castor oil ether; polyoxyalkylene alkyl amino ethers such as polyoxyethylene lauryl amino ether and polyoxyethylene stearyl amino ether; ethylene oxide-propylene oxide block or random copolymers; terminally alkyl etherified ethylene oxide-propylene oxide block or random copolymers; and terminally sucrose-etherified ethylene oxide-propylene oxide block or random copolymers.

[0103] Among those nonionic surfactants, branched polyoxyalkylene primary alkyl ethers, branched polyoxyalkylene secondary alkyl ethers, polyoxyalkylene alkenyl ethers, polyoxyalkylene alkyl phenyl ethers, polyoxyalkylene fatty acid esters, ethylene oxide-propylene oxide block copolymers, and terminally alkyl etherified ethylene oxide-propylene oxide block copolymers are preferred because of their superior performance in emulsifying silicone compounds in water. In addition, ethylene oxide-propylene oxide block or random copolymers and terminally alkyl etherified ethylene oxide-propylene oxide block copolymers are more preferred because of their performance of becoming tarry substances on the fibers during baking to protect the fibers from damage.

[0104] Anionic surfactants include salts of various acids, such as salts of fatty acids, salts of hydroxycarboxylic acids such as hydroxyacetic acid, potassium hydroxyacetate, lactic acid and potassium lactate; salts of polyoxyalkylene alkyl ether acetic acids, such as sodium salt of polyoxyalkylene tridecyl ether acetic acid; salts of carboxy-multisubstituted aromatic compounds, such as potassium trimellitate and potassium pyromellitate; salts of alkylbenzenesulfonic acids, such as salts of dodecylbenzenesulfonic acid; salts of polyoxyalkylene alkyl ether sulfonic acids, such as salts of polyoxyethylene 2-ethylhexyl ether sulfonic acid; salts of higher fatty acid amide sulfonic acids, such as salts of stearoyl methyl taurine, salts of lauroyl methyl taurine, salts of myristoyl methyl taurine and salts of palmitoyl methyl taurine; salts of N-acyl sarcosines, such as salts of lauroyl sarcosine; salts of alkyl phosphonic acids, such as salts of octyl phosphonate; salts of aromatic phosphonic acids, such as potassium salt of phenyl phosphonate; salts of alkyl phosphonic acid alkyl phosphate esters, such as salts of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester; salts of nitrogen-containing alkyl phosphonic acids, such as salts of aminoethyl phosphonic acid and its diethanolamine salt; salts of alkyl sulfates, such as salts of 2-ethylhexyl sulfate; salts of polyoxyalkylene sulfates, such as salts of polyoxyethylene 2-ethylhexyl ether sulfate; salts of long-chain sulfosuccinates, such as sodium di-2-ethylhexyl sulfosuccinate and sodium dioctyl sulfosuccinate; and long-chain N-acyl glutamates, such as monosodium N-lauroyl glutamate and disodium N-stearoyl-L-glutamate. Anionic surfactants may also include alkyl phosphoric acids and aryl phosphoric acids and their derivatives.

[0105] Cationic surfactants include, for example, quaternary ammonium salts, such as lauryl trimethyl ammonium chloride and oleyl methyl ethyl ammonium ethyl sulfate; and (polyoxyalkylene) alkyl amino ether salts, such as (polyoxyethylene) lauryl amino ether lactate, stearyl amino ether lactate and (polyoxyethylene) lauryl amino ether trimethyl phosphate.

[0106] Amphoteric emulsifiers include, for example, imidazoline amphoteric surfactants, such as sodium 2-undecyl-N,N-(hydroxyethyl carboxymethyl)-2-imidazoline and disodium 2-cocoyl-2-imidazolinium hydroxide-1-carboxylate ethoxylate; betaine amphoteric surfactants, such as 2-heptadecyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, lauryl dimethyl aminoacetate betaine, alkyl betaine, amide betaine and sulfobetaine; and amino acid amphoteric surfactants, such as N-lauryl glycine, N-lauryl-β-alanine and N-stearyl-β-alanine.

[0107] 5. Viscosity improver

[0108] In some embodiments, the sizing composition can include one or more viscosity modifiers. Generally, a viscosity modifier includes any composition that desirably improves the viscosity without inhibiting the action of the present invention. Viscosity modifiers can include natural polymers such as starch, cellulose, alginate, agar, carrageenan, collagen, gelatin, guar gum, and xanthan gum. Examples of cellulose polymers can include methylcellulose, hydroxypropylmethylcellulose, ethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose. Viscosity modifiers can also include synthetic acrylic-based polymers such as alkali-swellable (or soluble) emulsions (ASE), hydrophobically modified alkali-swellable emulsions (HASE), and hydrophobically modified ethoxylated urethane resins (HEUR). In some embodiments, the viscosity modifier can comprise aminocarboxylic acid substances such as carboxylates of alkylamines, carboxylates of arylamines, carboxylates of alkylarylamines, amino acids, and betaine compounds.

[0109] 6. Additional Components

[0110] In addition to the components mentioned above, the sizing composition of the present invention can also contain components provided that those components do not inhibit the action of the present invention. Those components can include antioxidants such as phenolic, amine, sulfur, phosphorus, or quinone compounds; antistatic agents such as sulfates, sulfonates of higher alcohols or higher alcohol ethers, phosphates of higher alcohols or higher alcohol ethers; lubricants such as polyethylene glycol, polyvinyl alcohol, alkyl esters of higher alcohols, ethers of higher alcohols, and waxes; antibacterial agents; antimicrobial agents; corrosion inhibitors; and humectants. In some embodiments, the lubricant can include polyethylene glycol having an average molecular weight between 100 and 10,000. More preferably, the lubricant can include polyethylene glycol having an average molecular weight between 800 and 8000. In a preferred embodiment, the lubricant can include polyethylene glycol having an average molecular weight between 1000 and 2000. In an embodiment, polyethylene glycol is present in the composition in an amount between 1% and 40% by weight based on the total weight of solids in the sizing composition.

[0111] In an embodiment, the carboxylate is present in the composition in an amount of from about 0.01% to about 80% by weight, based on the total weight of solids in the sizing composition. In an embodiment, the carboxylate is present in the composition in the following amounts by weight: less than, greater than, or about 0.01%, about 0.05%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 1.1%, about 1.2%, about 1.3%, about 1.4%, about 1.5%, about 1.6%, about 1.7%, about 1.8%, about 1.9%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, or about 80%.

[0112] Discussion

[0113] The fiber appearance (decoration) problems mentioned above as "markings" or other visible irregularities are typically addressed by implementing engineering controls during production, such as better sizing agent content control on the fiber and avoiding contaminants.

[0114] Amine-based curing agents are generally used to cure epoxy resins. They have been added to epoxy sizing agents to improve the properties of carbon fiber-vinyl ester composites as taught in US2013 / 0224470. These curing agents consist of polyamines containing primary and secondary amine groups. This reference does not teach the use of amine carboxylates as latent crosslinking agents for epoxy materials. Non-inhibited polyamines (the use of which is taught in these documents) are not suitable for conventional production due to their excessive reactivity towards epoxy groups in the sizing agent (even at ambient temperature), which presents serious complications such as the formation of highly insoluble, viscous, partially cured epoxy materials over time, the gelling of the sizing emulsion in the sizing bath, and the build-up on the surface of the dryer rollers.

[0115] JP 2013127132 A teaches the use of salts of tertiary amines for improving the adhesion of the matrix to carbon fibers. However, aside from the fact that the effect of the addition of these salts on the appearance of the fiber tow is not discussed, Comparative Example 3 of the present invention shows that tertiary amines are ineffective in making the tow darker because they cannot participate in the crosslinking reaction with epoxy resins.

[0116] The inventors of the present invention have found that the "darkness" of carbon fiber filaments generally depends on two parameters: the surface roughness of the filaments in the unsized state, and the sizing morphology / distribution in the sized state. It is extremely difficult to change and control the original carbon fiber surface roughness in a manner that can be repeatedly reproduced in a production environment, while the sizing morphology / distribution can be more easily changed and controlled. The inventors have also found that it is highly desirable and advantageous to reduce the brightness / gloss of the sized tows and make them darker in terms of masking the above-mentioned visible defects. Through intensive research, it has been found that the use of certain latent amine-based curing agents in epoxy-based sizing agents can result in a significantly darker appearance of the carbon fiber tows after the sizing agent has cured, thus solving the above-mentioned problems.

[0117] As shown below, it has been found that a certain structure of the carboxylate of an amine curing agent is particularly effective in reducing the luster / gloss of the fiber tows and imparting a darker appearance to the fiber tows when used in epoxy-based carbon fiber sizing agents.

[0118] From both Table 1 and Table 2 and the examples therein, it can be seen that the tow darkness can be effectively increased by adding a latent amine-based curing agent to an epoxy sizing formulation, applying the formulation to the fibers, and drying / curing at a selected temperature. The final drying temperature can be selected such that the epoxy-based formulation can cure. The final drying temperature can also be selected to be higher than the curing peak temperature obtained from DSC experiments. The final drying temperature can also be selected to be 1 °C to 50 °C higher than the curing peak temperature obtained from DSC experiments. The final drying temperature can also be selected to be 5 °C and 40 °C higher than the curing peak temperature obtained from DSC experiments.

[0119] A peak difference in gray scale of 10 can generally be discerned by the naked eye; thus, a gray scale peak of at least 125 is desirable, a gray scale peak of 115 is more desirable, and a gray scale peak below 105 is particularly desirable. As can be seen from the comparative examples, most of the non-inhibited (i.e., uncarboxylated) amine curing agents studied act to darken the fibers, but they are too reactive to be used in a production environment (as mentioned above), which can be seen when comparing, for example, the DSC onset / peak curing agent temperatures of Comparative Example 5 (non-inhibited Aradur 3986) and Example 15 (inhibited Aradur 3986). The latency of the inhibited curing agent depends both on the nature of the curing agent (type of amine groups present) and on the nature of the carboxylic acid used as the inhibitor (especially pKa and boiling point). The degree to which it may be desirable to inhibit the amine curing agent depends on processing parameters such as the fiber drying temperature and the nature of the drying (contact drying, non-contact drying) after the sizing application. As the type of non-inhibited curing agent taught in US2013 / 0224470, study Comparative Example 2. As shown, this curing agent is completely ineffective in darkening the fibers. As the type of tertiary amine additive described in JP 2013127132 A, study Comparative Example 3. This type of curing agent is ineffective in terms of tow darkness because the tertiary amine cannot participate in the epoxy crosslinking reaction but only catalyzes the chain extension / condensation reaction of the epoxy resin.

[0120] It is also desirable for the amine compound to have a certain degree of hydrophobicity, mainly due to the presence of the above-mentioned R group. In the case where there is only one R group and the R group is aliphatic, preferably, the R group is at least C 12 . As can be seen from Comparative Examples 8 and 9, in terms of darkening the fibers, among amines that are otherwise identical in structure, a larger R group (C 18 ) is more effective than a smaller C 12 group. It is also estimated that Aradur 340 has an R group based on C 13 , and Aradur 435 has an R group based on C 19 -C 20 . Without limiting the present invention, it is believed that the absence of a hydrophobic group in Jeffamine M600 (Comparative Example 2) makes it ineffective in darkening the fibers. However, the effectiveness of certain amines of this type (absence of R group), like Jeffamine M600 and O,O'-bis(3-aminopropyl)diethylene glycol (BADG), can be slightly improved by neutralizing the amine with a carboxylic acid bearing a hydrophobic group, like capric acid (Example 13).

[0121] Examples

[0122] In these studies, an unsized carbon fiber tow with 3,000 filaments of AS4C-3K (Hexcel, Stamford, Connecticut) was used. The amine curing agents ARADUR 340, ARADUR 435, and ARADUR 3986 were obtained from Huntsman (Salt Lake City, Utah). CARBOWAX TM SENTRY TM polyethylene glycol 1450 was obtained from Dow Chemical (Midland, Michigan). The GP sizing emulsion was obtained from Hexcel. Toximul TA-8 (tallow amine ethoxylate) was obtained from Stepan (Northfield, Illinois). All other materials were obtained from Sigma-Aldrich (St. Louis, Missouri).

[0123] Control and neat emulsion preparation

[0124] For Control 1, the general commercial sizing emulsion “GP” (Hexcel) based on bisphenol A epoxy resin was used. For Control 2, and also for use as the neat emulsion for curing studies, Carbowax 1450 was combined with the Control 1 emulsion at 10 wt.% relative to the epoxy resin.

[0125] Inhibited amine carboxylate preparation

[0126] The amine curing agent was reacted with an excess of carboxylic acid in aqueous solution at 60 °C and fully neutralized for 2 h. The stoichiometry was calculated based on the known structure and molecular weight, or, when the exact structure was unknown, based on the amine value of the curing agent reported by the supplier. The degree of neutralization was checked by pH measurement. These solutions of the latent curing agent were then added in the desired amounts to the diluted form (1 wt.% in water) of the neat emulsion (described above).

[0127] Sizing application and drying / curing

[0128] All emulsions were applied to the tow from the sizing bath at a 1 wt.% concentration and dried at different temperatures by non-contact drying (drying tower) or contact drying (steam drum, followed by a drying tower). When using simultaneous drying and curing, the drying temperature employed was matched or higher compared to the curing peak temperature determined by DSC (see next section), thereby also curing the sized tow.

[0129] Curing temperature determination

[0130] All emulsions were dried in vacuo at ambient temperature and small samples were run on a DSC (Discovery, TA Instruments) in air at a heating rate of 5 °C / min. The peak temperature of the exothermic curing reaction was recorded, as well as the onset temperature of this transition.

[0131] Method for Evaluating Tow Darkness

[0132] Prepare a plate with double-sided tape on its surface. Stretch the tow across the plate and press it into the double-sided tape. Image the tow via a Keyence VHX-5000 with a VH-Z100R lens and an OP-72402 ring light. Use a plate that rotates about a vertical axis to measure at different angles. Capture the mosaic image in 3D image stitching mode with a 100x lens magnification, full-ring illumination, monochrome capture mode, a manual 1.00 ms shutter speed, and 0 dB gain. After image capture, process the image via an internally scripted Matlab workflow. A 2.2 mm cross-section along the tow length and the full tow width constitutes each measurement region. Nine regions are selected for each tow. Figure 2 Depict exemplary tows, with nine regions selected for each tow; this figure is provided to depict the analysis method and does not necessarily represent fibers with Figure 1 or the data presented in Table 3. Record the gray-scale values at multiple positions within each of the nine regions. For each region, record the median gray-scale or peak gray-scale value between 0 and 255. For peak gray-scale measurement, calculate the histogram of the gray-scale values, smooth it, and report the maximum value from the smoothed curve. Report the average of the nine values from each region (Table 1). For median gray-scale measurement, calculate the average of the nine regions and report it as the median gray-scale darkness average in Table 3 and Figure 1 and. The values in Table 1 were measured at a 75-degree angle.

[0133] Controls 1 and 2

[0134] These emulsions do not contain a curing agent. They are applied to the carbon fiber tow at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C.

[0135] Example 1

[0136] Inhibit the amidoamine epoxy curing agent ARADUR 340 by neutralization reaction with acetic acid at a 1:3 amine:acid stoichiometry. Add a solution of this curing agent to the Control 2 emulsion to obtain an epoxy:amine salt stoichiometric ratio of 1:0.45. Apply the resulting emulsion to the carbon fiber tow at a 1 wt.% concentration and dry it by non-contact drying (drying tower) at 110 °C. Measure the average peak gray-scale of the tow and report it in Table 1.

[0137] Example 2

[0138] The amidoamine epoxy resin curing agent ARADUR 340 was inhibited with fumaric acid by a neutralization reaction at an amine:acid stoichiometry of 1:1.25. A solution of this curing agent was added to Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometric ratio of 1:0.45. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 150 °C. The average value of the peak gray scale of the tows was measured and reported in Table 1.

[0139] Example 3

[0140] The amidoamine epoxy resin curing agent ARADUR 340 was inhibited with fumaric acid by a neutralization reaction at an amine:acid stoichiometry of 1:1.25. A solution of this curing agent was added to Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometric ratio of 1:0.28. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 150 °C. The average value of the peak gray scale of the tows was measured and reported in Table 1.

[0141] Example 4

[0142] The amidoamine epoxy resin curing agent ARADUR 340 was inhibited with lactic acid by a neutralization reaction at an amine:acid stoichiometry of 1:1.1. A solution of this curing agent was added to Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C. The average value of the peak gray scale of the tows was measured and reported in Table 1.

[0143] Example 5

[0144] The amidoamine epoxy resin curing agent ARADUR 340 was inhibited with acetic acid by a neutralization reaction at an amine:acid stoichiometry of 1:3. A solution of this curing agent was added to Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 105 °C. The average value of the peak gray scale of the tows was measured and reported in Table 1.

[0145] Example 6

[0146] The amidoamine epoxy resin curing agent ARADUR 340 was inhibited with iminodiacetic acid by neutralization reaction at an amine:acid stoichiometry of 1:1.25. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.45. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by contact drying (drum) at 110 °C and then non-contact curing (drying tower) at 155 °C. The average value of the peak grey scale of the tow was measured and reported in Table 1.

[0147] Example 7

[0148] Dodecylamine was inhibited with iminodiacetic acid by neutralization reaction at an amine:acid stoichiometry of 1:1.25. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by contact drying (drum) at 110 °C and then non-contact curing (drying tower) at 155 °C. The average value of the peak grey scale of the tow was measured and reported in Table 1.

[0149] Example 8

[0150] Octadecylamine was inhibited with acetic acid by neutralization reaction at an amine:acid stoichiometry of 1:2. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 135 °C. The average value of the peak grey scale of the tow was measured and reported in Table 1.

[0151] Example 9

[0152] Dodecylamine was inhibited with acetic acid by neutralization reaction at an amine:acid stoichiometry of 1:2. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 135 °C. The average value of the peak grey scale of the tow was measured and reported in Table 1.

[0153] Example 10

[0154] The amidoamine epoxy resin curing agent ARADUR 435 was inhibited with fumaric acid by a neutralization reaction at an amine:acid stoichiometry of 1:1.1. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 160 °C. The average value of the peak gray scale of the tows was measured and reported in Table 1.

[0155] Example 11

[0156] The amidoamine epoxy resin curing agent ARADUR 435 was inhibited with fumaric acid by a neutralization reaction at an amine:acid stoichiometry of 1:1.1. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.18. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 160 °C. The average value of the peak gray scale of the tows was measured and reported in Table 1.

[0157] Example 12

[0158] The amidoamine epoxy resin curing agent ARADUR 435 was inhibited with monoethyl fumarate by a neutralization reaction at an amine:acid stoichiometry of 1:1.1. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 160 °C. The average value of the peak gray scale of the tows was measured and reported in Table 1.

[0159] Example 13

[0160] O,O'-Bis(3-aminopropyl)diethylene glycol (BADG) was inhibited with capric acid by a neutralization reaction at an amine:acid stoichiometry of 1:1.1. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C. The average value of the peak gray scale of the tows was measured and reported in Table 1.

[0161] Example 14

[0162] The epoxy - amine adduct curing agent ARADUR 3986 was inhibited by oxamic acid with an amine:acid stoichiometry of 1:1.2 through a neutralization reaction. A solution of this curing agent was added to the control 2 emulsion to obtain an epoxy resin:amine salt stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non - contact drying (drying tower) at 170 °C. The average value of the peak gray scale of the tow was measured and reported in Table 1.

[0163] Example 15

[0164] The epoxy - amine adduct curing agent ARADUR 3986 was inhibited by oxalic acid with an amine:acid stoichiometry of 1:1.1 through a neutralization reaction. A solution of this curing agent was added to the control 2 emulsion to obtain an epoxy resin:amine salt stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non - contact drying (drying tower) at 180 °C. The average value of the peak gray scale of the tow was measured and reported in Table 1.

[0165] Example 16

[0166] Octadecylamine was inhibited by ethoxy 4 - nonylphenyl ether glycolate with an amine:acid stoichiometry of 1:1.5 through a neutralization reaction. A solution of this curing agent was added to the control 2 emulsion to obtain an epoxy resin:amine salt stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non - contact drying (drying tower) at 125 °C. The average value of the peak gray scale of the tow was measured and reported in Table 1.

[0167] Example 17

[0168] The curing agent from Example 15 was used. A solution of this curing agent was added to the control 2 emulsion to obtain an epoxy resin:amine salt stoichiometric ratio of 1:0.52. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by contact drying (drum) at 125 °C and then by non - contact curing (drying tower) at 175 °C. The average value of the peak gray scale of the tow was measured and reported in Table 1.

[0169] Example 18

[0170] The fibers from Example 3 were woven into a plain weave fabric of 196 gsm. The darkness of 21 tows from the weft direction was analyzed and the average value of the peak gray scale was reported in Table 2.

[0171] Example 19

[0172] The amidoamine epoxy resin curing agent ARADUR 340 was inhibited with fumaric acid by a neutralization reaction at an amine:acid stoichiometry of 1:2. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 150 °C. The fiber was woven into a plain fabric of 196 gsm. The darkness of 21 tows from the weft direction was analyzed and the average of the peak gray levels was reported in Table 2.

[0173] Example 20

[0174] The epoxy-amine adduct curing agent ARADUR 3986 was inhibited with acetic acid by a neutralization reaction at an amine:acid stoichiometry of 1:1.1. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:1.5. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C. The average of the peak gray levels of the tow was measured and reported in Table 1.

[0175] Example 21

[0176] The same sizing formulation as in Example 20 was used, but the sized fiber was dried by non-contact drying (drying tower) at 160 °C. The average of the peak gray levels of the tow was measured and reported in Table 1.

[0177] Example 22

[0178] The epoxy-amine adduct curing agent ARADUR 3986 was inhibited with acetic acid by a neutralization reaction at an amine:acid stoichiometry of 1:1.1. A solution of this curing agent was added to the Control 2 emulsion to obtain an epoxy resin:amine salt stoichiometry ratio of 1:2. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C. The average of the peak gray levels of the tow was measured and reported in Table 1.

[0179] Example 23

[0180] The same sizing formulation as in Example 22 was used, but the sized fiber was dried by non-contact drying (drying tower) at 160 °C. The average of the peak gray levels of the tow was measured and reported in Table 1.

[0181] Comparative Example 1

[0182] The non-inhibited amidoamine epoxy resin curing agent ARADUR 340 was dissolved in the Control 2 emulsion to obtain an epoxy resin:amine stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C. The average of the peak gray levels of the tows was measured and reported in Table 1.

[0183] Comparative Example 2

[0184] The non-inhibited amine epoxy resin curing agent Jeffamine M-600 was dissolved in the Control 2 emulsion to obtain an epoxy resin:amine stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C. The average of the peak gray levels of the tows was measured and reported in Table 1.

[0185] Comparative Example 3

[0186] The non-inhibited tertiary amine-based emulsifier Toximul TA-8 was dissolved in the Control 2 emulsion to obtain an epoxy resin:amine stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 160 °C. The average of the peak gray levels of the tows was measured and reported in Table 1.

[0187] Comparative Example 4

[0188] The non-inhibited amidoamine epoxy resin curing agent ARADUR 435 was dissolved in the Control 2 emulsion to obtain an epoxy resin:amine stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C. The average of the peak gray levels of the tows was measured and reported in Table 1.

[0189] Comparative Example 5

[0190] The non-inhibited amine-epoxy condensate curing agent ARADUR 3986 was dissolved in the Control 2 emulsion to obtain an epoxy resin:amine stoichiometric ratio of 1:0.36. The resulting emulsion was applied to carbon fiber tows at a 1 wt.% concentration and dried by non-contact drying (drying tower) at 125 °C. The average of the peak gray levels of the tows was measured and reported in Table 1.

[0191] Comparative Example 6

[0192] Carbon fibers sized with the "GP" sizing (Control 1) from Table 1 were woven into a plain weave fabric of 196 gsm. The darkness of 21 tows from the weft direction was analyzed and the average of the peak gray levels was reported in Table 2.

[0193] Table 1

[0194] Table 2

[0195] Further experiments were conducted, in which the fiber darkness change was evaluated at different viewing angles ( angle) for the control and certain darker experimental fibers. As described above, for each fiber, nine different regions were selected; within each of the nine regions, the gray scale values were recorded at multiple points. The median gray scale value for each of the nine regions was determined. For each fiber, at each viewing angle, the average of the nine median gray scale values was calculated. The data are shown in Table 3, and the results are shown in Figure 1 . It was found that the darkness change of the darker experimental fibers was lower than that of the control.

[0196] Table 3

[0197] Those skilled in the art to which the present invention pertains will envision many modifications of the present invention and other embodiments thereof that have the benefit of the teachings presented in the foregoing description and the associated drawings. Accordingly, it is to be understood that the invention is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims.

[0198] Although specific terms are employed herein, they are used in a generic descriptive sense and not for purposes of limitation. Each embodiment disclosed herein is considered applicable to each of the other disclosed embodiments. All combinations and sub - combinations of the various elements described herein are within the scope of the embodiments.

Claims

1. An in - sizing composition, the in - sizing composition comprising: a. an epoxy - containing resin; and b. a carboxylate salt of an amine, wherein the amine has the following formula R n X m Q wherein: Q is an amine - containing group, the amine - containing group comprising at least one primary or secondary amine; X is a polyether group selected from: poly(propylene oxide) (PPO) compounds and poly(ethylene oxide) (PEO) compounds or mixtures thereof; m is an integer, where m≥0; R is an aryl or an alkyl, wherein each alkyl can independently be straight-chain or branched-chain, and wherein each alkyl can independently be saturated or unsaturated; R contains 0 - 10 heteroatoms; and R is unsubstituted or substituted with 1 - 5 substituents selected from the following: C 1 -C 12 alkyl, C 1 -C 12 heteroalkyl, C 6 -C 14 aryl and C 6 -C 14 heteroaryl; and n is an integer, and n≥0.

2. The composition according to claim 1, wherein Q is a monoamine.

3. The composition according to claim 1, wherein Q comprises multiple amino groups.

4. The composition according to claim 3, wherein Q comprises multiple primary or secondary amino groups.

5. The composition according to claim 1, wherein Q comprises a polyamidoamine.

6. The composition according to claim 1, wherein Q comprises an epoxy - amine adduct.

7. The composition according to any one of claims 1 - 6, wherein X comprises PPO.

8. The composition according to any one of claims 1 - 6, wherein X comprises PEO.

9. The composition according to any one of claims 1 - 8, wherein m≥1, m≥2, or m≥3.

10. The composition according to any one of claims 1 - 5, wherein X is absent.

11. The composition according to any one of claims 1 - 10, wherein at least one R is straight - chain.

12. The composition according to any one of claims 1 - 11, wherein at least one R is branched - chain.

13. The composition according to any one of claims 1 - 12, wherein at least one R is saturated.

14. The composition according to any one of claims 1 - 13, wherein at least one R is unsaturated.

15. The composition according to any one of claims 1 - 14, wherein R is unsubstituted.

16. The composition according to any one of claims 1 - 15, wherein R is substituted.

17. The composition according to any one of claims 1 - 16, wherein n≥2, or n≥3.

18. The composition according to any one of claims 1 - 17, wherein the carboxylate salt is derived from a monocarboxylic acid.

19. The composition according to any one of claims 1 - 18, wherein the carboxylate salt is derived from a polycarboxylic acid.

20. The composition according to any one of claims 1 - 19, wherein the carboxylate salt is derived from a polycarboxylic acid derivative having at least one free / unmodified acid group.

21. The composition according to any one of claims 1 - 20, wherein the epoxy resin:amine molar ratio is from about 10:1 to about 1:

10.

22. A carbon fiber, the carbon fiber being prepared by drying and curing on its surface a composition according to any one of claims 1 - 21.

23. A carbon - fiber - reinforced composite, the carbon - fiber - reinforced composite comprising the carbon fiber according to claim 22.

24. The carbon - fiber - reinforced composite according to claim 23, the carbon - fiber - reinforced composite comprising a resin matrix impregnated into the fibers.

25. A method for preparing a treated carbon fiber, the method Comprising the following steps: i) applying the composition according to any one of claims 1 - 21 to carbon fibers to form coated carbon fibers; ii) drying the coated carbon fibers, and iii) curing the coated carbon fibers; thereby forming treated carbon fibers.

26. The method according to claim 25, wherein step i) is carried out for about 5 seconds to 60 seconds.

27. The method according to claim 25 or 26, wherein step ii) is carried out at a temperature between about 100 °C and about 190 °C.

28. The method according to any one of claims 25 - 27, wherein step ii) is carried out for about 15 seconds to about 5 minutes.

29. The method according to any one of claims 25 - 28, wherein step iii) is carried out at a temperature between about 100 °C and about 190 °C.

30. The method according to any one of claims 25 - 29, wherein step iii) is carried out for about 15 seconds to about 5 minutes.

31. The method according to any one of claims 25 - 30, wherein steps ii) and iii) are carried out in parallel.

32. The method according to any one of claims 25 - 30, wherein steps ii) and iii) are carried out sequentially.

Images