Sizing agents for carbon fibers; carbon fiber and manufacturing processes for it, as well as composite materials

Abstract

A sizing agent for carbon fibers comprising a polyamine-polycarboxylic acid condensate (X) formed by the condensation of a polyamine (A) and a polycarboxylic acid (B), wherein the polyamine (A) is a polyamine which contains in one molecule a hydrocarbon group and three or more nitrogen atoms, wherein the total number of carbon atoms in one molecule is at least 4 and at most 63, and wherein the polycarboxylic acid (B) is a polycarboxylic acid with at least 2 and at most 24 carbon atoms, which is at least divalent and at most tetravalent, wherein the non-volatile component of the sizing agent for carbon fibers comprises the polyamine-polycarboxylic acid condensate (X) in a proportion of at least 50% by mass.

Description

TECHNICAL AREA

[0001] The present invention relates to a sizing agent for carbon fibers comprising a specific polyamine-polycarboxylic acid condensate, a carbon fiber, a manufacturing process for a carbon fiber and a composite material. TECHNICAL BACKGROUND

[0002] Fiber-reinforced thermoplastic resin composites are generally known as materials containing inorganic fibers, such as carbon fibers, and a matrix resin, such as a thermoplastic resin. This matrix resin is a base material with diverse applications, for example, in the fields of building materials and transportation equipment. To improve the adhesion between the inorganic fibers, such as carbon fibers, and the base material, such as a thermoplastic resin, a process is carried out in which a sizing agent is applied to the inorganic fibers.

[0003] Known sizing agents for inorganic fibers are disclosed, for example, in patent documents JP 2008 138296 A and JP 2020 007685 A. Patent document JP 2008 138296 A discloses a carbon fiber fuzz inhibitor containing a neutral salt of a polyalkylene-polyamine fatty acid condensate obtained by reacting a polyalkylene-polyamine with a saturated or unsaturated, unbranched or branched fatty acid having 8 to 24 carbon atoms. Patent document JP 2020 007685 A discloses a glass fiber bundling agent containing a polyethylene oxide and a polyalkylene-polyamine fatty acid condensate.The polyalkylene-polyamine fatty acid condensate is obtained by a reaction of a polyalkylene-polyamine and a saturated or unsaturated, straight-chain or branched-chain polyhydric fatty acid, resulting in a polyhydric polyalkylene-polyamine fatty acid amide, and subsequent neutralization with an organic or inorganic acid such as acetic acid.

[0004] Patent document JP S63 230542 A discloses a sizing agent for glass fibers which contains a condensation product of a polyethylene polyamine, octanoic acid or a derivative thereof and a bifunctional crosslinker as an essential component to bundle the fiber filaments and improve fiber processing. OVERVIEW OF THE INVENTIONAL PROBLEM

[0005] However, the problem with conventional sizing agents is that they do not satisfactorily improve the adhesion of inorganic fibers to a base material. SOLUTION TO THE PROBLEM

[0006] Therefore, the inventors of the present invention carried out investigations to solve the above-mentioned problem and thus came to the conclusion that a specific sizing agent for carbon fibers, which contains a specific polyamine-polycarboxylic acid condensate, is very suitable.

[0007] To solve the aforementioned problem and according to one aspect of the present invention, a sizing agent for carbon fibers comprises a polyamine-polycarboxylic acid condensate (X) formed by the condensation of a polyamine (A) and a polycarboxylic acid (B). The polyamine (A) is a polyamine containing a hydrocarbon group and three or more nitrogen atoms in one molecule, wherein the total number of carbon atoms in one molecule is at least 4 and at most 63. The polycarboxylic acid (B) is a polycarboxylic acid with at least 2 and at most 24 carbon atoms, which is at least divalent and at most tetravalent.

[0008] The sizing agent for carbon fibers can be the polyamine-polycarboxylic acid condensate (X) of the following formula (1). [Numerical Formula 1] 0.05≤_b1×b2a1×a2<1.0

[0009] In formula (1) it states a1 for the amine value measured for the polyamine (A), a2 for the content percentage (in mass%) of polyamine (A), if the sum of the content percentages of polyamine (A) and polycarboxylic acid (B) is assumed to be 100 mass%, b1 for the acid value measured for the polycarboxylic acid (B) and b2 for the content percentage (in mass%) of polycarboxylic acid (B) when the sum of the content percentages of polyamine (A) and polycarboxylic acid (B) is assumed to be 100 mass%.

[0010] The non-volatile component of the sizing agent for carbon fibers contains the polyamine-polycarboxylic acid condensate (X) in a ratio of at least 50% by mass.

[0011] The non-volatile component of the sizing agent for carbon fibers may contain the polyamine-polycarboxylic acid condensate (X) in a ratio of at least 80% by mass.

[0012] The sizing agent for carbon fibers may also contain Brønsted acid.

[0013] To solve the above-mentioned problem and according to another aspect of the present invention, the carbon fiber has the carbon fiber sizing agent applied to it.

[0014] To solve the above-mentioned problem and according to a further aspect of the present invention, a method for producing a carbon fiber comprises applying the carbon fiber sizing agent to a carbon fiber.

[0015] To solve the above-mentioned problem and according to a further aspect of the present invention, a composite material comprises carbon fiber and a thermoplastic resin.

[0016] The thermoplastic resin in the composite material can be at least one that is selected from a polyamide and a polypropylene. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0017] The present invention improves the adhesion of carbon fibers to a base material of a composite material. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of equipment for evaluating composite material cut surface properties, which is used in the evaluation of adhesion properties in the section "Examples". DESCRIPTION OF THE EXAMPLES OF EXECUTION<Erstes Ausführungsbeispiel>

[0018] A first embodiment of a sizing agent for carbon fibers according to the present invention (hereinafter also referred to as the sizing agent) is described below. The sizing agent contains a polyamine-polycarboxylic acid condensate (X). (Polyamine-polycarboxylic acid condensate (X)

[0019] The polyamine-polycarboxylic acid condensate (X) is formed by condensation of a polyamine (A) and a polycarboxylic acid (B).

[0020] The polyamine (A) is a polyamine which contains in one molecule a hydrocarbon group and three or more nitrogen atoms and in which the total number of carbon atoms in one molecule is at least 4 and at most 63.

[0021] There is no specific restriction regarding the polyamine (A) and specific examples of the same include, among others Tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, heptaethyleneoctamine, octaethylenenonamine, nonaethylenedecamine, pentapropylenehexamine, hexapropyleneheptamine, heptapropyleneoctamine, octapropylenenonamine, nonapropylendecamine, pentabutylenehexamine, hexabutyleneheptamine, Heptabutylenoctamin, Octabutylennonamine, Nonabutylendecamine, Pentapentylenhexamine, Hexapentylene heptamine, Heptapentylenoctamin, Octapentylene nonamine, Nonapentylene nonamine, Pentahexylenhexamine, Hexahexylenheptamine, Heptahexylenoctamin, Octahexylennonamine, Nonahexylendecamine, pentaheptylene hexamine, hexaheptylene heptamine, heptaheptylene octamin, octaheptylene nonamine and nonaheptylendecamine. Of these polyamines (A), one type of polyamine can be used alone, or two or more types of polyamine can be used in combination.

[0022] A polycarboxylic acid (B) is a polycarboxylic acid with at least 2 and at most 24 carbon atoms; it is at least divalent and at most tetravalent. There are no specific restrictions for polycarboxylic acids (B), and specific examples include, among others... (1) Dicarboxylic acids, such as oxalic acid, malonic acid, succinic acid, glutaric acid, fumaric acid, maleic acid, adipic acid, sebacic acid, and phellogenic acid; (2) tricarboxylic acids, such as aconitic acid; (3) aromatic dicarboxylic acids, such as benzoic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalene dicarboxylic acid; (4) aromatic tricarboxylic acids, such as trimellitic acid; and (5) aromatic tetracarboxylic acids, such as pyromellitic acid. Of these polycarboxylic acids (B), one type of polycarboxylic acid may be used alone, or several types of polycarboxylic acids may be used in combination.

[0023] The polyamine-polycarboxylic acid condensate (X) preferably conforms to formula (1) given below. In this case, the effect of improving the adhesion of carbon fibers to a base material of a composite material can be further enhanced by the sizing agent. [Numerical Formula 2] 0.05≤_b1×b2a1×a2<1.0

[0024] In formula (1) it states a1 for the amine value measured for the polyamine (A), a2 for the content percentage (in mass%) of polyamine (A), if the sum of the content percentages of polyamine (A) and polycarboxylic acid (B) is assumed to be 100 mass%, b1 for the acid value measured for the polycarboxylic acid (B) and b2 for the content percentage (in mass%) of polycarboxylic acid (B) when the sum of the content percentages of polyamine (A) and polycarboxylic acid (B) is assumed to be 100 mass%.

[0025] The amine value is a value obtained, for example, by measuring a quantity (mL) at the titration endpoint when a sample dissolved in isopropanol, a liquid mixture of xylene and isopropanol (volume ratio 1:1), water, or another solvent is potentiometrically titrated with a solution of 0.1 N hydrochloric acid, for example, in ethylene glycol / isopropanol (volume ratio 1:1), using an automatic potentiometric titration apparatus, wherein the number of mg of potassium hydroxide corresponding to the amount of hydrochloric acid required to neutralize the amino groups of an organic amine contained in 1 g of the sample is calculated using the following numerical formula (3). Amine value(KOH mg / g)=(A2×f2×5.61) / W2

[0026] In the numerical formula 3 it says A2 for the titration volume (mL) f2 for the titer of a 0.1 N potassium hydroxide solution and W2 for the amount (g) of the sample.

[0027] The acid value is a value obtained, for example, by measuring a quantity (mL) at the titration endpoint when a sample dissolved in isopropanol, a liquid mixture of xylene and isopropanol (volume ratio 1:1), water, or another solvent is potentiometrically titrated with a solution of 0.1 N potassium hydroxide, for example, in ethylene glycol / isopropanol (volume ratio 1:1), using an automatic potentiometric titration apparatus, wherein the number of mg of potassium hydroxide required to neutralize the acid groups of a phosphoric acid ester contained in 1 g of the sample is calculated using the following numerical formula (4). Acid value (KOH mg / g)=(A1×f1×5.61) / W1

[0028] In the numerical formula 4 it says A1 for the titration volume (mL), f1 for the titer of a 0.1 N potassium hydroxide solution and W1 for the amount (g) of the sample

[0029] There are no specific restrictions on the condensation reaction of polyamine (A) and polycarboxylic acid (B), as long as the reaction can form an amide bond and is carried out according to a known procedure. For example, it can be carried out by mixing the polyamine (A) and the polycarboxylic acid (B) as raw materials and then heating the mixture. The condensation reaction can be carried out in a nitrogen atmosphere or in another inert gas atmosphere.

[0030] The polyamine-polycarboxylic acid condensate (X) content in the sizing agent is at least 50% by mass of the non-volatile component of the sizing agent. This specification results in improved impregnation properties of the resin with respect to carbon fibers to which the sizing agent is applied when a nonwoven fabric is formed from the carbon fibers.

[0031] The polyamine-polycarboxylic acid condensate (X) content in the sizing agent is particularly preferably at least 80% by weight with respect to the non-volatile component of the sizing agent. Maintaining this level enables a further improvement in the adhesion of carbon fibers to a base material of a composite material, due to the action of the sizing agent.

[0032] The non-volatile component, as used here, refers to an absolute dry substance, i.e., a residue obtained by heating an object at 105°C for two hours to sufficiently remove a volatile component. (Brønsted acid)

[0033] Furthermore, the sizing agent according to the present embodiment can contain Brønsted acid. By including Brønsted acid in the sizing agent, the resin's impregnation capacity with respect to carbon fibers to which the sizing agent is applied is improved when a nonwoven fabric is formed from the carbon fibers.

[0034] A Brønsted acid is an acid that possesses a proton and can donate or dissociate this proton in an aqueous solution. A Brønsted acid differs from an acid that does not contain a proton, such as a Lewis acid.

[0035] There are no specific restrictions regarding Brønsted acid, and specific examples include alkyl etheracetic acids, such as polyoxyethylene (n=10)-lauryl ether acetic acid and polyoxyethylene (n=4,5)-lauryl ether acetic acid; alkyl amino acids, such as oleoyl sarcosinate and lauroyl sarcosinate; phosphate esters, such as phosphate esters of the 5-mol ethylene oxide adduct of 1-tridecanol and 1-hexadecanol phosphate esters; carboxylic acids, such as acetic acid, lactic acid, citric acid, lauric acid, and oleic acid; alkyl sulfonic acids, such as methanesulfonic acid; alkylbenzenesulfonic acids, such as dodecylbenzenesulfonic acid; and inorganic acids, such as sulfuric acid and phosphoric acid. Of these Brønsted acids, one type may be used alone, or two or more types may be used in combination. Of the above-mentioned, a monovalent Brønsted acid is preferable.

[0036] The proportion of Brønsted acid in the sizing agent, relative to the non-volatile component of the sizing agent, is preferably at least 0.05% by mass and at most 30% by mass, and particularly preferably at least 0.1% by mass and at most 20% by mass. Any combination of the aforementioned upper and lower limits may be used. Maintaining the proportion within these numerical ranges results in improved impregnation of the resin with respect to carbon fibers to which the sizing agent is applied when a nonwoven fabric is formed from the carbon fibers. (surfactant)

[0037] The sizing agent may also contain a surfactant. In this case, the formula stability of the sizing agent can be improved. Examples of surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. One type of surfactant can be used alone, or two or more types can be used in combination.

[0038] A known nonionic surfactant can be used appropriately. Specific examples of nonionic surfactants include, among others... (1) Compounds in which an alkylene oxide having 2 to 4 carbon atoms is added to an organic acid, an organic alcohol, an organic amine and / or an organic amide, for example, nonionic surfactants of the ether type, such as polyoxyethylene dilauric esters, polyoxyethylene oleic esters, polyoxyethylene oleic diesters, polyoxyethylene octyl ethers, polyoxyethylene lauryl ethers, polyoxyethylene lauryl ether methyl ethers, polyoxyethylene polyoxypropylene lauryl ethers, polyoxypropylene lauryl ether methyl ethers, polyoxyethylene oleyl ethers, polyoxybutylene oleyl ethers, polyoxyethylene polyoxypropylene nonyl ethers, polyoxypropylene nonyl ethers, polyoxyethylene polyoxypropylene octyl ethers, ethylene oxide adduct of 2-hexylhexanaol, polyoxyethylene 2-ethyl 1-hexyl ether, Polyoxyethylene isononyl ether, polyoxyethylene dodecyl ether, compound in which ethylene oxide is added to secondary dodecanol, polyoxyethylene tridecyl ether, polyoxyalkylene tetradecyl ether,(1) Polyoxyethylene laurylamino ether, polyoxyethylene lauric ether and polyoxyalkylene tristyrenized phenyl ether, (2) non-ionic surfactants of the polyoxyalkylene polyhydric alcohol fatty acid ester type, such as polyoxyalkylene sorbitan trioleate, polyoxyalkylene coconut oil, polyoxyalkylene castor oil, polyoxyalkylene castor wax, polyoxyalkylene castor wax trioctanoate, as well as maleic acid esters, stearic acid esters or oleic acid esters of polyoxyalkylene castor wax, (3) non-ionic surfactants of the alkylamide type, such as stearic acid diethanolamide and diethanolamine monolauramide, (4) non-ionic surfactants of the polyoxyalkylene fatty acid amide type, such as polyoxyethylene diethanolamine monoleylamide, polyoxyethylene laurylamine and polyoxyethylene bovine tallow, and (5) ether ester compounds, such as copolymer of Polyoxyethylene, dimethyl phthalate and lauryl alcohol.

[0039] A well-known anionic surfactant can be used appropriately. Specific examples of anionic surfactants include, among others...(1) Phosphoric acid ester salts of aliphatic alcohols, such as lauryl phosphoric acid ester salts, cetyl phosphoric acid ester salts, octyl phosphoric acid ester salts, oleyl phosphoric acid ester salts and stearyl phosphoric acid ester salts; (2) Phosphoric acid ester salts of adducts of at least one type of alkylene oxide selected from ethylene oxide and propylene oxide with an aliphatic alcohol, such as polyoxyethylene lauryl ether phosphoric acid ester salts, polyoxyethylene oleyl ether phosphoric acid ester salts and polyoxyethylene stearyl ether phosphoric acid ester salts; (3) Salts of aliphatic sulfonic acids or aromatic sulfonic acids, such as laurylsulfonic acid salts, myristylsulfonic acid salts, cetylsulfonic acid salts, oleylsulfonic acid salts, stearylsulfonic acid salts. Tetradecane sulfonic acid salts, dodecylbenzenesulfonic acid salts and secondary alkyl (C13 to C15) sulfonic acid salts, (4) sulfuric acid ester salts of aliphatic alcohols, such as lauryl sulfuric acid ester salts,Oleyl sulfuric acid ester salts and stearyl sulfuric acid ester salts, (5) Sulfuric acid ester salts of adducts of at least one type of alkylene oxide selected from ethylene oxide and propylene oxide, with an aliphatic alcohol, such as polyoxyethylene lauryl ether sulfuric acid ester salts, polyoxyalkylene (polyoxyethylene, polyoxypropylene) lauryl ether sulfuric acid ester salts and polyoxyethylene oleyl ether sulfuric acid ester salts, (6) Sulfuric acid ester salts of fatty acids, such as castor oil fatty acid sulfuric acid ester salts, sesame oil fatty acid sulfuric acid ester salts, tall oil fatty acid sulfuric acid ester salts, soybean oil fatty acid sulfuric acid ester salts, rapeseed oil fatty acid sulfuric acid ester salts, palm oil fatty acid sulfuric acid ester salts, lard fatty acid sulfuric acid ester salts, Beef tallow fatty acid sulfuric acid ester salts and whale oil fatty acid sulfuric acid ester salts, (7) Sulfuric acid ester salts of oils and fats, such as sulfuric acid ester salts of castor oil, sulfuric acid ester salts of sesame oil,Sulfuric acid ester salts of tall oil, sulfuric acid ester salts of soybean oil, sulfuric acid ester salts of rapeseed oil, sulfuric acid ester salts of palm oil, sulfuric acid ester salts of lard, sulfuric acid ester salts of beef tallow, and sulfuric acid ester salts of whale oil, (8) fatty acid salts, such as lauric acid salts, oleic acid salts, and stearic acid salts, and (9) succinic sulfide ester salts of aliphatic alcohols, such as dioctyl succinic sulfide salts. Examples of a counterion of the anionic surfactant include a potassium salt, a sodium salt, or another alkali metal salt, an ammonium salt, and triethanolamine or another alkanolamine salt.

[0040] A known cationic surfactant can be used appropriately. Specific examples of cationic surfactants include lauryl trimethylammonium chloride, cetyl trimethylammonium chloride, stearyl trimethylammonium chloride, behenyl trimethylammonium chloride, didecyl dimethylammonium chloride, 1,2-dimethylimidadazole, and triethanolamine.

[0041] A known amphoteric surfactant can be used appropriately. Specific examples of amphoteric surfactants include betaine-type amphoteric surfactants.

[0042] The following describes the processes and effects of the sizing agent according to the present embodiment.

[0043] (1-1) The sizing agent according to the present embodiment comprises a polyamine-polycarboxylic acid condensate in which the specific polyamine (A) and the specific polycarboxylic acid (B) are condensed to form an amide bond. This enhances the effect of the sizing agent improving the adhesion of carbon fibers to a base material of a composite material.

[0044] The polyamine polycarboxylic acid condensate has a high proportion of amino or amide groups; therefore, it is assumed that the sizing agent is strongly adsorbed onto the carbon fibers by interacting with, for example, hydroxy or carboxyl groups. The polyamine polycarboxylic acid condensate exhibits an anchoring effect by strongly adsorbing onto the carbon fibers, thus ensuring strong adhesion of a matrix resin to them. Since the polyamine polycarboxylic acid condensate is self-emulsifying, a larger amount of emulsifier is not required, and the proportion of polyamine polycarboxylic acid condensate used in the sizing agent can be increased.

[0045] (1-2) When a nonwoven fabric is formed from the carbon fibers to which the sizing agent has been applied, the impregnation capacity of a resin can be improved. In particular, if Brønsted acid is included in the sizing agent, the impregnation capacity of the resin with respect to the carbon fibers can be improved even further. <Zweites Ausführungsbeispiel>

[0046] Next, a second embodiment is described, in which a method for producing a carbon fiber according to the present invention is described. The same applies to the second embodiment as to the first embodiment, with the exceptions described below. In other words, the description of features identical to those of the first embodiment is omitted in the following description of the second embodiment.

[0047] The process for producing a carbon fiber according to the present embodiment comprises applying the sizing agent according to the first embodiment to a carbon fiber. There is no specific limitation regarding the amount of sizing agent applied (excluding solvents), and preferably the sizing agent is applied to the carbon fiber in an amount of at least 0.01% and at most 10% by mass. By specifying the amount within such a numerical range, an effect such as the bundle structure of the carbon fiber can be further improved. (Carbon fiber)

[0048] Examples of carbon fiber types include PAN-based carbon fibers, which are produced using acrylic fibers as raw material; pitch-based carbon fibers, which are produced using pitch as raw material; recycled carbon fibers; and carbon fibers produced using, for example, polyester fibers, polyethylene resin, phenolic resin, cellulose resin, or lignin resin as raw material.

[0049] To apply the sizing agent to the carbon fiber according to the first embodiment, a method commonly used in industry can be employed. Examples include, among others, a roller dipping process, a roller contact process, a spraying process, and a papermaking process. The carbon fiber to which the sizing agent has been applied can then be subjected to a drying treatment according to a known method.

[0050] In addition to the effects of the first embodiment, the following effects can be achieved with the method for producing a carbon fiber according to the present embodiment.

[0051] (2-1) The method for producing a carbon fiber according to the present embodiment comprises applying a sizing agent according to the first embodiment to a carbon fiber. The adhesion of the carbon fiber to a base material of a composite material can thus be improved by means of a simple method. <Drittes Ausführungsbeispiel>

[0052] Next, a composite material according to the present invention is described as a third embodiment. The same applies to the third embodiment as to the first and second embodiments, with the exceptions described below. In other words, the following description of the third embodiment omits the description of features identical to those of the first or second embodiment.

[0053] The composite material is obtained by impregnating the carbon fiber, to which the sizing agent has been applied according to the second embodiment, with a matrix resin as the base material. There is no specific restriction regarding the shape of the carbon fiber in the production of the composite material; examples include a long fiber shape, a short fiber shape, or a nonwoven shape. (Matrix resin)

[0054] The matrix resin is selected appropriately from matrix resins known in the context of the purpose or application of the composite material. Specific examples of the matrix resin include, but are not limited to, epoxy resins, vinyl ester resins, polyamide resins, polyolefin resins, polyurethane resins, polycarbonate resins, polyester resins, PEEK resins, fluorinated resins, phenoxy resins, phenolic resins, BMI resins, polyimide resins, polyimide resin precursors, and polyethersulfone resins. Specific examples of polyolefin resins include, but are not limited to, polypropylene resins and polyethylene resins. Of these, thermoplastic resins are preferred, and polypropylene resins and polyamide resins are particularly preferred, as they allow the effects of the present invention to be more effective.

[0055] The following effects can be achieved with the composite material according to the present invention.

[0056] (3-1) In the composite material according to the present invention, the sizing agent according to the first embodiment, which comprises the polyamine-polycarboxylic acid condensate, is applied to the carbon fiber. This allows a fiber-reinforced resin composite to be obtained due to the excellent adhesion between the carbon fiber and the matrix resin, which exhibits a variety of outstanding properties, particularly mechanical properties. Furthermore, the impregnability of the resin can be improved by forming a nonwoven fabric from the carbon fibers to which the sizing agent has been applied. In this way, a uniformly resin-impregnated composite material of excellent quality can be obtained.

[0057] The embodiments described above can be modified as follows. The embodiments described above and the modifications listed below can be combined within a technically feasible range.

[0058] In the sizing agent according to the embodiments described above, the addition of, for example, water or an organic solvent, a smoothing agent, an antioxidant or a preservative as a further component is not excluded, provided that the effect of the present invention is not impaired with regard to maintaining the effectiveness of the sizing agent and improving its applicability to the carbon fiber.

[0059] There is no specific restriction regarding the area in which the sizing agent is to be used according to the embodiments described above. For example, it can be used for a carbon fiber reinforced polymer (CFRP) material in which the carbon fibers are impregnated with a matrix resin, such as a polyimide resin. EXAMPLES

[0060] To illustrate the features and effects of the present invention more precisely, examples are given below; however, the present invention is not limited to these examples. In the following description of working examples and comparative examples, "parts" means mass fractions and "%" means mass percentage. Experimental Part 1 (Production of polyamine-polycarboxylic acid condensates) Polyamine-polycarboxylic acid condensate (A-1)

[0061] 1205 g of tetraethylenepentamine as a polyamine (A) and 795 g of oxalic acid as a polycarboxylic acid (B) were placed in a glass reaction vessel with a volume of 3 liters and dissolved, while the temperature was maintained at 90°C. Nitrogen was then introduced into the vessel contents, and the reaction was allowed to proceed at 160°C to 165°C under dehydration. The product was then cooled to room temperature, yielding a tetraethylenepentamine-oxalic acid condensate (A-1). Polyamine-polycarboxylic acid condensates (A-2 to A-7 and rA-1 to rA-4)

[0062] Using the respective ingredients listed in Table 1 and the same procedure as for the polyamine polycarboxylic acid condensate (A-1), polyamine polycarboxylic acid condensates (A-2 to A-7 and rA-1 to rA-4) were produced.

[0063] The types and proportions of the polyamines (A) and polycarboxylic acids (B) that constitute the raw materials for the polyamine-polycarboxylic acid condensates produced in this manner are listed in the columns "Polyamine (A)" and "Polycarboxylic acid (B)" of Table 1, respectively. The values ​​calculated using formula (1) above are given in the column "Calculation result formula (1)" of Table 1.

[0064] The tetraethylenepentamine listed in Table 1 was a product called "Tetraethylenepentamine (TEPA)" manufactured by Tosoh Corporation, and the pentaethylenehexamine was a product called "Pentaethylenehexamine (PEHA)" manufactured by Tosoh Corporation. Experimental Part 2 (Production of sizing agents) • Sizing agent from Example 1

[0065] By mixing as raw materials 99 parts (%) of the tetraethylenepentamine oxalic acid condensate (A-1) listed in Table 1 and 1 part (%) of dodecylbenzenesulfonic acid (C1) as Brønsted acid, a sizing agent according to Example 1 with the content specified in Table 2 was obtained. • Settlement agents according to Examples 2 to 20, of which Examples 17, 19 and 20 are not according to the invention, and Comparative Examples 1 to 5

[0066] The respective sizing agents according to Examples 2 to 20 and Comparative Examples 1 to 5 were produced by using as raw materials the polyamine polycarboxylic acid condensates from Table 1 and the Brønsted acids and other components from Table 2 as specified and mixing them with the content specified in Table 2.

[0067] The type and non-volatile fraction of each polyamine polycarboxylic acid condensate, the type and non-volatile fraction of each Brønsted acid, and the type and non-volatile fraction of each surfactant, which is the other component, contained in the sizing agents produced in this manner are listed in the columns "Polyamine polycarboxylic acid condensate", "Bronsted acid", and "Other component" of Table 2, respectively. The respective non-volatile fraction was determined as the amount of absolute dry matter obtained by subjecting an object to a two-hour heat treatment at 105°C to sufficiently remove any volatile fraction. [Table 1] category Polyamine (A) Polycarboxylic acid (B) Calculation result Formula (1) type Amine value [mg-KOH / g] Salary share (mass %) type Acidity [mg-KOH / g] Salary share (mass %) A-1 Tetraethylenepentamine 1330 60 Oxalic acid 1246 40 0,62 A-2 Pentaethylenehexamine 1240 67 Adipic acid 768 33 0,31 A-3 Pentaethylenehexamine 1240 85 Trimellitic acid 801 15 0,12 A-4 Tetraethylenepentamine 1330 53 Phellogenic acid 328 47 0,22 A-5 Pentaethylenehexamine 1240 37 Phthalic acid 675 63 0,93 A-6 Pentaethylenehexamine 1240 22 Phthalic acid 675 78 1,95 A-7 Tetraethylenepentamine 1330 95 Adipic acid 768 5 0,03 rA-1 Tetraethylenepentamine 1330 62 Caprylic acid - 38 - rA-2 Pentaethylenehexamine 1240 45 Stearic acid - 55 - rA-3 Ethylenediamine - 39 succinic acid - 61 - rA-4 Triethanolamine - 25 Isostearic acid - 75 - [Table 2] category Polyamine-polycarboxylic acid condensate Brønsted acid Further component Thermoplastic resin used for the evaluation Evaluation Type Mass fractions type Mass fractions type Mass fractions Impregnability Adherence Example 1 A-1 99 C-1 1 polyamide ⊚⊚ ⊚⊚ Example 2 A-2 80 C-2 20 polyamide ⊚⊚ ⊚⊚ Example 3 A-3 85 C-3 5 B-1 10 polyamide ⊚⊚ ⊚⊚ Example 4 A-4 92 C-2 0,1 B-2 7,9 polyamide ⊚⊚ ⊚⊚ Example 5 A-1A-5 2860 C-1C-3 33 B-3 6 polyamide ⊚⊚ ⊚⊚ Example 6 A-2A-3 5040 C-3C-5 28 polyamide ⊚⊚ ⊚⊚ Example 7 A-1 80 C-2C-4 55 B-5 10 Polypropylen ⊚⊚ ⊚⊚ Example 8 A-2 90 C-4 10 Polypropylen ⊚⊚ ⊚⊚ Example 9 A-3 95 C-5 1 B-2 4 Polypropylen ⊚⊚ ⊚⊚ Example 10 A-4 80 C-1 15 B-4 5 Polypropylen ⊚⊚ ⊚⊚ Example 11 A-3A-5 11.588 C-2 0,5 Polypropylen ⊚⊚ ⊚⊚ Example 12 A-4 100 Polypropylen ⊚ ⊚⊚ Example 13 A-5 100 polyamide ⊚ ⊚ ⊚ Example 14 A-2A-3 4040 B-2 20 polyamide ⊚ ⊚⊚ Example 15 A-5 60 B-1 40 polyamide ⊚ ⊚ Example 16 A-1A-2 3535 B-2 30 Polypropylen ⊚ ⊚ Example 17 A-3 40 B-3 60 polyamide ○ ⊚ Example 18 A-6 55 B-4 45 polyamide ⊚ ○ Example 19 A-7 40 B-1 60 Polypropylen ○ ○ Example 20 A-6 20 B-5 80 polyamide ○ ○ Comparative example 1 rA-1 100 polyamide × × Comparative example 2 rA-2 65 B-2 35 polyamide × × Comparative example 3 rA-3 30 B-5 70 polyamide × × Comparative example 4 rA-4 90 B-5 10 polyamide × × Comparative example 5 B-1 100 Polyamide × ×

[0068] Details regarding the Brønsted acids and the other components, as shown in Table 2, are as follows. (Brønsted acids) C-1: Dodecylbenzenesulfonic acid C-2: Acetic acid C-3: Oleic acid C-4: Methanesulfonic acid C-5: Lauric acid (Other components) B-1: 10-mol ethylene oxide adduct of dodecanol B-2: 8-mol ethylene oxide adduct of tetradecanol B-3: (on average) 9-mol ethylene oxide adduct of isotridecanol B-4: (on average) 34-mol ethylene oxide adduct of tristyrolated phenol B-5: 5-mol ethylene oxide adduct of dodecanol Experimental Part 2 (Evaluation) (Impregnation capability)

[0069] The sizing agent from each sample prepared in Experimental Part 2 was dissolved in 4900 parts of water (ion-exchanged) to produce an aqueous solution with a solids content of 2%. This aqueous solution was then applied by spraying to carbon fibers in nonwoven form, thus producing nonwoven carbon fibers coated with the sizing agent of the respective sample.

[0070] Two carbon fiber sheets, each obtained by cutting the nonwoven carbon fibers into 10 cm squares, and two Teflon sheets (polytetrafluoroethylene sheets manufactured by DuPont Inc.) were prepared. Then, a first Teflon sheet, a first carbon fiber sheet, 0.5 g of the thermoplastic resin used for evaluation (shown in Table 2), a second carbon fiber sheet, and a second Teflon sheet were layered and laminated in that order in a sandwich-like fashion.

[0071] The resulting laminate was compressed for 30 seconds at a pressure of 1 MPa using a hot press heated to 300°C (High-Temperature Hot Press 0-1t H400-01, manufactured by AS ONE, INC.). The amount of thermoplastic resin impregnated onto the Teflon sheet surfaces (i.e., the size of the area over which the thermoplastic resin exuded from surfaces had penetrated the Teflon sheets) was then visually assessed according to the criteria listed below. The results of the assessment are shown in the "Impregnation" column of Table 2. Similarly, the types of thermoplastic resins used are shown in the "Thermoplastic Resin Used for Assessment" column of Table 2.

[0072] • Evaluation criteria for impregnability ⊚⊚ (excellent): It can be stated that the thermoplastic resin bonds to the Teflon sheet sides over an area of ​​at least 1 cm. 2 impregnated. ⊚ (satisfactory): It can be determined that the thermoplastic resin bonds to the Teflon sheet sides over a surface area of ​​at least 0.1 cm². 2 , however less than 1 cm 2 impregnated. ◯ (acceptable): It can be determined that the thermoplastic resin adheres to the Teflon sheet sides over an area greater than 0 cm. 2 , however less than 0.1 cm 2 impregnated. × (bad): It cannot be determined that the thermoplastic resin impregnates the Teflon sheet sides. (Adherence)

[0073] The adhesion was assessed based on a tensile force measured using a microdroplet method and a commercially available apparatus for evaluating the interfacial properties of composite materials. Fig. Figure 1 shows a schematic view of an apparatus 10 for evaluating interface properties of composite materials.

[0074] The sizing agent prepared as described above for each example was dissolved in water to produce an aqueous solution with a solids content of 2%. This aqueous solution was then applied by dipping to filament carbon fibers in strand form, resulting in the production of stranded carbon fibers coated with the sizing agent of the respective example.

[0075] A single carbon fiber was extracted from the carbon fibers, and both ends of the tensioned carbon fiber 12 were fixed with adhesive 14 to a holder 11 of a plate-like four-sided frame. Next, the thermoplastic resin was applied as resin droplets 13 with a diameter of essentially 80 µm, according to each example shown in Table 2, and fixed by heating in a 300°C atmosphere for 3 minutes.

[0076] In a (not shown) apparatus base body, two plate-shaped cutting edges 17 and 18, whose vertical cross-section is each shaped to taper towards a side surface, are mounted such that their tip areas 17a and 18a face each other.

[0077] In a position where the carbon fiber 12, with the resin droplet 13 fixed to it, is sandwiched between the tip regions 17a and 18a of the two cutting edges 17 and 18, the holder 11 was mounted on a base plate 16, which is attached to the apparatus body. The base plate 16 is connected to a load cell 15, and a stress force acting on the base plate 16 is measured.

[0078] The load cell 15 measured a maximum tensile force F which arises when the resin droplet 13 is peeled from the carbon fiber 12 by the tip areas 17a and 18a of the cutting edges 17 and 18 when the holder 11 is moved at a speed of 15 mm / minute in the direction of a fiber axis.

[0079] Using the measured value, an interfacial shear strength τ was calculated using the numerical formula 5 given below. The same procedure was performed 20 times, and a mean value of the resulting interfacial shear strength was determined. Based on this mean value, the adhesion was evaluated according to the criteria given below. The evaluation results are listed in the "Adhesion" column of Table 2. τ=F / πDL

[0080] In the numerical formula 5 it says F represents the maximum tensile force (N) that arises when the resin droplet 13 is peeled from the carbon fiber 12, D for the diameter (in m) of the carbon fiber 12 and L for the diameter (in m) of the resin droplet 13 in the direction of extraction.

[0081] Assessment criteria for adhesion capacity ⊚⊚ (excellent): The interface shear force is at least 80 MPa. ⊚ (satisfactory): The interface shear force is at least 70 MPa, but less than 80 MPa. o (acceptable): The interface shear force is at least 60 MPa, but less than 70 MPa. × (bad): The interface shear force is less than 60 MPa.

[0082] As can be seen from the results presented in Table 2, the sizing agents in the respective examples were rated as acceptable or better with regard to both adhesion and impregnability. The present invention achieves the effect of improving both adhesion and impregnability. It was also found that an improvement in adhesion and impregnability occurs with glass fibers as well as with carbon fibers. REFERENCE MARK LIST 10 Apparatus for evaluating the interface properties of composite materials 11 bracket 12 Carbon fiber 13 resin droplets 14 Adhesive 15 stress cell 16 Substrat 17, 18 cutting

Claims

[1] A sizing agent for carbon fibers comprising a polyamine-polycarboxylic acid condensate (X) formed by condensation of a polyamine (A) and a polycarboxylic acid (B), wherein the polyamine (A) is a polyamine which contains in one molecule a hydrocarbon group and three or more nitrogen atoms, wherein the total number of carbon atoms in one molecule is at least 4 and at most 63, and wherein the polycarboxylic acid (B) is a polycarboxylic acid with at least 2 and at most 24 carbon atoms, which is at least divalent and at most tetravalent, wherein the non-volatile component of the sizing agent for carbon fibers comprises the polyamine-polycarboxylic acid condensate (X) in a proportion of at least 50% by mass. [2] Sizing agent for carbon fibers according to claim 1, wherein the polyamine-polycarboxylic acid condensate (X) satisfies the following formula (1), 0.05≤_b1×b2a1×a2<1.0 in formula (1) a1 for the amine value measured for the polyamine (A), a2 for the content percentage (in mass%) of polyamine (A), if the sum of the content percentages of polyamine (A) and polycarboxylic acid (B) is assumed to be 100 mass%, b1 for the acid value measured for the polycarboxylic acid (B) and b2 for the content percentage (in mass%) of polycarboxylic acid (B) when the sum of the content percentages of polyamine (A) and polycarboxylic acid (B) is assumed to be 100 mass%. [3] Sizing agent for carbon fibers according to claim 1 or 2, wherein the non-volatile component of the sizing agent for carbon fibers comprises the polyamine-polycarboxylic acid condensate (X) in a proportion of at least 80% by mass. [4] Sizing agent for carbon fibers according to any one of claims 1 to 3, which also contains a Brønsted acid. [5] Carbon fiber comprising the carbon fiber sizing agent applied to it according to any one of claims 1 to 4. [6] Method for producing a carbon fiber, comprising applying the carbon fiber sizing agent according to any one of claims 1 to 4 to a carbon fiber. [7] Composite material comprising the carbon fiber according to claim 5 and a thermoplastic resin. [8] Composite material according to claim 7, wherein the thermoplastic resin is at least one selected from a polyamide and a polypropylene.

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