JP7835962B2 - Treatment agents for carbon fiber precursors and their applications - Google Patents

Description

This invention relates to a treatment agent for carbon fiber precursors and its applications. More specifically, it relates to a treatment agent used in the production of carbon fiber precursors, a carbon fiber precursor using the treatment agent (hereinafter sometimes referred to as a precursor), and a method for producing carbon fiber using the treatment agent.

Carbon fiber, with its excellent mechanical properties, is widely used as a reinforcing fiber in composite materials with plastics called matrix resins, in applications such as aerospace, sports, and general industrial use.
The general method for manufacturing carbon fibers involves first producing a carbon fiber precursor (this manufacturing process is sometimes called the yarn spinning process). This carbon fiber precursor is then converted into flame-resistant fibers in an oxidizing atmosphere at 200-300°C (this process is sometimes referred to as the flame-retardant treatment process), and subsequently carbonized in an inert atmosphere at 300-2000°C (this process is sometimes referred to as the carbonization treatment process). (Hereafter, the flame-retardant treatment process and the carbonization treatment process together are sometimes referred to as the firing process.) In such a firing process, fusion of individual fibers occurs, which tends to cause problems such as fuzzing and yarn breakage, hindering productivity improvements.

To prevent the fusion of individual fibers during the firing process, a silicone-based treatment agent is applied during the production of the carbon fiber precursor. Numerous techniques have been proposed to apply the treatment agent uniformly in the form of an aqueous emulsion. (See Patent Documents 1-2)

Japanese Patent Publication No. 2012-46855 Japanese Patent Application Publication No. 2016-17231

However, when carbon fiber precursors produced with such treatment agents were stored for long periods, there was a problem of deterioration of the carbon fiber precursors over time. Therefore, when carbon fiber was produced by firing carbon fiber precursors that had been stored for a long period, problems arose such as the generation of fluff during the firing process and a decrease in the strength of the carbon fiber after firing.
In view of the above prior art background, the object of the present invention is to provide a carbon fiber precursor treatment agent that can suppress the deterioration of carbon fiber precursors when carbon fiber precursors manufactured by applying the treatment agent are stored for a long period of time, a carbon fiber precursor using the treatment agent, and a method for producing carbon fiber using the treatment agent.

As a result of diligent research to solve the above problems, the present inventors have found that a carbon fiber precursor treatment agent containing a silicone having an amino group (A) and an aromatic compound having a diphenylmethane skeleton (B), and satisfying at least one selected from specific condition 1 and specific condition 2, can suppress the deterioration of carbon fiber precursors when carbon fiber precursors produced with the treatment agent are stored for a long period of time, thus arriving at the present invention.

In other words, the carbon fiber precursor treatment agent of the present invention includes the following embodiments.
<1>
A treatment agent for carbon fiber precursors, comprising a silicone having an amino group (A) and an aromatic compound having a diphenylmethane skeleton (B), and satisfying at least one selected from the following conditions 1 and 2.
Condition 1: The acid value of the treatment agent is 0.1 to 30 mg KOH/g.
Condition 2: The treatment agent contains Brønsted acid compound (D), and the proportion of Brønsted acid compound (D) in the non-volatile content of the treatment agent is 0.05 to 10% by weight.
<2>
The carbon fiber precursor treatment agent according to <1>, wherein the aromatic compound (B) contains an aromatic compound having an oxyalkylene group.
<3>
The carbon fiber precursor treatment agent according to <1> or <2>, wherein the aromatic compound (B) contains an aromatic compound having at least one selected from a bisphenol A skeleton and a bisphenol F skeleton.
<4>
A treatment agent for carbon fiber precursors according to any one of <1> to <3>, comprising an aliphatic (poly)oxyalkylene derivative (C).
<5>
A treatment agent for carbon fiber precursors according to any one of <1> to <4>, comprising a Brønsted acid compound (D).
<6>
A treatment agent for carbon fiber precursors according to any one of <1> to <5>, which satisfies the above conditions 1 and 2.
<7>
A treatment agent for carbon fiber precursors according to any one of <1> to <6>, comprising an acetylene compound (E).
<8>
A treatment agent for carbon fiber precursors according to any one of <1> to <7>, wherein the proportion of the aromatic compound (B) in the nonvolatile content of the treatment agent is 10 to 99% by weight.
<9>
A carbon fiber precursor is obtained by attaching a carbon fiber precursor raw material to a carbon fiber precursor and a carbon fiber precursor treatment agent described in any of <1> to <8>.
<10>
A method for producing carbon fibers, comprising a flame-retardant treatment step of converting the carbon fiber precursor described in <9> into flame-retardant fibers, and a carbonization treatment step of further carbonizing the flame-retardant fibers.

The carbon fiber precursor treatment agent of the present invention can suppress the deterioration of carbon fiber precursors even when the carbon fiber precursors produced with the treatment agent are stored for a long period of time, and carbon fibers with excellent physical properties can be obtained even when using carbon fiber precursors that have been stored for a long period of time.
The carbon fiber precursor and carbon fiber manufacturing method of the present invention can produce carbon fibers with excellent physical properties even when using a carbon fiber precursor that has been stored for a long period of time.

The components of the carbon fiber precursor treatment agent (hereinafter sometimes simply referred to as the treatment agent) of the present invention will now be described.
[Silicone containing amino groups (A)]
The treatment agent of the present invention contains an amino group-containing silicone (A). The amino group-containing silicone (A) is not particularly limited as long as the main chain is an inorganic siloxane bond (-Si-O-Si-) and has an organic group having an amino group in the side chain and/or terminal. Examples of amino group-containing silicone (A) include amino-modified silicone and amino polyether-modified silicone, and it is more preferable to include an amino-modified silicone in order to achieve the effects of the present invention.
Furthermore, aminopolyether-modified silicone is a silicone having amino groups (including organic groups having amino groups) and polyether groups (including organic groups having polyoxyalkylene groups). Known amino-modified silicones and aminopolyether-modified silicones can be used. One or more types of silicone (A) having amino groups may be used.

The kinematic viscosity of the amino group-containing silicone (A) at 25°C is preferably 50 to 20,000 ^mm² /s in terms of uniform adhesion to fibers, suppression of treatment agent scattering, and imparting of bundle properties to fibers. The upper limit of the kinematic viscosity is more preferably 15,000 ^mm² /s, even more preferably 12,000 ^mm² /s, particularly preferably 10,000 ^mm² /s, and most preferably 3,000 ^mm² /s. On the other hand, the lower limit of the kinematic viscosity is more preferably 100 ^mm² /s, even more preferably 150 ^mm² /s, and particularly preferably 200 ^mm² /s. Also, for example, 100 to 15,000 ^mm² /s is more preferable, 150 to 10,000 ^mm² /s is even more preferable, and 200 to 3,000 ^mm² /s is particularly preferable.

The amino group (including an organic group having an amino group), which is a modifying group of the silicone (A) having an amino group, may be bonded to the side chain of the main chain silicone, to the end, or to both. However, from the viewpoint of protecting the fibers in the flame-retardant treatment process, it is preferable that it is bonded to the side chain (having an amino group on the side chain). Furthermore, the amino group may be of the monoamine type, diamine type, or polyamine type, and both may coexist in one molecule. However, from the viewpoint of uniformly applying the treatment agent to the inside of the fiber bundle in the flame-retardant treatment process and protecting the fibers by forming a film of the treatment agent, the monoamine type or diamine type is preferred, and the diamine type is more preferred.

The amino equivalent of the amino group-containing silicone (A) is preferably 300 to 10,000 g/mol, from the viewpoint of preventing adhesion and fusion between fibers. The upper limit of the amino equivalent is more preferably 9,500 g/mol, even more preferably 9,000 g/mol, and particularly preferably 8,000 g/mol. On the other hand, the lower limit of the amino equivalent is more preferably 500 g/mol, even more preferably 1,000 g/mol, and particularly preferably 1,500 g/mol. Also, for example, 500 to 9,000 g/mol is more preferable, and 1,000 to 8,000 g/mol is even more preferable.
Here, amino equivalent refers to the mass of the siloxane skeleton per amino group or ammonium group. The unit g/mol is the value converted to per mole of amino or ammonium groups. Therefore, a smaller amino equivalent value indicates a higher proportion of amino or ammonium groups within the molecule.

The amino group-containing silicone (A) may be a combination of multiple amino group-containing silicones with different amino equivalents and kinematic viscosities (at 25°C). When using two or more amino group-containing silicones, the above amino equivalent refers to the total amino equivalent of the amino group-containing silicone (A) (mixture), and the above kinematic viscosity at 25°C refers to the total kinematic viscosity of the amino group-containing silicone (A) (mixture).

Examples of silicones (A) having an amino group include the compound shown in the following general formula (1).

(In formula (1), ^R1 represents an alkyl group having 1 to 20 carbon atoms. ^R2 is a group represented by the general formula (2) below. ^R3 is ^R1 , ^R2 , or ^-OR9 ( ^R9 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms). a is 1 ≤ a ≤ 10000, and b is 0 ≤ b ≤ 1000. However, if b = 0, at least one of ^R3 is a group represented by the general formula (2) below. The order of each repeating unit enclosed by a and b is not limited, and the bonding pattern may be alternating, block-based, or random.)

In formula (1), ^R1 is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 5 carbon atoms, and even more preferably a methyl group. The multiple ^R1s in formula (1) may be the same or different. ^R3 is a group represented by ^R1 , ^R2 , or ^-OR9 , and is preferably ^R1 . The multiple ^R9s in formula (1) may be the same or different.
^R9 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably a hydrogen atom or a methyl group. a is a number from 1 to 10000, preferably 30 to 5000, and more preferably 50 to 2000. b is a number from 0 to 1000, preferably 1 to 500, and more preferably 2 to 100.

In formula (2), ^R4 and ^R6 are each independently an alkylene group having 1 to 6 carbon atoms, preferably an alkylene group having 1 to 3 carbon atoms. ^R5 , ^R7 and ^R8 are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, preferably a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and more preferably a hydrogen atom. c is a number from 0 to 6, preferably 0 to 3, and more preferably 0 to 1.

[Aromatic compounds having a diphenylmethane skeleton (B)]
The treatment agent of the present invention contains an aromatic compound (B) having a diphenylmethane skeleton (hereinafter sometimes referred to as aromatic compound (B)). Aromatic compound (B) is not particularly limited as long as it is an aromatic compound having a diphenylmethane skeleton, but in terms of achieving the effects of the present invention, at least one selected from a compound (B-1) having a structure in which an alkylene oxide is added to an aromatic compound having a hydroxyl group and a diphenylmethane skeleton, and an aromatic compound (B-2) having a diphenylmethane skeleton and an ester group is preferred, and a compound (B-1) having a structure in which an alkylene oxide is added to an aromatic compound having a hydroxyl group and a diphenylmethane skeleton is more preferred. One or more aromatic compounds (B) having a diphenylmethane skeleton may be used.

As the main skeleton of the aromatic compound (B) having a diphenylmethane skeleton, for example, diphenylmethane is used, and more preferably bisphenol. Specific examples of bisphenols include bisphenol A, AP, AF, B, BP, C, E, F, G, M, S, P, PH, TMC, Z, etc. Among these, at least one selected from the bisphenol A skeleton, bisphenol B skeleton, bisphenol E skeleton, and bisphenol F skeleton is preferred in terms of improving the convergence properties during flame retardation, and at least one selected from the bisphenol A skeleton and bisphenol F skeleton is more preferred.

Aromatic compound (B) having a diphenylmethane skeleton is preferable in terms of emulsification stability if it contains an aromatic compound having an oxyalkylene group. The oxyalkylene group in aromatic compound (B) having a diphenylmethane skeleton is preferably at least one selected from an oxyethylene group and an oxypropylene group, with an oxyethylene group or an oxyethyleneoxypropylene group being preferred, and an oxyethylene group being even more preferred.

The compound (B-1), which has a structure in which an alkylene oxide is added to an aromatic compound having a hydroxyl group and a diphenylmethane skeleton, is not particularly limited as long as it is not an aromatic compound (B-2) having a diphenylmethane skeleton and an ester group. However, in terms of improving the convergence during flame resistance, bisphenol A alkylene oxide adduct, bisphenol B alkylene oxide adduct, bisphenol E alkylene oxide adduct, and bisphenol F alkylene oxide adduct are preferred, bisphenol A ethylene oxide adduct, bisphenol E alkylene oxide adduct, and bisphenol F alkylene oxide adduct are more preferred, and bisphenol A ethylene oxide adduct is even more preferred.

In compound (B-1), which has a structure in which an alkylene oxide is added to an aromatic compound having a hydroxyl group and a diphenylmethane skeleton, the number of moles of alkylene oxide added is preferably 2 to 60 moles. The upper limit of the number of moles added is more preferably 30 moles, even more preferably 18 moles, and particularly preferably 10 moles. On the other hand, the lower limit of the number of moles added is more preferably 4 moles, even more preferably 6 moles, and particularly preferably 8 moles. Also, for example, 4 to 18 moles is more preferably, and 6 to 18 moles is particularly preferably.
The alkylene oxide preferably contains at least one selected from ethylene oxide and propylene oxide, and more preferably contains ethylene oxide. The alkylene oxide may be added randomly or in a blocked manner.

The aromatic compound (B-2) having a diphenylmethane skeleton and an ester group is not particularly limited as long as it has a diphenylmethane skeleton and an ester group, but examples include esters of aromatic compounds having a diphenylmethane skeleton and aliphatic carboxylic acids. One or more aromatic compounds (B-2) having a diphenylmethane skeleton and an ester group may be used.

The aliphatic carboxylic acid constituting the aromatic compound (B-2) having a diphenylmethane skeleton and an ester group is not particularly limited, but examples include aliphatic monocarboxylic acids having 4 to 24 carbon atoms and aliphatic polycarboxylic acids having 4 to 24 carbon atoms. The aliphatic carboxylic acid may be saturated or unsaturated, and may be linear or branched.

Examples of aliphatic monocarboxylic acids having 4 to 24 carbon atoms include pentanoic acid, hexanoic acid, octanoic acid, 2-ethylhexanoic acid, octicic acid, decanoic acid, dodecanoic acid (lauric acid), tridecanoic acid, isotridecanoic acid, hexadecanoic acid, octadecanoic acid (stearic acid), isooctadecanoic acid (isostearic acid), hydroxyoctadecanoic acid, 12-hydroxyoctadecanoic acid (12-hydroxystearic acid), octadecenoic acid, hydroxyoctadecenoic acid, octadecadienoic acid, octadecatrienoic acid, docosanic acid (behenic acid), tetracosanic acid, hexacosanic acid, octadocosanoic acid, octacosanic acid, ricinoleic acid, oleic acid, isostearic acid, isoarachinic acid, etc. Decanoic acid, dodecanoic acid, and tridecanoic acid are preferred in terms of compatibility with the aforementioned amino group-containing silicone (A).

Examples of aliphatic polycarboxylic acids having 4 to 24 carbon atoms include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, itaconic acid, mesaconic acid, and citraconic acid. Succinic acid and adipic acid are preferred in that they improve the convergence properties during flame resistance.

Examples of aromatic compounds (B-2) having a diphenylmethane skeleton and an ester group include diesters of bisphenol A alkylene oxide adduct and fatty acids, monoesters of bisphenol A alkylene oxide adduct and fatty acids, diesters of bisphenol B alkylene oxide adduct and fatty acids, monoesters of bisphenol B alkylene oxide adduct and fatty acids, diesters of bisphenol E alkylene oxide adduct and fatty acids, monoesters of bisphenol E alkylene oxide adduct and fatty acids, diesters of bisphenol F alkylene oxide adduct and fatty acids, and monoesters of bisphenol F alkylene oxide adduct and fatty acids. Among these, at least one selected from diesters of bisphenol A alkylene oxide adduct and fatty acids, diesters of bisphenol B alkylene oxide adduct and fatty acids, and diesters of bisphenol F alkylene oxide adduct and fatty acids is preferred in terms of improving the convergence properties during flame resistance.

[Aliphatic (poly)oxyalkylene derivatives (C)]
The treatment agent of the present invention may contain an aliphatic (poly)oxyalkylene derivative (C) (hereinafter sometimes referred to as aliphatic derivative (C)).
The aliphatic derivative (C) is not particularly limited as long as it is an aliphatic compound having a (poly)oxyalkylene group, but examples include an aliphatic alcohol alkylene oxide adduct (C-1) and an aliphatic alkylene oxide adduct having an ester group (C-2), with the aliphatic alcohol alkylene oxide adduct (C-1) being preferred in terms of emulsification stability. One or more aliphatic (poly)oxyalkylene derivatives (C) may be used. The aliphatic derivative (C) is other than the Brønsted acid compound (D) and acetylene compound (E) described later.

Examples of aliphatic alcohol alkylene oxide adducts (C-1) include alkylene oxide adducts of aliphatic alcohols that do not have an ester group.
The aliphatic alcohol constituting the aliphatic alcohol alkylene oxide adduct (C-1) is not particularly limited, but examples include aliphatic alcohols having 2 to 24 carbon atoms. The aliphatic alcohol may be saturated or unsaturated, linear or branched, and monohydric or dihydric or multihydric. In terms of emulsification stability, monohydric linear saturated aliphatic alcohols and monohydric branched saturated aliphatic alcohols are preferred. One or more types of aliphatic alcohol alkylene oxide adduct (C-1) may be used.
The upper limit of the aliphatic alcohol's carbon number is preferably 20, more preferably 18, and even more preferably 16. On the other hand, the lower limit of the carbon number is more preferably 4, even more preferably 6, and particularly preferably 8. Also, for example, 6 to 18 is preferred, and 8 to 16 is more preferred.

Examples of aliphatic alcohols constituting the aliphatic alcohol alkylene oxide adduct (C-1) include butyl alcohol, octyl alcohol, nonanol, lauryl alcohol, stearyl alcohol, cetyl alcohol, isobutyl alcohol, 2-ethylhexyl alcohol, isododecyl alcohol, isohexadecyl alcohol, isostearyl alcohol, isotetracosanyl alcohol, 12-eicosyl alcohol, vinyl alcohol, butenyl alcohol, hexadecenyl alcohol, oleyl alcohol, eicocenyl alcohol, linear secondary alcohols having 10 to 16 carbon atoms, glycerin, trimethylolpropane, sorbitol, ethylene glycol, propylene glycol, and butylene glycol. In terms of emulsification stability, lauryl alcohol, stearyl alcohol, isododecyl alcohol, isohexadecyl alcohol, isostearyl alcohol, and linear secondary alcohols having 10 to 16 carbon atoms are preferred, and linear secondary alcohols having 10 to 16 carbon atoms are more preferred.

The number of moles of alkylene oxide added to the aliphatic alcohol alkylene oxide adduct (C-1) is preferably 2 to 50 moles. The upper limit of the number of moles added is more preferably 40 moles, even more preferably 30 moles, and particularly preferably 20 moles. On the other hand, the lower limit of the number of moles added is more preferably 3 moles, even more preferably 4 moles, and particularly preferably 5 moles. Also, for example, 3 to 40 moles is more preferably, and 5 to 20 moles is particularly preferably.
The alkylene oxide preferably contains at least one selected from ethylene oxide and propylene oxide, and more preferably contains ethylene oxide. The alkylene oxide may be added randomly or in a blocked manner.

Specifically, examples of aliphatic alcohol alkylene oxide adducts (C-1) include polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene tetradecyl ether, polyoxyethylene cetyl ether, polyoxyethylene 2-ethylhexyl ether, polyoxyethylene isocetyl ether, polyoxyethylene isostearyl ether, polyoxyethylene 1-hexylhexyl ether, and polio Examples include oxyethylene 1-octylhexyl ether, polyoxyethylene 1-hexyloctyl ether, polyoxyethylene 1-pentylheptyl ether, polyoxyethylene 1-heptylpentyl ether, polyoxyethylene 1-hexylheptyl ether, polyoxyethylene 1-heptylhexyl ether, polyoxyethylene 1-pentylcaptyl ether, polyoxyethylene 1-capylpentyl ether, polyoxyethylene oleyl ether, linear secondary alcohol ethoxylates having 10 to 16 carbon atoms, oxyethylene-oxypropylene blocks, or random copolymers.

Examples of aliphatic alkylene oxide adducts (C-2) having an ester group include those with a structure in which an alkylene oxide is added to an aliphatic carboxylic acid (C-2-1) and those with a structure in which an alkylene oxide is added to an ester compound of an aliphatic carboxylic acid and a polyhydric alcohol (C-2-2). One or more types of aliphatic alkylene oxide adducts (C-2) having an ester group may be used.

The aliphatic carboxylic acid constituting the aliphatic alkylene oxide adduct (C-2) having an ester group is not particularly limited, but examples include aliphatic monocarboxylic acids having 4 to 24 carbon atoms and aliphatic polycarboxylic acids having 4 to 24 carbon atoms. The aliphatic carboxylic acid may be saturated or unsaturated, and may be linear or branched.

Examples of aliphatic monocarboxylic acids having 4 to 24 carbon atoms include pentanoic acid, hexanoic acid, octanoic acid, 2-ethylhexanoic acid, octicic acid, decanoic acid, dodecanoic acid (lauric acid), tridecanoic acid, isotridecanoic acid, hexadecanoic acid, octadecanoic acid (stearic acid), isooctadecanoic acid (isostearic acid), hydroxyoctadecanoic acid, 12-hydroxyoctadecanoic acid (12-hydroxystearic acid), octadecenoic acid, hydroxyoctadecenoic acid, octadecadienoic acid, octadecatrienoic acid, docosanic acid (behenic acid), tetracosanic acid, hexacosanic acid, octadocosanoic acid, octacosanic acid, ricinoleic acid, oleic acid, isostearic acid, and isoarachinic acid. In terms of emulsification stability, dodecanoic acid, oleic acid, and isostearic acid are preferred.

In the aliphatic alkylene oxide adduct (C-2) having an ester group, the number of moles of alkylene oxide added is preferably 2 to 50 moles. The upper limit of the number of moles added is more preferably 40 moles, even more preferably 30 moles, and particularly preferably 20 moles. On the other hand, the lower limit of the number of moles added is more preferably 3 moles, even more preferably 4 moles, and particularly preferably 5 moles. Also, for example, 3 to 40 moles is more preferably, and 5 to 20 moles is particularly preferably.
The alkylene oxide preferably contains at least one selected from ethylene oxide and propylene oxide, and more preferably contains ethylene oxide. The alkylene oxide may be added randomly or in a blocked manner.

Examples of structures in which an alkylene oxide is added to an aliphatic carboxylic acid (C-2-1) include the compounds obtained by adding an alkylene oxide to the aliphatic carboxylic acid mentioned above. In terms of emulsification stability, structures in which 1 to 20 moles of ethylene oxide are added to an aliphatic carboxylic acid having 8 to 18 carbon atoms are preferred.

The polyhydric alcohol constituting the structure (C-2-2) obtained by adding an alkylene oxide to an ester compound of an aliphatic carboxylic acid and a polyhydric alcohol is preferably a dihydric to tetrahydric alcohol having 2 to 6 carbon atoms, and among these, dihydric to trihydric alcohols having 2 to 6 carbon atoms are more preferred. Specifically, examples of such polyhydric alcohols include dihydric alcohols such as propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, and 1,6-hexanediol, trihydric alcohols such as glycerin and trimethylolpropane, and tetrahydric or higher alcohols such as pentaerythritol, sorbitan, and sorbitol.

Examples of structures (C-2-2) in which an alkylene oxide is added to an ester compound of an aliphatic carboxylic acid and a polyhydric alcohol include the compounds obtained by adding an alkylene oxide to the ester compounds of aliphatic carboxylic acids and polyhydric alcohols mentioned above. In terms of emulsification stability, alkylene oxide adducts of glycerin fatty acid esters and alkylene oxide adducts of sorbitan fatty acid esters are preferred.

[Brønsted acid compounds (D)]
The treatment agent of the present invention is preferred in that it exhibits the effects of the present invention and improves emulsification stability when it contains a Brønsted acid compound (D) (hereinafter sometimes referred to as compound (D)). A Brønsted acid compound (D) refers to a proton donor and includes organic carboxylic acid compounds, inorganic acids, organic sulfonic acid compounds, organic phosphate ester compounds, organic sulfuric acid ester compounds, and organic phosphonic acid compounds. A Brønsted acid compound (D) is defined as anything other than aromatic compounds (B) and acetylene compounds (E) described later.

Organic carboxylic acid compounds are organic compounds that have a carboxyl group in their molecular structure. Examples of organic carboxylic acid compounds are not particularly limited, but include aliphatic monocarboxylic acids, alkyl ether carboxylic acids, aliphatic polycarboxylic acids, aromatic carboxylic acids, aromatic polycarboxylic acids, and amino acids.

Examples of aliphatic monocarboxylic acids include acetic acid, lactic acid, butyric acid, crotonic acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, myristoleic acid, pentadecanoic acid, palmitic acid, palmitoleic acid, isocetyl acid, margaric acid, stearic acid, isostearic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, arachidic acid, isoeicosacid, gadoleic acid, eicosenoic acid, docosanic acid, isodocosanic acid, erucic acid, tetracosanic acid, isotetracosanic acid, nervonic acid, cerotic acid, montanic acid, and melissic acid.

Examples of alkyl ether carboxylic acids include those in which the alkyl group has 8 to 18 carbon atoms and the number of moles of polyoxyalkylene added is 1 to 50 moles. Examples of the alkyl group include octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, isotridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, and octadecyl group. Examples of the polyoxyalkylene group include polyoxyethylene group, polyoxypropylene group, and polyoxyethylene-polyoxypropylene group.

Examples of aliphatic polycarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebatic acid, undencanedioic acid, dodecanediic acid, tridecanediic acid, tetradecanediic acid, pentadecanediic acid, and their derivatives.

Examples of aromatic monocarboxylic acids include benzoic acid, cinnamic acid, naphthoic acid, toluic acid, and their derivatives.

Examples of aromatic polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, and their derivatives.

Amino acids are compounds that have both an amino group and a carboxyl group in their molecular structure, and examples include alanine, valine, leucine, isoleucine, phenylalanine, tryptophan, methionine, proline, glycine, tyrosine, serine, threonine, cysteine, asparagine, glutamine, lysine, arginine, histidine, aspartic acid, and glutamic acid.

Inorganic acids are acids whose components are nonmetallic atoms. Examples of inorganic acids include sulfuric acid, nitric acid, phosphoric acid, and hydrochloric acid.

Examples of organic sulfonic acid compounds include alkylbenzene sulfonic acid, polyoxyalkylene alkyl ether sulfonic acid, higher fatty acid amide sulfonic acid, alkyl sulfate monoester, and polyoxyalkylene sulfate monoester.

Examples of organic phosphate ester compounds include alkyl phosphate monoesters, alkyl phosphate diesters, polyoxyalkylene alkyl ether phosphate monoesters, polyoxyalkylene alkyl ether phosphate diesters, polyoxyalkylene alkylphenyl ether phosphate monoesters, and polyoxyalkylene alkylphenyl ether phosphate diesters.

Examples of organic sulfate ester compounds include alkyl sulfates, polyoxyalkylene alkyl sulfates, alkylphenyl sulfates, and polyoxyalkylene alkylphenyl sulfates.

Examples of organic phosphonic acid compounds include alkylphosphonic acids, aromatic phosphonic acids, and polyoxyalkylene alkyl ether phosphonic acids.

The pKa of the Brønsted acid compound (D) is preferably 0 to 7, more preferably 1 to 6.5, and even more preferably 2 to 6, from the viewpoint of equipment corrosion, safety, and suppression of crosslinking over time caused by the amino groups of the amino-modified silicone.

The Brønsted acid compound (D) preferably contains at least one selected from organic carboxylic acid compounds, inorganic acids, and organic phosphate ester compounds, in terms of improving emulsification stability, more preferably contains at least one selected from lactic acid, alkyl ether carboxylic acid, organic phosphate ester compounds, phosphoric acid, and acetic acid, and even more preferably contains at least one selected from alkyl ether carboxylic acid, organic phosphate ester compounds, acetic acid, and phosphoric acid. One or more Brønsted acid compounds (D) may be used.

[Acetylene compounds (E)]
The treatment agent of the present invention is preferable in that it contains an acetylene compound (E) in that it suppresses the penetration of the treatment agent into the interior of the fiber structure.
Acetylene compounds are compounds that have an acetylene group and a hydrophilic group such as a hydroxyl group in their molecular structure. Acetylene compounds (E) may be used alone or in combination of two or more types.

The acetylene compound (E) is preferably an acetylene surfactant, and more preferably at least one selected from acetylene alcohol (E1), acetylenediol (E2), a compound obtained by adding an alkylene oxide to acetylene alcohol (E3), and a compound obtained by adding an alkylene oxide to acetylenediol (E4). Among these, the compound obtained by adding an alkylene oxide to acetylene alcohol (E3) and the compound obtained by adding an alkylene oxide to acetylenediol (E4) are preferred, and the compound obtained by adding an alkylene oxide to acetylenediol (E4) is even more preferred.

Acetylene alcohol (E1) is a compound that has an acetylene group and one hydroxyl group in its molecular structure.
The acetylene alcohol (E1) is preferably a compound represented by the following general formula (3).
(In formula (3), R ¹⁰ and R ¹¹ are each independently alkyl groups having 1 to 8 carbon atoms.)

Acetylenediol (E2) is a compound that has an acetylene group and two hydroxyl groups in its molecular structure.
Acetylenediol (E2) is preferably a compound represented by the following general formula (4).
(In formula (4), ^R12 , ^R13 , ^R14 , and ^R15 are each independently alkyl groups having 1 to 8 carbon atoms.)

A compound (E3) obtained by adding alkylene oxide to acetylene alcohol is a compound in which alkylene oxide is added to the hydroxyl group of acetylene alcohol.
The compound (E3) obtained by adding an alkylene oxide to acetylene alcohol is preferably a compound represented by the following general formula (5).
(In formula (5), R ¹⁰ and R ¹¹ are each independently an alkyl group having 1 to 8 carbon atoms. R ¹⁶ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. AO represents an oxyalkylene group having 2 to 4 carbon atoms. n is a number from 1 to 50.)

A compound (E4) obtained by adding an alkylene oxide to acetylenediol is a compound in which an alkylene oxide is added to at least one of the hydroxyl groups of acetylenediol.
The compound (E4) obtained by adding an alkylene oxide to acetylenediol is preferably a compound represented by the following general formula (6).
(In formula (6), ^R12 , ^R13 , ^R14 , and ^R15 are each independently alkyl groups having 1 to 8 carbon atoms. ^R16 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. Note that the multiple ^R16s in formula (6) may be the same or different. AO represents an oxyalkylene group having 2 to 4 carbon atoms. m and n are each independently numbers from 1 to 50.)

In formulas (3) and (5), ^R10 and ^R11 are each independently an alkyl group having 1 to 8 carbon atoms. The alkyl group may be linear or have a branched structure. The number of carbon atoms in the alkyl group is preferably 1 to 7, more preferably 1 to 6, and even more preferably 1 to 5.
In formulas (4) and (6), ^R12 , ^R13 , ^R14 , and ^R15 are each independently alkyl groups having 1 to 8 carbon atoms. These alkyl groups may be linear or have a branched structure. The number of carbon atoms in these alkyl groups is preferably 1 to 7, more preferably 1 to 6, and even more preferably 1 to 5.

In formulas (5) and (6), ^R16 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2.
In formulas (5) and (6), AO represents an oxyalkylene group having 2 to 4 carbon atoms. That is, it represents an oxyethylene group, an oxypropylene group, or an oxybutylene group. As the oxyalkylene group, an oxyethylene group or an oxypropylene group is preferred, and an oxyethylene group is more preferred. The AO constituting (AO) _n or (AO) _m may be one type or two or more types. In the case of two or more types, it may be a block adduct, an alternating adduct, or a random adduct.

In formula (5), n is a number from 1 to 50. Preferably, n is from 1 to 45, more preferably from 1 to 40, and even more preferably from 1 to 35.
In formula (6), m and n are each independently a number from 1 to 50. m and n are each independently preferably from 1 to 45, more preferably from 1 to 40, and even more preferably from 1 to 35.

The HLB of the acetylene compound (E) is preferably 4 to 25 from the viewpoint of emulsification. The upper limit of the HLB is more preferably 20, and even more preferably 18. On the other hand, the lower limit of the HLB is more preferably 5, and even more preferably 6. The HLB in this invention can be experimentally determined by the ATLAS method proposed by Griffin et al.

Acetylene compounds (E) are known compounds and can be easily produced by known methods. For example, such compounds can be obtained by a method called the Reppe reaction, in which acetylene is reacted with a ketone or aldehyde under pressure in the presence of a catalyst such as an alkali or a metal compound.
Furthermore, the above-mentioned compound (E3) or compound (E4) can be obtained by addition polymerization of an alkylene oxide (e.g., ethylene oxide and/or propylene oxide) to acetylene alcohol (E1) or acetylenediol (E2), respectively, in the presence of a catalyst such as an alkali or a metal compound.

[Treatment agent for carbon fiber precursors]
The carbon fiber precursor treatment agent of the present invention contains a silicone having an amino group (A) and an aromatic compound having a diphenylmethane skeleton (B), and satisfies at least one selected from the following conditions 1 and 2.
Condition 1: The acid value of the treatment agent is 0.1 to 30 mg KOH/g.
Condition 2: The treatment agent contains Brønsted acid compound (D), and the proportion of Brønsted acid compound (D) in the non-volatile content of the treatment agent is 0.05 to 10% by weight.
The carbon fiber precursor treatment agent of the present invention is more preferable if it satisfies conditions 1 and 2, in that it better exhibits the effects of the present invention.

The carbon fiber precursor treatment agent of the present invention contains a silicone having amino groups (A) and an aromatic compound having a diphenylmethane skeleton (B). When the carbon fiber precursor produced by applying the treatment agent satisfies at least one of conditions 1 and 2, the deterioration of the carbon fiber precursor can be suppressed when it is stored for a long period of time. This is thought to be because the aromatic compound having a diphenylmethane skeleton (B) forms a protective layer on the surface of the carbon fiber precursor, and furthermore, (condition 1) the treatment agent has a specific acid value, and/or (condition 2) the proportion of Brønsted acid (D) in the nonvolatile content of the treatment agent is within a specific range, thereby suppressing crosslinking over time caused by the oxidation of the amino groups of the silicone having amino groups (A).

The acid value of the treatment agent of the present invention is preferably 0.1 to 30 mg KOH/g, in terms of easily suppressing the deterioration of the carbon fiber precursor over time and easily stabilizing the emulsification. The upper limit of the acid value is preferably in the order of (1) 28 mg KOH/g, (2) 25 mg KOH/g, (3) 20 mg KOH/g, (4) 15 mg KOH/g, and (5) 10 mg KOH/g. (The higher the number in parentheses, the more preferable it is.) On the other hand, the lower limit of the acid value is preferably in the order of (1) 0.2 mg KOH/g, (2) 0.3 mg KOH/g, (3) 0.4 mg KOH/g, (4) 0.5 mg KOH/g, and (5) 0.6 mg KOH/g. (The higher the number in parentheses, the more preferable.) For example, 0.2 to 28 mg KOH/g is more preferable, 0.3 to 25 mg KOH/g is even more preferable, 0.4 to 20 mg KOH/g is even more preferable, 0.5 to 15 mg KOH/g is particularly preferable, and 0.6 to 10 mg KOH/g is most preferable. The acid value of the treatment agent in this invention is determined by the method described in the examples.

The proportion of amino group-containing silicone (A) in the nonvolatile content of the treatment agent of the present invention is not particularly limited, but is preferably 1 to 90% by weight in terms of easily suppressing deterioration of the carbon fiber precursor over time and easily stabilizing the emulsion. The upper limit of this proportion is more preferably 88% by weight, even more preferably 85% by weight, and particularly preferably 80% by weight. On the other hand, the lower limit of this proportion is more preferably 5% by weight, even more preferably 10% by weight, and particularly preferably 15% by weight. Also, for example, 5 to 88% by weight is more preferable, 10 to 85% by weight is even more preferable, and 15 to 80% by weight is particularly preferable.
In this invention, the non-volatile content concentration is obtained by spreading 2.0 to 3.0 g of the treatment agent flat on an aluminum sheet (φ110 mm), drying it at 110°C under infrared lamp irradiation, accurately weighing the weight of the remaining portion on the aluminum sheet when the fluctuation range of the volatile content over 150 seconds reaches 0.15%, and calculating the ratio (percentage) of the remaining weight after heating to the weight before heating. In this invention, the non-volatile content refers to the remaining portion on the aluminum sheet when the fluctuation range of the volatile content over 150 seconds reaches 0.15%, as measured in the same procedure as for measuring the non-volatile content concentration.

The proportion of the aromatic compound (B) having a diphenylmethane skeleton in the nonvolatile content of the treatment agent of the present invention is not particularly limited, but is preferably 99% by weight or less in terms of easily suppressing the deterioration of the carbon fiber precursor over time and easily stabilizing the emulsion. The upper limit of this proportion is more preferably 95% by weight, even more preferably 90% by weight, and particularly preferably 85% by weight. On the other hand, the lower limit of this proportion is more preferably 10% by weight, even more preferably 15% by weight, and particularly preferably 20% by weight. Also, for example, 10 to 99% by weight is more preferable, 10 to 90% by weight is even more preferable, 15 to 95% by weight is particularly preferable, and 20 to 85% by weight is most preferable.

The proportion of aliphatic (poly)oxyalkylene derivative (C) in the nonvolatile content of the treatment agent of the present invention is not particularly limited, but is preferably 1 to 30% by weight in terms of easily suppressing the deterioration of the carbon fiber precursor over time and easily stabilizing the emulsification. The upper limit of this proportion is more preferably 25% by weight, even more preferably 20% by weight, and particularly preferably 15% by weight. On the other hand, the lower limit of this proportion is more preferably 2% by weight, even more preferably 3% by weight, and particularly preferably 5% by weight. Also, for example, 2 to 25% by weight is more preferable, 3 to 20% by weight is even more preferable, and 5 to 15% by weight is particularly preferable.

When the treatment agent of the present invention further contains a Brønsted acid compound (D), the proportion of the Brønsted acid compound (D) in the nonvolatile content of the treatment agent of the present invention is not particularly limited, but is preferably 0.05 to 10% by weight, as this is advantageous in suppressing the deterioration of the carbon fiber precursor over time and in stabilizing the emulsification. The upper limit of this weight percentage is more preferably 8% by weight, even more preferably 7% by weight, and particularly preferably 5% by weight. On the other hand, the lower limit of this weight percentage is more preferably 0.1% by weight, even more preferably 0.15% by weight, and particularly preferably 0.3% by weight. Also, for example, 0.1 to 8% by weight is more preferable, 0.15 to 7% by weight is even more preferable, and 0.3 to 5% by weight is particularly preferable.

When the treatment agent of the present invention further contains an acetylene compound (E), the proportion of the acetylene compound (E) in the nonvolatile content of the treatment agent of the present invention is not particularly limited, but is preferably 0.1 to 10% by weight in terms of suppressing the penetration of the treatment agent into the fiber structure. The upper limit of this weight percentage is more preferably 8% by weight, even more preferably 7% by weight, and particularly preferably 5% by weight. On the other hand, the lower limit of this weight percentage is more preferably 0.3% by weight, even more preferably 0.5% by weight, and particularly preferably 1% by weight. Also, for example, 0.3 to 8% by weight is more preferable, 0.5 to 7% by weight is even more preferable, and 1 to 5% by weight is particularly preferable.

[Other ingredients (F)]
The treatment agent of the present invention preferably further contains other nonionic surfactants as other components (F) because it can enhance emulsification stability. Other nonionic surfactants refer to nonionic surfactants other than aromatic compounds having a diphenylmethane skeleton (B), aliphatic (poly)oxyalkylene derivatives (C), and acetylene compounds (E).
Other nonionic surfactants include sorbitan esters such as sorbitan monopalmitate and sorbitan monooleate; glycerin fatty acid esters such as glycerin monostearate, glycerin monolaurate, and glycerin monopalmitate; and sucrose fatty acid esters.
The weight-average molecular weight of the other nonionic surfactants is preferably 2000 or less, more preferably 200 to 1800, more preferably 300 to 1500, and even more preferably 500 to 1000. One or more types of the other nonionic surfactants may be used.

When the treatment agent of the present invention contains other nonionic surfactants, the weight percentage of the other nonionic surfactants in the nonvolatile content of the treatment agent is not particularly limited, but is preferably 0.1 to 10% by weight in terms of emulsification stability. The upper limit of this percentage is more preferably 8.5% by weight, even more preferably 7.0% by weight, and particularly preferably 5.0% by weight. On the other hand, the lower limit of this percentage is more preferably 0.25% by weight, even more preferably 0.4% by weight, and particularly preferably 0.5% by weight. Also, for example, 0.25 to 8.5% by weight is more preferable, 0.4 to 7.0% by weight is even more preferable, and 0.5 to 5.0% by weight is particularly preferable.

[Other surfactants]
The treatment agent of the present invention may contain, to the extent that it does not impair the effects of the present invention, an aromatic compound having a diphenylmethane skeleton (B), an aliphatic (poly)oxyalkylene derivative (C), a Brønsted acid compound (D), an acetylene compound (E), and other surfactants other than nonionic surfactants. The other surfactants are used as emulsifiers, antistatic agents, etc. The other surfactants are not particularly limited, and known surfactants such as anionic surfactants, cationic surfactants, and amphoteric surfactants can be appropriately selected and used. The other surfactants may be one type or two or more types may be used in combination.

Examples of anionic surfactants include ether carboxylates, ether sulfates, sulfosuccinates, (poly)oxyethylene coconut oil fatty acid monoethanolamide sulfate sodium, alkyl-containing sulfonates, alkyl-containing phosphates, fatty acid salts, acylated amino acid salts, and amine neutralized fatty acids.

Examples of cationic surfactants include lauryltrimethylammonium chloride, myristyltrimethylammonium chloride, palmityltrimethylammonium chloride, stearyltrimethylammonium chloride, oleyltrimethylammonium chloride, cetyltrimethylammonium chloride, behenyltrimethylammonium chloride, coconut oil alkyltrimethylammonium chloride, beef tallow alkyltrimethylammonium chloride, stearyltrimethylammonium bromide, coconut oil alkyltrimethylammonium bromide, cetyltrimethylammonium methosulfate, and oleyldimethylethylammonium ethosulfate. Alkyl quaternary ammonium salts such as phosphate, dioctyldimethylammonium chloride, dilauryldimethylammonium chloride, distearyldimethylammonium chloride, octadecyldiethylmethylammonium sulfate; acylamide alkyl quaternary ammonium salts such as N-(2-hydroxyethyl)-N,N-dimethyl-N-stearoylamidopropylammonium nitrate, lanolin fatty acid amidopropyl ethyldimethylammonium ethosulfate, lauroylamidoethylmethyldiethylammonium methosulfate; alkylisoquinolinium salts such as laurylisoquinolinium chloride; lauryldimethylbenzylammonium Benzalkonium salts such as muchloride and stearyldimethylbenzylammonium chloride; pyridinium salts such as cetylpyridinium chloride; imidazolinium salts such as oleylhydroxyethylimidazolinium ethosulfate and laurylhydroxyethylimidazolinium ethosulfate; acyl basic amino acid alkyl ester salts such as N-cocoyl arginine ethyl ester pyrrolidone carboxylate and N-lauroyl lysine ethyl ester chloride; primary amine salts such as laurylamine chloride, stearylamine bromide, hydrogenated beef tallow alkylamine chloride and rosinamine acetate; cetylmethylamine sulfate, laurylmethylamine chloride Examples include secondary amine salts such as dilaurylamine acetate, stearylethylamine bromide, laurylpropylamine acetate, dioctylamine chloride, and octadecylethylamine hydroxide; tertiary amine salts such as dilaurylmethylamine sulfate, lauryldiethylamine chloride, laurylethylmethylamine bromide, diethanolstearylamideethylamine trihydroxyethyl phosphate, and stearylamideethylethanolamine urea polycondensate acetate; fatty acid amide guanidinium salts; and alkyltrialkylene glycol ammonium salts such as lauryltriethylene glycol ammonium hydroxide.

Examples of amphoteric surfactants include imidazoline-based amphoteric surfactants such as 2-undecyl-N,N-(hydroxyethylcarboxymethyl)-2-imidazoline sodium and 2-cocoyl-2-imidazolinium hydroxide-1-carboxyethyloxy disodium salt; betaine-based amphoteric surfactants such as 2-heptadecyl-N-carboxymethyl-N-hydroxyethylimidazolium betaine, lauryldimethylaminoacetic acid betaine, alkyl betaine, amide betaine, and sulfobetaine; and amino acid-type amphoteric surfactants such as N-laurylglycine, N-lauryl β-alanine, and N-stearyl β-alanine.

[Other ingredients]
The carbon fiber precursor treatment agent of the present invention may contain other components besides those described above, as long as they do not impair the effects of the present invention. Examples of other components include antioxidants such as phenolic, amine, sulfur, phosphorus, and quinone-based agents; antistatic agents such as quaternary ammonium salt type cationic surfactants and amine salt type cationic surfactants; smoothing agents such as alkyl esters of higher alcohols and waxes; antibacterial agents; preservatives; rust inhibitors; and hygroscopic agents.

Furthermore, the treatment agent of the present invention may contain one or more low molecular weight silicones. Examples of low molecular weight silicones include, for example, linear or cyclic silicones having 2 to 7 silicon atoms. Specific examples of low molecular weight silicones include octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, heptamethyloctyltrisiloxane, hexamethyldisiloxane, decamethyltetrasiloxane, dodecamethylpentasiloxane, and the like. These low molecular weight silicones may be substituted with groups represented by the general formula (2) above. These low molecular weight silicones may be included as trace components of the amino group-containing silicone (A).
The content of low molecular weight silicone in the treatment agent of the present invention is preferably 5 parts by weight or less per 100 parts by weight of silicone (A) having an amino group.

The carbon fiber precursor treatment agent of the present invention preferably contains a silicone having an amino group (A), an aromatic compound having a diphenylmethane skeleton (B), and optionally an aliphatic (poly)oxyalkylene derivative (C), a Brønsted acid compound (D), an acetylene compound (E), and other components (F) in a state in which they are dissolved, solubilized, emulsified, or dispersed in water.
There are no particular limitations on the weight percentage of water and the weight percentage of non-volatile matter in the carbon fiber precursor treatment agent. For example, these can be appropriately determined considering factors such as the transportation costs when transporting the carbon fiber precursor treatment agent of the present invention and the handling characteristics due to the emulsion viscosity. The weight percentage of water in the carbon fiber precursor treatment agent is preferably 0.1 to 99.9% by weight, more preferably 10 to 99.5% by weight, and particularly preferably 50 to 99% by weight. The weight percentage (concentration) of non-volatile matter in the carbon fiber precursor treatment agent is preferably 0.01 to 99.9% by weight, more preferably 0.5 to 90% by weight, and particularly preferably 1 to 50% by weight.

The carbon fiber precursor treatment agent of the present invention can be manufactured by mixing the components described above. The method for emulsifying and dispersing the components described above is not particularly limited, and known methods can be employed. Such methods include, for example, adding each component constituting the carbon fiber precursor treatment agent to warm water under stirring to emulsify and disperse, or mixing each component constituting the carbon fiber precursor treatment agent and gradually adding water while applying mechanical shear force using a homogenizer, homomixer, ball mill, etc. to perform phase inversion emulsification. Alternatively, a method may be used in which some components are emulsified and then the remaining components are dissolved and dispersed.

The carbon fiber precursor treatment agent of the present invention can be suitably used as a treatment agent for carbon fiber precursors (precursors).

[Carbon fiber residue, method for producing the same, and method for producing carbon fiber]
The carbon fiber precursor of the present invention is obtained by applying the above-mentioned treatment agent for carbon fiber precursors to a raw material carbon fiber precursor and then spinning it into yarn. The method for producing the carbon fiber precursor of the present invention includes a spinning step of applying the above-mentioned treatment agent for carbon fiber precursors to a raw material carbon fiber precursor and then spinning it into yarn.
The present invention provides a method for producing carbon fibers, comprising a flame-retardant treatment step for converting a carbon fiber precursor to which the above-mentioned carbon fiber precursor treatment agent has been applied into flame-retardant fibers, and a carbonization treatment step for further carbonizing the flame-retardant fibers.
The flame-retardant treatment step described above is preferably a flame-retardant treatment step in which a carbon fiber precursor is converted into flame-retardant fibers in an oxidizing atmosphere at 200 to 300°C, and the carbonization treatment step is preferably a step in which the flame-retardant fibers are further carbonized in an inert atmosphere at 300 to 2000°C.
According to the carbon fiber manufacturing method of the present invention, since the treatment agent for carbon fiber precursors of the present invention is used, high-quality carbon fibers can be produced even when the carbon fiber precursor produced with the treatment agent is stored for a long period of time.

The yarn-making process involves applying a treatment agent for carbon fiber precursors to the raw material carbon fiber precursor to produce the carbon fiber precursor, and preferably includes an adhesion treatment process and a stretching process.
The adhesion treatment process involves applying a treatment agent for carbon fiber precursors to the raw carbon fiber precursor after spinning the carbon fiber precursor. In other words, the treatment agent for carbon fiber precursors is applied to the raw carbon fiber precursor in the adhesion treatment process. Furthermore, when the raw carbon fiber precursor is stretched immediately after spinning, the high-magnification stretching after the adhesion treatment process is specifically called the "stretching process." The stretching process may be a moist heat stretching method using high-temperature steam, or a dry heat stretching method using a hot roller. Preferably, the stretching magnification in the stretching process is 2 to 20 times the total stretching magnification of the raw carbon fiber precursor immediately after spinning.

The carbon fiber precursor is preferably composed of acrylic fibers mainly comprising polyacrylonitrile, which is obtained by copolymerizing at least 95 mol% or more of acrylonitrile with 5 mol% or less of a flame-retardant promoting component. As the flame-retardant promoting component, vinyl group-containing compounds copolymerizable with acrylonitrile are suitably used. While there are no particular limitations on the single fiber fineness of the carbon fiber precursor, it is preferably 0.1 to 2.0 dtex, considering the balance between performance and manufacturing cost. Furthermore, while there are no particular limitations on the number of single fibers constituting the fiber bundle of the carbon fiber precursor, it is preferably 1,000 to 96,000, considering the balance between performance and manufacturing cost.

The carbon fiber precursor treatment agent may be applied to the raw material carbon fiber precursor at any stage of the yarn production process, but it is preferable to apply it once before the drawing process. It can be applied at any stage before the drawing process, for example, immediately after spinning. Furthermore, it can be applied again at any stage after the drawing process, for example, immediately after the drawing process, at the winding stage, or immediately before the flame-retardant treatment process. As for the application method, it may be applied using a roller or the like, or by immersion, spraying, etc.

In the adhesion treatment process, the application rate of the carbon fiber precursor treatment agent is preferably 0.1 to 5% by weight, and more preferably 0.3 to 1.5% by weight, relative to the weight of the carbon fiber precursor, in order to balance the effects of preventing adhesion and fusion between fibers with preventing deterioration of the carbon fiber quality due to the tar-like substances of the treatment agent in the carbonization treatment process. The application rate of the carbon fiber precursor treatment agent as used herein is defined as the percentage of the weight of the non-volatile components of the carbon fiber precursor treatment agent attached to the carbon fiber precursor relative to the weight of the carbon fiber precursor.

The flame-retardant treatment process is a process of converting carbon fiber precursors to flame-retardant fibers in an oxidizing atmosphere, for example, at 200 to 300°C, after the carbon fiber precursor treatment agent has been applied to them. The oxidizing atmosphere can usually be an air atmosphere. The temperature of the oxidizing atmosphere is preferably 230 to 280°C. In the flame-retardant treatment process, the carbon fiber precursors after the application treatment are subjected to heat treatment for, for example, 20 to 100 minutes (preferably 30 to 60 minutes) while applying a tension of, for example, a draw ratio of 0.90 to 1.10 (preferably 0.95 to 1.05). In this flame-retardant treatment, flame-retardant fibers having a flame-retardant structure are produced through intramolecular cyclization and oxygen addition to the ring.

The carbonization process is a process of further carbonizing the flame-resistant fibers in an inert atmosphere, for example, at 300 to 2000°C. In the carbonization process, it is preferable to first perform a preliminary carbonization process (first carbonization process) by heat-treating the flame-resistant fibers for several minutes in a firing furnace having a temperature gradient from 300°C to 800°C in an inert atmosphere such as nitrogen or argon, while applying a tension, for example, with a draw ratio of 0.95 to 1.15. Subsequently, in order to further advance carbonization and graphitization, a second carbonization process is performed in an inert atmosphere such as nitrogen or argon, heat-treating for several minutes while applying a tension, for example, with a draw ratio of 0.95 to 1.05 compared to the first carbonization process, thereby carbonizing the flame-resistant fibers. Regarding the control of the heat treatment temperature in the second carbonization process, it is preferable to set the maximum temperature to 1000°C or higher (preferably 1000 to 2000°C) while applying a temperature gradient. This maximum temperature is appropriately selected and determined according to the required properties (tensile strength, modulus of elasticity, etc.) of the desired carbon fiber.

In the carbon fiber manufacturing method of the present invention, if carbon fibers with an even higher elastic modulus are desired, a graphitization treatment step can be performed following the carbonization treatment step. The graphitization treatment step is usually carried out at a temperature of 2000 to 3000°C in an inert atmosphere such as nitrogen or argon, while applying tension to the fibers obtained in the carbonization treatment step.

The carbon fibers obtained in this way can be surface-treated to enhance their adhesion strength to the matrix resin when used in a composite material, depending on the purpose. Gas-phase or liquid-phase treatment can be employed as the surface treatment method; from a productivity standpoint, liquid-phase treatment using an electrolyte such as an acid or alkali is preferred. Furthermore, various sizing agents with excellent compatibility with the matrix resin can be added to improve the processability and handling of the carbon fibers.

The present invention will be specifically described below with reference to examples, but is not limited to the examples described herein. In the following examples, percentages (%) and parts refer to "weight percent" and "parts by weight" respectively, unless otherwise specified. Each characteristic value was measured based on the method described below.

<Application rate of treatment agent>
The application rate of the treatment agent for carbon fiber precursors was calculated by ethanol extraction using a Soxhlet extractor. However, for treatment agents containing silicone, the application rate was calculated using the following method.
The carbon fiber precursor, after being treated with the treatment agent, was alkali-dissolved in potassium hydroxide/sodium butyrate, then dissolved in water and adjusted to pH 1 with hydrochloric acid. Sodium sulfite and ammonium molybdate were added to this mixture to induce color development, and the silicon content was determined by colorimetric determination of silica-molybdenum blue (wavelength 815 mμ). Using the silicon content determined here and the silicon content in the treatment agent determined in advance by the same method, the application rate (weight %) of the carbon fiber precursor treatment agent was calculated.

<Acid value of treatment agent>
The acid value of the treatment agent was measured according to the neutralization titration method specified in JIS K0070, and the average value of five measurements was taken as the acid value of the treatment agent.

<Number of fibers in a carbon fiber bundle>
Carbon fiber precursors were stored under the following two conditions to produce carbon fibers, and the number of fibers was measured using the method described below.
Storage condition 1: Store at room temperature for 7 days. Storage condition 2: Store at room temperature for 12 months. Carbon fiber bundles were pulled out from the bobbin without tension, and any fuzz was collected until 50 fuzz was collected. The length of the carbon fiber bundles pulled out until 50 fuzz was collected was measured, and the number of fuzz per unit length (fuzz/m) was calculated from the measured length of the carbon fiber bundle as the number of fuzz present on the surface of the carbon fiber bundle, with ◎ and ○ being considered acceptable.
◎: The number of fibers is less than 3 per meter, indicating low fiber content and particularly good quality.
○: The number of fibers is 3 or more and less than 10 fibers per meter, indicating low fiber content and good quality.
×: The number of fibers is 10 or more per meter, indicating a high amount of fibers and poor quality.

<Carbon fiber strength>
Carbon fibers were prepared using carbon fiber precursors stored under the following two conditions. The tensile properties of the single fibers were measured according to the test method specified in JIS-R-7606, and the average value of 10 measurements was taken as the carbon fiber strength (GPa).
Storage condition 1: Store at room temperature for 7 days. Storage condition 2: Store at room temperature for 12 months. In addition, the retention rate of carbon fiber strength after time changes was calculated using the following formula.
(Retention rate (%)) = (Carbon fiber strength produced using carbon fiber precursor after 12 months of storage at room temperature) / (Carbon fiber strength produced using carbon fiber precursor after 7 days of storage at room temperature) × 100

<Inhibition of Degradation of Carbon Fiber Precursors>
In evaluating the fluffiness and carbon fiber strength of the carbon fiber bundles described above, the degradation suppression ability of the carbon fiber precursor was determined according to the following criteria. A pass was marked with ○, and a failing grade with ×.
Acceptance criteria: The number of fluffs in the carbon fiber bundle must be 0 or higher under both storage condition 1 and storage condition 2, and the carbon fiber strength retention rate must be 95% or higher.

[Example 1]
A silicone (A) having an amino group and an aromatic compound (B) having a diphenylmethane skeleton were mixed to achieve the non-volatile content composition of the treatment agent shown in Table 1. The mixture was heated to 60-80°C during emulsification, and water was gradually added while stirring with a stirring blade at a blade tip speed of 3 m/s to emulsify. After emulsification, a Brønsted acid compound (D) was dissolved and dispersed to prepare a treatment agent for carbon fiber precursors with a non-volatile content concentration of 30% by weight. The weight percentage of silicone (A) in the non-volatile content of the treatment agent was 15% by weight, the weight percentage of aromatic compound (B) having a phenylmethane skeleton was 84.5% by weight, and the weight percentage of Brønsted acid compound (D) was 0.5% by weight. The prepared treatment agent was then further diluted with water to obtain a diluted solution with a non-volatile content concentration of 3.0% by weight.
A carbon fiber precursor was prepared by copolymerizing a diluted solution with 97 mol% acrylonitrile and 3 mol% itaconic acid to obtain a raw material carbon fiber precursor. The non-volatile content of the treatment agent was applied to the precursor so that it was 1.0% by weight, and the precursor was then stretched (steam stretching, stretch ratio 2.1 times) to produce the carbon fiber precursor (single fiber fineness 0.8 dtex, 24,000 filaments). This carbon fiber precursor was flame-retardant treated in a flame-retardant furnace at 250°C for 60 minutes, and then converted into carbon fibers by firing in a carbonization furnace with a temperature gradient of 300 to 1400°C under a nitrogen atmosphere. The results of the evaluation of each characteristic value are shown in Table 1.

[Examples 2-31, Comparative Examples 1-10]
The non-volatile content composition was changed as shown in Tables 1 to 4. When adding aliphatic (poly)oxyalkylene derivatives (C), Brønsted acid compounds (D), and acetylene compounds (E), the treatment agent was prepared by dissolving and dispersing them after emulsification. Otherwise, the treatment agent for carbon fiber precursors, carbon fiber precursors, and carbon fibers were prepared and evaluated in the same manner as in Example 1. The results of the evaluation of each characteristic value are shown in Tables 1 to 4. Examples 9 and 19 are provided as reference examples.

The details of the non-volatile content composition shown in Tables 1-4 are as follows.
<Silicone containing amino groups (A)>
Amino-modified silicone A1: kinematic viscosity at 25°C: 90 ^mm² /s, amino equivalent: 3900 g/mol; Side-chain diamine type amino-modified silicone A2: kinematic viscosity at 25°C: 250 ^mm² /s, amino equivalent: 7600 g/mol; Side-chain diamine type amino-modified silicone A3: kinematic viscosity at 25°C: 1300 ^mm² /s, amino equivalent: 1700 g/mol; Side-chain diamine type amino-modified silicone A4: kinematic viscosity at 25°C: 1500 ^mm² /s, amino equivalent: 3800 g/mol; Side-chain diamine type amino-modified silicone A5: kinematic viscosity at 25°C: 20000 ^mm² /s, amino equivalent: 1800 g/mol; Side-chain diamine type amino-modified silicone A6: kinematic viscosity at 25°C: 1700 ^mm² /s, amino equivalent: 3800 g/mol, side-chain monoamine type aminopolyether modified silicone A7: kinematic viscosity at 25°C: 3300 ^mm² /s, amino equivalent: 1800 g/mol, side-chain aminopolyether type

<Aromatic compounds having a diphenylmethane skeleton (B)>
Aromatic compound B1 having a diphenylmethane skeleton: Aromatic compound B2 having a bisphenol A ether diphenylmethane skeleton with 8 moles of oxyethylene groups added: Aromatic compound B3 having a bisphenol A ether diphenylmethane skeleton with 10 moles of oxyethylene groups added: Aromatic compound B4 having a bisphenol F ether diphenylmethane skeleton with 10 moles of oxyethylene groups added: Aromatic compound B5 having a bisphenol A ether diphenylmethane skeleton with 10 moles of oxypropylene groups added: Aromatic compound B6 having a bisphenol A ether diphenylmethane skeleton with 17.5 moles of oxyethylene groups added: Diesterification reaction product of 1 mole of bisphenol A ether with 10 moles of oxyethylene groups added and 2 moles of lauric acid

<Aliphatic (poly)oxyalkylene derivatives (C)>
Aliphatic (poly)oxyalkylene derivative C1: A secondary alkyl ether with 12 to 14 carbon atoms in an alkyl group with 5 moles of oxyethylene groups added. Aliphatic (poly)oxyalkylene derivative C2: A secondary alkyl ether with 12 to 14 carbon atoms in an alkyl group with 9 moles of oxyethylene groups added. Aliphatic (poly)oxyalkylene derivative C3: A secondary alkyl ether with 12 to 14 carbon atoms in an alkyl group with 12 moles of oxyethylene groups added.

<Brønsted acid compound (D)>
Brønsted acid compound D1: Acetate Brønsted acid compound D2: Phosphate Brønsted acid compound D3: Dodecyl ether acetate with 10 moles of oxyethylene groups added.

<Acetylene compounds (E)>
Acetylene compound E1: Acetylene surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., trade name Orphine® E1010)
Acetylene compound E2: Acetylene surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., trade name Orphine® EXP-4123)
Acetylene compound E3: Acetylene surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., trade name Surfinol® 104E)

As can be seen from Tables 1 to 4, the carbon fiber precursor treatment agents of Examples 1 to 31 contain a silicone having an amino group (A) and an aromatic compound having a diphenylmethane skeleton (B), and satisfy at least one selected from conditions 1 and 2, thereby suppressing the deterioration of the carbon fiber precursor over time.
On the other hand, the carbon fiber precursor treatment agents of Comparative Examples 1 and 4-10 were not the carbon fiber precursor treatment agents of the present invention, and therefore could not suppress the deterioration of the carbon fiber precursor when the carbon fiber precursor produced with the treatment agents was stored for a long period of time. The carbon fiber precursor treatment agents of Comparative Examples 2-3 had poor emulsification stability and did not adhere uniformly to the precursor, so the carbon fiber precursor could not be produced normally and could not be used as carbon fiber precursor treatment agents.

The carbon fiber precursor treatment agent of the present invention is a treatment agent used in the production of the carbon fiber precursor treatment agent, and is useful for producing high-quality carbon fibers. The carbon fiber precursor treatment agent of the present invention has been treated with the treatment agent of the present invention and is useful for producing high-quality carbon fibers. High-quality carbon fibers can be obtained by the carbon fiber production method of the present invention.

Claims (9)

A treatment agent for carbon fiber precursors, comprising a silicone having an amino group (A) and an aromatic compound having a diphenylmethane skeleton (B), and satisfying at least one selected from the following conditions 1 and 2,
The aromatic compound (B) is a compound (B-1) having a structure in which an alkylene oxide is added to an aromatic compound having a hydroxyl group and a diphenylmethane skeleton (excluding aromatic compounds (B-2) having a diphenylmethane skeleton and an ester group).
The compound (B-1) having a structure in which an alkylene oxide is added to the aromatic compound having the hydroxyl group and the diphenylmethane skeleton is at least one selected from bisphenol A alkylene oxide adduct, bisphenol B alkylene oxide adduct, bisphenol E alkylene oxide adduct, and bisphenol F alkylene oxide adduct.
A treatment agent for carbon fiber precursors that satisfies the above condition 1.
Condition 1: The acid value of the treatment agent is 0.1 to 30 mg KOH/g.
Condition 2: The treatment agent contains Brønsted acid compound (D), and the proportion of Brønsted acid compound (D) in the non-volatile content of the treatment agent is 0.05 to 10% by weight. The carbon fiber precursor treatment agent according to claim 1, wherein the proportion of the aromatic compound (B) in the non-volatile content of the treatment agent is 5 to 99% by weight. The proportion of the amino group-containing silicone (A) in the non-volatile components of the treatment agent is 1 to 90% by weight.
The treatment agent for carbon fiber precursors according to claim 1, wherein the proportion of the aromatic compound (B) in the nonvolatile content of the treatment agent is 10 to 99% by weight. A treatment agent for carbon fiber precursors according to any one of claims 1 to 3, comprising an aliphatic (poly)oxyalkylene derivative (C). A treatment agent for carbon fiber precursors according to any one of claims 1 to 3, comprising a Brønsted acid compound (D). A treatment agent for carbon fiber precursors according to any one of claims 1 to 3, satisfying conditions 1 and 2. A treatment agent for carbon fiber precursors according to any one of claims 1 to 3, comprising an acetylene compound (E). A carbon fiber precursor obtained by attaching a carbon fiber precursor raw material to a carbon fiber precursor treatment agent according to any one of claims 1 to 3. A method for producing carbon fibers, comprising: a flame-retardant treatment step of converting the carbon fiber precursor described in claim 8 into flame-retardant fibers; and a carbonization treatment step of further carbonizing the flame-retardant fibers.