JP6752075B2 - Acrylic fiber treatment agent and its uses - Google Patents

Description

The present invention relates to an acrylic fiber treatment agent and its use. More specifically, a treatment agent used for producing acrylic fiber, an acrylic fiber for carbon fiber production using the treatment agent (hereinafter, may be referred to as a precursor), and a carbon fiber using the treatment agent. Regarding the manufacturing method.

Utilizing its excellent mechanical properties, carbon fiber is widely used as a reinforcing fiber for a composite material with a plastic called a matrix resin in aerospace applications, sports applications, general industrial applications, and the like.
As a method for producing carbon fibers, a method in which a precursor is converted into flame-resistant fibers in an oxidizing atmosphere at 200 to 300 ° C. and then carbonized in an inert atmosphere at 300 to 2000 ° C. is common. At the time of firing with these high heats, there is a problem that fusion of single fibers occurs and the quality and quality of the obtained carbon fibers are deteriorated.

In order to prevent this fusion, a silicone-based treatment agent having excellent heat resistance and excellent peelability due to fiber-to-fiber smoothness, particularly an amino-modified silicone-based treatment agent capable of further improving heat resistance by a cross-linking reaction, is used as a precursor. Many techniques have been proposed (for example, Patent Document 1 and the like), and they are widely used industrially.

However, on the other hand, the adhered silicone-based treatment agent falls off from the fibers and becomes a sticky substance, which is deposited on a drying roller or a guide in the precursor manufacturing process, and the fibers are wound or broken. There was a problem that it caused sexual deterioration. In addition, a part of silicon oxide is generated in the oxidizing atmosphere of the flame resistance process, and silicon nitride is generated when nitrogen is used as the inert gas in the inert atmosphere of the carbonization process, and these scales are deposited. It has a problem that the operability and operability are lowered and the firing furnace is damaged.
Furthermore, the excellent peelability of the silicone-based treatment agent due to the smoothness between fibers works effectively to prevent fusion between single fibers, while a firing process in which a large number of fiber bundles run in parallel at the same time. In the above case, since the width of each fiber bundle is widened by the smoothness of the silicone-based treatment agent, the distance between the fiber bundles and the adjacent fiber bundles is narrowed, and in some cases, fluff is generated due to the interference.

In order to avoid these problems, a treatment agent having a reduced content of a silicone compound, a treatment agent not using a silicone compound, and the like have been proposed. For example, there are a treatment agent in which an aromatic compound and an amino-modified silicone are combined (for example, Patent Document 2 and the like), and a treatment agent containing an aromatic ester as a main component (for example, Patent Document 3 and the like).

However, although these treatment agents have smoothness, operability, and operability, none of them satisfy all of the uniform adhesion to the inside of the fiber bundle, heat resistance, focusing property, and fusion prevention property. It was.

JP-A-2002-371477 Japanese Unexamined Patent Publication No. 2005-88884 Japanese Unexamined Patent Publication No. 2004-143645

In view of the conventional technical background, an object of the present invention is to suppress fusion between fibers and generation of fluff in the flame resistance treatment step, to have heat resistance and focusing property, and to have stable operability. It is an object of the present invention to provide an acrylic fiber treatment agent capable of obtaining the above, an acrylic fiber for producing carbon fiber using the treatment agent, and a method for producing carbon fiber using the treatment agent.

As a result of diligent studies to solve the above problems, the present inventors have obtained the finding that the above problems can be solved by an acrylic fiber treatment agent containing a specific ester compound in a specific ratio, and the present invention has been obtained. Reached.

That is, the acrylic fiber treatment agent of the present invention contains the following ester compound (A1), ester compound (A2) and ester compound (A3), and contains the following ester compound (A1), ester compound (A2) and ester compound (A3). The weight ratio of the ester compound (A1) is 40 to 60% by weight, the weight ratio of the ester compound (A2) is 25 to 45% by weight, and the weight ratio of the ester compound (A3) is 5 to 5 to the total. It is 25% by weight.
Ester compound (A1): Ester compound ester compound (A2) in which n = 0 in the following general formula (1): Ester compound ester compound (A3) in which n = 1 in the following general formula (1): The following general In the formula (1), the ester compound having n = 2

（式（１）中、Ｒ^１及びＲ²は、それぞれ独立してアルキル基である。Ｒ^７はアルキレン基である。Ｒ^３、Ｒ^４、Ｒ^５及びＲ^６は、それぞれ独立して水素原子又はメチル基である。ｍ^１及びｍ^２は、それぞれ独立して１〜５の数である。ＡＯ（ＯＡ）は炭素数２〜４のオキシアルキレン基を示す。）

(In formula (1), R ¹ and R ² are independently alkyl groups. R ⁷ is an alkylene group. R ³ , R ⁴ , R ⁵ and R ⁶ are independent hydrogen atoms, respectively. Alternatively, they are methyl groups. M ¹ and m ² are independently numbers 1 to 5. AO (OA) indicates an oxyalkylene group having 2 to 4 carbon atoms.)

The total weight ratio of the ester compound (A1), the ester compound (A2) and the ester compound (A3) to the non-volatile content of the treatment agent is preferably 10 to 70% by weight.

The treatment agent of the present invention preferably further contains a nonionic surfactant (B).

The weight ratio ((A1 + A2 + A3) / B) of the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3) to the nonionic surfactant (B) is 45/55 to 65. It is preferably / 35.

The treatment agent of the present invention preferably further contains an antioxidant (C).

The weight loss rate after heat-treating the non-volatile component of the treatment agent in air at 250 ° C. for 1 hour is preferably less than 50% by weight.

The acrylic fiber for carbon fiber production of the present invention is formed by adhering the above acrylic fiber treatment agent to the raw material acrylic fiber of the acrylic fiber for carbon fiber production.

The method for producing carbon fiber of the present invention includes a yarn-making process in which the above acrylic fiber treatment agent is attached to acrylic fiber, which is a raw material for acrylic fiber for carbon fiber production, to produce yarn, and flame resistance in an oxidizing atmosphere at 200 to 300 ° C. It includes a flame-resistant treatment step of converting into fibers and a carbonization treatment step of carbonizing the flame-resistant fibers in an inert atmosphere at 300 to 2000 ° C.

The acrylic fiber treatment agent of the present invention is excellent in heat resistance and focusing property, and by performing a treatment of attaching the acrylic fiber treatment agent to a precursor in advance, fusion between fibers and generation of fluff in the flame resistance treatment step can be suppressed. Furthermore, stable operability can be obtained. When the acrylic fiber for carbon fiber production of the present invention is used, fusion between the fibers and generation of fluff in the flame resistance treatment step are suppressed, and further, the operability is excellent. According to the method for producing carbon fibers of the present invention, fusion between fibers and generation of fluff in the flameproofing treatment step can be suppressed, and the operability is excellent.

[Acrylic fiber treatment agent]
The acrylic fiber treatment agent of the present invention is a treatment agent intended to be applied to acrylic fibers (carbon fiber precursors) used in carbon fiber production, and contains a specific ester compound in a specific ratio. .. The details will be described below.

[Ester compounds (A1), (A2), (A3)]
The acrylic treatment agent of the present invention essentially contains an ester compound (A1), an ester compound (A2) and an ester compound (A3). The ester compound (A1) is an ester compound in which n = 0 in the above general formula (1). The ester compound (A2) is an ester compound in which n = 1 in the above general formula (1). The ester compound (A3) is an ester compound in which n = 2 in the above general formula (1). As described above, by containing the three types of ester compounds (A1), (A2), and (A3) in which n = 0, 1, and 2 in the general formula (1), as compared with the case where each of them is contained alone. It can be satisfied with heat resistance, focusing property, prevention of fusion between fibers, suppression of fluff, and operability.

In the general formula (1), R ¹ and R ² are independently alkyl groups. The alkyl group preferably has 6 to 22 carbon atoms, and more preferably 8 to 18 carbon atoms. If the alkyl group has less than 6 carbon atoms, the heat resistance may be insufficient. On the other hand, when the number of carbon atoms exceeds 22, it may be difficult to emulsify in an aqueous system. The alkyl group may have a branch or may be linear.

In the general formula (1), R ⁷ is an alkylene group. The alkylene group preferably has 2 to 10 carbon atoms, and more preferably 3 to 8 carbon atoms. If the alkylene group has less than 2 carbon atoms, the heat resistance may be insufficient. On the other hand, when the number of carbon atoms exceeds 10, it may be difficult to emulsify in an aqueous system. The alkylene group may have a branch or may be linear.

In the general formula (1), R ³ , R ⁴ , R ⁵ and R ⁶ are independently hydrogen atoms or methyl groups, respectively. It is preferably a methyl group.
In the general formula (1), m ¹ and m ² are independently numbers 1 to 5. m ¹ and m ² are preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2.

In the general formula (1), AO (OA) represents an oxyalkylene group having 2 to 4 carbon atoms. The carbon number of AO is preferably 2 to 3, and more preferably 2. The AO constituting (AO) _m1 and (AO) _m2 may be one type or two or more types. In the case of two or more kinds, it may be either a block prism, an alternating prism or a random prism. The AO preferably contains an oxyethylene group indispensably. The ratio of the oxyethylene group to the total oxyalkylene group is preferably 40 mol% or more, more preferably 50 mol%, further preferably 60 mol% or more, and particularly preferably 80 mol% or more.

In order to exert the effect of the present application, it is necessary to set the ester compound (A1), the ester compound (A2) and the ester compound (A3) in a predetermined ratio. Specifically, the weight ratio of the ester compound (A1) to the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3) is 40 to 60% by weight. When the weight ratio of the ester compound (A1) is less than 40% by weight, the scratch resistance and the focusing property are insufficient. On the other hand, when the weight ratio of the ester compound (A1) exceeds 60% by weight, the heat resistance is insufficient and fusion is caused. The weight ratio of the ester compound (A1) is preferably 42 to 58% by weight, more preferably 45 to 55% by weight.

The weight ratio of the ester compound (A2) to the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3) is 25 to 45% by weight. If the weight ratio of the ester compound (A2) is less than 25% by weight, the desired performance cannot be balanced. On the other hand, when the weight ratio of the ester compound (A2) exceeds 45% by weight, the remarkable effects of heat resistance and focusing property cannot be obtained. The weight ratio of the ester compound (A2) is preferably 27 to 43% by weight, more preferably 30 to 40% by weight.

The weight ratio of the ester compound (A3) to the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3) is 5 to 25% by weight. When the weight ratio of the ester compound (A3) is less than 5% by weight, the heat resistance is insufficient. On the other hand, when the weight ratio of the ester compound (A3) exceeds 25% by weight, the oil agent cannot be uniformly adhered to the inside of the fiber bundle, and the focusing property is insufficient. The weight ratio of the ester compound (A3) is preferably 7 to 23% by weight, more preferably 10 to 20% by weight.

(Nonionic Surfactant (B))
The acrylic fiber treatment agent of the present invention preferably further contains a nonionic surfactant (B) from the viewpoint of aqueous emulsion stability. The nonionic surfactant (B) may be used alone or in combination of two or more.

Examples of the nonionic surfactant (B) include polyoxyalkylene linear chains such as polyoxyethylene hexyl ether, polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, and polyoxyethylene cetyl ether. Alkyl ether; Polyoxyalkylene branched primary alkyl ether such as polyoxyethylene 2-ethylhexyl ether, polyoxyethylene isocetyl ether, polyoxyethylene isostearyl ether; polyoxyethylene 1-hexylhexyl ether, polyoxyethylene 1- Polyoxyalkylene branched secondary alkyl ethers such as octylhexyl ether, polyoxyethylene 1-hexyl octyl ether, polyoxyethylene 1-pentyl heptyl ether, polyoxyethylene 1-heptyl pentyl ether; polyoxyethylene oleyl ether and the like. Polyoxyalkylene alkenyl ether; polyoxyalkylene alkyl phenyl ether such as polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene dodecylphenyl ether; polyoxyethylene tristyrylphenyl ether, polyoxyethylene distyrylphenyl Polyoxyalkylene alkylarylphenyl ethers such as ethers, polyoxyethylene styrylphenyl ethers, polyoxyethylene tribenzylphenyl ethers, polyoxyethylene dibenzylphenyl ethers, polyoxyethylene benzyl phenyl ethers; polyoxyethylene monolaurates, polyoxy Polyoxyalkylene fatty acids such as ethylene monooleate, polyoxyethylene monostearate, polyoxyethylene monomyristylate, polyoxyethylene dilaurate, polyoxyethylene diolate, polyoxyethylene dimyristylate, and polyoxyethylene distearate. Esters; sorbitan esters such as sorbitan monopalmitate and sorbitan monooleate; polyoxyalkylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monostearate and polyoxyethylene sorbitan monooleate; glycerin monostearate, glycerin monolaurate, glycerin mono Glycerin fatty acid ester such as palmitate; Polyoxyalkylene sorbitol fatty acid ester; Sugar fatty acid ester; Polyoxyalkylene castor oil ether such as polyoxyethylene castor oil ether; Polyoxyalkylene cured castor oil ether such as polyoxyethylene hydrogenated castor oil ether; Polyoxyalkylene such as polyoxyethylene laurylamino ether and polyoxyethylene stearylamino ether Alkyl amino ether; oxyethylene-oxypropylene block or random copolymer; terminal alkyl ether of oxyethylene-oxypropylene block or random copolymer; terminal sucrose ether of oxyethylene-oxypropylene block or random copolymer ; Polyoxyalkylene alkylamides such as polyoxyethylene laurylamide and polyoxyethylene stearylamide; and the like.

Among these nonionic surfactants (B), polyoxyalkylene branched primary alkyl ether, polyoxyalkylene branched secondary alkyl ether, and polyoxy because the above-mentioned ester compound is particularly excellent in aqueous emulsifying power. Terminal alkyl ethers of alkylene alkenyl ether, polyoxyalkylene alkyl phenyl ether, polyoxyalkylene hardened castor oil ether, polyoxyalkylene fatty acid ester, oxyethylene-oxypropylene block copolymer, and oxyethylene-oxypropylene block copolymer are preferable. In addition, polyoxyalkylene branched primary alkyl ethers, polyoxyalkylene hardened castor oil ethers, oxyethylene-oxypropylene blocks or random copolymers because they are less likely to tarl on the fibers and damage the fibers during the firing process. , Oxyethylene-oxypropylene block copolymer terminal alkyl ethers are more preferred.

(Other surfactants)
The acrylic fiber treatment agent of the present invention may contain a surfactant other than the above-mentioned nonionic surfactant (B) as long as the effect of the present invention is not impaired. Other surfactants are used as emulsifiers, antistatic agents and the like. The other surfactant is not particularly limited, and a known one can be appropriately selected and used from an anionic surfactant, a cationic surfactant and an amphoteric surfactant. Other surfactants may be used alone or in combination of two or more.

Examples of the anionic surfactant include fatty acids (salts) such as oleic acid, palmitic acid, sodium oleate, potassium palmitate, and triethanolamine oleate; hydroxyacetic acid, potassium hydroxyacetate, lactic acid, and lactic acid. Phosphonate-containing carboxylic acid (salt) such as potassium salt; polyoxyalkylene alkyl ether acetic acid (salt) such as polyoxyethylene tridecyl ether acetic acid (sodium salt); many carboxyl groups such as potassium trimellitate and potassium pyromellitic acid Salts of substituted aromatic compounds; alkylbenzene sulfonic acids (salts) such as dodecylbenzene sulfonic acid (sodium salt); polyoxyalkylene alkyl ether sulfonic acids (salts) such as polyoxyethylene 2-ethylhexyl ether sulfonic acid (potassium salt); Higher fatty acid amide sulfonic acid (salt) such as stearoylmethyl taurine (sodium), lauroyl methyl taurine (sodium), myristyl methyl taurine (sodium), palmitoyl methyl taurine (sodium); N-acylsulfonic acid such as lauroyl sarcosic acid (sodium) Acid (salt); alkylphosphonic acid (salt) such as octylphosphonate (potassium salt); aromatic phosphonic acid (salt) such as phenylphosphonate (potassium salt); 2-ethylhexylphosphonate mono 2-ethylhexyl ester (potassium salt), etc. Alkylphosphonic acid alkylphosphoric acid ester (salt); nitrogen-containing alkylphosphonic acid (salt) such as aminoethylphosphonic acid (diethanolamine salt); alkylsulfate ester (salt) such as 2-ethylhexyl sulfate (sodium salt); polyoxy Polyoxyalkylene sulfate esters (salts) such as ethylene 2-ethylhexyl ether sulfate (sodium salt); long-chain sulfosuccinates such as di-2-ethylhexyl sulfosuccinate, sodium dioctyl sulfosuccinate, sodium monosodium N-lauroyl glutamate, Long-chain N-acylglutamates such as N-stearoyl-L-disodium glutamate; etc. can be mentioned.

Examples of the cationic surfactant include lauryltrimethylammonium chloride, myristyltrimethylammonium chloride, palmityltrimethylammonium chloride, stearyltrimethylammonium chloride, oleyltrimethylammonium chloride, cetyltrimethylammonium chloride, behenyltrimethylammonium chloride, and coconut oil alkyltrimethyl. Ammonium chloride, beef fat alkyltrimethylammonium chloride, stearyltrimethylammonium bromide, coconut oil alkyltrimethylammonium bromide, cetyltrimethylammonium methsulfate, oleyldimethylethylammonium etosulfate, dioctyldimethylammonium chloride, dilauryldimethylammonium chloride, distearyldimethylammonium chloride , Octadecyl diethylmethylammonium sulfate, etc. Alkyl quaternary ammonium salts; (polyoxyethylene) laurylaminoether emulsion, stearylaminoether emulsion, di (polyoxyethylene) laurylmethylaminoether dimethyl phosphate, di (polyoxyethylene) (Polyoxyalkylene) such as (ethylene) lauryl ethylammonium etosulfate, di (polyoxyethylene) hardened beef alkylethylamine etosulfate, di (polyoxyethylene) laurylmethylammonium dimethyl phosphate, di (polyoxyethylene) stearylamine lactate, etc. Alkylaminoether salt; acyls such as N- (2-hydroxyethyl) -N, N-dimethyl-N-stearoylamide propylammonium nitrate, lanolin fatty acid amidopropylethyldimethylammonium etosulfate, lauroylamide ethylmethyldiethylammonium metosulfate, etc. Amidoalkyl quaternary ammonium salts; alkylethenoxy quaternary ammonium salts such as dipalmitylpolyethenoxyethylammonium chloride, distearylpolyethenoxymethylammonium chloride; alkylisoquinolinium such as laurylisoquinolinium chloride Salt; benzalconium salt such as lauryldimethylbenzylammonium chloride, stearyldimethylbenzylammonium chloride; benzyldimethyl {2- [2- (p-1,1,3,3-tetramethylbutylfe) Nooxy) etoxy] ethyl} benzethonium salts such as ammonium chloride; pyridinium salts such as cetylpyridinium chloride; imidazolinium salts such as oleylhydroxyethyl imidazolinium etosulfate and laurylhydroxyethyl imidazolinium etosulfate; N-cocoylarginine ethyl Acylbasic amino acid alkyl ester salts such as ester pyrrolidone carboxylate and N-lauroyl lysine ethyl ethyl ester chloride; primary amine salts such as lauryl amine chloride, stearyl amine bromide, cured beef alkylamine chloride, rosinamine acetate; cetyl Secondary amine salts such as methylamine sulfate, laurylmethylamine chloride, dilaurylamine acetate, stearylethylamine bromide, laurylpropylamine acetate, dioctylamine chloride, octadecylethylamine hydroxide; dilaurylmethylamine sulfate, lauryldiethylamine chloride , Lauryl ethyl methylamine bromide, diethanol stearylamide ethylamine trihydroxyethyl phosphate salt, stearylamide ethylethanolamine urea polycondensate acetate and other tertiary amine salts; fatty acid amide guanidinium salt; lauryltriethylene glycol ammonium hydrooxide Alkyltrialkylene glycol ammonium salt and the like can be mentioned.

Examples of the amphoteric surfactant include 2-undecyl-N, N- (hydroxyethylcarboxymethyl) -2-imidazoline sodium, 2-cocoyl-2-imidazolinium hydroxide-1-carboxyethyroxy disodium salt and the like. Imidazoline-based amphoteric surfactants; 2-heptadecyl-N-carboxymethyl-N-hydroxyethyl imidazolium betaine, lauryldimethylaminoacetic acid betaine, alkylbetaine, amide betaine, sulfobetaine and other betaine-based amphoteric surfactants; N- Examples thereof include amino acid-type amphoteric surfactants such as laurylglycine, N-lauryl β-alanine, and N-stearyl β-alanine.

(Antioxidant (C))
The acrylic fiber treatment agent of the present application preferably further contains an antioxidant from the viewpoint of imparting heat resistance to the treatment agent component. The antioxidant (C) is a component that effectively suppresses the thermal decomposition of the acrylic fiber treatment agent by heating in the flame resistance treatment step and enhances the effect of preventing fusion between fibers.

Examples of the antioxidant (C) include acidic phosphoric acid esters, phenol-based, amine-based, sulfur-based, phosphorus-based, quinone-based and other organic antioxidants. As the antioxidant, an organic antioxidant is preferable from the viewpoint of preventing contamination of the firing furnace. Examples of the organic antioxidant include 4,4'-butylidenebis (3-methyl-6-t-butylphenol, trioctadecylphosphite, N, N'-diphenyl-p-phenylenediamine, triethylene glycol bis [3-. (3-t-Butyl-4-hydroxy-5-methylphenyl) propionate], dioleyl-thiodipropionate and the like. These organic antioxidants may be used alone or in combination of two or more. Good.

(Modified silicone (D) having a modifying group containing a nitrogen atom)
The acrylic fiber treatment agent of the present invention may further contain a modified silicone (D) having a modifying group containing a nitrogen atom from the viewpoint of providing excellent smoothness between fibers.
The type of the modified silicone (D) is not particularly limited as long as it is a modified group containing a nitrogen atom. Examples of the modifying group containing a nitrogen atom include a modifying group containing an amino bond or an imino bond (that is, an amino group), a modifying group containing an amide bond (that is, an amide group), and the like. It may be a modifying group having a plurality of different bonds such as. The modifying group containing a nitrogen atom may be bonded to the side chain of the silicone which is the main chain, may be bonded to the terminal, or may be bonded to both. Further, it may have a polyoxyalkylene group (for example, a polyoxyethylene group, a polyoxypropylene group, a polyoxybutylene group, etc.) in the molecule.

Examples of the modified silicone (D) having a modifying group containing a nitrogen atom include amino-modified silicone, aminopolyether-modified silicone, amide-modified silicone, amidopolyether-modified silicone, and the like, and one type of modified silicone is used. Alternatively, a plurality of modified silicones may be used in combination.

The content of nitrogen atoms in the modified silicone (D) is preferably 0.35 to 3.2% by weight, more preferably 0.37 to 2.2% by weight, and 0.40 to 1.3% by weight. More preferred. If the content of nitrogen atoms is lower than 0.35% by weight, the emulsion stability may deteriorate when emulsified in an aqueous system. On the other hand, when the content of nitrogen atoms is higher than 3.2% by weight, the adhesiveness of the modified silicone (D) becomes high due to thermal cross-linking, which may cause gum-up.

Among these modified silicones (D), amino-modified silicones are excellent in the emulsion stability when emulsified in an aqueous system and in the effect of being used in combination with the ester compounds (A1), (A2) and (A3). preferable.

When the modified silicone (D) is an amino-modified silicone, the structure of the amino-modified silicone is not particularly limited. That is, the amino group which is a modifying group may be bonded to the side chain of silicone which is the main chain, may be bonded to the terminal, or may be bonded to both. Further, the amino group may be a monoamine type or a polyamine type, and both may coexist in one molecule.

The content of the amino group (NH ₂ ) in the amino-modified silicone (hereinafter referred to as "amino% by weight") is preferably 0.4 to 3.7% by weight, more preferably 0.42 to 2.5% by weight. 0.46 to 1.5% by weight is more preferable. If the amino weight% is lower than 0.4% by weight, the emulsification stability of the emulsion may deteriorate when emulsified in an aqueous system. On the other hand, if it is higher than 3.7% by weight, the adhesiveness of the amino-modified silicone becomes high due to thermal cross-linking, which may cause gum-up.

The viscosity of the amino-modified silicone at 25 ° C. is not particularly limited, but if the viscosity is too low, the treatment agent tends to scatter, and the emulsion becomes less stable when emulsified in an aqueous system, so that the treatment agent is transferred to the fiber. It may not be possible to apply evenly. As a result, fusion of fibers may not be prevented. On the other hand, if the viscosity is too high, gum-up due to stickiness may become a problem. Viscosity at 25 ° C. of the amino-modified silicone is preferably 100~15,000mm ² / s, more preferably 500~10,000mm ² / s, more preferably 1,000~5,000mm ² / s.

[Other ingredients]
The acrylic fiber treatment agent of the present invention may contain components other than the above-mentioned components as long as the effects of the present invention are not impaired. Other components include sulfate ester salts of higher alcohols / higher alcohol ethers, sulfonates, phosphoric acid ester salts of higher alcohols / higher alcohol ethers; smoothing agents such as alkyl esters of higher alcohols, higher alcohol ethers, waxes, etc. Antibacterial agents; preservatives; rust preventives; and hygroscopic agents.

Further, the acrylic fiber treatment agent of the present invention may contain a silicone component other than the modified silicone (D) having a modifying group containing a nitrogen atom as long as the effect of the present invention is not impaired. Specifically, dimethyl silicone, epoxy-modified silicone, alkylene oxide-modified silicone (polyether-modified silicone), epoxy polyether-modified silicone (see, for example, Patent No. 4616934), carboxy-modified silicone, carbinol-modified silicone, alkyl-modified silicone, Examples thereof include phenol-modified silicone, methacrylate-modified silicone, alkoxy-modified silicone, and fluorine-modified silicone.

Further, the acrylic fiber treatment agent of the present invention may contain an ester compound as long as the effect of the present invention is not impaired. Examples of the ester compound include an ester compound having three or more ester groups in the molecule described in Republished WO2007 / 066517, and a sulfur-containing ester described in the international application PCT / JP2013 / 75081. Compounds and the like can be mentioned.

[Ratio of each component in the treatment agent]
The acrylic fiber treatment agent of the present invention essentially contains the above-mentioned ester compound (A1), ester compound (A2) and ester compound (A3). The total weight ratio of the ester compound (A1), the ester compound (A2) and the ester compound (A3) to the non-volatile content of the treatment agent is preferably 10 to 70% by weight, more preferably 20 to 65% by weight, and 30 to 60% by weight. 62% by weight is more preferable, and 40 to 60% by weight is particularly preferable. When the weight ratio is less than 10% by weight, sufficient effects may not be obtained in heat resistance, focusing property, prevention of fusion between fibers, suppression of fluff, and operability. On the other hand, when the weight ratio exceeds 70% by weight, aqueous emulsification may be difficult.
The non-volatile component in the present invention refers to an absolute dry component when the treatment agent is heat-treated at 105 ° C. to remove a solvent or the like and reaches a constant amount.

When the acrylic fiber treatment agent of the present invention contains the nonionic surfactant (B), the weight ratio of the nonionic surfactant (B) to the non-volatile content of the treatment agent is preferably 5 to 60% by weight. 20 to 58% by weight is more preferable, 30 to 55% by weight is further preferable, and 35 to 50% by weight is particularly preferable.
From the viewpoint of aqueous emulsion stability, the weight ratio ((A1 + A2 + A3) / B) of the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3) to the nonionic surfactant (B) is , 45/55 to 65/35, more preferably 48/52 to 62/38, and even more preferably 50/50 to 60/40.

When the acrylic fiber treatment agent of the present invention contains the antioxidant (C), the weight ratio of the antioxidant (C) to the non-volatile content of the treatment agent is preferably 1 to 10% by weight, preferably 1 to 8% by weight. Is more preferable, 1 to 7% by weight is further preferable, and 1 to 5% by weight is particularly preferable.

When the modified silicone (D) is contained, the weight ratio ((A1 + A2 + A3) / D) of the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3) to the modified silicone (D) is 1/99. ~ 99/1 is preferable, 5/95 to 95/5 is more preferable, 10/90 to 90/10 is further preferable, and 15/85 to 85/15 is particularly preferable.

From the viewpoint of heat resistance in the flame-resistant treatment step and the effect of preventing fusion between fibers, the weight loss rate of the acrylic fiber treatment agent of the present invention after heat treatment in air at 250 ° C. for 1 hour is 50% by weight. It is preferably less than, more preferably less than 45% by weight, even more preferably less than 40% by weight. When the weight reduction rate is 50% or more, the treatment agent film remaining on the fibers in the flameproofing treatment step is reduced, and the effect of preventing fusion between fibers may not be sufficiently obtained.

In the acrylic fiber treatment agent of the present invention, the ester compound (A1), the ester compound (A2) and the ester compound (A3), and if necessary, the modified silicone (D) were dissolved, solubilized, emulsified or dispersed in water. It is preferably in a state.
The weight ratio of water to the total acrylic fiber treatment agent and the weight ratio of non-volatile content are not particularly limited. For example, it may be appropriately determined in consideration of the transportation cost when transporting the acrylic fiber treatment agent of the present invention, the handleability due to the viscosity of the emulsion, and the like. The weight ratio of water to the total acrylic fiber 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 ratio (concentration) of the non-volatile content to the entire acrylic fiber 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 acrylic fiber treatment agent of the present invention can be produced by mixing the components described above. The method for emulsifying and dispersing the components described above is not particularly limited, and a known method can be adopted. Examples of such a method include a method in which each component constituting the acrylic fiber treatment agent is put into warm water under stirring to emulsify and disperse, or a method in which each component constituting the acrylic fiber treatment agent is mixed and homogenizer or homogenizer is used. Examples thereof include a method of gradually adding water to emulsify the phase while applying a mechanical shearing force using a mixer, a ball mill or the like.

The acrylic fiber treatment agent of the present invention can be suitably used as a treatment agent (precursor treatment agent) for acrylic fibers (precursor) for carbon fiber production. It may be used as a spinning oil for acrylic fibers other than precursors.

[Acrylic fiber for carbon fiber production and carbon fiber production method]
The acrylic fiber for carbon fiber production (precursor) of the present invention is produced by adhering the above acrylic fiber treatment agent to the raw material acrylic fiber of the precursor. The method for producing a precursor of the present invention includes a silk-reeling step of adhering the acrylic fiber treatment agent to the raw acrylic fiber of the precursor to produce a silk yarn.
The method for producing carbon fiber of the present invention is a yarn-making step of adhering the above acrylic fiber treatment agent to the acrylic fiber as a raw material of the precursor to spin the precursor, and an oxidation of the precursor manufactured in the yarn-making step at 200 to 300 ° C. It includes a flame-resistant treatment step of converting into flame-resistant fibers in a sexual atmosphere, and a carbonization treatment step of carbonizing the flame-resistant fibers in an inert atmosphere at 300 to 2000 ° C.

The yarn-making step is a step of adhering an acrylic fiber treatment agent to the raw material acrylic fiber of the precursor to make the precursor, and includes an adhering treatment step and a drawing step.
The adhesion treatment step is a step of spinning the raw material acrylic fiber of the precursor and then adhering the acrylic fiber treatment agent. That is, the acrylic fiber treatment agent is attached to the raw material acrylic fiber of the precursor in the adhesion treatment step. Further, the raw material acrylic fiber of this precursor is drawn immediately after spinning, and the high-magnification drawing after the adhesion treatment step is particularly called a "drawing step". The stretching step may be a moist heat stretching method using high-temperature steam, or a dry heat stretching method using a hot roller.

The precursor is composed of an acrylic fiber containing polyacrylonitrile as a main component, which is obtained by copolymerizing at least 95 mol% or more of acrylonitrile and 5 mol% or less of a flame resistance promoting component. As the flame resistance promoting component, a vinyl group-containing compound having copolymerizability with acrylonitrile can be preferably used. The single fiber fineness of the precursor is not particularly limited, but is preferably 0.1 to 2.0 dTex from the viewpoint of the balance between performance and manufacturing cost. The number of single fibers constituting the fiber bundle of the precursor is also not particularly limited, but is preferably 1,000 to 96,000 from the viewpoint of the balance between performance and manufacturing cost.

The acrylic fiber treatment agent may be attached to the raw material acrylic fiber of the precursor at any stage of the silk reeling process, but it is preferable to attach the acrylic fiber treatment agent once before the drawing process. It may be attached at any stage before the drawing step, for example, immediately after spinning. Further, it may be reattached at any stage after the stretching step, for example, it may be reattached immediately after the stretching step, it may be reattached at the winding step, or it may be reattached immediately before the flameproofing treatment step. You may let me. Further, the modified silicone (D) may be lubricated separately from the acrylic fiber treatment agent. In that case, the acrylic fiber treatment agent and the modified silicone (D) may be refueled at the same time, or either of them may be refueled first. Regarding the attachment method, it may be attached using a roller or the like, or it may be attached by a dipping method, a spray method or the like.

When the modified silicone (D) is lubricated separately from the acrylic fiber treatment agent, the modified silicone (D) is dissolved, solubilized, emulsified or dispersed in water using the above-mentioned nonionic surfactant (B). It is preferably in a state (referred to as a modified silicone (D) -containing treatment agent).
The weight ratio of water to the total modified silicone (D) -containing treatment agent and the weight ratio of the non-volatile component are not particularly limited. For example, it may be appropriately determined in consideration of the transportation cost when transporting the modified silicone (D) -containing treatment agent of the present invention, the handleability due to the viscosity of the emulsion, and the like. The weight ratio of water to the entire modified silicone (D) -containing 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 ratio (concentration) of the non-volatile component to the total modified silicone (D) -containing treatment agent is preferably 0.01 to 99.9% by weight, more preferably 0.5 to 90% by weight, and 1 to 50% by weight. Especially preferable.
The modified silicone (D) -containing treatment agent can be produced by the same method as the acrylic fiber treatment agent described above.

In the adhesion treatment step, the application rate of the acrylic fiber treatment agent is to obtain the effect of preventing sticking between fibers and the effect of preventing fusion, and in the carbonization treatment step, the tarification of the treatment agent prevents deterioration of the quality of carbon fibers. From the balance with the above, it is preferably 0.1 to 2% by weight, more preferably 0.3 to 1.5% by weight, based on the weight of the precursor. If the application rate of the acrylic fiber treatment agent is less than 0.1% by weight, sticking and fusion between the single fibers cannot be sufficiently prevented, and the strength of the obtained carbon fibers may decrease. On the other hand, when the application rate of the acrylic fiber treatment agent is more than 2% by weight, the acrylic fiber treatment agent covers the single fibers more than necessary, so that the supply of oxygen to the fibers is hindered in the flame resistance treatment step, which is obtained. The strength of carbon fibers may decrease. The application rate of the acrylic fiber treatment agent referred to here is defined as a percentage of the weight of the non-volatile component to which the acrylic fiber treatment agent is attached to the weight of the precursor.

The flame-resistant treatment step is a step of converting the precursor to which the acrylic fiber treatment agent is attached into flame-resistant fibers in an oxidizing atmosphere at 200 to 300 ° C. The oxidizing atmosphere may usually be an air atmosphere. The temperature of the oxidizing atmosphere is preferably 230 to 280 ° C. In the flame resistance treatment step, the acrylic fiber after the adhesion treatment is subjected to a tension of a draw ratio of 0.99 to 1.10 (preferably 0.95 to 1.05) for 20 to 100 minutes (preferably 30). Heat treatment is performed for ~ 60 minutes). In this flame-resistant treatment, a flame-resistant fiber having a flame-resistant structure is produced through intramolecular cyclization and addition of oxygen to the ring.

The carbonization treatment step is a step of further carbonizing the flame-resistant fiber in an inert atmosphere at 300 to 2000 ° C. In the carbonization treatment step, first, in a firing furnace having a temperature gradient from 300 ° C. to 800 ° C. in an inert atmosphere such as nitrogen or argon, a tension having a draw ratio of 0.95 to 1.15 with respect to the flame-resistant fiber is obtained. It is preferable to carry out the pre-carbonization treatment step (first carbonization treatment step) by heat-treating for several minutes while applying the above. Then, in order to further promote carbonization and graphitization, a tension having a draw ratio of 0.95 to 1.05 is applied to the first carbonization treatment step in an inert atmosphere such as nitrogen or argon. The flame-resistant fiber is carbonized by performing a second carbonization treatment step while applying heat treatment for several minutes. Regarding the control of the heat treatment temperature in the second carbonization treatment step, 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 characteristics (tensile strength, elastic modulus, etc.) of the desired carbon fiber.

In the method for producing carbon fibers of the present invention, if a carbon fiber having a higher elastic modulus is 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 thus obtained can be surface-treated to increase the adhesive strength with the matrix resin when used as a composite material, depending on the purpose. A gas phase or liquid phase treatment can be adopted as the surface treatment method, and from the viewpoint of productivity, the liquid phase treatment with an electrolytic solution such as an acid or an alkali is preferable. Further, in order to improve the processability and handleability of the carbon fiber, various sizing agents having excellent compatibility with the matrix resin can be added.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the examples described here. The percentages and parts shown in the following examples are "% by weight" and "parts by weight" unless otherwise specified. The measurement of each characteristic value was performed based on the method shown below.

<Scratch resistance>
Using the TM type friction conjugation tester TM-200 (manufactured by Daiei Kagaku Seiki Co., Ltd.), the carbon fiber strands were rubbed 1000 times with a tension of 50 g through three mirror-finished chrome-plated stainless needles arranged in a zigzag pattern (reciprocating motion speed 300). (Times / min), the state of fluffing of the carbon fiber strands was visually determined according to the following criteria.
◎: No fluffing is seen as before rubbing ○: Several fluffs are seen but scratch resistance is good △: There is a little fluffing and the scratch resistance is slightly inferior ×: There is a lot of fluffing and significant single thread breakage Poor scratch resistance seen

<Fusion prevention>
Twenty locations were randomly selected from the carbon fibers, short fibers having a length of 10 mm were cut out from the carbon fibers, the fused state was observed, and the determination was made according to the following evaluation criteria.
⊚: No fusion ○: Almost no fusion Δ: Less fusion ×: More fusion

<Weight reduction rate>
Each treatment agent emulsion was collected on an aluminum cup having a diameter of φ60 mm so that the non-volatile content was 1 g, treated with a warm air dryer at 105 ° C. for 3 hours to remove water, and the sample was precisely weighed (W1). The obtained sample was heat-treated in a gear oven at 250 ° C. × 60 min, and the heat-treated sample was precisely weighed (W2). The weight loss rate was calculated by the following formula.
(W1-W2) / W1 × 100 = Weight loss rate (wt%)

<Fasciculation of fiber bundles>
At the time of winding and unwinding in the precursor silk reeling process, and at the inlet and outlet of the flame-resistant furnace in the flame-resistant process, the degree of focusing of fiber bundles was observed, and a comprehensive visual judgment was made according to the following evaluation criteria.
⊚: The fiber bundle has a uniform thickness, and no single fiber is scattered.
◯: The fiber bundle has a uniform thickness, and there is almost no variation in single fibers.
Δ: The fiber bundle has a uniform thickness, but some disjointed single fibers can be seen.
X: There are many loose single fibers, and single thread breakage is also seen.

<Silk reeling operability (roller dirt)>
The degree of contamination (gum-up) of the drying roller after the treatment agent was applied to 50 kg of the precursor was determined by the following evaluation criteria.
◎: There is no roller contamination due to gum-up, and there is no problem with silk reeling operability.
◯: There is little roller contamination due to gum-up, and there is no problem with silk reeling operability.
Δ: There is roller contamination due to gum-up, and the silk-reeling operability is slightly inferior.
×: Roller contamination due to gum-up is significant, single yarn is taken during silk reeling, and there is winding.

<Carbon fiber strength>
The measurement was performed according to the epoxy resin impregnated strand method specified in JIS-R-7601, and the average value of 10 measurements was taken as the carbon fiber strength (GPa).

[Synthesis of ester compounds]
(Synthesis Example A1-1)
While encapsulating nitrogen gas in a reactor, 1.0 mol of an adduct of 2 mol of ethylene oxide of bisphenol A and 2.0 mol of lauric acid were charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours to carry out an ester compound (A1-1-1). ) Was obtained.
(Synthesis Example A2-1)
With nitrogen gas sealed in the reactor, 2.0 mol of polyoxyethylene (2 mol) bisphenol A monolaurate and 1.0 mol of adipic acid were charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours to produce an ester compound (2 mol). A2-1) was obtained.
(Synthesis Example A3-1)
With nitrogen gas sealed in the reactor, 1.0 mol of polyoxyethylene (2 mol) bisphenol A monolaurate and 1.0 mol of adipic acid were charged, dehydrated and condensed at 190 ° C. for 3 hours, and then bisphenol A. The ester compound (A3-1) was obtained by charging 0.5 mol of an adduct of 2 mol of ethylene oxide and further dehydrating and condensing reaction at 190 ° C. for 3 hours.

(Synthesis Example A1-2)
While encapsulating nitrogen gas in a reactor, 1.0 mol of an adduct of 6 mol of ethylene oxide of bisphenol A and 2.0 mol of lauric acid were charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours to carry out an ester compound (A1-2). ) Was obtained.
(Synthesis Example A2-2)
With nitrogen gas sealed in the reactor, 2.0 mol of polyoxyethylene (6 mol) bisphenol A monolaurate and 1.0 mol of adipic acid were charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours to produce an ester compound (1 mol). A2-2) was obtained.
(Synthesis Example A3-2)
With nitrogen gas sealed in the reactor, 1.0 mol of polyoxyethylene (6 mol) bisphenol A monolaurate and 1.0 mol of adipic acid were charged, dehydrated and condensed at 190 ° C. for 3 hours, and then bisphenol A. The ester compound (A3-2) was obtained by charging 0.5 mol of an adduct of 6 mol of ethylene oxide of No. 1 and further performing a dehydration condensation reaction at 190 ° C. for 3 hours.

(Synthesis Example A1-3)
While encapsulating nitrogen gas in a reactor, 1.0 mol of an adduct of 2 mol of ethylene oxide of bisphenol A and 2.0 mol of stearic acid were charged, and the ester compound (A1-3) was subjected to a dehydration condensation reaction at 190 ° C. for 3 hours. ) Was obtained.
(Synthesis Example A2-3)
With nitrogen gas sealed in the reactor, 2.0 mol of polyoxyethylene (2 mol) bisphenol A monostearate and 1.0 mol of adipic acid were charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours to produce an ester compound (2 mol). A2-3) was obtained.
(Synthesis Example A3-3)
While encapsulating nitrogen gas in a reactor, 1.0 mol of polyoxyethylene (2 mol) bisphenol A monoesterate and 1.0 mol of adipic acid were charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours, and then bisphenol A. 0.5 mol of an adduct of 2 mol of ethylene oxide was further charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours to obtain an ester compound (A3-3).

(Synthesis Example A4)
With nitrogen gas sealed in the reactor, 1.0 mol of isooctyl alcohol and 1.0 mol of stearic acid were charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours to obtain an ester compound (A4).
(Synthesis Example A5)
With nitrogen gas sealed in the reactor, 1.0 mol of polyoxyethylene (10 mol) glycol and 2.0 mol of oleic acid were charged and subjected to a dehydration condensation reaction at 190 ° C. for 3 hours to obtain an ester compound (A4). It was.

[Nonionic Surfactant (B)]
Nonionic surfactant (B): Polyoxyethylene (18 mol) hardened castor oil ether / polyoxyethylene (9 mol) alkyl ether (alkyl groups C12 to C14) = 1/1 mixed.
[Antioxidant (C)]
Antioxidant (C): 4,4'-butylidenebis (3-methyl-6-tert-butylphenyl-di-tridecylphosphite)
[Modified Silicone (D)]
Amino-modified silicone (D1): (25 ° C. viscosity: 1300 mm ² / s, amino equivalent: 2000 g / mol, modified type: diamine)
Amino-modified silicone (D2): (25 ° C. viscosity: 4500 mm ² / s, amino equivalent: 1000 g / mol, modified type: diamine)
Amino-modified silicone (D3): (25 ° C. viscosity: 120 mm ² / s, amino equivalent: 5000 g / mol, modified type: monoamine)

[Examples 1 to 13, Comparative Examples 1 to 11]
Using the ester compound (A), nonionic surfactant (B), antioxidant (C), and amino-modified silicone (D) prepared above, water was used to obtain the non-volatile content composition shown in Tables 1 and 2. Acrylic fiber treatment agents, which are aqueous emulsions in which the proportion of nonionic content in the treatment agent is 20% by weight, were prepared by mixing and stirring. The numerical values in the table indicate the weight ratio of each component to the non-volatile content of the treatment agent. For example, the numerical values of A1-1 to A3-3 in the table indicate the weight ratio of the ester compounds A1-1 to A3-3 in the non-volatile content of the treatment agent. The numerical values in parentheses indicate the weight ratio of each ester compound to the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3).
Then, the prepared treatment agent was further diluted with water to obtain a treatment liquid having a non-volatile content concentration of 3.0% by weight.
Each treatment liquid was attached to a precursor (single fiber fineness 0.8 dtex, 24,000 filaments) so as to have an imparting rate of 1.0% by weight, and dried at 100 to 140 ° C. to remove water. The precursor after adhering to the treatment liquid was flame-resistant in a flame-resistant furnace at 250 ° C. for 60 minutes, and then calcined in a carbonization furnace having a temperature gradient of 300 to 1400 ° C. in a nitrogen atmosphere to convert it into carbon fibers. The evaluation results of each characteristic value are shown in Tables 1 and 2.

As shown in Tables 1 and 2, in the examples, the heat resistance and the focusing property are excellent, the fusion between fibers and the generation of fluff in the flame resistance treatment step can be suppressed, and the operation can be performed stably. It can be seen that high-strength carbon fibers can be obtained.
On the other hand, it can be seen that none of the comparative examples satisfy all of the above required characteristics. For example, in Comparative Example 2, although the fluff suppression and the focusing property are satisfactory, the fusion prevention property and the heat resistance are insufficient, and as a result, the strength of the carbon fiber is low.

Claims (8)

It contains the following ester compound (A1), ester compound (A2) and ester compound (A3).
The weight ratio of the ester compound (A1) to the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3) is 40 to 60% by weight, and the weight ratio of the ester compound (A2) is 25 to It is 45% by weight, and the weight ratio of the ester compound (A3) is 5 to 25% by weight.
Acrylic fiber treatment agent.
Ester compound (A1): Ester compound ester compound (A2) in which n = 0 in the following general formula (1): Ester compound ester compound (A3) in which n = 1 in the following general formula (1): The following general In the formula (1), the ester compound having n = 2

(In formula (1), R ¹ and R ² are independently alkyl groups. R ⁷ is an alkylene group. R ³ , R ⁴ , R ⁵ and R ⁶ are independent hydrogen atoms, respectively. Alternatively, they are methyl groups. M ¹ and m ² are independently numbers 1 to 5. AO (OA) indicates an oxyalkylene group having 2 to 4 carbon atoms.) The treatment agent according to claim 1, wherein the total weight ratio of the ester compound (A1), the ester compound (A2) and the ester compound (A3) to the non-volatile content of the treatment agent is 10 to 70% by weight. The treatment agent according to claim 1 or 2, further comprising a nonionic surfactant (B). The weight ratio ((A1 + A2 + A3) / B) of the total of the ester compound (A1), the ester compound (A2) and the ester compound (A3) to the nonionic surfactant (B) is 45/55 to 65. The treatment agent according to any one of claims 1 to 3, which is / 35. The treatment agent according to any one of claims 1 to 4, further comprising an antioxidant (C). The treatment agent according to any one of claims 1 to 5, wherein the weight loss rate after heat treatment of the non-volatile component of the treatment agent in air at 250 ° C. for 1 hour is less than 50% by weight. Acrylic fiber for carbon fiber production, which is obtained by adhering the acrylic fiber treatment agent according to any one of claims 1 to 6 to the raw material acrylic fiber for acrylic fiber for carbon fiber production. A yarn-making process in which the acrylic fiber treatment agent according to any one of claims 1 to 6 is attached to acrylic fiber, which is a raw material for acrylic fiber for carbon fiber production, to produce yarn, and a flame-resistant fiber in an oxidizing atmosphere at 200 to 300 ° C. A method for producing carbon fibers, which comprises a flame-resistant treatment step of converting to flame-resistant fiber and a carbonization treatment step of carbonizing the flame-resistant fiber in an inert atmosphere at 300 to 2000 ° C.