JP2021095659A - Sizing agent for carbon fiber and carbon fiber bundle - Google Patents

Abstract

To provide a sizing agent for carbon fiber having excellent stability to acidic substance.SOLUTION: A sizing agent for carbon fiber contains a polyamide aqueous dispersion containing an aqueous medium, a polyamide dispersed in the aqueous medium, and a polyalkylene polyamine alkylene oxide adduct with a melting point of 25°C or higher.SELECTED DRAWING: None

Description

The present disclosure relates to a sizing agent for carbon fibers, a carbon fiber or a fiber bundle to which the sizing agent is applied, and the like.

Composite materials reinforced with matrix resin using carbon fiber are lightweight yet have excellent strength, rigidity, dimensional stability, etc., so they are used for office equipment, automobiles, and computers (IC trays, laptop housings). It is widely deployed in general industrial fields such as), and its demand is increasing year by year.

Carbon fiber is one of the materials that have been widely applied as a composite material with resin because the strength of the resin is increased and the resin buffers the fragile fracture of the carbon fiber at the same time.

This carbon fiber is usually used as a fiber bundle composed of a large number of filaments, and because of its low elongation, the filament fibers are likely to be cut or fluffed due to mechanical friction or the like. There was a problem.

In order to solve these problems, it is common practice to apply a sizing agent to the surface of the carbon fiber. This is because the use of the sizing agent enhances the focusing property and reduces the generation of fluff and the cutting of the fiber in the carbon fiber.

The sizing agent is also being studied for the purpose of enhancing the affinity between the carbon fiber and the matrix resin. For example, Patent Document 1 discloses a method of improving the strength of a composite material by adhering a carboxylic acid-modified polyolefin-based sizing agent to a fiber.

When sizing a sizing agent to a carbon fiber bundle, the state of the sizing agent is required to be stable over time in the sizing step so that the focusing property and handleability of the carbon fiber bundle do not change. If the state of the sizing agent is not stable and the sizing agent aggregates with the passage of time in the sizing step, the state of adhesion to the carbon fiber bundle differs and the focusing property changes. Then, the impregnation property of the matrix resin into the carbon fiber bundle is not stable, and stable physical properties of the composite material cannot be obtained.

By the way, in the carbon fiber manufacturing process, in order to enhance the affinity between the carbon fiber and the sizing agent or the matrix resin, the carbonized fiber bundle is subjected to a surface oxidation treatment before the sizing treatment. As such a surface oxidation treatment, an electrolytic oxidation treatment that energizes in an electrolytic solution is generally used. However, if the electrolytic solution used for the electrolytic oxidation treatment is brought into the sizing step due to reasons such as insufficient washing with water after the electrolytic oxidation treatment, the hydrogen ion concentration (pH) of the sizing agent solution fluctuates. In many cases, an "acidic" electrolytic solution is used as the electrolytic solution used for the electrolytic oxidation treatment, and especially when an alkaline sizing agent is used, there is a problem that the pH decreases with time and the sizing agent tends to aggregate. there were. The sizing agent exemplified in the examples of Patent Document 1 is also alkaline, and it is considered that aggregation can be a problem.

Conventionally, various methods have been studied as a method for preventing aggregation of the sizing agent in the sizing process. For example, in Patent Document 2, after the surface-oxidized carbon fiber is immersed and run in an aqueous solution having a pH of 8 or more, it is run in an aqueous solution having a pH of 6 or less, and subsequently, the pH of the cleaning liquid is neutral. The post-treatment method of washing with water is disclosed until the above.

Alternatively, Patent Document 3 discloses a method of surface-treating carbon fibers by performing an electrolytic treatment in an aqueous solution having a pH of ≦ 7 and then immersing the carbon fibers in an aqueous solution having a pH> 7.

In these methods, as shown in Patent Document 2, oxides and the like produced by oxidizing the surface layer of carbon fibers by surface treatment are removed before entering the sizing step, so that a sizing agent associated with pH fluctuation can be used. This is a method to prevent agglomeration.

However, with these methods, if washing with water or washing with alkali is insufficient, oxides and the like remain on the surface of the carbon fibers, lowering the pH of the sizing agent in the sizing step, and as a result, the sizing liquid aggregates. There was a problem that it would end up. When the sizing agent aggregates, the impregnation property of the sizing agent into the carbon fiber bundle becomes insufficient, the sizing property deteriorates, fluffing is more likely to occur than before the agglutination, and the filament fibers are more easily cut. It ends up.

Further, in the case of washing with alkali, even if the oxide or the like can be removed, excess alkali may remain on the surface of the carbon fiber, and the adhesiveness between the carbon fiber and the matrix resin may be lowered.

Japanese Unexamined Patent Publication No. 2013-32600 Japanese Unexamined Patent Publication No. 61-152873 Japanese Unexamined Patent Publication No. 61-124674

The present inventors have conducted studies for the purpose of providing a sizing agent for carbon fibers having excellent stability against acidic substances.

The present inventors suppress the formation of polyamide agglomerates even in a pH range of neutral or lower if the polyamide aqueous dispersion contains a specific polyalkylene polyamine alkylene oxide adduct in addition to polyamide. We found the possibility of this, and by using this as a sizing agent, we thought that it would be a sizing agent with excellent stability against acidic substances, and repeated improvements. The findings obtained are disclosed herein.

The present disclosure includes, for example, the subjects described in the following sections.
Item 1.
A sizing agent for carbon fiber
A sizing agent for carbon fibers containing an aqueous polyamide dispersion, which comprises an aqueous medium, a polyamide dispersed in the aqueous medium, and a polyalkylene polyamine alkylene oxide adduct having a melting point of 25 ° C. or higher.
Item 2.
Polyamide is 6-nylon, 66-nylon, 610-nylon, 11-nylon, 12-nylon, 6/66 copolymerized nylon, 6/610 copolymerized nylon, 6/11 copolymerized nylon, 6/12 copolymerized nylon. , 6/66/11 copolymerized nylon, 6/66/12 copolymerized nylon, 6/66/11/12 copolymerized nylon, 6/66/610/11/12 copolymerized nylon, dimer acid-based polyamide, nylon-based Item 2. The sizing agent for carbon fiber according to Item 1, which is at least one selected from the group consisting of elastomers.
Item 3.
Item 2. The carbon according to Item 1 or 2, wherein the polyalkylene polyamine alkylene oxide adduct is a polyalkylene polyamine alkylene oxide adduct having a number average molecular weight of 5000 to 25000 and a solubility in water at 25 ° C. of 25% by mass or more. Sizing agent for fibers.
Item 4.
Item 3. The sizing agent for carbon fibers according to any one of Items 1 to 3, wherein 1 to 20 parts by mass of a polyalkylene polyamine alkylene oxide adduct is contained with respect to 100 parts by mass of polyamide.
Item 5.
Item 2. The sizing agent for carbon fibers according to any one of Items 1 to 4, wherein the polyalkylene polyamine alkylene oxide adduct is a polyalkylene polyamine alkylene oxide adduct having a structure in which alkylene oxide is addition-polymerized to polyethyleneimine.
Item 6.
Item 2. The sizing agent for carbon fibers according to any one of Items 1 to 5, wherein the average particle size of the polyamide is 1.0 μm or less.
Item 7.
Item 2. The sizing agent for carbon fibers according to any one of Items 1 to 6, wherein the amount of polyamide having a particle size of 2 μm or more is 15% by volume or less of the total amount of polyamide when the pH is lowered to 6.5.
Item 8.
A carbon fiber or a carbon fiber bundle treated with the carbon fiber sizing agent according to any one of claims 1 to 7.
Item 9.
A method for producing a sized carbon fiber or a carbon fiber bundle, which comprises treating with the sizing agent for carbon fiber according to any one of claims 1 to 7.

A sizing agent for carbon fibers having excellent stability against acidic substances is provided. Further, the carbon fiber or fiber bundle to which the sizing agent for carbon fiber is applied on the surface is excellent in bundling property and handleability, and also has good adhesiveness to the matrix resin, so that it is excellent in mechanical properties. Composite material can be obtained.

The present disclosure preferably includes, but is not limited to, a polyamide aqueous dispersion containing a specific polyalkylene polyamine alkylene oxide adduct, a sizing agent for carbon fibers containing the polyamide aqueous dispersion, and the like. This disclosure includes everything disclosed herein and recognizable to those skilled in the art.

The polyamide aqueous dispersion included in the present disclosure includes an aqueous medium, a polyamide dispersed in the aqueous medium, and a polyalkylene polyamine alkylene oxide adduct. The polyamide aqueous dispersion may be referred to as "the polyamide aqueous dispersion of the present disclosure".

Water is preferable as the aqueous medium, and various types of water such as tap water, industrial water, ion-exchanged water, deionized water, and pure water can be used. Deionized water and pure water are particularly preferable. Further, as the aqueous medium, a pH adjuster, a viscosity regulator, a fungicide and the like may be appropriately added to water, if necessary.

As the polyamide, a known one or one produced by a known method can be used. Commercially available products may be used.

More specifically, examples thereof include polyamides produced by a method such as polycondensation of diamine and dicarboxylic acid, polycondensation of ω-amino-ω'carboxylic acid, or ring-opening polymerization of cyclic lactam. That is, examples thereof include polyamides in which diamine and dicarboxylic acid are polycondensed, polyamides in which ω-amino-ω'carboxylic acid is polycondensed, and polyamides in which cyclic lactam is ring-opened polymerized. At the time of polycondensation or ring-opening polymerization here, a dicarboxylic acid or a monocarboxylic acid can be used as a polymerization regulator.

The polyamide in which diamine and dicarboxylic acid are polycondensed is, in other words, a polyamide having diamine and dicarboxylic acid as a monomer structural unit, and the polyamide in which ω-amino-ω'carboxylic acid is polycondensed is, in other words, ω. A polyamide having −amino-ω'carboxylic acid as a monomer structural unit, and a polyamide in which cyclic lactam is ring-open polymerized is, in other words, a polyamide having cyclic lactam as a monomer structural unit.

Examples of the diamine include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, and 1,10-diaminodecane. , Phenylenediamine, metaxylylenediamine and the like.

Examples of the dicarboxylic acid include glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonandicarboxylic acid, decandicarboxylic acid, tetradecanedicarboxylic acid, octadecanedicarboxylic acid, fumaric acid, phthalic acid, and xylylene dicarboxylic acid. Examples thereof include acids and dimeric acids (unsaturated dicarboxylic acids having 36 carbon atoms synthesized from unsaturated fatty acids containing linoleic acid and oleic acid as main components).

Examples of the ω-amino-ω'carboxylic acid include 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid and the like.

Examples of the cyclic lactam include ε-caprolactam, ω-enantractum, ω-lauryl lactam and the like.

The dicarboxylic acid used as the polymerization regulator is the same as the dicarboxylic acid used in the production of the polyamide, for example, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonandicarboxylic acid. , Decandicarboxylic acid, tetradecanedicarboxylic acid, octadecanedicarboxylic acid, fumaric acid, phthalic acid, pimelic acid, dimeric acid and the like. Examples of the monocarboxylic acid include caproic acid, heptanic acid, nonanoic acid, undecanoic acid, dodecanoic acid and the like.

In the present disclosure, among polyamides,-[NH (CH ₂ ) ₅ CO]-,-[NH (CH ₂ ) ₆ NHCO (CH ₂ ) ₄ CO]-,-[NH (CH ₂ ) ₆ NHCO (CH ₂ ) ₈ CO]-,-[NH (CH ₂ ) ₁₀ CO]-,-[NH (CH ₂ ) ₁₁ CO]-, _{and-[NH (CH 2} ) ₂ NHCO-D-CO]-( In the formula, D represents an unsaturated hydrocarbon having 34 carbon atoms), and a polyamide having at least one or two or more selected from the group consisting of structural units is preferably used.

Examples of such polyamides include nylon, specifically 6-nylon, 66-nylon, 610-nylon, 11-nylon, 12-nylon, 6/66 copolymerized nylon, 6/610 copolymerized nylon. , 6/11 Copolymerized Nylon, 6/12 Copolymerized Nylon, 6/66/11 Copolymerized Nylon, 6/66/12 Copolymerized Nylon, 6/66/11/12 Copolymerized Nylon, or 6/66/610 / 11/12 Copolymerized nylon and the like are exemplified. In addition, "/" here is a symbol used to indicate that it is a copolymer of each nylon. For example, 6/66 copolymerized nylon represents a copolymerized nylon of 6-nylon and 66-nylon.

Further, as an example of the polyamide that can be used, a dimer acid-based polyamide and a polyamide elastomer are also exemplified. Specific examples of the polyamide elastomer include a polyamide elastomer which is a copolymer of nylon and polyester or a copolymer of nylon and polyalkylene ether glycol. Examples of the polyalkylene ether glycol include polyethylene oxide glycol, polypropylene oxide glycol, polytetramethylene oxide glycol, polyhexamethylene oxide glycol and the like. Examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polytrimethylene naphthalate, and polybutylene naphthalate.

Polyamide can be used alone or in combination of two or more. The polyamide elastomer is not particularly limited, but a block copolymer containing a polyamide block and a polyether block is preferable. In particular, a block copolymer having a structure in which a polyamide and a polyether are copolymerized is preferable, and a block copolymer having a structure in which a polyamide and a polyether are copolymerized is particularly preferable. Examples of the constituent components of the polyether block include glycol compounds such as polyethylene oxide glycol, polypropylene oxide glycol, polytetramethylene oxide glycol and polyhexamethylene oxide glycol, and diamine compounds such as polyether diamine. Two or more kinds of these constituents may be used. As such a polyamide elastomer, several types having different molecular structures of the bonding portion between the polyamide block and the polyether block, that is, the bonding morphology, for example, "(polyamide block) -CO-NH- (polyamide block)" Examples thereof include a polyether block amide copolymer having a bonded form, a polyether ester block amide copolymer having a bonded form of "(polyamide block) -CO-O- (polyamide block)", and the like.

As the polyalkylene polyamine alkylene oxide adduct, for example, one having a structure in which an alkylene oxide is added to 1 to 3 active hydrogens in an amino compound is preferable. Specifically, for example, those having a structure in which alkylene oxide is addition-polymerized with amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and polyethyleneimine are preferable, and ethylene oxide / propylene oxide is particularly preferable. Is more preferably blocked or randomly subjected to addition polymerization. The polyethyleneimine may be either linear or branched.

The polyalkylene polyamine alkylene oxide adduct is not particularly limited, but a polyethyleneimine alkylene oxide adduct having a structure in which polypropylene oxide and polyethylene oxide are added as alkylene oxide components to polyethyleneimine in a block is particularly preferably used. ..

Further, as the polyethyleneimine alkylene oxide adduct, the following formula (1):

(In the formula, AO represents an alkylene oxide and n represents an integer), and those containing a repeating unit represented by the above are also preferably mentioned. Wherein the AO (alkylene oxide) _{is, -CH 2 CH 2 O -,} - CH 2 CH (CH 3) O-, or their block or random copolymers preferably.

The polyalkylene polyamine alkylene oxide adduct used in the aqueous polyamide dispersion of the present disclosure has a melting point of 25 ° C. or higher, preferably 25 to 100 ° C. The upper or lower limit of the range is, for example, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, It may be 97, 98, or 99 ° C. The range is, for example, more preferably 30 to 80 ° C, still more preferably 60 to 80 ° C.

The number average molecular weight of the polyalkylene polyamine alkylene oxide adduct is preferably 5000-25000. The upper or lower limit of the range is, for example, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, or 24000. May be good. The range is, for example, more preferably 1000 to 20000. When the number average molecular weight is 5000 or more, it works more preferably as a protective colloid around the particles as a polymer-type nonionic surfactant, and can preferably contribute to the stabilization of the aqueous dispersion. Further, when the number average molecular weight is 25,000 or less, not only contributes to the stabilization of the particles, but also the viscosity of the aqueous dispersion does not become too high, which can be a more practical and preferable viscosity.

The value of the number average molecular weight here is a value obtained by the measurement method described below. Number average molecular weight measurement method: A tetrahydrofuran solution containing a polyalkylene polyamine alkylene oxide adduct at a concentration of 0.2% by mass is prepared, and measurement is performed using a high performance liquid chromatograph. Then, a molecular weight marker (polystyrene) having a known molecular weight is measured under the same conditions, a calibration curve is created, and the number average molecular weight (Mn) is calculated. The measurement conditions are as follows.

Measuring machine: GPC-101 (Shodex)
Column: TSK GEL Multipore HZ-N manufactured by Tosoh Corporation
Column temperature: 40 ° C
Outflow: tetrahydrofuran Flow rate: 0.25 ml / min

The solubility of the polyalkylene polyamine alkylene oxide adduct in water is preferably 25% by mass or more, more preferably 26, 27, 28, or 29% by mass or more, and further preferably 30% by mass or more. Is. The solubility in water here is a value obtained as follows when examined using water at 25 ° C.

Solubility (% by mass) = A / (A + B) x 100
However, A: mass of polyalkylene polyamine alkylene oxide adduct B: mass of water in which the polyalkylene polyamine alkylene oxide adduct is dissolved.

Such a polyalkylene polyamine alkylene oxide adduct is commercially available as a polymer type nonionic surfactant, and for example, "Discol N" which is a polyalkylene polyamine alkylene oxide adduct manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. -518 ”can be used.

The polyalkylene polyamine alkylene oxide adduct may be used alone or in combination of two or more.

The amount of the polyalkylene polyamine alkylene oxide adduct used in the aqueous polyamide dispersion of the present disclosure is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the polyamide. The upper or lower limit of the range may be, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 parts by mass. Good. The range is, for example, more preferably 3 to 17 parts by mass, still more preferably 5 to 15 parts by mass.

Polyamide polyamine The polyamide aqueous dispersion containing no alkylene oxide adduct is usually anionic (for example, pH 9 to 10). When an acidic substance is added to the polyamide aqueous dispersion, polyamide agglomerates are likely to be formed, whereas the polyamide aqueous dispersion also containing a polyalkylene polyamine alkylene oxide adduct has a neutral region (for example, about pH 7 or more acidic). It can maintain a stable state up to pH). Therefore, not only the range of use of the aqueous polyamide dispersion can be expanded, but also it can be mixed with an acidic additive or the like, and various performance improvements and the like can be easily performed.

Although we do not want a theoretical limitation, the reason why the stable state can be maintained up to the neutral region by adding the polyalkylene polyamine alkylene oxide adduct to the aqueous polyamide dispersion is that it is a general polymer type non-ion. When using a sex surfactant, these polymer chains are only freely present around the particles and have a weak chemical stabilizing effect, whereas a polyalkylene polyamine alkylene oxide adduct having a nitrogen atom is used. In this case, nitrogen atoms are attracted to the carbonyl group on the surface of the polyamide particles, and the polyalkylene polyamine alkylene oxide adduct is present relatively close to the particle surface, which contributes to a greater stabilizing effect. Guess.

The method for producing the aqueous polyamide dispersion of the present disclosure is not particularly limited. For example, it can be produced by a method including a step of mixing an aqueous dispersion in which polyamide is dispersed (hereinafter, also referred to as a polyamide aqueous dispersion precursor) and a polyalkylene polyamine alkylene oxide adduct. It can also be produced by a method including a step of dispersing polyamide using an aqueous solution of a polyalkylene polyamine alkylene oxide adduct to obtain an aqueous dispersion.

The method for producing the polyamide aqueous dispersion precursor is not particularly limited, and any method may be used as long as the polyamide can be uniformly dispersed in the aqueous medium.

For example, a method in which polyamide powder obtained by pulverizing polyamide by a pulverization method such as a mechanical pulverization method, a freezing pulverization method, or a wet pulverization method is dispersed in an aqueous medium, or emulsified using polyamide and a basic substance. Examples thereof include a method of producing an aqueous dispersion, a method of emulsifying polyamide using a surfactant, and producing an aqueous dispersion.

Below, as a typical production example, a method of emulsifying using polyamide and a basic substance to produce an aqueous dispersion is shown.

In this production method, for example, a polyamide, a basic substance, and an aqueous medium are put into a container to prepare a mixed solution thereof.

The container used for preparing the mixture is a pressure-resistant container provided with a heating means for heating the polyamide to a temperature higher than the temperature at which it softens in an aqueous medium and a stirring means capable of applying a shearing force to the contents. Is preferable. For example, a pressure resistant autoclave with a stirrer is preferable.

Next, the polyamide, basic substance and aqueous medium are mixed in this container to obtain a mixed solution. Then, the mixed solution is heated to a temperature equal to or higher than the softening temperature of the polyamide and stirred to emulsify the mixture to obtain an emulsion. Cooling the emulsion to room temperature gives a polyamide aqueous dispersion precursor.

The basic substance is not particularly limited, and examples thereof include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, and amine compounds. The basic substance may be used alone or in combination of two or more. Of these, sodium hydroxide and / or potassium hydroxide are particularly preferably used from the viewpoint of excellent static stability of the dispersion.

The amount of the basic substance used is 0.1 to 2 mol per 1 mol of the terminal carboxyl group of the polyamide from the viewpoint of excellent static stability such as little change in the viscosity of the obtained aqueous dispersion with time. It is preferably 0.4 to 1 mol, more preferably 0.4 to 1 mol.

The amount of the polyamide used is not particularly limited, but is preferably set to 0.1 to 80 parts by mass with respect to 100 parts by mass of the obtained polyamide aqueous dispersion precursor, and is set to 20 to 60 parts by mass. It is more preferable to do so.

Further, as long as the effect of the present invention is not impaired, a polyamide aqueous dispersion precursor can be obtained by using a basic substance and a surfactant (dispersion stabilizer) in combination.

As a surfactant (dispersion stabilizer) used to obtain a polyamide aqueous dispersion precursor (that is, to disperse polyamide in an aqueous medium), the effect of the obtained polyamide aqueous dispersion of the present disclosure can be used. Additives such as anionic surfactants, nonionic surfactants, and polymer-based dispersants can also be used as long as they are not impaired.

Examples of the anionic surfactant include aliphatic polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkylphenyl ether sulfates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyldiphenyl sulfonates, and α-olefins. Examples thereof include sulfonates, alkyl sulfates, naphthalene sulfonate formalin condensates, dialkyl sulfosuccinates, polyoxyethylene alkyl ether acetates, rosin salts and fatty acid salts.

Examples of the nonionic surfactant include polyethylene glycol, ethylene oxide / propylene oxide copolymer, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl thioether, polyoxyethylene sorbitan fatty acid monoester, and polyoxy. Examples thereof include ethylene alkyl amide and polyglycerin ester.

Examples of the polymer-based dispersion stabilizer include polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyvinyl pyrrolidone, polyacrylic acid salt, polyacrylic acid ester salt, alginate, and salt of ethylene / acrylic acid copolymer. (Especially ammonium salt), styrene / maleic anhydride copolymer salt, styrene-maleic acid monoester copolymer salt, isobutylene / maleic anhydride copolymer salt, carboxymethyl cellulose salt and the like can be mentioned.

Among these additives, a nonionic surfactant and a polymer-based dispersion stabilizer are preferably used from the viewpoint of enhancing the stability of the obtained aqueous dispersion liquid of the present disclosure. Above all, the obtained aqueous dispersion of the present disclosure has excellent heat resistance, is not easily decomposed even when processed at a high temperature for a long time, and has good adhesion between the carbon fiber or fiber bundle treated with the aqueous dispersion and the matrix resin. In terms of points, ethylene oxide / propylene oxide copolymers, polyoxyethylene alkyl ethers (eg polyoxyethylene lauryl ethers, polyoxyethylene tridecyl ethers, polyoxyethylene cetyl ethers, polyoxyethylene stearyl ethers, polyoxyethylene oleyl ethers, poly). Oxyethylene myristel ether, polyoxyethylene octyldodecyl ether, etc.), ethylene / acrylic acid copolymer ammonium salt, styrene / maleic anhydride copolymer ammonium salt, styrene-maleic acid monoester copolymer ammonium salt, isobutylene / The ammonium salt of the maleic acid ester copolymer is preferably used.

These additives may be used alone or in combination of two or more.

The amount of the additive used is preferably less than 10 parts by mass, more preferably 0.1 to 8 parts by mass with respect to 100 parts by mass of the polyamide. However, the use of these additives may adversely affect the adhesiveness between the carbon fibers or fiber bundles treated with the obtained dispersion liquid and the matrix resin, so use a relatively large amount with reference to the above amount. It is desirable to set appropriately while avoiding.

In addition, these additives may be further added after the polyamide aqueous dispersion precursor is obtained in the manufacturing process.

By mixing the polyalkylene polyamine alkylene oxide adduct with the polyamide aqueous dispersion precursor prepared as described above, the polyamide aqueous dispersion of the present disclosure can be obtained. The method for mixing the polyamide aqueous dispersion precursor and the polyalkylene polyamine alkylene oxide adduct is not particularly limited. For example, the polyamide aqueous dispersion precursor and the polyalkylene polyamine alkylene oxide adduct are put into the same container and stirred. Then, a method of mixing and the like can be mentioned.

The concentration (w / w%) of the polyamide in the aqueous polyamide dispersion of the present disclosure is preferably, for example, 0.1 to 80% by mass, more preferably 1 to 60% by mass, and further preferably 5 to 5% by mass. It is 50% by mass. When the concentration of polyamide is 80% by mass or less, the stability of the aqueous polyamide dispersion can be further improved. Further, when the concentration is 0.1% by mass or more, the polyamide can be more easily adhered to the carbon fiber or the fiber bundle.

In the aqueous polyamide dispersion of the present disclosure, the average particle size of the dispersed polyamide (particles) is, for example, preferably less than 2 μm. The lower limit of the average particle size is not particularly limited, but is, for example, 0.05 μm or more. For example, it is more preferably less than 2 μm and 0.05 μm or more. The upper or lower limit of the range is, for example, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0. It may be 9.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1 μm. Further, as described above, the lower limit does not have to be set. For example, it can be more preferably 1.5 μm or less, 1.0 μm or less, or 0.8 μm or less. In the present specification, the average particle size of the polyamide is the volume average particle size measured by the laser diffraction type particle size distribution measurement method. That is, it is a volume average particle diameter value obtained when the polyamide aqueous dispersion is measured by a laser diffraction type particle size distribution measuring device.

Further, the aqueous polyamide dispersion liquid of the present disclosure is preferably one in which agglomerates of polyamide are unlikely to be formed when the pH is lowered by using an acidic substance. The degree of aggregation of polyamide can be indicated by, for example, the ratio (volume%) of the total polyamide amount (volume) to the polyamide amount (volume) having a particle size of 2 μm or more. The value is obtained by measuring the particle size distribution by the laser diffraction / scattering method. For example, when the pH is lowered to 6.5, the amount of polyamide having a particle size of 2 μm or more is preferably 15% by volume or less of the total amount of polyamide, and is 14, 13, 12, 11, or 10% by volume or less. Is more preferable, and 9, 8, 7, 6, 5, 4, or 3% by volume or less is further preferable. Further, for example, when the pH is lowered to 6.4, the amount of polyamide having a particle size of 2 μm or more is preferably 15% by volume or less of the total amount of polyamide, and is 14, 13, 12, 11, or 10% by volume. It is more preferably 9, 8, 7, 6, 5, 4, or 3% by volume or less. Further, for example, when the pH is lowered to 6.2, the amount of polyamide having a particle size of 2 μm or more is preferably 15% by volume or less of the total amount of polyamide, and is 14, 13, 12, 11, or 10% by volume. It is more preferably 9, 8, 7, 6, 5, 4, or 3% by volume or less.

As the acidic substance used to lower the pH of the aqueous polyamide dispersion, an acidic substance that does not affect the aggregation of the polyamide is preferable, and more specifically, for example, ammonium sulfate and the like are preferably mentioned.

The aqueous polyamide dispersion liquid of the present disclosure preferably includes, for example, one having a pH of less than 6.7 and an average particle size of the polyamide satisfying the above preferable range. The pH range is 6.65 or less, 6.6 or less, 6.55 or less, 6.5 or less, 6.45 or less, 6.4 or less, 6.35 or less, 6.3 or less, 6.25 or less, It may be 6.2 or less, 6.15 or less, or 6.1 or less. Further, as long as the average particle size of the polyamide satisfies the above preferable range, the lower limit of pH is not particularly limited. For example, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, or 6.

Further, the aqueous polyamide dispersion liquid of the present disclosure preferably includes, for example, one having a pH of less than 6.7 and containing no polyamide particles having an average particle diameter of 2 μm or more. The pH range is 6.65 or less, 6.6 or less, 6.55 or less, 6.5 or less, 6.45 or less, 6.4 or less, 6.35 or less, 6.3 or less, 6.25 or less, It may be 6.2 or less, 6.15 or less, or 6.1 or less. Further, the lower limit of pH is not particularly limited as long as it does not contain polyamide particles having an average particle diameter of 2 μm or more. For example, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, or 6.

In the present specification, the pH of the aqueous polyamide dispersion is a value measured at 25 ° C. using a pH meter.

The present disclosure also preferably includes a sizing agent for carbon fibers containing the above-mentioned aqueous polyamide dispersion. The sizing agent may be referred to as "the sizing agent of the present disclosure". Preferably, the sizing agent of the present disclosure is a sizing agent for carbon fibers composed of the above-mentioned aqueous polyamide dispersion.

By applying the sizing agent of the present disclosure to carbon fibers or fiber bundles and adhering the non-volatile component contained in the sizing agent to the carbon fibers or fiber bundles, the carbon fibers or fiber bundles can be sized. The non-volatile component is preferably a non-volatile component contained in the aqueous polyamide dispersion, and in this case, the non-volatile component is specifically the polyamide and the polyalkylene polyamine alkylene. Oxide adduct and other non-volatile components contained in the above-mentioned aqueous polyamide dispersion.

The amount of the non-volatile component attached to the carbon fiber or fiber bundle in which the non-volatile component is attached is preferably 0.1% by mass to 10% by mass in terms of dry mass with respect to the mass of the carbon fiber. When the amount of non-volatile component adhered is within this range, it becomes easy to uniformly size the fiber surface, fluffing and the like can be suppressed, and appropriate focusing property can be imparted during handling. The upper or lower limit of the adhesion amount range is, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2 , 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, or 9.5% by mass There may be. For example, it is more preferably 0.2% by mass to 5% by mass, and further preferably 0.2% by mass to 2% by mass. The amount of the non-volatile component adhered can be adjusted by adjusting the concentration of the non-volatile component in the sizing agent solution.

The amount of the non-volatile component contained in the sizing agent refers to the amount of residual material (solid content) when the sizing agent is heated at 120 ° C. for 60 minutes, and the sizing agent of the present disclosure is a carbon fiber made of the above-mentioned aqueous polyamide dispersion. In the case of a sizing agent for use, it is substantially the amount of the component excluding the dispersion medium from the sizing agent.

The amount of the non-volatile component adhering to the surface of the carbon fiber or the fiber bundle is determined as follows. That is, the carbon fiber or fiber bundle treated with the sizing agent is heated to 550 ° C. at 10 ° C./min in a nitrogen atmosphere and then fired at the same temperature for 10 minutes, and the reduced mass is applied to the surface of the carbon fiber or fiber bundle. The amount of non-volatile components attached.

The carbon fiber or fiber bundle to be sized is not particularly limited, but a particularly remarkable effect can be obtained when it is used as a fiber bundle in which a plurality of filaments (single yarns) are aggregated. In the present specification, the number of filaments constituting the fiber bundle is defined as a fiber bundle state if it is 10 or more, but it is preferably 100 or more, and more preferably 1,000 to 100. The number is preferably 000. Further, from the viewpoint of productivity and the like, the number is preferably 3,000 to 80,000, and more preferably 6,000 to 50,000. When the number of filaments constituting the fiber bundle is small, the flexibility of the fiber bundle tends to increase and the handleability tends to be improved, while the productivity of the reinforcing fiber tends to decrease. On the other hand, when the number of fibers is extremely large, it may be difficult to produce fiber bundles, and it tends to be difficult to sufficiently treat them with a surface treatment agent such as a sizing agent.

The overall shape of the fiber bundle is preferably a flat fiber bundle. When the fiber bundle is a flat fiber bundle, the sizing agent applied to the inside of the fiber bundle and the matrix resin used as a subsequent composite material are more easily diffused.

Further, since the time required for the sizing agent or the matrix resin to penetrate to the center of the fiber bundle is proportional to the square of the thickness of the fiber bundle, the fiber bundle is widened in order to complete the impregnation in a short time. , It is preferable to reduce the thickness of the fiber bundle. The thickness of the fiber bundle is preferably 200 μm or less. Further, from the viewpoint of handleability and moldability, the thickness of the fiber bundle is preferably 10 μm or more. Further, the thickness of the fiber bundle is preferably in the range of 30 μm to 150 μm, and more preferably in the range of 50 μm to 120 μm.

The width of such a fiber bundle is preferably 5 mm or more, and particularly preferably in the range of 10 mm to 100 mm. The flatness of the fiber bundle (width / thickness of the fiber bundle) is preferably in the range of 10 times or more, particularly 50 times to 400 times.

The average diameter of the fibers (single yarn) used in the present disclosure is preferably in the range of 0.001 μm to 100 μm, more preferably in the range of 3 μm to 20 μm. A more preferable range of the average diameter is 4 μm to 15 μm, and a particularly preferable range is 5 μm to 10 μm. If the fiber diameter is too small, the fiber component becomes bulky, and it tends to be difficult to increase the volume fraction of the fiber. On the other hand, if the fiber diameter is too large, it tends to be difficult to obtain fibers having high strength. When the fiber diameter is in the above range, a composite material having excellent mechanical strength can be obtained.

The carbon fiber attached to the sizing agent or the carbon fiber used for the fiber bundle of the present disclosure is not particularly limited, and any of pitch type, rayon type, acrylonitrile (PAN) type, single-walled carbon nanotube, multi-walled carbon nanotube, carbon nanofiber and the like. Although carbon fiber can be used, the PAN type is preferable in view of operability, process passability, mechanical strength and the like. The properties such as fineness and strength of the carbon fiber are not particularly limited, and any known carbon fiber can be used without limitation. The PAN-based carbon fiber can be produced, for example, by the following method.

<Precursor fiber>
As the precursor fiber of the carbon fiber, for example, a monomer containing acrylonitrile in an amount of preferably 90% by mass or more, more preferably 95% by mass or more, and another monomer in an amount of 10% by mass or less is used alone or copolymerized. Acrylo-based precursor fibers produced by spinning the spun solution are preferable. Examples of other monomers include itaconic acid and (meth) acrylic acid ester. Precursor fibers are obtained by washing, drying, stretching, and oiling the raw material fibers after spinning. The number of filaments of the precursor fiber is, for example, preferably 1000 or more, more preferably 12,000 or more, and even more preferably 24,000 or more in terms of production efficiency.

<Flame resistant treatment>
The obtained precursor fiber is heated in heated air at 200 ° C. to 300 ° C. for 10 minutes to 100 minutes for flame resistance treatment. In the flame resistance treatment, it is preferable to stretch the precursor fiber in the range of a draw ratio of 0.99 to 1.20.

<Carbonization treatment>
Carbon fibers can be obtained by carbonizing the flame-resistant precursor fibers at, for example, 300 ° C. to 2000 ° C. In order to obtain a carbon fiber bundle having a dense internal structure with higher tensile strength, a two-step carbonization step of low-temperature carbonization at 300 ° C to 1000 ° C and then high-temperature carbonization at 1000 ° C to 2000 ° C is performed. , It is preferable to carry out carbonization treatment. If a higher elastic modulus is required, the graphitization treatment may be further performed at a high temperature of 2000 ° C. to 3000 ° C.

<Surface oxidation treatment>
The carbon fibers obtained above are preferably surface-treated to improve the wettability with a sizing agent and, if necessary, a resin serving as a matrix. The surface treatment can be performed by any conventionally known method, but since the apparatus is simple and the control in the process is easy, it is generally industrially used to use electrolytic oxidation.

The amount of electricity for the surface treatment is preferably in the range of 10 coulombs to 150 coulombs per 1 g of carbon fiber. By adjusting the amount of electricity in this range, it is possible to obtain carbon fibers having excellent mechanical properties as fibers and having improved adhesiveness to the resin.

Examples of the electrolytic solution include nitric acid, sulfuric acid, ammonium sulfate and sodium hydrogen carbonate. Above all, it is preferable to use a strong acid or a strong acid salt such as nitric acid, sulfuric acid, and ammonium sulfate from the viewpoint of the strength of the obtained carbon fiber and the treatment efficiency. The electrolyte concentration of the electrolytic solution is preferably 0.1 or more, and more preferably 0.1 to 1 or more.

In the sizing treatment of carbon fibers, the concentration of the non-volatile component in the sizing agent is preferably 0.1% by mass to 25% by mass. The method for applying the sizing agent to the carbon fibers is not particularly limited, but a touch roll method, a dipping method, a spray method and other known methods can be used. Among them, a dipping method is preferably used for carbon fiber bundles having a large number of single fibers per bundle, which makes it easy to uniformly apply the sizing agent solution. The temperature of the sizing agent solution is preferably in the range of 10 ° C. to 50 ° C. in order to suppress fluctuations in the sizing agent concentration due to solvent evaporation. Further, the amount of the sizing agent adhered can also be adjusted by adjusting the amount of squeezing to squeeze out the excess sizing agent after applying the sizing agent.

The carbon fibers after the sizing treatment are subjected to a drying treatment in order to evaporate water or the like, which was a dispersion medium during the sizing treatment, to obtain carbon fibers having a sizing agent attached. It is preferable to use a vertical flow type hot air dryer for drying. The drying temperature is not particularly limited, but since water is used as the dispersion medium, it is preferably 100 ° C. to 250 ° C., more preferably 150 ° C. to 240 ° C. Further, after the drying step, a heat treatment step of 200 ° C. or higher may be performed. From the viewpoint of the adhesiveness of the obtained carbon fiber to the resin, the drying temperature is preferably 150 ° C. to 210 ° C. On the other hand, from the viewpoint of the quality of the obtained carbon fiber, the drying temperature is preferably 190 ° C. to 240 ° C., for example.

The drying time is not particularly limited, but is preferably, for example, 1 second to 300 seconds, and more preferably 5 seconds to 60 seconds.

In addition, in this specification, "including" also includes "consisting essentially" and "consisting of" (The term "comprising" includes "consisting essentially of" and "consisting of."). In addition, the various properties (property, structure, function, etc.) described for each of the above-described embodiments may be combined in any way in specifying the subject matter included in the present disclosure.

Hereinafter, the subject matter included in the present disclosure will be described in more detail, but the subject matter is not limited to the following examples.

Production of aqueous polyamide aqueous dispersion
Example 1
240 g of 6/66/12 copolymerized nylon (melting point 120 ° C.), 150 g of deionized water and 10 g of 10% sodium hydroxide aqueous solution as polyamide in a pressure resistant autoclave having an internal volume of 1 liter equipped with a turbine-type stirring blade having a diameter of 50 mm. It was prepared and sealed. Next, the stirrer was started, and the temperature inside the autoclave was raised to 160 ° C. while stirring at a rotation speed of 500 rpm. After stirring for another 30 minutes while maintaining the internal temperature at 160 ° C., the mixture was cooled, and 24.5 g of an aqueous dispersion of ethylene-acrylic acid copolymer ammonium salt (solid content concentration 29% by mass) and 198 g of deionized water were added. .. Further, after cooling to room temperature, 120 g of "Discol N-518" which is an aqueous solution of a polyalkylene polyamine alkylene oxide adduct manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (number average molecular weight: 16000, melting point 64.5 ° C., in water) Solubility was 30% by mass or more and less than 35% by mass, solid content concentration: 20% by mass) and 33.5 g of deionized water were added and mixed well to obtain a polyamide aqueous dispersion.

The solubility of the polyalkylene polyamine alkylene oxide adduct (Discol N-518) in water is as follows: Discol N-518 is dried, a predetermined amount is added to water, and the mixture is stirred at 25 ° C. for 5 hours. It was examined whether it would dissolve and calculated by the following formula.

Solubility (% by mass) = A / (A + B) x 100
However, A: mass of polyalkylene polyamine alkylene oxide adduct B: mass of water in which the polyalkylene polyamine alkylene oxide adduct is dissolved.

At 30% by mass, the solution was fluid, while at 35% by mass, a gel-like substance was formed and there was undissolved residue. Therefore, the solubility in water was judged to be 30% by mass or more and less than 35% by mass. ..

Further, the volume average particle size of the polyamide in the polyamide aqueous dispersion was measured using a diffraction type particle size distribution measuring device (Shimadzu Seisakusho Co., Ltd., trade name "SALD-2300") and found to be 0.53 μm.

Example 2
An aqueous polyamide dispersion was obtained in the same manner as in Example 1 except that the amount of "Discol N-518" used was 90 g and the amount of deionized water used was 47.8 g.
The volume average particle size of polyamide in this aqueous dispersion was measured using a diffraction type particle size distribution measuring device (Shimadzu Corporation, trade name "SALD-2300") and found to be 0.53 μm.

Comparative Example 1
A polyamide dispersion was obtained in the same manner as in Example 1 except that 53 g of deionized water was added instead of 120 g of "Discol N-518" (solid content concentration: 20% by mass).

Comparative Example 2
Instead of 120 g of "Discol N-518" (solid content concentration: 20% by mass), 24 g (number average molecular weight) of "Discol N-206" which is a polyalkylene polyamine alkylene oxide adduct manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 33,000, melting point less than 25 ° C, solubility in water 20% by mass or more and less than 25% by mass), and the amount of deionized water used was 96 g. Got

The solubility of Discol N-206 in water is a value examined in the same manner as the method for examining the solubility of Discol N-518 in water.

Comparative Example 3
In Example 1, 24 g of an ethylene oxide / propylene oxide copolymer (Pluronic F108 ADEKA Corporation) was used as a nonionic surfactant instead of 120 g of "Discol N-518" (solid content concentration: 20% by mass). A polyamide dispersion was obtained in the same manner as in Example 1 except that the amount of deionized water used was 96 g.

According to the catalog of Dai-ichi Kogyo Seiyaku Co., Ltd., both "Discol N-518" and "Discol N-206" used as the polyalkylene polyamine alkylene oxide adduct in the above example have the following formulas ( 1):

(In the formula, AO represents an alkylene oxide and n represents an integer.) It is described as a polyalkylene polyamine alkylene oxide adduct consisting of repeating units represented by.

Evaluation of Stability of Aqueous Polyamide Dispersion Liquid each of the aqueous polyamide dispersions (Examples 1 and 2 and Comparative Examples 1 to 3) obtained as described above was subjected to deionized water to have a polyamide concentration of 1 (w / w)%. 50 ml of the diluted polyamide aqueous dispersion was weighed out, and a 1 mol / L ammonium sulfate aqueous solution was gradually added as an acid component, and the amount of addition at which particle aggregation started was examined. Regarding the agglutination of particles, the agglutination state was confirmed by particle size distribution measurement using a diffraction type particle size distribution measuring device (Shimadzu Corporation, trade name “SALD-2300”).

Even if the pH of the polyamide dispersion was lowered to 6.4, those in which no agglomerates (particles of 2 μm or more) were not formed were evaluated as ◯, and those in which agglomerates were formed by 6.4 were evaluated as x.

When ammonium sulfate, which is an acidic component, is added to the polyamide dispersion to reduce the pH, agglomerates are formed at a pH of 7.2 in Comparative Example 1 and agglomerates are formed at a pH of 7.2 in Comparative Example 2. In Comparative Example 3, agglomerates were formed at a pH of 6.7, whereas in Example 1, the dispersed state could be maintained up to pH 6.2, that is, the dispersed state was maintained even at a pH of 6.4. It was found that the content of particles of 2 μm or more was 0% by volume, and in Example 2, the dispersed state could be maintained up to pH 6.4, and the content of particles of 2 μm or more was 0% by volume.

Further, in Comparative Example 1, when 3 mmol of ammonium sulfate, which is an acidic component, was added to the polyamide dispersion, aggregates were formed, and in Comparative Example 2, when 3 mmol of ammonium sulfate, which was an acidic component, was added to the polyamide dispersion, aggregates were formed. In Comparative Example 3, when 9 mmol of ammonium sulfate, which is an acidic component, was added to the polyamide dispersion, aggregates were formed at a pH of 6.7, whereas in Example 1, ammonium sulfate, which is an acidic component, was added to the polyamide dispersion up to 50 mmol. It can be seen that the dispersed state can be maintained even if it is added, and in Example 2, the dispersed state can be maintained even if ammonium sulfate, which is an acidic component, is added to the polyamide dispersion to 30 mmol.

The “content (%) of particles of 2 μm or more” in Table 1 represents the volume% with respect to the total amount of polyamide contained in the dispersion liquid.

From the above results, it was found that the aqueous polyamide dispersion containing the polyalkylene polyamine alkylene oxide adduct can maintain the dispersed state even in a low pH region (a region having a pH of about 7 or lower).

Manufacture of sizing agent for carbon fiber and carbon fiber bundle (1) Evaluation of the amount of non-volatile component adhered to the sizing agent The amount of non-volatile component adhered by the sizing agent treatment is 1.0 m of sizing-treated fiber bundle. Was collected, and these were heated to 550 ° C. at 10 ° C./min in a nitrogen atmosphere and then fired at the same temperature for 10 minutes. ..
Adhesion amount of non-volatile component of sizing agent = (ab) / b × 100 [mass%]
a: Fiber mass before firing treatment [g]
b: Fiber mass after firing treatment [g]

(2) Adhesiveness The adhesiveness was evaluated by the microdroplet method using the composite material interface characteristic evaluation device HM410 (manufactured by Toei Sangyo Co., Ltd.).

A single yarn was taken out from the sizing-treated carbon fiber bundle and set in the sample holder. A drop of polyamide 6 (matrix resin) melted at 230 ° C. was formed on a single yarn, cooled by air cooling and solidified to obtain a sample for measurement. The measurement sample was set in the device, the drop was sandwiched between the device blades, the single yarn was run on the device at a speed of 0.06 mm / min, and the maximum pull-out load F when the drop was pulled out from the single yarn was measured.

Then, the interfacial shear strength τ was calculated by the following formula, and the adhesiveness between the single yarn and the matrix resin was evaluated. The value of the interfacial shear strength is preferably 40 MPa or more.

Interfacial shear strength τ (unit: MPa) = F / πdl
(F: maximum pull-out load d: single thread diameter l: particle size in the drop pull-out direction)

(3) Evaluation of handleability As the handleability of the fiber, the amount of fluff generated during use was evaluated by the following measurements of Fuzz and MPF. The lower the value, the more the fluffing is suppressed and the better the quality of the fiber bundle.

(3-1) Evaluation of Fuzz The sizing-treated carbon fiber bundle was run between urethane sheets carrying a weight of 125 g at a speed of 50 feet / minute for 2 minutes, and the amount of carbon fibers accumulated in the urethane sheets was measured. , Calculated by the following formula. The value of Fuzz is preferably 500 or less, and more preferably 300 or less.

Fuzz value (μg / m) = Supplementary fluff amount (μg) / Evaluation fiber bundle length (m)

The urethane sheet on which a 125 g weight is placed has a structure of weight / urethane sheet / urethane sheet in order from the top, and a sizing-treated carbon fiber bundle is placed between the two layers of urethane sheets. It means that it was run.

(3-2) Evaluation of MPF
The sizing-treated carbon fiber bundle was run between the five pin guides at a speed of 50 feet / minute for 2 minutes under a tension of 200 g, and then passed between urethane sheets carrying a weight of 125 g. The amount of carbon fiber staying on the urethane sheet was measured and calculated by the following formula. The MPF value is preferably 1,600 or less, and more preferably 600 or less.

MPF value (μg / m) = Supplementary fluff amount (μg) / Evaluation fiber bundle length (m)

(4) Evaluation of bulk density A 300 mL graduated cylinder was filled with 30 g of sizing-treated carbon fiber bundle cut to a length of 14 mm, and the volume after 20 rotations up and down was determined. The bulk density was calculated from the mass of.

Regarding the measured bulk density, it was determined that those having a bulk density of 150 g / L or more were sufficiently focused.

Example 3
The aqueous polyamide dispersion obtained in Example 1 was diluted with water to obtain a sizing agent for carbon fibers having a concentration of non-volatile components of 2.0% by mass. The amount of the non-volatile component refers to the amount of residue (solid content) when the sizing agent is heated at 120 ° C. for 60 minutes.

<Manufacturing of sizing-treated fibers>
The polyacrylonitrile fiber was flame-resistant in air at 250 ° C. and then carbonized at a maximum temperature of 650 ° C. in a nitrogen gas atmosphere. Then, the carbon fibers produced by high-temperature carbonization at 1300 ° C. under a nitrogen atmosphere were surface-treated by electrolytic oxidation using a 10 wt% ammonium sulfate aqueous solution, and the unsized carbon fiber bundle (tensile strength: 5100 MPa, tensile elastic modulus:). 245 GPa, number of filaments: 24,000) was obtained. Next, the obtained unsized carbon fiber bundle was continuously immersed in a bath of the carbon fiber sizing agent, and the carbon fiber sizing agent was allowed to permeate between the filaments in the fiber bundle. This was dried under a drying condition of 180 ° C. for 15 seconds to obtain a carbon fiber bundle to which a non-volatile component of a carbon fiber sizing agent was attached. The amount of non-volatile components attached was 0.5% by mass. Table 2 shows the measurement results of interfacial shear strength, Fuzz, MPF, and bulk density, and the drying conditions during drying (time when the carbon fiber thread temperature was maintained at each temperature: measured by weaving a thermocouple into the carbon fiber during drying). Shown in.

The obtained carbon fiber bundle was a fiber bundle having excellent adhesiveness and excellent quality with low Fuzz and MPF. In addition, the bulk density was also good, and a sufficiently focused carbon fiber bundle could be obtained.

Comparative Example 4
As the sizing agent for carbon fibers, the amount of non-volatile component adhered to the sizing agent was the same as in Example 3 except that 3 mmol of ammonium sulfate was added using the polyamide aqueous dispersion of Comparative Example 1 to adjust the pH to 7.2. A carbon fiber bundle of 0.5% by mass was obtained. As shown in Table 1, the carbon fiber sizing agent used in Comparative Example 4 formed aggregates, so that it did not penetrate into the carbon fiber bundles and had almost no focusing property, so that the bulk density was judged to be ×. It was. Therefore, it was not possible to obtain a carbon fiber bundle whose characteristics can be evaluated.

Example 4
A carbon fiber bundle having a non-volatile component adhering amount of 0.5% by mass of the sizing agent was obtained in the same manner as in Example 3 except that the drying conditions at the time of drying were set to 200 ° C. for 15 seconds. Table 2 shows the measurement results of the interfacial shear strength, Fuzz, MPF, and bulk density, and the drying conditions at the time of drying.

Example 5
A carbon fiber bundle having a non-volatile component adhering amount of 0.5% by mass of the sizing agent was obtained in the same manner as in Example 3 except that the drying conditions at the time of drying were set to 220 ° C. for 15 seconds. Table 2 shows the measurement results of the interfacial shear strength, Fuzz, MPF, and bulk density, and the drying conditions at the time of drying.

Comparative Example 5
As the sizing agent for carbon fibers, the amount of non-volatile component adhered to the sizing agent was 0 in the same manner as in Example 3 except that the aqueous polyamide dispersion of Comparative Example 3 was used and 12 mmol of ammonium sulfate was added to adjust the pH to 6.7. A carbon fiber bundle of 1.6% by mass was obtained. As shown in Table 1, the carbon fiber sizing agent used in Comparative Example 5 does not permeate the carbon fiber bundle because it produces agglomerates and does not have sufficient focusing property, so that the bulk density is judged to be ×. became. Therefore, it was not possible to obtain a carbon fiber bundle whose characteristics can be evaluated.

The sizing-treated carbon fiber bundles obtained in Examples 3 to 5 were excellent in adhesiveness and excellent in quality with low Fuzz and MPF. The bulk density was also good, and the carbon fiber bundle was sufficiently focused.

Claims (9)

A sizing agent for carbon fiber
A sizing agent for carbon fibers containing an aqueous polyamide dispersion, which comprises an aqueous medium, a polyamide dispersed in the aqueous medium, and a polyalkylene polyamine alkylene oxide adduct having a melting point of 25 ° C. or higher. Polyamide is 6-nylon, 66-nylon, 610-nylon, 11-nylon, 12-nylon, 6/66 copolymerized nylon, 6/610 copolymerized nylon, 6/11 copolymerized nylon, 6/12 copolymerized nylon. , 6/66/11 copolymerized nylon, 6/66/12 copolymerized nylon, 6/66/11/12 copolymerized nylon, 6/66/610/11/12 copolymerized nylon, dimer acid-based polyamide, nylon-based The sizing agent for carbon fiber according to claim 1, which is at least one selected from the group consisting of elastomers. The polyalkylene polyamine alkylene oxide adduct according to claim 1 or 2, wherein the polyalkylene polyamine alkylene oxide adduct is a polyalkylene polyamine alkylene oxide adduct having a number average molecular weight of 5000 to 25000 and a solubility in water at 25 ° C. of 25% by mass or more. Sizing agent for carbon fiber. The sizing agent for carbon fibers according to any one of claims 1 to 3, wherein 1 to 20 parts by mass of a polyalkylene polyamine alkylene oxide adduct is contained with respect to 100 parts by mass of polyamide. The sizing agent for carbon fibers according to any one of claims 1 to 4, wherein the polyalkylene polyamine alkylene oxide adduct is a polyalkylene polyamine alkylene oxide adduct having a structure in which alkylene oxide is addition-polymerized to polyethyleneimine. The sizing agent for carbon fibers according to any one of claims 1 to 5, wherein the average particle size of the polyamide is 1.0 μm or less. The sizing agent for carbon fibers according to any one of claims 1 to 6, wherein the amount of polyamide having a particle size of 2 μm or more is 15% by volume or less of the total amount of polyamide when the pH is lowered to 6.5. A carbon fiber or a carbon fiber bundle treated with the carbon fiber sizing agent according to any one of claims 1 to 7. A method for producing a sized carbon fiber or a carbon fiber bundle, which comprises treating with the sizing agent for carbon fiber according to any one of claims 1 to 7.